Preparation Of Gas Diffusion Electrode With Pt/C Catalyst Of Low Pt Content And Its Application In Zinc Electro Winning

Zinc is one of the most widely applied non-ferrous metal.And electrowinning is currently the main method of industrial zinc hydrometallurgy.Traditional lead-silver anodes need to be improved due to problems such as high energy consumption,lead pollution,anode mud and acid fog.The hydrogen diffusion anode can catalyze the oxidation of hydrogen,thereby changing the anode reaction in the electrode process.Not only significantly reduce the cell voltage,but also can avoid the pollution caused by the dissolution of the lead anode.The research on hydrogen diffusion anode electrowinning of zinc is of great significance to reduce the energy consumption of zinc hydrometallurgy,improve the working environment,and improve the quality of zinc products.In this thesis,the hydrogen oxidation reaction catalyst under acidic conditions was prepared by the method of sodium gluconate and sodium hydroxide modification.Using carbon cloth as the current collector,the hydrogen diffusion anode was prepared,the electrowinning parameters were optimized,and the performance of the hydrogen diffusion anode was characterized.The main results obtained are as follows:First,using commercially available BP-2000 nano-carbon as a carrier and chloroplatinic acid as a platinum source,the chloroplatinate ions are complexed by adding sodium gluconate.The impregnation-thermal reduction method is adopted to make the chloroplatinate ions complexed with sodium gluconate adhere to the surface of the carrier,and a catalyst with low platinum loading was prepared.When the thermal reduction temperature is 500℃ and the molar ratio of sodium gluconate to chloroplatinic acid is 20:1,the prepared catalyst had high hydrogen oxidation reaction catalytic performance.The limiting current density of the catalyst with 5 wt%platinum loading is 3.3 mA/cm2.Further,the carbon support was modified with NaOH.The carbon carrier was etched with NaOH at high temperature,which increased the micropore volume by 2.5 times compared with that before modification.Using modified BP-2000 as a support,a catalyst with a platinum loading of 2 wt%was prepared.When the mass ratio of NaOH to carbon carrier is 1:5,the limiting current density of the catalyst obtained by reduction at 400℃ is 3.31 mA/cm2,which is equivalent to the commercial 20 wt%platinum carbon catalyst.The kinetic performance of the prepared catalyst was studied.The K-L equation obtained by fitting the linear polarization curve at different rotation speeds shows that the reaction has a number of transferred electrons close to 2.The exchange current density is 0.972 mA/cm2,and the Tafel slope is 30.7 mV dec-1,which are better than commercial platinum carbon.At 0.4 V,the mass activity is 2.502 A/mg,which is 30.9 times that of commercial platinum carbon.Transmission electron microscopy showed that the size of platinum nanoparticles supported by the catalyst was only 1.81 nm,which is considered to be the reason for the high activity of the catalyst.A new type of hydrogen diffusion anode was prepared by using carbon cloth as the current collector and the prepared low-load catalyst as the main component.The catalyst layer slurry ratio is:catalyst 0.6 g,isopropanol 15 mL,triton 0.87 mL,water 24 mL,and PTFE 1 mL.The prepared electrode has a three-layer structure of current collector-catalytic layer-current collector,with an average contact angle of 133.8°,and has appropriate hydrophilicity,hydrophobicity and conductivity.The preparation process of zinc electrowinning has been optimized.Under the conditions of electrode spacing of 2 cm,current density of 500 A/m2,sulfuric acid concentration of 150 g/L,and zinc sulfate concentration of 60 g/L,the main performance parameters are:cell voltage 1.16 V,The current efficiency is 74.62%,and the unit consumption is 1274.7 kWh/t.Based on the current industrial electrowinning zinc consumption of 3100 kWh/t,the energy saving is as high as 58.9%.The purity of the cathode product zinc is 94.2%.Not only the energy-saving effect is obvious,but the zinc purity is also improved,and the acid mist and other problems are avoided,showing a good industrial application prospect.