Preparation Of Activated Carbon From Shengli Lignite And Their Application In Electric Double Layer Capacitor

Activated carbons(ACs)were prepared by carbonization activation method and surface oxidation modification with nitric acid from Shengli lignite with KOH as activator.The pore structure and surface properties of ACs were characterized by means of scanning electron microscopy(SEM),X-ray diffraction(XRD),N2 adsorptiondesorption,Fourier transform infrared(FTIR)spectroscopy and X-ray photoelectron spectroscopy(XPS).The prepared ACs were used as electrode materials for electric double-layer capacitors(EDLC),and the electrochemical performances of ACs electrode materials were analyzed by galvanostatic charge-discharge(GCD),cyclic voltammetry(CV)and electrochemical impedance spectroscopy(EIS).The effects of preparation conditons and surface oxidation modification with nitric acid on the specific surface area,pore structure and electrochemical properties of EDLC were investigated systematically in this study.The electrochemical tests demonstrate that the prepared ACs exhibited good charge-discharge performance in 6 mol L-1 KOH,and the specific capacitance was higher than that of in TEABF4/PC electrolyte.The results show that the specific capacitance increases with the increase of the specific surface area of ACs,but the correlation between them are not linear.The specific capacitance of the AC electrodes decreased with the increase of current density,and the AC electrodes had a higher specific capacitance retention rate at high current density,exhibiting noticeable chargedischarge characteristics.Especifically,the Shengli lignite-based AC-K-4 caronized at 700 ℃,activated at 800 ℃ for 2 h with an activation ratio of 4 reached a specific surface area of 2550 m2 g-1 and a pore volume of 1.24 cm3 g-1,and the electrode possessed the specific capacitance of 213 F g-1 at the current density of 40 mA g-1,and maintained 175 F g-1 at of 200 mA g-1.Furthermore,the AC-K-4 electrode exhibited excellent cycle stability and keeped 96% coulomb efficiency over 1000 charge-discharge cycles,demonstrating a promising candidate as the electrode materials for EDLC.Additionally,the specific surface area and pore volume of ACs decreased after oxidation with nitric acid.However,surface oxygen-containing groups increase obviously,especially the hydroxyl and carboxyl groups.It is concluded that the specific capacitance of AC electrodes with 60% nitric acid surface oxidation reached 245 F g-1 at the current density of 40 mA g-1.The increased oxygen-containing groups improved the wettability of ACs in the electrolyte solution,resulting in a lower resistance to the transport of electrolyte ions within the micropores of ACs,which can remarkly enhance the energy density of the AC electrodes.