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 (similar to 3 degrees 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.