Degradation Mechanism of Calcium Iridium Oxide for Oxygen Evolution Reaction in Acid

The development of active and acid-stable iridium-based catalysts is crucial to meet the requirements of proton exchange membrane technologies for the sustainable production of hydrogen via water electrolysis. However, long-term stability remains a critical challenge. In this work, we focus on a Ca2IrO4 catalyst to develop a holistic picture of catalyst electronic and geometric structure evolution under various applied potentials by probing electrochemically active surface area, metal dissolution, Ir valence, and surface morphology. We observe an initial activity increase in parallel with increasing capacitance and minor iridium dissolution. Extensive chronoamperometry tests at oxidizing potentials lead to significant activity loss that occurs simultaneously with a dramatic drop in capacitance and a change in impedance. Using a combination of electrochemical and spectroscopic tools, we provide fundamental insights to these material degradation processes to enable future catalyst design with balanced activity and long-term stability.