Highly Effective Proton-Conductive Matrix-Mixed Membrane Based on a -SO₃H-Functionalized Polyphosphazene.

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Proton-exchange membrane (PEM) fuel cells require efficient proton-conductive electrolytes.
• Developing stable and high-performance organic polymers for PEMs is crucial for advancing fuel cell technology.

Purpose of the Study:

• To synthesize a novel polyphosphazene with sulfonic acid groups (PP-PhSO3H) for enhanced proton conductivity.
• To evaluate the potential of PP-PhSO3H in matrix-mixed membranes for PEM fuel cell applications.

Main Methods:

• Facile synthesis of PP-PhSO3H via polymerization of hexachlorocyclotriphosphazene (HCCP) and sulfonate p-phenylenediamine.
• Characterization of the polymer's stability and amorphous nature.
• Proton conductivity measurements under varying relative humidity and temperature.
• Preparation and testing of PP-PhSO3H-polyacrylonitrile (PAN) composite membranes.

Main Results:

• Synthesized PP-PhSO3H exhibits high proton conductivity (up to 6.64 × 10⁻² S cm⁻¹ at 353 K and 98% RH), significantly higher than its non-sulfonated analog.
• The PP-PhSO3H-PAN (3:1) composite membrane achieved a proton conductivity of 5.05 × 10⁻² S cm⁻¹ under similar conditions, comparable to current PEM electrolytes.
• The composite membrane demonstrated long-term reusability in continuous tests.

Conclusions:

• The developed PP-PhSO3H polymer is a promising material for high-performance PEM fuel cells.
• Simple polymeric synthesis of phosphazene-based sulfonated polymers offers an effective route to advanced proton-conductive membranes.
• Matrix-mixed membranes incorporating PP-PhSO3H show significant potential for practical PEM fuel cell applications.