Vol.5 No.4 2013

Research paper : Evaluating Uncertainty for the Standardization of Single Cell/Stack Power Generation Performance Tests for SOFC (A. Momma et al.)−256−Synthesiology - English edition Vol.5 No.4 (2013) type of support used. Figure 2(a) above represents the test results of an electrolyte-supported cell. This type of cell is characterized by relatively thin electrode films on both sides of the electrolyte, making it less affected by diffusion of reaction species and reaction products in the porous electrodes. In contrast, anode-supported and cathode-supported SOFC cells have a thicker porous medium and are therefore more susceptible to the effects of gas diffusion, raising the possibility that the operating-pressure dependence of the voltage of these types of cells would be substantively different from that of the electrolyte-supported cell mentioned above. Figure 2(b) shows the pressure dependence of the cell voltage measured in an anode-supported SOFC single cell. While the level of dependence observed on the lower pressure region is significantly different from what is observed above, the pressure dependence of the cell voltage at 1 atmospheric pressure is about 0.2 to 0.5 V/Pa, confirming its low impact on uncertainty for these types of cells as well. In contrast, the temperature distribution of SOFC is a very troublesome issue as far as uncertainty is concerned. In theory, the performance of SOFC at a certain temperature can be obtained simply by uniformly maintaining that particular temperature all over the object and conducting measurements. But in practice, taking measurements in such a condition is not always possible. Moreover, based on the actual usage of SOFC, it is arguable that a temperature distribution should be the norm. Therefore, for the purpose of this study we took measurements of the temperature distribution of a SOFC single cell, an example of which is shown in Fig. 3. In general, the temperature distribution varies depending on the setup in the electric furnace used and the method of temperature control Open circuitUf:50 %Uf:70 %Open circuitUf:50 %Uf:70 %Ambient pressure / MPaAmbient pressure / MPaCell Voltage / VCell Voltage / V(b)(a) ℃ H2:340 ml/mineffective area:113 cm2Tcell=700 ℃ H2:300 ml/mineffective area:100 cm2Fig. 2 Pressure dependence of the cell voltage at different fuel utilization rates(a) Electrolyte-supported cell; (b) Anode-supported cellUf:70 %Temperature / ℃Distance from center / mmDistance from center / mmTemperature at 600 ℃Temperature at 750 ℃74074274474674875074074575075576060504030201006050403020100590595600605610600 ℃ open circuit750 ℃ Uf = 70 %750 ℃ open circuitreforming temperature:600 ℃reforming temperature:550 ℃reforming temperature:500 ℃(a)(b)Fig. 3 Examples of temperature distribution measurement of a single cell Measurement by 0.25 sheath thermocouple (Okazaki Super Couple 1000H). (a) Electrolyte-supported cell (Active electrode area: 113 cm2. Fuel: pure hydrogen) (b) Anode-supported cell (Active electrode area: 113 cm2. Fuel: partially-reformed methane)


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