利用离子交换树脂合成炭材料.pdf

ORIGINAL PAPERThe production of activated carbon from cation exchangeresin for high-performance supercapacitorZhong Jie Zhang&Peng Cui&Xiang Ying Chen&Jian Wei LiuReceived:7 January 2013/Revised:4 February 2013/Accepted:8 February 2013/Published online:24 February 2013#Springer-Verlag Berlin Heidelberg 2013Abstract High-performance activated carbon for electro-chemical double-layer capacitors(EDLC)has been preparedfrom cation exchange resin by carbonization and subsequentactivation with KOH.The activation temperature has a keyrole in the determination of porous carbon possessing highsurface areas,and large pore structures.The porous carbonactivated at 700 C(carbon-700-1:4)has high surface area(2236 m2g1)and large total pore volume(1.15 cm3g1),which also displays best capacitive performances due to itswell-balanced micro-or mesoporosity distribution.In de-tails,specific capacitances of the carbon-700-1:4 sample are336.5 Fg1at a current density of 1 Ag1and 331.8 Fg1at2 Ag1.At high current density as 20 Ag1,the retention ofits specific capacitance is 68.4%.The carbon-700-1:4sample also exhibits high performance of energy density(46.7 Whkg1)and long cycle stability(8.9%loss after3,000 cycles).More importantly,due to the amount of wasteion-exchange resins increasing all over the world,the pres-ent synthetic method might be adopted to dispose them,producing high-performance porous carbons for EDLCelectrode materials.Keywords Cationexchangeresin.Activated carbon.Supercapacitor.Electrode materialsIntroductionSupercapacitors can provide a new technological solutionfor the energy storage needs in many industries.They de-liver high-power and energy densities increasingly closer torechargeable batteries and also bridge the gap between ca-pacitors and batteries 1.Since the first discovery ofcarbon-based supercapacitor by Becker in 1957 2,variouskinds of active materials have been designed and prepared,basically classified into carbon materials,conducting poly-mers,and metal oxides,as well as their hybrid systems 3.Among them,carbon materials have attracted more interestas electrode materials due to multiplex allotropes,accessi-bility,easy processability,low cost,chemical stability indifferent solutions(from strongly acidic to basic),and ablefor performance in a wide range of temperatures 4,5.In general,the increasing specific surface area and porevolume,aswellaswell-definedporesizedistributionofporouscarbons,are indispensable for acquiring a better capacitiveperformance by increasing energy density without sacrificingcycle life or high-power density 6,7.Porous carbons areusually obtained via the carbonization of natural or syntheticprecursors,followed by physical/chemical activation to enrichthe pore networks.Commonly,activating agents for physicalactivation include O2,CO2,or steam,while the chemicalElectronic supplementary material The online version of this article(doi:10.1007/s10008-013-2039-x)contains supplementary material,which is available to authorized users.Z.J.Zhang:P.Cui(*):X.Y.Chen(*)School of Chemical Engineering,Anhui Key Laboratoryof Controllable Chemistry Reaction&Material ChemicalEngineering,Hefei University of Technology,Hefei,Anhui 230009,Peoples Republic of Chinae-mail:e-mail:Z.J.Zhange-mail:Z.J.ZhangCollege of Chemistry&Chemical Engineering,Anhui Province Key Laboratory of Environment-friendlyPolymer Materials,Anhui University,Hefei 230039Anhui,Peoples Republic of ChinaJ.W.LiuDepartment of Physics and Astronomy,University of Kansas,Lawrence,KS 66045,USAe-mail:liuwku.eduJ Solid State Electrochem(2013)17:17491758DOI 10.1007/s10008-013-2039-xactivation utilizes KOH,H3PO4,ZnCl2,etc.In particular,chemical activation has outstanding advantages such as lowactivation temperatures,high yields,reduced activation time,and high surface area and pore volume 8.Of special interestis the use of KOH in chemical activation process,it can resultin activated carbons with balanced pore size distributions andhigh specific surface areas up to 3,000 m2g19.Variouskinds of carbon sources have been,so far,investigated usingKOH as an activating agent,such as graphene 10,mesoporous carbon 11,12,carbon nanofibers 13,straw14,etc.Further exploring low-cost and commercially avail-ablematerialsforpreparingporouscarbonsbytheactivationofKOH is still interesting and imperative.Ion-exchange resin is an insoluble matrix normally in theform of small beads based on cross-linked polystyrene and hasa highly developed structure of pores on the surface of whichare sites with easily trapped and released ions.They are widelyusedinseparation,purification,anddecontaminationprocesses15.Nowadays,the amount of waste ion-exchange resins isincreasing all over the world;therefore,the effective method towell dispose the waste resins is required 16.Considering the unit structure of cation exchange resin,especially the existence of phenyl groups,genuine carbonsare thus expected to form because of the high carbon contentof resin.Herein,we demonstrate a KOH-activated methodto prepare porous carbon,using cation exchange resin as thecarbon source.The mass ratio of cation exchange resin-to-KOH and activation temperature is emphatically studied.The resulting specific surface area,pore structure,and ca-pacitive performance of the as-obtained porous carbonswere well measured.ExperimentalAll the chemicals were purchased from Sinopharm Chemi-cal Reagent(Shanghai)Co.Ltd with analytical grade andused as received without further treatment.For research convenience,we adopted pure Sodium Form732 Cation Exchange Resin(cation exchange resin)as thestarting material because the regeneration of waste cationexchange resin can simply be realized by the treatment ofdiluted acid solution.The cation exchange resin was firstcarbonized at 600 C for 2 h under Ar flow,subsequentlywashed with deionized water(step 1),resulting in pristinecarbon,dominated as carbon-blank.The as-obtained samplewas further activated by KOH with designated mass ratios of1:1/1:2/1:3/1:4 at 600/700/800 C for 2 h under Ar flow(step2),giving rise to the formation of composite containing car-bon,potassium/potassium oxides/potassium carbonates aswell as some gases.After thoroughly being washed withdeionized water(step 3),the final activated carbonswith plentiful pores,named as carbon-600/700/800-1:1/1:2/1:3/1:4,were achieved.The whole schematicroute is depicted in Fig.1.Typical synthetic procedure for activated carbon from cationexchange resinFirst,certain amount of cation exchange resin was placed ina porcelain boat,flushing with Ar flow for 30 min,andfurther heated in a horizontal tube furnace up to 600C ata rate of 5 Cmin1and maintained at this temperature for2 h under Ar flow.After being washed with deionized water,the carbon-blank sample was obtained.Next,the above carbon-blank sample and KOH pelletswere mixed with designated mass ratios of 1:1/1:2/1:3/1:4and ground adequately in a mortar.The mixture was thenheated at 600/700/800 C for 2 h under Ar flow.Theresultant composites were immersed with dilute HCl solu-tion to remove soluble/insoluble substances,subsequentlywashed with deionized water.Finally,the samples weredried under vacuum at 120 C for 12 h to obtain thecarbon-600/700/800-1:1/1:2/1:3/1:4 samples.CharacterizationX-ray diffraction(XRD)patterns were obtained on a RigakuD/MAX2500V with Cu K radiation.Field emission scan-ning electron microscopy(FESEM)images were taken witha Hitachi S-4800 scanning electron microscope.X-ray pho-toelectron spectra(XPS)were obtained on a VG ESCALABMK II X-ray photoelectron spectrometer with an excitingsource of Mg K(1,253.6 eV).The specific surface areaand pore structure of the carbon samples were determinedby N2adsorptiondesorption isotherms at 77 K(Micrometrics ASAP 2020 system)after being vacuum-dried at 200 C overnight.The specific surface areas werecalculated by the conventional BrunauerEmmettTeller(BET)method.The pore size distribution curves wererecorded from the adsorption branch of the isotherm basedon the BarrettJoynerHalenda(BJH)model.Electrochemical measurementsIn order to evaluate the capacitive performances of the as-prepared carbon samples(4 mg)in electrochemical capac-itors,a mixture of 80 wt%the carbon sample,15 wt%acetylene black,and 5 wt%polytetrafluoroethylene binderwas fabricated using ethanol as a solvent.Slurry of theabove mixture was subsequently pressed onto nickel foamunder a pressure of 20 MPa,serving as the current collector.The prepared electrode was placed in a vacuum drying ovenat 120 C for 24 h.A three-electrode experimental setuptaking a 6 molL1KOH aqueous solution as electrolytewas used in cyclic voltammetry and galvanostatic charge1750J Solid State Electrochem(2013)17:17491758discharge measurements on an electrochemical working sta-tion(CHI660D,ChenHua Instruments Co.Ltd.,Shanghai).Here,the prepared electrode,platinum foil(6 cm2)andsaturatedcalomelelectrodewereusedastheworking,counter,and reference electrodes,respectively.Results and discussionWhen directly calcining cation exchange resin without theaddition of any KOH at 600C for 2 h,followed by thewashing with deionized water,the carbon-blank sample wasachieved.The corresponding XRD pattern is displayed inFig.2a,in which one broad and low-intensity diffractionpeak centers at ca.22.3,incredibly indicating the amor-phous and low-graphitization structure 17.Next,the car-bon-blank sample was activated by KOH with mass ratio of1:4 at 800 C for 2 h,subsequently with the washing withaqueous HCl and deionized water,the carbon-800-1:4 sam-ple was obtained,whose XRD pattern is shown in Fig.2c.To study the activation mechanism involved,the composite,i.e.,the carbon-800-1:4 sample before being washed,is alsodetected by XRD technique.The result in Fig.2b revealsthat the composite is composed of amorphous carbon andFig.1 Schematic routeshowing the production ofactivated carbon from cationexchange resin10203040506022.3o2 theta(deg.)Intensity(a.u.)*(c)(b)(a)*1020304050602 theta(deg.)43.4o25.0o800 oC700 oC600 oC(f)(e)(d)Intensity(a.u.)Fig.2 a XRD pattern of the carbon-blank;XRD patterns of the carbon-800-1:4 sample before(b)and after(c)being washed with aqueous HClsolution and deionized water to remove any unwanted impurities;dcarbon-600-1:4;e carbon-700-1:4;f carbon-800-1:4.Single asterisk(*)monoclinic K2CO31.5H2O(JCPDS card no.110655)J Solid State Electrochem(2013)17:174917581751monoclinic K2CO31.5H2O(JCPDS card no.110655).Thefinal product of K2CO31.5H2O well accords with the reac-tion mechanism commonly conceivable by scientists:theactivation of carbon with KOH proceeds as 6KOH+C2K+3H2+2K2CO3,followed by decomposition of K2CO3and/or reaction of K/K2O/K2CO3/CO2with carbon 18,19.XRD patterns of the carbon-600/700/800-1:4 samples aredisplayed in Fig.2df,respectively.The diffraction peakslocating at ca.25.0 can be indexed as(002)plane of graphite,while the one at ca.43.4 ascribe to(100)or(101)planes,often abbreviated as(10).Obviously,the two theta of thecarbon-600/700/800-1:4 samples have shifted to high degreecomparedwiththatofthecarbon-blanksample.Thatistosay,the lattice spacing of(002)plane after KOH activation hasbeenshortenedincontrasttothatofthepristinecarbon(BraggEq.2d sin=),primarily due to the intercalation of metallicpotassium 20.In addition,as increasing the activation tem-peratures from 600 to 800 C,keeping other reaction param-eters unchanged,the diffraction peaks at ca.25.0 graduallydisappear,whereas the ones at ca.43.4 almost remain.Thisindicates that higher activation temperature fairly favors forlarger dispersion of graphite layers,commonly resulting inhigh surface area 21.The shapes and sizes of the carbon-blank and carbon-600/700/800-1:4 samples were depicted by FESEM tech-nique.Figure 3a displays the representative FESEM imageof the carbon-blank sample,which consists of large numbersof irregular particles.The surfaces are clearly covered withabundant pores of several hundreds in sizes.However,as weknow,these pores are so large as to have neglectable contri-butions to the total pore volumes.After activated by KOH,these large pores vanish on the surfaces of the carbon-600/700/800-1:4 samples,and the particles seem to be morecompact,as shown in Fig.3bd.Even so,large quantity ofinvisibleporesinthescopeofmicrotomacro-scaleisbelievedto exist within the carbons,which will be detected by thefollowing N2adsorptiondesorption technique.The BrunauerEmmettTeller(BET)surface area and porestructure of the carbon-600/700/800-1:4 samples were inves-tigated by N2adsorptiondesorption isotherms,asdisplayed inFig.4ac.All present samples take on type IV isothermsaccording to IUPAC classification 22.At relatively low pres-sure(carbon-800-1:4carbon-600-1:4.The presenttrend of specific capacitance is not consistent with the BETsurface areas and total pore volumes of the carbon samplesshown in Table 1.In other words,there is no linear relation-ship between the surface area and the capacitance 3.It wasconfirmed that capacitance not only depends on surface areabut also on two other parameters:pore size distribution andsurface chemistry 32.Therefore,the carbon-700-1:4samplepossessing the maximum specific capacitance probably de-rives from the synergistic effects discussed above,especiallythe well-balanced micro-or mesoporosity distribution33.On the other hand,further increasing the scan ratefrom 20 to 100 mVs1leads to larger distortion of CV0200400600800100012001400321C1sO1s3-carbon-800-1:4 2-carbon-700-1:4 1-carbon-600-1:4 Binding Energy(eV)Relative Intensity(a.u.)survey(a)2822842862882902922943-carbon-800-1:4 2-carbon-700-1:4 1-carbon-600-1:4 289.4286.2288.3285.4284.5Binding Energy(eV)Relative Intensity(a.u.)123C1s(b)525528531534537540543532.8531.6534.0535.73-carbon-800-1:4 2-carbon-700-1:4 1-carbon-600-1:4 321Binding Energy(eV)Relative Intensity(a.u.)O1s(c)Fig.5 XPS spectra of the carbon-600/700/800-1:4 samples:a survey,b C1s,and c O1sTable 2 XPS peak analysis of the carbon samplesSampleC(at.%)O(at.%)Carbon-600-1:485.2814.72Carbon-700-1:487.9012.10Carbon-800-1:489.3610.641754J Solid State Electrochem(2013)17:17491758curves in shapes.The reason is that electrolytes cannotefficiently enter into micropores for the formation ofdouble-layer capacitance at high scan rates,especiallybeyond 100 mVs1.Figure7adisplaysthewholeCVcurvesofthecarbon-700-1:4 sample at scan rates of 10100 mVs1.It indicates thatalong with the increase of scan rates,the integral areasencircled by CV curves increase gradually,also accompany-ing with the improved deterioration of CV curves in shapes.Galvanostatic chargedischarge curves of the carbon-700-1:4sample measured at current densities from 1 to 20 Ag1areshown in Fig.7b.All chargedischarge curves take on goodtriangle shapes in the potential range of 0.90.1 V,anotherindication of well-performed EDLC.Furthermore,higher cur-rent density can lead to shorter charge/discharge time,mainlydue to the deficient ions moving at higher current den-sity between electrolyte and porous carbon.Figure 7cindi