(623c) In-Situ Analysis of Oxygen Evolution Reaction on CuO By Scanning Electrochemical Microscopy: Determining Active Sites Density and Microkinetics

The oxygen evolution reaction (OER) plays a pivotal role in electrochemical processes, serving as the anodic half-reaction in water electrolysis and electrochemical CO₂ conversion technologies. Recently, Cu composites have gathered significant attention as OER electrocatalysts due to their low costs and high performance. Particularly, CuO-based electrocatalysts have exhibited notable OER activities. The formation of metastable species (Cu^III) on CuO surfaces is known to serve as active sites for the OER with relatively fast kinetics. However, the lack of quantitative insights on the active sites limits further understanding of kinetics and the development of better performing CuO-based electrocatalysts. In this talk, I will discuss in-situ investigation of CuO surface during the OER in alkaline solution (pH 13) by using surface interrogation scanning electrochemical microscopy (SI-SECM). SI-SECM allows in-situ assessment of surface-adsorbed reaction intermediates on the catalysts. A tip electrode is placed above the CuO electrode with a small gap. Application of electrode potential at the CuO generates surface intermediates, which then oxidizes molecular probes dissolved in the solution. Coulometric detection of the oxidized molecular probes at the tip electrode enables titration of the surface intermediates. We identified the key potential of 0.72 V (vs. Ag/AgCl), corresponding to the saturation of active sites (Cu^III) on the CuO surface, leading to substantial increases in the OER activity. By combining with Tafel slopes and lattice constant, we confirmed rate determining step and estimated the active site density of about 25 Cu^III active sites/nm². Furthermore, a pseudo-first order rate constant of the intermediates for the OER was determined as k’=0.018 (±0.003) s^-1. The detailed understanding of the dynamics and kinetics of the OER on CuO would pave a road to further develop the high performing CuO-based OER electrocatalysts.