Porous Carbons Derived from Lignite Mixed with Zn 2+ -Doped Lignin for Electric Double-Layer Capacitor

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1 Int. J. Electrochem. Sci., 12 (217) , doi: / Interntionl Journl of ELECTROCHEMICAL SCIENCE Porous Crons Derived from Lignite Mixed with Zn 2+ -Doped Lignin for Electric Doule-Lyer Cpcitor Yn Wu, Xio-Yn Zho *, Jing-Pei Co **, Shn He, Zhi-Qing Ho, Hu-Yng Yu, Guo-Yu Sun, Xin-Yong Wei Key Lortory of Col Processing nd Efficient Utiliztion (Ministry of Eduction), Chin University of Mining & Technology, Xuzhou , Jingsu, Chin * E-mil: zhoxioyn@cumt.edu.cn ** E-mil: cojingpei@cumt.edu.cn, eyondco@hotmil.com, eyondco_2@163.com Received: 3 June 217 / Accepted: 11 July 217 / Pulished: 13 August 217 A series of porous crons (PCs) were prepred from lignin chelting with Zn 2+ nd mixed with lignite. KOH ws used s the ctivted gent during preprtion process. The influences of preprtion prmeters including the content of lignin chelted with Zn 2+, KOH/smple rtio nd ctivtion temperture on specific surfce re (SSA), pore size distriution nd electrochemicl performnces were investigted in this study. All the PCs were minly micropores through nitrogen dsorption isotherms test. The PCs derived from the lignin chelting with Zn 2+ present high SSA nd totl pore volume thn tht in the sence of Zn 2+. In ddition, the PC prepred from dding lignin to lignite hs lrger SSA thn the PC prepred from lignite. The PC prepred with Zn 2+ ccount for 3% of lignin mss, KOH/smple rtio of 3:1 nd ctivtion temperture of 7 o C hs the lrgest SSA of 3311 m 2 g - 1. When it ws used s electrode for electric doule-lyer cpcitor, the specific cpcitnce reched the highest vlue of F g -1 t current density of 4 ma g -1. The results demonstrte tht the lignin chelting with Zn 2+ then dd to the lignite cn significntly improve PCs performnce. Keywords: Lignin; Lignite; Porous crons; High surfce re; EDLC 1. INTRODUCTION The electric motors nd genertors invented in 187s led to prevlence of the electricl energy, especilly in the ge of electricity [1]. Nowdys, the oil resources scrcity nd the environment prolems re ecoming more nd more serious which re pushing people to find n environmentlly effective energy storge device [2]. The supercpcitor s promising energy storge

2 Int. J. Electrochem. Sci., Vol. 12, devices for electric power hve een ttrcting much ttention [3], which scried to its high energy density, long cycle life nd excellent reversiility [4, 5]. The supercpcitor cn e divided into electric doule-lyer cpcitor (EDLC), pseudocpcitive nd hyrid cpcitors ccording to its storge mechnism [2, 3, 6]. In generl, the electrode mterils is the core component to EDLC. The electrode mterils with high specific surfce re (SSA), optimized porous structures nd fvorite functionl groups hs excellent electrochemicl performnce. A series of porous crons (PCs) such s ctivted crons, cron nnotues, cron erogels, grphene sheets nd cron nnofiers [7-11] were used for EDLC. The PCs cn e prepred from wste te-leves, sugr cne gsse, col, pitch nd petroleum coke [12-17]. The preprtion methods of PCs include physicl nd chemicl ctivtion, mong which chemicl ctivtion is known s simple method for preprtion of PCs with high SSA nd porosity. Lignin is the second most undnt nturl polymer next to cellulose nd cn e used s precursor for PCs ttriute to its most undnt romtic polymer [18-2]. Hong et l. [21] reported tht the ZnCl 2 cn ct not only s solvent for lignin, ut lso cn integrted into the lignin. The metl ion hs the cpility of promoting the dehydrogention of the polymer nd ctlyzing chr formtion in the condensed phse [22]. Col re usully s the precursors for preprtion of PCs due to the low cost nd high cron content, especilly for tht rich in oxygen functionl group, such s lignite. But the high sh content in lignite hs gret impct on the qulity of PCs. When PCs ws used s electrode mterils for EDLC, the sh lso ffect the EDLC performnces [23]. Addition of certin cronceous mterils to the lignite my improve the performnce of PCs. KOH is one of the most effective compound for preprtion of ctivted crons. The PCs prepred from the mixture (lignin treted y ZnCl 2 then dd to the lignite) which my e hve high SSA when KOH ws used s ctivting gent. The PCs prepred through this method nd pplied in EDLC my hve excellent electrochemicl performnce, which re rrely reported. In this work, the lignin ws firstly mixed with ZnCl 2 solution to otin the lignin with Zn 2+. Then the PCs were prepred from the mixture which the lignin with Zn 2+ dd to lignite through croniztion-ctivtion method. The effects of Zn 2+ content, KOH/smple rtio nd ctivtion tempertures on the SSA nd electrochemicl performnce of the PCs for EDLC in 6 M KOH electrolyte were ddressed in detil. 2. EXPERIMENTAL 2.1. Mterils nd Regents Alkli lignin ws purchsed from TCI nd Shengli lignite ws collected from Inner Mongoli, Chin. The proximte nd ultimte nlyses of lignin nd lignite were shown in Tle 1. ZnCl 2 nd KOH re oth the nlyticl regents provided y Xilong Chemicl Co. Deionized wter ws used through ll the experiment.

3 Int. J. Electrochem. Sci., Vol. 12, Tle 1. Proximte nd ultimte nlyses of the lignin nd lignite. Smple Proximte nlysis (wt%) Ultimte nlysis (wt%,df) M r A d VM d FC d C H N S O Lignin Lignite A: sh; M: moisture; VM: voltile mtter; FC: fixed cron; r: s received sis; d: dried sis; df: dried nd sh free sis; : y difference Preprtion of the PCs Lignin ws dded to the ZnCl 2 solution nd the content of Zn 2+ ws clculted sed on the weight of the lignin. The lignin nd ZnCl 2 solution were stirred for 1 h in the wter th t 6 o C, nd then dried t 15 o C for 24 h. Susequently, the lignin with Zn 2+ ws mixed with lignite (the weight rtio ws 1:1). The mixture ws cronized t 6 o C for 2 h under Ar tmosphere in horizontl tue furnce t heting rte of 1 o C min -1. And the otined chr ws denoted s LC. The LC ws ctivted with KOH in horizontl tue furnce t 18 o C for 3 min nd then t prescried temperture of 6 to 9 o C for 1 h. The ctivted smples were oiled t 8 o C with 2 M HCl solution for 3 min, filtered nd rinsed y wrm deionized wter severl times, nd then wshed y room-temperture deionized wter until neutrl. The wshed smple ws dried in vcuum oven t 15 o C for 3 h nd the smple ws denoted s PC. All the smples nd their preprtion prmeters in this study re shown in Tle 2. The lignite without lignin is nmed SL nd the lignin without lignite is nmed LG. The preprtion condition of SL nd LG is the sme to PC-7. Tle 2. The preprtion prmeters of PCs (croniztion temperture of 6 o C nd ctivtion time of 6 min). Smple Rtio (KOH:LC) Content of zinc ions (%) Activtion temperture ( o C) PC-1 3:1-7 PC-2 3: :1 3 7 PC-4 3:1 5 7 PC-5 1:1 3 7 PC-6 2:1 3 7 PC-7 4:1 3 7 PC-8 5:1 3 7 PC-9 3:1 3 6 PC-1 3:1 3 8 PC-11 3: Cron Chrcteriztion Nitrogen dsorption-desorption isotherms were mesured t 77 K using n utomtic dsorption system in Quntchrome Autosor-IQ utomted gs sorption nlyzer. In order to

4 Int. J. Electrochem. Sci., Vol. 12, eliminte surfce contmintion, ll the smples were degssed t 3 o C for 1 h in vcuum condition efore dsorption. The SSA nd pore size distriutions were clculted y using the Brunuer-Emmett-Teller (BET) eqution nd the Density Functionl Theory (DFT), respectively. The totl pore volume (V t ) ws estimted t reltive pressure of P/P of.99. In ddition, the micropore surfces nd micropore volumes were mesured using the t-plot method. The mcroscopic fetures of smples were otined on Merlin Zeiss scnning electron microstructure (SEM) Electrochemicl Mesurements The electrodes were prepred y mixing PC, cetylene lck nd polytetrfluoroethylene (PTFE) inder t weight rtio of 85:1:5 in n gte mortr nd then the mixture ws pressed onto nickel fom under 6 MP in wfer shpe with dimeter of 13 mm. The electrodes were immersed with 6 M KOH solution under vcuum for 24 h to gurntee thorough wetting. Two of the electrodes were ssemled t room temperture nd seprted y polypropylene memrne, using MTI EQ-STC two-electrode testing type system. Cyclic voltmmetry (CV) nd electrochemicl impednce spectroscopy (EIS) were crried out on n Ivium Vertex electrochemicl worksttion. CV ws performed t voltge rnging from to 1 V t different scn rtes. EIS mesurement ws mesured t the open circuit voltge with mplitude of 1 mv nd the frequency rnge from 1-2 to 1 5 Hz. Glvnosttic chrge-dischrge (GCD) ws tested with the voltge from to.9 V y NEWARE cell test instrument. The specific cpcitnce (C s ) ws clculted from the glvnosttic dischrge curves ccording to Eq. (1) [24]. IΔt C s = 2 (1) mδv Where C s is the specific cpcitnce (F g -1 ), I is the current of dischrge, t is the dischrge time, m is one of the mss of electrodes mteril nd V is the voltge difference. The energy density (W h kg -1 ) nd power density (W kg -1 ) were clculted sed on the following formul [25]: 1 2 E = CV (2) 2 VI P= (3) m Where I is the dischrge current nd m is the ctive mss of the two-electrode cpcitor. 3. RESULTS AND DISCUSSION 3.1. Structurl Chrcteriztion of the PCs Morphology nd Microstructure of the PCs As shown in Fig. 1, lrge numer of Zn 2+ cn e found with uneven distriution tht due to the uneven lignin mixed with lignite. It lso suggests tht the Zn 2+ re successfully introduced into the precursor mixture. The imge of Fig. 1 displys n uneven surfce with mny smll pores nd no zinc

5 Int. J. Electrochem. Sci., Vol. 12, elements residul cn e oserved. ZnCl 2 evportes nd leve the position previously occupied y ZnCl 2 during the ctivtion process. The result is tht the PCs present high SSA, which is lso supported y the nitrogen dsorption-desorption isotherms. The PC-1 (Fig. 1c) hs porous structure with rugged surfce structure. Compred with, the PC-1 hs few pores demonstrting tht the mixture of lignite nd lignin chelting with Zn 2+ during the ctivtion process cn mke more pores thn tht in the sence of Zn 2+. c 1 m 1 m 1 m Figure 1. SEM imges of the LC contin 3% zinc ions (); (); PC-1 (c) Pore Structure of PCs It is well known tht the pore size distriution nd SSA re the importnt prmeters for EDLC. The perfect cron electrodes need proper pore size distriution nd reltively high SSA [26]. Thus it is necessry to study the pore structure of prepred PCs nd understnd the effects of preprtion conditions on the development of pore structure. Nitrogen dsorption-desorption nlysis were crried out to study the porosity of PCs. As exhiited in Fig. 2, the PCs re typicl of microporous mterils nd nitrogen dsorptiondesorption isotherms re elong to type I ccording to the clssifiction of the IUPAC [27]. The nitrogen dsorption shrply increses t reltive pressure elow.4, which illustrtes lrge numer of micropores in the PCs. A hysteresis loop cn e found t the P/P of.4-.9, which revels the presence of mesopores in PCs. In ddition, smll tils t the P/P ner 1. reveling the presence of mcropores. The SSA, pore volume nd verge pore size prmeters of the PCs re given in Tle 3. As shown in Fig. 2, the isotherms rises rpidly t low reltive pressure with the increse of the Zn 2+ mount, indicting tht the Zn 2+ plys n importnt role in microporous producing. It should e ttriuted to the dehydrtion of ZnCl 2 during the ctivtion process, which results in the croniztion nd romtiztion of cron skeleton nd pore-creting [24]. Some reserchers re using ZnCl 2 s ctivted gent for production of ctivted crons [2, 28-3]. The dsorption quntity incresed from PC-1 to, while the dsorption cpcity decresed with the increse of Zn 2+ content from 3% to 5%. It proly due to the excess Zn 2+ cuse some pores ecome lrger even collpse during ctivtion process nd leding to reduction of SSA.

6 STP (cm 3 g -1 ) STP (cm 3 g -1 ) STP (cm 3 g -1 ) Int. J. Electrochem. Sci., Vol. 12, PC-1 PC-2 PC Reltive pressure(p/p ) PC-5 PC-6 PC-7 PC Reltive pressure (P/P ) 12 c PC-9 PC-1 PC Reltive pressure (P/P ) Figure 2. Nitrogen dsorption-desorption isotherms of the PCs. The KOH-LC rtio lso hs significnt influence on the pore structure [14]. As listed in Tle 3, with KOH-LC rtio from 1:1 to 5:1, the SSA is 1257, 2351, 3311, 2842 nd 2518 m 2 g -1, nd the V t is.63, 1.19, 1.79, 1.54 nd 1.45 cm 3 g -1, respectively. The trend of SSA nd V t is incresed firstly nd

7 Int. J. Electrochem. Sci., Vol. 12, then decresed with the increse of KOH-LC rtio. The trend indicted tht the ctivtion y KOH could mke micropores etched into mesopores or mcropores. However, the excessive mounts of KOH could leds to pores collpse nd resulting in the reduction of SSA [31, 32]. It lso cn e seen tht the PC-7 hs higher SSA thn SL nd LG, indicting tht lignin chelting with Zn 2+ then dd to lignite cn improve the qulity of PCs. The lignin pyrolysis is wider thn lignite (Fig. 3 nd ). The lignin my e relese of CO 2 nd CO nd form some pores t low temperture. With the ctivtion process continues, more CO 2 nd CO re relesed from the mixture nd developed more pores. The results is tht the PC-7 hs lrge SSA (2842 m 2 g -1 ). Li et l. [33] prepred ctivted cron from lignite with ZnCl 2 nd the SSA of the s prepred ctivted cron ws only 124 m 2 g -1. Tle 3. Pore structure prmeters of the PCs otined under different preprtion conditions. Smple S BET S micro S non-micro c V tot d V micro V non-micro c (m 2 g -1 ) (m 2 g -1 ) (m 2 g -1 ) (cm 3 g -1 ) (cm 3 g -1 ) (cm 3 g -1 ) (nm) PC PC PC PC PC PC PC PC PC PC SL LG S BET : Specific surfce re from multiple BET method. S micro, V micro : Micropore surfce re micropore volume from t-plot method. c S non-micro, V non-micro : Difference of S BET nd S micro nd totl pore volume nd V micro, respectively. d V tot : Totl pore volume t P/P =.99. e D: Averge pore dimeter. D e

8 Weight loss(%) DTG (%/ o C) Weight loss (%) DTG (%/ o C) Int. J. Electrochem. Sci., Vol. 12, TG DTG Temperture ( o C) 1 TG. DTG Temperture ( o C) Figure 3. TG nd DTG curves of lignite () nd lignin (). Activtion temperture is lso n importnt fctor for controlling ctivtion extent [34]. The increse of ctivtion temperture from 6 o C to 7 o C cused the increse of oth the SSA nd mesopores size. However, the SSA decresed from 3311 to 2814 m 2 g -1 when the ctivtion temperture ws incresed from 7 o C to 9 o C, which is scried to the fct tht the ctivtion rection over 7 o C is fst nd thus results in over-etching [32, 35]. As cn e deduced from Fig. 4, the pore dimeters of ll the PCs concentrte in rnge of.5 to 5 nm, illustrting tht the PCs minly contined micropores nd mesopores, which is consistent with the nitrogen dsorption-desorption isotherms. Some reserchers reported tht micropores nd mesopores with pore width in certin rng is fvor for chrge storge in queous electrolytes [36-38].

9 Int. J. Electrochem. Sci., Vol. 12, dv(d) cm 3 nm -1 g dv(d) cm 3 nm -1 g PC-1 PC-2 PC Pore width (nm) dv(d) cm 3 nm -1 g Pore width (nm) PC-5 PC-6.42 PC-7 1. PC dv(d) cm 3 nm -1 g Pore width (nm) dv(d) cm 3 nm -1 g Pore width (nm) c dv(d) cm 3 nm -1 g PC-9 PC-1 PC Pore width (nm) Pore width (nm) Figure 4. Pore size distriutions of the PCs The Influence of Preprtion Conditions on the Electrochemicl Properties Effect of Zn 2+ Content The GCD mesurements were used to detect the electrochemicl performnces of the otined PCs. As cn e seen from Fig. 5, the curves of the PCs present closely liner nd symmetricl tringle

10 Specific cpcitnce (F g -1 ) Current (ma) Potentil (mv) Potentil (mv) Int. J. Electrochem. Sci., Vol. 12, with low ir voltge drops which indicte the good electrochemicl reversiility of the PCs [39]. The chrge-dischrge time of is much longer thn the others, suggesting the hs higher C s (28.43 F g -1 ). The good performnce of should e ttriuted to the highest SSA (Tle 3). The C s cn e clculted ccording to the Eq. (1). The C s vlues t the current density of 4 ma g -1 re , , nd F g -1 for the PC-1, PC-2, nd PC-4, respectively, demonstrting tht the is the most pproprite for energy storge PC-1 PC-2 PC ma g -1 1 ma g ma g -1 2 ma g ma g -1 3 ma g Time (s) 3 c Time (s) 1 d PC-1 PC-2 PC Current denisty (ma g -1 ) -5 PC-1 PC-2 PC Potentil (V) Figure 5. Effect of Zn 2+ content on the cpcitive performnces of PCs (PC-1~ PC-4). GCD curves of PCs t 4 ma g -1 (); GCD curves of t different current densities (); C s of PCs t different current densities (c); CV curves of PCs t scn rte of 2 mv s -1 (d). Fig. 5 displys the GCD curves of t different current densities. All the curves re still pproximte isosceles tringle t incresed current densities from 4 to 3 ma g -1, suggesting excellent electrochemicl reversiility [4]. The reltionship etween the current density nd C s is given in Fig. 5c. The C s decreses with the incresing of current density, which is due to the slow chrge-dischrge kinetics of the electrode mteril. Therefore, t the reltively high current density, the electrolyte ions hs not enough time to ccess the surfce of cron so tht lrge numer of ions ws not een well used [2]. The other one is tht the electrolyte ions diffusion in the porous suffered gret resistnce nd the ions cnnot fully enter the micropores under high current density [41].

11 Potentil (mv) Specific surfe re (m 2 g -1 ) Specific cpcitnce (F g -1 ) Int. J. Electrochem. Sci., Vol. 12, CV cn e further illustrte the electrochemicl performnce of the PCs. As seen in Fig. 5d, the CV curves show typicl similr rectngulr shpe without cler redox peks indicting n idel EDLC ehvior nd fst diffusion of electrolyte ions into/out of the electrode mterils [42]. In ddition, the CV curve of hs lrger re thn tht of PC-1, PC-2 nd PC-4. In generl, lrge SSA will hve high C s. The reltively high C s of is consistent with the result of GCD curves in Fig The Effect of KOH-LC Rtio As exhiits in Tle 3, the SSA nd V t were chnged with the increse of KOH-LC rtio which leding to the electrochemicl properties chnge. Fig. 6 shows the pproximte isosceles tringle shpe of the PC-5, PC-6,, PC-7 nd PC-8 curves, indicting tht the smples hve good electrochemicl stility nd reversiility. The C s t the current density of 4 ma g -1 of the PC-5, PC- 6,, PC-7 nd PC-8 is 21.1, , 28.43, nd F g -1, respectively. The reltively high C s of (KOH/LC = 3) is consistent with the high SSA nd pore volume. As shown in Fig. 6, the SSA incresed rpidly with the increse of KOH-LC rtio from 1 to 3 nd reched 3311 m 2 g -1 when the KOH/LC is 3. The SSA decresed when further incresed the rtio ove 3. The chnge in C s is similr to the SSA, suggesting the SSA hs importnt influences on the C s. The result is consistent with tht reported y Gmy [43]. It cn e seen in Fig. 6c tht ll the CV curves disply similr rectngles shpe without redox peks, indicting the typicl performnce of EDLC. Fig. 6d shows the CV curves of t different scn rtes from 2 to 1 mv s -1. The shpes of the CV curves devite from the rectngulr nd ecme more nd more olique with the increse of scn rte. It ecuse tht the increse of scn rte cused the voltge signl could not rech the pores effectively. In other words, this phenomenon should e ttriuted to the trdiness of the chrge-dischrge kinetics of the PC. Therefore, the electrolyte ions cnnot rech the PC surfce efficiently in short time [44, 45]. Compred with SL nd LG, the PC-7 hs lrger C s (Fig. 6e) which due to the PC-7 hs lrge SSA. The results illustrte tht the electrochemicl performnce improve fter dding lignin to lignite PC-5 PC-6 PC-7 PC Time (s) 1:1 2:1 3:1 4:1 5:1 Rtio 15

12 Potentil (mv) Current (ma) Current (ma) Int. J. Electrochem. Sci., Vol. 12, d 5 7 PC-5-5 PC-6 PC-7 PC Potentil (V) 1 8 e -7 2 mv s -1 5 mv s -1 8 mv s -1 1 mv s -1 2 mv s -1 3 mv s -1 5 mv s -1 1 mv s Potentil (V).8 1. LG SL PC Time (s) Figure 6. Effect of KOH-LC rtio on the cpcitive performnces of PCs. GCD curves of PCs with the current density of 4 ma g -1 (); SSA nd Cs t different rtios (); CV curves t scn rte of 2 mv s -1 (c); t vrious scn rtes from 2 mv s -1 to 1 mv s -1 (d); GCD curves of LG, SL nd PC-7 (e) The Effect of Activtion Tempertures In this study, the effects of ctivtion temperture on electrochemicl performnce of PCs re crried out under the condition tht KOH-LC rtio ws kept t 3. The GCD curves of PC-9,, PC- 1 nd PC-11 re displyed in Fig. 7. All the GCD curves show n pproximte isosceles tringle, indicting good EDLC fetures nd there is no frdy current cused y the redox rections. In ddition, the chrge-dischrge time of is longer thn PC-9, PC-1 nd PC-11, suggesting the PC- 3 hs higher C s under the sme current density. As shown in Fig. 7, the C s of is F g -1 t the current density of 4 ma g -1. At the current density of 3 ma g -1, the C s of is retin F g -1, which demonstrtes tht 7 o C is the est ctivtion temperture. The chnges re due to the different SSA nd pore structures of PCs (Tle 3). The CV curves of PC-9,, PC-1 nd PC-11 exhiit the pproximte rectngle shpes t 2 mv s -1 in Fig. 7c. The re of the CV curve for the is much lrger thn others, demonstrting the hs the est electrochemicl performnces.

13 Current (ma) -Z'' ( ) -Z'' ( ) Potentil (mv) Specific cpcitnce (F g -1 ) Int. J. Electrochem. Sci., Vol. 12, PC-9 PC-1 PC PC-9 PC-1 PC Time (s) c Current denisty (ma g -1 ) d PC-9-6 PC-1 PC Potentil (V) Z' ( ) PC-9 PC-1 PC Z' ( ) Figure 7. Effects of ctivtion tempertures on the cpcitive performnces of PCs. GCD curves of PCs t 4 ma g -1 (); the C s of PCs under different current densities (); CV curves of PCs t 2 mv s -1 (c); Nyquist plots of PCs (d). The EIS test ws crried out for further understnd the electrochemicl ehvior nd the effect of frequency on the cron electrodes. As shown in Fig. 7d, ll the smples hve idel electrochemicl cpcitnce chrcteristic. In the low frequency, the Nyquist plots present nerly liner indicting the idel cpcitive ehvior [46, 47]. There is cler semicircle in high frequency, indicting the interfce of the electrode exists ion diffusion resistnce [48]. The semi-circle of, PC-1 nd PC- 11 is smller thn PC-9, indicting the ion diffusion into the electrode surfce of, PC-1 nd PC- 11 is fster thn into PC-9. The energy density nd power density re clculted ccording to the Eqs. (2) nd (3). The plot of PCs with different ctivtion tempertures re shown in Fig. 8. As cn e seen, the energy density decresed slowly with the increse of power density, demonstrting tht in the high power density less energy ws relesed [49]. The energy density of is higher thn PC-9, PC-1 nd PC-11, indicting the possess etter electrochemicl performnces [2, 5]. This is due to the high SSA nd lrger verge pore dimeter of.

14 Energy density (W h kg -1 ) Int. J. Electrochem. Sci., Vol. 12, PC-9 PC-1 PC Power density (W kg -1 ) Figure 8. Rgone plot of PCs with different ctivtion tempertures. To compre the performnce of the PCs electrodes, summry of performnce of other PCs electrodes is presented in the Tle 4. The PC prepred in this work exhiits lrge SSA nd high Cs, demonstrting tht the lignite mixed with lignin chelting with Zn 2+ derived PCs re highly promising s electrode for EDLC nd show excellent electrochemicl performnce. Tle 4. PCs for EDLC electrodes. Rw mterils SSA (m 2 g -1 ) C s (F g -1 ) Electrolyte Ref. Lignite (5 ma g -1 ) 6 M KOH [33] HyperCol (1 ma g -1 ).5 M TEABF 4 /PC [14] Rice husk (1 ma g -1 ) 6 M KOH [51] Oil plm kernel shell (5 ma g -1 ) 1 M KOH [52] Ultr-Pure lignite (2 ma g -1 ) 6 M KOH [53] Lignin nd lignite (4 ma g -1 ) 6 M KOH This work 4. CONCLUSION The PCs with high SSA were prepred from lignite mixed with lignin chelting with Zn 2+ using KOH s ctivtion gent. The Zn 2+ content, KOH-LC rtio nd ctivtion temperture hd remrkle influence on the SSA nd C s of PCs. The C s incresed with long with the SSA nd the lrgest SSA reches to 3311 m 2 g -1. The ddition of lignin chelte with Zn 2+ to lignite my ffect the croniztionctivtion process of lignite nd improve the performnce of PCs. The prepred PCs s electrode mterils exhiit excellent electrochemicl performnce for EDLC. The present high C s of F g -1 t 4 ma g -1 nd the C s still retin high vlue of F g -1 t 3 ma g -1. Accordingly, the mixture of lignin nd lignite hs een demonstrted to e good precursor to prepre the ctivted cron nd excellent performnce electrodes for EDLC.

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