Nanoscale MOF-derived vacancy-engineered Co2P/N-doped coal-based carbon fibers for boosting hydrogen evolution

Abstract

Hydrogen has emerged as a promising clean energy source, driving extensive research into efficient electrocatalysts for the hydrogen evolution reaction (HER). This work reports the synthesis of a self-supported Co₂P/nitrogen-doped coal-based carbon fiber catalyst (Co₂P/N-C-CFs(S-ZIF-67)) with cobalt (Co) vacancies via pyrolysis of a nanoscale metal–organic framework (NMOF) precursor. Compared to conventional ZIF-67, the NMOF of S-ZIF-67 (40 nm) forms smaller Co₂P (7.3 nm), simultaneously generating hierarchical porosity with an increase in specific surface area. More importantly, the pyrolysis of S-ZIF-67 generates Co vacancies that optimize the electronic structure and increase the active site density of the catalyst. Density functional theory (DFT) calculations confirm that these Co vacancies lower the d-band center and promote electron transfer within the catalyst. Furthermore, N-C-CFs as a support provide both structural flexibility and tunable hydrogen adsorption Gibbs free energy (ΔG_H*). Consequently, Co₂P/N-C-CFs(ZIF-67) exhibits exceptional HER performance in 0.5 M H₂SO₄, requiring only 66 mV overpotential to reach a current density of 10 mA cm⁻², and demonstrates remarkable stability for 120 h at 20 mA cm⁻². Notably, it surpasses both Co₂P/N-C-CFs(ZIF-67) and commercial 20% Pt/C at high current densities. This study establishes an effective strategy for designing advanced HER catalysts through precise control of NMOF size and vacancy engineering.