2D MXene/MBene Superlattice with Narrow Bandgap as Superior Electrocatalyst for High-Performance Lithium-Oxygen Battery.

Lithium-oxygen (Li-O) battery with large theoretical energy density (≈3500 Wh kg) is one of the most promising energy storage and conversion systems. However, the slow kinetics of oxygen electrode reactions inhibit the practical application of Li-O battery. Thus, designing efficient electrocatalysts is crucial to improve battery performance. Here, TiC MXene/MoB MBene superlattice is fabricated its electrocatalytic activity toward oxygen redox reactions in Li-O battery is studied. It is found that the built-in electric field formed by a large work function difference between TiC and MoB will power the charge transfer at the interface from titanium (Ti) site in TiC to molybdenum (Mo) site in MoB. This charge transfer increases the electron density in 4d orbital of Mo site and decreases the d-band center of Mo site, thus optimizing the adsorption of intermediate product LiO at Mo site and accelerating the kinetics of oxygen electrode reactions. Meanwhile, the formed film-like discharge products (LiO) improve the contact with electrode and facilitate the decomposition of LiO. Based on the above advantages, the TiC MXene/MoB MBene superlattice-based Li-O battery exhibits large discharge specific capacity (17 167 mAh g), low overpotential (1.16 V), and superior cycling performance (475 cycles).