Xiaoliang Wei1 Zhengcheng Zhang3 2 Lu Zhang3 2

1, Indiana University-Purdue University, Indianapolis, Indiana, United States
3, Joint Center for Energy Storage Research, Argonne, Illinois, United States
2, Argonne National Laboratory, Argonne, Illinois, United States

Redox flow batteries are particularly attractive for stationary energy storage with potential impact to a variety of grid applications. High chemical cost or long-term cyclability have limited the conventional inorganic-based redox materials. In this regard, organic redox materials have recently demonstrated encouraging property and performance characteristics, promising to address these challenges.1 Solubility and chemical stability are among the most important properties of ROMs, the former determining the energy density and the latter of corresponding flow batteries. Currently, ROM candidates that satisfy these requirements simultaneously are rather limited.
Here, we will report our recent progress in the development of organic redox materials covering a diversity of structures and reaction mechanisms, such as diquats and phenazine in aqueous1-2 as well as dialkoxybenzenes in nonaqueous3 flow batteries. Our studies have unraveled the molecular-level fundamental mechanisms of low solubility and chemical instability via combined spectroscopic and computational methods. Rational materials design principles have been suggested and demonstrated to be effective in enabling new highly soluble, stable redox materials.

1. Hollas, A.; Wei, X. L.; Murugesan, V.; Nie, Z. M.; Li, B.; Reed, D.; Liu, J.; Sprenkle, V.; Wang, W., A biomimetic high-capacity phenazine-based anolyte for aqueous organic redox flow batteries. Nature Energy 2018, 3 (6), 508-514.
2. Huang, J.; Yang, Z.; Murugesan, V.; Walter, E.; Hollas, A.; Pan, B.; Assary, R. S.; Shkrob, I. A.; Wei, X.; Zhang, Z., Spatially Constrained Organic Diquat Anolyte for Stable Aqueous Flow Batteries. Acs Energy Lett 2018, 3, 2533–2538.
3. 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.