Variation of compression of seals in PEM fuel cells

Abstract

Seals or gaskets under compressive stress are used in PEM fuel cells (PEMFC) or stacks to prevent leaking of the liquid and gas inside the cell. The fuel cells are normally assembled with bolts or a combination of bolts and springs. As the seal is typically made of polymers, the level of the compressive stress on the seal during long term operation of the fuel cell depends on the stress relaxation property and any potential chemical degradation of the seal materials. In addition, the amount of compression applied to the seal may vary due to temperature changes during the fuel cell operation which causes thermal expansion and contraction of all components in the cell. To understand the sealing force existed in a fuel cell during operation, all these factors must be fully understood. In this study, the compression of the seal in a PEMFC was investigated experimentally. Specifically the compressive amount was measured in-situ, i.e. immediately after the assembly and during the normal operation of the PEMFC. The objective of this study is to gain an understanding of the variation of compressive strain applied to the seal as the temperature of the PEMFC changes and cycles. This information can then be used to estimate the sealing force in the cell and consequently the life prediction of the seal. Both the temperature and pressure are monitored during the tests. An interesting observation is that both the gap spacing and the outside dimensions jumped initially and did not follow the cell temperature's later rise to a maximum of 80oC. It's effect by the first gas inlet pressure.