Scalable Two-Step Synthesis of Nickel–Iron Phosphide Electrodes for Stable and Efficient Electrocatalytic Hydrogen Evolution

The development of efficient, durable, and inexpensive hydrogen evolution electrodes remains a key challenge for realizing a sustainable H2 fuel production via electrocatalytic water splitting. Herein, nickel–iron phosphide porous films with precisely controlled metal content were synthesized on Ti foil using a simple and scalable two-step strategy of spray-pyrolysis deposition followed by low-temperature phosphidation. The nickel–iron phosphide of an optimized Ni:Fe ratio of 1:4 demonstrated excellent overall catalytic activity for hydrogen evolution reaction (HER) in 0.5 M H2SO4, achieving current densities of −10 and −30 mA cm–2 at overpotentials of 101 and 123 mV, respectively, with a Tafel slope of 43 mV dec–1. Detailed analysis obtained by X-ray diffraction, electron microscopy, electrochemistry, and X-ray photoelectron spectroscopy revealed that the superior overall HER activity of nickel–iron phosphide as compared to nickel phosphide and iron phosphide was a combined effect of differences in the morphology (real surface area) and the intrinsic catalytic properties (electronic structure). Together with a long-term stability and a near-100% Faradaic efficiency, the nickel–iron phosphide electrodes produced in this study provide blueprints for large-scale H2 production.