Titanium Disulfide: A Promising Low-Dimensional Electrode Material for Sodium Ion Intercalation for Seawater Desalination

Abstract

This work introduces for the first time titanium disulfide (TiS 2 )/carbon nanotube (CNT) electrodes for desalination of high molarity saline water. Capitalizing on the two-dimensional layered structure of TiS 2 , cations can be effectively removed from a feedwater stream by intercalation. The TiS 2 −CNT hybrid electrode is paired in an asymmetric cell with microporous activated carbon cloth without an ion exchange membrane. By electrochemical analysis, the correlation between the state of charge and the stability of TiS 2 was investigated. By using post-mortem X-ray diffraction, the sodium-ion intercalation mechanism gives an insight into how the state of charge affects the structure and cyclic stability. Our system showed stable desalination performance over 70 cycles at high molar concentration (600 mM), with a cell salt removal capacity of 14 mg/g (equivalent to a sodium removal capacity of 35.8 mg/g normalized to the mass of TiS 2 −CNT). This novel approach of membrane-free hybrid Faradaic capacitive deionization paves the way toward energy-efficient desalination of seawater.

Potential‐Dependent, Switchable Ion Selectivity in Aqueous Media Using Titanium Disulfide

“…SEM and TEM micrographs of the binder‐free TiS 2 ‐10CNT electrode (Figure S2 A and B in the Supporting Information) show CNTs wrapped around TiS 2 sheets. This is an important feature to ensure electrode integrity of individual TiS 2 sheets during desalination and sufficient electrical conductivity throughout the electrode . As confirmed by the four‐point probe conductivity measurements, the electronic conductivity of TiS 2 was very low (<10 −4 S cm, which was the detection limit of the measuring device) compared to that of TiS 2 ‐10CNT (6.3±2.3 S cm).…”

“…The TiS 2 ‐10CNT (composite of TiS 2 and carbon nanotubes (CNTs) with a constant mass ratio of 9:1) binder‐free electrodes were prepared by filtration according to our previous publication . SEM and TEM micrographs of the binder‐free TiS 2 ‐10CNT electrode (Figure S2 A and B in the Supporting Information) show CNTs wrapped around TiS 2 sheets.…”

Faradaic Electrodes Open a New Era for Capacitive Deionization

“…In the CDI community, few studies express the energy consumption as the amount of salt removed for per unit of energy consumption (usually in terms of g Wh −1 ), [41] while most other studies represent it as the inverse (usually in terms of Wh g −1 , Wh L −1 , J mol −1 , or kT). [39,55,78,102,122] Here, we recommend and base all discussion below on the latter definition, with the corresponding calculation shown in the Equations (8) and (9) SP :…”

“…The unit of E s is J mol −1 , and the J mol −1 can also be converted into kT (an energy unit as the product of the absolute temperature and Boltzmann constant) by dividing the calculated energy (J mol −1 ) by the gas constant and absolute temperature RT (2.48 kJ mol −1 at 25°C). [55,122] These two metrics are meaningful for comparing different CDI systems and even other desalination technologies. [6] It can be seen from the definitions and desalination studies that there is an inverse relationship between charge efficiency and energy consumption.…”

“…Or, to put it another way, we can take their advantage of Na + removal and use another electrode for Cl − removal to achieve the balance. For example, Pattarachai et al [122] assembled a CDI cell of TiS 2 -CNT//K20-AC, in which the TiS 2 -CNT composite is for Na + intercalation, and the K20-AC was used for the removal of anions through electrosorption. As shown in Figure 24f, the CV of TiS 2 showed obvious redox peaks, Reproduced with permission.…”