Electrocapacitive Deionization: Mechanisms, Electrodes, and Cell Designs

Abstract

freshwater storage. [6,7] Figure 1 shows the annual average monthly blue water (fresh surface water and groundwater) scarcity.Regions like Australia, central America, North China, and North Africa face the highest freshwater scarcity. Two-thirds of the global population suffers from severe freshwater scarcity at least 1 month of the year, and half a billion people worldwide face severe freshwater scarcity all year around. [8] This issue will intensify in the future due to climate change and evergrowing water consumption.The earth's climate and the terrestrial water cycle have a close and complex relationship. [9] Climate change is causing parts of the water cycle to speed up as warming temperatures increase the water evaporation rate. Scientific evidence shows that global warming is now unequivocal. [10] Greenhouse gas emissions have steeply increased, directly affecting terrestrial water budgets. For example, water decreases have already been observed in western Africa, southwestern Australia, the Yellow River basin in China, and the Pacific Northwest of the United States of America. Such decreases affect freshwater availability directly. [8,11] In addition to the negative effects of climate change on freshwater access, the higher water consumption of our world population and economic activities are causing great additional freshwater stress. For example, agriculture consumes 50-60%, industries use 5-10%, and 10-20% is used for urban purposes. [12] Further, many of these activities may lead to polluted water, decreasing the available clean and freshwater. For these reasons, the United Nations declared freshwater as one of the many global challenges that need immediate action for sustainable development. [13] Depending on the total mass of dissolved solids in water, natural water is classified into brine water (>50 g L −1 ), saline water (30-50 g L −1 ), brackish water (0.5-30 g L −1 ), and freshwater (0-0.5 g L −1 ). [14] According to the World Health Organization, drinkable water should contain <0.25 g L −1 of salt, and the limitation on agriculture irrigation is 2 g L −1 . [15,16] There is a need to obtain freshwater by leveraging the tremendous amount of non-fresh water that can be made useable. This can be done by extracting undesirable ions from existing water in a desalination process. This process needs to be energy-efficient and cheap for sustainability and affordability. Water desalination is a promising and practical approach to maintaining an adequate potable water supply. [17,18] Capacitive deionization (CDI) is burgeoning as a cost-effective and energy-efficient

MXene‐Based Capacitive Deionization–Strong Competitor Among Faradaic Electrode Systems: Current Status and Future Perspectives

“…[8] The formula associated with the evaluation of E in the SP (equ 6) and BM (equ 7) operations are shown below where U is assigned for the voltage (V) during adsorption process. [33,34] It is usually expressed in the unit of W h g À 1 , W h L À 1 , W h m À 3 , and J mol À 1 . The product of Boltzmann constant (k) and absolute temperature (T) represents the consumed energy in kT, which is estimated by dividing energy (J mol À 1 ) with the gas constant (R) and T (RT room temperature = 2.48 kJ mol À 1 ).…”

“…The measurement of maximum SAC is based on the arrival of desalination process at the equilibrium stage when the effluent conductivity remains unchanged with time. The formula used to calculate gravimetric SAC in the SP and BM operations are shown in equation 1 and 2: [8,[33][34][35] SAC SP ¼ n R DC: dt m (1)…”

“…with the desalination/electrosorption or total cycling time (t, min) according to the equation 3. [8,[33][34][35] ASAR SP=BM ¼ SAC SP=BM t…”

Tailoring B, N-Enriched Carbon Nanosheets via a Gelation-Assisted Strategy for High-Capacity and Fast-Response Capacitive Desalination

“…Although 75% of the earth's area is covered by water, 97.5% of it is salt water and 89.6% of the remaining fresh water resources cannot be directly utilized by human beings, 1,2 which indicates the urgency of exploring efficient salt water desalination strategies to solve the water resource crisis. Capacitive deionization (CDI), a rising, low-cost, high-efficiency, and renewable water purification method, 3,4 can effectively adsorb the Na + from brackish water, thus showing potential application prospect for desalination.…”

“…Although 75% of the earth’s area is covered by water, 97.5% of it is salt water and 89.6% of the remaining fresh water resources cannot be directly utilized by human beings, , which indicates the urgency of exploring efficient salt water desalination strategies to solve the water resource crisis. Capacitive deionization (CDI), a rising, low-cost, high-efficiency, and renewable water purification method, , can effectively adsorb the Na + from brackish water, thus showing potential application prospect for desalination. , Generally, carbonaceous materials are the ideal electrodes for CDI due to their customizable structures and tunable surface properties, the commercial devices employing activated carbon as electrodes for CDI have emerged so far. – However, the poor capacity and sluggish response rate still require further exploration for advanced carbonaceous electrodes.…”