Development of nickel-based carbon tolerant bi-layer anodes for solid oxide fuel cells
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2012
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Abstract
A solid oxide fuel cell (SOFC) is an electrochemical device that continuously coverts the chemical energy of a fuel directly into electricity and heat at high efficiency ( ~ 70 %). Of all fuel cell types, a SOFC can operate with carbon monoxide, synthetic gas and other hydrocarbon fuels. The objective of this thesis is the development of Nickel- (Ni) based anodes for SOFC that can be operated directly with methane without significant deactivation. In the first part of this thesis, the effect of the cell support (i.e. anode- versus electrolyte-supported SOFC) was evaluated. With hydrocarbon fuel (e.g. methane), the type of support plays a significant role in determining the gas-phase composition at the anode functional layer. For the cells that are supported by the anode, Ni in the support catalyzes the cracking and reforming reactions of methane, resulting in a gas-phase composition that is more easily electrochemically oxidized at the anode functional layer. It was shown that methane is not directly converted into electricity, but the electrochemical conversion proceeds through the oxidation of hydrogen, carbon monoxide and carbon. Results show that the surface-chemical reactions play a significant role in determining the electrochemical activity of the anode and, for this reason, the type of support and current collector should be taken into account. Finally, the carbon that forms on a Ni/YSZ is a function of location within the anode. Specifically, the carbon that forms at the anode functional layer is reactive and hydrogenated, while the carbon that forms on the Ni support is stable and causes severe damage to the cell. By replacing the Ni of the anode conduction layer (ACL) with either a metal (Cu) or a perovskite-type material (La03Sr0_7 Ti03), it resulted in much improved stability in methane. The bi-layer anode - Cu/YSZ + Ni/YSZ - was operated at 100 mA cm-2 and 1023 K for nearly 5 days directly with methane. A small quantity of a reactive type of carbon was formed on the Cu/YSZ + Ni/YSZ bi-layer anode, and this carbon did not significantly degrade the cell performance.
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Bibliography: p. 193-206
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Buccheri, M. (2012). Development of nickel-based carbon tolerant bi-layer anodes for solid oxide fuel cells (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/5066