Formation of chlorate and perchlorate during electrochemical oxidation by Magnéli phase Ti(4)O(7) anode: inhibitory effects of coexisting constituents

Formation of chlorate (ClO(3)(−)) and perchlorate (ClO(4)(−)) as by-products in electrooxidation process has raised concern. In the present study, the formation of ClO(3)(−) and ClO(4)(−) in the presence of 1.0 mM Cl(−) on boron doped diamond (BDD) and Magneli phase titanium suboxide (Ti(4)O(7)) anodes were evaluated. The Cl(−) was transformed to ClO(3)(−) (temporal maximum 276.2 μM) in the first 0.5 h on BDD anodes with a constant current density of 10 mA cm(2), while approximately 1000 μM ClO(4)(−) was formed after 4.0 h. The formation of ClO(3)(−) on the Ti(4)O(7) anode was slower, reaching a temporary maximum of approximately 350.6 μM in 4.0 h, and the formation of ClO(4)(−) was also slower on the Ti(4)O(7) anode, taking 8.0 h to reach 780.0 μM. Compared with the BDD anode, the rate of ClO(3)(−) and ClO(4)(−) formation on the Ti(4)O(7) anode were always slower, regardless of the supporting electrolytes used in the experiments, including Na(2)SO(4), NaNO(3), Na(2)B(4)O(7), and Na(2)HPO(4). It is interesting that the formation of ClO(4)(−) during electrooxidation was largely mitigated or even eliminated, when methanol, KI, and H(2)O(2) were included in the reaction solutions. The mechanism of the inhibition on Cl(−) transformation by electrooxidation was explored.