Oliver Büchler

Thin BaCe0.8Gd0.2O3 − δ Protonic Electrolytes on Porous Ce0.8Gd0.2O1.9 – Ni Substrates

Thin proton-conducting electrolytes with 20 μm thickness and a nominal composition BaCe 0.8 Gd 0.2 O 3-δ were prepared over porous substrates composed of Ce 0.8 Gd 0.2 O 1.9 (CGO)-Ni. The fabrication method includes the simultaneous cofiring and solid-state reaction at 1300°C of three screen-printed layers: mixed conducting anode layer, CGO, and an upper-coated BaCO 3 layer. The resulting asymmetric membranes with 5 × 5 cm 2 geometry are gastight. The solid-state reaction resulted in the formation of (i) an electrolyte with large (∼2-5 μm) grains and high packing density and (ii) anode layer comprising finely grained BaCe 0.8 Gd 0.2 O 3-δ and Ni particles with a thickness around 5 μm. The layer morphology, phase distribution, and lattice composition has been investigated by X-ray diffraction, energy-dispersive spectroscopy scanning electron microscopy, and secondary-ion mass spectrometry. The preparation of the substrate by warm-pressing and tailoring of the porosity and sintering activity are also thoroughly described. DC-electrical conductivity and ac-electrochemical characterization showed that the supported Gd-doped barium cerate electrolyte produced by solid-state reaction has interesting proton-conduction properties for application in solid oxide fuel cells, hydrogen separation, and sensors.

Development of High Power Density Solid Oxide Fuel Cells (SOFCs) for Long-Term Operation

Solid oxide fuel cells (SOFCs) enable environmentally friendly energy to be produced with high efficiency. The market entry of SOFC systems depends on the functionality of the components and on the costs. The SOFC has not yet reached market maturity. This presentation focuses on the possibilities for manufacturing SOFCs with high power outputs and long-term durability by using manufacturing technologies feasible in industry. For the past 15 years, FZ Jülich has been developing large-size so-called anode-supported SOFCs (up to 200 x 200 mm²) with reproducibly high power output (> 2 A/cm² at 800°C). Novel technologies for high-capacity manufacturing such as tape casting and roller coating have been introduced. Additionally, newly developed thin-film techniques have led to power outputs of more than 3 A/cm² at 800°C and more than 1.5 A/cm² below 700°C. These high power densities open up new possibilities for the operation of SOFCs at low temperatures to ensure low degradation and therefore long lifetimes.

Preparation of Thin Functional Layers for Anode Supported SOFC by Roll Coating Process

A new method for the application of functional layers for solid oxide fuel cells was tested. So-called “roll coating” is a promising process for an industrial production of SOFCs, because it allows a high degree of automation. Nickel/yttria-stabilized zirconia (Ni/YSZ), YSZ, YSZ-LSM, and La0.65Sr0.3MnO3-δ (LSM) were used as materials for the anode, anode functional layer, electrolyte, cathode and current collector. The anode substrates were produced by tape casting. The anode and electrolyte were subsequently applied by roll coating on unsintered green tapes as well as presintered substrates. After co-sintering at 1400°C for 5h, half-cells with an electrolyte thickness of 10 µm were obtained. Finally, an LSM/YSZ cathode functional layer and an LSM current collector were deposited by screen printing and co-sintered at 1100°C for 3 h. The cells had current densities of 1.0 A/cm 2 at 800°C and 0.7 V, which is lower than the performance of screen-printed Julich standard cells with the same type of LSM/YSZ cathode. It is expected that the performance of roll-coated cells can be improved by further reducing the thickness of the functional layers. The results show that the anode-supported planar half-cells can be fabricated in a cost-effective way by combining roll coating with subsequent co-firing.