Can the substrate of the diamond anodes influence on the performance of the electrosynthesis of oxidants?

This work is focused on the evaluation of the performance of bulk electrosynthesis of chlorine oxoanions and peroxodisulfate with diamond electrodes, made with the same conductive-diamond coating deposited on three different substrates (niobium, tantalum and silicon). Results point out an important influence of the substrate on the efficiency of the processes. The diamond coatings on tantalum substrate lead to higher concentrations of hypochlorite and perchlorate from the electrolysis of synthetic brines. Specifically, the most remarkable influence has been observed at 1500 A m−2. This can be attributed to a production of large amounts of hydroxyl radicals which significantly contribute to the generation of hypochlorite and perchlorate by mediated oxidation of chloride and hypochlorite, respectively. On the contrary, the electrochemical production of peroxodisulfate is favored when using silicon as diamond substrate, as well at current densities higher than 1000 A m−2. Although the formation of peroxodisulfate depends on the production of hydroxyl radicals, this better performance of silicon (and even niobium) can be related to the decomposition of peroxodisulfate by means of its reaction with the excessively high concentrations of hydroxyl radicals produced with diamond coatings deposited on tantalum. These results are of extreme significance for the tailoring of electrodes for specific applications, because they demonstrate that the boron doping and the sp3/sp2 ratios are not the only inputs to be considered