Partition plate for alkaline water electrolysis

Abstract

A catalyst coated separator (1) for alkaline water electrolysis comprising a porous support (100) and, in order on at least one side of the support:-an optional porous polymer layer (200),-an alkali-stable non-porous polymer layer (300), and-a catalyst layer (400).

Description

TECHNICAL FIELD

[0001] The present invention relates to a separator for alkaline water electrolysis. BACKGROUND

[0002] Today, hydrogen is used in several industrial processes, for example as a raw material in the chemical industry and as a reducing agent in the metallurgical industry. Hydrogen is an essential building block for the manufacture of methanol used in the manufacture of ammonia and thus fertilizers and many polymers. Refineries that use hydrogen to process intermediate petroleum products are another field of use. However, hydrogen production from fossil fuels leads to a large amount of CO2 emissions.

[0003] Hydrogen is also being considered as an important future energy carrier, which means that it can store and deliver energy in a usable form. Hydrogen releases energy by undergoing an exothermic combustion reaction with oxygen to form water. During such a combustion reaction, no carbon-containing greenhouse gases are emitted.

[0004] In order to achieve a low-carbon society, the use of renewable energy, such as solar and wind power, is becoming increasingly important.

[0005] Electricity production from wind and solar power systems is highly dependent on weather conditions and is therefore variable, leading to imbalances in the supply and demand of electricity. In order to store surplus electricity, so-called "power-to-gas" technologies, in which electrical energy is used to produce gaseous fuels such as hydrogen, have attracted much attention in recent years. As electricity production from renewable sources will increase, the need for storage and transport of the generated energy will also increase.

[0006] Water electrolysis is an important manufacturing method in which renewable electricity can be converted into hydrogen. Hydrogen produced in this way is often referred to as "green hydrogen", emphasizing that no greenhouse gases are formed in its production process. Ammonia and steel made with green hydrogen are also referred to as "green ammonia" and "green steel".

[0007] In an alkaline water electrolysis (AWE) cell, a porous separator is used to separate the electrodes of different polarity to prevent short-circuiting between these electrodes and to prevent the recombination of hydrogen (formed at the cathode) and oxygen (formed at the anode) by avoiding gas crossover. In addition, the separator should also exhibit a high ionic conductivity in order to transport hydroxide ions from the cathode to the anode.

[0008] The separators for AWE disclosed, for example, in EP-A 1776490 (VITO), WO2009 / 147084 and WO2009 / 147086 (AGFA-GEVAERT NV and VITO) generally comprise a porous polymer layer disposed on a porous support. Inorganic particles such as zirconium oxide are added to the polymer layer to make it hydrophilic, thereby ensuring sufficient electrolyte permeability and minimizing the adhesion of gas bubbles on the surface of the polymer layer.

[0009] In a typical AWE cell, a separator is placed between two electrodes (anode and cathode). Hydrogen is formed at the cathode as a result of the hydrogen evolution reaction (HER), while oxygen is formed at the anode as a result of the oxygen evolution reaction (OER). Catalysts are used to minimize the overpotentials of both the OER and HER. These catalysts are typically deposited on the electrodes.

[0010] However, the catalyst can also be deposited on the surface of the separator to further reduce the overpotential. Separators in which the catalyst is deposited on one or both of their surfaces are generally referred to as catalyst-coated separators or catalyst-coated films.

[0011] Bladergroen et al., “Overview of Membrane Electrode Assembly Preparation Methods for Solid Polymer Electrolyte Electrolyzer”, 2012, DOI:10.5772 / 52947, disclosed the deposition of catalysts on non-porous membranes such as proton exchange membranes (PEMs).

[0012] However, in AWE, porous separators, such as those mentioned above, are typically used. DE102020208003 (FRAUNHOFER GES) discloses a method in which a catalytically active layer is deposited on the surface of a porous ZIRFON PERL membrane from AGFA-GEVAERT NV by plasma spraying. Utility model CN219315104 (UNIV TSINGHUA) discloses an apparatus for manufacturing catalyst-coated separators, wherein the catalyst is sprayed onto both sides of a porous separator. EP-A4105359 (SIEMENS AG) discloses catalyst-coated separators for PEM, AEM, and AWE. The catalyst is deposited by vapor deposition, for example, on a ZIRFON PERL separator.

[0013] In KR2022 / 0073190 (KOREA RES INST CHEMICAL TECH), a porous separator with a cross-linked PVA layer containing a metal catalyst is provided. The role of the metal catalyst is to further reduce HTO by converting hydrogen passing through the porous membrane into water through a catalytic reaction with oxygen, however, at the cost of reduced electrochemical efficiency. The PVA layer is also applied by ultrasonic spraying.

[0014] When a catalyst is deposited on the surface of a porous membrane, some catalyst may be deposited inside the membrane pores. When the catalyst is present inside such pores, hydrogen and / or oxygen may form inside the membrane. This can lead to an increase in sheet resistivity (a decrease in ionic conductivity) and / or an increase in gas cross-linking.

[0015] Therefore, a catalyst-coated separator for AWE is needed, wherein the catalyst does not deposit inside the pores of the separator. Summary of the Invention

[0016] One object of the present invention is to provide a catalyst-coated separator for alkaline water electrolysis, wherein the catalyst deposited inside the pores of the separator is minimal and has improved gas permeability.

[0017] This objective is achieved using the partition as defined in claim 1.

[0018] Other objects of the invention will become apparent from the following description. Attached Figure Description

[0019] Figure 1 schematically illustrates several embodiments of a catalyst-coated separator according to the present invention.

[0020] Figure 2 An embodiment of the electrolytic cell according to the present invention is illustrated schematically.

[0021] Figure 3 shows the comparative catalyst-coated separator S-1, which was prepared in Example 1. Figure 3.a ) and embodiment S-2 of the catalyst-coated separator according to the present invention ( Figure 3.b SEM cross-section of ).

[0022] Figure 4 shows the surface of the existing ZIRFON partition ( Figure 4.a ) and the surface of the partition S-3 containing a non-porous layer prepared in Example 2 ( Figure 4.b SEM image (top view). Detailed Implementation

[0023] Catalyst-coated separator The partition used in this article can also be referred to as a diaphragm or membrane.

[0024] The catalyst-coated separator for alkaline water electrolysis according to the present invention comprises a porous support (100) and, sequentially on at least one side of said support: - Optional porous polymer (200) containing polymer A, - Contains a non-porous layer (300) of polymer B, and - Catalyst layer (400).

[0025] It has been observed (see Examples) that the presence of a non-porous layer (300) between the porous support (100) or the porous layer (200) containing polymer A and the catalyst layer (400) will prevent the catalyst from depositing into the pores of the porous support or the porous layer containing polymer A.

[0026] Optional porous layers containing polymer A, non-porous layers containing polymer B, and catalyst layers can be applied independently to one or both sides of the porous support. If these layers are applied to both sides of the porous support, the optional porous layers (200 and 200'), non-porous layers (300 and 300'), and catalyst layers (400 and 400') can be the same or different from each other. Figure 1 ( Figures 1.a to 1.f Different embodiments of the catalyst-coated separator according to the present invention are schematically shown in the figure.

[0027] When only one catalyst layer is set, for example Figure 1.a , Figure 1.c and Figure 1.e The implementation scheme illustrated in the figure has been observed to achieve the highest improvement in electrolysis efficiency when the catalyst layer faces the cathode in the electrolytic cell.

[0028] The catalyst-coated separator according to the present invention preferably comprises one or two porous layers containing polymer A, said porous layers being disposed on one or both sides of a porous support, more preferably two porous layers containing polymer A being disposed on both sides of the porous support.

[0029] The total thickness of the catalyst-coated separator is preferably 50 to 750 µm, more preferably 75 to 500 µm, and most preferably 100 to 250 µm. The sheet resistivity of the separator typically increases with increasing separator thickness. However, a minimum thickness is often required to ensure that the separator has sufficient mechanical / physical properties and facilitates its manufacture and handling.

[0030] The gas permeability of the catalyst-coated separator is preferably less than 3 L / min.cm. 2 More preferably less than 1.5 L / min·cm 2 The optimal value is less than 0.5 L / min·cm. 2 A concentration of less than 0.1 L / min.cm is particularly preferred. 2 Gas permeability is preferably measured at 5 bar using a Porolux™ 1000 instrument. Excessive gas permeability may lead to an increase in HTO (the volume percentage of hydrogen present in the oxygen stream formed at the anode).

[0031] The maximum ionic conductivity requires the maximum electrolyte permeation within the separator. The porosity of the catalyst-coated separator is preferably 40% to 90%, more preferably 50% to 80%, and most preferably 60% to 70%.

[0032] The presence of a non-porous layer should not lead to a substantial increase in the sheet resistivity of the separator. At 25°C in a 30% by weight KOH aqueous solution, the sheet resistivity of the catalyst-coated separator is preferably less than 0.35 ohm / cm. 2 More preferably less than 0.25 ohm.cm 2 The optimal value is less than 0.10 ohm.cm 2 The surface resistivity is preferably measured using the Inolab® Multi9310 IDS instrument, which is available from VWR (an Avantor company) and is equipped with the TetraCon 925 conductivity cell, which is available from Xylem.

[0033] According to ASTM F316 measurements, the bubble point of the catalyst-coated separator is preferably at least 5 bar, more preferably at least 6 bar, most preferably at least 7 bar, and particularly preferably at least 8 bar.

[0034] Catalyst layer The catalyst-coated separator according to the invention comprises a catalyst layer (400). This catalyst layer is coated on a non-porous layer (300) such that the two layers are in direct contact. This means that under normal operating conditions, the catalyst layer cannot separate from the layer. When the catalyst layer is applied directly to the non-porous layer, the resulting catalytic surface is likely to be more uniform and smooth compared to when the catalyst is applied to the electrode. Therefore, a “true” zero-gap structure (see below) can be obtained, eliminating any voids between the separator and the catalyst layer. Such a smooth catalyst layer surface may help prevent localized temperature and / or current hotspots in the separator upon contact with the electrode, thereby ensuring more efficient electron transfer and preventing localized film degradation.

[0035] The catalyst layer facing the anode in the electrolytic cell contains one or more catalysts for the oxygen evolution reaction (OER), while the catalyst layer facing the cathode in the electrolytic cell contains one or more catalysts for the hydrogen evolution reaction (HER).

[0036] The thickness of the catalyst layer is preferably 0.5 to 200 µm, more preferably 1 to 100 µm, most preferably 5 to 75 µm, and particularly preferably 10 to 50 µm.

[0037] The catalyst is preferably selected from Ni, Ni / NiO, Ni-Fe, Ni-Co, Ni-Mn, Ni-Mo, Fe-Co, Ni-Zn, Ni-Al, Ni-Mo-Al, Ni-Co-Al, Ni-MnAl, Ni-Si, Ni-B, or Ni-Si-B. A single catalyst or a combination of catalysts can be used. Preferred catalysts on the cathode side of the separator are selected from Ni, Raney Ni, Ni-Fe, Ni-Co, and Ni-Mo. Preferred catalysts on the anode side of the separator are selected from NiO / OH and NiO.

[0038] The catalyst-coated separator may have a catalyst layer on one or both of its surfaces. When the catalyst layer is present on only one surface, the catalyst-coated separator is preferably oriented in the electrolytic cell such that the catalyst layer faces the cathode. It has been observed that such orientation results in a greater increase in electrolysis efficiency compared to orientation in which the catalyst layer faces the anode.

[0039] Non-porous layer containing polymer B The catalyst-coated separator according to the present invention comprises a non-porous layer comprising polymer B between a porous support or a porous layer comprising polymer A and a catalyst layer.

[0040] The presence of a non-porous layer has the following advantages: - The catalyst will not deposit into the pores of the porous support or porous layer; - The gas permeability of the catalyst-coated separator is reduced; and - Due to the smoothness of the non-porous layer, the contact with the catalyst layer (or electrode) is improved.

[0041] The nonporous layer containing polymer B, described below, is nonporous in the sense that it does not possess fixed pores in the traditional sense; that is, it does not have permanent, well-defined pores or channels as in porous materials. Instead, ion transport through this nonporous layer occurs through temporary, dynamic voids or free-volume regions between the individual polymer chains. These voids are formed due to the thermal motion and packing of the polymer chains. However, their structure and size are not static (or “fixed”). The size of these dynamic voids is typically less than 5 nm, on the order of angstroms, ranging from 0.1 to 5 nm (i.e., 1–50 Å). According to the well-known solution-diffusion model, the size and chemical properties of the voids allow for selective ion transport while filtering out larger species. Therefore, although the nonporous layer containing polymer B lacks fixed pores, the small dynamic spaces between the polymer chains allow for ion transport.

[0042] Importantly, the layer containing polymer B does not have fixed pores (with a defined pore size) and is therefore non-porous. When using porous layers, regardless of pore size, catalyst permeation into the separator cannot be prevented. Even if the average pore size of the porous layer is small, catalyst permeation cannot be completely avoided. In fact, the combination of the separator's pore size distribution and the catalyst particle size distribution, coupled with catalyst coating techniques (which may involve pressure application), inevitably leads to some degree of catalyst deposition within the pores of the porous layer. However, because there are no pores, the non-porous layer containing polymer B can completely eliminate catalyst permeation into the separator.

[0043] The non-porous layer containing polymer B must be able to withstand typical AWE conditions, such as prolonged exposure to 30% by weight of KOH at 80°C. Therefore, the non-porous layer preferably contains alkali-stable polymer B, thereby making the non-porous layer and thus the separator according to the invention suitable for alkaline water electrolysis. As used herein, an alkali-stable polymer refers to a polymer whose chain length degradation or change in polymer chemical properties is minimal after exposure to 6 M KOH at 120°C for 4 weeks.

[0044] Furthermore, the non-porous layer inevitably affects the sheet resistivity / conductivity of the separator. Therefore, the hydroxide permeability of the non-porous layer under AWE conditions must be sufficient.

[0045] Furthermore, the non-porous layer preferably comprises a hydrophilic polymer B, as this enhances the solubility of KOH (and water) in the non-porous layer and thus leads to a reduction in gas permeability without adversely affecting conductivity / surface resistivity. As measured below, the contact angle of water on the surface of the non-porous layer is preferably less than 90 degrees, more preferably less than 75 degrees, and most preferably less than 60 degrees. Particularly preferred is a contact angle of 40 to 60 degrees. It has been observed that less bubble adhesion occurs on the hydrophilic non-porous layer, resulting in lower surface resistivity.

[0046] Furthermore, the non-porous layer preferably has a smooth surface to improve contact with the catalyst layer (or electrode) and surface resistivity. A smooth surface also improves the contact between the separator surface and the electrodes in the electrolytic cell. It has been observed (see examples) that the surface of the non-porous layer is indeed smoother (lower roughness) than the surface of prior art separators without such a non-porous layer.

[0047] The hydroxide permeability of non-porous layers can be tuned, in particular, by the layer thickness, the properties of polymer B, the degree of crosslinking, the type of crosslinking agent, and by blending different polymers B into the non-porous layers. This allows for the use of a wide range of polymers with different swelling properties in aqueous alkaline media.

[0048] Polymer B is preferably cross-linked to further improve its long-term stability in the highly alkaline electrolyte of the electrolyzer using the separator.

[0049] The non-porous layer may also contain other components to optimize its properties or the coating process. However, the non-porous layer of the present invention preferably contains at least 50 parts by weight, more preferably at least 75 parts by weight, and most preferably at least 90 parts by weight of polymer B to ensure that the non-porous layer has sufficient hydroxide permeability and smoothness and maintains sufficient mechanical properties.

[0050] Other components include, for example, surfactants (see below), inorganic particles (see below), viscosity modifiers (see below), and combination catalysts.

[0051] The preferred composite catalyst is selected from NiO, Pt, Ir, IrO2 and stainless steel.

[0052] The thickness of the non-porous layer is preferably 0.01 to 50 µm, more preferably 0.1 to 30 µm, and most preferably 1 to 20 µm. Even more preferably, the thickness of the porous separator is 7 to 15 µm. When the thickness of the non-porous layer exceeds 50 µm, the overall resistivity of the membrane may become too high. On the other hand, when the thickness of the non-porous layer is less than 0.01 µm, the non-porous layer may not be able to cover the entire separator surface and may not be smooth enough to improve contact with the catalyst layer.

[0053] Polymer B Polymer B may be selected from, for example, optionally modified polybenzimidazole, polysulfone, polyethersulfone, polyetherketone, polyphenylene ether, polyether, polyacetal, styrene-based polymers and copolymers, and polyolefin-based polymers and copolymers. Preferred polymers have an all-carbon polymer backbone.

[0054] Polymer B is preferably functionalized with nonionic hydrophilic groups, wherein the modification is preferably selected from hydroxylation and ethoxylation. Preferred hydrophilic segments are selected from polyhydroxy segments and polyethylene oxide segments. These segments can be part of the polymer backbone or grafted onto the polymer backbone. The hydrophilic segments can be arranged in different geometries, such as block copolymers or graft copolymers. Polyethylene glycol-based polymers or copolymers are particularly preferred, including block copolymers such as polyolefin-ethylene glycol block copolymers or graft copolymers such as polyethylene glycol grafted onto polysulfone or polyethersulfone. Polymers containing multiple hydroxyl groups are most preferred. Typical examples of polymers containing multiple hydroxyl groups include polysaccharides and vinyl alcohol-based (co)polymers. Preferred polysaccharides include dextran and pullulan and their derivatives, as well as starch derivatives. Preferred vinyl alcohol-based (co)polymers include polyvinyl alcohol, polyethylene-vinyl alcohol copolymers, and polyethylene-ethyleneamine copolymers.

[0055] Polymer B is preferably selected from polyethylene glycol or copolymers thereof, polysaccharides, polyethylene-vinyl alcohol copolymers, polyethylene-vinylamine copolymers, and polyvinyl alcohol. A particularly preferred polymer B is polyvinyl alcohol (PVA) or a polyethylene-vinyl alcohol copolymer.

[0056] PVA is typically prepared by the hydrolysis of polyvinyl acetate. The properties of PVA are determined by the degree of hydrolysis. A preferred degree of hydrolysis is 50% to 100%, more preferably 70% to 99%, and most preferably 85% to 98%. It has been observed that non-porous layers of PVA containing a high degree of hydrolysis (i.e., above 85%) are more hydrophilic and have lower solubility in water.

[0057] The molecular weight of polymer B is preferably from 10 to 250 kDa, more preferably from 15 to 150 kDa, and most preferably from 50 to 125 kDa. It has been observed that non-porous layers containing polymer B with a high molecular weight (i.e., at least 15 kDa Mw) exhibit improved uniformity. Furthermore, when Mw is below 15 kDa, sufficient chain entanglement may not exist between the polymer chains, resulting in poorer film formation and lower overall durability of the separator. While higher molecular weight polymers will result in non-porous layers with better mechanical properties, excessively high molecular weights (i.e., above 150 kDa MW) may be more difficult to process.

[0058] surfactants Non-porous layers may contain surfactants to optimize the coating process, obtain a uniform non-porous layer, and / or optimize the surface properties of the non-porous layer. Surfactants may be added to reduce static and / or dynamic surface tension, improve wetting on the separator surface, improve the smoothness of the coating layer, and avoid coating defects such as orange peel, pits / fisheyes, spots, Bernard cells, and Marangoni flow.

[0059] Suitable surfactants include, for example, modified silicone surfactants, such as silicone-polyether graft copolymers and block copolymers or trisiloxanes. Preferred silicone polyether surfactants include Tego wet240, Tego wet KL 248, Dynol 960, Dynol 980 and Tego Foamex 822 supplied by Evonik; Byk 348 and Byk 3450 supplied by Byk Chemie; Coatosil 7607 and Silwet L77 supplied by Momentive; and Hydropalat WE 3220 supplied by BASF. Silicone surfactants with high hydrolytic stability include Byk 3420 supplied by Byk Chemie and Silwet HS312 and Silwet HS313 supplied by Momentive.

[0060] Another class of surfactants that can be used are fluorosurfactants, such as Tivida FL2500 or Tivida FL2700. However, the use of fluorosurfactants is less preferred due to health and safety concerns.

[0061] Other preferred surfactants include alkoxylated surfactants, such as alkyl ethoxylates or alkoxylated block copolymers. Examples include Lutensol AP6, Lutensol A8, Pluronic PE10500, and Kauropal K933 supplied by BASF; Emulgen 109P and Akypo RLM100 supplied by Kao; and Ecosurf EH 6 supplied by Dow Chemical.

[0062] Alternatively, a mixture of silicone additives and alkoxylated surfactants, such as Kauropal K933 and Tego foamex 822, can be used.

[0063] Acetylene derivatives, such as Dynol 604, Surfynol 104, Surfynol 420, and Surfynol 465, can be used to reduce the surface tension of the coating solution. Dynol 604 is an ethoxylated surfactant based on 2,5,8,11-tetramethyldodecane-6-yne-5,8-diol. Surfynol brands are based on 2,4,7,9-tetramethyl-5-decyn-4,7-diol. Alternatively, hydrogenated Surfynol derivatives, such as Surfynol AD01, can be used.

[0064] To optimize compatibility with polyvinyl alcohol, hydroxyl-functional surfactants, such as alkyl polyglucoside surfactants, such as Glucopon 420 or Glucopon 100DK supplied by BASF; Simulsol SL 826 supplied by Seppic SA; and surfactants based on glycidyl or polyglycerol, such as PGLAL ML04 and PGLAL ML08 supplied by Daicel Europe GmbH; and AEG 102 / 61 supplied by Lamberti, can also be used. Bio-based nonionic surfactants such as HoneySurf LF supplied by Holliferm can also be used.

[0065] In addition to nonionic surfactants, ionic surfactants (i.e., anionic, cationic, or amphoteric surfactants) can also be used to improve coating quality. Precursors to ionic surfactants that become ionic at low or high pH can also be used, such as carboxylated surfactants Akypo RLM45 and Akypo RLM100, which become anionic at alkaline pH, or surfactants with tertiary amine groups that become ionic at low pH. Suitable amphoteric surfactants include, for example, Euroglyc AMS supplied by EOC Surfactants, Arkopon T Paste 8015 supplied by Clariant, and amine oxide surfactants such as Makamine LO supplied by Verdant Specialty Solutions. Suitable anionic surfactants include Aerosol OT100 and Aerosol OT75E supplied by Solvay, Exodiss SE75 supplied by EOC Surfactants, or Marlon A365 supplied by Sasol.

[0066] Some surfactants can be designed as defoamers, such as silicone-based products or alkyl ethoxylates. Such surfactants typically have a low HLB (hydrophilic-lipophilic balance) value. Examples of defoamers include Tego Foamex 3062 or Tego Foamex 884 supplied by Evonik; Airase 5355 or Supread 2059 supplied by Elementis; and AF8014 supplied by Dow Chemical.

[0067] Viscosity modifier The viscosity of polymer B can be optimized by adding so-called thickeners or rheology modifiers to the polymer B solution.

[0068] Standard rheology modifiers can be used, such as thickeners based on ASE (alkali-swellable emulsion), HASE (hydrophobically modified alkali-swellable emulsion), or HEUR (hydrophobically ethoxylated polyurethane polymer). Examples of commercially available standard rheology modifiers include Tego Visco Plus 3000, Tegovisco Plus 3010, Tafigel PUR80, ADDITOLVXW6388E, BYK-LP R 21675, Rheovis AS 1130, Rheolate 278, and Rheolate 255.

[0069] Other rheology modifiers are selected from gelatin, dextran, starch, collagen derivatives, alginate, chitosan, collodion, and other polysaccharides such as xanthan gum, gum arabic, guar gum, casein, carrageenan, pectin, albumin, and cellulose-based thickeners such as methylcellulose, CMC (carboxymethyl cellulose), HPMC (hydroxypropyl methylcellulose), and HEC (hydroxyethyl cellulose). Other preferred thickeners include polyethylene glycol, polyglycerol, glycidyl ether or EO-PO copolymers, and polyvinylpyrrolidone. Specific examples of trade names for thickeners include Kelzan S, Kelzan T, Kelzan RD, Natrosol 250HR, Tylose CR1500, Satialgine S170, Tylose H4000P, Ambergum 3031, Walocel CRT10000, Dextran 60000, Biozan S, Polygel, Kelcogel, and Rheozan.

[0070] Highly preferred rheology modifiers include high molecular weight polyvinyl alcohol, vinyl alcohol copolymers, or branched polyvinyl alcohol, such as KURARAY POVAL 105 88 KX SB or KURARAY POVAL 20088 KX SB branched PVA structures corresponding to CAS Registry No. 1643793-45-6. Adding polyvinyl alcohol or vinyl alcohol copolymers as thickeners imparts good compatibility and does not significantly alter the properties of the layer.

[0071] Other thickeners that can be used include inorganic components such as clay, silica, or other metal oxide particles. Examples include Laponite JS, Laponite RD, Levasil 300, Cab-o-sil M5, Aerosil 300, Aerosil 200, Bindzil CC151 HS, Bindzil CC301, Luvotix HT, Luvogel 4, and Luvogel LD.

[0072] Porous supports The catalyst-coated separator according to the invention comprises a porous support. Such a porous support provides mechanical strength to the separator, thereby facilitating its production, operation, and integration into an electrolyzer.

[0073] The thickness of the porous support is preferably 350 µm or less, more preferably 200 µm or less, most preferably 100 µm or less, and particularly preferably 75 µm or less.

[0074] It has been observed that the ionic conductivity of the catalyst-coated separator increases as the thickness of the porous support decreases. However, to ensure sufficient mechanical properties of the catalyst-coated separator, the thickness of the porous support is preferably 20 µm or greater, more preferably 40 µm or greater.

[0075] The porous support is preferably a nonwoven fabric, a woven fabric, a mesh, or a felt, and more preferably a nonwoven or woven fabric.

[0076] Woven fabrics generally offer better dimensional stability, open area, and thickness uniformity. However, woven fabrics with a thickness of 100 µm or less are more complex to manufacture, resulting in higher costs. Nonwoven fabrics are less complex to manufacture, even for fabrics with a thickness of 100 µm or less. Furthermore, nonwoven fabrics can have larger open areas.

[0077] The opening area of ​​the porous support is preferably 30% to 80%, more preferably 40% to 70%, to ensure good permeation of the electrolyte into the support.

[0078] The fiber diameter of the fabric is preferably from 10 µm to 200 µm, more preferably from 20 µm to 150 µm, and most preferably from 30 µm to 100 µm. Fabrics with a smaller thickness preferably have a smaller fiber diameter. For example, fabrics with a thickness of 150 µm or less preferably contain fibers with a fiber diameter of 75 µm or less, more preferably 50 µm or less, and most preferably 35 µm or less.

[0079] To further reduce the thickness of the fabric, the ratio of yarn thickness to fiber diameter is preferably less than 2.0, more preferably 1.7 or less, and most preferably 1.4 or less. Thinner fabrics allow for the fabrication of thinner partitions.

[0080] Porous supports preferably include polymers such as, for example, polypropylene, polyethylene, polysulfone, polyphenylene sulfide, polyamide / nylon, polyethersulfone, polyphenylene sulfone, polyethylene terephthalate, polyetheretherketone, sulfonated polyetheretherketone, monochlorotrifluoroethylene, copolymers of ethylene with tetrafluoroethylene or chlorotrifluoroethylene, polyimide, polyetherimide, and meta-aramid.

[0081] A preferred porous support includes polyphenylene sulfide (PPS) or polyether ether ketone (PEEK).

[0082] Porous supports based on PPS or PEEK exhibit high tolerance to high temperatures and high concentrations of alkaline solutions, and high chemical stability against reactive oxygen species evolved from the anode during water electrolysis. Furthermore, PPS and PEEK can be readily processed into various forms, such as woven or nonwoven fabrics.

[0083] The density of the porous support is preferably between 0.1 and 0.7 g / cm³. 3 between.

[0084] The porous support is preferably a continuous web so that the manufacturing methods disclosed in EP-A 1776490 and WO2009 / 147084 can be used.

[0085] The width of the web is preferably between 30 and 300 cm, and more preferably between 40 and 200 cm.

[0086] Porous polymer layer containing polymer A The porous polymer layer comprises polymer A, which is capable of forming a three-dimensional porous network during the phase inversion step described below. Such a polymer will be described below.

[0087] The porous polymer layer may also contain inorganic particles. Such inorganic particles typically increase the hydrophilicity of the porous polymer layer, resulting in better permeability to electrolytes. Furthermore, inorganic particles have been observed to improve the polymer's alkali resistance. Such inorganic particles will be described below.

[0088] Porous polymer layers described for prior art porous separators, such as those disclosed in, for example, EP-A 3933069 or WO2023 / 280600 from AGFA-GEVAERTNV, can be used in the separator according to the invention. However, the porous layers in these prior art separators are characterized by a trade-off between minimum gas permeability and maximum ionic conductivity. Since a non-porous layer exists in the separator according to the invention, the porous polymer layer is no longer required to have minimum gas permeability, and the layer can be optimized to achieve maximum ionic conductivity.

[0089] The surface pore diameter of the porous layer should not be too large to avoid an uneven non-porous layer, nor too small to avoid delamination of the non-porous layer from the porous support and / or porous polymer layer. The average surface pore diameter is preferably from 0.001 to 10 µm, more preferably from 0.01 to 5 µm, and most preferably from 0.1 to 1 µm. The surface pore diameter is preferably measured using scanning electron microscopy.

[0090] Similarly, due to the presence of the non-porous layer, the pores of the porous polymer layer in the separator according to the present invention can be larger than the pores of the prior art separators mentioned above. The porous polymer layer may even include large finger-shaped pores.

[0091] The porous layer containing polymer A can be disposed on one or both sides of the porous support. When two porous polymer layers are disposed, the two layers can be the same or different from each other.

[0092] The porous layers containing polymer A disposed on both sides of the partition can be the same or different from each other. Such porous layers can differ in the following ways: - Composition, such as different polymers A or different inorganic particles; - Thickness, as disclosed, for example, in WO2023 / 208776 (AGFA-GEVEART NV); - Pore size or porosity, for example by applying different phase transition conditions to the two layers, as disclosed in EP-A 3652362 (AGFA-GEVAERT NV).

[0093] Polymer A The porous layer contains polymer A, which is capable of forming a three-dimensional porous network, a result of the phase inversion step during the preparation of the separator as described below. The phase inversion can be performed using an aqueous or organic medium to produce the porous structure.

[0094] When using an aqueous medium for phase transformation, polymer A is preferably a alkali-stable polymer that does not swell in an alkaline aqueous medium. Polymer A is preferably selected from high engineering plastics and polymers with a full carbon backbone.

[0095] High-performance engineering plastics typically consist of a backbone containing aromatic hydrocarbons. Preferred high-performance engineering plastics are polysulfone, polyethersulfone, polyimide, polyetherimide, polyamideimide, polyphenylene sulfide, polyphenylene ether, and polyetherketone.

[0096] Polymers containing a full carbon backbone, also known as polyhydrocarbons, are preferably selected from polymers based on polyolefins and polystyrene. Polyolefins can be fluorinated or chlorinated. Typical examples of fluorinated and chlorinated polyhydrocarbons include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), and polyvinylidene chloride (PVDC). Polyhydrocarbons can be pure hydrocarbons based on nonfunctionalized polyolefins such as polypropylene (PP) or low-density polyethylene. Polystyrene-based polymers can be pure polystyrene or styrene-based copolymers such as SEBS, also known as Kraton. TMFunctionalized polyolefins, such as hydrophobically modified polyvinyl alcohol derivatives, can also be used. Typical derivatives, such as hydrophobic polyacetals, for example, polyvinyl butyral, can be used as polymers in the porous layers according to the invention. Polyvinyl alcohol copolymers, especially those with high ethylene content, can also be used. In certain cases, non-swellable polyesters, such as polyethylene terephthalate and polybutylene terephthalate, can be used.

[0097] When using an organic medium as the phase inversion medium, a hydrophilic polymer stable to alkali can be used for the phase inversion, followed by crosslinking of the hydrophilic polymer to stabilize the layer in the alkaline medium. Polyvinyl alcohol is a particularly preferred polymer. Crosslinking with difunctional or polyfunctional aldehydes is particularly preferred to make the layer alkali-resistant.

[0098] Polymer A is preferably selected from polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, and polyphenylene sulfone, with polysulfone being the most preferred.

[0099] The porous layer may contain two, three or more different polymers A as described above.

[0100] The molecular weight (Mw) of polymer A is preferably between 1,000 and 250,000, more preferably between 25,000 and 250,000. When Mw is too low, the physical strength and durability of the porous layer may be insufficient. When Mw is too high, the viscosity of the coating solution may become too high.

[0101] Examples of polysulfone, polyethersulfone, and combinations thereof are disclosed in paragraphs

[0021] to

[0032] of EP-A 3085815.

[0102] The total amount of polymer A is preferably 5 to 40% by weight, more preferably 10 to 30% by weight, and most preferably 15 to 25% by weight, all relative to the total dry weight of the porous polymer layer.

[0103] Inorganic particles The porous polymer layer may also contain inorganic particles, for example, to improve the hydrophilicity and / or alkali stability of the porous polymer layer. Such inorganic particles may also be incorporated into non-porous layers to further optimize their properties.

[0104] The preferred inorganic particles are selected from metal oxides and metal hydroxides.

[0105] The preferred metal oxides are selected from titanium oxide, bismuth oxide, cerium oxide, and magnesium oxide.

[0106] Preferred metal hydroxides are selected from zirconium hydroxide, titanium hydroxide, bismuth hydroxide, cerium hydroxide, and magnesium hydroxide. A particularly preferred magnesium hydroxide is disclosed in paragraphs

[0040] to

[0063] of EP-A 3660188.

[0107] Other preferred inorganic particles include sulfates of calcium, barium, lead, or strontium, with barium sulfate particles being more preferred. Such barium sulfate particles are disclosed in EP-A 3994295.

[0108] Other inorganic particles that can be used include nitrides and carbides of elements in Group IV of the periodic table.

[0109] One or more different combinations of inorganic particles can be used.

[0110] Inorganic particles can be natural or synthetic substances.

[0111] The surface of inorganic particles can be untreated or treated with, for example, silane coupling agents, stearic acid, oleic acid or phosphate esters.

[0112] The shape of inorganic particles is not particularly restricted, as long as they are in granular form, and can be any irregular shape, spherical shape (such as true spheres and ellipsoids), plate shape (such as flakes and hexagonal plates), and fibrous shape.

[0113] The d50 particle size of the inorganic particles is preferably from 0.05 to 2.0 µm, more preferably from 0.1 to 1.5 µm, most preferably from 0.15 to 1.00 µm, and particularly preferably from 0.2 to 0.75 µm. The d50 particle size is preferably 0.7 µm or smaller, more preferably 0.55 µm or smaller, and most preferably 0.40 µm or smaller.

[0114] The total amount of inorganic particles is preferably 30 to 95% by weight, more preferably 50 to 92% by weight, and most preferably 60 to 90% by weight, all relative to the total dry weight of the porous layer containing polymer A. The amount of inorganic particles is preferably at least 65% by weight, more preferably at least 75% by weight, all relative to the total dry weight of the porous layer containing polymer A.

[0115] The weight ratio of inorganic particles to polymer in the porous layer containing polymer A is preferably 60 / 40 or higher, more preferably 70 / 30 or higher, and most preferably 75 / 25 or higher.

[0116] Preparation of catalyst-coated separators A preferred method for preparing the catalyst-coated separator according to the present invention includes the following steps: - Provides porous support (100), - Optionally, a coating solution described below is applied to the porous support and the applied coating solution is subjected to a phase inversion, thereby forming a porous polymer layer (200) on the porous support. - Apply a solution of polymer B onto a porous support or optionally a porous layer containing polymer A to form a non-porous layer (300) containing polymer B; and - A catalyst composition is applied to a non-porous layer to form a catalyst layer (400).

[0117] After applying the non-porous layer, a drying step is preferably performed to at least partially remove the solvent from the coating solution. Drying is preferably carried out at a temperature of 60 to 90°C for 5 to 20 minutes.

[0118] Optional porous layers containing polymer A, non-porous layers containing polymer B, and catalyst layers can be applied independently to one or both sides of the porous support. If these layers are applied to both sides of the porous support, the optional porous layers (200 and 200'), non-porous layers (300 and 300'), and catalyst layers (400 and 400') can be the same or different from each other.

[0119] The catalyst-coated separator according to the invention can also be prepared from a porous separator as described in WO2023 / 280600 or WO2023 / 208776, both from AGFA-GEVAERT NV. A polymer B solution is then applied to one or both sides of such a porous separator to form one or two non-porous layers containing polymer B, followed by the application of a catalyst composition onto the non-porous layers to form one or two catalyst layers.

[0120] Application of a non-porous layer containing polymer B The non-porous layer containing polymer B is preferably prepared by coating a porous support (100) or optionally a porous layer with a polymer B solution having a viscosity of at least 400 mPa·s, preferably at least 500 mPa·s, more preferably at least 800 mPa·s, and most preferably at least 1000 mPa·s, wherein the viscosity is at 20°C and 100 s⁻¹. -1 The measurements were taken at the shear rate.

[0121] Any coating technique can be used to apply the polymer B solution. Preferred coating techniques are selected from slot die coating, curtain coating, doctor blade coating, bar coating, air knife coating, cascade coating, extrusion coating, reverse roller coating, kiss coating, and dip coating. Highly preferred coating techniques are air knife coating, cascade coating, curtain coating, reverse roller coating, slot die coating, and kiss coating.

[0122] To achieve an efficient and cost-effective partition production process, it is preferable to apply a non-porous layer in a single coating step.

[0123] The solvent for the polymer B solution depends on the type of polymer B. When polymer B is a hydrophilic polymer such as PVA, the polymer B solution is preferably an aqueous solution. However, this aqueous solution may contain an organic water-soluble solvent, such as, for example, ethanol, isopropanol, DMSO, or mixtures thereof. However, water is the most preferred solvent.

[0124] Polymer B is preferably crosslinked. Crosslinking has been observed to improve the lifespan of non-porous layers in the electrolyzer. If polymer B is polyvinyl alcohol or an ethylene-vinyl alcohol copolymer, it is preferably crosslinked with difunctional or polyfunctional aldehydes such as glutaraldehyde and benzene-1,4-dialdehyde. The aldehyde functional groups react with the hydroxyl groups of the polyvinyl alcohol or ethylene-vinyl alcohol copolymer to form acetal bonds. For example, crosslinked polyvinyl alcohol can be obtained by gas-phase crosslinking of polyvinyl alcohol and glutaraldehyde, as described by KIM et al. (Journal of Power Sources 524 (2022) 231059). However, it is preferable to add the crosslinking compound together with a crosslinking catalyst (in the case of PVA and glutaraldehyde, an acid catalyst, such as H2SO4 or HCl) to the polymer B solution. The mixture is then stirred while crosslinking is being carried out. When the desired viscosity has been reached, the mixture is then coated onto a porous support or a porous polymer layer. To avoid an excessive increase in the viscosity of the mixture before coating, the crosslinking agent or acid catalyst can be added to the PVA solution just before coating. Alternatively, the crosslinked polyvinyl alcohol-coated separator can be obtained through the following synthesis procedure. A crosslinking mixture is prepared by adding polymer B, a crosslinking agent, and a catalyst to a suitable solvent at a pre-selected concentration. The crosslinking mixture is homogenized by stirring. The desired viscosity of the crosslinking mixture is obtained by adding a viscosity modifier or by selecting a sufficiently high initial polymer concentration. Next, the crosslinking mixture is immediately coated onto a substrate without waiting for crosslinking to occur. The coated substrate is then allowed to crosslink for a certain period of time before being dried in an oven.

[0125] Other cross-linking compounds, such as epoxides and sulfonamides, can also be used. Additionally, combinations of cross-linking compounds can be used.

[0126] After applying the non-porous layer, a drying step is preferably performed to at least partially remove the solvent from the coating solution. Drying is preferably carried out at a temperature of 60 to 90°C for 5 to 20 minutes.

[0127] In a cost-effective mass production process, it is preferable to apply a non-porous layer containing polymer B to at least one side of a porous support and / or a porous layer containing polymer A using a continuous roll-to-roll method.

[0128] Application of catalyst layer The catalyst can be applied by any of the methods disclosed in Bladergroen et al., “Overview of Membrane Electrode Assembly Preparation Methods for Solid Polymer Electrolyte Electrolyzer”, 2012, DOI: 10.5772 / 52947.

[0129] One well-known application method is the so-called decal method. In this method, a catalyst layer is first deposited on a temporary substrate, such as glass fiber reinforced Teflon. If two catalyst layers are applied, a spacer is then sandwiched between the two catalyst-coated decals, with the catalyst layers facing each other. The catalyst layer is then transferred from the decal to the spacer using a hot press, and the decal is subsequently removed.

[0130] The catalyst can also be placed directly on the surface of the separator, for example, by: - Electro-assisted catalyst deposition, such as electrodeposition, electrospraying, and electrophoretic deposition; - Applying catalysts by vapor, such as magnetron sputtering and chemical vapor deposition; - Plasma spraying; - Dry spraying; - Phase transformation; - Coating techniques, such as slot die coating, curtain coating, doctor blade coating, bar coating, air knife coating, cascade coating, extrusion coating, reverse roller coating, kiss coating, and dip coating. Preferred coating techniques are air knife coating, cascade coating, curtain coating, reverse roller coating, slot die coating, and kiss coating. - Printing, such as screen printing, gravure printing, inkjet printing, flexographic printing and 3D printing.

[0131] Preferred deposition methods are those that will not damage the non-porous polymer layer.

[0132] It is preferable to apply the catalyst layer online in the manufacturing equipment to provide an efficient and cost-effective production process.

[0133] When depositing a catalyst using coating or printing methods, the catalyst composition is coated or printed onto the surface of the separator. Such a catalyst composition contains one or more catalysts and may also contain binders, solvents, and other components such as surfactants.

[0134] Application of a porous layer containing polymer A An optional porous layer containing polymer A is provided on the porous support by applying a coating solution described below to at least one side of the porous support and performing a phase inversion on the applied coating solution to form at least one porous layer containing polymer A.

[0135] Prior to phase transformation, the applied coating solution preferably completely impregnates the porous support.

[0136] The methods disclosed in EP-A 1776490 and WO2009 / 147084 can be used to apply a porous layer to a porous support. Other suitable manufacturing methods that can be used are disclosed in EP-A 3272908, EP-A 3660188 and EP-A 3312306.

[0137] Paint solution The coating solution preferably contains polymer A and solvent as described above. The coating solution may also contain inorganic particles as described above.

[0138] The solvent for the coating solution is preferably an organic solvent in which the polymer resin can dissolve. Furthermore, the organic solvent is preferably miscible with water.

[0139] The solvent is preferably selected from N-methylpyrrolidone (NMP), N-ethylpyrrolidone (NEP), N-butylpyrrolidone (NBP), N,N-dimethylformamide (DMF), formamide, dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMAC), acetonitrile, and mixtures thereof. For health and safety reasons, N-butylpyrrolidone (NBP) is highly preferred.

[0140] The coating solution may also contain other components to optimize the properties of the resulting polymer layer, such as its porosity and the maximum pore diameter at its outer surface.

[0141] The coating solution preferably contains additives to optimize the pore size at the surface and interior of the porous layer. Such additives can be organic or inorganic compounds or combinations thereof.

[0142] Organic compounds that may affect pore formation in porous layers include polyethylene glycol, polyethylene oxide, polypropylene glycol, ethylene glycol, tripropylene glycol, glycerol, polyols, dibutyl phthalate (DBP), diethyl phthalate (DEP), di(undecyl) phthalate (DUP), isononanoic acid or neodecanoic acid, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate, polyethyleneimine, polyacrylic acid, methylcellulose, and dextran.

[0143] Preferred organic compounds that may affect pore formation in the porous layer are selected from polyethylene glycol, polyethylene oxide, and polyvinylpyrrolidone. Preferred polyethylene glycol has a molecular weight of 10,000 to 50,000, preferred polyethylene oxide has a molecular weight of 50,000 to 300,000, and preferred polyvinylpyrrolidone has a molecular weight of 30,000 to 1,000,000. A particularly preferred organic compound that may affect pore formation in the porous layer is glycerol. The amount of the compound that may affect pore formation is preferably between 0.1% by weight and 15% by weight, more preferably between 0.5% by weight and 5% by weight, relative to the total weight of the coating solution.

[0144] Inorganic compounds that may affect pore formation include calcium chloride, magnesium chloride, lithium chloride, and barium sulfate.

[0145] A combination of two or more additives that affect pore formation can be used.

[0146] The coating solutions applied to both sides of the porous support can be the same or different.

[0147] Application of coating solution The coating solution can be applied to the surface of the porous support using any coating or casting technique.

[0148] A preferred coating technique is extrusion coating. In a highly preferred embodiment, the coating solution is applied using a slit-die coating technique, wherein two slit-die coating dies are located on either side of a porous support.

[0149] The slit coating die can maintain the coating solution at a predetermined temperature, distribute the coating solution evenly on the support, and adjust the coating thickness of the applied coating solution.

[0150] In 100 s -1 The shear rate and the viscosity of the coating solution measured at 20°C are preferably at least 7.5 Pa·s, more preferably at least 15 Pa·s, and most preferably at least 30 Pa·s. The coating solution is preferably shear-thinned. At 1 s -1 Viscosity at shear rate and at 100 s -1 The viscosity-to-shear ratio is preferably at least 2, more preferably at least 2.5, and most preferably at least 5.

[0151] Upon application, the porous support is immediately impregnated with the coating solution. Preferably, the porous support is completely impregnated with the applied coating solution.

[0152] Phase transformation steps After a coating solution is applied to a porous support, the applied coating solution undergoes a phase inversion. In the phase inversion step, the applied coating solution is transformed into a porous layer.

[0153] In a preferred embodiment, both coating solutions applied to the porous support undergo phase inversion.

[0154] Porous hydrophilic layers can be prepared from the applied coating solution using any phase inversion mechanism.

[0155] The phase transition steps preferably include a so-called liquid-induced phase separation (LIPS) step, a gas-induced phase separation (VIPS) step, or a combination of VIPS and LIPS steps. The phase transition steps preferably include both VIPS and LIPS steps.

[0156] Both LIPS and VIPS are solvent-inducible phase transformation processes.

[0157] In the LIPS step, a porous support containing the coating solution is brought into contact with a non-solvent that is miscible with the solvent of the coating solution.

[0158] Typically, this is done by immersing a porous support containing a coating solution into a non-solvent bath (also known as a coagulation bath).

[0159] The non-solvent is preferably water; a mixture of water and an aprotic solvent selected from N-methylpyrrolidone (NMP), N-ethylpyrrolidone (NEP), N-butylpyrrolidone (NBP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and dimethylacetamide (DMAC); an aqueous solution of a water-soluble polymer such as PVP or PVA; or a mixture of water and an alcohol (such as ethanol, propanol, or isopropanol). Water is the most preferred non-solvent. However, when using a water-soluble hydrophilic polymer A, an organic solvent is preferred.

[0160] The temperature of the coagulation bath is preferably between 20 and 90°C, and more preferably between 40 and 70°C.

[0161] The transfer of solvent from the coated polymer A layer to the non-solvent bath, and the transfer of non-solvent into the polymer A layer, induces a phase inversion and the formation of a three-dimensional porous polymer network. The impregnation of the applied coating solution into the porous support results in the formation of a sufficiently adherent hydrophilic layer onto the porous support.

[0162] In the VIPS step, the porous support coated with the paint solution is exposed to non-solvent vapors, preferably humid air.

[0163] Preferably, the solidification step includes both the VIPS and LIPS steps. Preferably, the VIPS step is performed before the LIPS step. In a particularly preferred embodiment, the porous support coated with the paint solution is first exposed to humid air (VIPS step) and then immersed in a water bath (LIPS step).

[0164] A washing step may be performed after the phase inversion step, preferably the LIPS step in a coagulation bath.

[0165] A drying step may be performed after the phase inversion step or, optionally, the washing step.

[0166] A preferred method for preparing a porous polymer A layer on a porous support is described in paragraphs 117 to 129 of EP-A 3933069 (AGFA-GEVAERT NV). Figure 2 As shown in Figure 3.

[0167] Electrolytic cell The catalyst-coated separator for alkaline water electrolysis according to the present invention can be used in alkaline water electrolyzers.

[0168] Such an electrolyzer typically includes at least one electrolytic cell containing two electrodes: an anode (A) and a cathode (C), separated by a partition. An electrolyte exists between the two electrodes. A catalyst is typically disposed on the electrodes; however, in the electrolytic cell according to the invention, the catalyst is disposed on at least one side of the partition. Figure 2 An embodiment of the electrolytic cell according to the present invention is schematically presented.

[0169] If the catalyst is placed only on one side of the separator, the catalyst can also be applied to the electrode on the other side facing the separator.

[0170] The electrodes are preferably made of conductive materials selected from nickel, iron, mild steel, stainless steel, vanadium, molybdenum, copper, silver, manganese, platinum group elements, graphite, and chromium. The electrodes may be made of conductive alloys of two or more metals or mixtures of two or more conductive materials. A preferred material is nickel or a nickel-based alloy. Nickel exhibits good stability in strongly alkaline solutions, good electrical conductivity, and is relatively inexpensive.

[0171] The catalyst layer disposed on the electrode preferably comprises nickel, cobalt, iron, and platinum group elements. The catalyst layer may contain elemental metals, compounds (e.g., oxides), composite oxides, or alloys or mixtures of multiple metallic elements. Preferred catalyst layers include nickel plating, nickel-cobalt plating, nickel-iron plating, nickel-and-cobalt composite oxides (such as LaNiO3, LaCoO3, and NiCo2O4), platinum group element compounds (such as iridium oxide), or carbon materials (such as graphene).

[0172] A particularly preferred catalyst layer comprises Raney nickel. The Raney nickel structure is formed by selectively leaching aluminum or zinc from a Ni-Al or Ni-Zn alloy. The lattice vacancies formed during the leaching process result in a large surface area and a high density of lattice defects, which are active sites for electrocatalytic reactions.

[0173] Figure 2 A schematic diagram of an embodiment of an electrolytic cell according to the present invention is shown. A catalyst-coated separator is located between the anode (A) and the cathode (C). The separator includes a catalyst layer, a non-porous layer, and a porous polymer layer disposed on both sides of a porous support (see [reference]). Figure 1.f Since the catalyst-coated separator contains catalyst layers on both sides, there is no catalyst on the electrode.

[0174] When an electric current is supplied to the electrolytic cell, hydroxide ions in the electrolyte are oxidized to oxygen at the anode, while water is reduced to hydrogen at the cathode. The hydroxide ions formed at the cathode migrate to the anode through a separator. The separator prevents the hydrogen and oxygen formed during electrolysis from mixing.

[0175] The electrolyte solution is typically an alkaline solution. A preferred electrolyte solution is an aqueous solution of an electrolyte selected from sodium hydroxide or potassium hydroxide. Potassium hydroxide electrolyte is often preferred due to its high specific conductivity. The concentration of the electrolyte in the electrolyte solution is preferably 20 to 40% by weight relative to the total weight of the electrolyte solution.

[0176] The electrolyte temperature is preferably 50°C to 120°C, more preferably 75°C to 100°C, and most preferably 80°C to 90°C. However, higher temperatures, such as at least 100°C, more preferably 125°C to 165°C, may result in more efficient electrolysis.

[0177] In a so-called zero-gap electrolytic cell, the electrodes are positioned in direct contact with the separator, thereby reducing the space between the two electrodes. Mesh or porous electrodes are used so that the separator can be filled with electrolyte and efficiently remove the generated oxygen and hydrogen. Preferred porous electrodes and methods for preparing them are disclosed, for example, in paragraphs 23 to 84 of EP-A 3575442. The pore size of the porous electrode may affect the electrolysis efficiency. For example, EP-A 3575442 discloses that the preferred pore size of the porous electrode is from 10 nm to a maximum of 200 nm.

[0178] It has been observed that such zero-gap electrolyzers operate at high current densities.

[0179] However, it has been observed in WO2023 / 118088 (AGFA-GEVAERT NV) that in such zero-gap electrolytic cells, bubbles formed inside the separator may accumulate at the top of the separator. This accumulation of bubbles at the top of the separator may result in higher ionic resistance in that part of the cell. Temperature increases due to less efficient cooling of the electrolyte in this region of the electrolytic cell may even lead to separator burnout. Introducing a small distance between one side of the separator and at least one electrode may result in less bubble accumulation inside the separator. The distance (d1) between one side of the separator and the anode and the distance (d2) between the other side of the separator and the cathode may be the same or different. The distance between the surface of the separator and at least one electrode is preferably 50 to a maximum of 500 µm, more preferably 100 to a maximum of 250 µm.

[0180] Barros et al. (International Journal of Hydrogen Energy, Vol. 49, Part C, pp. 886-896) observed that a small distance between the separator surface and the electrode containing the catalyst layer reduces the supersaturation of dissolved gases in the electrolyte at the separator surface. High supersaturation at the separator surface can lead to higher gas diffusion through the separator. For example, high hydrogen supersaturation in the electrolyte at the cathode-facing surface of the separator can lead to higher HTO. A small distance d2 between the cathode and the cathode-facing separator surface reduces hydrogen supersaturation at the separator surface and thus reduces HTO. The optimal distance d2 was found to be around 100 µm.

[0181] The distance between the separator and the electrode can be achieved using so-called spacers. Such spacers are preferably hydrophilic to prevent air bubbles from adhering to them (static water contact angle of 90° or lower, preferably 45° or lower). Such spacers preferably have an open structure to ensure efficient ionic conductivity and bubble dispersal.

[0182] When the separator according to the invention is used in an electrolytic cell, the distance d2 between the porous surface of the separator (the surface of the porous support and / or the surface of the porous layer containing polymer A) and the electrode can be generated by a non-porous layer.

[0183] The non-porous layer of the catalyst-coated separator can also affect gas permeability. Therefore, when the catalyst-coated separator includes a catalyst layer deposited on a non-porous layer, it is preferable that the catalyst layer faces the cathode. This orientation can further reduce HTO.

[0184] A typical alkaline water electrolyzer consists of several electrolytic cells, also known as an electrolytic cell stack. Regarding cell configuration, two types of electrolyzers are generally used.

[0185] A monopole (or “tank”) electrolyzer consists of alternating positive and negative electrodes separated by partitions. The positive electrodes are all connected together in parallel, as are the negative electrodes, and the entire assembly is immersed in a single electrolyte bath (“tank”) to form a unit cell. Factory-scale electrolyzers are then constructed by electrically connecting these units in parallel. The total voltage applied to the entire electrolytic cell is the same as the total voltage applied to each individual unit cell.

[0186] On the other hand, in a bipolar electrolyzer, metal sheets (or "bipolar bodies") are electrically connected in series to adjacent cells. An electrocatalyst for the negative electrode is coated on one side of the bipolar body, and an electrocatalyst for the positive electrode of the adjacent cell is coated on the opposite side. In this case, the total cell voltage is the sum of the voltages of the individual unit cells. Therefore, such series-connected cells form a module that operates at a higher voltage and lower current than a cell-type (monopolar) design. To meet the requirements of large-scale electrolysis plants, these modules are connected in parallel to increase the current. Example

[0187] Materials ZIRFON is the ZirfonPerl UTP500 from AGFA-GEVAERT NV.

[0188] PVA is a high molecular weight polyvinyl alcohol with a molecular weight of 85-124 kDa and a degree of hydrolysis >99%, derived from ALDRICH.

[0189] Glutaraldehyde can be obtained from ALDRICH in a 25% by weight aqueous solution.

[0190] NiO is nickel oxide (99% purity), which can be obtained from BCR GMBH & CO.

[0191] PVP stands for polyvinylpyrrolidone, with a molecular weight of 8000, and is obtained from BCR GMBH&CO.

[0192] The NiO dispersion was prepared by mixing 60% NiO, 7.5% PVP, and 32.5% demineralized water by weight. The mixture was then milled on a stirred bead mill until the Z-average particle size was less than 200 nm.

[0193] Measurements Scanning electron microscopy (SEM) and energy-scattering X-ray spectroscopy (SEM-EDX) SEM cross-sections were prepared by cutting the sample and embedding it in epoxy resin. The sample was then mechanically polished and coated with a thin Pt-Pd layer. The surface sample was cut, attached to an aluminum stub with double-sided tape, and coated with a thin Pt-Pd layer.

[0194] Bubble point, minimum pore size, average pore size, gas permeability The pore diameter of the partition was measured using the so-called bubble point test method.

[0195] The bubble point test involves wetting the pores of a film with a wetting fluid and then measuring the minimum pressure required to completely wet the pores and overcome the surface tension between the wetting fluid and the pore walls. This pressure is called the bubble point pressure.

[0196] The theory of capillary action states that the height of the water column in a capillary is inversely proportional to the capillary diameter. Using the Young-Laplace equation, the pore diameter of a membrane can be correlated with the pressure required to force the wetting fluid out of the pores.

[0197] The procedure for the bubble point test is described in American Society for Testing and Materials (ASTM) Standard Method F316.

[0198] Position the filter so that the top is in contact with the liquid and the bottom is in contact with the air, and connect the filter holder to the regulated pressure source. Gradually increase the air pressure and observe the formation of bubbles on the liquid side. Below the bubble point, gas will only diffuse through the filter, but when the pressure is high enough to force the liquid out of the pores, overall flow will begin and bubbles will be visible.

[0199] The initial bubble test pressure determines the size (and location) of the maximum pore, while the open bubble point pressure determines the average pore size of the element.

[0200] The bubble point, average pore diameter, maximum pore diameter, and gas permeability of the separator were measured using a POROLUX 1000, which is available commercially from POROMETER.

[0201] Example 1 Preparation of catalyst-coated separators S-1 and S-2 Catalyst-coated separator S-1 was prepared by coating one side of a ZIRFON separator with a NiO dispersion.

[0202] The catalyst-coated separator S-2 was prepared as follows: First, a wet PVA solution with a thickness of 200 µm was coated onto one side of the ZIRFON separator, and then dried in an oven at 80 °C to form a dried PVA layer. Next, a NiO dispersion was coated onto the dried PVA layer.

[0203] Figure 3.a and Figure 3.b The SEM cross-sections of S-1 and S-2 are shown in the figure.

[0204] From these SEM cross-sections, it can be seen that the thicknesses of the NiO catalyst layer in S-1 and S-2, and the PVA layer in S-2, are 3-4 µm and 7-8 µm, respectively.

[0205] SEM-EDX was used to investigate whether NiO permeated into the pores of the ZIRFON separator. SEM-EDX analysis of the cross-sections of separators S-1 and S-2 revealed that for S-1, Ni could be detected 20-30 µm below the ZIRFON surface, while for S-2, no Ni was detected at or below the ZIRFON surface. This clearly indicates that the presence of a base-stable non-porous polymer layer between the catalyst layer and the surface of the porous separator prevents the catalyst from permeating into the pores of the porous separator.

[0206] Example 2 Preparation of partition S-3 The separator S-3 was prepared by coating one side of a ZIRFON separator with a 60 µm thick PVA solution (19% by weight in water) and then drying it in a standard oven at 80 °C for 15 minutes.

[0207] Figure 4 illustrates the effect of coating ZIRFON with PVA solution on the surface roughness of the separator. The surface of ZIRFON without a PVA layer (…). Figure 4.a ) and the surface of S-3 containing the PVA layer ( Figure 4.b The SEM top view clearly shows that a smoother diaphragm surface was observed on S-3.

[0208] As measured above, the gas permeability and bubble point of S-3 are 0.01 L / min·cm. 2 The values ​​are >8 bar, while for ZIRFON they are 3.8 and 1.9 bar, respectively. This clearly demonstrates that the presence of a non-porous PVA layer leads to a substantial reduction in gas permeability and an increase in bubble point.

Claims

1. A catalyst-coated separator for alkaline water electrolysis, comprising a porous support (100) and, sequentially, on at least one side of said support: - Optional porous layer (200) containing polymer A, - Contains a non-porous layer (300) of polymer B, and - Catalyst layer (400).

2. The catalyst-coated separator for alkaline water electrolysis according to claim 1, wherein polymer B is selected from polyethylene glycol or copolymers thereof, polysaccharides, polyethylene-vinyl alcohol copolymers, polyethylene-vinylamine copolymers, and polyvinyl alcohol.

3. The catalyst-coated separator for alkaline water electrolysis according to claim 1 or 2, wherein polymer B is polyvinyl alcohol or a polyvinyl alcohol copolymer.

4. The catalyst-coated separator for alkaline water electrolysis according to claim 3, wherein the polyvinyl alcohol has a molecular weight of 75 to 150 kDa.

5. The catalyst-coated separator for alkaline water electrolysis according to any one of the preceding claims, wherein the non-porous layer is cross-linked.

6. A catalyst-coated separator for alkaline water electrolysis according to any one of the preceding claims, wherein the thickness of the non-porous layer comprising polymer B is from 0.1 to 25 µm.

7. A catalyst-coated separator for alkaline water electrolysis according to any one of the preceding claims, wherein the thickness of the catalyst layer is 0.5 to 200 µm.

8. A catalyst-coated separator for alkaline water electrolysis according to any one of the preceding claims, wherein the catalyst is selected from Ni, NiO, Raney nickel, Ni-Fe, Ni-Co, Ni-Mo and NiO / NiOH.

9. A catalyst-coated separator for alkaline water electrolysis according to any one of the preceding claims, wherein the total thickness of the separator is 50 to 750 µm.

10. A catalyst-coated separator for alkaline water electrolysis according to any one of the preceding claims, wherein polymer A is selected from polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, and polyphenylene sulfone.

11. A method for preparing a catalyst-coated separator according to any one of the preceding claims, the method comprising the steps of: - Provides porous support (100), - Optionally, a coating solution containing polymer A is applied to the porous support and a phase inversion step is performed on the applied coating solution to form a porous layer (200) containing polymer A on the porous support. - Apply a polymer B solution to the porous support or the optional porous layer to form a non-porous polymer layer (300), and - A catalyst composition is applied to a non-porous layer to form a catalyst layer (400).

12. The method of claim 11, wherein the polymer B solution is at 20°C and 100 s -1 The viscosity measured at the shear rate is at least 400 mPa·s.

13. The method of claim 11 or 12, wherein the polymer B solution is applied by a single coating step.

14. An electrolytic cell for alkaline water electrolysis, the electrolytic cell comprising a catalyst-coated separator according to any one of claims 1 to 10.

15. Use of the catalyst-coated separator for alkaline water electrolysis according to any one of claims 1 to 10 in the production processes of green hydrogen, green ammonia, and green steel.

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