In search for structure of active site in iron-based oxygen reduction electrocatalysts.

Calculations to elucidate the structure of Fe-based electrocatalysts were performed. Lowest energy configurations for incorporation of nitrogen in bulk of graphene sheet as well as on edge were determined. Substitution of nitrogen in bulk graphene is endothermic, while on the edge it can be either exothermic, if hydrogen is present, or endothermic. Energies of various configurations for the incorporation of iron on the edge of the nitrided graphene sheet were also examined. In the absence of hydrogen, iron prefers to bond with nitrogen and a carbon atom. In the presence of hydrogen, however, iron was found to prefer bonding to two nitrogen atoms on the graphene edge.