Effect of pore characteristics on electrochemical capacitance of activated carbons

Abstract

Activated carbons (ACs) for electric double layer capacitors (EDLCs) were fabricated from waste tea leaves, activated with the pore-forming substances ZnCl2 then, carbonized at high-temperature in N2 atmosphere. The surface texture and porosity of the ACs were determined using transmission electron micros-copy and N2 adsorption/desorption studies. The surface area of the 20 wt % ZnCl2 treated sample was found to be 1029 m2g−1 and had a distribution of micropores and mesopores. The electrochemical properties of the ACs were evaluated by using cyclic voltammetry and galvanostatic charge-discharge studies. ACs from waste tea leaves exhibited excellent specific capacitance as high as 196 F g−1 in the 0.1 M Na2SO4 neutral electrolyte, with rectangular-like cyclic voltammetry curves at a cell potential of 1.5 V and good cyclability with a capacitance retention of 95% at a high current density of 100 mA g−1 for 2000 cycles. The results show that the pore texture properties and specific surface area of ACs are dominated by changing carbonization temperature and the amount of activating agent ZnCl2. The electrochemical performance is influenced mainly by surface area, but the pore size distribution becomes a dominating factor for specific capacitance of a carbon electrode material when the pore structure is in range of micropores/mesopores.