Electrochemical polymerization of Thiophene and

Polymer-Plastics Technology and Engineering

ISSN: 0360-2559 (Print) 1525-6111 (Online) Journal homepage: http://www.tandfonline.com/loi/lpte20

Electrochemical polymerization of Thiophene and poly(3-hexyl)thiophene, Nanocomposites with TiO2, and Corrosion protection behaviours Murat Ates & Aysegul Dolapdere To cite this article: Murat Ates & Aysegul Dolapdere (2015): Electrochemical polymerization of Thiophene and poly(3-hexyl)thiophene, Nanocomposites with TiO2, and Corrosion protection behaviours, Polymer-Plastics Technology and Engineering, DOI: 10.1080/03602559.2015.1036450 To link to this article: http://dx.doi.org/10.1080/03602559.2015.1036450

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Date: 27 October 2015, At: 16:22

Electrochemical polymerization of Thiophene and poly(3-hexyl)thiophene, Nanocomposites with TiO2, and Corrosion protection behaviours Murat Ates1,2, Aysegul Dolapdere1 1

Department of Chemistry, Faculty of Arts and Sciences, Namik Kemal University, Degirmenalti Campus, Tekirdag, Turkey, 2Department of Chemistry & Biochemistry, University of California Los Angeles, Los Angeles, California, USA

Downloaded by [University Town Library of Shenzhen] at 16:22 27 October 2015

Corresponding Author: E-mail: [email protected] and [email protected]

Abstract Thiophene (Th), 3-hexylthiophene (3HT) and their nanocomposites with TiO 2 were electropolymerized on Al1050 electrode by chronoamperometic technique. Different concentrations of Th and 3HT homopolymers and their nanocomposites with TiO2 (2% in total content) were characterized by attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), energy dispersion Xray analysis (EDX) and electrochemical impedance spectroscopy (EIS). The capacitive behaviours of modified electrodes were calculated from Nyquist, Bode-magnitude, Bodephase and Admittance plots. The optimum conditions of capacitive behaviours of homopolymers (PTh and P3HT) and their nanocomposite films of PTh/TiO 2 and P(3HT/TiO2) were electrocoated on an Al1050 electrode by chronoamperometric technique. The anti-corrosion tests for homopolymers and nanocomposite films were examined in 3.5% NaCl solution. The EIS and Tafel extrapolation results were comparatively studied. In all cases, polymer and nanocomposite films have protective behavior of Al1050 against corrosion. P(3HTh)/TiO2 nanocomposite films gave the highest protection effeciency (PE) = 98% because the amount of defects was much lower than that for the P(3HTh), PTh and PTh/TiO 2 films.

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KEYWORDS: Polythiophene, poly(3-hexylthiophene), TiO2, anti-corrosion, Nanocomposite, Al1050

1. INTRODUCTION Conducting polymers have superior advantages in electrochromic devices [1], solar cells


[2], nanomaterials [3], biosensors [4], drug delivery systems [5], computer software [6], light emmiting diodes [7], corrosion prevention [8], and rechargeable batteries [9] due to their optical, electrical and mechanical properties [10–11].

There are many conducting polymers such as polypyrrole, polyaniline, polythiophene that are used for the corrosion protection of metals in the literature [1214]. The substituted groups of thiophene was used to reduce the oxidation potential of the monomer and increase of the solubility in the solvent compared to the literature [15].

Poly(3-hexylthiophene) (P(3HT)) has better optoelectronic properties and processability. Due to these advantages, it was used in electronic and optoelectronic device applications [16-17]. Gunes et al. have studied the P(3HT)/TiO 2 nanocomposite films and their hybrid solar cell performances [18]. Nicho et al have studied P(3HT) coatings in 0.5 M H2SO 4 solution by using the drop-casting technique on mild steel type of 1018 [19].

Corrosion is defined as metal or alloy changes by chemical or electrochemical processes or physical changes due to environmental factors. Corrosion occurs with redox

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reactions. One of the reactions of oxidation or reduction prevents, the corrosion process stops. Conducting polymers may protect the substrate from corrosion with two mechanisms [20]. One of them supplies a barrier between the metal and the environment. The other supplies a passivation of the metal as anodic or cathodic protection. In literature, Poly(3-hexylthiophene) P(3HT) has the best corrosion protection compared to


the poly(3-octylthiophene) P(3HT) since the amount of defects was much lower than that for the P(3OT) films [21].

The type of Aluminum 1050 electrode has many advantages such as low density, thermal conductivities, good corrosion resistance, high ductility, strongly adherent and compact films [22].

In this work, PTh and P(3HT) and their TiO 2 nanocomposites were synthesized on GCE and characterized by CV, FTIR-ATR, SEM-EDX and EIS analysis. PTh and P(3HTh) electrodes on Al1050 were tested in 3.5% NaCl solution.

2. MATERIALS AND METHODS 2.1. Chemicals Thiophene (Th), 3-hexylthiophene (3HTh), oxalic acid (H2C2O4), titanium (IV) oxide (TiO2, ≥97%), cerium ammonium nitrate (CAN), nitric acid (HNO3), tetraethyl ammonium tetrafloroborate (TEABF4 ), tetrabutyl ammonium tetrafloroborate (TBABF4), sodium chloride (NaCl) and sodium hydroxide (NaOH) were purchased from SigmaAldrich (www.sigma-aldrich.com, Steinheim, Germany). Ethanol, acetonitrile (CH3CN,

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≥99.9%) and acetone (ACS, ISO) were supplied from Merck (www.merck.de, Darmstadt, Germany). Alumina polishing suspension (0.05 CB micron Gamma Type, CR85S) was obtained from Balkowski International. All chemicals were high grade reagents and used as received.


2.2. Instrumentation Digital microscope (TENSION), ultrasonic bath (Elma, E3OH, Elmasonic), deionized water equipment (purelab Option-Q, ELGA, DV25), accurate balance (OHAUS Pioneer), and vacuum oven (DRY-Line, VWR) were used in various experimental steps. FTIRATR spectra of PTh, P3HTh, PTh/TiO2 and P(3HTh)/TiO2 were recorded on a Perkin Elmer, spectrum One B model with ZnSe crystal attachment. Surface morphology analysis of PTh, P3HTh, PTh/TiO2 and P(3HTh)/TiO2 coated specimen surfaces was performed by scanning electron microscope (model Jeol JSM-6360 LV).

2.2.1. Electrochemical Studies An Iviumstat model potasiostat/galvanostat (software, iviumsoft and Faraday cage, BASI Cell Stand C3 ) was used for electrochemical and corrosion tests, which was equipped with a three-electrode electrochemical cell, employing a Al1050 electrode (geometric area: 2 cm2) as a working electrode, platinum disk as a counter electrode (geometric area: 0.020 cm2) and a saturated calomel electrode (SCE) as a reference electrode. All potentials were presented on the SCE scale. Prior to each electrochemical experiment, the specimen was mechanically polished with abrasive paper (1200, 1600 and 2000 grade) and cleaned in 1:1 acetone-ethanol mixture in an ultrasonic bath to remove impurities,

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rinsed with water and then dried in N 2 atmosphere. All experiments were carried out at room temperature.

2.2.2. EIS Analysis Electrochemical impedance spectroscopy (EIS) measurements were recorded at room


temperature (25 oC ± 1), using a conventional three electrode cell configuration. EIS measurements were conducted in monomer-free electrolyte solutions with a perturbation amplitude as 10 mV with a frequency range from 10 mHz to 100 kHz on an Iviumstat Model Potasiostat/Galvanostat (software; iviumsoft).

3. RESULTS & DISCUSSION 3.1. Electrosynthesis Of Pth, Pth/Tio2, P(3hth) And P(3hth)/Tio2 Films The electrogrowth of Th, Th/TiO2, 3HTh, and 3HTh/TiO2 shows that current decreases by time due to the chronoamperometric method. The chronoamperometric plots also show that polymerization was successfully performed on Al1050 electrode surface. In the literature, the oxidation and reduction peak potentials of the monomer changes with many factors such as used polymerization methods, type of solvent, or type of electrolyte etc. In our previous CV results, the oxidation and reduction peak potentials of Th were obtained as Epa= 1.2 V and Epc= -0.49 V in 0.1 M NaClO4 / CH3CN in the initial monomer concentration of [Th]0 = 0.5 M [23]. The initial monomer concentration of Th and 3HT were taken as [Th]0= 100 mM and [3HT]0= 50 mM, respectively (Fig. 1a and c). However, the initial monomer concentration of PTh/TiO 2 and P3HT/TiO2 nanocomposites were taken as [Th]0= 75 mM and [3HT]0= 75 mM, respectively. (Fig. 1b

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and d). The weight percent of TiO2 nanomaterials were inserted as 2% into the Th and 3HT polymer matrix content. All polymerizations were performed in 0.5 M oxalic acid solution.

3.2. SEM-EDX Analysis


SEM analysis were obtained for PTh, PTh/TiO2, P(3HTh) and P(3HTh)/TiO 2 nanocomposite films on a Al1050 electrode (Fig. 2). Polymer and nanocomposite films were electrocoated by chronoamperometric method. The obtained SEM images show significant changes by addition of TiO2 nanoparticles.

In the EDX analysis, Ti element was obtained as the weight percent of 0.15% and 0.30% for PTh/TiO2 and P(3HTh)/TiO2 films, respectively (Table 1).

3.3. FTIR-ATR Analysis PTh was chemically synthesized by using CAN as an initiator. In FTIR-ATR spectrum of PTh correspond to peak at 3256-2849 cm-1 for C-H stretching, at 1436 cm-1 for C=C stretching, at 1305 cm-1 for C-H bending and at 741 cm-1 for C-S stretching (Fig. 3a). The C-H stretching peaks at 3256-2849 cm-1 for PTh shift to 3237-2968 cm-1 for PTh/TiO2 nanocomposite films. The C=C stretching peak at 1436 cm-1 shift to 1424 cm-1 for PTh/TiO2 films. At 1326 cm-1 , C-H bending and at 738 cm-1, C-S stretching were obtained as shown in Fig. 3b. The peak at 1088 cm-1 refers to Ti-O-C structure.

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The FTIR spectrum of P(3HTh) film shows the peak at 3256 -2916 cm-1 is attributed to C-H stretching due to hexyl substituents of alkan group. The peaks at 1420 cm-1 , 1087 cm-1 and 739 cm-1 refer to C-H bending, C-C stretching and C-S peaks, respectively (Fig. 3c). For P(3HTh)/TiO2 nanocomposite film, the peak at 3339 cm -1 indicates the aromatic C-H stretching, 2988 cm-1 refer to C-H alkan stretching. The peaks


at 1421 cm-1, 1305 cm-1 , 1250 cm-1 and 725 cm-1 refer to C=C, C-H bending, C-C stretching and C-S peaks, respectively. In addition, the peak at 1121 cm-1 comes from TiO-C structure of P(3HTh)/TiO2 nanocomposites (Fig. 3d).

3.4. Electrochemical Impedance Spectroscopic Analysis The EIS measurements of uncoated Al1050 electrode, PTh and PTh/TiO2 nanocomposite films were taken by Nyquist, Bode-magnitude, Bode-phase and Admittance plots in 3.5% NaCl solution as shown in Fig. 4. Electrochemical investigations fully indicated that the PTh and its substituents had good capacitance behavior and cycle stability as an electrode material for supercapacitors [24].

The low frequency capacitance (Csp) values of PTh and P(3HTh) and their nanocomposites with TiO2 films (at 0.01 Hz) were calculated by the equation of Csp= (2×f×Zim) -1, where Csp is the specific capacitance; (Zim) is the slope of a plot of the imaginary component of impedance versus the inverse of the frequency (f) [25]. The highest specific capacitance (Csp) was obtained as Csp= 0.234 mFcm-2 for PTh/TiO2 nanocomposite films. The Csp values were obtained as Csp= 0.171 mFcm-2 and Csp= 0.101 mFcm-2 for PTh and the uncoated Al1050 electrode, respectively (Fig. 4a). Similar results

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were obtained from the Bode-magnitude plot, which was obtained by double layer capacitance (Cdl). A value of Cdl can be calculated from a Bode-magnitude plot as shown in Fig.4b by extrapolating the linear section to value ω = 1 (log ω = 0), employing the relationship IZI = 1 / Cdl. The highest C dl was obtained as Cdl= 0.043 mFcm-2 for PTh/TiO2 nanocomposite films. Cdl was obtained as Cdl= 0.015 mFcm-2 and Cdl= 0.026


mFcm-2 for PTh and the uncoated Al1050 electrode, respectively (Fig. 4b). The phase angle was obtained from Bode-phase for uncoated Al1050 electrode, PTh and PTh/TiO2 nanocomposite film plots as Ɵ= 86.63o (410.94 Hz), 82.51 o (704.83 Hz) and 80.98 o (106.66 Hz), respectively. If the phase angle closes to 90o, the ideal capacitance behavior is obtained. The conductivity values were obtained from the Admittance plot. Admittance is defined as the inverse of impedance. Therefore, the order of the conductivities were obtained as uncoated Al1050, PTh/TiO2 nanocomposite film and PTh, respectively (Fig. 4d).

The Nyquist, Bode-magnitude, Bode-phase, and Admittance plots of an uncoated Al1050 electrode, P(3HTh) and P(3HTh)/TiO2 nanocomposite films are given in Figure 5. The highest total impedance (Csp + Cdl) was obtained as 0.245 mFcm-2 for P(3HTh)/TiO2 nanocomposite films. The obtained results show that the total capacitance values (Csp+Cdl= 0.245 mFcm-2) and protection efficiency values of P(3HTh)/TiO 2 nanocomposite films (PE= 98%) are the higher values than P(3HTh) nanocomposite films (PE= 93% and Csp+Cdl= 0.199 mFcm-2). P(3HTh)/TiO2 nanocomposite films have the higher phase angle (Ɵ= 83.59o at 67.15 Hz) than P(3HTh) (Ɵ= 72.41o at 398.07 Hz). Specifically, PTh and its derivatives not only show the high environmentally stability of

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both theirs doped and undoped states together with their structure, but also are capable of storing charge in the electrical double layer. As well as in the polymer matrix can offer a higher energy storage capacity by the fast reversible faradaic reaction occuring near the electrode surface [26–28].


3.5. Tafel Analysis Tafel extrapolation plots of the uncoated Al1050, PTh and PTh/TiO2 nanocomposite films were taken in 3.5% NaCl solution as given in Figure 6. The main aim of this work is to obtain higher polarization resistance (R p) and lower corrosion current (icorr) values compared to uncoated Al1050 electrode. The coated materials of PTh and P(Th/TiO2) have more polarization resistance (Rp), and due to this increase, corrosion current (icorr) and corrosion rate (CR) decrease [29].

The corrosion current for an uncoated Al1050 electrode was decreased from 16.2 µAcm-2 to icorr= 0.655 µAcm-2 for PTh and icorr= 1.11 µAcm-2 for PTh/TiO2 nanocomposite film. Protection efficiency (P) can be calculated from the following formula [30, 31]; P= (io – i) / io × 100 where io is the uncoated corrosion current density and i is the coated electrode corrosion current density. The protection efficiency was obtained as PE= 95% for PTh and PE= 93% for PTh/TiO2 nanocomposite films. Corrosion rates were decreased from 0.1773 mm×y-1 to 0.0071 mm×y-1 for PTh and from 0.1773 mm×y-1 to 0.0121 mm×y-1 for PTh/TiO2 films. However, Rp values increased from 1160 Ω to 17090 Ω for PTh and from 1160 Ω to 15780 Ω for PTh/TiO2 nanocomposite films.

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The Tafel extrapolation results were given for uncoated Al1050 electrode, P(3HTh) and P(3HTh)/TiO2 nanocomposite films in Table 2. icorr values were decreased from 16.2 µAcm-2 for the uncoated Al1050 electrode to icorr= 1.09 µAcm-2 for P(3HTh) and from 16.2 µAcm-2 to icorr= 0.315 µAcm-2 for P(3HTh)/TiO2 nanocomposite films. Corrosion rate (CR/mm×y-1) was obtained using the expression:


Ccorr= [0.13×icorr(Eω)]/(Ad) Where Eω denotes the equivalent weight (g/eg), A represents area (cm -2) and d is density (g/cm3). In addition, corrosion rates were decreased significantly as shown in Table 2. Polarization resistance (R p) was obtained from the Stern-Geary formula: Rp= (βa×βb) / 2.303×Icorr (βa + βc), where Icorr represents corrosion current density, β a denotes the Tafel slope of the anode, and βc is the Tafel slope of the cathode. However, polarization resistance (R p) was increased from Rp= 1160 Ω to Rp= 4093 Ω for P(3HTh) and from Rp= 1160 Ω to R p= 21790 Ω for P(3HTh)/TiO2 nanocomposite films. The protection efficiency (PE) was obtained as 93% and 98% for P(3HTh) and P(3HTh)/TiO 2 films.

4. CONCLUSION In this study, Th and 3HTh and their TiO2 nanocomposites were electrocoated on GCE. The PTh, PTh/TiO2, P(3HTh) and P(3HTh)/TiO2 films were characterized by SEM-EDX, FTIR-ATR, and EIS analysis. The polymer and nanocomposites were also electrocoated on an Al1050 substrate. The modified films were inserted in 3.5% NaCl solution. The results show that PE was obtained as PE= 95% for PTh and PE= 93% for PTh/TiO2 films. PE was obtained as PE= 93% for P(3HTh) and PE= 98% for

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P(3HTh)/TiO2 films. All polymer and nanocomposite films were extremely effective in protecting the Al1050 substrate against 3.5% NaCl solution.

ACKNOWLEDGEMENTS Author thank to Serhat Tikiz (Afyon Kocatepe Univ., TUAM, Afyon, Turkey) for


SEM-EDX measurements and Dr. Argun Gokceoren (ITU, Istanbul, Turkey) for FTIRATR measurements.

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[11] Xu, Q.; Ihalainen, P.; Smatt, J.H.; Maattanen, A.; Sund, P.; Wilen, C.E.; Peltonen, J. Appl. Surf. Sci. 2014, 313, 237. [12] Deshpande, P.P.; Pravin, P.; Jadhav, N.G.; Gelling, V.J.; Sazou, D. J. Coat. Technol. Res. 2014, 11, 473. [13] Ai, L.; Liu, Y.; Zhang, X.Y.; Ouyang, X.H.; Ge, Z.Y. Synth. Met. 2014, 191, 41.


[14] 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. Electrochim. Acta, 2013, 95, 192. [15] Uygun, A.; Turkoglu, O.; Sen, S.; Ersoy, E.; Yavuz, A.G.; Batır, G.G. Current Applied Physics, 2009, 9, 866. [16] Perepichka, I.F.; Perepichka, D.F.; Meng, H.; Wudl, F. Advanced Materials, 2005, 17: 2281. [17] Chi-Ching, K.; Cheng-Ting, W.; Wen-Chang, C. Macromolecular Symposia, 2009, 279, 41. [18] Gunes, S.; Nenad, M.; Nedeljkovic, J.V.; Sariciftci, N.S. Journal of Nanoscience and Nanotechnology, 2008, 19: 424009. [19] Nicho, M.E.; Medrano-Baca, M.G.; Leon-silva, U.; Escalante, J.; GonzalezRodriguez, G.; Guizado-Rodriquez, M.; Linzago-Elizalde, I. Corrosion, 2011, 67, Article number: 105002. [20] Kashif, M.; Ahmad, N.; Ahmad, S. J. Solid State Electrochem. 2014, 18, 1855. [21] Medrano-Vaca, M.G.; Gonzalez-Rodriguez, J.G.; Nicho, M.E.; Casales, M.; SalinasBravo, V.M. Electrochim. Acta, 2008, 53, 3500. [22] Sherif EM.; Soliman MS.; El-Danaf EA.; Almajid AA. Int. J. Electrochem. Sci. 2013, 8, 1103-1116.

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[23] Ates, M. Int. J. Electrochem. Sci., 2009, 4, 980. [24] Sarac, A.S.; Geyik, H.; Parlak, E.A.; Serantoni, M. Prog. Org Coat. 2007, 59, 28. [25] Fiordipenti, P.; Pistoia, G. Electrochim. Acta, 1989, 34, 215. [26] Zhang, H.; Hu, L.; Tu, J.; Jiao, S. Electrochim. Acta, 2014, 120, 122. [27] Gnanakan, S.R.P.; Karthikeyan, K.; Amaresh, S.; Cho, S.J.; Park, G.J.; Lee, Y.S.


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Table 1. EDX results of the PTh, PTh/TiO2 , P(3HTh) and P(3HTh)/TiO2 on Al1050


electrodes Samples

Al

C

N

PTh

53.40 12.01 6.08

PTh/TiO2

68.53 8.57

P(3HTh)

56.74 9.13

O

Na

Au

F

17.58 0.50 0.25 10.18 ----

-----

-----

4.69

11.59 ----

-----

6.47

0.15

-----

-----

-----

11.35 ----

-----

7.06

------ 15.72 -----

----

13.73 0.30

P(3HTh)/TiO2 10.24 20.58 ------ 16.90 ---

14

Cl

S

Ti

20.84 17.71

Table 2. Tafel analysis results of uncoated Al1050, PTh and PTh/TiO2, P(3HTh), [3HTh]0= 50 mM, and P(3HTh)/TiO2, [3HTh]0= 75 mM nanocomposite films were obtained in 3.5% NaCl solution. Results were taken for the 1st day

Material

Ecorr/V

icorr/(µAcm-

βa/Vdec-

βc

2

1

/Vdec-1


)

Rp / Ω

CR/mm×y-

PE

1

/%

Al1050

-0.017

16.2

0.147

0.213

1160

PTh

-0.815

0.655

0.094

0.114

17090 0.0071

95.0

PTh/TiO2

-1.041

1.11

0.169

0.156

15780 0.0121

93.0

P(3HTh)

-0.759

1.09

0.023

0.208

4093

0.0010

93.0

0.315

0.035

0.306

21790 0.0003

98.0

P(3HTh)/TiO2 -0.691

15

0.1773

---

Figure 1. Electrogrowth Th and 3HT and their TiO 2 nanocomposite film formations were performed on Al1050 electrode by chronoamperometic method a) Th, [Th] 0 = 100 mM, b) Th/TiO2, [Th]0= 75 mM c) 3HT, [3HT]0= 50 mM, d) 3HTh/TiO2, [Th]0= 75 mM, All experiments were performed at constant potential of 1.7 V, time= 1200 s, in 0.5 M oxalic


acid solution. 2% TiO2 nanoparticles were inserted into the composite film.

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Figure 2. SEM images of a) PTh, b) PTh/TiO2, [Th]0= 100 mM c) P(3HT) and d) P(3HT)/TiO2, [3HT]0= 75 mM electrocoated on Al1050 electrode. Electropolymerization was performed in 0.5 M oxalic acid/CH 3 CN at constant potential of 0.9 V (1200 s) by chronoamperometric method. The weight percent of PTh/TiO 2 and P(3HTh)/TiO2 were


taken as 2% TiO2 in the total composition.

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Figure 3. FTIR-ATR spectrums of a) PTh, [Th]= 100 mM, b) PTh/TiO2, c) P(3HT) and d) P(3HT)/TiO2 electrocoated on Al1050 electrode. All films were chemically


synthesized by using CAN initiator.

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Figure 4. The EIS analysis of uncoated Al1050 electrode, PTh, [Th]= 100 mM, PTh/TiO2, [Th]= 75 mM electrocoated on Al1050. a) Nyquist, b) Bode-magnitude, c)


Bode-phase, d) Admittance plots.

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Figure 5. The EIS analysis of uncoated Al1050, P(3HT), [3HT]= 50 mM, P(3HT)/TiO 2, [3HT]= 75 mM electrocoated on Al1050 electrode. a) Nyquist, b) Bode-magnitude, c)


Bode-phase, d) Admittance plots.

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Figure 6. Tafel plots of a) uncoated Al1050, PTh, [Th]0= 100 mM and PTh/TiO2 films, [Th]0= 75 mM b) uncoated Al1050, P(3HT), [3HT]0= 50 mM, and P(3HT)/TiO2 films.


[3HT]0= 75 mM.

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