Tuning of metallic valence in CoMoP for promoting electrocatalytic hydrogen evolution

CoMoP_x-based electrocatalysts are promising for hydrogen evolution reaction (HER) but suffer from high overpotential and poor stability at large current density. Herein, we propose CoMoP@NF in lower valence states by thorough phosphorization which improves the adhesion of the catalysts on substrate and facilitates the Volmer step. The CoMoP@NF can reach 39 mV at 10 mA cm^-2, 119 mV at 100 mA cm^-2, and a low Tafel slope of 73.3 mV per decade. The decline of i-t test in 10 h at ~370 mA cm^-2 is only 1 mA cm^-2. Theoretical calculations confirm the rational design of CoMoP whose ΔG_H* is as low as 0.15 and 0.01 eV corresponding to (013) and (211) facets, respectively. Electrons transfer from Co to Mo results in middle d band center of CoMoP that promotes H adsorption and desorption.