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Impact of pH management on utilization and performance of anthraquinone/ ferrocyanide flow batteries

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Organic redox molecules in redox flow batteries (RFB) present a cost-efficient, environmentally friendly and earth abundant alternative to metal based ones. Their chemical stability is influenced by the pH, where RFB operation at highly acidic or alkaline, present a chemically harsh environment that increases the capacity fade. Operation under neutral or near-neutral conditions is therefore a pathway to longer battery lifetimes. Nonetheless, neutral conditions are difficult to maintain due to (electro-) chemical side reactions and a proper pH management is needed to mitigate the effect of these processes. In this work, we improved the chemical stability of a near-neutral system composed of 2,7-anthraquinone disulfonate (AQDS) and ferrocyanide by pH management. We apply different methods to control the pH variation during oxidation/reduction, such as the use of co-electrolytes with buffering properties and the increase in resting time to facilitate pH equilibration between the two electrolytes. We report a record-low capacity fade rate for AQDS of −0.025%/day for a stoichiometrically balanced flow battery that is validated with a record long operation period of more than 5 months without failure.

TidsskriftJournal of Power Sources
StatusUdgivet - aug. 2022

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