Insights of the Proton Transport Efficiency of a Membrane Electrode Assembly by Operando Monitoring of the Local Proton Concentration during Water Oxidation.

Direct estimation of the reaction environment, e.g., local pH at the anode side of a membrane electrode assembly (MEA) of zero gap electrolyzer, is essential to understand possible key factors, which are influencing the sustainable operation of industrial electrolyzers. Herein, we demonstrate a scanning electrochemical microscopy-based strategy to measure the local pH in the close vicinity of an operating MEA. Local proton concentration changes during the oxygen evolution reaction were monitored in the nonzero gap electrolyzer and MEA systems. The measurements constitute a methodology to evaluate the ion transport efficiency of the MEA. The strategy was extended to investigate the effect of an activation process, buffering of the electrolyte, and poisoning effect on the change in proton transport efficiency. This novel strategy enables the estimation of the actual pH of the MEA system during operation and is of great relevance in understanding the process conditions during sustainable fuel production.