Advanced Characterization of Proton Exchange Membrane Water Electrolyzers with Spatially‐Resolved X‐Ray Imaging

Abstract Electrocatalysis plays an increasing importance in mitigating chemical emissions, driving research on electrolysis for H 2 production. In this regard, it is a well‐known challenge for the electrochemistry community that the key catalyst components for both the oxygen and hydrogen evolution reactions (OER, HER) are expensive noble metals that urgently require optimization, especially with respect to the degradation of proton exchange water electrolyzer (PEMWE). Optimized design and strategies to reduce the degradation of multiple components are essential to avoid misuse of these catalysts. For this purpose, visualizing chemical and structural changes at an intermediate scale and linking them with degradation processes is crucial to bridge the gap between process‐scale PEMWE and lab‐scale research, which generally focuses on model systems. In this review, we present multiple synchrotron case studies, from operando to ex situ, discussing the approaches currently used in the field over the last few years. With the depth discussion of strategies to spatially resolve intermediate‐scale devices using synchrotron‐based hard X‐rays, we hope to guide further research in the electrochemistry community by adding specialized tools to the current set of characterization techniques.