Kinetics of decomposition of the solid electrolyte RbCu4Cl3I2

The processes of electrochemical decomposition of the solid electrolyte RbCu₄Cl₃I₂ at the vitreous carbon electrode and chemical decomposition of RbCu₄Cl₃I₂ by iodine has been investigated. The anodic decomposition of the electrolyte occurs in two steps. At first, the oxidizing electrode reaction of Cu⁺ ions up to Cu²⁺ ions takes place at potentials higher than 0.57 V and onto the electrode surface the layer of decomposition products is formed, including the compound of divalent copper RbCuCl₃. Then the oxidizing reaction of I ions occurs at potentials higher than approximately 0.67 V with deposition of the iodine layer onto the electrode surface. The deposition rate of the layers of decomposition products is controlled by instantaneous nucleation and two-dimensional growth of the deposit. It was shown that slow diffusion of the iodine in the reaction product layer is a limiting step in the chemical interaction of iodine with RbCu₄Cl₃I₂. For the compressed RbCu₄Cl₃I₂ sample investigated, iodine diffusion coefficient was calculated to be 6.2×10⁻⁷ cm² s⁻¹. Iodine loss from the glassy carbon surface is about 1.1×10⁻⁴ g cm⁻² s⁻¹ at the thickness of the RbCu₄Cl₃I₂ sample is equal to 2 mm.     

Caffeine as non-toxic corrosion inhibitor for copper in aqueous solutions of potassium nitrate

Different electrochemical methods were employed in order to confirm the ability of caffeine (1,3,7-trimethylxanthine) to inhibit the corrosion processes of copper in aqueous potassium nitrate solutions in the absence and in the presence of chloride. Some experiments were repeated in potassium perchlorate in order to compare the influence of the medium. The interaction between the organic compound and the electrode surface occurs independently of the electrode potential. However, maximum interaction was observed at 0.0 V (Ag/AgCl) in aerated solutions, and at −0.25 V (Ag/AgCl) in deaerated solutions.The presence of the organic compound adsorbed on the electrode surface was confirmed by comparing the voltammograms of copper electrode in the absence and presence of 1.5 mmol L⁻¹ of dissolved caffeine. The same results were observed by comparing polarization curves in the absence and in the presence of caffeine.Anodic currents decrease noticeably in the presence of the organic compound. Chronoamperometric experiments were conclusive to prove the inhibitor capability of caffeine to decrease the corrosion dissolution processes of copper under anodic polarization.     

Electrochemical synthesis of Ag nanoparticles supported on glassy carbon electrode by means of p-isopropyl calix[6]arene matrix and its application for electrocatalytic reduction of H2O2

The silver nanoparticles were prepared on the glassy carbon (GC) electrode, modified with p-iso propyl calix[6]arene, by preconcentration of silver ions in open circuit potential and followed by electrochemical reduction of silver ions. The stepwise fabrication process of Ag nanoparticles was characterized by scanning electron microscopy and electrochemical impedance spectroscopy. The prepared Ag nanoparticles were deposited with an average size of 70 nm and a homogeneous distribution on the surface of electrode. The observed results indicated that the presence of calixarene layer on the electrode surface can control the particle size and prevent the agglomeratione and electrochemical deposition is a promising technique for preparation of nanoparticles due to its easy-to-use procedure and low cost of implementation. Cyclic voltammetry experiments showed that Ag nanoparticles had a good catalytic ability for the reduction of hydrogen peroxide (H₂O₂). The effects of p-isopropyl calix[6]arene concentration, applied potential for reduction of Ag⁺, number of calixarene layers and pH value on the electrocatalytic ability of Ag nanoparticles were investigated. The present modified electrode exhibited a linear range from 5.0 × 10⁻⁵ to 6.5 × 10⁻³ M and a detection limit 2.7 × 10⁻⁵ M of H₂O₂ (S/N = 3) using amperometric method.     

Glassy carbon - A promising substrate material for pulsed laser deposition of thin Li1+xMn2O4−δ electrodes

The spinel LiMn₂O₄ is a promising candidate for future battery applications. If used as a positive electrode in a battery, the charging capacity of such a battery element is limited by the formation of a solid electrolyte interphase like layer between the electrolyte and the spinel. To study the electrolyte-electrode interaction during electrochemical cycling, spinel thin films are deposited as model electrodes on glassy carbon substrates by pulsed laser ablation. The obtained polycrystalline oxide thin films show a well defined surface morphology and are electrochemical active. Adhesion of these thin films on glassy carbon is in general poor, but can be improved considerably by a surface pretreatment or adding a thin metallic coating to the substrate prior deposition. The best adhesion is obtained for films deposited on argon plasma pretreated as well as Pt coated glassy carbon substrates. During the electrochemical characterization of Li_1.06Mn₂O_3.8 thin film electrodes, no additional reactions of the substrate are observed independent of the used electrolyte. The best cycle stability is achieved for films on Pt coated glassy carbon substrates.     

Selective determination of catecholamine in the presence of ascorbic acid or uric acid on the membrane of silver nanoparticles/poly l-phenylalanine

The silver ions and l-phenylalanine were co-deposited and formed a hybrid membrane on the surface of glassy carbon electrode by cyclic voltammetry. The membrane had good properties for catalyzing the redox of catecholamine neurotransmitters, including epinephrine (EP), norepinephrine (NE), and dopamine (DA). The electrochemical behaviors of these neurotransmitters were studied on this modified electrode. and therefore, an assay for each of them is set up and the detection limits for EP, NE, and DA are 7.2?×?10^?9, 6.4?×?10^?9, and 8.5?×?10^?9 mol L^?1, respectively. The proposed method can effectively eliminate the interference of the ascorbic acid and uric acid. The conditions which influenced the analyses were optimized. Using this method to determine the content of EP, NE, and DA in injections, the results were satisfactory.     

in situ FTIR Spectroscopic Characterization of Absorbed Species on Carbon Electrode,Part II: TCNE Anion Radical from Acetonitrile Solution

The reduction of tetracyanoethylene (TCNE) to its anion radicals on glassy carbon has been studied using in situ FTIR spectroscopy. In contrast to its adsorption behavior on a platinum electrode, TCNE was found to adsorb on a carbon surface not only as the dianion but also as the tricyanovinyl alcoholate (TVA) ion. A mechanism for the formation of the TVA ion involving the presence of surface functional groups on the carbon electrode is proposed.     

Surface modification of indium tin oxide films by amino ion implantation for the attachment of multi-wall carbon nanotubes

Amino ion implantation was carried out at the energy of 80 keV with fluence of 5 × 10¹⁵ ions cm⁻² for indium tin oxide film (ITO) coated glass, and the existence of amino group on the ITO surface was verified by X-ray photoelectron spectroscopy analysis and Fourier transform infrared spectra. Scanning electron microscopy images show that multi-wall carbon nanotubes (MWCNTs) directly attached to the amino ion implanted ITO (NH₂/ITO) surface homogeneously and stably. The resulting MWCNTs-attached NH₂/ITO (MWCNTs/NH₂/ITO) substrate can be used as electrode material. Cyclic voltammetry results indicate that the MWCNTs/NH₂/ITO electrode shows excellent electrochemical properties and obvious electrocatalytic activity towards uric acid, thus this material is expected to have potential in electrochemical analysis and biosensors.     

Electrochemical study and electrodeposition of copper in the hydrophobic tri-n-octylmethylammonium chloride ionic liquid media

The electrodeposition of metallic Copper in binary mixture ionic liquid/organic solvent (tri-n-octylmethylammonium chloride (TOMAC))/chloroform (CHCl₃) was investigated. The electrochemical behavior of Cu(II) in TOMAC/CHCl₃ at glassy carbon working electrode at room temperature was studied by cyclic voltammetry and spectroscopy impedance. The results from the cyclic voltammetry showed that the electrodeposition of metallic Cu in the binary mixture ionic liquid/organic solvent was an irreversible process and was controlled by the diffusion of Cu(II) on a glassy carbon working electrode. The average value of αn_α was found to be 0.23 at 25 °C and the diffusion coefficient (D₀) of Cu(II) was calculated to be 7.12 10^− 9 cm²/s at room temperature. The performance of TOMAC ionic liquid such as internal resistance has been investigated with electrochemical impedance spectroscopy (EIS). The scanning electron microscopy (SEM) micrographs was used to observe that the copper plating was moderately dense and contains fine crystallites with average sizes of about 1 μm at room temperature. Energy dispersive X-ray analysis (EDAX) profile showed that the obtained film was copper.     

Orientation of sp2 carbon nanoclusters in ion‐implanted polymethylmethacrylate as revealed by polarized Raman spectroscopy

Raman spectroscopy is widely used for the characterization of bonding type in carbon‐based materials, including carbonized surface layer in ion‐implanted polymers. Studies of the polarization properties of Raman scattering from amorphous carbonaceous materials, however, are very scarce. In this paper, we investigate the polarized Raman spectra of polymethylmethacrylate (PMMA) implanted with 50‐keV Si⁺ ions at fluences in the range 3.2 × 10¹⁴–1.0 × 10¹⁷ ions/cm² and for different visible excitation wavelengths. The spectra of the implanted samples are dominated by the D‐ and G‐bands of sp² carbon, which evidence strong carbonization of the ion‐modified layer. The multiwavelength excitation allowed us to resonantly probe the depolarization ratios for sp² clusters of different sizes. We established that the depolarization ratio ρ_G of the G‐band correlates with the sp² cluster size approaching the random orientation limit of 0.75 for the smallest clusters and a limiting value of 0.41 for the largest clusters. The experimental findings give evidence for a preferable orientation of the larger size clusters with their hexagonal planes perpendicular to the surface of the sample. A plausible explanation for such an arrangement is that the sp² clusters form tile‐like arrangements along the ion tracks. This finding may give clues for understanding of the strong transconductance of the ion‐modified layer, and open prospects for the application of polarized Raman spectroscopy as a characterization tool for surface morphology in ion‐implanted materials. Copyright © 2010 John Wiley & Sons, Ltd.     

Electrochemical luminescence of n-type ZnO semiconductor electrodes doped with rare earth metals under the anodic polarization

Electrochemical luminescence (ECL) at n-type ZnO semiconductor electrode was measured under anodic polarization. Scanning the potential imposed on the ZnO electrode, emission was suddenly observed around +20 V. Using the ZnO electrodes doped with rare earth metal ions as Sm³⁺, Eu³⁺, Dy³⁺, Ho³⁺ and Er³⁺, much brighter emission was obtained than the ECL of non-doped ZnO. These emission spectra are ascribed to the rare earth metal ions, respectively. This result would show that emission centers of doped ions were selectively excited by electrons that were injected from electrolyte to the electrode by avalanche breakdown under strong anodic bias on the ZnO.     

Electrocatalytic properties of glassy carbon electrodes modified with hydroxy derivatives of 9,10-anthraquinone for oxygen reduction reaction

The electrochemical and electrocatalytic behavior of glassy carbon electrodes modified by one mono and four dihydroxy derivatives of anthra-9,10-quinone compounds have been investigated by cyclic voltammetric technique. The stability of the modified electrodes was ascertained in acidic and neutral media. The surface morphology of modified electrode was characterized by scanning electron microscope. The influence of pH on the electrochemical and electrocatalytic behavior was studied and pH?6.0 or 7.0 was chosen as the optimum working pH by comparing the shift in oxygen reduction potential. The anthraquinone-adsorbed glassy carbon electrodes possess excellent electrocatalytic ability for oxygen reduction with overpotential ranging from 388 to 547?mV lower than that at a plain glassy carbon electrode. Hydrodynamic volatammetric studies were performed to determine the heterogeneous rate constants for the reduction of O₂ at the surface of the modified electrodes, mass specific activity of the anthraquinones used, and the apparent diffusion coefficient of O₂ in buffered aqueous O₂-saturated solutions.     

Influence of the surface electric field in ion-beam-surface interaction at grazing incidence

We have measured the polarization of light emitted after ion surface scattering at small angle of incidence. The measurements are carried out with H⁺-, H ₂ ⁺ - and He⁺-ions under UHV-conditions with mono- and polycrystalline targets. We explain the typical variation of the polarization as “post collision Stark interaction” (PCSI) in the surface electric field, which can force transitions between nearly degenerate terms. The electric field is composed of two different contributions, a strong but short range surface field which is “seen” by atomsand ions and a long range but weak field due to the image charge which is “seen” to first orderonly by ions. The influence of the electric field on H-Balmer radiation is negligible at typical survival distances r_s≧0.35nm. But in contrast to H-atoms He⁺-ions feel the additional influence of the image field leading to a strong alteration of the polarization of the emitted light. The polarization of the Balmer-radiation stemming from Coulomb exploding H ₂ ⁺ -beams is observed to be modified by the electric field of the “spectator proton”.     

Effect of annealing temperature on optical and electrochemical properties of chitosan–ZnO nanostructure

Chitosan–ZnO nanostructures were prepared by chemical precipitation method using different concentration of zinc chloride and sodium hydroxide solutions. Nanorod-shaped grains with hexagonal structure for samples annealed at 300 °C and porous structure with amorphous morphology for samples annealed at 600 °C were revealed in SEM analysis. X-ray diffraction patterns confirmed the hexagonal phase ZnO with crystallite size found to be in the range of ~24.15–34.83 nm. Blue shift of UV–Vis absorption shows formation of nanocrystals/nanorods of ZnO with marginal increase in band gap. Photoluminescence spectra show that blue–green emission band at 380–580 nm. The chitosan–ZnO nanostructures used on surface of a glassy carbon electrode gives the oxidation peak potential at ~0.6 V. The electrical conductivity of chitosan–ZnO composites were observed at 2.1?×?10^?5 to 2.85?×?10^?5?S/m. The nanorods with high surface area and nontoxicity nature of chitosan–ZnO nanostructures observed in samples annealed at 300 °C were suitable as a potential material for biosensing.     

Study by XPS of the chlorination of proteins aggregated onto tin dioxide during electrochemical production of hypochlorous acid

In solution, hypochlorous acid (HOCl) reacts with organic matter and notably with protein side-chains. In this study, HOCl was produced by an electrochemical way, by oxidation of chloride ions at a transparent tin dioxide electrode in the presence of a protein, the bovine serum albumin (BSA). A thick irregular layer is formed at the electrode when HOCl is produced at the SnO₂ surface. Indeed, SEM analyses show that an important deposit is formed during the anodic polarization of SnO₂ in the presence of chloride ions and proteins. Actually, two phenomena take place on the one hand the chlorination of the proteins due to the reaction of HOCl with some protein side-chains and on the other hand the aggregation of proteins onto the SnO₂ surface. The present X-ray photoelectron spectroscopy study points out the cross-linking of BSA molecules via formation of inter molecular sulfonamide groups. It also shows that the BSA chlorination is due on the one hand to the formation of sulfonyl chloride groups (-SO₂Cl) and on the other hand to formation of chloramine groups (N-Cl). The Cl2p and S2p photo-peak intensities allowed us to quantify the chloramines. It is found that, one BSA entity immobilized onto the SnO₂ surface contains about 50 chloramine groups.     

CO_2活化温度对N-C复合碳气凝胶结构及电化学性能的影响

采用CO2活化工艺对氮掺杂碳气凝胶(N-CA)的结构进行重整,并系统研究了活化温度对活化氮掺杂碳气凝胶(N-ACA)孔结构及电化学性能的影响。利用N2吸附数据、X-光电子能谱(XPS)和元素分析对样品的结构及元素组成进行表征。结果表明,随活化温度的升高,N-ACA的比表面积逐渐增大,其含有的氮原子分数逐渐减少,吡咯氮含量明显增加。利用循环伏安(CV)、电化学阻抗谱(EIS)等测试技术评价了碳气凝胶样品在6mol·L-1 KOH电解液中的电化学性能,结果发现,合理的孔结构与较高的吡咯氮含量是影响电容器比容量的关键因素。在5mV·s-1扫描速率下测试950-N-ACA电极的比电容值高达267.4F·g-1,经1000次充放电后比电容损失值在1.5%以内。     

Carbon–ionic liquid double-layer capacitors

A series of electrochemical capacitors, based on activated carbon powders (ACP, specific surface area 870 and 2600 m²/g) and ionic liquids as electrolytes, were prepared and tested. The ionic liquids consisted of 1-ethyl-3-methyl imidazolium (EMIm⁺), 1-butyl-3-methyl imidazolium (BMIm⁺) and 1-methyl-1-propyl pyrrolidinium (BMPy⁺) cations, as well as of tetrafluoroborate, hexafluorophosphate and bis((trifluoromethyl)sulfonyl) imide anions. A typical capacitor consisted of two electrodes each with a mass of ca. 15–30 mg, and showed a capacity of ca. 0.35–1.5 F; this leads to a specific capacity of the carbon electrode material within the range of 45 (ACP 870 m²/g)–180 F/g (ACP 2600 m²/g). The specific capacity expressed versus total surface of carbon material was within the range of 5.2–6.9 μF/cm². The electrochemical stability window of ionic liquids determined at the glassy carbon electrode is within the range of ca. 3.0–4.2 V. The energy stored in a capacitor based on activated carbons and ionic liquids may be high, due to a broad practical electrochemical stability window of ca. 3 V. Ionic liquids are characterised by negligible vapour pressure; such a capacitor emits no volatile organic compounds and may be regarded as environmentally friendly.     

Glassy carbon layer formed in diamond-like carbon films with femtosecond laser pulses

We report the first observation, to our knowledge, of a glassy carbon (GC) layer modified from diamond-like carbon (DLC) films with femtosecond (fs) laser pulses. The GC layer, which is confirmed by Raman spectroscopy, is produced most efficiently at low laser fluence near the ablation threshold of the DLC films. This surface modification depends little on the laser polarization and wavelength used. The fs laser-induced GC layer should be a new thin-film material useful for a variety of engineering applications due to its characteristics similar to those of DLC and the additional properties inherent in GC. PACS 61.80.Ba; 79.20.Ds; 42.62.Cf     

Hollow Silica Spheres Embedded in a Porous Carbon Matrix and Its Superior Performance as the Anode for Lithium‐Ion Batteries

Silica (SiO₂) is regarded as one of the most promising anode materials for lithium‐ion batteries due to the high theoretical specific capacity and extremely low cost. However, the low intrinsic electrical conductivity and the big volume change during charge/discharge cycles result in a poor electrochemical performance. Here, hollow silica spheres embedded in porous carbon (HSS–C) composites are synthesized and investigated as an anode material for lithium‐ion batteries. The HSS–C composites demonstrate a high specific capacity of about 910 mA h g^?1 at a rate of 200 mA g^?1 after 150 cycles and exhibit good rate capability. The porous carbon with a large surface area and void space filled both inside and outside of the hollow silica spheres acts as an excellent conductive layer to enhance the overall conductivity of the electrode, shortens the diffusion path length for the transport of lithium ions, and also buffers the volume change accompanied with lithium‐ion insertion/extraction processes.     

Fluorescence and Electrochemical Sensing of Pesticides Methomyl, Aldicarb and Prometryne by the Luminescent Europium-3-Carboxycoumarin Probe

This work describes the application of time resolved fluorescence in microtiterplates and electrochemical methods on glassy carbon electrode for investigating the interactions of europium-3-carboxycoumarin with pesticides aldicarb, methomyl and prometryne. Stern-volmer studies at different temperatures indicate that static quenching dominates for methomyl, aldicarb and prometryne. By using Lineweaver-Burk equation binding constants were determined at 303 K, 308 K and 313 K. A thermodynamic analysis showed that the reaction is spontaneous with ΔG being negative. The enthalpy ΔH and the entropy ΔS of reactions were all determined. A time-resolved (gated) luminescence-based method for determination of pesticides in microtiterplate format using the long-lived europium-3-carboxycoumarin has been developed. The limit of detection is 4.80, 5.06 and 8.01 μmol L⁻¹ for methomyl, prometryne and aldicarb, respectively. This is the lowest limit of detection achieved so far for luminescent lanthanide-based probes for pesticides. The interaction of the probe with the pesticides has been investigated using cyclic voltammetry (CV), differential pulse polarography (DPP), square wave voltammetry (SWV) and linear sweep voltammetry (LSV) on a glassy carbon electrode in I = 0.1 mol L⁻¹ p-toluenesulfonate at 25 °C. The diffusion coefficients of the reduced species are calculated. The main properties of the electrode reaction occurring in a finite diffusion space are the quasireversible maximum and the splitting of the net SWV peak for Eu(III) ions in the ternary complex formed . It was observed that the increase of the cathodic peak currents using LSV is linear with the increase of pesticides concentration in the range 5 × 10⁻⁷ to 1 × 10⁻⁵ mol L⁻¹. The detection limit (DL) were about 1.01, 2.23 and 1.89 μmolL⁻¹ for aldicarb, methomyl and prometryne, respectively. In order to assess the analytical applicability of the method, the influence of various potentially interfering species was examined. Influence of interfering species on the recovery of 10 μmol L⁻¹ pesticides has been investigated.     

Study of the oxygen electrode reaction using mixed conducting oxide surface layers. Part II: Small signal analysis

The oxygen gas electrode has been studied for a number of mixed conducting oxide surface layers on top of Gd₂Zr₂O₇ (TGZO) solid electrolytes. In part II of this paper we present the results of frequency dispersion measurements for the electrode reaction, supplying additional information to the results of current-overvoltage experiments presented in part I. For both kinds of experiments the same trends were observed for the electrode polarization. Best results are obtained for a surface layer of TGZO, while p-type mixed conducting oxides give less decreased values of the electrode polarization. High electrode capacitances were found in the case of mixed conducting surface layers (about 700 F/m²). The electrode reactions follow a Butler-Volmer type of equation. Most probably a diffusion process is rate controlling the overall charge transfer process.