Fabrication of nickel electrode coatings by combination of atmospheric and suspension plasma spray processes

Atmospheric plasma spray and suspension plasma spray were presented as two promising methods for manufacturing nickel cathode electrode coatings for alkaline water electrolysis, using micron- and submicron-sized powders, respectively. A combination of both processes was also successfully utilized as a novel method by deposition of a suspension plasma sprayed layer on an atmospheric plasma sprayed one to develop high performance electrodes. The coated electrodes were then characterized in terms of their microstructure, surface topography, wettability and steady state polarization curves. The highest electrocatalytic activity was obtained for an electrode coated by the combined method with the exchange current density and overpotential (η250) values of 6.2 × 10− 4 A/cm2 and − 386 mV, respectively. The high activity of this electrode was attributed to its large specific surface area with a high surface roughness value (Sa = 14.4 μm) comprising a multiscale micron/submicron-sized surface structure. It is expected that the dual microstructure of this electrode in addition to its superhydrophilic behaviour (with contact angles below 10°) enhances the activity by providing more reaction sites for hydrogen adsorption, promoting the diffusive mass transport of the reactants, and facilitating hydrogen bubble ascension from the pores.