A Highly Soluble Two-Electron Storage Viologen Negolyte for Neutral Aqueous Organic Redox Flow Batteries

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Aqueous organic redox flow batteries (AORFBs) are promising for large-scale renewable energy storage.
• Viologen species are effective negolytes, but often limited by one-electron redox processes.
• Achieving two-electron redox in viologens typically requires complex synthesis, hindering scalability.

Purpose of the Study:

• To develop a cost-effective, scalable negolyte for AORFBs with enhanced electrochemical performance.
• To investigate a novel viologen derivative, BTMEP-Vi, for its suitability in AORFBs.
• To analyze the electrochemical properties, stability, and degradation mechanisms of BTMEP-Vi.

Main Methods:

• Two-step synthesis of 3-(triethylammonio) propyl viologen tetrachloride (BTMEP-Vi).
• Electrochemical characterization including redox potential measurements.
• Assembly and testing of a flow battery utilizing BTMEP-Vi as the negolyte.
• Investigation of cycle stability and degradation pathways.

Main Results:

• BTMEP-Vi was synthesized efficiently from cost-effective materials.
• High water solubility (2.56 M) and two-electron reversible redox processes at -0.34 and -0.70 V vs SHE were observed.
• The assembled AORFB achieved a high voltage of 1.50 V and power density of 168.68 mW cm^-2.
• Cycle stability was assessed, and potential degradation mechanisms were elucidated.

Conclusions:

• BTMEP-Vi is a viable negolyte for high-performance AORFBs, overcoming limitations of single-electron redox systems.
• The straightforward synthesis and excellent electrochemical properties of BTMEP-Vi support its potential for commercial applications.
• Understanding degradation pathways is crucial for further optimizing the long-term stability of AORFBs.