Effect of Gas Leakage on the Performance of Planar Solid Oxide Fuel Cells

Abstract

Solid oxide fuel cell (SOFC) is a promising power source with its strong advantage being the use of solid oxide electrolyte. This allows long time operation of the cell without electrolyte depletion. Due to the solid nature of SOFCs, sealing of the cell to the peripheral attachments becomes an issue, especially in planar SOFC type. This defect in gas sealing causes gas-leakage to the outside, as well as, gas-crossover through the peripheral areas of the cell. These leakages lead to a reduction in the open-circuit voltage (OCV) and the overall cell performance. Most previous reports made on gas crossover were only based on H 2 crossover through the thin electrolyte membrane. In this work, the performance of a gas-leaked cell was compared with one with a gas-tight sealing. Both cells were 100 cm 2 planar SOFCs operated at 750 and supplied with H 2 and air gases at the anode and cathode respectively. The cells were supplied by a commercial SOFC producer in South Korea. Electrochemical Impedance Spectroscopy (EIS) and steady-state polarization (SSP) techniques were used in comparing the performance of the cells. An inert gas step addition (ISA) method [1] was also employed in determining quantitatively the partial pressure of water formed at the anode and its resulting internal short current. The ISA was first used to investigate the flow and partial pressure effect on the performance of a molten carbonate fuel cell (MCFC). The method adds nitrogen gas to the anode gas flow and the addition simultaneously increases the reactant gas flow until the added nitrogen arrives at the cell. The nitrogen addition port is placed ca. 5 m ahead of the anode electrode and is supplied through a 1/4-inch stainless tube, thus several seconds are required by the N 2 gas to reach the cell. The SSP behavior showed that the OCV and the polarization voltages recorded were higher in the gas-tight cell than in the gas-leaked cell. The impedance spectra, on the other hand, showed a remarkable decrease in the gas-leaked cell and was attributed to the decrease in the water-induced mass transfer resistance of the cell. Through the ISA method, the partial pressure of water formed at the anode as a result of the gas leak was quantitatively determined and was observed to be significantly higher in the case of the gas-leaked cell. Similarly, the computed internal short current was greater in the case of the gas-leaked cell. [1] C.-G. Lee, B.-S. Kang, H.-K. Seo, H.-C. Lim, J. Electroanal. Chem., 540 , 169–188 (2003).