Ordered Polypyrrole Nanowire Arrays Grown on a Carbon Cloth

Article

Ordered Polypyrrole Nanowire Arrays Grown on Carbon Cloth Substrate for High Performance Pseudocapacitor Electrode Zi-Hang Huang, Yu Song, Xinxin Xu, and Xiao-Xia Liu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b08830 • Publication Date (Web): 28 Oct 2015 Downloaded from http://pubs.acs.org on November 2, 2015

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ACS Applied Materials & Interfaces

Ordered Polypyrrole Nanowire Arrays Grown on Carbon Cloth Substrate for High Performance Pseudocapacitor Electrode

Zi-Hang Huang, Yu Song, Xin-Xin Xu*, Xiao-Xia Liu* Department of Chemistry, Northeastern University, Shenyang, 110819, China

Corresponding author: Xiao-Xia Liu, [email protected]; Xin-Xin Xu, [email protected]

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Abstract Highly aligned nanoarchitecture arrays directly grown on conducting substrates open up a new direction to accelerate Faradic reactions for charge storage as well as address “dead volume” limitations for high performance pseudocapacitor electrodes. Here we reported the electrochemical fabrication of well-ordered polypyrrole (PPy) nanowire arrays (NWAs) on surfaces of carbon fibers in untreated carbon cloth to construct hierarchical structures constituted by the three-dimensional conductive carbon fiber skeleton and the atop well-ordered electroactive polymer nanowires. Morphologies, wetting behaviors and charge storage performances of the polymer were investigated by scanning electron microscope (SEM), transmission electron microscope (TEM), contact angle (CA), cyclic voltammetry, galvanostatic charge-discharge

and

electrochemical

impedance

spectroscopy

(EIS).

The

well-ordered PPy NWAs electrode exhibited a high specific capacitance of 699 F/g at 1 A/g with excellent rate capability, 92.4% and 81.5% of its capacitance could be retained at 10 and 20 A/g, respectively. An extremely high energy density of 164.07 Wh/kg can be achieved by the PPy NWAs at the power density of 0.65 kW/kg. It also displayed a quite high energy density of 133.79 Wh/kg at a high power density of 13 kW/kg. The assembled symmetric supercapacitor (SSC) of PPy NWAs//PPy NWAs also exhibited excellent rate capability, only 19% of its energy density decreased when the power density increased 20 times from 0.65 to 13 kW/kg. Keywords: polypyrrole, nanowire arrays, electrochemical growth, supercapacitor, rate capability

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1. Introduction The development of high performance supercapacitors is highly desirable to meet the increasing demand for energy storage devices.1-4 Compare to electrical double layer capacitors, pseudocapacitors usually display higher capacitance as in which charges are stored through highly reversible Faradic reactions.5-8 However, this advantage may be offset by the poor rate capability due to the poor electrical conductivity of pseudocapacitive electrode materials. In addition, pseudocapacitive electrode materials, including conducting polymers and inorganic oxides, usually suffer from self-aggregation, leading to large “dead volume” which is inaccessible for electrolyte ions. Thus their charge storage capacity (specific capacitance) may be decreased and rate capability be further deteriorated. Advances in nanotechnology, especially highly aligned nanoarchitecture arrays grown on conducting substrates, open up new directions to address these limitations due to the fabrication of facile electron channels and short ion diffusion path for fast Faradic reactions. Tong and coworkers reported an electrochemical grown MnO2 nanorod array on conductive substrate which displayed good pseudocapacitive behaviors (with specific capacitance of 485.2 F/g at 3 A/g) attributed to the facilitated electron transportation and effective active species diffusion.9 Later, the authors designed a MnO2/Mn/MnO2 sandwich-like nanotube array with an increased specific capacitance of 955 F/g at 1.5 A/g thanks to the fabrication of electron superhighways by the middle Mn layer.10 Conducting polymers are promising functional materials for charge storage due to their advantages of low cost and high capacitance contribution. As one of the typical conducting polymers, polypyrrole (PPy) has aroused great attention because of its good charge storage performances in wide potential window and environmental stability. However, unlike polyaniline to which the fibrillar sturcture is intrinsic, it is very difficult for PPy to grow one dimensionally and so it is usually obtained in granular powders.11 A facile and controllable method for the growth of uniform PPy nanowire arrays (NWAs) will be of great interest. It was found that electrochemically grown PPy nanoarchitectures vary significantly by only changing the electrode

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substrate. For example, vertical aligned PPy conical nanocontainers were reported by Jiang’s group to be grown in the presence of D-camphorsulfonic acid on surfaces of hydrophilic Pt substrate while only conventional cauliflower-like PPy was obtained on surfaces of hydrophobic Au/Pt plate.12 The authors also reported the biphasic electrochemical growth of PPy nanofiber array in the presence of L-camphorsulfonic acid and found that pre-roughening process for electrode substrate is one of the key factors to form uniform aligned polypyrrole nanofibers.13 Vertically oriented PPy NWAs were also electrochemically grown on surfaces of Pd nano-islands coated Nafion substrate from phosphate buffer solutions containing p-toluenesulfonyl sodium and pyrrole, which displayed improved performances in direct methanol fuel cells.14-15 Well-oriented PPy NWAs were similarly prepared on Au nanoislands coated Pt plate which displayed a high specific capacitance of 566 F/g at 1.10 A/g.16 However, there is no report about PPy NWAs growth on untreated substrate, to the best of authors’ knowledge. Herein we report the electrochemical fabrication of well-ordered PPy NWAs on untreated carbon cloth thanks to the strong π-π interactions between pyrrole molecules and carbon substrate which facilitate formation of nucleation sites for electrochemical polymerization of pyrrole. The well-ordered PPy NWAs exhibited a high specific capacitance of 699 F/g at 1.0 A/g. 92.4% and 81.5% of its capacitance could be retained when the discharging current density increased 10 and 20 times from 1 A/g to 10 and 20 A/g, respectively, demonstrating its super rate capability. Benefiting from the wide charge storage potential window (1.3 V from -0.8 to 0.5 V vs. SCE), the PPy NWAs displayed an extremely high energy density of 164.07 Wh/kg at the power density of 0.65 kW/kg and a quite high energy density of 133.79 Wh/kg at a high power density of 13 kW/kg. A symmetric supercapacitor (SSC) of PPy NWAs//PPy NWAs was assembled to investigate the application of PPy NWAs for charge storage which also exhibited superior rate capability, 80.8 % of its capacitance can be retained when the charge-discharge current density increased 10 and 20 times from 1 A/g to 20 A/g. It also showed good cycling stability, 80.1% of its capacitance can be retained after 5000 charge-discharge cycles. 4


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2. Experimental 2.1 Materials All the reagents were purchased from Sinopharm Chemical Reagent Co., Ltd. and used as received, except pyrrole which was distilled prior to use. Carbon cloth and graphite foil were purchased from Fuel Cell Earth (American) and SGL group (Germany), respectively.

2.2 Electrochemical fabrication of ordered polypyrrole nanowire arrays and symmetric supercapacitor assembly Ordered PPy NWAs (mass loading: 0.21 ± 0.01 mg/cm2) was fabricated through electropolymerization of pyrrole on carbon cloth substrate in a solution of 0.2 M phosphate buffer (pH = 6.86) containing 0.145 M pyrrole and 0.02 M p-toluene sulfonate acid (TsOH) at a constant current of 1.0 mA/cm2 for 30 min with SCE and graphite foil as the reference and the counter electrode, respectively. Then the working electrode was washed thoroughly with distilled water and dried in vacuum at 60 °C for 24 h. To investigate the influence of TsOH concentration on PPy NWAs fabrication, electropolymerizations were also conducted in solutions containing 0, 0.005, 0.01, 0.04 and 0.08 M TsOH, respectively at 1.0 mA/cm2 for 30 min. Pyrrole was also polymerized at 1.4 and 1.8 mA/cm2 in a solution containing 0.02 M TsOH for 21 and 16

min,

respectively

to

ensure

that

same

charges

were

consumed.

Electropolymerizations at 1.0, 1.4 and 1.8 mA/cm2 were also conducted for 90, 150 and 150 s, respectively to investigate the influence of current density on PPy nucleation. A model symmetric supercapacitor (SSC) of PPy NWAs//PPy NWAs was assembled by using two identical pieces of PPy NWAs electrode as anode and cathode, respectively and 5 M LiCl as electrolyte.

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2.3 Characterizations Morphologies of the samples were investigated by using a scanning electron microscope (SEM, Ultra Plus, Carl Zeiss, Germany). Transmission electron microscope (TEM) measurements were carried out by using a Tecnai G2 20 TEM (FEI, USA). A Spectrum One Fourier transform infrared spectroscopy (FT-IR, Perkin-Elmer, USA) was used to obtain vibrational spectrum of the sample. Wetting behaviors of the materials were measured by contact angle (CA, TL100, Biolin Scientific, Finland). PPy mass loading was measured by the weight difference of the electrode before and after electropolymerization, using a Sartorius BT 25 S semi-microbalance with a sensitivity of 0.01 mg. Electrochemical properties of electrodes were investigated with multichannel electrochemical analyzer (VMP3, Bio-Logic-Science Instruments, France) in a three-electrode cell using 5 M LiCl aqueous solution as the electrolyte with SCE and graphite foil as the reference and counter electrode, respectively. Electrochemical impedance spectroscopy (EIS) measurements were conducted in a frequency range of 40 mHz to 50 kHz at open circuit potential. Charge storage behaviors of the model SSC were investigated in two-electrode configuration.

3. Results and discussions 3.1 Electrochemical growth of ordered PPy nanowire arrays PPy NWAs were fabricated through one-step electropolymerization of pyrrole on untreated carbon cloth substrate without any seed coating, at a constant current density of 1.0 mA/cm2, using p-toluene sulfonate acid (TsOH) as the “soft” template. Figure 1a-c shows the SEM images of the as-prepared PPy electrode. It can be seen that well-ordered PPy NWAs were vertically aligned on surfaces of the carbon fiber in the carbon cloth, forming a hierarchical structure constituted by the three-dimensional conductive carbon skeleton and the electroactive polymer nanowires. The fabrication process of aligned nanowires can be proposed as shown 6


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schematically in Fig 2. Firstly, pyrrole monomer and TsOH anions were absorbed on surfaces of carbon fibers in the carbon cloth due to the π-π interactions between aromatic rings of pyrrole as well as of TsOH with the sp2 carbon (Fig. 2b). Thereafter sufficient nucleation sites for the growth of PPy NWs can be provided by these π-π interactions (Fig. 2c). The TsOH anions doped in the initially formed PPy oligomers can protect them from random polymer growth. Instead, one-dimensional growth of PPy was promoted by the predominant polymerization on tips of the nuclei due to the highest electric field there originated from edge effects (Fig. 2d).14,16 The hierarchical structure of the three-dimensional distributed carbon fibers in carbon cloth and the upward grown PPy nanowires provides facile ion diffusion path as well as fast electron transport avenue, which are critical for high charge storage performances. FTIR spectrum of PPy NWAs is shown in Figure 1d. Typical characteristic vibrations of PPy can be seen, including the absorption bands at 1551 and 1400 cm-1 which related to the stretching vibrations of the pyrrole ring in the polymer.17-18 The bands at 1295 and 1207 cm−1 can be assigned to the stretching vibrations of sulfonic group in doped TsO− and C-N bond in the polymer, respectively.19-21 The absorption bands at 1039 and 924 cm-1 are attributed to the doping state of PPy and C-H deformation vibration, respectively.21-22 The peak at 1682 cm-1 is related to the adsorbed water molecules.23-24

3.2 Influence of TsOH concentration on PPy nanowire arrays growth To investigate the influence of TsOH concentration on PPy NWAs growth, electropolymerization of pyrrole was conducted in the presence of 0.005, 0.01, 0.02, 0.04 and 0.08 M TsOH, respectively, morphologies of the obtained polymers were investigated by SEM (Fig. 3a-e). It can be seen that the concentration of TsOH has significant influence on the polymer growth. PPy nanoparticles were formed in the presence of TsOH in relatively high concentration (0.08 M, Fig. 3a). Along with the decrease of TsOH concentration, one-dimensional polymer growth was directed, resulting in short nanorods (0.04 M TsOH, Fig. 3b) and well-ordered nanowire arrays

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(0.02~0.005 M TsOH, Fig. 3c-e). The length of PPy nanowire can be controlled by the concentration of TsOH. TEM images of PPy nanowires obtained in the presence of 0.02 and 0.005 M TsOH are shown in Fig. 3g and h. It can be clearly seen that the length of the nanowire increased from 600 nm for the polymer obtained in the presence of 0.02 M TsOH to 1.8 µm for PPy obtained in the presence of 0.005 M TsOH, with undetectable diameter change. It can be deduced that when there was as much as 0.08 M TsOH in the electropolymerization solution, its protection effect was so strong that even the longitudinal polymer growth was blocked, resulting in polymer nanoparticles. The block of polymer growth was also supported by the low polymerization potential in its chronopotentiometric curve (Fig. 3i). The protection function of TsOH gradually reduced along with the decrease of its concentration, leading to facilitated polymerization, which can be supported by the increased polymerization potential shown in Fig. 3i and elongated PPy nanowire. However, when electrochemical polymerization of pyrrole was conducted in the absence of TsOH, the obtained PPy existed mainly in irregular shapes with very few nanowires on top (Fig. 3f). Without TsOH in the solution, the initially formed PPy oligomers can also be partially protected by themselves from random polymer growth through self-templating. However, this self-protection effect is very weak indicated by the rapidly increased polymerization potential shown in Fig. 3i. So in the absence of TsOH, very few nanowires can be formed on top of the irregular shaped PPy. Insets in Fig. 3a∼f show the contact angle (CA) of the polymer with water. The irregular shaped PPy showed slightly hydrophobicity with a CA of 92.8° (insets in Fig. 3f), indicating that the specific interface energy of the wetted area under the water drop is larger than that of the free liquid surface over the drop.25 The nanoparticle and one-dimensional PPy showed increased hydrophobicity with increased CA of 106.8, 108.7, 118.3, 121.9 and 124.6° (insets in Fig. 3a∼e), respectively. Along with the progressively increase of surface roughness from irregular shaped PPy to nanoparticle and gradually enlogated one-dimensional nanowire, the wetted surface area under the drop will be increased. So the specific interface energy difference of the wetted surface area and the free liquid surface over the drop will be increased, leading to 8


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enhanced hydrophobicity.25

3.3 Influence of current density on PPy nanowire arrays growth Electropolymerization of pyrrole was also conducted at different current densities from 1.0 to 1.8 mA/cm2, in the solution of 0.2 M phosphate buffer (pH = 6.86) containing 0.145 M pyrrole and 0.02 M TsOH, to investigate its influence on PPy NWAs fabrication. Morphologies of the obtained polymers are shown in Fig. 4a-c. From Fig. 4a-c, it can be seen that PPy NWAs can grow at 1.0, 1.4 and 1.8 mA/cm2. However, it looks that the nanowire grew denser when the current density increased. Chronopotentiometric curves during pyrrole polymerization at different current densities are shown in Fig. 4d. The chronopotentiometric curve can be divided into three phases. Phase I (pink area) with a rapid potential increase should be related to double layer charging and pyrrole oxidation. The following phase (phase II, green area) with a moderate potential increase correspondeds to the nucleation of the polymer. The electropolymerization was ended in phase III (yellow area) which was related to the polymer growth. From Fig. 4d, it can be seen that the potential of phase II increased along with the increase of the current density. This will impede the ion transportation in the polymer and so be disadvantageous to its charge storage. SEM images of PPy grown in phase II stage at different current density are shown in insets of Fig. 4a-c, in which short PPy nanorods can be seen. Along with the increase of current density, PPy nucleation is facilitated. So more and more nanorods can be formed in phase II stage (insets of Fig. 4a-c), leading to denser PPy nanowires in the following polymer growth stage (phase III).

3.4 Electrochemical properties of PPy To investigate the influence of TsOH concentration and current density on electrochemical properties of the obtained PPy, cyclic voltammetry, galvanostatic charge-discharge and EIS experiments were conducted in a three-electrode cell containing 5 M LiCl aqueous electrolyte. The obtained cyclic voltammograms (CVs), 9



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galvanostatic charge-discharge profiles and Nyquist plots for the PPy obtained in the presence of TsOH in different concentrations are shown in Fig. 5a-c, with the oxidative peak current density on the CVs in inset of Fig. 5a and the combined series resistance (Rs) obtained from the crossing of the high-frequency domain end and the real component axis on Nyquist plots in inset of Fig. 5c. The specific capacitance C (F/g) of the polymer can be calculated based on galvanostatic charge-discharge experiments according to Equation 1: C = I×t/(∆ ∆U×m)

Equation 1

Where I and t are charge-discharge current (A) and time (s), respectively; ∆U and m are charge-discharge potential window (V) and mass loading of the polymer (g), respectively. The calculated specific capacitance of the PPy obtained in the presence of TsOH in different concentrations is shown in inset of Fig. 5b. As can be seen in Fig. 5a and b, the irregular shaped PPy obtained in the absence of TsOH as well as PPy nanoparticle and short nanorod obtained in the presence of comparatively high TsOH concentrations (0.08 and 0.04 M) displayed lower electroactvity and specific capacitance. This should be related to the low surface area of the polymer and so be disadvantageous to its contact with electrolyte for charge storage. When the TsOH concentration in electropolymerization solution decreased to 0.02 M, the obtained PPy NWAs displayed enhanced electroactivity and charge storage capacity (Fig. 5a and b). Although it showed slightly increased hydrophobicity compared to the above polymers (insets in Fig. 3a∼c and f), its charge storage performance was improved by the increased surface area and the established electron transportation channels through nanowires in the array for electrochemical reactions. The good charge storage behavior was also supported by the steepest slope of its Nyquist plot in the low-frequency domain (Fig. 5c). However, the charge storage performances deteriorated for the PPy NWAs with longer polymer wires obtained in the presence of TsOH in lower concentration (Fig. 5a and b), because of the enhanced hydrophobicity (Fig. 3d and e) which is disadvantage of the contact of the polymer with electrolyte. From the Nyquist plots shown in Fig. 5c, the PPy obtained in the presence of TsOH in different concentrations displayed similar Rs, except the 10


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nanoparticle PPy obtained in the solution containing 0.08 M TsOH, as well as the irregular shaped PPy obtained in the absence of TsOH, which displayed large Rs, showing their large combined series resistance. PPy NWAs were obtained at different current densities from 1.0 to 1.8 mA/cm2, however, with denser nanowires in the film obtained at higher current density (Fig. 4a-c). As can be seen in Fig. 5d and e, both of the electroactivity and the specific capacitance decrease for the denser nanowire obtained at higher current density. The PPy NWAs with different density displayed similar combined series resistance and similar slope in the low-frequency domain of their Nyquist plots (Fig. 5f), demonstrating their similar charge storage property. Based on galvanostatic charge-discharge experiment at 1.0 A/g, the well-ordered PPy NWAs obtained at 1.0 mA/cm2 in the solution of pH 6.86 (0.2 M phosphate buffer) containing 0.145 M pyrrole and 0.02 M TsOH displays a specific capacitance of 699 F/g. Significantly, the PPy NWAs can retain 92.4% and 81.5% of its capacitance when the charge-discharge current density increases 10 and 20 times from 1 to 10 and 20 A/g (Fig. 6a and b), respectively, showing its super rate capability. This is substantially better than or comparable to those of other nanostructured PPy and PPy films deposited on porous three-dimensional substrates. For example, potentiodynamically deposited PPy nanosheet displayed specific capacitance of 584 and 427 F/g at 5 and 20 mA/cm2, respectively with 73% capacitance retention when the charge-discharge current density increased 4 times.22 A galvanostatically fabricated hollow horn PPy displayed specific capacitance of 400 and 367 F/g at 3 and 24 A/g, respectively with 92% capacitance retention when the charge-discharge current density increased 8 times.26 PPy NWAs electrodeposited on Au nanoislands coated Pt plate displayed a high specific capacitance of 566 F/g at 1.10 A/g. However, when the current density increased 12.5 times to 13.75 A/g, only 45.7% of its capacitance can be retained (259 F/g).16 When core/shell nanotube arrays were formed through coating PPy on surfaces of SnO2 nanotubes, the polymer displayed a high rate capability, 84.6% of its capacitance can be retained when the current density increased 20 times from 1 to 20 A/g. However, the specific capacitance was only 260 F/g at 1 A/g.27 The PPy deposited on 3D nanoporous Au substrate displayed specific 11



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capacitance of 193 and 163 F/g at 2 and 20 A/g, with 84.4% capacitance retention for the 10 times increase of current density.28 Energy and power densities are two important factors for evaluating energy storage properties of supercapacitor electrodes. The energy density (E, Wh/kg) and power density (P, kW/kg) of PPy NWAs can be calculated by the following two Equations: E=1000 C∆ ∆U 2/2×3600

Equation 2

P=3600E/1000t

Equation 3

The calculated results are shown in the Ragone plot, together with values of other one-dimensional aligned pesudocapacitive material nanostructure arrays for comparison (Fig. 6c). Thanks to the high specific capacitance and the large charge storage potential window (1.3 V from -0.8 to 0.5 V vs. SCE), the well ordered PPy NWAs displayed an extremely high energy density of 164.07 Wh/kg at the power density of 0.65 kW/kg. Even at a high power density of 13 kW/kg, a quite high energy density of 133.79 Wh/kg can be achieved, illustrating its excellent energy storage property. This is higher than the PPy NWAs electrodeposited on Au nanoislands coated Pt plate which displayed the energy density of 100 and 50 Wh/kg at 0.9 and 15 kW/kg, respectively.16 This is also higher than one-dimensional aligned nanostructure arrays of other pesudocapacitive materials, including core-shell nanowire or nanotube arrays, such as PANI NWAs aligned on nitrogen-doped carbon fiber cloth (22.9 Wh/kg at 9.8 kW/kg, 20.3 Wh/kg at 36.5 kW/kg)29, ZnCo2O4 NWAs (12.5 Wh/kg at 0.8 kW/kg, 3.8 Wh/kg at 6.4 kW/kg)30, NiCo2O4@MnO2 core-shell NWAs (35 Wh/kg at 0.163 kW/kg, 8 Wh/kg at 3.5 kW/kg)31, CoO@PPy core-shell NWAs (43.5 Wh/kg at 0.09 kW/kg, 11.8 Wh/kg at 5.5 kW/kg)32, Ni(OH)@Fe2O3 core-shell NWAs (45.4 Wh/kg at 6.5 kW/kg, 12.7 Wh/kg at 65.5 kW/kg)33, Co3O4@Pt@MnO2 core-shell NWAs (74.6 Wh/kg at 0.5 kW/kg, 39.6 Wh/kg at 19.6 kW/kg)34 and MnO2@Mn@MnO2 core-shell nanotube arrays (87.5 Wh/kg at 1.25 kW/kg, 45 Wh/kg at 23 kW/kg)10. The high pesudocapacitive performance of the PPy NWAs can be attributed to the following two factors: 1) Facile ion diffusion paths are provided by the hierarchical structure of the three-dimensional conductive skeleton of carbon 12


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fibers in carbon cloth and the atop well-ordered PPy NWAs. 2) Fast electron transportation avenues are established by the vertically aligned PPy nanowires which grown directly on surfaces of conductive carbon fibers in carbon cloth substrate. Cyclic stability of the PPy NWAs was investigated by prolonged galvanostatic charge-discharge experiment at 50 A/g for 5000 cycles. As shown in Figure 6d, only 63% of PPy NWAs' capacitance can be retained after 5000 cycles. The polymer structural may be partially pulverized by the repeated high degree swelling and shrinking of PPy chains during charge-discharge in this large potential window, leading to the loss of active materials.35 The structure pulverization may be impeded by reducing the swelling-shrinking degree of the polymer through narrowing the potential window (see below). To evaluate the performance of the PPy NWAs electrode for application in supercapacitors, a model symmetric supercapacitor (SSC) of PPy NWAs//PPy NWAs was assembled by using two identical pieces of PPy NWAs electrode as anode and cathode, respectively and 5 M LiCl as electrolyte. The capacitive properties of PPy NWAs//PPy NWAs were investigated by constant current charge-discharge experiments at different current densities with an operating voltage of 1.3 V (Fig. 7a). Specific capacitance Cs of PPy NWAs//PPy NWAs can be calculated by Equation 4 (Fig. 7b): Cs = I×t/(U×m)

Equation 4

Where I and t are charge-discharge current (A) and time (s), respectively; U and m are operating voltage (V) and mass loading of the polymer in both of the electrodes (g), respectively. The PPy NWAs//PPy NWAs supercapacitor displays a specific capacitance of 140 F/g at the current density of 1 A/g. Significantly, the PPy NWAs//PPy NWAs can retain 80.8% of its capacitance when the charge-discharge current density increases 20 times from 1 to 20 A/g (Fig. 7b). The energy density (E, Wh/kg) and power density (P, kW/kg) of the SSC can be calculated by Equations 5 and 6: E=1000 CsU2/2×3600

Equation 5

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P=3600E/1000t

Equation 6

The calculated results are shown in the Ragone plot displayed in Fig. 7c. PPy NWAs//PPy NWAs displayed excellent rate capability, when the power density increased 20 times from 0.65 to 13 kW/kg, the energy density only decreased 19% from 32.9 to 26.6 Wh/kg. Cyclic stability of PPy NWAs//PPy NWAs was investigated by prolonged galvanostatic charge-discharge experiment at 20 A/g for 5000 times (Fig. 7d). The SSC displays a good stability with 80.1% capacitance retention after 5000 charge-discharge cycles. This is much better than the cyclic stability of PPy NWAs electrode (Fig. 6d). In fact, PPy NWAs needn’t work in the whole potential range of 1.3 V from -0.8 to 0.5 V in the SSC as the PPy NWAs in anode and cathode store charges in negative and positive potentials, respectively. To explore the stability of PPy NWAs in supercapacitor, prolonged charge-discharge experiments were conducted in the potential range of 0.05 to 0.5 V and -0.8 to 0.05 V, respectively for the charge balance stored in anode and cathode (Fig. 8a). After 5000 charge-discharge cycles, the PPy NWAs can maintain 120 % and 93 % of its initial capacitance in the potential range of 0.05 to 0.5 V and -0.8 to 0.05 V, respectively (Fig. 8b), showing much improved stability compare to in the large potential window from -0.8 to 0.5 V (Fig. 6d). This can be ascribed to the subdued structural pulverization due to the weakened swelling and shrinking of PPy chains during charge-discharge cycles.35

4. Conclusions In summary, well-ordered PPy NWAs were fabricated through one-step electropolymerization of

pyrrole

on untreated carbon cloth substrate for

supercapacitor electrode. “Dead volume” limitation can be addressed by the highly aligned nanoarchitecture arrays, so a high specific capacitance of 699 F/g at 1 A/g was achieved by the PPy NWAs. The hierarchical structure of the three-dimensional distributed carbon fibers in carbon cloth and the upward grown PPy nanowires also provides facile ion diffusion path as well as fast electron transport avenue, which are critical for high rate capability. 92.4% and 81.5% of the PPy NWAs' capacitance can

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be retained when the charge-discharge current density increased 10 and 20 times from 1 to 10 and 20 A/g, respectively. The assembled SSC of PPy NWAs//PPy NWAs also exhibited superior rate capability, when the power density increased 20 times from 0.65 to 13 kW/kg, its energy density only decreased 19% from 32.9 to 26.6 Wh/kg. The SSC displays a good stability with 80.1% capacitance retention after 5000 charge-discharge cycles.

Acknowledgements We gratefully acknowledge financial supports from the National Natural Science Foundation of China (Grant No. 21273029 and 21303010) and Research Foundation for Doctoral Program of Higher Education of China (Grant No. 20120042110024).

References (1) Li, S.; Huang, D.; Yang, J.; Zhang, B.; Zhang, X.; Yang, G.; Wang, M.; Shen, Y. Freestanding Bacterial Cellulose–Polypyrrole Nanofibres Paper Electrodes for Advanced Energy Storage Devices. Nano Energy 2014, 9, 309-317. (2) Wang, F.; Zhan, X.; Cheng, Z.; Wang, Z.; Wang, Q.; Xu, K.; Safdar, M.; He, J. Tungsten Oxide@Polypyrrole Core-Shell Nanowire Arrays as Novel Negative Electrodes for Asymmetric Supercapacitors. Small 2015, 11, 749-755. (3) Liu, Y.; Zhang, B.; Yang, Y.; Chang, Z.; Wen, Z.; Wu, Y. Polypyrrole-Coated α-MoO3 Nanobelts with Good Electrochemical Performance as Anode Materials for Aqueous Supercapacitors. J. Mater. Chem. A 2013, 1, 13582-13587. (4) Shi, Y.; Pan, L.; Liu, B.; Wang, Y.; Cui, Y.; Bao, Z.; Yu, G. Nanostructured Conductive Polypyrrole Hydrogels as High-Performance, Flexible Supercapacitor Electrodes. J. Mater. Chem. A 2014, 2, 6086-6091. (5) Zhao, Y.; Liu, J.; Hu, Y.; Cheng, H.; Hu, C.; Jiang, C.; Jiang, L.; Cao, A.; Qu, L. Highly Compression-Tolerant Supercapacitor Based on Polypyrrole-Mediated Graphene Foam Electrodes. Adv. Mater. 2013, 25, 591-595. (6) Abouali, S.; Garakani, M. A.; Zhang, B.; Xu, Z. L.; Heidari, E. K.; Huang, J. Q.; Huang, J.; Kim, J. K. Electrospun Carbon Nanofibers with in Situ Encapsulated Co3O4 Nanoparticles as Electrodes for High-Performance Supercapacitors. ACS Appl. Mater. Interfaces 2015, 7, 13503-13511. (7) Lu, X. F.; Chen, X. Y.; Zhou, W.; Tong, Y. X.; Li, G. R. α-Fe2O3@PANI Core-Shell Nanowire Arrays as Negative Electrodes for Asymmetric Supercapacitors. ACS Appl. Mater. Interfaces 2015, 7, 14843-14850. (8) Qian, Y.; Liu, R.; Wang, Q.; Xu, J.; Chen, D.; Shen, G. Efficient Synthesis of Hierarchical NiO Nanosheets for High-Performance Flexible All-Solid-State Supercapacitors. J. Mater. Chem. A 2014, 2, 1091710922. 15



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(9) Lu, X.; Zheng, D.; Zhai, T.; Liu, Z.; Huang, Y.; Xie, S.; Tong, Y. Facile Synthesis of Large-Area Manganese Oxide Nanorod Arrays as a High-Performance Electrochemical Supercapacitor. Energy Environ. Sci. 2011, 4, 2915-2921. (10) Li, Q.; Wang, Z. L.; Li, G. R.; Guo, R.; Ding, L. X.; Tong, Y. X. Design and Synthesis of MnO2/Mn/MnO2 Sandwich-Structured Nanotube Arrays with High Supercapacitive Performance for Electrochemical Energy Storage. Nano Lett. 2012, 12, 3803-3807. (11) Zhang, X.; Manohar, S. K. Bulk Synthesis of Polypyrrole Nanofibers by a Seeding Approach. J. Am. Chem. Soc. 2004, 126, 12714-12715. (12) Huang, J.; Quan, B.; Liu, M.; Wei, Z.; Jiang, L. Conducting Polypyrrole Conical Nanocontainers: Formation Mechanism and Voltage Switchable Property. Macromol. Rapid Commun. 2008, 29, 1335-1340. (13) Li, M.; Wei, Z.; Jiang, L. Polypyrrole Nanofiber Arrays Synthesized by a Biphasic Electrochemical Strategy. J. Mater. Chem. 2008, 18, 2276-2280. (14) Xia, Z.; Wang, S.; Li, Y.; Jiang, L.; Sun, H.; Zhu, S.; Su, D. S.; Sun, G. Vertically Oriented Polypyrrole Nanowire Arrays on Pd-plated Nafion® Membrane and its Application in Direct Methanolfuel Cells. J. Mater. Chem. A 2013, 1, 491-494. (15) Xia, Z.; Wang, S.; Jiang, L.; Sun, H.; Sun, G. Controllable Synthesis of Vertically Aligned Polypyrrole Nanowires as Advanced Electrode Support for Fuel Cells. J. Power Sources 2014, 256, 125-132. (16) Huang, J.; Wang, K.; Wei, Z. Conducting Polymer Nanowire Arrays with Enhanced Electrochemical Performance. J. Mater. Chem. 2010, 20, 1117-1121. (17) Tran, H. D.; Shin, K.; Hong, W. G.; D'Arcy, J. M.; Kojima, R. W.; Weiller, B. H.; Kaner, R. B. A Template-Free Route to Polypyrrole Nanofibers. Macromol. Rapid Commun. 2007, 28, 2289-2293. (18) Aradilla, D.; Estrany, F.; Armelin, E.; Oliver, R.; Iribarren, J. I.; Alemán, C. Characterization and Properties of Poly[N-(2-cyanoethyl)pyrrole]. Macromol. Chem. Phys. 2010, 211, 1663-1672. (19) Wang, Y.; Iqbal, Z.; Mitra, S. Rapidly Functionalized, Water-Dispersed Carbon Nanotubes at High Concentration. J. Am. Chem. Soc. 2006, 128, 95-99. (20) Bai, M. H.; Bian, L. J.; Song, Y.; Liu, X. X. Electrochemical Codeposition of Vanadium Oxide and Polypyrrole for High-Performance Supercapacitor with High Working Voltage. ACS Appl. Mater. Interfaces 2014, 6, 12656-12664. (21) Zhang, D.; Zhang, X.; Chen, Y.; Yu, P.; Wang, C.; Ma, Y. Enhanced Capacitance and Rate Capability of Graphene/Polypyrrole Composite as Electrode Material for Supercapacitors. J. Power Sources 2011, 196, 5990-5996. (22) Dubal, D. P.; Lee, S. H.; Kim, J. G.; Kim, W. B.; Lokhande, C. D. Porous Polypyrrole Clusters Prepared by Electropolymerization for a High Performance Supercapacitor. J. Mater. Chem. 2012, 22, 3044-3052. (23) Cammarata, L.; Kazarian, S. G.; Salter, P. A.; Welton, T. Molecular States of Water in Room Temperature Ionic Liquids. Phys. Chem. Chem. Phys. 2001, 3, 5192-5200. (24) Song, Y.; Xu, J.-L.; Liu, X.-X. Electrochemical Anchoring of Dual Doping Polypyrrole on Graphene Sheets Partially Exfoliated From Graphite Foil for High-Performance Supercapacitor Electrode. J. Power Sources 2014, 249, 48-58. (25) Wenzel, R. N. Resistance of Solid Surfaces to Wetting by Water. Ind. Eng. Chem. 1936, 28, 988-994. (26) Wang, J.; Xu, Y.; Yan, F.; Zhu, J.; Wang, J. Template-Free Prepared Micro/Nanostructured

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Page 16 of 26

Page 17 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Polypyrrole with Ultrafast Charging/Discharging Rate and Long Cycle Life. J. Power Sources 2011, 196, 2373-2379. (27) Grote, F.; Lei, Y. A Complete Three-Dimensionally Nanostructured Asymmetric Supercapacitor with High Operating Voltage Window Based on PPy and MnO2. Nano Energy 2014, 10, 63-70. (28) Hou, Y.; Chen, L.; Liu, P.; Kang, J.; Fujita, T.; Chen, M. Nanoporous Metal Based Flexible Asymmetric Pseudocapacitors. J. Mater. Chem. A 2014, 2, 10910-10916. (29) Yu, P.; Li, Y.; Yu, X.; Zhao, X.; Wu, L.; Zhang, Q. Polyaniline Nanowire Arrays Aligned on Nitrogen-Doped Carbon Fabric for High-Performance Flexible Supercapacitors. Langmuir 2013, 29, 12051-12058. (30) Wang, S.; Pu, J.; Tong, Y.; Cheng, Y.; Gao, Y.; Wang, Z. ZnCo2O4 Nanowire Arrays Grown on Nickel Foam for High-Performance Pseudocapacitors. J. Mater. Chem. A 2014, 2, 5434-5440. (31) Xu, K.; Li, W.; Liu, Q.; Li, B.; Liu, X.; An, L.; Chen, Z.; Zou, R.; Hu, J. Hierarchical Mesoporous NiCo2O4@MnO2 Core–Shell Nanowire Arrays on Nickel Foam for Aqueous Asymmetric Supercapacitors. J. Mater. Chem. A 2014, 2, 4795-4802. (32) Zhou, C.; Zhang, Y.; Li, Y.; Liu, J. Construction of High-Capacitance 3D CoO@Polypyrrole Nanowire Array Electrode for Aqueous Asymmetric Supercapacitor. Nano Lett. 2013, 13, 2078-2085. (33) Tian, W.; Wang, X.; Zhi, C.; Zhai, T.; Liu, D.; Zhang, C.; Golberg, D.; Bando, Y. Ni(OH)2 Nanosheet @ Fe2O3 Nanowire Hybrid Composite Arrays for High-Performance Supercapacitor Electrodes. Nano Energy 2013, 2, 754-763. (34) Xia, H.; Zhu, D.; Luo, Z.; Yu, Y.; Shi, X.; Yuan, G.; Xie, J. Hierarchically Structured Co3O4@Pt@MnO2 Nanowire Arrays for High-Performance Supercapacitors. Sci. Rep. 2013, 3, 2978. (35) Song, Y.; Liu, T. Y.; Xu, X. X.; Feng, D. Y.; Li, Y.; Liu, X. X. Pushing the Cycling Stability Limit of Polypyrrole for Supercapacitors. Adv. Funct. Mater. 2015, 25, 4626-4632.

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Figures

Figure 1 SEM images (a-c) and FT-IR spectrum (d) of PPy NWAs.

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Figure 2 Growth of PPy NWAs on carbon cloth: carbon cloth (a), absorption of pyrrole and TsOH on surface of carbon fiber in carbon cloth (b), nucleation of PPy on surface of carbon fiber (c), PPy NWAs on surface of carbon fiber (d), carbon cloth with PPy NWAs (e).

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Figure 3 SEM images of PPy obtained in the presence of TsOH in different concentration (a-f), the insets show the contact angle of the polymers with water. TEM images of PPy nanowire obtained in the presence of 0.02 M (g) and 0.005 M (h) TsOH. Chronopotentiometric curves during pyrrole polymerization in the presence of 0, 0.005, 0.01, 0.02, 0.04 and 0.08 M TsOH, respectively (i).

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Figure 4 SEM images of PPy NWAs obtained at different current density (a-c), the insets show SEM images of PPy grown in phase II stage. Chronopotentiometric curve during pyrrole polymerization at different current density (d).

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Figure 5 CVs measured at 50 mV/s (a), galvanostatic charge-discharge profiles at 1 A/g (b) and Nyquist plots (c) of PPy obtained in the presence of TsOH in different concentrations; insets show the oxidative peak current density on the CVs (a), specific capacitance (b) and combined series resistance (c) of the polymer obtained in solutions containing TsOH in different concentrations. CVs measured at 50 mV/s (d), galvanostatic charge-discharge profiles (e) and Nyquist plots (f) of PPy obtained at different current densities; insets show the oxidative peak current density on the CVs (d), specific capacitance (e) and combined series resistance (f) of the polymer obtained at different current densities.

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Figure 6 Galvanostatic charge-discharge profiles of PPy NWAs at different current densities (a). Specific capacitance of PPy NWAs measured at different current densities (b). Ragone plots of PPy NWAs, together with those of other one-dimensional aligned pseudocapacitive material nanostructure arrays for comparison (c). Cyclic stability of PPy NWAs, inset shows profiles of the first and the 5000th galvanostatic charge-discharge cycle (d).

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Figure 7 Galvanostatic charge-discharge profiles of PPy NWAs//PPy NWAs at different current densities (a). Specific capacitance of PPy NWAs//PPy NWAs measured at different current densities (b). Ragone plots of PPy NWAs//PPy NWAs (c). Cyclic stability of PPy NWAs//PPy NWAs, inset shows profiles of the first and the 5000th galvanostatic charge-discharge cycles (d).

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Figure 8 Galvanostatic charge-discharge profiles (a) and cyclic stability (b) of PPy NWAs in the potential range of -0.8 ∼ 0.05 V and 0.05 ∼ 0.5 V, respectively.

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TOC graphic

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Ordered Polypyrrole Nanowire Arrays Grown on a Carbon Cloth

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