Solubility-Enhancing Hydrotrope Electrolyte with Tailor-Made Organic Redox-Active Species for Redox-Enhanced Electrochemical Capacitors
Jinhwan Byeon, Jinhyuck Ko, Subin Lee, Da Hye Kim, Sung Won Kim, Dowon Kim, Wangsuk Oh, Sukwon Hong, Seung Joon Yoo
Abstract
The solubility of redox molecules is a critical factor that influences cell performance in redox-enhanced electrochemical capacitors (redox ECs). Unfortunately, commonly used organic redox molecules have low solubility in aqueous systems, limiting further performance enhancements. To solve this issue, a complex and costly synthesis is generally required. Here, we introduce the concept of a hydrotropic-supporting electrolyte (HSE) that can function as both a solubility-enhancing hydrotrope and an ion-conducting supporting electrolyte. Using the HSE, the solubility of hydroquinone (HQ) and anthraquinone-derivative (AQM-Br) increased up to 7- and 3-fold, respectively, compared to that in the aqueous H 2 SO 4 electrolyte. We develop a high-performance redox EC by implementing a bipolar AQM-Br with p -toluenesulfonic acid as the hydrotrope. Our mechanistic analysis provides insight into correlating the solute–hydrotrope interactions and hydrotrope efficiency. This work serves as a guideline for designing energy-dense redox-active electrolytes and for optimal selection of the HSE and redox-active electrolyte pairs.