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Scheme showing the inter-conversion of polyaniline between the leucoemeraldine and emeraldine oxidation states and the inter-conversion between the salt and base states.
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Polyaniline films were electrodeposited at pure aluminium from a tosylic acid solution containing aniline. These polymer films exhibited similar characteristics as pure polyaniline electrosynthesized at an inert platinum electrode, when removed from their respective substrates and dissolved in NMP. Both polymers had similar molecular weights and si...
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... number of quinoid rings, which range from zero to two in the elementary unit of four rings, with the other rings being benzenoid. The inter-conversion between the emeraldine base, with three benzenoid rings, and the leucoemeraldine base (LB), with four benzenoid rings, and the inter-conver- sion between the base and conducting salt can be seen in Fig. 1. In all cases, electroneutrality of the polymer is maintained by the presence of counter ...
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... with the polyaniline Á/Pt system. The steady- state pH values adopted by both systems are similar, indicating that the polymers formed in both cases undergo a de-doping process where H ' ions are released into the solution environment. However, this also suggests that a fraction of the formed polymer resides in the emeraldine salt (ES) state, Fig. 1, which is deprotonated in the chloride electrolyte thereby causing a decrease in the pH. The more rapid decrease in the pH of the polyaniline-coated aluminium electrode during the early stages of immersion may be connected with oxidation of the aluminium substrate. The ES form of the polymer is very permeable to water molecules that ...
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... as evidenced by an increase in the charge transfer resistance and a decrease in the capacitance. Indeed, clear evidence for the aluminium oxidation reaction could be obtained by removing the polymer coating. The substrate appeared white in coloration, which is consistent with the oxidation of aluminium and the generation of a thick Al 2 O 3 oxide (Eq. ...
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... polyaniline, anodic polarization mea- surements and local surface potential measurements, recorded using a scanning vibrating electrode technique, were performed. Representative polarization plots re- corded for uncoated aluminium and polyaniline coated aluminium in a highly aggressive 0.5 mol dm (3 NaCl, pH 5.85 electrolyte, are shown in Fig. 10. The plot depicted for the uncoated aluminium electrode is typical of the cathodic and anodic polarization behavior of pure aluminium; the corrosion potential lies at (/1.24 V (SCE), at higher potentials a passive region, with an average current of 3 mA cm (2 is obtained, and break- down and pitting of the electrode occurs at (/750 mV ...
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... data to support a corrosion protection mechanism for the polyaniline coating. There is an increase in the break- down potential of approximately 35 mV, but it is seen also that much higher rates of reduction and much higher mixed currents are accommodated at the poly- anilineÁ/Al composite. This can be seen more clearly from the data presented in Fig. 11 where a plot showing this mixed current as a function of the chloride concentration for polarization of aluminium and the polyaniline aluminium composite are presented. The mixed current shown for the uncoated aluminium electrode is equivalent to the corrosion current marking high rates of corrosion with increasing chloride concen- ...
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... corrosion current marking high rates of corrosion with increasing chloride concen- tration, while the origin of the mixed currents shown for the polyaniline Á/aluminium composite are less clear. These currents appear to be dominated by the high rates of reduction and the ability of the polymerÁ/ aluminium composite to catalyze reduction reactions (Fig. ...
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... the polymer and the aluminium substrate, the polymer was removed from part of the aluminium substrate and the surface potential across the coated and uncoated areas was mapped as a function of the potential applied to the electrode. Data from these surface potential measure- ments, obtained using a scanning vibrating probe technique, are shown in Fig. 12(a Á/c), as a function of the potential applied to the composite electrode. The uncoated area is marked by the circular area extending from 1580 to 0 mm (y-axis) and between 2800 and 4200 mm (x-axis) on the displacement scale. The correspond- ing bulk current, measured at each of the potentials, is shown in Fig. 12(d). For these measurements a ...
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... probe technique, are shown in Fig. 12(a Á/c), as a function of the potential applied to the composite electrode. The uncoated area is marked by the circular area extending from 1580 to 0 mm (y-axis) and between 2800 and 4200 mm (x-axis) on the displacement scale. The correspond- ing bulk current, measured at each of the potentials, is shown in Fig. 12(d). For these measurements a dilute chloride solution, 5 )/10 (3 mol dm (3 NaCl, with a relatively low conductivity was employed. This in turn means that much higher potentials are needed to nucleate corrosion on the aluminium electrode. The image presented in Fig. 12(a) was recorded at an applied potential of (/800 mV (SCE) which ...
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... correspond- ing bulk current, measured at each of the potentials, is shown in Fig. 12(d). For these measurements a dilute chloride solution, 5 )/10 (3 mol dm (3 NaCl, with a relatively low conductivity was employed. This in turn means that much higher potentials are needed to nucleate corrosion on the aluminium electrode. The image presented in Fig. 12(a) was recorded at an applied potential of (/800 mV (SCE) which corresponds to a potential at which the polyaniline-coated aluminium electrodes are stable and the bulk current recorded is a reduction current, Fig. 12(d). There is very little varia- tion, less than 50 mV, in the surface potential in this case. It is also interesting to ...
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... This in turn means that much higher potentials are needed to nucleate corrosion on the aluminium electrode. The image presented in Fig. 12(a) was recorded at an applied potential of (/800 mV (SCE) which corresponds to a potential at which the polyaniline-coated aluminium electrodes are stable and the bulk current recorded is a reduction current, Fig. 12(d). There is very little varia- tion, less than 50 mV, in the surface potential in this case. It is also interesting to note that there is no variation between the coated and uncoated surfaces, showing that both surfaces are polarized to a common mixed potential. Similar data were recorded at (/600 mV (SCE) showing that the polymer offers ...
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... no variation between the coated and uncoated surfaces, showing that both surfaces are polarized to a common mixed potential. Similar data were recorded at (/600 mV (SCE) showing that the polymer offers some corrosion protection to the underlying substrate under these conditions. However, on increasing the potential to a value of (/ 0.4 V (SCE), Fig. 12(b), breakdown of the electrode occurs. A bulk anodic current close to 0.1 mA cm (2 is recorded. Even though this high anodic current is measured there is no evidence of any variation between the surface potential of the coated and the adjacent uncoated parts of the electrode. Instead, it appears that the uncoated surface and the regions ...
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... right hand corner (7000 and (/1050 mm on the displacement scale) and in the lower center section of the image (2800 and 2630 mm on the displacement scale). On polarizing the composite to a higher potential, although higher bulk anodic currents are measured, the area accommodated by these reduction reactions appears to increase. This is seen in Fig. 11(c), where the image was recorded at (/0.2 V (SCE). In this case, the difference between the surface potential measured over the cathodic centers and that on the active surface was of the order of 630 mV. It is interesting to note that the cathodic event initially centered at 2800 and (/2630 mm on the displacement scale consumes the ...
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... data are in agreement with the current Á/ potential behavior seen in Fig. 10, where the anodic currents measured at potentials in the region of (/500 mV (SCE) in the 0.5 mol dm (3 NaCl solution appear to be limited by a diffusion process. This seems to be connected with dissolution of the underlying aluminium substrate and diffusion of these corrosion products through the polymer coating and into the bulk ...
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... process. This seems to be connected with dissolution of the underlying aluminium substrate and diffusion of these corrosion products through the polymer coating and into the bulk solution. Dissolution of the underlying aluminium substrate will lead to local detachment of the polymer from the substrate. The presence of the cathodic sites, Fig. 12(b and c), is consistent with reduction of the detached polymer form the emeraldine to the leucoemeraldine states, with this reduction reaction being catalyzed by the aluminium oxidation reaction. The expanding area accommodated by the reduced polymer on increasing the potential applied to the composite is consistent with the much ...
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... is also seen in Fig. 11, that much higher mixed currents are recorded for the polyaniline-coated electro- des. The mixed currents shown for the aluminium electrode are equivalent to the corrosion currents. However, the values shown for the polyaniline-coated aluminium are more difficult to analyze, as they are likely to be governed by a number of ...
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... to the leucoemeraldine form, the polymer can also catalyze the oxygen reduction reaction [30] and reduction of hydrogen may also occur at the polymer or at the aluminium substrate. However, these additional reduction reactions will drive the aluminium oxidation reaction. Although this may be beneficial, it is seen from the data presented in Fig. 12 that dissolution of this oxidized aluminium substrate can occur and that this attack propagates underneath the polymer leading to detachment of the polymer and reduction of the detached ...
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Citations
... These extra peaks can be related with overoxidation procedures. In this sense, it is well known that the presence of an additional peak between the leucoemeraldine and emeraldine base and the emeraldine and pernigraniline pair is related for the build-up of degradation products, for film overoxidation [30]. Fig. 3b and c are adequate examples of this issue. ...
... The behavior of the PAni/CG composite is similar PAni obtained in acid medium with conventional electrolyte, the pair of redox peaks around 0.05/0.20 V (peak A) was attributed to process of intercoversion of the leucoemeraldine oxidation to emeraldine, a shoulder that appears between peaks A and B can be considered training of intermediaries, such as intermediates of the quinoid/ benzenoid redox reaction, 32,33 another redox pair at about 0.55/ 0.85 V (peak B) corresponds to interconversion of the emeraldine to pernigraniline and the peak at 0.90 V (peak C) attributed to an anodic process occurring on the film surface. [32][33][34][35] Micrographic (Fig. 2c) observed the cauliflower-like PAni/CG with branched cavities. The microstructure analysis of PAni/CG thin films on different scales revealed sphericals structures repeated with a characteristic size of about 250 nm. ...
The electrosynthesis of polyaniline (PAni) and cashew gum (CG) composite was successfully performed by electrochemical methods (potential scanning and constant potential) in terms of pH, aniline (Ani), and polyelectrolyte concentrations. Our aim was to investigate the performance of a polyaniline-based ammonia sensor under different concentrations of ammonium gas, evidencing a color change from green to blue as in the presence of gas in a sensitive and reversible process. Films grown by cyclic voltammetry and chronoamperometry showed a cauliflower-like morphology, and a visual analysis detected a limit of 0.015 and 0.010 mol/L, respectively. The sensor demonstrated a fast response time of 20 seconds, a low detection limit, with a short regeneration time of less than 1 minute at room temperature. This polyaniline-based sensor is shown to be a portable, sensitive, dimensionally flexible, and cost-effective alternative for food packaging and other devices. The findings of this study contribute to the development of advanced ammonia detection technology.
... The synthesis of PAni is also considered to be relatively easy, with good environmental stability. However, the main disadvantage of PAni is its inferior electrochemical cycling stability [10][11][12]. Moreover, PAni is a redoxactive material with three distinguishable oxidation states, leucoemeraldine (fully reduced), emeraldine (half oxidized), and pernigraniline (fully oxidized), which can, in principle, exist as salts or bases. ...
Significant agricultural and industrial activities necessitate the regular monitoring of
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... It corresponds to the oxidation of the leucoemeraldine non-conducting PANI form to the emeraldine (see Figs. S2 and S3, Supplementary Note 1,2). The second peak, c1, located at 103 mV on the cathodic sweep of the curve corresponds to the transition of PANI from the emeraldine to pernigraniline state [52,71]. These redox processes are accompanied by the addition or elimination of protons, which also hints that PANI accumulates energy most efficiently in acidic media [52]. ...
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... It corresponds to the oxidation of the leucoemeraldine non-conducting PANI form to the emeraldine (see Figs. S2 and S3, Supplementary Note 1,2). The second peak, c1, located at 103 mV on the cathodic sweep of the curve corresponds to the transition of PANI from the emeraldine to pernigraniline state [52,71]. These redox processes are accompanied by the addition or elimination of protons, which also hints that PANI accumulates energy most efficiently in acidic media [52]. ...
... Thin polymeric PMAP films, synthesised by electro polymerization of various aromatic compounds, present numerous applications in advanced technology and in corrosion control. Series of studies [3,4] have reported that polymer films based on phenol and their derivatives [5], pyrrole [6][7][8][9], aniline and their derivatives such as PMAP [10][11][12], and other heterocyclic compounds reduced the corrosion rate of steel (and iron) in sulphuric acid and sodium chloride solutions. ...
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... Increasing the polymerization potential dissolves the oxide film and corrodes the aluminum, and this prevents the continuous polymer formation on the surface. PANI has been synthesized electrochemically on aluminum and its alloys, and studies have reported that PANI coating exhibited very good anti-corrosion properties and provided aluminum resistance against corrosion [36][37][38][39][40][41][42][43] . Tallman et al. [39] have explained the protection given by PANI to structural alloys for the aviation industry such as 2024-T3, 6061 and 7075, and reviewed the use of conductive polymers for corrosion control. ...
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We investigated the structural, conductive, and electrochemical properties of polyaniline-derived polymer/pristine aluminum composites by in situ polymerization. This research focused on the conductivity and electrochemical energy storage effects of Al particles used as reinforcing elements in composites and elucidating the interaction of polyaniline on the surface of Al particles by keeping the HCl acid dopant concentration and monomer-oxidant ratio constant. FTIR results revealed that polymerization was successfully synthesized by showing all the characteristic peaks of polyaniline, and the polymer matrix of composites produced in the presence of aluminum was polyaniline. SEM images also showed that Al particles were completely embedded or enclosed in the polymer matrix. Conductivity measurements revealed that the inclusion of Al particles with different mass ratios in the polyaniline matrix resulted in a decrease in conductivity compared to pure polyaniline, and these results were likely due to the thin yet highly stable and electrically-resistant protective oxide (Al2O3) film layer that rapidly formed on the aluminum surface in solution with low HCl concentration. Electrochemical characterizations of polyaniline and composites were investigated by galvanostatic charge discharge, cyclic voltammetry, and electrochemical impedance spectroscopy method. The results showed that composites produced with different aluminum content did not have good supercapacitor properties compared to pure polyaniline, due to the rapidly-forming surface oxide film layer which prevented an effective interaction between the polymer matrix and Al particles. Consequently, the composite has not contributed to the increase in capacitance with aluminum loading by redox reactions at the interfaces with functional groups. This confirms that the aluminum incorporated does not interact with the matrix structures of the composites, but is found in composites with a stable and protective passive oxide film layer that rapidly forms on its surface, thus having higher corrosion protection effectiveness.
... Since its anti-corrosion performance firstly found by DeBerry [5], PANI has also been considered to be an appropriate substitute for traditional toxic chromate coatings [6][7][8]. Unfortunately, pure PANI films are not an ideal choice for metal protection, because of their mass agglomeration and poor mechanical properties, prone to generate cracks to reduce anti-corrosion performance of PANI films [9,10]. To avoid these disadvantages, it is necessary to modify PANI films to enhance their anti-corrosion performance. ...
Composite coatings of poly(vinyl pyrrolidone) (PVP)-polyaniline (PANI) were prepared on 304 stainless steel (SS) for corrosion protection application by one-step electrodeposition. The composition and structure of the coatings were obtained by Fourier transform infrared spectra (FTIR), Raman spectroscopy, X-ray diffraction (XRD), UV–vis spectrum, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The electropolymerization rate of aniline is decreased and large aggregation of polyaniline particles can be significantly inhibited in the presence of PVP. It is suggested that 1.0 wt% PVP-PANI coating provides enhanced corrosion protection for 304 SS in 1 M H2SO4 solution. The interaction between PANI and PVP favors the formation of the compact structure and consequent high corrosion performance.
... The results observed exhibits the rate of polyaniline deposited graphene oxide polymerization that was rampant on the upper limit of the cyclic voltammetry and similar result has been reported [23]. Also, current density increases as number of cycles increases as seen in Fig. 2 when only 30 cycles were used and when 50 cycles were used in the case of Fig. 3, that behavior can be attributed to polyaniline growth which is in consistent with increasing the number of cycles similar observation has been reported in literature [25]. Scanning electron microscope (SEM) was further used to examine the surface of graphene oxide, polyaniline and electrochemically deposited graphene oxide on the surface of the polymer. ...
The synthesis and characterization of electrochemically deposited polyaniline-grafted graphene oxide was successfully carried out. Excellent electrochemical stability, thermal consistency, reversibility and lower internal resistance were noted at various current densities when graphene oxide was electrochemically deposited on the surface of conducting polyaniline at + 0.75 V. Electrochemical deposition of graphene oxide on the polyaniline was confirmed by scanning electron microscopy, Fourier transformed infrared spectroscopy, Raman scattering and UV/Vis spectroscopy measurements. The electrochemically deposited polyaniline-grafted graphene oxide is confirmed in various characterization techniques employed and has promising electrochemical features due to its good transparency and stability and hence can find various applications in the manufacture of electronic materials and in the construction of electrochemical sensors that are cheap, simple and environmental friendly.
... The band at 1279 cm-1 is attributed to the (C-N) stretching mode for the benzenoid ring For the 0.5 wt.% of PCO peaks observed at 1567 cm-1 and 1459 cm-1 are attributed to (C=N) and (C=C) stretching mode of vibration for the quinonoid and benzenoid units of PCO nanocomposites. The peaks at 1297 and 1279 cm-1 are assigned to N-H bending and C-N stretching mode of benzenoid ring [6]. These results suggest that nanocomposite was properly dispersed in the PANI matrix. ...
Polyaniline (PANI) doped cobalt oxide (CoO) nanocomposite was prepared by electrochemical deposition method. The Polyaniline nanocomposite was characterized by using UV-Visible absorption spectroscopy, Fourier transformation infrared spectroscopy (FT-IR), Field emission scanning electron microscope (FESEM). Absorption band gap are studied by UV-Visible spectroscopy. The FTIR result reveals the chemical interaction between PANI and nano composite. FESEM shows the shape changes from grain to flat surface structure and more porosity due to addition of nano concentration. These obtained results were confirmed that PANI nanocomposite is suitable candidature for energy storage devices.
