Liquid plasma spraying of NiO-YSZ anode layers applicable for SOFC

Abstract

Plasma spraying (PS) from liquid feedstocks is a promising alternative for fabricating the NiO-YSZ anodes for Solid Oxide Fuel Cell (SOFC). However, despite the inherent advantages of the PS process, the plasma sprayed anodes are still inferior to the conventional ones prepared by wet-ceramic techniques due to the difficulty of achieving the optimal porosity level. This study shows that due to recent development, the NiO-YSZ anode layers with desirable porosity and microstructure can now be effectively fabricated in a one-step process using PS equipment with a water-argon stabilized plasma torch. As a liquid feedstock, we utilized Ni nitrate (hexahydrate) solutions and YSZ suspensions with different ratios, using ethanol or water as solvents. We show that the ethanol-based feedstock provides a favorable microstructure and porosity of the resulted layers over the water-based one. In addition, apart from NiO and YSZ phases, the layers deposited with ethanol solvent contained even metallic Ni. Different ratios of Ni nitrate to YSZ in ethanol-based feedstocks greatly affected the layer’s characteristics; when the content of Ni nitrate was high, the resulting layers had a non-uniform morphology with a very porous microstructure. On the contrary, the equal contents of Ni nitrate and YSZ in the feedstock resulted in the most optimal layer's microstructure, chemical composition, and thus sufficient electrical resistance, making such material potentially useful as anode for SOFC.