Monomer Ratio and the Washing Post-Treatment

Subscriber access provided by LOUISIANA STATE UNIV

Article

Effect of Oxidant/Monomer Ratio and Washing Post-treatment on Electrochemical Properties of Conductive Polymers Jinxing Deng, Xue Wang, Jinshan Guo, and Peng Liu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/ie501366x • Publication Date (Web): 08 Aug 2014 Downloaded from http://pubs.acs.org on August 22, 2014

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Industrial & Engineering Chemistry Research is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 28

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

Industrial & Engineering Chemistry Research

Effect of Oxidant/Monomer Ratio and Washing Post-treatment on Electrochemical Properties of Conductive Polymers Jinxing Deng, Xue Wang, Jinshan Guo, Peng Liu* State Key Laboratory of Applied Organic Chemistry and Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, China

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Tel./Fax: 86-931-8912582.

ACS Paragon Plus Environment

1


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

Page 2 of 28

Abstract Polyaniline (PANI) and polypyrrole (PPy) were prepared via the chemical oxidative polymerization with various oxidant/monomer initial mole ratios (O/M) in hydrochloric acid aqueous solution and washing with water or ethanol to investigate the effect of the O/M ratio and washing process on their electrochemical performance as electrode materials for supercapacitors. Their morphologies were characterized with transmission electron microscopy (TEM). And the electrochemical performance of the PANI and PPy electrodes were studied by cyclic voltammogram and galvanostatic charge/discharge tests. It was found that the electrical conductivities and specific capacitances of the polymers were mainly dependent on the O/M ratio. An additional post-treatment of washing was considered as an unfavorable processing with the decrease in yield, conductivity and capacitance, except for the partial enhancement of the cyclic stabilities. This understanding will lead to better design of conductive polymer-based electrode materials for supercapacitors.

Keywords: Conductive polymers; chemical oxidative polymerization; oxidant/monomer ratio; washing post-treatment; electrochemical properties


2

Page 3 of 28

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


INTRODUCTION

Conductive polymers, particularly polyaniline (PANI) and polypyrrole (PPy), are an attractive class of versatile materials for a variety of applications,1 such as solar cells,2 battery electrodes,3 electrochromic devices,4 electromagnetic shielding devices,5 sensors,6 and anticorrosion coatings,7 due to their advantageous properties including high doping-dedoping rate during charge-discharge process, high charge densities (compared with high surface carbon), color changes associated with their oxidation state, adjustable electro-magnetic parameters, high and reversible change of electrical conductivity (adjustable in a wide range by choosing different redox state or a doping/dedoping process), good environmental stability, low cost and density (compared with noble metal oxides), easy synthesis through chemical and electrochemical processing.8 Chemical oxidative polymerization is the most major method for producing conductive polymers with the advantage of being a simple technique capable of producing bulk quantities of these polymers (dispersion, powder, and coating), of which the synthesis conditions also play an important role in the chemical, physical, thermal, electrical, morphological, and mechanical properties of the conductive polymers.9,10 It is useful and necessary to develop a systematic investigation aimed at establishing the relations between the characteristics of the intrinsically conductive polymers and a wide range of preparation variables. The effect of the chemical synthesis conditions, such as reacting temperature,11 reacting time,12 stirring rate,13 dopant or oxidant nature and concentration,14 oxidant/monomer mole ratio (O/M),15 and electrolyte16 had been investigated. However, most of which were mainly focused on the yield, conductivity, molecular weight, morphology, degreed of crystalline, and thermal behavior. By now, there is


3


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

Page 4 of 28

few work related to the electrochemical characteristics, as the most important parameter of supercapacitors,10 while the conductive polymers-based supercapacitor electrodes have attracted considerable attention due to their high energy, high power, and low equivalent series resistance (ESR).17,18 The other interesting importance is the electrical conductivity of the conductive polymers, often being considered as a criterion for whether a specific morphology is of interest, and for how successful a particular synthesis method is. However, the effect of the moisture in the conducting polymers on the conduction process is still unclear. Kang et.al reported that the electrical conductivity of PPy could be largely enhanced by washed with organic solvent in comparison with water, since the organic solvent can remove most of the residual water of the polymers.19 Alix et.al reported that the water content played an important role in the electrical transport properties of the conductive polymers and their electrical conductivity increased when water molecules were absorbed by the polymers.20 Pinto et al believed that the presence of water could lead to additional charge delocalization, the conductivity decreased with increasing the annealing temperature, and then recovered after upon exposure to moisture.21 Recently, nano-structured conductive polymers (nanowires, nanofibers, nanotubes and nanorods) have attracted intense interest due to their small size and high surface area, resulting in the enhanced properties for optoelectronic nanodevices.22 These nano-structured conductive polymers can be fabricated with “soft templates” such as DNA,23 organic dopants,24 or surfactants,25 and “hard templates” such as MnO2 hollow hierarchical nanostructures26 and V2O5 nanofibers.27 Huang et al developed a general chemical route to prepare PANI nanofibers without any templates by using interfacial polymerization and fast-fixing reaction, which can prevent the secondary growth effectively.13 Moreover, Wan’s group have discovered a controllable and universal approach to synthesize the nanostructures of conducting polymers through in-situ


4

Page 5 of 28

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


doping polymerization in the presence of dopants, namely by the self-assembly of dopantmonomer salt.28 It is well known that the bulk and granular PANI can be easily obtained through the traditional chemical oxidative polymerization;29 meanwhile, it yields intrinsically a small portion of nanofibers.30 The aniline dimer cation-radicals could act as effective surfactants to shape the PANI morphology, assisted by the excess APS without using any surfactants and acid,31,32 However, the presence of excess APS may cause over-oxidation and degradation,33 as well as the lower doping level without any additional acid, would decreased the electrical conductivity. In the present work, the morphology, conductivity, and electrochemical performance of the conductive polymers synthesized under different O/M ratios were investigated as well as the effect of the post-treatment, in which process the obtained products were washed completely with water or ethanol. It was found that the morphology, conductivity, and electrochemical performance of the conductive polymers were mainly determined by the O/M mole ratio, while the washing post-treatment with ethanol could deteriorate their conductivity, but enhance slightly their cycling stability as electrode materials for supercapacitors.

EXPERIMENTAL METHODS

Materials. Pyrrole and aniline (Shanghai Zhongqin Chemical Reagent Co. Ltd, Shanghai, China) were freshly distilled under reduced pressure prior to use. Ammonium peroxodisulfate (APS) (analytical reagent grade, Tianjin Chemical Reagent Co., Tianjin, China) as an oxidant was used as received. All other reagents were analytical reagent and used without further purification. Doubly deionized water was used through all the processes.


5


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

Carbon

black

was

obtained

from

Yiping

Chemical

Factory,

Page 6 of 28

Shanghai,

China.

Polyvinylidenefluoride (PVDF) was received Funuolin New Chemical Materials Co. Ltd. Zhejiang, China. Stainless steel mesh (150 meshes) was rinsed with acetone and hydrochloric acid to clean its surface prior to prepare the electrodes. Chemical oxidative polymerization. Aniline or pyrrole (0.2 mol/L) was oxidized with various proportions of APS at 0~5 °C in 1.0 mol/L HCl for 12 h. Generally, aniline or pyrrole was firstly dissolved in 50 ml 1.0 mol/L HCl with magnetic stirring for 10 min, and then the pre-cooled APS as an oxidant (with the O/M ratio of 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, or 1.75, respectively) in 50 mL 1.0 mol/L HCl was added to the above mixture drop by drop within 20 min, followed with stirring for 12 h. Upon the addition of APS, the mixture turned first to blue, green and then to dark-green for aniline in a few minutes, while it changed quickly to black for pyrrole. The polymers were collected on a filter, rinsed with distilled water until the filtrate became colorless (denoted as PANI-w or PPy-w), half of which were centrifugal washed with ethanol till the supernatant became colorless (denoted as PANI-e or PPy-e). These products were dried under vacuum at 45 °C to constant weight. The final polymer samples were identified by the notation PANIr or PPyr, where r is the initial O/M ratio. Characterization. The PANI and PPy samples were characterized by transmission electron microscope (JEOL, Tokyo, Japan) operating at an accelerating voltage of 100kV. The samples were dispersed in ethanol by ultrasonication and dropped onto the Cu grids covered with a polymer film for analysis. Thermogravimetric analysis (TGA) was conducted by a Diamond TG Thermal Analyzer (PERKIN ELMER, USA) under nitrogen flows from room temperature to 800 °C with a heating rate of 10 °C/min at nitrogen atmosphere.


6

Page 7 of 28

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


The electrical conductivities of the compressed PANI and PPy samples were measured using a RTS-2 four-point probe conductivity tester (Guangzhou four-point probe Technology Co. Ltd., Guangdong, China) at ambient temperature. The round shaped pellets (with thickness of 0.500~1.000 mm, measured with vernier caliper) were prepared by subjecting the dry polymer powder to a pressure of about 15 MPa using a steel die in a hydraulic press. The data are presented as the average of at least three measurements. Electrochemical measurements were carried out on a CHI660B electrochemical work station (CHI, Shanghai) in a standard one compartment three electrode configuration cell containing 1.0 mol/L H2SO4 solution as electrolyte at room temperature, where a composite electrode as working electrode, a platinum plate as counter electrode, and an Hg/Hg2Cl2 electrode as reference electrode. The working electrodes were prepared by mixing the active materials, carbon black and polyvinylidenefluoride (PVDF) with mass ratio of 80:15:5 in N, N-dimethylformamide (DMF). Then the slurry was uniformly painted on stainless steel mesh (current collector) with area of about 0.25 cm2 using a spatula, and pressed for 1 min under 1.0 MPa after drying to achieved a sufficient mechanical strength.34,35 The amount of the conductive polymers on the electrode surface was obtained from the weight difference before and after loading. The electrochemical performance of the working electrode was characterized with cyclic voltammetry (CV) and galvanostatic charge–discharge. CV tests were carried out between -0.2 V and 0.8 V at 100 mV/s for 1000 cycles. Galvanostatic charge–discharge curves were measured at a constant current density of 1A/g. The specific capacitance (Cm) of the electrode was calculated from the galvanostatic charge/discharge, according the following equation: Cm =


7


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

Page 8 of 28

where i, t, ∆v, and m are the constant current (A), the discharge time (s), the total potential deviation (1V), and the weight of active materials (g), respectively.

RESULTS AND DISCUSSION

Morphological analysis. The TEM images of the PANI-e and PPy-e samples are given in Figures 1 and 2. The obtained PANI samples were mainly composed of amorphous globular particles with average diameter of about 100 nm, which were apt to aggregate and stack together, which was the intrinsic characteristic of the conventional chemical oxidative polymerization of aniline.30 Besides the irregular particles, a small portion of nanofibers and nanotubes appeared in Figure 1a, b and c at lower initial O/M ratios, since it is favorable for forming nanotubes at a low concentration of APS due to the slow polymerization rate, which provides enough time for micelles to prolong linearly to form nanotubes because of the rigid PANI chains.32 Stirring is also found to greatly favor the heterogeneous nucleation of PANI, causing the formation of bigger and agglomerated particles.36 In addition, it is interesting to obtain the nanorod-shaped PANI with the initial O/M ratio of 1.25, of which the surfaces are not smooth with asperities along the rods (Figure 1e). Increasing the initial O/M ratio to 1.75, the irregular particles dominated its morphology (Figure 1g). With a high concentration of APS, the micelles aggregated and stacked quickly to form the amorphous morphology. The micelles might be formed by the anilinium cations due to its low surface energy and the hydrophobic benzene ring might act as the templates to form the PANI nanostructures, and then aniline or anilinium molecules were polymerized in the micelle/water interface via the chemical oxidation by APS.37 As the polymerization proceeded, the micelles elongated to


8

Page 9 of 28

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


produce the tubes/rods or accreted to form the big particles,38 drove by π-π stacking interaction, hydrogen bond, and/or van der Waals' force.39

Figure 1. TEM images of the PANI-e samples: (a) PANI0.25, (b) PANI0.50, (c) PANI0.75, (d) PANI1.00, (e) PANI1.25, (f) PANI1.50, and (g) PANI1.75. Figure 2 represents the irregular morphology of PPy as badly agglomerated particles; it is difficult to predict the actual morphology and the definite particle size of a single particle. These aggregates might be resulted from the poor dissolution of pyrrole in water. However, the particles seemed to agglomerate more seriously with increasing the initial O/M ratio.40


9


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

Page 10 of 28

Figure 2. TEM images of the PPY-e samples: (a) PPy0.25, (b) PPy0.50, (c) PPy0.75, (d) PPy1.00, (e) PPy1.25, (f) PPy1.50, and (g) PPy1.75. Yielding analysis. Figure 3 depicts the relationship between the product yielding and the initial O/M ratios for the PANI and PPy samples, wherein they behave the similar tendency. The yield of PANI prepared with the increased O/M ratio showed a steady increase up to 1.25, which was just the stoichiometric peroxydisulfate/aniline ratio, tending to fall thereafter, which is consistent with the results reported previously.32,41 Based on the stoichiometry of the oxidation reaction, 1.25 mol APS is needed for the polymerization of 1 mol aniline into the emeraldine form of PANI. Therefore, the product yielding is dependent on the amount of oxidant until the monomer is completely consumed when the O/M ratio is 1.25, and starts to decrease owing to the overoxidation as the feeding ratio of the oxidant is further increased.3,42 In addition, the yield slightly over 100% within the experimental error may be due to the addition of counterions, such SO42- or HSO4- anions, may participate in the protonation and doping of PANI along with the chloride anions.43 On the other hand, the yields of the samples washed with ethanol were slightly lower than those washed only with water, because the low-molecular-weight organic intermediates or oligomers had been removed through dissolving in ethanol,32 at the same time, the reaction would yield


10

Page 11 of 28

more oligomers at a high oxidant concentration. The same trend was seen for the PPy samples except that its highest yield was achieved with the initial O/M ratio of 1.50.

80

(a)

100 PANI-w PANI-e

80

Yield(%)

100

Yield (%)

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


60

40

20

20

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

PPy-w PPy-e

60

40

0.2

(b)

0.2

0.4

0.6

O/M Ratio

0.8

1.0

1.2

1.4

1.6

1.8

O/M Ratio

Figure 3. The yield of the PANI (a) and PPy (b) samples synthesized under various oxidant/monomer molar ratios. TGA analysis. The thermal decomposition of the PANI and PPy samples was investigated due to the yielding dependence of the O/M ratio, and the results are shown in Figure 4. It revealed a common feature with a three-step mass loss for all samples. For the PANI samples (Figure 4a, b), the three-step mass loss is the evaporation of moisture and dedoping from the samples at ~150 °C, the cross-linking of PANI chains at 200-350 °C,44 and carbonization by dehydrogenation and deammonianation to break the crosslinking structure at 450-650 °C. Whereas they are the evaporation of moisture at ~150 °C, decomposition of the dopant and the oligomers at 150400 °C, and the degradation of main chains at 400 °C for the PPy samples (Figure 4c, d). The first mass loss is followed immediately by the second degradation stage for both polymer, and then the third stage begins after a zone of thermal stability (350-450 °C) for PANI, while PPy does not exhibit any stability zone in the DTG curves. Notice that the TGA curves of the PANI samples (Figure 4a, b) displayed sharper decompositions than the PPy samples (Figure 4 c, d) before 450 °C, which might be resulted


11


from the more badly aggregate of PPy (Figure 2), hindering the removal of the volatile decomposition products.45 However, after which PANI showed a higher remaining weight percent about 40 wt.% at 800 °C, while 20 wt.% remaining at most for PPy.

100

100

(a)

(b)

PANI0.25

PANI0.25 PANI0.50

90

PANI0.50

90

PANI0.75

PANI0.75

PANI1.50 PANI1.75

60

60

50

40

40

200

300

400

500

600

700

PANI1.75

70

50

100

PANI1.25 PANI1.50

Weight (%)

Weight (%)

PANI1.25 70

PANI1.00

80

PANI1.00

80

100

800

200

300

400

500

600

700

800

Temperature (Cal.)

Temperature (Cal.)

100 100

(c)

PPy0.25

(d)

PPy0.25

PPy0.50

PPy0.50

PPy0.75

80

PPy0.75

80

PPy1.00

PPy1.00

PPy1.25

PPy1.25 PPy1.50

60

Weight (%)

Weight (%)

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

Page 12 of 28

PPy1.75

40

PPy1.50

60

PPy1.75 40

20

20

0

0 100

200

300

400

500

600

700

800

100

200

300

400

500

600

700

800

Temperature (Cal.)

Temperature (Cal.)

Figure 4. TGA curves of the PANI-e (a), PANI-w (b), PPy-e (c) and PPy-w (d) samples synthesized under various O/M ratios. The inset depicts the DTG curve of the samples synthesized under the O/M ratio of 0.25. It is also found that the samples, synthesized under the O/M ratio of 0.75, remained the least carbonized residues, and those synthesized under the O/M ratio of 0.25 exhibited the best thermal stability, which might be explained by the formation of the more oligomers under the higher O/M ratios as showed in Figure 3. What’s more, the samples washed with ethanol displayed the better


12

Page 13 of 28

thermal stability due to the removal of low molecular species compared to those without this additional washing process. Electrical conductivity. The electrical conductivity of the PANI-w and PANI-e samples increased initially at low O/M ratio and then decreased after attaining maximum value at an optimum molar ratio of 0.75 (Figure 5a), similar with the previous work.33 In addition, the highest conductivity of the PANI-e is in agreement with the highest doping level as determined by TGA (Figure 4). It was found that a high concentration of oxidant may lead to the evident deterioration in electrical conductivity. This decrease in conductivity can be partially attributed to the degradation which produced the shorter conjugation length of the polymers.46 On the other hand, the conductivity decreased after washing with ethanol, and the decrease is noticeable at the middle values of the O/M ratio. It might be due to the removal of the oligomers and/or partial dedoping during the washing with ethanol, as the yielding analysis (Figure 3a). Since dopant ions are in dynamic equilibrium between the polymer chains and solvent, the polymer can be dedoped by solvents which are Lewis bases with respect to HCl (e.g. ethanol and water). It was reported that PANI could be deposed by dialysis against water. 47,48

16 14

20

(b)

(a)

PANI-w PANI-e

PPy-w PPy-e

12

15

Conductivity (S/cm)

Conductivity (S/cm)

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


10 8 6 4

10

5

2 0

0

0.2

0.4

0.6

0.8

1.0

1.2

O/M Ratio

1.4

1.6

1.8

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

O/M Ratio

Figure 5. Conductivity of the PANI (a) and PPy (b) samples as a function of oxidant/monomer molar ratio and different washing processes.


13


As for the PPy samples (Figure 5b), the conductivity of the PPy-w samples decreased with the increasing of the O/M ratios. Furthermore, the difference between the PPy-w and PPy-e samples decreased with increasing the O/M ratio. After being washed with ethanol, the conductivity of PPy0.25 decreased from about 18 S/cm to less than 12 S/cm, indicating the ethanol-washing had significant influence on the conductivity of PPy synthesized at lower O/M ratios, as described above for the PANI samples. Capacitance property. Figures 6 and 7 display the charge-discharge curves of the samples at a current density of 1 A/g in 1.0 mol/L H2SO4 solution. The sudden potential drop at the starting of discharge is due to internal resistance of materials and electrolytes, especially for PANI electrodes, and a linear variation of the time dependence of the potential indicates the doublelayer capacitance behavior and a slope variation of the time dependence of the potential indicates a typical pseudocapacitance behavior, which resulted from the fast Faradic reaction.49 In addition, the charge-discharge curves are deviated from the idealized triangular-shape, attributed to the redox reactions of PANI and PPy electrodes. It was also found that the charge times were longer than the discharge times, particularly for PANI electrodes, implying that the reversibility and Coulombic efficiency of PPy are better than PANI, and the PPy electrodes showed more capacitance than PANI except for the only one at APS/monomer ratio 1.75.

0.8

0.8

(a)

(b)

PANI0.25 PANI0.50 PANI0.75 PANI1.00 PANI1.25 PANI1.50 PANI1.75

0.6

Potential (V)

0.6

Potential (V)

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

Page 14 of 28

0.4 PANI0.25 PANI0.50 PANI0.75 PANI1.00 PANI1.25 PANI1.50 PANI1.75

0.2 0.0 -0.2 0

100

200

0.4 0.2 0.0 -0.2

300

400

500

600

0

100

200

300

400

500

600

700

Time (s)

Time (s)


14

Page 15 of 28

(c)

Specific capacitance (F/g)

300

PANI-w PANI-e

270 240 210 180 150 0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

O/M Ratio

Figure 6. The galvanostatic charge-discharge curves of the PANI-e (a) and PANI-w (b) samples at a current density of 1 A/g, and the specific capacitance of PANI as a function of APS/aniline mole ratio (c).

0.8

(a)

PPy0.25 PPy0.50

0.6

PPy1.00

0.4

PPy1.25 PPy1.50

0.2

(b)

PPY0.25 PPY0.50

0.6

PPy0.75

Potential (V)

0.8

Potential (V)

PPy1.75

PPY0.75 PPY1.00

0.4

PPY1.25 PPY1.50 PPY1.75

0.2

0.0

0.0

-0.2

-0.2 0

200

400

600

800

0

200

Time (s)

400

600

800

Time (s)

400

(c)

PPY-w PPY-e

350

Specific capacitance (F/g)

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


300 250 200 150 100 0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

O/M Ratio

Figure 7. The galvanostatic charge-discharge curves of the PPy-e (a) and PPy-w (b) samples at a current density of 1 A/g, and the specific capacitance of PPy as a function of O/M ratio (c).


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

Page 16 of 28

The fast potential drop (about 0.05 to 0.2 V) at the starting of discharge is due to internal resistance of materials and electrolytes, which could block the diffusion of ions from solution to the active materials, and the IR drops of the PANI samples are obviously higher than those of the PPy samples, according with the result that the PPy electrodes showed the higher capacitance than the PANI electrodes except for the only one with O/M ratio of 1.75. The capacitance of the PANI-w and PPy-w samples exhibited two peak values as shown in Figure 6c and Figure 7c, while it increased to the maximum value 358 F/g and then decreased for PPy-e as shown in Figure 7c. It is well known that the capacitance is not only depended on the conductivity of electrode materials, but also their morphologies including specific surface area and pore size.50 It means that the specific surface area of the electrode materials also plays a key role in electrolyte ions transport and therefore affects the utilization of the electrode materials.51 Furthermore, the removal of the oligomers by washing with ethanol might result to tougher surfaces for the samples. However, almost all the specific capacitance of the conductive polymers after being washed with ethanol (PANI-e and PPy-e) were lower than those of the samples only being washed with water (PANI-w and PPy-w), which might be ascribed to the reason that the larger pore diameter was in favor of the penetration of electrolyte ions into the electrode, causing the enhancement of specific capacitance in spite of the smaller surface area.52 The cyclic voltammogram curves of the PANI0.50 and PPy0.50 at different scan rates in 1.0 M H2SO4 solution is shown in Figure 8. With an increase of scan rate, the anodic current shifts toward positive and the cathodic current shifts toward negative. Further, the CV curves of PPy has shown the typical features of capacitive behavior synchronizing both redox capacitive and double layer features.53 No evident redox peaks of conducting polymers were displayed in all the case, of which the reason might be that the highly disorder and aggregate structure of PANI and PPy would reduce the electrochemical reaction activity on the chains of polymers.54,55 It can be


16

Page 17 of 28

seen that the area surrounded by CV curves for PPy electrode are larger than that of the PANI electrode, indicating the more capacitance of PPy, which is in accordance with the result from charge-discharge tests (Figures 6 and 7).

2.5

12

(a) 2.0

10

1.5

8

4

0.5

Current (A/g)

Current (A/g)

(b)

6

1.0

0.0 -0.5

5 mv/s 10 mv/s 20 mv/s 50 mv/s 100mv/s

-1.0 -1.5

2 0


-2 -4 -6 -8

-2.0 -0.2

0.0

0.2

0.4

0.6

-10 -0.2

0.8

0.0

Potential (V)

0.2

0.4

0.6

0.8

Potential (V)

0.8

8

(c)

(d)

0.6

6

0.4 4

0.2 2

Current (A/g)

Current (A/g)

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


0.0 -0.2


-0.4 -0.6 -0.8 -1.0 -0.2

0.0

0.2

0.4

0.6

0 -2


-4 -6

0.8

-8 -0.2

0.0

Potential (V)

0.2

0.4

0.6

0.8

Potential (V)

Figure 8. The rate-dependent CV curves of the PANI0.50-e (a) and PANI0.50-w (b), PPy0.50-e (c) and PPy0.50-w (d) electrodes over a wide range of scan rates. Cyclic stability. The long-term cyclic stability of the electrodes were evaluated via repeating CV tests in 1.0 mol/L H2SO4 electrolyte at a scan rate of 100 mV/s for 1000 cycles and the results are shown in Figure 9. The capacitance retention of the PANI-e samples, PANI0.25-w, PANI0.50-w, and PANI1.50-w electrodes sharply decreased after the first 500 circles compared to the initial


17


value, and kept nearly the same in the subsequent 500 circles. The initial decline may be related to the shrinking and swelling of the nanostructures during the intercalating/deintercalating process of electrolyte ions and electron as well as the surface oxidation of the conducting polymer, which may be expelled from the electrode.56 However, the other PANI-w electrodes showed some different cyclic stability behaviors. Note that the capacitance retention increased to the maximum value at about 20 cycles, which was similar to the cyclic stability curves of the PPy-w electrodes (Figure 9b). What's more, a specific capacity fade of equal to or less than 10% was observed after 200 cycles or even 1000 cycles for the PPy-w electrodes, indicating the better cyclic ability of those PPy-w electrodes, compared to the PANI1.50-e electrode with the best stability among the PANI-e electrodes (remaining 67%). As shown in Figure 9b, the capacitance retention of some samples increased gradually for about initial 100 cycles due to the further activation process by doping with H2SO4,57 and then decreased steady. Furthermore, this increase in the initial cycles may be also attributed to the dense structure of original electrode materials, which hinder the electrolyte ions transfer during intercalating/deintercalating process, but they became looser after several cycles.58

(a)

120

(b)

150

PANI0.25-e

110

PPy0.25-e

140

PANI0.50-e PANI0.75-e PANI1.00-e

100

PANI1.25-e PANI1.50-e

90

PANI1.75-e PANI0.25-w

80

PANI0.50-w PANI0.75-w

70


Capacitance retention (%)


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

Page 18 of 28

PPy0.50-e PPy0.75-e PPy1.00-e

130

PPy1.25-e PPy1.50-e

120

PPy1.75-e PPy0.25-w

110

PPy0.50-w PPy0.75-w PPy1.00-w

100

PPy1.25-w

PANI1.50-w

60

PANI1.75-w

50

PPy1.50-w

90

PPy1.75-w

80 0

200

400

600

800

1000

1200

0

200

400

600

800

1000

1200

Cycle number

Cycle number

Figure 9. Variation of capacitance retention as a function of cycle number for the PANI (a) and PPy (b) electrodes in the 1.0 mol/L H2SO4 electrolyte at a scan rate of 100 mV/s.


18

Page 19 of 28

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


The capacitance retention of samples should relative to the maximum specific capacitance instead of the original value in view of the further activation process. It is found that PANI1.0-w and PPy1.0-w exhibited the best cyclic stability, having 95% of the maximum specific capacitance after 1000 cycles, and the PANI0.50-e and PPy0.75-e displayed the worst stability among the PANI and PPy samples, respectively. Therefore, the O/M ratio of 1.0 seems to be the optimum condition for both the polymers. On the other hand, the further activation process of electrodes is especially significant in the samples without additional washing with ethanol. In addition, the smaller difference of the cyclic stability is observed between the samples washed with ethanol. The exactly role of the additional washing seem to ambiguous that some PPy-e electrodes exhibit better cyclic stability compared to the corresponding PPy-w, while most of the PANI-w show a significantly improved ability compared to the PANI-e with the same O/M ratio. In other words, the negative effect of the additional washing treatment with ethanol on the cyclic stability of PANI is more obvious than that on PPy.

CONCLUSIONS

The oxidative polymerization of aniline and pyrrole was conducted by varying the feed ratio of ammonium peroxydisulfate in hydrochloric acid aqueous solutions. The morphology of both PANI and PPy were recorded by TEM technique; it was found that the amorphous particles dominated the morphology of both polymers besides some nano-fibers/tubes/rods appeared in PANI and the morphology of PPy was independent on the feeding ratio. The yields of PANI and PPy increased with the oxidant/monomer molar (O/M) ratio increased from 0.25 to 1.50. The washing condition also had been investigated in consideration of conductivity, specific


19


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

Page 20 of 28

capacitance, and cyclic stability. The maximum conductivity of was 10.1 S/cm of the PANI-e and 9.1 S/cm of the PPy-e at the same O/M ratio 0.75, and an additional washing treatment was benefic for the conductivity. In addition, the maximum specific capacitance of all samples were achieved when the O/M ratio of 0.50. The improvement of cycling stability of both polymers after being washed with ethanol was ascribed to the remove of the oligomers. After 1000 cycles, about 89.5% of the original capacitance was remained for the PPy0.50-e, which also exhibited the highest specific capacitance of 358 F/g, indicating that 0.50 is the optimal O/M ratio for PPy, and the PANI1.25-w electrode showed a better comprehensive performance with a high capacity retention (left 92 % finally) and a moderate capacitance 239 F/g. The additional washing treatment is harmful to the yield, conductivity and capacitance, except for the partially improved stability of PPy and PANI. Therefore, this present work is helpful to adopt a specific processing according to the desired properties of the conductive polymers.

AUTHOR INFORMATION Corresponding Author. * Corresponding Author. Tel./Fax: 86 0931 8912582. Email: [email protected]. Notes. The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was supported by the Natural Science Foundation of Gansu Province (Grant No. 1107RJZA213), and the Fundamental Research Funds for the Central Universities (No. lzujbky2011-21 and lzujbky-2013-237).


20

Page 21 of 28

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


REFERENCES (1) Lu, X. F.; Zhang, W. J.; Wang, C.; Wen, T. C.; Wei, Y. One-dimensional Conducting Polymer Nanocomposites: Synthesis, Properties and Applications. Prog. Polym. Sci. 2011, 36, 671. (2) Tai, Q. D.; Chen, B. L.; Guo, F.; Xu, S.; Hu, H.; Sebo, B.; Zhao, X. Z. In Situ Prepared Transparent Polyaniline Electrode and Its Application in Bifacial Dye-Sensitized Solar Cells. ACS Nano 2011, 5, 3795. (3) Fu, Z. H.; Wei, Z.; Lin, X. J.; Huang, T.; Yu, A. S. Polyaniline Membranes as Waterproof Barriers for Lithium Air Batteries. Electrochim. Acta 2012, 78, 195. (4) Ge, D. T.; Yang, L. L.; Tong, Z. Q.; Ding, Y. B.; Xin, W. H.; Zhao, J. P.; Li, Y. Ion Diffusion and Optical Switching Performance of 3D Ordered Nanostructured Polyaniline Films for Advanced Electrochemical/Electrochromic Devices. Electrochim. Acta 2013, 104, 191. (5) Wang, Y. Y.; Jing, X. L. Intrinsically Conducting Polymers for Electromagnetic Interference Shielding. Polym. Adv. Technol. 2005, 16, 344. (6) Huang, J. X.; Virji, S.; Willer, B. H.; Kaner, R. B. Polyaniline Nanofibers: Facile Synthesis and Chemical Sensors. J. Am. Chem. Soc. 2003, 125, 314. (7) Peng, C. W.; Chang, K. C.; Weng, C. J.; Lai, M. C.; Hsu, C. H.; Hsu, S. C.; Hsu, Y. Y.; Hung, W. I.; Wei, Y.; Yeh, J. M. Nano-casting Technique to Prepare Polyaniline Surface with Biomimetic Superhydrophobic Structures for Anticorrosion Application. Electrochim. Acta 2013, 95, 192. (8) MacDiarmid, A. G. Polyaniline and Polypyrrole: Where Are We Headed? Synth. Met. 1997, 84, 27.


21


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

Page 22 of 28

(9) Cortés, M. T.; Sierra, E. V. Effect of Synthesis Parameters in Polyaniline: Influence on Yield and Thermal Behavior. Polym. Bull. 2006, 56, 37. (10)

Ko, J. M.; Rhee, H. W.; Park, S. M.; Kim, C. M. Morphology and Electrochemical

Properties of Polypyrrole Films Prepared in Aqueous and Nonaqueous Solvents. J. Electrochem. Soc. 1990, 137, 905. (11)

Stejskal, J.; Riede, A.; Helmstedt, M. The effect of Polymerization Temperature on

Molecular Weight, Crystallinity, and Electrical Conductivity of Polyaniline. Synth. Met. 1998, 96, 55. (12)

Mayers, R. E. Chemical Oxidative Polymerization as a Synthetic Route to Electrically

Conducting Polypyrroles. J. Electr. Mater. 1986, 15, 61. (13)

Huang, J. X.; Kaner, R. B. Nanofiber Formation in the Chemical Polymerization of

Aniline: A Mechanistic Study. Angew. Chem. Int. Ed. 2004, 43, 5817. (14)

Sinha, S.; Bhadra, S.; Khastgir, D. Effect of Dopant Type on the Properties of Polyaniline.

J. Appl. Polym. Sci. 2009, 112, 3135. (15)

Blinova, N. V.; Stejskal, J.; Trchová, M. Polyaniline and Polypyrrole: A Comparative

Study of the Preparation. Eur. Polym. J. 2007, 43, 2331. (16)

Sbaite, P.; Huerta-Vilca, D.; Barbero, C.; Miras, M. C.; Mptheo, A.J. Effect of Electrolyte

on the Chemical Polymerization of Aniline. Eur. Polym. J. 2004, 40, 1445. (17)

Mastragostino, M.; Arbizzani, C.; Soavi, F. Conducting Polymers as Electrode Materials

in Supercapacitors. Solid State Ionics 2002, 148, 493. (18)

Snook, G. A.; Kaob, P.; Best, A. S. Conducting-polymer-based Supercapacitor Devices

and Electrodes. J. Power Source 2011, 196, 1.


22

Page 23 of 28

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


(19)

Kang, H. C.; Geckeler, K. E. Enhanced Electrical Conductivity of Polypyrrole Prepared

by Chemical Oxidative Polymerization: Effect of the Preparation Technique and Polymer Additive. Polymer 2000, 41, 6931. (20)

Alix, A.; Lemoine, V.; Nechtschein, M.; Travers, J. P. Water Absorption Study in

Polyaniline. Synth. Met. 1989, 29, 457. (21)

Pinto, N. J.; Shah, P. D.; Kahol, P. K. Conducting State of Polyaniline Films:

Dependence on Moisture. Phys. Rev. B1996, 53, 10690. (22)

Long, Y. Z.; Li, M. M.; Gu, C. Z.; Wan, M. X.; Duvail, J. L.; Liu, Z. W.; Fan, Z. Y.

Recent Advances in Synthesis, Physical Properties and Applications of Conducting Polymer Nanotubes and Nanofibers. Prog. Polym. Sci. 2011, 36, 1415. (23)

Ma, Y. F.; Zhang, J. M.; Zhang, G. J.; He, H. X. Polyaniline Nanowires on Si Surfaces

Fabricated with DNA Templates. J. Am. Chem. Soc. 2004, 126, 7097. (24)

Zhang, L.; Wan, M. Self-Assembly of Polyaniline—From Nanotubes to Hollow

Microspheres. Adv. Funct. Mater. 2003, 13, 815. (25)

Liu, Z.; Zhang, X. Y.; Poyraz, S.; Surwade, S. P.; Manohar, S. K. Oxidative Template for

Conducting Polymer Nanoclips. J. Am. Chem. Soc. 2010, 132, 13158. (26)

Fei, J. B.; Cui, Y.; Yan, X. H.; Yang, Y.; Wang, K. W.; Li, J. B. Controlled Fabrication of

Polyaniline Spherical and Cubic Shells with Hierarchical Nanostructures. ACS Nano 2009, 3, 3714. (27)

Zhang, X. Y.; Manohar, S. K. Narrow Pore-Diameter Polypyrrole Nanotubes. J. Am.

Chem. Soc. 2005, 127, 14156. (28)

Wan, M. A Template-Free Method towards Conducting Polymer Nanostructures. Adv.

Mater. 2008, 20, 2926.


23


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

(29)

Page 24 of 28

Avlyanov, J. K.; Josefowicz, J. Y.; MacDiarmid, A. G. Atomic Force Microscopy Surface

Morphology Studies of ‘In Situ’ Deposited Polyaniline Thin Films. Synth. Met. 1995, 73, 205. (30)

Huang, J. X.; Kaner, R. B. A General Chemical Route to Polyaniline Nanofibers. J. Am.

Chem. Soc. 2004, 126, 851. (31)

Chiou, N. R.; Lee, L. J.; Epstein, A. J. Self-Assembled Polyaniline Nanofibers/Nanotubes.

Chem. Mater. 2007, 19, 3589. (32)

Ding, H. J.; Shen, J. Y.; Wan, M. X.; Chen, Z. J. Formation Mechanism of Polyaniline

Nanotubes by a Simplified Template-Free Method. Macromol. Chem. Phys. 2008, 209, 864. (33)

Armes, S. P.; Miller, J. F. Optimum Reaction Conditions for the Polymerization of

Aniline in Aqueous Solution by Ammonium Persulphate. Synth. Met. 1988, 22, 385. (34)

Gao, Z.; Yang, W. L.; Liu, L. H. A New Partially Reduced Graphene Oxide

Nanosheet/Polyaniline Nanowafer Hybrid as Supercapacitor Electrode Material. Energy Fuel 2013, 27, 568. (35) and

Tsay, K. C.; Zhang, L.; Zhang, J. J. Effects of Electrode Layer Composition/Thickness Electrolyte Concentration on Both Specific Capacitance and Energy Density of

Supercapacitor. Electrochim. Acta 2012, 60, 428. (36)

Li, D.; Kaner, R. B. Shape and Aggregation Control of Nanoparticles: Not Shaken, not

Stirred. J. Am. Chem. Soc. 2006, 128, 968. (37)

Zhang, Z. M.; Wei, Z. X.; Wan, M. X. Nanostructures of Polyaniline Doped with

Inorganic Acids. Macromolecules 2002, 35, 5937. (38)

Harada, M.; Adachi, M. Surfactant-Mediated Fabrication of Silica Nanotubes. Adv. Mater.

2000, 12, 839.


24

Page 25 of 28

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


(39)

Boal, A. K.; Ilhan, F.; DeRouchey, J. E.; Albrecht, T. T.; Russell, T. P.; Rotello, V. M.

Self-assembly of Nanoparticles into Structured Spherical and Network Aggregates. Nature 2000, 404, 746. (40)

Blswas, M.; Roy, A. Thermal, Stability, Morphological, and Conductivity Characteristics

of Polypyrrole Prepared in Aqueous Medium. J. Appl. Polym. Sci. 1994, 51, 1575. (41)

Stejskal, J.; Omastova, M.; Fedorova, S.; Prokes, J.; Trchova, M. Polyaniline and

Polypyrrole Prepared in the Presence of Surfactants: A Comparative Conductivity Study. Polymer 2003, 44, 1353. (42)

Stejskal, J.; Kratochvíl, P. The Formation of Polyaniline and the Nature of Its Structures.

Polymer 1996, 37, 367. (43)

Stejskal, J.; Gilbert, R. G. Polyaniline. Preparation of a Conducting Polymer. Pure Appl.

Chem. 2002, 74, 857. (44)

Oka, O.; Kiyohara, O.; Morita, S.; Yoshino, K. Electrical and Mechanical Properties of

Crosslinked Polyanilines. Synth. Met. 1993, 55, 999. (45)

Cassignol, C.; Olivier, P.; Ricard, A. Influence of the Dopant on the Polypyrrole Moisture

Content: Effects on Conductivity and Thermal Stability. J. Appl. Polym. Sci. 1998, 70, 1567. (46)

Kapil, A.; Taunk, M.; Chand, S. Preparation and Characterization of Chemically

Synthesized Poly(N-methylaniline). Synth. Met. 2009, 159, 1267. (47)

Huang, J. X.; Virji, S.; Weiller, B. H.; Kaner, R. B. Polyaniline Nanofibers: Facile

Synthesis and Chemical Sensors. J. Am. Chem. Soc. 2003, 125, 314. (48)

Sutar, D. S.; Padma, N.; Aswal, D. K.; Deshpande, S. K.; Gupta, S. K.; Yakhmi, J. V.;

Preparation of Nanofibrous Polyaniline Films and Their Application as Ammonia Gas Sensor. Sensors and Actuators B 2007, 128, 286.


25


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

(49)

Page 26 of 28

Dubal, D. P.; Patil, S. V.; Gund, G. S.; Lokhande, C. D. Polyaniline–polypyrrole

Nanograined Composite via Electrostatic Adsorption for High Performance Electrochemical Supercapacitors. J. Alloy Compd. 2013, 552, 240. (50)

Tsay, K. C.; Zhang, L.; Zhang, J. J. Effects of Electrode Layer Composition/Thickness

and

Electrolyte Concentration on Both Specific Capacitance and Energy Density of

Supercapacitor. Electrochim. Acta 2012, 60, 428. (51)

Lee, J. G.; Kim, J. Y.; Kim, S. H. Effects of Microporosity on the Specific Capacitance of

Polyacrylonitrile-based Activated Carbon Fiber. J. Power. Sources 2006, 160, 1495. (52)

Muthulakshmi, B.; Kalpana, D. Electrochemical Deposition of Polypyrrole for Symmetric

Supercapacitors. J. Power. Sources 2006, 158, 1533. (53)

Zou, W. Y.; Wang, W.; Yin, Y. S. Supercapacitive Properties of Hybrid Films of

Manganese Dioxide and Polyaniline Based on Active Carbon in Organic Electrolyte. J. Power. Sources 2010, 195, 7489. (54)

Qu, L. T.; Shi, G. Q.; Yuan, J. Y.; Han, G. Y. Preparation of Polypyrrole Microstructures

by Direct Electrochemical Oxidation of Pyrrole in an Aqueous Solution of Camphorsulfonic Acid. J. Electroanal. Chem. 2004, 561, 149 (55)

Wang, Y. G.; Li, H. Q.; Xia, Y. Y. Ordered Whiskerlike Polyaniline Grown on the

Surface of Mesoporous Carbon and Its Electrochemical Capacitance Performance. Adv. Mater. 2006, 18, 2619. (56)

He, X. P.; Gao, B.; Wang, G. B.; Wei, J. T.; Zhao, C. A New Nanocomposite: Carbon

Cloth Based Polyaniline for an Electrochemical Supercapacitor. Electrochim. Acta 2013, 11, 210.


26

Page 27 of 28

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


(57)

Zhang, D. C.; Zhang, X.; Chen, Y.; Ma, Y. W. Enhanced Capacitance and Rate

Capability of Graphene/Polypyrrole Composite as Electrode Material for Supercapacitors. J. Power Source 2011, 196, 5990. (58)

Zhang, H. R.; Wang, J. X.; Chen, Y. Y.; Wang, Z.; Wang, S. C. Long-term Cycling

Stability of Polyaniline on Graphite Electrodes Used for Supercapacitors. Electrochim. Acta 2013, 105, 69.


27


For Table of Contents Only

(a)

120

(b)

150

PANI0.25-e

110

PPy0.25-e

140

PANI0.50-e PANI0.75-e PANI1.00-e

100

PANI1.25-e PANI1.50-e

90

PANI1.75-e PANI0.25-w

80


70




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

Page 28 of 28

PPy0.50-e PPy0.75-e PPy1.00-e

130

PPy1.25-e PPy1.50-e

120

PPy1.75-e PPy0.25-w

110

PPy0.50-w PPy0.75-w PPy1.00-w

100

PPy1.25-w

PANI1.50-w

60

PANI1.75-w

50

PPy1.50-w

90

PPy1.75-w

80 0

200

400

600

800

1000

1200

0

200

400

600

800

1000

1200

Cycle number

Cycle number


28

Monomer Ratio and the Washing Post-Treatment

Recommend Documents