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  5. 阴离子交换膜（AEM）电解水制氢技术近五年研究进展：材料创新与系统优化

阴离子交换膜（AEM）电解水制氢技术近五年研究进展：材料创新与系统优化

深度研究Mick发表于 2025年10月13日 10:3113阅读
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1. AEM电解水制氢的技术原理与发展背景

1.1 技术基本原理与核心优势

阴离子交换膜（AEM）电解水制氢技术，作为一种新兴的绿色制氢途径，其核心在于利用AEM作为电解质，在阴极还原水分子产生氢气（HER），在阳极氧化水分子产生氧气（OER），并伴随氢氧根离子（OH⁻）的传导。具体而言，在阴极，水分子接受电子生成氢气和氢氧根离子（2H₂O + 2e⁻ → H₂ + 2OH⁻）；在阳极，氢氧根离子失去电子并结合水分子生成氧气和水（2OH⁻ → ½O₂ + H₂O + 2e⁻）。OH⁻离子通过AEM从阴极迁移至阳极，完成电荷传输回路。

AEM电解水制氢技术结合了传统碱性电解（AWE）和质子交换膜电解（PEMWE）的优势，同时规避了两者的主要缺点1。相较于AWE，AEM电解槽采用固态聚合物电解质膜，无需循环腐蚀性液体碱液，简化了系统设计，提高了安全性，并允许更高的电流密度和更高的效率。此外，AEM电解槽可在较低温度下运行，降低了能耗。

与PEMWE相比，AEM技术的核心优势在于其碱性操作环境。PEMWE需要使用昂贵的贵金属催化剂（如Ir和Pt），因为在酸性环境中，非贵金属催化剂的稳定性差。而AEM的碱性环境使得非贵金属催化剂（如镍基、铁基、钴基材料）在HER和OER反应中表现出优异的活性和稳定性，从而显著降低了电解槽的成本12。例如，在AEMWE中，镍铁（NiFe）氧化物、氢氧化物或磷化物等非贵金属催化剂在OER反应中展现出与贵金属催化剂相当甚至更优的性能34，而铜镍（Cu-MoNi）异质结构催化剂在HER中也表现出卓越的活性和2000小时的稳定性5。这种对非贵金属催化剂的兼容性，以及无需昂贵双极板材料的需求，使得AEMWE在降低制氢成本方面具有巨大潜力，有助于实现2050年碳中和目标下的绿色氢能生产1。此外，AEM还可采用无氟烃基离子交换膜，进一步降低成本和环境影响6。

1.2 近五年发展驱动与行业需求

在应对全球气候变化和实现可持续发展的大背景下，绿色氢能作为一种清洁、高效的能源载体，正受到前所未有的关注。全球多个国家和地区都提出了雄心勃勃的绿色氢能发展目标，例如欧盟和美国均在其氢能路线图中强调了通过电解水制氢实现2050年碳中和的关键作用 1。这些目标对电解水制氢技术提出了更高的要求，尤其是在成本效益、效率和长期稳定性方面。

AEM电解水制氢技术正是在这一背景下迅速崛起。其战略地位主要体现在以下几个方面：首先，AEMWE与可再生能源（如太阳能、风能）的耦合具有天然优势。可再生能源的间歇性和波动性要求电解设备具有快速响应能力和宽泛的操作范围，AEMWE凭借其固态电解质结构和在较宽电流密度范围内的稳定运行特性，能够有效适应可再生能源的波动输出，实现电网负荷平衡，将不稳定的绿色电力转化为可储存、可运输的绿色氢能。

其次，AEM技术在规模化制氢中展现出巨大潜力。传统PEMWE依赖贵金属，其成本和稀缺性限制了大规模部署。而AEMWE对非贵金属催化剂的兼容性，以及对廉价材料（如不锈钢双极板）的适应性，使其在降低资本支出和运营成本方面具有显著优势，从而为绿色氢能的大规模商业化生产铺平道路 7。DOE设定的2026年氢气生产成本目标为2.0美元/GGE，而采用RuMoNi催化剂的AEM电解槽有望将成本降至0.85美元/GGE，显示出其强大的成本竞争力 8。

在2020-2025年间，多项关键政策和市场需求显著推动了AEM技术的发展。全球对减少温室气体排放的承诺、各国政府出台的氢能发展战略（如“氢能行动计划”、“国家氢能战略”等）以及对绿色技术研发的资金支持，都极大地刺激了AEM材料、催化剂和系统集成方面的创新。例如，欧盟的氢能战略旨在到2030年实现40 GW的电解水制氢能力，这需要大量的低成本、高效率电解技术。此外，市场对脱碳工业生产（如钢铁、化工）和绿色交通（燃料电池汽车、船舶）日益增长的需求，也加速了AEMWE技术的研发和产业化进程。众多研究机构和企业纷纷加大投入，致力于解决AEMWE在氢生产效率、长期稳定性和成本效益方面仍面临的挑战，以期将其推向更广泛的商业应用 79。

2. AEM材料的关键性能优化与结构设计

2.1 膜材料的离子传导机制与微观调控

AEM材料的性能核心在于其对氢氧根离子（OH⁻）的高效传导能力和优异的稳定性。OH⁻离子在AEM中的传导机制主要包括Grotthuss机制（质子跳跃机制）和车辆机制（直接扩散机制）。在Grotthuss机制中，OH⁻通过与膜中的水分子形成氢键网络，实现质子的连续跳跃式传输；而在车辆机制中，OH⁻则直接以水合离子的形式在膜内扩散。为了实现高效的OH⁻传导，AEM的微观结构设计至关重要，特别是亲水/疏水微相分离现象被认为是构建高效离子传输通道的关键因素 10。

理想的AEM应具备清晰且相互连通的亲水通道，以便OH⁻离子高效传输，同时具备稳定的疏水骨架以提供机械支撑。通过对AEM材料进行微观调控，可以优化其离子交换容量（IEC）、水合行为和离子通道结构，从而显著提升离子传导率。离子交换容量（IEC）是衡量膜中可交换离子基团数量的指标，较高的IEC通常意味着更多的OH⁻载体，有助于提高离子电导率。然而，过高的IEC也可能导致膜材料过度水合，降低机械强度或增加膨胀率。

水合行为，即膜材料对水分子的吸收和保持能力，直接影响OH⁻的传导效率。适度的水合有助于形成连续的氢键网络，促进Grotthuss传导。研究表明，通过引入不同长度的烷基侧链，可以影响SEBS-CQ（季铵化聚苯乙烯-聚乙烯-丁烯-聚苯乙烯三嵌段共聚物）离聚物的亲水-疏水相分离，从而优化水合膜的形态和水网络结构，显著提高离子电导率 10。

为了进一步优化离子传导率，研究人员探索了多种结构设计策略：

  1. 交联（Cross-linking）：通过在聚合物骨架中引入交联点，可以增强膜的机械稳定性，同时在一定程度上调控亲水区域的尺寸和连通性，防止过度溶胀，从而维持有效的离子传导路径。
  2. 接枝侧链（Grafting Side Chains）：在聚合物主链上接枝带有离子交换基团（如季铵基团）的侧链，是实现微相分离和构建高效离子通道的有效手段 10。侧链的长度、密度和化学性质直接影响离子基团的聚集程度和亲水通道的形成。例如，通过在聚合物上连接不同长度的烷基侧链，可以精确控制水相区域的纳米结构，形成更有效的离子传导路径 10。具有适当侧链设计的离子聚合物可以展现出清晰的亲水和疏水区域相分离，形成良好连接的水网络，从而获得更高的电导率，通常可达到0.1 S/cm (在60-80°C) 以上 1011。
  3. 微相分离调控：通过设计具有嵌段或接枝共聚物结构的AEM，可以诱导形成纳米尺度的亲水和疏水区域，形成连续的OH⁻传输通道。水含量增加时，亲水通道会扩张，形成更有效的离子导电路径 10。引入过量的烷基侧链可以增强纳米分离，形成更有序的结构和更长的水相关联长度 10。

然而，需要注意的是，尽管许多AEM的离子传导率已超过0.1 S/cm（在60-80°C），但其在高于60°C温度下的长期稳定性仍需进一步提升 11。

2.2 膜材料的多维度稳定性提升

AEM在实际应用中面临多重挑战，其中膜材料的稳定性是制约其商业化的关键因素。高性能AEM不仅需要优异的离子传导性，更需在碱性环境、机械应力和电化学反应等复杂工况下保持长期稳定。当前研究主要围绕提升膜的碱性稳定性、机械稳定性和电化学稳定性展开。

2.2.1 碱性稳定性

碱性稳定性是AEM最核心的挑战之一。在强碱性操作环境下，特别是高温条件下，AEM中的季铵盐（Quaternary Ammonium, QA）阳离子基团极易受到氢氧根离子（OH⁻）的亲核攻击，导致霍夫曼消除（Hofmann elimination）、亲核取代（nucleophilic substitution）以及位移反应等降解途径，从而造成离子交换基团的损失，进而导致离子电导率下降和膜性能衰减 11。季磷盐（Quaternary Phosphonium Salts, QPS）因其在某些应用中展现的抗菌活性而受到关注 12；而在AEM领域，季铵盐因其结构多样性和可调控性，是目前最常用的阳离子基团。

为提高季铵盐头基的抗降解能力，研究人员采取了多种策略：

  1. 改变季铵盐结构：

    • 空间位阻效应：通过在季铵基团周围引入较大体积的取代基，增加空间位阻，可以有效阻止OH⁻离子对中心氮原子的攻击，从而提高其稳定性。例如，N-甲基奎宁环鎓（N-methylquinuclidinium）等环状季铵结构被认为比线性季铵基团具有更高的稳定性，因为其氮原子被桥环结构所保护，不易发生霍夫曼消除反应 13。此外，异吲哚鎓（isoindolinium）基团也展现出优异的碱性稳定性，通过在芳香环上引入取代基可进一步提高稳定性一个数量级 14。
    • 电子效应：通过在季铵基团附近引入吸电子基团，可以降低氮原子的电负性，减弱OH⁻的亲核攻击能力。
    • 柔性间隔链：在聚合物骨架和季铵基团之间引入柔性烷基间隔链，可以使季铵基团更好地排列在亲水通道中，减少空间拥挤，并可能降低其受攻击的几率。然而，柔性间隔链也可能因其烷基部分被OH⁻攻击而断裂 15。

  2. 聚合物骨架设计：

    • 耐碱主链：选择本身具有优异碱性稳定性的聚合物骨架，例如聚芳醚砜（poly(arylene ether sulfone)）、聚苯并咪唑（polybenzimidazole, PBI）及其衍生物等。这些骨架通常具有较高的化学键能和惰性结构，能有效抵抗OH⁻的侵蚀。例如，聚苯乙烯基AEM与O-PBI共混膜在1 M KOH、85°C下浸泡六周后未观察到电导率损失，显示出优异的碱性稳定性 16。
    • 氟化骨架：在聚合物骨架中引入氟原子，可以降低聚合物的玻璃化转变温度，并诱导明显的相分离，有利于形成离子传输通道。同时，氟原子对骨架的保护作用也能提高其碱性稳定性。例如，一种含氟聚芴基AEM（PFPFTP-QA）在80°C、2 M KOH溶液中浸泡1000小时后，仍保持优异的碱性稳定性 17。

  3. 交联和复合策略：通过化学交联或物理共混的方式，可以有效限制聚合物链的运动，提高膜的结构稳定性。有机-无机复合膜也是提升稳定性的有效途径，例如将纳米尺寸的无机填料（如ZrO₂、SiO₂）引入聚合物基质中，可以形成致密的结构，减少OH⁻的渗透，同时改善膜的机械性能 18。一些聚合物如c-PAP（poly(aryl-r-aryl piperidinium)）AEMs及离子聚合物，在1 M NaOH, 80°C条件下可稳定超过2000小时 19。

2.2.2 机械稳定性

AEM在电解槽运行过程中会承受一定的机械应力，包括气体压力、水合-脱水循环引起的尺寸变化以及电流密度波动带来的热应力。因此，膜必须具备足够的机械强度、韧性和尺寸稳定性，以防止破裂或变形。

  1. 高分子骨架增强：高强度聚合物骨架是机械稳定性的基础。聚芳醚砜、聚苯并咪唑、聚醚醚酮（PEEK）等具有刚性骨架的聚合物，可以提供优异的机械支撑。
  2. 交联和共混：化学交联可以形成三维网络结构，显著提高膜的拉伸强度、杨氏模量和断裂伸长率。将AEM与高机械强度聚合物共混，如聚苯乙烯基AEM与O-PBI的共混，可以形成机械稳定的复合膜 16。
  3. 无机纳米填料复合：引入SiO₂、ZrO₂等无机纳米颗粒，可以作为增强相，提高膜的机械强度和尺寸稳定性，同时也能调控亲水/疏水相结构，优化离子传导。

2.2.3 电化学稳定性（抗自由基攻击）

在电解水过程中，特别是在氧气析出反应（OER）侧，可能会产生超氧自由基（O₂•⁻）和羟基自由基（•OH）等活性氧物种（ROS） 2021。这些高活性的自由基能够攻击聚合物骨架和季铵基团，导致膜的氧化降解，从而影响电解槽的长期运行性能。

  1. 自由基清除剂：在膜材料中掺入自由基清除剂，如某些抗氧化剂或无机纳米材料，可以捕获或猝灭活性氧物种，从而保护膜免受氧化降解。
  2. 抑制ROS生成：优化电催化剂和电极结构设计，尽可能降低ROS的生成量，是从源头上解决电化学稳定性问题的策略。
  3. 骨架抗氧化设计：选择对氧化降解具有较强抵抗力的聚合物骨架，减少易受自由基攻击的化学键或基团。

长期老化实验案例：

为验证AEM的稳定性，通常会进行严格的长期老化测试。例如，单个AEM水电解槽电池已在高达60°C和1 A/cm²的电流密度下运行数千小时 11。此外，如前文所述，含氟聚芴基AEM（PFPFTP-QA）在80°C、2 M KOH溶液中稳定运行1000小时 17。近期研究表明，具有环状季铵基团（如哌啶鎓、吡咯烷鎓）的AEM在80°C、2 M KOH溶液中浸泡一个月后，仍能保持较高的电导率和机械鲁棒性，其中哌啶鎓基AEM的性能优于吡咯烷鎓基AEM 15。这些长期老化数据为AEM的商业化应用提供了重要参考，但也指出，即便在取得了显著进展的情况下，提升AEM在超过60°C温度下的稳定性仍是未来研究的重点 11。

2.3 新型膜材料的开发与应用

为克服传统AEM在离子传导率、机械强度和化学稳定性方面的局限，研究人员不断探索新型膜材料的开发。这些新型材料通常结合了创新的结构设计和合成方法，以实现性能的显著提升。近五年的研究主要聚焦于辐射接枝膜、有机-无机复合膜以及微孔膜等。

2.3.1 辐射接枝膜

辐射接枝技术是一种“绿色”合成方法，通常在室温下进行，避免了催化剂和有毒溶剂的使用，最终产品具有良好的均一性和高品质 22。这种技术通过高能辐射（如电子束、γ射线）在聚合物基材（如聚乙烯-四氟乙烯共聚物 (ETFE) 23、聚偏氟乙烯 (PVDF)）上引入活性位点，再将带有离子交换基团（如乙烯基咪唑、乙烯基苄基氯）的单体接枝到基材上，随后进行季铵化反应，从而制备AEM。

辐射接枝膜的优势在于可以精确控制接枝程度和接枝链的结构，从而优化亲水和疏水区域的分布，形成高效的离子传输通道。例如，通过辐射接枝技术制备的咪唑基AEM，即便在较低水含量下也能保持较高的电导率，并具有良好的碱性耐久性 24。研究表明，辐射接枝技术能够有效调控亲水和疏水区域的形貌，例如形成“反胶束”或“胶束”结构，这些结构对AEM的电化学性能和耐久性至关重要 24。此外，辐射接枝还能通过在基聚物上接枝间隔链来提高AEM的化学稳定性 22。

2.3.2 有机-无机复合膜

有机-无机复合膜是将无机纳米材料（如二氧化硅、氧化锆、石墨烯氧化物等）引入到聚合物基体中，以期结合两者的优势：有机聚合物提供柔韧性和成膜性，无机组分则改善膜的机械强度、热稳定性、尺寸稳定性以及离子传导性。无机填料通常具有亲水性，可以在膜中形成额外的离子传输路径，并提高膜的吸水性，从而促进OH⁻传导 25。

例如，通过在交联膜中涂覆不同含量的亲水性极性纳米氧化锆，制备出有机-无机复合膜PBP-SH-Zrx。其中，CM PBP-SH-Zr4复合膜不仅在80°C下展现出167.7 mS cm⁻¹的良好离子电导率，而且在尺寸稳定性（溶胀率16.5%，吸水率206.4%）和碱性稳定性（在2 M NaOH中2200小时后仅降解16%）方面表现优异 18。这种复合策略可以缓解膜与催化剂层之间的“微间隙”问题，增强膜电极组件（MEA）的界面兼容性，从而降低电荷转移电阻，提高水分解性能 18。此外，无机填料还可以作为自由基清除剂，提高膜的抗氧化能力，进一步提升电化学稳定性。

2.3.3 微孔膜

微孔膜通过在聚合物骨架中引入特殊的结构单元，诱导形成纳米尺度的连通孔隙，从而为OH⁻传输提供明确的通道，同时有效抑制气体渗透。这些孔隙通常通过构象受限的刚性单元（如三蝶烯、交联Tröger碱结构）或半互穿聚合物网络（sIPN）的微相分离来创建。

半互穿聚合物网络AEMs（如PBP与微孔聚醚酮PEK-SBI的结合），利用亲水网络和疏水微孔段之间的不相容性，促进了相分离结构的形成，从而提高了氢氧根离子电导率 26。例如，sIPN-90/10 AEM在80°C下实现了122.4 mS cm⁻¹的离子电导率，同时保持低至12.2%的溶胀率，并在80°C、1 M NaOH溶液中浸泡30天后仍能保持94.7%的电导率，表现出良好的碱性稳定性 26。

更近期的研究利用具有刚性支化和微孔结构的奎宁环基AEMs，在80°C、10 M NaOH中实现了3100小时后99.95%的OH⁻电导率保留率 27。通过调整支化单元的刚性以限制链堆积，成功创建了微孔，使OH⁻在聚（三联苯-三蝶烯-奎宁环）膜中的扩散系数提高了1.6倍 27。这种微孔结构不仅提高了离子传导效率，还在高浓度碱液中表现出卓越的稳定性。通过原位交联方法，基于Tröger碱的微孔交联季铵膜QDTTB-Xs也被开发出来，它们具有高离子电导率和低钒离子渗透性，对于钒流电池等应用也展现出巨大的潜力 28。

这些新型膜材料的开发，在提高AEM的离子传导率、机械强度、化学稳定性和阻气性能方面取得了显著进展，为AEM电解水制氢技术的商业化应用奠定了坚实的基础。然而，如何实现这些高性能材料的低成本、大规模生产，并进一步提升其在苛刻条件下的长期耐久性，仍是未来研究的重要方向。

3. 电催化剂的开发与性能提升策略

3.1 OER催化剂的活性优化与机理争议

氧析出反应（OER）是电解水制氢过程中动力学最缓慢、过电位最高的半反应之一，其效率直接决定了整个电解系统的性能。因此，开发高性能、低成本的OER电催化剂对于AEM电解水制氢技术的商业化至关重要。镍铁（NiFe）基材料因其地球储量丰富、成本低廉且在碱性环境中表现出卓越的OER活性，已成为最有前景的非贵金属OER催化剂之一。

3.1.1 NiFe基催化剂的活性位点与机理争议

尽管NiFe基材料在OER中表现出色，但其精确的活性位点和催化机理仍存在争议。早期的研究普遍认为Ni是主要的活性中心，Fe的掺杂通过改变Ni的电子结构来提升催化活性。然而，越来越多的证据表明，Fe在NiFe基OER催化剂中扮演着更为核心的角色，甚至可能是真正的活性位点 2930。

  • Fe掺杂对Ni位点的调控：当Fe掺杂到Ni基材料（如NiOOH）中时，Fe原子可以调节Ni中心的电子结构，使其更容易被氧化形成高价态的Ni物种，从而促进OER反应。密度泛函理论（DFT）计算表明，Fe的引入能降低NiOOH的过电位，并将最优的电位决定步骤（PDS）从O解吸转移到OOH的形成 31。
  • Fe作为直接活性位点：一些研究认为，Fe本身就是OER的活性中心，尤其是在镍铁层状双氢氧化物（NiFe-LDH）中。氧同位素标记实验表明，在NiFe-LDH中，OER反应发生在Fe位点上，而非Ni位点 32。FeOOH在适当条件下也能表现出优异的OER活性，甚至有研究指出，双相FeOOH材料通过富集氧空位和混合价态，展现出当前报道的单组分铁氧化物/氢氧化物粉末催化剂中最高的OER性能，从而支持Fe作为OER活性位点的观点 30。此外，当Ni掺杂到Fe泡沫中时，OER过电位显著降低240mV，这归因于Ni掺杂活化了Fe泡沫表面，形成了多种活性位点，包括镍掺杂的氢氧化铁、氧化铁、氢氧化镍以及具有不同化学计量比的镍铁混合氢氧化物 33。
  • 双位点协同机制（DSSM）：最新的研究提出了NiFe双活性中心协同作用的机制。例如，Co和Y共掺杂的NiFeOOH催化剂，通过增加Ni位点的路易斯酸性来增强OH吸附，同时大尺寸Y原子引起晶格畸变并延长Fe─O─M键，削弱Fe位点对OH的结合。这种双位点调控减少了吸附差异，激活了NiFe双活性中心，促进了DSSM路径，将速率决定步骤的能量从传统AEM路径的2.51 eV降低到1.71 eV 34。

3.1.2 Co掺杂对导电性的增强

除了Fe掺杂外，钴（Co）的掺杂也被广泛研究以提升NiFe基OER催化剂的性能。Co的引入可以优化活性位点的电子结构，促进中间产物的吸附/脱附，例如，在Co-Fe（氧）氢氧化物中，Fe的引入可使Co的氧化还原电位发生阳极移动，表明两者之间存在强烈的电子相互作用 35。Co掺杂还可以诱导晶相转变，如Co掺杂镍硒化物从六方相NiSe（H-NiSe）到菱方相NiSe（R-NiSe）的转变，形成的H-NiSe/R-NiSe异质结构被发现可以降低裂解能，并促进电子转移过程，从而增强OER性能 36。

3.1.3 长期运行中的结构演变

NiFe基OER催化剂在长期运行过程中会经历复杂的结构演变，这对其耐久性至关重要。研究表明，NiFe基催化剂的OER活性与其在反应过程中形成的表面重构活性层密切相关。然而，这种动态重构也伴随着挑战。例如，Fe在长期运行中存在溶解或浸出的风险，这会导致催化剂失活。为解决这一问题，研究者们通过表面功能化（如负载四苯基卟啉，TPP）来稳定NiFe（氧）氢氧化物，TPP可以作为保护层抑制金属水合物在催化剂/电解液界面的溶解，同时促进活性位点Fe的再沉积，从而显著延长催化剂寿命，在AEM水电解中以1.41 mV/h的降解速率稳定运行115小时 37。此外，通过离子补偿重构设计NiFe基普鲁士蓝类似物（PBA）作为前驱体，成功制备了具有高稳定性的NiFeOₓHᵧ催化剂，该催化剂在500 mA cm⁻²下稳定运行超过500小时，有效抑制了Fe的流失 38。

3.1.4 不同制备方法对催化层厚度与活性的影响

NiFe基OER催化剂的制备方法对其形貌、晶体结构、比表面积和催化性能有着显著影响。常见制备方法包括电沉积、水热合成、共沉淀、化学浴沉积等。

  • 电沉积法：常用于制备薄膜或纳米结构催化剂，可以精确控制催化层的厚度和形貌。例如，通过针状阵列电沉积法制备的Co和Y共掺杂NiFeOOH催化剂，在1 A cm⁻²下仅需270 mV的超低过电位，并在1 A cm⁻²下稳定运行1500小时，初始电位保持率达98% 34。
  • 水热合成法：能够制备具有高比表面积和多孔结构的纳米材料，有利于暴露更多的活性位点和促进传质。例如，通过简便水热法合成的钒掺杂NiFeO/NF（镍泡沫）电极，在10 mA cm⁻²下表现出186 mV的低过电位，并且在AEM电解槽中实现1.0 A cm⁻²下1.711 V的电池电压，能量转换效率达73.30%，具有卓越的稳定性 39。
  • 共沉淀和热解法：可用于制备层状双氢氧化物（LDH）或金属有机骨架（MOF）衍生的催化剂。例如，通过MOF衍生的钴@介孔碳材料，其介孔结构和高比表面积为OER提供了丰富的活性位点，并表现出优异的催化性能 40。电纺丝技术制备的镍取代LaSrFeO多孔钙钛矿纳米纤维（ES-LSFN-0.5）展现出更大的比表面积、更高的孔隙率和更快的传质速率，其强化了憎气性，促进了氧气泡的快速脱离，有效降低了气泡过电位，从而在AEM水电解中100 mA cm⁻²电流密度下实现了100小时的优异稳定性 41。

总的来说，NiFe基OER催化剂的研究进展迅速，通过对活性位点的深入理解、精细的掺杂调控（如Co、V、Y、Mo、W、Sb等） 34394243以及创新制备方法的应用，其活性和稳定性均得到显著提升。然而，如何进一步优化其在苛刻工作条件下的长期稳定性，并实现工业规模的低成本制备，仍是未来研究的重点。

3.2 HER催化剂的非贵金属化与稳定性验证

析氢反应（HER）在AEM电解水制氢中是另一个关键的半反应。尽管HER的动力学通常比OER快，但高效、稳定且低成本的HER催化剂对于降低整个电解系统的能耗和成本至关重要。传统的HER催化剂以铂（Pt）基材料为金标准，但其稀缺性和高成本限制了其大规模应用。因此，非贵金属化是HER催化剂开发的核心方向。

3.2.1 Pt基催化剂的竞争优势与性能优化

在碱性HER中，Pt基催化剂因其优异的活性而仍被广泛应用作基准，并且在某些情况下，通过合金化或表面修饰可以进一步提升其性能。

  • PtNi合金：通过将Pt与廉价过渡金属Ni合金化，不仅可以降低Pt的用量，还能通过合金效应调节Pt的电子结构，优化氢吸附/脱附能，从而提升HER活性。例如，研究表明PtNi合金在碱性HER中表现出比纯Pt更高的质量活性。
  • Pt表面Ni(OH)₂修饰：在Pt表面修饰一层Ni(OH)₂，可以促进水解离，提供更多的H原子吸附位点，从而加速HER过程。这种策略通过协同效应，将Pt的高本征活性与Ni(OH)₂在碱性环境中促进水解离的能力结合起来，实现了更高的HER性能。
  • Pt单原子掺杂Ru/RuOₓ异质界面：最新的研究表明，通过在异质界面Ru/RuOₓ上掺杂Pt单原子，可以显著增强碱性HER活性。例如，Pt-Ru/RuOₓ催化剂在1 M KOH中表现出优异的HER过电位和稳定性，并且在AEMWE中达到1 A cm⁻²的电流密度仅需1.90 V，优于商业Pt/C 44。这种设计策略通过RuOₓ加速水解离，Pt单原子和金属Ru促进后续的H*结合，实现了性能与成本的平衡 44。

3.2.2 Ru基非贵金属催化剂

钌（Ru）基催化剂作为一种非铂族贵金属，在碱性HER中展现出优异的性能，被认为是极具潜力的Pt替代品。

  • 高分散Ru/C：将高分散的Ru纳米颗粒负载在碳载体上，可以最大化Ru的原子利用率并提供大量的活性位点。最新的研究通过将Ga单原子桥接在Ru簇上，形成了Ru-Ga/N-C催化剂，该催化剂在10 mA cm⁻²下的过电位仅为4 ± 1 mV，质量活性高达9.3 ± 0.5 A mg⁻¹，并在AEMWE中实现1 A cm⁻²工业电流密度下1.74 V的电池电压，且稳定运行超过170小时 45。Ga单原子作为电子桥，稳定了Ru簇，并优化了Ru-H键强度，同时亲氧Ga位点加速了水解离 45。
  • Ru/TiN纳米颗粒：将Ru纳米颗粒负载在TiN载体上（Ru NPs/TiN）可以实现高效率和高稳定性的HER。这种催化剂在63 mV过电位下展现出20 A mg⁻¹的高质量活性，并在AEM电解槽中以5 A cm⁻²的电流密度稳定运行超过1000小时，降解可忽略不计，远超商业电解槽的性能要求 46。结构分析表明，TiN基底有效改变了Ru纳米颗粒的性质，密度泛函理论计算也指出Ru颗粒与TiN基底之间的强吸附作用，以及通过颗粒-载体相互作用对氢吸附能的有利调节 46。
  • 原子级分散Ru与CoP：通过CoP优化原子级分散Ru位点的电子结构，可以在碱性和酸性介质中实现高效析氢。例如，NC@Ru₁-CoP催化剂在1 M KOH中达到10 mA cm⁻²的过电位仅为15 mV 47。实验和理论计算表明，Ru位点与CoP之间的强相互作用有效优化了Ru位点的电子结构，降低了氢结合能和水解离能垒 47。基于此催化剂的AEMWE在1.8 V下可达到1560 mA cm⁻²的工业级电流密度 47。

3.2.3 过渡金属磷化物（TMPs）

过渡金属磷化物（TMPs），如CoP、FeP、Ni₂P、MoP等，因其导电性良好、稳定性高以及与Pt相似的氢吸附特性，被认为是极具前景的非贵金属HER催化剂 48。

  • CoP基催化剂：CoP已被证实具有良好的HER活性。通过MOF衍生策略制备的FeP-CoP异质结构催化剂，在N和P双掺杂碳多孔纳米片上，在1000 mA cm⁻²下仅需175 mV的低过电位，并且在AEMWE中以1000 mA cm⁻²稳定运行超过1000小时，估算每公斤H₂的成本仅为0.79美元，达到美国能源部（DOE）设定的目标（2美元/公斤H₂） 49。这得益于d带中心的下移和界面Co-P-Fe桥接，触发了富电子的P位点，重新分配了电子密度，降低了HER的能垒 49。
  • NiMo基催化剂：Ni掺杂MoOₓ形成的NiₓMo₁₋ₓO₄纳米片，通过NiMo氧化物异质结构优化氢吸附，显示出卓越的碱性HER和HOR性能，在10 mA cm⁻²下HER过电位仅为16 mV，并在80 mA cm⁻²下稳定运行100小时 50。
  • 柔性WS₂超结构：柔性二硫化钨（WS₂）超结构被设计用于AEMWE的阴极催化剂，其特点是纳米片之间具有无键范德华相互作用，确保了优异的机械柔韧性，以及阶梯状边缘缺陷结构实现了高催化活性和有利的反应界面微环境 51。这种独特的柔性WS₂超结构能够有效抵御高密度气液交换的冲击并促进传质，在工业级电流密度下具有出色的长期耐久性。含有该催化剂的AEM电解槽在1 A cm⁻²下实现了1.70 V的电池电压，并稳定运行超过1000小时，衰减率可忽略不计（9.67 μV h⁻¹） 51。

3.2.4 腐蚀与失活机制

尽管非贵金属HER催化剂取得了显著进展，但在AEM电解工况（碱性/纯水环境）下的长期稳定性仍面临挑战。

  • 金属溶解/重构：许多非贵金属催化剂（如Ni、Fe、Co基材料）在长期电解过程中可能会发生溶解、晶体结构重构或表面氧化，导致活性位点减少和催化性能下降。例如，CoP催化剂在酸性溶液中进行HER时，原位分析表明其主要由近零价Co和还原态P组成，但仍可能存在多种有序和无序相，包含近零价和氧化态的Co以及还原态和氧化态的P，这些组分在操作中可能会发生动态变化 48。
  • 载体腐蚀：如果使用碳材料作为载体，在长期运行中，特别是在高电位下，碳载体可能会被氧化腐蚀，导致催化剂脱落和性能衰减。
  • 气体交叉与泡阻：AEM电解槽中氢气和氧气的交叉渗透会导致H₂在阳极或O₂在阴极被消耗，降低法拉第效率。同时，HER反应产生的氢气泡在电极表面的滞留（泡阻）会阻碍电解质与催化剂的接触，影响传质，尤其在高电流密度下。
  • 离子浸出与毒化：在纯水进料AEMWE中，缺乏电解液的缓冲能力可能导致局部pH波动，影响催化剂稳定性。此外，电解质中微量杂质离子也可能吸附在催化剂表面，导致毒化。

为了应对这些挑战，未来的研究需要进一步关注催化剂的抗腐蚀设计、载体的稳定性提升、气泡管理策略以及对AEMWE操作条件下催化剂动态演变的原位表征，以期实现非贵金属HER催化剂在实际应用中的长期高效稳定运行。

3.3 催化剂-膜界面的协同设计

在AEM电解水制氢技术中，除了优化膜材料和电催化剂本身的性能外，催化剂层与阴离子交换膜（AEM）之间的界面设计对整个电解槽的效率和稳定性也至关重要。高效的界面设计旨在最大化催化剂活性位点的利用率，优化OH⁻离子和水分子的传质，并降低界面电荷传输电阻。这通常通过界面工程、3D自支撑结构以及离子聚合物（ionomer）的精确匹配来实现52。

2.3.1 界面工程

界面工程通过改性催化剂层或膜表面，以提高两者之间的亲和性和传质效率。

  • 等离子体处理提升亲水性：通过等离子体处理（如氧等离子体）可以在催化剂层或膜表面引入亲水基团，从而改善界面润湿性，促进水分子和OH⁻离子的有效传输。增强的亲水性有助于形成更均匀的催化剂-离子聚合物混合层，减少“干区”的形成，确保催化剂颗粒被离子聚合物充分包覆。
  • 表面涂层改性：在催化剂表面或AEM表面施加特定的涂层，可以调节界面化学环境，优化局部pH值，或形成保护层以提高稳定性。例如，在NiFeOH催化剂上涂覆阴离子交换离子聚合物，可以调节膜与电极之间的局部pH环境，有效延长氢氧根阴离子向电极的扩散长度，从而显著降低Ni的溶解，将稳定性提高6倍53。这种界面工程策略揭示了离子聚合物不仅在离子传导中发挥作用，还在稳定电极-电解质界面方面具有关键功能，特别是在纯水进料的AEMWE中。

2.3.2 3D自支撑结构

传统的膜电极组件（MEA）通常通过将催化剂墨水涂覆到气体扩散层（GDL）或膜表面来制备，这种结构可能导致催化剂层较厚，传质阻力较大。3D自支撑电极结构，如泡沫金属（Ni泡沫、Ti泡沫）负载催化剂，能够提供：

  • 更低的传质阻力：开放的多孔结构有利于气体产物的快速逸出，减少气泡堵塞，并促进反应物的有效传输。
  • 更高的活性位点暴露：三维骨架能够支撑高负载量的催化剂，同时保持高比表面积，最大化催化剂的利用率。
  • 优异的导电性：金属泡沫基底本身具有优异的导电性，可以直接作为集流体，降低界面接触电阻。例如，将催化剂直接生长在镍泡沫上作为自支撑电极，可以显著提高OER和HER的性能，简化MEA的制备过程52。这种设计能够促进OH⁻离子传输和水供应，并提供额外的气泡释放通道。例如，具有纳米结构分层多孔非贵金属基电催化剂的AEM电解槽在10 cm²的活性面积下，仅需1.66 V即可达到10 mA cm⁻²的电流密度，并在300小时内保持95%-97%的优异稳定性54。

2.3.3 离子聚合物的匹配性

离子聚合物（ionomer）在催化剂层中扮演着至关重要的角色，它负责连接催化剂颗粒，形成OH⁻离子传导通道，并促进水分子向催化剂活性位点的传输。离子聚合物的化学性质、含量和分布对催化剂层的性能有着显著影响。

  • 离子聚合物含量优化：在催化剂层中，离子聚合物的含量需要进行优化。过高的离子聚合物含量会覆盖催化剂活性位点，增加传质阻力；过低的含量则会导致离子传导路径不连续，影响催化剂层的整体性能。研究表明，中等含量的离子聚合物可以导致最低的过电位、最高的有效表面积和最低的催化剂层电阻55。
  • 化学结构与AEM匹配：理想情况下，催化剂层中的离子聚合物应与AEM具有相似的化学骨架和离子交换基团，以确保良好的界面兼容性和OH⁻传输连续性。然而，最新的研究指出，对于支持电解质进料的AEMWE系统，离子聚合物并非离子传导的必需品，其主要作用在于维持催化剂层的结构和稳定性。这意味着可以选用与AEM化学结构不同的离子聚合物，从而为设计高活性、高稳定性的AEMWE提供新的途径，缓解对离子聚合物稳定性的顾虑55。
  • 离子聚合物层的设计：在AEMWE的低碱性甚至纯水进料条件下，离子聚合物除了在催化剂层中提供离子传导路径外，还可能形成离子聚合物中间层（Ionomer Interphase Layers, ITL）。研究表明，在阴极催化剂层和膜之间放置独立的离子聚合物顶层（ITL）作为中间层，可以最有效地提高低pH进料条件下的电池性能。ITL的作用被认为是离子传输的“缓冲器”，促进OH⁻从阴极向阳极的迁移，即使在pH 14的强碱性条件下也能发挥作用56。

2.3.4 膜电极界面图案化技术

膜电极界面图案化技术是一种通过微观结构设计来优化传质和电荷传输的创新方法。例如，通过机械应力诱导的离子通道缩短，可以在AEM表面形成特定的图案，以引导OH⁻离子更高效地传输。这种图案化处理可以创建微观的亲水/疏水区域，促进水渗透和离子传导，同时减少气体在界面的滞留，从而提高电解槽的整体性能。

综上所述，催化剂-膜界面的协同设计是提升AEM电解水制氢效率和耐久性的关键。通过精密的界面工程、创新的3D自支撑电极结构以及优化的离子聚合物匹配策略，可以有效解决传质、电荷传输和稳定性等方面的挑战，推动AEMWE技术走向更广泛的商业应用。

4. 膜电极组件（MEA）与系统集成优化

膜电极组件（MEA）是AEM电解水制氢系统的核心部件，其设计、制备和优化直接决定了电解槽的效率、耐久性和成本。MEA通常由阴离子交换膜、两层催化剂层（阴极和阳极）以及两层气体扩散层（GDL）组成。对MEA的系统性优化涵盖了结构设计、操作条件与系统管理以及实际工况下的耐久性验证，旨在提升整体性能并加速商业化进程。

4.1 MEA结构设计与性能提升

MEA的结构设计是实现高性能AEM电解水制氢的关键。当前，MEA的制备方法主要分为传统催化剂涂覆膜（Catalyst Coated Membrane, CCM）和新型3D有序/自支撑MEA两种，每种方法都有其独特的优势和挑战。

4.1.1 传统催化剂涂覆膜（CCM）

在传统CCM方法中，催化剂墨水（通常是催化剂粉末、离子聚合物和溶剂的混合物）直接涂覆在AEM两侧或气体扩散层（GDL）上，形成催化剂层。这种方法制备简单，易于批量生产。

  • 优点：
    • 制备相对简单：易于实现规模化生产，成本较低。
    • 膜与催化剂层接触紧密：理论上能提供较好的离子传输路径。
  • 挑战与限制：
    • 催化剂层厚度与孔隙率：催化剂层过厚会增加传质阻力，导致反应物和产物（OH⁻、H₂O、H₂、O₂）的传输受限，特别是在高电流密度下，H₂和O₂气泡的排出受阻，容易在催化剂层内形成“气堵”现象，覆盖活性位点，降低有效催化面积。而过薄的催化剂层可能活性位点不足，导致性能不佳。优化催化剂层的孔隙率至关重要，适当的孔隙率既能保证足够的活性位点暴露，又能提供有效的传质通道。
    • 离子聚合物分布不均：在制备过程中，离子聚合物在催化剂层中的分布可能不均匀，导致部分催化剂颗粒无法有效传导OH⁻离子，降低了催化剂利用率。
    • 界面接触电阻：催化剂层与气体扩散层之间的接触可能存在电阻，影响电子传输效率。
    • 机械稳定性：直接涂覆在膜上的催化剂层在高电流密度或长期运行中可能存在脱落的风险，影响MEA的耐久性。

4.1.2 3D有序/自支撑MEA

为了克服传统CCM的局限，研究人员积极开发新型3D有序/自支撑MEA结构。这些结构旨在通过改进电极的宏观和微观结构来优化传质、电荷传输和催化剂利用率。

  • 特点与优势：

    • 三维自支撑结构：催化剂直接生长在具有导电性的三维多孔基底（如镍泡沫、钛泡沫、多孔金属纤维毡）上，形成自支撑电极。这种结构可以显著增加电极的宏观比表面积，提供丰富的活性位点，并形成开放的通道，极大促进了H₂O/OH⁻的传质和H₂/O₂气体的快速排出，从而有效降低气泡阻力 5257。例如，在Ni纤维基PTL上，减小孔径和孔隙率可以使电流密度增加20% 57。
    • 优化传质与电荷传输：3D结构为水和离子的传输提供了更直接的路径，减少了扩散距离。同时，金属基底本身作为导电骨架，降低了催化剂层内的电子传输阻力，提升了电荷传输效率 52。
    • 高催化剂利用率：由于催化剂颗粒与导电基底和离子传输通道紧密结合，使得更多的催化剂活性位点得以有效利用。
    • 高机械稳定性：自支撑电极通常具有优异的机械强度，能够有效抵抗气泡冲刷和长期运行中的机械应力，避免催化剂脱落问题。
    • 简化MEA制备：在某些设计中，可以直接将自支撑电极与AEM进行压合，简化了MEA的制备流程。

  • 案例分析：

    • NiFe基OER催化剂直接生长在泡沫镍上：这种方法利用泡沫镍本身作为集流体和催化剂载体，构建了高效的OER电极。研究表明，与传统的涂覆型电极相比，自支撑电极在相同催化剂负载量下，可以实现更高的电流密度和更低的过电位。
    • 多孔输运层（PTL）的优化：PTL是MEA中的一个关键组件，其形态和组成对设备性能有显著影响。例如，有研究表明，使用低孔隙率的合金PTL，特别是如不锈钢PTL，与Ni纤维基PTL相比，电流密度可提高80% 57。这表明PTL材料本身也可能具有催化活性。然而，合金PTL的长期稳定性仍需关注，因为它们在测试后可能发生结构重构和腐蚀 57。
    • 微孔层（MPL）的引入：MPL作为PTL和催化剂层之间的中间层，可以通过调节孔径、厚度和结构，改善两相传输现象，增强催化剂利用率，并强化水毛细力，从而降低动力学和传输过电位 58。

4.1.3 大尺寸单电池的测试数据与挑战

MEA性能的最终衡量标准是在实际电解槽中的表现。研究人员通常使用小尺寸（如1 cm²、5 cm²）单电池进行实验室性能验证，但向大尺寸（如50 cm²、100 cm²甚至更大）扩展时会面临新的挑战。

  • 性能瓶颈：

    • 电流密度：目前在80°C、1M KOH条件下，某些高性能膜在1.8V下可达到5.25 A/cm² 59。然而，在大尺寸MEA中实现如此高的电流密度并保持均匀性仍然是一个挑战。
    • 均匀性与一致性：在大尺寸MEA的制备过程中，催化剂层的厚度、孔隙率、离子聚合物分布以及膜的厚度等参数很难保持高度均匀和一致。这种不均匀性会导致MEA内部电流分布不均，局部过热，甚至加速降解。
    • 水管理与气泡管理：随着MEA尺寸的增大，水在膜和电极中的传输路径变长，气泡的排出也变得更加困难。在大电流密度下，如何有效供给水并快速排出生成的H₂和O₂气泡，以避免气堵和局部“干区”的形成，是制约大尺寸MEA性能的关键问题。
    • 机械应力与膨胀：大尺寸AEM在吸水膨胀和工作温度变化下产生的机械应力更大，这可能导致MEA层间剥离、膜破裂或电极变形，影响长期稳定性。

  • 提升策略：

    • 优化制备工艺：开发先进的涂覆技术（如喷涂、狭缝涂布）和电极生长技术，以确保大尺寸MEA的均匀性和一致性。
    • 流场设计：优化电解槽的流场板设计，以实现反应物和产物在MEA表面的均匀分布和高效传输。
    • 集成多尺度建模：利用多尺度模型预测大尺寸MEA内的传质、电荷传输和热分布，指导结构优化和材料选择。

总的来说，MEA的结构设计正从传统的层状结构向更高效的3D有序/自支撑结构演进，以期通过优化内部微环境来提升传质、电荷传输和催化剂利用率。尽管在小尺寸单电池中已取得显著进展，但如何将这些性能优势扩展到大尺寸MEA并解决规模化制备中的均匀性、一致性以及水气管理等挑战，仍是AEM电解水制氢技术商业化道路上的重要课题。

4.2 操作条件与系统管理优化

除了MEA的结构优化，电解水制氢系统的操作条件和系统管理策略对AEMWE的性能、效率和耐久性也具有决定性影响。核心的优化方向包括电解质进料方式、温度、电流密度以及启停操作的管理。

4.2.1 电解质进料（纯水/稀碱液）对系统简化与长期稳定性的影响

当前AEMWE系统面临的一个关键选择是采用稀碱液进料还是纯水进料。

  • 稀碱液进料：

    • 优势：传统的AEMWE系统通常需要循环稀碱性电解液（如1 M KOH或更稀的NaOH溶液）来确保高离子电导率和催化剂的稳定运行。碱性环境能有效提升水解离速率和OH⁻传输效率，从而实现较高的电流密度和能量效率。
    • 挑战：然而，循环稀碱液系统引入了额外的成本和操作复杂性，包括电解液制备、储存、循环泵、冷却器以及防腐蚀材料（如不锈钢）。这些增加了系统的BOP（Balance of Plant）成本和维护需求，并且存在潜在的泄漏风险。此外，稀碱液进料通常意味着电极上离子聚合物的必要性降低，甚至可以省去离子聚合物，但同时可能带来局部pH梯度和离子传输不畅的问题。

  • 纯水进料（Alkali-Free Water Feed）：

    • 优势：纯水进料是AEMWE技术最具吸引力的发展方向之一 6。它能够显著简化系统设计，完全去除碱液循环系统，降低BOP成本和操作复杂性，提高安全性，并延长设备寿命 6。纯水进料系统还避免了对碱液处理和回收的需求，使得AEMWE更具环境友好性。
    • 挑战：在纯水进料条件下，AEMWE面临的最大挑战是电极反应动力学和离子传导效率的下降。由于缺乏体相电解液提供的OH⁻，HER和OER反应的局部pH值可能会急剧下降或升高，导致催化剂活性下降和稳定性恶化。此外，OH⁻的生成主要依赖水在催化剂表面的解离，需要更高效的OER催化剂和专门设计的离子聚合物来维持局部高pH环境和OH⁻的传输 6。
    • 性能突破：尽管存在挑战，纯水进料AEMWE已取得了显著的性能突破。例如，一些研究团队通过在电极中引入离子聚合物来增加局部OH⁻浓度，促进OER反应，实现了在纯水进料下高达1900 mA cm⁻²的电流密度（在1.90 V电压下） 60。这表明，通过精细的材料选择和电极结构设计，纯水进料AEMWE的性能可以达到甚至超越稀碱液进料系统的水平。

4.2.2 温度（30-80℃）对性能与降解的作用机制

操作温度是影响AEMWE性能的关键参数之一。

  • 对性能的影响：升高温度通常会加速电化学反应动力学，提高OH⁻在AEM中的传导率，并降低气体溶解度，从而降低电池电压和提高能量效率。在30-80℃范围内，通常表现出“热性能”的提升。
  • 对膜降解的影响：然而，高温也会加速AEM的化学降解（如季铵基团的霍夫曼消除和亲核攻击）和机械降解（如蠕变）。尤其是在80℃以上，许多现有AEM的稳定性会显著下降。因此，选择耐高温的AEM材料对于在较高温度下实现高效稳定运行至关重要。
  • 对催化剂团聚的影响：高温还可能加速催化剂颗粒的烧结和团聚，导致活性表面积减少，进而降低催化剂活性。例如，金属纳米颗粒在高温下容易发生Ostwald熟化，造成颗粒长大，影响长期稳定性。

4.2.3 电流密度（0.5-8 A/cm²）对性能与降解的影响

电流密度直接反映了制氢速率，是电解槽运行的关键指标。

  • 对性能的影响：提高电流密度可以增加氢气产量，但通常也会导致电池电压升高，因为欧姆损失、传质损失和电荷转移过电位都会随电流密度增加而增大。在高电流密度下，传质阻力（特别是水和OH⁻的传输以及气体产物的排出）成为主要的性能限制因素。
  • 对膜降解的影响：高电流密度会产生更多的热量，局部温度升高，可能加速膜的化学和机械降解。此外，高电流密度下活性氧物种（ROS）的生成量也可能增加，加剧膜的氧化降解。
  • 对催化剂团聚的作用机制：高电流密度下的强电场和高温环境可能导致催化剂颗粒的迁移和团聚，特别是对于负载在碳载体上的纳米催化剂。此外，剧烈的气体析出也会对催化剂层产生机械冲击，导致催化剂脱落或结构破坏。

4.2.4 启停操作对膜降解和催化剂团聚的影响

AEMWE系统与可再生能源耦合时，频繁的启停操作是不可避免的。

  • 膜降解：启停操作会导致MEA内部温度和湿度循环变化，引起膜的反复水合-脱水，从而产生尺寸变化和机械应力。这种应力循环可能导致膜的疲劳损伤，产生裂纹或孔洞，加速膜的机械降解。
  • 催化剂团聚/失活：在启停过程中，电极电位可能会发生剧烈波动，导致催化剂的氧化-还原循环，加速催化剂溶解、重构或团聚。例如，在低电流密度或停机状态下，电极可能会发生腐蚀，而在重新启动时，部分活性位点可能已经失活或结构改变。此外，启停操作期间，电解槽内可能形成瞬态的局部pH梯度或气体滞留，进一步加速催化剂的降解。

有效的系统管理策略包括：优化启停程序以减少电压波动和温度冲击；在膜中引入交联剂或无机填料以提高尺寸稳定性；以及开发对启停操作更具鲁棒性的催化剂材料和电极结构。通过对操作条件的精细控制和系统优化，AEMWE可以实现更长的寿命和更高的运行效率，为绿色氢能的商业化生产提供可靠保障。

4.3 实际工况下的耐久性验证

AEM电解水制氢技术的商业化成功，最终取决于其在实际运行工况下的长期稳定性和耐久性。因此，对MEA进行数千小时的连续运行测试，并深入分析其失效模式，对于指导材料和系统优化至关重要。

4.3.1 长期运行数据与性能衰减

近五年来的研究已积累了大量的AEMWE长期运行数据，尽管与商业化目标（通常要求数万小时的寿命）仍有差距，但已展示出显著的进步。例如：

  • NiFe-LDH基单电池：在1 A cm⁻²的电流密度下实现了1000小时的稳定运行，降解速率为84 µV h⁻¹ 61。该研究通过电化学数据与化学物理表征相结合，分析了NiFe-LDH基电池的性能和降解行为，发现即使存在Fe浸出、阴离子传导粘合剂化合物的变化以及催化剂本体形态改变，NiFe-LDH基单电池仍表现出高性能和耐久性，表明Ni-Fe相的导电性是获得高性能电解槽的关键因素 61。
  • Ir-Ru固溶体催化剂：在低碱性电解液（0.05 M KOH）中，采用Ir-Ru固溶体催化剂的AEMWE在1 A cm⁻²电流密度下达到1.75 V的电池电压，并表现出超过1000小时的优异耐久性 62。这得益于Ru上H*的高覆盖率，导致动力学缓慢和在高电流操作期间耐久性受限，而Ir-Ru固溶体通过氢溢流机制实现了快速的氢转移动力学 62。
  • N-甲基奎宁环鎓基AEM：基于这种新型季铵盐的PAQ-5 AEM在非贵金属AEM-WE中，实现了在2 V电压下8 A cm⁻²的高电流密度，并在梯度恒流测试中稳定运行超过2446小时，展现出卓越的稳定性 63。
  • 基准材料纯水进料AEMWE：使用市售催化剂、膜、离子聚合物和气体扩散层组成的AEM电解槽，在纯水进料、55 °C、0.5 A cm⁻²条件下，在经过初始活化后，性能衰减率为0.67 mV h⁻¹ 64。

这些数据表明，AEMWE在短中期（千小时级别）运行中的性能已接近甚至达到某些应用场景的需求。然而，与PEMWE商业化所需的数万小时寿命相比，AEMWE仍有显著提升空间 9。

4.3.2 失效模式分析

在长期运行过程中，AEMWE的性能衰减主要源于以下几种失效模式：

  1. 膜的化学降解：

    • 主链断裂：在高温强碱性环境下，AEM聚合物的主链可能发生断裂，特别是对于含有易水解键（如醚键、酯键）的聚合物。这会导致膜的机械强度下降，甚至碎片化。例如，季铵化聚苯醚（QPPO）基AEM在pH中性条件下、60°C纯水中浸泡10个月后会断裂成碎片，这归因于氧或OH•自由基攻击重排亚基上的甲基，形成醛或羧基附着在CH基团上 65。
    • 季铵基团降解：季铵基团在强碱性条件下易发生霍夫曼消除、亲核取代等反应，导致离子交换容量（IEC）下降，从而降低OH⁻传导率。这也是AEM最常见的化学降解机制。

  2. 催化剂脱落与团聚：

    • 脱落：长期运行过程中，气泡的冲刷、电极膨胀收缩产生的机械应力以及催化剂层与载体之间的结合力减弱，都可能导致催化剂颗粒从气体扩散层或集流体上脱落，减少活性位点。
    • 团聚/烧结：高温和高电流密度可能加速纳米催化剂颗粒的奥斯特瓦尔德熟化（Ostwald ripening）和烧结，导致颗粒尺寸增大，比表面积和活性位点数量减少。
    • 腐蚀与溶解：非贵金属催化剂（如NiFe基）在长期运行中可能发生部分金属元素的溶解或腐蚀，导致活性损失。例如，NiFe-LDH基电池中存在Fe浸出 61。

  3. 气体交叉（H₂/O₂混合）：

    • 膜的渗透性增加：膜的降解（如产生微孔或裂纹）会导致氢气和氧气更容易通过膜，造成气体交叉。气体交叉不仅降低法拉第效率，还可能引起安全隐患（H₂/O₂混合气体的爆炸风险）。
    • 局部压力不均：电解槽内部压力不均或气体产物排出不畅也可能导致气体在MEA内部堆积，增加交叉风险。

4.3.3 加速老化测试与实际工况的相关性

为了快速评估材料的耐久性，研究人员通常采用加速老化测试（Accelerated Stress Tests, ASTs）。

  • ASTs方法：常见的ASTs包括在更苛刻的条件下进行测试，例如：

    • 高温高浓度碱液浸泡：如在80℃、10 M NaOH或更高浓度的NaOH溶液中浸泡膜材料 66。这种测试主要用于评估膜的化学稳定性。例如，N-甲基奎宁环鎓基AEM在10 M NaOH、80°C下稳定超过1800小时未发生化学降解 66。
    • 电化学循环伏安测试（CV）：通过快速电压循环来模拟启停工况或电压瞬变，评估催化剂的稳定性。
    • 恒电流或恒电压连续运行：在高于正常工作电流密度或电压的条件下进行长期运行。

  • 相关性讨论：

    • 优点：ASTs能够在较短时间内提供材料性能变化趋势的初步评估，有助于筛选出具有潜力的材料。
    • 挑战：然而，ASTs的结果与实际工况之间的相关性仍需深入研究。苛刻的测试条件可能导致与实际运行中不同的降解机制，或者加速某些不具有代表性的失效模式。例如，高温高浓度的KOH溶液浸泡测试，可能无法完全模拟实际电解过程中膜内外的pH梯度、自由基攻击以及机械应力等复杂因素。因此，建立可靠的ASTs协议，并将其与实际工况下的长期运行数据进行比对和校准，是当前AEMWE耐久性研究的重要方向。

总而言之，AEMWE的耐久性验证已取得显著进展，但仍需更长的运行时间和更全面的失效分析，以应对复杂的实际工况挑战。未来研究应侧重于开发更具代表性的ASTs，并结合原位表征技术，深入理解降解机制，为高性能、长寿命AEMWE的商业化奠定基础。

5. 挑战与未来发展方向

5.1 当前技术瓶颈分析

尽管AEM电解水制氢技术在材料创新、催化剂开发和系统集成方面取得了显著进展，但其商业化应用仍面临一系列严峻的技术瓶颈。这些挑战主要体现在膜材料的稳定性、催化剂的耐久性、纯水进料系统的效率以及整体的商业化成本等方面。

5.1.1 膜材料的高温（>60℃）稳定性不足

AEM电解水制氢系统在较高温度下运行（如60-80°C）可以显著提高反应动力学、降低电池电压和提高能量效率。然而，目前大多数AEM材料，特别是其季铵基团，在高于60°C的强碱性环境中仍表现出稳定性不足的问题 17。高温会加速季铵基团的霍夫曼消除和亲核取代反应，导致离子交换容量下降和离子电导率衰减，进而影响电解槽的长期运行性能。尽管一些新型AEM（如含氟聚芴基AEM）在80°C、2 M KOH溶液中展现出千小时级别的稳定性，但要达到数万小时的商业运行寿命，高温下的化学稳定性仍需大幅提升 17。此外，高温还会加剧膜的机械降解，如蠕变和尺寸不稳定，增加MEA分层或破裂的风险。

5.1.2 催化剂长期耐久性（>5000 h）未达标

AEMWE对非贵金属催化剂的兼容性是其核心优势，但这些非贵金属催化剂在实际运行条件下的长期耐久性仍是主要挑战。目前，OER和HER催化剂在数百到数千小时的测试中表现出良好的活性和稳定性 5516768。例如，Ir-Ru固溶体催化剂在低碱性电解液中实现1000小时以上的耐久性 62，而MoC/Ni复合催化剂在双功能催化剂测试中展现出50小时的稳定性 69。更有研究报告了MoS/NiS催化剂在2 A cm⁻²下稳定运行2500小时 68，以及柔性WS₂超结构在1 A cm⁻²下稳定运行1000小时，衰减率可忽略不计 51。然而，这些测试时长距离商业化所需的5000小时甚至更长的寿命要求仍有差距。

催化剂的失效模式包括：

  • 金属元素溶解和重构：如NiFe基OER催化剂中Fe的浸出，以及催化剂活性位点的动态重构，可能导致活性下降 70。
  • 颗粒团聚和烧结：纳米催化剂颗粒易发生奥斯特瓦尔德熟化，导致比表面积减少和活性位点丧失。
  • 载体腐蚀：如果使用碳载体，在OER侧高电位下可能发生碳氧化，导致催化剂脱落。
  • 气泡脱附效率：尤其在高电流密度下，反应产物气泡（O₂和H₂）在催化剂表面的积累会导致活性位点覆盖，增加传质阻力，从而降低效率和加速局部降解 71。

5.1.3 纯水进料系统效率与碱液系统的差距

纯水进料（Alkali-Free Water Feed）是AEMWE实现系统简化和降低BOP成本的理想方向 6。然而，在缺乏体相碱性电解液缓冲的情况下，纯水进料系统面临更大的挑战。在OER和HER过程中，水解离产生的OH⁻在催化剂层中的传输路径变长，局部pH值可能出现剧烈波动，导致反应动力学受限。这通常会导致纯水进料AEMWE的能量效率低于使用稀碱液的系统。虽然部分研究通过优化催化剂层中的离子聚合物和电极结构取得了显著进展，如在超纯水进料下达到171 mA cm⁻²的电流密度 72，但要普遍实现与碱液系统相当甚至更高的效率，仍需在水解离机制、OH⁻传输通道和催化剂界面工程方面进行更深入的研究。

5.1.4 商业化成本分析

AEMWE的最终目标是实现具有竞争力的绿色氢气生产成本。虽然AEMWE在理论上能够使用非贵金属催化剂和廉价材料，从而降低成本，但目前膜和催化剂的制造成本仍是主要障碍。

  • 膜材料成本：高性能AEM的合成和规模化生产成本较高。
  • 催化剂成本：虽然非贵金属催化剂成本低于Pt/Ir，但其负载量通常较大，且长期稳定性不足导致的频繁更换也会增加运行成本。此外，为了达到高效率，部分催化剂仍需少量贵金属（如Ru 73）。
  • 整体系统成本（CAPEX和OPEX）：除了膜和催化剂，电解槽的其他部件（如多孔传输层 57）以及BOP（Balance of Plant）的成本也需要优化。尽管纯水进料有助于降低BOP成本，但如果系统效率低下或寿命不足，OPEX（运营成本）会显著增加。目前，AEMWE的成本尚未完全具备与传统碱性电解或PEMWE（考虑到其已达到的规模效应）竞争的优势。DOE设定的2026年氢气生产成本目标为2.0美元/GGE，而采用RuMoNi催化剂的AEM电解槽有望将成本降至0.85美元/GGE，显示出其强大的成本竞争力。

综上所述，当前AEM电解水制氢技术的核心挑战在于如何在保证高效率的前提下，大幅提升膜和催化剂在实际操作条件下的长期稳定性，并最终实现经济可行的规模化生产。解决这些瓶颈将是AEMWE走向商业成功的关键。

5.2 关键技术突破路径

面对AEM电解水制氢技术当前的技术瓶颈，未来的发展将聚焦于多学科交叉创新，通过新型表征技术、标准化评估协议的建立以及材料的颠覆性设计，来加速技术的成熟和商业化。

5.2.1 新型表征技术的发展

深入理解AEM电解水制氢过程中的复杂物理化学现象，特别是膜材料、催化剂和界面在操作条件下的动态变化，是实现技术突破的关键。为此，开发和应用新型原位表征技术显得尤为重要。

  • 原位中子散射解析离子-水-膜动态：中子散射技术对氢元素（包括水分子中的氢和离子传导介质中的氢）具有高灵敏度，能够穿透电解槽组件，实现对材料内部结构和动态过程的无损探测。原位中子散射（In-situ neutron scattering）可以用来：

    • 解析水合行为：研究AEM在不同温度、湿度和电流密度下的水合程度及水分子分布，揭示水在离子传导通道中的动态作用。
    • 追踪离子传输路径：通过氘代技术，区分不同形式的氢，进而解析OH⁻离子在膜内的微观传输路径和机制，以及水合离子团簇的形成和演变。
    • 监测微观结构变化：实时监测膜在运行过程中的微相分离结构、孔道结构和结晶度的变化，为膜材料的稳定性设计提供指导。
    • 界面动态：研究膜-催化剂界面处水分子和离子的传输行为，揭示界面传质阻力来源，为优化界面结构提供数据支持。

  • 同步辐射X射线技术：原位同步辐射X射线衍射（XRD）、X射线吸收谱（XAS）等技术可以用于实时监测催化剂在电化学反应过程中的晶体结构、电子态和局部原子排列的变化，从而揭示活性位点形成、演变及失活机制。

  • 电化学-质谱联用技术（EC-MS）：实时检测电解过程中气态产物（H₂、O₂）以及可能降解产物的生成，帮助分析副反应和降解路径。

  • 先进显微技术：原位透射电子显微镜（TEM）和扫描电子显微镜（SEM）结合能谱分析（EDS），可以对催化剂颗粒的团聚、形貌变化以及膜表面损伤进行纳米尺度的实时观察。

这些先进的原位表征技术将提供前所未有的微观洞察力，为理解失效机制、指导材料设计和优化电解槽运行提供关键数据支持。

5.2.2 标准化评估协议的建立

目前，AEM电解水制氢领域的研究成果评估标准不一，导致不同实验室和研究团队之间的数据难以直接比较，阻碍了技术的快速发展。建立一套全面、科学、规范的标准化评估协议对于推动AEMWE的商业化至关重要。

  • AEMWE性能测试规范：

    • 电化学性能测试：统一电流-电压曲线（I-V曲线）的测试条件（如温度、压力、电解质浓度、流速）、启动和活化程序、以及数据采集和处理方法。明确规定过电位、能量效率和法拉第效率的计算标准。
    • 长期耐久性测试：制定标准化的加速老化测试（ASTs）协议，包括测试温度、电流密度、测试时长、启停循环次数、以及性能衰减速率的评估指标（如电压衰减率 mV/h）。同时，需要明确ASTs与实际运行寿命的相关性评估方法。
    • 气体交叉率测试：统一气体渗透率的测量方法，包括测试气体、压力差和检测手段，确保对安全性能的准确评估。
    • 材料表征：对膜材料的离子电导率、离子交换容量（IEC）、机械强度、吸水率和溶胀率等关键参数，以及催化剂的比表面积、孔隙结构、晶体结构和元素组成等进行标准化测量。

  • 数据共享与数据库建设：建立一个开放的AEMWE性能数据库，汇集全球研究成果，为材料筛选、模型验证和技术路线评估提供依据。

5.2.3 创新材料设计与开发

材料创新是AEMWE技术突破的核心驱动力，未来的研究方向包括：

  • 耐碱交联网络AEM：

    • 新型高稳定性阳离子基团：开发除季铵盐之外，或对现有季铵基团进行结构优化（如空间位阻型、N-杂环型、多取代叔胺型）的新型阳离子基团，提高其在高温强碱环境下的化学稳定性。例如，使用具有柔性乙二醇交联剂的聚三联苯异靛红哌啶鎓共聚物（PTPBHIN-O）AEM，在80°C下具有高氢氧根电导率（151.69 mS cm⁻¹）和低溶胀率（10.53%），并且在80°C、3 M NaOH中处理1600小时后，仍能保持≥85%的氢氧根电导率，表明其优异的碱性稳定性 74。
    • 强韧交联骨架：通过设计高交联密度、刚性骨架或互穿网络结构，提高膜的机械强度、尺寸稳定性和抗氧化能力。例如，将聚苯乙烯基AEM与O-PBI共混，可以提高其氢氧根电导率（69 mS cm⁻¹@80°C）和机械稳定性 75。
    • 功能梯度膜：设计具有功能梯度的AEM，例如在阳极侧具有更高抗氧化性的结构，在阴极侧具有更高离子电导率的结构，以适应不同电极侧的运行环境。

  • 高活性无Pt催化剂：

    • 新型非贵金属合金/化合物：继续开发和优化NiFe基、Co基、Mo基、Ru基（如高分散Ru/C 11）以及过渡金属磷化物（TMPs）、硫化物、氮化物等非贵金属催化剂，重点关注其在纯水或低浓度碱性电解液中的HER和OER活性及稳定性。
    • 单原子/双原子催化剂：利用单原子或双原子催化剂的最大原子利用率和独特的电子结构，提高催化剂的本征活性和选择性。
    • 界面工程与缺陷调控：通过精准控制催化剂的表面重构、缺陷工程以及与载体或离子聚合物的界面相互作用，优化电子结构和传质路径。
    • 多功能催化剂：开发具有HER和OER双功能活性的催化剂，简化电解槽结构，降低成本。例如，将Co掺杂到NiFe-LDH中可以提高导电性并增强OER活性 11。

5.2.4 海水/低品位水直接电解的潜在应用

实现海水或低品位水（如工业废水、淡化盐水）的直接电解制氢，将是AEMWE技术的重大突破，因为它能彻底摆脱对淡水资源的依赖，进一步降低制氢成本。

  • 挑战：海水含有大量氯离子（Cl⁻），在电解过程中易发生氯析出反应（Chlorine Evolution Reaction, CER），与OER形成竞争，并可能对催化剂和膜材料造成腐蚀。同时，海水中存在的各种金属离子（如Na⁺、Mg²⁺、Ca²⁺）可能吸附在膜表面，堵塞离子通道，影响离子传导。
  • 突破路径：
    • 高选择性催化剂：开发对OER具有高选择性，能够有效抑制CER的催化剂。这可能需要通过材料设计来调节活性位点对水分子和氯离子的吸附强度。
    • 抗氯离子膜材料：设计对氯离子具有排斥作用或高耐受性的AEM，防止氯离子通过膜，保护阴极免受氯气污染。
    • 新型电解槽设计：探索分体式电解槽或新型膜电极结构，将OER和HER区域有效隔离，以应对海水复杂组分带来的挑战。
    • 预处理技术：虽然目标是直接电解，但在某些情况下，结合高效、低成本的预处理技术（如电化学脱盐）也可能是一种可行的方案。

AEMWE技术正快速发展，通过多方面的协同努力，有望克服现有瓶颈，实现更高效、更稳定、更经济的绿色氢能生产。

5.3 商业化前景与产业协同

AEM电解水制氢技术，凭借其独特的优势和快速发展的势头，在全球绿色氢能转型中占据着日益重要的战略地位。尽管目前仍面临技术挑战，但其商业化前景广阔，有望在2030年前实现大规模绿氢制备。

5.3.1 政策支持与市场驱动

全球对气候变化的关注和碳中和目标的设定，为绿色氢能产业的发展提供了强大的政策驱动力。欧盟、美国、中国、日本等主要经济体纷纷出台了氢能发展路线图和战略规划，明确了绿色氢能生产、运输和应用的长期目标。

  • 欧盟氢能战略：目标到2030年实现40 GW电解水制氢能力，并计划在欧洲建立大规模可再生氢的生产和消费市场，这将需要每年数百万吨的绿色氢气，为AEMWE技术提供了巨大的市场空间 1。
  • 美国氢能路线图：同样强调通过电解水制氢实现2050年脱碳目标，并设立了降低绿氢生产成本的具体目标（如2美元/公斤氢气）。美国能源部（DOE）的“H2@Scale”计划等，通过资金投入和技术示范，加速氢能技术的研发和商业化进程。有研究指出，采用RuMoNi催化剂的AEM电解槽有望将氢气生产成本降至0.85美元/GGE，远低于DOE设定的目标，预示着其强大的成本竞争力。
  • 其他国家与地区：中国、日本、韩国等亚洲国家也在大力推动氢能发展，将其视为能源结构转型的重要组成部分。例如，中国将氢能纳入国家战略性新兴产业，推动技术创新和产业布局。

这些政策支持和市场需求，不仅为AEMWE技术提供了明确的发展方向，也吸引了大量投资，加速了从实验室研究到工业应用转化的进程。

5.3.2 产业链布局与技术成熟度

AEM电解水制氢的商业化成功，依赖于完整的产业链布局和各环节技术的协同发展。目前，产业链的各个环节都在积极发展：

  • 膜材料供应商：一些公司和研究机构已经开始开发和生产商业化的AEM膜，并在离子传导率、机械强度和碱性稳定性方面取得了显著进步。例如，一些新型AEM已能在80°C、10 M NaOH中稳定超过1800小时，显示出优异的耐久性 66。
  • 催化剂制造商：针对OER和HER，非贵金属催化剂的开发已取得突破性进展，性能接近甚至部分超越贵金属催化剂。例如，通过三嗪交联和吡啶封端技术制备的AEM在AEMWE中表现出优异的性能，使电解槽在2V电压下达到3.0 A cm⁻²的电流密度，并在1.6 A cm⁻²的高电流密度下稳定运行约430小时，这超越了大多数AEMWEs的性能 76。高性能的缺陷工程铁镍羟基氧化物OER催化剂也在积极推广中 77。
  • 电解槽系统集成商：多家公司正在开发和测试商业化AEM电解槽，其电流密度和效率已接近甚至达到PEMWE的水平。例如，在80°C、5 wt% KOH下，AEMWE在1.8V电压下可实现5.23 A cm⁻²的电流密度 78。随着规模化生产技术的成熟，电解槽的成本有望进一步降低。
  • 上游原材料和下游应用：绿色氢能的生产成本下降，将进一步推动其在工业、交通、电力等领域的应用，形成良性循环。

5.3.3 产学研合作的关键作用

加速AEMWE技术的商业化落地，离不开产学研各方的紧密合作。

  • 基础研究与应用开发：高校和科研机构在膜材料设计、催化剂机理探索、新型表征技术等方面发挥着基础性作用。例如，通过原位中子散射等先进技术深入解析AEMWE运行机制，为材料创新提供理论指导。
  • 工程化与规模化：企业则在工程化设计、中试放大、规模化生产、成本控制以及系统集成方面具有优势。通过将实验室成果转化为可商业化的产品，并进行大规模的示范应用，验证技术的可靠性和经济性。
  • 标准化与规范：行业组织和标准化机构需要与产学研各方合作，制定统一的性能评估标准、测试方法和安全规范，以促进技术的互操作性和市场接受度。

通过建立创新的合作机制，例如联合实验室、产业联盟、政府引导基金等，可以有效整合资源、优化分工、加速技术成果转化。这种协同创新模式将有助于克服技术瓶颈，缩短研发周期，降低商业化风险，最终推动AEM电解水制氢技术在2030年前在全球范围内实现大规模的绿氢生产，为全球能源转型和可持续发展做出贡献。

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参考文献

1What is Next in Anion-Exchange Membrane Water Electrolyzers? Bottlenecks, Benefits, and Future.PubMed

Carlo Santoro, Alessandro Lavacchi, Piercarlo Mustarelli, et al.
ChemSusChem. 2022 Apr 22;15(8):e202200027. doi: 10.1002/cssc.202200027. Epub 2022 Mar 24.
As highlighted by the recent roadmaps from the European Union and the United States, water electrolysis is the most valuable high-intensity technology for producing green hydrogen. Currently, two commercial low-temperature water electrolyzer technologies exist: alkaline water electrolyzer (A-WE) and proton-exchange membrane water electrolyzer (PEM-WE). However, both have major drawbacks. A-WE shows low productivity and efficiency, while PEM-WE uses a significant amount of critical raw materials. Lately, the use of anion-exchange membrane water electrolyzers (AEM-WE) has been proposed to overcome the limitations of the current commercial systems. AEM-WE could become the cornerstone to achieve an intense, safe, and resilient green hydrogen production to fulfill the hydrogen targets to achieve the 2050 decarbonization goals. Here, the status of AEM-WE development is discussed, with a focus on the most critical aspects for research and highlighting the potential routes for overcoming the remaining issues. The Review closes with the future perspective on the AEM-WE research indicating the targets to be achieved.

2Developing Catalysts for Membrane Electrode Assemblies in High Performance Polymer Electrolyte Membrane Water Electrolyzers.PubMed

Sun Seo Jeon, Wonjae Lee, Hyeseong Jeon, et al.
ChemSusChem. 2024 Nov 25;17(22):e202301827. doi: 10.1002/cssc.202301827. Epub 2024 Sep 24.
Extensive research is underway to achieve carbon neutrality through the production of green hydrogen via water electrolysis, powered by renewable energy. Polymer membrane water electrolyzers, such as proton exchange membrane water electrolyzer (PEMWE) and anion exchange membrane water electrolyzer (AEMWE), are at the forefront of this research. Developing highly active and durable electrode catalysts is crucial for commercializing these electrolyzers. However, most research is conducted in half-cell setups, which may not fully represent the catalysts' effectiveness in membrane-electrode-assembly (MEA) devices. This review explores the catalysts developed for high-performance PEMWE and AEMWE MEA systems. Only the catalysts reporting on the MEA performance were discussed in this review. In PEMWE, strategies aim to minimize Ir use for the oxygen evolution reaction (OER) by maximizing activity, employing metal oxide-based supports, integrating secondary elements into IrO lattices, or exploring non-Ir materials. For AEMWE, the emphasis is on enhancing the performance of NiFe-based and Co-based catalysts by improving electrical conductivity and mass transport. Pt-based and Ni-based catalysts for the hydrogen evolution reaction (HER) in AEMWE are also examined. Additionally, this review discusses the unique considerations for catalysts operating in pure water within AEMWE systems.

3High-Efficiency Anion-Exchange Membrane Water Electrolyzer Enabled by Ternary Layered Double Hydroxide Anode.PubMed

Jooyoung Lee, Hyeonjung Jung, Yoo Sei Park, et al.
Small. 2021 Jul;17(28):e2100639. doi: 10.1002/smll.202100639. Epub 2021 Jun 3.
Developing high-efficiency and low-cost oxygen-evolving electrodes in anion exchange membrane (AEM) water electrolysis technology is one of the major challenges. Herein, it is demonstrated that the surface corrosion of a conventional Ni foam electrode in the presence of Fe and V cations can transform it into an electrode with a high catalytic performance for oxygen evolution reaction (OER). The corroded electrode consists of a ternary NiFeV layered double hydroxide (LDH) nanosheet array supported on the Ni foam surface. This NiFeV LDH electrode achieves an OER current density of 100 mA cm at an overpotential of 272 mV in 1 m KOH, outperforming the IrO catalyst by 180 mV. Density functional theory calculations reveal that the unique structure and the presence of vanadium in NiFeV LDH play a key role in achieving improved OER activity. When coupled with a commercial Pt/C cathode catalyst, the resulting AEM water electrolyzer achieves a cell current density as high as 2.1 A cm at a voltage of only 1.8 V in 1 m KOH, which is similar to the performance of the proton exchange membrane water electrolyzer obtained from the IrO and Pt/C catalysts pair.

4Partially amorphous NiFe layered double hydroxides enabling highly-efficiency oxygen evolution reaction at high current density.PubMed

Guijin Yang, Dongyang Fang, Yujun Fu, et al.
J Colloid Interface Sci. 2025 Jan 15;678(Pt C):717-725. doi: 10.1016/j.jcis.2024.09.151. Epub 2024 Sep 16.
Layered double hydroxide (LDH) serves as an innovative catalyst for water electrolysis, showcasing outstanding performance in the oxygen evolution reaction (OER) under alkaline conditions. However, it faces challenges due to its low electrical conductivity and limited accessibility to active sites. In this work, the flexibility advantages of disordered amorphous and ordered crystals in NiFe LDH were combined to improve OER performance and maintain long-term stability. This combination induces a variety of effects, including improving the intrinsic activity, changing the OER mechanism from adsorb evolution mechanism (AEM) to lattice oxygen mechanism (LOM), and promoting the reaction kinetics of the catalyst. Moreover, the porous structure of NiFe LDH can efficiently alleviate the issue of local acidic environment induced by prolonged OER reaction, satisfying the criteria for long-term stability. Therefore, the NiFe-2.0 LDH catalyst only requires an ultralow overpotential of 189 mV at a current density of 10 mA cm with Tafel slope of 43 mV dec. More importantly, the catalyst not only displays excellent electrocatalytic activity with an overpotential of 289 mV but also represents an outstanding stability over 80 h at an ultra-high current density of 1 A cm. This study provides a promising strategy for optimizing the catalytic activity and stability of catalyst at ampere current density, which is expected to achieve commercial applications.

5Micro-Galvanic-Driven Scalable Synthesis of Heterostructured Nanoarrays for Durable Anion Exchange Membrane Water Electrolysis.PubMed

Jian Sun, Lisong Zhong, Shan Chen, et al.
Small. 2025 Aug;21(34):e2503794. doi: 10.1002/smll.202503794. Epub 2025 Jul 10.
The scalable synthesis of alkaline hydrogen evolution (HER) electrocatalysts that integrate high activity with operational durability is essential for advancing practical anion exchange membrane water electrolysis (AEMWE). Herein, vertical Cu-MoNi heterostructures are fabricated via a self-driven galvanic-corrosion-coupled low-temperature reduction strategy, circumventing hydrothermal protocols for scalable electrode fabrication. The catalyst achieves a low overpotential of 276 mV and exceptional stability for up to 2000 h at an ampere-level current density of 1 A cm in 1 m KOH. Integrated in situ Raman and theoretical calculation unveil dual HER-enhancing mechanisms in Cu-MoNi: interfacial water restructuring activates O─H bond cleavage through electric-field-driven free water generation, while heterointerface charge redistribution synergistically lowers the dissociation barrier and optimizes hydrogen adsorption energy. When deployed as the cathode in an AEMWE device, the electrolyzer delivers industrial-grade current densities of 1 A and 3.2 A cm at low cell voltages of 1.74 and 2.0 V at 60 °C, respectively, while exhibiting durable operation over 1000 h at 500 mA cm. This study develops a scalable electrode fabrication protocol, advancing AEMWE technology for green hydrogen production within sustainable energy ecosystems.

6Anion-Exchange-Membrane Electrolysis with Alkali-Free Water Feed.PubMed

Mohsin Muhyuddin, Carlo Santoro, Luigi Osmieri, et al.
Chem Rev. 2025 Aug 13;125(15):6906-6976. doi: 10.1021/acs.chemrev.4c00466. Epub 2025 Aug 1.
Hydrogen is a green and sustainable energy vector that can facilitate the large-scale integration of intermittent renewable energy, renewable fuels for heavy transport, and deep decarbonization of hard-to-abate industries. Anion-exchange-membrane water electrolyzers (AEM-WEs) have several achieved or expected competitive advantages over other electrolysis technologies, including the use of precious metal-free electrocatalysts at both electrodes, fluorine-free hydrocarbon-based ionomeric membranes and bipolar plates based on inexpensive materials. Contrasting the analogous proton-exchange-membrane system (PEM-WE), where pure water is circulated (no support electrolyte), the current generation of AEM-WEs necessitates the circulation of a dilute aqueous alkaline electrolyte for reaching high energy efficiency and durability. For several reasons, including but not limited to lower cost of balance-of-plant, lower operating cost and improved device's lifetime, achieving high cell efficiency and performance using an alkali-free water feed is highly desirable. In this review, we develop and build a foundational understanding of AEM-WEs operating with pure water, as well as discuss the effects of operating with natural water feeds like seawater. After a discussion of the possible advantages of pure-water-fed AEM-WEs, we cover the thermodynamic and kinetic processes involved in AEM-WE, followed by a detailed review of materials and components and their integration in the device. We highlight the influence of electrolyte composition and alkali/electrolyte-free feed on the membrane-electrode assembly, ionomers, electrocatalysts, porous transport layer, bipolar plates and operating configuration. We provide evidence for how the pure water feed engenders several issues related to the degradation of device components and propose mitigation strategies.

7Anion-exchange membrane water electrolyzers and fuel cells.PubMed

Yaxiong Yang, Peng Li, Xiaobo Zheng, et al.
Chem Soc Rev. 2022 Nov 28;51(23):9620-9693. doi: 10.1039/d2cs00038e.
Anion-exchange membrane (AEM) water electrolyzers (AEMWEs) and fuel cells (AEMFCs) are technologies that, respectively, achieve transformation and utilization of renewable resources in the form of green hydrogen (H) energy. The significantly reduced cost of their key components (membranes, electrocatalysts, bipolar plates, ), quick reaction kinetics, and fewer corrosion problems endow AEM water electrolyzers and fuel cells with overwhelming superiority over their conventional counterparts (, proton-exchange membrane water electrolyzer/fuel cells and alkaline water electrolyzer/fuel cells). Limitations in our fundamental understanding of AEM devices, however, specifically in key components, working management, and operation monitoring, restrict the improvement of cell performance, and they further impede the deployment of AEM water electrolyzers and fuel cells. Therefore, a panoramic view to outline the fundamentals, technological progress, and future perspectives on AEMWEs and AEMFCs is presented. The objective of this review is to (1) present a timely overview of the market development status of green hydrogen technology that is closely associated with AEMWEs (hydrogen production) and AEMFCs (hydrogen utilization); (2) provide an in-depth and comprehensive analysis of AEMWEs and AEMFCs from the viewpoint of all key components (, membranes, ionomers, catalysts, gas diffusion layers, bipolar plates, and membrane electrode assembly (MEA)); (3) summarize the state-of-the-art technologies for working management of AEMWEs and AEMFCs, including electrolyte engineering (electrolyte selection and feeding), water management, gas and heat management, ; (4) outline the advances in monitoring the operations of AEMWEs and AEMFCs, which include microscopic and spectroscopic techniques and beyond; and (5) present key aspects that need to be further studied from the perspective of science and engineering to accelerate the deployment of AEMWEs and AEMFCs.

8A corrosion-resistant RuMoNi catalyst for efficient and long-lasting seawater oxidation and anion exchange membrane electrolyzer.PubMed

Xin Kang, Fengning Yang, Zhiyuan Zhang, et al.
Nat Commun. 2023 Jun 17;14(1):3607. doi: 10.1038/s41467-023-39386-5.
Direct seawater electrolysis is promising for sustainable hydrogen gas (H) production. However, the chloride ions in seawater lead to side reactions and corrosion, which result in a low efficiency and poor stability of the electrocatalyst and hinder the use of seawater electrolysis technology. Here we report a corrosion-resistant RuMoNi electrocatalyst, in which the in situ-formed molybdate ions on its surface repel chloride ions. The electrocatalyst works stably for over 3000 h at a high current density of 500 mA cm in alkaline seawater electrolytes. Using the RuMoNi catalyst in an anion exchange membrane electrolyzer, we report an energy conversion efficiency of 77.9% and a current density of 1000 mA cm at 1.72 V. The calculated price per gallon of gasoline equivalent (GGE) of the H produced is $ 0.85, which is lower than the 2026 technical target of $ 2.0/GGE set by the United Stated Department of Energy, thus, suggesting practicability of the technology.

9Recent Advances and Challenges in Anion Exchange Membranes Development/Application for Water Electrolysis: A Review.PubMed

Lu Liu, Hongyang Ma, Madani Khan, et al.
Membranes (Basel). 2024 Apr 5;14(4):85. doi: 10.3390/membranes14040085.
In recent years, anion exchange membranes (AEMs) have aroused widespread interest in hydrogen production via water electrolysis using renewable energy sources. The two current commercial low-temperature water electrolysis technologies used are alkaline water electrolysis (AWE) and proton exchange membrane (PEM) water electrolysis. The AWE technology exhibited the advantages of high stability and increased cost-effectiveness with low hydrogen production efficiency. In contrast, PEM water electrolysis exhibited high hydrogen efficiency with low stability and cost-effectiveness, respectively. Unfortunately, the major challenges that AEMs, as well as the corresponding ion transportation membranes, including alkaline hydrogen separator and proton exchange membranes, still face are hydrogen production efficiency, long-term stability, and cost-effectiveness under working conditions, which exhibited critical issues that need to be addressed as a top priority. This review comprehensively presented research progress on AEMs in recent years, providing a thorough understanding of academic studies and industrial applications. It focused on analyzing the chemical structure of polymers and the performance of AEMs and established the relationship between the structure and efficiency of the membranes. This review aimed to identify approaches for improving AEM ion conductivity and alkaline stability. Additionally, future research directions for the commercialization of anion exchange membranes were discussed based on the analysis and assessment of the current applications of AEMs in patents.

10Anion Exchange Membranes for Fuel Cells Based on Quaternized Polystyrene--poly(ethylene--butylene)--polystyrene Triblock Copolymers with Spacer-Sidechain Design.PubMed

Qun-Gao Chen, Ming-Tsung Lee
Polymers (Basel). 2022 Jul 13;14(14):2860. doi: 10.3390/polym14142860.
This work studied the polystyrene--poly(ethylene--butylene)--polystyrene (SEBS) triblock copolymers functionalized by butyl quaternary ammonium (CQ) groups and alkyl side chains of different chain lengths (C, n = 0 to 24). The hydrated membrane morphology was modeled by dissipative particle dynamics simulation at hydration levels from 10 to 30. A hydroxide model was devised to characterize the diffusivity of anions under the coarse-grained framework. In general, the ionomers with alkyl side chains provided ion conductivity of a similar level at a lower ion exchange capacity. All hydrated SEBS-CQ-C ionomers showed clear phase separation of the hydrophobic and hydrophilic domains, featuring 18.6 mS/cm to 36.8 mS/cm ion conductivity. The hydrophilic channels expanded as the water content increased, forming more effective ion conductive pathways. Introducing excess alkyl side chains enhanced the nano-segregation, leading to more ordered structures and longer correlation lengths of the aqueous phase. The membrane morphology was controlled by the length of alkyl side-chains as well as their tethering positions. Ionomers with functionalized side chains tethered on the same block resulted in well-connective water networks and higher conductivities. The detailed structural analysis provides synthesis guidelines to fabricate anion exchange membranes with improved performances.

11Anion-Exchange Membrane Water Electrolyzers.PubMed

Naiying Du, Claudie Roy, Retha Peach, et al.
Chem Rev. 2022 Jul 13;122(13):11830-11895. doi: 10.1021/acs.chemrev.1c00854. Epub 2022 Apr 20.
This Review provides an overview of the emerging concepts of catalysts, membranes, and membrane electrode assemblies (MEAs) for water electrolyzers with anion-exchange membranes (AEMs), also known as zero-gap alkaline water electrolyzers. Much of the recent progress is due to improvements in materials chemistry, MEA designs, and optimized operation conditions. Research on anion-exchange polymers (AEPs) has focused on the cationic head/backbone/side-chain structures and key properties such as ionic conductivity and alkaline stability. Several approaches, such as cross-linking, microphase, and organic/inorganic composites, have been proposed to improve the anion-exchange performance and the chemical and mechanical stability of AEMs. Numerous AEMs now exceed values of 0.1 S/cm (at 60-80 °C), although the stability specifically at temperatures exceeding 60 °C needs further enhancement. The oxygen evolution reaction (OER) is still a limiting factor. An analysis of thin-layer OER data suggests that NiFe-type catalysts have the highest activity. There is debate on the active-site mechanism of the NiFe catalysts, and their long-term stability needs to be understood. Addition of Co to NiFe increases the conductivity of these catalysts. The same analysis for the hydrogen evolution reaction (HER) shows carbon-supported Pt to be dominating, although PtNi alloys and clusters of Ni(OH) on Pt show competitive activities. Recent advances in forming and embedding well-dispersed Ru nanoparticles on functionalized high-surface-area carbon supports show promising HER activities. However, the stability of these catalysts under actual AEMWE operating conditions needs to be proven. The field is advancing rapidly but could benefit through the adaptation of new in situ techniques, standardized evaluation protocols for AEMWE conditions, and innovative catalyst-structure designs. Nevertheless, single AEM water electrolyzer cells have been operated for several thousand hours at temperatures and current densities as high as 60 °C and 1 A/cm, respectively.

12Antimicrobial potential of quaternary phosphonium salt compounds: a review.PubMed

Mahin K Ibrahim, Akash Haria, Namrashee V Mehta, et al.
Future Med Chem. 2023 Nov;15(22):2113-2141. doi: 10.4155/fmc-2023-0188. Epub 2023 Nov 6.
Given that mitochondrial dysregulation is a biomarker of many cancers, cationic quaternary phosphonium salt (QPS) conjugation is a widely utilized strategy for anticancer drug design. QPS-conjugated compounds exhibit greater cell permeation and accumulation in negatively charged mitochondria, and thus, show enhanced activity. Phylogenetic similarities between mitochondria and bacteria have provided a rationale for exploring the antibacterial properties of mitochondria-targeted compounds. Additionally, due to the importance of mitochondria in the survival of pathogenic microbes, including fungi and parasites, this strategy can be extended to these organisms as well. This review examines recent literature on the antimicrobial activities of various QPS-conjugated compounds and provides future directions for exploring the medicinal chemistry of these compounds.

13Alkali-Stable Cations and Anion Exchange Membranes.PubMed

Qihang Zhang, Rong Ren, Liqiang Yin, et al.
Chemistry. 2025 Mar 25;31(18):e202404264. doi: 10.1002/chem.202404264. Epub 2025 Feb 28.
Anion exchange membranes (AEMs) based energy conversion and storage devices have attracted attention as an innovative technology due to their advantageous alkaline catalytic kinetics and cost-effectiveness. AEMs play a crucial role in these devices and have shown significant progress in terms of ionic conductivity, mechanical properties, alkaline stability, and other essential characteristics. Nevertheless, their durability remains a limiting factor preventing the large-scale deployment of AEMs based devices. The attack of hydroxide ions on the cations is an inherent issue that needs to be addressed to enhance the lifetime of the AEMs. Therefore, the design of more stable cationic groups is essential to maintain the initial properties of AEMs and extend the device lifetime. This concept systematically summarizes the development and stability enhancement strategies of the cationic groups for AEMs in recent years, with particular emphasis on the emerging cyclic cationic groups. Furthermore, the stability differences of cations in small molecules versus AEMs are systematically discussed, as well as prospective research toward stable AEMs.

14Isoindolinium Groups as Stable Anion Conductors for Anion-Exchange Membrane Fuel Cells and Electrolyzers.PubMed

Kanika Aggarwal, Nansi Gjineci, Alexander Kaushansky, et al.
ACS Mater Au. 2022 Feb 23;2(3):367-373. doi: 10.1021/acsmaterialsau.2c00002. eCollection 2022 May 11.
Anion-exchange membrane (AEM) fuel cells (AEMFCs) and water electrolyzers (AEMWEs) have gained strong attention of the scientific community as an alternative to expensive mainstream fuel cell and electrolysis technologies. However, in the high pH environment of the AEMFCs and AEMWEs, especially at low hydration levels, the molecular structure of most anion-conducting polymers breaks down because of the strong reactivity of the hydroxide anions with the quaternary ammonium (QA) cation functional groups that are commonly used in the AEMs and ionomers. Therefore, new highly stable QAs are needed to withstand the strong alkaline environment of these electrochemical devices. In this study, a series of isoindolinium salts with different substituents is prepared and investigated for their stability under dry alkaline conditions. We show that by modifying isoindolinium salts, steric effects could be added to change the degradation kinetics and impart significant improvement in the alkaline stability, reaching an order of magnitude improvement when all the aromatic positions are substituted. Density functional theory (DFT) calculations are provided in support of the high kinetic stability found in these substituted isoindolinium salts. This is the first time that this class of QAs has been investigated. We believe that these novel isoindolinium groups can be a good alternative in the chemical design of AEMs to overcome material stability challenges in advanced electrochemical systems.

15Cycloaliphatic Quaternary Ammonium Functionalized Poly(oxindole biphenyl) Based Anion-Exchange Membranes for Water Electrolysis: Stability and Performance.PubMed

Sara Gjoshi, Paraskevi Loukopoulou, Michaela Plevova, et al.
Polymers (Basel). 2023 Dec 28;16(1):99. doi: 10.3390/polym16010099.
Mechanically robust anion-exchange membranes (AEMs) with high conductivity and long-term alkali resistance are needed for water electrolysis application. In this work, aryl-ether free polyaromatics containing isatin moieties were prepared via super acid-catalyzed copolymerization, followed by functionalization with alkaline stable cyclic quaternary ammonium (QA) cationic groups, to afford high performance AEMs for application in water electrolysis. The incorporation of side functional cationic groups (pyrrolidinium and piperidinium) onto a polymer backbone via a flexible alkyl spacer aimed at conductivity and alkaline stability improvement. The effect of cation structure on the properties of prepared AEMs was thoroughly studied. Pyrrolidinium- and piperidinium-based AEMs showed similar electrolyte uptakes and no obvious phase separation, as revealed by SAXS and further supported by AFM and TEM data. In addition, these AEMs displayed high conductivity values (81. 5 and 120 mS cm for pyrrolidinium- and piperidinium-based AEM, respectively, at 80 °C) and excellent alkaline stability after 1 month aging in 2M KOH at 80 °C. Especially, a pyrrolidinium-based AEM membrane preserved 87% of its initial conductivity value, while at the same time retaining its flexibility and mechanical robustness after storage in alkaline media (2M KOH) for 1 month at 80 °C. Based on H NMR data, the conductivity loss observed after the aging test is mainly related to the piperidinium degradation that took place, probably via ring-opening Hofmann elimination, alkyl spacer scission and nucleophilic substitution reactions as well. The synthesized AEMs were also tested in an alkaline water electrolysis cell. Piperidinium-based AEM showed superior performance compared to its pyrrolidinium analogue, owing to its higher conductivity as revealed by EIS data, further confirming the ex situ conductivity measurements.

16Novel side chain functionalized polystyrene/O-PBI blends with high alkaline stability for anion exchange membrane water electrolysis (AEMWE).PubMed

Linus Hager, Manuel Hegelheimer, Julian Stonawski, et al.
J Mater Chem A Mater. 2023 Oct 11;11(41):22347-22359. doi: 10.1039/d3ta02978f. eCollection 2023 Oct 24.
We report the synthesis of a polystyrene-based anion exchange polymer bearing the cationic charge at a C6-spacer. The polymer is prepared by a functionalized monomer strategy. First, a copper halide catalyzed C-C coupling reaction between a styryl Grignard and 1,6-dibromohexane is applied, followed by quaternization with -methylpiperidine and free radical polymerization. The novel polymer is blended with the polybenzimidazole O-PBI to yield mechanically stable blend membranes representing a new class of anion exchange membranes. In this regard, the ratio of the novel anion exchange polymer to O-PBI is varied to study the influence on water uptake and ionic conductivity. Blend membranes with IECs between 1.58 meq. OH g and 2.20 meq. OH g are prepared. The latter shows excellent performance in AEMWE, reaching 2.0 A cm below 1.8 V in 1 M KOH at 70 °C, with a minor degradation rate from the start. The blend membranes show no conductivity loss after immersion in 1 M KOH at 85 °C for six weeks indicating high alkaline stability.

17Fluorine-Containing Poly(Fluorene)-Based Anion Exchange Membrane with High Hydroxide Conductivity and Physicochemical Stability for Water Electrolysis.PubMed

Haeryang Lim, Gyeong Ho Han, Dae Hwan Lee, et al.
Small. 2024 Aug;20(32):e2400031. doi: 10.1002/smll.202400031. Epub 2024 Mar 18.
Improving the hydroxide conductivity and dimensional stability of anion exchange membranes (AEMs) while retaining their high alkaline stability is necessary to realize the commercialization of AEM water electrolysis (AEMWE). A strategy for improving the hydroxide conductivity and dimensional stability of AEMs by inserting fluorine atoms in the core structure of the backbone is reported, which not only reduces the glass transition temperature of the polymer due to steric strain, but also induces distinct phase separation by inducing polarity discrimination to facilitate the formation of ion transport channels. The resulting PFPFTP-QA AEM with fluorine into the core structure shows high hydroxide conductivity (>159 mS cm at 80 °C), favorable dimensional stability (>25% at 80 °C), and excellent alkaline stability for 1000 h in 2 m KOH solution at 80 °C. Moreover, the PFPFTP-QA is used to construct an AEMWE cell with a platinum group metal (PGM)-free NiFe anode, which exhibits the current density of 6.86 A cm at 1.9 V at 80 °C, the highest performance in Pt/C cathode and PGM-free anode reports so far and operates stably for over 100 h at a constant current of 0.5 A cm.

18Highly Hydrophilic Zirconia Composite Anion Exchange Membrane for Water Electrolysis and Fuel Cells.PubMed

Wenli Ma, Lin Tian, Qingqing Zhu, et al.
ACS Appl Mater Interfaces. 2024 Mar 6;16(9):11849-11859. doi: 10.1021/acsami.3c16283. Epub 2024 Feb 27.
To prepare anion exchange membranes with high water electrolysis and single fuel cell performance, an inorganic-organic composite (IOC) strategy with click cross-linked membranes coated with different contents of hydrophilic polar nanozirconia is proposed to fabricate composite membranes (CM) PBP-SH-Zrx. The performance test results showed that the CM PBP-SH-Zr4 not only has good through-plane ionic conductivity (167.7 mS cm, 80 °C), but also exhibits satisfactory dimensional stability (SR 16.5%, WU 206.4%, 80 °C), especially demonstrating excellent alkaline stability with only 16% degradation (2 M NaOH for 2200 h). In water electrolysis, the "microgap" between the membrane and catalyst layer (solid-solid interface) is alleviated, and the membrane electrode assembly (MEA) interfacial compatibility (liquid-solid-solid interface) is enhanced. The CM PBP-SH-Zr4 showed the lowest charge transfer resistance (R, 0.037 Ω cm) and a high current density of 2.5 A cm at 2.2 V, while the voltage drop was 0.361 mV h after 360 h of endurance (six start-stop cycles) at 60 °C and 500 mA cm, proving a good water electrolysis durability. Moreover, an acceptable peak power density of 0.464 W cm at 80 °C is achieved in a H/O fuel cell with a PBP-SH-Zr4-AEM. Therefore, the IOC strategy can enhance the membrane's comprehensive performance and interface compatibility of MEA and may promote the development of anion exchange membranes (AEMs) for water electrolysis and fuel cells.

19Poly(Aryl--Aryl Piperidinium) Copolymers for Anion Exchange Membrane Fuel Cells and Water Electrolyzers.PubMed

Nanjun Chen, Chuan Hu, Young Moo Lee
Acc Chem Res. 2025 Mar 4;58(5):688-702. doi: 10.1021/acs.accounts.4c00695. Epub 2025 Feb 10.
Next-generation cost-effective anion exchange membrane (AEM) fuel cells (AEMFCs) and AEM water electrolyzers (AEMWEs) have emerged as promising alternatives to costly proton exchange membrane (PEM) fuel cells and water electrolyzers due to the possibility of utilizing platinum-group-metal (PGM)-free catalysts and phasing out unsustainable perfluorosulfonic acid polymers. Anion exchange polyelectrolytes (AEPs), which can be utilized as AEMs or ionomers, are pivotal materials in AEM devices. Despite extensive exploration in the past decade, the application of AEPs has been significantly impeded by their poor ionic conductivity, insufficient alkaline stability, and unfavorable mechanical properties. Therefore, developing highly conductive and robust AEPs is critical to the success of AEMFCs and AEMWEs. (i) Our group has developed a series of highly conductive and durable poly(aryl--aryl piperidinium) (c-PAP) AEPs to address the aforementioned issues. c-PAP AEMs and ionomers enable outstanding OH conductivity (>160 mS cm at 80 °C), alkaline stability (1 M NaOH at 80 °C > 2000 h), dimensional stability, and mechanical properties (tensile strength > 80 MPa), giving them all the properties required for applications in AEM devices. (ii) Based on c-PAP AEMs and ionomers, we have developed high-performance AEMFCs and AEMWEs, as well as provided insights into the ionomer research and the design of membrane electrode assemblies. Typically, c-PAP AEMFCs reached the topmost peak power densities (PPDs) of 2.7 W cm at 80 °C in H-O along with 1000 h cell durability. Moreover, cathode-dried AEMWEs achieved a record-breaking current density of 17 A cm in 1 M KOH, and the cell can be run stably at a 1.5 A cm current density for over 2000 h. The remarkable performances achieved by this new class of c-PAP AEPs identify them as the most promising candidates for practical applications in AEMFCs and AEMWEs. In this account, we will elaborate on our strategies and methodologies associated with c-PAP AEPs and AEM devices, covering the screening and identification of highly durable cation head groups and molecular-engineering approaches to design c-PAP AEMs and ionomers. Moreover, we underscore our strategy in terms of developing highly efficient and durable AEMFCs and AEMWEs. We also elucidate different approaches for further enhancing the ion conductivity and mechanical stability of c-PAP AEMs, including the design of backbones and side chains, cross-linking, and reinforcement. We firmly believe that our series of studies has made substantial contributions to the fields of AEM, ionomers, AEMFCs, and AEMWEs, which have advanced AEM technology to be on par with PEM technology, opening a new avenue for commercialization of AEMFCs and AEMWEs.

20Reactive oxygen species accelerate degradation of anion exchange membranes based on polyphenylene oxide in alkaline environments.PubMed

Javier Parrondo, Zhongyang Wang, Min-Suk J Jung, et al.
Phys Chem Chem Phys. 2016 Jul 20;18(29):19705-12. doi: 10.1039/c6cp01978a.
Anion exchange membranes (AEM) based on polyphenylene oxide (PPO) suffered quaternary-ammonium-cation-site degradation in alkaline environments. Surprisingly, the degradation rate was considerably faster in the presence of molecular oxygen. We postulated that the AEM cation-site catalyzes the reduction of dioxygen by hydroxide ions to yield the superoxide anion radical and the highly reactive hydroxyl free radical. We substantiated our hypothesis by using a phosphorous-containing spin trap (5-diisopropoxy-phosphoryl-5-methyl-1-pyrroline-N-oxide) to detect the adducts for both free radicals in situ using (31)P-NMR spectroscopy.

21Detection of Reactive Oxygen Species in Anion Exchange Membrane Fuel Cells using In Situ Fluorescence Spectroscopy.PubMed

Yunzhu Zhang, Javier Parrondo, Shrihari Sankarasubramanian, et al.
ChemSusChem. 2017 Aug 10;10(15):3056-3062. doi: 10.1002/cssc.201700760. Epub 2017 Jun 28.
The objectives of this study were: 1) to confirm superoxide anion radical (O ) formation, and 2) to monitor in real time the rate of O generation in an operating anion exchange membrane (AEM) fuel cell using in situ fluorescence spectroscopy. 1,3-Diphenlisobenzofuran (DPBF) was used as the fluorescent molecular probe owing to its selectivity and sensitivity toward O in alkaline media. The activation energy for the in situ generation of O during AEM fuel cell operation was estimated to be 18.3 kJ mol . The rate of in situ generation of O correlated well with the experimentally measured loss in AEM ion-exchange capacity and ionic conductivity attributable to oxidative degradation.

22Radiation-Grafted Anion-Exchange Membrane for Fuel Cell and Electrolyzer Applications: A Mini Review.PubMed

Kean Long Lim, Chun Yik Wong, Wai Yin Wong, et al.
Membranes (Basel). 2021 May 27;11(6):397. doi: 10.3390/membranes11060397.
This review discusses the roles of anion exchange membrane (AEM) as a solid-state electrolyte in fuel cell and electrolyzer applications. It highlights the advancement of existing fabrication methods and emphasizes the importance of radiation grafting methods in improving the properties of AEM. The development of AEM has been focused on the improvement of its physicochemical properties, including ionic conductivity, ion exchange capacity, water uptake, swelling ratio, etc., and its thermo-mechano-chemical stability in high-pH and high-temperature conditions. Generally, the AEM radiation grafting processes are considered green synthesis because they are usually performed at room temperature and practically eliminated the use of catalysts and toxic solvents, yet the final products are homogeneous and high quality. The radiation grafting technique is capable of modifying the hydrophilic and hydrophobic domains to control the ionic properties of membrane as well as its water uptake and swelling ratio without scarifying its mechanical properties. Researchers also showed that the chemical stability of AEMs can be improved by grafting spacers onto base polymers. The effects of irradiation dose and dose rate on the performance of AEM were discussed. The long-term stability of membrane in alkaline solutions remains the main challenge to commercial use.

23Imidazolium-based anion exchange membranes for alkaline anion fuel cells: elucidation of the morphology and the interplay between the morphology and properties.PubMed

Yue Zhao, Kimio Yoshimura, Hideyuki Shishitani, et al.
Soft Matter. 2016 Feb 7;12(5):1567-78. doi: 10.1039/c5sm02724a. Epub 2015 Dec 14.
We investigated the morphology and swelling behavior of a new graft-type of anion exchange membrane (AEM) containing 2-methylimidazolium groups by using a contrast variation small angle neutron scattering (SANS) technique. These AEMs were prepared by radiation-induced grafting of 2-methyl-1-vinylimidazole and styrene into poly(ethylene-co-tetrafluoroethylene) (ETFE) films and subsequent N-alkylation with methyliodide, and possessed both high alkaline durability and high conductivity. Our results showed that the crystalline lamellar and crystallite structures originating from the pristine ETFE films were more or less conserved in these AEMs, but the lamellar d-spacing in both dry and wet membranes was enlarged, indicating an expansion of the amorphous lamellae due to the graft chains introduced in the grafting process and the water incorporated in the swelling process. For the first time, the swelling behavior of the AEMs was studied quantitatively in various water mixtures of water and deuterated water with different volume ratios (contrast variation method), and the morphology of these membranes was elucidated by three phases: phase (1) crystalline ETFE domains, which offer good mechanical properties; phase (2) hydrophobic amorphous domains, which are made up of amorphous ETFE chains and offer a matrix to create conducting regions; phase (3) interconnected hydrated domains, which are composed of the entire graft chains and water and play a key role in promoting the conductivity.

24A long side chain imidazolium-based graft-type anion-exchange membrane: novel electrolyte and alkaline-durable properties and structural elucidation using SANS contrast variation.PubMed

Yue Zhao, Kimio Yoshimura, Ahmed Mohamed Ahmed Mahmoud, et al.
Soft Matter. 2020 Sep 16;16(35):8128-8143. doi: 10.1039/d0sm00947d.
Newly designed styrylimidazolium-based grafted anion-exchange membranes (StIm-AEMs), in which imidazolium ionic groups are attached to styrene at the far side from the graft chains, were prepared by radiation-induced graft polymerization of p-(2-imidazoliumyl) styrene onto poly(ethylene-co-tetrafluoloethylene) (ETFE) films, followed by N-alkylation and ion-exchange reactions. StIm-AEM having an ion exchange capacity (IEC) of 0.54 mmol g-1 with a grafting degree (GD) of ∼18%, possesses practical conductivity (>50 mS cm-1) even with a very low water uptake (∼10%) and high stability over 600 h in a 1 M KOH solution at 80 °C. There exists a critical IEC (IECc) in the range of 0.7-0.8 mmol g-1 over which the membrane showed high water uptake, which resulted in pronounced susceptibility to hydrolysis. Using small-angle neutron scattering technique with a contrast variation method, we found the hydrophilic phase in StIm-AEMs with IECs lower and higher than IECc shows "reverse-micelles" with water domains dispersed in the polymer matrix and "micelles" with graft polymer aggregates dispersed in the water matrix, respectively. The further analysis of micelle structures using the hard-sphere liquid model and Porod limit analysis reveals that the interfacial structures of ionic groups are essential for the electrochemical properties and durability of StIm-AEMs. In addition, StIm-AEM with an IEC of 0.95 mmol g-1 and the maximum power density of 80 mW cm-2 in the hydrazine hydrate fuel cell test, exhibited long-term durability under constant current (8.0 mA) up to 455 h, which, thus far, is the best durability at 80 °C for platinum-free alkaline-type liquid fuel cells.

25Higher Acid Recovery Efficiency of Novel Functionalized Inorganic/Organic Composite Anion Exchange Membranes from Acidic Wastewater.PubMed

Muhammad Imran Khan, Abdallah Shanableh, Noureddine Elboughdiri, et al.
Membranes (Basel). 2021 Feb 14;11(2):133. doi: 10.3390/membranes11020133.
In this work, the synthesis of a series of the functionalized inorganic/organic composite anion exchange membranes (AEMs) was carried out by employing the varying amount of inorganic filler consist of -(trimethoxysilylpropyl)-,,-trimethylammonium chloride (TMSP-TMACl) into the quaternized poly (2, 6-dimethyl-1, 4-phenylene oxide) (QPPO) matrix for acid recovery via diffusion dialysis (DD) process. Fourier transform infrared (FTIR) spectroscopy clearly demonstrated the fabrication of the functionalized inorganic/organic composite AEMs and the subsequent membrane characteristic measurements such as ion exchange capacity (IEC), linear swelling ratio (LSR), and water uptake (W) gave us the optimum loading condition of the filler without undesirable filler particle aggregation. These composite AEMs exhibited IEC of 2.18 to 2.29 meq/g, LSR of 13.33 to 18.52%, and W of 46.11 to 81.66% with sufficient thermal, chemical, and mechanical stability. The diffusion dialysis (DD) test for acid recovery from artificial acid wastewater of HCl/FeCl showed high acid DD coefficient (U) (0.022 to 0.025 m/h) and high separation factor (S) (139-260) compared with the commercial membrane. Furthermore, the developed AEMs was acceptably stable (weight loss < 20%) in the acid wastewater at 60 °C as an accelerated severe condition for 2 weeks. These results clearly indicated that the developed AEMs have sufficient potential for acid recovery application by DD process.

26Semi-interpenetrating anion exchange membranes using hydrophobic microporous linear poly(ether ketone).PubMed

Jia Hui Chen, Wei Ting Gao, Yvonne Shuen Lann Choo, et al.
J Colloid Interface Sci. 2023 Mar 15;634:110-120. doi: 10.1016/j.jcis.2022.12.032. Epub 2022 Dec 11.
In order to realise high ionic conductivity and improved chemical stability, a series of anion exchange membranes (AEMs) with semi-interpenetrating polymer network (sIPN) has been prepared via the incorporation of crosslinked poly(biphenyl N-methylpiperidine) (PBP) and spirobisindane-based intrinsically microporous poly(ether ketone) (PEK-SBI). The formation of phase separated structures as a result of the incompatibility between the hydrophilic PBP network and the hydrophobic PEK-SBI segment, has successfully promoted the hydroxide ion conductivity of AEMs. A swelling ratio (SR) as low as 12.2 % at 80 °C was recorded for the sIPN containing hydrophobic PEK-SBI as the linear polymer and crosslinked structure with a mass ratio of PBP to PEK-SBI of 90/10 (sIPN-90/10). The sIPN-90/10 AEM achieved the highest hydroxide ion conductivity of 122.4 mS cm at 80 °C and a recorded ion exchange capacity (IEC) of 2.26 meq g. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) clearly revealed the improved phase separation structure of sIPN-90/10. N adsorption isotherm indicated that the Brunauer-Emmett-Teller (BET) surface area of the AEMs increased with the increase of microporous PEK-SBI content. Interestingly, the sIPN-90/10 AEM showed good alkaline stability for being able to maintain a conductivity of 94.7 % despite being soaked in a 1 M sodium hydroxide solution at 80 °C for 30 days. Meanwhile, a peak power density of 481 mW cm can be achieved by the hydrogen/oxygen single cell using sIPN-90/10 as the AEM.

27Quinuclidinium-Based Microporous Anion Exchange Membranes for Water Electrolysis.PubMed

Wenhao Zou, Gonggen Tang, Kang Peng, et al.
Angew Chem Int Ed Engl. 2025 Sep 14:e202514264. doi: 10.1002/anie.202514264.
Anion exchange membrane water electrolysis (AEMWE) is a promising green hydrogen production method; however, it is constrained by the moderate OH conductivity and inadequate alkaline stability of anion exchange membranes (AEMs). Here we report a series of quinuclidinium-based AEMs with branched and microporous structures, achieving 99.95% OH conductivity retention after 3100 h in 10 M NaOH at 80 °C. By tuning the rigidity of the branching units to limit chain packing, micropores were created to enhance OH transport, which improved the diffusion coefficient of OH by 1.6 times within the poly (terphenyl-triptycene-quinuclidinium) (PTPQ-Trip) membrane having the most rigid structure. An AEMWE configured with a PTPQ-Trip membrane and nickel-alloy catalysts can tolerate varied alkaline concentrations and deliver a hydrogen production current density of 2.8 A cm at 2.0 V in 5 M KOH, which can be continuously operated at 0.5 A cm and 30 °C for over 1200 h, with intentionally included stop/start interruptions. The assembled AEMWE demonstrated stable operation for 1400 h under alternating operational current densities and varying electrolyte temperatures. This work underscores the critical role of alkaline-resistant microporous AEMs and highlights the adaptability of AEMWE for hydrogen production using renewable electricity.

28In Situ Crosslinking of Tröger Base-Based Membranes with Improved Vanadium Flow Battery Property.PubMed

Jiachen Chu, Xiaokang Yang, Mengtao Wang, et al.
Macromol Rapid Commun. 2025 Jun;46(12):e2401129. doi: 10.1002/marc.202401129. Epub 2025 Mar 29.
The high conductivity of anion exchange membrane (AEM) remains a great challenge in achieving high-performance vanadium flow batteries. In this work, this is achieved by designing a series of microporous crosslinked quaternary ammonium membranes (QDTTB-Xs), which is synthesized by in situ reacting of iodomethane with a series of novel crosslinked microporous Tröger base membranes (DTTB-Xs) that prepared by condensation of 2, 6 (7)-diamino-triptycene and 2, 6 (7)-13-triamino-triptycene through in situ crosslinking. Compared with linear microporous QDTTB-0, the crosslinked QDTTB-X membranes showed higher conductivity. The QDTTB-35 membrane displays both higher coulombic efficiency and voltage efficiency, and 80% of energy efficiency is realized at 200 mA cm. Outperforming N117 and other reported anion exchange membranes. This is due to the increased triamino-triptycene molar ratio in the membrane resulting in both higher N concentration and improved micropores concentration. Moreover, positively charged N groups combined with the low swelling ratio also help in restricting the vanadium ions permeation. These results give great perspectives in designing high-performance AEMs for VRFB applications.

29Iron Is the Active Site in Nickel/Iron Water Oxidation Electrocatalysts.PubMed

Bryan M Hunter, Jay R Winkler, Harry B Gray
Molecules. 2018 Apr 14;23(4):903. doi: 10.3390/molecules23040903.
Efficient catalysis of the oxygen-evolution half-reaction (OER) is a pivotal requirement for the development of practical solar-driven water splitting devices. Heterogeneous OER electrocatalysts containing first-row transition metal oxides and hydroxides have attracted considerable recent interest, owing in part to the high abundance and low cost of starting materials. Among the best performing OER electrocatalysts are mixed Fe/Ni layered double hydroxides (LDH). A review of the available experimental data leads to the conclusion that iron is the active site for [NiFe]-LDH-catalyzed alkaline water oxidation.

30Identifying Fe as OER Active Sites and Ultralow-Cost Bifunctional Electrocatalysts for Overall Water Splitting.PubMed

Bo Li, Jun Zhao, Yishang Wu, et al.
Small. 2023 Sep;19(37):e2301715. doi: 10.1002/smll.202301715. Epub 2023 May 5.
Electrocatalysts based on Fe and other transition metals are regarded as most promising candidates for accelerating the oxygen evolution reaction (OER), whereas whether Fe is the catalytic active site for OER is still under debate. Here, unary Fe- and binary FeNi- based catalysts, FeOOH and FeNi(OH) , are produced by self-reconstruction. The former is a dual-phased FeOOH, possessing abundant oxygen vacancies (V ) and mixed-valence states, delivering the highest OER performance among all the unary iron oxides- and hydroxides- based powder catalysts reported to date, supporting Fe can be catalytically active for OER. As to binary catalyst, FeNi(OH) is fabricated featuring 1) an equal molar content of Fe and Ni and 2) rich V , both of which are found essential to enable abundant stabilized reactive centers (FeOOHNi) for high OER performance. Fe is found to be oxidized to 3.5+ during the *OOH process, thus, Fe is identified to be the active site in this new layered double hydroxide (LDH) structure with Fe:Ni = 1:1. Furthermore, the maximized catalytic centers enable FeNi(OH) @NF (nickel foam) as low-cost bifunctional electrodes for overall water-splitting, delivering excellent performance comparable to commercial electrodes based on precious metals, which overcomes a major obstacle to the commercialization of bifunctional electrodes: prohibitive cost.

31Direct and indirect role of Fe doping in NiOOH monolayer for water oxidation catalysis.PubMed

Manish Kumar, Simone Piccinin, Varadharajan Srinivasan
Chemphyschem. 2022 Jul 19;23(14):e202200085. doi: 10.1002/cphc.202200085. Epub 2022 May 31.
Water oxidation activity of pristine NiOOH is greatly enhanced by doping it with Fe. However, the precise role of Fe is still being debated. Using a first-principles DFT+U approach, we investigate the direct and indirect roles of Fe in enhancing the oxygen evolution reaction (OER) activity of NiOOH monolayers. Considering two Mars-Van-Krevelen mechanisms of OER based on the source of O-O bond formation, we show that a mechanism involving the coupling of lattice oxygen is generally more favorable than water nucleophilic attack on lattice oxygen. On doping with Fe, the overpotential of NiOOH is reduced by 0.33 V, in excellent agreement with experimental findings. Introducing Fe at active sites results in different potential determining steps (PDS) in the two mechanisms. The Ni sites in pristine and Fe-doped NiOOH have the same PDS regardless of the mechanism. The Fe sites not only have the lowest overpotential but also decrease the overpotential for Ni sites.

32Oxygen Isotope Labeling Experiments Reveal Different Reaction Sites for the Oxygen Evolution Reaction on Nickel and Nickel Iron Oxides.PubMed

Seunghwa Lee, Karla Banjac, Magalí Lingenfelder, et al.
Angew Chem Int Ed Engl. 2019 Jul 22;58(30):10295-10299. doi: 10.1002/anie.201903200. Epub 2019 Jun 17.
Nickel iron oxide is considered a benchmark nonprecious catalyst for the oxygen evolution reaction (OER). However, the nature of the active site in nickel iron oxide is heavily debated. Here we report direct spectroscopic evidence for the different active sites in Fe-free and Fe-containing Ni oxides. Ultrathin layered double hydroxides (LDHs) were used as defined samples of metal oxide catalysts, and O-labeling experiments in combination with in situ Raman spectroscopy were employed to probe the role of lattice oxygen as well as an active oxygen species, NiOO , in the catalysts. Our data show that lattice oxygen is involved in the OER for Ni and NiCo LDHs, but not for NiFe and NiCoFe LDHs. Moreover, NiOO is a precursor to oxygen for Ni and NiCo LDHs, but not for NiFe and NiCoFe LDHs. These data indicate that bulk Ni sites in Ni and NiCo oxides are active and evolve oxygen via a NiOO precursor. Fe incorporation not only dramatically increases the activity, but also changes the nature of the active sites.

33Nickel-Induced Activation of Iron Foam for the Oxygen-Evolution Reaction: A Multimodal Study of Structure and Dynamics.PubMed

Negah Hashemi, Mohammad Mahdi Najafpour
Inorg Chem. 2025 Jun 30;64(25):12824-12837. doi: 10.1021/acs.inorgchem.5c01959. Epub 2025 Jun 16.
Iron/nickel (hydr)oxides are widely recognized as efficient catalysts for the oxygen-evolution reaction (OER) in alkaline media. In this study, the effect of Ni on Fe foam toward OER activity is investigated. Treatment with nickel(II) nitrate induces the emergence of oxidation and reduction peaks, whose intensity and position are modulated by the nickel concentration on the iron foam surface. Remarkably, the OER onset potential exhibits a 240 mV reduction in overpotential upon the incorporation of nickel ions. In-situ Raman spectroscopy reveals the formation of γ-NiO(OH) during OER. Although substantial Fe ions are incorporated into the nickel (hydr)oxide matrix, reduced OER activity and a negative potential shift in the Ni(II)/(III) peak suggest Fe leaching during OER. Based on our findings, we propose a structure featuring multiple active sites, including nickel-doped iron hydroxide, iron oxide, nickel hydroxide, and mixed nickel/iron hydroxides with varying stoichiometries. This work highlights nickel-induced activation of iron foam to enhance OER performance, offering valuable insights for designing advanced, cost-effective, and durable electrocatalysts for applications such as water splitting and renewable energy storage systems.

34Cobalt and Yttrium Doping to Activate Dual-Site Mechanism of Amorphous NiFeOOH for Large-Current Water Electrooxidation.PubMed

Xiaojing Lv, Mingzhe Li, Hongye Qin, et al.
Adv Sci (Weinh). 2025 Sep 8:e12638. doi: 10.1002/advs.202512638.
The difference in hydroxyl adsorption between Ni and Fe sites in NiFeOOH limits the efficient dual-site synergistic mechanism (DSSM) during oxygen evolution reaction (OER). Here, a novel needle-array electrodeposition is reported for the scalable and efficient fabrication of Co and Y co-doped NiFeOOH catalyst. It achieves an ultralow overpotential of 270 mV at 1 A cm with a small Tafel slope of 30.7 mV dec. It maintains stable operation at 1 A cm for 1500 hrs with 98 % initial potential retention. When integrated into a 25 cm anion exchange membrane electrolyzer, the system only needs 2.13 V to achieve 1 A cm. XPS, XAS, and DFT studies reveal that Co and Y dopants increase the Lewis acidity of Ni sites, enhancing OH adsorption. Concurrently, the incorporation of large Y atoms induces lattice distortion and elongates Fe─O─M bonds, weakening OH binding at Fe sites. This dual-site modulation reduces adsorption disparity, activates NiFe dual-active centers, and promotes the DSSM pathway, as confirmed by in situ ATR-SEIRAS. The rate-determining step energy is lowered to 1.71 eV, significantly outperforming the conventional AEM pathway (2.51 eV). This work provides dual-site modulation into engineering high-performance NiFe-based OER catalysts for practical water electrolysis.

35Cobalt-iron (oxy)hydroxide oxygen evolution electrocatalysts: the role of structure and composition on activity, stability, and mechanism.PubMed

Michaela S Burke, Matthew G Kast, Lena Trotochaud, et al.
J Am Chem Soc. 2015 Mar 18;137(10):3638-48. doi: 10.1021/jacs.5b00281. Epub 2015 Mar 4.
Cobalt oxides and (oxy)hydroxides have been widely studied as electrocatalysts for the oxygen evolution reaction (OER). For related Ni-based materials, the addition of Fe dramatically enhances OER activity. The role of Fe in Co-based materials is not well-documented. We show that the intrinsic OER activity of Co(1-x)Fe(x)(OOH) is ∼100-fold higher for x ≈ 0.6-0.7 than for x = 0 on a per-metal turnover frequency basis. Fe-free CoOOH absorbs Fe from electrolyte impurities if the electrolyte is not rigorously purified. Fe incorporation and increased activity correlate with an anodic shift in the nominally Co(2+/3+) redox wave, indicating strong electronic interactions between the two elements and likely substitutional doping of Fe for Co. In situ electrical measurements show that Co(1-x)Fe(x)(OOH) is conductive under OER conditions (∼0.7-4 mS cm(-1) at ∼300 mV overpotential), but that FeOOH is an insulator with measurable conductivity (2.2 × 10(-2) mS cm(-1)) only at high overpotentials >400 mV. The apparent OER activity of FeOOH is thus limited by low conductivity. Microbalance measurements show that films with x ≥ 0.54 (i.e., Fe-rich) dissolve in 1 M KOH electrolyte under OER conditions. For x < 0.54, the films appear chemically stable, but the OER activity decreases by 16-62% over 2 h, likely due to conversion into denser, oxide-like phases. We thus hypothesize that Fe is the most-active site in the catalyst, while CoOOH primarily provides a conductive, high-surface area, chemically stabilizing host. These results are important as Fe-containing Co- and Ni-(oxy)hydroxides are the fastest OER catalysts known.

36Cobalt-Doping Induced Formation of Five-Coordinated Nickel Selenide for Enhanced Ethanol Assisted Overall Water Splitting.PubMed

Jinchang Xu, Jiaxi Ruan, Yongqi Jian, et al.
Small. 2024 Mar;20(11):e2305905. doi: 10.1002/smll.202305905. Epub 2023 Nov 5.
To overcome the low efficiency of overall water splitting, highly effective and stable catalysts are in urgent need, especially for the anode oxygen evolution reaction (OER). In this case, nickel selenides appear as good candidates to catalyze OER and other substitutable anodic reactions due to their high electronic conductivity and easily tunable electronic structure to meet the optimized adsorption ability. Herein, an interesting phase transition from the hexagonal phase of NiSe (H-NiSe) to the rhombohedral phase of NiSe (R-NiSe) induced by the doping of cobalt atoms is reported. The five-coordinated R-NiSe is found to grow adjacent to the six-coordinated H-NiSe, resulting in the formation of the H-NiSe/R-NiSe heterostructure. Further characterizations and calculations prove the reduced splitting energy for R-NiSe and thus the less occupancy in the t orbits, which can facilitate the electron transfer process. As a result, the Co -NiSe/NF shows a satisfying catalytic performance toward OER, hydrogen evolution reaction, and (hybrid) overall water splitting. This work proves that trace amounts of Co doping can induce the phase transition from H-NiSe to R-NiSe. The formation of less-coordinated species can reduce the t occupancy and thus enhance the catalytic performance, which might guide rational material design.

37Durable Nickel-Iron (Oxy)hydroxide Oxygen Evolution Electrocatalysts through Surface Functionalization with Tetraphenylporphyrin.PubMed

Sinwoo Kang, Changbin Im, Ioannis Spanos, et al.
Angew Chem Int Ed Engl. 2022 Dec 19;61(51):e202214541. doi: 10.1002/anie.202214541. Epub 2022 Nov 18.
NiFe-based oxides are one of the best-known active oxygen evolution electrocatalysts. Unfortunately, they rapidly lost performance in Fe-purified KOH during the reaction. Herein, tetraphenylporphyrin (TPP) was loaded on a catalyst/electrolyte interface to alleviate the destabilization of NiFe (oxy)hydroxide. We propose that the degradation occurs primarily due to the release of thermodynamically unstable Fe. TPP acts as a protective layer and suppresses the dissolution of hydrated metal at the catalyst/electrolyte interface. In the electric double layer, the nonpolar TPP layer on the NiFe surface also invigorates the redeposition of the active site, Fe, which leads to prolonging the lifetime of NiFe. The TPP-coated NiFe was demonstrated in anion exchange membrane water electrolysis, where hydrogen was generated at a rate of 126 L h for 115 h at a 1.41 mV h degradation rate. Consequently, TPP is a promising protective layer that could stabilize oxygen evolution electrocatalysts.

38Iron-Locked Hydr(oxy)oxide Catalysts via Ion-Compensatory Reconstruction Boost Large-Current-Density Water Oxidation.PubMed

Jiao Liu, Wei Du, Siying Guo, et al.
Adv Sci (Weinh). 2023 Jun;10(16):e2300717. doi: 10.1002/advs.202300717. Epub 2023 Apr 7.
Nickel-iron based hydr(oxy)oxides have been well recognized as one of the best oxygen-evolving catalysts in alkaline water electrolysis. A crucial problem, however, is that iron leakage during prolonged operation would lead to the oxygen evolution reaction (OER) deactivation over time, especially under large current densities. Here, the NiFe-based Prussian blue analogue (PBA) is designed as a structure-flexible precursor for navigating an electrochemical self-reconstruction (ECSR) with Fe cation compensation to fabricate a highly active hydr(oxy)oxide (NiFeO H ) catalyst stabilized with NiFe synergic active sites. The generated NiFeO H catalyst exhibits the low overpotentials of 302 and 313 mV required to afford large current densities of 500 and 1000 mA cm , respectively. Moreover, its robust stability over 500 h at 500 mA cm stands out among the NiFe-based OER catalysts reported previously. Various in/ex situ studies indicate that the Fe fixation by dynamic reconstruction process can reinforce the Fe-activated effect on the OER amenable to the industrial-level large current conditions against the Fe leakage. This work opens up a feasible strategy to design highly active and durable catalysts via thermodynamically self-adaptive reconstruction engineering.

39Boosting the Performance of Alkaline Anion Exchange Membrane Water Electrolyzer with Vanadium-Doped NiFeO.PubMed

Minsol Kwon, Jun Seok Ha, Dong Ho Lee, et al.
Small. 2025 Feb;21(7):e2410006. doi: 10.1002/smll.202410006. Epub 2025 Jan 7.
Developing efficient, economical, and stable catalysts for the oxygen evolution reaction is pivotal for producing large-scale green hydrogen in the future. Herein, a vanadium-doped nickel-iron oxide supported on nickel foam (V-NiFeO/NF) is introduced, and synthesized via a facile hydrothermal method as a highly efficient electrocatalyst for water electrolysis. X-ray photoelectron and absorption spectroscopies reveal a synergistic interaction between the vanadium dopant and nickel/iron in the host material, which tunes the electronic structure of NiFeO to increase the number of electrochemically active sites. The V-NiFeO/NF electrode exhibited superior electrochemical performance, with a low overpotential of 186 mV at a current density of 10 mA cm, a Tafel slope value of 54.45 mV dec, and minimal charge transfer resistance. Employing the V-NiFeO/NF electrode as an anode in an alkaline anion exchange membrane water electrolyzer single-cell, a cell voltage of 1.711 V is required to achieve a high current density of 1.0 A cm. Remarkably, the cell delivered an energy conversion efficiency of 73.30% with enduring stability, making it a promising candidate for industrial applications.

40MOF-Derived Cobalt@Mesoporous Carbon as Electrocatalysts for Oxygen Evolution Reaction: Impact of Organic Linker.PubMed

Aymen S Abu Hatab, Yahia H Ahmad, Muna Ibrahim, et al.
Langmuir. 2023 Jan 6. doi: 10.1021/acs.langmuir.2c02873.
Water electrolysis has attracted scientists' attention as a green route for energy generation. However, the sluggish kinetics of oxygen evolution reaction (OER) remarkably increases the reaction overpotential. In this work, we developed Co-based nanomaterials as cost-effective, highly efficient catalysts for OER. In this regard, different Co-based metal-organic frameworks (MOFs) were synthesized using different organic linkers. After annealing under inert atmosphere, the corresponding Co-embedded mesoporous carbon (Co/MC) materials were produced. Among them, Co/MC synthesized using 2-methyl imidazole (Co/NMC-2MeIM) expressed the highest surface area (412 m/g) compared to its counterparts. Furthermore, it expressed a higher degree of defects as depicted by Raman spectra. Co/NMC-2MeIM exhibited the best catalytic performance toward OER in alkaline medium. It afforded an overpotential of 292 mV at a current density of 10 mA cm and a Tafel slope of 99.2 mV dec. The superior electrocatalytic performance of Co/NMC-2MeIM is attributed to its high content of Co on the surface, high surface area, and enhanced electrical conductivity induced by nitrogen doping. Furthermore, its high content of pyridinic-N and high degree of defects remarkably enhance the charge transfer between the adsorbed oxygen species and the active sites. These results may pave the avenue toward further investigation of metal/carbon materials in a wide range of electrocatalytic applications.

41A Porous Perovskite Nanofiber with Reinforced Aerophobicity for High-Performance Anion Exchange Membrane Water Splitting.PubMed

Lu Li, Zhilin Zheng, Jiaxing Li, et al.
Small. 2023 Sep;19(38):e2301261. doi: 10.1002/smll.202301261. Epub 2023 May 24.
Perovskite oxides stand out as emerging oxygen evolution reaction (OER) catalysts on account of their effective electrocatalytic performance and low costs. Nevertheless, perovskite oxides suffer from severe bubble overpotential and inhibited electrochemical performance in large current densities due to their small specific surface areas and structural compactness. Herein, the study highlights the electrospun nickel-substituted La Sr FeO (LSF) porous perovskite nanofibers, that is, La Sr Fe Ni O (denoted as ES-LSFN-x, x = 0, 0.1, 0.3, and 0.5), as high-performance OER electrocatalysts. The most effective La Sr Fe Ni O (ES-LSFN-0.5) nanofibers suggest a larger specific surface area, higher porosity, and faster mass transfer than the counterpart sample prepared by conventional sol-gel method (SG-LSFN-0.5), showing notably increased geometric and intrinsic activities. The bubble visualization results demonstrate that the enriched and nano-sized porosity of ES-LSFN-0.5 enables reinforced aerophobicity and rapid detachment of oxygen bubbles, thereby reducing the bubble overpotential and enhancing the electrochemical performance. As a result, the ES-LSFN-0.5-based anion exchange membrane water electrolysis delivers a superior stability of 100 h while the SG-LSFN-0.5 counterpart degrades rapidly within 20 h under a current density of 100 mA cm . The results highlight the advantage of porous electrocatalysts in optimizing the performance of large current density water electrolysis devices by reducing the bubble overpotential.

42Iron-Doped Nickel Molybdate with Enhanced Oxygen Evolution Kinetics.PubMed

Jiayi Chen, Guoqiang Zhao, Yaping Chen, et al.
Chemistry. 2019 Jan 2;25(1):280-284. doi: 10.1002/chem.201803844. Epub 2018 Dec 11.
Electrochemical water splitting is one of the potential approaches for making renewable energy production and storage viable. The oxygen evolution reaction (OER), as a sluggish four-electron electrochemical reaction, has to overcome high overpotential to accomplish overall water splitting. Therefore, developing low-cost and highly active OER catalysts is the key for achieving efficient and economical water electrolysis. In this work, Fe-doped NiMoO was synthesized and evaluated as the OER catalyst in alkaline medium. Fe doping helps to regulate the electronic structure of Ni centers in NiMoO , which consequently promotes the catalytic activity of NiMoO . The overpotential to reach a current density of 10 mA cm is 299 mV in 1 m KOH for the optimal Ni Fe MoO , which is 65 mV lower than that for NiMoO . Further, the catalyst also shows exceptional performance stability during a 2 h chronopotentiometry testing. Moreover, the real catalytically active center of Ni Fe MoO is also unraveled based on the ex situ characterizations. These results provide new alternatives for precious-metal-free catalysts for alkaline OER and also expand the Fe-doping-induced synergistic effect towards performance enhancement to new catalyst systems.

43Understanding the Role of (W, Mo, Sb) Dopants in the Catalyst Evolution and Activity Enhancement of Co O during Water Electrolysis via In Situ Spectroelectrochemical Techniques.PubMed

Thanh Tran-Phu, Manjunath Chatti, Joshua Leverett, et al.
Small. 2023 Jun;19(25):e2208074. doi: 10.1002/smll.202208074. Epub 2023 Mar 18.
Unlocking the potential of the hydrogen economy is dependent on achieving green hydrogen (H ) production at competitive costs. Engineering highly active and durable catalysts for both oxygen and hydrogen evolution reactions (OER and HER) from earth-abundant elements is key to decreasing costs of electrolysis, a carbon-free route for H production. Here, a scalable strategy to prepare doped cobalt oxide (Co O ) electrocatalysts with ultralow loading, disclosing the role of tungsten (W), molybdenum (Mo), and antimony (Sb) dopants in enhancing OER/HER activity in alkaline conditions, is reported. In situ Raman and X-ray absorption spectroscopies, and electrochemical measurements demonstrate that the dopants do not alter the reaction mechanisms but increase the bulk conductivity and density of redox active sites. As a result, the W-doped Co O electrode requires ≈390 and ≈560 mV overpotentials to reach ±10 and ±100 mA cm for OER and HER, respectively, over long-term electrolysis. Furthermore, optimal Mo-doping leads to the highest OER and HER activities of 8524 and 634 A g at overpotentials of 0.67 and 0.45 V, respectively. These novel insights provide directions for the effective engineering of Co O as a low-cost material for green hydrogen electrocatalysis at large scales.

44Facilitating alkaline hydrogen evolution reaction on the hetero-interfaced Ru/RuO through Pt single atoms doping.PubMed

Yiming Zhu, Malte Klingenhof, Chenlong Gao, et al.
Nat Commun. 2024 Feb 16;15(1):1447. doi: 10.1038/s41467-024-45654-9.
Exploring an active and cost-effective electrocatalyst alternative to carbon-supported platinum nanoparticles for alkaline hydrogen evolution reaction (HER) have remained elusive to date. Here, we report a catalyst based on platinum single atoms (SAs) doped into the hetero-interfaced Ru/RuO support (referred to as Pt-Ru/RuO), which features a low HER overpotential, an excellent stability and a distinctly enhanced cost-based activity compared to commercial Pt/C and Ru/C in 1 M KOH. Advanced physico-chemical characterizations disclose that the sluggish water dissociation is accelerated by RuO while Pt SAs and the metallic Ru facilitate the subsequent H* combination. Theoretical calculations correlate with the experimental findings. Furthermore, Pt-Ru/RuO only requires 1.90 V to reach 1 A cm and delivers a high price activity in the anion exchange membrane water electrolyzer, outperforming the benchmark Pt/C. This research offers a feasible guidance for developing the noble metal-based catalysts with high performance and low cost toward practical H production.

45Oxophilic gallium single atoms bridged ruthenium clusters for practical anion-exchange membrane electrolyzer.PubMed

Chenhui Zhou, Jia Shi, Zhaoqi Dong, et al.
Nat Commun. 2024 Aug 8;15(1):6741. doi: 10.1038/s41467-024-51200-4.
The development of highly efficient and durable alkaline hydrogen evolution reaction (HER) catalysts is crucial for achieving high-performance practical anion exchange membrane water electrolyzer (AEMWE) at ampere-level current density. Herein, we report a design concept by employing Ga single atoms as an electronic bridge to stabilize the Ru clusters for boosting alkaline HER performance in practical AEMWE. Experimental and theoretical results collectively reveal that the bridged Ga sites trigger strong metal-support interaction for the homogeneous distribution of Ru clusters with high density, as well as optimize the Ru-H bond strength due to the electron transfer between Ru and Ga for enhanced intrinsic HER activity. Moreover, the oxophilic Ga sites near the Ru clusters tend to adsorb the hydroxyl species and accelerate the water dissociation for sufficient proton supplement in an alkaline medium. The Ru-Ga/N-C catalyst exhibits a low overpotential of 4 ± 1 mV (10 mA cm) and high mass activity of 9.3 ± 0.5 A mg at -0.05 V vs RHE. In particular, the Ru-Ga/N-C-based AEMWE in 1 M KOH delivers a voltage of only 1.74 V to reach an industrial current density of 1 A cm, and can steadily operate at 1 A cm for more than 170 h.

46Rationally designed Ru catalysts supported on TiN for highly efficient and stable hydrogen evolution in alkaline conditions.PubMed

Jia Zhao, Ricardo Urrego-Ortiz, Nan Liao, et al.
Nat Commun. 2024 Jul 29;15(1):6391. doi: 10.1038/s41467-024-50691-5.
Electrocatalysis holds the key to enhancing the efficiency and cost-effectiveness of water splitting devices, thereby contributing to the advancement of hydrogen as a clean, sustainable energy carrier. This study focuses on the rational design of Ru nanoparticle catalysts supported on TiN (Ru NPs/TiN) for the hydrogen evolution reaction in alkaline conditions. The as designed catalysts exhibit a high mass activity of 20 A mg at an overpotential of 63 mV and long-term stability, surpassing the present benchmarks for commercial electrolyzers. Structural analysis highlights the effective modification of the Ru nanoparticle properties by the TiN substrate, while density functional theory calculations indicate strong adhesion of Ru particles to TiN substrates and advantageous modulation of hydrogen adsorption energies via particle-support interactions. Finally, we assemble an anion exchange membrane electrolyzer using the Ru NPs/TiN as the hydrogen evolution reaction catalyst, which operates at 5 A cm for more than 1000 h with negligible degradation, exceeding the performance requirements for commercial electrolyzers. Our findings contribute to the design of efficient catalysts for water splitting by exploiting particle-support interactions.

47Optimizing the Electronic Structure of Atomically Dispersed Ru Sites with CoP for Highly Efficient Hydrogen Evolution in both Alkaline and Acidic Media.PubMed

Zhuoping Wang, Kai Chi, Shengxiong Yang, et al.
Small. 2023 Jul;19(28):e2301403. doi: 10.1002/smll.202301403. Epub 2023 May 14.
Developing efficient and stable electrocatalysts for hydrogen evolution reaction (HER) over a wide pH range and industrial large-scale hydrogen production is critical and challenging. Here, a tailoring strategy is developed to fabricate an outstanding HER catalyst in both acidic and alkaline electrolytes containing high-density atomically dispersed Ru sites anchored in the CoP nanoparticles supported on carbon spheres (NC@Ru -CoP). The obtained NC@Ru -CoP catalyst exhibits excellent HER performance with overpotentials of only 15 and 13 mV at 10 mA cm in 1 m KOH and 0.5 m H SO , respectively. The experimental results and theoretical calculations indicate that the strong interaction between the Ru site and the CoP can effectively optimize the electronic structure of Ru sites to reduce the hydrogen binding energy and the water dissociation energy barrier. The constructed alkaline anion exchange membrane water electrolyze (AAEMWE) demonstrates remarkable durability and an industrial-level current density of 1560 mA cm at 1.8 V. This strategy provides a new perspective on the design of Ru-based electrocatalysts with suitable intermediate adsorption strengths and paves the way for the development of highly active electrocatalysts for industrial-scale hydrogen production.

48Operando Spectroscopic Analysis of CoP Films Electrocatalyzing the Hydrogen-Evolution Reaction.PubMed

Fadl H Saadi, Azhar I Carim, Walter S Drisdell, et al.
J Am Chem Soc. 2017 Sep 20;139(37):12927-12930. doi: 10.1021/jacs.7b07606. Epub 2017 Sep 8.
Transition metal phosphides exhibit high catalytic activity toward the electrochemical hydrogen-evolution reaction (HER) and resist chemical corrosion in acidic solutions. For example, an electrodeposited CoP catalyst exhibited an overpotential, η, of -η < 100 mV at a current density of -10 mA cm in 0.500 M HSO(aq). To obtain a chemical description of the material as-prepared and also while effecting the HER in acidic media, such electrocatalyst films were investigated using Raman spectroscopy and X-ray absorption spectroscopy both ex situ as well as under in situ and operando conditions in 0.500 M HSO(aq). Ex situ analysis using the tandem spectroscopies indicated the presence of multiple ordered and disordered phases that contained both near-zerovalent and oxidized Co species, in addition to reduced and oxygenated P species. Operando analysis indicated that the active electrocatalyst was primarily amorphous and predominantly consisted of near-zerovalent Co as well as reduced P.

49MOF-on-MOF-Derived Ultrafine FeP-CoP Heterostructures for High-Efficiency and Durable Anion Exchange Membrane Water Electrolyzers.PubMed

Hua Zhang, Anran Chen, Zenghui Bi, et al.
ACS Nano. 2023 Dec 12;17(23):24070-24079. doi: 10.1021/acsnano.3c09020. Epub 2023 Nov 27.
The alkaline hydrogen evolution reaction (HER) in an anion exchange membrane water electrolyzer (AEMWE) is considered to be a promising approach for large-scale industrial hydrogen production. Nevertheless, it is severely hampered by the inability to operate tolerable HER catalysts consistently under low overpotentials at ampere-level current densities. Here, we develop a universal ligand-exchange (MOF-on-MOF) modulation strategy to synthesize ultrafine FeP and CoP nanoparticles, which are well anchored on N and P dual-doped carbon porous nanosheets (FeP-CoP/NPC). In addition, benefiting from the downshift of the d-band center and the interfacial Co-P-Fe bridging, the electron-rich P site is triggered, which induces the redistribution of electron density and the swapping of active centers, lowering the energy barrier of the HER. As a result, the FeP-CoP/NPC catalyst only requires a low overpotential of 175 mV to achieve a current density of 1000 mA cm. The solar-driven water electrolysis system presents a record-setting and stable solar-to-hydrogen conversion efficiency of 20.36%. Crucially, the catalyst could stably operate at 1000 mA cm over 1000 h in a practical AEMWE at an estimated cost of US$0.79 per kilogram of H, which achieves the target (US$2 per kg of H) set by the U.S. Department of Energy (DOE).

50An Effective Approach to Enhance Hydrogen Evolution Reaction and Hydrogen Oxidation Reaction by Ni Doping to MoO.PubMed

Lijie Zhu, Zhixin Li, Muzi Yang, et al.
Small. 2023 Dec;19(49):e2303481. doi: 10.1002/smll.202303481. Epub 2023 Aug 17.
The development of bifunctional catalysts that facilitate both the hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) in alkaline environment is crucial for realizing unitized regenerative anion-exchange membrane fuel cells. In this study, a novel strategy to modulate the electron density of MoO through Ni doping (sample named Ni Mo O ) is reported. Ni is incorporated to replace Mo atoms in MoO . Specifically, Ni Mo O is combined with optimal adsorption energy, along with MoO /Mo N hybrid with high conductivity. The resulting Ni Mo O supported on MoO /Mo N hybrid (sample named as Ni Mo O -H) exhibits excellent alkaline HER activity, with an overpotential of only 16 mV at 10 mA cm and a Tafel slope of 54 mV dec . In addition, the Ni Mo O -H demonstrates an ultrahigh HOR performance with a high exchange current density (3.852 mA cm ). The catalyst's breakdown potential of 0.23 V indicates its ability to withstand higher voltages without breaking down. As evidenced by the results, this characteristic leads to improved stability. These results are higher than those of the other catalysts reported, which indicates that the electron density of MoO can be effectively modulated through Ni doping, leading to excellent HER and HOR performance.

51Flexible tungsten disulfide superstructure engineering for efficient alkaline hydrogen evolution in anion exchange membrane water electrolysers.PubMed

Lingbin Xie, Longlu Wang, Xia Liu, et al.
Nat Commun. 2024 Jul 8;15(1):5702. doi: 10.1038/s41467-024-50117-2.
Anion exchange membrane (AEM) water electrolysis employing non-precious metal electrocatalysts is a promising strategy for achieving sustainable hydrogen production. However, it still suffers from many challenges, including sluggish alkaline hydrogen evolution reaction (HER) kinetics, insufficient activity and limited lifetime of non-precious metal electrocatalysts for ampere-level-current-density alkaline HER. Here, we report an efficient alkaline HER strategy at industrial-level current density wherein a flexible WS superstructure is designed to serve as the cathode catalyst for AEM water electrolysis. The superstructure features bond-free van der Waals interaction among the low Young's modulus nanosheets to ensure excellent mechanical flexibility, as well as a stepped edge defect structure of nanosheets to realize high catalytic activity and a favorable reaction interface micro-environment. The unique flexible WS superstructure can effectively withstand the impact of high-density gas-liquid exchanges and facilitate mass transfer, endowing excellent long-term durability under industrial-scale current density. An AEM electrolyser containing this catalyst at the cathode exhibits a cell voltage of 1.70 V to deliver a constant catalytic current density of 1 A cm over 1000 h with a negligible decay rate of 9.67 μV h.

52Advanced development of anion-exchange membrane electrolyzers for hydrogen production: from anion-exchange membranes to membrane electrode assemblies.PubMed

Yun Chao Lei, Jiayang Zhou, Wentao Zhou, et al.
Chem Commun (Camb). 2024 Oct 1;60(79):11000-11016. doi: 10.1039/d4cc03043e.
Anion-exchange membrane water electrolysis (AEMWE) has attracted attention owing to its operation in alkaline environments, which offers the advantage of not requiring the use of precious metals. Additionally, AEMWE exhibits higher kinetics in the hydrogen evolution reaction, enabling higher hydrogen production efficiency. The anion-exchange membrane (AEM) fabrication, catalyst design, and membrane electrode assembly (MEA) are crucial for enhancing the total water electrolysis performance. There is an urgent need to summarize the advances in the development of AEMWE to pave the way for the commercialization of AEMWE. In this review, first, the fundamental principles of AEMWE technology are introduced. Second, the optimization of AEM with high ion conductivity and high stability through innovative synthetic methods are discussed in detail. Third, the designs of catalysts to increase the reaction rates by regulating the OH-adsorption environment and relieving OH blockage are introduced. Last but not least, a systematic summary of the concepts of 3D-ordered MEA, 3D-unified MEA, and 3D-self-supported MEA is presented. This review would be helpful to enhance the overall performance of AEMWE and promote the development of green hydrogen energy.

53Stabilizing Pure Water-Fed Anion Exchange Membrane Water Electrolyzers through Membrane-Electrode Interface Engineering.PubMed

Sinwoo Kang, Yeongin Kim, Vincent Wilke, et al.
ACS Appl Mater Interfaces. 2024 Sep 11;16(36):47387-47395. doi: 10.1021/acsami.4c05327. Epub 2024 Aug 27.
Nickel-iron (oxy)hydroxide (NiFeOH) stands as a cutting-edge nonprecious electrocatalyst for the oxygen evolution reaction (OER). However, the intrinsic thermodynamic instability of nickel and iron as anode materials in pure water-fed electrolyzers poses a significant durability challenge. In this study, an anion exchange ionomer coating was applied to NiFeOH to modify the local pH between a membrane and an electrode. This effectively extended the diffusion length of hydroxide anions toward the electrode, establishing an alkaline local pH environment. Stability tests with the ionomer coating showed reduced Ni dissolution. Moreover, locally resolved current density measurements were used to demonstrate a notably lower degradation rate during stability testing, revealing a 6-fold increase in stability with the ionomer on NiFeOH. In situ Raman spectroscopy in a neutral pH electrolyte confirmed inhibited Ni oxidation with the ionomer, mitigating Ni dissolution and enhancing stability of state-of-the-art NiFeOH catalysts in pure water-fed water electrolyzers.

54Tensile nanostructured hierarchically porous non-precious transition metal-based electrocatalyst for durable anion exchange membrane-based water electrolysis.PubMed

Kailash Singh, Kaliaperumal Selvaraj
J Colloid Interface Sci. 2024 Jun 15;664:389-399. doi: 10.1016/j.jcis.2024.02.170. Epub 2024 Mar 7.
Electrochemical water electrolysis is a promising method for sustainable hydrogen production while transiting towards hydrogen economy. Among many, the Anion Exchange Membrane (AEM) based water electrolyzer is an emerging yet potentially affordable technology on maturity for producing large-scale hydrogen accommodating the usage of Non-Platinum Group Metal (non-PGM) based inexpensive electrocatalysts. Herein, we demonstrate the excellent performance of a bifunctional Nickel Copper Phosphide-Nickel sulphide (NCP-NS) electrocatalyst with a unique tensile nanostructure obtained via a facile, controlled ambient galvanic displacement route. An AEM electrolyzer with a larger active area of 10 cm stacked with the symmetric NCP-NS electrodes and a membrane demonstrates scalability with a requirement of a mere 1.66 V to reach a current density of 10 mA cm. The nickel-copper phosphide boosts the kinetics of charge transfer between the electrode and electrolyte interface, while a unique combination of a few nickel sulphide phases present in the catalyst provides sufficiently appropriate active sites for the overall water electrolysis. For the first time, we report a room temperature performance of ∼ 230 mA cm at 2 V for a non-PGM-based bifunctional electrocatalyst with exceptional durability for over 300 h of operation in an AEM water electrolyser with a retention rate of 95 %-97 % at a current density range of 80-800 mA cm.

55Role of the Ionomer in Supporting Electrolyte-Fed Anion Exchange Membrane Water Electrolyzers.PubMed

Emily K Volk, Arielle L Clauser, Melissa E Kreider, et al.
ACS Electrochem. 2024 Nov 6;1(2):239-248. doi: 10.1021/acselectrochem.4c00061. eCollection 2025 Feb 6.
While anion exchange membrane water electrolyzers (AEMWEs) have achieved significant performance advances in recent decades, overpotentials remain high relative to their proton exchange membrane water electrolyzer (PEMWE) counterparts, requiring AEMWE-specific catalyst layer design strategies to further advance this technology. In this work, the role of the ionomer in catalyst layer structure and quality, catalyst layer stability, and ion conduction for supporting electrolyte-fed AEMWEs is assessed for catalyst layers composed of NiFeO and PiperION TP85 from Versogen at variable ionomer contents (0-30 wt %) for tests up to 200 h. The results reveal that, for supporting electrolyte-fed AEM devices, the ionomer is not required for ion conduction through the catalyst layer. Instead, the ionomer is found to play a critical role in catalyst layer structure and stability, where intermediate ionomer contents lead to the lowest overpotentials, highest effective surface areas, and lowest catalyst layer resistances. Catalyst layer stability is found to be a function of both catalyst adhesion and ionomer loss. These results show that an ionomer may be selected which is not of the same chemistry as the anion exchange membrane, mitigating ionomer stability concerns throughout the catalyst layer and offering a pathway towards highly active and stable AEMWEs.

56Ionomer Interphase Layers Enable Efficient Anion-Exchange Membrane Water Electrolyzer Operation at Low pH.PubMed

Arthur P L Thévenot, Thilo Reiter, Trung Ngo Thanh, et al.
Energy Fuels. 2025 Apr 23;39(17):8203-8210. doi: 10.1021/acs.energyfuels.5c00396. eCollection 2025 May 1.
Anion-exchange membrane water electrolysis (AEMWE) is an emerging green hydrogen technology. As of today, AEM water electrolyzers operate using highly alkaline electrolytes. Design strategies to operate AEMWE systems sustainably under lower alkalinity toward pure water conditions have become a scientific priority. Under low-alkaline conditions, the alkaline-exchange ionomer (AEI) is, in addition to the AEM, the key ion-transport medium inside the AEMWE cell. While prior work addressed ion transport and the ionomer-catalyst interface at the anode in low-pH AEMWEs, a thorough investigation at the cathode side, including different AEI architectures, received limited attention. In this contribution, we explore the impact of AEI architectures in AEMWE cathodes using an ionomer and a membrane that are both commercially available. We demonstrate separate ionomer top layer (ITL) interphases placed between the cathode catalyst layer and the membrane as the most effective strategy toward high cell performance under low pH feeding. ITLs enabled performance benefits even at pH 14, which leads us to perceive their mechanistic role as an ion-transport buffer enabling ready ion migration from the cathode to the anode. Our insights on the ITL architecture will aid the design of AEMWE cells for sustained efficient operation under pure water feeds.

57Porous Transport Layers for Anion Exchange Membrane Water Electrolysis: The Impact of Morphology and Composition.PubMed

Melissa E Kreider, Ambar R Maldonado Santos, Arielle L Clauser, et al.
ACS Electrochem. 2025 Feb 7;1(6):897-909. doi: 10.1021/acselectrochem.4c00207. eCollection 2025 Jun 5.
Anion exchange membrane water electrolysis (AEMWE) is an emerging technology for the low-cost production of hydrogen. However, the efficiency and durability of AEMWE devices is currently insufficient to compete with other low-temperature electrolysis technologies. The porous transport layer (PTL) is a critical cell component that remains relatively unoptimized for AEMWE. In this study, we demonstrate that device performance is significantly affected by the morphology and composition of the PTL. For Ni fiber-based PTLs with a ∼2 μm CoO oxygen evolution reaction catalyst layer, decreasing the pore size and porosity resulted in a 20% increase in current density at 2 V in 1 M KOH supporting electrolyte. Alloy PTLs with even lower porosity had a higher performance; in particular, the stainless steel PTL gave an 80% increase in current density relative to Ni. Without CoO, the alloy PTLs still demonstrated high activity, indicating that the PTL material was catalytically active. However, characterization of the electrode and electrolyte after testing indicated that the alloy PTLs also underwent restructuring and corrosion processes that may limit long-term stability. This study demonstrates that the design of PTLs with improved morphology and composition is an important area of focus to achieve AEMWE performance targets.

58Versatile Decal-Transfer Method for Fabricating and Analyzing Microporous Layers in Polymer Electrolyte Membrane Water Electrolysis.PubMed

Gi Hong Jung, Youg Hwa Yun, Sieon An, et al.
Small. 2025 Jun;21(22):e2500086. doi: 10.1002/smll.202500086. Epub 2025 May 2.
Polymer electrolyte membrane water electrolysis (PEMWE) is hindered by the reliance on expensive iridium-based catalysts. To address this economic challenge, minimizing iridium usage while maintaining performance and durability is imperative. Achieving this goal requires enhanced catalyst utilization through improved electron, ion, and mass transport within the anode. Recent research has increasingly emphasized the development of microporous layers (MPLs) as a key strategy for enhancing the interface between the porous transport layer (PTL) and the catalyst layer (CL). However, standardized methodologies for MPL design and fabrication remain elusive. In this study, a decal-transfer method is presented as an effective method for introducing a uniform, thin MPL at the CL/PTL interface. By varying the MPL properties, including pore size, thickness, and back-layer structure, two-phase transport phenomena are investigated and established guidelines for optimal MPL design. The findings reveal that smaller micrometer-scale pores in the MPL enhance catalyst utilization and strengthen water capillary force, thereby reducing kinetic and transport overpotentials. Moreover, it is demonstrated that, unless the back layer hinders the in-plane mass transport beneath the flow field, its structural configuration has minimal influence on electrolysis performance. These results underscore the importance of the CL/PTL interface in determining the overall efficiency of PEMWE systems.

59Optimized Ion-Transport Properties of Diallylammonium-Cyclopolymerized Anion-Exchange Membranes for High-Performance Water Electrolysis.PubMed

Juyeon Choi, Hansoo Kim, Yujin Nam, et al.
Small. 2025 Aug 19:e07437. doi: 10.1002/smll.202507437.
Anion-exchange membranes (AEMs) are the key components of AEM-based water electrolysis (AEMWE) for green hydrogen production. Unfortunately, many AEMs have unsatisfactory ion conductivity, and the factors governing their ion transport remain unclear. To address these limitations, herein, a new pyrrolidinium-containing diallylammonium-cyclopolymerized (PDT) AEM is proposed. Cyclopolymerization between diallyldimethylammonium chloride and tetraallylammonium bromide (TAAB, crosslinker) monomers in a porous polytetrafluoroethylene support yielded a pore-filled crosslinked PDT membrane, whose structure is controlled by adjusting its TAAB content. The OH conductivity of the PDT membrane is more strongly correlated with its OH diffusivity (determined by its internal water content) than its OH partitioning (determined by its internal charge content). The optimized PDT membrane exhibited low gas crossover and high thermomechanical stability. Importantly, it displayed excellent AEMWE performance in both pure water (0.71 A cm at 1.8 V) and 1 m KOH (5.25 A cm at 1.8 V) at 80 °C with half-platinum-group metal electrodes, outperforming many previously reported and commercial AEMs, owing to its significantly high OH conductivity. The PDT membrane also demonstrated stable AEMWE performance in 1 m KOH at 60 °C for 300 h. This study offers an effective means to fabricate high-performance AEMs and sheds light on their ion-transport mechanisms.

60Construction of Integrated Electrodes with Transport Highways for Pure-Water-Fed Anion Exchange Membrane Water Electrolysis.PubMed

Lei Wan, Jing Liu, Ziang Xu, et al.
Small. 2022 May;18(21):e2200380. doi: 10.1002/smll.202200380. Epub 2022 May 1.
The design of high-performance and durable electrodes for the oxygen evolution reaction (OER) is crucial for pure-water-fed anion exchange membrane water electrolysis (AEMWE). In this study, an integrated electrode with vertically aligned ionomer-incorporated nickel-iron layered double hydroxide nanosheet arrays, used on one side of the liquid/gas diffusion layer, is fabricated for the OER. Transport highways in the fabricated integrated electrode, significantly improve the transport of liquid/gas, hydroxide ions, and electron in the anode, resulting in a high current density of 1900 mA cm at 1.90 V in pure-water-fed AEMWE. Specifically, three-electrode and single-cell measurement results indicate that an anion-exchange ionomer can increase the local OH concentration on the integrated electrodes surface and facilitate the OER for pure-water-fed AEMWE. This study highlights a new approach to fabricating and understanding electrode architecture with enhanced performance and durability for pure-water-fed AEMWE.

61Stability of Ni-Fe-Layered Double Hydroxide Under Long-Term Operation in AEM Water Electrolysis.PubMed

Irina Galkina, Alaa Y Faid, Wulyu Jiang, et al.
Small. 2024 Jun;20(26):e2311047. doi: 10.1002/smll.202311047. Epub 2024 Jan 25.
Anion exchange membrane water electrolysis (AEMWE) is an attractive method for green hydrogen production. It allows the use of non-platinum group metal catalysts and can achieve performance comparable to proton exchange membrane water electrolyzers due to recent technological advances. While current systems already show high performances with available materials, research gaps remain in understanding electrode durability and degradation behavior. In this study, the performance and degradation tracking of a NiFe-LDH-based single-cell is implemented and investigated through the correlation of electrochemical data using chemical and physical characterization methods. A performance stability of 1000 h, with a degradation rate of 84 µV h at 1 A cm is achieved, presenting the NiFe-LDH-based cell as a stable and cost-attractive AEMWE system. The results show that the conductivity of the formed Ni-Fe-phase is one key to obtaining high electrolyzer performance and that, despite Fe leaching, change in anion-conducting binder compound, and morphological changes inside the catalyst bulk, the NiFe-LDH-based single-cells demonstrate high performance and durability. The work reveals the importance of longer stability tests and presents a holistic approach of electrochemical tracking and post-mortem analysis that offers a guideline for investigating electrode degradation behavior over extended measurement periods.

62Durable Anion Exchange Membrane Water Electrolysis in Low-Alkaline Concentration Electrolyte.PubMed

Haifeng Shen, Fei-Yue Gao, Haobo Li, et al.
J Am Chem Soc. 2025 Jul 2;147(26):22677-22685. doi: 10.1021/jacs.5c04194. Epub 2025 Jun 23.
Anion-exchange-membrane water electrolysis (AEMWE) is a promising technology for scalable green hydrogen production. However, the conventional use of high-alkalinity conditions accelerates membrane degradation, emphasizing the need for low-alkalinity operation to ensure long-term stability. For a low-alkalinity electrolyte with a high water-dissociation energy barrier, Ru serves as an ideal cathodic catalyst owing to its strong Ru-H bond, which provides distinguished water dissociation ability. However, the trade-off is high *H coverage, causing sluggish kinetics and limited durability during high-current operation. Herein, we developed an Ir-Ru solid solution catalyst, which enables rapid hydrogen transfer kinetics through a hydrogen spillover mechanism at high current. As a result, AEMWE with the Ir-Ru solid solution achieved a cell voltage of 1.75 V at 1 A cm in 0.05 M KOH. Notably, the low-alkalinity AEMWE cell exhibited exceptional durability for over 1000 h, surpassing most of the previously reported data under similar operating conditions. Isotope labeling and in situ characterizations confirmed that dissociated *H spills from efficient water-dissociation sites on Ru to favorable hydrogen-desorption sites on Ir with lower *H coverage, significantly improving activity and stability at high current densities.

63Stable Anion Exchange Membrane Bearing Quinuclidinium for High-performance Water Electrolysis.PubMed

Liqiang Yin, Rong Ren, Lanlan He, et al.
Angew Chem Int Ed Engl. 2024 May 6;63(19):e202400764. doi: 10.1002/anie.202400764. Epub 2024 Apr 8.
Anion exchange membranes (AEMs) are core components in anion exchange membrane water electrolyzers (AEM-WEs). However, the stability of functional quaternary ammonium cations, especially under high temperatures and harsh alkaline conditions, seriously affects their performance and durability. Herein, we synthesized a 1-methyl-3,3-diphenylquinuclidinium molecular building unit. Density functional theory (DFT) calculations and accelerated aging analysis indicated that the quinine ring structure was exceedingly stable, and the S2 degradation mechanism dominated. Through acid-catalyzed Friedel-Crafts polymerization, a series of branched poly(aryl-quinuclidinium) (PAQ-x) AEMs with controllable molecular weight and adjustable ion exchange capacity (IEC) were prepared. The stable quinine structure in PAQ-x was verified and retained in the ex situ alkaline stability. Furthermore, the branched polymer structure reduces the swelling rate and water uptake to achieve a tradeoff between dimensional stability and ionic conductivity, significantly improving the membrane's overall performance. Importantly, PAQ-5 was used in non-noble metal-based AEM-WE, achieving a high current density of 8 A cm at 2 V and excellent stability over 2446 h in a gradient constant current test. Based on the excellent alkaline stability of this diaryl-quinuclidinium group, it can be further considered as a multifunctional building unit to create multi-topological polymers for energy conversion devices used in alkaline environments.

64Performance and Durability of Pure-Water-Fed Anion Exchange Membrane Electrolyzers Using Baseline Materials and Operation.PubMed

Grace A Lindquist, Sebastian Z Oener, Raina Krivina, et al.
ACS Appl Mater Interfaces. 2021 Nov 10;13(44):51917-51924. doi: 10.1021/acsami.1c06053. Epub 2021 Aug 10.
Water electrolysis powered by renewable electricity produces green hydrogen and oxygen gas, which can be used for energy, fertilizer, and industrial applications and thus displace fossil fuels. Pure-water anion-exchange-membrane (AEM) electrolyzers in principle offer the advantages of commercialized proton-exchange-membrane systems (high current density, low cross over, output gas compression, etc.) while enabling the use of less-expensive steel components and nonprecious metal catalysts. AEM electrolyzer research and development, however, has been limited by the lack of broadly accessible materials that provide consistent cell performance, making it difficult to compare results across studies. Further, even when the same materials are used, different pretreatments and electrochemical analysis techniques can produce different results. Here, we report an AEM electrolyzer comprising commercially available catalysts, membrane, ionomer, and gas-diffusion layers operating near 1.9 V at 1 A cm in pure water. After the initial break in, the performance degraded by 0.67 mV h at 0.5 A cm at 55 °C. We detail the key preparation, assembly, and operation techniques employed and show further performance improvements using advanced materials as a proof-of-concept for future AEM-electrolyzer development. The data thus provide an easily reproducible and comparatively high-performance baseline that can be used by other laboratories to calibrate the performance of improved cell components, nonprecious metal oxygen evolution, and hydrogen evolution catalysts and learn how to mitigate degradation pathways.

65Degradation of QPPO-based anion polymer electrolyte membrane at neutral pH.PubMed

Zhiming Feng, Gaurav Gupta, Mohamed Mamlouk
RSC Adv. 2023 Jul 5;13(29):20235-20242. doi: 10.1039/d3ra02889e. eCollection 2023 Jun 29.
The chemical stability of anion polymer electrolyte membranes (AEMs) determines the durability of an AEM water electrolyzer (AEMWE). The alkaline stability of AEMs has been widely investigated in the literature. However, the degradation of AEM at neutral pH closer to the practical AEMWE operating condition is neglected, and the degradation mechanism remains unclear. This paper investigated the stability of quaternized poly(-phenylene oxide) (QPPO)-based AEMs under different conditions, including Fenton solution, HO solution and DI water. The pristine PPO and chloromethylated PPO (ClPPO) showed good chemical stability in the Fenton solution, and only limited weight loss was observed, 2.8% and 1.6%, respectively. QPPO suffered a high mass loss (29%). Besides, QPPO with higher IEC showed a higher mass loss. QPPO-1 (1.7 mmol g) lost nearly twice as much mass as QPPO-2 (1.3 mmol g). A strong correlation between the degradation rate of IEC and HO concentration was obtained, which implied that the reaction order is above 1. A long-term oxidative stability test at pH neutral condition was also conducted by immersing the membrane in DI at 60 °C water for 10 months. The membrane breaks into pieces after the degradation test. The possible degradation mechanism is that oxygen or OH˙ radicals attack the methyl group on the rearranged ylide, forming aldehyde or carboxyl attached to the CH group.

66N-Methylquinuclidinium-Based Anion Exchange Membrane with Ultrahigh Alkaline Stability.PubMed

Mengying Zeng, Xianying He, Ju Wen, et al.
Adv Mater. 2023 Dec;35(51):e2306675. doi: 10.1002/adma.202306675. Epub 2023 Nov 10.
Anion-exchange-membrane (AEM) water electrolysis is a promising technology for hydrogen production from renewable energy sources. However, the bottleneck of its development is the poor comprehensive performance of AEM, especially the stability at highly concentrated alkaline condition and temperature. Herein, a new cationic group N-methylquinuclidinium with enhanced alkaline stability is proposed and hereby a full-carbon chain poly(aryl quinuclidinium) AEM is prepared. Compared with reported AEMs, it shows ultrahigh comprehensive alkaline stability (no chemical decomposition, no decay of conductivity) in 10 m NaOH aqueous solution at 80 °C for more than 1800 h, excellent dimensional stability (swelling ratio: <10% in pure water, <2% in 10 m NaOH) in OH form at 80 °C, high OH conductivity (≈139.1 mS cm at 80 °C), and high mechanical properties (tensile strength: 41.5 MPa, elongation at break: 50%). The water electrolyzer using the AEM exhibits a high current density (1.94 A cm at 2.0 V) when assembled with nickel-alloy foam electrodes, and high durability when assembled with nickel foam electrodes.

67Synergistic Configuration of Binary Rhodium Single Atoms in Carbon Nanofibers for High-Performance Alkaline Water Electrolyzer.PubMed

Natarajan Logeshwaran, Gyuchan Kim, Pandiarajan Thangavel, et al.
Adv Sci (Weinh). 2025 Jan;12(3):e2413176. doi: 10.1002/advs.202413176. Epub 2024 Nov 24.
Electrochemical alkaline water electrolysis offers significant economic advantages; however, these benefits are hindered by the high kinetic energy barrier of the water dissociation step and the sluggish kinetics of the hydrogen evolution reaction (HER) in alkaline media. Herein, the ensemble effect of binary types of Rh single atoms (Rh-N and Rh-O) on TiO-embedded carbon nanofiber (Rh-TiO/CNF) is reported, which serves as potent active sites for high-performance HER in anion exchange membrane water electrolyzer (AEMWE). Density functional theory (DFT) analyses support the experimental observations, highlighting the critical role of binary types of Rh single atoms facilitated by the TiO sites. The Rh-TiO/CNF demonstrates an impressive areal current density of 1 A cm, maintaining extended durability for up to 225 h in a single-cell setup. Furthermore, a 2-cell AEMWE stack utilizing Rh-TiO/CNF is tested under industrial-scale conditions. This research makes a significant contribution to the commercialization of next-generation high-performance and durable AEMWE stacks for clean hydrogen production.

68Suppressing Mo-Species Leaching in MoO/A-NiS Cathode for Stable Anion Exchange Membrane Water Electrolysis at Industrial-Scale Current Density.PubMed

Husileng Lee, Guoheng Ding, Linqin Wang, et al.
Adv Sci (Weinh). 2025 Jul;12(27):e2502478. doi: 10.1002/advs.202502478. Epub 2025 Apr 30.
The development of non-noble metal-based hydrogen evolving reaction (HER) electrocatalysts operating under high current density plays a critical role in the large-scale application of anion exchange membrane water electrolysis (AEM-WE). Herein, a porous and hybrid MoS/NiS is synthesized on nickel foam (NF) via a one-step hydrothermal method and studied its reconstruction process during alkaline HER conditions. Experimental results indicated that the MoS underwent an oxidative dissolution followed by a dynamic equilibrium between dissolution and redeposition of the amorphous MoO during HER. Meanwhile, S-vacancy-rich NiS (A-NiS) is exposed and acts as the real active site for HER. The obtained MoO/A-NiS catalyst exhibited high catalytic performance in three-electrode systems and single-cell AEM-WE. Finally, for a long-term durability test in the AEM electrolyzer, a dry cathode method is applied to suppress the Mo species leaching from the MoO/A-NiS electrode. Remarkably, the device assembled by MoO/A-NiS as the cathode catalyst and NiFe as the anode catalyst demonstrated a high stability of 2500 h at 2 A cm and 40 °C with a small aging rate of 30 µV h.

69A frogspawn inspired twin MoC/Ni composite with a conductive fibrous network as a robust bifunctional catalyst for advanced anion exchange membrane electrolyzers.PubMed

Zhongmin Wan, Linqing Wang, Yuheng Zhou, et al.
Nanoscale. 2024 Mar 14;16(11):5845-5854. doi: 10.1039/d3nr06242b.
Anion exchange membrane water electrolysis (AEMWE) is considered one of the most cost-effective methods for producing green hydrogen. However, the performance of AEMWE is still restrained by the slow reaction kinetics and poor ion/electron transport of catalysts. Herein, inspired by frogspawn, MoC nanoparticles coupled with Ni were embedded into a N-doped porous carbon nanofiber network (MoC/NCNTs@Ni) by chemical crosslinking electrospinning combined with carbonization. The unique bionic structure can guarantee favorable overall structural flexibility and fast ion/electron transport kinetics. As a result of the robust hydrogen binding energy of MoC, as well as the synergistic impact between Ni and MoC nanoparticles and the conductive network resembling frogspawn, the catalyst developed demonstrates excellent performance in both the HER and OER. When employed as a bifunctional catalyst in water electrolysis, MoC/NCNTs@Ni delivers overpotentials of 155 mV and 320 mV at 10 mA cm for the HER and OER, respectively. In addition, the MoC/NCNTs@Ni also displays excellent long-term durability during a continuous operation test under different currents for 50 h. The assembled AEMWE electrolyzers with MoC/NCNTs@Ni as both the anode and cathode can achieve a current density of 82.5 mA cm at 1.99 V, indicating great potential for industrial water splitting. These results give an insight for the development of advanced bifunctional electrocatalysts for the next generation of green and efficient H production by water electrolysis.

70Anode Catalysts in Anion-Exchange-Membrane Electrolysis without Supporting Electrolyte: Conductivity, Dynamics, and Ionomer Degradation.PubMed

Raina A Krivina, Grace A Lindquist, Sarah R Beaudoin, et al.
Adv Mater. 2022 Sep;34(35):e2203033. doi: 10.1002/adma.202203033. Epub 2022 Jul 30.
Anion-exchange-membrane water electrolyzers (AEMWEs) in principle operate without soluble electrolyte using earth-abundant catalysts and cell materials and thus lower the cost of green H . Current systems lack competitive performance and the durability needed for commercialization. One critical issue is a poor understanding of catalyst-specific degradation processes in the electrolyzer. While non-platinum-group-metal (non-PGM) oxygen-evolution catalysts show excellent performance and durability in strongly alkaline electrolyte, this has not transferred directly to pure-water AEMWEs. Here, AEMWEs with five non-PGM anode catalysts are built and the catalysts' structural stability and interactions with the alkaline ionomer are characterized during electrolyzer operation and post-mortem. The results show catalyst electrical conductivity is one key to obtaining high-performing systems and that many non-PGM catalysts restructure during operation. Dynamic Fe sites correlate with enhanced degradation rates, as does the addition of soluble Fe impurities. In contrast, electronically conductive Co O nanoparticles (without Fe in the crystal structure) yield AEMWEs from simple, standard preparation methods, with performance and stability comparable to IrO . These results reveal the fundamental dynamic catalytic processes resulting in AEMWE device failure under relevant conditions, demonstrate a viable non-PGM catalyst for AEMWE operation, and illustrate underlying design rules for engineering anode catalyst/ionomer layers with higher performance and durability.

71Combinatorial Use of Reference Electrodes and DRT for Disentangling AEM Electrolyzer Losses.PubMed

Suhas Nuggehalli Sampathkumar, Thomas Benjamin Ferriday, Samaneh Daviran, et al.
Energy Fuels. 2025 Aug 15;39(34):16485-16500. doi: 10.1021/acs.energyfuels.5c01799. eCollection 2025 Aug 28.
Anion exchange membrane water electrolyzers (AEMWEs) offer a promising alternative to proton exchange membrane (PEM) electrolyzers, leveraging non-precious-metal catalysts and alkaline electrolytes for cost reduction. However, challenges persist in achieving long-term durability, high current densities, and stable membrane performance. While previous studies have examined AEM development, a comprehensive structural-electrochemical analysis of AEMWE components under prolonged operation remains limited. This study presents a detailed structural and electrochemical characterization of a commercial AEMWE, where its full-cell performance was matched with the intrinsic half-electrode performance through the use of dual reference electrodes. The electrochemical analysis was supported by a thorough tomographic and spectroscopic investigation of each electrode, thereby providing for the first time a complete materials analysis of the commercial NiFeO anode and Raney nickel cathode. Electrochemical characterization using LSV, EIS, and a dual reference electrode setup revealed full-cell performance of 1.0 A cm at 2.2 V (ambient) and 1.1 A cm at 2.0 V (60 °C), with an HHV efficiency of 74.5% at 1.0 A cm. Long-term operation over 1000 h at 1.0 A cm, 60 °C, in 1.0 M KOH resulted in a substantial polarization resistance increase beyond 230 h, despite an unexpected continuous improvement in MEA performance due to membrane degradation. DRT analysis, coupled with reference electrode studies, was critical in isolating losses. Low-frequency peaks (1.5-25 Hz) were linked to bubble formation, while intermediate-frequency (50-2000 Hz) and high-frequency (>2000 Hz) processes corresponded to charge transfer and ionic transport. The NiFeO anode exhibited better charge transfer, whereas the Raney nickel cathode showed higher polarization resistance.

72Novel Pyrrolidinium-Functionalized Styrene-b-ethylene-b-butylene-b-styrene Copolymer Based Anion Exchange Membrane with Flexible Spacers for Water Electrolysis.PubMed

Ziqi Xu, Sofia Delgado, Vladimir Atanasov, et al.
Membranes (Basel). 2023 Mar 13;13(3):328. doi: 10.3390/membranes13030328.
Anion exchange membranes (AEM) are core components for alkaline electrochemical energy technologies, such as water electrolysis and fuel cells. They are regarded as promising alternatives for proton exchange membranes (PEM) due to the possibility of using platinum group metal (PGM)-free electrocatalysts. However, their chemical stability and conductivity are still of great concern, which is appearing to be a major challenge for developing AEM-based energy systems. Herein, we highlight an AEM with styrene-b-ethylene-b-butylene-b-styrene copolymer (SEBS) as a backbone and pyrrolidinium or piperidinium functional groups tethered on flexible ethylene oxide spacer side-chains (SEBS-Py2O6). This membrane reached 27.8 mS cm hydroxide ion conductivity at room temperature, which is higher compared to previously obtained piperidinium-functionalized SEBS reaching up to 10.09 mS cm. The SEBS-Py206 combined with PGM-free electrodes in an AWE water electrolysis (AEMWE) cell achieves 520 mA cm at 2 V in 0.1 M KOH and 171 mA cm in ultra-pure water (UPW). This high performance indicates that SEBS-Py2O6 membranes are suitable for application in water electrolysis.

73Platinum-Ruthenium Dual-Atomic Sites Dispersed in Nanoporous NiSe Enabling Ampere-Level Current Density Hydrogen Production.PubMed

Lebin Cai, Haoyun Bai, Cheng-Wei Kao, et al.
Small. 2024 Jun;20(26):e2311178. doi: 10.1002/smll.202311178. Epub 2024 Jan 15.
Alkaline anion-exchange-membrane water electrolyzers (AEMWEs) using earth-abundant catalysts is a promising approach for the generation of green H. However, the AEMWEs with alkaline electrolytes suffer from poor performance at high current density compared to proton exchange membrane electrolyzers. Here, atomically dispersed Pt-Ru dual sites co-embedded in nanoporous nickel selenides (np/PtRu-NiSe) are developed by a rapid melt-quenching approach to achieve highly-efficient alkaline hydrogen evolution reaction. The np/PtRu-NiSe catalyst shows ampere-level current density with a low overpotential (46 mV at 10 mA cm and 225 mV at 1000 mA cm), low Tafel slope (32.4 mV dec), and excellent long-term durability, significantly outperforming the benchmark Pt/C catalyst and other advanced large-current catalysts. The remarkable HER performance of nanoporous PtRu-NiSe is attributed to the strong intracrystal electronic metal-support interaction (IEMSI) between Pt-Se-Ru sites and NiSe support which can greatly enlarge the charge redistribution density, reduce the energy barrier of water dissociation, and optimize the potential determining step. Furthermore, the assembled alkaline AEMWE with an ultralow Pt and Ru loading realizes an industrial-level current density of 1 A cm at 1.84 volts with high durability.

74Cross-Linked Anion-Exchange Membranes with Dipole-Containing Cross-Linkers Based on Poly(terphenyl isatin piperidinium) Copolymers.PubMed

Lin Tian, Junmin Li, Qiao Liu, et al.
ACS Appl Mater Interfaces. 2022 Aug 31;14(34):39343-39353. doi: 10.1021/acsami.2c08221. Epub 2022 Aug 23.
To balance the ionic conductivity and dimensional stability of anion-exchange membranes (AEMs), several cross-linked ether-free poly(terphenyl isatin piperidinium) copolymers were synthesized using 1,2-bis(2-aminoethoxy)ethane as a cross-linker. By introducing an alkyl diamine-based hydrophobic cross-linker as a control, the effects of the dipolar-molecule-containing cross-linker on the comprehensive performance of the membranes were investigated. Cation-dipole interactions between the cations and the hydrophilic ethylene oxide cross-linker enhance the self-assembly capability of the cationic groups. The introduction of the rotatable ethylene oxide cross-linker facilitates the flexibility of the cross-linked networks, thereby promoting hydrophilic/hydrophobic phase separation and inhibiting excessive swelling of the corresponding AEMs simultaneously. The resulting PTPBHIN-O membrane showed a high hydroxide conductivity (151.69 mS cm) and low swelling ratio (10.53%) at 80 °C. Furthermore, owing to the cross-linked structure and ether-free polymer backbone with high alkali resistance, the membranes treated in 3 M NaOH at 80 °C for 1600 h maintained ≥85% of their hydroxide conductivity, indicating excellent alkaline stability. A H/O fuel cell based on the PTPBHIN-O AEM exhibited a maximum power density of 398 mW cm at 515 mA cm.

75Cationic groups in polystyrene/O-PBI blends influence performance and hydrogen crossover in AEMWE.PubMed

Linus Hager, Maximilian Schrodt, Manuel Hegelheimer, et al.
Chem Commun (Camb). 2024 Dec 17;61(1):149-152. doi: 10.1039/d4cc05067c.
This study examines the effect of various quaternary ammonium groups on AEMWE performance and hydrogen crossover in blends of quaternized polystyrenes with O-PBI. Due to their higher hydroxide conductivity (69 mS cm at 80 °C, 90% RH), trimethylammonium groups enable AEMWE to reach 1.0 A cm at 2.0 V. The trimethylammonium groups exhibit low hydrogen crossover, ranging from 1.5% to 0.3%, across current densities of 50 to 1000 mA cm. Low hydrogen crossover is essential for AEMWE in terms of safety and efficiency.

76Engineering Robust Triazine Crosslinked and Pyridine Capped Anion Exchange Membrane for Advanced Water Electrolysis.PubMed

Guoxiong Deng, Yiwen Liao, Yakai Lin, et al.
Angew Chem Int Ed Engl. 2024 Dec 20;63(52):e202412632. doi: 10.1002/anie.202412632.
Exploring high-performance anion exchange membranes (AEM) for water electrolyzers (AEMWEs) is significant for green hydrogen production. However, the current AEMWEs are restricted by the poor mechanical strength and low OH conductivity of AEMs, leading to the low working stability and low current density. Here, we develop a robust AEM with polybiphenylpiperidium network by combining the crosslinking with triazine and the capping with pyridine for advanced AEMWEs. The AEM exhibits an excellent mechanical strength (79.4 MPa), low swelling ratio (19.2 %), persistent alkali stability (≈5,000 hours) and high OH conductivity (247.2 mS cm) which achieves the state-of-the-art AEMs. Importantly, when applied in AEMWEs, the corresponding electrolyzer equipped with commercial nickel iron and nickel molybdenum catalysts obtained a current density of up to 3.0 A cm at 2 V and could be stably operated ~430 h at a high current density of 1.6 A cm, which exceeds the most of AEMWEs. Our results suggest that triazine crosslinking and pyridine capping can effectively improve the overall performance of the AEMWEs.

77Boosting Oxygen Evolution Reaction of (Fe,Ni)OOH via Defect Engineering for Anion Exchange Membrane Water Electrolysis Under Industrial Conditions.PubMed

Libo Wu, Minghui Ning, Xinxin Xing, et al.
Adv Mater. 2023 Nov;35(44):e2306097. doi: 10.1002/adma.202306097. Epub 2023 Sep 21.
Developing non-precious catalysts with long-term catalytic durability and structural stability under industrial conditions is the key to practical alkaline anion exchange membrane (AEM) water electrolysis. Here, an energy-saving approach is proposed to synthesize defect-rich iron nickel oxyhydroxide for stability and efficiency toward the oxygen evolution reaction. Benefiting from in situ cation exchange, the nanosheet-nanoflake-structured catalyst is homogeneously embedded in, and tightly bonded to, its substrate, making it ultrastable at high current densities. Experimental and theoretical calculation results reveal that the introduction of Ni in FeOOH reduces the activation energy barrier for the catalytic reaction and that the purposely created oxygen defects not only ensure the exposure of active sites and maximize the effective catalyst surface but also modulate the local coordination environment and chemisorption properties of both Fe and Ni sites, thus lowering the energy barrier from *O to *OOH. Consequently, the optimized d-(Fe,Ni)OOH catalyst exhibits outstanding catalytic activity with long-term durability under both laboratory and industrial conditions. The large-area d-(Fe,Ni)OOH||NiMoN pair requires 1.795 V to reach a current density of 500 mA cm at an absolute current of 12.5 A in an AEM electrolyzer for overall water electrolysis, showing great potential for industrial water electrolysis.

78Interfacially Assembled Anion Exchange Membranes for Water Electrolysis.PubMed

Hansoo Kim, Sungkwon Jeon, Juyeon Choi, et al.
ACS Nano. 2024 Nov 26;18(47):32694-32704. doi: 10.1021/acsnano.4c10212. Epub 2024 Nov 14.
High-performance and durable anion exchange membranes (AEMs) are critical for realizing economical green hydrogen production through alkaline water electrolysis (AWE) or AEM water electrosysis (AEMWE). However, existing AEMs require sophisticated fabrication protocols and exhibit unsatisfactory electrochemical performance and long-term durability. Here we report an AEM fabricated via a one-pot, in situ interfacial Menshutkin reaction, which assembles a highly cross-linked polymer containing high-density quaternary ammoniums and nanovoids inside a reinforcing porous support. This structure endows the membrane with high anion-conducting ability, water uptake (but low swelling), and mechanical and thermochemical robustness. Consequently, the assembled membrane achieves excellent AWE (0.97 A cm at 1.8 V) and AEMWE (5.23 A cm at 1.8 V) performance at 5 wt % KOH and 80 °C, significantly exceeding that of commercial and previously developed membranes, and excellent long-term durability. Our approach provides an effective method for fabricating AEMs for various energy and environmental applications.