Materials Letters 97 (2013) 97–99

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Materials Letters

0167-57

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n Corr

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journal homepage: www.elsevier.com/locate/matlet

Facile synthesis of mesoporous carbon nanofibres towards high-performanceelectrochemical capacitors

L. Yang, L.R. Hou, Y.W. Zhang, C.Z. Yuan n

Anhui Key Laboratory of Metal Materials & Processing, School of Materials Science & Engineering, Anhui University of Technology, Ma’anshan 243002, PR China

a r t i c l e i n f o

Article history:

Received 11 October 2012

Accepted 6 December 2012Available online 13 December 2012

Keywords:

Mesoporous carbon nanofibres

Carbon materials

Porous materials

Energy storage and conversion

7X/$ - see front matter & 2012 Elsevier B.V.

x.doi.org/10.1016/j.matlet.2012.12.018

esponding author. Tel.: þ86 555 2311871; fa

ail address: ayuancz@163.com (C.Z. Yuan).

a b s t r a c t

Mesoporous carbon nanofibres (CNFs) were prepared from furfuryl alcohol (FA) precursor coupled with

the SBA-15 template by vapor deposition polymerization strategy. The as-synthesized CNFs possessed

numerous disordered mesopores with the size of ca. 4 nm. Electrochemical data demonstrated that a

specific capacitance (SC) of 222 F g�1 could be delivered by the unique mesoporous CNFs at 0.5 A g�1,

and even 180 F g�1 at 6 A g�1. A SC degradation of ca. 2% after 1000 continuous charge–discharge

cycles at 6 A g�1 indicated that the mesoporous CNFs can be considered a good candidate for long-term

supercapacitors application.

& 2012 Elsevier B.V. All rights reserved.

1. Introduction

Mesoporous carbons with large uniform pores and highspecific surface area (SSA) are of significant interest, due to theirgreat potential applications in electrochemical double layer capa-citors (EDLCs) [1,2]. It is well established that the main physico-chemical properties of mesoporous carbons are principallycontrolled by their pore structure, and the morphologies ofmesoporous carbons (micro- and macrostructures) may criticallyaffect their physicochemical properties, especially serving as anelectrode material involving the electrolyte accessibility, iontransportation, electron conductivity, etc. [2]. Furthermore,carbon sources still play a great role in the adjustable SSAs, porevolumes, graphitic degrees and functional groups of final meso-porous carbon materials [3,4]. To efficiently prepare mesoporouscarbon materials with optimized pore sizes and large mesoporevolume fraction, template-strategy synthesis protocols have beenwell developed [2–6].

In the work, we prepared mesoporous carbon nanofibres(CNFs) by using SBA-15 as a hard template and non-graphitizable furfuryl alcohol (FA) as a carbon source via anefficient vapor deposition polymerization (VDP) strategy, whereno any additional acids were used for the monomer FA polymer-ization [3,6,7]. The good electrochemical performance of theunique mesoporous CNFs highlights their appealing applicationin electrochemical capacitors (ECs).

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2. Experimental

Mesoporous silica SBA-15 was synthesized as the reportedprocedure before [8]. Vapor deposition polymerization of the FA(98 wt%) was applied to prepare mesoporous CNRs as follows. 1 gof SBA-15 was placed in a Teflon holder located in the middle ofan autoclave, and 7 mL of FA was previously placed into thebottom of the autoclave. The autoclave was sealed and transferredinto an oven at 130 1C for 12 h, and then FA was vaporized andpolymerized into the poly(furfuryl alcohol) (PFA) in the pores ofSBA-15 [8]. The obtained PFA/SBA-15 composite (Fig. S1) wascalcinated at 800 1C in the nitrogen atmosphere, subsequentlyleached in HF (40 wt%) solution to remove the template. Then,mesoporous CNFs were obtained by filtering, washing, and dryingovernight.

The morphologies and microstructures of the sample wereexamined by scanning electron microscopy (SEM, LEO 1430VP,Germany), transmission electron microscope (TEM, Hitachi-600,Japan), N2 adsorption–desorption measurements (ASAP-2010 sur-face area analyzer) and Raman analysis by Laser Raman (T6400,Jobion Yzon Corp.). The working electrode was prepared bymixing 85 wt% of the CNFs, 5 wt% of acetylene black and 10 wt%of poly(tetrafluoroethylene), and the mixture was pressed onto anickel grid (1 cm2). Electrochemical performance of the samplewas evaluated in 6 M KOH aqueous solution on IVIUM electro-chemical workstation by cyclic voltammetry (CV) and chronopo-tentiometric charge and discharge (CD) tests in a three-electrodecell with a Pt foil and a saturated calomel electrode (SCE) as thecounter electrode and the reference electrode, respectively.The specific capacitances (SCs) of the electrode were calculatedon SC¼ It/DV, where I, t and DV were discharge current density,

L. Yang et al. / Materials Letters 97 (2013) 97–9998

discharge time and potential interval, respectively. Furthermore, aquasi-capacitor was fabricated by using two same mesoporousCNFs electrodes face to face in 6 M KOH aqueous electrolyte.

3. Results and discussion

Here, the worm-like SBA-15 (Fig. S2) was used as a hard templateto synthesize mesoporous CNFs, where the formed PFA layer via

VDP was converted to carbon phase inside the SBA-15 template bypyrolysis under calcination in the N2 atmosphere, and the templatewas finally removed. Fig. S3 demonstrates the typical XRD pattern ofthe resultant mesoporous CNFs. Two diffraction peaks observed at2y¼22.81 and 43.21 correspond to 002, 01 diffractions of the CNFs,respectively [3]. The strong intensity of the wide 002 diffractionpeak attributing to stacks of parallel layer planes suggests desirablegraphitizing degree of the fabricated CNFs, which can be verified bythe Raman data (Fig. S4). The typical SEM images of the as-preparedcarbon sample were shown in Fig. S5. Evidently, the CNFs with adiameter of ca. 150 nm and a length of several micrometers crosseach other. The most remarkable feature of the appearance of theseCNFs is a good resemblance to that of the corresponding template,suggesting a reliable replication.

The TEM images of the CNFs with different magnificationswere presented in Fig. 1a–d to demonstrate their microstructuresmore clearly. The obtained CNFs with a diameter of 150–200 nmpossess lots of uniform mesopores with the size of ca. 3–5 nm.Also, the SAED pattern (the inset in Fig. 1) shows a polycrystallinefeature of the CNFs, owing to the irregular orientation of graphitelayers. Unexpectedly, the unique CNFs present disordered meso-pores even in the short range, in sharp contrast with otherordered mesoporous carbon materials synthesized by using otheracids as initiators for FA polymerization [3,4], which should berelated to the different polymerization state of PFA without acid-catalyzed process.

200 nm

50 nm

Fig. 1. TEM images (a–d) and SAED pattern (the inse

Nitrogen sorption isotherm (Fig. 2a) for the mesoporous CNFsshows representative type-IV curves with hysteresis loop. Well-defined and steep step occurs approximately at P/P0¼0.40–0.80,which is associated with nitrogen filling of the mesopores owingto capillary condensation, reflecting a uniformity of mesoporesizes. Of note, the pore size distribution (Fig. 2b) is relativelynarrow, and mainly centers at 3.9 nm. Moreover, the BET SSA,average pore size and mesoporous volume of the mesoporousCNFs are quantitatively summarized as 267 m2 g�1, 6 nm and0.29 cm3 g�1, respectively. As we all know, such intriguing 1Dmesoporous nanofibrous feature is critical to ease the masstransfer of electrolytes within the pores for fast double-layercharging–discharging, greatly improving the accessible electrode/electrolyte interfaces, and accordingly enhancing their electro-chemical performance. Next, we apply the unique CNFs as anelectrode to highlight their merits for supercapacitors application.

Typical CV curves of the mesoporous CNFs electrode, at variousscan rates ranged from 5 to 50 mV s�1, are depicted in Fig. 3a.Notably, electrochemical response currents of the CV plots on thepositive sweeps are all nearly mirror-image symmetric to theircorresponding counterparts on the negative sweeps, and a rapidcurrent response on voltage reversal at each end potential alsocan be seen even at 50 mV s�1, indicating the intriguing EDLCperformance at high rates in 6 M KOH solution.

Typical charge–discharge curves of the mesoporous CNFs atvarious current densities ranged from 0.5 to 6 A g�1 were plottedin Fig. S6. Symmetrical triangle shape of linear charge–dischargecurves suggests high coulombic efficiency and good capacitivecharacteristics of the mesoporous CNFs electrode. The SCs of theunique CNFs at various current densities can be calculated basedon the CD plots (Fig. S6) and the typical data are collected inFig. S7. Obviously, unique mesoporous CNFs electrode exhibitsattractive SCs of 222, 211, 193, 186, 184, 180 and 180 F g�1 at 0.5,1, 2, 3, 4, 5 and 6 A g�1, respectively, suggesting its good rateproperty. The high SCs can be attributed not only to large

100 nm

20 nm

t in d) of the as-synthesized mesoporous CNFs.

Fig. 3. CV curves (a) and cycling performance (b) of the mesoporous CNFs.

Fig. 2. N2 adsorption–desorption isotherm (a) and pore size distribution (b) of the mesoporous CNFs.

L. Yang et al. / Materials Letters 97 (2013) 97–99 99

mesopores of the slim CNFs, which favors for a fast ionictransportation in pores, but also to large porous channelsbetween CNFs, which reserves enough electrolyte during fastcharge/discharge process. A mesoporous CNFs-based symmetricquasi-capacitor was further fabricated. The CV curves of thesymmetric EC, as depicted in Fig. S8, reveal its desirable electro-chemical capacitance in the potential range from 0.0 to 0.9 V.In addition, the cycling performance (Fig. 3b) of the mesoporousCNFs was estimated at 6 A g�1. A SC degradation of ca. 2% aftercontinuous 1000 charge–discharge cycles reveals good electro-chemical stability of the unique mesoporous CNFs at large currentdensities.

4. Conclusions

In summary, the mesoporous CNFs have been successfullysynthesized by a template-assisted strategy. The unique meso-porous CNFs delivered a SC of 180 F g�1 and good electrochemicalstability at 6 A g�1. The intriguing electrochemical performanceof the unique CNFs mainly stemmed from their large accessibleelectrode/electrolyte interfaces due to its mesoporous and slimnanofibrous nature.

Acknowledgments

This work was financially supported by National Natural ScienceFoundation of China (no. 51202004) and Graduate InnovationProgram of Anhui University of Technology (no. 011009).

Appendix A. Supplementary materials

Supplementary data associated with this article can be foundin the online version at http://dx.doi.org/10.1016/j.matlet.2012.12.018.

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