Fe-based electrocatalysts for oxygen reduction in PEMFCs using ballmilled graphite powder as a carbon support

Active Fe-based electrocatalysts were prepared using ballmilled graphite powder as a carbon support. The best performing catalysts were achieved by acid-washing, iron-loading, and pyrolyzing the ballmilled graphite powders. Only 1 h of ballmilling was required to produce optimal catalytic activity. High-energy ballmilling of pristine graphite powder under nitrogen was shown to reduce crystallite size, increase nitrogen content, increase surface area, increase degree of disorder, and inevitably introduce metallic impurities. Acid-washing treatment of ballmilled graphite powders reduced, but did not completely eliminate, metallic impurities. Iron enrichment and pyrolysis of acid-washed, ballmilled graphite powder was shown to increase catalytic activity, have little effect on crystallite size, increase surface area, and decrease degree of disorder. It was found that catalytic activity increases as crystallite size decreases, degree of disorder and nitrogen content increase, and micropore specific surface area increases. Fuel cell test results have shown that the order of increasing maximum power density follows the order of increasing catalytic activity. Interestingly, the optimal crystallite size parameter L-a (20-30 angstrom) and maximum activity for catalysts made with either ballmilled graphite powder or carbon black is almost the same. (c) 2008 The Electrochemical Society.