Apparatus and method for manufacturing acid-doped proton exchange membranes

Abstract

To provide an improved device and method for manufacturing an acid-doped proton exchange membrane for mass production, and also a method for continuous high-speed production of acid-doped polybenzimidazole and a PBI film.SOLUTION: A continuous automated process and a production line manufacture acid-doped polybenzimidazole, and a PBI polymer membrane film for use in a fuel cells, and the method includes preparing a PBI film membrane sheet for processing, a washing step, a drying procedure, and a doping step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Field of Invention The present invention relates to a method and apparatus for manufacturing an acid-doped proton exchange membrane for fuel cells. [Background technology]

[0002] Polymer electrolyte membranes, abbreviated as PEM and commonly known as proton exchange membranes, are combined with electrodes such as platinum-based electrodes to form a membrane electrode assembly (MEA), which is one of the key components of a correspondingly named PEM fuel cell. High-temperature PEM fuel cells have greater resistance to input gas impurities, particularly carbon monoxide, which is one of their major advantages over low-temperature fuel cells. However, their high operating temperatures, which can reach up to 200°C, require the use of special materials.

[0003] A good candidate for membrane materials used in high-temperature fuel cells is polybenzimidazole, PBI, a synthetic polymer with aromatic heterocyclic rings and excellent chemical and thermal stability. See also the paper, Improving the performance of high-temperature PEM fuel cells based on PBI electrolyte, Journal of Power Sources, 160(2006)27-36, by Seland F, Berning T, Boressen B, Tunold R, et al. This paper is reference [1] in the bibliography below.

[0004] PBI films exhibit relatively low proton conductivity, however, this can be significantly increased by doping the film polymer with a strong electrolyte. Various mineral acids, such as HBr, HCl, HClO4, HNO3, H2SO4, and H3PO4, are candidates for this purpose. Orthophosphate (H3PO4) is advantageous in that it has unique proton conductivity, low vapor pressure, and good chemical stability at high temperatures. Orthophosphate-doped PBI films exhibit a maximum directional electrical conductivity value of 0.26 S / cm at 200°C. Nevertheless, it is important to note that orthophosphate (H3PO4-PBI)-doped PBI films lose their mechanical properties as the acid content increases, which is why this parameter needs to be precisely controlled. For further information, please refer to the paper by Li Q, Jensen JO, Savinell RF, Bjerrum NJ et al., "High temperature proton exchange membranes based on polybenzimidazole for fuel cells," Progress in Polymer Science, 34(2009) 449-477. This paper is reference [2] in the bibliography below.

[0005] Typically, casting methods are used for PBI films and are disclosed, for example, in U.S. Patent Publications 2012 / 0115050, 2012 / 003564, 2008 / 268321, or International Publication 2000 / 44816. However, casting methods are not useful for high-speed production.

[0006] PBI membranes have been discussed in detail in the prior art. For example, U.S. Patent Application Publication 2016 / 0190625 (advertised as U.S. Patent No. 9,705,146) discloses a PBI membrane having porous and dense layers. U.S. Patent No. 5,945,233 discloses a PBI gel for fuel cells deposited on electrodes. U.S. Patent No. 6,042,968 discloses a PBI fabric for fuel cells. The fabric is immersed in acid and then heated to remove residual solvents such as N,N-dimethylacetamide (DMAc). However, the exemplary drying process is slow, taking almost several hours, which is unsuitable for mass production. U.S. Patent Application Publication 2012 / 0115050 discloses a method for washing acid-doped PBI membranes to remove the acid. However, the need to stretch the membrane does not enable continuous high-speed production, especially in roll-to-roll methods.

[0007] U.S. Patent Application Publication 2008 / 280182 discloses an acid doping step with doping times ranging from 5 minutes to 96 hours in the case of high concentrations of phosphoric acid. For doping, a temperature range of 20–100°C is disclosed. An example is given of doping with phosphoric acid at an 85% acid concentration for 95 hours. However, such long doping times are not useful for rapid production or continuous manufacturing. No rapid methods are disclosed.

[0008] U.S. Patent No. 4,927,909 discloses the continuous production of general PBI films, comprising a washing and removal of residual DMAc in a non-solvent bath, for example, in water, followed by a drying step in an oven. As an alternative to the water bath in the washing step, a bath containing up to 15%, but preferably 2-5%, of phosphoric acid is disclosed. However, its use in fuel cells is not disclosed, nor is any disclosure regarding final acid doping.

[0009] A continuous method for attaching membranes is disclosed in U.S. Patent Application Publication No. 2008 / 268321. However, a continuous method for producing membranes is not disclosed.

[0010] Patent No. EP1566251 discloses a film production method in which the film is cast between two supporting bands and then peeled off from there.

[0011] U.S. Patent Application Publication 2012 / 031992 discloses a method in which a second film is cast onto a first film to give a composite film. This method is slow in that the film is stored for at least one day for acid conversion.

[0012] U.S. Patent Application Publication 2014 / 0284269 discloses a method for casting PBI films. This method is not useful for continuous casting. Therefore, there is a need for improved and alternative methods for high-speed mass production. [Prior art documents] [Non-patent literature]

[0013] [Non-Patent Document 1] Seland F, Berning T, Boressen B, Tunold R, Improving the performance of high-temperature PEM fuel cells based on PBI electrolyte, Journal of Power Sources, 160 (2006) 27-36 [Non-Patent Document 2] Li Q, Jensen JO, Savinell RF, Bjerrum NJ, High temperature proton exchange membranes based on polybenzimidazole for fuel cells, Progress in Polymer Science, 34 (2009) 449-477 [Overview of the project]

[0014] One objective of the present invention is to provide improvements in the relevant technical field. In particular, one objective is to provide improved apparatus and methods for mass production. Another objective is to provide a method for the continuous, high-speed production of acid-doped polybenzimidazole (PBI) membranes.

[0015] These and further objectives are achieved using continuous automation methods and automated production lines for such methods, which are described in detail below.

[0016] A continuous automated method for producing acid-doped polybenzimidazole (PBI) polymer film membranes for use in fuel cells is described. As will become clear below, this method has the advantage of being fully automated with multiple sequential processing steps.

[0017] Typically, this method is controlled by a computer having corresponding measuring units functionally linked to a computer for measuring various parameters, including the production rate and temperature at various stages, and for controlling selective physical properties, including the temperature and acid concentration of the chemicals used at various processing stages, as well as other parameters indicating the purity of the chemicals used in the processing. Optionally, the replenishment and disposal or reuse of the liquids used in the processing are also computer-controlled to automatically maintain the predetermined conditions for the processing.

[0018] In this method, PBI film sheets are supplied for processing, particularly for doping with orthophosphate. Typical thickness parameters for undoped PBI film sheets for fuel cells are a film thickness dimension of 20-60 μm, and the length can be in any range depending on the requirements of the fuel cell stack design.

[0019] In principle, the doped PBI film membranes ultimately used in fuel cells can be supplied as separate sheets guided through processing steps, which appear to make production smoother, if the membrane sheets are supplied from a roll, such as a first roller, as a pseudo-endless film strip. In this case, the film strips are then gradually unfolded from the roll and guided through various processing steps by multiple additional rollers positioned accordingly.

[0020] One of the initial manufacturing steps of a membrane sheet is a washing step in which the membrane sheet is exposed to water. Typically, PBI membrane materials, when coated with a solution, contain residues of organic solvents such as N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or N-methyl-2-pyrrolidone (NMP)[2], which need to be removed from the membrane material. Clean water, such as deionized water, is effective for this process. For example, during its transport through the washing step, for example, when transported as a pseudo-endless strip, water is sprayed onto the membrane. However, a sufficiently efficient method for guiding the sheet, for example as a pseudo-endless strip, has been discovered, which involves guiding the sheet through a water bath into which it is immersed. To increase the efficiency of washing, it is possible to set up multiple water baths with progressively increasing cleanliness in the corresponding water containers for continuous washing, but it has been found that two sequentially arranged water baths are sufficient for removing solvents from the membrane sheet. It should be noted that DMAc is advantageous as a solvent for PBI compared to other solvents due to its good solubility and relatively low boiling point. See also [3, 4] in the bibliography below.

[0021] To increase the removal of DMAc, it has been found that any particular washing step is further efficient. In this optional step, which is the chemical reaction step before the membrane sheet is dried, the membrane sheet is exposed to water-diluted orthophosphoric acid having a concentration in the range of 0.01 wt% to 1 wt%. The low concentration of acid does not lead to any significant membrane doping and aids in the further removal of DMAc from the PBI membrane sheet by the chemical reaction forming acetic acid between DMAc and the diluted orthophosphoric acid. Due to the volatility of acetic acid, it easily dries the membrane, especially when the membrane is heated.

[0022] After the removal of DMAc and other impurities in the solution, the membrane sheet is subjected to a drying procedure. To accelerate this process, the membrane is conveniently dried at a high temperature above the ambient temperature in a drying device. An example is an oven or other type of heating zone where the temperature can be controlled and regulated. Optionally, the drying procedure includes two drying steps, for example, in the first and second zones of the drying device respectively.

[0023] The first step of any two-step drying is carried out at a temperature in the range 1 to 10 °C lower than the boiling point of water. For example, if the drying is carried out at standard atmospheric pressure where the boiling point of water is 100 °C, it is carried out in the first zone in the range of 90 to 99 °C. If the drying is carried out under different pressures, for example, under lower pressure conditions, the boiling point of water is correspondingly lower. Drying is carried out below the boiling point of water to evaporate water without forming water bubbles. Bubbles from water vapor in the membrane may create voids in the membrane material, which is undesirable.

[0024] The second step of any two-step drying is carried out at a temperature in the range 1 to 10 °C lower than the boiling point of DMAc, which boils at 166 °C at a standard atmospheric pressure of 100 kPa.

[0025] However, if the chemical reaction step is used after washing with water, acetic acid is produced, forming an azeotropic mixture with DMAc. In this case, the second step is conveniently performed at a temperature 1-10°C lower than the boiling point of the acetotropic mixture of acetic acid and DMAc, in order to evaporate the DMAc without foam formation. The boiling point of such an acetotropic mixture of acetic acid and DMAc is 171°C under standard atmospheric pressure.

[0026] Acetic acid itself has a standard boiling point of 116°C, and the temperature is sometimes selected between the evaporation of water and the evaporation of a DMAc or azeotropic mixture as an additional step.

[0027] The drying stage may also be provided as a drying tunnel, where the temperature in the zone gradually and smoothly increases in stages, so that the temperature of the membrane sheet, in the form of a membrane strip, rises as it is guided through the drying tunnel. Alternatively, the drying stage may comprise multiple subsequent heaters, such as ovens, having different temperatures, to provide the drying step.

[0028] As an optional step prior to the doping stage, the production line includes a pre-doping stage between the drying stage and the doping stage. In the pre-doping stage, the membrane sheet is exposed to orthophosphate at a concentration higher than 65% by weight, for example, in the range of 65–85% by weight, to dissolve the low molecular weight molecules of the PBI polymer in the membrane with orthophosphate. For example, the pre-doping stage includes a pre-doping container containing such orthophosphate to guide the membrane, for example, a strip, through the acid in the pre-doping container. By dissolving the low molecular weight molecules of the PBI polymer, the membrane polymer consists mainly of high molecular weight molecules, and the final doping stage is not contaminated with a considerable amount of such dissolved PBI. The useful temperature for the acid in the pre-doping stage is in the range of 40–80°C.

[0029] In the doping phase, a PBI membrane sheet, such as a strip, is optionally exposed to orthophosphate at a concentration higher than 85% by weight, for example, in the range of 86–99% by weight, for a period of 10 seconds to 5 minutes, or less than 5 minutes, in order to dope the membrane sheet with acid. For example, the doping phase includes a doping container containing such orthophosphate to guide the membrane, such as a strip, through the acid in the doping container.

[0030] By maintaining a high temperature, the doping time can be adjusted to a length suitable for production, such that the movement of the membrane sheet, or optionally selected strip, during the doping stage matches the transport rate of the other stages. For example, orthophosphate in the doping stage is maintained at a temperature above 75°C, e.g., in the range of 90-100°C.

[0031] During the doping phase, it was found that satisfactory doping levels could be achieved in less than 5 minutes, or even less than 1 minute, by increasing the temperature to a range of 90-100°C, such as 95-100°C, when using a 90% by weight acid concentration. In experiments at 100°C using 90% by weight orthophosphate, the required doping time was actually less than 1 minute, for example, as short as 10-30 seconds.

[0032] However, high temperatures and high doping levels are disadvantageous because they pose a risk of membrane material degradation and a corresponding decrease in tensile strength. In particular, doping levels are advantageous, cm 2 The orthophosphate content is less than 30 mg per membrane sheet, and even more conveniently, the transition from single-molecule to multi-molecule adsorption is approximately 12 mg / cm³. 2 Therefore, 10-15 mg / cm³ 2 It became clear that it was within the range.

[0033] For this reason, the combination of parameters such as acid concentration, temperature, and doping time must be carefully selected. Experiments at 100°C using 90% by weight orthophosphoric acid revealed that doping times of less than 1 minute, for example in the range of 5 to 30 seconds, were sufficient to maintain the tensile strength of the strip at the same time.

[0034] For manufacturing lines where pseudo-endless membrane strips are used, conveniently, recovery rollers are employed to recover the endless strips after doping. Such rollers are useful for transporting the doped membranes to the final fuel cell construct, where the membrane strips are cut to precise dimensions and inserted between the separator plates of the fuel cell.

[0035] As mentioned above, the manufactured membrane is useful for high-temperature polymer electrolyte membrane fuel cells (HT-PEMs), which operate at temperatures above approximately 120°C, differentiating HT-PEMs from low-temperature PEM fuel cells, the latter operating at temperatures below 100°C, e.g., 70°C. The typical operating temperature of a normal HT-PEM fuel cell is in the range of 120-200°C, e.g., 160-170°C. HT-PEM fuel cells are advantageous in that they can withstand relatively high CO concentrations, and therefore do not require a PrOx reactor between the reformer and the fuel cell stack. This is why a simple, lightweight, and inexpensive reformer can be used, which is suitable for purposes such as providing compact fuel cell systems for the automotive industry, for example, and for this purpose minimizes the overall size and weight of the system.

[0036] The present invention will be described below with reference to the drawings. [Brief explanation of the drawing]

[0037] [Figure 1] This is a schematic diagram of a continuous method for membrane doping. [Figure 2] This graph shows the adsorption isotherms of a PBI film in 85 wt% H3PO4 at various temperatures. [Figure 3]This graph shows the content of H3PO4 absorbed by the PBI membrane at 100°C for 1 minute, relative to the concentration of H3PO4. [Figure 4] This is a graph of the adsorption isotherm of a PBI film in 90% by weight H3PO4 at 100°C. [Figure 5] This graph shows the tensile strength of PBI membranes before and after doping using various processing parameters. [Modes for carrying out the invention]

[0038] The following describes a high-speed roll-to-roll method with precisely controlled production parameters for manufacturing high-quality membranes for fuel cells based on polybenzimidazole (PBI) sheet material and doped with orthophosphate (H3PO4). A production line for H3PO4-doped PBI membranes with desirable properties is presented below.

[0039] Figure 1 shows a typical production line using a roll-to-roll method, including washing and acid doping of PBI membranes.

[0040] A roll 1 of undoped pseudo-endless strips of PBI film sheet material is provided. Optionally, the PBI film is provided by casting or coating the PBI material onto a polymer film, such as a polyester film. The pseudo-endless polymer film sheet 18 is unwound from the roller 1 and placed by a guide roller 2 into a container 3 to which deionized water has been added. Typically, after coating onto the polymer film, the PBI film contains up to 20% by weight of a solvent, such as N,N-dimethylacetamide (DMAc), in the water container 3, where the majority of this solvent is removed.

[0041] Although the containers in Figure 1 are shown to be of equal size, this is usually not the case. Since the membrane strip is guided by rollers, and so that all parts of the strip move at the same speed, the length of the path through the bath in the various containers 3, 6-11 can be varied by changing the size of the individual containers, and correspondingly, the length of time required for the parts of the membrane strip to pass through the container can also be changed.

[0042] After the water container 3, the PBI film contains only a small amount of solvent, usually less than 2% by weight. The film is then easily peeled off the substrate, such as a polyester substrate, which is recovered on a film recovery roller.

[0043] A pseudo-endless membrane strip is guided via tension control rollers 5 to a second water container 6, which also contains deionized water. The water in the second container 6 is replenished continuously or periodically to maintain a low concentration of solvent in the second water container 6. The concentration of solvent removed in the first water container 3 is substantially higher than that in the second water container 6, which is why the water with a low concentration of solvent from the second water container 6 is conveniently used to replenish the water for the first water container 3. This water from the first water container 3 is then discarded into a water storage 16, which is optionally discharged or, if combined with a corresponding washing option, used for water reuse. The use of water from the second water container 6 for use in the first water container reduces the overall water consumption required in this method. For example, the replenishment process is continuous throughout this production method.

[0044] Despite the two-step cleaning of the PBI film, it may still contain some solvent residue, such as DMAc, due to the strong interaction between polar groups in the PBI and DMAc molecules (see also reference [2]).

[0045] To further remove the solvent, particularly any DMAc residue, a chemical reaction step is carried out in a low-acidity vessel 7, which contains diluted orthophosphoric acid at a concentration of less than 1% by weight in water.

[0046] The precise concentration of orthophosphoric acid in container 7 is determined by the volume of container 7 used and the volume of film rolled up through the container per specified time. In this container, a chemical reaction occurs between the solvent, particularly DMAc, and orthophosphoric acid. In the case of DMAc as the solvent, this method forms acetic acid, which is represented by the following formula, where DMAc is denoted as CH3CON(CH3)2.

[0047] 3CH3CON(CH3)2+3H2O+H3PO4→3CH3COOH+[(CH3)2NH2 + 3PO4 3-

[0048] Washing in this container 7 removes the solvent, particularly DMAc. This process is important because it prevents the products of acid hydrolysis of DMAc from entering the fuel cell stack.

[0049] Before final doping, the PBI membrane must be dried to remove all liquids other than orthophosphoric acid, particularly water, any remaining trace amounts of DMAc, and acetic acid. These have boiling points of 100, 166, and 118°C, respectively, under standard pressure. See also reference [5]. Other reaction products must also be removed. EP1551522, as in U.S. Patent Application Publication 2004 / 000470, points out that acetic acid forms an azeotropic mixture with DMAc that boils at 171°C.

[0050] Conveniently, to obtain proper drying results, two-zone ovens 8 and 9 are used, with the first zone maintained at approximately 100°C to remove water, and the second zone maintained at approximately 171°C to remove the acetic acid-DMAc mixture.

[0051] To avoid bubbles caused by the boiling of this liquid, which could create voids in the film, the temperature in the first container is maintained just below 100°C, for example, in the range of 90-98°C, and in the second zone, it is maintained just below 171°C, for example, in the range of 160-170°C. For example, in a multi-zone drying tunnel, evaporation of various liquids can be achieved without bubble formation by gradually raising the temperature.

[0052] After drying, the dried PBI film is moved through two subsequent containers 10 and 11 containing concentrated orthophosphate. The concentration in the first acid container 10 is over 65% by weight, but does not need to be as high as that in the second acid container, as the second container is used for final doping of the film. The first acid container 10 is maintained at a high temperature in the range of 40-80°C.

[0053] The role of the first acid container 10 is described below. Typically, PBI has a certain distribution of polymer molecular weights, and therefore both low and high molecular weight polymers are present. Low molecular weight PBI polymers dissolve at least partially in heat-concentrated orthophosphoric acid. To optimize the doping process, two containers 10 and 11 are used, in which the dissolution of low molecular weight PBI polymers occurs mainly or completely in the first container 10, thereby resulting in an acid concentration lower than the desired acid concentration in the second container 11 during the dissolution process. Since mainly low molecular weight polymers are removed from the first container, the film upon entering the second container 11 contains mainly higher molecular weight polymers. Thus, in the second container 11, the acid is maintained at a higher concentration because the degree of contamination is lower due to the dissolution of polymer residues. Higher concentrations are advantageous for doping, as will be described in more detail below.

[0054] Overall, the use of the cascade system of containers 10 and 11 helps in the regeneration of the optimized doping solution.

[0055] After doping the PBI membrane with orthophosphate in the doping container 11, the acid droplets of H3PO4-PBI on the membrane are removed by a sponge-covered roller 12, and the doped membrane is rolled up onto a roller 13.

[0056] The concentrations of DMAc and acetic acid in the water container 3 and the chemical reaction vessel 7 must be controlled to avoid excessive contamination of the working solution. If necessary, the liquids are removed into waste containers 16 and 17.

[0057] It is important to control the concentration of orthophosphate in the chemical reaction vessel 7 for membrane cleaning, in the pre-doping vessel 10 for reducing low molecular weight polymers, and in the doping vessel 11 for carrying out the overall complex doping treatment. Accordingly, a first replenishment vessel 14 containing deionized water and a second vessel 15 containing 99% by weight of H3PO4 are used to adjust the liquids in the various corresponding vessels for treatment to predetermined concentration levels.

[0058] Water containing DMAc as an impurity, and orthophosphate contaminated with the hydrolysis products of DMAc, are collected in waste containers 16 and 17, respectively, for further reuse.

[0059] Returning to the doping process and its mechanism, it should be noted that the doping of PBI with orthophosphate occurs via Coulomb forces through repeating units of a single polymer containing two acid molecules. Further acid accumulation within the PBI membrane occurs via hydrogen bonding. See also reference [2]. To achieve an optimized, consistent doping level and to prevent the membrane from losing its tensile strength, processing parameters such as time, temperature, and concentration of orthophosphate must be carefully considered. This will be discussed in more detail below with reference to experimental results.

[0060] Figure 2 shows the adsorption isotherms of the PBI membrane at 50 °C, 75 °C, and 100 °C in 85 wt% H3PO4. When doped in an 85 wt% orthophosphoric acid solution, a doping time of at least 2 hours is required at 50 °C to reach the plateau region of the orthophosphoric acid content. To reach the plateau region, a shortened doping time of 30 minutes is required at 75 °C, while at 100 °C, less than 5 minutes can be used. For high-speed production methods, short doping times are extremely advantageous.

[0061] To further shorten the doping time, it is advantageous for the concentration of orthophosphoric acid to be higher than 85 wt%.

[0062] Figure 3 shows the amount of orthophosphoric acid adsorbed by the PBI membrane when doped with various concentrations of H3PO4 in the range of 65 - 90 wt% at 100 °C. Note that the treatment time is fixed here at 1 minute.

[0063] According to Figure 3, the doping level increases exponentially and exceeds the maximum adsorption amount in Figure 1, about 11.5 mg / cm 2 The large increase is due to the change in mechanism from monolayer adsorption to multilayer adsorption. In the multilayer adsorption mode, the PBI membrane film becomes gel-like. A significant gel formation effect was observed at a doping level of about 30 mg / cm 2 At higher levels, the membrane dissolves in orthophosphoric acid.

[0064] Experimentally, the use of orthophosphoric acid at concentrations above 85 wt%, particularly 90 wt%, enabled a shortening of the doping time to up to 10 seconds.

[0065] Referring to Figure 4, which shows the adsorption isotherm of the PBI membrane in 90 wt% H3PO4 at 100 °C, the transition from the monolayer adsorption mechanism to the multilayer mechanism was clearly observed in the range of 10 - 15 mg / cm 2 An exemplary transition level of 12 mg / cm 2 is shown in Figure 4.

[0066] Therefore, when implementing such accelerated doping procedures, it must be noted that the PBI membrane still possesses sufficient tensile strength. To confirm this, highly doped PBI membranes were compared to PBI membranes doped under milder conditions, i.e., in 85 wt% H3PO4 at 50°C for 2 hours. The experimental results are shown in Figure 5.

[0067] As can be seen from Figure 5, experimentally prepared films doped at a high temperature of 100°C and with a high acid concentration of 90% by weight have at least the same tensile strength as films slowly doped at a lower temperature of 50°C and with a milder acid concentration of 85% by weight. However, this is only true when the doping time is 15 seconds or less. After 15 seconds, the tensile strength decreases, but the decrease is only gradual up to 45 seconds and is acceptable up to 1 minute.

[0068] This is consistent with Figure 4, where the transition from single-molecule to multi-molecule adsorption occurs between 12 and 18 seconds.

[0069] In conclusion, the method, through multi-stage cleaning of the membrane material and careful parameter adjustment, yields membrane doping content and tensile strength similar to that of slow doping methods, but this method has been demonstrated to be extremely suitable for mass production due to its much higher speed. In particular, the proposed high-speed doping method of PBI membranes with orthophosphate can be automated and used as part of the continuous production of fuel cells.

[0070] To summarize in comparison with some prior art, the following features can be noted: 1) Washing the PBI film in a diluted solution of orthophosphoric acid to decompose the residue in DMAc and to enable rapid and efficient drying (this differs from the disclosures in references [7, 8], in which the cast PBI film is simply washed in a non-solvent such as water and / or alcohol, which is why in these cases drying is required for a long time, e.g., 12 hours at 80°C (see reference [6]) to remove the DMAc bound to the PBI); 2) Use of a two-zone oven to remove various liquid components with different boiling points from the PBI film and to avoid foam formation within it; 3) In order to maintain its mechanical properties after doping, the processing parameters are strictly controlled, for example, to maintain adsorption in a monomolecular state in 90% by weight of H3PO4 at 100°C for less than 1 minute, for example, for 10-15 seconds (this differs from the disclosure in references [10-14], in which the PBI membrane is doped in a more diluted orthophosphoric acid solution at a lower temperature, which takes several hours and is therefore unsuitable for high-speed mass production).

[0071] References [1]Seland F,Berning T,Boressen B,Tunold R.Improving the performance of high-temperature PEM fuel cells based on PBI electrolyte.Journal of Power Sources,160(2006)27-36 [2] Li Q, Jensen JO, Savinell RF, Bjerrum NJ. High temperature proton exchange membranes based on polybenzimidazole for fuel cells. Progress in Polymer Science, 34 (2009) 449-477 [3] Li X, Qian G, Chen [4]Pu H,Wang L,Pan H,Wan D.Synthesis and characterization of fluorine-containing polybenzimidazole for proton conducting membranes in fuel cells.Journal of Polymer Science,48(2010)2115-2122 [5]Solvent Boiling Points Chart:https: / / www.brandtech.com / solventboilingpointschart / [6]Shen CH,Jheng LC,Hsu SLC,Wang JTW.Phosphoric acid-doped cross-linked porous polybenzimidazole membranes for proton exchange membrane fuel cells.Journal of Materials Chemistry,21(2011)156660-156665 [7]Oono Y,Sounai A,Hori M.Influence of the phosphoric acid-doping level in polybenzimidazole membrane on the cell performance of high-temperature proton exchange membrane fuel cells.Journal of Power Sources,189(2009)943-949 [8]Krishnan NN,Joseph D,Duong NMH,Konovalova A,Jang JH,Kim HJ,Nam SW,Henkensmeier D.Phosphoric acid doped crosslinked polybenzimidazole(PBI-OO)blend membranes for high temperatures polymer electrolyte fuel cells.Journal of Membrane Science,544(2017)416-424 [9]Kurungot S,Illathvarappil R,Bhange N,Unni SM.Process for the preparation PBI based electrode assembly(MEA)with improved fuel cell performance and stability.Patent US10,361,446B2,filed 09.12.2004

[10] Perry KA,More KL,Payzant EA,Meisner RA,Sumpter BG,Benicewicz BC.A comparative study of phosphoric acid-doped m-PBI membranes.Polymer Physics,52(2014)26-35

Claims

1. A continuous automated method for producing an acid-doped polybenzimidazole, PBI polymer film sheet (18) for use in fuel cells, comprising the following steps of automation: - Prepare a PBI film sheet (18) for processing; - In the washing steps (3, 6), expose the film sheet (18) to water in order to remove the solvent, for example, N,N-dimethylacetamide (DMAc), from the film sheet (18) with water; - In the drying procedure, the film sheet (18) is dried at a temperature exceeding the ambient temperature; - In the doping step (11), in order to dope the membrane sheet with orthophosphate, after the drying procedure, the membrane sheet is exposed to orthophosphate at a concentration higher than 85% by weight.

2. The method according to claim 1, wherein the method comprises supplying the orthophosphate at a temperature in the range of 90 to 100°C in the doping step (11).

3. The method according to claim 1 or 2, wherein the method includes doping for a period of 10 seconds to 5 minutes in the doping step (11).

4. The method according to any one of claims 1 to 3, wherein the method comprises supplying the membrane sheet (18) from a roll (1) as an endless strip, and the endless strip moving continuously on a roller (2) through the washing steps (3, 6), the drying step, and the doping step (11).

5. The method according to claim 1, wherein the method comprises providing the orthophosphoric acid at a temperature in the range of 90 to 100°C in the doping step (11), the method comprises performing doping in the range of 10 seconds to 5 minutes, or 10 seconds to less than 5 minutes in the doping step (11), and the method comprises providing the membrane sheet (18) from a roll (1) as an endless strip, and continuously moving the endless strip on a roller (2) through the washing steps (3, 6), the drying step, and the doping step (11).

6. The method according to any one of claims 1 to 5, wherein the drying procedure comprises two drying steps (8, 9), the first drying step (8) being carried out at a temperature in the range of 1 to 10°C below the boiling point of water, for example, in the range of 90 to 99°C at atmospheric pressure, in order to evaporate water without foam formation, and the second drying step (9) being carried out at a temperature in the range of 1 to 10°C below the boiling point of DMAc, or in the range of 1 to 10°C below the boiling point of an azeotrope of acetic acid and DMAc, in order to evaporate DMAc without foam formation.

7. The method according to any one of claims 1 to 6, wherein the method comprises, in a chemical reaction step (7) between the washing steps (3, 6) and the drying steps (8, 9), exposing the film sheet (18) to aqueously diluted orthophosphoric acid having a concentration in the range of 0.01% to 1% by weight, in order to further remove DMAc from the PBI film by forming acetic acid in the reaction of DMAc with diluted orthophosphoric acid.

8. The method according to any one of claims 1 to 7, wherein the method comprises, in the pre-doping step (10), between the drying steps (8, 9) and the doping step (11), exposing the membrane sheet to orthophosphoric acid at a concentration higher than 65% by weight but lower than the concentration in the doping step (11), thereby dissolving the low molecular weight molecules of the PBI polymer of the membrane with the orthophosphoric acid.

9. The method according to any one of claims 1 to 8, wherein the method comprises providing the washing step (3, 6) and the doping step (11) as liquid baths in separate containers (3, 6, 11), and immersing the membrane sheet (18) in the liquid.

10. An automated production line for a continuous automation method according to any one of claims 1 to 9, - Sheet receiving roller (2) that receives the PBI polymer film membrane sheet (18); - Washing (3, 6) to expose the membrane sheet (18) to water and remove the solvent, for example, N,N-dimethylacetamide (DMAc), from the membrane sheet (18) with water; - Drying apparatus (8, 9) for drying the film sheet (18) at a temperature exceeding the ambient temperature; - In order to dope the membrane sheet (18) with the acid, after the drying steps (8, 9), a doping container (11) is provided for exposing the PBI membrane sheet (18) to orthophosphoric acid at a concentration of 85% by weight or higher. A production line, including the production line.

11. The production line according to claim 10, wherein the sheet receiving roller is configured to receive the sheet (18) from the roll (1) as an endless strip, the production line includes the rollers (2, 5) for moving the endless strip over the rollers (2, 5) and through the washing (3, 6), the drying equipment (8, 9), and the doping container (11), and the automated production line for the continuous automated method is configured to supply orthophosphoric acid in the doping container at a temperature in the range of 90 to 100°C, and to perform doping in the doping container for a range of 10 seconds to 5 minutes or 10 seconds to less than 5 minutes.

12. A production line according to claim 10 or 11, comprising a first roll (1) for receiving a pseudo-endless strip of a PBI film sheet (18), and a plurality of correspondingly positioned additional rollers (2, 5) for unfolding the strip from the first roll (1) and simultaneously guiding the strip sequentially onto additional rollers (2, 5) through the various manufacturing steps described below: - The water containers (3, 6) containing water are used as part of a washing step to wash the strip through the water in one or more water containers (3, 6); A chemical reaction vessel including a dilution acid container (7) containing water-diluted orthophosphate having an orthophosphate concentration in the range of 0.01% to 1% by weight, for removing further DMA from the PBI membrane sheet by guiding the strip through the dilution acid in the dilution acid container (7) after the washing step, thereby forming acetic acid through a chemical reaction between DMA and water-diluted orthophosphate.

13. A production line according to any one of claims 10 to 12, comprising a first zone (8) and a second zone (9) of a drying apparatus having two corresponding drying steps for drying the strip and simultaneously guiding it through a first zone and then through a second zone, wherein the first zone is programmed to provide a drying temperature in the range of 1 to 10°C below the boiling point of water, for example, in the range of 90 to 99°C at atmospheric pressure, in order to evaporate water without foam formation in the first drying step, and the second zone is programmed to provide a temperature in the range of 1 to 10°C below the boiling point of DMAc, or in the range of 1 to 10°C below the boiling point of an azeotrope of acetic acid and DMAc, in order to evaporate DMAc without foam formation in the second drying step.

14. The pre-doping container (10) is used as part of the pre-doping step between the drying steps (8, 9) and the doping step (11), by guiding the strip through the acid in the pre-doping container (10) to dissolve the low molecular weight molecules of the PBI polymer of the film with orthophosphate, using orthophosphate at a concentration higher than 65% by weight, and - Doping the membrane sheet with the acid by guiding the strip through the acid in the doping container (11) after the pre-doping step, using orthophosphoric acid at a concentration higher than 85% by weight as part of the doping step, A production line according to any one of claims 10 to 13, including the production line according to any one of claims 10 to 13.

15. A production line according to claim 10 or 11, comprising a first roll (1) for receiving a pseudo-endless strip of a PBI film sheet (18), and a plurality of correspondingly positioned additional rollers (2, 5) for unfolding the strip from the first roll (1) and simultaneously guiding the strip sequentially onto additional rollers (2, 5) through the various manufacturing steps described below: - The water containers (3, 6) containing water as part of the washing step for washing the strip through the water in the water containers (3, 6); A chemical reaction vessel comprising a dilution acid container (7) containing water-diluted orthophosphate having an orthophosphate concentration in the water range of 0.01% to 1% by weight, in order to remove further DMAc from the PBI membrane sheet by guiding the strip through the dilution acid in the dilution acid container (7) to form acetic acid through a chemical reaction between DMAc and water-diluted orthophosphate; - A first zone (8) and a second zone (9) of a drying apparatus having two corresponding drying steps for drying the strip and simultaneously guiding it through a first zone and then through a second zone, wherein the first zone is programmed to provide a drying temperature in the range of 1 to 10°C below the boiling point of water, for example, in the range of 90 to 99°C at atmospheric pressure, in order to evaporate water without foam formation in the first drying step, and the second zone is programmed to provide a temperature in the range of 1 to 10°C below the boiling point of DMAc, or in the range of 1 to 10°C below the boiling point of an azeotropic mixture of acetic acid and DMAc, in order to evaporate DMAc without foam formation in the second drying step; - A pre-doping container (10) as part of a pre-doping step using orthophosphate at a concentration higher than 65% by weight to dissolve the low molecular weight molecules of the PBI polymer of the film by guiding the strip through the acid in the pre-doping container (10); - Doping container (11) as part of a doping step using orthophosphoric acid at a concentration higher than 85% by weight to dope the membrane sheet with the acid by guiding the strip through the acid in the doping container (11); - A recovery roller (13) for recovering the endless strip (18) after doping.

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