Modulating\nthe Coordination Environment of Cu-Embedded\nMo<i>X</i><sub>2</sub> (<i>X</i> = S, Se, and\nTe) Monolayers for Electrocatalytic Reduction of CO<sub>2</sub> to\nCH<sub>4</sub>: Un

The electrochemical CO<sub>2</sub> reduction reaction\n(CO<sub>2</sub>RR) is a promising approach to alleviating global warming\nand emerging\nenergy crises. Yet, the CO<sub>2</sub>RR efficiency is impeded by\nthe need for electrocatalysts with good selectivity and efficiency.\nRecently, single-atom catalysts (SACs) have attracted much attention\nin electrocatalysis and are more efficient than traditional metal-based\ncatalysts. In this study, we modeled a Cu single atom embedded on\nMo<i>X</i><sub>2</sub> (<i>X</i> = Se and Te)\nmonolayer with a single chalcogen (<i>X</i>) vacancy as\nSAC. Employing the dispersion-corrected density functional theory\n(DFT-D3) method, the electrocatalytic CO<sub>2</sub>RR activity of\nthe Cu-Mo<i>X</i><sub>2</sub> SACs is systematically investigated\nthrough significant descriptors, such as the Gibbs free energy change,\ncharge density difference, and COHP analysis. The stability of SACs,\nCO<sub>2</sub> adsorption configurations, and all possible reaction\npathways for the formation of C1 products (HCOOH, CO, CH<sub>3</sub>OH, and CH<sub>4</sub>) were examined. All of the Cu-Mo<i>X</i><sub>2</sub> SACs are stable and show high catalytic selectivity\nfor the CO<sub>2</sub>RR by significantly suppressing the hydrogen\nevolution reaction (HER). We found that the catalytic activity is\nmainly due to the level of antibonding states filling between the\nCu atom and *OCHOH intermediate. Among the C1 products, CH<sub>4</sub> is selectively produced in all three SACs. Notably, there is a decrease\nin the limiting potential (<i>U</i><sub><i>L</i></sub>) when <i>X</i> changes from S to Te in Cu-Mo<i>X</i><sub>2</sub>. Among these three SACs, Cu-MoTe<sub>2</sub> SAC is the most promising catalyst for reducing CO<sub>2</sub> to\nCH<sub>4</sub>, with as low as <i>U</i><sub><i>L</i></sub> of −0.34 V vs RHE. Our results demonstrate that the\nlocal coordination environment in SACs has a significant impact on\nthe catalytic activity of CO<sub>2</sub>RR.