Nitrogen doped graphene: influence of precursors and conditions of the synthesis
Heteroatoms doped graphenes, especially nitrogen doped graphenes, have attracted much attention due to their remarkable performance as parts of lithium-ion batteries, advanced catalyst supports, super capacitors and fuel cells. The performance of doped materials strongly depends on the level of doping. While the nitrogen doped graphenes are synthesized by various methods, the parameters influencing the level of doping are seldom studied. Here we prepare nitrogen doped graphenes by exfoliation of different graphite oxides (i.e. Staudenmaier, Hofmann and Hummers) in an ammonia atmosphere at various exfoliation temperatures (i.e. 600 degrees C, 800 degrees C and 1000 degrees C). We study the efficiency of nitrogen doping using characterization methods such as scanning electron microscopy, Raman spectroscopy, combustible elemental analysis and X-ray photoelectron spectroscopy. We show that the level of doping strongly depends on the type of the starting graphite oxide. This has very important implication on the fabrication of doped graphenes and we suggest that the graphite oxide preparation route must be always considered when one performs heteroatom doping of graphenes via a thermal exfoliation route. In addition, we present an optimized, scalable technique for fabrication of large quantities of highly nitrogen doped (>7 at.%) graphenes.