Ion-conductive polymers (ionomers) have been widely used as the solid-electrolyte in energy conversion devices, such as polymer-electrolyte fuel cells and water-splitting electrolyzers, to facilitate the selective transport of ions (e.g., protons). While ionomers are the ubiquitous choice as the polymer-electrolyte membrane (PEM), their role extends to electrodes where nanometer-thick ionomer films bind the catalysts and facilitate transport of ionic and gaseous species as well as water. When confined to sub-100nm thicknesses, ionomer structure changes drastically compared to PEM and is influenced strongly by the electro-catalyst interactions in electrodes. These electrodes are heterogeneous, porous catalyst layers fabricated from inks comprised of catalysts (e.g., C and Pt) and ionomer dispersion. Thus, morphology of catalyst layers is dictated by the ionomer-catalyst interactions in the inks, which ultimately affects the electrode properties. By studying these interactions both in dispersion phase and in film form on support, one can develop a better picture of the ionomer-catalyst interface and its role in device performance.<br/><br/>This talk will provide an overview of the current state of understanding of the fuel-cell electrodes with a focus on a class of Perfluorosulfonic acid (PFSA) ionomers. In particular, the properties of several ionomers are investigated in different solvent compositions by accounting for casting and processing effects. Then, we examine how these dispersions form films on supports (&lt;100 nm) and investigate the extent to which film properties are impacted by the solvent-ionomer interactions. The structural evolution of ionomers from dispersion to thin films is monitored using time-resolved grazing incidence x-ray scattering, which is complemented by physical and electrochemical properties of thin films cast on supports, including metallic surfaces relevant to electrodes. By examining factors impacting dispersion and film properties for various ionomers, we identify key chemical and processing parameters controlling their structure-functionality. These results are supported further by novel characterization techniques probing the ionomer-catalyst interface and ionic interactions with a fundamental understanding of the underlying causes of transport resistances in fuel-cell electrodes. The findings will be used to present strategies for tuning ionomer-catalyst interfaces for improved electrode performance in energy conversion devices.

Tuning catalyst ionomers for fuel-cell electrodes

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.