Dynamic interactions between adsorbates and catalyst surfaces over long-term OER stability testing in acidic media.

[Display omitted] • Dynamic Ir electronic and geometric structural change with surface adsorption. • pH-dependent oxygenate adsorption and Ir dissolution pathway. • Unfavorable adsorption coincides with distorted Ir linkage and decreased Ir valence state. The interaction between catalyst surfaces and adsorbed oxygen intermediates is critical to catalytic performance for electrochemical water oxidation to oxygen. However, the relationship between adsorption energetics and electrocatalytic activity is primarily assessed for pristine catalyst materials, which leaves much unknown about the dynamics of these properties in relationship to catalyst performance during long-term operation. In this work, we experimentally assess OH and O adsorption on Ca 2 IrO 4 nanoparticles and monitor their evolution during extensive chronoamperometry tests at highly oxidizing potentials in a range of low pH electrolytes. In situ x-ray absorption spectroscopy reveals changes for surface adsorbate energetics and local iridium structures with applied potentials. Increasingly unfavorable adsorption of OH and formation of O intermediates after long-term operation is correlated with severe metal dissolution, distorted [IrO 6 ] octahedral linkages, and a decreased average Ir valence. This work establishes connections between surface adsorption energetics, Ir structure, OER kinetics, and material stability outcomes. [ABSTRACT FROM AUTHOR]