The results thus obtained are as follows.
(1) A method to fabricate cells after the surfaces of electrolyte have been toughened was newly proposed, and it was identified that, in those ranges where boundary roughness was rather small, the power generation performance was increased remarkably as the roughness was increased. Because its effects approach gradually to a fixed value as the roughness increases, in this experiment, a surface roughness of approx. 0.5μm is considered optimum in order to maintain the mechanical strength of the cell. On the other hand, it was found from the measurement results obtained by a variation in working temperature that a considerably excellent voltage generation could be obtained even at the temperature of 900℃. When this cell is used, therefore, the working temperature can be lowered, which is effective to increase the reliability of the elemental parts of the power generator.
(2) From the measurements of impedance, the results that the internal resistance was lower for rougher cells could be obtained. In this case, from the SEM photos, it was observed that the boundary between the electrodes and electrolyte is structured complicatedly. Therefore, the major cause of increase in power generation performance is considered to be a substantial increase in contact area, i.e., increase in cell reaction site by the formation of three-dimensional structure in the boundary between the electrolyte and electrodes.
(3) By the surface finishing, the follow-up capability to load change was also improved. The problem with manufacture of this cell caused by increase in area and stacking must be studied further in the future.
(4) Except for the open circuit voltage, the voltage value for natural gas fuel was slightly lower than that for hydrogen. On the power generation itself, however, stable results were obtained. For the effects of a variation in steam partial pressure on the power generation performance including possibility of direct oxidation of methane on the electrode, the investigation must be performed further in the future.
Acknowledgement：
Authors' special thanks are due to the chief, Mr. Tetsuya Senda, and the staff, Mr. Kotani of the Materials and Processing Division of S.R.I. for giving us many useful hints and cooperating with us on the material property and material tests in conducting this work, and the former division director, Mr. Masanori Nomura of S.R.I. for giving us valuable advices on the whole aspect of this work.
References
1) Y.Kawagoe, et, al., Proceedings of General Meeting of Research Institute, the 57th(1991.6), 122-126 and the 59th(1992.6) 1-4. (in Japanese)
2) Y.Kawagoe, et al., Proceedings of the 65th General Meeting of Ship Research Institute, (1995.6), 5-8. (in Japanese)
3) Y.Kawagoe, et, al., The 4th Symposium on Solid Oxide Fuel Cells in Japan Extended Abstracts, (1995.12), 83-86. (in Japanese)
4) Y.Kawagoe, et al., Solid Oxide Fuel Cells V, the Electrochemical Society Inc., (1997.6), 549-556.
5) T. Hirota, M.Dokiya, et al., Solid Oxide Fuel Cells IV, the Electrical Society Inc., (1995.6), 791-800.
6) T. Aida, et al., ibid., 801-809.
