Mo-doped Ni2P hollow nanostructures: highly efficient and durable bifunctional electrocatalysts for alkaline water splitting

Abstract

The fabrication of an efficient bifunctional electrocatalyst towards alkaline overall water splitting is challenging, but in high demand. Herein, we report the construction of Mo-doped Ni₂P hollow nanostructures through a solvothermal method and in situ phosphorization strategy. The Mo-doped Ni₂P hollow nanostructures demonstrate excellent hydrogen evolution reaction (HER) activity in 1.0 M KOH solution with a low cathodic overpotential of 81 mV (10 mA cm⁻², glassy carbon) and a small Tafel slope of 53.4 mV dec⁻¹. First-principles density functional theory calculations reveal the mechanism of the alkaline HER. For pristine Ni₂P, the P site serves as the active center. After Mo doping, the active center transforms to a bridging Mo–Ni site and the corresponding Gibbs free energy of H* absorption (ΔG_H*) decreases from 0.33 eV (P site) to 0.21 eV (bridging Mo–Ni site). The optimal active site with a smaller ΔG_H* can accelerate the charge transfer process for H* intermedium and H₂ production. For the oxygen evolution reaction (OER), the Mo-doped Ni₂P hollow nanostructures require 270 mV to attain 20 mA cm⁻² (glassy carbon), with a small Tafel slope of 68.5 mV dec⁻¹. Impressively, both the HER and OER catalysis exhibit durable performance in alkaline electrolyte. When the Mo-doped Ni₂P hollow nanostructures are applied as bifunctional electrocatalysts for alkaline overall water splitting, the demanded cell voltage is only 1.54 V (10 mA cm⁻², nickel foam).