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High performance electrochemical supercapacitor from electrochemically synthesized nanostructured polyaniline
Materials Letters 60 (2006) 1466 – 1469 www.elsevier.com/locate/matlet
High performance electrochemical supercapacitor from electrochemically synthesized nanostructured polyaniline Vinay Gupta a,b,⁎, Norio Miura a a
Art, Science and Technology Center for Cooperative Research, Kyushu University, Kasuga-shi, Fukuoka 816-8580, Japan b Japan Science and Technology Agency, Saitama, 332-0012, Japan Received 12 September 2005; accepted 15 November 2005 Available online 7 December 2005
Abstract Polyaniline nanowires were electrochemically deposited on stainless steel electrode at the potential of 0.75 V vs. SCE and characterized by cyclic voltammetry in 1 M H2SO4 electrolyte for supercapacitive properties. A high specific capacitance of 775 F g− 1 was obtained at the sweep rate of 10 mV s− 1. A long-term cyclic stability of the polyaniline nanowires demonstrated its implications for the high performance supercapacitors. © 2005 Elsevier B.V. All rights reserved. Keywords: Polyaniline; Deposition; Nanowire; Cyclic voltammetry; Supercapacitor
Electrochemical supercapacitors are the charge-storage devices having high power density and long cyclic life [1–5]. The increasing pollution due to electrical vehicles and explosive growth of portable electronic devices have pushed the development of high performance supercapacitors as the urgent requirement. Supercapacitors store energy in the form of charge at the electrode/electrolyte interface and can be divided into two categories: (i) redox supercapacitors, in which the pseudocapacitance arises from faradic reactions occurring at the electrode interface and (ii) electric double layer capacitors (EDLCs), in which the capacitance arises from the charge separation at the electrode/electrolyte interface. The main materials that have been studied for the supercapacitor electrode are (i) carbons, (ii) metal oxides and (iii) polymers. The polymers are considered the most promising material in the supercapacitors. Among the polymers, such as polymethyl methacrylate (PMMA) [6], p-phenylenevinylene (PPV) [7], polypyrrole (PPy) [8–10] and polyaniline (PANI) [11–13], polyaniline is considered the most promising material
⁎ Corresponding author. KASTEC, Kyushu University, Kasuga-shi, Fukuoka 816-8580, Japan. Tel./fax: +81 92 583 7886. E-mail address: [email protected] (V. Gupta). 0167-577X/$ - see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.11.047
in the supercapacitors due to its high capacitive characteristics, low cost and ease of synthesis. The materials in the nano-size form with high surface area and high porosity give the best performances as the electrode materials for supercapacitors because of their distinctive characteristics of conducting pathways, surface interactions, and nanoscale dimensions. Therefore, the synthesis and the capacitive characterization of the high surface area nanomaterials such as nanotubes, nanowires, [14–16] etc. have been carried out extensively in the past few years. Consequently, different indirect methods were used to synthesized nanosized polyaniline, such as template synthesis [17], self-assembly [18], emulsions [19] and interfacial polymerization [20]. However, such methods require relatively large amounts of surfactants, which are rather tedious to recycle after polymerization, and it is difficult to attach nanosized polyaniline onto a substrate without involving large contact resistance. Therefore nanosized polyaniline synthesized by such methods is not suitable for supercapacitors applications. The best way is direct deposition of the nanostructured polyaniline onto a substrate electrode. In the present work, for the first time, we have performed cyclic votammetric measurements of the polyaniline nanowires electrochemically deposited directly on the stainless steel electrode for supercapacitor application.
V. Gupta, N. Miura / Materials Letters 60 (2006) 1466–1469
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Fig. 3. X-ray diffraction pattern of the original polyaniline nanowires.
Fig. 1. (a) and (b) SEM images of the polyaniline nanowires at different magnification.
The polyaniline was potentiostatically deposited on to 1 × 1 cm stainless-steel plates (SS) (grade 304, 0.2 mm thick) at 0.75 V vs. SCE. Research grade SS was obtained from the Nilaco® Corporation. Before the deposition, the SS was polished with emery paper to a rough finish, washed free of emery particles and then air-dried. The electrochemical deposition was performed using auto-lab® PGSTAT 30 instrument (Eco chemie, Netherlands) connected to a three-electrode cell. The three-electrode configuration contains platinum (Pt) as the counter electrode, saturated calomel electrode (SCE) as the reference electrode and SS as the working electrode. An electrolyte solution of 1 M H2SO4 + 0.05 M polyaniline was used for the electrochemical deposition of polyaniline nanowires on the SS electrodes. Subsequent to the deposition, the electrode was washed in distilled water and stirred by using a magnetic paddle. Thereafter, the electrodes were dried in oven at 40 °C for a day. The weight of the electrochemically deposited polyaniline was measured by means of Sartorius
Fig. 2. (a) and (b) Schematics of the possible growth process of the polyaniline nanowires.
microbalance (Model BP211D). The microstructure and the thickness of the deposit were evaluated by means of JEOL scanning electron microscope (FE-SEM, JEOL, JSM-6340F). The X-ray diffraction pattern was obtained by means of Rigaku X-ray diffractometer (model R1NT2100) using CuKα radiations. The photospectra was obtained by means of Rigaku UV– vis-NIR spectrophotometer (model ultraspec 3300 pro). The cyclic voltammetric measurements were performed in 1 M H2SO4 solution. Fig. 1 shows the SEM images of the polyaniline nanowires formed after 10 min deposition time. The diameter of the nanowires is in the range of 30∼60 nm. The thickness and the size of the nanowire film is ∼20 μm and 1 × 1 cm, respectively. The nanowire's network is highly porous with interconnectivity. A possible growth process of such nanowires is proposed as shown in Fig. 2(a) and (b). The polyaniline nanowires are expected to growth via seedling growth process, in which further polyaniline is deposited on the initially deposited nanosized granules (Fig. 2(a)). As the deposition progress, an aligned nanowire network is formed (Fig. 2(b)). A further deposition results in extended length and in the misalignment of nanowires and cross-links are formed [16]. Fig. 3 shows the X-ray diffraction spectra of the polyaniline nanowires. A very broad peak was observed centered at 2θ
Fig. 4. UV–vis-NIR spectra of polyaniline nanowires in dedoped state in NMP solution.
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Fig. 5. Cyclic voltammograms of polyanile nanowires at different sweep rates in 1 M H2SO4 electrolyte.
∼19° with a shoulder at 2θ∼26°. This suggests that the nature of the nanowires is amorphous. Fig. 4 shows the UV/visible photo spectra of the polyaniline nanowires in the dedoped state in N-methyl-2-pyrrolidone (NMP) solution. Before obtaining the photospectra, the polyaniline nanowires were washed in 0.1 M NH4OH solution. In this process, original green polyaniline becomes blue-purple, indicating that the doped emeraldine form has been deprotonated to emeraldine base. A few drops of this base formed a clear blue solution in the NMP, giving UV–visNIR absorbance photospectra with maxima at 638 and 332 nm,
Fig. 7. Cyclic-life data of the polyaniline nanowires capacitor. The specific capacitance was calculated for the cyclic voltammetry at the sweep rate of 100 mV s− 1 in 1 M H2SO4 electrolyte.
in excellent agreement with the literature results for indirectly prepared polyaniline nanostructures [21]. Fig. 5 shows the cyclic voltammogram of polyaniline nanowires/SS electrode in 1 M H2SO4 electrolyte in the potential range of 0 and 0.7 V vs. SCE. The near rectangularshaped cyclic voltammograms (CV) at low scan rate and high overall current suggests the highly capacitive behavior of the polyaniline nanowires. The CVs were also recorded in the same electrolyte with bare SS electrode, but no capacitive behavior was observed. Hence the capacitive behavior of polyaniline nanowires/SS electrode is entirely due to polyaniline nanowires. The CV current densities and the calculated specific capacitance values are shown in Fig. 6(a) and (b), respectively. The specific capacitance (SC) value of 775 F g− 1 was obtained at the scan rate of 10 mV s− 1 whereas the SC value of 562 F g− 1 was obtained at the high scan rate of 200 mV s− 1. This decrease of 25% in the specific capacitance at high scan rates is much lower than in the case of metal oxides where decrease of 50∼80% was reported between 10 and 200 mV s− 1 [22]. Moreover the CV current increases linearly with the increase in the scan rate as shown in Fig. 6 (a). This implies highly stable supercapacitive characteristics of the polyaniline nanowires. Fig. 7 shows the cyclic stability of the polyaniline nanowires at the sweep rate of 100 mV s− 1 for 1500 cycles. There is a small decrease in the specific capacitance value in the first 100 cycles and thereafter the specific capacitance remains almost constant. The decrease in the specific capacitance was 8% in the first 500 cycles and 1% in the subsequent 1000 cycles, indicating high stability of the electrode for long cyclic life. Acknowledgements
Fig. 6. (a) Cyclic voltammetric current density of polyaniline nanowires versus applied scan rate and (b) specific capacitance of polyaniline nanowires calculated from CV vs. the scan rate.
This present work was supported by Japan Science and Technology (JST) agency through “Core research for Evolution Science and Technology (CREST)” under the project “Development of advanced nanostructured materials for energy conversion and storage”.
V. Gupta, N. Miura / Materials Letters 60 (2006) 1466–1469
References [1] B.E. Conway, Electrochemical Supercapacitors, Scientific Fundamentals and Technological Applications, Kulwar Academic/Plenum Publishers, New York, 1997. [2] B.E. Conway, J. Electrochem. Soc. 138 (1991) 1539–1547. [3] C. Arbizzani, M. Mastragostino, B. Scosati, in: H.S. Nalwa (Ed.), Handbook of Organic Conductive Molecules and Polymers, vol. 4, Wiley, Chichester, UK, 1997, p. 595. [4] A.F. Burke, T.C. Murphy, in: D.H. Goughtly, B. Vyas, T. Takamura, J.R. Huff (Eds.), Materials for Energy Storage and Conversion: Batteries, Capacitors and Fuel Cells, Materials Research Society, Pittsburgh, 1995, p. 375. [5] S. Sarangapani, B.V. Tilak, C.P. Chen, J. Electrochem. Soc. 143 (1996) 3791–3799. [6] Y. Sun, S.R. Wilson, D.I. Schuster, J. Am. Chem. Soc. 123 (2001) 5348–5349. [7] J. Deng, X. Ding, W. Zhang, Y. Peng, J. Wang, X. Long, P. Li, A.S.C. Chan, Eur. Polym. J. 38 (2002) 2497–2501. [8] K.H. An, K.K. Jeon, J.K. Heo, S.C. Lim, D.J. Bae, Y.H. Lee, J. Electrochem. Soc. 149 (2002) A1058–A1062. [9] Q.W. Li, H. Yan, Y. Cheng, J. Zhang, Z.F. Liu, J. Mater. Chem. 12 (2002) 1179–1183.
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[10] M. Hughes, G.Z. Chen, M.S.P. Shaffer, D.J. Fray, A.H. Windle, Chem. Mater. 14 (2002) 1610–1613. [11] Y.K. Zhou, B.L. He, W.J. Zhou, J. Huang, X.H. Li, B. Wu, H.L. Li, Electrochim. Acta 49 (2004) 257–262. [12] Y.K. Zhou, B.L. He, W.J. Zhou, H.L. Li, J. Electrochem. Soc. 151 (2004) A1052–A1057. [13] K.R. Prasad, N. Munichand, J. Power Sources 112 (2002) 443–451. [14] V. Gupta, Norio Miura, J. Power Sources (in press). [15] K. Jurewicz, S. Delpeux, V. Bertagna, F. Béguin, E. Frakowiak, Chem. Phys. Lett. 347 (2001) 36–40. [16] V. Gupta, N. Miura, Electrochem. Commun. 7 (2005) 995–999. [17] Z. Niu, Z. Yang, Z. Hu, Y. Lu, C.C. Han, Adv. Funct. Mater. 13 (2003) 949–954. [18] H. Qiu, M. Wan, B. Matthews, L. Dai, Macromolecules 34 (2001) 675–680. [19] Z. Wei, M. Wan, Adv. Mater. 14 (2002) 1314–1317. [20] J. Huang, R.B. Kaner, J. Am. Chem. Soc. 126 (2004) 851–855. [21] D.M. Sarno, S.K. Manohar, A.G. MacDiarmid, Synth. Met. 148 (2005) 237–243. [22] K. Prasad, N. Miura, J. Power Sources 135 (2004) 354–360.
High performance electrochemical supercapacitor from electrochemically synthesized nanostructured polyaniline Vinay Gupta a,b,⁎, Norio Miura a a
Art, Science and Technology Center for Cooperative Research, Kyushu University, Kasuga-shi, Fukuoka 816-8580, Japan b Japan Science and Technology Agency, Saitama, 332-0012, Japan Received 12 September 2005; accepted 15 November 2005 Available online 7 December 2005
Abstract Polyaniline nanowires were electrochemically deposited on stainless steel electrode at the potential of 0.75 V vs. SCE and characterized by cyclic voltammetry in 1 M H2SO4 electrolyte for supercapacitive properties. A high specific capacitance of 775 F g− 1 was obtained at the sweep rate of 10 mV s− 1. A long-term cyclic stability of the polyaniline nanowires demonstrated its implications for the high performance supercapacitors. © 2005 Elsevier B.V. All rights reserved. Keywords: Polyaniline; Deposition; Nanowire; Cyclic voltammetry; Supercapacitor
Electrochemical supercapacitors are the charge-storage devices having high power density and long cyclic life [1–5]. The increasing pollution due to electrical vehicles and explosive growth of portable electronic devices have pushed the development of high performance supercapacitors as the urgent requirement. Supercapacitors store energy in the form of charge at the electrode/electrolyte interface and can be divided into two categories: (i) redox supercapacitors, in which the pseudocapacitance arises from faradic reactions occurring at the electrode interface and (ii) electric double layer capacitors (EDLCs), in which the capacitance arises from the charge separation at the electrode/electrolyte interface. The main materials that have been studied for the supercapacitor electrode are (i) carbons, (ii) metal oxides and (iii) polymers. The polymers are considered the most promising material in the supercapacitors. Among the polymers, such as polymethyl methacrylate (PMMA) [6], p-phenylenevinylene (PPV) [7], polypyrrole (PPy) [8–10] and polyaniline (PANI) [11–13], polyaniline is considered the most promising material
⁎ Corresponding author. KASTEC, Kyushu University, Kasuga-shi, Fukuoka 816-8580, Japan. Tel./fax: +81 92 583 7886. E-mail address: [email protected] (V. Gupta). 0167-577X/$ - see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.11.047
in the supercapacitors due to its high capacitive characteristics, low cost and ease of synthesis. The materials in the nano-size form with high surface area and high porosity give the best performances as the electrode materials for supercapacitors because of their distinctive characteristics of conducting pathways, surface interactions, and nanoscale dimensions. Therefore, the synthesis and the capacitive characterization of the high surface area nanomaterials such as nanotubes, nanowires, [14–16] etc. have been carried out extensively in the past few years. Consequently, different indirect methods were used to synthesized nanosized polyaniline, such as template synthesis [17], self-assembly [18], emulsions [19] and interfacial polymerization [20]. However, such methods require relatively large amounts of surfactants, which are rather tedious to recycle after polymerization, and it is difficult to attach nanosized polyaniline onto a substrate without involving large contact resistance. Therefore nanosized polyaniline synthesized by such methods is not suitable for supercapacitors applications. The best way is direct deposition of the nanostructured polyaniline onto a substrate electrode. In the present work, for the first time, we have performed cyclic votammetric measurements of the polyaniline nanowires electrochemically deposited directly on the stainless steel electrode for supercapacitor application.
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Fig. 3. X-ray diffraction pattern of the original polyaniline nanowires.
Fig. 1. (a) and (b) SEM images of the polyaniline nanowires at different magnification.
The polyaniline was potentiostatically deposited on to 1 × 1 cm stainless-steel plates (SS) (grade 304, 0.2 mm thick) at 0.75 V vs. SCE. Research grade SS was obtained from the Nilaco® Corporation. Before the deposition, the SS was polished with emery paper to a rough finish, washed free of emery particles and then air-dried. The electrochemical deposition was performed using auto-lab® PGSTAT 30 instrument (Eco chemie, Netherlands) connected to a three-electrode cell. The three-electrode configuration contains platinum (Pt) as the counter electrode, saturated calomel electrode (SCE) as the reference electrode and SS as the working electrode. An electrolyte solution of 1 M H2SO4 + 0.05 M polyaniline was used for the electrochemical deposition of polyaniline nanowires on the SS electrodes. Subsequent to the deposition, the electrode was washed in distilled water and stirred by using a magnetic paddle. Thereafter, the electrodes were dried in oven at 40 °C for a day. The weight of the electrochemically deposited polyaniline was measured by means of Sartorius
Fig. 2. (a) and (b) Schematics of the possible growth process of the polyaniline nanowires.
microbalance (Model BP211D). The microstructure and the thickness of the deposit were evaluated by means of JEOL scanning electron microscope (FE-SEM, JEOL, JSM-6340F). The X-ray diffraction pattern was obtained by means of Rigaku X-ray diffractometer (model R1NT2100) using CuKα radiations. The photospectra was obtained by means of Rigaku UV– vis-NIR spectrophotometer (model ultraspec 3300 pro). The cyclic voltammetric measurements were performed in 1 M H2SO4 solution. Fig. 1 shows the SEM images of the polyaniline nanowires formed after 10 min deposition time. The diameter of the nanowires is in the range of 30∼60 nm. The thickness and the size of the nanowire film is ∼20 μm and 1 × 1 cm, respectively. The nanowire's network is highly porous with interconnectivity. A possible growth process of such nanowires is proposed as shown in Fig. 2(a) and (b). The polyaniline nanowires are expected to growth via seedling growth process, in which further polyaniline is deposited on the initially deposited nanosized granules (Fig. 2(a)). As the deposition progress, an aligned nanowire network is formed (Fig. 2(b)). A further deposition results in extended length and in the misalignment of nanowires and cross-links are formed [16]. Fig. 3 shows the X-ray diffraction spectra of the polyaniline nanowires. A very broad peak was observed centered at 2θ
Fig. 4. UV–vis-NIR spectra of polyaniline nanowires in dedoped state in NMP solution.
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Fig. 5. Cyclic voltammograms of polyanile nanowires at different sweep rates in 1 M H2SO4 electrolyte.
∼19° with a shoulder at 2θ∼26°. This suggests that the nature of the nanowires is amorphous. Fig. 4 shows the UV/visible photo spectra of the polyaniline nanowires in the dedoped state in N-methyl-2-pyrrolidone (NMP) solution. Before obtaining the photospectra, the polyaniline nanowires were washed in 0.1 M NH4OH solution. In this process, original green polyaniline becomes blue-purple, indicating that the doped emeraldine form has been deprotonated to emeraldine base. A few drops of this base formed a clear blue solution in the NMP, giving UV–visNIR absorbance photospectra with maxima at 638 and 332 nm,
Fig. 7. Cyclic-life data of the polyaniline nanowires capacitor. The specific capacitance was calculated for the cyclic voltammetry at the sweep rate of 100 mV s− 1 in 1 M H2SO4 electrolyte.
in excellent agreement with the literature results for indirectly prepared polyaniline nanostructures [21]. Fig. 5 shows the cyclic voltammogram of polyaniline nanowires/SS electrode in 1 M H2SO4 electrolyte in the potential range of 0 and 0.7 V vs. SCE. The near rectangularshaped cyclic voltammograms (CV) at low scan rate and high overall current suggests the highly capacitive behavior of the polyaniline nanowires. The CVs were also recorded in the same electrolyte with bare SS electrode, but no capacitive behavior was observed. Hence the capacitive behavior of polyaniline nanowires/SS electrode is entirely due to polyaniline nanowires. The CV current densities and the calculated specific capacitance values are shown in Fig. 6(a) and (b), respectively. The specific capacitance (SC) value of 775 F g− 1 was obtained at the scan rate of 10 mV s− 1 whereas the SC value of 562 F g− 1 was obtained at the high scan rate of 200 mV s− 1. This decrease of 25% in the specific capacitance at high scan rates is much lower than in the case of metal oxides where decrease of 50∼80% was reported between 10 and 200 mV s− 1 [22]. Moreover the CV current increases linearly with the increase in the scan rate as shown in Fig. 6 (a). This implies highly stable supercapacitive characteristics of the polyaniline nanowires. Fig. 7 shows the cyclic stability of the polyaniline nanowires at the sweep rate of 100 mV s− 1 for 1500 cycles. There is a small decrease in the specific capacitance value in the first 100 cycles and thereafter the specific capacitance remains almost constant. The decrease in the specific capacitance was 8% in the first 500 cycles and 1% in the subsequent 1000 cycles, indicating high stability of the electrode for long cyclic life. Acknowledgements
Fig. 6. (a) Cyclic voltammetric current density of polyaniline nanowires versus applied scan rate and (b) specific capacitance of polyaniline nanowires calculated from CV vs. the scan rate.
This present work was supported by Japan Science and Technology (JST) agency through “Core research for Evolution Science and Technology (CREST)” under the project “Development of advanced nanostructured materials for energy conversion and storage”.
V. Gupta, N. Miura / Materials Letters 60 (2006) 1466–1469
References [1] B.E. Conway, Electrochemical Supercapacitors, Scientific Fundamentals and Technological Applications, Kulwar Academic/Plenum Publishers, New York, 1997. [2] B.E. Conway, J. Electrochem. Soc. 138 (1991) 1539–1547. [3] C. Arbizzani, M. Mastragostino, B. Scosati, in: H.S. Nalwa (Ed.), Handbook of Organic Conductive Molecules and Polymers, vol. 4, Wiley, Chichester, UK, 1997, p. 595. [4] A.F. Burke, T.C. Murphy, in: D.H. Goughtly, B. Vyas, T. Takamura, J.R. Huff (Eds.), Materials for Energy Storage and Conversion: Batteries, Capacitors and Fuel Cells, Materials Research Society, Pittsburgh, 1995, p. 375. [5] S. Sarangapani, B.V. Tilak, C.P. Chen, J. Electrochem. Soc. 143 (1996) 3791–3799. [6] Y. Sun, S.R. Wilson, D.I. Schuster, J. Am. Chem. Soc. 123 (2001) 5348–5349. [7] J. Deng, X. Ding, W. Zhang, Y. Peng, J. Wang, X. Long, P. Li, A.S.C. Chan, Eur. Polym. J. 38 (2002) 2497–2501. [8] K.H. An, K.K. Jeon, J.K. Heo, S.C. Lim, D.J. Bae, Y.H. Lee, J. Electrochem. Soc. 149 (2002) A1058–A1062. [9] Q.W. Li, H. Yan, Y. Cheng, J. Zhang, Z.F. Liu, J. Mater. Chem. 12 (2002) 1179–1183.
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[10] M. Hughes, G.Z. Chen, M.S.P. Shaffer, D.J. Fray, A.H. Windle, Chem. Mater. 14 (2002) 1610–1613. [11] Y.K. Zhou, B.L. He, W.J. Zhou, J. Huang, X.H. Li, B. Wu, H.L. Li, Electrochim. Acta 49 (2004) 257–262. [12] Y.K. Zhou, B.L. He, W.J. Zhou, H.L. Li, J. Electrochem. Soc. 151 (2004) A1052–A1057. [13] K.R. Prasad, N. Munichand, J. Power Sources 112 (2002) 443–451. [14] V. Gupta, Norio Miura, J. Power Sources (in press). [15] K. Jurewicz, S. Delpeux, V. Bertagna, F. Béguin, E. Frakowiak, Chem. Phys. Lett. 347 (2001) 36–40. [16] V. Gupta, N. Miura, Electrochem. Commun. 7 (2005) 995–999. [17] Z. Niu, Z. Yang, Z. Hu, Y. Lu, C.C. Han, Adv. Funct. Mater. 13 (2003) 949–954. [18] H. Qiu, M. Wan, B. Matthews, L. Dai, Macromolecules 34 (2001) 675–680. [19] Z. Wei, M. Wan, Adv. Mater. 14 (2002) 1314–1317. [20] J. Huang, R.B. Kaner, J. Am. Chem. Soc. 126 (2004) 851–855. [21] D.M. Sarno, S.K. Manohar, A.G. MacDiarmid, Synth. Met. 148 (2005) 237–243. [22] K. Prasad, N. Miura, J. Power Sources 135 (2004) 354–360.