Probing Electrocatalytic Gas Evolution Reaction at Pt by Force Noise Measurements. Part 2. Oxygen

Understanding O₂ bubble nucleation and growth during the oxygen evolution reaction (OER) is crucial to comprehend their influence on the location and distribution of catalytically active sites in the process. To achieve this goal, mapping the spatial variation of nanoscale dynamic individual steps at the electrocatalytic interfaces is vital, as it further enables a detailed understanding of the mechanism of the process. Here, we combine tapping mode AFM imaging with a Pt ultramicroelectrode to investigate oxygen bubble nucleation, growth, and detachment. Our AFM feedback error signal and topography data reveal that O₂ gas bubbles nucleate at step-edge sites and interact with catalytically active sites. This interaction between primary catalytic sites and bubble nucleation sites is the main reason for a decrease in the current density at a given high overpotential of the OER. Our findings advance the understanding of the complexity of phenomena involved in electrolytic gas evolution reactions on catalytic surfaces.