Degradation of PEMFC under Startup/Shutdown Cycling Operation

Degradation of PEMFC under Startup/Shutdown Cycling Operation
PEMFC; Durability
Issue Date
Gordon Research Conference
In this work, degradation mechanism of cathode of PEMFCs exposed to repetitive startup/shutdown cycles was studied by investigating effects of residual oxygen partial pressure in the flow channels on degradation of the cathode. In-situ degradation of the MEAs were examined by measuring polarization curves, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and linear sweep voltammetry (LSV) with repeating the on/off cycling. Single cell whose gas channels were kept with lower oxygen partial pressure exhibited better durability in the oxygen concentration range of 0 to 21 %. The CV and EIS results showed that as the residual oxygen partial pressure increased, the loss in electrochemically active surface area (EAS) and the increase in the charge transfer resistance (Rct) were faster during startup-shutdown cycling. However, changes in ohmic resistance (Rohm) and hydrogen crossover current density were not detectable, revealing that severe membrane degradation did not occur regardless of the residual oxygen partial pressure during startup-shutdown cycles. To elucidate the mechanism, EPMA, WDS, BSEM, on-line CO2 analysis, XPS, ICP, XRD, FETEM, SAED, EDX and FTIR were carried out before and after the durability test. The results revealed that pronounced Pt coarsening (agglomeration)/ oxidation/dissolution (detachment) and migration occurred along with corrosion of the carbon support at the majority of cathode catalyst layers. These changes contributed to the significant loss of Pt mass available for electrochemical reactions and active Pt surface area at the cathode, thus decaying the performance of the fuel cell. However, the degradation at the anode and membrane was not as severe as those observed at the cathode and did not show any dependence on residual oxygen concentration. Based on these results, a modified mechanism for the degradation of the cathode catalyst layer during the st
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