A Study Of Ti/SnO₂-Sb/PbO₂ Electrode Passivation During The Electrochemical Oxidation

The average gross occupancy volume of water resource in our country is very poor, and the water resource was seriously polluted, the pollution of the water resource may become one of the important factors that restrict the development of our country. The electrochemical oxidative destruction of toxic and biologically refractory organic pollutants in water is a prospect method, but it is restricted by the electrode materials. In most cases, the use of anodes is found in the harsh conditions. As a practical anode material should have the electrochemical activity and good selectivity. What is more important is that it must have good chemical and electrochemical stability. In recent years, Ti/SnO2—Sb /PbO2 electrode is used as a kind of excellent electrocatalytic material in view of its good conductivity, catalytic activity, high oxygen overpotential and low price in application to wastewater treatment, but the passivation still exists on Ti/SnO2—Sb /PbO2 electrode.Electrode passivation during the electrochemical oxidation of phenol has attracted a great deal of attention. However, many researches were focused on the Pt and BDD electrode. Therefore, we have studied the electrode passivation phenomenon in sulfuric acid solution on Ti/SnO2-Sb/PbO2 for finding the activity decrease reasons in order to improve the performance of electrodes. It will be of great theoretical and practical value in biodegradable organic wastewater treatment. The interlayer of Ti/SnO2– Sb was prepared by thermal decomposition and Ti/SnO2-Sb/PbO2 electrode was prepared byelectrodeposition. Through the XRD test we found that the lead oxide electrode prepared is consistent with standard spectrogram reported in the literature.The results were as follows:1. The deactivation reasons of Ti/SnO₂-Sb /PbO₂ electrode in sulfuric acid solution: We found that Ti/SnO₂-Sb /PbO₂ are stable in the electrolysis initial period by the accelerated life test. Because the interlayers of SnO2-Sb can prevent oxygen diffusion to the electrode surface. SnO2 is a semiconductor. Its conductivity can be improved greatly by Sb-doped. SnO2 has rutile structures. The lattice sizes and cell volumes of SbxOy and SnO2 are intervenient between TiO2 and PbO2, which ease the contradictions that TiO2 and PbO2 are difficult to form a solid solution due to much difference of the lattice size and cell volume. So it improves the bonding between the titanium substrate and the active coating PbO2 and increased the electrode service life. And ICP analysis, we found that this process is accompanied by the active element of lead dioxide dissolved consumption; SEM electrode can be seen, there are peeling or stripping phenomenon. The SEM test may see the coating detachment and mechanical damage. In late electrolysis, because there are a lot of the coating cracks and the intermediate level already could not play the protection role. Electrolytes and oxygen generated proliferated to the surface, forming TiO2 insulating layer, which caused the damage activity levels of lead dioxide electrodes, the electrode was deactivated.2. The deactivation reasons of Ti/SnO2-Sb /PbO2 electrode in the presence of organic substancesThe electrocatalytic performance of Ti/SnO2-Sb/PbO2 anode was investigated during the electrochemical oxidation of phenol in H2SO4 and Na2SO4 solution by cyclic voltammetry. The results have shown that excessive hydroxyl radicals are produced on the Ti/PbO2 electrode in H2SO4 and Na2SO4 solution, which have strong oxidation properties for phenol. In a low initial concentration of phenol, phenoxy radicals can be further oxidized large quantity of adsorbed hydroxylby radicals generated on electrode to benzoquinone and other intermediate products, and finally mineralized to CO2.In a high concentration phenol, little adsorbed hydroxy radicals are generated. Polymer products are formed by electropolymerization of phenolic radicals. The polymeric film is strong adhesion to the electrode surface and consequently diminishes the electrochemically active surface area of anode leading to the decrease of active sites. On the other hand, the polymeric film prevents the phenolic radicals from approaching the surface and inhibits the further oxidation of phenol.The deactivated electrode can be reactivated to a certain extent by applying high anodic potential polarization, because the organic compounds which adsorbed on electrode surface can be oxidized by hydroxyl radical. Furthermore, evolution of sufficient oxygen could remove the organic film mechanically; with the increase of electrolysis time, the organic film can be oxidized to carboxylic acids. The anodic activity can be restored due to the gradual oxidation of organic film.The deactivated electrode can be reactivated to a certain extent by applying high anodic potential polarization, because the organic compounds which adsorbed on electrode surface can be oxidized by hydroxyl radical. Furthermore, evolution of sufficient oxygen could remove the organic film mechanically; with the increase of electrolysis time, the organic film can be oxidized to carboxylic acids. The anodic activity can be restored due to the gradual oxidation of organic film.The deactivated electrode can be reactivated to a certain extent by applying high anodic potential polarization, because the organic compounds which adsorbed on electrode surface can be oxidized by hydroxyl radical. Furthermore, evolution of sufficient oxygen could remove the organic film mechanically; with the increase of electrolysis time, the organic film can be oxidized to carboxylic acids. The anodic activity can be restored due to the gradual oxidation of organic film.X-ray photoelectron spectroscopy (XPS) confirmed the exact organic substances that adsorbed on the electrode surface, which can gradually be oxidized along with the increase of electrolysis time.In brief, Lead dioxide electrode deactivation is the result of above several kinds of factors together. But the different stage and different environment play the leading role factor...