Unveiling the reaction selectivity mechanism of molybdenum and tungsten carbides as cathode catalysts for Li–CO2 batteries†

Abstract

The type of cathode catalysts and the adsorption behavior of molecules on the surface play a decisive role in the selectivity of the lithium–CO₂ battery electrochemical reaction. However, few researchers have revealed the regulatory mechanism from the perspective of electronic structures. In this work, the paths and products of the Li–CO₂ electrochemical reaction on Mo₂C(101) and W₂C(101) have been investigated by using the first-principles calculation. A surface covered by a molecular layer of CO₂ is proposed, and the feasibility of the model is thermodynamically proved. Based on the covered surface model, the reaction selectivity is consistent with the experimental results. Combined with electronic structure analysis, it is revealed that the d-orbital electrons of Mo in Mo₂C(101) are further activated after binding to CO₂. Metastable oxalate stabilization is achieved by enhancing the contribution of ionic bond components in the chemical bond with the key intermediate oxalate. The delocalized W-d orbital in W₂C(101) is hybridized with the p orbitals of C and O in *CO₂, weakening the CO bond in CO₂ and promoting the formation of carbonate. It provides a new idea for the construction of a Li–CO₂ battery reaction model and understanding the battery reaction selectivity.