Corrosion Behavior Of Metal Bipolar Plate Materials For Proton Exchange Membrane Fuel Cells

The main functions of bipolar plates in proton exchange membrane fuel cell (PEMFC) are to distribute and separate the cathodic and anodic reactant gases and to collect and transmit electric current. Metal bipolar plates have already received special attention due to their good machining properties. Unfortunately, the metal bipolar plates may be corroded in the PEMFC environments which comprise weakly acidic media and the reactant gases of cathode and anode. Thus, it is of great significance for the development and commercial applications of PEMFC to clarify the corrosion mechanism and characteristics of the typical metal bipolar plate materials and therewith to enhance their corrosion resistance. In this thesis, the corrosion behavior of stainless steels and some other metallic materials was investigated in simulated PEMFC environments. Moreover, the effect of surface treatments on corrosion resistance of stainless steels was also revealed. Some electrochemical measurement techniques, e.g. electrochemical impedance spectroscopy (EIS) and polarization curve, and surface analysis methods, e.g. scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS), were used in the study.Considering the low conductivity of the media in PEMFC, the effect of internal resistance of reference electrode system and solution conductivity on EIS was firstly studied. It was found that the large internal resistance of reference electrode system induced the capacitive high-frequency phase shift in EIS measurements.The corrosion behavior of type 316 stainless steel was investigated in the simulated fuel cell environments containing fluoride (F-) ions and sulfate (SO42-) ions, respectively. The results obtained under the cathodic conditions, i.e. oxygen aerated solutions, are as follows. 316 stainless steel can passivate spontaneously at corrosion potential in 0.01M hydrochloric acid (HCl) solutions with 0~0.1M F- ions, forming F- containing passive films on the surface. Low concentrations of F- ions (<0.01M) have no significant influence on the passivity of 316 stainless steel. In solutions containing 0.1M F- ions,...