2D-Mn₂C₁₂: An Optimal Electrocatalyst with Nonbonding Multiple Single Centers for CO₂-to-CH₄ Conversion

The CO₂ reduction reaction (CO₂RR) is a promising method that can both mitigate the greenhouse effect and generate valuable chemicals. The 2D-M₂C₁₂ with high-density transition metal single atoms is a potential catalyst for various catalytic reactions. Using an effective strategy, we screened 1s-Mn₂C₁₂ as the most promising electrocatalyst for the CO₂RR in the newly reported 2D-M₂C₁₂ family. A low applied potential of -0.17 V was reported for the CO₂-to-CH₄ conversion. The relative weak adsorption of H atom and H₂O in the potential range of -0.2 to -0.8 V, ensures the preferential adsorption of CO₂ and the following production of CH₄. The different loading amounts of Mn atoms on γ-graphyne (GY) were also investigated. The Mn atoms prefer doping in the nonadjacent triangular pores instead of the adjacent ones due to the repulsive forces between d-orbitals when the Mn loading is less than 32.3 wt % (5Mn). As the Mn concentration further increases, adjacent Mn atoms begin to appear, and the Mn@GY becomes metallic or half-metallic. The presence of four adjacent Mn atoms increases the d-band center of Mn@GY, particularly the d_z² center involved in CO₂ adsorption, thereby enhancing the adsorption capacity for CO₂. These findings indicate that 1s-Mn₂C₁₂ with high Mn atomic loadings is an excellent CO₂RR electrocatalyst, and it provides new insights for designing efficient CO₂RR electrocatalyst.