A binder free hierarchical mixed capacitive deionization electrode based on a polyoxometalate and polypyrrole for brackish water desalination.

Brackish water desalination using reverse osmosis and capacitive deionization at the water-energy nexus

Both brackish water desalination and seawater desalination processes are well established and in common use around the globe to create new water supply sources. The farther the location of the source water from the ocean or seashore, the lower the salinity (TDS) of the water and the lower the osmotic pressure that needs to be overcome when desalinated water is produced. This is one of the major reasons that brackish desalination is often considered less costly than seawater desalination. A number of project considerations, however, indicate that seawater desalination can be beneficial and more cost-effective than brackish water desalination. To make a fair comparison, we need to properly compare all major aspects of both types of projects to define the best and most appropriate desalination technology. While brackish water has less feed water TDS, it is more challenging to dispose of the produced concentrate. Also, although brackish water desalination needs less energy to overcome osmotic pressure, it usually requires more energy to draw the water from the well than it takes to pump seawater from the open ocean intake. Another factor is that the temperature of the brackish well water may be lower than the temperature of ocean water, giving seawater desalination an advantage in energy demand. In comparing brackish to seawater desalination, these major aspects should be evaluated: (1) Locations of seawater and brackish water plants, relative to the major consumers of the desalinated water, (2) Transportation (pumping and disposal) costs of the feed water and produced water, (3) Potential colocation of a seawater plant with a large industrial user (e.g., power plant) of the seawater for cooling or other purposes, (4) Produced quality of brackish water and seawater desalination in terms of major minerals and emerging contaminants, (5) Sustainability of the water source: capacity and depth of the brackish water wells, as well as the type of soil. (6) Technical and economic aspects of produced concentrate disposal, (7) Permitting process costs for brackish and seawater desalination, and (8) The economics of both brackish and seawater desalination treatment processes: capital costs, operational and maintenance (O&M) costs, lifetime water cost, and total water cost (TWC). This paper discusses the major evaluation criteria and considerations involved in properly comparing the economic and technical aspects of brackish and seawater desalination to determine the more favorable desalination technology for a given desalination project.

Cobalt oxide, nickel oxide and cobalt/nickel binary oxides were synthesised by electrodeposition. To fine tune composition of CoNi alloys, growth parameters including voltage, electrolyte pH/concentration and deposition time were varied. These produced nanomaterials were used as binder free electrodes in supercapacitor cells and tested using three electrode setup in 2 MKOH aqueous electrolyte. Cyclic voltammetry and galvanostatic charge/discharge were used at different scan rates (5–100 mV/s) and current densities (1–10 A/g) respectively to investigate the capacitive behaviour and measure the capacitance of active material. Electrochemical impedance spectroscopy was used to analyse the resistive/conductive behaviours of these electrodes in frequency range of 100 kHz to 0.01 Hz at applied voltage of 10 mV. Binary oxide electrode displayed superior electrochemical performance with the specific capacitance of 176 F/g at current density of 1 A/g. This hybrid electrode also displayed capacitance retention of over 83% after 5000 charge/discharge cycles. Cell displayed low solution resistance of 0.35 Ω along with good conductivity. The proposed facile approach to synthesise binder free blended metal electrodes can result in enhanced redox activity of pseudocapacitive materials. Consequently, fine tuning of these materials by controlling the cobalt and nickel contents can assist in broadening their applications in electrochemical energy storage in general and in supercapacitors in particular.

Desalination and disinfection of inland brackish ground water in a capacitive deionization cell using nanoporous activated carbon cloth electrodes

Capacitive deionization is a promising technique in sea water desalination. Compared with common electrodes, mixed capacitive-deionization electrodes exhibit better performance in sea water desalination because they integrate pseudocapacitance and electric double-layer capacitance in one system. Herein, a 3D binder-free mixed capacitive-deionization electrode was fabricated by direct electrodeposition of SiW12 O40 4- and polyaniline on a 3D exfoliated graphite carrier. In this electrode, SiW12 O40 4- /polyaniline composite particles with a size of about 100-120 nm are dispersed homogenously on the 3D exfoliated graphite carrier. Its specific capacitance reaches 352 F g-1 at 1 A g-1 . With increasing current from 1 to 20 A g-1 , the specific capacitance only decays by 32 %. When employed in sea water desalination, the performance of this mixed capacitive-deionization electrode is also excellent. At 1.2 V, the salt adsorption capacity of this mixed electrode reaches 23.1 mg g-1 with a salt adsorption rate of 1.38 mg g-1 min-1 in 500 mg L-1 NaCl. The performance of this electrode is well retained after 30 cycles. The excellent sea water desalination performance originates from the synergistic effect between SiW12 O40 4- and polyaniline. This work has developed polyoxometalate as a new material for capacitive-deionization electrodes.

Reverse osmosis pilot plants performance in brackish water desalination

Desalination of high salinity brackish water by an NF-RO hybrid system

Universal self-assembly of graphene-based composites as free-standing hierarchical electrodes for high-performance aqueous hybrid capacitors

Developing cost-effective brackish water and seawater desalination technology is crucial. Capacitive deionization (CDI) and inverted capacitive deionization (i-CDI) have been recognized as a promising desalination technology with low energy consumption for brackish water.Both systems use an electric field between two porous electrodes to remove and release ions in water reversibly.Recently, CDI has started using pseudocapacitive or battery electrode materials to enhance the desalination performance.Different from the desalination principle of electric double layers, the energy storage mechanisms of pseudocapacitive and battery materials generally involve ion intercalation/adsorption or compound formation for charge balance, leading to the faradaic desalination.Low cost and high theoretical capacity make PBAs and conducting polymers be the potential materials for the faradaic desalination application.In our previous studies, two dissimilar pseudocapacitive materials show a memory effect during brackish water desalination. This allows them to retain ion capturing or releasing states without an electric field, aiding water purification and resource recovery.Based on above viewpoints, two materials with fundamentally different electrochemical properties are demonstrated to construct a high-capacity, hybrid, faradaic deionization system with CuHCF (battery type) as the positive electrode and PPy (pseudocapacitive type) as the negative electrode.The deionization performance of this CuHCF//PPy cell can be improved by reversing the appropriate cell voltage during the discharge process.The plot of specific SRC against time for the above CuHCF//PPy cell with variations in the charging cell voltage but a fixed discharging cell voltage of 0 V. In addition, Fig. 1(b) shows the plot of specific SRC against time for the same cell with variations in the discharging cell voltage but a fixed charging cell voltage of 1.2 V. From Fig. 1(a), at all charging voltages, the SRC generally decreases with the charging time, indicating the ion repelling process. The order of charging cell voltage with respect to increasing the SRC value is: 0.6 V < 0.8 V < 1.0 V < 1.2 V, revealing the impact of the charging cell voltage. From Fig. 1(b), the SRC obviously increase with prolonging the discharging time, suggesting the ion capturing process. However, the order of discharging cell voltage with respect to increasing the SRC value is: -0.4 V < 0 V < −0.1 V< −0.2 V < −0.3 V. Note that a little inverted cell voltage leads to a higher salt-removing capacity and rate in comparison with a discharge cell voltage of 0 V. However, when the inverted voltage is set at −0.4 V, the SRC profile exhibits the unstable performance, probably due to the presence of certain irreversible reactions at this cell voltage.In the stability test, Fig 2 shows the CuHCF//PPy cell still maintained more than 90% of its original SRC after 50 cycles of testing.The mean SRC values of this CuHCF//PPy system obtained from the 8, 15, and 30 mM solutions reached 35.536, 58.824, and 101.84 mg g−1, respectively.This positive correlation between SRC and solution concentration reveals the higher utilization of the electroactive materials in more concentrated solutions and the very high SRC of the hybrid faradaic CuHCF//PPy system.From Fig 3 shows the SRC values of a CuHCF//PPy cell with the charging/discharging times of 30/30 min at the charging/discharging cell voltages of 1.2/−0.2 V in the 8, 15, and 30 mM NaCl solutions.The memory effect of electrochemically active materials can further extend the application of this system to concentrating valuable ions while purifying water, showing another advantage.The results of ion-removing and salt-concentrating experiment with the discharge/charge times = 10 min/10 min for 10 cycles. In this 10-cycle test, the total amount of salts transferred is up to 152.9 mg g−1, revealing the dual function of purifying water and concentrating salts through this hybrid battery//pseudo-capacitive system.This hybrid cell showed high salt removal capacities in the media containing various monovalent and divalent cations. In this work, the suitable working potential windows of both CuHCF and PPy were systematically evaluated by CV and GCD methods with the charge balance application. Moreover, this cell provides the ability in capturing other cations such as Mg2+ and Ca2+, further broadening its future potential applications. This methodology is a promising strategy for constructing a high-performance desalination cells consisting of various active materials. Figure 1

Facile preparation of binder–free electrode for electrochemical capacitors based on reduced graphene oxide composite film

Predicting the salt adsorption capacity of different capacitive deionization electrodes using random forest

The desalination of brackish ground water using cascade Rankine cycle is proposed. A pair of a Rankine cycle like steam Rankine cycle (SRC) and organic Rankine cycle (ORC) as a waste heat recovery. The single stage steam turbine for the SRC unit while the scroll expander for ORC unit is selected. Simulation of cascade RO system performance is considered using R245fa as a working fluid for ORC unit. The saturated steam from solar Scheffler disc will expand into steam turbine, where the reject heat from steam turbine will utilize for evaporation of ORC working fluid. The high-pressure RO pumps integrated with SRC and ORC turbines to provide net driving pressure to the RO module. This type of system is well suitable for desalination of brackish water due to moderate working temperature & pressure. Result shows that the pair of Rankine cycle will increase the overall (cascade) efficiency of the system. The basic input parameters are optimised with Taguchi approach. The performance of the system shows a good agreement with variation of mass flow rate of the steam in which the permeate flow rate from RO will increase along with the cycle efficiencies.

Comprehensive Summary Access to safe and clean water is fundamental to human health and economic development. While the practical impact of emerging technologies depends on their successful demonstration at large scales, capacitive deionization (CDI) has garnered significant attention as a promising approach for efficient desalination of seawater and brackish water. Among the various 2D materials explored for CDI (e.g., graphene, MXenes, covalent organic frameworks), their derived 2D/2D heterostructures, with unique lamellar morphology and interfacial engineering, offer an ideal platform for effectively modulating charge transfer behavior and ion diffusion. Despite a variety of 2D/2D heterostructures with diverse construction modes have been developed as CDI electrodes in recent years, a dedicated review focusing on the design strategies, synergistic effects, water desalination performance, and prevailing challenges remains lacking. In this review, we highlight the cutting‐edge research progress of 2D/2D heterostructures for CDI applications. After an overview of 2D materials and synthetic strategies of 2D/2D heterostructures, the relationships between the morphology/structure/composition and the water desalination performance are discussed in detail. Thereafter, we discuss current limitations and propose future directions for the rational design of 2D/2D heterostructures. This review will promote exploitation of 2D/2D heterostructures with an ideal performance of CDI towards water remediation. Key Scientists Significant progress has been made in the development of 2D/2D heterostructures for capacitive deionization (CDI) applications towards versatile ion capture. This collection of pioneering work underscores a clear trajectory in the field: the strategic construction of 2D/2D heterostructures is a powerful and versatile paradigm for advancing CDI. By intelligently combining different 2D materials, researchers have successfully engineered heterointerfaces with enhanced ion adsorption capacity, superior selectivity, and improved stability, paving the way for next‐generation, high‐performance desalination and water remediation technologies.

A methodology to investigate brackish groundwater desalination coupled with aquifer recharge by treated wastewater as an alternative strategy for water supply in Mediterranean areas

Inflating energy consumption of modern society demands sustainable energy storage device. Optimization of energy along with power density is the major concern for a sustainable energy storage device. Different types of materials are used for both supercapacitors and batteries. Usually carbon based materials are used as electric double layer capacitor (EDLC) and transition metal oxide and conducting polymers are used as pseudocapacitive type materials[1]. Transition metal oxides like Co3O4 [2] , NiCo2O4 [3]and Bi2O3[4] etc. are used as battery type materials. Hybridization of both battery and supercapacitor type materials can give high specific capacitance as well as high specific surface area and conductivity thus maximizing both energy density and power density of the electrode material. Metal organic frameworks (MOFs) are consisting of covalent bonds between transition metal ions and organic linkers containing carboxylic groups or imidazole groups[5]. These novel materials can provide very high specific surface area, good tailorability, and appreciable aspect ratio etc. A number of literature on MOF based energy storage device material are fabricated by binder method [6]. Use of binder lessens the conductivity and the active surface area of the electrode material. If a transition metal oxide is formed directly on a conducting substrate and over that, a MOF is formed then the morphology of the entire electrode will not only provide three-dimensional nanostructure but also high surface area, porosity and appreciable aspect ratio. Therefore, this approach can be proved as a highly fruitful for the synthesis of an excellent supercapattery device.In this work, an approach to synthesize a three-dimensional binder-free electrode material based on cobalt-metal organic frameworks (Co-MOF) grown over cobalt oxide is adopted. Cobalt oxide is grown over nickel sheet (Co3O4/Ni) via hydrothermal process followed by solvothermal process for the formation of Co-MOF@Co3O4/Ni using trimesic acid as organic linker. The structural, morphological and compositional confirmation was accomplished through X-ray diffraction (XRD) analysis, Field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS) analysis, respectively. The image delivers a three-dimensional micro-flower structure embedded with multidimensional polygons with good porosity and high specific surface area (Fig. 1). Herein the cobalt oxide forms a three-dimensional micro flower structure and the growth of MOF over that adds extra porosity, surface area and stability. The electrochemical characterization was accomplished through cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and electrochemical impedance spectroscopy (EIS) analysis using a three electrode system in 1M KOH solution. The Co-MOF@Co3O4/Ni binder-free electrode showed a battery type behavior i.e. redox peaks in both CV and GCD curve. The specific capacity obtained from cyclic voltammetry analysis was 539 mC/cm2 at scan rate of 5mV/s. This binder free and three-dimensional porous architecture electrode avoids the use of extra additive and provide large specific surface area and porosity for the easy access of electrolyte ions and charge storage and better electrical conductivity for the fast electron transportations. Hence, this novel three-dimensional binder-free Co-MOF@Co3O4/Ni electrode can be proved as an excellent candidate for supercapattery device.The detailed experimental results and discussion will be presented in the meeting. Acknowledgements: This research work is financially assisted by the Department of Science and Technology-Inspire (DST-Inspire) Fellowship (IF170869), by Govt. of India.