The Chemical Capacitance as a Fingerprint of Defect Chemistry in Mixed Conducting Oxides

Schmid, Alexander; Rupp, Ghislain M.; Slouka, Christoph; Navickas, Edvinas; Andrejs, Lukas; Hutter, Herbert; Volgger, Lukas; Nenning, Andreas; Fleig, Jürgen

doi:10.17344/acsi.2016.2302

Cited by 8 publications

(10 citation statements)

References 25 publications

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“…In literature, the notations e′, Ce Ce ¢ and Ce 3+ represent the same defect for this material. Also the chemical capacitance is a measure for the Ce 3+ concentration [50,51]. Therefore, also the increase of chemical capacitance in more reducing atmospheres is also in line with the literature defect chemical models [6,50,51].…”

Section: Separation Of Ionic and Electronic Conductivitysupporting

confidence: 80%

“…Also the chemical capacitance is a measure for the Ce 3+ concentration [50,51]. Therefore, also the increase of chemical capacitance in more reducing atmospheres is also in line with the literature defect chemical models [6,50,51]. In case of relatively small Ce 3+ concentrations, the model of doped bulk ceria predicts that chemical capacitance and electronic conductivity are proportional to p(O 2 ) −0.25 [5,51].…”

Section: Separation Of Ionic and Electronic Conductivitysupporting

confidence: 78%

“…Already the very good fit with only four parameters indicates that the circuit model is appropriate. In addition to electronic and ionic conductivities, the equivalent circuit fit delivers the chemical capacitance of the GDC film, which contains information on the concentration of Ce 3+ ions [50,51]. It is worth noting that the circuit model is only appropriate when the rate of electrochemically driven oxygen exchange at the GDC surface is much lower than the current carried by electronic and ionic charge carriers.…”

Section: Separation Of Ionic and Electronic Conductivitymentioning

confidence: 99%

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Low oxygen partial pressure increases grain boundary ion conductivity in Gd-doped ceria thin films

Nenning

Opitz

2019

J. Phys. Energy

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Grain boundaries play an important role in the transport properties of oxide ion conducting electrolytes and mixed ionic electronic conductors. Nevertheless, very little is known about the electrical grain boundary properties in thin films. In these, the separation of in-plane grain and grain boundary conductivity is more complicated due to the large capacitive effect of the insulating substrate. This can be overcome by using interdigitating electrodes with separation of few micrometres. By comparing grain and grain boundary conductivities of Gd-doped Ceria (GDC) thin films with 5 and 10 mol % Gd content, we can show that the much lower conductivity of 5% doped GDC is almost exclusively caused by a significantly higher grain boundary resistance. In reducing atmosphere, GDC becomes mixed ion and electron conducting and in such conditions, the employed Pt thin film electrodes are virtually blocking for oxygen anions and reversible for electrons. With impedance spectroscopy we can therefore simultaneously measure ionic and electronic conductivities under reducing conditions. Although the bulk vacancy concentration remains dominated by the extrinsic acceptor doping, the ionic conductivity of the films increases by up to one order of magnitude when going from oxidising to reducing atmosphere. This result is-although in such a clear manner not observed or predicted before-in line with the widely accepted grain boundary space charge model. It is concluded that an accumulation of Ce 3+ in the space charge zone weakens the oxygen vacancy depletion and therefore increases the grain boundary conductivity. The results are of high relevance for understanding and optimising the properties of GDC in anodes and electrolytes for solid oxide fuel cells, and potential new uses such as electrostrictive and memristive devices, for which oxygen partial pressure dependent ionic conductivity is an important new aspect.

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Section: Separation Of Ionic and Electronic Conductivitysupporting

confidence: 80%

Section: Separation Of Ionic and Electronic Conductivitysupporting

confidence: 78%

Section: Separation Of Ionic and Electronic Conductivitymentioning

confidence: 99%

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Low oxygen partial pressure increases grain boundary ion conductivity in Gd-doped ceria thin films

Nenning

Opitz

2019

J. Phys. Energy

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“…All the activation energies of RHF and RLF are around 1.50-1.60 eV. From an electrochemical point of view, as claimed by Maier et al [31] and Fleig et al [32], the change of the oxygen content in the electrode bulk results in a capacitive process; in the literature, it has been referred to as "chemical" capacitance (Cchem) [31] with values in a range from 10 −3 to 10 F.cm −2 [33], and should reflect the bulk defect chemical change inside the electrode material [32]. In our results, CLF is associated to this Cchem ( Fig.…”

Section: Influence Of the Electrolyte/electrode Interfacementioning

confidence: 55%

Influence of the electrode/electrolyte interface structure on the performance of Pr 0.8 Sr 0.2 Fe 0.7 Ni 0.3 O 3-δ as Solid Oxide Fuel Cell cathode

Giuliano

Nicollet

Fourcade

et al. 2017

Electrochimica Acta

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The effect of gadolinium-doped ceria (GDC) interlayer on the Pr0.8Sr0.2Fe0.7Ni0.3O3-δ (PSFN8273) cathode performance and stability in solid oxide fuel cell (SOFC) operating conditions is investigated. Two different symmetrical half-cells, with dense GDC electrolyte pellet (GDC/PSFN cell) and with GDC interlayer deposited on yttria stabilized zirconia pellet (YSZ) (YSZ/GDC/PSFN cell), are prepared and characterized by electrochemical impedance spectroscopy (EIS) as a function of temperature. The fitting of the data is carried out using an adapted Equivalent Circuit (EC). The polarization resistance (Rp) is higher for the YSZ/GDC/PSFN cell compared to GDC/PSFN cell. This increase is assigned to the interface microstructure. Then, the electrochemical properties of the half-cell with GDC interlayer are measured in threeelectrode configuration under dc cathodic overpotential. In addition, the long-term stability is evaluated through an ageing test applying a current density of −123 mA.cm −2 for 1000 hours at 700 °C under air. PSFN8273 appears to be stable as cathode with a decrease in overpotential of about 6% in the first 200 hours and a subsequently stabilization. These results mean that even if the GDC interlayer affect the cathode performance (in terms of Rp) it did not influence its stability, making PSFN8273 a suitable material as cathode for SOFC application.

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“…Lastly, when fitting the data with an equivalent circuit (depicted in the inset of Figure 10), the capacitance of the impedance arc (C chem ) can yield valuable information about the concentrations of point defects in the bulk. For acceptor doped ferrite perovskites, which have a relatively large amount of oxygen vacancies in reducing conditions, and relatively few reduced (from 3+ to 2+) Fe or Co ions, the amount of reduced ions can be calculated by Equation (2) [30,40].…”

Section: Electrochemical Characterizationmentioning

confidence: 99%

Novel Sample-Stage for Combined Near Ambient Pressure X-ray Photoelectron Spectroscopy, Catalytic Characterization and Electrochemical Impedance Spectroscopy

et al. 2020

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For an in-depth characterization of catalytic materials and their properties, spectroscopic in-situ (operando) investigations are indispensable. With the rapid development of advanced commercial spectroscopic equipment, it is possible to combine complementary methods in a single system. This allows for simultaneously gaining insights into surface and bulk properties of functional oxides, such as defect chemistry, catalytic characteristics, electronic structure, etc., enabling a direct correlation of structure and reactivity of catalyst materials, thus facilitating effective catalyst development. Here, we present a novel sample-stage, which was specifically developed to pave the way to a lab–based combination of near ambient pressure X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy with simultaneous catalytic operando measurements. This setup is designed to probe different (model) systems under conditions close to real heterogeneous catalysis, with a focus on solid oxide electrochemical cells. In a proof of concept experiment using an electrochemical model cell with the doped perovskite Nd0.6Ca0.4Fe0.9Co0.1O3-δ as working electrode, the precise control of the surface chemistry that is possible with this setup is demonstrated. The exsolution behavior of the material was studied, showing that at a lower temperature (500 °C) with lower reducing potential of the gas phase, only cobalt was exsolved, forming metallic particles on the surface of the perovskite-type oxide. Only when the temperature was increased to 600 °C and a cathodic potential was applied (−250 mV) Fe also started to be released from the perovskite lattice.

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The Chemical Capacitance as a Fingerprint of Defect Chemistry in Mixed Conducting Oxides

Cited by 8 publications

References 25 publications

Low oxygen partial pressure increases grain boundary ion conductivity in Gd-doped ceria thin films

Low oxygen partial pressure increases grain boundary ion conductivity in Gd-doped ceria thin films

Influence of the electrode/electrolyte interface structure on the performance of Pr 0.8 Sr 0.2 Fe 0.7 Ni 0.3 O 3-δ as Solid Oxide Fuel Cell cathode

Novel Sample-Stage for Combined Near Ambient Pressure X-ray Photoelectron Spectroscopy, Catalytic Characterization and Electrochemical Impedance Spectroscopy

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