Polyaniline-coated cellulose fibers decorated with silver nanoparticles

Cellulose fibers of 20 μm in diameter and aspect ratio of 2 or 10 were coated with protonated polyaniline (PANI) during the oxidation of aniline hydrochloride with ammonium peroxydisulfate in an aqueous medium. The presence of PANI has been proved by FTIR spectroscopy. The conductivity increased from 4.0 × 10⁻¹⁴ S cm⁻¹ to 0.41 S cm⁻¹ after coating the fibers with PANI. The percolation threshold in the mixture of original uncoated and PANI-coated fibers was reduced from 10 mass % PANI to 6 mass % PANI, as the aspect ratio changed from 2 to 10. The subsequent reaction with silver nitrate results in the decoration of PANI-coated cellulose fibers with silver nanoparticles of about 50 nm average size. The content of silver of up to 10.6 mass % was determined as a residue in thermogravimetric analysis. FTIR spectra suggest that the protonated emeraldine coating changed to the pernigraniline form during the latter process and, consequently, the conductivity of the composite was reduced to 4.1 × 10⁻⁴ S cm⁻¹, despite the presence of silver.     

Preparation of Proton Conductive Inorganic-Organic Hybrid Films Using Epoxycyclohexylethyltrimethoxysilane and Orthophosphoric Acid

Proton conductive inorganic-organic hybrid films, which show high proton conductivity at temperatures higher than 100°C with low humidification, have been prepared from epoxycyclohexylethyltrimethoxysilane (EHTMS), 3-glycidoxypropyltrimethoxysilane, and orthophosphoric acid by the sol-gel method. Self-supporting, flexible, and brownish transparent films with a thickness ranging from 150 to 300 μm were obtained. Differential thermal analyses and thermogravimetric measurements revealed that the films were stable up to about 200°C. Ionic conductivity of the films increased with an increase in the content of phosphoric acid in the films. The films with a molar ratio of P/Si = 1.75 retained a high conductivity of about 6 × 10^?4 S cm^?1 even after holding for 150 h under 0.7% relative humidity at 130°C. The conductivity of the films increased with an increase in the relative humidity and was about 1 × 10^?2 S cm^?1 under 20% relative humidity at 130°C.     

Lithium-ion conduction in elastomeric binder in Li-ion batteries

This paper describes two kinds of elastomeric binders which are styrene–butadiene (ST–BD) copolymer and 2-ethylhexyl acrylate–acrylonitrile (2EHA–AN) copolymer for electrode materials of rechargeable Li-ion batteries. These elastomeric binders were swollen by electrolyte solution (EC/DEC=1/2, 1 M LiPF₆), and 2EHA–AN copolymer retained larger amount of electrolyte solution than ST–BD copolymer. The Li-ionic conduction behavior was investigated for both copolymer films swollen by electrolyte solution. The Li-ion conductivity of ST–BD copolymer was 9.45 × 10⁻⁸ S·cm⁻¹ and that of 2EHA–AN copolymer was 1.25 × 10⁻⁵ S·cm⁻¹ at room temperature, and the corresponding amounts of activation energy were 0.31 and 0.26 eV, respectively. Because the observed activation energy in elastomeric binder was different from that in the bulk of electrolyte solution (0.09 eV), Li-ion conduction of the bulk of elastomeric binder swollen by electrolyte was affected by the polymer structure of binders. Electrochemical performance of cathode material, LiCoO₂, was investigated with three kinds of binders: ST–BD copolymer, 2EHA–AN copolymer, and poly(vinylidene fluoride). The initial charge–discharge capacity of the LiCoO₂ electrode with 2EHA–AN copolymer showed highest capacity, suggesting that Li⁺-ion conduction inside of the elastomeric binder contributes to the enhancement of charging and discharging capacity. This result indicates that elastomeric binder with sufficient Li-ionic conductivity can be an attractive candidate for improving cathode of lithium-ion battery.     

Conductivity of flowing polyaniline suspensions in electric field

The formation of chain structures by polarized polyaniline (PANI) particles suspended in silicone oil in the electric field has been monitored by recording suspension conductivity in the course of time. For that purpose, three types of PANI particles differing in the conductivity (3.1 × 10⁻³, 1.7 × 10⁻¹, and 2.0 × 10⁻¹ S cm⁻¹) have been chosen out of a series of nine samples prepared by controlled protonation of PANI base in orthophosphoric acid solutions. Relaxation times reflecting this process and characterizing the rate of the response to the electric field decreased with particle conductivity, indicating a higher polarizability of particles. At the same time, the maximum conductivity of suspension increased as a consequence of the electric and shear forces acting on the particles. In the shear fields, shorter relaxation times appeared than at rest. The simultaneous measurement of the shear stress confirmed that the conductivity investigation can reliably characterize the development of electrorheological structures.     

The kinetics of hydroxyl radical reactions with cyclopropane and cyclobutane

A laser flash photolysis/resonance fluorescence investigation has been carried out to study the kinetics of the overall reactions OH + cyclopropane (1) and OH + cyclobutane (2) in the temperature range 298–490 K and at 298 K, respectively. The following kinetic parameters have been determined: k₁ =(3.9 ±0.6) 10⁻¹²exp- (2.2 ± 0.1)kcal mol⁻¹/RT molecule⁻¹cm³s⁻¹, k₂(298 K) = (17.5 ± 1.5)10⁻¹³molecule⁻¹ cm³s⁻¹.     

Synthesis of proton conductive inorganic–organic hybrid membranes through copolymerization of dimethylethoxyvinylsilane with vinylphosphonic acid

Proton conductive inorganic–organic hybrid membranes were synthesized from dimethylethoxyvinylsilane (DMEVS), vinylphosphonic acid (VPA) and 3-glycidoxypropyltrimethoxysilane (GPTMS) through copolymerization followed by sol–gel process. The ratio of phosphorus to silicon in the copolymer almost corresponded to the charged molar ratio of VPA to DMEVS when the ratio of VPA to DMEVS was below 1/2. Self-standing, homogeneous, highly transparent membranes were synthesized from DMEVS–VPA copolymer and GPTMS via sol–gel condensation. Differential thermal analysis-thermogravimetry analyses indicated that these membranes were thermally stable up to 200 °C. The results of Fourier transform infrared and ¹³C NMR revealed that phosphonic acid groups of VPA were chemically bound to organosiloxane network. The copolymerization and condensation of (DMEVS–VPA)/GPTMS were confirmed by ³¹P and ²⁹Si NMR spectra. The proton conductivity of the hybrid membranes increased with phosphonic acid content. The membrane of (DMEVS–VPA)/GPTMS showed a remarkable conductivity of 6.3 × 10⁻² S cm⁻¹ at 130 °C and 100% relative humidity.     

Preparation and characterization of lithium ion conducting ionic liquid-based biodegradable corn starch polymer electrolytes

Thin films of biodegradable corn starch-based biopolymer electrolytes were prepared by solution casting technique. Lithium hexafluorophosphate (LiPF₆) and 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BmImTf) were employed as lithium salt and ionic liquid, respectively. With reference to the temperature dependence study, Arrhenius relationship was observed. The highest ionic conductivity of (6.00 ± 0.01) × 10⁻⁴ S cm⁻¹ was obtained at 80 °C. Based on x-ray diffraction (XRD) result, the peaks became broader with doping of ionic liquid revealing the higher amorphous region of the biopolymer electrolytes. Ionic liquid-based biopolymer electrolytes exhibited lower glass transition temperature (T _g).     

Measurement of the reaction rate constants of oxygen atoms with chlorine and iodomethane using a resonance fluorescence technique

The following reaction rate constants of oxygen atoms with iodomethane and chlorine were measured using resonance fluorescence under jet conditions at 298 K: k ₁ = (2.4 ± 0.5) × 10–15 and k ₂ = (6.9 ± 0.2) × 10⁻¹⁴ cm³/s, respectively.     

Lithium-conducting solid electrolytes of Li<Subscript>4</Subscript>GeO<Subscript>4</Subscript>-Li<Subscript>3</Subscript>PO<Subscript>4</Subscript> system with additions of zirconium ions

The effect of partial substitution of Zr⁴⁺ ions for Ge4+ ions in highly conducting lithium-cationic solid electrolyte Li_3.75Ge_0.75P_0.25O₄ is studied. It is found that the introduction of zirconium ions considerably raises the conductivity of basic electrolyte in the high-temperature range. For the optimal composition, the conductivity is 2.82 × 10⁻¹ S cm⁻¹ at 400°C and 1.55 S cm⁻¹ at 700°C. Possible reasons for the effects are discussed.     

Electrochemical preparation of poly(<Emphasis Type="Italic">p</Emphasis>-phenylene) thin films

We report the electrochemical preparation of poly(p-phenylene) (PPP) thin films with a polymerization degree of approximately 20 using biphenyl as starting material. The PPP films are prepared directly on a tin oxide electrode, presenting a positive charge carrier mobility of 5×10⁻⁷ cm² V⁻¹ s⁻¹.     

Investigation of the electrical resistance of single-walled carbon nanotube films in the temperature range 4.2–290 K

Electrical resistance of films made of the source material and purified HiPCO and Arc single-walled carbon nanotubes (SWCNTs) with a thickness of 20−40 μm is 2.4 to 45 Ω (electrical conductivity of 0.42 × 10³ to 5.03 × 10³ S/m) at room temperature. The films have been formed by vacuum microfiltration of SWCNT suspensions in toluene and characterized by Raman and X-ray photoelectron spectroscopy and scanning electron microscopy. The conductivity of the films at room temperature depends on the type and degree of purity of the material of nanotubes. The resistance of the films decreases with the increasing temperature over the range of 4.2–290 K, and the rate of the step-down decreases with increasing purity of the material of the nanotubes. The conductivity of the films is semiconducting in character, and the electron transport is consistent with three-dimensional hopping conductivity.     

Rubidium-conducting solid electrolytes in Rb2 ? 2xFe2 ? xVxO4 system

New solid rubidium-conducting electrolytes based on rubidium monoferrite in the system of Rb_{2 − 2x} Fe_2−x V _x O₄ are synthesized and studied. It is found that introduction of V⁵⁺ ions causes a drastic decrease in the electronic conductivity component prevalent in pure RbFeO₂ with a simultaneous increase in the ionic conductivity. The latter becomes predominant at an increase in the concentration of vanadium. The optimum compositions of the studied electrolytes feature a very high cationic rubidium conductivity (∼1.8 × 10⁻² S cm⁻¹ at 200°C, more than 10⁻¹ S cm⁻¹ at 700°C). The results are compared with the data obtained earlier for similar systems based on RbGaO₂ and RbAlO₂.     

Effect of chain aggregation on the conductivity and ESR spectra of polyaniline

Solutions of polyaniline in m-cresol with and without camphorsulfonic acid (CSA), as well as films cast from these solutions were studied by ESR spectroscopy at 133–423 K and by optical spectroscopy in the range λ = 350–1100 nm. An analysis of the optical and ESR spectra shows that in the solutions and films without CSA polyaniline is fully doped but the conductivity of these films is low (∼10⁻⁸ S cm⁻¹; cf. 100 S cm⁻¹ for the films with CSA). Compared with the CSA-containing samples, the samples without CSA are characterized by broader ESR lines and higher contribution of the Curie spins to the magnetic susceptibility. These facts indicate a weak aggregation of polyaniline chains without CSA, which leads to low conductivity. A formula was proposed, which describes the temperature dependence of the polyaniline ESR linewidth and allows the interchain distance and the mobility of electrons moving along polymer chains to be determined. The conductivity of polyaniline films is affected by moderate heating (363–388 K) of the films and solutions from which the films were cast. It was found that the interchain distances correlate with the conductivity of the films and with the broadening of their ESR lines caused by the effect of O₂. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2701–2711, December, 2005.     

The impedance of the Ag-CeF<Subscript>3</Subscript>/CeF<Subscript>3</Subscript> bicrystal-Ag system

The impedance spectra of CeF₃/CeF₃ bicrystal (two single crystals separated by a single intercrystalline boundary) between Ag-electrodes are studied over a 135 to 410 K temperature interval (including temperatures below room temperature). The bicrystal was prepared by thermal-diffusion welding under a pressure of 1.5 × 10⁷ Pa at 1473 K in vacuum (∼10⁻² Pa). It is shown that the intercrystalline boundary affects but insignificantly the bicrystal bulk impedance. The CeF₃/CeF₃ ionic conductivity is 3 × 10⁻⁶ S/cm at 293 K; it is mainly determined by transfer processes in the single crystal bulk.     

Enhanced electrochemical properties of polyethylene oxide-based composite solid polymer electrolytes with porous inorganic–organic hybrid polyphosphazene nanotubes as fillers

Solid composite polymer electrolytes consisting of polyethylene oxide (PEO), LiClO₄, and porous inorganic–organic hybrid poly (cyclotriphosphazene-co-4, 4′-sulfonyldiphenol) (PZS) nanotubes were prepared using the solvent casting method. Differential scanning calorimetry and scanning electron microscopy were used to determine the characteristics of the composite polymer electrolytes. The ionic conductivity, lithium ion transference number, and electrochemical stability window can be enhanced after the addition of PZS nanotubes. The electrochemical impedance showed that the conductivity was improved significantly. Maximum ionic conductivity values of 1.5 × 10⁻⁵ S cm⁻¹ at ambient temperature and 7.8 × 10⁻⁴ S cm⁻¹ at 80 °C were obtained with 10 wt.% content of PZS nanotubes, and the lithium ion transference number was 0.35. The good electrochemical properties of the solid-state composite polymer electrolytes suggested that the porous inorganic–organic hybrid polyphosphazene nanotubes had a promising use as fillers in SPEs and the PEO₁₀–LiClO₄–PZS nanotube solid composite polymer electrolyte might be used as a candidate material for lithium polymer batteries.     

Novel polymer electrolytes prepared by copolymerization of ionic liquid monomers

Ionic liquid monomer couples were prepared by the neutralization of 1‐vinylimidazole with vinylsulfonic acid or 3‐sulfopropyl acrylate. These ionic liquid monomer couples were viscous liquid at room temperature and showed low glass transition temperature (Tg) at ?83 °C and ?73 °C, respectively. These monomer couples were copolymerized to prepare ion conductive polymer matrix. Thus prepared ionic liquid copolymers had no carrier ions, and they showed very low ionic conductivity of below 10^?9 S cm^?1. Equimolar amount of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to imidazolium salt unit was then added to generate carrier ions in the ionic liquid copolymers. Poly(vinylimidazolium‐co‐vinylsulfonate) containing equimolar LiTFSI showed the ionic conductivity of 4 × 10^?8 S cm^?1 at 30 °C. Advanced copolymer, poly(vinylimidazolium‐co‐3‐sulfopropyl acrylate) which has flexible spacer between the anionic charge and polymer main chain, showed the ionic conductivity of about 10^?6 S cm^?1 at 30 °C, which is 100 times higher than that of copolymer without spacer. Even an excess amount of LiTFSI was added, the ionic conductivity of the copolymer kept this conductivity. This tendency is completely different from the typical polyether systems. Copyright © 2002 John Wiley & Sons, Ltd.     

Determination of the rate constants for the reaction Fe + O<Subscript>2</Subscript> = FeO + O in the forward and reverse directions

The results of our experimental studies and an analysis of the published data on the rate constant for the reaction Fe + O₂ = FeO + O in the forward (I) and reverse (−I) direction are reported. The data obtained in this work are described by the expressions k ₁ = 6.2 × 10¹⁴exp(−11100 K/T) cm³ mol⁻¹ s⁻¹ and k ₋₁ = 6.0 × 10¹³exp(−588 K/T) cm³ mol⁻¹ s⁻¹ (T = 1500–2500 K). The generalized expressions for the temperature dependences of these rate constants derived by combining our results with the literature data can be presented as k ₁ = 9.4 × 10¹⁴(T/1000)^0.022exp(−11224 K/T) cm³ mol⁻¹ s⁻¹ (T = 1500–2500 K) and k ₋₁ = 1.8 × 10¹⁴(1000/T)^0.37exp(−367 K/T) cm³ mol⁻¹ s⁻¹ (T = 200–2500 K).     

Novel composite polymer electrolytes based on poly(ether-urethane) network polymer and fumed silicas

Novel composite solid polymer electrolytes (CSPEs) and composite gel polymer electrolytes (CGPEs) have been prepared. CSPE consists of poly(ether-urethane) network polymer (PUN), fumed silicas and LiClO₄. The ionic conductivity of CSPEs can be enhanced nearly 20 times in comparison with the plain system without the addition of fumed silicas and can be above 1×10⁻⁵ S/cm at room temperature. The effects of both kinds of fumed silicas, viz. uSiO₂ with hydrophilic groups at the surface and mSiO₂ with hydrophobic groups at the surface on ionic conductivity were investigated. CGPE comprising of the CSPE and LiClO₄–PC solution with good mechanical strength exhibits ionic conductivity in the order of 10⁻³ S/cm at room temperature and above 3×10⁻⁴ S/cm at low temperature −40 °C.     

Spectroelectrochemistry of conducting polypyrrole and poly(pyrrole–cyclodextrin) prepared in aqueous and nonaqueous solvents

Conducting polypyrrole (PPy) and poly(pyrrole-2,6-dimethyl-β-cyclodextrin) [poly(Py-β-DMCD)] films were prepared by electrode potential cycling on a gold electrode in aqueous and nonaqueous (acetonitrile) electrolyte solutions containing lithium perchlorate. The resulting products were characterized with cyclic voltammetry, in situ UV–Vis spectroscopy, and in situ conductivity measurements. For the electrosynthesis of poly(Py-β-DMCD), a (1:1) (mole–mole) (Py-β-DMCD) supramolecular cyclodextrin complex of pyrrole previously characterized with proton NMR spectroscopy was used as starting material. A different cyclic voltammetric behavior was observed for pyrrole and the poly(Py-β-DMCD) complex in aqueous and nonaqueous solutions during electrosynthesis. The results show that in both solutions in the presence of cyclodextrin, the oxidation potential of pyrrole monomers increases. However, the difference of oxidation potentials for films prepared in aqueous solution is larger than for the films prepared in nonaqueous solution. In situ conductivity measurements of the films show that films prepared in acetonitrile solution are more conductive than those synthesized in aqueous solutions. Maximum conductivity can be observed for PPy and poly(Py-β-DMCD) films prepared in nonaqueous solution in the range of 0.10 < E _Ag/AgCl < 0.90 V and 0.30 < E _Ag/AgCl < 0.90 V, respectively. In situ UV–Vis spectroelectrochemical data for both films prepared potentiodynamically by cycling the potentials from −0.40 < E _Ag/AgCl < 0.90 V in nonaqueous solutions are reported. This paper is dedicated to Prof. Alan Bond on the occasion of his 65th birthday in recognition of his numerous contributions toward electrochemistry.     

FAD-modified SiO2/ZrO2/C ceramic electrode for electrocatalytic reduction of bromate and iodate

SiO₂/ZrO₂/C carbon ceramic material with composition (in wt%) SiO₂ = 50, ZrO₂ = 20, and C = 30 was prepared by the sol–gel-processing method. A high-resolution transmission electron microscopy image showed that ZrO₂ and the graphite particles are well dispersed inside the matrix. The electrical conductivity obtained for the pressed disks of the material was 18 S cm⁻¹, indicating that C particles are also well interconnected inside the solid. An electrode modified with flavin adenine dinucleotide (FAD) prepared by immersing the solid SiO₂/ZrO₂/C, molded as a pressed disk, inside a FAD solution (1.0 × 10⁻³ mol L⁻¹) was used to investigate the electrocatalytic reduction of bromate and iodate. The reduction of both ions occurred at a peak potential of −0.41 V vs. the saturated calomel reference electrode. The linear response range (lrr) and detection limit (dl) were: BrO₃ ⁻, lrr = 4.98 × 10⁻⁵–1.23 × 10⁻³ mol L⁻¹ and dl = 2.33 μmol L⁻¹; IO₃ ⁻, lrr = 4.98 × 10⁻⁵ up to 2.42 × 10⁻³ and dl = 1.46 μmol L⁻¹ for iodate.