Polyselenophene Nanohybrid Materials

Article pubs.acs.org/cm

In Situ Synthesis of Graphene/Polyselenophene Nanohybrid Materials as Highly Flexible Energy Storage Electrodes Jin Wook Park, Seon Joo Park, Oh Seok Kwon, Choonghyeon Lee, and Jyongsik Jang* J. Jang, J. W. Park, S. J. Park, and C. Lee Department of Chemical and Biological Engineering, Seoul National University, ENG 445 Seoul 151-742, Korea

O. S. Kwon Department of Chemical and Environmental Engineering School of Engineering and Applied Science, Yale University, New Haven, Connecticut 06520, United States S Supporting Information *

ABSTRACT: A new class of graphene−polyselenophene (PSe) hybrid nanocomposite was successfully synthesized using an in situ synthetic method. The synthesized graphene−PSe nanocomposite exhibited unique properties including a large voltage window, high conductivity, and good mechanical properties. The graphene−PSe nanohybrid reduced the dynamic resistance of electrolyte ions and enabled high charge−discharge rates, thereby enabling high-performance supercapacitance. The results were attributed to synergetic effects between graphene and conducting polymers (CPs), which enhanced charge transport, surface area, and hybrid supercapacitance by combining the properties of electrolytic double-layer capacitors (EDLCs) with those of psedocapacitors. Additionally, a flexible supercapacitor based on the graphene−PSe nanohybrid was successfully demonstrated. To fabricate binder-free supercapacitors, chemical vapor deposition (CVD) and vapor deposition polymerization (VDP) methods were employed. The fabricated all-solid-state supercapacitor exhibited outstanding mechanical and electrochemical performance, even after several bending motions. The novel graphene−PSe nanocomposite material is promising for new energy storage and conversion applications.

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INTRODUCTION

the development of redox-active materials with high specific capacitance and sufficient stability for use in pseudocapacitors. CPs are widely recognized as promising electrode materials due to their high specific capacitance and rapid redox-based charge−discharge behavior.7,8 For example, polypyrrole (PPy), polyaniline (PANI), and polythiophene (PT) have been actively studied and developed for use in batteries and supercapacitors. Among of those materials, PS is the most investigated materials owing to their facile electrochemical synthesis and good chemical stability.9−11 However, few examples of its close analogue, polyselenophene (PSe), have been reported. PSe is expected to exhibit various unique properties compared with other conducting polymers, particularly PT.12 For example, the band gap of PSe is lower than that of PT, thereby enabling greater interchain charge transfer in PSe via intermolecular Se−Se contacts. PSe also exhibits greater polarizability and enhanced planarity, and it accommodates

The development of portable, flexible, and lightweight energystorage devices has attracted attention in a wide range of emerging applications, such as wearable electronics, electronic newspapers, and other devices.1−3 A supercapacitor, also known as an electrochemical capacitor, is one of the most promising energy-storage devices due to its high power, high energy density, and long cycle life.4−6 Supercapacitors are generally divided into two main classes: electrochemical double-layer capacitors (EDLCs) and pseudocapacitors. EDLCs are based on carbon materials and function via a nonfaradaic process. Pseudocapacitors, in which conducting polymers (CPs) and transition metal oxides are commonly used, store charge faradaically. Charge transfer in pseudocapacitors can be induced by rapid redox reactions between the surface and the bulk of the electrodes. In general, EDLCs provide lower energy densities than redox supercapacitors because charge is stored only on the surface area of an active EDLC electrode. In contrast, pseudocapacitors use the entire mass of an electrode. For this reason, recent supercapacitor research has focused on © 2014 American Chemical Society

Received: February 17, 2014 Revised: March 14, 2014 Published: March 18, 2014 2354

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Figure 1. (a) Schematic illustration of the preparation of graphene−PSe nanocomposites. FE-SEM images of (b) rGO and (c) rGO/PSe nanocomposites. (Insets are the TEM images of rGO and rGO/PSe nanohybrid materials.) (d) Typical STEM image of graphene−PSe nanohybrids. Corresponding elemental mapping images of (e) C and (f) Se.

enable the practical development of high-performance supercapacitors. In this work, for the first time, we synthesized a new class of graphene−PSe nanocomposites for use as electrochemical energy storage materials. The synthesis of the hybrid electrode involved two main steps, as shown in Figure 1a. First, in situ polymerization of selenophene was carried out by mixing graphene oxide (GO) and selenophene monomer in water/ ethanol (50:1) and stirring vigorously in the presence of oxidant (FeCl3 5 wt % in deionized water). Next, reduction of GO via hydrazine treatment afforded reduced GO (rGO)/PSe nanocomposites. (See the Experimental Section for a detailed description of the synthetic method.) After reduction of GO/ PSe nanocomposites, the rGO/PSe nanocomposites maintained their original graphene sheet morphology, indicating that the PSe was highly coupled on the graphene sheets. The synthesized rGO/PSe nanohybrid material exhibited a broad potential window, a large surface area, and high conductivity based on the synergetic influence of graphene−PSe nanocomposites. The graphene−PSe nanohybrid supercapacitor electrodes improved the specific capacitance, energy, and power densities compared with individual PSe or rGO layers. To evaluate the practical application of the nanocomposite in a flexible energy-storage system, all solid-state supercapacitors were fabricated based on rGO/PSe nanohybrids using polyvinyl alcohol−sulfuric acid (PVA−H2SO4) hydrogel electrolyte. (See the Experimental Section for a detailed description of the fabrication of solid-state supercapacitors.) To fabricate binderfree supercapacitors, chemical vapor deposition (CVD) and

greater charge on doping due to the larger size of the Se atom compared with the S atom of PT. PSe materials have reportedly been recently used in various organic electronic devices such as solar cells, transistors, lasers, and photothermal therapy applications.13−16 However, reported synthetic methods require multiple steps and tedious conditions, limiting the practical use of PSe in energy devices. Therefore, the development of a facile and simple synthetic method is desired to enable implementation of PSe in energy devices. Graphene, which consists of a single layer or a few layers of graphitic carbon, is a potential candidate for EDLC electrodes due to its large theoretical surface area, good electronic conductivity, mechanical properties, and high electrochemical stability.17−19 Recently, nanocomposites of graphene with CPs have been investigated for their synergetic effects, including fast electron/ion transport in electrodes, enhanced surface area, and electrochemical stability, which lead to improved supercapacitance.20−24 However, the low energy and power densities of supercapacitors limit their practical application. Recently, widening the cell voltage (V) method by using tandem cells or organic electrolytes has been reported to enhance the device energy and power density.25−27 However, fabrication of tandem cells induces resistance between the cells, leading to lower electrical conductivity. Furthermore, organic electrolytes are undesirable in practical applications due to their poor conductivity and lack of environmental friendliness. Thus, design of novel hybrid materials with broad voltage window potential and rapid charge−discharge behavior is needed to 2355

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Figure 2. (a) Raman spectroscopy, (b) XRD patterns, and (c) ATR-FTIR spectra of GO, rGO, PSe, and rGO/PSe nanocomposites.

exhibited CC backbone stretching at ∼1609 cm−1 and a ring stretching mode at 1372 cm−1. The Raman spectrum of the rGO/PSe nanocomposites exhibited increased band intensity around 1357 cm−1, indicating an interaction between PSe and the rGO sheets. X-ray diffraction (XRD) patterns and attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) were also conducted for structural analysis of graphene−PSe nanocomposites, as shown in Figure 2b and c. The XRD pattern of GO exhibited a very sharp peak at 10.1° (d = 8.75 Å), indicating that the original graphite was successfully oxidized to form GO. A broad peak appeared at 24.8° (d = 3.59 Å), suggesting that rGO formation was achieved by reduction of GO using hydrazine. The rGO/PSe nanohybrids exhibited a broad peak at around 25.0° (d = 3.56), which corresponded to the PSe intermolecular distance in the rGO/ PSe nanocomposites. This result is deduced that the PSe was successfully coated on the rGO layer via strong intermolecular π−π interactions. ATR-FTIR spectra of the GO displayed characteristic absorption bands for oxide groups, including a CO stretching peak at 1733 cm−1, vibration and deformation peaks associated with O−H groups at 3391 cm−1 and 1417 cm−1, respectively, and a C−O (alkoyl) stretching peak at 1037 cm−1 as shown in Figure 2c. Most of the peaks related to oxygen-containing functional groups were not evident in the FTIR spectra of rGO, indicating that the reduction of GO was successful. The spectra of the rGO/PSe nanohybrids exhibited characteristic bands for a selenophene ring and graphene fundamental vibrations, which occurred at 1624 cm−1 (CC stretching), 1557 cm−1 (C−C stretching), 1196 cm−1 (C−Se stretching), and 1012 cm−1 (C− H deformation). The rGO/PSe nanocomposite peaks were shifted compared with those of isolated PSe and rGO due to interactions between the rGO layers and PSe. Overall, the spectra indicated that the PSe materials were successfully coated onto the surface of the rGO layer. The surface of rGO/PSe nanohybrids was further characterized by X-ray photoelectron spectroscopy (XPS), as shown

vapor deposition polymerization (VDP) methods were employed. This fabrication method is facile and cost-efficient technology. The fabricated solid-state supercapacitors were lightweight and exhibited high electrical performance. Furthermore, the solid-state rGO/PSe nanohybrid electrodes could be folded and bent without introducing any defects in the device, maintaining the structural integrity even after several bending cycles. In this study, we developed, for the first time, a novel graphene−PSe nanocomposite material with high supercapacitance and remarkable mechanical properties.

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RESULTS AND DISCUSSION The morphology of the rGO/PSe nanohybrid material was characterized using field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The FE-SEM images of rGO and rGO/PSe nanocomposites are shown in Figure 1b and c. We observed a rougher surface on the rGO/PSe nanocomposits than on the rGO sheets, indicating that the PSe was coated onto the rGO layer. The morphology of the as-synthesized materials was confirmed using TEM. (See the insets of Figure 1b and c.) The PSe was highly coupled to the graphene sheets, enabling the original morphology of the graphene sheets to be maintained. Scanning transmission electron microscopy (STEM) was conducted to obtain additional structural information about the graphene− PSe nanohybrid material (see Figure 1d). Elemental analysis (Figure 1e, f) indicated uniform distribution of C and Se. (The greater intensity of the elemental C signal compared with that of Se was attributed to the fact that the TEM sample grid was C based.) For greater insight into the structure of the rGO/PSe nanocomposites, Raman spectroscopy was carried out, as shown in Figure 2a. The Raman spectrum of GO exhibited D peaks at 1364 cm−1, and G peaks at 1610 cm−1. On the other hand, the Raman spectrum of the rGO showed two prominent bands, at 1356 cm−1 and 1602 cm−1, corresponding to the D and G bands, respectively. These results clearly indicated perfect reduction of GO to rGO. The Raman spectrum of PSe 2356

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Figure 3. CVs of (a) rGO/PSe nanocomposites at different scan rates and (b) rGO, PSe, and rGO/PSe nanocomposites at 50 mV s−1 in 1.0 M H2SO4 solution. (c) Galvanostatic charge−discharge curves of rGO, PSe, and rGO/PSe nanocomposites at 10 A g−1. (d) Specific capacitance data of rGO, PSe, and rGO/PSe nanocomposites at various current densities.

in Supporting Information Figure S1. The XPS survey scan spectrum exhibited the principal C 1s, O 1s, Se 3d, and Cl 2p core levels, without any evidence of impurities. The O 1s peak was attributed to physisorbed oxygen on the rGo/PSe nanonetworks, even after reduction GO. Cl atoms doped the rGO/PSe nanocomposites during oxidation polymerization of the selenophene monomer, as confirmed by the Cl 2p XPS profiles.28 Therefore, the rGO/PSe nanohybrid material was successfully synthesized and characterized. Electrochemical properties were studied using cyclic voltametry (CV) in a three-electrode cell. Figure 3a presents the CV curves of the rGO/PSe nanocomposites at various scan rates (50, 100, 150, 200, 250 mV s−1) for the potential voltage window of −0.8 to 1.1 V vs Ag/AgCl in 1 M H2SO4. The CV curves exhibited similar quasi-rectangular shapes with slight redox peaks, indicating combined contributions from faradaic pseudocapacitance and double-layer capacitance. For comparison under the same experimental conditions, the CV curves of individual components were obtained at a fixed scan rate of 50 mV s−1, as illustrated in Figure 3b. The CV curve of the PSeonly electrode exhibited a typically conductive polymer shape and a potential window similar to that of rGO/PSe nanocomposites. However, the CV curve of pure rGO sheets was shaped differently, with a relatively small area attributable to the agglomeration of rGO layers.29 (See Figure 1b.) In general, the area of the CV curve is proportional to the specific capacitance of the electrode material. To calculate the specific capacitance (SC), galvanostatic charge−discharge curves for rGO, PSe, and rGO/PSe nanocomposites were obtained. For direct performance comparison between the individual samples, a fixed current density (10 A g−1) was used, as illustrated in Figure 3c. The SC of the graphene-nanonetwork supercapacitor electrodes was calculated from the galvanostatic curves according to the following equation:

SC =

I Δt mΔV

(1)

where I = discharge current, t = discharge time, m = total mass of electrode active material, and V = voltage drop upon discharge. All curves suggested good reversibility during the charge− discharge process at the corresponding potential range. However, a short discharge duration was observed for the PSe nanomaterial due to its poor conductivity. On the other hand, the slopes of the discharge curves of rGO/PSe nanohybrids were nonlinear due to initial short-duration discharging associated with double layer capacitance followed by mixed discharging from both double-layer and faradaic capacitances.30,31 The discharge time was greater than that of individual components, indicating that the graphene−PSe nanohybrid electrode exhibited enhanced capacitance. The SC values were also determined at various current densities. (See Figure 3d and the detailed galvanostatic charge−discharge curves for each material in Supporting Information Figure S2.) The SC results were consistent with the CV curves. Notably, at higher current densities or faster charging, lower SCs were obtained, indicating that the energy-storage mechanism was based on electrochemical diffusion. At an applied current density of 0.1 A g−1, the SC of rGO/PSe nanocomposite was approximately 305.4 F g−1, which was much higher than that of pure rGO (165.8 F g−1) and PSe (72.2 F g−1). To further evaluate the increased electrochemical properties, we conducted Brunauer−Emmett−Teller (BET) surface area measurements. (See Supporting Information Figure S3.) Nitrogen isotherm adsorption measurement on the as-prepared PSe, rGO, and rGO/PSe nanocomposites revealed that graphene− PSe nanohybrids had a BET surface area of 95.06 m2 g−1, which was higher than that observed for pure PSe (19.57 m2 g−1) and rGO (63.5 m2 g−1). These results suggested that the rGO sheet served as a conductive channel, leading to enhanced conductivity (as shown in Figure 3b), enlarged surface area, 2357

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Figure 4. (a) Nyquist and (b) Ragone plots of rGO, PSe, and rGO/PSE nanocomposites.

Figure 5. (a) Photograph of the all solid-state supercapacitor. (The inset is a schematic image of the solid-state supercapacitor.) (b) CV curves at 200 mV s−1 with various bending angles and (c) galvanostatic charge−discharge curves at a current density of 4 A g−1 before (black) and after 100 bending cycles (red).

evaluate supercapacitor performance, we calculated the specific energy density (E) and power density (P), which are the two critical factors for practical application of electrochemical supercapacitors. The values of E and P were obtained based on the following equations:

and improved charge−discharge storage performance in graphene−PSe nanocomposite electrodes, which exhibited double-layer capacitance. Electrochemical impedance spectroscopy (EIS) measurements were carried out to further evaluate the electrochemical properties of the electrode material from 10 kHz to 10 mHz (see Figure 4a.) All Nyquist plots exhibited a semicircle over the high-frequency range and a linear section in the lowfrequency range. The size of the semicircle was determined by the charge transfer resistance (Rct) at the interface between the electrode material and the electrolyte. The diameter of the semicircle in the Nyquist plot for graphene−PSe nanocomposites was smaller than those for the individual components, indicating that rGO/PSe nanohybrids facilitated enhanced interfacial charge transfer in the electrode. The graphene−PSe nanohybrids with an rGO conductive layer induced facile ion and charge transfer. The Rct of pure rGO, pure PSe, and rGO/PSe nanocomposites obtained from the Nyquist plots were 16, 23, and 2 Ω, respectively. The Rct of the rGO/PSe nanohybrids was smaller than that of rGO and PSe, highlighting the beneficial influence of graphene−PSe nanocomposites in supercapacitor electrode applications. To further

E=

1 CΔV 2 2

(2)

P=

E Δt

(3)

where C is the specific capacitance, ΔV is the potential voltage range, and Δt is the discharge time. The E and P results are presented as Ragone plots in Figure 4b. Interestingly, the values of P and E for PSe were higher than those of an rGO capacitor, even though the rGO has a lower SC. Theoretically, the wide potential voltage range of PSe facilitates better supercapacitor performance. However, PSe electrodes exhibit poor conductivity, leading to low electrical performance, as discussed above. The rGO/PSe nanocomposites can deliver high power output in the 95−9500 W kg−1 range with minimal sacrifice of energy density (from 144.4 to 2358

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153.1 Wh kg−1). These results suggested greatly enhanced supercapacitance compared with that of individual components. We concluded that the rGO/PSe nanocomposites are promising for applications in the field of electrochemical energy storage. Next, the rGO/PSe nanocomposites were used to fabricate a flexible energy-storage device. Specifically, all solid-state supercapacitors based on rGO/PSe nanocomposites with two-electrode were symmetrically fabricated by sandwiching H2SO4−PVA-based hydrogel electrolyte between two pieces of rGO/PSe nanohybrid electrodes, as shown in Figure 5a. CVD and VDP were used to fabricate binder-free thin films of graphene−PSe nanohybrid materials. (A detailed description of the fabrication method is contained in the Experimental Section.) The thickness of the flexible film was 93 μm. (The thickness of the uncoated stainless steel substrate was 80 μm.) The as-prepared solid-state supercapacitors exhibited excellent flexibility and good mechanical properties. The electrochemical performance of the as-fabricated supercapacitor electrode was maintained under various bending angles up to 180°, indicating remarkable mechanical properties for the device (see Figure 5b.) The solid-state supercapacitors displayed CV curves with rectangular shapes that indicated ideal capacitance and fast charge−discharge behavior. The galvanostatic charge−discharge curves of the solid-state electrode were also obtained, as shown in Figure 5c. The discharge curves of the device were symmetrical compared with its charge curve counterparts, thereby indicating good capacitance and fast charge−discharge behavior. More importantly, the superior electrical performance of the solid-state device was maintained after 100 bending cycles. The calculated SC was 292.5 F g−1 prior to bending and 287.8 F g−1 after bending at a current density of 4 A g−1. The observed loss of electrical performance was only 1.6%.

Table 1. Comparison of the Electro-chemical Performance of Polythiophene Hybrid Materialsa electrode materials

specific capacitance (SC) (F/g)

reference

PT PT NP/OA dopant PT/surfactant composites MWCNT/PT Graphene-PT NCs rGO/PSe NCs

110 155 115 116 154 305.4

1 2 3 4 5 this work

a

PT = polythiophene, NP = nanoparticle, OA = organic acid, MWCNT = multiwalled carbon nanotube, NC = nanocomposite, rGO = reduced graphene oxide, PSe = polyselenophene.

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EXPERIMENTAL SECTION

Materials. Selenophene, copper(II) chloride, iron(III) chloride, and methyl orange (MO) were purchased from Aldrich and used as received without further purification. Synthesis of rGO/PSe Nanocomposite. GO was obtained from graphite powder using a modification of the Hummers and Offeman method.32 GO (4 mg/mL) was dispersed in 5 mL aqueous solution and then mixed with selenophene monomer (4 mg, 0.06 mmol) dissolved in EtOH (0.1 mL). The solution was sonicated for 1 min, and then iron chloride 1 mL (5 wt % in deionized water) was added to the mixture while stirring. After polymerization for 24 h, 2 mL of 35 wt % hydrazine solution was added dropwise to the GO/PSe nanocomposites over 1 h at 95 °C to reduce GO to rGO. The final product, rGO/PSe nanocomposite (5.3 mg, 66%), was obtained after filtration, purification with excess water, and drying in a vacuum oven at 25 °C. Fabrication of rGO/PSe Nanocomposite Electrodes. CV and galvanostatic charge/discharge experiments were performed first in a three-electrode cell containing 1 M H2SO4 solution using a Pt auxiliary electrode and a Ag/AgCl reference electrode. Mixtures of the hybrid nanostructure (4 mg, 97.5 wt %) and PVDF (0.1 mg, 2.5 wt %) dissolved in N-methyl pyrrolidone (0.1 mL) were coated onto stainless steel (area: 1 × 1 cm2) and used to measure the capacitance after vacuum drying for 12 h at 25 °C. Preparation of the rGO/PSe Solid-State Supercapacitor. GO was dispersed in aqueous solution (4 mg/mL) and then mixed with FeCl3 oxidant 1 mL (5 wt % in deionized water). Then, a piece of stainless steel substrate (area: 2 × 10 cm2) was immersed in the solution. Subsequently, the soaked stainless steel substrate was placed in a vapor deposition chamber and exposed to hydrazine vapor at 95 °C for 2 h. The as-prepared rGO film was placed in the vapor deposition chamber with selenophene monomer (10 μL) at 60 °C for 10 min. Fabrication of rGO All-Solid-State Supercapacitor Based on rGO/ PSe Nanohybrid. Polymer-gel electrolyte was prepared using the following typical method.33,34 First, 6 mL H2SO4 was added dropwise to 60 mL of deionized water, and then, 6 g PVA powder was added. The mixture was heated steadily to 85 °C under vigorous stirring until the solution clarified. After cooling to room temperature, the polymergel electrolyte was drop cast onto the rGO/PSe nanocomposite supercapacitor electrodes. The solid−solid-state rGO/PSe nanohybrid supercapacitor was then assembled by contacting two electrolytecoated rGO/PSe electrodes. The polymer−gel electrolyte acts as an also separator. The sandwiched electrodes were then left overnight until the polymer−gel electrolyte solidified. The electro-chemical properties of all solid-state supercapacitors were investigated from symmetric assembled structure in a two-electrode configuration using CV and galvanostatic charge/discharge experiments. CV tests were carried out at voltages in the range from −0.8 V to +1.1 V at a scan rate of 200 mV s−1. The galvanostatic charge/discharge curves were obtained at a current density of 4 A g−1. Instrumentation. The TEM images were taken with a JEOL JEM2100 microscope. For TEM observation, the samples were diluted with in ethanol and then the diluted solution was deposited on a copper grid coated with a carbon film. The FE-SEM images were obtained with a JEOL JSM-6700 F microscope. A specimen was coated

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CONCLUSION In summary, we successfully synthesized and characterized a new class of graphene−PSe nanohybrid materials for use as high-performance supercapacitive electrodes. The graphene− PSe nanocomposites were synthesized via a simple in situ method. The nanocomposites exhibited the unique properties of both graphene and conducting polymers, including a large voltage window, high conductivity, excellent mechanical properties, and high surface area. The graphene−PSe nanohybrids effectively reduced the dynamic resistance of electrolyte ions and facilitated high charge−discharge rates, leading to high-performance supercapacitance. The exceptional electrical performance was attributed to the synergetic effects of graphene and conducting polymers: (i) enhanced charge transport behavior and surface area, and (ii) hybrid supercapacitance that combined the properties of EDLCs and psedocapacitors. Furthermore, practical application of the graphene−PSe nanohybrid was demonstrated in the form of a flexible supercapacitor with a solid electrolyte. The fabricated all-solid-state supercapacitor electrode demonstrated remarkable flexibility and electrochemical performance. The electrochemical performance was maintained, even under repeated 180° bending motion, without any structural collapse or appearance of electrode defects. This novel graphene−PSe nanocomposite is a promising material for new types of flexible electrochemical applications. 2359

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(22) Zhang, K.; Zhang, L. L.; Zhao, X. S.; Wu, J. Chem. Mater. 2010, 22, 1392−1401. (23) Lee, J.-S.; Kim, S.-I.; Yoon, J.-C.; Jang, J.-H. ACS Nano 2013, 7, 6047−6055. (24) Huang, L.; Li, C.; Shi, G. J. Mater. Chem. A 2014, 2, 968−974. (25) Xu, Y.; Lin, Z.; Huang, X.; Liu, Y.; Huang, Y.; Duan, X. ACS Nano 2013, 7, 4042−4049. (26) Jiang, D.-e.; Jin, Z.; Henderson, D.; Wu, J. J. Phys. Chem. Lett. 2012, 3, 1727−1731. (27) Portet, C.; Taberna, P. L.; Simon, P.; Flahaut, E. J. Power Sources 2005, 139, 371−378. (28) Bhattacharyya, D.; Gleason, K. K. J. Mater. Chem. 2012, 22, 405−410. (29) Kwon, O. S.; Kim, T.; Lee, J. S.; Park, S. J.; Park, H.-W.; Kang, M.; Lee, J. E.; Jang, J.; Yoon, H. Small 2013, 9, 248−254. (30) Boukhalfa, S.; Evanoff, K.; Yushin, G. Energy Environ. Sci. 2012, 5, 6872−6879. (31) Cavaliere, S.; Subianto, S.; Savych, I.; Jones, D. J.; Roziere, J. Energy Environ. Sci. 2011, 4, 4761−4785. (32) Hummers, W. S.; Offeman, R. E. J. Am. Chem. Soc. 1958, 80, 1339−1339. (33) Meng, C.; Liu, C.; Chen, L.; Hu, C.; Fan, S. Nano Lett. 2010, 10, 4025−4031. (34) Yang, X.; Zhang, F.; Zhang, L.; Zhang, T.; Huang, Y.; Chen, Y. Adv. Funct. Mater. 2013, 23, 3353−3360.

with a thin layer of gold to eliminate charging effects. Raman spectra were recorded with a T64000 (Horiba Jobin Yvon). ATR-FTIR spectra were collected with a Thermo Scientific Nicolet 6700 FTIR spectrophotometer. X-ray diffraction (XRD) patterns were carried out with a New D8 Advance (Bruker). Nyquist plots were obtained for the three-electrode cell in the frequency range from 100 kHz to 10 mHz by using a Zahner Electrik IM6 analyzer. Significant data were extracted from the plot using the fitting software (ZMAN 2.3).

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ASSOCIATED CONTENT

S Supporting Information *

In situ synthesis of graphene/polyselenophene nanohybrid materials as highly flexible energy storage electrodes. This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Cao, Q.; Kim, H.-s.; Pimparkar, N.; Kulkarni, J. P.; Wang, C.; Shim, M.; Roy, K.; Alam, M. A.; Rogers, J. A. Nature 2008, 454, 495− 500. (2) Ju, S.; Facchetti, A.; Xuan, Y.; Liu, J.; Ishikawa, F.; Ye, P.; Zhou, C.; Marks, T. J.; Janes, D. B. Nat. Nanotechnol. 2007, 2, 378−384. (3) Nishide, H.; Oyaizu, K. Science 2008, 319, 737−738. (4) Lee, J. W.; Hall, A. S.; Kim, J.-D.; Mallouk, T. E. Chem. Mater. 2012, 24, 1158−1164. (5) Wang, D.-W.; Li, F.; Zhao, J.; Ren, W.; Chen, Z.-G.; Tan, J.; Wu, Z.-S.; Gentle, I.; Lu, G. Q.; Cheng, H.-M. ACS Nano 2009, 3, 1745− 1752. (6) Zhu, Y.; Murali, S.; Stoller, M. D.; Ganesh, K. J.; Cai, W.; Ferreira, P. J.; Pirkle, A.; Wallace, R. M.; Cychosz, K. A.; Thommes, M.; Su, D.; Stach, E. A.; Ruoff, R. S. Science 2011, 332, 1537−1541. (7) Mastragostino, M.; Arbizzani, C.; Soavi, F. J. Power Sources 2001, 97−98, 812. (8) Wang, G.; Zhang, L.; Zhang, J. Chem. Soc. Rev. 2012, 41, 797− 828. (9) Ambade, R. B.; Ambade, S. B.; Shrestha, N. K.; Nah, Y.-C.; Han, S.-H.; Lee, W.; Lee, S.-H. Chem. Commun. 2013, 49, 2308−2310. (10) Laforgue, A.; Simon, P.; Sarrazin, C.; Fauvarque, J.-F. J. Power Sources 1999, 80, 142−148. (11) Yin, Z.; Zheng, Q. Adv. Energy Mater. 2012, 2, 179−218. (12) Patra, A.; Bendikov, M. J. Mater. Chem. 2010, 20, 422−433. (13) Bertho, D.; Jouanin, C.; Lussert, J. M. Phys. Rev. B 1988, 37, 4039. (14) Chen, Z.; Lemke, H.; Albert-Seifried, S.; Caironi, M.; Nielsen, M. M.; Heeney, M.; Zhang, W.; McCulloch, I.; Sirringhaus, H. Adv. Mater. 2010, 22, 2371−2375. (15) Kim, B.; Shin, H.; Park, T.; Lim, H.; Kim, E. Adv. Mater. 2013, 25, 5483−5489. (16) Li, M.; Patra, A.; Sheynin, Y.; Bendikov, M. Adv. Mater. 2009, 21, 1707−1711. (17) Zhang, K.; Zhang, L. L.; Zhao, X. S.; Wu, J. Chem. Mater. 2010, 22, 1392−1401. (18) Liu, C.; Yu, Z.; Neff, D.; Zhamu, A.; Jang, B. Z. Nano Lett. 2010, 10, 4863−4868. (19) Zhang, L. L.; Zhou, R.; Zhao, X. S. J. Mater. Chem. 2010, 20, 5983−5992. (20) He, Y.; Chen, W.; Li, X.; Zhang, Z.; Fu, J.; Zhao, C.; Xie, E. ACS Nano 2012, 7, 174−182. (21) Yu, G.; Hu, L.; Liu, N.; Wang, H.; Vosgueritchian, M.; Yang, Y.; Cui, Y.; Bao, Z. Nano Lett. 2011, 11, 4438−4442. 2360

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