General urea-assisted synthesis of carbon-coated metal phosphide nanoparticles for efficient hydrogen evolution electrocatalysis

Elaborate design and synthesis of efficient and stable non-Pt electrocatalysts for some renewable energy-related conversion/storage processes is one of the major goals of sustainable chemistry. Herein, we report a facile, general, one-step synthetic method that leads to a family of non-noble metal hydrogen-evolving electrocatalysts that composed of metal phosphide nanoparticles embedded within nitrogen-doped carbon matrix. The synthesis of the materials is achieved via a facile one-step thermal treatment in inert atmosphere of homogeneously mixed urea, diammonium hydrogen phosphate and metal salts (e.g., ammonium molybdate for the synthesis of MoP). The use of inexpensive urea is crucial in the synthesis as it helps the deoxygenation-reduction of some metal salts and phosphor source (i.e., diammonium hydrogen phosphate) and undergoes in situ carbonization, leading to the formation of a composite material containing metal phosphide nanoparticles and nitrogen-doped carbon (NC) in one pot. Furthermore, we show that the resulting composite nanomaterials can serve as highly active, stable, noble metal-free electrocatalysts towards the hydrogen evolution reaction (HER). In particular, the MoP@NC material exhibits the best electrocatalytic activity in our study. This material affords a current density of 10 mA/cm2 at a low overpotential of 135 mV, exhibits excellent catalytic stability as long as 20 h, and gives nearly 100% Faradaic yield towards HER.