Boron-Formazanate Complexes as Tunable Redox-Active Materials for Non-Aqueous Redox Flow Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Conventional redox flow batteries (RFBs) face limitations due to expensive and potentially toxic transition metals.
• Main-group compounds present an earth-abundant and cost-effective alternative for RFB electrolytes.

Purpose of the Study:

• To evaluate boron-formazanate complexes as electrolytes in nonaqueous organic redox flow batteries (NAORFBs).
• To understand degradation mechanisms and guide the rational design of stable main-group electrolytes.

Main Methods:

• Electrochemical characterization of boron-formazanate complexes in static H-cells and flow batteries.
• Analysis of degradation pathways, including fluoride elimination.
• Modification of electrolyte structure to enhance stability.

Main Results:

• Boron-formazanate complexes exhibit two sequential reduction processes, with the first being highly stable.
• Degradation occurs in the two-electron reduced state, attributed to fluoride elimination.
• Introducing a B(Ph)2 unit significantly improved cycling performance and stability.

Conclusions:

• Main-group boron-formazanate complexes are viable candidates for NAORFBs.
• Structural modification is key to mitigating degradation and enhancing electrolyte longevity.
• This work provides a pathway for designing inexpensive and stable main-group electrolytes for energy storage.