Self-propagating synthesis of nitrogen-doped graphene as supercapacitor electrode materials

Doping heteroatoms into graphene is effective to open the energy bandgap and increase the free carrier density, thereby improving its electronic and electrochemical properties. In this paper, CO was selected as the carbon source for the preparation of graphene through the self-propagating reaction. During the reaction, a variety of hexamethyltetramine were used to dope N atoms into the graphene when different ratios of MgO/Mg were compared. Microstructural and electrochemical characterizations were conducted to study the effects of nitrogen doping as well as MgO/Mg ratio on the performance of the graphene as supercapacitor electrode. The Raman spectra show the presence of graphene after self-propagating reaction. The graphene doped from hexamethyltetramine shows the existence of pyridinic-N, pyrrolic-N, and graphitic-N. In general, the percentages of pyridinic-N in the materials increased with the usage of hexamethyltetramine. Given the same condition, the pyridinic-N content of the samples based on MgO/Mg ratio of 8 was higher than that of the samples using MgO/Mg ratio of 4. Besides, the specific surface areas of the samples increase as MgO/Mg increased. The introduction of nitrogen atoms in the graphene increased the active sites on its surface and consequently, the specific capacity, capacity retention rate and energy density of the supercapacitor. At the current density of 1Ag −1 , the specific capacity of N-SHS-8-3 was 153 Fg −1 and the capacity retention rate was 60% as the current density increased to 20Ag −1 .