Block Copolymer-Based Membranes for Vanadium Redox Flow Batteries: Synthesis, Characterization, and Performance

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Nafion membranes are standard for redox flow batteries but face cost and environmental concerns.
• Nonfluorinated polymers are being explored as sustainable alternatives for ion-exchange membranes.

Purpose of the Study:

• Synthesize and evaluate block copolymers of polysulfone (PSU) and polyphenylsulfone (PPSU) as precursors for vanadium redox flow battery (VRFB) membranes.
• Investigate the structure-property relationships of PSU/PPSU copolymers with varying molar ratios.

Main Methods:

• Block copolymers of PSU and PPSU were synthesized with PSU/PPSU molar ratios of 75/25, 60/40, and 50/50.
• Ex situ studies were conducted to assess vanadium ion permeability, chemical stability, and mechanical stability.
• Membrane performance was compared to commercial Nafion membranes.

Main Results:

• Copolymers with concentrated sulfonic groups (75/25 and 60/40) formed distinct hydrophobic/hydrophilic domains.
• The 50/50 copolymer exhibited a balanced sulfonation and homogeneous sulfonic group distribution.
• The 50/50 PSU/PPSU membranes demonstrated vanadium ion permeability and stability comparable to Nafion.

Conclusions:

• PSU/PPSU block copolymers are promising nonfluorinated alternatives for VRFB membranes.
• The 50/50 copolymer composition offers a balanced structure for high-performance ion-exchange membranes.
• These findings represent a significant advancement towards sustainable and high-performance VRFB technologies.