Performance And Parameters Of Single Chamber Thin-film Solid Oxide Fuel Cell Microstack

Single chamber solid oxide fuel cell (SC-SOFC) is a type of solid oxide fuel cell operating in a uniform mixture of fuel and oxygen, which has several advantages such as the elimination of the sealing process, simple gas management, good shock/mechanical resistances, high power density and so on. In particular, SC-SOFC has received considerable attention for the portable applications due to the sealing-free and high energy density. However, the study on the SC-SOFC stack is unsatisfactory. This paper provides a detailed study on the SC-SOFC stack essential parameters and technology.Cathode is an important factor limiting the performance of intermediate temperature fuel cell. La_0.7Sr_0.3MnO₃ (LSM) based cathodes are studied in single chamber condition using impedance spectroscopy. The performance of SDC-impregnated LSM is better than that of LSM/SDC and LSM/YSZ cathodes. The polarization resistances of composite LSM cathodes are much smaller than the ones of pure LSM cathode in the same condition. All of LSM based cathodes have catalytic active towards the partial oxidation of methane in some sense. The simulation of composite cathode structure shows that the TPB of SDC-impregnated LSM is higher than that of LSM/SDC, it correspond to the result of experiment. SDC-impregnated LSM has the highest overtemperature due to high TPB density and optimized microstructure.Flow rate concerns the mass transfer of the SC-SOFC stack. The results of the linear two-cell stack shows that the performance of the cell in the lower of gas flow increases as flow rate increase. At CH4/O2=1, when both CH4 and O2 flow rates=120sccm, or N2 flow rate=300sccm, the performamces of the two cells are similar with each other. The cell distance of stack influences the performances of the cells, because the electrodes which face the narrow gas path are in competition for mixture gas, so the performance of weak competitor will be influenced by the distance. When the cell distance is 2mm, cathode facing the narrow gas path is influenced obviously. When the cell distance is 3mm, the effect of the distance is weaker than that at 2mm; however the distance effect is increased as the amount of oxygen is decreased. When the cell distance is 4mm, the distance effect is the weakest. The critical distance of the stack with the cell diameter of 10mm is 4mm. Three-cell stack is used to study the heat effect in single chamber fuel cell. The heat from the partial oxidation of methane results in the increase of cell temperature. The heat effect can improve the performance of SC-SOFC; however it also results in the difference of the performance of the single cells in stack. This difference is disadvantageous to the stability of SC-SOFC stack.The results of cell couple shows that the critical distance should increase as the increase of single cell size. A large area of the cell can increase the fuel utilization efficiency. The fuel utilization efficiency is increase with the flow rate decreased, at 60-80sccm, the highest fuel utilization efficiency is 4.46%. However, the stack performance and fuel utilization efficiency have reverse trend as the variety of flow rate. In the cell couple with a YSZ separator, the effect of distance on cathode are eliminated. However, the effect of distance on anode appears in the cell couple. Because the anode reaction not only includes the partial oxidation reaction of methane, but also appeard the full oxidation reaction which is not tolerated in SC-SOFC. It also implies the anode is not selective.The cell-array microstack consistes of five single cells in series, it includes two stages. At 600oC, OCV of the stack is about 4.74V; at 700oC and CH4/O2=1, the maximum power output is about 420mW (total active electrode area is 1.4 cm2). The two stages design can increase the fuel utilization efficiency. The stack module consisted of four anode-supported YSZ-film fuel cells includes two stages and each stage includes two cells. The module generates OCV of 3.6V and power output of 228 mW at 700oC. The average maximum power density of each cell is ²03 mW cm-2. Each stage of stack module can operate normally. An annular microstack array consisting of four fuel cells are fabricated to improve the utilization of heating effect. The maximum power output is 380mW at 700oC, the average maximum power density of each cell is 190mW/cm2. The stack has a good stability. In order to analyze and contrast with the cell of stack, an additional single cell is arranged behind the stack. The fuel utilization efficiency has an increase of 0.25% because the addition of the additional single cell. The five-cell stack including annular microstack and additional single cell generates maximum power output of 390mW.