Electrochemical Performance of Nitrogen-Enriched Carbons in Aqueous and Non-Aqueous Supercapacitors

Abstract

Carbon materials with significant nitrogen contents were investigated as the electrode materials of supercapacitors. The preparation procedure involved the polymerization of melamine in the interlayer space of template fluorine mica and carbonization at 750, 850, and 1000 °C. Some samples were also stabilized prior to carbonization. We have shown previously that these carbons possess very interesting capacitive behavior in an acidic medium despite small surface areas. High capacitance values in H 2 SO 4 were attributed to the pseudocapacitive interactions between the protons and nitrogen atoms. This paper further discusses the results obtained in a base and an aprotic electrolyte, KOH and TEABF 4 /PC, respectively. Electrochemical properties were evaluated with cycling voltammetry, a galvanostatic charge/discharge technique, and electrochemical impedance spectroscopy. High capacitance values were obtained in proton-free KOH, and the presence of pseudocapacitive interactions between the ions of the electrolyte and the nitrogen atoms of the carbon matrix is proposed. Compared to those in sulfuric acid, greater capacitances of nonstabilized samples were obtained in KOH, i.e., for the sample carbonized at 1000 °C, the capacitance was 84.61 F/g in KOH vs 47.92 F/g in H 2 SO 4 . On the other hand, less porous but more nitrogen-rich stabilized samples gave better performances in H 2 SO 4, i.e., 62.24 F/g in H 2 SO 4 compared to 49.86 F/g in KOH for the sample stabilized and carbonized at 1000 °C. The sample heat-treated at 750 °C with a surface area of ca. 400 m 2 /g performs similarly in both electrolytes, i.e., ∼200 F/g. Significantly lower gravimetric capacitances were obtained in TEABF 4 /PC from the samples carbonized at 750 °C. On the other hand, the almost nonporous sample subjected to stabilization prior to carbonization at 1000 °C gave a capacitance of ∼20 F/g. Hence, we suggest that the faradaic interactions between the carbon electrode material and the electrolyte, although much less significant than those in H 2 SO 4 and KOH, play an important role in the nonaqueous electrolyte as well. Narrow micropores were detected by CO 2 adsorption/desorption, and their importance to the interpretation of capacitive behavior is also discussed.