First, the content introduction
Proton exchange membrane fuel cell (PEMFC) can directly convert chemical energy into electric energy by electrochemical method under isothermal conditions, and is not limited by Carnot cycle, with high energy conversion rate (40% ~ 60%), clean and pollution-free (the product is mainly water), so it is considered as the first choice for efficient and clean power supply system in 2 1 century. Bipolar plate, as the connecting part of single cells in PEMFC stack, mainly plays the role of isolating gas collusion between cells, distributing fuel and oxidant, supporting membrane electrodes and connecting single cells in series to form electronic circuits.
At present, the bipolar plate materials developed mainly include metal and carbon materials. The advantage of surface-modified metal bipolar plate is that it can be made into a thin plate (such as 0. 1 ~ 0.5 mm), and mechanical production methods such as stamping and shearing can be used to process the pores and flow fields, which is beneficial to reducing the cost of bipolar plate, but the corrosion problem of metal plate has not been well solved. At present, bipolar plates made of artificial graphite are actually used. The bipolar plate made of this material has good electrical conductivity and corrosion resistance. However, due to the requirement of air tightness of bipolar plate, the manufacturing process needs to go through many production processes such as resin impregnation, carbonization, graphitization and subsequent flow field treatment, so the manufacturing process is complex and the cost is high, which has become an important factor restricting the application of fuel cells.
In the laboratory, natural flake graphite is chemically or electrochemically treated to form expandable graphite, and the expandable graphite is expanded to obtain a worm-like substance, and the expanded graphite worm is shaped into a plate-like material with a certain density and good surface smoothness-the manufacturing process of flexible graphite plate is shown in Figure 1. Because the expansion process basically removes all unnatural chemical components in flake graphite, molding or rolling is only a mechanical combination of expanded graphite, and the final flexible graphite plate is basically pure graphite, which has the advantages of strong thermal stability, good electrical and thermal conductivity, corrosion resistance and good air tightness of natural graphite. At the same time, the flow field on the surface of flexible graphite bipolar plate can be directly manufactured by one-step molding, so its cost is greatly reduced.
Figure 1 Flowchart of Flexible Graphite Sheet Production
The strength of flexible graphite bipolar plate can reach 30MPa, which has been verified by laboratory. The helium permeability is (0.4 ~ 0.9) × 10-6 μ m2, the electrical conductivity reaches1.1×105s/m, and the thermal conductivity reaches129 w/(m k), all of which are superior.
Second, popularization and application
The actual test shows that the performance of the battery assembled by flexible graphite bipolar plate and artificial graphite bipolar plate is basically the same, while the cost of the former is only1/20 ~110 of the artificial graphite bipolar plate.
Three. Identification, awards and patents
From June 5th to February, 2004, the Ministry of Science and Technology organized experts to check and accept.