The electrochemical behaviour of polycrystalline silver electrodes in Na2CO3 solution and the effect of ClO− 4 ions

The electrochemical behaviour of polycrystalline silver electrodes in Na₂CO₃ solutions was studied under potentiodynamic and potentiostatic conditions and complemented with X-ray diffraction analysis. Potentiodynamic E/i anodic curves exhibit active passive transition prior to an oxygen evolution reaction. The active region involves a small peak AI followed by a major peak AII before the passive region. Peak AI is assigned to the formation of an Ag₂O layer while peak AII is due to the formation of an Ag₂CO₃ layer. The height of the anodic peaks increases with increasing Na₂CO₃ concentration, scan rate and temperature. The effect of increasing additions of NaClO₄ on the electrochemical behaviour of Ag in Na₂CO₃ solutions was investigated. The perchlorate ions stimulate the active dissolution of Ag, presumably as a result of the formation of soluble AgClO₄ salt. In the passive region, ClO⁻ ₄ ions tend to break down the dual passive film, leading to pitting corrosion at a certain critical pitting potential. The pitting potential decreases with ClO⁻ ₄ concentration. Potentiostatic current/time transients showed that the formation of Ag₂O and Ag₂CO₃ layers involves a nucleation and growth mechanism under diffusion control. However, in the presence of ClO⁻ ₄ ions, the incubation time for pit initiation decreases on increasing the anodic potential step. Received: 3 July 1998 / Accepted: 10 March 1999     

Electric capacity of electrochemical capacitors with composite electrodes based on the aluminum–active carbon system

The electric capacity of electrochemical capacitors with composite electrodes obtained by laser microstructuring was studied. The obtained electrodes allowed control of the contribution of the resistance of the electrode material and electrolyte to the total equivalent series resistance of the electrochemical capacitor. This allowed us to determine their effect on the resulting characteristics of the capacitors. The dependences of the specific electric capacity on the parameters of the composite structure of electrodes were studied, and the optimum parameters were found.     

The influence of thermal treatment on the electrochemical properties of carbon–Ni–Pd composites

Resorcinol–formaldehyde (RF) hydrogel and RF–nickel–palladium (RF–Ni–Pd) hydrogel were synthesized by sol–gel polycondensation followed by ambient drying. Carbon gel and carbon–nickel–palladium doped gels were prepared by carbonizing the RF and RF–Ni–Pd gels at 900 °C under a nitrogen atmosphere. The goal of this study was to determine the effect of oxidative thermal treatment on the electrochemical activity of nickel–palladium doped carbon gels (C–Ni–Pd). The scanning electron microscopy analysis, adsorption and X-ray diffraction measurements showed that the admixture of Ni and Pd to carbon matrix resulted in the modification of morphological, porous and crystalline features. It has been demonstrated that composite C–Ni–Pd composed of sphere-like granules incrusted with well-crystalline nickel and palladium particles exhibits electrochemical activity in 6 M KOH aqueous solution. Thermal treatment of the composite carried out in air at 450 °C brought about the improvement of electrochemical activity in the potential range of the hydrogen sorption/desorption reaction.     

Thermodynamic properties of the ternary oxides in the Eu–Ru–O system by using solid-state electrochemical cells

The Gibbs free energies of formation of Eu₃RuO₇(s) and Eu₂Ru₂O₇(s) have been determined using solid-state electrochemical technique employing oxide ion conducting electrolyte. The reversible electromotive force (e.m.f.) of the following solid-state electrochemical cells have been measured:

Influence of the technical process parameters on structural,mechanical and electrochemical properties of LiNi0.8Co0.15Al0.05O2 based electrodes – A review

The electrode manufacturing for lithium-ion batteries has been systematically evaluated. It has been shown that a proper tailoring of the electrodes can greatly improve both the electrochemical performance and the energy density of the battery. The pre-treatment of the electrode components, the degree of the electrode compacting and the mixing process have proven to have a strong impact on the electrochemical performance of the composite electrodes based on LiNi_0.80Co_0.15Al_0.05O₂. In addition, blending LiNi_0.80Co_0.15Al_0.05O₂ – NCA with lithium manganese oxide spinel (LiMn₂O₄, LMS) has exhibited beneficial effects on the discharge capacity of the blends, thus on the energy density and in the same time decreases the Mn dissolution from spinel structure. Moreover, the detailed study of the storage behaviour of LMS/NCA blend reveals that dissolved Mn from spinel structure is re-precipitable on NCA particles and so that less Mn²⁺ ions will be available in the electrolyte, which can migrate to the anode graphite and deposit thereof.     

Influence of the spin acceleration time on the properties of ZnO:Ga thin films deposited by sol–gel method

Journal of Sol-Gel Science and Technology - A detailed study of the structural, morphological, optical, and electrical properties of the spin-coated Ga-doped ZnO (GZO) films in which these...     

Clopyralid detection by using a molecularly imprinted electrochemical luminescence sensor based on the “gate-controlled” effect

A new strategy for trace analysis was proposed by preparing a molecularly imprinted polymer (MIP) sensor. The template molecules of clopyralid were determined based on “gate-controlled” electrochemiluminescence (ECL) measurement. A dense polymer film was electropolymerized on an electrode surface to fabricate the MIP–ECL sensor. The process of template elution and rebinding acted as a gate to control the flux of probes, which pass through the cavities and react on the electrode surface. ECL measurement was conducted in the luminol–H₂O₂ system. A linear relationship between ECL intensity and clopyralid concentrations in the range of 1?×?10^?9 mol/L to 8?×?10^?7 mol/L exists, and the detection limit was 3.7?×?10^?10 mol/L. The prepared sensor was used to detect clopyralid in vegetables. Recoveries of 97.9 % to 102.9 % were obtained. The sensor showed highly selective recognition, high sensitivity, good stability, and reproducibility for clopyralid detection.     

Iron porphyrin-modified electrodes: influence of the method of modification on the stability and electroactivity in oxidation of sulfite or hydrogensulfite in ethanol–water solutions

The aim of this work is to study four types of modification of a glassy carbon electrode by Fe(III)-tetrakis(p-tetraaminophenyl)porphyrin and determine the influence of the method of immobilization of the complex on glassy carbon in electrocatalytic properties for the sulfite and hydrogensulfite oxidation in ethanol–water. The first modification was deposition of a drop of solution containing the porphyrin on a glassy carbon electrode and evaporation of the solvent (dry-drop method). The second method was immersion of the electrode at 54°C in a solution of dimethylformamide containing the porphyrin for 2 h. The third method consisted of the same heating treatment but after formation of a chemical bond of 4-aminopyridine on the glassy carbon surface, which acts as an axial ligand for the first layer of porphyrin. The fourth method involves electropolymerization of the porphyrin on the electrode surface. Important differences in stability, the potential where the oxidation wave begins and selectivity of the electrode to sulfite or hydrogensulfite were observed. The behavior of the polymer-modified electrode is different in water compared to ethanol–water.     

Effect of substrate materials on the superconducting properties of electrophoretically deposited YBa2Cu3O7−x coatings

Coatings of the high-temperature superconductor YBa₂Cu₃O_7–x (x = 0.1–0.2) (YBCO), were deposited on commercial Ni,Ti and stainless steel substrates, by an electrophoretic deposition technique. Sintering and annealing procedures were followed in order to get strongly adherent superconducting films. The suitability of the used substrates was tested by measuring the stoichiometry and the superconducting properties of the deposited coatings by X-ray diffraction analysis (XRD), Raman spectroscopy and magnetization measurements with a superconducting quantum interference device (SQUID).     

Effect of a magnetic field on the rheological properties of the systems hydroxypropyl cellulose–ethanol and hydroxypropyl cellulose–dimethyl sulfoxide

With the use of viscometry, the cloud-point method, polarization microscopy, the turbidity-spectrum method, and a polarization photoelectric apparatus, the relaxation pattern of the rheological behaviors, phase transitions, and structures of the systems hydroxypropyl cellulose–ethanol and hydroxypropyl cellulose–dimethyl sulfoxide are studied. The regions of existence of isotropic and anisotropic phases and the concentration dependence of the sizes of supramolecular particles are determined. It is found that a magnetic field increases the viscosities of solutions. The concentration dependences of viscosity and particle size are described by curves with maxima.     

The effects of pretreatment of polycrystalline gold with OH<Superscript>•</Superscript> radicals on the electrochemical nucleation and growth of platinum

The nucleation and growth of platinum on polycrystalline gold was studied by chronoamperometry, cyclic voltammetry, and atomic force microscopy before and after treatment of the gold surface with hydroxyl (OH^•) radicals. Two different procedures of mechanical polishing of the gold surface (“coarse polish” and “fine polish”) were applied before the treatment with OH^• radicals. The nucleation and growth of Pt was much better reproducible on electrodes which underwent a “coarse polish”. The treatment of the Au surface with OH^• radicals decreased the number of active sites; however, the nucleation growth mode remained the same (3-D instantaneous). The spontaneous Pt deposition (no externally applied potential) on Au was unaffected by the treatment with OH^• radicals. In situ atomic force microscopy experiments showed that the Pt starts to grow only on some of the Au grains, most probably on those which have active sites on their surface. This leads to a roughening of the electrode surface upon Pt deposition. Treatment with OH^• radicals did only quantitatively diminish the amount of deposited Pt, but qualitatively the imaging of the Pt growth remained the same. Obviously, the OH^• radicals lead to a knockout (decreasing number) of active sites for Pt nucleation, while the nature of the remaining active sites stays unaffected.     

Effects of Fenton’s reagent and thermal modification on the electrochemical properties of graphite felt for microbial fuel cell

Research on Chemical Intermediates - Effective methods for graphite felt (GF) treatment based on Fenton’s reagent treatment and thermal modification have been used to improve microbial fuel...     

Improving the adhesion of polymethacrylate thin films onto indium tin oxide electrodes using a silane-based “Molecular Adhesive”

Indium tin oxide (ITO) is the most commonly used transparent conducting substance. It has been used in numerous applications such as light-emitting diodes. In most applications and studies, the ITO surface is further coated with additional layers. The interface between the ITO and the coating is of utmost importance since it affects the physical and chemical properties of the final device. Improving the adhesion between ITO and a coating layer can be achieved by applying a “molecular adhesive” as an inter-phasing molecular layer. In this study, we used 3-(trimethoxysilyl)propyl methacrylate as a “molecule adhesive” for better connection between ITO and a polymethacrylate layer. The samples were studied by electrochemistry, contact angle goniometry, atomic force microscopy, and nano scratch microscopy. These studies clearly show that a simple silanization process formed a thin molecular adhesive layer, which did not influence the physical and chemical properties of the final coated electrode and at the same time increased significantly the adhesion between the ITO and the polymethacrylate coating.