Encapsulating dual-phased Mo₂C-WC nanocrystals into ultrathin carbon nanosheet assemblies for efficient electrocatalytic hydrogen evolution

Mo₂C and WC are widely considered as promising electrocatalysts for hydrogen evolution reaction (HER) owing to their Pt-like electronic features. Herein, dual-phased Mo₂C-WC nanocrystals, densely and uniformly confined in ultrathin carbon nanosheet assemblies (abbreviated as Mo₂C-WC/NCAs), which are possible candidates for high-performance HER electrocatalysts, are fabricated through the in-situ pyrolysis of polymers containing Mo and W. When evaluated as HER electrocatalysts, Mo₂C-WC/NCAs requires a small overpotential of ~126 mV to drive a current density of 10 mA cm⁻², and low Tafel slopes of 72 mV dec^-1 and 59 mV dec^-1 in acidic and alkaline media, respectively. In addition, the Mo₂C-WC/NCAs exhibit robust catalytic stability up to 36 h. The introduction of dual-phased carbide heterostructures can modify the electronic structure and simultaneously facilitate the charge transfer of the catalysts, consistent with the density functional theory (DFT) calculations. This work highlights the in-situ construction of multi-phased hetero-metal carbide heterostructures for high-performance electrocatalysis.