Amphoteric-Side-Chain-Functionalized "Ether-Free" Poly(arylene piperidinium) Membrane for Advanced Redox Flow Battery

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Nonfluorinated membranes face stability challenges in redox flow batteries (RFBs).
• Existing membranes often lack the necessary ion-exchange capacity and conductivity for high-efficiency RFBs.

Purpose of the Study:

• To develop a stable, cost-effective, nonfluorinated membrane for RFBs.
• To enhance RFB efficiency through improved membrane properties.

Main Methods:

• Synthesized an ether-free poly(arylene piperidinium) (PBPip) membrane with amphoteric side chains.
• Evaluated membrane stability via oxidation tests and FTIR.
• Characterized ion-exchange capacity (IEC), area resistance, swelling rate, and VO2+ permeability.
• Tested membrane performance in vanadium redox flow batteries (VRFBs).

Main Results:

• The PBPip membrane exhibited excellent stability in strong oxidation environments with no degradation over 30 days.
• Achieved a high IEC of 4.19 mmol g⁻¹ and low area resistance (0.22 Ω cm²), comparable to Nafion 212.
• Demonstrated low swelling (13.9%) and low VO2+ permeability (1.31 × 10⁻⁸ cm² s⁻¹).
• VRFBs using this membrane showed high voltage efficiency (VE) and energy efficiency (EE) exceeding 80% at 200 mA cm⁻², with stable performance over 500 cycles.

Conclusions:

• The ether-free PBPip membrane with amphoteric side chains offers a promising solution for stable and efficient RFBs.
• This design overcomes limitations of traditional membranes, providing high ion conductivity and low vanadium ion crossover.
• The study presents a new strategy for designing high-performance membranes for next-generation energy storage systems.