Engineering Multilevel Porous Carbon Nanocages from ZnO@ZIFs with Embedded Ultrafine Mo2C Nanocrystals for Enhanced Hydrogen Evolution

Molybdenum carbide (Mo₂C) is a promising hydrogen evolution reaction (HER) catalyst, and conventional nanoparticles suffer from poor conductivity, large size, and low active-site utilization. Herein, a novel hollow carbon nanocage embedded with the Mo₂C nanocrystal catalyst (Mo₂C-HPCS) was developed through an in situ growth and self-sacrificial approach. ZnO nanospheres acted as sacrificial templates, releasing Zn²⁺ to coordinate with 2-methylimidazole (2-MIM) for ZIF-8 assembly and evaporating during pyrolysis to generate hollow structures. Simultaneously, MoO₄^2– species were uniformly incorporated into the ZIF-8 framework, ensuring a homogeneous Mo distribution. The resulting Mo₂C-HPCS possesses a multilevel porous N-doped carbon framework (NC) that enlarges the surface area, exposes more active sites, promotes electron transport, and prevents Mo₂C agglomeration. Mo₂C-HPCS delivers superior HER activity with a low overpotential of 99 mV at 10 mA cm^–2 in 1 M KOH. Density functional theory calculations confirm that Mo₂C_NC synergy optimizes the hydrogen adsorption free energy, accelerating HER kinetics.