Method of making a reinforced spacer

Abstract

A method for the production of a reinforced separator, comprising the steps of: - providing a porous support (6) on a pre-wetting casting drum (23); - applying a dope solution (3) comprising a polymeric resin and hydrophilic inorganic particles on one side of the porous support, other than the side of the porous support in contact with the pre-wetting casting drum; - phase-inverting (9, 1) the applied polymeric solution, thereby obtaining a reinforced separator; - removing the reinforced separator (7) from the casting drum; wherein the casting drum is pre-wetted with a non-solvent for the polymeric resin.

Description

[0001] Technical Field of the Invention

[0002] This invention relates to a method for preparing reinforced insulating components and their use in alkaline water electrolysis.

[0003] Background Art of the Invention

[0004] Today, hydrogen is used in several industrial processes, such as as a raw material in the chemical industry and a reducing agent in the metallurgical industry. Hydrogen is a fundamental building block in the production of ammonia and thus fertilizers, as well as in the production of methanol, which is used to produce many polymers. Refineries are another area of ​​application where hydrogen is used to process intermediate oil products.

[0005] Hydrogen is also considered an important future energy carrier, meaning it can store and transport energy in usable forms. It releases energy through an exothermic combustion reaction with oxygen, thereby forming water. This combustion reaction does not emit carbon-containing greenhouse gases.

[0006] In order to achieve a low-carbon society, the use of renewable energy sources such as solar and wind power is becoming increasingly important.

[0007] The generation of electricity from wind and solar power systems is highly dependent on weather conditions and therefore highly variable, leading to an imbalance between electricity supply and demand. To store excess electricity, so-called power-to-gas (PTO) technology, which uses electricity to produce gaseous fuels such as hydrogen, has received considerable attention in recent years. As the amount of electricity generated from renewable energy sources increases, the demand for the storage and transportation of this generated energy will also increase.

[0008] Alkaline water electrolysis is an important preparation method that can convert electricity into hydrogen gas.

[0009] In an alkaline water electrolysis cell, so-called separators or diaphragms are used to separate electrodes of different polarities to prevent short circuits between these electronically conductive components (electrodes) and to prevent the recombination of hydrogen (formed at the cathode) and oxygen (formed at the anode) by avoiding gas exchange. While performing all these functions, the separator should also be a highly ionic conductor for transporting hydroxide ions from the cathode to the anode.

[0010] The separator typically comprises a porous carrier. As disclosed in EP-A 23292 (Hydrogen Systems), such a porous carrier reinforces the separator to facilitate its operation and introduction into the electrolytic cell.

[0011] Due to their high tolerance to high temperatures and high concentrations of alkaline solutions, the preferred porous carriers are made of polypropylene (PP) or polyphenylene sulfide (PPS).

[0012] WO2009 / 147084 and WO2009 / 147086 (Agfa Gevaert and VITO) disclose a method for preparing reinforced spacers, in which a polymer solution, also known as a dope solution, is coated onto both sides of a porous support. However, this method is not optimal for preparing thin spacers. Coating the polymer solution onto both sides of a thin porous support (typical for such thin spacers) is critical and can lead to waviness in the spacer.

[0013] However, thin separators, including thinner porous carriers, lead to improved electrolysis efficiency due to their higher ionic conductivity.

[0014] A method in which a polymer solution is applied only to one side of a porous support typically uses a temporary support. For example, in the method disclosed in EP-A 232923 mentioned above, the stock solution is first applied to a temporary support. The porous support is then immersed in the applied polymer solution. After a coagulation step, the temporary support is removed from the resulting reinforced spacer.

[0015] An alternative to this temporary carrier is the so-called supporting casting drum. The casting drum supports the porous carrier on one side while a polymer solution is applied to the other side. After the coagulation step, the resulting spacer is then removed from the casting drum. However, as described in more detail below, this method also has several drawbacks, such as complexity and throughput.

[0016] Therefore, there is a need for a less complex and more cost-effective method for fabricating thin-reinforced spacers. Invention Overview

[0018] One object of the present invention is to provide a less complex and cost-effective method for preparing thin reinforced insulators with sufficient mechanical quality and improved ionic conductivity.

[0019] This objective is achieved by the method defined in claim 1.

[0020] Other objects of the invention will become apparent from the following description. Brief description of the attached diagram

[0022] Figure 1 This schematic diagram illustrates a prior art method for preparing reinforced insulating elements using a supported casting drum, wherein a polymer solution is coated on one side of a porous carrier.

[0023] Figure 2This schematic diagram illustrates another prior art method for preparing reinforced spacers using supporting casting belts, wherein a polymer solution is coated on one side of a porous carrier.

[0024] Figure 3 The schematic diagram illustrates a method for preparing a reinforced insulating element using a supported casting drum according to the present invention, wherein a polymer solution is coated on one side of a porous carrier.

[0025] Figure 4 The schematic diagram illustrates another method for preparing a reinforced insulating member using a supported embossed casting drum according to the present invention, wherein a polymer solution is coated on one side of a porous carrier.

[0026] Figure 5 Two embodiments of the isolator obtained using the method according to the present invention are illustrated. Invention Details

[0028] Method for preparing reinforced insulating components

[0029] A method for preparing a reinforced insulating element typically includes the following steps:

[0030] -Provide porous carriers,

[0031] - Apply a stock solution containing polymer resin, hydrophilic particles, and solvent to one side of a porous carrier.

[0032] - The applied stock solution undergoes a phase inversion.

[0033] The applied stock solution typically impregnates the porous support prior to the phase inversion step. Alternatively, the porous support can be immersed in the applied stock solution just before the phase inversion occurs.

[0034] Phase inversion typically occurs in a non-solvent environment within the polymer resin. This type of phase inversion is also known as liquid-induced phase separation (LIPS).

[0035] Figure 1 This invention discloses a prior art preparation method for preparing reinforced insulating components, wherein a stock solution is applied to one side of a porous carrier, and wherein a support casting drum is used.

[0036] A porous carrier (6) is provided on a casting drum (2). A stock solution is then applied (3) to the side of the porous carrier that is not in contact with the casting drum. The applied stock solution impregnates the porous carrier and comes into contact with the surface of the casting drum when the porous carrier is fully impregnated, and the surface of the casting drum rotates into a coagulation bath (1). The coagulation bath contains a non-solvent of the polymer resin for which the stock solution is applied, typically water.

[0037] The applied stock solution comes into contact with the non-solvent of the coagulation bath (1) only from one side. This usually results in a so-called asymmetric separator, which has small pores on the side in contact with the non-solvent and larger, less defined pores on the other side of the separator in contact with the casting drum.

[0038] The condensed stock solution (also known as a membrane) is at least partially embedded in a porous carrier (usually a fabric) and then further guided (7) to the washing section, the drying section and finally rolled up.

[0039] As the casting drum rotates out of the coagulation bath, its surface is wiped or scraped clean (8) and further dried in the drying zone (4) to provide a completely dry surface on which a porous carrier (6) is provided and the stock solution (3) is applied.

[0040] The extent to which the raw solution penetrates into the porous carrier depends on the pore area of ​​the carrier and the viscosity of the raw solution. However, most commonly, high penetration occurs, whereby the raw solution completely permeates the porous carrier and contacts the surface of the casting drum (2).

[0041] The separator (7) is released from the surface of the casting drum only when the phase transformation (condensation) of the applied stock solution is complete. The separator will remain attached to the casting drum as long as the applied stock solution has not completely solidified.

[0042] Because the applied solution only contacts the non-solvent on one side, a considerable amount of time will pass before the original solution in contact with the casting drum solidifies (cures) and the resulting separator can be released from the casting drum. As long as solidification is incomplete and the original solution in contact with the casting drum remains in a liquid state, the separator cannot delaminate or be released from the casting drum. Delamination will cause the applied original solution layer to crack.

[0043] The time required for complete coagulation of the stock solution depends on the thickness of the applied stock layer, the composition of the stock solution, the type of non-solvent, the temperature of the coagulation bath, and other process parameters. When using a rotary casting drum, the contact time between the applied stock solution and the non-solvent from the coagulation bath is determined by the drum's rotational speed. To ensure complete coagulation and release of the separator from the casting drum, the rotational speed and therefore the preparation speed are limited.

[0044] Increasing the diameter of the casting drum will prolong the contact time between the applied stock solution and the non-solvent in the coagulation bath, and increase the preparation speed.

[0045] Another way to increase the preparation speed is to use, for example... Figure 2 The flat annular belt shown, the flat belt (23), is typically made of stainless steel and runs on at least two rollers (21), one of which is driven. By using a longer belt (23), the contact time between the stock solution (3) applied to the porous support (6) and the non-solvent from the coagulation bath (1) is increased, thereby improving the preparation speed.

[0046] However, increasing the diameter of the casting drum or using a driven belt increases the complexity of the preparation method and thus increases the cost.

[0047] The above-mentioned problems are solved by the preparation method according to the invention, wherein the casting drum is uniformly pre-wetted with a small amount of non-solvent. Due to the presence of the non-solvent on the surface of the casting drum, when the applied stock solution comes into contact with the surface of the casting drum (after the porous carrier is fully impregnated), this will cause a phase inversion (condensation) of the applied stock solution. The porous carrier is almost immediately and completely impregnated by the applied stock solution after it is applied to the porous carrier. In this way, the separator can be delaminated from the casting drum more quickly, and a larger diameter drum or the use of a tape is not required.

[0048] The method for preparing the reinforced insulating member according to the present invention includes the following steps:

[0049] i) Provide a porous carrier (6) on the pre-wet casting drum (23);

[0050] ii) Apply the stock solution (3) containing polymer resin, hydrophilic inorganic particles and solvent to one side of the porous carrier, which is not the side of the porous carrier that is in contact with the pre-wet casting drum;

[0051] iii) Perform a phase inversion of the applied polymer solution (9, 1); and

[0052] iv) Remove the reinforcing isolation element (7) from the casting drum;

[0053] The feature is that the casting drum uses a non-solvent pre-wetting polymer resin.

[0054] As described below, the non-solvents mentioned can be a single solvent or a mixture of different solvents.

[0055] According to one embodiment of the invention, the casting drum is pre-wetted by applying a thin, non-solvent-based layer to the surface of the casting drum.

[0056] Non-solvent coatings can be applied to the casting drum using any coating technique, such as dip coating, doctor blade coating, extrusion coating, spray coating, and slide hopper coating.

[0057] The non-solvent layer contains less than 50 grams of non-solvent per square meter of casting drum surface area.

[0058] Preferably, the non-solvent used for pre-wetting the casting drum is the same non-solvent used in the liquid-induced phase inversion step (described below). In this case, the casting drum is preferably pre-wetted by dip coating, wherein, as Figure 3 The coating (2) is applied from the coagulation bath (1). The thickness of the applied non-solvent layer can be adjusted using an air knife or a metering roller (5).

[0059] When the non-solvent layer on the casting drum is too thick, the porous support may be over-wetted by the non-solvent, which may result in insufficient penetration of the applied feed solution into the porous support. Poor penetration of the feed solution into the porous support may cause the membrane (coagulated feed solution) to delaminate from the porous support after the coagulation step. Sufficient penetration of the feed solution into the porous support ensures adequate adhesion of the coagulated polymer layer to the porous support. Such good adhesion results in good mechanical properties of the separator, which is important for the operation of the separator and its introduction into the electrolytic cell.

[0060] The viscosity of the non-solvent is typically much lower than that of the dope solution. When the non-solvent layer on the casting drum is too thick, causing the porous fabric to be over-wetted by the non-solvent, uniform coating of the dope solution can become difficult due to the so-called slippage between the non-solvent and the dope solution. This may be because the shear force generated by viscous forces is insufficient to carry the entire dope package.

[0061] For these reasons, the thickness of the non-solvent layer on the casting drum is preferably lower than the thickness of the porous carrier. More preferably, the thickness of the non-solvent layer is less than 50% of the thickness of the porous carrier, and most preferably less than 20%.

[0062] According to another embodiment of the invention, such as Figure 4 As shown, an embossed roller is used as the casting drum.

[0063] The embossing roller or drum (23) rotates in the coagulation bath (1), where the grid or embossing is filled with a non-solvent. Excess non-solvent is preferably removed by a scraper or blade (8).

[0064] The amount or volume of non-solvent liquid drawn into an embossing drum depends on the geometry and depth of the embossed cells in the drum.

[0065] Embossed patterns can consist of lines, dots, or a combination of both. Dot patterns are often referred to as cell patterns.

[0066] Embossed cells can be quadrilaterals, pyramids, hexagons, or triple helices. Cells can also be interconnected through open channel embossing.

[0067] Cell count refers to the number of cell rows per linear centimeter. Cell depth refers to the depth of a cell. Cell volume (cm²) 3 / m 2 () refers to the amount of non-solvent that the embossing roller can absorb, and is determined by cell count and cell depth.

[0068] The preferred cell volume can be less than 25cm². 3 / m 2 or even less than 10cm 3 / m 2 This depends on the embossing pattern, depth, and line or cell density.

[0069] For quadrilateral cell patterns, a 25cm embossing depth can be achieved by using a cell count of 50 lines / cm and an embossing depth of 75μm. 3 / m 2 The cell volume. A 10cm cell can be obtained by using a cell count of 70 lines / cm and an embossing depth of 36μm. 3 / m 2 The volume of the cell.

[0070] Patterns, such as lines or dots, can be embossed mechanically or using lasers.

[0071] Figure 4 The enlarged images show the embossing drum (23), the porous carrier (6), and the resulting isolation element (7).

[0072] The porous carrier is composed of fabric fibers (described in more detail below), in Figure 4 The enlarged portion is depicted as a circle. This clearly illustrates the open area of ​​the porous carrier, allowing the original solution to penetrate well into the porous carrier. The reinforcing separator (7) consists of a porous carrier embedded in the condensed original solution.

[0073] The advantage of using an embossing casting drum is that the porous fabric (6) is little or not soaked in the pre-wetting liquid (10), which allows the original solution (3) to penetrate well into the fabric (6). Therefore, the fabric is well anchored or embedded in the membrane.

[0074] Another advantage of using a pre-wetting drum is that the rapid release of the original liquid from the drum, which has not yet fully condensed inside the fabric (7), allows for further solvent exchange on both sides, which can improve production speed.

[0075] As described in more detail below, the phase transformation step may also include a vapor-induced phase separation (VIPS) step. Figure 4 (9 in the middle)

[0076] When the surface tension of the non-solvent is too high to achieve good and uniform wetting of the drum surface (whether embossed or not) without dewetting spots, it may be necessary to add a surfactant to the pre-wetting solution to reduce its surface tension.

[0077] Preferably, the surface tension of the pre-wetted solution is less than 40 mN / m.

[0078] Thickeners can be added to the pre-wetted solution to increase its viscosity.

[0079] The viscosity of the pre-wetted solution is preferably below 50 mPa·s.

[0080] Casting drums or embossing drums are preferably made of abrasion-resistant materials with sufficiently high surface energy to achieve good spreading of the applied or scraped "pre-wet" solution. Materials that can be used as the drum surface include chrome plating, stainless steel, ceramics, etc.

[0081] The submersion portion of the drum or embossed drum in the condensation bath preferably reaches about 30 to 70% of the total circumference, more preferably about 40 to 60%.

[0082] Isolators for water electrolysis

[0083] The separator for water electrolysis obtained by the preparation method according to the present invention ( Figure 5 It includes a porous carrier (10) and a porous layer (20b). Such a spacer that includes a porous carrier is generally referred to as a reinforced spacer.

[0084] As described in more detail above, the preferred separator is prepared by applying a coating solution (commonly referred to as a stock solution) comprising a polymer resin, hydrophilic inorganic particles, and a solvent to one side of a porous carrier. A porous layer is then obtained after a phase inversion step, wherein the polymer resin forms a three-dimensional porous polymer network.

[0085] After the stock solution is applied to the surface of the porous carrier, the stock solution impregnates the carrier.

[0086] Following the phase inversion, the impregnation with the porous support ensures that the three-dimensional porous polymer network also extends into the porous support. This results in good adhesion between the porous hydrophilic layer and the porous support.

[0087] The preferred isolation element (100) is schematically shown. Figure 5 In the process, the stock solution (20a) is applied to one side of the porous support (10), and then preferably the support is completely impregnated with the applied stock solution. After the phase inversion step (50), a separator (100) comprising the support (10) and the porous layer (20b) is obtained.

[0088] Porous carriers are used to provide support and strength to the spacers during the preparation process, specifically in the coating and / or agglomeration steps described below. Using temporary carriers to reinforce the spacers during preparation also facilitates washing, rewinding, and other processes.

[0089] The porous carrier also provides strength and tear resistance to the separator during the conversion process (where, for example, the separator is cut into different formats) and during the assembly process (where the separator is introduced between the electrodes of the alkaline electrolyzer).

[0090] However, porous supports can adversely affect the ionic conductivity of the separator. Once placed in the electrolytic cell of an alkaline electrolyzer, it is not always necessary to reinforce the separator with porous supports. In particular, the so-called zero-gap configuration described below prevents the separator from vibrating due to escaping air bubbles and therefore avoids fatigue that could lead to cracks or tears in the separator.

[0091] According to another embodiment of the invention, as disclosed in unpublished EP-A20183861.2 (submitted by AgfaGevaert on July 3, 2020), the porous carrier can be substantially removed from the separator by an alkaline solution, more preferably by an electrolyte from an alkaline electrolyzer.

[0092] The alkaline solution or electrolyte in the alkaline electrolyzer is preferably a KOH aqueous solution of 10 to 40% by weight, more preferably 20 to 35% by weight. A particularly preferred alkaline solution or electrolyte is a 30% by weight KOH aqueous solution.

[0093] The temperature of the alkaline solution or electrolyte is preferably 50°C or higher, more preferably 80°C or higher.

[0094] The removal of porous carriers is preferably due to the carrier being dissolved in an alkaline solution or the electrolyte used in the electrolytic cell, or being degraded by the alkaline solution or the electrolyte used in the electrolytic cell.

[0095] As mentioned above, the presence of a porous carrier to enhance the spacer may adversely affect the ionic conductivity through the spacer. Preferably, the ionic conductivity of the spacer increases after the temporary carrier is removed.

[0096] The porous carrier can optionally be removed by treating the separator (100) with an alkaline solution (60) before assembly into the electrolyzer stack to obtain, as shown in the figure. Figure 5 The isolator (200) is shown schematically in the middle. (Reference) Figure 3 and Figure 4 Preferably, such alkaline treatment is carried out by guiding the separator (7) from the coagulation bath (1) to the alkaline bath.

[0097] The thickness of the separator is preferably 50 to 500 μm, more preferably 100 to 350 μm.

[0098] The pore size of the separator must be small enough to prevent the recombination of hydrogen and oxygen by avoiding gas exchange. On the other hand, a larger pore size is preferred to ensure efficient transport of hydroxide ions from the cathode to the anode. Efficient transport of hydroxide ions requires efficient permeation of the electrolyte into the separator.

[0099] The maximum aperture (PDmax) of the separator is preferably 0.05 to 2 μm, more preferably 0.10 to 1 μm, and most preferably 0.15 to 0.5 μm.

[0100] The pore size mentioned is preferably measured using the bubble point test method described in American Society for Testing and Materials Standard (ASMT) Method F316.

[0101] The porosity of the separator is preferably 30% to 70%, more preferably 40% to 60%. Separators with porosity within the above range generally have excellent ion permeability and excellent gas barrier properties because the pores of the membrane are continuously filled with electrolyte solution.

[0102] Apply the original solution

[0103] The coating or casting of the stock solution (3) on one side of the porous carrier (6) can be carried out using all known coating systems, preferably selected from rod or bar coating, extrusion coating and slot coating systems.

[0104] In a highly preferred embodiment, the stock solution is applied by slit coating. A slit coating die is typically used when applying the stock solution to one side of a carrier. The slit die is capable of maintaining the stock solution at a predetermined temperature, uniformly distributing the stock solution on the porous carrier, and adjusting the coating thickness of the applied stock solution by regulating the flow rate.

[0105] When used for slit die coating, the viscosity of the stock solution at the coating temperature and at 1s -1 The preferred shear rate is 1 to 500 Pa·s, more preferably 10 to 100 Pa·s.

[0106] The stock solution is preferably shear-thinned. Within 1 second... -1Viscosity at shear rate and at 100 s -1 The viscosity ratio at the shear rate is preferably at least 2, more preferably at least 2.5, and most preferably at least 5.

[0107] The porous carrier (6) is preferably a continuous web.

[0108] The porous carrier is preferably impregnated with the stock solution immediately after application. Preferably, the carrier is completely saturated with the applied stock solution.

[0109] Phase transformation steps

[0110] After the stock solution is applied to the carrier, a phase inversion is performed on the applied stock solution. In the phase inversion step, the applied stock solution is transformed into a porous hydrophilic layer.

[0111] Any phase inversion mechanism can be used to prepare porous hydrophilic layers from the applied stock solution.

[0112] The phase transformation step preferably includes a so-called liquid-induced phase separation (LIPS) step, a vapor-induced phase separation (VIPS) step, or a combination of VIPS and LIPS steps. The phase transformation step preferably includes both VIPS and LIPS steps.

[0113] Both LIPS and VIPS are solvent-inducible phase transformation processes.

[0114] In the LIPS step, a carrier coated with the stock solution is brought into contact with a non-solvent of the polymer resin of the stock solution, wherein the non-solvent is miscible with the solvent of the stock solution.

[0115] Typically, this is done by immersing a carrier coated with the original solution into a non-solvent bath, also known as a coagulation bath (1).

[0116] The non-solvent is preferably water, a mixture of water and an aprotic solvent selected from N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and dimethylacetamide (DMAC), an aqueous solution of a water-soluble polymer such as PVP or PVA, or a mixture of water and an alcohol such as ethanol, propanol or isopropanol.

[0117] Water is the preferred non-solvent.

[0118] The temperature of the coagulation bath is preferably 20 to 90°C, more preferably 40 to 70°C.

[0119] The transfer of solvent from the coated polymer layer to the non-solvent bath and the transfer of non-solvent into the polymer layer lead to a phase inversion and the formation of a three-dimensional porous polymer network. The impregnation of the applied stock solution into the support results in sufficient adhesion between the resulting hydrophilic layers on the support.

[0120] In the VIPS step, the carrier coated with the stock solution is exposed to non-solvent vapor, preferably humid air.

[0121] Preferably, the coagulation step includes both the VIPS and LIPS steps. Preferably, before immersion in the coagulation bath (LIPS step), the carrier coated with the stock solution is first exposed to humid air (VIPS step).

[0122] exist Figure 3 and Figure 4 In the preparation method shown, VIPS is performed in a region 9 between the slit coating die (3) and the surface of the non-solvent (20) in the coagulation bath (1), which is isolated from the environment by, for example, a heat-insulating metal plate (15).

[0123] The extent and rate of water transfer in the VIPS step can be controlled by adjusting the air velocity, relative humidity and temperature, and exposure time.

[0124] The exposure time can be adjusted by changing the distance between the slot coating die (3) and the surface of the non-solvent (20) in the coagulation bath (1) and / or the speed at which the elongated roll 6 is conveyed from the slot coating die to the coagulation bath.

[0125] The relative humidity in the VIPS area (9) can be regulated by the temperature of the condensation bath and by the isolation (15) of the VIPS area from the environment and from the condensation bath.

[0126] The air velocity can be adjusted by the rotational speed of the ventilator incorporated into the VIPS area (9).

[0127] A washing step can be performed after the phase inversion step, preferably after the LIPS step in a condensation bath.

[0128] A drying step may be performed after the phase inversion step or, optionally, the washing step.

[0129] Remove temporary carrier

[0130] In embodiments where a temporary carrier is used, as described below, the temporary carrier may be removed before or after the spacer is placed between the electrodes of the electrolytic cell.

[0131] When the temporary support is removed before the separator is placed in the alkaline electrolyzer, the dissolved material or degradation products of the porous support after it has been removed by the electrolyte in the alkaline electrolyzer will not adversely affect the electrocatalytic properties of the electrode or the electrolysis process. However, when the support is removed outside the electrolyzer, the additional enhancement provided to the operation or handling of the separator sheets during the assembly of the electrolyzer stack will be lost.

[0132] To remove the temporary carrier, it is preferable to apply an alkaline solution to the separator after the phase inversion step.

[0133] Preferably, the separator, including the porous carrier, is placed in a bath containing an alkaline solution.

[0134] After removing the alkalinity of the carrier, the resulting separator is preferably subjected to a washing step, and optionally followed by a drying step.

[0135] The alkaline solution is preferably a 20-40% by weight KOH aqueous solution, more preferably a 30% by weight KOH aqueous solution.

[0136] The preferred temperature for this alkaline solution is at least 50°C.

[0137] Porous carrier

[0138] Porous carriers are often used to reinforce spacers to ensure their mechanical strength.

[0139] The thickness of the carrier is preferably 20 μm to 400 μm, more preferably 40 μm to 200 μm, and most preferably 60 μm to 100 μm.

[0140] The porous carrier can be selected from porous fabrics, porous metal plates, and porous ceramic plates.

[0141] The porous carrier is preferably a porous fabric, and more preferably a porous polymer fabric.

[0142] Porous polymer fabrics can be woven or nonwoven. Woven fabrics generally have better dimensional stability and uniformity in pore area and thickness. However, the preparation of woven fabrics with a thickness of 100 μm or less is more complex, resulting in higher costs. Nonwoven fabrics are less complex to prepare, even with a thickness of 100 μm or less. Furthermore, nonwoven fabrics can have a larger pore area.

[0143] The open area of ​​the porous carrier is preferably 30 to 80%, more preferably 40 to 70%, to ensure good permeation of the electrolyte into the carrier.

[0144] Suitable porous polymer fabrics are made of polypropylene, polyethylene (PE), polysulfone (PS), polyphenylene sulfide (PPS), polyamide / nylon (PA), polyethersulfone (PES), polyphenylene sulfone (PPSU), polyethylene terephthalate (PET), polyether-ether ketone (PEEK), sulfonated polyether-ether ketone (s-PEEK), trichlorofluoroethylene (CTFE), copolymer of ethylene and tetrafluoroethylene (ETFE) or copolymer of ethylene and trichlorofluoroethylene (ECTFE), polyimide, polyetherimide and meta-aramid.

[0145] The preferred polymer fabric is made of polypropylene (PP) or polyphenylene sulfide (PPS), with polyphenylene sulfide (PPS) being the most preferred.

[0146] Polyphenylene sulfide (PPS) porous carriers exhibit high tolerance to high temperatures and high-concentration alkaline solutions, as well as high chemical stability against reactive oxygen species released from the anode during water electrolysis. Furthermore, PPS can be easily processed into various forms, such as woven or nonwoven fabrics.

[0147] The density of the porous support is preferably 0.1 to 0.7 g / cm³. 3 .

[0148] The porous carrier is preferably a continuous roll material so that it can be prepared by the methods disclosed in EP-A 1776490 and WO2009 / 147084.

[0149] The width of the roll is preferably 30 to 300 cm, more preferably 40 to 200 cm.

[0150] According to another embodiment of the invention, the porous carrier may also be a so-called temporary porous carrier as described above.

[0151] Since such a temporary carrier is removed in the electrolytic cell, it does not need to be resistant to highly alkaline electrolyte solutions.

[0152] To design fabrics that can be removed from the separator during alkaline treatment, the following methods are preferred:

[0153] - Introduce basic solubilizing groups onto the main polymer of the fabric fibers;

[0154] - Introducing basic reactive groups onto the main polymer of the fabric fibers; and

[0155] - Introduce alkaline degradable functional groups into the main chain of the main polymer of the fabric fiber.

[0156] Preferred basic solubilizing groups are functional groups with a pKa of 10 or less, more preferably 8 or less, and most preferably 6 or less. Particularly preferred basic solubilizing groups are selected from phenols, sulfonamides, carboxylic acids, phosphonic acids, phosphate esters, and sulfonic acids, with carboxylic acids being particularly preferred.

[0157] The preferred basic reactive groups are selected from esters and acid anhydrides, with esters being particularly preferred.

[0158] The preferred alkaline degradable group is ester.

[0159] The fabric fibers can be selected from natural polymers, synthetic polymers, or combinations thereof. The fabric is preferably selected from cotton fabrics, silk fabrics, flax fabrics, jute fabrics, hemp fabrics, modal fabrics, bamboo fabrics, pineapple fabrics, basalt fabrics, ramie fabrics, polyester fabrics, acrylic fabrics, glass fiber fabrics, aramid fiber fabrics, polyamide fabrics, polyolefin fabrics, polyurethane fabrics, and mixtures thereof.

[0160] Several strategies for designing alkali-soluble fabrics have been disclosed.

[0161] Post-modification of cotton to make it alkali-soluble is a well-known strategy for designing alkali-soluble cellulose-based fabrics, as disclosed in American Dyestuff Reporter, 50(19), 67-74(1961), and US3087775 (US Department of Agriculture). Polymers of the low-functionalized carboxymethyl cellulose type are particularly preferred.

[0162] Polyamides can be functionalized in the main chain with basic biodegradable functional groups, such as specific esters disclosed in US5457144 (Rohm and Haas Company), to design alkali-soluble polyamides.

[0163] Polyolefins can be functionalized or copolymerized with monomers containing basic reactive groups or basic solubilizing groups, preferably selected from acid anhydrides and carboxylic acids. Copolymers of ethylene with acrylic acid or methacrylic acid and polyethylene grafted with maleic anhydride are particularly preferred functionalized polyolefins.

[0164] In the most preferred embodiment, the fabric is of the polyester type because of its inherent alkaline degradability. Particularly preferred polyesters are selected from polyethylene terephthalate, polylactic acid, polycaprolactone, and copolymers thereof. Polylactic acid is particularly preferred due to its biodegradability and its availability from renewable resources.

[0165] Strategies for designing polyesters with enhanced alkali solubility and biodegradability have been disclosed, based on the introduction of hydrophilic blocks, preferably poly(ethylene glycol) segments, into the polyester structure as disclosed in JP7145509 (Toyo Boseki), optionally combined with additional water-solubilizing groups as disclosed in CN1439751 (Jinan Zhenghao Advanced Fiber Co.) and KR2018110827 (Toray Chemical Korea Inc.). A further strategy could be based on introducing reactive esters, such as oxalates, into the polyester backbone to make the fiber more sensitive to alkali treatment.

[0166] Polymer fabrics can be used alone, or in combination of two or more polymer fabrics, to prepare carriers.

[0167] After the support is removed by the electrolyte in the alkaline electrolyzer, the dissolved material from the support or the degradation products of the support preferably do not adversely affect the electrocatalytic properties of the electrode or the electrolysis process.

[0168] The carrier is preferably removed by at least 50% of the alkaline solution or the electrolyte of the alkaline electrolyzer, more preferably at least 75%, most preferably at least 90%, and particularly preferably at least 95%. In the most preferred embodiment, the carrier is completely removed by the electrolyte of the alkaline electrolyzer.

[0169] Preferably, the carrier is substantially removed after being placed in an alkaline solution or an electrolyte in an alkaline electrolytic cell for 24 to 48 hours. However, the carrier can also be substantially removed after 2 weeks or 1 month in an alkaline solution or an electrolyte in an alkaline electrolytic cell.

[0170] However, the temporary carrier must be resistant to the components used in the preparation method of the separator, especially the solvent.

[0171] For example, the temporary carrier must be solvent-resistant to the stock solution used in the following method for preparing the separator, preferably for at least 0.5 minutes, more preferably for at least 1 minute, most preferably for at least 2 minutes, and particularly preferably for at least 5 minutes, so that the coating step in which the stock solution is applied to the temporary carrier can be carried out.

[0172] After the following coagulation step, the solvent in the original solution is removed to ensure that the residual amount is very low (preferably <10 g / m³). 2 More preferably <5g / m 2 So that it no longer affects the carrier.

[0173] polymer resin

[0174] The porous layer contains a polymer resin.

[0175] The polymer resin forms a three-dimensional porous network, which is a result of the phase transformation step in the preparation of the separator as described below.

[0176] The polymer resin can be selected from fluoropolymers such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), olefin resins such as polypropylene (PP), and aromatic resins such as polyethylene terephthalate (PET) and polystyrene (PS). The polymer resin can be used alone, or two or more polymer resins can be used in combination.

[0177] PVDF and vinylidene fluoride (VDF) copolymers are preferred due to their antioxidant / reducing properties and film-forming properties. Among them, terpolymers of VDF, hexanefluoropropylene (HFP), and chlorotrifluoroethylene (CTFE) are preferred due to their excellent swelling properties, heat resistance, and adhesion to electrodes.

[0178] Another preferred polymer resin is aromatic resin because of its excellent heat and alkali resistance. Examples of aromatic resins include polyethylene terephthalate, polybutylene terephthalate, polybutylene naphthalate, polystyrene, polysulfone, polyethersulfone, polyphenylene sulfide, polyphenylene sulfone, polyacrylate, polyetherimide, polyimide, and polyamide-imide.

[0179] A particularly preferred polymer resin is selected from polysulfone, polyethersulfone and polyphenylsulfone, with polysulfone being the most preferred.

[0180] The molecular weight (Mw) of polysulfone, polyethersulfone, and polyphenylsulfone is preferably from 10,000 to 500,000, more preferably from 25,000 to 250,000. When Mw is too low, the physical strength of the porous layer may become insufficient. When Mw is too high, the viscosity of the stock solution may become too high.

[0181] Examples of polysulfone, polyethersulfone, and combinations thereof are disclosed in EP-A3085815, paragraphs

[0021] to

[0032] .

[0182] Polymer resins can be used alone, or two or more polymer resins can be used in combination.

[0183] Inorganic hydrophilic particles

[0184] The hydrophilic layer also contains hydrophilic particles.

[0185] The preferred hydrophilic particles are selected from metal oxides and metal hydroxides.

[0186] The preferred metal oxides are selected from zirconium oxide, titanium oxide, bismuth oxide, cerium oxide, and magnesium oxide.

[0187] Preferred metal hydroxides are selected from zirconium hydroxide, titanium hydroxide, bismuth hydroxide, cerium hydroxide, and magnesium hydroxide. Particularly preferred magnesium hydroxide is disclosed in EP-A 3660188, paragraphs

[0040] to

[0063] .

[0188] Another preferred hydrophilic particle is barium sulfate particles.

[0189] Other hydrophilic particles that can be used are nitrides and carbides of Group IV elements in the periodic table.

[0190] The hydrophilic 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 less than or equal to 0.7 μm, more preferably less than or equal to 0.55 μm, and more preferably less than or equal to 0.40 μm.

[0191] D50 particle size is also known as median diameter or the median of the particle size distribution. It is the particle size value at 50% of the cumulative distribution. For example, if D50 = 0.1 μm, then 50% of the particles are larger than 1.0 μm and 50% of the particles are smaller than 1.0 μm.

[0192] D50 particle size is preferably measured using laser diffraction, for example, using the Mastersizer from Malvern Panalytical.

[0193] 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.

[0194] The weight ratio of hydrophilic particles to polymer resin is preferably greater than 60 / 40, more preferably greater than 70 / 30, and most preferably greater than 75 / 25.

[0195] stock solution

[0196] The stock solution preferably contains the polymer resin, hydrophilic particles, and solvent as described above.

[0197] The solvent for the stock solution is preferably an organic solvent that can dissolve the polymer resin. Furthermore, the organic solvent is preferably miscible in water.

[0198] The solvent is preferably selected from N-methylpyrrolidone (NMP), N-ethylpyrrolidone (NEP), N-butylpyrrolidone (NBP), N,N-dimethylformamide (DMF), formamide, dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMAC), acetonitrile, and mixtures thereof.

[0199] The most preferred solvent, especially for health and safety reasons, is NBP.

[0200] The stock solution may further contain other components to optimize the properties of the resulting polymer layers, such as their porosity and the maximum pore size at their outer surface.

[0201] The stock solution preferably contains additives to optimize the pore size at the surface and interior of the porous layer. Such additives can be organic or inorganic compounds or combinations thereof.

[0202] Organic compounds that may affect pore formation in porous layers include polyethylene glycol, polyethylene oxide, polypropylene glycol, ethylene glycol, tripropylene glycol, glycerol, polyols, dibutyl phthalate (DBP), diethyl phthalate (DEP), di(undecyl) phthalate (DUP), isononanoic acid or neodecanoic acid, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate, polyethyleneimine, polyacrylic acid, methylcellulose, and dextran.

[0203] Preferred organic compounds that may affect pore formation in the porous layer are selected from polyethylene glycol, polyethylene oxide, and polyvinylpyrrolidone.

[0204] Preferred polyethylene glycol has a molecular weight of 10,000 to 50,000, preferred polyethylene oxide has a molecular weight of 50,000 to 300,000, and preferred polyvinylpyrrolidone has a molecular weight of 30,000 to 1,000,000.

[0205] Glycerol is a particularly preferred organic compound that may influence pore formation in porous layers.

[0206] The amount of compounds that may affect pore formation is preferably 0.1 to 15% by weight, more preferably 0.5 to 5% by weight, relative to the total weight of the stock solution.

[0207] Inorganic compounds that may affect pore formation include calcium chloride, magnesium chloride, lithium chloride, and barium sulfate.

[0208] A combination of two or more additives that affect pore formation can be used.

[0209] When two polymer layers are applied to a porous support, the stock solutions used for the two layers can be the same or different from each other.

[0210] Electrolytic cell

[0211] The separator for alkaline water electrolysis according to the present invention can be used in an alkaline water electrolysis cell.

[0212] An electrolytic cell typically consists of two electrodes separated by a separator: an anode and a cathode. The electrolyte exists between the two electrodes.

[0213] When electrical energy (voltage) is supplied to the electrolytic cell, hydroxide ions in the electrolyte are oxidized to oxygen at the anode, while water is reduced to hydrogen at the cathode. The hydroxide ions formed at the cathode migrate through the separator to the anode. The separator prevents the hydrogen and oxygen formed during electrolysis from mixing.

[0214] The electrolyte solution is typically an alkaline solution. A preferred electrolyte solution is an aqueous solution of an electrolyte selected from sodium hydroxide or potassium hydroxide. Potassium hydroxide electrolyte is generally preferred due to its high specific conductivity. The electrolyte concentration in the electrolyte solution is preferably 10 to 40% by weight, more preferably 20 to 35% by weight, relative to the total weight of the electrolyte solution. A very preferred electrolyte is a 30% by weight KOH aqueous solution. The temperature of the electrolyte solution is preferably 50°C to 120°C, more preferably 80°C to 100°C.

[0215] Electrodes typically include a substrate to which a so-called catalyst layer is provided. The catalyst layer may differ for the anode, which forms oxygen, and the cathode, which forms hydrogen.

[0216] Typical substrates are made of conductive materials selected from nickel, iron, mild steel, stainless steel, vanadium, molybdenum, copper, silver, manganese, platinum group elements, graphite, and chromium. The substrate can 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 exhibits good stability in strongly alkaline solutions, good conductivity, and is relatively inexpensive.

[0217] The catalyst layer provided on the anode preferably has a high oxygen production capacity. The catalyst layer preferably includes nickel, cobalt, iron, and platinum group elements. The catalyst layer may include these elements as elemental metals, compounds (e.g., oxides), composite oxides or alloys made of multiple metal elements, or mixtures thereof. Preferred catalyst layers include nickel plating, nickel-cobalt plating, or nickel-iron plating, composite oxides including nickel and cobalt such as LaNiO3, LaCoO3, and NiCo2O4, compounds of platinum group elements such as iridium oxide, or carbon materials such as graphene.

[0218] Raney nickel structures are formed by selectively leaching aluminum or zinc from Ni-Al or Ni-Zn alloys. The lattice vacancies formed during the leaching process result in a large surface area and a high lattice defect density, which are active sites for electrocatalytic reactions.

[0219] The catalyst layer may also include organic materials, such as polymers, to improve durability and adhesion to the substrate.

[0220] The catalyst layer provided on the cathode preferably has a high hydrogen production capacity. The catalyst layer preferably comprises nickel, cobalt, iron, and platinum group elements. To achieve the desired activity and durability, the catalyst layer may comprise metals, compounds such as oxides, composite oxides or alloys composed of multiple metal elements, or mixtures thereof. Preferred catalyst layers are formed from the following materials: Raney nickel; Raney alloys made from a combination of multiple materials (e.g., nickel and aluminum, nickel and tin); porous coatings made by spraying nickel or cobalt compounds using plasma thermal spraying; alloys and composite compounds of nickel and elements selected from, for example, cobalt, iron, molybdenum, silver, and copper; elemental metals and oxides of platinum group elements (e.g., platinum and ruthenium) with high hydrogen production capacity; mixtures of elemental metals or oxides of these platinum group element metals with compounds of another platinum group element (e.g., iridium or palladium) or rare earth metals (e.g., lanthanum and cerium); and carbon materials (e.g., graphene).

[0221] To provide higher catalyst activity and durability, the above materials can be laminated in multiple layers or contained within catalyst layers.

[0222] It may contain organic materials, such as polymers, to improve durability or adhesion to the substrate.

[0223] In a so-called zero-gap electrolyzer, the electrodes are placed in direct contact with the separator, thereby reducing the space between the two electrodes. Mesh or porous electrodes are used to allow the separator to be filled with electrolyte and used for efficient removal of the generated oxygen and hydrogen. Such zero-gap electrolyzers have been observed operating at high current densities.

[0224] As mentioned above, a typical alkaline water electrolyzer consists of several electrolytic cells, also known as an electrolytic cell stack.

Claims

1. A method for preparing a reinforced insulating member, comprising the following steps: - Provide a porous carrier (6) on the pre-wet casting drum (23); - Apply the stock solution (3) containing polymer resin and hydrophilic inorganic particles to one side of the porous carrier, which is not the side of the porous carrier that is in contact with the pre-wet casting drum; - The applied original solution undergoes a phase transformation (9, 1) to obtain a reinforced insulating component; and - Remove the reinforcing isolation element (7) from the casting drum; The casting drum is pre-wetted with the polymer resin using a non-solvent method, and the pre-wetted casting drum contains less than 50 grams of non-solvent per square meter of casting drum surface area.

2. The method according to claim 1, wherein the pre-wet casting drum is obtained by applying a non-solvent layer on the casting drum.

3. The method of claim 1, wherein an embossing casting drum is used.

4. The method according to claim 1, wherein the surface tension of the non-solvent is less than 40 mN / m.

5. The method of claim 1, wherein the non-solvent comprises a surfactant.

6. The method of claim 1, wherein the non-solvent comprises a thickener.

7. The method of claim 1, wherein the phase inversion step comprises a solvent-free liquid-induced phase separation (LIPS) step using the polymer resin of the stock solution.

8. The method of claim 7, wherein the non-solvent used for pre-wetting the casting drum is the same as the non-solvent used in the LIPS step.

9. The method of claim 7, wherein the phase transformation step further comprises a vapor-induced phase separation (VIPS) step.

10. The method of claim 1, wherein the polymer resin is selected from polysulfone, polyethersulfone, and polyphenylene sulfide.

11. The method according to claim 1, wherein the hydrophilic inorganic particles are selected from zirconium oxide particles, zirconium hydroxide particles, magnesium oxide particles, magnesium hydroxide particles, titanium oxide particles, titanium hydroxide particles, and barium sulfate particles.

12. The method of claim 1, wherein the porous carrier has an open area of ​​30 to 80%.

13. The method of claim 1, wherein the porous carrier has a thickness of 40 to 200 µm.

14. The method of claim 1, wherein the reinforcing spacer has a thickness of 100 to 350 µm.

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