Gaseous Nitrogen Oxides Catholyte for Rechargeable Redox Flow Batteries

Area of Science:

• Electrochemistry
• Energy Storage
• Materials Science

Background:

• Redox flow batteries (RFBs) require highly soluble redox compounds for improved energy density.
• High solute concentrations in electrolytes can negatively impact RFB performance.

Purpose of the Study:

• To design a high-potential catholyte for RFBs utilizing gaseous nitrogen oxides (NOx).
• To enable scalable energy storage by separating active species from the liquid electrolyte.

Main Methods:

• Designed a catholyte where charged and discharged species are gaseous NOx (NO and N2O3).
• Utilized a NOx symmetric H-cell for proof-of-concept testing.
• Investigated the electrochemical reaction: NO3- + 3NO <=> 2N2O3 + e-.

Main Results:

• Achieved a high potential of 0.5 V vs. Ag/Ag+.
• Demonstrated 200 stable cycles over 400 hours with >97% Coulombic efficiency.
• Observed negligible capacity decay, indicating excellent stability.

Conclusions:

• The NOx-based catholyte offers a promising approach for high-energy-density RFBs.
• Separating gaseous active species allows for independent scaling of energy and power.
• This system presents a low mass/charge ratio (152 g/mol e-) for efficient electron storage.