One-step synthesis of nickel and cobalt phosphide nanomaterials via decomposition of hexamethylenetetramine-containing precursors.

Dispersed pure phases of Ni2P and Co2P nanoparticles with high surface areas were prepared from one-step decomposition of hexamethylenetetramine (HMT)-containing precursors under an inert atmosphere. The solids before and after decomposition and the evolution of gas during the processes were studied by various characterization techniques. The HMT precursors underwent three decomposition stages: low-, moderate- and high-temperature stages. The formation of phosphides was observed at the high-temperature decomposition stage, in which Ni (Co) and P species were reduced by the decomposition products (C, H2 and CH4) of HMT to yield Ni (Co) phosphides, with the release of COx and H2O. Note that in contrast to the traditional H2-temperature-programmed reduction (H2-TPR) method, the HMT-based method produced CO as a major gas product rather than H2O. The better dispersions and higher surface areas of the as-prepared phosphide nanoparticles were achieved probably due to the mitigation of hydrothermal sintering.