Probing the electrochemical dynamics of soluble redox active polymers

It is an exciting time for exploring the synergism between the chemical and dimensional properties of redox nanomaterials for addressing the manifold performance demands faced by energy storage technologies. Our groups are interested in the development and implementation of a new strategy for non-aqueous flow batteries (NRFBs) for grid energy storage. Our motivation is to solve major challenges in NRFBs, such as the lack of membranes that simultaneously allow fast ion transport while minimizing redox active species crossover between anolyte (negative electrolyte) and catholyte (positive electrolyte) compartments. This pervasive crossover leads to deleterious capacity fade and materials underutilization. Redox active polymers (RAPs) are highlighted as soluble nanoscopic energy storing units that enable the simple but powerful size-exclusion concept for NRFBs. Crossover of the redox component is suppressed by matching high molecular weight RAPs with simple and inexpensive nanoporous commercial separators. In contrast to the vast literature on the redox chemistry of electrode-confined polymer films, studies on the electrochemistry of solubilized RAPs are incipient. Here, viologen-, ferrocene- and nitrostyrene-based polymers in various formats exhibit properties that make amenable their electrochemical exploration as solution-phase redox couples. A main finding is that RAP solutions store energy efficiently and reversibly while offering chemical modularity and size versatility. Beyond the practicality toward their use in NRFBs, the fundamental electrochemistry exhibited by RAPs is fascinating, showing clear distinctions in behavior from that of small molecules. Whereas RAPs conveniently translate the redox properties of small molecules into a nanostructure, they give rise to charge transfer mechanisms and electrolyte interactions that elicit distinct electrochemical responses. To understand how the electrochemical characteristics of RAPs depend on molecular features, including redox moiety, macromolecular size, and backbone structure, a range of techniques has been employed by our groups, including voltammetry at macro- and microelectrodes, rotating disk electrode (RDE) voltammetry, bulk electrolysis, and scanning electrochemical microscopy (SECM). Herein, we characterize the charge transfer mechanisms, identify the impact of backbone tether length and structure, demonstrate the role of the composition of the supporting electrolyte, and explore how electrostatic interactions and polyelectrolyte dynamics all affect the reactivity of soluble RAPs. Finally, new tools to study the energy storage capabilities of bulk RAP solutions and the possibility to interrogate single entities using SECM methods are highlighted as promising technologies to advance the electrochemical characterization of nanostructured macromolecular redox architectures.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2017

Author dc:creator

• Burgess, Mark

Contributors dc:contributor

• Rodríguez-López, Joaquín
• Moore, Jeffrey S.
• Sweedler, Jonathan
• Flaherty, David W.

• Redox active polymers
• Flow battery
• Electrochemistry
• Mechanisms

Statement dc:rights

• Copyright 2017 Mark Burgess

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/98249

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/98249