Preparation And Characterizations Of Biomass Activated Carbon As Supercapacitor Electrodes

Electrochemical supercapacitor is a new kind of energy storage system betweenconventional capacitors and rechargeable batteries. Duo to their characteristics of longcycle life, higher power density and fast charge-discharge rate capability, they havebeen widely used in electric vehicles, consumer electronics and storage fields.However, its main drawback is the high cost of the electrode material. The structuralcharacteristics of the electrode material affect the electrochemical performance of thecapacitor. In recent years, optimizing of the electrode material to improveperformance capacitance supercapacitors becomes a concerned issue in this direction.In this dissertation, the electrode materials with excellent electrochemical properties areobtained through carbonization and activation method by using the cheap biomass asraw material. The major research results are listed as following:Rice husks were converted into activated carbon by KOH activation, attemperatures between400and900℃and used in a two-electrode supercapacitor.The rice husks contain SiO2nano-crystals surrounded by an amorphous carbon matrix.The activated carbons maintained their size and shape after the synthesis process andthe ordering degree of carbon increased at elevated temperatures. The highest BETsurface area of the activated carbons was around3145m2g-1. Electrochemicalproperties of the studied samples were measured using a two electrode cell in6MKOH and1.5M tetraethylammonium tetrafluoroborate in acetonitrile. The materialsynthesized at800℃showed the highest gravimetric capacitance performance of367F g-1and174F g-1in aqueous and organic electrolytes, respectively. In contrast tothe commercial activated carbons, rice husk activated carbon, this material showedexcellent high-power handling ability and electrochemical cycle performance, after 30000cycles the capacitive value almost remained unchanged.Series of nanoporous carbons are prepared from sunflower seed shell (SSS) bycarbonization-activation process and used as electrode material for electrochemicaldouble-layer capacitor (EDLC). The surface area and porestructure of the nanoporouscarbons are characterized intensively using N2adsorption technique. The results showthat the pore-structure of the carbons is closely related to the activation temperatureand dosage of ZnCl2. Electrochemical measurements show that the carbons made at650℃activation temperature and at the ratio of1:2with ZnCl2have bettercapacitive behavior and higher capacitance retention ratio at high drain current. Thematerial synthesized at650℃showed the highest gravimetric capacitanceperformance of226F g-1in aqueous electrolytes. More importantly, the capacitiveperformances of these carbons are much better than ordered mesoporous carbons andcommercial wood based active carbon, thus highlighting the success of preparing highperformance electrode material for EDLC from SSS.