Bis(diisopropylamino)cyclopropenium-arene Cations as High Oxidation Potential and High Stability Catholytes for Non-aqueous Redox Flow Batteries.

This Article describes the development of 1,2-bis(diisopropylamino)-3-cyclopropenylium-functionalized (DAC-functionalized) benzene derivatives as high-potential catholytes for non-aqueous redox flow batteries. Density functional theory (DFT) calculations predict that the oxidation potentials (in CHCN) of various DAC-benzene derivatives will range from +0.96 to +1.64 V vs Fc, depending upon the substituents on the benzene ring. To test these predictions, a set of eight DAC-arene derivatives were synthesized and evaluated electrochemically. The molecule 1-DAC-4--butyl-2-methoxy-5-pentafluoropropoxybenzene was found to offer the optimal balance of high redox potential ( = +1.19 V vs Fc) and charge-discharge cycling stability (with 92% capacity retention over 116 h of cycling at 0.3 M concentration in a symmetrical flow cell). This optimal derivative was successfully deployed as a catholyte in a non-aqueous redox flow cell with butyl viologen as the anolyte to yield a 2.0 V battery.