Title

Polymer electrolyte fuel cells: Temperature-related topics

Date of Completion

January 2006

Keywords

Engineering, Chemical

Degree

Ph.D.

Abstract

The climbing cost of gasoline and the increasing need for renewable and environmentally friendly energy resources has turned polymer electrolyte fuel cells (PEFCs) into an attractive technology for power generation especially for applications related to transportation. The operational demand of a polymer electrolyte fuel cell (PEFC) vehicle requires the capability to start the stack under ambient conditions in which the cell temperature is lower than the desired operating temperature. This research provided a comprehensive understanding of the impact of low temperature operation on performance limiting phenomena and components using experimental as well as numerical analysis. The study offered, for the first time, fundamental information regarding the kinetics, proton conductivity in electrolyte/electrode, and mass transport directly from a PEFC operating at temperatures as low as 10°C. ^ Experimental evidences of the presence of thermo-osmotic water transport across a membrane electrode assembly (MEA) in a PEFC have been demonstrated. The presence of a temperature difference across the cell was found to cause a significant amount of water to transport through the MEA in the direction towards the colder side. The thermally driven water flux was found to be relatively large even for a small temperature differences (∼l°C); such flux was found to be comparable to electro-osmotic water transport. A physical model of thermo-osmosis is proposed. A quantitative comparison between the proposed model results and experimental data is provided. ^ High-temperature (∼200°C) PEFCs that use phosphoric acid-doped polybenzimidazole (PBI) membrane as electrolyte constitute a promising alternative for low-temperature (∼80°C) PEFCs by offering solutions to most of the shortcomings associated with the low operating temperature. However, the manufacturing cost of the fuel cell stack is still high, which makes the PEFC technology economically unattractive. Potential areas to reduce the cost of a PEFC include cost reduction of the bipolar plates. In this research, we have developed a porous interdigitated bipolar plate flow field design made from low-cost Toray™ paper. The developed bipolar plates offer significant advantages in reducing total stack cost and weight while providing the functionalities desired in a PEFC.^