Electrochemical ion pumping devices and methods of use thereof

Abstract

Disclosed herein are electrochemical ion pumping devices and methods of use thereof. Also disclosed are Ion diffusion across electrode and IBM films. Concentrations of the diluate and brine in experiments with spontaneous ion diffusion across commercial cation exchange membrane (CEM), cation electrode (CE), and conventional electro-sorption electrode without ion exchange polymer filler.

Description

[0001] ELECTROCHEMICAL ION PUMPING DEVICES

[0002] AND METHODS OF USE THEREOF

[0003] CROSS-REFERENCE TO RELATED APPLICATIONS

[0004] This US application claims priority to, and the benefit of, U.S. Provisional Patent Application No. 63 / 582,748, filed September 14, 2023, U.S. Provisional Patent Application No. 63 / 585,016, filed September 25, 2023, and U.S. Provisional Patent Application No. 63 / 664,770, filed June 27, 2024, which is incorporated by reference herein in its entirety.

[0005] STATEMENT OF GOVERNMENT SUPPORT

[0006] This invention was made with government support under grant / contract numbers N00014-23-1-2565 awarded by the Office of Naval Research. The government has certain rights in the invention.

[0007] BACKGROUND

[0008] Improved devices and methods for desalination and selective extraction of minerals and other valuable ions are needed. The devices, systems, and methods disclosed herein address these and other needs.

[0009] SUMMARY

[0010] In accordance with the purposes of the disclosed devices, methods, and systems as embodied and broadly described herein, the disclosed subject matter relates to electrochemical ion pumping devices and methods of use thereof.

[0011] Additional advantages of the disclosed devices, systems, and methods will be set forth in part in the description which follows, and in part will be obvious from the description. The advantages of the disclosed devices, systems, and methods will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosed systems and methods, as claimed.

[0012] The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

[0013] BRIEF DESCRIPTION OF THE FIGURES

[0014] The accompanying figures, which are incorporated in and constitute a part of this specification, illustrate several aspects of the disclosure, and together with the description, serve to explain the principles of the disclosure.

[0015] Figure 1. Description of “rocking chair” electrosorption for desalination with a “batch-mode”: In the first half cycle (upper left), all channels are filled with the feed water. Electrode “b” is the cathode and electrodes “a” and “c” are the anodes. Cations are pulled into electrode “a” from the two channels it contacts, whereas the anions migrate across the anion exchange membrane (AEM) to maintain charge neutrality in these two channels. To maintain the charge neutrality of the channels on the other side of the anion exchange membrane, cations are discharged from electrodes “a” and “c” to neutralize the migrating anions. The overall result is that the two middle channels are desalinated to become the diluate whereas the 1stand 4thchannels become brine. At the end of the first half cycle (upper right), electrode “b” is saturated (either fully or partially) and electrodes “a” and “c” are regenerated (either fully or partially). The diluate and brine will be drained from the system and the channels will then be refilled with the feed solution. Electrode “b” is switched to become the anode and electrodes “a” and “c” are switched to become the cathodes, which marks the beginning of the second half cycle (bottom right). Cations will be released from electrode “b” and enter electrodes “a” and “c”, thereby desalinating the two streams in contact with electrodes “a” and “c” and turning the two middle streams in contact with electrode “b” into brine. At the end of the second half cycle (bottom left), electrode “b” is fully or partially regenerated and electrodes “a” and “c” are fully or partially saturated. The channels with brine and diluate are then drained again, refilled with feed water, and the polarity of the voltages is switched to start the next cycle.

[0016] Figure 2. Description of CEIP for desalination: In the first half cycle (upper left), Electrodes “a” and “b” are the anode and cathode of circuit N, respectively. Whereas electrode “c” is the anode of circuit N+2 (the cathode of circuit N+2 is not shown). In each circuit, cations are discharged from the anode to the brine stream and adsorbed to the cathode from the diluate stream. Anions migrate across the anion exchange membrane from the diluate stream to the brine stream to maintain charge neutrality in both channels. Once the anodes are partially regenerated and the cathodes are partially saturated to the desired level (upper right), the circuits will be switched by an external control system. After the circuit switch (bottom right), electrode “a” switches from the anode of circuit N to the cathode of circuit N-l (anode of circuit N-l is not shown), electrode “b” switches from the cathode of circuit N to the anode of circuit N+l, whereas electrode “c” switches from the anode of circuit N+2 to the cathode of circuit N+l . Cation and anion transport in the second half cycle is similar to that in the first half cycle, except that they occur in a different cell pairs (and circuits).

[0017] Figure 3. Description of CEIP with a multi-cell stack. In the 1sthalf cycle (A), the terminal anode and odd-numbered circuits are active. In the 2ndhalf cycle (B), the terminal cathode and even-numbered circuits are active.

[0018] Figure 4. Description of CEIP with a single-cell stack. In the 1sthalf cycle (A), the terminal anode and circuit 1 are active. In the 2ndhalf cycle (B), the terminal cathode and circuit 2 are active.

[0019] Figure 5. Description of CEIP for Li separation and enrichment: In the first half cycle (upper left), Electrodes “a” and “b” are the anode and cathode of circuit N, respectively. Whereas electrode “c” is the anode of circuit N+2 (the cathode of circuit N+2 is not shown). In each circuit, Li+ions are discharged from the anode to the receiving solution (which becomes the Li-rich solution) and adsorbed to the cathode from the feed solution (which becomes the Li-lean solution. Anions migrate across the anion exchange membrane from the feed solution to the receiving solution to maintain charge neutrality in both channels. Once the anodes are partially regenerated and the cathodes are partially saturated to the desired level (upper right), the circuits will be switched by an external control system. After the circuit switch (bottom right), electrode “a” switches from the anode of circuit N to the cathode of circuit N-l (anode of circuit N-l is not shown), electrode “b” switches from the cathode of circuit N to the anode of circuit N+l, whereas electrode “c” switches from the anode of circuit N+2 to the cathode of circuit N+L Li+ion and anion transport in the second half cycle is similar to that in the first half cycle, except that they occur in a different cell pairs (and circuits). Once the anodes are again partially regenerated, and the cathodes are partially saturated to the desired level (bottom left), the circuit switch is performed again to perform the next cycle of ion pumping. In summary, the active ion pumping occurs in circuits N and N+2 in the first half cycle, and in circuits N-l and N+l in the 2ndhalf cycle.

[0020] Figure 6. Description of CEIP for desalination without ion exchange membranes: In the first half cycle (upper left), Electrodes “a” and “b” are the anode and cathode of circuit N, respectively. Whereas electrode “c” and “d” are the anode and cathode of circuit N+2, respectively. In each circuit, cations adsorb onto the cathode and anions adsorb onto the anode, thereby desalinating the streams between “a” and “b” and between “c” and “d”. When the electrodes are (fully or partially) saturated, which marks the end of the first half-cycle, we perform a circuit switch to enter the second half-cycle (bottom right) where “b” and “c” are now the anode and cathode of circuit N+l, “a” is the cathode of circuit N-l, and “d” is the anode of circuit N+3. In the second half-cycle, ions are discharged into the streams between two connected electrodes in active circuits, generating the brine. When the electrodes are (fully or partially) regenerated, which marks the end of the second half-cycle (bottom left), a circuit switch is performed to enter the first half-cycle of the next cycle.

[0021] Figure 7. Schematic of an electrode to be used in CEIP.

[0022] Figure 8. Schematic illustration of how an electrode can be fabricated.

[0023] Figure 9. Illustration of a full cycle extracting Li+from the feed solution and enriching the ions in the receiving solution.

[0024] Figure 10. Design of a Li-selective electrode comprising four major components: Li- intercalation material, carbon black (for improving conductivity), a conductive mesh current collector, and anion exchange polymer (AEP) filling the pores between the other three components.

[0025] Figure 11. Design of a Li-selective electrode comprising four major components: Li- intercalation material, carbon black (for improving conductivity), a conductive mesh current collector, and anion exchange polymer (AEP) filling the pores between the other three components.

[0026] Figure 12. Illustration of a full cycle for desalination using SCEIP. The cathode in each circuit temporally uptakes cations from the diluate stream and discharges to the adjacent brine stream when it is used as the anode in the next cycle

[0027] Figure 13. Conductivities of the diluate and brine streams over 150 mins of SCEIP operation.

[0028] Figure 14a-Figure 14f. Working principle and proof-of-concept for electrochemical ion pump (EIP). Figure 14a, Working principle of conventional electro- sorption (ES) with solution- switch. Figure 14b, Working principle of EIP with circuit-switch. The statistics of the half-cycle time for conventional electro- sorption are based on literature data as summarized in Table 1. Figure 14c, System design for asymmetric EIP (a-EIP) showing two consecutive circuits. Figure 14d, System design for symmetric EIP (s-EIP) showing two consecutive circuits. Both Figure 14c and Figure 14d show only part of a stack, whereas a full stack should include two terminal electrodes and possibly more circuits. Figure 14e, Photographic image and schematic of a complete s-EIP stack with a single cation electrode. Figure 14f, Performance of an s-EIP operated using a constant current density of 10 A nr2 and a half-cycle time of 2 s. A NaCl solution of 100 mM and a volume of 20 mL was used as the initial feed solution in both the diluate and brine channels. The top graph shows the applied current waveform. The middle graph presents the average voltages and current efficiencies of the charging and discharge half-cycles. The average voltage is calculated based on instant voltage (inset). The bottom graph shows the change in concentration of the diluate and the brine. The diluate concentration steadily decreased as ions were transfer to the brine over the 950 min s-EIP experiment.

[0029] Figure 15a-Figure 15d. Design, fabrication, and properties of cation adsorption electrodes (CE). Figure 15a, Illustration of cation electrode requirements and design. The fundamental requirements include (i) fast ion transport, (ii) high electrical conductivity, and (iii) minimal water permeation. The general design for a cation electrode meeting such requirements is a percolated activated carbon network connected to a current collector and filled with cation exchange polymer. Figure 15b, cation electrode fabrication strategy: the cation electrode was fabricated by preparing a composite film with a current collector embedded in a paste activated carbon particles and cation exchange polymer followed solvent evaporation (60 °C for 12 h) and hot-press (140 °C and 4000 psi) to form a water- impermeable dense film. The cation electrode was encapsulated with a frame of waterproof tape for assembly into an EIP stack. Figure 15c, Figure 15d, Focused-ion beam scanning electron microscopy images with energy dispersive spectroscopy mapping, as well as photographic images of the electrodes (Figure 15c) before and (Figure 15d) after hot-press.

[0030] Figure 16a-Figure 16f Behavior of a single-electrode s-EIP cell. Figure 16a, Ion flux and current efficiency at different current densities (6.25, 12.5, 50, and 125 A nr2). Figure 16b, Average circuit voltage of the s-EIP cell (blue data points) and contribution to the circuit voltage from desalination (red data points) at different current densities, with the later obtained by subtracting the average circuit voltage and the cell voltage of an electrolytic cell. The half-cycle time was 5 s for results shown in both Figure 16a and Figure 16b. Figure 16c, Potential distribution across different components of an active circuit in the charging (left) and discharge (right) half-cycles of an s-EIP process. Figure 16d, Temporal change of diluate and brine concentrations for an s-EIP process (50 A nr2) with a short half-cycle time of 5s (left) and a long half-cycle time of 500s (right). The gray datapoints represent concentrations of the respective solutions when the solutions were not part of an active circuit. Figure 16e, Representative time profiles of circuit voltage for charging and discharge half-cycles in an s- EIP process (50 A nr2) with different half-cycle times (0.5, 5, 50, and 500s). Figure 16f, Representative time profiles of cation electrode potential (vs. Ag / AgCl reference electrode) measured using 50 A nr2with different half-cycle times (0.5, 5, 50, and 500s) (Figure 26).

[0031] Figure 17a-Figure 17k. System design, behavior, and desalination performance of multi-electrode s-EIP stacks. Figure 17a, Photographic images of a 5-electrode s-EIP stack. The effective area for each cation electrode is 8 cm2. Figure 17b, Schematic of active circuit distribution in a full charging / discharge cycle for a 5-electrode s-EIP. Figure 17c, Figure 17d, Time profiles of salt concentration in the diluate and brine for multi-electrode (N=2, 3, 4, 5, 6) s-EIP with (Figure 17c) constant current operation with a current density of 8.1 A nr2, and (Figure 17d) constant voltage operation with a circuit voltage of 1.2V. Figure 17e, Summary of ion fluxes for multi -el ectrode (N=2, 3, 4, 5, 6) s-EIP with constant current (8.1 A nr2) and constant voltage (1.2 V) operations, as evaluated from the data presented in Figure 17c and Figure 17d. Results in this figure were obtained from experiments using a half-cycle time of 5 s, a feed concentration of 100 mM (NaCl) and a solution volume of 20 mL for both diluate and brine. Figure 17f, Distribution of average current densities for s-EIP with constant voltage operation (1.2 V) and different numbers of cation electrodes (N=2, 3, 4, 5, 6). Figure 17g, Illustration of charge transfer mechanisms (electrolysis vs. capacitive ion adsorption / desorption) across an s-EIP stack with constant voltage operation and many cation electrodes. Figure 17h, Distribution of average circuit voltages for s-EIP with constant current operation (8.1 A nr2) and different numbers of cation electrodes (N=2, 3, 4, 5, 6). Figure 17i, Illustration of charge transfer mechanisms across an s-EIP stack with constant current operation and many cation electrodes. Figure 17j , Comparison of performance in terms SECi and ion flux between s-EIP and various film electrode-based capacitive deionization (CDI) processes tested for desalination with a similar feed salinity (details can be found in Figure 30a-Figure 30b, Table 2). Figure 17k, Comparison of performance in terms of SECi and ion flux between s-EIP operated with constant current densities (8.1, 15, and 25 A nr2) and constant circuit voltages (0.4, 0.8, and 1.2 V). In both Figure 17j and Figure 17k, a process with a lower SECi and a high ion flux (i.e., toward the bottom right of the SECi vs. ion flux plot) is superior. Results in this figure were obtained from experiments using a half-cycle time of 5 s, a feed concentration of 100 mM (NaCl) and a solution volume of 20 mL for both diluate and brine.

[0032] Figure 18a-Figure 18b. Solution-switch in conventional electro-sorption. Figure 18a, Schematics of a conventional electro- sorption half-cell, which comprises the flow channel and the carbon electrode with macropores and micropores. The top schematic in Figure 18a splits the electro- sorption half-cell into three visually distinct domains for clearer representation of concentrations, even though the macropores and micropores should co-exist in a macroscopic domain as indicated by the bottom schematic in Figure 18a. Figure 18b, Semi-quantitative profiles of salt / ion concentration for different stages in a full charging / discharge cycle. , Cb, and Cdrepresent the salt concentrations of the feed, brine, and diluate streams, respectively, whereas Cmi toiis the total ion concentration in the micropores. The concentration arrow is only semi-quantitative and not to scale.

[0033] Figure 19. A typical full cycle of conventional electro-sorption (ES). During the charging half-cycles, the feed solution / diluate recirculates between the electro-sorption cell and the diluate tank. At the beginning of charging, no ion is stored in the electrode micropores. The feed solution is continually cycled between the external tank and the electrosorption cell. As charging commenced, ions in the feed solution are gradually adsorbed by the electrodes. By the end of the charging phase, the electrodes reach saturation at a certain applied voltage. To discharge and regenerate the electrodes, the diluate stream within the electro- sorption cell is replaced by the receiving solution (brine) and the direction of the circuit is reversed. Upon complete release of stored ions into the receiving solution, the discharge operation ends. At this stage, the electrode capacity reverts to its initial state, ready for the subsequent adsorption cycles.

[0034] Figure 20a-Figure 20c. Operation and desalination performance of a-EIP. Figure 20a, Working principle of asymmetrical electrochemical ion pump (a-EIP) with a pair of anion electrode (AE) and cation electrode (CE). Figure 20b, Performance of an s-EIP operated using a constant current density of 10 A m'2and a half-cycle time of 2 s. A NaCl solution of 100 mM with a volume of 20 mL was used as the initial feed solution in both the feed (diluate) and brine channels. The top graph shows voltages of different circuits. The middle graph shows the current efficiency of the charging half-cycles. The bottom graph shows the change in concentration of the diluate and the brine in >800 min s-EIP experiment. Figure 20c, Performance of s-EIP with constant current operation.

[0035] Figure 21a-Figure 21f. s-EIP operated with constant voltage operation. Figure 21a, Circuit voltage waveform (2V) over multiple charging / discharge cycles (half-cycle time: 2s). Figure 21b, current density over multiple charging / discharge cycles. Figure 21c, Figure 2 Id, the same data as Figure 21a and Figure 21b but for a much longer operation time. Figure 21e, Changes in the concentrations of the diluate, the brine, and electrolyte. Figure 21f, average current efficiency over long-term operation. Figure 22. Ion diffusion across electrode and IEM films. Concentrations of the diluate and brine in experiments with spontaneous ion diffusion across commercial cation exchange membrane (CEM), cation electrode (CE), and conventional electro-sorption electrode without ion exchange polymer filler. A NaCl solution of 100 mM and a volume of 20 mL was used as the initial feed solution in the brine channels. 20 mL of DI water was used as the feed solution in the diluate channel. The conventional electro- sorption electrode was fabricated using a blend comprising 80 wt% activated carbon (AC) and 20 wt% polyvinylidene fluoride (PVDF) without hot-pressing.

[0036] Figure 23a-Figure 23b. Electrochemical test of cation electrode before and after hot- press. Figure 23a, Cyclic voltammogram results for cation electrodes with and without hot- press. The scan rate was 1 mV s'1. Figure 23b, Nyquist plot for cation electrodes with and without hot-press from electro-impedance spectroscopy (right), highlighting the importance of hot-press to reduce ohmic resistances of the cation electrode.

[0037] Figure 24a-Figure 24b. Energy consumption of s-EIP. Figure 24a, Breakdown of energy consumed in s-EIP: desalination and electrolysis. In charging half-cycle, the oxygen evolution reaction (OER) at the terminal anode, the capacitive adsorption of cations at the cathode electrode, and ion transport through solution and anion exchange membrane (AEM) contribute to the overall circuit voltage. In discharge half-cycle, the hydrogen evolution reaction (HER) at the terminal cathode, capacitive desorption of cations at the anode electrode, and ion transport through solution and anion exchange membrane contribute to the overall circuit voltage. Figure 24b, Electrolytic cell for measuring the contribution from water electrolysis to circuit voltage. Each half-cell comprises one terminal electrode, one solution chamber, and half of an anion exchange membrane.

[0038] Figure 25. Breakdown of voltage drop from electrode to solution. The solid curves represent the overall potential in the bulk solution and the electrode. The external resistance is related to the electron transfer through the wires, carbon matrix, and across the interface between current collector and carbon. (pD+ (psrepresents the potential drop over the electrical double layer (Stern and Donnan). Excess potential is the driving force for the ions to transport across the electrode in a finite rate.

[0039] Figure 26. Schematic of an electrochemical cell for measuring CE potential. Using an electrochemical workstation (with dual -el ectrode operation) as the power source, the two electrical relays control the circuit switching. For charging, the working electrode (WE) serves as the cathode, with the CE on the left monitoring the electrode potential. For discharge, the working electrode functions as the anode, with the reference electrode on the right monitoring the electrode potential. The reference electrodes are Ag / AgCl electrodes.

[0040] Figure 27a-Figure 27c. Charge of solution pH and current efficiency under different current densities. Figure 27a, Figure 27b Solution pH of diluate and brine under (Figure 27a) different current densities (6.25, 12.5, 50, and 125 A nr2) and (Figure 27b) different halfcycle times (0.5, 5, 50, and 500 s). Figure 27c, Impact of half-cycle time on current efficiency.

[0041] Figure 28. Multi-electrode s-EIP with four cation electrodes: One half-cycle has three active circuits (top) while the other half-cycle has two active circuits (bottom). This differs from a multi-electrode s-EIP with odd number of electrodes (e.g., Figure 17b) where both half-cycles have the same number of electrodes.

[0042] Figure 29. pH of diluate and brine streams after 80 min in constant current vs. constant voltage mode. Substantial change of pH was observed in constant voltage mode to electrolysis. Specifically, OH' was generated in the diluate stream (thus pH increase) when the CE acted as a cathode, whereas H+was generated in the brine stream (thus pH decrease) when the CE acted as the anode.

[0043] Figure 30a-Figure 30b. Specific energy consumption of multi-electrode s-EIP. Figure 30a, Energy consumption of s-EIP with different numbers of cation electrodes (N = 0, 1, 2, 3, 4, 5). The system is essentially an electrolysis cell when N=0. Figure 30b, SECi as a function of number of cation electrodes for constant current and constant voltage modes. The red dashed line represents the SECi for desalination in for constant current mode (8.1 A m'2) as obtained by subtracting the contribution from electrolysis at terminal electrodes from the measured overall SECi.

[0044] Figure 31. Performance comparison between s-EIP and conventional electro-sorption. This figure is a replicate of Figure 17k with additional labels for data points from literature. Squares, circles and triangles represent CDI, MCDI and R-CDI, respectively. The important results and parameters for these data points, along with their references, are listed in Table 2.

[0045] Figure 32a-Figure 32c. Components and structures of EIP cells. Figure 32a, The components of an s-EIP cell. Figure 32b, The structure of the simplest s-EIP cell. Figure 32c, The structure of the simplest a-EIP cell. The dimensions of the components are as follows: 1) End plate: PTFE, 100 x 100 mm x 10 mm; 2) Silicon mat: 60 x 60 mm x 2 mm; 3) Terminal electrode: Graphite paper, 60 x 60 mm x 3 mm; 4) Spacer: External dimensions 60 x 60 mm, with a central circular area of 40 mm diameter, thickness 1 mm; 5) Anion exchange membrane: 60 x 60 mm; 6) Working electrode: external dimension 60 x 60 mm, effective electrode area 8 cm2.

[0046] Figure 33. An example terminal electrode-free (e.g., circular) asymmetric electrochemical ion pump (EIP).

[0047] Figure 34. An example terminal electrode-free (e.g., circular) symmetric electrochemical ion pump (EIP).

[0048] DETAILED DESCRIPTION

[0049] The devices, methods, and systems described herein may be understood more readily by reference to the following detailed description of specific aspects of the disclosed subject matter and the Examples included therein.

[0050] Before the present devices, methods, and systems are disclosed and described, it is to be understood that the aspects described below are not limited to specific synthetic methods or specific reagents, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.

[0051] Also, throughout this specification, various publications are referenced. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which the disclosed matter pertains. The references disclosed are also individually and specifically incorporated by reference herein for the material contained in them that is discussed in the sentence in which the reference is relied upon.

[0052] In this specification and in the claims that follow, reference will be made to a number of terms, which shall be defined to have the following meanings.

[0053] Throughout the description and claims of this specification the word “comprise” and other forms of the word, such as “comprising” and “comprises,” means including but not limited to, and is not intended to exclude, for example, other additives, components, integers, or steps.

[0054] As used in the description and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a composition” includes mixtures of two or more such compositions, reference to “an agent” includes mixtures of two or more such agents, reference to “the component” includes mixtures of two or more such components, and the like. “Optional” or “optionally” means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.

[0055] Ranges can be expressed herein as from “about” one particular value, and / or to “about” another particular value. By “about” is meant within 5% of the value, e.g., within 4, 3, 2, or 1% of the value. When such a range is expressed, another aspect includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

[0056] Values can be expressed herein as an “average” value. “Average” generally refers to the statistical mean value.

[0057] By “substantially” is meant within 5%, e.g., within 4%, 3%, 2%, or 1%.

[0058] “Exemplary” means “an example of’ and is not intended to convey an indication of a preferred or ideal embodiment. “Such as” is not used in a restrictive sense, but for explanatory purposes.

[0059] It is understood that throughout this specification the identifiers “first” and “second” are used solely to aid in distinguishing the various components and steps of the disclosed subject matter. The identifiers “first” and “second” are not intended to imply any particular order, amount, preference, or importance to the components or steps modified by these terms.

[0060] References in the specification and concluding claims to parts by weight of a particular element or component in a composition denotes the weight relationship between the element or component and any other elements or components in the composition or article for which a part by weight is expressed. Thus, in a compound containing 2 parts by weight of component X and 5 parts by weight component Y, X and Y are present at a weight ratio of 2:5, and are present in such ratio regardless of whether additional components are contained in the compound.

[0061] A weight percent (wt. %) of a component, unless specifically stated to the contrary, is based on the total weight of the formulation or composition in which the component is included.

[0062] The term “or combinations thereof’ as used herein refers to all permutations and combinations of the listed items preceding the term. For example, “A, B, C, or combinations thereof’ is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AB, BBC, AAABCCCC, CBBAAA, CAB ABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.

[0063] Devices and Methods

[0064] Described herein are devices and methods of use thereof. For example, disclosed herein are electrochemical ion pumping devices and methods of use thereof.

[0065] For example, disclosed herein are devices comprising a plurality of fluidly independent circuits, the plurality of fluidly independent circuits comprising alternating circuits of a charging circuit and a discharging circuit, wherein the total number of circuits in the device is 3 or more. In some examples, each charging circuit comprises an anion electrode, a cation electrode, and a feed solution, the feed solution being sandwiched between and in electrochemical contact with the anion electrode and the cation electrode. In some examples, each discharging circuit comprises a cation electrode, an anion electrode, and a receiving solution, the receiving solution being sandwiched between and in electrochemical contact with the cation electrode and the anion electrode. In some examples, the cation electrode is shared between a charging circuit and the following discharging circuit, and the anion electrode is shared between a discharge circuit and the following charging circuit, such that each pair of charging and discharging circuits includes three total electrodes. In some examples, each pair of charging and discharging circuits further comprises a first electrical relay switch and a second electrical relay switch. Each charging circuit and discharging circuit is fluidly independent. In some examples, each cation electrode is configured to adsorb and / or intercalate a target ion (e.g., a target cation). In some examples, each feed solution can be the same or different. In some examples, each feed solution comprises the target ion at an initial concentration. In some examples, each receiving solution comprises a counterion for the target ion. In some examples, each receiving solution comprises the target ion at a preliminary concentration. In some examples, when the device is operated in a charging mode, then the anion electrode and the cation electrode of each charging circuit are electrically connected to each other and a voltage source via the first and second electrical relay switches, and at least a portion of the target ion concentration is depleted from each of the feed solutions by being adsorbed and / or intercalated into the cation electrodes, such that the concentration of the target ion in the feed solutions decreases relative to the initial concentration. In some examples, when the device is operated in a discharging mode, then the cation electrode and the anion electrode of each discharging circuit are electrically connected to each other and the voltage source via the first and second electrical relay switches, at least a portion of the target ion adsorbed and / or intercalated in the cation electrode is released into the receiving solution, such that the concentration of the target ion in the receiving solution increases relative to the preliminary concentration.

[0066] Also disclosed herein are device comprising a plurality of fluidly independent circuits, wherein the total number of circuits in the device is 2 or more, and wherein each circuit comprises a receiving channel and a feed channel, the receiving channel being fluidly independent from the feed channel. In some examples, the receiving channel is defined by a first cation electrode and an anion exchange membrane, the receiving channel containing a receiving solution, such that the receiving solution is sandwiched between and in electrochemical contact with the first cation electrode and the anion exchange membrane. In some examples, the feed channel is defined by the anion exchange membrane and a second cation electrode, the feed channel containing a feed solution, the feed solution being sandwiched between and in electrochemical contact with the anion exchange membrane and the second cation electrode. In some examples, each pair of circuits further comprises a first electrical relay switch and a second electrical relay switch. In some examples, each cation electrode is shared between two neighboring circuits, but is only connected to one circuit in every half cycle via the first and second electrical relay switches. In some examples, each cation electrode is configured to adsorb and / or intercalate a target ion (e.g., a target cation). In some examples, each feed solution can be the same or different. In some examples, each feed solution comprises the target ion at an initial concentration. In some examples, each receiving solution comprises a counterion for the target ion. In some examples, each receiving solution comprises the target ion at a preliminary concentration. In some examples, each cation electrode functions as the cathode of one circuit to adsorb the target ion from the feed solution in its charging half-cycle, and as the anode of another circuit to release the target ions to the receiving solution in its discharge half-cycle, the switch of a cation electrode between two adjacent circuits is achieved by electrical relay switches; such that when a circuit is operated in a charging mode, then the target ions from the feed solution contacting one side of the cation electrode are electrochemically absorbed by said side of the cation electrode, and when the circuit is operated in discharging mode, then the target ions are released from the cation electrode into the receiving solution contacting the opposite side of the cation electrode. In some examples, when a circuit is operated in a charging mode, then the first cation electrode and the second cation electrode are electrically connected to each other and a voltage source via the first and second electrical relay switches, the voltage source being configured to apply a voltage to the first and second cation electrodes such that at least a portion of the target ion concentration is depleted from each of the feed solutions by being adsorbed and / or intercalated into the cation electrode, such that the concentration of the target ion in the feed solutions decreases relative to the initial concentration. In some examples, when the circuit is operated in a discharging mode, then the first cation electrode and the second cation electrode are electrically connected to each other and a voltage source via the first and second electrical relay switches, the voltage source being configured to apply a voltage to the first and second cation electrodes such that at least a portion of the target ion adsorbed and / or intercalated in the cation electrode is released into the receiving solution, such that the concentration of the target ion in the receiving solution increases relative to the preliminary concentration. For example, at any given time, half of the circuits or electrodes in the device can be charging and the other half of the circuits or electrodes in the device are discharging.

[0067] In some examples, the target ion comprises a critical mineral. Examples of critical minerals include, but are not limited to, aluminum, antimony, arsenic, barite, beryllium, bismuth, cerium, cesium, chromium, cobalt, copper, dysprosium, erbium, europium, gadolinium, gallium, germanium, graphite, hafnium, holmium, indium, iridium, lanthanum, lithium, lutetium, magnesium, manganese, neodymium, nickel, niobium, palladium, platinum, praseodymium, rhodium, rubidium, ruthenium, samarium, scandium, silicon, tantalum, tellurium, terbium, thulium, tin, titanium, tungsten, vanadium, ytterbium, yttrium, zinc, and zirconium.

[0068] In some examples, the target ion comprises a metal, such as an alkaline metal, a transition metal, a rare earth metal, or a combination thereof.

[0069] In some examples, the target ion comprises sodium, lithium, nickel, copper, cobalt, or a combination thereof. In some examples, the target ion comprises sodium, lithium, or a combination thereof.

[0070] Also disclosed herein are devices comprising a plurality of fluidly independent circuits, the plurality of fluidly independent circuits comprising alternating circuits of a charging circuit and a discharging circuit, wherein the total number of circuits in the device is 3 or more. In some examples, each charging circuit comprises a cation electrode, an anion electrode, and a feed solution, the feed solution being sandwiched between and in electrochemical contact with the anion electrode and the cation electrode. In some examples, each discharging circuit comprises an anion electrode, a cation electrode, and a receiving solution, the receiving solution being sandwiched between and in electrochemical contact with the cation electrode and the anion electrode. In some examples, the anion electrode is shared between a charging circuit and the following discharging circuit, and the cation electrode is shared between a discharge circuit and the following charging circuit, such that each pair of charging and discharging circuits includes three total electrodes. In some examples, each pair of charging and discharging circuits further comprising a first electrical relay switch and a second electrical relay switch. Each charging circuit and discharging circuit are fluidly independent. In some examples, each anion electrode is configured to adsorb and / or intercalate a target ion (e.g., a target anion). In some examples, each feed solution can be the same or different. In some examples, each feed solution can comprise the target ion at an initial concentration. In some examples, each receiving solution comprises a counterion for the target ion. In some examples, each receiving solution comprises the target ion at a preliminary concentration. In some examples, when the device is operated in a charging mode, then the anion electrode and the cation electrode of each charging circuit are electrically connected to each other and a voltage source via the first and second electrical relay switches, and at least a portion of the target ion concentration is depleted from each of the feed solutions by being adsorbed and / or intercalated into the anion electrodes, such that the concentration of the target ion in the feed solutions decreases relative to the initial concentration. In some examples, when the device is operated in a discharging mode, then the cation electrode and the anion electrode of each discharging circuit are electrically connected to each other and the voltage source via the first and second electrical relay switches, at least a portion of the target ion adsorbed and / or intercalated in the anion electrode is released into the receiving solution, such that the concentration of the target ion in the receiving solution increases relative to the preliminary concentration.

[0071] Also disclosed herein are devices comprising a plurality of fluidly independent circuits, wherein the total number of circuits in the device is 2 or more. In some examples, each circuit comprises a receiving channel and a feed channel, the receiving channel being fluidly independent from the feed channel. In some examples, the receiving channel is defined by a first anion electrode and a cation exchange membrane, the receiving channel containing a receiving solution, such that the receiving solution is sandwiched between and in electrochemical contact with the first anion electrode and the cation exchange membrane. In some examples, the feed channel is defined by the cation exchange membrane and a second anion electrode, the feed channel containing a feed solution, the feed solution being sandwiched between and in electrochemical contact with the cation exchange membrane and the second anion electrode. In some examples, each pair of circuits further comprises a first electrical relay switch and a second electrical relay switch. In some examples, each anion electrode is shared between two neighboring circuits, but is only connected to one circuit in every half cycle via the first and second electrical relay switches. In some examples, each anion electrode being configured to adsorb and / or intercalate a target ion (e.g., a target anion). In some examples, each feed solution can be the same or different. In some examples, each feed solution comprises the target ion at an initial concentration. In some examples, each receiving solution comprises a counterion for the target ion. In some examples, each receiving solution comprises the target ion at a preliminary concentration. In some examples, each anion electrode functions as the cathode of one circuit to adsorb the target ion from the feed solution in its charging half-cycle, and as the anode of another circuit to release the target ions to the receiving solution in its discharge half-cycle, the switch of an anion electrode between two adjacent circuits is achieved by electrical relay switches; such that when a circuit is operated in a charging mode, then the target ions from the feed solution contacting one side of the anion electrode are electrochemically absorbed by said side of the anion electrode, and when the circuit is operated in discharging mode, then the target ions are released from the cation electrode into the receiving solution contacting the opposite side of the anion electrode. In some examples, when a circuit is operated in a charging mode, then the first anion electrode and the second anion electrode are electrically connected to each other and a voltage source via the first and second electrical relay switches, the voltage source being configured to apply a voltage to the first and second anion electrodes such that at least a portion of the target ion concentration is depleted from each of the feed solutions by being adsorbed and / or intercalated into the anion electrode, such that the concentration of the target ion in the feed solutions decreases relative to the initial concentration. In some examples, when the circuit is operated in a discharging mode, then the first anion electrode and the second anion electrode are electrically connected to each other and a voltage source via the first and second electrical relay switches, the voltage source being configured to apply a voltage to the first and second anion electrodes such that at least a portion of the target ion adsorbed and / or intercalated in the anion electrode is released into the receiving solution, such that the concentration of the target ion in the receiving solution increases relative to the preliminary concentration. For example, at any given time, half of the circuits or electrodes in the device can be charging and the other half of the circuits or electrodes in the device are discharging.

[0072] In some examples, each of the feed solutions and / or receiving solutions further comprises a solvent, such as water (e.g., each of the feed solutions and / or receiving solutions is an aqueous solution).

[0073] In some examples, the feed solution is derived from natural sources or a waste streams.

[0074] In some examples, the feed solution comprises brackish water, salt lake brine, seawater, geothermal brine, oil and / or gas produced water, mining wastewater, leaching solution in battery recovery, or a combination thereof.

[0075] In some examples, the feed solution comprises a salt solution, produced water (e.g., from mining, fracking, oil recovery), brine, or a combination thereof.

[0076] In some examples, the feed solution comprises brine resulting from the power industry, chemical industry, food industry, oil and gas industry (e.g., hydraulic fracturing), desalination industry (e.g., inland brackish water desalination), mining industry, or a combination thereof.

[0077] The feed solution can comprise any type of water, treated or untreated. For example, the feed solution can comprise hard water, hard brine, sea water, brackish water, fresh water, flowback or produced water, wastewater (e.g., reclaimed or recycled), river water, lake or pond water, aquifer water, brine (e.g., reservoir or synthetic brine), slickwater, or a combination thereof. In some examples, the feed solution can comprise hard water, hard brine, sea water, brackish water, flowback or produced water, wastewater (e.g., reclaimed or recycled), brine (e.g., reservoir or synthetic brine), slickwater, or a combination thereof.

[0078] In some examples, the feed solution can comprise wastewater, such as industrial wastewater and / or wastewater from unconventional energy production. In some examples, the feed solution can comprise wastewater from gas and / or oil production from a subterranean formation (e.g., unconventional formation, conventional formation). In some examples, the feed solution can comprise wastewater from gas and / or oil production from an unconventional subterranean formation (e.g., shale formation). In some examples, the feed solution comprises unconventional oil wastewater (e.g., shale oil wastewater), unconventional gas wastewater (e.g., shale gas wastewater), conventional oil wastewater, conventional gas wastewater, or a combination thereof. In some examples, the feed solution comprises mining wastewater, flue gas desulfurization wastewater (this is from coal power plant), chemical industry wastewater, or a combination thereof.

[0079] In some examples, the plurality of circuits are stacked or arranged linearly, and the device further comprising one or more terminal electrodes (e.g., two or more terminal electrodes).

[0080] In some examples, the plurality of circuits are stacked or arranged circularly (e.g., to form at least part of a circle).

[0081] In some examples, the cation and / or anion electrodes enable fast transport of the target ion from the feed solution to the receiving solution, have minimal macropores to avoid direct mixing between the feed solution and the receiving solution, are electrically conductive to minimize resistive energy loss, or a combination thereof.

[0082] Also disclosed herein are methods of use of any of the devices disclosed herein. For example, the methods can comprise separating the target ion from the feed solution.

[0083] In some examples, the method comprises critical mineral extraction, for example from natural sources or recovery from waste streams. In some examples, the method comprises desalination.

[0084] In some examples, the method comprises the electrochemical adsorption of the target ions from the feed solution contacting one side of the cation or anion electrode, followed by the subsequent release of the target ions to the receiving solution contacting the opposite side of the cation or anion electrode.

[0085] In some examples, the method is continuous or semi-continuous.

[0086] In some examples, the charge / discharge half cycles have a cycle time of 0.1 seconds or more (e.g., 0.25 seconds or more, 0.5 seconds or more, 0.75 seconds or more, 1 seconds or more, 1.25 seconds or more, 1.5 seconds or more, 1.75 seconds or more, 2 seconds or more, 2.5 seconds or more, 3 seconds or more, 3.5 seconds or more, 4 seconds or more, 4.5 seconds or more, 5 seconds or more, 6 seconds or more, 7 seconds or more, 8 seconds or more, 9 seconds or more, 10 seconds or more, 15 seconds or more, 20 seconds or more, 25 seconds or more, 30 seconds or more, 35 seconds or more, 40 seconds or more, 45 seconds or more, 50 seconds or more, 55 seconds or more, 1 minute or more, 1.25 minutes or more, 1.5 minutes or more, 1.75 minutes or more, 2 minutes or more, 2.5 minutes or more, 3 minutes or more, 3.5 minutes or more, 4 minutes or more, 4.5 minutes or more, 5 minutes or more, 6 minutes or more, 7 minutes or more, 8 minutes or more, 9 minutes or more, 10 minutes or more, 15 minutes or more, 20 minutes or more, 25 minutes or more, 30 minutes or more, 35 minutes or more, 40 minutes or more, 45 minutes or more, 50 minutes or more, 60 minutes or more, 70 minutes or more, 80 minutes or more, or 90 minutes or more). In some examples, the charge / discharge half cycles have a cycle time of 100 minutes or less (e.g., 90 minutes or less, 80 minutes or less, 70 minutes or less, 60 minutes or less, 50 minutes or less, 45 minutes or less, 40 minutes or less, 35 minutes or less, 30 minutes or less, 25 minutes or less, 20 minutes or less, 15 minutes or less, 10 minutes or less, 9 minutes or less, 8 minutes or less, 7 minutes or less, 6 minutes or less, 5 minutes or less, 4.5 minutes or less, 4 minutes or less, 3.5 minutes or less, 3 minutes or less, 2.5 minutes or less, 2 minutes or less, 1.75 minutes or less, 1.5 minutes or less, 1.25 1 minute or less, 55 seconds or less, 50 seconds or less, 45 seconds or less, 40 seconds or less, 35 seconds or less, 30 seconds or less, 25 seconds or less, 20 seconds or less, 15 seconds or less, 10 seconds or less, 9 seconds or less, 8 seconds or less, 7 seconds or less, 6 seconds or less, 5 seconds or less, 4.5 seconds or less, 4 seconds or less, 3.5 seconds or less, 3 seconds or less, 2.5 seconds or less, 2 seconds or less, 1.5 seconds or less, 1.25 seconds or less, 1 seconds or less, 0.75 seconds or less, 0.5 seconds or less, or 0.25 seconds or less). The cycle time can range from any of the minimum values described above to any of the maximum values described above. For example, the charge / discharge half cycles have a cycle time of from 0.1 seconds to 100 minutes (e.g., from 0.1 second to 50 minutes, from 50 minutes to 100 minutes, from 0.1 seconds to 1 second, from 1 second to 1 minute, from 1 minute to 10 minutes, from 10 minutes to 100 minutes, from 0.1 seconds to 60 minutes, from 0.1 seconds to 30 minutes, from 0.1 seconds to 15 minutes, from 0.1 seconds to 10 minutes, from 0.1 seconds to 5 minutes, or from 0.1 seconds to 1 minute). In some examples, the charge / discharge half cycles have a cycle time of from 0.1 seconds to 10 minutes. In some examples, the charge / discharge half cycles have a cycle time of from 0.1 seconds to 1 minute.

[0087] In some examples, the charge / discharge half cycles are short.

[0088] A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims. The examples below are intended to further illustrate certain aspects of the systems and methods described herein, and are not intended to limit the scope of the claims. EXAMPLES

[0089] The following examples are set forth below to illustrate the methods and results according to the disclosed subject matter. These examples are not intended to be inclusive of all aspects of the subject matter disclosed herein, but rather to illustrate representative methods and results. These examples are not intended to exclude equivalents and variations of the present invention which are apparent to one skilled in the art.

[0090] Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.) but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in °C or is at ambient temperature, and pressure is at or near atmospheric. There are numerous variations and combinations of measurement conditions, e.g., component concentrations, temperatures, pressures and other measurement ranges and conditions that can be used to optimize the described process.

[0091] Example 1- Continuous Electrochemical Ion Pumping for Desalination and Selective Ion Extraction

[0092] Introduction. Electrochemical adsorption (or electrosorption) of ions from aqueous solution such as brackish water, seawater, and brines has important applications for desalination and selective extraction of minerals and other valuable ions. Electrosorption works by temporarily storing the ions in the electrodes in the charging step and releasing these ions in the discharge step. Specifically, in the charging step, a voltage is applied to a pair of electrodes to adsorb the cations to the negative electrode and the anions to the positive electrode. In the discharge step, the applied voltage is changed to release the adsorbed ions from the electrodes. Such a change can take different forms, e.g., the applied voltage can be reduced, set to zero (i.e., the electrodes are short-circuited), or reversed. The target ions are removed from a batch (or stream) of the feed solution in the charging step and released to a separate batch (or stream) of solution, thereby achieving separation.

[0093] Several mechanisms exist for electrochemical ion adsorption, including capacitive, which involves the formation of electrical double layers typically in activated carbon; intercalation, which involves insertion of ions into crystal lattice of electrode materials; and Faradaic, which involves redox reaction that changes valence of the adsorbed ions and / or certain elements of the electrode material. Electrode materials with these mechanisms have all been tested for desalination which does not require specificity in the removed ions. For selective ion extraction, however, intercalation and Faradaic mechanisms are more promising because the electrode materials can be selected or tailored to achieve selective adsorption of specific ions.

[0094] There are many configurations for electrosorption that have been reported in literature, herein, the two most widely investigated and practically promising system configurations are discussed: flow-by configuration and the so-called “rocking-chair” configuration.

[0095] In a flow-by configuration, the solution flows between two electrodes in both the charging and discharging steps. In the charging step, ions are from the influent stream and temporarily stored in the electrodes. In the discharge step, ions are discharged from the electrodes to another influent stream and the electrodes are consequently regenerated for the next cycle. For a desalination process, the effluent stream in the charging step is the product stream (also called the diluate), whereas the effluent stream in the discharge step is the brine stream. For selective extraction of ions, the effluent stream in the discharge step is the product stream enriched with the target ions to extract.

[0096] The “rocking chair” configuration typically uses symmetric electrodes that adsorb only cations (although anion adsorption electrodes may be developed). Most commonly, the electrodes used in such a configuration involve intercalation or Faradaic reaction mechanisms, even though activated carbon electrodes based on electrical double layer formation can also be used. In a simple two-channel “rocking chair” electrosorption system (Figure 1), a voltage is applied to a pair of cation intercalation electrodes contacting two solution chambers separated by an anion exchange membrane (AEM). The cations are removed from the solution in cathodic chamber via intercalation into the cathode and released from the anode into the solution of the anodic chamber, while the anions in the cathodic chamber transport through the anion exchange membrane to the anodic chamber. The applied voltage is flipped once the cathode is charged to the desired level. In desalination, the streams exiting the cathodic and anodic chambers are the desalinated stream and brine streams, respectively. In selective cation extraction, the feedwater flows through the anodic chamber whereas the product stream receiving the cations released from the electrodes flows through the anodic chamber.

[0097] Although the description in Figure 1 is based on a “batch-mode” operation, operation with continuous flow is similar, involving both voltage (polarity) switch and flow switch between each half cycle. The description above applies to two adjacent cells, with each cell comprising a cathode, an anode, and an anion exchange membrane, and with each electrode shared between two adjacent cells. This structure can be repeated to have many cells in a stack. The number of cells is the same as the number of anion exchange membranes and one less than the number of electrodes.

[0098] Regardless of configuration, these systems have a major challenge, which is the switch of streams between the charging and discharge steps. While the switching of streams can be achieved using valve control, the finite time for the solution in the cell to be completely replaced by new solution undermines the system performance due to the mixing between the diluate and brine (in desalination) or between the feed solution and receiving solution (in selective ion extraction). In desalination, for instance, this effect of finite switching time prevents the diluate stream salinity to reach a new steady state even with constant current. In selective ion extraction, the mixing between the feed solution and receiving solution is the “contamination” of the receiving solution by other non-target ions in the feed solution. One possible way to mitigate this challenge is to use electrodes with high adsorption capacity to minimize the switching time as compared to the charging and discharge time. However, attaining a leapfrog in electrodes’ adsorption capacity over the state-of-the-art is very difficult.

[0099] Herein, a new process called continuous electrochemical ion pumping (CEIP) is described for pseudo-continuous desalination and selective ion extraction to overcome the limitations resulting from the stream switching in existing electrosorption systems. The physical configuration of the CEIP is similar to that for “rocking chair” electrosorption. Specifically, cation adsorption electrodes (CAE) and anion exchange membranes (AEM) are placed parallel to each other alternately. A key innovation for CEIP, however, is its unique operation mode that switch circuits between two half cycles.

[0100] Desalination. The operation of a CEIP for desalination is described in Figure 2. At any time, an electrode belongs to one circuit (or a cell) in CEIP instead of being shared between two cells as in rocking chair electrosorption. In each circuit (cell), the anode discharges cations to the brine stream, the cathode adsorbs cations from the diluate stream, whereas the anions migrate across the anion exchange membrane from the diluate stream to the brine stream. Once the anode is partially regenerated and the cathode is partially saturated, the circuit is switched by turning the anode of the current circuit to the cathode of another circuit and the cathode of the current circuit to the anode of yet another circuit. Unlike in “rocking chair” electrosorption where the polarity of voltage and the flow streams (i.e., the arrangement of brine and diluate) are both switched, in CEIP, the polarity of voltage and the flow streams remain constant but only the circuits are switched. More details about how CEIP works throughout a cycle are provided in the caption of Figure 2.

[0101] Once the anodes are again partially regenerated, and the cathodes are partially saturated to the desired level (bottom left), the circuit is switched again to perform the next cycle of ion pumping. In summary, the active ion pumping occurs in circuits N and N+2 in the first half cycle, and in circuits N-l and N+l in the 2ndhalf cycle.

[0102] By switching circuits in CEIP instead of switching flows in “rocking chair” electrosorption, ion transport direction can always be maintained and the limitations due to solution mixing in flow switching can be circumvented. The unique operation mode of CEIP also allows working with a very low saturation of level for the electrodes, which in theory should have benefits in both kinetics and energy consumption as adsorption will become more “challenging” as the electrodes become more saturated. The circuit switching is controlled automatically by a logic board and the half cycle can be as short as Is or less and as long as needed.

[0103] The schematic in Figure 2 only shows one and half cells, but multiple cells can be stacked together to form a multi-cell stack (Figure 3). The N-cell stack comprises N anion exchange membranes (AEM), N-l cation adsorption electrodes (CAE), N-l dilute channels, N-l brine channels, two terminal electrodes for electrolysis, and two terminal electrode channels containing electrolyte solutions. In the 1sthalf cycle (Figure 3, panel A), electrolysis occurs in the terminal anode to produce H+to neutralize the anions coming from the adjacent diluate channel, the terminal cathode is not connected. In the 2ndhalf cycle (Figure 3, panel B), electrolysis occurs in the terminal cathode to produce OH' that transport across the anion exchange membrane to neutralize the cations released to the adjacent brine channel, whereas the terminal anode is not connected. In addition to utilizing water electrolysis in maintaining system neutrality, porous carbon (e.g., activated carbon, carbon black) can be added to the electrolyte for full capacitive adsorption / desorption operation. In the anode chamber, the positively charged porous carbon is able to adsorb anions, when the negatively charged porous carbon at the cathode adsorbs cations. The porous carbon of the cathode and anode are mixed on the outside of the cell and the porous electricity is regenerated.

[0104] A CEIP system can also function with a single-cell configuration (Figure 4) which comprises one cation adsorption electrode, two anion exchange membranes, one brine stream, one diluate stream, two terminal electrodes, and two electrolyte streams contacting the terminal electrodes. By making a single-cell stack with a large cell area and then assembling the single-cell stack in a spiral-wound configuration, a large specific area can be achieved for the active cation adsorption electrode.

[0105] Selective mineral extraction. The CEIP process can also be applied for continuous and selective extraction and enrichment of target ions from a complex mixture, provided that the ion adsorption electrodes are selective to the target ions (e.g., critical minerals and materials). Here lithium (Li) extraction from a feed stream containing a complex mixture of other cations is used as an example. The working principle is very much similar to what has been described for desalination in Figure 2, except that here the cation adsorption electrode is replaced with a Li-selective cation adsorption electrode which has a preferential adsorption / intercalation of Li+over other cations. Each cell comprises two Li-selective cation adsorption electrode, an anion exchange membrane, one receiving solution which later becomes the Li-rich solution, and a feed solution that later becomes the Li-lean solution. Specifically, the receiving solution could be a solution of Li salt (without other metal cations), whereas the feed solution can be any solutions with Li, including but are not limited to, salt lake brine, geothermal brine, produced water, mining wastewater, leaching solution in battery recovery, and seawater.

[0106] Like in CEIP for desalination, the stacks for CEIP for Li extraction can be a multi-cell stack (similar to that in Figure 3) and single-cell stack (similar to that in Figure 4). Selective CEIP can also be applied to extract and enrich other types of cations and anions, as long as the corresponding electrodes selective to those ions are available. When using CEIP for anion extractions, the anion exchange membrane in Figure 5 will be replaced by a cation exchange membrane (CEM).

[0107] Possible expansion of the process. The description above is based on the use of cation intercalation electrodes. However, the system design can also be used with anion intercalation electrodes by (1) replacing the cation intercalation electrodes with anion intercalation electrodes, (2) replacing the anion exchange membranes with cation exchange membranes, or (3) simultaneous use of cation exchange membranes and anion exchange membranes.

[0108] For desalination, the ion intercalation electrodes can also be replaced by activated carbon (AC) filled with ion exchange resins. Specifically, the cation intercalation electrodes can be replaced with activated carbon filled with cation exchange resins (to close up macropores); the anion intercalation electrodes can be replaced with activated carbon filled with anion exchange resins (to close up macropores). For desalination, both cation intercalation electrodes (or activated carbon filled with cation exchange resins) and anion interaction electrodes (or activated carbon filled anion exchange resins) can also be used at the same time without using any ion exchange membranes.

[0109] For cation electrodes, additional expansions include, but are not limited to: Cation exchange polymer plus activated carbon;

[0110] Cation exchange polymer plus cation intercalation material;

[0111] Anion exchange polymer plus cation intercalation material;

[0112] Anion exchange polymer plus cation intercalation material plus cation exchange polymer film;

[0113] Cation intercalation material plus hydrophobic, non-ionic polymers;

[0114] Cation intercalation material plus inorganic material (e.g., aluminum, titanium and alloys); and carbon electrode (either using activated carbon with binder or activated carbon cloth) with surface coated with an cation exchange polymer film.

[0115] For anion electrodes, additional expansions include, but are not limited to:

[0116] Anion exchange polymer plus activated carbon;

[0117] Anion exchange polymer plus cation intercalation material;

[0118] Cation exchange polymer plus anion intercalation material;

[0119] Cation exchange polymer plus anion intercalation material plus cation exchange polymer film;

[0120] Anion intercalation material plus hydrophobic, non-ionic polymers; and

[0121] Anion intercalation material plus inorganic material (e.g., aluminum, titanium and alloys)

[0122] 7. Carbon electrode (either using activated carbon with binder or activated carbon cloth) with surface coated with an cation exchange polymer film.

[0123] Electrode fabrication. Regardless of desalination or selective ion extraction, the ion adsorption electrodes used in CEIP should have the following characteristics:

[0124] (1) Electrically conductive so that electrical potentials can be applied to the electrodes.

[0125] (2) Have certain ion adsorption capacity to temporarily store ions before discharging them to the brine (in desalination) or receiving solution (in selective ion extraction). Due to the unique operation mode of CEIP, the performance may not be undermined even if the ion adsorption capacity is substantially lower than that for electrodes used in conventional flow-switching electrosorption.

[0126] (3) Devoid of macroscopic pores to minimize mixing between the two solutions contacting the two sides of the electrodes. There are three kinds of electrodes: 1. the macropores of the electrode are filled with an ion-exchange polymer (or other material); 2. using an ion exchange polymer to cover one side of the electrode, but the macropores of the electrode remain; 3. the electrode is prepared without macropores, which may be the case in intercalation electrodes used for lithium extraction.

[0127] An example structure of the electrodes that satisfy these requirements is shown in Figure 7.

[0128] One of the many possible approaches to fabricate electrodes with the above characteristics is described here (Figure 8).

[0129] Step 1 : Mix and ball-mill (optional) active electrode materials (e.g., activated carbon, cation intercalation materials, anion interaction materials, or other types) with conductive additives (e.g., carbon black). The active electrode materials provide the capacity for ion storage, and the conductive additives increase the electrical conductivity of the electrodes. The ball-milling will reduce the particle size and improve contact between active electrode materials and the conductive additive.

[0130] Step 2: Mix the powder mixture obtained from step 1 with a polymer solution. The polymer can be anion exchange polymer (or positively charged polyelectrolyte), cation exchange polymer (or positively charged polyelectrolyte), a non-ionic polymer, or a combination of these polymers in a mixture or as stratified layers. The resulting powder / polymer mixture is the electrode slurry.

[0131] Step 3: Cover a mesh, fibroid current collector (e.g., graphite, titanium) with the electrode slurry obtained from step 2 so that the current collected is fully or partially embedded in a film of the electrode slurry.

[0132] Step 4. Hot press the current collector-embedded film at high temperature and pressure to form the working film electrode.

[0133] Potential applications of CEIP. CEIP can be used for desalination and selective separation to either remove or enrich specific ions using electrodes that can adsorb those ions with specificity. For example, for extracting lithium ions, possible electrode materials can be inorganic particles comprising lithium, manganese, titanium, and oxygen (e.g., lithium manganese oxide, lithium titanium oxide, lithium titanium and manganese oxides). Other electrode materials can also be used.

[0134] Example 2 - Selective and Continuous Electrochemical Ion Pump (SCEIP) for Critical Mineral Extraction and Recovery

[0135] Introduction. As state-of-the-art technologies for critical mineral (CM) extraction, solvent extraction and adsorption have major limitations such as high chemical usage and operational complexity due to non-continuous operation. The use of organic solvents in solvent extraction and strong acids as the leaching solution in both processes poses significant occupational and environmental risks. Solvent extraction and adsorbent-based extraction involve two distinct steps, including an extraction (or adsorption) step and a stripping (or leaching) step, which induces significant operational complexity.

[0136] Electro-sorption (ES) is a promising electrochemical method for extracting critical minerals. Take Li for example, electro- sorption using Li intercalation materials has been demonstrated to be a promising direction for Li extraction from a variety of brines. In an electro- sorption process, Li intercalation electrodes, such as manganese oxide (Z-M CL) and lithium iron phosphate (LiFePCh), have been used to selectively adsorb Li+from a complex mixture of other ions and then release to a receiving solution.

[0137] While nanofiltration has been applied to effectively separate Li+and Mg2+, it has limited application scenarios due to (1) its undermined performance at high salinity and (2) its inability to separate Li+from other monovalent cations. Electrodialysis also suffers from similar limitations such as the challenge for achieving a high Li-specific selectivity (other than monovalent-divalent selectivity) and the loss of selectivity at high ionic strength. Compared to membrane-based process, such as nanofiltration (NF) or electrodialysis (ED), adsorption can typically achieve a much higher selectivity, and electro-sorption with intercalation electrodes thus also has the potential to become a highly selective Li extraction process.

[0138] Although electro-sorption based on intercalation-electrodes has advantages over nanofiltration or electrodialysis in achieving a high ion-specific selectivity, it is, to a certain extent, still a non-continuous process. Specifically, the operation of electro-sorption, regardless for selective ion adsorption or just general desalination, involves two distinct steps: the adsorption (or charging) step and the desorption (or discharge) step. The non- continuous operation of a conventional electro- sorption process creates a major challenge when switching the solutions (or the flows) between the feed solution and the receiving solution (i.e., the product stream). The inevitable mixing between the two solutions can significantly undermine the selectivity and recovery of the target ions. In addition, while the intercalation electrodes may capture the target ions with a high selectivity by storing them in the electrodes’ crystal lattice, competing ions are also stored in the “macropores” (i.e., pores between the particles of intercalation materials) and later released to the product stream, further compromising the selectivity. For these reasons, the electro- sorption research community has been trying to develop electrodes with higher capacity, as achieving more adsorption in the charging step can reduce the detrimental impacts due to flow switch and discharge of competing ions from macropores.

[0139] Technical Solution. Described herein is a technological platform to separate a critical mineral from aqueous solutions relevant to critical mineral extraction from natural sources or recovery from industrial waste streams. This technological platform, namely Selective and Continuous Electrochemical Ion Pump (SCEIP), an ion-selective electro- sorption process that can operate continuously without solution mixing and discharge of competing ions. Solution mixing and discharge of competing ions, which are unavoidable in conventional electrosorption with “flow switch”, are detrimental to both selectivity and energy efficiency of the critical mineral extraction process.

[0140] Herein, SCEIP is described with a focus on extracting lithium (Li) and nickel (Ni) which involve two fundamentally different mechanisms to achieve ion selectivity. There will be a Li-selective version of SCEIP, Selective and Continuous Electrochemical Lithium Pump (SCELiP) with the target application as Li-extraction from geothermal brine and produced water. There will also be a Ni-selective version of SCEIP, Selective and Continuous Electrochemical Lithium Pump, (SCENiP) with the target application as recovering Ni from spent solutions in electroplating industry (e.g., electroless and electrolytic baths).

[0141] Technical Description

[0142] Working Principle of SCEIP. A SCEIP stack comprises multiple cells with each cell having two ion-selective electrodes, an anion exchange membrane (AEM), one receiving solution which later becomes rich in the target ions, and a feed solution that later becomes lean in the target ions. Specifically, the receiving solution could be a pure solution containing only the target ions and their counter ions, whereas the feed solution can be any solutions containing the target ions (e.g., geothermal brine, produced water, mining wastewater, leaching solution in battery recovery). Here, the specific example of SCELiP is used as an example to describe the working principle of SCEIP, noting that the principle is the same for SCENiP and other metals except for the target ion species and the electrode design.

[0143] A full cycle of SCELiP is described in Figure 9. In the first half cycle (upper left), electrodes “a” and “b” are the anode and cathode of circuit N, respectively. Whereas electrode “c” is the anode of circuit N+2 (the cathode of circuit N+2 is not shown). In each circuit, Li ions are discharged from the anode to the receiving solution (Li-rich solution) and adsorbed to the cathode from the feed solution. Anions migrate across the anion exchange membrane from the feed solution to the receiving solution to maintain charge neutrality in both channels. Once the anodes are partially regenerated and the cathodes are partially saturated to the desired level (upper right), the circuits will be switched by an external control system. After the circuit switch (bottom right), electrode “a” switches from the anode of circuit N to the cathode of circuit N-l (anode of circuit N-l is not shown), electrode “b” switches from the cathode of circuit N to the anode of circuit N+l, whereas electrode “c” switches from the anode of circuit N+2 to the cathode of circuit N+L Li ions and anions’ transport in the second half cycle is similar to that in the first half cycle, except that they occur in different cells (and circuits). Once the anodes are again partially regenerated and the cathodes are partially saturated to the desired level (bottom left), the circuit is switched again to perform the next cycle of Li ion pumping. In summary, the active ion pumping occurs in circuits N and N+2 in the first half cycle, and in circuits N-l and N+l in the 2nd half cycle.

[0144] A unique feature of SCELiP (as compared to conventional electro- sorption) is to use “circuit switch” to replace “flow switch”. In other words, SCELiP replaces the more difficult and slower control of water flows with the easier and much faster control of the electron flows, which provides several key advantages. First, the absence of “flow switch” in SCELiP eliminates mixing between the feed solution and the receiving solution as well as the discharge of impurity cations from the macropores of the electrodes to the receiving solution — both phenomena are detrimental to selectivity in conventional electro-sorption. Second, because of the detrimental impacts of “flow switch”, high-capacity electrodes are strongly desired in conventional electro-sorption to minimize the time of “flow switch” as compared to the time of charging (adsorption). With SCELiP, however, high-capacity electrodes are unnecessary because there is no “flow switch” or its detrimental impacts in the entire process. Instead of adsorbing as much as Li ions to the electrode in the charging halfcycle and then releasing them to the receiving solution as in conventional electro- sorption, SCELiP only needs to capture a small amount of Li ions in the electrode for a very brief time (i.e., short half cycle time) and then release them to the receiving solution.

[0145] Not only does SCELiP not require high-capacity electrodes, but a very short halfcycle time can be used and a very low saturation level of the electrodes can be maintained, which is another advantage of the SCELiP. It is well known in desalination theory that charging the electrodes to a high saturation level is unfavorable in both kinetics and energy consumption. In the case of selective ion removal, high saturation level may even compromise selectivity. Operating with a low saturation level is impractical for conventional electro- sorption due to the detrimental impacts of “flow switch” but is completely feasible and actually desirable in SCELiP. With all these advantages considered, SCELiP has a strong potential to become a continuous, high selective, energy-efficient, and operationally simple and robust process for electrochemical Li extraction.

[0146] Electrode Design for SCELiP and SCENiP

[0147] SCELiP Electrode Design The Li-selective electrode in SCELiP is a symmetric thin film made of Li-intercalation materials, carbon black (for improving conductivity), a conductive mesh as current collector, and positively charged anion exchange polymers (AEP) filling the macropores in the electrode (Figure 10). The anion exchange polymer fully or partially blocks the macropores to prevent diffusional crossover of ions other than Li, and its positively charge helps to exclude competing cations from entering the film during charging (the electrode). Partial filling refers to the macropores of a very thin surface layer of electrode particles being filled. In addition, it is important to avoid the complete coverage of electrode particles by the anion exchange polymer, ensuring that the electrode particles remain exposed to the feed solution. When the Li-selective electrode is used as the cathode, Li ions in the feed solution will be inserted in the exposed Li-intercalation materials. The anion exchange resin does not fully cover the electrode surface, leaving the intercalation electrode material exposed to the solution. Other cations that cannot enter the crystal lattice of the intercalation materials will be rejected by the positive charge imparted by the anion exchange polymer. When the Li-selective electrode is used as anode, Li ions stored in the intercalation electrode will be released to the receiving solution.

[0148] Also described herein are composite electrodes, where the top layer is as described in the preceding paragraph but is very thin, and the support layer is a cation exchange membrane. In both designs, the conductive mesh only needs to contact the electrode materials, but not necessarily embedded in the film.

[0149] SCENiP Electrode Design For SCENiP, selective extraction of Ni can be achieved using some 2D pseudocapacitor materials (intercalation materials) such as TiS2, MoS2. For such materials, the electrodes are prepared in the same way as previously described for lithium intercalation material electrodes. Additionally, Ni selective electrodes for SCENiP can use other approach. Specifically, the Ni-selective electrode used in SCENiP is an asymmetric electrode integrating two functional layers (Figure 11). The base layer comprises a mixture of activated carbon (AC), carbon black, and cation exchange polymer (CEP). A mesh current collector is used to apply the potential to the base layer. The coating layer is a composite film made anion exchange polymer and a Ni-binding functional material (either polymer or inorganic particles) that forms a percolation network through the composite film.

[0150] When the Ni-selective electrode is used as the cathode, Ni ions in the feed solution will transport along the percolation network through the coating layer and enter the activated carbon-containing base layer. Other cations not binding to the functional material will be rejected by the positive charge imparted by the anion exchange polymer and thus cannot enter the activated carbon electrode. When the Ni-selective electrode is used as anode, Ni ions stored in the activated carbon electrode will be released to the receiving solution. The anions cannot enter the activated carbon electrode due to the exclusion by the cation exchange polymer, which maintain a high current efficiency for Ni discharge process.

[0151] It is emphasized that SCELiP and SCENiP are two of the many examples for SCEIP. SCEIP can be applied to extract many other ions using both approach 1 where intercalation electrodes for a specific ion are used (SCELiP as an example) and approach 2 where a selective same-charge polymer coating embedded with specific ion-binding additive is used to impart selectivity. Other ions that can be extracted using SCEIP include, but are not limited to, copper, cobalt, alkaline metals, transition metals, and rare earth metals.

[0152] Proof of Concept of SCEIP in Desalination. One major advantage of SCEIP is the unique way in which the charging and discharge is performed, not via switching the polarity in a circuit, but via switching the active circuits between adjacent half-cycles. This unique operation approach enables continuous separation and the elimination of flow switch, which improves separation performance, reduces operation complexity and the requirements on electrode capacity. While SCEIP can be pursued for the extraction of Li (SCELiP) and Ni (SCENiP), the feasibility of this unique circuit switch approach was confirmed in a recent study on desalination using the system shown in Figure 12. The data for desalination is shown in Figure 13.

[0153] Example 3 - Pseudo-continuous and Scalable Electrochemical Ion Pump with Circuit-Switch-Induced Ion Shuttling

[0154] Abstract. Despite the potential of electro- sorption to address many sustainability challenges, performance of conventional electro- sorption is hindered by the technical limitations associated with need to switch solutions in the flow channels between the charging and discharge half-cycles. It is shown herein that electrochemical ion pump (EIP), powered by the mechanism of circuit-switch-induced ion shuttling, offers a highly scalable approach to overcome the limitations of solution- switch and achieve pseudo-continuous ion separation with unidirectional ion flux. The feasibility EIP is demonstrated with symmetric and asymmetric configurations and a systematic investigation of symmetric EIP was performed with a single electrode and with multiple electrodes. Interesting system behaviors of multi-electrode EIP are unveiled that are critical to scaling up EIP for practical applications. Salient performance enhancement of EIP vs. conventional electro-sorption is also shown with various types of configurations for brackish water desalination. Beside its exceptional scalability and performance, the ability of EIP to operate with ultrashort halfcycles with minimum capacitance has a strong potential to shift the paradigm for electrode design in a broad range of electrochemical separation applications.

[0155] Introduction. Electrochemical separation has found wide applications in water treatment, desalination, and resource extraction due to its unique ability to achieve efficient, tunable, and selective separation (Alkhadra MA et al. Chem. Rev. 2022, 122, 13547-13635; Gamaethiralalage J et al. Energy Environ. Sci. 2021, 14, 1095-1120). Electro- sorption (ES) is an important class of electrochemical separation inspired by the mechanism of supercapacitor and battery for energy storage (Suss ME et al. Energy Environ. Sci. 2015, 8, 2296-2319; Biesheuvel P et al. arXiv preprint, 2017, arXiv: 1709.05925; Fleischmann S et al. Nature Energy, 2022, 7(3), 222-228; Breitsprecher K et al. Nature communications, 2020, 11(1), 6085; Prehal C et al. Nature Energy, 2017, 2(3), 1-8). Using capacitive or battery-type electrodes (Gabelich CJ et al. Environ. Sci. Technol. 2002, 36, 3010-3019; Porada S et al. ACS Appl. Mater. Interfaces, 2012, 4, 1194-1199; Lee J et al. ACS Omega, 2017, 2, 1653- 1659; Yu F et al. J. Mater. Chem. A, 2019, 7, 15999-16027; Su X et al. Nature communications, 2018, 9(1), 4701; Liu C et al. Nature Energy, 2017, 2(4), 1-8; Ge K et al. Nature Communications, 2024, 15(1), 1935), a general electro-sorption process comprises charging and discharge half-cycles (Porada S et al. Prog. Mater Sci. 2013, 58, 1388-1442; Zhao R et al. Energy Environ. Sci. 2012, 5, 9520-9527; Suss ME et al. Energy Environ. Sci. 2012, 5, 9511; Lee J et al. Energy Environ. Sci. 2014, 7, 3683-3689). In the charging halfcycle, charged ions or molecules are adsorbed by, and stored in, the electrodes. In the discharge half-cycle, the stored charged species are released to a receiving solution or brine.

[0156] Most electro-sorption processes are based on film electrodes, and charging is terminated when either the electrodes are saturated at an applied voltage or when the cell voltage becomes too high with an applied current (Wang L et al. Water Res. 2018, 129, 394- 401; Wang L et al. Environ Sci Technol. 2018, 52, 4051-4060; Zuo K et al. Nature Reviews Materials, 2023, 8(7), 472-490). Transitioning between charging and discharge half-cycles involves physically switching the solutions in the flow channels (Figure 14a), making these electro- sorption processes non-continuous (Do VQ et al. Energy Environ. Sci. 2023, 16, 3025-3039). Not only is this solution-switch operationally complex but it also results in unfavorable mixing and “wasted separation” (Figure 18a-Figure 18b and Note SI) (Do VQ et al. Energy Environ. Sci. 2023, 16, 3025-3039; Liu W et al. arXiv preprint, 2024, arXiv:2402.08234). Extensive research effort in electro-sorption has been devoted to developing high-capacity electrodes (Yu F et al. J. Mater. Chem. A, 2019, 7, 15999-16027; Liu T et al. Sci. Adv. 2020, 6, eaaz0906; Jain A et al. Environ. Sci. Technol. 2018, 52, 5859- 5867; Han B et al. Chem. Eng. J. 2019, 360, 364-384; Ji F et al. J. Mater. Chem. A, 2018, 7, 1768-1778). Although prioritizing capacity in electrode development may have started as a “methodological carryover” from energy storage research, electro-sorption with high- capacity electrodes reduces detrimental impacts of solution-switch by enabling more salt adsorption per half-cycle (Liu W et al. arXiv preprint, 2024, arXiv:2402.08234; Liu W et al. doi.org / 10.1021 / acs.est.4c02681). However, unlike energy storage, the primary goal of electro- sorption is separation and electrode capacity should not have been critical if it were not for the limitations associated with solution- switch.

[0157] Herein, an electrochemical separation process called electrochemical ion pump (EIP) is reported in which ion flux is unidirectional, solution-switch is eliminated, and the charging and discharge half-cycles can be ultrashort. The core working principle of EIP is the electrochemical adsorption of ions from the feed solution contacting one side of the electrode, followed by the subsequent release of the ions to the receiving solution contacting the opposite side of the electrode (Figure 14b). The unique operation of EIP enables electrochemical separation with half-cycle time and salt adsorption that are orders of magnitude lower than those in conventional film-electrode electro-sorption (Figure 14a, Figure 14b). Though governed by similar fundamental principles as film-electrode electrosorption and having discrete charging discharge half-cycles, the unidirectional ion flux and ultrashort half-cycle time render EIP pseudo-continuous. Herein, the concept of EIP is demonstrated for desalination using activated carbon electrodes. The working principle and system designs of EIP are described and its performance and system behaviors under different configurations and operation modes are examined, showing the great potential of EIP to transform electrochemical ion separation.

[0158] Working principle and proof of concept. The key to realize EIP with ultrashort half-cycle time and without physical solution- switch is to employ a unique system design and operation strategy called “circuit-switch”. In conventional electro- sorption, an electrode serves as the cathode and anode alternately within the same circuit and the switch is achieved by reversing the polarity of the applied voltage (Zuo K et al. Nature Reviews Materials, 2023, 8(7), 472-490; Srimuk P et al. Nature Reviews Materials, 2020, 5(7), 517-538). Such a switch of applied voltage direction is accompanied with the physical solution-switch, and they together demarcate the charging and discharge half-cycles (Figure 19). An electrode in EIP also functions as the cathode and anode alternately, but by changing the counter electrode it pairs with. In other words, an electrode in EIP is connected to two different electrodes in two different circuits in the charging and discharge half-cycles (Figure 14c, Figure 14d).

[0159] There are two EIP configurations, one with asymmetric electrodes (a-EIP) and the other with symmetric electrodes (s-EIP). In an a-EIP (Figure 14c), a complete circuit includes a flow channel sandwiched between two electrodes, a cation electrode (CE), and anion electrode (AE). In the charging half-cycle, the circuit N (in red) is connected through the feed channel where anions and cations are adsorbed by the anion electrode (electrodes i, anode) and cation electrode (electrode j, cathode), respectively, whereas electrode k functions as the anion electrode for circuit N+2. In the discharge half-cycle, the circuit N+l (in blue) connects electrodes j and k which release cations and anions to the brine channel, respectively, whereas electrode i functions as the cathode of circuit N-l and releases ions to the brine channel. Overall, each electrode shuttles ions from the feed solution to the brine.

[0160] In an s-EIP, a complete circuit comprises two cation electrodes, a feed channel, an anion exchange membrane (AEM), and a brine channel (Figure 14d). Each cation electrode is shared between two circuits but is only connected to one circuit in every half-cycle. When circuit N (in red) is connected, electrode j functions as the cathode in circuit N where electrode i serves as the anode. Electrode j adsorbs cations from the feed channel while electrode i releases cations that it previously adsorbed from the feed channel of circuit N-l. When circuit N+l (in blue) is connected, electrode j functions as the anode in circuit N+l where electrode k serves as the cathode. Electrode j releases cations to the brine channel while electrode k adsorbs from the feed channel cations that it will release to the brine channel in circuit N+2 in the subsequent half-cycle. In all connected circuits, anions migrate across the anion exchange membrane to maintain charge neutrality in both the feed and brine channels. Overall, each electrode functions as the cathode of one circuit to adsorb cations from the feed solution in its charging half-cycle, and as the anode of another circuit to release cations to the brine in its discharge half-cycle. For both configurations, the switch of an electrode between two adjacent circuits is achieved by electrical relays (Figure 14c, Figure 14d). This unique design of EIP replaces the slow physical solution-switch with the almost instantaneous circuit-switch. The time scale to change electron flows is orders of magnitude shorter than the hydraulic residence time.

[0161] As proof of concept, desalination experiments were performed with EIP cells of both configurations with minimum numbers of electrodes. Specifically, the s-EIP cell comprises two terminal electrodes, two anion exchange membranes, and a single cation electrode (Figure 14e), whereas the a-EIP cell comprises two terminal electrodes, an anion electrode, and a cation electrode (Figure 20a-Figure 20c and Note S3). With both configurations, a constant current density (10 A nr2) was applied in each circuit and near complete desalination of a representative brackish water (100 mM NaCl) was achieved with a current efficiency of -80% for both charging and discharge half cycles (Figure 14f and Figure 20b). The maximum voltage per half-cycle remained relatively stable for the discharge half-cycle but increased for the charging half-cycle over time due to the reduced feed channel resistance and the increase in salinity difference between the two channels. Similar current efficiency and performance stability were also observed in s-EIP experiments with constant voltage (2V, Figure 21a-Figure 2 If). While both s-EIP and a-EIP have been proven technically feasible, s- EIP is chosen for the rest of this study due to the simplicity of fabricating only one type of electrodes.

[0162] EIP electrode design. The electrodes for ElP-based desalination should satisfy three major requirements (Figure 15a). First, the electrodes should enable fast transport of the target ions from the feed solution to the brine. Second, the electrodes should have minimal macropores to avoid direct mixing between the feed solution and the brine and to mitigate water transport via osmosis. Third, the electrodes should be electrically conductive to minimize resistive energy loss. Following these criteria, EIP electrodes were fabricated by applying a paste of activated carbon and ion exchange polymer (IEP) mixture on a titanium mesh current collector, followed by solvent removal and hot press to obtain a thin film of activated carbon with macropores filled by ion exchange polymer (Figure 15b, and Methods). Another method for electrode preparation involves first coating a mixture of porous carbon, carbon black, and PVDF / or PTFE slurry onto a titanium mesh current collector. The solvent is then removed, followed by hot pressing to obtain a thin film electrode with macropores. Finally, a cation exchange polymer solution is sprayed onto the electrode surface, forming a dense ion exchange membrane layer. The ion exchange polymer fillers are Nafion for cation electrode and quaternized poly(p-phenylene oxide) for anion electrode (Wang L et al.

[0163] Environ. Sci. Technol. 2020, 54, 5874-5883), providing a fast ion transport pathway and serving as a binder to impart mechanical strength and flexibility, and a pore filler to eliminate macropores.

[0164] According to the cross-sectional micrograph, elemental mapping obtained using focused ion beam-scanning electron microscopy, and photographic images (Figure 15c, Figure 15d), hot-press helped the formation of a mechanically robust electrode with percolated network of activated carbon particles and minimum voids. The elimination of macropores is important for minimizing mixing between the two solutions contacting the electrode. Spontaneous ion diffusion across a hot-pressed EIP electrode under concentration gradient was minimal, much lower than conventional activated carbon electrodes without ion exchange polymer filler and even lower than a commercial ion exchange membrane (Figure 22). The electrodes showed nearly perfect capacitive behavior based on their cyclic voltammograms and electrochemical impedance spectra with and without hot-press (Figure 23a- Figure 23b), with hot-press slightly reducing the capacitance and ohmic resistance.

[0165] Behavior of single-electrode s-EIP. An s-EIP system with a single cation electrode can be operated over a wide range of current density (tested up to 120 A nr2) to achieve high ion fluxes while maintaining a high current efficiency of -80% (Figure 16a). Increasing the current density also increases the average voltage which is the temporal average of circuit voltages in the charging and discharge half-cycles (Figure 16b). However, only a small fraction of the circuit voltage is attributable to desalination, whereas most of the circuit voltage is attributable to water electrolysis half-reactions at the terminal electrodes (Figure 16b, Note S4 , and Figure 24a-Figure 24b). The contribution of desalination to the overall voltage includes the voltage drops due to ion transport resistances in the diluate channel, the brine channel, one anion exchange membrane, as well as the voltage drop from the cation electrode / solution interface to the current collector (Figure 16c, Figure 25) (Wang L et al. Environ Sci Technol. 2019, 53, 3366-3378). The distribution of the different contributions to the overall circuit voltage drop depends on multiple factors, including the current density, terminal electrode reactions, flow channel salinity, electrochemical properties of the cation electrode, and the half-cycle time.

[0166] The half-cycle time has substantial impacts on the behavior and performance of s-EIP. With a short half-cycle time (e.g., 5s), the concentration changes over time for both the diluate and brine appear to be continuous (Figure 16d). However, with a longer half-cycle time of 500s, the periodic behavior of s-EIP clearly emerges, with salt removal from the diluate and salt release to the brine occurring in two distinct half-cycles (Figure 16d). Strictly speaking, the periodic s-EIP behavior also exists, but is macroscopically negligible, in s-EIP with short half-cycle time. The observation of no concentration change in the solution outside the active circuit in an s-EIP with a half-cycle time of 500s confirms that the cation electrode exchanges ions dominantly with the solution within the active circuit.

[0167] Beside the periodicity of concentration change in solutions, varying half-cycle time also has a considerable impact on circuit voltage, and consequently, energy consumption. The impact of half-cycle time on circuit voltage is particularly salient when charging at a relatively high current density with a long half-cycle. With a current density of 50 A nr2, the charging and discharge voltage profiles were similar when the half-cycle time was increased from 0.5s to 5s. However, the circuit voltage at the start of the discharge half-cycle was appreciably lower with a half-cycle time of 50s and became very low (< IV) with a half-cycle of 500s (Figure 16e). Because the cation electrode was charged to a decent extent after 50s and a great extent after 500s, the stored capacitive energy provided driving force for ion release in discharge, thereby reducing the applied circuit voltage needed to sustain the same current density as compared to the case where fewer ions and energy were stored in the cation electrode.

[0168] Such an explanation is further supported by the measured profiles of cation electrode potential (vs. Ag / AgCl electrode as the reference) during charging and discharge with different half-cycle times (Figure 16f). These potential profiles reveal a positive open-circuit potential of ~0.3 V and an asymmetric potential difference between charging and discharge. Importantly, charging and discharge under this current density with a half-cycle time of 500s reduced the cation electrode potential in charging below the potential for hydrogen evolution reaction (Figure 24a) and increased the cation electrode potential beyond the potential for oxygen evolution reaction. Consequently, water electrolysis occurs at the cation electrode when a high current density with a long half-cycle time results in a high saturation level of the cation electrode, which is confirmed by a substantial increase of the diluate pH (Note S5, Figure 27a-Figure 27c).

[0169] Electrolysis compromises the current efficiency (or charge efficiency) by spending energy on electrolytic instead of capacitive charge transfer (Zhang C et al. Water Res. 2018, 128, 314-330; Liu X et al. Curr. Opin. Chem. Eng. 2019, 25, 67-74). Moreover, the presence of electrolysis has been shown to be detrimental to activated carbon electrodes by inducing irreversible reduction of electrode capacity (Cohen I et al. Electrochim. Acta 2013, 106, 91- 100; Cohen I et al. Electrochim. Acta 2015, 153, 106-114; Shapira B et al. Electrochim. Acta 2016, 220, 285-295). Therefore, the absence of electrolysis in s-EIP with a short half-cycle time even at high current density is a key advantage of s-EIP. This unique feature of s-EIP enables desalination to be operated at a current density much higher than conventional electro- sorption without generating detrimental electrolysis reactions at the cation electrode. In comparison, conventional electro-sorption, especially with activated carbon, can only be performed with low current density to prevent electrolysis because charging and discharge with a short half-cycle time is impractical due solution-switch (Zhang C et al. Water Res. 2018, 128, 314-330).

[0170] Design, behavior, and performance of multi-electrode s-EIP. The significant contributions of electrolysis half-reactions at terminal electrode to the circuit voltages of a single-electrode s-EIP system render single-electrode s-EIP energy inefficient as a desalination process. Fortunately, an s-EIP system can be easily scaled up by stacking multiple circuits between two terminal electrodes (Figure 17a). An s-EIP stack with N cation electrodes has N feed channels and brine channels, and V+1 anion exchange membranes and circuits. When N is an odd number, the number of active circuits is (A+l) / 2. For example, an s-EIP stack with 5 cation electrodes has 6 circuits in total and 3 active circuits at any moment (Figure 17b). When N is even, the numbers of active circuits in the two half-cycles differ by one (Figure 28). Herein, the level of stacking is defined based on the number of cation electrodes, N, i.e., an s-EIP stack with N cation electrodes is referred to herein as an N- electrode stack. Like the single-electrode s-EIP stack (Figure 14b), the multi-electrode stacks can also be operated using either constant voltage (CV) or constant current density (CC) mode.

[0171] With the same feed and brine stream flowrates, increasing the total area of cation electrode by circuit stacking increased desalination rate accordingly regardless of operation with a constant current (Figure 17c) or constant voltage mode (Figure 17d). The ion flux stayed constant as the number of electrodes increased for constant current operation (Figure 17e), which implies that the current efficiency was also constant regardless of the number of electrodes. However, increasing the number of electrodes increased the overall ion flux in a constant voltage operation, because the electrodes in the middle of the stack achieved better current efficiencies compared to those near the terminal electrodes. Interestingly, the ion flux for s-EIP with constant voltage operation with an even number (N) of cation electrodes is roughly the same as that for a system with N+l cation electrodes (Figure 17e), which can be explained by the current density distribution in a multi-electrode s-EIP stack operation using a constant voltage mode.

[0172] When a constant voltage of 1 ,2V was applied to each circuit of a multi-electrode s- EIP stack, the current densities systematically increased with increasing number of cation electrodes (Figure 17f). With a single-electrode s-EIP, which has two circuits each connecting to a terminal electrode, the current density for each circuit was low (< 7.5 A nr2), because most of the voltage drop was attributable to the electrolysis half-reactions. With a multi-electrode s-EIP, the current densities of the middle circuits without terminal electrode were higher than that of the terminal circuits. In general, the current density was higher the further away the circuit was from the terminal electrodes, as more charge transfer was attributable to capacitive ion adsorption / desorption instead of electrolysis (Figure 17g, Note S6). The electrolysis occurring at multiple electrodes (i.e., terminal electrodes and CEs) induced significant change in solution pH (Figure 29). The current densities, including that of the terminal circuits, increased systematically as the number of CEs increased.

[0173] For a single-electrode s-EIP operated using a constant current density (8.1 A nr2), the circuit voltages for the charging and discharge half-cycles were 1.17±0.01 V and 1.28±0.01V, respectively (Figure 17h). As discussed earlier, these circuit voltages include contributions from the half-reactions of water electrolysis at the terminal electrodes, which is strongly corroborated by the circuit voltage distributions for multi-electrode s-EIP with a constant current operation. With a two-electrode s-EIP, the voltage for the middle circuit, i.e., the circuit comprising only two CEs but not any terminal electrode, was only ~0.3 V, much lower than the voltages of the terminal circuits. Further increasing the number of CEs generated similar voltage profiles where the voltages of middle circuits remained roughly ~0.3 V and the terminal circuit voltages were substantially higher. In other words, the charge transfer through the CEs in a multi-electrode s-EIP with a constant current operation is dominantly attributable to capacitive ion adsorption / desorption. Only the charge transfer at the terminal electrodes is attributable to electrolysis half-reactions (Figure 17i).

[0174] Comparing the current density distribution of an s-EIP with a constant voltage operation vs. the voltage distribution of an s-EIP with a constant current appears to indicate that the impact of terminal electrode electrolysis propagates into the middle circuits in a constant voltage operation but not in a constant current operation. To quantify the performance of electrochemical desalination using s-EIP and other conventional electrosorption methods, the ion-specific energy consumption, SECi, (i.e., energy consumed to transfer a unit mole of ions) and ion flux was evaluated for different processes and compared in a “SECi vs. ion flux” plot. The almost overlapping “SECi vs. ion flux” tradeoff curves of s- EIP with constant current operation and that with constant voltage operation suggests that the two operation modes deliver closely comparable performance (Figure 17j). If the experimentally measured SECi contributions from electrolysis reactions at terminal electrodes are subtracted (Note S7, Figure 30a-Figure 30b), the SECi for s-EIP with constant current operation become less than half of that when contributions from terminal electrode electrolysis are included. These corrected values of SECi excluding contributions from terminal electrolysis can be attained with an s-EIP stack with many CEs.

[0175] Whether or not the contributions from electrolysis at terminal electrodes are considered, a 5-electrode s-EIP process with either constant current or constant voltage mode is far more efficient than conventional electro-sorption processes with solution-switch regardless of their configuration (Figure 17k, Figure 31, Table 2). Specifically, s-EIP delivered a substantially lower SECi and / or a much higher ion flux. Although the amount of salt adsorbed per half-cycle in an s-EIP process is very small (<1 mg / g salt / electrode), s- EIP’s performance is superior to conventional electro-sorption processes with high-capacity electrodes that can adsorb more >100 mg / g salt / electrode, which supports the hypothesis that electrode capacity is irrelevant to separation performance if the limitations of solution-switch can be overcome.

[0176] Conclusions. It is shown herein that sorption-based electrochemical separation can be operated using a circuit-switch strategy to enable unidirectional ion shuttling, ultrashort half- cycles, and greater performance in desalination. By controlling electron flows instead of liquid flows, the use of circuit-switch in EIP overcomes major limitations of physical solution- switch in conventional electro-sorption, which translates to operational simplicity and performance enhancement. Although EIP is demonstrated herein only for desalination, its general working principle should apply to other electro-sorption-based selective separation processes for contaminant removal as well as resource recovery and extraction, with a strong potential to enhance the separation performance in those applications. A key to developing EIP for those applications lies in fabricating EIP electrodes with ion-selective electrode materials instead of activated carbon. The results from this work challenge the general belief that salt adsorption capacity is critical to separation performance and should be prioritized in electrode development. The adoption of EIP can shift the paradigm of electrode fabrication by removing the constraint of capacity, allowing for focus on performance metrics with direct relevance to separation performance, such as ion transport resistance, electrical conductivity and, in the case of selective separation, selectivity toward the target ions.

[0177] Methods

[0178] Synthesis and characterization of working electrodes. LIQUion dispersion (LQ- 1115-1100 EW, 15% Nafion in a mixture of water and ethanol) was purchased from Ion Power, Inc, USA. Activated carbon (AC) powder with particle size of 5 ± 1 um and surface area of 1800 ±100 m2g'1was purchased from XFNANO., Ltd., USA. Titanium mesh (mesh size 100) was purchased from Jiangxin Wire Mesh Products Co., Ltd., China. Graphite paper was purchased from Beijing Jinglong Special Carbon Technology Co. China. Anion exchange polymer solution was prepared by dissolving quatemized poly(p-phenylene oxide) (QPPO, 10%) in a 1 : 1 dimethylacetamide / methanol mixture. The cation electrode (CE) slurry included 20 wt% activated carbon (AC), 40 wt% LIQUion dispersion, and 40 wt% ethanol. Anion electrode (AE) slurry was made of 10 wt activated carbon, 30 wt% QPPO solution, and 70 wt% methanol.

[0179] To fabricate the working electrodes, a slurry with ion exchange polymer and activated carbon particle was first coated on the center area of Ti-mesh current collector with a dimension of 60 mm x 60 mm, and then vacuum-dried at 60°C for 12 hours. After solvents have been removed, the cation electrode and anion electrode were pressed at 4000 psi with 140 °C and 160 °C, respectively. The mass loadings of cation electrode and anion electrode were both ~40 ± 2 mg cm'2. The electrodes were framed with waterproof tape (3M, USA). The effective area exposed on both sides of the electrode was ~8 cm2. To characterize the morphology and structure of the cation electrode, cryogenic Focused-Ion Beam Scanning Electron Microscopy (FIB-SEM, Thermo Scientific, USA) was performed using a FEI Scios DualBeam FIB / SEM system. Sample stage was cooled down to -180 °C with liquid nitrogen to minimize beam damage to the sample. Cyclic voltammetry tests were conducted using an electrochemical workstation over a voltage window of -0.7 to 0.7 V, with a scan rate of 1 mV s'1. Platinum and Ag / AgCl electrodes were utilized as the counter electrode and reference electrode, respectively. The electrolyte solution contains 1 M NaCl. The electrochemical impedances of the working electrodes were measured over a frequency range from 100 kHz to 10 mHz under open circuit potential. The mass loading of the working electrode (10 mm x 10 mm) for the electrochemical test was ~40 mg cm'2.

[0180] Assembly of symmetric and asymmetric EIP cells / stacks. The simplest s-EIP cell includes a pair of PTFE plates (as structural support), a pair of graphite terminal electrodes, two anion exchange membranes (AEMs), one cation electrode (CE), and four spacers. These components and their dimensions are described in Figure 32a-Figure 32c. The circuit-switch between charging and discharge half-cycles is controlled by two relays. The simplest a-EIP cell contains a pair of PTFE plates (as structural support), a pair of graphite terminal electrodes, two working electrodes (one cation electrode and one anion electrode) and three spacers. Multi-electrode s-EIP stacks were assembled by stacking multiple repeating units with each unit containing, from left to right, an anion exchange membrane, a spacer, a cation electrode, and another spacer. These stacked repeating units are terminated by an anion exchange membrane, sandwiched between two terminal electrode flow channels each comprising a terminal electrode and a spacer. An example of a 5-electrode s-EIP stack is illustrated in Figure 17b, with additional description of a 4-electrode s-EIP stack presented in Figure 28.

[0181] Desalination performance tests. Unless noted otherwise, all experiments were performed in semi-batch mode. Diluate (20 mL) circulates between the diluate tank and the diluate channels of the EIP cell / stack, while brine (20 mL) circulates between the brine tank and the brine channels of the EIP cell / stack. Electrolyte solution (200 mL) circulates between the terminal anode and cathode channels as well as the external electrolyte tank. The initial salt concentration of the feed solution in the diluate and brine channel s / tanks was 100 mM. The flow rate of both diluate stream and brine stream was 3.5 mL min'1. Conductivity, current and voltage were monitored with the Sensor Kit (Vernier Software & Technology, USA), which includes data collectors, conductivity sensors, current sensors, and voltage sensors. The salt concentration was calculated based on a calibration curve relating conductivity to salt concentration. Two key performance metrics were evaluated, including the ion flux, Jt(unit: pmol cm'2min'1), and the ion-specific energy consumption, SECi (unit: J pmol'1). Specifically, the ion flux can be calculated using the following equation: where c , cd, and cbare the molar salt concentration in feed, diluate, and brine streams, respectively; vdis the volume of diluate; A is the effective electrode area; and this the halfcycle time. The ion-specific energy consumption, SEC^ can be evaluated using the following equation: where Vc(i) and 7d(i) are the circuit voltages for charging and discharge at current density i, respectively; Ve(i) is the circuit voltage for the electrolytic cell at current density i; and the summation sign represents adding integrals from half-cycles over many cycles.

[0182] When the contribution from electrolysis to SECi is excluded, SECi can be evaluated using the following equation: where Ve(i) is the voltage drop due to electrolysis at current density i.

[0183] Note SI: Detrimental effects of solution-switch in conventional electro-sorption.

[0184] In conventional electro- sorption, the same flow channel accommodates the feed solution in the charging half-cycle and the receiving solution in the discharge half-cycle. Solution- switch must be performed between two consecutive half-cycles. For semi-continuous operation without emptying the cell, there are “wasted” adsorption and desorption, which undermines salt removal and energy efficiency. For example, at the end of a charging step, salts are released from the electrodes. However, there is feed solution remaining in the channel and the previously adsorbed salt ions will be released back to this portion of the feed solution, thus “wasting” part of the adsorption. At the end of a discharge step, charging will start to induce ion adsorption. However, there is receiving solution remaining in the flow channel and the previously desorbed ions will adsorb back to the electrode, thus “wasting” part of the desorption. This problem of wasted adsorption and desorption undermines salt removal and energy consumption. The mixing at the interface between the feed solution and receiving solution in the flow channel due to longitudinal diffusion also reduces the salt removal efficiency.

[0185] Even with batch operation where the flow channel is emptied in solution-switch to minimize “wasted separation” and longitudinal mixing, solution- switch still inevitably results in the unfavorable mixing of residual solution within the macropores with the new solution entering the flow channels (Figure 18a-Figure 18b). The “macropores” in the electrode serve as ion transport channels to the micropores. At the end of the charging half-cycle, the salt concentration of solution in the electrode macropores equals that of the diluate. Upon introduction of the receiving solution, mixing occurs between the residual solution in the macropores with a low concentration and the receiving solution with a higher concentration. At the end of the discharge half-cycle, the brine remaining in the electrodes macropores mixes with the feed solution entering the flow channels, raising the concentration of the solution in the feed channel beyond the feed concentration at the start of the charging halfcycle. Such mixing due to solution-switch compromises salt removal and increases energy consumption of electro- sorption for desalination.

[0186] Note S2: Operation of asymmetric EIP (a-EIP). An asymmetric EIP (a-EIP) cell requires at least one cation electrode (CE), one anion electrode (AE), and a pair of terminal electrodes (Figure 20a). Unlike s-EIP, a-EIP does not require an anion exchange membrane. The simplest a-EIP cell includes a pair of cation electrode and anion electrode, three circuits and three chambers. The electrolyte solution circulates in the chambers on both sides, which is identical to the s-EIP. In the charging half-cycle, circuit 2 is connected, charging the cation electrode and anion electrode by capacitive adsorption of cations and anions, respectively, reducing the feed channel salinity. In the discharge half-cycle, circuit 1 and circuit 3 are activated simultaneously for ion desorption (electrode discharge). Circuit 1 includes the terminal anode and anion electrode, where the anode undergoes oxygen evolution reaction (OER), and the anion electrode releases stored anions. Meanwhile, in circuit 3, the terminal cathode undergoes hydrogen evolution reaction (HER), and the cation electrode releases stored cations. Since the transfer of electrons on the terminal anode and terminal cathode must overcome the potential of the half-reaction of water electrolysis, the voltages of circuit 1 and circuit 3 are much higher than that of circuit 2 until the salinity in the feed (or diluate) channel becomes too low (Figure 20b). The calculated charging current efficiency was stable between 80% to 85%. The salt concentration in the feed solution linearly decreases over time and reaches ~0 after about 850 minutes. Unlike the s-EIP, the removed salts ultimately enter the electrolyte (volume = 200 mL). Increasing the current density from 12.5 A nr2to 50 A m’2linearly increases the ion flux of the a-EIP, while maintaining a stable current efficiency of -80% (Figure 20c).

[0187] Note S3: Contribution of electrolysis to energy consumption. The energy consumed by an s-EIP process can be attributed to desalination and water electrolysis. The desalination part includes resistive or capacitive contributions from the following phenomena, including cations entering the cation electrode (CE) from the feed (diluate) or being released from the cation electrode to the brine, anions passing through the anion exchange membrane, and ion transport in the feed (diluate) or brine, plus other contributions from electrical current due to resistances from external circuit and contact interfaces. A desalination unit includes one cation electrode, two solution chambers (dilute and brine), and one anion exchange membrane.

[0188] The electrolysis process also includes three contributions: oxygen evolution reaction (OER) at the terminal anode in the charging half-cycle, anions passing through the anion exchange membrane, and hydrogen evolution reaction (HER) at the terminal cathode in the discharge half-cycle. To subtract the contributions from electrolysis, experiments were performed using a electrolytic cell comprising a pair of terminal electrodes, anion exchange membrane, anode chamber, and cathode chamber. Currents were applied to the electrolytic cell at the same frequency as in an s-EIP process. The net energy consumption from the desalination contribution in an s-EIP process can be obtained by subtracting the energy consumption of the electrolysis cell from the total energy consumption. With a current constant, the energy consumption is proportional to voltage. The contributions from desalination to the cell voltage (VDesai) can thus be evaluated using the following equation: where Vc(i) and Vd(i) are the circuit voltages for charging and discharge at current density i, respectively; Ve(i) is the circuit voltage for the electrolytic cell at current density i; and this the half-cycle time. The summation sign represents adding integrals from half-cycles over many cycles.

[0189] Note S4: Change of diluate and brine pH. During the charging half-cycle of the s- EIP process, the terminal anode undergoes oxygen evolution reaction (OER), generating H+. With lower current densities or shorter half-cycle time, the porous electrode functions as a capacitor to enable ion adsorption (Figure 24a). Due to imperfect permselectivity of the anion exchange membrane (AEM), some H+ions produced at the terminal anode leak into the diluate stream, causing a slight decrease in diluate solution pH below the initial value (pH = 6.5) (Figure 27a, Figure 27b). In the discharging half-cycle, the charge transfer in the new circuit comprises the capacitive desorption of the porous electrode and the hydrogen evolution reaction (HER) at the terminal cathode. The OH' produced at the terminal cathode can pass through the anion exchange membrane into the brine, resulting in an alkaline pH in the brine stream. Hence, applying higher current densities or extending the half-cycle time exacerbates the electrolysis of water at the terminal electrode. Additionally, during the charging half-cycle, higher current densities and longer half-cycle times lead to an increase in the potential of the cation electrode, making water dissociation or HER more likely to occur, resulting in an increase in pH of the diluate stream. At a half-cycle time of 500s, the occurrence of electrode side reactions also causes an observable decrease in the current density (Figure 27c).

[0190] Note S5: Voltage distribution in constant current mode and current density distribution in constant voltage mode. Under constant current (CC) operation, each circuit transfers the same number of charge / ions, resulting in a linear enhancement in whole-stack ion removal rate as the number of circuits increases. In each cycle, the number of ions adsorbed and released by all cation electrodes remains consistent, thus maintaining the same saturation level of cation electrodes at the initial state of charging or discharge. For an s-EIP cell equipped with only one cation electrode, the voltages required for both charging and discharge circuits are primarily contributed by the electrolysis of water. With two cation electrodes, the new circuit formed by the two cation electrodes is dominated by capacitive adsorption / desorption (unless the electrode is saturated due to long-time charging at high current density). Therefore, for this new circuit (circuit 2), the required voltage to sustain the same current is substantially lower than that for the terminal circuit. As more cation electrodes are added to form an A-electrode s-EIP stack, circuits 2 to N-l all undergo capacitive adsorption / desorption, reducing the contribution of electrolysis at terminal electrodes to the overall energy consumption.

[0191] For constant voltage (CV) operation, the charge transfer across the cation electrodes in charging and discharging depends on the total resistance of the corresponding circuits. Similar to constant current operation, increasing the number of cation electrodes enhances the capacitive adsorption / desorption in circuits 2 to N-l. For circuits containing terminal electrodes (circuit 1 and circuit N), most energy (and voltage drop) is spent on inducing electrolysis at the terminal electrodes, and the current densities of the terminal circuits are thus relatively low. Using circuit 1 for example, all the current through terminal anode contributes to the oxygen evolution reaction (OER) and all the current through the counter electrode CE (CE #1, as the cathode) contributes to capacitive adsorption of Na Because the voltage drop for OER is significant compared to the applied voltage, the current density is low, and few ions are stored in the CE at the end of its charging half-cycle. When the CE is switched to become the anode, the anodic CE undergoes both capacitive desorption and OER, with the former consuming less energy and the later consuming more energy per charge transferred. Therefore, with the same applied voltage, the current density for circuit 2 is higher than that of circuit 1, and even more ions are stored in the cathodic CE (CE #2) of circuit 2. This cathodic CE of circuit 2 will later become the anodic CE of circuit 3 and undergoes even less electrolysis reaction and more capacitive adsorption, resulting in an even higher current density than circuit 2.

[0192] A similar analysis can also apply to the cathodic terminal circuit (circuit N) and its adjacent circuits. Briefly, the cathodic terminal circuit has the lowest current density because the of its largest contribution of electrolysis to the circuit voltage. Circuit N-l has a higher current density than the cathodic terminal circuit because of the larger contribution of capacitive adsorption / desorption to circuit voltage. Combining the behaviors of anodic and cathodic terminal circuits and their adjacent circuits explain the roughly symmetric distribution of current density in a multi-electrode s-EIP stack. Under the same voltage, the CEs are better utilized (i.e., undergoing more capacitive adsorption / desorption and less electrolysis) the further away they are located from the terminal electrodes. The behavior of a multi-stack s-EIP explains the concave profile of current density distribution observed in Figure 17h. It also explains the enhancement of overall current density as the number of CEs increases, as having more CEs leads to a large percentage of CEs away from the terminal electrodes.

[0193] Note S6: Specific energy consumption of multi-electrode s-EIP. In constant current mode, increasing the number of electrodes does not alter the voltage of the middle circuit. The total energy consumption of s-EIP exhibits a linear relationship with the number of electrodes (Figure 30a). Having zero electrodes represents a single electrolysis cell (including two terminal electrodes, one anion exchange membrane, and two solution channels). Regardless of the number of cation electrodes used, the calculated average circuit voltage is approximately 0.3 V at a current density of 8.1 A nr2. As the number of s-EIP electrodes increases, SECi gradually decreases and tends to approach a limit, which is the SECi calculated after subtracting the energy consumption of electrolysis (red dash line in Figure 30b). Thus, subtracting the energy consumption of electrolysis allows for the calculation of the SECi of s-EIP with any number of electrodes. Similar behavior was observed for constant voltage mode with which calculated SECi decreases with increasing number of electrodes due to the “dilution” of the detrimental impact of electrolysis (Figure 30b). Like constant current mode, it is expected that the SECi of s-EIP in a constant voltage mode will also approach a limit (that depends on applied voltage) as the number of electrodes continues to increase. Unlike constant current mode, however, it is technically challenging to subtract the electrolysis contributions from the SECi measured using an s-EIP system with a small number of electrodes in constant voltage mode. This is because the current density varies over time in a constant voltage mode. To subtract the contribution of terminal electrode electrolysis to overall circuit voltage, electrolysis experiments need to be performed using the time profile of current density that is consistent with that observed in constant voltage mode s-EIP experiments, which is technically challenging.

[0194] Table 1: Summary of literature data on charging time.

[0195] CDI: capacitive deionization; MCDI: membrane capacitive deionization:

[0196] Table 2: Summary of the literature data in Figure 17k.

[0197]

[0198] Note: R-CDI: rocking charging capacitive deionization; # It is assumed that the discharge time is the same as the charging time. Then, the ion flux obtained by recalculating from the total time; * SEC calculated by subtracting the energy consumed by electrolysis of water.

[0199] References

[0200] 1. Gao, M., Liang, W ., Yang, Z., Ao, T. & Chen, W. Flexible ultrathin Nitrogen- Doped carbon mediates the surface charge redistribution of a hierarchical tin disulfide nanoflake electrode for efficient capacitive deionization. J. Colloid Interface Sci. 650, 1244- 1252 (2023). 2. Shi, M. et al. Simple control of carbon mass loading in capacitive deionization for efficient deionized water production. Sep. Purif. Technol. 301, 121962 (2022).

[0201] 3. Wang, Y. et al. Amino acids functionalized vascular-like carbon fibers for efficient capacitive deionization. J. Colloid Interface Sci. 649, 97-106 (2023).

[0202] 4. Tang, Y. et al. Hollow mesoporous carbon nanospheres space-confining ultrathin nanosheets superstructures for efficient capacitive deionization. J. Colloid Interface Sci. 626, 1062-1069 (2022).

[0203] 5. Yan, L. et al. Ag-decorated monolithic carbon sponge with porous directional frameworks for chloride removal in flow-through capacitive deionization. Sep. Purif. Technol. 322, 124210 (2023). 6. Nguyen, T. K. A., Wang, T.-H. & Doong, R. Architectures of flower-like MoS2 nanosheet coated N-doped carbon sphere electrode materials for enhanced capacitive deionization. Desalination 540, 115979 (2022).

[0204] 7. Ren, P. et al. Conductive carbon additives: Friend or foe of capacitive deionization with activated carbon? Carbon N. Y. 213, 118191 (2023).

[0205] 8. He, M. et al. Hierarchical N-Doped porous 3D network electrode with enhanced capacitive deionization performance. Sep. Purif. Technol. 297, 121558 (2022).

[0206] 9. Feng, B., Khan, Z. U. & Khan, W. U. 3D graphene-supported N-doped hierarchically porous carbon for capacitive deionization of saline water. Environ. Sci. Nano 10, 1163-1176 (2023).

[0207] 10. Xu, H. et al. Fluorine-induced porous carbon nanosheets with abundant edgedefects for high-performance capacitive deionization. Desalination 538, 115919 (2022).

[0208] 11. Narayanan, A. et al. Designing of a Free-Standing Flexible Symmetric Electrode Material for Capacitive Deionization and Solid-State Supercapacitors. ACS Sustain. Chem. Eng. 11, 3750-3759 (2023).

[0209] 12. Ezzati, M., Hekmat, F., Shahrokhian, S. & Unalan, H. E. Titanium disulfide decorated hollow carbon spheres towards capacitive deionization. Desalination 533, 115766 (2022).

[0210] 13. Zhang, B. et al. Flexible 5-MnO2 nanosheet-infixed porous carbon nanofibers for capacitive deionization. Electrochim. Acta 443, 141929 (2023).

[0211] 14. Cai, Y., Zhang, L., Fang, R., Wang, Y. & Wang, J. Maximized ion accessibility in the binder-free layer-by-layer MXene / CNT film prepared by the electrophoretic deposition for rapid hybrid capacitive deionization. Sep. Purif. Technol. 292, 121019 (2022).

[0212] 15. Qiang, H., Shi, M., Wang, F. & Xia, M. Green synthesis of high N-doped hierarchical porous carbon nanogranules with ultra-high specific surface area and porosity for capacitive deionization. Sep. Purif. Technol. 308, 122918 (2023).

[0213] 16. Lei, J., Xiong, Y., Yu, F. & Ma, J. Flexible self-supporting CoFe- LDH / MXene film as a chloride ions storage electrode in capacitive deionization. Chem. Eng. J. 437, 135381 (2022).

[0214] 17. Li, R. et al. Laser-induced 3D porous flower-like Fe2O3 / reduced graphene oxide modified nickel foam electrode for enhanced capacitive deionization. Desalination 548, 116286 (2023). 18. Yu, J. et al. Enhanced capacitive deionization of a low-concentration brackish water with protonated carbon nitride-decorated graphene oxide electrode. Chemosphere 293, 133580 (2022).

[0215] 19. Cao, Y. et al. Large gap cob alt- vanadium oxide structure encapsulated in porous carbon for high performance capacitive deionization. Sep. Purif. Technol. 306, 122709 (2023).

[0216] 20. Chen, J. et al. Fungal hypha-derived freestanding porous carbon pad as a high- capacity electrode for water desalination in membrane capacitive deionization. Chem. Eng. J. 433, 133781 (2022).

[0217] 21. Liu, R., Yao, S., Shen, Y., Tian, Y. & Zhang, Q. Preparation of N-Doped Layered Porous Carbon and Its Capacitive Deionization Performance. Materials 16, (2023).

[0218] 22. Wang, S. et al. Freestanding Ti3C2Tx MXene / Prussian Blue Analogues Films with Superior Ion Uptake for Efficient Capacitive Deionization by a Dual Pseudocapacitance Effect. ACS Nano 16, 1239-1249 (2022).

[0219] 23. Shi, M. et al. Green double organic salt activation strategy for one-step synthesis of N-doped 3D hierarchical porous carbon for capacitive deionization. Chem. Eng. J. 453, 139764 (2023).

[0220] 24. Szabo, L. et al. Tailoring the Structure of Chitosan-Based Porous Carbon Nanofiber Architectures toward Efficient Capacitive Charge Storage and Capacitive Deionization. ACS Appl. Mater. Interfaces 14, 4004-4021 (2022).

[0221] 25. Liu, N. et al. Ti3C2-MXene Partially Derived Hierarchical 1D / 2D TiO2 / Ti3C2 Heterostructure Electrode for High-Performance Capacitive Deionization. Adv. Sci. 10, 2204041 (2023).

[0222] 26. Cao, R. et al. Improving capacitive deionization performance by using 02 plasma modified carbon black. Chem. Eng. J. 451, 138530 (2023).

[0223] 27. Molaei Aghdam, A., Mikaeili Chahartagh, N. & Delfani, E. High-Efficient Capacitive Deionization Using Amine-Functionalized ZIF-67@ 2D MXene: Toward Ultrahigh Desalination Performance. Adv. Mater. Technol. 8, 2300628 (2023).

[0224] 28. SONG, X. et al. Exceptional capacitive deionization desalination performance of hollow bowl-like carbon derived from MOFs in brackish water. Sep. Purif. Technol. 278, 119550 (2021). 29. Nguyen, N. T. et al. Water hyacinth as a green and sustainable material for carbon aerogel electrodes utilized in membrane capacitive deionization. CLEAN - Soil, Air, Water 51, 2200396 (2023).

[0225] 30. Yasin, A. S. et al. Design of zinc oxide nanoparticles and graphene hydrogel co-incorporated activated carbon for efficient capacitive deionization. Sep. Purif. Technol. 277, 119428 (2021).

[0226] 31. Zhao, C. et al. Titanium Dioxide Nanocluster Modified Lignite-Based Nanoporous Carbon for Capacitive Deionization. J. Electrochem. Soc. 170, 13503 (2023).

[0227] 32. Taha, M. M. et al. Controlled fabrication of mesoporous electrodes with unprecedented stability for water capacitive deionization under harsh conditions in large size cells. Desalination 511, 115099 (2021).

[0228] 33. Sun, J. et al. Enhanced capacitive deionization properties of activated carbon doped with carbon nanotube-bridged molybdenum disulfide. Chemosphere 310, 136740 (2023).

[0229] 34. Cai, Y., Wang, Y., Zhao, Y., Wang, S. & Wang, jixiao. Synergetic effects of different ion-doped polypyrrole layer coupled with P-cyclodextrin-derived hollow bottle-like carbon supporting framework for enhanced capacitive deionization performance. Electrochim. Acta 388, 138555 (2021).

[0230] 35. Zhang, C. et al. Boosting Capacitive Deionization Performance of Commercial Carbon Fibers Cloth via Structural Regulation Based on Catalytic-Etching Effect. ENERGY Environ. Mater. 6, el2276 (2023).

[0231] 36. Sayed, D. M., El-Deab, M. S. & Allam, N. K. Multi-walled vanadium oxide nanotubesmodified3D microporous bioderived carbon as novel electrodes for hybrid capacitive deionization. Sep. Purif. Technol. 266, 118597 (2021).

[0232] 37. Li, C.-P., Wu, Y.-Q., Gao, L.-X., Zhang, D.-Q. & An, Z.-X. Lignin-derived carbon nanofibers with the micro-cracking structure for high-performance capacitive deionization. J. Environ. Chem. Eng. 10, 108952 (2022).

[0233] 38. Zhang, H. et al. Nitrogen, phosphorus co-doped eave-like hierarchical porous carbon for efficient capacitive deionization. J. Mater. Chem. A 9, 12807-12817 (2021).

[0234] 39. Chen, C. et al. Enhanced electrochemical and capacitive deionization performances of single-layer graphene oxide / nitrogen-doped porous carbon / activated carbon fiber composite electrodes. J. Environ. Chem. Eng. 10, 108696 (2022). 40. Santos, C. et al. Low-energy consumption, free-form capacitive deionization through nanostructured networks. Carbon N. Y. 176, 390-399 (2021).

[0235] 41. Datar, S. D., Mane, R. S. & Jha, N. Zeolitic imidazolate framework-67 derived porous carbon electrodes for efficient capacitive deionization. Appl. Surf. Sci. 604, 154550 (2022).

[0236] 42. Wang, X. et al. Hierarchical MXene / Polypyrrole-D ecorated Carbon Nanofibers for Asymmetrical Capacitive Deionization. ACS Appl. Mater. Interfaces 14, 53150-53164 (2022).

[0237] 43. Liu, X. et al. Core-Shell MOF@COF Motif Hybridization: Selectively Functionalized Precursors for Titanium Dioxide Nanoparticle-Embedded Nitrogen-Rich Carbon Architectures with Superior Capacitive Deionization Performance. Chem. Mater. 33, 1657-1666 (2021).

[0238] 44. Tran, N. A. T., Moon, J., Kim, J. H., Park, J. T. & Cho, Y. NiCu bimetallic metal-organic framework to improve the desalination performance of capacitive deionization. Sep. Purif. Technol. 324, 124519 (2023).

[0239] 45. Li, Z., Mao, S., Yang, Y., Sun, Z. & Zhao, R. Controllable synthesis of a hollow core-shell Co-Fe layered double hydroxide derived from Co-MOF and its application in capacitive deionization. J. Colloid Interface Sci. 585, 85-94 (2021).

[0240] 46. Tang, Y. et al. Design of Uniform Hollow Carbon Nanoarchitectures: Different Capacitive Deionization between the Hollow Shell Thickness and Cavity Size. Adv. Sci. 10, 2206960 (2023).

[0241] 47. Feng, J., Liu, L. & Meng, Q. Enhanced electrochemical and capacitive deionization performance of metal organic framework / holey graphene composite electrodes. J. Colloid Interface Sci. 582, 447-458 (2021).

[0242] 48. Zhang, W. et al. Biobased polyporphyrin derived porous carbon electrodes for highly efficient capacitive deionization. Chemosphere 291, 133113 (2022).

[0243] 49. Liu, L. et al. Three-dimensional electrode design with conductive fibers and ordered macropores for enhanced capacitive deionization performance. Desalination 498, 114794 (2021).

[0244] 50. Chen, Z. et al. Dual-confinement effect in metal oxide nanoparticles / MXene- reduced graphene oxide for high capacitive deionization performance. Desalination 564, 116733 (2023). 51. Gong, X. et al. Defect-rich hierarchical porous carbon prepared by homogeneous activation for high performance capacitive deionization. Desalination 564, 116766 (2023).

[0245] 52. Zhang, W. et al. Efficient capacitive deionization with 2D / 3D heterostructured carbon electrode derived from chitosan and g-C3N4 nanosheets. Desalination 538, 115933 (2022).

[0246] 53. Dinh, V. C. et al. Development of a capacitive deionization stack with highly porous oxygen-doped carbon electrodes for brackish water desalination in remote coastal areas. Mater. Chem. Phys. 307, 128165 (2023).

[0247] 54. Wang, S., Chen, D., Zhang, Z.-X., Hu, Y. & Quan, H. Mesopore dominated capacitive deionization of N-doped hierarchically porous carbon for water purification. Sep. Purif. Technol. 290, 120912 (2022).

[0248] 55. Zhang, C. et al. Great truths are always simple: Preoxidation-tuned cellulosederived carbon fibers achieving ultrahigh areal desalination capacity in flow-through capacitive deionization. Chem. Eng. J. 471, 144526 (2023).

[0249] 56. Deng, D. et al. A novel layered activated carbon with rapid ion transport through chemical activation of chestnut inner shell for capacitive deionization. Desalination 531, 115685 (2022).

[0250] 57. Shi, M. et al. High-yield green synthesis of N-doped hierarchical porous carbon by Nitrate-Mediated organic salt activation strategy for capacitive Deionization: Universality and commerciality. Chem. Eng. J. 471, 144465 (2023).

[0251] 58. Zhang, G. et al. Interconnected N-doped MXene spherical shells for highly efficient capacitive deionization. Environ. Sci. Nano 9, 204-213 (2022).

[0252] 59. Li, C.-P. et al. Preparation of carbon foam from depolymerization-reforming lignin for capacitive deionization. Desalination 559, 116656 (2023).

[0253] 60. Wei, D. et al. Enhanced Pseudo-Capacitance Process in Nanoarchitectural Layered Double Hydroxide Nanoarrays Hollow Nanocages for Improved Capacitive Deionization Performance. ACS Appl. Mater. Interfaces 15, 24427-24436 (2023).

[0254] 61. Rangaraj, V. M., Yoo, J.-L, Song, J.-K. & Mittal, V. Three-dimensional (3D) MnMoO4@g-C3N4 / CNT hybrid composite electrode for hybrid capacitive deionization. Sep. Purif. Technol. 317, 123898 (2023). 62. Wang, D. et al. Internal Electric Field Induced by Superexchange Interaction on Mn4+-O2--Ni2+ Unit Enables Highly Efficient Hybrid Capacitive Deionization. Small 19, 2301717 (2023).

[0255] 63. Liu, S. et al. Preparation of nitrogen-doped hierarchical porous carbon electrodes for high performance capacitive deionization. Ionics (Kiel). 29, 2935-2945 (2023).

[0256] 64. Han, D.-C. et al. Efficient dual-ions hybrid capacitive system for superior deionization with enhanced kinetics match. Electrochim. Acta 436, 141380 (2022).

[0257] 65. Halabaso, E. R., Somnath Dayma, P., W. L. Salvacion, J. & Doong, R. Copper tungstate deposited reduced graphene oxide nanocomposite for highly efficient capacitive deionization. J. Electroanal. Chem. 938, 117441 (2023).

[0258] 66. Gao, L., Dong, Q., Hu, C. & Qiu, J. Surfactant-assisted self-assembly of flower-like ultrathin vanadium disulfide nanosheets for enhanced hybrid capacitive deionization. J. Colloid Interface Sci. 627, 1011-1020 (2022).

[0259] 67. Zhang, Y. et al. Core-shell 2D nanoarchitectures: engineering N, P-doped graphitic carbon / MXene heterostructures for superior capacitive deionization. J. Mater. Chem. A 11, 14356-14365 (2023).

[0260] 68. Du, J. et al. Synergistic effect of intercalation and EDLC electrosorption of 2D / 3D interconnected architectures to boost capacitive deionization for water desalination via MoSe2 / mesoporous carbon hollow spheres. Water Res. 235, 119831 (2023).

[0261] 69. Gang, H. et al. Surface redox pseudocapacitance boosting Fe / Fe3C nanoparticles-encapsulated N-doped graphene-like carbon for high-performance capacitive deionization. J. Colloid Interface Sci. 638, 252-262 (2023).

[0262] 70. Liu, X. et al. Unlocking Enhanced Capacitive Deionization of NaTi2(PO4)3 / Carbon Materials by the Yolk-Shell Design. J. Am. Chem. Soc. 145, 9242- 9253 (2023).

[0263] 71. Zhang, S., Wang, Y., Zhang, L., Fang, R. & Li, J. Ion-doped polypyrrole coupled core-shell hierarchical porous carbon electrode material with high desalination capacity for capacitive deionization. J. Environ. Chem. Eng. 11, 109684 (2023).

[0264] 72. Zhang, H., Tian, J., Cui, X., Li, J. & Zhu, Z. Highly mesoporous carbon nanofiber electrodes with ultrahigh specific surface area for efficient capacitive deionization. Carbon N. Y. 201, 920-929 (2023). 73. Fu, Z. et al. Local Electric Field Induced by Atomic-Level Donor- Acceptor Couple of O Vacancies and Mn Atoms Enables Efficient Hybrid Capacitive Deionization. Small 19, 2205666 (2023).

[0265] 74. Zhang, Y., Bu, X., Dong, X., Wang, Y. & Chen, Z. Nanofiltration combined with membrane capacitive deionization for efficient classification and recovery salts from simulated coal chemical industrial wastewater. Sep. Purif. Technol. 322, 124156 (2023).

[0266] 75. Xu, L. et al. Carbon nanotube bridged nickel hexacyanoferrate architecture for high-performance hybrid capacitive deionization. J. Colloid Interface Sci. 630, 372-381 (2023).

[0267] 76. Tu, X. et al. Ternary-metal Prussian blue analogues as high-quality sodium ion capturing electrodes for rocking-chair capacitive deionization. J. Colloid Interface Sci. 642, 680-690 (2023).

[0268] 77. Li, B. et al. Polyaniline-decorated porous carbons with engineered meso / macrochannels for high performance capacitive deionization. J. Mater. Chem. A 10, 24905-24914 (2022).

[0269] 78. Wang, K., Liu, Y., Xu, X., Jiao, Y. & Pan, L. In situ synthesis of ultrasmall NaTi2(PO4)3 nanocube decorated carbon nanofiber network enables ultrafast and superstable rocking-chair capacitive deionization. Chem. Eng. J. 463, 142394 (2023).

[0270] 79. Kong, W. et al. Nitrogen-doped hierarchical porous carbon obtained from silk cocoon for capacitive deionization. Diam. Relat. Mater. 129, 109388 (2022).

[0271] 80. Bao, Y., Hao, J., Zhang, S., Zhu, D. & Li, F. Structural / Compositional- Tailoring of Nickel Hexacyanoferrate Electrodes for Highly Efficient Capacitive Deionization. Small 19, 2300384 (2023).

[0272] 81. El-Deen, A. G. et al. Polystyrene sulfonate coated activated graphene aerogel for boosting desalination performance using capacitive deionization. Sep. Purif. Technol. 299, 121760 (2022).

[0273] Example 4 - Devices and Methods for Electrochemical Ion Pumping

[0274] The devices and methods described herein can be used for (1) desalination and (2) selective separation to either remove or enrich specific ions using electrodes that can adsorb those ions with specificity. The devices and methods described herein have advantages over capacitive deionization or conventional electrosorption (a process that has been commercialized) and even advantages over electrodialysis in some areas of selective separation.

[0275] An advantage of the devices and methods described herein is the way they operate, using "circuit switch" to replace "flow switch" to overcome many limitations in flow switch - based electro-sorption systems.

[0276] In some examples, the devices can have a terminal electrode-free design. A plate-and- frame stack has two terminal electrodes where electrolysis occurs to maintain the overall charge balance. Electrolysis typically costs substantially more energy than the capacitive adsorption / desorption occurring in the electrodes sandwiched between the two terminal electrodes. Terminal electrode-free cell design is a tubular cell design with the goal of eliminating the terminal electrode. In such a design, all the capacitive electrodes (or ion exchange membranes in symmetric EIP) are arranged in a way that forms a circular crosssection. The working mechanism of such a system is the same as the asymmetric and symmetric EIP described above, but without the terminal electrodes and the associated electrolysis.

[0277] An example terminal electrode-free (e.g., circular) asymmetric electrochemical ion pump (EIP) is shown in Figure 33.

[0278] An example terminal electrode-free (e.g., circular) symmetric electrochemical ion pump (EIP) is shown in Figure 34.

[0279] Other advantages which are obvious and which are inherent to the invention will be evident to one skilled in the art. It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

[0280] The devices and methods of the appended claims are not limited in scope by the specific devices and methods described herein, which are intended as illustrations of a few aspects of the claims and any devices and methods that are functionally equivalent are intended to fall within the scope of the claims. Various modifications of the devices and methods in addition to those shown and described herein are intended to fall within the scope of the appended claims. Further, while only certain representative method steps disclosed herein are specifically described, other combinations of the method steps also are intended to fall within the scope of the appended claims, even if not specifically recited. Thus, a combination of steps, elements, components, or constituents may be explicitly mentioned herein or less, however, other combinations of steps, elements, components, and constituents are included, even though not explicitly stated.

Claims

CLAIMSWhat is claimed is:

1. A device comprising a plurality of fluidly independent circuits: the plurality of fluidly independent circuits comprising alternating circuits of a charging circuit and a discharging circuit, wherein the total number of circuits in the device is 3 or more; wherein each charging circuit comprises an anion electrode, a cation electrode, and a feed solution, the feed solution being sandwiched between and in electrochemical contact with the anion electrode and the cation electrode; wherein each discharging circuit comprises a cation electrode, an anion electrode, and a receiving solution, the receiving solution being sandwiched between and in electrochemical contact with the cation electrode and the anion electrode; wherein the cation electrode is shared between a charging circuit and the following discharging circuit, and the anion electrode is shared between a discharge circuit and the following charging circuit, such that each pair of charging and discharging circuits includes three total electrodes, each pair of charging and discharging circuits further comprising a first electrical relay switch and a second electrical relay switch, each charging circuit and discharging circuit being fluidly independent; each cation electrode being configured to adsorb and / or intercalate a target ion (e.g., a target cation); each feed solution being the same or different and each comprising the target ion at an initial concentration; each receiving solution comprising a counterion for the target ion and comprising the target ion at a preliminary concentration; wherein: when the device is operated in a charging mode, then the anion electrode and the cation electrode of each charging circuit are electrically connected to each other and a voltage source via the first and second electrical relay switches, and at least a portion of the target ion concentration is depleted from each of the feed solutions by being adsorbed and / or intercalated into the cation electrodes, such that the concentration of the target ion in the feed solutions decreases relative to the initial concentration; andwhen the device is operated in a discharging mode, then the cation electrode and the anion electrode of each discharging circuit are electrically connected to each other and the voltage source via the first and second electrical relay switches, at least a portion of the target ion adsorbed and / or intercalated in the cation electrode is released into the receiving solution, such that the concentration of the target ion in the receiving solution increases relative to the preliminary concentration.

2. A device comprising a plurality of fluidly independent circuits: wherein the total number of circuits in the device is 2 or more; wherein each circuit comprises a receiving channel and a feed channel, the receiving channel being fluidly independent from the feed channel; the receiving channel defined by a first cation electrode and an anion exchange membrane, the receiving channel containing a receiving solution, such that the receiving solution is sandwiched between and in electrochemical contact with the first cation electrode and the anion exchange membrane; the feed channel defined by the anion exchange membrane and a second cation electrode, the feed channel containing a feed solution, the feed solution being sandwiched between and in electrochemical contact with the anion exchange membrane and the second cation electrode; each pair of circuits further comprising a first electrical relay switch and a second electrical relay switch, wherein each cation electrode is shared between two neighboring circuits, but is only connected to one circuit in every half cycle via the first and second electrical relay switches; each cation electrode being configured to adsorb and / or intercalate a target ion (e.g., a target cation); each feed solution being the same or different and each comprising the target ion at an initial concentration; each receiving solution comprising a counterion for the target ion and comprising the target ion at a preliminary concentration; wherein each cation electrode functions as the cathode of one circuit to adsorb the target ion from the feed solution in its charging half-cycle, and as the anode of another circuit to release the target ions to the receiving solution in its discharge half-cycle, the switch of a cation electrode between two adjacent circuits is achieved by electrical relay switches;such that when a circuit is operated in a charging mode, then the target ions from the feed solution contacting one side of the cation electrode are electrochemically absorbed by said side of the cation electrode, and when the circuit is operated in discharging mode, then the target ions are released from the cation electrode into the receiving solution contacting the opposite side of the cation electrode; wherein: when a circuit is operated in a charging mode, then the first cation electrode and the second cation electrode are electrically connected to each other and a voltage source via the first and second electrical relay switches, the voltage source being configured to apply a voltage to the first and second cation electrodes such that at least a portion of the target ion concentration is depleted from each of the feed solutions by being adsorbed and / or intercalated into the cation electrode, such that the concentration of the target ion in the feed solutions decreases relative to the initial concentration; and when the circuit is operated in a discharging mode, then the first cation electrode and the second cation electrode are electrically connected to each other and a voltage source via the first and second electrical relay switches, the voltage source being configured to apply a voltage to the first and second cation electrodes such that at least a portion of the target ion adsorbed and / or intercalated in the cation electrode is released into the receiving solution, such that the concentration of the target ion in the receiving solution increases relative to the preliminary concentration.

3. The device of claim 1 or claim 2, wherein the target ion comprises a critical mineral.

4. The device of any one of claims 1-3, wherein the target ion comprises a metal, such as an alkaline metal, a transition metal, a rare earth metal, or a combination thereof.

5. The device of any one of claims 1-4, wherein the target ion comprises sodium, lithium, nickel, copper, cobalt, or a combination thereof.

6. The device of any one of claims 1-5, wherein the target ion comprises sodium, lithium, or a combination thereof.

7. A device comprising a plurality of fluidly independent circuits: the plurality of fluidly independent circuits comprising alternating circuits of a charging circuit and a discharging circuit, wherein the total number of circuits in the device is 3 or more;wherein each charging circuit comprises a cation electrode, an anion electrode, and a feed solution, the feed solution being sandwiched between and in electrochemical contact with the anion electrode and the cation electrode; wherein each discharging circuit comprises an anion electrode, a cation electrode, and a receiving solution, the receiving solution being sandwiched between and in electrochemical contact with the cation electrode and the anion electrode; wherein the anion electrode is shared between a charging circuit and the following discharging circuit, and the cation electrode is shared between a discharge circuit and the following charging circuit, such that each pair of charging and discharging circuits includes three total electrodes, each pair of charging and discharging circuits further comprising a first electrical relay switch and a second electrical relay switch, each charging circuit and discharging circuit being fluidly independent; each anion electrode being configured to adsorb and / or intercalate a target ion (e.g., a target anion); each feed solution being the same or different and each comprising the target ion at an initial concentration; each receiving solution comprising a counterion for the target ion and comprising the target ion at a preliminary concentration; wherein: when the device is operated in a charging mode, then the anion electrode and the cation electrode of each charging circuit are electrically connected to each other and a voltage source via the first and second electrical relay switches, and at least a portion of the target ion concentration is depleted from each of the feed solutions by being adsorbed and / or intercalated into the anion electrodes, such that the concentration of the target ion in the feed solutions decreases relative to the initial concentration; and when the device is operated in a discharging mode, then the cation electrode and the anion electrode of each discharging circuit are electrically connected to each other and the voltage source via the first and second electrical relay switches, at least a portion of the target ion adsorbed and / or intercalated in the anion electrode is released into the receiving solution, such that the concentration of the target ion in the receiving solution increases relative to the preliminary concentration.

8. A device comprising a plurality of fluidly independent circuits:wherein the total number of circuits in the device is 2 or more; wherein each circuit comprises a receiving channel and a feed channel, the receiving channel being fluidly independent from the feed channel; the receiving channel defined by a first anion electrode and a cation exchange membrane, the receiving channel containing a receiving solution, such that the receiving solution is sandwiched between and in electrochemical contact with the first anion electrode and the cation exchange membrane; the feed channel defined by the cation exchange membrane and a second anion electrode, the feed channel containing a feed solution, the feed solution being sandwiched between and in electrochemical contact with the cation exchange membrane and the second anion electrode; each pair of circuits further comprising a first electrical relay switch and a second electrical relay switch, wherein each anion electrode is shared between two neighboring circuits, but is only connected to one circuit in every half cycle via the first and second electrical relay switches; each anion electrode being configured to adsorb and / or intercalate a target ion (e.g., a target anion); each feed solution being the same or different and each comprising the target ion at an initial concentration; each receiving solution comprising a counterion for the target ion and comprising the target ion at a preliminary concentration; wherein each anion electrode functions as the cathode of one circuit to adsorb the target ion from the feed solution in its charging half-cycle, and as the anode of another circuit to release the target ions to the receiving solution in its discharge half-cycle, the switch of an anion electrode between two adjacent circuits is achieved by electrical relay switches; such that when a circuit is operated in a charging mode, then the target ions from the feed solution contacting one side of the anion electrode are electrochemically absorbed by said side of the anion electrode, and when the circuit is operated in discharging mode, then the target ions are released from the cation electrode into the receiving solution contacting the opposite side of the anion electrode; wherein: when a circuit is operated in a charging mode, then the first anion electrode and the second anion electrode are electrically connected to each other and a voltage source via thefirst and second electrical relay switches, the voltage source being configured to apply a voltage to the first and second anion electrodes such that at least a portion of the target ion concentration is depleted from each of the feed solutions by being adsorbed and / or intercalated into the anion electrode, such that the concentration of the target ion in the feed solutions decreases relative to the initial concentration; and when the circuit is operated in a discharging mode, then the first anion electrode and the second anion electrode are electrically connected to each other and a voltage source via the first and second electrical relay switches, the voltage source being configured to apply a voltage to the first and second anion electrodes such that at least a portion of the target ion adsorbed and / or intercalated in the anion electrode is released into the receiving solution, such that the concentration of the target ion in the receiving solution increases relative to the preliminary concentration.

9. The device of any one of claims 1-8, wherein each of the feed solutions and / or receiving solutions further comprises a solvent, such as water (e.g., each of the feed solutions and / or receiving solutions is an aqueous solution).

10. The device of any one of claims 1-9, wherein the feed solution is derived from natural sources or a waste streams.

11. The device of any one of claims 1-10, wherein the feed solution comprises brackish water, salt lake brine, geothermal brine, seawater, oil and / or gas produced water, mining wastewater, leaching solution in battery recovery, or a combination thereof.

12. The device of any one of claims 1-11, wherein the plurality of circuits are stacked or arranged linearly, and the device further comprising one or more terminal electrodes (e.g., two or more terminal electrodes).

13. The device of any one of claims 1-11, wherein the plurality of circuits are stacked or arranged circularly (e.g., to form at least part of a circle).

14. The device of any one of claims 1-13, wherein the cation and / or anion electrodes enable fast transport of the target ion from the feed solution to the receiving solution, have minimal macropores to avoid direct mixing between the feed solution and the receiving solution, are electrically conductive to minimize resistive energy loss, or a combination thereof.

15. A method of use of the device of any one of claims 1-14.

16. The method of claim 15, wherein the method comprises separating the target ion from the feed solution.

17. The method of claim 15 or claim 16, wherein the method comprises critical mineral extraction, for example from natural sources or recovery from waste streams.

18. The method of any one of claims 15-17, wherein the method comprises desalination.

19. The method of any one of claims 15-18, wherein each of the feed solutions and / or receiving solutions further comprises a solvent, such as water (e.g., each of the feed solutions and / or receiving solutions is an aqueous solution).

20. The method of any one of claims 15-19, wherein the feed solution is derived from natural sources or a waste streams.

21. The method of any one of claims 15-20, wherein the feed solution comprises brackish water, salt lake brine, geothermal brine, seawater, oil and / or gas produced water, mining wastewater, leaching solution in battery recovery, or a combination thereof.

22. The method of any one of claims 15-21, wherein the method comprises the electrochemical adsorption of the target ions from the feed solution contacting one side of the cation or anion electrode, followed by the subsequent release of the target ions to the receiving solution contacting the opposite side of the cation or anion electrode.

23. The method of any one of claims 15-22, wherein the method is continuous or semi- continuous.

24. The method of any one of claims 15-23, wherein the charge / discharge half cycles are short.

25. The method of any one of claims 15-24, wherein the charge / discharge half cycles have a cycle time of from 0.1 seconds to 100 minutes.

26. The method of any one of claims 15-25, wherein the charge / discharge half cycles have a cycle time of from 0.1 seconds to 10 minutes or from 0.1 seconds to 1 minute.

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