Chlorine evolution at highly boron-doped diamond electrodes

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 HClO4) and at different pHs have been determined. together with the reaction orders with respect to Cl- and H+.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. (C) 2000 The Electrochemical Society.