Aluminate spinels for use as catalyst enhancement of solid oxide fuel cells
Zachariasen, Marley Sarria
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The 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.