Investigation On The Stacks Of Single Chamber Solid Oxide Fuel Cells

Single-chamber solid oxide fuel cell (SC-SOFC) is a novel type fuel cell with only one gas compartment where the oxidant and fuel are not separated. SC-SOFC relies on the selectivity of anode and cathode electrocatalysts to separate the electrochemical oxidation of fuel and reduction of oxidant. Recent years, with rapid development of SC-SOFCs research, the research in SC-SOFC stack is of great interest because of no sealing between anode and cathode.The properties of electrodes under single-chamber conditions and the optimization of electrodes properties were researched. By comparing the impedance spectra of cathode which was impregnated by the solution of Sm0.2Ce0.8(NO3)x with that of the non-impregnated cathode, it shows the ion impregnation technique can great reduce the cathode polarization resistance and will improve the performance of fuel cell. The result tested by four-probe method can eliminate the resistance of Ag wire efficiently; it is more precise than that tested by two-probe method. At different temperatures the tendency of the properties of cathode vary with various CH4/O2 ratio is different. At 750℃, the semicircle at lower frequency probably behaves as the rate-determining process of the electrode. For the anode symmetrical cell, the overheating of cell is not obvious because the anode is very thin. The gas diffusion resistance is also not obvious.The effects of mixed gas flow rate were studied. At a flow rate of 400 sccm, the performance of the stack has reached a higher level, which was used in the following measurements. According to the anode-facing-cathode configuration, the electrodes facing the narrow gas path are easy to be influenced. So the resistance of them will increase and the performance of cell will be influenced too.According to stack, the stack using two single cells was studied firstly. The power outputs of the stack from 1:1 to 1.5:1 are better than that from 1.75 to 2. However, I-V curves show the concentration polarization at higher current densities at CH4/O2 ratios of 1 and 1.25. Moreover, the fuel utilization of the stack at a CH4/O2 ratio of 1.5 is higher than the others. So the optimal methane-to-oxygen ratio is around 1.5 in order to achieve good performance. At 700℃and CH4/O2=1, the power output of stack is 371 mW and the maximum mass specific power is as high as 552 mW/g. According to the stack using three single cells, the optimal methane-to-oxygen ratio of is around 1. The performance of the stack increase obviously with the increase of temperature. At 800℃and CH4/O2=1, the power output of stack is 282 mW and the maximum mass specific power is as high as 282 mW/g. After the primary study for the stack using seven single cells, it shows that the any OCV of stack can be obtained by several series-wound single fuel cells. Also, the design of flow geometry is very important for the stack using several series-wound single fuel cells.The same or similar trends are obtained by comparing the result of the stack, such as the increase of OCV was observed as the CH4/O2 ratio increased. It is advantageous for commercial portable power generation in the future.