APPLICATION OF SYNTHETIC BORON-DOPED DIAMOND ELECTRODE IN ELECTROOXIDATION AND IN ELECTRO ANALYSIS

摘要

Boron-doped diamond (BDD) thin film electrodes, fabricated by chemical vapor deposition (typically from 1% CH_4 + 3 ppm trimethylboron in H_2, by the hot filament technique) on p-Si, Nb or Ti substrate, provide to electrochemists a new type of carbon electrode. A striking characteristic of polycrystalline BDD electrodes is the wide potential window for water discharge and the high anodic stability in strong acid media, compared to conventional carbon electrodes. Cyclic voltammetry, chronoamperometry and bulk electrolysis measurements have shown that in the potential region of water stability, some aromatic compounds can be oxidized directly on BDD electrode resulting in electrode fouling due to the formation of a polymeric film on its surface. However during electrolysis in the potential region of water decomposition (E>2.3 V vs SHE), indirect oxidation reactions can take place by electro-generated active intermediates, probably hydroxyl radicals, which can avoid electrode fouling. Depending on the hydrodynamic conditions, the value of applied current density and the organic concentration it is possible to obtain complete combustion of organics to CO_2 or partial oxidation to other aromatic compounds. A model is also proposed that permits to predict the evolution of chemical oxygen demand (COD) and current efficiency during the electrochemical oxidation of organic pollutants on BDD electrodes. This model is developed for an electrochemical reactor operating in a batch recirculation mode under galvanostatic conditions. A comparison with experimental data for the oxidation of different organic compounds (phenol, chloro-phenol, naphthol, pyridines, soluble polymers ...) under different experimental conditions shows good agreement. BDD electrodes has been also tested for the electroanalytical detection of phenolic compounds like 2-naphthol. Linear calibration curves have been obtained after a simple electrochemical anodic pretreatment. Finally typical examples of the potential application of BDD for the preparation of strong oxidants (Ag~(2+) in conc. HNO_3 and peroxodisulfuric acid) in electro-organic synthesis (benzoquinine and nicotinic acid) and in the electro-incineration of toxic pollutants (chlorophenol) will be presented.