RE-doped (RE = La, Ce and Er) Ni2P porous nanostructures as promising electrocatalysts for hydrogen evolution reaction

Abstract

The construction of an efficient non-noble-metal electrocatalyst towards alkaline hydrogen evolution is challenging but in great demand. The fabrication of a porous nanostructure and heteroatom doping are two productive strategies for developing effective electrocatalysts. In this contribution, we report the preparation of La, Ce and Er-doped Ni₂P porous nanostructures through a facile water bath method and phosphorization strategy. The Er-doped Ni₂P porous nanostructure exhibits superb hydrogen evolution reaction (HER) catalytic performance under alkaline conditions with a low cathodic overpotential of 87 mV (10 mA cm⁻², glassy carbon) and a small Tafel slope of 65.4 mV dec⁻¹. It also displays excellent electrochemical stability in alkaline electrolytes. First-principles density functional theory (DFT) calculations disclosed the mechanism of the alkaline HER catalysis. For pristine Ni₂P, the P site acts as the optimal active site with the Gibbs free energy of H* absorption (ΔG_H*) of 0.48 eV. After La, Ce and Er are doped, respectively, the P site is still the active center of the three doping systems. Notably, the ΔG_H* value is reduced from 0.48 eV to 0.23 eV (P site in La-doped Ni₂P), 0.20 eV (P site in Ce-doped Ni₂P) and 0.18 eV (P site in Er-doped Ni₂P), suggesting that doping with La, Ce and Er atoms plays a crucial role in decreasing the H* absorption energy on optimal P sites and the optimum active site with a smaller ΔG_H* can expedite the charge transfer rate for H* midbody and H₂ generation. This is particularly noticeable for Er doping, which is in accordance with the experimental result.