Carbon Corrosion in PEM Fuel Cells during Drive Cycle Operation

PEM fuel cells (PEMFCs) show great promise to increase the fuel efficiency for transportation applications; however, for this application, they must show performance and durability with the requirements for transportation. For transportation applications, the fuel cell will be subjected to frequent power cycling. For example, the DOE/Fuel Cell Tech Team (FCTT) protocol for durability includes load cycling from 0.02 A/cm2 to 1.2 A/cm2 every 0.5 min. The cathode catalyst and catalyst layer have been shown as susceptible to degradation causing loss of performance due to both loss of kinetics for the oxygen reduction reaction and loss of mass transport. Catalyst support-carbon corrosion can result in thinning of the catalyst layer contributing to degradation in performance. To examine the effect of power cycling in situ on carbon corrosion and electrode degradation, we directly measured the catalyst support degradation by measuring CO 2 in the cathode outlet by NDIR (Non-Dispersive Infra-Red) while operating a single-cell fuel cell. CO 2 present in air was removed by a lime bed prior to introduction to the fuel cell. We operated with a modified DOE/FCTT durability protocol using controlled voltage, and varied the potential limits to explore the effects of the upper potential limit, lower potential limit, the potential step size and time at potential. The upper potential limit was varied from 0.95 to 0.55V; the lower potential limit from 0.40V to 0.80V, with times ranging from 0.5 min to 5 min. The corrosion of three different types of carbon were explored, high surface area (E), vulcan (V), and graphitized (EA). The catalyst support carbon corrosion occurs under normal fuel cell operating conditions and is exacerbated by the voltage cycling inherent in these steps in potential. A series of carbon corrosion spikes during potential cycling is shown in Figure 1 for E-type carbon, varying the upper potential from 0.95 V to 0.60V while keeping the lower potential constant at 0.40V. Sharp spikes in the carbon corrosion rate are observed during a step increase in cell potential with the magnitude of the spikes decreasing as the high cell potential is reduced from 0.95 V to 0.6 V. The carbon corrosion rate at high cell potential (0.95V) decreases with time at potential, indicating formation of passivating carbon surface oxides. Carbon corrosion was measured during the drive cycle measurements for all three types of carbon, with the relative carbon corrosio