Abstract
Degradation of electrode microstructure is one of the key factors affecting long term performance of Solid Oxide Fuel Cell systems. Evolution of a multiphase system can be described quantitatively by the change in its interfacial energy. In this paper, we discuss free energy of a microstructure to showcase the anisotropy of its evolution during a long-term performance experiment involving an SOFC stack. Ginzburg Landau type functional is used to compute the free energy, using diffuse phase distributions based on Focused Ion Beam Scanning Electron Microscopy images of samples taken from nine different sites within the stack. It is shown that the rate of microstructure evolution differs depending on the position within the stack, similar to phase anisotropy. However, the computed spatial relation does not correlate with the observed distribution of temperature.
Highlights
IntroductionSolid Oxide Fuel Cells (SOFCs) are energy conversion devices, which provide electrical power by converting the chemical energy of fuels such as hydrogen, carbon monoxide, or carbohydrates (if internal or external reforming is used)
Solid Oxide Fuel Cells (SOFCs) are energy conversion devices, which provide electrical power by converting the chemical energy of fuels such as hydrogen, carbon monoxide, or carbohydrates. Despite their numerous advantages—high efficiency, wide variety of available fuels, and low pollution—the wider market application of SOFCs is still hindered by several issues, not the least of which the microstructure degradation affects the reliability of the ceramic porous electrodes
More decay of F is observed in the near-Triple Phase Boundary (TPB) elements, as a result of the Triple Phase boundary deterioration.The decline of FNiPore interfacial energy was most pronounced in the top cell samples, and least pronounced in the bottom cell, suggesting some relation to the temperature distribution
Summary
Solid Oxide Fuel Cells (SOFCs) are energy conversion devices, which provide electrical power by converting the chemical energy of fuels such as hydrogen, carbon monoxide, or carbohydrates (if internal or external reforming is used) Despite their numerous advantages—high efficiency, wide variety of available fuels, and low pollution—the wider market application of SOFCs is still hindered by several issues, not the least of which the microstructure degradation affects the reliability of the ceramic porous electrodes. One way to quantify the evolution of multiphase systems is by analyzing the change of its free energy This is the basis of Phase Field Models. We use Ginzburg-Landau type free energy functional to quantify the degradation observed during a previous long-term performance stack experiment. Relating these results to the framework of PFM modeling will allow for a quantitative description of the observed microstructure evolution
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