Deactivation and regeneration of Pt anodes for the electro-oxidation of phenol

Electro-oxidation tests with different electrolytes (Na₂SO ₄ NaCl H₂SO₄) and anode types (Pt Ti lined with Ir and Ta oxides PbO₂ activated carbon) were performed on aqueous solutions containing phenol to assess the mechanism and nature of electrode deactivation phenomena. For the Pt electrode the nature of the electro-deposited organic species was investigated by ATR-FTIR and FESEM-EDS analyses which showed adsorption of intermediate oxidation products (e.g. benzoquinone hydroquinone) is likely responsible for the early deactivation stages. Conversely in the longer term formation of polymeric films is promoted. Potentiostatic tests showed that anode regeneration can be achieved by anodic polarisation above 1.1 V (vs Hg/Hg₂SO₄). This reactivation was found to be easier in the presence of significant amounts of chloride ions. Conversely the deactivated state is maintained for the Ti/IrO ₂/Ta₂O₅ electrode even though anodic polarisation at high positive potentials is applied. Cyclic voltammetric curves on PbO₂ electrodes did not provide satisfactory results as the intensity of the lead-dioxide reduction peak was so high that peaks for phenol oxidation were hardly detectable. Finally the activated carbon based electrode was found to be promising as it enables simultaneous adsorption of the organic pollutant and oxidation of the pollutant itself to constitute a sort of self-regenerating adsorber unit.