Influence of Quaternary Ammonium Cation Chemistry on Interfacial Morphology of Anion-Conducting Block Copolymers at a Silver Interface

• Published in: Meeting abstracts (Electrochemical Society) Vol. MA2020-02; no. 37; p. 2365
• Main Authors: Buggy, Nora Catherine, Du, Yifeng, Kuo, Mei-Chen, Coughlin, E. Bryan, Herring, Andrew M.
• Format: Journal Article
• Language: English
• Published: 23.11.2020
• DOI: 10.1149/MA2020-02372365mtgabs
• ISSN: 2151-2043

The heterogeneous microstructure of the electrode in polymer electrolyte-based electrochemical devices features a complex mixture of interacting species, including ionomer, catalyst particles, and typically a conductive carbon support. The triple-phase boundary which forms between these three components significantly impacts the transport of water, ions, and reactant and product species to and from reaction sites. Hence, overall performance of the electrochemical device is significantly impacted by the structures that form in the electrode, which are driven by interactions between the ionomer and catalyst components. It is known that interactions at the ionomer-catalyst interface can facilitate restructuring of the ionomer morphology, ultimately affecting transport networks. Therefore, a more fundamental understanding of ionomer-catalyst interactions can aid in the development of ionomer chemistries that result in desirable interfacial morphologies and electrode structures. Since alkaline systems can leverage the ORR capabilities of non-noble metal catalysts beyond Pt, this work focuses on interactions with silver, which has been shown to have ORR activity akin to Pt catalysts. Our previous work has shown that the quaternary ammonium cations trimethylammonium (TMA) and methylpiperidinium (MPRD) both interact with silver and can affect bulk properties of the ionomer, including crystallinity and water uptake. To continue this study, a set of tunable block copolymers, post-functionalized with either TMA or MPRD, are used to investigate how cation chemistry influences the resulting interfacial morphology of the ionomer. Model interfaces between ionomer thin films and silver surfaces are fabricated and studied using a combination of environmental GISAXS and AFM to assess morphological characteristics such as domain size and orientation under relevant electrochemical device conditions. These efforts will lead to a better understanding of the ionomer-catalyst interface and will provide key insight toward rationally designing block copolymers for the alkaline electrochemical devices.