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 (Mo2C) has exhibited effective HER performance. However, the strong bonding strength of intermediate adsorbed H (Hads) with Mo active site slows down the HER kinetics of Mo2C. Herein, using phase-transition strategy, hexagonal ß-Mo2C could be easily transferred to cubic δ-Mo2C through electron injection triggered by tungsten (W) doping, and heterointerface-rich Mo2C-based composites, including ß-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 ß-Mo2C/MoO2 interface plays an important role in optimizing the electronic structure of Mo 3d orbital and hydrogen adsorption Gibbs free energy (ΔGH*), 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.