Ir-based oxygen evolution reaction catalysts: Role of microstructure and activation protocols

Currently, the most efficient electrocatalysts for the oxygen evolution reaction (OER) in proton exchange membrane water electrolyzers (PEMWE) are Ir-based materials. Their remarkable performance stems from an optimal balance between high catalytic activity, and chemical and electrochemical stability in an acidic environment. The limited availability of Ir is, however, of great concern considering the worldwide energy transition and wide application of water electrolysis to obtain green hydrogen. Hence, to reduce its consumption, there is a need to enhance the catalyst activity and stability – allowing their utilization in the Gigawatt-scale electrolyzer production. Because the structure of an “as-received” catalyst is altered after application, it is essential to induce adjustments of the catalyst surface, which is responsible for high OER activity, prior to performance evaluation of the catalyst. However, the absence of a standardized catalyst activation/conditioning protocol complicates the direct comparison of results across different studies. This work investigates the effect of three activation protocols applied to Ir-based catalysts synthesized via different liquid-phase deposition approaches. The effects of the catalyst background and the activation protocol on catalysts' surface structure and performance were elucidated. The performance of the catalysts thus obtained is benchmarked against PEMWE operation. • Ir catalyst composition and surface morphology are critical for oxygen evolution reaction (OER) kinetics. • The choice of activation protocol has a significant impact on catalyst performance. • Activation via potential cycling enhances kinetics of the OER by amorphous Ir oxide growth. • Activation at OER-relevant potentials preserves metallic active sites and limits oxide shell growth. • For OER optimization, it is recommended that catalysts be evaluated using three different activation protocols.