Theoretical Design and Structural Modulation of a Surface-Functionalized Ti 3 C 2 T x 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 TiO 2 /Ti 3 C 2 T x heterojunction (N-TiO 2 /Ti 3 C 2 T x ) was fabricated theoretically, with high conductivity and optimized electrocatalytic active sites. Based on the conductive substrate of Ti 3 C 2 T x , 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-TiO 2 /Ti 3 C 2 T x heterojunction optimized the adsorption for LiO 2 and Li 2 O 2 , 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-TiO 2 /Ti 3 C 2 T x 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.