In situ analysis of the oxygen evolution reaction on the CuO film in alkaline solution by surface interrogation scanning electrochemical microscopy: investigating active sites (CuIII) and kinetics

Abstract

This study examines the CuO film as a non-precious metal catalyst for the oxygen evolution reaction (OER) in an alkaline solution (pH 13) using surface interrogation scanning electrochemical microscopy (SI-SECM). We identified a key potential of 0.72 V (vs. Ag/AgCl), at which the saturation of Cu^III active sites on the CuO surface occurs (about 25 Cu^III active sites per nm²), marking a significant increase in electrocatalytic OER activity. SI-SECM and Tafel slope analysis revealed varying concentrations of adsorbed intermediates depending on the applied potential during the OER. The combination of these findings with active site analysis led to the identification of the rate-determining step (RDS) for the OER on the CuO film. Furthermore, SI-SECM with controlled time-delay experiments was conducted to determine a rate constant of the reaction intermediates of 0.018 (±0.003) s⁻¹. The results of this study highlight the potential of CuO as an effective and economical OER catalyst, offering critical insights for future development of CuO-based electrocatalysts.