Electrode for water electrolysis, membrane-electrode assembly comprising same, and electrolysis cell comprising membrane-electrode assembly

Abstract

The present invention relates to an electrode for water electrolysis, a membrane-electrode assembly comprising same, and an electrolysis cell comprising the membrane electrode assembly, and provides an electrode for water electrolysis comprising a substrate and a catalyst layer thereon comprising iridium oxide, and a membrane-electrode assembly and an electrolysis cell comprising the electrode.

Description

A water electrolysis electrode, a membrane electrode assembly including the same, and an electrolysis cell including the membrane electrode assembly.

[0001] [Cross-reference with related applications]

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0131049 dated September 26, 2024, and all contents disclosed in the document of said Korean patent application are incorporated herein as part of this specification.

[0003] [Technology Field]

[0004] The present invention relates to a water electrolysis electrode, a membrane electrode assembly including the same, and an electrolysis cell including the membrane electrode assembly.

[0005]

[0006] Hydrogen has the advantages of being suitable for storage and transportation and being eco-friendly, leading to various recent attempts to utilize it as an energy source. While various methods for producing hydrogen are known, the method of producing hydrogen through water electrolysis has the advantage of being environmentally friendly as it does not generate harmful byproducts.

[0007] Water electrolysis is a method of producing hydrogen and oxygen using electrons generated during the redox reaction of water.

[0008] Representative methods of water electrolysis include Alkaline Electrolysis (AEC) and Polymer Electrolyte Membrane Electrolysis (PEM). Among these, Alkaline Electrolysis is a method that electrolyzes water using an alkaline electrolyte and is the most commercialized technology among various electrolysis methods. Alkaline Electrolysis has the advantages of relatively low process operating costs, a simple production structure making it suitable for large-scale hydrogen production, and excellent durability. However, Alkaline Electrolysis has limitations, such as the need to continuously replenish the electrolyte consumed during the electrolysis process, corrosion problems caused by alkaline components, and low current density efficiency.

[0009] Meanwhile, Polymer Electrolyte Membrane (PEM) water electrolysis is a method that utilizes a polymer electrolyte membrane as the electrolyte. It features a structure in which an anode and a cathode are coated on either side of the polymer electrolyte membrane, and this is referred to as a Membrane Electrode Assembly. The principle of PEM water electrolysis is that water (H2O) is supplied to the anode and decomposed into oxygen gas, electrons, and hydrogen ions, while at the cathode, hydrogen ions that have passed through the polymer electrolyte membrane combine with electrons to be released as pure hydrogen gas.

[0010] The electrochemical performance of polymer electrolyte membrane water electrolysis is significantly influenced by key materials such as the polymer electrolyte membrane, catalyst, and electrode binder composed of an ionomer. It has the advantage of high energy efficiency because operation at high current densities is possible using precious metal catalysts, and the purity of the produced hydrogen is very high because it does not require an electrolyte component. In such polymer electrolyte membrane water electrolysis, since the oxygen evolution reaction is much slower than the hydrogen evolution reaction and requires a large overpotential, increasing the electrode activity of the anode is the most important consideration for improving overall cell performance. In particular, to maximize catalytic activity, it is important to increase the contact area of ​​the precious metal components constituting the catalyst layer of the anode and to have an appropriate distribution.

[0011] Meanwhile, the distribution of precious metal components within the catalyst layer is significantly influenced by the catalyst ink composition, catalyst content, distribution state, and coating process during the formation of the catalyst layer. Since there are limitations to controlling the appropriate distribution with conventionally known structures, methods to increase the amount of precious metal used are adopted to enhance catalytic activity. However, this increase in the amount of precious metal increases the cost of the precious metal catalyst, ultimately lowering the economic efficiency of the overall water electrolysis process. Therefore, there is a need to develop water electrolysis electrodes and membrane electrode assemblies that can secure high cell performance of polymer electrolyte membrane (PEM) while reducing the amount of precious metal catalyst used.

[0012] [Prior Art Literature]

[0013] [Patent Literature]

[0014] (Patent Document 1) KR 10-2023-0128481 A

[0015]

[0016] The problem to be solved by the present invention is to provide a water electrolysis electrode capable of reducing the loading amount of iridium oxide (IrO2) by controlling the distribution of iridium oxide on the surface of the catalyst layer and providing high electrolysis cell performance.

[0017] Another problem to be solved by the present invention is to provide a membrane electrode assembly having a high current density by including the above-mentioned water electrolysis electrode as an anode.

[0018] Another problem to be solved by the present invention is to provide an electrolysis cell having a high level of electrolysis efficiency.

[0019]

[0020] The present invention provides an electrolysis cell comprising a water electrolysis electrode, a membrane electrode assembly, and a membrane electrode assembly.

[0021] (1) The present invention comprises a substrate; and a catalyst layer positioned on the substrate and comprising iridium oxide, wherein the iridium loading amount of the catalyst layer is 0.1 mg / cm² 2 Above 0.4 mg / cm² 2 The present invention provides a water electrolysis electrode having the following: an iridium adsorption rate (Ir Coverage) of 70% or more within a scan size of 1 μm × 1 μm area in the adhesion mapping results obtained by atomic force microscopy analysis of the surface of the catalyst layer, and an average area of ​​iridium-island (Ir-island) of 3% or more within the said area.

[0022] (2) The present invention provides a water electrolysis electrode according to (1), wherein the iridium adsorption rate (Ir Coverage) within an area of ​​scan size 1 μm × 1 μm is 70% or more and 95% or less in the adhesion mapping results obtained by atomic force microscopy analysis of the surface of the catalyst layer, and the average area of ​​an iridium-island within the area is 3% or more and 50% or less.

[0023] (3) The present invention provides a water electrolysis electrode in which, in either (1) or (2), the surface roughness (Rq) within a scan size of 1 μm × 1 μm area is 20 nm or more in the topography results obtained by atomic force microscopy analysis of the surface of the catalyst layer.

[0024] (4) The present invention provides a water electrolysis electrode in which, in any one of (1) to (3), the surface roughness (Rq) within a scan size of 1 μm × 1 μm area is 20 nm or more and 1 μm or less in the topography results obtained by atomic force microscopy analysis of the surface of the catalyst layer.

[0025] (5) The present invention provides a water electrolysis electrode in which, in any one of (1) to (4), the catalyst layer further comprises one selected from an ionomer and an iridium oxide-ionomer aggregate.

[0026] (6) The present invention provides a water electrolysis electrode in which, in (5) above, the ionomer is one or more selected from the group consisting of perfluorinated ionomers, partially fluorinated ionomers and hydrocarbon ionomers.

[0027] (7) The present invention provides a water electrolysis electrode in which, in any one of (1) to (6), the substrate has a surface energy of 40 dyne / cm or less at 40°C.

[0028] (8) The present invention provides a water electrolysis electrode in which, in any one of (1) to (7), the substrate is one or more selected from the group consisting of polyether sulfone, cellulose acetate, polyvinylidene fluoride, polytetrafluoroethylene, polyamide, nylon and polyolefin.

[0029] (9) The present invention comprises an ion exchange separator; a cathode located on one side of the ion exchange separator; and an anode, which is a water electrolysis electrode according to any one of (1) to (8), located on the other side of the ion exchange separator, wherein the anode comprises a substrate and a catalyst layer located on the substrate and comprising iridium oxide, and the iridium loading amount of the catalyst layer is 0.1 mg / cm² 2 Above 0.4 mg / cm² 2 The present invention provides a membrane electrode assembly for water electrolysis having the following: an iridium adsorption rate (Ir Coverage) of 70% or more within a scan size of 1 μm × 1 μm area and an average area of ​​iridium-islands of 3% or more within the area, as shown in the adhesion mapping results obtained by atomic force microscopy analysis of the surface of the catalyst layer.

[0030] (10) The present invention provides a membrane electrode assembly in which, in (9) above, the ion exchange membrane is one or more selected from the group consisting of perfluorosulfonic acid, polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP).

[0031] (11) The present invention provides an electrolytic cell comprising a membrane electrode assembly according to (9) or (10) above.

[0032]

[0033] The water electrolysis electrode according to the present invention has the effect of having a high level of current density in membrane electrode assemblies and electrolysis cells to which it is applied, even though it contains a low loading amount of iridium, because the iridium adsorption rate and the total area of ​​iridium islands related to the distribution of iridium on the surface of the catalyst layer are controlled under specific conditions.

[0034]

[0035] The following drawings attached to this specification illustrate specific embodiments of the present invention and serve to further enhance understanding of the technical concept of the present invention together with the aforementioned description; therefore, the present invention should not be interpreted as being limited only to the matters described in such drawings.

[0036] Figure 1 is an image of the AFM analysis results of the water electrolysis electrode catalyst layer prepared in Example 1, showing (a) adhesion mapping and (b) topography.

[0037] Figure 2 is an AFM analysis result image of the water electrolysis electrode catalyst layer prepared in Example 2, showing (a) adhesion mapping and (b) topography.

[0038] Figure 3 is an image of the AFM analysis results of the water electrolysis electrode catalyst layer prepared in Example 3, showing (a) adhesion mapping and (b) topography.

[0039] Figure 4 is an AFM analysis result image of the water electrolysis electrode catalyst layer prepared in Comparative Example 1, showing (a) adhesion mapping and (b) topography.

[0040] Figure 5 is an AFM analysis result image of the water electrolysis electrode catalyst layer prepared in Comparative Example 2, showing (a) adhesion mapping and (b) topography.

[0041] Figure 6 is an AFM analysis result image of the water electrolysis electrode catalyst layer prepared in Comparative Example 3, showing (a) adhesion mapping and (b) topography.

[0042] FIG. 7 shows the current density (Current Density, A / cm²) according to the change in cell voltage (V) of the water electrolysis cells prepared in the examples and comparative examples. 2 It is a current-potential graph showing the change.

[0043]

[0044] Hereinafter, the present invention will be described in more detail to aid in understanding the invention. In this case, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0045]

[0046] terminology

[0047] The terms used in this specification are used merely to describe exemplary embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0048] In this specification, 'iridium adsorption rate' indicates the amount of iridium present on the surface of the catalyst layer, represented by the portion appearing in black when the lower limit of adhesion force is set to black and the upper limit to white in the adhesion mapping results obtained by Atomic Force Microscopy analysis, and is expressed as the ratio of the area of ​​the portion appearing as iridium to the total area, with the scan size (area) being the total area.

[0049] In this specification, 'iridium-island' refers to a black mass distinguished by a white area in the adhesion mapping results obtained by atomic force microscopy analysis, and 'average area of ​​iridium-island' refers to the average of the area ratios of each black mass to the total area, with the scan size being the total area.

[0050] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should not be understood as precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0051]

[0052] Measurement conditions

[0053] In this specification, 'iridium adsorption rate' and 'average area of ​​iridium-islands' can be obtained from adhesion mapping results obtained by atomic force microscopy (Dimension AFM, Bruker), and 'surface roughness' can be obtained from topography results obtained by atomic force microscopy (Dimension AFM, Bruker).

[0054] Specifically, the electrode was cut to an appropriate size and fixed to a holder using carbon tape, then loaded into an environmental AFM inside a glove box, and analysis was performed according to the standard operating procedure (SOP-06478-Ok) of the Environmental SPM (Icon-GB, Bruker) for the glove box environment. At this time, the AFM probe was set to TESPA-V2 (Typical tip radius: ~8 nm), the measurement mode to QNM (tapping PeakForce Quantitative Nanomechanical Mapping), the scan rate to 0.4–0.5 Hz, the PeakForce setpoint to 10 nN, and the Region of Interest (ROI) to 1 µm × 1 µm to obtain adhesion mapping and topography.

[0055] In the adhesion mapping image, the lower and upper limits of the adhesion force were fixed at 0 to 22 nN (△22 nN), and the iridium adsorption rate and the average area of ​​the iridium island were quantified by analyzing the adhesion mapping image using the Image J (National Institutes of Health, USA) program.

[0056] Surface roughness was determined by calculating the roughness values ​​of 3 points within the region of interest (scan size) after undergoing a plane fitting process in the topography, and then calculating the average value.

[0057]

[0058] water electrolysis electrode

[0059] The present invention provides a water electrolysis electrode that is applied as an anode constituting a membrane electrode assembly, even though the iridium distribution on the surface of the catalyst layer is controlled and contains a low loading amount of iridium, thereby enabling the membrane electrode assembly to maintain high electrolysis performance.

[0060] According to one embodiment of the present invention, the water electrolysis electrode comprises a substrate; and a catalyst layer positioned on the substrate and comprising iridium oxide, wherein the iridium loading amount of the catalyst layer is 0.1 mg / cm² 2 Above 0.4 mg / cm² 2 The following applies: in the adhesion mapping results obtained by atomic force microscopy analysis of the surface of the catalyst layer, the iridium adsorption rate (Ir Coverage) within a scan size of 1 μm × 1 μm area is 70% or more, and the average area of ​​the iridium-island within the area may be 3% or more.

[0061] The electrochemical performance of polymer electrolyte membrane water electrolysis is significantly influenced by key materials such as the polymer electrolyte membrane, catalyst, and electrode binder composed of an ionomer. It has the advantage of high energy efficiency because operation at high current densities is possible using precious metal catalysts, and the purity of the produced hydrogen is very high because it does not require an electrolyte component. In such polymer electrolyte membrane water electrolysis, since the oxygen evolution reaction is much slower than the hydrogen evolution reaction and requires a large overpotential, increasing the electrode activity of the anode is the most important consideration for improving overall cell performance. In particular, to maximize catalytic activity, it is important to increase the contact area of ​​the precious metal components constituting the catalyst layer of the anode and to have an appropriate distribution.

[0062] Meanwhile, the distribution of precious metal components within the catalyst layer is significantly influenced by the catalyst ink composition, catalyst content, distribution state, and coating process during the formation of the catalyst layer. Since there are limitations to controlling the appropriate distribution with conventionally known structures, methods to increase the amount of precious metal used are adopted to enhance catalytic activity; however, the relatively high cost of precious metal catalysts poses a problem that reduces the economic efficiency of the overall water electrolysis process.

[0063] However, a water electrolysis electrode according to one embodiment of the present invention comprises a catalyst layer containing iridium oxide, wherein the iridium adsorption rate and the total iridium-island area on the surface of the catalyst layer are limited under specific conditions, thereby controlling the distribution of iridium within the catalyst layer to 0.1 mg / cm² 2 Above 0.4 mg / cm² 2 A membrane electrode assembly and an electrolysis cell capable of having high cell performance of a polymer electrolyte membrane (PEM) even with the reduced iridium loading amount below can be provided.

[0064]

[0065] The above material may use a material having low surface energy at low temperatures, specifically having a surface energy of 40 dyne / cm or less at 40°C, specifically 15 dyne / cm or more and 40 dyne / cm or less. More specifically, the above material may be one or more selected from the group consisting of polyether sulfone, cellulose acetate, polyvinylidene fluoride, polytetrafluoroethylene, polyamide, nylon, and polyolefin, and even more specifically, the above material may be polytetrafluoroethylene.

[0066] The catalyst layer is located on the substrate and may include iridium oxide, and the iridium loading amount of the catalyst layer is 0.1 mg / cm² 2 Above 0.4 mg / cm² 2 The following applies: in the adhesion mapping results obtained by atomic force microscopy analysis of the surface of the catalyst layer, the iridium adsorption rate (Ir Coverage) within a scan size of 1 μm × 1 μm area is 70% or more, and the average area of ​​the iridium-island within the area may be 3% or more.

[0067] Reducing the amount of iridium, a precious metal, is one of the major challenges to be solved in the technical field to which this invention belongs. Furthermore, it is not enough to simply reduce the iridium loading amount; high electrolysis efficiency must be maintained while reducing the loading amount.

[0068] The present invention enables the simultaneous reduction of iridium loading and maintenance of high electrolysis efficiency by implementing a catalyst layer with controlled dispersion of surface iridium.

[0069] Specifically, in the present invention, the iridium loading amount of the catalyst layer is 0.40 mg / cm² 2 Below, 0.38 mg / cm² 2 Below, 0.36 mg / cm² 2 Below, 0.34 mg / cm² 2 Below, 0.32 mg / cm² 2 Below, 0.30 mg / cm² 2 Below, 0.28 mg / cm² 2 Below, 0.26 mg / cm² 2 Below, 0.24 mg / cm² 2 Below, 0.22 mg / cm² 2 Less than, or 0.20 mg / cm² 2 It may be less than, and also 0.10 mg / cm² 2 Above, 0.12 mg / cm² 2 Above, 0.14 mg / cm² 2 Above, 0.16 mg / cm² 2 Above, 0.18 mg / cm² 2 Above, or 0.20 mg / cm² 2 It may be above. If the iridium loading amount within the above range is not satisfied, the excessive use of iridium is undesirable from a cost and economic perspective, and this may act as a significant hindering factor to the commercialization of the PEM water electrolysis intended to be implemented in the present invention. In addition, the iridium loading amount is 0.10 mg / cm² 2 If it is less than that, it may be difficult to implement an electrolytic cell with sufficient current density and cell voltage.

[0070] In addition, the catalyst layer may have an iridium adsorption rate (Ir Coverage) of 70% or more within a scan size of 1 µm × 1 µm area in the adhesion mapping results obtained by atomic force microscopy analysis of the surface of the catalyst layer, and an average area of ​​iridium-islands within the area of ​​3% or more. Specifically, the iridium adsorption rate may be 70% or more, 75% or more, 80% or more, or 85% or more, and may be 95% or less, 90% or less, or 85% or less, and the average area of ​​the iridium-islets may be 3.0% or more, 3.2% or more, 3.4% or more, 3.6% or more, 3.8% or more, 4.0% or more, 4.2% or more, 4.4% or more, 4.6% or more, 4.8% or more, or 5.0% or more, and may be 50% or less, 40% or less, 35% or less, 30% or less, 25% or less, 20% or less, 15% or less, or 10% or less.

[0071] In the present invention, the iridium adsorption rate and the total area of ​​iridium islands on the surface of the catalyst layer represent an appropriate distribution of iridium within the catalyst layer, and when the iridium adsorption rate and the total area of ​​iridium islands on the surface of the catalyst layer are within the above range, an electrolysis cell having a sufficient current density can be realized even with a small amount of iridium loading, as described above.

[0072] Meanwhile, the iridium adsorption rate and the total iridium-island area on the surface of the catalyst layer may be influenced by the type of catalyst metal used in the process of forming the catalyst layer, the type and amount of ionomer and binder, the composition of the catalyst ink, the coating method, and the drying process. If the amount of catalyst metal included in the catalyst layer is excessively large, it is undesirable in terms of catalyst cost; conversely, if the amount of catalyst metal is excessively small, the electrical connectivity between catalysts is broken, increasing resistance and making it impossible to obtain a sufficient current density.

[0073] In addition, according to one embodiment of the present invention, the surface roughness (Rq) within a scan size of 1 μm × 1 μm in the topography results obtained by atomic force microscopy analysis of the surface of the catalyst layer may be 20 nm or more. Specifically, the surface roughness may be 20 nm or more, 22 nm or more, 24 nm or more, 26 nm or more, 28 nm or more, 30 nm or more, 32 nm or more, 34 nm or more, or 36 nm or more, or 1.0 μm or less, 0.8 μm or less, 0.6 μm or less, 0.4 μm or less, 0.2 μm or less, or 0.1 μm or less. When the surface roughness within the above range is satisfied, a sufficient contact area is secured, and the performance of the membrane electrode assembly and electrolysis cell to which it is applied may be excellent.

[0074] Additionally, the catalyst layer may further include either an ionomer or an iridium oxide-ionomer aggregate. Here, an iridium oxide-ionomer aggregate refers to a cluster formed by an ionomer attached to the surface of an iridium oxide particle.

[0075] The above-mentioned ionomer acts as a binder and can be included together with the catalyst metal during the preparation of the catalyst ink for forming the catalyst layer. It can be attached to the surface of the catalyst metal particles to prevent aggregation between the catalyst particles and to ensure that the catalyst particles are evenly distributed within the catalyst layer. However, catalytic activity can be significantly affected by the ratio between the ionomer content and the catalyst content, and to maintain excellent catalytic activity, it is important to ensure an appropriate distribution of catalyst particles and ionomer within the catalyst layer. The water electrolysis electrode according to the present invention can achieve excellent electrolysis efficiency without the influence of the ionomer by uniformly dispersing a low loading amount of iridium while maintaining the uniform dispersion of the catalyst ink for forming the catalyst layer through a high-energy dispersion process during its manufacturing process.

[0076] The above ionomer may be used without special limitation as long as it is commonly used in the industry, but, for example, it may be one or more selected from the group consisting of perfluorinated ionomers, partially fluorinated ionomers, and hydrocarbon ionomers.

[0077] For example, the perfluorinated ionomer may be a copolymer of poly(perfluorosulfonic acid), poly(perfluorocarboxylic acid), or fluorovinyl ether such as tetrafluoroethylene containing a sulfonic acid group, and a mixture thereof, and commercially available products may include Nafion, Flemion, Asiplex, 3M ionomer, Dow ionomer, Solvay ionomer, Sumitomo ionomer, and mixtures thereof.

[0078] In addition, the above-mentioned partial fluorinated ionomers may include, for example, sulfonated poly(arylene ethersulfone-co-vinylidene fluoride), sulfonated trifluorostyrene-graft-poly(tetrafluoroethylene) (PTFE-g-TES), styrene-graft-sulfonated polyvinylidene fluoride (PVDF-g-PSSA), copolymers containing dicarboxybiphenyl as a monomer, copolymers containing hexafluorobenzene as a monomer, and mixtures thereof.

[0079] In addition, the above hydrocarbon-based ionomer may include, for example, sulfonized imide, sulfonated aryl ether sulfone, sulfonated ether ether ketone, sulfonated benzimidazole, sulfonated sulfone, sulfonated styrene, sulfonated phosphazene, sulfonated ether ether sulfone, sulfonated ether sulfone, sulfonated ether ketone ketone, aryl ether benzimidazole, and mixtures thereof.

[0080] Meanwhile, the electrochemical performance of polymer electrolyte membrane water electrolysis can be significantly influenced by the catalytic metal and ionomer constituting the catalytic layer of the polymer electrolyte membrane and the anode. In a water electrolysis electrode according to one embodiment of the present invention, the catalytic metal iridium on the surface of the catalytic layer has adsorption rate and area conditions as described above, thereby maintaining an appropriate dispersion of iridium within the catalytic layer and enabling excellent activity even with a low loading amount of iridium.

[0081] In addition, according to one embodiment of the present invention, the thickness of the catalyst layer may be, for example, 7.0 μm or less, 6.9 μm or less, 6.7 μm or less, 6.5 μm or less, 6.3 μm or less, 6.1 μm or less, 6.0 μm or less, 5.9 μm or less, 5.7 μm or less, 5.5 μm or less, 5.3 μm or less, 5.1 μm or less, 5.0 μm or less, 4.9 μm or less, 4.7 μm or less, 4.5 μm or less, 1.0 μm or more, 1.3 μm or more, 1.5 μm or more, 1.7 μm or more, 1.9 μm or more, and 2.0 μm or more. When the thickness of the catalyst layer satisfies the aforementioned range, the problem of increased overpotential can be prevented by ensuring sufficient catalytic activity area and facilitating mass transfer within the catalyst layer, and excellent activity can be achieved without increasing electrical resistance while maintaining a uniform distribution of catalyst metal particles.

[0082] Meanwhile, the water electrolysis electrode according to one embodiment of the present invention can be manufactured by preparing a catalyst ink and coating it onto a substrate.

[0083] The above catalyst ink can be prepared by mixing iridium oxide and a solvent, and an ionomer may be further used.

[0084] The above solvent is not particularly limited as long as it is commonly used in the art, but, for example, one or more selected from the group consisting of water, alcohol, acetone, ethyl carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, fluoroethylene carbonate, dimethylacetamide, dimethyl sulfoxide, dimethylformamide, and N-methylpyrrolidone may be used, and specifically, a mixed solvent of water and alcohol may be used. When a mixed solvent of water and alcohol is used as the above solvent, water and alcohol may be used in a weight ratio of 1:1 to 3. Specifically, water and alcohol may be used in a weight ratio of 1:1, 1:1.5, or 3:7.

[0085]

[0086] The above alcohols are, for example, methanol, ethanol, 1-propanol, isopropyl alcohol, butanol, isobutanol, 2-butanol, tert-butanol, n-pentanol, isopenyl alcohol, 2-methyl-1-butanol, neopentyl alcohol, diethyl carbinol, methyl propyl carbinol, methyl isopropyl carbinol, dimethyl ethyl carbinol, 1-hexanol, 2-hexanol, 3-hexanol, 2-methyl-1-pentanol, 3-methyl-1-pentanol, 4-methyl-1-pentanol, 2-methyl-2-pentanol, 3-methyl-2-pentanol, 4-methyl-2-pentanol, 2-methyl-3-pentanol, 3-methyl-3-pentanol, 2,2-dimethyl-1-butanol, 2,3-dimethyl-1-butanol, Examples include 2,3-dimethyl-2-butanol, 3,3-dimethyl-1-butanol, 2-ethyl-1-butanol, 1-heptanol, 2-heptanol, 3-heptanol, and 4-heptanol, and mixtures thereof, but are not particularly limited thereto.

[0087] In addition, when using an ionomer in the preparation of the above catalyst ink, any ionomer commonly known in the art may be used without particular limitation, but the material described above may be used as an example. In addition, when using the above ionomer, the iridium oxide and the ionomer may be used in a weight ratio of 1:0.01 to 0.50, 1:0.02 to 0.35, 0.02 to 0.2, or 1:0.05 to 0.15.

[0088] In addition, the mixture for manufacturing the catalyst ink can be prepared using a mechano-fusion process, that is, a high-energy dispersion method. The mechano-fusion process is a method of diffusion immobilization in which thermal energy is added by applying mechanical energy to the surface of a parent particle and then applying thermal energy. For example, the mechano-fusion process may include a high-energy ball mill device, a planetary mill device, a stirred ball mill device, a vibrating mill device, etc. By utilizing the mechano-fusion process (high-energy dispersion method), catalyst particles within the catalyst composition can be uniformly dispersed and coating properties improved, allowing for the formation of a catalyst layer of a desired thickness and enabling a high level of electrolysis efficiency using a low loading amount of catalyst.

[0089] In addition, the mechano-fusion process may be preferably performed for 3 to 5 days for more uniform dispersion of catalyst particles, and may be repeated 1 to 4 times. Meanwhile, if the dispersion proceeds excessively to the extreme, the area of ​​the iridium-island within the catalyst layer obtained therefrom may actually decrease, and the mechano-fusion process under the above conditions may be advantageous for obtaining the desired average area of ​​the iridium-island.

[0090] In addition, the coating can be performed by methods such as bar coating, dip coating, spin coating, and spray coating, and preferably by a bar coating method. For example, the catalyst ink can be coated on one surface of a substrate using methods such as a Meyer bar, doctor blade, slot die, comma bar, and spin coat.

[0091]

[0092] Membrane electrode assembly

[0093] The present invention comprises an ion exchange membrane; a cathode located on one surface of the ion exchange membrane; and an anode located on the other surface of the ion exchange membrane, wherein the anode comprises a substrate and a catalyst layer located on the substrate and comprising iridium oxide, and the iridium loading amount of the catalyst layer is 0.1 mg / cm² 2 Above 0.4 mg / cm² 2 The present invention provides a membrane electrode assembly having the following: an iridium adsorption rate (Ir Coverage) of 70% or more within a scan size of 1 μm × 1 μm area and an average area of ​​iridium-islands of 3% or more within the area, as shown in the adhesion mapping results obtained by atomic force microscopy analysis of the surface of the catalyst layer.

[0094] The above membrane electrode assembly can be utilized in all electrochemical conversion devices, and the electrochemical conversion device may include a device capable of producing useful chemical substances through electrochemical conversion such as water electrolysis, carbon dioxide electrolysis, and fuel cells, and a device capable of being utilized for the reduction and conversion of carbon dioxide and NOx.

[0095] Electrochemical conversion, or electrolysis, refers to the decomposition of substances through redox reactions by applying a direct current voltage to a decomposition reaction that does not occur spontaneously. The anode acts as an oxidation electrode, oxidizing water to generate oxygen, thereby producing hydrogen ions. The hydrogen ions generated at the anode are transferred to the cathode through the separator, and the cathode acts as a reduction electrode, reacting with the electrons and hydrogen ions transferred from the anode to produce a product.

[0096] In a membrane electrode assembly, the anode is a portion that receives water (H2O), and when electricity is applied to the electrode catalyst layer, it electrolyzes water to generate oxygen, hydrogen ions, and electrons. It may include a catalyst that is active in the electrolysis of water, and the catalyst layer of the anode may include one or more selected from the group consisting of Pt, Au, Pd, Ir, Ag, Rh, Ru, Ni, Al, Mo, Cr, Cu, Ti, W, alloys thereof, or mixed metal oxides, such as RuO2, IrO2, etc., for the oxygen generation reaction.

[0097] In the membrane electrode assembly according to one embodiment of the present invention, the anode is the aforementioned water electrolysis electrode; that is, the membrane electrode assembly utilizes the aforementioned water electrolysis electrode as the anode. Accordingly, the anode in the membrane electrode assembly includes all the characteristics of the aforementioned water electrolysis electrode.

[0098]

[0099] The above ion exchange membrane is composed of an inert material that does not participate in electrochemical reactions itself, provides a pathway for ions to move between the anode and the cathode, and can serve to prevent physical contact between the anode and the cathode. The above ion exchange membrane may be a polymer electrolyte membrane and enables ion exchange that moves hydrogen ions generated in the catalyst layer of the anode to the catalyst layer of the cathode. The above ion exchange membrane may be one or more selected from the group consisting of perfluorosulfonic acid, polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene, and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP). The ion exchange membrane of the present invention may include a fluorine-based polymer, and the fluorine-based polymer has excellent hydrogen ion conductivity, so it can smoothly transport hydrogen ions generated from the anode.

[0100] According to one embodiment of the present invention, the thickness of the separator may be 30 μm or more and 140 μm or less. For example, the thickness of the separator may be 30 μm or more, 40 μm or more, 50 μm or more, 60 μm or more, 70 μm or more, 80 μm or more, 140 μm or less, 135 μm or less, 130 μm or less, 127 μm or less, 125 μm or less, 120 μm or less, 115 μm or less, 110 μm or less, 105 μm or less, and 100 μm or less. More specifically, the thickness of the separator may be 70 μm or more and 127 μm or less. When the thickness range of the separator is satisfied, the electrical resistance is reduced, the overvoltage is reduced, and the transport of hydrogen ions can proceed smoothly, thereby increasing the electrolysis efficiency.

[0101] In addition, the cathode serves as a hydrogen generating component, allowing hydrogen ions transferred from the anode to combine with electrons transferred through an external circuit to produce pure hydrogen. Such a cathode may be one commonly used in the industry and may be composed of, for example, platinum (Pt) or platinum-supported carbon (Pt / C).

[0102] According to one embodiment of the present invention, the membrane electrode assembly of the present invention has a current density of 2.4 A / cm² when the voltage of the reference cell below is 1.9 V at a temperature of 70°C. 2 It could be more than that.

[0103] [Reference Cell]

[0104] Anode catalyst: IrO2 (<0.4 mg / cm²) 2 )

[0105] Cathode catalyst: Pt / C

[0106] Catalyst layer active area: 4 cm 2

[0107] Separator: Nafion N115 (Thickness: 127 µm)

[0108] Porous diffusion layer: Ti-PTL (Thickness: 250 µm)

[0109] Gas diffusion layer: Sigracet 36BB, JNTG (Thickness: 270 µm)

[0110] Electrolyte: Ultrapure water (>18 MΩ) (30 ml / min)

[0111] The membrane electrode assembly of the present invention can be implemented to have an excellent level of current density value by including an anode comprising a catalyst layer with a controlled distribution of iridium and a low loading amount of iridium oxide. Specifically, under a temperature condition of 70°C, when the voltage of the reference cell below is 1.9V, the current density is 2.4 A / cm² 2The above may be the case, and having a current density within the above range means that the electrolysis cell including the membrane electrode assembly can have an excellent level of electrolysis efficiency. Generally, the current density value increases as the catalyst loading amount increases, but the membrane electrode assembly of the present invention can exhibit a high level of current density value despite a low catalyst loading amount. For example, the current density when the cell voltage is 1.9 V is 2.40 A / cm² 2 Above, 2.45 A / cm 2 Above, 2.50 A / cm 2 Above, 2.55 A / cm 2 Above or 2.60 A / cm 2 It could be more than that.

[0112]

[0113] electrolysis cell

[0114] The present invention provides an electrolytic cell comprising the membrane electrode assembly of the present invention described above. The electrolytic cell may include the membrane electrode assembly, a gas diffusion layer, a porous diffusion layer, and a separator.

[0115] Here, the above membrane electrode assembly is as described above.

[0116] The above gas diffusion layer may use a porous body made of carbon material such as carbon fiber cloth, carbon fiber felt, or carbon fiber paper, or a porous metal body made of a thin metal plate with a mesh structure such as expanded metal or metal mesh, and in the electrolysis cell of the present invention, the gas diffusion layer may use carbon fiber cloth.

[0117] The porous diffusion layer may include titanium felt. The porous diffusion layer can absorb processing errors occurring during the fabrication of the electrolysis cell by improving the contact force between the separator plate and the membrane electrode assembly and reducing the gap when the electrolysis cell is assembled. In addition, it acts as a flow path between the separator plate and the catalyst layer, thereby facilitating the smooth transport of fluid materials.

[0118] The above separator plate can serve to provide spatial separation between unit cells and can facilitate the transport and reaction of fluid materials by including a flow path. The above separator plate may include a corrosion-resistant metal material such as titanium or stainless steel.

[0119]

[0120] Examples

[0121] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0122] Example 1

[0123] (1) Manufacturing of anode electrode for water electrolysis

[0124] A catalytic ink was prepared and coated onto a substrate to manufacture a water electrolysis electrode.

[0125] First, IrO2 catalyst (Thermo-Fisher, Ir content: 84.5%, BET 25~35 m 2 A catalyst ink was prepared by performing a mechanofusion process for 2 days in a solution containing 2.625 g of 1-propanol, 1.965 g of Nafion binder (Nafion D-2020, Nafion content: 20 wt%, DuPont), 7.485 g of 1-propanol, and 2.925 g of distilled water.

[0126] The catalyst ink prepared above was coated onto a PTFE film using a bar coater. At this time, based on the wet thickness of the Mayer bar, the desired catalyst loading amount (iridium (Ir) loading amount 0.400 mg / cm²) 2 A Mayer bar was selected according to the thickness of the catalyst layer (2.2 μm) and coated at a speed of 10 mm / s at a temperature of 40°C, and dried in an 80°C oven for about 1 hour to prepare a water electrolysis anode electrode.

[0127]

[0128] (2) Manufacturing of cathode electrode

[0129] A catalyst ink was prepared by performing a mechanofusion process for 3 to 5 days in a solution containing 2.0 g of Pt / C catalyst (Tanaka, TEC10V50E), 3.7 g of Nafion binder (Nafion D-2020, Nafion content: 20 wt%, DuPont), 13.84 g of 1-propanol, and 0.46 g of distilled water, and the catalyst ink was coated onto a PTFE film. At this time, the desired catalyst loading amount (platinum loading amount 0.300 mg / cm²) based on the wet thickness of the Mayer bar 2 A Mayer bar was selected according to the ) and catalyst layer thickness (3.5 μm), coated at a speed of 10 mm / s at a temperature of 40°C, and dried in an 80°C oven for about 1 hour to prepare a cathode electrode.

[0130]

[0131] (3) Fabrication of membrane electrode assembly

[0132] The above-mentioned water electrolysis anode electrode and cathode electrode each have a cell active area (2 × 2 cm²) 2 The anode and cathode electrodes were placed against each other with a separator (Nafion N115, thickness: 127 μm) in between. The electrodes and the separator were placed between iron plates, and a membrane electrode assembly was manufactured by hot pressing (pressure: 0.5 ton) for about 5 minutes at a temperature of 140°C.

[0133]

[0134] Example 2

[0135] In Example 1, (1) 2.15 g of IrO2 catalyst was used when preparing the catalyst ink for manufacturing the water electrolysis anode electrode, and the mechano fusion process was repeated twice for 3 days, and the catalyst loading amount (iridium loading amount: 0.310 mg / cm²) when manufacturing the (1) water electrolysis anode electrode and (2) cathode electrode 2 , Platinum loading amount: 0.26 mg / cm² 2 A water electrolysis anode electrode, a cathode electrode, and a membrane electrode assembly were prepared in the same manner as in Example 1, except that a Mayer bar was selected and bar-coated according to the ) and catalyst layer thickness (1.6 μm).

[0136]

[0137] Example 3

[0138] In Example 2, (1) 2.51 g of IrO2 catalyst is used when preparing the catalyst ink for manufacturing the water electrolysis anode electrode, and when manufacturing the (1) water electrolysis anode electrode and (2) cathode electrode, the catalyst loading amount (iridium loading amount: 0.370 mg / cm²) 2 , Platinum loading amount: 0.27 mg / cm² 2 A water electrolysis anode electrode, a cathode electrode, and a membrane electrode assembly were prepared in the same manner as in Example 2, except that a Mayer bar was selected and bar-coated according to the ) and catalyst layer thickness (2.0 μm).

[0139]

[0140] Comparative Example 1

[0141] In Example 1, (1) 2.88 g of IrO2 catalyst was used when preparing the catalyst ink for manufacturing the water electrolysis anode electrode, and the ultrasonation process was carried out for 2 days, and when manufacturing the (1) water electrolysis anode electrode and (2) cathode electrode, the catalyst loading amount (iridium loading amount: 1.260 mg / cm²) 2 , Platinum loading amount: 0.40 mg / cm² 2 A water electrolysis anode electrode, a cathode electrode, and a membrane electrode assembly were prepared in the same manner as in Example 1, except that a Mayer bar was selected and bar-coated according to the ) and catalyst layer thickness (5.0 μm).

[0142]

[0143] Comparative Example 2

[0144] In Example 1, (1) 1.95 g of IrO2 catalyst was used when preparing the catalyst ink for manufacturing the water electrolysis anode electrode, and the ultrasonation process was carried out for 2 days, and when manufacturing the (1) water electrolysis anode electrode and (2) cathode electrode, the catalyst loading amount (iridium loading amount: 0.260 mg / cm²) 2 , Platinum loading amount: 0.41 mg / cm² 2 A water electrolysis anode electrode, a cathode electrode, and a membrane electrode assembly were prepared in the same manner as in Example 1, except that a Mayer bar was selected and bar-coated according to the ) and catalyst layer thickness (1.4 μm).

[0145]

[0146] Comparative Example 3

[0147] In Example 1, when manufacturing (1) the water electrolysis anode electrode and (2) the cathode electrode, the catalyst loading amount (iridium loading amount: 0.099 mg / cm²) 2 , Platinum loading amount: 0.22 mg / cm² 2A water electrolysis anode electrode, a cathode electrode, and a membrane electrode assembly were prepared in the same manner as in Example 1, except that a Mayer bar was selected and bar-coated according to the ) and catalyst layer thickness (1.0 μm).

[0148]

[0149] Experimental Example 1

[0150] Surface and cross-sectional analyses were performed on each water electrolysis anode electrode prepared in the examples and comparative examples, and the results are shown in Table 1 and Figures 1 to 6 below.

[0151] The iridium adsorption rate, average iridium island area, and surface roughness of the catalyst layer surface were measured using Atomic Force Microscopy (AFM).

[0152] Specifically, the analysis was performed using an atomic force microscope (Dimension AFM, Bruker) in the following manner.

[0153] The electrode was cut to an appropriate size and fixed to a holder using carbon tape, then loaded into an environmental AFM inside a glove box, and analysis was performed according to the standard operating procedure (SOP-06478-Ok) for the Environmental SPM (Icon-GB, Bruker) in a glove box environment. At this time, the AFM probe was set to TESPA-V2 (Typical tip radius: ~8 nm), the measurement mode to QNM (tapping PeakForce Quantitative Nanomechanical Mapping), the scan rate to 0.4–0.5 Hz, the PeakForce setpoint to 10 nN, and the Region of Interest (ROI) to 1 µm × 1 µm to obtain adhesion mapping and topography.

[0154] In the attachment mapping image, the lower and upper limits of the adhesion force were fixed at 0 to 22 nN (△22 nM), and the attachment mapping image was analyzed using the Image J (National Institutes of Health, USA) program to quantify the iridium adsorption rate and the average area of ​​the iridium island.

[0155] Surface roughness was determined by calculating the roughness values ​​of 3 points within the region of interest (scan size) after undergoing a plane fitting process in the topography, and then calculating the average value.

[0156]

[0157] As shown in Table 1 above, it can be confirmed that Examples 1 to 3 have a reduced Ir loading amount, and the Ir adsorption rate, average Ir-island area, and surface roughness of the catalyst layer surface are significantly increased compared to the comparative example, and it was confirmed that all the physical properties presented in the claims are satisfied.

[0158]

[0159] Experimental Example 2

[0160] Water electrolysis cells were fabricated using the membrane electrode assemblies prepared in the above examples and comparative examples, and current density, cell voltage, and mass activity were measured. The results are shown in Table 2 and Figure 7 below.

[0161] (1) Electrolytic cell

[0162] The water electrolysis cell was manufactured by stacking an end plate / current collector / separator (bipolar plate, senpentine flow channel structure, Pt coating) / porous transport layer (Pt-coated PLT) / membrane electrode assembly / gas diffusion layer (36BB, SGL) / separator (bipolar plate) / current collector / end plate.

[0163]

[0164] (2) Current density (A / cm²) 2 )

[0165] Starting from a set initial potential (0V), the voltage was varied at a constant scanning rate of 10 mV / s to a specific potential (2V), and the current value corresponding to 1.9V was read and set as the current density. At this time, the flow rate of water injected into the cell was 10 mL / min, and the temperature of the cell was 70℃.

[0166]

[0167] (3) Cell voltage (V)

[0168] Starting from a set initial potential (0V), the current-potential curve is measured while varying the voltage at a constant scan rate of 10 mV / s up to a specific potential (2V), and 1.5 A / cm 2 The voltage value corresponding to was read and used as the cell voltage. At this time, the flow rate of water injected into the cell was 10 mL / min, and the cell temperature was set to 70℃.

[0169]

[0170] (4) Mass activity (A / mg) Ir )

[0171] The current density value measured in (2) was calculated by dividing it by the Ir loading amount.

[0172]

[0173] As shown in Table 2 and Figure 6, it was confirmed that Examples 1 to 3 showed significantly improved current density, cell voltage, and mass activity compared to Comparative Examples 1 and 2, and that the current density was significantly improved compared to Comparative Example 3. In particular, it was confirmed that the current density and mass activity increased significantly and the cell voltage decreased even compared to Comparative Example 1, which had about three times more Ir loading.

Claims

1. Recording; and A catalyst layer comprising iridium oxide, located on the above-mentioned substrate, and The iridium loading amount of the catalyst layer is 0.1 mg / cm² 2 Above 0.4 mg / cm² 2 Below, A water electrolysis electrode having an iridium adsorption rate (Ir Coverage) of 70% or more within a scan size area of ​​1 µm × 1 µm and an average area of ​​iridium-islands of 3% or more within the said area, based on adhesion mapping results obtained by atomic force microscopy analysis of the surface of the catalyst layer.

2. In Paragraph 1, A water electrolysis electrode having an iridium adsorption rate (Ir Coverage) of 70% or more and 95% or less within a scan size area of ​​1 µm × 1 µm in the adhesion mapping results obtained by atomic force microscopy analysis of the surface of the catalyst layer, and an average area of ​​iridium-islands of 3% or more and 50% or less within the said area.

3. In Paragraph 1, A water electrolysis electrode having a surface roughness (Rq) of 20 nm or more within a scan size of 1 μm × 1 μm area in the topography results obtained by atomic force microscopy analysis of the surface of the catalyst layer.

4. In Paragraph 1, A water electrolysis electrode having a surface roughness (Rq) of 20 nm or more and 1 μm or less within a scan size of 1 μm × 1 μm in the topography results obtained by atomic force microscopy analysis of the surface of the catalyst layer.

5. In Paragraph 1, A water electrolysis electrode in which the catalyst layer further comprises one selected from an ionomer and an iridium-ionomer aggregate.

6. In Paragraph 5, A water electrolysis electrode in which the above ionomer is one or more selected from the group consisting of perfluorinated ionomers, partially fluorinated ionomers, and hydrocarbon ionomers.

7. In Paragraph 1, The above description describes a water electrolysis electrode having a surface energy of 40 dyne / cm or less.

8. In Paragraph 1, The above description is a water electrolysis electrode comprising one or more selected from the group consisting of polyether sulfone, cellulose acetate, polyvinylidene fluoride, polytetrafluoroethylene, polyamide, nylon, and polyolefin.

9. Ion exchange membrane; A cathode located on one side of the above-mentioned ion exchange membrane; and It includes an anode located on the other side of the ion exchange membrane, and The above anode comprises a substrate and a catalyst layer located on the substrate and comprising iridium oxide, and The iridium loading amount of the catalyst layer is 0.1 mg / cm² 2 Above 0.4 mg / cm² 2 Below, A membrane electrode assembly for water electrolysis having an iridium adsorption rate (Ir Coverage) of 70% or more within a scan size of 1 µm × 1 µm area and an average area of ​​iridium-islands of 3% or more within the said area, based on adhesion mapping results obtained by atomic force microscopy analysis of the surface of the catalyst layer.

10. In Paragraph 9, The above ion exchange membrane is a membrane electrode assembly in which one or more are selected from the group consisting of perfluorosulfonic acid, polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene, and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP).

11. An electrolytic cell comprising a membrane electrode assembly according to claim 9.

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