Mapping electrochemically driven gas exchange of mixed conducting SrTi0.7Fe0.3O3−δ and Ce0.8Gd0.2O1.9 thin films by 18O tracer incorporation under reducing atmosphere

Nenning, Andreas; Navickas, Edvinas; Velicsanyi, Peter; Opitz, Alexander Karl; Hutter, Herbert; Fleig, Jürgen

doi:10.1016/j.ssi.2014.10.024

Cited by 5 publications

(7 citation statements)

References 27 publications

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“…The main conductance increase of the non-etched Ni/TiO 2 /YSZ samples is thus caused by the much larger active area for the electrochemical reaction due to in-plane electron conduction in TiO 2 . A very similar situation can be found for ceria based mixed conducting anodes [37,38]. The rate-limiting process is probably a combination of lateral transport of electrons and electrochemical reaction at the surface of mixed conducting TiO 2 .…”

Section: Discussionsupporting

confidence: 66%

Comparison of electrochemical hydrogen oxidation on different metal/ceramic model anodes and mechanistic implications

et al. 2019

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Micro-patterned metal/ceramic model thin film electrodes were used to investigate the hydrogen oxidation mechanism on various metal/ion conductor combinations such as Ni/yttria-stabilized zirconia (YSZ), Pt/YSZ, Ni/scandia-stabilized zirconia, Ni/titania/YSZ. For all electrode types besides those with a continuous titania interlayer a triple phase boundary (TPB) and an area pathway could be separated. Moreover, activation energies as well as hydrogen and water reaction orders were determined for both pathways and compared with previously published data on Ni/YSZ. It was found that when varying the electronically conducting phases on YSZ the activation energy of the TPB path remains virtually the same. However, changing the ion conductor significantly influenced the activation energy, indicating a rate-limiting step on the electrolyte. However, the stark difference in water reaction order of Ni/YSZ and Pt/YSZ electrodes shows that the metal phase is also actively participating in the reaction chain. It is suggested that the electrolyte surface is responsible for the ratelimiting electrochemical redox reaction while the metal interacts with the gas phase molecules and thus supplies the reactants. For samples with a thin mixed conducting titania layer on YSZ, the electrochemical behavior drastically changed, which can be explained by an extension of the reaction zone away from the TPB.

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Section: Discussionsupporting

confidence: 66%

Comparison of electrochemical hydrogen oxidation on different metal/ceramic model anodes and mechanistic implications

et al. 2019

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“…Mapping of 18 O exchange on similar electrodes revealed that the Pt film is not permeable for oxygen and therefore reduces the electrochemically active area of the STF electrode. 26 At the triple phase boundary (TPB), however, the oxygen exchange is catalyzed by the platinum, 42,44 causing the much smaller electrode arc with Pt on top. The contributions of the STF surface and the TPB can be separated by measuring electrodes of all 9 geometries shown in Figure 1e.…”

Section: Resultsmentioning

confidence: 99%

The Electrochemical Properties of Sr(Ti,Fe)O_3-δfor Anodes in Solid Oxide Fuel Cells

Nenning

Volgger

Miller

et al. 2017

J. Electrochem. Soc.

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Reduction-stable mixed ionic and electronic conductors such as Sr(Ti,Fe)O 3-δ (STF) are promising materials for application in anodes of solid oxide fuel cells. The defect chemistry of STF and its properties as solid oxide fuel cell (SOFC) cathode have been studied thoroughly, while mechanistic investigations of its electrochemical properties as SOFC anode material are still scarce. In this study, thin film model electrodes of STF with 30% and 70% Fe content were investigated in H 2 +H 2 O atmosphere by electrochemical impedance spectroscopy. Lithographically patterned thin film Pt current collectors were applied on top or beneath the STF thin films to compensate for the low electronic conductivity under reducing conditions. Oxygen exchange resistances, electronic and ionic conductivities and chemical capacitances were quantified and discussed in a defect chemical model. Increasing Fe content increases the electro-catalytic activity of the STF surface as well as the electronic and ionic conductivity. Current collectors on top also increase the electrochemical activity due to a highly active Pt-atmosphere-STF triple phase boundary. Furthermore, the electrochemical activity depends decisively on the H 2 :H 2 O mixing ratio and the polarization. Acceptor-doped mixed ionic and electronic conductors are a promising class of materials for application in solid oxide fuel cell (SOFC) electrodes and they are widely investigated as SOFC cathodes due to their low polarization resistance.1-3 Some of these materials are chemically stable and mixed conducting also in humidified hydrogen atmosphere, 4 which makes them applicable in SOFC anodes. Several mixed conductors, such as acceptor doped (La,Sr)(Cr,Mn)O 3 , [5][6][7][8] donor-doped SrTiO 3 9,10 and Sr(Ti,Fe)O 3-δ -Ce 0.9 Gd 0.1 O 2-δ (STF-GDC) composites 11 were investigated in form of porous SOFC anodes. Most of these studies revealed moderately low polarization resistances. In STF-GDC composites, for example, the anode polarization resistance was <0.2 cm 2 at 800• C, and the overall performance increased with increasing Fe content. However, the usually ill-defined geometry of porous electrodes makes the analysis of specific materials parameters such as electronic and ionic conductivity or oxygen exchange activity very challenging.Thin film model electrodes have well defined and controllable geometry and comparatively simple pathways of electron and oxygen ion migration. This strongly facilitates identification of reaction pathways and quantification of the oxygen exchange activity of the material's surface. [12][13][14][15][16][17][18] Mechanistic studies using thin film model electrodes have so far been performed mainly in oxidizing atmosphere. Thorough studies of the mechanisms of electrochemical oxygen exchange in reducing atmospheres are still largely missing, not only for STF, but for most reduction stable mixed conductors, except for (Gd or Sm) doped ceria [19][20][21][22][23][24] and a study on (La,Sr)FeO 3-δ. 25 The typically low electronic conductivity of accep...

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“…Therefore, in an attempt to measure diffusion coefficients of sulphur in GDC by means of ToF-SIMS, sulphur incorporation experiments were performed on macroscopic GDC 10 polycrystals over several days of exposure. To increase the rate of surface sulphur incorporation and to suppress possible back reactions with water [ 44 , 45 ], a dry hydrogen atmosphere was chosen. The resulting depth profiles are plotted in Figure 4 .…”

Section: Resultsmentioning

confidence: 99%

The Sulphur Poisoning Behaviour of Gadolinia Doped Ceria Model Systems in Reducing Atmospheres

et al. 2016

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An array of analytical methods including surface area determination by gas adsorption using the Brunauer, Emmett, Teller (BET) method, combustion analysis, XRD, ToF-SIMS, TEM and impedance spectroscopy has been used to investigate the interaction of gadolinia doped ceria (GDC) with hydrogen sulphide containing reducing atmospheres. It is shown that sulphur is incorporated into the GDC bulk and might lead to phase changes. Additionally, high concentrations of silicon are found on the surface of model composite microelectrodes. Based on these data, a model is proposed to explain the multi-facetted electrochemical degradation behaviour encountered during long term electrochemical measurements. While electrochemical bulk properties of GDC stay largely unaffected, the surface polarisation resistance is dramatically changed, due to silicon segregation and reaction with adsorbed sulphur.

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Mapping electrochemically driven gas exchange of mixed conducting SrTi0.7Fe0.3O3−δ and Ce0.8Gd0.2O1.9 thin films by 18O tracer incorporation under reducing atmosphere

Cited by 5 publications

References 27 publications

Comparison of electrochemical hydrogen oxidation on different metal/ceramic model anodes and mechanistic implications

Comparison of electrochemical hydrogen oxidation on different metal/ceramic model anodes and mechanistic implications

The Electrochemical Properties of Sr(Ti,Fe)O_3-δfor Anodes in Solid Oxide Fuel Cells

The Sulphur Poisoning Behaviour of Gadolinia Doped Ceria Model Systems in Reducing Atmospheres

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Mapping electrochemically driven gas exchange of mixed conducting SrTi0.7Fe0.3O3−δ and Ce0.8Gd0.2O1.9 thin films by 18O tracer incorporation under reducing atmosphere

Cited by 5 publications

References 27 publications

Comparison of electrochemical hydrogen oxidation on different metal/ceramic model anodes and mechanistic implications

Comparison of electrochemical hydrogen oxidation on different metal/ceramic model anodes and mechanistic implications

The Electrochemical Properties of Sr(Ti,Fe)O3-δfor Anodes in Solid Oxide Fuel Cells

The Sulphur Poisoning Behaviour of Gadolinia Doped Ceria Model Systems in Reducing Atmospheres

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The Electrochemical Properties of Sr(Ti,Fe)O_3-δfor Anodes in Solid Oxide Fuel Cells