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

Abstract

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 (UL) of CO2RR and will not change the reaction products. While surface metal modification not only reduced the UL of CO2RR, but also changed the reaction products. The V modified Nb2CO2 (VL) 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.