Method for producing a ternary polymer blend, polymer blend, membrane, use of a membrane and electrode

Abstract

The present invention relates to a method for producing a ternary polymer blend, in particular a ternary ionomer blend, comprising the following steps: - Providing at least a partially phosphoronized starting polymer; - Providing a hydrophobic and / or fluorinated starting polymer; - Providing another, in particular sulfonated, starting polymer; - Production of a ternary polymer blend from the three starting polymers.

Description

[0001] The present invention relates to a method for producing a ternary polymer blend, in particular a ternary ionomer blend. The invention further relates to a polymer blend, in particular an ionomer blend, as well as a membrane and the use of a membrane. The invention also relates to an electrode.

[0002] As part of the energy transition, alternative methods of electricity generation are increasingly being developed. Fuel cells represent an important area in this development. These convert the chemical reaction energy of a supplied fuel and an oxidant into electrical energy. In a fuel cell, the anode is separated from the cathode by a membrane. A key function of this membrane is to prevent the diffusion of fuel from the anode to the cathode, which would result in a loss of fuel for the reaction.

[0003] Simultaneously, the membrane must possess high chemical stability with respect to both the fuels used and the reaction products to prevent membrane degradation and aging effects. These two essential characteristics—namely, the prevention of diffusion through the membrane and high chemical resistance—are crucial for the operation of such a fuel cell. Furthermore, the membrane must exhibit sufficient mechanical stability. In particular, the membrane must not be too brittle to avoid breakage.

[0004] The ionic conductivity of a membrane plays a particularly important role in its quality across different temperature ranges. Ionically conductive polymers are often highly polar and therefore brittle as membranes. To counteract this brittleness, these materials can be blended, i.e., mixed, with softer materials. However, such softer materials are often hydrophobic, so compatibility between the two blend components is not guaranteed.

[0005] Against this background, the object of the present invention is to provide an alternative method for producing polymer blends, in particular for the production of cationically conductive membranes, which can also be called cation exchange membranes. Preferably, such membranes should be ionically conductive over a wide temperature range, especially at temperatures well above 100°C.

[0006] This problem is solved in a process for producing a ternary polymer blend, in particular a ternary ionomer blend, which comprises the following steps: - Providing at least a partially phosphoronized starting polymer; - Providing a hydrophobic and / or fluorinated starting polymer; - Providing another, in particular sulfonated, starting polymer; - Production of a ternary polymer blend from the three starting polymers.

[0007] The invention is based on the idea that such polymers can be mixed to form homogeneous blend membranes. In addition to high homogeneity, polymers produced using this method preferably also exhibit favorable mechanical properties. In particular, the brittleness can be reduced by using a fluorinated starting polymer.

[0008] Simultaneously, high ionic conductivity is observed both at temperatures below 100°C and in the temperature range above 100°C. This is primarily due to the fact that phosphonic acid groups exhibit intrinsic proton conductivity and are therefore not dependent on water. Consequently, membranes made from such polymers also exhibit ionic conductivities at temperatures above 100°C.

[0009] In a further embodiment, the at least partially phosphonated starting polymer can be a phosphonated terphenyl and / or a phosphonated styrene, in particular polypentafluorostyrene (PWNx). Specifically, the degree of phosphonation of the at least partially phosphonated starting polymer can be at least 30% and / or at most 100%. The degree of phosphonation can depend on the proportions of the individual starting polymers. For example, it has been found that with a degree of phosphonation of 75% in the at least partially phosphonated starting polymer, a mass fraction of at least 40% of the hydrophobic and / or fluorinated starting polymer is required to obtain favorable mechanical properties. If the degree of phosphonation is 60%, a proportion of 30 wt% of the hydrophobic and / or fluorinated starting polymer may be sufficient to achieve favorable mechanical properties.

[0010] In a further embodiment, the hydrophobic and / or fluorinated starting polymer can be PVDF or a copolymer, in particular a block copolymer of the form PVDF-HFP. Preferably, PVDF has the following structure:

[0011] The copolymer, in particular the block copolymer, can have the form PVDF-HFP, which is preferably characterized by the following structural formula:

[0012] For example, a block copolymer PVDF-HFP with Mn = 130 kDa and Mw = 400 kDa can be used. Such block copolymers are available, for example, from Sigma Aldrich under the name poly(vinylidene fluoride-co-hexafluoropropylene) under product number 427160.

[0013] PVDF is typically produced from hydrogen fluoride and methyl chloroform. These can be synthesized to chlorodifluoroethane and further to vinylidene fluoride. Vinylidene fluoride can be converted to polyvinylidene fluoride in highly purified water under controlled pressure and temperature conditions using a catalyst.

[0014] Preferably, the additional starting polymer is sulfonated and / or has at least one sulfonic acid group in its structure. This configuration is based on the consideration that sulfonic acid groups are hydrophilic, whereas the hydrophobic and / or fluorinated starting polymer, for example PVDF, is very hydrophobic. It has been found that a sulfonated additional starting polymer results in lower proportions of PVDF or a hydrophobic and / or fluorinated starting polymer being sufficient to achieve an improvement in mechanical properties compared to the phosphonated starting polymer (e.g., PWNx). Blends of sulfonated and phosphonated polymers have shown that, in most cases, the strength of the sulfonic acid groups is greater than the acid strength of the phosphonic acid groups. This pK a-In contrast to phosphonated and sulfonated polymers, the phosphonic acid group undergoes protonation, leading to an increase in the conductivity of such a blend of these two polymers.

[0015] Preferably, the further starting polymer has the following form: R1 = H or F R4 = H or SO3H

[0016] In a specific embodiment, the further starting polymer can have the following structure:

[0017] Alternatively, the other starting polymer can have the following structure:

[0018] The phosphonated starting polymer can have a mass fraction of at least 30%, particularly at least 40%, preferably at least 45%, and / or at most 70%, particularly at most 60%, preferably at most 55%, of the polymer blend, i.e., of the total amount of the three starting polymers. The hydrophobic and / or fluorinated starting polymer can have a mass fraction of at least 5%, particularly at least 10%, and / or at most 35%, particularly at most 30%, of the polymer blend. Preferably, the other starting polymer has a mass fraction of at least 10%, particularly at least 20%, and / or at most 50%, particularly at most 30%, of the polymer blend. Such proportions, based on the total amount of the three starting polymers, result in favorable mechanical properties according to tests, with favorable conductivity also being measured.

[0019] In a further embodiment of the process according to the invention, the starting polymers can be provided as a solution, or in a solution.

[0020] Specifically, the starting polymers can each be provided separately dissolved in DMSO. The starting polymers can be provided in a solution of at least 5% and / or at most 10%. The polymer blend can then be prepared by mixing the three solutions together before the solvent evaporates. Preferably, the solvent is a dipolar aprotic solvent. The blends have been shown to exhibit surprisingly high conductivity and good mechanical stability. The typically high brittleness of the phosphonated blend components can be significantly reduced. The hydrophobic and / or fluorinated starting polymer appears to act as a plasticizing component in the ternary polymer blend. Examples of specific mixing ratios of ternary polymer blends can be found in the table below. The other starting polymer is designated as SFS in the table.. PWN75 / SFS / PVDF(m / m / m) Thickness / µm Conductivity / m5 cm -1 Water absorption / wt% 6 / 0 / 4 25 18,0 113 0 / 8 / 2 35 22,2 243 6 / 3 / 1 45 28,5 28 6 / 2 / 2 65 33,7 27 6 / 1 / 3 29 27,2 32 5 / 4 / 1 60 35,0 20 5 / 3 / 2 61 38,0 16 5 / 2 / 3 46 20,3 29 4 / 5 / 1 45 18,3 40 4 / 4 / 2 38 20,2 33 4 / 3 / 3 62 26,2 12 Nafion212 30 80 33

[0021] The first two rows of the table show binary polymer blends: one consisting of a phosphonated starting polymer and a hydrophobic and / or fluorinated starting polymer, and the second consisting of a sulfonated starting polymer and a hydrophobic and / or fluorinated starting polymer. It is evident that a ternary polymer blend, as shown in various mixing ratios in the following rows, achieves significantly higher conductivity and simultaneously significantly reduced water absorption.

[0022] The problem underlying the invention is further solved by a polymer blend, in particular an ionomer blend, produced according to a method as described above.

[0023] Furthermore, the invention provides a membrane, in particular a cation exchange membrane, made from or consisting of such a polymer blend. The invention also relates to an electrode made from or consisting of such a polymer blend.

[0024] Precise adjustment of properties is possible using an electrode made from a ternary polymer blend, particularly an ionomer blend. For example, hydrophobicity can be adjusted to improve water management.

[0025] Preferably, the membrane, electrode, or polymer blend comprises at least two microphases. Preferably, the membrane may also comprise three microphases, each consisting at least predominantly of one of the starting polymers.

[0026] In other words, such a polymer blend can possess microphase-separating properties, meaning that several different microphases are formed. The microphases can be configured such that the distance between two opposing interfaces to another microphase is, in particular, on average at least 10 nm and / or at most 1000 nm. In such a case, the phases are in the nanometer range, which is why they can also be referred to as nanophases. In other words, the polymer blend in this case forms a nanostructure, wherein the individual regions, when viewed in cross-section, preferably have extensions in one direction of less than 1000 nm and / or at least 10 nm. Particularly preferably, the extensions in one direction are, in particular, on average less than 200 nm, more preferably less than 150 nm, and more preferably less than 100 nm.Such a nanophase structure can be detected, for example, by High-Angle Angular Dark-Field Imaging (HAADF)-Scanning Transmission Electron Microscopy (STEM).

[0027] The membrane or electrode or polymer blend can have a conductivity of at least 20 mS / cm, in particular at least 25 mS / cm, preferably at least 30 mS / cm, and most preferably at least 32 mS / cm.

[0028] Furthermore, the invention relates to the use of such a membrane, in particular as a cation exchange membrane, or such an electrode in an electrochemical device. In particular, the membrane or the electrode can be used in a fuel cell and / or in a battery, in particular in a redox flow battery, and / or in an electrolyzer.

[0029] It is also conceivable, in principle, to use a system in which a first starting polymer with a high ion exchange capacity, a second starting polymer with a medium ion exchange capacity as a binder, and a third starting polymer as a plasticizer are used. PVDF or PVDF-HFP can be used as the plasticizer component. This is based on the consideration that such a polymer dissolves in the same or similar solvents as the sulfonated and phosphonate starting polymers used. It is also conceivable to use a membrane made from such a ternary polymer blend as an anion-conducting system, i.e., as an anion exchange polymer.

[0030] For further details of the invention, reference is made to the dependent claims and to the following description of an exemplary embodiment with reference to the drawing. The drawing shows: Fig.1. Structural formulas of various possible starting polymers for the production of a ternary polymer blend according to the present invention; and Fig. 2 The ternary system for the production of a polymer blend in a schematic representation.

[0031] The Fig. Figure 1 shows the structural formula of various starting polymers for the production of a ternary polymer blend. The figure on the left initially shows a partially phosphonated starting polymer, which is designated PWNx in this case. The degree of phosphonation can be at least 0.3 and / or at most 1.0. In other words, at least 30% and / or at most 100% of the repeating units can be phosphonated.

[0032] In addition, two examples of a hydrophobic and fluorinated starting polymer are shown. First, PVDF is a starting polymer that is both hydrophobic and fluorinated. Next, a block copolymer is shown, which is designated PVDF-HFP.

[0033] A method for producing PWNx is described, for example, in the paper “Protonated phosphonic acid electrodes for high power heavy-duty vehicle fuel cells”, Katie H. Lim, Albert S. Lee, Vladimir Atanasov, Jochen Kerres, Eun Joo Park, Santosh Adhikari, Sandip Maurya, Luis Delfin Manriquez, Jiyoon Jung, Cy Fujimoto, Ivana Matanovic, Jasna Jankovic, Zhendong Hu, Hongfei Jia and Yu Seung Kim, nature energy, volume 7, March 2022, 248-259.

[0034] Two preferred sulfonated starting polymers, designated SFS001 and SFS028, are presented. These can optionally be used for the preparation of a ternary polymer blend according to the present invention. The preparation of these starting polymers is described in “Preparation and characterisation of sulfonated partially fluorinated statistical poly(arylene ether sulfone)s and their blends with PBI”, Schönberger, Hein, Kerres, Solid State Ionics, 178 (2007), 547-554.

[0035] To produce the ternary polymer blend, the three starting polymers are first dissolved separately in a bipolar aprotic solvent, e.g., DMSO. These solutions can be at least 5% and / or at most 10%. The solutions are then mixed together in the desired mass ratio. To produce the membranes, the blend solutions are spread onto glass plates using a doctor blade. The blade height is adjusted so that the resulting membranes have a thickness of 40 µm before the solvent is evaporated in a convection oven at a temperature of 100 to 110°C. After solvent evaporation, the membranes are removed from the glass plate and post-treated. This post-treatment preferably begins with an acid, particularly sulfuric acid, preferably at least 1% and / or at most 20%, especially 10%, sulfuric acid.Post-treatment can then be carried out in deionized water until almost all residual solvent has been removed from the membrane. The membranes can then be dried, and the membrane thickness can be determined, for example, using a micrometer.

[0036] The Fig. Figure 2 schematically illustrates the interaction of the individual components in the polymer blend, using a blended membrane made of PWN, PVDF, and SFS as an example. The phosphonated starting polymer (PWN) ensures conductivity even at temperatures above 100°C. The hydrophobic and / or fluorinated starting polymer, here PVDF, provides favorable mechanical properties. The third, sulfonated starting polymer, referred to here as SFS, acts as a binder and simultaneously ensures good conductivity at temperatures below 100°C. The combination of these three starting polymers significantly improves the properties of the blended membrane. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited non-patent literature

[0000] Protonated phosphonic acid electrodes for high power heavy-duty vehicle fuel cells", Katie H. Lim, Albert S. Lee, Vladimir Atanasov, Jochen Kerres, Eun Joo Park, Santosh Adhikari, Sandip Maurya, Luis Delfin Manriquez, Jiyoon Jung, Cy Fujimoto, Ivana Matanovic, Jasna Jankovic, Zhendong Hu, Hongfei Jia and Yu Seung Kim, nature energy, volume 7, March 2022, 248-259

[0033] Preparation and characterisation of sulfonated partially fluorinated statistical poly(arylene ether sulfone)s and their blends with PBI“, Schönberger, Hein, Kerres, Solid State Ionics, 178 (2007), 547-554

[0034]

Claims

[1] Method for producing a ternary polymer blend, in particular a ternary ionomer blend, comprising the following steps: - Providing at least a partially phosphoronized starting polymer; - Providing a hydrophobic and / or fluorinated starting polymer; - Providing another, in particular sulfonated, starting polymer; - Production of a ternary polymer blend from the three starting polymers. [2] Method according to claim 1, characterized by that the at least partially phosphoronized starting polymer is a phosphoronized terphenyl and / or a phosphoronized styrene, in particular polypentafluorostyrene (PWN) x ). [3] Method according to claim 2, characterized by that the degree of phosphonation of the at least partially phosphonated starting polymer is at least 30% and / or at most 100%. [4] Method according to any one of the preceding claims, characterized by that the hydrophobic and / or fluorinated starting polymer is PVDF or a copolymer, in particular a block copolymer of the form PVDF-HFP. [5] Method according to any one of the preceding claims, characterized by that the further starting polymer is sulfonated. [6] Method according to any one of the preceding claims, characterized by , that the further starting polymer has the following form: where: R1 = H or F R4 = H or SO3H [7] Method according to claim 6, characterized by , that the further starting polymer has the following structure: or that the further starting polymer has the following structure: [8] Method according to any one of the preceding claims, characterized bythat the phosphonated starting polymer has a mass fraction of at least 30%, in particular at least 40%, preferably at least 45%, and / or at most 70%, in particular at most 60%, preferably at most 55%. [9] Method according to any one of the preceding claims, characterized by that the hydrophobic and / or fluorinated starting polymer has a mass fraction of at least 5%, in particular at least 10%, and / or at most 35%, in particular at most 30%, of the polymer blend. [10] Method according to any of the preceding claims, characterized by that the further starting polymer has a mass fraction of at least 10%, in particular at least 20%, and / or at most 50%, in particular at most 30%, of the polymer blend. [11] Method according to any of the preceding claims, characterized by that the starting polymers are provided as a solution or in a solution. [12] Method according to claim 11, characterized by that the starting polymers are provided dissolved in DMSO, and / or that the starting polymers are provided in a solution of at least 5% and / or at most 10%. [13] Polymer blend, in particular ionomer blend, produced by a method according to any of the preceding claims. [14] Membrane, in particular cation exchange membrane or electrode, made of or consisting of a polymer blend according to claim 13. [15] Membrane or electrode according to claim 14, characterized by that it has at least two microphases. [16] Membrane or electrode according to claim 15, characterized by , that the microphases are designed such that the distance between two opposing interfaces to another microphase is, in particular, on average at least 10 nm and / or at most 1,000 nm. [17] Membrane or electrode according to any one of claims 14 to 16, characterized by that the membrane has a conductivity of at least 20 mS / cm, in particular at least 25 mS / cm, preferably at least 30 mS / cm, most preferably at least 32 mS / cm. [18] Use of a membrane or an electrode according to any one of claims 14 to 17, in particular as a cation exchange membrane, in an electrochemical device, in particular in a fuel cell and / or in a battery and / or in an electrolyzer.

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