Water electrolysis catalyst, method for preparing same, and membrane electrode assembly using same

Abstract

The invention provides a water electrolysis catalyst, a preparation method thereof and a membrane electrode assembly using the catalyst. An embodiment water electrolysis catalyst includes an iridium oxide containing a rutile phase and an iridium-nickel oxide containing a hexagonal phase. A method of making a water electrolysis catalyst includes preparing a mixture including an iridium precursor, a nickel precursor, and cysteamine hydrochloride, drying the mixture, grinding the dried mixture, and firing the ground product, where the water electrolysis catalyst includes a rutile phase-containing iridium oxide and a hexagonal phase-containing iridium-nickel oxide.

Description

Technical Field

[0001] The present disclosure relates to a catalyst including rutile phase iridium oxide and hexagonal phase iridium-nickel oxide, a method for preparing the same, and a membrane electrode assembly using the catalyst. Background Art

[0002] Hydrogen energy has recently attracted much attention as an alternative to existing fossil fuels. Hydrogen energy can be easily obtained by electrolyzing water and is environmentally friendly because water is produced when hydrogen burns.

[0003] There are several types of water electrolysis, and among them, a membrane electrode assembly (MEA) using an exchange membrane has attracted attention due to its high efficiency. Cation exchange membrane water electrolysis is a reaction that uses electrical energy to decompose water into hydrogen and oxygen, and has the advantage of quickly converting electrical energy into chemical energy. In the case of new renewable energy, it is difficult to fully utilize new renewable energy because the power generation amount does not remain consistent depending on the environment and conditions. Therefore, if the remaining new renewable energy is converted into hydrogen (i.e., chemical energy) through cation exchange membrane water electrolysis and then stored, new renewable energy with inconsistent power generation amounts can be fully utilized.

[0004] Cation exchange membrane water electrolysis has the advantage of being able to produce hydrogen with high efficiency and purity. In water electrolysis, hydrogen generation and oxygen generation reactions occur simultaneously, and a catalyst is necessary for the effective occurrence of each reaction. However, when using a cation exchange membrane, a large overvoltage is applied to the oxidation electrode, and since the ionomer is a strongly acidic material, most catalysts cannot maintain their performance and suffer from degradation and oxidation problems.

[0005] Currently, iridium (Ir) is well-known as a material having good performance and durability in the oxygen generation reaction in cation exchange membrane water electrolysis. However, iridium is a precious metal with extremely small reserves and extremely small production amounts, which causes quantity and financial limitations in constructing a large-scale water electrolysis system. In the past, in order to reduce the production cost of hydrogen through the development of catalysts, methods of using highly active catalysts to save power consumption and methods of using highly durable catalysts to extend the catalyst replacement cycle have been proposed. In addition, since iridium, a precious metal, is very expensive, methods of reducing the amount of iridium used have been studied.

[0006] As various iridium-based catalysts are studied, the importance of the structure and environmental factors of iridium as a catalyst active site has been mentioned. In particular, the importance of structural connectivity, symmetry, and the nature of oxygen ligands in catalyst activity or stability has emerged, and research on molten salt synthesis has been carried out, but there has been no research on iridium catalysts containing nickel (Ni).

[0007] The above information disclosed in this background art section is only for enhancing the understanding of the background art of the present invention, and thus it may include information that does not form the prior art that is already known. Summary of the Invention

[0008] Embodiments of the present disclosure can solve problems related to the prior art, and one embodiment of the present disclosure provides a water electrolysis catalyst including iridium-nickel oxide, which has a reduced iridium usage amount by adding nickel and has higher activity and durability than conventionally reported iridium catalysts.

[0009] Another embodiment of the present disclosure provides a method for preparing a water electrolysis catalyst including iridium-nickel oxide using an iridium precursor, a nickel precursor, and cysteamine hydrochloride.

[0010] Yet another embodiment of the present disclosure provides a membrane electrode assembly (MEA) including a water electrolysis catalyst.

[0011] Embodiments of the present disclosure are not limited to the above embodiments. Embodiments of the present disclosure will become clearer from the following description.

[0012] One embodiment of the present disclosure provides a water electrolysis catalyst including rutile-phase iridium oxide and hexagonal-phase iridium-nickel oxide.

[0013] In a preferred embodiment, when analyzed by X-ray diffraction (XRD), the iridium oxide may include peaks of at least one of the (110), (101), (200), and (211) crystal planes.

[0014] In another preferred embodiment, when analyzed by X-ray diffraction (XRD), the iridium-nickel oxide may include peaks at at least one diffraction angle 2θ of 18° to 20°, 33.0° to 34.5°, 35.0° to 37.0°, and 46° to 48°.

[0015] In yet another preferred embodiment, the iridium oxide may have a nanoneedle-like structure, and the iridium-nickel oxide may have a hexagonal platelet-shaped structure.

[0016] In yet another preferred embodiment, the iridium oxide having a nanoneedle structure can be located on at least a part of the surface of the iridium-nickel oxide having a hexagonal plate-like structure or physically connected to at least a part of the surface of the iridium-nickel oxide having a hexagonal plate-like structure.

[0017] Another embodiment of the present disclosure provides a method for preparing a water electrolysis catalyst, the method comprising preparing a mixture comprising an iridium precursor, a nickel precursor, and cysteamine hydrochloride, drying the mixture, grinding the dried mixture, and firing the ground product.

[0018] In a preferred embodiment, the iridium precursor may include at least one selected from the group consisting of: iridium(III) chloride (IrCl 3 ), iridium(III) chloride hydrate (IrCl 3 ·xH 2 O), potassium hexachloroiridate(IV) (K 2 IrCl 6 ), potassium hexachloroiridate(IV) hydrate (K 2 IrCl 6 ·xH 2 O), and combinations thereof.

[0019] In another preferred embodiment, the nickel precursor may include at least one selected from the group consisting of: nickel sulfate, nickel chloride, nickel bromide, nickel acetylacetonate, nickel cyclohexanebutyrate, nickel ethylhexanoate, nickel octanoate, and combinations thereof.

[0020] In yet another preferred embodiment, the iridium precursor and the nickel precursor may be configured such that the number of moles of iridium is greater than the number of moles of nickel.

[0021] In yet another preferred embodiment, the iridium precursor and the nickel precursor may be configured such that the molar ratio of iridium: nickel is from 1.1:1 to 3:1.

[0022] In yet another preferred embodiment, the preparation of the mixture may be carried out in an aqueous solution containing sodium nitrate (NaNO 3 ).

[0023] In a further preferred embodiment, the firing of the ground product may be carried out at a temperature of 450 °C to 650 °C.

[0024] In another further preferred embodiment, when firing the abrasive product, the temperature of the abrasive product can be raised to a target temperature of 450 °C to 650 °C at a heating rate of 10 °C per minute, and then the target temperature can be maintained for 30 minutes to 2 hours.

[0025] Another embodiment of the present disclosure provides a membrane electrode assembly, which includes a positive electrode, a negative electrode, and an electrolyte membrane inserted between the positive electrode and the negative electrode.

[0026] Other aspects and preferred embodiments of the present invention are discussed below.

[0027] The above features and other features of the embodiments of the present invention are discussed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above features and other features of the embodiments of the present disclosure will now be described in detail with reference to some exemplary embodiments thereof shown in the accompanying drawings, in which the drawings are given by way of example only and thus do not limit the present disclosure, and wherein:

[0029] Figure 1 Shows the X-ray diffraction analysis results of a catalyst prepared according to a preparation example of an embodiment of the present disclosure;

[0030] Figure 2 Shows an image of the appearance of the catalyst in the control group observed by a transmission electron microscope according to a test example of an embodiment of the present disclosure;

[0031] Figure 3 Shows an image of the appearance of the catalyst in Comparative Example 2 observed by a transmission electron microscope according to a test example of an embodiment of the present disclosure;

[0032] Figure 4 Shows an image of the appearance of the catalyst in Example 1 observed by a transmission electron microscope according to a test example of an embodiment of the present disclosure;

[0033] Figure 5 Shows an image of the appearance of the catalyst in Comparative Example 3 observed by a transmission electron microscope according to a test example of an embodiment of the present disclosure;

[0034] Figure 6 Shows the evaluation results of the activity of the catalyst in a three-electrode system according to a test example of an embodiment of the present disclosure;

[0035] Figure 7 Shows the evaluation results of the performance of the catalyst in a membrane electrode assembly according to a test example of an embodiment of the present disclosure; and

[0036] Figure 8 Shows the evaluation results of the durability of the catalyst in a membrane electrode assembly according to a test example of an embodiment of the present disclosure.

[0037] It should be understood that the drawings are not necessarily drawn to scale and present a slightly simplified representation of various preferred features illustrating the basic principles of the embodiments of the present invention. Specific design features of the embodiments of the present disclosure disclosed herein (including, for example, specific dimensions, orientations, positions, and shapes) will be determined in part by the particular intended application and use environment.

[0038] In the drawings, throughout several views of the drawings, reference numerals refer to the same or equivalent components of the present disclosure. Detailed Description

[0039] From the following description of the embodiments given with reference to the drawings, the above objects, other objects, advantages, and features of the embodiments of the present disclosure will become apparent. However, the present disclosure is not limited to the embodiments disclosed herein and can be implemented in various different forms. These embodiments are provided so that the description of the present disclosure is thorough and will fully convey the scope of the present disclosure to those skilled in the art.

[0040] In the drawings, even if the same or similar elements are shown in different drawings, they are denoted by the same reference numerals. In the drawings, for clarity of description, the dimensions of the structures may be enlarged compared to their actual sizes. In the following description of the embodiments, terms such as "first" and "second" may be used to describe various elements, but do not limit these elements. These terms are only used to distinguish one element from other elements. For example, without departing from the scope and spirit of the present invention, the first element may be referred to as the second element, and similarly, the second element may be referred to as the first element. Singular representations may cover plural representations unless they have an apparently different context meaning.

[0041] In the following description of the embodiments, terms such as "comprising", "including", and "having" should be construed as indicating the presence of the features, quantities, steps, operations, elements, or components, or combinations thereof, stated in the description, and they do not exclude the presence or addition of one or more other features, quantities, steps, operations, elements, components, or combinations thereof. In addition, it should be understood that when a component such as a layer, film, region, or plate is said to be "on" another component, the component may be "directly on" the other component, or other components may be interposed between the two components. Similarly, it should be understood that when a component such as a layer, film, region, or plate is said to be "under" another component, the component may be "directly under" the other component, or other components may be interposed between the two components.

[0042] Unless otherwise specified, all numerical values, values and / or representations used in the specification to denote amounts of components, reaction conditions, polymer compositions, and blends are approximate values, which reflect the various uncertainties in measurements when obtaining such values from substantially different things, and thus it should be understood that they are modified by the term "about". In addition, it should be understood that if a numerical range is disclosed in the specification, such a range includes all continuous values from the minimum value to the maximum value of the range, unless otherwise stated. Further, if such a range refers to integers, the range includes all integers from the smallest integer to the largest integer, unless otherwise stated.

[0043] In the following description of embodiments, it should be understood that when describing a range of a variable, the variable includes all values within the described range, including the described endpoints of the range. For example, it should be understood that the range of "5 to 10" includes not only the values of 5, 6, 7, 8, 9, and 10, but also any sub-ranges such as the sub-range of 6 to 10, the sub-range of 7 to 10, the sub-range of 6 to 9, and the sub-range of 7 to 9, as well as any values between the valid integers within the described range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, and 6.5 to 9. In addition, for example, it should be understood that the range of "10% to 30%" includes not only all integers containing values of 10%, 11%, 12%, 13%,..., 30%, but also any sub-ranges, such as the sub-range of 10% to 15%, the sub-range of 12% to 18%, and the sub-range of 20% to 30%, as well as any values between the valid integers within the described range, such as 10.5%, 15.5%, and 25.5%.

[0044] One embodiment of the present disclosure relates to a water electrolysis catalyst, which includes rutile-phase iridium oxide and hexagonal-phase iridium-nickel oxide.

[0045] In an embodiment of the present disclosure, the iridium oxide may contain a rutile phase and may be represented by the chemical formula [IrO x . Here, x may be a value that makes the iridium oxide (IrO x ) electrically neutral.

[0046] In this specification, the term "rutile phase" is one of the crystal structures of nanoparticles and may represent the two-dimensional layer structure observed in titanium dioxide (TiO 2 ) and the like. The rutile phase may have an elliptical crystal structure with different aspect ratios, and the macroscopic shape of the particles in the rutile phase may be long and thin nanoneedle-like.

[0047] In an embodiment of the present disclosure, when analyzed by X-ray diffraction (XRD), the iridium oxide may include peaks of at least one of the (110), (101), (200), and (211) crystal planes.

[0048] In an embodiment of the present disclosure, the iridium-nickel oxide may be hexagonal and may be represented by the chemical formula [Ir 2 NiO x . Here, x may be a value that makes the iridium-nickel oxide (Ir 2 NiO x ) electrically neutral.

[0049] In this specification, the term "hexagonal phase" is one of the crystal structures of nanoparticles and, different from the rutile phase, may represent a hexagonal crystal structure. The macroscopic shape of the particles in the hexagonal phase may be hexagonal plate-like.

[0050] In an embodiment of the present disclosure, when analyzed by X-ray diffraction (XRD), the iridium-nickel oxide may include peaks at at least one diffraction angle 2θ of 18° to 20°, 33.0° to 34.5°, 35.0° to 37.0°, and 46° to 48°.

[0051] In one embodiment, when analyzed by X-ray diffraction (XRD), the iridium-nickel oxide may include peaks at diffraction angles 2θ of about 19.0°, about 33.7°, about 35.8°, and about 47°.

[0052] In an embodiment of the present disclosure, the iridium-nickel oxide may be characterized in that iridium atoms and nickel atoms form a hexagonal close-packed (HCP) crystal structure.

[0053] In an embodiment of the present disclosure, the iridium oxide may microscopically have a rutile phase and may macroscopically have particles with a nanoneedle-like structure.

[0054] In an embodiment of the present disclosure, the iridium-nickel oxide may microscopically have a hexagonal phase and may macroscopically have particles with a hexagonal plate-like structure.

[0055] In an embodiment of the present disclosure, the iridium oxide may be located on at least a part of the surface of the iridium-nickel oxide or physically connected to at least a part of the surface of the iridium-nickel oxide. The water electrolysis catalyst according to an embodiment of the present disclosure may include at least one iridium-nickel oxide, and the iridium oxide may be located on at least a part of the surface of the iridium-nickel oxide, physically connected to at least a part of the surface of the iridium-nickel oxide, or located near at least a part of the surface of the iridium-nickel oxide.

[0056] The water electrolysis catalyst according to an embodiment of the present disclosure may not include a separate iridium oxide. In addition, the water electrolysis catalyst according to an embodiment of the present disclosure may not include a separate iridium-nickel oxide.

[0057] In an embodiment of the present disclosure, water electrolysis may include polymer electrolyte membrane (PEM) water electrolysis. PEM water electrolysis is an electrochemical reaction in which water is separated into hydrogen and oxygen by externally supplied electricity, and may have characteristics such as a fast hydrogen production rate, high hydrogen purity, and flexible operation. Generally, PEM water electrolysis may be performed in a stacked form in which unit cells are stacked and assembled to meet the required hydrogen production amount, and the membrane electrode assembly may be located in the innermost part of the stack, but is not limited thereto.

[0058] The water electrolysis catalyst according to an embodiment of the present disclosure may exhibit improved durability under acidic conditions, i.e., actual water electrolysis conditions.

[0059] Another embodiment of the present disclosure relates to a method for preparing a water electrolysis catalyst, the method including preparing a mixture containing an iridium precursor, a nickel precursor, and cysteamine hydrochloride, drying the mixture, grinding the dried mixture, and firing the ground product.

[0060] In an embodiment of the present disclosure, the iridium precursor may include at least one selected from the group consisting of: iridium(III) chloride (IrCl 3 ), iridium(III) chloride hydrate (IrCl 3 ·xH 2 O), potassium hexachloroiridate(IV) (K 2 IrCl 6 ), potassium hexachloroiridate(IV) hydrate (K 2 IrCl 6 ·xH 2 O), and combinations thereof, and may include, for example, iridium(III) chloride hydrate (IrCl 3 ·xH 2 O), but is not limited thereto.

[0061] In an embodiment of the present disclosure, the nickel precursor may include at least one selected from the group consisting of: nickel sulfate, nickel chloride, nickel bromide, nickel acetylacetonate, nickel cyclohexanebutyrate, nickel 2-ethylhexanoate, nickel octanoate, and combinations thereof, and may include, for example, nickel chloride, but is not limited thereto.

[0062] In an embodiment of the present disclosure, cysteamine hydrochloride may be substantially essential for forming a hexagonal-phase-containing iridium-nickel oxide.

[0063] Among the iridium precursor and nickel precursor in the embodiments of the present disclosure, the number of moles of iridium in the iridium precursor can be greater than the number of moles of nickel in the nickel precursor. Specifically, the iridium precursor and the nickel precursor can have an iridium:nickel molar ratio of 1.1:1 to 3:1, 1.3:1 to 3:1, 1.5:1 to 3:1, 1.7:1 to 3:1, or 2:1 to 3:1, and can be, for example, 2:1 to 3:1. When the iridium:nickel molar ratio is about 1:1 or the number of moles of nickel is greater than the number of moles of iridium, impurities in the form of nickel oxide without iridium are synthesized. Therefore, the number of moles of iridium can be greater than the number of moles of nickel, or the iridium:nickel molar ratio can be limited within the above range.

[0064] In an embodiment of the present disclosure, the mixture can be prepared in an aqueous solution containing sodium nitrate (NaNO 3 ), and thus, it can be characterized in that the mixture is not affected by the surrounding gas environment during heat treatment.

[0065] In an embodiment of the present disclosure, the ground product can be fired at a temperature of 450 °C to 650 °C, 500 °C to 650 °C, or 550 °C to 650 °C, and can be fired at a temperature of, for example, 550 °C to 650 °C.

[0066] In an embodiment of the present disclosure, when firing the ground product, the temperature of the ground product can be raised to a target temperature of 450 °C to 650 °C at a heating rate of 10 °C / minute, and then the target temperature can be maintained for 30 minutes to 2 hours. Preferably, the target temperature can be 550 °C to 650 °C, and the holding time can be about 1 hour.

[0067] Another embodiment of the present disclosure relates to a membrane electrode assembly (MEA), which includes a positive electrode, a negative electrode, and an electrolyte membrane. The electrolyte membrane contains a water electrolysis catalyst and is interposed between the positive electrode and the negative electrode.

[0068] In an embodiment of the present disclosure, the MEA can include a polymer electrolyte membrane configured to conduct protons, and a positive electrode (i.e., an air electrode) and a negative electrode (i.e., a fuel electrode) applied to two surfaces of the electrolyte membrane, such that hydrogen and oxygen can react.

[0069] In an embodiment of the present disclosure, water supplied to the negative electrode is separated into oxygen, protons, and electrons. The protons can migrate through the membrane to the positive electrode (which is a reduction electrode), and the electrons can move to the positive electrode through an external circuit and a power source. At the positive electrode, the protons and electrons can react together to produce hydrogen.

[0070] In an embodiment of the present disclosure, the electrolyte membrane can include a water electrolysis catalyst substantially the same as the above-mentioned water electrolysis catalyst, and thus its detailed description will be omitted because it is considered unnecessary.

[0071] In an embodiment of the present disclosure, at least one surface of the electrolyte membrane may be coated with a water electrolysis catalyst, but is not limited thereto.

[0072] In an embodiment of the present disclosure, a porous transport layer (PTL) or a gas diffusion layer (GDL) and an additional gasket may be stacked outside the MEA where the negative electrode and the positive electrode are located, respectively, but the embodiments of the present disclosure are not limited thereto. A separator or a bipolar plate (including a flow field through which reactants or products flow, or a structure that can replace the flow field) may be connected to the outer surface of the PTL or GDL, but the embodiments of the present disclosure are not limited thereto.

[0073] In the case of polymer electrolyte membrane water electrolysis, since the negative electrode maintains a high voltage of 1.7V or more for water decomposition, corrosion of the GDL formed of carbon may occur, and as a result, the PTL formed of corrosion-resistant titanium may be mainly stacked on the negative electrode. The fuel cell is designed so that there is no corrosion reaction of carbon at the negative electrode under normal operating conditions, and therefore the GDL can be stacked on the negative electrode, but when a problem occurs in the hydrogen supply or under transient or continuous high voltage conditions, corrosion of this carbon material may occur. The catalyst material of the embodiment of the present disclosure has excellent catalytic activity and durability, and when the catalyst material is applied to a water electrolysis cell or a fuel cell, the above-mentioned corrosion or abnormal operation can be prevented.

[0074] The membrane electrode assembly in the embodiment of the present disclosure may be a membrane electrode assembly for a fuel cell.

[0075] Hereinafter, other embodiments of the present disclosure will be described in more detail through the following preparation examples and test examples. The following preparation examples and test examples are only used to exemplarily describe the embodiments of the present disclosure and are not intended to limit the scope and spirit of the present invention.

[0076] Preparation Example: Synthesis of Catalyst

[0077] 667 mg of iridium precursor (IrCl 3 ·xH 2 O), 265 mg of nickel precursor (NiCl 2 6H 2 O), 20 g of sodium nitrate (NaNO 3 ) and 500 mg of cysteamine hydrochloride dissolved in 300 mL of distilled water was stirred at 90° C. for 2 hours and then dried in an oven at 80° C.

[0078] The obtained dry powder was finely ground and then fired in a tube furnace. The temperature of the tube furnace was increased to the target firing temperatures of 400 °C, 500 °C, 600 °C, and 700 °C at a rate of 10 °C / min, and then the tube furnace was maintained at each target firing temperature for 1 hour. Thereafter, the salts remaining in the fired catalyst were removed using distilled water.

[0079] The control group was set as the catalyst fired without mixing the nickel precursor.

[0080] The crystal structures of the catalysts according to the control group, Example 1 (obtained at a firing temperature of 600 °C), Comparative Example 1 (obtained at a firing temperature of 400 °C), Comparative Example 2 (obtained at a firing temperature of 500 °C), and Comparative Example 3 (obtained at a firing temperature of 700 °C) were analyzed using peak area analysis based on X-ray diffraction (XRD), and the analysis results are shown in Table 1 and Figure 1 in.

[0081] Table 1

[0082]

[0083] Reference Figure 1 , it can be seen that rutile-phase iridium oxide (IrO x ) was synthesized in the control group. In the case of low-temperature firing, for example, in Comparative Example 1 where the firing temperature was 400 °C and in Comparative Example 2 where the firing temperature was 500 °C, it was determined that rutile-phase iridium oxide (IrO x ) [(110), (101), (200), and (211) crystal planes showed high intensity] and nickel oxide (nickel oxide) (NiO) [(111) and (200) crystal planes showed high intensity] were synthesized.

[0084] Meanwhile, in the case of Example 1 where the firing temperature was 600 °C, it was determined that hexagonal-phase iridium-nickel oxide (Ir 2 NiO x ) representing new peaks began to be synthesized at the positions of diffraction angles 2θ of 19.0°, 33.7°, 35.8°, and 47°, and the existing rutile phase began to disappear.

[0085] Furthermore, in the case of Comparative Example 3 where the firing temperature was 700 °C, it was determined that rutile-phase iridium oxide (IrO x ) was not present at all, and iridium-nickel oxide (Ir 2 NiO x ) with a complete hexagonal crystal system was synthesized.

[0086] Test Example 1: Evaluation of the Appearance of Catalyst Particles

[0087] The results of the catalyst particles of the control group, Comparative Example 2, Example 1, and Comparative Example 3 observed using a transmission electron microscope (TEM) are shown in Figures 2 to 5 .

[0088] Refer to Figure 2 , it can be determined that in the control group without adding nickel, IrO in the form of thin nanoneedles is formed 2 .

[0089] Refer to Figure 3 , it can be determined that in Comparative Example 2 where the firing temperature is 500 °C, like the control group, IrO in the form of thin nanoneedles is formed 2 , and this is consistent with the detection of the rutile phase IrO Figure 1 peak in the XRD pattern of x .

[0090] Refer to Figure 4 , it can be determined that in Example 1 where the firing temperature is 600 °C, the hexagonal phase, that is, the hexagonal plate-like structure, begins to form, and this is consistent with the onset of the hexagonal phase peak in the XRD pattern of Figure 1 . More specifically, in Example 1, it can be determined that IrO in the form of nanoneedles 2 (represented by circles) remains on the surface of the hexagonal plate-like structure, and this indicates the coexistence of the hexagonal phase and the rutile phase.

[0091] Refer to Figure 5 , it can be determined that in Comparative Example 3 where the firing temperature is 700 °C, the hexagonal plate-like structure appears more clearly, and IrO in the form of nanoneedles is no longer observed 2 . This is consistent with the result that no rutile peak is observed and only a new peak (i.e., the hexagonal phase peak) is observed in the XRD pattern of Figure 1 .

[0092] Test Example 2: Evaluation of catalytic activity using a three-electrode system

[0093] By using a 1 M sulfuric acid (H 2 SO 4 ) solution as the electrolyte and applying the catalyst to a glassy carbon rotating disk electrode (RDE), a three-electrode system was used to evaluate the activity of the catalyst synthesized in the preparation examples. A Pt coil was used as the counter electrode, and an RHE electrode was used as the reference electrode, and the current density of the catalyst was measured using linear sweep voltammetry (LSV) (without iR compensation) at a voltage of 1.2 V to 1.75 V and a scan rate of 10 mV / s. The measurement results are shown in Figure 6 .

[0094] Refer toFigure 6 , it can be determined that the performance of the catalyst with added nickel is superior to that of the catalyst in the control group without added nickel. Specifically, it can be determined that the performance of the catalyst of Example 1 is significantly superior to that of the catalyst of Comparative Example 2, and the performance of the catalyst in Comparative Example 3, which is completely transformed into the hexagonal phase, decreases rapidly.

[0095] That is, the catalyst of Example 1 (at the moment when the phase transition from the rutile phase to the hexagonal phase occurs) exhibits the best performance.

[0096] Test Example 3: Evaluation of the water electrolysis performance of the membrane electrode assembly

[0097] The performance of the catalyst was evaluated under the conditions of a membrane electrode assembly (MEA) as an actual water electrolysis device.

[0098] The control group was set as a membrane electrode assembly using a catalyst synthesized by the same method as in the above Preparation Example without using a nickel precursor and cysteamine hydrochloride.

[0099] The manufacturing method and cell test method for each of the membrane electrode assemblies including the respective catalysts are as follows.

[0100] To evaluate the membrane electrode assembly, the catalyst synthesized in the Preparation Example was coated on the membrane, and Nafion 212 was used as the membrane. The catalyst was directly coated on the membrane by spraying with a spray gun (Infinity, Harder & Steenbeck). Ir 2 NiO x was coated as the oxidation electrode catalyst at 1.0 mg catalyst / cm 2 and 40 wt% Pt / C was coated as the reduction electrode catalyst at 0.1 mg Pt / cm 2 . As the diffusion layer, Ti felt was used for the oxidation electrode and carbon paper was used for the reduction electrode. When assembling the membrane electrode assembly, hot pressing was not used, and a pressure of 80 kgf cm was applied when fixing the membrane electrode assembly into a single cell. Distilled water was made to flow to the oxidation electrode at 10 mL / min. The temperature of the cell and distilled water was maintained at 80 °C.

[0101] The activity of the catalyst was evaluated by measuring the average voltage of the catalyst for 3 minutes at a specific current density from 0 A / cm 2 to 2 A / cm 2 , and the results are shown in Figure 7 .

[0102] Reference Figure 7, it can be determined that the membrane electrode assembly including the catalyst of Example 1 (where the hexagonal phase starts to form) exhibits the best activity, and this is consistent with the best performance of the catalyst of Example 1 in the three-electrode system confirmed in Test Example 2.

[0103] In addition, the durability of the membrane electrode assembly was evaluated by measuring the voltage change for 90 hours at a current density of 1 A / cm 2 , and the results are shown in Figure 8 .

[0104] Reference Figure 8 shows that it can be determined that the durability of the membrane electrode assembly including the catalyst of Example 1 fired at 600 °C is the best compared to the control group.

[0105] It is obvious from the above description that, compared with conventional catalysts including iridium oxide, the water electrolysis catalyst including iridium-nickel oxide according to the embodiments of the present disclosure may have excellent activity and durability and reduced iridium usage, and thus is very useful.

[0106] The method for preparing the catalyst according to the embodiments of the present disclosure can achieve the nanoparticle structure of the catalyst while finely adjusting the nanoparticle structure, which is difficult to achieve using the molten salt synthesis method, and this preparation method is advantageous in preparing the catalyst according to the embodiments of the present disclosure including iridium oxide having a nanoneedle structure and iridium-nickel oxide having a hexagonal plate-like structure.

[0107] The effects of the embodiments of the present disclosure are not limited to the above effects. The effects of the embodiments of the present disclosure should be understood to include all effects that can be inferred from the above description.

[0108] The embodiments have been described in detail with reference to the preferred embodiments of the present invention. However, those skilled in the art will understand that changes can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined in the appended claims and their equivalents.

Claims

1. A water electrolysis catalyst comprising: Iridium oxide containing rutile phase; as well as Iridium-nickel oxide containing a hexagonal phase.

2. The water electrolysis catalyst according to claim 1, wherein The iridium oxide includes a peak of at least one crystal plane selected from the group consisting of (110), (101), (200), and (211) crystal planes based on an analysis of X-ray diffraction.

3. The water electrolysis catalyst according to claim 1, wherein The iridium-nickel oxide includes at least one peak of a diffraction angle 2θ selected from the group consisting of 18° to 20°, 33.0° to 34.5°, 35.0° to 37.0°, and 46° to 48° based on an analysis of X-ray diffraction.

4. The water electrolysis catalyst according to claim 1, wherein The iridium oxide has a nano needle structure; and The iridium-nickel oxide has a hexagonal plate structure.

5. The water electrolysis catalyst according to claim 4, wherein The iridium oxide having a nanoneedle structure is located on a portion of a surface of the iridium-nickel oxide having a hexagonal plate structure.

6. The water electrolysis catalyst according to claim 4, wherein The iridium oxide having the nanoneedle structure is physically connected to a portion of the surface of the iridium-nickel oxide having the hexagonal plate structure.

7. A method for preparing a water electrolysis catalyst, the method comprising: preparing a mixture comprising an iridium precursor, a nickel precursor, and cysteamine hydrochloride; drying the mixture; Grind the dry mixture; as well as Firing of ground products; and Wherein, the water electrolysis catalyst comprises: Iridium oxide containing a rutile phase; and Iridium-nickel oxide containing a hexagonal phase.

8. The method according to claim 7, wherein: The iridium precursor includes at least one component selected from the group consisting of IrCl3, IrCl3·xH2O, K2IrCl6 and K2IrCl6·xH2O.

9. The method according to claim 7, wherein: The nickel precursor includes at least one component selected from the group consisting of nickel sulfate, nickel chloride, nickel bromide, nickel acetylacetonate, nickel cyclohexanebutyrate, nickel ethylhexanoate, and nickel octanoate.

10. The method according to claim 7, wherein: The iridium precursor and the nickel precursor are configured such that the number of moles of iridium is greater than the number of moles of nickel.

11. The method according to claim 7, wherein: The iridium precursor and the nickel precursor are configured such that a molar ratio of iridium:nickel is 1.1:1 to 3:

1.

12. The method according to claim 7, wherein: The preparation of the mixture is carried out in an aqueous solution containing sodium nitrate.

13. The method according to claim 7, wherein: Firing the ground product is performed at a temperature of 450°C to 650°C.

14. The method according to claim 7, wherein: When the ground product is fired, the temperature of the ground product is increased to a target temperature of 450° C. to 650° C. at a heating rate of 10° C. / min, and then the target temperature is maintained for 30 minutes to 2 hours.

15. A membrane electrode assembly comprising: positive electrode; negative electrode; as well as An electrolyte membrane is interposed between the positive electrode and the negative electrode and contains a water electrolysis catalyst, wherein the water electrolysis catalyst includes an iridium oxide containing a rutile phase and an iridium-nickel oxide containing a hexagonal phase.

16. The membrane electrode assembly according to claim 15, wherein: The iridium oxide includes a peak of at least one crystal plane selected from the group consisting of (110), (101), (200), and (211) crystal planes based on an analysis of X-ray diffraction.

17. The membrane electrode assembly according to claim 15, wherein: The iridium-nickel oxide includes at least one peak of a diffraction angle 2θ selected from the group consisting of 18° to 20°, 33.0° to 34.5°, 35.0° to 37.0°, and 46° to 48° based on an analysis of X-ray diffraction.

18. The membrane electrode assembly according to claim 15, wherein: The iridium oxide has a nano needle structure; and The iridium-nickel oxide has a hexagonal plate structure.

19. The membrane electrode assembly according to claim 18, wherein: The iridium oxide having a nanoneedle structure is located on a portion of a surface of the iridium-nickel oxide having a hexagonal plate structure.

20. The membrane electrode assembly according to claim 18, wherein: The iridium oxide having the nanoneedle structure is physically connected to a portion of the surface of the iridium-nickel oxide having the hexagonal plate structure.

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