Fe–C–N Oxygen-Reduction Catalysts Prepared by Mechanochemical Reaction

Abstract

Fe-C-N oxygen-reduction catalysts were prepared by mechanochemical reaction of Fex N (x=2-4) and graphite under Ar using high-energy ballmilling. The activity of the catalyst toward the oxygen reduction reaction (ORR) depends on the ballmilling time and on the Fex N precursor content. Heat-treatment up to 600°C does not significantly affect the activity, but the activity strongly decreases as the samples are heat-treated above 800°C in argon. The onset potential of a typical sample ballmilled for 12 h is 0.72 V versus reversible hydrogen electrode. About 20% of the product of oxygen reduction is H2 O2 and the other 80% is water. The X-ray diffraction pattern of the ballmilled material shows the formation of Fe7 C3 and disordered carbon, which presumably contains nitrogen, because the ball mills are sealed and the nitrogen cannot escape. This work demonstrates that mechanochemical synthesis is a useful technique for the preparation of Fe-C-N ORR catalysts. © 2008 The Electrochemical Society.