5:00 PM - ES01.05.04
A New Class of Redox-Active Heterocyclic Rings Applied for Negolytes in Nonaqueous Redox Flow Batteries
Soeun Kim1,2,Jin Hyeok Jang3,Jungmin Joo3,Hye Ryung Byon1,2
Korea Advanced Institute of Science and Technology (KAIST)1,KAIST Institute for NanoCentury2,Pusan National University3
Redox flow batteries (RFBs) are one of the promising energy storages with a grid scale owing to their decoupled energy and power density, which lead to scalability and flexibility in design. To aim at higher energy density more than that of the current technology of vanadium RFBs, the redox-active molecules should have higher solubility and larger voltage gap than vanadium ions. The nonaqueous electrolyte media are also essential to offer wide electrochemical windows (> 2 V). Many redox-active organic materials have been studied for the role of posolyte in nonaqueous medium ,., while only a few negolytes have been designed in this system,,. Herein, we present a new category of fused heterocyclic rings that can be employed as the negolyte. Our attempts to introduce various substituents to the core cyclic ring altered the electrochemical and chemical reversibility. The degree of molecular planarity and Lewis acidity/basicity of redox-active heterocyclic molecules critically determine the reversibility in cyclic voltammetry profile. The decorations of functionality also shift the redox potential and the number of electrons transferred. In addition, the asymmetric structure of heterocyclic rings may increase the solubility in the nonaqueous media. Through the fundamental studies on the design of heterocyclic rings and the corresponding electrochemical/chemical analyses, we demonstrated the optimum negolyte that can potentially provide high energy density and cyclic stability in nonaqueous RFBs. This study gives the guideline to develop new redox-active organic molecules for the application of RFBs.
 Hu, B.; DeBruler, C.; Rhodes, Z.; Liu, T. L. Long-Cycling Aqueous Organic Redox Flow Battery (AORFB) toward Sustainable and Safe Energy Storage. J. Am. Chem. Soc. 2017, 139 (3), 1207−1214.
 Huskinson, B.; Marshak, M. P.; Suh, C.; Er, S.; Gerhardt, M. R.; Galvin, C. J.; Chen, X.; Aspuru-Guzik, A.; Gordon, R. G.; Aziz, M. J. A metal-free organic-inorganic aqueous flow battery. Nature, 2014, 505 (7482), 195−198.
 Zhang, J.; Yang, Z.; Shkrob, I. A.; Assary, R. S.; Tung, S. o.; Silcox, B.; Duan, W.; Zhang, J.; Su, C. C.; Hu, B.; Pan, B.; Liao, C.; Zhang, Z.; Wang, W.; Curtiss, L. A.; Thompson, L. T.; Wei, X.; Zhang, L. Annulated Dialkoxybenzenes as Catholyte Materials for Nonaqueous Redox Flow Batteries: Achieving High Chemical Stability through Bicyclic Substitution. Adv. Energy Mater. 2017, 7, 1701272
 Liu, T.; Wei, X.; Nie, Z.; Sprenkle, V.; Wang, W. A Total Organic Aqueous Redox Flow Battery Employing a Low Cost and Sustainable Methyl Viologen Anolyte and 4-HO-TEMPO Catholyte. Adv. Energy Mater. 2016, 6 (3), 1501449
 Sevov, C. S.; Hickey, D. P.; Cook, M. E.; Robinson, S. G.; Barnett, S.; Minteer, S. D.; Sigman, M. S.; Sanford, M. S. Physical Organic Approach to Persistent, Cyclable, Low-Potential Electrolytes for Flow Battery Applications. J. Am. Chem. Soc. 2017, 139 (8), 2924−2927.
 Wei, X.; Xu, W.; Huang, J.; Zhang, L.; Walter, E.; Lawrence, C.; Vijayakumar, M.; Henderson, W. A.; Liu, T.; Cosimbescu, L.; Li, B.; Sprenkle, V.; Wang, W. Radical Compatibility with Nonaqueous Electrolytes and Its Impact on an All-Organic Redox Flow Battery. Angew. Chem., Int. Ed. 2015, 54 (30), 8684−8687.
 Duan, W.; Huang, J.; Kowalski, J. A.; Shkrob, I. A.; Vijayakumar, M.; Walter, E.; Pan, B.; Yang, Z.; Milshtein, J. D.; Li, B.; et al. Wine-Dark Sea” in an Organic Flow Battery: Storing Negative Charge in
2,1,3-Benzothiadiazole Radicals Leads to Improved Cyclability. ACS Energy Lett. 2017, 2, 1156−1161