KINETIC-STUDY OF ELECTROCATALYTIC REDUCTION OF HYDROGEN-PEROXIDE AT IRON(III) PORPHYRIN MODIFIED GLASSY-CARBON ELECTRODE IN ALKALINE-MEDIUM USING THE ROTATION-SCAN METHOD

Reduction of hydrogen peroxide at a glassy carbon (GC) electrode modified with sigma-bonded pyrrole iron(III) octaethylporphyrin complex, (OEP)Fe(Pyr), was studied by cyclic voltammetry and a rotating disk electrode. In 0.1N NaOH solution, it is shown that such an (OEP)Fe(Pyr)/GC electrode has a significant catalytic activity towards hydrogen peroxide reduction (E(D) = -0.80 V, k = 0.066 cm s(-1)); however, the electrode stability is low. The deactivation is observed when the reaction charge (Q) is passing through the (OEP)Fe(Pyr)/GC disk electrode. A linear rotation scan method is applied to study the kinetic process by determining the disk electrochemical response (i(D)) to rotation rate (omega) at a definite disk potential (E(D)). Considering that the number of adsorbed electroreduced catalyst molecules (Red) varies according to the disk potential, a factor theta(= Gamma(Red)/(Gamma(Red) + Gamma(Ox))) is introduced to describe the electrode surface area fraction for electroreduced species. The obtained Koutecky-Levich equation is applicable whatever the potential is.

THE ANODIC-OXIDATION OF HYDRAZINE ON GLASSY-CARBON ELECTRODE

The anodic oxidation kinetics of hydrazine (N2H4) on glassy carbon (GC) electrode was examined by cyclic voltammetry, rotating disk and ring-disc electrode techniques. The possible mechanisms of N2H4 oxidation in both aqueous and nonaqueous solutions are proposed.

Electrochemical oxidation of glycine by doped nickel hydroxide modified electrode

The electrocatalytic oxidation of glycine by doped nickel hydroxide modified electrodes and their use as sensors are described. The electrode modification was carried out by a simple electrochemical coprecipitation and its electrochemical properties were investigated. The modified electrode presented activity for glycine oxidation after applying a potential required to form NiOOH (similar to 0.45 V vs Ag/AgCl). In these conditions a sensitivity of 0.92 mu A mmol(-1) L and a linear response range from 0.1 up to 1.2 mmol L(-1) were achieved in the electrolytic Solutions at PH 12.6. Limits of detection and quantification were found to be 30 and 110 mu mol L(-1), respectively. Kinetic studies performed with rotating disk electrode (RDE) and by chronoamperometry allowed to determine the heterogeneous rate constant of 4.3 x 10(2) mol(-1) Ls(-1), Suggesting that NiOOH is a good electrocatalyst for glycine oxidation. NiOOH activity to oxidize other amino acids was also investigated, (c) 2008 Elsevier B.V. All rights reserved.

Well-Alloyed PtFe/C Nanocatalysts of Controlled Composition and Same Particle Size: Oxygen Reduction and Methanol Tolerance

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Electrochemical measurements of oligonucleotides in the presence of chromosomal DNA using membrane-covered carbon electrodes

Substantial improvements in the selectivity of electrochemical measurements of trace nucleic adds are obtained by using membrane-covered carbon disk electrodes. Access to the electrode surface can be manipulated via a judicious choice of the membrane molecular weight cutoff (MWCO). The resulting separation step, performed in situ at the electrode surface, adds a new dimension of selectivity based on molecular size to electroanalysis of nucleic acids, Transport properties are evaluated with respect to the oligonucleotide length and membrane MWCO. A highly selective response is observed for synthetic oligonucleotides in the presence of otherwise interfering chromosomal DNAs. Discrimination among oligonucleotides of different lengths is also possible, Short accumulation periods (1-5 min) are sufficient for convenient measurements of low milligram per liter concentrations.

A comparison of charge-transfer mechanisms at rotated disk electrode for biomimetic binuclear and tetranuclear oxo-manganese complex in aqueous solution

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Scheme of squares: Part II. Systems formalism for sinusoidal perturbations

We extend here the formalism developed in Part I (for the potentiostatic response) to the admittance analysis of the scheme of squares. The results are applicable, as before, to several configurations of the electrode such as the rotating disk or the planar. All that one has to do is “to plug in” the appropriate matrices relating the interfacial concentrations to the fluxes.

Estimation of Cavitation Erosion with Incubation Periods and Material Properties

A detailed study of the normalized correlations between the incubation period tc and the properties of various materials tested in a rotating disk device indicates that, at very high intensities, the strength properties influence the duration of tc. The analysis of extensive data from other laboratories for cavitation and liquid impingement erosion also indicates that, while both energy and strength properties influence the duration of tc, the latter ones predominate for a majority of cases. A fatigue-type failure occurs during tc. For estimating the time required to pierce a metallic specimen in a rotating device a relationship tp = 160 tc0.44 is proposed. A detailed study of normalized correlations between erosion resistance (inverse of erosion rate) and tc values of different materials tested in the rotating disk shows that correlations are good. Analysis of data from eight other investigators clearly points out the validity and the usefulness of this type of prediction.

Similarities in Different Experiments of Erosion Caused by Cavitation and Liquid Impingement

Correlations of erosion resistances of materials tested in different equipment are reported. Analysis of the authors' data from rotating disk and venturi equipment indicates that there exists a good correlation between the erosion resistances of materials tested at different intensities. The study indicates that time effects on erosion are important in correlations of this type. The erosion resistances of materials tested in two different devices exhibit good correlations indicating a quantitative similarity between different forms of erosion. The investigations also show that the prediction of erosion resistances of materials in a field device may be made with the data from a laboratory device which may not fully reproduce the flow conditions in the field. These conclusions are also checked with data reported from other laboratories.

Evaluation of Erosion Resistance of Metallic Materials and the Role of Material Properties in Correlations

A study of the correlations between material properties and normalized erosion resistance (inverse of erosion rates) of various materials tested in the rotating disk and the flow venturi at various intensities indicates that different individual properties influence different stages of erosion. At high and low intensities of erosion, energy properties predominate the phenomenon, whereas at intermediate intensities strength and acoustic properties become more significant. However, both strength and energy properties are significant in the correlations for the entire spectrum of erosion when extensive cavitation and liquid impingement data from several laboratories involving different intensities and hydrodynamic conditions are considered. The use of true material properties improved the statistical parameters by 3 to 37%, depending on the intensity of erosion. It is possible to evaluate qualitatively the erosion resistances of materials based on the true stress-true strain curves.

A characteristic based numerical method with tracking for nonlinear wave equations

Many physical problems can be modeled by scalar, first-order, nonlinear, hyperbolic, partial differential equations (PDEs). The solutions to these PDEs often contain shock and rarefaction waves, where the solution becomes discontinuous or has a discontinuous derivative. One can encounter difficulties using traditional finite difference methods to solve these equations. In this paper, we introduce a numerical method for solving first-order scalar wave equations. The method involves solving ordinary differential equations (ODEs) to advance the solution along the characteristics and to propagate the characteristics in time. Shocks are created when characteristics cross, and the shocks are then propagated by applying analytical jump conditions. New characteristics are inserted in spreading rarefaction fans. New characteristics are also inserted when values on adjacent characteristics lie on opposite sides of an inflection point of a nonconvex flux function, Solutions along characteristics are propagated using a standard fourth-order Runge-Kutta ODE solver. Shocks waves are kept perfectly sharp. In addition, shock locations and velocities are determined without analyzing smeared profiles or taking numerical derivatives. In order to test the numerical method, we study analytically a particular class of nonlinear hyperbolic PDEs, deriving closed form solutions for certain special initial data. We also find bounded, smooth, self-similar solutions using group theoretic methods. The numerical method is validated against these analytical results. In addition, we compare the errors in our method with those using the Lax-Wendroff method for both convex and nonconvex flux functions. Finally, we apply the method to solve a PDE with a convex flux function describing the development of a thin liquid film on a horizontally rotating disk and a PDE with a nonconvex flux function, arising in a problem concerning flow in an underground reservoir.

Ag nanoparticles-anchored reduced graphene oxide catalyst for oxygen electrode reaction in aqueous electrolytes and also a non-aqueous electrolyte for Li-O-2 cells

Silver nanoparticles-anchored reduced graphene oxide (Ag-RGO) is prepared by simultaneous reduction of graphene oxide and Ag+ ions in an aqueous medium by ethylene glycol as the reducing agent. Ag particles of average size of 4.7 nm were uniformly distributed on the RGO sheets. Oxygen reduction reaction (ORR) is studied on Ag-RGO catalyst in both aqueous and non-aqueous electrolytes by using cyclic voltammetry and rotating disk electrode techniques. As the interest in non-aqueous electrolyte is to study the catalytic performance of Ag-RGO for rechargeable Li-O-2 cells, these cells are assembled and characterized. Li-O-2 cells with Ag-RGO as the oxygen electrode catalyst are subjected to charge-discharge cycling at several current densities. A discharge capacity of 11 950 mA h g(-1) (11.29 mA h cm(-2)) is obtained initially at low current density. Although there is a decrease in the capacity on repeated discharge-charge cycling initially, a stable capacity is observed for about 30 cycles. The results indicate that Ag-RGO is a suitable catalyst for rechargeable Li-O-2 cells.

Ir nanoparticles-anchored reduced graphene oxide as a catalyst for oxygen electrode in Li-O-2 cells

Iridium nanoparticles-anchored reduced graphene oxide (Ir-RGO) was prepared by simultaneous reduction of graphene oxide and Ir3+ ions and its catalytic activity for oxygen electrode in Li-O-2 cells was demonstrated. Ir particles with an average size of 3.9 nm were uniformly distributed on RGO sheets. The oxygen reduction reaction (ORR) was studied on an Ir-RGO catalyst in non-aqueous electrolytes using cyclic voltammetry and rotating disk electrode techniques. Li-O-2 cells with Ir-RGO as a bifunctional oxygen electrode catalyst were subjected to charge-discharge cycling at several current densities. A discharge capacity of 9529 mA h g(-1) (11.36 mA h cm(-2)) was obtained initially at a current density of 0.5 mA cm(-2) (393 mA g(-1)). A decrease in capacity was observed on increasing the current density. Although there was a decrease in capacity on repeated discharge-charge cycling initially, a stable capacity was observed for about 30 cycles. The results suggest that Ir-RGO is a useful catalyst for rechargeable Li-O-2 cells.

固体力学进展及应用: 庆贺李敏华院士90华诞文集

《固体力学进展及应用：庆贺李敏华院士90华诞文集》收录了近代固体力学基础理论及其应用领域的重要科技成果和最新进展。作者是在同体力学领域工作多年的资深研究员，他们来自各行各业，有丰富的科研与丁作经验。他们提供的论文在相当程度上反映当前同体力学的发展现状与成就，并能看出发展趋势，对未来研究的课题选择有参考价值。《固体力学进展及应用：庆贺李敏华院士90华诞文集》还收集了李敏华院士的珍贵照片和纪念李敏华院士90华诞的庆贺和回忆文章，具有重要的史料价值。

Grafenoan oinarrituriko aire elektrodoa metal/aire baterietarako

Metal-aire baterietarako grafenoan oinarritutako aire elektrodoaren diseinua eta fabrikazioa. Hasteko, grafenoan eutsitako katalizatzaileen sintesia eta haien analisi elektrokimikoa 'Rotating Disk Electrode' teknikaren bidez burutu dira. Ondoren, katalizatzaile eta egitura desberdineko elektrodoen fabrikazioa eta jokaeraren analisia egin dira bifuntzionala den geruza bikoitzeko elektrodoa lortzeko.