Annual Reviews of Heat Transfer
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Ernest G. Cravalho Fritz Pierre, Jr. ABSTRACT The performance of low temperature fuel cells, such as proton exchange membrane fuel cells (PEMFC) and phosphoric acid fuel cells (PAFC), is largely controlled by the microstructures that make up the catalyst layer of the air/oxygen electrode. In state of the art fuel cells, the microstructures are formed by conventional fabrication techniques like rolling, printing, or spraying the catalyst ink onto a gas backing layer or an electrolyte membrane. Conventional fabrication techniques provide little control over the geometry and distribution of these structures within the catalyst layer. Consequently, catalyst layers are not ideal structures that operate only under activation control. Instead, fuel cell electrodes suffer from low catalyst utilization and contain microstructures that are not optimal for transport of reactants and products. Microfabrication is a proposed method for constructing electrodes that address the limitations posed by existing fabrication techniques. The advantage of microfabrication comes from its ability to provide greater control over the geometry and distribution of the microstructures that make up the catalyst layer. This added control, allows for a more efficient use of the catalyst at the desired operating conditions of the fuel cell. The first half of this chapter provides a brief review of fuel cell technology as well as an introduction to the kinetic and transport equations that are often used to model the physics within the active regions of the cell. In the second half of this chapter one embodiment of the microfabricated electrode concept is described. A simple 1-D model is then presented to demonstrate the possible improvement in fuel cell performance that a microfabricated air electrode can provide. 529-576 pages |
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