Catalytic mechanism of sulfur-nitrogen doping metal single-atom graphene-based catalysts for the conversion of CO2 to CH4: A computational study

The conversion of CO2 into renewable fuel (CH4) has significant environmental and economic benefits. Graphene-supported single-atom catalysts (SACs) show promise as electrocatalysts for the carbon dioxide reduction reaction (CO2RR). In this study, using spin-polarized density functional theory (DFT) calculations, we investigate the potential for converting CO2 to CH4 on the representative SACs, specifically graphene-supported TM-N-S (transition metal-nitrogen-sulfur). The results show that TM-N-S can break the scaling relationship between the adsorption energy of *CHO and *OCH2. The free energy profiles indicate that among the candidate TM-N-S SACs, Fe, Co, and Ni-N-S stand out with low overpotentials of 0.23, 0.40, and 0.39 V, respectively. Compared with the competing hydrogen evolution reaction (HER), they exhibit higher CO2 selectivity and catalytic activity. Analysis of electronic structure and charge variations reveals the origin of CO2RR activity and the binding strength between catalyst and intermediate. This work uncovers the potential mechanism of CO2RR, providing valuable insights into the conversion of CO2 to CH4 via TM-N-S catalysis and offering novel perspectives for the design and screening of efficient SACs for CO2RR.