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.

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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 (UL) 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 UL 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.