Separator for alkaline water electrolysis

Abstract

To provide a separator with minimal strain, high ionic conductivity, and good gas separation properties. [Solution] A separator (1) for alkaline electrolysis, comprising a porous support (10), a first porous layer (20b) provided on one side of the porous support, and a second porous layer (30b) provided on the other side of the porous support, wherein the first porous layer and the second porous layer partially penetrate the porous support, and each layer has overlay thicknesses d1 and d2, respectively, the overlay thickness being defined as the portion of each porous layer that does not penetrate the porous support, a) d1 being smaller than the overlay thickness (d2) of the second porous layer, and b) d1 being at least 20 μm.

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing a separator for alkaline water electrolysis and to a separator obtained by this method. [Background technology]

[0002] Currently, 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 a fundamental component of methanol, which is used in ammonia production, and by extension, fertilizer production, as well as in the production of many polymers. In oil refineries, hydrogen is used in the processing of intermediate oil products, which is another area of ​​application.

[0003] Hydrogen is also considered an important future energy carrier. This means that hydrogen can store and deliver energy in a stable form. Energy is released through exothermic combustion reactions using oxygen, which form water. No carbon-containing greenhouse gases are released during such combustion reactions.

[0004] To realize a low-carbon society, renewable energy sources such as solar and wind power are becoming increasingly important.

[0005] Electricity generation from wind and solar power systems is highly dependent on weather conditions. Because weather conditions are constantly changing, the balance between electricity supply and demand can be disrupted. So-called power-to-gas technology, which uses electricity to generate gaseous fuels such as hydrogen for storage, has recently attracted considerable attention. As electricity generation from renewable energy sources increases, so does the demand for storing and transporting the generated energy.

[0006] Alkaline water electrolysis is an important manufacturing process that can convert electricity into hydrogen.

[0007] In alkaline water electrolysis cells, a separator or diaphragm is used to separate electrodes with different polarities, prevent short circuits between these electron-conducting parts (electrodes), and avoid gas crossing, thereby preventing the recombination of hydrogen (formed at the cathode) and oxygen (formed at the anode). The separator must perform all of these functions while also being a highly ionic conductor that transports hydroxyl ions from the cathode to the anode.

[0008] The separator typically comprises a porous support. Such a porous support, as disclosed in Patent Document 1 (Hydrogen System), reinforces the separator to facilitate its operation and introduction into the electrolyzer.

[0009] Patent document 2 (Kawasaki / De Nora / ThyssenKrupp) discloses a film equipped with a porous support and a polymer porous film impregnated into a porous support. A film-forming solution is applied to one surface of the support, but in some cases, this results in a double coating film of porous layers with significantly different thicknesses on both surfaces of the support.

[0010] Patent document 3 (VITO) discloses a process for preparing a reinforced separator. This process results in a film with symmetrical properties. The process includes the steps of: preparing a porous support as a web and a suitable doping solution; inducing the web in a vertical position; coating both sides of the web equally with the doping solution to produce a web-coated support; and applying a symmetrical surface pore formation step and a symmetrical solidification step to the doped web to produce a reinforced film.

[0011] Patent documents 4 and 5 (Agfa-Gevaert and VITO) disclose manufacturing methods for producing reinforced films having the symmetrical properties described in Patent Document 3. The porous support used in these manufacturing methods has a thickness of more than 190 μm.

[0012] The advantage of films with symmetrical properties is improved robustness, because the occurrence of defects on one side of the support does not negatively impact the overall performance of the film.

[0013] Patent document 6 (Agfa-Gevaert) discloses a reinforced separator with symmetrical properties, which comprises a porous support with a thickness of 150 μm or less, and a membrane thickness of less than 250 μm. The membrane has improved ionic conductivity and sufficient mechanical properties. By adjusting the viscosity of the doping solution, a membrane with sufficient flatness and low distortion was obtained.

[0014] However, it has been observed that during the manufacturing process of double-sided reinforced separators, problems with support structure / flatness remain, potentially resulting in strained separators. Such strain can lead to performance issues in electrolytic devices.

[0015] Therefore, there is still a need for membranes with minimal strain, high ionic conductivity, and sufficient gas separation properties. [Prior art documents] [Patent Documents]

[0016] [Patent Document 1] EP-A 232923 [Patent Document 2] EP-A 3312306 [Patent Document 3] EP-A 1776490 [Patent Document 4] WO2009 / 147084 [Patent Document 5] WO2009 / 147086 [Patent Document 6] EP-A 3933069 [Overview of the project]

[0017] An object of the present invention is to provide a separator having minimal strain, high ionic conductivity, and good gas separation properties. Surprisingly, when the separator has different overlay thicknesses d1 and d2 as defined in claim 1, it has been found that the separator has minimal strain, high ionic conductivity, and sufficient gas separation properties.

[0018] Another object of the present invention is to provide a method for preparing such a separator.

[0019] A further object of the present invention will become apparent from the description hereinafter.

Brief Description of the Drawings

[0020] [Figure 1] It is a diagram schematically showing an embodiment of a separator according to the present invention. [Figure 2] It is a diagram schematically showing an embodiment of a method for manufacturing a separator according to the present invention. [Figure 3] It is a diagram schematically showing another embodiment of a method for manufacturing a separator according to the present invention. [Figure 4] It is a microscopic image of a cross-sectional view of a separator according to the present invention, illustrating d1 and d2 by showing a plurality of distances represented by d1(1), d1(2), d1(3), d2(1), d2(2), d2(3) for the overlay thicknesses d1 and d2. The average can be calculated by drawing a plurality of lines. [Figure 5] It is an image of a separator showing strain.

Modes for Carrying Out the Invention

[0021] Separator for Alkaline Electrolysis The separator (1) for alkaline water electrolysis according to the present invention comprises a porous support (10) and a first (20b) porous layer and a second (30b) porous layer provided on each side of the porous support, as follows a) The first porous layer has an overlay thickness (d1) that is smaller than the overlay thickness (d2) of the second porous layer, and b) The overlay thickness (d1) of the first porous layer is at least 20 μm, preferably at least 30 μm, more preferably at least 35 μm, and most preferably at least 40 μm. It is characterized by the following.

[0022] The porous layer overlay is defined as the portion of the porous layer that does not penetrate the porous support (see Figure 1). The thickness of the porous layer overlay can be determined by microscopy, as further described.

[0023] Surprisingly, it was found that strain reduction is possible when the overlay thicknesses d1 and d2 are different from each other. The overlay thickness d1 of the first porous layer is at least 20 μm. If d1 is less than 20 μm, the fibers of the porous support may protrude through the overlay of the porous layer, resulting in excessively high gas permeability. Excessively high gas permeability can lead to excessive electrolyte flow, which can carry dissolved gases to the unsuitable side of the electrolytic device, potentially leading to an increase in HTO (volume %) of hydrogen present in oxygen formed at the anode.

[0024] Preferably, the overlay thickness ratio d1 / d2 is less than 0.8, more preferably less than 0.6, and most preferably less than 0.4. If d1 / d2 is greater than 0.8, the separator may have distortion.

[0025] The total thickness (D) of the separator is preferably 250 μm or less, more preferably 225 μm or less, most preferably 175 μm or less, and particularly preferably 150 μm or less. If the thickness of the separator is less than 100 μm, the physical strength of the separator may be insufficient, and if the thickness exceeds 250 μm, the electrolysis efficiency may decrease.

[0026] The gas permeability of the membrane is preferably 1 to 7 L / min·cm.2 More preferably 1.5 to 6.5 L / min·cm 2 Most preferably 2-5.5 L / min·cm 2 The gas permeability can be measured at 5 bar using a Porolux™ 1000 instrument.

[0027] The separator preferably has an ionic resistance (also called area resistivity) of 0.1 ohm·cm in a 30 wt% KOH aqueous solution at 80°C. 2 Less than 0.07 ohm·cm², more preferably 0.07 ohms·cm². 2 It is less than [value]. Ion resistance can be determined using an Inolab® Multi 9310 IDS instrument (available from VWR, a division of Avantor) fitted with a TetraCon 925 conductivity cell (available from Xylem).

[0028] As described in more detail below, the separator according to the present invention is preferably prepared by coating both surfaces of a porous support with a coating solution. This coating solution, also called a dope solution, typically comprises a polymer resin, hydrophilic inorganic particles, and a solvent. Subsequently, a porous layer is obtained after a phase transition step, in which the polymer resin forms a three-dimensional porous polymer network.

[0029] A separator according to the present invention having different overlay thicknesses on both sides of a porous support is preferably obtained by adjusting the flow rate in a slot coating die, which will be described in more detail.

[0030] When applying the doping solution to both surfaces of a porous support, the doping solution penetrates the porous support. Preferably, the porous support is completely impregnated with the doping solution.

[0031] The first porous layer and the second porous layer provided to the porous support may have the same composition or different compositions, and may have the same foaming point or different foaming points.

[0032] After the phase transition, penetration into the porous support ensures that the three-dimensional porous polymer network extends into the porous support as well. This results in good adhesion between the porous layer and the porous support.

[0033] A suitable separator (1) is schematically shown in Figure 1.

[0034] The doping solution has been applied to both sides of the porous support (10), and the applied doping solution has completely penetrated the porous support. The applied doping layers are referred to as 20a and 30a.

[0035] After the phase conversion process (50), a separator (1) is obtained, which comprises a porous support (10) and porous layers (20b, 30b) on each side surface of the support.

[0036] The separator contains pores with a diameter small enough to prevent gas crossing. On the other hand, a larger pore diameter is preferable to ensure efficient transport of hydroxyl ions from the cathode to the anode. Efficient transport of hydroxyl ions requires that the electrolyte penetrate the separator efficiently.

[0037] The pores are preferably characterized using the foaming point test method described in the American Society for Testing and Materials (ASMT) Method F316. This technique is based on replacing the wetting solution embedded in the separator with a pressurized inert gas. In this way, only the material passing through the pores is measured.

[0038] The most difficult part for gas to replace liquid along the entire pore path is the narrowest part of the pore, also known as the pore gap. The pore diameter measured by the foaming point test is the diameter of the pore gap, regardless of where the pore gap is located in the pore path.

[0039] All pore sizes referenced herein are measured using the foaming point test method described above.

[0040] The maximum pore size (PDmax) of the separator is preferably 0.05 to 2 μm, more preferably 0.10 to 1 μm, and most preferably 0.2 to 0.6 μm.

[0041] The average pore size of the separator is preferably 0.01 to 1 μm, more preferably 0.02 to 0.5 μm, and most preferably 0.05 to 0.25 μm.

[0042] The foaming point test method can be adapted to measure the maximum pore size (PDmax) on both sides of the separator by using a grid to support one side of the separator during measurement. Then, another measurement is performed using a grid to support the other side of the separator.

[0043] The two sides of the separator may have the same maximum pore diameter or different maximum pore diameters.

[0044] A suitable separator has a maximum pore diameter PDmax(1) on one side and a maximum pore diameter PDmax(2) on the other side, where both PDmax(1) and PDmax(2) are 0.05 to 2 μm, more preferably 0.10 to 1 μm, and most preferably 0.15 to 0.5 μm, and the ratio PDmax(1) / PDmax(2) is 0.9 to 1.1, more preferably 0.95 to 1.05.

[0045] However, the separator may also have substantially different maximum pore sizes PDmax(1) and PDmax(2), for example, to prevent bubbles from being trapped inside the separator. For example, the separator may have a maximum pore size PDmax(1) of 0.05 to 0.3 μm, more preferably 0.08 to 0.25 μm, and most preferably 0.1 to 0.2 μm on one side, and a maximum pore size PDmax(2) of 0.2 to 6.5 μm, more preferably 0.2 to 1.50 μm, and most preferably 0.2 to 0.5 μm on the other side. The ratio of PDmax(2) to PDmax(1) is preferably 1.1 to 20, more preferably 1.25 to 10, and most preferably 2 to 7.5. A smaller PDmax(1) ensures efficient separation of hydrogen and oxygen, while a larger PDmax(2) ensures good penetration of the electrolyte into the separator, resulting in sufficient ionic conductivity.

[0046] The porosity of the separator is preferably 30-80%, more preferably 50-70%. Separators having a porosity within the above range typically have excellent ion permeability and excellent gas barrier properties because the pores of the membrane are continuously filled with the electrolyte.

[0047] porous support Porous supports are used to reinforce separators and ensure their mechanical strength.

[0048] It has been observed that ion conductivity through the reinforcing separator increases as the thickness of the porous support decreases. Therefore, the thickness of the porous support is preferably 150 μm or less, more preferably 125 μm or less, most preferably 100 μm or less, and particularly preferably 75 μm or less.

[0049] However, in order to ensure sufficient mechanical properties of the reinforced separator, the thickness of the porous support is preferably 20 μm or more, more preferably 40 μm or more, and most preferably 50 μm or more.

[0050] The porous support can be selected from the group consisting of porous cloth and porous ceramic plate.

[0051] The porous support is preferably a nonwoven fabric, woven fabric, mesh, or felt, more preferably a nonwoven fabric or woven fabric.

[0052] The porous support is preferably a porous cloth, or more preferably a porous polymer cloth.

[0053] Porous polymer fabrics can be either woven or nonwoven. Woven fabrics typically offer better dimensional stability, as well as uniformity of opening ratio and thickness. However, manufacturing woven fabrics with a thickness of 100 μm or less is more complex and results in a more expensive fabric. Manufacturing nonwoven fabrics, even with a thickness of 100 μm or less, is not nearly as complex. Woven fabrics can have a larger opening ratio.

[0054] To ensure that the electrolyte penetrates the support well, the opening ratio of the porous support is preferably 30-80%, more preferably 40-70%.

[0055] The fabric preferably has a fiber diameter of 20 μm to 200 μm, more preferably 40 μm to 150 μm, and most preferably 60 μm to 100 μm. Thinner fabrics preferably have a smaller fiber diameter. For example, a fabric with a thickness of 150 μm or less preferably has a fiber diameter of 75 μm or less, more preferably 50 μm or less, and most preferably 35 μm or less.

[0056] To further reduce the thickness of the fabric, the ratio of mesh thickness to fiber diameter is preferably less than 2.0, more preferably 1.7 or less, and most preferably 1.4 or less. The thinner the fabric, the thinner the separator that can be prepared.

[0057] Suitable porous polymer fabrics are prepared from polypropylene (PP), polyethylene (PE), polysulfone (PSU), polyphenylene sulfide (PPS), polyamide / nylon (PA), polyethersulfone (PES), polyphenylsulfone (PPSU), polyethylene terephthalate (PET), polyether-etherketone (PEEK), sulfonated polyether-etherketone (s-PEEK), monochlorotrifluoroethylene (CTFE), copolymers of ethylene and tetrafluoroethylene (ETFE) or chlorotrifluoroethylene (ECTFE), polyimides, polyetherimides, and m-aramids.

[0058] Suitable polymer fabrics are prepared from polypropylene (PP), polyetheretherketone (PEEK), or polyphenylene sulfide (PPS), most preferably from polyetheretherketone (PEEK) or polyphenylene sulfide (PPS).

[0059] PPS or PEEK-based porous supports exhibit high resistance to high temperatures and high-concentration alkaline solutions, as well as high chemical stability against reactive oxygen species released from the anode during water electrolysis processes. Furthermore, PPS and PEEK can be easily processed into various shapes, such as woven or nonwoven fabrics.

[0060] The density of the porous support is preferably 0.1 to 0.7 g / cm³. 3 That is the case.

[0061] The porous support is preferably a continuous web that enables the manufacturing process as described in EP-A 1776490 and WO2009 / 147084.

[0062] The width of the web is preferably 30 to 300 cm, more preferably 40 to 200 cm.

[0063] polymer resin The porous layer preferably contains a polymer resin.

[0064] As a result of the phase conversion process in the preparation of the separator, the polymer resin forms a three-dimensional porous network, as described below.

[0065] The polymer resin can be selected from fluororesins, such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), olefin resins, such as polypropylene (PP), and aromatic hydrocarbon resins, such as polyethylene terephthalate (PET) and polystyrene (PS). The polymer resin is used alone. It is also possible to use two or more types of polymer resins in combination.

[0066] PVDF and vinylidene fluoride (VDF) copolymers are preferred due to their oxidation / reduction resistance and film-forming properties. Of these, terpolymers of VDF, hexanefluoropropylene (HFP), and chlorotrifluoroethylene (CTFE) are preferred due to their excellent swelling properties, heat resistance, and adhesion to electrodes.

[0067] Another suitable polymer resin is aromatic hydrocarbon resin due to its excellent heat resistance and alkali resistance. Examples of aromatic hydrocarbon resins include polyethylene terephthalate, polybutylene terephthalate, polybutylene naphthalate, polystyrene, polysulfone, polyethersulfone, polyphenylene sulfide, polyphenylsulfone, polyacrylate, polyetherimide, polyimide, and polyamide-imide.

[0068] Particularly preferred polymer resins are selected from the group consisting of polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, and polyphenylsulfone, with polysulfone being the most preferred.

[0069] The molecular weight (Mw) of the polymer resin is preferably 10,000 to 500,000, more preferably 25,000 to 250,000. If Mw is too low, the physical strength of the porous layer may be insufficient. If Mw is too high, the viscosity of the doping solution may become too high.

[0070] Examples of polysulfones, polyethersulfones, and combinations thereof are disclosed in EP-A 3085815, paragraphs

[0021] to

[0032] .

[0071] inorganic hydrophilic particles The hydrophilic layer preferably contains hydrophilic inorganic particles.

[0072] Suitable hydrophilic inorganic particles are selected from metal oxides and metal hydroxides.

[0073] Suitable metal oxides are selected from the group consisting of zirconium oxide, titanium oxide, bismuth oxide, cerium oxide, and magnesium oxide.

[0074] Suitable metal hydroxides are selected from the group consisting of zirconium hydroxide, titanium hydroxide, bismuth hydroxide, cerium hydroxide, and magnesium hydroxide. Particularly suitable magnesium hydroxides are disclosed in EP-A 3660188, paragraphs

[0040] to

[0063] .

[0075] Other suitable hydrophilic inorganic particles are barium sulfate particles as disclosed in EP-A 3994295.

[0076] Other usable hydrophilic particles are nitrides and carbides of Group IV elements in the periodic table.

[0077] The hydrophilic inorganic particles preferably have a D50 particle size of 0.05 to 2.0 μm, more preferably 0.1 to 1.5 μm, most preferably 0.15 to 1.00 μm, and particularly preferably 0.2 to 0.75 μm. The D50 particle size is preferably 0.7 μm or less, preferably 0.55 μm or less, and more preferably 0.40 μm or less.

[0078] The D50 particle size is also known as the median diameter or the median of the particle size distribution. This is the particle size value at which the cumulative distribution reaches 50%. For example, if D50 = 1.0 μm, then 50% of the particles are Larger than 1.0 μm, and 50% are smaller than 1.0 μm.

[0079] The D50 particle size is preferably measured using laser diffraction, for example, with a Mastersizer from Malvern Panalytical.

[0080] The amount of hydrophilic particles relative to the total dry weight of the porous layer is preferably at least 50% by weight, and more preferably at least 75% by weight.

[0081] The weight ratio of hydrophilic particles to polymer resin is preferably greater than 60 / 40, more preferably greater than 70 / 30, and most preferably greater than 75 / 25.

[0082] Preparation of separators A preferred method for preparing the separator described above involves the following steps: - The process of applying the doping solution described below to both sides of the porous substrate, and -A step of initiating a phase change with the coated doping solution, thereby forming a first porous layer and a second porous layer on one and the other side of the porous support, respectively. It includes and is characterized by the following: a) The first porous layer has an overlay thickness (d1) that is smaller than the overlay thickness (d2) of the second porous layer.

[0083] The separator according to the present invention is preferably obtained by the method described above.

[0084] In a preferred embodiment, the overlay thickness (d1) of the first porous layer is at least 20 μm, preferably at least 30 μm, more preferably at least 35 μm, and most preferably at least 40 μm.

[0085] Preferred methods for manufacturing reinforced separators are disclosed in EP-A 1776490, WO2009 / 147084, and EP-A 3652362. These methods result in web-reinforced separators in which the web, i.e., the porous support, is successfully embedded in the separator without the web appearing on the surface of the separator.

[0086] Other available manufacturing methods are disclosed in EP-A 3272908.

[0087] Dope liquid The doping solution preferably comprises the polymer resin as described above, the hydrophilic inorganic particles as described above, and a solvent.

[0088] The solvent in the doping solution is preferably an organic solvent capable of dissolving the polymer resin. Furthermore, the organic solvent is preferably miscible with water.

[0089] 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.

[0090] For health and safety reasons, a very suitable solvent is N-butylpyrrolidone (NBP).

[0091] The doping solution may further contain other components to optimize the properties of the resulting polymer layers, such as their porosity and the maximum pore size on their outer surface.

[0092] The doping solution preferably contains additives to optimize the pore size on the surface and inside of the porous layer. Such additives may be organic compounds, inorganic compounds, or a combination thereof.

[0093] Organic compounds that can influence pore formation in porous layers include polyethylene glycol, polyethylene oxide, polypropylene glycol, ethylene glycol, tripropylene glycol, glycerol, polyhydric alcohols, dibutyl phthalate (DBP), diethyl phthalate (DEP), diundecyl phthalate (DUP), isononanoic acid or neodecanoic acid, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate, polyethyleneimine, polyacrylic acid, methylcellulose, and dextran.

[0094] Suitable organic compounds that can influence pore formation in the porous layer are selected from polyethylene glycol, polyethylene oxide, and polyvinylpyrrolidone.

[0095] A suitable polyethylene glycol has a molecular weight of 10,000 to 50,000, a suitable polyethylene oxide has a molecular weight of 50,000 to 300,000, and a suitable polyvinylpyrrolidone has a molecular weight of 30,000 to 1,000,000.

[0096] A particularly suitable organic compound that can influence pore formation in porous layers is glycerol.

[0097] The amount of compound that can influence pore formation is preferably 0.1 to 15% by weight, more preferably 0.5 to 5% by weight, relative to the total weight of the dope solution.

[0098] Inorganic compounds that can influence pore formation include calcium chloride, magnesium chloride, lithium chloride, and barium sulfate.

[0099] Two or more additives that can influence pore formation can be used in combination.

[0100] The doping solution applied to each side of the porous support can be the same or different.

[0101] Doping The doping solution can be applied to the surface of a substrate, preferably a porous support, by any coating or casting technique.

[0102] The preferred coating technique is extrusion coating.

[0103] In a very preferred embodiment, the doping solution is applied by a slot die coating technique, in which case two slot coating dies (Figures 2-3, 200-300) are positioned on each side of the porous support.

[0104] The slot coating die can maintain the dope solution at a predetermined temperature, uniformly distribute the dope solution over the support, and adjust the coating thickness of the applied dope solution.

[0105] The viscosity of the dope solution is measured at a shear rate of 100 s -1 and a temperature of 20 °C, and is preferably 1.0 to 30.0 Pa·s, more preferably 5.0 to 20.0 Pa·s, and most preferably 7. 5 to 15.0 Pa·s.

[0106] The dope solution is preferably shear-thinning. The ratio of the viscosity at a shear rate of 1 s -1 to the viscosity at a shear rate of 100 s -1 is preferably at least 2, more preferably at least 2.5, and most preferably at least 5.

[0107] The flow rate Q of the dope solution in the slot coating die can be the same or different.

[0108] To prepare the separator according to the present invention, the dope solution is preferably applied by adjusting the flow rate Q of the slot coating die such that the flow rate Q1 in the first slot coating die (200) is different from the flow rate Q2 in the second slot coating die (300). The difference in flow rates Q1 - Q2 is denoted as ΔQ. The sum of the flow rates Q1 + Q2 is denoted as Q TOT and is denoted as such.

[0109] When there is no difference in the flow rate (ΔQ is zero) or only a slight difference, there is a high possibility that the separator will be distorted.

[0110] When the difference in the flow rate is too large, the overlay thickness (d1) of the first porous layer becomes 20 μm, and there is a possibility that the gas permeability of the separator will become too high. ΔQ = Q TOT In this case, the substrate may be coated only on one side.

[0111] The difference in flow velocity ΔQ is preferably greater than zero. TOT Smaller. The difference in flow velocity at the slot coating die is preferably such that Q1 / Q2 is greater than 0 and less than 1. Q1 / Q2 is preferably 0.1 to 0.9, more preferably 0.2 to 0.8, and most preferably 0.3 to 0.7.

[0112] The aperture ratio of a porous support can be determined by how large the difference in flow velocity can be. A higher aperture ratio may require a larger ΔQ to reduce strain. A lower aperture ratio in a porous support may require a smaller ΔQ to achieve minimal strain.

[0113] The separator according to the present invention is preferably obtained by adjusting the flow velocity Q of the doping liquid in the slot coating die such that the flow velocity Q1 in the first slot coating die (200) is different from the flow velocity Q2 in the second slot coating die (300), and more preferably Q1 / Q2 is 0.1 to 0.9, more preferably 0.2 to 0.8, and most preferably 0.3 to 0.7.

[0114] The porous support is preferably a continuous web, which is transported downward between the slot coating dies (200, 300) as shown in Figures 2 and 3.

[0115] Immediately after coating, the porous support is impregnated with a doping solution.

[0116] Preferably, the porous support is completely impregnated with the coated dope solution.

[0117] Phase conversion process After applying the doping solution to the porous support, the applied doping solution is subjected to a phase conversion. In the phase conversion process, the applied doping solution is transformed into a porous hydrophilic layer.

[0118] In a preferred embodiment, both doping solutions coated on a porous support are subjected to phase conversion. .

[0119] A porous hydrophilic layer can be prepared from a coated dope solution using any phase conversion mechanism.

[0120] The phase transition process preferably includes a so-called liquid-induced phase separation (LIPS) process, a vapor-induced phase separation (VIPS) process, or a combination of a VIPS process and a LIPS process. The phase transition process preferably includes both a VIPS process and a LIPS process.

[0121] Both LIPS and VIPS are non-solvent-inducible phase inversion processes.

[0122] In the LIPS process, a porous support, coated on both sides with a doping solution, is brought into contact with a non-solvent that is miscible with the solvent of the doping solution.

[0123] Typically, this is done by immersing a porous support, whose sides are coated with a doping solution, in a non-solvent bath (also called a coagulation bath).

[0124] The non-solvent is preferably water, a mixture of water and an aprotic solvent selected from the group consisting of 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.

[0125] The non-solvent is most preferably water.

[0126] The coagulation bath temperature is preferably 20 to 90°C, more preferably 40 to 70°C.

[0127] The transfer of solvent from the coated polymer layer to the non-solvent bath, and the transfer of the non-solvent to the polymer layer, leads to phase transition and the formation of a three-dimensional porous polymer network. The penetration of the coated dope solution into the porous support results in sufficient adhesion of the resulting hydrophilic layer to the porous support.

[0128] In a preferred embodiment, a continuous web (100) with each side coated with doping fluid is transported vertically downward toward the solidification bath, as shown in Figures 2 and 3.

[0129] In the VIPS process, the porous support coated with the doping solution is exposed to a non-solvent vapor, preferably humid air.

[0130] Preferably, the solidification process included both a VIPS process and a LIPS process. Preferably, the VIPS process was performed before the LIPS process. In a particularly preferred embodiment, the porous support coated with the doping solution was first exposed to humid air (VIPS process) and then immersed in a water bath (LIPS process).

[0131] In the manufacturing method shown in Figure 2, VIPS is performed within region 400, between the slot coating dies (200, 300), and on the non-solvent surface of the solidification bath (800), while being shielded from the environment, for example, by a thermally separated metal plate (500).

[0132] The degree and rate of water movement in the VIPS process can be controlled by adjusting the air velocity, relative air temperature, and temperature, as well as the exposure time.

[0133] The exposure time can be adjusted by changing the distance d between the slot coating die (200, 300) and the non-solvent surface of the solidification bath (800), and / or the rate at which the extended web 100 is transported from the slot coating die toward the solidification bath.

[0134] The relative temperature of the VIPS region (400) can be adjusted by the temperature of the solidification bath and by shielding the VIPS region (400) from the environment and from the solidification bath.

[0135] The air velocity can be adjusted by the rotation speed of the ventilator (420) in the VIPS region (400).

[0136] The VIPS process, performed on one side of the separator and on the other side of the separator that yields the second porous polymer layer, can be the same (Figure 2) or different (Figure 3).

[0137] A phase transition step, preferably a LIPS step in a solidification bath, can be followed by a washing step.

[0138] After a phase conversion process or an optional washing process, an optional drying process is performed.

[0139] Manufacturing of separators Figures 2 and 3 schematically illustrate a preferred embodiment for manufacturing a separator according to the present invention.

[0140] The porous support is preferably a continuous web (100).

[0141] The web is pulled out from the feed roller (600) on which it was wound and guided downward between two coating units (200) and (300) in a vertical position.

[0142] These coating units are used to coat each side of the web with the dope solution. The coating thickness on each side of the web can be adjusted by optimizing the flow rate, viscosity of the dope solution, and distance between the coating unit and the web surface, as described above. Suitable coating units are described in EP-A 2296825, paragraphs

[0043] ,

[0047] ,

[0048] ,

[0060] ,

[0063] , and Figure 1.

[0143] Next, the web, with both sides coated with the doping solution, is transported downwards over a distance d towards the coagulation bath (800).

[0144] In the coagulation bath, the LIPS process is carried out.

[0145] The VIPS process is performed in the VIPS region before entering the coagulation bath. In Figure 2, the VIPS region (400) is identical on both sides of the coated web, whereas in Figure 3, the VIPS regions (400(1)) and (400(2)) on each side of the coated web are different.

[0146] The relative temperature (RH) and air temperature in the VIPS region can be optimized using thermally separated metal plates. In Figure 2, the VIPS region (400) is completely shielded from the environment by such metal plates (500). Therefore, the RH and air temperature are determined primarily by the temperature of the solidification bath. The air velocity in the VIPS region can be adjusted by a ventilator (420).

[0147] In Figure 3, the VIPS regions (400(1)) and (400(2)) are distinct from each other. The VIPS region (400(1)) on one side of the coated web, which includes a metal plate (500(1)), is identical to the VIPS region (400) in Figure 2. The VIPS region (400(2)) on the other side of the coated web is different from region (400(1)). There is no metal plate shielding the VIPS region (400(2)) from the environment. However, the VIPS region (400(2)) is shielded from the solidification bath by a thermally separated metal plate (500(2)). Also, there is no ventilator in the VIPS region 400(2). As a result, the VIPS region (400(1)) has a higher RH and air temperature compared to the other VIPS region (400(2)).

[0148] High RH and / or high air velocity in the VIPS region typically result in larger maximum pore diameters.

[0149] In one VIPS region, the RH is preferably more than 85%, more preferably more than 90%, and most preferably more than 95%, while in the other VIPS region, the RH is preferably less than 80%, more preferably less than 75%, and most preferably less than 70%.

[0150] After the phase separation process, the reinforced separator is then transported to the roll-up system (700).

[0151] The liner can be provided to one side of the separator, and then the separator and the installed liner can be rolled up.

[0152] electrolyzer The alkaline water electrolysis separator according to the present invention can be used in an alkaline water electrolysis apparatus.

[0153] An electrolysis cell typically consists of two electrodes, an anode and a cathode, separated by a separator. The electrolyte is located between the two electrodes.

[0154] When an electric current is supplied to the electrolysis cell, the hydroxyl ions in the electrolyte are oxidized to oxygen at the anode, and water is reduced to hydrogen at the cathode. The hydroxyl ions formed at the cathode move to the anode through the separator. The separator prevents the mixing of hydrogen gas and oxygen gas formed during electrolysis.

[0155] The electrolyte is typically an alkaline solution. A suitable electrolyte 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 is preferably 20 to 40% by weight of the total weight of the electrolyte.

[0156] 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, even higher temperatures, for example, at least 100°C, more preferably 125°C to 165°C, can also result in more efficient electrolysis.

[0157] The electrode typically includes a substrate with a so-called catalyst layer. The catalyst layer can be different for the anode, where oxygen is formed, and the cathode, where hydrogen is formed.

[0158] Typical substrates are made of conductive materials selected from the group consisting of nickel, iron, mild steel, stainless steel, vanadium, molybdenum, copper, silver, manganese, platinum group elements, graphite, and chromium. The substrate may also be made of a conductive alloy of two or more metals or a mixture of two or more conductive materials. Preferred materials are nickel or nickel-based alloys. Nickel has good stability in strong alkaline solutions, good conductivity, and is relatively inexpensive.

[0159] The catalyst layer preferably contains nickel, cobalt, iron, and platinum group elements. The catalyst layer may contain these elements as elemental metals, compounds (e.g., oxides), composite oxides or alloys made of multiple metallic elements, or mixtures thereof. Suitable catalyst layers include plated nickel, nickel-cobalt or nickel-iron plated alloys, composite oxides containing nickel and cobalt, such as LaNiO3, LaCoO3, and NiCo2O4, compounds of platinum group elements, such as iridium oxide, or carbon materials, such as graphene.

[0160] Particularly suitable catalyst layers include 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 leaching result in large surface area and high density lattice defects, which serve as active sites for electrocatalytic reactions.

[0161] Suitable porous electrodes and methods for preparing them are disclosed, for example, in EP-A 3575442, paragraphs 23-84.

[0162] The pore size of a porous electrode can affect the electrolysis efficiency. For example, EP-A 3575442 discloses that a suitable pore size for a porous electrode is 10 nm to a maximum of 200 nm.

[0163] The catalyst layer may also contain organic substances such as polymers to improve durability and adhesion to the substrate.

[0164] In so-called zero-gap electrolytic cells, the electrodes are positioned in direct contact with the separator, thereby reducing the space between the two electrodes. Mesh-type or porous electrodes are used to allow the separator to be filled with electrolyte and to efficiently remove the formed oxygen and hydrogen gases. Such zero-gap electrolytic cells have been observed to operate at higher current densities.

[0165] However, in such zero-gap electrolytic cells, it has been observed that bubbles formed inside the separator can accumulate at the top of the separator. Such accumulation of bubbles at the top of the separator can increase ionic resistance in that part of the cell. The resulting temperature rise due to reduced efficiency of electrolyte cooling in that region of the electrolysis cell could even lead to combustion of the separator.

[0166] It has been observed that introducing a short distance between one side of the separator and at least one electrode reduces the accumulation of air bubbles inside the separator. The distance between one side of the separator and the anode and the distance between the other side of the separator and the cathode can be the same or different.

[0167] The distance between the separator surface and at least one electrode is preferably 50 to a maximum of 500 μm, more preferably 100 to a maximum of 250 μm.

[0168] The distance between the separator and the electrode can be achieved by using a so-called spacer.

[0169] Such spacers are preferably hydrophilic (static water contact angle of 90°C or less, preferably 45°C or less) in order to prevent air bubbles from adhering to them.

[0170] Such spacers preferably have an open structure to ensure the rapid and sufficient discharge of air bubbles.

[0171] A typical alkaline water electrolysis apparatus includes multiple electrolytic cells, which are also referred to as an electrolytic cell stack.

[0172] Regarding the three-dimensional arrangement of cells, two types of electrolytic devices are typically used.

[0173] A unipolar (or "tank-type") electrolytic apparatus consists of alternating anodes and anodes separated and fixed by a separator. All anodes are coupled in parallel, as are the anodes. This entire assembly is immersed in a single electrolyte bath ("tank") to form a unit cell. These units are then electrically connected in series to create a plant-scale electrolytic apparatus. The total voltage applied to the entire electrolytic cell is the same as that applied to the individual unit cells.

[0174] On the other hand, in a bipolar electrolytic device, a metal sheet (or "bipolar") electrically connects adjacent cells in series. The electrolytic catalyst for the negative electrode is coated on one side of the bipolar, and the electrolytic catalyst 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, a stack of such cells connected in series forms a module that operates at a higher voltage and lower current than a tank-type (unipolar) design. To meet the requirements of large-scale electrolysis plants, these modules are connected in parallel to increase the current.

[0175] Membrane electrode assemblies (MEAs) can also be used in electrolytic devices. Such MEAs are typically prepared by applying a separator, preferably one without a reinforcing support, to at least one porous electrode. Such MEAs are disclosed, for example, in EP-A 2831312 (Agfa Gevaert), EP3277862 (De Nora), and WO2020 / 158719 (Nippon Shokubai). Such MEAs can also be used in the electrolysis method according to the present invention.

[0176] The catalyst layer mentioned above can also be provided on the surface of the separator to produce a so-called catalyst-coated film (CCM).

[0177] Such a CCM can result in improved contact between the film surface and the catalyst layer, leading to higher electrolysis efficiency.

[0178] The catalyst layer can be applied to the film surface using any precipitation technique, such as coating, spraying, inkjet printing, gravure printing, screen printing, 3D printing, or vapor deposition. [Examples]

[0179] material All materials used in the following examples, unless otherwise specified, are standard materials such as ALDRICH CHEMICAL Co. (Belgium) and ACROS (Belgium). It was readily available from a supplier. The water used was deionized water.

[0180] PPS-Fabric, a 100μm thick polyphenylene sulfide woven fabric.

[0181] The particles are ZrO2, zirconium oxide, and have a D50 particle size of less than 1 μm, as measured by a Mastersizer available from Malvern Panalytical.

[0182] Polysulfone, Udel P1700 NT LCD, polysulfone resin available from Solway.

[0183] Glycerol, pore-enlarging agent, distributed by MOSSELMAN.

[0184] NBP, N-butyl-pyrrolidone, distributed by Taminco.

[0185] measurement Flatness / Distortion. The flatness / distortion of the separator was evaluated by visual inspection. Figure 5 illustrates the distortion observed in the separator.

[0186] Overlay thickness. The overlay thickness of the porous layer is determined by optical microscopy. Before imaging, the film is embedded in epoxy resin and mechanically polished. Imaging is performed using a Zeiss Discovery V12 stereomicroscope with ring light. Calibrated images are analyzed with the Image Pro 10 measurement tool. The overlay thickness is measured by drawing multiple lines perpendicularly from the edge of the film toward the outer edge of the mesh fibers, as shown in Figure 4. For illustration, Figure 4 shows multiple distances for d1 and d2, represented as d1(1), d1(2), d1(3), d2(1), d2(2), and d2(3). The average of d1 and d2 is calculated from all the distances measured at 10 different points on 5 images of 2 cm cross-sections of three different samples.

[0187] Viscosity. 100s of dope solution -1 The viscosity at 20°C was measured using a Kinexus LAB+ Rheometer, available from Malvern Panalytical, with a "cup and bob" geometry.

[0188] Gas permeability. Gas permeability was measured at 5 bar using a Porolux™ 1000 instrument.

[0189] Example 1 Preparation of separators S-1 to S-3 The dope solution was prepared by mixing the components listed in Table 1. [Table 1]

[0190] 100s of dope solution -1 The viscosity, as measured above, is 10.50 Pa·s.

[0191] Separators S-1 to S-3 were prepared as schematically shown in Figure 2. The doping solution was coated onto both sides of a 1.3 m wide PPS cloth at a speed of 3 m / min using a slot die coating technique. The flow rate in the slot coating dies (200-300, Figure 2) was adjusted as shown in Table 2. The coated support was then transported to a water bath (solidification bath, 800) maintained at 50°C. The VIPS process was performed in a closed area (400, d=7 cm, RH=98%, aerated) before entering the water bath. The coated support was then immersed in the water bath for 2 minutes, during which liquid-induced phase separation (LIPS) occurred. After an in-line washing process in water at 65°C for 5 minutes, the resulting separator was rolled up without drying and then cut into the desired form.

[0192] The resulting separators S-1 to S-3 have overlay thicknesses d1 and d2 and a total thickness D, as shown in Table 2. The gas permeability and strain evaluation of the separators are shown in Table 2, as evaluated as described above. A strain indicated as OK means that the strain present in the separator is the minimum possible. [Table 2]

[0193] The results in Table 2 clearly show that preparing separators by coating them with different flow rates Q1 and Q2 in a slot coating die results in separators with an overlay thickness d1 smaller than the overlay thickness d2.

[0194] If the overlay thickness d1 is less than 20 μm, the gas permeability becomes too high. This is because the fibers of the porous support begin to protrude through the porous layer.

[0195] The film strain is considered sufficiently good when d1 / d2 is less than 0.8.

Claims

1. A separator (1) for alkaline electrolysis, comprising a porous support (10), a first porous layer (20b) provided on one side of the porous support, and a second porous layer (30b) provided on the other side of the porous support, wherein the first porous layer and the second porous layer partially penetrate the porous support, and each layer has overlay thicknesses d1 and d2, respectively, the overlay thickness being defined as the portion of each porous layer that does not penetrate the porous support. below a) d1 is smaller than the overlay thickness (d2) of the second porous layer, and b) d1 is at least 20 μm. The separator characterized by the above.

2. The separator according to claim 1, wherein d1 / d2 is 0.8 or less.

3. A separator according to claim 1 or claim 2, having a thickness of 250 μm or less.

4. The porous support is the separator according to any one of the prior claims, wherein the porous support has a thickness of 50 to 150 μm.

5. The porous support having an opening ratio of 30 to a maximum of 80%, the separator according to any one of the prior claims.

6. Measured at 5 bar, the flow rate is 2–5.8 L / min·cm². ２ A separator according to any one of the prior claims, having gas permeability.

7. In a 30% by weight KOH aqueous solution, at 80°C, 0.1 ohm·cm ２ A separator according to any one of the prior claims, having an ion resistance of less than 1.

8. The separator according to any one of the prior claims, wherein the first porous layer and the second porous layer comprise a polymer resin and hydrophilic inorganic particles.

9. The separator according to claim 8, wherein the polymer resin is at least one selected from the group consisting of polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, and polyphenylsulfone.

10. The separator according to claim 8 or 9, wherein the hydrophilic inorganic particles are selected from at least one of the group consisting of zirconium oxide, zirconium hydroxide, magnesium oxide, magnesium hydroxide, titanium oxide, titanium hydroxide, and barium sulfate.

11. A method for manufacturing a separator for alkaline water electrolysis, comprising the following steps: - A step of coating both sides of a porous support (10) with a doping solution containing a polymer resin, hydrophilic inorganic particles, and a solvent, and - A step of performing a phase change with the coated doping liquid, thereby forming the first porous layer (20b) on one side of the porous support and the second porous layer (30b) on the other side of the porous support, Including the following: The first porous layer has an overlay thickness (d1) that is smaller than the overlay thickness of the second porous layer (d2). The method characterized by the above.

12. The first doping solution has a flow rate Q. １ The second doping liquid is coated onto one side of the porous support, and this allows the flow rate Q of the second doping liquid on the other side of the porous support to be ２ A slower method according to claim 11.

13. Q １ / Q ２ The method according to claim 12, wherein is 0.1 to 0.

9.

14. The method according to any one of claims 11 to 13, wherein the overlay thickness (d1) of the first porous layer is at least 20 μm.

15. Alkaline water electrolysis apparatus comprising a separator positioned between the cathode and the anode as defined in any one of claims 1 to 10.

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