196,787 research outputs found
Nickel based electrocatalysts for oxygen evolution in high current density,alkaline water electrolysers
No full textA number of nickel based materials are investigated as potential oxygen evolution catalysts under conditions close to those met in modern, high current density alkaline water electrolysers. Microelectrodes are used to avoid distortion of voltammetric data by IR drop even at the high current densities employed in such water electrolysers. High surface area nickel metal oxides prepared by cathodic deposition and mixed oxides prepared by thermal methods are considered. A mixed Ni/Fe oxide is the preferred electrocatalyst. The influence of hydroxide ion concentration and temperature on the voltammetry is defined. Preliminary stability tests in a zero gap cell with an OH? conducting membrane show no significant increase in overpotential during 10 days operation in 4 M NaOH electrolyte at a current density of 1 A cm?2 at 333 K
Electrodeposited lead dioxide coatings
No full textLead dioxide coatings on inert substrates such as titanium and carbon now offer new opportunities for a material known for 150 years. It is now recognised that electrodeposition allows the preparation of stable coatings with different phase structures and a wide range of surface morphologies. In addition, substantial modification to the physical properties and catalytic activities of the coatings are possible through doping and the fabrication of nanostructured deposits or composites. In addition to applications as a cheap anode material in electrochemical technology, lead dioxide coatings provide unique possibilities for probing the dependence of catalytic activity on layer composition and structure (critical review, 256 references)
The influence of the medium on Pb(II) removal on a 3-dimensional electrode.
No full textThe removal of Pb(II) ions from aqueous solutions of perchlorate, nitrate, tetrafluoroborate, chloride and sulfate, pH2, has been investigated in a cell with a reticulated vitreous carbon cathode. It is confirmed that the Pb(II) may always be removed. There are, however, marked differences in the conditions necessary and the performance attained by the system (eg, rate of removal, current efficiency), even with these nominally similar, aqueous acid media. The origin of these differences are investigated
Review of: The Diplomacy Of Involvement: American Economic Expansion Across The Pacific, 1784-1900 by David M. Pletcher
No full textThis article reviews Review of: The Diplomacy Of Involvement: American Economic Expansion Across The Pacific, 1784-1900 by David M. Pletcher
A microelectrode study of the mechanism of the reactions of silver(II) with manganese(II) and chromium(III) in sulphuric acid
No full textThe variation of the steady state limiting current for the Ag(I)/Ag(II) oxidation wave with the radius of the microdisc electrode, concentration and temperature has been used to probe the kinetics and mechanisms for the reactions of silver(II) with manganese(II) and chromium(III) in 10 mol dm?3 sulphuric acid. It is shown that the current density for the silver(I) mediated oxidation of manganese(II) is controlled by the diffusion of manganese(II) to the surface except for microelectrodes with radii below 5 ?m. On the other hand, the current density for the mediated oxidation of chromium(III) is determined by the rate of the Ag(II)/Cr(III) reaction over a range of conditions. In contrast to the Ag(II)/water reaction, its kinetics can be fitted to a mechanism where the initial electron transfer from Cr(III) to the Ag(II) is the rate determining step.<br/
The electrosynthesis of diaryliodonium salts
No full textA simple, one-step procedure for the synthesis of diaryliodonium salts is described. It is shown that the electrochemical oxidation of an aryl iodide at a carbon felt anode in acetic acid/25% acetic anhydride/5% sulfuric acid in the presence of an arene leads to a diaryliodonium salt in good yield. The method allows the preparation of unsymmetrical, as well as symmetrical diaryliodonium salts
Studies of the electrodeposition of platinum metal from a hexachloroplatinic acid bath
No full textThe mechanism of platinum deposition onto carbon from a bath containing H2PtCl6 in 0.1 M HCl is discussed. Although voltammograms show multiple cathodic waves, it is shown that they all result from the reduction of Pt(IV) to Pt(0) and there is no evidence for Pt(II) as a stable intermediate at any potential; the multiple waves arise because the hexachloroplatinic acid exists in solution as a mixture of kinetically inert Cl?/H2O complexes. The nucleation of the Pt centres on carbon is a very slow process even with a large overpotential and this leads to surfaces with well dispersed hemispherical nuclei. Moreover, each Pt centre appears to grow only to a limiting size before growth ceases.<br/
The influence of deposition conditions and dopant ions on the structure, activity, and stability of lead dioxide anode coatings
No full textbeta-lead dioxide layers have been electroplated onto gold from nitric acid solutions and the influence of lead (II) concentration, dopant ions in the bath, pH, temperature, current density, and deposition time on the characteristics of the deposits and their properties as anode materials for synthesis and effluent treatment have been examined. The most adhesive, abrasion resistant and chemically stable deposits were prepared in 0.5 M Pb(NO3)(2)/1 M HNO3 at a temperature of 333 K and using a current density of 5 mA cm(-2); these deposits had a morphology consisting of angular crystallites but they were rather inactive as anode materials. In many other conditions, deposits were made up of overlapping hemispherical centers. Such layers were significantly less stable in open-circuit conditions and were both dissolved slowly in acids and reduced by dimethyl sulfoxide in acidic solutions. On the other hand, they supported the anodic oxidation of organic molecules. Bismuth (III) was a preferred dopant ions; it led to a preference for deposits consisting of hemispherical centers even in conditions where angular crystallites were formed in the absence of Bi (III). The Bi (III) doped coatings represent the best compromise between stability and the ability to support anodic oxidations
The electrodeposition and electrocatalytic properties of copper-palladium alloys
No full textThe codeposition of copper and palladium from solutions of CuSO4 and PdSO4 in 0.6 M HClO4 is investigated using microdisc voltammetry. It is shown that good quality coatings of CuPd may be deposited and the composition may be controlled either through the deposition potential or the Cu(II)/Pd(II) ratio in solution. While the deposits seem to be amorphous and the copper can be dissolved anodically, the voltammetry indicates that the palladium stabilises the copper to dissolution. The CuPd alloys are effective catalysts for nitrate reduction in alkaline media
A microelectrode study of competing electrode reactions in the commercial process for the hydrodimerization of acrylonitrile to adiponitrile
No full textThe hydrodimerization of acrylonitrile to adiponitrile is a commercial electrolytic process carried out in a narrow gap, undivided, bipolar cell and with a multiphase electrolyte. As a consequence of the process chemistry, the electrolyte contains oxygen, iron (III), and Pb(II) and the reduction of these species along with hydrogen evolution compete with the reduction of acrylonitrile at the cathode surfaces. This paper defines the cathode reactions which can occur and considers the influence of additives to the electrolyte and of pH changes induced by the cathode reaction itself on the relative importance of the competing electrode reactions
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