As one of electrochemical energy storage devices,aqueous flow batteries appear promising which manifest design flexibility,energy and power decoupling,high safety and low cost.The water-soluble electrolyte molecule is the core material in an aqueous flow battery system,and its properties largely determine the performance of the entire battery.A number of scientific problems of currently developed redox electrolyte molecules urgently need to be solved in order to advance the development of aqueous flow batteries with high power density,high energy density and long-term cycling stability,such as sluggish redox kinetics,low solubility,severe cross-membrane contamination,and poor stability.This dissertation mainly focuses on the electrolyte materials of aqueous flow batteries.Various properties of electrolyte molecules can be improved by rational design,preparation and characterization for the application of high-performance aqueous flow batteries.The main contents are as follow:(1)Taking 2,5-dihydroxy-3,6-dimethyl-1,4-benzoquinone(DMBQ)electrolyte molecule as an example,its redox kinetics can be effectively enhanced by two strategies:chemical structure modification and inexpensive catalyst,thereby improving the battery performance such as power density and energy efficiency.On the one hand,the two methyl groups of DMBQ are replaced with two methoxy groups by chemical synthesis.This method reduces the energy gap of the molecule and improves the redox kinetics.On the other hand,self-made catalyst is coated on the electrode surface which provides more electrochemically active sites and higher conductivity,thereby enhancing the redox kinetics.Through electrochemical characterization,both strategies significantly reduce the redox electron transfer resistance of benzoquinone derivatives and greatly improved the power density and energy efficiency of aqueous flow batteries;(2)Two-electron reversible storage of methyl viologen(MV2+)in water is solved by the surfactant solubilization strategy.By simply mixing MV2+and the surfactant dodecyl trimethyl ammonium chloride(DTAC),the doubly reduced MVO can enter the micelles formed by the surfactant and becomes soluble in water,thus effectively achieving the two-electron reversible storage.The CV results of the MV2+ and DTAC mixture show two pairs of relatively symmetrical redox peaks.The battery exhibits two charge-discharge platforms.These results confirm the availability of surfactant solubilization;(3)BTMAE-Vi was synthesized by introducing oxygen-containing quaternary aminated side chains on viologen(MV)molecules.This molecular modification strategy increases the volume,charge and polarity of electrolyte molecules,thus reducing its cross-membrane contamination while increasing the water solubility.The battery shows extremely high capacity retention rate of 99.996%/cycle when BTMAE-Vi only involves single-electron redox process;(4)EuCl3-based molecule is reported as anode electrolytes for aqueous flow batteries.Furthermore,coordination chemistry strategy is exploited to regulate the redox behavior,solubility,and stability of Eu3+.A typical complex,EuDTPA,is screened out which features a low potential,high solubility and stability.The battery exhibits a high voltage of 1.56 V and a high capacity retention rate of 99.997%/cycle,enabling the application of high-voltage,long-cycle aqueous flow batteries. |