Abstract
In order to evaluate the suitability of graphite composite materials for use as bipolar plates in fuel cells, polypropylene (PP) was melt compounded with expanded graphite as conductive filler to form composites with different filler contents of 10–80 wt %. Electrical resistivity, thermal conductivity, and mechanical properties were measured and evaluated as a function of filler content. The electrical and thermal conductivities increased with filler content. Tensile and flexural strengths decreased with the incorporation of expanded graphite in PP. With higher graphite contents, however, both strength values remained more or less unchanged and were below the values of pure PP. Young’s-modulus and flexural modulus increased almost linearly with increasing filler content. The results of the thermogravimetric analysis confirmed the actual filler content in the composite materials. In order to evaluate the wettability and suitability for adhesive joining of graphite composites, contact angle measurements were conducted and surface tensions of composite surfaces were calculated. The results showed a significant increase in the surface tension of graphite composites with increasing filler content. Furthermore, graphite composites were adhesively joined and the strength of the joints was evaluated in the lap-shear test. Increasing filler content in the substrate material resulted in higher tensile lap-shear strength. Additionally, the influence of surface treatment (plasma and chemical) on surface tension and tensile lap-shear strength was investigated. The surface treatment led to a significant improvement of both properties.
Highlights
Fuel cells seem to be promising energy converters, which are more economically and environmentally friendly than common energy converters, e.g., heat engines
The results showed a significant increase in the surface tension of graphite composites with increasing filler content
Metals have much higher density than polymers, which leads to a high weight of fuel cell stacks, and they are susceptible to corrosion, which can lead to problems in fuel cell operation
Summary
Fuel cells seem to be promising energy converters, which are more economically and environmentally friendly than common energy converters, e.g., heat engines. A fuel cell consists of two bipolar plates, which are firmly joined together providing efficient and reliable power generation. The most commonly used materials for the manufacturing of fuel cells are metals, due to their high electrical and thermal conductivity and better processability than polymer materials. Metals have much higher density than polymers, which leads to a high weight of fuel cell stacks, and they are susceptible to corrosion, which can lead to problems in fuel cell operation. Polymers filled with conductive fillers can be considered as very good alternative to metals. Polymer composites can guarantee sufficient electrical and thermal conductivity and good processability of bipolar plates with low weight of the fuel cell and can successfully replace metals in fuel cell applications in the future
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