Date of Graduation

5-2026

Document Type

Thesis

Degree Name

Bachelor of Science in Chemical Engineering

Degree Level

Undergraduate

Department

Chemical Engineering

Advisor/Mentor

Dr. Keisha Walters

Committee Member

Dr. Keisha Walters

Second Committee Member

Dr. Hyunjin Moon

Third Committee Member

Dr. Xiaoyu Wang

Fourth Committee Member

Dr. Tammy Lutz-Rechtin

Abstract

Polymer electrolytes for supercapacitor applications require a balance between mechanical robustness and electrochemical performance. In this study, cellulose acetate (CA) films were modified with additives such as polyetherimide (PEI) and polyethylene glycol (PEG) to test how compositional changes influence mechanical performance, ionic conductivity, and electrochemical charge storage. Films were cast using phase inversion, soaked in a 1 M NaCl aqueous solution, and characterized using Fourier-transform infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and tensile testing. Films were also evaluated based on fluid uptake for insight into electrolyte retention.

Characterizations show that the addition of PEI increased ionic conductivity by an order of magnitude, from 2.3·10-4 S/cm in a neat CA film to 4.7·10-3 S/cm in a 20 wt% PEI film, due to enhanced ion transport pathways from enhanced porosity. Mechanical performance also improved and was found optimal at 10 wt% PEI with the highest Young’s modulus, ultimate tensile strength, and percent elongation, which can be attributed to an improved polymer compatibility and stress distribution. The addition of PEG (up to 5 wt%) into the film containing the optimal PEI weight percentage (10 wt%) was found to further enhance transport properties. With added PEG, ionic conductivity reached a maximum at 2 wt% PEG (PEG2) of 8.5·10-3 due to increased electrolyte retention and polymer chain mobility.

However, the incorporation of PEG into the film significantly decreased specific capacitance, decreasing from 0.5223 F/g at 0 wt% PEG (PEG0) to 0.0980 at 1 wt% PEG (PEG1) due to the disruption of electric double-layer formation. These results show a trade-off between ionic transport and charge storage. While PEG can increase mechanical robustness and transport pathways, its effect of capacitance limits its usefulness in supercapacitor devices. As a result, the optimal formulation was determined to be PEG0/CA90, providing the best overall performance for a supercapacitor device.

Keywords

supercapacitors; energy storage; polymers; transport phenomena; capacitance; ionic conductivity

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