Search

Chemically synthesized layered manganese dioxide (δ-MnO2) modified by poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) dispersion were used as cathode materials for aqueous Zn-ion batteries (AZIBs). A comparative study of electrochemical properties of cathodes with pristine MnO2and materials chemically modified by conducting polymers in different forms was performed with cycling voltammetry and galvanostatic charge-discharge curves in Zn2+-containing electrolyte solutions. The results of electrochemical tests indicate the significant improvement in specific capacity of electrodes in the sequence MnO2, MnO2/PEDOT and MnO2/PEDOT:PSS composites. The MnO2/PEDOT:PSS electrode delivered a specific discharge capacity of 278 mAh·g−1at a current density 0.3 A·g−1after 100 cycles, whereas for MnO2/PEDOT and MnO2electrodes the values were 238 and 121 mAh·g−1(capacity retention is 99%, 99.5% and 89%, respectively). These specific capacity values obtained for manganese dioxide-based cathodes are demonstrating the positive role of intrinsically conducting polymer, especially in case of surface modification of electroactive particles by PEDOT:PSS dispersion.

A new composite anode material of Ag and polymeric carbon was prepared by heat‐treating the mixture of polyacrylonitrile and AgNO3. They were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), electrochemical impedance spectroscopy (EIS) and electrochemical measurements. It was found that the addition of Ag was favorable for the improvement of electrochemical performance of the composite in comparison with the virginal polymeric carbon. These improvements were due to an increase of electronic conductivity, alloying of lithium with Ag and smaller particle size of the composites. The optimal amount of Ag addition is 5% based on the molar ratio of the monomer unit. Copyright © 2006 John Wiley & Sons, Ltd.

Abstract: Reduction potentials for the first electron transfer to a broad selection of nitrogen containing bi- and polydentate molecules considered as potential ligands have been determined. Results are compared with data obtained with semiempirical and UV-Vis spectroscopic data. Close correlations for the investigated molecules are observed. Systematic differences in properties of molecules with and without the keto moiety can be explained by invoking molecular orbital and surface interaction arguments. Similar structural arguments can be used to explain the behaviour of 2,4,6-tripyridin-2–yl[1,3,5]triazine. UV-Vis data match closely those derived from HOMO-LUMO calculations for these molecules.

A new inverse emulsion protocol has been developed for the synthesis of polyaniline (PANI), which can be dissolved completely in common organic solvents such as chloroform. Benzoyl peroxide is used as the oxidizing agent and toluene + 2-propanol−water is used as the solvent. Dodecylbenzenesulfonic acid (DBSA) has been selected as the dopant because it also functions as the surfactant. Cyclic voltammetry and spectroelectrochemical investigations were carried out to study the electroactivity, UV−Vis response, and metal-to-insulator transition of the chemically synthesized PANI as a function of applied electrode potential. At more positive potentials, cyclic voltammograms of PANI in aqueous acids show two oxidation waves caused by redox processes of PANI as observed with electrochemically prepared PANI. Peak position and shape are influenced by the slow anion exchange rate. Electrical conductivity of the material is relatively high as the minimum resistance value is nearly 10 Ω. SEM investigations show that the amount of DBSA in the feed strongly influences the morphology of the polymer. In situ UV−Vis spectroscopy measurements reveal good electrochromic reversibility for the polymer very similar to the response of PANI synthesized electrochemically.

Abstract Three kinds of silicon-containing disordered carbons have been prepared by pyrolysis of polysiloxanes with different amounts of phenyl side groups. X-ray powder diffraction, X-ray photoelectron spectroscopy and electrochemical capacity measurements were performed to study their behaviors. Graphite crystallites, micropores, and silicon species affect their electrochemical performances. All of them present high reversible capacities, >372 mAh/g. Since the graphite crystallites are very small, they contribute very little to reversible capacity. The number of micropores produced by gas emission during the heat-treatment process decides whether they exhibit reversible capacity. Si mainly exists in the form C–Si–O and influences the irreversible capacity. There is no evident capacity fading in the first ten cycles, indicating promising properties for these disordered carbons.

Electrochemical reduction potentials of a broad selection of nitrogen-containing molecules suitable as bridging dipodal and tripodal ligands in coordination and organometallic chemistry are reported and compared with results of semiempirical calculations. Trends of electrode potentials observed experimentally agree with respective calculated data, deviations can be explained by invoking peculiarities of the involved molecular orbitals and ligand–electrode surface interactions.

Improving the preparation technology and electrochemical performance of cathode materials for lithium ion batteries is a current major focus of research and development in the areas of materials, power sources and chemistry. Sol-gel methods are promising candidates to prepare cathode materials owing to their evident advantages over traditional methods. In this paper, the latest progress on the preparation of cathode materials such as lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, vanadium oxides and other compounds by sol-gel methods is reviewed, and further directions are pointed out. The prepared products provide better electrochemical performance, including reversible capacity, cycling behavior and rate capability in comparison with those from traditional solid-state reactions. The main reasons are due to the following several factors: homogeneous mixing at the atomic or molecular level, lower synthesis temperature, shorter heating time, better crystallinity, uniform particle distribution and smaller particle size at the nanometer level. As a result, the structural stability of the cathode materials and lithium intercalation and deintercalation behavior are much improved. These methods can also be used to prepare novel types of cathode materials such as nanowires of LiCoO 2 and nanotubes of V 2O 5, which cannot be easily obtained by traditional methods. With further development and application of sol-gel methods, better and new cathode materials will become available and the advance of lithium ion batteries will be greatly promoted.

Modification of natural graphite for anode materials has been a recent focus of research and development. Here we report that a common natural graphite, whose electrochemical performance is very poor, can be modified by solutions of (NH 4) 2S 2O 8, concentrated nitric acid solution, or green chemical solutions such as aqueous solutions of hydrogen peroxide and ceric sulfate. All treatments result in marked improvement of the electrochemical performance, including reversible capacity, coulombic efficiency in the first cycle, and cycling behavior. The main reason is the effective removal of active defects in natural graphite, formation of a new dense surface film consisting of oxides, improvement of the graphite stability, and introduction of more nanochannels/micropores. As a result, these changes inhibit the decomposition of electrolytes, prevent the movement of graphene planes along the a-axis direction, and provide more passages and storage sites for lithium. They are mild and the uniformity of the product can be well controlled. Pilot experiments show economic promise for their application in industry to manufacture anode materials for lithium ion batteries.

Graphitic anode materials for lithium ion batteries processed under high humidity conditions show severe performance losses. The sensitivity of these materials towards humidity can be significantly reduced by adsorbing metal ions like silver or copper ions, with subsequent heat treatment of these composites. Results of X-ray photoelectron spectroscopy, high-resolution electron microscopy, thermogravimetry, and differential thermal analysis indicate that the deposited metals exist in metallic and carbide, M xC (M=Cu or Ag), forms. They remove or cover (i.e. deactivate) active hydrophilic sites at the surface of the graphite. These composites absorb less water during processing. The electrochemical performance, including reversible capacity, coulombic efficiency in the first cycle, and cycling behavior, is markedly improved. This approach provides a potentially powerful method to manufacture lithium ion batteries under less demanding conditions.

In situnear-infrared (NIR) spectroelectrochemical studies during growth and dedoping/redoping of polyaniline (PANI) in the range between 1200 to 3000 nm are carried out in 1 M aqueous solutions of HCl, H2SO4, and HClO4acids andp-toluene sulfonic acid (PTSA). The results show three characteristic absorption bands around 1440, 1900, and 2500 nm. The band at 2500 nm is characteristic of mobile charge carriers. The PANI prepared in HClO4keeps memory of the size of the doping anion (ClO4–) and can be redoped only with the same or smaller anions (Cl–and SO42–or HSO4–) while it cannot be redoped to any significant extent by a larger anion (PTSA–).

Mild oxidation of a natural graphite in an ammonium peroxydisulfate solution yields promising anode materials. X-ray photoelectron spectroscopy, FTIR spectroscopy, electron paramagnetic resonance, thermogravimmetry, differential thermal analysis, high resolution electron microscopy and surface area measurements provided results suggesting that oxidation eliminates some reactive structural defects in this graphite. In addition, the surface of natural graphite is recoated with a dense layer of oxides forming an effective passivating film to prevent the decomposition of electrolyte and the movement of graphene molecules along its a-axis. Consequently, its thermostability and the EPR signal increase. In addition, the numbers of nanosized pores and channels increases, which provide more inlets and outlets for lithium intercalation and deintercalation and more sites for lithium storage. As a result, the reversible lithium capacity and the coulombic efficiency in the first cycle increase significantly and the cycling behaviour improves markedly. The reproducibility of product properties can be well controlled, and this method is promising for industry.

Hydrogen permeation and corrosion inhibition characteristics of isomers of phenylenediamine, toluidine, and nitroaniline were studied on mild steel in 1M HCl. The Tafel extrapolation method was used to determine the inhibition efficiency, while the Devanathan–Stachurski technique was used to determine the hydrogen permeation rate. The adsorption of these compounds on mild steel from 1M HCl obeys Langmuir's adsorption isotherm for toluidine and nitroaniline and Temkin's adsorption isotherm for phenylenediamine. Inhibition efficiency was found to be more for isomers of phenylenediamine followed by those of nitroaniline and toluidine. All the isomers of these three organic compounds inhibit the corrosion of and hydrogen permeation through mild steel in HCl in the order ortho > meta > para for phenylenediamine and nitroaniline and meta > ortho > para for toluidine.

The mode of interaction with and the mechanism of the dioxygen reduction reaction at six transition metal α,β,γ,δ-tetra(4-pyridyl)porphyrins (MeTPyPs) deposited on carbon and silver supporting electrodes were investigated with cyclic voltammetry, FTIR and UV-vis spectroscopy and resonance Raman spectroscopy. Results indicate a strong influence of both the ligand and the central metal ion upon the reduction electrocatalysis in terms of electrode overpotentials. Spectroelectrochemical results support a two-electron pathway resulting in hydrogen peroxide as the primary reduction product. A significant influence of the central ion on the vibrational behaviour and the dioxygen reduction mechanism was not found.

The mode of interaction with and the mechanism of the dioxygen reduction reaction at six transition metal α,β,γ,δ-tetra(4-pyridyl)porphyrins (MeTPyPs) deposited on carbon and silver supporting electrodes were investigated with cyclic voltammetry, FTIR and UV-vis spectroscopy and resonance Raman spectroscopy. Results indicate a strong influence of both the ligand and the central metal ion upon the reduction electrocatalysis in terms of electrode overpotentials. Spectroelectrochemical results support a two-electron pathway resulting in hydrogen peroxide as the primary reduction product. A significant influence of the central ion on the vibrational behaviour and the dioxygen reduction mechanism was not found. Copyright © 1999 John Wiley & Sons, Ltd.

The electrooxidation of a series of vicinal and terminal aliphatic diols ranging from ethanediol to hexanediol including an unsaturated diol at a polycrystalline gold electrode in contact with an alkaline electrolyte solution has been studied. Significant differences found in the oxidation activity are rationalized based on the molecular structure and the different electrosorption behaviour as deduced from additional adsorption measurements.

An alternative concept of an integrated water electrolysis/hydrogen-hydrogen fuel cell using metal electrocatalysts and a solid polymer electrolyte is described. Instead of operating both electrodes as hydrogen and oxygen electrodes respectively the electrodes are used as oxidation and reduction electrodes in both modes of operation. A more suitable selection of electrocatalysts and an improved cell design are possible; both can increase the efficiency of the cell considerably. New results on the electrocatalytic activity of various noble-metal containing catalysts with respect to both oxygen evolution and hydrogen oxidation in a proton exchange membrane-cell at 80°C are reported. Kinetic data derived from Tafel plots of the oxygen evolution polarization curves agree closely with those of experiments with aqueous sulphuric acid electrodes. This agreement allows the determination of kinetic parameters for electrocatalysts difficult to prepare in solid smooth electrodes but easy to be made into porous deposits. Polarization curves of the hydrogen oxidation reaction clearly indicate a relative activity rating of the studied catalysts. In cycling tests the lifetime stability of the new bifunctional oxidation electrode was determined. Polarization data obtained under these conditions agree with those obtained in earlier experiments where electrodes were exposed to only one type of oxidation reaction. During a test of 10 cycles (30 min of electrolyser and 30 min of fuel cell mode each) no changes in the electrode potential were observed. With the conventional cell design employing a hydrogen and an oxygen electrode both catalyzed with platinum and a current density of 100 mA cm-2 a storage efficiency of 50% was calculated; with the alternative concept of oxidation and reduction electrodes and selected oxidation catalysts this was improved to 57%. With further improvements these efficiencies seem possible even at current densities of 500 mA cm-2.

The electrochemical corrosion behaviour of sixteen currently marketed amalgams for dental fillings was studiedin vitro under experimental conditions closely resembling those of clinical application. Depending upon the type of amalgam and the treatment of the filling the electrochemical corrosion currents varied over several orders of magnitude; their change as a function of time was also very different. Suggestions are made for a stability rating of the products based on the results obtained.

A survey of representative studies on the oxidation of mono- and polyhydric alcohols on gold and platinum electrodes is given, with a special attention to the reaction mechanisms and the effect of the molecular structure of these compounds on their electrocatalytic reactivity.

The mechanism of the dioxygen interaction with and reduction reaction at iron α,β,γ,δ-tetra(4-pyridyl) porphyrin (FeTPyP)deposited on carbon and silver supporting electrodes was investigated with cyclic voltammetry and FTIR, UV-vis and resonance Raman spectroscopies. Results indicate a strong influence of the ligand upon the reduction electrocatalysis. Spectroelectrochemical results support a two-electron pathway resulting most probably in hydrogen peroxide as the primary reduction product.

The mechanism of the dioxygen interaction with and reduction reaction at iron α,β,γ,δ-tetra(4-pyridyl) porphyrin (FeTPyP) deposited on carbon and silver supporting electrodes was investigated with cyclic voltammetry and FTIR, UV-vis and resonance Raman spectroscopies. Results indicate a strong influence of the ligand upon the reduction electrocatalysis. Spectroelectrochemical results support a two-electron pathway resulting most probably in hydrogen peroxide as the primary reduction product. © 1998 John Wiley & Sons, Ltd.