UBC Theses and Dissertations
Performance characterization of the high temperature direct alcohol fuel cell Fan, Simon Shun Ming
A fuel cell that promotes the direct use of alcohol fuels such as methanol and ethanol is attractive because these fuels are friendlier than other fuels, such as gasoline, to the end-user and are renewable. Therefore, these fuel cells continue to receive much interest from academia and industry who actively seek alternative energy sources and comprehensive energy supply solutions. However, one of the barriers to the performance improvement of the alcohol fuel cell is the CO-like poisoning intermediates that hinder the alcohol electro-oxidations. This thesis project has validated several different advanced approaches to eliminate the CO-like intermediates from the catalyst surface. A 3-electrode electrochemical glass cell, a half-cell and a single fuel cell have been used to study the effects of these approaches (i.e., introduction of oxidant additives, increased operating temperature, electrochemical pulse techniques, and fuel starvation) on intermediates. A 3-way relationship between the onset potential for electro-oxidation of alcohols, the CO oxidizing potential, and temperatures was determined, and conditions required for a performance benefit were identified. A higher temperature Direct Alcohol Phosphoric Acid Fuel Cell (DAPAFC) using Phosphoric Acid/Silicon Carbide (SiC) as an electrolyte/separator was investigated. Parametric studies were conducted to determine the effects of factors such as higher temperature operation (120-180ºC), etc. A reduced performance gap between PtRu and Pt catalyst at higher temperatures ((>120°C) was shown. Comprehensive studies were also conducted to demonstrate the performance effects of the gas diffusion layer and the micro-porous layer. It was shown that the structure improvement of the phosphoric acid electrode assembly significantly improved the durability and could also improve the cell performance. A higher temperature Direct Alcohol Alkaline Fuel Cell (DAAFC) was also developed to demonstrate the effectiveness of the alcohol electro-oxidation in alkaline medium. An advantage for this system was the use of pure fuel operation which provides at least a 10% improvement in performance compared to dilute fuel operation. In general, the higher temperature direct alcohol vapor fed fuel cells show significantly improved performance using a simple inexpensive separator approach. It appears that this is a new approach which could have a number of advantages.
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