Blatter Radicals as Bipolar Materials for Symmetrical Redox-Flow Batteries

Jelte S. Steen, Jules L. Nuismer, Vytautas Eiva, Albert E.T. Wiglema, Nicolas Daub, Johan Hjelm, Edwin Otten (Corresponding author)

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Redox-active organic molecules are promising charge-storage materials for redox-flow batteries (RFBs), but material crossover between the posolyte and negolyte and chemical degradation are limiting factors in the performance of all-organic RFBs. We demonstrate that the bipolar electrochemistry of 1,2,4-benzotriazin-4-yl (Blatter) radicals allows the construction of batteries with symmetrical electrolyte composition. Cyclic voltammetry shows that these radicals also retain reversible bipolar electrochemistry in the presence of water. The redox potentials of derivatives with a C(3)-CF3substituent are the least affected by water, and moreover, these compounds show >90% capacity retention after charge/discharge cycling in a static H-cell for 7 days (ca. 100 cycles). Testing these materials in a flow regime at a 0.1 M concentration of the active material confirmed the high cycling stability under conditions relevant for RFB operation and demonstrated that polarity inversion in a symmetrical flow battery may be used to rebalance the cell. Chemical synthesis provides insight in the nature of the charged species by spectroscopy and (for the oxidized state) X-ray crystallography. The stability of these compounds in all three states of charge highlights their potential for application in symmetrical organic redox-flow batteries.

Original languageEnglish
Pages (from-to)5051-5058
Number of pages8
JournalJournal of the American Chemical Society
Issue number11
Publication statusPublished - 23 Mar 2022

Bibliographical note

Funding Information:
Financial support from The Netherlands Organisation for Scientific Research (NWO) (VIDI grant to E.O.) is gratefully acknowledged. We thank F. de Vries for the X-ray diffraction studies, W. Tang for measurement of diffusion coefficients and standard rate constants, Dr. J. E. M. N. Klein and T. Jo (UV–vis) and Prof. W .R. Browne (EPR) for access to their spectroscopic facilities at the University of Groningen, and Prof. R. A. J. Janssen (Eindhoven University of Technology) for access to a flow battery setup.

Publisher Copyright:
© 2022 American Chemical Society. All rights reserved.


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