Catalyst complex having effect of reducing gas permeation and polymer electrolyte membrane comprising same

Abstract

The present invention relates to a catalyst composite and a polymer electrolyte membrane comprising the same, which are prepared by compounding platinum, a metal having a higher ionization tendency than platinum, and a functional support, and which has an effect of reducing gas permeating from a counter electrode when applied to a polymer electrolyte membrane.

Description

Technical Field

[0001] This invention relates to a catalyst complex for a polymeric electrolyte membrane contained in a membrane electrode assembly of a water electrolysis device. More particularly, it relates to a catalyst complex and a polymeric electrolyte membrane comprising the catalyst complex, which is prepared by compositing a single platinum or platinum with a metal having a greater ionization tendency than platinum on a functional support, and when applied to a polymeric electrolyte membrane, has the effect of reducing gas permeation from the counter electrode.

[0002] Furthermore, the present invention relates to a polymeric electrolyte membrane contained in a membrane electrode assembly of a water electrolysis apparatus. In particular, the present invention relates to an enhanced composite electrolyte membrane for water electrolysis in which the concentration gradients of hydrogen-suppressing additives and antioxidants are independently adjusted, thereby enabling the functional additives to function most effectively, since the dominant reactions in the anode-side electrolyte membrane and the cathode-side electrolyte membrane in the water electrolyzer are different.

[0003] Furthermore, the present invention relates to a polymeric electrolyte membrane contained in a membrane electrode assembly of a water electrolysis apparatus. In particular, the present invention relates to a reinforced composite electrolyte membrane for water electrolysis in which the layer design and additive distribution are adjusted by controlling the pore size of the reinforcing substrate and the particle size of the additives, thereby enabling the functional additives to function most effectively in the water electrolyzer (cell) without additional coating processes. Background Technology

[0004] Water electrolysis is an environmentally friendly hydrogen production technology that uses water splitting to produce hydrogen. As a solution to the environmental problems caused by energy production using fossil fuels, the importance of water electrolysis is increasingly prominent. Therefore, research is underway on catalysts or electrolyte membranes, electrodes, separators, etc., for continuous water splitting.

[0005] Especially for polymer electrolyte membranes, the following requirements must be met: high hydrogen ion conductivity, low electronic conductivity, minimal movement of reactant gases or water relative to ion migration, and mechanical and chemical stability.

[0006] In recent years, driven by considerations such as improving the efficiency of water electrolysis, saving raw materials, and facilitating the preparation process, the development of polymer electrolyte membranes has been trending towards increasingly thinner membranes. However, while thinner membranes offer performance advantages, they also lead to increased gas permeation through the counter electrode, resulting in reduced durability.

[0007] Therefore, there is a need to develop a technology that can reduce gas permeation while maintaining a relatively thin polymer electrolyte membrane.

[0008] In water electrolysis systems, hydrogen can permeate from the cathode to the anode under high pressure conditions exceeding 30 bar. When more than 4% of hydrogen cross-permeates in the oxygen environment towards the anode, the mixture of oxygen and hydrogen poses an explosion risk. To prevent explosions, efforts are being made to prevent hydrogen cross-permeation by adding additives that block hydrogen permeation to the electrolyte membrane.

[0009] Unlike fuel cell systems, the main deterioration site is also located at position ① where hydrogen and oxygen are mixed ( Figure 6 This refers to the electrolyte membrane region near the anode electrode. Unlike fuel cells, free radical-induced degradation has a relatively small impact on water electrolysis, and the amount of free radical-induced degradation occurring in the anode direction is also less. However, the electrolyte membrane region near the cathode electrode, i.e., location ② (… Figure 6 This is the region where hydrogen peroxide is generated, therefore, deterioration caused by free radicals occurs more frequently. Summary of the Invention

[0010] The problem that the invention aims to solve The present invention is proposed to solve the above-mentioned problems by providing a catalyst complex and a polymeric electrolyte membrane containing the catalyst complex, which is applied to the polymeric electrolyte membrane contained in the membrane electrode assembly of a water electrolysis device, thereby reducing the gas permeating from the reverse electrode.

[0011] Furthermore, the present invention is proposed to solve the above-mentioned problems, and aims to provide an enhanced composite electrolyte membrane for water electrolysis. Since the dominant reactions in the electrolyte membrane on the anode side and the electrolyte membrane on the cathode side in the water electrolyzer are different, the concentration gradients of hydrogen inhibitors and antioxidants can be independently adjusted, thereby enabling the functional additives to play their role most effectively.

[0012] Furthermore, the present invention is proposed to solve the above-mentioned problems, and aims to provide an enhanced composite electrolyte membrane for water electrolysis, which adjusts the layer design and additive distribution by controlling the pore size of the reinforcing substrate and the particle size of the additives, so that the functional additives can play their most effective role in the water electrolyzer (cell) without additional coating processes.

[0013] The technical problems of this invention are not limited to those mentioned above. Those skilled in the art can clearly understand other technical problems not mentioned through the following description.

[0014] means for solving problems According to one embodiment of the present invention, a catalyst composite is provided for use in a polymeric electrolyte membrane for water electrolysis. The catalyst composite comprises: a single platinum catalyst or a composite catalyst, the composite catalyst comprising platinum and a metal with a greater ionization tendency than platinum; and a functional support on which the catalyst is loaded, the functional support being selected from one or more of the following: a) a support acting as an antioxidant; b) a support acting to improve ion transport characteristics and catalyst activity; c) a support acting to improve catalyst stability; d) a support functioning to modify the hydrophilic or hydrophobic properties of the polymeric electrolyte membrane; e) a support acting to improve water content; and f) a three-dimensional mesh structure support acting to improve the durability and long-term stability of the polymeric electrolyte membrane.

[0015] The characteristic is that the metal with a greater ionization tendency than platinum is selected from one or more of barium (Ba), magnesium (Mg), aluminum (Al), manganese (Mn), zinc (Zn), chromium (Cr), iron (Fe), cadmium (Cd), cobalt (Co), nickel (Ni), tin (Sn), and lead (Pb), and the metal is composited on the platinum.

[0016] The characteristic is that the carrier a) is selected from one or more of CeO2, Ce2O3 and LaCeO7.

[0017] The characteristic is that the carrier b) is selected from one or more of YSZ, SDC, LST, BYZ, BCZY, Gd2O3, Nd2O3 and La2Zr2O7.

[0018] The characteristic is that the carrier c) is selected from one or more of IrO2, NiO, SnO2 and TiO2.

[0019] The carrier (e) is a polymer with a mesh or network structure, which is a hydrogel polymer or a superabsorbent polymer (SAP).

[0020] The feature is that the particle size of the functional carrier is less than 1 μm.

[0021] Another embodiment of the present invention includes a method for preparing a catalyst composite with a gas permeation reduction effect. This method is for preparing a catalyst composite for use in a polymer electrolyte membrane for water electrolysis. The preparation method includes the following steps: pulverizing a functional support to a particle size of less than 1 μm (S100); mixing the pulverized functional support with a platinum precursor and a metal precursor with a greater ionization tendency than platinum in a certain proportion to form a mixture (S200); and subjecting the mixture to reduction, drying, and heat treatment to composite the functional support with platinum and the metal with a greater ionization tendency than platinum (S300).

[0022] According to another embodiment of the present invention, an ionomer dispersion comprising a catalyst complex includes a solid ionomer, one or more solvents, and the catalyst complex according to the above.

[0023] The characteristic is that the pH of the ionomer dispersion is below 3.0.

[0024] The catalyst complex is characterized by comprising 0.05 to 5% by weight relative to the total weight of the ionomer dispersion.

[0025] Another embodiment of the present invention includes a polymeric electrolyte membrane comprising: a porous carrier layer; and an ionomer layer, prepared by impregnating and coating the ionomer dispersion onto the porous carrier layer and then drying it.

[0026] According to another embodiment of the present invention, a membrane electrode assembly comprising the polymer electrolyte membrane and a water electrolysis device comprising the membrane electrode assembly are included.

[0027] In addition, according to another embodiment of the present invention, an enhanced composite electrolyte membrane for water electrolysis is provided, characterized in that the enhanced composite electrolyte membrane for water electrolysis comprises: a first ionomer layer disposed on the anode side; a second ionomer layer disposed on the cathode side; and a composite layer formed by at least partially impregnating one or more of the first ionomer and the second ionomer onto a porous substrate between the first ionomer layer and the second ionomer layer, wherein the first ionomer layer and the composite layer respectively contain hydrogen-suppressing additives at different concentrations (satisfying B-1>B>0 when the concentration of the first ionomer layer is B-1 and the concentration of the composite layer is B), and the second ionomer layer and the composite layer respectively contain antioxidants at different concentrations (satisfying B-2>B>0 when the concentration of the second ionomer layer is B-2 and the concentration of the composite layer is B).

[0028] Alternatively, the first ionomer layer, the second ionomer layer, and the composite layer may each contain different concentrations of hydrogen-suppressing additives (where B-1 is the concentration of the first ionomer layer, B-2 is the concentration of the second ionomer layer, and B is the concentration of the composite layer, satisfying B-1≥B-2>B>0), and the first ionomer layer, the second ionomer layer, and the composite layer may each contain different concentrations of antioxidants (where B-2≥B-1>B>0, where B-1 is the concentration of the first ionomer layer, B-2 is the concentration of the second ionomer layer, and B is the concentration of the composite layer).

[0029] Alternatively, the hydrogen suppression additive may include: a catalyst composite comprising platinum (Pt) particles and a functional support supporting the platinum particles; or a catalyst composite comprising platinum (Pt) particles and metal particles with a greater ionization tendency than the platinum (Pt) particles and a functional support supporting the catalyst.

[0030] Alternatively, the antioxidant may include a cerium (Ce)-based free radical scavenger, which is cerium oxide.

[0031] Alternatively, a third ionomer layer may be formed on the outer surface of the first ionomer layer in a manner between the anode and the first ionomer layer, and the first ionomer layer, the third ionomer layer and the composite layer may each contain hydrogen-suppressing additives at different concentrations (satisfying B-3≥B-1>B>0 when the concentration of the first ionomer layer is B-1, the concentration of the third ionomer layer is B-3 and the concentration of the composite layer is B).

[0032] Alternatively, a fourth ionomer layer may be formed on the outer surface of the second ionomer layer in a manner between the cathode and the second ionomer layer, and the second ionomer layer, the fourth ionomer layer and the composite layer may each contain antioxidants of different concentrations (satisfying B-2≥B-4>B>0 when the concentration of the second ionomer layer is B-2, the concentration of the fourth ionomer layer is B-4 and the concentration of the composite layer is B).

[0033] Alternatively, the outer surface of the first ionomer layer may also include a third ionomer layer formed between the anode and the first ionomer layer, and the outer surface of the second ionomer layer may also include a fourth ionomer layer formed between the cathode and the second ionomer layer.

[0034] Alternatively, the first ionomer layer, the second ionomer layer, the third ionomer layer, the fourth ionomer layer, and the composite layer may each contain different concentrations of hydrogen-suppressing additives (satisfying B-3≥B-1≥B-2≥B-4≥B>0 when the concentration of the first ionomer layer is B-1, the concentration of the second ionomer layer is B-2, the concentration of the third ionomer layer is B-3, the concentration of the fourth ionomer layer is B-4, and the concentration of the composite layer is B).

[0035] Alternatively, the first ionomer layer, the second ionomer layer, the third ionomer layer, the fourth ionomer layer, and the composite layer may each contain different concentrations of antioxidants (satisfying B-2≥B-4≥B-3≥B-1≥B>0 when the concentration of the first ionomer layer is B-1, the concentration of the second ionomer layer is B-2, the concentration of the third ionomer layer is B-3, the concentration of the fourth ionomer layer is B-4, and the concentration of the composite layer is B).

[0036] Alternatively, the composite layer may be a composite layer in which one or more of a first ionomer and a second ionomer are at least partially impregnated into at least two or more stacked porous substrates between the first ionomer layer and the second ionomer layer.

[0037] Alternatively, the porous substrate may contain at least one fluorinated polymer, which is polytetrafluoroethylene (PTFE), poly(ethylene-co-tetrafluoroethylene) (EPTFE), expanded polytetrafluoroethylene (e-PTFE), polyvinylidene fluoride (PVDF), expanded polyvinylidene fluoride (e-PVDF), expanded poly(ethylene-co-tetrafluoroethylene) (eEPTFE), or a mixture thereof.

[0038] Alternatively, the composite layer may include at least one ionomer inner layer between at least two porous substrates, the composition of which is the same as that of the first ionomer layer or the second ionomer layer.

[0039] The enhanced composite electrolyte membrane for water electrolysis according to an embodiment of the present invention described above can be applied to a membrane electrode assembly (MEA) for water electrolysis or a water electrolysis system including the membrane electrode assembly (MEA).

[0040] In addition, according to another embodiment of the present invention, an enhanced composite electrolyte membrane for water electrolysis is provided, characterized in that the enhanced composite electrolyte membrane for water electrolysis comprises: a first ionomer layer disposed on the anode side and formed of a first ionomer composition; and a composite layer formed by impregnating the first ionomer composition at least partially onto a porous substrate laminated on one side of the first ionomer layer, the first ionomer composition comprising a hydrogen-suppressing additive, the hydrogen-suppressing additive comprising: a first additive having a particle size smaller than the maximum pore size of the porous substrate; and a second additive having a particle size larger than the maximum pore size, the first additive being impregnated into the porous substrate and located within the composite layer, and the second additive being located within the first ionomer layer.

[0041] Alternatively, the enhanced composite electrolyte membrane for water electrolysis may further include: an intermediate layer, located between the first ionomer layer and the composite layer, formed from the first ionomer composition, in which the second additive aggregates at a higher concentration than the first additive.

[0042] Alternatively, the hydrogen-suppressing additive may include: a composite comprising platinum (Pt) particles and a functional support supporting the platinum particles; or a composite comprising platinum (Pt) particles and metal particles with a greater ionization tendency than the platinum (Pt) particles and a functional support supporting the catalyst.

[0043] Alternatively, in the particle size distribution, the particle size (diameter size) of the hydrogen-suppressing additive that corresponds to a percentage greater than 0 and less than X is below the maximum pore size of the porous substrate, where X is 50 to 80.

[0044] Alternatively, the enhanced composite electrolyte membrane for water electrolysis may further include: a second ionomer layer disposed on the cathode side, formed of a second ionomer composition, and laminated on the other side of the porous substrate (the side opposite to the side on which the first ionomer layer is laminated), wherein the second ionomer composition is at least partially impregnated into the porous substrate.

[0045] Alternatively, the composite layer may be a composite layer in which one or more of a first ionomer composition and a second ionomer composition are at least partially impregnated onto at least two or more stacked porous substrates between the first ionomer layer and the second ionomer layer.

[0046] Alternatively, the porous substrate may contain at least one fluorinated polymer, which is polytetrafluoroethylene (PTFE), poly(ethylene-co-tetrafluoroethylene) (EPTFE), expanded polytetrafluoroethylene (e-PTFE), polyvinylidene fluoride (PVDF), expanded polyvinylidene fluoride (e-PVDF), expanded poly(ethylene-co-tetrafluoroethylene) (eEPTFE), or a mixture thereof.

[0047] Alternatively, the composite layer may include at least one ionomer inner layer between at least two porous substrates, the ionomer inner layer being formed from the first ionomer composition or the second ionomer composition.

[0048] The enhanced composite electrolyte membrane for water electrolysis according to an embodiment of the present invention described above can be applied to a membrane electrode assembly (MEA) for water electrolysis or a water electrolysis system including the membrane electrode assembly (MEA).

[0049] In another embodiment, the present invention provides a method for preparing an enhanced composite electrolyte membrane for water electrolysis. The method includes the following steps: preparing a porous substrate and a hydrogen-suppressing additive, wherein the porous substrate is prepared by adjusting the average pore size and the maximum pore size, and the hydrogen-suppressing additive comprises a first additive having a particle size smaller than the maximum pore size of the porous substrate and a second additive having a particle size larger than the maximum pore size; preparing a first ionomer composition comprising the hydrogen-suppressing additive and a first ionomer dispersed in a solvent; coating the first ionomer composition to form a first ionomer layer; and attaching the porous substrate to one side of the first ionomer layer, thereby forming a composite layer in which the first ionomer composition is at least partially impregnated into the porous substrate by utilizing capillary effect.

[0050] Alternatively, in the step of preparing the porous substrate and the hydrogen-suppressing additive, in the particle size distribution, the particle size (diameter size) of the hydrogen-suppressing additive that is greater than 0 and less than X% is less than or equal to the maximum pore size of the porous substrate, where X is 50 to 80.

[0051] Alternatively, in the step of forming the composite layer, the first additive is contained in the first ionomer composition and impregnated into the interior of the porous substrate, and the second additive aggregates at the interface between the porous substrate and the first ionomer layer to form an intermediate layer between the first ionomer layer and the composite layer, and in the first ionomer composition, the second additive aggregates at a higher concentration than the first additive.

[0052] Alternatively, after the step of forming the composite layer, the following step may be included: coating a second ionomer composition containing a second mixture of the second ionomer dispersed in a solvent onto the other side of the porous substrate (the side opposite to the side on which the first ionomer layer is stacked).

[0053] Alternatively, in the step of coating the second ionomer composition, the second ionomer composition may be at least partially impregnated onto the porous substrate.

[0054] The present invention also provides an enhanced composite electrolyte membrane for water electrolysis prepared by the above preparation method.

[0055] Invention Effects According to the present invention as described above, the catalyst complex according to the present invention is made by combining platinum, a metal having a greater ionization tendency than platinum, and a functional support, thereby reducing the gas permeating from the counter electrode when applied to a polymer electrolyte membrane, resulting in improved durability of the polymer electrolyte membrane.

[0056] Furthermore, the present invention has the following characteristics: firstly, the functional support is pulverized to the nanoscale of less than 1 μm and then mixed with a metal precursor as a catalyst to prepare a catalyst composite, thereby minimizing the phenomenon of catalyst detachment from the functional support and exhibiting excellent dispersion stability in the ionomer dispersion.

[0057] Furthermore, this invention prepares a polymer electrolyte membrane by adjusting the pH of the ionomer dispersion containing the catalyst complex to a certain level, thereby preventing wrinkles, cracks, and ruptures in the prepared polymer electrolyte membrane.

[0058] According to the present invention as described above, its effect is that, in order to manage the deterioration and explosion risk of the water electrolysis system to the greatest extent, the hydrogen inhibitor is mainly located in the anode direction to prevent hydrogen and oxygen from mixing at a certain concentration or higher. Conversely, the antioxidant is mainly located in the cathode direction to achieve effective free radical removal.

[0059] According to the present invention as described above, the following effects are achieved: even without additional layer coating processes, the performance and safety of the unit can be ensured by controlling the particle size of the additives and the pore size of the porous substrate based on existing processes, and by positioning the functional additives used to reduce hydrogen permeation in the most effective location.

[0060] The effects of the present invention are not limited to those mentioned above, but also include other effects that can be clearly understood by those skilled in the art through the entire description, but which are not explicitly mentioned. Attached Figure Description

[0061] Figure 1 This is a schematic diagram showing the catalyst complex according to the present invention.

[0062] Figure 2 These are example diagrams illustrating functional supports that can be applied to catalyst complexes according to the present invention. The upper diagram is an example diagram of a support e) having a mesh or network structure, and the lower diagram is an example diagram of a support f) having a lattice or three-dimensional mesh structure.

[0063] Figure 3 This is a schematic diagram illustrating the effect of the method for preparing the catalyst complex according to the present invention. The upper part shows the case where an unpulverized functional support is used, indicating that a large amount of catalyst (Pt, Pt-M) is lost during the preparation of polymer electrolyte membranes such as the dispersion process. The lower part shows the case where a pulverized functional support is used, indicating that the loss of catalyst (Pt, Pt-M) is minimized during the preparation of polymer electrolyte membranes such as the dispersion process.

[0064] Figure 4This is a flowchart illustrating a method for preparing the catalyst complex according to the present invention.

[0065] Figure 5 This is a schematic diagram illustrating how easily polymer materials undergo volume changes due to pH (the sensitivity of volume changes with pH).

[0066] Figure 6 This is a schematic diagram of a water electrolysis (PEMWE) system based on a polymer electrolyte membrane.

[0067] Figure 7 This is a schematic diagram of a polymer electrolyte membrane-based fuel cell (PEMFC) system.

[0068] Figure 8 This is a schematic diagram of an enhanced composite electrolyte membrane for water electrolysis according to a preferred embodiment of the present invention.

[0069] Figure 9 This is a schematic diagram of an enhanced composite electrolyte membrane for water electrolysis according to another preferred embodiment of the present invention.

[0070] Figure 10 This is a schematic diagram illustrating the cross-sectional structure of an electrolyte membrane according to an embodiment of the present invention, and the behavior of the hydrogen-suppressing additive according to particle size during the formation of the composite layer.

[0071] Figure 11 This is a conceptual diagram representing the difference in flux between hydrogen and oxygen along the thickness direction of the electrolyte membrane.

[0072] Figure 12 The images show a cross-sectional photograph (left) of the electrolyte membrane according to a preferred embodiment of the present invention, and an EDS composition analysis image (right) of its rectangular region.

[0073] Figure 13 This is a conceptual diagram of the preparation process when two layers of a polymer material are stacked using a roll-to-roll (RTR) process. Detailed Implementation

[0074] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The advantages, features, and methods of achieving the present invention will become apparent from the accompanying drawings and the detailed embodiments described below. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in different ways. These embodiments are provided merely to complete the disclosure of the present invention and to fully inform those skilled in the art of its scope, which is defined only by the scope of the claims. Throughout this specification, the same reference numerals refer to the same components.

[0075] Unless otherwise defined, all terms used in this specification (including technical and scientific terms) are to be used in the sense commonly understood by one of ordinary skill in the art to which this invention pertains. Furthermore, terms already defined in commonly used dictionaries should not be idealized or over-interpreted unless explicitly and specifically defined. The terminology used in this specification is for illustrative purposes only and is not intended to limit the invention. In this specification, the singular form also includes the plural form unless specifically mentioned in the context.

[0076] The use of “comprises” and / or “comprising” in this specification does not exclude the presence or addition of more than one other component, step, action and / or element besides those mentioned.

[0077] This invention relates to: a catalyst composite (1) for use in PEMWE, i.e., water electrolysis (WE) systems based on polymer electrolyte membranes (PEM), which has the effect of reducing gas permeation; an electrolyte membrane structure (2) for independently adjusting the concentration gradient of hydrogen inhibitors and antioxidants; and an electrolyte membrane structure and process (2) for adjusting the layer design and additive distribution by controlling the pore size of the reinforcing substrate and the particle size of the additives. Hereinafter, the former (1) will be described first.

[0078] <Catalyst complex with gas permeation reduction effect (1)> Figure 1 This is a schematic diagram illustrating a catalyst complex according to an embodiment of the present invention, such as... Figure 1 As shown, the catalyst composite according to the present invention comprises: a single platinum (Pt) catalyst or a composite catalyst, the composite catalyst comprising platinum and a metal (M) with a greater ionization tendency than platinum; and a functional support on which the single catalyst or the composite catalyst is supported.

[0079] Specifically, the metal with a greater ionization tendency than platinum can be one or more selected from barium (Ba), magnesium (Mg), aluminum (Al), manganese (Mn), zinc (Zn), chromium (Cr), iron (Fe), cadmium (Cd), cobalt (Co), nickel (Ni), tin (Sn), and lead (Pb). When such a metal with a high ionization tendency is included, these metals will be preferentially oxidized before platinum, thereby reducing the oxidation of platinum.

[0080] More specifically, such as Figure 1 As shown, the catalyst is configured as a metal including platinum (Pt) and a Pt-M (metal with a greater tendency to ionize than platinum) composite of platinum and the aforementioned metal (M).

[0081] The functional carrier can specifically be selected from one or more of the following a) to f): a) a carrier that acts as an antioxidant; b) a carrier that improves ion transport characteristics and catalyst activity; c) a carrier that improves catalyst stability; d) a carrier that modifies the hydrophilic or hydrophobic properties of the polymer electrolyte membrane; e) a carrier that improves water content; and f) a three-dimensional mesh structure carrier that improves the durability and long-term stability of the polymer electrolyte membrane.

[0082] That is, the catalyst complex according to the present invention has the following morphology: a catalyst comprising platinum (Pt) and a metal in the form of Pt-M (a metal with a greater tendency to ionize than platinum) is supported on the above-mentioned functional support. Supporting on the functional support includes both the case where it is located on the inner surface of the functional support and the case where it is located on the outer surface of the functional support.

[0083] The carrier a) is a carrier that can act as an antioxidant (radical scavenger), specifically selected from one or more of CeO2, Ce2O3 and LaCeO7.

[0084] The support b) can be a material with chemical structures such as ABO3, AO2, ABO4, and A2B2O7, doped with elements of different ionic radii, thereby utilizing oxygen vacancies to increase cation and anion transport characteristics and improve catalytic activity. Specifically, it can be one or more selected from YSZ, SDC, LST, BYZ, BCZY, Gd2O3, Nd2O3, and La2Zr2O7.

[0085] The support c) is a support that still has excellent stability under conditions such as fuel shortage, high electrochemical drive, and acidic environment, and can be selected from one or more of IrO2, NiO, SnO2 and TiO2.

[0086] Here, YSZ (also known as Y Dopped Zirconia or Yttria Stabilized Zirconia) refers to yttrium-doped zirconium oxide (or, also known as yttrium-stabilized zirconium oxide).

[0087] The SDC (Sm Dopped Ceria) refers to samarium-doped cerium oxide.

[0088] The LST mentioned above (also known as La Dopped SrTiO3 or Lanthanum strontium titanate) refers to [(La x Sr 1-x TiO 3-δ ].

[0089] The BYZ (yttrium doped barium zirconate) refers to yttrium-doped barium zirconate.

[0090] The BCZY (yttrium-doped barium cerium zirconium oxide) refers to yttrium-doped barium cerium zirconate.

[0091] CeO2 and Ce2O3 are cerium oxide, LaCeO7 is lanthanum cerium oxide, Gd2O3 is gadolinium oxide, Nd2O3 is neodymium oxide, La2Zr2O7 is lanthanum zirconium oxide, IrO2 is iridium oxide, NiO is nickel oxide, SnO2 is tin oxide, and TiO2 is titanium oxide.

[0092] The carrier e) is a polymer with a mesh or network structure, which can increase the water content by trapping water in the polymer network. Specifically, it can be a hydrogel polymer or a superabsorbent polymer (SAP). (Refer to...) Figure 2 Above, you can see an example diagram of a carrier (e) with a mesh or lattice structure.

[0093] The superabsorbent polymer (SAP) may specifically be one or more selected from polyacrylate, polyacrylamide copolymer, ethylene maleic anhydride copolymer, cross-linked carboxymethyl cellulose, polyvinyl alcohol copolymer, cross-linked polyethylene oxide, starch-grafted copolymer of polyacrylonitrile, and alginate.

[0094] The carrier f) is preferably a lattice-like or three-dimensional mesh structure that serves as a macroscopic framework within a polymer electrolyte membrane. (Refer to...) Figure 2 Below, you can see an example diagram of a carrier f) with a lattice or three-dimensional mesh structure.

[0095] Furthermore, in the catalyst composite according to the present invention, the molar ratio of catalyst to functional support can be between 0.3:1 and 4:1. If the catalyst ratio is below this range, the effect of reducing gas permeation may not be significant; if it is above this range, a large amount of catalyst cannot be loaded onto the functional support, which is therefore not preferred.

[0096] In addition, the molar ratio of platinum and metals with a greater tendency to ionize than platinum in the catalyst can satisfy 0.3:1 to 19:1.

[0097] Furthermore, the particle size of this functional support can be below 1µm, more specifically, it can be 500nm to 50nm. If the particle size is greater than 1µm, the specific surface area is small, resulting in fewer reaction sites and thus reduced efficiency. If the particle size is below 50nm, it is similar to the particle size of Pt and metal catalysts, and therefore cannot function as a support for Pt and metal catalysts.

[0098] During the preparation of polymeric electrolyte membranes, such as in the dispersion process, a large amount of catalyst may detach from the functional support. Furthermore, reducing the particle size of the functional support to the nanoscale (below 1 µm) is preferable in terms of achieving uniform dispersion even with lower energy consumption. Therefore, it is preferable to pulverize the functional support to the nanoscale (below 1 µm) as described above, and then composite it with the catalyst.

[0099] Figure 3 This is a schematic diagram illustrating the pulverization effect of the functional support in the preparation method of the catalyst complex according to the present invention. The upper part shows the case of using an unpulverized functional support, indicating that a large amount of catalyst (Pt, Pt-M) is detached during the preparation of polymer electrolyte membranes such as the dispersion process. The lower part shows the case of using a pulverized functional support, indicating that the detachment of catalyst (Pt, Pt-M) is minimized during the preparation of polymer electrolyte membranes such as the dispersion process.

[0100] Therefore, the method for preparing the catalyst complex according to the present invention is characterized by using a pulverized functional support. This will be described in more detail below.

[0101] Figure 4 This is a flowchart illustrating a method for preparing a catalyst complex according to an embodiment of the present invention.

[0102] like Figure 4As shown, the method for preparing the catalyst complex according to the present invention includes the following steps: pulverizing a functional support to a particle size of less than 1 μm (S100); mixing the pulverized functional support with a platinum precursor and a metal precursor with a greater ionization tendency than platinum in a certain proportion to form a mixture (S200); and reducing, drying and heat-treating the mixture to make the functional support composite with platinum and a metal with a greater ionization tendency than platinum (S300).

[0103] In the step (S200) of forming the mixture, the platinum precursor and the metal precursor with a greater tendency to ionize than platinum are preferably precursors in the liquid phase.

[0104] The specific reduction, drying, and heat treatment conditions of the composite step (S300) are preferably set to appropriate conditions based on the functional carrier used and the type of metal other than platinum. For reference, here, reduction refers to the process of adding a reducing agent to the mixture to reduce the platinum precursor and the metal precursor. Through such a reduction process, the composite of the functional carrier, platinum, and a metal with a greater ionization tendency than platinum is achieved.

[0105] Furthermore, in the composite step (S300), the mixture can be washed and filtered before drying and heat treatment to separate the catalyst composite formed through the reduction process. Additionally, after drying the separated catalyst composite, it can be washed and filtered again, and then dried and heat-treated to obtain the final catalyst composite.

[0106] In addition, the present invention includes an ionomer dispersion containing a solid ionomer, one or more solvents, and the catalyst complex.

[0107] Here, the solid ionomer may be a fluorine-based ionomer, a hydrocarbon-based ionomer, a perfluorosulfonic acid-based ionomer, or a mixture thereof, and more preferably, it contains a perfluorosulfonic acid-based ionomer.

[0108] The solvent may be distilled water, an alcohol-based solvent, or a mixture thereof, wherein the alcohol-based solvent may be one or more of methanol, ethanol, propanol, and butanol.

[0109] The solid ionomer and the solvent can be mixed in a weight ratio of 0.1:1 to 1:1. If the amount of solid ionomer added is lower than this ratio, it is difficult to prepare a high-performance polymer electrolyte membrane; if the amount of solid ionomer added is higher than this ratio, it will be difficult to disperse even in the dispersion process due to excessive addition.

[0110] Furthermore, the pH of the ionomer dispersion can be controlled by adjusting the type and ratio of solvent, preferably within the range of 0.01 to 3.0, and more specifically, preferably within the range of 0.8 to 2.5. This is because polymeric materials are prone to volume changes due to pH (volume change sensitivity). More specifically, when the pH of the ionomer dispersion is greater than 3.0, if it is used to prepare a polymeric electrolyte membrane, the polymeric material will swell, leading to unevenness such as wrinkles, cracks, and fissures in the final polymeric electrolyte membrane during the subsequent shrinkage process.

[0111] Figure 5 This is a schematic diagram used to illustrate how polymer materials easily undergo volume changes due to pH. It can be seen that when the pH increases, the material swells and expands in volume (swelling phenomenon), while when the pH decreases, the material shrinks in volume.

[0112] Furthermore, the catalyst complex can be included at 0.05 to 5% by weight relative to the total weight of the ionomer dispersion; more specifically, it can be included at 0.5 to 3% by weight, and even more specifically, at 0.5 to 2% by weight. When the content is below the above range, the effect of reducing gas permeation may not be significant; when the content is above the above range, it may reduce the ionic conductivity of the polymer electrolyte membrane. Therefore, it is preferable to include the catalyst complex within an appropriate range that both improves the effect of reducing gas permeation and ensures the ionic conductivity of the polymer electrolyte membrane.

[0113] The present invention includes a polymeric electrolyte membrane comprising: a porous carrier layer; and an ionomer layer, which is prepared by impregnating and coating the ionomer dispersion onto the porous carrier layer and then drying it.

[0114] In addition, according to one embodiment of the present invention, the polymer electrolyte membrane may further include additional ionomer layers disposed on the upper and lower parts of the porous carrier layer to form a reinforced composite membrane morphology with a three-layer structure. In this case, the additional ionomer layers are composed of pure ionomers and can be formed simultaneously when the ionomer dispersion is impregnated and coated on the porous carrier layer to form the ionomer layer.

[0115] The polymeric electrolyte membrane according to the present invention is characterized by having a dimensional change rate (MD) of less than 4% and a thickness change rate (TD) of less than 5%, and a thickness change rate of less than 45%, exhibiting excellent long-term stability and durability. As a preferred embodiment, the MD can be 3-4%, and the TD can be 3.5-5%.

[0116] In addition to adjusting the pH of the ionomer dispersion, the unevenness of the prepared polymer electrolyte membrane, such as wrinkles, cracks, and fissures, can also be reduced by adjusting the thickness of the polymer electrolyte membrane. If the polymer electrolyte membrane becomes too thick, surface unevenness will be exacerbated; therefore, it is preferable to prepare a multi-layered thin-layer structure to reduce shrinkage / expansion stress. As an example, a 5-layer 20μm structure is more conducive to stress release than a 100μm single-layer structure, thus being preferred in the preparation of a uniform polymer electrolyte membrane.

[0117] The following analysis describes specific embodiments of the present invention.

[0118] Example 1: Preparation of catalyst complex CeO2, serving as a functional support, was pulverized to a particle size below 500 nm and dispersed. Then, the nanoscale functional support was mixed with liquid platinum precursor (H2(PtCl6)) and liquid cobalt precursor (CoCl2) in a 4:1 molar ratio, and thoroughly stirred. A reducing agent was then added to reduce the precursors, thereby preparing a functional support, platinum, and cobalt integrated catalyst composite. The prepared catalyst composite was then separated by washing and filtration, followed by heat treatment at 130°C for 3 hours and drying at 80°C, ultimately yielding a functional support integrated with platinum and / or platinum-cobalt catalyst composite.

[0119] Comparative Example 1: Preparation of Catalyst Complex (Functional Support Pulverization ×) The catalyst complex was prepared using the same method as in Example 1, but uncrushed CeO2 was used as the functional support. For reference, the particle size of the uncrushed CeO2 was 20 μm.

[0120] Preparation Examples 1 to 4: Preparation of Polymer Electrolyte Membranes A perfluorosulfonic acid ionomer (3M, product name EW725) with SO3 groups was added to a solvent consisting of distilled water and ethanol at a weight ratio of 1:1 (ionomer: solvent) and mixed. Then, different amounts of the catalyst composite from Example 1 were added according to each preparation example and mixed. The mixture was then placed in a paste mixer and dispersed at 2,000 rpm for 30 minutes to prepare an ionomer dispersion. The specific contents of the catalyst composite are shown in Table 1 below.

[0121] [Table 1]

[0122] Polymer electrolyte membranes were prepared using the ionomer dispersions prepared in this manner. The preparation methods were identical for both. Specifically, after the ionomer dispersion was first coated onto a polymer membrane (PET), an adjustable thickness coater was used to coat it to a certain thickness. Then, a porous carrier, PTFE (Polytetrafluoroethylene), was impregnated onto the first-coated ionomer dispersion, followed by a second coating of the ionomer dispersion. Subsequently, the membrane was dried sequentially at 40°C for the first time, at 80°C for the second time, and then heat-treated sequentially within the range of 120–200°C to finally obtain the polymer electrolyte membrane.

[0123] Experimental Example 1: Ionic conductivity based on the content of catalyst complex The ionic conductivity of the polymer electrolyte membranes prepared in Examples 1 to 4 was measured under RH 100% conditions. The measurement results are shown in Table 2 below.

[0124] [Table 2]

[0125] As shown in Table 2 above, the ionic conductivity of the polymer electrolyte membrane decreases with increasing catalyst complex content. Therefore, when applying the catalyst complex to the polymer electrolyte membrane to reduce gas permeation, it is important to adjust its content to avoid excessively low ionic conductivity of the polymer electrolyte membrane. The catalyst complex should ideally be present at 0.05–5% by weight, more preferably 0.5–3% by weight, and even more preferably 0.5–2% by weight relative to the total weight of the ionomer dispersion. If the content is lower than this, the gas permeation effect may be insignificant; if the content is higher, the ionic conductivity of the polymer electrolyte membrane becomes too low.

[0126] Experimental Example 2: Reduction rate of platinum content Using the catalyst complex of Comparative Example 1, the catalyst complex of Example 1, the polymeric electrolyte membrane prepared using the catalyst complex of Comparative Example 1, and the polymeric electrolyte membrane prepared using the catalyst complex of Example 1 as examples, the platinum content was determined by ICP (Inductively Coupled Plasma Spectrometry) analysis, and the reduction rate (%) of platinum content was calculated using the measured values. The calculation results are shown in Table 3 below. For reference, the preparation method of the polymeric electrolyte membrane was the same as that of Preparation Example 1.

[0127] [Table 3]

[0128] As shown in Table 3 above, when using the catalyst complex of Comparative Example 1, the platinum content decreased by 37.3% after preparing the polymer electrolyte membrane. Conversely, when using the catalyst complex of Example 1 of the present invention, the platinum content decreased by 4.5% after preparing the polymer electrolyte membrane. It can be confirmed that the amount of platinum detachment in Example 1 is much less than that in Comparative Example 1. That is, it can be confirmed that when the functional support is pulverized to a nanometer scale of less than 1 μm, catalyst detachment is minimized during the preparation of the polymer electrolyte membrane, such as in the dispersion process.

[0129] Preparation Examples 5 to 8: Preparation of Polymer Electrolyte Membranes (pH Adjustment) The preparation was carried out in the same manner as in Preparation Examples 1 to 4, except that the pH of the ionomer dispersion was not specifically adjusted in Preparation Examples 1 to 4. In this case, the polymer electrolyte membrane was prepared by adjusting the pH of the ionomer dispersion. The pH was adjusted by adjusting the ratio of water to ethanol as the solvent. The details are shown in Table 4 below.

[0130] In Table 4 below, the pH values ​​of the ionomer dispersions in Preparation Examples 1 to 4 were measured without special pH adjustment, while those in Preparation Examples 5 to 8 were measured after pH adjustment.

[0131] [Table 4]

[0132] Experimental Example 3: Dimensional Change Rate, Thickness Change Rate, and Surface State of Polymer Electrolyte Membranes To measure the dimensional change rate, thickness change rate, and surface condition of the polymeric electrolyte membranes prepared in Examples 1 to 8, each membrane was cut into 5cm × 5cm pieces and then placed in room temperature and hot water for at least 12 hours. The dimensional change (MD), thickness (TD), and surface condition were then measured before and after placement. The change rate was calculated, and the surface condition was visually observed. Thickness was measured at five points, and the length changes of MD and TD after swelling were also measured. The measurement results are shown in Table 5 below.

[0133] For reference, a large rate of change in size and thickness of polymeric electrolyte membranes indicates a large change in state after placement, which can be considered equivalent to a polymeric electrolyte membrane that is not preferred in terms of long-term stability and durability.

[0134] [Table 5]

[0135] As shown in Table 5 above, it can be seen that when polymeric electrolyte membranes prepared using ionomer dispersions with a pH of 3.0 or lower (Preparation Examples 1, 2, and 4 to 8) are used, the dimensional change rates (MD) are ≤4% and TD is ≤5%. Conversely, when polymeric electrolyte membranes prepared using ionomer dispersions with a pH >3.0 are used (Preparation Examples 3 and 4), the MD is ≥4.5 and the TD is ≥5.5.

[0136] Regarding the thickness change rate, it can also be seen that when polymeric electrolyte membranes prepared using ionomer dispersions with a pH of 3.0 or lower (Preparation Examples 1, 2, and 4 to 8) are used, the thickness change rate is 45% or lower. Conversely, when polymeric electrolyte membranes prepared using ionomer dispersions with a pH of 3.0 or higher (Preparation Examples 3 and 4) are used, the thickness change rate is 49% or higher.

[0137] Furthermore, in the surface state of polymer electrolyte membranes (Preparation Examples 3 and 4) prepared using ionomer dispersions with a pH exceeding 3.0, inhomogeneity and cracking were observed.

[0138] Preparation Example 9: Preparation of Polymer Electrolyte Membranes (Catalyst-Free Composites) The polymer electrolyte membrane was prepared in the same manner as in Preparation Example 1, but without the use of a catalyst complex.

[0139] Experimental Example 4: Hydrogen permeability based on whether or not a catalyst complex is present To measure the hydrogen permeability of the polymeric electrolyte membranes prepared in Examples 1 and 9, each membrane was fixed in a 5cm × 5cm fixture, and a system was constructed as follows: hydrogen was supplied to one side and nitrogen to the other side under conditions of 50% RH and 70°C. A hydrogen detector was then installed at the gas outlet on the nitrogen supply side to measure the vol% of hydrogen that permeated through the electrolyte membrane to the nitrogen supply side over time. The measurement results are shown in Table 6 below.

[0140] [Table 6]

[0141] As shown in Table 6 above, it can be seen that in the case of the polymeric electrolyte membrane of Preparation Example 9, which does not contain the catalyst complex, the hydrogen permeation increases with increasing operating time. Conversely, in the case of the polymeric electrolyte membrane of Preparation Example 1, which contains the catalyst complex of the present invention, the hydrogen permeation is low even with increasing operating time. This confirms that the polymeric electrolyte membrane of Preparation Example 1 exhibits a gas permeation reduction effect.

[0142] Preparation Examples 10 to 12: Preparation of Polymer Electrolyte Membranes (Modifying Functional Supports) The polymer electrolyte membrane was prepared in the same manner as in Example 1, but a catalyst complex was prepared by changing only the type of functional support. Details are shown in Table 7 below. For reference, the preparation method of the catalyst complex was the same as in Example 1, except for the type of functional support.

[0143] [Table 7]

[0144] Experimental Example 5: Hydrogen permeability based on the type of functional support for the catalyst complex Hydrogen permeability was measured using the polymeric electrolyte membranes prepared in Examples 1 and 9 to 12. The measurement method was the same as in Experiment 4, but only the amount of hydrogen was measured when the running time was 200 h. The measurement results are shown in Table 8 below.

[0145] [Table 8]

[0146] As shown in Table 8 above, it can be seen that, compared with the polymer electrolyte membrane of Preparation Example 9 which does not contain the catalyst complex, the polymer electrolyte membranes of Preparation Examples 10 to 13 which contain the catalyst complex of the present invention have low hydrogen permeation, thus confirming that they exhibit a gas permeation reduction effect.

[0147] Next, the electrolyte membrane structure (2) in which the concentration gradients of hydrogen inhibitors and antioxidants are independently regulated in the PEMWE, i.e., water electrolysis (WE) system based on polymer electrolyte membrane (PEM), will be described.

[0148] <Electrolyte membrane structure with independently adjustable concentration gradients of hydrogen-suppressing additives and antioxidants (2)> The enhanced composite electrolyte membrane for water electrolysis, with independently adjustable concentration gradients of hydrogen-suppressing additives and antioxidants according to a preferred embodiment of the present invention, relates to an electrolyte membrane that ensures safety and durability by effectively blocking hydrogen.

[0149] As an enhanced composite electrolyte membrane for water electrolysis comprising a first ionomer layer, a second ionomer layer, and a composite layer, functional additives for hydrogen inhibition and oxidation are introduced not only into the ionomer layer (electrolyte layer) but also into the composite layer (reinforcement layer). The first ionomer layer is disposed on the anode side, the second ionomer layer is disposed on the cathode side, and the composite layer is formed by at least partially impregnating one or more of the first ionomer and the second ionomer onto a porous substrate between the first ionomer layer and the second ionomer layer.

[0150] As described above, functional additives are incorporated into all layers. However, since the dominant reactions in the anode-side and cathode-side electrolyte membranes of the water electrolyzer differ, the concentration gradients of the additives for reducing hydrogen (capture) and those for anti-oxidation should be independently configured. In other words, this invention relates to an electrolyte membrane that imparts a concentration gradient in a manner that allows the functional additives to function most effectively.

[0151] refer to Figure 6 Position ① corresponds to a location where hydrogen gas cross-permeating from the cathode and excess oxygen gas from the anode can easily be converted into water (H2O). Specifically, this position highlights the role of platinum (Pt), which, according to the surface adsorbed mechanism, facilitates the reaction that converts hydrogen and oxygen gas into water.

[0152] In addition, position ② is where H2O2 is generated from oxygen cross-permeating from the anode, which actively forms free radicals and causes membrane degradation. Therefore, when forming an antioxidant gradient, the higher the concentration set at this position, the better.

[0153] The cross-permeation of hydrogen and oxygen is a phenomenon in which hydrogen is generated on the cathode side and oxygen is generated on the anode side, creating a concentration gradient of each gas, and then permeating through diffusion. When pressure is applied on the cathode side, permeation to the anode side is promoted (30~40 bar). If differential pressure is applied to reduce system cost, the cross-permeation phenomenon will be further aggravated.

[0154] Examples of energy elements based on polymer electrolyte membranes include proton exchange membrane fuel cells (PEMFC) and proton exchange membrane water electrolyzers (PEMWE), but they have different technical concerns regarding degradation or cross-permeation. Figure 6 This is a schematic diagram of a water electrolysis system. Figure 7 This is a schematic diagram of a fuel cell system.

[0155] For fuel cell systems, the most significant degradation factor is the free radicals generated by oxygen. To suppress this free radical degradation, antioxidants are typically added. The primary degradation area is location ① of the electrolyte membrane near the cathode electrode. Figure 7 Therefore, the region where the antioxidant should be present in high concentration is also the ionomer layer on the cathode side, i.e., position ①.

[0156] From the perspective of gas permeation, hydrogen permeates and encounters oxygen and metals to form free radicals. Therefore, it is necessary to prevent hydrogen permeation. In most fuel cell systems, the purpose of introducing platinum (Pt) additives is to block the permeated hydrogen, thereby inhibiting the formation of free radicals.

[0157] Conversely, in water electrolysis systems, hydrogen permeates from the cathode to the anode under pressure exceeding 30 bar. When more than 4% of cross-permeated hydrogen is present in the oxygen environment at the anode, the mixing of oxygen and hydrogen increases the risk of explosion. To prevent explosions, attempts are being made to prevent hydrogen cross-permeation by adding additives that block hydrogen permeation to the electrolyte membrane.

[0158] Unlike fuel cell systems, the main degradation site is also located at position ① where hydrogen and oxygen are mixed (…). Figure 6 This refers to the electrolyte membrane region near the anode electrode. Unlike fuel cells, free radical-induced degradation is a minor issue during water electrolysis, and it occurs only in small amounts in the anode direction. However, the electrolyte membrane region near the cathode, i.e., location ② (… Figure 6 () is the location where hydrogen peroxide is generated, and free radical degradation occurs relatively frequently.

[0159] Therefore, in order to minimize the risk of deterioration and explosion in this water electrolysis system, the present invention places the hydrogen inhibitor primarily in the anode direction to prevent hydrogen and oxygen from mixing at a certain concentration, and places the antioxidant primarily in the cathode direction to achieve effective free radical removal.

[0160] The present invention is characterized in that, in the reinforced composite electrolyte membrane structure composed of a first ionomer layer, a second ionomer layer and a composite layer, the hydrogen-suppressing additive and the antioxidant have different (opposite trend) concentration gradients.

[0161] Figure 8 This is a schematic diagram of an enhanced composite electrolyte membrane structure according to an embodiment of the present invention. The first ionomer layer on the anode side is labeled B-1, the middle composite layer is labeled B, and the second ionomer layer on the cathode side is labeled B-2.

[0162] Since a high concentration gradient is required in the region near the anode, when the concentration of the first ionomer layer is B-1 and the concentration of the composite layer is B, a hydrogen-suppressing additive can be included in such a way that B-1>B>0. Conversely, since a high concentration gradient is required in the region near the cathode, when the concentration of the second ionomer layer is B-2 and the concentration of the composite layer is B, an antioxidant can be included in such a way that B-2>B>0.

[0163] As mentioned above, in order to reduce hydrogen permeation and inhibit degradation, the concentration (B-1) of the hydrogen inhibitor in the first ionomer layer near the anode side needs to be higher than the concentration (B) in the composite layer. For the composite layer composed of porous substrate in the reinforced composite electrolyte membrane structure, since it is a region where hydrogen and oxygen stay for a relatively long time during migration, a certain degree of hydrogen inhibitor (B>0) is also required in the composite layer.

[0164] In addition, sometimes hydrogen-suppressing additives and antioxidants are introduced into the entire three-layer structure. When the concentration of the first ionomer layer is B-1, the concentration of the second ionomer layer is B-2, and the concentration of the composite layer is B, hydrogen-suppressing additives are contained in such a way that B-1≥B-2>B>0 is satisfied. When the concentration of the first ionomer layer is B-1, the concentration of the second ionomer layer is B-2, and the concentration of the composite layer is B, antioxidants are contained in such a way that B-2≥B-1>B>0 is satisfied.

[0165] According to one embodiment of the present invention, the hydrogen inhibition additive may be Pt / Ceria, that is, a catalyst complex in which a platinum catalyst is supported on cerium oxide, and the antioxidant may be a cerium (Ce)-based free radical scavenger, that is, Ceria (cerium oxide).

[0166] When Pt / Ceria, the hydrogen-suppressing additive, is primarily introduced to the anode side, it offers advantages in the following aspects: Due to the high oxygen concentration on the anode side caused by the oxygen generation reaction, there are more sites for hydrogen cross-permeating from the opposite side to react with the additive (Pt / Ceria) and the oxygen / hydrogen, thus increasing the reaction rate (H+). 2（g） +1 / 2O 2（g） →H2O （g） The hydrogen migration rate is about twice that of oxygen, so the probability or frequency of the above reaction occurring on the anode side is higher. Since platinum (Pt) can assist the anode electrode material (IrO2, etc.) in the oxygen generation reaction, it can act as a catalyst for the oxygen generation reaction to a certain extent, thereby reducing the polarization resistance of the battery cell and helping to improve performance.

[0167] In particular, regarding the performance of individual battery cells, it has been confirmed that although the surface hydrogen ion conductivity of the electrolyte membrane with Pt / Ceria is low, the performance can be maintained at or above the same level in the environment of water electrolysis electrochemical reaction after the battery cell is assembled.

[0168] In addition, when Ceria, the antioxidant, is mainly introduced to the cathode side, performance can be maintained by introducing Pt / Ceria while significantly reducing hydrogen permeation (H2 in O2), thereby maximizing one of the key parameters, selectivity.

[0169] In this invention, selectivity (S) is a measure of ion migration through the membrane, namely ionic conductivity (σ), and hydrogen permeability through the electrolyte membrane (P), representing the selective mass transport performance of the electrolyte membrane. In this case, the electrolyte membrane should effectively transport ions while suppressing hydrogen permeation, and is therefore expressed by the following formula.

[0170] (Unit: mS cm) -1 barrer -1 ) Reference Figure 9 The electrolyte membrane of the present invention may further include a third ionomer layer on the outer side of the first ionomer layer. Figure 9 The B-3 is formed between the anode and the first ionomer layer. At this time, when the concentration of the first ionomer layer is B-1, the concentration of the third ionomer layer is B-3, and the concentration of the composite layer is B, the hydrogen-suppressing additive can be contained in such a way that B-3≥B-1>B>0.

[0171] The third ionomer layer, in contact with the anode, is where the oxygen concentration is highest, thus providing the most reaction sites for oxygen, hydrogen, and the hydrogen suppressant additive. Therefore, it is advantageous for the third ionomer layer (B-3) to have a higher concentration of the hydrogen suppressant additive than the first ionomer layer (B-1). Furthermore, although the oxygen concentration is high, the anode supplies water as fuel, creating a high-humidity environment that makes it difficult for hydrogen peroxide and free radicals to form.

[0172] Furthermore, the electrolyte membrane of the present invention may further include a fourth ionomer layer on the outer side of the second ionomer layer. Figure 9 The B-4 is formed between the cathode and the second ionomer layer. At this time, when the concentration of the second ionomer layer is B-2, the concentration of the fourth ionomer layer is B-4, and the concentration of the composite layer is B, it is possible to contain an antioxidant in a manner that satisfies B-2≥B-4>B>0.

[0173] The cathode direction, due to its low humidity and oxygen cross-permeability, is an environment conducive to hydrogen peroxide generation, leading to active free radical formation. Therefore, the fourth ionomer layer, like the second ionomer layer, also needs to contain a higher antioxidant concentration than the composite layer (B-4>B). Furthermore, the second ionomer layer has the highest oxygen concentration permeating from the anode side towards the cathode, decreasing towards the fourth ionomer layer. Therefore, it is advantageous for the second ionomer layer to have a higher antioxidant content than the fourth ionomer layer (B-2≥B-4).

[0174] Furthermore, it can be assumed that all of the above-described embodiments of the third and fourth ionomer layers are applied. In this case, when the concentration of the first ionomer layer is B-1, the concentration of the second ionomer layer is B-2, the concentration of the third ionomer layer is B-3, the concentration of the fourth ionomer layer is B-4, and the concentration of the composite layer is B, the hydrogen-suppressing additive can be contained in a manner that satisfies B-3≥B-1≥B-2≥B-4≥B>0.

[0175] Similarly, when the concentration of the first ionomer layer is B-1, the concentration of the second ionomer layer is B-2, the concentration of the third ionomer layer is B-3, the concentration of the fourth ionomer layer is B-4, and the concentration of the composite layer is B, it is possible to contain antioxidants in a manner that satisfies B-2≥B-4≥B-3≥B-1≥B>0.

[0176] Furthermore, the composite layer of the electrolyte membrane of the present invention can be composed of at least two or more stacked porous substrates between a first ionomer layer and a second ionomer layer. The outermost outer layer of the stacked porous substrates is in contact with the ionomer layers on both sides, and the composition constituting the contacted ionomer layers is at least partially impregnated to form the composite layer.

[0177] In a so-called multi-layer structure using two or more porous substrates, multiple thin ionomer layers can be stacked, resulting in lower expansion and shrinkage rates of the electrolyte membrane. Furthermore, since two or more porous substrates that contribute most to mechanical strength are incorporated, the underlying strength is increased. Moreover, in roll-to-roll (RTR) film fabrication processes, thinner coatings and drying are possible, maximizing drying efficiency and facilitating the removal of residual solvents and other impurities.

[0178] The porous substrate may contain at least one fluorinated polymer, preferably polytetrafluoroethylene (PTFE), poly(ethylene-co-tetrafluoroethylene) (EPTFE), expanded polytetrafluoroethylene (e-PTFE), polyvinylidene fluoride (PVDF), expanded polyvinylidene fluoride (e-PVDF), expanded poly(ethylene-co-tetrafluoroethylene) (eEPTFE), or a mixture thereof, more preferably expanded polytetrafluoroethylene (e-PTFE).

[0179] In the case of a porous substrate with two or more layers, the stacked porous substrates can be a continuous stacked structure in direct contact, or at least two porous substrates can be spaced apart by a predetermined distance to form an internal space, and an ionomer inner layer formed of an ionomer composition can be inserted therein. In this case, the ionomer inner layer can be composed of one or more of the same components as the ionomer layer on the anode or cathode side, i.e., one or more of the first ionomer layer / second ionomer layer.

[0180] The enhanced composite electrolyte membrane for water electrolysis according to the present invention can be prepared by a method comprising the following steps: 1) Prepare a first ionomer dispersion comprising a first ionomer, a solvent and an additive, and a second ionomer dispersion comprising a second ionomer, a solution and an additive; 2) Coat the first ionomer dispersion onto a substrate such as a carrier membrane; 3) A porous substrate is laminated onto the side coated with the first ionomer dispersion to perform a composite based on ionomer impregnation; 4) Coat the second ionomer dispersion onto the other side of the porous substrate (the side opposite to the side that contacts the first ionomer dispersion); and 5) The prepared electrolyte membrane is dried and heat-treated.

[0181] At this point, the drying and heat treatment steps can also be performed between other steps.

[0182] By adjusting the types and contents of additives in the first and second ionomer dispersions, the concentration gradients of the two additives (hydrogen inhibitor and antioxidant) between the first ionomer layer, the composite layer, and the second ionomer layer can be achieved independently.

[0183] When additional layers such as the third ionomer layer and the fourth ionomer layer are formed, steps 2) to 5) above can be performed as a cycle to carry out the additional layer process.

[0184] Next, the electrolyte membrane structure and process (3) applied to PEMWE, namely water electrolysis (WE) system based on polymer electrolyte membrane (PEM), which adjusts the layer design and additive distribution by controlling the pore size of the reinforcing substrate and the particle size of the additives, will be described.

[0185] Layer design and additive distribution can be adjusted by controlling the pore size of the reinforcing substrate and the particle size of the additives. Electrolyte membrane structure and process (3) This invention relates to an enhanced composite electrolyte membrane composed of a porous substrate and an ionomer layer. By controlling the particle size (diameter of the particles) of the hydrogen-suppressing additives contained in the ionomer layer and the pore size (average / maximum) of the porous substrate, the additives can be differentiated in the electrolyte membrane according to their particle size. At the same time, an intermediate layer in which large-particle additives are concentrated can be formed without additional processing.

[0186] Capillary action refers to the phenomenon where, when a capillary is placed in a liquid, the liquid inside the capillary rises or falls due to the attraction between molecules and the attraction between molecules and the capillary wall.

[0187] Figure 10This is a schematic diagram illustrating the cross-sectional structure of an electrolyte membrane according to an embodiment of the present invention, and the behavior of the hydrogen-suppressing additive according to particle size during the formation of the composite layer.

[0188] The hydrogen-suppressing additive included in the first ionomer composition can be divided into a first additive having a particle size smaller than the maximum pore size of the porous substrate, and a second additive having a particle size larger than the maximum pore size. (Reference) Figure 10 During the composite process of the ionomer layer and the porous substrate, i.e., the formation of the composite layer, the ionomer composition is impregnated into the pores of the porous substrate due to capillary forces. At this time, particles smaller than the pore size of the porous substrate enter the pores, while particles larger than the pore size accumulate at the interface between the ionomer layer and the composite layer. Figure 10 The second layer), thus forming an independent layer with a high concentration of large particles.

[0189] Through this process, a first additive smaller than the maximum pore size of the porous substrate is impregnated into the pores of the porous substrate, thereby being located in the composite layer ( Figure 10 Within the third layer, a second additive larger than the maximum pore size of the porous substrate remains in the first ionomer layer. More specifically, under capillary force, an intermediate layer is formed where the concentration of the second additive is higher than the concentration of the first additive. Figure 10 The second layer), and the first ionomer layer other than the intermediate layer ( Figure 10 In the first layer, large and small particles, i.e., the first additive and the second additive, coexist.

[0190] Hydrogen-suppressing additives induce the reaction of hydrogen and oxygen into water within the electrolyte membrane. Therefore, placing the additive near the point where hydrogen and oxygen meet maximizes the hydrogen suppression effect. Under the same thickness, concentration, and steady-state conditions, the flux of the reactants can be calculated using the following formula (see reference). Figure 11 Due to differences in diffusion coefficient and molecular weight, oxygen flux is slower than hydrogen flux. Therefore, within the electrolyte membrane, the two will meet on the side near the anode electrode, resulting in a dense distribution of the additive at that location. Figure 11 The area indicated by shading in the middle is valid, and this area corresponds to the intermediate layer area according to the invention.

[0191]

[0192] in, C * R : Catalyst layer reactant concentration C 0 R Bulk (flow channel) reactant concentration δ: Electrode (diffusion layer) thickness D eff Effective reactant diffusion coefficient To form the intermediate layer region, as mentioned earlier, it is necessary to relatively control the pore size of the porous substrate and the particle size (diameter) of the hydrogen-suppressing additive. The pore size of the porous substrate can be controlled during the preparation of substrates such as e-PTFE by the composition of the precursor material or process conditions, while the particle size of the additive can be controlled during the preparation process by ball milling by a combination of conditions such as bead size, flow rate, milling time, and the initial particle size of the additive, but is not limited to the methods described above.

[0193] When analyzing the particle size distribution of hydrogen-suppressing additive particles that have undergone particle size control, from the smallest to the largest particles, a curve resembling a normal distribution is typically observed. Preferably, in this particle size distribution, the particle size of the additive that represents more than 0 and less than X% (the percentage (%) refers to the proportion of particles with that size to the total number of particles) is below the maximum pore size of the porous substrate. In this case, the benchmark X value can be between 50 and 80. In other words, relative to the total number of hydrogen-suppressing additive particles, the proportion of the first additive can be between 50% and 80%, while the proportion of the second additive can be between 20% and 50%.

[0194] That is, additives smaller than the maximum pore size of the porous substrate are impregnated into the interior of the porous substrate due to capillary force, thereby forming a composite layer. These particles correspond to particles that account for 50 to 80% of the total number of additive particles in the particle size distribution. The remaining relatively large additive particles cannot enter the pores of the porous substrate and thus accumulate at the interface between the ionomer layer and the composite layer to form an intermediate layer, or remain on the ionomer layer in the bulk state.

[0195] The additives introduced into the porous substrate are located within the composite layer of the electrolyte membrane. In the reinforced composite electrolyte membrane structure, the composite layer composed of the porous substrate is a region where hydrogen and oxygen reside for a relatively long time during migration. Therefore, a certain level of hydrogen-suppressing additives is also required within the composite layer. Thus, it is necessary to control the distribution so that, based on particle size distribution, the top 50% to 80% of the additives are abundantly distributed within the composite layer. At this point, due to enhanced capillary forces, the extent of the intermediate layer can also be expanded.

[0196] Conversely, if the particle size distribution exceeds 50%, and the additive (second additive) with a particle size larger than the maximum pore size of the porous substrate is abundant, the excessive additive particles cannot impregnate the interior of the porous substrate. Instead, the ionomer composition enters the pores of the porous substrate, but the large additive particles hinder the impregnation, leading to a slower overall impregnation rate and weakened capillary force, thus posing a risk of a reduced intermediate layer area. Furthermore, if the proportion of the second additive is less than 20%, the insufficient amount of particles forming the intermediate layer makes it difficult to achieve a sufficiently thick intermediate layer.

[0197] Figure 12 The images show a cross-sectional photograph (left) of the electrolyte membrane according to a preferred embodiment of the invention, and an EDS compositional analysis image of platinum (Pt) over a rectangular region of the membrane (right). Reference Figure 12 The EDS composition analysis image on the right confirms that a platinum (Pt) dense layer is formed near the interface between the first ionomer layer (lower 1 / 4 region) and the composite layer (lower 1 / 4 to 2 / 3 region), which corresponds to the "intermediate layer" of this invention.

[0198] Furthermore, the present invention can also be applied to a three-layer structure, wherein, based on the first ionomer layer-composite layer structure, a second ionomer layer composed of a second ionomer composition is further included on the other side of the porous substrate of the composite layer (the side opposite to the side where the first ionomer layer is formed). In this case, it is possible that only the first ionomer composition is impregnated into the porous substrate to form the composite layer, and the second ionomer layer is stacked separately; or it is possible that the second ionomer composition constituting the second ionomer layer is also at least partially impregnated into the porous substrate to form a composite layer containing both the first and second ionomer compositions.

[0199] Furthermore, the composite layer of the electrolyte membrane of the present invention can be composed of at least two or more stacked porous substrates between a first ionomer layer and a second ionomer layer. The outermost outer layer of the stacked porous substrates is in contact with the ionomer layers on both sides, and the composition constituting the contacted ionomer layers is at least partially impregnated, thereby forming the composite layer.

[0200] The porous substrate may contain at least one fluorinated polymer, preferably polytetrafluoroethylene (PTFE), poly(ethylene-co-tetrafluoroethylene) (EPTFE), expanded polytetrafluoroethylene (e-PTFE), polyvinylidene fluoride (PVDF), expanded polyvinylidene fluoride (e-PVDF), expanded poly(ethylene-co-tetrafluoroethylene) (eEPTFE), or a mixture thereof, more preferably expanded polytetrafluoroethylene (e-PTFE).

[0201] In the case of a porous substrate with two or more layers, the stacked porous substrates can be a continuous stacked structure in direct contact, or at least two porous substrates can be spaced apart by a predetermined distance to form an internal space, and an ionomer inner layer formed of an ionomer composition can be inserted therein. In this case, the ionomer inner layer can be composed of one or more of the same components as the ionomer layer on the anode or cathode side, i.e., one or more of the first ionomer layer / second ionomer layer.

[0202] In addition, according to a preferred embodiment of the present invention, a method for preparing an enhanced composite electrolyte membrane for water electrolysis is provided.

[0203] Figure 13 This is a conceptual diagram of the fabrication process involving stacking two layers of a polymer material using a roll-to-roll (RTR) process. The same process is repeated when forming three or more layers. In this manner, in order to prepare... Figure 10 The structure shown on the left, consisting of four layers, requires three RTR cycles: first coating, second coating, third substrate adhesion, and fourth coating.

[0204] However, by controlling the pore size of the porous substrate and the particle size of the additives, the present invention can naturally form a second layer, i.e. an intermediate layer, even when only the first layer is coated, during the process of attaching the third layer to the substrate and performing the composite process. Therefore, it has the advantage of being able to form a film through only two RTR cycle processes.

[0205] Specifically, the preparation method of the present invention includes the following steps: preparing a porous substrate with adjusted pore size and a hydrogen-suppressing additive with adjusted particle size and distribution; preparing an ionomer composition; forming an ionomer layer by an RTR coating process; and attaching a porous substrate to the ionomer layer to form a composite layer (composite).

[0206] The porous substrate may contain at least one fluorinated polymer, preferably polytetrafluoroethylene (PTFE), poly(ethylene-co-tetrafluoroethylene) (EPTFE), expanded polytetrafluoroethylene (e-PTFE), polyvinylidene fluoride (PVDF), expanded polyvinylidene fluoride (e-PVDF), expanded poly(ethylene-co-tetrafluoroethylene) (eEPTFE), or mixtures thereof. More preferably, the porous substrate may be expanded polytetrafluoroethylene (e-PTFE). The porous substrate can be prepared by adjusting the maximum pore size and the average pore size, which can be controlled during the preparation of e-PTFE by the composition of the precursor material, process conditions, etc.

[0207] For additives, particle size and its distribution are controlled. Specifically, the particle size distribution is configured to include a first additive with a particle size smaller than the maximum pore size of the porous substrate and a second additive with a particle size larger than the maximum pore size. While the overall distribution can be adjusted, the particle size distribution can also be configured by preparing a first additive with a small particle size and a second additive with a large particle size separately, and then adjusting the mixing ratio between them. The particle size of the additives can be controlled by processes such as ball milling, and the target particle size distribution can be obtained by combining technical conditions such as bead size, flow rate, grinding time, and initial particle size used in this process.

[0208] By adjusting the particle size and distribution, the hydrogen-suppressing additive containing the first additive and the second additive is mixed or compounded with the first ionomer to prepare a first mixture, which is then dispersed in a solvent to prepare the first ionomer composition.

[0209] The first ionomer composition prepared by means of, Figure 13 The roll-to-roll (RTR) film-forming process is shown to coat the substrate such as a carrier film or release film to form a first ionomer layer, which is then dried and heat-treated at an appropriate level.

[0210] A porous substrate with adjusted pore size is attached to one side of the prepared first ionomer layer. Then, through capillary effect, the first ionomer composition impregnates into the pores of the porous substrate, thereby forming a composite layer. At this time, in order to obtain a certain capillary force and impregnation rate, it is necessary to ensure the fluidity of the first ionomer composition. Therefore, drying / heat treatment can be performed under relatively mild conditions during the formation of the first ionomer layer, or it can be performed after the composite with the porous substrate as needed.

[0211] In the composite layer formation step, namely the composite process of the ionomer layer and the porous substrate, the first additive in the first ionomer composition is contained within the first ionomer composition and impregnates into the interior of the porous substrate. The second additive, with a particle size larger than the maximum pore size of the porous substrate, does not impregnate into the interior of the porous substrate but accumulates at the interface between the first ionomer layer and the porous substrate, thereby forming an intermediate layer in which the second additive exists at a high concentration. Thus, the effect of forming two layers in a single coating process can be achieved.

[0212] Furthermore, a second ionomer layer can be formed on the other side of the porous substrate, that is, on the side opposite to where the first ionomer layer is formed. The second ionomer layer is also formed by an RTR coating process of a second ionomer composition in which the second ionomer is dispersed in a solvent. It is possible to composite the porous substrate with only the first ionomer composition (forming a composite layer), or it can be configured such that, during the formation of the second ionomer layer, the second ionomer composition is impregnated onto the other side of the porous substrate, so that both the first and second ionomer compositions participate in the formation of the composite layer.

[0213] The present invention provides an enhanced composite electrolyte membrane for water electrolysis prepared by the preparation method described above, and also provides a membrane electrode assembly (MEA) comprising the enhanced composite electrolyte membrane for water electrolysis and a water electrolysis system.

[0214] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, those skilled in the art will understand that the present invention can be implemented in other specific ways without changing the technical concept or essential features of the invention. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

Claims

1. A catalyst composite with a gas permeation reduction effect, said catalyst composite being applied to a polymer electrolyte membrane for water electrolysis, characterized in that, The catalyst complex comprises: Catalysts, including single platinum catalysts or composite catalysts, said composite catalysts comprising platinum and a metal with a greater ionization tendency than platinum; and Functional support, on which the catalyst is loaded, The functional carrier is selected from one or more of the following functional carriers: a) A carrier that enables antioxidant activity; b) Supports that enhance ion transport properties and catalyst activity; c) Supports that enhance catalyst stability; d) A carrier that modifies the hydrophilic or hydrophobic properties of polymer electrolyte membranes; e) A carrier that enhances water content; and f) A three-dimensional mesh structure carrier that enhances the durability and long-term stability of polymer electrolyte membranes.

2. The catalyst composite with gas permeation reduction effect according to claim 1, characterized in that, The metal with a greater ionization tendency than platinum is selected from one or more of barium (Ba), magnesium (Mg), aluminum (Al), manganese (Mn), zinc (Zn), chromium (Cr), iron (Fe), cadmium (Cd), cobalt (Co), nickel (Ni), tin (Sn), and lead (Pb). The metal is composited onto the platinum.

3. The catalyst composite with gas permeation reduction effect according to claim 1, characterized in that, The carrier a) is selected from one or more of CeO2, Ce2O3 and LaCeO7.

4. The catalyst composite with gas permeation reduction effect according to claim 1, characterized in that, The carrier b) is selected from one or more of YSZ, SDC, LST, BYZ, BCZY, Gd2O3, Nd2O3 and La2Zr2O7.

5. The catalyst composite with gas permeation reduction effect according to claim 1, characterized in that, The carrier c) is selected from one or more of IrO2, NiO, SnO2 and TiO2.

6. The catalyst composite with gas permeability reduction effect according to claim 1, characterized in that, The carrier e) is a polymer with a mesh or network structure, such as a hydrogel polymer or a superabsorbent polymer (SAP).

7. The catalyst composite with gas permeation reduction effect according to claim 1, characterized in that, The particle size of the functional carrier is less than 1 μm.

8. A method for preparing a catalyst complex with a gas permeation reduction effect, said preparation method being a method for preparing a catalyst complex for use in polymer electrolyte membranes for water electrolysis, characterized in that, The preparation method includes the following steps: The functional carrier is pulverized to a particle size of less than 1 μm; The pulverized functional carrier is mixed with a platinum precursor and a metal precursor with a greater ionization tendency than platinum in a certain proportion to form a mixture; and The mixture is subjected to reduction, drying, and heat treatment to combine the functional carrier with platinum and metals with a greater tendency to ionize than platinum.

9. An ionomer dispersion comprising a catalyst complex, characterized in that, The ionomer dispersion comprises: Solid ionomers; One or more solvents; and The catalyst complex according to any one of claims 1 to 7.

10. The ionomer dispersion containing the catalyst complex according to claim 9, characterized in that, The pH of the ionomer dispersion is below 3.

0.

11. The ionomer dispersion containing the catalyst complex according to claim 9, characterized in that, The catalyst complex is contained in 0.05 to 5% by weight relative to the total weight of the ionomer dispersion.

12. A polymeric electrolyte membrane, characterized in that, The polymeric electrolyte membrane comprises: Porous carrier layer; and The ionomer layer is prepared by impregnating and coating the porous carrier layer with the ionomer dispersion of claim 9 and then drying it.

13. A membrane electrode assembly, characterized in that, The membrane electrode assembly includes the polymer electrolyte membrane as described in claim 12.

14. A water electrolysis device, characterized in that, The water electrolysis device includes the membrane electrode assembly as described in claim 13.

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