Ex situ and in situ stability studies of PEMFC catalysts

We explore ex situ and in situ fuel cell catalyst degradation test methods and the impact of catalyst degradation on fuel cell performance. A series of platinum-loaded carbons with two different carbon supports are aged ex situ in an isothermal oven and in situ using a 1.2-V fuel cell accelerated test. The ex situ combustion test and in situ 1.2 V accelerated fuel cell test both show that the rate and extent of carbon combustion for samples with the same platinum loading increases as the surface area of the carbon increases, presumably because platinum deposits as smaller particles, covering more of the carbon surface. In addition, the rate of reaction/loss of carbon is shown to increase significantly if humidity is introduced into the environment, a concern for long-term polymer electrolyte membrane fuel cell (PEMFC) operation because PEMFCs operate in a hot, humidified, oxygenated environment. Finally, graphitized carbon black supports with the same surface area and platinum loading as ungraphitized supports show much greater stability in both the ex situ and in situ tests, suggesting that carbon surface chemistry plays a strong role in oxidative stability under fuel cell conditions. (c) 2005 The Electrochemical Society.