SOFC/CeO2 Doped Electrolyte Deposition Using Suspension Plasma Spraying

Abstract

Ceria (CeO2) based electrolytes have been considered for use in solid oxide fuel cells (SOFC) for more than 20 years. There are however some limitations to this usage that this study has tried to address, indeed the study objective has been that of synthesizing and thermal spraying thin layers (50 - 100 µm) of doped CeO2 by the technique of suspension plasma spraying, using radio frequency (RF) plasma technology. Various dopant combinations and concentrations have been selected for this work in order to increase the useful partial oxygen pressure range for satisfactory ionic conductivity development, thereby increasing the anionic conductivity and preventing CeO2 reduction in fuel cell service. Ceria possesses the fluorite crystal structure at low temperatures but does not have enough oxygen vacancies to be a good ionic conductor. In ceria the cerium have 4+ oxidation state within the fluorite structure, and by substituting a certain amount of Ce4+ ions by trivalent dopant ions, oxygen vacancies are induced into the structure. Recent studies have demonstrated that at low temperatures doped ceria seems to be a better electrolyte than doped zirconia. Also, it seems that dopants with ionic radii close to Ce4+ ions give rise to better ionic conductivities. The doped ceria conductivity increases with the dopant concentration because more oxygen vacancies are created, but at higher concentrations vacancy ordering occurs which results in decreased ionic conductivity.

High Velocity Thermal Spraying of Powders and Suspensions Containing Micron, Submicron and Nanoparticles for Functional Coatings

“…Most of these approaches considered the fabrication of thin films or the achievement of a fine coating structure. Spraying suspensions containing nano oxide ceramic powders using plasma spray technique were published by several authors [4], [5], [6]. A first experimental approach to insert suspensions into a modified HVOF system was patented in 2005 and published in 2006 by Gadow and Killinger [7], [8].…”