Stoichiometric Control of Electrocatalytic Amorphous Nickel Phosphide to Increase Hydrogen Evolution Reaction Activity and Stability in Acidic Medium

This work describes the electrocatalysis of amorphous nickel phosphide (Ni‐P) electrodeposited onto copper metal foil, for its use as a non‐noble metal catalyst for the hydrogen evolution reaction (HER) in 0.5 M H2SO4. Although electrodeposition offers many advantages over conventional high temperature and high pressure fabrication techniques, there are very few reports on the preparation of Ni‐P electrocatalysts via electrodeposition. This Ni‐P electrocatalyst exhibits good activity in acidic medium, with a potential of –222 mV to achieve 10 mA cm–2 cathodic current density. This potential is comparable to that of electrodeposited Pt black (–104 mV), and much better than that of electrodeposited Ni (–480 mV). An unusual long‐term stability in acidic medium was demonstrated by the –222 mV potential remaining constant after 5000 cyclic voltammetric sweeps in 0.5 M H2SO4. Importantly, the stoichiometry of the nickel phosphide films can be easily varied from an atomic % of phosphorus from 15 % to as high as 24 % by modifications to the electrodeposition conditions. Such a high phosphorous loading is greater than is generally reported with electrodeposited Ni‐P materials. In addition, we observed Ni‐P films electrodeposited at lower temperatures (∼ 3 °C) result in higher phosphorous loading, which gives rise to enhanced stability as well as activity. Electrodeposited amorphous Ni‐P can therefore be used as an active, stable and Earth‐abundant metal catalyst for the HER in acidic electrolytes. Even after 5000 cyclic voltammetric sweeps, electrodeposited nickel phosphide shows high activity and stability towards hydrogen evolution reaction (HER) in acidic electrolyte. Modifications to the deposition conditions could easily elevate the phosphorus loading on the film up to circa 24 at%, which provided enhanced activity.