Ruth Bieringer

Gaskets: Important Durability Issues

In the past, the construction and optimization of single fuel cell components was often considered most important and relatively little attention has been paid to the sealing of the cells. Enduring sealing solutions though are a prerequisite for functionality, continuous operation and achievement of high efficiencies. The requirements for the applied sealing materials are multifarious; some of them are common to all types of polymer electrolyte fuel cells (PEFCs), while others depend on the type of fuel cell in question. Besides the usual requirements for sealing materials such as optimized relaxation behavior and a good processability allowing for inexpensive mass production, all suitable sealing materials must have a general fuel cell compatibility. First, the materials must not contain potential catalyst poisons which might migrate and deactivate the catalyst layer of the PEFC; second the materials must not contain any substances which might reduce the performance of the PEFC; and finally the materials must not contain any components which might be eluted and thus have the potential to block pores of the gas-diffusion layer, coat other active surfaces, or interfere in whatever way with the electrochemistry of the cell. The differences among the three main types of polymer-electrolyte-based fuel cells (PEFC, direct methanol fuel cell, high-temperature PEFC) for the sealing material are, on the one hand, the different temperatures at which the cells are operated and on the other hand, the different media against which the materials need to be resistant (water, fuel: H2, O2, reformate, methanol, formic acid, phosphoric acid, coolants). The resulting catalogue of requirements necessitates an in-depth understanding of the material behavior within the cell; therefore fundamental investigations need to emphasize a profound understanding of the deterioration mechanisms (e.g., oxidative and thermal processes, hydrolysis, chemical nature of the neighboring parts, influence of surrounding media, etc.). Many times the existing and commonly employed methods for evaluating the sealing performance of a gasket are found not to be sufficient, so either known methods have to be adapted or completely new methods have to be set up. With the resulting knowledge base optimized sealing solutions can be developed, including new materials and composites as well as innovative gasket designs.