茶叶的碳化 做超级电容

Electrochimica Acta 87 (2013) 401–408Contents lists available at SciVerse ScienceDirectElectrochimicaActaj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /e l e c t a c taPromising activated carbons derived from waste tea-leaves and their application in high performance supercapacitors electrodesChao Peng a ,b ,c ,Xing-bin Yan a ,b ,∗,Ru-tao Wang a ,b ,Jun-wei Lang a ,b ,Yu-jing Ou b ,Qun-ji Xue baLaboratory of Clean Energy Chemistry and Materials,Lanzhou Institute of Chemical Physics,Chinese Academy of Science,Lanzhou 730000,PR China bState Key Laboratory of Solid Lubrication,Lanzhou Institute of Chemical Physics,Chinese of Academy of Sciences,Lanzhou 730000,PR China cSchool of Petrochemical Engineering,Lanzhou University of Technology,Lanzhou 730050,PR Chinaa r t i c l ei n f oArticle history:Received 29May 2012Received in revised form 17September 2012Accepted 18September 2012Available online 8 October 2012Keywords:Activated carbon Tea-leavesSupercapacitors Carbonization Activationa b s t r a c tIn this paper,five types of waste tea-leaves,which come from five of the most typical tea in China,are first used to prepare activated carbons (ACs)by high-temperature carbonization and activation with KOH.The resulting ACs show typical amorphous character,and display porous structures with high specific surface areas ranging from 2245m 2g −1to 2841m 2g −1.As the electro-active electrode materials,the as-made five ACs exhibit ideal capacitive behaviors in aqueous KOH electrolyte,and the maximal specific capacitance is as high as 330F g −1at the current density of 1A g −1.Furthermore,they all show excellent electrochemical cycle stability with ∼92%initial capacitance being retained after 2000cycles.The desirable capacitive performances enable the waste tea-leaves to act as a new biomass source of carbonaceous materials for high performance supercapacitors and low-cost energy storage devices.© 2012 Elsevier Ltd. All rights reserved.1.IntroductionChina is the homeland of tea,which has been producing and drinking for thousands of years.According to statistics available,the production quantity of Chinese tea was about 1,450,000tons in only 2010,and about 400,000tons were exported u-ally,after people drink tea,most of the waste tea-leaves (WTLs)are discarded as useless materials.However,as we know,the chem-ical compositions of TLs mainly contain 3.5–7.0%of the inorganic substance and 93.0–96.5%of the organism.Thus,the disuse of the WTLs is a kind of huge wasting of resources,and it is very necessary to recycle the WTLs.Nowadays,considering the business cost and energy/environmental concerns,the use of biomass materials to pro-duce activated carbons (ACs)becomes one of the hot topics.Until now,various biomass materials,such as dates’stones,coconut shells,pitch coke,wood,rice husk,walnut shell,banana peel and fungi [1–10],have been used as the precursors to produce ACs,and as-obtained ACs have been served as electrode materials,catalyst carriers and adsorbents [6,7,9–15].As a kind of energy storage/conversion devices,supercapacitors exhibit higher power density and longer cycling life than com-mon batteries,and much higher energy density compared with∗Corresponding author.Tel.:+869314968055;fax:+869314968055.E-mail address:xbyan@ (X.-b.Yan).traditional dielectric capacitors [16,17].On the basis of the charge storage mechanism,supercapacitors are basically classified into the electric double-lay capacitors (EDLCs,capacitance from the electro-static charge accumulation at the electrode–electrolyte interface),pseudocapacitors (capacitance from fast and reversible redox pro-cesses at the electroactive material surface)and hybrid capacitors (attributed to the EDL capacitance and the pseudocapacitance)[18].In present,various carbon materials are widely used for super-capacitors’electrode materials,including ACs,carbon nanotubes,carbon nanofibers and graphene sheets and so on [7,19–21].Espe-cially,ACs with porous structure and high specific surface area have attracted much interest due to an array of their exceptional char-acteristics including moderate cost,good chemical stability and high electrical conductivity.Generally,AC materials for supercap-acitors electrodes are fabricated by a straightforward and feasible two-process that consists of carbonization followed by activation.Pyrolysis is occurred in an inert gas atmosphere,such as nitrogen and argon [10,22].Whereas,activation is usually carried out via a high temperature process that involves the chemical etching agent of zinc chloride,potassium hydroxide,potassium carbonate and phosphoric acid [1,7,23–25].Among them,potassium hydroxide as an activator has been successfully used to enhance the porosity of the carbon fibers,carbon nanotubes and graphene and to improve their supercapacitive performances [20,26,27].In this paper,we choose five types of typical Chinese TLs,includ-ing Bi luo chun,Tie guan yin,Pu’er tea,Long jing and Mao feng,as the precursors to prepare ACs by high-temperature carbonization in0013-4686/$–see front matter © 2012 Elsevier Ltd. All rights reserved./10.1016/j.electacta.2012.09.082402 C.Peng et al./Electrochimica Acta87 (2013) 401–408argon atmosphere followed by KOH activation.The electrochemical properties of as-made ACs were estimated by cyclic voltammetry (CV),galvanostatic charge/discharge(GCD)and electrochemical impedance spectroscopy(EIS).As the results,as-made porous ACs show very high specific surface areas and high specific capacitance. Among them,the Bi luo chun-derived AC exhibits the highest spe-cific capacitance of330F g−1under a three-electrode system.In addition,these porous AC electrodes all show good cycling stabil-ity.These properties possibly enable these WTLs to act as a new biomass source of carbonaceous materials for high-performance supercapacitors.2.Experimental2.1.Preparation of activated carbonBi luo chun(B),Tie guan yin(T),Pu’er tea(P),Long jing(L)and Mao feng(M),were purchased from a local tea-shop.The TLs were first marinated in boiling water means that the TLs were soaked in the boiling water until the water temperature reach to room temperature.The dried WTLs were pyrolyzed at600◦C for2h in a horizontal tube furnace with an argonflow of40sccm,to obtain carbon-ated products(denoted as X-C,X is corresponding to the B,T,P, L and M).KOH activation of the X-C was as follows:briefly,a given mass of X-C was impregnated using KOH aqueous solution(the mass ratio of KOH/X-C was4),followed by an evaporation step at80◦C under vacuum atmosphere.The dried KOH/X-C mixture was heated at800◦C for1h in the horizontal tube furnace with the same argonflow and a raising speed of5◦C/min.After being cooled down to room temperature inflowing argonflow,the prod-uct was neutralized by the1M HCl solution until a pH value of7was reached.Subsequently,as-obtained AC(denoted as X-AC)wasfil-tered,washed with ultra-pure water,and dried at60◦C in ambient for10h.2.2.Structural characterizationThe morphology and microstructure of the obtained prod-ucts were investigated using afield emission scanning electron microscope(FE-SEM,JSM-6701F).The chemical compositions of thefive carbon samples were analyzed by Fourier transformation infrared spectroscopy(FTIR)using a Bruker IFS66V FTIR spec-trometer.Crystallite structures were determined by a powder X-ray diffraction(XRD,X’Pert Pro,Philips)using Cu K␣radia-tion from10◦to70◦.Nitrogen adsorption–desorption isotherm measurements were performed on a Micrometitics ASAP2020 volumetric adsorption analyzer at77K.Prior to the adsorption experiments,all X-AC samples were adopted through degassing process at200◦C for4h to eliminate the surface gaseous contami-nants.The Brunauer–Emmett–Teller(BET)method was utilized to calculate the specific surface area of each sample and the pore-size distribution was derived from the adsorption branch of the corresponding isotherm using the Barrett–Joyner–Halenda(BJH) method.The total pore volume was estimated from the amount adsorbed at a relative pressure of P/P0=0.99.2.3.Electrode preparation and electrochemical measurementsThe working electrodes were prepared as follows:typically, 80wt.%of X-AC was mixed with7.5wt.%of acetylene black(>99.9%) and7.5wt.%of conducting graphite in an agate mortar until a homogeneous black powder was obtained.To this mixture,5wt.% of poly(tetrafluoroethylene)was added with a few drops of ethanol. After briefly allowing the solvent to evaporate,the resulting paste was pressed at10MPa to the nickel gauze with a nickel wire for an electric connection.The assembled electrodes were dried for16h at 80◦C in air.Each electrode contained about8mg of X-AC material and had a geometric surface area of about1cm2.The electrochemical measurements of each as-prepared elec-trode were carried out by an electrochemical working station (CHI660D,Shanghai,China)using a three-electrode system in2M KOH electrolyte at room temperature.A platinum sheet electrode and a saturated calomel electrode served as the counter electrode and the reference electrode.The CV measurements were conducted with a potential window from−1.1V to−0.1V at different sweep rates ranging from5mV s−1to200mV s−1.EIS analyses were recorded with using another electrochemi-cal working station(Autolab,Switzerland)from10kHz to0.1Hz with alternate current amplitude of10mV,at open circuit poten-tial and in2M KOH aqueous electrolyte.GCD measurements were run on from−1.1V to−0.1V at different current densities.The corresponding specific capacitance was calculated from:C=I( E/ t)×m(1)where C is the specific capacitance,I is the constant discharging current,dE/dt indicates the slope of the discharging curves,and m is the mass of the corresponding electrode material.3.Results and discussion3.1.Structure and morphology of thefive type X-ACsIn China,Bi luo chun(B),Tie guan yin(T),Pu’er tea(P),Long jing (L)and Mao feng(M)arefive of the most typical tea.Fig.1shows the photographs of thefive TLs before and after water marinat-ing.For an example of Long jing,Fig.2shows a typical preparation schematic of porous AC derived from the dried WTLs by pyrolyzing under argon atmosphere and KOH activation.As we mentioned before,KOH activation has been widely used on various carbon materials,to increase surface area and improve electrochemical performance.When the activation temperature is higher than700◦C,chemical reactions are mostly as the process: 6KOH+2C→2K+3H2+2K2CO3,and subsequent decomposition of K2CO3and/or reactions of K/K2CO3/CO2with the carbon[28,29]. In our synthesis,through the activation of the carbonated X-Cs with KOH at800◦C for1h,obvious weight-loss occurred and the yields offive types X-ACs are around0.5.We believe that,owing to the loss of carbon,a large amount of nano-scale pores will be generated in thefinal products.The nitrogen adsorption and desorption isotherms of the X-AC samples are showed in Fig.3A.According to the IUPAC classifica-tion,the B-AC and the P-AC exhibit type I isotherm curves[30].The major nitrogen adsorption occurs at relative pressures less than0.3. Relatively horizontal adsorption plateau appears at higher P/P0val-ues,indicating that the micropores are dominant in the B-AC and the P-AC.Certainly,there are still some mesopores in the two ACs because of the appearance of small hysteresis,as well as the little deviation from almost horizontal plateau in the isotherm curves [31].On the contrary,the samples of T-AC,L-AC and M-AC exhibit type IV isotherm curves with an obvious hysteresis loop associated with capillary condensation taking place in mesopores[32].Table1summarizes the specific surface area(SSA),pore volume and average pore size.It is obvious that KOH etching can build a lot of nano-scale pores,as a result that the all X-ACs have very high BET SSAs ranging from2245m2g−1to2941m2g−1and large pore volumes ranging from1.069cm3g−1to1.366cm3g−1,as well as the BJH pore size ranging from2.67nm to3.20nm.The BJH pore size distributions forfive ACs(Fig.3B)do not display a complete distribution near the lower pore size limit,indicates the existence of micropores.Among them,the B-AC sample shows the highestC.Peng et al./Electrochimica Acta87 (2013) 401–408403Fig.1.Photographs offive WTLs marinated in water:(A)Bi luo chun,(B)Tie guan yin,(C)Pu’er tea,(D)Long jing,and(E)Mao feng.Insets show the as-boughtTLs.Fig.2.Scheme of the production of the X-AC(X is the L here).SSA,the smallest pore diameter and the largest pore volume,which is one of the advantages of using KOH as an activating agent.Fig.4shows the XRD patterns of the as-prepared X-ACs.All XRD patterns show a broaden diffraction peak centered at43◦, corresponding to the(100)diffractions of graphitic carbon with the amorphous character.Considerable intensity of thefive types X-ACs in the low-angle scatter indicates the presence of a high den-sity of pores[27].FE-SEM images of the surface morphologies of the as-prepared X-ACs are shown in Fig.5.It can be seen that,on thefive types of particle surfaces,the number of the macropores is few,indicating the nano-scale pores are dominant in thefive samples.Among them,as seen from Fig.4D,a particle of the L-AC exhibits an obvious mesoporous surface,which is consistent with the observation from its nitrogen adsorption–desorption isotherm.In addition,the surface chemical component and the atomic concentrations of thefive carbon samples were evaluated XPS anal-yses as well,and the high-resolution C1s XPS spectra of all the carbon samples are present in Fig.6a–e.The deconvolution of C1sTable1BET measurements and the specific capacitances of thefive types of X-Cs and the correspondingfive types of X-ACs.Samples BET Surface area(m2g−1)Pore volume(cm3g−1)BJH pore size(nm)Specific capacitance(F g−1)B-C110.00921.5320B-AC2841 1.366 2.67330T-C130.01116.0712T-AC2540 1.255 2.99305P-C70.00544.8715P-AC2245 1.069 2.76293L-C80.00817.1820L-AC2607 1.350 3.20280M-C60.00317.0416M-AC2521 1.252 3.02275404 C.Peng et al./Electrochimica Acta 87 (2013) 401–408Fig.3.(A)Nitrogen adsorption–desorption isotherms for the five types of X-ACs.(B)Pore size distributions,which are calculated by the BJHmethods.Fig.4.XRD patterns of the five types of X-ACs.spectrum gives four peaks representing carbon atoms bonded to carbon and oxygen atoms.These four peaks are related to C C C bonds (284.7eV),C O bonds (286.4eV),C O bonds (287.7eV)and O C O bonds (289.7eV),respectively [33–35].The C O,C O and O C O fractions are as high as 21.58%,8.84%and 10.16%in B-AC sample,respectively,indication a significant amount of oxygen-containing groups.Furthermore,qualitative identification of functional groups was examined by FT-IR spectroscopy.Fig.6f shows the FT-IR spectra of five ACs materials over the range of 4000–400cm −1.It is clear seen that all spectra are very simi-lar.A broad band of O H stretching vibration presents at around 3,443cm −1,and bands at 1657,1438and 1050cm −1are corre-sponded to COO −anion stretching,C C vibrations in aromatic rings and C O stretching of ester [9,36,37].These oxygen-containing functional groups,such as pyrone-like functionalities (part of C O and C O)in the porous surfaces of carbon materials can make effects on the electrochemical capacitivebehaviors.Fig.5.SEM images of the as-prepared X-ACs:(A)B-AC,(B)T-AC,(C)P-AC,(D)L-AC and (E)M-AC.C.Peng et al./Electrochimica Acta 87 (2013) 401–408405Fig.6.The C 1s XPS spectra of activated carbon materials:(a)B-AC,(b)T-AC,(c)P-AC,(d)L-AC and (e)M-AC;(f)FTIR spectra of five ACs derived from waste tea-leaves.3.2.Electrochemical performances of the five types X-ACsFig.7shows the CV curves of five X-Cs and the corre-sponding five X-ACs electrodes obtained in 2M KOH electrolyte solution with a sweep rate of 5mV s −1.The X-Cs electrodes exhibit low current density responses (the peak current den-sities are all on the order of ∼10−3A g −1).Moreover,their CV curves all have an obvious induced current in negative potential and little response current in positive potential.However,com-pared with the X-Cs electrodes,the current density responses and the CV curve areas of the X-ACs electrodes are both much larger than those of the X-Cs electrodes.This indicates thatthe electrochemical performances of the X-ACs are remarkably enhanced owing to the KOH activation.Also,for the X-ACs electrodes,their CV curves exhibit ideal rectangular shape with-out obvious polarization from −1.1V to −0.1V.In addition,as seen from their CV plots,there is one pair of weak redox peaks (around −0.52V/−0.42V)and slightly polarization occurs on the positive and negative potential.The existence of redox peaks and polarizations are attributed to a certain number of oxygen-containing functional groups on the X-ACs surfaces.Of course,these results might be also due to the transition between quinone/hydroquinone groups,which is typical for carbon materi-als [38].Fig.7.CV curves for the five types of X-Cs before and after KOH activation,obtained at a sweep rate of 5mV s −1and in a 2M KOH aqueous electrolyte.A,B,C,D and E represent to the B-,T-,P-,L-and M-AC electrodes.406 C.Peng et al./Electrochimica Acta 87 (2013) 401–408Fig.8.GCD curves of the five types of X-Cs before and after KOH activation,obtained at a constant current density of 1A g −1,in the 2M KOH aqueous electrolyte and from −1.1V to −0.1V.A–E represent the B-,T-,P-,L-and M-AC electrodes.Fig.8displays the steady-state GCD curves for the five types X-Cs and their corresponding X-ACs at a constant current den-sity of 1A g −1.As shown in the GCD curves,the charge–discharge times of the X-ACs electrodes are much longer than those of the X-Cs electrodes,suggesting that the electrochemical capacitances of the X-ACs are remarkably enhanced by the KOH activation.Also,their plots present good linearity and symmetrical triangle,indicating good electric double-lay capacitor behaviors.According to the formula (1),the specific capacitance values can be calcu-lated,which are listed in Table 1.The specific capacitances of the five X-ACs electrodes are ranging from 275F g −1to 330F g −1.The values are comparable with those for most biomass-derived ACs (100–370F g −1)in aqueous electrolytes [6,7,10,39–42].More-over,as seen from Table 1,there is disproportion between the specific capacitance and the specific surface area.It is due to that not all pores are effective in charge accumulation at the electrode–electrolyte interface [17,43,44].Fig.9A displays the CV curves of B-AC electrode at various volt-age sweep rates.As the curves show,even the voltage sweep rate up to 100mV s −1,the CV curve still retain the rectangular shape,this result illuminates the unrestricted motion of electrolyte in the pores at the slow double-layer formation situation [45,46].How-ever,and the curve becomes deformed when the potential sweep rate rises to 200mV s −1.The phenomenon is attributed to the ohmic resistance for electrolyte motion in porous carbon,in which the storage charge has been recognized to be distributed for the double layer formation mechanism [45–47].Fig.9B shows the GCD plots of B-AC electrode at different current densities.It can be seen that all curves are still highly symmetrical and linear at increased current densities from 1A g −1to 10A g −1,which is a typical characteristic of an ideal capacitor.Also,with the increase in the current den-sity,the specific capacitance decreases gradually from 330F g −1at 1A g −1to 238F g −1at 10A g −1.The results indicate the as-prepared B-AC electrode has excellent capacitive behavior.In our system,the B-AC possesses the high specific surface area (2841m 2g −1),small BJH pore size (2.67nm)and abundant oxygen-containing groups.Thus,the high specific capacitance of B-AC results from the simultaneous function of the electric doubleFig.9.(A)CV curves of the B-AC electrode at different sweep rates,and (B)GCD curves for the B-AC electrode at different current densities.C.Peng et al./Electrochimica Acta 87 (2013) 401–408407Fig.10.Nyquist plots of the five types of X-ACs electrodes.Inset is the enlarged plots of the high-frequency region.layer capacitance and the pseudo-capacitance obtained from the oxygenated groups on the porous surface of carbon materials.The EIS data were analyzed using Nyquist plots,which show the frequency response of the electrode/electrolyte system and are the plots of the imaginary component (Z )of the impedance against the real component (Z ).From the Nyquist plots shown in Fig.10,allFig.11.Cycle life of the five types of X-ACs electrodes at a constant current den-sity of 5A g −1and in the 2M KOH aqueous electrolyte:(A)variation of the specific capacitance,and (B)variation of the Coulomb efficiency.the plots of the X-ACs electrodes display a small semicircle at high frequency followed by a transition to linearity at low frequency.The semicircle at higher frequency region should be related to the Faradaic process of the charge-transfer at the electrode/electrolyte interface,and the slope of lines at lower frequency region should be ascribed to the diffusion of the electrolyte ions in the electrode pores [48–50].Also,the vertical lines closed to 90◦at low frequency suggest the pure capacitive behavior and fast transfer character of electrolyte ions in the structure of the carbon electrode [50,51].The cycle lifetime for the five types of X-ACs electrodes was monitored by a chronopotentiometry measurement at 5A g −1in 2M KOH electrolyte.As shown in Fig.11A,for all the electrodes,almost no decay up to 2000cycles and about 92%of the initial specific capacitances still is retained.It indicates that all the X-ACs exhibit long-term cycle stability and good electrochemical reproducibility due to the excellent electrical conductivity.Fig.11B shows the Coulomb efficiency as a function of cycle number,which was calculated using following equation [52,53]:Á(%)=T dT c×100T d and T c are discharge time and charge time,respectively.In Fig.10B,the values of Coulomb efficiency are 1.02,1.00,1.00,1.00and 1.00corresponding to the B-,T-,P-,L-and M-AC after 2000cyclic charge–discharge processes,respectively.It is obviously seen that the values of T d and T c of five types X-ACs are approximately equal after 2000cycles,further indicating the five types X-ACs have good electrochemical stability and coulomb efficiency.4.ConclusionsIn summary,porous ACs materials have been successfully produced from five types of WTLs through high-temperature car-bonization followed by KOH activation.The resulting ACs all show high specific capacitances and excellent cycle stability in aqueous electrolytes.Because the five teas are considered to be the most well-known representative for Chinese teas,we think that other teas could be also used to prepare porous ACs via the same route,and they should have good capacitive properties.Considering their abundance and their recycling,WTLs would act as a new biomass source for preparing ACs for high-performance supercapacitors and low-cost energy storage devices.AcknowledgmentsThis work was supported by the Top Hundred Talents Program of Chinese Academy of Sciences.References[1]Y.A.Alhamed,Activated Carbon from Dates’Stone by ZnCl 2Activation,Journalof King Abdulaziz University:Engineering Sciences 17(2006)75.[2]C.J.Kirubakaran,K.Krishnaiah,S.K.Seshadri,Experimental study of the produc-tion of activated carbon fromcoconut shells in a fluidized bed reactor,Industrial and Engineering Chemistry Research 30(1911)2411.[3]S.Mitani,S.I.Lee,S.H.Yoon,Y.Korai,I.Mochida,Activation of raw pitch cokewith alkali hydroxide to prepare high performance carbon for electric double layer capacitor,Journal of Power Sources 133(2004)298.[4]H.Benaddi,T.J.Bandosz,J.Jagiello,J.A.Schwarz,J.N.Rouzaud,D.Legras,F.Béguin,Surface functionality and porosity of activated carbons obtained from chemical activation of wood,Carbon 38(2000)669.[5]Y.P.Guo,H.Zhang,N.N.Tao,J.R.Qi,Z.C.Wang,H.D.Xu,Adsorption of malachitegreen and iodine on rice husk-based porous carbon,Materials Chemistry and Physics 82(2003)107.[6]Y.P.Guo,J.R.Qi,Y.Q.Jiang,S.F.Yang,Z.C.Wang,H.D.Xu,Performance of elec-trical double layer capacitors with porous carbons derived from rice husk,Materials Chemistry and Physics 80(2003)704.[7]K.Kuratani,K.Okuno,T.Iwaki,M.Kato,N.Takeichi,T.Miyuki,T.Awazu,M.Majima,T.Sakai,Converting rice husk activated carbon into active material for capacitor using three-dimensional porous current collector,Journal of Power Sources 196(2011)10788.408 C.Peng et al./Electrochimica Acta87 (2013) 401–408[8]Z.H.Hu,E.F.Vansant,Synthesis and characterization of a controlledmicropore-size carbonaceous adsorbent produced from walnut shell,Microporous Materials3(1995)603.[9]Y.K.Lv,L.H.Gan,M.X.Liu,W.Xiong,Z.J.Xu,D.Z.Zhu,D.S.Wright,A self-template synthesis of hierarchical porous carbon foams based on banana peel for supercapacitor electrodes,Journal of Power Sources209(2012) 152.[10]H.Zhu,X.L.Wang,F.Yang,X.R.Yang,Promising carbons for supercapacitorsderived from fungi,Advanced Materials23(2011)2745.[11]J.Klinik,B.Samojeden,T.Grzybek,W.Suprun,H.Papp,R.Gläser,Nitrogenpromoted activated carbons as DeNOx catalysts.2.The influence of water on the catalytic performance,Catalysis Today176(2011)303.[12]J.P.S.Sousa,M.F.R.Pereira,J.L.Figueiredo,Catalytic oxidation of NO to NO2onN-doped activated carbons,Catalysis Today176(2011)383.[13]M.Ghaedi,S.Z.Amirabad,F.Marahel,S.N.Kokhdan,R.Sahraei,M.Nosrati,A.Daneshfar,Synthesis and characterization of Cadmium selenide nanoparticles loaded on activated carbon and its efficient application for removal of Muroxide from aqueous solution,Spectrochimica Acta,Part A83(2011)46.[14]R.Mehta,K.Daga,P.Gehlot,Adsorption Studies of Pb(II)from Aqueous Solu-tion by Using Activated Carbon of Datura stramonium as An Adsorbent,Asian Journal of Chemistry23(2011)5194.[15]Z.N.Wang,L.Zhan,M.Ge,F.Xie,Y.L.Wang,W.M.Qiao,X.Y.Liang,L.C.Ling,Pithbased spherical activated carbon for CO2removal fromflue gases,Chemical Engineering Science66(2011)5504.[16]A.Davies,A.P.Yu,Material advancements in supercapacitors:from activatedcarbon to carbon nanotube and graphene,Canadian Journal of Chemical Engi-neering89(2011)1321.[17]L.L.Zhang,Z.B.Lei,J.T.Zhang,X.N.Tian,X.S.Zhao.Supercapacitors:ElectrodeMaterials Aspects,/10.1002/0470862106.ia816[18]P.Simon,Y.Gogotsl,Materials for electrochemical capacitors,Nature Materials7(2008)845.[19]H.Zhang,G.P.Cao,Y.S.Yang,Carbon nanotube arrays and their composites forelectrochemical capacitors and lithium-ion batteries,Energy&Environmental Sciences2(2009)932.[20]V.Barranco,M.A.Lillo-Rodenas,A.Linares-Solano,A.Oya,F.Pico,J.Iba˜nez,F.Agullo-Rueda,J.M.Amarilla,J.M.Rojo,Amorphous Carbon Nanofibers and Their Activated Carbon Nanofibers as Supercapacitor Electrodes,Journal of Physical Chemistry C114(2010)10302.[21]J.Yan,T.Wei,B.Shao,F.Q.Ma,Z.J.Fan,M.L.Zhang,C.Zheng,Y.C.Shang,W.Z.Qian,F.Wei,Electrochemical properties of graphene nanosheet/carbon black composites as electrodes for supercapacitors,Carbon48(2010)1731.[22]S.Mitani,S.I.Lee,K.Saito,S.H.Yoon,Y.Korai,I.Mochida,Activation of coal tarderived needle coke with K2CO3into an active carbon of low surface area and its performance as unique electrode of electric double-layer capacitor,Carbon 43(2005)2960.[23]J.Górka,A.Zawislak,J.Choma,M.Jaroniec,KOH activation of mesoporouscarbons obtained by soft-templating,Carbon46(2008)1159.[24]B.S.A.N.Girgis,A.El-Hendawy,Porosity development in activated carbonsobtained from date pits under chemical activation with phosphoric acid,Micro-porous and Mesoporous Materials52(2002)105.[25]T.Budinova,E.Ekinci,F.Yardim,A.Grimm,E.Björnbom,V.Minkova,M.Gora-nova,Characterization and application of activated carbon produced by H3PO4 and water vapor activation,Fuel Processing Technology87(2006)899. [26]B.Xu,F.Wu,Y.F.Su,G.P.Cao,S.Chen,Z.M.Zhou,Y.S.Yang,Competitive effectof KOH activation on the electrochemical performances of carbon nanotubes for EDLC:Balance between porosity and conductivity,Electrochimica Acta53 (2008)7730.[27]Y.W.Zhu,S.Murali,M.D.Stoller,K.J.Ganesh,W.W.Cai,P.J.Ferreira,A.Pirkle,R.M.Wallace,K.A.Cychosz,M.Thommes,D.Su,E.A.Stach,R.S.Ruoff,Carbon-based supercapacitors produced by activation of graphene,Science332(2011) 1537.[28]E.Raymundo-Pi˜nero,P.Azaïsa,T.Cacciaguerraa,D.Cazorla-Amorósb,A.L.Solanob,F.Béguin,KOH and NaOH activation mechanisms of multiwalled car-bon nanotubes with different structural organization,Carbon43(2005)786.[29]M.A.Lillo-Ródenas, D.Cazorla-Amorós, A.Linares-Solano,Understandingchemical reactions between carbons and NaOH and KOH:An insight into the chemical activation mechanism,Carbon41(2003)267.[30]K.S.W.Sing,D.H.Everett,R.A.W.Haul,L.Moscou,R.A.Pierotti,J.Rouquerol,T.Siemieniewska,Reporting physisorption data for gas solid systems with special reference to the determination of surface-area and porosity(recommendations 1984),Pure and Applied Chemistry57(1985)603.[31]Y.A.Alhamed,H.S.Bamufleh,Sulfur removal from model diesel fuel using gran-ular activated carbon from dates’stones activated by ZnCl2,Fuel88(2009)87.[32]H.Y.Liu,K.P.Wang,H.Teng,A simplified preparation of mesoporous carbon a ndthe examination of the carbon accessibility for electric double layer formation, Carbon43(2005)559.[33]J.T.Chen,G.G.Zhang,B.M.Luo,D.F.Sun,X.B.Yan,Q.J.Xue,Surface amorphiza-tion and deoxygenation of graphene oxide paper by Ti ion implantation,Carbon 49(2011)3141.[34]ng,X.B.Yan,W.W.Liu,R.T.Wang,Q.J.Xue,Influence of nitric acidmodification of ordered mesoporous carbon materials on their capacitive per-formances in different aqueous electrolytes,Journal of Power Sources204 (2012)220.[35]czarek,A.Cizewski,I.Stepniak,Oxygen-doped activated carbonfibercloth as electrode material for electrochemical capacitor,Journal of Power Sources196(2011)7882.[36]M.Anbia,S.E.Moradi,The examination of surface chemistry and porosity ofcarbon nanostructured adsorbents for1-naphthol removal from petrochemical wastewater streams,Journal of Chemical Engineering29(2012)743.[37]A.M.Stephan,T.P.Kumar,R.Ramesh,S.Thomas,S.K.Jeong,K.S.Nahm,Pyroliticcarbon from biomass precursors as anode materials for lithium batteries,Mate-rials Science and Engineering A430(2006)132.[38]X.B.Yan,J.T.Chen,J.Yang,Q.J.Xue,M.Philippe,Fabrication of free-standingelectrochemically active,and biocompatible graphene oxide-polyaniline and graphene-polyaniline hybrid paper,ACS Applied Materials&Interfaces2 (2010)2521.[39]B.Xu,Y.F.Chen,G.Wei,G.P.Cao,H.Zhang,Y.S.Yang,Activated carbon withhigh capacitance prepared by NaOH activation for supercapacitors,Materials Chemistry and Physics124(2010)504.[40]X.Li,W.Xing,S.P.Zhuo,J.Zhou,F.Li,S.Z.Qiao,G.Q.Lu,Preparation of capacitor’selectrode from sunflower seed shell,Bioresource Technology102(2011)1118.[41]E.Raymundo-Pi˜nero,M.Cadek,F.Béguin,Tuning carbon materials for super-capacitors by direct pyrolysis of seaweeds,Advanced Functional Materials19 (2009)1032.[42]T.E.Rufford,D.Hulicova-Jurcakova,Z.H.Zhu,G.Q.Lu,Nanoporous carbonelectrode from waste coffee beans for high performance supercapacitors,Elec-trochemistry Communications10(2008)1594.[43]W.J.Gao,Y.Wan,Y.Q.Dou,D.Y.Zhuo,Synthesis of Partially Graphitic OrderedMesoporous Carbons with High Surface Areas,Advanced Engineering Materials 1(2011)115.[44]K.Kierzek,E.Frackowiak,G.Lota,G.Gryglewicz,J.Machnikowski,Electrochem-ical capacitors based on highly porous carbons prepared by KOH activation, Electrochimica Acta49(2004)515.[45]L.H.Wang,M.Toyoda,M.Inagaki,Dependence of electric double layer capac-itance of activated carbons on the types of pores and their surface areas,New Carbon Materials23(2008)111.[46]Z.M.Sheng,J.N.Wang,J.C.Ye,Synthesis of nanoporous carbon with controlledpore size distribution and examination of its accessibility for electrode double layer formation,Microporous and Mesoporous Materials111(2008)307. [47]R.D.Levie,On porous electrodes in electrolyte solutions,Electrochimica Acta8(1963)751.[48]S.B.Tang,i,L.Lu,Li-ion diffusion in highly(003)oriented LiCoO2thinfilmcathode prepared by pulsed laser deposition,Journal of Alloys and Compounds 449(2008)300.[49]J.C.Zhao,B.Tang,J.Cao,J.C.Feng,P.Liu,J.Zhao,J.L.Xu,Effect of hydrothermaltemperature on the structure and electrochemical performance of manganese compound/ordered mesoporous carbon composites for supercapacitors,Mate-rials and Manufacturing Processes27(2012)119.[50]W.H.Wang,X.D.Wang,Investigation of Ir-modified carbon felt as the positiveelectrode of an all-vanadium redoxflow battery,Electrochimica Acta52(2007) 6755.[51]M.Ghaemi,F.Ataherian,A.Zolfaghari,S.M.Jafari,Charge storage mecha-nism of sonochemically prepared MnO2as supercapacitor electrode:Effects of physisorbed water and proton conduction,Electrochimica Acta53(2008) 4607.[52]V.S.Jamadade,V.J.Fulari,C.D.Lokhande,Supercapacitive behavior of elec-trosynthesized marygold-like structured nickel doped iron hydroxide thinfilm, Journal of Alloys and Compounds509(2011)6257.[53]S.G.Kandalkar,D.S.Dhawale,C.K.Kim,C.D.Lokhande,Chemical synthesis ofcobalt oxide thinfilm electrode for supercapacitor application,Synthetic Metals 160(2010)1299.。