Advanced Functional Materials for Intermediate-Temperature Ceramic Fuel Cells
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Low to intermediate-temperature solid oxide fuel cell (SOFC, 500 oC-700 oC) based on doped ceria (DCO) electrolyte has attracted much attention during the last decade. However, DCO suffers from electronic conduction caused byreduction of Ce (IV) to Ce (III) at high temperatures and low oxygen partial pressures and has a high grain-boundary resistivity. Co-doping has been chosen as the focus of this PhD study to investigate the feasibility of overcoming these technical problems.
For different purposes, two co-doping strategies have been implemented to improve the properties of the singly doped ceria. Sr addition has been used with the aim of enhancing the ionic conductivity of Ce0.8Sm0.2O2-δ. The Sr addition greatly improves the microstructure of the space charge layers and the space charge potentials. The total conductivity of Sm and Sr co-doped ceria is higher than that of Ce0.8Sm0.2O1.9, and Ce0.8(Sm0.7Sr0.3)0.2O2-δ has the highest total conductivity. Sm and Lu co-doped ceria with composition of Ce1-x(Sm3Lu2)x/5O2-δ was investigated to validate the concept of critical dopant ionic radius. The elastic strain and critical dopant ionic radius may have an immediate effect on the grain bulk ionic conduction characteristics.
As the basis of the ceramic electrolyte processing, the effect of the powder synthesis routes, including Polyvinyl alcohol (PVA)-assisted sol-gel process,Polyethylene glycol (PEG)-assisted sol-gel process, citrate sol-gel process and oxalate co-precipitation process (OCP), on the microstructure and the ionic conductivity of the Ce0.85Sm0.075Nd0.075O2-δ (SNDC) electrolyte has beeninvestigated. OCP process results in higher relative density and ionic conductivity, lower grain-boundary resistance and activation energy.
Sm0.5Sr0.5CoO3-δ (SSC) cathode was investigated for SOFCs based on Ce0.85Sm0.075Nd0.075O2-δ (SNDC) electrolyte. Kinetics of oxygen reduction reaction (ORR) on porous SSC cathode was investigated by AC impedance spectra. Finally, novel BaZr0.1Ce0.7Y0.2O3-δ (BZCYO)-Ce0.8Y0.2O2-δ (YDC) composite ceramic electrolyte having both proton and oxygen ion conduction was studied. The composite ceramic electrolyte shows an enhanced ionic conductivity and chemical stability against reduction.
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. , vii, 49 p.
IdentifiersURN: urn:nbn:se:kth:diva-51479ISBN: 978-91-7501-145-5OAI: oai:DiVA.org:kth-51479DiVA: diva2:464160
2011-12-19, F3, KTH, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Mogensen, Mogens, Research Professor
Bergman, Bill, Professor
QC 201112132011-12-132011-12-122011-12-13Bibliographically approved
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