Regioisomeric Engineering for Multicharge and Spin Stabilization in Two-Electron Organic Catholytes

Journal of the American Chemical Society, vol. 147, pp. 2115–2128

Abstract

High Resolution Image Download MS PowerPoint Slide Developing multicharge and spin stabilization strategies is fundamental to enhancing the lifetime of functional organic materials, particularly for long-term energy storage in multiredox organic redox flow batteries. Current approaches are limited to the incorporation of electronic substituents to increase or decrease the overall electron density or bulky substituents to sterically shield reactive sites. With the aim to further expand the molecular toolbox for charge and spin stabilization, we introduce regioisomerism as a scaffold-diversifying design element that considers the collective and cumulative electronic and steric contributions from all of the substituents based on their relative regioisomeric arrangements. Through a systematic study of regioisomers of near-planar aromatic cyclic triindoles and nonplanar nonaromatic cyclic tetraindoles, we demonstrate that this regioisomeric engineering strategy significantly enhances the H-cell cycling stability in the above two new classes of 2e – catholytes, even when current strategies failed to stabilize the multicharged species. Density functional theory calculations reveal that the strategy operates by redistributing the charge and spin densities while highlighting the role of aromaticity in charge stabilization. The most stable 2e – catholyte candidate was paired with a viologen derivative anolyte to achieve a proof-of-concept all-organic flow battery with 1.26–1.49 V, 98% capacity retention, and only 0.0117% fade/h and 0.00563% fade/cycle over 400 cycles (192 h), which is the highest capacity retention ever reported over 400 cycles in a multielectron all-organic flow battery setup. We anticipate regioisomeric engineering to be a promising strategy complementary to conventional electronic and steric approaches for multicharge and spin stabilization in other functional organic materials.

Authors 4

1. Tim K. Schramm Aachen Department of Chemistry

   RWTH Aachen University · University of California, Berkeley

   Affiliation as printed

   Department of Chemistry, RWTH Aachen University, Landoltweg 1, Aachen 52074, Germany

   Department of Chemistry, University of California, Berkeley, California 94720, United States

2. Martin Head‐Gordon

   Lawrence Berkeley National Laboratory · University of California, Berkeley

   Affiliation as printed

   Chemical Science Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, United States

   Department of Chemistry, University of California, Berkeley, California 94720, United States

3. James Shee

   Rice University

   Affiliation as printed

   Department of Chemistry, Rice University, Houston, Texas 77005, United States

4. F. Dean Toste corresponding

   Lawrence Berkeley National Laboratory · University of California, Berkeley

   Affiliation as printed

   Chemical Science Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, United States

   Department of Chemistry, University of California, Berkeley, California 94720, United States

   Joint Center for Energy Storage Research (JCESR), 9700 South Cass Avenue, Argonne, Illinois 60439, United States