Influence Mechanism Of Gas Flow Distribution And Gas Components On Single Chamber Fuel Cell Microstacks

SC-SOFC has received considerable attention for the portable applications due tothe sealing-free and simple gas management. However, current researches focusprimarily on the single cells. Studies of the SC-SOFC stack are also confined to the lowpower output. This paper provides a detailed study on the SC-SOFC stack essentialparameters, including the gas flow field distribution, gas supply method and gascomponent of SC-SOFC, by using the theoretical and experimental methods. ASC-SOFC stack with dual gas supply method is proposed for the first time.As the SC-SOFC worked in the fuel and air mixture, gas flow distribution is animportant factor limiting the cell performance. Numerical simulation and experimentalverification are studied with different gas flow distribution. Results showed that thepartial pressure of oxygen at the cathode side of the cell with gas flow direction facingthe anode was very low, which was caused by the catalytic reaction at the anode. Theperformance of the cells with gas flow direction facing the cathode and parallel to theelectrodes were nearly the same. Numerical simulation of the SC-SOFC stack wasstudied due to the gas competition between the anode and cathode. The cell distance ofan anode-facing-cathode two cell stack influences the performances of the cells.Numerical simulation showed that the partial pressure of oxygen and surface temperatureof the cathode facing the narrow gas path is influenced obviously with smaller spacing.While the oxygen partial pressure of the cathode on the outside is influenced with largerspacing. Numerical simulation of the two cell stack with anode-facing-anodeconfiguration was also studied. Results showed that the heat released by the exothermicreaction of the anodes is concentrated between the cells, which is propitious to achievethe thermally self-sustained of SC-SOFC stack.Numerical simulation showed that the performances of the cells of SC-SOFC microstack with traditional gas supply method are seriously limited by the uneven flowgeometry, where the downstream portion of the stack is exposed to by-products resultingfrom fuel oxidation in the upstream portion of the stack. In view of this problem, a novelgas supply method with multi-point gas vents in the gas tube is proposed in this paper.The traditional gas supply method was also investigated for comparison. Experimentalresults showed that the single cells could obtain a uniform open-circuit voltage andpower output by using the separated gas supply method. For the traditional gas supplymethod, the cell at the outlet position yielded inferior performance compared to that ofthe inlet cell. Finally, the stack operated with the multi-point gas supply methodproduced a higher power output than that operated with the traditional gas supplymethod. In view of the gas competition between the anode and cathode, dual gas supplymethod for anode and cathode by using multi-point gas transmission tubes is proposed.The performance of the cell with dual gas supply method was increased by67%than thatof the conventional SC-SOFC. As a result, several SC-SOFC micro-stacks with two gastubes were studied. The cells with an anode-facing-cathode configuration were connectedin serial by zigzag sliver sheets. The maximum power output are192,230and276mWat CH₄flow rate of50,70and100sccm, respectively. The performance of SC-SOFCmicro-stacks with congener-electrode-facing configuration was better than that of theanode-facing-cathode configuration stack. A two-cell SC-SOFC stack with cellsembedded in plane configuration demonstrated a maximum power output of1.04W atthe flow rate of260sccm CH₄and130sccm O₂. Finally, a scaled-up stack with six cellsin series generated an OCV of6.4V and a maximum power output of8.18W.Consider of carbon deposition and oxidation of Ni metal at the Ni/YSZ anode inCH₄/O₂gas mixture, influencing mechanism of CH₄/O₂gas component over Ni/YSZanode was studied by using gas mass spectrometer. Results showed that completeoxidation of CH₄was the main reaction with the CH₄/O₂ratio of1. Partial oxidationreaction of CH₄was the main reaction with higher CH₄/O₂ratio. Neither carbondeposition occurs nor nickel protoxide be observed at CH₄/O₂ratio of2.5at700°C,which is a reasonable proportion of CH₄and O₂for the Ni/YSZ anode of SC-SOFC.