Surface Chemistry-Engineered Nb 2 CT x MXene Enables Reversible CO 2 Redox in Li-CO 2 Batteries

Li-CO2 batteries hold potential due to the advantages in energy density and CO2 utilization, with their application limited by the CO2 reduction/evolution reaction kinetics (CRR/CER). Herein, Nb2CTx MXene is explored as an electrocatalyst for Li-CO2 batteries, with its surface microenvironment engineered by functionalizing with -O, -F, -Cl, -Br, and -I terminations to optimize the catalytic activity. Theoretical and experimental analyses reveal that chlorine functionalization (Nb2CClx) enhances the adsorption of Li, CO2, and Li2CO3, promotes d-orbital electron delocalization in Nb atoms, and increases electron donation capability. Moreover, Li2CO3 formed on Nb2CClx displays an elongated Li–O bond and a reduced dissociation energy. Consequently, the Nb2CClx-based Li-CO2 battery delivers a discharge capacity of 15521.2 mAh g–1, an overpotential of 1.50 V, and an extended lifetime of over 157 cycles. These findings underscore the importance of surface chemistry in designing catalytically active MXene-based electrocatalysts for reversible Li-CO2 batteries.