Method for recovering ionomer and catalyst material from a catalyst material-ionomer mixture

Abstract

A method for recovering ionomer and catalyst material from a catalyst material-ionomer mixture comprises the following steps: dispersing the catalyst material-ionomer mixture in a solvent to obtain a mixture of a catalyst material dispersion and an ionomer solution; adding counterions to the mixture of the catalyst material dispersion and the ionomer solution to improve dissolution of the ionomer; and separating the catalyst material dispersion from the ionomer solution.

Description

[0001] 120201 P1348PC

[0002] METHOD FOR RECOVERING IONOMER AND CATALYST MATERIAL FROM A CATALYST MATERIAL-IONOMER MIXTURE

[0003] The present invention relates to a method for recovering ionomer and catalyst material from a catalyst material-ionomer mixture, and to the use of a catalyst material and / or ionomer isolated by the method for manufacturing a membrane electrode assembly for a fuel cell. The present invention relates in particular to a method for recovering ionomer and catalyst material (especially carbon-supported platinum, Pt / C) from electrode material that is lost during the manufacturing process of a membrane electrode assembly (MEA) for use in a fuel cell.

[0004] US Patent 8,124,261 B2 discloses a process for recovering the ionomer of a polymer electrolyte membrane (PEM) and the catalyst materials from a membrane electrode assembly (MEA). In this process, fragments of an MEA are first dispersed in an alcohol / water mixture, using specific alcohols such as n-butanol and sec-butanol. The fragments are then sieved. The remaining ionomer / catalyst material / solvent dispersion is then separated into a catalyst material-containing fraction and an ionomer-containing fraction using known filtration techniques. The solvent is recovered. The filtered-off catalyst material is also recovered, for example, by burning the filter and the carbon particles in air. However, this process alters the catalyst material, preventing its direct reuse. The ionomer is also recovered by ultrafiltration.

[0005] However, there is currently no way to separate raw materials used in fuel cell systems or electrolysis cells without damaging them. 120201 P1348PC

[0006] The raw material yield in the production of a MEA or CCM (catalyst-coated membrane) depends on the individual manufacturing steps. The steps of producing a catalyst dispersion (mixing), applying this dispersion to a carrier film (coating), pressing electrodes onto a membrane and simultaneously removing the carrier film (transfer process), and other possible steps (cutting, punching, etc.) each have a material utilization rate of 90–99.9% according to current technology. The overall process is therefore estimated at approximately 95%, meaning that 5% of the materials used cannot be utilized in the product. These materials are a cost driver for fuel cells and electrolyzers, and their recycling is currently inefficient and potentially environmentally harmful.

[0007] One object of the present invention is to improve a method for recovering ionomer and catalyst material from a catalyst material-ionomer mixture.

[0008] This problem is solved by the features of the independent patent claim. Further preferred embodiments of the invention are the subject of the dependent patent claims.

[0009] According to a first aspect of the present invention, a process for recovering ionomer and catalyst material from a catalyst material-ionomer mixture comprises the following steps:

[0010] Dispersing the catalyst material-ionomer mixture in a solvent to obtain a mixture of a catalyst material dispersion and an ionomer solution;

[0011] Addition of counterions, in some embodiments the addition of an alkaline salt, to the mixture to improve the dissolution of the ionomer; and

[0012] Separation of the catalyst material dispersion from the ionomer solution. 120201 P1348PC

[0013] This eliminates the need, in some designs, to dissolve a precious metal contained in the catalyst material, which in some designs is or contains a catalytically active material. Furthermore, this allows for the separation of raw materials from the catalyst material-ionomer mixture, such as ink, offcuts, or similar components, directly within the catalyst dispersions and electrodes. This significantly reduces production losses, leads to a competitive financial advantage, and also protects the environment, as no fluorine is produced, unlike during the combustion of polymers.If aged material, which has been physically altered, for example, by thousands of hours of use in fuel cells, is used, this material can be processed more easily using the inventive method than pure metal obtained by combustion or by electrochemical / electrochemical processes.

[0014] Furthermore, in some embodiments, this allows the original state of the materials in the catalyst material-ionomer mixture to be maintained or restored without burning organic materials or dissolving the precious metals through the use of acids, potentials, or similar agents. The solvents used, and optionally alkali salts or bases which may contain the counterions, can be purified in a batch process for reuse in the process according to the invention, thus creating a closed, energy-efficient cycle. In some embodiments, this can lead to cost savings and also represent an environmentally friendly way to avoid carbon dioxide and fluorine emissions, such as those produced during the combustion of fluoropolymers.

[0015] The catalyst material-ionomer mixture can be supplied wet or dry before dispersion. 120201 P1348PC

[0016] In some designs, when the catalyst material-ionomer mixture is dispersed in the solvent, the ionomer component can be completely dissolved (from the catalyst material).

[0017] In some designs, the catalyst material-ionomer mixture and the solvent are stirred during dispersion.

[0018] An ionomer is a polymer consisting of a neutral backbone with ionized groups (side chains) repeatedly bonded to the backbone, giving the polymer a certain ionic character. Typically, no more than 15 mol% of the molecule is ionized. If a higher percentage of the molecule is ionized, the polymer belongs to a different class of material (polyelectrolyte).

[0019] In some formulations, adding counterions in the dissolved state of the ionomer can eliminate its ionic character, thereby also eliminating its attraction to the catalyst material particles. This allows the catalyst material and ionomer components of the catalyst-ionomer mixture to be separated. The elimination of the ionomer's attraction to the catalyst material particles can be deduced, for example, when using NaOH as an alkaline salt, from the experimentally observed viscosity of the ionomer dissolved in NaOH approaching zero, since viscosity is a known result of the cross-linking of (ionic) polymers.

[0020] Any terms used herein, such as "comprises," "includes," "includes," "has," "with," or any other variant thereof, are intended to cover non-exclusive inclusion. For example, a method or apparatus that includes or has a list of elements is not necessarily limited to those elements but may include other elements not expressly listed or inherent in such method or apparatus. 120201 P1348PC

[0021] Furthermore, unless explicitly stated otherwise, "or" refers to an inclusive or and not an exclusive "or". For example, a condition A or B is satisfied by any of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present). The terms "a" or "an" as used here are defined as "one or more". The terms "another" and "another", as well as any other variant thereof, are to be understood as "at least one more". The term "plural" as used here is to be understood as "two or more".

[0022] The terms "configured" or "set up" to perform a specific function (and their respective variations) are understood within the meaning of the invention to mean that the corresponding device or apparatus already exists in a configuration or setting in which it can perform the function, or at least that it is adjustable—i.e., configurable—so that it can perform the function after appropriate adjustment. Configuration can be achieved, for example, by adjusting parameters of a process sequence or by using switches or similar devices to activate or deactivate functionalities or settings. In particular, the device or apparatus can have several predetermined configurations or operating modes, so that configuration can be carried out by selecting one of these configurations or operating modes.Preferred embodiments of the invention and their further developments are described below, which, unless expressly excluded, can be combined with each other as desired and with the second aspect of the invention described below.

[0023] In some formulations, the solvent contains water or is water, whereby after the addition of the counterions the mixture of the catalyst material- 120201 P1348PC

[0024] The dispersion and the ionomer solution with the counterions is heated to a temperature in the range of 180 °C to 220 °C, in some versions 200 °C, (and held at this temperature for a predetermined period of time).

[0025] In some formulations, the solvent contains water and a water-soluble alcohol, in others te / t-butanol. After the counterions are added, the mixture of the catalyst material dispersion and the ionomer solution containing the counterions is heated to a temperature in the range of 70 °C to 110 °C, or 90 °C in some formulations. This heating or holding of the mixture at this temperature can be carried out, for example, for a period of three hours.

[0026] The addition of water-soluble alcohol allows the process to be carried out at lower temperatures in some variations. Since the alcohol is partially hydrophilic, it dissolves in water. Furthermore, due to its alkyl groups, the alcohol also exhibits hydrophobic properties.

[0027] The version that does not contain alcohol in the solvent can be environmentally friendly in that no alcohol is required. Conversely, the version that does contain alcohol in the solvent can be environmentally friendly in that less energy is needed for heating.

[0028] In some formulations, the solvent contains esters, ethers, alkylamines, alkylimines, or aziridines, or a mixture of two or more of the aforementioned solvents. This allows the partially hydrophobic / hydrophilic ionomer to be dissolved at lower temperatures than when water is used as the solvent.

[0029] In some versions, the addition of counterions involves the addition of an alkaline salt, where the alkaline salt is NaOH, NaCl, KCl, NaNH2, KNO3, CsCl, 120201 P1348PC

[0030] may contain CaCl2 or a mixture of two or more of the aforementioned alkaline salts.

[0031] In some formulations, the ionomer is an ionic polymer of perfluorosulfonic acid (PFSA ionomer) or contains a hydrocarbon skeleton with hydrocarbon side chains carrying sulfonic acid groups (hydrocarbon ionomer).

[0032] In this case, the framework consists in particular of a PTFE (polytetrafluoroethylene, “Teflon”) framework with PTFE side chains that terminate with a sulfonic acid group.

[0033] There are several types of PFSA ionomers that differ from other PFSA ionomers in their side chain length, side chain repetition, side chain type, and PTFE backbone variation, and which can also be used as ionomers in the process according to the invention. Examples include Nation (registered trademark), Aquivion (registered trademark), 3M (registered trademark), and HOPI (registered trademark), which are available in various types based on the repetition of their side chain length (measured by equivalent weight).

[0034] In some versions, the catalyst material contains platinum supported on carbon (Pt / C) or a platinum alloy.

[0035] In this process, indium oxide and / or ruthenium oxide and / or nickel and / or rhodium and / or another catalytically active metal may be added to the platinum supported on carbon.

[0036] Furthermore, instead of carbon, a different carrier material, such as aluminium oxide, can be used.

[0037] In some designs, the catalyst material dispersion is separated from the ionomer solution by filtration. A filter for filtering out particles (of the catalyst material) larger than 0.2 pm can be used for this purpose. 120201 P1348PC

[0038] This allows for the creation of a ionomer solution and a catalyst material dispersion that are separated from each other.

[0039] Alternatively or additionally, the separation of the catalyst material dispersion or the separation of the catalyst material can also be carried out using an electric and / or magnetic field, particularly in a case where the catalyst material contains magnetic components.

[0040] In some designs, the catalyst material-ionomer mixture is lost during the execution of a process for manufacturing a membrane electrode assembly for use in a fuel cell (and is removed from the process flow).

[0041] In some configurations, the catalyst material-ionomer mixture can fall off during the production of a catalyst dispersion, during the application of the catalyst dispersion to a support film, during the pressing of electrodes onto a membrane and simultaneous removal of the support film, or during the cutting of the coated membrane.

[0042] In some embodiments, the process also includes isolating the catalyst material from the catalyst material dispersion and isolating the ionomer from the ionomer solution.

[0043] In some formulations, isolating the catalyst material involves removing the solvent, for example, by drying the separated catalyst material dispersion, in some formulations to obtain a catalyst material powder. This drying can be carried out, for example, at a temperature of 50 °C. In some formulations, isolating the ionomer involves removing the solvent, for example, by evaporation, in some formulations using a rotary evaporator, or by freeze-drying. 120201 P1348PC

[0044] In some embodiments, the process also involves a reactivation of the ionomer in the ionomer solution, in some embodiments using sulfuric acid, before isolating the ionomer, in some embodiments to convert it back into its expellee form.

[0045] A second aspect of the present invention relates to the use of a catalyst material and / or ionomer isolated according to a method described above for the production of a membrane electrode assembly for a fuel cell.

[0046] The features and advantages described in relation to the first aspect of the invention and its advantageous embodiment also apply, at least where technically meaningful, to the second aspect of the invention and its advantageous embodiments, and vice versa.

[0047] Further advantageous developments result from the following description of preferred embodiments. This is shown, in part schematically:

[0048] Fig. 1 is a flowchart illustrating a process for recovering ionomer and catalyst material from a catalyst material-ionomer mixture according to one embodiment, and

[0049] Fig. 2 is a representation illustrating various steps of the process for recovering ionomer and catalyst material from a catalyst material-ionomer mixture according to one embodiment.

[0050] Fig. 1 shows a flowchart to illustrate a process for recovering ionomer and catalyst material from a catalyst material-ionomer mixture according to one embodiment of the invention.

[0051] The catalyst material-ionomer mixture 10, 20 illustrated in Fig. 2 preferably falls during the execution of a process for the production of a membrane electrode assembly for use in a fuel cell (i.e., in-line) as 120201 P1348PC

[0052] loss occurs (and is removed from the process flow), particularly during the production of a catalyst dispersion, during the application of the catalyst dispersion to a carrier film, during the pressing of electrodes onto a membrane and simultaneous removal of the carrier film, or during the cutting of the coated membrane.

[0053] With reference to Fig. 1, in step S10 of the process, the catalyst material-ionomer mixture 10, 20 is dispersed in a solvent 40 to obtain a mixture of a catalyst material dispersion and an ionomer solution.

[0054] In this process, the catalyst material-ionomer mixture 10, 20 can be dispersed for 30 min in an fe / t-butanol-water mixture under stirring, and the amount of solvent can correspond to approximately 95% of the total mass of the catalyst material-ionomer mixture 10, 20.

[0055] In section “A” of Fig. 2, the catalyst material ionomer mixture 10, 20 is illustrated in a container 30 filled with solvent 40.

[0056] The catalyst material 10 can, for example, contain platinum supported on carbon or a platinum alloy. Indium oxide and / or ruthenium oxide and / or nickel and / or rhodium may be added to the platinum supported on carbon. The catalyst material 10 may also contain other metal compounds or metal alloys.

[0057] Solvent 40 can be, for example, water or contain water. In other formulations, solvent 40 can contain water and a water-soluble alcohol, for example, te / t-butanol. In still other formulations, solvent 40 can contain esters, ethers, alkylamines, alkylimines, or aziridines, or a mixture of two or more of the aforementioned solvents.

[0058] Ionomer 20 can be an ionic polymer of perfluorosulfonic acid or an ionic ionomer having a hydrocarbon backbone with hydrocarbon side chains bearing sulfonic acid groups. 120201 P1348PC

[0059] The catalyst material-ionomer mixture 10, 20 consists of a network of ionomers 20, wherein particles of the catalyst material 10, as shown in section “A” of the Fig.

[0060] Figure 2 illustrates that the ionomers are surrounded by ionomers 20. In this state, the ionomer 20 cannot be separated by filtration because the network is too large and the ionomer 20 is attracted to the particles of the catalyst material 10.

[0061] In section “B” of Fig. 2, the catalyst material-ionomer mixture 10, 20 is shown in the container 30 filled with solvent 40 in a state of ionomer 20 completely dissolved (free from the particles of the catalyst material 10), which is achieved by dispersion. In other words, in section “B” of Fig. 2, the container 30 contains a mixture of a catalyst material dispersion and an ionomer solution.

[0062] In step S20 of the process, counterions 50, in particular an alkaline salt containing the counterions 50, are added to the mixture of the catalyst material dispersion and the ionomer solution in order to improve the dissolution of the ionomer 20 by eliminating the ionic character of the ionomer 20 through the counterions 50.

[0063] The alkaline salt can contain NaOH, NaCl, KCl, NaNFh, KNO3, CsCl, or CaCl₂, or a mixture of two or more of the aforementioned alkaline salts. The alkaline salt can be added in the form of an alkaline solution.

[0064] In this process, an amount of an alkaline solution containing the counterions 50 can be added, the ratio of which is 1:1 to the amount of ionomer 20 used.

[0065] Afterwards, the mixture of the catalyst material dispersion and the ionomer solution together with the counterions 50 or the alkaline solution, especially in a case where this contains NaOH and the solvent 40 contains water and a water-soluble alcohol, can be heated, for example, to 90 °C for 3 h.

[0066] In section “C” of Fig. 2, the state is illustrated in which the ionic character of the ionomer 20 120201 P1348PC is increased by the addition of the counterions 50.

[0067] is suspended and the particles of the catalyst material 10 and the ionomer 20 are present separately in the solvent 40 with the remaining counterions 50.

[0068] The mixture of the catalyst material dispersion and the ionomer solution with the counterions 50 can then be cooled to room temperature, for example.

[0069] If, however, no counterions 50 are added, after a certain time the state shown in the section labelled “B” of Fig. 2 returns to the undissolved state shown in the section labelled “A” of Fig. 2.

[0070] In step S30 of the process, the catalyst material dispersion is separated from the ionomer solution, in particular by means of filtration. For example, a filter can be used to filter out particles of catalyst material 10 that are larger than 0.2 pm. This allows a separate ionomer solution and catalyst material dispersion to be obtained.

[0071] In section “D” of Fig. 2, a state is illustrated in which the catalyst material 10 and the ionomer 20 are separated after filtration. In step S40 of the process, the catalyst material is isolated from the catalyst material dispersion and the ionomer 20 is isolated from the ionomer solution.

[0072] In this process, isolating the catalyst material 10 may involve removing the solvent, for example by drying, in some embodiments at a temperature of 50 °C, and isolating the ionomer 20 may involve removing the solvent, for example by evaporation, in some embodiments using a rotary evaporator, or by freeze-drying. 120201 P1348PC

[0073] Furthermore, the process can involve reactivating the ionomer 20 in the ionomer solution, for example using sulfuric acid, before isolating the ionomer 20.

[0074] The (in-line) isolated catalyst matenal 10 and / or the (in-line) isolated ionomer 20 is preferably subsequently recycled and used in the production process for manufacturing a membrane electrode assembly for a fuel cell, from which it had previously been obtained as waste.

[0075] The inventive method allows, in particular, the recycling of the catalyst material-ionomer mixture generated as waste during the production process for manufacturing the membrane electrode assembly, thereby protecting the environment. 120201 P1348PC

[0076] REFERENCE SIGN LIST

[0077] 10 catalyst material 20 ionomer

[0078] 30 containers

[0079] 40 solvents

[0080] 50 counterions

Claims

120201 P1348PC REQUIREMENTS 1. A process for recovering ionomer (20) and catalyst material (10) from a catalyst material-ionomer mixture (10, 20), comprising the steps: Dispersing the catalyst material-ionomer mixture (10, 20) in a solvent (40) to obtain a mixture of a catalyst material dispersion and an ionomer solution; Addition of counterions (50) to the mixture of the catalyst material dispersion and the ionomer solution to improve dissolution of the ionomer (20); and Separation of the catalyst material dispersion from the ionomer solution.

2. Method according to the preceding claim, wherein the solvent (40) contains water or is water and, after the addition of the counterions (50), the mixture of the catalyst material dispersion and the ionomer solution with the counterions (50) is heated to a temperature in the range of 180 °C to 220 °C.

3. The method according to claim 1, wherein the solvent (40) contains water and a water-soluble alcohol and, after the addition of the counterions (50), the mixture of the catalyst material dispersion and the ionomer solution with the counterions (50) is heated to a temperature in the range of 70 °C to 110 °C.

4. The method of claim 1, wherein the solvent (40) contains esters, ethers, alkylamines, alkylimines or aziridines or a mixture of two or more of the aforementioned solvents.

5. Method according to any of the preceding claims, wherein the addition of counterions (50) includes the addition of an alkaline salt.

6. A method according to the preceding claim, wherein the alkaline salt contains NaOH, NaCI, KCl, NaNH2, KNO3, CsCI or CaCL or a mixture of two or more of the aforementioned alkaline salts. 120201 P1348PC 7. A method according to any of the preceding claims, wherein the ionomer (20) is an ionic polymer of perfluorosulfonic acid or contains a hydrocarbon skeleton with hydrocarbon side chains having sulfonic acid groups.

8. Method according to any of the preceding claims, wherein the catalyst material (10) comprises carbon-supported platinum or a platinum alloy.

9. A method according to the preceding claim, wherein the catalyst material (10) contains platinum supported on carbon, to which indium oxide and / or ruthenium oxide and / or nickel and / or rhodium is added.

10. Method according to any of the preceding claims, wherein the separation of the catalyst material dispersion from the ionomer solution is carried out by filtration.

11. Method according to any of the preceding claims, wherein the catalyst material ionomer mixture (10, 20) is lost during the execution of a method for producing a membrane electrode assembly for use in a fuel cell.

12. Method according to the preceding claim, wherein the catalyst material ionomer mixture (10, 20) falls off during the production of a catalyst dispersion, during the application of the catalyst dispersion to a support film, during the pressing of electrodes onto a membrane and simultaneous removal of the support film, or during the cutting of the coated membrane.

13. Method according to any one of the preceding claims, further comprising isolating the catalyst material (10) from the catalyst material dispersion and isolating the ionomer (20) from the ionomer solution. 120201 P1348PC 14. Method according to the preceding claim, wherein the isolation of the catalyst material (10) comprises drying the separated catalyst material dispersion and / or the method further comprises reactivation of the ionomer (20) in the ionomer solution prior to isolating the ionomer (20).

15. Method according to the preceding claim, wherein the reactivation of the ionomer (20) is carried out using sulfuric acid.

16. Use of a catalyst material (10) and / or ionomer (20) isolated according to a method according to one of claims 13 to 15 for the production of a membrane electrode assembly for a fuel cell.

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