The graphite material plate has a good electrical conductivity,thermal conductivity,and corrosion resistance,so it’s widely used as the bipolar plate of full cell. However,there are some small hole,during the production process,and the size of the holes are different. The main reason is that some coal tar which is used as binder will be oxidation or volatilization during the making process. And this situation will have a bad influence on the graphite plate The porosity of graphite plate is about 18.2%~24.4%.
Now,the most common method is using some organic compound to fill in the hole of graphite plate,such as phenolic resin, paraffin, asphalt, polymer, etc. to achieve the purpose of sealing,but it can increase the resistance of graphite plate. The new way to meet the requirement is to use the
Na2SiO3 solution, acid leaching and heating to treat the graphite plate,it can improve the fuel cell performance and reduce the porosity.
The immersion time and pressure have a big influence to the result. the effect will be better with the pressure increasing and the time extending. However ,the higher pressure need higher strength and better sealing effect,and also difficult to operate.
By this way,the porosity can down to 3.3% from 18.2%,and it will not influence the resistance. Some scholars did the testing on the different resistance between the before and after dipping,it’s about 6.34ρ /( Ψ ·cm) before impregnation and it’s about 6.36ρ /( Ψ ·cm) after the impregnation.
The properties of the graphite plate after impregnation is better than the ones before impregnation,and it also can be proved by the electric reactor performance test.
The graphite plate after impregnation can increase the voltage to 40mV above,it’s under the same situation with the same current density to the graphite plate without impregnation,it can guarantee the fuel cell property.