Josep Claret

Electrochemical reduction of oxygen on thin-film Pt electrodes in 0.1 M KOH

The electroreduction of oxygen has been studied on thin-film platinum using the rotating disk electrode technique. The kinetic parameters of oxygen reduction were determined for Pt films over the range of thickness from 1 to 50 nm. The kinetics of oxygen reduction were found to be slightly influenced by the platinum film thickness.

Oxygen electroreduction on titanium-supported thin Pt films in alkaline solution

Abstract The electrochemical reduction of oxygen at thin Pt films prepared on titanium substrate has been studied in alkaline solution. Tafel plots with two different slope regions were observed for oxygen reduction in 0.1 M KOH. At low current densities the slope was around − 60 mV dec −1 , whereas at high current densities the slope was varying between −260 and −490 mV dec −1 . The oxygen reduction behaviour at Pt/Ti electrodes was qualitatively the same in comparison to that of Pt/GC electrodes. Cyclic-voltammetric experiments revealed that the potential of the hydrogen adsorption-desorption peaks and the platinum oxide reduction peak shifted towards positive potentials with the increasing Pt film thickness in 0.1 M KOH and 0.5 M H 2 SO 4 . The coverage of platinum surface with oxygen-containing species ( Θ ox ) was found to be dependent on Pt film thickness. Θ ox plays an important role in determining the oxygen reduction kinetics at platinum electrodes.

Pattern morphologies in zinc electrodeposition

Abstract A systematic experimental study of quasi two-dimensional zinc electrodeposition in an electrochemical cell with parallel electrodes is reported. The well-known different growth regimes, from anisotropically dendritic to irregularly disordered fractal, described previously in radial cells, are shown together with a novel mixed texture composed of dendritic backbones with ramified open branches. Experiments conducted by varying the cell thickness and electrode separation show significant effects by the current on the pattern morphology. Finally, the self-similarity of the electrodeposits is examined for two different growth regimes.

Growth and forms in quasi-two-dimensional electrocrystallization

Abstract A review on the morphologies and corresponding growth dynamics observed in quasi-two-dimensional electrocrystallization is presented. Emphasis is devoted to the understanding of the specific and growth mode-dependent role played by the different transport mechanisms, i.e. diffusion, migration and convection, as well as the chemical processes. The role of chemical reactions is decissive for the understanding of the well-known morphological transitions and is at the origin of the finger-like texture.

Chiral shape and enantioselective growth of colloidal particles of self-assembled meso-tetra(phenyl and 4-sulfonatophenyl)porphyrins

The self-assembly of diprotonated phenyl and 4-sulfonatophenyl meso-tetrasubstituted porphyrins gives a spontaneous chiral symmetry breaking, but only for H2TPPS3−, which forms helicoidal colloidal particles; the selection of the resulting chirality sign by the hydrodynamic forces of a stirring vortex can be demonstrated.

Phase transitions in mercury + quinoline derivative systems: The anodic formation of Hg(I)-8-hydroxyquinoline-5-sulfonic acid chelate

Abstract The anodic behaviour of a mercury electrode in 8-hydroxyquinoline-5-sulfonic acid (QH) aqueous solutions has been analyzed using different electrochemical techniques. The product obtained in the electrode process has been identified as Hg 2 Q 2 . At low QH concentrations a strong adsorption of both reactant and product is observed, while at high QH concentrations an electrodeposition process, including a two-dimensional phase transition, is observed. Two structures seem to be formed on the electrode surface by means of a mixed adsorption/nucleation mechanism.

Stirring competes with chemical induction in chiral selection of soft matter aggregates

Chirality, the absence of mirror symmetry, can be equally invoked in relation to physical forces and chemical induction processes, yet a competition between these two types of influence is rarely reported. Here we present a self-assembled soft matter system in which chiral selection is controlled by the combined independent action of a chiral dopant and vortical stirring, which are arbitrarily coupled, either constructively or destructively. In the latter case, perfect compensation, that is, absence of a net chiral effect, is realized. The induced enantiomorphic excess is measured in terms of the statistical imbalance of an ensemble of submillimetre domains, where achiral molecules self-assemble with a well-defined orientational chirality that is unambiguously resolved using optical microscopy. The possibility of combining top-down and bottom-up strategies to induce a chiral predominance in a supramolecular system of achiral components should be recognized as a new twist in the process of chiral recognition, selection and control.

Some effects of cell dimensions on zinc electrodeposits

Abstract Some specific effects of cell dimensions on the morphology of zinc electrodeposits in a parallel cell are reported. At high concentration values, a transition from mixed to string-like structures is observed as cell thickness is increased. Homogeneous patterns which are observed at low concentration values seem to be the most stable against modification of cell parameters.

Phase transitions in mercury-quinoline derivative systems. Electrochemical adsorption and nucleation processes in 8-hydroxyquinoline solutions

Abstract The deposition of the 8-hydroxyquinoline mercurous complex on a mercury electrode in aqueous solutions has been studied. A pure adsorption monolayer is formed and followed by the nucleation and growth deposition of a second complex structure. A phase transition seems to take place at very low coverages by this second structure.

Electrochemical behaviour of squaric acid on single-crystal platinum electrodes with basal orientations in aqueous sulphuric acid medium

Abstract The electro-oxidation of squaric acid (SQA) on basal platinum single-crystal surfaces in aqueous 0.5 M H 2 SO 4 solutions has been studied. Voltammetric results show that two different processes occur in the overall reaction. In the potential range 0.7–0.8 V vs. reversible hydrogen electrode, the oxidation of strongly bonded species formed after adsorption of SQA at less positive potentials takes place. This process is a structure-sensitive reaction and its characteristics allow us to assume that CO-like species are the stable adsorbed residues. At more positive potentials, the direct oxidation of SQA takes place overlapping with the oxidation of the platinum surface; Pt(110) is the most active electrode for this reaction. Its sensitivity to the surface structure indicates that this reaction involves the interaction of SQA molecules with the first platinum surface oxides. Only a slight inhibition effect on the direct oxidation of SQA due to strongly adsorbed CO is observed on Pt(100) and Pt(110) electrodes.