Regulating the 4d-band center of Mo atoms in β-Mo2C to promote lithium-oxygen reactions

Abstract

Lithium-air batteries have attracted much attention because of their high energy density. However, the sluggish kinetics of the Li-O reaction leads to high charge/discharge overpotentials and poor reversibility. Therefore, exploring efficient and low-cost cathode catalysts in promoting the Li-O reaction is crucial. Herein, the first principles calculation method, for the first time, is used to study the catalytic performance based on Pt-like β-Mo2C by modifying the C sites with B, N, and O. The N modification decreases the d-band center of Mo atoms from 0.11 eV (β-Mo2C) to −0.23 eV, resulting in optimal adsorption energy and charge transfer. In comparison, B and O have a negative effect. The N modification changes the rate-determining step of the entire catalytic process from the decomposition of LiO2 (β-Mo2C, B-β-Mo2C, O-β-Mo2C) to the decomposition of Li2O2. The electronic structure and Bader charge analysis show that N-modified β-Mo2C has a significantly lower work function than other structures, which increases the charge transfer ability between the catalyst and LiO2. This work provides a valuable scheme for adjusting the transition metal electronic structure in low-cost MXene for lithium-air batteries.