Sebastian Molin

Structural and electrical properties of Sr(Ti, Fe)O3-δ materials for SOFC cathodes

Doped strontium titanates are very versatile materials. Iron doped SrTiO3 can be used, for example, as a material for resistive gas sensors and fuel cell electrodes. In this paper, two compositions based on Fe doped SrTiO3 were studied as possible candidates for cathode application in SOFCs. Namely, SrTi0.65Fe0.35O3 and SrTi0.50Fe0.50O3 were examined. A chemical reactivity between electrode and YSZ electrolyte material was investigated, since Sr containing cathode materials in contact with YSZ electrolyte are prone to form insulating phases. Electrical conductivity of bulk samples showed relatively low total conductivities of 0.4 S cm−1 and ~2 S cm−1 for STF35 and STF50 respectively. Suitability for cathode application was studied by Electrochemical Impedance Spectroscopy in a symmetrical electrode configuration. Area specific resistance (ASR) was determined in the temperature range from 600°C to 800°C. At 790°C samples show polarization ASR of approximately 0.1u2009Ωxa0cm2. It can be expected that further reduction of electrode ASR can be obtained by introduction of ceria barrier layer and tailoring of the electrode microstructure.

The comparison of SrTi0.98Nb0.02O3–δ-CeO2 and SrTi0.98Nb0.02O3–δ-YSZ composites for use in SOFC anodes

Composites of Nb-doped strontium titanate mixed with yttria-stabilized zirconia or cerium oxide in 50:50, 70:30 and 85:15 weight ratios were evaluated as possible anode/electrolyte interface materials for solid oxide fuel cells in terms of chemical compatibility, electrical conductivity and mechanical properties. It has been shown that composite samples prepared by typical powder-mixing methods remain single-phase up to 1400°C. The electrical conductivity of these composites, regardless of their composition and fabrication conditions, is lower than the conductivity of pure SrTi0.98Nb0.02O3–δ, but in most cases sufficient for solid oxide fuel cells anode application. The best properties are found for samples reduced at 1400°C for 10xa0h in H2 atmosphere. The observations made by scanning electron microscope suggest that the grains of both phases are well-distributed throughout the whole volume of the investigated samples, and that the composites with CeO2 better adhere to the electrolyte surface. The electrical results confirm that composites with at most 30 wt % of YSZ/CeO2 phase fulfill the anode requirements. However, the fuel cell performance tests indicate that the application of composite with CeO2 results in the lower power density than the application of the composite with YSZ.

The Comparison of SrTi0.98Nb0.02O3-delta - CeO2 and SrTi0.98Nb0.02O3-delta - YSZ Composites for Use in SOFC Anodes

Composites of Nb-doped strontium titanate mixed with yttria-stabilized zirconia or cerium oxide in 50:50, 70:30 and 85:15 weight ratios were evaluated as possible anode/electrolyte interface materials for solid oxide fuel cells in terms of chemical compatibility, electrical conductivity and mechanical properties. It has been shown that composite samples prepared by typical powder-mixing methods remain single-phase up to 1400°C. The electrical conductivity of these composites, regardless of their composition and fabrication conditions, is lower than the conductivity of pure SrTi0.98Nb0.02O3–δ, but in most cases sufficient for solid oxide fuel cells anode application. The best properties are found for samples reduced at 1400°C for 10xa0h in H2 atmosphere. The observations made by scanning electron microscope suggest that the grains of both phases are well-distributed throughout the whole volume of the investigated samples, and that the composites with CeO2 better adhere to the electrolyte surface. The electrical results confirm that composites with at most 30 wt % of YSZ/CeO2 phase fulfill the anode requirements. However, the fuel cell performance tests indicate that the application of composite with CeO2 results in the lower power density than the application of the composite with YSZ.

Conductivity improvement of Ce0.8Gd0.2O1.9 solid electrolyte

Abstract Solid oxide fuel cells based on doped ceria electrolytes offer operating temperatures of ∼600 °C. During recent years much attention was aimed at successful powder preparation with high sinter activity and high conductivity. The properties of ceria electrolyte are very sensitive to impurities introduced during powder and electrolyte fabrication. One of the most successful and commercially available processes for the production of clean powders is based on the addition of several percent metallic cations that will react with impurities and segregate into the triple points of grain boundaries. In this work the results obtained from doping of CGO20 by 2% Ca and prepared by different routes were presented. The way of introducing Ca seemed to play an important role.

Assesment of (Mn,Co)33O4 powders for possible coating material for SOFC/SOEC interconnects

In this work (Mn,Co)3O4 spinel powders with different Mn:Co ratio (1:1 and 1:2) and from different commercial suppliers are evaluated for possible powder for production of interconnect coatings. Sinterability of the powders is evaluated on pressed pellets sintered in oxidizing and in reducing/oxidizing atmospheres. For selected powder, coatings are then prepared by the electrophoretic deposition method on Crofer 22 APU stainless steel coupons. Effects of dispersant/iodine content and deposition voltage and times are evaluated. Thickness as a function of deposition parameters is described. Results show that with appropriate powder it is possible to produce adherent protective coating with a well-controlled thickness.

Perovskites in Solid Oxide Fuel Cells

Perovskite oxides comprise large families among the structures of oxide compounds, and several perovskite-related structures are also known. Because of their diversity in chemical composition, properties and high chemical stability, perovskite oxides are widely used for preparing solid oxide fuel cell (SOFC) components. In this work a few examples of perovskite cathode and anode materials and their necessary modifications were shortly reviewed. In particular, nickel-substituted lanthanum ferrite and iron-substituted strontium titanate as cathode materials as well as niobium-doped strontium titanate, as anode material, are described. Electrodes based on the modified perovskite oxides are very promising SOFC components.

Metal Supported Solid Oxide Fuel Cells - Selected Aspects

Metal supported solid oxide fuel cells are regarded as next generation fuel cells. In this configuration, the use of stainless steel allows lowering the cost of fuel cell fabrication and provides improvement in durability. Recent research progress brings promising results but many issues still must be overcome. In this paper some research insight into the description of properties of porous substrates and fabrication issues of porous metal supported fuel cells are highlighted.

FABRICATION AND CHARACTERIZATION OF ANODE SUPPORTED SOLID OXIDE FUEL CELLS

In this work, slurry spraying is evaluated as a deposition method of thin electrolytes for solid oxide fuel cells. This method is cost effective, uncomplicated and have several advantages in respect to widely used screen printing method. Influence of deposition parameters: slurry concentration, spraying pressure are discussed. Anode supported cells are produced with three different electrolyte thicknesses: 5, 10 and 20 μm showing flexibility of the developed method. Prepared fuel cells achieve satisfactory power densities of almost 1 W cm-2 at 800°C. As evidenced by impedance spectroscopy, performance of cells is determined by the polarization resistance. Cross sections of cells show that all electrolyte layers are of high quality. Slurry spraying is a feasible method for fabrication of functional cells and can be easily scaled for large quantity production.