New highly soluble triarylamine-based materials as promising catholytes for redox flow batteries

A series of arylamines bearing oligoethylene glycol ether solubilizing moieties were designed and comprehensively evaluated as promising catholyte materials for non-aqueous redox flow batteries (RFBs). The triphenylamine core maintains the chemical stability of the radical cation, the ethylene glycol chains enhance the solubility up to complete miscibility with organic solvents, and the electron-withdrawing bromine substituents increase the redox potential of the compounds up to 0.61 V vs. Ag/AgNO3. The best material showed 99% coulombic efficiency in combination with good stability in over 50 charge-discharge cycles in laboratory RFB cells. The designed triarylamine-based catholyte materials appear promising for the development of next-generation high-voltage and high-capacity RFBs.