Probing Ionomer Interactions with Electrocatalyst Particles in Solution

Abstract

The interaction between ionomer (ion-conducting polymer) and catalyst particles in porous electrodes of electrochemical energy-conversion devices is a critical yet poorly understood phenomenon that controls device performance. This interaction stems from that in the electrode precursor inks, which also governs porous-electrode morphology during formation. In this letter, we probe the origin of this interaction in solution to unravel the ionomer/particle agglomeration process. Quartz-crystal microbalance studies detail ionomer adsorption (with a range of charge densities) to model surfaces under a variety of solvent environments, and isothermal-titration-calorimetry experiments extract thermodynamic binding information to platinum-and carbon-black nanoparticles. Results reveal that under the conditions tested, ionomer binding to platinum is similar to carbon, suggesting that adsorption to platinum-on-carbon catalyst particles in inks is likely dictated mostly by hydrophobic interactions with the carbon surface. Furthermore, water-rich solvents (relative to propanol) promote ionomer adsorption. Finally, ionomer dispersions change with time, yielding dynamic binding interactions.

Co3O4|CoP Core–Shell Nanoparticles with Enhanced Electrocatalytic Water Oxidation Performance

“…The widespread ionomer used in the preparation of the catalyst ink is Nafion, also known as perfluorosulfonic acid (PFSA), which exhibits very good mechanical and electrochemical stability. Nafion is usually comprised of a hydrophobic Teflon network and a hydrophilic sulfonic acid group as a side chain. , Nafion can act as a good binder if it disperses uniformly and hence binds with catalyst particles. The dispersion structures have a strong influence on the self-assembly of ionomer agglomeration, the properties of the catalyst layer after drying, and the adsorption of the ionomer to the catalyst particles …”

Linking Perfluorosulfonic Acid Ionomer Chemistry and High-Current Density Performance in Fuel-Cell Electrodes

“…The ionomer in ink dispersions influences both electrostatic and non-electrostatic specific interactions, with the former stemming from the inherent acidity of the ionomer ( i.e. , similar to an inorganic acid) and the latter stemming from the specific hydrophobic/hydrophilic interactions with the catalyst particles, particularly through hydrophobic ionomer backbone interactions with the graphitic Vulcan carbon support …”

Impact of Platinum Primary Particle Loading on Fuel Cell Performance: Insights from Catalyst/Ionomer Ink Interactions

“…Importantly, the surface chemistry of the catalyst particles (i.e., platinum-nanoparticle loading and distribution and carbon type) alters how the ionomer interacts with them, as evidenced by rheological measurements . Furthermore, calorimetry and ionomer adsorption measurements reveal that, when subject to no applied potentials, the binding strengths of the ionomer are higher on hydrophobic (carbon) surfaces than on platinum surfaces when using Nafion (a prototypical ionomer; although depending on the ionomer charge density, the magnitude of this relationship may change) . One therefore expects that as the PPL varies (i.e., the surface area of platinum nanoparticles relative to carbon particles), the ionomer/catalyst particle interaction strengths in an ink will differ (decreasing interaction with the increasing platinum surface area), which could impact the CL microstructure and device power output.…”