Date of Award:

12-2023

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Chemistry and Biochemistry

Committee Chair(s)

Tianbiao Liu

Committee

Tianbiao Liu

Committee

Gang Li

Committee

Yi Rao

Committee

Tuan Trinh

Committee

Christo Sevov

Abstract

Since the fast growth of the global population, energy scarcity has become a new threat to modern society. Those commonly seen resources like fossil, coal, and natural gas are nonrenewable energies, which cannot be replenished by human-scale time. In contrast, wind, solar, and hydropower are the three main renewable green energies under development with great efforts around the world. However, the intermittent character of these powers raises a new question: how to store them properly on large scales? By 2021, more than 90% of the electricity storage was taken by Lithium-ion batteries (LIBs). The usage of lithium brings concerns about its limited amount and high reactivity, and thus urgent to look for a replacement.

Under this situation, redox-flow batteries (RFBs) were recognized as a promising class for large-scale renewable energy storage. Unlike conventional solid- state batteries in daily portable devices, RFBs use electrolytes, which is a kind of solution that contains dissolved redox-active materials, for electricity storage. The general construction of RFBs contains two electrolyte tanks and a center reaction site that has been divided into two polars by a separator (membrane). Such an architecture separates the power-producing site and the energy-storing site, which is a merit that cannot be accomplished by LIBs. This character offers the chance to change one parameter while holding the other one intact within a single device. The study of RFBs has passed through decades with the two most advanced designs, all vanadium RFBs (VRFBs) and Zinc-Bromine RFBs (ZBRFBs), that have been commercialized. Nevertheless, due to the high cost of vanadium and toxicity for both vanadium and bromine species, the development focus has switched from inorganic materials to organic materials. Organic compounds incorporate earth-abundant elements like C, H, O, N, etc., and have high flexibility to fabricate their structures. By modifying the organic molecules, they could achieve desired solubilities (energy), redox potentials (energy & power), and material stabilities (lifetime).

The efforts in my graduate studies have been put into designing two aqueous- based viologen materials and studying the chemical stability of (2,2,6,6- tetramethylpiperidin-1-yl)oxyl (TEMPO). Inclusive analysis of physiochemical and electrochemical properties and battery demonstrations have been made using numerous techniques. After the work with material development, a further study on desalination RFBs has been made to establish a relationship between the battery parameter and the desalination performance.

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