Phase and composition controllable synthesis of nickel phosphide-based nanoparticles via a low-temperature process for efficient electrocatalytic hydrogen evolution

Nickel phosphide has been shown to be active toward hydrogen evolution reaction (HER). In this paper, we demonstrate the phase and composition controllable synthesis of nickel phosphide-based nanoparticles (NiP-based NPs) via a low-temperature phosphidation reaction (250 °C) using NaH2PO2 as the phosphorus source and the as-prepared Ni(OH)2 precursor as the nickel source. Interestingly, by changing the NaOH concentration and nickel source used to fabricate Ni(OH)2 precursors, we could adjust the phases and compositions of as-synthesized NiP-based nanocatalysts from Ni5P4, Ni2P to Ni12P5. The different steric hindrance and the electrostatic repulsion of synthesized β-Ni(OH)2 precursors result in the formation of three NiP phases with various Ni:P ratios. Electrochemical characterizations reveal that the NiP-based NPs with P-rich phase (Ni5P4+Ni2P) exhibit remarkable electrocatalytic HER property, with low overpotential (η) of 111 mV to reach a current density of 10 mA cm−2 in a 0.5 M H2SO4 media, which is superior than those of pure Ni2P (η = 118 mV) and the Ni-rich NiP-based counterpart (Ni12P5+Ni2P) (η = 131 mV). This is attributed to the stronger ensemble effect of P and more active sites provided by P-rich NiP-based NPs. Our results demonstrate that by tailoring the surface properties of Ni(OH)2 precursors, the phases and compositions of NiP-based nanoparticles could be easily tuned, which provides a simple, economic, and green strategy to optimize the HER performance of transition metal phosphide-based electrocatalysts.