ARTICLE pubs.acs.org/JPCC
Controllable Assembly of Polyaniline Nanostructures and Improving Their Electrochemical Performance by High Gravity Jiazang Chen,*,†,‡ Bo Li,†,§ Jianfeng Zheng,† Jianghong Zhao,† Huanwang Jing,†,§ and Zhenping Zhu*,† †
State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China National Engineering Research Center for Phosphate Resources Development and Utilization, Wuhan Institute of Technology, Wuhan 430073, China § College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, China ‡
ABSTRACT: A novel strategy is proposed for controllable synthesis of polyaniline nanofibers by introducing high gravity into the interfacial polymerization system. During the polymerization of the aniline monomers, overgrowth and aggregation of the polyaniline nanofibers were effectively suppressed by virtue of high gravity. By adjustment of high gravity levels, polyaniline nanofibers with various diameters can be obtained, and the diameter of the nanofibers becomes smaller as the gravitational acceleration increases (from 9.8 m/s2 to 78.4 m/s2). By application of these materials as hole conductor media in quasi-solidstate dye-sensitized solar cells, it was found that the electrochemical behaviors are strongly dependent on the high gravity that is applied for the synthesis of the polyaniline nanofibers. Electrochemical impedance spectroscopy characterization indicates that both of the transport properties of charge in the bulk of the electrolyte and charge transfer on the counter electrode are affected by the diameter of the nanofibers. The quasi-solid-state photovoltaic devices employing the polyaniline nanofibers obtained under a high gravity level of 78.4 m/s2 achieved energy conversion efficiency of 1.375%, which is ∼76% higher than that obtained under normal gravitational acceleration on Earth (9.8 m/s2).
1. INTRODUCTION Polyaniline (PANI) is considered as one of the most promising and versatile conducting polymers due to its relatively facile processability, electrical conductivity, and environmental stability.17 For example, it can play a role as catalyst for conversion of redox couples in dye-sensitized solar cells (DSSCs)812 as well as hole conductor media in solidstate photovoltaic devices.1319 Among the various types of PANI, one-dimensional (1D) PANI nanostructures such as nanofibers (NFs) with controllable morphologies are especially interesting.2023 Up to now, many techniques have been developed for the synthesis of PANI nanostructures. The interfacial polymerization method is a special approach because it does not rely on templates, structure-directing molecules, or specific dopants and therefore simplifies the synthesis procedures.20,24,25 This method produces PANI NFs on the interface of an immiscible organic/aqueous biphasic system, in which the reactants, aniline monomers, oxidant, and a doping acid such as HCl, are separated by the interface between the organic solvent and the aqueous phase.24,26 In a typical reaction of interfacial polymerization, PANI NFs were first formed by oxidation of the aniline monomers with oxidant on the interface followed by protonate doping and then diffusion into the aqueous layer.24,25,27 Diffusion becomes a key step in the interfacial polymerization. Diffusion of as-formed PANI NFs into the aqueous layer can suppress the r 2011 American Chemical Society
overgrowth and aggregation of the nanostructures.24,25,28 Generally, diffusion is driven by the hydrophilicity of the emeraldine salt, which is the protonate doping state of the base PANI.27 However, because of the hysteretic step of protonate doping, overgrowth and aggregation of PANI nanostructures seemingly cannot be avoided.27 Therefore, to suppress the overgrowth and aggregation, it is of great importance to promote the diffusion of the PANI NFs from the organic/aqueous interface into the bulk of the aqueous phase. Here we develop an approach to improve the conventional interfacial polymerization and effectively suppress the overgrowth and aggregation during the polymerization. In this way, the PANI NFs in the system were compulsorily diffused and dispersed into the bulk of the aqueous phase by external force. The effect of external force on the morphologies of the interfacial polymerization products was investigated in detail. In addition, the work also reported the application of the synthesized NFs as the hole conductor media in quasi-solid-state DSSCs. Although the energy conversion efficiency of these cells with liquid electrolytes has already reached as high as ∼12%,29 the technological problems such as device sealing, precipitation of salts in the electrolyte at low temperature, evaporation of liquid Received: July 17, 2011 Revised: September 30, 2011 Published: October 17, 2011 23198
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Figure 1. Schematic diagrams for concentration distribution of interfacial polymerization product by intrinsic diffusion (a) and compulsory dispersion (b). The X in the diagram represents the distance along the axial direction from the interface (base point) to the bottom of the reactor, and Y, the concentration of PANI NFs.
electrolyte at high temperature, corrosion, and lack of long-term stability still limit the practical applications. To solve these problems, it is of great importance to solidify or quasisolidify the electrolyte. PANI has become one of the promising alternatives among hole conductor materials, and some encouraging results have been obtained from photovoltaic devices with PANI composite electrolytes.13,15,18,19 However, certain problems such as charge transport and transfer still need further investigation. Here we investigate the effect of the NF diameter on the charge transport properties in the cell based on PANI composite electrolyte, and the photoelectrochemical properties in the photovoltaic devices.
2. DEVELOPMENT OF HIGH GRAVITY-ASSISTED INTERFACIAL POLYMERIZATION According to the Fick’s law, diffusion of PANI NFs was controlled by the concentration gradient and mobility of the emeraldine salt in the aqueous layer. In a certain system of interfacial polymerization, the neonatal or protonated PANI NFs would first accumulate in the vicinity of the aqueous/organic interface before they dispersed into the aqueous phase by the hydrophilicity of emeraldine salt. Figure 1a shows the schematic diagram of concentration distribution of PANI NFs along the axial direction of the reactor. In the vicinity of the interface, where the concentration is very high, overgrowth and aggregation cannot be ignored because of the reaction of the NFs with aniline monomers and interaction of NFs themselves. While in the bulk of the aqueous layer, overgrowth and aggregation of PANI NFs could be effectively avoided from the absence of aniline monomers and very low concentration of NFs. Moreover, the growing concentration of PANI by the continuous polymerization of the monomers in the interface can aggravate the interaction. To alleviate the overgrowth and aggregation, it is rational to promote the diffusion of the neonatal PANI NFs toward the axial direction of the reactor and the dispersion of NFs into the bulk of the aqueous phase. Thus, the concentration distribution of the as-synthesized NFs in the aqueous layer will be ameliorated, as shown in Figure 1b. To realize this goal, high gravity was introduced as an external force to compulsorily disperse the nanofibers.
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Figure 2. Scheme of the equipment for high gravity-assisted interfacial polymerization. R1 and R2 in the vial respectively represent the organic and aqueous phase.
High gravity-related methods are very common in many process industries, such as mining processing, chemical industry, and bioengineering.3033 Here high gravity is used as external force to draw the as-formed PANI from the interface into the aqueous layer and preclude overgrowth and aggregation. The schematic diagram for the equipment to achieve high gravity is shown in Figure 2. Various high gravity levels (g0 ) can be obtained by adjusting the rotational speed of the rotor according to the geometric parameters of the equipment and the mathematical expression presented.
3. EXPERIMENTAL SECTION 3.1. High Gravity-Assisted Interfacial Polymerization of Polyaniline Nanofibers. Synthesis of PANI NFs was conducted
in a 10-mL glass vial. Typically, 0.4 mmol of ammonium peroxydisulfate (APS) and 1.6 mmol of aniline were separately dissolved in 5 mL of hydrochloric acid solution (1 M) and 5 mL of n-hexane. Then the organic solution was added into the aqueous solution carefully to form a biphase system. The resulting biphase system was subjected to the centrifugal separator to perform the high gravity-assisted interfacial polymerization of aniline monomers, as shown in Figure 2. High gravity with various gravitational accelerations can be obtained by adjusting the rational speed. Here the high gravity levels used are 9.8 m/s2 (normal gravitational acceleration on Earth, 1 g), 19.6 m/s2 (2 g), 39.2 m/s2 (4 g), and 78.4 m/s2 (8 g), and the resulting PANI NFs were labeled as P1g, P2g, P4g, and P8g, respectively. For all the experiments, the reaction time was 30 min. After the reaction, the PANI NFs were filtered out, washed with water and acetone, and then dried at 60 °C. Morphology of the products was characterized by transmission electron microscopy (TEM) carried out on a JEOL JEM-2010 electron microscope. The surface area of the nanofibers was measured by nitrogen adsorption desorption isotherms using the BrunauerEmmettTeller (BET) method (TriStar 3000). 3.2. Fabrication of DSSCs. Dye-sensitized TiO2 photoelectrodes for fabrication of DSSCs were prepared according to our previous procedure.34 The composite electrolyte was prepared by mixing 50 mg of PANI NFs with 0.5 mL of organic solution (denoted OS) containing ionic liquid (1-propyl-3-methylimidazolium iodide, PMII). The OS was prepared by dissolving 0.6 M of PMII, 0.02 M of iodine (I 2 ), 23199
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4. RESULTS AND DISCUSSION 4.1. Effect of High Gravity on the Morphologies of Polyaniline Nanofibers. Effects of external force on the morpholo-
Figure 3. Effect of high gravity levels on diameters of PANI NFs. (ad) TEM images and (e) average diameters of PANI NFs obtained under the gravitational accelerations of 9.8 m/s2, 19.6 m/s2, 39.2 m/s2, and 78.4 m/s2. All the samples were obtained at the time when the reactions continued to 30 min.
and 0.5 M of 4-tert-butylpyridine (TBP) into acetonitrile (ACN). Next, the composite electrolyte was coated onto the dye-sensitized TiO2 electrodes at 60 °C to ensure that the ionic liquid could penetrate into the porous structure and evaporate the ACN. Then the TiO 2 electrode with the composite electrolyte was assembled with a platinized fluorine-doped tin dioxide (FTO) glass. For a good comparison, the cell with liquid electrolyte (that was OS) was also fabricated here. 3.3. Fabrication of Symmetric Cells. Assembly of the symmetric cell can be described as follows. First, an adhesive tape (100 μm in thickness) with a hole was attached on a platinized electrode, and the composite electrolyte was then coated on the platinized film at 60 °C. Next, the platinized electrode with the electrolyte was assembled with another platinized electrode. 3.4. Electrochemistry and Photoelectrochemistry. The photovoltaic performance of the DSSCs were characterized by recording the photocurrentvoltage on a Keithley 2601 source meter under illumination of A.M. 1.5 G (100 mW/cm2). The illumination was provided by performing a San-Ei solar simulator. Electrochemical impedance measurements of the cells were performed with a computer-controlled Zahner Im6ex potentiostat with a frequency range of 0.01100k Hz.
gies of the synthesized PANI nanostructures were studied by fixing all the experimental parameters including the composition of both the organic and aqueous phases, configuration of the reactors, and the reaction duration time. In the present work, 0.08 M APS, 1 M HCl, and n-hexane were adopted as oxidant, dopant, and organic solvent, respectively. The concentration of aniline monomers in the organic solvent is 0.32 M, and the reaction time for each sample is 30 min. Formation of PANI NFs took place on the interface of the aqueous/organic biphase. A variety of high gravity levels from 9.8 to 78.4 m/s2 were used to investigate the effect of the external force on the diameters of the PANI NFs. Figure 3ad presents the TEM images of the asprepared PANI NFs under various high gravity levels, and the average diameter of these materials are summarized in Figure 3e and Table 1. It is clear that high gravitational acceleration is preferable to produce thin PANI NFs. Under normal gravitational acceleration (9.8 m/s2), the average diameter of the PANI NFs is ∼100 nm. The relatively large diameter of the product indicates that the NFs severely overgrew and aggregated during the polymerization reaction. When high gravity was applied, the average diameters of the uniform PANI NFs become smaller and the size distribution becomes narrower as the gravitational acceleration increases (Figure 3e and Table 1). For example, the average diameters of the products synthesized under high gravity levels of 19.6, 39.2, and 78.4 m/s2 are 83, 55, and 37 nm, respectively. Moreover, the surface area of the PANI NFs increased as the high gravity levels increase from 1 g (normal gravitational acceleration) to 8 g (78.4 m/s2). The respective surface area for P1g, P2g, P4g, and P8g PANI NFs are 22.7, 24.2, 33.4, and 36.7 m2/g. The effects of external force on the morphology of PANI can be explained as follows. When the high gravity was absent, in other words, when dispersion of as-formed PANI was merely driven by diffusion and normal gravity (on Earth), the dispersion rate was low. Because of the relatively long duration in the vicinity of interface, the formed PANI NFs would function as nucleation centers for secondary growth of PANI and finally grow into thick fibers. As the gravitational acceleration increases, the external force acting on the PANI can promote the dispersion of the NFs into the aqueous layer, where the aniline monomers are almost absent, and the density of PANI NFs becomes lower. Therefore, further polymerization of aniline monomers onto the PANI or the interaction between the NFs can be terminated. 4.2. Charge Transport Properties. Having characterized the influence of high gravity on the morphology of PANI NFs, we next investigated the electrochemical behaviors of the cells based on PANI composite electrolyte. Generally, one-dimensional nanostructures having less boundaries will facilitate charge transport, and the PANI NFs themselves in the composite electrolyte would provide efficient routes for charge transport. To gain insight into the effect of PANI NF diameter and to remove the impact of the photoelectrode, charge transport in the bulk of the electrolyte and charge transfer resistance on the counter electrode was characterized using electrochemical impedance spectroscopy in a symmetric cell.35 In this case, the configuration of the cell was simplified, and contribution from several operational circuit elements such as charge transport in the bulk of the TiO2 and interfacial charge transfer on the 23200
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Table 1. Feature of the PANI NFs Obtained under Various Gravitational Accelerations and the Charge Transport Resistance and Charge Transfer Resistance for the Corresponding Composite Electrolytes PANI
diameter of
specific area of
W
Rct
NFs
NFs (nm)
NFs (m2/g)
(Ω cm2)
(Ω cm2)
P1g
100
22.7
P2g
83
24.2
839.6
1952
P4g
55
33.4
565.3
1408
P8g
37
36.7
599.0
1204
1115
1980
Figure 5. Photocurrentvoltage characteristics of the DSSCs with various electrolytes.
Figure 4. (a) Schematic diagram and the equivalent circuit of the symmetric cell for measurement of the charge transport resistance in the bulk of electrolyte and charge transfer resistance on the counter electrode. (b) Nyquist plots of cells with various PANI NF electrolyte. Rs: the series resistance; Rct: the charge transfer resistance; CPE: double layer capacitance; W is the Warburg diffusion impedance.
semiconductorelectrolyte interface (SEI) were eliminated. Figure 4a presents the scheme and equivalent circuit of the symmetric cell employed in the impedance study. The symmetric cell consists of a series resistance (Rs), a Warburg impedance (W), which represents the diffusion of hole carriers in the bulk of the composite electrolyte, and a charge transfer resistance (2Rct) on both sides of the electrodeelectrolyte interface, which describes the ability for catalytic conversion between tri-iodide and iodide ions. Furthermore, two constant phase elements (CPEs) should be separately connected in parallel with the two RCT elements to form the Rs (RctCPE)W network. Figure 4b shows the Nyquist diagrams of the cell consisting of various PANI electrolytes. It is clear that the sum of charge
transport resistance (W) and charge transfer resistance (2Rct) decrease as the PANI NFs become thinner. By fitting the impedance data with the equivalent circuit, the detailed parameters for W and Rct on the counter electrode were evaluated and are listed in Table 1. As shown, the values of W decreased from 1115 Ω cm2 for the P1g electrolyte to 565.3Ω cm2 for the P4g electrolyte. At the same time, charge transfer resistance also decreased from 1980 Ω cm2 for the P1g electrolyte to 1024 Ω cm2 for the P8g electrolyte. The significantly decrease in both W and Rct suggest that the composite electrolyte with PANI NFs obtained under high gravity are beneficial for charge transport in the bulk of the electrolyte and charge transfer on the electrode. It is well-known that PANI is not only electrically conductive for the transport of charge carriers3638 but also electrocatalytically active for conversion of iodine-containing redox couples in DSSCs.8,9,11 Here in our case, the Rct value (larger than 1200 Ω cm2) is much higher than that obtained from a common symmetric cell consisting of liquid electrolyte (usually less than 10 Ω cm2),35,39 which indicates that the charge transfer between electrolyte and electrode is not efficient. Thus, during transport of hole carriers in the composite electrolyte containing ionic liquid, conversion of I3 into I ions (that is I3 + 2e T 3I and/or I3 + I f I 3 3 3 I2 3 3 3 I f I + I3) in the bulk of the electrolyte will take place under the catalysis of PANI NFs,15,19 which means that transport of charge in the bulk of the composite electrolyte is under the dual action of diffusion of charge carriers (mass transfer) and the catalytic conversion of the redox couples (charge transfer). The PANI NF with smaller diameter possesses higher specific area, which provides more catalytically active sites for conversion of iodide-containing redox couples and, at the same time, alleviates the burden of charge transfer on the electrodeelectrolyte interface, resulting in a relatively low charge transport resistance and charge transfer resistance. 4.3. Photovoltaic Performance. Figure 5 presents the photocurrentvoltage curves of the as-fabricated DSSCs with various PANI electrolytes measured under illumination of 100 mW/cm2. Certain photovoltaic parameters such as open-circuit voltage (VOC), short-circuit current density (JSC), fill factor (FF), and energy conversion efficiency (η) of the photovoltaic device are listed in Table 2. In addition, photovoltaic parameters obtained from a cell with liquid electrolyte are also presented in Table 2. Clearly, all the photovoltaic parameters, including the FF and η of the DSSCs, are strongly affected by the diameter of the PANI NFs used in the composite electrolyte. The cell with P8g PANI 23201
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Table 2. Photovoltaic Parameters of DSSCs with Various Electrolytes VOC (mV)
JSC (mA/cm2)
FF
η (%)
P1g
614
2.71
0.469
0.781
P2g P4g
645 686
2.82 2.95
0.495 0.542
0.898 1.095
electrolyte
P8g
727
3.13
0.604
1.375
Liquid
734
12.32
0.662
5.983
NF composite electrolyte exhibits the best performance (highest VOC, JSC, FF, and η) among the solid-state photovoltaic devices, showing a 1.375% energy conversion efficiency. Following a descending order in performance is the cell using P4g PANI NFs, which exhibits an efficiency of 1.095%. The cell with P1g PANI NFs exhibits the lowest energy conversion efficiency; the detailed photovoltaic parameters for the cell are 614 mV, 2.71 mA/cm2, and 0.469 for the VOC, JSC, and FF, respectively, and the η is 0.781%. The cell with liquid electrolyte exhibits an energy conversion efficiency of 5.983% and JSC of 12.32 mA/cm2, which is at least 3 times larger than that obtained from solid-state DSSCs. By comparison of these photovoltaic parameters with that obtained from a cell with liquid electrolyte, the significant parameters are JSC, FF, and η. The photovoltaic parameters (VOC, JSC, FF, and η) of the devices are very sensitive to the electrolyte. Many publications indicate that the photovoltaic performance of the DSSCs degraded when the liquid electrolytes were solidified because of the poor charge transport properties of the hole conductor. The very large charge transport resistance in the bulk of the composite electrolyte and the charge transfer resistance on the counter electrode significantly increase the internal resistance of the cell, resulting in a low value of FF.40 Furthermore, because of the very large resistance for diffusion of the hole carriers in the composite electrolyte, the accumulation of electron acceptor in the vicinity of the SEI can aggravate the recombination of the electron in the semiconductor with the hole carriers, negatively resulting in a low charge collection efficiency and electron lifetime41 and consequently lowering the photocurrent density and open-circuit voltage of the cell.4042 Similarly, by comparison of these four photovoltaic devices with PANI composite electrolyte, the cells with thinner PANI NF can facilitate charge transport, reduce the internal dissipating power, and alleviate the recombination of the photogenerated charges, resulting in relatively high values of VOC, JSC, FF, and η.
5. CONCLUSION Polyaniline nanofibers with various diameters can be obtained simply by adjusting the high gravity levels during the procedure of polymerization from aniline monomers. The overgrowth and aggregation of polyaniline nanofibers are effectively suppressed when high gravity was applied. Electrochemical impedance results obtained from symmetric cells show that the charge transport and transfer are strongly dependent on the diameter of the polyaniline nanofibers. By application of the polyaniline nanoibers as hole conductor materials in dye-sensitized solar cells, the photovoltaic device exhibits higher energy conversion efficiency as the diameter of the materials become smaller. In summary, high gravity has been applied to improve conventional interfacial polymerization for the first time. We believe that
high gravity can provide a novel and wide scope to assist the assembly of nanostructures.
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected] (J.C.);
[email protected] (Z.Z.).
’ ACKNOWLEDGMENT J.C. thanks Dr. Yinghua Xu (Zhejiang Univ. Technol.) for some fruitful discussion on impedance results. ’ REFERENCES (1) MacDiarmid, A. G. Rev. Mod. Phys. 2001, 73, 701. (2) Huang, W.-S.; Humphrey, B. D.; MacDiarmid, A. G. J. Chem. Soc., Faraday Trans. 1 1986, 82, 2385–2400. (3) Mandic, Z.; Rokovic, M. K.; Pokupcic, T. Electrochim. Acta 2009, 54, 2941–2950. (4) Kuila, B. K.; Nandan, B.; Bohme, M.; Janke, A.; Stamm, M. Chem. Commun. 2009, 5749–5751. (5) Li, G. R.; Feng, Z. P.; Zhong, J. H.; Wang, Z. L.; Tong, Y. X. Macromolecules 2010, 43, 2178–2183. (6) Mondal, S. K.; Barai, K.; Munichandraiah, N. Electrochim. Acta 2007, 52, 3258–3264. (7) Gupta, V.; Miura, N. Electrochem. Solid State Lett. 2005, 8, A630–A632. (8) Li, Q.; Wu, J.; Tang, Q.; Lan, Z.; Li, P.; Lin, J.; Fan, L. Electrochem. Commun. 2008, 10, 1299–1302. (9) Li, Z. P.; Ye, B. X.; Hu, X. D.; Ma, X. Y.; Zhang, X. P.; Deng, Y. Q. Electrochem. Commun. 2009, 11, 1768–1771. (10) Ameen, S.; Akhtar, M. S.; Kim, Y. S.; Yang, O. B.; Shin, H. S. J. Phys. Chem. C 2010, 114, 4760–4764. (11) Sun, H. C.; Luo, Y. H.; Zhang, Y. D.; Li, D. M.; Yu, Z. X.; Li, K. X.; Meng, Q. B. J. Phys. Chem. C 2010, 114, 11673–11679. (12) Qin, Q.; Tao, J.; Yang, Y. Synth. Met. 2010, 160, 1167–1172. (13) Tan, S. X.; Zhai, J.; Wan, M. X.; Meng, Q. B.; Li, Y. L.; Jiang, L.; Zhu, D. B. J. Phys. Chem. B 2004, 108, 18693–18697. (14) Tan, S. X.; Zhai, J.; Xue, B. F.; Wan, M. X.; Meng, Q. B.; Li, Y. L.; Jiang, L.; Zhu, D. B. Langmuir 2004, 20, 2934–2937. (15) Ikeda, N.; Teshima, K.; Miyasaka, T. Chem. Commun. 2006, 1733–1735. (16) Kim, H. S.; Wamser, C. C. Photochem. Photobiol. Sci. 2006, 5, 955–960. (17) Kim, Y. K.; Sung, Y. E.; Xia, J. B.; Lira-Cantu, M.; Masaki, N.; Yanagida, S. J. Photochem. Photobiol. A: Chem. 2008, 193, 77–80. (18) Chen, P. Y.; Lee, C. P.; Vittal, R.; Ho, K. C. J. Power Sources 2010, 195, 3933–3938. (19) Lee, C. P.; Chen, P. Y.; Vittal, R.; Ho, K. C. J. Mater. Chem. 2010, 20, 2356–2361. (20) Huang, J. X.; Virji, S.; Weiller, B. H.; Kaner, R. B. J. Am. Chem. Soc. 2003, 125, 314–315. (21) Guo, Y. P.; Zhou, Y. Eur. Polym. J. 2007, 43, 2292–2297. (22) Marie, E.; Rothe, R.; Antonietti, M.; Landfester, K. Macromolecules 2003, 36, 3967–3973. (23) Huang, K.; Wan, M. X. Chem. Mater. 2002, 14, 3486–3492. (24) Huang, J. X.; Kaner, R. B. J. Am. Chem. Soc. 2004, 126, 851–855. (25) Huang, J. X.; Kaner, R. B. Chem. Commun. 2006, 367–376. (26) Huang, J. X. Pure Appl. Chem. 2006, 78, 15–27. (27) Mattoso, L. H. C.; MacDiarmid, A. G.; Epstein, A. J. Synth. Met. 1994, 68, 1–11. (28) Huang, J.; Kaner, R. B. Angew. Chem., Int. Ed. 2004, 43, 5817–5821. (29) Chiba, Y.; Islam, A.; Watanabe, Y.; Komiya, R.; Koide, N.; Han, L. Y. Jpn. J. Appl. Phys. Part 2 2006, 45, L638–L640. 23202
dx.doi.org/10.1021/jp206814k |J. Phys. Chem. C 2011, 115, 23198–23203
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ARTICLE
(30) Nabighian, M. N.; Ander, M. E.; Grauch, V. J. S.; Hansen, R. O.; LaFehr, T. R.; Li, Y.; Pearson, W. C.; Peirce, J. W.; Phillips, J. D.; Ruder, M. E. Geophysics 2005, 70, 63ND–89ND. (31) Stankiewicz, A. Chem. Eng. Res. Des. 2006, 84, 511–521. (32) Linko, M.; Haikara, A.; Ritala, A.; Penttila, M. J. Biotechnol. 1998, 65, 85–98. (33) Chen, Y.-S.; Wang, Y.-H.; Liu, H.-S.; Hsu, K.-Y.; Tai, C. Y. Ind. Eng. Chem. Res. 2010, 49, 8832–8840. (34) Chen, J.; Li, B.; Zheng, J.; Zhao, J.; Jing, H.; Zhu, Z. Electrochim. Acta 2011, 56, 4624–4630. (35) Hauch, A.; Georg, A. Electrochim. Acta 2001, 46, 3457–3466. (36) Sirringhaus, H.; Brown, P. J.; Friend, R. H.; Nielsen, M. M.; Bechgaard, K.; Langeveld-Voss, B. M. W.; Spiering, A. J. H.; Janssen, R. A. J.; Meijer, E. W.; Herwig, P.; de Leeuw, D. M. Nature 1999, 401, 685–688. (37) Lee, K.; Cho, S.; Heum Park, S.; Heeger, A. J.; Lee, C.-W.; Lee, S.-H. Nature 2006, 441, 65–68. (38) Lee, S. H.; Lee, D. H.; Lee, K.; Lee, C. W. Adv. Func. Mater. 2005, 15, 1495–1500. (39) Murakami, T. N.; Gratzel, M. Inorg. Chim. Acta 2008, 361, 572–580. (40) Wang, Q.; Moser, J. E.; Gratzel, M. J. Phys. Chem. B 2005, 109, 14945–14953. (41) Fabregat-Santiago, F.; Bisquert, J.; Cevey, L.; Chen, P.; Wang, M. K.; Zakeeruddin, S. M.; Gratzel, M. J. Am. Chem. Soc. 2009, 131, 558–562. (42) Kern, R.; Sastrawan, R.; Ferber, J.; Stangl, R.; Luther, J. Electrochim. Acta 2002, 47, 4213–4225.
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