Electrode for water electrolysis and structure for forming electrode for water electrolysis

Abstract

The present invention relates to: an electrode for water electrolysis comprising an electrolyte membrane and an electrode layer formed on at least one surface of the electrolyte membrane, wherein the electrode layer has a surface roughness (Sa) of 30 nm to 90 nm and includes one or more cracks having a maximum width of 1 μm to 5 μm on the surface thereof; and a structure for forming an electrode for water electrolysis, the structure comprising a transfer substrate and an electrode layer formed on at least one surface of the substrate, wherein the electrode layer comprises iridium oxide particles and an ionomer, and has an adhesion energy of 60 aJ or more as measured by atomic force microscopy with respect to the surface of the electrode layer.

Description

Electrode for water electrolysis and structure for forming an electrode for water electrolysis

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0193017 filed on December 20, 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 an electrode for water electrolysis that exhibits excellent characteristics at the electrode surface, the electrolyte membrane, and the electrode layer interface, thereby demonstrating excellent performance and durability, and a structure for forming an electrode for water electrolysis that can manufacture said electrode.

[0005] 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.

[0006] Representative methods of water electrolysis include alkaline electrolysis (AEC) and polymer electrolyte membrane (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. On the other hand, polymer electrolyte membrane electrolysis utilizes polymer electrolyte membranes as the electrolyte, primarily employing cation exchange membranes. Polymer electrolyte membrane electrolysis offers the advantage of high energy efficiency because it allows operation at high current densities using precious metal catalysts, and the purity of the produced hydrogen is very high as it does not require an electrolyte component. Therefore, various studies on water electrolysis using polymer electrolyte membranes are currently being conducted.

[0007] Meanwhile, water electrolysis using polymer electrolyte membranes involves oxygen evolution at the anode and hydrogen evolution at the cathode, and hydrogen production efficiency is determined by the efficiency of both reactions. Pt / C catalysts are known to exhibit high efficiency for hydrogen evolution, while precious metal catalysts such as iridium are known to exhibit high efficiency for oxygen evolution. However, precious metal catalysts like iridium suffer from a problem where their durability decreases as the electrochemical reaction progresses, and since they are also expensive, various efforts are being made to develop catalysts for oxygen evolution and anodes for water electrolysis that can minimize iridium usage while ensuring durability. For example, there are prior studies that aim to secure the durability of catalyst particles by applying doping or coating films to iridium catalyst particles to reduce the iridium loading per unit area. However, applying doping or coating to particles in this manner increases the difficulty of the manufacturing process and does not result in sufficient improvements in terms of activity and durability. Therefore, it is necessary to develop a new structure of electrode for water electrolysis that can minimize the use of the aforementioned iridium while simultaneously improving performance.

[0008] To solve the above-mentioned problem, the present invention can provide an electrode for water electrolysis that uses iridium oxide particles having a coating layer as an electrode catalyst and optimizes the manufacturing conditions of the electrode layer, thereby providing excellent surface characteristics of the electrode and simultaneously excellent performance and durability of the electrode.

[0009] In addition, the present invention can provide a structure capable of forming a water electrolysis electrode that can simultaneously improve the performance and durability of the water electrolysis electrode by improving the interface characteristics between the electrolyte membrane and the electrode layer.

[0010] In addition, the present invention can provide a water electrolysis cell comprising the above-mentioned electrode for water electrolysis.

[0011] To solve the above-mentioned problem, the present invention provides an electrode for water electrolysis, a structure for forming an electrode for water electrolysis, and a water electrolysis cell.

[0012] More specifically, (1) the present invention provides an electrode for water electrolysis comprising an electrolyte membrane and an electrode layer formed on at least one surface of the electrolyte membrane, wherein the surface roughness (Sa) of the electrode layer is 30 nm or more and 90 nm or less, and there is one or more cracks having a maximum width of 1 μm or more and 5 μm or less on the surface of the electrode layer.

[0013] (2) The present invention provides an electrode for water electrolysis in which the surface roughness (Sa) of the electrode layer is 50 nm or more and 73 nm or less, in accordance with (1).

[0014] (3) The present invention provides an electrode for water electrolysis in which, in (1) or (2), the maximum length of the crack is 120 μm or more and 500 μm or less.

[0015] (4) The present invention provides an electrode for water electrolysis in which, in any one of (1) to (3), the electrode layer comprises iridium oxide particles.

[0016] (5) The present invention provides an electrode for water electrolysis in which, in any one of (1) to (4), the iridium oxide particles comprise a coating layer formed on at least a portion of the particle surface.

[0017] (6) The present invention provides an electrode for water electrolysis in which, in any one of (1) to (5), the coating layer comprises titanium oxide.

[0018] (7) The present invention provides an electrode for water electrolysis in which, in any one of (1) to (6), the thickness of the electrode layer is 1 μm or more and 15 μm or less.

[0019] (8) The present invention provides an electrode for water electrolysis in which, in any one of (1) to (7), the electrolyte membrane is a cation exchange membrane.

[0020] (9) The present invention provides a water electrolysis electrode characterized in that, in any one of (1) to (8), the water electrolysis electrode is an anode.

[0021] (10) The present invention provides a structure for forming an electrode for water electrolysis, comprising a transfer substrate and an electrode layer formed on at least one surface of the substrate, wherein the electrode layer comprises iridium oxide particles and an ionomer, and the adhesion energy measured by atomic force microscopy on the surface of the electrode layer is 60 aJ ​​or more.

[0022] (11) The present invention provides a structure for forming an electrode for water electrolysis, wherein the iridium oxide particles in (10) contain 40% or more of crystalline iridium oxide.

[0023] (12) The present invention provides a structure for forming an electrode for water electrolysis, wherein the ionomer percentage of the electrode layer is 20% or more and 40% or less in accordance with (10) or (11).

[0024] (13) The present invention provides a structure for forming an electrode for water electrolysis, wherein in any one of (10) to (12), the surface roughness (Ra) of the electrode layer is 40 nm or more and 70 nm or less.

[0025] (14) The present invention provides a structure for forming an electrode for water electrolysis, wherein in any one of (10) to (13), the stiffness of the electrode layer is 300 N / m or less.

[0026] (15) The present invention provides a structure for forming an electrode for water electrolysis, wherein in any one of (10) to (14), the iridium oxide particles comprise 60 weight% or more of amorphous iridium oxide.

[0027] (16) The present invention provides a structure for forming an electrode for water electrolysis in which, in any one of (10) to (15), the ionomer % of the electrode layer is greater than 40% and less than or equal to 90%.

[0028] (17) The present invention provides a structure for forming an electrode for water electrolysis, wherein in any one of (10) to (16), the surface roughness (Ra) of the electrode layer is 75 nm or more and 200 nm or less.

[0029] (18) The present invention provides a structure for forming an electrode for water electrolysis, wherein in any one of (10) to (16), the stiffness of the electrode layer is 40 N / m or less.

[0030] (19) The present invention provides a water electrolysis cell comprising an electrode for water electrolysis according to any one of (1) to (9).

[0031] The electrode for water electrolysis according to the present invention has excellent surface characteristics as the surface roughness (Sa) of the electrode layer satisfies certain conditions and has narrow cracks, thereby simultaneously improving the performance and durability of the electrode. In particular, the electrode for water electrolysis according to the present invention can exhibit an excellent elastic modulus as the surface of the electrode layer possesses the aforementioned characteristics, thereby maintaining excellent durability of the electrode.

[0032] In addition, the structure for forming a water electrolysis electrode according to the present invention has high adhesion energy on the surface of the electrode layer and a high ionomer ratio, thereby minimizing separation at the interface between the electrode layer formed from the surface and the electrolyte membrane, and advantageously inducing cation exchange during the electrolysis process, which can improve the mechanical stability and performance of the water electrolysis electrode formed from the structure.

[0033] Figure 1 shows the distribution of intrinsic physical properties of each component within the electrode layer obtained during the process of measuring the ionomer % in the present invention.

[0034] FIG. 2 is a graph showing the distribution of each component within the electrode layer and the degree of coexistence of each component obtained from the AFM analysis results on the electrode layer surface of Example 1-1 (5 cycles) and Example 1-2 (7 cycles), Comparative Example 1-1 (0 cycles), Comparative Example 1-3 (10 cycles), and Comparative Example 1-4 (15 cycles).

[0035] FIG. 3 is a graph showing the distribution of each component within the electrode layer and the degree of coexistence of each component obtained from the AFM analysis results on the surface of the electrode layer of Example 2-1 (3 cycles), Comparative Example 2-1 (0 cycles), Comparative Example 2-2 (5 cycles), and Comparative Example 2-3 (10 cycles).

[0036] Figure 4 shows the TEM image of the electrode interface for water electrolysis of Comparative Example 1-1 after operation.

[0037] Figure 5 shows the electrode interface for water electrolysis of Comparative Example 1-2 observed by TEM image after operation.

[0038] Figure 6 is a TEM image of the electrode interface for water electrolysis of Example 1-2 after operation.

[0039] Figure 7 shows an intensity map image representing the distribution of iridium obtained from XRF analysis results of the electrode layer of the water electrolysis electrodes of Example 2-1 and Comparative Example 2-1.

[0040] Figure 8 shows the electrode interface for water electrolysis of Comparative Example 2-1 observed by TEM image before operation.

[0041] Figure 9 shows the water electrolysis electrode interface of Comparative Example 2-1 observed by TEM image after 1,000 hours of operation.

[0042] Figure 10 shows the electrode interface for water electrolysis of Example 2-1 observed by TEM image before operation.

[0043] Figure 11 is a TEM image of the electrode interface for water electrolysis of Example 2-1 after 1,500 hours of operation.

[0044] FIG. 12 is an SEM observation of the electrode surface according to Examples 3-1 to 3-3 of the present invention.

[0045] Figure 13 shows the electrode surface according to Comparative Example 3-1 of the present invention observed by SEM.

[0046] Figure 14 shows the electrode surface according to Comparative Example 3-2 of the present invention observed by SEM.

[0047] Figure 15 shows the electrode surface according to Comparative Example 3-3 of the present invention observed by SEM.

[0048] The present invention will be described in more detail below.

[0049] 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.

[0050]

[0051] In the present invention, "structure for forming an electrode for water electrolysis" refers to a structure for forming an electrode layer of an electrode for water electrolysis. More specifically, the structure refers to a structure having an electrode layer formed thereon to be transferred onto a substrate for transfer, and an electrode for water electrolysis can be manufactured by transferring the electrode layer of the structure to a separate substrate, specifically an electrolyte membrane. In the present invention, the electrode for water electrolysis may be a membrane-electrode assembly in which an electrolyte membrane and an electrode layer are combined.

[0052] In the present invention, the fact that the iridium oxide particles have a crystalline structure may mean that the iridium oxide particles contain crystalline iridium oxide in an amount of 40 wt% or more, 45 wt% or more, 50 wt% or more and 100 wt% or less, 99.5 wt% or less, 99 wt% or less, 97 wt% or less, 95 wt% or less, or 90 wt% or less. The iridium oxide particles having a crystalline structure contain such a large amount of crystalline iridium oxide and can be described as crystalline iridium oxide particles themselves. The relative proportion of the crystalline iridium oxide can be measured and calculated through quantitative analysis using XRD.

[0053] In the present invention, the fact that the iridium oxide particles have an amorphous structure may mean that the iridium oxide particles contain amorphous iridium oxide in an amount of 60 wt% or more, 65 wt% or more, 70 wt% or more, 75 wt% or more, 78 wt% or more, or 80 wt% or more, and 100 wt% or less, 99.5 wt% or less, 99 wt% or less, 97 wt% or less, 95 wt% or less, or 90 wt% or less. The iridium oxide particles having an amorphous structure contain such a large amount of amorphous iridium oxide and can be described as amorphous iridium oxide particles themselves. The relative proportion of the amorphous iridium oxide can be measured and calculated through quantitative analysis using XRD.

[0054]

[0055] In the present invention, the ionomer %, adhesion energy, roughness (Ra), and stiffness of the electrode layer of a structure for forming an electrode for water electrolysis can be measured using an atomic force microscope. More specifically, the measurement conditions of the atomic force microscope for measuring the above characteristics are as follows.

[0056] [Measurement Conditions]

[0057] 1) Equipment and Software: Use of NX-10 (Park Systems) and Smart Scan - XEI Analysis software

[0058] 2) Sample preparation conditions: Constant temperature and humidity conditions of 23°C and 45% relative humidity. After cutting the sample to an appropriate size, secure it to a holder using carbon tape and load it into the atomic force microscope (AFM) system.

[0059] 3) Measurement Mode: Use non-contact mode for measuring roughness and pinpoint force-distance tapping mode for measuring stiffness, utilizing an AFM probe (NCHR, tip radius <10 nm) according to standard operation.

[0060] 4) Measurement Area: Observe the sample with an optical microscope and acquire data from a 5㎛ x 5㎛ area with 3 points per sample at locations free of foreign matter.

[0061] 5) Other conditions: Sampling per line is 512, scan speed is 0.2 Hz, speed in force-distance tapping mode for measuring stiffness is set to 15 µm / s, and load is set to 100 nN.

[0062]

[0063] Electrode for water electrolysis

[0064] The present invention provides an electrode for water electrolysis comprising an electrolyte membrane and an electrode layer formed on at least one surface of the electrolyte membrane, wherein the surface roughness (Sa) of the electrode layer is 30 nm or more and 90 nm or less, and there is one or more cracks having a maximum width of 1 μm or more and 5 μm or less on the surface of the electrode layer.

[0065]

[0066] The electrode for water electrolysis provided by the present invention satisfies a certain condition for the surface roughness (Sa) of the electrode layer and has one or more cracks on the surface with a maximum width of 1 μm or more and 5 μm or less, thereby allowing the water electrolysis reaction on the surface of the electrode layer to proceed smoothly and the performance of the electrode to be excellent at the same time.

[0067]

[0068] The surface roughness (Sa) of the electrode layer may refer to the arithmetic mean height of the surface, and more specifically, may refer to the average difference in height from the mean plane. The surface roughness (Sa) may be measured using an atomic force microscope (AFM). The surface roughness of the electrode layer of the electrode for water electrolysis provided by the present invention may be 30 nm or more and 90 nm or less, and preferably 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, or 50 nm or more, and 90 nm or less, 85 nm or less, 80 nm or less, 75 nm or less, or 73 nm or less. When the surface roughness (Sa) of the electrode layer is within the range described above, an appropriate uneven structure is formed on the surface of the electrode layer, thereby simultaneously producing effects of improved durability and performance. Meanwhile, the surface roughness (Sa) of the electrode layer may be measured in an area of ​​the electrode layer where cracks described later are not formed.

[0069]

[0070] In addition, the electrode for water electrolysis provided by the present invention may have one or more cracks on the surface of the electrode layer having a maximum width of 1 μm or more and 5 μm or less. The cracks can be confirmed by observing the surface of the electrode layer, and equipment such as a scanning electron microscope (SEM) may be used for the surface observation. The maximum width of the cracks refers to the width of the widest crack among a plurality of cracks present in the observed image, and the maximum width of the cracks may be 1 μm or more and 5 μm or less, and preferably 1 μm or more and 5 μm or less, 4.5 μm or less, 4 μm or less, 3.5 μm or less, 3 μm or less, 2.5 μm or less, or 2 μm or less. In addition, the maximum length of the crack may be 120 μm or more and 500 μm or less, and preferably 120 μm or more and 500 μm or less, 450 μm or less, 400 μm or less, 350 μm or less, 300 μm or less, 250 μm or less, or 200 μm or less. The maximum length of the crack may refer to the length of the longest crack connected to each other in an image (x500) of the observed electrode layer surface. When the electrode for water electrolysis has the crack characteristics described above, the durability of the electrode layer may be excellent because there are fewer cracks present on the surface of the electrode layer. Furthermore, by having such crack characteristics, the electrode for water electrolysis provided by the present invention may have uneven characteristics on the surface of the electrode layer, which can increase the adhesion of the electrode surface for water electrolysis. Meanwhile, in the electrode for water electrolysis provided by the present invention, the maximum width value of the crack may appear low as the cohesive force between the catalyst particles included in the electrode layer and the ionomer is controlled to be low. In addition, the electrode for water electrolysis of the present invention may have excellent elasticity of the electrode itself by having the surface characteristics described above, and the excellent elasticity of the electrode itself contributes to the durability of the electrode for water electrolysis, thereby enabling the electrode to have excellent durability.

[0071]

[0072] In the electrode for water electrolysis provided by the present invention, the electrode layer performs the role of exhibiting activity for the water electrolysis reaction, and to this end, the electrode layer may include iridium oxide particles. The iridium oxide particles can act as catalyst particles to induce the smooth progress of the water electrolysis reaction. In particular, iridium oxide particles are known to possess excellent catalytic activity for the water electrolysis reaction. Meanwhile, the iridium oxide particles may have a rutile structure or an amorphous structure.

[0073]

[0074] In the present invention, the iridium oxide particles may comprise a coating layer formed on at least a portion of the particle surface. When iridium oxide particles are used with a coating layer formed on their surface in this manner, the durability of the catalyst particles can be improved while minimizing the decrease in activity that may occur during the water electrolysis reaction.

[0075] The above iridium oxide may be represented as IrO2, and the iridium oxide particles may have the form of secondary particles formed by the aggregation of multiple primary particles having an average particle size of 0.1 nm or more and 20 nm or less, preferably 1 nm or more and 5 nm or less. Additionally, the average particle size of the secondary particles may be 0.1 µm or more and 20 µm or less, and preferably 0.1 µm or more, 0.5 µm or more, or 1 µm or more, while being 20 µm or less, 10 µm or less, 5 µm or less, or 3 µm or less. Furthermore, if the iridium oxide particles are crystalline, their specific surface area is 30 m² 2 / g or more and 80m 2 It may be less than / g, preferably 33m 2 / g or more, 35m 2 / g or more, 37m 2 / g or more or 40m 2 / g or more and 80m 2 / g or less, 77m 2 / g or less, 75m 2 / g or less, 73m 2 / g or less, 70m 2 / g or less, 67m 2 / g or less or 65m 2 It may be less than / g. Meanwhile, if the iridium oxide particles are amorphous, their specific surface area is 60 m² 2 / g or more and 130m 2 It may be less than / g, preferably 65m 2 / g or more, 70m 2 / g or more, 75m 2 / g or more or 80m 2 / g or more and 130m 2 / g or less, 125m 2 / g or less, 120m 2 / g or less, 115m 2 / g or less, 110m 2 / g or less or 105m 2 It may be less than / g. When the iridium oxide particles satisfy the above-described conditions, the durability of the catalyst particles may be superior, and the formation of the coating layer may also be easier.

[0076] The above coating layer can suppress the leaching of iridium during the water electrolysis process, thereby improving the durability of the iridium oxide particles. The above coating layer may include titanium oxide.

[0077] The titanium oxide mentioned above may be TiO2, Ti2O3, or TiO, and preferably may be TiO2. When titanium oxide is used as a component of the coating layer, the effect of improving durability can be maximized. Meanwhile, the coverage rate of iridium oxide particles by the coating layer may be 30% or more and 120% or less, and more specifically, 30% or more, 33% or more, 35% or more, 36% or more, 37% or more, 38% or more, 40% or more, 43% or more, 45% or more, 47% or more, 50% or more, 52% or more, or 55% or more, and 120% or less, 110% or less, 100% or less, 98% or less, 95% or less, 93% or less, 90% or less, 87% or less, 85% or less, 83% or less, 80% or less, 77% or less, 75% or less, 73% or less, 70% or less, 67% or less, 65% or less, 63% or less, or 60% or less.

[0078]

[0079] Meanwhile, the coverage rate in this specification can be defined as shown in Formula 1 below.

[0080] [Equation 1]

[0081] Coverage rate (%) =

[0082] In the above Equation 1,

[0083] m coat represents the total weight of the coating layer, and

[0084] m sub represents the total weight of the substrate particles on which the coating layer is formed before coating, and

[0085] t represents the thickness of the coating layer, and

[0086] SSA refers to the specific surface area of ​​the substrate particles,

[0087] ρ coat represents the theoretical true density value of the coating layer component.

[0088]

[0089] The coverage ratio of the present invention represents the ratio of the actual weight of the formed coating layer to the theoretical weight of the coating layer, assuming that a coating layer of thickness t is formed completely and uniformly on the substrate particle. Therefore, the coverage ratio of the present invention is a concept distinct from the geometric coverage ratio, which refers to the ratio of the area where the coating layer is formed to the surface area of ​​the substrate particle, and may refer to a mass-based ratio of the coating amount relative to the theoretical amount. More specifically, the substrate particle may be an iridium oxide particle, and the coating layer component may include titanium oxide (TiO2). In this case, the theoretical true density value of the titanium oxide (TiO2) is 4.2 g / cm³. 3 It can be applied. In addition, the thickness t of the coating layer can be measured by observing the catalyst with a TEM image, and the total weight of the coating layer can be measured through ICP analysis.

[0090]

[0091] Meanwhile, the atomic ratio of O / Ti in the coating layer, which can be confirmed through XPS analysis, may be 1.2 or more and 5.0 or less, and preferably 1.2 or more, 1.4 or more, 1.6 or more, 1.8 or more, 2.0 or more, 2.2 or more, 2.4 or more, 2.6 or more, 2.8 or more, or 3.0 or more, and may be 5.0 or less, 4.8 or less, 4.6 or less, 4.4 or less, 4.2 or less, 4.0 or less, 3.8 or less, 3.6 or less, or 3.4 or less.

[0092] In addition, the oxygen content in the coating layer, which can be confirmed through XPS analysis, may be 30 at% or more and 70 at% or less, and preferably 30 at% or more, 33 at% or more, 35 at% or more, 37 at% or more, 40 at% or more, 43 at% or more, 45 at% or more, 47 at% or more, or 50 at% or more, and may be 70 at% or less, 67 at% or less, 65 at% or less, 63 at% or less, 60 at% or less, 57 at% or less, or 55 at% or less.

[0093] In addition, the titanium content in the coating layer, which can be confirmed through XPS analysis, may be 5 at% or more and 40 at% or less, and preferably 5 at% or more, 7 at% or more, 10 at% or more, 11 at% or more, 12 at% or more, 13 at% or more, 14 at% or more, 15 at% or more, or 16 at% or more, and may be 40 at% or less, 37 at% or less, 35 at% or less, 33 at% or less, 30 at% or less, 27 at% or less, 25 at% or less, 23 at% or less, or 21 at% or less.

[0094] In addition, the carbon content in the coating layer, which can be confirmed through XPS analysis, may be 10 at% or more and 30 at% or less, and preferably 10 at% or more, 12 at% or more, or 14 at% or more, and may be 30 at% or less, 27 at% or less, 25 at% or less, 23 at% or less, 20 at% or less, 18 at% or less, or 15 or less.

[0095] When the content of each component within the coating layer and the ratios between them satisfy the conditions described above, the effect of improving durability by the coating layer can be maximized. Meanwhile, the carbon in the coating layer may originate from residual carbon of the organic precursor used in the process of forming the coating layer.

[0096] Meanwhile, the above XPS analysis can be performed under the following conditions.

[0097] (1) XPS analysis conditions

[0098] 1) XPS Analysis Equipment: K-alpha+, Thermo Fisher Scientific Inc.

[0099] 2) X-ray source conditions: monochromatic Al Kα (1486.6 eV)

[0100] 3) Calibration Standard: CF2 and IrO2 Reference Standards

[0101] 4) Surface charge compensation: default FG03 mode(150μA, 0.5V)

[0102] 5) Sample Pretreatment: Proceed without pretreatment / sputtering

[0103] 6) Analysis Mode: CAE (Constant Analyzer Energy) Mode

[0104] 7) X-ray spot size: 400㎛

[0105] 8) Sample shape: Measured in powder form

[0106] (2) Quantification conditions

[0107] 1) Software: Avantage Software (version 5.992)

[0108] 2) Peak Background: Smart method applied

[0109] 3) Regarding the titanium peak: Since there is an overlapping region between the Ir 4f and Ti 3s peaks, the Ir 4f content was calculated using peak fitting (estimation of the Ti 3s peak region from the Ti 2p peak region).

[0110]

[0111] The thickness of the coating layer may be 0.1 nm or more and 2 nm or less, preferably 0.1 nm or more, 0.2 nm or more, or 0.3 nm or more, and 2 nm or less, 1.5 nm or less, 1.3 nm or less, 1.2 nm or less, 1.1 nm or less, 1.0 nm or less, or 0.9 nm or less. In the present invention, the coating layer may be formed through an atomic film deposition method, and accordingly, the coating layer may be formed thinly and uniformly.

[0112]

[0113] The iridium (Ir) content based on the total weight of the iridium oxide particles may be 60 wt% or more and 95 wt% or less when the iridium oxide particles are crystalline, and preferably 65 wt% or more or 70 wt% or more and 90 wt% or less. In addition, when the iridium oxide particles are amorphous, it may be 50 wt% or more and 85 wt% or less, and preferably 55 wt% or more or 60 wt% or more and 80 wt% or less. If the proportion of iridium is too low, sufficient catalytic activity may not be exhibited, and if the proportion of iridium is too high, the role of the coating layer may not be sufficiently performed. Meanwhile, the iridium content can be measured through XRF analysis.

[0114] The titanium (Ti) content based on the total weight of the iridium oxide particles may be 0.5 wt% or more and 10 wt% or less, and preferably 0.5 wt% or more, 1.0 wt% or more, or 1.5 wt% or more, and 10 wt% or less, 9 wt% or less, 8 wt% or less, or 7 wt% or less. Meanwhile, the titanium content may be measured through XRF analysis.

[0115]

[0116] The electrode layer may include an ionomer along with iridium oxide particles. The ionomer may be a fluorinated polymer, such as tetrafluoroethylene, into which a sulfonic acid functional group has been introduced. Hydrogen ions can move through the ionomer, and the ionomer can facilitate the movement of hydrogen ions while inhibiting the gas permeation of hydrogen and oxygen, thereby allowing the water electrolysis reaction to proceed properly. As the ionomer, those known to be capable of implementing the above functions may be used, and as an example, Nafion's ionomer may be used.

[0117]

[0118] The thickness of the electrode layer may be 1 μm or more and 15 μm or less, preferably 1 μm or more, 2 μm or more, 4 μm or more, or 6 μm or more, and 15 μm or less, 13 μm or less, 12 μm or less, 10 μm or less, or 8 μm or less. When the thickness of the electrode layer is within the above-described range, the performance for the water electrolysis reaction relative to the amount of iridium used can be maximized. The thickness of the electrode layer can be directly measured through cross-sectional SEM analysis.

[0119]

[0120] The electrode layer may be formed on an electrolyte membrane, and the electrolyte membrane may be a cation exchange membrane. A conventionally used cation exchange membrane may be used as the cation exchange membrane. The electrode for water electrolysis may be a membrane-electrode assembly formed by joining a membrane and an electrode.

[0121]

[0122] The electrode for water electrolysis provided by the present invention may be an anode. During the water electrolysis process, an oxygen evolution reaction is performed at the anode, and the electrode for water electrolysis of the present invention may exhibit excellent catalytic activity for the oxygen evolution reaction.

[0123]

[0124] In the electrode for water electrolysis of the present invention, the iridium content per unit area of ​​the electrode for water electrolysis is 0.1 mg / cm² 2 Above and 2 mg / cm² 2 It may be less than or equal to, preferably 0.1 mg / cm² 2 ≥ or 0.2 mg / cm² 2 Above, and 2 mg / cm² 2 Less than 1.5 mg / cm² 2 Less than 1.0 mg / cm² 2 Less than or equal to 0.5 mg / cm² 2 The following may apply. The electrode for water electrolysis according to the present invention has a relatively low iridium content per unit area and can achieve excellent performance even with a small iridium loading amount.

[0125]

[0126] Structure for forming electrodes for water electrolysis

[0127] The present invention provides a structure for forming an electrode for water electrolysis comprising a transfer substrate and an electrode layer formed on at least one surface of the substrate, wherein the electrode layer comprises iridium oxide particles and an ionomer, and the adhesion energy measured using an atomic force microscope on the surface of the electrode layer is 60 aJ ​​or more.

[0128]

[0129] The above-described electrode for water electrolysis can be formed from the above-described structure for forming the electrode for water electrolysis. More specifically, the above-described electrode for water electrolysis can be manufactured by transferring an electrode layer formed on the above-described structure for forming the electrode for water electrolysis to an electrolyte membrane.

[0130]

[0131] In the structure for forming an electrode for water electrolysis according to the present invention, the adhesion energy of the electrode layer may be 60 aJ ​​or more and 150 aJ or less. When the iridium oxide particles in the electrode layer have a crystalline structure, the adhesion energy of the electrode layer may be 60 aJ ​​or more, 65 aJ or more, 70 aJ or more, 75 aJ or more, or 80 aJ or more, and 150 aJ or less, 140 aJ or less, 130 aJ or less, 120 aJ or less, or 110 aJ or less.

[0132] When the iridium oxide particles of the electrode layer have an amorphous structure, the adhesion energy of the electrode layer may be 60aJ or more, 65aJ or more, 70aJ or more, 75aJ or more, or 80aJ or more, and 150aJ or less, 140aJ or less, 130aJ or less, 120aJ or less, 110aJ or less, 100aJ or less, or 90aJ or less.

[0133] By ensuring that the above-mentioned adhesion energy falls within the aforementioned range, excellent durability, mechanical stability, and performance can be provided when the electrode layer is transferred to the electrolyte membrane.

[0134] The adhesive energy may be measured through atomic force microscopy analysis of the surface of the electrode layer, and more specifically, may be measured through atomic force microscopy analysis under the conditions described above. More specifically, under the conditions described above, the measurement mode is set to force-distance spectral mode, and the maximum tensile force can be measured by bringing the AFM tip over the specimen surface, driving it vertically until the maximum load is reached, and then recording the force-distance curve while returning it to its original position until it is completely separated from the specimen. Based on the maximum tensile force measured in this process, the tensile section of the force-distance curve during the separation of the tip and the specimen can be integrated over the curve area to convert it into adhesive energy per unit area. The adhesive energy may be a value calculated by averaging measurements taken 3 to 5 times at randomly selected different points for each specimen.

[0135]

[0136]

[0137] The structure for forming an electrode for water electrolysis according to the present invention comprises iridium oxide particles and an ionomer within the electrode layer, and the ionomer percentage measured using an atomic force microscope on the surface of the electrode layer may be 20% or more and 90% or less. As such, the surface of the structure for forming an electrode for water electrolysis according to the present invention has a relatively high ionomer ratio, and this high ionomer ratio on the surface may lead to a high ionomer ratio at the interface when the electrode layer is subsequently transferred to an electrolyte membrane. A high ionomer ratio at the interface of the electrode for water electrolysis can optimize the ionomer distribution at the interface to improve interface stability, which may lead to improved performance and durability of the electrode for water electrolysis.

[0138] Meanwhile, the above ionomer % may be 20% or more and 90% or less, and the specific numerical range may differ depending on whether the iridium oxide particles in the electrode layer have a crystalline structure or an amorphous structure.

[0139] More specifically, when the iridium oxide particles in the electrode layer have a crystalline structure, the ionomer % may be 20% or more, 21% or more, 22% or more, 23% or more, 24% or more, 25% or more, 26% or more, 27% or more, 28% or more, or 29% or more, and 40% or less, 38% or less, 36% or less, 35% or less, 34% or less, 33% or less, 32% or less, 31% or less, or 30% or less.

[0140] In addition, when the iridium oxide particles have an amorphous structure, the ionomer % may be greater than 40%, 40.5% or more, or 41% or more, and 90% or less, 85% or less, 80% or less, 75% or less, 70% or less, 65% or less, 60% or less, 55% or less, 50% or less, 47% or less, 45% or less, or 43% or less.

[0141] When the above ionomer % is within the range described above, the interface characteristics between the electrode layer and the electrolyte membrane of the water electrolysis electrode formed from the above structure for forming the water electrolysis electrode may be superior.

[0142] Meanwhile, the above ionomer % refers to the relative ratio of ionomer exposed on the surface of the electrode layer, which can be measured and calculated using an atomic force microscope. Among the components of the electrode layer, the ionomer has relatively high adhesion energy and relatively low stiffness compared to iridium oxide, and the degree of exposure (phase fraction) of the ionomer, iridium oxide, and the coating layer components described below, which are constituents of the electrode layer, on the surface of the electrode layer can be quantitatively quantified using force-distance mapping data. More specifically, the above quantification can be performed through the following process.

[0143] 1) After preparing individual standard samples of each ionomer (e.g., Nafion), iridium oxide, and coating layer component (e.g., titanium oxide), the intrinsic physical properties (adhesion energy and stiffness) of each component are measured using an atomic force microscope. More specifically, the intrinsic physical properties of each component may exhibit a distribution shape as shown in Fig. 1.

[0144] 2) Subsequently, force-distance mapping is performed on the surface of the electrode layer to obtain adhesion energy and stiffness values ​​for each pixel of the surface image, and the adhesion energy and stiffness values ​​for each pixel are statistically classified by comparing them with the standard property distribution of each component obtained earlier. The probability (contribution) that the property value of each pixel corresponds to the ionomer, iridium oxide, or coating layer component is evaluated. In this statistical classification step, a Gaussian distribution can be used, or a machine learning model trained by inputting standard sample data can be used. As for machine learning methods, techniques for binary classification of conventional data, such as Support Vector Machines (SVM), can be used.

[0145] 3) Finally, the ionomer percentage for each sample can be calculated by weighted summing the contribution of each component for each pixel across the entire surface of the electrode layer being measured. The ionomer percentage may represent the exposure tendency of the ionomer on the electrode surface. That is, a higher ionomer percentage may indicate a higher proportion of ionomer exposed on the electrode surface.

[0146]

[0147] In the structure for forming an electrode for water electrolysis according to the present invention, when the iridium oxide particles in the electrode layer have a crystalline structure, the surface roughness (Ra) of the electrode layer may be 40 nm or more and 70 nm or less, and preferably 40 nm or more, and 70 nm or less, 65 nm or less, or 60 nm or less.

[0148] When the iridium oxide particles in the electrode layer have an amorphous structure, the surface roughness (Ra) of the electrode layer may be 75 nm or more and 200 nm or less, preferably 75 nm or more or 77 nm or more, and may be 200 nm or less, 180 nm or less, 160 nm or less, 140 nm or less, 120 nm or less, 100 nm or less, 90 nm or less, or 85 nm or less.

[0149] The surface roughness (Ra) described above can be measured using the same atomic force microscope device and procedure as previously described. More specifically, a two-dimensional height image of the specimen surface can be acquired using a tapping mode, and the arithmetic mean roughness can be calculated by performing standard line correction on the acquired height data. For each specimen, the average of 3 to 5 repeated measurements taken at different points can be used as the surface roughness (Ra) value.

[0150]

[0151] In the structure for forming an electrode for water electrolysis according to the present invention, when the iridium oxide particles in the electrode layer have a crystalline structure, the stiffness of the electrode layer may be 300 N / m or less, preferably 100 N / m or more, 120 N / m or more, 140 N / m or more, or 150 N / m or more, and may be 300 N / m or less, 290 N / m or less, 280 N / m or less, or 270 N / m or less.

[0152] When the iridium oxide particles in the electrode layer have an amorphous structure, the stiffness of the electrode layer may be 40 N / m or less, preferably 1 N / m or more, 3 N / m or more, 5 N / m or more, 7 N / m or more, 8 N / m or more, 9 N / m or more, 10 N / m or more, 11 N / m or more, 12 N / m or more, 13 N / m or more, or 14 N / m or more, and may be 40 N / m or less, 35 N / m or less, 30 N / m or less, 25 N / m or less, 23 N / m or less, 20 N / m or less, or 18 N / m or less.

[0153] The above stiffness can be measured using the same atomic force microscope device and procedure as previously described. More specifically, after selecting the initial linear response region (elastic deformation region) after the tip and specimen come into contact in the force-distance curve, the slope is obtained by linearly regressing the relationship between force and displacement, and this can be defined as the local stiffness (effective spring constant). For accurate pinpoint nanomechanical mapping, a sapphire standard can be used as the calibration sample, and the force-slope can be corrected before measurement, and the sensitivity and spring constant of the cantilever can be calibrated. For each specimen, the average of 3 to 5 repeated measurements taken at different points can be used as the above stiffness value.

[0154]

[0155] In the structure for forming an electrode for water electrolysis according to the present invention, the ionomer may be the same as the ionomer of the electrode for water electrolysis described above. Meanwhile, the ionomer may be used in the form of a dispersion mixed with a solvent such as water or n-propyl alcohol and catalyst particles, i.e., in the form of ink. More specifically, the structure for forming an electrode for water electrolysis can be manufactured by applying the ink to a transfer substrate and drying it.

[0156]

[0157] In the present invention, the transfer substrate may be a perfluorinated polymer such as polytetrafluoroethylene or a hydrocarbon polymer such as ethylenetetrafluoroethylene, and preferably, polytetrafluoroethylene may be used.

[0158] The transfer process for forming a water electrolysis electrode from the structure for forming a water electrolysis electrode of the present invention can be performed through heat press lamination, and accordingly, the transfer substrate preferably has heat resistance and non-stick properties at high temperatures for smooth bonding by heat press lamination. The heat press lamination process can be performed under temperature conditions of 100 to 200°C, preferably 130 to 150°C, and accordingly, the transfer substrate must have properties that do not exhibit bending or melting phenomena due to heat within the said temperature range. In addition, to minimize the phenomenon where the electrode layer does not separate from the transfer substrate during the transfer process after forming the electrode layer on the transfer substrate, it is preferable for the transfer substrate to have low surface energy, and more specifically, it may be preferable for it to have a surface energy of 30 dyne / cm or less or 20 dyne / cm or less.

[0159]

[0160] water electrolysis cell

[0161] The present invention provides a water electrolysis cell comprising the aforementioned electrode for water electrolysis.

[0162]

[0163] The above-mentioned electrode for water electrolysis may be an anode, and accordingly, the above-mentioned water electrolysis cell may include an anode for water electrolysis and a cathode for water electrolysis according to the present invention.

[0164]

[0165] More specifically, the anode for water electrolysis may have an anode layer formed on one side of an electrolyte membrane, and the cathode for water electrolysis may have a hydrogen generation catalyst coated on the opposite side of the electrolyte membrane. Accordingly, the anode and cathode for water electrolysis may constitute a membrane-electrode assembly.

[0166] In addition, the water electrolysis cell of the present invention may include a gas diffusion layer formed on both sides of the membrane-electrode assembly and a separator formed on the outer side of the gas diffusion layer.

[0167] The above gas diffusion layer may be a porous diffusion layer that allows the formed gas to move smoothly, and the above separator may serve to protect the water electrolysis cell while distinguishing it from other cells.

[0168]

[0169] Hereinafter, the present invention will be described in more detail through examples and experimental examples to specifically explain the invention, but the present invention is not limited by these examples and experimental examples. The embodiments according to the present invention may be modified in various different forms, and the scope of the present invention should not be interpreted as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the invention to those with average knowledge in the art.

[0170]

[0171] ingredient

[0172] Crystalline iridium oxide particles with a specific surface area of ​​52 m² 2 It was used that had a particle size of 1 / g, an average particle size of primary particles of 2 nm, and an average particle size of secondary particles of 1 μm. It was confirmed that the iridium content of the crystalline iridium oxide particles was 85 wt% and the crystal content was 50 wt% or more.

[0173] Amorphous iridium oxide particles with a specific surface area of ​​100 m² 2A particle with a particle size of 1 / g, an average particle size of 5 nm for primary particles, and an average particle size of 0.5 μm for secondary particles was used. It was confirmed that the iridium content of the amorphous iridium oxide particles was 74 wt% and the amorphous content was 80 wt% or more.

[0174]

[0175] (1) Structure for forming electrodes for water electrolysis

[0176]

[0177] Example 1-1

[0178] 2.5 g of prepared crystalline iridium oxide particles were loaded onto a square tray. Then, the tray was placed into a chamber within an ALD machine, and the chamber temperature was set to 100°C and the process pressure to 1 Torr. Subsequently, tetrakis(dimethylamino)titanium, a titanium precursor at 50°C, was pulse-injected into the chamber for 360 seconds along with 60 sccm of nitrogen gas as a carrier gas, followed by purging for 800 seconds. Then, water was pulse-injected for 2 seconds and purged again for 540 seconds. This process was defined as one cycle, and the cycle was repeated 5 times to produce iridium oxide particles with a coating layer formed thereon. An ink composition was prepared by mixing manufactured iridium oxide particles, water as a solvent, n-propyl alcohol, and Nafion D2020 as an ionomer in a weight ratio of 1:2:0.5 (catalyst content in the ink composition was 13.6 wt%), and the ink composition was coated onto a PTFE film to form an electrode layer, thereby preparing a structure for forming an electrode for water electrolysis.

[0179]

[0180] Examples 1-2

[0181] A structure for forming an electrode for water electrolysis was prepared by carrying out the same procedure as in Example 1-1 above, except that the atomic film deposition cycle was repeated 7 times.

[0182]

[0183] Comparative Example 1-1

[0184] A structure for forming an electrode for water electrolysis was prepared by carrying out the same procedure as in Example 1-1 above, except that crystalline iridium oxide particles without a coating layer were used.

[0185]

[0186] Comparative Example 1-2

[0187] A structure for forming an electrode for water electrolysis was prepared by carrying out the same procedure as in Example 1-1 above, except that the atomic film deposition cycle was repeated three times.

[0188]

[0189] Comparative Examples 1-3

[0190] A structure for forming an electrode for water electrolysis was prepared by carrying out the same procedure as in Example 1-1 above, except that the atomic film deposition cycle was repeated 10 times.

[0191]

[0192] Comparative Examples 1-4

[0193] A structure for forming an electrode for water electrolysis was prepared by carrying out the same procedure as in Example 1-1 above, except that the atomic film deposition cycle was repeated 15 times.

[0194]

[0195] Comparative Examples 1-5

[0196] A structure for forming an electrode for water electrolysis was prepared by carrying out the same procedure as in Example 1-1 above, except that the atomic film deposition cycle was repeated 30 times.

[0197]

[0198] Example 2-1

[0199] 2.5 g of prepared amorphous iridium oxide particles were loaded onto a square tray. Then, the tray was placed into a chamber within an ALD machine, and the chamber temperature was set to 100°C and the process pressure to 1 Torr. Subsequently, tetrakis(dimethylamino)titanium, a titanium precursor at 50°C, was pulse-injected into the chamber for 720 seconds along with 60 sccm of nitrogen gas as a carrier gas, followed by purging for 800 seconds. Then, water was pulse-injected for 4 seconds and purged again for 540 seconds. This process was defined as one cycle, and the cycle was repeated three times to produce iridium oxide particles with a coating layer formed thereon. An ink composition was prepared by mixing manufactured iridium oxide particles, water as a solvent, n-propyl alcohol, and Nafion as an ionomer in a weight ratio of 1:0.9:0.15 (catalyst content in the ink composition was 13.6 wt%), and the ink composition was coated onto a PTFE film to form an electrode layer, thereby preparing a structure for forming an electrode for water electrolysis.

[0200]

[0201] Comparative Example 2-1

[0202] A structure for forming an electrode for water electrolysis was prepared by carrying out the same procedure as in Example 2-1 above, except that amorphous iridium oxide particles without a coating layer were used.

[0203]

[0204] Comparative Example 2-2

[0205] A structure for forming an electrode for water electrolysis was prepared by carrying out the same procedure as in Example 2-1 above, except that the atomic film deposition cycle was repeated 5 times.

[0206]

[0207] Comparative Example 2-3

[0208] A structure for forming an electrode for water electrolysis was prepared by carrying out the same procedure as in Example 2-1 above, except that the atomic film deposition cycle was repeated 10 times.

[0209]

[0210] (2) Electrode for water electrolysis

[0211]

[0212] Example 3-1

[0213] 2.5 g of prepared crystalline iridium oxide particles were applied and loaded onto a square tray. Then, the tray was placed into a chamber within an ALD apparatus, and the chamber temperature was set to 100°C and the process pressure to 1 Torr. Subsequently, tetrakis(dimethylamino)titanium, a titanium precursor at 50°C, was pulse-injected into the chamber for 360 seconds along with 60 sccm of nitrogen gas as a carrier gas, followed by purging for 800 seconds. Then, water was pulse-injected for 2 seconds and purged again for 540 seconds. This process was defined as one cycle, and the cycle was repeated three times to produce a catalyst for water electrolysis. An ink composition was prepared using the produced catalyst, and the ink composition was coated onto a PTFE film to form an electrode layer. Finally, the electrode layer formed on the film was transferred to an electrolyte membrane (fluorine-based cation exchange membrane) at 140°C to produce an electrode for water electrolysis. For the ink solvent used, a mixed solvent of water and n-propanol was used in a weight ratio of 3:7, Nafion was used as the ionomer, and the ionomer / catalyst weight ratio was 10%.

[0214]

[0215] Example 3-2

[0216] In the above Example 3-1, an electrode for water electrolysis was prepared by carrying out the same procedure, except that the atomic film deposition cycle was repeated five times.

[0217]

[0218] Example 3-3

[0219] In the above Example 3-1, an electrode for water electrolysis was prepared by carrying out the same procedure, except that the atomic film deposition cycle was repeated 7 times.

[0220]

[0221] Examples 3-4

[0222] In the above Example 3-1, an electrode for water electrolysis was prepared by carrying out the same procedure, except that the atomic film deposition cycle was repeated 10 times.

[0223]

[0224] Comparative Example 3-1

[0225] An electrode for water electrolysis was manufactured by carrying out the same procedure as in Example 3-1 above, except that the atomic film deposition cycle was not performed.

[0226]

[0227] Comparative Example 3-2

[0228] In the above Example 3-1, an electrode for water electrolysis was prepared by carrying out the same procedure, except that the atomic film deposition cycle was repeated 30 times.

[0229]

[0230] Comparative Example 3-3

[0231] In the above Example 3-1, an electrode for water electrolysis was manufactured by carrying out the same procedure, except that the atomic film deposition cycle was performed only once.

[0232]

[0233] Experimental Example 1. Confirmation of surface characteristics of the electrode layer of the manufactured structure for forming electrodes for water electrolysis.

[0234] The ionomer %, adhesion energy, roughness (Ra), and stiffness were measured on the surface of the electrode layer of the structures for forming electrodes for water electrolysis prepared in the above examples and comparative examples using an atomic force microscope. In addition, the ionomer % was measured separately for each electrode for water electrolysis. The specific measurement methods for each characteristic are as follows.

[0235]

[0236] (1) Atomic force microscope measurement conditions

[0237] 1) Equipment and Software: NX-10 (Park Systems) and Smart Scan - XEI Analysis software were used.

[0238] 2) Sample preparation conditions: Constant temperature and humidity conditions of 23℃ and 45% relative humidity. After cutting the sample to an appropriate size, it was fixed to a holder using carbon tape and loaded into the atomic force microscope equipment.

[0239] 3) Measurement mode: According to standard operation, a non-contact mode was used to measure roughness and a pinpoint force-distance tapping mode was used to measure stiffness using an AFM probe (NCHR, tip radius <10 nm).

[0240] 4) Measurement area: Data was acquired in a 5㎛ x 5㎛ area with 3 points per sample for locations free of foreign matter by observing the sample with an optical microscope.

[0241] 5) Other conditions: Sampling per line was 512 and the scan speed was 0.2 Hz. The speed in the force-distance tapping mode for measuring stiffness was set to 15 µm / s and the load to 100 nN.

[0242]

[0243] (2) Parameter measurement conditions

[0244] 1) Ionomer%

[0245] In accordance with the above description, the intrinsic properties of adhesion energy and stiffness for each intrinsic standard sample of ionomer, iridium oxide, and titanium oxide were determined, and the ionomer percentage in each sample was calculated using these values. Images obtained for the electrode layer surfaces of Example 1-1 (5 cycles) and Example 1-2 (7 cycles), and Comparative Example 1-1 (0 cycles), Comparative Example 1-3 (10 cycles), and Comparative Example 1-4 (15 cycles) are shown in FIG. 2. Images obtained for the electrode layer surfaces of Example 2-1 (3 cycles), Comparative Example 2-1 (0 cycles), Comparative Example 2-2 (5 cycles), and Comparative Example 2-3 (10 cycles) are shown in FIG. 3.

[0246] 2) Adhesion energy

[0247] Measurements were taken in accordance with the above description, and for each specimen, the average of five repeated measurements taken at randomly selected different points was used as the adhesion energy value.

[0248] 2) Roughness (Ra)

[0249] Measurements were taken in accordance with the above description, and for each specimen, multiple scans were performed five times at randomly selected different points, and the average value was used as the roughness value.

[0250] 3) Stiffness

[0251] Measurements were taken in accordance with the above description, and for each specimen, the average of five repeated measurements taken at randomly selected different points was used as the stiffness value.

[0252]

[0253] The results measured through the above process are summarized in Tables 1 and 2 below.

[0254] ALD Cycle Collection (Ra, nm) Stiffness (N / m) Adhesion Energy (aJ) Ionomer % Comparative Example 1-10 57.74 43.23 9.41 6.7 Comparative Example 1-23 71.24 28.53 5.11 9.1 Example 1-15 40.42 64.79 0.82 9.7 Example 1-27 591 59.51 08.32 4.2 Comparative Example 1-3 10 56.23 96.42 5.91 0.2 Comparative Example 1-4 15 49.73 23.72 6.17.7 Comparative Example 1-5 30 38.24 22.15 8.16.8

[0255] ALD Cycle Collection (Ra, nm) Stiffness (N / m) Adhesion Energy (aJ) Ionomer % Comparative Example 2-10 73.9 10.3 47.9 33.9 Example 2-13 77.1 16.3 81.1 41.2 Comparative Example 2-25 375 5.5 37.1 8.6 Comparative Example 2-3 10 40.4 43.9 35.5 11.2

[0256]

[0257] First, looking at the distribution of ionomer, iridium oxide, and titanium oxide on the surface of the electrode layer through Figures 2 and 3, it can be confirmed that as the atomic film deposition cycle increases, the ionomer does not clump together and phase-separates with iridium and titanium, resulting in an evenly mixed heterojunction. When the atomic film deposition cycle exceeds a certain number, the phase separation disappears again, and a surface characteristic appears in which the titanium is not exposed and the iridium is exposed overall. The degree of coexistence of each component in Figures 2 and 3 represents the distribution between the three components on the surface of each sample as a triangular graph. It can be seen that in the case of the electrode layer surface of the example where a suitable coating layer is formed, the three components are distributed somewhat uniformly, whereas in the case of the comparative example, the uniformity of the distribution of the three components is lower.

[0258] In addition, as confirmed by the results in Tables 1 and 2, it can be seen that when iridium oxide particles with an appropriate coating layer formed using atomic layer deposition are used, the adhesion energy of the electrode layer is improved and the surface characteristics of the electrode layer are improved. This improvement in the surface characteristics of the electrode layer leads to excellent interfacial characteristics when the electrode layer is transferred to an electrolyte membrane to form an electrode for water electrolysis, thereby simultaneously improving the performance and durability of the electrode for water electrolysis.

[0259]

[0260] Experimental Example 2. Confirmation of electrochemical properties of a water electrolysis electrode formed from a structure for forming a water electrolysis electrode

[0261] An electrode for water electrolysis was prepared using the structures of the above examples and comparative examples, and its electrochemical properties were evaluated. More specifically, an electrode for water electrolysis was prepared by transferring an electrode layer onto a fluorine-based cation exchange membrane at 140°C using the previously prepared structure for forming an electrode for water electrolysis.

[0262] For the water electrolysis electrodes manufactured through the above process, the initial performance and cell degradation rate were measured and calculated. More specifically, a cell evaluation was performed using the manufactured electrodes. A Pt / C catalyst was used as the cell cathode; the cathode was formed on the side opposite to the surface where the electrode layer was formed on the previously manufactured water electrolysis electrode, and a titanium felt was used as the gas diffusion layer for the anode, while a carbon gas diffusion layer was used as the gas diffusion layer for the cathode. The cell evaluation condition was 3 A / cm² 2 Constant current, temperature of 80℃, water flow rate of 10–40 mL / min, and cell area of ​​4 cm 2 It was conducted for 100 hours.

[0263] 1) LSV (Linear Sweep Voltammetry): Starting from a set initial voltage (1.2V), the current-voltage curve is measured while varying the voltage at a constant scan rate of 10mV / s until a specific voltage (2V) is reached, and the initial performance of the cell is the current density value corresponding to 1.9V (Unit: A / cm²). 2 Measured by reading ).

[0264] 2) Cell degradation rate: 2 x 2 cm 2 Supplying water to the cell at 80℃, 3A / cm 2 A constant current was applied in 100-hour intervals. Subsequently, using the linear scan potential method under the same conditions as the initial performance measurement above, 0.04 A / cm² 2 From 3A / cm 2 Measure the cell voltage value up to 3A / cm 2 The cell degradation rate (unit: mV / khr) at 1,000 hours was calculated by dividing the change in current cell voltage relative to the initial cell voltage by the evaluation time.

[0265]

[0266] The results are summarized in Tables 3 and 4 below.

[0267] Initial performance (J@1.9V(A / cm) 2 Cell Degradation Rate (mV / khr) Comparative Example 1-12.84 30.0 Comparative Example 1-22.97 28.5 Example 1-12.90 15.7 Example 1-22.80 6.2 Comparative Example 1-32.45 20.0 Comparative Example 1-42.21 30.0 Comparative Example 1-52.33 36.0

[0268] Initial performance (J@1.9V(A / cm) 2 Cell degradation rate (mV / khr) Comparative Example 2-12.7389.0 Example 2-12.761.3 Comparative Example 2-22.77200.2 Comparative Example 2-32.83630.0

[0269]

[0270] As confirmed in the table above, it was confirmed that the electrode for water electrolysis according to the embodiment of the present invention exhibits superior effects compared to the comparative examples in terms of cell degradation rate and initial performance. More specifically, the electrodes for water electrolysis of Examples 1-1 to 1-2 were superior in both electrode performance and durability compared to the electrodes for water electrolysis of Comparative Examples 1-3 to 1-5. In the case of the electrodes for water electrolysis of Comparative Examples 1-1 and 1-2, similar results were shown in terms of performance, but inferior results were shown in terms of durability compared to the examples. In the case of the electrode of Example 2-1, the performance was at a similar level compared to Comparative Examples 2-1 to 2-3, but significantly superior results were shown in terms of durability.

[0271] From this, it was confirmed that the excellent surface characteristics of the structure for forming a water electrolysis electrode lead to excellent interfacial characteristics of the water electrolysis electrode manufactured therefrom, thereby providing simultaneous improvement in performance and durability.

[0272]

[0273] Experimental Example 3. Evaluation of Iridium Elution Occurrence Before and After Operation (Crystalline Iridium Oxide)

[0274] In Experimental Example 2 above, after evaluating the constant current of the electrodes for water electrolysis of Comparative Examples 1-1 and 1-2 and the electrodes for water electrolysis of Example 1-2, the interface between the electrode layer and the electrolyte membrane was cut to a certain thickness by microtoming to process it into a cross-sectional sample. First, a primary thin film sample was fabricated through microtoming, then a curable epoxy layer was impregnated to fix the electrode layer and the electrolyte membrane, and subsequently, a precise thin film cross-section of less than 100 nm was formed through ultra-microtoming. The cross-section of the thin film was observed using TEM images (Talos F200X, ThermoFischer, acceleration voltage 200 kV) to confirm whether iridium leaching occurred from the electrode layer.

[0275] The interface image for Comparative Example 1-1 is shown in FIG. 4, the interface image for Comparative Example 1-2 is shown in FIG. 5, and the interface image for Example 1-2 is shown in FIG. 6.

[0276] Referring to Figures 4 to 6, it can be seen that in the case of the water electrolysis electrode of Comparative Example 1-1, the iridium oxide catalyst was leached out in the form of particles after the constant current evaluation, whereas in the water electrolysis electrode of Example 1-2, no leaching of iridium occurred. Meanwhile, although there was no leaching of iridium confirmed in the TEM image of the water electrolysis catalyst of Comparative Example 1-2, as confirmed in Experimental Example 2, it showed inferior results compared to the example in terms of cell degradation rate, so it can be inferred that fine leaching of iridium occurred, even though it is not observed in the TEM image.

[0277]

[0278] Experimental Example 4. Evaluation of Iridium Elution Occurrence Before and After Operation (Amorphous Iridium Oxide)

[0279] In Experimental Example 2 above, after evaluating the constant current for the water electrolysis electrode of Comparative Example 2-1 and the water electrolysis electrode of Example 2-1, it was confirmed whether iridium leaching occurred at the interface between the electrode layer and the electrolyte membrane.

[0280] 1) Evaluation of changes in iridium content of the electrode layer using XRF analysis

[0281] After applying a constant current under the conditions of Experimental Example 2 to the water electrolysis electrode of Comparative Example 2-1 for 1,000 hours and to the water electrolysis electrode of Example 2-1 for 1,500 hours, the surface of the electrode layer before and after the application of the constant current was analyzed by XRF. The analysis conditions are as follows.

[0282] (1) Analysis equipment: ED-XRF (Rigaku, X-ray tube: Pd target, Secondary target: Cu, Mo, Al, Quantification program: RPF-SQX SW)

[0283] (2) Analysis process: After checking the power of the equipment, the He gas was opened to set the pressure inside the equipment to 1 to 2 bar. After that, the X-ray was turned on, and a warm-up was performed for about 2 hours. Then, an application for calibration was selected, and the analytical element and concentration to be measured were selected and compared with the calibration curve measurement results of the standard sample. The analysis sample was inserted by fixing the electrolyte membrane, before and after the application of constant current, to a PP holder.

[0284] Through the XRF analysis above, an intensity map image showing the distribution of iridium on the electrode layer was obtained and is shown in Fig. 7. In addition, the average intensity values ​​of each element are summarized in Table 5 below.

[0285] Hourly Intensity (cps) IrFS Comparative Example 2-10hr 295.6 1.6 0.08 1000hr 170.1 2.3 41.2 Example 2-10hr 301.2 1.3 0.1 1500hr 282.2 1.8 24.4

[0286] Referring to the results in Figure 7 and Table 5, it can be seen that the electrode for water electrolysis according to Example 2-1 of the present invention does not show a significant change in iridium content even when used for a longer period of operation compared to Comparative Example 2-1, whereas the electrode for water electrolysis according to Comparative Example 2-1 shows a decrease of approximately 42.5% in iridium intensity after 1,000 hours of operation. In other words, it can be seen that the electrode for water electrolysis of the present invention has superior durability during long-term operation compared to the electrode for water electrolysis of the Comparative Example.

[0287]

[0288] 2) Interface observation using TEM image analysis

[0289] The interface between the electrode layer and the electrolyte membrane before and after the above long-term operation was observed using TEM images. Specifically, the interface between the electrode layer and the electrolyte membrane was cut to a certain thickness using microtoming to process it into a cross-sectional sample. First, a primary thin film sample was fabricated through microtoming, then a curable epoxy layer was impregnated to fix the electrode layer and the electrolyte membrane, and subsequently, a precise thin film cross-section of less than 100 nm was formed through more precise ultra-microtoming. The above thin film cross-section was observed using TEM images (Talos F200X, ThermoFischer, acceleration voltage 200 kV).

[0290] The pre-operation image of Comparative Example 2-1 obtained through the above process is shown in FIG. 8, and the post-operation image is shown in FIG. 9. In addition, the pre-operation image of Example 2-1 is shown in FIG. 10, and the post-operation image is shown in FIG. 11. The porosity was calculated for each electrode layer, and the calculated porosity is indicated in FIG. 8 to FIG. 11, respectively.

[0291] The above porosity was calculated by analyzing TEM images, and more specifically, by referring to ASTM E2109-01 Standard Test Methods for Determining Area Percentage Porosity in Thermal Spray Coatings. Using freeware software (Image J), ​​the Ir catalyst portion, represented in dark colors, and the pore or binder portion, represented in bright colors, were distinguished in the TEM image. Since selecting an arbitrary grayscale value from the 256 grayscale levels could result in calculations varying depending on the overall brightness of the image, the point where the slope changes on the overall grayscale distribution curve was selected as the standard for brightness / darkness. Through this process, the electrode portion was selected in the overall TEM image, excluding the separator, at a ratio of approximately 256 x 100 pixels, and the porosity was calculated by determining the ratio of the bright area distinguished according to the above standard for brightness / darkness using Image J.

[0292] Referring to the results of Figures 8 to 11 above, it can be seen that in the electrode for water electrolysis of the comparative example, the porosity of the electrode layer increased significantly as a large amount of iridium was leached, whereas in the electrode for water electrolysis of the example, a relatively small amount of iridium was leached, resulting in a relatively small increase in porosity. In other words, just as with the previous XRF analysis results, it was confirmed through the TEM image analysis that the electrode for water electrolysis of the present invention has superior durability compared to the electrode for water electrolysis of the comparative example.

[0293]

[0294] Experimental Example 5. Confirmation of electrochemical properties of the manufactured electrode for water electrolysis

[0295] For the water electrolysis electrodes prepared in Examples 3-1 to 3-4 and Comparative Examples 3-1 to 3-3, the initial performance, iridium loading amount, and cell degradation rate were measured and calculated. Cell evaluation was performed using the prepared electrodes. A Pt / C catalyst was used as the negative electrode of the cell; the negative electrode was formed on the side opposite to the surface where the electrode layer was formed on the previously prepared water electrolysis electrode, and titanium felt was used as the gas diffusion layer of the anode, while a carbon gas diffusion layer was used as the gas diffusion layer of the negative electrode. The cell evaluation condition was 3 A / cm² 2 Constant current, temperature of 80℃, water flow rate of 10–40 mL / min, and cell area of ​​4 cm 2 It was conducted for 100 hours.

[0296] 1) LSV (Linear Sweep Voltammetry): Measures the current-voltage curve while varying the voltage at a constant scan rate of 10 mV / s until a specific voltage (2 V) is reached, starting from a set initial voltage (1.2 V), and 3 A / cm 2 The voltage value corresponding to was read, and the initial performance (unit: V) was measured.

[0297] 2) Cell degradation rate: 2 x 2 cm 2 Supplying water to the cell at 80℃, 3A / cm 2 A constant current was applied in 100-hour intervals. Subsequently, using the linear scan potential method under the same conditions as the initial performance measurement above, 0.04 A / cm² 2 From 3A / cm 2 Measure the cell voltage value up to 3A / cm 2 The cell degradation rate (unit: mV / khr) at 1,000 hours was calculated by dividing the change in current cell voltage relative to the initial cell voltage by the evaluation time.

[0298] 3) Iridium Loading Amount: Using the PTFE release film used during the above manufacturing process, the weight of the release film before and after transfer was measured, and the iridium loading amount (unit: mg / cm²) was determined based on this. 2) was calculated. The weight ratio of iridium in the electrode layer was confirmed through the ink composition. For the ink solvent used, a mixed solvent of water and n-propanol mixed in a weight ratio of 3:7 was used, Nafion was used as the ionomer, and the ionomer / catalyst weight ratio was set to 10%.

[0299]

[0300] The results are summarized in Table 6 below.

[0301] Initial performance (cell voltage @ 3A / cm 2 )Iridium loading amount (mg / cm²) 2 Cell degradation rate (mV / khr) Example 3-11.9 160.4 28.5 Example 3-21.9 20.4 15.7 Example 3-31.9 240.3 86.2 Example 3-41.9 770.4 220 Comparative Example 3-11.9 20.4 30 Comparative Example 3-21.9 70.4 136 Comparative Example 3-31.9 40.4 29

[0302] As confirmed in the table above, it was confirmed that the electrode for water electrolysis according to the embodiment of the present invention exhibits significantly superior durability compared to the electrode of the comparative example in terms of cell degradation rate.

[0303] Experimental Example 6. Evaluation of Surface Characteristics of Electrode for Water Electrolysis

[0304] Surface roughness, adhesion, and crack characteristics were verified for the electrode surfaces of Examples 3-1 to 3-4 and Comparative Examples 3-1 to 3-3. More specifically, the surface roughness and adhesion were measured in non-contact mode (scan rate: 0.2 Hz) using an AFM system (NX-10, Park System), and the crack characteristics were verified by observing the electrode surface with SEM images (magnification: x500 and x5000). Meanwhile, the surface roughness and adhesion were measured in three regions for each example and comparative example, and the average values ​​were calculated.

[0305] The results are summarized in Table 7 below. In addition, SEM images of the electrode surfaces of Examples 3-1 to 3-3 are shown in Fig. 12, SEM images of the electrode surface of Comparative Example 3-1 are shown in Fig. 13, SEM images of the electrode surface of Comparative Example 3-2 are shown in Fig. 14, and SEM images of the electrode surface of Comparative Example 3-3 are shown in Fig. 15.

[0306] Surface Roughness (Sa, nm) Adhesion (aJ) Max Crack Length (㎛) Max Crack Width (㎛) Example 3-17 135 300 1.9 Example 3-26 44 216 01 Example 3-35 94 81 201 Example 3-45 54 01 402 Comparative Example 3-17 539 100 0.71 Comparative Example 3-2 Measurement Omitted Measurement Omitted 94 0.33 Comparative Example 3-31 06.6 Measurement Omitted 300 3.0

[0307] Through the results of the simulation, it was confirmed that the electrode for water electrolysis of the present invention has excellent surface characteristics, and in particular, the surface roughness (Sa) and crack characteristics satisfy the conditions of the present invention, resulting in excellent adhesion and thus excellent electrode durability. In particular, this excellent electrode durability can also lead to the example showing superior results compared to the comparative example in terms of cell degradation rate in Experimental Example 5.

Claims

1. Electrolyte membrane; and Includes an electrode layer formed on at least one surface of the above electrolyte membrane; The surface roughness (Sa) of the electrode layer is 30 nm or more and 90 nm or less, and An electrode for water electrolysis characterized by having one or more cracks on the surface of the electrode layer having a maximum width of 1 μm or more and 5 μm or less.

2. In Paragraph 1, An electrode for water electrolysis having a surface roughness (Sa) of the electrode layer of the above-mentioned electrode of 50 nm or more and 73 nm or less.

3. In Paragraph 1, An electrode for water electrolysis having a maximum crack length of 120㎛ or more and 500㎛ or less.

4. In Paragraph 1, The electrode for water electrolysis comprises an electrode layer containing iridium oxide particles.

5. In Paragraph 4, The above-mentioned iridium oxide particles comprise a coating layer formed on at least a portion of the particle surface, forming an electrode for water electrolysis.

6. In Paragraph 5, The above coating layer is an electrode for water electrolysis comprising titanium oxide.

7. In Paragraph 1, An electrode for water electrolysis having a thickness of 1 μm or more and 15 μm or less of the electrode layer.

8. In Paragraph 1, The above electrolyte membrane is a cation exchange membrane and is an electrode for water electrolysis.

9. In Paragraph 1, The above-mentioned electrode for water electrolysis is characterized as being an anode.

10. Recording for transfer; and Includes an electrode layer formed on at least one surface of the above-described surface; and The above electrode layer comprises iridium oxide particles and an ionomer, and A structure for forming an electrode for water electrolysis, wherein the adhesion energy measured using an atomic force microscope on the surface of the electrode layer is 60 aJ ​​or more.

11. In Paragraph 10, The above iridium oxide particles are a structure for forming an electrode for water electrolysis, comprising 40 weight percent or more of crystalline iridium oxide.

12. In Paragraph 11, A structure for forming an electrode for water electrolysis, wherein the ionomer percentage of the electrode layer is 20% or more and 40% or less.

13. In Paragraph 11, A structure for forming an electrode for water electrolysis, wherein the surface roughness (Ra) of the electrode layer is 40 nm or more and 70 nm or less.

14. In Paragraph 11, A structure for forming an electrode for water electrolysis, wherein the stiffness of the electrode layer is 300 N / m or less.

15. In Paragraph 10, The above iridium oxide particles are a structure for forming an electrode for water electrolysis, comprising 60 weight% or more of amorphous iridium oxide.

16. In Paragraph 15, A structure for forming an electrode for water electrolysis, wherein the ionomer percentage of the electrode layer is greater than 40% and less than or equal to 90%.

17. In Paragraph 15, A structure for forming an electrode for water electrolysis, wherein the surface roughness (Ra) of the electrode layer is 75 nm or more and 200 nm or less.

18. In Paragraph 15, A structure for forming an electrode for water electrolysis, wherein the stiffness of the electrode layer is 40 N / m or less.

19. A water electrolysis cell comprising an electrode for water electrolysis according to any one of claims 1 to 9.

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