Ion-conductive polymers (ionomers) have been widely used as the solid-electrolyte in electrochemical energy conversion devices, such as polymer electrolyte fuel cells (PEFCs), redox flow batteries and water-splitting devices. Ionomers such as perfluorosulfonic-acid (PFSA) are the benchmark separator-electrolyte in these devices, including polymer electrolyte fuel cells (PEFCs), due their high proton conductivity and chemical-mechanical stability. In PEFCs, however, ionomers play another key role in Catalyst Layer (CL) structure, where they exist as nanometer-thick electrolyte “thin films" to provide transport pathways to the catalytic particles. Once confined to these nanometer thicknesses (&lt; 100 nm), ionomer properties change drastically from the bulk (solid-electrolyte), and are significantly more influenced by its interfaces with the free surface (air) and the catalytic surface, such as carbon/platinum. Key is to understand how intrinsic morphology of an ionomer and its transport properties change throughout throughout this thickness range, which has implications for improving catalyst-layer performance. As an example, mass-transport limitations observed in fuel-cells are commonly associated with the transport resistances at the ionomer thin-film, mitigation of which requires a fundamental understanding of ionomer interfaces. Despite an ever-growing number of studies on ionomer membranes for solid-electrolytes, it is of great importance to characterize catalyst ionomers by studying them in thin film form, in an effort to explore factors controlling their structure and transport properties. In particular, there is need for developing not only novel characterization techniques for thin films and but also better model systems for dispersion-cast thin films that can mimic catalyst ionomer structure, behavior and environment, from solution properties to film formation, and to multiple interfaces and environmental conditioning. This talk summarizes recent progress in ionomer thin-film research, with a focus on key roles of chemistry, ion-exchange capacity, and cation interactions in ionomer structure/property relationship relavant to catalyst-layer performance. In addition, I will discuss recent developments in advanced characterization techniques, including the in-situ Grazing-Incidence X-ray scattering (GIXS), and how they can be used to probe various interactions in ionomer thin films.<br/>

Ionomer thin films in catalyst layers

256th National Meeting (2018)

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