Iron-Nitrogen Coordination in Modified Graphene Catalyzes a Four-Electron-Transfer Oxygen Reduction Reaction

It is shown that iron-nitrogen (Fe/N) coordination in an Fe/N-modified graphene (Fe/N-graphene) electrocatalyst catalyzes a four-electron transfer oxygen reduction reaction (ORR). The Fe/N-graphene is synthesized by heat-treating graphene oxides in the presence of an Fe/N complex at 900 degrees C for just 45 s. When the heat-treatment period is increased, the Fe/N coordination bonds are broken and the number of electrons involved in the ORR decreases. Extended X-ray absorption fine structure analysis and X-ray absorption spectroscopy (XAS) show that both a complete sp(2) graphitic structure and a high density of Fe/N coordination structures exist in the Fe/N-graphene material, which is in contrast to the carbon-based catalyst prepared by using the conventional pyrolysis method. XAS analysis also reveals that back-donation from Fe atoms coordinated with N to an O antibonding pi* orbital occurrs, promoting the four-electron transfer ORR.