Strong polybenzimidazole (PBI) gel films with high conductivity

Abstract

Disclosed is a polybenzimidazole gel film which exhibits high proton conductivity and high tensile strength at break. This is formed from a high percentage of a tetraaminobiphenyl monomer and a naphthalic acid monomer.

Description

[0001] Related applications

[0002] This application claims the right to U.S. Provisional Patent Application Serial No. 63 / 491301, filed March 21, 2023, which is incorporated herein by reference for all purposes. Background Technology

[0003] Polybenzimidazole (PBI) membranes have been considered for various electrochemical applications. Traditionally, PBI membranes for electrochemical applications are prepared by solution casting in N,N'-dimethylacetamide (DMAc) to form a dense membrane, which is then imbibing in the desired electrolyte – a process known as the "conventional absorption method." Conventional PBI membranes are best known for their performance as high-temperature polymeric electrolyte membranes, suitable for fuel cell applications. They have also been considered for devices such as electrochemical hydrogen separators, SO2 depolarization electrolyzers, and redox flow batteries. Unfortunately, these conventional PBI membranes exhibit limitations in absorbing electrolyte solutions (less than 100 mS·cm). -1 It exhibits extremely low ionic conductivity at current loads above approximately 100 mAcm. -2 It exhibits low-power operation. Furthermore, the traditional absorption methods for PBI membranes are time-consuming and environmentally unfriendly technologies, increasing the cost of membrane manufacturing.

[0004] Recently, a method for preparing PBI membranes has been developed, which involves directly casting a polymeric composition containing a PBI polymer dissolved in a polyphosphoric acid (PPA) solvent. The PPA solvent is then hydrolyzed to phosphoric acid (PA, H3PO4), a poor solvent for PBI, which causes the casting solution to gel into a PBI membrane, absorbing PA as the membrane forms. Unfortunately, these second-generation polymer membranes have been found to require improvement because membranes exhibiting high mechanical properties (e.g., tensile properties) show low proton conductivity, while membranes exhibiting high proton conductivity exhibit poor low strength properties.

[0005] There is still a need in this field for PBI gel membranes with high mechanical properties and high ionic conductivity. Summary of the Invention

[0006] According to one embodiment, a gel membrane is disclosed, comprising a PBI polymer and a PA-containing absorbent solution. The gel membrane exhibits a high proton conductivity of approximately 180 mS / cm or higher at 160°C and also exhibits excellent mechanical properties, such as a tensile strength at break of approximately 5 MPa or higher, measured with a 10 N load cell at a crosshead speed of 5 mm / min. The PBI repeating unit of the gel membrane comprises the reaction product of a tetraaminobiphenyl monomer and a naphthalenedicarboxylic acid monomer.

[0007] A method for forming a gel membrane is also disclosed. This method may include forming a polymerization solution comprising PPA and PBI forming monomers, including tetraaminobiphenyl monomer and naphthalenedicarboxylic acid monomer. The tetraaminobiphenyl monomer and naphthalenedicarboxylic acid monomer constitute about 70 mol% or more of the PBI forming monomer in the solution. After monomer polymerization, the resulting solution may be treated to hydrolyze at least a portion of the PPA, thereby causing the membrane to gel. Attached Figure Description

[0008] The remainder of this specification sets forth in more detail the full and advantageous disclosure of the subject matter, including its best mode of presentation for those skilled in the art, including with reference to the accompanying drawings, wherein:

[0009] Figure 1 An embodiment of an electrochemical cell in which the PBI membrane described herein can be incorporated is shown.

[0010] Figure 2 A proton exchange PEM fuel cell that can incorporate the PBI membrane described herein is shown.

[0011] Figure 3 A proton exchange PEM electrolyzer in which the PBI membrane described herein can be incorporated is shown. Detailed Implementation

[0012] Reference will now be made in detail to various embodiments of the disclosed subject matter, one or more of which are described below. Each embodiment is provided by way of explanation and not limitation of the subject matter. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to this disclosure without departing from the scope or spirit of the subject matter. For example, features illustrated or described as part of one embodiment may be used in another embodiment to produce further embodiments.

[0013] This disclosure generally relates to PBI gel membranes exhibiting both strong mechanical properties and high proton conductivity, and methods for forming such gel membranes. More specifically, PBI gel membranes can exhibit high tensile strength at break while maintaining high ionic conductivity, enabling them to be used to form fuel cells, electrolyzers, and other products that can provide high-power operation under high current load conditions.

[0014] The improved physical robustness and high proton conductivity of the disclosed gel membrane, combined with its superior properties, enable more durable membranes and broader applications of technologies incorporating this membrane. For example, as disclosed herein, fuel cells incorporating PBI gel membranes can withstand multiple start-stop cycles even at extremely low external temperatures without membrane damage. This capability has proven highly beneficial in applications such as the automotive industry and home appliances. The enhanced mechanical durability, combined with the high proton conductivity of the disclosed gel membrane, is also advantageous in the production of membrane electrode assemblies and fuel cell stacks. For instance, considerable forces act on the gel membrane during the lamination of fuel cell stacks, and the high tensile properties of the disclosed gel membrane can be advantageous under these conditions. The disclosed membrane can better withstand the forces acting on the gel membrane encountered during device assembly, thereby improving quality control and reducing production costs.

[0015] The disclosed gel membrane can operate at high current densities. For example, in some embodiments, the disclosed gel membrane can exhibit proton conductivity of about 180 mS / cm or higher, about 190 mS / cm, about 200 mS / cm or about 220 mS / cm or higher at 160°C, for example, a proton conductivity of about 180 mS / cm to about 500 mS / cm.

[0016] According to ASTM D638, measured at a crosshead speed of 5 mm / min with a load of 10 N, the disclosed gel films can also exhibit high tensile strength at break. For example, PBI gel films can exhibit tensile strength at break of about 5 MPa or greater, about 6 MPa or greater, or even higher in some embodiments, such as about 5 MPa to about 10 MPa.

[0017] Previously, a combination of high proton conductivity and high tensile strength at break has not been achieved because improving one property often reduces the other. For example, Table 1 below provides the tensile strength at break and proton conductivity at 160°C for several representative PBI films previously described in the art. As shown, none of these previously known films achieve the high proton conductivity and high tensile strength at break exhibited by publicly disclosed PBI films.

[0018] Table 1

[0019] Membrane type Tensile strength at break (MPa) Conductivity at 160℃ literature p-PBI 2.0 270 Chem. Mater., Vol. 17, No. 21, 2005 s-PBI 2.4 220 Macromolecules,Vol.43,No.16, 2010 m / p-PBI (7:1) 7.0 170 ACS Appl. Energy Mater. 2019, 2, 1720−1726 i-AB-PBI 0.4 202 Journal of Polymer Science, Part A: Polymer Chemistry 2014, 52, 619–628 diOH-PBI 1.8 350 Macromolecules, Vol. 42, No. 22, 2009 6F-PBI 0.8 90 Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 47, 4064–4073 (2009) 2,5 Py-PBI 1.8 200 Fuel Cells, 2005, 5(2), 287-295 2,6 Py-PBI 1.8 100 Fuel Cells, 2005, 5(2), 287-295

[0020] To form a PBI gel film, a polymeric composition comprising PPA and PBI forming monomers can be formed. The monomer content of the polymeric composition can typically be low, for example, about 10 wt% or less of the total weight of the monomer and PPA combination, such as about 8 wt% or less, about 5 wt% or less, about 4 wt% or less, or about 3 wt% or less, and in some embodiments, for example, about 1 wt% to about 4 wt% or about 2 wt% to about 3 wt%.

[0021] More specifically, the PBI forming monomer of the polymer composition may include at least one tetraaminobiphenyl monomer and at least one naphthalenedicarboxylic acid monomer.

[0022] Examples of tetraaminobiphenyl monomers that can be used to form PBI gel films may include, but are not limited to, 3,3′,4,4′-tetraaminobiphenyl; 3,3′,4,4′-tetraaminodiphenyl sulfone; 3,3′,4,4′-tetraaminodiphenyl ether; 3,3′,4,4′-tetraaminodiphenylmethane; and 3,3′,4,4′-tetraaminodiphenyldimethylmethane and their salts, such as mono-, di-, tri-, and tetra-hydrochlorides, and any combination of tetraaminobiphenyl monomers.

[0023] Examples of naphthalene dicarboxylic acid monomers may include, but are not limited to, 1,4-naphthalene dicarboxylic acid; 1,5-naphthalene dicarboxylic acid; 2,6-naphthalene dicarboxylic acid; 2,7-naphthalene dicarboxylic acid; 1,8-dihydroxynaphthalene-3,6-dicarboxylic acid; or any combination thereof.

[0024] In one embodiment, the PBI-forming monomers of the polymer composition may comprise only tetraaminobiphenyl monomer and naphthalic acid monomer. However, this is not mandatory; in one embodiment, the polymer composition may also include one or more other PBI-forming monomers in addition to at least one tetraaminobiphenyl monomer and at least one naphthalic acid monomer. When present, the polymer composition may contain an amount of about 30 mol% or less of all the PBI-forming monomers in the polymer composition as other PBI-forming monomers. Thus, in some embodiments, the tetraaminobiphenyl and naphthalic acid monomers of the polymer composition (and the resulting PBI polymer) may together comprise about 70 mol% or more of the total PBI-forming monomers of the polymer composition, for example, about 80 mol% or more, about 90 mol% or more, about 95 mol% or more, or about 97 mol% or more, or about 98 mol% or more. Based on the total amount of PBI forming monomers in the polymer composition, the amount of other PBI forming monomers can typically be about 30 mol% or less, for example, about 0.1 mol% to about 20 mol%, or about 0.5 mol% to about 10 mol%.

[0025] Other PBI forming monomers may include one or more aromatic and heteroaromatic tetraamino monomers. Examples of other aromatic and heteroaromatic tetraamino monomers that may be used to form PBI films may include, but are not limited to, 2,3,5,6-tetraaminopyridine; 1,2,4,5-tetraaminobenzene; 3,3′,4,4′-tetraaminobenzophenone; and 3,3′,4,4′-tetraaminodiphenyldimethylmethane and its salts, such as mono-, di-, tri-, and tetra-hydrochlorides, as well as any combination of aromatic or heteroaromatic tetraamino monomers.

[0026] Other PBI-forming monomers may include one or more aromatic or heteroaromatic polycarboxylic acids or their esters, acid anhydrides or acyl chlorides and / or one or more aromatic or heteroaromatic diaminocarboxylic acids. Esters of polycarboxylic acids, such as C1-C20 alkyl esters or C5-C12 aryl esters of polycarboxylic acids, may be used.

[0027] Examples of aromatic dicarboxylic acid monomers may include, but are not limited to, 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; 2,4- Dihydroxyphthalic acid; 3,4-dihydroxyphthalic acid; diphenyl sulfone-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 Formic acid; tetrasulfonated phthalic acid; tetrasulfonated isophthalic acid; tetrasulfonated terephthalic acid; biphenylic acid; diphenyl ether 4,4′-dicarboxylic acid; benzophenone-4,4′-dicarboxylic acid; biphenyl-4,4′-dicarboxylic acid; 4-trifluoromethyl phthalic acid; 2,2-bis(4-carboxyphenyl)hexafluoropropane; 4,4′-stilbenedicarboxylic acid; and 4-carboxycinnamic acid or any combination thereof.

[0028] Examples of aromatic tricarboxylic acids and their esters, anhydrides and acyl chlorides include, but are not limited to, 1,3,5-phenyltricarboxylic acid (pyromellitic acid); 1,2,4-phenyltricarboxylic acid (trimethoxylic acid); (2-carboxyphenyl)iminodiacetic acid; 3,5,3′-biphenyltricarboxylic acid; 3,5,4′-biphenyltricarboxylic acid; or any combination thereof.

[0029] Examples of aromatic tetracarboxylic acids and their esters, anhydrides and acyl chlorides include, but are not limited to, 3,5,3′,5′-biphenyltetracarboxylic acid; benzene-1,2,4,5-tetracarboxylic acid; benzophenone tetracarboxylic acid; 3,3′,4,4′-biphenyltetracarboxylic acid; 2,2′,3,3′-biphenyltetracarboxylic acid; 1,2,5,6-naphthotetracarboxylic acid; 1,4,5,8-naphthotetracarboxylic acid; or any combination thereof.

[0030] Heteroaromatic carboxylic acids can include heteroaromatic dicarboxylic acids, heteroaromatic tricarboxylic acids, and heteroaromatic tetracarboxylic acids, including their respective esters, such as C1-C20 alkyl esters, C5-C12 aryl esters, or anhydrides or acyl chlorides of heteroaromatic carboxylic acids. Examples of heteroaromatic carboxylic acids include, but are not limited to, 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; and their C1-C20 alkyl esters or C5-C12 aryl esters, or their anhydrides or acyl chlorides, or any combination thereof.

[0031] In one embodiment, the polymeric composition may include a diaminocarboxylic acid monomer, examples of which include, but are not limited to, monohydrochloride and dihydrochloride derivatives of diaminobenzoic acid, and 4,4′-diphenyl ether of 1,2-diamino-3′-carboxylic acid, or any combination thereof.

[0032] The polymerization composition may also include PPA. PPA that can be used in the polymerization composition may include, for example, commercially available PPA from Riedel-de Haen. PPA may include PA concentrate grade of 100% or higher. At high concentrations, individual H3PO4 units are polymerized by dehydration, and PPA can be produced using formula H... n+2 P n O 3n+1 (n>1) represents.

[0033] PPA[H n+2 P n O 3n+1 The P2O5 content of (n>1) can be calculated by a pH meter to be about 70 wt% or higher, for example, about 75 wt% or higher, or about 82 wt% or higher, for example, about 70 wt% to about 86 wt% in some embodiments.

[0034] The polymerization composition can be in the form of a solution, dispersion or suspension of monomers in PPA, depending on the nature of the compound to be polymerized and any other components of the polymerization solution.

[0035] Polymerization can be carried out at a certain temperature for a period of time until the monomers undergo suitable polymerization, which can typically be determined by an increase in the viscosity of the composition. This increase in viscosity can be determined by visual inspection, by measuring the intrinsic viscosity, or by any other suitable method. For example, in some embodiments, polymerization can continue until the polymeric composition exhibits an intrinsic viscosity of about 0.8 dL / g or higher, for example, about 1.0 dL / g or higher, or about 1.5 dL / g or higher. Polymerization temperatures can typically be about 220°C or lower, for example, about 200°C or lower, and in some embodiments, about 100-195°C. Polymerization can be carried out over a period of several minutes (e.g., about 5 minutes) to up to several hours (e.g., about 100 hours). In one embodiment, the polymeric composition can be heated gradually, for example, in three or more steps, each lasting about 10 minutes to about 5 hours, with each step increasing the temperature by about 15°C or higher. Of course, specific polymerization conditions can vary, typically depending on the reactivity and concentration of the specific monomers, as will be apparent to those skilled in the art, and specific polymerization conditions are not required for film formation.

[0036] After polymerization, PBI can dissolve in PPA solvent, and the PBI polymer solution can be processed to form a membrane. Typically, membrane formation may include the initial formation of a membrane precursor with the desired thickness. In some embodiments, the viscosity of the PBI polymer solution can be adjusted, and / or, depending on the desired formation method, to form the membrane precursor to the desired thickness. For example, the solution can be combined with PA (most typically concentrated PA, e.g., 85% PA) to adjust the viscosity of the polymer solution to the desired value and promote the formation of the membrane precursor.

[0037] The membrane precursor can be formed according to any suitable formation method, such as, but not limited to, casting, spraying, blade coating, etc. Similarly, the membrane precursor can be formed to any suitable thickness. For example, the membrane precursor can be formed to a thickness of about 20 micrometers (μm) to about 4000 μm, in one embodiment, for example, about 30 μm to about 3500 μm, or in some embodiments, about 50 μm to about 1000 μm.

[0038] To promote the gelation of the membrane precursor and the formation of a PBI gel membrane, the PBI polymer solution can be treated in the presence of water and / or moisture to hydrolyze at least a portion of the PPA in the solution. Once hydrolyzed, the PPA will form PA or a mixture of PA and water, leading to sol-gel transfer of the PBI polymer solution and membrane gelation, since the PBI polymer is less soluble in PA compared to PPA.

[0039] Hydrolysis can be carried out at a temperature sufficient to gel the membrane for a sufficient time, thereby becoming self-supporting and allowing operation without damage, while introducing a high liquid content (e.g., about 60 wt% or more of the total solid-liquid content of the gel membrane). For example, the hydrolysis treatment can be carried out at temperatures of about 0 to about 150°C, for example, about 10 to about 120°C, or about 20 to about 90°C, for example, at ambient temperature in some embodiments (e.g., in an environment with a relative humidity of about 35% to 100%).

[0040] Hydrolysis can be carried out by contacting the membrane precursor with H2O (e.g., in liquid or vapor form) and / or in the presence of other components. For example, the membrane precursor can be contacted with water vapor and / or liquid water and / or vapor and / or aqueous PA solutions (e.g., the PA solution may have a PA concentration of about 10 wt% to about 90 wt%, for example, about 30 wt% to about 70 wt% or about 45 wt% to about 55 wt%). The treatment can be carried out at standard pressure, but this is not required for the gelation method; in some embodiments, the hydrolysis treatment can be carried out at varying pressures.

[0041] In one implementation, hydrolysis can be carried out in a climate-controlled environment where the H2O content can be strictly controlled. For example, the water content of the local environment can be controlled by controlling the temperature or saturation of the fluid in contact with the precursor membrane. For example, a carrier gas such as air, nitrogen, carbon dioxide, or other suitable gas can carry a controlled amount of H2O (such as water vapor) to contact the precursor membrane.

[0042] Hydrolysis time can vary depending on parameters such as H2O content and contact method, precursor film thickness, and contact temperature. Generally, hydrolysis can be carried out over a period of seconds to minutes (e.g., when superheated steam is used) or over a period of days (e.g., when hydrolysis is carried out at ambient temperature and low relative humidity). 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. For example, in embodiments where the hydrolysis of at least a portion of the PPA in the PBI polymer solution is carried out at room temperature (e.g., about 20°C) and a relative humidity of about 20%-100%, for example, about 40%-80% in ambient air, the treatment time can typically be from about 5 hours to about 200 hours.

[0043] Following hydrolysis of at least a portion of the PPA in the PBI polymer solution, the polymer can gel and form a PBI gel film. In one embodiment, the PBI gel film can have a thickness of about 15 to about 3000 μm, for example, about 20 to about 2000 μm, or about 20 to about 1500 μm, but any particular film thickness is not critical and can depend on the thickness of the membrane precursor. In some embodiments, the PBI film can have a thickness less than the membrane precursor thickness. After hydrolysis, the PBI gel film can be self-supporting even at high liquid contents, which is believed to be due to the intramolecular and intermolecular polymer structures present in the gel polymer matrix.

[0044] In one embodiment, the gel membrane thus formed may have a PBI solids content of about 4 wt% to about 40 wt%, for example, about 8 wt% to about 30 wt%, or about 10 wt% to 25 wt% of the total weight of the membrane, including the liquid content.

[0045] In one embodiment, the PBI gel membrane can be cross-linked, which can reduce the permeability of the gel membrane without significantly affecting its electrochemical properties. There are no particular limitations on the cross-linking method or the points at which the gel membrane is cross-linked during the formation process.

[0046] In one embodiment, the PBI gel film can be simply crosslinked by heating in the presence of atmospheric oxygen. Crosslinking can also be affected by radiation, such as infrared (IR) radiation (wavelengths from about 700 nm to 1 mm), including near-IR (wavelengths from about 700 to 2000 nm or energy ranges from about 0.6 to 1.75 eV).

[0047] To crosslink the membrane, PBI polymerization can introduce reactive functional groups onto the polymer chain, allowing it to crosslink itself or alternatively, to combine with a crosslinking agent, i.e., a multifunctional compound that can react with one or more functional groups (e.g., amines) of the PBI polymer. The crosslinking agent can include any suitable function to implement crosslinking. Suitable crosslinking agents are not particularly limited, and examples include, but are not limited to, epichlorohydrins, diepoxides, diisocyanates, α,ω-dihaloalkanes, diacrylates, and bisacrylamide; specific examples include, but are not limited to, α,α'-dichloro-p-xylene, chloromethyl methyl ether, di(chloromethyl) ether, terephthaloyl chloride, succinoyl chloride, and dimethyl succinate, as well as combinations of crosslinking agents. In one embodiment, 1-20 equivalents of crosslinking agent can be used for each available aromatic ring, but the crosslinking implementation of the membrane is not limited to any particular crosslinking density.

[0048] In one embodiment, the PBI gel membrane may absorb an ion transporter (e.g., a supporting electrolyte) together with the PA remaining in the membrane after gelation. For example, the PBI membrane may absorb inorganic acids (e.g., strong inorganic acids) such as hydrochloric acid, nitric acid, fluorosulfonic acid, or sulfuric acid, or mixtures thereof, or strong organic acids such as acetic acid, formic acid, p-toluenesulfonic acid, or trifluoromethanesulfonic acid, or mixtures thereof, as well as mixtures of different types of acids, such as combinations of inorganic and organic acids. Other examples of ion transporters that can be absorbed in the membrane may include, but are not limited to, sodium chloride, potassium chloride, sodium hydroxide, potassium hydroxide, sodium sulfide, potassium sulfide, and combinations thereof. For example, ion transporters may include H₂SO₄, HBr, HBr / HCl mixtures, HCl, NaS₂, NaS₂ / NaBr mixtures, Br₂ in HBr, Br₂ in H₂SO₄, and Br₂ in HBr / H₂SO₄ mixtures. 2 In one embodiment, tetraalkylammonium supports the absorption of cations into the membrane, such as tetraethylammonium (Et4N). + ) and tetrabutylammonium (Bu4N) + ) are two non-limiting examples. Tetrafluoroborate (BF4) − ), perchlorate (ClO4) − ) or hexafluorophosphate (PF6) − Solutions of or combinations thereof are other examples of ion transport agents that can be absorbed into membranes.

[0049] There is no particular limitation on the concentration of the ion transporter in the gel membrane. In some embodiments, it can typically be up to about 25 mol / L (M), 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.

[0050] PBI gel membranes can be absorbed with ion transporters using any suitable method. For example, in one embodiment, the PBI gel membrane can be absorbed with ion transporters by immersing it in an ion transporter solution for several minutes to several hours or several days, optionally in an elevated temperature environment.

[0051] The gel membrane may include one or more additives, which may be introduced into the membrane during precursor membrane formation, membrane gelation, or together with the addition of an ion transporter. For example, small organic molecules, such as small C1-C4 alcohols (e.g., glycerol), small organic acids, urea, etc., may be introduced into the PBI gel membrane together with or as a substitute for the absorption of the ion transporter.

[0052] In one embodiment, the gel membrane may typically incorporate particles, such as titanium dioxide or PBI particles, in an amount of about 2 wt% or less of the membrane weight, which can reduce the membrane porosity. For example, during the gelation of the PBI gel membrane, nanoscale particles of PBI can be introduced into the polymer matrix by adding the particles to the polymer solution during hydrolysis.

[0053] Gel membranes can be used for any purpose. Representative applications of PBI gel membranes may include, but are not limited to, use in fuel cells, electrolysis, capacitors, and battery systems.

[0054] For example, in one embodiment, the PBI gel membrane can be combined with other electrochemical battery components known in the art. Figure 1 An embodiment of an electrochemical cell 20 is shown, which may incorporate the PBI gel membrane described herein. As shown, the electrochemical cell 20 may include a cathode 22 and an anode 24 separated by a PBI gel membrane 25, which may absorb a suitable supporting electrolyte / ion transport agent as a proton exchange membrane (PEM).

[0055] The electrochemical cell 20 may also include porous layers 26 and 27 adjacent to one or both of the electrodes 22 and 24, which can improve the contact between chemical reactants and products and the electrodes 22 and 24. For example, when considering a flow of gaseous reactants or products, the porous layer 26 may be a gas diffusion layer. The gas diffusion layer may be fibers, particles, or a combination thereof, providing a uniform gas distribution on the electrode surface and facilitating electron transport between the electrodes and external circuitry. For example, the gas diffusion layer may be formed from carbon fibers, for example, in a woven or nonwoven form. The porous layers 26 and 27 may optionally include multiple sublayers with different porosities (e.g., micropores, mesopores, and / or micropores) in any desired combination, further refining and defining the flow field of the fluid at the electrodes and facilitating the desired interactions between the electrode active material and the half-reacted reactants and products.

[0056] The electrochemical cell 20 can also define flow fields 28, 29 on each side of the cell, which can transport and / or remove reactants and products from the cell. For example, in Figure 1 In the example shown, flow fields 28 and 29 are defined by channels formed in bipolar plates 21 and 23, respectively. Bipolar plates 21 and 23 can be any design and construction known in the art, such that they typically combine electrical connections, thermal control for heat dissipation, and prevention of leakage to the outside of battery 20 to provide the desired flow fields 28 and 29.

[0057] Although Figure 1The representative electrochemical cell 20 shown includes inflow and outflow on each side of the cell 20, but those skilled in the art will understand that in various embodiments, one side or the other side of the cell will not require flow to / from that side of the cell.

[0058] A single electrochemical cell 20 can be used alone or in combination with other cells to provide a battery stack. The battery stack can include any number of individual electrochemical cell units, for example, 10 or more, 50 or more, or hundreds of individual cells combined into a single battery stack.

[0059] In one embodiment, the PBI gel membrane can be incorporated into a fuel cell, wherein the electrochemical cell is designed to utilize electrical energy generated by the cell's half-reaction. (See also...) Figure 2 One embodiment of the hydrogen fuel cell shown includes a positive electrode 34 and a negative electrode 36 separated by a proton-conducting PBI gel membrane 32. During operation of the fuel cell, hydrogen can be fed 35 to the negative electrode side of the cell, while oxygen (e.g., air) 37 can be fed to the positive electrode side of the cell.

[0060] At the negative electrode 36, hydrogen can undergo the following half-reaction:

[0061]

[0062] The PBI gel membrane 32 allows the transfer of protons formed at the negative electrode 36 to the positive electrode 34, and the generated electrons e - They can be utilized as they travel from the negative terminal 36 through the circuit to the positive terminal 34.

[0063] At the positive electrode 34, protons, oxygen, and electrons can react according to the following half-reaction:

[0064]

[0065] Then, the water and any unreacted gases from the input flow 37 are discharged from the positive electrode side of the battery 39, while the unreacted hydrogen is discharged from the negative electrode side of the battery 31.

[0066] The disclosed PBI gel membrane can also be used in electrolyzers that utilize electro-promoted chemical reactions. For example, see reference... Figure 3 One embodiment of the proton exchange PBI gel membrane PEM water electrolyzer shown includes a cathode 44 and an anode 46 separated by a PBI gel membrane 42. In the illustrated embodiment, water can be fed 45 to the anode side of the electrolyzer. In some embodiments, water can be fed to both sides of the cell to improve the hydration of the PBI gel membrane 42.

[0067] At the anode 46, water undergoes a half-reaction:

[0068]

[0069] PBI gel membrane 42 allows protons formed at anode 46 to be transported to cathode 44.

[0070] At cathode 44, protons and electrons react according to a half-reaction:

[0071]

[0072] Then, oxygen and unreacted water are discharged from the anode side of the tank 41, and hydrogen is discharged from the cathode side of the tank 49. Generally, the products can be discharged with water as long as the supplied water volume is sufficient to remove them from the tank. Subsequently, oxygen and hydrogen products can be separated from the water as needed.

[0073] While the examples above illustrate representative products that may introduce publicly disclosed PBI gel membranes, those skilled in the art will readily understand that publicly disclosed gel membranes can be used in a variety of applications.

[0074] This disclosure can be better understood with reference to the embodiments listed below.

[0075] Example

[0076] Materials and methods

[0077] 3,3',4,4'-Tetraaminobiphenyl (TAB, polymer grade, ~97.5%) was donated by BASF Fuel Cell, Inc. and used as is. Naphthalene-1,4-dicarboxylic acid (HPLC grade, >98.00%) was purchased from AK Scientific and used as is. PPA (115%) was supplied by FMC Corporation and used as is.

[0078] A typical polymerization consists of a molar equivalent mixture of tetraaminobiphenyl (TAB) and a dicarboxylic acid, which is added to PPA, mixed with a top-mounted stirrer, and purged with dry nitrogen. The contents are heated in a high-temperature silicone oil bath, with the temperature controlled by a programmable temperature controller featuring heating, cooling, and holding functions. The reaction temperature is gradually increased from room temperature to 120°C, 150°C, 170°C, and 190°C. In a typical polymerization reaction, the final reaction temperature is approximately 190°C and maintained for 12 hours. Once the reaction is complete (determined by visually inspecting the viscosity), the polymer solution is cast onto a transparent glass plate with a controlled gate thickness of 15 mils using a scraper. The cast solution is then hydrolyzed into a gel film in a humidity chamber conditioned to 55% relative humidity at 25°C.

[0079] Membrane composition

[0080] The composition of each PBI gel membrane was determined by measuring the relative amounts of polymer solids, water, and acid in each membrane. The PA content of the gel membrane was determined by titrating the membrane sample with a standardized sodium hydroxide solution (0.10 M) using a Metrohm 716 DMS Titrino automatic titrator. After titration, the sample was thoroughly washed with deionized water and dried under reduced pressure overnight at 120°C. The dried sample was then weighed to determine the polymer solids content of the membrane.

[0081] The polymer weight percentage and PA weight percentage were determined by Equations 1 and 2:

[0082]

[0083] Among them W 样品 W is the weight of the sample before titration. 干 This is the weight of the finally dried sample after titration. M 酸 It is the molecular weight of PA, while V NaOH and c NaOH This refers to the volume and concentration of sodium hydroxide solution required to neutralize PA to the first equivalence point. Calculate the number of PA moles per mole of PBI repeating unit (or PA doping level X, PA / RU in the table below) according to equation (3):

[0084]

[0085] Where V NaOH and c NaOH W is the volume and concentration of sodium hydroxide solution required to neutralize PA to the first equivalent point. 干 M is the final weight of the dried sample after titration. 聚合物 It is the molecular weight of the repeating unit of the polymer.

[0086] The monomer concentration is determined as the weight ratio of the total amount of monomer (g) in the polymerization mixture to the total amount of monomer and PPA (g) in the polymerization mixture × 100.

[0087] Tensile properties

[0088] The tensile properties of the gel film were tested at room temperature using an Instron Model 5543A system with a load of 10 N and a crosshead speed of 5 mm / min. Dog bone-shaped specimens (V-shaped specimens) were cut according to ASTM standard D638 and preloaded to 0.1 N before testing.

[0089] Proton conductivity

[0090] Using a Zahner IM6e electrochemical workstation, the proton conductivity of the membrane was measured by four-probe electrochemical impedance spectroscopy at an amplitude of 5 mV within a frequency range of 1 Hz to 100 kHz. The experimental data were fitted using a two-component model with an ohmic resistor connected in parallel with a capacitor. The membrane conductivity at different temperatures was calculated using the following equation (4) based on the membrane resistance obtained from the model simulation:

[0091]

[0092] Where d is the distance between the two internal probes, l is the film thickness, w is the film width, and R... m The ohmic resistance was determined by model fitting. The membrane sample underwent two heating cycles to 180°C. The reported conductivity data were recorded on the second heating ramp after water was removed from the membrane during the first heating cycle.

[0093] Example 1

[0094] As described above, 1,4-naphthalene-PBI (n-PBI) membranes were polymerized and hydrolyzed. 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 the reaction was carried out under a nitrogen atmosphere for 36 hours. The solution was coated onto a glass plate with a 15 mil gate thickness using a doctor blade, followed by hydrolysis to produce a gel membrane.

[0095]

[0096] The properties of the membrane are described in Table 2 below.

[0097] Table 2

[0098] Monomer concentration (wt.%) Mol PA / RU Acid content (wt.%) PBI content (wt.%) Water content (wt.%) Conductivity @160℃ (mS / cm) Tensile strength (MPa) 2.2 52.7 56.7 4.2 39.1 240 6.5

[0099] As shown, the gel membrane has a proton conductivity of 240 mS / cm and an average tensile strength of 6.5 MPa.

[0100] Example 2

[0101] 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 polymerization was carried out as described above according to the following reaction scheme to form n-PBI. The polymerization reaction was carried out at 190 °C under a nitrogen atmosphere for 36 hours. The solution was applied to a glass plate with a 15 mil gate thickness using a doctor blade, and subsequently hydrolyzed to produce a gel film.

[0102] The properties of the membrane are shown in Table 3 below.

[0103] Table 3

[0104] Monomer concentration (wt.%) Mol PA / RU Acid content (wt.%) PBI content (wt.%) Water content (wt.%) Conductivity @160℃ (mS / cm) Tensile strength (MPa) 2.5 46.2 65.0 5.2 29.8 260 9.2

[0105] As shown, the gel membrane has a higher PBI solids content than the membrane of Example 1, and exhibits a proton conductivity of 260 mS / cm and an average tensile strength of 9.2 MPa.

[0106] Comparative Example 3

[0107] As described above, terephthalic acid is used instead of naphthaleneacetic acid to polymerize p-PBI (p-PBI) membranes.

[0108] 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 the mixture was reacted under a nitrogen atmosphere for 36 hours. The solution was applied to a glass plate with a 15 mil gate thickness using a doctor blade and subsequently hydrolyzed to produce a gel film.

[0109] The properties of the membrane are shown in Table 4 below.

[0110] Table 4

[0111] Monomer concentration (wt.%) Mol PA / RU Acid content (wt.%) PBI content (wt.%) Water content (wt.%) Conductivity @160℃ (mS / cm) Tensile strength (MPa) 3.0 32.3 57.3 5.6 37.1 270 2.0

[0112] As shown, the gel membrane has a proton conductivity of 270 mS / cm, but exhibits an average tensile strength of only 2.0 MPa.

[0113] Comparative Example 4

[0114] As mentioned above, sulfonated-PBI (s-PBI) membranes are polymerized using sulfonated terephthalic acid instead of naphthalic acid.

[0115] 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 the mixture was reacted under a nitrogen atmosphere for 36 hours. The solution was applied to a glass plate with a 15 mil gate thickness using a doctor blade and subsequently hydrolyzed to produce a gel film.

[0116] The properties of the membrane are shown in Table 5 below.

[0117] Table 5

[0118] Monomer concentration (wt.%) Mol PA / RU Acid content (wt.%) PBI content (wt.%) Water content (wt.%) Conductivity @ 160℃ (mS / cm) Tensile strength (MPa) 3.5 35.3 67.2 7.5 25.3 220 2.4

[0119] As shown above, the gel membrane has a conductivity of 220 mS / cm, but exhibits an average tensile strength of only 2.4 MPa.

[0120] Comparative Example 5

[0121] As described above, the dihydroxy-PBI (diOH-PBI) membrane utilizes dihydroxy terephthalic acid instead of naphthalic acid for polymerization.

[0122] 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 the mixture was reacted under a nitrogen atmosphere for 36 hours. The solution was applied to a glass plate with a 15 mil gate thickness using a doctor blade, and subsequently hydrolyzed to produce a gel film.

[0123] The properties of the membrane are shown in Table 6 below.

[0124] Table 6

[0125] Monomer concentration (wt.%) Mol PA / RU Acid content (wt.%) PBI content (wt.%) Water content (wt.%) Conductivity @ 160℃ (mS / cm) Tensile strength (MPa) 2.8 25.4 38.7 5.3 56.0 275 1.8

[0126] As shown, the gel membrane has a conductivity of 275 mS / cm, but exhibits an average tensile strength of only 1.8 MPa.

[0127] Comparative Example 6

[0128] As shown above, the m / p-PBI membrane is polymerized using isophthalic acid / terephthalic acid in a 7:1 weight ratio instead of naphthalic acid.

[0129] 11.27 g tetraaminobiphenyl (TAB, 52.3 mmol), 7.64 g isophthalic acid (IPA, 46.0 mmol), and 1.09 g terephthalic acid (TPA, 6.6 mmol) were added to 230 g PPA, and the mixture was reacted under a nitrogen atmosphere for 36 hours. The solution was applied to a glass plate with a 15 mil gate thickness using a doctor blade, and subsequently hydrolyzed to produce a gel film.

[0130] The properties of the membrane are shown in Table 7 below.

[0131] Table 7

[0132] Monomer concentration (wt.%) Mol PA / RU Acid content (wt.%) PBI content (wt.%) Water content (wt.%) Conductivity @ 160 ℃ (mS / cm) Tensile strength (MPa) 8.0 9.5 52.6 17.5 29.9 170 7.0

[0133] As shown, this gel film, which has a much higher polymer solids content than that of Examples 1 and 2, exhibits a high average tensile strength of 7.0 MPa, but only shows a proton conductivity of 170 mS / cm.

[0134] Example 7

[0135] As described above, a copolymer membrane (1:1 n / p-PBI membrane) was polymerized using 1,4-naphthalenedicarboxylic acid and terephthalic acid in a 1:1 ratio as the diacid components. Therefore, 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 TAB+NDA = 27.75 mmol, or 75 mol% of total monomers) were added to 243 g of polyphosphoric acid, and the reaction was carried out under a nitrogen atmosphere for 36 hours. The solution was applied to a glass plate with a 15 mil gate thickness using a doctor blade, and subsequently hydrolyzed to produce a gel membrane.

[0136] The properties of the membrane are shown in Table 8 below.

[0137] Table 8

[0138] Monomer concentration (wt.%) Mol PA / RU Acid content (wt.%) PBI content (wt.%) Water content (wt.%) Conductivity @160 ℃ (mS / cm) Tensile strength (MPa) 3.0 38.4 63.0 6.0 38.4 250 6.2

[0139] As shown, the gel membrane has a conductivity of 250 mS / cm and an average tensile strength of 6.2 MPa.

[0140] Example 8

[0141] 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 polymerization was carried out as described above according to the following reaction diagram to form n-PBI. Polymerization was conducted at 190 °C for 25 hours under a nitrogen atmosphere. The solution was applied to a glass plate with a 15 mil gate thickness using a doctor blade, and subsequently hydrolyzed to produce a gel film.

[0142] The properties of the membrane are shown in Table 9 below.

[0143] Table 9

[0144] Monomer concentration (wt.%) Mol PA / RU Acid content (wt.%) PBI content (wt.%) Water content (wt.%) Conductivity @160℃ (mS / cm) Tensile strength (MPa) 2.75 43.9 59.3 4.92 35.7 219 5.08

[0145] As shown above, the gel membrane has a proton conductivity of 219 mS / cm and an average tensile strength of 5.08 MPa.

[0146] Example 9

[0147] 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 polymerization was carried out as described above according to the following reaction diagram to form n-PBI. Polymerization was conducted at 190 °C for 25 hours under a nitrogen atmosphere. The solution was applied to a glass plate using a doctor blade with a 15-mil grid thickness, and subsequently hydrolyzed to produce a gel film.

[0148] The properties of the membrane are shown in Table x below.

[0149] Table 10

[0150] Monomer concentration (wt.%) Mol PA / RU Acid content (wt.%) PBI content (wt.%) Water content (wt.%) Conductivity @ 160 ℃ (mS / cm) Tensile strength (MPa) 3.0 37.7 56.15 5.44 38.39 250 9.54

[0151] As shown above, the gel membrane has a proton conductivity of 250 mS / cm and an average tensile strength of 9.54 MPa.

[0152] While certain embodiments of the disclosed subject matter have been described using specific terminology, such description is for illustrative purposes only, and it should be understood that changes and variations may be made without departing from the spirit or scope of the subject matter.

Claims

1. A gel membrane comprising polybenzimidazole and an absorbent solution containing phosphoric acid, said polybenzimidazole comprising a reaction product of tetraaminobiphenyl monomer and a reaction product of naphthalic acid monomer, said polybenzimidazole membrane exhibiting a proton conductivity of about 180 mS / cm or higher at 160 °C and exhibiting a tensile strength at break of about 5 MPa or greater as measured with a 10 N load at a crosshead speed of 5 mm / min.

2. The gel membrane according to claim 1, wherein, The tetraaminobiphenyl monomer is selected from the group consisting of 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 mono-, di-, tri- or tetra-hydrochlorides, and any combination thereof.

3. The gel membrane according to claim 1 or claim 2, wherein, 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.

4. The gel film according to any one of the preceding claims, wherein, The tetraaminobiphenyl monomer and the naphthalenedicarboxylic acid monomer together account for approximately 70 mol% or more of all monomers in the polybenzimidazole.

5. The gel membrane according to any one of the preceding claims further comprises a reaction product of one or more other monomers, said one or more other monomers including aromatic tetraamino monomers; heteroaromatic tetraamino monomers; aromatic polycarboxylic acids or their esters, anhydrides or acyl chlorides; heteroaromatic polycarboxylic acids or their esters, anhydrides or acyl chlorides; aromatic diaminocarboxylic acids; heteroaromatic diaminocarboxylic acids; or any combination thereof.

6. The gel film according to any one of the preceding claims, wherein, The solid content of the gel membrane is approximately 4 wt% to approximately 40 wt%.

7. The gel film according to any one of the preceding claims, wherein, The polybenzimidazole is cross-linked.

8. The gel film according to any one of the preceding claims, wherein, The absorbed solution also contains inorganic acids, organic acids, or mixtures 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.

9. The gel membrane according to any one of the preceding claims further comprises small organic molecules or particles.

10. A fuel cell comprising a gel membrane according to any one of the preceding claims.

11. A method for forming a gel film, comprising: A polymerization solution is formed, the polymerization solution comprising polyphosphoric acid and polybenzimidazole forming monomers, the polybenzimidazole forming monomers comprising tetraaminobiphenyl monomer and naphthalic acid monomer, the tetraaminobiphenyl and the naphthalic acid monomers comprising a total of about 70 mol% or more of the polybenzimidazole forming monomers; Construct the polymerization conditions for polymerizing the polybenzimidazole monomer in the polymerization solution; and Hydrolysis of at least a portion of the polyphosphoric acid causes gelation of the gel membrane.

12. The method according to claim 11, wherein, The monomer content of the polymerization solution is about 10 wt% or less of the total weight of the polybenzimidazole forming monomer and the polyphosphoric acid.

13. The method of claim 11 or claim 12, further comprising shaping the gel film precursor prior to the step of constructing the polymerization conditions.

14. The method according to any one of claims 11-13, further comprising crosslinking the gel membrane.

15. The method according to any one of claims 11-14, further comprising causing the gel membrane to absorb an ion transport agent.

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