Modulating the Coordination Environment of Cu-Embedded MoX2 (X = S, Se, and Te) Monolayers for Electrocatalytic Reduction of CO2 to CH4: Unveiling the Origin of Catalytic Activity

The electrochemical CO₂ reduction reaction (CO₂RR) is a promising approach to alleviating global warming and emerging energy crises. Yet, the CO₂RR efficiency is impeded by the need for electrocatalysts with good selectivity and efficiency. Recently, single-atom catalysts (SACs) have attracted much attention in electrocatalysis and are more efficient than traditional metal-based catalysts. In this study, we modeled a Cu single atom embedded on MoX₂ (X = Se and Te) monolayer with a single chalcogen (X) vacancy as SAC. Employing the dispersion-corrected density functional theory (DFT-D3) method, the electrocatalytic CO₂RR activity of the Cu-MoX₂ SACs is systematically investigated through significant descriptors, such as the Gibbs free energy change, charge density difference, and COHP analysis. The stability of SACs, CO₂ adsorption configurations, and all possible reaction pathways for the formation of C1 products (HCOOH, CO, CH₃OH, and CH₄) were examined. All of the Cu-MoX₂ SACs are stable and show high catalytic selectivity for the CO₂RR by significantly suppressing the hydrogen evolution reaction (HER). We found that the catalytic activity is mainly due to the level of antibonding states filling between the Cu atom and *OCHOH intermediate. Among the C1 products, CH₄ is selectively produced in all three SACs. Notably, there is a decrease in the limiting potential (U_L) when X changes from S to Te in Cu-MoX₂. Among these three SACs, Cu-MoTe₂ SAC is the most promising catalyst for reducing CO₂ to CH₄, with as low as U_L of -0.34 V vs RHE. Our results demonstrate that the local coordination environment in SACs has a significant impact on the catalytic activity of CO₂RR.