Improved 3D porous structures of Ni electrodes prepared by high-pressure cold spray and post annealing for water splitting

For improving the performance of water splitting, high pressure cold spray was applied to prepare Ni electrodes with controlled 3D porous structures. Al was added as pore former to endow the Ni electrodes with porous structures. Heat treatment was performed to improve the adhesion of the prepared coatings and thus boost the durability of the obtained Ni electrodes. The electrochemical results and characterizations revealed that porous Ni electrodes were successfully obtained. The porosity of obtained electrodes was increased with the addition of Al. Alloy phases such as NiAl and Ni3Al were detected after heat treatment. An oxide layer was found surrounding Ni layers after chemical leaching. The thickness of oxide layer was found increased with heating temperature and Al addition. NiO, Ni(OH)2 and NiOOH were found in the leached samples. With porous coatings, the electrodes possessed an improved current density of HER/OER. The Tafel slops of HER/OER were about 120mv/dec which indicated that the rate of water splitting was controlled by Volmer step. Due to the existence of oxide layers and unconnected pores, some samples exhibited Warburg diffusion behavior. Benefitting from the loose and porous microstructure, N30A sintered at 400 °C performed the best catalytic activity for HER/OER, and is considered the best sample for water splitting in alkaline condition.