LiClO4 Acetonitrile Research Articles

Electrochemical synthesis of polyaniline on mild steel in acetonitrile–LiClO4 and corrosion performance

Polyaniline film could not be obtained on mild steel by direct electrooxidation of aniline in LiClO4 containing acetonitrile medium (ACN–LiClO4), because sufficient passivity of the surface could not be provided. This non-passivated metal undergoes intense dissolution, in potential region at which the monomer oxidation happens and this event prevents the formation of stable polymer film on the surface. Therefore, the electrode surface was coated with very thin polyaniline (PANi), polypyrrole (PPy) primer coatings, in monomer containing aqueous oxalic acid solution, and then the synthesis of top PANi film was achieved in aniline containing ACN–LiClO4 successfully. The corrosion behavior of PANi/PANi and PPy/PANi coated MS samples were investigated in 3.5% NaCl solution, properly. For this aim, anodic polarization curves and open circuit potential–time (Eocp–t) variation and electrochemical impedance spectroscopy (EIS) techniques were used. It was shown that PPy/PANi coating could provide much better protection for longer periods than PANi/PANi coating against the corrosion of MS. This behavior was explained with better barrier property of PPy/PANi. After 240h of immersion time in corrosive test solution, the protection efficiency value was 97.0%, for PPy/PANi coated electrode.

Polythienobenzothiophenes, a new family of electroactive polymers: electrosynthesis, spectral characterization and modelling

New conducting polymers, including poly[thieno[3,2-b][1]benzothiophene] (poly-TBT) and poly [6-methoxythieno[3,2-b][1]benzothiophene] (poly-MeOTBT) were electrosynthesized by anodic oxidation of the corresponding monomers in 0.1 M LiClO4 acetonitrile solution. Poly-TBT and poly-MeOTBT electroactive films were formed on platinum electrodes and characterized spectroscopically. FT-IR studies show that both polymers present couplings occurring on the thiophene moiety and the phenyl ring, with a step-like structure. MALDI-TOF mass spectrometry indicates that poly-TBT and poly-MeOTBT films are mainly constituted of short-chain oligomers. The results of molecular orbital (MO) calculations performed on the basis of a radical-cation electropolymerization mechanism are in good agreement with our spectral data.

LiClO4‐Catalyzed Highly Diastereoselective Synthesis of cis‐Aziridine Carboxylates.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Electrochemical Behavior of Polythiophene Films: Effect of Electrolyte Concentration and the Nature of the Alkyl Substituent

The electrochemical behavior of poly(3-methylthiophene) and poly(3-octylthiophene) films in solutions of 0.05–0.5 M LiClO4 in acetonitrile is studied using cyclic voltammetry and chronoamperometry. An analysis of data on the current relaxation following a film perturbation by a pulsed small voltage reveals the presence of two constituents of the current relaxation for either polymer, each constituent exponentially depending on the time. Effect of the electrode potential and electrolyte concentration on the current relaxation parameters are studied. Results of additional studies of poly(3-methylthiophene) films by a faradaic impedance method conform to the chronoamperometry data and permit a more reliable interpretation of them.

Evolution from gravimetric to viscoelastic response of poly(3-methylthiophene)-loaded acoustic wave resonators

Acoustic wave resonators are used to explore the relationship between ion and solvent populations (composition) and shear moduli (dynamics) for poly(3-methylthiophene) films. The films were electropolymerized from monomer solutions in acetonitrile–LiClO4 and subsequently characterized in a monomer-free electrolyte. Crystal impedance spectra provide a diagnostic for the rigid s. viscoelastic behaviour. Very thin films contain two types of zone, with different electrochemical responses and solvation characteristics. The more compact type of zone significantly influences the characteristics of very thin films. The more open, solvated type of zone dominates the characteristics of thicker films. Gravimetric interpretation of resonator frequency response shows that redox driven ion and solvent transfers exhibit compensatory motion: anions driven into the film to maintain electroneutrality displace some of the solvent present in undoped films. These transfers can be temporally resolved by variation of the potential scan rate in cyclic voltammetric experiments: solvent transfers more slowly. Resonator responses for thicker films are interpreted using a model in which a finite viscoelastic film contacts a semi-infinite Newtonian fluid. Compensatory motion of anions and solvent is again manifested through redox state independent film thickness; replacement of some solvent by denser dopant anions results in increased film density. Film shear moduli at 10 MHz are characteristic of lossy, viscoelastic materials. The storage shear modulus increases significantly (almost by a factor of two) upon p-doping of the film. The loss shear modulus, which is the larger component of the two, increases only marginally upon film doping.

Improvement of the Electrosynthesis and Physicochemical Properties of Poly(3,4-ethylenedioxythiophene) Using a Sodium Dodecyl Sulfate Micellar Aqueous Medium

Electrosynthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) films was performed in a micellar aqueous solution containing sodium dodecyl sulfate (SDS) by cyclic voltammetry, chronoamperometry, and chronopotentiometry on a platinum electrode. The electrocatalytic effect of SDS was characterized by a significant decrease of the EDOT oxidation potential (Ep) in the micellar medium relative to 0.1 M LiClO4 acetonitrile as well as aqueous solutions. Linear variation of Ep with SDS concentration indicated the formation of a pseudocomplex (Keq = 5.4 × 103 M-1). PEDOT films were characterized electrochemically and spectroscopically (UV−visible, X-ray photoelectron spectroscopy, IR, Raman spectra). Regular, well-ordered, and adherent films were obtained in SDS medium. The PEDOT film morphologies investigated by atomic force microscopy suggested the possible presence of columnar structures when the electrosynthesis is performed in the micellar medium.

Electrochemical characterization in nonaqueous electrolyte of polyaniline electrochemically prepared from aqueous media

Polyaniline film electrodes were characterized in nonaqueous electrolyte following their electrochemical preparation in aqueous media. More specifically, polyaniline films were deposited galvanostatically at the surface of platinum or gold electrodes by anodic electrochemical polymerization from a 0.5 M aniline – 1 M HCl aqueous solution. The polyaniline film electrode was then dried and its electrochemical behavior was evaluated in nonaqueous electrolyte (LiClO4–acetonitrile). Stable cyclic voltammograms were recorded between −0.1 and 1 V in the nonaqueous media, which represents a much wider range than in aqueous acidic media. In the latter case the positive potential limit must be restricted to about 0.7 V in order to avoid oxidative degradation of the polymer. Electrochemical impedance spectroscopy was used to determine the charge capacity of the polyaniline film electrode as a function of film thickness and electrode potential. A linear relationship was observed between the low-frequency capacitance of the polyaniline electrode and the amount of deposited polymer (e.g., charge used to grow the polymer). This indicates that even for the thickest film (deposited charge of 10 C/cm2) most of the polyaniline is electrochemically accessible at the low frequency of 5 mHz. The thinnest polyaniline film electrode (deposited charge of 0.2 C/cm2) was also characterized by the electrochemical quartz crystal microbalance technique and it was found that ionic transport is dominated by the movement of anions. Keywords: conducting polymer, polyaniline, nonaqueous electrolyte, capacitance, electrochemical impedance spectroscopy, cyclic voltammetry, electrochemical quartz crystal microbalance.

Lithium Intercalation in Nanoporous Anatase TiO2 Studied with XPS

Intercalation of lithium ions in nanoporous anatase TiO2 was studied with XPS using a novel electrochemical preparation technique. The electrolyte was 0.5 M LiClO4 in acetonitrile (not water-free). The electrochemical insertion of lithium ions creates reduced Ti ions (Ti3+), which was observed as a new well-resolved state in the Ti 2p core level spectrum shifted 2.1 eV to lower binding energy. The new Ti 2p state was reversible when the electrode was deintercalated. Changes in the O 1s core spectra were also observed and discussed in terms of hydrated lithium ions in the Helmholtz layer, or formation of Li2O/LiOH.

Effects of Salt on Isomerization of Stilbene Cation Radicals. Direct Observation of their Cis → Trans Conversion

Abstract Unimolecular cis → trans conversion of stilbene cation radicals generated from 9,10-dicyanoanthracene-biphenyl co-sensitization under air was directly observed in the presence of salt such as LiClO4 in acetonitrile, and the activation parameters of this process were determined by means of transient spectroscopy. It is proposed that the salt reduces the rate of charge recombination between the olefin cation radical and the resulting superoxide anion by complexing with the latter anion.

Anodic Dissolution of Metallophthalocyanine Layers and Their Intrinsic Oxidation

AbstractVoltammetric measurements at a PtRRDE, where vacuumdeposited MePc‐layers (70–700 nm) are present at the disc, were performed in 0.1 M LiClO4 in acetonitrile. Any dissolved MePcz+‐species can be rereduced at the ring. Anodic dissolution was found to be the only process in the case of FePc and CoPc at relatively negative potentials. The cations dissolve layer by layer. For NiPc and CuPc, three different anodic processes can be distinguished: I) Anodic insertion of anions into the solid without any dissolution of cationic species. II) A further insertion of anions at more positive potentials, which is accompanied by a slow dissolution of the material. This is indicated by a relatively weak cathodic ring current. Lattice dynamics in the course of the anodic insertion of anions leads to a destabilization of the solid. III) A strong ring current shows the anodic dissolution of the whole MePc‐layer at even more positive potentials. It is accompanied by a chemical dissolution to release the anions, which were inserted in the course of steps I and II. The consequences with respect to the long term stability of MePc are discussed.

Investigation of Ion and Solvent Transport Accompanying Redox Reactions of Polyvmylferrocene Films Using an in situ Electrochemical Quartz Crystal Microbalance Technique

Abstract The in situ electrochemical quartz crystal microbalance (in situ EQCM) technique has been applied to study ion and solvent transport accompanying the redox reaction of polyvmylferrocene (PVF) film coated on quartz crystal electrodes in aqueous and acetonitrile media. The dependence of apparent formal potentials (Epolyf)app of the Fc°/Fc+ redox couple (Fc° and Fc+ represent the reduced and oxidized sites, respectively, in the PVF film) upon the concentration of supporting electrolyte has been also examined in comparison with those of solution-phase ferrocene derivatives. The PVF film is ideally permselective to ClO4− anion in both aqueous and acetonitrile media. The PVF oxidation (or reduction of polyvinylferricenium ion) in aqueous media is accompanied by the ingress (or egress) of one ClO4− ion per redox site and some solvent (ca. one H2O per redox site). In LiClO4 acetonitrile media, during the oxidation process ClO4− ion with some solvent inserts into the film and the reverse phenomenon occurs during the reduction process. The results demonstrate that a combination of the in situ EQCM measurement and the measurement of the dependence of (Epolyf)app on the concentration of supporting electrolyte makes possible to elucidate quantitatively the ion and/or solvent transport process across the polymer film/ solution interface during the redox reaction.

Electrosynthesis and analytical characterization of films obtained by oxidation of 2,6-diaminopyridine

The oxidation of 2,6-diaminopyridine in acetonitrile–LiClO4 at a platinum electrode leads to the formation of two different films (I and II), depending on the deposition potential. Electroanalytical investigations revealed in ECE mechanism operating for film I formation and provided evidence for nucleation and growth in film II deposition. UV and ESCA spectroscopic characterization revealed the different natures of the films.

Electrochemical preparation and study of thin poly( N-vinylcarbazole) layers

The growth of poly(N-vinylcarbazole) (PVCZ) films was followed under the conditions of potentiostatic square wave multipulse electropolymerization of N-vinylcarbazole in a medium of LiClO4 in acetonitrile. The time dependence of the polymer mass during the initial film growth and the changes in the oxidation level of PVCz during this process were derived from oscilloscopic I-t curves. Two polymerization stages were found: in the first, a thin layer of very compact (PVCZ) is formed, on which, in the second stage, a polymer with a globular structure grows. The thickness and morphology of the film is controlled by the frequency of the square wave potential pulses. The transition to the globular polymer is caused by polymerization via the vinyl groups of N-vinylcarbazole, initiated by H+ ions.Photogeneration of charge carriers was studied on non-conducting PVCz (polymerized only through the vinyl groups) formed in the bulk of a non-aqueous polymerization solution as a side product of electropolymerization. The intrinsic charge carrier photogeneration is depicted as a multistage process which can be described within the framework of the ballistic model. The dissociation of electron-hole pairs is in good agreement with predictions based on the Onsager theory of geminate recombination. The pair separation distance was determined as 2.8 nm.

Mechanism of oxidation of cyclohexane by the radical cation of pyridine N-Oxide

Oxidation of pyridine N-oxide in the presence of cyclohexane was studied on platinum and carbon glass rotating disk electrodes using the method of cyclic voltammetry in 0.2 N LiClO4 in acetonitrile. It was hypothesized that the electrochemically generated N-oxide radical cation reacts with cyclohexane according to the mechanism of hydrogen atom cleavage.

Electrochemical, electrochromic, and conductive properties of poly(N-alkyldiphenylamine) polymers

Chemically prepared poly(N-alkyldiphenylamine) polymers are conductive and electrochemically reversibly dopable in organic and aqueous solutions; cast polymer films exhibit multiple, reversible colour changes in 1 M LiCLO4 in acetonitrile or 1 M HClO4 aqueous under potential cycling between 0.0 and 1.0 vs. Ag/AgCl or when dipped in aqueous solutions having different pH.