Sodium silicate/graphite conductive composite bipolar plates for proton exchange membrane fuel cells

The flexural strength, pore size distribution, resistance to acid corrosion and thermal properties of sodium silicate/graphite composite bipolar plates for proton exchange membrane fuel cells (PEMFC) were investigated in this paper. The experiment results show that when the graphite content is greater than 40 wt.%, the flexural strength of composite bipolar plate can attain 15 MPa and this composite bipolar plate was not broken during machining the flow fields. The large amount of porosity in this composite bipolar plate is from the silica gel capillary pores because of the solidification of sodium silicate, which makes it possess a humidifying function during PEMFC operation. The corrosion current is about 10−4.5 A cm−2 from the polarization curves for this composite bipolar plate, which shows that this composite bipolar plate is acid-resistant. Na+ ions leached from this composite bipolar plate is only a small percentage of the total Na+ ion content in the composite bipolar plate after 1 M H2SO4 solution corrosion at 30 °C for 1 h. Na+ ions in the acidic corrosion solution increased a little with temperature from 30 to 80 °C. In addition, this composite bipolar plate was thermally stable from room temperature to 400 °C.