Abstract

With global climate change becoming a chronic situation, humanity needs to come up with efficient, sustainable, and clean alternative energy sources that can truly create markets capable of competing with the fossil fuel industry. Being one of the fundamental constituents of the greater part of the planet, Hydrogen emerges as one of the best alternative fuels, offering comparable –or higher- energy levels, as well as cleaner combustion results, when compared with our everyday sources of energy. Also, water is both the primary source and resultant, which means full sustainability. The process of producing Hydrogen gas, however, is not as giving. Huge amounts of energy are consumed daily to produce amounts of Hydrogen gas that can barely cover the currently-low market demand. Thus, the need to develop more efficient Hydrogen production systems is dire. Being the gigantic nuclear fusion reactor it is, the Sun supplies our planet with more energy per day than all of industrial energy sources combined. Harvesting such energy is made available by pyroelectric as well as semiconducting materials. With the invention of the transistor, the world’s focus on the latter materials increased greatly, and huge amounts of research has been taken out ever since. It is now a global ultimatum to develop semiconducting systems that can efficiently convert the energy of the Sun to electrical energy to be used in the electrolysis of water for the production of Hydrogen gas. In this thesis, an Earth-abundant material, Zirconium, was used to develop semiconducting electrodes for that exact purpose. Because nanostructuring offers new properties un-attainable at the macro scale, in the first part of this thesis, a comprehensive study was taken out to develop protocols for the synthesis of semiconducting Zirconium Oxide nanotubes (NTs) with different lengths, diameters, wall thicknesses, and morphologies. It was shown that, using the cheap electrochemical anodization method, Zirconia NTs with hexagonal as well as circular cross sections were synthesized, depending on the concentrations of water and etchant in the electrochemical bath. The control of length, diameter, and wall thickness was also attained through controlling the applied potential, anodization time, as well as the solvent composition of the electrolyte. With the aims of using these NTs in solar water splitting, the smallest wall thickness, as well as the best structure, were the main drives behind choosing the optimum electrolyte-potential-time combination for NT synthesis. Thus, the synthesis of semiconducting, widely stable Zirconia NTs was successful. Zirconia NTs are wide band gap semiconductors, limiting their optical absorption to the Ultra Violet region (<10%) of the solar spectrum. Thus, their use in solar water splitting proves to be inefficient. It was, thus, the aim of the second part of this thesis to cheaply modify the synthesized nanostructured electrodes. Atomic Layer Deposition (ALD) was used to deposit very thin layers of Zirconium Nitride, another Earth-abundant compound, to drive Oxygen/Nitrogen diffusion, and eventually attain an oxynitride layer on the surface of the oxide NTs. This so-called Zirconium Oxynitride layer is known to have visible-light absorption characteristics, which would greatly increase the efficiency of the resulting photoanodes. Indeed, the chemical composition was proven to be a mixed oxide-nitride layer through X-ray Photoelectron Core and Valence Band Spectroscopy. UV-Vis and Tauc optical analysis proved the shift in the optical band gap of the oxide NTs from 3.8 to 2.4 eV. Photoelectrochemical analysis showed a higher catalytic activity for the composite photoanodes as compared to the bare oxide NTs. Electrochemical Impedance Spectroscopy showed that the increase in photogenerated carriers, as well as the decrease in the hole potential barrier at the photoelectrode/electrolyte interface in the composite electrodes, may be the main reasons behind the performance enhancement witnessed in these electrodes.

Department

Nanotechnology Program

Degree Name

MS in Nanotechnology

Graduation Date

2-1-2015

Submission Date

September 2015

First Advisor

Allam, Nageh K.

Committee Member 1

El-Shabasy, Adel

Committee Member 2

El-Refai, Joumana

Extent

104 p.

Document Type

Master's Thesis

Rights

The author retains all rights with regard to copyright. The author certifies that written permission from the owner(s) of third-party copyrighted matter included in the thesis, dissertation, paper, or record of study has been obtained. The author further certifies that IRB approval has been obtained for this thesis, or that IRB approval is not necessary for this thesis. Insofar as this thesis, dissertation, paper, or record of study is an educational record as defined in the Family Educational Rights and Privacy Act (FERPA) (20 USC 1232g), the author has granted consent to disclosure of it to anyone who requests a copy.

Institutional Review Board (IRB) Approval

Not necessary for this item

Comments

The only true provider of success and straightness in one’s path is ALLAH subhanahu wa ta’ala. However, because causality is a fundamental concept in the creation of this world, ALLAH renders humans, and other, the main causes behind one’s success. This being said, I owe all my success in taking out this study to my advisor, Dr. Nageh Allam. I am indeed grateful to his constant financial and logistical support to my project, including buying all the materials I used to finish my studies, as well as obtaining access for me to work at the Laser Dynamics Lab (LDL) at the Georgia Institute of Technology to take out critical experiments. I am also indebted to him for his extreme care to teach me, as well as all other group members, and constantly drive us towards better status, even if this often caused him great distress. In this sense, I am thankful to Prof. Mostafa El-Sayed, as well as his only Egyptian PhD student, Mustafa, for making life extremely easy for me and my peers at the US. Coming second to Dr. Nageh’s support is the support by my father, mother, brother, and my wife. Indeed, my upper family was always beside me whenever I needed support throughout my studies, even if it sometimes irritated them, or made them fall into a financial dilemma, or simply angered them. Also, my wife; what she endured during my three-year experience was not part of our vows. Her constant support, positivity, and ingenious sink of technical and social ideas that saved a lot of my days are truly invaluable. Of course, our baby son, Malek, also had to endure a lot. May ALLAH make it easy upon them all. I am forever indebted to them. I’d also like to specially mention my quarter back: Ahmad Mohyeldin. Meeting at the Fellowship’s office before starting our first semester, Ahmad and I grew very strong ties until we travelled together to the US, where we became true brothers. Ahmad has always been there for me to set up that elusive experiment, or take out that anodization or photoelectrochemical experiments when I was absent. This work owes much to Ahmad. I hope I can join him with my PhD studies to always be fellows in this grand journey of life. I would also like to thank all my peers at the Energy Materials Lab and beyond, especially Basamat, Hafez and Ali, for helping me achieve this degree, whilst providing the friendliest working atmosphere. In addition, the constant support of Justin, Mike, Steven, and Paul from LDL is gratefully acknowledged. Indeed, the generous acceptance of the respected members of my examination committee: Prof. Adel El-Shabasy, Dr. Joumana El-Refai, and Dr. Ahmed El-Gendy, is well acknowledged. I thank them all for being very facilitating throughout the process of submission and defense, as well as for their valuable advice and constructive criticism before and after the defense. Finally, the financial support by the American University in Cairo, as well as the US National Science Foundation, are also acknowledged.

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