Abstract
A quaternary amine‐functionalized naphthalene diimide (NDI) moiety is synthesized and considered as a redox‐active species for application in aqueous organic redox flow batteries. For the first time, this NDI is characterized electrochemically in aqueous solutions, using cyclic and rotating disk electrode voltammetry, bulk electrolysis, as well as 1H‐nuclear magnetic resonance (1H‐NMR) spectroscopy. The molecule reaches a solubility of 0.68 m in water and reversibly delivers two electrons at attractive potentials for flow battery applications. Further exploration with 1H‐NMR reveals a strong dimerization of the NDI species with an equilibrium constant of 146 m−1. Using diffusion NMR coupled with rotating disk electrode voltammetry, it is shown that the dimer retains limited redox‐activity, yielding two electrons per dimer unit. However, using galvanostatic bulk electrolysis, close to the theoretical capacity is obtained, indicating a fast dissociation reaction of the reduced dimer. Finally, the NDI species shows excellent stability; after constant cycling for 1 week, no degradation is detected. In conclusion, NDI is demonstrated to be a highly attractive candidate for aqueous redox flow batteries.
Highlights
AQDS in logical climate change, transitioning from the use of fossil fuels— its oxidized form has been shown to self-associate in solution, which are known to make up for a majority of greenhouse gas emissions—to renewable energy sources is given considerable forming a redox-inactive dimer that somewhat impedes its use in electrochemical applications.[24,32]
To make napthalene diimides (NDIs) water-soluble at higher pH, the material was dissolved in chloroform through which chloromethane was bubbled, after which the pure NDI with quaternary amine sidechains precipitated out of solution
At pH values below 8.1, which is a likely condition for the actual flow battery operation, the amine sidechains will be protonated, yielding solubilizing positive charges to the molecule without methylation
Summary
(AQDS) coupled with HBr/Br2 was seminally demonstrated in 2014,[27] and due to its fulfillment of many of the above criteria, There is a growing concern for Earth’s ecological development AQDS has been thoroughly studied since and is often considered over the last decades. The ORCID identification number(s) for the author(s) of this article been considered for aqueous flow battery applications. The molecule is referred to as NDI in this article
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