Activity and Durability of Iridium Nanoparticles in the Oxygen Evolution Reaction

Unsupported iridium (Ir) nanoparticles, a benchmark catalyst in acidic electrolyzers, are investigated for oxygen evolution activity in rotating disk electrode (RDE) half-cells. Mercury underpotential deposition, used to evaluate the electrochemical surface areas (ECAs) of Ir, produces similar values prior to and following oxygen evolution testing and irreversible surface oxidation; stable ECA measurements allow for the study of site-specific activities prior to and following accelerated stress tests. Durability testing results in increasing activity losses due to particle growth at moderate potential and Ir dissolution at higher potential. Although the prolonged formation of oxygen bubbles may destabilize the catalyst layer, accelerated stress tests in hydrogen peroxide and formic acid confirm that the losses are primarily potential dependent. This study establishes RDE testing protocols for Ir in oxygen evolution. The observed durability losses have significant implications on acidic electrolyzers, particularly at low Ir loadings.