Investigation of the influence of the anode composition of DSA-type electrodes on the electrocatalytic oxidation of phenol in neutral medium

Abstract

In this paper, phenol oxidation was used as a probe reaction to carry out a systematic investigation of the electrocatalytic activity of DSA-type anodes with nominal compositions equal to Ti/Ru0.3M0.7O 2 and Ti/Ir0.7M0.3O2 (M = Ti and Sn) in 1.0 mol L-1 NaClO4. Under CV conditions, phenol oxidation favors polymerization that completely blocks the electrode activity after few cycles independently of the anode material. The following intrinsic catalytic efficiency was observed under CV conditions: Ti/Ru 0.3Ti0.7O2 ≫Ti/Ru0.3Sn 0.7O2 > Ti/Ir0.7Ti0.3O 2 > Ti/Ir0.7Sn0.3O2. However, electrolysis experiments (i = 40/80 mA cm-2) run in laboratory-scale showed that the proper choice of anode material can improve the yields of CO2 as final product. HPLC and TOC techniques were used in order to quantity the electrode efficiency. It is important to emphasize that all anodes presented good ability to oxidize the phenolic portion, and a TOC reduction as high as 80% was observed for the Ti/ Ru0.3Ti0.7O 2 electrode. Benzoquinone formed in the beginning of the electrolysis is continuously oxidized as the reaction proceeds. Malic, tartaric and malonic acids were also identified as other by-products of phenol oxidation.