Structural development on Ru and RuO2 electrodes during oxygen evolution – a soft X-ray absorption spectroscopy approach

• The paper describes an operando application of the soft XAS of oxygen evolution on Ru based electrodes. • The energy dispersive XAS spectra follow the formation of surface oxygen containing species. • The energy dispersive XAS spectra also reflect local electronic structure. • Experiments confirm the confinement of OER on Ru oxides to cus sites binding the intermediates through e g contributing orbitals. • OER process is controlled by the 3rd electron transfer at high overpotentials. Time resolved in-situ X-ray absorption spectroscopy (XAS) in soft X-ray region was used to characterize polarized interphase on Ru and Ru oxide based electrodes under oxygen evolution reaction (OER) conditions. XAS spectra were used to align the type and population of oxygen-containing species formed at electrodes at anodic potentials with local electronic structure of the OER catalyst. The soft XAS data do not identify a single rate limiting process for OER at potentials negative to 1.7 V vs. RHE. Individual intermediates of the oxygen evolution process coexist at the surface at potentials preceding the actual OER onset. The OER is accompanied with redistribution of the electron density resulting for a start of the catalytic cycle reflecting the transfer of the electrons from water to the external circuit during catalyzed water oxidation. The observed spectral behavior indicates a confinement of the OER to the coordination unsaturated sites ( cus ) at the surface.