Performance Of Electroactive Anode Materials For Aqueous Organic Redox Flow Battery

In recent years,with the widespread use of renewable energy,it is urgent to develop economical and efficient large-scale energy storage technologies.Among various electrochemical energy storage technologies,aqueous redox flow battery(ARFB)has been widely concerned by researchers due to its low cost,high flexibility,long life,high efficiency,safety and pollution-free characteristics.Due to the fact that organic materials have abundant sources and customizable physicochemical properties and are easy to be synthesized on a large scale,the exploration of organic molecules as energy-storage materials of ARFBs has become current research focus.In this work,we have developed a class of insoluble π-conjugated quinazine compounds to improve the energy density of ARFBs.Their electrochemical properties in aqueous solution were investigated.And then,aqueous redox-targeting flow battery(RTFB)and hybrid redox flow battery(HRFB)were assembled by employing them as solid-state anodic energy-storage materials.The main contents of this dissertation are as follows:(1)Firstly,2,3-dichloro-1,4-naphthoquinone(DANQ)was prepared using Gabriel amine synthesis method with2,3-diamino-1,4-naphthoquinone(DANQ)as an initial reactant.Then,an aromatic heterocyclic compound,tribenzo [a,c,i] phenazine-10,15-dione(TBPDO),was prepared via Schiff-base condensation approach.The structure and morphology of TBPDO were characterized by nuclear magnetic resonance(NMR),infrared spectroscopy(IR)and electron microscopy.The electrochemical properties and stability of TBPDO in aqueous solution were investigated using various electrochemical methods.In addition,electrochemical kinetic parameters of TBPDO were measured to explore its possible redox mechanism and potential flow cell applications.(2)Based on the principle of redox-targeting reaction,we have designed and assembled a novel aqueous RTFB employing TBPDO as an anodic solid energy-storage material,a mixture of 2,6-DHAQ and lawsone as a redox-active anolyte(i.e.redox mediator for redox-targeting reaction),and potassium ferrocyanide/ferrocyanide as a catholyte,respectively.This RTFB displays an open circuit voltage(OCV)of ~1.09 V.The charge-discharge cycling results show that the capacity retention rate still remains 80% after 21 cycles at a constant current density of 5m A cm-2.The capacity retention rate per cycle is up to 99.82%(equivalent to 98.56% per day).The material utilization reaches80%.The average Coulomb efficiency(CE)is 99.51% while energy efficiency(EE)is above 80%,revealing high cycling stability of the RTFB.In addition,we also determine the NMR spectra of TBPDO at different SOCs to speculate the possible mechanisms of electrochemical and redox-targeting reactions of TBPDO in the aqueous RTFB.(3)A π-conjugated organic molecule HATTNQ containing multiple electroactive quinazine units was synthesized via Schiff-base condensation reaction using DANQ and hexanone cyclohexane as the initial reactants.The structure and physicochemical properties of HATTNQ were characterized and its electrochemical properties in aqueous solution were investigated.Furthermore,an alkaline aqueous organic HRFB was constructed by pairing an HATTNQ-coated porous carbon felt anode with potassium ferrocyanide catholyte.The HRFB cell shows high specific capacity and high power density,excellent rate performance,outstanding cycling stability and high energy efficiency,which is expected to be used to store renewable energy on a large scale in the future.