Synthesis and characterization of nitrogen-doped 3D graphene foam prepared by inductively-coupled plasma-assisted chemical vapor deposition

In this work, we developed a new CVD process for the direct synthesis of N-doped graphene based on thermal CVD with inductively-coupled plasma (ICP) assistance using pure nitrogen (N₂) gas source. 3D N-doped graphene foam (GP foam) was fabricated by CVD with ICP on Ni foam using acetylene (C₂H₂) carbon source and hydrogen (H₂) gas carrier at 700-1000°C. The effects of various synthesis parameters including N₂/C₂H₂/H₂ gas flow ratio, ICP power, pressure, temperature and time on N-doped graphene structure have been systematically studied. Ni foam template was then etched in 3M HCl for an hour before subsequent characterizations by Raman spectroscopy, X-ray photoemission spectroscopy (XPS) and scanning/transmission electron microscopy (SEM/TEM). An optimal condition for high-quality N-doped graphene foam structure was found to be N₂/C₂H₂/H₂ of 7/4/84, ICP power of 200 W, pressure of 0.7 Tor, temperature of 900°C and time of 1 minute. Rama spectra exhibited dominant 2D and G peaks with low D peak and notable D´ peak at 1624 cm^-1, indicating successful N-doping of few-layer graphene structure. The presence of N atoms and N-doping concentration in graphene was confirmed by XPS. SEM/TEM data confirm that the structures are nanometer-thick N-doped 3D graphene structure with good crystallinity. Therefore, the CVD with ICP process is a new promising method for direct synthesis of N-doped graphene due to advantages including the use of non-toxic nitrogen source, high crystallinity of produced N-doped graphene structure and well controlled N-doping process.