Effect of the operating conditions on the oxidation mechanisms in conductive-diamond electrolyses

The electrochemical window of conductive-diamond electrodes is large enough to produce hydroxyl radicals with high efficiency, and this species seems to be directly involved in the oxidation mechanisms that occur on diamond surfaces. To verify the role of these radicals in the conductive-diamond electrolyses of organic and inorganic aqueous solutions, several experiments were carried using two well-known processes, which were selected as models: the electrosynthesis of peroxodiphosphate and the treatment of phenolic wastes in sulfate supporting media. Results show that there is an abrupt change in the efficiencies and product conversions of the processes with the anodic potential, although there is no change in the nature of the reaction intermediates or final products. Working at high anodic potentials led to very efficient processes in both cases. The changes observed have been interpreted in terms of the oxidation mechanisms involved in the process, taking into account the contribution of hydroxyl radicals for higher potentials and the formation of stable oxidants through the oxidation of the electrolyte by these radicals. (c) 2007 The Electrochemical Society.