Mechanism of Perchlorate Formation on Boron-Doped Diamond Film Anodes

This research investigated the mechanism of perchlorate (ClO4-) formation from chlorate (ClO3-) on boron-doped diamond (BDD) film anodes by use of a rotating disk electrode reactor. Rates of ClO4- formation were determined as functions of the electrode potential (2.29-2.70 V/standard hydrogen electrode, SHE) and temperature (10-40 degrees C). At all applied potentials and a ClO3- concentration of 1 mM, concentration. Experimental and density functional theory (DFT) ClO4- production rates were zeroth-order with respect to ClO4- results indicate that ClO3- oxidation proceeds via a combination of direct electron transfer and hydroxyl radical oxidation with a measured apparent activation energy of 6.9 +/- 1.8 kJ.mol(-1) at a potential of 2.60 V/SHE. DFT simulations indicate that the ClO4- formation mechanism involves direct oxidation of ClO3- at the BDD surface to form ClO3 center dot, which becomes activationless at potentials > 0.76 V/SHE. Perchloric acid is then formed via the activationless homogeneous reaction between ClO3 center dot; and OH center dot in the diffuse layer next to the BDD surface. DFT simulations also indicate that the reduction of ClO3 center dot can occur at radical sites on the BDD surface to form ClO3- and ClO2, which limits the overall rate of ClO4- formation.