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

Abstract 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 (Mo 2 C) 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 Mo 2 C. Herein, using phase‐transition strategy, hexagonal β‐Mo 2 C could be easily transferred to cubic δ‐Mo 2 C through electron injection triggered by tungsten (W) doping, and heterointerface‐rich Mo 2 C‐based composites, including β‐Mo 2 C, δ‐Mo 2 C, and MoO 2 , 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‐Mo 2 C/MoO 2 interface plays an important role in optimizing the electronic structure of Mo 3d orbital and hydrogen adsorption Gibbs free energy (Δ G H* ), enabling these Mo 2 C‐based composites to have excellent intrinsic catalytic activity like low overpotential ( η 10 = 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.