Investigation of Carbon Corrosion Behavior and Kinetics in Proton Exchange Membrane Fuel Cell Cathode Electrodes

The corrosion behavior and kinetics of high surface area Ketjen black carbon (HSC) supported membrane electrode assemblies (MEAs) have been investigated in this work. Carbon corrosion rate derived from CO2 evolution was used to quantify carbon weight loss. It was found that the presence of Pt catalyst on the carbon support enhanced carbon corrosion; but the accelerating impact diminished gradually with time. Carbon corrosion rate of HSC supported MEAs is a strong time and weight loss dependent function. It appears a significant decrease in the corrosion rate as the carbon weight loss exceeds 25%. It is believed that center-hollow corrosion behavior and heterogeneous carbon structure may be responsible for this discontinuity of carbon corrosion rate. As the amorphous carbon matrix in the central region of carbon particles has been consumed (at ∼34% carbon weight loss), the corrosion rate of HSC supported MEAs acts as graphite-like corrosion behavior. Samples with specific levels of carbon weight loss were analyzed by scanning electron microscopy in order to investigate the effect of carbon corrosion on the thickness of fuel cell electrodes. The results suggest that the carbon weight loss is not linearly proportional to electrode thickness reduction. This nonlinear relation indicates more than one corrosion mechanisms playing a role and supports a multi-step carbon corrosion behavior.