| Electrowinning is the most energy-consuming part in zinc hydrometallurgy process.It will transform anode reaction from oxygen evolution reaction to hydrogen oxidation reaction（HOR）,by replacing lead-based anodes in industrial production with hydrogen diffusion anodes,which can greatly reduce the cell voltage of zinc electrowinning and bring huge economic and environmental benefits.Gas diffusion electrodes（GDE）are used as anodes in the electrolytic cell operating in a highly acidic environment for zinc electrowinning,presenting an extreme operating condition that demands higher stability for the HOR catalyst.In this thesis,titanium felt was selected as the substrate,and the Pt-metal oxide mixed coating was loaded on the titanium felt as the catalytic layer for zinc electrowinning GDE.The preparation process parameters of PtTi catalytic coating and GDE were investigated.On this basis,a PtSnTi coating with improved performance was prepared,and the performance enhancement mechanism of the PtSnTi coating was investigated.The primary research results obtained in this thesis are as follows:（1）The PtTi catalytic coating was prepared on the titanium felt substrate by dip-pyrolysis method.The effects of the type of Ti precursor type,the mass ratio of Ti and Ptelements and the pyrolysis temperature on the coating structure,as well as the HOR performance of the coating in 1.5 M sulfuric acid solution were explored.The optimal preparation parameters of the PtTi coating were determined as follows:tetrabutyl titanate was used as titanium source,chloroplatinic acid as platinum source,the mass ratio of Ptto Ti elements in the dipping solution was controlled at 1:1,and the pyrolysis temperature was 500.The PtTi coating prepared under this condition exhibited the highest HOR catalytic activity after 3000 cycles of cyclic voltammetry（CV）test.（2）Based on the PtTi coating with the best performance.a GDE with the structure of"titanium felt catalytic layer-titanium felt diffusion layer-carbon cloth diffusion layer"was prepared.The effects of the hydrophobic agent PTFE loadings and the porosity of the titanium felt diffusion layer on the cell voltage were investigated.For the selected titanium felt porosity,the lowest cell voltage for zinc electrowinning was achieved when both catalyst and diffusion layers have a PTFE loading of 3 mg PTFE cm-2.The optimized PtTi-coated GDE with a working area of 4 cm×4 cm was subjected to zinc electrowinning test for 3×16h.The average operating cell voltage was 1.237V and the average direct current unit consumption was 1059 k Wh/t zinc,which can save energy by 66.90%compared with the average consumption of about 3200 k Wh/t zinc for traditional anodes.（3）The PtSnTi coating with improved performance was prepared by dipping-pyrolysis method,and its preparation parameters were optimized.The optimum composition for PtSnTi coating was Pt:Sn:Ti=1:0.5:0.5,and the optimum pyrolysis temperature was 500.The PtSnTi-coated gas diffusion electrode with a working area of 4 cm×4 cm was subjected to zinc electrowinning test for 3×16 h,with an average cell voltage of 1.203 V and an average direct current unit consumption of 1028 k Wh/t zinc.Compared with the PtTi coated GDE,the average cell voltage was reduced by 34 m V,and compared with the unit power consumption of industrial lead-silver anode of about 3200k Wh/t zinc,the energy consumption reduced by 67.88%.A 28×8 h long-time zinc electrowinning test was carried out on the PtSnTi coated GDE in an industrial electrolyte,and the electrode still maintained excellent stability.The performance improvement mechanism of the PtSnTi coating was investigated,indicating that charge transfer occurred between Sn oxides and Ptelements in the PtSnTi coating,increasing the proportion of elemental Ptand its antioxidation ability.Simultaneously,Ptparticles formed a moderately exposed interface structure on the surface,contributing to the balance between the coating activity and stability. |
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