Intrinsically active nickel electrodes with large porous surface areas have shown promise for producing hydrogen by alkaline water electrolysis. In this study, Ni powder and NiO suspensions were sprayed on Inconel 600 substrates with an atmospheric plasma gun, producing single (Ni, NiO) and double layer (Ni-NiO) coatings. Top surface morphologies were examined, revealing both micro and nano scale features. Based on kinetic parameters obtained from steady-state polarization measurements, APS-SPS coated electrodes are the most catalytically active and thus have the most potential for hydrogen evolution. It is believed that the nanoscale structure increases effective surface area while the microporous structure facilitates mass transport and overcomes hydrogen bubble blockage.

In this study, atmospheric and suspension plasma spraying are used to create nickel-based electrodes with enhanced surface area as required for hydrogen production. Optimal spraying conditions were determined using a Taguchi design-of-experiments approach. Electrochemical double-layer capacitance measurements by cyclic voltammetry show that suspension plasma spray coatings have more surface area than coatings produced by atmospheric plasma spraying. SEM micrographs show that the surface microstructure of the sample with the largest surface area contains high amounts of cauliflower-like aggregates with an average diameter of 10 µm. In general, the combination of melted, semi-melted, and resolidified particles leads to the formation of deposits with high porosity, rougher surfaces, and consequently larger surface areas.

This study compares two methods for modeling the breakup of droplets during suspension plasma spraying. One is based on Taylor analogy breakup, the other on Kelvin-Helmholtz Rayleigh Taylor breakup. A three-dimensional model with two-way coupling is used to simulate flow within the plasma plume and interactions between suspension droplets, and a Reynolds stress model is used to simulate gas field turbulence. After breakup and vaporization, the solid suspended particles are tracked through the domain to determine the characteristics of coating particles. The numerical results are validated against experiments using high-speed imaging.