Performance of sol–gel Titanium Mixed Metal Oxide electrodes for electro-catalytic oxidation of phenol

Mixed metal oxides SnO₂–RuO₂–IrO₂, Ta₂O₅–IrO₂ and RhO₂–IrO₂ were immobilised on a Ti substrate using sol–gel techniques. The Ti mixed metal oxides were characterized in terms of morphology using scanning electron microscopy. Cyclic voltammetric responses of phenol at Ti/SnO₂–RuO₂–IrO₂, Ti/Ta₂O₅–IrO₂ and Ti/RhO₂–IrO₂ electrodes were evaluated and showed significantly low potentials for Ti/Ta₂O₅–IrO₂ (+100 mV), Ti/SnO₂–RuO₂–IrO₂ (+200 mV) and Ti/RhO₂–IrO₂ (−100 mV). The degradation of phenol in aqueous solution and its intermediates were investigated by bulk electrolysis and quantitatively assessed by HPLC analysis to elucidate the decomposition pathways and to develop a kinetic model for the electro-catalytic oxidation of phenol over Ti mixed metal oxides. Ring compounds, benzoquinone/hydroquinone, catechol, and short chain organics, carboxylic acids, have been identified as intermediate products for the electro-catalytic oxidation of phenol. Fundamental kinetic data were obtained for the conversion of phenol at these electrodes and was found to proceed in accordance with the pseudo-first-order kinetics with respect to the phenol concentration.