Carbon Nanofibers Prepared via Electrospinning

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Transcript of Carbon Nanofibers Prepared via Electrospinning

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    Michio Inagaki , * Ying Yang , and Feiyu Kang

    Carbon Nanofi bers Prepared via Electrospinning

    Prof. M ProfesSappo E-mail: [email protected] Prof. Y. Yang Department of Electrical EngineeringTsinghua UniversityBeijing 100084China, State Key Laboratory of Control and Simulation of Power System and Generation EquipmentsTsinghua UniversityBeijing 100084, China Prof. F. Kang Department of Materials Science and EngineeringTsinghua UniversityBeijing 1

    DOI: 10

    1. Introduction

    Fibrous carbon materials have attracted the attention of scien-tists and engineers. [ 1 , 2 ] In the 1960s carbon fi bers were developed as onand tcarbotrile (with addititempetion. resinschemcarbofrom grownconsilater carbotion oThe dnm fo

    such assimple afrom pospun na

    A fundamental setup for elecmatically shown in Figure 1 . Ais charged by a DC or AC hience between the syringe anamong the charges on the susyringe (spinneret) competestends to stabilize the drop. Oat which surface charge repufrom the spinneret under a cojet decreases in diameter withand the surface charge repulsion continually draw on it, until

    jet s to

    Carbon nanofi bers prepared via electrospinning and following carboniztion are summarized by focusing on the structure and properties in relato their applications, after a brief review of electrospinning of some polmers. Carbon precursors, pore structure control, improvement in electrconductivity,and metal loading into carbon nanofi bers via electrospinnidiscussed from the viewpoint of structure and texture control of carbon

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    00084, China

    .1002/adma.201104940

    a point is reached where the axis of the jet bends, and thebegins whipping. As the solvent evaporates, the jet solidifi e

    r. 2012, 24, 25472566. Inagaki sor Emeritus of Hokkaido Universityro 060-8628, Japan

    e of the important industrial materials for modern science echnology, and which have been produced from various n precursors via the melt-spinning process. Polyacryloni-PAN) has been used as the principal precursor associated different modifi cations in processing, such as the use of ves, oxidative stabilization of as-spun PAN fi bers at a low rature, and stretching during stabilization and carboniza-

    Isotropic and anisotropic mesophase pitches and phenolic have also been precursors for carbon fi bers. A catalytic ical vapor deposition (CVD) process has also produced n fi bers with a structure and properties that are different those produced via melt-spinning, which is called vapor- carbon fi ber (VGCF). In the center of VGCFs, thin tubes

    sting of straight carbon layers were found, [ 3 ] which were reported to be formed via arc-discharging [ 4 ] and named n nanotubes (CNTs). [ 5 , 6 ] The process used for the produc-f VGCFs was successfully applied to synthesize CNTs. [ 7 ] iameters of CNTs are in the nanometer range, e.g., 7 r single-wall CNTs, in contrast to the micrometer-range

    have attrA few coucts on techniqupolymer

    In thielectrospstructura brief ening, anin pore loading of contrnanofi becarbon ncally acton carbo

    2. Elec

    2.1. Setutrospinning of polymers is sche- viscoelastic solution of polymers

    gh voltage due to potential differ-d grounded target. The repulsion rface of the drop at the tip of the with the surface tension, which nce a critical condition is reached lsion dominates, a jet is drawn nstant fl ow rate . The accelerating increasing external applied fi eld W

    diameters of carbon fi bers. CNTs are con-sidered to be an important material for the development of modern nanotech-nology in the 21st century, because carbon fi bers have supported the development of modern technology since the 1960s.

    Electrospinning has been used to pro-duce nanofi bers of various polymers with diameters from a few tens of nanometers to a few micrometers in different forms

    nonwoven mats (webs), yarns, etc. It is a relatively nd low-cost strategy to produce continuous nanofi bers lymer solutions or melts. Over the past decade, electro-nometer- to sub-micrometer-sized polymer nanofi bers acted much attention in both research and commerce. mpanies started to develop electrospun nanofi ber prod-the basis of large-scale electrospinning setups. This e was reviewed from different viewpoints, focusing on nanofi bers. [ 817 ] s review, we focuse on carbon nanofi bers prepared via inning and carbonization by summarizing on their

    e and properties in relation to their applications, after xplanation on the setup and conditions for electrospin-d some polymer nanofi bers. Carbon precursors, control structure, improvement in electrical conductivity, metal of carbon nanofi bers are discussed from the viewpoint ol of structure and texture in the resultant carbon rs. Although one of the applications of electrospun anofi bers is the support for catalysts and electrochemi-

    ive materials, loading and deposition of these materials n nanofi bers are not included here.

    trospinning of Polymers

    p and Conditions for Electrospinning

    a-tion

    y-ical ng are .

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    form tcolleceters an exaelectrosmall

    Motheir ntrospiconditThe eBy usdifferesucceshollowporoupropefrom

    Theof a ramesh stant sform. two pwere enhandeveloin partion oblies a

    Theof restors; p

    Michio Inagaki is the pro-

    Aichi Institute of Technology. esearch activities are in the fi elds of science and engi-ng on carbon materials, and are highlighted by The Carbon Award from American Carbon Society in 2004.

    Ying Yang is the professor of Tsinghua University. She received her PhD from Tsinghua University, Beijing, China in 2007. She was a post doctoral associate in Department of Chemical Engineering at Massachusetts Institute of Technology from 2008 to 2009.

    Feiyu Kang was born in 1962, received doctoral degree from Hong Kong University of Science and Technology.

    Figure hin fi bers, which are deposited on the grounded target (or tor). The diameters of polymer fi bers are around nanom-(nanofi bers), from few tens nanometers to micrometers mple of polymer nanofi bers, although it is still diffi cult to spin polymer into uniform nanofi bers with diameter as as several nanometers up to now. re than 100 kinds of polymers have been used to produce anofi bers via electrospinning in the past 20 years. Elec-

    nning process of various polymers was discussed on the ion to control fi ber diameter in nanometer scale. [ 8 , 11 , 1315 ]

    His rneeriSGL

    1 . Scheme of fundamental setup for electrospinning. linelibrary.com 2012 WILEY-VCH Verlag GmbH & Co

    lectrospun polymer fi bers are usually smooth solid fi bers. ing a spinneret consisting of two coaxial capillaries and nt polymer solution in each capillary, nanofi bers were sfully prepared with core-shell structure [ 1820 ] or with structure. [ 21 ] The use of volatile solvent resulted in

    s nanofi bers. [ 2224 ] The mechanical and thermodynamic rties of electrospun polymer nanofi bers were discussed the electrospinning conditions. [ 17 ] electrospun polymer fi bers can be collected in the form ndom nonwoven mat (web) by using fl at metallic plate or as a collector. By using a round collector rotating in a con-peed the continuous fi bers can be collected in an aligned By using a spinneret with single nozzle and immiscible olymer solutions, side-by-side bicomponent nanofi bers prepared. [ 25 ] The use of multi-needle spinneret can ce the production rate of polymer nanofi bers. [ 26 ] Recent pments in designs for the collection of spun nanofi bers, ticular, the mass production of nanofi bers and the fabrica-f various forms, from nonwoven form to yarn, 3D assem-nd patterned structures, were reviewed. [ 15 ] spinnability of a polymer solution and the morphology

    ulting fi bers are known to depend strongly on three fac-roperties of polymer solution, processing condition and

    condelectclear

    atmospincludestant, vthe polyture), stives (suoxide) Pvent of fessor emeritus of Hokkaido University and Toyohashi University of Technology. He received his PhD from the Nagoya University, Japan, in 1963. He worked in different universities, Nagoya University, Toyohashi University of Technology, Hokkaido University, and . KGaA, Weinheim

    He now is a full professor in Department of Materials Science and Engineering, and also a dean in Graduate School at Shenzhen, Tsinghua University. His research is focusing on nanocarbon materials, graphite, thermal

    uctive materials, lithium ion battery, super-capacitors, ric vehicles, porous carbon and adsorption, indoor air ing and water purifi cation.

    here condition. The fi rst factor, solution properties, s surface tension, electrical conductivity, dielectric con-iscosity of the polymer solution, depending strongly on mer (its concentration, molecular weight and architec-

    olvent (vapor pressure, diffusivity in air, etc) and addi-rfactants, salts, etc). In electrospinning of poly(ethylene EO, a marked solvent effect was reported; a mixed sol-

    ethanol with deionized water in either 1/1 or 3/1 volume

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    inning of PAA solution and then imidization of the un PAA fi bers. Concentration or viscosity of the PAA

    was found to be one of the most effective variables on rol of morphology of electrospun PI fi bers. [ 45 ] Diameter I fi bers synthesized ranges from several tens nanom-everal hundreds nanometer. The applied voltage and ing rate of the precursor solution may have an infl u- the diameter, even though the effect is not drastic. By alts to PAA solution and controlling humidity condi-rafi ne uniform nanofi bers were prepared with a narrow nanoscale diameters (33 5 nm). [ 46 ] is a thermoplastic polymer which can be easily proc-to various forms. PVDF was electrospun from its

    of a mixed solvent of acetone and DMAc under sev-centrations from 12 to 18 wt%. [ 55 ] Webs of electrospun bers were prepared from its mixed solutions of DMF one, [ 56 ] fi ber diameter ranging from 50 to 300 nm from VDF solution of 8/2 DMF/acetone. Its porous fi bers pared via electrospinning accompanied by phase sepa-uring electrospinning process, which was induced by ylene oxide) and water mixed into PVDF solution. [ 57 ] inyl alcohol) (PVA) is a water-soluble polyhydroxy and has been used as a carbon precursor in funda-researches, even though it is easily decomposed at a perature and gives a low carbon yield. PVA nanofi bers

    ratio had to be used. [ 27 ] The second factor, processing condition, includes fl ow rate of the polymer solution controlled by syringe pump, sand distalast factoas air, Nelectrospreportedfi bers ofPVC andPVC. [ 283

    polymer tors and rate of atives in distance reportedof polymuniversaneous th

    2.2. Poly

    The polynanofi beimide (P(PVDF) been elec

    PAN fi bers winanofi be(i.e., diamsitive to tfound totrospun concentrsolution.ymer interal nanby manithe carbofi bers instability as strong

    On aeffects oapplied Dsolution are studiresultanttration inwas alsoand entavoltage dshown in

    Recenthrough adopted,

    Dependences of diameter of polyacrylonitrile fi ber on concen-f the precursor solution and applied voltage for spinning. [ 33 ] with permission from Elsevier.

    Adv. Mater. 2012 WILEY-VCH Verlag GmbH & Co. K

    electrospelectrospsolutionthe contof the Peter to sthe feedence onadding stions ultrange of

    PVDFessed insolutioneral conPVDF fi and aceta 15% Pwere preration dpoly(eth

    Poly(vpolymermental high tem

    trength of electric fi eld controlled by power supply, nce between the spinneret tip and the collector. The r, atmosphere condition, includes the gas used (such 2 , Ar, vacuum) and its fl ow rate, and humidity in the inning hood. Humidity in spinning atmosphere was to affect the morphology and porosity of electrospun various polymers, polystyrene PS, poly(vinyl chloride) poly(methyl methacrylate) PMMA, poly(vinyl chloride) 0 ] However, most of the works on electrospinning of nanofi bers focused on the control of the fi rst two fac-ignored the atmosphere effect. Concentration and fl ow combination of precursor polymer and solvent, addi-the solution, power voltage applied for spinning, and between the spinneret tip and the collector are usually as parameters to be controlled. Although a wide variety ers have been studied for electrospinning, there are no l ranges for these parameters to synthesize homoge-in fi bers found until now.

    mer Nanofi bers

    mer nanofi bers which have been converted to carbon rs are rather limited, as polyacrylonitrile (PAN), poly-I), poly(vinyl alcohol) (PVA), poly(vinyliden fl uoride) and pitch, although so many kinds of polymers have trospun. has been commonly electrospun into high-quality th various diameters [ 31 ] and also converted to carbon rs, as explained in the following sections. Morphology

    eter and uniformity) of the electrospun fi bers is sen-hree factors mentioned, but the solution properties are be dominant. [ 3236 ] Generally, the diameter of the elec-fi bers decreases dramatically with decreasing poly mer ation and with increasing electrical conductivity of Up to now, it is still diffi cult to electrospin PAN pol-o uniform nanofi bers with diameter as small as sev-ometers. [ 37 ] A special alignment can be also achieved pulating the distribution of electric fi eld. [ 38 ] Moreover, n nanotubes are embedded into the electrospun PAN

    order to improve the mechanical properties, thermal and electrical conductivity, since the pure fi bers are not as desired. [ 3942 ]

    N,N-dimethylformamide (DMF) solution of PAN, f the concentration of the polymer solution and the

    C voltage between the electrode immersed into the and the target on the diameter of PAN nanofi bers ed. [ 33 ] Solution concentration governs the diameter of fi bers, as shown in Figure 2 a). Effect of PAN concen- DMF solution on diameter of electrospun nanofi bers

    reported to depend on molecular weight of PAN [ 43 ] nglement density of the polymeric solution. [ 44 ] Applied id not appreciably affect on the fi ber diameter, [ 33 ] as Figure 2 b). tly, PI fi bers are prepared by many researchers electrospinning. [ 4554 ] Generally, three-step method is which include polymerization of polyamic acid (PAA),

    Figure 2 . tration oReprinted

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    with various diameters (50250 nm) were easily electrospun from its 715 wt% aqueous solution. [ 58 , 59 ] From a 12 wt% PVA aqueounanofi bPVA aqdiametaverage290 nmconditining ofon-strinPVA.

    In ccursor For pitpitch tzation DMF-inin THFused foas explcursorsTHF saged mponentspinnahigher nanofi b

    3. CarElectr

    In Tabnanofi bof pubsolutionanofi bpurposerence frequenin the poly(vin(PBI) lignin w

    In onanofi bappliedpotentisuch ascarbonthe funbons dDuringthey shthe dec

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    tors, an

    3.1. Stru

    PAN nasolutionwere stunanofi bcarbonicarbon spacingof 0.93.cluded tbeing obased cwt% PAdodecylrim of tthe headiametemately 220 nmon 1000having to havecarbon tubes (Mcarbon around PAN-baonly a nanofi btion beh343423adsorptfocusinnature a

    Corea doubland poand conup to 1by elecand PM0.5 mmtreatmePAN/PMopore v0.47 cmwas alm

    Mixinemploywas disthermabonizedratio in

    s solution containing 1.0 wt% MWCNT, the composite ers were prepared by electrospinning. [ 60 ] Effect of pH of ueous solution was discussed on the morphology and

    er of its fi bers electrospun from a 7 wt% solution. [ 61 ] The diameter of PVA nanofi bers electrospun at pH 7.2 was and it became thinner with increasing pH under basic

    ons. Under acidic conditions, however, the electrospin- PVA solution was not continuous and PVA with beads-g structures was obtained due to the protonation of

    ontrast to PVA, pitch has several advantages as the pre-for carbon nanofi bers; high carbon yield and low cost. ches, however, a proper solvent, which dissolves the o high enough concentration and has a proper vapori-point, has to be selected for its electrospinning. The soluble fraction of a petroleum-derived isotropic pitch solution and a binary solvent of DMF and THF were r the spinning of pitch to convert to carbon nanofi bers,

    ained in the next section. Molecular structure of the pre- was shown to have an effect on spinnability of their

    olution by using two pitches with different weight-aver-olecular weights of 2380 and 556. [ 62 ] THF-soluble com- of the pitch with the lower molecular weight gave better bility on its 40 wt% THF solution, but the pitch with the molecular weight resulted in more microscopic carbon ers

    bon Nanofi bers Synthesized Via ospinning

    le 1 , the papers reporting on the preparation of carbon ers via electrospinning process are listed in the order lished year by summarizing key points on precursor n, spinning condition, treatments to convert to carbon ers and their characteristics. [ 63141 ] In Table 1 , the main

    e of the papers is also indicated together with the ref-number. As carbon precursors, PAN and pitches were tly used, probably because both of them are also used production of commercial carbon fi bers. In addition, yl alcohol) (PVA), polyimides (PIs), polybenzimidazol

    poly(vinylidene fl uoride) (PVDF), phenolic resin and ere used.

    rder to convert electrospun polymer nanofi bers to carbon ers, carbonization process at around 1000 C has to be . In principle, any polymer with a carbon backbone can ally be used as a precursor. For the carbon precursors, PAN and pitches, so-called stabilization process before

    ization is essential to keep fi brous morphology, of which damental reaction is oxidation to change resultant car-

    iffi cult to be graphitized at high temperatures as 2500 C. stabilization and carbonization of polymer nanofi bers, owed signifi cant weight loss and shrinkage, resulting in rease of fi ber diameter. , the results obtained in these papers are reviewed ding into the sections based on the purposes of the h works; fundamental structure and properties of the . KGaA, Weinheim

    d composite nanofi bers with carbon nanotubes.

    cture and Properties

    nofi bers were prepared by electrospinning from DMF , on which structure and electromagnetic properties died. [ 6365 ] Structural analysis was performed on carbon

    ers, which were prepared from PAN/DMF solution by zation at 750 C followed by 1100 C. [ 77 ] The resultant nanofi bers had average diameter of 110 nm, interlayer d 002 of 0.368 nm and Raman band intensity ratio I D /I G From SEM and TEM observations, the fi ber was con-o have skin-core heterogeneity; in the skin carbon layers riented predominantly parallel to the fi ber surface. PAN-arbon nanofi ber bundles, which were prepared from 10 N/DMF solution added 5 wt% acetone and 0.01 wt%

    ethyldimethylammonium bromide, and collected on the he rotating disc covered with Al foil, were subjected to t treatment at 1400, 1800, and 2200 C for 1 h. [ 107 ] The r of nanofi bers composing the bundles was approxi-330 nm for as-spun, 250 nm for 1000 C-treated and for 1800 C-treated. TEM images are shown in Figure 3 C-treated and 2200 C-treated nanofi bers, the latter

    d 002 of 0.344 nm and I D /I G of larger than 1.0. Aiming better alignment of basic structural units of hexagonal layers along the fi ber axis, multi-walled carbon nano-

    WCNTs) were embedded into electrospun PAN-based nanofi bers, although the improvement was observed just MWCNTs. [ 97 ] TEM observation on MWCNTs-embedded sed nanofi bers by in-situ heating up to 750 C showed local orientation of carbon layers. [ 142 ] On PAN-based ers web after the activation by steam at 800 C, adsorp-avior of benzene vapor was studied at a temperature of K under a pressure up to 4.0 kPa, confi rming a high

    ion in comparison with activated carbon fi ber A-10. [ 82 ] By g on PAN, electrospinnability, environmentally benign nd commercial viability were recently reviewed. [ 143 ]

    -shell polymeric nanofi bers were electrospun through ed capillary, PAN/DMF solution in the outer capillary ly(methyl methacrylate) PMMA in the inner capillary, verted to hollow carbon nanofi bers by carbonization

    100 C. [ 81 ] Similar hollow nanofi bers were synthesized trospinning of emulsion-like DMF solution of PAN MA in different ratios through a single capillary of

    diameter, followed by carbonization at 1000 C and heat nt up to 2800 C, [ 84 ] as shown in Figure 4 . By changing

    MA ratio, mesopore volume could be controlled; mes-olume V meso changed from 0.18 cm 3 g 1 for 9/1 ratio to 3 g 1 for 5/5 ratio, although micropore volume V micro ost constant of 0.34 cm 3 g 1 . [ 84 ] g of poly(vinylpyrrolidone) (PVP) into PAN was also

    ed to control pore structure in the nanofi bers. [ 103 ] PVP solved out from as-spun fi bers at 100 C under hydro-l condition and the resultant PAN nanofi bers were car- at 1000 C after stabilization. The change of PAN/PVP the precursor solution from 0.8/0.2 to 0.8/1.0 resulted

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    Table 1 . Preparation of carbon nanofi bers via electrospinning.

    Ref. (Purpose a) ) Precursor and additives/solvent

    Spinning conditions b) Stabilization, carbonization and activation Carbon nanofi bers synthesized and functionalities

    [ 6365 ] (Structure) PAN/DMF 15 kV//15 cm/ no stabilization, carbonized at 600, 800,

    1000, 1200 C for 1/2h in vacuum92.5 164 nm 2 , = 490 S m 1 , magnetoresis-tance (1000 C) of -0.75 at 1.9 K and 9T

    [ 66 ] (Composite) [PAN + SWCNT]/DMF 25 kV//15 cm/0.9 mm stabilized at 200 C, carbonized at 1100 o C homogeneous and straight SWCNTs in PAN, stiffening of PAN

    [ 67 ] (EDLCs) 10 wt%PAN/DMF 1025 kv/// stabilized at 280 C, carbonized & activated at 700-800 C in N 2 + steam

    200400 nm dia., S BET 1230 m 2 g 1 , V total 0.55cc g 1 ,

    173 F g 1 at 10 mA g 1 in 30vol% KOH

    [ 68 ] (Properties) 12 wt%PI/(THF + MeOH) 1315 kV/20 g h 1 /67 cm/0.41 mm/

    imidization at 150250 C, carbonized at 7001000 and 2200 o C

    electrical conductivity: from 2.5 and

    5.3 S cm 1 , tensile strength: from 5.0

    and 73.9 MPa by 1000 and 2200 o C

    [ 69 ] (Properties) Pitch/THF carbonization & activation S BET 20602220 m 2 g 1 , microporous

    [ 70 , 71 ] (EDLCs) PBI/DMAc 1025 kV/// 700850 C for 1/2h in N 2 + 30vol% steam 100-500nm dia., 800 C-treated S BET 1220 m 2 g 1 , V micro 0.71mL g 1 , 175F g 1 in 30wt%KOH

    [ 72 ] (Properties) DMF-insoluble pitch/THF 18 kV/3mL h 1 /10 cm/

    0.88 mm

    stabilized at 300 C, carbonized at 700, 1000, 1200 C for 1h

    dumb-bell like cross-section with (46) (23) m, electrical conductivity 83S/cm

    [ 73 ] (Composite) [6.7 wt%PAN + 3.3 wt% Fe-acac]/DMF

    30 kV//30 cm/ stabilized at 250 C, Fe reduction at 500550 C in H 2 , carbonized at 1100 o C

    MWCNTs grown by CVD of hexane at 700 C on nanofi bers

    [ 74 ] (EDLCs) 10 wt%PAN/DMF 20 kV////300 rpm stabilized at 280 C, carbonized & activated at 800 C for 1/41h in N 2 + steam

    200350 nm dia., S BET = 1160 m 2 g 1 , V total = 0.64 cc g 1 , 134 F g 1 in 6N KOH with

    1 mA cm 2

    [ 75 ] (EDLCs) PI/(THF + MeOH) 1315 kV/// imidized at 350 C, carbonized at 1000 C and activated at 650800 C in N 2 + steam

    S BET = 9411450 m 2 /g, V micro = 0.370.56cc g 1 750 C-activated: 175F g 1 in 30wt% KOH

    [ 76 ] (Composite) [7 wt%PAN + 235 wt% MWCNT]/DMF

    30 kV//30 cm//10 m/s stabilized at 220 C for 2h in air, carbonized at 850 C for 1/2h in Ar

    100300nm dia., 5% MWCNT composite

    shows max. strength 80MPa

    [ 77 ] (Properties) 8 wt%PAN/DMF 0.9 kV/cm///0.1 mm/

    5 m s 1 stabilized at 250 C, carbonized at 1100 C 1h

    110 nm dia., 89.4%C, d 002 = 0.368 nm, I D /I G = 0.9, weaker than commercially available fi bers

    [ 78 ] (EDLCs) 20 wt%PBI/DMAc ///0.5 mm/300 rpm carbonized & activated at 700, 750, 800,

    850 C in N 2 + 30% steam for 1/2h800 C-treated: S BET = 1220m 2 g 1 , V micro = 0.71 cc g 1 , 202F g 1 in 1M H 2 SO 4 with

    1 mA cm 2 , good rate performance

    [ 79 ] (Properties) [20 wt%PI + Fe-acac (03.0 wt%)]/DMAc

    615 kV/2050 m min 1 ///

    carbonized at 4001200 C for 1h -Fe and Fe 3 O 4 are formed above 800 C, d 002 = 0.34 nm, I D /I G = 1.8 by 3wt% atfter 1200 o C

    [ 80 ] (LIBs) PAN/DMF 25 kV//300 rpm//

    0.5 mmstabilize at 280 C for 1h, carbonized at 7002800 C

    1000 C-treated C dis = 450 mAh g 1 but C irr = ca. 500 mAh g 1 in 1M LiClO 4 EC/DEC with

    30 mA g 1

    [ 81 ] (Structure) PAN/DMF(shell) and

    PMMA/Acetone(core)0.3 kV cm 1 //18 cm/

    0.31.65 mm

    stabilized at 250 C carbonized at 1100 C for 1h

    hollow carbon nanofi bers

    [ 82 ] (Properties) 10 wt% PAN/DMF 20 kV//18 cm// stabilized at 280 oC, carbonized at 80 C,

    activated at 800 C in 30% steam for 1hS BET = 1193m 2 g 1 , V micro = 0.455 cc g 1 high adsorptivity for benzene vapor

    [ 83 ] (EDLCs) [PAN + Ru-acac]/DMF 20 kV//18 cm/0.5 mm/300 rpm

    stabilized at 280 C, carbonized & activated at 800 C in N 2 + 30 vol% steam

    200-900nm dia., Ru metal (215 nm)-

    embedded, 7.31wt% Ru: 391F g 1 (261F g 1

    pseudocapactitance)

    [ 84 ] (Properties) [PAN + PMMA(5/5, 7/3, 9/1)]/DMF

    20 kV///0.5 mm/

    300 rpmstabilized at 280 C for 1h, carbonized at 1000 & 2800 o C

    PAN/PMMA = 5/5 and 1000 C-carbonized: S BET = 940 m 2 g 1 , V meso = 0.47 & V micro = 0.35 cc g 1

    [ 85 ] (EDLCs) [10wt%PAN + 155 wt% ZnCl 2 ]/DMF

    25 kV////300 rpm stabilized at 280 C, carbonized at 800 C for 1h in Ar, repeatedly wash by HCl

    S BET = 310550 m 2 g 1 , V total = 0.170.34cc g 1 , 140 F g 1 in 6M KOH

    [ 86 ] (Properties) [PI + 1, 3, 5wt%TEA]/DMF 1923 kV//15 cm/ stabilized by oxidation, carbonized at 1000 C for 1 h in Ar

    80 nm dia. from 18wt%PAA solution, conduc-

    tivity of the mat under 22,000Pa pressure was

    16S/cm

    [ 87 ] (Properties) [9.1wt%PAN + SiO 2 ]/ 18 kV/1.0 mL h 1 //1.27 mm/300 rpm

    stabilized at 250 C for 8h, carbonized at 1050 C for 1h in N 2 , washed out Si by HF

    fi ber diameter increases, bead, bead-on-string

    and fi ber structures, S BET = 340 m 2 g 1 , V total = 0.472 cc g 1

    [ 88 ] (Properties) [PAN + PI (10/0, 7/3, 5/5, 3/7, 0/10)]/DMF

    20 kV////ca. 300 rpm stabilized at 280 C for 1 h, carbonized at 1000 C in Ar

    carbon yield increases, decreases and I D /I G increases with increasing PI content

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    Ref. (Purpose a) ) Precursor and additives/solvent

    Spinning conditions b) Stabilization, carbonization and activation Carbon nanofi bers synthesized and functionalities

    [ 89 ] (Properties) [Ph + PVB]/MeOH 15 kV/0.010.20 mL min 1 /10-20cm/1.0 mm

    cured by adding formaldehyde, carbonized at

    900 C for 2 h in N 2 fl exible carbon nanofi ber fabric by adding PVB,

    S BET = 495 m 2 g 1

    [ 90 ] (LIBs) [PAN + Co(OAc) 2 ]/DMF 1011 kV/2.5 L m 1 /12 cm/0.6 mm

    stabilized at 230 C, carbonized at 600 C for 10h

    100300 nm dia., 40wt%Co loaded, high dis-

    charge capacity > 750 mAh/g & good cyclability

    [ 91 ] (LIBs) [PAN + Fe-acac]/DMF 1214 kV/4 L min 1 /12 cm/

    stabilize at 240 C, carbonized at 500700 C for 10h

    Fe 3 O 4 -included, interesting cycle performance

    [ 92 ] (Properties) [8 wt%PAN + 4.8 wt% Pd(OAc) 2 ]/DMF

    30 kV//30 cm/ stabilized at 230 C for 3 h, reduced Pd 2 + at 300 C, carbonized at 1100 C in Ar

    200500 nm dia., Pd ( 37nm size) dispersed, high sensitivity for H 2 O 2 and NADH

    [ 93 ] (Fuel cells) PAN/DMF 13.7 kV//12 cm/ stabilized at 280 C in air, carbonized at 1200 C for 1h in Ar

    150 nm dia., = 50S/cm, electrochemical deposition of Pt(50-200 nm), high electro-

    catalytic activity and stability

    [ 94 ] (EDLCs) [10 wt%PAN + 3 wt%MWCNT]/DMF

    20 kV/1 mL h 1 / 15 cm/

    0.5 mm/300 rpm

    stabilized at 280 C, carbonized and activated at 800 C, coated by polypyrole

    PAN-based: S BET = 742m 2 g 1 , 141 F g 1 , PAN/CNT: S BET = 1170m 2 g 1 , 180 F g 1 , PPy/PAN/CNT: 333 F g 1

    [ 95 ] (EDLCs) [10 wt%PAN + 10 wt% V 2 O 5 ]/DMF

    20 kV/1 mL h 1 /

    130 rpm/17 cm/1.27 mm

    stabilized at 250 C for 8h, carbonized and activated with KOH at 800 C in Ar

    V(5wt%)-embedded, S BET = 2800 m 2 g 1 , 107F g 1 in 1M (C 2 H 5 ) 4 NBF 4 /PC with 20 A g 1

    [ 96 ] (Properties) [10 wt%PAN + V 2 O 5 ]/DMF 15 kV/1 mL h 1 / 17 cm/1.27 mm/130 rpm

    stabilized at 250 C for 8h, carbonized at 1050 C for 1h, activated by KOH at 750 C

    V(25wt%, 80nm)-embedded, S BET = 2780 m 2 g 1 , H 2 adsorption = 2.41wt% at 303K &10 MPa

    [ 97 ] (Structure) [PAN + 2.5, 5, 25 wt% MWCNTs]/DMF

    12 kV//15 cm/

    0.5 mm/1000 rpmstabilized at 250 C 1h in air, carbonized at 750, 1200 C for 1h in N 2

    little improvement in carbon layer alignment

    around MWCNTs

    [ 98 ] (Properties) [10 wt%PAN + 0.51.5 wt%Mn(OAc)]/DMF

    20 kV/1 mL h 1 / 18 cm/

    0.5 mm/300 rpm

    stabilized at 280 C, carbonized at 1000 C, activated at 800 C in N 2 + 30 vol%H 2 O

    Mn(0.23wt%)-embedded: S BET = 1230 m 2 g 1 , V micro = 0.42 cc g 1 , toluene adsorption = 68g/100g

    [ 99 ] (LIBs) [8 wt%PAN + Mn(OAc) 2 ]/DMF

    14 kV/0.75 mL h 1 /

    15 cm/

    stabilized at 280 C in air, 700 C for 1h MnO + Mn 3 O 4 -loaded porous nanofi bers: 800450mAh g 1

    [ 100 ] (LIBs) [PAN + (poly- L -lactic acid) + Si(17:3:6)]/DMF

    21 kV/0.75 mL h 1 /

    15 cm/

    stabilize at 280 C for 8h in air, 700 C for 1h in Ar

    Si nanoparticle-loaded, C dis = 1100 and C irr = 240 mAh g 1

    [ 101 ] (Properties) [PAN + pitch]/(DMF + THF) 25 kV/// Carbonization at 1000 C, steam activation at 700-1000 C for 1h

    Improvement in spinnability by PAN, S BET = 732-1877 m 2 g 1 , V total = 0.3-1.1 cc g 1

    [ 102 ] (EDLCs) [PAN + CA]/DMF 800 C for 0h without CA: S BET = 742 m 2 g 1 , pore 2.0 nm, 141F g 1 with 15wt%CA: S BET = 1160 m 2 g 1 , pore 2.8 nm, 245F g 1

    [ 103 ] (Structure) [PAN + PVP]/DMF 10 kV///1015 cm/800 m

    dissolved PVP by hot water, stabilized at

    270 C and carbonized at 1000 o CS BET 330-570 m 2 g 1 ,

    [ 104 ] (LIBs) PAN/DMF, TBT/mineral oil,

    (PAN/TBT = 1/1)20 kV/15 & 5 L min 1 /15 cm/1.2 & 0.5 mm

    dissolved out mineral oil in n-octane,

    carbonized at 1000 C for 5 [email protected] nanotube, 200 nm dia. with ca.

    100 nm Sn, reversible capacity 737 mAh g 1

    [ 105 ] (EDLCs) [7.2 wt% PAN + 0.8 wt% MWCNT]/DMF

    30 kV//30 cm/ stabilized at 240 C, carbonized at 700 C, activated at 650 C with H 2 O 2 vapor

    PAN: S BET = 930 m 2 g 1 , = 0.86S cm 1 , 170F g 1 in H 2 SO 4 PAN/MWCNT: S BET = 810 m 2 g 1 , = 5.32S cm 1 , 310F g 1

    [ 106 ] (LIBs) [PAN + PMMA + tin octoate]/DMF

    stabilized at 250 C, multichannel tubular with 2 m dia. & 150 nm channels, reversible capacity 648 mAh g 1

    [ 107 ] (Properties) 10 wt%PAN/(DMF + acetone + bromide)

    20 kV/1.5 mL/h 1 / 22 cm/

    0.55 mm/ 1500 rpm

    stabilized at 280 C, carbonized at 1000 C in vacuo, heated to 14002200 C for 1h

    bundles, 2200 C-treated: d 002 = 0.344 nm, I D /I G > 1, // = 840, strength = 542 MPa, Youngs modulus = 58GPa

    [ 108 ] (EDLCs) [PAN + 0, 35, 100, 135 wt% Ni(OAc)]/DMF

    35 kV/0.5 mL h 1 /

    20 cm/0.6 mm

    stabilized at 280 C in air, carbonized at 1000 C for 1h

    22.4 wt%Ni: 164 F/g in 6 M KOH at 2 mV s 1

    scan

    [ 109 ] (EDLCs) [10 wt%PAN + 1, 3, 5 wt%Ni(NO 3 ) 2 ]/DMF

    25 kV//20 cm//350 rpm stabilized at 280 C in air, carbonized at 1000 C, leached excess Ni in 4M NaOH

    S BET = 480682 m 2 g 1 , V meso = 0.210.32cc 1 , V micro = 0.190.23 cc g 1 for 15 wt%Ni-salt added,

    [ 110 ] (LIBs) [7 wt%PAN + 5, 10, 15 wt%ZnCl 2 ]/DMF

    14 kV/0.5 mL h 1 / 15 cm/ stabilized at 280 C for 2.5 h, carbonized at 700 C for 1h in N 2 , washed out Zn by HCl

    15 wt% ZnCl 2 -mixed gives S BET = 438 m 2 g 1 , V total = 0.29 and V micro = 0.24 cc g 1 , C dis = 400 mAh g 1 at 10th cycle

    Table 1. Continued.

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    [ 111 ] (LIBs) [10 wt%PAN + (030 wt%)Si]/DMF

    17 kV/0.75 mL h 1 /

    15 cm/

    stabilized at 280 C in air for 5.5 h, carbonized at 700 C for 1h in Ar

    C dis = 855 and C irr = 321 mAh g 1 with 100 mA g 1 in 1M LiPF 6 /(EC + EMC)

    [ 112 ] (LIBs) [PVA + Si[/(H 2 O + Na alkyl- benzenesulfonate)

    20 kV/1 mL h 1 / 11cm/ dried on copper current collector and then

    heated at 500 C for 2 h in ArSi nanoparticles (40 nm) embedded in

    irregular pores, C dis increase with cycles, C dis = 892 mAh g 1 after 50 cycles

    [ 113 ] (LIBs) 8 wt%PAN + (15, 30, 50 wt%) Si( > 70 nm)]/DMF

    21 kV/0.75 mL h 1 /

    15 cm//

    stabilized at 280 C in air for 5 h, carbonized at 700 C for 1 h in N 2

    30 wt%Si precursor: C dis = 1281mAh g 1 , C irr = 260 mAh g 1 , for 1st cycle, but C dis = 318 mAh g 1 for 50th.

    [ 114 ] (Properties) [10 wt%PAN + 1, 2, 3 wt% (FeSO 4 + FeCl 3 )]/DMF

    25 kV//20 cm// stabilized at 280 C in air for1h, immersed into 4M NaOH, carbonized at 1000 C

    containing 3wt% iron oxide: S BET = 550 m 2 g 1

    [ 115 ] (Properties) [10 wt%PAN + 15 wt% SiWA or SiMoA]/DMF

    25 kV//20 cm// stabilized at 280 C in air, carbonized at 1000 C, sashed in 4 M NaOH

    A3-sized webs consisting of 100-300 nm fi bers,

    for SiMoA-contained fi ber: 1.7 10 3 S cm 1

    [ 116 ] (LIBs) [7 wt%PAN + 0, 5, 10, 20 wt% fumed SiO 2 ]/DMF

    21 kV/0.8 mL h 1 /

    15 cm/

    stabilized at 280 C for 2.5 h, carbonized at 700 or 1000 C, washed out SiO 2 by HF

    C irr = 593 mAh g 1 for 20wt% SiO 2 , large irreversible capacity

    [ 117 ] (LIBs) [10 wt%PAN + 30 wt% Ni(OAc) 2 ]/DMF

    12.5 kV/0.5 mL h 1 /

    15 cm/

    stabilized 280 C for 6 h in air, carbonized at 600 C for 8h in Ar

    dispersed Ni with 20nm size, C dis = 795 mAh g 1 and C irr = 225 mAh g 1 in LiPF 6 electrolyte

    [ 118 ] (LIBs) [8 wt%PAN + 15, 30, 50 wt% Mn(OAc) 2 ]/DMF

    21 kV/// stabilized at 280 C for 5 h, carbonized at 700 C for 1 h in Ar

    MnO x ( 10 nm)-embeddedwith, C dis = 785 mAh g 1 in 1M LiPF 6 (EC/EMC = 1/1) with 50 mA g 1

    [ 119 ] (Properties) [15 wt%PAN-itaco acid

    copolymer]/DMF

    25kV//40cm/ 0.4 mm/

    200 rpm

    stretched in hot water, stabilized under

    tension, carbonized at 10001500 o C

    aligned carbon nanofi ber bundles, expecting

    high mechanical strength

    [ 120 ] (LIBs) [8 wt%PAN + poly- L -lactic acid]/DMF

    17 kV/0.5 mL h 1 / 15 cm/ stabilized at 280 C for 5.5 h in air, carbonized at 800 C for 1 h

    S BET = 235 m 2 g 1 , V total = 0.114 cc g 1 , V micro = 0.086 cc g 1 , C dis = 435 mAh g 1 after 50 cycles

    [ 121 ] (Properties) [Ph + PVB, piridine and/or Na 2 CO 3 ]/MeOH

    15 kV/0.01 mL min 1 /

    15 cm/0.5 mm

    cured by adding formaldehyde, carbonized

    at 900 C for 2 h in N 2 addition of PVB improves spinnability, addition

    of electrolyte (pyridine and Na 2 CO 3 allows

    thinner fi bers

    [ 122 ] (LIBs) [PVA + SnCl 2 ]/H 2 O 25 kV/1.0 mL h 1 / 15 cm/1 mm

    carbonized at 500 C for 3 h in Ar/H 2 including ca. 1nm Sn, C dis = 382 mAh g 1 at 20th cycle

    [ 123 ] (LIBs) [PVA + SnCl 2 ]/H 2 O 35 kV/1.0 mL h 1 / 20 cm/1 mm

    carbonized at 550 C for 3 h in Ar/H 2 Sn/SnO x containing fi bers, 735 and 510 mA h 1 in 1st and 40th cycle.

    [ 124 ] (LIBs) [8 wt%PAN + 50 wt% Cu(OAc) 2 ]/DMF

    10.5 kV/0.5 mL h 1 /

    15 cm/

    stabilized at 280 C 5.5 h, carbonized at 600 C for 8 h in Ar

    fcc-Cu particles embedded in fi bers, C dis = 617 and C irr = 253 mAh g 1 in LiPF 6 (EC/EMC = 1/1) with 50 mA g 1

    [ 125 ] (Properties) 50 wt%Polycarbosilane/THF 10 kv/4 mL h 1 /10 cm/

    0.8 mm

    carbonized in Ar + Cl 2 at 800 or 90 C for 2 or 3 h,

    S BET = 3116 m 2 g 1 , high storage capacity of H 2 as 3.86% at 17bar and 77K

    [ 126 ] (Properties) [10 wt%PAN + 7wt% CoFe 2 O 4 ]/DMF

    20 kV/5 mL h 1 /15 cm/

    0.8 mm/800 rpm

    stabilized at 25 C for 2 h in air, carbonized

    at 100 C for 4 h in Ar

    Superparamagnetic, saturation magnetization

    of 63emu/g

    [ 127 ] (Properties) [Lignin + Pt-(acac)]/ethanol 12 kV//2025 cm/ stabilized at 20 C for 36 h in air fl ow, carbonized at 6001000 C

    400 nm 1 m, 0.6wt%Pt-loaded: S BET = 1200 m 2 g 1 , V micro = 0.52 cc g 1 ,

    [ 128 ] (EDLCs) 10 wt%PAN/DMF 25 kV/// Stabilized at 28 C, 1h, carbonized & activated

    by steam at 800 Cca. 900 nm dia., microporous, S BET = 550 m 2 g 1 , V micro = 0.35cc g 1 , Na-ion capture = 3.2 mg g 1

    [ 129 ] (LIBs) [PAN + Si]/DMF 15 kV/1 mL/h/25 cm/ carbonized at 800, 1000, 120 C for 1 h in Ar Si(5080 nm)-embedded, 120 C-treated: C dis = 500 mAh g 1 and better capacity retention of

    78% after 50th cycle.

    [ 130 ] (Properties) 9 wt%PAN/DMF 1525 kV//1525 cm/ stabilized at 30 C, carbonized at 800140 C, 380-530nm, tensile strength = 3.5 GPa, Youngs modulus = 172 GPa after 140 C,

    [ 131 ] (EDLCs) [PAN + PVP]/DMF PAN/DMF and PVP/DMF

    20 kV//15 cm/ stabilized at 30 C, carbonized to 97 C, acti-

    vated by CO 2 at 850 C

    blend & side-by-side fi bers of PAN/PVP,

    interconnected membranes, the latter

    ca. 220F g 1 in 1M H 2 SO 4

    [ 132 ] (Properties) 30 wt% Ph (novolac-type)/

    MeOH

    25 kV//20 cm/ cured in formaldehyde + HCl, carbonized at 80 C for 2 h

    100450 nm dia., narrow pore size in

    0.40.7 nm, V tota l = 0.91cc g 1 , I D /I G = 0.88

    Table 1. Continued.

    Ref. (Purposea)) Precursor and additives/solvent

    Spinning conditionsb) Stabilization, carbonization and activation Carbon nanofi bers synthesized and functionalities

    Adv. Mater. 2012, 24, 25472566

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    IEW Table 1. Continued.

    Ref. (Purpo a) b)

    [ 57 ] (Proper r

    [ 133 ] (LIBs) h

    [ 134 ] (Prope

    [ 62 ] (Propet

    [ 135 ] (Prope u

    a

    [ 136 ] (EDLC

    [ 137 ] (EDLC

    [ 138 ] (EDLC

    [ 139 ] (Prope

    [ 140 ] (Prope

    [ 141 ] (Prope

    a) Classifi eVoltage/fl oPMMA: poMWCNT: mlamide, TBX-100: surfpore size, dnamide ad

    in the cand totaPAN solside-by-sPVP bletheir actnanofi beto cocoo

    The Dpitch introspun eter. [ 69 , 72

    out to bthe solvevolatilizase ) Precursor and additives/solvent

    Spinning conditions Stabilization, carbo

    ties) [PVDF + PEO]/(DMF + water) 22.5 kV//40 cm/ stabilized and defl uocarbonized at 1000 C

    [4 wt%PAN + 8 wt% LiFePO 4 precursor]/DMF

    15 kV//15 cm/ 0.012 inch stabilized 28 C for 5

    C 18h in Ar

    rties) PAN/DMF 17 kV///1.27 mm stabilized at 26 C, ca

    1h, activated by H 3 PO

    ies) 40 & 45 wt% pitches (M w = 2380 & 556)/THF

    25 kV/3 mL h 1 /10cm/

    0.88 mm

    carbonized at 100 C

    steam/N 2 at 700, 800

    rties) 10 wt% PAN/DMF 30 kV/1.5 mL h 1 /

    35 cm/

    hot-pressed at 20 C

    at 27 C, carbonized library.com 2012 WILEY-VCH Verlag GmbH & Co.

    ) 10 wt%[PAN + TEOS (7/3)]/DMF

    20 kV//25 cm// stabilized at 28 C in

    900, 1000 C

    ) 10 wt%[PAN + -CD] + 3 wt% AgNO 3 /DMF

    25 kV//// stabilized at 28 C for

    steam/N 2 ,

    ) [2050 wt%Pitch/THF ] + PAN/DMF (7/3)

    20 kV//25 cm// sabilized and carboni

    rties) [10wt%PAN + (1, 5, 10 wt %Fe 3 O 4 + X100]/DMF

    1112kV/2mL

    h 1 /17cm//

    stabilized at 25 C for

    700, 90 C for 1 h

    rties)10 wt%PAN/DMF 20kV/1mL h 1 /

    15cm/0.5 mm/

    stabilized at 28 C, ca

    30 vol% steam at 80

    rties)

    30 wt%Ph + 0.9 wt%PVB + 0.1 wt%Na 2 CO 3 /MeOH

    25kV/1mL h 1 /20 cm// immersed into forma

    solution, carbonized

    d into structure, properties, electrochemical capacitors (EDLCs), lithium-ion rechargeabw rate/distance between nozzle and collector/needle diameter, and collector rotation ly(methyl methacrylate), PVB: poly(vinyl butyral), PVP: poly(vinyl pyrrolidone), CA: cellultiwalled carbon nanotube, DMF: N,N-dimethylformamide, THF: tetrahydrofurane, DM

    T: tributyltin, acac: acetylacetonate, OAc: acetate. SiWA: silicotungstic acid, SiMoA: silactant Triton X-100, : electrical conductivity, S BET : BET surface area, V total : total pore vo 002 : interlayer spacing, I D /I G : intensity ratio of D-band to G-band in Raman spectrum, C

    enine dinucleotide, M w : weight-averaged molecular weight, Ms: saturation magnetizatio

    arbon nanofi bers with S BET from 237 to 571 m 2 g 1 l pore volume V total from 0.10 to 0.19 cm 3 g 1 . PVP/utions were separately fed into the spinneret to form ide bicomponent nanofi bers and compared with PAN/nd nanofi bers after carbonization up to 970 C and ivation at 850 C in CO 2 . [ 131 ] Side-by-side bicomponent rs changed the cross-section morphology from round n-like shape by PVP extraction. MF-insoluble fraction of a petroleum-derived isotropic

    THF solution (40 wt% pitch) was successfully elec-to form the web of carbon fi bers with 2-6 m diam- ] The diffi culty to prepare thinner fi ber was pointed e resulted from the low boiling point (6567 C) of nt THF, the viscosity of the jet increasing due to the tion of THF during electrospinning. After activation,

    the web2200 m 2

    binary sfi bers wisteam atconsistinsoluble c556 gavethe carbpitch asgiving Sactivatednanofi bepolycarband chlonization and activation Carbon nanofi bers synthesized and functionalities

    ized with DBU at 5 C,

    for 1h2.3 m dia., pores with ca. 100 nm in 4.3 pores m 2 , high electrode performance for redox reaction

    in air, carbonized at70 LiFePO 4 /C composite nanofi bers + beads, 160 mAh g 1 in 1M LiPF 6 EC/EMC

    rbonized at 105 C for

    4 at 75 C for 3hactivated by using 80 wt% H 3 PO 4 : S BET = 621 m 2 g 1 , V total = 0.501cc g 1 , V micro = 0.071cc g 1 , NO gas sensitive

    for 1h, activated by

    , 90 C for 1hM w had a strong effect on spinnability, S BET = 2053 m 2 g 1 after 90 C activation of pitch A

    with M w = 2380

    nder 400kPa, stabilized

    t 1000 C

    the mats consisting of carbon nanofi bers with

    380 nm diameter and having the bulk density

    of 1.211.23 g cc 1 KGaA, Weinheim

    air, carbonized at 800, 80 C-treated: 150nm diameter, microporous

    with S BET = 1200 m 2 g 1 , w micro = 0.6 nm, 160130F/g in 6M KOH

    1h, activated at 80 C in PAN/30% -CD: 350 nm diameter, SBET = 1096 m 2 g 1 , microporous, 150F g 1 in 6 M

    KOH, < 20 nm Ag dispersed

    zation at 1000 C S BET = 966 m 2 g 1 , V pore = 0.38cc g 1 , w micro = 1.6 nm, 130 F g 1 , 100 kW kg 1 , 15 Wh kg 1

    20 min, carbonized at 290270 nm diameter, Fe 3 O 4 nanoparticles

    dispersed, = 9.2 S cm 1 and M s = 16 emn g 1 (10 wt%, 90 C)

    rbonized & activated in

    CS BET = 710 m 2 g 1 , V micro = 0.345 cc g 1 , > 60% removal of NO, no (NO + NO 2 ) detected

    ldehyde and HCl

    at 80 C for 2 h100-450nm diameter, S BET = 812 m 2 /g 1 , V micro = 0.91cc g 1 , w micro = 0.4-0.7 nm, H 2 O & EtOH vapor adsorption

    le batteries (LIBs), fuel cells and composites with carbon nanotubes. b) if any. PAN: poly(acrylonitrile, PI: polyimide. PBI: poly(benzimidazole), ulose acetate, Ph: phenolic resin, SWCNT: single-wall carbon nanotube,

    Ac: dimethylacetamide, EtOH: ethanol, MeOH: methanol, TEA: triethy-icomolybdic acid, TEOS: tetraethoxy orthosilicate, -CD: -cyclodextrin, lume, V micro : micropore volume, V meso : mesopore volume, w micro : micro- dis : reversible discharge capacity, C irr : irreversible capacity, NADH: nicoti-n

    s were microporous, showing very high S BET as g 1 . By mixing PAN with a pitch, spinnability using a olvent DMF + THF (1/1) was improved, resulting in the th the diameter of 750 nm. [ 101 ] After activation by using 900 C, S BET of 1877 m 2 g 1 and V total of 1.11 cm 3 g 1 , g of both micro- and meso-pores, were obtained. THF-omponent of the pitch with a low molecular weight of better spinnability on its 40 wt% THF solution, but

    on nanofi bers prepared from a high molecular weight 2380 showed higher development of micropores, BET of 2053 m 2 g 1 , after carbonization at 1000 C and at 900 C in steam/N 2 fl ow. [ 62 ] Highly porous carbon rs were obtained by electrospinning of THF solution of osilane, followed by pyrolysis at different temperatures rination to extract Si. [ 125 ] The nanofi bers pyrolyzed at

    Adv. Mater. 2012, 24, 25472566

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    REV

    Figure 3 .2200 C

    900 C m 2 g 1 a high s77 K.

    Polyinanofi bof PMDrelativelductivitA thermlacetamlacetnatwith 24was decto a-Fe ture pa0.34 nmof PANdiamete

    Poly(the soluof whiccyelo[5,1000 CThey cothe intwith 10

    liquid-liquid phase separation and the micro-

    Adv. Mate TEM images of PAN-based carbon nanofi bers after heat treatment at 1000 C[107] 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

    (b). Reprinted with permission from Elsevier.

    and chlorinated at 850 C had very high S BET as 3116 and V total of 1.66 cm 3 g 1 , which were reported to have torage capacity for hydrogen as 3.86 wt% at 17 bar and

    mide (PI) was also spun to prepare carbon ers. [ 68 , 75 , 79 , 86 , 88 ] Carbon nanofi bers prepared from a PI A/ODA with the diameter less than 2-3 m could give y high tensile strength as 74 MPa and electrical con-y of 5.3 S cm 1 after the heat treatment at 2200 C. [ 68 ]

    otropic PI (Matimid 5218) dissolved into dimethy-ide (DMAc) together with 0.33.0 wt% iron(III) acety-e (AAI) was spun to nanofi bers in the atmosphere % humidity and then carbonized at 4001200 C. [ 79 ] It lared that AAI worked as a catalyst after decomposing and Fe 3 O 4 during carbonization, although the struc-

    rameters changed a little, d 002 decreasing from 0.37 to , Lc(002) increasing from 1.0 to 4.2 nm. The addition

    in PI solution improved spinnability and decreased the r of resultant carbon fi bers. [ 88 ] vinylidene fl uoride) (PVDF) nanofi bers were spun from tion of DMF with poly(ethylene oxide) (PEO) and water, h the webs were dehydrofl uorized by using 1,8-diazabi-4,0]undec-7-ene at 90 C, followed by carbonization at for 1 h in N 2 to convert to carbon nanofi ber webs. [ 57 ] ntained three kinds of pores; the largest pores were

    erstices among nanofi bers, intermediate-sized pores 0-300 nm size were formed on the fi ber surface due to

    Na 2 CO 3 , without

    of these carbon nanofi benanofi bers with a narrow were prepared from novopinning of its methanol soand carbonization at 800 applied, the nanofi bers hadg 1 and relatively low I D /I G

    Electrical conductivity w800 C-carbonized PAN-b1000 C-treated nanofi bertoresistance, -0.75 at a temfi eld of 9 T. [ 65 ] Although thphology was survived undinto account that these nanbonization when these procommercial PAN-based cananofi ber bundles preparethe conductivity of 840 S 61 S cm 1 in perpendicuPAN-based carbon nanofichanges sensitive to NO gainto 80 wt% H 3 PO 4 aqueotreatment at 750 C in Ar. [

    Mechanical property mcarried out on PAN-basbending modulus was meresonance method and W

    r. 2012, 24, 25472566 2555wileyonlinelibrary.com

    followed by carbonization at 800 C activation. [ 141 ] Electrical conductivity r fabrics was 5.29 S cm 1 . Carbon pore size distribution of 0.40.7 nm lac-type phenolic resin via electros-lution, curing in formaldehyde/HCl

    C. [ 132 ] Even though no activation was S BET of 812 m 2 g 1 , V total of 0.91 cm 3 of 0.88. as measured to be 4.9 S cm 1 on

    ased carbon nanofi bers [ 63 ] and the s showed a large negative magne-perature of 1.9 K under a magnetic e papers have said that fi brous mor-er the heat treatment, it has to take ofi bers are not stabilized before car-

    perties were compared with those of rbon fi bers. The PAN-based carbon

    d by carbonization at 2200 C showed cm 1 in parallel with fi ber axis, but

    lar to the fi ber axis. [ 107 ] Electrospun bers showed electrical conductivity s after activation through immersion us solution for 12 h and then heat-

    134 ] easurements on single fi bers were ed carbon nanofi bers. [ 77 ] Averaged asured to be 63 GPa by mechanical eibull fracture stress was 640 MPa IEW

    (a) and

    pores were due to the decomposition of PEO during carbonization. Dehydrofl uorination process was found to be the key to retain the pore morphology in as-spun fi bers during carbonization.

    For electrospinning of phenolic resin (novolac type), its concentration had to be selected, the solution with more than 65 wt% was diffi cult to be spun and that with less than 50 wt% gave fi bers having beads. [ 89 ] Spinnability of phenolic resin solution was improved by the addition of a small amount of poly(vinyl butyral) (PVB) with a molecular weight (M w ) of 110,000, 1 to 3 wt%. The resultant carbon nanofi ber fabrics prepared at 900 C were fl exible and had S BET of ca. 500 m 2 /g. Addition of a high molecular weight PVB (M w of 340,000) markedly improved the spinnability of phenolic resin solution due to decreasing solution viscosity and the addi-tion of an electrolyte (pyridine or Na 2 CO 3 ) allowed to give thinner fi bers because of increasing electrical conductivity of the pre-cursor solution; 0.1 wt% Na 2 CO 3 resulting in the carbon nanofi bers with an average diam-eter of 110 nm and S BET of 790 m 2 g 1 . [ 121 ] Microporous carbon nanofi bers having V micro of 0.9 cm 3 g 1 were prepared from novolac-type phenol-formaldehyde by adding PVB and

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    and Yougiving 1in mechby the gbe pointis randonanofi bezation, eical propwere pre

    Loadiwere permetal naimproveium-ion

    failure probability of 63%. Tensile strength and Youngs us measured on the bundles of electrospun PAN-based nanofi bers were 542 MPa and 58 GPa, respectively. [ 107 ] mechanical properties reported on electrospun carbon

    bers are much inferior to commercially available PAN-carbon fi bers. Since oxidative stabilization of PAN fi bers en known to be the most important unit-process for ased carbon fi bers, optimization of stabilization con-for electrospun PAN nanofi bers has to be studied in Relatively high tensile strength and Youngs modulus

    eported on electrospun single nanofi bers prepared from PAN/DMF solution, followed by stabilization at 300 C in air and carbonized at 800, 1100, 1400 and 1700 C

    130 ] Tensile strength depended strongly on heat treatment ature, showing the maximum of 2.30 GPa at 1400 C,

    . SEM images as-spun (a), 1000 C-carbonized (b) and 2800 C-treated (c) fi bture of PAN/PMMA = 5/5. [ 84 ] Reprinted with permission from Elsevier. KGaA, Weinheim

    ngs modulus increased with increasing temperature, 81 GPa at 1700 C, as shown in Figure 5 . These changes anical properties with heat treatment were explained rowth of crystallite in nanofi bers. However, it has to ed out that orientation of crystallites in the nanofi bers mly oriented, not axial. Stretching on as-spun PAN r bundles was applied before and during their stabili-xpecting well-developed nanotexture and high mechan-erties, [ 119 , 143 ] although no detailed experimental data sented regrettably. ng of nanoparticles of various metals and metal oxides formed via electrospinning process. Various transition noparticles were loaded to carbon nanofi bers in order to the performance of electrochemical capacitors and lith- rechargeable batteries, and also loading of platinum to

    ers and TEM image of 2800 C-treated fi ber (d) prepared from

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    capacitors was studied either by control-ling pore structure in the nanofi bers as the

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    carbon as descpinningPt acetycarboninanofi bpreparePd acetstabiliz1100 Clytic acnanopavia elecacid-moby stananofi bnetic p45 to 6nanofi bsolutionstabilizcarbon increasembeddning ofV 2 O 5 . [ 96

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    the capa currecarbon taining 800 C Side-by8 wt% Pmeasurblended

    PAN(MWCNconsistiformanMWCNelectricaEDLC polypyrto furthembeddtance in

    nanofi ber webs was carried out for fuel cell applications, ribed separately in the following sections. By electros- of lignin/ethanol solution containing 0.2 and 0.4 wt% lacetonate, followed by stabilization at 200 C in air and zation at 6001000 C, microporous Pt-loaded carbon ers were obtained. [ 127 ] Pd-loaded carbon nanofi bers were d from 8 wt% PAN/DMF solution containing 4.8 wt% ate Pd(OAc) 2 by electrospinning, accompanying by the ation in steps from 230 to 300 C and carbonization at . [ 92 ] The resultant nanofi bers showed high electrocata-

    tivity toward the reduction of H 2 O 2 . Magnetic CoFe 2 O 4 rticles were embedded in PAN-based carbon nanofi bers trospinning of PAN/DMF solution with dispersed oleic difi ed CoFe 2 O 4 nanoparticles with 5 nm size, followed

    bilization and carbonization. [ 126 ] CoFe 2 O 4 -embedded ers were superparamagnetic because of nanosized mag-articles and saturation magnetization increased from 3 emu g 1 by carbonization. SiO 2 -embedded carbon ers were prepared by electrospinning of PAN/DMF s containing different amounts of SiO 2 , followed by

    ation and carbonization. [ 87 ] SiO 2 particles embedded in nanofi bers were washed out by HF, but S BET and V total ed only to 340 m 2 g 1 and 0.472 cm 3 g 1 . Vanadium-ed carbon nanofi bers were prepared by electrospin- PAN/DMF solutions containing different amounts of ] After activation by using KOH at 750 C, nanoporous er were obtained, S BET reaching to 2780 m 2 g 1 , V total to 3 g 1 and V micro to 1.52 cm 3 g 1 , which gave a hydrogen

    capacity of 2.41 wt% at 303 K and 10 MPa. Mn-loaded nanofi bers, which were activated by steam at 850 C

    . Dependences of tensile strength and Youngs modulus of carbon nanofi beron temperature. [ 130 ] Reprinted with permission from Elsevier. 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

    respectively, from 0.86 S cwithout MWCNTs. [ 105 ] selected as carbon precursnanofi ber webs were preacetamide (DMAc) solutioactivation at 700850 C steam. Dependences of aqueous electrolyte on disthe webs activated at diffcapacitance of about 202 vated at 800 C with discwhich had S BET of 1220 mof 0.20 cm 3 g 1 .

    d V micro of 0.42 cm 3 g 1 , gave relatively high adsorption for toluene at 289 K. [ 98 ]

    ctrode Materials for Electrochemical Capacitors

    carbon materials are essential for the electrodes of elec-ical capacitors, including electric double-layer capaci-

    commercially available capacitors, activated carbons are nly used. For the improvement of capacitor perform-arious carbon materials have been proposed, activated fi bers, templated carbons, carbon nanotubes etc. [ 144 ]

    tion of electrospun carbon nanofi bers to electrochemical

    r. 2012, 24, 25472566 2557wileyonlinelibrary.com

    eased to 5.32 S cm and 310 F g , m 1 and 170 F g 1 for the nanofi bers Polybenzimidazol (PBI) was also or for electrospinning. [ 70 , 71 , 78 ] Carbon

    pared by electrospinning of dimethyl n of PBI (20 wt%), carbonization and in a fl ow of N 2 containing 30 vol% EDLC capacitance in 1 M H 2 SO 4 charge current density are shown on erent temperatures in Figure 6 . The F g 1 was measured on the webs acti-harge current density of 1 mA cm 2 , 2 g 1 , V micro of 0.71 cm 3 g 1 and V meso IEW

    electrode for electric double-layer capacitors (EDLCs) or by loading fi ne metal particles to the nanofi bers via electrospinning in order to add some pseudocapacitance. Advantage of electrospinning is that it can produce webs, which make their activation and formation of electrode for capacitors easy.

    Webs of PAN-based carbon nanofi bers, which were prepared by electrospinning, sta-bilization, carbonization and activation at 700, 750 and 800 C in a fl ow of N 2 containing 30 vol% steam, were used as electrodes of EDLC using 30 wt% KOH aqueous solution. [ 5 ] The 700 C-activated webs gave a high capaci-

    173 F g 1 at low discharge current density as 10 mA at high current density as 1000 mA g 1 the 800 C-acti-ebs gave a high capacitance as 120 F g 1 : the former

    T of 1230 m 2 g 1 consisting of micropores but the latter

    T of 850 m 2 g 1 consisting of mesopores. Similar results tained in other papers. [ 74 ] The importance of the pres-mesopores was reported in many papers using different

    aterials. [ 145 ] PAN-based carbon nanofi bers prepared by PAN with 15 wt% cellulose acetate (CA) gave S micro of g 1 and S meso of 241 m 2 g 1 , and consequently showed citance of 245 F g 1 in 6M KOH aqueous solution with t density of 1 mA cm 2 . [ 102 ] Electrospun PAN-based nanofi bers prepared from PAN/DMF solution con-PVP by carbonization at 970 C in N 2 and activation at in CO 2 were tested in 1 M H 2 SO 4 aqueous solution. [ 131 ] side bicomponent carbon nanofi bers prepared by using VP gave the capacitance of 221 F g 1 , higher than that

    ed on carbon nanofi bers prepared from PAN solution with PVP. DMF solution dispersed multiwalled carbon nanotubes Ts) was successfully spun and carbonized to get webs

    ng of carbon nanofi bers which gave improved EDLC per-e in aqueous electrolytes. [ 94 , 105 ] The addition of 3 wt%

    Ts in precursor PAN increased S BET to 1170 m 2 g 1 and l conductivity to 0.98 S cm 1 , consequently increased apacitance to 180 F g 1 in 6M KOH. [ 94 ] Coating of le (PPy) on these MWCNT-embedded nanofi bers led

    er increase in capacitance to 333 F g 1 . For MWCNT-ed carbon nanofi bers, electrical conductivity and capaci- 1 M H 2 SO 4 incr 1 1

    on car-

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    oa

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    imide (PI)-derived carbon nanofi ber webs were also as electrode materials of EDLC using 30 wt% KOH s solution and showed a relatively high capacitance of 1 with a high current density of 1000 mA cm 2 . [ 75 ] The or for spinning was pyromellitic dianhydride (PMDA) -oxydianiline (ODA) dissolved in a mixed solution of d methanol. The PI webs obtained after spinning were

    . Dependences of electric double-layer capacitance on discharge density for polybenzimidazol-derived carbon nanofi ber webs heat-t different temperatures. [ 78 ] (a) 700 o C, (b) 750 o C, (c) 800 o C and

    C. Reprinted with permission from Elsevier.

    Figure 7solution.nelibrary.com 2012 WILEY-VCH Verlag GmbH & Co. K

    much larNi loadinnanofi berDMF soluat 800 C0.71.2 n

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    Carbon nfollowingium-ion rto use anand an obe expectwhich isbecause degree. Fto anodebe avoidewebs, rewas obtaithan natu

    lly imidized by heating up to 350 C and carbonized C. All webs activated in air fl ow containing 40 vol%

    at a temperature of 650800 C gave a peculiar behavior: ance increased with increasing current density up to 10 2 and then decreased.

    ition of inorganic salts into PAN infl uenced on the pore re of the resultant carbon nanofi bers. [ 85 , 108110 ] Electros-g from PAN/DMF solutions containing 1-15 wt% ZnCl 2 d in microporous carbon nanofi bers without any activa-ocess after removing Zn compounds by HCl. [ 85 , 110 ] Addi- 5 wt% Ni(NO 3 ) 2 4H 2 O into PNA/DMF solution resulted increase in S BET , mainly due to the increase in mes-

    , without any activation process after carbonization. [ 109 ] ructure control in microporous carbon nanofi bers was y mixing of tetraethoxy orthosilicate and AgNO 3 into 6 , 137 ] and by changing concentration of carbon precursor AN. [ 138 ] principle of electrochemical capacitors, i.e. , physical

    tion/desorption of electrolyte ions in solution, was for water purifi cation (capacitive de-ionization) by using t carbon materials. [ 146 ] Electrochemical adsorption

    y of Na + of electrospin PAN-based carbon fi ber webs, was measured in NaCl aqueous solution, was compared ious carbon materials in Figure 7 . They showed the f 3.2 mg g 1 , which was comparable with those for notube fi lm and carbon aerogel.

    er to add pseudo-capacitance to electric double-layer ce, loading of Ru on electrospun carbon nanofi bers d out. [ 83 ] By the addition of Ru acetylacetonate into the AN/DMF solution, metallic Ru particles with 215 nm embedded in the nanofi bers. Nanofi bers loaded by Ru showed the capacitance of 391 F g 1 in 6M KOH solution, although the nanofi bers without Ru loading F g 1 . Carbon nanofi bers containing nanoparticles of Ni were prepared through electrospinning of PAN/tion added 35, 100 or 135 wt% nickel acetate. [ 117 ] The

    tained had a diameter of about 150 nm and fi ne Ni were deposited on their surfaces. The nanofi ber webs wt% Ni loading showed the capacitance of 164 F g 1 H with a current density of 250 mA g 1 , which was

    ger than about 50 F g 1 for the nanofi ber webs without g. Imbedding of metallic V into PAN-based carbon s were performed through electrospinning of PAN/tion containing V 2 O 5 . [ 95 ] After activation using KOH , S BET reached 2800 m 2 g 1 , due to micropores with

    m and mesopores with 24 nm.

    Electrochemical adsorption capacity of Na ion in NaCl 8 ] GaA, Weinheim

    e Materials for Lithium-Ion Rechargeable Batteries

    anofi ber webs prepared through electrospinning and carbonization have an advantage for anode of lith-echargeable batteries (LIBs), because of no necessity electric conductive additive, such as acetylene black, rganic binder, such as PTFE. However, they can not ed to give low irreversible capacity, as natural graphite currently used in commercially available batteries, most of carbon nanofi bers have low graphitization ew papers reported the results of their application

    of LIBs, but a high irreversible capacity could not d. On 1000 C-treated PAN-based carbon nanofi ber versible discharge capacity C dis of 450 mAh g 1 ned with a current density of 30 mA g 1 , a little higher ral graphite, but irreversible capacity C irr was as high

    Adv. Mater. 2012, 24, 25472566

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    c) 2 ) was used, carbon nanofi bers containing crystalline d Mn 3 O 4 nanoparticles were obtained after carboniza-00 C, which had steady cyclic performance. [ 99 , 118 ] The carbon nanofi bers include MnO x nanoparticles in trix with pores, as shown in Figure 10 a), and give high with good cyclic performance, the nanofi bers prepared g 50 wt% Mn(OAc) 2 giving a steady capacity value of 0 mAh g 1 , much higher than the nanofi bers prepared Mn(OAc) 2 , as shown in Figure 10 b). When ferric acety-e was added into PAN/DMF solution, Fe 3 O 4 -loaded anofi bers were obtained. [ 91 ] After the carbonization at the resultant carbon fi bers included crystalline Fe 3 O 4 with about 20 nm size, of which content was calcu-1 wt%. C dis of the nanofi bers decreases rapidly during

    cycles and then tends to increase with increasing cycle, gher discharge capacity than that without Fe 3 O 4 . bers of LiFePO 4 /C composite were obtained fi bers via electrospinning of PAN/DMF solution

    as 500 mAh g 1 . [ 80 ] High temperature treatment of the webs could not improve LIB performance. Pores were introduced into carPAN/DMpores wand incrent denminute to createS BET as at the fi r

    Manysome enanofi bcarbon with Si PVA/H 2a surfacyclic peLiPF 6 /E15 wt% in Figurwith a rwith cycafter thecapacitypared w

    Sn-loa Sn cocontaineH 2 O solcarbonizresultanparticlesin porewebs shlarge C irsmaller nanofi bnanofi boil, folloat the cin Ar/Hto decomnanofi bretical cnanofi bPMMA of abou100 nmcontent covered nanofi bdensity

    Loadimostly tion. [ 90 , 9

    metallicin 1 M

    Charge-discharge curves and cyclic performance of the carbon webs prepared from 15 wt% Si-dispersed PAN/DMF solu-eprinted with permission from Royal Society of Chemistry.

    Adv. Mater 2012 WILEY-VCH Verlag GmbH & Co. K

    (Mn(OAMnO antion at 7resultanttheir macapacity by addinabout 60without lacetonatcarbon n600 C, particleslated as 3fi rst few giving hi

    Nanofias nano

    bon nanofi bers by adding poly- L -lactic acid (PLLA) in F solution. [ 100 , 120 ] Addition of PLLA created micro-

    ithout activation process, V micro being 0.086 cm 3 g 1 , reased C dis to 435 mAh g 1 after 50th cycle with a cur-

    sity of 50 mA g 1 . [ 120 ] Addition of fumed SiO 2 with particles in PAN/DMF solution was carried out in order pores after leaching out of SiO 2 , but it showed a low

    92 m 2 g 1 and very high C irr , more than 1000 mAh g 1 , st cycle. [ 116 ] works applying electrospinning are aiming to load lectrochemically active metallic particles to carbon ers in order to improve LIB performance. Si-loaded nanofi bers were prepared from PAN/DMF solution nanoparticles (ca. 70 nm) [ 100 , 111 , 113 , 129 ] and also from O solution dispersed Si nanoparticles (ca. 40 nm) with ctant. [ 112 ] Galvanostatic charge-discharge curves and rformance with a current density of 100 mA g 1 in 1 M C + EMC solution are shown on the webs prepared from Si mixed PAN/DMF solution by carbonization at 700 C e 8 . C dis for the 1st cycle is very high as 855 mAh g 1 elatively large C irr of 312 mAh g 1 . C dis decreases slowly ling, 781 mAh g 1 after 10th cycle and 773 mAh g 1 20th cycle, which is much higher than the theoretical for graphite and also than carbon nanofi ber webs pre-ithout Si addition. ading via electrospinning was performed by adding mpound into the precursor solution. [ 104 , 106 , 122 , 123 ] Sn-d carbon nanofi ber webs were prepared from PVA/ution dissolved SnCl 2 by electrospinning and following ation in Ar/H 2 (95/5 v/v). [ 122 , 123 ] The diameter of the t nanofi bers was about 4 m and contained Sn/SnO x of about 20-40 nm size, most of which were located

    s of carbon nanofi bers, as shown in Figure 9 a). The ow relatively high C dis as 735 mAh g 1 but relatively

    r for the 1st cycle (457 mAh g 1 ), although C irr becomes after the 2nd cycle (Figure 9 b). Sn-encapsulated carbon ers were prepared through electrospinning of PAN ers containing tributyltin (TBT) dissolved into a mineral wed by extracting the mineral oil, most of which located ore of the fi ber, in n -octane and by heating at 1000 C 2 atmosphere to carbonize the outer PAN sheath and

    pose the TBT core to metallic Sn. [ 104 ] The resultant ers showed high C dis as 737 mAh g 1 (91% of the theo-apacity), even after 200 cycles. Sn-encapsulated carbon ers were also prepared from PAN/DMF containing and tin octoate. [ 106 ] The nanofi bers had the diameter t 2 m and consisted of hollow channels with about diameter containing metallic Sn nanoparticles. Sn in these nanofi bers was 66 wt% and its particles were by carbon layer with a thickness of about 5 nm. The

    ers showed a high C dis as 648 mAh g 1 with a current of 100 mA g 1 even after 140 cycles. ng of Co, Fe, Mn, Ni and Cu was carried out by adding their acetates into PAN/DMF solu-

    1 , 99 , 114 , 115 , 117 , 118 , 124 ] Carbon nanofi bers containing either Co, Ni or Cu nanoparticles delivered relatively high C dis LiPF 6 /EC + DEC electrolyte. [ 90 , 117 , 124 ] When Mn acetate

    Figure 8 . nanofi bertion. [ 111 ] R

    . 2012, 24, 25472566IEW

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    containH 3 PO 410200at 700 EC + EMcomposolutiowith P

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    ing phosphate precursor (LiCO 2 CH 3 , Fe(CO 2 CH 3 ) 2 and in equal mole ratio) with a wide range of diameters of nm, together with beads. [ 133 ] The nanofi bers carbonized C gave the highest C dis of 160 mAh g 1 in 1 M LiPF 6 /C solution as cathode. Nanofi bers of Li 2 ZnTi 3 O 8 /C

    sites were synthesized via electrospinning of an ethanol n of tetrabutyl titanate, zinc acetate and lithium acetate VP, followed by calcination at 750 C in air. [ 147 ]

    mposite With Carbon Nanotubes

    s carbon nanotubes (CNTs) were included in carbon bers via electrospinning for the reinforcement of their nical properties. [ 66 , 76 , 107 ] Carbon nanofi bers were pre-by electrospinning of PAN/DMF solution, in which

    t% single-wall carbon nanotubes (SWCNTs) were dis-, stabilizing in air and carbonizing at 1100 C. [ 66 ]

    SWCNTstaining teter of 50which wSWCNTthat contubes (Mspun carwhich thnanofi beaxis, but and winwithin thMWCNTulus of 3

    . TEM image of Sn/SnO x -containing carbon nanofi bers (a) and erformance in 1 M LiPF 6 /EC + DMC electrolyte solution with a cur-sity of 30 mA g 1 . [ 123 ] Reprinted with permission from Elsevier. Figure 10

    performanprepared tion. [ 118 ] RKGaA, Weinheim

    were distributed in parallel to the fi ber axis, main-heir straight shape, in PAN nanofi bers with the diam-200 nm. Elastic modulus of SWCNT/PAN nanofi bers, as evaluated using AFM, increased with increasing

    content, from 60 GPa for PAN fi ber to 140 GPa for taining 4 wt% SWCNT. Multi-walled carbon nano-WCNTs) were also successfully included into electro-bon nanofi bers prepared from PAN/DMF solution, in e content of MWCNTs were 2-35 wt%. [ 76 ] In as-spun rs, most MWCNTs are aligned well along the fi ber slightly-curved MWCNTs resulted in curved nanofi bers ding or helical MWCNTs could not be embedded e nanofi bers. The PAN nanofi bers containing 5 wt% s showed tensile strength of 80 MPa and tensile mod-.1 GPa. The fi brous morphology was maintained after

    . TEM image of MnO x -loaded carbon nanofi ber (a) and cyclic ce in 1 M LiPF 6 EC/DEC electrolyte (b) for carbon nanofi bers

    by adding 0. 10, 30 and 50 wt% Mn(OAc) 2 into PAN/DMF solu-eprinted with permission from Elsevier.

    Adv. Mater. 2012, 24, 25472566

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    K

    REduring stabilization and carbonization by expecting superior

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    been reup to 15

    Stabiis knowof carbocarbon stabilize600110the optfrom stunits ofbonizatand oxychanges

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    on nanotubes were grown on the surface of electrospun nanofi bers. [ 73 ] Fe-loaded carbon nanofi bers were pre-

    rom PAN/DMF solutions containing 3.3 and 6.7 wt% yleacetonate Fe(acac) 3 by electrospinning, stabilization, on of Fe 3 + to metallic Fe at 500550 C in H 2 and car-ion at 1100 C in Ar. Metallic Fe particles with 1020 nm persed in the nanofi bers. On the surface of the carbon ers thus prepared, MWCNTs were grown by catalytic hexane, of which the length depended on the period of

    c CVD.

    cussions

    bon Precursors

    production of carbon materials, the selection of pre-is the most crucial, because it determines the nanote-f the resultant carbon under ordinary carbonization ns, such as the heat treatment under atmospheric pres-he nanotexture formed during carbonization process, s classifi ed into random, planar, axial and point orienta- the basis of the scheme of preferred orientation of the

    ructural units of carbon layers, is known to govern the ral development by further treatment at high tempera-d, as a consequence, to infl uence on various properties,

    s electrical, mechanical and chemical properties. [ 1 , 148 ] rbon materials prepared from various precursors have assifi ed into two groups, based on whether the struc-hange to graphite (three-dimensionally ordered struc- easy or not at high temperatures above 2500 C, calling izing and non-graphitizing carbons, [ 1 ] even though some are known to show different behaviors. diameter of electrospun carbon nanofi bers is 100 to

    m, which might give some infl uence on the formation texture during their carbonization process and also on

    ral modifi cation at high temperatures. Size of carbon valuated as La by X-ray diffraction was experimentally to depend strongly on the particle size of spherical materials. [ 148 ] PAN-derived carbon fi bers prepared via inning, stabilization and carbonization have a random ture and are non-graphitizing (called general-purpose In order to improve nanotexture to axial orientation, ng of the as-spun fi bers is known to be necessary during heat treatments, and the resultant PAN-based carbon ive higher strength and Youngs modulus (high-perform-ade). [ 2 ] The carbon prepared in the gallery of layer-struc-ontmorillonite (template carbonization) is easily con-

    o graphite at a high temperature as 2800 C, because the is of PAN is performed in monolayer of carbon atoms

    template layers. [ 149 ] Therefore, the formation of nano-in nano-sized fi brous carbons (carbon nanofi bers) and ange in structure and properties with high temperature nt might be a little different from our knowledge based e-sized particles of carbons with different nanotextures. sed continuous nanofi bers were prepared under tension

    r. 2012, 24, 25472566 2561wileyonlinelibrary.comGaA, Weinheim

    VIEW

    cal properties. However, no structural studies had orted yet and the heat treatment had been done only 0 C.

    ization of PAN fi bers with micrometer-sized diameters to be the most important process on the production

    n fi bers. [ 2 ] In most literatures working on PAN-based anofi bers, however, as-electrospun PAN fi bers were at 280 C in air and carbonized at a temperature of

    0 C in inert atmosphere. It might be needed to explore mum condition for stabilization and carbonization uctural view points, such as the size of basis structural carbon layers and their orientation in nanofi bers, car-n yield, content of foreign atoms, hydrogen, nitrogen en, which remain even after carbonization, and also in diameter and its distribution. atic polyimides (PIs) are interesting carbon precursors they give a wide range of structure, from well-crystallized fi lm to amorphous carbon with random nanotexture, ing a combination of the starting dianhydride and the . [ 150 ] However, one kind of polyimide (a combination of litic anhydride and 4,4 -oxydianiline, PMDA/ODA) was sed for electrospinning. [ 75 , 86 ] Even when starting from DA, the thickness of its fi lm is known to govern the ability: thin fi lms with less than 25 m thickness can rted to highly crystalline graphite by high temperature t, but thicker fi lms can not, which is explained by the

    on of precursor molecules in the fi lm. [ 150 ] Studies on PIs by coupling with heat treatment at high temper-d detailed structural analyses may give a more wide

    nanotextures in the resultant carbon nanofi bers and, ently, may open more wide applications, because of the ty to have a controlled structure from graphite to amor-or applications requiring high electrical conductivity, PIs are worthwhile to be tested as a precursor. is less costly than other carbon precursors, such as PAN but not many reports discuss its use for electrospin-ce pitch is a mixture of various hydrocarbons, certain nts might be needed to be selected for electrospinning n to the solvent selected, as the DMF-insoluble part of with THF. [ 72 ] Mesophase pitch, which is used as a pre-r commercial mesophase-pitch-based carbon fi bers, is ile to be used for electrospinning, even though a stabi-rocess is needed to get pitch-based carbon nanofi bers,

    expected to lower its graphitizability. gh poly(vinyl alcohol) PVA has a very low carboni-

    ield (few wt%), it might be an interesting precursor water can be used as a solvent. [ 112 , 122 , 123 ] lic resins are often used as carbon precursor, which

    n-graphitizing carbon in a conventional carbonization with the advantage of a relatively high carbonization wever, it is rarely used in studies on carbon nanofi bers ospinning. [ 89 , 121 , 132 ]

    Structure Control

    cases, electrospun carbon nanofi bers were prepared rm of webs (mats), which is an advantage for various

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    t kinds of pores are formed; large pores (maybe better them spaces), macropores ( > 50 nm size), mesopores m size) and micropores ( < 2 nm size). spaces are formed due to entangling of different ers and disperse widely in their size and morphology. ores are very diffi cult to control and characterize mainly they are fl exible (fl exible interparticle pores). [ 1 ] The nsity or porosity of the webs is the parameter that is determine and effective for characterizing these large However, information on the bulk density or porosity been presented in most literature reporting on electro-rbon nanofi ber webs. It has to be emphasized that their e in the webs is very important for applications: they are s for electrolytes in energy storage devices to diffuse aller pores to be adsorbed, but a too large amount of akes the volumetric storage capacity small. When elec-ing conditions are not appropriate, bead-like particles ed together with fi brous particles and rigidly bound

    nections between nanofi bers are formed after carboni-which may result in a rigid macropore system. o-, meso- and micropores are formed in each nanofi ber rigid (rigid intraparticle pores). Most micropores and esopores are intrinsically formed in fi brous carbon par-ring the carbonization process due to the evolution of

    t gaseous species, such as hydrocarbons of various sizes, 2 , etc., and thus strongly depends on the carbon pre-sed and carbonization conditions. To increase and con-

    amount of micropores, a conventional activation process n applied in many works by using either steam, KOH, O 4 as an activation reagent on electrospun nanofi bers ir carbonization (Table 1 ). The addition of ZnCl 2 , which

    e of reagents for conventional activation, into a PAN/lution before electrospinning was also adopted, but no ced improvement of S BET was obtained. [ 85 ] For appli-

    o the electrode of electrochemical capacitors, the acti-rocess was applied on electrospun carbon nanofi bers from PAN, [ 67 , 74 , 128 ] PBI, [ 70 , 71 , 78 ] and PI. [ 75 ] By the activa-AN-based carbon nanofi bers in a fl ow of N 2 containing

    steam at 800 C, S BET increased to 1160 m 2 g 1 , V total to 3 g 1 and capacitance to 134 F g 1 in 6M KOH aqueous te with a current density of 1 mA cm 2 . [ 75 ] By the activa-

    PBI-derived carbon nanofi bers at 800 C, capacitance of 1 in 1 M H 2 SO 4 aqueous electrolyte was obtained with te performance. [ 78 ] Also the addition of cellulose acetate N was tried to control pore structure without activation , giving certain increases in S BET from 740 to 1160 m 2 g 1 capacitance from 141 to 245 F g 1 in 6M KOH with a density of 1 mA cm 2 . [ 102 ] By the activation of carbon

    ers, micropores are supposed to be formed on their which is expected to be advantageous for adsorption/ion. For commercially available activated carbon fi bers their advantages for adsorption/desorption of gases due resence of micropores on their surface are now well

    [ 1 ] Good rate performance in electrochemical capacitors orted on electrospun carbon nanofi ber webs, [ 74 , 78 ] prob-e to the formation of micropores on the nanofi ber sur-t its experimental evidence is not reported yet. KGaA, Weinheim

    only by sacrifi cing micropores. It might be interesting template, either surfactants or MgO precursors into

    pinning precursor solution, which can leave mesopores bonization. [ 151 ] of the macropores and some of the mesopores have to duced into fi brous particles intentionally, by using either ional carbon precursor, which gives pores after carboni-ecause of its low carbonization yield, such as PMMA in introduce tubular macropores, [ 84 ] or an additional sol-

    electrospinning solution, such as water in DMF. [ 57 ] nly micro- and mesopores of the electrodes in EDLCs are nt for adsorption of electrolyte ions, but also the diffu-ons to micro- and/or meso-pore surfaces to be adsorbed n to give a strong infl uence on capacitor performance, rly charge/discharge process with high rates. The pres-

    mesopores, in addition to micropores, has been pointed e important for getting good rate performance, in other igh retention in capacitance with high rate charge/dis-. Obtaining webs consisting of carbon nanofi bers may f the merits of the process via electrospinning, because

    der and electroconductive additives (commonly carbon re not needed to form electrode sheets and the presence spaces between nanofi bers may be advantageous for sion of electrolyte ions to the micro- and meso-pores in rs. However, it has to be mentioned that the webs usu-

    e a low bulk density, which may lead to low volumetric nce. ptimum conditions for electrode carbon, including its

    ucture, is not yet clearly understood and they might be t for charge/discharge conditions and also for electro-s. It also has to be pointed out that direct comparison the capacitance values reported is very diffi cult because termination procedure is not standardized. [ 144 ] In order the merits of using carbon nanofi bers prepared via elec-ing clearly under the present situation, more detailed are strongly demanded on pore structure control, not control of meso- and micropores in nanofi bers, but also characterization and the control of large spaces in the addition, wettability of the resultant carbon nanofi ber

    th electrolyte solutions, either aqueous or non-aqueous, e studied, which might depend on precursor and car-on temperature.

    rove