Stability and Effects of Subsurface Oxygen in Oxide-Derived Cu Catalyst for CO₂ Reduction

Here, oxide-derived copper (OD-Cu) catalysts are promising candidates for the electrochemical CO₂ reduction reaction (CO₂RR) due to the enhanced selectivity toward ethylene over methane evolution, which has been linked to the presence of subsurface oxygen (O_sb). In this work, O_sb is investigated with theoretical methods. Although O_sb is unstable in slab models, it becomes stabilized within a "manually" reduced OD-Cu nanocube model which was calculated by self-consistent charge density functional tight binding (SCC-DFTB). The results obtained with SCC-DFTB for the full nanocube were confirmed with subcluster models extracted from the nanocube, calculated with both density functional theory (DFT) and SCC-DFTB. The higher stability of O_sb in the nanocube is attributed to the disordered structure and greater flexibility. The adsorption strength of CO on Cu(100) is enhanced by O_sb withdrawing electron density from the Cu atom, resulting in reduction of the σ-repulsion. Hence, the coverage of CO may be increased, facilitating its dimerization.