PEDOT Nanotubes Electrochemically Synthesized on Flexible

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PEDOT Nanotubes Electrochemically Synthesized on Flexible Substrates: Enhancement of Supercapacitive and Electrocatalytic Properties Bruna M. Hryniewicz, and Marcio Vidotti ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.8b00694 • Publication Date (Web): 11 Jul 2018 Downloaded from http://pubs.acs.org on July 13, 2018

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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.

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ACS Applied Nano Materials

PEDOT Nanotubes Electrochemically Synthesized on Flexible Substrates: Enhancement of Supercapacitive and Electrocatalytic Properties

Bruna M. Hryniewicz and Marcio Vidotti* Grupo de Pesquisa em Macromoléculas e Interfaces, Departamento de Química, Universidade Federal do Paraná, CP 19032, 81531-980, Curitiba, PR, Brazil. *[email protected]

KEYWORDS: PEDOT nanotubes, electrochemical synthesis, methyl orange, supercapacitors, electrocatalysis.

ABSTRACT

PEDOT nanotubes were successfully electrodeposited onto stainless steel mesh electrodes in the presence of methyl orange template for the first time. It was found that the pH of the reaction medium is a key parameter to tune up the final morphology of the electrodeposited material. The modified electrodes were characterized by electrochemical, spectroscopic and scanning electron microscopy and transmission electron microscopy techniques. It was observed that the PEDOT

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nanotubes were formed all around the electrode in acidic conditions, while a globular morphology was verified in the synthesis in neutral medium. To better understand the mechanism of nanotube formation, the current-time transients obtained in the synthesis were fitted accordingly to a theoretical model and the total current was deconvoluted into components that describe the polymer 3D growth and EDOT oxidation onto PEDOT surface. The cyclic voltammetry of the modified electrodes exhibited an intense pseudocapacitive behavior and their properties were also tested by galvanostatic charge/discharge cycles. The maximum specific capacitance obtained herein was 307.3 F g-1 at a current density of 0.8 A g-1 and a capacity retention of 77% was obtained after 2500 galvanostatic charge/discharge cycles, with no drastic changes in the capacitance when the electrode was folded or twisted. The PEDOT nanotubes were also tested for the electrocatalytic reduction of 2-nitrophenol isomer, which was evaluated by spectroelectrochemical method. The constant rate obtained (1.07x10-3 s-1) could be compared with works employing chemical catalysis, indicating that the nanotube morphology provides excellent eletrocatalytical properties, the kinetic experiments were corroborated by the study of the interfacial electrochemical features by using electrochemical impedance spectroscopy experiments in an innovative methodology.

INTRODUCTION

Nanostructured materials have been severely studied to achieve the properties enhancement or even new characteristics compared with bulk materials. Many efforts have been focused in the synthesis of novel nanostructures for application in sensors, circuit integration, biomedical devices, sustainable energy and microfluidics.1 Amongst different materials,


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conducting polymers are certainly of great interest for the construction of nanostructured devices. Poly(3,4-ethylenedioxythiophene) (PEDOT) is one of the most interesting conducting polymer as it possesses high conductivity (4500 S/cm),2 moderate band gap with low redox potentials, environmental stability and facility of synthesis, that can be either chemically or electrochemically.3 PEDOT has been applied in chemical and electrochemical sensors,4-6 electrochromism7 and in the supercapacitors construction.8-9 Nanostructured PEDOT has been reported from different synthetic procedures, for example, the synthesis of PEDOT nanotubes or nanofibers was already described by using chemical methods using a reverse cylindrical micelle of sodium bis(2-ethylhexyl) sulfosuccinate (AOT)10, aqueous micellar solution of sodium dodecyl sulfate (SDS),11 by vapor-phase polymerization,2, 12-13 using aluminum anodic oxidation membrane,12 by electrochemical synthesis using cetyltrimethylammonium bromide (CTAB),14 among others.15-17

The methyl-orange (MO) aggregates have been extensively used for chemical polymerization in nanostructures. In some conditions, MO molecules form insoluble cylindrical or rectangular aggregates that can work as hard template for the formation of nanotubular conducting polymers.18-20 PEDOT, polypyrrole and polyaniline nanotubes were synthesized by using the chemical polymerization18,

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although solely polypyrrole nanotubes were

electrochemically synthesized employing MO as template.22 The electrochemical synthesis of nanomaterials has many advantages in comparison with the chemical method since the product is obtained directly at the electrode surface and it is not necessary any further modification step which could modify the material morphology, reflecting the loss of the advantages gained by the nanostructure. Also, the electrochemical synthesis is cleaner as it is employed less amount of chemicals and the possibility of secondary reactions is far diminished, which is not simple in the


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in the chemical synthesis. Finally, experimental parameters are easily controllable such as applied potential, deposition methodology, current and time, this aspect is of great importance for the tune up the physical chemical properties of the nanomaterial.

Different materials grown by electrodeposition have been exploited in the supercapacitors development, as oxides and hydroxides of transition metals, layered transition metal chalcogenides, conducting polymers and composites.23-27 Amongst them, conducting polymers have attracted attention as supercapacitor electrode materials due to their interesting properties such as reversibility during redox processes, mechanical flexibility, low cost and high conductivity.8 There are many works that report the use of PEDOT modified electrodes in the supercapacitors development that achieved good stability and high specific capacitances.9, 28-30 However, the swelling and shrinking mechanisms of the conducting polymers are common drawbacks that can decrease the stability in long term charge/discharge cycles.8,

31-32

A good

alternative to overcome these issues is the fabrication of nanostructures, for example, the nanotube or nanofiber morphology can shorten the diffusion distance of ionic transport and increase the specific area, leading to the better capacitive performance and superior stability in long term charge/discharge cycles.13 A good strategy to fabricate high performance supercapacitors relies on flexible electrodes,33 these substrates are very important for the rapid development of flexible electronics, such as touch screens and wearable sensors. Allied to this, conducting polymers are the most promising materials for foundation of flexible electrodes due to the high redox active-specific capacitance and inherent elastic polymeric nature.34

Another important feature of the conducting polymers relies on their versatility, besides the use of PEDOT in the supercapacitors development, it can be also employed for the chemical


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and electrochemical catalysis of nitrophenol isomers, which is very important since the 2nitrophenol and 4-nitrophenol are listed in United States Enviromental Protection Agency (USEPA) as hazardous pollutants and present high toxicity, facility of propagation in water and soil and difficult biological decomposition.35-36 As reported before, composites with PEDOT synthesized in the presence of polystyrene sulfonate (PEDOT:PSS) and gold or platinum nanoparticles were found to be good catalyst for the chemical reduction of 4-nitrophenol.37-38 Notwithstanding, PEDOT:PSS composite was very efficient on the simultaneous electrocatalysis of nitrophenol isomers on the construction of electrochemical sensors.39 Nonetheless, to the best of our knowledge the kinetic analysis by “in situ” UV-Vis spectroscopy of

nitrophenol

electrocatalysis has not been reported so far and this study can be of benefit of different areas of catalysis and electrochemistry. In this work, PEDOT nanotubes were electrochemically synthesized directly on stainless steel mesh electrodes by using MO aggregates as template. The tuning up of the morphology was performed by changing the pH of the reaction medium and the amount of deposited material. The modified electrodes were characterized by scanning electron microscopy and transmission electron microscopy. The electrochemical behavior of the nanotubes was studied by analysis of the current-time transients for the polymerization and by cyclic voltammetry. The supercapacitive properties of the nanotubes was investigated by charge/discharge cycles. Also, the synthesized material was tested for electrocatalysis of 2-nitrophenol, that was investigated by spectroelectrochemical method and electrochemical impedance spectroscopy measurements.

RESULTS AND DISCUSSION


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Material Characterization MO is and acid-basic indicator and its form in aqueous solution can be changed by the acidification of the medium. It is known that in concentrations above 5 mmol L-1, MO molecules are associated in a planar geometry containing five to seven units.18 Above pH 4.4, the β-azonitrogen of the molecules are hydrated, and the MO is found in form of a yellow salt. However, in pH below 3.1 the MO molecules have two different charges that promote intramolecular interactions,40 forming a precipitate that can be used as a template for the polymerization. The aggregation of MO in acid aqueous solution was summarized in Figure 1 (a).18 In the literature, the formation of MO aggregates was observed with both Fe3+ and H+ ions showing different shapes, such as rectangular and cylindrical.18-20 The aggregation of MO is characterized by a blue-shift in the UV-Vis spectra of aqueous solution, as seen in Figure 1(b).41 In our case, it was observed the formation of parallelepiped-like aggregates, some of them with a conical head, as seen in Figure 1(c-e) of TEM and SEM images of aggregates formed in pH 2 and in Figure S1 for the aggregates formed in pH 4.


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Figure 1. (a) Scheme of MO aggregation in acid aqueous solution. (b) UV-Vis spectra of MO aqueous solutions 60 µmol L-1 in pH 2, pH 4 and pH 7. Representative (c) Representative TEM and (d, e) SEM images of MO aggregates formed in aqueous solution pH 2.

The electrochemical synthesis of PEDOT nanotubes in the presence of MO aqueous solution was done in potentiostatic conditions with a charge control of 0.5 C cm-2 and 5.0 C cm-2 to verify how the amount of electrodeposited material would affect the morphology of the modified electrodes, also, the pH of the electrolytes was adjusted to 2, 4 and 7 for each synthesis. Lower deposition charges were tested, anyway, it was not observed the formation of PEDOT nanotubes in these cases. In Figure 2 are shown the SEM images of the PEDOT-NT electrodeposited under the different conditions described. The PEDOT-NT-pH2 modified electrode exhibited the nanotube morphology all over the electrode surface. The morphology of the PEDOT-NT-pH4 electrodes present both tubes and globules, the latter one vastly observed in the electrodeposition of conducting polymer films.16 On the other hand, it was not evidenced the formation of any nanotube morphology at the PEDOT-NT-pH7 sample. In the modified electrodes synthesized with the charge of 5 C cm-2 an interesting behavior was observed. When the synthesis was made in pH 2 and pH 4, nanotubes with an extremely rough surface were formed, but the synthesis in pH 7 only generated the globular structure of PEDOT with MO aggregates adsorbed. Interestingly, the MO structures remained at the electrode surface even after the washing process of the electrode with copious amount of ethanol.


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Figure 2. Representative SEM images of electrodes modified with 0.5 C cm-2 and 5 C cm-2 in two different magnifications.

The formation of MO aggregates in neutral solution are totally dependent of H+ ions generated from the electrolysis of the solvent, as explained by Lu et al.22 In this case, the formation of PEDOT nanotubes only occur after the formation of MO aggregates. As seen in Figure 2, the electrosynthesis performed in pH 7 (at 0.5 C cm-2 of charge) produced PEDOT in globular morphology, due to the absence of MO aggregates in the initial stages of polymerization. As the synthesis go forth and the applied potential is high enough (1.25 V), the electrolysis of water takes place, generating H+ locally on the electrode surface favoring by this way the MO aggregation, as observed in the PEDOT-NT-pH7 sample at 5 C cm-2.


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In the electrosynthesis performed at pH 2, MO aggregates are already formed when the potential of 1.25 V is applied, so the polymerization occurs around the aggregates, while in pH 4 only few MO aggregates are present in the reaction medium at the initial stages of polymerization, in this case both nanotubular and globular morphologies were generated. Further SEM images of pristine PEDOT synthesized with charge control of 0.5 C cm-2 and 5 C cm-2 are shown in Figure S2 and the globular morphology was verified as well, also TEM images of PEDOT-NT-pH2 and PEDOT-NT-pH4 deposited onto the electrode surface (Figure S3) show the internal cavity of nanotubes and the high roughness of the surface. It is also observed the great dispersion of nanotube size, with average diameters around 300 nm for PEDOT-NT-pH2 and 680 nm for PEDOT-NT-pH4. The Raman spectroscopy was employed to further characterize the as-synthesized materials. In Figure S4 are shown the spectra of the materials synthesized with the charge control of 0.5 C cm-2. Characteristic vibrations of PEDOT structure are observed in all spectra, such as the bands in 988 cm-1 attributed to oxyethylene ring deformation, in 1440 cm-1 attributed symmetrical Cα=Cβ(-O) stretching, in 1520 cm-1 related to the asymmetrical C=C stretching42 and in 1576 cm-1 assigned to the CH2 bending.43 The slight shifts observed can be attribuited to differences in organization of the polymeric chains, anyway, this result indicates that all materials are molecularly similar and the presence of MO during synthesis does not affect the structure of the PEDOT chain. To better understand the different morphologies obtained in this work the kinetic profile of the electropolymerization was properly studied by means of the mechanism of formation. Classically, the growth of conducting polymers onto electrodes can be divided into different processes that occur at the electrode/electrolyte interface.45 In the first stage, the molecules


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diffuse from the bulk to the electrode interface where they are oxidized, followed by the oligomerization process. When the oligomeric high-density region is stablished, clusters are deposited onto the electrode forming the growing nuclei. After this time, the current reaches a plateau and this region is often attributed as the nucleation and growth steps.45 In Figure 3 are present the current-time transients for the electropolymerization of the PEDOT in presence and absence of MO and each synthesis was performed with the same charge control of 0.5 C cm-2. The shapes of the curve profiles are dependent on nucleation and growth steps so the differences between the plots are attributed to modifications in the growth mechanism.

4

PEDOT PEDOT-NT-pH2 PEDOT-NT-pH4 PEDOT-NT-pH7

-2

3 j / mA 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

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2 1 0

100

200 300 400 Time / seconds

500

Figure 3. Current vs time transients for the polymerization of the different modified electrodes synthesized with charge control of 0.5 C cm-2 The current-time transients were fitted according to a theoretical model that was used to describe very well the shapes of the current-time plots of polypyrrole deposits46-47. The potentiostatic formation of a new phase involves the presence of two simultaneous electrode reactions. In our case, one is related to the 3D nucleation and growth of PEDOT limited by the mass transfer reaction, named as J3D, and other is the faradaic process of EDOT oxidation at the


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PEDOT surface growing nuclei, named as JEO. The total current can be described as the addition of both contributions, as can be seen in equation 1.46-48 Jtotal = JEO + J3D (1) The contribution of PEDOT diffusion limited 3D nucleation and growth (J3D) and the EDOT oxidation on the growing PEDOT surface (JEO) can be described as follows:48 JEO (t) = P1 1-exp -P2 t-

1-exp(-P3t) P3

and J3D (t) = P4t-1/2 1-exp -P2 t-

(2) (3)

1-exp(-P3t) P3

With: P1=

2C0 M 1/2

P2

πρ

8πco 1/2 ρ

zFk EO (4) N0 πD (5)

P3 = A (6) P4 = zFD1/2 c0 / (7) where c0 is the EDOT bulk concentration, ρ is the density of deposit, M is the molar mass of the deposit, zF is the molar mass charge transferred during the EDOT oxidation, kEO is the constant rate of the EDOT oxidation reaction on PEDOT surface, D is the EDOT diffusion coefficient, A is the PEDOT nucleation rate and N0 is the number density of active sites for PEDOT nucleation on electrode surface.


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Substituting equations (2) and (3) in (1), Jtotal can be parametrized according to equation 8:46-48 Jtotal (t) = (P1+P4t-1/2 ) 1-exp -P2 t-

1-exp(-P3t) P3

(8)

A nonlinear curve fit was used to obtain the values of P1, P2, P3 and P4 from the experimental current-time transients. Only PEDOT-NT-pH2 and PEDOT-NT-pH4 could be represented by this theoretical model, as seen in Figure S5. For other electrodes (PEDOT-NTpH7 and PEDOT), the parameters obtained by fitting the experimental data showed extremely high standard errors, so the results are unreliable. It is important to mention that for the better fitting, the effects of double layer capacitance in the j-t curves (observed as a drop in the current at the early stages of the electropolymerization) were removed as they are not related with the nucleation and growth of the polymer45. It is not possible to infer some parameters present in equations 4 to 7, as the density and molar mass of the deposit and the molar charge transferred during the oxidation, anyway, according to the values of P1, P2, P3 and P4 obtained through the fitting (see Table S1), the Jtotal can be deconvoluted in the JEO and J3D contributions using equations 2 and 3. The fitting data and the JEO and J3D contributions are shown in Figure 4(a) for PEDOT-NT-pH2 and Figure 4(c) for PEDOT-NT-pH4, along with SEM images of the modified electrodes, respectively as Figure 4(b) and 4(d).


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Figure 4. Deconvolution of Jtotal in the JEO and J3D contributions and representative SEM images of (a, c) PEDOT-NT-pH2 and (c,d) PEDOT-NT-pH4 modified electrodes.

From Figure 4(a) it is possible to note that the current of PEDOT-NT-pH2 electropolymerization is totally dependent of the 3D nucleation and growth processes, indicating that PEDOT deposition actually occurs over the electrode surface by simultaneous multiple nucleation of cones and the subsequent 3D growth, as verified in SEM image of the same material (Figure 4(b)). PEDOT-NT-pH4 modified electrode exhibited a Jtotal dependent of both JEO and J3D during all the electropolymerization time (Figure 4(c)), indicating that the nucleation is not so


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instantaneous as observed in PEDOT-NT-pH2 and this process is accompanied by the oxidation of some EDOT monomers, which might help the subsequent PEDOT growth. The overlap of both mechanism can be a result of the presence of few MO aggregates during the initial stages of polymerization. In this case, some EDOT monomers are oxidized simultaneously over the aggregates and adsorbed onto the electrode surface, while other monomers are free to be oxidized separately from the template at the PEDOT growing surface, which might result in the different structures observed (Figure 4(d)). In fact, analyzing the P3 values obtained by fitting the current-time transients, is possible to infer that the nucleation rate of PEDOT-NT-pH2 is 1.4 times higher than PEDOT-NT-pH4, corroborating with the mentioned above.

Supercapacitive properties The modified electrodes were electrochemically characterized by cyclic voltammetry in 1 mol L-1 NaCl, as shown in Figure 5 at a sweep rate of 20 mV s-1, all of them electrosynthesized to 0.5 C cm-2. The voltammograms at different scan rates are shown in Figure S6. In all voltammograms the modified electrodes exhibited a pseudocapacitive behavior with discrete redox waves, clearly the PEDOT-NT-pH2 showed the highest current density, as due to the unique nanotube morphology the electroactive sites are highly exposed. PEDOT-NT-pH7 modified electrode presented a less rectangular voltammogram, corroborating with the absence of nanotubes on the electrode surface. PEDOT-NT-pH4 material has shown a discrete enlargement of the redox behavior but still far from the pure nanotubes modified electrode.


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The CVs of PEDOT and PEDOT-NT-pH2 modified electrodes were deconvoluted in the surface capacitive and diffusion-controlled intercalation process,49-50 according to equations 9 and 10: I(V) = k1 υ + k2 υ1/2 (9) or I(V)/υ1/2 k1 υ1/2 + k2 (10) where I(V) is the current at a fixed potential, k1 υ and k2 υ1/2 correspond to the current contributions of the surface capacitive effects and diffusion-controlled intercalation process, respectively, being the sweep rate of the voltammogram. By plotting I(V)/υ1/2 versus υ1/2 it is possible to determine the values of k1 and k2 and separate the fraction of the total current arising from capacitive effects at each potential. In Figure 5 the total current of the CV at 20 mV s-1 was deconvoluted in the capacitive contribution (shade area). By comparing the stored charge in the shaded area and the total charge, we find that PEDOT and PEDOT-NT-pH7 have the smallest capacitive contribution to the total current (46% and 57%, respectively), while both PEDOT-NTpH2 and PEDOT-NT-pH4 have significative higher capacitive effects, with 64% and 67% of the total stored charge, respectively. These results indicate that the nanotube morphology has an important role in order to increase the double layer capacitance, which result in higher specific capacitances, as it will be discussed later on.


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6

6

PEDOT

-1

0

j/Ag

-1

j/Ag

PEDOT-NT-pH2

3

3

-3

0 -3 -6

-6 -1.2

-0.8

-0.4

0.0

0.4

-1.2

0.8

6

PEDOT-NT-pH4

0.0

0.4

0.8

PEDOT-NT-pH7

-1

3

0

j/Ag

-1

3

-3

0 -3 -6

-6 -1.2

-0.4

E / V vs Ag/AgCl/Cl sat


6

-0.8

-

-

j/Ag

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

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-0.8

-0.4

0.0

0.4 -


0.8

-1.2

-0.8

-0.4

0.0

0.4

0.8

-


Figure 5. Voltammograms in 1 mol L-1 NaCl of the modified electrodes synthesized with charge control of 0.5 C cm-2, scan rate of 20 mV s-1. The capacitive contribution to the total current is shown by the shaded area. The supercapacitive properties of the modified electrodes were tested by galvanostatic charge/discharge (GCD) experiments at different current densities in a three-electrode cell configuration. The GCD curves at 0.8 A g-1 for different electrodes are shown in Figure 6(a) and the GCD curves at different current densities are shown in Figure S7. All GCD curves present a discharge process with a deviation from the linearity due to the redox processes intrinsic of the conducting polymers.8 The specific capacitances were calculated from the GCD curves using equation 11.51


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Cm=

I × ∆T (11) ∆V×m

where Cm is the specific capacitance, I is current, ∆" is the discharge time, ∆# is the potential window of the galvanostatic discharge discounting the IR drop, according to previous reported study

52

and and m is the mass of the electrodeposited material, which was approximately 0.5

mg for all electrodes. The specific capacitances obtained in this work are listed on Table S2 and the effect of the current density on specific capacitances is shown in Figure 6(b).


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(a)

0.6


-


0.9

0.3 0.0 -0.3 -0.6 -0.9

0

150 300 450 600 750 900

Specific Capacitance / F g

-1

time / seconds

(b)

320


280 240 200 160 120 0.5

1.0 1.5 2.0 2.5 -1 Current Density / A g

100 Capacity 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

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3.0

(c)

80 77%

60 40 20 0

0

500 1000 1500 2000 2500 Cycle number

Figure 6. (a) GCD curves of the modified electrodes at 0.8 A g-1 in 1 mol L-1 NaCl (b) Specific capacitances calculated from GCD curves. (c) Capacity retention of PEDOT-NT-pH2 modified electrode over 2500 GCD cycles at current density of 3 A g-1


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The highest specific capacitance obtained in this work was 307.3 F g-1 at 0.8 A g-1, for the PEDOT-NT-pH2 modified electrode. This value is higher than other PEDOT-based modified electrodes recently published, as PEDOT:MWCNT:PTS (199 F g-1 at 0.5 A g-1);53 PEDOT nanofibers synthesized by evaporative vapor-phase polymerization (160 A g-1 at a current density of 1 A g-1);2 PEDOT nanopaper electrode (90 F g-1 at a current density of 1 mA cm-2);54 PEDOT/non-woven fabric composites (169 F g-1 at 0.2 A g-1)55 and PEDOT vapor-phase polymerized (134 F g-1 at 1.0 A g-1).56 The PEDOT-NT-pH2 modified electrode also exhibited the highest discharge time and a small IR drop, indicating the potentiality of this material in the construction of a high energy density supercapacitor. The capacity retention over 2500 cycles at current density of 3 A g-1 is shown in Figure 6(c). It is known that conducting polymers have poor capacity retention in long term GCD cycles because of the material swelling and shrinking during these processes.8, 31 Anyway, the nanotube morphology can shorten the diffusion distances for the ionic transport, leading to extended GCD cycles.13 PEDOT-NT-pH2 electrode provided a capacity retention of 77% over 2500 cycles, which is very satisfactory for a conducting polymer that was not synthesized with other species, as inorganic or organic compounds to form a composite. The specific capacitances of flexible electrodes in different strains are important parameters to develop flexible devices, so the electrochemical performance of the electrode during mechanical deformations should be evaluated. In this work, the flexibility properties were investigated with the electrode bent at 90º in horizontal and vertical directions and twisted, as seen in Figure 7(a). It was found a similar voltammogram profile when the electrode is in the normal position or under flex, with a slight decrease of the current density in the twisted position (Figure 7(b)). In Figure 7(c) are shown the GCD curves for the electrode in the different


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positions and the discharge time of the normal and 90º folded electrode were quite similar. Anyway, in the twisted position there was a slight decrease in the discharge time, which led to a smaller specific capacitance (87% of the normal capacitance). Moreover, the capacity retention of PEDOT-NT-pH2 modified electrode bent at 90º in horizontal direction confirm that the bending stress has little influence in the supercapacitive behavior, reaching a value of 99% of the initial capacitance after 100 GCD cycles alternating in the normal and bent positions (Figure 7(d)).

Figure 7. (a) Electrode in normal, 90º horizontal, 90º vertical and twisted positions. (b) CV and (c) GCD curves at 3 A g-1 of PEDOT-NT-pH2 electrode in different bending conditions. (d) Capacity retention of PEDOT-NT-pH2 modified electrode under bending conditions. The red and black dots symbolize the cycles with the electrode bent at 90º in horizontal direction and in normal position, respectively.


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Electrocatalytic properties Besides the excellent performance of the modified electrodes in the supercapacitors construction, the materials were tested for an additional application. As studied before,39 the PEDOT modified electrodes are capable of electrocatalyzing reactions involving nitrophenol isomers by reducing the nitro group to amino group, with many intermediate steps. Herein, the PEDOT nanotubes were tested for the electrocatalytic reduction of 2-nitophenol and the interfacial processes occurring at the electrode surface were investigated. In Figure 8(a) it is observed the cyclic voltammetry of PEDOT-NT-pH2 in presence of different concentrations of 2-nitrophenol in biphtalate buffer (pH 4), the same electrolyte used in previously reported data.39 In the voltammograms it is possible to verify a cathodic process in approximately -0.8 V described as the reduction of nitro group to hydroxylamine derivatives. Anyway, even with a high concentration of 2-nitrophenol, the reduction process was very discreet since the current (both capacitive and faradaic) in the PEDOT nanotubes voltammogram is very high due to the great amount of material, for a sensor development it must be considered less amount of material to achieve similar currents and it is important to note that the analytical performance and the proper sensor development by using the PEDOT-NTs are not the scope of the present work. Anyway, the physical chemical properties of this new electrosynthesized interface can be addressed in terms of heterogeneous electrocatalysis, where the intrinsic properties of the nanostructured

material

could

offer

several

advantages.57-58

In

this

way,

the

spectroelectrochemistry method was chosen to better evaluate the electrocatalytical performance of the PEDOT-NT modified electrodes. The UV-Vis spectra were taken during the application of a constant potential of -0.9 V and the electrochemical cell was assembled directly in the cuvette.


21


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The initial concentration of 2-nitrophenol in all experiments was 220 µmol L-1 in biphtalate buffer pH 4. In Figure 8(b) are shown the UV-Vis spectra obtained for the electrocatalysis of 2nitrophenol during various times of reaction. It is possible to distinguish two different bands, the first one in 350 nm is related to the 2-nitrophenol59 initially present in the medium and the decrease of this band is observed during the electrocatalysis, due to the isomer consumption at the reduction process. The second band in 450 nm is related to the azo derivative formed during the 2-nitrophenol reduction, as studied before.39 The band in 350 nm was chosen to proceed the kinetic analysis (Figure 8(c)), according to the equation of the pseudo-first order reaction (equation 12): At =$A0 -A∞ %ekapp t +A∞ (12) where At is the absorbance as function of time, A0 is the initial absorbance, &' is the absorbance in the infinite, kapp is the apparent constant rate and t is time. The experiments were performed with five different electrodes of the same material to evaluate the reproducibility and reliability of the results. In Figure 8(d) are shown the average kapp obtained for the different modified electrodes with the standard deviations. All calculated values from the kinetic analysis are shown in Table S3.


22

0.4

-1

0 mmol L

0.3

0.6 mmol L

(a)

(b) 0.3

-1

Absorbance

0.6

0.0 -0.3 -0.6 -1.2

-0.8 -0.4 0.0 0.4 E / V vs Ag/AgCl/Cl sat

0.2 0.1 0.0 320

0.8

360

400

440

480

520

Wavelength / nm

0.40

1.2

(c) 0.9


(d)

-3

kapp/ 1x10 s

-1

0.36 A-A0

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


i / mA

Page 23 of 37

0.32

0.6 0.3

0.28 0

10

20

30

40

0.0

Time / minutes

Figure 8. (a) Cyclic voltammetry of PEDOT-NT-pH2 electrode in the presence of different concentrations of 2-nitrophenol (maximum of 0.6 mmol L-1 in biphtalate buffer). (b) “In situ” UV–vis spectra obtained for the electrocatalytic reduction of 2-nitrophenol by PEDOT-NT-pH2a modified electrode in biphtalate buffer pH 4. (c) Kinetic analysis of 2-nitrophenol reduction and (d) apparent constant rates obtained from the kinetic analysis, S/N =5.

It is noticeable that PEDOT, PEDOT-NT-pH4 and PEDOT-NT-pH7 modified electrodes presented almost the same value of kapp, indicating similar electrocatalytical interfaces, depicted by the presence of the globular PEDOT on the surface, as observed in the SEM images. However, the PEDOT-NT-pH2 modified electrode presented a superior value of k when


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compared to the other modified electrodes, with an average kapp of 1.07x10-3 s-1, indicating a higher electroactive surface. The direct comparison of kapp obtained in this work to others in the literature is not simple, because for an electrochemical reaction the constant rate is directly related to the rate of electron transfer and no works were found that evaluate the electrocatalysis of nitrophenol by kinetic measurements. Anyway, this value could be compared to works employing heterogeneous catalysis through chemical reactions. The kapp obtained in this work is comparable and has the same order of magnitude that some recent published works as Fe3O4/SiO@Ag particles (kapp of 5.5x10-3 s-1),60 core-shell composite microspheres Au-polypyrrole/fly ash (kapp 6.4x10-3 s-1) 61 and Fe oxychlorides (kapp 2.5x10-3 s-1).62 Although these works obtained higher apparent constant rates, the electrocatalysis has some advantages compared to the conventional heterogeneous catalysis, as the versatility over different reactions, the selectivity resulted from the control of the working potential, the possibility of automation and the facile recovery and reuse of the catalyst. The study of the electrocatalytical properties of the material can be extended through electrochemical impedance spectroscopy (EIS) experiments using 2-nitrophenol as a probe. The measurements were done in -0.9 V, the same potential used for the spectroelectrochemical experiments. In Figure 9(a) are shown the Nyquist plots obtained for the different modified electrodes and it is possible to observe the formations of two depressed arcs in all plots. This behavior was observed before in EIS experiments with PPy modified electrodes in potentials above 0.0 V

63

and also in thicker films of conducting polymers.64-65 Each arc is related with

different charge transfer processes. The arc in higher to medium frequencies is ascribed as the capacitance of the polymeric film and resistance for the electron transfer between the steel mesh and the conducting polymer, which is significative since the polymer is in neutral state at -0.9 V,


24

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while the arc in low frequencies is related with the PEDOT/electrolyte interface. The equivalent circuit used to fit the experimental data was described before,64-67 with some modifications since the Warburg diffusion element was not observed. The equivalent circuit is shown inset in Figure 9(a) and is formed by a resistance of the solution (Rs), a high frequency bulk PEDOT resistance (Rf), a constant-phase element accounting for bulk PEDOT capacitance (Cf), a second constant phase element describing the non-ideal double-layer capacitance (Cdl) and a charge transfer resistance (Rct).64, 66 The parameters obtained through fitting the EIS data are shown in Table 1.

Table 1. EIS parameters obtained from fitting the experimental data. Modified electrode

Rs / Ω

Rf / Ω

Cf / µF sn-1

Rct / Ω

Cdl / mF sn-1

PEDOT

18.73

102.3

20.71

129.7

12.8

PEDOT-NT-pH2

22.48

144.4

12.30

31.60

57.0

PEDOT-NT-pH4

25.23

116.0

8.96

79.73

22.0

PEDOT-NT-pH7

25.64

161.6

7.40

119.2

12.6

The values of Rs were quite similar for all electrodes, since the electrolytes and the connections were the same in the analysis. All the electrodes synthesized in the presence of MO present higher values of Rf and smaller values of Cf in comparison with pure PEDOT, since some MO molecules, that are less conductive than the polymer, can be trapped into the polymeric matrix hiding some electroactive sites in the material. PEDOT-NT-pH2 modified electrode exhibited a smaller charge transfer resistance in comparison with other modified


25


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electrodes indicating that the nitrophenol reduction is favored at the nanotubes surface. This result is consistent with the higher apparent constant rate obtained for PEDOT-NT-pH2 electrode in the spectroelectrochemical experiments and indicates that the better electrocatalytical performance of this electrode is related with the interfacial kinetic of the electron transfer between the polymer and 2-nitrophenol and with the nature of the polymeric film.68 It is also observed higher double layer capacitances for PEDOT-NT-pH2 and PEDOT-NT-pH4 compared to PEDOT and PEDOT-NT-pH7, which is in agreement with the fractions of the capacitive effects to the total current, verified in the voltammograms in Figure 7. This could be an evidence of a higher electroactive surface area of the nanotubes compared to the polymeric films, increasing the number of ions that can be accommodated in the electrochemical double layer, the best comparison between these parameters can be found in Figure 9(b), where both Rct and Cdl values of the PEDOT and PEDOT-NT-pH2 modified electrodes are shown. The schematic representation of the different interfaces of those electrodes are shown in Figure 9(c).


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Figure 9. (a) Nyquist plots of the samples and the fitted results using a ZVIEW electrochemical software. (inset) Equivalent circuit used to fit the EIS data. (b) Comparison between Rct and Cdl values of PEDOT and PEDOT-NT-pH2 modified electrodes; (c) Processes occurring at electrode/polymer and polymer/electrolyte interfaces in presence of 2-nitrophenol.


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CONCLUSION PEDOT nanotubes were electrochemically synthesized by using methyl-orange aggregates as a template for polymerization. It was found that the pH of the reaction medium totally influence the final morphology. The nanotube morphology was obtained for the materials synthesized in pH 2 and pH 4 with charge control of 0.5 C cm-2 and 5 C cm-2, as observed in SEM and TEM images. It was found that the synthesis at pH 7 generated PEDOT in globular morphology and MO aggregates remained adsorbed at the polymeric surface synthesized with higher deposition charge. The electropolymerization was studied by the analysis of the current-time transients and the total current was deconvoluted into the 3D growth and EDOT oxidation contributions. The modified electrodes were tested for supercapacitors construction and an excellent specific capacitance was reached (307.3 F g-1 at 0.8 A g-1) for the PEDOT-NT-pH2 modified electrode. Finally, the modified electrodes were employed for the electrocatalytical reduction of 2nitrophenol. The reaction was accompanied by UV-Vis spectroscopy and the kinetic analysis revealed an apparent constant rate in the same order of magnitude of previous reported catalysis by chemical reduction. The electrocatalytic behavior was further investigated through EIS measurements using 2-nitrophenol as a probe, which indicated a smaller charge transfer resistance for the PEDOT-NT-pH2 modified electrode.

METHODS Chemicals and materials: All solutions were prepared by using ultrapure water by a MilliQ system (R = 18.2 MΩ·cm). The EDOT (97% Aldrich) was purified by distillation under low pressure and bubbled with N2 stream. Methyl orange (MO - Aldrich), H2SO4 (Synth), HNO3


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(Synth), NaCl (Aldrich), potassium biphtalate (Aldrich) and KNO3 (Aldrich) were used as received. All the electrochemical measurements were done in IviumStat potentiostat using stainless steel mesh (Geometric Area of 1.4 cm²) as working electrode, a large area platinum foil as counter electrode and the Ag/AgCl/Cl-sat reference electrode. Electrochemical synthesis: The reaction medium was composed by 100 mmol L-1 of EDOT, 5 mmol L-1 of MO and 8 mmol L-1 of KNO3 with pH adjusted to 2, 4 and 7 with 1 mol L-1 HNO3, generating the modified electrodes PEDOT-NT-pH2, PEDOT-NT-pH4 and PEDOT-NT-pH7, respectively. The synthesis was made without MO to produce the pristine PEDOT.

The

electrochemical synthesis was performed under potentiostatic conditions (1.25 V) with charge control of 0.5 C cm-2 and 5 C cm-2. This methology is very interesting as by controlling the charge passed through the synthesis it is possible to obtain similar amounts of electrodeposited material in all electrodes and provide a proper comparison between them. Characterizations: The electrochemical characterizations was performed in 1 mol L-1 NaCl and 1 mol L-1 H2SO4. Firstly, the electrodes were characterized by cyclic voltammetry at different scan rates (10 - 100 mV s-1). The galvanostatic charge/discharge curves were performed with current densities ranging from 0.8 A g-1 to 3 A g-1. The mass loading of the modified electrode was measured by gravimetric weight difference in a sensitive microbalance (Mettler Toledo XSE205DU). The morphologies of PEDOT nanotubes were investigated by Scanning Electron Microscope (SEM) in a TESCAN VEGA3 LMU and Transmission Electron Microscope (TEM) in a JEOL JEM 1200EX-II, the images showed herein are the representative ones, at least five different points from different synthesis were tested to assure homogeneity and reproducibility. The spectroscopic characterization was performed in a Confocal Raman


29


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Microscopy Witec Alpha 300R. The spectra were taken at least at five different points of the sample to verify the reproducibility. Electrocatalysis of 2-nitrophenol: UV-Vis spectroscopy was employed to evaluate the electrocatalytic properties of the materials on the 2-nitrophenol reduction. The experiments were performed in situ during the application of -0.9 V in biphtalate buffer pH 4 with 220 µmol L-1 of 2-nitrophenol, using the PEDOT modified electrodes with charge control of 0.5 C cm-2 as working electrode, a platinum foil as counter electrode and Ag/AgCl/Cl-(sat) as reference electrode. The spectra were taken each minute and the experiment was performed five times. The EIS measurements were performed with the frequency ranging from 10 kHz to 10 mHz with an applied ac voltage of 10 mV and dc potential equal to -0.9 V in biphtalate buffer pH 4 with 220 µmol L-1 of 2-nitrophenol. A ZVIEW software was used to fit the experimental EIS data.

ASSOCIATED CONTENT Supporting Information. Figure S1. TEM images of MO aggregates formed in pH 4 aqueous solution. Figure S2. SEM images of pristine PEDOT synthesized with charge control of 0.5 C cm-2 and 5 C cm-2. Figure S3. TEM images and diameter distribution of PEDOT-NT-pH2 and PEDOT-NT-pH4 modified electrode with charge control of 0.5 C cm-2. Figure S4. Raman spectra of modified electrodes with charge control of 0.5 C cm-2 along with the spectrum of MO aggregates.


30

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Figure S5. Current-time transients of (a) PEDOT-NT-pH and (b) PEDOT-NT-pH4 modified electrodes with charge control of 0.5 C cm-2, along with fitted curve and the obtained R2. Figure S6. CV at different scan rates of (a) PEDOT, (b) PEDOT-NT-pH2, (c) PEDOT-NT-pH4, (d) PEDOT-NT-pH7 modified electrodes. Figure S7. GCD curves at different current densities of (a) PEDOT, (b) PEDOT-NT-pH2, (c) PEDOT-NT-pH4, (d) PEDOT-NT-pH7 modified electrodes. Table S1. Parameters obtained from fitting current-time transients (Figure 6) using equation 7. Table S2. Specific capacitances calculated from GCD curves in 1 mmol L-1 NaCl. Table S3. Pseudo-first order rate constants obtained in the kinetic analysis of 2-nitrophenol electrocatalytic reduction.

AUTHOR INFORMATION Corresponding Author Prof. Dr. Marcio Vidotti Grupo de Pesquisa em Macromoléculas e Interfaces, Departamento de Química, Universidade Federal do Paraná, CP 19032, 81531-980, Curitiba, PR, Brazil.


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[email protected]

ACKNOWLEDGMENT The authors thank the Brazilian agencies Fundação Araucária (308/2014), CAPES and CNPq for the financial support and Centro de Microscopia Eletrônica (CME-UFPR) for the SEM and TEM facilities. Also, INCT in Bioanalytics (FAPESP grant no. 2014/50867-3 and CNPq grant no. 465389/2014-7) is kindly acknowledged.

REFERENCES 1. Im, S. G.; Kusters, D.; Choi, W.; Baxamusa, S. H.; Sanden, M. C. M. v. d.; Gleason, K. K., Conformal Coverage of Poly(3,4-Ethylenedioxythiophene) Films with Tunable Nanoporosity via Oxidative Chemical Vapor Deposition. ACS Nano 2008, 2, 1959-1967. 2. D’Arcy, J. M.; El-Kady, M. F.; Khine, P. P.; Zhang, L.; Lee, S. H.; Davis, N. R.; Liu, D. S.; Yeung, M. T.; Kim, S. Y.; Hammond, P. T.; Kaner, R. B., Vapor-Phase Polymerization of Nanofibrillar Poly(3,4-Ethylenedioxythiophene) for Supercapacitors. ACS Nano 2014, 8, 15001510. 3. Groenendaal, L. B.; Jonas, F.; Freitag, D.; Pielartzik, H.; Reynolds, J. R., Poly(3,4Ethylenedioxythiophene) and Its Derivatives: Past, Present, and Future Adv. Mater. 2000, 12, 481-494. 4. Atta, N. F.; Galal, A.; El-Ads, E. H., Gold Nanoparticles-Coated Poly(3,4-EthyleneDioxythiophene) for the Selective Determination of Sub-Nano Concentrations of Dopamine in Presence of Sodium Dodecyl Sulfate. Electrochim. Acta 2012, 69, 102-111. 5. Gonçalves, A. R.; Ghica, M. E.; Brett, C. M. A., Preparation and Characterisation of Poly(3,4-Ethylenedioxythiophene) and Poly(3,4-Ethylenedioxythiophene)/Poly(Neutral Red) Modified Carbon Film Electrodes, and Application as Sensors for Hydrogen Peroxide. Electrochim. Acta 2011, 56, 3685-3692. 6. Jang, J.; Chang, M.; Yoon, H., Chemical Sensors Based on Highly Conductive PEDOT Nanorods. Adv. Mater. 2005, 17, 1616-1620. 7. Cutler, C. A.; Bouguettaya, M.; Reynolds, J. R., PEDOT Polyelectrolyte Based Electrocromic Films via Eletrostatic Adsorption. Adv. Mater. 2002, 14, 684-688. 8. Snook, G. A.; Kao, P.; Best, A. S., Conducting-Polymer-Based Supercapacitor Devices and Electrodes. J. Power Sources 2011, 196, 1-12. 9. Kelly, T. L.; Yano, K.; Wolf, M. O., Supercapacitive Properties of PEDOT and Carbon Colloidal Microspheres. ACS Appl. Mater. Interfaces 2009, 1, 2536-43. 10. Zhang, X.; Lee, J.-S.; Lee, G. S.; Cha, D.-K.; Kim, M. J.; Yang, D. J.; Manohar, S. K., Chemical Synthesis of PEDOT Nanotubes. Macromolecules 2006, 39, 470-472.


32

Page 33 of 37 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


11. Han, M. G.; Foulger, S. H., Facile Synthesis of Poly(3,4-Ethylenedioxythiophene) Nanofibers from an Aqueous Surfactant Solution. Small 2006, 2, 1164-9. 12. Back, J.-W.; Lee, S.; Hwang, C.-R.; Chi, C.-S.; Kim, J.-Y., Fabrication of Conducting PEDOT Nanotubes Using Vapor Deposition Polymerization. Macromol. Res. 2011, 19, 33-37. 13. Liu, R.; Cho, S. I.; Lee, S. B., Poly(3,4-Ethylenedioxythiophene) Nanotubes as Electrode Materials for a High-Powered Supercapacitor. Nanotechnology 2008, 19, 215710. 14. Li, Y.; Wang, B.; Chen, H.; Feng, W., Improvement of the Electrochemical Properties via Poly(3,4-Ethylenedioxythiophene) Oriented Micro/Nanorods. J. Power Sources 2010, 195, 3025-3030. 15. Nair, S.; Hsiao, E.; Kim, S. H., Melt-Welding and Improved Electrical Conductivity of Nonwovenporous Nanofiber Mats of Poly(3,4-Ethylenedioxythiophene) Grown on Electrospun Polystyrene Fiber Template. Chem. Mater. 2009, 21, 115-121. 16. Patra, S.; Barai, K.; Munichandraiah, N., Scanning Electron Microscopy Studies of PEDOT Prepared by Various Electrochemical Routes. Synth. Met. 2008, 158, 430-435. 17. Park, E.; Kwon, O. s.; Park, S. j.; Lee, J. s.; You, S.; Jang, J., One-Pot Synthesis of Silver Nanoparticles Decorated Poly(3,4-Ethylenedioxythiophene) Nanotubes for Chemical Sensor Application. J. Mater. Chem. 2012, 22, 1521-1526. 18. Dai, T.; Lu, Y., Water-Soluble Methyl Orange Fibrils as Versatile Templates for the Fabrication of Conducting Polymer Microtubules. Macromol. Rapid Commun. 2007, 28, 629633. 19. Li, Y.; Bober, P.; Trchová, M.; Stejskal, J., Polypyrrole Prepared in the Presence of Methyl Orange and Ethyl Orange: Nanotubes Versus Globules in Conductivity Enhancement. J. Mater. Chem. C 2017, 5, 4236-4245. 20. Kopecká, J.; Kopecký, D.; Vrňata, M.; Fitl, P.; Stejskal, J.; Trchová, M.; Bober, P.; Morávková, Z.; Prokeš, J.; Sapurina, I., Polypyrrole Nanotubes: Mechanism of Formation. RSC Adv. 2014, 4, 1551-1558. 21. Yang, X.; Zhu, Z.; Dai, T.; Lu, Y., Facile Fabrication of Functional Polypyrrole Nanotubes via a Reactive Self-Degraded Template. Macromolecular Rapid Communications 2005, 26, 1736-1740. 22. Yang, X.; Dai, T.; Zhu, Z.; Lu, Y., Electrochemical Synthesis of Functional Polypyrrole Nanotubes via a Self-Assembly Process. Polymer 2007, 48, 4021-4027. 23. Lei, W.; He, P.; Zhang, S.; Dong, F.; Ma, Y., One-Step Triple-Phase Interfacial Synthesis of Polyaniline-Coated Polypyrrole Composite and Its Application as Electrode Materials for Supercapacitors. J. Power Sources 2014, 266, 347-352. 24. Mariappan, V. K.; Krishnamoorthy, K.; Pazhamalai, P.; Sahoo, S.; Kim, S.-J., Electrodeposited Molybdenum Selenide Sheets on Nickel Foam as a Binder-Free Electrode for Supercapacitor Application. Electrochim. Acta 2018, 265, 514-522. 25. Wang, N.; Sun, B.; Zhao, P.; Yao, M.; Hu, W.; Komarneni, S., Electrodeposition Preparation of NiCo2O4 Mesoporous Film on Ultrafine Nickel Wire for Flexible Asymmetric Supercapacitors. Chem. Eng. J. 2018, 345, 31-38. 26. Chen, J.; Wang, Y.; Cao, J.; Liu, Y.; Zhou, Y.; Ouyang, J. H.; Jia, D., Facile CoElectrodeposition Method for High-Performance Supercapacitor Based on Reduced Graphene Oxide/Polypyrrole Composite Film. ACS Appl. Mater. Interfaces 2017, 9, 19831-19842. 27. Fan, X.; Wang, X.; Li, G.; Yu, A.; Chen, Z., High-Performance Flexible Electrode Based on Electrodeposition of Polypyrrole/MnO2 on Carbon Cloth for Supercapacitors. J. Power Sources 2016, 326, 357-364.


33


Page 34 of 37

28. Xie, Y.; Du, H.; Xia, C., Porous Poly(3,4-Ethylenedioxythiophene) Nanoarray Used for Flexible Supercapacitor. Microporous Mesoporous Mater. 2015, 204, 163-172. 29. Alhashmi Alamer, F., A Simple Method for Fabricating Highly Electrically Conductive Cotton Fabric without Metals or Nanoparticles, Using PEDOT:Pss. J. Alloys Compd. 2017, 702, 266-273. 30. Zhang, H.; Li, J.; Gu, C.; Yao, M.; Yang, B.; Lu, P.; Ma, Y., High Performance, Flexible, Poly(3,4-Ethylenedioxythiophene) Supercapacitors Achieved by Doping Redox Mediators in Organogel Electrolytes. J. Power Sources 2016, 332, 413-419. 31. Ghosh, S.; Maiyalagan, T.; Basu, R. N., Nanostructured Conducting Polymers for Energy Applications: Towards a Sustainable Platform. Nanoscale 2016, 8, 6921-47. 32. Osterholm, A. M.; Ponder, J. F., Jr.; Kerszulis, J. A.; Reynolds, J. R., Solution Processed PEDOT Analogues in Electrochemical Supercapacitors. ACS Appl. Mater. Interfaces 2016, 8, 13492-8. 33. Lehtimäki, S.; Suominen, M.; Damlin, P.; Tuukkanen, S.; Kvarnstrom, C.; Lupo, D., Preparation of Supercapacitors on Flexible Substrates with Electrodeposited PEDOT/Graphene Composites. ACS applied materials & interfaces 2015, 7, 22137-22147. 34. Shown, I.; Ganguly, A.; Chen, L.-C.; Chen, K.-H., Conducting Polymer-Based Flexible Supercapacitor. Energy Sci. Eng. 2015, 3, 2-26. 35. Ni, Y.; Wanga, L.; Kokot, S., Simultaneous Determination of Nitrobenzene and NitroSubstituted Phenols by Differential Pulse Voltametry and Chemometrics. Analytica Chimica Acta 2001, 431, 101-113. 36. Shen, J.; Zhang, Y.; Xu, X.; Hua, C.; Sun, X.; Li, J.; Mu, Y.; Wang, L., Role of Molecular Structure on Bioelectrochemical Reduction of Mononitrophenols from Wastewater. Water Res. 2013, 47, 5511-9. 37. Kumar, S. S.; Kumar, C. S.; Mathiyarasu, J.; Phani, K. L., Stabilized Gold Nanoparticles by Reduction Using 3,4-Ethylenedioxythiophene-Polystyrenesulfonate in Aqueous Solutions: Nanocomposite Formation, Stability, and Application in Catalysis. Langmuir 2007, 23, 34013408. 38. Harish, S.; Mathiyarasu, J.; Phani, K. L. N.; Yegnaraman, V., Synthesis of Conducting Polymer Supported Pd Nanoparticles in Aqueous Medium and Catalytic Activity Towards 4Nitrophenol Reduction. Catal. Lett. 2008, 128, 197-202. 39. Hryniewicz, B. M.; Orth, E. S.; Vidotti, M., Enzymeless PEDOT-Based Electrochemical Sensor for the Detection of Nitrophenols and Organophosphates. Sens. Actuators, B 2018, 257, 570-578. 40. Sapurina, I.; Li, Y.; Alekseeva, E.; Bober, P.; Trchová, M.; Morávková, Z.; Stejskal, J., Polypyrrole Nanotubes: The Tuning of Morphology and Conductivity. Polymer 2017, 113, 247258. 41. Buwalda, R. T.; Jonker, J. M.; Engberts, J. B. F. N., Aggregation of Azo Dyes with Cationic Amphiphiles at Low Concentrations in Aqueous Solution. Langmuir 1999, 15, 10831089. 42. Garreau, S.; Louarn, G.; Buisson, J. P.; Froyer, G.; Lefrant, S., In Situ Spectroelectrochemical Raman Studies of Poly(3,4-Ethylenedioxythiophene) (Pedt). Macromolecules 1999, 32, 6807-6812. 43. Tran-Van, F.; Garreau, S.; Louarn, G.; Froyer, G.; Chevrot, C., Fully Undoped and Soluble Oligo(3,4-Ethylenedioxythiophene)S: Spectroscopic Study and Electrochemical Characterization. J. Mater. Chem. 2001, 11, 1378-1382.


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44. Zhang, A.; Fang, Y., Influence of Adsorption Orientation of Methyl Orange on Silver Colloids by Raman and Fluorescence Spectroscopy: pH Effect. Chem. Phys. 2006, 331, 55-60. 45. Randriamahazaka, H.; Noël, V.; Chevrot, C., Nucleation and Growth of Poly(3,4Ethylenedioxythiophene) in Acetonitrile on Platinum under Potentiostatic Conditions. J. Electroanal. Chem. 1999, 472, 103-111. 46. Licona-Sánchez, T. d. J.; Álvarez-Romero, G. A.; Mendonza-Huizar, L. H.; Galán-Vidal, C. A., Nucleation and Growth Kinetics of Electrodeposited Sulfate-Doped Polypyrrole: Determination of the Diffusion Coefficient of SO42- in the Polymeric Membrane. J. Phys. Chem. B 2010, 114, 9737-9743. 47. Licona-Sánchez, T. d. J.; Álvarez-Romero, G. A.; Palomar-Pardavé, M.; Galán-Vidal, C. A.; Páez-Hernández, M. E.; Silva, M. T. R.; Romero-Romo, M., Influence of the Cation Nature of the Sulphate Salt on the Electrochemical Synthesis of Sulfate-Doped Polypyrrole. Int. J. Electrochem. Sci. 2011, 6, 1537-1549. 48. Palomar-Pardavé, M.; Scharifker, B. R.; Arce, E. M.; Romero-Romo, M., Nucleation and Diffusion-Controlled Growth of Electroactive Centers Reduction of Protons During Cobalt Electrodeposition. Electrochim. Acta 2005, 50, 4736-4745. 49. Wang, J.; Polleux, J.; Lim, J.; Dunn, B., Pseudocapacitive Contributions to Electrochemical Energy Storage in TiO2 (Anatase) Nanoparticles. J. Phys. Chem. C 2007, 111, 14925-14931. 50. Wang, F.; Wu, X.; Yuan, X.; Liu, Z.; Zhang, Y.; Fu, L.; Zhu, Y.; Zhou, Q.; Wu, Y.; Huang, W., Latest Advances in Supercapacitors: From New Electrode Materials to Novel Device Designs. Chem. Soc. Rev. 2017, 46, 6816-6854. 51. Zhang, S.; Pan, N., Supercapacitors Performance Evaluation. Adv. Energy Mater. 2015, 5, 1401401. 52. Xu, R.; Wei, J.; Guo, F.; Cui, X.; Zhang, T.; Zhu, H.; Wang, K.; Wu, D., Highly Conductive, Twistable and Bendable Polypyrrole–Carbon Nanotube Fiber for Efficient Supercapacitor Electrodes. RSC Advances 2015, 5, 22015-22021. 53. Zhou, H.; Liu, G.; Liu, J.; Wang, Y.; Ai, Q.; Huang, J.; Yuan, Z.; Tan, L.; Chen, Y., Effective Network Formation of PEDOT by in-Situ Polymerization Using Novel Organic Template and Nanocomposite Supercapacitor. Electrochim. Acta 2017, 247, 871-879. 54. Wang, Z.; Tammela, P.; Huo, J.; Zhang, P.; Strømme, M.; Nyholm, L., SolutionProcessed Poly (3,4-Ethylenedioxythiophene) Nanocomposite Paper Electrodes for HighCapacitance Flexible Supercapacitors. J. Mater. Chem. A 2016, 4, 1714-1722. 55. Bai, X.; Hu, X.; Zhou, S., Flexible Supercapacitors Based on 3D Conductive Network Electrodes of Poly(3,4-Ethylenedioxythiophene)/Non-Woven Fabric Composites. RSC Adv. 2015, 5, 43941-43948. 56. Tong, L.; Skorenko, K. H.; Faucett, A. C.; Boyer, S. M.; Jian Liu; Mativetsky, J. M.; Bernier, W. E.; Jr., W. E. J., Vapor-Phase Polymerization of Poly(3,4-Ethylenedioxythiophene) (PEDOT) on Commercial Carbon Coated Aluminum Foil as Enhanced Electrodes for Supercapacitors. J. Power Sources 2015, 297, 195-201. 57. Menzel, N.; Ortel, E.; Kraehnert, R.; Strasser, P., Electrocatalysis Using Porous Nanostructured Materials. Chemphyschem : a European journal of chemical physics and physical chemistry 2012, 13, 1385-94. 58. Mao, H.; Liu, X.; Chao, D.; Cui, L.; Li, Y.; Zhang, W.; Wang, C., Preparation of Unique PEDOT Nanorods with a Couple of Cuspate Tips by Reverse Interfacial Polymerization and their Electrocatalytic Application to Detect Nitrite. J. Mater. Chem. 2010, 20, 10277.


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Page 36 of 37

59. Goyal, A.; Bansal, S.; Singhal, S., Facile Reduction of Nitrophenols: Comparative Catalytic Efficiency of MFe2O4 (M = Ni, Cu, Zn) Nano Ferrites. Int. J. Hydrogen Energy 2014, 39, 4895-4908. 60. Shin, K. S.; Cho, Y. K.; Choi, J.-Y.; Kim, K., Facile Synthesis of Silver-Deposited Silanized Magnetite Nanoparticles and their Application for Catalytic Reduction of Nitrophenols. Appl. Catal., A 2012, 413-414, 170-175. 61. Sun, X.; Sun, L.; Zheng, Y.; Lin, Q.; Su, H.; Li, F.; Qi, C., One-Pot Fabrication of CoreShell Fly Ash@Polypyrrole/Au Composite Microspheres and their Performance for the Reduction of Nitrophenol. Synth. Met. 2016, 220, 635-642. 62. ElShafei, G. M. S.; Al-Sabagh, A. M.; Yehia, F. Z.; Philip, C. A.; Moussa, N. A.; Eshaq, G.; ElMetwally, A. E., Metal Oxychlorides as Robust Heterogeneous Fenton Catalysts for the Sonophotocatalytic Degradation of 2-Nitrophenol. Appl. Catal., B 2018, 224, 681-691. 63. Waller, A. M.; Compton, R. G., Simultaneous Alternating Current Impedance/Electron Spin Resonance Study of Electrochemical Doping in Polypyrrole. J. Chem. Soc., Faraday Trans.1 1989, 85, 977. 64. Barreira, S. V. P.; García-Morales, V.; Manzanares, J. A.; Pereira, C. M.; Silva, F., Electrochemical Impedance Spectroscopy of Polyelectrolyte Multilayer Modified Electrodes. J. Phys. Chem. B 2004, 108, 17973-17982. 65. Silva, T. H.; Garcia-Morales, V.; Moura, C.; Mazanares, J. A.; Silva, F., Electrochemical Impedance Spectroscopy of Polyelectrolyte Multilayer Modified Gold Electrodes: Influence of Supporting Electrolyte and Temperature. Langmuir 2005, 21, 7461-7467. 66. Vyas, R. N.; Wang, B., Electrochemical Analysis of Conducting Polymer Thin Films. Int. J. Mol. Sci. 2010, 11, 1956-72. 67. Fernández-Sánchez, C.; McNeil, C. J.; Rawson, K., Electrochemical Impedance Spectroscopy Studies of Polymer Degradation: Application to Biosensor Development. TrAC, Trends Anal. Chem. 2005, 24, 37-48. 68. Rodriguez-Calero, G. G.; Lowe, M. A.; Burkhardt, S. E.; Abruna, H. D., Electrocatalysis of 2,5-Dimercapto-1,3,5-Thiadiazole by 3,4-Ethylenedioxy-Substituted Conducting Polymers. Langmuir 2011, 27, 13904-9.


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PEDOT Nanotubes Electrochemically Synthesized on Flexible

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