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Decoupling Solvent Effects: Perfluorinated Sulfonic Acid Structure and Catalyst Layer Stability in PEM Water
Jong-Hyeok Park1,2, Jin-Soo Park1,2,3
1Department of Civil, Environmental, and Biomedical Engineering, The Graduate School, Sangmyung University, Cheonan 31066, Republic of Korea.
Membranes
|January 27, 2026
Summary
Using a propylene-glycol solvent, this study isolates ionomer structure effects on catalyst layers for water electrolysis. Shorter side-chain ionomers offer improved performance and durability by optimizing film formation and reducing degradation.
Area of Science:
- Electrochemistry
- Materials Science
Background:
- Perfluorinated sulfonic acid ionomer (PFSI) dispersions are crucial binders in catalyst layers (CLs) for proton-exchange membrane (PEM) water electrolysis.
- Solvent choice significantly impacts PFSI behavior, confounding comparisons of different ionomer structures and their effects on CL performance.
Purpose of the Study:
- To isolate the effects of ionomer structure (side-chain architecture and equivalent weight) on hydrogen evolution reaction (HER) catalyst layers.
- To establish a standardized solvent platform (propylene glycol) for reliable comparisons of PFSI binders.
Main Methods:
- Utilized a propylene-glycol (PG) single-solvent system to prepare PFSI dispersions for five different ionomers.
- Characterized catalyst layers using electrochemical testing (current density, ohmic overpotential) and surface analysis (contact angle measurements).
- Assessed durability through Accelerated Stress Test-2 (AST-2) and analyzed material changes via transmission electron microscopy (TEM).
Main Results:
- PG solvent collapses ionomer aggregates and reduces catalyst-ionomer agglomerates, facilitating film formation independent of equivalent weight.
- Hydrophobicity and aerophobicity of CLs correlate with ionomer structure, with decreasing equivalent weight increasing sulfonic acid density.
- Short-side chain (SSC) and mid-side chain (MSC) ionomers exhibited higher current densities and better durability compared to long-side chain (LSC) Nafion under PG conditions.
- TEM analysis revealed significant Pt growth in LSC Nafion-based CLs, while SSC/MSC ionomers showed minimal degradation.
Conclusions:
- Ionomer structure, specifically side-chain architecture and equivalent weight, is the primary determinant of catalyst layer performance and stability when solvent effects are controlled.
- Short-side chain (SSC) ionomers with an equivalent weight around 980 are recommended for optimal performance and stability in PEM water electrolysis.
- Mid-side chain (MSC) ionomers maximize current density while offering moderate stability.
Keywords:
catalyst layerionomer thin-film formationperfluorosulfonic acid ionomerproton exchange membrane water electrolysisside-chain chemistryMore Related Videos
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