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Significant improvement of ionic conductivity of high-graphene oxide-loading ice-templated poly (ionic liquid) nanocomposite electrolytes
Accepted Manuscript Significant improvement of ionic conductivity of high-graphene oxide-loading icetemplated poly (ionic liquid) nanocomposite electrolytes Fu Jie Yang, Yi Fu Huang, Ming Qiu Zhang, Wen Hong Ruan PII:
S0032-3861(18)30751-1
DOI:
10.1016/j.polymer.2018.08.039
Reference:
JPOL 20846
To appear in:
Polymer
Received Date: 1 April 2018 Revised Date:
11 August 2018
Accepted Date: 18 August 2018
Please cite this article as: Yang FJ, Huang YF, Zhang MQ, Ruan WH, Significant improvement of ionic conductivity of high-graphene oxide-loading ice-templated poly (ionic liquid) nanocomposite electrolytes, Polymer (2018), doi: 10.1016/j.polymer.2018.08.039. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Graphical Abstract In the ice-templated graphene oxide / poly (ionic liquid) nanocomposite electrolyte, a superhighway for ion conduction consisted of "PIL&GO nanosheets" could be built at a high
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loading of GO, which contributed to significant improvement of the ionic conductivity.
ACCEPTED MANUSCRIPT 1
Significant Improvement of Ionic Conductivity of High-Graphene Oxide-Loading Ice-Templated
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Poly (Ionic Liquid) Nanocomposite Electrolytes
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Fu Jie Yang, Yi Fu Huang*, Ming Qiu Zhang and Wen Hong Ruan*
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Key Laboratory for Polymeric Composite and Functional Materials of Ministry of Education, GD
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HPPC Lab, School of Chemistry, Sun Yat-Sen University, Guangzhou 510275, P. R. China
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*Corresponding authors:
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Dr. Yi Fu Huang and Dr. Wen Hong Ruan
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Materials Science Institute
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Sun Yat-Sen University
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Guangzhou 510275
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P. R. China
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E-mails: [email protected]; [email protected]
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Manuscript submitted to Polymer, 2 April, 2018
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ACCEPTED MANUSCRIPT 1
Significant Improvement of Ionic Conductivity of High-Graphene Oxide-Loading Ice-Templated
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Poly (Ionic Liquid) Nanocomposite Electrolytes
3 Fu Jie Yang, Yi Fu Huang*, Ming Qiu Zhang and Wen Hong Ruan*
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Key Laboratory for Polymeric Composite and Functional Materials of Ministry of Education, GD
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HPPC Lab, School of Chemistry, Sun Yat-Sen University, Guangzhou 510275, P. R. China
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Abstract: Poly (ionic liquid)s are an emerging family of promising polymer electrolytes. In this study,
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a nanocomposite electrolyte based on ice-templated high-graphene oxide-loading poly (ionic liquid)
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(GO / PIL) was prepared to significantly improve ion transport of PIL. X-ray diffraction patterns
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exhibited that GO was well-loaded in the as-prepared composites event at high content of 50 wt%. The
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Raman and UV-Vis spectra demonstrated the strong interaction between GO and PIL. Morphology
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observations showed that PIL could well contact with GO, forming so-called "PIL&GO nanosheets"
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that were connected in an ionic-conducting network, which facilitated the ion transport in the PIL, as
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revealed by conductive atomic force microscope investigation. As a result, with a superhighway for
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ions built, PIL-based composite electrolyte obtained a higher ionic conductivity of 3.1×10-4 S cm-1 at 50
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wt% GO, 775% of that of pure PIL electrolyte. Such ice-templated nanocomposite electrolytes possess
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potential applications for various electrochemical devices.
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Keywords: Nanocomposite electrolyte; Ionic conductivity; Poly (ionic liquid)s
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1 Introduction To adapt to the rapid development of flexible electrochemical devices, polymer electrolytes have
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been urgently developed, with superior advantages of high safety, excellent mechanical properties, and
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environment-friendly production. [1-3] A typical polymer electrolyte mainly consists of polar polymer
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(e.g. PMMA [4], PVDF [5], PEO [6], PAN [7], PVC [8]) as solid-state solvent with incorporated
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electrolyte salt for providing solvated ions. Since the first work of Wright et al [9], overcoming poor
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ion-transport ability of the polymer electrolytes has still been a big challenge, which greatly hinders
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their practical applications. [10, 11] Poly (ionic liquid)s (PILs), an emerging family of high
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performance polymer electrolyte, have attracted extensive attention. [12-14] These PILs can be
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prepared by polymerization of ionic liquid (IL) monomers and are anticipated to take advantages of
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both the mechanical durability of polymer and electrochemical properties of ionic liquid. [15, 16]
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However, the ionic conductivity of PILs is surprisingly far below that of IL unpolymerized. [17]
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Structurally, a PIL molecule, behaving as a chain-like ionic conductor, owns mobile cations or
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anions and the repeating counterionic species covalently bonded to the polymer backbone. Common
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methods to improve the ionic conductivity of PIL electrolyte are to decrease the glass transition
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temperature (Tg) of polymer backbone, like plasticizing [18], copolymerizing [19], and interpenetrating
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[20], to increase the PIL chain motion. Unlimited to the above methods, it has been reported that
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preparation of nanocomposite electrolyte by adding functional nanoparticles (e.g. TiO2 [21], SiO2 [22],
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Al2O3 [18]) into the PILs also works because an ionic conductive network could be constructed by
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nanofillers and ions could align and transport faster along the networks. The emerging nanocomposite
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electrolyte has provided a simple, facial strategy of tuning the properties of the polymer electrolyte
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without modifying the chemical structure of polymer chains. Among reported functional nanomaterials,
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ACCEPTED MANUSCRIPT graphene oxide (GO) is an ideal candidate owing to two-dimensional (2D) structure with the high ionic
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conductivity of ~10-2 S cm-1 , as well as the oxygen-containing groups on GO basal planes could
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well-dissociate the salts. [23] Inspired by the superior properties of GO nanosheets in last decades, the
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introduction of GO into PIL has gained great interests in recent years. [24, 25] Because of the π-ion
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interaction between GO and IL, the GO can be well exfoliated. [26] By functionalizing the GO with IL
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(IL-FG), Mai et al showed modified GO was an excellent additive to improve the ionic conductivity of
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polymer electrolyte by ~150% with 0.6 wt% IL-FG. [27, 28] Lin et al have fabricated a GO / PIL
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composite electrolyte by direct solution-blending method and observed that the ionic conductivity
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could be improved by 141% when addition 2 wt% GO. But when GO content was over 2wt%, the
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steric effects of GO occurred and lead to the decrease of ionic conductivity. [29] It is obvious that the
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aggregation of GO nanosheets is detrimental to the ion transport. To increase the loading of GO with
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well-dispersion in the PILs becomes a main issue.
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Ice-templated assembly technology to construct 3D structure has provided a viable route for
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obtaining well-dispersed GO nanosheets in water-soluble polymers (e.g. PVA [30], PEO [31], Nation
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[32]), since GO can have a molecular-level dispersion in aqueous solution. Kim et al have obtained
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well-dispersed GO even at a high content up to 50 wt% in ice-templated GO / PVA. [33] This gives us
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a hint that the high content GO / PILs nanocomposites electrolyte could be obtained by ice-templated
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method. However, the studies on ice-templated structure based composite polymer electrolyte have not
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been reported yet. Herein, a new nanocomposite electrolyte of GO / PIL is prepared by ice-templating
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in this work. X-ray diffraction (XRD) analysis is used to study the exfoliation of GO nanosheets in the
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GO / PILs. The interaction between the GO and PIL is investigated by Raman spectra, UV-Vis spectra,
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and differential scanning calorimetry (DSC) techniques. Morphology of GO / PIL composites is
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electron microscopy (SEM). Subsequently, the ionic conductivities of GO / PIL electrolytes are
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measured using AC impedance spectra and the relevant mechanism is also revealed through
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tunneling-AFM (TUNA) analysis. It is hoped that the as-prepared high-GO-content PIL electrolytes
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could offer new insight into the development of the advanced nanocomposite polymer electrolytes.
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2 Experimental
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2.1.
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polymerization
poly
(1-propyl-3-vinyl-imidazolium)
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Firstly, a certain amount of N-vinylimidazole (1.88 g, AR, Aladdin agent) and chloropropane (1.48
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g, AR, Aladdin agent) were dissolved in 5 mL distilled methylbenzene under nitrogen atmosphere, and
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stirred at 50 oC for a period of 48 h. Then 0.04 mg AIBN dissolved into 5 mL methylbenzene was
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added, under vigorous stirring at 65oC for 48h. [21] After that, the resulting precipitate was filtrated,
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and repeatedly washed for several times with anhydrous ether, and further purified via the Soxhlet
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extraction.
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2.2. Preparation of ice-templated GO / poly (ionic liquid) (PIL) nanocomposite electrolytes
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Firstly, the as-synthesized PVImCl (20 mg) was entirely dissolved into 10 mL distilled water and
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stirred for at least 24hr at room to obtain a precursor aqueous solution. Then, 10 mL GO aqueous
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solution with a series of 0.2, 0.9, 2, 8 mg mL-1 was slowly added to the precursor aqueous solution
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dropwise under vigorous stirring for 24hr to obtain aqueous dispersions with various content of GO
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(see Fig. S1). The graphite oxide powder for preparing GO aqueous solution was prepared from flake
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graphite (99.8% purity, XF NANO) using modified Hummers method. [34] The aqueous dispersions
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were transferred into plastic petri dishes, frozen for 6 h at -80 oC, and freeze-dried by a LGJ-12
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ice-templated GO / PVIm composites were prepared. For comparisons, the pure PIL and pure GO were
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obtained from the corresponding aqueous solutions (1mg mL-1) by the ice-templating, respectively.
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Finally, to introduce the counter ions into PVIm to prepare poly (ionic liquid) (PIL), the GO / PVIm
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composite was immersed into I- / I3- solution using acetonitrile as solvent for more than 24 hr at room
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temperature, and then the solvents was removed in a vacuum oven at 50 oC for 12 hr, to obtain the
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resulting product of GO / PIL nanocomposite electrolytes.
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2.3. Characterizations
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Wide-angle XRD patterns were recorded using a Rigaku DMAX 2200 X-ray diffractometer with
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Cu-Kα radiation (40 kV, 40 mA, 10o min−1 from 5o to 60o). The zeta potential of the sample aqueous
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solution was measured using a Brooken Heaven PALS zeta potential analyzer. Raman scattering signals
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of the samples were recorded on a Raman spectroscope (Renishaw inVia). The excitation wavelength
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was 514 nm with a scanning range from 500 to 2500 cm−1. UV-Vis absorption spectroscopy was
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conducted on a Shimadzu UV-3600 spectrophotometer at room temperature. The measurement of glass
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transition temperatures (Tgs) of the samples was performed on a differential scanning calorimeter (DSC,
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TA/Q10).
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The morphology images of samples were obtained on Bruker atomic force microscope (AFM,
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Multimode 8). Before the test, the ice-templated sample was spin-coated on a cleavage surface of mica.
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Scanning electron microscopy (SEM) images of the samples were obtained using a Hitachi S-4800
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field emission electron microscope equipped with an energy dispersive X-ray fluorescence
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spectrometer for element analysis. Transmission electron microscopy (TEM) analysis was conducted
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using a FEI Tecnai G2 Spirit electron microscope.
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workstation (CH Instruments Inc.) in a symmetrical cell composed of the sample, and two transparent
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conductive Pt electrodes at room temperature, using the AC impedance method over the frequency
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range from 1 Hz to 106 Hz. The values of σ could be calculated as bellows: σ = L / RS · A. Where L, RS
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and A were the thickness between two electrodes, the internal resistance of the electrolyte, and the area
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of the electrode-electrolyte contact, respectively. [35] The tunneling-AFM (TUNA) measurements were
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also performed on the Bruker atomic force microscope. The as-prepared ice-templated samples were
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spin-coated on the conductive layer of an ITO glass substrate for tunneling-AFM analysis.
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3 Results and discussion
The X-ray diffraction (XRD) technology was firstly used to investigate the GO dispersion in
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ice-templated GO / PIL composites [31, 33]. As shown in Fig. 1, the XRD patterns of ice-templated PIL
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exhibited a broad peak at 22o, indicating that the PIL was amorphous. With the addition of GO, there
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were no characteristic diffraction signals of GO appeared even loading 50 wt% of GO. However, a
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characteristic peak of GO at 10.5o was appeared when the content of GO was up to 80 wt%, similar to
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the appearance of characteristic peak at 11.2o of ice-templated GO without PIL, which indicated that
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aggregation of GO nanosheets occurred. Compared to the published literature which showed the
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apparent aggregation of GO nanosheets over the content of 2 wt%, [29] this study demonstrated that
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the GO nanosheets could be well-loaded in the PIL composite even at the highest GO loading of 50
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wt% through ice-templated process.
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Ice-templated GO Ice-templated 80wt% GO / PIL Ice-templated 50wt% GO / PIL
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Ice-templated 10wt% GO / PIL
Ice-templated PIL
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2θ ( C)
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Fig. 1. XRD patterns of the ice-templated PIL, GO and various GO / PIL composite materials with
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different loading of GO.
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Ice-templated GO / PIL
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Ice-templated GO / PIL Ice-templated GO
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Raman shift (cm )
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Fig. 2. Investigation on the internal interactions of ice-templated 50wt% GO / PIL composites. (a)
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UV-vis absorption spectra of ice-templated PIL and 50wt% GO / PIL; (b) Raman spectra of
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ice-templated GO and 50wt% GO / PIL.
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In Fig. 2, the interaction between GO and PIL in ice-templated composites was investigated by
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using UV-Vis and Raman techniques. Fig. 2a depicted the UV-Vis spectra of solid PIL and GO / PIL. 8
ACCEPTED MANUSCRIPT The UV-Vis spectrum of PIL exhibited a characteristic absorption peak at 210 nm which was assigned
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to π–π* transitions. Interestingly, the π–π* transition of PIL appeared at 210 nm was red shifted to
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higher wavelength of 223 nm in the spectra of GO / PIL, indicating that there was a strong interaction
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between GO and PIL. Besides, a shoulder peak at 295 nm was attributed to n-π* transitions of GO.
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Further, Raman spectroscopy (Fig. 2b) was also used to confirm the interactions involved between GO
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and PIL. An eminent band at 1360 cm-1 corresponding to sp3 (D band) and a band at 1607 cm-1 for the
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sp2 (G band) could be observed for pure GO. Compared with the peaks of GO, the two characteristic
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peaks of GO / PIL were significantly blueshifted to 1351 cm-1 and 1590 cm-1, respectively, indicating
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that the PIL changes the sp2-sp3 hybridization of GO nanosheets when the π-π stacking between
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imidazole rings and carbon rings occurred, since the GO is good electron-donating π system and the
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imidazolium cation of PIL is electron-deficient π system. [36] Therefore, the surface of GO nanosheets
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could be interacted with PIL via the π-π interaction which made them positively charged. It was further
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confirmed that the positive zeta potential of GO / PIL aqueous dispersions (30.72 ± 0.5 mV) showed
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higher than the negative zeta potential value of pure GO aqueous dispersions (-13.5 ± 1.5 mV).
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Moreover, the value of ID / IG had a slight decrease from 0.81 for pure GO to 0.77 for GO / PIL, as the
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π-π stacking extended the π-conjugated structure of GO corresponding to G band intensity. [37]
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Meanwhile, in case of the GO / PIL composite, the oxygen functional groups (such as carboxyl groups)
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on the GO could act as the charge compensating anions and were linked to the positively charged
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imidazole rings of PIL through electrostatic interaction. [26] It implied that the transport of counter
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ions within the PIL would be benefited.
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Fig.3 showed the morphologies of ice-templated GO / PIL composites. The appearance of obtained
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GO / PIL composites were a brown and sponge-like material, as exhibited in Fig. 3a (1). A typical SEM
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(3), respectively. It was shown that the ice-templated composite owned macroporous structure and the
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uniform distribution of N element on it was experimentally mapped out. Compared to the SEM image
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of pure GO (Fig. S2), the presence of N element in GO / PIL exhibited that GO nanosheets were
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well-loaded with PIL. The TEM image of GO / PIL composite (Fig. 3b) revealed the easy formation of
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layer structure in the composite, in which GO nanosheets and PIL were attached each other owing to
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strong interaction between GO and PIL (see Fig.2). In addition, the atomic force microscopy (AFM)
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image and height curve in Fig. 3c exhibited the flat configuration of GO / PIL with an average height of
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~2.0 nm. The increased thickness of GO / PIL nanosheet (relative to GO of~0.9 nm, Fig. S3) mainly
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ascribed to the absorbed PIL layer.
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Fig. 3. (a) Structure and morphology of ice-templated 50wt% GO / PIL composite: (1) optical image of
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a piece of sponge-like 50wt% GO / PIL composite, (2) a representative SEM image of 50wt% GO /
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PIL, with (3) corresponding elemental mapping image of N element; (b) TEM image of ice-templated
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50wt% GO / PIL; (c) AFM image of ice-templated GO / PIL at 50wt% GO content on a mica substrate,
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with the corresponding height profile (bottom) along the white line showing thicknesses of the
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nanosheets.
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To further investigate the structure of GO / PIL nanosheets in ice-templated composites, DSC
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measurements of composites with different GO content were conducted (Fig. 4). The glass transition 10
ACCEPTED MANUSCRIPT temperature (Tg) of ice-templated PIL was 174 oC. Tg of PIL in the GO / PIL composites were gradually
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increased with the addition of GO and finally became infinite when GO content was up to 50 wt%. It
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was demonstrated that chain mobility of PIL was hindered due to more PIL chains were fixed by GO
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when GO content was increased. The SEM images of corresponding samples manifested that the pore
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structures of ice-templated composites became more ordered and pore walls became thinner with the
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increase of GO content. Combining the DSC results with morphology observation, it inferred that PIL
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was evenly attached on the skeleton of GO sponge with the increase of GO loading. A so-called
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"PIL&GO nanosheets" could be formed in the ice-templated structure composites when addition of GO
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was up to a certain amount.
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Ice-templated 5wt% GO / PIL
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Ice-templated 80wt% GO / PIL
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140
160
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o
Temperature ( C)
Fig. 4. DSC curves of ice-templated PIL and various GO / PIL composites combining with the SEM
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observation.
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a
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0
20
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b
-3.2
log σ (S cm -1 )
-1 σ (S cm )
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2.7
Ice-templated PIL Ice-templated 30wt% GO / PIL Ice-templated 50wt% GO / PIL Ice-templated 80wt% GO / PIL
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3.0
3.1
3.2
3.3
1000/T (1/K)
GO content (wt%)
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Fig. 5. (a) The effect of GO loading on ionic conductivities (σs) of composite electrolytes based on
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ice-templated GO / PIL; (b) Influence of the temperature on ionic conductivities of ice-templated GO / 11
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PIL composite electrolytes.
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Table 1 The corresponding activation energy (Ea) of ice-templated GO / PIL composite electrolytes. Activation energy (Ea, kJ mol-1)
Ice-templated PIL
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Ice-templated 30wt% GO / PIL
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Ice-templated 50wt% GO / PIL
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The ionic conductivities (σs) of ice-templated GO / PIL electrolytes with different GO loading
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were also studied by EIS measurement (Fig. 5a). It was noticeable that the σ significantly increased
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with the addition of GO and reached 3.1×10-4 S cm-1 at 50 wt% GO via ice-templated technique, which
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was approximately 775% increase compared to that of the pure PIL (4.0×10-5 S cm-1). However,
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without the ice-templated assistance, the highest ionic conductivity of GO / PIL just reached 7.1×10-5 S
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cm-1 for a GO content of 3wt% with the directly addition of GO into PIL electrolyte (see Fig. S5). The
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ion transport of PIL electrolyte was poor due to the electrostatic effect of positively-charged main
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chains on anions in the system. In the GO / PIL systems, the positively-charged polymer chains of PIL
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strongly interacted with the GO (see Fig. 2 and Fig. 4) and led to the well-loaded GO via the
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ice-templated process. Finally, the polymer chains could be mostly fixed at the certain GO loading and
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resulted "PIL&GO nanosheets" (see Fig. 3b and c). These "PIL&GO nanosheets" would promote the
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ion transport since the carboxyl groups of GO could efficiently weaken the electrostatic effect of PIL
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chains on the anions. Therefore, the σ values dramatically increased with the loading of GO. In addition,
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the σ decreased at higher content of GO, due to the aggregation of GO nanosheets that was confirmed
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by Fig. 1. Ionic conductivity-temperature plots of the ice-templated PIL and GO / PIL electrolytes with
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different GO loading were conducted (Fig. 5b) and corresponding activation energy (Ea) were
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calculated (Table 1). The ionic conductivity-temperature curves of the PIL and GO / PIL electrolytes
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ACCEPTED MANUSCRIPT follow an Arrhenius behavior. The Ea of PIL electrolyte is 18.96 kJ mol-1. The Ea of ice-templated GO /
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PIL composite electrolyte was significantly decreased with the addition of GO, and then reached to the
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lowest Ea of 4.33 kJ mol-1 at the loading 50wt%GO. However, the excess GO resulted in the increase of
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the Ea of the GO / PIL composite electrolyte, which was well consistent with the influence of GO
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content on the ionic conductivity. A lower Ea value for a polymer electrolyte indicates that ions in the
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systems can move more easily along the ionic channels. Therefore, the ion transport of PIL electrolyte
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system can be significantly improved by loading certain high content of GO.
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TUNA current (nA)
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Fig. 6. Investigation of ion transport of the ice-templated GO / PIL composite electrolytes using
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conductive atomic force microscope (C-AFM). (a) and (c) are the height images of ice-templated PIL
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electrolyte and 50wt% GO / PIL electrolyte, respectively; (b) and (d) are TUNA current image of
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ice-templated PIL electrolyte and 50wt% GO / PIL electrolyte, respectively. 1 and 2 are current-voltage
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(I-V) curves at different conductive regions (1: high conductivity; 2: low conductivity).
DC sample bais (mV)
DC sample bia (mV)
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To investigate the mechanism on the significantly increased ionic conductivity in GO / PIL
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electrolytes, the conductive AFM (C-AFM) measurement was used to microscopically analyze the ion
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ACCEPTED MANUSCRIPT transport of GO / PIL electrolytes. It was found that the sample of PIL (Fig. 6a) exhibited relatively a
211
flat morphology. The sample of GO / PIL (Fig. 6c), by contrast, showed a distinct morphology which
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consisted of several layers of "PIL&GO nanosheets" . It was reported that the ionic transport of
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electrolytes was reflected by color regions in TUNA images, i.e., the fast-ion channels at the dark color
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regions and the slow-ion channels at the light color regions. [38] According to these, the TUNA images
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of PIL electrolyte (Fig. 6b) revealed that a relatively low ionic transport with small and disconnected
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ionic channels existed in the samples. On the contrary, the TUNA images of the GO / PIL electrolyte
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(Fig. 6d) demonstrated excellent ion conduction of "PIL&GO nanosheets" with large area of connected
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ionic channels, indicating that ions in the system could move more easily along the "PIL&GO
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nanosheets". In addition, the current-voltage (I-V) tests showed that TUNA current signals of
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"PIL&GO nanosheets" (Fig. 6d (1)) were much higher than that of the region without GO (Fig. 6d (2)).
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Moreover, based on the Ohm’s law (i.e., R = V / I), the conductivity of the sample was proportional to
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the slope (k) of the relative I-V fitting curve. It could be seen that the k value of the I-V curve on the
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region 1 was extremely higher than that of the region 2, which indicated that the ion transport could be
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facilitated on the surface of "PIL&GO nanosheets". Thus, the addition of GO could significantly
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increase the σ of PIL.
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Fig. 7. The schematic drawing of the effect of GO on significant improvement of ion transport of
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ice-templated GO / PIL composite electrolytes.
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Based on the above investigations, the effect of GO on significant improvement of ion transport of
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ice-templated GO / PIL composite electrolytes was revealed and summarized by the schematic drawing
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of Fig. 7. In the PIL electrolyte, migration of anions could be hindered by electrostatic interaction since
232
the polymer chains of PIL consisted of positively-charged imidazole rings. Fig. 7a showed that the ion
233
transport path zigzagged and prolonged, so the ionic conductivity of PIL electrolyte had a very low
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value (see Fig. 5). In the GO / PIL electrolytes, the GO could be well loaded into the PIL matrix via the
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ice-templated process and formed the so-called "PIL&GO nanosheets" (see Fig. 1-4). These "PIL&GO
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nanosheets" could weaken electrostatic effect of PIL main chains on the anions and accelerate the ion
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transport in PIL, thus a relatively shorter ion transport path could be built in the GO / PIL systems (Fig.
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7b) and higher ionic conductivity could be obtained (see Fig. 5). When the addition of GO reached a
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certain amount, the chains of PIL were mostly fixed on the GO surface and the electrostatic effect on
240
anions had been significantly decreased, and "PIL&GO nanosheets" could be connected to form
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ion-conducting networks. As a result, a superhighway for ion transport built in the GO / PIL electrolyte
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(Fig. 7c), which was ascribed to the significant improvement on the σ of GO / PIL electrolyte (see Fig.
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5 and Fig. 6).
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Conclusions In this study, GO / PIL nanocomposite electrolytes are prepared by ice-templating method. GO can
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be dispersed and well-loaded in the PIL matrix even at the high content of 50 wt%. There are strong
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interactions between GO and PIL, resulting in positively-charged polymer chains of PIL attached on
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the GO surface and forming so-called "PIL&GO nanosheets" at high GO loading. The ionic
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conductivity of GO / PIL electrolyte increases with the addition of GO because more polymer chains of
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PIL can be fixed on the GO to decrease the electrostatic effect of PIL on the anions and to accelerate
251
the ion transport. A superhighway of ion conductive networks consisted of "PIL&GO nanosheets" can
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be built at certain loading of GO (≥50 wt%). As a result, the ionic conductivity of GO / PIL electrolyte
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can be significantly improved. 50 wt% GO / PIL electrolyte has the ionic conductivity of 3.1×10-4 S
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cm-1, which is 7.75 times than that of the pure PIL electrolyte. This type of nanocomposite electrolyte
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can meet the requirement of assembling electrochemical devices, such as dye-sensitized solar cells or
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lithium ion battery.
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Acknowledgement
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The authors are grateful for the support of the National Natural Science Foundation of China
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(Grant: 51473186, 51703090), the Natural Science Foundation of Guangdong, China (Grants:
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2015B090925002) and the Science and Technology Program of Guangzhou, China (Grant:
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201508010052, 201604010105), and the Fundamental Research Funds for the Central Universities
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(Grant: 161gpy17).
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ACCEPTED MANUSCRIPT References
266
[1] E. Glynos, L. Papoutsakis, W. Pan, E.P. Giannelis, A.D. Nega, E. Mygiakis, G. Sakellariou, S.H.
267
Anastasiadis, Nanostructured polymer particles as additives for high conductivity, high modulus solid
268
polymer electrolytes, Macromolecules 50 (2017) 4699-4706.
269
[2] Z.G. Xue, D. He, X.L. Xie, Poly(ethylene oxide)-based electrolytes for lithium-ion batteries, J.
270
Mater. Chem. A 3 (2015) 19218-19253.
271
[3] D.W. Shin, M.D. Guiver, Y.M. Lee, Hydrocarbon-based polymer electrolyte membranes:
272
importance of morphology on ion transport and membrane stability, Chem. Rev. 117(6) (2017)
273
4759-4805.
274
[4] P. Pal, A. Ghosh, Influence of TiO2 nano-particles on charge carrier transport and cell performance
275
of PMMA-LiClO4 based nano-composite electrolytes, Electrochim. Acta 260 (2018) 157-167.
276
[5] M. Muthuvinayagam, C. Gopinathan, Characterization of proton conducting polymer blend
277
electrolytes based on PVdF-PVA, Polymer 68 (2015) 122-130.
278
[6] B. Jinisha, K.M. Anilkumar, M. Manoj, V.S. Pradeep, S. Jayalekshmi, Development of a novel type
279
of solid polymer electrolyte for solid state lithium battery applications based on lithium enriched poly
280
(ethylene oxide) (PEO)/poly (vinyl pyrrolidone) (PVP) blend polymer, Electrochim. Acta 235 (2017)
281
210-222.
282
[7] N. Voigt, L. van Wullen, The mechanism of ionic transport in PAN-based solid polymer electrolytes,
283
Solid State Ionics 208 (2012) 8-16.
284
[8] S. Ramesh, A.K. Arof, Structural, thermal and electrochemical cell characteristics of poly(vinyl
285
chloride)-based polymer electrolytes, J. Power Sources 99 (2001) 41-47.
286
[9] D.E. Fenton, J.M. Parker and P.V. Wright, Complexes of alkali metal ions with poly(ethylene oxide).
287
Polymer 14 (1973) 589.
288
[10] X.J. Yan, B. Peng, B.W. Hu, Q. Chen, PEO-urea-LiTFSI ternary complex as solid polymer
289
electrolytes, Polymer 99 (2016) 44-48.
290
[11] W. Liu, S.W. Lee, D.C. Lin, F.F. Shi, S. Wang, A.D. Sendek, Y. Cui, Enhancing ionic conductivity
291
in composite polymer electrolytes with well-aligned ceramic nanowires, Nat. Energy 2 (2017).
292
[12] Y.J. Men, D. Kuzmicz, J.Y. Yuan, Poly(ionic liquid) colloidal particles, Curr. Opin. Colloid In 19(2)
293
(2014) 76-83.
AC C
EP
TE D
M AN U
SC
RI PT
265
17
ACCEPTED MANUSCRIPT [13] I. Osada, H. de Vries, B. Scrosati, S. Passerini, Ionic-liquid-based polymer electrolytes for battery
295
applications, Angew. Chem. Int. Edit. 55 (2016) 500-513.
296
[14] A. Eftelchari, T. Saito, Synthesis and properties of polymerized ionic liquids, Eur. Polym. J. 90
297
(2017) 245-272.
298
[15] S. Wang, Q.X. Shi, Y.S. Ye, Y. Xue, Y. Wang, H.Y. Peng, X.L. Xie, Y.W. Mai, Constructing
299
desirable ion-conducting channels within ionic liquid-based composite polymer electrolytes by using
300
polymeric ionic liquid-functionalized 2D mesoporous silica nanoplates, Nano Energy 33 (2017)
301
110-123.
302
[16] D. Kuzmicz, P. Coupillaud, Y. Men, J. Vignolle, G. Vendraminetto, M. Ambrogi, D. Taton, J.Y.
303
Yuan, Functional mesoporous poly(ionic liquid)-based copolymer monoliths: From synthesis to
304
catalysis and microporous carbon production, Polymer 55(16) (2014) 3423-3430.
305
[17] F. Fan, W.Y. Wang, A.P. Holt, H.B. Feng, D. Uhrig, X.Y. Lu, T. Hong, Y.Y. Wang, N.G. Kang, J.
306
Mays, A.P. Sokolov, Effect of molecular weight on the ion transport mechanism in polymerized ionic
307
liquids, Macromolecules 49 (2016) 4557-4570.
308
[18] X.E. Wang, H.J. Zhu, G.M.A. Girard, R. Yunis, D.R. MacFarlane, D. Mecerreyes, A.J.
309
Bhattacharyya, P.C. Howlett, M. Forsyth, Preparation and characterization of gel polymer electrolytes
310
using poly(ionic liquids) and high lithium salt concentration ionic liquids, J. Mater. Chem. A 5 (2017)
311
23844-23852.
312
[19] J.R. Nykaza, A.M. Savage, Q.W. Pan, S.J. Wang, F.L. Beyer, M.H. Tang, C.Y. Li, Y.A. Elabd,
313
Polymerized ionic liquid diblock copolymer as solid-state electrolyte and separator in lithium-ion
314
battery, Polymer 101 (2016) 311-318.
315
[20] B.Y. Huang, Y.D. Zhang, M.M. Que, Y.B. Xiao, Y.Q. Jiang, K. Yuan, Y.W. Chen, A facile in situ
316
approach to ion gel based polymer electrolytes for flexible lithium batteries, Rsc Adv. 7 (2017)
317
54391-54398.
318
[21] X.J. Chen, Q. Li, J. Zhao, L.H. Qiu, Y.G. Zhang, B.Q. Sun, F. Yan, Ionic liquid-tethered
319
nanoparticle/poly(ionic liquid) electrolytes for quasi-solid-state dye-sensitized solar cells, J. Power
320
Sources 207 (2012) 216-221.
321
[22] S. Ketabi, K. Lian, Effect of SiO2 on conductivity and structural properties of PEO-EMIHSO4
322
polymer electrolyte and enabled solid electrochemical capacitors, Electrochim. Acta 103 (2013)
323
174-178.
AC C
EP
TE D
M AN U
SC
RI PT
294
18
ACCEPTED MANUSCRIPT [23] M.R. Karim, K. Hatakeyama, T. Matsui, H. Takehira, T. Taniguchi, M. Koinuma, Y. Matsumoto, T.
325
Akutagawa, T. Nakamura, S. Noro, T. Yamada, H. Kitagawa, S. Hayami, Graphene oxide nanosheet
326
with high proton conductivity, J. Am. Chem. Soc. 135 (2013) 8097-8100.
327
[24] Y.J. Men, X.H. Li, M. Antonietti, J.Y. Yuan, Poly(tetrabutylphosphonium 4-styrenesulfonate): a
328
poly(ionic liquid) stabilizer for graphene being multi-responsive, Polym. Chem.-Uk 3(4) (2012)
329
871-873.
330
[25] Y.Y. Wang, C.Y. Li, T. Wu, X.X. Ye, Polymerized ionic liquid functionalized graphene oxide
331
nanosheets as a sensitive platform for bisphenol a sensing, Carbon 129 (2018) 21-28.
332
[26] Y.K. Yang, C.E. He, R.G. Peng, A. Baji, X.S. Du, Y.L. Huang, X.L. Xie, Y.W. Mai, Non-covalently
333
modified graphene sheets by imidazolium ionic liquids for multifunctional polymer nanocomposites, J.
334
Mater. Chem. 22 (2012) 5666-5675.
335
[27] Y.S. Ye, H. Wang, S.G. Bi, Y. Xue, Z.G. Xue, Y.G. Liao, X.P. Zhou, X.L. Xie, Y.W. Mai, Enhanced
336
ion transport in polymer-ionic liquid electrolytes containing ionic liquid-functionalized nanostructured
337
carbon materials, Carbon 86 (2015) 86-97.
338
[28] Y.S. Ye, H. Wang, S.G. Bi, Y. Xue, Z.G. Xue, X.P. Zhou, X.L. Xie, Y.W. Mai, High performance
339
composite polymer electrolytes using polymeric ionic liquid-functionalized graphene molecular
340
brushes, J. Mater. Chem. A 3 (2015) 18064-18073.
341
[29] B.C. Lin, T.Y. Feng, F.Q. Chu, S. Zhang, N.Y. Yuan, G. Qiao, J.N. Ding, Poly(ionic liquid)/ionic
342
liquid/graphene oxide composite quasi solid-state electrolytes for dye sensitized solar cells, Rsc Adv. 5
343
(2015) 57216-57222.
344
[30] M. Yang, N.F. Zhao, Y. Cui, W.W. Gao, Q. Zhao, C. Gao, H. Bai, T. Xie, Biomimetic architectured
345
graphene aerogel with exceptional strength and resilience, Acs Nano 11 (2017) 6817-6824.
346
[31] H. Lu, C.W. Li, B.Q. Zhang, X. Qiao, C.Y. Liu, Toward highly compressible graphene aerogels of
347
enhanced mechanical performance with polymer, Rsc Adv. 6 (2016) 43007-43015.
348
[32] L. Estevez, A. Kelarakis, Q.M. Gong, E.H. Da'as, E.P. Giannelis, Multifunctional
349
graphene/platinum/nafion hybrids via ice templating, J. Am. Chem. Soc. 133 (2011) 6122-6125.
350
[33] S. Kim, Y. Azuma, Y. Kuwahara, T. Ogata, S. Kurihara, Preparation of graphene oxide/polyvinyl
351
alcohol microcomposites and their thermal conducting properties, Mater. Lett. 139 (2015) 224-227.
352
[34] W.S. Hummers, R.E. Offeman, Preparation of graphitic oxide, J. Am. Chem. Soc. 80 (1958)
353
1339-1339.
AC C
EP
TE D
M AN U
SC
RI PT
324
19
ACCEPTED MANUSCRIPT 354
[35] G.M. Hou, M.Q. Zhang, Y.F. Huang, W.H. Ruan, A TiO2/PEO composite incorporated with in situ
355
synthesized hyper-branched poly(amine-ester) and its application as a polymer electrolyte, Rsc Adv. 6
356
(2016) 83406-83411.
357
[36]
358
Poly(3,4-ethylenedioxythiophene)-ionic liquid functionalized graphene/reduced graphene oxide
359
nanostructures: improved conduction and electrochromism, ACS Appl. Mater. Interfaces 3(4) (2011)
360
1115-1126.
361
[37] Z. Liu, J.Q. Liu, D. Li, P.S. Francis, N.W. Barnett, C.J. Barrow, W.R. Yang, Probing the tunable
362
surface chemistry of graphene oxide, Chem. Commun. 51 (2015) 10969-10972.
363
[38] Y.F. Huang, W.H. Ruan, D.L. Lin, M.Q. Zhang, Bridging redox species-coated graphene oxide
364
sheets to electrode for extending battery life using nanocomposite electrolyte, Acs Appl. Mater. Inter. 9
365
(2017) 909-918.
M.
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A.G.
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S.
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ACCEPTED MANUSCRIPT Highlights 1. High content of GO was well-loaded in the PIL composites through ice-templated process. 2. A so-called "PIL&GO nanosheets" with excellent ion transport was formed at high loading of GO.
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S0032-3861(18)30751-1
DOI:
10.1016/j.polymer.2018.08.039
Reference:
JPOL 20846
To appear in:
Polymer
Received Date: 1 April 2018 Revised Date:
11 August 2018
Accepted Date: 18 August 2018
Please cite this article as: Yang FJ, Huang YF, Zhang MQ, Ruan WH, Significant improvement of ionic conductivity of high-graphene oxide-loading ice-templated poly (ionic liquid) nanocomposite electrolytes, Polymer (2018), doi: 10.1016/j.polymer.2018.08.039. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Graphical Abstract In the ice-templated graphene oxide / poly (ionic liquid) nanocomposite electrolyte, a superhighway for ion conduction consisted of "PIL&GO nanosheets" could be built at a high
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loading of GO, which contributed to significant improvement of the ionic conductivity.
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Significant Improvement of Ionic Conductivity of High-Graphene Oxide-Loading Ice-Templated
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Poly (Ionic Liquid) Nanocomposite Electrolytes
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Fu Jie Yang, Yi Fu Huang*, Ming Qiu Zhang and Wen Hong Ruan*
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Key Laboratory for Polymeric Composite and Functional Materials of Ministry of Education, GD
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HPPC Lab, School of Chemistry, Sun Yat-Sen University, Guangzhou 510275, P. R. China
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*Corresponding authors:
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Dr. Yi Fu Huang and Dr. Wen Hong Ruan
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Materials Science Institute
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Sun Yat-Sen University
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Guangzhou 510275
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P. R. China
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E-mails: [email protected]; [email protected]
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Manuscript submitted to Polymer, 2 April, 2018
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ACCEPTED MANUSCRIPT 1
Significant Improvement of Ionic Conductivity of High-Graphene Oxide-Loading Ice-Templated
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Poly (Ionic Liquid) Nanocomposite Electrolytes
3 Fu Jie Yang, Yi Fu Huang*, Ming Qiu Zhang and Wen Hong Ruan*
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Key Laboratory for Polymeric Composite and Functional Materials of Ministry of Education, GD
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HPPC Lab, School of Chemistry, Sun Yat-Sen University, Guangzhou 510275, P. R. China
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Abstract: Poly (ionic liquid)s are an emerging family of promising polymer electrolytes. In this study,
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a nanocomposite electrolyte based on ice-templated high-graphene oxide-loading poly (ionic liquid)
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(GO / PIL) was prepared to significantly improve ion transport of PIL. X-ray diffraction patterns
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exhibited that GO was well-loaded in the as-prepared composites event at high content of 50 wt%. The
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Raman and UV-Vis spectra demonstrated the strong interaction between GO and PIL. Morphology
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observations showed that PIL could well contact with GO, forming so-called "PIL&GO nanosheets"
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that were connected in an ionic-conducting network, which facilitated the ion transport in the PIL, as
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revealed by conductive atomic force microscope investigation. As a result, with a superhighway for
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ions built, PIL-based composite electrolyte obtained a higher ionic conductivity of 3.1×10-4 S cm-1 at 50
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wt% GO, 775% of that of pure PIL electrolyte. Such ice-templated nanocomposite electrolytes possess
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potential applications for various electrochemical devices.
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Keywords: Nanocomposite electrolyte; Ionic conductivity; Poly (ionic liquid)s
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1 Introduction To adapt to the rapid development of flexible electrochemical devices, polymer electrolytes have
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been urgently developed, with superior advantages of high safety, excellent mechanical properties, and
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environment-friendly production. [1-3] A typical polymer electrolyte mainly consists of polar polymer
5
(e.g. PMMA [4], PVDF [5], PEO [6], PAN [7], PVC [8]) as solid-state solvent with incorporated
6
electrolyte salt for providing solvated ions. Since the first work of Wright et al [9], overcoming poor
7
ion-transport ability of the polymer electrolytes has still been a big challenge, which greatly hinders
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their practical applications. [10, 11] Poly (ionic liquid)s (PILs), an emerging family of high
9
performance polymer electrolyte, have attracted extensive attention. [12-14] These PILs can be
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prepared by polymerization of ionic liquid (IL) monomers and are anticipated to take advantages of
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both the mechanical durability of polymer and electrochemical properties of ionic liquid. [15, 16]
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However, the ionic conductivity of PILs is surprisingly far below that of IL unpolymerized. [17]
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Structurally, a PIL molecule, behaving as a chain-like ionic conductor, owns mobile cations or
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anions and the repeating counterionic species covalently bonded to the polymer backbone. Common
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methods to improve the ionic conductivity of PIL electrolyte are to decrease the glass transition
16
temperature (Tg) of polymer backbone, like plasticizing [18], copolymerizing [19], and interpenetrating
17
[20], to increase the PIL chain motion. Unlimited to the above methods, it has been reported that
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preparation of nanocomposite electrolyte by adding functional nanoparticles (e.g. TiO2 [21], SiO2 [22],
19
Al2O3 [18]) into the PILs also works because an ionic conductive network could be constructed by
20
nanofillers and ions could align and transport faster along the networks. The emerging nanocomposite
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electrolyte has provided a simple, facial strategy of tuning the properties of the polymer electrolyte
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without modifying the chemical structure of polymer chains. Among reported functional nanomaterials,
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ACCEPTED MANUSCRIPT graphene oxide (GO) is an ideal candidate owing to two-dimensional (2D) structure with the high ionic
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conductivity of ~10-2 S cm-1 , as well as the oxygen-containing groups on GO basal planes could
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well-dissociate the salts. [23] Inspired by the superior properties of GO nanosheets in last decades, the
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introduction of GO into PIL has gained great interests in recent years. [24, 25] Because of the π-ion
27
interaction between GO and IL, the GO can be well exfoliated. [26] By functionalizing the GO with IL
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(IL-FG), Mai et al showed modified GO was an excellent additive to improve the ionic conductivity of
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polymer electrolyte by ~150% with 0.6 wt% IL-FG. [27, 28] Lin et al have fabricated a GO / PIL
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composite electrolyte by direct solution-blending method and observed that the ionic conductivity
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could be improved by 141% when addition 2 wt% GO. But when GO content was over 2wt%, the
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steric effects of GO occurred and lead to the decrease of ionic conductivity. [29] It is obvious that the
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aggregation of GO nanosheets is detrimental to the ion transport. To increase the loading of GO with
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well-dispersion in the PILs becomes a main issue.
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Ice-templated assembly technology to construct 3D structure has provided a viable route for
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obtaining well-dispersed GO nanosheets in water-soluble polymers (e.g. PVA [30], PEO [31], Nation
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[32]), since GO can have a molecular-level dispersion in aqueous solution. Kim et al have obtained
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well-dispersed GO even at a high content up to 50 wt% in ice-templated GO / PVA. [33] This gives us
39
a hint that the high content GO / PILs nanocomposites electrolyte could be obtained by ice-templated
40
method. However, the studies on ice-templated structure based composite polymer electrolyte have not
41
been reported yet. Herein, a new nanocomposite electrolyte of GO / PIL is prepared by ice-templating
42
in this work. X-ray diffraction (XRD) analysis is used to study the exfoliation of GO nanosheets in the
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GO / PILs. The interaction between the GO and PIL is investigated by Raman spectra, UV-Vis spectra,
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and differential scanning calorimetry (DSC) techniques. Morphology of GO / PIL composites is
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electron microscopy (SEM). Subsequently, the ionic conductivities of GO / PIL electrolytes are
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measured using AC impedance spectra and the relevant mechanism is also revealed through
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tunneling-AFM (TUNA) analysis. It is hoped that the as-prepared high-GO-content PIL electrolytes
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could offer new insight into the development of the advanced nanocomposite polymer electrolytes.
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2 Experimental
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2.1.
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polymerization
poly
(1-propyl-3-vinyl-imidazolium)
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Firstly, a certain amount of N-vinylimidazole (1.88 g, AR, Aladdin agent) and chloropropane (1.48
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g, AR, Aladdin agent) were dissolved in 5 mL distilled methylbenzene under nitrogen atmosphere, and
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stirred at 50 oC for a period of 48 h. Then 0.04 mg AIBN dissolved into 5 mL methylbenzene was
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added, under vigorous stirring at 65oC for 48h. [21] After that, the resulting precipitate was filtrated,
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and repeatedly washed for several times with anhydrous ether, and further purified via the Soxhlet
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extraction.
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2.2. Preparation of ice-templated GO / poly (ionic liquid) (PIL) nanocomposite electrolytes
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Firstly, the as-synthesized PVImCl (20 mg) was entirely dissolved into 10 mL distilled water and
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stirred for at least 24hr at room to obtain a precursor aqueous solution. Then, 10 mL GO aqueous
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solution with a series of 0.2, 0.9, 2, 8 mg mL-1 was slowly added to the precursor aqueous solution
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dropwise under vigorous stirring for 24hr to obtain aqueous dispersions with various content of GO
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(see Fig. S1). The graphite oxide powder for preparing GO aqueous solution was prepared from flake
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graphite (99.8% purity, XF NANO) using modified Hummers method. [34] The aqueous dispersions
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were transferred into plastic petri dishes, frozen for 6 h at -80 oC, and freeze-dried by a LGJ-12
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ice-templated GO / PVIm composites were prepared. For comparisons, the pure PIL and pure GO were
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obtained from the corresponding aqueous solutions (1mg mL-1) by the ice-templating, respectively.
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Finally, to introduce the counter ions into PVIm to prepare poly (ionic liquid) (PIL), the GO / PVIm
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composite was immersed into I- / I3- solution using acetonitrile as solvent for more than 24 hr at room
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temperature, and then the solvents was removed in a vacuum oven at 50 oC for 12 hr, to obtain the
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resulting product of GO / PIL nanocomposite electrolytes.
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2.3. Characterizations
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Wide-angle XRD patterns were recorded using a Rigaku DMAX 2200 X-ray diffractometer with
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Cu-Kα radiation (40 kV, 40 mA, 10o min−1 from 5o to 60o). The zeta potential of the sample aqueous
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solution was measured using a Brooken Heaven PALS zeta potential analyzer. Raman scattering signals
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of the samples were recorded on a Raman spectroscope (Renishaw inVia). The excitation wavelength
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was 514 nm with a scanning range from 500 to 2500 cm−1. UV-Vis absorption spectroscopy was
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conducted on a Shimadzu UV-3600 spectrophotometer at room temperature. The measurement of glass
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transition temperatures (Tgs) of the samples was performed on a differential scanning calorimeter (DSC,
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TA/Q10).
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The morphology images of samples were obtained on Bruker atomic force microscope (AFM,
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Multimode 8). Before the test, the ice-templated sample was spin-coated on a cleavage surface of mica.
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Scanning electron microscopy (SEM) images of the samples were obtained using a Hitachi S-4800
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field emission electron microscope equipped with an energy dispersive X-ray fluorescence
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spectrometer for element analysis. Transmission electron microscopy (TEM) analysis was conducted
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using a FEI Tecnai G2 Spirit electron microscope.
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workstation (CH Instruments Inc.) in a symmetrical cell composed of the sample, and two transparent
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conductive Pt electrodes at room temperature, using the AC impedance method over the frequency
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range from 1 Hz to 106 Hz. The values of σ could be calculated as bellows: σ = L / RS · A. Where L, RS
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and A were the thickness between two electrodes, the internal resistance of the electrolyte, and the area
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of the electrode-electrolyte contact, respectively. [35] The tunneling-AFM (TUNA) measurements were
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also performed on the Bruker atomic force microscope. The as-prepared ice-templated samples were
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spin-coated on the conductive layer of an ITO glass substrate for tunneling-AFM analysis.
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3 Results and discussion
The X-ray diffraction (XRD) technology was firstly used to investigate the GO dispersion in
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ice-templated GO / PIL composites [31, 33]. As shown in Fig. 1, the XRD patterns of ice-templated PIL
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exhibited a broad peak at 22o, indicating that the PIL was amorphous. With the addition of GO, there
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were no characteristic diffraction signals of GO appeared even loading 50 wt% of GO. However, a
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characteristic peak of GO at 10.5o was appeared when the content of GO was up to 80 wt%, similar to
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the appearance of characteristic peak at 11.2o of ice-templated GO without PIL, which indicated that
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aggregation of GO nanosheets occurred. Compared to the published literature which showed the
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apparent aggregation of GO nanosheets over the content of 2 wt%, [29] this study demonstrated that
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the GO nanosheets could be well-loaded in the PIL composite even at the highest GO loading of 50
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wt% through ice-templated process.
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Ice-templated PIL
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20
30
40
50
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2θ ( C)
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Fig. 1. XRD patterns of the ice-templated PIL, GO and various GO / PIL composite materials with
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different loading of GO.
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Ice-templated GO / PIL Ice-templated GO
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800
1000
1200
1400
1600
1800
2000
-1
Raman shift (cm )
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Fig. 2. Investigation on the internal interactions of ice-templated 50wt% GO / PIL composites. (a)
115
UV-vis absorption spectra of ice-templated PIL and 50wt% GO / PIL; (b) Raman spectra of
116
ice-templated GO and 50wt% GO / PIL.
117
In Fig. 2, the interaction between GO and PIL in ice-templated composites was investigated by
118
using UV-Vis and Raman techniques. Fig. 2a depicted the UV-Vis spectra of solid PIL and GO / PIL. 8
ACCEPTED MANUSCRIPT The UV-Vis spectrum of PIL exhibited a characteristic absorption peak at 210 nm which was assigned
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to π–π* transitions. Interestingly, the π–π* transition of PIL appeared at 210 nm was red shifted to
121
higher wavelength of 223 nm in the spectra of GO / PIL, indicating that there was a strong interaction
122
between GO and PIL. Besides, a shoulder peak at 295 nm was attributed to n-π* transitions of GO.
123
Further, Raman spectroscopy (Fig. 2b) was also used to confirm the interactions involved between GO
124
and PIL. An eminent band at 1360 cm-1 corresponding to sp3 (D band) and a band at 1607 cm-1 for the
125
sp2 (G band) could be observed for pure GO. Compared with the peaks of GO, the two characteristic
126
peaks of GO / PIL were significantly blueshifted to 1351 cm-1 and 1590 cm-1, respectively, indicating
127
that the PIL changes the sp2-sp3 hybridization of GO nanosheets when the π-π stacking between
128
imidazole rings and carbon rings occurred, since the GO is good electron-donating π system and the
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imidazolium cation of PIL is electron-deficient π system. [36] Therefore, the surface of GO nanosheets
130
could be interacted with PIL via the π-π interaction which made them positively charged. It was further
131
confirmed that the positive zeta potential of GO / PIL aqueous dispersions (30.72 ± 0.5 mV) showed
132
higher than the negative zeta potential value of pure GO aqueous dispersions (-13.5 ± 1.5 mV).
133
Moreover, the value of ID / IG had a slight decrease from 0.81 for pure GO to 0.77 for GO / PIL, as the
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π-π stacking extended the π-conjugated structure of GO corresponding to G band intensity. [37]
135
Meanwhile, in case of the GO / PIL composite, the oxygen functional groups (such as carboxyl groups)
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on the GO could act as the charge compensating anions and were linked to the positively charged
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imidazole rings of PIL through electrostatic interaction. [26] It implied that the transport of counter
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ions within the PIL would be benefited.
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Fig.3 showed the morphologies of ice-templated GO / PIL composites. The appearance of obtained
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GO / PIL composites were a brown and sponge-like material, as exhibited in Fig. 3a (1). A typical SEM
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142
(3), respectively. It was shown that the ice-templated composite owned macroporous structure and the
143
uniform distribution of N element on it was experimentally mapped out. Compared to the SEM image
144
of pure GO (Fig. S2), the presence of N element in GO / PIL exhibited that GO nanosheets were
145
well-loaded with PIL. The TEM image of GO / PIL composite (Fig. 3b) revealed the easy formation of
146
layer structure in the composite, in which GO nanosheets and PIL were attached each other owing to
147
strong interaction between GO and PIL (see Fig.2). In addition, the atomic force microscopy (AFM)
148
image and height curve in Fig. 3c exhibited the flat configuration of GO / PIL with an average height of
149
~2.0 nm. The increased thickness of GO / PIL nanosheet (relative to GO of~0.9 nm, Fig. S3) mainly
150
ascribed to the absorbed PIL layer.
151 152
Fig. 3. (a) Structure and morphology of ice-templated 50wt% GO / PIL composite: (1) optical image of
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a piece of sponge-like 50wt% GO / PIL composite, (2) a representative SEM image of 50wt% GO /
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PIL, with (3) corresponding elemental mapping image of N element; (b) TEM image of ice-templated
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50wt% GO / PIL; (c) AFM image of ice-templated GO / PIL at 50wt% GO content on a mica substrate,
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with the corresponding height profile (bottom) along the white line showing thicknesses of the
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nanosheets.
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To further investigate the structure of GO / PIL nanosheets in ice-templated composites, DSC
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measurements of composites with different GO content were conducted (Fig. 4). The glass transition 10
ACCEPTED MANUSCRIPT temperature (Tg) of ice-templated PIL was 174 oC. Tg of PIL in the GO / PIL composites were gradually
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increased with the addition of GO and finally became infinite when GO content was up to 50 wt%. It
162
was demonstrated that chain mobility of PIL was hindered due to more PIL chains were fixed by GO
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when GO content was increased. The SEM images of corresponding samples manifested that the pore
164
structures of ice-templated composites became more ordered and pore walls became thinner with the
165
increase of GO content. Combining the DSC results with morphology observation, it inferred that PIL
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was evenly attached on the skeleton of GO sponge with the increase of GO loading. A so-called
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"PIL&GO nanosheets" could be formed in the ice-templated structure composites when addition of GO
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was up to a certain amount.
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Ice-templated PIL
o
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Ice-templated 5wt% GO / PIL
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Ice-templated 10wt% GO / PIL
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Ice-templated 50wt% GO / PIL
Ice-templated 80wt% GO / PIL
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120
140
160
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200
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o
Temperature ( C)
Fig. 4. DSC curves of ice-templated PIL and various GO / PIL composites combining with the SEM
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observation.
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-2.8
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a
-3.0
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-3.4 -3.6 -3.8 -4.0 -4.2 -4.4
10-5
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0
20
40
b
-3.2
log σ (S cm -1 )
-1 σ (S cm )
10
60
80
100
2.7
Ice-templated PIL Ice-templated 30wt% GO / PIL Ice-templated 50wt% GO / PIL Ice-templated 80wt% GO / PIL
2.8
2.9
3.0
3.1
3.2
3.3
1000/T (1/K)
GO content (wt%)
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Fig. 5. (a) The effect of GO loading on ionic conductivities (σs) of composite electrolytes based on
174
ice-templated GO / PIL; (b) Influence of the temperature on ionic conductivities of ice-templated GO / 11
ACCEPTED MANUSCRIPT 175
PIL composite electrolytes.
176
Table 1 The corresponding activation energy (Ea) of ice-templated GO / PIL composite electrolytes. Activation energy (Ea, kJ mol-1)
Ice-templated PIL
18.96
Ice-templated 30wt% GO / PIL
8.80
Ice-templated 50wt% GO / PIL
4.33
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Ice-templated 80wt% GO / PIL
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The ionic conductivities (σs) of ice-templated GO / PIL electrolytes with different GO loading
178
were also studied by EIS measurement (Fig. 5a). It was noticeable that the σ significantly increased
179
with the addition of GO and reached 3.1×10-4 S cm-1 at 50 wt% GO via ice-templated technique, which
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was approximately 775% increase compared to that of the pure PIL (4.0×10-5 S cm-1). However,
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without the ice-templated assistance, the highest ionic conductivity of GO / PIL just reached 7.1×10-5 S
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cm-1 for a GO content of 3wt% with the directly addition of GO into PIL electrolyte (see Fig. S5). The
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ion transport of PIL electrolyte was poor due to the electrostatic effect of positively-charged main
184
chains on anions in the system. In the GO / PIL systems, the positively-charged polymer chains of PIL
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strongly interacted with the GO (see Fig. 2 and Fig. 4) and led to the well-loaded GO via the
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ice-templated process. Finally, the polymer chains could be mostly fixed at the certain GO loading and
187
resulted "PIL&GO nanosheets" (see Fig. 3b and c). These "PIL&GO nanosheets" would promote the
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ion transport since the carboxyl groups of GO could efficiently weaken the electrostatic effect of PIL
189
chains on the anions. Therefore, the σ values dramatically increased with the loading of GO. In addition,
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the σ decreased at higher content of GO, due to the aggregation of GO nanosheets that was confirmed
191
by Fig. 1. Ionic conductivity-temperature plots of the ice-templated PIL and GO / PIL electrolytes with
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different GO loading were conducted (Fig. 5b) and corresponding activation energy (Ea) were
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calculated (Table 1). The ionic conductivity-temperature curves of the PIL and GO / PIL electrolytes
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ACCEPTED MANUSCRIPT follow an Arrhenius behavior. The Ea of PIL electrolyte is 18.96 kJ mol-1. The Ea of ice-templated GO /
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PIL composite electrolyte was significantly decreased with the addition of GO, and then reached to the
196
lowest Ea of 4.33 kJ mol-1 at the loading 50wt%GO. However, the excess GO resulted in the increase of
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the Ea of the GO / PIL composite electrolyte, which was well consistent with the influence of GO
198
content on the ionic conductivity. A lower Ea value for a polymer electrolyte indicates that ions in the
199
systems can move more easily along the ionic channels. Therefore, the ion transport of PIL electrolyte
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system can be significantly improved by loading certain high content of GO.
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1
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TUNA current (nA)
2.1
200
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0
100
200
0.9 -200
-100
0
100
200
202 203
Fig. 6. Investigation of ion transport of the ice-templated GO / PIL composite electrolytes using
204
conductive atomic force microscope (C-AFM). (a) and (c) are the height images of ice-templated PIL
205
electrolyte and 50wt% GO / PIL electrolyte, respectively; (b) and (d) are TUNA current image of
206
ice-templated PIL electrolyte and 50wt% GO / PIL electrolyte, respectively. 1 and 2 are current-voltage
207
(I-V) curves at different conductive regions (1: high conductivity; 2: low conductivity).
DC sample bais (mV)
DC sample bia (mV)
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To investigate the mechanism on the significantly increased ionic conductivity in GO / PIL
209
electrolytes, the conductive AFM (C-AFM) measurement was used to microscopically analyze the ion
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ACCEPTED MANUSCRIPT transport of GO / PIL electrolytes. It was found that the sample of PIL (Fig. 6a) exhibited relatively a
211
flat morphology. The sample of GO / PIL (Fig. 6c), by contrast, showed a distinct morphology which
212
consisted of several layers of "PIL&GO nanosheets" . It was reported that the ionic transport of
213
electrolytes was reflected by color regions in TUNA images, i.e., the fast-ion channels at the dark color
214
regions and the slow-ion channels at the light color regions. [38] According to these, the TUNA images
215
of PIL electrolyte (Fig. 6b) revealed that a relatively low ionic transport with small and disconnected
216
ionic channels existed in the samples. On the contrary, the TUNA images of the GO / PIL electrolyte
217
(Fig. 6d) demonstrated excellent ion conduction of "PIL&GO nanosheets" with large area of connected
218
ionic channels, indicating that ions in the system could move more easily along the "PIL&GO
219
nanosheets". In addition, the current-voltage (I-V) tests showed that TUNA current signals of
220
"PIL&GO nanosheets" (Fig. 6d (1)) were much higher than that of the region without GO (Fig. 6d (2)).
221
Moreover, based on the Ohm’s law (i.e., R = V / I), the conductivity of the sample was proportional to
222
the slope (k) of the relative I-V fitting curve. It could be seen that the k value of the I-V curve on the
223
region 1 was extremely higher than that of the region 2, which indicated that the ion transport could be
224
facilitated on the surface of "PIL&GO nanosheets". Thus, the addition of GO could significantly
225
increase the σ of PIL.
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Fig. 7. The schematic drawing of the effect of GO on significant improvement of ion transport of
228
ice-templated GO / PIL composite electrolytes.
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Based on the above investigations, the effect of GO on significant improvement of ion transport of
230
ice-templated GO / PIL composite electrolytes was revealed and summarized by the schematic drawing
231
of Fig. 7. In the PIL electrolyte, migration of anions could be hindered by electrostatic interaction since
232
the polymer chains of PIL consisted of positively-charged imidazole rings. Fig. 7a showed that the ion
233
transport path zigzagged and prolonged, so the ionic conductivity of PIL electrolyte had a very low
234
value (see Fig. 5). In the GO / PIL electrolytes, the GO could be well loaded into the PIL matrix via the
235
ice-templated process and formed the so-called "PIL&GO nanosheets" (see Fig. 1-4). These "PIL&GO
236
nanosheets" could weaken electrostatic effect of PIL main chains on the anions and accelerate the ion
237
transport in PIL, thus a relatively shorter ion transport path could be built in the GO / PIL systems (Fig.
238
7b) and higher ionic conductivity could be obtained (see Fig. 5). When the addition of GO reached a
239
certain amount, the chains of PIL were mostly fixed on the GO surface and the electrostatic effect on
240
anions had been significantly decreased, and "PIL&GO nanosheets" could be connected to form
241
ion-conducting networks. As a result, a superhighway for ion transport built in the GO / PIL electrolyte
242
(Fig. 7c), which was ascribed to the significant improvement on the σ of GO / PIL electrolyte (see Fig.
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5 and Fig. 6).
244
Conclusions In this study, GO / PIL nanocomposite electrolytes are prepared by ice-templating method. GO can
246
be dispersed and well-loaded in the PIL matrix even at the high content of 50 wt%. There are strong
247
interactions between GO and PIL, resulting in positively-charged polymer chains of PIL attached on
248
the GO surface and forming so-called "PIL&GO nanosheets" at high GO loading. The ionic
249
conductivity of GO / PIL electrolyte increases with the addition of GO because more polymer chains of
250
PIL can be fixed on the GO to decrease the electrostatic effect of PIL on the anions and to accelerate
251
the ion transport. A superhighway of ion conductive networks consisted of "PIL&GO nanosheets" can
252
be built at certain loading of GO (≥50 wt%). As a result, the ionic conductivity of GO / PIL electrolyte
253
can be significantly improved. 50 wt% GO / PIL electrolyte has the ionic conductivity of 3.1×10-4 S
254
cm-1, which is 7.75 times than that of the pure PIL electrolyte. This type of nanocomposite electrolyte
255
can meet the requirement of assembling electrochemical devices, such as dye-sensitized solar cells or
256
lithium ion battery.
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Acknowledgement
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The authors are grateful for the support of the National Natural Science Foundation of China
260
(Grant: 51473186, 51703090), the Natural Science Foundation of Guangdong, China (Grants:
261
2015B090925002) and the Science and Technology Program of Guangzhou, China (Grant:
262
201508010052, 201604010105), and the Fundamental Research Funds for the Central Universities
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(Grant: 161gpy17).
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ACCEPTED MANUSCRIPT References
266
[1] E. Glynos, L. Papoutsakis, W. Pan, E.P. Giannelis, A.D. Nega, E. Mygiakis, G. Sakellariou, S.H.
267
Anastasiadis, Nanostructured polymer particles as additives for high conductivity, high modulus solid
268
polymer electrolytes, Macromolecules 50 (2017) 4699-4706.
269
[2] Z.G. Xue, D. He, X.L. Xie, Poly(ethylene oxide)-based electrolytes for lithium-ion batteries, J.
270
Mater. Chem. A 3 (2015) 19218-19253.
271
[3] D.W. Shin, M.D. Guiver, Y.M. Lee, Hydrocarbon-based polymer electrolyte membranes:
272
importance of morphology on ion transport and membrane stability, Chem. Rev. 117(6) (2017)
273
4759-4805.
274
[4] P. Pal, A. Ghosh, Influence of TiO2 nano-particles on charge carrier transport and cell performance
275
of PMMA-LiClO4 based nano-composite electrolytes, Electrochim. Acta 260 (2018) 157-167.
276
[5] M. Muthuvinayagam, C. Gopinathan, Characterization of proton conducting polymer blend
277
electrolytes based on PVdF-PVA, Polymer 68 (2015) 122-130.
278
[6] B. Jinisha, K.M. Anilkumar, M. Manoj, V.S. Pradeep, S. Jayalekshmi, Development of a novel type
279
of solid polymer electrolyte for solid state lithium battery applications based on lithium enriched poly
280
(ethylene oxide) (PEO)/poly (vinyl pyrrolidone) (PVP) blend polymer, Electrochim. Acta 235 (2017)
281
210-222.
282
[7] N. Voigt, L. van Wullen, The mechanism of ionic transport in PAN-based solid polymer electrolytes,
283
Solid State Ionics 208 (2012) 8-16.
284
[8] S. Ramesh, A.K. Arof, Structural, thermal and electrochemical cell characteristics of poly(vinyl
285
chloride)-based polymer electrolytes, J. Power Sources 99 (2001) 41-47.
286
[9] D.E. Fenton, J.M. Parker and P.V. Wright, Complexes of alkali metal ions with poly(ethylene oxide).
287
Polymer 14 (1973) 589.
288
[10] X.J. Yan, B. Peng, B.W. Hu, Q. Chen, PEO-urea-LiTFSI ternary complex as solid polymer
289
electrolytes, Polymer 99 (2016) 44-48.
290
[11] W. Liu, S.W. Lee, D.C. Lin, F.F. Shi, S. Wang, A.D. Sendek, Y. Cui, Enhancing ionic conductivity
291
in composite polymer electrolytes with well-aligned ceramic nanowires, Nat. Energy 2 (2017).
292
[12] Y.J. Men, D. Kuzmicz, J.Y. Yuan, Poly(ionic liquid) colloidal particles, Curr. Opin. Colloid In 19(2)
293
(2014) 76-83.
AC C
EP
TE D
M AN U
SC
RI PT
265
17
ACCEPTED MANUSCRIPT [13] I. Osada, H. de Vries, B. Scrosati, S. Passerini, Ionic-liquid-based polymer electrolytes for battery
295
applications, Angew. Chem. Int. Edit. 55 (2016) 500-513.
296
[14] A. Eftelchari, T. Saito, Synthesis and properties of polymerized ionic liquids, Eur. Polym. J. 90
297
(2017) 245-272.
298
[15] S. Wang, Q.X. Shi, Y.S. Ye, Y. Xue, Y. Wang, H.Y. Peng, X.L. Xie, Y.W. Mai, Constructing
299
desirable ion-conducting channels within ionic liquid-based composite polymer electrolytes by using
300
polymeric ionic liquid-functionalized 2D mesoporous silica nanoplates, Nano Energy 33 (2017)
301
110-123.
302
[16] D. Kuzmicz, P. Coupillaud, Y. Men, J. Vignolle, G. Vendraminetto, M. Ambrogi, D. Taton, J.Y.
303
Yuan, Functional mesoporous poly(ionic liquid)-based copolymer monoliths: From synthesis to
304
catalysis and microporous carbon production, Polymer 55(16) (2014) 3423-3430.
305
[17] F. Fan, W.Y. Wang, A.P. Holt, H.B. Feng, D. Uhrig, X.Y. Lu, T. Hong, Y.Y. Wang, N.G. Kang, J.
306
Mays, A.P. Sokolov, Effect of molecular weight on the ion transport mechanism in polymerized ionic
307
liquids, Macromolecules 49 (2016) 4557-4570.
308
[18] X.E. Wang, H.J. Zhu, G.M.A. Girard, R. Yunis, D.R. MacFarlane, D. Mecerreyes, A.J.
309
Bhattacharyya, P.C. Howlett, M. Forsyth, Preparation and characterization of gel polymer electrolytes
310
using poly(ionic liquids) and high lithium salt concentration ionic liquids, J. Mater. Chem. A 5 (2017)
311
23844-23852.
312
[19] J.R. Nykaza, A.M. Savage, Q.W. Pan, S.J. Wang, F.L. Beyer, M.H. Tang, C.Y. Li, Y.A. Elabd,
313
Polymerized ionic liquid diblock copolymer as solid-state electrolyte and separator in lithium-ion
314
battery, Polymer 101 (2016) 311-318.
315
[20] B.Y. Huang, Y.D. Zhang, M.M. Que, Y.B. Xiao, Y.Q. Jiang, K. Yuan, Y.W. Chen, A facile in situ
316
approach to ion gel based polymer electrolytes for flexible lithium batteries, Rsc Adv. 7 (2017)
317
54391-54398.
318
[21] X.J. Chen, Q. Li, J. Zhao, L.H. Qiu, Y.G. Zhang, B.Q. Sun, F. Yan, Ionic liquid-tethered
319
nanoparticle/poly(ionic liquid) electrolytes for quasi-solid-state dye-sensitized solar cells, J. Power
320
Sources 207 (2012) 216-221.
321
[22] S. Ketabi, K. Lian, Effect of SiO2 on conductivity and structural properties of PEO-EMIHSO4
322
polymer electrolyte and enabled solid electrochemical capacitors, Electrochim. Acta 103 (2013)
323
174-178.
AC C
EP
TE D
M AN U
SC
RI PT
294
18
ACCEPTED MANUSCRIPT [23] M.R. Karim, K. Hatakeyama, T. Matsui, H. Takehira, T. Taniguchi, M. Koinuma, Y. Matsumoto, T.
325
Akutagawa, T. Nakamura, S. Noro, T. Yamada, H. Kitagawa, S. Hayami, Graphene oxide nanosheet
326
with high proton conductivity, J. Am. Chem. Soc. 135 (2013) 8097-8100.
327
[24] Y.J. Men, X.H. Li, M. Antonietti, J.Y. Yuan, Poly(tetrabutylphosphonium 4-styrenesulfonate): a
328
poly(ionic liquid) stabilizer for graphene being multi-responsive, Polym. Chem.-Uk 3(4) (2012)
329
871-873.
330
[25] Y.Y. Wang, C.Y. Li, T. Wu, X.X. Ye, Polymerized ionic liquid functionalized graphene oxide
331
nanosheets as a sensitive platform for bisphenol a sensing, Carbon 129 (2018) 21-28.
332
[26] Y.K. Yang, C.E. He, R.G. Peng, A. Baji, X.S. Du, Y.L. Huang, X.L. Xie, Y.W. Mai, Non-covalently
333
modified graphene sheets by imidazolium ionic liquids for multifunctional polymer nanocomposites, J.
334
Mater. Chem. 22 (2012) 5666-5675.
335
[27] Y.S. Ye, H. Wang, S.G. Bi, Y. Xue, Z.G. Xue, Y.G. Liao, X.P. Zhou, X.L. Xie, Y.W. Mai, Enhanced
336
ion transport in polymer-ionic liquid electrolytes containing ionic liquid-functionalized nanostructured
337
carbon materials, Carbon 86 (2015) 86-97.
338
[28] Y.S. Ye, H. Wang, S.G. Bi, Y. Xue, Z.G. Xue, X.P. Zhou, X.L. Xie, Y.W. Mai, High performance
339
composite polymer electrolytes using polymeric ionic liquid-functionalized graphene molecular
340
brushes, J. Mater. Chem. A 3 (2015) 18064-18073.
341
[29] B.C. Lin, T.Y. Feng, F.Q. Chu, S. Zhang, N.Y. Yuan, G. Qiao, J.N. Ding, Poly(ionic liquid)/ionic
342
liquid/graphene oxide composite quasi solid-state electrolytes for dye sensitized solar cells, Rsc Adv. 5
343
(2015) 57216-57222.
344
[30] M. Yang, N.F. Zhao, Y. Cui, W.W. Gao, Q. Zhao, C. Gao, H. Bai, T. Xie, Biomimetic architectured
345
graphene aerogel with exceptional strength and resilience, Acs Nano 11 (2017) 6817-6824.
346
[31] H. Lu, C.W. Li, B.Q. Zhang, X. Qiao, C.Y. Liu, Toward highly compressible graphene aerogels of
347
enhanced mechanical performance with polymer, Rsc Adv. 6 (2016) 43007-43015.
348
[32] L. Estevez, A. Kelarakis, Q.M. Gong, E.H. Da'as, E.P. Giannelis, Multifunctional
349
graphene/platinum/nafion hybrids via ice templating, J. Am. Chem. Soc. 133 (2011) 6122-6125.
350
[33] S. Kim, Y. Azuma, Y. Kuwahara, T. Ogata, S. Kurihara, Preparation of graphene oxide/polyvinyl
351
alcohol microcomposites and their thermal conducting properties, Mater. Lett. 139 (2015) 224-227.
352
[34] W.S. Hummers, R.E. Offeman, Preparation of graphitic oxide, J. Am. Chem. Soc. 80 (1958)
353
1339-1339.
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[35] G.M. Hou, M.Q. Zhang, Y.F. Huang, W.H. Ruan, A TiO2/PEO composite incorporated with in situ
355
synthesized hyper-branched poly(amine-ester) and its application as a polymer electrolyte, Rsc Adv. 6
356
(2016) 83406-83411.
357
[36]
358
Poly(3,4-ethylenedioxythiophene)-ionic liquid functionalized graphene/reduced graphene oxide
359
nanostructures: improved conduction and electrochromism, ACS Appl. Mater. Interfaces 3(4) (2011)
360
1115-1126.
361
[37] Z. Liu, J.Q. Liu, D. Li, P.S. Francis, N.W. Barnett, C.J. Barrow, W.R. Yang, Probing the tunable
362
surface chemistry of graphene oxide, Chem. Commun. 51 (2015) 10969-10972.
363
[38] Y.F. Huang, W.H. Ruan, D.L. Lin, M.Q. Zhang, Bridging redox species-coated graphene oxide
364
sheets to electrode for extending battery life using nanocomposite electrolyte, Acs Appl. Mater. Inter. 9
365
(2017) 909-918.
M.
Deepa,
A.G.
Joshi,
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Bhandari,
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Srivastava,
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ACCEPTED MANUSCRIPT Highlights 1. High content of GO was well-loaded in the PIL composites through ice-templated process. 2. A so-called "PIL&GO nanosheets" with excellent ion transport was formed at high loading of GO.
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3. The ionic conductivity of PIL electrolyte was significantly improved by 775% with loading of 50
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wt% GO.