Abstract
The expanding grow in global population and intensified industrialization has resulted in a huge demand for freshwater sources. Therefore, considering the limited sources of freshwater, the exploitation of alternative sources is vital. Practical approach to ensure the adequate supply of fresh water is to produce it through wastewater treatment and/or water desalination. The latter is developing all over the world as brackish water and sea water is ubiquitous. However, desalination of high salinity water with the current technologies such as thermal distillation and reverse osmosis are based on the extraction of water molecules from solutions which consume a huge amount of energy and requires immense infrastructure. In lower water salinity instead, it is more efficient to develop alternative techniques which remove smaller quantity of salt molecules rather than water molecules. Therefore, electrochemical process such as Capacitive deionization (CDI) is a promising technology to desalinate the water with low to medium salinity. In CDI upon potential difference between electrodes, ions migrate to the electrodes due to the electrostatic forces. Salt removal happens during the charging step in the oppositely charged electrodes and the electrodes regenerate during discharging step. In traditional CDI architectures, desalination relies on electrosorption of the ions within the pores of the electrode materials (Electrical double layer mechanism, EDL). Thus, electrosorption- based removal is inherently limited as specific surface area improvement is restricted, and the capacity cannot exceed some certain value. Therefore, faradaic electrodes incorporated into the traditional CDI systems, expecting to achieve higher desalination capacity and lower energy consumption owing to their different ions capturing mechanisms. However, the importance of cell architectures remained unclear. In this thesis, a systematic study demonstrates to elucidate the relationship between the ‘cell architecture’ and the ‘electrode materials’ to establish a promising roadway for future CDI studies. Moreover, the structural and composition of the electrodes’material are rationally designed and fabricated to maximize their performances while their long-term stabilities are maintained. The introductory chapters (Chapter 1 and Chapter 2) elaborate on the necessities of the water desalination, the contribution of materials and their involved mechanisms in CDI systems, and an in-depth literature review on the current technologies and their limitations. In Chapter 3, we focus on Membrane CDI consisting of symmetric designed carbon electrodes for salt adsorption via simple electrical double layer mechanism. The composition is adjusted iv to enhance the ion capturing capacity and the novel 3D printing technique is used to fabricate free-standing graphene oxide/carbon nanotubes with designed macrostructures. Chapter 4 to Chapter 6, showcase the application of faradaic-based electrodes within Hybrid CDI architectures. In our HCDI systems, one of the conventional EDL electrodes is replaced by faradaic electrodes comprising Co3O4, WS2, and Prussian Blue to enhance the sodium storage capacity which proves the remarkable improvement comparing to the EDL systems. However, due to the imbalanced ion storage capacities of anode and cathode in such systems, in Chapter 7, two new architectures of cation-selective CDI and Dual ion deionization comprising NASICON-structured electrodes are introduced. The achievements drawn from this thesis is concluded in Chapter 8, and the future research directions is suggested, accordingly. The proposed strategies together with the remarkable results in this thesis could be a leading way for further research projects and could be an effective solution for global water shortages in future.