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

Lithium-oxygen (Li-O₂) 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-O₂ battery. Thus, designing efficient electrocatalysts is crucial to improve battery performance. Here, Ti₃C₂ MXene/Mo_4/3B_2-x MBene superlattice is fabricated its electrocatalytic activity toward oxygen redox reactions in Li-O₂ battery is studied. It is found that the built-in electric field formed by a large work function difference between Ti₃C₂ and Mo_4/3B_2-x will power the charge transfer at the interface from titanium (Ti) site in Ti₃C₂ to molybdenum (Mo) site in Mo_4/3B_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 LiO₂ at Mo site and accelerating the kinetics of oxygen electrode reactions. Meanwhile, the formed film-like discharge products (Li₂O₂) improve the contact with electrode and facilitate the decomposition of Li₂O₂. Based on the above advantages, the Ti₃C₂ MXene/Mo_4/3B_2-x MBene superlattice-based Li-O₂ battery exhibits large discharge specific capacity (17 167 mAh g^-1), low overpotential (1.16 V), and superior cycling performance (475 cycles).