Manufacture of high performance solid oxide fuels cells (SOFCs) with atmospheric plasma spraying (APS)

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 the substrate a tape-casted FeCr alloy was used. It turned out that all layers can be applied by this technique, however, the APS cathode layer, although applied by suspension plasma spraying led to cells with rather low performance. Much better cell characteristics could be obtained by using screen-printed LSCF cathodes, which do not need any additional thermal treatment. Anode layers with high electrochemical activity were produced by separate injection of NiO and YSZ powders. The manufacturing of gastight electrolyte layers was a key-issue of the present development. As APS ceramic coatings typically contain microcracks and pores their leakage rate is not sufficiently low for SOFC applications. Based on the understanding of the formation of defects during spraying an optimized spraying process was developed which led to highly dense coatings with the appearance of a bulk, sintered ceramic. Open cell voltages above 1 V proofed the low leakage rates of the rather thin (< 50 μm) coatings. With these cells having a screen-printed cathode an output power of 500 mW/cm2 could be achieved at 800 °C. It turned out that the long-term stability of the metal substrate based APS SOFCs was rather poor. The aging of the cells was probably due to interdiffusion of anode and substrate material. Hence, diffusion barrier was applied by APS between substrate and anode. These layers were very effective in reducing the degradation rate. For these cells the output power reached 800 mW/cm2