Influence of iron on structure and catalyst activity of nitrogen-functionalized graphene nanoflakes

A cost effective alternative catalyst to platinum for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells is iron nanoparticles deposited into nitrogen-rich stacked graphene sheets. In this work graphene nanoflakes with high levels of nitrogen (HN-GNFs) are grown from the plasma phase and iron functionalities are added by a wet-chemical method. The amount of iron is varied to study the structural and electrochemical effects on the catalyst. The amount of iron in the sample and on the surface is measured and proven to have no effect on the qualitative surface conditions of HN-GNFs, as the iron is imbedded into the HN-GNFs. Electrochemical studies with a rotating disk electrode reveal that the addition of iron is beneficial in acid and neutral environments, with improvements of over 0.3V to the onset potential and 1.85mAcm−2 to the current density at 0V versus a reversible hydrogen electrode when the iron catalysts are compared to untreated HN-GNFs. The iron did not improve the catalytic performance in alkaline environments, with untreated HN-GNFs already showing good activity towards the ORR.