Preparation And Electrochemical Properties Of Al / Pb / Pb0 -Mn0 ₂ Composite Anode Materials

The Pb-Ag(0.5%-1.0%) and Pb-Ag(0.2%-0.3%)-Ca(0.06%-0.1%) anode materials has been widely used in zinc electrowinning industry at present. However, these materials have some defects, such as high oxygen evolution overpotential, large density makes difficult to assemble, high consumption of silver. For the past few years, the lead dioxide electrode has attracted many attentions of the researchers because of its good corrosion resistance and electrical conductivity. But the oxygen evolution overpotential of lead dioxide electrode is high. Some researchers put forward some new type of modified lead dioxide anode aiming at reducing oxygen evolution overpotential, and reducing the energy consumption of zinc electrowinning process.The Al/Pb-WC-Ce02/Pb02-Mn02-Ce02 inert anode materials were prepared by pulse composite electrodeposition. The relationship between prepare conditions and electrochemical properties of electrode were studied, exploring the oxygen evolution reaction mechanism and corrosion behavior of electrode in zinc electrolyte through kinds of electrochemical measurement, such as anodic polarization curves, electrochemical impedance spectroscopy (EIS) and Tafel curves. The optimal preparation conditions determined by single factor experiment were:Mn(NO3)2 30 g·L-1, current density 125 mA·cm-2, temperature 50-60℃, CeO240 g·L-1, pulse work time 400 ms.A proper amount of MnO2 in coating can reduce the oxygen evolution overpotential of electrode. CeO2 in coating can refine grains and improve the amount of active point. The tafel slope b values of electrode were greater than 0.12 V, which indicated that the oxygen evolution process of electrode was controlled by the formation and adsorption of intermediate product (S-OHads).From EIS under open circuit potential (OCP), the corrosion behavior of anode materials were controlled by charge transfer resistance and the diffusion process of corrosion products, together.The deposition process of anode were studied through cyclic voltammetry method.The results showed that the Pb(Ⅱ) in acidic solution combined with hydroxyl radicals forming a new active intermediate, and then it was oxidized to Pb(Ⅳ). The deposition potential decreased when Pb2+ and Mn2+ were composite oxidation deposition. There was one reduction peak in reduction branch, incorporation with the XRD analysis, it showed that the crystallization of MnO2 was poor in anode materials.The cell voltage, current efficiency and electrode life of different kinds of anode were compared in simulation zinc electrolyte. The results showed that the cell voltage and current efficiency of aluminum substrate PbO2-MnO2-CeO2 is better than that of traditional Pb-Ag(0.75 wt%) anode, which illustrated that the PbO2-MnO2-CeO2 electrode had a better electrocatalytic activity. However, the results of accelerated life test showed that the corrosion resistance of PbO2-MnO2-CeO2 electrode is lower than Pb-Ag(0.75 wt%) anode for 400 h. That may be some cracks appeared on the electrode surface resulting in the degradation of electrode.