Highly Stable, Low Gas Crossover, Proton-Conducting Phenylated Polyphenylenes

Area of Science:

• Polymer Science and Engineering
• Electrochemistry
• Materials Science

Background:

• Proton exchange membranes (PEMs) are critical components in electrochemical devices like fuel cells.
• Current PEMs, such as Nafion, face challenges including high cost, limited performance under low humidity, and degradation.
• Development of alternative PEMs with enhanced properties is crucial for advancing electrochemical technologies.

Purpose of the Study:

• To investigate novel sulfonated phenylated polyphenylenes as potential polyaromatic-based proton exchange membranes.
• To evaluate the ion exchange capacity, water solubility, proton conductivity, and stability of these new ionomers.
• To compare the performance and durability of these membranes against Nafion in fuel cell applications.

Main Methods:

• Synthesis and characterization of two classes of sulfonated phenylated polyphenylenes.
• Measurement of ion exchange capacity and water solubility at elevated temperatures.
• Assessment of proton conductivity under various humidity conditions (fully hydrated and reduced relative humidity).
• Evaluation of resilience to free radical attack and in situ chemical stability via accelerated stress tests.
• Fabrication and testing of membrane-electrode assemblies in fuel cells to determine in situ proton conductivity and peak power densities.

Main Results:

• The novel ionomers possess high ion exchange capacities and are insoluble in water at elevated temperatures.
• High proton conductivity was observed under both fully hydrated and reduced relative humidity conditions.
• The membranes demonstrated significant resilience to free radical attack.
• Fuel cells utilizing these membranes exhibited higher in situ proton conductivity and peak power densities compared to Nafion.
• Accelerated stress tests showed lower gas crossover and degradation rates for the new membranes versus Nafion.

Conclusions:

• Sulfonated phenylated polyphenylenes represent a promising class of materials for proton-conducting applications.
• These polyaromatic membranes offer superior performance and stability compared to conventional Nafion systems.
• Molecularly designed sulfonated phenylated polyphenylenes hold significant potential for next-generation electrochemical technologies.