Fabrication of a stable Ti/Pb-TiOxNWs/PbO2 anode and its application in benzoquinone degradation

Abstract

To delay passivation of a titanium (Ti) substrate as well as enhance adhesion between an electrodeposited PbO2 coating and the Ti substrate, a titanium-lead composite oxide nanowire (Pb-TiOxNWs) intermediate layer was formed in situ on the surface of porous Ti by alkali etching, ion substitution, and high-temperature calcination. At the same time, Ti/PbO2 and Ti/TiO2NWs/PbO2 electrodes with porous Ti as a matrix were prepared for comparison. The surface structure and morphology of the prepared intermediate layer and the PbO2 coating were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The influences of the composite oxide intermediate layer on the electrochemical performance of the PbO2 electrode were analyzed by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and AC impedance spectroscopy (EIS). Accelerated lifetime tests were performed for electrodes with and without different intermediate layers. The results showed that PbOx was incorporated into the titanium dioxide three-dimensional network structure, resulting in formation of Pb-TiOxNWs. The surface of the Ti/Pb-TiOxNWs/PbO2 electrode was denser due to the smaller particle size of PbO2. The preferred crystal orientation of β(110) was observed for PbO2 deposited on Ti/Pb-TiOxNWs. The oxygen evolution potential reached a maximum of 2.19 V for Ti/Pb-TiOxNWs/PbO2. Accelerated life tests showed that compared with Ti/PbO2 and Ti/TiO2NWs/PbO2, the electrode life of Ti/Pb-TiOxNWs/PbO2 was increased by 91.7% and 35.3%, respectively. Therefore, it can be concluded that significantly improved morphology and electrochemical performance were achieved for titanium-based PbO2 electrodes by the addition of a Pb-TiOxNWs intermediate layer. In particular, the electrochemical stability of the PbO2 coating electrodes was improved markedly by the Pb-TiOxNWs intermediate layer. The electrodes were used for electrochemical oxidation of benzoquinone in wastewater (100 mg/L). It was found that chloride ions played a critical role in improving the current efficiency of electro-oxidative degradation. Under the same conditions, the COD removal rate in the presence of NaCl was 45% higher than in the presence of sulfate. The results of HPLC analysis of the intermediate products indicated that the oxidants electro-generated by chloride ions had stronger ring-opening and mineralization capabilities than those electro-generated by sulfate ions.