Oxygen nonstoichiometry and exchange kinetics of Ba0.5Sr0.5Co0.8Fe0.2O3−δ

Bucher, Edith; Egger, Andreas; Ried, Peter; Sitte, Werner; Holtappels, Peter

doi:10.1016/j.ssi.2008.01.089

Cited by 185 publications

(148 citation statements)

References 20 publications

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“…In addition, higher activation energy was reported for the bulk diffusion (86 AE 8 kJ mol À1 ) than that for the exchange kinetics (64 AE 12 kJ mol À1 ) in temperature range of 550-750 C measured by electrical conductivity relaxation method. 27 The two values are all closed to those obtained through the model. For the investigated BSCF membrane, the L c values defined by Eq.…”

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confidence: 69%

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Permeation model and experimental investigation of mixed conducting membranes

Zhu

Liu

et al. 2011

AIChE Journal

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A simple oxygen permeation model was developed based on the theoretical analysis of the role of interfaces of mixed conducting membranes. The developed model equations contain three resistance constants, which can be determined by correlating oxygen permeation flux to oxygen partial pressure on each side. A series of experimental measurements of oxygen fluxes of Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3À membranes over a wide range of temperature and oxygen partial pressures were tested for the regression of three resistance constants with good correlation (R > 0.997). With this model, the interfacial exchange resistances of each side can be well distinguished from the bulk-diffusion resistance under a wide-temperature range. The kinetics parameters, including interfacial exchange coefficients on each side and ionic diffusion coefficient, can be obtained through the three resistance constants. Parametric studies can predict the influences of membrane thickness, oxygen partial pressures on oxygen flux, distribution of permeation resistances, and characteristic thickness.

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confidence: 69%

“…Here, for the comparison purpose, the chemical diffusion coefficients and vacancy diffusion coefficients are converted to self-diffusion coefficients according to Ref. 27. The chemical exchange coefficients were treated similarly.…”

Section: Kinetic Parametersmentioning

confidence: 99%

Permeation model and experimental investigation of mixed conducting membranes

Zhu

Liu

et al. 2011

AIChE Journal

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“…[4][5][6][7][8] The ALSmodel is an analytical 1D-model developed for semi-infinite thickness, porous, mixed-conducting cathodes with high ionic-electronic conductivity and no gas phase diffusion limitations. It is generally accepted that for thick cathodes the oxygen surface-exchange and the solid-state diffusion processes are coupled and can be described by the following equation, mathematically equivalent to a Gerischer impedance:…”

Section: Resultsmentioning

confidence: 99%

“…Many publications have assessed the D and k values of MIEC materials, most commonly by; electrical conductivity relaxation (ECR) measurements for dense bulks [4][5][6][7][8] and temperature for LSCF cathodes. 17 Here it should be pointed out that the well-known ALS model can only be applied if the measured impedance shows a Gerischer impedance, which indicates that the surface-exchange and the oxygen bulk diffusion are strongly coupled.…”

Section: -3mentioning

confidence: 99%

“…[1][2][3] The surface-exchange coefficient (k) and the oxygen diffusion coefficient (D) provide key information about the oxygen transport mechanism that dominates the cathodic ORR. Many publications have assessed the D and k values of MIEC materials, most commonly by; electrical conductivity relaxation (ECR) measurements for dense bulks [4][5][6][7][8] or thin-films 9,10 (k δ , D δ ) and by oxygen tracer diffusion experiments for thin-films 11 or powder 12 (k * , D * ). The oxygen transport parameters are usually determined by ex situ experiments for model systems (i.e.…”

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Oxygen Transport Kinetics of Mixed Ionic-Electronic Conductors by Coupling Focused Ion Beam Tomography and Electrochemical Impedance Spectroscopy

Almar

Szász

Weber

et al. 2017

J. Electrochem. Soc.

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The oxygen reduction reaction of mixed ionic-electronic conducting (MIEC) cathodes Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF) and La 0.58 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) is investigated by detailed electrochemical impedance spectroscopy and focused ion beam tomography. The oxygen transport parameters of these materials are usually determined for model systems, such as dense bulks or thin films. However in the present study, probable differences regarding the time and thermal history of the samples (e.g. ambient poisoning gases, grain coarsening, secondary phase or surface segregation, etc.) were avoided by the in situ sintering of electrodes with nominal stoichiometry under synthetic air. The microstructural parameters of the electrodes are obtained by 3D FIB-SEM reconstruction tomography and subsequently used in combination with the Adler-Lane-Steele analytical model to calculate a simulated cathode resistance. Large discrepancies are observed compared to the electrochemical impedance measurements. In particular, the electrochemical impedance measurements do not show a Gerischer behavior, as expected for MIEC materials controlled by a coupled surface-exchange and bulk diffusion. Analysis by distribution function of relaxation times (DRT) reveals four individual processes taking place, indicating a surface-exchange controlled behavior with a reaction zone similar to the particle size. Bulk diffusion (D) and surface-exchange (k) coefficients from literature are critically discussed and tentative surface-exchange coefficients (k) for both MIECs are given. High-temperature devices such as solid oxide fuel cells (SOFCs) and oxygen transport membranes (OTMs) are promising systems for working towards zero-emissions power generation. The selected materials require high chemical and microstructural stability, as well as high catalytic activity during the oxygen reduction reaction (ORR), under normal operational conditions (i.e. operational temperature and oxygen partial pressure). Particularly interesting are the mixed ionic-electronic conducting (MIEC) materials, based on the ABO 3 perovskite structure. Their material properties can be flexibly customized, giving solid solutions with high ionic-electronic conductivity and hence good transport properties. More specifically, La 0.58 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) has become established as the stateof-the-art SOFC cathode, while Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF) has presented outstanding oxygen permeation flux in its cubic phase. 1-3The surface-exchange coefficient (k) and the oxygen diffusion coefficient (D) provide key information about the oxygen transport mechanism that dominates the cathodic ORR. Many publications have assessed the D and k values of MIEC materials, most commonly by; electrical conductivity relaxation (ECR) measurements for dense bulks [4][5][6][7][8] and temperature for LSCF cathodes. 17 Here it should be pointed out that the well-known ALS model can only be applied if the measured impedance shows a Gerischer impedance, which indicates tha...

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