Catalysts for oxygen reduction from heat-treated carbon-supported iron phenantroline complexes

Oxygen reduction catalysts were prepared by heat treatment of carbon supported iron phenantroline complexes in Ar or NH3. The optimum carbon black loading with iron was found to be 2%, the optimum heat treatment temperature was about 800 °C. X-ray diffractogramms and TEM showed the occurrence of crystalline species at higher catalyst loadings; however, these species seem not to contribute significantly to the catalytic activity. From the slope of the Koutecky–Levich plot, an average number of 3.7 electrons transferred per oxygen molecule was calculated, which is consistent with RRDE data. A Tafel slope of about 120 mV (decade)−1 indicates that the first electron transfer is rate determining.