Para-Substituted Triphenylamine as a Catholyte for Zinc–Organic Aqueous Redox Flow Batteries
Xiaowei Wang, Wei Tang, Kian Ping Loh
Abstract
Aqueous organic redox flow batteries (RFBs) have emerged as one the most promising technologies for grid-scale energy storage because of their sustainability, safety, and high power densities. Herein, by the molecular engineering of aqueous irreversible triphenylamine (TPA) to form 4,4′,4″-trihydroxytriphenylamine (P3), a reversible two-electron transfer system based on an enol/keto redox couple was obtained, with a high kinetic rate constant of 1.1 × 10–2 cm2 s–1. P3 was used as the catholyte and paired with a zinc anolyte in an aqueous RFB, which yields a high working voltage of ∼1.4 V with good cycling behavior. A capacity of 22.5 Ah L–1 can be obtained using a mixed solvent (DMF/H2O = 1:5, volume ratio) and the battery shows a minor self-discharge rate at full state of charge. This work demonstrates that irreversible or instable redox-active organic molecules can be converted into reversibly reactive analogues by molecular engineering, thereby broadening the range of redox-active materials for organic aqueous RFBs.