# Electrolyte Engineering in Redox-Enhanced Electrochemical Capacitors with Zn Anodes: The Role of Colorimetric Indicators

## TL;DR

Researchers developed color-changing dyes for use in zinc-ion capacitors, improving performance and allowing real-time diagnostics.

## Contribution

The use of triphenylmethane dyes as colorimetric indicators in electrolytes for redox-enhanced zinc-ion capacitors is novel.

## Key findings

- Colorimetric indicators enable proton-electron transfer, supporting health diagnostics and redox reactions.
- Dye-based electrolytes extend Zn||Zn cell lifespan to 4,000 hours with 87.7% capacity retention after 20,000 cycles.
- RZICs achieve 152.4 mAh g−1 capacity within a 0.2–1.6 V window using phenol–quinone transformation.

## Abstract

Triphenylmethane dyes as colorimetric indicators were developed for fabricating functional electrolytes in redox-enhanced zinc-ion hybrid capacitors (RZICs), integrating pH buffering, electrochromic response, and redox activity.The colorimetric indicators exhibit proton-electron transfer behavior, where proton transfer enables health state diagnostics and electron transfer facilitates reversible redox reactions.The dye-containing electrolytes provide a wider voltage window, high capacity, and long cycling stability for high-performance RZIC devices.Incorporating colorimetric indicators extends the cycling lifespan of Zn||Zn cells to 4,000 h, allowing RZICs to deliver a capacity of 152.4 mAh g−1 within a 0.2-1.6 V voltage window, with 87.7% capacity retention after 20,000 cycles.

Triphenylmethane dyes as colorimetric indicators were developed for fabricating functional electrolytes in redox-enhanced zinc-ion hybrid capacitors (RZICs), integrating pH buffering, electrochromic response, and redox activity.

The colorimetric indicators exhibit proton-electron transfer behavior, where proton transfer enables health state diagnostics and electron transfer facilitates reversible redox reactions.

The dye-containing electrolytes provide a wider voltage window, high capacity, and long cycling stability for high-performance RZIC devices.

Incorporating colorimetric indicators extends the cycling lifespan of Zn||Zn cells to 4,000 h, allowing RZICs to deliver a capacity of 152.4 mAh g−1 within a 0.2-1.6 V voltage window, with 87.7% capacity retention after 20,000 cycles.

The online version contains supplementary material available at 10.1007/s40820-026-02116-9.

The increasing demand for high-performance energy devices has prompted the exploration of advanced electrolytic solutions for aqueous energy storage. Redox-enhanced Zn-ion capacitors (RZICs) overcome the limitations of conventional electrochemical capacitors by integrating redox-active molecules into the electrolyte, which enables higher energy density and expanded voltage windows. In this study, we developed organic dye-based colorimetric indicators for the fabrication of functional electrolytes in RZICs. The structural responsiveness of these dyes, driven by proton–electron transfer through electrochromic dynamics, allows real-time monitoring and optimization of the RZICs. The acid–base equilibrium of colorimetric indicators supports pH buffering, resulting in an extended lifespan of Zn||Zn cells up to 4,000 h. The conjugated aromatic structure of the indicators enhances their adsorption onto activated carbon, thereby minimizing the self-discharge in RZICs. Additionally, the phenol–quinone transformation increases the capacity of RZICs to 152.4 mAh g−1 within an optimized voltage window of 0.2–1.6 V, while promoting electrochemical kinetics and suppressing anode degradation. The results advance the design and customization of redox electrolytes with colorimetric properties for supercapacitive energy storage.

The online version contains supplementary material available at 10.1007/s40820-026-02116-9.