Polyethylene-carbon material for polymer electrolyte membrane fuel cell bipolar plates

Abstract

Bipolar plates are the interconnects between cells within a fuel cell stack. They must be highly electrically conductive in order to maximize the voltage across the stack and must be highly thermally conductive to aid cooling of the stack. Traditionally, bipolar plates are made from graphite or stainless steel; both have drawbacks such as low mechanical strength and corrosion problems, respectively. In order to overcome the problems associated with these common materials and to improve on the electrical and thermal conductivity aspects as well as decrease costs and improve manufacturability, a mixture of polyethylene and carbon was investigated. Composites of polyethylene and carbon were mixed using a two-roll mill and injection moulded. Micrographs of the polyethylene-carbon (PE-C) blends show how the microstructure of the polyethylene network and carbon particles provide increased mechanical properties but further addition of carbon leads to the degradation of these properties. Increasing carbon content led to an ever-increasing electrical conductivity. The material was tested for tensile and flexural properties, resulting in a maximum tensile and flexural strength of ∼24 MPa (at 26 wt% carbon in polyethylene) and ∼35 MPa (at 40 wt% carbon in polyethylene), respectively. The samples displayed electrical conductivity, with a maximum of 1.19 S/cm in-plane and 1.05 S/cm through-plane being achieved at a carbon loading of 65 wt%. The PE-C composite displayed low densities of 1.56 g/cm3 and desirable mechanical strength close to the US Department of Energy target level of 44.26 MPa for flexural strength. It was concluded that PE-C composites with different types of carbon and carbon fibres should be tested in order to reach the electrical conductivity target levels of 100 S/cm.