Preparation Of Cyclodextrin-derived Multi-heteroatom Doped Carbon And Poly Aniline Composites For Supercapacitors

The combustion of fossil fuels causes environmental pollution and fossil fuels are non-renewable resources.Massive use of fossil fuels results in energy shortage.It is urgent to find clean and alternative new energy sources.In the development of renewable energy,the fluctuation of power generation and the limitation of natural conditions affect its development.Research and development of high performance energy storage materials is of great significance to solve the energy shortage problem.Among various energy storage devices,supercapacitors(SCs)and batteries are the most promising devices.Batteries have high energy density,but their development is limited by the low power density and poor reversibility.SCs have attracted wide attention due to their advantages of high power density,good reversibility and fast charging and discharging.They have been widely used in trams and trolleys.However,due to their low energy density,improving its energy density is still the key to our research.In this paper,?-cyclodextrin(?-CD)was used as precursor.Methylene blue(MB)and methyl orange(MO)were used as nitrogen and sulfur sources.Multi-heteroatom doping materials(CDC+MB/MO)were obtained by simple physical mixing,and polyaniline(PANI)was deposited on CDC+MB to get composites,which was used in SCs.The main work of this paper is as follows:(1)CDC was obtained by carbonization and activation of environmentally friendly biomass ?-CD.The hydrothermal temperature(T=180?,200? and 220?)and alkali-carbon ratio(M=1:1,2:1 and 3:1)were preliminarily screened by morphological and structural characterization.CDC-200(CDC-2:1)had the best spherical morphology and graphitization degree(IF/ID=0.83),so hydrothermal temperature(200?)and alkali-carbon ratio(2:1)were chosen as the optimum conditions.And multi-heteroatom doping was operated by a simple physical mixing of using CDC of the best condition to adsorb MB/MO,and then excess MB/MO were washed to get CDC+MB/MO.And a series of characterization were made.CDC+MB/MO(IG/ID=0.89 and 0.88)had higher graphitization degree than CDC.The nitrogen content(1.51%and 1.37%)and sulfur content(0.94%and 0.82%)of CDC+MB/MO and pore size distribution were known.A series of characterizations showed that MB and MO were doped by a special adsorption layer formed on the surface of CDC.(2)The effect of hydrothermal temperature and alkali-carbon ratio on the capacitance performance of CDC were investigated in three-electrode system.The results showed that the optimal conditions were 200? and 2:1,which were consistent with the characterization results.The conclusion was further validated by the test in the two-electrode system.In this condition,the influence of acidity and alkalinity of electrolyte(6 M KOH,0.5 M Na2SO4 and 1 M H2SO4)on the capacitance performance of CDC was investigated,and the subsequent experiments were carried out in 1 M H2SO4.The optimum capacitance and energy density of CDC were 328.6 F·g-1 and 7.81 Wh·kg-1,respectively.CDC showed good adsorption properties for MB and MO,with the maximum adsorption capacity of 495 and 363.4 mg·g-1,respectively.The electrochemical properties of CDC+MB and CDC+MO were tested in three-electrode and two-electrode systems.At the current density of 0.1 A·g-1,the maximum specific capacitance of CDC+MB and CDC+MO were 419.9 and 449 F·g-1,respectively.Compared with CDC+MO,CDC+MB had a higher energy density of 8.34 Wh·kg-1,which was slightly higher than that of CDC,but it was still not satisfied with practical application.(3)The material CDC+MB+PANI was obtained by electrodeposition of PANI onto CDC+MB.Scanning electron microscopy(SEM)proved that there were substances deposited on the surface of CDC.By comparing with pure PANI,the synthesized substance was proved to be PANI by the FTIR and Raman spectra.And then the electrochemical properties of CDC+MB+PANI were investigated.In the three-electrode system,CDC+MB+PANI had a high specific capacitance,reaching 557 F·g-1 in 1 M H2SO4 aqueous solution in 0.1 A·g-1.It had excellent rate performance.In the two-electrode system,it had a high energy density of 30.33 Wh·kg-1 in the wide voltage range of 0 to 1.4 V.Compared with the unmodified CDC,the energy density of CDC+MB+PANI increased by 3.88 times,the power density increased by 1.4 times and the capacitance increased by 69.6%.This work can make use of the adsorbed wasted materials to save resources.The competitive electrode materials were obtained by simple operation of electrodeposition to get PANI composites.This method provides a new idea for the synthesis of SCs electrode materials.