Mechanistic Insights into 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 extra-terrestrial exploration, it can enable the conversion of 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 V 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 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 on 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.