Phase‐Transition of Mo2C Induced by Tungsten Doping as Heterointerface‐Rich Electrocatalyst for Optimizing Hydrogen Evolution Activity

Electrochemical hydrogen evolution reaction (HER) from water splitting driven by renewable energy is considered a promising method for large-scale hydrogen production, and as an alternative to noble-metal electrocatalysts, molybdenum carbide (Mo₂C) has exhibited effective HER performance. However, the strong bonding strength of intermediate adsorbed H (H_ads) with Mo active site slows down the HER kinetics of Mo₂C. Herein, using phase-transition strategy, hexagonal β-Mo₂C could be easily transferred to cubic δ-Mo₂C through electron injection triggered by tungsten (W) doping, and heterointerface-rich Mo₂C-based composites, including β-Mo₂C, δ-Mo₂C, and MoO₂, are presented. Experimental results and density functional theory calculations reveal that W doping mainly contributes to the phase-transition process, and the generated heterointerfaces are the dominant factor in inducing remarkable electron accumulation around Mo active sites, thus weakening the Mo─H coupling. Wherein, the β-Mo₂C/MoO₂ interface plays an important role in optimizing the electronic structure of Mo 3d orbital and hydrogen adsorption Gibbs free energy (ΔG_H*), enabling these Mo₂C-based composites to have excellent intrinsic catalytic activity like low overpotential (η₁₀ = 99.8 mV), small Tafel slope (60.16 dec^-1), and good stability in 1 m KOH. This work sheds light on phase-transition engineering and offers a convenient route to construct heterointerfaces for large-scale HER production.