Combining Operando SAXS and Ex Situ Photoemission Spectroscopy for Tracking the Degradation Process of Pt/C Electrocatalysts

Abstract The durability of Pt/C electrocatalysts remains a central challenge for proton-exchange membrane fuel cells (PEMFCs), where Pt nanoparticle agglomeration and dissolution drive the loss of electrochemically active surface area (ECSA) during operation. Although ECSA loss is driven by coupled changes in Pt nanoparticle morphology and surface chemical state, these two contributions are difficult to separate. Here, we report a combined characterization using synchrotron-based operando small-angle X-ray scattering (SAXS) and ex situ photoemission spectroscopy to correlate nanoparticle growth with the evolution of surface chemical states in high-surface-area carbon-supported Pt catalysts. Operando SAXS reveals an overall increase in the apparent diameter of Pt nanoparticles during accelerated stress test (AST) cycling, consistent with irreversible particle growth. This increasing trend is periodically interrupted by decreases in the apparent diameter after each electrochemical cleaning step inserted between AST segments. Further ex situ photoemission analysis of the degraded Pt/C electrodes reveals Pt–O(H)-related surface signatures that depend on the preceding AST and cleaning conditions. These findings highlight the importance of combining hard X-ray operando scattering with ex situ soft X-ray surface-sensitive spectroscopy to relate the evolution of surface adsorption to that of nanoparticle morphology during electrocatalyst degradation.