Boron-doping on the surface mediated low-valence Co centers in cobalt phosphide for improved electrocatalytic hydrogen evolution

Rationally engineering the surface structure of transition metal phosphides (TMPs) could regulate valence state of metal centers (Mδ+) with optimized binding strength of H2O and H* and relative Gibbs free energy (ΔGH*) in alkaline hydrogen evolution reaction (HER). However, the precise location of such metal centers is still challenging due to the limited synthetic methodology. Herein we report the surface-layer-confined doping of boron on cobalt phosphide nanowire arrays (B-CoP) via a controllable surface redox reaction. Nanowire CoP decorated with B-doped surface layer structure has proved to be an outstanding HER electrocatalyst, with an overpotential of 112 mV at 100 mA cm−2. X-ray absorption near edge structure (XANES) and X-ray photoelectron spectroscopy (XPS) analysis, and theoretical results demonstrate that B-doping induced electron redistribution of Co with electron-rich features. Such low-valence Co centers coordinated with B can achieve strong affinity toward H2O molecules and optimized ΔGH* to accelerating reaction kinetics.