Author ORCID Identifier

0000-0003-0332-8055

Document Type

Dissertation

Date of Award

12-31-2025

Degree Name

Doctor of Philosophy in Mechanical Engineering - (Ph.D.)

Department

Mechanical and Industrial Engineering

First Advisor

Eon Soo Lee

Second Advisor

Zhiming Ji

Third Advisor

Dibakar Datta

Fourth Advisor

Mengqiang Zhao

Fifth Advisor

Joshua Young

Abstract

The development of advanced electrochemical energy conversion and storage systems is crucial for achieving sustainable energy security. As alternatives to precious metal-based catalysts in electrochemical systems, especially for the oxygen reduction reaction (ORR), Nitrogen-doped Graphene with Metal-organic Frameworks (N-G/MOF) nanocatalysts have shown exceptional promise in recent years. This research advances the understanding of N-G/MOF nanocatalysts by systematically examining their structural features, degradation traits, correlated performance losses, and other aspects related to catalytic activities.

First, nitrogen-doped graphene (N-G) nanocatalysts were thoroughly investigated, resolving their physical properties, the influence of synthesis parameters, molecular-level material structures, and chemical and electronic structural details of key Nitrogen-functional groups in N-G. Then, a critical analysis was conducted on graphene/MOF hybrid materials, focusing on N-G/ZIF-8 composites, to evaluate their functionalities and performance trends in fuel cells, batteries, and supercapacitors. Subsequently, an experimental study investigated the ORR activities on N-G/MOF nanocatalysts, explaining the direct correlations between the shapes of linear sweep voltammetry (LSV) curves and corresponding ORR steps in alkaline and acidic electrolytes. Afterward, the electrocatalytic performance loss of N-G/MOF nanocatalysts was experimentally evaluated and linked to material degradation induced by exposure to different oxidative species like H2O2 and H2O2-derived species. A separate experimental study investigated the structural stability of ZIF-8 in aqueous environments containing various oxidative species that are typically present under electrochemical conditions. Finally, through an experimental investigation, several chemical changes occurring from the precursors (N-G and ZIF-8) to the synthesized N-G/MOF nanocatalysts were identified, which are attributed to the enhancement of electrocatalytic activities toward ORR.

Through these integrated theoretical and experimental studies, this research elucidated the structural and chemical traits that govern the superior electrochemical performance of N-G/MOF nanocatalysts, demonstrated how LSV data plots can be interpreted to understand ORR mechanisms on carbon-based catalysts, showed roles of ORR intermediates in performance degradation, provided insights into the structural stability of ZIF-8 in electrochemical environments, and identified key synthesis-driven chemical changes that contribute to improved catalytic properties of N-G/MOF nanocatalysts. Collectively, these findings offer critical insights for the rational design of next-generation N-G/MOF nanocatalysts with enhanced activity and durability for electrochemical energy conversion and storage applications.

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