Desalination battery electrodes containing Prussian blue compounds

Abstract

The present invention relates to a desalination cell electrode comprising a Prussian blue compound. The desalination cell comprises: an electrode comprising a material having at least one compound of the following formula: x M I y M II z (CN)6, where A is Na, Li or K, 0≤x≤2, M I It is the first metal, M II is a second metal, 1≤y, and z≤2. The material is configured to reduce calcium carbonate formation and / or carbon dioxide gas formation during operation of the desalination cell. The first metal may be Fe, Mn, Co, Sc, Ti, Cr, or Zn. The second metal is Fe, Mn, Co, Sc, Ti, Cr, or Zn. The first metal may be different from the second metal.

Description

Technical Field

[0001] The present disclosure relates to desalination cell electrodes comprising a Prussian blue compound configured to reduce calcium carbonate formation and / or carbon dioxide gas formation. Background Art

[0002] As the world's population increases, the demand for high-quality drinking water is growing. However, there are limited sources of freshwater on land, some of which are currently severely depleted. The quality of other sources can be compromised by industrial and agricultural processes, as well as urban expansion.

[0003] In view of the above, technologies are being developed to obtain fresh water from abundant ocean water sources. However, these water sources are saline water containing high concentrations of dissolved salts, making them unsuitable for human consumption, agricultural use, or industrial processes. Saline water needs to be desalinated to reduce its concentration of dissolved solids (e.g., salt) so that it can be used as a drinking water source.

[0004] Efforts to desalinate water date back thousands of years. For example, the earliest recorded attempts involved evaporation of brine by sailors at sea. The earliest large-scale modern desalination methods of multi-stage flash evaporation were developed in the mid-20th century. However, desalination processes still suffer from common problems. These problems include, but are not limited to, relatively high energy requirements, environmental issues, and material problems associated with corrosion of membranes. These problems have prevented desalination from being widely used to provide drinking water from saltwater resources. Summary of the invention

[0005] According to one embodiment, a desalination cell is disclosed. The desalination cell comprises: an electrode comprising a material having at least one compound of the following formula: x M I y M II z (CN)6, where A is Na, Li or K, 0 ≤ x ≤ 2, M I It is the first metal, M IIis a second metal, 1 ≤ y and z ≤ 2. The material is configured to reduce calcium carbonate formation and / or carbon dioxide gas formation during operation of the desalination cell. The first metal may be Fe, Mn, Co, Sc, Ti, Cr or Zn. The second metal is Fe, Mn, Co, Sc, Ti, Cr or Zn. The first metal may be different from the second metal. The second metal may constitute 5 to 50 mol% of the total molar concentration of the first and second metals. In one or more embodiments, the second metal may be Ni, V or a combination of Ni and V. 5 to 50 mol% of the first and / or second metal may be substituted by one or more 4d series elements, one or more 5d series elements or a combination thereof. In certain embodiments, x is equal to 0, the first metal is Fe and the second metal is Co. The ratio of z to y may be 2:1. The at least one compound may be FeCo2(CN)6. In certain embodiments, x is equal to 0, the first metal is Fe, and the second metal is Mn. The ratio of z to y may be 1.6:1. The at least one compound may be FeMn 1.6 (CN)6.

[0006] In another embodiment, a desalination cell is disclosed. The desalination cell comprises a material having at least one compound of the following formula: Fe4[M(CN)6]3, wherein M is a metal. The material is configured to reduce calcium carbonate formation and / or carbon dioxide gas formation during operation of the desalination cell. In one or more embodiments, M is Mn, Co, Sc, Ti, Cr, Zn, or a combination thereof, or, M is Ni, V, or a combination of Ni and V. 5 to 50 mol % of M may be substituted by one or more 4d series elements, one or more 5d series elements, or a combination thereof. The at least one compound may be Fe4[Co(CN)6]3 or Fe4[Mn(CN)6]3.

[0007] In yet another embodiment, a desalination cell is disclosed, which has an electrode comprising a first Prussian blue compound and a second Prussian blue compound different from the first Prussian blue compound. The first and second Prussian blue compounds collectively operate in a collective voltage window during operation of the desalination cell, wherein the voltage window of the first Prussian blue compound is less than the collective voltage window, and the voltage window of the second Prussian blue compound is less than the collective voltage window. The first Prussian blue compound decomposes into a first decomposed phase mixture during operation of the desalination cell. The second Prussian blue compound decomposes into a second decomposed phase mixture during operation of the desalination cell. The first and second decomposed phase mixtures are different from each other. The first and second Prussian blue compounds are independently selected from compounds of the first formula: A x M I y M IIz (CN)6, where A is Na, Li or K, 0 ≤ x ≤ 2,M I It is Fe, M II is one or more metallic elements, 1 ≤ y ,and z ≤ 2, or a compound of the second formula: Fe4[M(CN)6]3, where M is one or more metal elements. The collective voltage window can be 0.0 to 1.4 V vs. SHE. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 A schematic diagram depicting a non-limiting example of a desalination cell according to one or more embodiments.

[0009] Figure 2 is a graph plotting reaction data for the reaction between FeCo2(CN)6 and calcium bicarbonate. DETAILED DESCRIPTION

[0010] Embodiments of the present disclosure are described herein. However, it is to be understood that the disclosed embodiments are merely examples and that other embodiments may present various alternative forms. The drawings are not necessarily to scale; some features may be magnified or minimized to show the details of a particular component. Therefore, the specific structural and functional details disclosed herein should not be interpreted as limiting, but only as a representative basis for teaching those skilled in the art to utilize the embodiments in various ways. As understood by those of ordinary skill in the art, the various features illustrated and described with reference to any of the accompanying drawings may be combined with the features illustrated in one or more other drawings to produce an embodiment that is not explicitly illustrated or described. The combination of illustrated features provides a representative embodiment for typical applications. However, various combinations and modifications of features consistent with the teachings of the present disclosure may be desirable for specific applications or implementations.

[0011] Except in the examples or where otherwise expressly indicated, all numerical quantities in this specification indicating the amount of material or reaction conditions and / or conditions of use should be understood to be modified by the word "approximately" to describe the broadest scope of the present invention. It is generally preferred to implement within the numerical limits shown. In addition, unless explicitly indicated to the contrary, percentages, "parts" and ratio values ​​are by weight; a group or class of materials is described as suitable or preferred for a given purpose related to the present invention, meaning that a mixture of any two or more members of the group or class is also suitable or preferred; describing ingredients in chemical terms refers to the ingredients when added to any combination specified in the specification, and does not necessarily exclude chemical interactions between the ingredients of the mixture after mixing.

[0012] The first definition of an acronym or other abbreviation applies to all subsequent uses of the same abbreviation herein and to normal grammatical variations of the initially defined abbreviation mutatis mutandis. Unless expressly indicated to the contrary, measurements of properties are determined by the same techniques as previously or subsequently mentioned for the same property.

[0013] It must also be noted that as used in the specification and the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. For example, a component mentioned in the singular is intended to include plural components.

[0014] The terms "substantially", "usually" or "approximately" used herein refer to the amount or value involved may be a specified specific value or some other value near it. These terms can be used to modify any numerical value disclosed or claimed herein. Generally, the term "approximately" indicating a specific numerical value is intended to indicate within ± 5% of the numerical value. As an example, the phrase "about 100" refers to the range of 100 ± 5, i.e., the range of 95 to 105. Generally, when the term "approximately" is used, it is expected that similar results or effects according to the present invention can be obtained within the range of ± 5% of the numerical value shown. The term "substantially" may modify the numerical value or relative characteristics disclosed or claimed in the present disclosure. In such a case, "substantially" may mean that the numerical value or relative characteristics modified by it are within ± 0%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5% or 10% of the numerical value or relative characteristics.

[0015] It should also be appreciated that integer ranges explicitly include all integers therebetween. For example, the integer range 1 to 10 explicitly includes 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. Similarly, the range 1 to 100 includes 1, 2, 3, 4 ... 97, 98, 99, 100. Similarly, when any range is proposed, the difference between the upper and lower limits divided by 10 is the value therebetween that can be taken as an alternative upper or lower limit. For example, if the range is 1.1. to 2.1, the following values ​​1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 and 2.0 can be selected as the lower or upper limit.

[0016] In the examples given herein, the concentrations, temperatures, and reaction conditions (e.g., pressure, pH, flow, etc.) may be implemented as + or -50% of the values ​​shown, rounded to or truncated to two significant figures of the values ​​provided in the example. In one refinement, the concentrations, temperatures, and reaction conditions (e.g., pressure, pH, flow, etc.) may be implemented as + or -30% of the values ​​shown, rounded to or truncated to two significant figures of the values ​​provided in the example. In another refinement, the concentrations, temperatures, and reaction conditions (e.g., pressure, pH, flow, etc.) may be implemented as + or -10% of the values ​​shown, rounded to or truncated to two significant figures of the values ​​provided in the example.

[0017] For all compounds expressed as empirical chemical formulas with a number of letter and number subscripts (e.g., CH2O), the value of the subscript may be + or -50% of the value indicated, rounded or truncated to two significant figures. For example, if CH2O is indicated, the formula C (0.8-1.2) H (1.6-2.4) O (0.8-1.2) In one refinement, the value of the subscript may be + or - 30% of the value shown, rounded or truncated to two significant figures. In another refinement, the value of the subscript may be + or - 20% of the value shown, rounded or truncated to two significant figures.

[0018] The term "and / or" as used herein means that all elements of the group may be present or only one element. For example, "A and / or B" means "only A, or only B, or A and B". In the case of "only A", the term also covers the possibility that B is not present, i.e., "only A, but no B".

[0019] It is also to be understood that the invention is not limited to the specific embodiments and methods described below, as specific components and / or conditions may, of course, vary. Furthermore, the terminology used herein is for the purpose of describing particular embodiments of the invention only and is not intended to be limiting in any way.

[0020] The term "comprising" is synonymous with "including," "having," "containing," or "characterized by." These terms are inclusive and open-ended and do not exclude additional, unrecited elements or method steps.

[0021] The phrase "consisting of" excludes any element, step or ingredient not specified in the claim. When this phrase appears in a clause of the body of a claim rather than immediately following the preamble, it limits only the elements listed in that clause; it does not exclude other elements from the claim as a whole.

[0022] The phrase "consisting essentially of" limits the scope of a claim to the specified materials or steps and those that do not materially affect the basic and novel characteristics of the claimed subject matter.

[0023] With respect to the terms "comprising," "consisting of," and "consisting essentially of," when any of these three terms are used herein, the disclosed and claimed subject matter may include use of either of the other two terms.

[0024] The term "one or more" means "at least one," and the term "at least one" means "one or more." The terms "one or more" and "at least one" include "plurality" as a subset.

[0025] A group or class of materials described as suitable for a given purpose in connection with one or more embodiments means that mixtures of any two or more members of the group or class are suitable. Describing ingredients in chemical terms refers to the ingredients when added to any combination specified in the specification and does not necessarily exclude chemical interactions between the ingredients of the mixture once mixed. The first definition of an acronym or other abbreviation applies to all subsequent uses of the same abbreviation herein and to the normal grammatical variations of the initially defined abbreviation, mutatis mutandis. Unless expressly indicated to the contrary, measurements of properties are determined by the same techniques as previously or later mentioned for the same property.

[0026] The growing population on earth has led to an increasing demand for clean fresh water suitable for human consumption, agricultural use and industrial use. Fresh water refers to an aqueous solution with a low salt concentration (e.g., less than 1%). Due to the limited fresh water sources, many attempts have been made to make fresh water from abundant ocean water by desalination. Desalination is the process of removing mineral components from salt water. Removing salt and other chemicals from salt water requires electrical energy or thermal energy to separate the salt water into two streams. The two streams are a fresh water stream containing a low concentration of dissolved salts and a second stream of concentrated brine with a high concentration of dissolved salts.

[0027] Various desalination technologies have been developed, such as evaporation, freezing, distillation, reverse osmosis, ion exchange and electrodialysis. These technologies still have certain disadvantages that hinder their widespread use and limit their success. For example, reverse osmosis usually requires a large amount of input electrical energy, so that this technology is quite expensive. In addition, reverse osmosis utilizes selective membranes, which are prone to fouling or unwanted accumulation of mineral deposits on the membrane surface. The membrane therefore needs to be frequently replaced to cause maintenance requirements and increased costs.

[0028] Electrodialysis is another membrane desalination technology that uses ion exchange membranes. Electrodialysis can be expensive and has no barrier effect against microbial contamination. However, membraneless technologies present other challenges. For example, freeze-thaw often relies on long-term natural sub-zero temperatures and is therefore limited to specific climatic conditions. Multiple-effect distillation utilizes several stages or groups of effects during which the feed water is heated by steam in tubes onto which salt water is sprayed. But this technology carries high operating costs unless waste heat is available for the desalination process, and high temperatures can increase corrosion and scaling.

[0029] The newly developed concept includes an electrochemical desalination method, such as a desalination cell or electrochemical device. The desalination cell uses electrical energy input to extract sodium and chloride ions and other impurity ions from salt water to produce fresh water. The cell thus constitutes a dual ion electrochemical deionization technology, including sodium and chloride dual ion electrochemical electrodes, to which a voltage is applied to separate the salt water into fresh water with a relatively low concentration of dissolved salts and a concentrated brine stream.

[0030] It is desirable to provide a water treatment system utilizing a desalination cell. A non-limiting example of a water treatment system utilizing a desalination cell may include a container for retaining a liquid solution, such as salt water or desalinated water, two electrodes, a power source, a salt water inlet, and a fresh water outlet. Additional components are contemplated, such as additional inlets, outlets, etc. The two electrodes may be separated by an exchange membrane. The exchange membrane may be an anion or cation exchange membrane. The exchange membrane may include a separator on either or both sides.

[0031] The container can be a container, compartment, housing, tank, can, barrel, box, etc. of any shape, size or configuration that can obtain, retain, hold and / or release liquid solutions, such as salt water, brackish water, seawater, offshore seawater, fresh water, sweet water, drinking water, desalted water, polluted water, industrial water, etc. The container is spacious enough to hold enough aqueous solutions for desalination. Accordingly, the size is therefore different with specific applications. The container can be large enough to serve industrial applications. The container can be made of different materials that can withstand corrosion, temperature fluctuations, pH changes, pressure changes and withstand other chemical, mechanical and / or physical conditions.

[0032] The container may be made of glass, plastic, composite material, metal, ceramic or a combination of materials. The container may have one or more protective coatings. The container may be made of materials configured to minimize the occurrence of water contamination. The container may be made of one or more materials that are non-toxic and meet drinking water standards.

[0033] The electrodes are arranged in the battery pack to be in fluid communication with the water in the container. The electrodes are at least partially immersed in the aqueous solution. The electrodes can be completely immersed in the aqueous solution. The electrodes can be placed on opposite sides of the container, centrally placed in the container, or both on the same side of the container. The electrodes can be placed adjacent to each other or separated by a certain distance in the presence of a diaphragm and an exchange membrane (anion exchange membrane or cation exchange membrane).

[0034] The electrodes may be made of the same or different materials, depending on the operating conditions and the device design. The first electrode, the second electrode, or both electrodes may be made of expanded graphite. Graphite is a crystalline carbon allotrope and an example of a semimetal. Graphite represents the most stable form of carbon under standard conditions. Graphite is an electrical conductor with highly anisotropic acoustic and thermal properties and is self-lubricating. Graphite has a layered planar structure. A single layer of graphite is called graphene. The electrodes may include a graphite having sufficient capacity to accommodate Na + Expanded graphite with an interlayer distance of ions. Expanded graphite can be formed by changing and / or expanding the interlayer distance of original graphene layers.

[0035] Due to the expanded interlayer distance, expanded graphite can absorb cations and anions from salt water, sea water, brackish water, etc. Expanded graphite can absorb cations, including but not limited to Na + Mg 2+ 、Al 3+ 、Si 4+ , K + , Ca + Sc 3+ 、Ti 2+ / 3+ / 4+ 、V 2 + / 3+ / 4+ / 5+ Cr 3+ / 6+ , Mn 2+ / 3+ / 4+ , Fe 2+ / 3+ 、Ni 2+ / 3+ / 4+ , Cu 2+ 、Zn 2+ Sn 2+ / 4+ , Pb 4+ etc., and anions, including but not limited to monoanionic species such as F - , Cl - Br - ,I - , S - / 2- , anionic complexes such as ClO4 - 、ClO3 - 、ClO2 - BrO4 - BrO3 - 、SO4 2 -、SiO3 2- , CN - , metal-containing anions such as MX y Ozn- where M = Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Mo, Sn, Cs, and Pb; X = F, Cl, Br, I, N, and P; and 0 < y ≤ 5; 0 ≤ z ≤ 5; 1 ≤ n ≤ 4, etc.

[0036] The electrodes of the desalination cell can be configured to act as host materials for ion intercalation. Intercalation refers to the reversible inclusion of one or more ions into a material having a layered structure. The space between the layers can be used to temporarily store one or more types of ions (such as alkali metal and alkaline earth metal ions). The electrodes can include an intercalation active material to enable the electrodes to act as host materials for ion intercalation. The intercalation active material can be configured to intercalate cations, anions, or both. Cation host materials can include Prussian blue and / or Prussian blue analog compounds (such as compounds based on hexacyanoferrate (HCF) or hexacyanomanganate (HCM), such as NiHCF, NiCuHCF, and MnHCM). In the cathode, anode, or both, an exemplary loading of the intercalation active material can be about 0.01 to 100 mg / cm 2 , 0.05 to 50 mg / cm 2 or 0.1 to 10 mg / cm 2 .

[0037] In addition to the active material, one or both of the electrodes can also include one or more conductive agents, one or more polymer binders, and / or other components. The (one or more) electrodes can include an intercalation active material in an amount of about 70 to 99 wt%, 75 to 97 wt%, or 60 to 95 wt% based on the total weight of the electrode. The electrodes can include one or more conductive agents in an amount of about 1 to 40 wt%, 2.5 to 30 wt%, or 5 to 20 wt% based on the total weight of the electrode. The electrodes can include one or more polymer binders in an amount of about 1 to 30 wt%, 2.5 to 20 wt%, or 5 to 15 wt%.

[0038] Non-limiting examples of conductive agents can include carbon black, conductive carbon black, amorphous carbon, carbon fiber, (one or more) quaternary ammonium salts, (one or more) alkyl sulfonates, (one or more) halogen-free cationic compounds, etc., or combinations thereof.

[0039] Non-limiting examples of polymer binders may be polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), poly(methyl methacrylate) (PMMA), polyethylene glycol (PEO), polyimide, polydopamine, poly(ethylene glycol) diacrylate, polymethylpentene, nylon, metal-aramid, polyetherimide, copolyester, polyetherketone, carboxymethyl cellulose, styrene-butadiene rubber (SBR), copolymers and blends such as poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP), poly(vinylidene fluoride) ethylene-chlorotrifluoroethylene) (PVdF-CTFE), poly(methyl methacrylate-vinyl acetate) (PMMA-VAc), poly(ethylene glycol) diacrylate (PEGDA), poly(methyl methacrylate-acrylonitrile-vinyl acetate) (PMMA-AN-VAc), poly(methyl methacrylate-co-butyl acrylate) (PMMA-co-BA), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate-co-polyethylene glycol (PEDOT-co-PEG), etc., or a combination thereof.

[0040] Calcium carbonate (CaCO3) accumulation on the surface of the electrodes of desalination cells can make it more difficult to transport alkali and alkaline earth metal ions in and out of the embedded host structure. One of the reactions that can lead to the formation of CaCO3 may involve calcium bicarbonate (Ca(HCO3)2). Calcium bicarbonate decomposes into water (H2O) and carbon dioxide (CO2). Calcium is often present in ionic form in water sources (also known as "hard water"). Hard water can cause desalination cell performance to decrease.

[0041] Therefore, it is beneficial to soften hard water in a desalination cell to remove calcium ions according to the following reaction (1):

[0042] 0.5 Ca + HCO3→ 0.5CaCO3+ 0.5CO2+ 0.5H2O (1)

[0043] Prussian blue (PB) compounds and Prussian blue analog (PBA) compounds have a large amount of void space into which monovalent and / or divalent cations can be easily inserted. In one or more embodiments, PB compounds and PBA compounds are collectively referred to as PB compounds. When brine or hard water is input into a desalination system for cleaning, it is possible to introduce Na + , K + , Ca 2+ and / or Mg 2+ The ions are pushed into electrodes containing one or more PB compounds, leaving behind clean water that can be collected and reused.

[0044] A non-limiting example of a desalination cell 100 for a water treatment device is depicted in Figure 1The desalination cell 100 includes electrodes 102 and 104 and an anion exchange membrane (AEM) 106 located between the electrodes 102 and 104. The AEM 106 separates separate water compartments 108 and 110. The electrodes 102 and 104 are connected to a voltage source 112. The battery cell 100 also includes one or more water inlets 114 and water outlets 116.

[0045] One or more inlets 114 and one or more outlets 116 can be used to introduce or release salt water or desalinated water. The number of one or more inlets 114 and one or more outlets 116 for each chamber 108 and 110 can be the same or different. For example, the water compartment 108 can have one more inlet than the water compartment 110. One or more inlets 114 can be located between the AEM 106 and the electrodes 102 and 104. One or more inlets 114, one or more outlets 116, or both can be centered between the AEM 106 and the electrodes 102 and 104. One or more inlets 114 can be located directly opposite the one or more outlets 116. Alternatively, the one or more inlets 114 and one or more outlets 116 of the same compartment 108 or 110 can be staggered so that the one or more inlets 114 and one or more outlets 116 are not aligned or located on the same axis. One or more inlets 114, one or more outlets 116, or both can have the same or different diameters. One or more inlets 114, one or more outlets 116, or both may connect the battery pack 100 to the reservoir 122, the reservoir 123, or both.

[0046] The desalination cell 100 and additional battery cells disclosed herein may be connected to one or more water reservoirs 122 for storing salt water or desalinated water, one or more pumps 124 configured to control the flow of water to and from the desalination cell 100, one or more valves 126 connected to one or more pumps 124, and / or one or more devices 128 configured to check, measure or monitor water quality, such as a pH meter, a water softener, etc. The reservoir 122 may be a container, compartment, housing, tank, tank, cylinder, box, etc. of any shape, size or configuration capable of obtaining, retaining, containing and / or releasing a liquid solution, such as salt water, brackish water, seawater, pelagic seawater, fresh water, sweet water, drinking water, polluted water, industrial water, etc. The one or more pumps 124 may be automatic, manual, or both. The one or more pumps 124 may be in one or more inlet pipes, one or more outlet pipes, a stream connected to the water reservoir 122 and / or 123, or a combination thereof.

[0047] The desalination cell 100 may include two symmetrical electrodes 102, 104 that include the same or similar chemistry and electrode material loading. Alternatively, the desalination cell 100 may include an asymmetric electrode configuration such that the electrode 104 is at least partially or completely made of a different material than the electrode 106. The electrode materials may share similar structural characteristics, such as the same space group, but with different ions such as Na + , Ca 2+ or Mg 2+ The concentration may vary.

[0048] The desalination cell 100 can be operated in the following manner. A positive voltage V can be applied to the desalination cell 100 to release cations such as Na from one of the electrodes 102 and 104. + The cations may be dispersed with the salt water in one of the water compartments 108 and 110, in particular the brine compartment 118, which contains a salt water solution having a first dissolved salt concentration c1. The salt water in the brine compartment 118 may be supplied via one of the water inlets 114. Since the cations cannot pass through the AEM 106, the Na in the brine compartment 118 + The concentration increases. Anions such as Cl - are attracted and pass through the AEM 106 to neutralize cations in the brine compartment 118. At the same time, cations such as Na + The ions are embedded in the other side of the electrodes 102 and 104 due to the electrical neutrality and applied voltage bias. This process creates a clean water compartment 120 on the opposite side of the AEM 106 containing fresh or desalinated water having a second dissolved salt concentration c2 such that c1>c2.

[0049] The desalination cell 100 can be operated cyclically (intercalation and deintercalation) with water flowing continuously. Under continuous flow, desalinated water from the clean water compartment 120 can be stored in a reservoir 122. Alternatively, the desalination cell 100 can be operated as a batch desalination device, in which a limited amount of water can be supplied to the compartment to purify in a smaller scale operation. Alternatively or additionally, a semi-continuous water flow can be supplied to the desalination cell 100 so that the water compartments 108 and 110 can be refilled with additional salt water and can be reversed in the next cycle. In an alternative embodiment, the desalination cell 100 can be designed as a cylindrical tubular cell. Both compartments 108 and 110 can be used for water purification in the reverse direction of operation.

[0050] In one non-limiting example, continuous collection of clean water in successive cycles can be provided by utilizing a clean water reservoir 122 and a recirculation loop for water purification. During startup, electrodes 102 and 104 are at similar states of charge (e.g., 50%), then electrode 102 is discharged (towards 0%) and electrode 104 is charged to 100% SOC. In the first cycle, the first target ions, including Na+ , K + Mg 2+ , Ca 2+ and Pb 2+ Etc. Due to cation-anion attraction (neutralization), anions are added to the brine compartment 118. The clean water compartment 120 thus contains desalinated water, which can be collected. The next cycle causes the ions to be flushed out of the electrodes 102 and 104 to discharge the waste water. The electrodes 102 and 104 can also be used for the next water purification cycle.

[0051] Since the desalination cell is a type of electrochemical cell, in which a voltage is applied, the intercalated ions have the potential to react with other species present to form undesirable byproducts. PB compounds have a cyanide (CN - ), where six cyanide groups are usually coordinated to a transition metal such as Fe, Cu, Ni, Mn, etc. to form a local octahedral coordination. As mentioned above, since the desalination unit is designed to collect Ca from hard water (with high Ca and Mg content), 2+ , when voltage is applied to the electrochemical cell, CaCO3 formation can occur. The Ca2+ inserted into the bulk electrode 2+ Ions may cause undesirable side reactions (e.g. scale formation) when in contact with PB compounds. 2+ The ion source may come from the Ca2+ already present in the embedded host. 2+ ions or Ca dissolved in water located in the desalination cell 2+ ions. Scale accumulation embedded in the bulk electrode can cause electrode surface passivation, which slows or prevents ion and / or electron transport necessary for the operation of the electrochemical cell. Another potential negative side effect is CO2 gas evolution. If the carbon source is generated from cyanide (CN) groups rather than from carbonates dissolved in the water source by decomposition of one or more PB compounds in the electrode, the associated electrode degradation may result in reduced capacity of the desalination cell. Generally, scale formation is a greater problem at high temperatures, where reduced carbonate solubility causes precipitation of calcium carbonate, which accumulates into an undesirable scale coating.

[0052] In view of the above, an electrode material comprising one or more PB compounds that are relatively stable to calcium bicarbonate is needed. This stability reduces the possibility of unwanted side reactions between the PB compound and other compositions present in the desalination cell, including other electrode materials. These side reactions occur between calcium ions and the PB embedding body to form unwanted byproducts (such as scale and CO2 gas precipitation). In one or more embodiments, a specific PB compound is found to reduce the unwanted side reactions between the electrode material comprising the PB compound and the bicarbonate compound, thereby improving the operation of the desalination cell. Reducing scale accumulation can be used in many specific applications of desalination cells, such as but not limited to human consumption, whole house applications, coffee machines, dishwashers, agricultural purposes and industrial purposes.

[0053] In one or more embodiments, a PB compound having a first or second general compound is disclosed. The first general compound is A x M I y M II z (CN)6, where A is Na, Li or K, where 0 ≤ x ≤ 2, where M I and M II wherein y is Fe, Cu, Ni, Co and / or Mn, wherein 1 ≤ y, and wherein z ≤ 2. The second general formula compound is Fe4[M(CN)6]3, wherein M is equal to Fe, Cu, Ni, Co or Mn. The publicly available materials database interface reaction toolkit available at materialsproject.org includes reaction data between the first and second general formula compounds and calcium bicarbonate (CB). In one or more embodiments, such reaction data are analyzed and examined to test the stability of the first and second general formula compounds to CB.

[0054] Figure 22 is a graph 200 that plots reaction data for the reaction between FeCo2(CN)6 and calcium bicarbonate. The X-axis 202 of the graph 200 is the relative mole fractions of FeCo2(CN)6 and calcium carbonate given by the equation [x in x·CaH2C2O6+ (1-x)·FeCo2C6N6]. For example, if x equals 0, the mole fraction of calcium carbonate is 0% and the mole fraction of FeCo2(CN)6 is 100%. In other words, when x equals 0, the mixture is pure FeCo2(CN)6. As another example, if x equals 1, the mole fraction of calcium carbonate is 100% and the mole fraction of FeCo2(CN)6 is 0%. In other words, when x equals 1, the mixture is pure calcium carbonate. The Y-axis 204 of the graph 200 shows the reaction enthalpy in eV / atom.

[0055] In one or more embodiments, the Interface Reactions Toolkit available from the Materials Project's open access materials database (https: / / materialsproject.org / #apps / interfacereactions) is used to analyze the interface reactions that can generate CaCO3. Figure 2 The stable chemical reaction between FeCo2(CN)6 and Ca(HCO3)2 (calcium bicarbonate) is shown in Table 1. Table 1 shows the results of this analysis. According to this analysis, CaCO3 is first x ) is 0.434 (i.e., 56.6% PB compound reacts with 43.4% calcium bicarbonate) as a decomposition product, where the reaction enthalpy (E rxn ) is -1.010 eV / atom.

[0056]

[0057] In one or more embodiments, Figure 2 The analytical framework developed in Table 1 is used to further examine other PB compounds having the first or second general formula compounds disclosed above. The analysis includes determining the mole fraction (x) at which CaCO3 first appears as a decomposition product. If the decomposition reaction includes consuming more calcium bicarbonate (CB) relative to the amount of PB compound, then such electrode material will be more desirable for combating scale formation (i.e., increasing the CB / PB ratio) because less electrode material is degraded per unit of CB. The analysis may also include analyzing the reaction enthalpy ( E rxn ). Relatively corrected E rxnMakes scaling reactions (CaCO3 formation) more difficult to occur. The analysis can also examine other relevant decomposition products. Other decomposition products (such as Ca(FeO2)2) may have the same or similar blocking or accumulation effects as CaCO3, thereby hindering ion transport. The analysis can also check whether undesirable CO2 gas evolution may occur in specific PB compounds. When CaCO3 formation is reduced, other byproducts produced (such as transition metal carbonates, metal oxides, etc.) can be checked.

[0058] Table 2 shows the characteristics of PB compounds available from the Materials Project. The space groups of the PB compounds of Table 2 were found to be F-43m or Fm-3m (They are all cubic structures). The convex hull distance of most PB compounds ( E hull ) is obviously different from other stable compounds in the material database, such as oxides, nitrides, carbides, metals, etc. E hull When the value of is 0, the given compound T Equivalent to thermodynamically "stable" at 0 K. Such compounds will not decompose into other chemical species because they lie on the convex hull of a given chemical compound. E hull Compounds with less than 25 meV / atom can be obtained experimentally at room temperature. However, as can be seen in Table 2, almost all of the compounds listed have extremely high E hull values, as their predicted decomposition species include very stable metal nitrides, carbon, and / or nitrogen (N2). Although many of the compounds listed in Table 2 can be obtained using experimental synthesis and found to be practically stable, the reported values ​​of these compounds are limited by the presence of more stable phase mixtures listed in Table 2. E hull Quite high. Finally, Table 2 provides the DFT band gaps of the compounds specified in Table 2, where most of the compounds except K2FeNiC6N6 are found to be highly conductive with 0 or small band gaps (less than 0.2 eV), and thus capable of transporting electrons during the intercalation electrochemical reaction. This feature can be used to appropriately adjust or reduce the amount of additives in the electrode composition.

[0059] As shown in Table 2 below, the space groups, convex hull distances ( E hull ), stable decomposed phase mixtures and band gaps ( E gIn one or more embodiments, the PB compound contains two to three transition metal cations (i.e., Fe, Co, Cu, and Ni), 0 to 2 alkali metals (i.e., Li, Na, and K), and six cyanides (CN - ).

[0060]

[0061] Ni-based PB compounds can be used as electrode materials. Although a DFT band gap of ~1.5 eV (semiconductor) is reported for K2FeNiC6N6 in Materials Project, the reported DFT band gap may have some error. According to one theory, when K2FeNiC6N6 loses some K + ions, it may become more conductive (i.e., transform from a semiconductor to a metal).

[0062] Compound annotation <![CDATA[FeCoC6N6]]> Alkali metal free (K) <![CDATA[FeCuC6N6]]> No alkali metals (Li, Na or K) <![CDATA[FeNiC6N6]]> Alkali metal free (K) <![CDATA[Fe4[Fe(CN)6]3]]> Reported in 2014, 4, 42991

[0063] Table 3.

[0064] In Table 4, the chemical reactivity of the compounds listed in Table 2 with calcium bicarbonate is examined. Instead of listing the first occurrence of a given mole fraction of CaCO3 ( x ) (similar to Table 1), only the relevant decomposition species are listed in Table 4, such as CaCO3, MCO3, Ca(FeO2)2, CO2, metals and metal oxides. Table 4 also provides the CB / PB ratio and the reaction enthalpy. Also in the chemical reactions shown in Table 4, all PB compounds are abbreviated as "PB" and calcium bicarbonate is abbreviated as "CB". In Table 4, the reaction of PB compounds with calcium bicarbonate (CB; Ca(HCO3)2, equivalent to Ca + 2HCO3→ H2O + CaCO3+ CO2) to form CaCO3 is reported, using the Interface Reaction Toolkit of the Materials Project database.

[0065]

[0066] As observed from Table 4, the change of alkali metal ions (i.e., K vs. Na) can significantly affect the final reaction products. Based on this observation, it is expected that all alkali metal ions Li are removed from the bulk of the electrode during the activation cycle. + 、Na + and K +For example, it was observed that Na2FeCuC6N6 resulted in the formation of Na2Ca2(CO3)3 and K2FeCuC6N6 resulted in the formation of K2Ca2(CO3)3. It is also difficult to determine whether Na2Ca2(CO3)3 accumulates at the electrode surface similar to CaCO3. Both Na2FeCuC6N6 and K2FeCuC6N6 are expected to lose Na from the embedding host. + and K + , which does not affect the results of this analysis, regardless of the products formed when reacting with calcium bicarbonate Ca(HCO3)2 as shown in Table 4.

[0067] In Table 5, FeCoC6N6, FeCuC6N6, and FeNiC6N6 are additionally analyzed in combination with the restated information from Table 4 for FeCo2C6N6, FeCu2C6N6, and FeNi2C6N6 PB compounds, directly comparing FeCoC6N6, FeCuC6N6, and FeNiC6N6 vs. FeCo2C6N6, FeCu2C6N6, and FeNi2C6N6 (with additional transition metals in the PB compounds). Here is a comparison based on analysis of the data from Table 5: (1) (FeCo2C6N6 vs. FeCoC6N6) FeCo2C6N6 results in less CaCO3 and CoCO3 formation; (2) (FeCu2C6N6 vs. FeCuC6N6) same amount of CaCO3 and CO2, but FeCu2C6N6 forms more Cu; and (3) (FeNi2C6N6 vs. FeNiC6N6) similar amounts of carbonate and CO2.

[0068]

[0069] Initial analysis showed that FeCo2C6N6 is a beneficial compound to mitigate CaCO3 formation and limit CO2 gas formation. The CB / PB ratios of these six compounds and E rxn Similarly, they vary from 0.77 to 1.00 and -0.914 to -1.010 eV / atom, respectively. Based on the analysis of Table 5, decreasing the Co content (FeCo2C6N6 to FeCoC6N6) causes more CaCO3 and CoCO3 to form. According to Table 5, FeCuC6N6, FeNiC6N6, FeCu2C6N6, and FeNi2C6N6 lead to the formation of CO2 gas. In addition, the Cu-containing PB compounds have metallic Cu as the final decomposition product. This partially explains the instability of the Cu-containing PB compounds, where Cu can be further oxidized to CuO and / or ionized to Cu 2+. Although the Ni-containing PB compounds in Table 5 do not result in Ni formation (i.e., improved stability relative to the Cu-containing PB), the Ni-containing PB compounds are predicted to result in CO2 gas evolution. Finally, FeMn2C6N6 and FeMnC6N6 are analyzed in Table 5. Although the Mn-substituted PB compounds result in significantly more CaCO3 (and MnCO3), the CB / PB ratio of FeMn2C6N6 and E rxn FeMn2C6N6 forms MnO as a byproduct, while FeMnC6N6 does not form MnO. Based on the analysis in Table 5, FeMn 1.6 C6N6 can be used as a compound to reduce or eliminate the formation of MnO. In summary, in one or more embodiments, FeCo2(CN)6 and FeMn 1.6 (CN)6 compounds are recommended for desalination applications to reduce scale formation. Although Mn-containing compounds may lead to higher carbonate formation, we found that FeMn 1.6 The CB / PB ratio and reaction enthalpy of C6N6 are both higher than the other candidates listed in Table 5. This analysis predicts that FeCo2C6N6 forms minimal CaCO3, while some Co may be converted to CoCO3 upon contact with calcium bicarbonate.

[0070] In one or more embodiments, Fe4[M(CN)6]3 compounds, where M = Fe, Ni, Cu, Co, and Mn, are analyzed as shown in Table 6. Substitution of Fe with Ni or Cu may result in less CaCO3, but more Ca(FeO2)2 and CO2 gas formation. In addition, Ni substitution inhibits CaCO3 formation, but results in extremely high CO2 gas release. In addition, Fe4[Cu(CN)6]3 forms Cu as one of the byproducts, which can be further oxidized to CuO or Cu 2+ , especially for environments similar to desalination cells (i.e., aqueous, sudden pH changes, and / or when voltage is applied). Substituting Fe with Co or Mn produces less CaCO3 and no CO2, but the amount of MCO3 (CoCO3 and MnCO3) increases. Analysis of the decomposition products shows that Co and Mn substitutions are beneficial for desalination applications in terms of anti-degradation. Based on the analysis of Table 6, the CB / PB ratio of Fe4[Fe(CN)6]3 is high. However, Fe4[Fe(CN)6]3 results in the highest amount of CaCO3 as shown in Table 6 (and also forms CO2 gas as a byproduct).

[0071] Table 6 shows the analysis of Fe4[M(CN)6]3 compounds, where M = Fe, Ni, Cu, Co, and Mn. The chemical reactions of these compounds with calcium bicarbonate (CB; Ca(HCO3)2, equivalent to Ca + 2HCO3→ H2O + CaCO3+ CO2) to form CaCO3 were examined using the Interfacial Reaction Toolkit in the MaterialsProject database.

[0072]

[0073] As shown in Table 7, other metal substitution options were explored. In one or more embodiments, other 3d metals from the periodic table, including Sc, Ti, V, Cr, and Zn, were explored as shown in Table 7. Table 7 shows that FeM x Analysis of (CN)6 (where x = 1 or 2) and Fe4[M(CN)6]3 compounds where M = Sc, Ti, V, Cr or Zn.

[0074]

[0075] Among the chemical compounds analyzed in Table 7, FeScC6N6, FeTiC6N6 or FeCrC6N6 produced acceptable amounts of CaCO3 and no CO2, but formed Sc2O3, TiO2 or Cr2O3 as by-products. 3+ and Ti 4+ Further oxidation is unlikely, but Cr 3+ May be oxidized to Cr 4+ or Cr 6+ . FeZnC6N6 results in increased amounts of CaCO3, with no Zn metal or binary oxide formation occurring. A similar phenomenon occurs with Fe4[M(CN)6]3 compounds, where M = Sc, Ti, and Cr, which form Sc2O3, TiO2, and Cr2O3, respectively. In one or more embodiments, Sc or Cr substitution effectively inhibits CaCO3 formation. Similar to FeZnC6N6 as a desirable compound, although Fe4[Zn(CN)6]3 produces more carbonates (i.e., CaCO3 and ZnCO3), it does not form any Zn metal or binary oxides as final decomposition products.

[0076] In one or more embodiments, the desalination cell includes: an electrode comprising one or more PB compounds configured to effectively inhibit the formation of CaCO3 and CO2 gases. Non-limiting examples of such PB compounds may include A x M I y M II z(CN)6, where A is Na, Li or K, 0 ≤ x ≤ 2, M I It is Fe, M II is one or more metal elements, 1 ≤ y, and z ≤ 2, and Fe4[M(CN)6]3, wherein M is one or more metal elements. In one or more embodiments, M II Mn, Co, Sc, Ti, Cr, Zn, or a combination thereof. In one or more embodiments, M is Mn, Co, Sc, Ti, Cr, Zn, or a combination thereof.

[0077] Other elemental metals may be used for M II and M. These metals may effectively inhibit the formation of CaCO3, but may cause some CO2 to precipitate, depending on the chemical compound, operating voltage, temperature and / or pH. In one or more embodiments, these metals include Ni, V and combinations thereof. Based on the analysis herein, these metals may cause CaCO3 to be inhibited, but some CO2 to be formed as a byproduct. According to one theory, the thermodynamic stability of PB compounds supports this result, in which a more stable phase mixture (e.g., C, N2 and CO2) is present.

[0078] In one or more embodiments, the desalination cell electrode may include a material having at least one compound of the formula: x M I y M II z (CN)6, where A is Na, Li or K, 0 ≤ x ≤ 2, M I It is the first metal, M II is a second metal, 1 ≤ y, and z ≤ 2. The first metal can be Fe, Mn, Co, Sc, Ti, Cr, Zn, Ni and V. The second metal can be Fe, Mn, Co, Sc, Ti, Cr, Zn, Ni and V. The first metal may be different from the second metal. In another embodiment, the first and second metals can be a mixture of two or more of Fe, Mn, Co, Sc, Ti, Cr, Zn, Ni and V. One or more of these metals can exist in 5 to 50 mol % of the total molar concentration of the metal in the PB compound. In one or more embodiments, 5 to 50 mol % of the first and / or second metals are substituted by one or more 4d series elements, one or more 5d series elements or a combination thereof.

[0079] In one or more embodiments, the desalination cell electrode may include a material having at least one compound of the formula: Fe4[M(CN)6]3, wherein M is a metal. In one or more embodiments, M is Mn, Co, Sc, Ti, Cr, Zn, Ni, V, or a combination thereof. In one or more embodiments, 5 to 50 mol% of M may be substituted with one or more 4d series elements, one or more 5d series elements, or a combination thereof.

[0080] In one or more embodiments, two or more PB compounds can be used in the desalination electrode. When two or more desalination electrodes each cover a different operating voltage window, the use of these two or more desalination electrodes can be used to increase the overall voltage operating window of the desalination electrode. For example, the operating voltage windows of NiHCFe, CuHCFe, CoHCFe and MnHCFe in terms of V vs. SHE are 0.0 to 0.8, 0.2 to 1.2, 0.6 to 1.3 and 0.65 to 1.35, respectively. In one embodiment, NiHCFe and CoHCFe can be used in combination to cover an overall voltage window of 0.0 to 1.3. The voltage window covered by the two or more PB compounds can have lower limits of 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 and upper limits of 1.0, 1.1, 1.2, 1.3 and 1.4. It can be based on the operation of different salts (such as MCl x ) to select the two or more PB compounds based on different starting potentials of the desalination cell. In one or more embodiments, the use of two or more PB compounds can provide a larger voltage window to remove the desired salt species. The use of two or more PB compounds can be applied to a single electrode within a single desalination cell. In other embodiments, the desalination cells can be combined together to form a series of cells or many cells in parallel, and different PB compounds can be applied to electrodes within different cells to reduce hot spots for scale accumulation in different cells (e.g., upstream cells exposed to a higher salinity percentage).

[0081] Although exemplary embodiments are described above, these embodiments are not intended to describe all possible forms covered by the claims. The words used in the specification are descriptive rather than restrictive words, and it is to be understood that various changes can be made without departing from the spirit and scope of the present disclosure. As described above, the features of various embodiments can be combined to form further embodiments of the present invention that are not clearly described or illustrated. Although various embodiments may have been described as providing advantages or taking precedence over other embodiments or prior art embodiments in terms of one or more desired characteristics, it will be recognized by those of ordinary skill in the art that one or more features or characteristics can be compromised to achieve the desired overall system properties, depending on the specific application and implementation. These properties may include, but are not limited to, cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, availability, weight, manufacturability, ease of assembly, etc. Therefore, if any embodiment is described as not as desirable as other embodiments or prior art embodiments in terms of one or more characteristics, these embodiments are not outside the scope of the present disclosure and may be desirable for specific applications.

Claims

1. A desalination cell comprising: An electrode comprising a material having at least one compound of the formula: From x M I y M II z (CN)6, Where A is Na, Li or K, 0≤x≤2, M I It is the first metal, M II is the second metal, 1≤y, and z≤2, The material is configured to reduce calcium carbonate formation and / or carbon dioxide gas formation during operation of a desalination cell, The first metal is Fe, Mn, Co, Ti, Cr or Zn, and the second metal is Sc.

2. The desalination cell of claim 1, wherein the second metal constitutes 5 to 50 mole % of the total molar concentration of the first and second metals.

3. A desalination cell comprising: An electrode comprising a material having at least one compound of the formula: Fe4[M(CN)6]3, Where M is the metal, The material is configured to reduce calcium carbonate formation and / or carbon dioxide gas formation during operation of a desalination cell, wherein M is Mn, Co, Sc, Ti, Cr, Zn or a combination thereof.

4. The desalination cell of claim 3, wherein the at least one compound of the following formula is Fe4[Co(CN)6]3.

5. The desalination cell of claim 3, wherein the at least one compound of the formula is Fe4[Mn(CN)6]3.

6. A desalination cell comprising: An electrode comprising a first Prussian blue compound and a second Prussian blue compound different from the first Prussian blue compound, the first and second Prussian blue compounds collectively operate in a collective voltage window during operation of a desalination cell, wherein the voltage window of the first Prussian blue compound is less than the collective voltage window, and the voltage window of the second Prussian blue compound is less than the collective voltage window, the first Prussian blue compound decomposes into a first decomposed phase mixture during operation of the desalination cell, the second Prussian blue compound decomposes into a second decomposed phase mixture during operation of the desalination cell, and the first and second decomposed phase mixtures are different from each other, wherein the first and second Prussian blue compounds are independently selected from compounds of the first formula: From x M I y M II z (CN)6, Where A is Na, Li or K, 0≤x≤2, M I It is Fe, M II is Sc, 1≤y, and z≤2, Or a compound of the second formula: Fe4[M(CN)6]3, Wherein M is one or more metal elements, and the metal elements are selected from Mn, Co, Sc, Ti, Cr, Zn or a combination thereof.

7. The desalination cell of claim 6, wherein the collective voltage window is 0.0 to 1.4 V vs. SHE.

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