Pc

Ca

b

a

ARAA

KACRC

1

arri(ptUhd[tteEp

mpoa

0h

Journal of Analytical and Applied Pyrolysis 104 (2013) 372–377

Contents lists available at ScienceDirect

Journal of Analytical and Applied Pyrolysis

journa l h om epage: ww w.elsev ier .com/ locate / jaap

reparation and characterization of high surface area activatedarbons from co-pyrolysis product of coal-tar pitch and rosin

heng Zenga, Qilang Lina,∗, Changqing Fangb,∗, Dongwei Xua, Zhichao Maa

College of Materials Science and Engineering, Fuzhou University, Fuzhou 350116, PR ChinaCollege of Printing and Packing Engineering, Xi’an University of Technology, Xi’an 710048, PR China

r t i c l e i n f o

rticle history:eceived 4 April 2013ccepted 14 June 2013vailable online 26 June 2013

a b s t r a c t

Co-pyrolysis product of coal-tar pitch and rosin was used as a precursor to prepare high surface areaactivated carbons (ACs) by KOH activation. The influences of AC precursor origin, KOH/AC precursorweight ratio and activation time on the pore characteristics of the ACs were investigated, and meanwhiletheir electrochemical performance was studied. The results show that adding rosin results in a decrease

eywords:ctivated carbonoal-tar pitchosinhemical activation

in the C/H atomic ratio of AC precursor as well as a significant increase in its mesophase content, whichfavors the porosity development in ACs during KOH activation. The effect of adding rosin on the porositycharacteristics of the ACs can be illustrated by increases in the BET surface area from 1846 to 2847 m2/gand the total pore volume from 1.09 to 1.57 cm3/g. In addition, the ACs possess good electrochemicalperformance, as indicated by that they have a maximum specific capacitance of 203 F/g and exhibit goodrectangular-shaped I–V curves in cyclic voltammetry.

. Introduction

Activated carbons (ACs) with a highly developed surface areare widely used in numerous fields such as gas separation, solventecovery, organic pollution removal and catalyst support [1–3]. Inecent years, there is a growing interest in the applications of ACsn the fields of gas storage and electric double-layer capacitorsEDLCs) [4]. Commercial ACs, which have a low surface area andoor adsorption properties, cannot be applied to these fields and,herefore, it is necessary to fabricate high surface area ACs [5,6].p to now, mesocarbon microbeads (MCMB) and mesophase pitchave been considered to be the most suitable precursors for the pro-uction of high surface area ACs by potassium hydroxide activation7–11]. These ACs, which possess well-developed crystalline struc-ure, high mesopore content, high electronic conductivity, goodhermal stability, and satisfactory oxidation resistance [12–14], arespecially suited for applications in the fields of gas storage andDLCs. However, the high cost of traditional MCMB and mesophaseitch restricts the development and application of these ACs.

MCMB and mesophase pitch are two kinds of carbonaceousesophases prepared by thermolysis (pyrolysis) of aromatic com-

ounds such as pitch, coal tar and crude oil [15–17]. The formationf carbonaceous mesophase generally involves nucleation, growth,nd coalescence of mesophase spheres, which is accompanied by

∗ Corresponding authors. Tel.: +86 591 22866531; fax: +86 591 22866531.E-mail addresses: linqilang@hotmail.com (Q. Lin), fcqxaut@163.com (C. Fang).

165-2370/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.jaap.2013.06.010

© 2013 Elsevier B.V. All rights reserved.

simultaneous aromatic polymerization reactions; it is difficult tocontrol the polymerization reactions at pyrolysis temperatures,leading to the high cost of MCMB and mesophase pitch [18]. Asa solution, MCMB were prepared in high yield by co-pyrolysis ofcoal-tar pitch and rosin in our previous work [19]; the co-pyrolysisproduct had high mesophase content and low C/H atomic ratio aswell as low cost. It is known that the decrease in C/H atomic ratioof AC precursor is beneficial to the porosity development in ACs[20,21]. Therefore, the co-pyrolysis product seems to be a suit-able precursor for the low-cost production of high surface areaACs. In this paper, we attempted the preparation of ACs from theco-pyrolysis product by KOH activation, and then structures andelectrochemical performance of the ACs were studied.

2. Experimental

2.1. Raw materials

Coal-tar pitch was purchased from Wuhan Steel Co., Ltd.(Wuhan, China). Rosin was supplied by Ninghua Forest ChemicalsCo., Ltd. (Ninghua, China). The properties of pitch and rosin used inthis study can be seen in our previous study [19].

2.2. Preparation of AC precursors

Coal-tar pitch was mixed with certain amount of rosin in a cylin-drical steel reactor equipped with a motor driven stirrer. The stirrerwas started at 100 ◦C at a speed of 50 rpm. The speed of the stirrer

C. Zeng et al. / Journal of Analytical and Applied Pyrolysis 104 (2013) 372–377 373

AC p

wawrprts

2

cic5tcaiAutbwAarC8

A

w

2

bp(cwbtpo

Fig. 1. Optical textures of the three

as raised to 240 rpm at 150 ◦C and maintained for 30 min under nitrogen flow of 100 mL min−1. The pitch–rosin mixture sampleas loaded into a Pyrex tube, and then heated up to 450 ◦C at a

ate of 5 ◦C min−1 under a nitrogen stream and kept for 2 h. The co-yrolysis product obtained was labeled CP0, CP5 and CP10 when theosin content was 0 wt%, 5 wt% and 10 wt% of coal-tar pitch, respec-ively. The co-pyrolysis product was pulverized to <0.2 mm particleize and used as AC precursor.

.3. Preparation of ACs

Chemical activation with KOH was carried out using a mechani-al mixing method. The AC precursor sample was mixed with KOHn the desired proportions. The sample was placed in a corundumrucible, and heated in nitrogen atmosphere at a heating rate of◦C min−1 until the desired carbonization temperature and main-

ained under these conditions for 1, 1.5 or 2 h. The treatments werearried out in a tube furnace with an inner diameter of 50 mm under

nitrogen flow of 30 dm3 h−1. The activated sample was neutral-zed with a 0.5 mol/L HCl solution to eliminate the residual alkali.fter that, the sample was washed with hot distilled water (85 ◦C)ntil the PH of the filtrating solution was adjusted to 6–7. Finally,he cleaned sample was dried in vacuum at 110 ◦C for 24 h, followedy grinding and sieving to <0.2 mm particle size. The resultant ACsere labeled following the scheme: three groups of numbers afterC precursor (CP0, CP5, or CP10) make reference to the chemicalgent/AC precursor weight ratio, carbonization temperature, andesidence time. Thus, CP0-5-850-1.5 refers the AC obtained from theP0 after activation with KOH, in a ratio to the CP0 (5:1), treated at50 ◦C for 1.5 h. The activation yield (AY) of the AC was calculated:

Y (%) = W1

W0× 100, (1)

here W0 is the mass of AC precursor and W1 the mass of the AC.

.4. Preparation of electrode and cell capacitor

The electrode consisted of 80 wt% of AC, 10 wt% of acetylenelack and 10 wt% PTFE (polytetrafluoroethylene). Electrodes wereunched out of activated carbon sheet, and the disk electrodes1.5 cm2) were then mounted onto a Ni-current collector in a Teflonell holder. For the cell capacitor construction, two disk electrodesere mounted face-to-face into the holder with a separator in

etween. After the electrolyte solution of 6 M KOH was introduced,he capacitors were sealed. The capacitors were kept at room tem-erature for 24 h before electrochemical measurements. The massf the AC in a single electrode is about 12 mg.

recursors. (a) CP0, (b) CP5, (c) CP10.

2.5. Characterization

The carbon, hydrogen, and nitrogen weight percentages of sam-ples were determined using a Vario EL III elemental analyzer. Thesolubility in quinoline was determined according to ASTM D2318.

The AC precursor sample was mounted in epoxy resin, andsmoothed using fine grade silicon carbide paper, then polishedusing a cloth pad with alumina powder. Optical textures of thesample were observed from the polished surfaces using DDM-300Cpolarized-light microscope. The mesophase content was deter-mined using a point-counting procedure.

Textural characterization of the ACs was performed by N2adsorption at 77 K in a micromeritics ASAP 2020 apparatus. TheBET surface area (SBET) was determined from isotherms usingthe Brunauer–Emmett–Teller equation (BET). Total pore volume(Vtot) was defined as the volume of liquid nitrogen correspond-ing to the amount adsorbed at a relative pressure of P/P0 = 0.99.The micropore volume (Vmic) was obtained from application ofDubinin–Radushkevich (DR), and the mesopore volume (Vmes)was calculated as the difference between Vtot and Vmic. The poresize distribution was calculated from N2 adsorption isotherm byBerrret–Toyner–Hslena (BJH) method.

For the electrochemical analysis, charge–discharge tests wereperformed at a constant current density of 10 mA cm−2 in thepotential range of 0–1.2 V, and cyclic voltammetry (CV) measure-ments were performed between −1 V to 0 V with scanning rate from5 mV/s to 40 mV/s. All the electrochemical measurements wereconducted at ambient temperature. Specific capacitance of the sin-gle electrode was calculated from the CV curves according to thefollowing equation:

C =∫

idV

SmV, (2)

where C is the specific capacitance (F/g), i is the instantaneous cur-rent, V is the potential (V), S is the potential scanning rate (V/s), andm is the mass of active material on one electrode (g).

3. Results and discussion

3.1. Properties of AC precursors

Fig. 1 illustrates the SEM images of the AC precursors (CP0, CP5,and CP10). It is found that the three AC precursors all contain acertain number of irregular particles with sizes of 50–200 �m. Theparticles of the CP0 exhibit sharp edges and corners (Fig. 1a). How-ever, the particles of the CP5 and the CP10 have no obvious edges

and corners (Fig. 1b and c). The facts indicate that the rosin additionresults in decreased hardness of the AC precursor. The reason forthis is related to the characteristics of the AC precursors. The opti-cal textures of the AC precursors before pulverization were given in

374 C. Zeng et al. / Journal of Analytical and Applied Pyrolysis 104 (2013) 372–377

Table 1Main properties of the AC precursors.

Sample Elemental analysis (wt%) C/H QI (%) MC (%)

C H N

CP0 93.10 3.86 1.24 2.01 57.41 63.18CP5 92.42 4.07 1.22 1.89 48.38 92.46CP10 91.98 4.19 1.17 1.83 42.06 87.09

M

owthtfp

Iadccihmbcotttiwo

3

3

KtTiI5h1CCAspotcwtdbsccs

0.0 0.2 0.4 0.6 0.8 1.00

100

200

300

400

500

600

700

800

900

1000

1100

V (

cm

3/g

ST

P)

P/P0

CP0-5-850 -1.5

CP5-5-850 -1.5

CP10-5-850-1.5

1 2 3 4 5 6

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Dif

fere

nti

al

po

re v

olu

me

(c

m3

/g)

Pore size ( nm)

icantly increases with increasing KOH/CP10 weight ratio. Porositycharacteristics and activation yields of the ACs were summarized inTable 2. The activation yield of the AC is decreased from 64% to 35%when the KOH/pitch weight ratio KOH/pitch weight ratio increases

0.0 0.2 0.4 0.6 0.8 1.0

0

200

400

600

800

1000

1200

V (

cm

3/g

ST

P)

P/P0

CP10-3-850 -1.5

CP10-5-850 -1.5

CP10-7-850 -1.5

1 2 3 4 5 6

0.0

0.2

0.4

0.6

0.8

1.0

Dif

fere

nti

al

po

re v

olu

me

(c

m3

/g)

Pore size (nm)

C: mesophase content; C/H: the atomic ratio of C to H; QI: quinoline insolubles.

ur previous work [19]; the CP0 had a content of bulk mesophaseith various morphologies, whereas the CP5 contained a high con-

ent of irregular-shaped mesophase and the CP10 had a relativelyigh content of MCMB. Therefore, the high mesophase contents ofhe AC precursors (CP5 and CP10) seem to be responsible for theormation of the particles without obvious edges and corners afterulverization.

Table 1 shows the main properties of the above AC precursors.t can be seen that the AC precursor possesses lower C/H ratio withn increase in added rosin content from 0 to 10 wt%, showing aecrease in its aromaticity. Moreover, the quinoline insoluble (QI)ontent of the AC precursor decreases with increasing added rosinontent. The AC precursor had higher cycloparaffin content withncreasing added rosin content [19]. It is generally accepted that theigh cycloparaffin content is beneficial in the formation of solubleesophase constituents during the pyrolysis of pitch. This should

e responsible for the decrease in the QI content of the AC pre-ursor with increasing added rosin content. Furthermore, it can bebserved that the CP5 and CP10 have much higher mesophase con-ent that CP0, which confirms that the rosin addition contributeso the development of carbonaceous mesophase. Compared withhe CP5, the CP10 has lower mesophase content. The reason for thiss related to its lower C/H ratio and higher cycloparaffin content,

hich could reduce the polymerization velocity for hydrogenationf coal-tar pitch upon pyrolysis [15].

.2. Porosity of ACs

.2.1. Effect of AC precursor originThe AC precursor (CP0, CP5, or CP10) was mixed with the

OH in a 5:1 KOH/AC precursor weight ratio, and then the mix-ure was treated at 850 ◦C for 1.5 h to obtain the resultant AC.he adsorption–desorption isotherms and the inset correspond-ng pore size distribution profile for the ACs were given in Fig. 2.t can be observed in the isotherms that the ACs from CP5 (CP5--850-1.5) and CP10 (CP10-5-850-1.5) have a wider knee and aigher N2 adsorption capacity than the AC from CP0 (CP0-5-850-.5). In addition, the pore size distribution profile shows that theP10-5-850-1.5 owns more micropores and mesopores than theP0-5-850-1.5. Porosity characteristics and activation yields of theCs were summarized in Table 2. The CP5-5-850-1.5 has the highestpecific surface area and pore volume, whereas the CP10-5-850-1.5ossesses the largest mesopore percentage. This indicates that therigin of AC precursor has a great effect on the porosity charac-eristics of the ACs. The AC precursors (CP5 and CP10) have higherontents of carbonaceous mesophase and lower C/H ratio than CP0,hich favors the porosity development in ACs [20]. Compared with

he CP5-5-850-1.5, the CP10-5-850-1.5 has a larger average poreiameter and a lower specific surface area. This can be explainedy the fact that CP10 has a higher number of MCMB with smallerize [19], which would lead to an increase in the activation effi-

iency of KOH, thus contributing to the pore enlargement. When aertain number of enlarged pores are formed in the AC, its specificurface area would decrease.

Fig. 2. N2 adsorption–desorption isotherms and the inset corresponding pore sizedistributions for the ACs prepared at 850 ◦C from the different AC precursors (CP0,CP5, and CP10).

3.2.2. Effect of KOH/AC precursor weight ratioThe study of the influence of the KOH/AC precursor weight ratio

on the activation process was carried out by mixing samples of theCP10 with KOH in 3:1, 5:1, and 7:1 KOH/CP10 weight ratios, main-taining 850 ◦C as the activation temperature and 1.5 h as residencetime in all cases. The N2 adsorption–desorption isotherms and theinset corresponding pore size distribution profile of the resultantACs were shown in Fig. 3. It is found that the shapes of the N2adsorption–desorption isotherms are varied dramatically with theincrease of KOH/CP10 weight ratio. Meanwhile, a great enhance-ment of N2 adsorption capacity can be achieved by increasing theKOH/CP10 weight ratio. The pore size distribution profile reflectsthat the KOH/AC precursor weight ratio has a great effect on thedevelopment of mesopores. The mesopore volume of the AC signif-

Fig. 3. N2 adsorption–desorption isotherms and the inset corresponding pore sizedistribution profile for the ACs prepared at 850 ◦C from the CP10 in differentKOH/CP10 weight ratios (3:1, 5:1, and 7:1).

C. Zeng et al. / Journal of Analytical and Applied Pyrolysis 104 (2013) 372–377 375

Table 2Porosity characteristics and activation yields of the ACs prepared from the co-pyrolysis products by KOH activation.

Sample SBET (m2/g) Vtot (cm3/g) Vmic (cm3/g) Vmes (cm3/g) MP (%) D (nm) AY (%)

CP0-5-850-1.5 1846 1.09 0.79 0.30 27.5 1.81 41.6CP5-5-850-1.5 2847 1.57 1.11 0.46 29.3 2.20 43.0CP10-5-850-1.5 2270 1.36 0.9 0.46 33.8 2.39 40.8CP10-3-850-1.5 1628 0.90 0.85 0.05 5.6 1.34 64.5CP10-7-850-1.5 2360 1.91 1.03 0.88 46.1 3.24 43.0CP10-7-850-1.0 1855 1.28 0.92 0.34 26.6 1.84 55.1

M

fhKtuvpab

3

At(titboaibPtsaTd

Fdt

CP10-7-850-2.0 2304 1.89 0.99

P: mesopore percentage; D: average pore diameter; AY: activation yield.

rom 3:1 to 7:1. In addition, the AC possesses high surface area,igh micropore volume and considerable mesoporisty when theOH/CP10 weight ratio is higher than 5:1. It can be seen that both

he surface area and the pore volume of the AC increase contin-ously with the KOH/CP10 weight ratio and reach the maximumalues at a ratio of 7:1. Similar results were obtained by Ahmad-our and Duong [22]. Pore widening normally begins when therere a number of opened pores in the structure, therefore, it starts toe significant when the chemical ratio is reasonably high [23–25].

.2.3. Effect of activation timeThe influence of activation time on the texture of the resultant

Cs was studied through activation of the samples for differentime (1 h, 1.5 h, and 2.0 h), maintaining the KOH/CP10 weight ratio7:1) and the activation temperature (850 ◦C) constant. Fig. 4 showshe N2 adsorption–desorption isotherms and the inset correspond-ng pore size distribution profile of the ACs. When the activationime is 1 h, the isotherms of the ACs show the major adsorptionelow P/P0 = 0.1 and the minimum adsorption in the P/P0 rangef 0.1–1.0, indicating the ACs are mainly microporous. When thectivation time is 1.5 h, the isotherms of the ACs show a linearncrease in adsorption until P/P0 = 0.4 after the marked adsorptionelow P/P0 = 0.05, and then a gradual increase in adsorption after/P0 = 0.4. In addition, the pore size distribution profile shows thathe AC possesses more developed pore structure and wider pore

ize distribution with increasing activation time. Porosity char-cteristics and activation yields of the ACs were summarized inable 2. It can be observed that the activation yield of the ACecreases with increasing activation time, which is due to the

0.0 0.2 0.4 0.6 0.8 1.0

0

200

400

600

800

1000

1200

V (

cm

3/g

ST

P)

P/P0

CP10-7-850 -1.0

CP10-7-850 -1.5

CP10-7-850-2.0

1 2 3 4 5 6

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Dif

fere

nti

al

po

re v

olu

me

(c

m/g

)

Pore size (nm)

ig. 4. N2 adsorption–desorption isotherms and the inset corresponding pore sizeistribution for the ACs prepared from the CP10 at 850 ◦C for different activationime (1 h, 1.5 h, and 2.0 h).

0.90 47.6 3.32 40.7

results of KOH etching at high temperatures. Compared with text-ural parameters of the CP10-7-850-1.5, the specific surface areaand micropore volume of the CP10-7-850-2.0 decrease unobviously,and their mesopore volume and average pore diameter increaseslightly. This indicates that most KOH have been depleted whenthe activation time is 1.5 h.

3.3. Electrochemical performance

The four ACs (CP0-5-850-1.5, CP5-5-850-1.5, CP10-5-850-1.5,and CP10-7-850-1.5) were used to prepare electrodes, and their typ-ical CV curves are shown in Fig. 5. The voltage sweep range was from−1 V to 0 V and the scanning rates were 5, 10, 20 and 40 mV/s. Itis known that achieving rectangular-shaped CV curves over a widerange of scanning rates is the ultimate goal in EDLCs. This behav-ior is important for practical applications involving high energy andpower density. The four CV curves show typical capacitor-like char-acteristics in the form of almost rectangular cyclic behavior, andredox peaks were not observed. This suggests that the ACs show agood capacitor performance in a voltage range of −1 V to 0 V. Thefacts indicate that the charge–discharge responses of the electricdouble layer are highly reversible. At the same scanning rate, moreideal capacitive behavior was observed for the CP10-7-850-1.5 witha steeper current change at the switching potential, showing betterrectangular-shaped I–V curves. The slower changes at the switchingpotentials in the CV measurement of the CP0-5-850-1.5 stem fromthe slower reorganization of the double layer, owing to the highercontent of micropores and slower ionic motions in the micropores[26].

The specific capacitance at a scanning rate of 5 mV/s was cal-culated according to Eq. (2). The measured specific capacitancesof CP0-5-850-1.5, CP5-5-850-1.5, CP10-5-850-1.5 and CP10-7-850-1.5 are 108, 172, 180 and 203 F/g, respectively. This indicates therosin addition is beneficial to increase the specific capacitance ofthe AC. It is found that the surface area and pore volume of theACs increase significantly after adding the rosin, and especiallytheir average pore diameter and mesopore volume are furtherenhanced with increasing rosin content. The CP5-5-850-1.5 has thehighest surface area (2847 m2/g) and pore volume (1.57 cm3/g),and the CP10-7-850-1.5 possesses the largest mesopore volume(0.88 cm3/g), which should be responsible for the high specificcapacitances of the two ACs. In general, the specific capacitance ofcarbon material is linked to the electrical conductivity, the surfacearea, the porosity of the carbon, the accessibility of the electrolytefor penetrating into the carbon pores and the electrolyte proper-ties [27,28]. Micropores with small diameter may not be accessibleto electrolyte solution, and the ions cannot enter those pores,thus, the surface area of those non-accessible micropores will notcontribute to the total double-layer capacitance of the material

[29].

Fig. 6 shows the charge–discharge profiles of the electrodes fromthe above four ACs. It is found that their chronopotentiograms weretriangular, indicating a typical behavior of capacitive electrodes.

376 C. Zeng et al. / Journal of Analytical and Applied Pyrolysis 104 (2013) 372–377

-1.0 -0.8 -0.6 -0.4 -0.2 0.0-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

Cu

rre

nt

/A·c

m-2

Potenti al /V

40 mV/s20 mV/s10 mV/s

5 m V/s

-1.0 -0.8 -0.6 -0.4 -0.2 0.0-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

40 mV/s20 mV/s10 mV/s

Cu

rre

nt

/A·c

m-2

Potenti al /V

5 m V/s

-1.0 -0.8 -0.6 -0.4 -0.2 0.0-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

Cu

rre

nt

/A· c

m-2

40 mV/s20 mV/s10 mV/s

5 m V/s

-1.0 -0.8 -0.6 -0.4 -0.2 0.0-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

Cu

rre

nt

/A· c

m-2

40 mV/s20 mV/s10 mV/s

5 m V/s

(a) (b)

(c) (d)

F t ACs

T1tocht

FC

Poten tial / V

ig. 5. CV curves at various scanning rates for the capacitors prepared with differen

he electrodes from the three ACs (CP5-5-850-1.5, CP10-5-850-.5, and CP10-7-850-1.5) have much higher charge and dischargeimes than that from CP0-5-850-1.5. It is known that the charger discharge time, especially discharge time, is proportional to the

apacitance of AC. Compared with CP0-5-850-1.5, they possess aigher surface area and mesopore volume, leading to the forma-ion of larger effective surface area, and thus have longer discharge

0 10 0 20 0 30 0 40 0 50 0 60 00.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Po

ten

tia

l /V

Time /s

ab c

d

ig. 6. The charge–discharge curves of the four AC electrodes. (a) CP0-5-850-1.5, (b)P5-5-850-1.5, (c) CP10-5-850-1.5, (d) CP10-7-850-1.5.

Poten tial / V

. (a) CP0-5-850-1.5, (b) CP5-5-850-1.5, (c) CP10-5-850-1.5, (d) CP10-7-850-1.5.

time. In addition, a certain voltage drop can be observed in thecharge–discharge profile of the electrodes from CP5-5-850-1.5. Thisis mainly due to the presence of the internal resistance of the capac-itor [30].

4. Conclusions

This study has demonstrated that the co-pyrolysis product ofcoal-tar pitch and rosin was a suitable precursor for the low-costproduction of high surface area activated carbons (ACs) by KOHactivation. The adding rosin results in a decrease in the C/H atomicratio of the AC precursor as well as a significant increase in itsmesophase content. The effect of AC precursor origin on the poros-ity characteristics of the ACs can be illustrated by increases inthe BET surface area from 1846 to 2847 m2/g, the total pore vol-ume from 1.09 to 1.57 cm3/g and the average pore diameter from1.81 to 2.39 nm. In addition, the main factor affecting the poros-ity characteristics of the ACs is the KOH/AC precursor weight ratio.It is recommended that a KOH/AC precursor weight ratio of 7:1,an activation temperature of 850 ◦C and a residence time of 1.5 hare the optimum parameter values for producing high surface areaACs with good electrochemical performance. The resulting AC hasthe maximum specific capacitance of 203 F/g and exhibit goodrectangular-shaped I–V curves in cyclic voltammetry.

Acknowledgements

The authors gratefully acknowledge financial support form theNational Natural Science Foundation of China (Grant No. 51272045)

nd Ap

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nd the Natural Science Foundation of Fujian Province of ChinaGrant No. 2010J01280).

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