Studies On The Polypyrrole/graphite-gas Diffusion Layer Contact Resistance

Fuel cell (FC) is an electrical device which can directly convert chemical energy into electrical energy. It 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. Bipolar plate can be divided into two kinds: metallic and graphitic. With the advantages of anticorrosion and low density, graphite bipolar plate has become a promising material. However, the graphitic bipolar-gas diffusion layer contact resistance can cause significant ohmic overpotential in a FC stack. Therefore, it is important to develop methods which can effectively decrease the contact resistance. To increase the contact area between composite graphite bipolar plate and gas diffusion layer, we used nano-sized polypyrrole(PPy), a highly conductive material to coat bipolar plates. We first compared the contact resistance of composite graphite plates coated with different PPy. The effect of different polymerization conditions including polymerization time, polymerization temperature, dopant concentration and pyrrole concentration on the contact resistance was investigated. In addition, we compared results of contact resistance at different compaction pressures. SEM was used to observe the morphology of nano-sized PPy. Modification of composite graphite with nano-sized PPy can reduce the contact resistance between the plate and gas diffusion layer remarkably. Besides, the method used proves to be economical and time effective. These will be valuable in improving FC's efficiency and promoting its wide application.