Molybdenum Carbide‐Oxide Heterostructures: In Situ Surface Reconfiguration toward Efficient Electrocatalytic Hydrogen Evolution

Heterostructured Mo₂ C-MoO_x on carbon cloth (Mo₂ C-MoO_x /CC), as a model of easily oxidized electrocatalysts under ambient conditions, is investigated to uncover surface reconfiguration during the hydrogen evolution reaction (HER). Raman spectroscopy combined with electrochemical tests demonstrates that the Mo^VI oxides on the surface are in situ reduced to Mo^IV , accomplishing promoted HER in acidic condition. As indicated by density functional theoretical calculations, the in situ reduced surface with terminal Mo=O moieties can effectively bring the negative ΔG_H* on bare Mo₂ C close to a thermodynamic neutral value, addressing difficult H* desorption toward fast HER kinetics. The optimized Mo₂ C-MoO_x /CC only requires a low overpotential (η₁₀ ) of 60 mV at -10 mA cm^-2 in 1.0 m HClO₄ , outperforming Mo₂ C/CC and most non-precious electrocatalysts. In situ surface reconfiguration are shown on W₂ C-WO_x , highlighting the significance to boost various metal-carbides and to identify active sites.