Novel synthesis of dispersed molybdenum and nickel phosphides from thermal carbonization of metal- and phosphorus-containing resins

Abstract

Dispersed pure phases of MoP and Ni₂P nanoparticles supported by carbon were synthesized by carbonization of metal- and phosphorus-containing resins under an inert atmosphere. The solid products and the evolution of gases during the carbonization process were investigated by various techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), N₂ adsorption–desorption analysis, and mass spectrometry (MS). The resins underwent two carbonization stages: the low-temperature carbonization stage (<650 °C) and the high-temperature carbonization stage (≥650 °C). There was an initial reduction of Mo and Ni precursors in the low-temperature region. However, the formation of phosphides was observed in the high-temperature carbonization stage, in which Mo(Ni) and PO_x species were further reacted with the carbonization products (C, H₂ and CH₄) to yield Mo(Ni) phosphide. Note that compared with the traditional H₂-temperature-programmed reduction (H₂-TPR) method, this novel synthesis route produced a large amount of CO_x besides H₂O, leading to a lower water vapor pressure. In addition, the residual carbon produced from resin can play a role in bonding of nanoparticle aggregation. Therefore, the better dispersions and higher surface areas of the as-prepared phosphide nanoparticles were attributed to the mitigation of hydrothermal sintering and the intimate contact between phosphide nanoparticles and carbon species.