Surface Modification Of Fe-Cr-Ni Alloy And304Stainless Steel As Bipolar Plates For PEMFC

Bipolar plate is one of key components in Proton Exchange membrane fuel cell(PEMFC), which accounts for60~80%weight of cell and40%of the cost. Bipolarplate performs a critical function of distributing and separating the reactant gases,collecting and transmitting electric current, supporting the MEA. Metal materials arethe promising candidate materials for bipolar plate of PEMFC due to their highconductivity, ease stamping manufacture, low material and production costs. However,their interfacial contact resistances (ICR) are high and corrosion resistances are not atdesired levels for real PEMFC working conditions. Therefore, surface modification hasbeen investigated intensively for decreasing the ICR and increasing corrosionresistance of metal material for bipolar plate. Generally, depositing conductive andanticorrosive films on metal plate would be a feasible and effective way to improve itsconductivity and corrosion resistance. However, coatings on metal plate are proveninsufficiently due to pin-hole defect and the poor adhesion force. Furthermore, an extracost hinders the application of metal bipolar plat. In this paper, Composite coatingswith good conductivity and corrosion resistance is in situ generated in metal platesurface by surface modification.In our previous work, it is found that an in situ surface modification technology,or acid treatment-heat treatment-electrochemical treatment (process(a-b-c)) on theFe-Cr-Ni alloy, shows advantages over others. So optimizing the parameters of heattreatment is carried out in this work. We obtain the optimal parameters as in anoxygen atmosphere,250℃, holding time for2hours. The Fe-Cr-Ni alloy samplewith optimized process(a-b-c) exhibits the lowest corrosion current density,3×10-8A·cm-2, and the smallest ICR,9.4m·cm-2at the compaction force of240N·cm-2. The composition and morphology analysis included XPS，AES，EPMAand FESEM of Fe-Ni-Cr alloy indicated that a composite coating is in situ formed inthe sample surface with process(a-b-c). And the coating is mainly composed ofCr2O3, C，Ni and Cr7C3. Finally, we use Fe-Ni-Cr alloy with optimized process(a-b-c)to assemble the single PEMFC. The single cell shows the highest output powerdensity over0.8W.cm-2. In order to further reduce the cost, surface modification of commercial SS304is carried out according to the similar method as Fe-Ni-Cr alloy. The sample withprocess(a-b-c) exhibits the lowest corrosion current density,3×10-7A·cm-2, and thesmallest ICR,10.11m·cm-2at the compaction force of240N·cm-2. By thecomposition and morphology analysis included XPS，AES，EPMA and FESEM ofSS304with process(a-b-c), it is concluded that a protectively thin composite coatingis in-stu formed in the sample surface which is mainly consisted of Cr2O3and C.Therefore, SS304sample with process(a-b-c) shows good conductivity andanti-corrosion.