Real-time observation of intermediate species in electrochemical oxygen evolution reactions on CoOx through soft X-ray absorption spectroscopy

• Species at electrode interface during OER were observed in real-time and operando . • The observation was achieved by wavelength-dispersive soft X-ray absorption spectroscopy. • A prominent evolution of XAS peaks attributed to the intermediates were observed. • he real-time XAS at solid-liquid interface will be highly useful for analysing electrocatalysis. • Abstruct. • Real-time monitoring of oxygen species during the OER on cobalt oxide, one of the major OER electrocatalysts, were achieved through operando observation using wavelength-dispersive X-ray absorption spectroscopy (XAS) at the oxygen K-edge. The XAS spectra were collected every 3 s during electrode potential sweeping for the OER, and oxygen intermediate species related to the rate-determining step of the OER were detected just below the onset potential. Moreover, the cobalt L-edge XAS results demonstrate that the Co 3 O 4 species dominates the surface of the electrode at a relatively high potential region, where the OER occurs. The present technique has significant potential for application in the analysis of solid-liquid interfaces, whose fundamental understanding is useful for further improvement of electrocatalysis.