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

Lithium-oxygen (Li-O 2 ) battery with large theoretical energy density (≈3500 Wh kg -1 ) 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 2 battery. Thus, designing efficient electrocatalysts is crucial to improve battery performance. Here, Ti 3 C 2 MXene/Mo 4/3 B 2-x MBene superlattice is fabricated its electrocatalytic activity toward oxygen redox reactions in Li-O 2 battery is studied. It is found that the built-in electric field formed by a large work function difference between Ti 3 C 2 and Mo 4/3 B 2-x will power the charge transfer at the interface from titanium (Ti) site in Ti 3 C 2 to molybdenum (Mo) site in Mo 4/3 B 2-x . 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 2 at Mo site and accelerating the kinetics of oxygen electrode reactions. Meanwhile, the formed film-like discharge products (Li 2 O 2 ) improve the contact with electrode and facilitate the decomposition of Li 2 O 2 . Based on the above advantages, the Ti 3 C 2 MXene/Mo 4/3 B 2-x MBene superlattice-based Li-O 2 battery exhibits large discharge specific capacity (17 167 mAh g -1 ), low overpotential (1.16 V), and superior cycling performance (475 cycles).