Enhanced tungstate electrochromism via formation of transparent conductive networks

Indium tin oxide (ITO) nanopowder was added to a polymer film containing WO₃ · H₂O particles to enhance electron conductivity and complimentary Li ion kinetics in an electrochromic device. Film conductivity increased dramatically with ITO content, suggesting the formation of conductive ITO networks in the film. The improved electron conductivity leads to a substantial increase of the effective Li⁺ ion diffusion coefficient in the composite film, from 10⁻¹¹ to 10⁻⁹ cm²/s. Electrochromic contrast studies revealed that the presence of the ITO networks leads to enhanced blue/green color contrast.     

Polymerization of 3-Methoxythiophene in a Direct-Current Discharge

Thin polymer films were obtained from 3-methoxythiophene at the cathode in a dc discharge. It was found using Fourier transform IR spectroscopy that thiophene rings were the main structural units of the polymer; aliphatic fragments and oxygen-containing groups were also present. The polymer based on 3-methoxythiophene was found to exhibit p-type intrinsic conduction with an activation energy of 0.045 eV. The conductivity of the polymer at 20°C was 10⁻⁸ Ω⁻¹ cm⁻¹, and doping with iodine resulted in a rise in conductivity to 10⁻³ Ω⁻¹ cm⁻¹.__________Translated from Khimiya Vysokikh Energii, Vol. 39, No. 5, 2005, pp. 382–385.Original Russian Text Copyright © 2005 by Drachev, Gil’man, Krasovskii, Costa-Belobrzeckaja.     

Electropolymerization of ionic liquid substituted polyphenylene as supercapacitors materials

A new type of polyphenylene, ionic liquid (IL) 1,3-methylimidazolium hexafluorophosphate substituted, has been prepared by electrodeposition on Au electrode surface via pulse galvanostatic method in 1-butyl-3-methylimidazolium hexafluorophosphate solution. The obtained polymer film had a spherulitic morphology with smallest grains of around 500 nm. Infrared spectrometry revealed that polyphenylene was deposited to a certain extent. The capacitive behavior of the IL substituted polyphenylene was investigated by cyclic voltammetry (CV) and galvanostatic charge–discharge method in 0.2 mol L⁻¹ H₂SO₄ aqueous solutions or pure IL [bmim]PF₆. The specific capacitance of the polymer at the charge–discharge current density of 1 mA cm⁻² equaled 206 F g⁻¹ in acidic aqueous solution or 164 F g⁻¹ in [bmim]PF₆. Additionally, excellent charge–discharge cycle stability (over 85% value of specific capacitance remained after 600 charge–discharge cycles) and power characteristics of the polymer electrode were observed in both electrolytes.     

Etude des propriétés de conduction électrique des polyphosphates: Li3Ba2(PO3)7, LiPb2(PO3)5, LiCs(PO3)2, et αLiK(PO3)2

The electrical conductivity of the crystallized polyphosphates Li₃Ba₂(PO₃)₇, LiPb₂(PO₃)₅, LiCs(PO₃)₂, and αLiK(PO₃)₂ has been determined at different temperatures by impedance spectroscopy. The conductivity, σ, spreads within a range of 1.59 × 10⁻⁸ to 1.79 × 10⁻⁷ S cm⁻¹ at 573 K, and from 1.71 × 10⁻⁵ to 9.86 × 10⁻⁴ S cm⁻¹ at 773 K. The transport should be assumed in the majority by the lithium ions with regard to the structural characteristics of these polyphosphates. The results are discussed and compared to the conductivity properties of other lithium ion conductors.     

Inorganic–organic hybrid polymers with pendent sulfonated cyclic phosphazene side groups as potential proton conductive materials for direct methanol fuel cells

A synthetic method is described to produce a proton conductive polymer membrane with a polynorbornane backbone and inorganic–organic cyclic phosphazene pendent groups that bear sulfonic acid units. This hybrid polymer combines the inherent hydrophobicity and flexibility of the organic polymer with the tuning advantages of the cyclic phosphazene to produce a membrane with high proton conductivity and low methanol crossover at room temperature. The ion exchange capacity (IEC), the water swelling behavior of the polymer, and the effect of gamma radiation crosslinking were studied, together with the proton conductivity and methanol permeability of these materials. A typical membrane had an IEC of 0.329 mmol g⁻¹ and had water swelling of 50 wt%. The maximum proton conductivity of 1.13 × 10⁻⁴ S cm⁻¹ at room temperature is less than values reported for some commercially available materials such as Nafion. However the average methanol permeability was around 10⁻⁹ cm s⁻¹, which is one hundred times smaller than the value for Nafion. Thus, the new polymers are candidates for low-temperature direct methanol fuel cell membranes.     

Novel composite polymer electrolytes based on poly(ether-urethane) network polymer and modified montmorillonite

Novel composite solid polymer electrolytes (CSPEs) and composite gel polymer electrolytes (CGPEs) have been prepared. CSPE consists of poly(ether-urethane) network polymer, which is superior to poly(ethylene oxide) in mechanical stability due to its cross-linked structure, modified montmorillonite (MMMT) and LiClO₄, and CGPE with good mechanical strength comprises of the CSPE and LiClO₄–PC (propylene carbonate) solution. The ionic conductivity can be enhanced after the addition of MMMT, and CGPE exhibits ionic conductivity in the order of 10⁻³ S/cm at room temperature. The temperature dependence of the ionic conductivity of the CSPE follows the Vogel–Tamman–Fulcher (VTF) equation. The effects of MMMT on the interactions in these systems and the possible conduction mechanisms are also discussed.     

Ternary blends of poly(ethylene oxide) and acrylate-based copolymers: Crystallinity, miscibility, interactions and proton conductivity

In the present work, blends of poly(ethylene oxide) (PEO), poly(acrylonitrile-co-methyl acrylate) (PANMA) and poly(4-vinylphenol-co-2-hydroxyethyl methacrylate) (PVPh-HEM) were studied by DSC, FTIR and electrochemical impedance spectroscopy (EIS). PEO/PANMA blends were found to be immiscible, while PEO/PVPh-HEM blends are miscible and PVPh-HEM/PANMA exhibits partial miscibility behaviour. The ternary PEO/PANMA/PVPh-HEM blends exhibited miscible compositions for PVPh-HEM and PEO-rich systems. The miscibility observed is a direct consequence of the hydrogen bond interactions among the polymer chains, in which the phenol groups in PVPh-HEM interact with both PEO and PANMA chains. The proton conductivity of a selected membrane based on the ternary blend containing 60% PEO and doped with H₃PO₄ aqueous solution reached 8 × 10⁻³ Ω⁻¹ cm⁻¹ at room temperature and 3 × 10⁻² Ω⁻¹ cm⁻¹ at 80 °C.     

Ion Transfer in CdF<Subscript>2</Subscript>-based Iso- and Polyvalent Solid Solutions

The ionic conductivity of solid solution Cd_0.77Sr_0.23F₂ is 1.6 × 10⁻⁴ S/cm at 500 K. The conduction mechanism changes from a vacancy mechanism to an interstitial one at 523–553 K. In solid solutions Cd_0.9R_0.1F_2.1 (R = La-Lu, Y), the activation enthalpy of conduction decreases from 0.9 to 0.8 eV with decreasing ionic radius of R³⁺, raising the 500-K conductivity from 6 ×10⁻⁶ S/cm for La³⁺to 6 × 10⁻⁵ S/cm for Lu³⁺. For crystalline Cd_0.95In_0.05F_2.05, ionic and electronic conductivities at 313 K equal 5 × 10⁻⁴ and 5 − 10⁻⁶ S/cm.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 627–632.Original Russian Text Copyright © 2005 by Sorokin, Buchinskaya, Sul’yanova, Sobolev.     

Potentiostatic preparation of poly-1,3-dimethoxybenzene films. Kinetics and bilayer structure

The anodic oxidation of 1,3-dimethoxybenzene (MDMB) on a platinum electrode in non-aqueous tetrabutylammonium perchlorate (TBAP) + acetonitrile solutions begins at 1100 mV. Under polarization at constant potential a polymer film is formed at potentials above than 1700 mV. The empirical kinetics of the formation and growth of this film were investigated using microgravimetry and coulometry. Under all experimental conditions the polymerization rate R_p changes after 10 s of polarization, and this behavior can be described by the empirical equationsR_p = k[MDMB]^0.3[TBAP]^0.4t_pol <10sR′_p = k′[MDMB]^0.9[TBAP]^0.5t_pol 10 s The apparent activation energy is 25 ± 1 kJ mol⁻¹ in both cases. The electrogenerated polymer film has a bilayer structure: a inner compact adherent golden layer, and an outer powdery brown layer.     

Low-potential facile electrosyntheses of free-standing poly(5-methoxyindole) film with good fluorescence properties

High-quality free-standing poly(5-methoxyindole) (P5MIn) films were synthesized electrochemically by direct anodic oxidation of 5-methoxyindole (5MIn) in boron trifluoride diethyl etherate (BFEE). P5MIn films obtained from this medium showed good electrochemical behavior and good thermal stability with a conductivity of 0.12 S cm⁻¹. P5MIn films were insoluble in water, acetone and tetrahydrofuran. The structure of the polymer was studied by UV–visible spectroscopy and FT-IR spectroscopy, which indicated that the polymerization occurred at C₍₂₎ and C₍₃₎ position. Fluorescent spectral studies indicate that solid P5MIn film is a good blue emitter. Thermal stability of P5MIn film is higher than poly(5-methylindole) and poly(5-chloroindole) obtained from BFEE. To the best of our knowledge, this is the first report on the electrosyntheses of free-standing P5MIn films.     

Determination of Nitric Oxide by Glassy Carbon Electrodes Modified with Poly(Neutral Red)

Nitric oxide can be oxidized to NO⁻₂ (then to NO⁻₃) and reduced to N₂O at a glassy carbon electrode modified with the film of poly(neutral red). When the modified electrode is further coated with a thin Nafion film, the interference of NO⁻₂ can be almost thoroughly eliminated, and the electrode can be employed to detect nitric oxide.     

Electrochemical behavior of polypyrrole/ kodak aq composite polymeric films

The anodic polymerization of pyrrole (P) onto glassy carbon in an aqueous solution of the Kodak-AQ poly(ester sulfonic acid) polyelectrolyte gives a PP/AQ composite film. While incorporated as charge compensators during the anodic growth of PP, the entangled AQ⁻ chains cannot easily diffuse out upon reduction. The composite layer, resulting from such unique use of AQ ionomers (as electrolyte and dopant) possesses the features of both its conducting polymer and cation exchanger components. These include effective loading of hydrophobic cations, potential switch effect or permselective response. For example, the uptake of Ru(bpy)²⁺₃ by the AQ anion, residing in the conducting polymer, is facilitated by an electrochemical event (reduction of the film to PP⁰/AQ⁻). Similarly, the redox switchable PP component offers electrochemical control of the release of loaded cations. These and other attractive properties of PP/AQ composite layers are explored by cyclic voltammetry, chronocoulometry, potentiometry and flow injection amperometry.     

In situ surface plasmon study of the electropolymerization of Fe(vbpy)3 onto a gold surface

Sequential multilayer electropolymerization of Fe(vbpy)₃²⁺ (vbpy=4-vinyl-4′-methyl-2,2′-bipyridine) onto a thin gold electrode was followed in situ with surface plasmon spectroscopy (SPS) using a 1 mW HeNe laser at 6328 Å. The robustness of the gold film electrode necessary for electrochemical deposition in 0.10 M tetraethylammonium perchlorate+acetonitrile is imparted by use of a thin film of 3-mercaptopropyl-trimethoxysilane attached to a SF10 slide to which the metal is covalently bonded. As each polymer layer is deposited by cycling a potentiostat from 0.0 to −1.75 and back to 0.0 V, a plasmon spectrum (reflectivity versus prism angle) is obtained. SP analysis of the angular shift of the spectrum, which increases as the polymer layer thickens, yields an estimate of both the thickness and index of refraction of the polymer film. We found that the plasmon spectrum shifts to higher angles as the polymer layer thickens, along with a progressive decrease in the depth of the resonance minimum. Our modeling shows this unusual spectral behavior involving the resonance minimum is consistent with a Fe(vbpy)₃²⁺ chromophore absorption at 6328 Å, along with thickening of the polymer film. This work demonstrates that SPS is a viable in situ technique for obtaining thickness measurements of electrodeposited thin films.     

Effect of Dibenzo-18-crown-6 on the Polymer Electrolyte/Lithium Anode Interface

Photocured polymer electrolytes, applied onto a porous polypropylene separator, with conduction by lithium cations (1 × 10⁻⁴ S cm⁻¹ at 20°C) are designed. The polymer is formed from a 1 : 1 mixture of oligourethane dimethacrylate and polypropylene glycol monomethacrylate, which are capable of undergoing polymerization via double bonds in a liquid organic electrolyte (0.5 M LiClO₄) in a 1 : 1 mixture of propylene carbonate and dimethoxyethane. The polymer electrolyte comprises a polymer composition (20 wt %), a liquid electrolyte (78 wt %), and a photoinducer (2 wt %). Effect of insertion of dibenzo-18-crown-6 into the electrolyte on its electrochemical characteristics (on the electrolyte/Li interface) is investigated. Dependences of the bulk conductivity and exchange currents at the interface on the temperature and storage duration are studied at different crown ether contents.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 646–650.Original Russian Text Copyright © 2005 by Yarmolenko, Efimov.     

Is small particle size more important than carbon coating? An example study on LiFePO4 cathodes

Based on careful analysis of nine papers by different research groups, we show, for the first time, that in LiFePO₄-based cathode materials the electrode resistance depends solely on the mean particle size. The effect of carbon coating is marginal, it suffices that each LiFePO₄ particle is point-contacted with a reasonable number of carbon black particles usually added in the course of electrode preparation. We present a simple but general theoretical model that consistently explains this unexpected result. The main reason for the relatively small importance of carbon coatings is the fact that the ionic conductivity (ca. 10⁻¹¹–10⁻¹⁰ S cm⁻¹ at RT) is much smaller than the electronic (>10⁻⁹ S cm⁻¹ at RT). The present finding could be of significant importance not only for further optimization of LiFePO₄ cathodes, but also for preparation of other cathode materials in which the ionic conductivity is much lower than the electronic.     

A study by voltammetry and the photocurrent response method of copper electrode behavior in acidic and alkaline solutions containing chloride ions

The electrochemical behavior of Cu electrodes in Cl⁻ solutions was studied in a wide range of pH. The results were compared with those obtained in solutions containing F⁻, Br⁻, I⁻ and So²⁻₄ ions at pH 8.5, and discussed in terms of the competitive formation of Cu₂O and CuCl films on the Cu surface and the influence of CuCl on the properties of Cu₂O. At pH 8.5 or higher, Cu₂O was formed first, whereas at pH 5.7 or lower the Cu₂O film was formed on the Cu surface under the CuCl layer which was formed initially. It is believed that the Cu₂O films doped with Cl⁻ ions exhibited poor protective properties against Cu corrosion.     

C60 trianion-mediated electrocatalysis and amperometric sensing of hydrogen peroxide

Heterogeneous electrocatalytic reduction of hydrogen peroxide (H₂O₂) by C₆₀ is reported for the first time. C₆₀ is embedded in tetraoctylammonium bromide (TOAB) film and is characterized by scanning electron microscopy and cyclic voltammetry. Electrocatalytic studies show that the trianion of C₆₀ mediates the electrocatalytic reduction of H₂O₂ in aqueous solution containing 0.1 M KCl. Application of such film modified electrode as an amperometric sensor for H₂O₂ determination is also examined. The sensor shows a fast response within 1 s and a linear response is obtained (R = 0.9986) in the concentration range from 3.33 × 10⁻⁵ to 2.05 × 10⁻³ mol L⁻¹ for H₂O₂, with the detection limit of 2 × 10⁻⁵ mol L⁻¹ and the sensitivity of 1.65 μA mM⁻¹. A good repeatability and stability is shown for the sensor during the experiment.     

Preparation and electrical properties of new oxide ion conductors Ce6−xDyxMoO15−δ (0.0 ≤ x ≤ 1.8)

Ce_6−xDy_xMoO_15−δ (0.0 ≤ x ≤ 1.8) were synthesized by modified sol–gel method. Structural and electrical properties were investigated by means of X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The XRD patterns showed that the materials were single phase with a cubic fluorite structure. Impedance spectroscopy measurement in the temperature range between 350 °C and 800 °C indicated a sharp increase in conductivity for the system containing small amount of Dy₂O₃. The Ce_5.6Dy_0.4MoO_15−δ detected to be the best conducting phase with the highest conductivity (σ_t = 8.93 × 10⁻³ S cm⁻¹) is higher than that of Ce_5.6Sm_0.4MoO_15−δ (σ_t = 2.93 × 10⁻³ S cm⁻¹) at 800 °C, and the corresponding activation energy of Ce_5.6Dy_0.4MoO_15−δ (0.994 eV) is lower than that of Ce_5.6Sm_0.4MoO_15−δ (1.002 eV).     

The second order hyperpolarizability of cis azobenzene isomer

The second order hyperpolarizability of cis azobenzene isomer (γ_c) was obtained by measuring the third harmonic generation (THG) variation of an azobenzene doped polymer film when the film was optically pumped to create a large amount of cis isomers via photoisomerization. A steady state theory was developed to treat the THG intensity variation by considering the optical pump induced redistribution and reorientation of azobenzene in the polymer film and the contribution of cis isomer to the THG signal. The ratio of γ of cis and trans molecule, (γ_c/γ_t), was found to be 0.51. After the γ_t was obtained from the time-resolved optical Kerr effect (OKE) measurement, γ_c was deduced to be 5.6 × 10⁻³³ esu. The result shows that the optical nonlinearity of cis isomer is clearly not negligible.     

Solvation Phenomena of Potassium Thiocyanate in Methanol–Water Mixtures

This paper reports the results of a variety of experiments carried out for understanding the solvation behavior of potassium thiocyanate in methanol–water mixtures. Electrical conductivity, speed of sound, viscosity, and FT-Raman spectra of potassium thiocyanate solutions in 5 and 10% methanol–water (w/w) mixtures were measured as functions of concentration and temperature. The conductivity and structural relaxation time suggest the ion–solvent and solvent-separated ion–ion associations increase as the salt concentration increases in the mixtures. The Raman band shifts due to the C–O stretching mode of methanol for the solvent mixtures reveal the formation of methanol–water complexes. The significant changes in the Raman bands for the C–N, C–S and O–H stretching modes indicate the presence of SCN⁻−solvent interactions through the N-end, “free” SCN⁻ and the solvent-shared ion pairs as potassium thiocyanate is added to the methanol–water mixtures. The relative changes corresponding to H–O–H bending and C–O stretching frequencies indicate that K⁺ is preferentially solvated by water in these solvent mixtures. The appearance and increase of the intensity of a broad band at ≈940 cm⁻¹ upon salt addition was attributed to the SCN⁻–H₂O–K⁺ solvent-shared ion pairs. No Raman spectral evidence for K⁺(H₂O)_n species was observed. The preferential solvation of K⁺ and SCN⁻ in the methanol−water mixtures was verified by the application of the Kirkwood−Buff theory of solutions. This theory confirms that K⁺ is strongly preferentially solvated by water, whereas SCN⁻ is preferentially solvated by the methanol component.