Synthetic Boron-doped Diamond Thin Film Research Articles

Complementary Mechanism Model for the Electrochemical Mineralization

Comninellis and his research group have elucidated a theoretical model that permits us to predict the chemical oxygen demand (COD) and instantaneous current efficiency (ICE), during the electrochemical oxidation of organic pollutants on a synthetic boron-doped diamond thin film electrodes (BDD) in a batch recirculation system under galvanostatic conditions. Several studies highlight the good correlation between theoretical predictions and empirical data, but it was noted that some data, from some experiments, were not in agreement with the theoretical model, since it achieved efficiencies above 100%. Recently, few studies have reported phenomena that occur in electrocatalytic systems which were not deducted in the first models. Thus, we emphasize that the mineralization of organic compounds on BDD electrodes involves not only hydroxyl radicals but also the molecular oxygen present in air, in saturated aqueous solutions or strong oxidants generated from simultaneous reactions. Therefore, this highlights summarizes the results reported by other electrochemists until nowadays to understand the electrochemical oxidation mechanisms. Keywords: Dissolved oxygen, Hydroxyl radicals, Complementary mechanism model, Strong oxidant species, electrochemical oxidation, galvanostatic, organic pollutants, anode, hydroxyl radicals, biodegradable

Electrochemical oxidation of water on synthetic boron-doped diamond thin film anodes

Electrolysis in aqueous 1 M HClO4 and 1 M H2SO4 solutions has been carried out under galvanostatic conditions using boron-doped diamond electrodes (BDD). Analyses of the oxidation products have shown that in 1 M 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. Finally, a simplified mechanism involving hydroxyl radicals formed by water discharge has been proposed for water oxidation on boron-doped diamond anodes.

Electrochemical oxidation of phenol at boron-doped diamond electrode

The electrochemical oxidation of phenol at synthetic boron-doped diamond thin film electrode (BDD) has been studied in acid media by cyclic voltammetry, chronoamperometry and bulk electrolysis. The results have shown that in the potential region of water stability ( E<2.3 V vs. SHE) they can occur direct electron transfer reactions on BDD surface that results in electrode fouling due to the formation of a polymeric film on its surface. While during electrolyses in the potential region of water decomposition ( E>2.3 V vs. SHE), indirect oxidation reactions can take place by electrogenerated active intermediates, probably hydroxyl radicals, which can avoid electrode fouling. Depending on the values of applied current, and phenol concentration it is possible to obtain the complete combustion of phenol to CO 2 or the partial oxidation of phenol to other aromatic compounds (benzoquinone, hydroquinone, catechol).

Anodic oxidation of 2-naphthol at boron-doped diamond electrodes

The anodic oxidation of 2-naphthol in acid media was investigated at a synthetic boron-doped diamond thin film electrode (BDD) using cyclic voltammetry and bulk electrolysis. The results have shown that in the potential region, where the supporting electrolyte is stable, reactions involving simple electron transfer, such as oxidation of 2-naphthol to naphthoxy radical and 1,4-naphthoquinone occur. Polymeric materials, which lead to electrode fouling, are also formed in this potential region. Electrolysis at high positive potentials in the region of electrolyte decomposition causes complex oxidation reactions by electrogenerated hydroxyl radicals leading to the complete incineration of 2-naphthol. 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 2-naphthol is a fast reaction and it is under diffusion control.

Electrochemical Oxidation of 4-Chlorophenol for Wastewater Treatment: Definition of Normalized Current Efficiency (ϕ)

The electrochemical behavior of lead dioxide and synthetic boron-doped diamond thin film electrodes (BDDs) has been studied in acid media containing 4-chlorophenol (4-CP) by bulk electrolysis under different experimental conditions. In order to quantify the electrochemical activity of a given electrode, for the electrochemical oxidation of organic compounds (4-CP), the current efficiency of the anodic oxidation has been normalized taking into consideration mass-transport limitations. The normalized current efficiency (ϕ) has been defined as the ratio between the current efficiency of the investigated anode to the current efficiency of an ideal anode which has a very fast oxidation rate, resulting in a complete combustion of organics to carbon dioxide. The results have shown that even if the complete combustion of 4-chlorophenol has been achieved at both lead dioxide and boron-doped diamond anodes, the latter give higher ϕ. The difference in reactivity of the electrogenerated hydroxyl radicals on the anode surface, has been proposed to explain the high ϕ values obtained using boron-doped diamond anodes. © 2001 The Electrochemical Society. All rights reserved.