A robust polybenzimidazole (PBI) gel film with high conductivity.

Abstract

The present disclosure provides a polybenzimidazole (PBI) gel film exhibiting both high proton conductivity and high tensile strength at fracture. The polybenzimidazole (PBI) gel film of the present disclosure is manufactured using a polybenzimidazole-forming monomer containing high proportions of tetraaminobiphenyl monomer and naphthalenedicarboxylic acid monomer.

Description

[Technical Field]

[0001] (Cross-reference of related applications) This application claims priority under U.S. Provisional Patent Application No. 63 / 491,301, filed March 21, 2023. The entire disclosure of the above application is incorporated herein by reference. [Background technology]

[0002] Polybenzimidazole (PBI) membranes have been considered for use in a variety of electrochemical applications. Conventionally, PBI membranes used in electrochemical applications have been manufactured by a process (referred to as the "conventional impregnation process") in which a high-density membrane is formed by solution casting using N,N'-dimethylacetamide (DMAc), followed by impregnation of the formed membrane with the desired electrolyte. Conventional PBI membranes are particularly well known for their performance as high-temperature polymer electrolyte membranes suitable for fuel cell applications. Furthermore, conventional PBI membranes have been considered for use in devices such as electrochemical hydrogen separation systems, sulfur dioxide (SO2) depolarization electrolytic cells, and redox flow batteries. Unfortunately, these conventional PBI membranes exhibit extremely low ionic conductivity (100 mS·cm) when impregnated with electrolyte solutions. -1 (Less than) indicates a current load of approximately 100 mA·cm². -2 It has been found that output performance decreases when the value exceeds a certain limit. Furthermore, the conventional impregnation process used to manufacture PBI films is a time-consuming and environmentally unfriendly technology, which increases the cost of the PBI film manufacturing process.

[0003] Very recently, a method for producing PBI films has been developed that includes the step of directly casting a polymerized composition in which a PBI polymer is dissolved in a polyphosphate (PPA) solvent. In this method, the PPA solvent is hydrolyzed to phosphoric acid (PA, H3PO4), which has low solubility for PBI, thereby inducing gelation of the casting solution into a PBI film, and thus forming a PA-impregnated PBI film. Unfortunately, such second-generation polymer films still need improvement because, when formed to have high mechanical properties (e.g., tensile strength), they have low proton conductivity, and when formed to have high proton conductivity, their tensile strength is undesirably low.

[0004] Polybenzimidazole (PBI) gel films exhibiting both high ionic conductivity and high mechanical properties are in demand in this field. [Overview of the project] [Means for solving the problem]

[0005] According to one embodiment, a gel film comprising a polybenzimidazole (PBI) polymer and an impregnation solution containing phosphoric acid (PA) is disclosed. The gel film of this disclosure exhibits a high proton conductivity of about 180 mS / cm or more at 160°C and excellent mechanical properties, for example, a breaking point tensile strength of about 5 MPa or more when measured using a 10 N load cell at a crosshead speed of 5 mm / min. The repeating units of the PBI in the gel film of this disclosure include reaction products of tetraaminobiphenyl monomer and reaction products of naphthalenedicarboxylic acid monomer.

[0006] Furthermore, a method for producing the gel film of this disclosure is also disclosed. The method of this disclosure includes the step of preparing a polymerization solution containing polyphosphate (PPA) and polybenzimidazole (PBI) forming monomers. The polybenzimidazole (PBI) forming monomers include tetraaminobiphenyl monomer and naphthalenedicarboxylic acid monomer. The tetraaminobiphenyl monomer and naphthalenedicarboxylic acid monomer account for about 70 mol% or more of the polybenzimidazole (PBI) forming monomers in the polymerization solution. After polymerizing the polybenzimidazole forming monomers, the gelation of the gel film can be induced by treating the resulting solution to hydrolyze at least a portion of the polyphosphate (PPA). [Brief explanation of the drawing]

[0007] A complete and feasible disclosure of the present invention (including the best mode) for those skilled in the art is described in more detail in the remainder of this specification with reference to the accompanying drawings.

[0008] [Figure 1] Figure 1 shows one embodiment of an electrochemical cell that can incorporate the polybenzimidazole (PBI) gel membrane of the present disclosure. [Figure 2] Figure 2 shows a proton exchange PEM fuel cell that can incorporate the polybenzimidazole (PBI) gel membrane of the present disclosure. [Figure 3] Figure 3 shows a proton-exchange PEM electrolytic cell into which the polybenzimidazole (PBI) gel membrane of the present disclosure can be incorporated. [Modes for carrying out the invention]

[0009] The following describes in detail various embodiments of the present invention and one or more examples thereof. Each example is provided for illustrative purposes and does not limit the present invention. In fact, it will be apparent to those skilled in the art that various modifications and variations of the present invention are possible without departing from the scope and spirit of the invention. For example, features exemplified or described as part of one embodiment can be used together with another embodiment to create yet another embodiment.

[0010] This disclosure relates to polybenzimidazole (PBI) gel films that generally exhibit both high mechanical properties and high proton conductivity, and to methods for producing the same. More specifically, the PBI gel films of this disclosure can exhibit high tensile strength at fracture while maintaining high ionic conductivity, thereby enabling the manufacture of fuel cells, electrolytic cells, and other products that can provide high power operation under high current load conditions.

[0011] The PBI gel film of this disclosure, with its combination of high proton conductivity and improved physical robustness, enables extended gel film life and a wide range of applications for technologies incorporating this gel film. For example, a fuel cell incorporating the PBI gel film of this disclosure can withstand numerous start-up and stop-down cycles without damaging the gel film, even at extremely low external temperatures. Such performance can be proven to be particularly beneficial in automotive and residential electrical appliance applications. The combination of high mechanical durability and high proton conductivity of the PBI gel film of this disclosure is also advantageous in the manufacture of membrane electrode assemblies and fuel cell stacks. For example, considerable forces act on the gel film during the stacking of fuel cell stacks, and the high tensile properties of the PBI gel film of this disclosure are advantageous under such conditions. Furthermore, the PBI gel film of this disclosure can withstand forces applied to the gel film during device assembly, leading to improved quality control and reduced manufacturing costs.

[0012] The PBI gel film of the present disclosure can operate at a high current density. For example, the PBI gel film of the present disclosure can exhibit a proton conductivity of about 180 millisiemens / cm (mS / cm) or more, about 190 mS / cm or more, about 200 mS / cm or more, or about 220 mS / cm or more at 160°C. In some embodiments, for example, it can exhibit a proton conductivity of about 180 mS / cm to about 500 mS / cm.

[0013] In addition, the PBI gel film of the present disclosure can exhibit a high breaking tensile strength when measured at a crosshead speed of 5 mm / min using a 10 N load cell in accordance with ASTM D638. For example, the PBI gel film of the present disclosure can exhibit a tensile strength at break of about 5 megapascals (MPa) or more, about 6 MPa or more, or in some embodiments, even higher, for example, about 5 MPa to about 10 MPa.

[0014] Since the proton conductivity and the breaking tensile strength tend to decrease when one is increased, a combination of high proton conductivity and high breaking tensile strength has not been achieved so far. For example, Table 1 below shows the breaking tensile strength and the proton conductivity at 160°C for some representative PBI films known in the art. As shown in Table 1, none of the PBI films known in the art achieve the combination of high proton conductivity and high breaking tensile strength as exhibited by the PBI film of the present disclosure.

[0015]

Table 1

[0016] To form the PBI gel film of this disclosure, a polymerization composition containing polyphosphate (PPA) and a PBI-forming monomer is prepared. The monomer content of the polymerization composition is generally low, for example, about 10% by weight or less, for example, about 8% by weight or less, about 5% by weight or less, about 4% by weight or less, or about 3% by weight or less, relative to the total weight of the combination of the PBI-forming monomer and PPA, and in some embodiments, for example, about 1% to about 4% by weight, or about 2% to about 3% by weight.

[0017] More specifically, the PBI-forming monomers of the polymerization composition may include at least one tetraaminobiphenyl monomer and at least one naphthalenedicarboxylic acid monomer.

[0018] Examples of tetraaminobiphenyl monomers used to form the PBI gel film of this disclosure include, but are not limited to, 3,3',4,4'-tetraaminobiphenyl, 3,3',4,4'-tetraaminobiphenyl, 3,3',4,4'-tetraaminodiphenyl sulfone, 3,3',4,4'-tetraaminodiphenyl ether, 3,3',4,4'-tetraaminodiphenylmethane, 3,3',4,4'-tetraaminodiphenyldimethylmethane, their monohydrochlorides, their dihydrochlorides, their trihydrochlorides, their tetrahydrochlorides, and any combination thereof.

[0019] Examples of naphthalenedicarboxylic acid monomers, but not limited to these, include 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,8-dihydroxynaphthalene-3,6-dicarboxylic acid, and any combination thereof.

[0020] In one embodiment, the PBI-forming monomers in the polymerization composition consist only of tetraaminobiphenyl monomer and naphthalenedicarboxylic acid monomer. However, this is not essential, and in one embodiment, the polymerization composition may contain one or more additional PBI-forming monomers in addition to at least one tetraaminobiphenyl monomer and at least one naphthalenedicarboxylic acid monomer. In this case, the additional PBI-forming monomer may be included in the polymerization composition in an amount of about 30 mol% or less of all PBI-forming monomers in the polymerization composition. Thus, the tetraaminobiphenyl monomer and naphthalenedicarboxylic acid monomer (and therefore of the resulting PBI polymer) in the polymerization composition may, in some embodiments, constitute about 70 mol% or more of the total amount of PBI-forming monomers in the polymerization composition, for example, about 80 mol% or more, about 90 mol% or more, about 95 mol% or more, about 97 mol% or more, or about 98 mol% or more. The amount of additional PBI-forming monomers may generally be about 30 mol% or less of the total amount of PBI-forming monomers in the polymerization composition, for example, about 0.1 mol% to about 20 mol%, or about 0.5 mol% to about 10 mol%.

[0021] The additional PBI-forming monomers may include one or more aromatic tetraamino monomers and heteroaromatic tetraamino monomers. Examples of aromatic tetraamino monomers and heteroaromatic tetraamino monomers that can be used to form the PBI gel film of this disclosure include, but are not limited to, 2,3,5,6-tetraaminopyridine, 1,2,4,5-tetraaminobenzene, 3,3',4,4'-tetraaminobenzophenone, 3,3',4,4'-tetraaminodiphenyldimethylmethane, their monohydrochlorides, their dihydrochlorides, their trihydrochlorides, their tetrahydrochlorides, and any combination thereof.

[0022] The additional PBI-forming monomers include one or more aromatic polycarboxylic acids or heteroaromatic polycarboxylic acids, or their esters, anhydrides, or acid chlorides, and any combination thereof. Suitable esters of polycarboxylic acids include C1-C20 alkyl esters and C5-C12 aryl esters.

[0023] Examples of aromatic dicarboxylic acid monomers, though not limited to these, include pyridine-2,5-dicarboxylic acid, pyridine-3,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid, pyridine-2,4-dicarboxylic acid, 4-phenyl-2,5-pyridinedicarboxylic acid, 3,5-pyrazoledicarboxylic acid, 2,6-pyrimidinedicarboxylic acid, 2,5-pyrazinedicarboxylic acid, 2,4,6-pyridinetricarboxylic acid, benzimidazole-5,6-dicarboxylic acid, 5-hydroxyisophthalic acid, 4-hydroxyisophthalic acid, 2-hydroxyterephthalic acid, 5-aminoisophthalic acid, 5-N,N-dimethylaminoisophthalic acid, 5-N,N-diethylaminoisophthalic acid, 2,5-dihydroxyterephthalic acid, 2,6-dihydroxyisophthalic acid, 4,6-dihydroxyisophthalic acid, 2,3-dihydroxyphthalic acid, and 2,4-dihydroxy Examples include phthalic acid, 3,4-dihydroxyphthalic acid, diphenylsulfone-4,4'-dicarboxylic acid, isophthalic acid, terephthalic acid, phthalic acid, 3-fluorophthalic acid, 5-fluoroisophthalic acid, 2-fluoroterephthalic acid, tetrafluorophthalic acid, tetrafluoroisophthalic acid, tetrafluoroterephthalic acid, 3-sulfophthalic acid, 5-sulfoisophthalic acid, 2-sulfoterephthalic acid, tetrasulfophthalic acid, tetrasulfisophthalic acid, tetrasulfoterephthalic acid, diphenic acid, diphenyl ether 4,4'-dicarboxylic acid, benzophenone-4,4'-dicarboxylic acid, biphenyl-4,4'-dicarboxylic acid, 4-trifluoromethylphthalic acid, 2,2-bis(4-carboxyphenyl)hexafluoropropane, 4,4'-stilbenidicarboxylic acid, 4-carboxycinnamic acid, or any combination thereof.

[0024] Examples of aromatic tricarboxylic acids and their esters, acid anhydrides, or acid chlorides include, but are not limited to, 1,3,5-benzenetricarboxylic acid (trimesic acid), 1,2,4-benzenetricarboxylic acid (trimellitic acid), (2-carboxyphenyl)iminodiacetic acid, 3,5,3'-biphenyltricarboxylic acid, 3,5,4'-biphenyltricarboxylic acid, or any combination thereof.

[0025] Examples of aromatic tetracarboxylic acids and their esters, acid anhydrides, or acid chlorides include, but are not limited to, 3,5,3',5'-biphenyltetracarboxylic acid, benzene-1,2,4,5-tetracarboxylic acid, benzophenonetetracarboxylic acid, 3,3',4,4'-biphenyltetracarboxylic acid, 2,2',3,3'-biphenyltetracarboxylic acid, 1,2,5,6-naphthalenetetracarboxylic acid, 1,4,5,8-naphthalenetetracarboxylic acid, or any combination thereof.

[0026] Examples of heteroaromatic carboxylic acids include heteroaromatic dicarboxylic acids, heteroaromatic tricarboxylic acids, and heteroaromatic tetracarboxylic acids, each of which includes esters such as C1-C20 alkyl esters or C5-C12 aryl esters, or acid anhydrides or acid chlorides of heteroaromatic carboxylic acids. Examples of heteroaromatic carboxylic acids, but not limited to these, include pyridine-2,5-dicarboxylic acid, pyridine-3,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid, pyridine-2,4-dicarboxylic acid, 4-phenyl-2,5-pyridinedicarboxylic acid, 3,5-pyrazoledicarboxylic acid, 2,6-pyrimidinedicarboxylic acid, 2,5-pyrazinedicarboxylic acid, 2,4,6-pyridinetricarboxylic acid, benzimidazole-5,6-dicarboxylic acid, their C1-C20 alkyl esters, their C5-C12 aryl esters, their acid anhydrides, their acid chlorides, or any combination thereof.

[0027] In one embodiment, the polymerization composition may include a diaminocarboxylic acid monomer. Examples of diaminocarboxylic acid monomers, but are not limited to, diaminobenzoic acid, its monohydrochloride or dihydrochloride derivative, 1,2-diamino-3'-carboxylic acid, 4,4'-diphenyl ether, and any combination thereof.

[0028] Furthermore, the polymerization composition may contain PPA. An example of PPA usable in polymerization compositions is commercially available PPA from Riedel-de Haen, for example. PPA may contain concentrated grade phosphoric acid (PA) exceeding 100%. At high concentrations, individual H3PO4 units polymerize by dehydration. PPA is represented by the following formula: H n+2 P n O 3n+1 (n>1)

[0029] PPA[H n+2 P n On +1 (n>1) is a P2O5 content calculated by acid titration that is approximately 70% by weight or more, for example, approximately 75% by weight or more, or approximately 82% by weight or more, and in some embodiments, for example, approximately 70% by weight to approximately 86% by weight.

[0030] Polymerization compositions can generally be in the form of a solution, dispersion, or suspension of monomers in PPA, depending on the properties of the compound being polymerized and any additional components of the polymerization solution.

[0031] Polymerization can be carried out at a predetermined temperature and time until proper polymerization of the monomers occurs, and polymerization can generally be determined by an increase in the viscosity of the composition. The increase in viscosity can be confirmed by visual inspection, measurement of intrinsic viscosity, or other suitable means. For example, in some embodiments, polymerization can be continued until the polymerized composition exhibits an intrinsic viscosity of about 0.8 dL / g or more, for example, about 1.0 dL / g or more, or about 1.5 dL / g or more. The polymerization temperature is generally about 220°C or less, for example, about 200°C or less, and in some embodiments, for example, about 100°C to 195°C. Polymerization can be carried out over a period of time from a few minutes (e.g., about 5 minutes) to several hours (e.g., about 100 hours). In one embodiment, the polymerized composition can be heated in stages. For example, the polymerized composition can be heated in three or more stages, each stage lasting about 10 minutes to about 5 hours, with the temperature increasing by about 15°C or more in each stage. Naturally, it will be apparent to those skilled in the art that specific polymerization conditions can generally be modified depending on the reactivity and concentration of the specific monomer, and that no specific polymerization conditions are required for film formation.

[0032] After polymerization, PBI exists as a solution in a PPA solvent, and a film can be formed by processing this PBI polymer solution. Generally, film formation involves the initial formation of a film precursor having a desired thickness. In some embodiments, the viscosity of the PBI polymer solution can be adjusted to form a film precursor of a desired thickness and / or according to a desired formation method. As an example, the formation of a film precursor can be facilitated by adjusting the viscosity of the polymer solution to a desired value by combining the PBI polymer solution with PA (most typically concentrated PA, e.g., 85% PA).

[0033] The film precursor can be formed according to any suitable formation process, including but not limited to casting, spray coating, and knife coating. Similarly, the film precursor can be formed to any suitable thickness. For example, in one embodiment, the film precursor can be formed to a thickness of about 20 micrometers (μm) to about 4,000 μm, and in some embodiments, for example, to a thickness of about 30 μm to about 3,500 μm, or about 50 μm to about 1,000 μm.

[0034] To induce gelation of the membrane precursor and form a PBI gel membrane, the PBI polymer solution is treated in the presence of water and / or moisture to hydrolyze at least a portion of the PPA in the PBI polymer solution. Hydrolysis causes PPA to form PA or a mixture of PA and water, thereby changing the PBI polymer solution from a sol to a gel and inducing membrane gelation. This is because PBI polymer is less soluble in PA compared to PPA.

[0035] Hydrolysis is carried out at a temperature and time sufficient to gel the film, thereby enabling it to be handled independently and without damage while maintaining a high liquid content (e.g., a liquid content of about 60% by weight or more relative to the total solid and liquid components of the gel film). For example, the hydrolysis process can be carried out at temperatures of about 0°C to about 150°C, for example, about 10°C to about 120°C, or about 20°C to about 90°C, and in some embodiments, for example, at ambient temperature (e.g., in a contact environment with relative humidity of about 35% to 100%).

[0036] Hydrolysis can be carried out by contacting the membrane precursor with H2O, for example, in liquid or vapor form, and / or in the presence of other components. For example, the membrane precursor can be contacted with water vapor, liquid water, vapor, and / or aqueous PA (e.g., PA solutions having PA concentrations of about 10% to about 90% by weight, e.g., about 30% to about 70% by weight, or about 45% to about 55% by weight). The hydrolysis treatment can be carried out under standard pressure, but this is not a requirement for the gelation process, and in some embodiments, the hydrolysis treatment can be carried out under modified pressure.

[0037] In one embodiment, hydrolysis can be carried out in a temperature and humidity controlled environment in which the H2O content can be precisely controlled. For example, the moisture content of the local environment can be controlled by adjusting the temperature or saturation of the fluid brought into contact with the precursor membrane. For example, a carrier gas such as air, nitrogen, carbon dioxide, or another suitable gas can be used to transport a controlled amount of H2O (e.g., vapor) to contact the precursor membrane.

[0038] The hydrolysis treatment time generally varies depending on parameters such as the H2O content and form at contact, the thickness of the precursor film, and the contact temperature. Generally, hydrolysis can be carried out over a period of several seconds to several minutes when using superheated steam, and over a period of several days when carried out at ambient temperature and with low relative atmospheric moisture. In some embodiments, hydrolysis can be carried out over a period of about 10 seconds to about 300 hours, for example, from about 1 minute to about 200 hours. As an example, in one embodiment in which at least partial hydrolysis of PPA in a PBI polymer solution is performed at room temperature (e.g., about 20°C) with ambient air having a relative atmospheric moisture content (i.e., relative humidity) of about 20% to 100%, for example, about 40% to about 80%, the treatment time may generally be about 5 hours to about 200 hours.

[0039] When at least a portion of the PPA in a PBI polymer solution is hydrolyzed, the PBI polymer gels, forming a PBI gel film. In one embodiment, the PBI gel film can have a thickness of about 15 μm to about 3000 μm, for example, about 20 μm to about 2000 μm, or about 20 μm to about 1500 μm. However, any particular thickness of the PBI gel film is not important, and the thickness of the PBI gel film may depend on the thickness of the precursor. In some embodiments, the PBI gel film may have a thickness thinner than the thickness of the film precursor. After hydrolysis, the PBI gel film can stand on its own, even with a high liquid content, which is thought to be due to the intramolecular and intermolecular polymer structures present within the gelled polymer matrix.

[0040] In one embodiment, the PBI solid content of the formed PBI gel film may be about 4% to about 40% by weight, for example, about 8% to about 30% by weight, or about 10% to about 25% by weight, relative to the total weight of the film containing the liquid component.

[0041] In one embodiment, the PBI gel film can be crosslinked, thereby reducing the permeability of the gel film without significantly affecting its electrochemical properties. The mode of crosslinking is not particularly limited. The timing of crosslinking the gel film in the gel film formation process is not particularly limited.

[0042] In one embodiment, the PBI gel film can be easily crosslinked by heating in the presence of atmospheric oxygen. Crosslinking can also be induced by the action of radiation, such as infrared (IR) radiation (having wavelengths of approximately 700 nm to approximately 1 mm) including near-infrared (IR) radiation (having wavelengths of approximately 700 nm to approximately 2000 nm or energies in the range of approximately 0.6 to approximately 1.75 eV).

[0043] To crosslink a PBI gel film, reactive functionalities can be incorporated into the polymer chain of the PBI polymer, either so that the PBI polymer crosslinks with itself, or so that it crosslinks with a crosslinking agent, i.e., a polyfunctional compound (e.g., an amine) that can react with one or more functional groups of the PBI polymer. The crosslinking agent may include any suitable functionalities that cause crosslinking. Suitable crosslinking agents include, but are not limited to, epichlorohydrins, diexoxides, diisocyanates, α,ω-dihaloalkanes, diacrylates, and bisacrylamides, with specific examples including α,α'-dichloro-p-xylene, chloromethyl methyl ether, bis(chloromethyl) ether, terephthaloyl chloride, succinyl chloride, dimethyl succinate, and any combination thereof. In one embodiment, 1 to 20 equivalents of the crosslinking agent can be used per available aromatic ring. However, embodiments in which the gel film is crosslinked are not limited to any particular crosslinking density.

[0044] In one embodiment, the PBI gel film is impregnated with an ion transport agent, such as a supporting electrolyte, together with PA remaining in the gel film after gelation. For example, the PBI gel film can be impregnated (filled) with a mineral acid (e.g., a strong inorganic acid) such as hydrochloric acid, nitric acid, fluorosulfonic acid, sulfuric acid, or any combination thereof, or a strong organic acid such as acetic acid, formic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid, or any combination thereof, or a mixture of various types of acids, e.g., a combination of a mineral acid and an organic acid. Other examples of ion transport agents that can be impregnated into the PBI gel film include, but are not limited to, sodium chloride, potassium chloride, sodium hydroxide, potassium hydroxide, sodium sulfide, potassium sulfide, and any combination thereof. As an example, ion transport agents include H2SO4, HBr, HBr / HCl mixture, HCl, NaS2, NaS2 / NaBr mixture, Br2 in HBr, Br2 in H2SO4, Br2 in HBr / H2SO4 mixture, etc. In one embodiment, a tetraalkylammonium-supported cation is impregnated into the PBI gel film. Two non-limiting examples of tetraalkylammonium-supported cations are tetraethylammonium (Et4N + ) and tetrabutylammonium (Bu4N + ). Further examples of ion transport agents that can be impregnated into the PBI gel film include solutions of tetrafluoroborate (BF 4- ), perchlorate (ClO 4- ), or hexafluorophosphate (PF 6- ), or any combination thereof.

[0045] The concentration of the ion transport agent in the PBI gel film is not particularly limited and generally can be up to about 25 moles per liter (M), and in some embodiments, for example, about 0.1 M to about 25 M, about 0.5 M to about 10 M, or about 1 M to about 5 M.

[0046] The PBI gel membrane can be impregnated with an ion transporter according to any suitable method. For example, in one embodiment, the PBI gel membrane can be impregnated with an ion transporter by immersing it in a solution of the ion transporter in a high-temperature environment for a period of time of any choice from several minutes to several hours or several days.

[0047] The PBI gel film may contain one or more additives that can be incorporated into the PBI gel film during precursor film formation, film gelation, or impregnation with an ion transporter. For example, low molecular weight C1-C4 alcohols (e.g., glycerol), small organic molecules, or low molecular weight organic acids such as urea can be incorporated (impregnated) into the PBI gel film together with the ion transporter, or in place of the ion transporter.

[0048] In one embodiment, the PBI gel film can contain particles, such as titanium dioxide or PBI particles, generally in an amount of about 2% by weight or less, thereby reducing the porosity of the film. For example, nano-sized PBI particles can be incorporated into the polymer matrix during the gelation of the PBI gel film by adding them to the polymer solution during hydrolysis.

[0049] The PBI gel film of this disclosure can be suitably used in a wide range of applications. Typical applications of the PBI gel film of this disclosure include, but are not limited to, use in fuel cells, electrolytic cells, capacitors, and battery systems.

[0050] In one embodiment, the PBI gel membrane of the present disclosure can be combined with other electrochemical cell components known in the art. Figure 1 shows one embodiment of an electrochemical cell 20 into which the PBI gel membrane of the present disclosure can be incorporated. As shown, the electrochemical cell 20 comprises a PBI gel membrane 25 and cathodes 22 and anodes 24 separated from each other by the PBI gel membrane 25. The PBI gel membrane 25 can be impregnated with a suitable supporting electrolyte / ion transporter as a proton exchange membrane (PEM).

[0051] Furthermore, the electrochemical cell 20 includes porous layers 26, 27 adjacent to one or both of the electrodes 22, 24. The porous layers 26, 27 can improve contact between the chemical reactants and chemical products and the electrodes 22, 24. For example, when considering the flow of gaseous reactants or products, the porous layer 26 can be a gas diffusion layer. The gas diffusion layer can be fibrous, particulate, or a combination thereof to provide a uniform distribution of gas on the electrode surface and facilitate electron transport between the electrode and the external electrical circuit. As an example, the gas diffusion layer can be formed from carbon fibers in the form of a woven or nonwoven fabric, for example. The porous layers 26, 27 may optionally include a plurality of sublayers having various porosity levels (e.g., microporosity, mesoporosity, and / or microporosity) in any desired combination to further refine and define the fluid flow field at the electrodes and facilitate desired interactions between the electrode active material and the half-reacting reactants and products.

[0052] Furthermore, the electrochemical cell 20 can have flow fields 28, 29 defined on each of its sides, which can deliver reactants and products to the electrochemical cell 20 and / or remove reactants and products from the electrochemical cell 20. For example, in the embodiment shown in Figure 1, the flow fields 28, 29 are defined by channels formed in the bipolar plates 21, 23, respectively. The bipolar plates 21, 23 can generally be any design and configuration known in the art to provide the desired flow fields 28, 29 in combination with one or more of the following: electrical connection, temperature control by thermal removal, and prevention of leakage of the electrochemical cell 20 to the outside.

[0053] The typical electrochemical cell 20 shown in Figure 1 includes inflow and outflow on each side of the electrochemical cell 20, but it will be understood by those skilled in the art that in various embodiments, one side or the other side of the electrochemical cell 20 does not require inflow / outflow on that side.

[0054] A single electrochemical cell 20 may be used alone, or one electrochemical cell 20 may be combined with other electrochemical cells 20 to form a cell stack. A cell stack can contain any number of individual electrochemical cell units; for example, a single cell stack may be formed by combining 10 or more, 50 or more, or several hundred individual cells.

[0055] In one embodiment, the PBI gel membrane of the present disclosure can be incorporated into a fuel cell designed to utilize the electrical energy generated in a cell half-reaction of an electrochemical cell. Referring to Figure 2, one embodiment of a hydrogen fuel cell is shown, which comprises a proton-conducting PBI gel membrane 32 and a cathode 34 and an anode 36 separated from each other by the PBI gel membrane 32. When the hydrogen fuel cell is in operation, hydrogen is supplied to the anode side of the cell (35) and oxygen (e.g., air) is supplied to the cathode side of the cell (37).

[0056] At anode 36, hydrogen reacts according to the following half-reaction. 2H2→4H + +4e -

[0057] The PBI gel film 32 transports protons generated at the anode 36 to the cathode 34, and electrons e generated at the anode 36 - This is used when passing through the circuit from anode 36 to cathode 34.

[0058] At cathode 34, protons, oxygen, and electrons react according to the following half-reactions. O2 + 4H + +4e - →2H2O

[0059] Subsequently, the water and unreacted gases in the input flow (37) are discharged from the cathode side of the cell (39), and the unreacted hydrogen is discharged from the anode side of the cell (31).

[0060] The PBI gel membrane of this disclosure is also useful in electrolytic cells that use electricity to accelerate chemical reactions. For example, referring to Figure 3, one embodiment of a PEM-type water electrolytic cell is shown, comprising a PBI gel membrane 42 which is a proton exchange membrane (PEM), and a cathode 44 and an anode 46 separated from each other by the PBI gel membrane 42. In the illustrated embodiment, water is supplied to the anode side of the electrolytic cell (45). In some embodiments, water is supplied to both sides of the cell to improve hydration of the PBI gel membrane 42.

[0061] At anode 46, water reacts according to the following half-reaction. 2H2O → 4H + +O2+4e -

[0062] The PBI gel film 42 transports protons formed at the anode 46 to the cathode 44.

[0063] At cathode 44, protons and electrons react according to the following half-reactions. 4H + +4e - →2H2

[0064] Next, oxygen and unreacted water are released from the anode side of the cell (41), and hydrogen is released from the cathode side of the cell (49). In general, the products can be discharged from the electrolytic cell along with water, as long as a sufficient amount of water is supplied to the electrolytic cell to purge them. The oxygen and hydrogen products can then be separated from the water, if necessary.

[0065] While the above examples illustrate typical products into which the PBI gel film of this disclosure can be incorporated, those skilled in the art will readily understand that the PBI gel film of this disclosure can be used in a variety of applications.

[0066] This disclosure can be better understood by referring to the following examples.

[0067] Examples

[0068] Materials and methods

[0069] 3,3',4,4'-Tetraaminobiphenyl (TAB, polymer grade, approximately 97.5%) was purchased from BASF Fuel Cell, Inc. and used as is. Naphthalene-1,4-dicarboxylic acid (HPLC grade, purity >98.00%) was purchased from AK Scientific and used as is. PPA (115%) was purchased from FMC Corporation and used as is.

[0070] A typical polymerization composition consisted of a molar equivalent mixture of tetraaminobiphenyl (TAB) and dicarboxylic acid species, which was added to PPA, mixed with an overhead stirrer, purged with dry nitrogen, and heated in a high-temperature silicone oil bath. The temperature was controlled by a programmable temperature control device with heating and immersion functions. The reaction temperature was gradually increased from room temperature to 120°C, 150°C, 170°C, and 190°C. In a typical polymerization, the final reaction temperature was approximately 190°C and maintained for 12 hours. After confirming the completion of the reaction by visual inspection of viscosity, the polymer solution was cast onto a clear glass plate using a doctor blade with a gate thickness of 15 mils. This cast solution was hydrolyzed in a humidity chamber adjusted to 25°C and 55% relative humidity to produce a PBI gel film.

[0071] Membrane composition

[0072] The composition of each PBI gel membrane was determined by measuring the relative amounts of polymer solids, water, and acid in each membrane. The phosphate (PA) content of each PBI gel membrane was determined by titrating each membrane sample with a standard sodium hydroxide solution (0.10 M) using a Metrohm 716 DMS Titrino automatic titrator. After titration, each membrane sample was thoroughly washed with deionized water (DI water) and dried under reduced pressure at 120°C overnight. The dried samples were then weighed to determine the polymer solids content in each membrane.

[0073] The polymer wt% and phosphate (PA) wt% were determined by the following formulas 1 and 2.

[0074]

number

[0075]

number

[0076] In the above formula, W sample This is the weight of the sample before titration, W dry This is the weight of the final dried sample after titration, and M acid This is the molecular weight of phosphate (PA), and V NaOH and C NaOH This represents the volume and concentration of sodium hydroxide solution required to neutralize PA to the first equivalence point. The number of moles of PA per mole of polybenzimidazole (PBI) repeating unit (or PA doping level, X, PA / RU in the table below) was calculated using the following formula (3).

[0077]

number

[0078] In the above formula, V NaOH and C NaOH This is the volume and concentration of sodium hydroxide solution required to neutralize PA to the first equivalence point, W dry This is the final weight of the dried sample after titration, and M polymer This is the molecular weight of the polymer repeating unit.

[0079] The monomer concentration was calculated as the weight ratio of the total amount of monomers (g) in the polymerization mixture to the total amount of monomers and PPA (g) in the polymerization mixture multiplied by 100.

[0080] Tensile properties

[0081] The tensile properties of the PBI gel film described herein were tested at room temperature using an Instron 5543A system with a 10N load cell and a crosshead speed of 5 mm / min. Dogbone-shaped samples were cut according to ASTM standard D638 (Type V sample), and a preload of 0.1N was applied before testing.

[0082] Proton conductivity

[0083] The proton conductivity of the PBI gel film described herein was measured by four-electrode electrochemical impedance spectroscopy using a Zahner IM6e electrochemical workstation, at a frequency range of 1 Hz to 100 kHz and an amplitude of 5 mV. The experimental data was fitted to a two-component model in which a capacitor and an ohmic resistor were connected in parallel. The conductivity of the PBI gel film described herein at various temperatures was determined using the film resistance obtained from model simulations, according to the following formula.

[0084]

number

[0085] In the above formula, d represents the distance between the two internal probes, l represents the thickness of the membrane, w represents the width of the membrane, and R m The ohmic resistance is shown, determined by model fitting. The film sample was heated in two stages up to 180°C. The reported conductivity data was recorded during the second heating cycle, after water was removed from the film during the first heating cycle.

[0086] Example 1

[0087] A 1,4-naphthalene-PBI (n-PBI) gel film was polymerized and hydrolyzed as described above. 2.74 g of tetraaminobiphenyl (TAB, 12.8 mmol) and 2.76 g of naphthalene-1,4-dicarboxylic acid (NDA, 12.8 mmol) were added to 245 g of PPA and reacted under a nitrogen atmosphere for 36 hours. This solution was coated onto a glass plate using a doctor blade with a gate thickness of 15 mils, and then hydrolyzed to produce a gel film.

[0088] [ka]

[0089] The properties of this gel film are shown in Table 2 below.

[0090] [Table 2]

[0091] As shown in Table 2, this gel film exhibited a proton conductivity of 240 mS / cm and an average tensile strength of 6.5 MPa.

[0092] Example 2

[0093] 3.11 g of tetraaminobiphenyl (TAB, 14.5 mmol) and 3.14 g of naphthalene-1,4-dicarboxylic acid (1,4-NDA, 14.5 mmol) were added to 243 g of PPA, and an n-PBI gel film was prepared by polymerization in the same manner as described above according to the following reaction scheme. Polymerization was carried out under a nitrogen atmosphere at 190°C for 36 hours. This solution was coated onto a glass plate using a doctor blade with a gate thickness of 15 mils, and then hydrolyzed to prepare a gel film.

[0094] The properties of this gel film are shown in Table 3 below.

[0095] [Table 3]

[0096] As shown in Table 3, this gel film has a higher PBI solid content compared to the gel film of Example 1. Furthermore, this gel film exhibited a proton conductivity of 260 mS / cm and an average tensile strength of 9.2 MPa.

[0097] Comparative Example 3

[0098] Para-PBI (p-PBI) gel films were polymerized using terephthalic acid instead of naphthalenedicarboxylic acid in the same manner as described above.

[0099] 4.23 g of tetraaminobiphenyl (TAB, 19.7 mmol) and 3.27 g of terephthalic acid (TPA, 19.7 mmol) were added to 243 g of PPA and reacted under a nitrogen atmosphere for 36 hours. This solution was coated onto a glass plate using a doctor blade with a gate thickness of 15 mils, and then hydrolyzed to produce a gel film.

[0100] The properties of this gel film are shown in Table 4 below.

[0101] [Table 4]

[0102] As shown in Table 4, this gel film exhibited a proton conductivity of 270 mS / cm, but its average tensile strength was a low 2.0 MPa.

[0103] Comparative Example 4

[0104] A sulfonated PBI (s-PBI) gel film was polymerized using sulfonated terephthalic acid instead of naphthalenedicarboxylic acid, in the same manner as described above.

[0105] 3.89 g of tetraaminobiphenyl (TAB, 18.1 mmol) and 4.86 g of monosodium 2-sulfoterephthalate (s-TPA, 18.1 mmol) were added to 241 g of PPA and reacted under a nitrogen atmosphere for 36 hours. This solution was coated onto a glass plate using a doctor blade with a gate thickness of 15 mils, and then hydrolyzed to produce a gel film.

[0106] The properties of this gel film are shown in Table 5 below.

[0107] [Table 5]

[0108] As shown in Table 5, this gel film exhibited a proton conductivity of 220 mS / cm, but its average tensile strength was a low 2.4 MPa.

[0109] Comparative Example 5

[0110] Dihydroxy-PBI (diOH-PBI) gel films were polymerized using dihydroxyterephthalic acid instead of naphthalenedicarboxylic acid, in the same manner as described above.

[0111] 3.64 g of tetraaminobiphenyl (TAB, 17.0 mmol) and 3.36 g of 2,5-dihydroxyterephthalic acid (DiOH-TPA, 17.0 mmol) were added to 243 g of PPA and reacted under a nitrogen atmosphere for 36 hours. This solution was coated onto a glass plate using a doctor blade with a gate thickness of 15 mils, and then hydrolyzed to produce a gel film.

[0112] The properties of this gel film are shown in Table 6 below.

[0113] [Table 6]

[0114] As shown in Table 6, this gel film exhibited a proton conductivity of 275 mS / cm, but its average tensile strength was a low 1.8 MPa.

[0115] Comparative Example 6

[0116] Instead of naphthalenedicarboxylic acid, a meta / para-PBI (m / p-PBI) gel film was polymerized using isophthalic acid:terephthalic acid in a weight ratio of 7:1, in the same manner as described above.

[0117] 11.27 g of tetraaminobiphenyl (TAB, 52.3 mmol), 7.64 g of isophthalic acid (IPA, 46.0 mmol), and 1.09 g of terephthalic acid (TPA, 6.6 mmol) were added to 230 g of PPA and reacted under a nitrogen atmosphere for 36 hours. This solution was coated onto a glass plate using a doctor blade with a gate thickness of 15 mils, and then hydrolyzed to produce a gel film.

[0118] The properties of this gel film are shown in Table 7 below.

[0119] [Table 7]

[0120] As shown in Table 7, this gel film had a significantly higher polymer solids content compared to Examples 1 and 2. This gel film exhibited a high average tensile strength of 7.0 MPa, but its proton conductivity was a low 170 mS / cm.

[0121] Example 7

[0122] A copolymer (1:1 n / p-PBI) gel film was polymerized using 1,4-naphthalenedicarboxylic acid and terephthalic acid in a 1:1 ratio as the diacid components, in the same manner as described above. 3.9638 g of tetraaminobiphenyl (TAB, 18.5 mmol), 1.9996 g of naphthalene-1,4-dicarboxylic acid (NDA, 9.25 mmol), and terephthalic acid (9.25 mmol) (total of TAB + NDA = 27.75 mmol, or 75 mol% of the total monomer content) were added to 243 g of polyphosphate and reacted under a nitrogen atmosphere for 36 hours. This solution was coated onto a glass plate using a doctor blade with a gate thickness of 15 mils, and then hydrolyzed to produce a gel film.

[0123] The properties of this gel film are shown in Table 8 below.

[0124] [Table 8]

[0125] As shown in Table 8, this gel film exhibited a proton conductivity of 250 mS / cm and an average tensile strength of 6.2 MPa.

[0126] Example 8

[0127] 2.39 g of tetraaminobiphenyl (TAB, 11.1 mmol) and 2.41 g of naphthalene-1,4-dicarboxylic acid (1,4-NDA, 11.1 mmol) were added to 170.2 g of PPA, and an n-PBI gel film was prepared by polymerization in the same manner as described above according to the following reaction scheme. Polymerization was carried out under a nitrogen atmosphere at 190°C for 25 hours. This solution was coated onto a glass plate using a doctor blade with a gate thickness of 15 mils, and then hydrolyzed to prepare a gel film.

[0128] The properties of this gel film are shown in Table 9 below.

[0129] [Table 9]

[0130] As shown in Table 9, this gel film exhibited a proton conductivity of 219 mS / cm and an average tensile strength of 5.08 MPa.

[0131] Example 9

[0132] 2.61 g of tetraaminobiphenyl (TAB, 12.1 mmol) and 2.63 g of naphthalene-1,4-dicarboxylic acid (1,4-NDA, 12.1 mmol) were added to 169.76 g of PPA, and an n-PBI gel film was prepared by polymerization in the same manner as described below according to the reaction scheme. Polymerization was carried out in a nitrogen atmosphere at 190°C for 25 hours. This solution was coated onto a glass plate using a doctor blade with a gate thickness of 15 mils, and then hydrolyzed to prepare a gel film.

[0133] The properties of this gel film are shown in Table 10 below.

[0134] [Table 10]

[0135] As shown in Table 10, this gel film exhibited a proton conductivity of 250 mS / cm and an average tensile strength of 9.54 MPa.

[0136] While specific embodiments of the present invention have been described using specific terminology, it should be understood that such descriptions are for illustrative purposes only and can be modified and altered without departing from the spirit or scope of the invention.

Claims

1. It is a gel film, It comprises polybenzimidazole and an impregnation solution containing phosphoric acid, The polybenzimidazole comprises a reaction product of tetraaminobiphenyl monomer and a reaction product of naphthalenedicarboxylic acid monomer. The gel film exhibits a proton conductivity of approximately 180 mS / cm or higher at 160°C, and a tensile strength at the breaking point of approximately 5 MPa or higher when measured using a 10 N load cell at a crosshead speed of 5 mm / min.

2. The gel film according to claim 1, The tetraaminobiphenyl monomer is selected from the group consisting of 3,3',4,4'-tetraaminobiphenyl, 3,3',4,4'-tetraaminodiphenylsulfone, 3,3',4,4'-tetraaminodiphenyl ether, 3,3',4,4'-tetraaminodiphenylmethane, 3,3',4,4'-tetraaminodiphenyldimethylmethane, their monohydrochlorides, their dihydrochlorides, their trihydrochlorides, their tetrahydrochlorides, and any combination thereof, and a gel membrane.

3. A gel film according to claim 1 or 2, The naphthalenedicarboxylic acid is selected from the group consisting of 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,8-dihydroxynaphthalene-3,6-dicarboxylic acid, and any combination thereof, in a gel film.

4. A gel film according to any one of claims 1 to 3, A gel film comprising the tetraaminobiphenyl monomer and the naphthalenedicarboxylic acid monomer, each accounting for approximately 70 mol% or more of all monomers of the polybenzimidazole.

5. A gel film according to any one of claims 1 to 4, Further comprising reaction products of one or more further monomers, The gel film comprises one or more further monomers including aromatic tetraamino monomers, heteroaromatic tetraamino monomers, aromatic polycarboxylic acids or their esters, anhydrides or acid chlorides, heteroaromatic polycarboxylic acids or their esters, anhydrides or acid chlorides, aromatic diaminocarboxylic acids, heteroaromatic diaminocarboxylic acids, or any combination thereof.

6. A gel film according to any one of claims 1 to 5, The gel film is a gel film having a solid content of approximately 4% to 40% by weight relative to the total weight of the gel film.

7. A gel film according to any one of claims 1 to 6, The aforementioned polybenzimidazole is cross-linked in a gel membrane.

8. A gel film according to any one of claims 1 to 7, The impregnation solution further contains mineral acids, organic acids, or combinations thereof, such as hydrochloric acid, nitric acid, fluorosulfonic acid, sulfuric acid, acetic acid, formic acid, p-toluene, sulfonic acid, trifluoromethanesulfonic acid, sodium chloride, potassium chloride, sodium hydroxide, potassium hydroxide, sodium sulfide, potassium sulfide, tetraethylammonium, tetrabutylammonium, tetrafluoroborate, perchlorate, hexafluorophosphate, or any combination thereof, in a gel film.

9. A gel film according to any one of claims 1 to 8, A gel film further containing small organic molecules or microparticles.

10. A fuel cell comprising a gel membrane according to any one of claims 1 to 9.

11. A method for manufacturing a gel film, A step of preparing a polymerization solution, wherein the polymerization solution contains polyphosphate and a polybenzimidazole-forming monomer, the polybenzimidazole-forming monomer comprises a tetraaminobiphenyl monomer and a naphthalenedicarboxylic acid monomer, and the tetraaminobiphenyl monomer and the naphthalenedicarboxylic acid monomer constitute about 70 mol% or more of the polybenzimidazole-forming monomer, The steps include establishing polymerization conditions for the polymerization of the polybenzimidazole-forming monomer in the polymerization solution, A method comprising the step of inducing gelation of a gel film by hydrolyzing at least a portion of the polyphosphate.

12. The method according to claim 11, A method wherein the monomer content in the polymerization solution is about 10% by weight or less relative to the total weight of the polybenzimidazole-forming monomer and the polyphosphate.

13. A method according to claim 11 or 12, A method further comprising the step of forming a gel film precursor before the step of establishing the polymerization conditions.

14. A method according to any one of claims 11 to 13, A method further comprising the step of crosslinking the gel film.

15. A method according to any one of claims 11 to 14, A method further comprising the step of impregnating the gel membrane with an ion transport agent.

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