Electrochemical Impedance Spectroscopy (EIS) on Pressurized SOFC

Abstract

Former experiments at DLR on planar solid oxide fuel cell short stacks (SOFC) showed a considerable increase of performance at elevated pressure (1). This increase in power is due to numerous and interacting effects at both electrodes. To fully understand this behaviour it is not enough to characterize the short stacks only by current voltage curves. There needs to be further analysis by resistance measurements in order to obtain a better understanding. Electrochemical impedance spectroscopy (EIS) is a promising method to analyze the pressure-induced effects. A deduction from single cell results to stack results is hardly possible since stacks are mainly operated at higher fuel utilizations than single cells. EIS measurements on stacks have already been performed at ambient conditions by (2) but the influence of pressure can not be estimated by using stack results at ambient pressure. Impedance spectroscopy showed that with increasing pressure the individual resistances and therefore the losses in the stack decrease. This paper presents the results of the examination of a SOFC short stack at elevated pressures of up to 8bar with current voltage curves and impedance spectroscopy to examine the influence of pressure on the various resistances and losses within the stack. 1. S. Seidler, M. Henke, J. Kallo, W.G. Bessler, U. Maier and K.A. Friedrich, Pressurized solid oxide fuel cells: Experimental studies and modeling. Journal of Power Sources, 196, p. 7195-7202 (2011). 2. M. Lang, T. Weckesser, C. Auer, P. Jentsch, K.A. Friedrich, C. Westner, SOFC Stacks for Mobile Applications. ECSTransactions, 25 (2), p 97-104 (2009)