Theses and Dissertations at Montana State University (MSU)
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Item Aluminate spinels for use as catalyst enhancement of solid oxide fuel cells(Montana State University - Bozeman, College of Engineering, 2019) Zachariasen, Marley Sarria; Chairperson, Graduate Committee: Stephen W. SofieThe growing necessity to find clean, efficient power sources has led to the advancement of technology in various fields of renewable energy. The field of electrochemical energy conversion, better known has Hydrogen Fuel Cell energy, has shown promise in replacing fossil fuels. This technology is fuel flexible, emits no harmful products, and generates power at efficiencies double or triple that of the Carnot combustion cycle widely used in automotive propulsion and large scale combustion power generation. However, the power production is limited by the short life expectancy of the components used to convert the chemical energy of the fuel into an electrical current. Two mechanisms work simultaneously during fuel cell operation to degrade the anodic electrode of the cell. The coarsening of the catalyst metal particles reduces the total active area of the anode while contaminants from the fuel deposit on the anodes remaining active areas, blocking fuel from the locations where the reaction takes place. Recent studies have shown that doping the industry standard fuel cell anode, Ni/YSZ, with a compound known as Aluminum Titanate (ALT) increases the overall resiliency of the cell. When heat-treated, ALT disassociates in to aluminum and titanium oxides which are then able to go into solution with the material components of the anode. These new secondary phases were shown to increase the strength and overall power output of the cell while decreasing the rate at which the catalyst coarsens. The electrochemical enhancements were attributed to the aluminum based secondary phase, known as nickel aluminate, a spinel structured compound which undergoes unusual reduction and catalytic transport kinetics. This work assesses the viability of transferring these enhancement effects to various other cermet anode systems by individually exchanging the ceramic ion conductor and metal electrocatalyst. The electrochemical performance and degradation, as well as mechanical properties, were evaluated for Ni/GDC anodes doped with ALT and alumina. In addition, synthesis and reduction behavior of cobalt and copper aluminate spinels were analyzed for similarities with nickel aluminate.Item Investigation of chemical anchoring of nickel catalyst networks by aluminum titanate additives(Montana State University - Bozeman, College of Engineering, 2011) Law, Cameron Hunter; Chairperson, Graduate Committee: Stephen W. Sofie; Stephen W. Sofie was a co-author of the article, 'Anchoring of infiltrated nickel electro-catalyst by addition of aluminum titanate' in the journal 'Journal of the Electrochemical Society' which is contained within this thesis.; Stephen W. Sofie was a co-author of the article, 'Chemical anchoring of infiltrated nickel metal catalysts for improved stability at high temperature' in the journal 'Journal of the Electrochemical Society' which is contained within this thesis.; Stephen W. Sofie was a co-author of the article, 'Investigation of aluminum titanate for chemical anchoring of infiltrated nickel catalyst in solid oxide fuel cell anode systems' in the journal 'Journal of Power Sources' which is contained within this thesis.; Stephen W. Sofie, Zane Townsend and Max Lifson were co-authors of the article, 'Sintering performance of YSZ ceramics with transitionmetal oxide sintering aid' in the journal 'TMS Supplemental Proceedings' which is contained within this thesis.Electrocatalysts are incorporated into a plethora of technologies and material systems such as catalytic converters, reforming systems, multilayer ceramic capacitors, and solid oxide fuel cells (SOFCs). In SOFCs, nickel is commonly the catalyst of choice due to its chemical stability, high catalytic activity, and lower cost. While traditional SOFCs have a bulk mixture of nickel and yttria stabilized zirconia (YSZ) with at least 33 vol% nickel, solution infiltrated anode SOFCs have several benefits including lower nickel vol% to satisfy percolation, better mechanical strength and CTE matching that can improve redox cycling. Coarsening of the fine nickel metal catalyst with microstructures below 1 micrometer have shown a strong propensity to coarsen from thermal migration at temperatures above 700°C. This migration induced degradation by decreasing particle surface area and nickel network connectivity for electrical conduction. Utilizing metastable oxide additives as a minor dopant in the anode cermet system, novel methods of anchoring the metal phase to porous YSZ ceramic scaffolds have been identified as a means to engineer infiltrated anodes for improved performance. Less than 10 wt% aluminum titanate (ALT-Al 2TiO 5), added to YSZ by mechanical mixing, has shown a stepwise process in the formation of NiAl 2O 4 at 1100°C and ZrTiO 4 at 1205°C for chemically binding the nickel phase to YSZ. XRD, SEM, TEM, and EDS characterization coupled with FIB sample preparation has been utilized to identify the size, morphology, composition and temperature at which the anchoring phases form. Area specific resistance tests of component anodes indicate a decrease in degradation of at least 521%/1000 hr compared to infiltrated specimens without the ALT additive. Electrochemical tests of electrolyte supported cells (ESC) show higher initial performance of cells doped with ALT and at least a 1400%/1000 hr reduction in performance degradation at the same nickel loading content.