Elucidating Instabilities Contributing to Capacity Fade in Bipyridine‐Based Materials for Non‐aqueous Flow Batteries. Issue 6 (19th January 2022)

• Record Type: Journal Article
• Authors: Kolesnichenko, Claudina X.; Pratt, Harry D.; Small, Leo J.; Anderson, Travis M.
• Is Part Of: ChemElectroChem. Volume 9:Issue 6(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-01-19
• Subjects: Bipyridinium -- Capacity fade -- Decomposition pathway -- Iron bipyridine -- Non-aqueous redox flow battery; Electrochemistry -- Periodicals; 541.37
• DOI: 10.1002/celc.202101490
• Languages: English
• ISSNs: 2196-0216

Abstract

Abstract: Metal‐based non‐aqueous redox flow batteries have the potential for long‐term energy storage if stability requirements can be achieved. One such stability issue in metal coordination complexes arises from ligand shedding in the anolyte upon reduction. Recognizing that the free ligands are relatively more stable than the metal coordination complex under highly reducing conditions, we evaluated a family of metal‐free bipyridinium materials as flow battery anolytes with the corresponding iron coordination complex as the catholyte. Bipyridinium compounds were functionalized for increased electrochemical stability, cycled in flow cells to understand efficiencies, and analyzed for degradation products. Methylation of the bipyridine nitrogens increased electrochemical stability yet left the reduced molecule susceptible to radical‐induced bond cleavage. Subsequent functionalization of bipyridine with carbomethoxy groups resulted in good battery performance with 96 % Coulombic and 90 % voltage efficiency, and improved cycling stability over a methoxy‐substituted anolyte with 14 % vs 36 % capacity fade in the first charge‐discharge cycle. Abstract : Better without metal : High‐stability non‐aqueous redox flow battery materials are imperative for integration into the electric grid. One such source of instability in metal‐based electroactive materials is ligand shedding during cycling. Development of electrochemically stable, unbound ligands can circumvent the issue, but stability must be understood. Here, sources of capacity fade in flow cells using substituted bipyridinium anolyte materials were designed and elucidated and improved stability of a carbomethoxy group over a methoxy‐substituted molecule was found.