Preparation Of Activated Carbon Electrode Materials For High-performance Supercapacitor

Supercapacitor, a new class of electrical energy storage device with high power density, long cycle life, good stability and rapid charge/discharge rates etc., has attracted intense attention. The performances of supercapacitor are largely dependent on the properties and structures of the electrode materials. Compared with other kinds of electrode materials, carbon materials are one of the first application scope of electrode candidates for supercapacitor. Nitrogen-doped porous carbon materials have been found to cause an increase in electric conductivity and concurrently ameliorate surface wettability as well as adsorption properties that facilitate an electrochemical reaction on the carbon surface, thus improving the electrochemical performances of electrode materials, and have been proved to be intriguing electrode materials for supercapacitor. Hence, we have prepared porous activated carbons?ACs? through a simple chemical activation method using green, environmental protection and cheap carbon precursors as raw materials. The morphology, structure and electrochemical properties of the materials are characterized in detail. The main research contents and results are as follows:1. Cotton-based porous activated carbons?CACs? have been prepared through a simple chemical activation method using cotton fiber as carbon source and ZnCl₂ as activating agent. By optimizing the carbonization temperature and the amount of ZnCl₂ activating agent, a maximum specific surface area up to 2548.6 m2g-1for CAC2 sample was obtained when the cotton/ZnCl₂ mass ratio is 1:2 at the carbonization temperature of 900 ?. As an electrode material for supercapacitor, the CAC2 has high capacitive performance with a specific capacitance of 239 F g-1in 2M KOH aqueous electrolyte in three-electrode systems at a current density of 0.5 A g-1. Furthermore, the as-assembled CAC2//CAC2 symmetric supercapacitor device with an wide operation voltage of 0 to 1.8 V in 0.5 M Na₂SO₄ aqueous electrolyte delivers a high energy density of 13.75 Wh kg-1 and an excellent cycling performance?only 7% capacitance loss after 5000 cycles?.2. We report an effective synthetic route to prepare the nitrogen-doped rapeseed residues activated carbons?N-RCs? by ZnCl₂ activation method to improve the surface performances of materials. The resulting porous carbon N-RC2 exhibits ahigher specific surface area and larger pore volume when the rapeseed residues/ZnCl₂ mass ratio is 1:2. As an electrode material for supercapacitor, the N-RC2 electrode possesses a maximum capacitance of 250 F g-1 in 6 M KOH aqueous electrolyte in three-electrode systems. The as-assembled N-RC2//N-RC2 symmetric supercapacitor device with an wide operation voltage of 0 to 1.8 V in 0.5 M Na₂SO₄ aqueous electrolyte delivers a high energy density of 13.55 Wh kg-1. Furthermore, the asymmetric supercapacitor also exhibites a good cycling stability with 92.8% specific capacitance retained at a current density of 5 A g-1after 5000 cycles.3. Isolated soy protein as nitrogen precursor is used to prepare nitrogen-doped activated carbon materials?N-PACs? through high-temperature carbonization and activation with ZnCl₂. By optimizing the carbonization temperature and the amount of ZnCl₂ activating agent, the resulting carbon material?N-PAC-2? exhibits a loose and porous morphology. The N-PAC2 electrode possesses a maximum capacitance of 216 F g-1in 6 M KOH aqueous electrolyte in three-electrode systems. Furthermore, the as-assembled N-PAC-2//N-PAC-2 symmetric supercapacitor device with an wide operation voltage of 0 to 1.8 V in 0.5 M Na₂SO₄ aqueous electrolyte delivers a high energy density of 13.95 Wh kg-1, and the device retained about 93% of the initial capacitance after 5000 cycles, suggesting satisfactory cycling stability.