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

Abstract 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 Co 2+ ions from Co(NO 3 ) 2 ⋅6H 2 O were oxidized to Co 3+ ions in the ethanol‐water solution. Meanwhile, NO 3 − ions from Ni(NO 3 ) 2 ⋅6H 2 O and Co(NO 3 ) 2 ⋅6H 2 O triggered the ethanol‐water solution to release OH − ions, which subsequently reacted with Ni 2+ , Co 2+ and Co 3+ ions to generate NiCo‐OH precipitation. Subsequently, in the phosphorization step NiCo‐OH was converted to NiCoP nanosheets by NaH 2 PO 2 at a low temperature of 350 °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.