| Super-capacitor is a type of novel energy storage device whose capacity is almost 20~200 times of that of conventional capacitor, with excellent pulse discharging property, high capacity of energy-storage (>2.5 W?h?kg-1), high power (>500 W?kg-1),light weight, long cyclic life (>10,000), wide range of temperature (-40℃~60℃) and quick charge and discharge (<3 min) etc.. Super-capacitors have been widely used for the power supply of electric vehicles, internal combustion engines and other heavy vehicle engines'starting system for instantaneous large current power supply, solar cell auxiliary power, aerospace equipments with power supply, standby power supply and so on. Super-capacitors have broad market prospects, particularly in the environmental protection electric vehicle industry with great market potential, and have aroused widespread attention. Today, with the non-renewable oil resources and worsening environmental problems arising, it is very meaningful for the study on the preparation of super-capacitor electrode materials to produce high performance super-capacitors. Carbon micro-spheres have good chemical stability, thermal stability, and good electrical conductivity and thermal conductivity properties. It is a kind of new materials with broad prospects for application. The introduction of new methods for the synthesis of carbon micro-spheres with special structure, morphology and performance, and the choice of excellent raw materials for preparation of carbon micro-spheres have become hotspot in the research field of spherical materials. Starch is from the corn, cassava, potato, sweet potato, rice, wheat, and other plants, the major component of starch is polysaccharides with high carbon content. Starch is a renewable, environmentally friendly carbon source with low price and abundant source, particularly, it is the advantage resources of Guangxi province. Starch and Modified starch have a special texture. Porous starch (also known as micro starch) is a type of modified starch with special honeycomb pore structure, and it is the enzyme or acid hydrolysis product of degeneration. In this paper, starch and porous starch were used for the preparation of porous carbon electrode materials which have excellent electrochemical performance for super-capacitors, and hollow porous carbon micro-spheres which preserved the morphology and pore structure of porous starch. The genetic mechanism of the morphology of porous carbon spheres from porous starch was also discussed. The main contents of this paper are as follows:(1) Two original Starch (corn starch and cassava starch) and two modified starch (graft copolymer starch and cationic starch) were used as carbon source, after pre-carbonization, a KOH activation was utilized for the preparation of porous carbon materials used in electrochemical capacitor in accordance with alkali/carbon=2, the heating rate of 1℃/min, and being kept at 850℃for 1.5 h. We used the JSM-6460LV scanning electron microscopy (SEM) for the observation of the morphology of porous carbon materials; and Autosorb-6B surface area and pore Analyzer for the characterization of porous carbon material surface area and pore size distribution of pore structure parameters (gas adsorption N2), and the D/max2500v/pc X-ray diffractometer to test microcrystalline structure of porous carbon materials. Experimental two-electrode super-capacitor was assembled in the 30 wt% aqueous solution of KOH electrolyte to test cyclic voltammetry (CV) and EIS (EIS) with IM6-electrochemical workstation; battery tester was used to test charge and discharge performance (voltage range of 0.05 to 1.2 V). The experimental results showed that: using starch or modified starch as carbon source, porous carbon materials with large specific surface area (1330 to 1510 m2/g) can be prepared by activating their pre-carbonization product with KOH activation method. The porous carbon materials have plenty of micro-pores and meso-pores, and narrow pore size distribution (mainly distributed in the range of 1~ 3 and 5~ 6 nm), microcrystalline graphite was also formed. For these samples, cyclic voltammetry curves showed good capacitive characteristics of rectangular shape, particularly cationic starch porous carbon materials showed the best capacitive characteristics, it could maintain good rectangular shape even with the high scan rate of 100 mV/s. The results of ac impedance spectroscopy (EIS) showed that, for the four starch porous carbon electrode materials, the value of axis intercept along the real axis at high frequency was very small, they showed a good capacitive characteristics and power characteristics, and the results of ac impedance spectroscopy and cyclic voltammetry were in consistent with each other, the two results all showed that the capacitive performance of cationic starch porous carbon material was the best of the four starch porous carbon electrode materials; the specific capacitance of the four porous carbon materials exceeded more than 170 F/g at the current density of 0.37 A/g. The specific capacitance of cationic starch porous carbon material even reached up to 194 F/g, its capacitance could remain 94% of its initial value, up to 184 F/g even when the current density increased to 7.4 A/g; it showed the good performance of rate discharge. The electrochemical performance was good using starch porous carbon materials as super capacitor electrode materials.(2) Porous starch was prepared from corn starch; porous carbon micro-spheres were prepared using porous starch as carbon source, using Na2SnO3, Na2CO3 and Na2SiO3 as the coating agent, carbonized at 600℃for 3 h at a heating rate of 2℃/min in a inert atmosphere (Ar). Under the same conditions, porous carbon micro-spheres were prepared without coating for comparison; the genetic mechanisms of morphology and pore structure of the carbon micro-spheres were discussed. Using JSM-6460LV type scanning electron microscopy (SEM) and FEI Quanta FEG-200 field emission scanning electron microscopy observed the morphology of porous carbon samples. The elements of analysis of the coated porous starch were carried out using JENSIS60S type X-ray spectrometer; using D/max2500v/pc X-ray diffractometer and invia confocal laser microscopy-Raman spectrometer for the analysis of microcrystalline structure of the porous carbon micro-spheres. The experimental results show that, porous hollow carbon micro-spheres with unique morphology can be obtained from Na2SnO3 and Na2SiO3 coated porous starch. Porous carbon micro-spheres retained the morphology and pore-structure of the porous starch, and realized inheritance of morphology from porous starch to carbon micro-spheres. However, porous hollow carbon micro-spheres can not be obtained without coating or with Na2CO3 coating. The porous carbon micro-spheres were composed of amorphous carbon. The inorganic compounds like Na2SiO3 etc. can form polyhydroxy colloid in water; the colloid can form hydrogen bounds on the surface of porous starch, the coating agent can be adsorbed easily. There is plenty of hydrogen bounds on the surface of porous starch, a uniform protective layer can be formed on the surface of porous starch; the inorganic coating can strengthen the skeleton of porous starch, and keep the porous starch granules from destroying, so the inheritance of morphology and pore structure from porous starch to porous carbon micro-spheres can be realized.
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