Investigation On Properties Of Modifed Metallic Bipolar Plate

PEMFCs(Proton Exchange Membrane Fuel Cells)are regarded as most potential power sources for transportation and portable application because of high power density,fast start-up at ambient temperature and low operation temperature.Bipolar plate is one of the most important and expensive components in PEMFCs.Metal is one kind of widely studied materials to substitute for traditional machined-graphite using as bipolar plates for PEMFCs.Metallic bipolar plates has been become major research focuses on the development of PEMFCs.However,the insufficient corrosion resistance and/or higher interfacial contact resistance still prevent from the large scale commercialization for PEMFCs.In this paper,intensive studies involving in surface modification methods,microstructure,corrosion behavior and surface conductivity were carried out.Nb-alloyed coating is prepared on surface of pure titanium TA2 by plasma surface alloying.Especially,the coating is metallurgical combined with the substrate TA2,and uniform in thickness as well as dense in microstructures.No pinhole and microcrack,even interfacial defect is found.The results of electrochemical measurements show that the Nb-alloyed coating is self-passivated in the simulated PEMFC environments,and the passive current densities is lower than that of the untreated TA2.Stable passive films with n-type semiconductor are formed on the Nb-alloyed coating after potentiostatic polarization at anode and cathodic operation potential for PEMFC,which results in a slightly increase in interfacial contact resistance at the given compaction force.Chemical deposition method is used to prepare Ag coating on stainless steel 316L and T4003.Ag coating with 2?3?m in thickness is combined with stainless steel substrate by Cu interlayer.Compared with the untreated 316L and T4003,corrosion current density of Ag-modified T4003 is decreased up to 2-3 magnitude order,while that of Ag 316L almost remain unchanged.Low porosity in uniform Ag-modified coating leads to accelerated corrosion of the substrate.The surface conductivity of 316L and T4003 is significantly improved,and is closed to that of graphite.In addition,the contact angle of 316L and T4003 is also increased by the Ag coating with low surface energy.