Synthesis of nitrogen-doped multilayer graphene from milk powder with melamine and their application to fuel cells

We reported on the facile synthesis of N-doped multilayer graphene (N-MLG) from milk powder that uses melamine as a nitrogen-doping source with Fe2+ ions as catalytic growth agents. We showed that milk powder could be used as a precursor for large-scale N-MLG synthesis through heat treatment at 1000 °C under N2 atmosphere for 45–120 min. In addition, heating time has a remarkable effect on N content and type in N-MLG. The resulting N-MLG exhibited higher catalytic activity than undoped graphene and carbon nanotubes (CNTs), as well as comparable catalytic activity to commercial Pt/C catalyst toward oxygen reduction reaction (ORR). Furthermore, the catalytic activity was sensitive to N content and type, particularly the ratio of pyridinic-N to total N atoms. Results showed that Fe atoms in N-MLG were found to function not as synergetic catalysts for ORR but as catalytic growth agents for N-MLG formation, thereby promoting and stabilizing N atoms. The present method could lead to the synthesis of bulk amounts of N-MLG, which is promising for applications in electrochemical energy devices, such as fuel cells and metal–air batteries.