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Title:Metal–organic framework based non-precious metal electrocatalysts for the oxygen reduction reaction
Author(s):Al-Zoubi, Talha
Director of Research:Yang, Hong
Doctoral Committee Chair(s):Yang, Hong
Doctoral Committee Member(s):Flaherty, David W; Gewirth, Andrew A; Kenis, Paul JA
Department / Program:Chemical & Biomolecular Engr
Discipline:Chemical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Redox reactions
Metal organic frameworks
Chemical structure
Abstract:Proton-exchange membrane fuel cells (PEMFCs) are devices capable of converting the chemical energy stored in hydrogen into electrical energy for several applications. Their high energy conversion efficiency and environmentally friendly emissions have designated them as viable candidates to replace fossil fuel-based technologies, particularly in transportation applications. However, the high cost associated with the platinum-based catalyst required to drive the sluggish kinetics of the cathodic oxygen reduction reaction (ORR) have rendered these devices impractical on a large scale. To address this, the development of non-platinum group metal (non-PGM) catalysts is a research area of great relevance. This thesis serves to (1) address the mechanism surrounding non-PGM electrocatalysts and provide a method to understand the structure-property relationship, and (2) study strategies in the synthesis of non-PGM electrocatalyst for greater homogeneity in the as-made active structures. The first part of this thesis work involves the use of the zeolitic imidazolate framework ZIF-8 as a model precursor to understanding the role of temperature on the conversion of metal organic frameworks (MOFs) to an active catalyst. The experimental data together with the DFT calculations suggests that the proximity of carbon-encapsulated neighboring iron structures can play a role in activating surface carbon atoms leading to the cleavage of the OOH bond, a key step in the ORR. In the second part of this thesis, the use of cadmium as a sacrificial metal instead of the widely-used zinc is presented. The use of cadmium allows for the synthesis of an active non-PGM electrocatalyst at a lower pyrolysis temperature, resulting in an abundance of single atom sites. Furthermore, at a higher pyrolysis temperature, the catalyst synthesized with cadmium as the sacrificial metal exhibited noteworthy activity in both a three-electrode half-cell test and a membrane electrode assembly (MEA) study. Lastly, a MOF immobilization strategy is introduced which involved the use of Ketjen black carbon as a support to effectively anchor the MOF precursors prior to thermal treatment. This would allow for a greater dispersion of the single atom metal sites and curb sintering during thermal treatment. It was demonstrated that there was an exclusive formation of single atom iron structures after the pyrolysis using this strategy. The work in this thesis provides the basis for a fresh outlook on the current work in the area of non-PGM electrocatalysts for the cathodic ORR. Through this work, we seek to expand on the understanding of these catalyst materials on a fundamental level and to propose strategies to design and develop highly active catalysts.
Issue Date:2021-04-08
Rights Information:Copyright 2021 Talha Al-Zoubi
Date Available in IDEALS:2021-09-17
Date Deposited:2021-05

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