SOFCs for mobile applications require short starting times and capability of withstanding several and severe cycles. For such applications metallic cassette type cells with low weight and thermal capacity are beneficial where the active cell part is set in interconnects consisting of two sheets of ferritic steel. These cells are stacked serially to get higher voltage and power. This approach needs interconnect sheets that are electrically insulated from each other to prevent electrical short circuit. The technology discussed here is to use brazed metals, as sealants, and ceramic layers, as electrical insulators, which are vacuum plasma sprayed on the cassette rims. For reliable insulating layers, a variety of deposits were developed, starting from cermet-spinel multilayers with various compositions and constituents, where reactive metals (such as Ti, Zr) were part of the coatings, to pure ceramic layers. The qualities and characteristics of these coatings were investigated which included electric insulation at room temperature and at 800 °C (SOFC operating temperature), wettability of different brazes towards these deposits, phase stability and peeling strength. The single steps of development, characteristics of the insulating layers for SOFCs as well as some challenges that have to be taken into account in the process are described.

High temperature fuel cells of SOFC type as direct converter of chemical into electrical energy show a high potential for reducing considerably the specific energy consumption in different application fields. Of particular interest are advanced light-weight planar cells for electricity supply systems in cars and other mobile systems. Such cells, in one current design, consist mainly of metallic parts, e.g. of ferrite steels. These cells shall operate in the temperature range of 700 to 800 °C where oxidation and diffusion processes can be of detrimental effect on cell performance for long-term operation. Problems arise in particular by diffusion of Cr-species from the inter-connect or the casing into the electrolyte/cathode interface forming insulating phases and the mutual diffusion of substrate and anode material, e.g. iron and chromium from the ferrite into the anode and nickel from the anode into the ferrite which in both cases reduces performance and system lifetime. Protecting intermediate layers, can reduce such effects considerably if they are dense, stable and of high electronic conductivity. Perovskite-type layers (e.g. doped LaCrO 3 ) applied with high-velocity Direct Current-Vacuum Plasma Spraying (DCVPS) promise to solve reliably such problems.

DC plasma spraying with its products has gained a high technical importance. With the availability of technically reliable high-frequency plasma torches whose basic development can be traced back to about 40 years ago, some of the disadvantages of the DC spray method are no longer existing or can be avoided to a great extent. This paper describes the principle, construction, and function of high-frequency plasma torches in which the plasma is generated by induction and metallic electrodes are not required (as is the case with conventional DC plasma torches). Typical examples of HF plasma spray application are discussed. Paper includes a German-language abstract.

Solid oxide fuel cells (SOFC) are expected to gain a high importance as direct converters for transforming chemical into electrical energy. They have the potential of working with considerably higher efficiency and much less environmental problems compared to systems used so far. SOFCs of present technology operate at temperatures in the range of 950 °C. Besides an increase in performance and stability, a main precondition for a technical breakthrough of SOFCs is a drastic reduction of their production costs. Approaches are the use of less-expensive materials, new SOFC designs with thinner components and the improvement of presently applied production routes, or their replacement by other techniques such as thermal spray methods. DC- and RF-VPS show very attractive properties particularly if the cell will be manufactured in one consecutive combined process. The state of SOFC spray design will be described together with results of the process adaptation and the SOFC components development.

The central components for solid oxide fuel cells (SOFC) are the electrodes-electrolyte multilayer arrangement (PEN) and the separating bipolar plates. The PEN (Positive electrode- Electrolyte-Negative electrode) assembly consists of a dense gastight yttria-stabilized zirconia (YSZ) electrolyte and porous electrodes for which usually Ni-YSZ cermet anode and Sr-doped LaMnO 3 cathode layers are used. The various PEN units are connected in a cell stack by bipolar plates which are either metallic or ceramic ones. Furthermore, a protective layer on the metallic bipolar plates consisting of a chromium alloy is required to prevent chromium evaporation leading to a rapid and strong degradation of the SOFC performance. At the DLR Stuttgart both the DC and the RF vacuum plasma spraying technique have been further developed and adapted to meet the requirements for the manufacture of the different SOFC components. The DCVPS process using specially developed Laval-like nozzles is especially appropriate to the production of thin and dense coatings as required for the electrolyte and the protective layers. However, applying special spray parameters and nozzles it is also possible to deposit porous electrode layers. The production of the entire PEN arrangement in one consecutive DC-VPS process is the objective of the actual development. On the other hand, the RF plasma spray technique is suitable for the near net-shape production of bulk components such as the metallic bipolar plate. The development of the deposition processes for the production of SOFC components using DC and RF plasma spray methods and the results obtained concerning PEN fabrication, deposition of protective layers and the near net-shape production of metallic bipolar plates are presented in the paper.