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

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 (ε_d) on the surface of doped Ni₂P catalyst have a significant linear correlation with the hydrogen adsorption energy (ΔG_H*). As a result, the ε_d 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 ε_d 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.