Enhanced Electrochemical Stability of a Zwitterionic-Polymer-Functionalized Electrode for Capacitive Deionization

Jung, Youngsuk,Yang, Yooseong,Kim, Taeyoon,Shin, Hyun Suk,Hong, Sunghoon,Cha, Sungmin,Kwon, Soonchul American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.7

<P>In capacitive deionization, the salt-adsorption capacity of the electrode is critical for the efficient softening of brackish water. To improve the water-deionization capacity, the carbon electrode surface is modified with ion-exchange resins. Herein, we introduce the encapsulation of zwitterionic polymers over activated carbon to provide a resistant barrier that stabilizes the structure of electrode during electrochemical performance and enhances the capacitive deionization efficiency. Compared to conventional activated carbon, the surface-modified activated carbon exhibits significantly enhanced capacitive deionization, with a salt adsorption capacity of similar to 2.0 x 10(-4) mg/mL and a minimum conductivity of similar to 43 mu S/cm in the alkali-metal ions solution. Encapsulating the activated-carbon surface increased the number of ions adsorption sites and the surface area of the electrode, which improved the charge separation and deionization efficiency. In addition, the coating layer suppresses side reactions between the electrode and electrolyte, thus providing a stable cyclability. Our experimental findings suggest that the well-distributed coating layer leads to a synergistic effect on the enhanced electrochemical performance. In addition, density functional theory calculation reveals that a favorable binding affinity exists between the alkali metal ion and zwitterionic polymer, which supports the preferable salt ions adsorption on the coating layer. The results provide useful information for designing more efficient capacitive-deionization electrodes that require high electrochemical stability.</P>

Continuous braciksh water desalination via rocking chair capacitive deionization

이재한,윤제용 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.1

Capacitive deionization (CDI) is an electrochemical desalination technology using porous electrode materials. Although it is considered as a high energy efficient and eco-friendly process, a separated released the absorbed ion step is requried in typical capacitive deionization system, and resulting in cost-intensive process. In this study, we investigated “Rocking chair capacitive deionization” that consists of two cation selective porous carbon electrodes and an anion exchange membrane, and it allowed a continuous process by a rocking-chair ion movement during constant current operation. Moreover, the RCDI has an efficient energy consumption and high salt adsorption capacity.

Improved ionic sorption performance of TiO₂/Carbon electrodes for capacitive deionization application

이윤지,정경열,최재환,민병호 한국공업화학회 2016 한국공업화학회 연구논문 초록집 Vol.2016 No.1

Capacitive deionization (CDI) is an high potential desalination technology with a relatively high-energy-efficient and eco-friendly process, and its performance strongly depends on the characteristics of porous electrode. High-surface activated carbon powders (ACPs) are frequently used as the electrode materials for CDI. The surface properties of carbonbased electrodes also affect the performance of CDI electrodes. The existence of hydrophilic surface functional groups is good for improving the ionic sorption capacitance. In this work, the surface of ACPs was modified with TiO₂ through a sol-gel method. In terms of the ionic sorption capacitance, the quantity of TiO₂ coated was optimized. The surface and electrochemical properties of TiO₂/ACP electrodes were characterized by SEM, TEM, CV and EIS measurements. It was clear that the specific capacitance of ACP electrodes could be improved by the coating of TiO₂. Detailed performance for the desalination was studied.

Enhanced electrical and mass transfer characteristics of acid-treated functionalized carbon nanotubes (a-CNTs) and its desalination application in capacitive deionization (CDI)

이재영,정상호,강힌빛,이재광 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.1

Capacitive deionization (CDI) has attracted significant attention for next generation water treatment due to its low energy consumption and small environmental impact in comparison to widely established methods. For CDI technology to move forward, however, the development of carbon electrodes having superb electrosorption behavior is essential. In this study, we demonstrate the functionalization of carbon nanotubes (CNTs) via acid treatment and show its improved electrochemical characteristics as a carbon electrode in a CDI process. Our results suggest that the activation effectively improves the wettability of the acid-treated CNTs (a-CNTs) via the addition of oxygen functional groups, leading to a higher electric double layer capacitance.

Electrochemical analysis of slurry electrodes for flow-electrode capacitive deionization

Choo, Ko Yeon,Yoo, Chung Yul,Han, Moon Hee,Kim, Dong Kook Elsevier 2017 Journal of Electroanalytical Chemistry Vol.806 No.-

<P><B>Abstract</B></P> <P>Due to recent advancements in electrochemical devices such as batteries, fuel cells, and supercapacitors, novel electrochemical processes for industrial plant scale including water treatment and desalination are being actively investigated. Slurry electrodes for flow-electrode capacitive deionization (FCDI) are representative process technology with continuous and easy scale-up characteristics. These characteristics are feasible as slurry electrodes can be flowed in microchannels, instead of stacking conventional electrodes fixed on plates. However, the electrochemical properties of slurry electrodes for electrochemical process engineering have not been clearly identified, compared to those of conventional fixed electrodes. In the present study, we investigated the electrochemical properties of capacitive slurry electrodes with changes in carbon content and electrolyte salt concentration using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and deionization/regeneration cycle tests with newly fabricated button-type cells. The CV patterns were rectangular, symmetrical, and reversible at a scan rate of 2mV/s, indicating electrical double-layer capacitive behavior. The results of the EIS and cycle tests demonstrated that increasing the carbon content and electrolyte salt concentration in slurry electrodes improved the cell efficiency due to the higher capacitance and lower total resistance.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Novel electrochemical cells suitable for slurry electrodes were developed. </LI> <LI> The electrochemical properties of slurry electrodes were affected by their composition. </LI> <LI> Increasing the carbon content of slurry electrodes led to a higher capacitance. </LI> <LI> Increasing the electrolyte salt concentration of slurry electrodes improved the cell efficiency. </LI> </UL> </P>

Theoretical insight into the structure-property relationship of mixed transition metal oxides nanofibers doped in activated carbon and 3D graphene for capacitive deionization

Yasin, Ahmed S.,Mohamed, Ahmed Yousef,Mohamed, Ibrahim M.A.,Cho, Deok-Yong,Park, Chan Hee,Kim, Cheol Sang Elsevier 2019 CHEMICAL ENGINEERING JOURNAL -LAUSANNE- Vol.371 No.-

<P><B>Abstract</B></P> <P>Over the last two decades, the capacitive deionization (CDI) technique has been developed into a high performance, low-cost, and environmental-friendly desalination technology. The development of novel advanced nanostructures via the hybridization of diverse carbon materials to improve the performance of CDI technology has attracted considerable attention. In this study, the combination of graphene hydrogel and ZrO<SUB>2</SUB>-doped TiO<SUB>2</SUB> nanofibers as efficient dopants into activated carbon (AC), has been achieved through a simple electrospinning technique followed by a post annealing process. The strong interactions between the graphene hydrogel, nanofibers and AC were found to enhance the wettability as well as the electrical conductivity of the AC. The morphology and electrochemical performance of the as-synthesized composite were characterized by field-emission scanning electron microscopy (FE-SEM), Transmission electron microscopy (TEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). What’s more, the X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and synchrotron X-ray absorption structures (XAS) are performed to investigate the atomic and electronic structure of titania and zirconia in order to understand their phase stability. We observed the appearance of anatase structure of titania and cubic structure of zirconia after doping the AC and graphene hydrogel with the nanofibers. The water contact angle of the composite was examined and found to be less than 3°. The introduced nanocomposite showed high electrosorption capacity of 9.34 mg g<SUP>−1</SUP> at the initial solution conductivity of ∼100 μS cm<SUP>−1</SUP>, which is much higher compared to the other surveyed materials; these results should be attributed to its significant hydrophilicity, high specific capacitance, and reduced charge transfer resistance.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Unique three-dimensional graphene/mixed transition metal oxides modified activated carbon was prepared and characterized. </LI> <LI> The nanocomposite electrode shows low charge transfer resistance and high specific capacitance. </LI> <LI> Analysis of synchrotron-based hard X-ray absorption spectroscopy. </LI> <LI> The fabricated nanocomposite exhibits a high electrosorption capacity of 9.34 mg g<SUP>−1</SUP>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Incorporating zirconia nanoparticles into activated carbon as electrode material for capacitive deionization

Yasin, Ahmed S.,Mohamed, Ibrahim M.A.,Amen, Mohamed T.,Barakat, Nasser A.M.,Park, Chan Hee,Kim, Cheol Sang Elsevier 2019 Journal of alloys and compounds Vol.772 No.-

<P><B>Abstract</B></P> <P>In recent years, capacitive deionization (CDI) has attracted intensive research due to its environmentally-friendly nature and low power requirement. Although the characteristics of titania (TiO<SUB>2</SUB>) and zirconia (ZrO<SUB>2</SUB>) are almost the same, ZrO<SUB>2</SUB> has not attracted the same attention since the characteristics of the carbonaceous material need to be modified to enhance its performance as an electrode in CDI cells. In this study, the wettability and electrochemical behavior of activated carbon (AC), as a widely used, effective, and inexpensive material, was distinctively improved by doping with zirconia nanoparticles. The introduced AC/ZrO<SUB>2</SUB> nanocomposite was fabricated using the alkaline hydrothermal method. Investigation of the surface morphology, phase and crystallinity by SEM, TEM, XPS, and XRD demonstrated the successful doping of AC by zirconia nanoparticles. Interestingly, the wettability measurement showed excellent enhancement, since the water contact angles of pristine and doped AC are 45° and 148°, respectively. The electrochemical experiments demonstrated that the synthesized composite (AC/ZrO<SUB>2</SUB>) has a specific capacitance of 282.8 F g<SUP>−1</SUP>, which is higher than that for AC (207.5 F g<SUP>−1</SUP>). Due to the significant improvement in wettability and specific capacitance, the desalination performance and the salt ion electrosorption capacity were also enhanced: 40.4% and 68.5%, and 2.82 and 4.79 mg/g for AC and AC/ZrO<SUB>2</SUB>, respectively. Moreover, the introduced AC/ZrO<SUB>2</SUB> revealed 99% remaining desalination retention suggesting high stability. Overall, this study demonstrates ZrO<SUB>2</SUB> is an effective, stable, and environmentally safe material for improving the performance of carbonaceous CDI electrodes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> ZrO<SUB>2</SUB> NPs/AC is introduced as effective CDI electrode material. </LI> <LI> The salt removal efficiency has been improved to 68.5%. </LI> <LI> Good performance is due to improving the specific capacitance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Enhanced electrical and mass transfer characteristics of acid-treated carbon nanotubes for capacitive deionization

정상호,강한빛,조이 오콘,이재광,이재영 한국물리학회 2015 Current Applied Physics Vol.15 No.11

Capacitive deionization (CDI) has attracted significant attention for the next generation water treatment due to its low energy consumption and environment friendly properties in comparison to widely established methods. For CDI technology to move forward, however, the development of carbon electrodes having superb electrosorption behavior is essential. In this study, we demonstrate the functionalization of carbon nanotubes (CNTs) via acid treatment shows enhanced electrochemical characteristics and effectively improves the wettability of the acid-treated CNTs (a-CNTs) via the addition of oxygen functional groups, leading to a higher electric double layer capacitance. Furthermore, defect formation in a-CNTs increases the conductivity and decreases the mass transfer resistance during CDI operation. CDI measurements confirmed a 270% increase in performance of a-CNTs in contrast to pristine CNTs (p- CNTs), attributable to the improved characteristics outlined above.

Enhanced electrical and mass transfer characteristics of acid-treated carbon nanotubes for capacitive deionization

Chung, S.,Kang, H.,Ocon, J.D.,Lee, J.K.,Lee, J. Elsevier 2015 Current Applied Physics Vol.15 No.11

Capacitive deionization (CDI) has attracted significant attention for the next generation water treatment due to its low energy consumption and environment friendly properties in comparison to widely established methods. For CDI technology to move forward, however, the development of carbon electrodes having superb electrosorption behavior is essential. In this study, we demonstrate the functionalization of carbon nanotubes (CNTs) via acid treatment shows enhanced electrochemical characteristics and effectively improves the wettability of the acid-treated CNTs (a-CNTs) via the addition of oxygen functional groups, leading to a higher electric double layer capacitance. Furthermore, defect formation in a-CNTs increases the conductivity and decreases the mass transfer resistance during CDI operation. CDI measurements confirmed a 270% increase in performance of a-CNTs in contrast to pristine CNTs (p-CNTs), attributable to the improved characteristics outlined above.

Pretreatment for capacitive deionization: Feasibility tests using activated filter media and granule activated carbon filtration

김희곤,최예슬,이순재,이기봉,정경원,최재우 한국공업화학회 2021 Journal of Industrial and Engineering Chemistry Vol.93 No.-

Dissolved organic matter and scaling are the main causes of electrode fouling, blocking activated carbonpores and reducing their performance. However, limited information exists on fouling by low molecularweight organic matter in the capacitive deionization (CDI) process. This study therefore systematicallyinvestigated for thefirst time a pretreatment process to prevent the accumulation of organic andinorganic matter as well as scaling in the CDI process. During various pretreatments, activatedfiltermedia and granule activated carbon were considered promising for drinking water treatment. The higherthe turbidity and organic matter concentration in the CDI feed solution was, the greater the reduction ofsalt removal efficiency, production rate, and energy consumption became. Divalent ions, such as Ca2+, hadno noticeable effect on CDI treatment performance because of the neutralization effect of the dispersant,whereas iron had a noticeable effect on CDI electrode fouling. The results of this study are foreseen to helpminimize its negative impact by reducing organic matter fouling and enabling water reuse.