Two‐Electron Tetrathiafulvalene Catholytes for Nonaqueous Redox Flow Batteries

Tetrathiafulvalene (TTF) exhibits two reversible oxidation steps and is used as a novel multi-electron catholyte for nonaqueous organic redox flow batteries. To increase solubility in polar solvents, TTF derivatives with side chains are synthesized. 4-Methoxymethyl tetrathiafulvalene emerges promising two-electron because it liquid at room temperature miscible acetonitrile. Bulk-electrolysis experiments UV-vis-NIR absorption spectroscopy reveal excellent cycling stability the first second electrochemical oxidations. In doubly oxidized state, show about 1% loss of state charge per day, due to extrinsic effects. symmetric battery, 4-methoxymethyltetrathiafulvalene shows volumetric capacity only 0.2% cycle coulombic efficiency (CE) 99.6%. an asymmetric battery pyromellitic diimide anolyte, 0.8% cycle, CE > 99% each cycle.