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
H2SO4 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.
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