Triacylphosphines as Phosphorus Sources for the Synthesis of Transition Metal Phosphide Nanoparticles

Abstract

Transition metal phosphide (TMP) nanoparticles (NPs) have emerged as a versatile material for a wide array of energy conversion/storage applications due to their robustness and a broad range of available compositions, stoichiometries, and crystalline structures. Combined with size and shape control, this opens many possibilities to tailor NPs’ electronic, physical, and chemical properties. One of the main hurdles towards broader implementation of TMP NPs consists in their challenging synthesis further exacerbated by the limited choice of available phosphorus precursors. On the one hand, the synthesis of TMP NPs can be carried out using various alkyl- or arylphosphines, which require prolonged heating at high temperatures, while on the other hand, the use of highly reactive P(SiMe3)3, white phosphorus, or PH3 poses additional obstacles associated with their hazardous nature, high cost, and limited availability. In this work, we report the use of acylphosphines as a new class of phosphorus sources for the synthesis of nickel and cobalt phosphide NPs. We demonstrate that they react with respective metal chlorides at moderate temperatures as low as 250 °C yielding amorphous/poorly crystalline NPs, which can later be crystallized at 305 °C. After ligand stripping with HPF6, the prepared NPs were shown to be an effective electrocatalyst for the hydrogen evolution reaction in the acidic medium exhibiting overpotentials as low as 50 mV at a current density of 10 mA/cm², which is among the lowest overpotentials for these materials and is quite competitive to commercial platinum-based catalysts.