Assessment of doped ceria as electrolyte

Dalslet, Bjarke Thomas; Blennow, Peter; Hendriksen, Peter Vang; Bonanos, Nikolaos; Lybye, Dorthe; Mogensen, Mogens Bjerg

doi:10.1007/s10008-006-0135-x

Cited by 117 publications

(94 citation statements)

References 28 publications

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“…This behavior is not noted when a higher load of 300 mA cm −2 is applied, due to the fact that the leakage current density becomes null when enough current density is extracted, and the whole electronic current introduced at the electrodes converts into ionic current in the electrolyte. As effectively summarized by Dalslet et al, 3 the electrolyte becomes a better (ion-transferring) electrolyte at increasing the current load.…”

Section: Discussionmentioning

confidence: 92%

“…• C. [1][2][3][4][5] Associated to a high ionic conductivity, however, these materials show mixed ionic and electronic conductive (MIEC) properties, and their electronic conductivity increases when exposed to reducing atmospheres. The MIEC character of the electrolyte, in turn, results in the onset of electronic leakage currents (or short circuit currents) and low open-circuit voltage values.…”

mentioning

confidence: 99%

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A Distributed Charge Transfer Model for IT-SOFCs Based on Ceria Electrolytes

Rahmanipour

Pappacena

Boaro

et al. 2017

J. Electrochem. Soc.

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A distributed charge transfer model for IT-SOFCs with MIEC electrolyte and composite electrodes is developed. A physically-based description of the electronic leakage current in the electrolyte is included, together with mass and charge conservation equations. The model is applied to simulate experimental polarization curves and impedance spectra collected on IT-SOFCs consisting of SDC electrolytes, Cu-Pd-CZ80 infiltrated anodes and LSCF/GDC composite cathodes. Hydrogen electro-oxidation experiments are examined (H 2 /N 2 humidified mixtures, 700 • C, 30-100% H 2 molar fraction). A significant increase of the ohmic resistance measured in the impedance spectra is revealed at decreasing the H 2 partial pressure or increasing the voltage (from 0.71 cm 2 at 100% H 2 to 0.81 cm 2 at 30% H 2 ). Good agreement between the calculated and experimental polarization and EIS curves is achieved by fitting the exchange current density and the capacitance of each electrode. Model and theoretical analyses allow to rationalize the observed shift of the ohmic resistance, highlighting the key-role played by the electronic leakage current. Overall, the model is able to capture significant kinetic features of IT-SOFCs, and allows to gain insight into relevant parameters for the optimal design of the cell (electrochemically active thickness, current and potential distribution, mass diffusion gradients). Samaria doped Ceria (SDC) and Gadolinia doped Ceria (GDC) are reference electrolyte materials for intermediate temperature solid oxide fuel cell (IT-SOFC) applications, thanks to their high ionic conductivity between 500• C and 700• C. 1-5 Associated to a high ionic conductivity, however, these materials show mixed ionic and electronic conductive (MIEC) properties, and their electronic conductivity increases when exposed to reducing atmospheres. The MIEC character of the electrolyte, in turn, results in the onset of electronic leakage currents (or short circuit currents) and low open-circuit voltage values. The leakage current has a chemical origin and is due to the partial reduction of Ce 4+ ions to Ce 3+ ions, prompted by the different chemical potential at the electrodes: this current is active also in the absence of an electric field applied on the cell, since it stems from the spontaneous transfer of ions across the lattice structure. As a consequence, the effects of the leakage current are not confined to the electrolyte, but extend to the electrodes, and entail a complex relationship with the current drawn from the cell. 6 Deeper insight can therefore be achieved by mathematical modeling.In the literature, comprehensive models can be found, which take into account the MIEC properties of Ce-based electrolytes. Starting from continuum rigorous descriptions, a series of models has been derived for the prediction of impedance spectra collected on MIEC electrolytes, the most important examples being those by Jamnik and Maier, 7 by the group of Haile 8,9 and by Atkinson et al. 10 These models propose closed-form, equivalent circuit-l...

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Section: Discussionmentioning

confidence: 92%

mentioning

confidence: 99%

A Distributed Charge Transfer Model for IT-SOFCs Based on Ceria Electrolytes

Rahmanipour

Pappacena

Boaro

et al. 2017

J. Electrochem. Soc.

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“…The latter point follows from the conductivities of CGO being ≈0.001 S/cm at 350 °C [21] while the conductivity of the molten KNO 3 at 350 °C is 0.699 S/cm [36], which means at 350 °C the reduced serial resistance observed for the KNO 3 impregnated sample may be explained by the current passing through the KNO 3 instead of the CGO electrolyte . Unfortunately it has despite of extensive search not been possible to find information on the conductivity of K 2 O and solid KNO 3 at 300 °C, for this reason it cannot be estimated here, if an alternative current path is a realistic explanation of the reduced serial resistance observed on the impregnated cell stacks at 300 °C.…”

mentioning

confidence: 93%

“…The stacks were subjected to electrochemical impedance spectroscopy and conversion/polarisation experiments while the gas composition was monitored by a mass spectrometer (MS) and a chemiluminiscense detector (CLD). The cell stacks differed from each other in the way they were impregnated: one stack had no impregnation, one stack was impregnated with KNO 3 and one stack was impregnated with K 2 O. LSF was chosen as electrode material, since LSF as a mixed conductor [18] [19] has been evaluated to be a promising material for intermediate temperate solid oxide electrodes [20] while CGO was chosen as an electrolyte, as CGO has superior oxygen ion-conductivity below 600 °C when compared to yttria stabilized zirconia [21]. KNO 3 /K 2 O was chosen for impregnation, as potassium is known to act both as a NO x -storage compound [22] and also to improve simultaneous NO x and soot removal [23,24], the latter being of interest for future development of the electrochemical deNO x technique.…”

mentioning

confidence: 99%

NO x conversion on porous LSF15–CGO10 cell stacks with KNO3 or K2O impregnation

Traulsen

Bræstrup

2012

J Solid State Electrochem

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In the present work it was investigated how addition of KNO 3 or K 2 O affected the NO x conversion on LSF15-CGO10 (La 0.85 Sr 15 FeO 3 -Ce 0.9 Gd 0.1 O 1.95 ) composite electrodes during polarisation. The LSF15-CGO10 electrodes were part of a porous 11-layer cell stack with alternating layers of LSF15-CGO10 electrodes and CGO10 electrolyte. The KNO 3 was added to the electrodes by impregnation, and kept either as KNO 3 in the electrode or thermally decomposed into K 2 O before testing. The cell stacks were tested in the temperature range 300-500 °C in 1000 ppm NO, 10% O 2 and 1000 ppm NO + 10% O 2 . During testing the cells were characterized by electrochemical impedance spectroscopy (EIS) and the NO conversion was measured during polarization at -3 V for 2 h. The concentration of NO and NO 2 was monitored by a chemiluminiscence detector, while the concentration of O 2 , N 2 and N 2 O was detected on a mass spectrometer. A significant effect of impregnation with KNO 3 or K 2 O on the NO x conversion was observed. In 1000 ppm NO both impregnations caused an increased conversion of NO into N 2 in the temperature range 300-400 °C with a current efficiency up to 73%. In 1000 ppm NO + 10% O 2 no formation of N 2 was observed during polarisation, but the impregnations altered the conversion between NO and NO 2 on the electrodes. Both impregnations caused increased degradation of the cell stack, but the exact cause of the degradation has not been identified yet.

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“…S δ = (16) Considering the separation of the Boltzmann distribution and Maxwell's demon, the generalized expression obtained from Equations (12) and Equation (13) …”

Section: Additional Thermodynamic Law Based On the Advanced Model Of mentioning

confidence: 99%

Bell’s Non-Locality Theorem Can Be Understood in Terms of Classical Thermodynamics

Miyashita¹

2017

JMP

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Bell's non-locality theorem can be understood in terms of classical thermodynamics, which is already considered to be a complete field. However, inconsistencies in classical thermodynamics have been discovered in the area of solid-oxide fuel cells (SOFCs). The use of samarium-doped ceria electrolytes in SOFCs lowers the opencircuit voltage (OCV) to less than the Nernst voltage. This low OCV has been explained by Wagner's equation, which is based on chemical equilibrium theory. However, Wagner's equation is insufficient to explain the low OCV, which should be explained by fluctuation and dissipation theorems. Considering the separation of the Boltzmann distribution and Maxwell's demon, only carrier species with sufficient energy to overcome the activation energy can contribute to current conduction, as determined by incorporating different constants into the definitions of the chemical and electrical potentials. Then, an energy loss equal to the activation energy will occur because of the interactions between ions and electrons. This energy loss means that an additional thermodynamic law based on an advanced model of Maxwell's demon is needed. In this report, the zero-point energy can be explained by this additional thermodynamic law, as can Bell's non-locality theorem.

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Assessment of doped ceria as electrolyte

Cited by 117 publications

References 28 publications

A Distributed Charge Transfer Model for IT-SOFCs Based on Ceria Electrolytes

A Distributed Charge Transfer Model for IT-SOFCs Based on Ceria Electrolytes

NO x conversion on porous LSF15–CGO10 cell stacks with KNO3 or K2O impregnation

Bell’s Non-Locality Theorem Can Be Understood in Terms of Classical Thermodynamics

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