Scholarship & Research
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Item Operando optical and quantitative electrochemical studies of solid oxide fuel cell anode degradation and regeneration(Montana State University - Bozeman, College of Letters & Science, 2022) Pomeroy, Elias Deen; Chairperson, Graduate Committee: Robert Walker; This is a manuscript style paper that includes co-authored chapters.Solid Oxide Fuel Cells (SOFCs) are high temperature (600-1000 °C) devices that can generate electricity with extremely high efficiencies from a wide variety of fuels, including H 2, CH 4, Biogas, and crushed coal. Unfortunately, the SOFC anodes are highly sensitive to gas phase contaminants, including sulfur and carbon containing fuels. Sulfur is ubiquitous in all carbon containing fuels, with concentrations as low as a few parts per million to as high as 1% by mass. At all concentrations sulfur substantially decreases SOFC performance. Conventional models propose that sulfur decreases fuel cell performance by blocking anode active sites, preventing electrochemical reactions, and reducing surface area for heterogeneous catalysis. Carbon containing fuels can rapidly degrade SOFCs due to graphitic carbon formation. Graphite blocks active sites on the anode, causes damage within the anode microstructure, and removes electrocatalytic material via metal dusting. Studies presented in this work used operando optical techniques and quantitative electrochemistry to study degradation and remediation of SOFC anodes. First, since typical electrochemical techniques infer microstructural changes rather than directly measuring surface area, a traditional electrochemical technique, chronocoulometry (CC), was adapted to SOFCs for the first time to measure the electrochemically active area of the anode. This technique showed that active area is temperature dependent, and that sulfur participates in electrochemical reactions, decreasing performance with sluggish oxidation kinetics, rather than simply blocking active sites. Carbon monoxide, on the other hand, decreased the number of active sites, rather than participating in electrochemical reactions, either by blocking active sites or forming carbon. Then, a comparative study was undertaken of different methodologies of carbon remediation, comparing electrochemical oxidation, molecular oxygen, and steam as methods to remove graphite accumulated on SOFC anodes. This study found that with all methods, CO 2 played a key role in removing carbon, that both electrochemical oxidation and steam removed carbon more globally than oxygen, and that imaging the entire cell is critical for understanding the complex, spatially and temporally heterogeneous chemistry occurring across SOFC anodes. Finally, sulfur was employed to passivate SOFC anodes operating on dry methane, significantly reducing carbon formation with only slight decreases in electrochemical performance.Item The reactive form of a C-S bond-cleaving CO 2-fixing flavoenzyme(Montana State University - Bozeman, College of Letters & Science, 2019) Mattice, Jenna Rose; Chairperson, Graduate Committee: Jennifer DuBois; Thesis includes a paper of which Jenna R. Mattice is not the main author.Atmospheric carbon dioxide (CO 2) is used as a carbon source for building biomass in plants and most engineered synthetic microbes. Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), the most abundant enzyme on earth, is used by these organisms to catalyze the first step in CO 2 fixation. 1,2 Microbial processes that also fix carbon dioxide or bicarbonate have more recently been discovered. My research focuses on a reaction catalyzed by 2-KPCC (NADPH:2-ketopropyl-coenzyme M oxidorectuase/ carboxylase), a bacterial enzyme that is part of the flavin and cysteine-disulfide containing oxidoreductase family (DSORs) which are best known for reducing metallic or disulfide substrates. 2-KPCC is unique because it breaks a comparatively strong C-S bond, leading to the generation of a reactive enolacetone intermediate which can directly attack and fix CO 2. 2-KPCC contains a phenylalanine in the place where most other DSOR members have a catalytically essential histidine. This research focuses on studying the unique reactive form of 2-KPCC in presence of an active site phenylalanine.