Sergio Ferro

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.

Characterization of IrO2-SnO2 Films Prepared by Physical Vapor Deposition at Ambient Temperature

The synthesis of thin-film electrodes of IrO2-SnO2 was carried out at room temperature by rf-magnetron sputtering, and their characterization was attained through electrochemical (cyclic voltammogram, electrochemical impedance spectrometry, polarization curves) as well as structural tests (Rutherford backscattering spectroscopy, X-ray diffraction, SEM). Further information was obtained studying the catalytic properties of films towards the chlorine evolution reaction, which has been taken into account as a model reaction. Films appear amorphous, and the fact that their density is in good agreement with the weighted average of component oxide densities may indicate that no solid solution has formed. As a result of their compact structure, coatings richer in iridium oxide do not show a high availability in electrocatalytic sites; tin oxide addition appears fundamental in terms of catalytic activity and cost of materials. The “valve metal” oxide acts as a dispersing phase for the “noble metal” oxide: the number of electroactive sites increases significantly when moving from IrO2 100xa0% to IrO2-SnO2 50:50xa0% mol, and the active material thickness increases too, reaching more than 100 active monolayers. However, a high (re)activity generally involves a high tendency to dissolution: iridium and tin sites dissolve with the same ease and, in fact, the IrO2-SnO2 50:50xa0% mol is both the most active and the less stable among the studied coatings.

Electronic structure of boron doped diamond: An x-ray spectroscopic study

The valence and conduction band electronic structure of boron-doped diamond has been measured using soft x-ray emission and absorption spectroscopy. The experimental results reveal p-type doping in the diamond film through the appearance of states in the band-gap. Structure distortion was observed around the doping center, while the long range order of the diamond structure remains. A chemically shifted C 1s level explains why one of the absorption features seems to appear below the valence band maximum. An excitonic feature was observed in the boron-doped diamond, similar to that observed in pure diamond, indicating that the exciton binding energy remains the same upon B-doping.