Stability Study of Nitrogen-Modified Carbon Composite Catalysts for Oxygen Reduction Reaction in Polymer Electrolyte Membrane Fuel Cells

The objectives of this paper are to evaluate the nature of the active sites, the stability and degradation mechanism of nitrogen-modified carbon composite (NMCC) catalysts for oxygen reduction reaction in polymer electrolyte membrane (PEM) fuel cells. Two NMCC catalysts were synthesized using our previously reported method (ECS Transactions 11 (1) (2007) 241) at pyrolysis temperatures of 800 and 1100 degrees C, respectively. The catalyst pyrolized at 800 degrees C containing pyridinic nitrogen showed higher initial activity but much lower stability due to the protonation reaction in the acidic environment. The catalyst pyrolized at 1100 degrees C mainly containing graphitic (quaternary) nitrogen exhibited good long-term stability. The proposed nitrogen-modified active sites (pyridinic and graphitic nitrogen) for the non-precious metal catalysts can explain both the observed activity and stability of the catalysts.