Y. Meas

Effect of Cd, Ni, Zn and Co ions on electrode reactions of the leadacid battery

Abstract The influence of metallic ions Cd(II), Ni(II), Zn(II) and Co(II) on gassing and maintenance behaviour of both lead and lead dioxide electrodes has been studied using linear potential sweep voltammetry and charge and discharge curves. The experiments were made using a Pb-0.6%Ca alloy and commercial electrodes in 5 M H 2 SO 4 electrolytic solution. Charge efficiencies were enhanced and a lower maintenance was required when the battery contained Cd(II) and Zn(II) ions, but the opposite occurred with Ni(II) and Co(II) ions.

Formation of ion-translocating oligomers by nigericin

SummaryAt pH 4.0, >10−7m nigericin was found capable of conducting net charge transfer across bimolecular lecithin membranes, with a stoichiometry of three uncharged ionophore moieties per cation. At neutral or alkaline pH, nigericin catalyzed the transfer of net charge through dimer forms. In agreement with these results, quantitative analysis of nigericin-potassium complexes formed at pH 4.0 showed a 3∶1 ratio, and a 2∶1 ratio at neutral or alkaline pH. A 1∶1 stoichiometry was observed when the ionophore complex was not transferred from methanol-water to chloroform. Moreover,1H-NMR spectra of nigericin-cation complexes formed at pH 4.0, displayed clear-cut chemical shift variations different to those observed at neutral or alkaline pH. Thus, it is apparent that acid pH causes a transition from dimeric to trimeric forms of nigericin-cation complexes. The membrane conductance increased up to ten times when negatively charged phosphatidyl glycerol was used, while the conductance decreased in positively charged cetylpyridinium containing membranes at pH 4.0. These results suggest that the nigericin-K+ oligomeric complex is positively charged. In this respect, pKa values around 8.0 were obtained for the nigericin carboxylate group in media of different dielectric constant, indicating that this chemical group is undissociated under these conditions. Moreover, the values for the complex formation constants as well as the ΔG values calculated for the dimers and trimers indicated that such ionophore cation oligomeric complexes are thermodynamically stable.

Electrochemical preparation of a Pt-Ru alloy

Abstract The electrochemical reduction of Pt(IV) and Ru(III), in separated and mixed solutions, has been studied on a platinum electrode in 1 N HCl solution. The chronoamperometric and chronocoulometric results showed that the simultaneous reduction of Ru(III) and Pt(IV) occurs, leading to alloy formation. The voltammogram of the obtained alloy is in agreement with such a conclusion.

Depot en sous-tension de cuivre sur des electrodes de platine ruthenisee

The characterization of ruthenium deposited on platinum electrodes by hydrogen or oxygen adsorption is difficult, thus the use of UDP of copper is suggested. Different electrodes, with increasing factor of roughness (3 30, a multilayer growth of copper, before the completion of the first monolayer, is observed.

Pourbaix-type diagram of Fe(III) and Fe(II) phenanthroline complexes

Abstract A potential ( E h )—pH diagram has been derived for the Fe(III)—Fe(II)—1, 10-phenanthroline system in sulphuric acid medium. The stability of [Fe(III)—1, 10-phenanthroline], [Fe(II)—1, 10-phenanthroline] [Fe(III)—sulphate] and [Fe(II)—sulphate] complexes discussed. With the aid of this diagram, several experimental results obtained here and others published elsewhere are analysed.

Arrangement of bismuth on a ruthenium electrode

Abstract The deposit of Bi adatoms by UPD on Ru, was systematically studied as function of the potential and time of deposition. The UPD Bi was characterized by a monolayer peak at 0.60 V and with an UPD shift Δ E p = 0.36 V. The electrochemical behaviour of the Bi adsorbed layer, the stoichiometry for the Ru/Bi system and a possible rearrangement of Bi, are discussed.

Effect of metallic deposits on the photocurrent and stability of semiconducting n-CdTe electrodes in aqueous media

Abstract The catalytic effect of metallic deposits of Pt, Bi, Hg, Au, Pb, Fe and Cu upon the oxidation of hydroquinone on illuminated CdTe electrodes has been studied. The photocurrents and stability factors have also been studied. The photocurrents and stability factors have been found to depend upon the nature of the metals deposited as well as their deposition methods. Those metals that displace the anodic peak potential towards more cathodic values were found to catalyze the oxidation reaction.

Influence of samarium on the electrocatalytic activity of platinum electrodes for the hydrogenation of benzene

The hydrogenation of benzene on platinum electrodes in 0.5 M sulfuric acid as supporting electrolyte has been studied in the presence and the absence of samarium in solution. The hydrogenation overpotential of preadsorbed benzene was diminished to ∼ 90 mV with samarium in the solution and the hydrogenation current was significatively increased. These results are interpreted in terms of a synergic effect of samarium on hydrogen adsorption and, consequently, on the electrocatalytic activity of the platinum electrode for the hydrogenation of benzene.

Electrocatalytic effect of metal ions on lead and lead dioxide electrode reactions

The electrochemical reactions which take place on lead and lead dioxide electrodes of a lead-acid battery are highly influenced by the presence in the electrolytic solution of ions Cd(II), Ni(II), Zn(II) and Co(II). Current density-potential curves were obtained in this work by using a Pb/Ca alloy. It was observed that Co(II) and Ni(II) ions catalyzed both hydrogen and oxygen evolution reactions. On the other hand, Cd(II) and Zn(II) ions decreased the hydrogen evolution rate.AbstractНа электрохимические реакции, протекающие на электродах свинца и двуокиси свинца в свинцово-кислых аккумуляторах, сильно влияет присутствие в электролитическом растворе ионов Cd(II), Ni(II), Zn(II) и Co(II). Кривые плотность тока-потенциал получены, используя сплавы Pb/Ca. Найдено, что металлические ионы Co(II) и Ni(II) катализируют реакции выделения как водорода, так и кислорода. С другой стороны, металлические ионы Cd(II) и Zn(II) уменьшают скорость реакции выделения водорода.

Diagramme potentiel-pH pour le système Fe(III)-Fe(II)/H2O en présence de 1,10 phénanthroline

Resume Le diagramme potential (Eh—pH pour le systeme Fe(III)Fe(II)/H2O a ete construit pour une concentration de 1,10 phenanthroline total de 10−1 mole l−1 et a 298 K. La stabilite des complexes [Fe(III)—1,10 phenanthroline] et [Fe(II)—1,10 phenanthroline] en milieu acide est discutee.