Nanostructured polyaniline synthesized using interface polymerization and its redox activity in a wide pH range

Purely nanostructured polyaniline with the conductivity of 7.2 S cm^?1 was synthesized via the quick addition of the oxidant of the solid ammonium peroxydisulfate into a cooled solution containing aniline and hydrochloric acid without any templates. The morphology of polyaniline is constructed of interwoven fibers with an average diameter of about 50 nm with lengths varying from 250 nm to 370 nm. In general, the conventional polyaniline completely lost its electric activity including conductivity and redox activity at pH 6; however, the polyaniline reported here shows two pairs of redox peaks on its cyclic voltammogram in 1.0 M NaCl solution with pH 7.0, which is similar to that of the conventional polyaniline in the more acidic solutions; and it still holds the redox activity until pH 9.0. The pH dependence of conductivity of polyaniline is also improved compared to that of the conventional polyaniline. The ESR measurements show that the deprotonated polyaniline still holds rather high unpaired spin densities. The ¹H NMR spectra of polyaniline synthesized using interface polymerization are different those of the conventional polyaniline. The electrochemical behavior and spectra of polyaniline synthesized via the quick addition of an oxidant solution into a solution of aniline were reported and discussed.     

Self-dispersed polyaniline derivative extending electrochemical activity to neutral media

Self-dispersed poly-N-[5-(8-quinolinol)ylmethyl]aniline, which can be easily dispersed in some organic solvents without any dispersant, has been prepared by oxidative polymerization of 5-(anilinomethyl)-8-hydroxyquinoline. Although its conductivity only reaches 1.45 × 10^?3 S cm^?1, it possesses good redox reversibility in aqueous electrolyte ranging from pH 1.0 to 7.0, and its cyclic voltammetry curves also show good cycling stability in the aqueous medium of pH 5.0. It will be a promising material for several applications such as biosensors due to increasing the operating pH window in aqueous media.     

Novel properties of polyaniline nanofibers coated with polycatechol

Polyaniline nanofibers coated with polycatechol, FcPAn/polycatechol, have been prepared with two steps by using repeated potential cycling. First, aniline in a solution containing ferrocenesulfonic acid (Fc) was polymerized on a platinum electrode to form polyaniline nanofibers (FcPAn); second, catechol was polymerized on the polyaniline nanofibers to form FcPAn/polycatechol. The scanning electron microscopy (SEM) images show that the diameters of FcPAn and FcPAn/polycatechol fibers are in the range of 40–60 and 70–90 nm, respectively. The IR and XPS spectra of FcPAn/polycatechol indicate that OH groups and ferrocenesulfonic acid are contained in FcPAn/polycatechol. FcPAn/polycatechol has a good electrochemical activity in the wide pH range. The cyclic voltammogram identifies that FcPAn/polycatechol in the Na₂SO₄ solution with pH 11.0 still has the electrochemical activity at the scan rate of 60 mV s⁻¹. The conductivity of FcPAn/polycatechol is 0.48 S cm⁻¹, which is slightly affected by water. FcPAn/polycatechol nanofibers with the diameter of 70–90 nm have a higher catalytic activity to the electrochemical oxidation of ascorbic acid, compared with FcPAn/polycatechol fibers with the diameter of 140–210 nm.     

Electrosynthesis of polyaniline films on titanium by pulse potentiostatic method

Polyaniline (PANI) was synthesized on titanium electrode from aqueous solution containing 0.3 mol L⁻¹ aniline and 1 mol L⁻¹ HNO₃ by pulse potentiostatic method. The chronoamperogram during polymerization process of aniline was recorded. The effects of the synthesis parameters, such as anodic pulse duration (t_a), cathodic pulse duration (t_c), lower limit potential (E_c) and upper limit potential (E_a), on the morphology and electroactivity of the PANI films were investigated by scanning electron microscopy (SEM) and cyclic voltammetry (CV). SEM results present that flake, mica-like, quasi-fibrous and nano-fibrous PANI film could be synthesized with various polymerization parameters. Under the following conditions, t_a = 0.8 s, t_c = 0.1 s, E_c = 0 V and E_a = 1.0 V, high quality nano-fibrous PANI film with the best electroactivity was obtained. The CV results show that the PANI films with different morphologies, which were prepared under the same anodic polymerization charge, have obvious different characteristics. This means that the PANI films with different morphologies have different electrochemical activity.     

Preparation and characterization of polyaniline film on stainless steel by electrochemical polymerization as a counter electrode of DSSC

Polyaniline (PANI) films were electrodeposited on stainless steel 304 (SS) from 0.5 M H₂SO₄ solution containing 0.3 M aniline by potentiostatic techniques to prepare a low cost and non-fragile counter electrode in dye-sensitized solar cell (DSSC). The compact layer, micro-particles, nanorods and fibrils were observed on the top of PANI films with different applied potentials (E_appl) by SEM. Then the conductivity and electrochemical test illuminated that a polyaniline film with the highest conductivity and best electrocatalytic activity for I₃^?/I^? reaction was electrodeposited at 1.0 V E_appl. Finally, the photoelectric measurement showed that the energy conversion efficiency of DSSC with the PANI electrode was increased with the E_appl decreasing. And the efficiency of DSSC with PANI counter electrode at 1.0 V was higher than that with Pt electrode, owing to the loosely porous structure, high conductivity and excellent catalytic activity of PANI electrode.     

Polypyrrole nanowire modified graphite (PPy/G) electrode used in capacitive deionization

With high specific capacitance and good conductivity, polypyrrole nanowire modified graphite (PPy/G) electrode has great promising applications in capacitive deionization (CDI). Preparation parameters of modified electrode such as concentration of supporting electrolyte solution (LiClO₄), concentration of monomer (pyrrole, Py), pH of polymerization medium, polymerization potential and time have significant effects on the electrode adsorption capacity of NaCl. The experimental results indicate that the optimal preparation condition of the PPy/G electrode used for CDI is 0.10 M LiClO₄, 0.19 M Py and pH 5.91 which was controlled by phosphates buffer solution (PBS, 0.10 M), polymerized at 0.85 V vs saturated calomel electrode (SCE) with polymerization time of 150 s. The obtained electrode has an area specific capacitance of 0.188 F/cm² determined by cyclic voltammetry (CV) method in 1.0 M HClO₄ at a scanning rate of 0.05 V/s. In addition, the desalination experiments of the electrode were carried out in 500 ppm NaCl solution at a working voltage of 1.4 V. The experimental results indicate that the NaCl can be removed from the feed solution by electroadsorbing of the electrode with good desalination stability and the electrode can be regenerated efficiently by its electrodesorbing.     

Spectroscopic and thermal properties of the copolymer of aniline with dithiodianiline

Electrochemical copolymerization of aniline (ANI) with dithiodianiline (DTDA), an aniline derivative containing –S–S– links was carried out in 2 M H₂SO₄ using cyclic voltammetry. The cyclicvoltamogram (CV) of the deposited copolymer was recorded in monomer free background electrolyte. A close comparison of the CV characteristics of the films deposited during polymerization of mixture of ANI and DTDA clearly the copolymer deposition. The UV–VIS spectroscopy, spectroelectrochemical studies, thermal analysis and FTIR spectroscopic analysis were used to identify the differences between the copolymer and PANI in the optical, thermal properties and structure. The copolymer was found to have a branched structure in comparison with PANI. The copolymer exhibit different colors upon changing applied potentials.     

The electrocatalytic oxidation of ascorbic acid on polyaniline film synthesized in the presence of ferrocenesulfonic acid

The catalytic oxidation of ascorbic acid on the two kinds of polyaniline electrodes (PAn and PAnFc films) has been carried out by cyclic voltammetry, constant potential and constant current methods. PAnFc and PAn films were synthesized in the presence and absence of ferrocenesulfonic acid, respectively. For the electrolysis of ascorbic acid at pH 5.64, the anodic peak potential of ascorbic acid shifts from 0.32 V (vs. SCE) on the bare platinum electrode to 0.05 V on both PAn and PAnFc electrodes. The oxidation current of ascorbic acid on the PAnFc electrode is 31 times as high as on the bare platinum electrode at the electrolysis of the constant potential. The exchange current density is 1.3 mA cm⁻² on the PAnFc electrode and 1.0 mA cm⁻² on the PAn electrode. The catalytic effect is caused by polyaniline itself. Ferrocenesulfonic acid doped in polyaniline plays an important role in enhancing the catalytic activity of polyaniline in the solution of pH >5.     

Effect of Fenton reagent on the synthesis of polyaniline

Polyaniline has been prepared using Fenton reagent. The in situ visible spectra during the polymerization process show that the polymerization of aniline was carried out through an intermediate at 530 nm. The absorption band of the resulting product, polyaniline, appears at 700 nm. The conductivity of polyaniline prepared using Fenton reagent can reach 1.04×10⁻² S cm⁻¹, which is strongly dependent on the concentrations of FeSO₄, H₂SO₄ and polymerization time. The cyclic voltammogram of polyaniline prepared using Fenton reagent is much different from that of polyaniline prepared normally, and has the good electrochemical reversibility and a fast charge transfer characteristic in the solution with pH 4.0. The FTIR spectrum indicates that no absorption band attributed to N–H stretching vibrations is present in polyaniline.     

Fuzzy nanofibrous network of polyaniline electrode for supercapacitor application

Fuzzy nanofibrous network of polyaniline electrode is successfully electrosynthesized for supercapacitor application. The nanofibre network of polyaniline electrode is characterized using Fourier transforms infrared spectroscopy (FTIR), scanning electron microscope (SEM) and optical absorption studies. Network of polyaniline is highly porous with interconnected fuzzy nanofibres having diameter typically between 120 and 125 nm. The supercapacitive performance of polyaniline electrode is tested using cyclic voltammetry (C-V) technique in H₂SO₄ electrolyte within potential range of ?100 to 800 mV. The effect of scan rate on the capacitance of polyaniline electrode is studied. The highest specific capacitance of 839 F g^?1 at the voltage scan rate of 10 mV s^?1 is achieved. Additionally stability and charging–discharging of polyaniline electrode are studied.     

Synthesis of sulfonated polyaniline by polymerization of the aniline heterodimer 4-aminodiphenylamine-2-sulfonic acid

The aniline heterodimer 4-aminodiphenylamine-2-sulfonic acid has been polymerized in aqueous ammonium persulfate solution to yield a new form of sulfonated polyaniline (SPAn). This polymer, obtained as a green powder, is soluble in aqueous base (violet solution) and polar solvents (green solution, turning blue on standing). Its FTIR, UV–VIS and EPR spectra are quite similar to those of SPAn obtained by direct ring-sulfonation of polyaniline. The room temperature dc conductivity of the polymer is about 1.3×10⁻⁵ S/cm, indicative of considerable disorder in the sample. Cyclic voltammetry in 1.0 M HCl shows two redox peaks at E_1/2,1=0.50 V and E_1/2,2=0.68 V against Ag/AgCl electrode, characteristic of SPAn.     

Transmembrane redox reactions through polyaniline membrane doped with fullerene C60

Polyaniline (PANI)-C₆₀ membranes were chemically synthesized with fullerene C₆₀ content of 0.2, 0.5, 1, 2 and 3 mol% (relative to aniline fragment) respectively, and then systematically characterized with FTIR, field emission scanning electron microscopy (FESEM), XPS and electrochemical impedance spectroscopy (EIS). It is demonstrated that electron/ion coupled transport across PANI-C₆₀ membrane is possible in the presence of oxidizing agent at one side of the membrane and reducing agent at the other side. If 0.05 M acidic solution of FeCl₃ was used as the oxidizing agent and 0.3 M ascorbic acid as the reducing agent, a typical value of transmembrane transport rate of redox equivalents was 3.1 × 10⁻⁸ mol s⁻¹ cm⁻² with the membrane containing 0.5% C₆₀. This value was one order higher than that for HCl doped PANI membrane at identical conditions, which can be explained by superimposed C₆₀ doping and acid doping. The 0.5% content of C₆₀ is optimal and at higher content the rates of transmembrane redox transport decrease.     

Synthesis and photovoltaic application of donor–acceptor type copolymers containing 9-cyanomethylenefluorene derivatives with chemically tunable electronic properties

Four 9-cyanomethylenefluorene derivatives were synthesized as a new class of electron-deficient building blocks for donor–acceptor (D–A) type alternating copolymers. UV–vis absorption spectroscopy, cyclic voltammetry and density functional theory calculations show that the substituent X at the cyanomethylene unit, depending on its electron-withdrawing ability (X = –H, –CONMe₂, –COOiBu and –CN), can continuously control the LUMO energy level of the monomer. D–A type copolymers were synthesized using the derivatives and an oligothiophene as the electron-donating block. The photovoltaic performance of D–A copolymer:PCBM bulk heterojunction devices shows the importance of LUMO level alignment to achieve efficient charge separation at the donor/acceptor interface. After optimization, the power conversion efficiency of the device with X = –H reached 1.14% with V_OC of 0.61 V, J_SC of 3.24 mA cm^?2 and FF of 0.58 under the irradiation of AM1.5 simulated solar light. The electronic properties of the copolymers correlated well with the electron-withdrawing ability of the monomers while the structure of the π-conjugated backbone was preserved, demonstrating the advantage of the chemically tunable monomer design.     

In-situ electrochemical polymerization of multi-walled carbon nanotube/polyaniline composite films for electrochemical supercapacitors

Multi-walled carbon nanotube (MWCNT)/polyaniline (PANI) composite films were prepared by in-situ electrochemical polymerization of an aniline solution containing different MWCNT contents. The supercapacitive behaviors of these films were investigated with cyclic voltammetry (CV), charge–discharge tests, and ac impedance spectroscopy. The results revealed that the MWCNT/PANI films show much higher specific capacitance (SC), better power characteristic, better cyclic stability, and more promising for applications in supercapacitors than a pure PANI film electrode. The highest specific capacitance value of 500 F g^?1 was obtained for the MWCNT/PANI composite film containing MWCNT of 0.8 wt.%. The improvement mechanisms of the capacitance of the composites are also discussed in detail.     

Potentiodynamic deposition of polyaniline on non-platinum metals and characterization

Polyaniline (PANI) was potentiodynamically deposited on stainless steel (SS), Ni, Ti, Al and Pb electrodes from aqueous solutions of NaClO₄, oxalic acid and H₂SO₄ of different concentrations. Platinum was also used as a substrate for the purpose of comparison. Although, the non-platinum metals showed reactivity in the electrolytes, the adsorption of aniline monomer occurred leading to initiation and growth of PANI during repeated potential sweeps. The nature of voltammograms of the non-platinum metals during PANI deposition differed from that of the Pt electrode. Subsequent to potentiodynamic deposition, the electrodes were studied for their electrochemical activity in 0.5 M H₂SO₄ without and with dissolved redox species. On all metals, the PANI exhibited the potentiodynamic peak at about 0.2 V corresponding to transition from leucoemaraldine (LE) state to emeraldine (EM) state at low scan rates. However, this peak disappeared on repetition of potential scan and also at high scan rates. The PANI deposited on non-platinum metals showed response to dissolved redox species, viz. hydroquinone/quinone, ferrous/ferric, ferrocyanide/ferricyanide, as reflected in the potentiodynamic and ac impedance measurements. However, the peak potential separation of cyclic voltammograms was very large.     

Self-assembled polyaniline nanotubes and nanoribbons/titanium dioxide nanocomposites

Self-assembled polyaniline (PANI) nanotubes, accompanied with nanoribbons, were synthesized by the oxidative polymerization of aniline with ammonium peroxydisulfate in an aqueous medium, in the presence of colloidal titanium dioxide (TiO₂) nanoparticles of 4.5 nm size, without added acid. The morphology, structure, and physicochemical properties of the PANI/TiO₂ nanocomposites, prepared at various initial aniline/TiO₂ mole ratios, were studied by scanning (SEM) and transmission (TEM) electron microscopies, FTIR, Raman and inductively coupled plasma optical emission (ICP-OES) spectroscopies, elemental analysis, X-ray powder diffraction (XRPD), conductivity measurements, and thermogravimetric analysis (TGA). The electrical conductivity of PANI/TiO₂ nanocomposites increases in the range 3.8 × 10^?4 to 1.1 × 10^?3 S cm^?1 by increasing aniline/TiO₂ mole ratio from 1 to 10. The morphology of PANI/TiO₂ nanocomposites significantly depends on the initial aniline/TiO₂ mole ratio. In the morphology of the nanocomposite synthesized using aniline/TiO₂ mole ratio 10, nanotubes accompanied with nanosheets prevail. The nanocomposite synthesized at aniline/TiO₂ mole ratio 5 consists of the network of nanotubes (an outer diameter 30–40 nm, an inner diameter 4–7 nm) and nanorods (diameter 50–90 nm), accompanied with nanoribbons (a thickness, width, and length in the range of 50–70 nm, 160–350 nm, and ～1–3 μm, respectively). The PANI/TiO₂ nanocomposite synthesized at aniline/TiO₂ mole ratio 2 contains polyhedral submicrometre particles accompanied with nanotubes, while the nanocomposite prepared at aniline/TiO₂ mole ratio 1 consists of agglomerated nanofibers, submicrometre and nanoparticles. The presence of emeraldine salt form of PANI, linear and branched PANI chains, and phenazine units in PANI/TiO₂ nanocomposites was proved by FTIR and Raman spectroscopies. The improved thermal stability of PANI matrix in all PANI/TiO₂ nanocomposites was observed.     

Preparation and characterization of a polypyrrole hybrid film with [Ni(dmit)2]2−, bis(1,3-dithiole-2-thione-4,5-dithiolate)nickellate(II)

The synthesis of a hybrid material obtained by electropolymerization of a solution of pyrrole and [NEt₄]₂[Ni(dmit)₂] (dmit = 1,3-dithiole-2-thione-4,5-dithiolato) in acetonitrile solution is reported. The material was characterized by cyclic voltammetry, UV–vis and infrared spectroscopies, scanning electron microscopy (SEM), atomic force microscopy (AFM) and thermal gravimetric analysis (TGA). The FTIR spectroscopy showed that the [Ni(dmit)₂]²⁻ anion has been inserted in the polypyrrole framework and was not destroyed or modified during the polymerization process. The voltammetric analysis indicated that the material has electroactivity and undergoes redox processes associated with the conducting polymer and the counteranion. The cyclic voltammetry results also suggest that the counteranion is not trapped in the PPy matrix undergoing anion exchange during the redox cycle of PPy. The PPy/[Ni(dmit)₂]²⁻ exhibits good thermal stability and a intrinsic conductivity value in the range of semiconductors (10⁻³ S cm⁻¹).     

On the polymerization of 2-aminodiphenylamine: An electrochemical and spectroscopic study

The electrochemical oxidation of 2-aminodiphenylamine (2ADPA) was performed by cyclic scanning of the potential in aqueous HCl solutions. A mixture of oligomeric compounds, named poly(2ADPA), was deposited on the surface of the electrode. The chemical structures present in poly(2ADPA) containing phenazine units and open-ring units were assigned by ¹H NMR spectroscopy. CV results revealed that the redox transformation of poly(2ADPA) from the fully reduced to the fully oxidized state occurs under a single voltammetric peak. The SEM images obtained for the polymer deposited on platinum substrates showed a “fallen leaves” morphology. In situ FTIR spectroscopy experiments carried out during the reversible oxidation of the polymer revealed that the conversion of aromatic rings (1500 cm⁻¹) into quinoid structures (1524–1590 cm⁻¹) is of major significance. Besides, the transformation of secondary aromatic amines (1301 cm⁻¹) into fully oxidized imines and polaronic structures (1470, 1389, 1330 and 1250 cm⁻¹) has been observed.     

Studies on electrochemical copolymerization of aniline with o-phenylenediamine and degradation of the resultant copolymers via electrochemical quartz crystal microbalance and scanning electrochemical microscope

Electropolymerization of aniline in sulfuric acid solution in the presence of o-phenylenediamine (oPD) of various concentrations was investigated via the electrochemical quartz crystal microbalance (EQCM) technique. It was found that the polymerization occurred more favorably at high aniline-to-oPD molar ratios (F₁, 20 or above). The stabilities of the resultant copolymers against degradation were efficiently improved compared with that of polyaniline (PANI). The first-order kinetic constants for polymer degradation were estimated to be 2.07 × 10⁻³ s⁻¹ for polyaniline, and 3.91 × 10⁻⁴ and 1.28 × 10⁻⁴ s⁻¹ for copolymers with F₁ values of 50 and 20, respectively. The degradation product, benzoquinone, was also detected at the tip electrode of a scanning electrochemical microscope (SECM).     

Electrochemical performance of a high cation-deficiency Li2Mn4O9/active carbon supercapacitor in LiNO3 electrolyte

A hybrid supercapacitor based on spinel Li₂Mn₄O₉ and activated carbon (AC) was fabricated. The electrochemical performance of the capacitor was studied by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge in different aqueous electrolytes such as 1 M LiNO₃, Li₂SO₄, NaNO₃ and KNO₃ solution. A maximum specific capacitance of 261 F g^?1 was obtained for the Li₂Mn₄O₉ single electrode between 0 and 1.4 V. The Li₂Mn₄O₉/AC hybrid supercapacitor showed a sloping voltage profile from 0 to 1.4 V and delivered an energy density of 53 Wh kg^?1 based on the total weight of the active electrode materials. The hybrid capacitor exhibited a desirable profile and maintained over 80% of its initial energy density after 1000 cycles, indicating that Li₂Mn₄O₉ has excellent cycling performance and structural stability in aqueous electrolyte. The hybrid supercapacitor also exhibited an excellent rate capability, even at a power density of 1250 W kg^?1, it had a specific energy 29 Wh kg^?1 compared with 48 Wh kg^?1 at the power density of about 417 W kg^?1.