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 electro-catalytic reactions. A surface-functionalized nitrogen-doped two-dimensional N-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-O-2 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.