Operando and Postmortem Study of Iridium-Decorated Titanium-Based Catalysts in PEM Water Electrolysis

Understanding the dynamic degradation of oxygen- evolution electrocatalysts under realistic operating conditions is essential for advancing the performance and efficiency of proton exchange membrane (PEM) water electrolyzers. By combining operando Small-Angle and Wide-Angle X-ray Scattering (SAXS/ WAXS) with electrochemical measurements, the evolution of iridium nanoparticles supported on TiO2, TiC, and TiN, loaded on full membrane electrode assemblies, and undergoing accelerated stress testing in these assemblies has been monitored in real time. SAXS analysis shows pronounced Ostwald ripening of Ir on TiO2, resulting in particle growth from 1.5 to 2.2 nm and a corresponding loss of electrochemically active surface area. In contrast, Ir supported on TiC remains morphologically stable. However, the TiC support undergoes severe degradation, losing approximately 80% crystallinity and releasing Ti species that migrate across the membrane. TiN exhibits an intermediate behavior, showing partial oxidation, moderate Ir growth, and limited Ti migration. Postmortem transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy corroborate results from operando analyses. Results confirm the dissolution and oxidation of Ti in TiC and TiN, as well as the structural stability ofTiO2, and better describe the boundaries of the trade-off between nanoparticle stability and support robustness. Moreover, results underscore the need to design catalyst−support systems capable of simultaneously suppressing Ir ripening and mitigating support corrosion. Finally, this study demonstrates the capabilities of operando SAXS/WAXS analysis from full membrane electrode assemblies to elucidate degradation pathways and inform the development of durable, next-generation anode catalysts for PEM electrolyzers.