Rocking-Chair Capacitive Deionization for Continuous Brackish Water

Subscriber access provided by TUFTS UNIV

Article

Rocking Chair Capacitive Deionization for Continuous Brackish Water Desalination Jaehan Lee, Kyusik Jo, Jiho Lee, Sung Pil Hong, Seonghwan Kim, and Jeyong Yoon ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/acssuschemeng.8b02123 • Publication Date (Web): 06 Jul 2018 Downloaded from http://pubs.acs.org on July 6, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 25 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

ACS Sustainable Chemistry & Engineering

1

2

Rocking Chair Capacitive Deionization for

3

Continuous Brackish Water Desalination

4

Jaehan Lee,†,‡ Kyusik Jo,† Jiho Lee,† Sung Pil Hong,† Seonghwan Kim,†,‡ Jeyong Yoon*,†,‡ †

5

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

6

Chemical Process, Seoul National University (SNU), 1 Gwanak-ro, Gwanak-gu, Seoul 08826,

7

Republic of Korea

8 9

‡

Asian Institute for Energy, Environment & Sustainability (AIEES), Seoul National University (SNU), 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea

10 11 12 13 14 15 16

Jeyong Yoon (corresponding author)

17

E-mail: [email protected]; Phone: +82-2-880-8927; Fax: +82-2-876-8911

18 19

Keywords: desalination, electrochemical process, capacitive deionization, Nafion, activated carbon

20 1

ACS Paragon Plus Environment

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 48 49 50 51 52 53 54 55 56 57 58 59 60

21

Abstract

22

Capacitive deionization (CDI) is considered an alternative desalination technology due to its

23

easy operation, high energy efficiency and environmentally friendly process. However, a

24

separate regeneration step is required in typical CDI technologies that releases the absorbed

25

ions on the electrodes which results in an inefficient and cost-intensive process. This study

26

proposed a novel CDI system referred to as “rocking chair capacitive deionization (RCDI)”

27

that has a continuous brackish water desalination process which consists of a pair of Nafion

28

coated activated carbon electrodes and an anion exchange membrane. The coated Nafion

29

contributed to the cation selectivity of the carbon electrode, and it enabled a continuous

30

desalination process during constant current operation through a rocking chair ion movement.

31

From the desalination tests that included the analysis of the CDI Ragone plot, the RCDI has a

32

high salt adsorption capacity (maximum of 44.5 mg g-1) with continuous operation.

33

Furthermore, the RCDI desalted brackish water under rapid operation conditions (up to ±30.0

34

A m-2) which is a constant current operation condition that is several times higher than that of

35

previously reported desalination technologies using battery materials. Consequently, this

36

study proposes a new strategy for a continuous desalination CDI system that provides a high

37

performance and energy efficient desalination process for brackish water.

38

2


Page 2 of 25

Page 3 of 25 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


39

Introduction

40

The demand for fresh water is increasing due to the rapid population growth and enhanced

41

living standards in the world; hence, water scarcity is becoming a serious issue across the

42

world.1-2 Currently, the desalination of salt water is considered as one of the feasible methods

43

to provide fresh water. However, well-developed desalination processes such as reverse

44

osmosis (RO), electrodialysis (ED), and distillation require not only large-scale infrastructure

45

but also have a high cost for controlling fouling during operations. Therefore, it is desirable

46

to develop a novel desalination technology with simple equipment, easy operation and high

47

energy efficiency.3-5

48

Among the various desalination technologies, capacitive deionization (CDI) is considered as

49

one of the promising desalination technologies because of its energy-efficient, eco-friendly,

50

facile operation. CDI is an electrochemical desalination technology to produce fresh water

51

from salt water, and the charged ions of the source water are removed by capacitive

52

electrosorption.6-14 Typically, CDI consists of two porous electrodes that have high surface

53

areas, and the feed stream flows between the electrodes. When applying a potential between

54

the two electrodes, cations and anions in the feed stream are adsorbed onto the surfaces of the

55

electrodes by forming an electrical double layer which results in the production of deionized

56

water. After charging the cell, adsorbed ions are released by discharging or applying a reverse

57

potential which creates a brine solution. However, further applications of conventional CDI

58

are limited due to its low salt adsorption capacity (0.1 to 15 mg g-1), low charge efficiency

59

(30 to 70%), and poor cycling stability. Moreover, CDI requires a separate regeneration step

60

to release the absorbed ions on the electrodes resulting in an inefficient, time-intensive

61

process.15-18 To overcome the limitations of these disadvantages, various attempts have been 3



62

reported including using novel cell architectures, such as water desalination with a wire-

63

electrode, flow-electrode CDI (FCDI), and multi-channel flow stream membrane CDI.19-23

64

A wire-based capacitive desalination is constructed by coating a porous carbon material onto

65

conductive wire electrode pairs. In this system, a feed stream splits into two compartments

66

(dilute and concentrated), and the solution in the dilute compartment is continuously

67

deionized by the wire-electrodes which is then dipped into the solution in the concentrated

68

compartment where the adsorbed ions are released. FCDI is a novel CDI architecture that

69

uses flowable carbon suspensions as electrode rather than static electrodes. FCDI enables a

70

continuous desalination process through a consistent supply of flow-electrodes that are

71

regenerated in separate components either through a short circuit or discharge by applying a

72

reverse potential. Multi-channel flow stream membrane CDI (MC-MCDI) is a recently

73

reported CDI system in which the cell consists of middle and side channels separated by ion

74

exchange membranes. This newly designed CDI enables a semi-continuous desalination

75

process that alternately produces a dilute and concentrated solution at the middle and side

76

channels.

77

Recently, continuous electrochemical desalination technologies that have been developed

78

using battery materials for continuous operation are referred to as a rocking chair desalination

79

battery, battery electrode deionization, and cation intercalation desalination (CID).24-28 These

80

technologies consist of two battery electrodes that react with a cation and anion exchange

81

membrane. The cation selectivity of the battery materials enables continuous ion removal.

82

Although these technologies have a high desalination capacity (approximately 30 to 100 mg

83

g-1) with efficient energy consumption, they have limited performance in terms of the

84

desalination rate (below 5.0 A m-2 in constant current operation) because the ion 4


Page 4 of 25

Page 5 of 25 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


85

capturing/releasing process is based on a chemical reaction. Additionally, improving the

86

cycling life of the battery material still remains a challenge.

87

In addition to these approaches, this study proposes a continuous CDI system based on the

88

rocking-chair ion movement using Nafion coated activated carbon electrodes referred to as

89

“rocking chair capacitive deionization (RCDI), which has a superior desalination rate and

90

stability compared to previous continuous desalination systems using battery materials.

91

Figure 1 shows the schematic of the RCDI and the operation mechanism during the constant

92

current operation. The RCDI consists of two cation selective resin-coated electrodes and an

93

anion exchange membrane similar to electrodialysis (ED) combined with an activated carbon

94

electrode system which is a device for extracting energy from salinity gradients.29 One

95

electrode uses an electrode on which the cations are adsorbed by a pre-treatment before

96

operation, and there are two flow channels (arbitrarily called channel A and channel B)

97

separated by an anion exchange membrane. It is noted that the pre-treatment electrode is

98

located in channel A. In the RCDI system, the carbon electrodes selectively

99

adsorbed/desorbed cations due to the cation selective resin (Nafion) coating. During constant

100

current operation, cations in the channel B solution are adsorbed onto the negative electrode,

101

whereas cations adsorbed onto the carbon electrode in channel A are released into the solution,

102

and the anions in the channel B solution pass through the anion exchange membrane due to

103

the charge neutrality. When a reverse current is applied, the movement of cations and anions

104

are reversed. Consequently, the RCDI system enables desalination in both the constant and

105

reversed constant current operation with a rapid ion removal rate compared to battery-based

106

desalination technologies due to this movement of ions and the fast formation of electrical

107

double layers (EDLs) on the surface of the carbon electrode. This study shows the efficiency 5



108

of the RCDI system using activated carbon electrodes coated with Nafion by evaluating the

109

salt adsorption capacity (SAC), average salt adsorption rate (ASAR), charge efficiency,

110

energy consumption, and stability performance which are performance parameters in the CDI

111

process.

112 113

114

Experimental Section

115

Preparation and characterization of the Nafion coated activated carbon electrodes

116

The activated carbon electrodes were fabricated as follows. Activated carbon (MSP-20X,

117

Kansai Coke and Chemicals, Japan), acetylene black (Super P, Timcal, Switzerland) as a

118

conducting agent, and poly(tetrafluoroethylene) (PTFE, Sigma-Aldrich, USA) as a binder

119

were dispersed and mixed in a pure ethanol solvent for 30 min. The resulting slurry was

120

rolled using a rolling machine to obtain a sheet type electrode with a thickness of 300 µm and

121

dried in a vacuum oven (120 ˚C for 12 h). The fabricated electrode was cut into a square

122

shape (dimensions: 2.0 x 2.0 cm; weight: 55.9±0.9 mg) and attached onto graphite sheets

123

using carbon paint (DAG-T-502, Ted Pella, USA). Then, 0.2 mL of Nafion solution (Nafion-

124

117 solution, Sigma-Aldrich, USA) were coated onto the surface of the activated carbon

125

electrode by the dropping casting method. The pristine and Nafion coated activated carbon

126

electrodes were characterized by scanning electron microscopy (FESEM, JEOL JSM 6700 F,

127

Japan). The cyclic voltammetry tests were conducted on a battery cycler (WBC S3000, WonA

128

tech Co., Korea) in a three-electrode system (Figure S1).

129 6


Page 6 of 25

Page 7 of 25 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


130

Cell construction

131

Figure 2 shows an illustration of the RCDI module. It consists of two Nafion coated

132

activated carbon electrodes, nylon spacers (dimensions: 2.0 x 2.0 cm; thickness: 0.2 µm), and

133

an anion exchange membrane (AMV; AGC engineering Co., Japan). A graphite electrode was

134

used as a current collector. Before assembling the cell, one Nafion coated activated carbon

135

electrode was pretreated. The pre-treated positive electrode was prepared by electrical

136

conduction at a constant current (-10.0 A m-2) for 1 h in a three electrode system. As shown in

137

Figure 3, the Nafion coated electrode was used as a working electrode, and stainless steel

138

mesh was prepared as a counter electrode. The reference electrode was a silver/silver chloride

139

(KCl saturated) electrode, and the cell was put into a 100 mM NaCl solution.

140 141

Desalination performance tests

142

For the desalination performance tests, the RCDI was operated in the two channel pass

143

mode shown in Figure 2. Feed solutions were supplied in the two channels by a peristaltic

144

pump with a volumetric flow rate of 2 mL min-1. The pre-treated Nafion coated AC electrode

145

was located on the channel A side, and the desalination process was conducted under various

146

constant current conditions with a cell voltage range of -1.2 V to +1.2 V or -1.0 V to +1.0 V

147

using a battery cycler. The current direction was reversed when the cell voltage reached the

148

voltage limitations. The conductivity of the treated solution was measured by a flow-type

149

conductivity meter (3573-10C, HORIBA, Japan). The salt adsorption capacity at one cycle

150

(SAC) was calculated by equation (1) as follows:

151

= × −

7


(1)


Page 8 of 25

152

, where Mw is the molecular weight of NaCl (58.44 mg mmol-1); Me is the total weight of the

153

pristine activated carbon electrodes (g); t2-t1 is the operation time of one cycle during the

154

constant and reversed constant current operation steps; Ci is the NaCl concentration of the

155

initial source solution (mM); Cd is the NaCl concentration of the desalted water (mM), and Q

156

is the flow rate (mL min-1).

157

The average salt adsorption rate (ASAR) was estimated by equation (2) as follows:

=

158

159 160

163 164

165

(2)

, where t2 – t1 is the cycle time. The charge efficiency at one cycle (Q) was examined by equation (3) as follows: % =

161

162

×

#

# |"|

× 100

(3)

, where F is the faradaic constant (96485 C mole-1), and I is the applied current (A). The total energy consumption per salt adsorption mass at one cycle (Et) was calculated by equation (4) as follows:

# - . /

& '( )*+ = , ×

#

(4)

166

, where I is the applied current (A); V is the cell voltage during operation (V); Ci is the NaCl

167

concentration of the initial source solution (mM); Cd is the NaCl concentration of the desalted

168

solution (mM), and Q is the flow rate (mL min-1).

169 170

8


Page 9 of 25 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


171

Results and Discussion

172

Figure 4 shows the morphologies of the pristine and Nafion coated activated carbon

173

electrodes. As shown in Figure 4 (a) & (b), the activated carbon and acetylene black powder

174

covered the surface, and they were bound together with the PTFE polymer. On the other hand,

175

they were not observed in Figure 4 (c) because of the Nafion coating layer. From the side-

176

view images of the Nafion coated electrode (Figure 4 (d) & (e)), the thickness of the coating

177

layer was approximately 1 µm which well covered the top of the carbon electrode. The

178

selective transport of cations between the feed solution and the surface of the carbon

179

electrode during operations is attributed to the thin cation-exchange polymer layer.30

180

Figure 5 shows the effluent conductivity changes of channel A and channel B and the

181

voltage-current profiles during the constant current operation with a cell voltage range of -1.2

182

V to 1.2 V ((a) & (b)) and -1.0 V to 1.0 V ((c) & (d)) at a current density of ±12.5 A m-2 in the

183

RCDI. As seen in Figure 5 (a) & (b), the effluent conductivity changes are stable both for the

184

adsorption and desorption steps showing a typical constant current operation in CDI.9

185

Additionally, it was confirmed that both channel A and channel B have opposite conductivity

186

properties during a cycle indicating that desalted water can be continuously produced. It

187

should be noted that the Nafion, which is a cation selective polymer resin, was well coated

188

onto the electrode surface at a thickness of approximately 1 µm. This thin layer enables the

189

cation selective adsorption onto the surface of the activated carbon electrode without any

190

other signification changes in the electrochemical performance shown in the cyclic

191

voltammetry curve (Figure S1). Therefore, cations are selectively adsorbed onto the surface

192

of the Nafion coated activated carbon. In addition, cations adsorbed onto the electrode by the

9



193

pre-treatment before operations enable the rocking-chair ion movement which means that the

194

RCDI can desalt salt water both in the constant and reverse constant current operation.

195

The desalination performance of the RCDI was confirmed with a voltage range of -1.2 V to

196

1.2 V. The salt adsorption capacity during one cycle was 29.3 ± 0.1 mg g-1. This value is

197

higher than that in a similar constant current operation condition for a MCDI result (17.4 mg

198

g-1) reported in previous studies.31-32 The charge efficiency, which represents the efficiency of

199

the removed ions compared to the total charge amount during operations, is around 90%

200

indicating that most of the charge during operations was used for the ion adsorption onto the

201

surface of the electrode. The energy consumption of the RCDI cell can be calculated by the

202

cell voltage profile at the constant current operation, The energy consumption per removed

203

ion during one cycle is 4.8 kT (23.9 kJ mol-1) which is lower than the reported value for

204

brackish water desalination with MCDI (10 to 50 kT).9,

205

consumption step and a recovery step in the operation of the RCDI. In detail, the constant

206

current operation starts with energy recovery until the cell voltage reaches 0 V (∆G < 0) and

207

then switches to energy consumption in a cell voltage range from 0 to 1.2 V (∆G > 0). When

208

a reverse constant current is applied, the energy is recovered when the cell voltage reaches 0

209

V and is consumed when the voltage ranges from 0 V to -1.2 V.

33

Note that there is an energy

210

Figure 5 (b) shows the cell voltage change over a voltage window of -1.2 V to 1.2 V. As can

211

be seen, the slop of the cell voltage profile vividly changes from around -0.8 V indicating that

212

a side reaction (e.g., water splitting) occurred after fully releasing the adsorbed cation on the

213

surface of the electrodes. This result presents the ion adsorption capacity of the RCDI can be

214

limited by the one side of the electrode. Moreover, the amount of adsorbed cations by the pre-

215

treatment is one of the limiting factors during operations because it leads to the occurrence of 10


Page 10 of 25

Page 11 of 25 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


216

this side reaction. The effect of the side reaction is also seen in the conductivity curves

217

(Figure 5 (a)) with the appearance of peaks at the end of the concentrated solution. One

218

solution to avoid this side reaction was to adjust the voltage range. Figure 5 (c) & (d) shows

219

the conductivity and voltage curve during the constant current operation with a cell voltage

220

range of -1.0 V to 1.0 V because this produces a stable conductivity and linear changes in the

221

cell voltage during the cycles. This observation suggests that it is possible to operate the

222

RCDI stably and to prevent a side reaction by controlling the cell voltage range.

223

Figure 6 (a) & (b) shows the conductivity changes with different current densities and the

224

CDI Ragone plot of the RCDI at various salt concentrations under the constant current

225

operation. As can be seen in Figure 6 (a), the higher current operation produces an effluent

226

with large conductivity changes, and similar conductivity changes are observed for both

227

channel A and channel B. These results indicate that the salt concentration of the effluent can

228

be controlled by the operating conditions; the salt concentration of the effluent decreases

229

when increasing the current and vice versa. To further evaluate the results of the RCDI at

230

various operating conditions compared with the results of the conventional MCDI, a CDI

231

Ragone plot, which is an analysis tool to evaluate the desalination performance of CDI, is

232

shown in Figure 6 (b) that compares the RCDI results with previously reported MCDI results

233

from our group.32 Note that the CDI Ragone plot in this study is represented by the salt

234

adsorption capacity (SAC) and the average salt adsorption rate (ASAR) which is an essential

235

parameter in CDI obtained by dividing the SAC by the duration of the total cycle operation

236

time including the ion adsorption and desorption steps proposed by Zhao et al.34 More

237

detailed SAC performances at different operation conditions are given in the Supporting

238

information (Table S1). The CDI Ragone plot shows that both the SAC and ASAR increased 11



239

when the source water concentration was higher. This performance enhancement can be

240

explained by the increased capacity of the electrode and the decreased electrolyte resistance

241

in the higher influent concentration. The maximum SAC in RCDI observed at the low current

242

operation (10.0 A m-2) in the high influent concentration (50 mM) was 44.6 mg g-1 which is

243

higher than the mSAC of MCDI (22.8 mg g-1). Moreover, the RCDI has an excellent ASAR

244

comparable to that of the conventional MCDI. The cell architecture including one electrode,

245

on which the cations are adsorbed by a pre-treatment, enabled continuous desalination during

246

both the constant and reverse constant current operation. Hence, this system can achieve a

247

higher SAC during the total cycle operation compared with the conventional MCDI which

248

has a separate regeneration step. Additionally, the RCDI can be operated under a rapid

249

operation condition (±30.0 A m-2 in 50 mM NaCl) with a remarkable SAC (17.5 mg g-1)

250

indicating that it is possible to deionize salt water under fast operation conditions compared

251

with previous continuous desalination systems using battery materials (constant current

252

operation conditions: ±1.4 to ±5.0 A m-2).24,25,27 Consequently, the RCDI architecture enables

253

a rapid desalination performance with continuous operation.

254

Figure 7 shows the results of the stability tests in the RCDI. To investigate the repeatability

255

and the characteristics of the RCDI system, a cycling test (35 cycles) was done at a constant

256

current operation with a current density of ± 12.5 A m-2 in 10 mM NaCl solution. From the

257

results of the conductivity and voltage data, the SAC and charge efficiency during the cycling

258

test are shown in Figure 7 (a). Impressively, the SAC slightly increased with the increase of

259

cycles, and it stabilized after 26 cycles. This result can be explained as follows: the charge

260

balance between the pre-adsorbed cation and the capacity of the opposite electrode is

261

adjusted by repeating the operation. As shown in Figure 7 (b) & (c), linear voltage profiles 12


Page 12 of 25

Page 13 of 25 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


262

and more steady conductivity changes were observed at the end of the test compared with the

263

beginning step. Adjusting the charge balance reduces the side reaction and enhances the

264

charge efficiency during the operation. From the results of the cycling performance test, the

265

RCDI has a promising stable performance in repeated operation. However, it should be noted

266

that the source water used in this study was not a real condition, and a membrane fouling

267

could be an important issue during operation. Further research is required to investigate the

268

fouling effects using a feed solution containing organic/inorganic compounds and the long-

269

term stability.

270

271

Conclusion

272

In this study, a novel continuous desalination system for CDI was investigated. It is simple

273

and easy to operate using a Nafion coated activated carbon electrode. With the cation

274

exchange resin coating, the Nafion coated activated carbon can selectively adsorb and desorb

275

cations. As a result, continuous operation is possible in the RCDI system with the

276

spontaneous diffusion of anions. This system had a high maximum SAC (44.6 mg g-1)

277

compared to the conventional CDI system. Additionally, it is possible for the system to

278

operate in a rapid current operation (maximum: ± 30.0 A m-2) with excellent cycling stability.

279

The RCDI can be easily scaled up by increasing the size of the electrodes; moreover, it is

280

possible to reduce the installation expense by replacing the Nafion with an inexpensive cation

281

exchange resin. We believe the proposed RCDI in this study can be used in a variety of

282

applications such as desalination and water softening as well as an analysis tool in CDI

283

technologies.

13



284 285

286

Acknowledgement

287

This study was supported by the Technology Innovation Program (10082572, Development

288

of Low Energy Desalination Water Treatment Engineering Package System for Industrial

289

Recycle Water Production) funded By the Ministry of Trade, Industry & Energy (MOTIE,

290

Korea), the Basic Science Research Program through the National Research Foundation of

291

Korea (NRF) funded by the Ministry of Education (NRF-2016R1D1A1A02937469), and by

292

the Ministry of Environment, Republic of Korea, as a “Global Top Project (E617-00211-

293

0608-0).

294

295

296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311

References (1) Shannon, M. A.; Bohn, P. W.; Elimelech, M.; Georgiadis, J. G.; Mariñas, B. J.; Mayes, A. M. Science and technology for water purification in the coming decades. Nature 2008, 452 (7185), 301-310. (2) Anderson, M. A.; Cudero, A. L.; Palma, J. Capacitive deionization as an electrochemical means of saving energy and delivering clean water. Comparison to present desalination practices: Will it compete? Electrochim. Acta 2010, 55 (12), 3845-3856. (3) Kim, S. J.; Ko, S. H.; Kang, K. H.; Han, J. Direct seawater desalination by ion concentration polarization. Nat. Nanotechnol. 2010, 5 (4), 297-301. (4) Elimelech, M.; Phillip, W. A. The future of seawater desalination: energy, technology, and the environment. Science 2011, 333 (6043), 712-717. (5) Kim, S.; Kim, C.; Lee, J.; Kim, S.; Lee, J.; Kim, J.; Yoon, J. Hybrid Electrochemical Desalination System Combined with an Oxidation Process. ACS Sustainable Chem. Eng. 2018, 6 (2), 1620-1626. (6) 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 Environ. Sci. 2015, 8 (8), 2296-2319.

14


Page 14 of 25

Page 15 of 25 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

312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357


(7) Seo, S.-J.; Jeon, H.; Lee, J. K.; Kim, G.-Y.; Park, D.; Nojima, H.; Lee, J.; Moon, S.-H. Investigation on removal of hardness ions by capacitive deionization (CDI) for water softening applications. Water Res. 2010, 44 (7), 2267-2275. (8) Suss, M. E.; Baumann, T. F.; Bourcier, W. L.; Spadaccini, C. M.; Rose, K. A.; Santiago, J. G.; Stadermann, M. Capacitive desalination with flow-through electrodes. Energy Environ. Sci. 2012, 5 (11), 9511-9519. (9) Zhao, R.; Biesheuvel, P.; Van der Wal, A., Energy consumption and constant current operation in membrane capacitive deionization. Energy Environ. Sci. 2012, 5 (11), 9520-9527. (10) Farmer, J. C.; Fix, D. V.; Mack, G. V.; Pekala, R. W.; Poco, J. F. Capacitive deionization of NaCl and NaNO3 solutions with carbon aerogel electrodes. J. Electrochem. Soc. 1996, 143 (1), 159-169. (11) Kim, C.; Lee, J.; Kim, S.; Yoon, J. TiO2 sol–gel spray method for carbon electrode fabrication to enhance desalination efficiency of capacitive deionization. Desalination 2014, 342, 70-74. (12) Yeh, C.-L.; Hsi, H.-C.; Li, K.-C.; Hou, C.-H. Improved performance in capacitive deionization of activated carbon electrodes with a tunable mesopore and micropore ratio. Desalination 2015, 367, 60-68. (13) Fan, C.-S.; Tseng, S.-C.; Li, K.-C.; Hou, C.-H. Electro-removal of arsenic (III) and arsenic (V) from aqueous solutions by capacitive deionization. J. Hazard. Mater. 2016, 312, 208-215. (14) Zhang, C.; He, D.; Ma, J.; Tang, W.; Waite, T. D. Faradaic reactions in capacitive deionization (CDI)-problems and possibilities: A review. Water Res. 2018, 128, 314-330. (15) 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 Environ. Sci. 2013, 6 (12), 3700-3712. (16) Porada, S.; Zhao, R.; Van Der Wal, A.; Presser, V.; Biesheuvel, P. Review on the science and technology of water desalination by capacitive deionization. Prog. Mater. Sci. 2013, 58 (8), 1388-1442. (17) Kim, T.; Yoon, J. Relationship between capacitance of activated carbon composite electrodes measured at a low electrolyte concentration and their desalination performance in capacitive deionization. J. Electroanal. Chem. 2013, 704, 169-174. (18) Gao, X.; Omosebi, A.; Landon, J.; Liu, K. Surface charge enhanced carbon electrodes for stable and efficient capacitive deionization using inverted adsorption– desorption behavior. Energy Environ. Sci. 2015, 8 (3), 897-909. (19) Porada, S.; Sales, B.; Hamelers, H.; Biesheuvel, P. Water desalination with wires. The J. Phys. Chem. Lett. 2012, 3 (12), 1613-1618. (20) Jeon, S.-I.; Park, H.-R.; Yeo, J.-G.; Yang, S.; Cho, C. H.; Han, M. H.; Kim, D. K. Desalination via a new membrane capacitive deionization process utilizing flow-electrodes. Energy Environ. Sci. 2013, 6 (5), 1471-1475. (21) Cho, Y.; Lee, K. S.; Yang, S.; Choi, J.; Park, H.-R.; Kim, D. K. A novel threedimensional desalination system utilizing honeycomb-shaped lattice structures for flowelectrode capacitive deionization. Energy Environ. Sci. 2017, 10 (8), 1746-1750. (22) Kim, C.; Lee, J.; Srimuk, P.; Aslan, M.; Presser, V. Concentration- gradient multichannel flow stream membrane capacitive deionization cell for ultra- high desalination capacity of carbon electrodes. ChemSusChem 2017, 10, 4914-4920. 15



358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387

(23) Kim, C.; Srimuk, P.; Lee, J.; Aslan, M.; Presser, V. Semi-continuous capacitive deionization using multi-channel flow stream and ion exchange membranes. Desalination 2018, 425, 104-110. (24) Lee, J.; Kim, S.; Yoon, J. Rocking chair desalination battery based on Prussian Blue electrodes. ACS Omega 2017, 2 (4), 1653-1659. (25) Kim, T.; Gorski, C. A.; Logan, B. E. Low energy desalination using battery electrode deionization. Environ. Sci. Technol. Lett. 2017, 4 (10), 444-449. (26) Smith, K. C.; Dmello, R. Na-Ion Desalination (NID) Enabled by Na-Blocking Membranes and Symmetric Na-Intercalation: Porous-Electrode Modeling. J. Electrochem. Soc. 2016, 163 (3), A530-A539. (27) Porada, S.; Shrivastava, A.; Bukowska, P.; Biesheuvel, P.; Smith, K. C. Nickel hexacyanoferrate electrodes for continuous cation intercalation desalination of brackish water. Electrochim. Acta 2017, 255, 369-378. (28) Smith, K. C. Theoretical evaluation of electrochemical cell architectures using cation intercalation electrodes for desalination. Electrochim. Acta 2017, 230, 333-341. (29) Vermass, D. A.; Bajracharya, S.; Sales, B. B.; Saakes, M., Hamelers, B.; Nijmeijer, K. Clean energy generation using capacitive electrodes in reverse electrodialysis, Energy Environ. Sci. 2013, 6, 643-651. (30) Kim, Y.-J.; Choi, J.-H. Improvement of desalination efficiency in capacitive deionization using a carbon electrode coated with an in-exchange polymer, Water Res. 2010, 44, 990-996. (31) Kim, S.; Lee, J.; Kim, C.; Yoon, J. Na2FeP2O7 as a novel material for hybrid capacitive deionization. Electrochim. Acta 2016, 203, 265-271. (32) Kim, T.; Yoon, J. CDI ragone plot as a functional tool to evaluate desalination performance in capacitive deionization. RSC Adv. 2015, 5 (2), 1456-1461. (33) Dykstra, J.; Zhao, R.; Biesheuvel, P.; Van der Wal, A. Resistance identification and rational process design in Capacitive Deionization. Water Res. 2016, 88, 358-370. (34) Zhao, R.; Satpradit, O.; Rijnaarts, H.; Biesheuvel, P.; Van der Wal, A. Optimization of salt adsorption rate in membrane capacitive deionization. Water Res. 2013, 47 (5), 19411952.

388

16


Page 16 of 25

Page 17 of 25 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

389


Associated content

390

Supporting information

391

Cyclic voltammetry of the electrodes and additional salt adsorption capacity data

392

393

17



Figure 1. Schematic diagram of the rocking chair capacitive deionization (RCDI). The RCDI system consists of a pre-treated Nafion coated activated carbon electrode in channel A, a Nafion coated activated carbon electrode in channel B, and anion exchange membrane. During the constant current operation in the RCDI, the positive compartment solution is concentrated by the released cations from the carbon electrode in channel A and by the anions from the channel B solution driven by diffusion, whereas the channel B solution is diluted. The channel A solution is diluted by the reverse movement of cations and anions during the reverse current operation. 101x57mm (300 x 300 DPI)


Page 18 of 25

Page 19 of 25 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


Figure 2. (a) Illustration of the RCDI module for the desalination tests and (b) the RCDI cell. 114x50mm (300 x 300 DPI)



Figure 3. Schematic of the cell geometry for the pre-treatment electrode (Na ion adsorbed electrode). 76x48mm (300 x 300 DPI)


Page 20 of 25

Page 21 of 25 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


Figure 4. The scanning electron microscopy (SEM) images of the pristine activated carbon ((a) & (b)) and Nafion coated activated carbon electrodes ((c) ~ (e)). 63x101mm (300 x 300 DPI)



Figure 5. The effluent conductivity changes of channel A (black solid line) and channel B (blue dash line), and a curve of the voltage & current vs. time during the constant current desalination tests (i = ±12.5 A m2) in a voltage range of -1.2 to 1.2 V ((a) & (b)) and -1.0 to 1.0 V ((c) & (d)). The initial concentration of the NaCl solution was 10 mM. 83x62mm (300 x 300 DPI)


Page 22 of 25

Page 23 of 25 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


Figure 6. (a) The conductivity profiles at different current densities (solid line: channel A; dash line: channel B). (b) CDI Ragone plot of the RCDI system with respect to the source water concentration (10, 20, and 50 mM NaCl) under constant current adsorption/desorption operations with a cell voltage range of -1.2 to 1.2 V. The CDI Ragone plot is representative of the salt adsorption capacity (SAC) and average salt adsorption capacity (ASAR). The MCDI data at 10 and 50 mM were constructed from Ref. [32]. 45x78mm (300 x 300 DPI)



Figure 7. Representative stability performance of the RCDI system. The test was conducted for 35 cycles under constant current adsorption/desorption operations in 10 mM NaCl solution (current: ±12.5 A m-2, voltage range:-1.2 to 1.2 V). (a) The changes in the salt adsorption capacity and charge efficiency during the cycling process. (b) Cell voltage & current vs. time plot. (c) The conductivity changes of the effluent from channel A and channel B. 50x101mm (300 x 300 DPI)


Page 24 of 25

Page 25 of 25 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


TOC only synopsis The RCDI is a new strategy for a sustainable desalination technology with a continuous and energy efficient brackish water deionization process. 84x47mm (300 x 300 DPI)


Rocking-Chair Capacitive Deionization for Continuous Brackish Water

Recommend Documents