Research Of Surface Modification On Stainless Steel As Bipolar Plate Of PEMFC

PEMFC is a device that can translate chemical energy in fuel and oxidant effectively into electric energy directly. PEMFC may be popular used on electrical source in the area of mobile power supply and immobile power plant in the future because of its high energy consistency and low pollution. As one of the critical components, bipolar plates can determine the output power and life of PEMFC. So it need not only high conductivity, well anti-corrosion ability, low density, high mechanical performance and resistance permeating of gas, but also low material cost, good machinability and stability on size. Simultaneously, bipolar plate must be a well conductor of heat, in order to ensure homogeneous temperature distribution and get rid of superfluous heat. Presently, metal bipolar plate has taken up a broad market of this area by its excellent machinability and anti-permeating of gas. But the coexistence of conductivity and corrosion resistance blocks its development in bipolar plate area.In this paper, preparation of chemical conversion coatings and chemical Ag plating were operated on 316 stainless steel in order to do surface chemical modification. The mixed treatment solution is composed by AgNO₃ and HNO₃, in a specific concentration.The results indicate that the contact resistance of 316 SS with chemical conversion coatings can reach to approximately 20mΩ·cm² when the pressure achieves 150N·cm^-2. Comparing with the 316 SS untreated, its contact resistance decreases nearly 10 times while the corrosive current does change sharply in the environment of PEMFC. Though it decreases a little, after silvering the contact resistance can reach to about 16mΩ·cm². A lot of holes can be found distributing on the surface of the steel under the apparatus of super depth microscope . After treatment, most of the holes are mantled. EDS explains that a bit of Ag is founded in the corrosive holes on the surface of SS. XRD expresses that Fe_0.64Ni_0.36 enhances the conductivity. And some atoms are existing on the surface steadily. Open Circuit Potential-Time plots show that the open circuit potential of SS after modification has become higher in simulated PEMFC environment. Dynamic potential polarization plot and steady potential oxidation plots display that the stainless steel improves its self-corrosion potential in a high degree after treatment. And the corrosion current density also decreases nearly two degree in quantity. Oxidation on steady potential plots also show us the improved corrosion resistance in simulated proton exchange membrane fuel cell (PEMFC) environment after surface treatment.