Separator and a method of preparation thereof

Abstract

The present invention provides a separator. More particularly, the present invention provides a multi-layered separator comprising a base layer, an optional middle layer, a top layer and an optional surface layer. Further, the present invention provides that the top layer is a polymer composite layer, wherein the polymer composite layer comprises non-functionalized or functionalized polymers, a nanomaterial, and an inorganic salt. The present invention also provides a process of preparation of the said multi-layered separator.

Description

[0001] SEPARATOR AND A METHOD OF PREPARATION THEREOF

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a separator. More particularly, the separator is a multi-layered separator for alkaline water electrolysis. Further, the present invention relates to a process of preparation of the said separator for alkaline water electrolyzer.

[0004] BACKGROUND OF THE INVENTION

[0005] Hydrogen serves diverse roles in industrial processes, acting as a raw material in the chemical and metallurgical sectors. Its significance extends to the production of ammonia for fertilizers, methanol for polymers, and its usage in refining intermediate oil products. Moreover, hydrogen is under exploration as a crucial future energy carrier, offering a means to store and deliver energy without releasing carbon-containing greenhouse gases. With society's focus on achieving a low carbon future, the prominence of renewable energies such as solar and wind power is on the rise. Nevertheless, the variable nature of these sources introduces challenges, leading to imbalances in electricity supply and demand. To mitigate this, power-to-gas technology has gained significant interest, converting excess electricity into gaseous fuels like hydrogen, and addressing the growing need for energy storage and transportation.

[0006] Bound to the hydrogen economy, alkaline water electrolysis technology plays a significant role in the development of hydrogen as a clean and renewable energy carrier, offering a promising pathway towards a more sustainable energy future. In AWE, hydrogen gas (H2) was produced from water (H2O) by passing an electric current through an alkaline electrolyte solution. This process involves an electrolyzer cell with two electrodes (cathode and anode) submerged in an alkaline electrolyte solution, typically potassium hydroxide (KOH) or sodium hydroxide (NaOH). When a direct current is applied, hydrogen ions (H+) migrate to the cathode, where they gain electrons to form hydrogen gas (H2), while hydroxide ions (OH") migrate to the anode by passing through a porous separator, where they lose electrons to form oxygen gas (O2). This process is known for its relatively high efficiency in generating pure hydrogen gas suitable for various applications. In an alkaline water electrolysis cell, the separator serves and fulfils the crucial role of inhibiting the recombination of H2 (generated at the cathode) and O2 (produced at the anode). It prevents gas crossover and resists the possibility of a short circuit that occurs between these electrodes. To achieve these vital functions, the separator must exhibit exceptional ionic conductivity and high alkaline stability. At present, many published and patent literature report the manufacture of separators by mixing zirconium oxide or magnesium oxide with Polysulfone solution and carrying out a non-solvent-induced phase separation process to obtain porous separator with controlled thickness and pore size.

[0007] Publication No. US10975483B2 (Asahi Kasei Corp, Japan, 2021) discloses diaphragm for alkaline water electrolysis, which comprises a porous polymer membrane made of polymer resin and hydrophilic inorganic particles. The porosity of the porous polymer membrane ranges between 30 % to 60 %, with an average pore size at both surfaces ranging from 0.5 to 2.0 pm. The coating liquid made of polymer resin and hydrophilic inorganic particles in the specified solvent is applied to both surfaces of a substrate to achieve specific porosity and pore size.

[0008] Publication No. US-11613820-B2 (Nippon Shokubai Co Ltd., Japan, 2023) specifically relates to a low-cost diaphragm for alkaline water electrolysis with reduced dissolution of an inorganic component and a method for producing the same. To achieve good stability of inorganic compound, magnesium hydroxide is used in the diaphragm for alkaline water electrolysis and it does not cause dissolution in an alkali solution as early as possible.

[0009] Publication No. US-10358729-B2 (VITO NV, USA, 2019) discloses an ion permeable web- reinforced separator comprising two separator elements separated by a substantially hollow bypass channel. Wherein, the separator elements each comprise a binder and a metal oxide or hydroxide dispersed therein and the separator elements have a bubble point of at least 1 bar (0.1 MPa) and a back-wash resistance of at least 1 bar (0.1 MPa) and optionally have a specific resistance less than 4 Q-cm at 30° C.

[0010] In other words, the conventional separator (diaphragm) has a limitation of ion permeability which in fact leads to rise in electrolyte resistance. This is due to the high separator thickness and insufficient hydrophilicity of these conventional separators. Hence, there is a need of an improved separator having specific thickness, pore size, mechanical strength, resistance to alkaline environment, and hydrophilicity which will result in better the performance of ion permeability and gas permeability of an electrolyzer. Additionally, the simplified method reduces the cost of preparation of the said separator.

[0011] OBJECTIVES OF THE INVENTION

[0012] The main objective of the present invention is to provide a multi-layered separator.

[0013] Another objective of the present invention is to provide a multi-layered separator having increased hydrophilicity, higher mechanical stability and lower membrane resistance.

[0014] Another objective of the present invention is to provide a method for the synthesis of a multilayered separator.

[0015] Another objective of the present invention is to provide a cost-effective multi-layered separator.

[0016] Another objective of the present invention is to provide a polymer composite material for a top layer of a multi-layered separator.

[0017] SUMMARY OF THE INVENTION

[0018] This summary provides a simplified introduction to the present invention detailed in the following Detailed Description. It aims to present an overview of the subject matter without identifying key or essential features of the claimed invention or aiding in the determination of its scope:

[0019] Accordingly, the present invention provides a multi-layered separator comprising: a. a base layer formed by a fabric matrix, b. optionally, a middle layer formed by a binding layer, c. a top layer formed by a polymer composite layer, and d. optionally, the top layer is coated with a surface layer.

[0020] The present invention provides a process of preparation of a multi-layered separator, wherein the process comprises the following steps: a. obtaining a fabric matrix comprising a thermally and chemically stable woven or nonwoven material to form a base layer, b. optionally, applying a hydrophilic polymer on the base layer to form a middle layer; c. coating a polymer composite layer on the middle layer or the base layer to form a top layer, and d. optionally, coating the top layer with a surface layer; wherein the polymer composite layer comprises at least, one non-functionalized or functionalized polymer, one additive, and one inorganic salt.

[0021] DETAILED DESCRIPTION OF THE INVENTION

[0022] At the very outset of the detailed description, it may be understood that the ensuing description only illustrates a particular form of this invention. However, such a particular form is only exemplary embodiment, and without intending to imply any limitation on the scope of this invention. Accordingly, the description is to be understood as an exemplary embodiment and teaching of invention and not intended to be taken restrictively.

[0023] It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present disclosure.

[0024] Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the methods. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed within the methods, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the methods.

[0025] Certain ranges are presented herein with numerical values being preceded by the term “about.” The term “about” is used herein to provide literal support for the exact number that it precedes, as well as a number that is near to or approximately the number that the term precedes. In determining whether a number is near to or approximately a specifically recited number, the near or approximating unrecited number may be a number which, in the context in which it is presented, provides the substantial equivalent of the specifically recited number. In an embodiment, “about” can mean within one or more standard deviations, or within ± 30%, 25%, 20%, 15%, 10% or 5% of the stated value.

[0026] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, preferred methods and materials are described.

[0027] For the purposes of the present invention, the following terms are defined below:

[0028] The articles "a" and "an" are used herein to refer to one or to more than one (i.e. to at least one) of the grammatical object of the article.

[0029] By way of example, “an element” means one element or more than one element. As used herein, the term “comprises” or “comprising” is generally used in the sense of include, that is to say permitting the presence of one or more features or components.

[0030] The terms “separator” and “diaphragm” can be used interchangeably for the present invention.

[0031] Other objects, feature, and aspects of the present invention are disclosed in or are obvious from, the following detailed description. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only and is not to be construed as limiting the broader aspects of the present invention.

[0032] The present invention provides a flexible and multi-layered separator with low area resistance for alkaline water electrolyzer, wherein the separator is designed with reduced thickness and optimized bubble point pressure to produce high purity hydrogen. In the present invention, the separator design is balanced to achieve lower membrane resistance with high gas blocking capability. The overall performance of the electrolyzer comprising the multi-layered separator is balanced by optimizing the thickness and hydrophilicity of the separator. The pore blockage through formation of gas bubbles is reduced by increasing the hydrophilicity of the separator. The present invention addresses enhancing the hydrophilicity of the separator and in turn improves the overall performance of the electrolyzer by reducing the resistance of the separator. Accordingly, the present invention provides a multi-layered separator comprising: a. a base layer formed by a fabric matrix, b. optionally, a middle layer formed by a binding layer, c. a top layer formed by a polymer composite layer, and d. optionally, the top layer is coated with a surface layer.

[0033] In an embodiment of the present invention, the thickness of the separator varies with the thickness of the fabric matrix.

[0034] In an embodiment of the present invention, the thickness of the separator ranges from 100 to 500 pm, depending on thickness of the fabric.

[0035] In another embodiment of the present invention, the pore diameter of the separator varies depending on the thickness of the separator.

[0036] In another embodiment of the present invention, the pore diameter of the separator ranges from 25 to 300 nm.

[0037] In another embodiment of the present invention, the separator has a bubble point pressure ranging from 3 to 25 bar.

[0038] In another embodiment of the present invention, the separator has a contact angle ranging from 50 to 70 degrees.

[0039] In another embodiment of the present invention, the separator has an area resistance ranging from 0.10 to 0.30 (1 cm2.

[0040] In an embodiment of the present invention, the fabric matrix comprises woven or non-woven matrix made of a thermally and chemically stable material.

[0041] In an embodiment, the fabric matrix is selected from, but not limited to, Meta-Aramids (such as Nomex and Conex), Para-Aramids (such as Kevlar and Twaron), Polytetrafluoroethylene (PTFE), Polyacrylonitrile (PAN), Polyphenylene Sulfides (PPS), or a combination thereof. In a preferred embodiment, the fabric matrix is Polyphenylene Sulfides (PPS).

[0042] In an embodiment of the present invention, the fabric matrix has a thickness ranging from 50 to 500 pm.

[0043] In an embodiment of the present invention, the separator comprises an optional binding layer.

[0044] In an embodiment, the binding layer comprises a hydrophilic polymer. The binding layer forms a thin coating of the hydrophilic polymer that is crosslinked over the fabric matrix of the base layer to achieve higher surface hydrophilicity and enhanced bonding between the base layer and the polymer composite layer.

[0045] In an embodiment of the present invention, the hydrophilic polymer is present in an amount ranging from of 1-10 wt.%.

[0046] In a preferred embodiment, the hydrophilic polymer is present in a concentration range of 1-5 wt.%.

[0047] In an embodiment of the present invention, the hydrophilic polymer is selected from, but not limited to, Polyvinyl Alcohol, Polydopamine, Polyethyleneimine (PEI), Polyethylene Glycol, Polyvinylpyrrolidone (PVP), Polyacrylic Acid (PAA), Poly(N-vinylcaprolactam), Poly(2- hydroxyethyl methacrylate) (PHEMA), Carboxymethyl Cellulose (CMC), Sodium Alginate, Gelatin, Chitosan, or a combination thereof.

[0048] In an embodiment of the present invention, the hydrophilic polymer is mixed with a suitable solvent and casted on the surface of fabric matrix to obtain the binding layer.

[0049] In an embodiment of the present invention, the binding layer achieves higher surface hydrophilicity and enhanced bonding between the base layer and the top layer.

[0050] In an embodiment of the present invention, the thickness of the binding layer ranges from 0.1- 5 pm and the binding layer is completely embedded into the fabric matrix of the base layer. In the microstructure level, the binding layer is deposited over the threads of the fabric matrix of the base layer and helps to achieve good binding between the polymer composite of the top layer and the fabric matrix of the base layer. In addition, it simplifies to achieve membrane microstructure with the desired pore size ranging from 10 nm to 500nm.

[0051] In an embodiment of the present invention, the top layer is a polymer composite layer.

[0052] In an embodiment of the present invention, the top layer is coated on the middle layer or on the base layer.

[0053] In an embodiment of the present invention, the polymer composite layer comprises at least, one non-functionalized or functionalized polymer, one additive and one inorganic salt.

[0054] In an embodiment of the present invention, the non-functionalized or functionalized polymer is present in an amount ranging from 10-20 wt.%. In an embodiment, the non-functionalized or functionalized polymer is present in an amount selected from 10 wt.%, 12 wt.%, 14 wt.%, 16 wt.%, 18 wt.%, and 20 wt.%.

[0055] In an embodiment of the present invention, the functionalized polymer contains at least 50% of the functional end groups.

[0056] In an embodiment of the present invention, the functional end groups are specifically hydroxyl functionalized end groups, but not limited to, carboxyl acid, sulfonic acid, phosphonic acid and other functional groups that impart hydrophilicity.

[0057] In another embodiment, the hydroxyl end groups are present in the functionalized polymer in an amount ranging from 50% to 80%.

[0058] In an embodiment of the present invention, the non-functionalized polymer is selected from, but is not limited to, Poly(ether sulfones), Bisphenol-A Polysulfone, Polyphenylene sulfone, Polyimides, Polyketones, Polysulfides, and other polymers.

[0059] In an embodiment of the present invention, the functionalized polymer is selected from, but is not limited to, Poly(ether sulfones), Bisphenol-A Polysulfone, Polyphenylene sulfone, Polyimides, Polyketones, Polysulfides, and other polymers, functionalized with end groups selected from but not limited to, hydroxyl, carboxyl acid, sulfonic acid, phosphonic acid and other functional groups.

[0060] In a preferred embodiment, the functionalized polymer is Poly(ether sulfones) functionalized with hydroxyl functional group.

[0061] In an embodiment of the present invention, the functionalized polymer has good alkaline stability and film forming ability.

[0062] In an embodiment of the present invention, the functionalized polymer has high mechanical, thermal and chemical stability.

[0063] In an embodiment of the present invention, the additive is present in an amount ranging from 0.1-5 wt.%.

[0064] In an embodiment, the additive is present in an amount selected from 0.1 wt.%, 0.5 wt.%, 1 wt.%, 1.5 wt.%, 2 wt.%, 2.5 wt.%, 3 wt.%, 3.5 wt.%, 4 wt.%, 4.5 wt.%, and 5 wt.%. In a preferred embodiment, the additive is present in an amount ranging from 0.1-3 wt.%.

[0065] In an embodiment of the present invention, the additive comprises a nanomaterial, a pore forming agent, or a combination thereof.

[0066] In an embodiment of the present invention, the nanomaterial is present in an amount ranging from 40-50 wt.% of the weight of the additive.

[0067] In a preferred embodiment, the nanomaterial is present in an amount of 40 wt.% of the additive.

[0068] In an embodiment of the present invention, the nanomaterial is selected from, but not limited to, carbon-based nanoparticles such as functionalized graphene oxide, cellulose nanofibers, carbon nanotubes, metal / metal oxide nanoparticles, silica / ceramic nanoparticles, dendrimers, hybrid compounds, or a combination thereof.

[0069] In an embodiment of the present invention, the metal oxide nanoparticles are selected from the group comprising of, but not limited to, titanium dioxide, silicon dioxide, aluminium oxide, zinc oxide, tin oxide, iron oxides, tantalum oxide, zirconium oxide, hafnium oxide, nickel oxide, cobalt oxide, manganese oxides, copper oxides, and chromium oxide, which are inherently hydrophilic due to their hydroxyl-rich surfaces.

[0070] In a preferred embodiment, the nanomaterial is hydroxy functionalized graphene oxide.

[0071] In an embodiment of the present invention, the pore forming agent is present in an amount ranging from 50-60 wt.% of the weight of the additive.

[0072] In a preferred embodiment, the pore forming agent is present in an amount of 60 wt.% of the additive.

[0073] In an embodiment of the present invention, the pore forming agent is a polymer that is selected from, but not limited to, Polyvinylpyrrolidone (PVP) of different molecular weight, Polyethylene Glycol (PEG), Polyvinyl alcohol (PVA), other material with pore forming property, or a combination thereof.

[0074] In a preferred embodiment, the pore forming agent is Polyvinylpyrrolidone (PVP).

[0075] In an embodiment of the present invention, individually the nanomaterial is present at a concentration ranging from 0.1 to 3 wt.% of the polymer composite and the pore forming agent is present at a concentration ranging from 0.1 to 5 wt.% of the polymer composite.

[0076] In a preferred embodiment, in combination, the nanomaterial is present in an amount of 2 wt.% of the polymer composite and the pore forming agent is present in an amount of 3 wt.% of the polymer composite.

[0077] In an embodiment of the present invention, the inorganic salt is present in an amount ranging from 70-90 wt.%.

[0078] In an embodiment, the inorganic salt is present in an amount selected from 70 wt.%, 72 wt.%, 74 wt.%, 76 wt.%, 78 wt.%, 80 wt.%, 82 wt.%, 84 wt.%, 86 wt.%, 88 wt.%, and 90 wt.%. In a preferred embodiment, the inorganic salt is present in an amount ranging from 80-85 wt.%.

[0079] In an embodiment of the present invention, the inorganic salt is selected from, but is not limited to, zirconium dioxide (ZrCh), nickel oxide, barite (BaSC ), cerium dioxide, zirconia toughened alumina, titanium dioxide, aluminium oxide (AI2O3), and yttria-stabilized zirconia (YSZ).

[0080] In a preferred embodiment, the inorganic salt is Yttria-stabilized zirconia.

[0081] In an embodiment of the present invention, the inorganic salt exhibits excellent chemical stability in highly alkaline environments.

[0082] In an embodiment of the present invention, the inorganic salts are inert and support to provide a stable, porous structure to achieve ionic conductivity, durability, and overall performance.

[0083] In an embodiment of the present invention, the particle size of the inorganic salt ranges between 0.1 nm to 1 pm. In another embodiment, the particle size of the inorganic salt ranges between 0.13 and 0.50 pm.

[0084] In an embodiment of the present invention, the particle size of the inorganic salt in a slurry, comprising the inorganic salt and a solvent, ranges from 5 nm to 200 nm.

[0085] In an embodiment of the present invention, the inorganic salt has the ability to disperse easily in an organic solvent.

[0086] In an embodiment of the present invention, the solvent is an organic solvent that includes but is not limited to N-Methyl-2-Pyrrolidone (NMP), Dimethylacetamide (DMAc), water, hydrocarbons such as pentane, hexane, cyclohexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, toluene, benzene, xylene, mesitylene, tetrahydrofuran, chlorobenzene, dichlorobenzene, tri chlorobenzene, dichloromethane, N,N- dimethylformamide (DMF) nitrobenzene, cyanobenzene, acetonitrile, alcohols such as methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, or a combination thereof. In an embodiment of the present invention, the surface layer comprises at least one hydrophilic polymer and optionally a nanoparticle. The surface layer forms a thin coating on the top polymer composite layer in order to achieve higher surface hydrophilicity.

[0087] In a preferred embodiment, the surface layer comprises at least one hydrophilic polymer and at least one nanoparticle

[0088] In an embodiment of the present invention, the hydrophilic polymer is present in the surface layer in an amount ranging from 1-10 wt%.

[0089] In a preferred embodiment, the hydrophilic polymer is present in an amount ranging from of 1-5 wt%.

[0090] In an embodiment of the present invention, the hydrophilic polymer is selected from, but not limited to, Polyvinyl Alcohol, Polydopamine, Polyethyleneimine (PEI), Polyethylene Glycol, Polyvinylpyrrolidone (PVP), Polyacrylic Acid (PAA), Poly(N-vinylcaprolactam), Poly(2- hydroxyethyl methacrylate) (PHEMA), Carboxymethyl Cellulose (CMC), Sodium Alginate, Gelatin, Chitosan, or a combination thereof.

[0091] In a preferred embodiment, the hydrophilic polymer is a combination of Polydopamine and Polyethyleneimine.

[0092] In an embodiment of the present invention, the nanoparticle is present in the surface layer in an amount ranging from 0.01-2 wt%.

[0093] In a preferred embodiment, the nanoparticle is present in an amount of 0.5 wt.% in order to ensure optimized and better performance.

[0094] In an embodiment of the present invention, the nanomaterial is selected from, but not limited to, carbon-based nanoparticles such as functionalized graphene oxide, cellulose nanofibers, carbon nanotubes, metal / metal oxide nanoparticles, silica / ceramic nanoparticles, dendrimers and other hybrid compounds.

[0095] In a preferred embodiment, the nanoparticle is hydroxy functionalized graphene oxide. In an embodiment of the present invention, the thickness of the surface layer ranges from 0.1- 5 pm.

[0096] In an aspect, the present invention provides a process of preparation of a multi-layered separator, wherein the process comprises the following steps: a. obtaining a fabric matrix comprising a thermally and chemically stable woven or nonwoven material to form a base layer, b. optionally, applying a hydrophilic polymer on the base layer to form a middle layer, wherein the hydrophilic polymer is mixed with a solvent and is casted on the fabric matrix to obtain the middle layer as a binding layer; c. coating a polymer composite layer on the middle layer or the base layer to form a top layer, and d. optionally, coating the top layer with a surface layer comprising at least one hydrophilic polymer and optionally a nanoparticle, wherein the hydrophilic polymer and optionally the nanomaterial are mixed with a solvent and casted on the top layer as the surface layer; wherein the polymer composite layer comprises at least, one non-functionalized or functionalized polymer, one additive, and one inorganic salt.

[0097] In an embodiment, the hydrophilic polymer is present in an amount ranging from 1-10 wt%.

[0098] In a preferred embodiment, the hydrophilic polymer is present in an amount ranging from of 1-5 wt%.

[0099] In an embodiment of the present invention, the process of preparing the polymer composite layer comprises the following steps: a. mixing at least one non-functionalized or functionalized polymer and at least one inorganic salt in a solvent to obtain a dispersion, and b. adding at least one additive while stirring the dispersion to obtain the polymer composite layer.

[0100] In an embodiment of the present invention, the non-functionalized or functionalized polymer is present in an amount ranging from 10-20 wt.%, the additive is present in an amount ranging from 0.1-5 wt.%, and the inorganic salt is present in an amount ranging from 70-90 wt.%. The polymer and the additive are present in different proportions together with inorganic salts.

[0101] In an embodiment of the present invention, the functionalized polymer contains at least 50% of the functional end groups.

[0102] In another embodiment, the hydroxyl end groups are present in the functionalized polymer in an amount ranging from 50% to 80%.

[0103] In an embodiment of the present invention, the non-functionalized or functionalized polymer is dissolved in an organic solvent at a temperature in the range of 25 to 100 °C under stirring at a speed of 500 to 1000 rpm for a period of 60 to 300 minutes to obtain a functionalized polymer solution, wherein the concentration of the functionalized polymer ranges from 10 w / v% to 20 w / v% in 50 mL of solvent.

[0104] In an embodiment of the present invention, the inorganic salt is added to the functionalized polymer solution under stirring at a speed ranging from 900 to 1100 rpm for a period of 60 to 300 minutes at a temperature ranging from 30 to 50 °C to obtain a dispersion, wherein the concentration of the inorganic salt ranges from 80% to 85% in 50 mL of the dispersion.

[0105] In an embodiment of the present invention, the additive is added to the dispersion under stirring at a speed ranging from about 900 to 1000 rpm for a period of 60 to 180 minutes at a temperature ranging from 30 to 50°C to obtain the polymer composite layer composition, wherein the concentration of the additive ranges from 0.1% to 2% in 50 mL of the polymer composite layer.

[0106] In an embodiment of the present invention, the solvent is an organic solvent that includes but is not limited to N-Methyl-2-Pyrrolidone (NMP), Dimethylacetamide (DMAc), water, hydrocarbons such as pentane, hexane, cyclohexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, toluene, benzene, xylene, mesitylene, tetrahydrofuran, chlorobenzene, dichlorobenzene, tri chlorobenzene, dichloromethane, N,N- dimethylformamide (DMF) nitrobenzene, cyanobenzene, acetonitrile, alcohols such as methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, or a combination thereof. In another aspect, the present invention provides a polymer composite layer for a separator comprising at least, one non-functionalized or functionalized polymer, one additive and one inorganic salt.

[0107] In an embodiment, the polymer composite layer comprises the non-functionalized or functionalized polymer in an amount ranging from 10-20 wt.%, the additive in an amount ranging from 0.1-5 wt.%, and the inorganic salt present in an amount ranging from 70-90 wt.%.

[0108] In a preferred embodiment, the additive is present in an amount ranging from 0.1-3 wt.%, and the inorganic salt is present in an amount ranging from 80-85 wt.%.

[0109] In an embodiment of the present invention, the additive comprises a nanomaterial, a pore forming agent, or a combination thereof.

[0110] In an embodiment of the present invention, the nanomaterial is present in an amount ranging from 40-50 wt.% of the additive and the pore forming agent is present in an amount ranging from 50-60 wt.% of the additive.

[0111] In an embodiment of the present invention, the nanomaterial is a carbon-based nanoparticle selected from the group comprising of functionalized graphene oxide, cellulose nanofibers, carbon nanotubes, metal / metal oxide nanoparticles, silica / ceramic nanoparticles, dendrimers and hybrid compounds; and the pore forming agent is a polymer selected from the group comprising of Polyvinylpyrrolidone (PVP), Polyethylene Glycol (PEG), Polyvinyl alcohol (PVA), or a combination thereof.

[0112] In an embodiment of the present invention, the functionalized polymer contains at least 50% of functional end groups on the non-functionalized polymer selected from the group comprising of Poly(ether sulfones), Bisphenol-A Polysulfone, Polyphenylene sulfone, Polyimides, Polyketones, and Polysulfide. In an embodiment, the functional end groups are selected from but not limited to, hydroxyl, carboxyl acid, sulfonic acid, phosphonic acid and other functional groups. In an embodiment, the inorganic salt is selected from the group comprising of zirconium dioxide (ZrCh), nickel oxide, barite (BaSCU), cerium dioxide, zirconia toughened alumina, titanium dioxide, aluminium oxide (AI2O3), and yttria-stabilized zirconia (YSZ).

[0113] In another aspect, the present invention provides a separator for use in an alkaline water electrolyzer, but not limited to other applications where selective ion transport and chemical stability are critical factors. The separator of the present invention is used in chemical processing for the separation of reactants and products, used in devices designed to separate and purify gases, also used as a separator in flow batteries to prevent the mixing of different electrolyte solutions.

[0114] The present invention thus provides a separator with a microstructure that includes a strong bonding between the base layer and the top layer through the presence of the middle binding layer. The fabric matrix of the base layer is surface modified with enhanced functionality, wherein surface modification is done by application of the middle layer on the base layer. The hydrophilic materials present in the middle layer forms a coating on the base layer that act as the barrier for gas crossover.

[0115] The present invention thus ensures:

[0116] • optimization of the thickness and porosity of the separator to obtain a stable porous separator having improved mechanical stability with strong barrier to gas permeability, by providing a multi-layered separator; and

[0117] • simplification of the method of manufacture of the separator that enables cost reduction in comparison to existing separators.

[0118] The details of the characterization techniques followed to ensure the advancement in the separator performance are as follows:

[0119] 1. Thickness:

[0120] Sample thickness was measured through digital thickness gauze with an accuracy of 1 pm. Higher thickness above 500 microns increases separators resistance, whereas thickness below 300-250 microns for specific separator microstructure leads to higher H2 permeability. Thus, the separator exhibits lower performance for higher separator thickness. 2. Average pore diameter and Bubble point pressure

[0121] The average pore diameter (Bubble Point Diameter) and Bubble point pressure (BPP) of the porous separators were measured following the test procedure based on ASTM D6767 (Standard Test Method for Pore Size Characterization). Higher BPP (because of smaller pore diameter) ensures that there is no / lower gas crossover, and vice versa. Again, very low pore diameter results in low performance. Hence, an optimized balance is required to be maintained between BPP and pore diameter.

[0122] 3. Contact angle analysis to determine separator wettability or hydrophilicity: Contact angle of the membrane sample was measured through Optical contact angle goniometer. Lower the contact angle, better is the wetting, and higher is the performance of the separator.

[0123] 4. Area resistance:

[0124] The membrane area resistance was assessed through electrochemical workstation. Linear sweep voltammetry tests were performed in a custom-made test cell with an effective area of 4 cm2. The membranes to be tested were positioned between two compartments of the test cell and were exposed to 30 wt.% KOH solution on both compartments. Current measurements were recorded over a standard voltage range at 25°C, and area resistance was calculated from the current -voltage plot. The higher the resistance, the lower is the performance of the separator.

[0125] 5. Electrolysis test for performance analysis:

[0126] The membrane water electrolysis performance was assessed using a standard test electrolyzer. The electrochemical workstation monitored the electrolyzer current density at different voltage ranging between 1.0 V. to 5.0 V. Purity of the gases (hydrogen content at the anode and the oxygen content at the cathode) were analyzed using a gas chromatograph.

[0127] 6. Long term stability test:

[0128] Long-term stability tests were carried out for 30 cycles with each 8 hours per cycle at 80°C maintaining a steady current density of 1.0 A / m2in a 30 wt.% KOH solution. The electrolyte solution was periodically renewed during the tests, without changing the separator. The bubble point pressure (BPP) and area resistance of the separator that underwent 30 cycles of operation was measured to examine its stability. The higher the stability, the higher is the performance of the separator.

[0129] The multi-layered separator of the present invention thus provides the following advantages:

[0130] • Increased hydrophilicity,

[0131] • Enhanced ion permeability

[0132] • Improved mechanical strength,

[0133] • Reduced membrane resistance,

[0134] • Reduced Hydrogen permeability,

[0135] • Reduced production cost, and

[0136] • Improved electrolyzer performance.

[0137] Experimental

[0138] Although the content of the present invention is further specifically explained using Examples, the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded. Values of various manufacturing conditions and evaluation results in the following Examples mean preferable values of an upper limit or a lower limit in the embodiments of the present invention, and a preferable range may be a range defined by a combination of the above-described upper limit or the above-described lower limit and the values of the following Examples or a combination of the values of Examples.

[0139] In the examples 1-6 below, polymers and inorganic salts were mixed together with the solvent at specific ratios at room temperature to have a dope solution. Additives were then added either in a single dose or in multiple batches to obtain the dope solution required for polymer composite layer. Separator manufacture were carried out through casting machine to load the polymer composite layer over the fabric. Further, a surface layer was introduced over the polymer composite layer in order to enhance the performance of separator. Performance of the separator was studied and compared as per characterization methods listed above.

[0140] Example 1

[0141] Polyether sulfone (PES) is dissolved in NMP solvent at 30°C to obtain a polymer solution of concentration ranging between 10-15%. The inorganic fillers, specifically Yttria-stabilized zirconia was mixed with polymer solution and stirred to obtain uniform dispersion. The percentage of inorganic fillers in the separator was 85 wt.%. This solution obtained was casted over the base layer made of woven PPS support material using slot die casting machine to form a polymer composite layer in the wet form. After casting, polymer composite layer in the wet form was soaked in non-solvent mixture comprising water and 5% NMP at room temperature to obtain the solidified final separator applied in alkaline water electrolyser. The properties of the separator are analysed and shown in Table 1.

[0142] Example 2

[0143] The procedure of example 1 is followed with addition of Polyvinylpyrrolidone (PVP as the pore forming agent) into the dispersion in the percentage varying between 1-2 wt.% to obtain casting solution for polymer composite layer. This solution was casted over the woven PPS support material constituting the base layer using slot die casting machine to form a polymer composite layer in the wet form. The properties of the separator are analysed and shown in Table 1.

[0144] Example 3

[0145] The procedure of example 2 is followed with addition of graphene oxide (nanomaterial) as an additive. Polyether sulfone is dissolved in NMP solvent at 30°C to obtain a polymer solution. The inorganic fillers Yttria-stabilized zirconia was mixed with polymer solution and stirred to obtain uniform dispersion. Further, additives comprising hydroxyl functionalized graphene oxide and Polyvinylpyrrolidone (PVP) were added into the dispersion and casted over the woven PPS support. After casting, polymer composite layer in the wet form was soaked in nonsolvent mixture as in Example 1.

[0146] The resulting separators properties are analysed and shown in Table 1.

[0147] Example 4 (Comparative)

[0148] The procedure of example 1 is followed, replacing the use of Yttria-stabilized zirconia with Zirconium dioxide, besides no additives were added into the dope solution composition. Polyether sulfone was dissolved in NMP solvent and the inorganic fillers Zirconium dioxide was mixed with polymer solution to obtain uniform dispersion. Further, they were casted similar to the example 1 and the results are shown in Table 1.

[0149] Table 1 : Properties of the separators as in example 1, 2, 3 and comparative example 4

[0150] Example 5

[0151] The procedure according to the example 3 was followed, with the addition of polydopamine as a surface layer. The polydopamine layer crosslinked with polyethyleneimine (PEI) at specific concentration is coated over the surface of polymer composite layer as specified in example 3.

[0152] Co-deposition of PDA with PEI for a specific time forms a uniform functional coating with high permeability and stability and the results are shown in Table 2.

[0153] Example 6 The procedure according to the example 5 was followed, with the addition of graphene oxide reinforced polydopamine hybrid nanocomposite as a surface layer. The polydopamine / PEI layer with graphene oxide for a thin hybrid nanocomposite layer on the surface of polymer composite layer as in example 2. Deposition of hybrid nanocomposite layer PDA with PEI imparted coating and alkaline stability to the separator as besides stable properties as shown in Table 2.

[0154] Table 2: Properties of the separators as in example 5 and 6, and comparative example 4

Claims

We claim,1. A multi-layered separator comprising: a. a base layer formed by a fabric matrix, b. optionally, a middle layer formed by a binding layer, c. a top layer formed by a polymer composite layer, and d. optionally, the top layer is coated with a surface layer.

2. The multi-layered separator as claimed in claim 1 , wherein the separator has a thickness ranging from 100 to 500 pm and a pore diameter ranging from 25 to 300 nm.

3. The multi-layered separator as claimed in claim 1, wherein the fabric matrix is selected from the group comprising of Meta-Aramids, Para-Aramids, Polytetrafluoroethylene (PTFE), Polyacrylonitrile (PAN), Polyphenylene Sulfides (PPS), or a combination thereof.

4. The multi-layered separator as claimed in claim 1, wherein the binding layer comprises a hydrophilic polymer in an amount ranging from 1-10 wt.%, and wherein the binding layer has a thickness ranging from 0.1-5 pm.

5. The multi-layered separator as claimed in claim 4, wherein the hydrophilic polymer is selected from the group comprising of Polyvinyl Alcohol, Polydopamine, Polyethyleneimine (PEI), Polyethylene Glycol, Polyvinylpyrrolidone (PVP), Polyacrylic Acid (PAA), Poly(N-vinylcaprolactam), Poly(2-hydroxyethyl methacrylate) (PHEMA), Carboxymethyl Cellulose (CMC), Sodium Alginate, Gelatin, Chitosan, or a combination thereof.

6. The multi-layered separator as claimed in claim 1, wherein the polymer composite layer comprises at least, one non-functionalized or functionalized polymer, one additive and one inorganic salt.

7. The multi-layered separator as claimed in claim 6, wherein the polymer composite layer comprises the non-functionalized or the functionalized polymer in an amount ranging from 10-20 wt.%, the additive in an amount ranging from 0.1-5 wt.%, and the inorganic salt in an amount ranging from 70-90 wt.%.

8. The multi-layered separator as claimed in claim 6, wherein the functionalized polymer contains at least 50% of functional end groups selected from the group comprising of hydroxyl, carboxyl acid, sulfonic acid, and phosphonic acid.

9. The multi-layered separator as claimed in claim 6-8, wherein the non-functionalized polymer is selected from Poly(ether sulfones), Bisphenol-A Polysulfone, Polyphenylene sulfone, Polyimides, Polyketones, and Polysulfides, and wherein the functionalized polymer is selected from Poly(ether sulfones), Bisphenol-A Polysulfone, Polyphenylene sulfone, Polyimides, Polyketones, and Polysulfides, functionalized with the functional end groups.

10. The multi-layered separator as claimed in claim 6, wherein the additive comprises a nanomaterial, a pore forming agent, or a combination thereof, wherein the nanomaterial is present in an amount ranging from 40-50 wt.% of the additive and the pore forming agent is present in an amount ranging from 50-60 wt.% of the additive.

11. The multi-layered separator as claimed in claim 10, wherein the nanomaterial is a carbon-based nanoparticle selected from the group comprising of functionalized graphene oxide, cellulose nanofibers, carbon nanotubes, metal / metal oxide nanoparticles, silica / ceramic nanoparticles, dendrimers, hybrid compounds, or a combination thereof.

12. The multi-layered separator as claimed in claim 10, wherein the pore forming agent is a polymer selected from the group comprising of Polyvinylpyrrolidone (PVP), Polyethylene Glycol (PEG), Polyvinyl alcohol (PVA), or a combination thereof.

13. The multi-layered separator as claimed in claim 6, wherein the inorganic salt is selected from the group comprising of zirconium dioxide (ZrCh), nickel oxide, barite (BaSCU), cerium dioxide, zirconia toughened alumina, titanium dioxide, aluminium oxide (AI2O3), and yttria-stabilized zirconia (YSZ), and wherein the inorganic salt has a particle size ranging between 0.1 nm and 1 pm.

14. The multi-layered separator as claimed in claim 1, wherein the surface layer comprises at least one hydrophilic polymer and optionally a nanoparticle, wherein the hydrophilic polymer is present in an amount ranging from 1-10 wt.% and the nanoparticle is present in an amount ranging from 0.01-2 wt.%, and wherein thickness of the surface layer ranges from 0.1-5 pm.

15. A process of preparation of a multi-layered separator as claimed in claim 1, wherein the process comprises: a. obtaining a fabric matrix comprising a thermally and chemically stable woven or non-woven material to form a base layer; b. optionally, applying a hydrophilic polymer on the base layer to form a middle layer, wherein the hydrophilic polymer is mixed with a solvent and is casted on the fabric matrix to obtain the middle layer as a binding layer; c. coating a polymer composite layer on the middle layer or the base layer to form a top layer; and d. optionally, coating the top layer with a surface layer comprising at least one hydrophilic polymer and optionally a nanoparticle; wherein the hydrophilic polymer and optionally the nanomaterial are mixed with a solvent and casted on the top layer as the surface layer; wherein the polymer composite layer comprises at least, one non-functionalized or functionalized polymer, one additive and one inorganic salt.

16. The process as claimed in claim 15, wherein the polymer composite layer is prepared by a process comprising: a. mixing at least one non-functionalized or functionalized polymer and at least one inorganic salt in a solvent to obtain a dispersion, and b. adding at least one additive while stirring the dispersion to obtain the polymer composite layer.

17. The process as claimed in claim 16, wherein the process comprises:• dissolving the non-functionalized or functionalized polymer in the organic solvent at a temperature in the range of 25 to 100°C under stirring at a speed of 500 to 1000 rpm for a period of 60 to 300 minutes to obtain a functionalized polymer solution,• adding the inorganic salt to the functionalized polymer solution under stirring at a speed ranging from 900 to 1100 rpm for a period of 60 to 300 minutes at a temperature ranging from 30 to 50°C to obtain a dispersion, and• adding the additive into the dispersion under stirring at a speed ranging from about 900 to 1000 rpm for a period of 60 to 180 minutes at a temperature ranging from 30 to 50°C to obtain the polymer composite layer.

18. The process as claimed in claim 15-17, wherein the hydrophilic polymer is present in an amount ranging from 1-10 wt.%, and the hydrophilic polymer is selected from the group comprising of Polyvinyl Alcohol, Polydopamine, Polyethyleneimine (PEI), Polyethylene Glycol, Polyvinylpyrrolidone (PVP), Polyacrylic Acid (PAA), Poly(N- vinylcaprolactam), Poly(2-hydroxyethyl methacrylate) (PHEMA), Carboxymethyl Cellulose (CMC), Sodium Alginate, Gelatin, Chitosan, or a combination thereof; wherein the non-functionalized polymer is selected from the group comprising of Poly(ether sulfones), Bisphenol-A Polysulfone, Polyphenylene sulfone, Polyimides, Polyketones, and Polysulfides; wherein the functionalized polymer is selected from Poly(ether sulfones), Bisphenol-A Polysulfone, Polyphenylene sulfone, Polyimides, Polyketones, and Polysulfides, functionalized with functional end groups selected from the group comprising of hydroxyl, carboxyl acid, sulfonic acid, and phosphonic acid; and wherein the inorganic salt is selected from the group comprising of zirconium dioxide (ZrCh), nickel oxide, barite (BaSCU), cerium dioxide, zirconia toughened alumina, titanium dioxide, aluminium oxide (AI2O3), and yttria-stabilized zirconia (YSZ).

19. The process as claimed in claims 15-16, wherein the solvent is an organic solvent selected from the group comprising of N-Methyl-2-Pyrrolidone (NMP), Dimethylacetamide (DMAc), water, pentane, hexane, cyclohexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, toluene, benzene, xylene, mesitylene, tetrahydrofuran, chlorobenzene, di chlorobenzene, tri chlorobenzene, dichloromethane, N,N-dimethylformamide (DMF) nitrobenzene, cyanobenzene, acetonitrile, alcohols such as methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, or a combination thereof.

20. A polymer composite layer for a separator comprising at least, one non-functionalized or functionalized polymer, one additive and one inorganic salt.

21. The polymer composite layer as claimed in claim 20, wherein the non-functionalized or the functionalized polymer is present in an amount ranging from 10-20 wt.%, the additive is present in an amount ranging from 0.1-5 wt.%, and the inorganic salt is present in an amount ranging from 70-90 wt.%.

22. The polymer composite layer as claimed in claims 20, wherein the additive comprises a nanomaterial, a pore forming agent, or a combination thereof; wherein the nanomaterial is present in an amount ranging from 40-50 wt.% of the additive and the pore forming agent is present in an amount ranging from 50-60 wt.% of the additive, wherein the nanomaterial is a carbon-based nanoparticle selected from the group comprising of functionalized graphene oxide, cellulose nanofibers, carbon nanotubes, metal / metal oxide nanoparticles, silica / ceramic nanoparticles, dendrimers and hybrid compounds; and wherein the pore forming agent is a polymer selected from the group comprising of Polyvinylpyrrolidone (PVP), Polyethylene Glycol (PEG), Polyvinyl alcohol (PVA), or a combination thereof.

23. The polymer composite layer as claimed in claim 20, wherein the functionalized polymer contains at least 50% of functional end groups on the non-functionalized polymer selected from the group comprising of Poly(ether sulfones), Bisphenol-A Polysulfone, Polyphenylene sulfone, Polyimides, Polyketones, and Polysulfides, and the functional end groups are selected from the group comprising of hydroxyl, carboxyl acid, sulfonic acid, phosphonic acid and other functional groups; and wherein the inorganic salt is selected from the group comprising of zirconium dioxide (ZrCh), nickel oxide, barite (BaSCU), cerium dioxide, zirconia toughened alumina, titanium dioxide, aluminium oxide (AI2O3), and yttria-stabilized zirconia (YSZ).

24. Use of a separator in an alkaline water electrolyzer, in chemical processing for separation of reactants and products, in devices to separate and purify gases, and in flow batteries.

Images