Development and Characterization of Conductive Materials for PEMFC Bipolar Plates

The aim of this work was to develop and characterize electrically conductive bipolar plates (BPPs) used in proton exchange membrane fuel cells (PEMFCs). These BPPs were made from highly conductive blends of polyethylene terephthalate (PET) and polyvinylidene fluoride (PVDF), as matrix phase. The conductive materials were developed from carefully formulated blends composed of conductive carbon black powder (CB) mixed with pure PET, PVDF, or with PVDF/PET systems. They were first developed by twin screw extrusion (TSE) process then compression molded to give BPP final shape. Focus was made on the effect of crystallization of PVDF and PET polymers on the electrical through-plane resistivity of BPPs. It was observed that lower resistivity was obtained with PVDF/CB blends due to the higher interfacial energy between the PVDF matrix and CB and also the higher density and crystallinity of PVDF, compared to those of PET. For the different systems studied, slow cooling rates helped to attain the lowest values of through-plane resistivity since higher PET crystallinity led to smaller amorphous region in which CB was more concentrated. In addition, BPPs made from (PVDF/PET)/CB blends led to lower through-plane resistivity when the PVDF/PET phase had a co-continuous morphology. This is mainly due to the selective localization of the CB in the PET phase leading to a denser conductive carbon network. The lowest through-plane resistivity was around 0.3 Ohm.cm obtained with a (50/50 PVDF/PET)/CB filled with 30 wt% CB.