| Stainless steel is often chosen as the PEMFC metallic bipolar plate materials because of its excellent corrosion resistance and easy processing properties. However, the corrosion of stainless steel bipolar plates under PEMFC working conditions becomes a major factor of restricting its application. In addition, the passivation film of the stainless steel surface, an increase of contact resistance inside the battery.In order to improve the poor corrosion resistance of electro-plating layer because of the pinholes, this article investigated the composite coating layers on 304L stainless steel, which a silver layer was deposited by electroplating and then a floor gold covering layer by electroplating or sputttering. The coated bipolar plate showed low interfacial contact resistance. Under the fuel cell stack compacting pressures, the interfacial contact resistance between the bipolar plate and Toray 060 carbon paper was 2.7～3.1 m·cm2.The 304L stainless steel bipolar plates also showed improved corrosion resistance in simulated proton exchange membrane fuel cell(PEMFC) environment.Compared to 304L stainless steel, the corrosion potential of the gold coating 304L stainless steel by electroplating or sputtering on a silver based layer were increased respectively by 0.45V and 0.49V, and the corrosion current density about 10-6～10-7.5 A/cm2 , which is two orders of magnitude lower than that of the bare metal in 0.05mol/L H2SO4+5×10-6mol/L HF.In addition, some research in the flow field structure of bipolar plate was did. Non-uniform fluid flow channel design by reversing the fluid flow between the double-effect mode conversion was proposed, based on the respective characteristics of fluid flow in the flow field between fuel cell mode (discharge mode) and water electrolysis mode (charging mode),so as to achieve high efficiency of fuel cell mode and water electrolysis mode. A sheet metal stamping bipolar plate of fuel cell was also proposed,composed of three plates, respectively, the above and below plates as the anode and cathode flow field plates, the middle plate as the coolant plate. Two polar plates that had the same serpentine flow field was connected to the two sides of coolant plate by their contact surface and sealing material placed in their border groove. A cooling liquid flow channel was formed between the back flow channel groove of cathode flow field plate and flow channel of the middle field plate.Finally, Compared experimental test of a single cell stamped from 0.2mm thick 304L SS, simulation results of the add-on PEMFC module of Fluent was closer to experimental results. Testing verification confirmed the validity of the model. Different contact resistance and humidity at room temperature were analyzed as well as gas distribution in the flow channels of cathode and anode by simulation of fuel cell,based on 304L stainless steel flow field plate of silver-gold composite coatings. |
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