Following structural changes in iridium nanoparticles during oxygen evolution electrocatalysis with operando X-ray total scattering

Understanding the structure of nanoparticles under (electro)catalytic operating conditions is crucial for uncovering structure-property relationships. By combining operando X-ray total scattering and PDF analysis with operando small angle X-ray scattering, we obtain comprehensive structural information on ultra-small (< 3 nm) iridium nanoparticles and track their changes during the acidic oxygen evolution reaction. When subjected to electrochemical conditions at reducing potentials, the metallic Ir nanoparticles are found to be decahedral clusters. Upon electrochemical oxidation, iridium oxide forms, containing small rutile-like clusters composed of edge- and corner-connected [IrO6] octahedra of very confined range. These rutile domains are less than 1 nm. Combined with SAXS analysis of the particle size, we find that the iridium oxide phase active in the oxygen evolution reaction (OER) lacks crystalline order.