Department of Mechanical Engineering , University of California Merced , California 95343 , United States.
Department of Chemical Engineering, College of Engineering , University of the Philippines Diliman , Quezon City 1101 , Philippines.
ACS Appl Mater Interfaces. 2019 Sep 18;11(37):33748-33758. doi: 10.1021/acsami.9b06889. Epub 2019 Sep 5.
Traditional understanding of electrocatalytic reactions generally focuses on either covalent interactions between adsorbates and the reaction interface (i.e., electrical double layer, EDL) or electrostatic interactions between electrolyte ions. Here, our work provides valuable insights into interfacial structure and ionic interactions during alkaline oxygen evolution reaction (OER). The importance of inner-sphere OH adsorption is demonstrated as the IrO activity in 4.0 M KOH is 6.5 times higher than that in 0.1 M KOH. Adding NaNO as a supporting electrolyte, which is found to be inert for long-term stability, complicates the electrocatalytic reaction in a half cell. The nonspecially adsorbed Na in the outer compact interfacial layer is suggested to form a stronger noncovalent interaction with OH through hydrogen bond than adsorbed K, leading to the decrease of interfacial OH mobility. This hypothesis highlights the importance of outer-sphere adsorption for the OER, which is generally recognized as a pure inner-sphere process. Meanwhile, based on our experimental observations, the pseudocapacitive behavior of solid-state redox might be more reliable in quantifying active sites for OER than that measured from the conventional EDL charging capacitive process. The interfacial oxygen transport is observed to improve with increasing electrolyte conductivity, ascribing to the increased accessible active sites. The durability results in a liquid alkaline electrolyzer which shows that adding NaNO into KOH solution leads to additional degradation of OER activity and long-term stability. These findings provide an improved understanding of the mechanistic details and structural motifs required for efficient and robust electrocatalysis.
传统的电催化反应理解通常集中在吸附物与反应界面（即双电层，EDL）之间的共价相互作用或电解质离子之间的静电相互作用上。在这里，我们的工作为碱性析氧反应（OER）过程中的界面结构和离子相互作用提供了有价值的见解。证明内球 OH 吸附的重要性，因为在 4.0 M KOH 中的 IrO 活性比在 0.1 M KOH 中的活性高 6.5 倍。添加作为支持电解质的 NaNO，其发现对长期稳定性是惰性的，这使半电池中的电催化反应变得复杂。建议在外部紧密界面层中非特异性吸附的 Na 通过氢键与 OH 形成比吸附的 K 更强的非共价相互作用，从而降低界面 OH 的迁移率。该假设强调了 OER 中外球吸附的重要性，而 OER 通常被认为是一个纯粹的内球过程。同时，根据我们的实验观察，固态氧化还原的赝电容行为可能比从传统的 EDL 充电电容过程测量更可靠地定量 OER 的活性位点。观察到界面氧传输随着电解质电导率的增加而改善，这归因于增加了可及的活性位点。在液体碱性电解质中进行的耐久性测试表明，在 KOH 溶液中添加 NaNO 会导致 OER 活性和长期稳定性的额外降解。这些发现为高效和稳健的电催化所需的机理细节和结构基元提供了更好的理解。
