Alkaline water electrolysis separator

Abstract

A separator (1) for alkaline electrolysis comprising a porous support (100) and a porous layer (200) provided on the porous support, characterized in that the separator has a lateral bubble point of at least 0.2 bar, measured according to the method described in the specification.

Description

[Technical Field]

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

[0002] Today, hydrogen is used in several industrial processes, for example, its use as a raw material in the chemical industry and as a reducing agent in the metallurgical industry. Hydrogen is the basic building block for the production of ammonia and, in turn, methanol, which is used in the production of fertilizers and many polymers. Refineries, where hydrogen is used to process intermediate oil products, are another area of ​​use.

[0003] Hydrogen is also considered an important future energy carrier, meaning that it can store and deliver energy in a usable form. Energy is released through an exothermic combustion reaction with oxygen, thereby forming water. No greenhouse gases, including carbon, are emitted during such a combustion reaction.

[0004] In order to realize a low-carbon society, renewable energy utilizing 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, resulting in large fluctuations and imbalances between the supply and demand of electricity. To store surplus electricity, so-called power-to-gas technologies, in which electricity is used to produce gaseous fuels such as hydrogen, have attracted much interest in recent years. As the generation of electricity from renewable energy sources increases, so too does the demand for storage and transportation of the generated energy.

[0006] Alkaline water electrolysis is an important manufacturing process in which electricity may be converted into hydrogen.

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

[0008] Separators typically include a porous support that reinforces the separator, thereby facilitating its handling and installation in an electrolytic cell, as disclosed in US Patent No. 5,929,999 (Hydrogen Systems).

[0009] Patent Document 2 (VITO) discloses a process for preparing a reinforced separator. This process results in a membrane with symmetrical properties. The process includes the steps of providing a porous support as a web and a suitable dope solution, guiding the web in a vertical position, coating both sides of the web equally with the dope solution to produce a web-coated support, and subjecting the dope-coated web to a symmetrical surface pore-forming step and a symmetrical coagulation step to produce a reinforced membrane comprising a porous support and two porous polymer layers on either side of the support.

[0010] US Pat. No. 5,629,999 and US Pat. No. 5,629,999 (Agfa Gevaert and VITO) disclose manufacturing methods for producing reinforced membranes with symmetrical properties as described in US Pat. No. 5,629,999.

[0011] Patent Document 5 (Kawasaki, De Nora Permelec, Thyssen Krupp discloses a separator that is made by applying a dope solution to one side of a porous support followed by a symmetrical pore formation process, resulting in a separator with substantially identical pores on both sides of the separator.

[0012] Patent Document 6 (Nippon Shokubai) also discloses a separator reinforced with a porous support.

[0013] However, it has been observed that voids located at the interface between the porous polymer layer and the porous support can lead to the formation of bubbles inside the separator. The formation of bubbles can lead to a decrease in ionic conductivity through the separator and therefore to a decrease in the electrolysis efficiency. These bubbles can accumulate at the top of the separator placed in the electrolytic cell (lateral movement of bubbles in the separator), leading to so-called hot spots or even to the burning of the separator. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] European Patent Application Publication No. 232923 [Patent Document 2] European Patent Application Publication No. 1776490 [Patent Document 3] International Publication No. 2009 / 147084 Brochure [Patent Document 4] International Publication No. 2009 / 147086 Brochure [Patent Document 5] European Patent No. 3312306 [Patent Document 6] European Patent No. 3660188 Summary of the Invention

[0015] It is an object of the present invention to provide a reinforced separator that may achieve more efficient water electrolysis by reducing lateral movement of gas bubbles within the separator.

[0016] This object is achieved by the separator defined in claim 1.

[0017] Further objects of the present invention will become apparent from the following description. [Brief explanation of the drawings]

[0018] [Figure 1] 1 shows a schematic diagram of the lateral and longitudinal directions of a separator used in the present invention. [Figure 2] 1 shows a schematic diagram of one embodiment of a separator according to the present invention. [Figure 3] 2 shows a schematic representation of another embodiment of a separator according to the present invention. [Figure 4] 1 shows SEM photographs of a comparative (top) and inventive (bottom) separator showing the presence (top) and absence (bottom) of voids (150) at the interface between the porous layer and the porous support. [Figure 5] 1 shows a schematic of the lateral diffusion of gas bubbles in a separator in a "zero gap" electrolysis cell. [Figure 6] 2A and 2B are schematic diagrams illustrating some examples of pore size distribution in the thickness direction of a separator. [Figure 7] 4 is a schematic diagram showing one embodiment of a method for producing the separator shown in FIG. 3. [Figure 8] 4 is a schematic diagram illustrating another embodiment of a method for producing the separator shown in FIG. 3. [Figure 9] 1 shows a schematic of a measurement method for determining the lateral bubble point. DETAILED DESCRIPTION OF THE INVENTION

[0019] Alkaline water electrolysis separator The separator (1) for alkaline electrolysis according to the present invention comprises a porous support (100); and a porous layer (200) provided on the side of the porous support, and characterized in that the separator has a lateral bubble point of at least 0.2 bar, preferably at least 0.35 bar, more preferably at least 0.5 bar, measured according to the method described below.

[0020] FIG. 1 shows a schematic diagram of the lateral (L1) and longitudinal (L2) directions of a separator (1) used herein.

[0021] 2 shows a schematic representation of an embodiment of a separator according to the present invention in which a porous layer (200) is provided on the side of a porous support (100). The porous layer (200) is preferably provided on the side of the porous support, as described below.

[0022] 3 shows a schematic representation of another embodiment of the separator according to the present invention, in which a first (250) porous layer is provided on one side of the porous support (100) and a second (250') porous layer is provided on the other side of the porous support (100). The first (250) and second (250') porous layers may be the same or different from each other. The porous layers are preferably provided on both sides of the porous support, as described below.

[0023] The thickness (t2) of the separator is preferably 50 to 750 μm, more preferably 75 to 500 μm, most preferably 100 to 250 μm, and particularly preferably 125 to 200 μm. Increasing the thickness of the separator typically increases the physical strength of the separator. However, increasing the thickness of the separator also typically decreases the electrolysis efficiency due to increased ionic resistance.

[0024] The thickness of the separator can affect the lateral bubble point, as it is affected by the shrinkage phenomenon (see below): a smaller thickness typically results in a higher lateral bubble point.

[0025] The separator preferably has a resistance of 0.1 ohm.cm in a 30 wt % aqueous KOH solution at 80°C. 2 Less than 0.07ohm.cm is preferable 2 It has the following ionic resistance: The ionic resistance may be determined using an Inolab® Multi 9310 IDS instrument available from VWR, part of Avantor, equipped with a TetraCon 925 conductivity cell available from Xylem.

[0026] As described in more detail below, separators according to the present invention are preferably prepared by applying a coating solution, also referred to herein as a dope solution, to one or both sides of a porous support.

[0027] The dope solution preferably includes a polymer resin, hydrophilic inorganic particles, and a solvent.

[0028] A porous layer is then obtained after a phase inversion step in which the polymer resin forms a three-dimensional porous polymer network.

[0029] When the dope solution is applied to one or both sides of the porous support, the dope solution preferably penetrates the porous support. The porous support is more preferably completely impregnated with the dope solution. Such impregnation of the porous support with the dope solution ensures that, after phase inversion, the three-dimensional porous polymer network also extends into the porous support, resulting in improved adhesion between the porous layer and the porous support.

[0030] However, during the preparation of the separator, the porous layer and the porous It has been observed that voids may form at the interface between the support and the porous support. The occurrence of such voids (150) at the interface between the porous support (100) and the porous layers (250, 250') provided on both sides of the support is evident from the SEM photograph (top) in Figure 4.

[0031] If the voids are large enough, bubbles may form within them. These bubbles may rise to the top of the electrolytic cell if the voids are interconnected laterally through the separator. The diffusion of such bubbles "inside" the separator to the top of the electrolytic cell, in this case with a zero-gap configuration, is shown in Figure 5 (LB). The accumulation of bubbles at the top of the electrolytic cell may result in higher ionic resistance within that portion of the cell. The temperature rise due to lower cooling efficiency within that region of the electrolytic cell may even result in separator combustion.

[0032] The lateral bubble, measured as described below, is determined by the lateral (L1) diffusion of bubbles within the separator, as opposed to the commonly known bubble point, also described below, which is a measure of the longitudinal (L2) diffusion of bubbles through the separator.

[0033] It has now been observed that with a separator having a lateral bubble point of at least 0.2 bar, preferably at least 0.35 bar, more preferably at least 0.5 bar, measured according to the method described below, fewer gas bubbles are formed inside the separator, thereby causing fewer gas bubbles (which can negatively affect electrolysis efficiency) to accumulate at the top of the electrolysis cell.

[0034] It has been found that the above mentioned lateral bubble point can be affected by: - composition of the dope solution; - composition and structure of the porous support; - Residual solvent in the porous support. These parameters are described in more detail below.

[0035] The separator contains pores with a pore size small enough to prevent recombination of hydrogen and oxygen by avoiding gas crossover along the length of the separator, while the pore size may not be too small to ensure efficient penetration of electrolyte into the separator to ensure efficient transport of hydroxyl ions from the cathode to the anode.

[0036] Porosity is preferably characterized using the bubble point test method described in American Society for Testing and Materials (ASMT) Method F316. This technique relies on displacing a wetting liquid embedded in the separator by applying an inert pressurized gas. Only through-pores are measured by this method.

[0037] The most difficult part for a gas to move a liquid along the entire pore path is the narrowest part of the pore, also known as the pore throat. The pore diameter measured by the bubble point test is the diameter of the pore throat, regardless of where the pore throat is located within the pore path.

[0038] The pores preferably have a maximum pore diameter (Pdmax) of 0.05 to 2 μm, more preferably 0.10 to 1 μm, and most preferably 0.15 to 0.5 μm, as measured by the bubble point test method.

[0039] FIG. 6 shows a schematic diagram of so-called through-pores a to e having various shapes. The through-pores are pores that allow transport from one side of the separator to the other side of the separator. Pore throats (p) are shown for the different pore geometries. For clarity, the porous support and porous layer of the separator are not shown separately in FIG. 6. The separator of FIG. 6 can be the separator shown in FIG. 2 or FIG. 3.

[0040] The pore throat may be located in: - the outer surface of the separator (a); - "inside" the separator (b, c, e); or - both on the outer surface of the separator and on the "inside" of the separator (d).

[0041] According to a preferred embodiment, the pore throat is located at a distance d3 and / or d4 from one or both outer surfaces of the separator. Distances d3 and d4 may be the same or different. Distances d3 and d4 are preferably 0 to 15 μm, more preferably 0 to 10 μm, from outer surfaces A″ and B″ of the separator, respectively.

[0042] The pore sizes on both outer surfaces may be substantially the same or different from each other. Substantially the same, as referred to herein, means that the ratio of the pore sizes on both surfaces is between 0.9 and 1.1. The pore size on the outer surface of the separator may also be measured by scanning electrode microscopy (SEM), as disclosed in EP 3652362.

[0043] For the pore shape (a) in FIG. 6, the pore diameter measured by SEM on the outer surface of the separator will correspond to the maximum pore diameter PDmax measured by the bubble point test method.

[0044] However, when the pore throat is located inside the separator (see pore shapes (b), (c), (d), and (e) in Figure 6), the maximum pore diameter (PDmax) measured by the bubble point test method is smaller than the pore diameter measured on the outer surface using SEM.

[0045] The bubble point test method may 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 the measurement. A separate measurement is made using a grid to support the other side of the separator.

[0046] Additionally, the PDmax measured on both sides of the separator may be substantially the same or different from each other.

[0047] Preferred separators having substantially the same pore size on both sides as measured by bubble point testing are disclosed in EP 1776480, US Pat. No. 5,649,999 and US Pat. No. 5,649,999.

[0048] A preferred separator having different pore sizes on both sides, as measured by the bubble point test method, is disclosed in EP 3652362. The maximum pore size PDmax(1) at the outer surface of the first porous layer is preferably 0.05 to 0.3 μm, more preferably 0.08 to 0.25 μm, and most preferably 0.1 to 0.2 μm. The maximum pore size PDmax(2) at the outer surface of the second porous layer is preferably 0.2 to 6.5 μm, more preferably 0.2 to 1.50 μm, and most preferably 0.2 to 0.5 μm. 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 electrolyte penetration in the separator, resulting in sufficient ionic conductivity.

[0049] The porosity of the separator is preferably 30 to 70%, more preferably 40 to 60%.

[0050] Separators with porosities in the above range generally have excellent ion permeability and gas barrier properties because the pores of the diaphragm are continuously filled with the electrolyte. A porosity of 80% or more will result in too low mechanical strength of the separator and too high electrolyte penetration, the latter of which will result in an increase in HTO (the weight percent of hydrogen present in the oxygen formed at the anode).

[0051] The separator preferably has a pressure of 200 to 800 l / bar.hm 2 , more preferably 300 to 600 l / bar.hm 2 It has a water permeability of . porous support

[0052] The porous support (100) is used to reinforce the separator and ensure its mechanical strength.

[0053] The thickness (t1) of the porous support is preferably 350 μm or less, more preferably 200 μm or less, most preferably 100 μm or less, and particularly preferably 75 μm or less.

[0054] Ionic conductivity through reinforced separators has been observed to increase as the thickness of the porous support decreases.

[0055] 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.

[0056] The porous support may be selected from the group consisting of a porous fabric and a porous ceramic plate.

[0057] The porous support is preferably a porous fabric, more preferably a porous polymer fabric, which is often referred to as a polymer mesh.

[0058] Porous polymer fabrics can be woven or nonwoven. Woven fabrics typically have better dimensional stability and uniformity of open area and thickness. However, the production of woven fabrics with a thickness of 100 μm or less is more complicated and results in more expensive fabrics. The production of nonwoven fabrics is relatively simple, even for fabrics with a thickness of 100 μm or less. Nonwoven fabrics can also have a larger open area.

[0059] Suitable porous polymer fabrics are prepared from polypropylene (PP), polyethylene (PE), polysulfone (PS), polyphenylene sulfide (PPS), polyamide / nylon (PA), polyethersulfone (PES), polyphenylsulfone (PPSU), polyethylene terephthalate (PET), polyetheretherketone (PEEK), sulfonated polyetheretherketone (s-PEEK), monochlorotrifluoroethylene (CTFE), copolymers of ethylene with tetrafluoroethylene (ETFE) or chlorotrifluoroethylene (ECTFE), polyimide, polyetherimide, polyarylene, and m-aramid.

[0060] The porous support preferably has high resistance to high temperatures and highly concentrated alkaline solutions, and also has high chemical stability against active oxygen generated from the anode during the water electrolysis process.

[0061] Preferred porous supports are prepared from polypropylene (PP), polyphenylene sulfide (PPS) and polyether-ether ketone (PEEK).

[0062] The lateral bubble point of the separator has been observed to increase when the separator includes a PEEK or polyarylene porous support.

[0063] The open area of ​​the porous support is preferably 30 to 80%, more preferably 40 to 70%, to ensure good penetration of the electrolyte into the support.

[0064] The porous support is preferably a continuous web, which allows for manufacturing processes such as those disclosed in US Pat. Nos. 5,629,999 and 5,729,999.

[0065] The width of the web is preferably 30 to 300 cm, more preferably 40 to 200 cm.

[0066] It has been observed that the use of porous supports containing residual solvent in the preparation of separators can result in an increase in the lateral bubble point.

[0067] Residual solvent may be a result of the manufacturing process of the porous support, or may be a result of treating the porous support with one or more solvents.

[0068] Residual solvents are preferably selected from the group consisting of toluene, phenol, butyrolactone, dichlorobenzene, N-methylpyrrolidone, N-ethylpyrrolidone, N-butylpyrrolidone, chloro-N-methylaniline and oleicamide.

[0069] The residual solvent is more preferably selected from the group consisting of butyrolactone, N-methylpyrrolidone, N-ethylpyrrolidone, N-butylpyrrolidone, chloro-N-methylaniline and oleicamide.

[0070] Residual solvents are most preferably selected from N-methylpyrrolidone, N-ethylpyrrolidone, N-butylpyrrolidone, chloro-N-methylaniline and oleicamide.

[0071] The amount of residual solvent is preferably at least 25 ppm, more preferably at least 50 ppm, most preferably at least 75 ppm, and especially preferably at least 100 ppm.

[0072] The method for treating the porous support preferably comprises the following steps: - immersing the porous support in at least one of the above-mentioned solvents, The solvent is partially removed from the porous support.

[0073] The temperature of the solvent in the immersion step depends on the type of solvent, in particular its boiling point. Immersion is preferably carried out at a temperature of at least 50°C, more preferably at least 75°C, and most preferably at least 100°C.

[0074] The immersion time is preferably 12 hours or more, more preferably 1 day or more, and most preferably 1 week or more.

[0075] The solvent is then partially removed from the porous support to obtain the desired amount of residual solvent, which may be done by wiping the solvent from the porous support and / or drying the porous support.

[0076] polymer resin The porous layer preferably comprises a polymer resin.

[0077] The polymer resin forms a three-dimensional porous network, which is the result of a phase inversion process in the preparation of the separator, as described below.

[0078] The polymer resin may 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, or two or more of the polymer resins may be used in combination.

[0079] 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.

[0080] Another preferred polymer resin is an aromatic hydrocarbon resin due to its excellent heat resistance and alkali resistance. Examples of aromatic hydrocarbon resins include, for example, polyethylene terephthalate, polybutylene terephthalate, polybutylene naphthalate, polystyrene, polysulfone, polyethersulfone, polyphenylene sulfide, polyphenylsulfone, polyacrylate, polyetherimide, polyimide, and polyamideimide.

[0081] Particularly preferred polymer resins are selected from the group consisting of polysulfone, polyethersulfone and polyphenylsulfone, with polysulfone being most preferred.

[0082] The molecular weight (Mw) of polysulfone, polyethersulfone, and polyphenylsulfone 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 solution may be too high.

[0083] Examples of polysulfones, polyethersulfones and combinations thereof are disclosed in European Patent Application Publication No. 3085815, paragraphs

[0021] to

[0032] .

[0084] It has been observed that the amount of polymer resin in the dope solution can affect the lateral bubble point: too little polymer resin can result in void formation and / or too high porosity, both of which result in too low a lateral bubble point.

[0085] inorganic hydrophilic particles The porous layer preferably contains hydrophilic particles. After phase inversion, a hydrophilic porous polymer layer is obtained. A sufficient amount of hydrophilic particles is added to the porous layer to ensure sufficient wetting of the separator by the electrolyte.

[0086] Preferred hydrophilic particles are selected from metal oxides and metal hydroxides.

[0087] Preferred metal oxides are selected from the group consisting of zirconium oxide, titanium oxide, bismuth oxide, cerium oxide and magnesium oxide.

[0088] Preferred metal hydroxides are zirconium hydroxide, titanium hydroxide, bismuth hydroxide, hydroxide The magnesium hydroxide is selected from the group consisting of cerium hydroxide and magnesium hydroxide. Particularly preferred magnesium hydroxide is disclosed in Patent Document 6, paragraphs

[0040] to

[0063] .

[0089] Another preferred hydrophilic particle is barium sulfate particle.

[0090] Other hydrophilic particles that may be used are nitrides and carbides of elements from Group IV of the periodic table.

[0091] The hydrophilic particles preferably have a D 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. 50 particle size. D 50 The particle size is preferably 0.7 μm or less, preferably 0.55 μm or less, more preferably 0.40 μm or less.

[0092] D 50 Particle size is also known as the median diameter or mean value of the particle size distribution. 50 The particle size is the value of the 50% particle size in the cumulative distribution. For example, D 50 = 0.1um, 50% of the particles are larger than 1.0um and 50% are smaller than 1.0um.

[0093] D 50 Particle size is preferably measured using laser diffraction, for example using a Mastersizer from Malvern Panalytical.

[0094] 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.

[0095] 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.

[0096] Preparation of the separator A preferred method for preparing the separator according to the first aspect comprises the following steps: - applying a dope solution as described below to the side of the porous support (100); and - forming a porous layer (200) by performing a phase inversion on the applied dope solution.

[0097] The applied dope solution preferably completely impregnates the porous support before phase inversion occurs.

[0098] Another preferred method for producing a reinforced separator is disclosed in U.S. Patent Nos. 5,669,992 and 5,669,992 for a symmetric separator, and in European Patent No. 3,652,362 for an asymmetric separator. These methods result in a web-reinforced separator, in which the web, i.e., the porous support, is well embedded in the separator without the web appearing on the surface of the separator.

[0099] Other manufacturing methods which may be used are disclosed in EP 3272908, WO 02 / 04999 and WO 02 / 04999.

[0100] Dope Solution The dope solution preferably includes a polymer resin as described above, hydrophilic particles as described above, and a solvent.

[0101] The solvent of the dope solution is preferably an organic solvent capable of dissolving the polymer resin, and further, the organic solvent is preferably miscible with water.

[0102] 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.

[0103] For health and safety reasons, highly preferred solvents are N-butyl-pyrrolidone (NBP) and methyl 5-(dimethylamino)-2-methyl-5-oxopentanoate.

[0104] The type of solvent used can affect the lateral bubble point.

[0105] The dope solution may further contain other ingredients to optimize the properties of the resulting polymer layers, such as their porosity and the maximum pore size at their outer surface.

[0106] The doping solution preferably contains additives to optimize the surface and internal pore size of the porous layer. Such additives may be organic or inorganic compounds, or a combination thereof.

[0107] Organic compounds that may 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.

[0108] Preferred organic compounds that may affect pore formation in the porous layer are selected from polyethylene glycol, polyethylene oxide and polyvinylpyrrolidone.

[0109] Preferred polyethylene glycols have a molecular weight of 10,000 to 50,000, preferred polyethylene oxides have a molecular weight of 50,000 to 300,000, and preferred polyvinylpyrrolidones have a molecular weight of 30,000 to 100,000.

[0110] A particularly preferred organic compound that may affect pore formation in the porous layer is glycerol.

[0111] The amount of the compound that may affect 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.

[0112] Inorganic compounds that may affect pore formation include calcium chloride, magnesium chloride, lithium chloride and barium sulfate.

[0113] A combination of two or more additives that affect pore formation may be used.

[0114] The dope solutions applied to both sides of the porous support may be the same or different.

[0115] Dope solution application The dope solution may be applied to the side of the porous support by any application technique.

[0116] A well-known technique involves immersing the porous support in a dope solution that is applied onto a temporary support. After a layer separation step, the temporary support is removed and the porous support (100) is and a separator (1) comprising a porous layer (200) provided on the side of the porous support.

[0117] The dope solution is preferably applied to the side of the porous support by any coating or casting technique.

[0118] The preferred coating technique is extrusion coating.

[0119] In a highly preferred embodiment, the dope solution is applied by a slot die coating technique, with seven slot coating dies (FIGS. 7 and 8, 600 and 600') positioned on either side of the porous support.

[0120] The slot coating die can maintain the dope solution at a predetermined temperature, distribute the dope solution uniformly on the substrate, and adjust the coating thickness of the applied dope solution.

[0121] shear rate 100s -1 and the viscosity of the dope solution measured at a temperature of 20°C is at least 20 Pa.s, more preferably at least 30 Pa.s, and most preferably at least 40 Pa.s.

[0122] The dope solution is preferably shear thinning. Shear rate: 100 s -1 Viscosity at shear rate 1s -1 is preferably at least 2, more preferably at least 2.5, and most preferably at least 5.

[0123] The porous support is preferably a continuous web, which is preferably transported downward between slot coating dies (600, 600') as shown in FIGS.

[0124] Immediately after application, the porous support is impregnated with the dope solution.

[0125] Preferably, the porous support is completely impregnated with the applied dope solution.

[0126] If the dope solution is applied to only one side of the support, a single slot coating die located on one side of the support may be used.

[0127] Phase inversion process After applying the dope solution onto the porous support, the applied dope solution is subjected to a phase inversion process, in which the applied dope solution is converted into a porous layer.

[0128] In a preferred embodiment, both dope solutions applied to the porous support are subjected to phase inversion.

[0129] Any phase inversion mechanism may be used to prepare the porous layer from the applied dope solution.

[0130] 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. Preferably, the phase inversion process comprises both a VIPS process and a LIPS process.

[0131] Both LIPS and VIPS are non-solvent induced phase inversion processes.

[0132] In the LIPS process, the porous support coated with the dope solution is contacted with a non-solvent that is miscible with the solvent of the dope solution.

[0133] Typically, this is done by immersing the dope solution coated porous support in a non-solvent bath, also called a coagulation bath.

[0134] The non-solvent is preferably water, a mixture of water and an aprotic solvent selected from the group consisting of N-methylpyrrolidone (NMP), 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.

[0135] The non-solvent is most preferably water.

[0136] The temperature of the coagulation bath is preferably 20 to 90°C, more preferably 40 to 70°C.

[0137] The migration of the solvent from the coated polymer layer to the non-solvent bath and from the non-solvent to the polymer layer results in solidification of the polymer resin and the formation of a three-dimensional porous polymer network.

[0138] In a preferred embodiment, the continuous web (100) coated with the dope solution is transported downward in a vertical position towards a coagulation bath (800), as shown in FIGS.

[0139] In the VIPS process, the porous support coated with the dope solution is exposed to a non-solvent vapor, preferably humid air.

[0140] Preferably, the solidification step includes both the VIPS step and the LIPS step. Preferably, the VIPS step is performed before the LIPS step. In a particularly preferred embodiment, the porous support coated with the dope solution is first exposed to humid air (VIPS step) before being immersed in a water bath (LIPS step).

[0141] In the manufacturing method shown in Figure 7, VIPS is performed in the region 400 between the slot coating die (600, 600') and the surface of the non-solvent in the coagulation bath (800), which region is shielded from the environment using, for example, an insulating metal plate (500).

[0142] The degree and rate of water movement in the VIPS process can be controlled by adjusting the air velocity, air relative humidity and temperature, and exposure time.

[0143] The exposure time may be adjusted by varying the distance d between the slot coating die (600, 600') and the surface of the non-solvent in the coagulation bath (800) and / or the speed at which the elongated web 100 is transported from the slot coating die toward the coagulation bath.

[0144] The relative humidity within the VIPS region (400) may be controlled by the temperature of the coagulation bath and the shielding of the VIPS region (400) from the environment and the coagulation bath.

[0145] The velocity of the air may be regulated by the rotational speed of the ventilator (420) within the VIPS region (400).

[0146] The VIPS steps performed on one side of the separator and on the other side of the separator resulting in the seventh porous polymer layer may be the same as each other (FIG. 2) or different (FIG. 8).

[0147] After the phase inversion step, preferably the LIPS step in a coagulation bath, a washing step may be performed.

[0148] Preferably, the phase inversion step or the optional washing step is followed by a drying step.

[0149] Separator manufacturing 7 and 8 show a schematic representation of a preferred embodiment for producing a separator according to the present invention.

[0150] The porous support is preferably a continuous web (100).

[0151] The web is unwound from the supply roller (700) and guided downwards in a vertical position between the two coating units (600) and (600').

[0152] In these coating units, the dope solution is coated on both sides of the web. The coating thickness on both sides of the web can be adjusted by optimizing the viscosity of the dope solution and the distance between the coating unit and the surface of the web. Preferred coating units are described in EP 2296825, paragraphs

[0043] ,

[0047] ,

[0048] ,

[0060] ,

[0063] , and FIG. 1.

[0153] The web, coated on both sides with the dope solution, is then transported a distance d downwards towards the coagulation bath (800).

[0154] In the coagulation bath, the LIPS process takes place.

[0155] The VIPS process takes place in a VIPS zone prior to entering the coagulation bath. In Figure 7, the VIPS zone (400) is the same on both sides of the coated web, while in Figure 8, the VIPS zones (400(1)) and (400(2)) are different on both sides of the coated web.

[0156] The relative humidity (RH) and air temperature within the VIPS region may be optimized using insulating metal plates. In Figure 7, the VIPS region (400) is completely shielded from the environment by such metal plates (500). Therefore, the RH and air temperature are primarily determined by the temperature of the coagulation bath. The air velocity within the VIPS region may be regulated by a ventilator (420).

[0157] In FIG. 8, VIPS regions 400(1) and 400(2) are different from each other. The VIPS region 400(1) on one side of the coated web, including the metal plate 500(1), is identical to the VIPS region 400 in FIG. 7. 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 now shielded from the coagulation bath by the insulating metal plate 500(2). Additionally, there is no ventilator within VIPS region 400(2). This results in the VIPS region 400(1) having a higher RH and air temperature compared to the RH and air temperature of the other VIPS region 400(2).

[0158] High RH and / or high air velocity in the VIPS region typically results in larger maximum pore sizes.

[0159] The RH in one VIPS region is preferably more than 85%, more preferably more than 90%, and most preferably Preferably it is greater than 95%, while the RH in other VIPS regions is preferably less than 80%, more preferably less than 75%, and most preferably less than 70%.

[0160] After the phase separation process, the reinforced separator is then transported to a winding system (750).

[0161] After providing a liner on one side of the separator, the separator and applied liner may be rolled up.

[0162] electrolytic cell The separator for alkaline water electrolysis according to the present invention may be used in an alkaline water electrolysis cell.

[0163] An electrolytic cell typically consists of two electrodes, an anode and a cathode, separated by a separator. An electrolyte is present between both electrodes.

[0164] When electrical energy (voltage) is applied to an 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 through a separator to the anode. The separator prevents mixing of the hydrogen gas and oxygen gas formed during electrolysis.

[0165] The electrolyte solution is typically an alkaline solution. A preferred electrolyte solution is an aqueous solution of an electrolyte selected from sodium hydroxide or potassium hydroxide. Potassium hydroxide electrolytes are often preferred due to their higher specific conductivity. The concentration of the electrolyte in the electrolyte solution is preferably 20 to 40 wt % based on the total weight of the electrolyte solution. The temperature of the electrolyte solution is preferably 50 to 120°C, more preferably 75 to 100°C.

[0166] The electrodes typically comprise a substrate provided with a so-called catalyst layer, which may be different for the anode, where oxygen is formed, and the cathode, where hydrogen is formed.

[0167] Typical substrates are made from 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 from 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 electrical conductivity, and is relatively inexpensive.

[0168] The catalytic layer disposed on the anode preferably has a high oxygen generating capacity. The catalytic layer preferably contains nickel, cobalt, iron, and a platinum group element. The catalytic layer may contain these elements as elemental metals, compounds (e.g., oxides), composite oxides, or alloys of multiple metal elements, or mixtures thereof. Preferred catalytic 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.

[0169] Raney nickel structures are 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.

[0170] The catalyst layer may also include organic materials such as polymers to improve durability and adhesion to the substrate.

[0171] The catalytic layer provided on the cathode preferably has a high hydrogen production capacity. The catalytic layer preferably contains nickel, cobalt, iron, and a platinum group element. To achieve desired activity and durability, the catalytic layer may contain a metal, a compound such as an oxide, a composite oxide or alloy of multiple metal elements, or a mixture thereof. Preferred catalytic layers are formed from Raney nickel; a Raney alloy consisting of a combination of multiple materials (e.g., nickel and aluminum, nickel and tin); a porous coating prepared by plasma spraying a nickel compound or a cobalt compound; an alloy or composite compound of nickel with an element selected from cobalt, iron, molybdenum, silver, and copper; elemental metals and oxides of platinum group elements (e.g., platinum and ruthenium) with high hydrogen production capacity; a mixture of elemental metals or oxides of these platinum group element metals with a compound of another platinum group element (e.g., iridium or palladium) or a compound of a rare earth metal (e.g., lanthanum and cerium); and a carbon material (e.g., graphene).

[0172] To provide greater catalytic activity and durability, the above materials may be stacked in multiple layers or may be included in a catalyst layer.

[0173] Organic materials such as polymeric materials may be included to improve durability or adhesion to the substrate.

[0174] In so-called zero-gap electrolysis cells, the electrodes (cathode 950 and anode 950') are placed in direct contact with the separator (1), thereby reducing the space between both electrodes. Mesh-type or porous electrodes are used to allow the separator to fill with electrolyte and efficiently remove the formed oxygen and hydrogen gases. Such zero-gap electrolysis cells have been observed to operate at higher current densities. Such a zero-gap electrolysis cell is shown schematically in Figure 9.

[0175] A typical alkaline water electrolyser contains several electrolysis cells, also called a stack of electrolysis cells as described above. [Example]

[0176] material All materials used in the following examples were readily available from standard sources such as Aldrich Chemical Co (Belgium) and Acros (Belgium) unless otherwise stated. Water used was deionized water.

[0177] Fabric 1 is a PPS fabric containing 60 ppm residual solvents, of which 33 ppm comes from N-methylpyrrolidone, N-ethylpyrrolidone, N-butylpyrrolidone, and chloro-N-methylaniline.

[0178] Fabric 2 is a PPS fabric containing 149 ppm residual solvents, of which 96 ppm comes from N-methylpyrrolidone, N-ethylpyrrolidone, N-butylpyrrolidone, and chloro-N-methylaniline.

[0179] Fabric 3 is a PEEK fabric.

[0180] Fabric 4 is a polyarylene fabric.

[0181] measurement Lateral Bubble Points The method for measuring the lateral bubble point is shown schematically in FIG.

[0182] The separator was dried in a Mettler moisture meter for at least 2 minutes until its weight was constant and then punched to the exact outer circular size (300). A second punch of smaller diameter (10 mm) was then used to prepare a concentric hole (350) in the sample.

[0183] The washer-shaped sample (310) was covered from its bottom side with tape or a flat closed circular sheet having the same outer diameter (380).

[0184] This capped washer-shaped sample was then immersed in Porofil™, a porometer wetting fluid, and placed in the measurement cell of a Porometer 3G with a "grid" (390) at the bottom and a rubber O-ring (370) on top. Both the porometer wetting fluid and the porometer are commercially available from Quantachrome.

[0185] The increasing gas pressure of the porometer is now forced in a lateral direction (see arrows in Figure 9) and the pore size distribution is measured across the internal (lateral) structure.

[0186] Preparation of separators S-1 to S-7 Separators S-1 to S-7 were prepared on polymer fabrics according to Table 1, as shown schematically in Figure 7, using a dope solution containing 40 wt% polysulfone, 10 wt% zirconium oxide, and 50 wt% N-butylpyrrolidone or N-ethylpyrrolidone.

[0187] The dope solution was coated on both sides of the polymer fabric using a slot die coating technique at a speed of 3 m / min.

[0188] The coated fabric was then transported towards a water bath maintained at 65°C.

[0189] The VIPS step was carried out in an enclosed area prior to entering the water bath.

[0190] The coated support was then placed in a water bath for 2 minutes, during which time liquid-induced phase separation (LIPS) occurred.

[0191] The thickness of the obtained separator is shown in Table 1.

[0192] The lateral bubble point (LBP) and bubble point (BP) of S-1 to S-7 were measured as described above and are shown in Table 1. [Table 1]

[0193] From the results in Table 1, it is clear that the residual solvent content of the polymer fabric and the type of polymer fabric affect the lateral bubble point, while the bubble point remains fairly constant.

[0194] A thinner separator also results in a higher lateral bubble point.

[0195] It has been observed that electrolysis efficiency using separators having a lateral bubble point of at least 0.2 bar, measured as described above, is well maintained during operation.

Claims

1. A separator (1) for alkaline electrolysis comprising a porous support (100) and a porous layer (200) provided on the porous support, the separator having a lateral bubble point of at least 0.2 bar, the lateral bubble point being: (a) drying the separator for at least 2 minutes until it reaches a constant weight; (b) drilling a circular outer size from the separator and attaching it to the porometer measuring cell; Drill concentric holes into the tubular outer size to obtain washer-shaped samples; preparing a washer-shaped sample from the separator by (c) covering the washer-shaped sample from its bottom side with tape or a flat closed circular sheet having the same outer shape as the washer-shaped sample to create a covered-bottom washer-shaped sample; (d) immersing the bottom side of the capped washer sample in a porometer wetting fluid and placing the capped washer sample in a porometer measurement cell with the porometer grid located on the bottom side of the capped washer sample and the porometer rubber O-ring on top; (e) increasing the gas pressure in the porometer to determine the pressure at which the gas penetrates laterally through the separator, which pressure is the lateral bubble point; is measured by Separator.

2. 10. The separator of claim 1 having a lateral bubble point of at least 0.5 bar.

3. 3. The separator of claim 1 or 2, wherein the porous support comprises polyetheretherketone (PEEK) or a polyarylene polymer fabric.

4. 4. The separator according to claim 1, wherein the porous support contains at least 50 ppm of a residual solvent selected from the group consisting of toluene, phenol, butyrolactone, dichlorobenzene, N-methylpyrrolidone, N-ethylpyrrolidone, N-butylpyrrolidone, chloro-N-methylaniline, and oleicamide.

5. A separator described in any one of claims 1 to 4, wherein the porous layer includes a first porous layer (250) provided on a first side of the porous support and a second porous layer (250') provided on a second side of the porous support.

6. The separator of claim 5 , wherein the first porous layer and the second porous layer are the same.

7. The separator according to any one of claims 1 to 6, wherein the porous layer comprises a polymer resin and hydrophilic inorganic particles.

8. 8. The separator of claim 7, wherein the polymer resin is selected from the group consisting of polysulfone, polyethersulfone, and polyphenylsulfide.

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

10. The hydrophilic inorganic particles have a particle size D of 0.7 μm or less. 50 The separator of claim 9 having the formula:

11. The separator according to any one of claims 1 to 10, wherein the thickness (t2) of the separator is 100 to 500 µm.

12. The separator according to any one of claims 1 to 11, wherein the porous support has a thickness (t1) of 100 µm or less.

13. 200-800l / bar / h / m 2 The separator according to any one of claims 1 to 12, having a water permeability of 0.1 to 0.25 MPa.

14. An alkaline water electrolysis device comprising a separator as defined in any one of claims 1 to 13 located between the cathode and anode of the alkaline water electrolysis device.

15. 15. The alkaline water electrolysis device of claim 14, having a zero gap configuration.

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