| Electrode material is a key factor for improving supercapacitors performance. Asmall resistance of electrolyte ion diffusion in the electrode material is necessary tohigher power output. Upto now, porous carbon is the best one among the carbonelectrode materials in practical utility. How to realize the optimal electrochemicalpropereis of the porous carbon is a great challenge for the researchers. The work aimsto design and prepare a sort of porous carbon with needle-like mesoporous structureand high conductivity, and then a composite consisting of the porous carbon andmetallic oxide, and subsequently construct a supercapacitor system with high specificenergy and high specific power. Electrolyte ions transfer in such a straight mesopores,the ion diffusion resistance is really low. As a result, the porous carbon will show anexcellent rate performance. In this work, porous carbons were prepared from differentcarbon precursors by needle-like Mg(OH)2/MgO (MgO is the product of the Mg(OH)2pyrolysis) templates. Some testing techniques, such as N2adsorption, X-ray diffraction,Transmission electron microscope (TEM), cyclic voltammetry (CV) and galvanostaticcharge/discharge, were used to characterize the structure and property of theexperiment samples. The effect of manufacturing parameters on the characteristics ofthose samples, such as pore structure and morphology, were studied in detail, and therelation between the structure characteristics and the capacitive capability was alsoinvestigated.Firstly, mesoporous carbon was prepared from soluble starch. The highest valueof total pore volume is3.5cm3g-1, in which80%is mesopore volume. Carbonizationtechnics affect the structure and electrochemical property greatly. The prepared carbonmaterials shows a relative high specific capacitance and an excellent rate capability.Specific capacitance normalized by specific surface area and pore diameter show alogarithmic relationship. With the pore diameter increasing, the specific capacitancenormalized by specific surface area increases quickly in the range of5-12nm, thenapproaches a constant value gradually. It is found that a graphite-like domain can beformed in the porous carbon due to the presence of needle like template, and amechanism that the needle-like template act as a director reagent is proposed. Then, in order to obtain a higher specific capacitance, porous carbons with largemicropores and abundant mesopores were prepared from resorcinol/formaldehyde-based organic aquagel and coal tar pitch. Due to the needle like template, largemicropores are formed in the inner of the basic carbon particles, resulting in that theprepared porous carbon shows a large specific surface area. Those micropores and themesopores remained after removing template in the porous carbon might form acolumnar cactus-like pore texture, which is favorable to improve the utilization ratio ofthe miropores under a high charge/discharge current. Through small amounts of NaOHactivation, the specific surface area of the porous carbon increased greatly, resulting ina great improvement of the capacitance. In6M KOH solution, the porous carbon madefrom coal tar pitch oxidized with nitricacid/vitriol shows a highest specific capacitanceof282F g-1, which could be retained65%under a current density of50A g-1.Further, mesoporous carbon/MnO2composite was prepared by the method thatcarbon reduces potassium permanganate directly. Amorphous MnO2is loaded in thepore inner of mesoporous carbon, and the composite shows a porous characteristic.The basic feature of pore size distribution of the composite is similar as that of themesoporous carbon. Carbon acts as the conductive framework, thus the compositeshows a more better rate capability than powder MnO2. An asymmetric aqueoussupercapacitor system is constructed by the carbon/MnO2composite as anode materialand the porous carbon with high capacitance as cathode material, and shows a highspecific energy and high specific power characteristic. |
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