Start/Stop Induced Carbon Corrosion in Polymer Electrolyte Fuel Cells

The effect of different operating parameters on carbon corrosion in polymer electrolyte fuel cells was investigated by applying single triangular potential pulses to cells operated in H₂/N₂ mode. Corrosion rates were determined by integration of the resulting CO₂ concentration peaks in the cathode exhaust gas. A significant effect of the lower voltage limit was observed which was attributed to a partial inhibition of the platinum catalyzed corrosion pathway through the formation of a stable oxide layer on the platinum surface. Humidity variation experiments showed a linear correlation between carbon corrosion rate and water vapor partial pressure. However, corrosion rate strongly decreased at low relative humidity, showing that both absolute and relative water content influence corrosion. Since the distinction between the influence of absolute and relative water content is not clear yet, interpretation of temperature effects is difficult. In case of fully humidified gases, corrosion rates showed an exponential-like increase with increasing temperature. In order to assess the relevance for real start-up and shut-down processes, carbon corrosion rates were compared to degradation data obtained in application oriented start/stop cycling experiments, which were carried out by alternating purging of the anode compartment with hydrogen and air. Generally, fuel cell performance loss rates are in good agreement with corrosion rates determined in potential pulse experiments. Due to the high complexity of real start-up and shut-down processes, however, potential pulse experiments can not provide an accurate prediction of start/stop induced degradation behavior.