Preparation And Electrochemical Properties Of The Carbon-based Composite Electrode Materials For Supercapacitor

With the depletion of fossil energy,and the increased environmental pollution caused by burning of fossil fuels,people are hoping to find a renewable,clean energy instead of fossil fuels to meet the needs of future human social and economic development.Energy storage,as a clean,efficient and practical intermediate step,has attracted much attention from the majority of researchers.Current common energy storage device are batteries and super-capacitors.Supercapacitor(SC)has much higher specific energy density than normal capacitor and greater power density than the battery,and with long cycle life,wide temperature range,and safety.In recent years,supercapacitors have a wide applications range in aerospace,aviation,information,communication,defense and other fields.To date,there are three types of supercapacitor electrode materials including carbon materials,metal oxides and conducting polymers.Electrode materials as the main factor to determine the performance of supercapacitor got more and more attention.A Ni-Al layered double hydroxides(LDH),mutil-wall carbon nanotubes(CNT)and reduced graphene oxide sheets(GNS)ternary nanocomposite electrode material has been developed by a facile one-step ethanol solvothermal method.The obtained LDH/CNT/GNS composite displayed a three-dimensional(3D)architecture with flower-like Ni-Al LDH/CNT nanocrystallites gradually self-assembled on GNS nanosheets.GNS was used as building blocks to construct 3D nanostructure,and the LDH/CNT nanoflowers in turn separated the two-dimensional(2D)GNS sheets which preserved the high surface area of GNSs.Furthermore,the generated porous networks with small mesopores and narrow pore size distribution in the LDH/CNT/GNS composite were also demonstrated by the N2-adsorption/desorption experiment.Such morphology would be favorable to the Faradaic redox reaction and mass transfer of the electrode.As supercapacitor electrode material,the LDH/CNT/GNS hybrid exhibited excellent electrochemical performance,including ultrahigh specific capacitance(1562 F/g at 5 mA/cm2)and excellent rate capability,good charge-discharge stability and long-term cycling life,which could be applied in energy storage/conversion devices.Carbon Nanotube/Fe3O4(CNT/Fe3O4)nanocomposite with well-dispersed Fe3O4 nano-cubes inlaid on the surfaces of carbon nanotubes,was synthesized through an easy and efficient hydrothermal method.The electrochemical behaviors of the nanocomposite were analyzed by cyclic voltammetry(CV),electrochemical impedance spectroscopy(EIS)and chronopotentiometry in 6 M KOH electrolyte.Results demonstrated that CNT as the supporting material could significantly improve the supercapacitor performance of the CNT/Fe3O4 composite.Comparing with pure Fe3O4,the resulting composite exhibited improved specific capacitances of 119 F/g at 10 mA/cm2(3 times than that of pure Fe3O4),excellent cyclic stability.The much improved electrochemical performances could be attributed to the good conductivity of CNTs as well as the anchored Fe3O4 particles on the CNTs.The GNS/SnO2 composites were synthesized using stannous chloride to restore the semi-reduction GO(SRGO)under a simple hydrothermal reduction procedure.First GO was pre-reduced by glucose for a certain time to get SRGO,which keeps the good water-solubility of GO and has numbers of functional groups.The higher electrostatic attraction makes Sn2+ions adsorbed on the the functional groups of SRGO and finally turn to SnO2 in the hydrothermal reduction process.The SEM and TEM tests showed SnO2 nanoparticles tightly anchor on the graphene sheets.What's more,GNS/SnO2 composites showed excellent supercapacitor performances:the specific capacitance reached 368 F/g at a current density of 5 mA/cm2,the highest energy density was 184 Wh/kg,and capacity retention was more than 95%after cycling 500 cycles with a constant current density of 50 mA/cm2.The experimental results and the thorough analysis described in this work not only provide a potential electrode material for supercapacitors but also give us a new way to solve the reunification of the graphene sheets.Reduced Graphene Oxide/Zn-Al Layerd Double Hydroxide(GNS/Zn-Al LDH)multilayer films were fabricated through an electrochemical technology.X-ray diffraction(XRD),scanning electron microscopy(SEM)and atomic force microscopy(AFM)were used to characterize the microstructures of the films.Results showed that this method was a feasible way to construct multilayer films.The electrochemical test was studied with assembly supercapacitor in 1 mol/L KOH electrolyte.The GNS/Zn-Al LDH multilayer films presented excellent cycling performance with a specific capacitor of 178 F/g at a scan rate of 5 mV/s.The testing results showed a potential supercapacitor electrode material.