Operando X-ray characterization platform to unravel catalyst degradation under accelerated stress testing in CO2 electrolysis

Membrane-electrode assembly (MEA)-based CO₂ electrolysis technology has a promising future to realize the industrial-scale production of diverse value-added chemical commodities. One crucial metric for CO₂ electrolysis is stability. However, comprehensive but distinguishable degradation mechanisms of catalyst and electrode in the MEA are still missing when assembled in the electrolyzer. Herein, a customized operando synchrotron X-ray characterization platform was first established to track the time- and space-resolved evolution of ions and water movements, crystal structure, and particle size of the catalyst in the entire MEA. Based on the model catalysts of Au and Ag, we reveal that the crystalline phase stability of catalyst and catalyst-substrate interaction together determine cathode durability. The D-ratio (i.e., diameter ratio achieved from a deep analysis of small/wide angle X-ray scattering) is a good descriptor to evaluate the structure stability of catalyst on electrode. Au catalysts with a more stable crystal structure and strong catalyst-substrate interaction possess a smaller D-ratio change as well as a better durability under a pulse-driven accelerated stress test in contrast to Ag catalysts, which degrade due to agglomeration and Ostwald ripening. This work demonstrates the broad capability of the newly developed operando X-ray characterization platform to unveil catalyst and electrode degradation in MEA-based devices.