Preparation And Electrochemical Performance Of Biomass-based Porous Carbons For Supercapacitor

Supercapacitor has been recognized as a new energy storage device which has higherenergy densities than conventional electrolytic capacitors and higher power density thanbatteries, long lifecycle, rapid charge-discharge rate, etc, and bridges between traditionalelectrolytic capacitors and batteries. Presently, supercapacitor has been widely used inenergy storage, hybrid electric vehicles and composite systems. Generally, the performanceof supercapacitor is strongly dependent on the characteristics of the electrode materials andthe types of electrolyte.In this paper, porous carbons (PCs) were prepared from rice husk by one–step zincchloride (ZnCl2) activation assisted with microwave and conventional heating, respectively.Their electrochemical performance of PCs was investigated in detail. The morphologiesand patterns of the PCs were determined by field emission scanning electron microscopy,transmission electron microscopy and X-ray diffraction. The pore structure and surfacearea of PCs were investigated by nitrogen adsorption-desorption. The electrochemicalperformance of PC electrodes in6mol/L KOH aqueous and l mol/L Et4NBF4/PC organicelectrolyte were performed via galvanostatic charge/discharge, cyclic voltammetry andelectrochemical impedance spectroscopy. The main conclusions are following.PCs were prepared rapidly from rice husk by ZnCl2activation at600W of microwavepower and20min of activation time. With the increasing mass ratio of ZnCl2/rice huskfrom1/1to5/1, the total volume pore and average pore size of PCs increases from0.75cm3/g to2.07cm3/g, and from2.02nm to5.99nm, respectively. The specific surface areaof PCs passes through a maximum, reaches1727m2/g at a ZnCl2/rice husk mass ratio aslow as3/1and then drops to1380m2/g. The Dapof PC3/1–Mreaches3.46nm with a Vtof1.58cm3/g and mesopore percentage of99.4%. For6mol/L KOH aqueous electrolyte,PC4/1–Mshows the highest specific capacitance and energy density, reaching182F/g and6.23Wh/kg after1000cycles at the current density of50mA/g. For l mol/L Et4NBF4/PCorganic electrolyte, PC4/1-Mhas the highest specific capacitance of94F/g and the highestenergy density of23.4Wh/kg at the current density of50mA/g.PCs were also made at a rate of5K/min to850℃, and held at850℃for1h byconventional heating. The specific surface area of PCs passes through a maximum with theincreasing mass ratio of ZnCl2/rice husk from1/1to4/1, and reaches1768m2/g at aZnCl2/rice husk mass ratio as low as2/1. With the ZnCl2/rice husk mass ratio from1/1to 4/1, the average pore size of PCs rises from1.90nm to3.46nm, the total pore volumefrom0.71cm3/g to1.38cm3/g, mesopore percentage from8.5%to85.2%, respectively.The specific capacitance of PC4/1–Conly drops from245F/g to233F/g with the increasingcurrent density from50mA/g to2000mA/g with a high capacitance retention of95.1%in6mol/L KOH aqueous electrolyte. The specific capacitance and energy density of PC4/1–Creaches99F/g and24.4Wh/kg, respectively, at the current density of50mA/g in l mol/LEt4NBF4/PC organic electrolyte.