Preparation Of Ti-based Oxygen Evolution Anode Based On Doping Modification And Its Application

Metallic manganese is an important raw material,which is widely used in metallurgy,chemical industry,aerospace and agriculture,etc.The production of manganese metal using electrodeposition method faces the problems of low current efficiency(65?70%)and high specific energy consumption(5600?7000 kW·h/t).Anode is one of the most important devices for manganese production.The specific energy consumption and the quality of the product of manganese production are significantly influenced by the properties of the anode.Oxygen evolution reaction(OER)occurred on the anode results in high overpotential that increases the specific energy consumption of manganese electrodeposition.Therefore,developing an anode with high electrocatalytic properties and low-cost is very important for the energy efficient electrodeposition of metallic manganese.This work aimed at improving the electrocatalytic properties and reducing the cost of the traditional Ti/IrO2 anode by doping Ru,Si and Zr.XRD,XPS,FESEM,LSV,CV and EIS measurements were performed to investigate the influence of Ru,Si,Zr on the composition,morphology and electrocatalytic properties of the oxide coating.The modification mechanism of Ru,Si and Zr for Ti/IrO2 anode was explained.The relationship between preparation condition,surface properties and electrocatalytic properties was explored.The corrosion mechanism of the anode in sulphuric acid solution was investigated.Manganese electrodeposition experiments were performed in an anion-exchange membrane electrolysis reactor using Ti-based anode.The influence of operating condition on the current efficiency,specific energy consumption,crystallization structure and morphology of Mn metal was explored.The corrosion mechanism of the electrodeposited manganese metal during the manganese electrodeposition process was investigated.The energy-saving mechanism of manganese electrodeposition using anion-exchange membrane was analyzed.The obtained results indicate that the electrocatalytic activity of the Ti/IrO2 anode increased,while the service lifetime decreased by doping Ru.The improved apparent activity can be attributed to the increased active surface area and the enhanced activity of each active site.The electrocatalytic activity and stability of the Ti/IrO2 anode improved by the appropriate addition of Si.The crystallization of the active IrO2 was promoted by doping Si,which increased the active surface area.Doping Si into the IrO2 coating decreased the activity of each active site.The improved apparent activity can be attributed to the increased active surface area.The apparent activity of the prepared Ti/IrO2-ZrO2 anode is higher than the Ti/IrO2 anode.The crystallization of the active IrO2 is influenced by the addition of Zr.With increasing Zr content of the coating,the crystalline IrO2-ZrO2 coating would transform to the amorphous structure.The electrocatalytic activity of the amorphous coating was higher than the crystalline one,but showed lower service lifetime.The active surface area increased,while the activity of each active site decreased by doping Zr.The improved apparent activity can be attributed to the increased active surface area.Based on the modification mechanism of Ru,Si and Zr,Ti/IrO2-RuO2-ZrO2 and Ti/IrO2-RuO2-SiO2 anodes were prepared.The surface morphology and electrochemical properties of these two anodes were investigated.The obtained results reveal that the electrocatalytic properties of Ti/IrO2-ZrO2 and Ti/IrO2-SiO2 were improved by doping Ru.According to the comparison of the electrocatalytic properties and the cost of Ti/IrO2,Ti/IrO2-RuO2,Ti/IrO2-SiO2,Ti/IrO2-ZrO2,Ti/IrO2-RuO2-ZrO2 and Ti/IrO2-RuO2-SiO2 anodes,the Ti/IrO2-RuO2-SiO2 anode with molar ratio of Ir:Ru:Si=9:21:70 was regarded as the best anode.Under the applied current density of 50 mA/cm2,the potential of this anode for OER was 1.33 V vs.SCE and the service lifetime was expected to be higher than 4 years.Corrosion mechanism of the Ti/IrO2-RuO2-SiO2 anode for oxygen evolution reaction in sulfuric acid solution was revealed by accelerated life tests,physical characterization and electrochemical measurements.The electrolysis process of the anode was divided into four stages,including penetration stage,stable stage,slow deactivation stage and sharp deactivation stage.The synergistic effect of the large dissolution of the active components and the localized oxidation of the Ti substrate is regarded as the main reason for the failure of the Ti/IrO2-RuO2-SiO2 anode.The relationship between preparation condition,surface properties and electrocatalytic properties of the Ti/IrO2-RuO2-SiO2 anode were investigated by the variation of the precursor concentration,calcination temperature and calcination time.The obtained results indicate that the preparation condition impacts on the crystallinity,size of the active crystal,pores and cracks of the coating,which has significant influence on the electrocatalytic properties of the anode.The electrocatalytic activity of the amorphous coating was higher,while its service lifetime was much lower than the crystalline coating.The manganese electrodeposition experimental results reveal that the current density,electrolysis time,Mn2+ concentration,(NH4)2SO4 concentration and SeO2 concentration impact on the current efficiency,specific energy consumption and the morphology of the deposited Mn metal.While,they have not influence on the crystallization structure of the deposited Mn metal.The operating condition of pH=7.5,temperature of 40?,Mn2+concentration of 30 g/L,cathode current density of 350 A/m2,(NH4)2SO4 concentration of 110 g/L and SeO2 concentration of 0.03 g/L was regarded as the best condition for manganese electrodeposition.Under this condition,the current efficiency was 78.3%and the specific energy consumption was 4346-4433 kW h/t after electrolyzing for 24 h.Compared with the traditional approach,the current efficiency increased by about 10%and the specific energy consumption decreased by about 27%.