Influence of the oxygen partial pressure on the reduction of CeO2 and CeO2ZrO2 ceramics

Huang, Shuigen; Li, L.; Biest, Omer Van der; Zhang, Fei

doi:10.1016/j.solidstatesciences.2005.02.005

Cited by 37 publications

(29 citation statements)

References 25 publications

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“…In the system Ce-Zr-O different phases such as fluorite-type (Ce,Zr)O 2−δ solid solutions, tetragonally distorted ZrO 2 -rich fluorite structures or pyrochlore Ce 2 Zr 2 O 7 occur depending on Zr/Ce ratio, p O 2 , and temperature [13][14][15][16][17]. Pyrochlore formation is assumed to result in lower redox entropy since possible site occupancies of oxygen vacancies are limited with respect to oxygen vacancy sites in the fluorite structure of pure ceria [17][18][19][20][21].…”

Section: Introductionmentioning

confidence: 99%

Ceria: Recent Results on Dopant-Induced Surface Phenomena

et al. 2017

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Abstract:Redox studies on dense zirconia-doped ceria pellets were carried out by thermogravimetric investigations and dilatometry. Up to 1600 K reduction parameters determined by both methods correspond to each other. At higher temperatures, however, thermogravimetry overestimates the degree of reduction since mass loss is not only due to oxygen exsolution but also to selective evaporation of CeO 2 whose vapour pressure is considerably higher than that of ZrO 2 . As a consequence surface segregation of zirconia occurs in (Ce,Zr)O 2−δ pellets leading to a porous surface zone of Ce 2 Zr 2 O 7 pyrochlore which gradually grows in thickness. Surface enrichment of zirconia is detrimental for splitting CO 2 or H 2 O since re-oxidation temperatures of (Ce,Zr)O 2−δ are known to be shifted towards lower temperatures with increasing ZrO 2 content. Thus, very harsh reduction conditions should be avoided for the (Ce,Zr)O 2−δ redox system. The kinetics investigations comprised the high temperature reduction step (T ∼ = 1600 K) and the "low" temperature oxidation reaction with a carbon dioxide atmosphere (T ∼ = 1000 K). The reduction kinetics (at around 1600 K and an oxygen activity of 7 × 10 −4 in the gas phase) directly yield the (reduction) equilibrium exchange rate of oxygen in the order of 10 −7 mol·O/(cm 3 ·s) as the kinetics are surface controlled. The oxidation step at around 1000 K, however, occurs in the mixed control or in the diffusion control regime, respectively. From oxygen isotope exchange in combination with SIMS depth profiling oxygen exchange coefficients, K, and oxygen diffusivities, D, were determined for so-called equilibrium experiments as well as for non-equilibrium measurements. From the obtained values for K and D the (oxidation) equilibrium exchange rates for differently doped ceria samples were determined. Their dependency on the oxygen activity and the nature and the concentrations of a tetravalent dopant (Zr) and trivalent dopants (La, Y, Sm) could be semi-quantitatively rationalised on the basis of a master equation for the equilibrium surface exchange rate.

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Section: Introductionmentioning

confidence: 99%

Ceria: Recent Results on Dopant-Induced Surface Phenomena

et al. 2017

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“…19 It is also possible to retain more tZrO 2 phase by decreasing the sintering temperature since the CeO 2 reduction is also dependent on the temperature. 17 For the ZrO 2 -WC composites however, the reduction of CeO 2 in combination with the residual tensile stresses caused the high amount of m-ZrO 2 in the Y 2 O 3 + CeO 2 co-stabilized ZrO 2 -WC composites.…”

Section: Constituent Phasesmentioning

confidence: 98%

Development of ZrO2–WC composites by pulsed electric current sintering

Huang

Vanmeensel

Biest

et al. 2007

Journal of the European Ceramic Society

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“…Solid oxide fuel cells (SOFCs) can produce electrical power with high efficiency and reduce emissions of pollution such as CO 2 and NO x . However, current SOFCs based on yttria-stabilized zirconia (YSZ) generally operate at high temperatures (above 900 o C) for good performance.…”

Section: Introductionmentioning

confidence: 99%

“…This method creates an oxidation atmosphere (dry CH 4 ) instead of a reduction atmosphere (H 2 ), as expressed above in Equations [2] and [3]. This paper discusses the interrelationship between the ceria structure change and the atmosphere at the anode.…”

Section: Introductionmentioning

confidence: 99%

Structural Stability of GDC Electrolyte for Low-Temperature SOFCs Depending on Fuels

Ko¹,

Lee²,

Hyun³

2009

ECS Trans.

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GDC (Gd 0.1 Ce 0.9 O 1-X ) has been considered as a low-temperature SOFC electrolyte. However, ceria cannot be efficiently used with hydrogen and wet hydrocarbon fuels because its structure change (Ce +4 →Ce +3 ) causes a decline of mechanical strength under a reduction atmosphere. In this work, the structural stability test of the GDC electrolyte for low-temperature SOFCs was investigated under reduction and oxidation atmospheres depending on the fuels. Each structural stability test was examined under reduction (H 2 ) and oxidation (dry CH 4 ) atmospheres at 650 o C. Micro-cracks and pinholes were observed on the electrolyte surface and at the fracture after completing the test with hydrogen fuel, but in the case of dry methane, only small amounts of defects were found at the fracture. This study clearly confirmed from the XPS data that many more Ce +4 ions transform into Ce +3 ions under the reduction (H 2 ) atmosphere (1, 2).

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Influence of the oxygen partial pressure on the reduction of CeO2 and CeO2ZrO2 ceramics

Cited by 37 publications

References 25 publications

Ceria: Recent Results on Dopant-Induced Surface Phenomena

Ceria: Recent Results on Dopant-Induced Surface Phenomena

Development of ZrO2–WC composites by pulsed electric current sintering

Structural Stability of GDC Electrolyte for Low-Temperature SOFCs Depending on Fuels

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