The electrochemical behavior of synthetic boron-doped diamond thin-film electrode ͑BDD͒ has been studied in acid media containing 4-chlorophenol ͑4-CP͒ by cyclic voltammetry, chronoamperometry, and bulk electrolysis. The results have shown that in the potential region of supporting electrolyte stability occur reactions involving the oxidation of 4-CP to phenoxy radical and 1,4-benzoquinone. Polymeric materials, which result in electrode fouling, are also formed in this potential region. Electrolysis at high anodic potentials, in the region of electrolyte decomposition, complex oxidation reactions can take place involving electrogenerated hydroxyl radicals, leading to the complete incineration of 4-chlorophenol. Electrode fouling is inhibited under these conditions. The experimental results have been also compared with a theoretical model. This model is based on the assumption that the rate of the anodic oxidation of 4-CP is a fast reaction. Finally, high-pressure liquid chromatographic analyses revealed that the main intermediate products of 4-CP oxidation were 1,4-benzoquinone, maleic acid, formic acid, and oxalic acid.

The chlorine evolution reaction has been studied at highly boron-doped diamond thin film electrodes. The comparison of this carbonaceous material with graphite and glassy carbon points out the similar behavior in terms of diagnostic parameters and related mechanisms, without the mechanical fragility of these materials. Tafel slopes at different chloride concentrations in solution (from 0.1 to 4 M NaCl in 0.01 M HClO 4 ) and at different pHs have been determined, together with the reaction orders with respect to Cl Ϫ and H ϩ . All measurements were carried out at a constant ionic strength. The electrode characterization has been done by means of cyclic voltammetry, showing a detailed picture for the chloride oxidation and the reduction of the evolved chlorine. Significant surface modifications occur when the electrode works as an anode for oxygen evolution, while chlorine evolution does not seem to cause severe changes. As shown by tests carried out following a method suggested in the literature, the faradaic yield for chlorine production is expected to be very high. In dilute chloride media and at neutral-weakly alkaline pH, a faradaic yield of about 65% has been found; this makes use of highly doped diamond electrodes in, e.g., seawater electrolysis, quite promising.

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. #

No abstract

No abstract