| With the rapid development of portable and automotive equipments,many renewable and efficient energy-storage devices have attracted much attention.Supercapacitor,a new energy-storage device,has been widely applied in many fields due to its good energy storage and safety.There are two kinds of principles for different electrodes.One is double layer capacitor which is in the form of double-layer energy storage and the other one is the pseudocapacitor,also known as faraday capacitor,which produces redox reaction on the surface of electrode during charge/discharge process.It is important to choose the electrodes for supercapacitor.Based on the two principles,porous carbon electrode and carbon-based composite electrode are prepared in this paper,respectively,combining double-layer capacitance and pseudo-capacitance each other to achieve better electrochemical performance of supercapacitor.The precursor of carbon electrode selected in this paper is sodium alginate,a biomass polysaccharide extracted from brown algae,which has been widely used in many fields such as food,medicine and so on because of its environmental protection,cheap price and non-toxic properties.In the preparation of the electrode,the sodium alginate aerogel with self-supporting skeleton was prepared by one-step template method and the structure of the egg-shell was formed by the crosslinking of calcium chloride.This structure of the aerogel was stable after carbonization at high temperature.Calcium ions,acted as crosslinkers,is combined with nearby carbon and oxygen atoms to form calcium carbonate particles,which are coated inside the carbon materials.After removing it by acid etching method,the porous free-standing carbon electrode was obtained.What's more,sodium alginate is a kind of oxygen rich material and it still contains a large number of oxygen-functional groups after high temperature carbonization.These groups produce pseudocapacitance effect and enhance the electrochemical properties of the electrode.At the same time,this article explores the effect of the content of its oxygen-functional groups on the electrochemical performance by changing the carbonization temperature,and then we construct a porous oxygen-doping and free-standing carbon material with excellent ratio and energy storage properties,its specific capacitance reach 419.3 F g-1(0.5 A g-1 current density).The whole preparation is nontoxic,environmentally friendly,and the electrochemical performance is higher than the other researches.The capacitors based on the double-layer principle have excellent powder density,but the energy density is lower than that prepared by pseudo-capacitance effect.At the same time,thepreparation of free-standing capacitor has become a hot spot in rencent research.In this paper,a ternary composite of manganese hydroxide and polyaniline was prepared on the surface of buckypaper by two-step method using buckypaper as free-standing substrate.The MnOOH nanorods array enables the conductive polyaniline grows on the surface of MnOOH and buckypaper,respectively,which provides good conductive pathes for the whole electrode.Because of the porous structure of polyaniline,it would provides the active position for the intercalation/deintercalation of ions.The electrochemical performance of ternary electrode is much higher than that of the electrodes made of polyaniline or manganese hydroxide on the surface of buckypaper.Due to complementing and cooperating with three kinds of material,the he electrochemical performance of the electrode made of the ternary composites is much higher than that of the electrode made of polyaniline or manganese hydroxide grown on the surface of buckypaper.The specific capacitance reaches 567.5 F g-1. |
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