Design and evaluation of mixed ionic/electronic conducting polymers for energy storage devices and organic electrochemical transistors
File(s)
Author(s)
Yu, Hang
Type
Thesis
Abstract
Over the past decade, significant progress has been made in the field of organic mixed ionic-electronic conductors (OMIECs)—often π-conjugated polymers (CPs). These advancements include the development of high-performance p- and n-type mixed conducting polymers, and in-depth investigations into their operational mechanisms using operando characterisation techniques and multi-scale simulations. This thesis aims to contribute to this field by exploring the influence of side chains and electrolytes on the performance of mixed conducting polymers.
The first two results chapters, Chapters 3 and 4, investigate the impact of amphiphilic side chains on the charge transport and storage properties of oxy-bithiophene-based p-type CPs. In Chapter 3, the introduction of alkyl blocks between the backbone and the glycol side chains, termed “alkyl spacers”, aimed to enhance the charge transport and storage properties of the polymers. However, experimental results show an opposite outcome. Using molecular dynamics simulation, the mechanism for this deterioration is identified as the coupling between adjacent non-polar alkyl spacers in polar environments, which induces the backbone to twist. In Chapter 4, the backbone twisting issue was resolved by relocating the alkyl blocks to the outer end of the glycol blocks, termed “alkyl tips”. The new design strategy successfully prevents the backbone twisting and improves the charge transport and storage properties of the polymers.
Chapter 5 discusses the impact of electrolyte concentration on the reversibility of electron bipolarons in an archetypal naphthalenediimide (NDI)-based n-type CP. This study shows that, in contrast to the immediate bipolaron loss after the first charging/discharging cycle in dilute aqueous electrolytes, bipolarons can be reversibly and completely achieved in concentrated electrolytes. Furthermore, this study demonstrates distinctions in ion transport mechanisms between dilute and concentrated electrolytes, advancing our understanding of the mechanism of bipolaron loss.
The first two results chapters, Chapters 3 and 4, investigate the impact of amphiphilic side chains on the charge transport and storage properties of oxy-bithiophene-based p-type CPs. In Chapter 3, the introduction of alkyl blocks between the backbone and the glycol side chains, termed “alkyl spacers”, aimed to enhance the charge transport and storage properties of the polymers. However, experimental results show an opposite outcome. Using molecular dynamics simulation, the mechanism for this deterioration is identified as the coupling between adjacent non-polar alkyl spacers in polar environments, which induces the backbone to twist. In Chapter 4, the backbone twisting issue was resolved by relocating the alkyl blocks to the outer end of the glycol blocks, termed “alkyl tips”. The new design strategy successfully prevents the backbone twisting and improves the charge transport and storage properties of the polymers.
Chapter 5 discusses the impact of electrolyte concentration on the reversibility of electron bipolarons in an archetypal naphthalenediimide (NDI)-based n-type CP. This study shows that, in contrast to the immediate bipolaron loss after the first charging/discharging cycle in dilute aqueous electrolytes, bipolarons can be reversibly and completely achieved in concentrated electrolytes. Furthermore, this study demonstrates distinctions in ion transport mechanisms between dilute and concentrated electrolytes, advancing our understanding of the mechanism of bipolaron loss.
Version
Open Access
Date Issued
2023-12-20
Date Awarded
2024-04-01
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Nelson, Jenny
Barnes, Piers
Sponsor
China Scholarship Council
European Research Council
Grant Number
File No. 201906150122
Grant Agreement No. 742708
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)