Supercapacitors Prepared from Melamine-Based Carbon

Abstract

The electrochemical performance of supercapacitors made of a carbon material with a moderate amount of nitrogen atoms embedded in a carbon matrix is reported. Melamine was polymerized in the interlayer spaces of mica and afterward carbonized at various temperatures between 650 and 1000 °C. Elemental analysis and an XPS study showed that the nitrogen content of samples stabilized at 250 °C for 4 h prior to carbonization was generally higher if compared to their nonstabilized counterparts and that the nitrogen species were located preferably at the edges of graphene sheets. To understand the relationship between the capacitive performance and the porosity of stabilized and nonstabilized samples, the nitrogen adsorption/desorption method was also employed. Supercapacitors with the electrodes manufactured from these carbon materials showed a very good capacitive performance in 1 M sulfuric acid. The maximum gravimetric specific capacitance of 204.8 F g-1 was obtained from a sample carbonized at 750 °C. Specific capacitances per surface area were also calculated, and, as a result, the stabilized samples provided higher values than the nonstabilized samples, for example, 3.66 F m-2 for a sample stabilized and carbonized at 1000 °C. We associate the high values of capacitances in sulfuric acid with the pseudocapacitance that originates from an interaction between the nitrogen species and the protons of the electrolyte. This claim was verified by another measurement, where a neutral electrolyte (3 M NaCl) was used instead of sulfuric acid. We observed a decrease in capacitance with the surface area, and the values of capacitances per surface area were close to the values for activated carbons. Thus, the capacitance in NaCl can be attributed to the electrostatic interaction of ions on the double-layer rather than the pseudocapacitive interaction.