Surface Modification Of 304 Stainless Steel As Bipolar Plates For PEMFC

Proton Exchange Membrane Fuel Cell?PEMFC?is the most common fuel cell in our recent research,it is widely used in transportation and portable power terms.Graphite is the most commonly used bipolar plate material in PEMFC,but its application is restricted because of the big volume,high processing costs as well as their brittleness and other problems.Metallic material is the best candidate for commercial production for its good mechanical properties,electrical and thermal conductivity.Using the metal material instead of graphite can reduce their production costs.Stainless steel is one kind of widely investigated bipolar plate materials,but its corrosion resistances and interfacial contact resistances?ICR?can not meet the requirements of PEMFC work environment,therefore,surface modification has been investigated.At present,depositing conductive and anticorrosive film on the metal is the most commonly method to improve its surface properties,but in the long-running process of the battery the film is easy to fall off due to its film defects and poor adhesion strength,so battery performance is affected.In this paper,composite surface modification is used for SS304,composite coatings with good conductivity and corrosion resistance is in situ generated in metal plate surface.In our previous work,a complex treatment process with acid treatment-heat treatment-electrochemical treatment was study for metal material.In this paper we use this complex treatment to deal with SS304,and optimiz the parameters of acid treatment and electrochemical treatment.Finally we obtain the best parameters as in a mixed acid?HNO3:HCl:HF=12:2:1?concentration of 30%?volume ratio of acid to water?and the polarization treatment 2h.After the optimized treatment the SS304exhibits the lowest corrosion current density,2.8×10^-8A·cm^-2,and the smallest ICR,4.29m?·cm^-2 at the compaction force of 240N·cm^-2.Using XPS,AES,FESEM to analysis its surface composition and morphology,we find that a composite coating is in-stu formed in the surface after complex treatment.The coating is mainly composed of Cr₂O₃,C and it is thin and dense,and some Cr-N-C=O may also exist.So the SS304has better corrosion resistance and conductivity.The single cell is tested with SS304 as bipolar plate by complex treatment.The output power density is 0.38W.cm² for the single cell with working temperature of65?and excessive coefficient of 1.5:2.0 for anode and cathode as well as 100%relative humidification for gas.