Understanding the doping effect on hydrogen evolution activity of transition-metal phosphides: Modeled with Ni2P

Our calculations reveal a linear relationship of the charge transfer and d-band center with the H adsorption on the doped catalysts. It indicated that the catalytic activity of the metal doped Ni2P could described by the change of the charge transfer on the dopants with respect to the Ni atom, where the Co and Fe doped Ni2P could present higher catalytic activities due to the closer of H Gibbs free energy to zero. [Display omitted] •The increment of Bader charge and d-band center on Ni2P shows a linear correlation with ΔGH*.•The εd of Ni atom is found to locate near the optimal region caused by Fe and Co heteroatoms.•Co-Ni2P and Fe-Ni2P electrodes were proved to exhibit comparable HER activity with Pt/C. Investigating the correlations between the changes of electronic structure and catalytic activity is a major requisite for the design and synthesis of the electrocatalysts with promising performance. Herein by using Ni2P as a model electrocatalyst, which is one of the most promising catalysts toward hydrogen evolution reaction (HER), the intrinsic issues in electrochemical HER performance affected by doping heteroatoms (i.e., Sn, Pb, Ti, Nb, V, Li, Cr, Na, Mn, Fe, and Co) are systemically investigated via first-principles calculations and coupled with experimental validation. The results reveal that the increment of Badar charge (ΔQ) and d-band center (εd) on the surface of doped Ni2P catalyst have a significant linear correlation with the hydrogen adsorption energy (ΔGH*). As a result, the εd of Ni atom is found to locate near the optimal region caused by Fe and Co heteroatoms, suggesting that the Fe and Co doped Ni2P should have the best catalytic activity toward HER. Furthermore, the experimental validation process is performed by the synthesis and characterization of the corresponding heteroatom doped Ni2P. The X-ray photoelectron spectroscopy (XPS) reveals that the charge transfer and the shift of εd on the activate site of the doped Ni2P catalyst are consistent with the theoretical analysis. The electrochemical tests demonstrate that Co- and Fe-doped Ni2P catalysts exhibit a Pt-like performance with 31 mV overpotentials at 10 mA cm−2, which is in good agreement with the proposed theory. Our results suggest that the charge redistribution on the surface of the catalysts induced by doping effect is the key to improve their activity, which can be used to guide the design of catalysts in other related catalysis.