Accelerated degradation of bipolar plates in the PEMFC
Abstract: The aging of bipolar plates in the polymer electrolyte membrane fuel cell was evaluated using different accelerated degradation tests. From previous studies, it is well known that the startups and shutdowns of a polymer electrolyte membrane fuel cell is the primary cause of fuel cell component degradation. Therefore, the aim of these tests was to simulate the number of startups/shutdowns that normally occur during the lifetime of a polymer electrolyte membrane fuel cell, e.g. for automobile applications. The tests were carried out in situ in order to be as realistic and close to operational conditions in real applications as possible. Mechanical stress and degradation normally occurring during polymer electrolyte membrane fuel cell operation was thereby included. The accelerated degradation tests were designed for maximum fuel cell stress, including use of the no purge and the air purge strategy, short cycle duration as well as an increased number of startups/shutdowns. Since the no purge strategy avoids prevention of local H 2/O2 fronts, this strategy was implemented first. Other strategies e g the air purge strategy, where air is used to purge the anode, where also implemented. Parameters influencing the tests were varied and the cathode gas was changed between O2 and air depending on the test. Electrochemical methodology was implemented for the detection of corrosion in the tests and for analysis/ studies of the test results. These techniques include cell voltage/current readings, polarization curves, electrochemical impedance spectroscopy, contact resistance and current density decrease at constant cell voltage. In addition, scanning electron microscope was used to visualize the actual corrosion of the bipolar plates. It was found that implementation of the air purge strategy resulted in localized corrosion, i.e. oxide film formation, on the surface of the bipolar plates increasing both the corrosion resistance and the interfacial contact resistance.
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