Spatial distribution of carbon accumulation on solid oxide fuel cells operating under methane
Neuburger, Daniel Miller.
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With the looming threat of climate change, new technologies that can reduce the use of fossil fuels are desirable. One such technology is the solid oxide fuel cell (SOFC). SOFCs convert chemical energy directly into electrical energy, so they can be much more efficient than traditional sources of electrical power generation. SOFCs utilize an oxide-ion conducting electrolyte to generate electricity by reducing molecular oxygen at the cathode and oxidizing fuel at the anode. High temperatures (<650 °C) are required to catalyze oxide conduction through the electrolyte. High temperatures enable SOFCs to use a variety of fuels, but these same conditions also accelerate unfavorable reactions that can cause anode degradation. Research described in this dissertation examined the effects of carbon accumulation in SOFC anodes on overall device performance, and the spatial variation in anode degradation. Fuel was introduced to the fuel cell using a single fuel inlet. This method of fuel introduction created spatial variance in factors such as fuel concentration, and this variance was expected to affect carbon accumulation on the anode. Carbon accumulation is a major contributor to anode degradation through a variety of mechanisms including mass transport obstruction, anode delamination from the electrolyte, and metal dusting, a process describing anode disintegration induced by carbon growth disrupting the anode's electronically conducting network. The amount of carbon accumulation on the surface of the anode was analyzed in operando using Raman spectroscopy. Spectroscopic results showed that more carbon accumulated on the anode further from the fuel inlet than closer to it. In situ electrochemical measurements coupled with post mortem visual and FEM analysis suggested that severe anode degradation occurred early in an experiment, affecting spectroscopic results. We infer that the highest amount of carbon accumulation occurs close to the fuel inlet causing fast and severe anode degradation, decreasing the amount of carbon that can accumulate in further trials when the majority of the spectroscopic data was collected. These results suggest that spectroscopic results should be analyzed with experimental factors such as anode location and trial sequence specifically in mind.