Design And Performance Study Of Manganese-based Complex For Redox Flow Batteries

With the improvement of science and technology and development of economy,the demand for renewable energy sources is growing rapidly.However,most renewable energy sources（e.g.,solar,wind,geothermal,etc.）need to be equipped with highly safe,low-cost and long-life energy storage as a reliable backup power source.Redox flow battery（ARFB）is considered as one of the most flexible energy storage systems due to their special structure,excellent scalability,flexibility,low-cost and decoupling properties between energy and power.In this work,we designed and developed high-potential manganese-based composite materials and Mn-MOF as the cathode of a aqueous hybrid-flow batteries（AHFBs）.The main results are listed as following:1.Ethylenediaminetetraacetic acid disodium salt（EDTA-2Na）were selected as ligands to coordinate with Mn（III）,and Mn^（III）EDTA were synthesized in Na OH solution at 0℃.Then,Mn^（III）EDTA and methyl viologen（MV）were used as the cathodic and anodic active electrolyte to assemble an aqueous redox flow battery（RFB）and its electrochemical performances were investigated.The results show that the potential of the Mn^（III）EDTA complex is 1.01 V and the coulombic efficiency of this RFB reaches 96%at 25℃.After 100 charge-discharge cycles,the charge-discharge capacity is retained at 48.6%of initial value and the average capacity retention rate per cycle is about 99.5%.2.Sodium methanesulfonate（MSA-Na）was used as the conjugation ligand to prepare manganese-based complex,which was used as cathode to pair with the MV anode in the course of assembling the aqueous redox flow batteries.As proved in the experimental results,the RFB shows the best electrochemical performances when the molar ratio of Mn and MSA is 1:5.The open circuit voltage reaches 1.316 V and the energy efficiency is ca.74%at a current density of 30 m A cm^-2.The Coulomb efficiency exceeds 90%and the capacity retention rate is kept at 99.2%per cycle over100 consecutive cycles.3.Ni/Mn based bimetallic organic frameworks（Ni/Mn-MOF）were synthesized and utilized as the anode of RFB by using 6-quinoxaline carboxylic acid as an organic ligand,and manganese chloride and nickel chloride as raw metal salt.The potential of Ni/Mn-MOF is 0.527 V in 0.5M KOH solution.In three-electrode system,the capacity of Ni/Mn-MOF is 23.81 m Ah g^-1 at a current density of 1 A g^-1.And Assembled with the negative electrode 2,2’-bis（3-hydroxy-1,4-naphthoquinone）（bislawsone）into an RFB battery.After paired with bislawsone,the voltage is 1.101 V and the capacity is 55.8 m Ah g^-1 at a current density of 1 A g^-1.After 1000charge-discharge cycles,the charge-discharge capacity is retained at 58.3%of initial value and the average capacity retention rate per cycle is about99.96%.4.Manganese based metal-organic frameworks（Mn-MOF）were synthesized by a hydrothermal method using 1,3,5-benzentricarboxylic acid as organic linker and manganese nitrate was used as the metal ion salt,which were used in both hybrid-flow batteries and supercapacitors.The fabricated hybrid supercapacitor have an excellent specific capacitance of89 F g^-1 at a current density of 0.5 A g^-1,the specific capacitance retained91.8%of the initial capacitance after successive 10,000 charge-discharge cycles at a current density of 1 A g^-1.When paired with the bislawsone anode,the capacity is 49.17 m Ah g^-1 at a current density of 1 A g^-1.After500 charge-discharge cycles,the capacity increased by approximately27.8%.