Enhancement of Electrocatalytic Activity of Ti₃C₂T_x MXene by in-situ Tunable Interfacial Anion Doping and Structural Modification for Hydrogen Evolution Reaction

2D-layered MXenes have attracted increasing attention as promising low-cost, stable electrocatalysts for hydrogen production through electrolysis. However, poor intrinsic chemical activities, and limited active site densities currently inhibit MXenes as practical electrocatalysts for hydrogen evolution reaction (HER). Herein, these limitations are overcome by <i>in-situ</i> tunable interfacial chemical doping and structural modification with nonmetallic electron donors—by nitrosulfurization through simple heat treatment with thiourea as a nitrogen and sulfur source in 2D titanium carbide (Ti₃C₂T_x) MXene. Through this process, XPS analysis indicates that the substitution of nitrogen and sulfur occurs at the basal plane with controllable chemical compositions ranging from 2 - 4 at. % (Sulfur), and 5-15 at. % (Nitrogen). It is observed by HRTEM, SEM, and AFM that structure of the MXene is changed from planar nanosheets to hexagonal-nanoplate-decorated nanosheets. Moreover, it is confirmed by XRD that the interlayer spacing is increased after interfacial doping, which is expected to increase the diffusivity of electrolytes into the layers and enhance the electrocatalytic activity. The optimal modified Ti₃C₂T_x MXene exhibits a high concentration of Ti-S and Ti-N bonds as well as the lowest overpotential of –260 mV and a Tafel slope of 85 mV/dec at a current density of 10 mA/cm² in 0.5 M H₂SO₄, which is three times lower than pristine MXene (overpotential: -770 mV, and Tafel slope: 247 mV/dec). This strategy to improve the electrocatalytic activity of Ti₃C₂T_x MXene for hydrogen evolution by a simple <i>in-situ</i> interfacial chemical doping and structural modification will open the possibility of manipulating the electrocatalytic performance of a broad range of MXenes.