Theoretical study on catalytic performance of Ti2B monolayer as cathodes of Li-O2 and Na-O2 batteries promoted by surface functionalization

Abstract

Alkali metal–oxygen batteries with high theoretical energy density are regarded as one of the promising next-generation batteries. The suitable catalyst is the key to realize the application of alkali metal–oxygen batteries. In this study, two-dimensional (2D) Ti2B monolayer with extremely high Young’s modulus (1024.7 N·m−1) was investigated as cathode catalysts of Li-O2 and Na-O2 batteries by density functional theory (DFT) calculations. The electrocatalytic performance can be further improved by surface functionalization, and the catalytic activities based on total overpotentials are in order: Ti2BF2 (1.244/1.131 V) < Ti2BCl2 (1.383/1.247 V) ≈ Ti2BS2 (1.373/1.256 V) < Ti2B (9.514/9.191 V) for both Li-O2 and Na-O2 batteries. Furthermore, there is a volcanic relationship between overpotentials and the binding energies of peroxides and substrates. The energy evolution of four-electron steps on these materials reveals that surface functionalization regulated catalytic activities by balancing the adsorption strength of alkali metal and oxygen, and the disproportionation side reactions on surface functionalized Ti2B monolayers are thermodynamically unfavorable. Besides, the densities of states (DOSs) and alkali metal migration behaviors of these materials indicate their good electronic and ionic conductivities. Our study of functionalized Ti2B monolayer cathode catalysts may shed light on the application of 2D transition metal borides to alkali metal–oxygen batteries.