(547c) Design Considerations for Pemfc Cathode Air Filters

Platinum catalyst used in PEM fuel cells experience performance degradation such as reduction in efficiency and life as a result of airborne contaminants. Current research provides evidence for fuel cell performance degradation when operated in an environment with contaminant concentrations similar to urban and military environments. Carbon monoxide and benzene concentrations at city centers have been measured as high as 20 ppm and 50 ppm respectively. Military application of fuel cells may require operation in environments with high concentrations of organic vapors and chemical warfare agents. These contaminants have both short and long term effects on fuel cell performance. The cathode air filter will utilize a novel material developed at Auburn University. Microfibrous materials are a sinter-locked network of micron diameter fibers (1-20 um) used to entrap small particulate (10-300 um). The production of these media involves a high speed specialized wet-lay processes facilitating the entrapment of fine particulates in the microfibrous carrier. Microfibrous materials are suitable for trace contaminant removal applications by virtue of their high contacting efficiency (90% sorbent utilization in 4mm layer) and low pressure drop (0.45? H2O at 27 cm/s face velocity). Microfibrous materials can also be added at the end of a packed bed. This design exhibits both a high capacity and high contacting efficiency which provides a thinner overall bed depth and a lower pressure drop than a packed bed alone. The focus of this study is to create an algorithm for designing a cathode air filter for fuel cell applications that specifies thickness of a composite bed and the ratio of microfibrous layer and packed bed layer. This algorithm must consider contaminate concentration of raw air stream, maximum contaminate concentration entering stack, affinity of contaminate to adsorbant, filter operation time, desired fuel cell power output, compressor limitations, and spatial limitations (thickness and area). Modeling of the filter will be accomplished using an exact breakthrough equation integrated to include two layers, the Ergun equation, and a modified Ergun equation applicable to microfibrous materials. This algorithm will then design a filter which will be tested to confirm pressure drop, the capability of removing trace contaminants, and allowance of the necessary flow rate for fuel cell operation.