Understanding Chlorite, Chlorate and Perchlorate Formation When Generating Hypochlorite Using Boron Doped Diamond Film Electrodes

This research used density functional theory for investigating reactions on boron doped diamond (BDD) film electrodes that contribute to unwanted byproduct formation during hypochlorite generation. Clusters containing 10 carbon atoms were used to simulate the diamond electrode surface. The simulations included reactions with hydrogen terminated surfaces, and with surface sites produced by anodic polarization, namely: ≡C*, =C*H, ≡C-O* and =CH-O*. The activation energies for oxidation of chlorine oxyanions via direct electron transfer and via reaction with hydroxyl radicals were calculated. Oxychlorine radicals (ClO*, ClO2*, ClO3*) were found to chemically adsorb to both secondary and tertiary carbon atoms on the BDD surface. These chemisorbed intermediates could react with hydroxyl radicals to regenerate the original chlorine oxyanion (ClO−, ClO2−, ClO3−), and produce ≡C-O* and =CH-O* sites on the BDD surface. The ≡C-O* and =CH-O* sites also reacted with oxychlorine radicals to form chemisorbed intermediates, which could then be converted to higher oxidation states (ClO2−, ClO3−, ClO4−) via reaction with hydroxyl radicals.