Methods and apparatus for removing impurities from electrolytes

Abstract

This disclosure provides methods and apparatus for preparing electrolytes containing unwanted impurities at pg / L levels. The methods typically involve electrochemically reducing the impurities to a precipitated, plated, or volatilized form, and removing the reduced form from the electrolyte. This disclosure describes the methods and apparatus for implementing such methods, as well as electrochemical solutions derived from or potentially derived from such methods.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 749,459, filed October 23, 2018, which is incorporated herein by reference. Technical Field

[0003] This disclosure relates to methods and apparatus for purifying electrolytes, and purified electrolytes prepared therefrom, said electrolytes including electrolytes containing redox active materials. Background Technology

[0004] In redox flow battery systems and general battery systems, the presence of specific impurities, including those containing arsenic, antimony, tin, and other such metals, is a well-known problem. For example, U.S. Patent Nos. 9,647,290 and 9,985,311 and U.S. Patent Application Publication No. 2018 / 0102561 discuss problems related to the precipitation of arsenic, antimony, and germanium from vanadium redox flow battery systems and describe the need to maintain the levels of these materials and other metals and metalloids, including Cr, Mn, Fe, Co, Ni, Cu, Zn, and Mo, by selecting raw materials.

[0005] Both U.S. Patent Application Publications 2010 / 0143781 and 2010 / 0261070 describe the problem of Hg, Ni, Co, and Cu impurities in iron-chromium redox flow battery electrolytes and attempt to remedy or avoid these material problems using zinc amalgam or other inorganic reducing agents. These methods appear to be very suitable for solutions containing acidic iron ions and chromium.

[0006] In vanadium systems, or in other systems involving a wider variety of chemicals, general methods for providing such solutions are few, if any, available. In particular, no issues have been raised or described in the chemistry involving metal ligand coordination compounds as described herein, nor have any methods for reducing these types of impurities in such systems been presented previously.

[0007] This application addresses these and other issues. Summary of the Invention

[0008] This disclosure relates to methods and apparatus for reducing impurity levels, electrolytes derived from or potentially derived from these methods and apparatus, and batteries, electrochemical cells and / or systems, fuel cells, electrochemical storage systems, and redox flow batteries and flow battery systems incorporating these electrolytes.

[0009] Specific embodiments of this disclosure provide a method for preparing an electrolyte with reduced impurity levels, the method comprising:

[0010] (1) Under conditions sufficient to produce an electrolyte for electrochemical treatment, an impurity is electrochemically reduced, the impurity being present in an initial electrolyte at an initial concentration, the initial electrolyte further comprising a redox-active electrolyte, and the electrochemically treated electrolyte containing a reduced form of the redox-active electrolyte and a reduced form of the impurity; and optionally further comprising

[0011] (2) Separate the impurities in the reduced form from the electrochemically reduced solution.

[0012] This provides a final electrolyte having a final concentration of impurities that is lower than the initial concentration of impurities in the initial electrolyte.

[0013] In some embodiments, the concentration of the redox active electrolyte in the redox active electrolyte is in the range of 0.5M to 5M or a subrange thereof.

[0014] In a particular embodiment, the impurity concentration in the final electrolyte is at a predetermined threshold level, wherein the predetermined threshold level is:

[0015] (i) one or more given impurities less than about 10 mg / L (“mg / L”), less than 5 mg / L, less than 2.5 mg / L, less than 1 mg / L, less than 500 μg / L (“μg / L”), less than 250 μg / L, less than 100 μg / L, less than 50 μg / L, less than about 40 μg / L, less than about 30 μg / L, less than about 20 μg / L, less than about 10 μg / L, less than about 5 μg / L, or less than about 1 μg / L; or

[0016] (ii) One or more given impurities less than about 10 mg / mol, less than 5 mg / mol, less than 2.5 mg / mol, less than 1 mg / mol, less than 500 μg / mol, less than 250 μg / mol, less than 100 μg / mol, less than 50 μg / mol, less than about 40 μg / mol, less than about 30 μg / mol, less than about 20 μg / mol, less than about 10 μg / mol, less than about 5 μg / mol, or less than about 1 μg / mol in the redox-active electrolyte. In some embodiments, a predetermined threshold level is less than 5 μg / L or 5 μg / mol for Sb and As, and less than 10 μg / L or 5 μg / mol for Ge and Sn. In some embodiments, the impurity is in the form of antimony, arsenic, germanium, tin, or combinations thereof. In other aspects, impurities may also include Hg, Cr, Mn, Fe, Co, Ni, Cu, Zn, or Mo.

[0017] Depending on the nature of the impurities, the properties of the electrolyte (e.g., based on pH and the properties of the accompanying redox-active material), and the reduction conditions employed, reduced impurities can be separated from the electrolyte by plating, precipitation, or volatilization. In certain aspects of these methods, electrochemical reduction is carried out at a redox potential that is more negative than the reduction potential of the impurities.

[0018] In those embodiments where the reducing impurity provides a volatile reducing impurity during reduction, for example, wherein the reducing impurity comprises one or more of arsine (AsH3), germanane (GeH4), stanane (SnH4), or antimonide (SbH3), the additional method further includes conditioning the electrochemically treated electrolyte by one or both of the following:

[0019] (a) Heating the electrolyte of the electrochemical treatment, for example, at a temperature in the range of 20°C to about 105°C; or

[0020] (b) The electrolyte for the electrochemical treatment or the heated solution described in (a) is purged or bubbled with an inert gas such as nitrogen or argon.

[0021] The heating and purging steps can be provided individually, simultaneously, or sequentially. These operations can be performed with or without the conditions of electrochemical reduction, preferably minimizing or avoiding the re-oxidation of reducing impurities at elevated temperatures.

[0022] While any or all of these foregoing steps may be performed while the electrolyte has been placed in the battery, electrochemical single cell and / or system, fuel cell, electrochemical storage system, and redox flow battery and flow battery system, in a preferred embodiment, these methods are performed, for example in a tank or other container, before delivery to such a system, to simplify the operation of the battery, fuel cell, or flow battery.

[0023] These electrolytes can be processed and operated as provided in the methods described to date, i.e., wherein the redox active electrolyte is charged in its reduced form, but additional steps may be performed to at least partially discharge the reduced redox active electrolyte, most preferably removing all reduced impurities in one step.

[0024] Therefore, additional embodiments include those that further include methods for oxidizing the reduced form of the redox-active electrolyte in the final electrolyte. Such oxidation can be carried out as follows: (i) using an oxidizing gas, such as a gas mixture containing air or oxygen; (ii) using an oxidizing chemical reagent, such as hydrogen peroxide; (iii) electrochemically; or (iv) a combination thereof. It should be understood that, regardless of the method chosen, the selection of the oxidant should not, for example, impair the integrity of the purified electrolyte by introducing other impurities.

[0025] These methods are generally applicable to most chemical systems, including vanadium or iron-chromium systems, as well as those containing redox-active metal ligand coordination compounds as described elsewhere in this document, redox-active organic materials as described elsewhere in this document, or combinations thereof.

[0026] This disclosure also includes compositions derived from or potentially derived from the purification of these methods. That is, and to avoid confusion, this disclosure covers those compositions whether or not they are actually prepared by these methods. As a separate embodiment, such electrolytes contain a suitable redox-active electrolyte material at a concentration of at least 0.7 M, with impurity levels lower than those otherwise described herein. Such impurities may include one or more of As, Ge, Hg, and Sb, and / or Ag, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, Ge, Ir, Mg, Mn, Mo, Ni, Pb, Pd, Pt, Re, Ru, Sb, Sc, Sn, Sr, V, and Zn. In specific embodiments, these solutions contain one or more of antimony, arsenic, germanium, and / or tin at levels less than 5 μg / L or 5 μg / mol of redox-active electrolyte in the redox-active electrolyte.

[0027] Furthermore, flow batteries that include one or more of the disclosed electrolytes are also within the scope of this disclosure.

[0028] Additional embodiments of this disclosure include apparatuses that can be used to implement these methods and manufacture these purified electrolyte compositions. These apparatuses include those comprising at least one electrochemical single cell, said electrochemical single cell comprising a first half-cell chamber and a second half-cell chamber separated by a cation exchange membrane, wherein:

[0029] (i) The first half-cell chamber includes a first electrode, preferably a carbon electrode, in contact with a first aqueous electrolyte containing a redox-active material and reducible impurities; and

[0030] (ii) The second half-cell chamber contains a second electrode in contact with a second aqueous electrolyte, the second aqueous electrolyte containing one or more salts containing a non-protic cation at a concentration of at least 0.1 M, and the second electrode contains a catalyst for generating O2, preferably containing nickel, such as Ni foam, stainless steel mesh, stainless steel felt, Ni oxide, Ni hydroxide, Ni hydroxyl oxide, or Ni-Fe oxide.

[0031] Additional embodiments include electrochemical single cells comprising a first half-cell chamber and a second half-cell chamber separated by a cation exchange membrane, wherein:

[0032] (i) The first half-cell chamber contains a first electrode, preferably a carbon electrode, in contact with a first aqueous electrolyte containing redox active materials and reducible impurities, such as carbon cloth, carbon felt, or carbon paper; and

[0033] (ii) The second half-cell chamber includes a second electrode in contact with a second aqueous electrolyte, the second aqueous electrolyte having a pH of at least 2 and containing one or more salts of aprotic cations having a concentration of at least 0.1 M.

[0034] (iii) The second electrode contains a catalyst for generating O2, preferably at least one or a combination of oxides of cobalt, iridium, iron, manganese, nickel, ruthenium, tin or platinum, most preferably IrO2.

[0035] In other embodiments, the electrochemical single cell includes a first half-cell chamber and a second half-cell chamber separated by a membrane, wherein

[0036] (i) The first half-cell chamber contains a first electrode in contact with a first aqueous electrolyte containing a redox-active material and reducible impurities; and

[0037] (ii) The second half-cell chamber contains a second electrode containing a catalyst for generating O2; and the second half-cell chamber does not contain (does not contain) an aqueous electrolyte.

[0038] Other embodiments include methods for implementing the disclosed method, including operating the disclosed electrochemical single cell, such methods include operating the electrochemical device described herein by passing sufficient current through the single cell to reduce the concentration of reducible impurities in the first aqueous electrolyte to a predetermined level, for example, to a level described elsewhere herein. Attached Figure Description

[0039] This application will be further understood when read in conjunction with the accompanying drawings. Exemplary embodiments of the subject matter are shown in the drawings for illustrative purposes; however, the subject matter disclosed herein is not limited to the specific methods, apparatus, and systems disclosed. Furthermore, the drawings are not necessarily drawn to scale. In the drawings:

[0040] Figure 1 This is a dot plot showing the percentage of arsenic removal as a function of redox potential (ORP) after charging the negative electrode electrolyte. As measured by ICP-OES, above a specific solution potential, over 99% of arsenic is removed from the conditioned solution. Figure 2 Each point in the table represents a single experiment in which the negative electrode electrolyte was charged to the solution potential indicated on the x-axis (relative to Ag / AgCl) at 45°C. The charged electrolyte was conditioned at 65°C for several hours while bubbling with flowing nitrogen, and then discharged by heating to reflux under the same gas flow conditions. The arsenic content in the electrolyte was analyzed using ICP-OES.

[0041] Figure 2 This is a dot plot of the arsenic concentration in the negative electrode electrolyte during a charging period of approximately 40 hours at 65°C.

[0042] Figures 3 (A-C) illustrate several potential implementations of the HERM device.

[0043] Figure 3(A) illustrates a device configuration in which the second electrolyte is acidic and the membrane assembly comprises a cation exchange membrane (CEM) having an associated non-conductive layer (NCL), as described, for example, in International Application No. PCT / US2018 / 054798, the contents of which are incorporated herein by reference in whole or at least with respect to the design and operating conditions of the disclosed device. Note that this embodiment incorporates protons (H... + The injection of protons into the treated redox electrolyte (as shown here, but not limited to, using metal ligand coordination compounds containing titanium) lowers the pH of the electrolyte, as described elsewhere herein. Also note that the acidic secondary electrolyte for the electrode is shown as IrO2, which is an example of a more general metal oxide electrode as described elsewhere herein.

[0044] Figure 3(B) illustrates a second type of device configuration, in which the second electrolyte is alkaline, allowing the use of a less expensive electrode catalyst (in this example, Ni). Alkali metal cations (in this example, Na) + / K + The presence and injection of the mixture enable electron injection without altering the pH of the redox electrolyte being treated.

[0045] Figure 3(C) illustrates a third type of device configuration. In this design, a carbon anode with an iridium oxide catalyst is used instead of a carbon cathode. The anode is separated from the cathode by two cation exchange membranes, forming a third compartment. In this third compartment, a strongly buffered alkaline solution converts the proton current generated by the anode into an alkali metal ion current. This architecture prevents the proton current from degrading the negative electrode electrolyte, but requires a more complex single-cell design.

[0046] Figure 4 The cathode described in Example 5 is shown after electrochemical reduction. Detailed Implementation

[0047] This disclosure relates to electrolytes (positive electrolytes or negative electrolytes or both) and methods for their preparation. In particular, this disclosure relates to the preparation of electrolytes containing impurity levels below a predetermined threshold level.

[0048] This disclosure will be more readily understood through reference to the following description, which is incorporated herein by reference in conjunction with the accompanying drawings and embodiments, all of which form part of this disclosure. It should be understood that this disclosure is not limited to the specific products, methods, conditions, or parameters described and / or shown herein, and the terminology used herein is for illustrative purposes only and is not intended to limit any claimed subject matter. Similarly, unless specifically stated otherwise, any description of possible mechanisms or modes of action or reasons for improvement is intended to be illustrative only, and this disclosure is not bound by the correctness or incorrectness of any such suggested mechanisms or modes of action or reasons for improvement. Throughout this document, it is recognized that the descriptions and embodiments relate to methods for preparing impurity-reduced electrolytes comprising redox-active electrolytes, the impurity-reduced electrolytes themselves, electrochemical devices, and methods of using such electrochemical devices that can be used to implement said methods. Embodiments or descriptions used to describe or characterize any of these categories should be understood to refer to all of these categories. In other words, in the context of the features or implementations described and / or claimed in this disclosure in relation to a system or apparatus or a method of making or using a system or apparatus, it should be understood that such descriptions and / or claims are intended to extend these features or implementations to implementations in each of these contexts (i.e., systems, apparatuses, methods, and compositions).

[0049] It should be understood that the specific features of the invention described herein in the context of individual embodiments for clarity may also be combined or provided in a single embodiment. That is, unless obviously incompatible or specifically excluded, each individual embodiment is considered to be combinable with any other embodiment, and such a combination is considered another embodiment. Conversely, the various features disclosed in the context of individual embodiments for brevity may also be provided individually or in any sub-combination. Finally, while an embodiment may be described as part of a series of steps or a more general structure, each said step may also be considered, in itself, as an independent embodiment that can be combined with other steps.

[0050] When a list is presented, unless otherwise stated, it should be understood that each individual element in the list and each combination of the list is a separate implementation. For example, a list of implementations presented as “A, B, or C” will be interpreted as including implementations “A”, “B”, “C”, “A or B”, “A or C”, “B or C”, and “A, B, or C”.

[0051] This disclosure relates in particular to electrochemical methods and apparatus for reducing unwanted impurities from redox-active electrolytes, in some cases of which the methods and apparatus are capable of reducing some impurities to low mg / L or mg / mol or even μg / L or μg / mol levels. This disclosure also relates to electrolyte compositions having such reduced impurity levels and redox cells incorporating such electrolytes.

[0052] Description of general methods

[0053] Therefore, specific embodiments of this disclosure provide a method for preparing an electrolyte with reduced impurity levels. Such a method includes, under conditions sufficient to produce an electrochemically treated electrolyte, at least electrochemically reducing impurities contained in an initial electrolyte that also contains a redox-active electrolyte, the impurities being present at an initial concentration, wherein the electrochemically treated electrolyte contains both a reduced form of the redox-active electrolyte and a reduced form of the impurities. In related embodiments, the method may further include separating the reduced form of the impurities from the electrochemically treated solution to provide a final electrolyte having a final concentration of the impurities lower than the initial concentration of the impurities.

[0054] These methods involve electrochemically reducing impurities to produce a reduced form of the impurity. In some embodiments, the electrochemical reduction is carried out in an electrochemical single cell using techniques in the art. The impurity may be soluble in the electrolyte or may exist as a solid in a redox-active electrolyte. Those skilled in the art will be able to readily implement the electrochemical reduction using techniques in the art and the teachings herein. Typically, electrochemical reduction is carried out by passing an electric current through an electrolyte. Desiredly, the reduction is carried out at a redox potential that is more negative than the reduction potential of the impurity. The desired redox potential is selected based on the impurity to be removed from the electrolyte.

[0055] A discussion of the intended meanings of the terms “electrolyte,” “redox-active electrolyte,” “impurity,” and “impurity in reduced form” is provided elsewhere in this document. Furthermore, the method is applicable regardless of whether the initial electrolyte containing impurities and the redox-active electrolyte has a pH that makes it alkaline, neutral, or acidic, reflecting the properties of the specific redox-active electrolyte used.

[0056] Obviously, the nature and initial concentration of impurities depend on the nature and concentration of the redox active electrolyte and other materials used to prepare the initial electrolyte. For example, vanadium-containing electrolytes are known to contain metallic elements such as Sb, As, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, or Sn. These same types of impurities can be present in other metal-containing redox active electrolytes. In other embodiments, the impurities comprise one or more forms of antimony, arsenic, germanium, mercury, tin, or combinations thereof.

[0057] In certain embodiments of these implementations, the concentration of the redox-active electrolyte is at least 0.5 M, and the redox-active electrolyte is particularly those containing a metal or metalloid. Other specific concentrations are described elsewhere in this document within the context of the final redox-active electrolyte.

[0058] The methods described herein enable the final concentration of impurities in the final electrolyte to be adjusted to a predetermined threshold level. For example, in some embodiments, the final concentration of impurities in the final electrolyte can be any impurity level described herein, but in preferred embodiments, these impurity levels are limited in the following ways:

[0059] (i) less than about 50 μg of impurities per liter of final electrolyte, preferably less than 10 μg / L, more preferably less than 5 μg / L, and even more preferably less than 1 μg / L; or

[0060] (ii) The amount of impurities is less than about 50 μg / mol relative to the redox active electrolyte in each mole of the final electrolyte, preferably less than 10 μg / mol, more preferably less than 5 μg / mol, and even more preferably less than 1 μg / mol. These levels have been achieved for various impurities using the conditions described herein. In a specific independent embodiment, for example, the method provides a final electrolyte containing germanium at levels of less than 10 μg / L or 10 μg / mol, and / or tin at levels of less than 10 μg / L or 10 μg / mol, and / or arsenic at levels of less than 5 μg / L or 5 μg / mol, and / or antimony at levels of less than 5 μg / L or 5 μg / mol, and / or mercury at levels of less than 5 μg / L or 5 μg / mol. Of course, as described elsewhere herein, the method can provide a final electrolyte that may also contain one or more of these impurities at higher levels.

[0061] The methods are further characterized by their efficiency in removing impurities and reducing their initial levels to a final predetermined level. Thus, in some embodiments, the final impurity level shows a 50% reduction in impurities relative to its initial level. In other independent embodiments, the methods provide a final redox active electrolyte in which the final impurity concentration is at least 75%, 80%, 85%, 90%, 95%, 98%, 99%, or 99.9% lower than the concentration in the initial solution.

[0062] In some embodiments, impurities are removed or their concentration is reduced when the reduced form of the impurities is separated by plating onto or within the cathode of an electrochemical single cell. In other embodiments, the treatment results in the precipitation of the reduced form of the impurities from the electrochemically treated electrolyte. Once precipitated, the reduced form of the impurities can be removed by known methods such as filtration, decantation, or removal of solids from the solution. In some embodiments, the precipitated reduced form of the impurities is removed by coagulation sedimentation, filtration, or membrane separation. In yet another embodiment, the precipitated reduced form of the impurities is removed by filtration. Filtration can be performed by passing the electrolyte containing the reduced form of the impurities through a filter, for example, a chelating resin, or a column filled with chelating resin beads.

[0063] In other embodiments, the nature of the impurity makes the impurity in its reduced form a volatile hydride. In particular, such impurities include, for example, antimony, arsenic, germanium, or tin; that is, the volatile hydride is arsine (AsH3), germanane (GeH4), stanane (SnH4), or antimony (SbH3).

[0064] Obviously, for electrochemical reduction to be effective, it must be carried out in the presence of a redox-active electrolyte at a redox potential that is more negative than the reduction potential of the impurity. Since different impurities have different reduction potentials, those skilled in the art should select an appropriate reduction potential for the target impurity. For the purposes of this invention, it is not important whether the impurity is directly reduced under the applied conditions or indirectly reduced by a redox-active material in its reduced form (or vice versa), as long as the impurity is reduced. Although it is possible that the presence of a given redox-active electrolyte may affect the reduction potential of the impurity, generally speaking, the reduction potential of the impurity can be determined or is known regardless of the presence of the redox-active electrolyte, and for this reason, determining the exact reduction potential will be within the capabilities of those skilled in the art. Furthermore, the effect of pH on the standard reduction potential is known, and those skilled in the art will be able to accurately predict the appropriate potential used to achieve the desired conversion.

[0065] In cases where the treatment results in the formation of volatile reducing impurities such as volatile hydrides, additional steps may help remove these volatile substances, especially when they are generated in large containers. Such a "conditioning" step may include heating the electrochemically treated electrolyte at a temperature above ambient temperature under an inert atmosphere until the electrochemically treated electrolyte, or the final electrolyte, reaches its boiling point. For most commercially relevant systems, the boiling point of the final aqueous electrolyte is approximately 105°C to approximately 110°C. Therefore, in some embodiments, such heating can be applied to temperatures within the ranges of 20°C to 25°C, 25°C to 30°C, 30°C to 35°C, 35°C to 40°C, 40°C to 45°C, 45°C to 50°C, 50°C to 55°C, 55°C to 60°C, 60°C to 65°C, 65°C to 70°C, 70°C to 75°C, 75°C to 80°C, 80°C to 85°C, 85°C to 90°C, 90°C to 95°C, 95°C to 100°C, 100°C to 105°C, or 105°C to 110°C, or temperatures encompassing one or more of these ranges, such as 35°C to 95°C, or more preferably 45°C to 85°C. Further understanding is that, for aqueous systems, increasing the temperature of the electrolyte can promote the oxidation of the redox-active electrolyte or reducing impurities during charging, leading to hydrogen evolution. To avoid this, a temperature should be chosen that prevents such oxidation (e.g., keeping the electrolyte charged and / or preventing the escaping hydrides from oxidizing back to a soluble, non-volatile state). Alternatively or additionally, the operator may maintain the electrolyte at an appropriate potential (i.e., more negative than the reduction potential of impurities and / or redox-active electrolytes) during the heating process.

[0066] In addition to heating, or as an alternative to heating, such a "conditioning" step may include purging or bubbling the electrochemically treated electrolyte or heated solution with an inert gas such as nitrogen or argon. Furthermore, it is important to keep the reduced impurities in their volatile form. Purging may also be performed using mixing at a rate sufficient to remove the reduced form of the impurities. The inventors have found that purging, optionally performed with mixing, promotes the efficient transfer of dissolved reduced form impurities to the gas phase and their removal from the electrolyte.

[0067] During application, heating and / or bubbling may be performed simultaneously or sequentially through one or more cycles.

[0068] Once at least a portion of the reduced form of impurities has been removed, and the impurity level in the final electrolyte is at an appropriate level, the redox-active material may be in its fully reduced / charged state. Whether for safety or any other reason (e.g., to minimize unintentional oxidation accompanied by hydrogen evolution during transport of the final electrolyte), it may be desirable to reduce the state of charge of the final electrolyte (i.e., to at least partially discharge the redox-active electrolyte). This can be achieved by any suitable oxidation method. For example, this can be done chemically by purging with an oxidizing gas such as air or oxygen or by using a chemical oxidant such as hydrogen peroxide, or electrochemically by using a hydrogen evolution catalyst (e.g., activated carbon, carbon cloth, carbon felt, carbon paper, Ti mesh, Ti felt, drawn Ti mesh, Pt-plated Ti mesh, or combinations thereof), or by some combination of these methods. It is preferable to choose the reagents or methods used for such oxidation so that no harmful substances are introduced.

[0069] Oxidation can be carried out at ambient temperature or at a lower or higher temperature. In a particular embodiment, the final electrolyte is re-oxidized to its boiling point at one or more temperatures above 65°C, preferably above about 85°C, and more preferably above about 105°C. In certain cases, the application of heating and / or bubbling may also be helpful and may indeed be intentionally used to further concentrate the redox-active electrolyte in the final redox-active solution.

[0070] Electrochemical device (HERM device)

[0071] Therefore, this disclosure focuses on methods for removing these reducible impurities and electrolytes for impurity reduction, but it also covers apparatus / systems that can be used to implement these methods.

[0072] For effectiveness, the chemical process requires a device / system that "injects" electrons into an electrolyte containing redox-active materials at a potential sufficient to reduce reducible impurities. The effect or nature of counter-cations that necessarily accompany the injected electrons has not been discussed previously. However, the specific choice of the device / system used (hereinafter referred to as a "HERM device" or hybrid electrochemical removal module device) depends on the electrolyte being "cleaned" (i.e., a solution containing redox-active materials in which impurities are removed). The choice of system also needs to consider the state of charge of the redox-active materials and that the amount of impurities (even at 100 mg / L or 100 ppm) will be very small relative to the redox-active materials in any actual electrolyte being cleaned (typically greater than 0.5 M). For example, consider a hypothetical one-liter electrolyte solution containing 1 M of redox-active materials at a 50% charge state and 100 ppm of reducible impurities. Almost all the electrons pumped into such a system will be used to reduce the redox-active materials, and only a small proportion will be used to reduce the reducible impurities. The number of electrons required to reduce the charged state of the redox-active material may be several orders of magnitude larger than the number of electrons required to reduce the reducible material. Furthermore, in any such system, these electrons will be accompanied by an equal amount of countercations.

[0073] Perhaps more importantly, regardless of whether the electrolyte being treated is acidic or alkaline, injecting hydrogen ions at these levels typically results in a concentration far exceeding the hydrogen ion content of the electrolyte being treated (even at pH 2, [H+]). + [=0.01M]. Such injection has a significant effect on altering the pH of the treated electrolyte. This can be addressed by adjusting the electrolyte pH with an appropriate base after the reduction step, but even adding a base may introduce significant impurities into the purified electrolyte. A simpler solution is to use a HERM device, which simultaneously injects alkali metal or alkaline earth metal (or other aprotic) cations with electrons.

[0074] Previously described apparatuses for balancing the pH of a system include those described in WO 2015 / 048074 ('074 application), the contents of which are incorporated herein by reference for all purposes, but at least for the teachings therein regarding the hardware and methods of use. '074 application teaches apparatus and methods for simultaneously balancing both the electron and proton content of a working electrolyte. As described therein, apparatuses described as rebalancing single cells or balancing single cells describe apparatus and methods for injecting both electrons and protons into a redox-active electrolyte. While primarily described in relation to a working flow battery, the description also describes the rebalancing single cell as a standalone apparatus. Several embodiments discussed in '074 application and set forth herein include embodiments in which the balancing single cell comprises:

[0075] (1) A first half-cell chamber and a second half-cell chamber, wherein the first half-cell chamber contains a first electrode in contact with a first aqueous electrolyte of a redox flow cell; and wherein the second half-cell chamber contains a second electrode in contact with a second aqueous electrolyte, the second electrode containing a catalyst for generating O2. In some of these embodiments, the pH of the second aqueous electrolyte is at least 2, preferably greater than about 7, and more preferably in the range of about 9 to about 14. In other embodiments, no second electrolyte is added.

[0076] (2) A first half-cell chamber having a first electrode in contact with a first aqueous electrolyte of a redox flow cell; a second half-cell chamber containing a second electrode in contact with a second aqueous electrolyte, the second electrode containing a consumable carbon electrode material for generating O2 and / or CO2. The two half-cell chambers are separated by an ion-exchange polymer membrane.

[0077] (3) A first half-cell chamber having a first electrode in contact with a first aqueous electrolyte of a redox flow cell; a second half-cell chamber containing a second electrode containing a catalyst for generating O2, but the electrode not in contact with a second aqueous electrolyte. The two half-cell chambers are separated by an ion-exchange polymer membrane.

[0078] In these embodiments, the first aqueous electrolyte is described as the negative working electrolyte (“negative electrode electrolyte”) comprising a redox flow cell. In various embodiments, the electrochemistry associated with the second half-cell of the equilibrium single cell at acidic or neutral pH is described with respect to formula (1):

[0079] 2H₂O→2O₂+4H + +4e - (1)

[0080] Furthermore, at a more alkaline pH, the electrochemistry associated with the second half-cell of the equilibrium single cell is described by equation (2):

[0081] 4OH - →2H₂O + O₂ + 4e⁻ (2)

[0082] The corresponding electrochemical reactions associated with the first half-cell can be described in equation (3):

[0083] M n +e - →M n-1 (3)

[0084] as well as

[0085] IMP n+ +ne - →IMP 0 (4)

[0086] or

[0087] IMP n+ +ne - +n H + →IMP.H n (5)

[0088] Where M n and M n-l These respectively represent the oxidized and reduced forms of the redox-active material in the negative electrode electrolyte, corresponding in this application to the redox-active material in the solution to be treated, wherein "IMP" n+ This refers to the initial form of impurities (e.g., As). 3+ ), and IMP 0 and IMP.H n These refer to the reduced metal form or hydride form of the impurity, respectively. In the context of this invention, two such reaction schemes can be seen in equations (6) and (7):

[0089] As+3H + +3e - →AsH3 (6)

[0090] As + 3H₂O + 3e - →AsH3+3OH - (7)

[0091] Because the '074 application involves the simultaneous balance of electron and proton content in the working electrolyte, in both cases, the transport of protons through the membrane from the second half-cell of a pH-corrected single cell to the first half-cell is referred to as providing charge balance to the negative electrode electrolyte. As a result of this design, the '074 application describes that when the second half-cell chamber contains a second electrode comprising a catalyst for O2 generation operating in an alkaline environment, the two half-cell chambers are separated by a bipolar membrane consisting of a cation-exchange ionomer membrane and an anion-exchange ionomer membrane sandwiching a metal oxide membrane that promotes water dissociation. It is precisely through the use of the bipolar membrane that the balanced single cell is described as operating simultaneously with an alkaline electrolyte configured within the second half-cell.

[0092] However, in the case of this invention, for the reasons described above, it is less desirable to simultaneously pump in electrons and protons (as described in application '074), and it is more desirable to simultaneously pump in electrons and other aprotic cations into the electrolyte. Therefore, the apparatus described in application '074 can be reconfigured to simultaneously pump in electrons and aprotic cations by introducing alkali metal or alkaline earth metal cations (or even ammonium cations) into the second electrolyte at a concentration sufficient to prevent pH adjustment of the first aqueous electrolyte after electrochemical treatment. In a preferred embodiment, the alkali metal or alkaline earth metal cations (or even ammonium cations) in the second electrolyte are present at a much higher concentration (e.g., more than 10, 100, 500, 1000, 5000, or 10,000 times the proton concentration in the second electrolyte). In a particular embodiment, these aprotic cations may be alkali metal or alkaline earth metal cations, such as Li. + Na + K + 、[NH n R 4-n ] + (R = alkyl) or mixtures thereof. These aprotic cations may be present in the second aqueous electrolyte at concentrations ranging from at least 0.1 M to their saturation concentration, or in the range of 0.1 M to 0.2 M, 0.2 M to 0.3 M, 0.3 M to 0.4 M, 0.4 M to 0.5 M, 0.5 M to 0.6 M, 0.6 M to 0.7 M, 0.7 M to 0.8 M, 0.8 M to 0.9 M, 0.9 M to 1 M, 1 M to 1.25 M, 1.25 M to 1.5 M, 1.5 M to 2 M or higher, or any combination thereof. Exemplary counterions of these cations include hydroxide, phosphate, or sulfate.

[0093] In the context of this invention, a similar system (including its hardware aspects) as described in application '074 can be used as a HERM device, which is attached to a flow battery as described in application '074, or to a tank or container, and / or is separate from the operating system. Since the HERM device is not used in conjunction with the operating flow battery system, the voltage and other efficiencies of the HERM device are not critical to the economics of such a flow battery system.

[0094] In a specific embodiment of this disclosure, an electrochemical single cell includes a first half-cell chamber and a second half-cell chamber separated by a membrane, wherein:

[0095] The first half-cell chamber contains a first electrode, preferably a carbon electrode, in contact with a first aqueous electrolyte containing a redox-active electrolyte (e.g., a negative electrode electrolyte) and reducible impurities; and the first electrode is made of carbon cloth, carbon felt, or carbon paper.

[0096] The second half-cell chamber contains a second electrode in contact with a second aqueous solution, which is preferably acidic but has a pH of at least 2. The second electrode contains a catalyst for generating O2, preferably at least one or a combination of oxides of cobalt, iridium, iron, manganese, nickel, ruthenium, tin, or platinum, with IrO2 being the most preferred.

[0097] Therefore, in other embodiments, this disclosure envisions an electrochemical single cell comprising a first half-cell chamber and a second half-cell chamber separated by a membrane, wherein:

[0098] The first half-cell chamber contains a first electrode, preferably a carbon electrode, in contact with a first aqueous electrolyte containing redox active materials and reducible impurities; and

[0099] The second half-cell chamber contains a second electrode in contact with a second aqueous solution. The second electrode contains a catalyst for generating O2, preferably containing nickel, such as Ni foam, stainless steel mesh, stainless steel felt, Ni oxide, Ni hydroxide, Ni hydroxyl oxide, or Ni-Fe oxide.

[0100] In certain embodiments of these implementations, the membrane is a cation exchange membrane (“CEM”). In these implementations, the membrane is not a bipolar membrane as described in application '074 and does not contain an introduced anion exchange membrane. Materials that can be used for these cation exchange membranes include perfluorinated or polyfluorosulfonic acid (PFSA) membranes. TM AQUIVION TM Or FLEMION TMThe membrane comprises a copolymer of tetrafluoroethylene, optionally comprising perfluoropolyvinyl ether; sulfonated hydrocarbon membranes (sulfonated polyether ether ketone, sulfonated polyphenylene sulfone). Other exemplary perfluorinated membrane materials include copolymers of tetrafluoroethylene and one or more fluorinated acid-functionalized comonomers. Other available perfluorinated electrolytes include copolymers of tetrafluoroethylene (TFE) and FSO2—CF2CF2CF2CF2-O-CF=CF2.

[0101] In some embodiments, the second aqueous electrolyte does not contain redox active materials. In other embodiments, the second aqueous electrolyte contains aprotic cations at the level discussed elsewhere herein for this purpose. Preferably, the type and proportion of aprotic cations in the second solution approximates or substantially matches the type and proportion of the electrolyte being treated (in the first half-cell). The term "approximately matches" means that the distribution of cation content in the redox-containing electrolyte does not need to be adjusted after treatment. The migration rate of the corresponding cations across the membrane may require a slightly different relative proportion of cations in the second electrolyte compared to the corresponding proportion in the treated electrolyte. If necessary, the ability to determine these differences can be assessed by those skilled in the art without excessive experimentation.

[0102] In other independent embodiments, the pH of both the first aqueous electrolyte and the second aqueous electrolyte is less than seven, about seven, or greater than seven. Such apparatus and methods can be used to process highly acidic redox-active electrolytes, such as those present in vanadium or iron-chromium flow batteries; and alkaline or pH-neutral redox-active electrolytes, such as those based on metal-ligand coordination compounds, such as titanium-based anode electrolyte materials (and also including the broader range of anode electrolytes described herein).

[0103] Preferably, the pH difference between the first aqueous electrolyte and the second aqueous electrolyte is less than 5 pH units. In other independent embodiments, the electrolyte difference is less than 4, 3, 2, or 1 pH unit. If higher, a strategy using a pH buffer layer may also be employed, such as that described in PCT / US2018 / 054798 filed October 8, 2018.

[0104] As described above, the second electrode typically contains a catalyst for generating O2. In certain embodiments of these works, the second electrode contains a metal oxide catalyst suitable for the electrochemical generation of O2 from water. In addition to their ability to generate O2, these oxidizing catalysts are preferably corrosion-resistant at the pH considered in this application, are poor catalysts for reducing water to hydrogen, or both. Catalysts that corrode under the acidic or alkaline oxidizing conditions of the operating second aqueous electrolyte have the potential to cross-convert into the first pH-correcting half-cell, interfering with the intended effect of the pH-correcting single cell, or worse, interfering with the operation of the flow cell. If such a cross-converting catalyst is further an effective catalyst for generating hydrogen under the reducing conditions of the first half-cell, it is conceivable that hydrogen evolution in the first half-cell or at the negative electrode of the operating flow cell could lead to safety problems. Therefore, the present invention contemplates the preferred use of oxides of cobalt, iridium, iron, manganese, nickel, ruthenium, tin, or combinations thereof for the second electrode. Iridium oxides are particularly preferred because of their good catalytic activity for O2 evolution and their high corrosion resistance.

[0105] When the second half-chamber contains an alkaline electrolyte, catalysts such as nickel or nickel-iron oxides are particularly preferred because they exhibit good catalytic activity for O2 evolution and are highly corrosion-resistant in alkali. Suitable materials include Ni foam, stainless steel mesh, stainless steel felt, Ni oxide, Ni hydroxide, Ni hydroxyl oxide, or Ni-Fe oxide.

[0106] In some embodiments, the second electrode of the HERM device comprises carbon. Such electrodes are well known in the art and include graphitic carbon, glassy carbon, amorphous carbon, boron- or nitrogen-doped carbon, diamond-like carbon, carbon onions, carbon nanotubes, carbon cloth, carbon felt, carbon paper, and graphene. Carbon materials can release O2, and although at a fairly high overpotential, the carbon electrode itself will inevitably be oxidized to CO2. Thus, the carbon electrode is semi-consumable. In other embodiments, the second electrode may also comprise a Ti mesh, Ti felt, drawn Ti mesh, stainless steel mesh, and stainless steel felt.

[0107] In other embodiments, the electrochemical single cell includes a first half-cell chamber and a second half-cell chamber separated by a membrane, wherein

[0108] (i) The first half-cell chamber contains a first electrode in contact with a first aqueous electrolyte containing a redox-active material and reducible impurities; and

[0109] (ii) The second half-cell chamber contains a second electrode containing a catalyst for generating O2; and wherein the second half-cell chamber does not contain (does not contain) an aqueous electrolyte.

[0110] In this configuration, the water required for the O2 precipitation reaction is supplied by water originating from the aqueous electrolyte in the first half-chamber, which is transported across the membrane. To avoid mass transfer confinement, water transport across the membrane needs to be faster than water consumption at the metal oxide catalyst. The membrane on the second half-chamber side uses a metal oxide O2 precipitation catalyst (e.g., IrO). x The coating process results in the direct oxidation of water transported across the membrane from the first half-chamber into molecular oxygen and protons. This configuration greatly simplifies the design of the electrochemical device. For example, the metal oxide catalyst on the membrane can be directly interfaced with the titanium endplate, eliminating the need for a titanium mesh that acts as the flow field for the second aqueous electrolyte. The only additional design feature would be the outlet for the molecular oxygen evolved at the metal oxide catalyst. Furthermore, water must be periodically added to the negative electrode electrolyte tank to compensate for the water consumed in the O2 evolution reaction. Optionally, this replenishment water can be generated in situ by combining evolved O2 from the second half-chamber with H2 evolved in the second half-chamber of the electrochemical single cell of the HERM device and in the negative electrode electrolyte compartment of the first single cell. This water production method can be catalyzed by noble metal catalysts (e.g., Pt, Pd, etc.).

[0111] Additional embodiments provide methods for operating any of the HERM devices described herein, each method comprising applying a potential to the first and second electrodes of the device and supplying a current to the device in the presence of the treated aqueous electrolyte. Specific conditions for such operation are described elsewhere herein. When operating to remove impurities from an electrolyte containing these redox-active materials, parasitic hydrogen evolution does not impede its primary function. This allows for the use of less expensive materials, such as stainless steel, in the construction of the electrodes.

[0112] Other implementations include incorporating the batteries, electrochemical single cells, fuel cells, and / or flow batteries described herein into larger systems, such as systems comprising a single-cell stack, tanks and piping for containing and transferring electrolytes, control hardware and software (which may include safety systems), and at least one power conditioning unit as part of an energy storage system. In such systems, the tanks contain electroactive materials. The control software, hardware, and optional safety systems include all sensors, mitigation equipment, and electronic / hardware controls and protections to ensure the safe, autonomous, and efficient operation of the flow battery or other energy storage system.

[0113] Such a storage system may also include a power conditioning unit at the front end of the energy storage system to convert input and output power into voltage and current optimal for the energy storage system or application. For an example of a grid-connected energy storage system, during a charging cycle, the power conditioning unit converts the input AC power into DC power at the appropriate voltage and current for the electrochemical stack. During a discharging cycle, the stack generates DC power, and the power conditioning unit converts it back into AC power at an appropriate voltage and frequency suitable for the grid application. Such an energy storage system is well-suited for continuous charging or discharging cycles lasting several hours. Therefore, the system is suitable for smoothing energy supply / demand curves and providing mechanisms for stabilizing intermittent generation assets (e.g., derived from renewable energy). It should be understood that various embodiments of the invention include those energy storage applications where such long charging or discharging durations are valuable. For example, non-limiting examples of such applications include those where the system of the invention is connected to the grid, including renewable energy integration, peak load shifting, grid firming, baseload generation / consumption, energy arbitrage, transmission and distribution asset deferral, weak grid support, and / or frequency regulation. Additionally, the device or system can be used to provide stable power for applications not connected to the power grid or microgrid, such as as a power source for remote camps, forward operating bases, off-grid telecommunications, or remote sensors.

[0114] Redox active electrolyte with reduced impurities

[0115] This disclosure also includes the final electrolytes obtainable by the disclosed methods. These embodiments include electrolytes containing redox-active electrolytes and impurities at levels as disclosed herein, regardless of whether such electrolytes are prepared by the methods disclosed herein (“derived” from the methods disclosed herein). As used herein, the term “derived” reflects the fact that a given electrolyte can be prepared by the methods of the present invention (i.e., possessing the characteristics of the electrolytes described herein), but is actually prepared by alternative methods.

[0116] These final "impurity-reduced" electrolytes contain at least one redox-active electrolyte, one or more impurities at the levels described herein, and optionally other additives (surfactants, viscosity modifiers, buffers, and non-redox-active molecules / substances electrolytes) suitable for the desired properties of the material.

[0117] The selection of the at least one redox active material is flexible and includes, for example, salts of vanadium, iron, chromium, or various metal ligand coordination compounds. These latter types of materials are described elsewhere herein. In particular, this disclosure highlights the utility of the method of the invention and the resulting redox active electrolyte, wherein the redox active material comprises a titanium-containing metal ligand coordination compound, especially as a negative electrode electrolyte.

[0118] In the inventors' experience with commodity chemicals, significant impurities are typically found in the raw materials, which then correspond to impurities in the final batch-formulated electrolyte. Caustic alkalis are a common source of impurities. Typical impurity ranges derived from common precursor materials are given in Tables 1A and 1B below. Depending on the method used, these impurities can accumulate in the final flow battery electrolyte at elevated concentrations. Comparative data for titanium-catechin salt derivatives prepared from commercial sources are also shown in Table 2.

[0119] For example, if multiple equivalents of economical-grade NaOH are used in the synthesis of organic redox active materials, the resulting materials may be rich in impurities such as Ni. Electrolytes formulated from such materials may tend to exhibit precipitation or elevated parasitic hydrogen evolution in flow batteries.

[0120]

[0121]

[0122]

[0123] Impurities derived from vanadium sources may be even higher:

[0124]

[0125] In these redox-active electrolytes, including those with reduced impurities, the concentration of the at least one redox-active material is at least 0.7 M. In various embodiments, the concentration of the at least one redox-active material is defined by one or more ranges from 0.7 M to 0.8 M, 0.8 M to 0.9 M, 0.9 M to 1 M, 1 M to 1.2 M, 1.2 M to 1.4 M, 1.4 M to 1.6 M, 1.6 M to 1.8 M, 1.8 M to 2 M, 2 M to 2.2 M, 2.2 M to 2.4 M, 2.4 M to 2.6 M, 2.6 M to 2.8 M, 2.8 M to 3 M, 3 M to 3.5 M, or 3.5 M to 4 M. The final impurity level in the redox-active solution is relevant only in the context of these practically available concentrations (or higher), and should be interpreted in that context.

[0126] Although impurities are generally described as containing one or more of Ag, As, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, Ge, Hg, Ir, Mg, Mn, Mo, Ni, Pb, Pd, Pt, Re, Ru, Sb, Sc, Se, Sn, Sr, Te, V, and Zn, in specific embodiments, impurities are described as containing one or more of As, Ge, Hg, and Sb.

[0127] In this context, in some embodiments, the levels of these impurities may be defined based on a mass basis relative to the total mass of the redox active electrolyte (independent of the amount of redox active electrolyte in the solution), typically based on ppm or ppb. Alternatively, they may be defined based on a weight basis per unit volume of the redox active electrolyte, for example, based on mg / L or μ / L. When the density of the redox active electrolyte is 1 g / L, the corresponding ppm vs. mg / L and ppb vs. μg / L values ​​are equal.

[0128] Therefore, in an independent embodiment, the redox-active electrolyte contains one or more given impurities less than about 10 mg / L (“mg / L”), less than 5 mg / L, less than 2.5 mg / L, less than 1 mg / L, less than 500 μg / L (“μg / L”), less than 250 μg / L, less than 100 μg / L, less than 50 μg / L, less than about 40 μg / L, less than about 30 μg / L, less than about 20 μg / L, less than 10 μg / L, less than 5 μg / L, or less than 1 μg / L. Furthermore, for clarity, these descriptions are intended to apply individually and independently to each material described as an impurity. For example, under these described limitations, a specific composition specifying As, Sb and Ge may contain, for example, less than 5 μg / L of As, less than 10 μg / L of Sb and less than 50 μg / L of Ge.

[0129] In some embodiments, the electrolyte contains one or more of As, Ge, Hg, and Sb at a concentration of less than about 50 μg / L. In other preferred embodiments, the electrolyte contains one or more of Ag, As, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, Ge, Hg, Ir, Mg, Mn, Mo, Ni, Pb, Pd, Pt, Re, Ru, Sb, Sc, Sn, Sr, V, and Zn at a concentration of less than about 5 μg / L. In other preferred embodiments, the electrolyte contains one or more or a combination of Sb, As, Ge, and Sn at a concentration of less than about 5 μg / L. In other preferred embodiments, the electrolyte contains As, Hg, or a combination thereof at a concentration of less than about 5 μg / L. In other preferred embodiments, the electrolyte contains Sb, As, or a combination thereof at a concentration of less than about 5 μg / L. In other preferred embodiments, the electrolyte contains Ge, Sn, or a combination thereof at a concentration of less than about 10 μg / L.

[0130] However, since the primary source of foreign impurities is typically a metal used as a redox-active metal (e.g., vanadium) or a redox-active metal ligand coordination compound (e.g., in titanocatechin), the levels of these impurities can also (and perhaps more appropriately) be defined on a mass basis relative to the amount of redox-active electrolyte in the redox-active electrolyte. In such a case, the relevant basis becomes the parts by weight of impurities relative to each mole of redox-active electrolyte in the redox-active electrolyte (i.e., based on mg / mol or μg / mol). Furthermore, when the concentration of the redox-active electrolyte in the redox-active electrolyte is 1 M, the values ​​of mg / mol or μg / mol are numerically equal to ppm or ppb, respectively. However, in practice, additional embodiments include the following, wherein the impurity level is described with respect to the concentration of redox active electrolyte in the redox active electrolyte in mg / L or μg / L per mole (e.g., the limitation of 10 μg impurity / L solution per 0.8M redox active electrolyte would correspond to [10 μg / L] / [0.8 mol / L] or 12.5 μg impurity / mol redox active electrolyte).

[0131] Therefore, in an independent embodiment, using a 1M standard, the redox-active electrolyte contains less than about 10 mg of one or more given impurities per mole of redox-active electrolyte (hereinafter referred to as "mg / mol"), or less than 5 mg / mol, less than 2.5 mg / mol, less than 1 mg / mol, less than 500 μg / mol, less than 100 μg / mol, less than 50 μg / mol, less than 40 μg / mol, less than 30 μg / mol, less than 20 μg / mol, less than about 10 μg / mol, less than 5 μg / mol, or less than 1 μg of one or more given impurities per mole of redox-active electrolyte.

[0132] Similarly, in some embodiments, the electrolyte contains one or more of As, Ge, Hg, and Sb in amounts less than about 50 μg / mol. In other preferred embodiments, the electrolyte contains one or more of Ag, As, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, Ge, Hg, Ir, Mg, Mn, Mo, Ni, Pb, Pd, Pt, Re, Ru, Sb, Sc, Sn, Sr, V, and Zn in amounts less than about 5 μg / mol. In other preferred embodiments, the electrolyte contains one or more or a combination of Sb, As, Ge, and Sn in amounts less than about 5 μg / mol. In other preferred embodiments, the electrolyte contains As, Hg, or a combination thereof in amounts less than about 5 μg / mol. In other preferred embodiments, the electrolyte contains Sb, As, or a combination thereof in amounts less than about 5 μg / mol. In other preferred embodiments, the electrolyte contains Ge, Sn, or a combination thereof in amounts less than about 10 μg / mol.

[0133] Applications of electrolyte electrochemical (redox) systems with reduced impurities

[0134] The redox-active electrolyte of the present invention can also be used in flow batteries or fuel cell applications. Therefore, this disclosure covers flow batteries comprising at least one half-cell containing one of the impurity-depleted electrolytes described herein; and systems comprising such flow batteries.

[0135] the term

[0136] Throughout this specification, terms are given their normal meanings as will be understood by those skilled in the art. However, to avoid misunderstanding, the meanings of specific terms will be specifically defined or clarified.

[0137] In this disclosure, the singular forms “a,” “an,” and “the” include plural referents, and unless the context clearly indicates otherwise, a reference to a particular numerical value includes at least that particular value. Thus, for example, a reference to “a material” refers to at least one of such material and its equivalents known to those skilled in the art, and so on.

[0138] When a value is expressed as an approximation using the antecedent "about," it will be understood that the particular value forms another implementation. Generally, the term "about" is used to indicate an approximation that may vary depending on the desired properties sought by the disclosed subject matter and is interpreted based on its function in the specific context in which it is used. Those skilled in the art will be able to interpret this in a conventional manner. In some cases, the number of significant figures used for a particular value can be a non-limiting method for determining the range of the term "about." In other cases, the expected range of the term "about" available for each value can be determined using the rank used in a series of values. Where applicable, all ranges are inclusive and composable. That is, a reference to a value within a range includes every value within that range.

[0139] Unless otherwise specified, the term "aqueous" refers to a solvent system containing at least about 98 wt% water relative to the total weight of the solvent. In some applications, soluble, miscible, or partially miscible (emulsified with surfactants or other means) co-solvents may also be present, which, for example, extend the range of water's fluidity (e.g., alcohol / diol). When specified, additional independent embodiments include those in which the "aqueous" solvent system contains at least about 55 wt%, at least about 60 wt%, at least about 70 wt%, at least about 75 wt%, at least about 80%, at least about 85 wt%, at least about 90 wt%, at least about 95 wt%, or at least about 98 wt% water relative to the total solvent. In some cases, the aqueous solvent may consist substantially of water and may be substantially free of or completely free of co-solvents or other substances. The solvent system may be at least about 90 wt%, at least about 95 wt%, or at least about 98 wt% water, and in some embodiments, it is free of co-solvents or other substances.

[0140] Unless otherwise specified, the term "non-aqueous" refers to a solvent system containing less than about 10% by weight of water and typically containing at least one organic solvent. Additional independent embodiments include those in which the "non-aqueous" solvent system contains less than about 50% by weight, less than about 40% by weight, less than about 30% by weight, less than about 20% by weight, less than about 10% by weight, less than about 5% by weight, or less than about 2% by weight of water relative to the total solvent.

[0141] As used herein, the terms “aqueous electrolyte,” “electrolyte,” and variations thereof (often referred to as “electrolyte”) are intended to indicate a solvent system comprising at least one material having a higher conductivity than a solvent system not containing that material.

[0142] The terms "electrochemically active electrolyte" or "redox active electrolyte" and their variations have their normal meanings for those skilled in the art of electrochemistry. These terms are generally intended to refer to those electrolyte compositions (compounds or solutions) capable of redox transitions (i.e., changing their oxidation or valence state by capturing or releasing at least one electron when a potential is applied). In the context of metal ligand coordination compounds, the metal may have multiple accessible valence states and be referred to as redox active, or the ligand may be able to accept / release electrons and be referred to as redox active, or redox active materials may contain one or both of a redox active metal and a ligand.

[0143] The electrolyte may contain various redox active materials. Examples of electrolytes include vanadium-based electrolytes containing vanadium ions as active materials for both electrodes, iron-chromium electrolytes containing iron ions as positive electrode active materials and chromium ions as negative electrode active materials, manganese-titanium electrolytes containing manganese ions as positive electrode active materials and titanium ions as negative electrode active materials, manganese-titanium electrolytes containing both manganese and titanium ions for both electrodes, and so on.

[0144] In some embodiments, the electrochemically active electrolyte comprises a metal ligand coordination compound. In other embodiments, the electrochemically active electrolyte comprises a metal ligand coordination compound comprising a redox-active metal ion and / or a redox-inert metal ion. Preferably, the redox-active or redox-inert metal ion is Al, Ca, Co, Cr, Sr, Cu, Fe, Mg, Mn, Mo, Ni, Pd, Pt, Ru, Sn, Ti, V, Zn, or Zr, or a combination thereof. In other embodiments, the electrochemically active electrolyte comprises an organic active material. Preferably, the organic active material is carbon, an aromatic hydrocarbon, or a combination thereof. Examples of aromatic compounds include, but are not limited to, quinones, hydroquinones, ionines, and pyridines. pyridine, acridine Or catechol. In some preferred embodiments, the electrolyte comprises a vanadium-based electrolyte.

[0145] As used herein, the term "redox couple" is a commonly accepted term among general electrochemists and refers to the oxidized (electron acceptor) and reduced (electron donor) forms of a substance in a given redox reaction. Fe(CN)6 3- / Fe(CN)6 4-A redox couple is a non-limiting example. Similarly, the term "redox-active metal ion" is intended to indicate a change in oxidation state that a metal undergoes under operating conditions. As used herein, the term "redox couple" can refer to a pair of organic materials or a pair of inorganic materials.

[0146] In addition to redox active materials, the electrolyte may also contain additional components such as solvents, buffers, supporting electrolytes, viscosity modifiers, wetting agents, etc. The electrolyte may also contain metallic elements, including heavy metals, as impurities, as defined herein. Examples of solvents include aqueous solutions containing at least one of H₂SO₄, K₂SO₄, Na₂SO₄, H₃PO₄, H₄P₂O₇, K₂HPO₄, Na₃PO₄, K₃PO₄, HNO₃, KNO₃, HCl, NaNO₃, NaOH, or KOH. Alternatively, the solvent may be an organic acid solvent.

[0147] As used herein, the term "impurity" is used in its accepted sense to refer to an unwanted substance, typically containing a metal or metalloid, that is not intended to participate in the operation of an electrochemical single cell, as is the case in the context of fuel cells or flow batteries, and in many cases, is detrimental to the safe and efficient use of the electrochemical single cell. It is often present by chance, introduced as an impurity (in the conventional sense of the term) along with the intended material. For example, as described elsewhere herein, in some systems, the presence of foreign arsenic, antimony, and other such materials forms precipitates during the operation of a flow battery. While not considered to contribute in any way to the operation of a flow battery or fuel cell, their presence can adversely affect performance. The distinction between impurities and those defined as unwanted or inappropriate aspects of the selected redox active electrolyte is important because metals or metalloids that may be considered or even chosen as redox active materials in some applications can be considered impurities when present in other electrolytes. For example, in an electrolyte composition in which a titanium-containing metal ligand coordination compound is the selected redox active electrolyte, the presence of vanadium in the same electrolyte may be considered an impurity, even though vanadium is indeed chosen as the primary redox active electrolyte in other systems.

[0148] As used herein, the term "reduced form of impurity" refers to an impurity form having an oxidation state lower than that of the impurities in the initial electrolyte. For example, when most metals or metalloids are present in solution as cations or carry a positive charge, such impurities, as used herein, are considered to be in their corresponding reduced form if their metallic form (i.e., having a zero valence state) or hydride form, such as arsine, antimony, germane, etc., have a negative valence state. Reduced form of impurities can include any type of reduced impurity. In some embodiments, the reduced form of impurity is volatile. In other embodiments, the reduced form of impurity is a volatile hydride. Common reduced form impurities include, but are not limited to, arsine (AsH3), germane (GeH4), stanane (SnH4), antimony (SbH3), or combinations thereof. In some embodiments, the reduced form of impurity is AsH3. In other embodiments, the reduced form of impurity is GeH4. In other embodiments, the reduced form of impurity is SnH4. In other embodiments, the reduced form of impurity is SbH3. In other embodiments, the reduced form of impurity is elemental mercury.

[0149] As used herein, the term "inorganic material" may include "metal ligand coordination compound" or simply "coordination compound," as is known to those skilled in the art of electrochemistry and inorganic chemistry. A (metal ligand) coordination compound may comprise a metal ion bound to an atom or molecule. The bound atom or molecule is referred to as a "ligand." In certain non-limiting embodiments, the ligand may comprise a molecule containing C, H, N, and / or O atoms. In other words, the ligand may comprise an organic molecule. In some embodiments, the coordination compound comprises at least one ligand that is not water, hydroxide, or a halide ion (F). - Cl - ,Br - I - However, the invention is not limited to these embodiments. Additional embodiments include those metal ligand coordination compounds described in U.S. Patent No. 9,768,463, which are incorporated herein by reference in their entirety, at least for the purposes of their teachings concerning coordination compounds.

[0150] As used herein, the terms “negative electrode” and “positive electrode” are electrodes defined relative to each other such that the negative electrode operates, or is designed or intended to operate, at a potential more negative than the positive electrode in both charging and discharging cycles (and vice versa), regardless of the actual potential at which they operate. The negative electrode may or may not operate at a negative potential relative to the reversible hydrogen electrode, or is designed or intended to operate at a negative potential relative to the reversible hydrogen electrode.

[0151] In this disclosure, the negative electrode associated with the first aqueous electrolyte of the balance cell may contain the same or different materials as the negative electrode of the operating flow cell, even though they share a common electrolyte. Conversely, the positive electrode associated with the second aqueous electrolyte of the balance cell will almost certainly contain a different material than the positive electrode of the operating flow cell; in this case, the positive electrolyte of the flow cell will almost certainly be compositionally different from the second electrolyte of the balance cell and will be physically separate from it.

[0152] The terms "negative electrode electrolyte" and "positive electrode electrolyte" generally refer to electrolytes associated with the negative and positive electrodes, respectively. However, as used herein, the terms "negative electrode electrolyte" and "positive electrode electrolyte" are reserved for the corresponding electrolytes in flow batteries. As envisioned herein, the negative electrode working electrolyte (negative electrode electrolyte) of a flow battery comprises a coordination compound or a metal-ligand coordination compound. In a specific embodiment, the negative electrode electrolyte comprises a metal-ligand coordination complex having the following formula:

[0153] M(L 1 ) x (L 2 ) y (L 3 ) z m

[0154] in:

[0155] M can be Al, Ca, Ce, Co, Cr, Fe, Mg, Mn, Mo, Si, Sn, Ti, V, W, Zn, or Zr;

[0156] L 1 L 2 and L 3 Each of these can be independently an ascorbate, catechol, citrate, glycolate, or a polyol (including ligands derived from ethylene glycol, propylene glycol, or glycerol), gluconate, glycine, α-hydroxyalkanoate (e.g., α-hydroxyacetic acid, or derived from glycolic acid), β-hydroxyalkanoate, γ-hydroxyalkanoate, malate, maleate, phthalate, pyrogallolate, sarcosine, salicylate, or lactate.

[0157] x, y, and z are independently 0, 1, 2, or 3, and 1 ≤ x + y + z ≤ 3;

[0158] And m can be +1, 0, -1, -2, -3, -4 or -5.

[0159] Related and independent embodiments provide (a) x = 3, y = z = 0; (b) x = 2, y = 1, z = 0; (c) x = 1, y = 1, z = 1; (d) x = 2, y = 1, z = 0; (e) x = 2, y = z = 0; or (f) x = 1, y = z = 0. In some preferred embodiments, M is Al, Cr, Fe, or Ti, and x + y + z = 3. In a more preferred embodiment, the negative electrode electrolyte comprises a titanium metal-ligand coordination compound. In other preferred embodiments, the negative electrode electrolyte comprises a vanadium metal-ligand coordination compound.

[0160] In other embodiments, the redox-active material is described with respect to compounds having the following formula:

[0161] M n Ti(L1)(L2)(L3)

[0162] Wherein: L1 is a catechol salt, and L2 and L3 are each independently selected from catechol, ascorbate, citrate, glycolate, polyol, gluconic acid, glycine, hydroxyalkanoate, acetate, formate, benzoate, malate, maleate, phthalate, sarcosine, salicylate, oxalate, urea, polyamine, aminophenol, acetylacetone, or lactate; each M is independently Na, Li, or K; n is 0 or an integer from 1 to 6; and the condition is that when both L1 and L2 are catechol, L3 is not oxalate, urea, catechol, or acetylacetone.

[0163] In some embodiments, the catechol group comprises 1,2-dihydroxybenzene, 1,2,3-trihydroxybenzene, 1,2,4-trihydroxybenzene, or mixtures thereof. Preferred embodiments include compositions having the following formula.

[0164] M n Ti (catechin ion) 2 (hydroxycatechin ion) or M n Ti (catechin)3.

[0165] In other embodiments, the redox-active composition is or comprises one or more compositions having the following formula.

[0166] M n Ti(L1)(L2)(L3)

[0167] Wherein: L1 is a catechol group, and L2 and L3 are each independently selected from catechol groups, ascorbic acid groups, citrate groups, glycolate groups, polyols, gluconic acid groups, glycine groups, hydroxyalkanoates, acetate groups, formate groups, benzoate groups, malate groups, maleate groups, phthalate groups, sarcosinate groups, salicylate groups, oxalate groups, urea groups, polyamines, aminophenol groups, acetylacetone groups, or lactate groups; each M is independently Na, Li, or K; n is 0 or an integer from 1 to 6. L1, L2, or L3 may also contain compounds having a structure according to Formula I or their oxidized or reduced forms:

[0168]

[0169] in

[0170] Ar is a 5- to 20-membered aromatic moiety that optionally contains one or more cyclic O, N, or S heteroatoms;

[0171] X1 and X2 are independently -OH, -NHR2, -SH or their anions, and X1 and X2 are adjacent to each other;

[0172] R1 is independently H or C each time it appears. 1-6 Alkoxy, C 1-6 Alkyl, C 1-6 alkenyl, C 1-6 Alkyne, 5-6 aryl or heteroaryl, boric acid or its salt, carboxylic acid or its salt, carboxylic acid ester, cyano, halogen, hydroxyl, nitro, sulfonate, sulfonic acid or its salt, phosphonate, phosphonic acid or its salt, or polyethylene glycol (preferably polyethylene glycol);

[0173] R2 is independently H or C 1-3 Alkyl; and

[0174] n can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.

[0175] Other suitable active materials may include "organic active materials." Organic active materials may comprise molecules or supramolecular structures that do not contain transition metal ions. It should also be understood that organic active materials are intended to comprise molecules or supramolecular structures dissolved in aqueous solutions. Suitable organic active materials are capable of undergoing oxidation state changes during the operation of the electrochemical energy storage system. Therefore, the molecules or supramolecular structures can accept or donate electrons during system operation.

[0176] The terms “catechin ion,” “hydroxyacetic acid ion,” “polyol,” “hydroxyalkanoate ion,” “benzoate ion,” “phthalate ion,” “urea,” and “polyamine” reflect that these ligands can optionally be selected independently from at least one of H, C. 1-6 Alkoxy, C 1-6 Alkyl, C 1-6 alkenyl, C 1-6Alkyne, 5-6 aryl or heteroaryl, boric acid or its salt, C 0-6 The fact that alkylene carboxylic acids or their salts, cyano, halogen, hydroxyl, nitro, sulfonate, sulfonic acid or its salts, phosphonate, phosphonic acid or its salts, or polydiol (preferably polyethylene glycol) groups are substituted.

[0177] Alkanoic acid groups include α, β, and γ forms. Polyamines include, but are not limited to, diamines and triamines, such as ethylenediamine, ethylenediaminetetraacetic acid (EDTA), and diethylenetriaminepentaacetic acid (DTPA). Catechol groups include all compositions containing a 1,2-dihydroxybenzene moiety. Such moieties include hydroxycatechol groups (including pyrogallol groups) and substituents listed herein. Substituents include, but are not limited to, alkyl, alkenyl, and alkynyl groups (each referring to branched or linear structures and optionally substituted with one or more carboxyl, halogen, hydroxyl, or other electron-withdrawing or electron-donating groups). Substituents also include 5- to 6-membered aryl or heteroaryl groups, including phenyl, pyridyl, furanyl, pyrroleyl, imidazolyl, triazole, or thiophene. Electron-withdrawing or electron-donating substituents may be added to the periphery of the aromatic ring to modulate the redox potential of the redox-active ligand.

[0178] The terms “parts per million (ppm)” and “parts per billion (ppb)” are defined relative to the total mass of the electrolyte to which these terms are applied, based on a mass criterion. As elsewhere herein, the terms “mg / mol” and “μg / mol” refer to the concentration of impurities relative to the amount of redox-active electrolyte in the same redox-active electrolyte.

[0179] The term "pile," "single-cell pile," or "electrochemical single-cell pile" refers to a collection of individually electrochemical cells that are electrically connected. These cells may be connected in series or in parallel. The cells may be fluidly connected or not.

[0180] aspect

[0181] Aspect 1: A method for preparing an electrolyte with reduced impurity levels, the method comprising...

[0182] a. Under conditions sufficient to produce an electrolyte for electrochemical treatment, an impurity is electrochemically reduced, the impurity being present in an initial electrolyte at an initial concentration, the initial electrolyte further comprising a redox-active electrolyte at a concentration of at least 0.5 M, the electrochemically treated electrolyte containing a reduced form of the redox-active electrolyte and a reduced form of the impurity;

[0183] b. Separate the reduced form of the impurity from the solution subjected to the electrochemical treatment.

[0184] This provides a final electrolyte having a final concentration of the impurities that is lower than the initial concentration of the impurities.

[0185] Aspect 2. The method according to Aspect 1, wherein the final concentration of the impurities in the final electrolyte is at a predetermined threshold level, the predetermined threshold level being:

[0186] (i) one or more of the following given impurities: less than about 10 mg / L, less than 5 mg / L, less than 2.5 mg / L, less than 1 mg / L, less than 500 μg / L, less than 250 μg / L, less than 100 μg / L, less than 50 μg / L, less than about 40 μg / L, less than about 30 μg / L, less than about 20 μg / L, less than about 10 μg / L, less than about 5 μg / L, or less than about 1 μg / L; or

[0187] (ii) One or more of the following impurities per mole of redox active electrolyte: less than about 10 mg (“mg / mol”), less than 5 mg / mol, less than 2.5 mg / mol, less than 1 mg / mol, less than 500 μg / mol, less than 250 μg / mol, less than 100 μg / mol, less than 50 μg / mol, less than about 40 μg / mol, less than about 30 μg / mol, less than about 20 μg / mol, less than about 10 μg / mol, less than about 5 μg / mol, or less than about 1 μg / mol.

[0188] Aspect 3. The method according to aspect 1 or 2, wherein the impurity comprises antimony, arsenic, germanium, tin or a combination thereof.

[0189] Aspect 4. The method according to any one of Aspects 1 to 3, wherein the electrochemical treatment is carried out in an electrochemical single cell.

[0190] Aspect 5. The method according to aspect 4, wherein the impurities in the reduced form are separated by plating within the cathode of the electrochemical single cell.

[0191] Aspect 6. The method according to any one of Aspects 1 to 5, wherein the impurities in the reduced form are precipitated from the electrolyte of the electrochemical treatment.

[0192] Aspect 7. The method according to aspect 6, wherein the impurities in the reduced form of the precipitate are removed by filtration.

[0193] Aspect 8. The method according to any one of Aspects 1 to 4, wherein the impurity in the reduced form is a volatile hydride.

[0194] Aspect 9. The method according to aspect 8, wherein the volatile hydride is arsine (AsH3), germanane (GeH4), stanane (SnH4), antimony (SbH3), or a combination thereof.

[0195] Aspect 10. The method according to any one of Aspects 1 to 9, wherein the electrochemical treatment is an electrochemical reduction performed at a redox potential that is more negative than the reduction potential of the impurity.

[0196] Aspect 11. The method according to any one of Aspects 1 to 10, further comprising conditioning the electrochemically treated electrolyte by the following steps:

[0197] (a) Heating the electrolyte of the electrochemical treatment in a temperature range of 20°C to about 105°C;

[0198] (b) purging the electrochemically treated electrolyte or the heated solution described in (a) with an inert gas; or

[0199] (c) The combination of (a) and (b).

[0200] Aspect 12. The method according to aspect 11, wherein the temperature of the heating step (a) is in the range of about 35°C to about 95°C, or more preferably about 45°C to about 85°C.

[0201] Aspect 13. The method according to aspect 11 or 12, wherein the inert gas is nitrogen or argon.

[0202] Aspect 14. The method according to any one of aspects 11 to 13, wherein steps (a) and (b) are performed simultaneously.

[0203] Aspect 15. The method according to any one of aspects 11 to 13, wherein steps (a) and (b) are performed sequentially.

[0204] Aspect 16. The method according to any one of Aspects 1 to 15 further includes oxidizing the redox active electrolyte in the reduced form of the final electrolyte.

[0205] Aspect 17. The method according to aspect 16, wherein the oxidation is carried out by purging the final electrolyte with an oxidizing agent such as oxygen, preferably air.

[0206] Aspect 18. The method according to any one of Aspects 1 to 15, wherein the oxidation is carried out using hydrogen peroxide.

[0207] Aspect 19. The method according to any one of Aspects 16 to 18, wherein the oxidation is carried out while the final electrolyte is heated.

[0208] Aspect 20. The method according to aspect 16 or 19, wherein the oxidation is carried out at a temperature of about 65°C or higher, preferably at a temperature of about 85°C or higher, and more preferably at a temperature of about 105°C or higher.

[0209] Aspect 21. The method according to aspect 19, wherein the oxidation is carried out using a hydrogen evolution catalyst.

[0210] Aspect 22. The method according to aspect 21, wherein the hydrogen evolution catalyst is activated carbon, carbon cloth, carbon felt, carbon paper, Ti mesh, Ti felt, drawn Ti mesh, Pt-plated Ti mesh, or a combination thereof.

[0211] Aspect 23. The method according to any one of Aspects 1 to 22, wherein the redox active electrolyte comprises:

[0212] (i) Metal ligand coordination compounds, including Al, Ca, Co, Cr, Sr, Cu, Fe, Mg, Mn, Mo, Ni, Pd, Pt, Ru, Sn, Ti, V, Zn or Zr;

[0213] (ii) Organic active materials, preferably carbon, aromatic hydrocarbons such as quinones, hydroquinones, ionines, and pyridines. pyridine, acridine Or catechins; or

[0214] Combinations of (iii), (i), or (ii).

[0215] Aspect 24. The method according to aspect 23, wherein the redox active electrolyte comprises a metal ligand coordination compound comprising the group Co, Cr, Cu, Fe, Mn, Mo, Ru, Sn, Ti, V or Zr.

[0216] Aspect 25. An electrolyte prepared according to any one of Aspects 1 to 24.

[0217] Section 26. Electrolyte, comprising:

[0218] (i) a redox active electrolyte with a concentration of at least 0.5 M, preferably containing a metal or metalloid, more preferably a metal ligand coordination compound containing titanium; and

[0219] (ii) Impurities, which are present in an amount of less than about 500 μg / L of the electrolyte or less than 500 μg / mol of the redox active electrolyte.

[0220] Aspect 27. The electrolyte according to aspect 25 or 26, comprising one or more of As, Ge, Hg and Sb in amounts less than about 50 μg / L.

[0221] Aspect 28. The electrolyte according to any one of Aspects 25 to 27 comprises antimony, arsenic, germanium, tin or a combination thereof in a concentration of less than about 20 μg / L, less than about 15 μg / L, less than about 10 μg / L or less than about 5 μg / L.

[0222] Aspect 29. The electrolyte according to any one of Aspects 25 to 28, comprising one or more or a combination of antimony, arsenic, germanium, and tin in a concentration of less than about 5 μg / L.

[0223] Aspect 30. An electrochemical single cell comprising an electrolyte according to any one of Aspects 25 to 29.

[0224] Aspect 31. A redox flow battery comprising at least one electrochemical single cell according to aspect 30.

[0225] Aspect 32. An electrochemical single cell comprising a first half-cell chamber and a second half-cell chamber separated by a cation exchange membrane, wherein:

[0226] The first half-cell chamber includes a first electrode, preferably a carbon electrode, in contact with a first aqueous electrolyte containing redox active materials and reducible impurities; and

[0227] The second half-cell chamber contains a second electrode in contact with a second aqueous electrolyte, the second aqueous electrolyte containing one or more salts containing a non-protic cation at a concentration of at least 0.1 M, and the second electrode contains a catalyst for generating O2, preferably containing nickel, such as Ni foam, stainless steel mesh, stainless steel felt, Ni oxide, Ni hydroxide, Ni hydroxyl oxide, or Ni-Fe oxide.

[0228] Aspect 33. An electrochemical single cell comprising a first half-cell chamber and a second half-cell chamber separated by a cation exchange membrane, wherein:

[0229] The first half-cell chamber contains a first electrode, preferably a carbon electrode, in contact with a first aqueous electrolyte containing redox active materials and reducible impurities, and is made of carbon cloth, carbon felt, or carbon paper; and

[0230] The second half-cell chamber includes a second electrode in contact with a second aqueous electrolyte, the second aqueous electrolyte having a pH of at least 2 and containing one or more salts of aprotic cations having a concentration of at least 0.1 M.

[0231] The second electrode contains a catalyst for generating O2, preferably at least one or a combination of oxides of cobalt, iridium, iron, manganese, nickel, ruthenium, tin or platinum, most preferably IrO2.

[0232] Aspect 34. The electrochemical single cell according to aspect 32 or 33, wherein the reducible impurity forms a volatile reduced form during electrochemical reduction, such as arsine (AsH3), germanane (GeH4), tinane (SnH4), or antimonide (SbH3).

[0233] Aspect 35. The electrochemical device according to any one of aspects 32 to 34, wherein the second aqueous electrolyte comprises Na + and / or K + Ions and have a pH of at least 7.

[0234] Aspect 36. A method of operating an electrochemical device according to any one of aspects 32 to 35, comprising passing a sufficient current through the single cell under conditions sufficient to reduce the concentration of reducible impurities in the first aqueous electrolyte to a predetermined level in the first aqueous electrolyte, preferably less than 10 μg / L.

[0235] Example

[0236] The following examples are provided to illustrate some of the concepts described within this disclosure. While each example is thought to provide a specific individual implementation of the composition, preparation method, and use, these examples should not be considered as limiting the more general implementation described herein.

[0237] Example 1:

[0238] As described above, in a particular embodiment, the electrochemical single cell includes a first half-cell chamber and a second half-cell chamber separated by a membrane, wherein:

[0239] The first half-cell chamber contains a first electrode, preferably a carbon electrode, in contact with a first aqueous electrolyte containing a redox-active electrolyte (e.g., a negative electrode electrolyte) and reducible impurities; and

[0240] The second half-cell chamber contains a second electrode in contact with a second aqueous solution, which is preferably acidic but has a pH of at least 2. The second electrode contains a catalyst for generating O2, preferably at least one or a combination of oxides of cobalt, iridium, iron, manganese, nickel, ruthenium, tin, or platinum, with IrO2 being the most preferred.

[0241] To illustrate an exemplary implementation in this context, experiments have been conducted in which an iridium oxide catalyst with a carbon electrode coated on a cation exchange membrane is used as the anode, and carbon cloth is used as the cathode, which is separated from the membrane by a non-conductive layer (see Figure 3(A)). This non-conductive layer is composed of an electronically insulating but fluid-permeable material such as a mesh or foam. Melamine foam has been found to be suitable for the operation of this non-conductive layer. As described elsewhere herein, the non-conductive layer separates the reduction of the negative electrode electrolyte from the acid flow originating from the anode, which can lead to degradation of the negative electrode electrolyte. In this configuration, the electrochemical single cell is used as a flow cell, in which a redox-active electrolyte (negative electrode electrolyte) solution containing titanium ligand coordination compounds (e.g., titanium-catechol salt complexes) is flowed through the cathode. Water for the anode is supplied by diffusion from the negative electrode electrolyte. In practice, this design has so far been limited to charging the redox-active electrolyte at a current density of approximately 30 or 40 mA / cm². This current density appears to be limited by acid transport to the cathode, leading to degradation of the titanium complexes. Despite these initial limitations, such a construction has been shown to provide proof of concept for the principles described herein, providing a final redox active electrolyte comprising a titanium-catechol salt complex at a concentration exceeding 0.7 M, wherein the level of arsenic, as an exemplary impurity, is less than 10 μg / L.

[0242] Example 2:

[0243] As described above, in certain other embodiments, the electrochemical single cell includes a first half-cell chamber and a second half-cell chamber separated by a membrane, wherein:

[0244] The first half-cell chamber contains a first electrode, preferably a carbon electrode, in contact with a first aqueous electrolyte containing redox active materials and reducible impurities; and

[0245] The second half-cell chamber contains a second electrode in contact with a second alkaline aqueous solution (anolyte), the second electrode containing a catalyst for generating O2, preferably containing nickel, such as Ni foam, stainless steel mesh, stainless steel felt, Ni oxide, Ni hydroxide, Ni hydroxyl oxide, or Ni-Fe oxide.

[0246] In this exemplary embodiment, the anolyte is a concentrated solution of sodium hydroxide, potassium hydroxide, phosphate buffer, or a mixture thereof (see Figure 3(B)). The anode consists of a common alkaline oxidation catalyst, in these cases nickel or nickel-coated steel. The cathode is a carbon electrode. The cathode and anode are connected by a cation exchange membrane such as NAFION. TMPerfluorosulfonic acid resin or sulfonated polyether ether ketone (s-PEEK) is used as a separator. This single cell is also designed as a flow cell, in which a redox-active electrolyte solution (negative electrode electrolyte) containing a titanium ligand coordination compound (e.g., titanium-catechol salt complex) and an anolyte are pumped through the single cell. Furthermore, as described in Example 1, acceptable results were obtained.

[0247] Example 3:

[0248] Using Ni foam anode (346g / m) 2 1.6mm thickness, porosity: ≥95%, 80~110ppi; MTI Corporation), Nafion N117 cation exchange membrane and carbon cloth cathode constructed a 25cm 2 HERM apparatus. 1M KOH was used as the anolyte. The apparatus was used to purify a 1.2M Ti-catechol salt negative electrode electrolyte, which, as measured by ICP-OES, contained 3.1 ppm As and 2.9 ppm Sn. The negative electrode electrolyte was charged at 180 mA / cm². 2 The solution potential was lowered to -1.36 V vs Ag / AgCl. The electrolyte was conditioned by bubbling with nitrogen and magnetically stirring at 45°C for 16 hours, followed by reflux and further bubbling with nitrogen for 20 hours. At the end of these conditioning steps, ICP-OES revealed less than 1.0 ppb of As and 1.6 ppm of Sn, representing a reduction in the concentrations of these impurities of >99% and 45%, respectively.

[0249] Example 4:

[0250] A 25cm anode was constructed using a carbon cloth anode facing an IrO2-coated surface of a Nafion N117 film. 2 HERM apparatus. A melamine foam non-conductive layer is placed between the membrane and the carbon cloth cathode. This apparatus is used to purify a 1.2 M Ti-catechol salt negative electrode electrolyte containing 3.1 ppm As. The negative electrode electrolyte is charged at 40 mA / cm². 2 The solution potential was lowered to -1.34 V vsAg / AgCl. The electrolyte was conditioning by bubbling with nitrogen and magnetically stirring at 65°C for 2.5 hours. After this conditioning step, the electrolyte was found to contain 6.7 ppb As, representing a >99% reduction in As concentration.

[0251] Example 5:

[0252] The 1.2 M Ti-catechol salt anode electrolyte, contaminated with more than 20 mg / L of Zn, was purified. Charging this electrolyte to -1.42 V vs Ag / AgCl resulted in a substantial Zn coating on the carbon cathode of the HERM device. Figure 4 (Zn plated on HERM cathode)

[0253] As will be understood by those skilled in the art, many modifications and variations of the invention are possible in light of these teachings, and all of these are contemplated herein.

[0254] The disclosure of each patent, patent application, and publication cited or described in this document is incorporated herein by reference in its entirety for all purposes.

Claims

1. A method for preparing an electrolyte with reduced impurity levels, the method comprising: a. Under conditions sufficient to produce an electrolyte for electrochemical treatment, an impurity is electrochemically reduced, the impurity being present in an initial electrolyte at an initial concentration, the initial electrolyte further comprising a redox-active electrolyte at a concentration of at least 0.5 M, the electrolyte for electrochemical treatment containing a reduced form of the redox-active electrolyte and a reduced form of the impurity, wherein the conditions include, while passing an electric current through the electrolyte, the injection of aprotic cations into the electrolyte through a cation exchange membrane, wherein the aprotic cations include alkali metal cations, alkaline earth metal cations, or organic ammonium cations, and wherein the redox-active electrolyte is a metal-ligand coordination complex comprising Al, Ca, Co, Cr, Sr, Cu, Fe, Mg, Mn, Mo, Ni, Pd, Pt, Ru, Sn, Ti, V, Zn, or Zr; b. Heating the electrochemically treated electrolyte within a temperature range of 30°C to 105°C; c. Purge the electrolyte or the heated solution of the electrochemical treatment with an inert atmosphere; as well as d. Separate the reduced form of the impurities from the solution after the electrochemical treatment to provide the final electrolyte. The concentration of the impurities in the final electrolyte is less than 500 μg / L, or the impurities per mole of redox active electrolyte in the redox active electrolyte solution are less than 500 μg.

2. The method according to claim 1, wherein the impurity comprises antimony, arsenic, germanium, tin, or a combination thereof.

3. The method according to claim 1, wherein the electrochemical treatment is performed in an electrochemical single cell.

4. The method of claim 3, wherein the impurities in the reduced form are separated by plating within the cathode of the electrochemical single cell.

5. The method of claim 1, wherein the reduced form of the impurity precipitates from the electrolyte of the electrochemical treatment.

6. The method of claim 5, wherein the impurities in the reduced form of the precipitate are removed by filtration.

7. The method according to claim 1, wherein the impurity in the reduced form is a volatile hydride.

8. The method according to claim 7, wherein the volatile hydride is arsine AsH3, germanane GeH4, tinane SnH4, antimony hydrogen SbH3, or a combination thereof.

9. The method of claim 1, wherein the electrochemical treatment is an electrochemical reduction performed at a redox potential that is more negative than the reduction potential of the impurity.

10. The method according to claim 1, wherein the temperature of the heating step is in the range of 35°C to 95°C.

11. The method according to claim 1, wherein the temperature of the heating step is in the range of 45°C to 85°C.

12. The method according to claim 1, wherein the inert atmosphere is nitrogen or argon.

13. The method according to claim 1, wherein steps b and c are performed simultaneously.

14. The method of claim 1, wherein steps b and c are performed sequentially.

15. The method of claim 1, further comprising oxidizing the reduced form of the redox active electrolyte in the final electrolyte.

16. The method of claim 15, wherein the oxidation is performed by purging the final electrolyte with an oxidizing agent.

17. The method of claim 16, wherein the oxidant is oxygen or air.

18. The method of claim 15, wherein the oxidation is performed using hydrogen peroxide.

19. The method of claim 15, wherein the oxidation is performed while the final electrolyte is heated.

20. The method of claim 15, wherein the oxidation is carried out at a temperature of 65°C or higher.

21. The method of claim 20, wherein the temperature is 85°C or higher.

22. The method of claim 21, wherein the temperature is 105°C or higher.

23. The method of claim 15, wherein the oxidation is carried out using a hydrogen evolution catalyst.

24. The method according to claim 23, wherein the hydrogen evolution catalyst is activated carbon, carbon cloth, carbon felt, carbon paper, Ti mesh, Ti felt, or a combination thereof.

25. The method of claim 24, wherein the Ti mesh comprises drawn Ti mesh, Pt-plated Ti mesh, or a combination thereof.

26. The method of claim 1, wherein the redox electrolyte is a metal ligand coordination complex of the following formula: M(L 1 ) x (L 2 ) y (L 3 ) z m in: M is Al, Ca, Co, Cr, Fe, Mg, Mn, Mo, Sn, Ti, V, Zn, or Zr; L 1 L 2 and L 3 Each of these can be independently classified as ascorbate, catechol, citrate, glycolate, polyol, gluconate, glycine, α-hydroxyalkanoate, β-hydroxyalkanoate, γ-hydroxyalkanoate, malate, maleate, phthalate, pyrogallate, sarcosine, salicylate, or lactate. x, y, and z are each independently 0, 1, 2, or 3, and 1 ≤ x + y + z ≤ 3; and m can be +1, 0, -1, -2, -3, -4, or -5.

27. The electrolyte prepared by the method according to any one of claims 1 to 25, comprising: (i) a redox-active electrolyte with a concentration of at least 0.5 M, wherein the redox-active electrolyte is a metal-ligand coordination complex comprising Al, Ca, Co, Cr, Sr, Cu, Fe, Mg, Mn, Mo, Ni, Pd, Pt, Ru, Sn, Ti, V, Zn, or Zr; and (ii) Impurities, which are present in an amount of less than 500 μg / L of the electrolyte or less than 500 μg / mol of the redox active electrolyte.

28. The electrolyte according to claim 27, wherein the final concentration of the impurities is: (i) one or more of the following given impurities: less than 10 mg / L, less than 5 mg / L, less than 2.5 mg / L, less than 1 mg / L, less than 500 μg / L, less than 250 μg / L, less than 100 μg / L, less than 50 μg / L, less than 40 μg / L, less than 30 μg / L, less than 20 μg / L, less than 10 μg / L, less than 5 μg / L, or less than 1 μg / L; or (ii) One or more of the following given impurities relative to the redox active electrolyte: less than 10 mg / mol, less than 5 mg / mol, less than 2.5 mg / mol, less than 1 mg / mol, less than 500 μg / mol, less than 250 μg / mol, less than 100 μg / mol, less than 50 μg / mol, less than 40 μg / mol, less than 30 μg / mol, less than 20 μg / mol, less than 10 μg / mol, less than 5 μg / mol, or less than 1 μg / mol.

29. The electrolyte according to claim 27, wherein the redox active electrolyte further comprises an organic active material.

30. The electrolyte according to claim 29, wherein the organic active material is carbon or an aromatic hydrocarbon.

31. The electrolyte according to claim 29, wherein the organic active material is quinone, hydroquinone, zirconia, or pyridine. pyridine, acridine Or catechins.

32. The electrolyte according to claim 27, wherein the redox active electrolyte comprises a metal ligand coordination compound, wherein the metal ligand coordination compound comprises Co, Cr, Cu, Fe, Mn, Mo, Ru, Sn, Ti, V or Zr.

33. The electrolyte of claim 32, wherein the metal ligand coordination compound comprises Ti.

34. The electrolyte according to claim 27, comprising one or more of As, Ge, Hg and Sb in a concentration of less than 50 μg / L.

35. The electrolyte according to claim 27, comprising any one or a combination of antimony, arsenic, germanium, and tin at a concentration of less than 20 μg / L, less than 15 μg / L, less than 10 μg / L, or less than 5 μg / L.

36. The electrolyte according to claim 27, comprising one or more or a combination of antimony, arsenic, germanium, and tin at a concentration of less than 5 μg / L.

37. An electrochemical single cell comprising the electrolyte according to claim 27.

38. A redox flow battery comprising at least one electrochemical single cell according to claim 37.

39. The electrochemical single cell according to claim 37, comprising a first half-cell chamber and a second half-cell chamber separated by a cation exchange membrane, wherein: The first half-cell chamber includes a first electrode in contact with a first aqueous electrolyte containing redox active material and reducible impurities; and The second half-cell chamber includes a second electrode in contact with a second aqueous electrolyte, the second aqueous electrolyte containing one or more salts containing a non-proton cation at a concentration of at least 0.1 M, and the second electrode containing a catalyst for generating O2.

40. The electrochemical single cell according to claim 39, wherein the first electrode is a carbon electrode.

41. The electrochemical single cell of claim 39, wherein the catalyst comprises nickel.

42. The electrochemical single cell according to claim 41, wherein the catalyst is Ni foam, stainless steel mesh, stainless steel felt, Ni oxide, Ni hydroxide, Ni oxide with hydroxyl group, or Ni-Fe oxide.

43. The electrochemical single cell according to claim 40, wherein: The carbon electrode is made of carbon cloth, carbon felt, or carbon paper.

44. The electrochemical single cell of claim 39, wherein the second aqueous electrolyte has a pH of at least 2.

45. The electrochemical single cell of claim 39, wherein the catalyst comprises oxides of platinum or cobalt, iridium, iron, manganese, nickel, ruthenium, tin, or combinations thereof.

46. ​​The electrochemical single cell according to claim 45, wherein the catalyst is IrO2.

47. The electrochemical single cell according to claim 39, wherein the reducible impurity forms a volatile reduced form during electrochemical reduction.

48. The electrochemical single cell according to claim 47, wherein the volatile reducing form is arsine AsH3, germane GeH4, tinane SnH4, or antimonide SbH3.

49. The electrochemical single cell of claim 39, wherein the second aqueous electrolyte comprises Na + and / or K + It contains ions and has a pH of at least 7.

50. A method of operating an electrochemical cell according to claim 39, comprising reducing the concentration of reducible impurities in the first aqueous electrolyte to a predetermined level in the first aqueous electrolyte, thereby allowing sufficient current to pass through the single cell.

51. The method of claim 50, wherein the predetermined level is less than 10 μg / L.

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