CO₂ reduction mechanism on the Nb₂CO₂ MXene surface: Effect of nonmetal and metal modification

Electrochemical CO₂ reduction to fuels offers a path to simultaneously address both CO₂ emission and renewable energy storage challenges. Developing high efficient, selectivity and low overpotential nonprecious CO₂ reduction reaction (CO₂RR) catalysts is one of key factors for renewable energy. Herein, we explored the CO₂RR as well as its side reaction (hydrogen evolution reaction (HER)) properties of pure Nb₂CO₂, nonmetal doping, and metal modification Nb₂CO₂ systems by using density functional theory calculations. Results indicated that the O terminal Nb₂C (Nb₂CO₂) is more stable than that of the F and OH terminals. The reaction Gibbs free energy diagrams indicated that the pure Nb₂CO₂ is not suitable as catalyst for HER and CO₂RR. Nonmetal doping can reduce potential limiting (U_L) of CO₂RR and will not change the reaction products. While surface metal modification not only reduced the U_L of CO₂RR, but also changed the reaction products. The V modified Nb₂CO₂ (V_L) system is identified as the best CO₂RR catalyst with against HER among modified systems with accounting HER side reaction. The charge transfers and electronic structure analysis indicates that the surface metal d have a strong interaction with Nb₂CO₂, leading the intermediates *COOH receive extra electrons from metal d bonding orbitals, which harm the ability of *COOH gaining electrons from proton, and therefore changed the reaction products.