M. Panizza and G. Cerisola
Electrochemical oxidation of 2-naphthol with in situ electrogenerated active chlorine
Electrochimica Acta 48 (2003) 1515-1519

ABSTRACT
The electrochemical oxidation of 2-naphthol mediated by active chlorine electrogenerated in situ on a Ti-Ru-Sn ternary oxide has been studied by galvanostatic electrolysis under different experimental conditions. Measurements of chemical oxygen demand (COD), HPLC and GC analyses have been used to follow the oxidation. In the absence of NaCl, only a small fraction of 2-naphthol was oxidized by direct electrolysis, while its complete mineralization was obtained in the case of chlorine-mediated electrolysis. In particular, the rate of naphthol oxidation was found to increase with chloride concentration, pH and to be independent of current density. Analysis of oxidation product has shown that initially organochlorinated compounds have been formed which have been further completely oxidized.

L. Ouattara, T. Diaco, I. Duo, M. Panizza, G. Foti, and Ch. Comninellis
Dimensionally Stable Anode-Type Anode Based on Conductive p-Silicon Substrate
Journal of The Electrochemical Society 150 (2003) D41-D45

ABSTRACT
In the search for a good dimensionally stable anode-type electrode, p-silicon (1-3 mohm cm) has been chosen as the substrate material due to its high anodic stability and its reasonable cost compared to titanium and tantalum. Several p-Si/IrO₂ electrodes have been prepared by thermal decomposition at different temperature. The effect of preparation temperature on the morphological and electrochemical properties has been investigated by scanning electron microscopy analysis, X-ray diffraction, and cyclic voltammetries in 1 M HClO₄ showing that p-Si/IrO₂ prepared at 450°C presents a high surface area and a low degree of crystallinity, while increasing the calcination temperature resulted in a decrease of true area and an increase in crystallite size. The activity of p-Si/IrO₂ electrodes for simple electron transfer reactions and for complex electrode reactions has been also studied by cyclic voltammetry and linear polarization in solutions containing the hydroquinone/benzoquinone redox couple and various organic compounds (isopropanol, tert-butanol, methanol). Finally, the anodic stability of a p-Si/IrO₂ electrodes prepared at 450°C has been tested by an accelerated service life test. p-Silicon based electrodes were shown to have the highest standardized service life compared with that of titanium- or tantalum-based electrodes.

M. Panizza, L. Ouattara, E. Baranova and Ch. Comninellis
DSA-type anode based on conductive porous p-silicon substrate
Electrochemistry Communications 5 (2003) 365-368

ABSTRACT
Porous silicon (PS) thin films have been prepared by electrochemical anodization of p-Si in HF–H₂O–EtOH solution and they have been used as substrate material for the preparation of iridium oxide based electrodes (PS/IrO₂) using the thermal decomposition technique. The morphology and the electrochemical behaviour of the PS/IrO₂ have been studied and the results have been compared with IrO₂ electrodes deposited on a sandblasted p-silicon (p-Si/IrO₂). SEM analyses have revealed that the PS/IrO₂ electrodes are porous, rough and IrO₂ appears to be deposited within some silicon pores, while the p-Si/IrO₂ present a `mud-cracked' surface. Cyclic voltammetries in 1 M HClO₄ have shown that the PS/IrO₂ presents higher surface area than p-Si/IrO₂.

M. Panizza and G. Cerisola
Influence of anode material on the electrochemical oxidation of 2-naphthol. Part 1: Cyclic voltammetry and potential step experiments
Electrochimica Acta 48 (2003) 3491-3497

ABSTRACT
The anodic oxidation of 2-naphthol has been studied by cyclic voltammetry and chronoamperometry, using a range of electrode materials such as Ti-Ru-Sn ternary oxide, lead dioxide and boron-doped diamond anodes. The results show that polymeric films, which cause electrode fouling, are formed during oxidation in the potential region of supporting electrolyte stability. IR spectroscopy verified the formation of this organic film. While the Ti-Ru-Sn ternary oxide surface cannot be reactivated, PbO₂ and boron-doped diamond can be restored to their initial activity by simple anodic treatment in the potential region of electrolyte decomposition. In fact, during the polarization in this region, complex oxidation reactions leading to the complete incineration of polymeric materials can take place on these electrodes due to electrogenerated hydroxyl radicals. Moreover, it was found that boron-doped diamond deactivation was less pronounced and its reactivation was faster than that of the other electrodes.

1. P.-A. Michaud, M. Panizza, L. Ouattara, T. Diaco, G. Foti and Ch. Comninellis
Electrochemical oxidation of water on synthetic boron-doped diamond thin film anodes
Journal of Applied Electrochemistry 33 (2003) 151-154

ABSTRACT
Electrolysis in aqueous 1M HClO₄ and 1M H₂SO₄ solutions has been carried out under galvanostatic conditions using boron-doped diamond electrodes (BDD). Analyses of the oxidation products have shown that in 1M HClO₄ the main reaction is oxygen evolution, while in H₂SO₄ the main reaction is the formation of H₂S₂O₈. In both electrolytes small amounts of O₃ and H₂O₂ are formed. The accelerated service-life test at high anodic current density (1A cm-2) showed that diamond is consumed during anodic polarisation. A mechanism involving hydroxyl radicals and CO₂ formation has been proposed to explain the anodic corrosion of BDD. A simplified mechanism for water oxidation on boron-doped diamond is also proposed.

G. Siné, L. Ouattara, M. Panizza and Ch. Comninellis
Electrochemical behaviour of fluorinated boron-doped diamond
Electrochemical and Solid State Letters 6 (2003) D9-D11

ABSTRACT
The surface properties and the electrochemical behavior of a fluorinated boron-doped diamond (F-BDD) electrode prepared by plasma treatment in CF4-He mixture has been studied by X-ray photoelectron spectroscopy and cyclic voltammetry in acidic media. The results have shown the presence of carbon-fluorine bonding (C—CF and C—F) on the surface of F-BDD, which made the surface more hydrophobic. It was also found that hydrogen evolution was shifted to more cathodic potentials for fluorinated diamond, as compared with untreated BDD. Finally, the higher cathodic overpotential for hydrogen evolution permitted nickel deposition and nitrate reduction.

M. Panizza, G. Siné, I. Duo, L. Ouattara and Ch. Comninellis
Electrochemical polishing of boron-doped diamond in organic media
Electrochemical and Solid State Letters 6 (2003) D17-D19

ABSTRACT
The electropolishing of a boron-doped diamond ~BDD! film deposited by chemical vapor deposition has been studied in acetic acid-H2SO4 media. The electropolished surface has been characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. The results have shown that in 1 M H2SO4 no polishing of the surface occurred even after prolonged time; on the contrary, in electrolyte containing 3 M acetic acid in 1 M H2SO4 the morphology changed rapidly. The surface became smoother and the roughness decreased as the typical results of a polishing process. All the non-diamond impurities were also removed by the electropolishing treatment in acetic acid media.

M. Panizza, G. Cerisola
A comparative study on direct and indirect electrochemical oxidation of polyaromatic compounds
Annali di Chimica, Journal of Analytical and Environmental Chemistry 93 (2003) 977-984

ABSTRACT
This study has been performed to investigate the treatment of an industrial wastewater containing naphthalene- and anthraquinone-sulfonic acids, by direct and indirect electrolyses. The direct electrochemical oxidation has been carried out using boron-doped diamond and lead dioxide anodes, while the indirect electrolyses has been mediated by active chlorine electrogenerated on a platinum anode, or by hydrogen peroxide electrogenerated on a graphite felt cathode. For each type of electrolyses the effects of operating parameters, such as anode material, current density, chloride concentration, ferrous ions concentrations have been also investigated. Measurements of Chemical Oxygen Demand (COD) and colour fading have been used to compare the results of different electrolyses. Experimental data showed that the complete COD and colour removals have been obtained only by direct oxidation or by active chlorine mediated electrolyses. On the contrary using electrogenerated hydrogen peroxide the solution has been presented a residual COD and colour. In particular, it found that faster oxidation rate has been obtained by direct oxidation using a boron-doped diamond anodes at low current density.