To improve the mechanical strength of sealants for solid oxide fuel cell (SOFC) stacks, several fillers were proposed in this work as reinforcement for a glass-ceramic sealant based on the system BaO-CaO-SiO2. The chosen reinforcement additives were metallic particles including nickel, a nickel-chromium alloy and silver, as well as ceramics such as gadolinium-doped ceria particles and yttrium-stabilized zirconia particles or fibers. The glass-ceramic sealant, with and without reinforcements, was used to join two parts made of stainless steel (Crofer22APU). A torsion test was used to measure the shear strength of the joined samples. The shear strength measurement by torsion gave reliable and reproducible results for all the joined samples. The lowest shear strength was found for the glass-ceramic sealant without any reinforcement. The composite prepared of a combination of glass matrix and 20 wt.-% Ni powder seems to be the best candidate sealant, able to fulfill all the requirements of a SOFC sealant. The samples made with this composite sealant presented the highest shear strength values as prepared and also after aging the sample in air atmosphere for 500 hours at 800 degrees C.

Glass-ceramic composites are used as sealants for high temperature applications, e.g. in planar solid oxide fuel cell (SOFC) stacks. This study focuses on the implementation of more than one sheet of different composite materials within the individual joint between two adjacent plates, producing a multilayer or a, so called, laminate sealant. Each sheet should be tailored for a specific function and, in combination with the other layers, fulfil the overall requirements for the joining of SOFC stacks. In a first attempt to improve the bonding strength, different laminar combinations were screen-printed to yield a triple layer design. Varied filler materials were used, e.g. yttria-stabilised zirconia fibres and particles, and silver particles together with a glass matrix based on the system BaO-CaO-SiO2. The joining partners were steel plates of ferritic chromium-containing steel (Crofer22APU). The multilayer designs tested were based on two material combinations: one with ceramic and one with metal fillers. The three layers were set up by establishing two sheets of identical type on the outer sides, and one reinforcement layer in the centre plane. It was especially with a design with outer layers containing ceramic fillers in which an electrical insulation ability greater than 1 k Omega cm(2) and gas-tightness of 10(-9) mbar ls(-1) were achieved.

The glass–ceramic sealants developed at Forschungszentrum Juelich already meet several of the requirements for their potential use in SOFC stacks. The adequate choice of glass materials and adaptation of the joining and design parameters are essential for stack assembling. Successful long time operation of stacks depends on sufficiently high bond strength between sealant and other components. Currently one of the major problems has been to find a glass–ceramic sealant with appropriate strength withstanding operation conditions. Therefore a reinforcement concept was developed based on addition of silver particles, YSZ fibers or particles as fillers in glass matrix from the system BaO–CaO–SiO2. Additionally different screen‐printed laminar combinations were prepared as double and triple layer design. The double layer design consists in one with ceramic filler and another one with metal filler addition. Triple layer design was set up by establishing two identical films on the outer sides and one different reinforcement layer in the center plane. In order to evaluate the multilayer designs' strength, tensile tests were carried out on circular butt‐joints. The three layers combination showed best performance. Samples could be qualitatively compared in a relative ranking. Changes in the tensile test configuration were proposed to improve future evaluation.

A comparative microstructural study between Ni–Ce0.9Gd0.1O1.95 (Ni–CGO) anodes obtained from NiO–CGO nanocomposite powders prepared by in situ one-step synthesis and by mechanical mixture (two-step synthesis) of NiO and CGO powders is reported. The open porosity and microstructure of sintered and reduced pellets were investigated as a function of the citric acid content used as pore forming agent. Nanosized crystallites for the one-step and two-step routes were around 18nm and 24nm against 16nm and 37nm, for CGO and NiO, respectively. Overall results show that both routes provided suitable microstructures either for anode-support, or for functional anodes for solid oxide fuel cells (SOFCs), with more versatile characteristics in the case of the one-step route. The electrical characterization of selected NiO–CGO samples, carried out between 90 and 260°C by impedance spectroscopy, confirms electrical percolation of both phases in the composites. However, based on combined microstructural and impedance data, it seems clear that the one-step processing route is the best approach to make SOFC anodes with improved performance.

The development of novel high-performance cathodes is essential to reduce Solid Oxide Fuel Cell (SOFCs) operation to low and intermediate temperatures. To that end, the performance of CeO2-based composite cathodes is very attractive. In the present work, LSM (La0.8Sr0.2MPO3), LSCF (La0.5Sr0.5CO0.5Fe0.2O3) and SDC (Ce0.8Sm0.2O19) powders were synthesized by different synthesis methods and used to prepare SOFC composite film cathodes. LSM-SDC and LSCF-SDC composite powders were obtained by milling. Composite films were deposited onto yttria stabilized zirconia (YSZ) electrolytes and characterized by scanning electron microscopy. Preliminary performance tests were carried out using a single cell having a LSCF-SDC cathode. I - V curves indicated that the cell had qualitatively good performance with maximum power density of 19 mW/cm(2) at 800 degrees C. The preparation of LSM and LSCF composites by mixing SDC, synthesized by the method proposed herein is an innovative alternative for the production of high performance ceramic materials for SOFC cathodes.

Infrared spectroscopy is certainly one of the most important analytical techniques available nowadays for scientists. One of the greatest advantages of infrared spectroscopy is that virtually any sample in any physical state can be analyzed. The technique is based on the vibrations of atoms of a molecule. An infrared spectrum is obtained by passing infrared radiation through a sample and determining what fraction of the incident radiation is absorbed at a particular energy. The energy at which any peak in an absorption spectrum appears corresponds to the frequency of a vibration of a part of a sample molecule (Stuart, 2004).

In this study, a chemical route was adopted to obtain strontium-doped lanthanum manganite (LaSrMnO3 or LSM) powders in order to prepare LaSrMnO3-4YSZ (4 mol% Y2O3) composite films by the suspension spin coating method onto 4YSZ and 8YSZ/8YSZ-NiO substrates with or without the application of a zirconia interlayer in the film/substrate interface. The multilayers were sintered at 1150 degrees C for 6 h and the effect of the interlayer on the morphological properties of the films has been investigated by scanning electron microscopy. The results show that in the less roughn substrates the application of the interlayer (similar to 500 nm) not only improved the adhesion in the film/substrate interface, but also avoided new coating failures. All the films were porous, crack-free and with a thickness below 30 mu m, desirable features for application as SOFC cathodes.

The CeO2-based electrolyte low temperature SOFCs require special electrodes with a higher performance and compatibility. The performance of the CeO2-based composite anodes depends on microstructural features such as particle size, tripe phase boundaries (TPB), surface area, and percolation. Some of the primary parameter can be manipulated during the materials synthesis. In this work the compound NiO-Ce0.9Gd0.1O1.95 (NiO-CGO), used as anode in SOFC, was synthesized by two different processes. Both of them are based on the polymeric precursor method. Characterized by simultaneous thermogravimetry-differential thermal analysis, X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and dilatometry. The refinement of the XRD data indicated that the composite sample synthesized by the process called "one step synthesis" produced smaller crystallite size in comparison to the sample attained by the two steps process. Simple preliminary performance tests were done with single cells in which such I-V curves indicated that the cell with one step anode had better performance. "One step synthesis" product, in situ nanocomposite, presented similar fine grained particle sizes for both phases Ni and CGO, which would be beneficial to the electrochemical activity, also indicated by first performance tests. (C) 2010 Elsevier B.V. All rights reserved.

In this work compounds of gadolinium-doped ceria, Ce0.9Gd0.1O1.95 (CGO) and NiO were synthesized by polymeric precursor method. NiO-Ce0.9Gd0.1O0.95 composite was attained by mixture of the powders of the both phases calcinated already. The precursor powders were characterized by simultaneous thermogravimetry-differential thermal analysis and the calcined materials were studied by X-ray diffraction, scanning electronic microscopy, Fourier transform infrared spectroscopy and dilatometry. The refinement of the diffraction data indicated that the powders were crystallized in the wanted phases. All the produced powders had nanometric and sub micrometric features. The produced composite showed good characteristics for the use as anode for SOFC.

In the development of solid oxide fuel cells, the components most in need of improvement are still the sealants. Over the last decade, several types of sealants have been investigated for use under high temperatures, such as compressive, compliant, and rigidly bonded seals. Of these three types, rigidly bonded glass-ceramic seals are the most promising. Their properties can be tailored to match the requirements of SOFC sealants. These include the coefficient of thermal expansion, joining temperature, crystallization behavior, electrical insulation, and gas-tightness. Nevertheless, in the past, the developed sealant compositions failed to demonstrate sufficient mechanical strength. This property is extremely important to avoid catastrophic failure of the rigid seals during SOFC operation. Additionally, there is a lack of standardized methods to characterize the mechanical strength of joined components in the research community. This makes it difficult to rely on the results of the state of art measurements, to reproduce them, and indeed to compare them. In order to improve the mechanical strength of glass-ceramic sealants, this work proposes reinforcing the glass-ceramic sealant with different metallic and ceramic particles. A new concept of laminate sealant, known as a multilayer design, was developed in an attempt to combine the properties of two types of composites in one joint. In addition, three possible methods for mechanical strength characterization were developed. The reinforcement concept is mainly based on adding fillers to the glass matrix named “87”, which is a composition from the system BaO-CaO-SiO2. The chosen fillers were metallic particles including nickel (Ni), nickel-chromium (NiCr) (80-20), copper (Cu), and silver (Ag), as well as ceramic fillers such as gadolinium-doped ceria (CGO) particles and yttrium-stabilized zirconia (YSZ) particles or fibers. These materials were tested in different weight concentrations in the glass matrix to form the composites. This approach showed that adding filler materials (metallic or ceramic) improved the mechanical strength values. The multilayer design was also proven to be effective in combining the properties of two different composite layers in one joint. Electrically insulating samples with sufficient mechanical strength were produced with single layers of reinforced sealant as well as with the multilayer approach. In developing the mechanical strength test, three types of measurements were investigated: tensile test, shear bond test, and torsion test. The first two tests were developed in-house and the third test was performed within a bilateral cooperation with Politecnico di Torino in Italy. The torsion test obtained the most reliable and reproducible results for the joined samples. The values for shear strength obtained by this method were close to what was expected according to theory and computer simulations. The torsion test method was therefore deemed the most appropriate mechanical strength test for this purpose. The analysis performed in this work indicated that the combination glass 87 and 20 wt.-% Ni fulfilled the requirements for SOFC sealants. The samples made with this composite sealant exhibited the highest shear strength values, and they remained gastight and electrically insulating after 500 h at 800 C.