Hybrid Electrochemical Desalination System Combined with an

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Hybrid Electrochemical Desalination System Combined with an Oxidation Process Seonghwan Kim, Choonsoo Kim, Jaehan Lee, Seoni Kim, Jiho Lee, Jiye Kim, and Jeyong Yoon ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b02789 • Publication Date (Web): 18 Dec 2017 Downloaded from http://pubs.acs.org on December 19, 2017

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ACS Sustainable Chemistry & Engineering

Hybrid Electrochemical Desalination System Combined with an Oxidation Process

Seonghwan Kima,b, Choonsoo Kima, Jaehan Leea,b, Seoni Kima, Jiho Leea, Jiye Kima, and Jeyong Yoona,b∗

a

School of Chemical and Biological Engineering, College of Engineering, Institute of

Chemical Processes (ICP), Seoul National University (SNU), Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea b

Asian Institute for Energy, Environment & Sustainability (AIEES), Seoul National

University (SNU), Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea

∗

Corresponding author e-mail: [email protected] (Phone: +82-2-880-8941; Fax: +82-2-876-

8911) ACS Paragon Plus Environment

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ABSTRACT

Here, we report a novel hybrid electrochemical desalination system synchronized with an oxidation process for the first time. As one of breakthrough in electrochemical desalination systems, the oxidation process is demonstrated as a strategy to overcome the drawbacks of electrochemical

desalination

systems

associated

with

the

difficulties

of

anion

adsorption/intercalation. This hybrid system consists of a cation-selective battery material in the desalination component, an oxidant generating anode in the oxidation component and an anion exchange membrane that offers a channel for the diffusion of anions. During the operation, cations are intercalated into the battery material and reactions occur on the anode to generate reactive chlorine species (e.g., Cl2, HOCl and •Cl), reactive oxygen species (e.g., H2O2, •OH and O3). Simultaneously, the anions in the desalination component diffuse into the oxidation component to maintain the neutrality in each component. By utilizing the diffusion of anions through anion exchange membrane, the desalination process can be performed with only the cation-selective battery material, leading to enhancement of desalination capacity, and generated oxidants on the anode can be utilized in electrochemical water treatment process. As a primary result, a specific capacity of approximately 33 mAh g-1 was successfully utilized as the desalination capacity with a coulombic efficiency of over 96% in 7.2 g L-1 of NaCl, indicating 28 mg of Na was desalted per gram of cation selective battery material and 44 mg of Cl diffused. Through the combination of an oxidation process with a desalination system using energy storage materials, the research and application of the electrochemical water treatment system is expected to be expanded.

Keywords: hybrid desalination system, desalination and oxidation, electrochemical water treatment, cation-selective battery materials, TiO2 nanotube

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INTRODUCTION

In recent decades, the lack of available water, which threatens nearly 80% of the world’s population, has been considered a critical challenge for mankind. Nearly 3.9 billion people are expected to suffer from limited access to water according to the projections that 90% of all available water will be depleted by 2025.1-3 Electrochemical water treatment has emerged as a possible solution due to its high energy efficiency, eco-friendliness, and lack of required hazardous chemicals.4-6 The electrochemical processes for water treatment have been demonstrated in such as capacitive deionization (CDI), electrochemical oxidation and electrodialysis for heavy metal removal, wastewater treatment and water recycling.7-11 Above all, CDI, a representative electrochemical desalination system, has been developed via the successful convergence of materials used for energy storage with electrochemical systems for water treatment.12-18 This technique achieves electrochemical desalination using the operational principle used for energy storage in supercapacitors and batteries, which provides an energy-efficient desalination process. In CDI, carbon-based materials have been extensively utilized due to their versatility such as high surface area and non-specific adsorption/desorption. However, as investigation for the improvement of high deionization performance has matured, materials for sodium ion battery were introduced in order to overcome an insufficient ion storage capacity in the electrical double layer capacitance of carbon based materials. A hybrid CDI (HCDI) consisted of sodium manganese oxide that is a representative material for sodium ion battery and activated carbon successfully showed a remarkable enhancement in the desalination capacity. Nevertheless, the HCDI system cannot fully make use of the capacity of materials for sodium ion battery due to the relatively low capacity of activated carbon. Finding compounds that can stably function in aqueous solutions is a challenge in electrochemical deionization systems with battery materials, and each material is required to ACS Paragon Plus Environment


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capture cations or anions, respectively. In the case of cation-selective battery materials, various potential compounds for the intercalation of cations have been investigated, such as λ-MnO2, Na0.44MnO2, NaFePO4, Na2FeP2O7, NaTi2(PO4)3 and Prussian blue analogues.19-22 Meanwhile, finding suitable compounds to capture anions is difficult. In most applications, the reaction of silver/silver chloride has been used (Ag0 + Cl- ⇌ AgCl). However, the possibility of using it in desalination systems with battery materials is limited due to the following reasons: i) the necessity of a noble metal; ii) the reaction can be used only with Cl-; and iii) the possibility of active material dissolution.18, 23-26 To overcome these drawbacks, recently advanced materials such as Bi/BiOCl electrode for chloride storage, heterogeneous organometallic electrode and functionalized electrode for electro-mediation

have been

reported.27-32 For example, the selective electrochemical separation was demonstrated through a symmetric Faradaic system with redox-functionalized electrodes.32 Furthermore, innovative systems for deionization, a rocking chair desalination battery and a cation intercalation desalination (CID) system, which consist of a pair of cation-selective battery materials have been introduced.33-34 Thus, developing a novel materials and systems that overcomes the current drawbacks is an important and promising issue in the field of electrochemical desalination. Here, we report a novel hybrid electrochemical desalination system synchronized with an oxidation process, as one of breakthrough to overcome the difficulties of anion adsorption/intercalation (Figure 1). During the operation of this hybrid system, cations are intercalated into the cation-selective battery material by an applied electrical potential in the desalination component, and reactions occur on the anode to generate the oxidants, including the reactive chlorine species in the oxidation component. Simultaneously, the anions in the desalination component diffuse into the oxidation component through the anion exchange membrane to maintain the neutrality in each component. By utilizing the diffusion of anions through anion exchange membrane, the desalination process can be performed with only the cation-selective battery material, leading to enhancement of desalination capacity, and ACS Paragon Plus Environment

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generated oxidants on the anode can be utilized in electrochemical water treatment process. In this study, a sodium manganese oxide (Na0.44MnO2), which is a representative material from sodium ion batteries, was selected as the electrode for intercalation/deintercalation with cations. A cathodic polarized TiO2 nanotubes (NTs), which can be simply fabricated via anodizing process and electrochemical reduction, was used as the anode for the reactive chlorine species (e.g., Cl2, HOCl and •Cl), reactive oxygen species (e.g., H2O2, •OH and O3) without the use of precious metals (e.g., iridium, ruthenium and platinum).35



EXPERIMENTAL SECTION

Preparation of sodium manganese oxide (Na0.44MnO2) and TiO2 nanotubes on a meshed Ti substrate (m-TiO2 NTs) Na0.44MnO2 was synthesized via a solid-state reaction with Na2CO3 and Mn2O3 according to a procedure reported in the literature.13 A Na0.44MnO2 electrode was fabricated by a slurry mixture of a prepared powder (80 wt%), carbon black (Super-PTM, TIMCAL Graphite and Carbon Inc., Switzerland, 10 wt%) and polytetrafluoroethylene (PTFE, Sigma-Aldrich, USA, 10 wt%). The m-TiO2 NTs were fabricated following the anodization and cathodic polarization procedures reported in the literature.35 Anodization was performed in an electrolyte of H2O (2.5 wt%)/NH4F (0.2 wt%) with ethylene glycol for 5 h under a constant voltage (40 V) at room temperature.

Characterization of the prepared Na0.44MnO2 and m-TiO2 NTs The prepared electrodes were characterized by field emission scanning electron microscopy (FE-SEM, JSM 6700F, JEOL Ltd, Japan), and the crystalline structure was analyzed by Xray powder diffraction (HR-XRD, Bruker D8 Discover X-ray Diffractometer, Germany). Electrochemical characterization of the prepared electrodes was measured by CV and staircase linear sweep voltammetry (SLSV) with a potentiostat (PARSTAT 2273, Princeton Applied Research, USA). Galvanostatic charge/discharge was conducted with a battery cycler (WBCS 3000, WonA Tech Co., Korea).

Installation of the hybrid electrochemical desalination system for deionization and oxidant generation Figure 2 describes components of the hybrid electrochemical desalination system. The hybrid electrochemical desalination system consists of a cation-selective battery material in the ACS Paragon Plus Environment

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desalination and an anode providing the oxidant generation function in the oxidation component. The two components are divided by an anion exchange membrane (AMV, AGC engineering Co., Japan) that offers a channel for the diffusion of anions. Na0.44MnO2 and mTiO2 NTs were used for the desalination and oxidation, respectively. As shown in the FESEM images of Na0.44MnO2 and m-TiO2 NTs (Figure 3 (a) – (d)), Na0.44MnO2, which had a mean diameter of approximately 300 nm and a length of 1 – 2 µm, and the TiO2 NTs grown via electrochemical anodization appear to be highly ordered. The outer diameter of m-TiO2 NTs was approximately 100 nm, and the wall thickness was 20 nm. The length of m-TiO2 NTs was approximately 15 µm. Prior to the installation of the system, the Na0.44MnO2 electrode was treated by a pre-charging process in which a potential of 0.9 V (vs. Ag/AgCl) was applied for 30 min to provide defect sites for Na in Na0.44MnO2, and m-TiO2 NTs was treated by cathodic polarization that gives an electro-catalytic activity with colorization (Figure 3 (e)).13, 35 The system consisted of a pair of 4 cm2 electrodes, a pair of spacers on each electrode and the anion exchange membrane.

Operation of the hybrid electrochemical desalination system for deionization and oxidant generation The desalination component in the hybrid electrochemical desalination system was operated in batch mode, and the oxidation component was operated in a single pass mode with a flow rate of approximately 2 mL min-1 under a constant current of approximately 20 mA g-1 based on the total mass of Na0.44MnO2. Note that the mass of the electrode is presented as the total mass of the electrode, including Na0.44MnO2, Super-P and PTFE. The feed water contained an approximate NaCl concentration of 6 g L-1. In addition, the system was tested in the NaCl concentration range from 3 g L-1 to 35 g L-1 based on the salinity levels of brackish water and sea water under a constant current of approximately 50 mA g-1. To evaluate this hybrid system in an electrolyte containing diverse ions, the performance was tested in synthetic



brackish water (total amount of salt: ~ 2.8 g L-1, Na+: 874 mg L-1, Ca2+: 63 mg L-1, Mg2+: 86 mg L-1, Cl-: 1547 mg L-1 and SO42-: 220 mg L-1).

Analysis of the hybrid electrochemical desalination system for deionization and oxidant generation The feed concentration was measured by a conductivity meter (3573-10C, HORIBA, Ltd, Japan). The deionization performance was expressed as the mass of the deionized NaCl salt per the total mass of Na0.44MnO2. The amount of deionized ions was estimated based on the change in the concentration of the cations and anions in the deionization cell measured via ion chromatography (IC, DX-120, DIONEX Co., Ltd., USA). The amount of accumulated reactive chlorine in the oxidation cell was measured by the N,N-diethyl-p-phenylenediamine (DPD) colorimetric method using a spectrophotometer (DR/2010, HACH Co., USA) at a wavelength of 530 nm.9 The coulombic efficiencies for deionization in desalination part and chlorine generation in oxidation part were estimated by Equation (1): η =

n×V×F×C I×t

(1)

where i indicates each ion in synthetic brackish water (Na+, Ca2+, Mg2+, Cl- and SO42-) or generated Cl2, n is the number of consumed charges, V is the volume of the electrolyte (L), F is the Faraday constant (96485 C equivalent-1), C is the concentration of deionized ion or generated chlorine (mg L-1), I is the applied current (A), and t is the operation time. All the experiments were carried out in duplicate or triplicate to examine their reproducibility.


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Results and Discussion

Figure 4 shows the conductivity (a) and cell voltage profiles (b) for the desalination component of the hybrid electrochemical desalination system operated in 7.2 g L-1 of NaCl. Note that the potential of Na0.44MnO2 is expressed as that of the negative electrode (Vcell=VmTiO2 NTs

- VNa0.44MnO2). As shown in Figure 4 (a), exemplary deionization characteristics under

constant current operation (20 mA g-1 based on the total mass of Na0.44MnO2) in batch mode were observed through the gradual change that varied with the operation time (corresponding to the applied charge) in the effluent conductivity. For instance, the effluent conductivity consistently decreased during the deionization process and reverted to its initial state during the regeneration process. Based on the conductivity change in the desalination process, this hybrid electrochemical desalination system showed a coulombic efficiency of over 96%. This considerable coulombic efficiency indicated that the deionization in this hybrid system is performed by the intercalation of Na+ into Na0.44MnO2 and the simultaneous diffusion of Clinto the oxidation component through the anion exchange membrane. This result indicated the Na0.44MnO2 specific capacity of approximately 33 mAh g-1 was successfully utilized for a desalination capacity of approximately 32 mAh g-1 (due to the coulombic efficiency of 96%). Converting the values to the salt adsorption capacity (SAC), which is the representative parameter for electrochemical deionization performance, showed that approximately 28 mg of Na was deionized by one gram of intercalation in Na0.44MnO2 and approximately 44 mg of Cl was deionized via diffusion through the anion exchange membrane. On the other hand, in the oxidation component, the conductivity variation was relatively insignificant (Figure S1). Interestingly, sudden drops in the effluent conductivity were measured during the regeneration process, which was attributed to bubbling from the hydrogen evolution reaction in the oxidation component. This observation suggested the hybrid system has the potential to merge hydrogen generation and desalination technologies. ACS Paragon Plus Environment


In Figure 4 (b), a distinct characteristic in the cell voltage profile of the hybrid system under constant current operation was observed. In the initial stage of the desalination process, the cell voltage drastically increased to approximately 2 V. The initial cell voltage was mainly affected by the potential for oxidation reaction (oxygen/chlorine evolution reaction) on the mTiO2 NTs. As the desalination proceeded, the voltage gradually increased to approximately 2.7 V. The gradual increase of the cell voltage was affected by the potential of Na0.44MnO2 due to the intercalation of the Na+. Conversely, in the regeneration process, the cell voltage decreased from -1.5 V to -2.5 V, resulting from the potential for reduction reaction (proton intercalation/hydrogen evolution reaction) on the m-TiO2 NTs. This explanation was supported by the potentials for the oxidation and reduction of the m-TiO2 NTs in the cyclic voltammetry (CV) measurement (Figure S2), and the potential variation (approximately 0.8 V) during the process well matched the working potential of Na0.44MnO2 in the CV measurement (Figure S3). Overall, based on the result in Figure 4 (a) and (b), this hybrid system showed energy consumption of approximately 47 ± 2 kT (energy per removed ion) 7.2 g L-1 of NaCl for desalination and oxidation processes. In respect to desalination process, comparatively high energy consumption is required compared to conventional CDI or MCDI system (20 kT for MCDI). However, it is expected that the m-TiO2 NTs is attributed to the overpotential for generating oxidants, and the energy consumption could be reduced via the further research of the anode material.


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Figure 5 (a) and (b) show the discharging curves and desalination capacity of Na0.44MnO2 in the hybrid electrochemical desalination system, respectively (in the range of 3 g L-1 to 35 g L1

NaCl, which represents salinity levels from brackish water to sea water; current density of

50 mA g-1 based on Na0.44MnO2). As shown in Figure 5 (a), Na0.44MnO2 exhibited a high specific capacity with the increasing NaCl concentration, which allowed more ions to be accessible to the interfaces of the electrode. For instance, the specific capacity in 3 g L-1 of NaCl was approximately 18 mAh g-1, whereas the capacity increased to approximately 40 mAh g-1 at 35 g L-1 (more than twice the specific capacity). This result implied that twice as many Na+ can be intercalated into Na0.44MnO2. In Figure 5 (b), the capacity of the deionized Na+ via intercalation into Na0.44MnO2 (gray) and the capacity of the diffused Cl- via the anion exchange membrane (white) are presented as a function of the concentration of NaCl. Notably, approximately 34 mg of Na was deionized by one gram of Na0.44MnO2, and approximately 53 mg of Cl was deionized by diffusion through the anion exchange membrane in 35 g L-1 of NaCl. Approximately 14 mg of Na was deionized by one gram of Na0.44MnO2, and approximately 22 mg of Cl was deionized via diffusion in 3 g L-1 of NaCl. A primary reason for this desalination performance is the nature of this hybrid system. Because an oxidation process was utilized as a counterpart of the desalination system, the anions were deionized by spontaneous diffusion into the oxidation component without using the anode to capture the anions. The desalination capacity was estimated by Equation (2): 1 Q Desalination

=

1 (qCations+qDiffusion )⁄mCathode

(2)

where QDesalination is the desalination capacity of the system (mg g-1), qCations is the amount of deionized cations (mg), qDiffusion is the amount of diffused anions (mg), and mCathode is the mass of the cathode used to capture cations (g). Hence, this hybrid system can achieve a desalination performance in a novel way to fully use the capacity of the cathode in



comparison with a conventional system that consists of a cathode and anode, which is estimated by Equation (3): 1 QDesalination

=q

1 Cations ⁄mCathode

+q

Anions

1 ⁄mAnode

(3)

where QDesalination, qCations and mCathode correspond to those in Equation (2), qAnions is the amount of deionized anions (mg), and mAnode is the mass of the anode used to capture anions (g). In addition, utilizing an oxidation process demonstrated a new electrochemical desalination system that does not use the anode to capture anions. This provides an opportunity to overcome the limitations associated with selecting materials for anion capture. Figure 5 (c) presents the correlation between the specific capacity of Na0.44MnO2 (Figure 5 (a)) and its desalination capacity (Figure 5 (b)) in the hybrid electrochemical desalination system. As shown in Figure 5 (c), this hybrid system showed a high average efficiency of approximately 98% (the ratio of the desalination capacity to the specific capacity). This high efficiency implies that this hybrid system fully uses the specific capacity of the electrode. Note that the efficiency at each concentration of NaCl was calculated using the total consumed coulombs for the deionized NaCl in Figure 5 (b) per the specific capacity of Na0.44MnO2 in Figure 5 (a).


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Table 1 presents the overall performance of the hybrid electrochemical desalination system for desalination and oxidation in synthetic brackish water (sodium: 874 mg L-1, calcium: 63 mg L-1, magnesium: 86 mg L-1, chloride: 1547 mg L-1, sulfate: 220 mg L-1). Deionization occurred on Na0.44MnO2 and, simultaneously, oxidation occurred on the m-TiO2 NTs. As shown in Table 1, this hybrid system demonstrated an effective deionization capability with a coulombic efficiency of approximately 98% based on the cations (Na+, Mg2+ and Ca2+). Approximately 68% of the charges were consumed to capture the Na+, which composed the majority of the synthetic brackish water. Notably, despite Na0.44MnO2 being a representative host material for sodium intercalation, approximately 30% of the charges were consumed to capture the Mg2+ and Ca2+. The high removal ratio for the divalent ions (Mg2+ and Ca2+) is possibly explained by their smaller or equivalent atomic size and the high electrostatic force of divalent ions compared to that of Na+.18, 36 However, no notable difference was observed in the removal ratio of the anions (chloride and sulfate), which may indicate that the anions do not selectively diffuse through the anion exchange membrane due to their similar ionic mobility in water (Cl-: 7.91 x 10-8 m2 s-1 V-1, SO4-2: 8.29 x 10-8 m2 s-1 V-1).37 Furthermore, as shown in Table 1, this hybrid system demonstrated a coulombic efficiency of approximately 66% for chlorine generation in the synthetic brackish water, and the rest of the charges were presumed to be utilized for oxygen evolution. This result indicated that the m-TiO2 NTs efficiently function as the anode for chlorine generation in low concentrations of synthetic brackish water (~ 1,547 mg L-1 of Cl-), and this conclusion is supported by the staircase linear sweep voltammetry (SLSV) in Figure S4.38-39 The m-TiO2 NTs exhibited a lower onset potential in the presence of Cl-, which provided insight into the preference for chlorine evolution over oxygen evolution. Although the theoretical potential of the oxygen evolution at a neutral pH (0.62 V vs. Ag/AgCl) is much lower than that of the chlorine evolution (1.16 V vs. Ag/AgCl), the chlorine evolution was noted to be kinetically favorable due to the abstraction of four electrons for the oxidation of H2O to O2.40 The high efficiency of the chlorine generation on the m-TiO2 NTs can be ACS Paragon Plus Environment


attributed to the well-organized nanotube structure or intrinsic properties (e.g., affinity for oxygen, working potential and over potential), and the efficient chlorine generation allows for the efficient mass transfer of Cl- from the bulk to the interface (Figure 3 (b)). The efficiency of the m-TiO2 NTs for chlorine generation led to stability in this hybrid system without the accumulation of anions that diffused from the desalination component.


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CONCLUSION

In this study, a novel hybrid electrochemical desalination system was synchronized with an oxidation process for the first time and successfully demonstrated the spontaneous diffusion of anions through the anion exchange membrane and a simultaneous chlorine generation reaction via intercalation into a selective-cation battery material. By combining the oxidation process with the desalination system, this electrochemical desalination system showed a superior desalination capacity and efficiency and provided a new strategy to overcome the limitations of the materials used to capture anions. As a primary result, a specific capacity of approximately 33 mAh g-1 in the cation-selective battery material was successfully utilized for the desalination capacity with a coulombic efficiency of over 96% in 7.2 g L-1 of NaCl. This result indicated that approximately 28 mg of Na was desalted by 1 gram of the cationselective battery material and approximately 44 mg of Cl diffused through the anion exchange membrane. Additionally, this hybrid system showed a coulombic efficiency of approximately 98% and 66% in synthetic brackish water (total of 2.8 g L-1 of diverse ions) for desalination and oxidation, respectively. Through the combination of an oxidation process with a desalination system using energy storage materials, the research and application of the electrochemical water treatment system is expected to be expanded.



ACKNOWLEDGMENTS This research was supported by a grant (code 17IFIP-B065893-05) from the Industrial Facilities & Infrastructure Research Program funded by the Ministry of Land, Infrastructure and Transport of the Korean government, the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF2016R1D1A1A02937469) and the Korea Ministry of Environment as “Global Top Project (E617-00211-0608-0)”.


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REFERENCES

1.

Service, R. F., Desalination freshens up. Science (New York, NY) 2006, 313 (5790),

1088. 2.

Elimelech, M.; Phillip, W. A., The future of seawater desalination: energy,

technology, and the environment. Science 2011, 333 (6043), 712-717. 3.

Vörösmarty, C. J.; McIntyre, P. B.; Gessner, M. O.; Dudgeon, D.; Prusevich, A.;

Green, P.; Glidden, S.; Bunn, S. E.; Sullivan, C. A.; Liermann, C. R., Global threats to human water security and river biodiversity. Nature 2010, 467 (7315), 555-561. 4.

Yoon, H.; Lee, J.; Kim, S.-R.; Kang, J.; Kim, S.; Kim, C.; Yoon, J., Capacitive

deionization with Ca-alginate coated-carbon electrode for hardness control. Desalination 2016, 392, 46-53. 5.

Comninellis, C., Electrocatalysis in the electrochemical conversion/combustion of

organic pollutants for waste water treatment. Electrochimica Acta 1994, 39 (11-12), 18571862. 6.

Oren, Y., Capacitive deionization (CDI) for desalination and water treatment—past,

present and future (a review). Desalination 2008, 228 (1), 10-29. 7.

Martinez-Huitle, C. A.; Ferro, S., Electrochemical oxidation of organic pollutants for

the wastewater treatment: direct and indirect processes. Chemical Society Reviews 2006, 35 (12), 1324-1340. 8.

Porada, S.; Zhao, R.; Van Der Wal, A.; Presser, V.; Biesheuvel, P., Review on the

science and technology of water desalination by capacitive deionization. Progress in Materials Science 2013, 58 (8), 1388-1442. 9.

Jeong, J.; Kim, C.; Yoon, J., The effect of electrode material on the generation of

oxidants and microbial inactivation in the electrochemical disinfection processes. Water Research 2009, 43 (4), 895-901.



10.

Sadrzadeh, M.; Mohammadi, T., Sea water desalination using electrodialysis.

Desalination 2008, 221 (1), 440-447. 11.

Sillanpää, M.; Shestakova, M., Electrochemical Water Treatment Methods:

Fundamentals, Methods and Full Scale Applications. 1st ed.; Butterworth-Heinemann: 2017; Vol. 1, p 310. 12.

Suss, M.; Porada, S.; Sun, X.; Biesheuvel, P.; Yoon, J.; Presser, V., Water

desalination via capacitive deionization: what is it and what can we expect from it? Energy & Environmental Science 2015, 8 (8), 2296-2319. 13.

Lee, J.; Kim, S.; Kim, C.; Yoon, J., Hybrid capacitive deionization to enhance the

desalination performance of capacitive techniques. Energy & Environmental Science 2014, 7 (11), 3683-3689. 14.

Kim, S.; Lee, J.; Kim, C.; Yoon, J., Na2FeP2O7 as a novel material for hybrid

capacitive deionization. Electrochimica Acta 2016, 203, 265-271. 15.

Yin, H.; Zhao, S.; Wan, J.; Tang, H.; Chang, L.; He, L.; Zhao, H.; Gao, Y.; Tang, Z.,

Three‐dimensional graphene/metal oxide nanoparticle hybrids for high‐performance capacitive deionization of saline water. Advanced Materials 2013, 25 (43), 6270-6276. 16.

Porada, S.; Borchardt, L.; Oschatz, M.; Bryjak, M.; Atchison, J.; Keesman, K.;

Kaskel, S.; Biesheuvel, P.; Presser, V., Direct prediction of the desalination performance of porous carbon electrodes for capacitive deionization. Energy & Environmental Science 2013, 6 (12), 3700-3712. 17.

Zhang, D.; Yan, T.; Shi, L.; Peng, Z.; Wen, X.; Zhang, J., Enhanced capacitive

deionization performance of graphene/carbon nanotube composites. Journal of Materials Chemistry 2012, 22 (29), 14696-14704. 18.

Pasta, M.; Wessells, C. D.; Cui, Y.; La Mantia, F., A desalination battery. Nano

Letters 2012, 12 (2), 839-843. 19.

Kim, H.; Hong, J.; Park, K.-Y.; Kim, H.; Kim, S.-W.; Kang, K., Aqueous

rechargeable Li and Na ion batteries. Chemical Reviews 2014, 114 (23), 11788-11827. ACS Paragon Plus Environment

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20.

Slater, M. D.; Kim, D.; Lee, E.; Johnson, C. S., Sodium‐Ion Batteries. Advanced

Functional Materials 2013, 23 (8), 947-958. 21.

Jo, C.; Park, Y.; Jeong, J.; Lee, K. T.; Lee, J., Structural effect on electrochemical

performance of ordered porous carbon electrodes for Na-ion batteries. ACS Applied Materials & Interfaces 2015, 7 (22), 11748-11754. 22.

Smith, K. C.; Dmello, R., Na-Ion desalination (NID) enabled by Na-blocking

membranes and symmetric Na-intercalation: porous-electrode modeling. Journal of The Electrochemical Society 2016, 163 (3), A530-A539. 23.

Lee, J.; Yu, S.-H.; Kim, C.; Sung, Y.-E.; Yoon, J., Highly selective lithium recovery

from brine using a λ-MnO2–Ag battery. Physical Chemistry Chemical Physics 2013, 15 (20), 7690-7695. 24.

Pasta, M.; Battistel, A.; La Mantia, F., Batteries for lithium recovery from brines.

Energy & Environmental Science 2012, 5 (11), 9487-9491. 25.

Trócoli, R.; Battistel, A.; Mantia, F. L., Selectivity of a lithium‐recovery process

based on LiFePO4. Chemistry–A European Journal 2014, 20 (32), 9888-9891. 26.

Kim, S.; Lee, J.; Kang, J. S.; Jo, K.; Kim, S.; Sung, Y.-E.; Yoon, J., Lithium recovery

from brine using a λ-MnO2/activated carbon hybrid supercapacitor system. Chemosphere 2015, 125, 50-56. 27.

Achilleos, D. S.; Hatton, T. A., Selective Molecularly Mediated Pseudocapacitive

Separation of Ionic Species in Solution. ACS Applied Materials & Interfaces 2016, 8 (48), 32743-32753. 28.

Su, X.; Hatton, T. A., Redox-electrodes for selective electrochemical separations.

Advances in Colloid and Interface Science 2017, 244, 6-20. 29.

Su, X.; Hatton, T. A., Electrosorption at functional interfaces: from molecular-level

interactions to electrochemical cell design. Physical Chemistry Chemical Physics 2017, 19 (35), 23570-23584.



30.

Su, X.; Kulik, H. J.; Jamison, T. F.; Hatton, T. A., Anion‐Selective Redox

Electrodes: Electrochemically Mediated Separation with Heterogeneous Organometallic Interfaces. Advanced Functional Materials 2016, 26 (20), 3394-3404. 31.

Nam, D.-H.; Choi, K.-S., Bismuth as a New Chloride-Storage Electrode Enabling the

Construction of a Practical High Capacity Desalination Battery. Journal of the American Chemical Society 2017, 139 (32), 11055-11063. 32.

Su, X.; Tan, K.-J.; Elbert, J.; Rüttiger, C.; Gallei, M.; Jamison, T. F.; Hatton, T. A.,

Asymmetric Faradaic systems for selective electrochemical separations. Energy & Environmental Science 2017, 10 (5), 1272-1283. 33.

Lee, J.; Kim, S.; Yoon, J., Rocking Chair Desalination Battery Based on Prussian

Blue Electrodes. ACS Omega 2017, 2 (4), 1653-1659. 34.

Porada, S.; Shrivastava, A.; Bukowska, P.; Biesheuvel, P.; Smith, K. C., Nickel

Hexacyanoferrate Electrodes for Continuous Cation Intercalation Desalination of Brackish Water. Electrochimica Acta 2017, 255, 369-378. 35.

Kim, C.; Kim, S.; Choi, J.; Lee, J.; Kang, J. S.; Sung, Y.-E.; Lee, J.; Choi, W.; Yoon,

J., Blue TiO2 Nanotube Array as an oxidant generating novel anode material fabricated by simple cathodic polarization. Electrochimica Acta 2014, 141, 113-119. 36.

Kim, S.; Yoon, H.; Shin, D.; Lee, J.; Yoon, J., Electrochemical selective ion

separation in capacitive deionization with sodium manganese oxide. Journal of Colloid and Interface Science 2017, 506, 644-648. 37.

Bard, A. J.; Faulkner, L. R., Electrochemical methods: principles and applications.

Electrochemical Methods: Principles and Applications 2001, 386-428. 38.

Kuhn, A.; Mortimer, C., The efficiency of chlorine evolution in dilute brines on

ruthenium dioxide electrodes. Journal of Applied Electrochemistry 1972, 2 (4), 283-287. 39.

Rajkumar, D.; Kim, J.-G.; Kim, K. K., A study on electrochemical, oxidation of

catechol in chloride medium for wastewater treatment application. Environ. Eng. Res. 2004, 9 (6), 279-287. ACS Paragon Plus Environment

Page 20 of 29

Page 21 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


40.

Hoganson, C. W.; Babcock, G. T., A metalloradical mechanism for the generation of

oxygen from water in photosynthesis. Science 1997, 277 (5334), 1953-1956.


ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

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Table 1. The overall performance of the hybrid electrochemical desalination system combined with an oxidation process in synthetic brackish water (total concentration of 2.8 g L-1, Na+: 874 mg L-1, Ca2+: 63 mg L-1, Mg2+: 86 mg L-1, Cl-: 1547 mg L-1 and SO42-: 220 mg L-1; current density: 50 mA g-1 based on Na0.44MnO2, 3.5 mA cm-2 based on m-TiO2 NTs). Ci: initial concentration, Cf: final concentration, ∆C: ratio of concentration changes.

Desalination Component

Oxidation Component

Na+

Ca2+

Mg2+

Cl-

SO42-

Cl2

Ci / mg L-1

874

63

86

1547

220

0

Cf / mg L-1

616 ± 1

29 ± 1

47 ± 1

1033 ± 8

137 ± 1

173

∆C / %

30

54

46

33

38

−

68

10

20

88

10

Coulombic Efficiency / %

66 98 (Total)


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Figure 1. Schematic of a novel hybrid electrochemical desalination system synchronized with an oxidation process. During the operation for the desalination and oxidation, cations are intercalated into the cation-selective battery material by the electrical potential in the desalination component, and in the oxidation component, reactions occur on the anode to generate oxidant, including reactive chlorine species. Simultaneously, the anions in the desalination component diffuse into the oxidation component through the anion exchange membrane to maintain the neutrality in each component.



Figure 2. Schematic of the hybrid electrochemical desalination system combined with an oxidation process. This hybrid system consists of a deionization component with a cation-selective electrode material and an oxidant generation component with an anode, and these two components are separated by an anion exchange membrane (1: current collector, 2: cation selective electrode, 3: oxidant generating electrode, 4: spacer, 5: anion exchange membrane).


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Figure 3. FE-SEM images of Na0.44MnO2 and top-view (b), side-view (c) and mesh Ti substrate (d) of m-TiO2 NTs used as the electrode materials in the hybrid electrochemical desalination system. The colorization of the m-TiO2 NTs (e), anodized m-TiO2 NTs (on left) and m-TiO2 NTs treated by cathodic polarization (on right).



Figure 4. Effluent conductivity profile in the desalination component (a) and current-voltage profile (b) of the hybrid electrochemical desalination system operated in a NaCl concentration of 7.2 g L-1 under a constant current operation (20 mA g-1 based on Na0.44MnO2). Note that the potential of Na0.44MnO2 was expressed as that of the negative electrode (Vcell = Vm-TiO2 NTs - VNa0.44MnO2).


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Figure 5. Discharging curves (a) and desalination capacity (b) of Na0.44MnO2 in the hybrid electrochemical desalination system (in the range of 3 g L-1 to 35 g L-1 of NaCl; current density: 50 mA g-1 based on Na0.44MnO2) and the correlation between the specific capacity and the desalination capacity (c) of Na0.44MnO2 in the hybrid electrochemical desalination system. Inset of (a): the specific capacity measured in the discharging curves based on the NaCl concentration.


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For Table of Contents Use Only

Synopsis: Hybrid electrochemical desalination system synchronized with oxidation process provides a strategy to fully utilize the capacity of electrode for desalination.


Hybrid Electrochemical Desalination System Combined with an

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