Next-generation aqueous flow battery chemistries

The battery industry is seeking solutions for large-scale energy storage that are affordable, durable, and safe. Aqueous redox flow batteries (RFBs) have the inherent properties to meet these requirements. While much has been learned over the past decade on the properties of redox materials, the focus of next-generation systems must be primarily on lowering redox material cost and increasing durability. In this context, in addition to inexpensive materials such as iron salts, redox couples based on small organic molecules have shown significant promise. A considerable level of understanding has been gained on the factors affecting the durability of aqueous RFB systems, specifically relating to molecular stability and crossover. New molecular classes, substituent strategies, and cell configurations have been identified to enhance the durability of systems in the future. Next-generation systems will also need to focus on designing molecules for achieving high energy efficiency and power density as well. Furthermore, the application of computational methods for screening of chemical stability could accelerate discovery of new molecular architectures.     

Protonation of CH3N3 and CF3N3 in Superacids: Isolation and Structural Characterization of Long‐Lived Methyl‐ and Trifluoromethylamino Diazonium Ions

The methylamino diazonium cations [CH₃N(H)N₂]⁺ and [CF₃N(H)N₂]⁺ were prepared as their low‐temperature stable [AsF₆]^? salts by protonation of azidomethane and azidotrifluoromethane in superacidic systems. They were characterized by NMR and Raman spectroscopy. Unequivocal proof of the protonation site was obtained by the crystal structures of both salts, confirming the formation of alkylamino diazonium ions. The Lewis adducts CH₃N₃?AsF₅ and CF₃N₃?AsF₅ were also prepared and characterized by low‐temperature NMR and Raman spectroscopy, and also by X‐ray structure determination for CH₃N₃?AsF₅. Electronic structure calculations were performed to provide additional insights. Attempted electrophilic amination of aromatics such as benzene and toluene with methyl‐ and trifluoromethylamino diazonium ions were unsuccessful.