Date of Award

Winter 2021

Project Type

Dissertation

Program or Major

Chemical Engineering

Degree Name

Doctor of Philosophy

First Advisor

Xiaowei Teng

Second Advisor

Nivedita Gupta

Third Advisor

Young Jo Kim

Abstract

Aqueous energy storage has been an important part of battery research for its cost-effective, environmentally benign, and robust nature. Iron-based materials, including iron hydroxides and iron oxides, are widely investigated as electrode materials for their extremely low cost and sufficient discharge capacity. Iron-based electrode materials were often operated in strong alkaline electrolytes, experiencing either slow reaction kinetics, severe side reactions, or significant capacity loss over cycling. This research focused on the application of iron-based materials in aqueous electrolytes with low alkalinity. This research showed that the synthesized γ-FeOOH measured with a cocktail electrolyte of sodium sulfate and sodium hydroxide demonstrated an enhanced discharge capacity and improved capacity retention, compared with the results measured in sodium hydroxide electrolyte. The investigation on the charge storage mechanism using in-situ XRD, XPS, as well as electrochemical methods showed that a green rust phase formed in the discharge stage in the cocktail electrolyte played an important role in the enhancing of electrochemical performance of γ-FeOOH, promoting Fe2+/Fe3+ one-electron transfer reaction with an enhanced capacity. The green rust phase also reduced the formation of the electrochemically inert Fe3O4 phase during the discharge process, promoting cycling performance. This research on the performance of iron-based materials in cocktail electrolytes opens up a new field in utilizing iron-based materials for aqueous battery applications.

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