Water mediated proton conduction in a sulfonated microporous organic polymer

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Polymer membranes (PEMs) are crucial for fuel cells (FCs), acting as separators and proton conductors.
• Conventional PEMs suffer from water loss at high temperatures due to microphase separation.
• Porous materials offer improved water retention and proton conductivity.

Purpose of the Study:

• To investigate the proton conductivity of sulfonated microporous polymer PAF-1.
• To evaluate the impact of gas-phase sulfonation on PEM performance.
• To understand the relationship between water uptake and conductivity in porous PEMs.

Main Methods:

• Post-synthetic sulfonation of microporous polymer PAF-1 via gas phase.
• Proton conductivity measurements under various hydrous conditions.
• Analysis of water uptake and its effect on charge carrier concentration and activation barriers.

Main Results:

• Sulfonated PAF-1 achieved proton conductivities up to 10⁻¹ S cm⁻¹ under hydrous conditions.
• Gas-phase sulfonation effectively introduced a high concentration of -SO₃H groups.
• Conductivity strongly correlated with water uptake, but activation barriers remained consistent across relative humidities.

Conclusions:

• Microporous polymer PAF-1, when sulfonated, demonstrates excellent potential as a PEM for fuel cells.
• Gas-phase sulfonation is a critical method for enhancing proton conductivity in these materials.
• Homogeneous water storage in porous structures dictates interpore conductivity and overall performance.