Development Of Osaka Gas Type Planar Sofc

M. Iha, A. Shiratori, O. Chikagawa

H. Takagi and Y. Sakabe R&D division Murata Mfg. Co., Ltd. 2288 Oshinohara Yasu, Shiga, 520-23

K. Akagi

Fundamental Reseach Lab. Osaka Gas Co., Ltd. 1, Awata-cho, Chudoji Shimogyou-ku, Kyoto, 600

1 .Introduction

Osaka Gas Co. has been developing a planar type SOFC (OG type SOFC) which has a suitable structure for stacking (1-3). Murata Mfg. Co. has begun to develop the OG type SOFC stack through joint program since 1993. Figure 1 shows OG type cell structure. Because each cell is sustained by cell holders acting air manifold, the load of upper cell is not put on the lower cells. Single cell is composed of 3-layered membrane and LaCrOj separator. 5 single cells are mounted on the cell holder, connected with Ni felt electrically, and bonded by glassy material sealant. We call the 5-ceIl stack a unit. Stacking 13 units, we succeeded 870 W generation in 1993. But the power density was low, 0.11 Wcm'2 because of crack in the electrolyte and gas leakage at some ce!Is(4).

Then we concentrated our efforts on developing the fabricating method of the cell without any crack and the unit without gas leakage. As a result, the crack-free cells could be obtained by examining them before unit fabrication using acoustic micrography technique(5). After the units fabrication, the sealant check before stacking is introduced to prevent gas leakage while generating (6).

In this paper, the authors present the performance of single cell, an unit (5-cell stack) and two units (10-cell stack) of which gas tightness are proved with above acoustic technique and sealant check.

Cell holder(manifold) 3-layered membrane Fuel

Figure 1 Osaka gas type cell structure

2.Experimental 2.1.Singl cell

8mol% Y203 doped Zr02 (YSZ) were employed for electrolyte. The length of electrolyte membrane was 12 cmx 12cm and the thickness was 300 jim. The materials used for anode and cathode are NiO/YSZ and (LaSr)Mn03/YSZ, respectively. These electrodes powder were prepared in the paste form with vehicles, and screen-printed onto the electrolyte membrane, followed by firing respectively. (LaSr)Cr03 was used for separator, which was bonded to the 3-layered membrane by conductive ceramics bond and glassy material sealant.

The I-V characteristics were measured at 1000 °C using H2 gas humidified by water at 30 °C as fuel and air as oxidant gas. The fuel utilization were 40 % and 70 %, and the air utilization was 25% at 36 A (0.3Acm"2).

2.2.Units fabrication and measure

Single cells preparing beforehand were bonded to cell holders acting the air manifold. Each cells is connected electrically by Ni felt. The sealant between single cells and manifold was glassy materials, and bonded over the glass transition temperature. 5-celI stack is showed in figure 2. We call this 5-cell stack a unit. After the unit fabrication, gas leakage characteristics of each unit was examined at room temperature by the sealant check technique(6). The crack-free units were then selected.

Figure 2 OG type 5-cell stack ( a unit)

The performance of crack-free units was measured at 1000 °C using H2 gas humidified by water at 30 °C as fuel and air as oxidant gas. The fuel utilization was 20 %, and the thermal cycle characteristics to room temperature was studied.

10-cell stack using crack-free two units was measured at 950 °C. Fuel utilization was 40% using fuel mentioned above.

3.Results 3.1 .Single cell

The I-V/P characteristics are showed in figure 3. The maximum power was 33 W at 40 % fuel utilization, and the power density was 0.27 Wcm"2. Terminal voltage at j = 0.3 Acm"2 fell down from 0.703 V to 0.657 V when fuel utilization was changed from 40 % to 70%, the difference was nearly equal to calculated Nernst loss. As a result, the ability of the anode was considered enough to be used at 70% fuel utilization.

Polarization in the electrodes at 0.3 Acm"2 was 166 mV. This value was nearly equal to that of polarization which was measured by a current interrupt method using small size cells (3.14 cm of effective electrode area). Consequently, the electrode ability does not decrease if the cell size come large to 120 cm"2.

10 20 30 40 Current, l/A

Fig. 3 I-V/P characteristics of single cell Fig. 4 I-V/P characteristics of 5-celI 3.2.Qne unit (5-cell stack)

Figure 4 shows the results of 5-cell stack (one unit). The maximum power was 146 W (the power density was 0.24 Wcm"2). There was fuel gas leakage at the portion of the fuel inlet to the stack. So, apparent fuel utilization was 20 %, but substantial fuel utilization may be 40 % in consideration of pressure loss between inlet and outlet in the cell.

10 20 30 40 Current, l/A

Fig. 3 I-V/P characteristics of single cell Fig. 4 I-V/P characteristics of 5-celI 3.2.Qne unit (5-cell stack)

Figure 4 shows the results of 5-cell stack (one unit). The maximum power was 146 W (the power density was 0.24 Wcm"2). There was fuel gas leakage at the portion of the fuel inlet to the stack. So, apparent fuel utilization was 20 %, but substantial fuel utilization may be 40 % in consideration of pressure loss between inlet and outlet in the cell.

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