A Study On The Graphite/Polymer Composite Bipolar Plates In PEMFC

Polymer electrolyte membrane fuel cell (PEMFC) is recognized as a new alternative to the present power sources because of its high efficiency, low emission, high energy and power density. Bipolar plate is an important part in FC, which distributes fuel and oxidant for FC and provides electronic connection between single cells. Its cost accountes for about 40% of a FC stack, while the high cost of FC is a key obstacle to its wide application. Therefore, searching materials and manufacturing methods for high performance and low cost bipolar plate has been very important. With the above background, new materials and manufacturing methods for bipolar plates are explored in this study.Graphite/polymer composite plate was manufactured using compression molding method. Compared with injection moulding commonly used, our method is more competitive for much lower equipment cost and high graphite content allowed in the plate, which then leads to lower cost of the plate and higher plate conductivity.Low-cost phenolic resin (PF) and polypropylene (PP) were chosen to compound with natural graphite. The composite plate was manufactured using the compression moulding. The variation of electrical properties, gas tightness, mechanical properties and corrosion resistance with compression technological conditions, polymer content and rheological behavior of melt polymer was also studied. The composite plate with PP content 20wt% or PF content 10wt% can meet the demand for the bipolar plate materials.High temperature PEMFC is the new developing direction. Silicone resin was selected to mix with natural graphite for its excellent thermal stability. The compression moulding technical conditions was established. TGA results show that the NG/silicone resin composite has excellent thermal stability. Its application temperature is higher than currently used composite bipolar plate. When the silicone resin content is 10wt%, the composite plate can meet the demand for the bipolar plate materials.Contact resistance mainly accountes for the ohmic polarization. The results show that the contact resistance is greatly affected by the polymer content and the hydrophobic degree of carbon paper. It is also found that it is sensitive to the polymer content because of polymer enrichment on the surface of plate. And the compression moulding technical conditions have little effects on the contact resistance.A new idea of polymer gradient composite plate was proposed. Gradient composite plates were prepared based on compression moulding. The results show the gradient composite plate can greatly decrease the contact resistance with little increase of bulk resistance. The gas-tightness and mechanical properties of high polymer content composite plate are also maintained. The overall properties of the gradient composite plate are improved compared to the non-gradient composite plate.