Scalable production of foam-like nickel–molybdenum coatings via plasma spraying as bifunctional electrocatalysts for water splitting

Abstract

Foam-like NiMo coatings were produced from an inexpensive mixture of Ni, Al, and Mo powders via atmospheric plasma spraying. The coatings were deposited onto stainless-steel meshes forming a highly porous network mainly composed of nanostructured Ni and highly active Ni₄Mo. High material loading (200 mg cm⁻²) with large surface area (1769 cm² per cm²) was achieved without compromising the foam-like characteristics. The coatings exhibited excellent activity towards both hydrogen evolution (HER) and oxygen evolution (OER) reactions in alkaline media. The HER active coating required an overpotential of 42 mV to reach a current density of −50 mA cm⁻² with minimum degradation after a 24 h chronoamperometry test at −10 mA cm⁻². Theoretical simulations showed that several crystal surfaces of Ni₄Mo exhibit near optimum hydrogen adsorption energies and improved water dissociation that benefit the HER activity. The OER active coating also consisting of nanostructured Ni and Ni₄Mo required only 310 mV to achieve a current density of 50 mA cm⁻². The OER activity was maintained even after 48 h of continuous operation. We envisage that the development of scalable production techniques for Ni₄Mo alloys will greatly benefit its usage in commercial alkaline water electrolysers.