A Composite Membrane Based on Sulfonated Polystyrene Implanted in a Stretched PTFE Film for Vanadium Flow Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Science

Background:

• Ion-selective membranes are critical for Vanadium Flow Battery (VFB) efficiency.
• Nafion™ is a common but expensive material, driving the search for alternatives.
• Mimicking Nafion's dual-phase structure is a promising approach.

Purpose of the Study:

• To develop a novel, low-cost composite membrane as a Nafion™ alternative for VFBs.
• To investigate the relationship between material composition and membrane performance.
• To evaluate the suitability of the new membrane for VFB applications.

Main Methods:

• Synthesizing a composite membrane by polymerizing sulfonated styrene within a porous PTFE matrix.
• Varying polystyrene content and sulfonation degree to control ion-exchange capacity (IEC).
• Characterizing membrane properties including vanadium permeability and proton conductivity.
• Testing the membrane's performance in a single-cell VFB.

Main Results:

• Achieved IEC values ranging from 0.96 to 1.84 mmol/g.
• Developed a membrane with balanced vanadium permeability (approx. 5.5 × 10⁻⁶ cm²/min) and proton conductivity (approx. 50 mS/cm) at 21-23% polystyrene and 94% sulfonation.
• Demonstrated stable VFB cycling with 81% energy efficiency.

Conclusions:

• The new composite membrane offers a promising, cost-effective alternative to Nafion™ for VFBs.
• The scalable production method facilitates wider adoption of advanced VFB technology.
• Optimized material composition leads to balanced ion transport and high energy efficiency.