Controllable synthesis of nitrogen-doped mesoporous carbons for supercapacitor applications

Abstract

Nitrogen-doped mesoporous carbons (NMC) have been controllably synthesized through a solvent evaporation induced self-assembly (EISA) method, where a novel nitrogen-doped carbon precursor is used, followed by thermo-polymerization and pyrolysis of this precursor. In this precursor, dicyandiamide is covalently integrated into low-molecular weight and soluble phenolic resins. The configuration of nitrogen and the effects of nitrogen on the structure and porosity before and after KOH activation are deeply investigated for the obtained NMC. The nitrogen functional groups are found to facilitate the KOH activation process, especially when the aperture is suitable for molten KOH immersion, leading to the formation of much more micropores and mesopores on the surface of the carbons. As a result, a large specific surface area of 2828.8 m² g⁻¹ in activated NMC (A-NMC) is significantly greater than that of activated mesoporous carbon without nitrogen (1244.6 m² g⁻¹), and the mesoporous ratio in A-NMC is as high as 44.1%. Meanwhile, supercapacitor electrodes based on the obtained A-NMC exhibit a specific capacitance as high as 388 F g⁻¹ at the current density of 0.5 A g⁻¹, while only 213.6 F g⁻¹ is achieved by the nitrogen-free activated mesoporous carbons based electrode. Moreover, the A-NMC shows a good rate capability (70% of the capacitance retained at a high current density up to 50 A g⁻¹) and an excellent cycling stability (no capacitance loss over 5000 cycles). The method demonstrated in this work is hopeful to open up a new route of designing nitrogen-doped mesoporous carbons for supercapacitor applications with good rate capability and excellent cycling stability.