Influence of reactivation on the electrochemical performances of activated carbon based on coconut shell

Coconut shell-based activated carbon (AC) were prepared by CO₂ activation, and then the ACs with higher mesopore ratio were obtained by steam activation and by impregnating iron catalyst followed by steam activation, respectively. The AC with the highest mesopore ratio (AC_hmr) shows superior capacitive behavior, power output and high-frequency performance in supercapacitors. The results should attribute to the connection of its wide micropores and mesopores larger than 3 nm, which is more favorable for fast ionic transportation. The pore size distribution exhibits that the mesopore ratios of the ACs are significantly increased by reactivation of steam or catalyst up to 75% and 78%, respectively. As evidenced by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic measurements, the AC_hmr shows superior capacitive behaviors, conductivity and performance of electrolytic ionic transportation. The response current densities are evidently enhanced through the cyclic voltammery test at 50 mV/sec scan rate. The electrochemical impedance spectroscopy demonstrates that the conductivity and ion transport performance of the ACs are improved. The specific capacitances of the ACs were increased from 140 to 240 F/g at 500 mA/g current density. The AC_hmr can provide much higher power density while still maintaining good energy density, and demonstrate excellent high-frequency performances. The pore structure and conductivity of the AC_hmr also improve the cycleability and self-discharge of supercapacitors. Such AC_hmr exhibits a great potential in supercapacitors, particularly for applications where high power output and good high-frequency capacitive performances are required.