Krivina Raina A, Lindquist Grace A, Yang Min Chieh, Cook Amanda K, Hendon Christopher H, Motz Andrew R, Capuano Christopher, Ayers Katherine E, Hutchison James E, Boettcher Shannon W
Department of Chemistry and Biochemistry and Materials Science Institute, University of Oregon, Eugene, Oregon 97403, United States.
Oregon Center for Electrochemistry, University of Oregon, Eugene, Oregon 97403, United States.
ACS Appl Mater Interfaces. 2022 Apr 27;14(16):18261-18274. doi: 10.1021/acsami.1c22472. Epub 2022 Apr 18.
Among existing water electrolysis (WE) technologies, anion-exchange-membrane water electrolyzers (AEMWEs) show promise for low-cost operation enabled by the basic solid-polymer electrolyte used to conduct hydroxide ions. The basic environment within the electrolyzer, in principle, allows the use of non-platinum-group metal catalysts and less-expensive cell components compared to acidic-membrane systems. Nevertheless, AEMWEs are still underdeveloped, and the degradation and failure modes are not well understood. To improve performance and durability, supporting electrolytes such as KOH and KCO are often added to the water feed. The effect of the anion interactions with the ionomer membrane (particularly other than OH), however, remains poorly understood. We studied three commercial anion-exchange ionomers (Aemion, Sustainion, and PiperION) during oxygen evolution (OER) at oxidizing potentials in several supporting electrolytes and characterized their chemical stability with surface-sensitive techniques. We analyzed factors including the ionomer conductivity, redox potential, and pH tolerance to determine what governs ionomer stability during OER. Specifically, we discovered that the oxidation of Aemion at the electrode surface is favored in the presence of CO/HCO anions perhaps due to the poor conductivity of that ionomer in the carbonate/bicarbonate form. Sustainion tends to lose its charge-carrying groups as a result of electrochemical degradation favored in basic electrolytes. PiperION seems to be similarly negatively affected by a pH drop and low carbonate/bicarbonate conductivity under the applied oxidizing potential. The insight into the interactions of the supporting electrolyte anions with the ionomer/membrane helps shed light on some of the degradation pathways possible inside of the AEMWE and enables the informed design of materials for water electrolysis.
在现有的水电解（WE）技术中，阴离子交换膜水电解槽（AEMWEs）显示出通过用于传导氢氧根离子的碱性固体聚合物电解质实现低成本运行的前景。与酸性膜系统相比，电解槽内的碱性环境原则上允许使用非铂族金属催化剂和成本较低的电池组件。然而，AEMWEs仍未得到充分发展，其降解和失效模式尚未得到很好的理解。为了提高性能和耐久性，通常会向进水添加诸如KOH和KCO等支持电解质。然而，阴离子与离聚物膜（特别是除OH以外的其他离子）之间相互作用的影响仍然知之甚少。我们在几种支持电解质中，在氧化电位下对三种商业阴离子交换离聚物（Aemion、Sustainion和PiperION）进行了析氧反应（OER）研究，并用表面敏感技术对它们的化学稳定性进行了表征。我们分析了包括离聚物电导率、氧化还原电位和pH耐受性等因素，以确定在OER过程中是什么决定了离聚物的稳定性。具体而言，我们发现，在存在CO/HCO阴离子的情况下，电极表面的Aemion氧化更易发生，这可能是由于该离聚物在碳酸盐/碳酸氢盐形式下的电导率较差。由于在碱性电解质中有利于发生电化学降解，Sustainion往往会失去其载流基团。在施加的氧化电位下，PiperION似乎同样受到pH下降和低碳酸盐/碳酸氢盐电导率的负面影响。对支持电解质阴离子与离聚物/膜相互作用的深入了解有助于揭示AEMWE内部一些可能的降解途径，并有助于为水电解材料的明智设计提供依据。
