Preparation And Performance Test Of Carbon Microspheres With Starch As Carbon Source

Because of good conductive, thermal conductivity, chemical stability, large specific surface area and developed pore structure characteristic, hollow carbon spheres are used as electrode materials for supercapacitors, adsorbent materials and catalyst carrier, But the synthesis method is the template method, while the process is complex, So developing a new and simple process to prepare the hollow carbon spheres and to investigate the supercapacitor performance of the materials.Pretreatment of starch with potassium carbonate/potassium bicarbonate solution as carbon source, the hollow carbon microspheres were acquired by carbonation. The influence factors in the formation of hollow carbon microsphere were detailed studied. Results showed that the formation of hollow carbon microspheres were influenced by pH values of pretreatment, concentration of potassium carbonate/potassium bicarbonate, heating rate and carbonization temperature. At the same time, the formation mechanism of hollow carbon microspheres were discussed in this paper, potassium carbonate/potassium bicarbonate in the carbonization process can hinder starch gelatinized and maintain the spherical morphology of starch granules. Meanwhile, the water vapour and carbon dioxide within starch particles formed in situ template during the carbonization, thereby the hollow structure of the carbon spheres were formed.The hollow carbon microspheres for electrode materials of supercapacitor were studied. The microstructure, pore structure and activity of functional groups of the hollow carbon microspheres were detailed studied. Then optimum experimental conditions were as follows:the concentration of starch is 3%, buffer solution concentration is 0.5 mol L-1, alkaline system (pH=9-12), the reaction time is 15 h, the heating rate is 1 ℃ min-1, carbonization temperature is 800 ℃ and holding time is 10 h. The morphology of hollow carbon microspheres is easy to control and the average particle size is 7.55 μm with thickness of 2.55 μm. The sample exhibits large specific surface area of 517.5 m2g-1 and pore volume of 0.265 cm3 g-1.Derived from the CV curves, a symmetrical supercapacitor of HCS-10 exhibits a maximum specific capacitance of 317 F g-1 at a slow scan rate of 5 mV s-1 and a high rate capacitance of 222.2 F g-1 at a fast scan rate of 300 mV s-1 with the potential window of 1.0 V by using 6 M KOH solution as the electrolyte. Galvanostatic charge-discharge displays a high capacitance of 265.4 F g-1 at 1 A g-1 and a high rate capacitance of 137.9 F g-1 even at a high current density of 100 A g-1.The high capacitance retention of 99.6% over 25000 charge/discharge cycles further confirms the cycling stability and rate performance with varied current densities of 1,2,5,10 and 1 Ag-1. Also, the presence of oxygen-containing groups broadens the working voltage up to 1.5 V. Notably, the highest power density of 100 kW kg-1 is achieved at current density of 100 A g-1 and working voltage of 1.0 V. Cycling tests deliver a compatible data at 1.4 V and 10 Ag-1, a high capacitance of 286 F g-1 with a high energy density of 77.88 Wh kg-1 and a large power density of 14 kW kg-1. The excellent supercapacitive performances of HCS-10 will possibly fit the growing demands for the energy storage devices.