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Current Density, mAJar?

Fig. 6 Oxygen self-diffusion for selected cathode materials

different current densities. Cathode B is such a material with good performance (2.4 il-cm2 at 500°C) however some improvement is still required to achieve values of less than 1 £2-cm2.

The performance of a cell with cathode A is shown in figure 7. The OCV was considerably lower owing to significant porosity when the electrolyte was thinner (200 pm). The thinner electrolyte had a reduced resistance, which raised overall performance. Also shown in the figure is a calculated performance curve for a dense electrolyte with negligible thickness.

Fig. 7 Cell performance with cathode A. Measured OCV lower due to interconnected porosity.

Cathode performance is also being increased by using improved microstructures. Steele[4] has recently been demonstrated that a thin 1-p.m LSCF layer between the electrolyte and a coarser porous thick LSCF electrode exhibited only 0.4 ii-cm2 interface resistance.

Conclusions

Cathode performance is being improved by using better materials and/or microstructures. Fabrication of thin dense electrolytes is also necessary to achieve high cell performances.

Acknowledgements

This work is supported by the OTT-DOE under Contract No.W-31-109-ENG-38. References

[1] M. Sahibzada et.al., Proc. of 2nd.European SOFC Forum, Oslo, Norway, May 1996, p687-696

[2] B.C.H. Steele et al., Proc. of the Fuel Cell Seminar, San Diego, CA, Nov. 1994, p479-482

[3] C. Milliken et al., EPRI/GRI Fuel Cell Workshop, Tempe, AZ, Apr. 2-3,1996

[4] B.C.H. Steele, private communication, July 1996.

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