Effect of the iron precursor on the insitu functionalization of deposited graphene nanoflakes for catalyst applications

Graphene nanoflakes (GNF), a stack of 5 to 20 layers of graphene sheets with typically 100 nm side lengths, are the product of methane decomposition using an argon ICP thermal plasma. GNFs are good candidates to support non-noble catalytic sites for the oxygen reduction reaction. This material has a high crystallinity allowing the graphene to be acid resistant, together with a high electrical conductivity, these properties providing a good basis for a stable catalyst material in fuel cells. The GNFs are functionalized with nitrogen to support iron atoms and create catalytic sites dispersed at the atomic level on the nano-structured powders. The iron functionalization step is realized in situ as a post-processing step within the synthesis reactor through the vaporization of two different Fe precursors in the core of the plasma. The first consists of pure iron powders carried by a nitrogen flow; this method having the advantage of avoiding impurities during the functionalization step. The second precursor is an iron(II) acetate solution also carried by a nitrogen flow, with the iron already in atomic form once dissociated in the thermal plasma core. The effects of the type of precursor, the power of the plasma, and the reactor chamber pressure on the iron functionalization are studied in the present contribution. The structure, composition, and activity of the resulting catalyst are also fully characterized.