Study On The Single-mode Microwave Assisted Synthesis And Properties Of Carbon Aerogel For Supercapacitor Electrode Materials

The supercapacitor(electrochemical capacitors or electric double layer capacitor)is a novel energy storage device between battery and capacitor, which have the advantages of both. Because of their high power density, high-capacity, fast charge-discharge rate, long cycle life,economic environment, supercapacitors have been applied in many fields, such as telecommunications, national defense technology,public transportation. The electrode material is the core factor influencing the performance of supercapacitor. Thus, development of high-performing electrode materials become the focus of research of supercapacitor. In this paper, synthesis and electrochemical performance of carbon aerogels and PANI/CA composite electrodes are studied. For the shortcomings of the long synthetic cycle of CA, low capacitance of carbon materials, poor cycle life of conductive polymer, we took a systematic study aiming at improving the synthesis efficiency and the electrochemical performance of electrode materials.Single-mode microwave synthesis instrument can greatly shorten the reaction time of sol-gel reaction. It needs more than 7 days to prepare organogel by traditional heating method, but useing microwave radiation only requires 40 minutes. Carbon aerogels were prepared from resorcinol and formaldehyde, using Na OH as catalyst,via sol-gel process, high temperature carbonization and atmospheric pressure drying technology with solvent replacement.The concentration of reactants and microwave irradiation time are two critical factors affecting the performance of aerogels. SEM and XRD test showed that reagent concentration of resorcinol-formaldehyde has a great influence to the morphology of samples. When the reactant concentration increased from 25 w.t.% to 30 w.t% and 40 w.t.%, 3D network construction with microspheres change to blocky structural,causing the reduction of porosity and local micro crystallites. The optimum performance appeared when the mass concentration of the reactant was 25% and the microwave irradiation time was 40 min, the specific capacitance equal to 91.76 F/g at the current of 3 m A.Aging organogel with trifluoroacetic acid(TFA) helps to improve network strength of the carbon aerogel and prevent the collapse of pore structure in the carbonization process. The particle size of carbon aerogels diminish after aging by TFA. When Vacetone:VTFA=97:3, the specific capacitance of the carbon aerogel equal to111.74 F/g at 3 m A, 21.8% higher than the CA without pickling aging. After 1000 times cycle, the specific capacitance attenuation rate of only 0.49%.Adding appropriate amount of PEG in the so-gel process can effectively increase the specific surface area and pore volume of the micro/ mesoporous. When putting1 w.t.% PEG into the precursor solution, the SBET of the material increased from 596m2/g to 1030 m2/g. Electrochemical tests demonstrate that the sample with 0.5 w.t.%PEG in the precursor solution exhibits the best electrochemical performance. The average specific capacitance is as high as 136.08 F/g at 3 m A in 6 mol/L KOH electrolyte, 48.3% higher than the CA without PEG modified. After 1000 times cycle,the decay rate of the specific capacitance is just 0.5%.At 800?,using potassium hydroxide as activator,we prepared carbon aerogel with high specific surface area and outstanding electrochemical properties. When mKOH:mCA=1:3, through grinding at room temperature and then activating at 800?for 2 hours, the specific capacitance of the carbon aerogel can reach 162.95 F/g at the current of 3 m A. It is 77.6% higher than the CA without activation by KOH and24.7% more than the sample which activated by means of immersing in potassium hydroxide solution. After 1000 times cycle, the decay rate of the specific capacitance of it is only 0.6%.This paper describes the synthesis of polyaniline doping with 1 M HCl by chemical oxidizing process. PANI/CA as a composite is simply prepared by chemicalin-situ polymerization. XRD and electrochemical measurement shows that adding a spot of CA can improve the degree of order and electrochemical property of polyaniline. When mCA:mAn=1%, the composite electrode material PANI/CA2 exhibits preferable electrochemical properties and the average capacitance is as high as 471.42F/g, 17.5% higher than the PANI(Cm=388.84 F/g). After charge and discharge 100 times under a constant current of 3 m A, the specific capacitance decay of PANI/CA is1.7% while the pure PANI is 3.5%.