Alkaline water electrolysis separator

Abstract

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, the first and second porous layers partially penetrating the porous support, and each layer having an overlay thickness d1 and d2, respectively, the overlay thickness being defined as the portion of each porous layer that does not penetrate the porous support, characterized in that a) d1 is smaller than the overlay thickness (d2) of the second porous layer, and b) d1 is at least 20 μm.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a separator for alkaline water electrolysis and a separator obtained by the 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 basic component of methanol, which is used in ammonia production and therefore in fertilizer production and in many polymer production processes. In refineries, hydrogen is used in the processing of middle oil products, which is another area of ​​use.

[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 an exothermic combustion reaction with oxygen, which forms water. No carbon-containing greenhouse gases are released during such a combustion reaction.

[0004] In order to realize a low-carbon society, renewable energy that uses natural energy such as solar and wind power is becoming increasingly important.

[0005] Electricity generation from wind and solar power systems is highly dependent on weather conditions. These constantly changing weather conditions create an imbalance between the supply and demand of electricity. To store surplus electricity, so-called power-to-gas technology, which uses electricity to generate gaseous fuels such as hydrogen, has attracted significant attention in recent years. As electricity generation from renewable energy sources increases, the demand for storing and transporting the generated energy will also increase.

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

[0007] In alkaline water electrolysis cells, so-called separators or membranes are used to separate electrodes of opposite polarity, to prevent short circuits between these electronic conductors (electrodes), and to prevent recombination of hydrogen (formed at the cathode) and oxygen (formed at the anode) by avoiding gas crossover. While performing all these functions, the separator must also be a high ionic conductor to transport hydroxyl ions from the cathode to the anode.

[0008] Separators typically include a porous support that reinforces the separator and facilitates its handling and installation in an electrolyser, as disclosed in US Pat.

[0009] Patent document 2 (Kawasaki / De Nora / ThyssenKrupp) discloses a membrane with a porous support and a polymeric porous membrane impregnated in the porous support. A membrane-forming solution is applied to one of the surfaces of the support, sometimes resulting in a double coating 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, which results in a membrane with symmetrical properties. The process includes the steps of providing a porous support as a web and a suitable dope, guiding the web in a vertical position, coating both sides of the web equally with the dope to produce a web-coated support, and subjecting the dope-coated web to a symmetrical surface pore-forming step and a symmetrical solidification step to produce a reinforced membrane.

[0011] US Patent No. 5,629,999 and US Patent No. 5,629,999 (Agfa-Gevaert and VITO) disclose manufacturing methods that produce reinforced membranes with symmetrical properties as described in US Patent No. 5,629,999. The porous supports used in these manufacturing methods have a thickness of more than 190 μm.

[0012] The advantage of membranes with symmetrical properties is improved robustness, since the occurrence of defects on one side of the support is not detrimental to the overall performance of the membrane.

[0013] Patent document 6 (Agfa-Gevaert) discloses a reinforced separator with symmetrical characteristics, which has 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 dope 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, distortion / flatness of the support may remain an issue, resulting in a distorted separator. Such distortion may result in performance issues in the electrolytic device.

[0015] Therefore, there remains a need for membranes with minimal strain, high ionic conductivity, and adequate 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 Summary of the Invention

[0017] The object of the present invention is to provide a separator with minimal distortion, high ionic conductivity, and good gas separation properties. Surprisingly, it has been found that when the separator has different overlay thicknesses d1 and d2 as defined in claim 1, the separator has minimal distortion, 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] Further objects of the present invention will become apparent from the following description. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a diagram schematically illustrating an embodiment of a separator according to the present invention. [Figure 2] 1A to 1C are diagrams schematically illustrating an embodiment of a method for manufacturing a separator according to the present invention. [Figure 3] 4A to 4C are diagrams schematically illustrating another embodiment of a method for manufacturing a separator according to the present invention. [Figure 4] 1 is a micrograph of a cross section of a separator according to the present invention illustrating overlay thicknesses d1 and d2 by showing multiple distances represented as d1(1), d1(2), d1(3), d2(1), d2(2), and d2(3). By drawing multiple lines, an average can be calculated. [Figure 5] 10 is an image of a separator showing distortion. DETAILED DESCRIPTION OF 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 porous layer (20b) and a second porous layer (30b) provided on each side of the porous support, and is a) the first porous layer has an overlay thickness (d1) that is less 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:

[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 porous layer overlay thickness can be determined microscopically, as further described.

[0023] Surprisingly, it has been found that distortion can be reduced 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 too high gas permeability. Too high gas permeability may result in too much electrolyte flow, which may carry dissolved gases to the wrong side of the electrolyzer, resulting in an increase in HTO (volume percentage of hydrogen present in the oxygen formed at the anode).

[0024] Preferably, the ratio of the overlay thicknesses 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 be reduced.

[0026] The gas permeability of the membrane is preferably 1 to 7 L / min cm2 , more preferably 1.5 to 6.5 L / min cm 2 , most preferably 2 to 5.5 L / min cm 2 Gas permeability can be measured using a Porolux™ 1000 instrument at 5 bar.

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

[0028] As described in more detail below, separators according to the present invention are preferably prepared by applying a coating liquid, also called a dope, to both surfaces of a porous support. The coating liquid typically comprises a polymer resin, hydrophilic inorganic particles, and a solvent. A porous layer is then obtained after a phase inversion process, 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 the porous support is preferably obtained by adjusting the flow rate in the slot coating die, as will be described in more detail further below.

[0030] When the dope is applied to both surfaces of the porous support, the dope penetrates the porous support, and the porous support is preferably completely impregnated with the dope.

[0031] The first and second porous layers provided on the porous support can have the same or different compositions and can have the same or different bubble points.

[0032] After phase inversion, infiltration into the porous support ensures that the three-dimensional porous polymer network also extends into the porous support, which results in good adhesion between the porous layer and the porous support.

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

[0034] The dope solution has been applied to both sides of the porous support 10, and the porous support is completely permeated with the applied dope solution. The applied dope layers are designated 20a and 30a.

[0035] After the phase inversion step (50), a separator (1) is obtained comprising a porous support (10) and a porous layer (20b, 30b) on each side of the support.

[0036] The separator contains pores with a pore size small enough to prevent gas crossover, while a larger pore size is preferred to ensure efficient transport of hydroxyl ions from the cathode to the anode, which requires efficient electrolyte penetration into the separator.

[0037] The pores are preferably characterized using the bubble point test method described in the American Society for Testing and Materials (ASMT) method F316. This technique is based on the displacement of the wetting liquid embedded in the separator by using pressurized inert gas. In this way, only the flow through the pores is measured.

[0038] The most difficult part for gas to displace liquid along the entire pore path is the most constricted part of the pore, also known as the pore space. The pore size measured by the bubble point test is the diameter of the pore, regardless of where the pore is located along the pore path.

[0039] All pore sizes referenced herein are measured using the Bubble Point Test Method described above.

[0040] The maximum pore diameter (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 bubble point test method can be adapted to measure the maximum pore diameter (PDmax) on both sides of the separator by using a grid to support one side of the separator during the measurement, and then performing another measurement with the grid supporting the other side of the separator.

[0043] Both sides of the separator can have the same or different maximum pore sizes.

[0044] A suitable separator has a maximum pore size PDmax(1) on one side and a maximum pore size 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 have substantially different maximum pore diameters PDmax(1) and PDmax(2), for example, to prevent air bubbles from being trapped inside the separator. For example, the separator may have a maximum pore diameter 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 diameter 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 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 to 80%, more preferably 50 to 70%. A separator with a porosity within the above range typically has excellent ion permeability and excellent gas barrier properties, since the pores of the membrane are continuously filled with the electrolyte.

[0047] porous support The porous support is used to reinforce the separator and ensure its mechanical strength.

[0048] It has been observed that as the thickness of the porous support decreases, the ionic conductivity through the reinforced separator increases. 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 especially preferably 75 μm or less.

[0049] However, 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 may be selected from the group consisting of a porous cloth and a porous ceramic plate.

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

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

[0053] Porous polymer fabrics can be woven or nonwoven. Woven fabrics typically have better dimensional stability and uniformity of opening rate and thickness. However, the manufacture of woven fabrics with a thickness of 100 μm or less is more complicated, resulting in more expensive fabrics. The manufacture of nonwoven fabrics is not as complicated, even for fabrics with a thickness of 100 μm or less. Also, nonwoven fabrics can be used for fabrics with a thickness of 100 μm or less. Woven fabrics can have a greater open area.

[0054] To ensure good penetration of the electrolyte into the support, the opening ratio of the porous support is preferably 30 to 80%, more preferably 40 to 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 smaller fiber diameters. 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 gauze 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 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 tetrafluoro(fluor)ethylene (ETFE) or chlorotrifluoro(fluor)ethylene (ECTFE), polyimide, polyetherimide, and m-aramid.

[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 and PEEK porous supports have high resistance to high temperatures and highly concentrated alkaline solutions, and high chemical stability against the active oxygen released from the anode during the water electrolysis process. In addition, 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 / cm 3 is.

[0061] The porous support is preferably a continuous web which allows for manufacturing processes 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 comprises a polymer resin.

[0064] The polymer resin forms a three-dimensional porous network as a result of a phase inversion process in the preparation of the separator, 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 may be used alone. Alternatively, two or more polymer resins can be used in combination.

[0066] PVDF and vinylidene fluoride (VDF) copolymers are preferred due to their oxidation / reduction resistance and film-forming properties. Among 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 an 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 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 dope may be 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 hydroxide is 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 hydrophilic particles that can be used are nitrides and carbides of elements from Group IV of 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. It is the particle size value at which the cumulative distribution is 50%. For example, if D50=1.0 um, then 50% of the particles are Greater than 1.0um, 50% smaller than 1.0um.

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

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

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

[0082] Preparation of the separator A suitable method for preparing the separator described above comprises the following steps: - applying a dope solution as described below to both sides of a porous substrate; and - performing a phase inversion on the applied dope, thereby forming a first porous layer and a second porous layer on one side and the other side of the porous support, respectively; and characterized by the following: a) The first porous layer has an overlay thickness (d1) that is less than the overlay thickness (d2) of the second porous layer.

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

[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] Suitable methods for producing reinforced separators are disclosed in EP-A 1776490, WO2009 / 147084, and EP-A 3652362. These methods result in web-reinforced separators, where the web, i.e., the porous support, is well embedded in the separator without the web emerging from the surface of the separator.

[0086] Another possible preparation method is disclosed in EP-A 3272908.

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

[0088] The solvent of the dope is preferably an organic solvent in which the polymer resin can be dissolved. Moreover, the organic solvent is preferably water-miscible.

[0089] The solvent is preferably selected from N-methyl-pyrrolidone (NMP), N-ethyl-pyrrolidone (NEP), N-butyl-pyrrolidone (NBP), N,N-dimethylformamide (DMF), formamide, dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMAC), acetonitrile, and mixtures thereof.

[0090] For health and safety reasons, a highly preferred solvent is N-butyl-pyrrolidone (NBP).

[0091] The dope may further contain other ingredients to optimize the properties of the resulting polymer layers, for example, their porosity and maximum pore size at their outer surface.

[0092] The dope preferably contains additives to optimize the pore size at the surface and inside of the porous layer, which can be organic or inorganic compounds, or a combination thereof.

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

[0094] Suitable organic compounds capable of influencing pore formation in the porous layer are selected from polyethylene glycol, polyethylene oxide, and polyvinylpyrrolidone.

[0095] Suitable polyethylene glycols have a molecular weight of 10,000 to 50,000, suitable polyethylene oxides have a molecular weight of 50,000 to 300,000, and suitable polyvinylpyrrolidones have a molecular weight of 30,000 to 1,000,000.

[0096] A particularly suitable organic compound capable of influencing pore formation in the porous layer is glycerol.

[0097] The amount of the compound capable of influencing pore formation is preferably 0.1 to 15% by weight, more preferably 0.5 to 5% by weight, based on the total weight of the dope solution.

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

[0099] Two or more additives capable of affecting pore formation can be used in combination.

[0100] The dope provided on each side of the porous support can be the same or different.

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

[0102] A preferred coating technique is extrusion coating.

[0103] In a highly preferred embodiment, the dope is applied by a slot die coating technique, where two slot coating dies (200-300, Figures 2-3) are positioned on each side of the porous support.

[0104] The slot coating die is capable of maintaining the dope at a predetermined temperature, distributing the dope evenly across the substrate, and controlling the coating thickness of the applied dope.

[0105] The viscosity of the dope solution is -1 and a temperature of 20°C, the viscosity 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 is preferably shear-thinning. -1 Viscosity vs. shear rate at 100 s -1 is preferably at least 2, more preferably at least 2.5, and most preferably at least 5.

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

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

[0109] If there is no difference in flow rate (ΔQ is zero) or only a small difference, the separator is likely to be distorted.

[0110] If the difference in flow rate is too large, the overlay thickness (d1) of the first porous layer will be 20 μm, which may cause the separator to have too high gas permeability. ΔQ=Q TOT In this case, the substrate may be coated on only one side.

[0111] The difference in flow rate ΔQ is preferably greater than zero and Q TOT The difference in flow rates 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 open area of ​​a porous support can be determined by how large the difference in flow rates can be. The more open area, the larger the ΔQ may be required to reduce strain. The less open area a porous support has, the smaller the ΔQ may be to achieve minimal strain.

[0113] The separator according to the present invention is preferably obtained by a method in which the flow rate Q of the dope solution at the slot coating die is adjusted so that the flow rate Q1 at the first slot coating die (200) is different from the flow rate Q2 at the second slot coating die (300), 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 that is transported downwardly between slot coating dies (200, 300) as shown in Figures 2-3.

[0115] Immediately after coating, the porous support is impregnated with the dope.

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

[0117] Phase inversion process After the dope is applied to the porous support, the applied dope is subjected to a phase inversion process, in which the applied dope is converted into a porous hydrophilic layer.

[0118] In a preferred embodiment, both dopes coated on the porous support are subjected to a phase inversion. .

[0119] Any phase inversion mechanism can be used to prepare the porous hydrophilic layer from the coated dope.

[0120] The phase inversion process preferably comprises 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 inversion process preferably comprises both a VIPS process and a LIPS process.

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

[0122] In the LIPS process, a porous support coated on both sides with a dope solution is contacted with a non-solvent that is miscible with the dope solution's solvent.

[0123] Typically, this is done by immersing the porous support, coated on both sides with the dope, 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-ethyl-pyrrolidone (NEP), N-butyl-pyrrolidone (NBP), dimethylformamide (DMF), dimethylsulfoxide (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 migration of the solvent from the coated polymer layer to the non-solvent bath and back into the polymer layer leads to phase inversion and the formation of a three-dimensional porous polymer network. The penetration of the coated dope into the porous support results in good adhesion of the resulting hydrophilic layer to the porous support.

[0128] In a preferred embodiment, the continuous web (100), coated on each side with dope, is transported downward in a vertical position towards the coagulation bath, as shown in Figures 2-3.

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

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

[0131] In the manufacturing process shown in FIG. 2, VIPS is performed in region 400 between the slot coating dies (200, 300) and on the non-solvent surface of the coagulation bath (800), while being shielded from the environment by, for example, a thermally isolated 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, and 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 coagulation bath (800) and / or the speed at which the stretched web 100 is transported from the slot coating die towards the coagulation bath.

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

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

[0136] The VIPS steps performed on one side of the separator and the other side of the separator that results in the second porous polymer layer can be the same (FIG. 2) or different (FIG. 3) from each other.

[0137] After the phase inversion step, preferably the LIPS step in a coagulation bath, a washing step can be performed.

[0138] After the phase inversion step, or the optional washing step, an optional drying step is performed.

[0139] Separator manufacturing 2-3 illustrate a preferred embodiment for producing a separator according to the present invention.

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

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

[0142] These coating units are used to coat the dope onto each side of the web. The coating thickness on each side of the web can be adjusted by optimizing the flow rate, viscosity of the dope, and the 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 FIG. 1.

[0143] The web, coated on both sides with the dope, is then transported downwards over a distance d towards the coagulation bath (800).

[0144] In the coagulation bath, the LIPS process takes place.

[0145] The VIPS process occurs in a VIPS zone prior to entry into the coagulation bath. In Figure 2, the VIPS zone (400) is identical on both sides of the coated web, while in Figure 3, the VIPS zones (400(1)) and (400(2)) on each side of the coated web are different.

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

[0147] In FIG. 3, VIPS regions 400(1) and 400(2) are different from each other. VIPS region 400(1), including metal plate 500(1), on one side of the coated web is identical to VIPS region 400 in FIG. 2. VIPS region 400(2) on the other side of the coated web is different from region 400(1). There is no metal plate shielding VIPS region 400(2) from the environment. However, VIPS region 400(2) is now shielded from the coagulation bath by thermally isolated metal plate 500(2). Also, there is no ventilator in VIPS region 400(2). As a result, VIPS region 400(1) has a higher RH and air temperature than the other VIPS region 400(2).

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

[0149] The RH in one VIPS region is preferably greater than 85%, more preferably greater than 90%, and most preferably greater than 95%, while the RH in the other VIPS region 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 a roll-up system (700).

[0151] A liner can be provided on one side of the separator and then the separator and applied liner can be rolled up.

[0152] electrolyzer The separator for alkaline water electrolysis 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. An electrolyte is present between the electrodes.

[0154] When an electric current is applied to the electrolysis cell, 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 migrate to the anode through a separator, which prevents mixing of the hydrogen and oxygen gases 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 wt % based on the total weight of the electrolyte.

[0156] The temperature of the electrolyte is preferably 50° C. to 120° C., more preferably 75° C. to 100° C., and most preferably 80 to 90° C. However, even higher temperatures, for example at least 100° C., more preferably 125 to 165° C., can also result in more efficient electrolysis.

[0157] The electrodes typically comprise a substrate provided with a so-called catalyst layer, which 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 can 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 a platinum group element. The catalyst layer can contain these elements as simple metals, compounds (e.g., oxides), composite oxides or alloys made of multiple metal elements, or mixtures thereof. Suitable catalyst layers include plated nickel, plated alloys of nickel and cobalt or nickel and iron, 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] A particularly suitable catalyst layer comprises Raney nickel. The Raney nickel structure is formed by selectively leaching aluminum or zinc from Ni-Al or Ni-Zn alloys. The lattice vacancies formed during leaching result in a large surface area and a high density of lattice defects, which are active sites for electrocatalytic reactions to occur.

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

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

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

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

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

[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 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.

[0168] The distance between the separator and the electrodes can be achieved using so-called spacers.

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

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

[0171] A typical alkaline water electrolysis system includes multiple electrolysis cells, also referred to as a stack of electrolysis cells.

[0172] With respect to cell configuration, two types of electrolyzers are typically used.

[0173] A monopolar (or "tank-type") electrolyzer consists of alternating anodes and cathodes, separated and fixed by separators. The cathodes are all coupled together 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 electrolyzer. The total voltage applied to the entire electrolysis cell is the same as that applied to each individual unit cell.

[0174] On the other hand, in bipolar electrolyzers, metal sheets (or "bipolar") electrically connect adjacent cells in series. An electrocatalyst for the negative electrode is coated on one side of the bipolar electrode, 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. A stack of such series-connected cells therefore forms a module that operates at a higher voltage and lower current than a tank-type (monopolar) design. To meet the requirements of large electrolysis plants, these modules are connected in parallel to increase the current.

[0175] Membrane electrode assemblies (MEAs) can also be used in electrolysis 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), EP 3277862 (De Nora), and WO 2020 / 158719 (Nippon Shokubai). Such MEAs can also be used in the electrolysis method according to the present invention.

[0176] The above mentioned catalyst layer may also be provided on the surface of the separator, resulting in a so-called catalyst coated membrane (CCM).

[0177] Such CCMs can provide improved contact area between the membrane surface and the catalyst layer, leading to higher electrolysis efficiency.

[0178] The catalyst layer can be applied to the membrane surface by any deposition technique, such as coating, spraying, inkjet printing, gravure printing, screen printing, 3D printing, vapor deposition techniques, and the like. [Example]

[0179] material All materials used in the following examples were obtained from standard suppliers such as Aldrich Chemical Co. (Belgium) and Acros (Belgium) unless otherwise specified. The water used was deionized water.

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

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

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

[0183] Glycerol, a pore expander, sold by MOSSELMAN.

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

[0185] measurement Flatness / Distortion. The flatness / distortion of the separator was assessed 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. Prior to imaging, the membrane is embedded in epoxy resin and mechanically polished. Images are taken with a Zeiss Discovery.V12 stereo microscope using a ring light. Calibrated images are analyzed with the measurement tool in Image Pro 10. The overlay thickness is measured by drawing multiple lines perpendicularly from the membrane edge to the outer edge of the mesh fibers, as shown in Figure 4. For illustration, Figure 4 shows multiple distances for d1 and d2, denoted as d1(1), d1(2), d1(3), d2(1), d2(2), and d2(3). The average values ​​of d1 and d2 are calculated from all the distances measured at 10 different points on five images of 2-cm-long cross sections of three different samples.

[0187] Viscosity: 100s of dope -1 and viscosities at 20°C were measured using a Kinexus LAB+ Rheometer available from Malvern Panalytical using "cup and bob" geometry.

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

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

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

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

[0192] The resulting separators S-1 to S-3 have overlay thicknesses d1 and d2 and total thickness D as shown in Table 2. The separator gas permeability and distortion were evaluated as described above and are shown in Table 2. Distortion indicated as OK means that the separator had minimal distortion. [Table 2]

[0193] From the results in Table 2, it is clear that preparing separators by coating with a slot coating die using different flow rates Q1 and Q2 results in separators having an overlay thickness d1 that is less than the overlay thickness d2.

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

[0195] The distortion of the film is good enough when d1 / d2 is lower 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, the first porous layer and the second porous layer partially penetrating the porous support, and each layer having an overlay thickness 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 less than the overlay thickness (d2) of the second porous layer; and b) d1 is at least 20 μm; d1 / d2 is 0.8 or less; The separator, characterized in that

2. 10. The separator of claim 1 having a thickness of 250 μm or less.

3. 3. The separator according to claim 1, wherein the porous support has a thickness of 50 to 150 μm.

4. 3. The separator according to claim 1, wherein the porous support has an opening ratio of 30 to a maximum of 80%.

5. 2 to 5.8 L / min cm measured at 5 bar 2 The separator according to claim 1 or 2, having a gas permeability of

6. 0.1 ohm cm in a 30 wt % KOH aqueous solution at 80°C 2 3. The separator of claim 1, having an ionic resistance of less than 0.1%.

7. The separator according to claim 1 or 2, wherein the first porous layer and the second porous layer contain a polymer resin and hydrophilic inorganic particles.

8. The separator according to claim 7 , wherein the polymer resin is at least one selected from the group consisting of polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, and polyphenylsulfone.

9. 8. The separator according to claim 7, wherein the hydrophilic inorganic particles are at least one selected from the group consisting of zirconium oxide, zirconium hydroxide, magnesium oxide, magnesium hydroxide, titanium oxide, titanium hydroxide, and barium sulfate.

10. A method for producing a separator for alkaline water electrolysis, comprising the following steps: - coating a dope solution containing a polymer resin, hydrophilic inorganic particles and a solvent onto both sides of the porous support (10); - performing a phase inversion on the applied dope, 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 less than the overlay thickness of the second porous layer (d2); d1 is at least 20 μm, and d1 / d2 is 0.8 or less; The method, characterized in that

11. The first dope solution flows at a flow rate Q 1 The second dope solution is applied to one side of the porous support at a flow rate Q 2 The method of claim 10, wherein the

12. Q 1 / Q 2 The method of claim 11, wherein is 0.1 to 0.

9.

13. 3. An alkaline water electrolysis apparatus comprising a separator as defined in any one of claims 1 or 2 located between a cathode and an anode.

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