Desalination with porous electrodes : Mechanisms of ion transport and adsorption

Dykstra, J.E.

doi:10.18174/443551

Cited by 3 publications

(3 citation statements)

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“…Another informative way to present the breakdown of energy consumption in CDI and MCDI processes is to plot cumulative specific energy consumptions as a function of σ for the full charging/discharge cycle (Figure 3C,D), similar to what has been shown by Dykstra et al 76,77 Surprisingly, even though the charge efficiency of MCDI is higher than that of CDI, SEC of the two processes, both achieving the same separation and with the same current density, are very similar (without considering possible Faradaic reactions). This may be explained by the fact that the additional ΔV D,mem and ΔV i,mem in MCDI is offset by the significant reduction of ΔV i,mA due to the much higher macropore concentration enabled by the IEMs.…”

Section: ■ Thermodynamic Energy Efficiencymentioning

confidence: 76%

Energy Efficiency of Capacitive Deionization

Wang

Dykstra

Lin

2019

Environ. Sci. Technol.

209

138

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Capacitive deionization (CDI) as a class of electrochemical desalination has attracted fast-growing research interest in recent years. A significant part of this growing interest is arguably attributable to the premise that CDI is energy efficient and has the potential to outcompete other conventional desalination technologies. In this review, systematic evaluation of literature data reveals that while the absolute energy consumption of CDI is in general low, most existing CDI systems achieve limited energy efficiency from a thermodynamic perspective. We also analyze the causes for the relatively low energy efficiency and discuss factors that may lead to enhanced energy efficiency for CDI.

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Section: ■ Thermodynamic Energy Efficiencymentioning

confidence: 76%

Energy Efficiency of Capacitive Deionization

Wang

Dykstra

Lin

2019

Environ. Sci. Technol.

209

138

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“…One of the most effective strategies to keep a high desalination performance is the inclusion of IEMs in the CDI cell, a cell design we refer to as MCDI. These IEMs are placed in front of the electrodes and contribute to maintaining the desalination performance in two ways: the membranes effectively slow down the transport of dissolved oxygen to the electrodes and consequently limit the rate of carbon oxidation and the related pH changes. , However, during long-term operation, dissolved oxygen will eventually oxidize the electrically positively polarized electrode (anode), and oxygen-containing surface groups will form. , Whereas these groups would have negatively affected the desalination performance in CDI (without membranes) due to enhanced coion expulsion during desalination, in MCDI, the desalination performance does not decline because IEMs prevent coions from leaving the electrode region. , Furthermore, Faradaic reactions during MCDI operation were also confirmed in our previous work by microscopic physics-based modeling of pH changes . This study predicted only minor pH changes during desalination in MCDI when non-Faradaic processes, including the effect of different mobilities of various ions on transport rates, combined with acid–base reactions and the presence of chemical surface groups in the micropores are taken into account.…”

Section: Introductionmentioning

confidence: 99%

Unravelling pH Changes in Electrochemical Desalination with Capacitive Deionization

Arulrajan

Dykstra

Wal

et al. 2021

Environ. Sci. Technol.

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Membrane capacitive deionization (MCDI) is a water desalination technology employing porous electrodes and ion-exchange membranes. The electrodes are cyclically charged to adsorb ions and discharged to desorb ions. During MCDI operation, a difference in pH between feed and effluent water is observed, changing over time, which can cause the precipitation of hardness ions and consequently affect the long-term stability of electrodes and membranes. These changes can be attributed to different phenomena, which can be divided into two distinct categories: Faradaic and non-Faradaic. In the present work, we show that during long-term operation, as the electrodes age over time, the magnitude and direction of pH changes shift. We studied these changes for two different feed water solutions: a NaCl solution and a tap water solution. Whereas we observe a pH decrease during the regeneration with a NaCl solution, we observe an increase during regeneration with tap water, potentially resulting in the precipitation of hardness ions. We compare our experimental findings with theory and conclude that with aged electrodes, non-Faradaic processes are the prominent cause of pH changes. Furthermore, we find that for desalination with tap water, the adsorption and desorption of HCO3 –and CO3 2– ions affect the pH changes.

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“…A CDI unit comprises two porous electrodes (often carbon electrodes) and a separator (either a porous dielectric material or an open channel) [ 26 ]. Typically, the electrodes are treated to a potential difference of 1–1.4 V [ 27 ]. The saline or contaminated water passes between the positive and negative electrodes, where the unwanted ions in the water move into an electric double layer (EDL) along the electrode–water interface, thereby removing the unwanted salts or contaminants [ 28 ] via electrosorption on the electrode surfaces ( Figure 1 a).…”

Section: Introductionmentioning

confidence: 99%

A Comparison of Capacitive Deionization and Membrane Capacitive Deionization Using Novel Fabricated Ion Exchange Membranes

2023

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Another technique for desalination, known as membrane capacitive deionization (MCDI), has been investigated as an alternative. This approach has the potential to lower the voltage that is required, in addition to improving the ability to renew the electrodes. In this study, the desalination effectiveness of capacitive deionization (CDI) was compared to that of MCDI, employing newly produced cellulose acetate ion exchange membranes (IEMs), which were utilized for the very first time in MCDI. As expected, the salt adsorption and charge efficiency of MCDI were shown to be higher than those of CDI. Despite this, the unique electrosorption behavior of the former reveals that ion transport via the IEMs is a crucial rate-controlling step in the desalination process. We monitored the concentration of salt in the CDI and MCDI effluent streams, but we also evaluated the pH of the effluent stream in each of these systems and investigated the factors that may have caused these shifts. The significant change in pH that takes place during one adsorption and desorption cycle in CDI (pH range: 2.3–11.6) may cause problems in feed water that already contains components that are prone to scaling. In the case of MCDI, the fall in pH was only slightly more noticeable. Based on these findings, it appears that CDI and MCDI are promising new desalination techniques that has the potential to be more ecologically friendly and efficient than conventional methods of desalination. MCDI has some advantages over CDI in its higher salt removal efficiency, faster regeneration, and longer lifetime, but it is also more expensive and complex. The best choice for a particular application will depend on the specific requirements.

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Desalination with porous electrodes : Mechanisms of ion transport and adsorption

Cited by 3 publications

References 168 publications

Energy Efficiency of Capacitive Deionization

Energy Efficiency of Capacitive Deionization

Unravelling pH Changes in Electrochemical Desalination with Capacitive Deionization

A Comparison of Capacitive Deionization and Membrane Capacitive Deionization Using Novel Fabricated Ion Exchange Membranes

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