Detailed Electrochemical Characterisation of Large SOFC Stacks

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Abstract

As solid oxide fuel cell (SOFC) technology is moving closer to a commercial break through, lifetime limiting factors, determination of the limits of safe operation and methods to measure the “state-of-health” of operating cells and stacks are becoming of increasing interest. This requires application of advanced methods for detailed electrochemical characterisation during operation. An operating stack is subject to steep compositional gradients in the gaseous reactant streams, and significant temperature gradients across each cell and across the stack, which makes it a complex system to analyse in detail. Today one is forced to use mathematical modelling to extract information about existing gradients and cell resistances in operating stacks, as mature techniques for local probing are not available. This type of spatially resolved information is essential for model refinement and validation, and helps to further the technological stack development.
Further, more detailed information obtained from operating stacks is essential for developing appropriate process monitoring and control protocols for stack and system developers. An experimental stack with low ohmic resistance from Topsoe Fuel Cell A/S was characterised in detail using electrochemical impedance spectroscopy. An investigation of the optimal geometrical placement of the current probes and voltage probes was carried out in order to minimise measurement errors caused by stray impedances. Unwanted stray impedances are particularly problematic at high frequencies. Stray impedances may be caused by mutual inductance and stray capacitance in the geometrical set-up and do not describe the fuel cell. Three different stack geometries were investigated by electrochemical impedance spectroscopy. Impedance measurements were carried out at a range of ac perturbation amplitudes in order to investigate linearity of the response and the signal-to-noise ratio. Separation of the measured impedance into series and polarisation resistances was possible.
Original languageEnglish
Title of host publicationProceedings of 10th European SOFC Forum
Number of pages10
Publication date2012
Pages56/203-65/203
Publication statusPublished - 2012
Event10th European SOFC Forum - Kultur- und Kongresszentrum Luzern, Luzern, Switzerland
Duration: 26 Jun 201229 Jun 2012

Conference

Conference10th European SOFC Forum
LocationKultur- und Kongresszentrum Luzern
CountrySwitzerland
CityLuzern
Period26/06/201229/06/2012

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