Prospects of graphite - polypropylene/epoxy blend composite for high performance bipolar plate in polymer electrolyte membrane fuel cell

Abstract

Conductive polymer composites (CPCs) are very promising candidate materials for bipolar plates (BPs) in polymer electrolyte membrane fuel cells (PEMFCs). However, a major challenge facing application of CPCs in PEMFC BPs is the difficulty in achieving high electrical conductivity while maintaining adequate mechanical strength. Therefore, a good balance between electrical conductivity and mechanical strength is critical in the development of high-performance CPC BPs. In this study, CPCs consisting of polypropylene (PP)/epoxy blend filled with graphite were investigated for application as BP material, which will combine electrical conductivity and mechanical strength that meet the performance requirements for PEMFC BPs. The CPCs, with 30 – 80 wt% graphite powder, were produced by melt mixing followed by compression molding. The morphology, in-plane electrical conductivity, and flexural strength of the composites were investigated using the scanning electron microscopy, four-point probe method, and three-point bending test, respectively. The results obtained were compared with the technical targets for PEMFC BPs by the United States Department of Energy (DOE). All the PP/epoxy/graphite composites exhibited flexural strength that satisfies the DOE target of > 25 MPa while the composite with 80 wt% graphite content showed the best in-plane electrical conductivity.

Polymer based flow field plates for polymer electrolyte membrane fuel cell and the scope of additive manufacturing: A techno‐economic review

“…The resulting fluorinated ethylene‐propylene/graphite composite FFP, which contained 65 wt% graphite, exhibited a high electrical conductivity of 550 Scm −1 . Despite their performance, defects observed in the graphite powder slightly increased after ball‐milling, which strongly agglomerated in the polymer matrix as a result of direct mixing without using a twin‐screw extruder 100 …”

Comparative study of flexural and physical properties of graphite-filled immiscible polypropylene/epoxy and high-density polyethylene/epoxy blends

“…29 Details of compounding procedure for the composites have been described elsewhere. 23,25 Specimens for characterizations, with generic designation M/EP/xSG, where M = polyolefin (i.e., PP or HDPE), EP = epoxy, and x = weight percent of SG (Table 1), were fabricated by compression molding at 200 o C and 2 tonnes for 10 min. The processes involved in the fabrication of the composite samples are summarized in Figure 1.…”

“…Co-continuity of PP/EP and HDPE/EP blend structure, which can be attributed to the close-to-symmetric composition of the blends, has been reported in previous studies. 23,25 Also, the interface between the two component polymers is distinct in HDPE/EP blend than in PP/EP blend, which indicates a poor interfacial adhesion in HDPE/EP blend compared to PP/EP blend.…”

“…26,27 This can have significant influence on the behavior of their blend systems and cause blends of these polyolefins with the same polymer to exhibit considerably different properties. In our previous studies, 23,25,28 it was found that graphite-filled epoxy (PP/EP) and high-density polyethylene (HDPE/EP) blends (polyolefin: epoxy = 55:45) exhibited higher in-plane and through-plane electrical conductivities than several filled single polymers reported in the literature. Higher electrical performance of PP/EP and HDPE/EP composites was attributed to co-continuous structure of the blends, which favored concentration of filler in the epoxy, leading to more conducting pathways within the composites.…”

“…Potential of filled blends of polyolefins such as polypropylene (PP) and polyethylene (PE) with epoxy or novolac resin to achieve higher electrical conductivities than filled single polymers at the same filler loadings has been reported. 17,[23][24][25] Although, the unit structures in PP and PE are similar, they exhibit different properties such as degree of crystallinity, surface tension, and viscosity. 26,27 This can have significant influence on the behavior of their blend systems and cause blends of these polyolefins with the same polymer to exhibit considerably different properties.…”