Mutually Activated 2D Ti0.87O2/MXene Monolayers Through Electronic Compensation Effect as Highly Efficient Cathode Catalysts of Li–O2 Batteries

Abstract

2D materials exhibit remarkable electrochemical performance as the cathode catalyst in lithium–oxygen batteries (LOBs). Their catalytic capability mainly derives from their 2D surface with tunable surface chemistry and unique electronic states. Herein, Ti_0.87O₂ and Ti₃C₂ MXene monolayers are applied to construct a face/face 2D heterostructure to enhance the catalytic performance in LOBs. It is demonstrated that electronic compensation from the O-terminated MXene to Ti_0.87O₂ side is achieved through the built-in electric field and the overlap of Ti 3d and O 2p orbitals between Ti_0.87O₂ and MXene units. As a result, the ORR/OER catalytic activity is improved in Ti_0.87O₂/MXene heterojunction due to the modulated p-band center that optimizes the s–p coupling with the key intermediate LiO₂. The Ti_0.87O₂/MXene cathode presents a structural stability and long-term cycling life of 425 cycles (2534 h) at 200 mA g⁻¹ and 407 cycles at 1000 mA g⁻¹ with a fixed capacity of 600 mAh g⁻¹, being nearly five and three times higher than that of pure Ti_0.87O₂ and MXene cathodes, respectively.