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solid oxide fuel cell (SOFC) with a thin-film yttria-stabilized zirconia (YSZ) electrolyte was developed and tested. This novel SOFC shows a similar multilayer set-up as other current anode-supported SOFCs and is composed of a Ni/8YSZ anode, a gas-tight 8YSZ electrolyte layer, a dense Sr-diffusion barrier layer and a LSCF cathode. To increase the power density and lower the SOFC operating temperature, the thickness of the electrolyte layer was reduced from around 10 μm in current cells to 1 μm, using a nanoparticle deposition method. By using the novel 1 μm electrolyte layer, the current density of our SOFC progressed to 2.7, 2.1 and 1.6 A/cm at operation temperatures of 800, 700 and 650°C, respectively, and out-performs all similar cells reported to date in the literature. An important consideration is also that cost-effective dip-coating and spin-coating methods are applied for the fabrication of the thin-film electrolyte. Processing of 1 μm layers on the very porous anode substrate material was initially experienced as very difficult and therefore 8YSZ nanoparticle coatings were developed and optimized on porous 8YSZ model substrates and transferred afterwards to regular anode substrates. In this paper, the preparation of the novel SOFC is shown and its morphology is illustrated with high resolution SEM pictures. Further, the performance in a standard SOFC test is demonstrated. [ABSTRACT FROM AUTHOR]

High-performance solid oxide fuel cells require a thin and gas-tight electrolyte membrane that must be coated on a porous and relatively rough support. A pretreatment of the delivered submicronmeter electrolyte powder of 8 mol%-yttria-stabilized zirconia (8YSZ) yielded a reduced sintering mismatch between the anode substrate made from NiO/8YSZ and the electrolyte coating. Furthermore, it also enhanced the powder packing inside the green film. Constrained sintering usually leads to inadequate film density and an unfavorable pore deformation and orientation. It was demonstrated that these limitations can be resolved by using a coshrinking substrate in a planar cell design. Relative densities of >97% were achieved, which are higher than those for free-standing layers. Additionally, the camber behavior was investigated in dependence of the temperature program with and without gravity effects, giving an overall suggestion for the cofiring parameters of the electrolyte. [ABSTRACT FROM AUTHOR]

The article presents a research on the behaviour upon re-oxidation to determine the redox stability of anode-supported of solid oxide fuel cells (SOFCs). The study covered the influences of reoxidation parameters such as temperature, time of re-oxidation, air flow rate and substrate thickness for SOFCs. A list of materials is provided, along with the experimental procedure and discussion topics.

Abstract: Nonstoichiometric yittrium-substituted SrTiO3 samples with a nominal composition of Sr x Y0.07TiO3± δ (x =0.87–1.01) and Sr0.895Y0.07Ti x O3 − δ (x =1.00–1.20) were prepared and investigated. Phase impurities were found in samples with too high A-site or B-site deficiency. The electrical properties of the samples sintered in reducting atmosphere at different temperatures were analyzed with a view to their potential use as anode materials for solid oxide fuel cells (SOFCs). The redox properties of selected samples were investigated in detail. Samples with small A-site deficiency were considered to be the best candidates for SOFC anode materials. [Copyright &y& Elsevier]

Abstract: The overall performance of ionic conducting electrolyte layers is a key factor for determining the power density of solid oxide fuel cells (SOFCs). The aim of this work is to investigate high performance SOFC electrolyte layers developed in our lab via a low cost wet-chemical processing method. In this paper, SOFCs with bulk ionic conductivity dominated thin-film electrolyte demonstrate superior electrochemical performances. Conventional materials for SOFCs are applied in this work: Ni–YSZ cermet as the anode, yttria-stabilized zirconia (YSZ) as the electrolyte, gadolinia-doped ceria (CGO) as the Sr-diffusion barrier layer, and LSCF or LSC as the cathode. At 0.7 V and 600 °C, single cells with an active LSCF and LSC cathode area of 4 × 4 cm2 obtain a power density of 0.7 and 1.4 W cm−2, respectively. According to electrochemical impedance spectroscopy (EIS), the ohmic resistance of the single cells is almost one order of magnitude lower than the conventionally fabricated SOFCs. Due to the improved performance of the electrolyte, SOFCs are able to deliver high power output at reduced operating temperature and increased cell voltage. [Copyright &y& Elsevier]

Abstract: The application of a thin film electrolyte layer with a thickness in the micrometer range could greatly improve current solid oxide fuel cells (SOFCs) in terms of operating temperature and power output. Since the achievable minimal layer thickness with conventional powder coating methods is limited to ∼5μm, a variety of thin film methods have been studied, but results on regular large-scale anode substrates are still lacking in the literature. In this paper, a wet coating process is presented for fabricating gas-tight 1–2μm thick 8YSZ electrolyte layers on a regular NiO/8YSZ substrate, with a rough surface, a high porosity and a large pore size. These layers were deposited in a similar way as conventional suspension based layers, but the essential difference includes the use of coating liquids (nano-dispersion, sol) with a considerably smaller particle size (85nm, 60nm, 35nm, 6nm). Successful deposition of such layers was accomplished by means of an innovative coating process, which involves the preparation of a hybrid polyvinyl alcohol/8YSZ membrane by dip-coating or spin-coating and subsequently burning out the polymer part at 500°C. Results from He leak tests confirmed that the sintered layers posses a very low number of defects and with values in the range 10−4–10−6 (hPadm3)/(scm2) the gas-tightness of the thin film layers is satisfactory for fuel cell operation. Moreover, preliminary results have also indicated a potential reduction of the sintering temperature from 1400°C to the range 1200–1300°C, using the presented coating process. [Copyright &y& Elsevier]

Abstract: Donor-substituted SrTiO3 ceramic materials were investigated as the anodes of solid oxide fuel cells (SOFCs). Sr0.89Y0.07TiO3−δ (SYT) samples with good electrical conductivity and redox stability were prepared. The thermal and chemical expansions of SYT are both compatible with YSZ electrolyte. Half cells consisting of a flat anode substrate and an electrolyte layer with outer dimensions of 5cm×5cm were fabricated, Ni particles were infiltrated on the pore walls within the ceramic anode framework, and the redox stability of the half cell was tested by He leakage tests after redox cycling. Ti diffusion but no Sr migration was found between the anode and electrolyte layers. Sr0.895Y0.07Ti x O3±δ (x =1.00–1.20)–YSZ composites with a volume ratio 2:1 were prepared to investigate the influences of this interdiffusion between YSZ and SYT materials. The results indicate that the conductivity of SYT decreases because of the Ti diffusion, and a small amount of Ti excess can solve this problem. [Copyright &y& Elsevier]

Abstract: It was shown in part I (Variation of the cathode composition) [A. Mai, V.A.C. Haanappel, S. Uhlenbruck, F. Tietz, D. Stöver, Solid State Ionics 176 (2005), 1341], that an interlayer is needed between yttria-stabilised zirconia (YSZ) electrolytes and (La,Sr)(Co,Fe)O3−δ (LSCF) cathodes in order to prevent undesired chemical reactions between these materials. This interlayer makes it possible to benefit from the superior electrochemical properties of the LSCF perovskites in solid oxide fuel cells (SOFCs). In this study the influence of a Ce0.8Gd0.2O2−δ (CGO) interlayer on the electrochemical performance of LSCF-type SOFCs is investigated in more detail. For screen-printed and sintered interlayers the grain size as well as the sintering temperature affected the electrochemical performance. The use of a fine powder with a mean particle size of d 50 =0.2 μm and sintered at 1250 °C resulted in the best performance. Furthermore, reactive sputtering resulted in dense CGO interlayers at low deposition temperatures, which led to improved properties regarding diffusion inhibition and electrochemical performance. SOFCs with sputtered interlayers gave power densities of up to 0.9 W/cm2 at 700 °C and 0.7 V, with H2 +3% H2O as fuel gas (approx. 10% fuel utilisation). [Copyright &y& Elsevier]

Abstract: The properties and the applicability of iron- and cobalt-containing perovskites were evaluated as cathodes for solid oxide fuel cells (SOFCs) in comparison to state-of-the-art manganite-based perovskites. The materials examined were La1−x−y Sr x Co0.2Fe0.8O3− δ (x =0.2 and 0.4; y =0−0.05), La0.8Sr0.2FeO3− δ , La0.7Ba0.3Co0.2Fe0.8O3− δ and Ce0.05Sr0.95Co0.2Fe0.8O3− δ . The main emphasis was placed on the electrochemical properties of the materials, which were investigated on planar anode-supported SOFCs with 8 mol% yttria-stabilised zirconia (8YSZ) electrolytes. An interlayer of the composition Ce0.8Gd0.2O2− δ was placed between the electrolyte and the cathode to prevent undesired chemical reactions between the materials. The sintering temperatures of the cathodes were adapted for each of the materials to obtain similar microstructures. In comparison to the SOFCs with state-of-the-art manganite-based cathodes, SOFCs with La1− x − y Sr x Co0.2Fe0.8O3− δ cathodes achieved much higher current densities. Small A-site deficiency and high strontium content had a particularly positive effect on cell performance. The measured current densities of cells with these cathodes were as high as 1.76 A/cm2 at 800 °C and 0.7 V, which is about twice the current density of cells with LSM/YSZ cathodes. SOFCs with La0.58Sr0.4Co0.2Fe0.8O3− δ cathodes have been operated for more than 5000 h in endurance tests with a degradation of 1.0–1.5% per 1000 h. [Copyright &y& Elsevier]

The concept of anode-supported planar solid oxide fuel cells (SOFCs) involves different fabrication procedures and several sintering steps. This contribution is an attempt towards minimizing the number of sintering steps. By adopting an improved technique a pre-firing step was eliminated. Cells obtained following this co-firing technique showed relatively higher power density (∼1 A cm-2 at 0.7 V) at an operating temperature of 800 °C compared to the cells prepared by the conventional technique. In the present investigation, cells as large as10 cm×10 cm were prepared and characterized following the new co-firing approach. Detailed microstructural, leak-rate testing (gastightness of the sintered electrolyte film) and electrochemical characterizations were carried out. [Copyright &y& Elsevier]

Abstract: Compression seals based on metal/mica composites were investigated under solid oxide fuel cell (SOFC) operating conditions. Since a compressive force has to be permanently applied in this sealing concept, the mechanical properties of the sealing materials and the SOFC components also became important for maintaining gas tightness. Leakage tests with a sandwich arrangement of mica paper and embossed metallic profiles show leak rates of <1 × 10-4mbarl/mms under an applied normalized compressive load of 2.7N/mm (0.7MPa). Also under thermal cycles between ambient temperature and 800°C this leak rate does not change due to the elastic response of the seal. Compression tests with the seals in contact with SOFC membranes reveal no damage to the membranes. First results of leakage tests with SOFC stacks are presented, which may serve as a reference for future leakage tests of alternative sealing systems. [Copyright &y& Elsevier]

The continuing development of new materials suitable for solid oxide fuel cells operating at about 650–800 °C is of great interest in recent days. The present investigation deals with the development of a perovskite composition–LaNi0.6Fe0.4O3 (LNF)–prepared following two combustion synthesis routes: citrate-gel (LNC) and urea (LNU). The powders were sintered over a wide temperature range (900–1400 °C) and sintering behavior for LNC and LNU was compared. The thermal expansion coefficient (TEC), electrical and microstructural characteristics of LNF was thoroughly investigated. Electrical conductivities were found to be one and a half times higher than that of most commonly used cathode material, La(Sr)MnO3. Moreover, the TEC value of LNF was found to be ≈11.4×10-6 K-1 at 800 °C. The study opens up a possibility of using LNF as a promising cell component for SOFC. [Copyright &y& Elsevier]