The Solvent Effect on Ionomer Self-Assembly: From Molecular Morphology to Catalyst Layer Performance

Area of Science:

• Electrochemistry
• Materials Science
• Chemical Engineering

Background:

• The catalyst-bound ionomer layer (CBIL) is crucial for proton exchange membrane fuel cell (PEMFC) performance.
• Ionomers in CBILs exhibit complex solvation behaviors and phase-separated structures.
• Understanding solvent effects on CBIL architecture is key to optimizing electrode properties.

Purpose of the Study:

• To elucidate how solvent composition and polarity influence ionomer solvation and phase separation within the CBIL.
• To investigate the impact of these changes on CBIL architecture, slurry properties, and electrode performance.
• To correlate CBIL characteristics with proton exchange membrane fuel cell polarization performance.

Main Methods:

• Analysis of ionomer solvation diameters and phase-separated structures under varying solvent conditions.
• Characterization of CBIL architecture on catalyst aggregates and slurry network heterogeneity.
• Measurement of pore distribution in coatings and electrode polarization performance.
• Zeta potential measurements to assess surface properties and interaggregate interactions.

Main Results:

• Water-rich solvents lead to ionomer morphological collapse, reduced exclusion volumes, and constrained -SO3H group extension.
• Denser CBIL structures with highly negative zeta potentials (<-70 mV) were observed, weakening interaggregate network strength.
• Main-chain collapse and side-chain curling reduced surface sulfur content, mitigating platinum poisoning.
• Elevated CBIL zeta potentials enhanced interaggregate repulsion, suppressing overaggregation and improving polarization performance.

Conclusions:

• Solvent composition critically regulates CBIL architecture and properties by controlling ionomer solvation and phase separation.
• Optimized CBIL structures, driven by solvent choice, significantly enhance PEMFC electrode polarization performance.
• The findings offer a pathway to mitigate platinum poisoning and improve fuel cell durability through tailored ionomer layer design.