Graphite is charactered by good conductivity, good heat conduction and rust-resistance, but graphite contains many pores during their manufacturing process inevitably. H2 and O2 will be mixed if the graphite bipolar plates which contain pores are used in PEMFC ( proton exchange membrane fuel cell) , and the performance of fuel cell is low . Graphite bipolar plates were impregnated by thick Na2SiO3 solution in vacuum and pressure. Na2SiO3 in graphite plate was turned into SiO2 after being reacted with acid and heated. Porosity of graphite plate dropped to 3. 3 %from 18. 2%.No H2 leakage occurred at the pressure of 0 . 3 MPa.The resistance of graphite plate after impregnation did not rise. The voltage of fuel cell used the graphite plates added 40 mV at the same current density.
Graphite plates are widely used as bipolar plates for proton exchange membrane fuel cells because of their good electrical conductivity, thermal conductivity and corrosion resistance. But as a result of the graphite plate in the process of burning coal tar as the binder will be oxidized or volatile, are caused by the size of the holes graphite products, the porosity is about 18.2% ~ 24.3%, such a high rate of stomata use graphite plate. At present, more and more researchers in the world are using organic materials such as phenol resin, paraffin, asphalt, and so on to fill the hole of graphite plate, which can reduce the porosity and achieve the purpose of sealing graphite plate. The advantages of organic matter are large molecular weight, long molecular chain and good deformation performance. However, due to the organic matter seems to penetrate into the graphite plate hole, and even penetrate into the graphite layer, forming a composite material, thus increasing the graphite plate body resistance and surface resistance. The theory of voltage of single proton exchange membrane fuel cell is only 1.229 V, the greater the material resistance of the battery, the output power is small, therefore, most of the organic material is not suitable for the impregnation of proton exchange membrane fuel cell with graphite bipolar plate.
