Electrode for water electrolysis and membrane electrode assembly comprising same

Abstract

The present invention relates to an electrode for water electrolysis and a membrane electrode assembly comprising same, wherein the electrode for water electrolysis comprises a catalyst layer comprising a catalyst containing metallic iridium and iridium oxide, wherein the full width at half maximum of the metallic iridium peak and the iridium loading amount of the catalyst layer satisfy specific conditions.

Description

Electrode for water electrolysis and membrane electrode assembly including the same

[0001] [Cross-reference with related applications]

[0002] The present invention claims the benefit of priority based on Korean Patent Application No. 10-2024-0133179 filed on September 30, 2024, and includes all contents disclosed in the document of said Korean patent application as part of this specification.

[0003] [Technology Field]

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

[0005] With the recent worsening environmental and energy issues, the utilization of hydrogen as a new renewable energy source is anticipated. For example, the development and commercialization of hydrogen-fueled devices such as hydrogen engines and fuel cells are underway.

[0006] In order to efficiently utilize hydrogen as an energy source, it is necessary to ensure its stable and safe production and supply. Until now, hydrogen production has been carried out through methods such as the steam reforming of fossil fuels; however, due to environmental concerns and the depletion of fossil fuels, the importance of hydrogen generation processes via water electrolysis is increasing. Hydrogen generation processes via water electrolysis are broadly classified into alkaline water electrolysis, solid polymer water electrolysis, and steam electrolysis. Among these, solid polymer water electrolysis is expected to see future development because it can produce water tanks with higher efficiency compared to alkaline water electrolysis.

[0007] Meanwhile, in solid polymer water electrolysis, an electrolysis device is used in which a single cell is constructed by sandwiching a solid polymer electrolyte membrane (PEM) or a proton exchange membrane as the electrolyte with anode and cathode electrodes and a power supply, and multiple electrolysis cells are stacked. Proton-conducting fluoropolymer-based ion exchange membranes (perfluorocarbon sulfone membranes) are frequently used as the solid polymer electrolyte membrane. Additionally, a catalyst layer composed of a water electrolysis catalyst is used as the anode and cathode electrodes. Recently, a catalyst-coated membrane (CCM), in which an electrode membrane composed of a mixture of water electrolysis catalyst particles and a solid electrolyte (ionomer) is attached to the electrolyte, is being used as a component of the water electrolysis device.

[0008] Among the components of solid polymer water electrolysis devices, expensive iridium catalysts are primarily used for water splitting in the oxygen generation electrode. Since the cost of iridium catalysts in solid polymer water electrolysis devices is very high, the commercialization of solid polymer water electrolysis technology is being delayed. Therefore, to commercialize solid polymer water electrolysis devices, there is a need for membrane electrode assemblies that reduce the amount of iridium used in the anode while maintaining high water electrolysis performance.

[0009] [Prior Art Literature]

[0010] [Patent Literature]

[0011] (Patent Document 1) KR2023-0081887A

[0012] The problem that the present invention aims to solve is to provide an electrode for water electrolysis that can achieve high activity and high durability while reducing the amount of iridium used.

[0013] To solve the above-mentioned problem, 1) the present invention provides a water electrolysis electrode comprising a catalyst layer including iridium in a metallic state and iridium oxide, wherein the iridium in a metallic state has a peak full width at half maximum of 0.20 to 10.00°, the peak full width at half maximum is a value measured at 47.00 to 48.00° on the x-axis, plotted with 2θ on the x-axis and intensity on the y-axis using data measured by X-ray diffraction analysis, and the iridium loading amount of the catalyst layer is 0.100 to 0.800 mg / cm².

[0014] 2) The present invention can provide an electrode for water electrolysis in which the full width at half maximum of the peak is 0.25 to 7.00°, in accordance with 1).

[0015] 3) The present invention may provide an electrode for water electrolysis comprising 0.0001 to 1.0000 weight% of iridium in a metallic state in the above 1) or 2).

[0016] 4) The present invention can provide an electrode for water electrolysis in which, in any one of 1) to 3), the iridium loading amount of the catalyst layer is 0.100 to 0.600 mg / cm².

[0017] 5) The present invention may provide an electrode for water electrolysis in which, in any one of 1) to 4), the iridium oxide is in an amorphous form or a rutile form.

[0018] 6) The present invention may provide an electrode for water electrolysis in which, in any one of 1) to 5), the iridium oxide has a BET specific surface area of ​​20.0 to 70.0 m² / g.

[0019] 7) The present invention may provide a water electrolysis electrode in which, in any one of 1) to 6), the catalyst layer has an average thickness of 1.00 to 10.00 μm.

[0020] 8) The present invention may provide an electrode for water electrolysis comprising an ionomer in the catalyst layer in any one of 1) to 7).

[0021] 9) The present invention may provide an electrode for water electrolysis in any one of 1) to 8), wherein the catalyst layer comprises 0.10 to 30.00 parts by weight of the ionomer with respect to 100 parts by weight of the catalyst.

[0022] 10) The present invention may provide an electrode for water electrolysis comprising, in any one of 1) to 9), a coating layer comprising titanium oxide, wherein the catalyst is formed on at least a portion of the iridium oxide.

[0023] 11) The present invention can provide an electrode for water electrolysis in which, in the above 10), the coating layer has an average thickness of 0.1 nm or more and 2.0 nm or less.

[0024] 12) The present invention may provide a water electrolysis electrode in any one of 1) to 11), wherein the water electrolysis electrode is an oxygen generating electrode.

[0025] 13) The present invention may provide a membrane electrode assembly comprising an electrode for water electrolysis according to any one of 1) to 12).

[0026] The electrode for water electrolysis according to the present invention can achieve high activity and high durability while reducing the amount of iridium used compared to conventional electrodes.

[0027] Figure 1 shows the iridium in a metallic state included in the catalyst layer of the oxygen generating electrode of Example 1 measured by X-ray diffraction analysis, and a graph was created using the measured data with 2θ on the x-axis and intensity on the y-axis.

[0028] Figure 2 shows the iridium in a metallic state included in the catalyst layer of the oxygen generating electrode of Example 5 measured by X-ray diffraction analysis, and a graph was created using the measured data with 2θ on the x-axis and intensity on the y-axis.

[0029] Figure 3 shows the iridium in a metallic state contained in the catalyst layer of the oxygen generating electrode of Comparative Example 1 measured by X-ray diffraction analysis, and a graph was created using the measured data with 2θ on the x-axis and intensity on the y-axis.

[0030] 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.

[0031]

[0032] In the present invention, the “peak full width at half maximum of iridium in a metallic state” is plotted with the x-axis 2θ and the y-axis as intensity using data measured by X-ray diffraction analysis, and can be measured at 47.00 to 48.00° on the x-axis.

[0033] Specifically, the X-ray diffraction analysis of the catalyst can be measured using a coupled 2 theta / theta mode with a Bruker D8 Endeavor instrument. A Si cavity holder can be used for powder mounting. The target is Cu ka (1.5418 Å), the detector is LYNXEYE_XE)T (1D mode), the divergence slit is 0.5°, and the measurement conditions allow for measurements at 6 seconds every 0.06° in the range of 5.00° ≤ 2θ ≤ 95.00°, and at 2 seconds every 0.10° in the range of 39.00° ≤ 2θ ≤ 49.00°.

[0034]

[0035] In the present invention, the “content of components within the catalyst layer” can be measured using an energy-dispersive fluorescence X-ray analyzer (XRF, Rigaku NEX-GC). Specifically, the absolute amount of components within the catalyst layer measured by the energy-dispersive fluorescence X-ray analyzer (XRF, Rigaku NEX-GC) can be quantified to calculate the relative ratio.

[0036]

[0037] In the present invention, the “form of iridium oxide” can be confirmed using a transmission electron microscope (HITACHI H7650).

[0038]

[0039] In the present invention, the “BET specific surface area” can be measured by the BET gas adsorption method. Specifically, the specific surface area of ​​the particle can be measured based on the amount of nitrogen gas adsorbed on the particle surface at liquid nitrogen temperature.

[0040]

[0041] In the present invention, the “average thickness” can be measured using a field emission scanning electron microscope (FE-SEM, JEOL JSM7610F). The thickness of the particles confirmed through the analysis of surface and cross-sectional images can be calculated as an average value.

[0042]

[0043] 1. Electrode for water electrolysis

[0044]

[0045] An electrode for water electrolysis according to one embodiment of the present invention comprises a catalyst layer comprising a catalyst including iridium in a metallic state and iridium oxide, wherein the iridium in a metallic state has a peak full width at half maximum of 0.20 to 10.00°, the peak full width at half maximum is a value measured at 47.00 to 48.00° on the x-axis, plotted with 2θ on the x-axis and intensity on the y-axis using data measured by X-ray diffraction, and the iridium loading amount of the catalyst layer is 0.100 to 0.800 mg / cm².

[0046]

[0047] If the electrode for water electrolysis satisfies the full width at half maximum of the peak of the iridium in the metallic state but does not satisfy the iridium loading amount of the catalyst layer, the activity of the electrode for water electrolysis is reduced.

[0048] If the electrode for water electrolysis satisfies the iridium loading amount of the catalyst layer but does not satisfy the full width at half maximum of the peak of the iridium in the metallic state, the durability of the electrode for water electrolysis is reduced under conditions where the iridium loading amount of the electrode for water electrolysis is reduced.

[0049]

[0050] The above-mentioned electrode for water electrolysis may include a support that supports a catalyst layer.

[0051]

[0052] When the above-mentioned electrode for water electrolysis is applied to a membrane electrode assembly, the catalyst layer may be positioned to face the separator.

[0053]

[0054] An electrode for water electrolysis according to one embodiment of the present invention may be an electrode for oxygen generation.

[0055]

[0056] Hereinafter, an electrode for water electrolysis according to one embodiment of the present invention will be described in detail.

[0057]

[0058] 1) Catalyst layer

[0059]

[0060] The catalyst layer includes a catalyst comprising iridium in a metallic state and iridium oxide.

[0061]

[0062] The catalyst layer above may include an ionomer.

[0063]

[0064] The thickness of the catalyst layer may be 1.00 to 10.00 μm, preferably 1.00 to 5.00 μm, more preferably 1.50 to 4.00 μm, and more preferably 1.80 to 3.00 μm. If the above conditions are satisfied, the characteristic of transferring hydrogen ions to the separator while maintaining electrical connection within the electrode can be improved.

[0065]

[0066] (1) catalyst

[0067]

[0068] The catalyst plays a role in promoting water electrolysis and contains iridium in a metallic state and iridium oxide.

[0069]

[0070] The iridium in the metallic state may have a peak full width at half maximum (FWHM) of 0.20 to 10.00°, preferably 0.25 to 7.00°, and more preferably 0.30 to 5.00°. If the FWHM of the peak is less than the conditions described above, a problem arises in which durability is reduced under conditions where the iridium loading amount of the electrode for water electrolysis is reduced. Furthermore, if the FWHM of the peak exceeds the conditions described above, it cannot contain iridium in the metallic state.

[0071]

[0072] If the above catalyst does not contain iridium in the metallic state, the activity of the catalyst is relatively reduced.

[0073]

[0074] The catalyst may contain iridium in the metallic state in an amount of 0.0001 to 1.0000 wt%, preferably 0.0001 to 0.5000 wt%, and more preferably 0.0001 to 0.1000 wt%. When the above conditions are satisfied, the durability of the electrode for water electrolysis is improved under conditions where the iridium loading amount of the electrode for water electrolysis is reduced.

[0075]

[0076] The above iridium oxide may be in an amorphous or rutile form. Among these, the rutile form, which has excellent durability, is preferred.

[0077]

[0078] The above iridium oxide may be included as a remainder so that the total content of the catalyst is 100 weight%.

[0079]

[0080] The iridium oxide may have a BET specific surface area of ​​20.0 to 70.0 m² / g, preferably 40.0 to 65.0 m² / g, and more preferably 45.0 to 60.0 m² / g. If the above conditions are satisfied, the dispersion of the catalyst can be facilitated when preparing the catalyst layer composition, and it can be easy to secure an active surface area for the catalytic reaction.

[0081]

[0082] The loading amount of iridium in the catalyst layer may be 0.100 to 0.800 mg / cm², preferably 0.100 to 0.600 mg / cm², and more preferably 0.200 to 0.500 mg / cm². If the above conditions are satisfied, sufficient catalytic reactivity can be secured while minimizing the use of iridium oxide. However, if the loading amount of iridium is less than the above conditions, the activity of the electrode for water electrolysis decreases. In addition, if the loading amount of iridium is greater than the above conditions, the manufacturing cost of the electrode for water electrolysis increases.

[0083]

[0084] In addition to iridium oxide, the catalyst may include one or more selected from ruthenium, platinum, platinum-nickel alloy, platinum-cobalt alloy, and platinum-nickel-cobalt alloy.

[0085]

[0086] Meanwhile, the catalyst may include a coating layer formed on at least a portion of the iridium oxide and comprising titanium oxide.

[0087] The above coating layer suppresses iridium leaching during the water electrolysis process, thereby improving the durability of the catalyst itself.

[0088] 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.

[0089]

[0090] The coating layer may have an average thickness of 0.1 nm or more and 2.0 nm or less. Preferably, it may be 0.1 nm or more, 0.2 nm or more, 0.3 nm or more, 2.0 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. If the above conditions are satisfied, the durability of the catalyst can be improved, while preventing or minimizing the decrease in the activity of the catalyst.

[0091] The above coating layer may be formed through atomic film deposition, and accordingly, the coating layer may be formed thinly and uniformly.

[0092]

[0093] (2) Ionomer

[0094]

[0095] The ionomer attaches to the surface of the catalyst and prevents aggregation between catalysts, thereby helping the catalyst to be evenly distributed in the catalyst layer.

[0096]

[0097] The catalyst layer may contain 0.10 to 30.00 parts by weight, preferably 1.00 to 25.00 parts by weight, and more preferably 3.00 to 20.00 parts by weight, of the ionomer relative to 100 parts by weight of the catalyst. If the above conditions are satisfied, the catalyst is made to adhere to each other while being evenly distributed within the electrode, thereby preventing the catalyst from detaching and falling off the electrode.

[0098]

[0099] The above ionomer may be a polymer in which sulfonic acid groups are introduced into the backbone of polytetrafluoroethylene. The above ionomer may be a commercially available product, and specifically, one or more selected from Nafion D-2020, Nafion D-2021, Nafion D-520, or Aquivion may be used.

[0100]

[0101] The loading amount of the ionomer in the catalyst layer may be 0.001 to 0.200 mg / cm², preferably 0.005 to 0.150 mg / cm², and more preferably 0.010 to 0.120 mg / cm². If the above conditions are satisfied, the activity of the electrode for water electrolysis can be maintained while preventing the catalyst from detaching and desorbing from the electrode.

[0102]

[0103] 2) Support

[0104]

[0105] The above support is for supporting the catalyst layer, and the catalyst layer may be positioned on the support.

[0106]

[0107] The above support may be a polymer membrane or a metal mesh, and specifically may be polytetrafluoroethylene, polyimide, titanium mesh, platinum-plated titanium mesh, or nickel mesh.

[0108]

[0109] 2. Membrane electrode assembly

[0110]

[0111] A membrane electrode assembly according to another embodiment of the present invention includes an electrode for water electrolysis according to one embodiment of the present invention.

[0112]

[0113] Specifically, the above membrane electrode assembly may have a structure in which an oxygen generating electrode, a separator, and a hydrogen generating electrode are sequentially stacked.

[0114]

[0115] When electrical energy is applied to the water supplied to the above membrane electrode assembly, negatively charged oxygen atoms adhere to the oxygen generating electrode and positively charged hydrogen atoms adhere to the hydrogen generating electrode, thereby separating the atoms, and hydrogen molecules generated from the hydrogen generating electrode can be collected to extract hydrogen.

[0116]

[0117] Hereinafter, a membrane electrode assembly according to another embodiment of the present invention will be described in detail.

[0118]

[0119] 1) Electrode for oxygen generation

[0120]

[0121] The above oxygen generating electrode may be a water electrolysis electrode according to one embodiment of the present invention.

[0122]

[0123] As the description of the above-mentioned electrode for water electrolysis has been provided above, it will be omitted.

[0124]

[0125] 2) Separator

[0126]

[0127] The separator separates the oxygen generation electrode and the hydrogen generation electrode, and can serve as a pathway for hydrogen ions generated at the oxygen generation electrode to move to the hydrogen generation electrode.

[0128]

[0129] The above separation membrane may be a cation exchange membrane or a porous membrane.

[0130]

[0131] The above separation membrane may be one or more selected from perfluorosulfonic acid, polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene, or polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP).

[0132] As the above-mentioned separator, a commercially available product can be used, and specifically, DuPont’s Nafion® N-115 can be used.

[0133]

[0134] The thickness of the above-described membrane may be 30 to 140 μm, preferably 50 to 130 μm, and more preferably 70 to 127 μm. If the above conditions are satisfied, the electrical resistance is reduced, which reduces the overvoltage, and the transport of hydrogen ions can proceed smoothly, thereby increasing the electrolysis efficiency.

[0135]

[0136] 3) Electrode for hydrogen generation

[0137]

[0138] The hydrogen generation electrode may include a gas diffusion layer and a catalyst layer located on the gas diffusion layer.

[0139]

[0140] The above gas diffusion layer may include one or more selected from a gas diffusion medium and a microporous layer.

[0141] The above gas diffusion medium has pores larger than the microporous layer and may include one or more selected from the group consisting of non-woven carbon paper, carbon felt, nickel foam, titanium foam, and insulating mesh.

[0142] The above microporous layer may include one or more materials selected from the group consisting of carbon powder and thermally expandable graphite.

[0143] In the case where the above gas diffusion layer includes both a gas diffusion medium and a microporous layer, the gas diffusion layer may include the gas diffusion medium, a microporous layer located on the gas diffusion medium, and a catalyst layer located on the microporous layer.

[0144]

[0145] The catalyst layer may include a catalyst and an ionomer.

[0146] The catalyst plays a role in promoting water electrolysis. The catalyst may include one or more of platinum, platinum-nickel alloy, platinum-cobalt alloy, or platinum-nickel-cobalt alloy. Additionally, the catalyst may be in a form supported on a support, and the support may be a carbon-based support, and the carbon-based support may include one or more selected from carbon black, carbon nanotubes, graphite, graphene, activated carbon, porous carbon, carbon fiber, and carbon nanowire.

[0147] The above ionomer is attached to the surface of the catalyst and prevents aggregation between catalysts, thereby helping the catalyst to be evenly distributed in the catalyst layer.

[0148]

[0149] The catalyst layer may comprise 1.0 to 80.0 parts by weight, preferably 30.0 to 80.0 parts by weight, and more preferably 60.0 to 80.0 parts by weight, of the ionomer relative to 100 parts by weight of the catalyst. If the above conditions are satisfied, the catalyst can be evenly distributed within the electrode while adhering to one another, thereby preventing the catalyst from detaching and falling off the electrode.

[0150]

[0151] The catalyst layer may have a catalyst of 0.100 to 0.750 mg / cm², preferably 0.100 to 0.650 mg / cm², and more preferably 0.100 to 0.500 mg / cm². If the above conditions are satisfied, it can rapidly combine with hydrogen ions delivered through the membrane to promote a hydrogen generation reaction.

[0152]

[0153] The above ionomer may be a polymer in which sulfonic acid groups are introduced into the backbone of polytetrafluoroethylene. The above ionomer may be a commercially available product, and specifically, one or more selected from Nafion D-2020, Nafion D-2021, Nafion D-520, or Aquivion may be used.

[0154]

[0155] The catalyst layer may have an ionomer of 0.070 to 0.580 mg / cm², preferably 0.070 to 0.500 mg / cm², and more preferably 0.070 to 0.390 mg / cm². If the above conditions are satisfied, the catalyst is evenly distributed within the electrode and adheres to one another, thereby preventing the catalyst from detaching and falling off the electrode.

[0156]

[0157] Hereinafter, preferred embodiments are presented to aid in understanding the present invention; however, the above embodiments are merely illustrative of the description, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the description, and that such variations and modifications fall within the scope of the appended claims.

[0158]

[0159] Example 1

[0160] Preparation of Electrode Catalyst Composition for Water Electrolysis

[0161] A mixed solution was prepared by sequentially adding 100.00 parts by weight of a catalyst (iridium content: 83.0 wt% or more, BET specific surface area: 57.0 m² / g, form: rutile), 75.00 parts by weight of an ionomer solution (Nafion D-2020, composition: Nafion 20 wt%, deionized water 34 wt%, 1-propanol 46 wt%), 170.77 parts by weight of deionized water, and 423.46 parts by weight of 1-propanol to a vial.

[0162] Next, 48 g of ZrO2 balls (average particle size: 3.00 mm) were added to the entire amount of this mixed solution, and after ultrasonic treatment for 20 minutes, ball milling was performed at a speed of 250 rpm for 3 days. After that, the ZrO2 balls (average particle size: 3.00 mm) were removed. Then, 48 g of yttrium-stabilized ZrO2 balls (average particle size: 0.65 mm) were added, and ball milling was performed at a speed of 300 rpm for 2 hours to prepare an electrode catalyst composition for water electrolysis.

[0163] <Manufacture of Oxygen Generation Electrode>

[0164] At 40 ℃, this electrode catalyst composition for water electrolysis was coated onto a polytetrafluoroethylene membrane (average thickness: 142 μm) using a bar coater at a speed of 10 mm / s. Afterwards, an oxygen generating electrode (average thickness of catalyst layer: 1.80 μm) was prepared by drying in an oven (internal temperature: 80 ℃) for 1 hour.

[0165] <Manufacture of Hydrogen Generation Electrode>

[0166] A mixed solution was prepared by sequentially adding 100.00 parts by weight of platinum (Pt / C, TEC10V50E of Tanaka) supported on carbon (carbon black, Vulcan XC-72R), 185.00 parts by weight of an ionomer solution (Nafion D-2020, composition: Nafion 20 wt%, deionized water 34 wt%, 1-propanol 46 wt%), 23.00 parts by weight of deionized water, and 690.50 parts by weight of 1-propanol.

[0167] Next, 48 g of ZrO2 spheres (average particle size: 3.00 mm) were added to the entire mixed solution, and after ultrasonic treatment for 20 minutes, ball milling was performed at a speed of 250 rpm for 2 days. After that, the ZrO2 spheres (average particle size: 3.00 mm) were removed, and a composition for a hydrogen generation electrode was prepared.

[0168] At 40 ℃, this composition for a hydrogen generation electrode was coated onto a polytetrafluoroethylene film (average thickness: 142 μm) using a bar coater at a speed of 10 mm / s. Afterwards, the composition was dried in an oven (internal temperature: 80 ℃) for 1 hour to produce a hydrogen generation electrode (average thickness of the catalyst layer: 4.50 μm).

[0169] <Manufacturing of Membrane Electrode Assembly>

[0170] The oxygen generating electrode and the hydrogen generating electrode were each cut to a size of 2 cm × 2 cm. A laminate was manufactured by sequentially stacking the oxygen generating electrode, a separator (Dupont’s Nafion® N-115, average thickness: 127 μm), and the hydrogen generating electrode. Then, the laminate was placed between two steel plates, and the oxygen generating electrode and the hydrogen generating electrode were transferred onto the separator by applying high pressure of 0.5 tons at 140°C for 5 minutes. After removing the polytetrafluoroethylene membrane from each electrode, a membrane electrode assembly was manufactured.

[0171] Manufacture of water electrolysis cells

[0172] A water electrolysis cell was manufactured by sequentially stacking an end plate, a current collector, a separator, a porous transfer layer, the membrane electrode assembly, a gas diffusion layer, a separator, a current collector, and an end plate.

[0173] Here, the porous transfer layer was positioned facing the oxygen generating electrode within the membrane electrode assembly and used titanium coated with platinum on its surface (average thickness: 270 μm, manufacturer: Bekaert). The gas diffusion layer was positioned facing the hydrogen generating electrode within the membrane electrode assembly and used carbon fiber (average thickness: 270 μm, manufacturer: SGL Carbon), trade name: Sigracet 36BB). Platinum-coated titanium (Serpentine Euro) was used as the separator.

[0174]

[0175] Example 2

[0176] Preparation of Electrode Catalyst Composition for Water Electrolysis

[0177] An electrode catalyst composition for water electrolysis was prepared in the same manner as in Example 1, except that the thickness of the catalyst layer in Example 1 was changed as shown in Table 1 below.

[0178] <Manufacture of Oxygen Generation Electrode>

[0179] An oxygen generation electrode catalyst composition was prepared in the same manner as in Example 1, except that the electrode catalyst composition for water electrolysis prepared above was used.

[0180] <Manufacture of Hydrogen Generation Electrode>

[0181] A hydrogen generation electrode was prepared using the same method as in Example 1.

[0182] <Manufacturing of Membrane Electrode Assembly>

[0183] A membrane electrode assembly was prepared in the same manner as in Example 1, except that the oxygen generating electrode and hydrogen generating electrode prepared above were used.

[0184] Manufacture of water electrolysis cells

[0185] A water electrolysis cell was manufactured in the same manner as in Example 1, except that the membrane electrode assembly manufactured above was used.

[0186]

[0187] Example 3

[0188] Preparation of Electrode Catalyst Composition for Water Electrolysis

[0189] An electrode catalyst composition for water electrolysis was prepared in the same manner as in Example 1, except that the content of the catalyst, ionomer solution, deionized water, and 1-propanol, and the thickness of the catalyst layer were changed as shown in Table 1 below.

[0190] <Manufacture of Oxygen Generation Electrode>

[0191] An oxygen generation electrode catalyst composition was prepared in the same manner as in Example 1, except that the electrode catalyst composition for water electrolysis prepared above was used.

[0192] <Manufacture of Hydrogen Generation Electrode>

[0193] A hydrogen generation electrode was prepared using the same method as in Example 1.

[0194] Manufacture of water electrolysis cells

[0195] A water electrolysis cell was manufactured in the same manner as in Example 1, except that the membrane electrode assembly manufactured above was used.

[0196]

[0197] Example 4

[0198] Preparation of Electrode Catalyst Composition for Water Electrolysis

[0199] An electrode catalyst composition for water electrolysis was prepared in the same manner as in Example 1, except that the content of the catalyst, ionomer solution, deionized water, and 1-propanol, and the thickness of the catalyst layer were changed as shown in Table 1 below.

[0200] <Manufacture of Oxygen Generation Electrode>

[0201] An oxygen generation electrode catalyst composition was prepared in the same manner as in Example 1, except that the electrode catalyst composition for water electrolysis prepared above was used.

[0202] <Manufacture of Hydrogen Generation Electrode>

[0203] A hydrogen generation electrode was prepared using the same method as in Example 1.

[0204] <Manufacturing of Membrane Electrode Assembly>

[0205] A membrane electrode assembly was prepared in the same manner as in Example 1, except that the oxygen generating electrode and hydrogen generating electrode prepared above were used.

[0206] Manufacture of water electrolysis cells

[0207] A water electrolysis cell was manufactured in the same manner as in Example 1, except that the membrane electrode assembly manufactured above was used.

[0208]

[0209] Example 5

[0210] Preparation of catalysts for water electrolysis

[0211] 2.5 g of catalyst (iridium content: 83.0 wt% or more, BET specific surface area: 57.0 m² / g, form: rutile) was applied onto a square tray. Then, the tray was placed into a chamber within an atomic layer deposition (ALD) apparatus. At this time, the temperature inside the chamber was set to 100 ℃ and the process pressure to 1 Torr. Subsequently, tetrakis(dimethylamino)titanium, a titanium precursor at 50 ℃, was pulse-injected into the chamber for 360 seconds along with 60 sccm of nitrogen gas as a carrier gas, and after purging for 800 seconds, 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 prepare a catalyst for water electrolysis. The above-mentioned water electrolysis catalyst had a coating layer containing titanium oxide formed on at least a portion of iridium oxide, and said coating layer contained titanium oxide (TiO2).

[0212] Preparation of Electrode Catalyst Composition for Water Electrolysis

[0213] A mixed solution was prepared by sequentially adding 100.00 parts by weight of the above-mentioned water electrolysis catalyst, 40.00 parts by weight of an ionomer solution (Aquivion D72, composition: Aquivion 25 wt%, deionized water 75 wt%), 237.80 parts by weight of deionized water, and 238.02 parts by weight of 1-propanol to a vial.

[0214] <Manufacture of Oxygen Generation Electrode>

[0215] An oxygen generation electrode catalyst composition was prepared in the same manner as in Example 1, except that the electrode catalyst composition for water electrolysis prepared above was used.

[0216] <Manufacture of Hydrogen Generation Electrode>

[0217] A mixed solution was prepared by sequentially adding 100.00 parts by weight of platinum (Pt / C, TEC10V50E of Tanaka) supported on carbon (carbon black, Vulcan XC-72R), 185.00 parts by weight of an ionomer solution (Nafion D-2020, composition: Nafion 20 wt%, deionized water 34 wt%, 1-propanol 46 wt%), 23.00 parts by weight of deionized water, and 690.50 parts by weight of 1-propanol.

[0218] Next, 48 g of ZrO2 spheres (average particle size: 3.00 mm) were added to the entire mixed solution, and after ultrasonic treatment for 20 minutes, ball milling was performed at a speed of 250 rpm for 2 days. After that, the ZrO2 spheres (average particle size: 3.00 mm) were removed, and a composition for a hydrogen generation electrode was prepared.

[0219] At 40 ℃, this composition for a hydrogen generation electrode was coated onto a polytetrafluoroethylene film (average thickness: 142 μm) using a bar coater at a speed of 10 mm / s. Afterwards, the composition was dried in an oven (internal temperature: 80 ℃) for 1 hour to produce a hydrogen generation electrode (average thickness of the catalyst layer: 4.50 μm).

[0220] <Manufacturing of Membrane Electrode Assembly>

[0221] The oxygen generating electrode and the hydrogen generating electrode were each cut to a size of 2 cm × 2 cm. A laminate was manufactured by sequentially stacking the oxygen generating electrode, a separator (Dupont’s Nafion® N-115, average thickness: 127 μm), and the hydrogen generating electrode. Then, the laminate was placed between two steel plates, and the oxygen generating electrode and the hydrogen generating electrode were transferred onto the separator by applying high pressure of 0.5 tons at 140°C for 5 minutes. After removing the polytetrafluoroethylene membrane from each electrode, a membrane electrode assembly was manufactured.

[0222] Manufacture of water electrolysis cells

[0223] A water electrolysis cell was manufactured by sequentially stacking an end plate, a current collector, a separator, a porous transfer layer, the membrane electrode assembly, a gas diffusion layer, a separator, a current collector, and an end plate.

[0224] Here, the porous transfer layer was positioned facing the oxygen generating electrode within the membrane electrode assembly and used titanium coated with platinum on its surface (average thickness: 270 μm, manufacturer: Bekaert). The gas diffusion layer was positioned facing the hydrogen generating electrode within the membrane electrode assembly and used carbon fiber (average thickness: 270 μm, manufacturer: SGL Carbon), trade name: Sigracet 36BB). Platinum-coated titanium (Serpentine Euro) was used as the separator.

[0225]

[0226] Comparative Example 1

[0227] Preparation of Electrode Catalyst Composition for Water Electrolysis

[0228] An electrode catalyst composition for water electrolysis was prepared in the same manner as in Example 1, except that the content of the catalyst, ionomer solution, deionized water, and 1-propanol, as well as the type of catalyst and the thickness of the catalyst layer, were changed as shown in Table 2 below.

[0229] Here, the catalyst used was iridium oxide (Thermo-Fisher Scientific Product No. 043396, iridium content: 84.5 wt% or more, BET specific surface area: 25.0 to 35.0 m² / g, form: amorphous).

[0230] <Manufacture of Oxygen Generation Electrode>

[0231] An oxygen generation electrode catalyst composition was prepared in the same manner as in Example 1, except that the electrode catalyst composition for water electrolysis prepared above was used.

[0232] <Manufacture of Hydrogen Generation Electrode>

[0233] A hydrogen generation electrode was prepared using the same method as in Example 1.

[0234] <Manufacturing of Membrane Electrode Assembly>

[0235] A membrane electrode assembly was prepared in the same manner as in Example 1, except that the oxygen generating electrode and hydrogen generating electrode prepared above were used.

[0236] Manufacture of water electrolysis cells

[0237] A water electrolysis cell was manufactured in the same manner as in Example 1, except that the membrane electrode assembly manufactured above was used.

[0238]

[0239] Comparative Example 2

[0240] Preparation of Electrode Catalyst Composition for Water Electrolysis

[0241] An electrode catalyst composition for water electrolysis was prepared in the same manner as in Example 1, except that the content of the catalyst, ionomer solution, deionized water, and 1-propanol, and the thickness of the catalyst layer were changed as shown in Table 2 below.

[0242] <Manufacture of Oxygen Generation Electrode>

[0243] An oxygen generation electrode catalyst composition was prepared in the same manner as in Example 1, except that the electrode catalyst composition for water electrolysis prepared above was used.

[0244] <Manufacture of Hydrogen Generation Electrode>

[0245] A hydrogen generation electrode was prepared using the same method as in Example 1.

[0246] <Manufacturing of Membrane Electrode Assembly>

[0247] A membrane electrode assembly was prepared in the same manner as in Example 1, except that the oxygen generating electrode and hydrogen generating electrode prepared above were used.

[0248]

[0249] Comparative Example 3

[0250] Preparation of Electrode Catalyst Composition for Water Electrolysis

[0251] An electrode catalyst composition for water electrolysis was prepared in the same manner as in Example 1, except that the content of the catalyst, ionomer solution, deionized water, and 1-propanol, as well as the type of catalyst and the thickness of the catalyst layer, were changed as shown in Table 2 below.

[0252] Here, the catalyst used was iridium oxide (Thermo-Fisher Scientific Product No. 043396, iridium content: 84.5 wt% or more, BET specific surface area: 25.0 to 35.0 m² / g, form: amorphous).

[0253] <Manufacture of Hydrogen Generation Electrode>

[0254] A hydrogen generation electrode was prepared using the same method as in Example 1.

[0255] <Manufacturing of Membrane Electrode Assembly>

[0256] A membrane electrode assembly was prepared in the same manner as in Example 1, except that the oxygen generating electrode and hydrogen generating electrode prepared above were used.

[0257] Manufacture of water electrolysis cells

[0258] A water electrolysis cell was manufactured in the same manner as in Example 1, except that the membrane electrode assembly manufactured above was used.

[0259]

[0260] Experimental Example 1

[0261] The full width at half maximum of metallic iridium contained in the catalyst layer of the oxygen generation electrode of Example 1 and Comparative Example 1 was measured by the following method.

[0262] First, iridium in a metallic state was measured using X-ray diffraction analysis, and a graph was constructed using the measured data with 2θ on the x-axis and intensity on the y-axis, and the full width at half maximum of the peak was measured at 47.00 to 48.00° on the x-axis.

[0263] Specifically, the X-ray diffraction analysis of the catalyst was measured using a coupled 2 theta / theta mode with a Bruker D8 Endeavor instrument. A Si cavity holder was used for powder mounting. The target was Cu ka (1.5418 Å), the detector was LYNXEYE_XE)T (1D mode), the divergence slit was 0.50°, and the measurement conditions were 6 seconds at 0.06° intervals in the range of 5.00° ≤ 2θ ≤ 95.00°, and 2 seconds at 0.10° intervals in the range of 39.00° ≤ 2θ ≤ 49.00°.

[0264] The measured values ​​were listed in Table 1 and Table 2 below.

[0265]

[0266] In addition, Figure 1 shows the iridium in a metallic state included in the catalyst layer of the oxygen generating electrode of Example 1 measured by X-ray diffraction analysis, and a graph was created using the measured data with 2θ on the x-axis and intensity on the y-axis. From this graph, the full width at half maximum of the peak at 47.00 to 48.00° on the x-axis was measured and listed in Table 1 below.

[0267] Figure 2 shows the iridium in a metallic state included in the catalyst layer of the oxygen generating electrode of Example 5 measured by X-ray diffraction analysis, and a graph was created using the measured data with 2θ on the x-axis and intensity on the y-axis. From this graph, the full width at half maximum of the peak at 47.00 to 48.00° on the x-axis was measured and listed in Table 2 below.

[0268] Figure 3 shows the iridium in a metallic state contained in the catalyst layer of the oxygen generating electrode of Comparative Example 1 measured by X-ray diffraction analysis, and a graph was constructed using the measured data with 2θ on the x-axis and intensity on the y-axis. From this graph, the full width at half maximum of the peak at 47.00 to 48.00° on the x-axis was measured and listed in Table 2 below.

[0269]

[0270] Experimental Example 2

[0271] The loading amount of the components of the catalyst layer of the oxygen generation electrode was measured using an energy-dispersive fluorescence X-ray analyzer (XRF, Rigaku NEX-CG), and the absolute amount of the measured components was quantified to calculate the relative ratio. The results are listed in Tables 1 and 2 below.

[0272]

[0273] Experimental Example 3

[0274] The physical properties of the water electrolysis cells of the examples and comparative examples were measured in the following manner, and the results are listed in Table 1 and Table 2 below.

[0275]

[0276] 1) Current density (unit: A / cm², @1.9 V vs. RHE): Starting from a set initial potential (0 V), the current-potential curve was measured while varying the voltage at a constant scan rate of 10 mV / s up to a specific potential (2 V or 3 V). Then, the current value corresponding to 1.9 V was read, and the value obtained by dividing the current value by the electrode area was defined as the current density. At this time, the flow rate of the electrolyte (ultrapure water (18 MΩ)) injected into the water electrolysis cell was 30 ml / min, the electrode size was 4 cm², and the temperature of the water electrolysis cell was 60 ℃.

[0277]

[0278] In the present invention, if the current density is 2.0 A / cm² or higher, it was determined that the activity of the electrode for water electrolysis is excellent.

[0279]

[0280] 2) Cell voltage (unit: V, @ 1.5 A / cm²): Starting from a set initial potential (0 V), the current-potential curve was measured while varying the voltage at a constant scan rate of 10 mV / s up to a specific potential (2 V or 3 V). The voltage value corresponding to 6 A was set as the cell voltage.

[0281]

[0282] In the present invention, if the cell voltage is 1.810 V or less, it was determined that the activity of the electrode for water electrolysis is excellent.

[0283]

[0284] 3) Ohmic resistance (R ohm , Unit: Ohm-㎠, @ 0.2 A / ㎠): Using the electrochemical impedance measurement method, the impedance response was measured by applying an alternating current (AC) signal from a high frequency (30,000 Hz) to a low frequency (1 Hz) range at the potential at which the electrochemical reaction begins. In this case, the x-intercept of the linear portion of the Nyquist plot in the high-frequency region (500 Hz to 3,000 Hz) was taken as the ohmic resistance value.

[0285] In the present invention, if the ohmic resistance is 0.165 Ohm-cm² or less, the electrical resistance value of the membrane electrode assembly is low, so it is determined that the electrical conductivity is excellent.

[0286]

[0287] 4) Degradation Rate 1 (Unit: mV / kh, △V / Evaluation Time): A constant current durability evaluation was conducted for more than 300 hours at a water electrolysis cell temperature of 60 ℃ while applying a constant current of 6.0 A (1.5 A / cm²). The water electrolysis cell voltage values ​​were measured at the start and end of the constant current evaluation, and the change in the water electrolysis cell voltage values ​​during the evaluation time was measured. The difference in cell voltage before and after the durability evaluation was divided by the evaluation time to determine the degradation rate.

[0288]

[0289] In the present invention, if the degradation rate is 100 mV / kh or less, it was determined that the durability of the water electrolysis cell is excellent.

[0290]

[0291] 5) Degradation rate 2 (Unit: mV / kh, △V / evaluation time): A constant current durability evaluation was conducted for more than 414 hours at a water electrolysis cell temperature of 80 ℃ while applying a constant current of 12.0 A (3.0 A / cm²). The water electrolysis cell voltage values ​​were measured at the start and end of the constant current evaluation, and the change in water electrolysis cell voltage values ​​during the evaluation time was measured. The difference in cell voltage before and after the durability evaluation was divided by the evaluation time to determine the degradation rate.

[0292]

[0293] In the present invention, if the degradation rate is 100 mV / kh or less, it was determined that the durability of the water electrolysis cell is excellent.

[0294]

[0295] 6) R ohm Factor: Calculated by substituting the ohmic resistance and the thickness of the separator used in the manufacture of the membrane electrode assembly into the following formula.

[0296]

[0297] R ohm Factor (Unit: Ohm-cm) = {Ohmic Resistance (Unit: Ohm-cm²)} / {Separator Thickness (Unit: cm)}

[0298] Classification Example 1 Example 2 Example 3 Example 4 Oxygen Generation Electrode Mixed Solution Catalyst Full Width (°) of Iridium Peak in Metallic State 0.5 to 1.5 0.5 to 1.5 0.5 to 1.5 0.5 to 1.5 Content (Weight%) Approx. 0.1 Approx. 0.1 Approx. 0.1 Approx. 0.1 Iridium Oxide Content (Weight%) Approx. 99.9 Approx. 99.9 Approx. 99.9 Content (Parts by Weight) 100.00 100.00 100.00 100.00 100.00 Ionomer Solution Content (parts by weight) 75.00 75.00 60.00 25.00 Deionized Water Content (parts by weight) 17 0.77 17 0.77 15 1.54 16 8.75 -Propanol Content (parts by weight) 42 3.46 42 3.46 45 7.69 40 0.69 Catalyst Layer Iridium Loading Amount (mg / cm²) 0.31 00.38 00.42 00.38 Ionomer Loading Amount (mg / cm²) 0.05 60.06 80.07 50.023 Thickness (㎛) 1.8 02.5 02.6 01.80 Physical Property Evaluation Current Density (Unit: A / cm², @ 1.9 V) 2.17 2.24 2.02 2.21 Cell Voltage (Unit: V, @ 1.5 A / ㎠)1.7911.7791.8091.783R ohm (Unit: Ohm-㎠, @ 0.2 A / ㎠) 0.136 0.145 0.163 0.145 Degradation Rate 1 (Unit: mV / kh, △V / Evaluation Time) 14.56 4.21 8.45 5.7R ohm Factor (R ohm / Membrane thickness)10.74 11.43 12.85 11.43

[0299] Classification Example 5 Comparative Example 1 Comparative Example 2 Comparative Example 3 Oxygen generating electrode mixed solution catalyst Full width at half maximum (°) of iridium peak in metallic state 1.0 to 1.5 0.1 0.5 to 1.5 0.1 Content (weight%) approx. 0.1 approx. 2.0 approx. 0.1 approx. 2.0 Iridium oxide content (weight%) approx. 99.9 approx. 98.0 approx. 99.9 approx. 98.0 Content (parts by weight) 100.00 100.00 100.00 100.00 100.0 Ionomer Solution Content (parts by weight) 40.00 75.00 25.00 75.00 Deionized Water Content (parts by weight) 237.80 111.43 168.75 40.00 -Propanol Content (parts by weight) 238.02 285.14 400.69 118.33 Catalyst Layer Iridium Loading Amount (mg / cm²) 0.32 00.28 00.09 90.99 Ionomer Loading Amount (mg / cm²) 0.05 40.05 00.00 60.175 Thickness (㎛) 1.74 1.6 00.8 00.99 Physical Property Evaluation Current Density (Unit: A / cm², @ 1.9 V) 2.07 2.31 1.89 1.92 Cell Voltage (Unit: V, @ 1.5 A / ㎠)1.8101.7621.8301.819R ohm (Unit: Ohm-㎠, @ 0.2 A / ㎠) 0.129 0.144 0.158 0.168 Degradation Rate 1 (Unit: mV / kh, △V / Evaluation Hour) -25 3.3 -9 1.7 Degradation Rate 2 (Unit: mV / kh, △V / Evaluation Hour) -0.26---R ohm Factor (R ohm / Membrane thickness)10.16 11.37 12.44 13.23

[0300] Referring to Tables 1 and 2, Examples 1 to 4 satisfy both the full width at half maximum of the peak of metallic iridium contained in the catalyst being 0.2 to 10.0° and the iridium content in the catalyst layer being 0.100 to 0.800 mg / cm², so it was predicted that excellent performance and durability would be achieved, as the current density is high and the degradation rate is low.

[0301] Example 5 utilized a catalyst comprising iridium in a metallic state and iridium oxide, wherein the catalyst comprises a coating layer formed on at least a portion of the iridium oxide and containing titanium oxide. Although the degradation rate of Example 5 was evaluated under harsher conditions compared to Examples 1 to 4, no degradation occurred, suggesting that significantly superior durability could be achieved. Furthermore, the catalyst became more active after the degradation rate evaluation, resulting in improved cell performance compared to the initial cell performance, and the degradation rate showed a negative value.

[0302] In Comparative Example 1, since the full width at half maximum of the peak of iridium in the metallic state contained in the catalyst is less than 0.2°, it was predicted that even if the iridium content in the catalyst layer satisfies 0.100 to 0.800 mg / cm², the degradation rate of the water electrolysis device is excessively high and excellent durability cannot be secured.

[0303] Comparative Example 2 satisfies the condition that the peak full width at half maximum of iridium in the metallic state contained in the catalyst is 0.2 to 10.0°, but since the iridium content in the catalyst layer is less than 0.100 mg / cm², it was predicted that high activity could not be secured due to the low current density.

[0304] Comparative Example 3 has a peak full width at half maximum of metallic iridium contained in the catalyst of less than 0.2° and an iridium content in the catalyst layer exceeding 0.800 mg / cm². It was predicted that Comparative Example 3 could not secure high activity because the amount of iridium used in the electrode of the water electrolysis device was too high and the current density was low.

Claims

1. A catalyst layer comprising a catalyst including iridium in a metallic state and iridium oxide, and The iridium in the above metallic state has a peak full width at half maximum of 0.20 to 10.00°, and The full width at half maximum of the above peak is plotted using data measured by X-ray diffraction analysis with 2θ on the x-axis and intensity on the y-axis, and is a value measured at 47.00 to 48.00° on the x-axis, and An electrode for water electrolysis having an iridium loading amount of the catalyst layer of 0.100 to 0.800 mg / cm².

2. In Claim 1, An electrode for water electrolysis having a peak full width at half maximum of 0.25 to 7.00°.

3. In Claim 1, The above catalyst is a water electrolysis electrode comprising 0.0001 to 1.0000 weight% of the iridium in the metallic state.

4. In Claim 1, An electrode for water electrolysis having an iridium loading amount of the catalyst layer of 0.100 to 0.600 mg / cm².

5. In Claim 1, The above iridium oxide is an electrode for water electrolysis in an amorphous or rutile form.

6. In Claim 1, The above iridium oxide is a water electrolysis electrode having a BET specific surface area of ​​20.0 to 70.0 m² / g.

7. In Claim 1, The above catalyst layer is an electrode for water electrolysis having an average thickness of 1.00 to 10.00 μm.

8. In Claim 1, The above catalyst layer is an electrode for water electrolysis comprising an ionomer.

9. In Claim 8, The above catalyst layer comprises 0.10 to 30.00 parts by weight of the ionomer with respect to 100 parts by weight of the catalyst, for a water electrolysis electrode.

10. In Claim 1, The above catalyst is formed on at least a portion of the iridium oxide, and the electrode for water electrolysis comprises a coating layer including titanium oxide.

11. In Claim 10, The above coating layer is an electrode for water electrolysis having an average thickness of 0.1 nm or more and 2.0 nm or less.

12. In Claim 1, The above-mentioned electrode for water electrolysis is an electrode for water electrolysis that is an electrode for oxygen generation.

13. A membrane electrode assembly comprising an electrode for water electrolysis according to claim 1.

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