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Investigation of oxygen reduction reaction kinetics on Sm(0.5)Sr(0.5)CoO(3-delta) cathode supported on Ce(0.85)Sm(0.075)Nd(0.075)O(2-delta) electrolyte
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.ORCID-id: 0000-0003-3060-9987
2011 (engelsk)Inngår i: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 196, nr 22, s. 9195-9203Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Sm(0.5)Sr(0.5)CoO(3-delta) (SSC) cathode prepared by a glycine-nitrate process (GNP) is investigated for solid oxide fuel cells (SOFCs) based on Ce(0.85)Sm(0.075)Nd(0.075)O(2-delta) (SNDC) electrolyte. SSC forms cubic perovskite structure after being annealed at 1100 degrees C for 5 h. SSC cathode and SNDC electrolyte can retain their own structure and there is no reaction between the two compositions. The microstructure of the cathode and the interfaces between cathodes and SNDC electrolytes are studied by scanning electron microscopy (SEM) after sintering at various temperatures. Impedance spectroscopy measurements reveal that area specific resistances (ASRs) of SSC-SNDC30 cathode are much lower than those of SSC cathode. Kinetics of oxygen reduction reaction (ORR) on porous SSC cathode is investigated by analysis of impedance spectra. Medium-frequency conductivities show no dependency on oxygen partial pressure (Po(2)), which can be attributed to the oxygen ions transfer across the electrode/electrolyte interface. The dependencies of low-frequency conductivities on oxygen partial pressure (Po(2)) vary in the range from ca. 0.31 to ca. 0.34 and increase with the increasing temperatures. The low-frequency electrode process is a mixing process involving oxygen reduction reaction related to atomic oxygen and oxygen ions conduction step together with total charge-transfer step. IR-compensated current density (i)-overpotential (eta) relationship is established and the exchange current densities i(0) originated from high-field approximations are much higher than those of low-field approximations and a.c. impedance data under OCV state. It demonstrates the polarization overpotential has great effect on the kinetics of ORR. The polarization current is observed to increase with time in the long-term stability measurement, which can be ascribed to the propagation process of oxygen vacancies.

sted, utgiver, år, opplag, sider
2011. Vol. 196, nr 22, s. 9195-9203
Emneord [en]
Solid oxide fuel cells, Cathode, Oxygen reduction reaction, Area specific resistance
HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-45576DOI: 10.1016/j.jpowsour.2011.07.012ISI: 000295602400013Scopus ID: 2-s2.0-80052483639OAI: oai:DiVA.org:kth-45576DiVA, id: diva2:454447
Merknad
QC 20111107Tilgjengelig fra: 2011-11-07 Laget: 2011-10-31 Sist oppdatert: 2017-12-08bibliografisk kontrollert
Inngår i avhandling
1. Advanced Functional Materials for Intermediate-Temperature Ceramic Fuel Cells
Åpne denne publikasjonen i ny fane eller vindu >>Advanced Functional Materials for Intermediate-Temperature Ceramic Fuel Cells
2011 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

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.

sted, utgiver, år, opplag, sider
Stockholm: KTH Royal Institute of Technology, 2011. s. vii, 49
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-51479 (URN)978-91-7501-145-5 (ISBN)
Disputas
2011-12-19, F3, KTH, Lindstedtsvägen 26, Stockholm, 10:00 (engelsk)
Opponent
Veileder
Merknad
QC 20111213Tilgjengelig fra: 2011-12-13 Laget: 2011-12-12 Sist oppdatert: 2011-12-13bibliografisk kontrollert

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