Metal coordination determines the catalytic activity of IrO2 nanoparticles for the oxygen evolution reaction

H2 production through water electrolysis is a promising strategy for storing sunlight energy. For the oxygen evolution reaction, iridium oxide containing materials are state-of-the-art due to their stability in acidic conditions. Moreover, precious metal content can be reduced by using small nanoparticles that show high catalytic activities. We performed DFT calculations on 1.2 nm large IrO2 Wulff-like stoichiometric nanoparticle model (IrO2) with aim of determining factors controlling activity nanoparticles. Results at reaction conditions tetra- and tricoordinated centers not fully oxidized, major species being IrO(OH) IrO(OH)2, respectively. Although computed overpotential all present relatively similar reactivities, low coordinated tend more active than pentacoordinates sites well-defined facets. These coordination likely abundant amorphous nanoparticles, which could one explaining higher observed non-crystalline materials.