Probing Ionomer Interactions with Electrocatalyst Particles in Solution

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 determines device performance: electrode morphology is controlled by ionomer/particle interactions in precursor inks during electrode formation. In this Letter, we probe the origin of this interaction in inks to unravel the complexities of ionomer/particle adsorption interactions. 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 entropic interactions with the carbon surface. Furthermore, water-rich solvents (relative to mixed water/propanol) promote ionomer adsorption. Finally, ionomer dispersions change with time, yielding dynamic binding interactions.

Automated summary

The interaction between ionomer and catalyst particles in porous electrodes of electrochemical-energy-conversion devices is crucial for performance, with ionomer adsorption being influenced mainly by entropic interactions with the carbon surface. Solvents with higher water content promote ionomer adsorption, and ionomer dispersions change with time, leading to dynamic binding interactions.