Abstract
Ceramic electrolytes formed by Bi (4 mol%)-doped 8YSZ, i.e., Y2O3 (8 mol%)-doped ZrO2, were synthesized by a simple co-precipitation route, using ammonia solution as precipitating agent. The amorphous as-synthesized powders convert into zirconia-based single phase with fluorite structure through a mild calcination step at 500 °C. The calcined powders were sintered at very low temperatures (i.e., 900–1100 °C) achieving in both cases very high values of relative densities (i.e., >95%); the corresponding microstructures were highly homogeneous and characterized by micrometric grains or sub-micrometric grains for sintering at 1100 °C and 900 °C, respectively. Very interesting electrochemical properties were determined by Electrochemical Impedance Spectroscopy (EIS) in the best samples. In particular, their total ionic conductivity, recorded at 650 °C, are 6.06 × 10-2S/cm and 4.44 × 10-2S/cm for Bi (4 mol%)-doped 8YSZ sintered at 1100 °C and 900 °C, respectively. Therefore, Bi was proved to be an excellent sintering aid dopant for YSZ, highly improving its densification at lower temperatures while increasing its total ionic conductivity.
Highlights
Solid oxide fuel cells (SOFCs), being able to directly convert chemical energy of hydrocarbon fuels into electricity, are regarded as the generation of energy conversion devices mainly for them high efficiency, low environmental impact and high fuel flexibility [1]
A first possibility to fulfill this target is to use ceramic electrolytes based on different classes of materials such as doped and/or co-doped ceria [8,9,10] or the very recently proposed rhombohedral Bismuth oxide [11], whilst a second strategy consists of improving the properties of existing yttria-doped zirconia ceramics by further adding selected dopants [12]
The as-synthesized sample was sintered at 900 °C and 1100 °C and the electrochemical behavior was ascertained by Electrochemical Impedance Spectroscopy
Summary
Solid oxide fuel cells (SOFCs), being able to directly convert chemical energy of hydrocarbon fuels into electricity, are regarded as the generation of energy conversion devices mainly for them high efficiency, low environmental impact and high fuel flexibility [1]. The state-of-the-art material that better fulfill these requirements is the fluorite-structured yttria (8 mol%) doped-zirconia (8YSZ), which has been widely applied in a variety of fields, with specific interest as electrolyte in solid oxide fuel cells (SOFC) [2,3] It found application in composites with interesting thermal properties [4] and as porous ceramic material [5,6]. A first possibility to fulfill this target is to use ceramic electrolytes based on different classes of materials such as doped and/or co-doped ceria [8,9,10] or the very recently proposed rhombohedral Bismuth oxide [11], whilst a second strategy consists of improving the properties of existing yttria-doped zirconia ceramics by further adding selected dopants [12] To this regard, several reviews about SOFC materials can be found in literature. The obtained results highlighted the very positive effect of Bi2O3 in the samples both on powders sinterability and on sintered pellets electrochemical properties
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