Ion-conductive membrane, component having ion-conductive membrane, and method of forming same

Abstract

This disclosure provides an ion-conducting membrane (10), a component (100) having the ion-conducting membrane (10), and methods for manufacturing the membrane (10) and the component (100). The ion-conducting membrane (10) comprises a homogeneous blend (12) and one or more additives (14). The selected polymer(s) are present at a weight percent ranging from 1% to 40%. The ion-conducting membrane (10) of the present invention combines advances in materials chemistry, nanotechnology, and manufacturing to simultaneously increase device power and efficiency. The ion-conducting membrane (10) of the present invention overcomes limitations in currently known technology without sacrificing advantageous properties. The membrane (10) of the present invention provides nonlinear performance improvements in electrochemical devices, resulting in cost reductions at the overall system level.

Description

[Technical Field]

[0001] The present disclosure relates to ion-conducting membranes. In particular, the present disclosure relates to ion-conducting membranes, components having ion-conducting membranes as one of their parts, and methods of forming the ion-conducting membranes and components. [Background technology]

[0002] Ion-conducting membranes are solid materials that allow the transport of ions through them. They are used in devices used in applications such as energy generation, energy conversion, and energy storage. Ion-conducting membranes are also electrical insulators. They determine the power output (energy extraction rate) and efficiency of energy devices. Ion-conducting membranes differ from separators, which allow the transport of flammable organic liquids throughout the device through micropores. The stability of the ion-conducting membrane determines the operating window of the device.

[0003] Ion-conducting membranes can be effectively used in energy generation, conversion, and storage. Fuel cells are energy conversion devices that convert fuel into electricity. Electrolyzers function inversely to fuel cells in that they generate fuel (such as H2) when supplied with electricity. Batteries store energy. At a given energy density, the power density of a battery is fixed, and vice versa. Flow batteries combine features of both batteries and fuel cells into a single device. As in the case of fuel cells, where the fuel is stored separately from the stack, in a flow battery, energy is stored in a separate tank in chemical form and flowed to the stack, which converts this chemical energy into electrical energy. Highly efficient ion-conducting membranes can improve the performance of the device and extend its use.

[0004] The first ion-conducting membranes developed were used in low-temperature polymer electrolyte membrane (LT-PEM) fuel cells, also known as proton exchange membrane (PEM) fuel cells. Nafion®, developed by DuPont in 1970, has become the industry standard due to its exceptional chemical stability and ionic conductivity under humidified conditions. However, Nafion® can only conduct cations, has poor selectivity among cations, and requires a water management system. It can also only operate below 120°C, limiting the types of devices in which it can be used. The use of Nafion® is also limited by its cost. Ion-conducting membranes containing polybenzimidazole (PBI) have been developed for operation under anhydrous conditions. PBI-based ion-conducting membranes utilize acid doping to transfer protons (H) along the polymer backbone. + ) traps. Increasing the ionic conductivity of PBI-based membranes comes at the expense of their strength. Crosslinking increases membrane strength, but often at the expense of other properties. Crosslinking generally occurs at the expense of PBI's protonated amide bonds being bonded to another polymer, making the site inaccessible for proton hopping, resulting in increased strength. Conductivity, selectivity, and strength are orthogonal properties in current material systems, and an improvement in one property is offset by a decrease in a related property.

[0005] Ion conductors for metal batteries (lithium-air, lithium-sulfur, aluminum-air, zinc-air, etc.) generally use ceramic electrolytes. The anode and cathode sides pose various challenges in the construction of such devices. In many cases, the presence and growth of dendrites and electrode instability due to the electrolyte, as well as active material crossover, degrade the performance of such batteries. Metal anodes, such as lithium, are prone to certain The metal anode is bonded or deposited with a ceramic electrolyte through techniques. Dendrites grow from the surface of the metal anode through the electrolyte. Multiple dendrites can grow and spread through the bulk electrolyte. The cathode side uses an electrode with different properties compared to the anode. Furthermore, the interface between the cathode and anode must be engineered to selectively allow the desired ions. Modern metal batteries and modern solid-state batteries are subcategories of this type of battery and use solid ionic conductors such as those mentioned above, in some cases Nafion®. These limitations limit the power that can be extracted from these battery systems.

[0006] Flow battery electrolytes often use multivalent catholyte and anolyte solutions. Therefore, the use of ion-conducting membranes that can selectively transport only specific types of cations or anions is beneficial in flow batteries. Such membranes should have two important performance parameters: high ionic conductivity and high ionic selectivity for the major ions responsible for their function.

[0007] First-generation separators, also known as nonzero gap separators, are physical separators using diaphragms. Such porous separators suffer from the drawback of high crossover, which limits the device's operating window. Second-generation membranes were based on perfluorosulfonic acid (PFSA). PFSA-based membranes sacrifice selectivity due to Donnan's membrane equilibrium, an equilibrium derived from the second law of thermodynamics that allows only fully ionized electrolytes to cross the permeability barrier. Teflon-like membranes with a hydrophobic backbone and ionogenic groups, SO3 -The structure of PFSA-based membranes with a cation-containing structure leads to conditions of Donnan equilibrium. When equilibrium is reached, all cations in a system containing water or a polar solvent will diffuse from one phase (or region) to the other. In the presence of multi-cation systems, such as flow batteries, increasing the charge / discharge rate under dynamic conditions will also force countercations through the membrane, limiting the maximum current density that can be drawn. This leads to permanent capacity degradation of the battery.

[0008] High-temperature proton exchange membranes (HT-PEMs) based on anhydrous proton conduction have been developed to alleviate some of the limitations of low-temperature proton exchange membrane fuel cell (LT-PEM) systems. Therefore, there is a need for ion-conducting membranes that can maintain their conductivity at higher temperatures without compromising selectivity or their mechanical resilience. Second-generation membranes were constructed around PBI, with improved proton conductivity achieved by impregnating the PBI with phosphoric acid. A drawback of such phosphoric acid-based PBIs is that high levels of acid content are required for high conductivity, which leads to deterioration of mechanical properties. Some techniques used in the prior art include crosslinking, post-treatment, functionalization of PBI, and the use of additives such as graphene oxide (GO). However, GO is reduced above 160 °C to reduced graphene oxide (r-GO), which is electronically conductive. This leads to a loss of conductivity, limiting the amount of graphene oxide that can be added to the system. If a permeating network is present, it can short-circuit the system. The stacking of multi-layer graphene hinders proton transport through the thickness direction.

[0009] In direct methanol fuel cells (DMFCs), second-generation membranes limit the concentration of methanol used as the input fuel due to methanol crossover. DMFCs are limited by the use of methanol concentrations between 1 and 3 molar as the fuel feed. At such low concentrations, a high degree of dilution with water is required. Price and cost-performance analysis indicates that methanol concentrations above 10 M are required to be competitive with other competing technologies, such as diesel generators. (Feng, Yan, et. al., "A selective electrocatalyst-based direct methanol fuel cell operated at high concentrations of methanol," Science Advances, vol. 3, pp. 1–7 (2017).)

[0010] The first and second generation anion conductors share some common drawbacks, such as a figure-of-merit tradeoff between anion conductance and mechanical properties. - ) tends to be large compared to protons, so the premium for this trade-off remains high. A common method for introducing anionic charge carriers or ionomeric groups involves quaternization of the polymer backbone with quaternary ammonium functional groups. When operating in a strongly alkaline medium, such as potassium hydroxide or sodium hydroxide, the interaction between the strong base and the anionic ionogenic groups attached to the polymer chain leads to chemically induced mechanical degradation. This mechanism is known as Hoffmann degradation. A common prior art goal is to obtain a conducting membrane that is mechanically strong and maintains stable anionic conductance over a wide range of temperatures.

[0011] Currently known membranes have technical limitations regarding how they can operate individual devices, and currently no membranes exist that overcome these limitations while being compatible across a wide variety of target device types. The orthogonal property requirements of selectivity, conductivity, and strength impose limitations on device operating conditions. Primarily, these types of membranes are polymer chemistry driven by specific applications and limited operating conditions. The membranes, compositions, and methods for their manufacture disclosed herein offer improved strength, selectivity, and conductivity over known membranes in a variety of applications, including high temperatures and other challenging operating conditions. Summary of the Invention [Problem to be solved by the invention]

[0012] This Summary is provided to conveniently introduce a selection of ideas that are further described in the Detailed Description of the Disclosure. This Summary is not intended to identify key or essential inventive ideas of the subject matter, nor is it intended to delineate the scope of the disclosure. [Means for solving the problem]

[0013] The present disclosure relates to an ion-conducting membrane comprised of a homogeneous blend of polybenzimidazole (PBI) and one or more polymers selected from the group consisting of polyvinylidene difluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) PVDF-HFP, chitosan, and functionalized chitosan. The one or more additives are selected from the group consisting of graphene oxide (GO), functionalized graphene oxide (functionalized GO), and hexagonal boron nitride (h-BN). The selected one or more polymers are present in a weight percent range of 1% to 40%, while the weight percent of the selected additive is in a range of 0.5% to 80%. The additive is dispersed in the homogeneous blend with a dispersion amount of greater than 80% and an aggregate amount of less than 30%. The ion-conducting membrane has a conductivity of 1 S / cm at 30°C. 2 The ionic conductance per area may be greater than 0.05.

[0014] Also taught herein is a component including an ion-conducting membrane comprising a homogeneous blend of PBI and one or more polymers selected from the group consisting of PVDF, PVDF-HFP, chitosan, and functionalized chitosan, wherein the weight percentage of the one or more polymers is in the range of 1% to 40%. The ion-conducting membrane of the component has one or more additives selected from the group consisting of graphene oxide, functionalized graphene oxide, and h-BN, wherein the weight percentage of the one or more additives is in the range of 0.5% to 80%. The additive is dispersed in the homogeneous blend with a dispersion amount of greater than 80% and an aggregate amount of less than 30%, and the membrane has an ionic conductance per area of ​​1 S / cm at 30°C. 2 It's super.

[0015] A method for producing an ion-conducting membrane in accordance with the teachings of the present invention includes mixing a PBI polymer and one or more polymers selected from the group consisting of PVDF, PVDF-HFP, chitosan, and functionalized chitosan with N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (NDF), and / or N,N-dimethylformamide (NDMf). The process includes dissolving the graphene oxide in one or more solvents selected from the group consisting of DMAc, DMF, DMSO, N-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), phosphoric acid, polyphosphoric acid, formic acid, KOH, and ethanol. This process forms a homogeneous polymer solution in which the weight percentage of the selected polymer or polymers is in the range of 1% to 40%. One or more additives selected from the group consisting of graphene oxide, functionalized graphene oxide, and hexagonal boron nitride (h-BN) are dispersed in one or more solvents selected from the group consisting of DMAc, DMF, DMSO, NMP, THF, phosphoric acid, polyphosphoric acid, formic acid, KOH, and ethanol to form an additive dispersion in which the weight percentage of the one or more additives is in the range of 0.5% to 80%. The polymer solution and additive dispersion are then homogeneously mixed to obtain a pre-forming solution. A sheet is formed from the pre-forming solution, and the solvent is removed to obtain a sheet having an ionic conductance per area of ​​1 S / cm at 30°C. 2In one embodiment, an ion-conducting membrane is obtained in which the additive is dispersed with a dispersion amount of more than 80% and an aggregate amount of less than 30%.

[0016] To further clarify the advantages and features of the present disclosure, a more particular description of the present disclosure will be provided with reference to specific embodiments thereof, which are illustrated in the accompanying drawings. It should be understood that these drawings depict only typical embodiments of the present disclosure, and therefore should not be considered limiting of the scope of the present disclosure. The present disclosure will be described and explained with additional specificity and detail through the use of the accompanying drawings.

[0017] These and other features, aspects, and advantages of the exemplary embodiments can be better understood by reading the following detailed description in conjunction with the accompanying drawings, in which like reference numerals represent like parts throughout. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 shows a membrane (10) containing additives (14) of different dimensions (in the nano- to mesoscale range), different shapes, and size distributions according to one embodiment of the present disclosure. [Figure 2A] FIG. 2A shows a membrane (10) having a linear gradient of additive (14) dispersion according to one embodiment of the present disclosure. [Figure 2B] FIG. 2B shows a membrane (10) having a non-linear gradient of additive (14) dispersion according to one embodiment of the present disclosure. [Figure 2C] FIG. 2C shows a membrane (10) with another non-linear gradient of additive (14) dispersion, according to one embodiment of the present disclosure. [Figure 3A] FIG. 3A shows a membrane (10) integrated with two nano / micro fiber layers according to one embodiment of the present disclosure. [Figure 3B] FIG. 3B shows a membrane (10) with an embedded nano / micro fiber layer according to one embodiment of the present disclosure. [Figure 3C]FIG. 3C shows a membrane (10) having an integrated nano / micro fiber layer and bonded to an electrode according to one embodiment of the present disclosure. [Figure 4A] FIG. 4A shows the placement of additives (14) at different length scales in a membrane (10) according to one embodiment of the present disclosure. [Figure 4B] FIG. 4B shows a nanofiber porous mat (20) with nanoadditives (14) according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0019] In the figures, features of the figures are numbered and identified as follows: 10 membrane; 12 polymer blend; 14 one or more additives; 20 nanofiber mat; 22 nanofiber; 30 substrate / electrode / electrolyte; and 100 component.

[0020] Additionally, those skilled in the art will understand that elements in the figures may be depicted in a simplified manner and not necessarily drawn to scale. Furthermore, with respect to the construction of a device, one or more components of the device may be represented in the figures by conventional symbols, and the figures may show only certain details relevant to an understanding of an embodiment of the invention so as not to obscure the figures with details that are readily apparent to one of ordinary skill in the art having the benefit of this description.

[0021] Disclosed herein is an ion-conducting membrane 10, a component 100 having the ion-conducting membrane 10, and methods for making the membrane 10 and the component 100. The ion-conducting membrane 10 conducts different types of charged species, including positive ions, which may be cations, more specifically protons (H+) and transition metal ions, and negatively charged particles, including hydroxyl (OH-) ions.

[0022] The ion-conducting membrane 10 can be used in electrochemical devices, including flow batteries, fuel cells, electrolyzers, and advanced metal batteries. The membrane 10 disclosed herein has advantageous properties when utilized in at least one of the above-listed electrochemical devices.

[0023] FIG. 1 illustrates an ion-conducting membrane (10). The disclosed ion-conducting membrane (10) comprises a homogeneous blend (12) of two or more polymers having one or more additives (14) dispersed throughout. As used herein, "homogenous blend" refers to a solid material in which the raw components are intermixed at a molecular level, such that the raw components are indistinguishable from their physical appearance on length scales greater than the molecular dimensions. PBI is one of the polymers in the homogeneous blend (12).

[0024] Polybenzimidazole (PBI) contains repeating benzimidazole units. A typical chemical name for a PBI polymer is "poly[2,2'-(m-phenylene)-5,5'-bibenzimidazole]" and is commonly known as meta-PBI. Other known PBIs are para-PBI, PBI-OO, O-PBI, and AB-PBI. For the purposes of this disclosure, PBI refers to all of the different types of PBIs listed above.

[0025] PBI has excellent mechanical properties and thermochemical stability. It has a high glass transition temperature (T) of 430°C. g Its melting point is also very high, i.e., above 600° C. The cost of PBI is about two orders of magnitude lower compared to Nafion®.

[0026] In addition to PBI, the intimate blend (12) also includes one or more other polymers. The one or more other polymers may include poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP), chitosan, functionalized chitosan, or any combination of these polymers. Chitosan, as used herein, is a linear polysaccharide composed of randomly distributed β-(1→4)-linked D-glucosamine (deacetylated units) and N-acetyl-D-glucosamine (acetylated units). Furthermore, chitosan and functionalized chitosan may also be described in Shanta Pokhrel et al., “Functionalization of chitosan polymers and their applications,” Journal of Macromolecular Science, Part A Pure and Applied Chemistry, vol. 56, pp. 450-475 (2019).

[0027] In the intimate blend (12), the polymers are present in certain ratios. The weight percent of one or more polymers in the intimate blend (12) ranges from 1% to 40%. In some embodiments, the weight percent of the various polymers may vary to any percentage within the range of 1% to 40%. As used herein, the "weight percent" of the raw materials is used to refer to the percentage of the raw materials that is present in the intimate blend (12). "Cents" means the mass of the feedstock as a percentage of the mass of the PBI. More specifically, the "mass percent" of a feedstock component is calculated by dividing the mass of the feedstock component by the mass of the PBI and multiplying by 100. As used herein, the percent, m f , is defined as follows:

number

[0028] In addition to the polymer, the ion-conducting membrane 10 also includes one or more additives 14. As used herein, "additive 14" refers to any ingredient that is part of the membrane 10, that is mixed with the homogeneous blend 12, and that is distinguishable from its physical appearance on length scales greater than molecular dimensions. In various embodiments of the membrane 10 formulation of the present disclosure, the weight percent of the one or more additives 14 may vary anywhere from 0.5% to 80%.

[0029] The one or more additives (14) can include graphene oxide (GO), functionalized graphene oxide (functionalized GO), hexagonal boron nitride (h-BN), or any combination thereof. The functional groups of GO can include OH - group, NH - 2 units, COOH - The weight percent of the additive (14) may be in the range of 0.5% to 80%. In some embodiments, the weight of the additive (14) may be greater than the weight of the PBI. In such cases, the primary component of the membrane (10) will be the additive (14), with the polymer blend (12) acting as a support material.

[0030] The advantageous properties of the disclosed membrane 10 are a result of the additive 14 added, the ratio of additive 14, and the membrane 10 formation process, all of which act synergistically to promote the permeation of desirable ions through the membrane 10 and prevent the permeation of undesirable species.

[0031] One goal of the present disclosure is to increase the number of active pathways for desired ions by lowering the energy barrier for ion transport and increasing the freedom of movement. The ion-conducting membrane (10) has an internal structure resembling a randomly distributed fractal network of nanoscale additives (14) in a polymer matrix. The nanoscale morphology and ion channel interaction and access created by the specific processing techniques disclosed herein result in a nonlinear increase in the power output and energy efficiency of electrochemical devices incorporating the ion-conducting membrane (10).

[0032] Another object of the present disclosure is the use of additives (14) to help increase conductance per unit area and reduce permeability of undesirable species, such as vanadium ions in vanadium redox flow batteries and methanol molecules in direct methanol fuel cells. The additives (14) act as nanoscale reinforcements. The additives (14) can enhance mechanical, thermal, and electrochemical stability. The interaction energy between the polymers of the blend (12) and the additives (14), along with processing parameters, determines the non-agglomerated dispersion, thus resulting in high dispersion and low agglomerate content. Some dimensions of the additives (14) can be nanometer-scale. In some embodiments, at least one dimension of the additives (14) is in the range of 1 nm to 1000 nm.

[0033] The degree of dispersion, measured by the amount of dispersion, and the degree of aggregation, measured by the amount of aggregation, are advantageously The amount of dispersion and agglomeration of the additive 14 present in the membrane 10 is measured as described by Tyson, BM, et al., "A quantitative method for analyzing the dispersion and agglomeration of nanoparticles in composite materials," Composites: Part B, vol. 42, pp. 1395-1403 (2011).

[0034] For best results, the dispersion level of the one or more additives (14) should be as high as possible (ideally close to 100%) and the agglomerate level should be as low as possible (ideally close to 0%). The dispersion level of the ion-conductive membrane (10) is greater than 80% and the agglomerate level is less than 30%. In some embodiments, the ion-conductive membrane (10) has a dispersion level of greater than 85% and an agglomerate level of less than 15%.

[0035] Typically, a key performance parameter for a membrane (10) used in an electrochemical device is its ionic conductivity. The performance of an electrochemical device is measured in S / cm 2 The current density is determined primarily by the conductance per area, measured in units of 1 S / cm. The membranes (10) described in this disclosure have a current density of 1 S / cm when measured at 30° C. 2 The ion-conducting membrane (10) has a conductance per area of ​​greater than 1 S / cm under operating conditions. The conductance per area is the ionic conductivity per unit area of ​​the membrane (10). In some embodiments, the ion-conducting membrane (10) has a conductance per area of ​​greater than 1 S / cm under operating conditions. 2 For example, for membranes (10) formed for use in HT-PEM fuel cells, the area conductance is greater than 50 S / cm in the temperature range of 160°C to 200°C. 2 The height may be

[0036] In any electrochemical application, the stability of the membrane 10 during long-term operation is of great importance, and the membranes 10 described herein are stable for periods of at least 2000 hours or 2000 cycles under corresponding operating conditions, in some cases.

[0037] Another embodiment of the present disclosure is a method for forming an ion-conducting membrane 10. The method includes preparing a preformed solution, forming the membrane 10 on a substrate, and removing the solvent. In some embodiments, if the membrane 10 is formed on a substrate other than the substrate used in the end use application, the method may further include separating the membrane 10 from the substrate.

[0038] The preformed solution is formed by combining at least two parts. The first part is a homogeneous solution obtained by mixing two or more polymers in a solvent. The second part is an additive (14) dispersion in which the additive (14) is dispersed in the solvent. The solvent used herein can be an organic solvent or a combination of one or more solvents. The one or more solvents can be selected from the group consisting of DMAc, DMF, DMSO, NMP, THF, phosphoric acid, polyphosphoric acid, formic acid, KOH, and ethanol. The solvents used in the first and second parts can be the same or different. In some embodiments, the same solvent is used for both parts. In some embodiments, a combination of two or more solvents can be used.

[0039] The PBI is an essential part of the homogeneous solution of polymers. The polymer that constitutes the first part together with the PBI can be one or more polymers selected from the group consisting of PVDF, PVDF-HFP, chitosan, and functionalized chitosan. The weight percentage of the selected polymer or polymers is in the range of 1% to 40%. The weight ratio of polymer to solvent is adjusted to obtain the desired viscosity of the final preformed solution. The weight fraction of polymer in the final polymer solution is less than 0.2.

[0040] In some embodiments, a small amount of lithium chloride (LiCl) is added to facilitate dissolution of the polymer. The weight percent of LiCl is 10% or less. The LiCl added at this stage is ultimately removed from the membrane 10 in the solvent removal step.

[0041] The second part or additive (14) dispersion can include one or more additives (14) selected from the group consisting of GO, functionalized GO, and h-BN. The solvent can be one or more solvents selected from the group consisting of DMAc, DMF, DMSO, NMP, THF, phosphoric acid, polyphosphoric acid, formic acid, KOH, and ethanol. The weight percentage of the one or more additives (14) ranges from 0.5% to 80%. The weight ratio of additive (14) to solvent is adjusted to obtain the desired viscosity of the final preformed solution.

[0042] A homogeneous solution of the polymer is prepared by dissolving the selected polymer in the solvent by stirring and heating. The temperature of dissolution varies from 30°C to 250°C. The heating process may involve multiple steps of increasing the temperature at different rates and soaking at multiple set temperatures for different durations.

[0043] In some embodiments, an autoclave equipped with a mechanical stirrer is used to dissolve the polymer in the solution. Various dissolution parameters, such as the polymer-to-solvent mass ratio, the total volume of the polymer-solvent mixture, the stirring speed, the maximum temperature and pressure of the mixture in the autoclave, are selected to obtain a homogeneous solution. The maximum temperature of the mixture inside the autoclave can be 230° C. or less at a pressure of 3 bar or less.

[0044] A dispersion of additive (14) in a solvent is prepared by subjecting one or more additives (14) and the solvent to alternating stirring and mechanical sonication, with the stirring speed, stirring duration, and sonication duration selected to obtain the required dispersion.

[0045] In the next step, the additive (14) dispersion is mixed with the homogeneous polymer solution to form a preformed solution. Good mixing is achieved by alternately stirring and sonicating the preformed solution. The stirring speed, stirring duration, and sonication duration are selected to obtain a preformed solution with the desired viscosity. The viscosity of the preformed solution is in the range of 20 centipoise to 3000 centipoise.

[0046] The membrane 10 is formed by casting the preformed solution onto a suitable substrate with a doctor blade. The gap between the edge of the doctor blade and the surface of the substrate onto which the membrane 10 is cast is adjusted to form a membrane 10 of the desired thickness. The casting speed is adjusted to form a monolithic membrane 10 without pinholes. Once cast with the doctor blade, the preformed solution forms a sheet. This sheet is then heated in a hood equipped with an electric or infrared heater to uniformly evaporate the solvent and form the membrane 10. The rate of heat-up, maximum temperature, and duration of soaking the membrane 10 at the set temperature are adjusted to form a membrane 10 free of residual solvent or defects. The maximum heating temperature is in the range of 30°C to 250°C. In some embodiments, the as-cast membrane 10 is heated in a hot air oven to evaporate the solvent. A heat-up and soaking sequence is selected to remove all solvent.

[0047] After heat treatment, the membrane 10 is separated from the substrate, which can be accomplished using a variety of liquids, such as water, isopropyl alcohol, methanol, ethanol, dilute inorganic acids, or mixtures thereof.

[0048] In some embodiments, the membrane 10 is formed by spraying a preformed solution onto a suitable substrate. The viscosity of the preformed solution is in the range of 20 centipoise to 3000 centipoise. The membrane 10 is then heated to a temperature in the range of 30°C to 250°C to remove the solvent.

[0049] In some embodiments, the membrane (10) is also formed by electrospinning a preformed solution onto a suitable substrate. The viscosity of the preformed solution is in the range of 20 centipoise to 3000 centipoise. The formed fibers are subsequently post-processed.

[0050] In some embodiments, the membrane (10) has a dispersion content of greater than 80% and an aggregate content of less than 20%, and the membrane (10) has an ionic conductance per area of ​​1 S / cm at 30° C. 2 It's super.

[0051] The ion-conducting membrane 10 can be tailored for use in multiple articles of manufacture, such as various devices and systems. Devices manufactured using such membranes 10 include batteries, metal-air batteries, redox flow batteries, fuel cells, high-temperature proton exchange membrane 10 (HT-PEM) fuel cells, electrolyzers, different types of electrolyzers, direct-vapor fuel-cells, direct methanol fuel cells (DMFCs), high-temperature direct steam fuel cells, high-temperature direct methanol fuel cells (HT-DMFCs), metal alkaline-earth batteries, ammonia generators, and lithium ion extraction reactors.

[0052] In some embodiments, the ion-conducting membrane (10) may be used in a flow battery. The ion-conducting membrane (10) used in such applications has the objective of having high ionic conductivity for desired ions, more specifically protons, and low permeability to any undesired species. For example, in an all-vanadium redox flow battery, V 2+ , V 3+ , V 4+ , and V 5+ are the species involved in the chemical reaction. The membrane (10) + ), it is also desirable that the membrane (10) prevent crossover of the vanadium ions listed above through the membrane (10).

[0053] Another important performance parameter of the ion-conducting membrane (10) in a flow battery is the areal conductivity of the membrane (10), since the current density of the membrane (10) depends on the areal conductance. The areal conductance is expressed in S / cm 2The conductance is specified in units of 1 S / cm and is a measure of the degree to which the membrane 10 allows protons to be conducted through the membrane itself, per unit area of ​​the membrane 10. For reasonable performance in an electrochemical device, the membrane 10 should have a conductance per unit area of ​​at least 1 S / cm. 2 The area conductance can be increased by decreasing the thickness of the membrane 10 (the dimension of the membrane 10 parallel to the permeation of ions through the membrane 10), and therefore it is a property that depends on the thickness of the membrane 10. A parameter that is independent of the dimensions of the membrane 10 is "ionic conductivity," specified in units of S / cm. Although the area conductance can be increased by decreasing the thickness of the membrane 10, mechanical properties such as tensile strength (UTS) may be compromised by decreasing the thickness. Therefore, it is generally best not to indiscriminately decrease the thickness of the membrane 10 in order to increase the area conductance.

[0054] If the membrane 10 allows undesired species, such as vanadium ions in the example of a vanadium redox flow battery, to permeate through itself, the flow battery loses its energy storage capacity. This is referred to as capacity fade of the flow battery. Capacity fade can be prevented by preventing the flow of undesired ions through the membrane 10. Permeability is a parameter that quantifies the permeation of undesired species through the membrane 10. Permeability is measured in units of cm. 2 / min. A parameter that takes into account both ionic conductivity and permeability is selectivity. Selectivity is defined as the ratio of ionic conductivity to permeability, which is S × min / cm 3 It is specified in units of .

[0055] Typical selectivity values ​​for commercial membranes (10) commonly used in flow batteries are 10 at room temperature, even with high ionic conductivities of 0.1 S / cm. 5 S×min / cm 3The reason for this is that these membranes (10) readily allow undesired species to permeate, resulting in very high permeability. Thus, for a membrane (10) used in a typical vanadium redox flow battery with an ionic conductivity of 0.1 S / cm, for example, V 4+ The transmittance of -6 cm 2 / min, resulting in a selectivity of 1 x 10 5 S×min / cm 3 By more effectively blocking the permeation of undesired species, the selectivity of the membrane 10 can be increased. For example, decreasing the permeability by an order of magnitude can increase the selectivity of the membrane 10 by the same order of magnitude.

[0056] During operation in a flow battery, the ion-conducting membrane 10 typically exists in a flowing liquid electrolyte. For example, in a vanadium redox flow battery, the liquid electrolyte can be a solution of a vanadium salt in an acid. The acid can be sulfuric acid. Under such conditions, the membrane 10 undergoes a dimensional change. This dimensional change is known as swelling. The swelling of the membrane 10 is controlled by the presence of PVDF or PVDF-HFP in the blend 12. By varying the weight percent of PVDF or PVDF-HFP, the swelling of the membrane 10 can be controlled. Another advantage of blending with PVDF or PVDF-HFP is that the membrane 10 may be able to function even in high concentrations of H2SO4, such as greater than 5M. A combination of PVDF and PVDF-HFP may have a similar effect on swelling and function at high H2SO4 concentrations.

[0057] PBI has imidazole units in its polymer backbone. The imidazole units in the PBI polymer's polymer backbone act as both acid and base sites, depending on its chemical environment. When immersed in an acid medium, such as H2SO4 or H3PO4, the PBI membrane 10 acts as a cation-conducting membrane 10. This process is called protonation of the membrane 10. When protonated, the PBI membrane 10 repels positively charged ions according to Donnan's exclusion principle. When immersed in a base, such as NaOH or KOH, the PBI acts as an anion host.

[0058] PVDF and PVDF-HFP are inherently hydrophobic. When blended with PBI, the hydrophobicity of PVDF or PVDF-HFP causes the imidazole rings to preferentially complex with or protonate acid molecules. It is desirable to have as many active sites as possible in the membrane 10. Active sites in the ion-conducting membrane 10 refer to sites on the polymer chain that host active ions. However, the presence of excess PVDF in the polymer blend 12 reduces the total number of active sites or deteriorates the mechanical properties of the membrane 10. Therefore, the weight percent of PVDF or PVDF-HFP is kept below 20%. In some embodiments, the additive 14 used in the ion-conducting membrane 10 to be used in a flow battery includes graphene oxide, functionalized graphene oxide, or a combination thereof. Graphene oxide and functionalized graphene oxide have a layered structure. OH - , N.H. - 2, and COOH - The functional groups of functionalized graphene oxide, such as , are intercalated between the layers and form weak bonds with the layers.

[0059] In some embodiments, the ion-conducting membrane (10) may be used in a HT-PEM fuel cell. A HT-PEM fuel cell is a fuel cell that uses hydrogen (H) as fuel and operates at high temperatures, e.g., up to 250°C. The ion-conducting membrane (10) to be used in a HT-PEM fuel cell is intended to have high ionic conductivity for protons and low permeability for hydrogen gas molecules. The ion-conducting membrane (10) used in a HT-PEM fuel cell is intended to have high ionic conductivity for protons at high temperatures, e.g., up to 250°C, and high mechanical strength, e.g., high tensile strength, at these high temperatures. Since area conductance is inversely proportional to its thickness, it is also desirable that the membrane (10) have low permeability to H molecules, since H crossover leads to a low open circuit potential in HT-PEM fuel cells.

[0060] HT-PEM fuel cell membranes (10) are typically impregnated with an acid, H3PO4, to create active sites. The process of impregnating the membrane (10) with acid is also known as "acid-loading" or "acid-uptake." HT-PEM fuel cell membrane (10) The active site of the + The term "acid loading" refers to the sites on the polymer chains that host cations (ions) and the free volume of trapped acid within the membrane 10. A membrane 10 with a high acid loading has a high number of active sites. A high acid loading also softens the membrane 10. The softening of the membrane 10 leads to a deterioration of its mechanical properties. At high temperatures, the deterioration of the mechanical properties of the membrane 10 becomes more severe.

[0061] In some embodiments, an ion-conducting membrane (10) suitable for use in an HT-PEM fuel cell includes PVDF, PVDF-HFP, or a combination thereof in a homogeneous blend (12) with PBI. One of the additives (14) is h-BN. The other additive (14) can be one or more of graphene oxide and functionalized graphene oxide.

[0062] h-BN has a multilayer structure similar to graphene. It consists of alternating boron (B) and nitrogen (N) atoms forming hexagonal rings. Protons can travel through the centers of the hexagonal rings in the atomic layers of h-BN, while other large molecules are blocked. This structure makes the h-BN-containing film (10) impermeable to all chemical species except protons. The centers of the hexagonal rings of BN in successive atomic layers overlap each other. Therefore, the structure of h-BN can be considered "porous" to protons. Melting point T m h-BN has high thermal stability, with a temperature above 2800°C. Therefore, a membrane (10) containing h-BN can operate at high temperatures due to its high thermal stability. The highly "porous" nature of h-BN for proton conduction allows for a higher mass percentage of additive (14) in the membrane (10), increasing the amount of agglomerates.

[0063] Due to the layered atomic structure of the h-BN contained in the membrane 10, phosphate molecules can be intercalated between the layers of the h-BN, and the increased interaction between the nano-additive 14 and the phosphate molecules reduces acid leaching from the membrane 10.

[0064] In some embodiments, the ion-conducting membrane (10) usable in an HT-PEM fuel cell has a weight percent of one or more polymers in the range of 1% to 20%. The weight percent of the additive (14) is in the range of 1% to 20%. The amount of h-BN is greater than the weight of one or more other additives (14). In some embodiments, the weight of h-BN is 10 times greater than the weight of one or more other additives (14). The amount of dispersion is greater than 90% and the amount of aggregates is less than 30%. The area conductance is 1 S / cm at a temperature of 30°C. 2 and up to 60 S / cm at 200°C. 2 is.

[0065] Electrolyzers produce hydrogen (H2) and O2 gases from water (H2O). Electrolyzers that use membranes (10) to produce H2 can use either cation exchange membranes (10) or anion exchange membranes (10). Electrolyzers that use anion exchange membranes (10) (AEM) are known as AEM electrolyzers. The electrolyte used in AEM electrolyzers is hydroxide. Such hydroxide solutions are also known as alkalis. Alkalis include sodium hydroxide (NaOH) and potassium hydroxide (KOH). The performance of such electrolyzers depends on the concentration of the alkali solution used. Electrolyzers The efficiency of the decomposer increases with increasing alkali concentration. The alkali concentrations typically used in electrolyzers range from 5% to 40%, where the percentage is expressed as the ratio of the mass of alkali to the volume of water. The primary limitation of AEM is the degradation of the membrane (10) at high alkali concentrations.

[0066] The membranes (10) used in AEMs are typically made from polymers functionalized with quaternary amine groups. The quaternization reaction functionalizes the polymer to create ionogenic sites to enable operation in alkaline media. Highly concentrated alkaline solutions attack the -NH groups of the anion exchange membrane (10) via Hoffmann degradation, which involves the removal of -C=O groups from the polymer backbone in the presence of a strong base.

[0067] The PBI polymer membrane (10) can operate in a highly alkaline solution. However, the highly alkaline solution softens the PBI polymer. To improve the mechanical strength by structural reinforcement, a functionalized GO additive (14) is dispersed in the membrane (10). The functionalized GO acts by reacting with OH groups within the membrane (10). - The active OH groups present in GO are functionalized to create additional active sites and pathways for hosting and transporting functional groups. - The ability of PBI to host higher concentrations of alkaline solutions makes the functionalized GO less susceptible to Hofmann degradation.

[0068] The ion-conducting membrane (10) disclosed herein can be used in an AEM electrolyzer. Within the ion-conducting membrane (10), a functionalized GO additive (14) is dispersed to maximize the number of active sites and the mechanical resilience of the membrane (10). The mass percentage of the functionalized GO is selected to be within the range of 1% to 80%. In the ion-conducting membrane (10), chitosan, functionalized chitosan, or a combination thereof is used with PBI to create a homogeneous polymer blend (12). The chitosan or functionalized chitosan strengthens the PBI-functionalized GO matrix through a continuous network of hydrogen bonds, which acts as a bridge between the GO nanosheets and the PBI polymer matrix in aqueous solution, resulting in better dispersion of the sites and additive (14) within the membrane (10). The mass percentage of the chitosan, functionalized chitosan, or a combination thereof in the polymer blend (12) is within the range of 1% to 40%.

[0069] Unlike conventional hydrogen fuel cells, DMFCs typically use dilute methanol in liquid form as fuel. The methanol is diluted with HO. The methanol concentration in water typically used in known DMFCs is in the 1M to 3M range. Therefore, the energy density of DMFCs is very low. High concentrations of methanol cannot be used in DMFCs due to crossover of methanol molecules through the membrane 10. A membrane 10 that can prevent the permeation of methanol molecules through the membrane itself allows for the use of higher concentrations of methanol fuel in DMFCs. For membranes 10 with sufficiently low methanol permeability, the methanol concentration in the fuel supply can be as high as 15M. Therefore, membranes 10 to be used in DMFCs should have high ionic conductivity for protons and very low permeability for methanol molecules. The size of methanol molecules is larger than that of protons. Methanol crossover through the membrane 10 can be prevented by creating an obstacle to the flow of methanol through the membrane 10. One objective of the present disclosure is to form a membrane (10) that preferentially provides pathways that offer high resistance to the flow of methanol, but minimal resistance to the flow of protons.

[0070] In some embodiments, the ion-conducting membranes (10) disclosed herein are suitable for use in DMFCs. The raw material components, compositions, and methods are selected to form the ion-conducting membranes (10) suitable for use in DMFCs. The ion-conducting membranes (10) disclosed herein are also suitable for use in DMFCs operating at temperatures up to 230°C. PVDF, PVDF-HFP, or a combination thereof, blended with PBI and dispersed with one or more additives (14) selected from the group consisting of h-BN, GO, and functionalized GO, are also suitable for use in DMFCs. The thermal stability, ionic conductivity, and mechanical properties are enhanced. This improves the performance of DMFCs at high temperatures. Operation at high temperatures allows for operation of DMFCs with or without a reformer. DMFC In this case, higher efficiency is obtained.

[0071] Herein, the membrane (10) includes another polymer along with PBI. PVDF, PVDF-HFP, or a combination of PVDF and PVDF-HFP can be used as the other polymer as part of the homogeneous polymer blend (12). The weight percentage of the PVDF, PVDF-HFP, or combination thereof is in the range of 1% to 35%. The membrane (10) includes one or more additives (14) selected from the group consisting of GO, functionalized GO, and h-BN. The addition of h-BN enables high temperature operation. The weight percentage of the one or more additives (14) is in the range of 1% to 80%. The membrane (10) has a dispersion content greater than 90% and an aggregate content less than 20%. The membrane (10) has an area conductance of 1 S / cm. 2 The tensile strength of the membrane (10) is greater than 50 MPa.

[0072] To achieve low permeability of methanol molecules while maintaining high conductance per unit area, the ion-conducting membrane 10 is formed with a gradient along the direction of methanol flow. The gradient can include a gradient of dispersion or chemical composition. Different possible gradients of dispersion of one or more additives 14 in the polymer blend 12 are shown in Figures 2A, 2B, and 2C. Figure 2A shows a continuously varying dispersion along the thickness of the membrane 10. Figures 2B and 2C show a varying dispersion along the thickness of the membrane 10, with valleys and peaks, respectively, in the dispersion profile along the thickness of the membrane 10. The gradient was achieved by forming multiple sub-membranes 10 of different compositions and combining them to form a monolithic membrane 10. In some embodiments, the ion-conducting membrane 10 includes multiple smaller sub-membranes 10 of varying thicknesses to achieve a gradient in conductivity and a gradient in methanol permeability. The membrane 10 formation process is designed to integrate sub-membranes 10 to form a single monolithic membrane 10 during the process of forming the ion-conducting membrane 10. The raw material components, composition, dispersion amount, and aggregate amount of each sub-membrane 10 are varied to achieve the desired gradient.

[0073] The physical structure of some of the components of an electrochemical device can be as simple as an ion-conducting membrane 10 used in a flow battery, or as complex as a membrane electrode assembly (MEA) or catalyst-coated membrane 10 (CCM) used in a fuel cell. The physical structure of some electrochemical device components, such as advanced metal batteries, can be much more complex than that of a fuel cell. Challenges always relate to the nature of the active species and the components that handle those active species.

[0074] Advanced metal batteries use metallic lithium as the anode, achieving higher energy density than conventional lithium-ion batteries. Instead of graphite, which is intercalated with lithium ions, metallic lithium is used as the anode in lithium metal batteries. Advanced lithium metal batteries use sulfur as one of the cathode components. Sulfur is not an intercalation compound like graphite. Other components used in advanced metal batteries are often selected from conventional technologies due to the difficulty in obtaining compatible components. For example, lithium-sulfur batteries still use liquid electrolytes with separators. Sulfur used as the cathode tends to form polysulfides, such as Li2S, Li2S2, Li2S3, Li2S4, Li2S6, Li2S8, and S8. These polysulfides are actually part of the active material in the battery. When the active material migrates into the electrolyte, the battery capacity decreases. The formation of metallic lithium dendrites that can penetrate the separator is another significant issue for lithium-sulfur batteries.

[0075] Electrochemical devices such as aluminum-air batteries, also known as aluminum-air fuel cells, have a significant challenge: corrosion of the aluminum electrodes. Some other electrochemical devices, such as those used to extract metallic lithium from aqueous salt solutions, use solid electrolytes. Solid electrolytes exposed to highly corrosive saltwater environments are susceptible to accelerated degradation. The component (100) disclosed herein is designed to address the above-mentioned challenges associated with one or more electrochemical devices.

[0076] Some of the components 100 disclosed herein necessarily include a membrane 10 and one or more physical structures. The physical structures may include a layer of nanofibers 22, an electrode, a solid electrolyte, or an interfacial layer used in conjunction with the membrane 10. The ingredients, composition, and method of formation of the membrane 10 and physical structures in different embodiments may vary depending on the application.

[0077] In certain embodiments, a component 100 is disclosed that includes a membrane 10 flanked on both sides by layers of nanofibers 22. The flanking layers of nanofibers 22 may be integrated with the largest surface of the membrane 10 oriented perpendicular to the flow of ions / molecules through the membrane 10.

[0078] In one particular embodiment, a component (100) is disclosed in which two membranes (10) are adjacent to each other on either side of a layer of nanofibers (22), with the membranes (10) being adjacent to each other on their largest faces, which are also generally perpendicular to the flow of ions / molecules through the membranes (10).

[0079] In certain other embodiments, a component (100) is disclosed in which a membrane (10) is adjacent to one side of the device electrode and adjacent to the opposite side of the membrane (10) to a layer of nanofibers (20). This adjacency occurs on the largest surface of the membrane (10) that is perpendicular to the flow of ions / molecules through the membrane (10). One such embodiment is shown in Figure 3C.

[0080] In almost all of the above embodiments, the membrane (10) comprises a homogeneous blend (12) of PBI and one or more polymers selected from the group consisting of PVDF, PVDF-HFP, chitosan, and functionalized chitosan. The weight percentage of the one or more polymers is in the range of 1% to 40%. One or more additives (14) selected from the group consisting of graphene oxide, functionalized graphene oxide, and h-BN are used. The weight percentage of the one or more additives (14) is in the range of 0.5% to 80%. The additives (14) are dispersed in the polymer blend (12) with a dispersion amount of greater than 80% and an aggregate amount of less than 30%. The membrane (10) has an ionic conductance per area of ​​1 S / cm at 30°C. 2 It's super.

[0081] FIG. 3A shows a component 100 comprising an ion-conducting membrane 10 and two nanofiber layers 20. The membrane 10 acts as a thin, dense interlayer sandwiched between two porous nanofiber layers 20. This type of component physical structure can be advantageous in metal-electrode flow batteries, where the outer nanofibers 22 can absorb more electrolyte because the nanofibers 22 provide more accessible conduction paths for ions. The dense interlayer acts as a barrier to non-active ions. When stacks are fabricated, the membrane 10 must be able to withstand compressive forces without fracture or through-thickness pinhole defects. The outer porous nanofiber layers 20 can withstand compressive forces and prevent direct punctures in the inner dense interlayer. The component 100 shown in FIG. 3A can be used in electrochemical devices, including electrolyzers, advanced metal batteries, and flow batteries.

[0082] The method for forming the component (100) includes the following steps: In a first step, a preformed solution of a first viscosity containing a homogeneous polymer solution and an additive (14) dispersion is prepared; In a second step, a porous, free-standing nanofiber layer (20) is formed by electrospinning the preformed solution of the first viscosity; In a third step, the solvent in the porous nanofiber layer (20) is partially removed; In a fourth step, another preformed solution of a second viscosity suitable for spray coating is prepared; In a fifth step, the preformed solution of the second viscosity is sprayed onto one side of the nanofiber layer (20), thereby forming a thin, dense sheet of the polymer additive (14) blend (12) on the nanofiber layer (20); In a sixth step, the solvent is partially removed from the thin, dense sheet; and In a seventh step, the preformed solution of the first viscosity is electrospun onto the formed thin, dense sheet. Finally, any residual solvent is removed from this physical structure to form the desired component.

[0083] Depending on the application, the ingredients and composition of the pre-formed solution can be tailored to form a structure that is asymmetric about a plane passing through the center of the membrane 10. The plane of symmetry referred to herein is coplanar with the largest area surface of the membrane 10. The ionic conduction properties of the membrane 10 and nanofiber layer 20 can be tailored by varying the ingredients and composition of the pre-formed solution.

[0084] FIG. 3B shows an example of a component 100 having two ion-conducting membranes 10 and a porous nanofiber layer 20. The nanofiber layer 20 is sandwiched between two dense ion-conducting membranes 10. This type of membrane 10 configuration may be useful in high-temperature fuel cells, alkaline fuel cells, and alkaline electrolyzers, where maintaining ionic conductivity is a key requirement. The porous core 20 acts as a host for the electrolyte (acidic or basic medium), thereby increasing conductance per area by trapping more strong acids or bases within it. Because fibers are stronger than films, higher acid or base loadings can be achieved with fibers. The fibers are then trapped in a dense layer, which serves the dual role of retaining more acid or base within the membrane 10 and acting as an external permeation barrier. The dense outer layer reduces electrolyte leaching, allowing for more stable performance over time.

[0085] The method for forming the component (100) shown in FIG. 3B includes the following steps: In a first step, preform solutions of different first, second, and third viscosities are prepared as described above; in a second step, a porous, free-standing nanofiber layer (20) is formed by electrospinning the preform solution of the first viscosity; in a third step, the solvent in the porous nanofiber layer (20) is partially removed; in a fourth step, a preform solution of a second viscosity suitable for spray coating is sprayed onto the nanofiber layer (20); in a fifth step, the solvent is partially removed; in a sixth step, a preform solution of a third viscosity is sprayed onto both sides of the nanofiber layer (20) to form a second sheet; and in a seventh step, residual solvent is removed to form the desired component.

[0086] In some embodiments, the sheet-forming techniques in the fourth and sixth steps may be replaced with alternative sheet-forming techniques, such as dip coating. In some other embodiments, the sheet-forming techniques in the fourth and sixth steps may be replaced with alternative sheet-forming techniques, such as solution casting. Depending on the application, the ingredients and composition of the pre-formed solution may be tailored to form structures that are asymmetric about a plane through the center of the porous layer. The ionic conductivity properties of the membrane 10 and nanofiber layer 20 can be tailored by varying the ingredients and composition of the pre-formed solution.

[0087] FIG. 3C shows a disclosed component (100) adjacent to a device electrode (30) on one side of the membrane (10) and adjacent to a layer of nanofibers (20) on the other side. This adjacency is on the largest surface side of the membrane (10) that is perpendicular to the flow of ions / molecules through the membrane (10). The component can have high conductivity for ions, including protons, lithium ions, and aluminum ions. The component can also have high conductivity for ions such as polysulfides, metal ions other than lithium, such as sodium ions (Na + ), hydroxide ion (OH - ), and may have low permeability to chemical species including magnesium ions.

[0088] The method for forming the component (100) shown in FIG. 3C includes the following steps: In a first step, preformed solutions of first and second viscosities are prepared as described above; in a second step, the solution of the first viscosity is sprayed directly onto a substrate to form a sheet. The substrate (30) may include electrodes, solid electrolytes, and other interfacial layers of an electrochemical device; in a third step, the solvent in the sheet is partially removed; in a fourth step, the preformed solution of the second viscosity is electrospun onto the surface of the sheet to form the nanofiber layer (20); and in a final step, the residual solvent is completely removed. In some embodiments, the sheet is formed on the selected substrate by solution casting or dip coating.

[0089] According to various embodiments of the present disclosure, additives (14) of different length scales may be incorporated into the polymer blend (12) in any suitable shape or size, as shown in Figure 4A. The nanofiber mat (20) shown in Figure 4B may also be made of a multitude of nanofibers (22), which may also include additives (14) in the matrix that forms the nanofiber mat (20) in various embodiments. [Example]

[0090] In one experiment, 9.6 g of PBI and 1.06 g of PVDF were dissolved in 61.79 g of DMAc in a glass beaker on a hot plate equipped with a magnetic stirrer. The temperature was slowly increased from room temperature to 140 °C over 16 hours while stirring to form a homogeneous solution of the polymer. In a parallel experiment, 0.19 g of graphene oxide was dispersed in 7 g of DMAc by sonication followed by stirring at room temperature to form an additive dispersion.

[0091] The additive dispersion was then added to the homogeneous polymer solution and mixed to form a preformed solution. The preformed solution was then cast onto a glass plate using a doctor blade method to form a sheet. The sheet was heated to 150°C to remove the solvent, forming membrane (10). The membrane (10) was then peeled off from the substrate using water.

[0092] The thickness of the membrane (10) was measured using a screw gauge to be 40 μm. The membrane (10) was further characterized for permeability, dispersion amount, aggregate amount, and conductivity.

[0093] The permeability of the membrane (10) was measured as described in So-Won Choi, et al. “Hydrocarbon membranes (10) with high selectivity and enhanced stability for vanadium redox flow battery applications: Comparative study with sulfonated poly(ether sulfone)s and sulfonated poly(thioether ether sulfone)s,” Electrochimica Acta, vol. 259, pp. 427–439 ​​(2018).

[0094] Briefly, a thickness of 40 μm and a cross-sectional area of ​​1.847 cm 2 The membrane (10) was attached to a cell with two compartments. One compartment contained 35 ml of a solution of VOSO4·5H2O salt in 2 M H2SO4. The concentration of VOSO4·5H2O salt in the 2 M H2SO4 solution was 1.66 M. The other compartment contained 2 The solution contained 35 ml of MgSO4 salt in 2 M H2SO4. The concentration of MgSO4 salt in the 2 M H2SO4 solution was 1.66 M. A membrane (10) was installed between the two solutions to allow the flow of ions from both compartments to each other. The solution containing MgSO4 was continuously stirred for 48 hours. After 48 hours, V 4+ The solution in the MgSO4 compartment was analyzed by UV-visible spectrophotometer to determine the concentration of ions. 4+ The concentration of the ions was determined to be 0.00282 M. The permeability of the membrane (10) was 5.03 × 10 -8 cm 2 / min.

[0095] To measure the ionic conductivity of the membrane (10), a flow cell was constructed as shown in M. Raja, et al., “Binder-free thin graphite fiber mat sandwich electrode architectures for energy-efficient vanadium redox flow batteries,” Catalysis Today, vol. 370, pp. 181–188 (2021).

[0096] For the ionic conductivity measurement, a 40 μm thick membrane (10) with dimensions of 7 cm × 7 cm was used. The effective area of ​​the membrane (10) was 25 cm. 2 The membrane (10) was pretreated with 3M H2SO4 for 2 hours before incorporating the membrane (10) into the flow cell. For the measurement, 3M H2SO4 was circulated through the flow cell using a peristaltic pump. Electrochemical impedance spectroscopy (EIS) measurements were performed on the flow cell in the frequency range of 200 kHz to 100 mHz. The real part of the membrane (10) impedance, with the imaginary part of the impedance set to zero, was considered to be the membrane (10) resistance. The conductivity was calculated from the resistance value. In one measurement, the membrane (10) resistance was 63 mΩ. The conductance per area was 635 mS / cm 2 The ionic conductivity was calculated to be 2.54 mS / cm. The selectivity was 5.04 x 10 4 S×min / cm 3 It was calculated that:

[0097] Tensile testing of the ionic conductivity of the membrane (10) was performed as specified in ASTM D882-18, Standard Test Method for Tensile Properties of Thin Plastic Sheeting, ASTM International, West Conshohocken, PA, (2018).

[0098] A clean, dry membrane (10) with a thickness of 40 μm was cut into strips 300 mm long and 6 mm wide. The gauge length of the sample was 250 mm. The sample was clamped to a universal testing machine with a 100 N load cell. As recommended by the standard, a strain rate of 25 mm / min was used in the uniaxial tensile test. The tensile strength (UTS) was calculated using the maximum load obtained from the tensile test. In one measurement, the UTS was calculated to be 42 MPa.

[0099] The ion-conducting membranes 10 disclosed herein and related devices incorporating these membranes 10 can enhance ionic conductivity of desired ions while simultaneously inhibiting the transport of undesired chemical moieties. Through the selection of additives 14 to the polymer blend 12, the membrane 10 can be engineered to have the transport properties desired for its application in an electrochemical system. For applications in devices with acidic or basic operating conditions, both the polymer blend 12 and the additives 14 can be selected and tailored to achieve either anion transport or cation transport.

[0100] Although the present disclosure has been described using specific language, no limitations are intended because of this. As will be apparent to those skilled in the art, various operational modifications may be made to the present methods for the purpose of carrying out the inventive concepts taught herein.

[0101] The drawings and the above description provide examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. It is understood that, alternatively, certain elements may be divided into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, the order of the methods described herein may be changed and is not limited to the order described herein. Furthermore, the operations in any flow diagram need not be performed in the order shown, and not all operations necessarily need to be performed. Also, operations that are independent of other operations may be performed in parallel with other operations. The scope of the embodiments is in no way limited by these specific examples. Numerous modifications, such as differences in structure, dimensions, and use of materials, are possible, whether or not explicitly stated herein. The scope of the embodiments is at least as broad as indicated by the following claims.

Claims

1. An ion-conducting membrane (10), (a) an intimate blend (12) of polybenzimidazole (PBI) with one or more polymers selected from the group consisting of polyvinylidene difluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), chitosan, and functionalized chitosan, wherein the weight percent of the one or more polymers is in the range of 1% to 40% based on the weight of the PBI; and (b) one or more additives (14) selected from the group consisting of graphene oxide, functionalized graphene oxide, and hexagonal boron nitride (h-BN), in a weight percentage ranging from 0.5% to 80% relative to the weight of the PBI; Including, The additive (14) is dispersed in the homogeneous blend (12) with a dispersion amount of greater than 80% and an aggregate amount of less than 30%, and the ion-conducting membrane (10) has an ionic conductance per area of ​​less than 1 S / cm at 30°C. ２ An ion-conducting membrane (10) that is super.

2. the one or more polymers selected from the group consisting of PVDF, PVDF-HFP, or a combination thereof, wherein the weight percent of the one or more polymers is in the range of 1% to 20% relative to the weight of the PBI; and the additive (14) comprises h-BN and one or more additives (14) selected from the group consisting of graphene oxide and functionalized graphene oxide, the total weight percent of the h-BN and the one or more additives (14) combined is in the range of 1 to 20% based on the weight of the PBI, the weight of h-BN is 10 times the weight of the one or more additives (14), the dispersion amount of the one or more additives (14) is greater than 90%, and the aggregate amount of the additives (14) is less than 30%; and The ionic conductance per area of ​​the membrane (10) is 1 S / cm at 30°C. ２ and a maximum of 60 S / cm at a temperature of 200°C. ２ The ion-conducting membrane (10) of claim 1, wherein:

3. one or more polymers selected from the group consisting of chitosan and functionalized chitosan, the weight percentage of which is in the range of 2% to 40% relative to the weight of the PBI; and the one or more additives (14) comprising functionalized graphene oxide, the weight percentage of which is in the range of 1% to 80% relative to the weight of the PBI; wherein the dispersion amount of the one or more additives (14) is greater than 90% and the aggregate amount of the one or more additives (14) is less than 10%; and The ionic conductance per area of ​​the membrane (10) is 1 S / cm at 30°C. ２ The ion-conducting membrane (10) of claim 1, wherein the tensile strength is greater than 50 MPa.

4. one or more polymers selected from the group consisting of PVDF and PVDF-HFP, the weight percent of which is in the range of 1% to 35% relative to the weight of PBI; the additive (14) comprises h-BN and one or more additives (14) selected from the group consisting of graphene oxide and functionalized graphene oxide, and the total weight percent of the h-BN and the one or more additives (14) combined is in the range of 1 to 80% based on the weight of the PBI; the dispersion amount of the additive (14) is greater than 90% and the aggregate amount of the one or more additives (14) is less than 20%; The ionic conductance per area of ​​the membrane (10) is 1 S / cm at 30°C. ２ and the tensile strength is greater than 50 MPa; 10. The ion-conducting membrane of claim 1, wherein the membrane has a gradient in size, shape, amount, or a combination thereof, of the one or more additives, the gradient being in a direction perpendicular to the maximum area of ​​the membrane.

5. A component (100) comprising an ion-conducting membrane (10), said ion-conducting membrane (10) comprising: (a) an intimate blend (12) of polybenzimidazole (PBI) with one or more polymers selected from the group consisting of polyvinylidene difluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), chitosan, and functionalized chitosan, wherein the weight percent of the one or more polymers is in the range of 1% to 40% based on the weight of the PBI; and (b) one or more additives (14) selected from the group consisting of graphene oxide, functionalized graphene oxide, and hexagonal boron nitride (h-BN), in a weight percentage range of 0.5% to 80% relative to the weight of the PBI; wherein the one or more additives (14) are dispersed in the blend (12) at a dispersion volume of greater than 80% and an aggregate volume of less than 30%, and the membrane (10) has an ionic conductance per area of ​​less than 1 S / cm at 30°C. ２ Super, component (100).

6. 6. The component (100) of claim 5, wherein a layer (20) of nanofibers is adjacent to each side of the ion-conducting membrane (10) in a direction perpendicular to the flow of ions through the ion-conducting membrane (10).

7. 6. The component (100) of claim 5, wherein one ion-conducting membrane (10) is adjacent to the layer of nanofibers (20) on one side of the layer and another ion-conducting membrane (10) is adjacent to the layer of nanofibers (20) on the opposite side in a direction perpendicular to the flow of ions through the ion-conducting membrane (10).

8. 6. The component (100) of claim 5, wherein the ion-conducting membrane (10) is adjacent to a substrate on one side and a layer of nanofibers on the opposite side in a direction perpendicular to the flow of ions through the ion-conducting membrane (10).

9. A method for producing an ion-conductive membrane (10), comprising: dissolving a polybenzimidazole (PBI) polymer and one or more polymers selected from the group consisting of polyvinylidene difluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), chitosan, and functionalized chitosan in one or more solvents selected from the group consisting of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), phosphoric acid, polyphosphoric acid, formic acid, KOH, and ethanol to form a homogeneous polymer solution, wherein the weight percentage of the selected one or more polymers is in the range of 1% to 40% based on the weight of the PBI; dispersing one or more additives (14) selected from the group consisting of graphene oxide, functionalized graphene oxide, and hexagonal boron nitride (h-BN) in the one or more solvents to form an additive dispersion, wherein the weight percentage of the one or more additives (14) is in the range of 0.5% to 80% based on the weight of the PBI; homogeneously mixing the polymer solution and the additive dispersion to obtain a preformed solution; forming a sheet; and removing the solvent to obtain the ion-conductive membrane (10); The additive (14) is dispersed in the ion-conductive membrane (10) with a dispersion amount of more than 80% and an aggregate amount of less than 30%, and the membrane (10) has an ionic conductance per area of ​​1 S / cm at 30°C. ２ A method for producing an ion-conducting membrane (10) that is above 1000 nm in diameter.

10. selecting the one or more polymers from the group consisting of PVDF, PVDF-HFP, wherein the weight percent of the one or more polymers is in the range of 1% to 20% relative to the weight of PBI; dissolving the PBI and the one or more selected polymers in one or more solvents selected from the group consisting of DMAc, DMF, DMSO, NMP, THF, phosphoric acid, polyphosphoric acid, formic acid, KOH, and ethanol to form the homogeneous polymer solution, wherein the mass ratio of solid content to liquid content in the polymer solution is less than 0.2; selecting the one or more additives (14) selected from the group consisting of graphene oxide and functionalized graphene oxide and dispersing them in the one or more solvents to form the additive dispersion, wherein the weight percent of the one or more additives (14) is in the range of 0.5% to 10% relative to the weight of the PBI; mixing the homogenous polymer solution and the additive dispersion by stirring and sonication to form the preformed solution; solvent casting the preformed solution to form a sheet; and removing said one or more solvents; 10. The method of claim 9, comprising:

11. selecting PVDF, PVDF-HFP, or a combination thereof, wherein the weight percent of said one or more polymers relative to PBI is in the range of 1% to 20% relative to the weight of PBI; dissolving the PBI and the one or more selected polymers in one or more solvents selected from the group consisting of DMAc, DMF, DMSO, NMP, THF, phosphoric acid, polyphosphoric acid, formic acid, KOH, and ethanol to form the homogeneous polymer solution, wherein the mass ratio of solid content to liquid content in the polymer solution is up to 0.2; selecting h-BN and one or more additives (14) selected from the group consisting of graphene oxide and functionalized graphene oxide, wherein the total weight percent of the h-BN and the one or more additives (14) combined is in the range of 1% to 20% based on the weight of the PBI, and the weight of the h-BN is 10 times or more the weight of the other one or more additives (14); dispersing the h-BN and dispersing the one or more additives (14) in the one or more solvents to form the additive dispersion, wherein the mass ratio of the one or more additives (14) to the selected one or more solvents is at most 2:98; mixing the homogenous polymer solution and the additive dispersion by stirring and sonication to form the preformed solution; solvent casting the preformed solution to form a sheet; and removing said one or more solvents; 10. The method of claim 9, comprising:

12. selecting the chitosan, functionalized chitosan, or combination thereof, wherein the weight percent of chitosan, functionalized chitosan, or combination thereof is in the range of 2% to 40% based on the weight of PBI; dissolving the selected polymer and PBI in one or more solvents selected from the group consisting of DMAc, DMF, DMSO, NMP, THF, phosphoric acid, polyphosphoric acid, formic acid, KOH, and ethanol to form the homogeneous polymer solution, wherein the mass ratio of solid content to liquid content in the polymer solution is up to 0.2; selecting the one or more additives (14) comprising functionalized graphene oxide, wherein the weight percent of the one or more additives (14) is in the range of 1% to 80% relative to the weight of the PBI; dispersing the one or more additives (14) in the one or more solvents to form the additive dispersion; mixing the homogenous polymer solution and the additive dispersion by stirring and sonication to form the preformed solution; solvent casting the preformed solution to form a sheet; and removing said one or more solvents; 10. The method of claim 9, comprising:

13. (a) selecting PVDF, PVDF-HFP, or a combination thereof, wherein the weight percent of the one or more polymers is in the range of 1% to 35% relative to the weight of PBI; (b) dissolving the PBI and the one or more selected polymers in one or more solvents selected from the group consisting of DMAc, DMF, DMSO, NMP, THF, phosphoric acid, polyphosphoric acid, formic acid, KOH, and ethanol to form the homogeneous polymer solution, wherein the mass ratio of solid content to liquid content in the polymer solution is up to 0.2; (c) selecting the one or more additives (14) from the group consisting of graphene oxide, functionalized graphene oxide, and h-BN, wherein the weight percent of the one or more additives (14) is in the range of 1% to 80% based on the weight of the PBI; (d) dispersing the selected additive (14) in the one or more solvents to form the additive dispersion, wherein the weight percent of the one or more additives (14) is in the range of 1% to 80% based on the weight of the PBI; (e) mixing the homogenous polymer solution and the additive dispersion by stirring and sonication to form the preformed solution; (f) solvent-casting the pre-formed solution to form a sheet to partially remove the one or more solvents; (g) repeating steps (a) through (f) to stack the sheets until a predetermined number of sheets is reached, independently varying the weight ratio of polymer to PBI and the weight ratio of additive (14) to PBI to form multilayer films (10) with different additive (14) contents, while maintaining the dispersion content greater than 90% and the aggregate content less than 10% in all the layers; and (h) complete removal of all residual solvent; 10. The method of claim 9, comprising:

14. A method for manufacturing a component (100) comprising an ion-conducting membrane (10), said method comprising: dissolving a polybenzimidazole (PBI) polymer and one or more polymers selected from the group consisting of polyvinylidene difluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), chitosan, and functionalized chitosan in one or more solvents selected from the group consisting of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), phosphoric acid, polyphosphoric acid, formic acid, KOH, and ethanol to form a homogeneous polymer solution, wherein the weight percentage of the selected one or more polymers is in the range of 1% to 40% based on the weight of the PBI; dispersing one or more additives (14) selected from the group consisting of graphene oxide, functionalized graphene oxide, and hexagonal boron nitride (h-BN) in the one or more solvents to form an additive dispersion, wherein the weight percentage of the one or more additives (14) is in the range of 0.5% to 80% based on the weight of the PBI; homogeneously mixing the polymer solution and the additive dispersion to obtain a preformed solution; forming a sheet from the preformed solution; and removing the solvent from the sheet to obtain the ion-conducting membrane (10); The additive (14) is dispersed with a dispersion amount of more than 80% and an aggregate amount of less than 30%, and the ionic conductance per area of ​​the membrane (10) is 1 S / cm at 30°C. ２ The super method.

15. controlling the viscosity of the preformed solution within the range of 20 centipoise to 3000 centipoise by independently varying the ratio of polymer to solvent in the polymer solution and the ratio of additive (14) to solvent in the additive dispersion; The method of forming the component (100) of claim 14, comprising:

16. Electrospinning the pre-formed solution of a first viscosity to form one individual layer of nanofibers (20); spraying the pre-formed solution of a second viscosity onto the free-standing layer of nanofibers (20) to form the sheet; and electrospinning the pre-formed solution of the first viscosity onto the sheet opposite the discrete layer of nanofibers (20) to form a second layer of nanofibers (20); wherein removing the solvent includes partially removing the solvent after each step of forming the individual layers of the component, and completely removing the solvent after formation of the component is complete; and 16. The method of claim 15, wherein the component comprises an ion-conducting membrane having two nanofiber layers adjacent to its largest surface area side, each layer located on one of the two sides of the ion-conducting membrane.

17. electrospinning the pre-formed solution of a first viscosity to form a layer of nanofibers (20) and partially removing the solvent; spraying or dip-coating the pre-formed solution of the second viscosity onto the side of the nanofiber layer (20) having the largest surface area and partially removing the solvent; repeating the spraying or dip coating process on the other side of the nanofiber layer (20); and completely removing the solvent; 16. The method of claim 15, wherein the component comprises two ion-conducting membranes adjacent a layer of nanofibers.

18. spraying or dip-coating the pre-formed solution of a first viscosity onto a surface of a substrate (30) to form a sheet of an ion-conducting membrane (10); Electrospinning the pre-formed solution of a second viscosity to form a layer of nanofibers (20) on the surface of the sheet; and removing the solvent; wherein removing the solvent includes partially removing the solvent after each step of forming the individual layers of the component (100), and completely removing the solvent after the formation of the component (100) is complete; and 16. The method of claim 15, wherein the ion-conducting membrane is adjacent to the substrate on one of its largest surfaces and adjacent to a layer of nanofibers on an opposite surface.

19. An article of manufacture comprising an ion-conducting membrane (10) according to any one of claims 1 to 4.

20. 20. The article of manufacture of claim 19, the article of manufacture includes an electrochemical system; The article of manufacture, wherein the electrochemical system comprises a redox flow battery, a high temperature proton exchange membrane fuel cell, an electrolyzer, a direct steam fuel cell, a direct methanol fuel cell, a high temperature direct steam fuel cell, a high temperature direct methanol fuel cell, an alkaline earth metal cell, a fuel cell, or a battery.

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