Hierarchical porous nitrogen doping activated carbon with high performance for supercapacitor electrodes

Abstract

Hierarchical porous nitrogen doping activated carbon materials were designed and prepared by carbonization of electrospun composite carbon nanofibers and subsequent chemical activation. The porous carbons were activated by potassium hydroxide (KOH) and the optimal activation weight ratio for carbons was investigated for this process. It is found that activation weight ratios played an important role on the porous structures and capacitive properties. The morphology, pore structure and surface physicochemical properties of the carbon samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption/desorption isotherm analysis. The sample with the activation weight ratio of 4 possessed a large 2217 m² g⁻¹ specific surface area and held a high 1.443 cm³ g⁻¹ volume value as well as a hierarchical porous structure. A symmetrical supercapacitor was fabricated using 6 mol L⁻¹ KOH as the electrolyte and the electrochemical properties were evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), galvanostatic charge–discharge (GCD) and life cycle measurements. The results indicate that the sample with an activation weight ratio of 4 obtained high specific capacitances of 255, 238, 230, 215 and 198 F g⁻¹ at the current densities of 0.2, 0.5, 1.0, 5.0 and 10 A g⁻¹, respectively. Furthermore, the sample materials presented good cycling behavior with respect to the specific capacitance value, which hardly decreased during 8000 cycles. This is considerably promising for this type of porous material to be far-reaching applied in the field of electrode materials for supercapacitors.