Pairing nitroxyl radical and phenazine with electron-withdrawing/-donating substituents in “water-in-ionic liquid” for high-voltage aqueous redox flow batteries

作     者：Zhifeng Huang Rolf Hempelmann Yiqiong Zhang Li Tao Ruiyong Chen Zhifeng Huang;Rolf Hempelmann;Yiqiong Zhang;Li Tao;Ruiyong Chen

作者机构：Transfercenter Sustainable ElectrochemistrySaarland University and KIST Europe66125SaarbruckenGermany State Key Laboratory of Chem/Bio-Sensing and Chemometrics College of Chemistry and Chemical Engineering Hunan UniversityChangsha410082HunanChina College of Materials Science and Engineering Changsha University of Science and TechnologyChangsha410114HunanChina Materials Innovation FactoryDepartment of ChemistryUniversity of LiverpoolLiverpoolL697ZDUnited Kingdom 

出 版 物：《Green Energy & Environment》 (绿色能源与环境（英文版）)

年 卷 期：2024年第9卷第4期

页      面：713-722页

核心收录：

学科分类：0820[工学-石油与天然气工程] 07[理学] 070304[理学-物理化学(含∶化学物理)] 0817[工学-化学工程与技术] 0703[理学-化学] 

基　　金：support from China Postdoctoral Science Foundation(Grant No.2021M690960) China CSC abroad studying fellowship.R.C.thanks the KIST Europe basic research funding“new electrolytes for redox flow batteries”and the partial financial support from the CMBlu Energy AG.Y.Z.thanks to the support received from the National Natural Science Foundation of China(Grant No.22002009) the Natural Science Foundation of Hunan Province(Grant No.2021JJ40565). 

主　　题：Aqueous redoxflow batteries Water-in-ionic liquid electrolytes High-voltage aqueous batteries Organic redox-active materials 

摘      要：Aqueous redox-active organic materials-base electrolytes are sustainable alternatives to vanadium-based electrolyte for redoxflow batteries(RFBs)due to the advantages of high ionic conductivity,environmentally benign,safety and low cost.However,the underexplored redox properties of organic materials and the narrow thermodynamic electrolysis window of water(1.23 V)hinder their wide applications.Therefore,seeking suitable organic redox couples and aqueous electrolytes with a high output voltage is highly suggested for advancing the aqueous organic RFBs.In this work,the functionalized phenazine and nitroxyl radical with electron-donating and electron-withdrawing group exhibit redox potential of-0.88 V and 0.78 V vs.Ag,respectively,in“water-in-ionic liquidsupporting electrolytes.Raman spectra reveal that the activity of water is largely suppressed in“water-in-ionic liquiddue to the enhanced hydrogen bond interactions between ionic liquid and water,enabling an electrochemical stability window above 3 V.“Water-in-ionic liquidsupporting electrolytes help to shift redox potential of nitroxyl radical and enable the redox activity of functionalized phenazine.The assembled aqueous RFB allows a theoretical cell voltage of 1.66 V and shows a practical discharge voltage of 1.5 V in the“water-in-ionic liquidelectrolytes.Meanwhile,capacity retention of 99.91%per cycle is achieved over 500 charge/discharge cycles.A power density of 112 mW cm^(-2) is obtained at a current density of 30 mA cm^(-2).This work highlights the importance of rationally combining supporting electrolytes and organic molecules to achieve high-voltage aqueous RFBs.