Doping and reduction of graphene oxide using chitosan-derived volatile N-heterocyclic compounds for metal-free oxygen reduction reaction

We developed a fast, simple, scalable and safe method for the metal-free reduction and nitrogen-doping of graphene oxide (GO) using volatile nitrogen-containing heterocyclic compounds. In this method, chitosan and graphene oxide were simultaneously annealed without making any physical contact between them under a flow of argon using chemical vapor deposition (CVD). Based on the established knowledge of chitosan thermal decomposition, in-situ formed volatile nitrogen-containing heterocyclic compounds interact with graphene oxide to produce N-doped reduced graphene oxide (NrGO). In order to study the effect of temperature on the nitrogen content distribution and on the carbon/oxygen ratio, we annealed the graphene oxide and chitosan at 300, 450 and 600 °C. We fully characterized the synthesized materials (NrGOs) by XPS, Raman, FT-IR, HR-SEM, AFM, XRD and UV–Vis techniques. On the basis of XPS analysis, we achieved the highest nitrogen-doping level at 4.3 atom % at 450 °C with an atomic ratio of C/O as high as 16, which, to our knowledge, is the highest value reported so far at this temperature. Electrochemical characterizations demonstrate electrocatalytic activity of this NrGO towards the oxygen reduction reaction (ORR) in alkaline electrolytes, with a high reaction onset potential of 0.78 V vs. RHE.