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) ([P6,6,6,14]2[CoCl4]) with carbon nanotubes (CNTs) was utilized to obtain the Co2P/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 [P6,6,6,14]2[CoCl4] can form Co2P without adding other reagent and CNTs can improve the electrical conductivity and contribute to the formation of cobalt phosphide.