N-doped hierarchically micro- and mesoporous carbons with superior performance in supercapacitors

Highlights: • N-Doped Hierarchically Micro- and Mesoporous Carbons were prepared through hard template method and chemical activation. • The surface area is up to 3056 m² g⁻¹. • Superior capacitive performance (417 F g⁻¹ at a current density of 0.5 A g⁻¹) was obtained. A series of N-doped carbons with hierarchically micro- and mesoporous structure were prepared by using silica nanoparticles as the template, ethylenediamine (EDA) and CCl₄ as carbon and nitrogen sources, and potassium hydroxide (KOH) as the activation agent. The obtained carbons were characterized with N₂ adsorption, transmission electronic microscope (TEM), X-ray photoelectron spectroscopy (XPS), elemental analysis as well as electrochemical methods. It was found that the nitrogen-doped carbon (NC) without being activated shows lower capacitive performance due to the low surface area (287 m² g⁻¹) while the carbon activated at 800 °C (NC800) shows the best capacitive performance and the capacitance can reach up to 417 F g⁻¹ at a current density of 0.5 A g⁻¹ due to the ultra-high surface area (3056 m² g⁻¹), large mesopores (∼3 nm) and the proper nitrogen content. The large surface area is beneficial to the double-layer capacitance while the nitrogen content attributes to the pseudocapacitance. The larger mesopores and micropores are in favor of the decrease of mass transfer resistance. After 5000 cycles at a current density of 3 A g⁻¹, the capacitance of NC800 can still maintain 97.6% of original capacitance. The energy density can reach up to 11.2 Wh Kg⁻¹ at the power density of 125.1 W kg⁻¹.