Novel method for producing PBI film without organic solvents

Abstract

The objective is to provide a novel method for producing PBI films starting from gel PBI films polymerized and cast in a PPA process. [Solution] This method involves neutralizing a gel PBI that has absorbed acid in a series of water baths, and then subjecting it to controlled drying together with a substrate to obtain a PBI film without using organic solvents.

Description

[Technical Field]

[0001] Description of research funded by the U.S. federal government. This invention was made with government assistance under DE-AR0000767 granted by the Department of Energy. The government has certain rights in this invention.

[0002] 1) Field of invention The present invention relates to a novel method for producing a PBI film starting from a gel PBI membrane polymerized and cast in a PPA process, wherein the acid-absorbing gel PBI is neutralized in a series of water baths and, optionally together with a substrate or porous material, undergoes controlled drying to obtain a PBI film without the use of organic solvents. [Background technology]

[0003] 2) Description of related technologies Polybenzimidazole (PBI) is a glassy thermoplastic with particularly excellent thermal stability (Tg at 427°C), broad chemical resistance, and the ability to function as a proton acceptor or proton donor. PBI has unique properties that make it suitable for transferring protons, hydrogen, and water. For these reasons, PBI is very suitable for applications that are often used at high temperatures, such as H2 / CO2 separation membranes, fuel cell proton exchange membranes, and permeable vaporization dehydration membranes for organic chemicals.

[0004] A novel synthetic process for manufacturing high molecular weight PBI, the "PPA process", was developed at Rensselaer Polytechnic Institute with the cooperation of BASF Fuel Cell GmbH. In the general synthesis of PBI by this method, a combination of tetraamine and dicarboxylic acid in polyphosphoric acid (PPA) in a dry environment is required. The sequential polycondensation reaction is typically carried out at about 200 °C for 16 - 24 hours in a nitrogen atmosphere, and a high molecular weight polymer is produced. This solution is cast directly from PPA as a thin film on a substrate, and when water is absorbed, PPA hydrolyzes in situ to form phosphoric acid. It should be noted that for PBI, PPA is a good solvent, while PA is a poor solvent. Under controlled hydrolysis conditions, a highly doped and mechanically stable PBI gel film is produced.

[0005] In one commercial application, a PA-doped m-PBI fuel cell membrane has been manufactured, which maintains thermal and physical stability during operation at high temperatures. In the PPA process, membranes with much higher proton diffusion coefficients and conductivities are produced, having a proton transport structure superior to that of conventionally absorbed PBI membranes. In addition, intrinsic viscosity data indicates that the PPA process produces polymers with much higher molecular weights. Improved membrane morphology and increased molecular weight have shown that the polymer can hold much more phosphoric acid than conventional cast PBI membranes. An increase in the doping level of PA can typically improve the conductivity of the membrane and further enhance the performance of the battery.

[0006] PBI films are known to have very excellent properties such as high temperature stability, non-flammability, and high chemical resistance. So far, the manufacturing method of PBI films has involved polymerization, dissolution of the obtained polymer in an organic solvent such as dimethylacetamide (DMAc), casting of the film, and removal of the solvent by a series of washings. Summary of the Invention Problems to be Solved by the Invention

[0007] Therefore, the object of this disclosure is to provide a novel and improved method for producing PBI films starting from a gel PBI membrane polymerized and cast in a PPA process. As described below in this disclosure, the acid-absorbing gel PBI may be neutralized in a series of water baths, subjected to controlled drying, and optionally applied between two porous materials or onto a suitable substrate to obtain a PBI film without the use or utilization of organic solvents. In addition, PBI gels synthesized in a PPA process can be used with a wider range of monomers due to their low solubility in organic solvents. Thus, the present invention provides for the first time access to a wider range of PBI chemicals that can be processed into films. [Means for solving the problem]

[0008] The above objective is achieved in accordance with this disclosure by providing, in one embodiment, a method for producing a PBI film. This method may include forming a gel PBI film via a PPA process, rinsing the gel PBI film, constraining the gel PBI film in at least the XY plane, and drying the rinsed gel PBI film, and no organic solvents are used throughout the method. Furthermore, the gel PBI film may be rinsed with a washing solution. Furthermore, the rinsed gel PBI film may be applied to at least one substrate. Furthermore, the rinsed gel PBI film may be applied to a porous substrate. Furthermore, the constrainment of the PBI film may involve applying tension to the PBI film in the X, Y, or Z plane. Furthermore, the PBI film may be formed via a continuous forming process. Furthermore, the polybenzimidazole in the PBI film may consist of the following repeating units: [ka] [ka] The formula includes one or more of the following, or any combination thereof, where n and m are Each of these is independently 1 or more, approximately 10 or more, or approximately 100 or more. Furthermore, this method can be used to form a film.

[0009] In further embodiments, a PBI film is formed. The film may be formed by: forming a gel PBI film via a PPA process; rinsing the gel PBI film; constraining the gel PBI film in at least the XY plane; and drying the rinsed gel PBI film to form a PBI film, wherein no organic solvent is used throughout the entire method for forming the film. Furthermore, the film may be used as a coating. Furthermore, the film may have a thickness of 5 to 150 μm. Furthermore, the film has a breaking stress of at least 25 MPa. Furthermore, the polybenzimidazole in the PBI film has the following repeating units: [ka] [ka] The formula may include one or more of these, or any combination thereof, where n and The values ​​of 'b' and 'm' are, independently, 1 or more, about 10 or more, or about 100 or more. Furthermore, the film may contain a PBI polymer that is substantially insoluble in organic solvents. Furthermore, the film may absorb organic or inorganic acids or bases to form an ion-conducting film.

[0010] The structure designed to carry out the present invention, along with other features of the present invention, will be described below. The present invention will be more readily understood by reading the following specification and by referring to the accompanying drawings which form part of the present invention and illustrate examples of the present invention. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 shows a graph of the cell cycling current in the film of this disclosure. [Figure 2] Figure 2 shows a further graph of the cell cycle current in the film of this disclosure. [Figure 3] Figure 3 shows the oxidative stability test of VRFB in the film of this disclosure. [Figure 4] Figure 4 shows the polymerization scheme of s-PBI in PPA and the crosslinking modification reaction of the membrane. [Figure 5] Figure 5 shows the ex-situ properties of the s-PBI gel film compared to the dense m-PBI film (Table 1). [Figure 6] Figure 6 shows the performance of the film of this disclosure compared to a commercially available film. [Figure 7] Figure 7 shows a graph of the measured out-of-device properties of the film of this disclosure compared to a typical PBI gel film. [Figure 8] Figure 8 shows the entire process of measuring the film of this disclosure outside of the apparatus. [Figure 9] Figure 9 shows the transmittance compared to the conductivity for para-PBI. [Figure 10] Figure 10 shows the transmittance compared to the conductivity in Mrp PBI. [Figure 11] Figure 11 shows the results of cell tests on films formed according to this disclosure. [Figure 12] Figure 12 shows the voltage efficiency (VE), Coulomb efficiency (CE), and energy efficiency (EE) for a 1.7× stretched para-PBI. [Figure 13] Figure 13 shows the voltage efficiency (VE), Coulomb efficiency (CE), and energy efficiency (EE) for a 1.5× stretched para-PBI. [Figure 14] Figure 14 shows the voltage efficiency (VE), Coulomb efficiency (CE), and energy efficiency (EE) for dry para-PBI. [Figure 15]Figure 15 shows the voltage efficiency (VE), Coulomb efficiency (CE), and energy efficiency (EE) for the stretched s-PBI. [Figure 16] Figure 16 shows the voltage efficiency (VE), Coulomb efficiency (CE), and energy efficiency (EE) for dry s-PBI. [Figure 17] Figure 17 shows the voltage efficiency (VE), Coulomb efficiency (CE), and energy efficiency (EE) in the VRB test cell of Comparative Example 1 of dense m-PBI absorbed in the conventional manner. [Figure 18] Figure 18 shows the mechanical properties of a para-PBI film formed via a PPA process and treated via the method of this disclosure. [Figure 19] Figure 19 shows the mechanical properties of a Di-OH-PBI film formed according to this disclosure. [Figure 20] Figure 20 shows the mechanical properties of an s-PBI copolymer film formed according to this disclosure. [Figure 21] Figure 21 shows the mechanical properties of a meta / para-PBI copolymer film formed according to this disclosure. [Figure 22] Figure 22 shows a comparative example using m-PBI cast in an organic solution. [Figure 23] Figure 23 shows a continuous PBI film formation process that can be used in this disclosure. [Figure 24] Figure 24 shows that films produced by the method disclosed herein exhibited lower creep resistance than films produced by a standard PPA process. [Figure 25] Figure 25 shows the polarization curve for H2 in air. [Figure 26] Figure 26 shows the polarization curve in H2 / O2. [Modes for carrying out the invention]

[0012] Those skilled in the art will understand that one or more embodiments of the present invention may satisfy certain purposes, while one or more other embodiments may satisfy certain other purposes. Each purpose may not be equally applicable in all respects to all embodiments of the present invention. For this reason, the aforementioned purposes may be considered selective with respect to any one embodiment of the present invention. These and other purposes and features of the present invention will become more fully apparent by reading the following detailed description in conjunction with the accompanying drawings and examples. However, it should be understood that the above summary of the present invention and the following detailed description are of preferred embodiments and do not limit the embodiments of the present invention or other alternative embodiments of the present invention. In particular, it should be understood that although the present invention is described herein with reference to several specific embodiments, the description is illustrative of the present invention and is not intended to limit the present invention. Those skilled in the art will be able to conceive of various modifications and applications without departing from the spirit and scope of the present invention as described by the accompanying claims. Similarly, other purposes, features, benefits, and advantages of the present invention will become apparent from this summary and certain embodiments described below and will be readily apparent to those skilled in the art. Such purposes, features, benefits, and advantages will become apparent from the above, either alone or in conjunction with the attached examples, data, drawings, and all reasonable inferences derived therefrom.

[0013] The present invention will be described in more detail below with reference to the drawings. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the subject matter of this disclosure pertains. Any methods, devices, and materials similar to or equivalent to those described herein may be used in the practice or testing of the subject matter disclosed herein, but this specification describes representative methods, devices, and materials.

[0014] Unless otherwise specified, the terms and phrases used in this document, as well as their variations, should be interpreted in a non-restrictive rather than restrictive sense, unless explicitly stated otherwise. Similarly, groups of items connected by the conjunction "and" should not be interpreted as requiring all of these items to exist within the group, but rather as "and / or" unless explicitly stated otherwise. Likewise, groups of items connected by the conjunction "or" should not be interpreted as requiring mutual exclusivity within the group, but rather as "and / or" unless explicitly stated otherwise.

[0015] Furthermore, while items, elements, or components of this disclosure may be described or requested in the singular form, unless expressly limited to the singular, the plural form is also considered to be within the scope of this disclosure. The presence of broadening words and phrases, such as “one or more,” “at least,” “but not limited to,” or other similar phrases, in some cases should not be construed as meaning that a narrower case is intended or required where such broadening phrases may not exist.

[0016] This invention describes in detail a novel method for producing PBI film without using organic solvents. By eliminating the need for organic solvents, a novel PBI film production route is provided that is cheaper, takes less time, significantly reduces worker exposure, and generates less chemical waste than conventional methods. This novel non-solvent process is scalable. This allows for integration, and since the use of organic solvents in the past limited the types of chemicals that could be incorporated into PBI films, it also makes it possible to create films with a wider range of PBI chemicals.

[0017] This specification provides a method and process for obtaining a chemically resistant and thermally stable PBI film synthesized for the first time without the use of organic solvents. Previously, the synthesis of PBI films was an expensive and time-consuming process involving harsh chemicals. This disclosure provides a method that does not require the use of organic solvents, thereby making it a "greener" and more environmentally friendly method. This method is also considered safer because it reduces worker exposure to organic solvents. By overcoming the need for organic solvents, the method for producing PBI films becomes cheaper and faster.

[0018] PBI films manufactured without organic solvents reduce associated solvent purchase costs and eliminate the costly and time-consuming disposal of hazardous waste generated from the use of organic solvents. The method for obtaining PBI films according to this disclosure is simpler and provides a wider range of PBI chemicals than those previously available. Importantly, commercial applications of this disclosure include, but are not limited to, aerospace coatings, wire coatings, microelectronics packaging, protective windows and glass coatings, gas separation membranes, high-temperature materials / films, high-chemical-resistant films, and ion exchange membranes.

[0019] In one aspect of this disclosure, sulfonated polybenzimidazole (s-PBI) gel films were prepared and shown to have high stability in concentrated sulfuric acid and oxidative vanadium (V) (V) solutions. These films were considered candidates for use in vanadium redox flow batteries and were compared with commonly used meta-polybenzimidazole (m-PBI) films cast from N,N'-dimethylacetamide (DMAc) solution "conventionally absorbed". The s-PBI films exhibited high conductivity and low performance degradation in in-cell tests.

[0020] Redox flow batteries are used to convert electrical energy into chemical energy, which can then be converted back into electrical energy as needed. These devices can store energy on a grid scale. However, at present, the high cost of manufacturing these devices limits the widespread adoption of flow batteries. This cost can be mitigated by reducing the size of the electrochemical stack. To effectively achieve this and maintain high power density, the battery must be able to operate under high current loads. Conventional membranes used in flow batteries are insufficient ion conductors and cannot maintain operation under these conditions, thus requiring larger stacks. This disclosure provides, in part, a high-performance PBI-based battery with high conductivity and low intra-cell resistance that enables high-performance battery operation under high current load conditions. These characteristics allow for the use of smaller and lower-cost electrochemical stacks.

[0021] PBI gel films synthesized from the PPA process may be neutralized and allowed to absorb electrolytes commonly used in flow batteries. This established process and use of PBI films leverages the excellent physical properties that make them suitable for such applications.

[0022] In one case, PBI gel membranes were fabricated for use with a sulfate electrolyte commonly used in redox flow batteries. These membranes exhibit higher ionic conductivity than any previously reported literature on this subject, and can be used in batteries for renewable energy sectors and / or for backup / energy disruption reduction during peak usage in existing power grids.

[0023] This disclosure enables higher-performance flow batteries operating under high-current loads. These operating conditions reduce the need for large electrochemical stacks, thereby lowering the overall cost of commercial flow battery devices. Furthermore, the films of this disclosure exhibit superior performance due to their high ionic conductivity, which reduces the overall construction cost by decreasing the required stack size.

[0024] Figures 1 and 2 show improved performance of the PBI gel film at higher current densities. By using and manufacturing devices with these films, which inherently possess higher ionic conductivity, it is possible to improve the battery's rate characteristics. The overall battery cost can be dramatically reduced due to the smaller required stack size. Note: All data shown is for PBI films unless marked "BOM".

[0025] Furthermore, the film of this disclosure does not decompose in vanadium(V) oxide solution. The applicants understand that no hydrocarbon film with this level of chemical stability exists, suggesting that the PBI gel film is advantageous for long-term use devices. Figure 3 shows the oxidation stability test of VRFB in the film of this disclosure.

[0026] The increasing demand in the energy sector has created a new need for large-scale energy storage devices that are more significant in grid management and backup power, and that can be seamlessly integrated with new renewable energy devices. Redox flow batteries have the potential to efficiently store large amounts of energy while also meeting cost expectations. In vanadium redox flow batteries (VRBs), the main cost is attributable to the vanadium electrolyte. This cost can be offset by a less expensive cell stack design. Currently, commercially available VRBs use PFSA films as stack components, which limits their further development due to their low selectivity and high cost. To reduce the cost of VRBs and improve overall performance, there has been a surge in film development tailored to the specific needs of VRBs.

[0027] Phosphate (PA)-doped polybenzimidazole (PBI) membranes are best known for their performance in high-temperature polymer electrolyte membranes (HT-PEMs). However, PBI membranes have been shown to be a preferred candidate for several novel devices, including electrochemical hydrogen separation, SO2 depolarized electrolyzers, and redox flow batteries.

[0028] To date, research on PBI membranes for flow batteries has focused on meta-polybenzimidazole (m-PBI) and its derivatives. These membranes are manufactured by forming a dense film through solution casting in N,N'-dimethylacetamide (DMAc), followed by absorption of the desired electrolyte into the film, a process referred to as the "conventional absorption process." Membranes produced by this method typically have pore sizes in the range of 0.5 nm to 2.0 nm, which is significantly smaller than the pore sizes (2 to 4 nm) found in PFSA (e.g., Nafion®) type membranes. This reduction in pore size allows for a dramatic decrease in vanadium ion transmittance compared to PFSA membranes, despite their extremely low conductivity (<20 mS·cm) when absorbing a typical VRB electrolyte solution. -1 This can also be a cause of [unspecified problem]. The focus of these recent studies is to increase the proton conductivity of m-PBI dense films while maintaining their inherently low transmittance. These techniques include pre-swelling the PBI film with concentrated phosphoric acid before doping with sulfuric acid, creating a spongy porous structure using vapor-induced phase inversion and non-solvent-induced phase separation, and grafting various substituents onto the PBI polymer backbone. To the best of the applicant's knowledge, the PPA process as an alternative membrane for redox flow batteries... No research has been conducted on the use of PBI gel membranes formed from this material.

[0029] Conventional absorption processes for PBI membranes are time-consuming, environmentally unfriendly, and costly. However, Xiao et al. developed a novel PPA process for producing PBI gel membranes, consisting of directly casting a polymerization solution containing PBI polymer in polyphosphate (PPA). Subsequently, by exposing the cast solution to moisture in the air or under controlled humidity conditions at room temperature, the PPA solvent, a good solvent for PBI, is hydrolyzed to phosphoric acid (PA), a poor solvent for PBI. This process induces a gel transition in the solution, forming a PBI gel membrane that has essentially absorbed phosphoric acid. These membranes, while "pre-absorbed" of phosphoric acid, have been shown to be able to undergo acid exchange of the absorbed electrolyte. Garrick et al. exchanged phosphoric acid in a sulfonated para-polybenzimidazole (s-PBI) membrane with a 50 wt% sulfuric acid solution for testing in an SO2 depolarization electrolysis apparatus used for hydrogen production. This membrane exhibited high stability in concentrated sulfuric acid, even at 120°C. Furthermore, the film resistance in the SO2 depolarization electrolysis apparatus was found to be almost negligible compared to the anode overpotential, which is attributed to the high ionic conductivity of s-PBI. Due to the particularly excellent stability of the PBI derivative and its high conductivity, s-PBI polymer gel films are considered a possible alternative film for vanadium redox flow batteries with improved rate characteristics. [Examples]

[0030] material 3,3',4,4'-Tetraaminobiphenyl (TAB, polymer grade, approximately 97.5%) was donated by BASF Fuel Cell, Inc. and used as received. Monosodium 2-sulfoterephthalate (purity >98.00%) was purchased from TCI and used as received. Polyphosphate (115%) was supplied by FMC Corporation and used as received. a,a'-Dichloro-p-xylene (purity >98.0%) was purchased from TCI and used as received.

[0031] Polymer synthesis and film manufacturing A typical polymerization involves adding 10.71 g of tetraaminobiphenyl (TAB, 50 mmol) and 13.44 g of monosodium 2-sulfoterephthalate (s-TPA, 50 mmol) to 580 g of polyphosphate, mixing with an overhead stirrer, and purging with dry nitrogen. The contents are heated in a high-temperature silicone oil bath, and the temperature is controlled by a programmable temperature controller with lamp and soak functions. In a typical polymerization, the final reaction temperature is approximately 195°C and is maintained for 12 hours. After the reaction is complete and the viscosity is visually confirmed, the polymer solution is cast onto a transparent glass plate using a doctor blade, controlling the gate thickness to 15 mils. The cast solution is hydrolyzed to form a film in a humidity chamber controlled at 55% RH at 25°C.

[0032] acid exchange The cast membrane was placed in a DI water bath, and the pH of the water was monitored using pH test paper. The water bath was changed every 8 hours until a pH of 7 was recorded. At this point, the membrane was placed in a 2.6 molar sulfuric acid bath for 24 hours to ensure acid doping equilibrium, or the membrane was further modified by a cross-linking reaction.

[0033] Crosslinking after film formation After removing PA from the PBI gel membrane, the membrane was immersed in a bath of 0.0523 M α,a'-dichloro-p-xylene solution in methanol. The bath was covered, heated to 30°C, and stirred with a magnetic stirrer bar. The crosslinking reaction was typically allowed to proceed for 6 hours. The membrane was then washed at least three times with DI water and methanol. The membrane was then subjected to 2.6 M The samples were transferred to a sulfuric acid (SA) bath for 24 hours to dope them with acid.

[0034] Membrane composition The composition of the sulfuric acid-doped PBI membrane was specified by measuring the relative amounts of polymer solids, water, and acid in the membrane. The sulfuric acid (SA) content of the membrane was specified by titrating the membrane sample with a standard solution of sodium hydroxide (0.10 M) using a Metrohm 888 DMS Titrando automatic titrator. After titration, the sample was thoroughly washed with DI water and dried under reduced pressure at 120 °C overnight. Next, the dried sample was weighed to specify the polymer solids of the membrane.

[0035] Using Equations 1 and 2, the weight percent of the polymer and the weight percent of sulfuric acid can be specified, respectively:

Equation

[0036] The number of moles of sulfuric acid per mole of repeating unit of PBI (or, SA doping level, X) was calculated from the following equation:

Equation

[0037] conductivity By immersing the film in a 2.6M sulfuric acid solution and a 1.5M VOSO4 + 2.6M sulfuric acid solution, the film absorbs sulfuric acid and V 4+ Ions were absorbed. The in-plane conductivity of the film was measured in the frequency range of 1 Hz to 50 kHz by four-terminal electrochemical impedance spectroscopy (EIS) using a FuelCon (TrueData EIS PCM) electrochemical workstation. A typical film sample of 1.0 cm × 4.0 cm was fixed to the four-electrode head used for this measurement method. The conductivity of the film was calculated using the following formula:

number

[0038] Vanadium transmittance Vanadium (IV) (VOSO4) crossover, PermeGear "S Measurements were performed using an idbyside-type direct transmission cell. This cell has two 45 mL chambers separated by the membrane under test. The chamber temperature was controlled to 25°C using a circulating water bath. In a typical test experiment, 1.5 M VOSO4 in 2.6 M sulfuric acid was placed in the donor chamber, and 1.5 M MgSO4 in 2.6 M sulfuric acid was placed in the receptor chamber. Vanadium(IV) has a strong absorption characteristic at 248 nm, and this characteristic was used to measure the concentration in the receptor chamber at various time intervals using a Shimadzu UV-2450 UV / Vis spectrometer. 2+ The transmittance can be calculated using Fick's law of diffusion, equation 5.

number

[0039] Figure 4 shows the polymerization scheme of s-PBI in PPA and the crosslinking modification reaction of the film. The rate characteristics of a flow battery depend heavily on the conductivity of the film. m-PBI films produced by conventional absorption processes have relatively low conductivity, which limits stable operation at high current densities. In this specification, the inventors are considering the use of s-PBI, a highly proton-conducting film, in vanadium redox flow batteries.

[0040] Figure 5 shows the out-of-device characteristics of the s-PBI gel film compared to the dense m-PBI film (Table 1).

[0041] Table 1 shows the external membrane properties of s-PBI gel membranes (both uncrosslinked and crosslinked) and m-PBI membranes formed from conventional absorption processes. See Figure 5. The room-temperature conductivity of the membranes was measured using 2.6M sulfuric acid and V(IV) / H under typical cell operation conditions. + The evaluation was performed in both solutions. The s-PBI gel membrane exhibited remarkably high conductivity compared to the m-PBI membrane in both sulfuric acid and acid electrolyte solutions, with values ​​of 13.1 mS·cm, respectively. -1 Compared to 537-593 mS·cm -1 , and 12.2 mS·cm -1 Compared to 240-242 mS·cm -1The slight difference between the two s-PBI films is likely a result of crosslinking. s-PBI-x in Table 1 is an s-PBI film that underwent crosslinking modification after hydrolysis of the film. The crosslinking agent forms bonds with imidazole nitrogen and may slightly inhibit the proton pathway through the hydrogen bond network. The decrease in conductivity of the gel film in vanadium electrolyte solution compared to the absorbed solution is thought to be due to two factors. First, vanadium ions may interact with the film through an attractive force with negatively charged sulfonate groups (pKa approximately -2), thereby inhibiting the flow of protons. Furthermore, PBI The dramatic decrease in the conductivity of the gel film is most likely due to the inherent conductivity of the electrolyte solution containing vanadium ions.

[0042] Since the primary factor in proton conductivity is ion mobility, it is not surprising that increasing vanadium concentration decreases the proton conductivity of the electrolyte solution solely due to the increase in viscosity. PBI gel membranes have a very open configuration that enhances proton conductivity not only by enabling proton transport via the Grotthuss mechanism but also by the mobility of the electrolyte within the membrane. Therefore, proton transport through the membrane is also affected by the increase in viscosity due to the incorporation of vanadium ions. .

[0043] Nevertheless, the mobility of electrolytes in PBI gel membranes is a valid argument for why the permeability of vanadium is significantly higher than in the corresponding dense membrane. This result is not unexpected, even when considering the polymer solids content of the membrane. As can be seen in Table 1, s-PBI has a relatively small amount of polymer per unit volume of electrolyte in the membrane compared to m-PBI. Given the high permeability of vanadium ions in PBI gel membranes, the inventors devised a mitigation method that can chemically crosslink the PBI chains together to fill voids and limit chain mobility. At first glance, the permeability of s-PBI-x is not ideal, but this slight modification has an effect compared to the unmodified type without dramatically affecting conductivity. Since this technique is not affected by the selected PBI derivative, it can be used to improve the properties of PBI membranes as needed. Currently, general gravimetric and rheological techniques have large errors in the case of cast absorption gel membranes, so the inventors have not found an easy method to determine the crosslinking density of gel membranes. However, to confirm the occurrence of crosslinking, a 50 mg sample of the neutralized and dried film was heated under reflux in 800 mL of N,N'-dimethylacetamide for 48 hours. Under these conditions, no film degradation or discoloration of the solution was observed in the crosslinked sample, but dissolution was observed in the original polymer film. Furthermore, a comparison of the swelling rates of the crosslinked and uncrosslinked films yielded noteworthy results. When a non-acidic solvent (N,N'-dimethylacetamide) was used to reliably suppress unwanted solvent-polymer interactions, it was found that the uncrosslinked gel (3.94 wt% increase) absorbed approximately 0.75 wt% more solvent than the crosslinked film (3.25 wt% increase). The restriction of chain mobility by chemical crosslinking inhibits solvent swelling of the polymer gel, resulting in less weight increase due to solvent uptake.

[0044] s-PBI gel films were synthesized via the PPA process, yielding stable films in sulfuric acid and oxidizing V(V) solutions. These films exhibited high conductivity and good cell performance, particularly at high current densities. However, these films inherently possess high vanadium ion penetration due to their open morphology and low polymer solids content. Vanadium penetration was shown to be inhibited by chemical crosslinking, but it remains high compared to dense films. However, this crosslinking method is applicable to many PBI chemicals and can be used to further reduce penetration in PBI gel films without significantly impairing proton conductivity.

[0045] Currently, PBI gel films used in flow batteries offer superior performance compared to those described in the literature. However, redox species penetration reduces the long-term overall efficiency of the battery. One further aspect of this disclosure mitigates the high penetration transport characteristics typical of films without significantly impairing performance.

[0046] PBI gel membranes exhibited particularly excellent performance in redox flow batteries. Membranes formed through this process can be neutralized and doped with common electrolytes used in these applications. The use of these membranes offers cost advantages compared to membranes in the literature, due to their inherently high ionic conductivity, enabling operation under high current load conditions. Under these conditions, the stack size can be significantly reduced, alleviating the very high cost of commercialization. While the out-of-the-box membranes offer high performance, their redox pair permeability hinders long-term efficiency.

[0047] Through novel unidirectional and bidirectional stretching methods, the redox pair transport mechanism can be inhibited without significantly impairing the overall performance.

[0048] One aspect of this disclosure provides post-modification improvements to novel membranes used in redox flow batteries. Under these processing techniques, membrane transport The properties are altered without affecting the ionic conductivity of protons.

[0049] In one embodiment, this disclosure provides a film that can function under high current loads, can reduce the overall cost of the battery, and improves long-term efficiency by reducing the penetration of redox active species. Such a film can be used in the renewable energy sector and / or for backup during peak use in existing power grids / for reducing energy transmission interruptions.

[0050] The novel processing technique for the formed films enables improved performance by reducing the transport of reactive species. These films exhibit superior performance compared to films commonly used in current commercially available vanadium redox flow batteries. See Figure 6, which shows the performance of the films disclosed in this disclosure compared to commercially available non-PBI films. Note: All data shown is for PBI films unless marked "BOM".

[0051] Figure 7 shows a graph of the measured out-of-device properties of the film of this disclosure compared to a typical PBI gel film. Novel processing techniques make it possible to significantly alter the film properties. These types of changes are not common in commercially available films and provide end-users with flexibility when designing new devices or modifying existing ones. The transmittance of the film of the following disclosure can be characterized as follows:

number

[0052] Figure 8 shows the entire process of measuring the film of this disclosure outside of the apparatus.

[0053] Figure 9 shows a comparison of transmittance compared to conductivity for Para-BPI.

[0054] Figure 10 shows a comparison of transmittance with conductivity in Mrp BPI. Figure 11 shows the cell test results of films formed according to this disclosure. Overall, PBI films formed according to this disclosure showed high conductivity and stability in concentrated SA. Furthermore, the transmittance of the para-PBI film was 4.55E-08cm². 2 The voltage can be reduced to / s, while the proton conductivity is maintained at 246 mS / cm with a 2.6 M SA. Furthermore, the VRB operated with a modified para-PBI film was 100-450 mA / cm. 2 It exhibits a Coulomb efficiency of over 98% under high cycle current densities within the specified range.

[0055] Example 1: Para-PBI, stretching rate = 1.7 Para-PBI membranes, manufactured using the PPA process, were first rinsed in a series of deionized water baths to remove phosphate. Before proceeding, pH indicator paper was used to confirm that all acids had been removed. The membranes were cut to dimensions of 10 cm × 12 cm and folded twice to form four layers. Using an Instron 5843 tensile testing machine, the membranes were stretched to 1.7 times their original length. Next, they were sandwiched between two porous glass plates, clamped around the edges to maintain the x and y dimensions, and dried overnight. The following day, the dried, dense PBI film was removed and immersed in a 2.6 M sulfuric acid solution for 24 hours before characterization. The in-plane ionic conductivity was measured at 175 mS / cm at room temperature.

[0056] The transmission of vanadium (VOSO4) was measured using a PermeGear "side-by-side" direct transmission cell. The cell contains two 45 mL chambers separated by the membrane sample. The test temperature was controlled to 25°C using a circulating water bath. In the experiment, 1.5 M VOSO4 in 2.6 M sulfuric acid was placed in the donor chamber, and 1.5 M MgSO4 in 2.6 M sulfuric acid was placed in the receptor chamber. The vanadium(IV) concentration in the receptor chamber was measured at various time intervals using a Shimadzu UV-2450 UV / Vis spectrometer as absorbance at 248 nm. Next, the transmittance of VO2+ was calculated using Fick's law of diffusion:

number

[0057] A VRB (Vanadium Redox Flow Battery) test cell was placed on a 24cm² sheet. 2The cell was assembled with a specific working area, and for the liquid electrolyte, interdigitated flow fields machined from carbon plates were used. The membrane was sandwiched between commercially available carbon paper electrodes heat-treated at 400°C in air for 30 hours, and a polytetrafluoroethylene (PTFE) film was used as a gasket. The cell had two reservoirs on each side, each containing 100 mL of electrolyte solution consisting of 1.60 M vanadium species with an average oxidation state of 3.55 and a total sulfur content of 4.2 M. The electrolyte was circulated within the cell at a constant flow rate of 120 mL / min by two acid-resistant membrane pumps. The charge / discharge cycle performance was measured at 72 mA / cm using a multi-channel potentiostat (Model BT2000, Arbin Instruments Inc., College Station, TX). 2 ~484mA / cm 2 Measurements were taken at a constant current density within the specified range. Voltage efficiency (VE), Coulomb efficiency (CE), and energy efficiency (EE) were measured and recorded. See Figure 12.

[0058] Example 2: Para-PBI, stretching rate = 1.5 The para-PBI membrane, manufactured by the PPA process, was first rinsed in a series of deionized water baths to remove phosphate. Before proceeding, pH indicator paper was used to confirm that all acids had been removed. Next, the neutralized membrane was cut into 10 cm x 12 cm sections and folded twice to form four layers. Using an Instron 5843 tensile testing machine, the membrane was stretched to 1.5 times its original length. Next, it was sandwiched between two porous glass plates, the edges were clamped to maintain the x and y dimensions, and it was dried overnight. The following day, the dried, dense PBI film was removed. The material was immersed in a 2.6 M sulfuric acid solution for 24 hours before characterization. The in-plane ionic conductivity was measured at 207.6 mS / cm at room temperature. The transmittance of VOSO4 was tested as described in Example 1, yielding 4.55 × 10⁻⁶. -8 cm 2 It was found to be / s.

[0059] A VRB test cell was assembled as described herein. Voltage efficiency (VE), Coulomb efficiency (CE), and energy efficiency (EE) were measured and recorded. See Figure 13.

[0060] Example 3: Para-PBI, stretching rate = 0 The para-PBI membrane, manufactured by the PPA process, was first rinsed in a series of deionized water baths to remove phosphate. Before proceeding, pH indicator paper was used to confirm that all acids had been removed. The wet thickness was measured as 356.67 ± 5.8 μm. The membrane was cut to dimensions of 45.72 cm × 30.48 cm. The wet membrane was sandwiched between two porous polyethylene sheets, and the edges were clamped to maintain the dimensions in the x and y directions. The sandwiched membrane was placed upright on a benchtop and dried at room temperature. After 24 hours, the clamps and porous sheets were removed to obtain a dried, dense PBI film. This film had a uniform thickness of 30 μm.

[0061] Example 3A: Flow battery data doped with 2.6M SA The dried film was immersed in 2.6 M sulfuric acid for 24 hours, and then its characteristics were evaluated. The in-plane ionic conductivity was measured at room temperature at 95.17 mS / cm. The transmittance of VOSO4 was tested as described in Example 1, and was 2.65 × 10⁻⁶. -8 cm 2 It was measured as / s.

[0062] A VRB test cell was assembled as described in Example 1. Voltage efficiency (VE), Coulomb efficiency (CE), and energy efficiency (EE) were measured and recorded. See Figure 14.

[0063] Example 3B: Doping with 85% by weight of phosphoric acid The dried film was immersed in 85% by weight phosphoric acid for 24 hours, and then its characteristics were evaluated. The ionic conductivity in the thickness direction (through-plane) was determined by 4-terminal AC impedance spectroscopy using Zahn. Measurements were taken using an er IM6e spectrometer with an amplitude of 5 mV over a frequency range of 1 Hz to 100 kHz. A two-component model consisting of an ohm resistor and a capacitor in parallel was used to fit the experimental data. The conductivity of the film at different temperatures was calculated from the film resistance obtained from model simulations using the following formula:

number

[0064] Example 4: s-PBI, stretching ratio=1.5 11.0824 g of 3,3',4,4'-tetraaminobiphenyl (TAB, 51.72 mmol), 13.9034 g of monosodium 2-sulfoterephthalate (2STPA, 51.85 mmol), and 600 g of polyphosphate (PPA) were added to a 1000 mL reaction vessel equipped with an overhead mechanical stirrer (4% by weight of monomers). Polymerization was carried out at 220 °C for 48 hours under a nitrogen atmosphere. The solution was then treated with a doctor blade. The film was coated onto a glass substrate with a gate thickness of 20 mils and subsequently hydrolyzed for 24 hours. The s-PBI film, which had absorbed phosphoric acid, was rinsed in a series of deionized water baths to remove the phosphoric acid. Before proceeding, pH indicator paper was used to confirm that all acid had been removed. It was cut to dimensions of 10 cm × 12 cm and folded twice to form four layers. The film was stretched to 1.5 times its original length using an Instron 5843 tensile testing machine. Next, it was sandwiched between two porous glass plates, the edges were clamped to maintain the dimensions in the x and y directions, and it was dried overnight. The following day, the dried, dense PBI film was removed and characterized after being placed in a 2.6 M sulfuric acid solution for 24 hours. The in-plane ionic conductivity was measured at 179.7 mS / cm at room temperature. The transmittance of VOSO4 was tested as described in Example 1 and was 2.60 × 10⁻⁶. -9 cm 2 It was measured as / s.

[0065] A VRB test cell was assembled as described in Example 1. Voltage efficiency (VE), Coulomb efficiency (CE), and energy efficiency (EE) were measured and recorded. See Figure 15.

[0066] Example 5: s-PBI, stretch rate=0 11.0824 g of 3,3',4,4'-tetraaminobiphenyl (TAB, 51.72 mmol), 13.9034 g of monosodium 2-sulfoterephthalate (2STPA, 51.85 mmol), and 600 g of polyphosphate (PPA) were added to a 1000 mL reaction vessel equipped with an overhead mechanical stirrer (4 wt% monomer input). Polymerization was carried out at 220 °C for 48 hours in a nitrogen atmosphere. The solution was coated onto a glass substrate with a gate thickness of 20 mil using a doctor blade and subsequently hydrolyzed for 24 hours. The phosphoric acid-absorbing s-PBI film was rinsed in a series of deionized water baths to remove the phosphoric acid. Before proceeding, pH indicator paper was used to confirm that all acids had been removed. The wet thickness was measured to be 251.8 ± 34 μm. A wet film was sandwiched between two porous polyethylene sheets, and the edges were clamped to maintain the dimensions in the x and y directions. It was dried overnight. After 24 hours, the clamps and porous sheets were removed to obtain a dry, dense PBI film. This film had a uniform thickness of 37.7 μm. The dried film was placed in 2.6 M sulfuric acid for 24 hours and then characterized. The in-plane ionic conductivity was measured at 65.71 mS / cm at room temperature. The transmittance of VOSO4 was tested as described herein and was 7.76 × 10⁻⁶. -9 cm 2 It was measured as / s.

[0067] A VRB test cell was assembled as described herein. Voltage efficiency (VE), Coulomb efficiency (CE), and energy efficiency (EE) were measured and recorded. See Figure 16.

[0068] Example 6: Di-OH-PBI, stretching rate=0 6.615 g of 3,3',4,4'-tetraaminobiphenyl (TAB, 30.87 mmol), 6.119 g of 2,5-dihydroxyterephthalic acid (DiOH-TPA, 30.88 mmol), and 401.29 g of polyphosphate (PPA) were added to a reaction vessel and stirred with an overhead mechanical stirrer under a nitrogen atmosphere. Polymerization was carried out at 220°C for 24 hours under a nitrogen atmosphere. The solution was coated onto a glass substrate with a gate thickness of 20 mil using a doctor blade and subsequently hydrolyzed for 24 hours. The phosphoric acid-absorbing film was rinsed in a series of deionized water baths to remove the phosphoric acid. Before proceeding, pH indicator paper was used to confirm that all acids had been removed. The wet thickness was measured to be 404.44 ± 10 μm. The wet film was sandwiched between two porous polyethylene sheets, the edges were clamped to maintain the x and y dimensions, and it was dried overnight. After 24 hours, the clamps and porous sheet were removed to obtain a dry, dense PBI film. This film had a uniform thickness of 31.1 μm. The dry film was placed in 2.6 M sulfuric acid for 24 hours and then characterized. The in-plane ionic conductivity was measured at 218.48 mS / cm at room temperature. The transmittance of VOSO4 was tested as described herein and was 3.92 × 10⁻⁶. -8 cm 2 It was measured as / s.

[0069] Comparative Example 1 (Para-PBI of gel) Para-PBI membranes, manufactured by the PPA process, were first rinsed multiple times in a deionized water bath to remove phosphate. Before proceeding, pH indicator paper was used to confirm that all acids had been removed. Next, the neutralized membranes were placed in a 2.6 M sulfuric acid solution for at least 24 hours and then characterized. The VOSO4 transmittance was tested as described herein and was found to be 5.73 × 10⁻⁶. -7 cm 2 It was measured as / s.

[0070] Comparative Example 2 (s-PBI of gel) 11.0824 g of 3,3',4,4'-tetraaminobiphenyl (TAB, 51.72 mmol), 13.9034 g of monosodium 2-sulfoterephthalate (2STPA, 51.85 mmol), and 600 g of polyphosphate (PPA) were added to a 1000 mL reaction vessel equipped with an overhead mechanical stirrer (4 wt% monomer input). Polymerization was carried out at 220 °C for 48 hours in a nitrogen atmosphere. The solution was coated onto a glass substrate with a gate thickness of 20 mil using a doctor blade and subsequently hydrolyzed for 24 hours. The s-PBI membrane, which had absorbed phosphoric acid, was rinsed in a series of deionized water baths to remove the phosphoric acid. pH indicator paper was used to confirm that all acid had been removed. The s-PBI membrane was placed in 2.6 M sulfuric acid for 24 hours and then characterized. The transmittance of VOSO4 was tested as described herein and was 4.89 × 10⁻⁶. -7 cm 2 It was measured as / s.

[0071] Comparative Example 3 (Di-OH-PBI in gel) 6.615 g of 3,3',4,4'-tetraaminobiphenyl (TAB, 30.87 mmol), 6.119 g of 2,5-dihydroxyterephthalic acid (diOH-TPA, 30.88 mmol), and 401.29 g of polyphosphate (PPA) were added to a reaction vessel and stirred with an overhead mechanical stirrer under a nitrogen atmosphere. Polymerization was carried out at 220°C for 24 hours under a nitrogen atmosphere. The solution was coated onto a glass substrate with a gate thickness of 20 mil using a doctor blade and subsequently hydrolyzed for 24 hours. The phosphoric acid-absorbing film was rinsed in a series of deionized water baths to remove the phosphoric acid. The removal of all acid was confirmed using pH indicator paper. The film was placed in 2.6 M sulfuric acid for 24 hours and then characterized. The VOSO4 transmittance was tested as described in Example 1 and was 7.23 × 10⁻⁶. -7 cm 2 It was measured as / s.

[0072] Comparative Example 4 (Meta-PBI) A commercially available meta-PBI film, prepared by casting and drying an N,N-dimethylacetamide solution, was used as is. The film was immersed in a 2.6 M sulfuric acid solution for 24 hours and then characterized. The in-plane ionic conductivity was measured at 13.1 mS / cm at room temperature.

[0073] A VRB test cell was assembled as described in Example 1. Voltage efficiency (VE), Coulomb efficiency (CE), and energy efficiency (EE) were measured and recorded at 72 mA / cm². See Figure 17. At higher power densities, the cell did not have practical performance and was inoperable. This is because the voltage is related to the conductivity of the film, and in the case of this film, the conductivity is very low.

[0074] Another aspect of this disclosure includes refining a method for forming PBI films. PBI films are known to possess excellent properties such as high temperature stability, non-flammability, and high chemical resistance. To date, methods for producing PBI films have involved polymerization, dissolution of the resulting polymer in an organic solvent such as dimethylacetamide (DMAc), casting of the film, and removal of the solvent by a series of washes.

[0075] This disclosure, in one aspect, describes a gel PB polymerized and cast in a PPA process. This invention provides a novel method for producing PBI films starting from a film. A PBI gel, which has absorbed an acid, is neutralized in a series of water baths and subjected to controlled drying between porous materials to obtain a PBI film without the use of organic solvents. In addition, PBI gels synthesized by the PPA process can be used with a wider range of monomers due to their low solubility in organic solvents. Therefore, this invention provides, for the first time, access to a wider range of PBI chemicals that can be processed into films.

[0076] The improved methods provided herein are based on polybenzimidazole (PBI) membranes, more specifically, on PBI gel membranes. As used herein, the term “gel” refers to any polymer matrix that can incorporate high liquid content and maintain a self-supporting structure. For example, the PBI gel membranes described herein can incorporate about 60% by weight or more, about 65% by weight or more, about 75% by weight or more, about 80% by weight or more, or about 85% by weight or more of liquid, on a weight basis of the composite membrane (total solid plus liquid content), without impairing the structure of the polymer matrix. In one embodiment, the PBI gel membrane can incorporate about 60% to about 95% by weight of liquid while maintaining a self-supporting semi-rigid structure. That is, it can be manipulated to exhibit flexibility without impairing the structure of the polymer matrix. In addition, the PBI gel membrane can have the liquid removed from the gel by treatment, and then be re-swelled by re-absorbing the liquid without impairing the structure of the polymer matrix.

[0077] The film formed by the method of the present invention, in one embodiment, provides high conductivity and low resistance, enabling high-performance operation under high-current load conditions, which can lead to applications such as batteries using smaller and cheaper electrochemical stacks that provide the same or better performance compared to other technologies. For example, the redox flow battery film described may, in some embodiments, exhibit in-plane ionic conductivity of about 100 mS / cm or more, about 200 mS / cm or more, or about 300 mS / cm or more in a 2.6 M sulfuric acid solution. The crosslinked film may exhibit extremely high in-plane ionic conductivity of about 300 mS / cm or more, about 400 mS / cm or more, or about 500 mS / cm or more. For example, the redox flow battery may, in some embodiments, exhibit in-plane ionic conductivity of about 100 mS / cm to about 600 mS / cm in a 2.6 M sulfuric acid solution.

[0078] In addition, batteries incorporating the disclosed film can operate at high current densities, for example, about 100 mA / cm² or more, and in some embodiments, at current densities of about 100 mA / cm² to about 500 mA / cm². Furthermore, batteries incorporating the described redox flow battery film can operate at high efficiency. For example, at a current density of 242 mA / cm², a redox flow battery incorporating the described film can exhibit a Coulomb efficiency (CE) of about 90% or more, for example, about 93% to about 99% in some embodiments; an energy efficiency (EE) of about 75% or more, for example, about 78% to about 85% in some embodiments; and a voltage efficiency (VE) of about 80% or more, for example, about 81% to about 87%. At a current density of 483 mA / cm², the described redox flow battery can exhibit CE of 90% or more, for example, about 94% to about 98% in some embodiments; EE of 65% or more, for example, about 65% to about 75% in some embodiments; and VE of 65% or more, for example, about 66% to about 77%.

[0079] As further described herein, the disclosed gel film is formed by a method comprising hydrolysis of a PPA polymer solvent and subsequent solidification of the PBI polymer in the hydrolysis product (PA). This in situ hydrolysis and polymer solidification is thought to result in the formation of a regular polymer matrix with a different molecular structure from conventional organic solution-cast PBI films, which are cast as a solution in an organic solvent and then solidified by removing the organic solvent, for example, by heating. In particular, the PBI gel film structure is more It is believed that the open, regular framework of the PBI matrix provides a stable gel film that exhibits the improved electrochemical properties described.

[0080] To form a PBI gel film that can be used in the methods of this disclosure, a polymerization composition comprising PPA and a selected PBI-forming compound, such as a PBI-forming monomer, can be formed. The monomer content of the polymerization composition may generally be low, for example, about 10% by weight or less, about 8% by weight or less, or about 5% by weight or less in some embodiments.

[0081] The PBI polymer of the PBI gel film may have any PBI structure commonly known in the art and can be formed by polymerization of a PBI-forming compound comprising at least one aromatic or heteroaromatic tetraamino compound and at least one aromatic or heteroaromatic polycarboxylic acid or its ester, anhydride, or acid chloride, or at least one aromatic or heteroaromatic diaminocarboxylic acid. Heteroaromatic compounds as defined herein include aromatic systems containing at least one nitrogen, oxygen, sulfur, or phosphorus atom in the aromatic ring.

[0082] Examples of aromatic and heteroaromatic tetraamino compounds that can be used to form PBI gel films include, but are not limited to, 2,3,5,6-tetraaminopyridine, 3,3',4,4'-tetraaminodiphenylsulfone, 3,3',4,4'-tetraaminodiphenyl ether, 3,3',4,4'-tetraaminobiphenyl, 1,2,4,5-tetraaminobenzene, 3,3',4,4'-tetraaminobenzophenone, 3,3',4,4'-tetraaminodiphenylmethane, and 3,3',4,4'-tetraaminodiphenyldimethylmethane, as well as salts thereof, such as mono-, di-, tri-, and tetrahydrochloride salts, and any combination of aromatic or heteroaromatic tetraamino monomers.

[0083] In one embodiment, the aromatic polycarboxylic acid may include a dicarboxylic acid. The dicarboxylic acid may be used alone or in combination with one or more additional polycarboxylic acid compounds, such as tricarboxylic acid and / or tetracarboxylic acid. When incorporated, the content of the tricarboxylic acid or tetracarboxylic acid may generally be about 30 mol% or less, based on the amount of one or more dicarboxylic acid compounds, for example, about 0.1 mol% to about 20 mol%, or about 0.5 mol% to about 10 mol%. Esters of polycarboxylic acids, such as C1-C20 alkyl esters or C5-C12 aryl esters of polycarboxylic acids, may be used. The anhydride of the polycarboxylic acid or the acid chloride of the polycarboxylic acid may be polymerized according to the disclosed method.

[0084] Examples of aromatic dicarboxylic 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, 5-hydroxyisophthalic acid, 4-hydroxyisophthalic acid, 2-hydroxyterephthalic acid, 5-aminoisophthalic acid, and 5-N,N-dimethyl Diaminoisophthalic 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, 1,8-dihydroxynaphthalene-3,6-dicarboxylic 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, tetra Examples include lafluoroterephthalic acid, 3-sulfophthalic acid, 5-sulfoisophthalic acid, 2-sulfoterephthalic acid, tetrasulfophthalic acid, tetrasulfoisophthalic acid, tetrasulfoterephthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic 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'-stilbendicarboxylic acid, and 4-carboxycinnamic acid, or any combination thereof.

[0085] Examples of aromatic tricarboxylic acids, as well as their esters, acid anhydrides, and 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; and 3,5,4'-biphenyltricarboxylic acid; or any combination thereof.

[0086] Examples of aromatic tetracarboxylic acids, as well as their esters, acid anhydrides, and 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; and 1,4,5,8-naphthalenetetracarboxylic acid; or any combination thereof.

[0087] Examples of heteroaromatic carboxylic acids include heteroaromatic dicarboxylic acids, heteroaromatic tricarboxylic acids, and heteroaromatic tetracarboxylic acids, and include corresponding esters such as C1-C20 alkyl esters and C5-C12 aryl esters of heteroaromatic carboxylic acids, or acid anhydrides or acid chlorides. Examples of heteroaromatic carboxylic acids, but not limited to, 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, and further, their C1-C20 alkyl esters or their C5-C12 aryl esters, or their acid anhydrides, or their acid chlorides, or any combination thereof.

[0088] In one embodiment, the polymerization composition may include, but are not limited to, diaminobenzoic acid and mono and dihydrochloride derivatives of said acid, as well as 1,2-diamino-3'-carboxylic acid 4,4'-diphenyl ether, or any combination thereof.

[0089] The PPA that can be used in the polymerization composition may be a commercially available PPA, for example, from Riedel-de Haen. The PPA may include concentrated grades of PA(H3PO4) exceeding 100%. At high concentrations, individual H3PO4 units are polymerized by dehydration, and the PPA is of the formula H n+2 P n O 3n+1 It can be expressed as (n>1).

[0090] PPA[H n+2 P n O 3n+1(n>1) may, when calculated by acid titration, have a P2O5 content of about 70% by weight or more, for example, about 75% by weight or more, or about 82% by weight or more, for example, about 70% to about 86% by weight, in some embodiments. The polymerization composition may generally be in the form of a monomer / compound solution or a monomer / compound dispersion / suspension in PPA, depending on the properties of any additional components of the compound to be polymerized and the polymerization solution.

[0091] Polymerization may be carried out at a certain temperature and for a certain period of time until the compound is properly polymerized, and the occurrence of polymerization can generally be determined by an increase in the viscosity of the polymerized composition. The increase in viscosity can be determined by visual inspection, through the determination of the intrinsic viscosity, or by any other suitable means. For example, polymerization may 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 in some embodiments, or about 1.5 dL / g or more. The polymerization temperature may generally be about 220°C or less, for example, about 200°C or less, and for some embodiments, about 100°C to 195°C. Polymerization may be carried out over a period of time ranging from a few minutes (e.g., about 5 minutes) to a few hours (e.g., about 100 hours). In one embodiment, the polymerized composition may be heated in a stepwise manner, for example, in three or more steps, each step lasting from about 10 minutes to about 5 hours, with the temperature increasing by about 15°C or more for each step. As will be obvious to those skilled in the art, specific polymerization conditions can generally be varied depending on the reactivity and concentration of the specific monomer, and specific polymerization conditions are not required for the formation of redox flow cell films.

[0092] Examples of PBI polymer repeating units in PBI gel films include, but are not limited to: [ka] [ka] [ka] Or any combination thereof, where in some embodiments, n and m are independently 1 or more, about 10 or more, or about 100 or more.

[0093] The PBI polymers of the films disclosed herein may contain any repeating units, including any derivatizations commonly known in the art, examples of which are well within the knowledge of those skilled in the art, and representative examples of which are, for example, described in U.S. Patent Application Publication 2013 / 0183603 by Benicewicz, et al., incorporated herein by reference.

[0094] After polymerization, the polymer may be dissolved in a PPA solvent, and this PBI polymer solution can be processed to form a gel film precursor having a desired thickness. Beneficially, the polymer solution, the gel film precursor formed from the polymer solution, the final gel film, and the redox flow cell film can be organic solvent-free.

[0095] The film precursor may be formed according to any suitable formation process, but is not limited to casting, spray coating, or knife coating. For example, in one embodiment, the gel film precursor may be formed to a thickness of about 20 micrometers (μm) to about 4000 μm, and in some embodiments, it may be formed to a thickness of about 30 μm to about 3500 μm, or about 50 μm to about 1000 μm.

[0096] To solidify the polymer and form a PBI gel film, 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. Upon hydrolysis, the PPA hydrolyzes to form PA and water, and since the PBI polymer is less soluble in PA than PPA, this causes a sol-gel transition of the PBI polymer solution and solidification of the polymer.

[0097] The hydrolysis treatment may be carried out at a temperature and time sufficient to solidify the gel film so that it becomes self-supporting and can be operated without being damaged, while maintaining a high liquid content (e.g., a liquid content of about 60% by weight or more of the total solid and liquid content of the film). For example, in some embodiments, the hydrolysis treatment may be carried out at a temperature 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, for example, at ambient temperature (for example, in a contact environment with relative humidity of about 35% to 100%).

[0098] Hydrolysis may be carried out by contacting the gel film precursor with H2O, for example, in the form of liquid or vapor, and / or in the presence of other components. For example, the gel film precursor may be contacted with water vapor and / or liquid water and / or steam and / or an aqueous PA solution (e.g., a PA solution with 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 process may be carried out under standard pressure, but this is not a requirement of the formation process, and in some embodiments, the hydrolysis process may be carried out under modified pressure.

[0099] In one embodiment, hydrolysis may be carried out in a controlled environment where the H2O content can be tightly controlled. For example, the moisture content of the local environment may 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 another suitable gas may carry H2O, such as steam, in a controlled amount for contact with the precursor membrane.

[0100] The hydrolysis treatment time can generally vary depending on parameters such as the H2O content and the form of contact, film thickness, and contact temperature. Generally, the hydrolysis treatment may be carried out for a period of several seconds to several minutes, for example, when the hydrolysis treatment is performed using superheated steam, or, as an alternative, for example, when the hydrolysis treatment is performed at ambient temperature and with a low relative atmospheric moisture content, it may be carried out for several days. In some embodiments, the hydrolysis treatment may be carried out for about 10 seconds to about 300 hours, for example, about 1 minute to about 200 hours. For example, in an 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 (i.e., relative humidity) content 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.

[0101] When at least a portion of the PPA in the PBI polymer solution is hydrolyzed, the polymer can solidify, forming a PBI gel film. In one embodiment, the PBI gel film may 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, but no particular thickness is essential. In some embodiments, the PBI gel film may have a thickness less than the thickness of the film precursor. As mentioned earlier, 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 in the solidified polymer matrix.

[0102] In one embodiment, the as-formed PBI gel film may have a PBI solid content of about 5% to about 40% by weight of the total weight of the film, including the liquid content, for example, about 8% to about 30% by weight or about 10% to about 25% by weight. The as-formed PBI gel film may be self-supporting and, for example, in some embodiments, when specifying a PBI gel film (e.g., polybenzimidazole) with a thickness of 403 μm and a PBI content of 5% by weight, it may have a Young's modulus of about 2.0 MPa or more, for example, about 3.0 MPa or more or about 4.5 MPa or more.

[0103] One obvious application of the method disclosed herein is redox flow cell films, but the method of the present invention is not limited to this aspect and can be used not only for PBI films but also for the manufacture of fibers, fibrils, resins, resin beads, paper, microporous resins, sizing agents, coatings, and molding resins. Furthermore, the PBI films disclosed herein can be used in aerospace structures, adhesives, carbon fiber laminates, insulation, syntactic foams, and fabrics. Specific applications, though not limited to them, include aircraft fire seals, firefighting protective equipment, sock hoods, high-temperature gloves, aluminum-coated rescue equipment, flight suits, hazardous work coveralls, filtration systems, glass handling belts, expansion joints, gaskets, packings, resin fillers, motor insulation, filament wound composites, lacing for reinforcing fibers, chopped fiber reinforcements for resin matrices, acid scavenging applications, sizing agents, heat shields, transformer wraps, asbestos substitutes, composites, battery separators, pipe insulation, microelectronics processing, wire coatings, gas separation films, protective windows and glass coatings, and high-temperature substrate fils.

[0104] If desired, the PBI gel membrane may be crosslinked, thereby reducing the membrane permeability of redox ion pairs of the battery electrolyte solution without significantly affecting the desired electrochemical properties of the membrane. The method of crosslinking and the timing of crosslinking during the formation process are not particularly limited. For example, the gel membrane may be crosslinked after rinsing / washing the as-formed gel membrane and before the absorption of the supporting electrolyte into the membrane. However, in other embodiments, the membrane may be crosslinked before rinsing / washing or after the absorption of the supporting electrolyte into the membrane.

[0105] In one embodiment, the PBI gel film may be crosslinked simply by heating in the presence of atmospheric oxygen. Crosslinking may also be carried out by the action of radiation, including near-infrared (IR) rays (radiation with wavelengths of about 700 nm to about 2000 nm or energies in the range of about 0.6 to about 1.75 eV) and IR (having wavelengths of about 700 nm to about 1 mm).

[0106] To perform crosslinking, the PBI polymer may contain reactive functional groups in its polymer chains, either to crosslink with itself or with a crosslinking agent, i.e., a polyfunctional compound that can react with one or more functional groups (e.g., amines) of the PBI polymer. The crosslinking agent may contain any suitable functional group for crosslinking. Suitable crosslinking agents are not particularly limited, and examples include, but are not limited, epichlorohydrins, diexoxides, diisocyanates, α,ω-dihaloalkanes, diacrylates, and bisacrylamides. Specific examples, but are not limited, include, α,α'-dichloro-p-xylene, chloromethyl methyl ether, bis(chloromethyl) ether, terephthaloyl chloride, succinyl chloride, and dimethyl succinate, as well as combinations with crosslinking agents. In one embodiment, 1 to 20 equivalents of crosslinking agent may be used per available aromatic ring, but the crosslinked embodiment of the film is not limited to any particular crosslinking density.

[0107] Furthermore, the PBI of this disclosure may absorb a supporting electrolyte. The choice of supporting electrolyte may generally depend on the specific characteristics of the redox flow battery in which the membrane is used, and may include acidic, basic, and even neutral types (e.g., water). For example, the 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 supporting electrolytes that may be absorbed by the membrane include, but are not limited to, sodium chloride, potassium chloride, sodium hydroxide, potassium hydroxide, sodium sulfide, potassium sulfide, and combinations thereof. Examples of supporting electrolytes include H2SO4, HBr, HBr / HCl mixture, HCl, NaS2, NaS2 / NaBr mixture, Br2 in HBr, Br2 in H2SO4, and Br2 in HBr / H2SO4 mixture. In one embodiment, a tetraalkylammonium supporting cation may be absorbed into the membrane, and Et4N + and Bu4N + These are two unspecified examples. Tetrafluoroboric acid (BF 4- ), perchloric acid (ClO 4- ), or hexafluorophosphate (PF 6- Solutions of these, or combinations thereof, are further examples of supporting electrolytes that may be absorbed into the membrane.

[0108] The concentration of the supporting electrolyte in the membrane is not particularly limited, and generally, the solution absorbed by the membrane may contain the supporting electrolyte at concentrations up to about 25 moles / liter (M) 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.

[0109] The film may be made to absorb the supporting electrolyte by any appropriate method. For example, In one embodiment, absorption of the supporting electrolyte into the film may be carried out by immersing the film in a solution of the supporting electrolyte in an environment where the temperature is optionally raised, for a period of time ranging from several minutes to several hours or several days.

[0110] This disclosure details a novel method for producing PBI films without the use of organic solvents. By eliminating the need for organic solvents, a novel PBI film production route is provided that is cheaper, faster, and generates less chemical waste than conventional methods. This novel solvent-free method can also be used to produce films from a wider range of PBI chemicals.

[0111] The PBI-based films of this disclosure have a variety of applications. In the case of films to be used as ion conductors in electrochemical applications, the dry film may be further processed to "re-swell" the film and allow it to absorb a base, acid, or other ion conductor, and therefore the film is not limited to applications in redox flow cells. Upon re-swelling, the film exhibits low transmittance to redox pairs and other materials, while still exhibiting high ion conductivity for electrochemical applications.

[0112] The following examples better illustrate this disclosure.

[0113] Example 7: Para-PBI film The para-PBI membrane, manufactured by the PPA process, was first rinsed with a detergent to remove phosphoric acid. The detergent may consist of various solutions including weakly basic water, deionized water, or other suitable detergents known to those skilled in the art. In one embodiment, the detergent may be a series of deionized water baths. Before proceeding, pH indicator paper was used to confirm that all acids had been removed. See Figure 18. The wet thickness was measured as 356.67 ± 5.8 μm, and the membrane was cut to dimensions of 45.72 cm × 30.48 cm. The wet membrane was sandwiched between two porous polyethylene sheets, the periphery was clamped to maintain the x and y dimensions, and it was dried overnight. After 24 hours, the polyethylene sheets were removed to obtain a dried, dense PBI film. This film had a uniform thickness of 30 μm. The film showed a retention rate of over 85 wt% when measured by thermogravimetric analysis (TGA) at 500°C in a nitrogen atmosphere.

[0114] The mechanical properties of the dense film were measured using an Instron 5843 tensile testing machine. Five samples were cut according to the ASTM D638 (Type V) standard, and the modulus of elasticity (measured as slope at 1% strain), fracture stress, and fracture strain were measured. Figure 18 shows the tensile test results of para-PBI films manufactured according to this disclosure.

[0115] Example 8: Di-OH-PBI film 401.30 g of polyphosphate was added to a reaction vessel containing 6.6161 g (30.88 mmol) of 3,3',4,4'-tetraaminobiphenyl and 6.1177 g (30.88 mmol) of 2,5-dihydroxyterephthalic acid. Polymerization was started at 40°C for 1 hour with stirring under a nitrogen atmosphere, then increased to 140°C over 2 hours, immersed at 140°C for 4 hours, increased to 195°C over 3 hours, and immersed at 195°C for 14 hours. Next, the solution was applied to a polyester film using a doctor blade and subsequently hydrolyzed at room temperature and 55% relative humidity.

[0116] Next, the Di-OH-PBI membrane was rinsed in a series of deionized water baths to remove phosphate, and before proceeding, pH indicator paper was used to confirm that all acids had been removed. The wet thickness was measured to be 348.33 ± 43.4 μm. The wet membrane was sandwiched between two porous polyethylene sheets, the edges were clamped to maintain the dimensions in the x and y directions, and it was dried overnight. After 24 hours, the polyethylene sheets were removed to obtain a dried, dense PBI film. The lumen had a thickness of 24.67 ± 3.8 μm.

[0117] The mechanical properties of the dense film were measured using an Instron 5843 tensile testing machine. Four samples were cut according to the ASTM D638 (Type V) standard, and the modulus of elasticity (measured as slope at 1% strain), fracture stress, and fracture strain were measured. See Figure 19.

[0118] Example 9: s-PBI film 384 g of polyphosphate was added to a reaction vessel containing 7.1063 g (33.17 mmol) of 3,3',4,4'-tetraaminobiphenyl and 8.8937 g (33.16 mmol) of monosodium 2-sulfoterephthalate. Polymerization was carried out at 190°C for 48 hours with stirring under a nitrogen atmosphere. Next, the solution was applied to a polyester film using a doctor blade and subsequently hydrolyzed at room temperature and 55% relative humidity.

[0119] Next, the s-PBI membrane was rinsed in a series of deionized water baths to remove phosphate, and before proceeding, pH indicator paper was used to confirm that all acids had been removed. The wet thickness was measured to be 276.33 ± 22.59 μm. The wet membrane was sandwiched between two porous polyethylene sheets, the edges were clamped to maintain the dimensions in the x and y directions, and it was dried overnight. After 24 hours, the polyethylene sheets were removed to obtain a dried, dense PBI film. This film had a thickness of 33.0 ± 3.0 μm.

[0120] The mechanical properties of the dense film were measured using an Instron 5843 tensile testing machine. Five samples were cut according to the ASTM D638 (Type V) standard, and the modulus of elasticity (measured as slope at 1% strain), fracture stress, and fracture strain were measured. See Figure 20.

[0121] Example 10: Meta / para-PBI copolymer film 1027 g of polyphosphate was added to a reaction vessel containing 64.2810 g (300.00 mmol) of 3,3',4,4'-tetraaminobiphenyl, 43.6118 g (262.52 mmol) of isophthalic acid, and 6.2303 g (37.50 mmol) of terephthalic acid. The mixture was polymerized at 190°C for 20 hours with stirring under a nitrogen atmosphere. Next, the solution was applied to a polyethylene film using a doctor blade and subsequently hydrolyzed at room temperature and 55% relative humidity.

[0122] Next, the meta / para-PBI copolymer membrane was rinsed in a series of deionized water baths to remove phosphate, and before proceeding, pH indicator paper was used to confirm that all acids had been removed. The wet thickness was measured to be 197 ± 15.70 μm. The wet membrane was sandwiched between two porous polyethylene sheets, the edges were clamped to maintain the dimensions in the x and y directions, and it was dried overnight. After 24 hours, the polyethylene sheets were removed to obtain a dried, dense PBI film. This film had a thickness of 62.67 ± 7.97 μm.

[0123] The mechanical properties of the dense film were measured using an Instron 5843 tensile testing machine. Five samples were cut according to the ASTM D638 (Type V) standard, and the modulus of elasticity (measured as slope at 1% strain), fracture stress, and fracture strain were measured. See Figure 21.

[0124] Example 11: Para-PBI film dried on a single support substrate In this example, the para-PBI membrane, manufactured by the PPA process, was first rinsed in a series of deionized water baths to remove phosphate, and before proceeding, pH indicator paper was used to confirm that all acid had been removed. The wetted thickness was measured to be 350 □ m. The wetted membrane was then supported by a single support structure. The material was clamped and fixed onto a single porous polyethylene sheet, maintaining its dimensions in the x and y directions, and then dried. After 8 hours, a dried, dense PBI film remained, which was removed from the porous polyethylene sheet. The film had a thickness of 42 □ m and was observed to be of high quality, appearing to be consistent with the film produced in Example 1 above.

[0125] Comparative Example 5: Commercially available meta-PBI film cast from an organic solvent. Commercially available m-PBI (m-PBI) solution-cast (from N,N-dimethylacetamide) was obtained and used as is. The mechanical properties of the dense film were measured using an Instron 5843 tensile testing machine. Eight samples were cut according to ASTM D638 (Type V) standards, and the modulus of elasticity, yield stress, yield strain, fracture stress, and fracture strain at 1% strain were measured. See Figure 22.

[0126] In addition, PBI films manufactured in accordance with this disclosure may be re-doped with phosphoric acid. These re-doped films may exhibit better creep resistance and may be directly applicable to fuel cell applications at least.

[0127] Example 12: Dry para-PBI film doped with 85% by weight phosphoric acid Para-PBI membranes manufactured by the PPA process were first rinsed in a series of deionized water baths to remove phosphoric acid (PA). Before proceeding, pH indicator paper was used to confirm that all acids had been removed. The wet thickness was measured as 356.67 ± 5.8 μm, and the membrane was cut to dimensions of 45.72 cm × 30.48 cm. The wet membrane was sandwiched between two porous polyethylene sheets, the edges were clamped to maintain the x and y dimensions, and it was dried overnight. After 24 hours, the polyethylene sheets were removed to obtain a dry, dense PBI film. This film had a uniform thickness of 30 μm. The dried film was placed in 85 wt% phosphoric acid for 24 hours, after which characterization and fuel cell testing were performed. The film thickness after PA doping was 150 μm.

[0128] The ionic conductivity in the thickness direction was measured using a Zahner IM6e spectrometer with a 5mV amplitude and 4-terminal AC impedance spectroscopy over a frequency range of 1Hz to 100kHz. A two-component model consisting of an ohm resistor and a capacitor in parallel was used to fit the experimental data. The conductivity of the film at different temperatures was calculated from the film resistance obtained from model simulations using the following formula:

number

[0129] Compressive creep and creep recovery tests were performed using a TA Instrument RSAIII dynamic mechanical analyzer. Membrane samples with a diameter of approximately 7 mm and a thickness of approximately 1.2–1.7 mm were cut. Before the creep test, all samples were pre-conditioned at 180°C for 24 hours. In a typical experiment, a constant compressive force equivalent to a stress level of 0.1 MPa was applied to the sample, held for 20 hours, and then the force was removed over 3 hours. All experiments were conducted at 180°C, and strain and stress were recorded as functions of time. Creep compliance was calculated by dividing the time-dependent strain by the applied stress. The values ​​were calculated as follows. In this experiment, the creep test was repeated three times for each film. In one embodiment, the film of this disclosure may have a breaking stress of at least 25 MPa. Figure 24 shows that the film produced by this method exhibited significantly better (lower) creep resistance than a standard PPA process film.

[0130] A membrane electrode assembly (MEA) consisting of a phosphate-doped para-PBI membrane is placed at 10 cm 2 The cells were assembled into a single-cell hardware unit and tested using a commercially available fuel cell test station (Fuel Cell Technology, Inc.). This device was controlled by self-programmed LabView software (National Instruments in Austin, TX). Before testing, the cells were heated to 160°C and 0.2 A / cm² while supplying H2 to the anode and air to the cathode. 2 A trial run of at least 24 hours was conducted by operating at the specified current density. Polarization curves were recorded at 160, 180, and 200°C at stoichiometric flow rates of H2 / air = 1.2 / 2.0 and H2 / O2 = 1.2 / 2.0. Figure 25 shows the polarization curve for H2 / air, and Figure 26 shows the polarization curve for H2 / O2.

[0131] These examples disclose the placement of a PBI gel membrane in contact with a substrate such as a porous sheet during the drying process. The substrate may include a variety of materials, such as porous or non-porous substrates. In addition, the disclosure also discloses that various PBI gels may be sandwiched between two porous sheets, between a porous sheet and a non-porous sheet, or simply in contact with a single porous or non-porous sheet without placing a sheet on the opposite side of the PBI gel membrane. The membrane may be dried in a continuous process with or without the use of a support sheet. As shown in Figure 23, a flow of drying gas may be used on one or both sides of the supported or freestanding membrane to accelerate the drying process.

[0132] With respect to processing, the PBI film of this disclosure may be constrained and / or tensioned with respect to the X, Y, and Z planes. In this specification, “constrained” may be used to mean simply fixing the PBI film properly without applying stretching or tension to the PBI film to stretch the film from its original shape. On the other hand, “tensioned” may be used to mean applying stretching or tension to the PBI film to make it taut across the entire film surface with respect to the X and / or Y planes, or to stretch its length with respect to the X and / or Y planes. In a preferred embodiment, the PBI film is constrained and / or tensioned with respect to the X, Y, and Z planes, but is not constrained and not tensioned with respect to the Z plane. Furthermore, drying of the film may simply be air-drying of the PBI film. However, in a further embodiment, a drying gas, air, or a gas such as nitrogen may be supplied to the constrained or tensioned film to accelerate the drying process. Furthermore, the PBI film may be constrained in the width direction, and a dry gas, air, or nitrogen may pass over one or both sides of the tensioned film.

[0133] This disclosure also directly affects the application of film processing in PBI films formed according to this disclosure. In one embodiment, this disclosure may be combined with a continuous film formation process known to those skilled in the art. For example, as shown in Figure 23, a continuous forming process 100 may be used to form a PBI film 102 via a continuous process, in which case a pre-formed PBI film 102 may be directly deposited on a film tensioner surface 104 that can simultaneously or separately restrain the film in the X, Y, and / or Z planes or apply tension to the PBI film 102 by pulling it in the X, Y, and / or Z planes. Alternatively, the PBI film 102 may be formed by coating a substrate surface 106 known to those skilled in the art, such as a quench drum, air roller, or porous surface, as a solution 105 in a bath containing a mixture of phosphoric acid and water to aid in completing the sol-gel process, and additionally, removing the phosphoric acid and replacing it with water. An additional step may be added in which the casting solution and the substrate are immersed in the water bath. Thus, all methods of this disclosure can be adapted to a continuous assembly process for either pre-formed or newly formed PBI films 102 under the command of the controller 108. A drying gas, represented by arrow A, may be applied to the upper surface 110 and / or lower surface 112 of the PBI film throughout the process 100. Furthermore, serpentine rolls 114 may be used to assist in applying tension to the PBI film 102 as it passes along the continuous forming process 100, and to allow for further drying. After the PBI film 102 has been tensioned and dried, the film may be further processed by cutting, winding, etc., as known to those skilled in the art, to process the PBI film 102 116.

[0134] This disclosure offers several advantages to the PBI industry. Firstly, no organic solvents are used in the formation process. Secondly, this disclosure opens the way for PBI polymers that have previously received little attention precisely because they could not be dissolved in organic solvents. This method makes it possible to use a wider variety of chemicals.

[0135] Furthermore, using the method disclosed herein, films with a thickness of 5 to 150 microns, more preferably 5 to 100 microns, and even more preferably 10 to 50 microns can be formed.

[0136] While the subject matter of the present invention has been described in detail with respect to specific embodiments and methods thereof, it will be understood that those skilled in the art will readily be able to obtain modifications, variations, and equivalents to such embodiments by understanding the above. Therefore, the scope of this disclosure is illustrative and not limiting, and this disclosure does not exclude modifications, variations, and / or additions to the subject matter of the present invention that would be readily apparent to those skilled in the art by using the teachings disclosed herein.

[0137] Other embodiments of this disclosure include, for example, the following: [1] Dry PBI film having a breaking stress of 25 MPa or more. [2] PBI is the following repeating unit: [ka] [ka] [ka] A dry PBI film according to [1], comprising one or more of the following, wherein n and m are each independently 1 or more. [3] VOSO4 transmittance is 2.6 × 10 -9cm 2 / s~4.89×10 -7 cm 2 A dry PBI film as described in [1] or [2], which is / s. [4] A cross-linked dry PBI film as described in any of [1] to [3]. [5] A redox flow battery comprising a dried PBI film as described in [1] having absorbed a supporting electrolyte. [6] The redox flow battery according to [5], wherein the supporting electrolyte comprises sulfuric acid. [7] The redox flow battery according to [5] or [6], wherein the concentration of the supporting electrolyte is 0.1 M to 25 M. [8] A vanadium redox flow battery, which is a redox flow battery as described in any of [5] to [7]. [9] The PBI film is 100 mA / cm² 2 ~450mA / cm 2 A redox flow battery as described in any of [5] to [8], exhibiting a Coulomb efficiency of 98% or higher under the battery cycle current density.

Claims

1. 2.6 x 10 －９ cm ２ / s ~ 4.89 x 10 －７ cm ２ / s VOSO ４ A redox flow battery comprising a polybenzimidazole (PBI) film that exhibits transmittance, The PBI film that has absorbed the supporting electrolyte has a current of 100 mA / cm². ２ ~450 mA / cm ２ A redox flow battery exhibiting a Coulomb efficiency of over 98% under the following battery cycle current density.

2. The redox flow battery according to claim 1, wherein the supporting electrolyte contains sulfuric acid.

3. The redox flow battery according to claim 1, wherein the supporting electrolyte comprises a mixture of an organic acid and an inorganic acid.

4. The redox flow battery according to claim 1, wherein the supporting electrolyte comprises sodium chloride, potassium chloride, sodium hydroxide, potassium hydroxide, sodium sulfide, potassium sulfide, or a combination thereof.

5. The redox flow battery according to claim 1, wherein the supporting electrolyte is present at a concentration of 0.1 to 25 M.

6. The redox flow battery according to claim 1, wherein the PBI film comprises a PBI polymer that is insoluble in organic solvents.

7. The redox flow battery according to claim 1, which is a vanadium redox flow battery.

8. The redox flow battery according to claim 1, wherein the PBI film comprises sulfonated polybenzimidazole.

9. The redox flow battery according to claim 1, wherein the PBI film exhibits an conductivity of 537 mS / cm to 593 mS / cm in 2.6 M sulfuric acid.

10. The redox flow battery according to claim 1, exhibiting an energy efficiency of approximately 65% ​​or more and a voltage efficiency of approximately 65% ​​or more.

11. The PBI film has the following repeating units: 【Chemistry 1-1】 [Chemistry 1-2] The formula includes one or more of the following, where n and m are each independently 1 or more, as described in claim 1. A redox flow battery.

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