Nanoengineered materials for energy conversion & storage applications: a density Functional Theory Study
All praise is due to Allah. We praise Him, seek for His assistance and forgiveness and we seek refuge with Him from evils of our souls and our misdeeds. No one can mislead whosoever Allah guides and none can guide whosoever Allah causes to go astray. And as our Prophet ( )صلى الله عليه وسلمsaid: “He who does not thank people does not thank Allah†we shall abide and obey. This being said, I am utterly grateful and thankful to all who supported and guided me through the journey of the masters degree. A special appreciation goes to my father and my mother (may allah grant them jannah tul Firdous) who backed me heart and soul throughout my life in each and every single aspect of life with hearts full of unconditional love; they literally sacrificed everything to make me the way who I am now. Comes second to my parents is the support of my beloved wife who brightened up my life from day one of our marriage. She was always there for me, helped me a lot in my research and writing the thesis was not possible without her support and encouragement. Her persistent positivity and brilliant academic and social ideas made my life easier, full of hope and optimism. Also, I thank my lovely sister for her support and care. For my son Al-Baraa, I would like to thank him for his endurance during my thesis writing period. I would like to thank Prof. Nageh for being my mentor and advisor. Since I joined the Energy Materials Laboratory (EML), Prof. Nageh guided and taught me how to be a researcher. His guidance and support went beyond academia to enlighten my personal and social life. Indeed, he was and will always be a caring big brother beside being a dedicated, professional, bright, and an inspiring role-model scientist and advisor; despite all of the hardships that face any researcher in the MENA region. I would also thank Dr. Moustafa Youssef for his efforts in my training on the different ab-initio platforms and their post-treatments. Also, the role and the support of my brothers and colleagues in the EML is invaluable. I also want to thank all the instructors who taught me the graduate courses and the AUC employees who facilitated the administrative work. Finally, I want to thank Al-Ghurair Foundation and the AUC for their financial support during my graduate studies period.
Abstract
The conventional approach for the development of novel materials has become long relative to the desired product development cycle. Thus, the sluggish pace of the development of materials within the conventional approach hinders the rapid transformation of the scientific outcomes into useful technological products. To this end, the field of hierarchical materials informatics evolved to bridge this gap. In this field, the multiscale material internal structure is considered the starting point and the core of this approach. This being said, the density functional theory (DFT) was used to generate useful materials data for the advancement of the hierarchical materials data-bases towards the novel efficient data-driven materials design approach. In this study, the DFT was employed to tackle energy materials arena as the global community is heading towards the renewable energies paradigm to secure the pillars of sustainability. Photoelectrochemical (PEC) water splitting proved to be one of the most trailblazing technologies serving this dazzling aspiration. Development of efficient photoelectrodes through defect engineering of wide-bandgap metal oxides has been the prime focus of materials scientists for decades. However, tuning the properties of m-ZrO2 was scarcely addressed in the context of photoelectrochemical (PEC) water splitting. In addition, the effect of carbon defects in wide-bandgap metal oxides for PEC applications raised numerous controversies and still elusive. To this end, herein, the effect of various carbon defects in mZrO2 for PEC applications was investigated using the density functional theory to probe the thermodynamic, electronic, and optical properties of the defective structures. The defect formation energies revealed that elevating the temperature promotes and facilitates the formation of carbon defects. Moreover, the binding energies confirmed the stability of all studied complex carbon defects. Furthermore, the band edge positions against the redox potentials of water species exemplified that all the studied defective structures can serve as photoanodes. Additionally, CO3c (carbon atom substituted O3c site) was the only defective structure that exhibited slight straddling of the redox potentials of water species. Importantly, all the defective structures enhanced the light absorption to different extents. Also, it is reported that CO3cVO3c (carbon atom substituted O3c associated with O3c vacancy) defective m-ZrO2 enjoyed low direct bandgap (1.9 eV), low defect formation energy, low exciton binding energy, high mobility of charge carriers, fast charge transfer, and low recombination rate. Concurrently, its optical properties were excellent in terms of high absorption, low reflectivity and improved static dielectric constant. Hence, the study recommends CO3cVO3c defective m-ZrO2 as the leading candidate defective structure to serve as a photoanode for PEC applications. Also, DFT was used to investigate the performance of energy storage electrodes. The DFT proved to be a reliable tool for investigating the quantum capacitance performance of the EDL supercapacitor electrodes. DFT was used to give insights on the capacitance performance of graphene, graphite, carbon nanotubes (CNTs), and N-doped graphene. The results revealed that the quantum capacitance of the CNTs was very high in both positive and negative potential windows and that the N-doping greatly enhanced the capacitance performance of the pristine graphene.