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Table 3 Thickness of a 'green' For the SOFC-Concept of Forschungszentrum cathode 240x240 mm" in size Jülich, the sintered composite comprising of a thick anode and a thin-film electrolyte up to 250x250 mm2 had to be coated with the cathode and then used for stack integration. Table 3 documents the constancy of the coating thickness for such large cathodes. In order to verify the homogeneity of the electrochemical activity, 10 electrolyte foils with 19.5 mm diameter were distributed in the coating area and subjected to standard coating. The results of their electrochemical measurements are given in Fig. 3. All specimens are within a certain scatter. For -0.8 A/cm" the standard deviation is 8 mV and the maximum deviation 13 mV. This deviation is also strongly influenced by the inaccuracy of the electrochemical characterization. As a result of the inaccuracy, the microstructure can be regarded as homogeneous over the entire coated area.

summary

In this paper the potential of Wet Powder Spraying for the production of SOFC electrodes was demonstrated. Anodes and cathodes with an excellent initial electrochemical performance and an enhanced long-term stability could be manufactured with high reproducibility. The outstanding advantage of this process is its ability to coat flat or curved substrates of any size so that SOFC technology can be "up-scaled" to any size. Cathode manufacture was demonstrated for sizes up to 240x240 mm", with a maximum deviation in layer thickness of about ±13% and a constant electrochemical activity, so that the microstructure can be assumed as homogeneous.

references

1 E. Syskakis, B. Robens, A. Naoumidis. 'Structural and High Temperature Electrical Properties of LaYSrxMn03 Perovskite Materials'. Journal de Physique IV. Colloque C7. Supplement au Journal de Physique III. "Euromal", Vol. 3. Nov. 1993 1429fT

Average value

Standard deviation

Maximum deviation

69.4 pm

3.9 pm

± 9.3 pm

2 G. Stochniol. E. Syskakis, A. Naoumidis, 'Chemical Compatibility between Strontium-Doped Lanthanum Manganite and Yttria-Stabilized Zirconia'. J. Am. Ceram. Soc. 78 [4] (1995) 929ff

3 A. Ruder, H.P. Buchkremer. H. Jansen. W. Mallener. D. Stöver, "Wet Powder Spraying - a Process for the Production of Coatings', Surface and Coatings Technology 53 (1992) 71 ff

4 M. Fflbi. H.P. Buchkremer. D. Stöver. "Wet Powder Spraying - a new PM-Route for Processing Fiber Reinforced MMC's'. Proceedings of the World Congress PM'94: Paris 6.-9.6.1994.483ff

5 H.P. Buchkremer, U. Diekmann. L.G.J, de Haart. H. Kabs. U. Stimming and D. Stöver, 'Realisation of an Anode Supported Planar SOFC System", this conference

6 J. Divisek. L.G.J, de Haart. P. Holtappels. Th. Lennartz. W. Mallener. U. Stimming and K. Wippermann. "The kinelics of electrochemical reactions on high temperature fuel cell electrodes', J. Power Sources 49 (1994) 257-270

7 R. Wilkenhöner. Th. Haubcr. U. Stimming. W. Malliiner, H.P. Buchkremer, 'Cathode Processing by Wet Powder Spraying". Proceedings of the "2. European SOFC Forum'. Oslo. Norway, 6.-10.5.1996,

—cathode — anode anode : Ni. 40 vol.% 8YS2 cathode : LSM, 40 wt.% 8YSZ

temperature :950°C calhoda-atmosphere: air anode-atmosphere :

25 50 75

absolut value of the overpotential [mV]

0 0

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