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Electrochemical Reaction (electrochemical + reaction)
Selected AbstractsChemInform Abstract: 57Fe Moessbauer Study of the Electrochemical Reaction of Lithium with Triclinic Iron Vanadate.CHEMINFORM, Issue 11 2001S. Denis Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Rotating Ring-Disk Study of the Oscillating Electrochemical Reaction of Iodide at Gold.CHEMINFORM, Issue 5 2001Joseph E. Vitt Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Voltammetric Determination of Phenylglyoxylic Acid in Urine Using Graphite Composite ElectrodeELECTROANALYSIS, Issue 2 2006Navrátil Abstract A composite electrode prepared from graphite powder and epoxy resin was applied as a working electrode for the determination of phenylglyoxylic acid (one of the metabolites of styrene) in human urine. Cathodic differential pulse stripping voltammetry was used and optimum conditions have been found giving the limit of determination about 5,mg L,1. All results were compared with those obtained using hanging mercury drop electrode. For the confirmation of suggested mechanism of the electrochemical reaction the elimination voltammetry with linear scan was used. [source] The Influence of Mass Transfer on a Porous Fuel Cell ElectrodeFUEL CELLS, Issue 1-2 2004Y.-P. Sun Abstract A one-dimensional model for a porous fuel cell electrode using a liquid electrolyte with dissolved reactant is presented. The model consists of a Poisson, second-order ordinary differential equation, describing the effect of the electric field and a one-dimensional; Fickian diffusion, second-order ordinary differential equation describing the concentration variation associated with diffusion. The model accounts for mass transport and heterogeneous electrochemical reaction. The solution of this model is by the approximate Adomian polynomial method and is used to determine lateral distributions of concentration, overpotential and current density and overall cell polarisation. The model is used to simulate the effects of important system and operating parameters, i.e. local diffusion rates, and mass transport coefficients and electrode polarisation behaviour. [source] Selective control of voltage polarity in a single-chamber solid-oxide fuel cell using the same catalytic electrodes with different sizesIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 5 2008Akiyoshi Nagata Member Abstract The selective control of the voltage polarity in a single-chamber solid-oxide fuel cell (SC-SOFC) constituting the anode and cathode arranged at the same electrolyte surface of yttria-stabilized zirconia (YSZ) or samaria-doped ceria (SDC) and which can operate in a flowing mixture of hydrogen and oxygen is discussed on the basis of the dissociation and adsorption reactions due to the catalytic materials and electrode configurations. The open circuit voltage (OCV) of SC-SOFC showed the highest value when the H2:O2 ratio was around 2:1, which might be equal to the mol ratio of oxygen and hydrogen based on the reaction of water formation by the electrochemical reaction in the cell. The voltage polarity of the cell using the Pt and LSM (La0.7Sr0.3MnO3) catalysts was the same as in the conventional SOFC such that in the Pt catalysis the anode became negative whereas in the LSM catalysis the cathode was independent of the electrode configurations. In SC-SOFC using the same Pt catalyst, the larger Pt electrode functioned as the cathode desorbing the oxide ion conducting in YSZ or SDC. As a result, it was confirmed that the voltage polarity of SC-SOFC could be selectively controlled by making use of the same catalytic electrodes with different sizes, and that the I,V characteristic of the cell improved by using SDC with Pt electrodes with a surface area ratio of 2:1. © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] A parametric study of multi-phase and multi-species transport in the cathode of PEM fuel cellsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 8 2008Nada Zamel Abstract In this study, a mathematical model is developed for the cathode of PEM fuel cells, including multi-phase and multi-species transport and electrochemical reaction under the isothermal and steady-state conditions. The conservation equations for mass, momentum, species and charge are solved using the commercial software COMSOL Multiphysics. The catalyst layer is modeled as a finite domain and assumed to be composed of a uniform distribution of supported catalyst, liquid water, electrolyte and void space. The Stefan,Maxwell equation is used to model the multi-species diffusion in the gas diffusion and catalyst layers. Owing to the low relative species' velocity, Darcy's law is used to describe the transport of gas and liquid phases in the gas diffusion and catalyst layers. A serpentine flow field is considered to distribute the oxidant over the active cathode electrode surface, with pressure loss in the flow direction along the channel. The dependency of the capillary pressure on the saturation is modeled using the Leverette function and the Brooks and Corey relation. A parametric study is carried out to investigate the effects of pressure drop in the flow channel, permeability, inlet relative humidity and shoulder/channel width ratio on the performance of the cell and the transport of liquid water. An inlet relative humidity of 90 and 80% leads to the highest performance in the cathode. Owing to liquid water evaporation, the relative humidity in the catalyst layer reaches 100% with an inlet relative humidity of 90 and 80%, resulting in a high electrolyte conductivity. The electrolyte conductivity plays a significant role in determining the overall performance up to a point. Further, the catalyst layer is found to be important in controlling the water concentration in the cell. The cross-flow phenomenon is shown to enhance the removal of liquid water from the cell. Moreover, a shoulder/channel width ratio of 1:2 is found to be an optimal ratio. A decrease in the shoulder/channel ratio results in an increase in performance and an increase in cross flow. Finally, the Leverette function leads to lower liquid water saturations in the backing and catalyst layers than the Brooks and Corey relation. The overall trend, however, is similar for both functions. Copyright © 2007 John Wiley & Sons, Ltd. [source] Intelligent structure design of membrane cathode assembly for direct methanol fuel cellINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 12 2005K. Furukawa Abstract The performance and the structural model of membrane electrode assembly (MEA) have been developed and experimentally verified with fundamental calculations of the direct methanol fuel cell (DMFC). The model provides information concerning the influence of the operating and structural parameters. The composition and performance optimization of MEA structure in DMFC has been investigated by including both electrochemical reaction and mass transport process. In the experimentation, the effect of Nafion content and loading method in the catalyst layer of cathode for DMFC was investigated. For the spray method electrode (SME), the cell performance and cathode performance using a dynamic hydrogen electrode (DHE) as a reference electrode was improved in comparison with those of the PME electrode by decreasing cathode potential. From ac impedance measurements of the cathode, the adsorption resistance of the SME electrode was decreased compared with that of the PME electrode. The higher cell performance was mostly dependent on the adsorption resistance. In the modelling, the cathode overpotential was decreased with increasing ionomer content, due to increasing ionic conductivity for proton transfer and the larger reaction site. The resistance to oxygen transport was increased at the same time, and became dominant at higher ionomer loadings, leading to an increase in the voltage loss. The ratio of ionomer to void space in the cathode affected the cathode polarization, which had the lowest resistance of oxygen diffusion at the ratio of 0.1,0.2. Copyright © 2005 John Wiley & Sons, Ltd. [source] Oxidation of bisnaphthols to spironaphthalenones, revisitedJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2008Ahmad Khoramabadi-Zad Bis(2-hydroxy-1-naphthyl)methane derivatives have been efficiently converted to their corresponding spirans through three methods, i.e. oxidation by TCCA under mild reaction conditions, Ph3Bi catalyzed air oxidation, and by electrochemical reaction. The first two methods are diastereoselective and give either of the two possible diastereomers, while the electrochemical method produces equal amounts of these diastereomers. [source] Modelling and parameter comparison of equivalent circuits on the basis of impedance measurements of stainless steelsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 4 2006M. Slemnik Abstract In our former work [1] we have discussed the impedance of differently heat treated steels X20Cr13 in 0.1 M H2SO4, undergoing an active passive transition. Impedance spectra were interpreted in terms of a model by Armstrong [2, 3], describing the electrochemical reaction at interfaces with adsorbed intermediates. The present work was performed in order to study this phenomenon in more detail, with computer simulations of a new created and more convenient equivalent circuit in comparison with the former model. Computer simulations of equivalent circuits were also made in the region of passivity which was also continuation of our earlier work [4]. In this sense the entire study for these steels was completed by collating distinctive parameter values, demonstrating electrochemical characteristics of steel X20Cr13, undergoing different heat treatments in the active-passive and passive region. [source] Inhibition Mechanism of TbIII on Horseradish Peroxidase ActivityCHEMISTRY & BIODIVERSITY, Issue 10 2008Shaofen Guo Abstract The inhibition mechanism of TbIII on horseradish peroxidase (HRP) in vitro was discussed. The results from MALDI-TOF/MS and X-ray photoelectron spectroscopy (XPS) showed that TbIII mainly interacts with the O-containing groups of the amides in the polypeptide chains of the HRP molecules and forms the complex of TbIII,HRP, and, in the complex, the molar ratio TbIII/HRP is 2,:,1. The results from CD and atomic force microscopy (AFM) indicated that the coordination effect between TbIII and HRP can lead to the conformation change in the HRP molecule, in which the contents of , -helix and , -sheet conformation in the peptide of the HRP molecules is decreased, and the content of the random coil conformation is increased. Meanwhile, the coordination effect also leads to the decrease in the content of inter- and intrapeptide-chain H-bonds in the HRP molecules, resulting in the HRP molecular looseness and/or aggregation. Thus, the conformation change in the HRP molecules can significantly decrease the electrochemical reaction of HRP and its electrocatalytic activity for the reduction of H2O2. [source] Application of Nanoparticles in Electrochemical Sensors and BiosensorsELECTROANALYSIS, Issue 4 2006Xiliang Luo Abstract The unique chemical and physical properties of nanoparticles make them extremely suitable for designing new and improved sensing devices, especially electrochemical sensors and biosensors. Many kinds of nanoparticles, such as metal, oxide and semiconductor nanoparticles have been used for constructing electrochemical sensors and biosensors, and these nanoparticles play different roles in different sensing systems. The important functions provided by nanoparticles include the immobilization of biomolecules, the catalysis of electrochemical reactions, the enhancement of electron transfer between electrode surfaces and proteins, labeling of biomolecules and even acting as reactant. This minireview addresses recent advances in nanoparticle-based electrochemical sensors and biosensors, and summarizes the main functions of nanoparticles in these sensor systems. [source] The Effect of the Anode Loading and Method of MEA Fabrication on DMFC PerformanceFUEL CELLS, Issue 3 2007T. V. Reshetenko Abstract The influence of the Pt-Ru anode loading and MEA preparation techniques on direct methanol fuel cell (DMFC) performance is studied. Two different anode catalyst layer preparation techniques are employed. One is the direct coating of anode catalyst ink on a membrane to form a catalyst coated membrane, CCManode, and the other is the coating of the ink on the diffusion layers, which generates a catalyst coated substrate, CCSanode. The power density of a combined CCManode/CCScathode MEA is higher than for a CCSanode/CCScathode MEA. The main difference in the performance is observed in the high current density region, where two-phase flow is present and mass transfer processes govern the performance. The CCManode and CCSanode have different macroscopic structures, while showing the same microscopic morphology. Based on their morphological differences, it is expected that the combination of the CCManode and carbon paper provides the more homogeneous removal of CO2 at high currents. The authors suggest that the application of the CCManode with an optimal anode loading improves anode mass transfer, reduces methanol crossover, and enhances the electrochemical reactions. [source] Electrochromic Polymer-Dispersed Liquid-Crystal Film: A New Bifunctional Device,ADVANCED FUNCTIONAL MATERIALS, Issue 6 2005P. Nicoletta Abstract Polymer-dispersed liquid crystals (PDLCs) are liquid-crystal dispersions within a polymer matrix. These films can be changed from an opaque to a transparent state by applying a suitable alternating-current electric field. PDLCs have attracted the interest of researchers for their applications as light shutters, smart windows, and active displays. For such applications, electrochromic devices, which change color as a result of electrochemical reactions, have also become a recent focus of research. Herein, we report our preliminary results on bifunctional devices based on PDLCs that host electrochromic guest molecules. Such devices allow both an independent and fast switching from a scattering opaque state to a transmissive transparent state owing to liquid-crystal reorientation and a color change from white (pale yellow) to dark blue, due to either oxidation or reduction of the electrochromic molecules. [source] Comparison of real-time methods for maximizing power output in microbial fuel cellsAICHE JOURNAL, Issue 10 2010L. Woodward Abstract Microbial fuel cells (MFCs) constitute a novel power generation technology that converts organic waste to electrical energy using microbially catalyzed electrochemical reactions. Since the power output of MFCs changes considerably with varying operating conditions, the online optimization of electrical load (i.e., external resistance) is extremely important for maintaining a stable MFC performance. The application of several real-time optimization methods is presented, such as the perturbation and observation method, the gradient method, and the recently proposed multiunit method, for maximizing power output of MFCs by varying the external resistance. Experiments were carried out in two similar MFCs fed with acetate. Variations in substrate concentration and temperature were introduced to study the performance of each optimization method in the face of disturbances unknown to the algorithms. Experimental results were used to discuss advantages and limitations of each optimization method. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Electrochemical Microstructuring with Short Voltage PulsesCHEMPHYSCHEM, Issue 1 2007Rolf Schuster Prof. Dr. Abstract The application of short (nanosecond) voltage pulses between a tool electrode and a workpiece immersed in an electrolyte solution allows the three-dimensional machining of electrochemically active materials with submicrometer resolution. The method is based on the finite charging time constant of the double-layer capacitance, which varies approximately linearly with the local separation between the electrode surfaces. Hence, the polarization of the electrodes during short pulses and subsequent electrochemical reactions are confined to regions where the electrodes are in sufficiently close proximity. This Minireview describes the principles behind electrochemical microstructuring with short voltage pulses, and its current achievements and limitations. [source] | ||||||||||||||||