Date of Award

12-2024

Degree Name

Doctor of Philosophy

Department

Mechanical and Aerospace Engineering

First Advisor

Muralidhar K. Ghantasala, Ph.D.

Second Advisor

Ramakrishna Guda, Ph.D.

Third Advisor

Bade Shrestha, Ph.D.

Fourth Advisor

Elena A. Rozhkova, Ph.D.

Keywords

Catalyst modification, electrochemical performance, materials charactrazation, MOF supported catalyst, PEM fuel cell, reduced graphene oxide

Abstract

The requirement for low cost and efficient catalysts for fuel cells motivated the proposed research on Nitrogen-doped reduced graphene oxide (N-rGO) integrated with transition metal zeolitic imidazolate frameworks (ZIFs). Synthesis, characterization and performance evaluation of the newly synthesized nitrogen-doped graphene oxide-based catalysts for Proton Exchange Membrane Fuel Cells (PEMFCs) constitutes the main objective of this thesis.

The synthesis of N-rGO combined with cobalt, nickel, or iron ZIFs was carried out using wet chemical methods followed by one step pyrolysis at 900°C, resulting in catalysts with highly porous structures and uniform metal nanoparticle distribution. These were characterized for structure, microstructure, composition and porosity using different techniques viz., Fourier Transform Infrared Spectroscopy, Raman Spectroscopy, X-Ray Diffraction, Scanning Electron Microscopy, Energy Dispersive Spectroscopy, X-ray Photoelectron Spectroscopy, and Brunauer– Emmett–Teller (BET) methods. A detailed analysis and correlation of these properties provided insight into different characteristics of these materials.

The electrochemical performance of these catalysts were evaluated using Cyclic Voltammetry, Linear sweep voltammetry (LSV), and Koutecky-Levich study techniques. Notably, N-rGO-Fe-ZIF-900 exhibits an onset potential of 0.79 V and a limiting current density comparable to Pt/C, underscoring its potential as a viable alternative. Iron based catalyst provided relatively the best performance compared to Co and Ni catalysts.

Further, the preparation of membrane electrode assemblies (MEAs) and their integration into a PEMFC setup allowed for a comprehensive assessment of catalyst performance under realworld conditions. Open circuit potential (OCP) measurements, polarization curves, and electrochemical impedance spectroscopy (EIS) were carried out to evaluate these catalysts. NrGO- Fe-ZIF-900 showed superior initial voltage stability, maintaining over 1005 mV OCP, and demonstrated 95% of the performance of Pt/C. The EIS analysis revealed that N-rGO-Fe-ZIF-900 had a lower charge transfer resistance, indicating enhanced electrochemical kinetics compared to Pt/C.

This work not only demonstrated the potential of N-rGO and transition metal-doped catalysts for PEMFC applications but also provides insights into their electrochemical behavior and stability. Despite the promising results, challenges such as thermal stability and long-term durability remains concerns, which require further optimization.

In conclusion, this dissertation provided an in-depth study of nitrogen-doped graphene oxide with transition metal (Co, Ni and Fe) based MOF catalysts and their potential to be alternatives to platinum-based catalysts in PEM fuel cell technology.

Access Setting

Dissertation-Open Access

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