Electrochemical oxidation of p-chlorophenol on SnO2-Sb2O5 based anodes for wastewater treatment

The influence of an IrO2 interlayer between the Ti substrate and the SnO2-Sb2O5 coating on the electrode service life and on the efficiency of p-chlorophenol (p-CP) oxidation for wastewater treatment has been investigated. The results have shown that if the loading of the SnO2-Sb2O5 coating relative to the IrO2 interlayer loading (gamma ratio defined by Equation 1) is high (gamma = 20-30) the service life of the electrode can be increased without modification of the ability of this electrode to perform p-CP oxidation. This suggests that the oxidation of p-CP using a Ti/IrO2/SnO2-Sb2O5 electrode with high gamma ratio (gamma > 20) occurs only through the SnO2-Sb2O5 component of the electrode, with no interference of the IrO2 interlayer. However, the electrode potential at a given current density is considerably lower in the case of the Ti/IrO2/SnO2-Sb2O5 electrode. In order to explain this decrease in electrode potential we speculate that water is firstly discharged on IrO2, which is present in small amounts on the surface, forming hydroxyl radicals at a relatively low potential. These active hydroxyl radicals then migrate (spill over) towards the SnO2-Sb2O5 coating, where they are physiosorbed and react with p-CP leading to complete combustion.