Dissertation Defense: A Mechanistic Interpretation for Charge Storage in Conducting Polymers

Committee

• Vishnu-Baba Sundaresan, Chair (Mechanical)
• Marcello Canova (Mechanical)
• Carlos Castro (Mechanical)
• Anne Co (Chemistry)

Abstract

This research focuses on the characterization of active redox sites in p-doped conducting polymers (CP) and applies this knowledge to develop a mechanistic interpretation for charge storage in CPs. The scientific goal of this thesis is to develop a novel understanding of ion transport and associated mechanics in CPs and leverage this knowledge to design electrodes with templating techniques that can produce polypyrrole-based membranes with charge storage capacity near its theoretical limit and yet undergo minimal mechanical strain during charging and discharging cycles. The specific translation of ion transport into mechanical deformation is analyzed using static and dynamic characterization techniques. The polypyrrole (PPy) membranes from this research can be fabricated into a flexible supercapacitor to demonstrate its advantages in energy storage applications. The hypothesis of this research is that polypyrrole membranes fabricated using phospholipid vesicles as soft-templates have higher specific surface area/volume (SA:V) ratio and decreased density, resulting in reduced mechanical strain. Additionally it is proposed that morphology effects ion ingress/egress and distribution throughout the polymer matrix. The higher SA:V ratio and improved ion transport kinetics is expected to lead to higher storage capacity, smaller strain during charging/discharging, and increased operational lifetime. The higher charge storage capacity of phospholipid-templated polypyrrole membranes would manifest itself as higher specific capacitance and offer systemic advantages as sensors and battery/supercapacitor electrodes. Contemporary knowledge does not account for redox sites and their influence on charge storage capacity of CPs. The inability to determine a filling efficiency was limited by a lack of understanding of the polymerization mechanism, which has been expanded on through this work. Further, the ability to experimentally determine ion transport dependent strain has been limited by a lack of contemporary techniques to map surface topography and charge storage simultaneously. The limitation has been overcome in this research through the use of correlated electrochemical characterization (CA/CV) and shear force (SF) imaging.