Quantitative analysis of carbon corrosion during fuel cell start-up and shut-down by anode purging

Abstract

The corrosion of the carbon support during start-up and shut-down of polymer electrolyte fuel cells was systematically quantified to elucidate effects related to the propagation of the gas front through the anode compartment and to determine the influence of relevant operating parameters. Measurements with different reactant gas concentrations and gas flow rates suggest that the gas exchange process is dominated by a homogeneous displacement of the anode gas in case of start/stop operation at OCV. The influence of additional effects such as direct recombination of hydrogen and oxygen, diffusion on the channel and land scale and pseudocapacitive effects seems to be negligible under the investigated conditions. With an external load applied during the gas exchange process (discharge mode), shut-down induced carbon corrosion strongly differs from the behavior at OCV. The virtually constant corrosion rates obtained below a critical purge gas flow rate in the discharge mode are attributed to a significant contribution of electrochemical hydrogen consumption. Temperature and humidity variation measurements demonstrate that the carbon corrosion behavior during real start/stop processes can differ considerably from the correlations obtained under controlled potential conditions in H2/N2 mode. Thus, potential cycling experiments only provide limited information about start/stop durability under application relevant conditions.