Theoretical Design and Structural Modulation of a Surface-Functionalized Ti₃C₂T_<i>x</i> MXene-Based Heterojunction Electrocatalyst for a Li-Oxygen Battery.

Abstract

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/Ti₃C₂T_<i>x</i> heterojunction (N-TiO₂/Ti₃C₂T_<i>x</i>) was fabricated theoretically, with high conductivity and optimized electrocatalytic active sites. Based on the conductive substrate of Ti₃C₂T_<i>x</i>, 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/Ti₃C₂T_<i>x</i> 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 <i>in situ</i> differential electrochemical mass spectrometry, <i>ex situ</i> Raman spectra, and SEM tests, the N-TiO₂/Ti₃C₂T_<i>x</i> 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.