Azoniafluorenones: A New Family of Two-Electron Storage Electrolytes for Sustainable Near-Neutral pH Aqueous Organic Flow Battery
: Artault, Maxime; Gonzalez, Gabriel; Damlin, Pia; Toivola, Juho; Mailman, Aaron; Hannonen, Jenna; Pihko, Petri M.; Peljo, Pekka
Publisher: WILEY-V C H VERLAG GMBH
: WEINHEIM
: 2024
: Advanced Energy Materials
: ADVANCED ENERGY MATERIALS
: ADV ENERGY MATER
: 2401635
: 14
: 37
: 10
: 1614-6832
: 1614-6840
DOI: https://doi.org/10.1002/aenm.202401635
: https://doi.org/10.1002/aenm.202401635
: https://research.utu.fi/converis/portal/detail/Publication/457435012
Fluorenones are suitable candidates for negolytes in flow batteries, as they demonstrate the ability to store 2 electrons, and can achieve reversibility, solubility, and stability with appropriate molecular design. However, limitations persist such as the use of alkaline media, high redox potentials, and a limited scope for optimization. Herein, azoniafluorenones is reported as a novel class of negolytes. They can be readily accessed in a highly modular fashion from inexpensive commercially available materials (e.g., boronic acids). Variations in the substitution patterns reveal the 3-substituted N-alkylated AZON3, which demonstrates excellent solubility at neutral pH (1.64 m) with two low reversible redox potentials (-0.31 and -0.58 V vs Ag/AgCl). AZON3 exhibits high stability when evaluated at high concentration in a neutral supporting electrolyte (1 m in 3 m KCl), paired with BTMAP-Fc on the positive side. Capacity retentions of 99.95% and 99.91% per cycle (99.35% and 99.21% per day) are achieved when cycling with 1 and 2 electrons, respectively, coupled with high volumetric capacity of 46.4 Ah L-1 (87% of capacity utilization).A highly promising class of energy storage materials is identified for flow batteries (FBs). Starting from commercially available and inexpensive building blocks, azoniafluorenones (AZONs) can be accessed in a few steps and the molecular structure optimized through electrochemical studies. The optimal AZONs display a high solubility and stability in battery tests, affording high charge densities, and they work in neutral media. image
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This project has received funding from the European Union – NextGenerationEU instrument and is funded by Research Council Finland under grant numbers 348326 (P.P.) and 348328 (P.M.P.). Support from the European Union's Horizon2020 Research and Innovation programme under grant agreement No 875565 (Project CompBat) is also acknowledged. GG gratefully acknowledges the financial support from the University of Turku Graduate School. P.P. gratefully acknowledges the Academy Research Fellow funding (grant no. 315739, 343791, 320071, and 343794) from Research Council Finland, and European Research Council through a Starting grant (agreement no. 950038).
