Study Of Zn/Fe Redox Flow Battery

Global warming is a serious threat to the survival and development of human society.Only by vigorously developing and utilizing new energy sources such as solar energy and wind energy can the climate be prevented from continuing to warm.However,new energy utilization requires reliable energy storage devices.Among all kinds of energy storage technologies,the redox flow battery has attracted wide attention because of its unique advantages.The Zn/Fe flow battery is rich in resouces and is advantages to reduce the cost.This paper mainly studies the performance of zinc negative electrode,iron positive electrode and Zn/Fe whole battery,the specific content is as follows:The thermodynamics and kinetics of Zn/Zn²⁺anode were studied.The effects of various ionic liquids,electrolyte flow rates and current density on the morphology of cathode zinc were investigated.At the same concentration,the open circuit potential of zinc sulfate is greater than that of zinc chloride.In general,the open circuit potential of both increases with the increase of zinc ion concentration.The diffusion coefficient of zinc ion in 0.04 mol L^-1 Zn Cl₂+2 mol L^-1Na Cl solution is 6.96×10^-6cm²s^-1.The exchange current density of the Zn/Zn²⁺electrode process is 8.9×10^-3A cm^-2.The standard rate constant is 9.2×10^-4cm s^-1.The test of zinc symmetric battery showed that the surface of the original zinc sheet became rough after the battery cycle,and its microstructure was related to many factors,including electrolyte flow rate,electrolyte composition and current density.The thermodynamics and kinetics of iron positive electrode are studied.The supporting medium will affect the Fe²⁺/Fe³⁺form potential,which is greater in ammonium chloride solution than in ammonium sulfate.In addition,the coordination reaction will affect the formal potential of the Fe²⁺/Fe³⁺form potential.For example,the formal potential of Fe（CN）₆^3-/Fe（CN）₆^4-decreases relative to that of Fe²⁺/Fe³⁺,and Fe（bpy）₃³⁺/Fe（bpy）₃²⁺gets bigger.In 0.002 mol L^-1 Fe SO₄+0.001mol L^-1 Fe₂（SO₄）₃+0.25 mol L^-1 H₂SO₄ solution,the diffusion coefficients of Fe³⁺and Fe²⁺are6.92×10^-6cm²s^-1and 9.18×10^-6cm²s^-1 respectively.In 0.01 mol L^-1 K₃（CN）₆+0.01 mol L^-1K₄（CN）₆+1 mol L^-1 KCl solution,the diffusion coefficients of Fe（CN）₆^4-and Fe（CN）₆^3-are3.68×10^-6cm²s^-1and 2.16×10^-6cm²s^-1respectively.In the solution of 0.025 mol L^-1Fe（Bpy）Cl₃+0.025 mol L^-1 Fe（Bpy）Cl₂+0.1 mol L^-1 H₂SO₄+1 mol L^-1 Na₂SO₄,the diffusion coefficients of Fe（bpy）₃²⁺and Fe（bpy）₃³⁺are 2.12×10^-6cm²s^-1and 1.12×10^-6cm²s^-1 respectively.The standard rate constants of Fe（bpy）₃³⁺/Fe（bpy）₃²⁺,Fe（CN）₆^3-/Fe（CN）₆^4-and Fe³⁺/Fe²⁺on the platinum-plate electrode at 300 K were measured as 4.56×10^-4cm s^-1,5.02×10^-4cm s^-1and 4.47×10^-4cm s^-1 respectively.The performance of zinc-iron battery was studied.The performance of neutral zinc negative battery and bipyridine iron positive battery was investigated.The performance of the battery combined with alkaline zinc cathode and Fe（CN）₆^3-/Fe（CN）₆^4-positive electrode was investigated.Due to the large pore size（25 microns）of the CELGARD 3501 microporous membrane,it can not effectively prevent the cross contamination of positive and negative active substances,resulting in battery failure.Nafion 115 membrane can effectively prevent the cross contamination of Zn/Zn²⁺-Fe（bpy）₃Cl₂/Fe（bpy）₃Cl₃ battery active substances.Due to the large size of Fe（bpy）₃³⁺/Fe（bpy）₃²⁺ions,it is easy to cause the blockage of the membrane,which has a great impact on the long-term operation performance of the battery.Relatively,the cycle life of alkaline zinc-K₃Fe（CN）₆/K₄Fe（CN）₆ battery is better.