A. De Battisti

Ruthenium dioxide-based film electrodes

Oxygen evolution from acid solutions has been investigated on two kinds of RuO2-based electrodes; compact and cracked (porous) films. The kinetic study has been carried out by means of potentiostatic curves. A method is suggested to estimate the surface concentration of active sites. The reaction order with respect to active sites and the activation energy have been determined. The mechanism is shown to differ on the two kinds of film in relation to theS(site)-OH bond strength and the surface concentration of intermediates. The behaviour of films on silica glass substrates is reported for the first time.

Electrochemical Incineration of Glucose as a Model Organic Substrate. II. Role of Active Chlorine Mediation

The electrochemical incineration of glucose mediated by active chlorine in alkaline media has been studied under different elec trolysis conditions. For the sake of comparison, the electrolysis has been carried out in the presence of 1 M Na 2SO4 1 0.01 M NaOH at Pt, SnO2-Pt composite electrodes and PbO2 electrodes in the absence of sodium chloride. At the first two electrode materials, only partial oxidation could be achieved and complete mineralization was observed only at PbO 2 electrode. While the other parameters remain constant, addition of NaCl to the solution causes a sharp increase of the reactivity of glucose and its oxidat ion intermediates, toward the electrochemical incineration. At a NaCl concentration as low as 1 g dm 23 , the mediation of the incineration process by active chlorine is already significant. A maximum is achieved at [NaCl] 5 5 g dm 23 (in 0.01 M NaOH). At this sodium chloride concentration, the chemical oxygen demand of glucose solutions has been found to decrease faster, the lower the solution temperature and the higher the current density. This acceleration of the mineralization is accompanied by an increase of faradaic efficiency.

Electrochemical oxidation of trans-3,4-dihydroxycinnamic acid at PbO2 electrodes: direct electrolysis and ozone mediated reactions compared

A comparative study of the oxidative degradation of trans-3,4-dihydroxycinnamic acid was carried out using three different methods, two of which have in common the use of electrogenerated ozone as a potential oxidant: (i) direct electrolysis; (ii) external cell chemical reactions with O3; and (iii) a ‘cathodic oxidation’ in which an O2/O3 mixture is fed into the cathodic compartment containing the organic substrate; H2O2 produced reacts with ozone to yield radicals that bring about the demolition of the organic compound. The nature products formed by the direct electrochemical oxidation depends on potential. The degradation of the dihydroxy-acid is observed only at relatively high potentials, where radical oxygen species are formed in a high amount by the oxidation of water. At relatively lower potentials the process shows stirring dependence and leads essentially to one oxidation product which is adsorbed on the electrode. A comparative examination of the results, considering also the requested amount of ozone as a parameter, shows that the external cell and cathodic oxidation are the most efficient methods. This confirms our previous data on the oxidation of phenolic compounds, and the cathodic oxidation with ozone emerges as a promising approach in the abatement of pollutants.

Electrochemical treatment of bisphenol-A containing wastewaters

The effectiveness of electrochemical methods in purification of synthetic wastewaters containing bisphenol-A has been tested. The role of electrode material and electrolysis parameters have been considered. The kinetics of bisphenol oxidation have been followed using different analytical techniques and a degradation mechanism has been proposed.

Electrochemical Incineration in the Presence of Halides

The influence of different halides on electrochemical incineration of oxalic acid was studied. Experiments were initially carried outat a Pt electrode in alkaline media, in which case, in the absence of mediating effects, a slow electroxidation was observed.However, with halides, the rate of the electrochemical incineration was increased significantly, following the order F

Influence of anions on oxygen/ozone evolution on PbO2/spe and PbO2/Ti electrodes in neutral pH media

The formation of O2/O3 on PbO2 from the electrolysis of water in neutral solutions is shown here to present some analogies and some differences with respect to the same process in acid media. The electrolyte composition affects the current efficiency for O3 formation (η) and the cell potential (E) of a Membrel type electrochemical assembly. An improvement in η and a decrease in E is observed upon addition of relatively low amounts of Na2SO4 or NaClO4 in pure water. We observe no effect of NaNO3 on either parameters. In agreement with literature data in acid solutions, F− causes an increase in both η and E. The results of electrochemical kinetic investigations with electrodes of PbO2 electrodeposited on Ti confirm the above data. Current—potential curves constructed from measurements in NaNO3 show a region of Tafel linearity with slopes of 2RT/F and RT/F in the low and high currents range, respectively. Addition of Na2SO4 and NaClO4 to NaNO3 has an effect on the process at more positive potentials only: the RT/F slope decreases toward a value of RT/2F as the concentration of the “foreign” salt is increased. As an explanation of the observed behaviour, the possibility is advanced that a step following the discharge of water is rate determining at high positive potentials with the adsorption of intermediates described by Temkin conditions. The composition of the electrolyte is expected to influence the yield of ozone formation by affecting the coverage and free energy of adsorbed oxygen intermediates.

Adsorption of butyronitrile at the Hg/aqueous solution interface: Evidence for field dependent solvent-adsorbate surface interaction

Abstract The adsorption of butyronitrile from aqueous solutions of not specifically adsorbed electrolytes on a polarized Hg electrode has been studied by means of electrocapillary and capacity measurements. Adsorption has been found to follow a Frumkin isotherm with particle-particle attraction decreasing as the charge becomes more positive than the value of maximum adsorption. Explanation is given in terms of solvent-adsorbate surface interaction being a function of the interfacial electric field. Results are compared with two limiting electrical models for the adsorption layer. The latter is shown to be probably best described by a transition between the two models as the electric field is changed from negative to positive values. Qualitative discussion is also given in terms of Mohilners surface solution. Conclusions as drawn from the latter are shown not to differ from those obtainable from the experimental results being treated in terms of Frumkins isotherm.

Electrochemical oxidation of oxalic acid in the presence of halides at boron doped diamond electrode

Aim of this work is to discuss the electrochemical oxidation of oxalic acid (OA), analyzing the influence of NaCl and NaBr. Experiments were carried out at boron-doped diamond (BDD) electrodes, in alkaline media. BDD electrodes have a poor superficial adsorptivity so their great stability toward oxidation allows the reaction to take place with reactants and intermediates in a non-adsorbed state. The process is significantly accelerated by the presence of a halogen salt in solution; interestingly, the mediated process does not depend on applied current density. Based on the results, bromide was selected as a suitable mediator during OA oxidation at BDD. Br- primarily acts in the volume of the solution, with the formation of strong oxidants; while Cl- action has shown lower improvements in the OA oxidation rate at BDD respect to the results reported using Pt electrode. Finally, the parameters of removal efficiency and energy consumption for the electrochemical incineration of OA were calculated.

Influence of the Valve Metal Oxide on the Properties of Ruthenium Based Mixed Oxide Electrodes II . Coatings

Depth profiling of RuO{sub 2}/TiO{sub 2} mixed oxide coatings supported on titanium foil, was performed by means of Rutherford backscattering spectrometry and x-ray photoelectron spectroscopy. Results of the two techniques indicate the occurrence of surface segregation of the valve-metal oxide and a general enrichment with it across the first 100-150 nm. The segregation phenomenon takes place for all of the coating compositions investigated. However, it seems less pronounced for Ru contents higher than 60/ac. The nature of the ruthenium salt used in the coating preparation seems to affect the extent of the surface enrichment.

Influence of the valve metal oxide on the properties of ruthenium based mixed oxide electrodes: Part I. Titanium supported RuO2/Ta2O5 layers

Abstract RuO2/Ta2O5 mixed oxide electrodes have been investigated by XPS-AES techniques and X-ray diffractometry and their electrochemical behaviour for the oxygen evolution reaction has been studied. The surface analysis indicated a relative insensitivity of the surface composition to the changes of the Ru/Ta ratio in the bulk of the coatings. The diffractometric study showed the existence of a RuO2 rutile phase and a Ta2O5 amorphous phase in the electrode materials. no evidence for solid solutions was found. The influence of the noble metal concentration in the coatings on their catalytic activity has been studied for different oxide loadings. Maxima of Activity for a Ru/Ta atom ratio close to 1 have been found for coating thicknesses of 1 μm. Thicker layers exhibit an activity increasing with the noble metal content. The correlation between anodic charge density, q*, and current density, i, for the oxygen evolution reaction has been tested and definite trends related to the morphology of the electrode material have been assessed.