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Oliveira Silva R.,Jülich Research Center | Malzbender J.,Jülich Research Center | Schulze-Kuppers F.,Jülich Research Center | Schulze-Kuppers F.,Julich Aachen Research Alliance JARA Energy | And 4 more authors.
Journal of the European Ceramic Society | Year: 2017

New oxygen transport membrane materials based on SrTi1-xFexO3-δ, synthesized through solid state reaction and processed via tape casting were characterized with respect to their mechanical behaviour via depth-sensitive indentation and ring-on-ring flexural testing. The elastic moduli obtained by indentation with 1 N load for SrTi1-xFexO3-δ (x = 0.25, 0.35, 0.5) specimens were 147 ± 10 GPa, 123 ± 6 GPa and 158 ± 10 GPa, respectively. Fracture stress was accessed by ring-on-ring testing performed at 100 N/min and the obtained results were 92 ± 9 MPa, 117 ± 15 MPa, and 100 ± 15 MPa for SrTi0.75Fe0.25O3, SrTi0.65Fe0.35O3, and SrTi0.5Fe0.5O3 respectively. Ring-on-ring tests conducted at different loading rates gave access to subcritical crack growth sensitivity and aided the prediction of the materials’ lifetime through stress-time-probability diagrams, where SrTi1-xFexO3-δ (x = 0.25, 0.35, 0.5) may resist for 1 year with a failure probability of 0.1% at least 15 MPa, 22 MPa, and 12 MPa respectively. © 2017 Elsevier Ltd


Udomsilp D.,Christian Doppler Laboratory | Udomsilp D.,Jülich Research Center | Roehrens D.,Christian Doppler Laboratory | Roehrens D.,Jülich Research Center | And 7 more authors.
Materials Letters | Year: 2017

Metal-supported solid oxide fuel cells (MSCs) have gained high attention as they offer a possibility to utilize solid oxide fuel cells (SOFCs) in mobile applications such as auxiliary power units in heavy duty vehicles. Cathode reliability is one of the main issues of MSC development, since cathodes tend to degrade rapidly after being in-situ activated during onset of the stack operation. In the present study, a novel sintering route for La0.58Sr0.4Co0.2Fe0.8O3−δ (LSCF) cathode material was developed. Sintering of the screen printed cathodes was performed before stack operation at 950 °C in reducing Ar atmosphere for 3 h. Under these conditions, severe oxidation of the metallic substrate and the Ni in the anode was avoided reliably. For proof of concept, phase stability and microstructure of the MSC cathodes were characterized. The results reveal that cathode layers sintered in Ar exhibit substantially improved adherence and mechanical stability compared to conventionally processed MSC cathodes, making them ready for systematic investigation of electrochemical performance. © 2016 Elsevier B.V.


Deibert W.,Jülich Research Center | Deibert W.,Julich Aachen Research Alliance JARA Energy | Ivanova M.E.,Jülich Research Center | Ivanova M.E.,Julich Aachen Research Alliance JARA Energy | And 6 more authors.
Journal of Membrane Science | Year: 2015

La5.4WO12-δ (LaWO) is a promising membrane candidate for a variety of H2-related applications due to its appreciable levels of mixed proton-electron conduction and its stability in moist reducing atmospheres at elevated temperatures. Governed by Wagner theory, the H2 permeation performance of a membrane can be enhanced by reducing its thickness. Therefore, the present work deals with preparing LaWO supported membranes with reduced thickness and optimised microstructure. Combining a dense membrane with a porous supporting layer is associated with mismatched sintering rates, which ultimately lead to bending effects. Therefore, the sintering behaviour of both the dense membrane and the porous substrate must be carefully adjusted to each other. For this purpose, single and co-fired membrane and substrate layers were produced by tape casting. Sintering experiments were carried out with an optical dilatometer. The shrinkage and microstructural evolution of the layers were evaluated in terms of the anisotropic shrinkage forces and the membrane rigidness counteracting the substrate shrinkage. The results were used to develop asymmetric LaWO membranes with optimal microstructure. High membrane density was combined with a substrate porosity of ∼30% and minimised bending (40 μm). The LaWO membrane-substrate assembly displayed a He leakage of 10-5 hPa dm3 cm-2 s-1, which is a value that satisfies further practical demands. © 2015 The Authors. Published by Elsevier B.V.


Dellen C.,Jülich Research Center | Dellen C.,Julich Aachen Research Alliance JARA Energy | Gehrke H.-G.,Jülich Research Center | Gehrke H.-G.,Julich Aachen Research Alliance JARA Energy | And 12 more authors.
Journal of Power Sources | Year: 2016

A detailed time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis of the lithium de-/intercalation in thin films of the insertion cathode material lithium cobalt oxide is presented. The LiCoO2 (LCO) thin films are deposited by radio frequency magnetron sputtering at 600 °C, having a (003) preferred orientation after the deposition. The thin electrode films are cycled with liquid electrolyte against lithium metal, showing 80-86% extractable capacities. After disassembling the cells, the depth resolved elemental distribution in the LCO is investigated by ToF-SIMS and glow discharge optical emission spectroscopy. Both techniques show a stepwise lithium distribution in charged state, leading to a lithium depleted layer close to the surface. In combination with the electrochemical results, the qualitative comparison of the different lithium depth profiles yields a reversible lithium extraction in the depleted area below the stability limit for bulk materials of LCO. For bulk LCO, a phase change normally occurs when the lithium concentration in LixCoO2 is lower than x = 0.5. As a possible cause for the inhibition of the phase change, the preferred orientation and thus pinning of the crystal structure of the film by the substrate is proposed. © 2016 Elsevier B.V. All rights reserved.


Tsai C.-L.,Jülich Research Center | Tsai C.-L.,Julich Aachen Research Alliance JARA Energy | Dashjav E.,Jülich Research Center | Dashjav E.,Julich Aachen Research Alliance JARA Energy | And 10 more authors.
Journal of Electroceramics | Year: 2015

Al-substituted Li7La3Zr2O12 (LLZ:Al) was synthesized via conventional solid state reaction. Different dwell times at sintering temperature of 1200 °C led to a varying Li content in LLZ:Al which significantly affected the Li-ion conductivity. Electrochemical impedance spectroscopy and X-ray diffraction were used to characterize the sintered pellets which showed a maximum total ionic conductivity of ~3 × 10−4 S cm−1 at room temperature although the samples were composed of cubic and tetragonal LLZ:Al, with the tetragonal phase as its major phase. Inductively coupled plasma optical emission spectroscopy revealed that the Li content steadily decreased from 7.5 to 6.5 Li per formula unit with increasing sintering time. The highest conductivity was observed from the sample with the lowest Li concentration at 6.5 per formula unit. Scanning electron microscopy images revealed the formation of large grains, about 500 μm in diameter, which additionally could be the reason for achieving high total Li-ion conductivity. Electrochemical tests showed that mixed phase LLZ:Al is stable against metallic Li up to 8 V. © 2015, Springer Science+Business Media New York.


Lobe S.,Jülich Research Center | Lobe S.,Julich Aachen Research Alliance JARA Energy | Dellen C.,Jülich Research Center | Dellen C.,Julich Aachen Research Alliance JARA Energy | And 13 more authors.
Journal of Power Sources | Year: 2016

Thin film batteries based on solid electrolytes having a garnet-structure like Li7La3Zr2O12 (LLZ) are considered as one option for safer batteries with increased power density. In this work we show the deposition of Ta- and Al-substituted LLZ thin films on stainless steel substrates by r.f. magnetron sputtering. The thin films were characterized by XRD, SEM and time-of-flight-secondary ion mass spectrometry (ToF-SIMS) to determine crystal structure, morphology and element distribution. The substrate temperature was identified to be one important parameter for the formation of cubic garnet-structured LLZ thin films. LLZ formation starts at around 650 °C. Single phase cubic thin films were obtained at substrate temperatures of 700 °C and higher. At these temperatures an interlayer is formed. Combination of SEM, ToF-SIMS and XRD indicated that this layer consists of γ-LiAlO2. The combined total ionic conductivity of the γ-LiAlO2 interlayer and the LLZ thin film (perpendicular to the plane) was determined to be 2.0 × 10-9 S cm-1 for the sample deposited at 700 °C. In-plane measurements showed a room temperature conductivity of 1.2 × 10-4 S cm-1 with an activation energy of 0.47 eV for the LLZ thin film. © 2016 Elsevier B.V.


Udomsilp D.,Jülich Research Center | Udomsilp D.,Julich Aachen Research Alliance JARA Energy | Roehrens D.,Jülich Research Center | Roehrens D.,Julich Aachen Research Alliance JARA Energy | And 6 more authors.
ECS Transactions | Year: 2015

DC conductivity experiments were carried out in order to characterize the area specific resistances (ASR) of various multilayer-structures. They represent the contacting interface between cathode and interconnector of state-of-the-art planar anode-supported SOFCs. The investigation focused on quantifying the influence of various chromium evaporation protection layer materials (MnOx, MnCo1.9Fe0.1O4 (MCF)), perovskitic cathode contact layers (LCC10, LCC12, LSCF), operational parameters during stack joining and the effect of pre-annealing of multi-layer samples on the overall ASR of the model system. The results demonstrate the influence of different material combinations as well as the duration of heat treatment during the joining process on the cell resistance, whereas we have not observed an obvious effect of pre-annealing. © The Electrochemical Society.


Berger C.M.,Jülich Research Center | Berger C.M.,Julich Aachen Research Alliance JARA Energy | Hospach A.,Jülich Research Center | Hospach A.,Siemens AG | And 6 more authors.
ECS Transactions | Year: 2015

In a rechargeable oxide battery (ROB) a solid oxide cell (SOC) is combined with an integrated iron oxide base storage for oxygen ions. The cell is operated at 800°C alternately as fuel cell and as electrolyser and the storage material regulates the oxygen partial pressure at the fuel electrode in a range of approximately 10-21-10-18 bar. Repeated charging (electrolysis) and discharging (fuel cell mode) can lead to a degradation of the storage material (particle coarsening, layer formation). In this study the influence of additions of Al2O3, CeO2, Mn3O4, Cr2O3, TiO2, SiO2, and MgO to the Fe2O3 base on these detrimental effects is analysed. Hence, compacted samples are repeatedly oxidised and reduced in a laboratory furnace, where the conditions present in the ROB are simulated. Using XRD and laser microscopy it was found that among the tested oxides only MgO and Al2O3 could mitigate the degradation phenomena to some extent. © The Electrochemical Society.


Tsai C.-L.,Jülich Research Center | Tsai C.-L.,Julich Aachen Research Alliance JARA Energy | Dashjav E.,Jülich Research Center | Dashjav E.,Julich Aachen Research Alliance JARA Energy | And 10 more authors.
Journal of Electroceramics | Year: 2015

Al-substituted Li7La3Zr2O12 (LLZ:Al) was synthesized via conventional solid state reaction. Different dwell times at sintering temperature of 1200 °C led to a varying Li content in LLZ:Al which significantly affected the Li-ion conductivity. Electrochemical impedance spectroscopy and X-ray diffraction were used to characterize the sintered pellets which showed a maximum total ionic conductivity of ~3 × 10−4 S cm−1 at room temperature although the samples were composed of cubic and tetragonal LLZ:Al, with the tetragonal phase as its major phase. Inductively coupled plasma optical emission spectroscopy revealed that the Li content steadily decreased from 7.5 to 6.5 Li per formula unit with increasing sintering time. The highest conductivity was observed from the sample with the lowest Li concentration at 6.5 per formula unit. Scanning electron microscopy images revealed the formation of large grains, about 500 μm in diameter, which additionally could be the reason for achieving high total Li-ion conductivity. Electrochemical tests showed that mixed phase LLZ:Al is stable against metallic Li up to 8 V. © 2015 Springer Science+Business Media New York


Tsai C.-L.,Jülich Research Center | Tsai C.-L.,Julich Aachen Research Alliance JARA Energy | Roddatis V.,University of Gottingen | Chandran C.V.,Leibniz University of Hanover | And 10 more authors.
ACS Applied Materials and Interfaces | Year: 2016

Al-contaminated Ta-substituted Li7La3Zr2O12 (LLZ:Ta), synthesized via solid-state reaction, and Al-free Ta-substituted Li7La3Zr2O12, fabricated by hot-press sintering (HP-LLZ:Ta), have relative densities of 92.7% and 99.0%, respectively. Impedance spectra show the total conductivity of LLZ:Ta to be 0.71 mS cm-1 at 30 °C and that of HP-LLZ:Ta to be 1.18 mS cm-1. The lower total conductivity for LLZ:Ta than HP-LLZ:Ta was attributed to the higher grain boundary resistance and lower relative density of LLZ:Ta, as confirmed by their microstructures. Constant direct current measurements of HP-LLZ:Ta with a current density of 0.5 mA cm-2 suggest that the short circuit formation was neither due to the low relative density of the samples nor the reduction of Li-Al glassy phase at grain boundaries. TEM, EELS, and MAS NMR were used to prove that the short circuit was from Li dendrite formation inside HP-LLZ:Ta, which took place along the grain boundaries. The Li dendrite formation was found to be mostly due to the inhomogeneous contact between LLZ solid electrolyte and Li electrodes. By flatting the surface of the LLZ:Ta pellets and using thin layers of Au buffer to improve the contact between LLZ:Ta and Li electrodes, the interface resistance could be dramatically reduced, which results in short-circuit-free cells when running a current density of 0.5 mA cm-2 through the pellets. Temperature-dependent stepped current density galvanostatic cyclings were also carried out to determine the critical current densities for the short circuit formation. The short circuit that still occurred at higher current density is due to the inhomogeneous dissolution and deposition of metallic Li at the interfaces of Li electrodes and LLZ solid electrolyte when cycling the cell at large current densities. © 2016 American Chemical Society.

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