Electrochemical Tailoring of Fibrous Polyaniline and Electroless

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Electrochemical Tailoring of Fibrous Polyaniline and Electroless Decoration with Gold and Platinum Nanoparticles Muhammad E Abdelhamid, Graeme Andrew Snook, and Anthony Peter O'Mullane Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b02058 • Publication Date (Web): 16 Aug 2016 Downloaded from http://pubs.acs.org on August 19, 2016

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Electrochemical Tailoring of Fibrous Polyaniline and Electroless Decoration with Gold and Platinum Nanoparticles Muhammad E. Abdelhamid,†,* Graeme A. Snook,* Anthony P. O’Mullane.‡ †School of Applied Sciences, RMIT University, GPO Box 2476V, Melbourne, VIC 3001, Australia *Mineral Resources, Commonwealth Science and Industrial Research Organisation (CSIRO), Private Bag 10, Clayton, VIC 3169, Australia. ‡School of Chemistry, Physics, and Mechanical Engineering, Queensland University of Technology, GPO Box 2434, Brisbane, QLD 4001, Australia

ABSTRACT. Presented in this work is a facile and quick electrochemical method to control the morphology of thick PANi films, without the use of templates. By stepping the polymerisation potential from high voltages to a lower (or series of lower) voltage(s), the morphology of the polymer was successfully controlled and fibrous structures, unique to each potential step, were achieved. In addition, the resultant films were tested electrochemically for its viability as an electrode material for flexible batteries and supercapacitors. Furthermore, the PANi film was decorated with gold and platinum nanoparticles via an

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electroless deposition process for possible electrocatalytic applications, whereby the oxidation of hydrazine at the composite was investigated.

INTRODUCTION Conducting polymers, such as polyaniline (PANi), are researched intensively due to their unique chemical and physical properties, such as wide range of conductivity, facile processability, flexibility and low cost 1. As a result, they have been utilised in many applications such as photovoltaics, gas sensing and anti-corrosive coatings 2-4 and extensively investigated as a replacement for traditional electrode materials, such as metals and metal oxides, in energy storage/conversion devices 4. PANi can be easily produced via chemical or electrochemical oxidative polymerisation

1, 5

. Producing nanostructured PANi has also been

studied due to improved properties over the bulk material 6-7, however developing facile and reproducible methods for the controlled growth of nanostructured PANi is an ongoing research effort. Generally, nano-structured conducting polymers exhibit higher electrical conductivity, larger surface area, shorter path length for ion transport and improved electrochemical activity storage/generation field

8

9-10

and hence they are promising materials in the energy

. Controlling PANi’s morphology can be achieved through many

different methods ranging from template-based to template-free methods 3, 11-12. Incorporation of various metal nanoparticles, such as Pt into PANi has also received much attention

13-18

, Au

19-22

, Ag

23-24

and Cu

25-26

,

27

. In particular, the synthesis of Pt

nanoparticles/PANi composites is of interest as Pt exhibits excellent catalytic properties in addition to PANi’s high conductivity

28

. Such a composite has displayed an excellent

performance in oxidising small organic molecules 14, 18, 29-30. The advantage of dispersing the metal nanoparticles into a CP matrix is the prevention of the agglomeration of the nanoparticles into large clusters. This results in a larger specific area for catalytic reaction to 2 ACS Paragon Plus Environment

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occur as well as maintaining the electrical connectivity with the electrode 20. As expected, the nanoparticles arrangement exhibits an enhanced electrocatalytic activity compared to the bulk metal

31-32

. The PANI/Pt composite has been utilised in various electrocatalytic oxidations,

such as hydrazine

27

, methanol

14, 29

, formic acid

14, 33

, hydrogen

15

, in addition to oxygen

reduction 34-35. The aim of this work is to develop a facile and quick approach to control the morphology of thick PANi films without the use of physical or chemical templates. PANi was therefore polymerised electrochemically from its protic salt precursor via a two-step constant potential method. The method involved applying a high potential to initiate the nucleation step, then stepping the polymerisation potential to a lower (or series of lower) potential(s) for the polymer growth step. This allowed for successful control over the morphology of the polymer and yielded distinctive fibrous structures that are unique to each potential step. Furthermore, the resultant film was tested electrochemically for its viability as an electrode material for energy storage devices. An extra step was undertaken to deposit gold and platinum nanoparticles via electroless deposition onto the PANi film for possible electrocatalytic applications such as the oxidation of hydrazine, which is a potential fuel source for environmentally friendly zero emission fuel cells 36-37, according to equation 1. Although the electroless deposition of Pt and Au in isolation has been reported, the possible formation of a PANi film decorated by bimetallic Au/Pt nanomaterials using this approach is investigated. It has been shown previously that the formation of bimetallic Au/Pt nanoparticles can be beneficial for electrocatalytic activity and biosensing applications due to the synergy between these two metals 38-39.

+ 4 + 4 (1)


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EXPERIMENTAL SECTION Materials and Instruments. Aniline, chloroauric acid (HAuCl4), and chloroplatinic acid (H2PtCl6) were purchased from Sigma-Aldrich. Ethanol and perchloric acid (70%) were purchased from Merck Millipore (EMSURE ACS). 18.2 MΩ cm Milli-Q water was also used for making up solutions. 1 cm2 Indium tin oxide glass electrode (ITO, Delta technologies LTD) was used as the working electrode and platinum wire was used as the counter electrode. Both were cleaned via ultrasonication in ethanol for 10 min and subsequently rinsed with ethanol and acetone. Ag/AgCl (3 M KCl Aqueous) was used as a reference electrode in all experiments unless otherwise stated. Electropolymerisation of polyaniline was conducted with a CH Instruments Bipotentiostat (700E) using different polymerisation conditions. Anilinium Perchlorate Synthesis. The protic aniline salt (i.e. anilinium perchlorate) was synthesised according to previous methods reported by Snook et al. 5 and Abdelhamid et al. 3. Briefly, an equimolar amount of perchloric acid (in 2:3 v/v water:ethanol) was added drop wisely to a round bottom flask containing aniline (in ethanol) under constant stirring and controlled temperature under 0˚C to prevent the oxidation of the amine group. After the reaction was complete, a suspension of beige coloured powder was obtained. The product was filtered under vacuum and subsequently washed with cold water and cold ethanol in order to remove any excess or unreacted chemicals. The filtered product was then dried in a vacuum oven for overnight to obtain a dry needle-like powder. Fabrication of Polymer Electrodes and Decoration with Metal Nanoparticles.

The

polymerisation methods involved immersing a freshly cleaned ITO electrode into 1 M aqueous anilinium perchlorate where a constant potential was applied under the following conditions; (a) 0.75 V for 30 minutes (1.57 C cm−2) “film 1”, (b) 0.75 V for 5 minutes (0.26 4 ACS Paragon Plus Environment

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C cm-2) then switched to 0.60 V for 25 minutes (1.37 C cm-2) for a total of 1.63 C cm−2 “film 2”, (c) 0.75 V for 5 minutes (0.26 C cm-2) then switched to 0.50 V for 25 minutes (0.88 C cm2

) for a total of 1.14 C cm−2 “film 3”, and (d) 0.75 V for 5 minutes (0.26 C cm-2) then

switched to 0.60 V for 15 minutes (0.80 C cm-2) followed by 0.50 V for 10 minutes (0.33 C cm-2) for a total of 1.39 C cm−2 “film 4”. These potential sequences are illustrated in figure 1. The deposited films were then rinsed in water to remove unreacted monomer and oligomers. The deposited film was decorated with gold-platinum nanoparticles via electroless deposition. The PANi film was immersed in an equimolar solution of 10 mM HAuCl4 and H2PtCl6 in 1 M aqueous perchloric acid for 30 seconds. This caused the PANi film to turn dark green. The film was then rinsed with water three times to stop metal deposition and remove excess acids. Electrochemical Characterisation. The electrochemical characterisation of PANi films was performed via cyclic voltammetry (CV) and charge/discharge techniques in a standard threeelectrode cell containing 1 M perchloric acid. For cyclic voltammetry, the scan rate was 20 mV s−1. While in charge/discharge tests, the cells were charged and discharged galvanostatically at current densities of 1.5, 1.0, and 0.5 mA cm−2 to a cell voltage of 0.9 V (for charging), and 0.05 V (for discharging). The electrochemical impedance spectroscopy measurements (EIS) were conducted using FRA software from AutoLab using AutoLab potentiostat in the range of 10 mHz to 10 kHz at two potentials (-0.10 V and 0.25 V) in addition to a single frequency measurement while swiping the potential from -0.15 V to 1.00V. RESULTS AND DISCUSSION The different electrochemical polymerization conditions resulted in an interesting variation in the morphology of the PANi films (figure 1). When the polymerization was conducted at a 5 ACS Paragon Plus Environment

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single potential (i.e. 0.75 V), thin intricate and closely packed PANi fibres were produced with an average fibre diameter of about 0.2 µm (figure 1bi). On the other hand, when the polymerisation was carried out by initiating the process at 0.75 V and then stepping the potential to a lower value (i.e. 0.60 V), the PANi fibres were still intricate but thicker and loosely packed with an average diameter of 0.4 µm (figure 1bii). Moreover, when the potential was switched to a much lower potential of 0.50 V (where the corresponding polymerisation current is more than 3 times lower than the initial polymerisation step), the PANi film morphology changed dramatically from a well-defined fibrous structure into a layered and denser structure, in particular for the surface of the film (figure 1biii). This may be attributed to the formation and deposition of oligomers at such a low voltage. However, when the electropolymerisation process was conducted at three consecutive switching potentials (i.e. 0.75 V (5 min) 0.60 V (15 min) 0.50 V (10 min)), a neuron-like network structure was produced as a result of combining these consecutive potentials, that results in different morphologies. The polymerization process was always initiated at 0.75 V as it was found to be the minimum potential required to start the nucleation step and provide enough nucleation sites to produce a high-quality PANi mat. However, when the polymerization process was initiated at lower potentials, such as 0.50 V, low-quality PANi fibres were produced. This is due to a significantly lower number of nucleation sites created at this low potential.


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Figure 1. a) Diagram plotted over a single linear sweep voltammogram showing the different methods and steps of the electrochemical polymerisation and the corresponding polymerisation current at each potential step. b) SEM micrographs showing the morphology of PANi as a result of applying different polymerisation approaches; (i) constant potential at 0.75 V for 30 minutes, (ii) 0.75 V for 5 minutes then switched to 0.60 V for 25 minutes, (iii)


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0.75 V for 5 minutes then switched to 0.50 V for 25 minutes, and 0.75 V for 5 minutes then switched to 0.60 V for 15 minutes followed by 0.50 V for 10 minutes. Figure 2 shows the cyclic voltammograms (CVs) and the oxidation and reduction potentials of the four different PANi electrodes in 1 M perchloric acid recorded at 20 mV s−1. The three characteristic oxidation peaks are present in all PANi electrodes, where the first and third peaks (~0.3 and ~0.7 V vs Ag/AgCl) correspond to the emeraldine and pernigraniline oxidation states of PANi while the origin of the second “middle” peak (~0.5 V vs Ag/AgCl) is still a source of some debate. According to the literature, it has been attributed to either the degradation of the polymer during cycling or to self-cross linking between PANi chains during potential cycling

40

. However, the presence of this peak in the first potential cycle

which is maintained at the same intensity for subsequent cycles suggests that self-cross linking is the more likely mechanism rather than PANidegradation. If degradation of the film was the dominant mechanism, then the peak should be absent or negligible in the first cycle and increase with the number of cycles, which is not the case. By comparing the second oxidation peak and the overall current densities of the PANi electrodes, one can deduce the relative intensity of the packing “density” of the PANi film and the exposed “active” surface area that contribute to the redox activity of the film. For example, the current density recorded for film 2 (figure 2b) is the largest and the second oxidation peak is not as prominent as in the other three films. This could be interpreted as this particular PANi film being less packed and less cross-linked, hence exhibiting higher active surface area, which is confirmed by the SEM image (figure 1bii). The current density passed through film 3 (figure 2c) is the lowest and the second peak is more prominent in relation to the other two oxidation peaks which could be attributed to the higher degree of cross-linking and hence lower surface area due to the dense packing of the polymer fibres (figure 1biii). It is also interesting to note that although similar charge was passed during the deposition process for films 1 (1.57 C cm8 ACS Paragon Plus Environment

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2

) and 2 (1.63 C cm-2), the current density for the redox processes is higher for film 2. In

addition, the charge passed for the formation of film 4 (1.39 C cm-2) is lower than that for film 1 yet the current density for the redox processes is comparable. This indicates that the morphology of the PANi film has a significant impact on its electrochemical properties.

Figure 2. Cyclic voltammograms recorded at 20 mV s-1 in 1 M perchloric acid of PANi films deposited via different approaches; (a) 0.75 V for 30 minutes, (b) 0.75 V for 5 minutes then switched to 0.60 V for 25 minutes, (c) 0.75 V for 5 minutes then switched to 0.50 V for 25


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minutes, and (d) 0.75 V for 5 minutes then switched to 0.60 V for 15 minutes followed by 0.50 V for 10 minutes.

EIS measurements were undertaken to illustrate the electrochemical behaviour of the resultant PANi film 2 at different potentials in its undoped (-0.1 V) and doped (0.25 V) states, at a single frequency of 0.1 Hz (figure 3a, b). This sample was chosen as it demonstrated the highest passage of current density for all the films that were fabricated. The ionic resistance of the film was measured to be 36.80 ± 0.03 Ω and 4.00 ± 0.05 Ω at -0.1 V and 0.25 V, respectively, by fitting the data to an equivalent circuit model (figure 4). This equivalent circuit model consists of four elements. The elements are a resistance (R1) and a sub-circuit connected in series. The R1 represents a combination of the resistance of the solution as well as the electronic resistance of the polymer. The sub-circuit is composed of a constant phase element (CPE1) connected in parallel to a resistance (R2) and a Warburg element (Wo1). Here, CPE1 and R2 are attributed to the distributed capacitance and the ionic resistance, respectively, as a result of counter ion migration across the interface between the PANi surface and the electrolyte solution the bulk of the polymer

43-44

41-42

. Wo1 represents the ionic diffusion of the ions into

. The capacitance of the film was surveyed by measuring the

impedance of the film at a range of frequencies (i.e. 1 mHz to 1 MHz) while sweeping the potential from -0.15 V to 1 V at 20 mV s-1 (figure 3c). The EIS survey demonstrates the contrast in capacitance exhibited by the PANi film when it is doped and undoped. While the capacitance at -0.1 V was ca. 36.5 mF, the film exhibited a higher capacitance of ca. 330.5 mF at 0.25 V. Comparable results were obtained from the data fitting of the low-frequency domain of the Nyquist plots where the capacitance (CPE1) of the PANi film at -0.1 V was 37.2 ± 0.1 m F compared to 333.8 ± 0.2 mF at 0.25 V.


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Figure 3. Nyquist plots of PANi at (a) -0.1 V “un-doped”, and (b) 0.25 V “doped” at 0.1 Hz to 1 MHz and the fitting data that resulted from the equivalent circuit. (c) capacitance vs potential survey of PANi film at 20 mV s-1 at 0.1 Hz showing the effective capacitive region of the film.


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Figure 4. The equivalent circuit model of the PANi film. Figure 5 shows the charge/discharge curves of film 2 which was chosen as it has the highest active area as determined by the CV data in Figure 2. The behaviour of the increase and decrease of the charging potential and discharging potential, respectively, is characteristic of materials used as electrodes in rechargeable batteries. Furthermore, the faradaic processes are evident and manifested as sharp increases and kinks in the potential data due to the oxidation/reduction of PANi. This proves that a polyaniline film could in principle be used as an electrode material for energy storage devices. A charge (C) capacity of 0.88 mAh cm−2 and discharge (DC) capacity of 0.84 mAh cm−2 were obtained at a charging/discharging current density of 1 mA cm−2. The capacity of the film is comparable to literature values that range from 0.1 mAh cm−2 to 5 m Ah cm−2

45-46

. Employing other

charging/ discharging rates (1.5 mA cm−2 & 0.5 mA cm−2) gave almost similar capacity values (i.e. C1.5 = 0.86 mAh cm−2, DC1.5 = 0.78 mAh cm−2 & C0.5 = 0.92 mAh cm−2, CD0.5 = 0.85 mAh cm−2). This might be due to the resultant PANi film exhibiting less self-crosslinking and low packing, resulting in a relatively high electrochemically accessible surface area and shorter path length for ion transportation leading to an increase in the number of electrochemically active sites 3. The connotation of this work is that electrochemically tailored PANi could be utilised as an electrode material for flexible energy storage devices.


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Figure 5. Charge/ discharge curves showing the periodic change in voltage and capacity as a result of applying; (a) 1.5 mA cm−2, (b) 1 mA cm−2, and (c) 0.5 mA cm−2 while charging and discharging. The process of the electroless decoration of the PANi film with gold and platinum nanoparticles was successful. Figures 6a shows evenly distributed metal nanoparticles (small white spherical particles) that cover the thin underlying PANi film as well as the thick PANi fibres (figure 6b). Here, the PANi film acts as a reactive substrate for the metal to deposit. The metal undergoes reduction from its cationic form, in chloroauric acid and chloroplatinic acid, into Au0 and Pt0 atoms, while the PANi undergoes further oxidation to the


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pernigraniline form as evidenced by a significant colour change in the film to a dark bluegreen colour. This could be confirmed by looking at figure 6e, where the dark patches are thin PANi film, the light patches are the surface of ITO electrode and the bright white dots are metal nanoparticles. There is a complete absence of any nanoparticles on the ITO patches (light areas), and the SEM image clearly indicates that the deposition of the nanoparticles occurs exclusively on the PANi film and not the ITO surface. The average diameter of the metal nanoparticles was measured to be ranging from 15 nm (TEM, figure 7) to 200 nm (SEM, figure 6) however, occasionally, clusters of nanoparticles were formed (figure 6d, f) with diameters ranging from 1 µm to 3.5 µm. TEM images confirm the deposition of bimetallic nanoparticles on PANi’s surface with even smaller sizes (figure 7a). However, in the bimetallic particles, the gold concentration is significantly higher than for platinum as shown by the EDS measurements where the percentage of Au and Pt is estimated, from the EDS spectra, to be 92.9% for Au and 7.1% for the Pt (figure 7c).


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Figure 6. SEM micrographs showing; (a, b, and c) almost evenly distributed gold and platinum nanoparticles on PANi as a result of the electroless deposition from their acid precursors, (d, and f) microcluster formation on PANi fibres and mat regions respectively, and (e) the exclusive deposition of the nanoparticles on PANi (dark patches) and the absence of nanoparticles from ITO regions (light patches). 15 ACS Paragon Plus Environment

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Figure 7. TEM micrographs showing; a) high magnification of gold/platinum nanoparticles on PANi with about 15 nm diameter and smaller nanoparticles (slightly lighter dots) incorporated in the polymer. b) low magnification of the composite showing the three sites where EDS measurements were taken (c). In order to further verify the deposition of both gold and platinum on the polymer surface, XPS measurements were conducted (figure S1). The XPS spectra confirmed the presence of


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both metals as both peak regions attributed to the 4f orbitals were detected at 84.1 eV (gold) and 72.7 eV (platinum) with well separated asymmetric spin-orbital components by 3.7 eV (for gold) and 3.4 eV (for platinum). The XPS data is in agreement with EDS as the amount of platinum detected is also low compared to gold. The potential at which gold is reduced from [AuCl4]-to metallic gold is around 1.00 V (vs RHE) 47-48 which is higher than platinum’s reduction potential from [PtCl6]²- (i.e. 0.73 to 0.76 V vs RHE) 49. This difference in reduction potential indicates the deposition of gold is thermodynamically more favourable than that for Pt by ca. 0.27 V which explains the higher gold coverage of PANi from an equimolar solution of [AuCl4]-and [PtCl6]²-. Another consideration is the pathway each metal deposition process takes during the process. In the case of gold, the reduction of the metal salt occurs via one step (3-electrons) reaction (equation 2) 47-48, while for the platinum salt it is reduced via a more sluggish pathway of two 2-electron reduction steps (4-electrons) reaction (equations 3, and 4) 49.

[ ] + 3 + 4 +1.002

[ ] + 2 [ ] + 2 +0.726

[ ] + 2 + 4 +0.758

…(2) …(3) …(4)

The electrocatalytic activity of the PANi/Au-Pt composite towards hydrazine oxidation was evaluated via cyclic voltammetry. First, the cyclic voltammetric experiment was performed on PANi/Au-Pt in 1 M H2SO4 in the absence of hydrazine (figure S2). There is a distinct increase in current from -0.20 to -0.40 V which can be attributed to the hydrogen evolution reaction. Over the potential range of 0 to 1.20 V the cyclic voltammogram is consistent with PANi. However, when 0.1 M hydrazine was introduced, a change in the cyclic voltammogram was observed with an increase in the oxidation current at ~0.88 V (figure S2). This behaviour is associated with the oxidation of hydrazine as reported previously for PANi/Pt composites 27. 17 ACS Paragon Plus Environment

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In order to determine the role of the gold nanoparticles in such electrochemical behaviour, separate PANi/Au and PANi/Pt composites were prepared via the same method and were examined in the presence of hydrazine. The PANi/Pt composite exhibited the same behaviour as PANi/Au-Pt (figure S3a) while PANi/Au gave no apparent response towards the oxidation of hydrazine as shown in figure S3b. This is in contrast to previous studies that showed the catalytic activity of Au nanoparticles on various substrates, such as GC, TiO2 and PANi for this reaction.50-52 However, the reason for the apparent absence of the catalytic activity is unclear, but may be attributed to the thick PANi layer hindering electron transfer from the Au nanoparticles and the underlying electrode. This is in agreement with a study by Li et al.53 where they studied the effect of thickness of the supporting conducting polymer, polypyrrole in their case, on the current response for hydrazine oxidation at PPy/Au. They found that the current response for hydrazine was enhanced when the PPy thickness was 60 nm or less but diminished when the thickness increased.53 This would explain the low catalytic activity of the metal decorated PANi films here and indicates that thick films that are appropriate for energy storage applications do not translate to highly effective electrocatalytically active composites.

However the ability to deposit bimetallic nanoparticles on a conducting

polymer via a one-step electroless deposition approach may be useful for other combinations of polymer and nanoparticles.

CONCLUSIONS Solid polyaniline films were electrochemically prepared and morphologically tailored. The method involved applying and switching to a series of consecutive constant potentials to electrochemically oxidise aniline into PANi. The morphology varied dramatically when different potentials and approaches were used. When a single potential was used, a film


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comprised of dense fibres was obtained, while switching between two or three consecutive potentials produced a wide range of morphologies (e.g. loosely packed fibres to an amorphous dense structure, and neuron-like fibres). It appears that the lower the potential used in the growth step, the denser and more amorphous the PANi film became. One particular film was chosen (i.e. film 2 deposited to 1.63 C cm−2) to be tested electrochemically as it exhibited the most interesting morphology and relatively higher surface area than the other films (according to cyclic voltammetric data). The electrochemical properties of the film were measured via CV, EIS and charging/discharging techniques in order to assess the feasibility of the produced films to be used in electrochemical energy storage devices. The EIS data highlighted the effective potential window where the polymer exhibits its highest capacitance and lowest ionic resistance to be between about 0.05 V and 0.70 V. Also, an equivalent circuit model was developed to obtain accurate insight of how the PANi film behaved. The charging/discharging curves demonstrated that the average capacity of the polymer is 88.6 mAh cm−2 at 1 C rate (i.e. 1 mA cm−2), which suggests the developed PANi is suitable as an electrode material for flexible batteries and supercapacitors. Furthermore, the spontaneous electroless deposition of evenly distributed gold and platinum nanoparticles on PANi was successful where SEM, TEM, and XPS confirmed the deposition of both elements exclusively on PANi. The deposition happened via the reduction of the metal ions onto the PANi surface into neutral atoms and the consequent oxidation of PANi. In future work thinner films of PANi could be employed for electrocatalytic experiments and forcontrol over the deposition ratio of Pt and Au, the concentration of each corresponding precursor can be varied and/or the Pt (IV) precursors could be substituted with Pt (II) species for faster one-step reduction to Pt metal. The ability to electrochemically tailor conducting polymers and deposit bimetallic nanoparticles in a simple step could in principle be applied to many other composites for energy storage and electrocatalytic applications.


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AUTHOR INFORMATION Corresponding Author Dr Graeme A. Snook Mineral Resources, Commonwealth Science and Industrial Research Organisation (CSIRO),

Private Bag 10, Clayton, VIC 3169, Australia.

Email: [email protected]

Associate Professor Anthony P. O’Mullane School of Chemistry, Physics, and Mechanical Engineering, Queensland University of Technology, GPO Box 2434, Brisbane, QLD 4001, Australia Email: [email protected]

Funding Sources A.P.O’M. gratefully acknowledges the Australian Research Council for funding through a Future Fellowship (FT FT110100760). G.A.S. acknowledges the funding from the CSIRO Office of the Chief Executive Julius Career Award.

ACKNOWLEDGMENT M.E.A. acknowledges the CSIRO for the provision of a PhD stipend. The authors acknowledge the facilities, and the scientific and technical assistance, of the Australian Microscopy and Microanalysis Research Facility at the RMIT Microscopy & Microanalysis Facility.


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REFERENCES 1. Abdelhamid, M. E.; O'Mullane, A. P.; Snook, G. A., Storing energy in plastics: a review on conducting polymers & their role in electrochemical energy storage. RSC Advances 2015, 5 (15), 11611-11626. 2. Ćirić-Marjanović, G., Recent advances in polyaniline research: Polymerization mechanisms, structural aspects, properties and applications. Synthetic Metals 2013, 177 (0), 1-47. 3. Abdelhamid, M. E.; Murdoch, T.; Greaves, T. L.; O'Mullane, A. P.; Snook, G. A., High-throughput approach for the identification of anilinium-based ionic liquids that are suitable for electropolymerisation. Physical Chemistry Chemical Physics 2015. 4. Snook, G. A.; Kao, P.; Best, A. S., Conducting-polymer-based supercapacitor devices and electrodes. Journal of Power Sources 2011, 196 (1), 1-12. 5. Snook, G. A.; Greaves, T. L.; Best, A. S., A comparative study of the electrodeposition of polyaniline from a protic ionic liquid, an aprotic ionic liquid and neutral aqueous solution using anilinium nitrate. Journal of Materials Chemistry 2011, 21 (21), 7622-7629. 6. Pan, L.; Qiu, H.; Dou, C.; Li, Y.; Pu, L.; Xu, J.; Shi, Y., Conducting Polymer Nanostructures: Template Synthesis and Applications in Energy Storage. International Journal of Molecular Sciences 2010, 11 (7), 2636-2657. 7. Ćirić-Marjanović, G., Polyaniline Nanostructures. In Nanostructured Conductive Polymers, John Wiley & Sons, Ltd: 2010; pp 19-98. 8. Wu, C. G.; Bein, T., Conducting polyaniline filaments in a mesoporous channel host. Science (Washington, D. C.) 1994, 264 (5166), 1757-9. 9. Arico, A. S.; Bruce, P.; Scrosati, B.; Tarascon, J.-M.; van Schalkwijk, W., Nanostructured materials for advanced energy conversion and storage devices. Nat. Mater. 2005, 4 (5), 366-377. 10. Wu, H.; Yu, G.; Pan, L.; Liu, N.; McDowell, M. T.; Bao, Z.; Cui, Y., Stable Li-ion battery anodes by in-situ polymerization of conducting hydrogel to conformally coat silicon nanoparticles. Nat Commun 2013, 4. 11. Yu, X.; Li, Y.; Kalantar-zadeh, K., Synthesis and electrochemical properties of template-based polyaniline nanowires and template-free nanofibril arrays: Two potential nanostructures for gas sensors. Sensors and Actuators B: Chemical 2009, 136 (1), 1-7. 12. Zhang, L.; Liu, P., Facile Fabrication of Uniform Polyaniline Nanotubes with Tubular Aluminosilicates as Templates. Nanoscale Research Letters 2008, 3 (8), 299-302. 13. Qi, Z.; G. Pickup, P., High performance conducting polymer supported oxygen reduction catalysts. Chemical Communications 1998, (21), 2299-2300. 14. Napporn, W. T.; Laborde, H.; Léger, J. M.; Lamy, C., Electro-oxidation of C1 molecules at Pt-based catalysts highly dispersed into a polymer matrix: effect of the method of preparation. Journal of Electroanalytical Chemistry 1996, 404 (1), 153-159. 15. Croissant, M. J.; Napporn, T.; Léger, J. M.; Lamy, C., Electrocatalytic oxidation of hydrogen at platinum-modified polyaniline electrodes. Electrochimica Acta 1998, 43 (16– 17), 2447-2457. 16. Kitani, A.; Akashi, T.; Sugimoto, K.; Ito, S., Electrocatalytic oxidation of methanol on platinum modified polyaniline electrodes. Synthetic metals 2001, 121 (1-3), 1301-1302. 17. Kessler, T.; Castro Luna, A. M., A catalytic platinum–ruthenium–polyaniline electrode for methanol oxidation. Journal of Applied Electrochemistry 2002, 32 (7), 825-830.


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18. Niu, L.; Li, Q.; Wei, F.; Chen, X.; Wang, H., Formation optimization of platinummodified polyaniline films for the electrocatalytic oxidation of methanol. Synthetic Metals 2003, 139 (2), 271-276. 19. Wang, J.; Neoh, K. G.; Kang, E. T., Preparation of Nanosized Metallic Particles in Polyaniline. Journal of Colloid and Interface Science 2001, 239 (1), 78-86. 20. Daniel, M.-C.; Astruc, D., Gold Nanoparticles: Assembly, Supramolecular Chemistry, Quantum-Size-Related Properties, and Applications toward Biology, Catalysis, and Nanotechnology. Chemical Reviews 2004, 104 (1), 293-346. 21. Sarma, T. K.; Chowdhury, D.; Paul, A.; Chattopadhyay, A., Synthesis of Au nanoparticle-conductive polyaniline composite using H2O2 as oxidising as well as reducing agent. Chemical Communications 2002, (10), 1048-1049. 22. Hatchett, D. W.; Josowicz, M.; Janata, J.; Baer, D. R., Electrochemical Formation of Au Clusters in Polyaniline. Chemistry of Materials 1999, 11 (10), 2989-2994. 23. Tsakova, V.; Milchev, A., Nucleation of silver on a polyaniline-coated platinum electrode. Electrochimica Acta 1991, 36 (7), 1151-1155. 24. de Barros, R. A.; de Azevedo, W. M.; de Aguiar, F. M., Photo-induced polymerization of polyaniline. Materials Characterization 2003, 50 (2–3), 131-134. 25. Ivanov, S.; Tsakova, V., Influence of copper anion complexes on the incorporation of metal particles in polyaniline Part I: Copper citrate complex. Journal of Applied Electrochemistry 2002, 32 (6), 701-707. 26. Ivanov, S.; Tsakova, V., Influence of copper anion complexes on the incorporation of metal particles in polyaniline Part II: Copper oxalate complex. Journal of Applied Electrochemistry 2002, 32 (6), 709-715. 27. O'Mullane, A. P.; Dale, S. E.; Day, T. M.; Wilson, N. R.; Macpherson, J. V.; Unwin, P. R., Formation of polyaniline/Pt nanoparticle composite films and their electrocatalytic properties. J. Solid State Electrochem. 2006, 10 (10), 792-807. 28. Hopkins, A. R.; Rasmussen, P. G.; Basheer, R. A., Characterization of Solution and Solid State Properties of Undoped and Doped Polyanilines Processed from Hexafluoro-2propanol. Macromolecules 1996, 29 (24), 7838-7846. 29. Luna, A. M. C., A novel electrocatalytic polyaniline electrode for methanol oxidation. Journal of Applied Electrochemistry 2000, 30 (10), 1137-1142. 30. Venancio, E. C.; Napporn, W. T.; Motheo, A. J., Electro-oxidation of glycerol on platinum dispersed in polyaniline matrices. Electrochimica Acta 2002, 47 (9), 1495-1501. 31. Mikhaylova, A. A.; Molodkina, E. B.; Khazova, O. A.; Bagotzky, V. S., Electrocatalytic and adsorption properties of platinum microparticles electrodeposited into polyaniline films. Journal of Electroanalytical Chemistry 2001, 509 (2), 119-127. 32. Malinauskas, A., Electrocatalysis at conducting polymers. Synthetic Metals 1999, 107 (2), 75-83. 33. Gholamian, M.; Contractor, A. Q., Oxidation of formic acid at platinum microparticles dispersed in a polyaniline matrix. Journal of Electroanalytical Chemistry and Interfacial Electrochemistry 1990, 289 (1), 69-83. 34. Lai, E. K. W.; Beattie, P. D.; Holdcroft, S., Electrocatalytic reduction of oxygen by platinum microparticles deposited on polyaniline films. Synthetic Metals 1997, 84 (1), 87-88. 35. Coutanceau, C.; Croissant, M. J.; Napporn, T.; Lamy, C., Electrocatalytic reduction of dioxygen at platinum particles dispersed in a polyaniline film. Electrochimica Acta 2000, 46 (4), 579-588. 36. Yamada, K.; Yasuda, K.; Fujiwara, N.; Siroma, Z.; Tanaka, H.; Miyazaki, Y.; Kobayashi, T., Potential application of anion-exchange membrane for hydrazine fuel cell electrolyte. Electrochemistry Communications 2003, 5 (10), 892-896.


Page 23 of 34

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37. Serov, A.; Kwak, C., Direct hydrazine fuel cells: A review. Applied Catalysis B: Environmental 2010, 98 (1–2), 1-9. 38. Wang, S.; Wang, X.; Jiang, S. P., Self-assembly of mixed Pt and Au nanoparticles on PDDA-functionalized graphene as effective electrocatalysts for formic acid oxidation of fuel cells. Physical Chemistry Chemical Physics 2011, 13 (15), 6883-6891. 39. Kang, Q.; Yang, L.; Cai, Q., An electro-catalytic biosensor fabricated with Pt–Au nanoparticle-decorated titania nanotube array. Bioelectrochemistry 2008, 74 (1), 62-65. 40. Geniès, E. M.; Lapkowski, M.; Penneau, J. F., Cyclic voltammetry of polyaniline: interpretation of the middle peak. Journal of Electroanalytical Chemistry and Interfacial Electrochemistry 1988, 249 (1–2), 97-107. 41. Zaban, A.; Aurbach, D., Impedance spectroscopy of lithium and nickel electrodes in propylene carbonate solutions of different lithium salts A comparative study. Journal of Power Sources 1995, 54 (2), 289-295. 42. Aurbach, D.; Zaban, A., Impedance Spectroscopy of Nonactive Metal Electrodes at Low Potentials in Propylene Carbonate Solutions: A Comparison to Studies of Li Electrodes. Journal of The Electrochemical Society 1994, 141 (7), 1808-1819. 43. Yang, C. R.; Song, J. Y.; Wang, Y. Y.; Wan, C. C., Impedance spectroscopic study for the initiation of passive film on carbon electrodes in lithium ion batteries. Journal of Applied Electrochemistry 2000, 30 (1), 29-34. 44. Snook, G. A.; Best, A. S., Co-deposition of conducting polymers in a room temperature ionic liquid. J. Mater. Chem. 2009, 19 (24), 4248-4254. 45. Genies, E. M.; Lapkowski, M.; Santier, C.; Vieil, E., Proceedings of the International Conference of Science and Technology of Synthetic Metals Polyaniline, spectroelectrochemistry, display and battery. Synthetic Metals 1987, 18 (1), 631-636. 46. Jugović, B.; Gvozdenović, M.; Stevanović, J.; Trišović, T.; Grgur, B., Characterization of electrochemically synthesized PANI on graphite electrode for potential use in electrochemical power sources. Materials Chemistry and Physics 2009, 114 (2–3), 939-942. 47. Lingane, J. J., Standard potentials of half-reactions involving + 1 and + 3 gold in chloride medium. Journal of Electroanalytical Chemistry (1959) 1962, 4 (6), 332-342. 48. Bard, A. J.; Parsons, R.; Jordan, J., Standard potentials in aqueous solution. CRC press: 1985; Vol. 6. 49. Bard, A. J.; Faulkner, L. R.; Leddy, J.; Zoski, C. G., Electrochemical methods: fundamentals and applications. Wiley New York: 1980; Vol. 2. 50. Wang, G.; Zhang, C.; He, X.; Li, Z.; Zhang, X.; Wang, L.; Fang, B., Detection of hydrazine based on Nano-Au deposited on Porous-TiO2 film. Electrochimica Acta 2010, 55 (24), 7204-7210. 51. Hosseini, H.; Ahmar, H.; Dehghani, A.; Bagheri, A.; Fakhari, A. R.; Amini, M. M., Au-SH-SiO2 nanoparticles supported on metal-organic framework (Au-SH-SiO2@Cu-MOF) as a sensor for electrocatalytic oxidation and determination of hydrazine. Electrochimica Acta 2013, 88, 301-309. 52. Xin, M.; Lin, H.; Yang, J.; Chen, M.; Ma, X.; Liu, J., Preparation of Polyaniline/Au0 Nanocomposites Modified Electrode and Application for Hydrazine Detection. Electroanalysis 2014, 26 (10), 2216-2223. 53. Li, J.; Lin, X., Electrocatalytic oxidation of hydrazine and hydroxylamine at gold nanoparticle—polypyrrole nanowire modified glassy carbon electrode. Sensors and Actuators B: Chemical 2007, 126 (2), 527-535.


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Figure 1. a) Diagram plotted over a single linear sweep voltammogram showing the different methods and steps of the electrochemical polymerisation and the corresponding polymerisation current at each potential step. b) SEM micrographs showing the morphology of PANi as a result of applying different polymerisation approaches; (i) constant potential at 0.75 V for 30 minutes, (ii) 0.75 V for 5 minutes then switched to 0.60 V for 25 minutes, (iii) 0.75 V for 5 minutes then switched to 0.50 V for 25 minutes, and 0.75 V for 5 minutes then switched to 0.60 V for 15 minutes followed by 0.50 V for 10 minutes. 120x186mm (220 x 220 DPI)

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Figure 2. Cyclic voltammograms recorded at 20 mV s-1 in 1 M perchloric acid of PANi films deposited via different approaches; (a) 0.75 V for 30 minutes, (b) 0.75 V for 5 minutes then switched to 0.60 V for 25 minutes, (c) 0.75 V for 5 minutes then switched to 0.50 V for 25 minutes, and (d) 0.75 V for 5 minutes then switched to 0.60 V for 15 minutes followed by 0.50 V for 10 minutes. 164x241mm (300 x 300 DPI)


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Figure 3. Nyquist plots of PANi at (a) -0.1 V “un-doped”, and (b) 0.25 V “doped” at 0.1 Hz to 1 MHz and the fitting data that resulted from the equivalent circuit. (c) capacitance vs potential survey of PANi film at 20 mV s-1 at 0.1 Hz showing the effective capacitive region of the film. 177x248mm (300 x 300 DPI)


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Figure 4. The equivalent circuit model of the PANi film. 120x47mm (220 x 220 DPI)


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Figure 5. Charge/ discharge curves showing the periodic change in voltage and capacity as a result of applying; (a) 1.5 mA cm−2, (b) 1 mA cm−2, and (c) 0.5 mA cm−2 while charging and discharging. 196x244mm (300 x 300 DPI)


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Figure 6. SEM micrographs showing; (a, b, and c) almost evenly distributed gold and platinum nanoparticles on PANi as a result of the electroless deposition from their acid precursors, (d, and f) microcluster formation on PANi fibres and mat regions respectively, and (e) the exclusive deposition of the nanoparticles on PANi (dark patches) and the absence of nanoparticles from ITO regions (light patches). 202x281mm (300 x 300 DPI)


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Figure 7. TEM micrographs showing; a) high magnification of gold/platinum nanoparticles on PANi with about 15 nm diameter and smaller nanoparticles (slightly lighter dots) incorporated in the polymer. b) low magnification of the composite showing the three sites where EDS measurements were taken (c). 84x180mm (220 x 220 DPI)


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Figure S1. The deconvoluted XPS spectra for 4f 7/2 and 4f 5/2 peaks for a) gold, and b) platinum confirming the deposition of both elements during the electroless deposition on PANi. 99x137mm (220 x 220 DPI)


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Figure S3. Cyclic voltammograms at 20 mV s−1 of a) PANi/Pt composite, and b) PANi/ Au in 0.1M hydrazine in 1 M H2SO4. 99x138mm (220 x 220 DPI)


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Electrochemical Tailoring of Fibrous Polyaniline and Electroless

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