Rosa Albalat

Electrodeposition of zinc-nickel alloy coatings: influence of a phenolic derivative

The electroplating of Zn−Ni alloy films from a chloride bath has been studied under different plating conditions, both in the absence and presence of a phenolic derivative. Under the conditions examined, the electrodeposition of the alloys belonged to the anomalous type. The morphology and composition of the deposits varied with current density, temperature, bath composition and additive concentration. The results show that the additive modifies the structure and surface topography of the deposits to a large extent and produces smoother deposits. The corrosion resistance of the alloys has been analyzed by means of salt-spray tests.

Zinc-nickel coatings: Relationship between additives and deposit properties

The electroplating of zinc-nickel alloys from a chloride bath containing two brighteners (a phenolic derivative and an unsaturated aromatic compound) and a levelling agent (an aromatic carboxylate) has been studied under different plating conditions. The composition and morphology of the alloys depended on the concentration of all the additives and also on the temperature. As a general effect, these additives smooth the deposit and refine the grain size. By means of scanning electron microscopy, it was possible to classify the deposit morphologies according to the type and concentration of the additives. The resistance of the alloys to corrosion was studied by means of a neutral salt-spray test.

Autonomously Moving Catalytic Microellipsoids Dynamically Guided by External Magnetic Fields

Advances toward the realization of smarter transport systemsrequire the design of artificial microengines with versatilemagneticproperties,capableofdistinguishingthedirectionsofmotion, and to make complete 1808 turns without losingcontrol.Here we report on a new technique for realizingparamagnetic catalytic microellipsoids, displaying all pre-viously mentioned properties. Our approach is based on theuseofjanusparamagneticellipsoidalparticleshalf-coatedwitha thin Pt layer and immersed in a H

Electrochemical nucleation of nickel on vitreous carbon electrodes : the influence of organic additives

The initial stages of the electrodeposition of nickel onto vitreous carbon from ethanol/water chloride solutions was studied in the presence and absence of some organic compounds. The influence of both additives and metal concentration was investigated by cyclic voltammetry, potential step experiments and differential capacity measurements. The role of the additives in the deposition process related to their adsorption, both on vitreous carbon and on vitreous carbon/nickel deposited electrodes, is also discussed.

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.

Stability of bismuth adlayers on Pt(111) electrodes in the presence of adsorbed organic compounds

The interactions of bismuth adlayers with adsorbed organic compounds on Pt(111) surfaces have been examined using voltammetric techniques. Evidence is provided that adsorbed CO affects bismuth adatoms giving rise to different adsorption states. After CO stripping, a potential excursion to negative potentials allows the surface diffusion of bismuth adatoms to take place in order to attain their most stable state on the Pt(111) surface. A similar effect on the bismuth adlayer is also carried out by tetrahydroxy-p-benzoquinone, an organic compound that exhibits a completely different behavior from that observed for CO adspecies on Pt(111) electrodes.

Electrochemical behaviour of oxocarbons on single crystal platinum electrodes Part IV. Rhodizonic acid in 0.5 M sulphuric acid medium

The electrochemical behaviour of rhodizonic acid on Pt(111), Pt(100) and Pt(110) surfaces has been studied in sulphuric acid solutions by cyclic voltammetry and in situ FTIR spectroscopy. The direct oxidation process takes place at potentials positive to the desorption of strongly bonded adsorbates. For the three orientations, polyketonic compounds and finally carbon dioxide are the oxidation products. Reduction processes can take place at lower potentials, leading to the formation of tetrahydroxyquinone and hexahydroxybenzene, also detected by FTIR. These species seem to be adsorption intermediates in the case of Pt(111), transforming from one to another depending on potential. A small amount of carbon monoxide is observed on this orientation. Significantly higher CO adsorptions have been obtained for Pt(110) (linear CO) and Pt(100) (linearly and bridge bonded). Other adsorbates seem to be formed after adsorption experiments, which give no detectable infrared absorption.

Electrochemical behaviour of oxocarbons on single crystal platinum electrodes Part 3. Croconic acid oxidation on Pt(111) surfaces in acid medium

Abstract The electrochemical behaviour of croconic acid (CRA) on Pt(111) electrodes has been studied in acid medium by cyclic voltammetry. Its oxidation proceeds via a dual path mechanism. The direct oxidation path takes place at potentials higher than 0.9 V, probably involving incipient surface oxide formation. The formation of strongly adsorbed species upon CRA adsorption is influenced by the concentration of CRA and the adsorption potential. At open circuit, only CO ads is formed, while at controlled potentials lower than 0.40 V, other adsorbates, probably with more than one carbon atom, exist. These are oxidized to CO in the range 0.4–0.6 V. The activity for poison formation at open circuit is much lower for concentrations higher than 1 mM. FTIR experiments clearly indicate that carbon monoxide is not formed at potentials lower than 0.40 V. Linearly- and bridge-bonded CO adspecies appear at potentials higher than 0.40 V, which are oxidized to CO 2 before the direct oxidation of CRA begins. A band at 1780 cm −1 indicates the presence of leuconic acid at potentials between 0.95 and 1.22 V as a product of the latter process. At higher potentials, CRA is completely oxidized to CO 2 .

Electrocatalytic oxidation of mesoxalic acid on a polycrystalline platinum electrode in acid medium

Abstract The adsorption and electrooxidation reaction of mesoxalic acid adsorbed molecules on a polycrystalline platinum electrode, in acid medium, have been studied by potentiodynamic and potentiostatic techniques. The mesoxalic acid adsorption features and the number of sites per molecule have been determined. This organic acid oxidizes through an irreversible four electron reaction. A mechanism is postulated according to the experimental kinetic parameters.

Electrochemical behaviour of oxocarbons on single crystal platinum electrodes Part II. Croconic acid oxidation on Pt(S)-[n(100) × (111)] surfaces in 0.5 M sulphuric acid medium☆

Abstract The electrochemical behaviour of croconic acid at platinum single crystal electrodes with Pt(100) and Pt(2n-1,1,1) orientations has been studied in 0.5 M H2SO4 by cyclic voltammetry. Experiments with croconic acid in solution show two main processes: the oxidation of surface poisons at around 0.8 V, and the oxidation of the acid, between 0.9 and 1.25 V. While the currents involved in the first process tend to increase with the terrace width, the process at higher potentials gives maximum current density for short terraces (3–6 atoms width). Adsorption experiments have shown that, although strongly adsorbed species are formed from croconic acid even under open circuit conditions, the application of a polarization significantly increases the amount of poison formed. For each surface, maximum amounts of irreversibly adsorbed species are formed at potentials around 0.4–0.5 V. The greatest amount of strongly adsorbed species is obtained with the Pt (100) electrode, for which adsorbed CO seems to be the only adsorbate. For stepped surfaces, some other intermediates may also be formed.