Radical Stabilization of a Tripyridinium–Triazine Molecule Enables Reversible Storage of Multiple Electrons

• Published in: Angewandte Chemie International Edition 2021-09, Vol.60 (38), p.20921-20925
• Main Authors: Huang, Jinghua, Hu, Shuzhi, Yuan, Xianzhi, Xiang, Zhipeng, Huang, Mingbao, Wan, Kai, Piao, Jinhua, Fu, Zhiyong, Liang, Zhenxing
• Format: Article
• Language: English
• Subjects: aqueous; Diffusion coefficient; Diffusion rate; Electron transfer; Electrons; multi-electron storage; Organic chemistry; pyridinium; radical stabilization; Radicals; Rechargeable batteries; Specific capacity; Triazine
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202107216

A novel organic molecule, 2,4,6‐tris[1‐(trimethylamonium)propyl‐4‐pyridiniumyl]‐1,3,5‐triazine hexachloride, was developed as a reversible six‐electron storage electrolyte for use in an aqueous redox flow battery (ARFB). Physicochemical characterization reveals that the molecule evolves from a radical to a biradical and finally to a quinoid structure upon accepting four electrons. Both the diffusion coefficient and the rate constant were sufficiently high to run a flow battery with low concentration and kinetics polarization losses. In a demonstration unit, the assembled flow battery affords a high specific capacity of 33.0 Ah L−1 and a peak power density of 273 mW cm−2. This work highlights the rational design of electroactive organics that can manipulate multi‐electron transfer in a reversible way, which will pave the way to development of energy‐dense, manageable and low‐cost ARFBs. A tripyridinium–triazine molecule featuring multiple redox centers was developed with a capacity as high as six electrons per molecule. The electronic coupling between the pyridinium and triazine units can effectively delocalize the charge of the radicals, thereby stabilizing the reactive intermediate and enabling reversible storage of multiple electrons.