Phosphonium-Based Ionic Liquid: A New Phosphorus Source toward Microwave-Driven Synthesis of Nickel Phosphide for Efficient Hydrogen Evolution Reaction

Employing phosphonium-based ionic liquid, tetrabutylphosphonium chloride [P4444]Cl as novel phosphorus source and reaction medium, a facile approach for fabricating nanostructured Ni2P and Ni12P5 was developed upon microwave heating in 1–2 min or conventional heating at 350 °C for 3 h. In a microwave-driven approach, controlling counteranions of various nickel salts could conveniently tune the phase of as-synthesized nickel phosphides. Ni(acac)2 and Ni(OAc)2·4H2O as Ni source could yield Ni2P nanoparticles, while NiCl2·6H2O and NiSO4·7H2O offered Ni12P5 nanocrystals. The synthesized products were characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Their electrocatalytic behavior toward hydrogen evolution reaction in acidic medium was investigated. The as-synthesized Ni2P nanoparticles presented more excellent catalytic efficiency than Ni12P5. Ni2P nanoparticles from Ni(acac)2 require overpotentials of only 102 mV to reach 10 mA cm–2 with a sma...