Nickel Phosphide-based Compound For Efficient Electrocatalytic Water Spiltting

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?Ni-P-based NPs?via a low-temperature phosphidation reaction?250oC?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?₂precursors,we could adjust the phases and compositions of as-synthesized Ni-P-based nanocatalysts from Ni₅P₄,Ni₂P to Ni₁₂P₅.The different steric hindrance and the electronstatic repulsion of synthesized?-Ni?OH?₂ precursors result in the formation of three Ni-P phases with various Ni:P ratios.Electrochemical characterizations reveal that the Ni-P-based NPs with P-rich phase?Ni₅P₄+Ni₂P?exhibit remarkable electrocatalytic HER property,with low overpotential???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??=118 mV?and the Ni-rich Ni-P-based counterpart(Ni₁₂P₅+Ni₂P)??=131 mV?.This is attributed to the stronger ensemble effect of P and more active sites provided by P-rich Ni-P-based NPs.Our results demonstrate that by tailoring the surface properties of Ni?OH?₂ precursors,the phases and compositions of Ni-P-based nanoparticles could be easily tuned,which provides a simple,economic,and green strategy to optimize the HER performance of transtion metal phosphide-based electrocatalysts.In addition,we also prepared Co,Fe-doped Ni-P-based LDHs by simple coprecipitation of aqueous solution.The phase morphology characterization and the electrocatalytic properties measurement indicate that P-doping and the synergistic effect of different transition metal ions is conducive to the electrocatalytic oxygen evolution?OER?of the layered materials.When the anode current density of the ternary NiCoFe-P LDHs reaches 10 mA cm^-2,the overpotential???is only 274 mV in1 M KOH media.This is attributed to P element increases the conductivity and wettability of the material,promoting the electron transfer.The interdoping of different transition metal elements changes the electronic structure of the material and increases the active sites of the material.