Reversible fuel cell performance and degradation

This thesis presents the development of a test stand to characterize the performance of reversible solid oxide fuel cells. The test stand was used in two different studies to determine the behavior of commercially available solid oxide fuel cells under varying steam percentage input and to compare the degradation incurred during fuel cell operation to that during electrolysis operation. The development of this test stand included construction of a water vapor delivery system using steam entrained in a hydrogen flow and a circuit built from high power op-amps to allow biasing of the fuel cell in both fuel cell and electrolysis mode. The test stand allows the steady state characteristics to be evaluated over a wide voltage range through current/voltage sweeps and the small signal behavior to be examined in-situ through the use of electrochemical impedance spectroscopy. These tests, as well as post-operation field emission scanning electron microscope observation, were used to determine that the cells perform comparably in both modes of operation though the cell resistance tends to be higher in electrolysis mode. It was also found that during extended operation these cells degrade significantly to the point of mechanical failure in electrolysis mode and thus may not be suitable for long term electrolysis operation. The equipment developed here can perform similar tests on newly designed reversible fuel cells to determine whether different materials choices or cell construction provide superior reversible performance and durability.

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