The potential of atmospheric plasma spraying (APS) technology has been investigated for the manufacture of anode, electrolyte and cathode of a solid oxide fuel cell. As substrates tape-casted or commercial available porous plates both made of a FeCr-alloy were used. The functional layers were applied by atmospheric plasma spraying, however, it turned out that screen printed LSCF cathodes performed better than thermally sprayed versions. Anode layers with high electrochemical activity could be produced by APS using separate injections of NiO and YSZ powders. The manufacturing of gas-tight electrolyte layers was a key-issue of the present development. With adequate processing conditions and advanced gun technology it was possible to produce highly dense ceramic coatings with a very low amount of micro-cracks and pores. These electrolytes gave high open cell voltages above 1 V corresponding to the low measured leakage rates (<10-3 mbar*l/s) of the rather thin (<50 µm) coatings. Additional layers have been applied to reduce the interdiffusion especially of species from the metallic substrates into the anode. These layers could significantly reduce degradation of the cells. SOFCs with a power density at 800°C well above 0.7 W/cm² could be produced by the developed technology.

Atmospheric plasma spraying is a cost effective way to produce SOFC components. Doing so, sinter steps can be avoided, which is essential once a metallic support is used for the SOFC. Several properties are required regarding the micro structure of an optimized anode layer. Here gas permeability, electrochemistry, electronic conductivity, coefficient of thermal expansion as well as thermal shock resistance has to be considered. Different types of powder feedstock were investigated to develop an atmospheric plasma sprayed anode layer: (i) NiO or Ni together with YSZ as starting materials, (ii) agglomerates in which NiO and YSZ are already mixed on a sub-micrometer range, (iii) blended NiO/YSZ powder, (iv) separate injection of the individual NiO and YSZ powders, respectively into the plasma by two separate powder lines. The performance of APS anodes are measured in single fuel cell tests. Anode layers sprayed by a separate injection of the individual NiO and YSZ powders into the plasma show the best results.

Atmospheric plasma-spraying (APS) is an attractive process for the production of solid oxide fuel cell layers. However, especially the manufacture of gas-tight electrolyte layers is a major challenge as typical APS ceramic coatings contain microcracks and pores which allow an easy penetration of gases. To overcome this problem a detailed understanding of the formation of microcracks and pores in the coating was developed. These ideas and the conclusions made will be described in detail. Major influencing factors were identified to be substrate temperature, particles temperature and velocity, particle size, and the way the plasma gun is moved. According to the outcome of these considerations spraying experiments have been performed with different yttria stabilized zirconia (YSZ) powders including spray dried and fused and crushed types. Porous, tape-casted metallic plates were used as substrates. Employed measures for the coating optimization lead to a significant reduction of both length and opening of the microcracks. These results were in accordance with the outcome of leakage tests. It was possible to improve the leakage rates by several orders of magnitude and to achieve sufficiently low values for an application as solid oxide fuel cell electrolyte without any subsequent thermal treatment.

In order to reduce the manufacturing costs of SOFC layer systems the atmospheric plasma-spray (APS) process is an attractive technique. Especially the deposition of high performance cathodes, which are essential for a high power density of the SOFC, are of major importance. The cathode functional layer (CFL) has to provide a high amount of triple-phases boundaries to allow the cathodic oxidation reaction. A typical materials mixture used for such a CFL is the perovskite (La0.65,Sr0.3)MnO3 (LSM) and the fully Y 2 O 3 -stabilized zirconia (YSZ). A sufficiently porous layer has to be formed where both components are mixed on a sub-micrometer scale. In addition to the tough challenge concerning the creation of a suitable microstructure of a CFL deposited by an APS process two additional difficulties have to be solved: i.) a decomposition of the perovskite and ii.) a chemical reaction between the LSM and the YSZ during the atmospheric plasma-spray process must be avoided. Suitable spray processing strategies were developed to overcome these problems. Cathode functional layers were produced by an atmospheric plasma-spray process using a multi-cathode Triplex-APS torch. Coatings are characterized by SEM, EDX, XRD and the porosity was determined by digital image analysis. SOFC layer systems with the new developed CFL are tested in single fuel cell tests.