Peptide-Controlled Assembly of Anion Exchange Ionomer Thin Films on Electrode Surfaces for Promoting Microphase Separation and Ionic Conductivity

Abstract

In electrochemical devices such as water electrolyzers and fuel cells, the network and morphology of the conductive ionomers within electrodes are critical for ion delivery and mass transport, significantly influencing the device performance. Most studies investigate these materials as bulk polymer electrolyte membranes and comparatively little attention has been given to their behavior on electrode surfaces as thin films. Anion exchange membrane fuel cells and water electrolyzers (AEMFCs and AEMWEs) would allow the use of non-precious group metals and enable low-cost systems, yet, even less is known about thin films of anion exchange ionomer (AEI). Protein engineering is emerging as a powerful nanomanufacturing tool to control the organization of components on electrodes. In this work, we propose that it can be applied to ionomer control, demonstrating that sequence defined elastin-like peptides assembled on electrode surfaces, and/or solvent vapor annealing processing, alters the microstructure configuration of assembled thin films of anion exchange ionomer. It is observed that peptides form a uniform monolayer on the metal surface, and moderately sized microphase separated ionic domains of the AEI are obtained either by modifying the electrode with peptides or solvent vapor annealing, which correlate with an increased in-plane ionic conductivity of the thin film. Interestingly, the use of peptide-modified electrodes in conjunction with solvent vapor annealing yields excessively large ionic grains that correlates with compromised ionic conductivity. Overall, we show that sequence defined peptides could serve as a tool for controlling electrode architecture, and judicious use of peptides, or solvent vapor annealing, have the potential to control the microstructure of thin AEI films and lead to structure-function understanding.