Investigation of Electrochemical Mechanisms in Redox-Active Polymer Thin-Films

Abstract

Thin-film redox-active polymers, such as polyaniline and polythiophene, exhibit high rate energy storage, and have recently been demonstrated for their utility in electrochemical desalination. In order to improve the effectiveness of redox-active polymer films for electrochemical desalination, we need to understand the fundamental electrochemical mechanisms occurring in these materials. In particular, we are interested in understanding how the deposition technique impacts the polymer structure and in turn the type and quantity of ions binding to the film under applied potential in aqueous solutions. Furthermore, investigating the influence of thickness of these polymer films can further the understanding of their electrochemical mechanisms and rate capabilities. Here, we deposit thin-film redox-active polymers using nitrogen and sulfur heterocyclic monomers, and demonstrate control over the polymer film thickness from 1 – 20 nm by tuning the deposition parameters. We characterize rate capability of charge storage of the polymer films over this thickness range, and employ a range of characterization techniques, including electrochemical quartz crystal microbalance (EQCM), to study the fundamental electrochemical mechanisms at play in aqueous solutions. Mechanistic and performance studies are carried out in aqueous solutions containing various cations (e.g. Li+, Na+, K+) and anions (e.g. SO4 2-, Cl-, Br-). The insights from this study will help to inform the development of thin-film polymers for enhanced electrochemical desalination. Figure 1