A Self-Assembled Flower-Like Structure of Nickel-Cobalt Phosphide Nanosheets Supported on Nickel Foam for Electrochemical Hydrogen Evolution Reaction

In this study, flower-like nickel-cobalt phosphide (NiCoP) on Ni foam (flower-like NiCoP/NF) was fabricated via a two-step process, including hydrothermal and phosphorization. Hydrogen evolution reaction (HER) measurements show that such flower-like NiCoP/NF is a highly efficient and stable electrocatalyst, which can keep high activity for more than 20 h at ambient temperature. Scanning electron microscope (SEM) images show that flower-like NiCoP/NF uniformly covered the Ni foam surface. In the hydrothermal step, X-ray photoelectron spectroscopy (XPS) results show that partial Co2+ ions from Co(NO3)(2)center dot 6H(2)O were oxidized to Co3+ ions in the ethanol-water solution. Meanwhile, NO3- ions from Ni(NO3)(2)center dot 6H(2)O and Co(NO3)(2)center dot 6H(2)O triggered the ethanol-water solution to release OH- ions, which subsequently reacted with Ni2+, Co2+ and Co3+ ions to generate NiCo-OH precipitation. Subsequently, in the phosphorization step NiCo-OH was converted to NiCoP nanosheets by NaH2PO2 at a low temperature of 350 degrees C. The two-step method employed in the present work avoids an addition of alkali sources or precipitators to the hydrothermal reaction solution, which is favorable for environmental protection strategies and sustainable development principles.