Catalyst paste for an electrolyzer
Patent Information
- Application Number
- PCT/EP2026/055944
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2025-03-26
- Filing Date
- 2026-03-04
- Publication Date
- 2026-10-01
Smart Images
Figure EP2026055944_01102026_PF_FP_ABST
Abstract
Description
[0001] 2024 PF00832
[0002] 1
[0003] Description
[0004] Catalyst paste for an electrolyzer
[0005] Technical field
[0006] The present invention relates to catalyst pastes for electrolyzers, membrane electrode units with such a catalyst paste, and methods for producing such a catalyst paste, in particular to provide improved flow behavior for their processing and application.
[0007] State of the art
[0008] Various technologies can be used to produce hydrogen through the electrolysis of water. One industrially established technology is polymer electrolyte membrane water electrolysis (PEMWE), also known as proton exchange membrane electrolysis. This typically uses a polymer membrane based on perfluorinated ionomers.
[0009] However, the use of fluoropolymers has proven to be disadvantageous from an environmental perspective. Furthermore, existing solutions often result in high manufacturing and energy costs, as well as technical challenges due to ongoing mechanical, thermal, and / or chemical degradation. Approaches to developing fluorine-free membrane electrode assemblies (MEAs) are currently based on the sulfonation of materials such as PEEK, PPX, or PI.
[0010] However, it was found that under electrolysis conditions, these materials exhibit, among other things, low chemical stability and significant swelling, which can even lead to water solubility due to the high ion exchange capacity necessary for sufficient ion transport. To reduce water solubility, approaches are known that involve ionic cross-linking of the molecular chains. Im2024 PF00832
[0011] 2
[0012] In contrast to the more stable covalent bonds, such cross-links, however, form unfavorable points of attack for chemical degradation.
[0013] Description of the invention
[0014] Within an electrolyzer, the conversion of substances takes place at planar catalyst electrodes with the aid of an electric current. The conversion rate is proportional to the charge flowing, so the current density is the measure of the area utilization at a predefined current intensity. Accordingly, an electrode is typically designed as a planar structure. The electrode materials can be directly laminated or coated onto the membrane, or they can be designed as gas diffusion electrodes, in which case the electrode material is typically applied in paste form.
[0015] It was recognized according to the invention that various challenges arise with regard to processability in both the production and application of such high-performance catalyst pastes. Depending on the material combination used, the paste can exhibit unfavorable rheological properties, particularly concerning flowability and shear behavior. The high viscosity of the paste, which is associated with the increased proportion of electrode materials, complicates processing, handling, and use. Such non-flowable pastes consequently pose a conveying problem in process chains, with slump-resistant pastes having to be manually transferred between machines. The low flowability of such pastes under shear thus limits their application range, rendering them unsuitable for automated processes.
[0016] Similarly, such pastes require both grinding or comminution of catalyst agglomerates and successive dispersion of fine-particulate colloids and aggregates. Conventional mixing devices and / or 2024 PF00832
[0017] 3
[0018] Crushing devices are unsuitable due to the lack of flow properties of the highly viscous pastes, meaning they can only be processed on manual three-roll mills under high mechanical stress. Furthermore, such pastes require an additional premixing process, necessitating the use of at least two machines for production. This can result in long downtimes and metal losses due to the complex cleaning processes.
[0019] According to the invention, it was further recognized that the use of electrically conductive solids, which can be present in the paste as a support material for the catalyst material, leads to structural instability. This is because catalyst material, particularly carbon-based such as carbon black, can form structures due to electrostatic interactions that strongly influence the flow and agglomeration behavior.
[0020] For example, in low-viscosity systems, unstabilized carbon black particles, due to their high specific surface energy, tend to agglomerate and settle, and cannot be uniformly dispersed or stabilized in the media using simple dispersants. Even the addition of common stabilizers such as fatty acids or fatty alcohols failed to produce sufficient film formation with electrostatic repulsion to stabilize the carbon black particles. This leads to collision agglomeration or build-up agglomeration between particles in high-speed mixing systems, resulting in large agglomerates that impair the stability of the catalyst paste.
[0021] Accordingly, there is a need to provide high-performance catalyst pastes with sufficient chemical and mechanical stability, suitable for manufacturing processes with the fastest possible 2024 PF00832
[0022] 4
[0023] suitable for throughput times and minimal machine and personnel costs.
[0024] Based on the known prior art, one object of the present invention is therefore to provide an improved catalyst paste for an electrolyzer. In particular, one object may be to provide a highly viscous or highly loaded catalyst paste with improved flow and shear behavior and sufficient stability.
[0025] This task is solved by the independent claims. Advantageous further developments result from the dependent claims, the figures, and the description.
[0026] Accordingly, a catalyst paste for an electrolyzer is proposed, comprising an organic solvent, a polymer-based binder, and particulate catalyst material. According to the invention, the catalyst paste comprises styrene-maleic anhydride (SMA).
[0027] The addition of styrene-maleic anhydride to the catalyst paste enables almost complete wetting of the exposed surface of the catalyst material in the dispersion and significantly increases the flowability of the catalyst paste, even with high solids content. The styrene-maleic anhydride thus acts as a shear thinner, improving both the homogeneous production and processing of the catalyst paste.
[0028] It was discovered that styrene-maleic anhydride copolymer undergoes instantaneous hydrolysis in water, advantageously generating functional anchor groups, namely ionically conductive carboxylic acid groups. In addition to improved rheological properties, this also enables mechanical and chemical stabilization of a compound optionally incorporated into the catalyst paste. 2024 PF00832
[0029] 5
[0030] This can be provided on an existing electrically conductive carrier material. For example, it can prevent the formation of structures when using carbon blacks such as conductive carbon blacks, thereby improving flowability. This is because it has been recognized that an interplanar nn-interaction exists between the aromatics of the styrene-maleic anhydride and the polycyclic aromatic hydrocarbons (PAHs) contained in the carbon black, which increases the interaction with the styrene-maleic anhydride on the surface. Accordingly, due to its structure, the styrene-maleic anhydride can provide very good dispersing properties for the catalyst paste.
[0031] In other words, the addition of styrene-maleic anhydride improves the stability of the catalyst paste while simultaneously providing improved flowability. This not only significantly simplifies the manufacturing process but also allows for higher web speeds and essentially automated production, without intermittent mechanical pressure being applied to the catalyst paste. Furthermore, this method enables the production of electrodes that are free of per- and polyfluoroalkyl substances (PFAS).
[0032] Furthermore, the improved rheological properties can also improve system efficiency, especially since the contact resistance of the contact structure can be reduced. In this way, a voltage saving of approximately 100 mV to 150 mV can be achieved.
[0033] Preferably, the styrene-maleic anhydride (SMA) is present in the range between 0.5 percent and 12 percent based on the weight of the catalyst. In particular, the styrene-maleic anhydride (SMA) can be used as an additive in the range between 0.5 percent and 12 percent based on the weight of the catalyst.
[0034] 6
[0035] Styrene-maleic anhydride (SMA) can be present in concentrations of 4% and 5% based on the weight of the catalyst. Alternatively, SMA can also provide the binder, in which case it is preferably present in concentrations between 5% and 12% based on the weight of the catalyst.
[0036] The percentages given here therefore correspond to weight percentages based on the catalyst content in the catalyst paste. The addition of styrene-maleic anhydride (SMA) as an additive already has a beneficial effect on the shear and flow behavior, enabling catalyst pastes to be produced and used even with high viscosity and a high solids content.
[0037] Preferably, styrene-maleic anhydride (SMA) is used as a binder. This makes it particularly advantageous to provide a catalyst paste without fluorine-containing plastisols as a binder. Thus, styrene-maleic anhydride (SMA) can serve as a replacement for conventionally used PFSA.
[0038] In this way, not only can the costs for production and disposal be significantly reduced.
[0039] Furthermore, a catalyst paste with significantly improved environmental friendliness can be provided, especially since no fluorochemicals that could be released into the environment during the manufacturing process are used. For example, no hydrogen fluoride is produced during combustion in a recycling process, thus eliminating the need for a corresponding, complex gas scrubbing procedure. Potential corrosion problems can also be significantly reduced as a result.
[0040] By eliminating the use of a fluorine-containing binder, improved temperature resistance can also be achieved compared to fluorine-based materials, 2024 PF00832
[0041] 7
[0042] This allows for higher operating temperatures and improved cell efficiencies. In tests where the catalyst paste was added to a solution containing 10 percent H2O2 by weight, long-term chemical stability was demonstrated at temperatures up to 80 °C.
[0043] As described above, the addition of styrene-maleic anhydride (SMA) also allows the catalyst paste to be produced with a high solids content. Accordingly, the solids content in the catalyst paste is preferably in the range of 10 percent to 50 percent by weight. The high percentage of
[0044] The high solids content and the associated high viscosity of the catalyst paste are made possible by the shear-thinning behavior of styrene-maleic anhydride (SMA).
[0045] In this way, an improved current density can be provided while maintaining the same surface area. Complete wetting of the catalyst material also improves the availability of the catalyst material, and in particular, of a carbon-supported catalyst such as carbon black. Experiments have shown that higher current densities of more than 2.5 A / cm² are possible. 2 could be achieved.
[0046] To prevent the styrene-maleic anhydride (SMA) from being inadvertently washed out gradually during the downstream electrolysis process, it is preferably present as a water-insoluble long chain. It has been found that this not only provides an excellent dispersing agent for carbon blacks but also allows it to function as an electrode binder. The higher molecular weight further contributes to its water insolubility. However, it was also found that the 2024 PF00832
[0047] 8
[0048] Styrene-maleic anhydride (SMA) can be instantly hydrolyzed in water, thereby forming advantageous carboxylic acid functionalities.
[0049] Alternatively or additionally, styrene-maleic anhydride (SMA) can be used as a mixture with a
[0050] Polysulfone resin is used. In this way, a resin with improved mechanical properties can be provided, while the functionalization due to the styrene-maleic anhydride (SMA) still provides sufficient ionic conductivity. The organic polymer binder styrene-maleic anhydride (SMA) is advantageously combinable with other fluorine-free organic polymers such as polysulfones (PPSU, PSU, PPS). The polysulfones can optionally also be functionalized with sulfonic acid (-RHSO3).
[0051] The solvent in the catalyst paste is organic. The solvent may preferably contain lactones, lactams, lactols, diols, or mixtures thereof. Preferably, the catalyst paste comprises a diol and / or a lactam as the solvent.
[0052] The catalyst paste particularly preferably comprises a mixture of diol and lactam, wherein these are present in a ratio of 1 : 4 and 1 : 1 , 2, preferably between 1 : 1 , 7 and 1 : 2 , 3, based on the weight percent.
[0053] Platinum and / or ruthenium are preferably used as catalyst materials for the cathode, or iridium for the anode. For example, a catalyst paste may contain platinum, ruthenium, or an alloy of platinum and ruthenium for the cathode, while iridium or iridium oxide may be used as the catalyst material for the anode.
[0054] Iridium(III) oxide, iridium(V) oxide, IrCy, or iridium black is specified. Alternatively or additionally, palladium can also be used for the cathode side. Likewise, ruthenium can also be used for the anode side, for example, in an alloy with iridium oxide. 2024 PF00832
[0055] 9
[0056] A particularly noteworthy feature is that the catalyst paste can be used for both the cathode and anode sides, with only the catalyst material being adjusted. This significantly simplifies the production of an electrolyzer.
[0057] The catalyst material is preferably combined with a carbon-based support material. As described above, the support material can be carbon black or conductive carbon black. The aforementioned preferred catalyst materials can accordingly be supported on carbon, preferably as an alloy of platinum and ruthenium or as iridium black.
[0058] According to another aspect of the invention, a membrane electrode unit for a polymer electrolyte membrane water electrolyzer is proposed, comprising a polymer-based membrane, a cathode and an anode, wherein the cathode and / or the anode is made from the catalyst paste according to the invention.
[0059] Due to the advantageous flow properties of the catalyst paste, it can be applied directly to the membrane. The binder in the catalyst paste ensures that the catalyst paste, or the catalyst material, is fixed to the membrane. Although various binders can be used, it is preferred that styrene-maleic anhydride be used as the binder, thus eliminating the need for, for example, PFSA-based binders.
[0060] The catalyst material, preferably as a carbon-supported variant, can be directly laminated or coated onto the membrane or designed as a gas diffusion electrode. Thus, the catalyst paste or 2024 PF00832
[0061] 10
[0062] The catalyst ink, with electrically conductive properties, is applied as a layer to a pre-formed, electrically conductive solid substrate using a doctor blade, spraying, or screen printing. After application of the catalyst paste, pores advantageous for water electrolysis are created in the catalyst layer by removing the solvent from the binder of the wet film layer. After drying, one or more further layers of the catalyst paste can then be applied.
[0063] to be worn.
[0064] Accordingly, the dimensions can be varied as desired, enabling efficient mass production of membrane electrode units.
[0065] Preferably, both the cathode and the anode are made from the catalyst paste, wherein the catalyst material for the cathode and the anode are different from each other. As described above, a catalyst material comprising platinum, ruthenium and / or palladium can be selected for the cathode to achieve a
[0066] to provide hydrogen evolution reaction.
[0067] Similarly, a catalyst material may be chosen for the anode which includes iridium, iridium oxide, iridium (III) oxide, iridium (V) oxide, IrO2, iridium black or an alloy of iridium-ruthenium oxide to provide an oxygen evolution reaction.
[0068] Preferably, the catalyst paste has a layer thickness between 2 µm and 20 µm, more preferably between 5 µm and 15 µm or about 10 µm. Due to the shear-thinning behavior of the styrene-maleic anhydride, the catalyst paste can be applied as a very thin layer, while still providing sufficient chemical and mechanical stability with good ionic and electronic conductivity. 2024 PF00832
[0069] 11
[0070] According to a further aspect of the present invention, a method for producing a catalyst paste according to the invention is proposed, wherein the catalyst material is present in a dispersion and is mixed with the styrene-maleic anhydride (SMA).
[0071] As described above, the addition of styrene-maleic anhydride (SMA) has a shear-thinning effect on the catalyst paste or mixture, which significantly improves the processing of the catalyst paste. Furthermore, SMA stabilizes the catalyst material, preventing the formation of agglomerates during production or the deagglomeration of broken agglomerates. In other words, the catalyst material is dispersed in a stable manner, and the flowability of the catalyst paste is simultaneously improved.
[0072] Preferably, the mixture of the catalyst material and the styrene-maleic anhydride (SMA) is milled after or during mixing. Due to its advantageous flow properties, the catalyst paste can be produced using high-speed mixing equipment. Vacuum dispersers, forced-action mixers, or rotor-stator systems are preferably used. Alternatively, planetary ball mills, roller mixers, or planetary mixers are also suitable. Depending on the agglomerate state of the catalyst material or the carbon-supported catalyst material, a roller mixer for simultaneous comminution or a bead mill for subsequent comminution can be used instead of an intensive mixer, for example, to comminute a catalyst powder that is already highly agglomerated.
[0073] Mixing can be carried out until a target viscosity in the range between 100 cps and 150,000 cps is reached, preferably in the range between 500 cps and 2,000 cps. 2024 PF00832
[0074] 12
[0075] preferably at a shear rate of 100 / s and at a temperature of 25 °C. Preferably, the catalyst paste has a target viscosity of at least 500 cps, preferably about 1000 cps, at 25 °C. This target viscosity simplifies processing of the catalyst paste while still providing sufficient mechanical and chemical stability. The unit cps, centipoise, is familiar to those skilled in the art and is 0.001 Pa*s. The target viscosity ranges specified above are therefore preferably in the range of 0.1 Pa*s to 150 Pa*s, particularly in the range of 0.5 Pa*s to 2 Pa*s at a shear rate of 100 / s.
[0076] Preferably, the catalyst material is combined with a carbon-based support material and exists as a dispersion in a mixture with the solvent and the binder. In other words, the components of the catalyst paste are preferably included during the mixing process to support or enable the dispersion of the catalyst material. Styrene-maleic anhydride (SMA) is preferably used as the binder, thus eliminating the need for fluorine-based plastisols.
[0077] The solvent can be used as a binder to enable a more homogeneous dispersion. Preferably, the styrene-maleic anhydride (SMA) is present in the form of water-insoluble long chains, which are preferably mixed with polysulfone. In this way, a resin with good mechanical properties and functionalization by the styrene-maleic anhydride (SMA) can be provided.
[0078] Brief description of the characters
[0079] Preferred further embodiments of the invention are explained in more detail by the following description of the figures. Figures 2024 PF00832 show:
[0080] 13
[0081] Figure 1 shows a characteristic curve for the voltage versus current density for a reference electrode and a styrene-maleic anhydride (SMA) stabilized electrode.
[0082] Detailed description of preferred embodiments. Preferred embodiments are described below with reference to the figures. Identical, similar, or equivalent elements in the different figures are designated with identical reference symbols, and repeated descriptions of these elements are sometimes omitted to avoid redundancy.
[0083] Figure 1 shows characteristic curves for voltage (V) versus current density (A / cm²). 2The characteristic curves shown were recorded for a PEMWE cell with an active area of 25 cm², with the results shown for each cathode electrode. In this example, styrene-maleic anhydride (SMA) was used as an additive at a level of two percent based on the weight of the catalyst.
[0084] It can be seen that the electrochemical performance is not affected by the addition of styrene-maleic anhydride (SMA). In fact, the result was even a higher current density at the same potential.
[0085] Furthermore, in one example, it was found that the addition of styrene-maleic anhydride (SMA) to a carbon-supported catalyst material made of a platinum-ruthenium alloy significantly improved its stability. In a sedimentation test, the supported catalyst material remained completely dispersed even after seven days, whereas in a control sample of the same supported catalyst material with a conventional surfactant, no dispersion could be detected. 2024 PF00832
[0086] 14
[0087] Furthermore, in tests where the catalyst paste was added to a solution with 10 percent H2C>2 based on weight, permanent chemical stability was demonstrated at temperatures up to 80 °C.
[0088] The catalyst paste according to the invention has thus proven to be particularly stable during storage within a production environment. Furthermore, the electrochemical properties were not impaired or even improved by the addition of styrene-maleic anhydride (SMA), and this addition provides a catalyst paste that is largely insensitive to temperature.
[0089] Where applicable, all individual features shown in the exemplary embodiments can be combined and / or exchanged without leaving the scope of the invention.
Claims
2024 PF00832 15 Patent claims 1. Catalyst paste for an electrolyzer, comprising - an organic solvent, - a polymer-based binder, and - particulate catalyst material, characterized by the fact that the catalyst paste styrene-maleic anhydride (SMA) comprises .
2. Catalyst paste for an electrolyzer, wherein the styrene-maleic anhydride (SMA) is present in the range between 0.5 percent and 12 percent based on the weight of the catalyst.
3. Catalyst paste according to claim 1 or 2, wherein the styrene maleic anhydride (SMA) is present as an additive in the range between 0.5 percent and 4 percent based on the weight of the catalyst, or wherein the binder is the styrene maleic anhydride (SMA) and is present in the range between 5 percent and 12 percent based on the weight of the catalyst.
4. Catalyst paste according to one of the preceding claims, wherein the solids content in the catalyst paste is in the range between 10 percent and 50 percent based on the weight of the catalyst paste.
5. Catalyst paste according to one of the preceding claims, wherein the styrene maleic anhydride (SMA) is present as a water-insoluble long chain and / or wherein the styrene maleic anhydride (SMA) is present as a mixture with a polysulfone resin.
6. Catalyst paste according to any one of the preceding claims, wherein the solvent comprises diol and / or lactam. 2024 PF00832 16 7. Catalyst paste according to any of the preceding claims, wherein the catalyst material comprises platinum and / or ruthenium for a cathode or iridium for an anode.
8. Catalyst paste according to one of the preceding claims, wherein the catalyst material is combined with a carbon-based support material.
9. Membrane electrode assembly for a polymer electrolyte membrane water electrolyzer, comprising a polymer-based membrane, a cathode and an anode, wherein the cathode and / or the anode is made from the catalyst paste according to any of the preceding claims.
10. Membrane electrode assembly according to claim 9, wherein the cathode and the anode are made from the catalyst paste, wherein the catalyst material for the cathode and the anode are different from each other.
11. Membrane electrode assembly according to claim 9 or 10, wherein the catalyst paste has a layer thickness between 2 µm and 20 µm, preferably between 5 µm and 15 µm or about 10 µm.
12. Method for producing a catalyst paste according to any one of claims 1 to 8, wherein the catalyst material is in a dispersion and is mixed with the styrene-maleic anhydride (SMA).
13. Method according to claim 12, wherein the mixture of the catalyst material and the styrene-maleic anhydride (SMA) is ground after or during mixing.
14. Method according to claim 12 or 13, wherein the mixing is carried out until a target viscosity in the range between 100 cps and 150,000 cps is achieved, preferably in the range between 500 cps and 2,000 cps at 25 °C and a shear rate of 100 / s. .2024 PF00832 17 15. Method according to any one of claims 12 to 14, wherein the catalyst material is combined with a carbon-based support material and is present as a dispersion in a mixture with the solvent and the binder.