MnO₂ And CNTs Enhance The Electrodeposition Preparation And Electrochemical Characteristics Of PbO₂ Composite Anode

At present,Pb-?0.5-1.0wt%?Ag alloy is widely used as anode in zinc electrowinning process,but there are still some problems objectively,such as weak electrocatalytic activity for oxygen evolution,high energy consumption,poor corrosion resistance and low mechanical strength.Lead dioxide?PbO₂?,as an inert metal oxide with metal conductivity,has high electrocatalytic activity,good conductivity and strong corrosion resistance,which can well meet the requirements of strong corrosive sulfuric acid medium in zinc electrowinning industry and is a kind of anode material for non-ferrous metal electrowinning with important exploration and research value.In this paper,a controllable composite anode of?-PbO₂,active particles MnO₂ and CNTs dispersively doped?-PbO₂ were prepared on the surface of Pb-0.6wt%Sb?PS?by anodic composite electrodeposition technology.The synergistic effect of matrix metal oxides and second-phase active particles were fully utilized to improve the electrocatalytic activity of oxygen evolution,reduce DC power consumption and prolong the service life of zinc electrowinning process.The research contents are supported by the National Natural Science Foundation of China and the Key Projects of Yunnan Science and Technology Program.Firstly,the kinetics of electrodeposition of PbO₂ in lead mesylate-methanesulfonate system was studied by hydrodynamic voltammetry with rotating disc electrode.Reaction rate constants and diffusion coefficients of PbO₂ electrodeposition were determined by Levich equationi_L?28?.062nFAD₀^2/3v^-1/6w^1/2C₀^*.It was found that the electrodeposition of PbO₂ was obviously reversible,and the reaction was controlled by the mixture of diffusion and electrochemical processes.The reaction rate constant of PbO₂ increased first and then decreased with the concentration increase of Pb???,methanesulfonic acid and solution temperature.The concentration increase of Pb???,methanesulfonic acid diffused the Pb???in solution to the surface of disc electrode and reduced the diffusion coefficient,while increasing the solution temperature will increase the diffusion coefficient.Under different conditions,the prepared PbO₂ on the surface of disc electrodes is mainly?-PbO₂,with a small amount of cubic?-PbO₂.Raising the solution temperature is conducive to promoting the formation of?-PbO₂.Secondly,????-PbO₂ deposits were prepared on PS substrates in methanesulfonic acid system by anodic composite electrodeposition.The effects of Pb???concentration,M methanesulfonic acid concentration,current density and solution temperature on the electrocatalytic activity,corrosion characteristics,crystal structure and surface microstructure of PS/PbO₂ composite anodes in simulated zinc electrowinning solution were investigated.Current density and solution temperature separately determine the electron transfer and diffusion process of PbO₂ electrodeposition reaction on PS substrate surface and affect its growth rate and nucleation rate,resulting in the difference of crystal structure between?-PbO₂ and?-PbO₂.The deposition layer prepared at 25?solution temperature is mainly?-PbO₂ crystal,with the highest microhardness of 426.2 Hv.Increasing solution temperature is conducive to the transformation of metastable?-PbO₂crystal form to?-PbO₂ crystal form and the direct deposition and growth of?-PbO₂crystal form.The deposit layer prepared at solution temperature of 60?is mainly?-PbO₂ crystal form.Corresponding composite anode has the best reversibility(i⁰:9.128×10^-88 A·cm^-2),best corrosion resistance(i_corr:3.76×10^-44 A·cm^-2)and best electrocatalytic activity of oxygen evolution in simulated zinc electrowinning solution.Its anodic oxygen evolution overpotentials at 300 A·m^-2?400 A·m^-2?500 A·m^-22 current densities were 0.844 V,0.907 V and 0.928 V,respectively.Thirdly,after the deposition of?-PbO₂ on PS substrate,the dispersive doped?-PbO₂with MnO₂ and CNTs was prepared by anodic composite electrodeposition in methanesulfonic acid system.For grinding of MnO₂ active particles and surface active treatment of CNTs,the particle size was reduced by ultrasonic cavitation effect in 30minutes,Zeta potential on the particle surface was increased and uniform distribution of particles in electrolyte was promoted.The mechanism of modification of co-deposition of MnO₂ and?-PbO₂ was that MnO₂ was on the grain boundary of?-PbO₂.After adsorption,it was gradually coated by new nucleation and growth of?-PbO₂.The modification mechanism of the co-deposition of CNTs and?-PbO₂ is to provide reaction nucleation active sites for the deposition reaction after CNTs adsorbed on the surface of?-PbO₂,accelerating heterogeneous nucleation rate,making the nucleation and growth of?-PbO₂around the edge of CNTs,and forming a staggered spatial network structure by using lead dioxide and active particles themselves.After which the grain gap of deposit layer is filled,grain size is refined and structure is more compact and uniform.When MnO₂ and CNTs were dispersed and embedded in?-PbO₂,the electrocatalytic activity of the corresponding composite anode decreased to 0.613 V,0.677 V and 0.693 V at 300 A·m^-2?400 A·m^-2?500 A·m^-22 current densities respectively.At the same time,the corrosion potential increases,the corrosion current density decreases and the corrosion resistance increases.Finally,six PS/?-PbO₂/?-PbO₂-MnO₂?CNTs?composite anodes with different deposition time of????-PbO₂ were prepared by precisely controlling the solution temperature.The electrochemical characteristics and current efficiency,direct current consumption,cell voltage and corrosion life of the new anodes before and after 8 days electrowinning in simulated zinc electrowinning solution were systematically studied.The composite anode with long deposition time of?-PbO₂ dioxide has stronger corrosion resistance,and the composite anode with long deposition time of?-PbO₂ has lower oxygen evolution potential and higher electrocatalytic activity.After 8 days of electrowinning,the electrocatalytic activity of the composite anode with long deposition time of?-PbO₂ film on the surface of the new type anode has been further improved in a shorter electrowinning time.Compared with Pb-0.8wt%Ag alloy,the current efficiency,cell voltage and direct current consumption of the composite anode with optimum performance increased by 2.1%,299 mV and 323.54 kWt/?t.Zn?after 8 days electrowinning in simulated zinc electrowinning solution.In addition,the service life of new type of anode was 68.2 h at 20000 A·m^-22 high current density and estimated service life was 109120 h at 500 A·m^-22 normal current density.