Theoretical Design and Structural Modulation of a Surface-Functionalized Ti3C2Tx MXene-Based Heterojunction Electrocatalyst for a Li–Oxygen Battery

Two-dimensional MXene with high conductivity has metastable Ti atoms and inert functional groups on the surface, greatly limiting application in surface-related electrocatalytic reactions. A surface-functionalized nitrogen-doped two-dimensional TiO2/Ti3C2Tx heterojunction (N-TiO2/Ti3C2Tx) was fabricated theoretically, with high conductivity and optimized electrocatalytic active sites. Based on the conductive substrate of Ti3C2Tx, the heterojunction remained metallic and efficiently accelerated the transfer of Li+ and electrons in the electrode. More importantly, the precise regulation of active sites in the N-TiO2/Ti3C2Tx heterojunction optimized the adsorption for LiO2 and Li2O2, facilitating the sluggish kinetics with a lowest theoretical overpotential in both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Employed as an electrocatalyst in a Li–oxygen battery (Li–O2 battery), it demonstrated a high specific capacity of 15 298 mAh g–1 and a superior cyclability with more than 200 cycles at 500 mA g–1, as well as the swiftly reduced overpotential. Furthermore, combined with the in situ differential electrochemical mass spectrometry, ex situ Raman spectra, and SEM tests, the N-TiO2/Ti3C2Tx heterojunction electrode presented a superior stability and reduced side reaction along with the high performance toward the ORR and OER. It provides an efficient insight for the design of high-performance electrocatalysts for metal–oxygen batteries.