Mechanism of Selective Ion Removal in Membrane Capacitive Deionization for Water Softening

Wang, Li; Lin, Shihong

doi:10.1021/acs.est.9b00655

Cited by 134 publications

(70 citation statements)

References 45 publications

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“…[19][20][21][22] In general, the performance of CDI in sea waterd esalination is influenced greatly by the capacitance of the electrode material. [23][24][25][26][27][28] Am aterial with large surface area and high capacitance is more favorable for CDI. [29][30][31] Up to now,s ome carbon-based materials have been employed as electrode materials in CDI, includinga ctive carbon, graphene, nanotubes, anda erogels.…”

Section: Introductionmentioning

confidence: 99%

A Polyoxometalate‐Based Binder‐Free Capacitive Deionization Electrode for Highly Efficient Sea Water Desalination

Liu

Zhang

et al. 2020

Chemistry A European J

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Capacitive deionization is a promising technique in sea water desalination. Compared with common electrodes, mixed capacitive‐deionization electrodes exhibit better performance in sea water desalination because they integrate pseudocapacitance and electric double‐layer capacitance in one system. Herein, a 3D binder‐free mixed capacitive‐deionization electrode was fabricated by direct electrodeposition of SiW12O404− and polyaniline on a 3D exfoliated graphite carrier. In this electrode, SiW12O404−/polyaniline composite particles with a size of about 100–120 nm are dispersed homogenously on the 3D exfoliated graphite carrier. Its specific capacitance reaches 352 F g−1 at 1 A g−1. With increasing current from 1 to 20 A g−1, the specific capacitance only decays by 32 %. When employed in sea water desalination, the performance of this mixed capacitive‐deionization electrode is also excellent. At 1.2 V, the salt adsorption capacity of this mixed electrode reaches 23.1 mg g−1 with a salt adsorption rate of 1.38 mg g−1 min−1 in 500 mg L−1 NaCl. The performance of this electrode is well retained after 30 cycles. The excellent sea water desalination performance originates from the synergistic effect between SiW12O404− and polyaniline. This work has developed polyoxometalate as a new material for capacitive‐deionization electrodes.

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Section: Introductionmentioning

confidence: 99%

A Polyoxometalate‐Based Binder‐Free Capacitive Deionization Electrode for Highly Efficient Sea Water Desalination

Liu

Zhang

et al. 2020

Chemistry A European J

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“…CDI and CAPMIX technologies are EDLC-based technology. Both technologies have been widely investigated in the field of water technology in the past years, and several EDLC cell architectures have been proposed for both systems, e.g., flow-by CDI [69][70][71][72][73] , Membrane CDI 72,74,75 , flow-through electrode 76 , flow-electrode CDI 77,78 , and wire-shaped electrode 19,22,79 . Conventionally, a flow-by CDI is considered as the "conventional" design for CDI application, while the Membrane CDI is the conventional design for CAPMIX application.…”

Section: Principles Of Capacitive Deionization (Cdi) and Capacitive Mmentioning

confidence: 99%

“…However, besides the electrode behavior, the IEMs could also influence Λ | . For instance, the IEMs show a selectivity towards specific ions based on their valence 71,75 or size 71 . The individual effect of the electrodes and the IEMs is challenging to distinguish in CO2-MCDI experiments.…”

Section: Absorption Efficiency In Co2-mcdimentioning

confidence: 99%

“…CO2-CDI is based on capacitive deionization (CDI), i.e., a technology widely developed in the last decade for water desalination 17,[70][71][72][73]75,77,178 . An MCDI cell is composed of two capacitive electrodes, both covered by an ion exchange membrane, i.e., an anion exchange membrane (AEM) for the anode, and a cation exchange membrane (CEM) for the cathode.…”

Section: Introductionmentioning

confidence: 99%

“…Besides the role of the electrodes, the ion exchange membranes (IEMs) can potentially affect Λ | . Studies demonstrated the importance of IEMs on the ion selectivity in MCDI cells 71,75 , an effect of which was never investigated in CO2-MCDI with a CO2-sparged solution.…”

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confidence: 99%

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Capacitive processes for carbon capture and energy recovery from CO2 emissions : Shaping a new technology going from water to gas applications

Legrand¹

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Nonetheless, how can we convert a water technology into a gas technology? The first step is to identify a strategy to produce ions from CO2 gas. As CO2 gas is not an ion, the CDI and CAPMIX cells are not directly usable with gas streams. Nevertheless, ions can be generated from CO2 by sparging CO2 gas in water, a process in which bicarbonate ions are formed (see Box 1). 1.3.2. Electrochemical pH swing CO2 capture can be achieved by generating a pH swing between two chambers in an electrochemical cell. The electrochemical pH swing has been mostly investigated in electrodialysis cell 62,63 and bipolar electrodialysis cell 49,53-55. The CO2 absorption takes place in the alkaline compartment (high pH) through the reaction of CO2 with hydroxide (CO + OH → HCO), whereas the CO2 desorption takes place in the acidic compartment (HCO + H → CO). Fig. 1.6 shows an example of CO2 capture with bipolar electrodialysis. Supercapacitive swing adsorption (SAA) is an electrical double-layer capacitor (EDLC) for CO2 capture 58-61. The concept consists of adsorbing CO2 on the cathode in a gas channel while charging the EDLC cell in a highly concentrated NaCl solution. Fig. 1.8 shows an illustration of the SAA concept. Three mechanisms have been suggested for the CO2 gas adsorption in the electrodes, i.e. (a) adsorption of gas molecules at gas-solid interface, (b) adsorption of gas molecules at the gas-liquid interface, and (c) adsorption of ionized gas molecule 61. Adsorption at the gas-solid interface would occur when CO2 gas is adsorbed in non-filled electrode pores stimulated by a change of affinity between the pore wall and CO2 during the charging step of the cell. Adsorption at the gas-liquid interface would occur due to an increased CO2 solubility in the electrical double layer (EDL) by charging the capacitive cell. Finally, ionization adsorption occurs through the adsorption where ϵ. is the dielectric constant, ϵ 0 is the permittivity of free space, R the gas constant, T the temperature, F the Faraday constant and c 4 the ion concentration in the bulk solution. Finally, the Stern layer represents the layer of solution separating the diffuse layer, and the carbon matrix surface. In theory, ions are surrounded by a hydration shell, and therefore, the charged ions are not infinitely close to the electrode surface. IEMs are ionomer, i.e., charged polymer, which primarily act as selective charge barriers. Ideally, only anions can be transported through the AEM, and only cations can be transported through the CEM (counter-ion transport). IEMs are mainly used in CDI to improve the charge efficiency (in Membrane CDI or MCDI) 70,72 and are required in CAPMIX to generate an electrical potential.

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Electrochemically Mediated Sustainable Separations in Water

Tan

Hatton

2022

Sustainable Separation Engineering

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Mechanism of Selective Ion Removal in Membrane Capacitive Deionization for Water Softening

Cited by 134 publications

References 45 publications

A Polyoxometalate‐Based Binder‐Free Capacitive Deionization Electrode for Highly Efficient Sea Water Desalination

A Polyoxometalate‐Based Binder‐Free Capacitive Deionization Electrode for Highly Efficient Sea Water Desalination

Capacitive processes for carbon capture and energy recovery from CO2 emissions : Shaping a new technology going from water to gas applications

Electrochemically Mediated Sustainable Separations in Water

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