Dynamic Surface Evolution and O Diffusion in High-Index Cu ₂ O Surfaces for Enhanced Electrochemical CO ₂ Reduction

High-index Cu2O surfaces are attractive catalysts for electrochemical CO2 reduction (eCO2RR), owing to their rich distribution of coordinatively unsaturated active sites that enable efficient C2+ product formation at low overpotentials. In this work, we employ ab initio molecular dynamics (AIMD) simulations to investigate the surface restructuring behavior of pristine and oxide-derived (OD) high-index Cu2O[(200), (210), and (211)] surfaces, with O removal extending up to the third subsurface layer. The calculated energy profiles show an initial drop followed by equilibration, indicating surface restructuring. Surface roughness analysis reveals a progressive downward shift of Cu atoms with increasing O vacancies. Structural evolution is primarily driven by the diffusion of near-surface Cu and O atoms, while deeper bulk atoms remain largely immobile. Notably, subsurface O diffusion alters the coordination environment of Cu atoms, leading to agglomeration on oxide-derived surfaces. These changes directly impact the adsorption behavior of key C–C coupling intermediate *CO–*CO, which governs C2 product formation. Our findings highlight that controlled O removal enables modulation of surface coordination and reactivity, offering an atomistic understanding of how OD surface evolution governs catalytic performance in eCO2RR.