Free Ionomer Controls Adsorption in Electrolyzer Inks

Abstract

Abstract The ionomer/catalyst interface in proton-exchange-membrane water-electrolyzer (PEMWE) anode catalyst layers governs multi-species transport and reaction kinetics, and originates from ionomer adsorption onto catalyst particles during ink formation. These inks contain iridium oxide (IrOx) catalyst and PEM ionomer (typically perfluorosulfonic acid, PFSA) dispersed in water:alcohol solvent mixtures, deposited to form the catalyst layer upon solvent evaporation. Despite the importance of ink formulation controlling ionomer adsorption, a systematic investigation spanning industrially relevant formulations (including concentrated inks used in roll-to-roll manufacturing) is missing. Here, we investigate the influence of IrOx concentration, ionomer-to-catalyst (I:C) ratio, and solvent composition on PFSA adsorption using thermal gravimetric analysis. PFSA adsorption is independent of IrOx concentration, being instead determined by free-ionomer concentration and solvent identity, across both dilute and concentrated inks. We further show that I:C ratio is a poor descriptor, with free-ionomer weight percentage providing a more meaningful metric that collapses adsorption data onto a single isotherm. In water-rich solvents, adsorption is primarily limited by electrostatic repulsion, whereas, in alcohol-rich solvents, solvation forces and surface-coverage effects dominate. We additionally characterize ink stability (sedimentation, x-ray scattering) and single-cell performance. These results extend to PFSA-based catalyst inks (including high-surface-area carbons), offering practical implications for ink formulation across deposition methods.

The authors' abstract, as published at the source. Journal of The Electrochemical Society, 2026 · DOI ↗