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 throughplane being achieved at a carbon loading of 65 wt%. The PE-C composite displayed low densities of 1.56 g/cm 3 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.

A review of performance degradation and failure modes for hydrogen-fuelled polymer electrolyte fuel cells

“…While the BPP must have high mechanical strength, low susceptibility to material dissolution, low susceptibility to the release of metal ions, and high corrosion resistance, the bulk electrical conductivity must be high and the interfacial contact resistance (ICR) must be kept low [120]. As an indication, targets set for mechanical strength and electrical conductivity are 44.26 MPa and 100 S/cm, respectively [121]. These attributes have to be achieved with materials and processes that are compatible with low cost and high volume manufacturability concepts.…”

“…[125]. The conductivity of SS316 is, for example, ∼51 S/cm [121]. It has been shown that those grades of SS with a higher content of Cr and Ni, SS904L for example, result in the formation of thinner passive oxide films with low ICR.…”

Hybrid conductive filler/polycarbonate composites with enhanced electrical and thermal conductivities for bipolar plate applications

“…Several thermoplastic materials such as polypropylene (PP) , polyethylene , polycarbonate (PC) , and polyphenylene sulfide have been studied as the matrix for CPCs, including bipolar plate applications . Different carbon‐based fillers such as carbon fiber (CF) , graphite (G) , carbon nanotube (CNT) , and graphene (Gr) have been used as conductive fillers.…”

Conductive materials for polymeric bipolar plates: Electrical, thermal and mechanical properties of polyethylene-carbon black/graphite/magnetite blends

“…1 where the main aims were to decrease bipolar plate mass and cost and to increase mechanical strength whilst providing sufficient electrical and thermal conductivity. The study mixed high-density polyethylene (HDPE) with Monarch 800 carbon black 2 suitable for injection moulding and tested for the aforementioned properties.…”