Effect of the N content of Fe/N/graphene catalysts for the oxygen reduction reaction in alkaline media

In this work a series of N-modified graphene composites with different N/C ratios have been synthesised. The incorporation of Fe atoms into the N-modified graphene composites leads to the formation of Fe/N/C ensembles on the outer graphene layers along with Fe3C and metallic Fe phases in the bulk of the graphite nanoplates as revealed by X-ray absorption and XPS analyses. The adequate choice of the N/C atomic ratio of precursors to prepare Fe/N/graphene based materials is crucial to obtain electrocatalysts with an optimal performance for the ORR. The activity for the oxygen reduction reaction (ORR) of the Fe/N-graphene based electrocatalysts increases with increasing amount of accessible nitrogen, that is, with the amount of nitrogen by surface area.