Unveiling the Anion Effect of Potassium Salts on Lawsone-Based Anolytes for Aqueous Redox Flow Batteries

<title>Abstract</title> <p>Aqueous organic redox flow batteries (AORFBs) attract a significant attention for large-scale energy storage systems owing to their intrinsic safety, low cost, and design flexibility. Among various organic redox couples, 2-hydroxy-1,4-naphthoquinone (Lawsone) and ferrocyanide (FeCN) combination exhibits a promising electrochemical performance. However, its practical application is hindered by capacity decay arising from side reactions occurring under strongly alkaline conditions. Although chemical modification of Lawsone proposes to improve cycling stability, such approaches generally require complex synthesis and increase material cost. In this work, supporting electrolyte composition is adjusted to alleviate the strongly alkaline environment without modifying the active material. Specifically, hydroxide is partially replaced with chloride to reduce alkalinity of electrolyte and the effects of potassium salt anions on electrochemical behavior and battery performance of Lawsone anolyte is investigated. Contrary to the initial expectation, conventional 1 M KOH electrolyte exhibits superior electrochemical kinetics, leading to higher capacity utilization and improved cycling stability than the mixed electrolyte (0.8 M KCl + 0.2 M KOH). AORFB employing 1 M KOH retains 72% of its initial capacity after 100 cycles, whereas mixed electrolyte preserves only 42%. These findings indicate that electrochemical performance is governed not only by electrolyte alkalinity but also by the nature of supporting electrolyte anion.</p>