Copper-containing polymethylsilsesquioxane nanocomposites in catalytic olefination reaction

New copper-containing organosilicon hybrid materials were synthesized by the reaction of branched polymethyl- silsesquioxane with copper nanoparticles prepared by the metal-vapor synthesis. Hybrid materials showed a high activity in the catalytic olefination of p-chlorobenzaldehyde hydrazone with polyhaloalkanes such as CBrCl₃, CBr₄ and CF CBr to afford the corresponding halostyrenes in the yields above 80%. The structure and composition of the prepared nanocomposites were studied by X-ray using synchrotron radiation to show that the active sites of the catalysts are mixed copper(I)–copper(II) oxides (Cu–Cu₂O–CuO) in nature.     

On the effect of montmorillonite in the curing reaction of epoxy nanocomposites

The procedure for the fabrication of epoxy-based polymer layered silicate nanocomposites is important in respect of the nanostructure that is developed. To further our understanding of this, the influence of an organically modified clay (montmorillonite, MMT) on the curing kinetics of an epoxy resin has been studied by differential scanning calorimetry. Clay loadings of 10 and 20 mass% are used, and isothermal as well as dynamic cures have been investigated. For both cure schedules the effect of the MMT is to advance the reaction. Kinetic analysis yields values for the activation energy, but shows that the reaction cannot be described simply by the usual autocatalytic equation. The glass transition of the cured nanocomposites is lower than that for the cured neat resin, a result that is attributed to homopolymerisation taking place in addition to the epoxy–amine reaction.     

Investigation of the electrode reaction of chromium(III) at the lead dioxide electrode

Summary Using the electro-deposited lead dioxide electrode as an indicator electrode, the electrode reaction of chromium(III) was investigated in unbuffered solution covering a pH range of about 2 to 8. Reduction and oxidation peaks, the heights of which increase with chromium(III) concentration, were observed. It was found that the electrode reaction of chromium(III) at the lead dioxide electrode depends on the pH of the solution and that the reaction at a pH lower than 3 differs from that at a pH higher than 3. The lead dioxide electrode seems to be useful for the determination of chromium(III).

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Untersuchung der Elektrodenreaktion von Chrom(III) an der Bleidioxid-Elektrode

Zusammenfassung Mit der elektrolytisch belegten Bleidioxidelektrode als Indicatorelektrode wurde die Elektrodenreaktion von Chrom(III) in ungepufferter Lösung im pH-Bereich 2 bis 8 untersucht. Reduktions- und Oxidationspeaks, deren Höhe mit der Chrom(III)- Konzentration zunahm, wurden beobachtet. Es ergab sich, daß die Elektrodenreaktion vom pH der Lösung abhängt und im pH-Bereich unter und über 3 unterschiedlich ist. Die Bleidioxidelektrode scheint für die Bestimmung von Chrom(III) geeignet zu sein.

     

Investigation of the electrode reaction of EDTA and other complexanes at the lead dioxide electrode in aqueous solutions

Summary By using an electrodeposited lead dioxide electrode as an indicator electrode, the electrode reaction of ethylenediaminetetraacetic acid (EDTA) and other complexanes was investigated in unbuffered solution covering a pH range of about 2–12. Well-defined anodic and cathodic peaks, the heights of which increase with EDTA concentration, were observed. In an anodic single-sweep process, one anodic pre-peak appeared only at a pH higher than 4. It was found that in the cathodic process lead dioxide on the electrode is reduced to lead ion which reacts with EDTA to form the complex and in the anodic process the lead complex is oxidized again and deposited onto the electrode as lead dioxide. The height of the anodic and cathodic peaks is directly proportional to the EDTA concentration. The lead dioxide electrode seems to be useful for determining a chelating agent such as the EDTA-type complexanes.

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Untersuchung der Elektrodenreaktion von EDTA und anderen Komplexanen in wäßriger Lösung an der Bleidioxidelektrode

Zusammenfassung Mit Hilfe der elektrolytisch belegten PbO₂-Elektrode wurde die Elektrodenreaktion von EDTA (sowie von IDA, NTA und DTPA) in ungepufferter Lösung im pH-Bereich 2–12 untersucht. Gut ausgebildete anodische und kathodische Peaks wurden beobachtet, deren Höhe mit der EDTA-Konzentration zunimmt. Im anodischen single-sweep-Prozeß erschien nur ein anodischer Vorpeak bei pH>4. Es wurde festgestellt, daß bei dem kathodischen Vorgang PbO₂ an der Elektrode zu Pb-Ion reduziert wird, das mit EDTA unter Komplexbildung reagiert, während an der Anode der Pb-Komplex wieder oxidiert und PbO₂ abgeschieden wird. Die Peakhöhen sind der EDTA-Konzentration direkt proportional. Die PbO₂-Elektrode erscheint daher von Nutzen für die Bestimmung von Komplexanen vom Typ des EDTA.

     

Polypyrrole-cobalt-carbon nanocomposites as efficient counter electrode materials for dye-sensitized solar cells

In this work, we demonstrate a new kind of Pt-free counter electrode for dye-sensitized solar cells(DSCs). Polypyrrole-cobalt-carbon(PPY-Co-C) nanocomposites, with the advantages of low cost and simple preparation, show favorable catalytic activity in promoting tri-iodide reduction. The DSC composed of the PPY-Co-C nanocomposite electrode exhibits an acceptable energy conversion efficiency of 6.01%, a considerable short-circuit photocurrent of 15.33 mA cm-2, and a low charge-transfer resistance of 1.5 Ω cm2. The overall performance of PPY-Co-C is superior to the carbon counterparts and comparable with the platinum reference, rendering them efficient and promising counter electrode materials for DSCs.     

Experimental analysis of the reaction layer structure in a gas diffusion electrode

The micro-structure of the reaction layer and the performance of a PTFE-bonded gas diffusion electrode having different PTFE contents have been studied experimentally using electrochemical techniques and a mercury pore sizer. A more practical image of the structure has resulted in comparison with any of the models postulated previously. Maximum performance was obtained at 30% PTFE content for oxygen reduction with ca. 75% utilization of platinum clusters, where an activation process is controlling the performance. The reaction layer consists of two distinctive pore distributions with a boundary of ca. 0.1 μm. The smaller pore (primary pore) was assigned to the space in-between the primary particles in their agglomerate and the larger one (secondary pore) to that in-between the agglomerates. Platinum clusters of ca. 80% were located in the primary pores and most of the PTFE was in the secondary pores. On the basis of the experimental results, a schematic micro-structure for the reaction layer is proposed. It was possible to determine the degree of occupation of each pore by the electrolyte or gas from the experimental results. It was revealed that the primary pore works as a reaction volume while the secondary pore works as main gas channels, e.g. 80% of the former is occupied by electrolyte and 30% of the latter contains gas at the composition of maximum performance. Increased gas channels and high utilization of platinum clusters are essential for a high-performance gas diffusion electrode. They were achieved by dispersing efficiently both the catalysed carbon black and the PTFE.     

Photocatalytic reaction on photofuel cell titania electrode

Benzoic acid-doped titania electrodes were prepared from titanium alkoxide sols containing benzoic acid in order to examine the photocatalytic reaction of the fuel material concentrated on the titania surface of a photofuel cell electrode. This doping was developed in order to understand the physicochemical processes on the titania rather than to advance the practical use of the photofuel cells. The observed photocurrent and CO₂ and H₂O productions indicated that the oxidation of the benzoic acid enhanced the generation of electricity during the UV irradiation. Benzoic acid molecules should be oxidized by oxygen molecules and holes on the titania surface. The steam treatment of the electrodes improved the benzoic acid oxidation and the photocurrent because it promoted the titania densification and enhanced the interaction between the benzoic acid and titania. The benzoic acid-doped titania is a valid model of the fuel material concentrated in the porous titania when using benzoic acid as the fuel material. The contact between the benzoic acid and titania is important in order to obtain a high photofuel electric conversion.     

Calorimetry of electrode reaction under linear sweep-current polarization

The mathematical-physical equation concerning the process of calorimetry of electrode reactions was deduced, and the corresponding solutions were obtained respectively for the period of the electrochemical polarization and that of the natural cooling. The calorimetry of the anodic oxidation of ferrocyanide to ferricyanide under linear sweep-current polarization was carried out, the obtained apparent enthalpy change of the electrode reaction agreed well with that obtained by the calorimetry with constant currents. The developed calorimetry with linear sweep-current and the data processing method are applicable for quick determination of apparent enthalpy changes of electrode reactions.     

外控恒电流对BZ电化学反应体系动力学行为的影响

在使用探头对BZ反应体系进行观测时,原来纯粹的BZ反应系变成了由两个子系通过扩散过程耦合成的一类特殊电化学体系,所用的探头能否如实反映该体系的真实振荡行为值得探讨。本文基于FKN机理及Oregonator模型,分别对Pt电极BZ反应体系建立了动力学模型,讨论了两子系出现极限环振荡的动力学行为不一致性及外控电极电流的影响。     

多菌灵在羧甲基纤维素钠/蒙脱土修饰电极上的电化学行为及测定

制备了羧甲基纤维素钠/蒙脱土修饰电极,研究了多菌灵在该修饰电极上的电化学行为并用方波伏安法对其进行测定。实验结果表明,多菌灵在修饰电极上出现了一个不可逆氧化峰,该氧化过程受扩散控制,多菌灵浓度在2.0×10-6～6.0×10-5mol/L范围内,方波伏安法的氧化峰电流与多菌灵浓度呈现良好的线性关系,检出限为8.5×10-7mol/L,可用于检测溶液中多菌灵含量。     

A novel composite electrode for oxygen evolution reaction

FeOOH nanowires were prepared and characterized with X-ray diffraction spectroscopy and scanning electron microscopy. A composite electrode consisting of FeOOH and Ni foam (FeOOH/Ni-foam) was fabricated, and its catalytic performance for oxygen evolution reaction (OER) was evaluated and compared with nanowire NiCo₂O₄/Ni-foam electrode. The mass current density of OER on FeOOH/Ni-foam is around three times of that on NiCo₂O₄/Ni-foam. Ni foam played a key role for the high activity of the FeOOH/Ni-foam. A synergistic mechanism of FeOOH and Ni was proposed to account for the superior catalytic performance of the FeOOH/Ni-foam electrode. Considering the low cost, abundant resource and environment-benign property of FeOOH, the FeOOH/Ni-foam electrode would be a promising anode for OER.     

Silica aerogel-iron oxide nanocomposites: recoverable catalysts in conjugate additions and in the Biginelli reaction

Ferrihydrite silica aerogels containing 11-13% iron and a surface area of 500-600 m²/g are catalysts for the title reactions. They are recovered and reused without loss of activity.     

Pt dendrimer nanocomposites for oxygen reduction reaction in direct methanol fuel cells

Dendrimer-encapsulated Pt nanoparticles (G4OHPt) were prepared by chemical reduction at room temperature. The G4OHPt, with average diameters of ca. 2.7 nm, were characterized by X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. Electrocatalytic behavior for oxygen reduction reaction was investigated using a rotating disk electrode configuration in an acidic medium, with and without the presence of methanol (0.01, 0.1, and 1 M). Kinetic studies showed that electrodes based on Pt nanoparticles encapsulated inside the dendrimer display a higher selectivity for ORR in the presence of methanol than electrodes based on commercial Pt black catalysts. Also, the dendritic polymer confers a protective effect on the Pt in the presence of methanol, which allows its use as a cathode in a direct methanol fuel cell operating at different temperatures. Good performance was obtained at 90 °C and 2 bar of pressure with a low platinum loading on the electrode surface.     

Mechanism and reaction rate of the Karl-Fischer titration reaction: Part II. Rotating ring-disk electrode measurements

A platinum disk-platinum ring electrode was used to investigate the kinetics of the oxidation of the monomethyl sulfite ion (which is the oxidizable species in the Karl-Fischer reagent) by triiodide and iodine, generated with controlled current at the disk electrode. The experimental conditions were such, that the technique for measurement of homogeneous pseudo-first order reactions could be used. The results are in reasonable agreement with those of the potentiometric investigations as described in part I. The reaction rate constant of triiodide is approximately 600 1² mol^?2 s^?1; for iodine the rate constant is approximately 7×10⁶.     

Understanding the oxophilic effect on the hydrogen electrode reaction through PtM nanostructures

Journal of Solid State Electrochemistry - Carbon-supported PtM nanostructured materials (M = Cr, Co, Ni, Cu, Mo, Y, Sm, Gd) were investigated for the hydrogen evolution/oxidation...     

Kinetic analysis of the hydrogen oxidation reaction on Pt-black/Nafion electrode

The hydrogen oxidation reaction on Pt-black/Nafion electrode was investigated using a rotating disk electrode and cyclic voltammetry technique. The voltammetric results demonstrated that the electrode can be prepared with good reproducibility and that Pt-black particles without direct contact with Nafion were still electrochemically active in taking part in the H-adsorption/desorption process. For hydrogen oxidation, the limiting current density was reduced by the presence of Nafion coating. The H₂ diffusion resistance in Nafion film was avoided when the film thickness was less than 0.2 μm for a Pt-black loading of 20 μg. Moreover, the uncertainties in the kinetic results were discussed.     

A knowledge-based system for the automatic chronopotentiometric elucidation of electrode reaction mechanisms

A knowledge-based system for the elucidation of electrode reaction mechanisms based on chronopotentiometric experiments is described. The system runs the diagnostic experiments and uses the results in the reasoning process. New mechanistic knowledge can be added directly to its knowledge base in the form of production rules. The system is fully modular and its domain- specific modules can easily be changed for application to other electrochemical techniques. Correct operation of the system is demonstrated with the familiar reduction mechanisms of cadmium (II), zinc (II), cystamine and cinnamaldehyde.