Highly Efficient Nb2C MXene Cathode Catalyst with Uniform O-Terminated Surface for Lithium-Oxygen Batteries

Highly-efficient cathode catalysts are the key to improve high rate cycle stability, avoid side reactions, and lower the overpotential of lithium-oxygen batteries (LOBs). MXenes are predicted to be one of the most impressive materials for energy applications. In this work, the catalytic capability of Nb2C MXene is demonstrated with a uniform O-terminated surface as a cathode material for LOBs. The easily fabricated uniform O-terminated surface, high catalytic activity of Nb2CO2 sites, and unique reaction kinetics contribute to the excellent electrocatalytic performance of Nb2C MXene. The uniform O-terminated surface on Nb2C MXene is obtained after heat treatment. Density functional theory calculations reveal the superior catalytic activity of Nb2CO2 compared to other anchor groups and bare surfaces. The calculations also reveal the multinucleation and growth/decomposition mechanism for discharge products on the Nb2CO2 surface. This mechanism is believed to account for the results characterized by ex situ and in situ measurements. The spatial-direction accumulated porous discharge products at high current density contribute to the excellent high-rate cycle stability. For example, the cathodes exhibit cycle stability for 130 cycles at an ultrahigh current density of 3 A g(-1). The present work provides insights into the modulation of catalytic capabilities, and the rational design of high-performance MXenes based electrocatalysts.