Synthesis of Nickel Phosphide Electrocatalysts from Hybrid Metal Phosphonates

Transition-metal phosphides (TMPs) have recently emerged as efficient and inexpensive electrocatalysts for electrochemical water splitting. The synthesis of nanostructured phosphides often involves highly reactive and hazardous phosphorous-containing compounds. Herein, we report the synthesis of nickel phosphides through thermal treatment under H 2 (5%)/Ar of layered nickel phenylphosphonate (NiPh) or methylphosphonate (NiMe) that act as single-source precursors. Ni 12 P 5, Ni 12 P 5 -Ni 2 P, and Ni 2 P nanoparticles (NPs) with sizes of ca. 15–45 nm coated with a thin shell of carbonaceous material were produced. Thermogravimetric analysis coupled with mass spectrometry (TG–MS) showed that H 2, H 2 O, P 2, and —C 6 H 5 are the main compounds formed during the transformation of the precursor under argon and no hazard phosphorous-containing compounds are created, making this a simple and relatively safe route for fabricating nanostructured TMPs. The H 2 most likely reacts with the —PO 3 groups of the precursor to form H 2 O and P 2, and the latter subsequently reacts with the metal to produce the phosphide. The Ni 12 P 5 -Ni 2 P and Ni 2 P NPs efficiently catalyze the hydrogen evolution reaction (HER), with Ni 2 P showing the best performance and generating a current density of 10 mA cm –2 at an overpotential of 87 mV and exhibiting long-term stability. Co 2 P and CoP NPs were also synthesized following this method. This approach may be utilized to explore the rich metal phosphonate chemistry for fabricating phosphide-based materials for electrochemical energy conversion and storage applications.