Synthesis Of Electroactive Conjugated Organic Materials And Their Applications In Electrochemical Energy Storage

Electricity generated by clean renewable energy sources such as solar,wind and geothermal is growing rapidly all over the world.Therefore,it is necessary to develop a large-scale electrical-energy-storage（EES）system to buffer the impact of intermittent renewable energy on the stable operation of the improve the electric grids.Among many EES systems,aqueous flow batteries（RFBs）and hybrid flow batteries（AHFBs）have attracted extensive attention of researchers.Because RFBs are limited by the narrow electrochemical stability window of their aqueous electrolytes and the solubility of electroactive species,and the achievable specific capacity of AHFB systems is usually limited by the low areal specific capacity of solid-state electrodes.Therefore,the concept of redox-targeting reactions has recently been proposed and applied in the field of flow batteries to improve energy density.Redox-targeted flow batteries（RTFBs）utilize thermodynamically-allowed targeted chemical reactions between redox mediators in liquid electrolytes and solid-state electrode materials to store electrical energy.It requires high redox potential matching and similar electrochemical reaction rates between solid electrode materials and redox mediators.Due to their low redox potential,high specific capacity,reversible electrochemical kinetics,abundant sources and environmental sustainability,phenazine derivatives are an ideal class of electrochemical energy storage materials.In this paper,two redox active conjugated phenazine derivatives-1,2:3,4-dibenzophenazine（DPHZ）and benzo[a]hydroxyphenazine-7/8-carboxylic acid（BHPC）were developed.On this basis,AHFB,RTFB and capacity-enhancing aqueous flow batteries were designed and constructed.The main contents of this dissertation are as follows:（1）An insoluble electroactive conjugated organic material DPHZ was synthesized via keto-amine condensation reaction condensation reaction.The electrochemical properties of DPHZ in acidic,alkaline and neutral electrolytes were investigated by cyclic voltammetry.Then,the properties of DPHZ//K₄[Fe（CN）₆]alkaline AHFB were established and systematically explored.The hybrid flow battery has an open circuit voltage of 1.21 v.After 2250 cycles at a current density of 5 A g^-1,about95.7%of the initial discharge capacity is retained,the capacity retention rate is～99.998%per cycle,the average coulombic efficiency is about98.4%,and the energy efficiency is 92.6%.（2）A soluble electroactive conjugated organic material benzo[a]hydroxyphenazine-7/8-carboxylic acid（BHPC）was synthesized via Schiff-Base condensation reaction.The electrochemical properties and reaction mechanism of BHPC were investigated by cyclic voltammetry.Then the performance of BHPC//K₄[Fe（CN）₆]ARFB was established and explored.The liquid flow battery has an open circuit voltage of 1.27 V and retains 100%of the initial discharge capacity with little attenuation under 100 charge/discharge cycles at a current density of40 m A cm^-2.The average coulomb efficiency of the battery is 99.9%and the energy efficiency is 83.3%.And at 100%state of charge（SOC）,the maximum power density is 220 m W cm^-2.（3）The targeted chemical reaction between BHPC and DPHZ was verified by introducing porous insulating material MgO.Based on this,an aqueous RTFB and an aqueous organic liquid flow battery with DPHZ solid-state negative electrode are designed and established.DPHZ is a solid-state anode energy storage material and BHPC is an anode redox electrolyte.The performance of the battery is explored.The results show that the solid-state anode energy storage material DPHZ significantly improves the capacity of the battery,and it has good redox stability.