The nature of active sites of Ni2P electrocatalyst for hydrogen evolution reaction

Abstract Nano-scaled Ni 2 P particles were synthesized by ligand stabilization method and applied for hydrogen evolution reaction (HER). X-ray diffraction (XRD), transmission electron microscope (TEM), and X-ray absorption fine structure (XAFS) spectroscopy were employed to examine structural properties of Ni 2 P nanoparticles. The electrocatalytic HER activity and stability for the Ni 2 P nanocatalyst were tested in 0.5M H 2 SO 4 , and the Ni 2 P electrocatalyst exhibited a low onset potential for the HER at around −0.02 V vs. RHE, a little more negative compared to the Pt catalyst which shows almost 0 V vs. reversible hydrogen electrode (RHE), and the Tafel slope of 75 mV per decade, i.e. following Volmer step as a rate-determining step. Density functional theory (DFT) calculations for hydrogen adsorption over Ni 2 P surfaces (0 0 1) and (0 0 2) revealed that the hydrogen adsorption might occur via two reaction pathways: consecutive or simultaneous hydrogen adsorption. The consecutive hydrogen adsorptions on threefold hollow (TFH)-Ni site followed by on P(II) site on a Ni 2 P (0 0 1) surface led to a lower reaction barrier than simultaneous hydrogen adsorption. These results thus demonstrated that the Volmer step might follow consecutive adsorption mechanism over the Ni 2 P surface.