Investigation On Electrochemical Behavior Of Fe³⁺Ion In CaCl₂-NaCl-Fe₂O₃ Molten Salt Using Yttria Stabilized Zirconia Solid Electrolyte

Electrolyzing molten electrolyte containing iron oxide by using inert electrode can obtain iron and oxygen,which is a short green process for the production of metal iron.In order to establish a reasonable electrolysis process,it is necessary to understand the electrochemical reduction mechanism of iron ions.MgO or Y₂O₃ doped ZrO₂ is an oxygen ion conducting solid electrolyte,which has the characteristics of high oxygen ion conductivity and low electronic conductivity at high temperatures,strong anti melt erosion,and is often used together with flowing air flow to build stable O^2-|YSZ|Pt|O₂?air?reference electrode at high temperatures to carry out electrochemical study related the oxygen.However,this reference electrode is rarely used in the electrochemical basic research for the molten salt system.In this paper,a novel and simple integrated yttria stabilized zirconia?YSZ?cell with O^2-|YSZ|Pt|O₂?air?reference electrode?RE?from a YSZ tube with a closed end.The electrochemical behavior of Fe³⁺ion in the CaCl₂-NaCl eutectic salt containing dissolved Fe₂O₃ was studied by cyclic voltammetry?CV?,square wave voltammetry?SWV?,chronopotentiometry?CP?,chronoamperometry?CA?and other electrochemical techniques.The reduction mechanism of Fe³⁺ions was analysed,and the exchange electron number of electrode reaction and the Fe³⁺diffusion coefficient were calculated.The possibility of applying Zr O₂?Y₂O₃?solid electrolyte in molten salt electrochemistry basic research was discussed.It is expected to provide a simple structure,convenient use and the unified reference electrode with good stability for the study of electroactive oxide component in the molten salt.Firstly,the effects of different temperatures?1273,1323,1373 and 1393K?and Fe₂O₃concentrations?0.2%,0.5%and 1%mass fraction?on Fe³⁺electrochemical behavior on the Pt working electrode in Fe₂O₃-CaCl₂-NaCl molten salt were investigated by CV,SWV,CP,CA and other electrochemical techniques.The results show that,when doing CV and SWV analyses on the molten salt in the range of proper scanning,the peak current of Fe³⁺reduction increases with the increase in sacn rate or frequency,but the peak potential does not change,the reduction reaction of Fe³⁺to Fe on the Pt electrode is one step and diffusion controlled reversible process.The electrochemical parameters,such as the resistance of the Fe₂O₃-CaCl₂-NaCl molten salt system,the exchange electron number of the electrode reaction on the Pt electrode and the diffusion coefficient of the Fe³⁺,and so on,are obtained.It is also found the diffusion coefficient of Fe³⁺ions increases with the increase in temperature and Fe₂O₃ concentration.The diffusion activation energy of Fe³⁺ions is obtained through the Fe³⁺diffusion coefficients at 1273,1323,1373 and 1393K.Then,the electrochemical behavior of Fe³⁺on the Fe electrode and Mo electrode in0.5%Fe₂O₃-CaCl₂-NaCl molten salt was studied at 1273K by linear sweep voltammetry?LSV?,CV,SWV and EIS electrochemical techniques.It is found that the Fe electrode and the Mo electrode have poor reversibility and stability under this condition.The above results also show that it is possible to use the novel integrated electrochemical cell with O^2-|YSZ|Pt|O₂?air?as reference electrode for electrochemistry basic research under certain condition.Under choosing suitable inert working electrode,it could be expected to provide simple,convenient and stable unified reference electrode for studying the electrochemical properties of electroactive oxide components in other molten salt systems.