Unraveling Low Overpotential Pathways for Electrochemical CO2 Reduction to CH4 on Pure and Doped MoS2 Edges

The electrochemical reduction of carbon dioxide (CO2) has received considerable attention from the scientific community for its promising applications in the selective production of useful hydrocarbons, such as synthetic natural gas, i.e., methane (CH4). In the field of extraterrestrial exploration, it can enable the conversion of the metabolite CO2 as well as that present in the Martian atmosphere into CH4, which can be used as fuel. In this work, we investigate vertically aligned 2H molybdenum disulfide (MoS2) and its edge-doped alternatives as heterogeneous electrocatalysts for the reduction of CO2 using density functional theory (DFT) calculations. Via a comprehensive reaction pathway analysis, we show that the edges of MoS2 offer a significantly low overpotential of 0.62 V for CO2 reduction to CH4 as compared to a value of 0.86 V on copper, a prominent electrocatalyst. Furthermore, by screening 8 dopants (Al, Co, Cr, Cu, Fe, Mn, Ni, and Rh), we find that Al-doped MoS2 yields CH4 at a remarkably low overpotential of 0.41 V, owing to a different potential-determining step (PDS) (*COOH → *CO) as compared to the PDS on pure MoS2 (*CO → *CHO). Other promising dopants include Ni and Rh, offering overpotentials of 0.58 and 0.62 V, respectively, for CH4 production. Investigation of the competing hydrogen evolution reaction (HER) reveals that, while the CO2RR is significantly more favorable on Al-doped MoS2, the HER outcompetes the CO2RR on pure, Ni-doped, and Rh-doped MoS2. Mechanistic insights obtained by comparing various reaction pathways (via *COOH/*HCOO and *CH2/*CH3OH) are complemented by density of states and charge density difference calculations, which rationalize the favored mechanism for each catalyst considered. Overall, our thorough, DFT-based mechanistic investigation of CO2 reduction on pure and doped MoS2 presents Al-doped MoS2 edges as a promising material for the thermodynamically facile electroreduction of CO2 to CH4.