Study On The Relationship Between Doping Modification And Properties Of Titanium / Aluminum Electrode

In the electrolysis industry, the electrode plays as the "heart" role. Along with the development of electrochemical and hydrometallurgical industry, the requirements of the electrode materials continue to increase. Now the graphite, lead and lead-based alloys, titanium, platinum group metals and metal oxides are commonly used. Lead electrode is widely used because of its good performance and economy. However, There are some lacks of it such as high oxygen evolution potential, poor electrical conductivity and poor mechanical properties, the anode can dissolve easily and pollute the electrolyte solution; titanium as the valve metal has been widely applied because of its high strength, low cost, corrosion resistance and other characteristics of the chlor-alkali industry, however, titanium has high electrode resistance and it is passivized easily. In sulfuric acid system (electro winning zinc is in acidic environment), the surface of the precious metal-oxide coating is easy to fall off, so the electrode life is short. Therefore, in order to overcome these shortcomings, this paper presents the design of new Ti/Al composite structure with intermediate plating layer, and dope rare earth elements in the PbO2electrode surface which can not only improve the mechanical properties, but also improve the conductivity of the electrode, reduce the oxygen evolution potential and prolong electrode life.In this study, it breaks the traditional lead dioxide electrode which only with a single titanium metal as matrix material for the electrode structure model, This design chooses Ti/Al layered composite materials instead of the traditional single base material and lead electrode material. Traditional titanium electrode use iridium, ruthenium and other precious metals as active coating,it has high electrode cost and not suitable using in sulfate system, in order to reduce costs and expand the scope of application of titanium electrode. In this study, selects the lead dioxide as electrode coating, and doped with rare earth elements. Meanwhile, choose the antimony-oxide as the intermediate layer between the base material and lead dioxide. Through by the above means can change the electrical conductivity and the cohesive force of the substrate and the coating, to improve the electro catalytic activity, lower cell voltage, to improve product quality, saving energy, reducing pollution.The interface of Ti/Al area, middle layer and the surface microstructure and phase composition of active layer has been analyzed in this study, the impact of the rare earth elements doped on the surface coating was explored.The influence mechanism, and the catalytic performance of composite electrode was investigated. From the experimental analysis point of view, with the four-probe method to test the resistance of the base material, The feature of the matrix、intermediate layer and the surface coating were tested by SEM、EDS、XRD;Analysis interface phase composition area, the middle layer and the surface of the active layer has been analyzed, the impact of the rare earth elements doped on the surface coating was explored.Finally, the electrochemical workstation was used as performance testing tools to examine the catalytic performance of the composite electrode.The main research results are as follows:(1) The resistivity of Ti/Al composite matrix prepared with thermal diffusion method is significantly lower than the Ti electrode, only a fourth of Ti; They come to be realizing metallurgical-type combination. With the proliferation temperature increases. The thickness of the diffusion layer increase, the phase turns to Ti:Al=1:1from Ti:Al=1:3; the polarization potential of the Composite-Coated Electrodes reduced by about25%at the same current density relative to Ti through voltameter(2) Add Sn-Sb to the intermediate layer improves the adhesion condition of the substrate and coating, and it can prevents the active oxygen into the surface of the electrode substrate; It was showed by XRD that the SnO2in the intermediate layer has a rutile structure, The Sb can be form N type semiconductor solid solution with TiO2; The concentration of the carrier increasing and the conductivity improves; It can be known that the sizes of the oxides in the interlayer were at Nano scale sizes, the average particle size is from5nm to6nm; and the blunt potential decrease about15%after add the intermediate layer, from2.6V～2.8V down to2.25V～2.4V, which indicate that the intermediate layer can enhance the electrode electrochemical properties.(3) Through the orthogonal experiment design, it is concluded that when the current density was at4.1A·dm-2, deposition time at2.5h, The temperature at60℃, the electroplated layer appear to the best electrochemical performance.(4) After doping rare earth, the particles on the surface of electrodes turn smaller, and the coating structure is more compact. This small compact structure can improve the micro current distribution on the surface of the coating, scatter crystal stress, reduce the coating surface crack, then improves the catalytic activity of the composite substrate. For an example, when add Yb element, the life of the electrode increase to47hours, nearly32%increased than the electrode without rare earth, the slot voltage decreased0.3v which shows that rare earth has played an important role in saving energy and reducing consumption.