Metal and phosphonium-based ionic liquid: A new Co and P dual-source for synthesis of cobalt phosphide toward hydrogen evolution reaction

Abstract Phosphonium-based ionic liquid, containing cobalt ion, was applied as novel phosphorus and metal dual-source for fabrication of cobalt phosphide. Trihexyl(tetradecyl)phosphonium tetrachlorocobaltate(II) ([P 6,6,6,14 ] 2 [CoCl 4 ]) with carbon nanotubes (CNTs) was utilized to obtain the Co 2 P/CNTs via one step phosphidation. This material exhibits a good catalytic activity toward hydrogen evolution reaction (HER) including an onset overpotential of 85 mV, a Tafel slope of 47 mV dec −1 , current densities of 10 and 20 mA cm −2 at overpotentials of 150 and 178 mV, and it has a good stability to keep the HER activity. All experimental results confirmed that [P 6,6,6,14 ] 2 [CoCl 4 ] can form Co 2 P without adding other reagent and CNTs can improve the electrical conductivity and contribute to the formation of cobalt phosphide.