Over the last decade transition metal phosphide (TMP) nanoparticles (NPs) have emerged as a material of interest for a variety of energy conversion/storage applications such as photovoltaics, electrical capacitors, thermoelectrics, ion batteries, etc. One of the important rapidly developing research avenues for this class of materials is their application in various catalytic processes including photocatalysis, organic catalysis, electrocatalysis for CO₂-conversion, hydrogen evolution and oxygen reduction reactions, etc.

Over the years their performance characteristics are steadily approaching those of state-of-the-art noble metal-based systems, however, unlike NPs composed of precious metals, TMPs comprise widely abundant elements, which drastically reduces the cost of their broad large-scale implementation. In addition, a significant number of TMP NPs exhibit excellent robustness and broad flexibility of their physiochemical and electronic properties due to a vast number of available stoichiometries and crystalline structures, which can be further expanded by alloying, doping, as well as size- and shape-control.

One of the main obstacles hindering the further development of TMP catalysts is their challenging synthesis and the limited choice of available phosphorus sources. Historically, such NPs were prepared on various supports at high (> 500 °C) temperatures, which greatly increases the required energy input. The introduction of colloidal syntheses helped to resolve this issue as well as opened new possibilities to manipulate the properties of TMP NPs. The majority of works reported so far utilized various trialkyl- or triarylphosphines (mainly trioctylphosphine), and their combinations with trioctylphosphine oxide and related metal complexes. Due to the low reactivity of these phosphorus sources, the synthesis protocols required keeping the reaction at high temperatures (albeit significantly lower than previous approaches – 300-360 °C) for several hours. On the other side of the reactivity spectrum are P(SiMe₃)₃, white phosphorus, and PH₃ gas, but they pose significant hazards due to their high flammability and toxicity as well as high cost.

In this work, we report the synthesis of new reactive phosphorus precursors through a one-pot procedure employing inexpensive starting materials with high yields and purity and their use in the preparation of nickel, and cobalt phosphides at moderate (250-300 °C) temperatures. We demonstrate that unlike commonly used trialkylphosphines, upon reaction with metal chlorides the new phosphine derivatives directly form metal phosphides without the intermediate formation of metallic NPs, which in turn allows controlling the size and crystallinity degree of phosphide NPs by varying the synthesis temperature and the type of acyl substitutes of the phosphine. Finally, we studied the performance of the ligand-exchanged TMP NPs as electrocatalysts for hydrogen evolution in the acidic and basic media, respectively. We show that among the synthesized TMP NPs the lowest HER overpotential was demonstrated by Ni₂P/Ni₁₂P₅ NPs (50 mV) in an acidic medium and Co₂P NPs (160 mV) in a basic medium.