Engineering Defects, Strain, and Janus Structures in Transition Metal Dichalcogenides for Enhanced Hydrogen Evolution Reaction Electrocatalysis

Transition metal dichalcogenides (TMDCs) have emerged as promising alternatives to platinum-group catalysts for the hydrogen evolution reaction (HER), yet their practical application is limited by intrinsically inert basal planes, poor conductivity, and insufficient active sites. This review systematically summarizes recent advances in enhancing HER performance through defect engineering, strain engineering, and Janus structure manipulation in TMDCs. Defect engineering (e.g., sulfur vacancies, grain boundaries, and doping) optimizes hydrogen adsorption free energy (ΔG_H) and charge transfer kinetics, while strain engineering tunes electronic band structures to reduce energy barriers. Janus TMDCs, with their broken symmetry and built-in electric fields, further improve the catalytic activity by stabilizing intermediates and lowering overpotentials. We critically analyze synergistic strategies (e.g., defect-strain coupling) and discuss dominant synthesis methods including liquid-phase exfoliation (LPE), chemical vapor deposition (CVD), and room-temperature atomic substitution. Finally, we outline challenges and prospects for designing high-performance TMDCs catalysts for large-scale green hydrogen production.