Effect Of Introduction Of Intermediate Layers And Addition Of Neodymium Oxide On Properties Of Ti-based Pbo2 Coated Electrodes

Electrochemical oxidation technology to deal with bio-refractory organic wastewater has been proved to be an effective and promising approach for wastewater treatment.However,the core component—anode oxidation electrodes have became a major obstacle to its practical application and extension,because its stability,efficiency and benefits can not meet the needs of the project.Lead dioxide is often deposited onto titanium using anodize deposition method as electrode material for the treatment of refractory organic wastewater because PbO₂ has some excellent characteristics such as good conductivity,excellent chemical stability,low cost,effective degradation of organic pollutant and so on.In fact,PbO₂ electrodes have some great technical advantages in preconditioning high concentration organic wastewater process while this kind of electrodes also has some defects such as poor durability,low catalytic activity,poor binding in practical applications.Some researchers have confirmed that introduction of the appropriate intermediate layers and modification by using of rare earth compounds are effective technical approaches to solve the above shortcomings.This paper aims at that it’s to improve the performance of the electrode in adding different intermediate layers by the controllable electrodeposition methods;the mechanism of deactivation of lead dioxide coated electrodes with different interlayers in sulfuric acid solution were investigated;and the effect of neodymium oxide on properties of Ti-based PbO₂ coated electrodes was studied systematically by adding ions and compounds too.The main results of the investigation are as follows:（1）The Ti/Ni/PbO₂ and the Ti/Cu-Ni/PbO₂ were prepared by introduction of a nickel-plating intermediate layer and a copper-nickel composite interlayer which theboth interlayers were sequential deposited.Compared with Ti/PbO₂ electrode,surface morphology,element composition,crystal structure,stability and catalytic performance of electrodes were characterized.Some results show that the stability of these electrodes were improved by introduction of the both intermediate layers,and the accelerated lives of these three electrodes were 36 h,30h and 26 h,respectively.The surface potential distribution and electrode’s conductivity are also improved,cell voltage and energy consumption were simultaneously reduced,and the surface potential distribution of electrodes were 1.5²V,2³V and 6⁶.5V,respectively.The per unit energy consumption of COD removal were 112kW·h/kg,139.3kW·h/kg and218.6kW·h/kg,respectively.In addition,the deposition rate of the active layer of the Ti/Ni/PbO₂ electrode was increased,the grain of the active layer was refined,the catalytic activity of the coated electrode was improved owe to introduction of a nickel intermediate layer,and the removal rates of COD reaches to 62.1% and 52.6%,respectively in simulated phenol waste water.（2）The Ti/MnO₂/PbO₂ electrodes and the Ti/α-PbO₂/PbO₂ electrodes were anodized by introduction of a MnO₂ intermediate layer and a α-PbO₂ intermediate layer,respectively.The surface morphology,element composition,crystal structure,stability and catalytic performance were analyzed.Results shows that the stability of the electrodes is improved by introduction of the α-PbO₂ inter-layers,and the accelerated lives of the both electrodes were 33 h and 26 h respectively.The surface potential distribution and electrodes conductivity is improved,the cell voltage and the energy consumption are reduced by introduction of the both intermediate layers compared with Ti/PbO₂ electrodes without intermediate layer,and the surface potential distribution of electrodes were 5.0⁵.5V,5.5⁶.0V and 6⁶.5V,respectively.The per unit energy consumption for COD removal are 146.8 kW·h/kg,171.2kW·h/kg and 218.6kW·h/kg,and the COD removal rates for simulated phenol wastewater are 54.7%,57.5% and 52.6%,respectively.（3）The oxygen deactivation process of electrodes with different interlayers were analyzed in sulfuric acid medium.Results indicate that these electrodes have similar failure characteristic that the particles of the active layer of electrodes were corroded or partially fallen out with the increase of the electrolysis time,and the equivalentelement fitting value of coated electrodes were changed significantly before and after deactivation.At the same time,it can be concluded that the compact structure,high bonding strength and good active oxygen barrier capacity of middle layers were beneficial to improve the stability of the electrode on the basis of effect study of electrodes with or without different intermediate layers.Among the four the middle layers,the comprehensive performance of the electrode with nickel plating interlayer was the best that the test life time of Ti/Ni/PbO₂ electrodes is the longest,the test life time of the Ti/Cu-Ni/PbO₂ electrode was became short because of the poor compactness and bonding of copper-nickel composite sub-layer,the compact α-PbO₂ intermediate layer structure help to increased its life time,and the electrode with a MnO₂ inter-layer reduces its life time because more cracks stem from electrocrystallization stress.（4）The PbO₂ electrodes were prepared by adding rare earth Nd³⁺ and Nd₂O₃ and the adding effect disciple was investigated.These results indicate that the electrocatalytic activity of the electrode prepared when the amount of Nd³⁺ was 50mg/L is the highest that the removal rate of COD reach to 54.56%,the degradation rate of phenol is 89.78%,and the concentration of rare earth Nd³⁺has a non monotonic effect on the electrocatalytic activity of electrodes.The Nd₂O₃ oxide was not detected in the lead dioxide electrodes prepared by adding rare earth Nd₂O₃ composite,but it has some influence on the crystallization process of PbO₂.The amount of inactive α-PbO₂ in the deposited electrode increase with increase of Nd₂O₃ adding amount that it will reduce the catalytic activity of lead dioxide electrodes,so that the removal rate of COD and the degradation rate of phenol becomes lower than that of the lead dioxide electrodes without Nd₂O₃ addition.