Effect of porosity and crystallinity of activated carbons for electrochemical capacitors

Abstract

Activated carbons (ACs) are usually utilized for the electrochemical capacitor due to their inherent properties, such as large surface area, high chemical stability, and good electrical conductivity. In this study, the commercial and chemically activated ACs with various surface areas were prepared and evaluated for their capacitance. The capacitances were generally increased as increasing the surface areas, but the highest surface area always did not lead to the highest capacitance. The Brunauer–Emmett–Teller specific surface area of chemically activated coconut-ACs (2,209 m ^2 /g) was lower than chemically activated wood-ACs (2,903 m ^2 /g), but the capacitance was higher. It was found that the major factor for the capacitance was not only the surface area, but also the electrical conductivity. The electrical conductivity is usually associated with crystallinity, which is represented by the nanographitic domain size and crystalline thickness along the c -axis (L _c ). The crystalline structure enhances the electron mobility, increasing the capacitance. The conductivities of prepared ACs were measured at different pressures, and their crystalline structure was confirmed by Raman spectroscopy and x-ray diffraction.

Keywords

• activated carbon
• supercapacitor
• electrochemical capacitor
• capacitance
• conductivity
• crystallization