Free-standing COF proton exchange membrane

For high-current-density flow batteries

Sulfonic acid functionalization enables free-standing membrane formation and builds continuous hydrogen-bonding networks for rapid proton transport in flow batteries.

Di, Mengting · Siwen, Lu · Sun, Xiaojun · Li, Zhang · Gao, Li · Yiran, Li · Jie, Liu · Hu, Lei · Ruan, Xuehua · Jiang, Xiaobin · Yan, Xiaoming · He, Gaohong

Chemical Engineering Journal 2026

Specifications

Tensile strength

{'zh': '50', 'en': '50'} MPa

Bending curvature

{'zh': '3500', 'en': '3500'} m⁻¹

Proton conductivity

{'zh': '332', 'en': '332'} mS cm⁻¹

Energy efficiency

{'zh': '70', 'en': '70'} %

Advantages

Free-standing film formation

Sulfonic acid groups induce framework twisting, weakening interlayer π-π stacking and facilitating strain dissipation, allowing COFs that otherwise yield only non-processable powders to be fabricated into flexible free-standing membranes.

High mechanical strength

The free-standing membrane achieves a tensile strength of 50 MPa and bending curvatures up to 3500 m⁻¹, meeting deformation requirements during device assembly and operation.

Rapid proton conduction

High-density sulfonic acid groups establish continuous hydrogen-bonding networks within sub-nanometer channels that promote rapid proton migration via the Grotthuss mechanism, achieving a proton conductivity of 332 mS cm⁻¹.

High efficiency at high current density

The membrane achieves an energy efficiency of 70% in vanadium flow batteries at a high current density of 500 mA cm⁻², suitable for high-power energy storage.

Applications

• Flow battery energy storage：Used as a separator in flow batteries, enabling high-current-density operation with high efficiency.
• PEM fuel cells：Can replace Nafion as a PEM, offering high proton conductivity and mechanical robustness.