Since proton exchange membrane fuel cell (PEMFC) not only has the general characteristics of fuel cell (such as high energy conversion, environment friendly, etc.), but also has the characteristics of rapid start-up at room temperature, long life, high specific power and specific energy, etc. It has become one of the research hotspots in the world. Bipolar plate is the key component of PEMFC, which has an important influence on its volume, weight and performance. At present, the research on bipolar plate mainly focuses on the material and flow field design, especially the material design.
The currently widely used bipolar plate has three types of graphite plate, metal plate and composite material plate.
Graphite bipolar plate is divided into porous graphite plate and injection graphite plate. Porous graphite plates are usually prepared from carbon or graphite powder and graphitized resins. Porous graphite plate has the advantages of good chemical stability, high conductivity and good gas resistance in fuel cell environment. But the processing period of the graphitization is long, and the processing difficulty of the flow field makes the manufacturing cost high and the price is high. Graphite powder or carbon powder and resin (phenolic resin epoxy resin etc.) are used in injection molding graphite bipolar plate. Conductive adhesive is formed by graphitization. Injection molding, grouting and other methods, can be directly processed into a flow field, compared with machine processing has the advantages of low cost, short cycle and so on. However, the post-formed graphitization process increases the cost. In addition, that shrinkage of the resin in the graphitization process lead to the deformation of the graphite plate, therefore, strict temperature control is required in the graphitization process, and the temperature control can lead to serious deformation. Graphite bipolar plates with good conductivity and corrosion resistance have laid a good beginning for the commercialization of PEMFC and are widely used as polar plate materials for PEMFC. However, its poor mechanical strength and high processing cost make it lack of sufficient competitive force in the industrial application of PEMFC.
Compared with graphite materials, metal materials have better conductive and heat conduction properties, so that the output power of fuel cells can be improved and the heat management of fuel cells can be improved, and the gas barrier function of metals makes them become the physical phase materials of preventing oxidation and reducing agents. Aluminum, stainless steel, titanium and nickel are the most commonly used PEMFC metal bipolar plate materials in the world. At first, its thickness is about 3 ~ 5 mm, the processing quantity is large, the cost is high, the volume is high, and the quality is also large. In order to reduce the volume and mass of the bipolar plate, the invention is beneficial to mass production, and the volume ratio power and mass ratio power of the fuel cell are improved, and the thin-layer metal bipolar plate is a better choice. And the thickness of the bipolar plate can reach 0.1-0.3 mm, so that the specific energy and the specific power of the battery pack can be greatly improved.
The composite plate is a thin metal plate or other high strength conductive plate as a separator, the thickness of which is generally 0.1 × 0.3 mm, the frame is made of plastic, polysulfone, carbonate, etc., and the frame is bonded to the metal plate by conductive adhesive. The porous thin carbon plate, graphite plate or graphite linoleum prepared by injection molding and baking is used as flow field plate. In this way, not only the power of volume ratio and mass ratio of battery pack can be improved, but also the advantages of graphite plate and metal plate can be combined. The composite bipolar plate has the characteristics of corrosion resistance, small volume, light weight and high strength, which is one of the developing trends.
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