DOI: 10.1002/chem.201501245

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Controllable Preparation of Polyaniline–Graphene Nanocomposites using Functionalized Graphene for Supercapacitor Electrodes Xianbin Liu, Yuying Zheng,* and Xiaoli Wang[a] Abstract: In order to explore the effect of graphene surface chemistry on electrochemical performance based on polyaniline–graphene hybrid material electrodes, four different polyaniline–graphene nanocomposites were fabricated with graphene oxide, reduced graphene oxide, aminated graphene and sulfonated graphene as carriers, respectively. The nanocomposites feature various structures and morphologies, which could be used to more deeply understand the morphology and structure effects caused by surface chemistry on electrochemical performance. The experimental results reveal that functionalized electronegative gra-

Introduction In recent years, increasing attentions has been focused on research on supercapacitors owing to the advantages of their high power density, rapid charge–discharge processes and long life cycles, which make them possible substitutes for lithium ion batteries.[1] The properties of supercapacitors are mainly determined by the electrode materials.[2] Despite many significant advances achieved in electrode materials for supercapacitors, some shortcomings, such as the low specific capacitance in carbon materials, poor cycling stability in conducting polymers and low electrical conductivity in metal oxides, still limit their practical applications.[3] Therefore, further efforts are required to improve the electrochemical performance of electrode materials, meeting the demand of both high power density and energy density. It has been shown that nanostructured composites that combine unique properties of individual nanostructures, could present the most desired properties.[4] Most importantly, these nanocomposites have a well-defined nanostructure, relatively high specific area and short ion diffusion pathways through the synergistic effect, which lead to enhanced capacitance and cycling stability.[5] Therefore, the effective manipulation of the morphologies of nanocomposites seems to be a very promising strategy in the fabrication of high performance supercapacitor electrodes. Nanocomposites of polyaniline with carbon materials (such as active carbon, carbon nanotubes, graphene) are attractive [a] X. Liu, Y. Zheng, X. Wang College of Materials Science and Engineering Fuzhou University, Fuzhou, 350116 (China) E-mail: [email protected] Chem. Eur. J. 2015, 21, 10408 – 10415

phene was conducive to the vertical and neat growth of polyaniline (PANI) nanorods. The array architecture endowed the PANI–GS nanocomposite with a large ion-accessible surface area and high-efficiency electron- and ion-transport pathways. Meanwhile, the introduction of sulfonic acid functional groups accelerated the redox reaction with doping and dedoping of the PANI. Thereby, the PANI–GS nanocomposite exhibited a high specific capacitance of 863.2 F g¢1 at a current density of 0.2 A g¢1 and the excellent rate capability of 67.4 % (581.6 F g¢1 at 5 A g¢1), which were much better than the other three nanocomposites produced.

and promising because polyaniline possesses a series of merits such as easy synthesis, low cost, environmental friendliness and excellent electrochemical performances; meanwhile, carbon materials with high specific surface area could act as ideal substrates to host the polyaniline.[1c, 6] In addition, the high conductivity of carbon facilitates the redox reactions of polyaniline during charge–discharge process.[7] Therefore, when polyaniline is composited with graphene—an outstanding carbon material—the capacitance of nanocomposites show a clear boost of magnitude.[8] Different nanostructures, such as nanoparticles,[9] nanofibers,[10] nanowires,[11] and other hierarchically featured structures,[12] have been prepared to improve the capability of polyaniline–graphene nanocomposites. The reported capacitances have ranged from 500 to 3400 F g¢1 but have not been directly comparable. It is obvious that graphene surface-functionalized groups are very important to the performances of polyaniline–graphene nanocomposites.[5b, 13] The different groups have diverse effects on the electronic properties. The groups in the graphene oxide can hinder the electrical conductivity but can provide doping for the redox process.[13c, 14] Nitrogen-functionalized groups as electron donors have been reported to affect the pseudocapacitive generation.[15] Functional groups act as active sites and affect the nucleation process of polyaniline, leading to different morphologies, porous distributions, and thus the capacitance of PANI can vary remarkably.[16] However, both effects induced by the different groups have not been systematically investigated to date. In this study, we prepared four types of functionalized graphene, using graphene oxide (GO), reduced graphene oxide (G), aminated graphene (GN) and sulfonated graphene (GS), as the basis materials for the polyaniline–graphene nano-

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Full Paper composites. The different roles played by the functional groups on the surfaces in adsorption of monomers for polymerization was demonstrated. The effect of different functional groups on the morphology and electrochemical performances was investigated and elaborated in detail. This study will provide an instructive suggestion to the fabrication of highperformance nanocomposites for practical application.

Results and Discussion The structural features of the different functionalized graphene samples were analyzed using the FT-IR spectra. As shown in Figure 1, the peaks at 3436, 1735, 1630, 1380 and 1124 cm¢1, which are attributed to the ¢OH, ¢C(O)¢, ¢COOH, ¢CO¢OH and ¢C¢OH, respectively, indicated the success of the GO preparation. After treatment with a hydrothermal process, both the peak intensities of C¢O and C=O were significantly weakened, demonstrating that GO was reduced to G. When added with an ammonia solution, GN was generated by nucleophilic replacement with two absorption peaks at 1648 and 2850–2920 cm¢1. In the FT-IR spectrum for GS, the two characteristic peaks at 1040 and 1090 cm¢1 were from the symmetric and antisymmetric stretching of the sulfonic group, respectively.[17] Raman spectra were used to further study the structural changes of the obtained samples. As shown in Figure 2 a, all the curves exhibit two apparent peaks: 1320 and 1598 cm¢1, which correspond with the D and G modes. The D mode indicates the edges and/or defects of sp2 domains while the G mode indicates the E2g mode of the sp2 carbon atoms.[18] The intensity ratio of ID/IG was used to evaluate the disorder of graphitic materials. All the values of ID/IG for GO (1.52), GN (1.41) and GS (1.47) are larger than that for G (0.78), indicating the functionalization has increased the edges and/or defects of graphene. As shown in Figure 2 b, the characteristic peaks of pure PANI are located at 1176, 1228, 1386 and 1486 cm¢1. The reappearance of similar peaks illustrates the presence of PANI in the four nanocomposites. Moreover, the red shift of the

Figure 1. FT-IR spectra of GO, G, GN, GS. Chem. Eur. J. 2015, 21, 10408 – 10415

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Figure 2. a) Raman spectra of GO, G, GN and GS; b) Raman spectra of pure PANI, PANI–GO, PANI–G, PANI–GN and PANI–GS.

peak from 1386 to 1340 cm¢1 in the nanocomposites has notably occurred, because of the strong interaction between the functional groups and PANI molecular chains, which may facilitate the electron transfer in the interface of PANI and graphene.[19] To investigate the elements and functional groups, the XPS spectra were analyzed (Figure 3). It can be seen in Figure 3 a that C, N and O element could be detected in the four nanocomposites. The O 1 s peak in the PANI–G and PANI–GN may be due to the surface-absorbed oxygen. The weak peak at approximately 168 eV belongs to S 2 p indicates that the ¢SO3H functional group was present in the PANI–GS nanocomposite. The high-resolution C 1 s, N 1 s and S 2 p regions in PANI–GS were further analyzed. Figure 3 b shows that the C 1 s main peak was resolved into five peaks: 284.8 (C¢C), 285.4 (C¢N), 286.5 (C¢O), 287.8 (C=O) and 288.9 eV (p–p*). In Figure 3 c, the N 1 s was split into three peaks located at 399.3, 399.8 and 400.9 eV, which are attributed to quinonoid amine (¢N=), benzenoid amine (¢NH¢) and nitrogen cationic amine (¢NH + ), respectively.[20] The total proportion of ¢N= and ¢NH + could be up to 50.1 %, which indicated the high electrical conductivity of PANI in PANI–GS. The S 2 p spectrum is shown in Figure 3 d. The sulfur atom gives rise to a spin-split doublet: S 2 p1/2 and S 2 p3/2, which originate from the sulfonic group ¢SO3H with spin-orbit coupling.[21] Further characterization of GO using atomic force microscopy was carried out. As shown in Figure 4 a, the GO with a size of 1–3 mm could provide large amounts of active points for the absorption of aniline monomers. The morphological observations of samples were carried out using field-emission scanning electron microcopy. Figure 4 b shows pure PANI with randomly stacked nanorods. The morphologies were quite different when using different functionalized graphene as substrates. It was clearly observed that PANI was uniformly coated on the surface of G with inconspicuous salient point in the PANI–G nanocomposite (Figure 4 c). However, some generated short PANI nanorods were cross-linked in the PANI–GN nanocomposite. Besides, some insular PANI nanosheets were deposited on the surface (Figure 4 d). The PANI nanorods became longer but lay on all sides in the PANI–GO nanocomposite, even some re-

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Figure 3. a) XPS curves of PANI–G, PANI–GN, PANI–GO and PANI–GS; b) C 1 s, c) N 1 s, and d) S 2 p region spectra of PANI–GS.

united nanorod clusters were accumulated on the PANI nanorods (Figure 4 e). In contrast, in the PANI–GS nanocomposite, the PANI nanorods, the sizes of which are approximately 80 nm in length and 20 nm in diameter, grew uniformly and vertically on the GS surface (Figure 4 f). Due to the diverse functional groups, the morphology of PANI on the surface of graphene evolves from a dense nanocladding to the straight and neat nanorods with hieratical structure. Based on the above experimental results, the formation of different morphologies may be explained by the nucleation mechanism during the polymerization process (Scheme 1). There are two competitive nucleation modes: homogeneous

nucleation and heterogeneous nucleation.[22] The electronegativity of the functional groups on graphene surfaces plays a decisive role in the concentration distribution, which affects the subsequent nucleation and growth. It was originally thought that PANI nanorods could not be generated on substrates in such a monomer concentration (0.02 m).[14] However, when graphene with the functional groups possessing negative electricity, the protonated aniline monomers with positive electricity could be attracted and transferred to the surface of graphene. The migrated aniline monomers, which increased the surface local concentration of monomers, were apt for the heterogeneous nucleation to form PANI nanorods on the graphene surface. For a more electronegative surface, more aniline monomers underwent heterogeneous nucleation. The PANI would grow along one dimension due to the incessant polymerization of adsorbing aniline monomers. Meanwhile, homogeneous nucleation in the bulk solution was suppressed at a low concentration. It is known that electronegative intensities follow the trend ¢SO3H >¢OH >¢NH2. Therefore, when the aniline monomers were paired with GS, heterogeneous nucleation was stimulated to form uniform and vertical PANI nanorods. Whereas the aniline monomers were paired with G, the PANI claddings were polymerized by homogeneous nucleation and deposited on the surface of G.

Scheme 1. Schematic illustration of the formation process of PANI growth on the graphene surface based on different functional groups.

Figure 4. a) AFM image of GO; FE-SEM images of: b) pure PANI (scale bar: 100 nm), c) PANI–G (scale bar: 500 nm), d) PANI–GN (scale bar: 500 nm), e) PANI–GO (scale bar: 500 nm), and f) PANI–GS (scale bar: 500 nm). Insets: the corresponding high-magnification views; scale bar: 100 nm. Chem. Eur. J. 2015, 21, 10408 – 10415

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The microstructures of the four nanocomposites were further characterized by nitrogen adsorption and desorption at 77 K. As shown in Figure 5, all of the isotherms have the type IV, characteristic with a small hysteresis loop at a relatively high pressure, indicating that these nanocomposites possessed abundant mesopores. Table 1 displays the results of the BET surface area and average pore diameter. The simple nanocladding layer in PANI–G led to a small specific surface area of 20.103 m2 g¢1. With the formation of PANI nanorods in the PANI–GN and PANI–GO, the values slightly increased to 27.884 and 36.579 m2 g¢1, respectively. G-NS had the largest specific surface area of 49.023 m2 g¢1 and the smallest pore diameter of 3.9 nm, which 10410

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Figure 5. Nitrogen adsorption–desorption isotherms of the four nanocomposites: a) PANI–G; b) PANI–GN; c) PANI–GO; d) PANI–GS.

were attributed to the vertical and straight arrangement of PANI nanorods on the surface of graphene. The compositions of the nanocomposites were studied by thermal gravimetric analysis (TGA). As shown in Figure 6, all the samples have a little mass loss around 100 8C caused by the removal of surface-absorbed water molecules. From 100 to 550 8C, G (curve a) almost shows no mass loss and still keeps about 89.3 % weight residual at 800 8C, indicating the excellent thermal stability of G. However, the pure PANI (curve f) shows dramatic weight losses from 100 to 550 8C; this is ascribed to the degradation and decomposition of PANI molecular chains. The maximum weight loss is 55.8 % at 800 8C. In comparison, the nanocomposites show gradual weight loss between 100 and 550 8C. The increased thermal stability of nanocomposites could be explained by the introduction of graphene to PANI molecular chains. The weight residuals for PANI–G (curve b), PANI–GO (curve c), PANI–GN (curve d) and PANI–GS (curve e) are 71.1, 71.4, 71.8 and 72.6 % at 800 8C, respectively. According to calculations reported in a previous publication,[23] the PANI

Table 1. Surface and porosity characteristics of PANI–G, PANI–GN, PANI–GO and PANI–GS. Sample

BET surface area [m2 g¢1]

Average pore diameter [nm]

PANI–G PANI–GN PANI–GO PANI–GS

20.103 27.884 36.579 49.023

16.2 10.8 6.2 3.9

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content in the nanocomposites is equal to 40.4, 39.7, 38.8 and 37.0 %, respectively. To compare the performances of the four nanocomposites, cyclic voltammetry (CV), galvanostatic charge–discharge and electrochemical impedance spectroscopy were performed. The CV curves at a scan rate of 5 mV s¢1 are shown in Figure 7 a. All of the CV curves show two pairs of the redox peaks which is a feature of redox transitions of PANI. Remarkably, the PANI–GS exhibited the highest current peaks. The hierarchical structure in the PANI–GS nanocomposite provides more channels for the diffusion of electrolyte ions to electrode surface, which can improve the utilization of PANI. In addition, the ¢SO3H functional group with the proton may accelerate the doping and dedop-

Figure 6. TGA curves of: a) G, b) PANI–G, c) PANI–GO, d) PANI–GN, e) PANI–GS, and f) pure PANI.

ing during the redox process.[24] It should be noted that the peaks were very flat in PANI–GO, which may be caused by the low electrical conductivity of GO and the dense layer of PANI. Therefore, with both the unique nanostructure and the synergistic effect, the PANI–GS shows excellent capacitive characteristics. Figure 7 b displays the galvanostatic charge–discharge curves at a current density of 1 A g¢1. The results show that PANI–GS had the longest discharging duration, following by PANI–GN, PANI–GO and PANI–G, which were mainly determined by the morphologies of the nanocomposites. Furthermore, the IR drop of the PANI–GO was much larger than those of the other three nanocomposites, leading to a somewhat distorted shape. Low internal resistance is very favorable in high-

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Figure 7. a) Cyclic voltammograms at a scan rate of 5 mV s¢1, and b) galvanostatic charge–discharge curves at a current density of 1 A g¢1 of PANI–G, PANI–GO, PANI–GN and PANI–GS.

performance energy-storage devices with less energy being wasted during the charge–discharge processes. Thus, the PANI–GS nanocomposite with a low internal resistance could Figure 8. a) Plots of specific capacitance as a function of the current be suitable for supercapacitor electrodes. The rate capabilities densities, and b) Nyquist plots in the frequency range of 105 to 10¢2 Hz of of the nanocomposites were evaluated by discharging processPANI–G, PANI–GO, PANI–GN and PANI–GS. es at different current densities. As depicted in Figure 8 a, the PANI–GS nanocomposite showed the highest rate performance with 67.4 % of the capacitance maintained as current density a semicircle in the high-frequency region. However, the curve increases from 0.2 to 5 A g¢1, while only 65.6, 53.1 and 63.0 % for the PANI–GS nanocomposite had the largest slope in the of the specific capacitance remained for PANI–G, PANI–GO and low-frequency region, demonstrating an ideal capacitive bePANI–GN, respectively. havior. The Warburg region, where the electrochemical reaction determined by ion diffusion at the electrolyte/electrode These results demonstrate that specific capacitance and rate capability of PANI–GS are markedly promoted compared with interface, was negligible while it could be relatively long in the those of other three nanocomposites. More importantly, the PANI–G, PANI–GO and PANI–GN nanocomposites. The negligible Warburg region suggests a low ion diffusion resistance (poelectrochemical performances of PANI–GS electrode are highly competitive with other previously reported polyaniline–gralarization impedance). This may be related to the well-aligned phene electrodes (Table 2). It is well known that the pseudocananorods with a length of 80 nm in PANI–GS, which could create more channels for the fast kinetic diffusion of the elecpacitance mainly comes from redox reaction on the surface of PANI. Therefore, our PANI nanorods–GS electrode with the relatrolyte ions.[5a] In the high-frequency region, the semicircle reptively high specific surface area and electrical conductivity, resented the electron-transfer kinetics during the redox prowhich accelerate the charge diffusion and transfer during the cess. Calculations show that the charge-transfer resistance of charge–discharge process, shows much higher specific capacitance and excellent rate capability. Table 2. Comparisons of the electrochemical performances for polyaniline–graphene nanocomposites. Electrochemical impedance Rate Electrolyte Reference Materials and Capacitance spectroscopy was used to furcapability morphology [F g¢1] ther investigate the variation of PANI nanoparticle–graphene 257 (0.1 A g¢1) 56.42 % (1 A g¢1) 1 m H2SO4 [25] charge-transfer kinetics and elechollow G@PANI@G 682.75 (0.5 A g¢1) 46.77 % (10 A g¢1) 1 m H2SO4 [26] tron transport. Figure 8 b shows PANI nanowire–GO 555 (0.2 A g¢1) 40.90 % (2 A g¢1) 1 m H2SO4 [4a] that Nyquist plots for the four PANI nanofiber–graphene 480 (0.1 A g¢1) 48.78 % (1 A g¢1) 2 m H2SO4 [8b] mesoporous PANI–graphene 749 (0.5 A g¢1) 73 % (5 A g¢1) 1 m H2SO4 [27] nanocomposites are basically ¢1 ) – 1 m H SO [28] PANI wire–CFGO 525 (0.3 A g 2 4 the same with a straight line in PANI nanorods–GS 863.2 (0.2 A g¢1) 67.4 % (5 A g¢1) 1 m H2SO4 this work the low-frequency region and Chem. Eur. J. 2015, 21, 10408 – 10415

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Full Paper PANI–GS was 5.3 W. Such a low value implies that the PANI–GS nanocomposite displays fast electron transport. The introduction of ¢SO3H functional groups not only increases the wettability of electrolyte but also facilitates the dedoping, leading to high electrical conductivity. To recap, all of the data collected support the result that the favorable morphology and structure effected by the ¢SO3H facilitate fast kinetics of diffusion and transfer, and improve the electrochemical performances. To further evaluate the practical application of the nanocomposites with different morphologies, an asymmetric supercapacitor was fabricated to investigate the energy density and the power density. Figure 9 displays the Ragone plots of energy density versus power density for the four nanocomposites at various charge–discharge current densities. Figure 10. Cycling performances of PANI–GS at 10 mV s¢1 for 1 000 cycles. Inset: the comparison of CV curves between the 1st and 10 000th cycles.

Figure 9. The Ragone plots of energy density versus power density of PANI– G, PANI–GO, PANI–GN and PANI–GS at various charge–discharge current densities.

The supercapacitor used the PANI–GS as positive electrode exhibited the highest energy density of 11.3 Wh kg¢1 at a current density of 0.2 A g¢1, and the power density maintained a relatively high value of 83 kW kg¢1. Additionally, as an electrode with great advantages, the PANI–GS was tested at a current density of 1 A g¢1 to study its stability. As shown in Figure 10, after 1000 cycles, the supercapacitor maintained 85.6 % of its original specific capacitance. Even after 10 000 cycles performed at a scan rate of 10 mV s¢1, the specific capacitance still retained 78.4 % of its initial value, as shown in the inset of Figure 10; this reveals a good electrochemical stability. It is worth noting that the specific capacitance rose with an increasing cycle number in the beginning due to the activation of the electrode.

Conclusions In summary, we have successfully developed a series of polyaniline–graphene nanocomposites, featuring controllable structures and morphologies. Due to the diversity of the functionalized graphene, the morphology of PANI on the surface of graphene evolves from a dense nanocladding to straight and neat nanorods. Experimental results show that the introduction of electronegative functional groups on the surface of graphene is extremely significant for preparing high performance supercapacitor electrodes, and is beneficial for the growth of Chem. Eur. J. 2015, 21, 10408 – 10415

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straight and neat PANI nanorods. Moreover, functional groups with protons could accelerate the redox reaction with the doping and dedoping of PANI. Thus, PANI–GS has a large specific surface area of 49.023 m2 g¢1. As a supercapacitor electrode, the PANI–GS nanocomposite showed the best electrochemical performances compared with the PANI–G, PANI–GN and PANI–GO nanocomposites. The high specific capacitance of 863.2 F g¢1 and the excellent rate capability of 67.4 % were achieved in the PANI–GS nanocomposite. Such a verified effect could provide an opportunity for the design of novel composite materials with controllable structures and enhanced performances.

Experimental Section Materials Natural flake graphite (325 meshes) was purchased from the Institute of Shenghua (China). The other chemicals were supplied by Sinopharm Chemical Reagent Co. Ltd (China). Aniline was purified by double distillation under a reduced pressure, and others were used without any treatment.

Synthesis of the four types of functionalized graphene GO was firstly synthesized from the natural flake graphite by an improved hummers method.[29] The other three functionalized graphene samples were synthesized using GO as the precursor. G and GN were obtained through a hydrothermal method. Briefly, 60 mL GO solution (1 mg mL¢1) was added to 100 mL Teflon autoclave and heated to 180 8C for hydrothermal reaction, followed by washing and drying to obtain G. The GN was obtained through adding 2 mL ammonia solution into GO solution. GS was prepared following the procedures described in the literature.[17, 30] Briefly, the GO was sulfonated with the aryl diazonium salt of sulfanilic acid and hydrothermally reduced to produce the GS.

Synthesis of the four polyaniline-graphene nanocomposites The polyaniline–graphene nanocomposites were synthesized by in suit oxidation polymerization of aniline in the presence of obtained functionalized graphene. First, 200 mg functionalized graphene

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Full Paper was ultrasonically dispersed in 75 mL HClO4 solution (1 mol L¢1). Then 20 mL ethanol was added to the mixture, subsequently 0.186 mL aniline monomer was added at ¢10 8C. After stirring for 30 min, 0.3 g of the oxidizing agent ammonium persulfate was dissolved in 25 mL HClO4 solution and added and reacted for 24 h. The products were washed clean with copious amounts of water and ethanol, followed by drying for 24 h at 60 8C under vacuum.

Characterization The as-prepared GO was characterized by atomic force microscope (Agilent 5500, USA). The structures of synthesized samples were investigated by Fourier transform infrared spectrometry (Thermo Nicolet 5700 system, USA), Raman spectrometry (Renishaw Invia, UK) and X-ray photoelectron spectrophotometry (ESCALAB 250, USA). Field-emission scanning electron microscope images of the nanocomposites were obtained on a scanning electron microscope (Zeiss SUPRA 55, Germany) operated at an acceleration voltage of 2 kV with InLens detector. The Brunauer–Emmett–Teller (BET) surface area and pore distributions were measured on a NOVA 2000e surface area and pore-size analyzer, respectively. The thermogravimetric data (TGA) were obtained using thermogravimetric analysis (TA SDT-Q600, USA) at a heating rate of 10 8C min¢1 under nitrogen atmosphere.

Electrochemical measurements The cyclic voltammograms (CVs), galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS) were carried out by using a CHI 660D electrochemical workstation (China) with a three-electrode system, consisting of a nanocomposite loaded on glassy carbon electrode as the working electrode, a platinum sheet as the counter electrode and an Ag/AgCl electrode as the reference electrode in 1 m H2SO4 electrolyte at room temperature. The working electrode was prepared as follows: the glassy carbon electrode (F = 3 mm) was pretreated by polishing and ultrasonic cleaning. Nanocomposite (2 mg) was dispersed in 1 mL ethanol containing 10 mL of Nafion solution (5 wt % in water) to form a homogenous solution. The solution (20 mL) was then dropped onto the pretreated glassy carbon electrode and dried at 60 8C. The CVs were recorded at a potential range of ¢0.2–0.8 V with the scan rate of 5 mV s¢1. The galvanostatic charge–discharge was carried out at current density ranged from 0.2 to 5 A g¢1, and the specific capacitance (C) could be calculated with Equation (1). The EIS measurements were conducted at open circuit potential with an amplitude of 10 mV in the frequency range of 10¢2 to 105 Hz. Energy density (E) and power density (P) were derived from the discharge curves based on an asymmetric supercapacitor. The values were calculated using Equations (2) and (3), respectively:



IDt DVm

ð1Þ

1 E ¼ CDV 2 2

ð2Þ

E Dt

ð3Þ



where I [A], Dt [s] and DV [V] are the discharge current, time and potential window in the charge–discharge curve, respectively, and m [g] is the mass of the active material. The asymmetric supercapacitor was constructed by sandwiching a filter paper soaked with 1 m H2SO4 electrolyte between the positive and negative electroChem. Eur. J. 2015, 21, 10408 – 10415

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des. The positive electrode was fabricated by mixing the as-prepared nanocomposite, acetylene black, and polytetrafluoroethylene with the mass ratio 80:15:5 to obtain a homogeneous slurry. The slurry was coated on the stainless steel mesh and dried at 60 8C for 24 h under vacuum. The mass loading was approximately 3 mg cm¢2. The negative electrode was prepared by using active carbon as active materials. In order to achieve the optimal properties, the mass loading of active carbon was adjusted according to Equation (4):

Q þ ¼ Q¢ !

mþ C¢   DV ¢ ¼ m¢ C þ   DV þ

ð4Þ

Acknowledgements This work was supported by Scientific and Technological Innovation Project of Fujian Province (Grant No. 2012H6008), Scientific and Technological Innovation Project of Fuzhou City (Grant No. 2013-G-92). Keywords: electrochemistry · graphene · nanocomposites · nanostructures · supercapacitor electrodes

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Received: March 30, 2015 Published online on June 12, 2015

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Controllable Preparation of Polyaniline-Graphene Nanocomposites using Functionalized Graphene for Supercapacitor Electrodes.

In order to explore the effect of graphene surface chemistry on electrochemical performance based on polyaniline-graphene hybrid material electrodes, ...
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