Oxydation électrochimique du phénol sur des électrodes du type métal support/dépôt conducteur
Electrochemistry can bring important contributions to current applications, such as organic synthesis or wastewater treatment. In an environmental context, electrochemical processes are interesting substitutes to the conventional wastewater treatment techniques (STEP). In this work, we have studied different types of electrodes, in order to develop a predictive model, so as to propose an electrode concept suitable for these two processes. The metal support/conducting oxide electrodes can behave in two distinct ways. The electrode can be active, and thereby directly take part to the oxidation of the organic product, or it can be inert and oxidise the organics through hydroxyl radicals produced during water electrolysis. We have studied the behavior of several electrodes, such as Ti/IrO2, Ti/CoMn204, Ti/SnO2-Sb2O5, Ti/PbO2, Pb/PbO2, Ti/PbO2-Bi2O5, Ti/IrO2/PbO2 and Pt (massive electrode) during electrochemical oxidation processes. The analysis of the formation of hydroxyl radicals showed a strong •OH formation for inert electrodes (PbO2, PbO2-Bi2O5, SnO2-Sb2O5), whereas the •OH formation was lower in case of active electrodes (IrO2, Pt). The electrochemical oxidation of phenol allowed us to show the efficiency and the features of two different types of electrodes. Ti/IrO2 selectively oxidises phenol into intermediate products, where Pb/PbO2 leads to total oxidation (combustion) of phenol to CO2. Finally, the formation of a polymer film at the surface of the electrodes was clearly shown by cyclic voltametry and oxygen evolution measurements. This film was shown to have a passivation effect on the Ti/CoMn2O4 electrode, and lead to a considerable decrease of its efficiency.