Preparation And Properties Analysis Of Biomass Carbon Electrodes

As a new type of green energy storage device,supercapacitors not only have the advantages of conventional capacitors and electrochemical batteries,but also exhibit the characteristics of long cycle life and fast charging/discharging rate,and thus show a great prospect in modern energy storage devices.Due to their high specific surface area,good chemical stability and relatively low cost,the carbon materials have been widely studied as the most commonly used electrode materials for supercapacitors.The renewable biomass is an ideal raw material for the preparation of carbon materials because of its abundant storage,low price and easy obtainment.In this dissertation,the porous carbon materials were prepared from common biomass wastes,such as corn straw and phoenix tree leaves,and then they were decorated by gold nanoparticles to serve as electrode materials for supercapacitors.The morphologies,crystal structures and distributions of pore size of the fabricated materials were characterized by X-ray diffractometer（XRD）,X-ray photoelectron spectrometer（XPS）,scanning electron microscope（SEM）,transmission electron microscope（TEM）,specific surface area and porosity analyzer,and moreover,the electrochemical properties were investigated by cyclic voltammetry（CV）,galvanostatic charge-discharge（GCD）,electrochemical impedance spectroscopy（EIS）and cyclic performance measurements.The main contents and results of this work are summarized as follows:（1）The porous carbon materials were synthesized from the corn straw via a hydrothermal method combining with the KOH activation.The electrochemical properties of the porous carbon were evaluated in Li₂SO₄ electrolyte with different concentrations using a three-electrode testing system.It was shown that the porous carbon materials exhibited the enhanced electrochemical properties in the 0.5 mol L^-1 Li₂SO₄ electrolyte and the specific capacitance could reach 224 F g^-1 at a current density of 0.5 A g^-1.Moreover,the specific capacitance retention could still maintain 94.1%after 1500 charging/discharging cycles,indicating a good cycling characteristic.（2）The corn straw-based biomass porous carbon materials were decorated by gold nanoparticles via a simple in-situ reduction method,and a 3D honeycomb-like structure was observed in the fabricated composites,which could significantly improve their conductivities and electrochemical properties.It could be found that the composite had a high specific capacitance of 347 F g^-1 in 6 mol L^-1 KOH electrolyte and there was almost no decrease of specific capacitance after 4000 charging/discharging cycles,suggesting an excellent cycling stability.Moreover,a large energy density of 14.61 Wh kg^-11 was achieved at a power density of500.9 W kg^-1 via a two-electrode testing system.（3）The 3D honeycomb-like porous carbon composites（Au-PPC）with different gold-nanoparticle loads were synthesized from the phoenix tree leaves by an in-situ reduction method,and focusing on the effects of gold-nanoparticle load on the electrochemical performance.It was found that the Au-PPC-5 showed the best electrochemical properties and it had a high specific capacitance of 440 F g^-1 at a current density of 0.5 A g^-11 in 6 mol L^-1 KOH electrolyte,meanwhile a capacitance retention of 100%was achieved after 2000 cycles.The maximum energy densityof Au-PPC-5 was 19.47 Wh kg^-11 at the power density of 499.86 W kg^-1,which indicates it possessed an excellent electrochemical performance.