Molybdenum-driven electronic restructuring of iron carbides unlocks faster volmer kinetics in alkaline hydrogen evolution

Abstract

The development of efficient, earth-abundant electrocatalysts for the hydrogen evolution reaction (HER) is paramount for sustainable green hydrogen production. Herein, we report a Mo-doped Fe₂C-carbon composite synthesized via a scalable pyrolysis strategy. The optimized catalyst exhibits HER activity in 0.1 M KOH, requiring a low overpotential (∼260 mV) to reach 10 mA cm⁻², long-term stability and displaying a Tafel slope of 90 mV dec⁻¹ in 0.1 M KOH. Post-mortem X-ray photoelectron spectroscopy (XPS) reveals an in situ electrochemical reduction of the surface into metallic Fe⁰ and Mo⁰ states during the reaction. We demonstrate that the precise incorporation of Mo atoms into the Fe₂C lattice modulates the electronic structure, effectively downshifting the d-band center to optimize the Gibbs free energy of hydrogen adsorption while accelerating the Volmer step. While FeMoNC2 facilitates water dissociation through its oxophilic nature, we find FeMo-NC3 leads to a decline in activity due to phase segregation. This work highlights the importance of in situ structural evolution, and electronic tuning in designing high-performance bimetallic carbide catalysts.