Abstract

There is a rapidly growing interest, both nationally internationally, in the development of fuel cells for a wide range of applications, including as stationary power sources and for use in electrically powered vehicles. This research proposal is directed towards optimizing electrocatalyst performance in solid oxide fuel cells (SOFCs), systems which run at temperatures of ca. 800 °C and involve the electrochemical oxidation of methane and other hydrocarbons at the anode, and the reduction of oxygen from air at the cathode. One of the world leaders in SOFC development, and the only Canadian company in this area, is Global Thermoelectric of Calgary, who are supporting this research work. The key objective of this proposed research project is to establish the structural and compositional characteristics of the SOFC electrodes which are essential to yielding the highest oxygen reduction and hydrocarbon fuel oxidation rates. The explicit long-term goal of our research in this area is the knowledgeable design of better-performing (more catalytic and more stable) low cost electrode materials for the SOFC, so that an environmentally clean, competitive high power and energy density system results.

INTRODUCTION TO FUEL CELLS

Fuel cells are high efficiency energy sources, which cleanly convert chemical energy into electricity. They were developed originally for use in the US aerospace program, where a high power:weight ratio was required and no toxic gases or effluents would be generated. More recently, with the emphasis on a cleaner environment and reduced emissions, a pronounced resurgence of interest in fuel cells is occurring internationally.

There are several types of fuel cells currently under development, categorized partly by the temperature of their operation. In low temperature systems, the proton exchange membrane fuel cell (PEMFC) is the most advanced, operating at ca. 70 °C. Hydrogen gas is oxidized at the anode, producing protons, which cross an electronically insulating, wet, polymeric membrane separator (the PEM), encountering OH- (produced from oxygen reduction at the cathode) and forming water at the cathode, which is siphoned off. In other PEM fuel cells currently under development, methanol is the fuel which is oxidized at the anode, with protons again crossing the membrane and water being formed at the cathode. The PEMFC is the type of fuel cell currently being developed by Ballard Power Systems (BPS) in Vancouver (in partnership with Toyota, Ford, and DaimlerChrysler), currently the world leader in PEMFC development.

Other types of fuel cells operate at higher temperatures. Most notably, the solid oxide fuel cell (SOFC), which runs at temperatures typically of 800 °C or more, is based on an anode and cathode separated by a thin, solid layer of yttrium-stabilized zirconia (YSZ). YSZ is an ionically conducting (at high temperatures), but electronically insulating, ceramic material. At the cathode, O2-, generated by the reduction of oxygen, passes through the YSZ solid electrolyte to the anode, where it combines with the oxidized products generated at the anode. Although the SOFC is not as close to commercialization, it can be operated with hydrogen, methane and higher hydrocarbons as the fuel, an extremely important feature in relation to the Alberta economy.

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