J.L. Vázquez

Electrochemical oxidation of benzoic acid at boron-doped diamond electrodes

The electrochemical oxidation of benzoic acid (BA) has been studied on boron-doped diamond electrodes on acid medium by cyclic voltammetry and bulk electrolysis. The results showed that in the potential region where the supporting electrolyte is stable, reactions occur, resulting in the loss of activity due to electrode fouling. Electrolysis at high anodic potentials in the region of electrolyte decomposition causes complex oxidation reactions that lead to incineration of BA. There is no indication of electrode fouling. Salicylic acid, 2,5-hydroxybenzoic acid and hydroquinone have been detected at trace level by HPLC as soluble products during the electrolysis of BA.

Platinum particles deposited on synthetic boron-doped diamond surfaces. Application to methanol oxidation

Two methods have been used for the deposition of Pt particles on synthetic boron-doped diamond (BDD) surfaces: chemical deposition and electrodeposition under potentiostatic conditions. However, electrodeposition leads much higher platinum dispersion than chemical deposition. The mechanism of nucleation and growing of the electrodeposited platinum was investigated by means of chronoamperometric studies in acid medium. The electrodeposition on diamond surfaces shows a mechanism of progressive nucleation as deduced from the chronoamperometric studies in acid medium. The stability of the deposited platinum is very low and the platinum particle are dissolved/detached by cycling. The modified BDD electrodes by deposition of platinum have been tested for the oxidation of methanol, showing that multi-step deposition results in higher values of surface and mass activities for methanol oxidation than one-step deposition process.

Optimization studies on a Fe/Cr redox flow battery

Abstract The performance of a Fe/Cr redox flow battery which operates in bipolar mode is described. The optimization studies on electrolyte composition, temperature and membrane type are presented. These studies have achieved a coulombic efficiency of 97% and an energy efficiency of 73% for an electrolyte composition of 2.3 M HCl + 1.25 M FeCl2 + 1.25 M CrCl3, working at 44 °C with a current density of 40 mA/cm2 and using the Nafion 117 membrane. A maximum discharge power density of 73 mW/cm2 has been obtained.

Electrochemical behaviour of aqueous SO2 at Pt electrodes in acidic medium. A voltammetric and in situ Fourier transform IR study Part I. Oxidation of SO2 on Pt electrodes with sulphur-oxygen adsorbed species

Abstract The electrochemical oxidation of aqueous SO2 at platinum electrodes has been studied in an acidic medium by means of cyclic voltammetry and in situ Fourier transform IR (FTIR) spectroscopy. In the potential zone ranging from 0.55 to 1.50 V (vs.RHE), the oxidation reaction of SO2 takes place at a Pt surface initially covered by a sulphur-oxygen adsorbate. In situ FTIR spectroscopy yields a band at 1271 cm−1, which could be assigned to adsorbed SO2. However, (bi)sulphate is detected as the only SO2 oxidation product. The generation of S(VI) species occurs during both the forward and the reverse sweeps. The different voltammetric responses obtained in each case are attributed to the oxidation of SO2 on a Pt electrode with different surface states.

Corrosion behaviour at the interface of steel bars embedded in cement slurries: effect of phenol polymer coatings

Direccion General de Ensenanza Superior e Investigacion Cientifica (PB97-0130); Generalitat Valenciana (GV-1159/93) AE97-2).

Determination by Fluorimetric Titration of the Ionization Constants of Ciprofloxacin in Solution and in the Presence of Liposomes

Abstract A fluorescence titration method was applied for the determination of pKa of ciprofloxacin (CPX) in solution. Values of 6.18 ± 0.05 and 8.76 ± 0.03 were obtained for pKa1 and pKa2, respectively. The method was used to determine the ionization constants in the presence of liposomes of dipalmitoylphosphatidylcholine (DPPC) and DPPC with 10 mol% of dipalmitoylphosphatidylglycerol. A dependence on the surface charge of liposomes was found which supported the existence of a basic electrostatic interaction between CPX and the phospholipid bilayer. Both pK values for the N-4 butyl-piperazinyl derivative (BCPX) of the parent compound were also determined in solution and in the presence of liposomes. The competition of both drugs for the same binding site as 1-anilino-8-naphtalene sulfonate demonstrate that the interaction is governed by electrostatic forces.

Evaluation of the Electrocatalytic Activity of Antimony-Doped Tin Dioxide Anodes toward the Oxidation of Phenol in Aqueous Solutions

Financial support by the Generalitat Valenciana (GRUPOS04/75 and GV05/136) and Ministerio de Ciencia y Tecnologia (MAT2004- 01479) projects are gratefully acknowledged. Universidad de Alicante assisted in meeting the publication costs of this article.

Voltammetric and in situ FTIRS study of the electrochemical oxidation of aniline from aqueous solutions buffered at pH 5

The electrochemical oxidation of aniline at low concentration was carried out in phosphate buffer solutions of pH 5. Both electrochemical and spectroscopic results indicate that during the initial stages of aniline oxidation, a dimerisation process takes place. The dimer has been identified as p-aminodiphenylamine (ADPA). No evidence supporting the formation of other dimerisation products, such as benzidine or hydrazobenzene has been found. The hydrolysis of ADPA seems to be a very slow process at pH 5 and, consequently, the formation of hydroquinone/p-benzoquinone has not been observed. ADPA is poorly soluble in aqueous medium and a part of these species precipitates on the electrode surface when formed. This precipitated dimer could act as an active centre for the further growth of the polymeric chains.

Electrochemical behaviour of aqueous sulphur dioxide at polycrystalline Pt electrodes in acidic medium. A voltammetric and in-situ FT-IR study Part II. Promoted oxidation of sulphur dioxide. Reduction of sulphur dioxide

The promoted electro-oxidation of aqueous sulphur dioxide at platinum electrodes has been studied in acidic medium with the aid of cyclic voltammetry and in-situ FT-IR spectroscopy. Promotion of SO2 oxidation is achieved when adsorbed SO2 is reduced previously to adsorbed sulphur. On a platinum surface covered by sulphur in this way, an enhancement of SO2 oxidation is attained. Spectroscopic evidence demonstrates that, like oxidation of SO2 in the oxygen adsorption region, soluble S(VI) is the ultimate reaction product of the catalysed SO2 oxidation. The electroreduction of SO2 has been dealt with by using the same techniques. Besides a surface process converting adsorbed SO2 into adsorbed sulphur, bulk SO2 reduces irreversibly giving rise to a diffusion-limited voltammetric peak. The absence of significant IR bands in the potential region at which reduction of bulk SO2 takes place, allows discarding the generation of S-H containing species. A sulphur + polysulphide mixture is suggested as the ultimate product, yet whether this mixture is formed directly in the electron-transfer step or stems from chemical decomposition of sulphur-oxygen short lifetime intermediates is not clear. Reduction of SO2 leads to a progressive accumulation of sulphur on the platinum surface. An excess of adsorbed sulphur negatively affects the kinetic stages of both oxidation and reduction of bulk SO2.

Electrochemical behaviour of amino acids on Pt(h,k,l): a voltammetric and in situ FTIR study. Part 1. Glycine on Pt(111)

Abstract A spectroelectrochemical study of the adsorption and oxidation of glycine on a Pt(111) electrode has been carried out in 0.1 M HClO4 solution. Two types of adsorbate were identified. On the one hand, strongly adsorbed cyanide which comes from the oxidative adsorption of the molecule. This adsorbate has been isolated and characterized. On the other hand reversibly adsorbed glycinate anions, which adsorb at potentials above 0.3 V, have been detected. As in the case of acetate anions, glycinate is two-fold coordinated to the Pt(111) surface through the carboxylate group. The analysis of the potential dependent band centre frequencies and integrated band intensities suggests that lateral interactions between adsorbed glycinate anions are at the origin of the small frequency shift observed with increasing potential.