A Multielectron and High-Potential Spirobifluorene-Based Posolyte for Aqueous Redox Flow Batteries

Area of Science:

• Electrochemistry and Materials Science
• Renewable Energy Storage

Background:

• Growing energy demand necessitates advanced renewable energy storage.
• Aqueous organic redox flow batteries (AORFBs) require improved positive electrolytes.
• Current AOFB positive electrolytes face limitations in redox potential and electron concentration.

Purpose of the Study:

• To develop novel organic positive electrolytes for AORFBs.
• To address limitations in redox potential and stability of existing materials.
• To explore the use of unexpected side reactions for material development.

Main Methods:

• Synthesis of spatially twisted chlorinated spirobifluorene ammonium salts (CSFAs).
• In-situ generation of CSFAs via a green chlorination-protection pathway during flow battery cycling.
• Electrochemical characterization and long-term cycling performance evaluation in a full AORFB.

Main Results:

• CSFAs exhibit a unique one-step four-electron transfer capability.
• Achieved an unprecedented redox potential of 1.05 V (vs. SHE) with high resistance to nucleophilic attacks.
• A CSFA-Cl based flow battery demonstrated >99.4% coulombic efficiency and 95% capacity utilization over 250 cycles.

Conclusions:

• Spatially twisted chlorinated spirobifluorene ammonium salts are effective positive electrolytes for AORFBs.
• The study showcases the potential of utilizing side reactions for novel redox species discovery.
• This approach can lead to the development of more versatile and efficient energy storage materials.