Mechanisms of diffusive charge transport in redox active polymer solutions

Bello Fernandez, Liliana

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https://hdl.handle.net/2142/121250 Copy

Description

Title

Mechanisms of diffusive charge transport in redox active polymer solutions

Author(s)

Bello Fernandez, Liliana

Issue Date

2023-07-12

Director of Research (if dissertation) or Advisor (if thesis)

Sing, Charles E

Doctoral Committee Chair(s)

Sing, Charles E

Committee Member(s)

• Schroeder, Charles M
• Rodriguez-Lopez, Joaquin
• Statt, Antonia

Department of Study

Chemical & Biomolecular Engr

Discipline

Chemical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• redox active polymers
• computation
• polymer physics theory, polyelectrolyte

Abstract

Due to the strong demand to switch towards renewable sources of energy, we investigate redox active polymer solutions as a target material to be employed in redox flow battery systems. Given the lack of molecular level understanding in redox active polymer solutions, we created a combined Brownian dynamics and kinetic Monte Carlo simulation to fundamentally understand charge transport in redox active polymer solutions. This work provides fundamental insight of the conformational effects relevant in redox active polymer solutions and how this interplays with charge transport mechanisms such as intra-chain charge hopping, segmental motions, inter-chain charge hopping, and translational diffusion depending on the polymer concentration, salt concentration, and charge valency. This work provides molecular level insight that is not easily accessible via experimental studies that will help us design RAPs for more efficient charge transport. We simulated single chain and multi-chain systems for various rates of self-exchange characterized by average adjacent charge hopping time ⟨τ ̃A⟩ and average non-adjacent charge hopping time ⟨τ ̃B⟩ to probe the various charge hopping mechanisms. We showed the existence of three distinct regimes of charge hopping mechanisms delineated by the polymer coil size R and effective overlap concentration c∗eff using an implicit salt model. We then extended our model to consider the role of salt concentration and valency by including salt explicitly in our system. We showed that the role of salt concentration on charge transport centers around its role in polymer swelling and this interplays with the charge valency of our system, where higher valency leads to more polymer swelling and increasing salt concentration generally leads to less polymer swelling. Lastly, we collaborated with the Rodriguez-Lopez and Ewoldt group to investigate high valency RAP solutions with different rates of self-exchange. We showed that just changing the rate of self-exchange plays an important role in how many monomers can become oxidized upon contacting a model electrode surface. There is also some role of salt ii concentration given that it affects the polymer coil size and how quickly a polymer chain can diffuse from a surface. Overall, this work provides a molecular level understanding of the charge transport mechanisms in redox active polymer solutions that will aid in the design of RAPs for improved battery performance.

Graduation Semester

2023-08

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Liliana Bello Fernandez

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