Effect Of Activating Agents For Producing Activated Carbon For Supercapacitors
Activated carbon with large specific surface area and high porisity has been widely applied as the energy storage material for supercapacitors. The low-cost property is one of the most promising advantages for applying activated carbon on the commercial energy storage devices since activated carbon can be produced using the waste biomass. The activating agent is considered to be the most important factor for producing efficient activated carbon, since activation is the key process for determining the amount of acitve sites and pore structures for activated carton. However, the effect of the activating agent on physical and electrochemical features of activated carbon has never been carefully discussed in previous literatures. In this work, six acitvating agents of KOH, NaOH, HCl, H3PO4, ZnCl2 and FeCl3 are applied for producing activated carbon using the cost-free waste coffee grounds. The functional groups, the ratio of defect to graphene, and the surface area as well as the pore structure for the activated carbon produced using different activating agents are carefully investigated. The KOH-activated carbon electrode shows the highest specific capacitance of 105.3 F/g, which is five-fold of the specific capacitance for the commercial activated carbon electrode (21.8 F/g), owing to the less hydrophobic functional groups, the moderate defect to graphene ratio, and the largest specific surface area as well as the high porisity for the homemade KOH-activated carbon. The symmetric supercapacitor composed of the KOH-activated carbon electrode shows a specific capacitance of 19.28 F/g and the maximun energy density of 6.94 Wh/kg at the power density of 350 W/kg. The specific capacitance retention of 133% and the Coulombic efficiency of higher than 80% are also achieved for the homemade activated carbon-based symmetric supercapacitor in the 8000 times charging/discharging process.
Keyword; Activating Agent; Energy Density; Waste Coffee Grounds; Surface Area; Symmetric Supercapacitor