Date of Award:

5-2020

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Chemistry and Biochemistry

Advisor/Chair:

Tianbiao Liu

Co-Advisor/Chair:

Lance C. Seefeldt

Third Advisor:

Bradley S. Davidson

Abstract

Nowadays, the utilization of renewable energy resources such as solar and wind energy has been realized to be a sustainable and environmentally benign strategy to alleviate the world’s severe dependency on traditional fossil fuels, and thus enables the environmental recovery and sustainable development of the economy. The massive commercialization of solar and wind energy raises the demands for advanced energy storage technologies, among which the redox flow battery has been recognized as a promising solution due to it is low cost, safe, environmentally benign, and easy to be scaled up. All vanadium redox flow battery stands for the most important system in the market. However, the high price of raw material (V2O5), active materials crossover leaded self-discharge, and hazardous electrolyte limit its broad application. Therefore, it is urgent to explore new active materials that are cheaper, more stable and more sustainable. Redox active organic molecules are great candidates to meet those requirements. The metal-free molecules are normally composed of elements of C, H, O, N,etc., which have massive resources from nature. With the rational molecular design, the organic molecules could be very tolerant of side reactions and chemical decomposition. Their electrochemical and physicochemical properties (such as redox potential, solubility and so on) can also be tuned by molecular engineering. My efforts have been putting on design highly water-soluble and stable ferrocene derivative and other metal-free molecules, for example, viologen, (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO), and anthraquinone derivatives. Their electrochemical properties and battery performance were evaluated with comprehensive techniques. Besides, we systematically studied the chemical decomposition mechanism of these active materials by UV-Vis monitoring, NMR characterization, and half-cell long term cycling. Elucidating the active material decomposition mechanism helps us to improve the molecular structure design for more stable organic redox active materials developing in the future.

Electrocatalysis is a process where electrochemical reactions happen on the surface of the electrodes which deliver or accept electrons. Electrocatalysis could provide another solution for valuable product synthesis with environment protection especially when it is integrated with renewable energy. I have been focusing on electrocatalytic CO2 and N2 fixation to synthesis carbohydrate and ammonia in aqueous media. Using CO2 and water as the reactant, nitrogenase as the catalyst, we electrochemically synthesized formate with high efficiency. I also carefully examined the catalytic activity of Mo2N for nitrogen reduction reaction (NRR). 15N2 isotope labeling experiment revealed that instead of catalytic N2 reduction, the ammonia formation is from nitride decomposition. The present results raise an urgent alert to the application of other metal nitrides or even nitrogen contained materials for electrocatalytic N2 reduction reactions.

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Included in

Chemistry Commons

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