An investigation of the formation of chlorate and perchlorate during electrolysis using Pt/Ti electrodes: The effects of pH and reactive oxygen species and the results of kinetic studies

The characteristics of chlorate (ClO3−) and perchlorate (ClO4−) formation were studied during the electrolysis of water containing chloride ions (Cl−). The experiments were performed using an undivided Pt/Ti plate electrode under different pH conditions (pH 3.6, 5.5, 7.2, 8.0 and 9.0). ClO3− and ClO4− were formed during electrolysis in proportion to the Cl− concentration. The generation rates of ClO3− and ClO4− under acidic conditions (pH 3.6 and 5.5) were lower than in basic pH conditions (pH 7.2, 8.0 and 9.0). However, the pH of the solution did not influence the conversion of ClO3− to ClO4−. The effects of intermediately formed oxidants on the production of ClO3− and ClO4− were observed using sodium thiosulfate (Na2S2O3) as the active chlorine scavenger and tertiary butyl alcohol (t-BuOH) as the hydroxyl radical (OH) scavenger. The results revealed that electrolysis reactions that involved active chlorine contributed dominantly to ClO3− production. The direct oxidation reaction rate of Cl− to ClO3− was 13%. The OH species that were intermediately formed during electrolysis were also found to significantly affect ClO3− and ClO4− production. The key formation pathways of ClO3− and ClO4− were studied using kinetic model development.