Green preparation of nickel phosphides as catalysts for green hydrogen production Gwaza Eric Ayom and Neerish Revaprasadu University of Zululand, South Africa The splitting of water to produce hydrogen is a green route explored towards replacing the heavy use of fossil fuels on our planet. This technology is however weighed down by the use of scarce and exotic noble metal catalysts. Ni 2 P is an important material for water-splitting reactions; however, its synthesis is usually tedious or requires toxic reagents. We report a facile, simple and green route for the preparation of a phase pure nickel phosphide, through a solvent-less synthetic protocol. The decomposition of different sulfur-based complexes (dithiocarbamate, xanthate and dithiophosphonate) of nickel was investigated in the presence and absence of triphenylphosphine (TPP). The optimization of reaction parameters (nature of precursor, ratio of TPP, temperature and time) indicated that phosphorus and sulfur-containing inorganic dithiophosphonate complexes and triphenylphosphine (1:1 mole ratio) yield pure nickel phosphide, whereas different phases of nickel sulfide were obtained from dithiocarbamate and xanthate precursors in presence or absence of TPP. Furthermore, the route was employed to also demonstrate transition metal doping in Ni 2 P. A plausible explanation of the sulfide or phosphide phase formation will be discussed, and the performance of Ni 2 P and doped Ni 2 P was investigated as an electrocatalyst for overall water-splitting reactions. The performance was also compared with Ni 2 P, prepared by other routes. The prepared nickel phosphide required overpotentials of 174 and 316 mV along with Tafel slopes of 115 and 95 mV/dec to achieve a current density of 10 mA/cm 2 for HER and OER, respectively. The good performance of the solvent-less prepared nickel phosphide electrode provides a framework for applications in energy conversion and storage technologies.
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© The Author(s), 2023
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