| Proton exchange membrane fuel cell (PEMFC) is a new clean power generation system with advantages of high proficiency, good durability, non-pollution, quiet operation, fast start-up time and low operating temperature (typically between70and80℃). It gets much attention from the world. Bipolar plates are key components of PEMFC which account for about60-80%of total weight and29-45%of stack cost, respectively. To meet working requirements, bipolar plates should exhibit several properties including high electrical conductivity, good corrosion resistance, good mechanical properties, low cost, and low permeability. To date, there are still no materials which can meet the commercial application of bipolar plates. In this paper, electrically conducting polyaniline (PANI) coating was deposited on stainless steel304(SS) by electropolymerization and the target is to find a promising material with good corrosion resistance and conductivity used for bipolar plates.PANI coating was deposited on stainless steel304(SS) by potentiostatic and galvanostatic methods. Its feasibility used for bipolar plates was studied. The effect of depositing parameters on the structure and properties of coatings was examined and the optimal condition was obtained. The optical microscope (OM), scanning electron microscope (SEM), Fourier transform infrared (FT-IR) spectroscopy and X-ray diffraction (XRD) were used to examine its morphology and structure. Potentiodynamic and potentiostatic tests, electrochemical impedance spectroscopy (EIS) were conducted to investigate its corrosion resistance. And our home-made electrical conductivity testing equipment was used to examine its interfacial contact resistance.First, PANI coating was deposited by different conditions. FT-IR and XRD result confirmed the polymerization of aniline and its good crystallization. The optimal depositing condition of PANI was obtained by the result of surface morphology analysis and potentiodynamic tests. For the PANI coatings obtained under optimal conditions, the corrosion potentials were both over400mV and the corrosion densities were four orders of magnitude less than bared SS.Afterwards, the following research objects were the SS and the PANI coatings deposited under optimal conditions by potentiostatic and galvanostatic methods. Their long-term corrosion behavior was determined by potentiostatic tests in simulated PEMFC environments. OM, SEM and energy dispersive spectrometer (EDS) were used to characterize the change of coating morphologies. Inductively coupled plasma atom emission spectroscopy (ICP-AES) was used to determine the metal ion concentration in the solution after corrosion. As a result, the anode condition is more corrosive than the cathode one, and PANI coated SS exhibits better stability and higher corrosion resistance in the simulated PEMFC working conditions than the bared one.Corrosion protection mechanism of PANI was investigated by the pre-existing corrosion data and open-circuit potential (OCP) test, EIS test and the existing mechanisms reported by other researchers. The bared SS exhibited the poorest corrosion resistance during long-term immersion test. Passive film formed on the surface of bared SS at the first4hours and dissolved at last. PANI coating deposited by potentiostatic method showed good corrosion resistance for short term, while electrolyte penetrated the coating and corroded the substrate after four hours of immersion. PANI coating deposited by galvanostatic method displayed the best durability.Lastly, the conductivity of PANI coating was examined. ICR of bared sample at140N cm-2was much lower than that of PANI coated one. After potentiostatic tests, PANI coated sample showed better conductivity, due to the formation of thinner passive film. In actual fuel cell acidic conditions, conductivity of PANI coating is expected to be higher considering the flowing channel structure of bipolar plates and the test condition. Therefore, the ICR may satisfy the U.S. Department of Energy (DOE)2015targets on metallic bipolar plates. |
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