Investigating the influence of catholyte salinity on seawater battery desalination
Introduction
The increasing demand for potable water has remained a major global issue for decades [1]. Many countries in the Middle East, North Africa, East Asia, North America, and Australia have built seawater desalination plants due to the lack of freshwater resources such as river water, rainwater, and groundwater [2]. Since the early 2000s, RO has been widely adopted to produce clean water owing to its high energy efficiency and productivity compared to previous thermal desalination technologies [3,4]. However, membrane-based desalination technologies are still energy-intensive and environmentally detrimental [[5], [6], [7]]. For instance, the development of RO has gradually reduced the energy consumption from ~10 to 3 kWh/m3; however, this is still higher than the theoretical minimum energy consumption of ~0.8 kWh/m3 [[8], [9], [10], [11], [12], [13]]. Additionally, a high concentration of RO brine, together with toxic chemicals, is inevitably discharged into the sea, which could adversely impact the environment [7]. Hence, there is great interest in the development of more energy-efficient and cleaner desalination technologies [[14], [15], [16]].
Alternative desalination technologies based on electrochemistry, such as capacitive deionization (CDI), membrane capacitive deionization (MCDI), electro-deionization (EDI), and electrode forward osmosis, have been actively investigated [[17], [18], [19]]. In the early stages of development, these electrochemical desalination technologies seemed to have relatively low energy consumption compared to RO under brackish water conditions (<30 mM NaCl) [20]. However, a recent modeling study has reported that RO could outperform CDI even in brackish water desalination [21], while other studies reported remarkably low or competitive energy demands of electrochemical processes [22,23]. Further, one of the drawbacks of CDI is its low salt adsorption capacity (~30 mg/g for brackish water desalination), as it adsorbs dissolved ions through a non-Faradaic reaction with a low charge capacity [24]; thus, it is unlikely feasible for seawater desalination, which requires a significantly large salt adsorption capacity [25].
The recently proposed seawater battery (SWB) system utilizes the sodium ions present in seawater [[26], [27], [28]]. The SWB extracts sodium ions from seawater during the charging of the battery by storing electrical energy in the anode (i.e., sodium metal); therefore, it has a higher theoretical salt adsorption capacity (~2520 mg/g) than that of CDI [29]. During charging, the counter ions (mostly chlorine ions) are extracted from the cathode compartment by chlorine gas evolution [30]. Thus, the SWB could extract over 70% of the dissolved ions from seawater due to the large quantity of sodium (~30%) and chlorine ions (~55%) present in seawater [31]. Additionally, the SWB is rechargeable as only the sodium ions can enter or leave the SWB anode [18,20]. Thus, the desalination aspect of the SWB has received interest from environmental engineers engaged in water desalination [32,33]. However, only a few studies using a single desalination compartment of catholyte have been conducted [33,34].
A novel SWB-D system consisting of the SWB, desalination compartment, and catholyte compartment was introduced by combining the SWB with additional membrane filtration systems, such as nanofiltration (NF) and RO, to remove residual ions [35]. According to a study [35], the SWB-D system successfully reduced the total energy consumption for desalination from 2.83 (using only RO) to 1.35 kWh/m3 (RO combined with SWB-D). However, several aspects remain unexplored regarding the practical application of the SWB-D system for water desalination. Most studies primarily focused on material development, such as electrolyte synthesis or electrode replacement [29,36,37]. Additionally, only a fixed catholyte of a synthetic electrolyte [32] or seawater [35] has been used to evaluate the salt removal and electrochemical profiles. Hence, the SWB-D system still requires further investigation through comprehensive research using various catholytes.
In this regard, we investigated the influence of cathode compartments on the performance of the SWB-D system and discussed its implications and practical applications for water desalination based on the following objectives: 1) evaluating the effect of different catholytes—three natural water resources with different salinities (RO retentate, brackish water, or river water) on the charging/discharging and desalination efficiencies of the SWB-D system; 2) evaluating the quality and quantity of the desalinated/catholyte solution under different catholyte conditions; and 3) providing a guideline for the catholyte selection for the SWB-D system.
Section snippets
Seawater battery coin cell assembly
SWB (SWB2465, 4TOONE, Republic of Korea) was assembled using a previously described procedure [35]. The coin cell compartments consisted of seven components in the following order: 1) the coin bottom equipped with a NASICON (Na3Zr2Si2PO12; CE&Chem Co. Ltd., Republic of Korea) membrane with a diameter of 16 mm and a thickness of 1 mm [38], 2) polyethylene (PE; Celgard, Republic of Korea) separator with a 19 mm diameter, 3) 200 μL of a mixed organic electrolyte (1 M NaCF3SO3) dissolved in
Feed water characteristics
The salinity of C1 was expected to be the most influential factor in water desalination using the SWB-D system as it determines the solution resistance of C1 and ion migration rate from C2 to C1. The ionic conductivity of the three catholytes was in the range of 0.28 ± 0.08–90.55 ± 0.04 mS/cm, which was selected based on that of the C2 solution (22.20 ± 0.52 mS/cm) (Table 1). A fixed feed water of NF permeate was used in C2 as a previous study has shown that an ion conductivity of >48.7 mS/cm
Conclusion
Here, we explored the influence of the feed water of the cathode compartment on the performance of the SWB-D system. Each type of feed water yielded different charging and discharging performances based on the resistivity and salinity of the feed water. This study proposes the necessary consideration for the catholyte solution to improve the desalination efficiency of SWB. The major findings are summarized as follows:
- •
High-saline feed water maintained the high step-currents during charging
CRediT authorship contribution statement
Sanghun Park: Writing - Original draft preparation, Methodology, Visualization
Mayzonee Ligaray: Methodology, Conceptualization
Youngsik Kim: Investigation, Validation
Kangmin Chon: Investigation, Validation
Moon Son: Supervision, Writing - Reviewing and editing
Kyung Hwa Cho: Supervision, Conceptualization.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Funding
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) [grant number 2020R1A4A1019568].
References (54)
- et al.
Desalination by using alternative energy: review and state-of-the-art
Desalination
(2007) - et al.
State-of-the-art of reverse osmosis desalination
Desalination
(2007) - et al.
Optimal design and operation of reverse osmosis desalination process with membrane fouling
Chem. Eng. J.
(2011) - et al.
Exploring the environmental impact assessment commissioners' perspectives on the development of the seawater desalination project
Desalination
(2018) - et al.
Environmental impact of desalination technologies: a review
Sci. Total Environ.
(2020) Reverse osmosis applications: prospect and challenges
Desalination
(2016)- et al.
A review on RO membrane technology: developments and challenges
Desalination
(2015) - et al.
A comprehensive review of energy consumption of seawater reverse osmosis desalination plants
ApEn
(2019) Energy use for membrane seawater desalination - current status and trends
Desalination
(2018)- et al.
Energy consumption and membrane replacement cost for seawater RO desalination plants
Desalination
(2003)
Renewable energy-driven innovative energy-efficient desalination technologies
ApEn
Emerging desalination technologies for water treatment: a critical review
Water Res.
Renewable energy-driven desalination technologies: a comprehensive review on challenges and potential applications of integrated systems
Desalination
Seawater desalination by over-potential membrane capacitive deionization: opportunities and hurdles
Chem. Eng. J.
In-sight studies on concentration polarization and water splitting during electro-deionization for rapid production of ultrapure water (@ 18.2 MΩ cm) with improved efficiency
J. Membr. Sci.
Comparison of energy consumption in desalination by capacitive deionization and reverse osmosis
Desalination
Review on the science and technology of water desalination by capacitive deionization, Prog
Mater. Sci.
Hybrid seawater desalination-carbon capture using modified seawater battery system
J. Power Sources
Development of coin-type cell and engineering of its compartments for rechargeable seawater batteries
J. Power Sources
A modified method for the determination of chemical oxygen demand (COD) for samples with high salinity and low organics
Bioresour. Technol.
Evaluating membrane fouling potentials of dissolved organic matter in brackish water
Water Res.
Influence of cations on the proton leakage through anion-exchange membranes
J. Membr. Sci.
Water permeation through anion exchange membranes
J. Power Sources
Understanding chemical reactions between carbons and NaOH and KOH: an insight into the chemical activation mechanism
Carbon
Large-scale stationary energy storage: seawater batteries with high rate and reversible performance
Energy Storage Mater.
Na ion-conducting ceramic as solid electrolyte for rechargeable seawater batteries
Electrochim. Acta
Optimization of a nanofiltration and membrane capacitive deionization (NF-MCDI) hybrid system: experimental and modeling studies
Desalination
Cited by (13)
Research and applications of rechargeable seawater battery
2024, Journal of Energy StorageContinuous desalination and high-density energy storage: Na metal hybrid redox flow desalination battery
2024, Chemical Engineering JournalInsights into desalination battery concepts: current challenges and future perspectives
2023, Chemical CommunicationsDistillation performance in a novel minichannel membrane distillation device
2023, Chemical Engineering JournalSeawater battery desalination with sodium-intercalation cathode for hypersaline water treatment
2022, DesalinationCitation Excerpt :The SWB-D system has several unique properties compared to other electrochemical desalination approaches, such as CDI [33,34], battery deionization (BDI; also known as cation intercalation desalination) [16,18–23,35], flow-electrode desalination [36–39], electrodialysis [40–43], and desalination battery (DB) [44–47]. First, SWB-D can directly desalinate water having salinity higher than that of the seawater (>0.6 M NaCl) [3,10], while the applications of CDI and BDI are often limited to brackish water desalination (<0.05 mM NaCl) [20,22]. Second, the SWB-D system can store energy during the full cycle of desalination [5], whereas energy is only consumed for other processes, except DB.
Seawater battery desalination with a reverse osmosis membrane for simultaneous brine treatment and energy storage
2022, Journal of Cleaner ProductionCitation Excerpt :The SWB coin cell was installed in the anode compartment with the sodium superconducting solid electrolyte (NASICON) membrane facing the desalination compartment, where saline water was treated. Thus, the NASICON membrane transferred only sodium ions during charging by completely blocking the inflow of water and other ions into the SWB coin cell, where sodium metals were stored (Park et al., 2021). The AEM or RO membrane physically separated the desalination compartment from the cathode compartment.