Biomass Waste-based Porous Carbonmaterials And The High Electrochemical Performance For Supercapacitor

Supercapacitors, also known as electrochemical capacitors or ultracapacitors are electrochemical storage devices whose range of energy and power densities can complement the function of batteries and conventional capacitors for storing and delivering energy. In recent years, supercapacitors have attracted more and more attention due to their high power density, fast charging/discharging rate, long cycle life, environmental benignity and simple principles. They are able to store and release energy within a very short period, being perfectly adapted for the quality of electricity required by energy efficient industrial equipment, electric and hybrid electric vehicles and smart-grid applications. To enhance the capacitance of electrochemical capacitors（ECs）, a typical strategy is to utilize carbon electrodes with large surface areas and appropriate pore-size distributions. Carbon materials that possess a porous structure with a large surface area, high conductivity, and long-term cycle ability are needed to achieve the stable and reversible electrical energy storage capacity and high energy storage ability for the applications of supercapacitor.Herein, the biomasswaste has been used as low-cost precursor to produce high performance porous carbon for supercapacitor. The biomasswaste was carbonized at mild conditions followed by activation with low amount of ZnCl₂ andFeCl₃ or direct carbonization. The prepared activated carbons were characterized to determine their pore texture, surface chemistry, and electrochemical characteristics. Results were compared with published findings for activated carbons prepared from other biomass residues and wastes. The main research contents and results are as follows:1.In this work, we present a facile approach to prepare nitrogen-doped porous carbon materials via one-step carbonizing biowaste soybean curd residue（SCR） as the biomass carbon precursor. The morphology, structure and textural properties of the carbon materials are investigated by field emission scanning electron microscopy, transmission electron microscopy, N2 sorption isotherms, and X-ray photoelectron spectroscopy, respectively. The SCR carbonized at 700 oC exhibits high charge storage capacity with a specific capacitance of 215 F g-1 at a current density of 0.5 Ag-1 and good stability over 5000 cycles. Moreover, the assembled symmetric supercapacitor device possesses an energy density of 9.95 Wh kg-1 at a power density of 236 W Kg-1, which is higher than that of commercially available supercapacitors. The high supercapacitor performance of the porous carbon can be due to the high surface area and effective nitrogen-doping, indicating it can be a great potential for supercapacitors.2. High capacitance property and low cost are the pivotal requirements for practical application of supercapacitors. In this paper, a low cost and high capacitance property nitrogen-doped porous carbon with high specific capacitance is prepared. The as-prepared nitrogen-doped porous carbon are employing potato waste residue（PWR） as the carbon source, zinc chloride（ZnCl₂） as the activating agent and melamine as nitrogen doping agent. The morphology and structure of the carbon materials are studied by scanning electron microscopy（SEM）, N2 adsorption/desorption, X-ray diffraction（XRD） and Raman spectra. The surface area of the nitrogen-doped carbon which prepared under 700 oC is found to be 1052 m2/g, and the specific capacitance as high as 255 F g-1 in 2 M KOH electrolyte is obtained utilize the carbon as electrode materials. The electrode materials also show excellent cyclability with 93.7% coulombic efficiency at 5A g-1 current density of for 5000 cycles.3. In this study, sunflower marrow is used as raw material to prepare porous carbon via a simple carbonization method activated by ZnCl₂ and FeCl₃ mixture. The as-prepared porous sunflower marrow carbons（PSMCs） show large number of mesoporous and masoporous, maximum specific surface area of 1628.5 m2 g-1 and large pore volume of 2.34 cm3 g-1. As an electrode material for supercapacitor, the PSMCs possess high specific capacitance of 252.5 F g-1 at 0.5 A g-1. A symmetric supercapacitor used PSMCs as electrodes exhibits energies density of 12.4 Wh kg-1 at a power density of 817 W kg-1 operated in the voltage range of 0-2.0V in 0.5 mol L-1 Na₂SO₄ aqueous electrolyte. Also, the carbon material shows excellent cycleability retains about 97% initial capacitance after 5000 cycles...