Takashi Yasuo

Degradation phenomena in the cathode of a solid oxide fuel cell with an alloy separator

A study is made of the cathode degradation phenomena in a solid oxide fuel cell that uses an alloy separator. Under the action of the discharge current, chromium diffuses from the alloy to the cathode and moves to the cathode/electrolyte interface. The cathode polarization increases in correlation with the intensity of chromium at the cathode/electrolyte interface. The increase in cathode polarization by the discharge current is due to chromium filling the pores at the cathode/electrolyte interface. This restricts diffusion of oxygen gas and decreases the number of electrode reaction sites. Chromium displacement at the cathode/electrolyte interface appears to be caused by the decrease in oxygen activity at the cathode/electrolyte interface.

Improvement of thermal cycle characteristics of a planar-type solid oxide fuel cell by using ceramic fiber as sealing material

Abstract The objective of this paper is to improve the endurance of solid oxide fuel cell (SOFC) against thermal cycles by reducing the stress caused by the difference in thermal expansion coefficients of alloy separator and electrolyte. The thermal cycle characteristics were improved by using a ceramic fiber for the sealing material. The ceramic fiber seemed to play the role of suppressing electrolyte-cracking by relaxing the stress set up during thermal cycles. The appropriate structure for the sealing material was investigated with 200 mm×150 mm×4 combined-cell single-layer modules. The glass was arranged around the internal manifold to suppress gas leakage, and the ceramic fiber was arranged around the electrolyte to prevent the glass from contacting the electrolyte. It was confirmed that the thermal cycle characteristics can be improved and that good cell performance can be maintained by adopting this gas seal structure.

Surface treatment of alloy separator in a planar-type solid oxide fuel cell

Abstract In the process of improving the performance of planar-type solid oxide fuel cells it is found necessary to apply an appropriate surface treatment to the alloy separator that can diffuse chromium to the cathode. Cathode polarization shows a correlation with the intensity of the chromium. With heat treatment and polishing to remove the surface oxide layer, the amount of chromium diffusing from the alloy is suppressed and cell performance is raised. Accordingly, a 150 mm2 single cell has been operated stably for about 3000 h.

Development status of planar SOFCs at Sanyo

A 2 kW class combined cell stacked module (182 cm{sup 2} X 4X 17) was examined. An output power of 2.47 kW and output power density of 0.20 W/cm{sup 2} were obtained at the current density of 0.3 A/cm{sup 2}. The temperature uniformity is an important factor to develop large scale SOFC modules. Therefore, in this 2 kW class module, one cell was divided into four smaller unit cells to decrease temperature difference across these cells. Moreover, an internal heat-exchanging duct was arranged to spend the surplus heat effectively in the middle of the module. As for the basic research, the followings were investigated to improve thermal cycle characteristics. One was to adopt a silica/alumina-based sealing, material in order to absorb the thermal expansion difference between the electrolyte and the separator. Deterioration was quite small after 12 thermal cycles with a 150 by 150 mm single cell. The other was to use a heat-resisting ferritic alloy as a separator in a 50 by 50 mm single cell in order to decrease the thermal expansion coefficient of the separator. High performance was obtained for 2000 hours at 900{degrees}C in an endurance test and deterioration was quite small after a thermal cycle.