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Electrostatically Limited PFSA Ionomer Adsorption to Catalyst Particles in Catalyst Inks
Siddharth Rajupet1,2, Niki Jacquin1,2, Sarah A Berlinger2
1Department of Chemical and Biomolecular Engineering, University of California, Berkeley, California94720-1462, United States.
ACS Applied Materials & Interfaces
|August 9, 2026
Summary
Controlling perfluorosulfonic-acid (PFSA) ionomer adsorption onto catalyst particles is key for fuel cell performance. Electrostatic repulsion limits adsorption, but this can be tuned by modifying particle surface charge.
Area of Science:
- Materials Science
- Electrochemistry
- Surface Chemistry
Background:
- Optimizing catalyst-layer structure and performance in membrane-electrode assemblies is critical.
- Understanding and controlling ionomer adsorption in catalyst inks is essential for this optimization.
Purpose of the Study:
- To systematically quantify perfluorosulfonic-acid (PFSA) ionomer adsorption on diverse catalyst particles.
- To establish the dominant mechanism limiting ionomer adsorption and provide a framework for rational design.
Main Methods:
- Quantified ionomer adsorption on various particles (carbon, Pt/C, functionalized carbons, IrOx).
- Utilized potentiometric titration and a kinetic adsorption model.
- Calculated electric double-layer interactions using DLVO theory adapted for PFSA systems.
Main Results:
- Adsorption extent varied by nearly an order of magnitude across particle types.
- Ionomer adsorption self-quenches when an energy barrier exceeds ~25 kBT due to electrostatic repulsion.
- Particles reached a common limiting surface-charge density, independent of particle type.
- Adsorption was successfully tuned via surface functionalization.
Conclusions:
- Electrostatic interactions are the dominant mechanism limiting PFSA ionomer adsorption.
- A common limiting surface-charge density is achieved across different particle types.
- Surface functionalization offers a method to systematically tune ionomer adsorption.
- Findings provide a framework for designing catalyst inks and improving ionomer distribution.
