ELECERODE COMPRISING TERNARY ALLOY CATALYST FOR WATER ELECTROLYSIS AND METHOD FOR PREPARING THE SAME

Description

DESCRIPTION OF GOVERNMENT-SPONSORED RESEARCH

This invention was carried out with the support of Ministry of Science and ICT under a research project of Unique Project identification number: 2710006542 and Project identification number: 00431630 titled “Development of high crystalline mesoporous carbon based catalyst and MEA for highly efficient and durable hydrogen fuel cells”, as part of the research project of “Development of Nanomaterial technology” managed by the National Research Foundation of Korea from Apr. 1 to Dec. 31, 2024.

This invention was carried out with the support of Ministry of Science and ICT under a research project of Unique Project identification number: 2710006319 and Project identification number: 00409901 titled “Development of low precious metal materials for PEM water electrolysis through structural and interfacial control”, as part of the research project of “Development of Nanomaterial technology” managed by the National Research Foundation of Korea from Apr. 1 to Dec. 31, 2024.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No. 10-2024-0157846, filed on Nov. 8, 2024, the entire contents of which are hereby incorporated by this reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present specification discloses an electrode including a ternary alloy catalyst for water electrolysis and a method for preparing the same.

Description of the Related Art

As a measure to mitigate global warming caused by the indiscriminate use of fossil fuels, extensive research has been conducted into the use of renewable energy along with hydrogen as a renewable energy carrier. However, since renewable energy sources such as wind and solar are intermittent and time-varying, a bottleneck occurs when producing electricity directly from such sources. Therefore, utilization needs to be increased by developing energy conversion systems connected to renewable energy. Various water electrolysis systems are being developed by converting hydrogen, which is clean energy, into energy in order to replace fossil energy. Compared to typical hydrogen production methods such as steam reforming, water electrolysis operates under relatively mild conditions and produces only hydrogen and oxygen without emitting pollutants. Further, when water electrolysis is driven by electricity produced from a renewable energy source, an environmentally friendly hydrogen production system can be constructed. In particular, proton exchange membrane water electrolysis (PEMWE) is recognized as a promising technology for producing green hydrogen without emitting pollutants, and shows a higher hydrogen production rate with higher purity than anion exchange membrane water electrolysis.

However, in consideration of the acidic operating environment of PEMWE, considerable challenges arise from the dependence on platinum group metals as electrode materials for water electrolysis. Specifically, platinum (Pt) is recognized as the most effective electrocatalyst for the hydrogen evolution reaction (HER), which is the key half-reaction in water electrolysis. However, the scarcity and high cost of platinum (Pt) increases the manufacturing costs of membrane electrode assemblies (MEAs), thereby ultimately hindering the scale-up and industrial commercialization of PEMWE. Therefore, the development of non-platinum (Pt)-based electrocatalysts and electrodes is essential for achieving low-cost water electrolysis. As an alternative to platinum (Pt), ruthenium (Ru) has recently been attracting attention as an electrocatalyst because its price is about 2.4-fold lower than that of platinum (Pt) (Pt: $973.9/oz, Ru: $400.0/oz). Further, since the hydrogen bond strength of ruthenium (Ru) (65 kcal/mol) is similar to that of platinum (Pt) (62 kcal/mol), it is likely to exhibit similar reaction rates according to the Sabatier principle. However, pure ruthenium (Ru) has a problem in that the intrinsic HER performance thereof is lower than that of platinum (Pt). In addition, although electrodes for PEMWE in the related art have been manufactured by drop casting or spraying a catalyst powder, these methods are composed of multiple steps, and thus, have a disadvantage in that a relatively long manufacturing time is required and it is difficult to prepare atomically uniform thin films. Accordingly, there is a need for develop an electrode that exhibits excellent water electrolysis performance while replacing platinum (Pt) and a method for preparing the same with simplified preparation steps.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an electrode including a ternary alloy catalyst for water electrolysis, which exhibits excellent water electrolysis performance and is prepared through simplified steps, and a method for preparing the same.

In one aspect, exemplary embodiments of the present invention provide an electrode catalyst for water electrolysis, including a ternary metal thin film of ruthenium-gold-molybdenum (Ru—Au—Mo) formed on a substrate.

In one aspect, exemplary embodiments of the present invention provide an electrode for water electrolysis, including the electrode catalyst for water electrolysis.

In one aspect, exemplary embodiments of the present invention provide a method for preparing the electrode catalyst for water electrolysis, the method including: forming a ternary metal thin film of ruthenium-gold-molybdenum (Ru—Au—Mo) on a substrate by co-sputtering.

According to exemplary embodiments of the present invention, an electrode catalyst exhibiting excellent water electrolysis performance by including a ternary metal which replaces platinum (Pt) can be provided, and a method for preparing the same can be provided, in which the preparation steps are simplified by co-sputtering.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating the thicknesses of catalysts according to an embodiment of the present invention.

FIGS. 2A, 2B, and 2C are microscopic images illustrating the shape of a catalyst according to an embodiment of the present invention.

FIG. 3 is a graph of catalyst components and contents obtained as a result of energy dispersive X-ray spectroscopy (EDS) of a catalyst according to an embodiment of the present invention.

FIG. 4 is a graph of the polarization curves of catalysts according to an embodiment of the present invention.

FIG. 5 is a graph illustrating the HER overpotential (η) at a current density of −10 mA/cm².

FIG. 6 is a Tafel plot corresponding to the polarization curves of catalysts according to an embodiment of the present invention.

FIG. 7 is a Nyquist plot of catalysts according to an embodiment of the present invention.

FIGS. 8A, 8B, 8C, and 8D are microscopic images illustrating the shape of a catalyst according to an embodiment of the present invention.

FIG. 9 is a graph of catalyst components and contents obtained as a result of energy dispersive X-ray spectroscopy (EDS) of a catalyst according to an embodiment of the present invention.

FIG. 10 is a graph illustrating the X-ray diffraction patterns of catalysts according to an embodiment of the present invention.

FIGS. 11A, and 11B are graphs illustrating X-ray photoelectron spectroscopy (XPS) profiles of catalysts according to an embodiment of the present invention.

FIG. 12 is a graph of the polarization curves of catalysts according to an embodiment of the present invention.

FIG. 13 is a graph illustrating the HER overpotential (η) at a current density of −10 mA/cm².

FIG. 14 is a graph illustrating the current-voltage (i-V) polarization curves of catalysts according to an embodiment of the present invention.

FIG. 15 is a graph illustrating the mass activity of the catalyst at a cell voltage of 1.8 V_cell in comparison with the Prior Literature.

DETAILED DESCRIPTION OF THE INVENTION

With respect to the terms used in the present specification, general terms currently and widely used are selected in consideration of function in the present invention, but the terms may vary according to an intention of a technician skilled in the art, a precedent, or the advent of a new technology, and the like. Further, in a specific case, there is also a term arbitrarily chosen by the applicant, and in this case, the meanings thereof will be described in detail in the corresponding part of the Detailed Description of the present invention. Accordingly, the term used in the present specification should not be defined merely as a simple name of the term, but should be defined based on the meaning of the term and overall content of the present invention.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person with ordinary skill in the art to which the present invention pertains. Generally understood terms should be interpreted as having the same meaning as they have in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless expressly defined in the present invention.

Numerical ranges are inclusive of the numerical values defined in the present invention. Every maximum numerical limitation given throughout the present specification includes all lower numerical limitations as if the lower numerical limitation were expressly written. Every minimum numerical limitation given throughout the present specification includes all higher numerical limitations as if the higher numerical limitation were expressly written. Any numerical limitation given throughout the present specification shall include all the better numerical ranges within the broader numerical range, as if the narrower numerical limitation were expressly written.

As used herein, the words “comprising,” “having,” “containing,” are inclusive or open-ended and do not exclude additional unrecited elements or method steps. As used herein, the term “or combinations thereof” refers to all permutations and combinations of items listed prior to the term. For example, “A, B, C, or combinations thereof” means A, B, C, AB, AC, BC or ABC, and it is intended to include at least one of BA, CA, CB, CBA, BCA, ACB, BAC or CAB where order is important in a particular context. With this example, combinations containing repetitions of one or more items or terms may be included, such as BB, AAA, MB, BBC, AAABCCCC, CBBAAA, CABABB, and the like. A person of ordinary skill in the art will understand that there is typically no limit to the number of items or terms in any combination, unless the context makes it clear otherwise.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to accompanying drawings. However, it is obvious that the present invention is not limited by the following embodiments.

Electrode Catalyst for Water Electrolysis and Electrode for Water Electrolysis, Including the Same

In one aspect, exemplary embodiments of the present invention provide an electrode catalyst for water electrolysis, including a ternary metal thin film of ruthenium-gold-molybdenum (Ru—Au—Mo) formed on a substrate.

The present inventors have discovered that the strong interaction between the ternary metals results in excellent performance compared to monometallic and bimetallic catalysts, thereby completing the present invention.

According to an embodiment of the present invention, the ternary metal is deposited on the substrate by co-sputtering. The co-sputtering is a technique for depositing multiple targets at the same time, and can sputter two or more targets at the same time, unlike typical sputtering which sputters and deposits one target.

According to an embodiment of the present invention, the ternary metal forms an alloy structure. Alloys exhibit unique electronic, catalytic and optical properties due to the synergistic effects induced by hetero-junction charge transfer from one metal to another. The present inventors have discovered that an alloy structure formed by the ternary metal contributes to improving the HER performance, thereby completing the present invention.

According to an embodiment of the present invention, the atomic concentration of the ruthenium (Ru) is 65 to 85 atomic % based on the total atomic concentration of the ternary metal. More specifically, the atomic concentration of the ruthenium (Ru) may be 65 atomic % or more, 70 atomic % or more, 75 atomic % or more, and 77.68 atomic % or more; 85 atomic % or less, 80 atomic % or less, and 77.68 atomic % or less, based on the total atomic concentration of the ternary metal, but is not limited thereto.

According to an embodiment of the present invention, the atomic concentration of the gold (Au) is 7 to 12 atomic % based on the total atomic concentration of the ternary metal. More specifically, the atomic concentration of the gold (Au) may be 7 atomic % or more, 7.5 atomic % or more, 8 atomic % or more, 8.5 atomic % or more, 9 atomic % or more, 9.5 atomic % or more, 10 atomic % or more, 10.5 atomic % or more, 11 atomic % or more, and 11.16 atomic % or more; 12 atomic % or less, 11.9 atomic % or less, 11.8 atomic % or less, 11.7 atomic % or less, 11.6 atomic % or less, 11.5 atomic % or less, 11.4 atomic % or less, 11.3 atomic % or less, 11.2 atomic % or less, and 11.16 atomic % or less, based on the total atomic concentration of the ternary metal, but is not limited thereto.

According to an embodiment of the present invention, the atomic concentration of the molybdenum (Mo) is 5 to 25 atomic % based on the total atomic concentration of the ternary metal. More specifically, the atomic concentration of the molybdenum (Mo) may be 5 atomic % or more, 6 atomic % or more, 7 atomic % or more, 8 atomic % or more, 9 atomic % or more, 10 atomic % or more, 11 atomic % or more, and 11.16 atomic % or more; 25 atomic % or less, 24 atomic % or less, 23 atomic % or less, 22 atomic % or less, 21 atomic % or less, 20 atomic % or less, 19 atomic % or less, 18 atomic % or less, 17 atomic % or less, 16 atomic % or less, 15 atomic % or less, 14 atomic % or less, 13 atomic % or less, 12 atomic % or less, and 11.16 atomic % or less, based on the total atomic concentration of the ternary metal, but is not limited thereto.

According to an embodiment of the present invention, the ternary metal thin film has a thickness of 50 to 500 nm. More specifically, the ternary metal thin film may have a thickness of 50 nm or more, 100 nm or more, 150 nm or more, and 200 nm or more; 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 200 nm or less, and 150 nm or less, but the thickness is not limited thereto.

According to an embodiment of the present invention, the substrate is a porous support or wafer.

The porous support may be a “porous transport layer (PTL)”, and the PTL refers to a porous conductive support used to effectively transfer and discharge reactant gases or water supplied to the electrodes and reactant gases and water generated from the electrodes. The PTL includes one or more of stainless steel, iron (Fe), magnesium (Mg), aluminum (Al), and titanium (Ti). The wafer is a disk-shaped substrate made by thinly slicing a single crystal pillar obtained by growing silicon (Si), gallium arsenide (GaAs), or the like. The composition of the wafer is Ti/Si or Ti/TiN/Si.

According to another embodiment of the present invention, provided is an electrode for water electrolysis, including the electrode catalyst for water electrolysis.

Method for Preparing Electrode Catalyst for Water Electrolysis

In one aspect, exemplary embodiments of the present invention provide a method for preparing the electrode catalyst for water electrolysis, the method including: forming a ternary metal thin film of ruthenium-gold-molybdenum (Ru—Au—Mo) on a substrate by co-sputtering.

Electrodes for PEMWE in the related art were prepared by drop-casting or spraying a catalyst powder through steps such as (1) nanoparticle catalyst synthesis, (2) mixing with an ionomer solution to prepare a catalyst slurry, and (3) loading the slurry onto a membrane or porous transport layer (PTL). As described above, methods for preparing an electrode for PEMWE in the related art have the disadvantages in that a relatively long preparation time is required because the method includes various steps, and it is difficult to prepare atomically uniform thin films.

Meanwhile, in contrast, a thin film deposition method such as sputtering, chemical vapor deposition and electrodeposition may prepare a catalyst layer directly on a substrate with a high coverage, and the thin film structure is effective in improving cell performance by increasing catalyst utilization. Since sputtering among these methods may form a thin film with high quality and reproducibility within a short process time, the step of preparing an electrode is simplified. Unlike typical porous transport electrode (PTE) preparation methods, sputtering does not require a polymer binder, and thus may improve electrical conductivity during water electrolysis. In addition, the thin film structure contributes to promoting the mass transfer of reactants and products. Furthermore, the sputtering method may easily expand the electrode area, and thus is suitable for water electrolysis to produce large amounts of hydrogen. Despite these advantages, the use of sputtering as a method for preparing an electrode for HER has not yet been extensively investigated.

The present inventors have discovered that a preparation method thereof with simplified preparation steps can be provided by co-sputtering, thereby completing the present invention. In particular, an atomically uniform alloy-based catalyst may be easily prepared using co-sputtering of multiple targets, and the atomic concentration of the alloy may be controlled by adjusting the sputtering power conditions. This one-port process also provides considerable advantages for the preparation of porous transport electrodes (PTEs) for PEMWE.

According to an embodiment of the present invention, the sputtering powers of the ruthenium (Ru), gold (Au), and molybdenum (Mo) are each individually adjusted. The inventors have discovered that the atomic composition of the electrode catalyst according to an embodiment of the present invention can be easily adjusted by controlling the sputtering power of each target, and that the activity of the ternary metal can also be adjusted through the sputtering power of each target, thereby completing the present invention.

According to an embodiment of the present invention, the sputtering power of the ruthenium (Ru) is 50 to 90 W. More specifically, the sputtering power of the ruthenium (Ru) may be 50 W or more, 55 W or more, 60 W or more, 65 W or more, and 70 W or more; 90 W or less, 85 W or less, 80 W or less, 75 W or less, and 70 W or less, but is not limited thereto.

According to an embodiment of the present invention, the sputtering power of the gold (Au) is 5 to 30 W. More specifically, the sputtering power of the gold (Au) may be 5 W or more, and 10 W or more; 30 W or less, 25 W or less, 20 W or less, 15 W or less, and 10 W or less, but is not limited thereto.

According to an embodiment of the present invention, the sputtering power of the molybdenum (Mo) is 20 to 50 W. More specifically, the sputtering power of the molybdenum (Mo) may be 20 W or more, 25 W or more, and 30 W or more; 50 W or less, 45 W or less, 40 W or less, 35 W or less, and 30 W or less, but is not limited thereto.

EXAMPLES

Hereinafter, the present invention will be described in detail through Examples. However, the following Examples are merely examples for helping a general understanding of the present invention, and the contents of the present invention are not limited to the following Examples.

<Preparation Example 1> Preparation of Electrode Catalyst for Water Electrolysis

Prior to sputtering deposition, a Ti foil was pretreated with 5 wt % of oxalic acid at 70° C. for 30 minutes to remove a native oxide layer. A pretreated Ti support was placed in a sputtering chamber and pressurized at 15 m Torr. Subsequently, a ternary metal thin film of ruthenium-gold-molybdenum (Ru—Au—Mo) was deposited on the Ti foil substrate using radio-frequency magnetron sputtering. The sputtering powers (P_metal) of the ruthenium (Ru), gold (Au), and molybdenum (Mo) were each individually adjusted. The sputtering area of the Ti foil was 1.5 cm², and the co-sputtering was performed for 1800 seconds.

<Preparation Example 2> Preparation of Electrode for Water Electrolysis

Further, a Ti PTL (Bekaert, 250 μm, porosity: 60%) was used as a PTL to manufacture a ruthenium-gold-molybdenum (Ru—Au—Mo) ternary metal-based porous transport electrode (PTE) for PEMWE. The Ti PTL was also treated using the same method as the Ti foil. The optimized sputtering conditions were applied to the pretreated Ti PTL with a surface area of 4 cm² to manufacture a ruthenium-gold-molybdenum (Ru—Au—Mo) ternary metal-based porous transport electrode (PTE).

<Experimental Example 1> Thickness Measurement of Monometallic Catalyst

Each element of ruthenium (Ru), gold (Au), and molybdenum (Mo) was deposited on a Ti/TiN/Si wafer by sputtering for 1800 seconds. The sputtering power (P_metal) for each target element was adjusted to 25, 45, 70, 80, 90, and 100 W for ruthenium (Ru), to 15, 20, 25, 45, and 60 W for gold (Au), and to 15, 25, 45, 60, 70, 90, and 110 W for molybdenum (Mo).

FIG. 1 is a graph illustrating the thicknesses of catalysts according to an embodiment of the present invention. From FIG. 1, it can be confirmed that the thickness of each element, ruthenium (Ru), gold (Au), and molybdenum (Mo), varies depending on the metal type and sputtering power (P_metal).

<Experimental Example 2> Shape Measurement of Monometallic Catalyst

Ruthenium (Ru) was deposited on a Ti/TiN/Si wafer by sputtering for 1800 seconds. The sputtering power (P_Ru) for ruthenium (Ru) was adjusted to 30, 70, and 90 W for ruthenium (Ru). For the shape of the catalyst, the morphology and cross-section thereof were measured using a scanning electron microscope (SEM, Inspect F50, ELECMI). FIGS. 2A to 2C are microscopic images illustrating the shape of a catalyst according to an embodiment of the present invention (30, 70, and 90 W, respectively).

From FIG. 2A to FIG. 2C, it can be confirmed that a ruthenium (Ru) thin film prepared at a sputtering power (P_Ru) of 30 W has a thickness of 97 nm, which increases to 250 nm at 90 W.

<Experimental Example 3> Composition Analysis of Bimetallic Catalyst

A bimetallic thin film of ruthenium-gold (Ru—Au) was prepared in the same manner as in Preparation Example 1, except that molybdenum (Mo) was not used. The sputtering power (P_metal) for each target element was fixed at 70 W for ruthenium (Ru) and adjusted to 0, 10, 30, and 50 W for gold (Au). The composition of the catalyst was analyzed by energy-dispersive X-ray spectroscopy (EDS) (Talos F200X, Thermo Scientific, USA). FIG. 3 is a graph of catalyst components and contents obtained as a result of energy dispersive X-ray spectroscopy (EDS) of a catalyst according to an embodiment of the present invention.

From FIG. 3, it can be confirmed that in the bimetallic thin film of ruthenium-gold (Ru—Au), the atomic proportion of gold (Au) gradually increases as the sputtering power (P_Au) increases.

<Experimental Example 4> Evaluation of Electrochemical Characteristics of Bimetallic Catalyst

A bimetallic thin film of ruthenium-gold (Ru—Au) was prepared in the same manner as in Preparation Example 1, except that molybdenum (Mo) was not used. The sputtering power (P_metal) for each target element was fixed at 70 W for ruthenium (Ru) and adjusted to 0, 10, 30, and 50 W for gold (Au).

The electrochemical characteristics of the thin film electrode catalyst were measured in a 1.0 M H₂SO₄ acidic solution. The electrode catalyst was used as a working electrode with an active area of 0.264 cm². The counter electrode and the reference electrode were a Pt wire and Ag/AgCl (KCl-saturated), respectively. Cyclic voltammetry (CV) was performed to measure the HER performance of the electrode catalyst in a potential range from the open circuit potential to −0.4 V vs. Ag/AgCl at a scan rate of 5 mV/s. The Nyquist plot of the electrode catalyst was obtained by potentiostatic electrochemical impedance spectroscopy (PEIS) at −75 mV in a frequency range of 100 mHz to 100 kHz. The potentials obtained by all measurements were converted to the reversible hydrogen electrode (RHE) scale.

FIG. 4 is a graph of the polarization curves of catalysts according to an embodiment of the present invention. FIG. 5 is a graph illustrating the HER overpotential (η) at a current density of −10 mA/cm². FIG. 6 is a Tafel plot corresponding to the polarization curves of catalysts according to an embodiment of the present invention. FIG. 7 is a Nyquist plot of catalysts according to an embodiment of the present invention. Here, # in RuAu # represents the sputtering power (P_Au) in watts.

From FIG. 4, it can be confirmed that RuAu10 with a sputtering power (P_Au) of 10 W has the maximum HER performance compared to pure ruthenium (Ru) and other samples. From FIG. 5, it can be confirmed that the overpotential (η) of pure ruthenium (Ru) is 84.5 mV, and the HER overpotential (η) decreases when the sputtering power (P_Au) is 10 W. However, it can be confirmed that as the sputtering power (P_Au) increases further, the overpotential (η) also increases, reaching 85.0 mV in the case of RuAu50. Although gold (Au) has good electrical conductivity, the HER performance of the bimetallic electrode catalyst of ruthenium-gold (Ru—Au) may deteriorate due to the weak hydrogen adsorption characteristics of gold (Au).

From FIG. 6, it can be seen that the Tafel slopes of the pure ruthenium (Ru) and the bimetallic electrode catalysts of ruthenium-gold (Ru—Au) were in a range of 60 to 70 mV/dec, and the HER proceeded via the Volmer-Heyrovsky mechanism. In addition, RuAu10 with a sputtering power (P_Au) of 10 W exhibited a Tafel slope of 61.9 mV/dec, indicating that it had a faster reaction rate for HER among the electrode catalysts. From FIG. 7, it can be confirmed that among the electrode catalysts with a sputtering power (P_Au) of 10 W, the reaction rate for HER is faster.

Based on these results, RuAu10, prepared with a ruthenium (Ru) sputtering power (P_Ru) of 70 W and a gold (Au) sputtering power (P_Au) of 10 W, was adopted as the optimal bimetallic electrode catalyst in subsequent experiments.

<Experimental Example 5> Shape Measurement of Trimetallic Catalyst

A trimetallic thin film of ruthenium-gold-molybdenum (Ru—Au—Mo) prepared in Preparation Example 1 was prepared. The sputtering power (P_metal) for each target element was fixed at 70 W for ruthenium (Ru), fixed at 10 W for gold (Au), and adjusted to 0, 20, 30, and 110 W for molybdenum (Mo). For the shape of the catalyst, the morphology thereof was measured using a scanning electron microscope (SEM, Inspect F50, ELECMI). FIGS. 8A to 8D are microscopic images illustrating the shape of a catalyst according to an embodiment of the present invention (0, 20, 30, and 110 W, respectively).

From FIGS. 8A to 8D, it can be confirmed that the surfaces of the trimetallic thin films of ruthenium-gold-molybdenum (Ru—Au—Mo) are somewhat rough and all show similar morphologies regardless of the sputtering power (P_Mo).

<Experimental Example 6> Composition Analysis of Trimetallic Catalyst

A trimetallic thin film of ruthenium-gold-molybdenum (Ru—Au—Mo) prepared in Preparation Example 1 was prepared. The sputtering power (P_metal) for each target element was fixed at 70 W for ruthenium (Ru), fixed at 10 W for gold (Au), and adjusted to 0, 20, 30, 50, 60, 70, 90, and 110 W for molybdenum (Mo). The composition of the catalyst was analyzed by energy-dispersive X-ray spectroscopy (EDS) (Talos F200X, Thermo Scientific, USA). FIG. 9 is a graph of catalyst components and contents obtained as a result of energy dispersive X-ray spectroscopy (EDS) of a catalyst according to an embodiment of the present invention. Here, # in RuAuMo # represents the sputtering power (P_Mo) in watts.

TABLE 1
	Gold (Au)	Molybdenum (Mo)	Ruthenium (Ru)
PMo/W	(%)	(%)	(%)

0	10.44	0	89.56
20	11.48	5.02	83.5
30	11.16	11.16	77.68
50	7.2	23.32	69.48
60	6.91	29.67	63.42
70	6.6	35.28	58.12
90	5.97	43.92	50.11
110	5.3	50.1	44.6

From FIG. 9, it was found that in the trimetallic thin film of ruthenium-gold-molybdenum (Ru—Au—Mo), as the sputtering power (P_Mo) increases, the atomic proportion of molybdenum (Mo) increases and the atomic proportion of ruthenium (Ru) decreases. This trade-off relationship between ruthenium (Ru) and molybdenum (Mo) concentrations may be attributed to their similar deposition trends as a function of sputtering time. Conversely, in the trimetallic thin film of ruthenium-gold-molybdenum (Ru—Au—Mo), the composition of gold (Au) atoms is maintained in a range of 6 to 12%, so that it can be confirmed that it is least affected by the sputtering power (P_Mo).

<Experimental Example 7> Crystal Structure Analysis of Trimetallic Catalyst

A trimetallic thin film of ruthenium-gold-molybdenum (Ru—Au—Mo) prepared in Preparation Example 1 was prepared. The crystal structure of the catalyst was analyzed using grazing incidence X-ray diffraction (GIXRD, D8 Advance, Bruker). FIG. 10 is a graph illustrating the X-ray diffraction patterns of catalysts according to an embodiment of the present invention.

From FIG. 10, in the case of a pure ruthenium (Ru) thin film, the Ru (100), Ru (002), and Ru (101) peaks were detected at 38.3°, 42.1°, and 44.1°, respectively. The broad peak observed for ruthenium (Ru) may be attributed to random growth that produces small particles of ruthenium (Ru) through sputtering. As the sputtering power (P_Mo) increased, the intensity of these ruthenium (Ru) peaks gradually decreased and a new peak appeared at 41.3°, which shifted slightly to 40.4°. Such a peak shift in the XRD pattern may be expected to originate from the formation of an alloy structure in the trimetallic thin film of ruthenium-gold-molybdenum (Ru—Au—Mo). In particular, in the RuAu10Mo110 sample, in which the atomic proportion of molybdenum (Mo) is 44.8 atomic %, the Ru (100), Ru (002), and Ru (101) peaks became negligible, whereas the peaks corresponding to metallic molybdenum (Mo) became clear.

<Experimental Example 8> Electronic Structure Analysis of Trimetallic Catalyst

A trimetallic thin film of ruthenium-gold-molybdenum (Ru—Au—Mo) prepared in Preparation Example 1 was prepared. The electronic structure of the catalyst was analyzed using X-ray photoelectron spectroscopy (XPS, PHI 5000 Versa Probe, ULVAC-PHI). FIG. 11 is a set of graphs illustrating X-ray photoelectron spectroscopy (XPS) profiles of catalysts according to an embodiment of the present invention. More specifically, FIGS. 11A and 11B are graphs illustrating the Ru 3p spectrum and the Au 4f spectrum, respectively, of a catalyst according to an embodiment of the present invention.

From FIG. 11A, it can be confirmed that the Ru 3p_1/2 and 3p_3/2 spectra of the bimetallic thin film of RuAu10 and the trimetallic thin film of RuAu10Mo # were separated into three peaks corresponding to the Ru⁰ peak and two Ru satellite peaks. Compared with metallic Ru (461.2 eV), the Ru⁰ peak of RuAu10 shifts to a higher binding energy, indicating that there is an electronic interaction between ruthenium (Ru) and gold (Au). This peak shift is due to electron transfer from ruthenium (Ru) to gold (Au) along with the formation of a ruthenium-gold (Ru—Au) alloy. In addition, the Ru⁰ peak of the trimetallic thin film of RuAu10Mo # shifted slightly in the negative direction compared to RuAu10.

From FIG. 11B, it can be confirmed that both the bimetallic thin film of RuAu10 and the trimetallic thin film of RuAu10Mo # exhibit an Au 4f peak shift compared to metallic Au (84.0 eV). This confirms that the co-sputtering of Ru, Au, and Mo forms an alloy structure. Interestingly, in terms of electronegativity, a positive peak shift for Au 4f was observed in all samples, despite the higher electronegativity of Au (EN: 2.54) than Ru (EN: 2.20) and Mo (EN: 2.16). This shift may be attributed to a small fraction of gold (Au) analyzed by energy dispersive X-ray spectroscopy (EDS), which led to a decrease in the electron density of gold (Au) in the RuAu10Mo # deposit.

As a result of XRD and XPS analysis, it was revealed that the sputtering method was suitable for preparing Ru, Au, and Mo alloy structures.

<Experimental Example 9> Evaluation of Electrochemical Characteristics of Trimetallic Catalyst

A trimetallic thin film of ruthenium-gold-molybdenum (Ru—Au—Mo) prepared in Preparation Example 1 was prepared. The sputtering power (P_metal) for each target element was fixed at 70 W for ruthenium (Ru), fixed at 10 W for gold (Au), and adjusted to 0, 20, 30, 70, and 110 W for molybdenum (Mo).

The electrochemical characteristics of the thin film electrode catalyst were measured in a 1.0 M H₂SO₄ acidic solution. The electrode catalyst was used as a working electrode with an active area of 0.264 cm². The counter electrode and the reference electrode were a Pt wire and Ag/AgCl (KCl-saturated), respectively. Cyclic voltammetry (CV) was performed to measure the HER performance of the electrode catalyst in a potential range from the open circuit potential to −0.4 V vs. Ag/AgCl at a scan rate of 5 mV/s. The potentials obtained by all measurements were converted to the reversible hydrogen electrode (RHE) scale.

FIG. 12 is a graph of the polarization curves of catalysts according to an embodiment of the present invention. FIG. 13 is a graph illustrating the HER overpotential (η) at a current density of −10 mA/cm². Here, the dashed line represents the overpotential (η) for Pt^[48] ([48] J N Hansen, H Prats, K K Toudahl, N M Secher, K Cahn, J Kibsgaard, ACS energy letters, 2021, 6, 1175-1180.)

From FIG. 12, it can be confirmed that bimetallic RuAu and trimetallic RuAuMo electrocatalysts have better HER activity than monometallic ruthenium (Ru) in an acidic medium. From this, it can be seen that an alloy structure containing various elements contributes to improving the HER performance. From FIG. 13, it can be confirmed that at a sputtering power (P_Au) of 30 W, the overpotential (η) is minimized to 50.4 mV, but as the sputtering power (P_Au) increases further, the activity deteriorates (for RuAu10Mo110, overpotential (η)=81.1 mV).

According to the images in FIGS. 8A to 8D, it can be seen that the surfaces of the trimetallic thin films of ruthenium-gold-molybdenum (Ru—Au—Mo) all showed similar morphologies regardless of the sputtering power (P_Mo), and therefore, the difference in HER activity is due to the composition and crystal structure of RuAuMo. According to the half-cell system results, the RuAu10Mo30 electrocatalyst showed the best HER performance due to easy charge transfer in an acidic medium, and was adopted as a reduction electrode (cathode) catalyst for PEMWE.

<Preparation Example 3> Preparation of Membrane Electrode Assembly for Water Electrolysis

A membrane electrode assembly (MEA) for proton exchange membrane water electrolysis (PEMWE) was prepared, which was composed of a reduction electrode (cathode), an oxidation electrode (anode), and a proton exchange membrane (PEM, N212, DuPont Co.) disposed in a zero-gap configuration between the two electrodes.

More specifically, the reduction electrode (cathode) was composed of a RuAuMo film deposited on the Ti PTL prepared in Preparation Example 2 by sputtering. For the oxidation electrode (anode), a catalyst slurry containing an iridium oxide (IrO₂) powder (Alfa Aesar, 99.9% metal-based), deionized water, a Nafion ionomer (Alfa Aesar, 5% Nafion®), and isopropanol was spray-coated onto the PEM. The loading amount of iridium oxide (IrO₂) was 1.0 mg/cm². A RuAuMo-based reduction electrode (cathode), an iridium oxide (IrO₂)-coated PEM, and a Ti PTL oxidation electrode (anode) were assembled by hot pressing for 2 minutes. The active area of the MEA was 1.0 cm².

<Experimental Example 10> Evaluation of Single Cell Performance

Proton exchange membrane water electrolysis (PEMWE) single cell tests were performed at 80° C. Deionized water was preheated to the same temperature and injected into the oxidation electrode (anode) side at a flow rate of 15 ml/min. Before investigating single cell performance, a single cell was electrochemically activated by performing chronoamperometry (CA) at 1.55 V for 30 minutes. After activation, the performance of the PEMWE cell was evaluated by measuring the current-voltage (i-V) polarization curves from the open circuit voltage to 2.2 V. In addition, potentiostatic electrochemical impedance spectroscopy (PEIS) measurements were performed at 1.5, 1.8 and 2.1 V, and a frequency range was 100 mHz to 100 kHz.

Metal loading amounts were analyzed using inductively coupled plasma mass spectrometry (ICP-MS, NexION 2000, Perkin Elmer). As a result of the inductively coupled plasma mass spectrometry (ICP-MS) analysis, the total amount of Ru, Au, and Mo loaded on the Ti PTL was 30.96 μg/cm² for RuAu10Mo30.

FIG. 14 is a graph illustrating the current-voltage (i-V) polarization curves of catalysts according to an embodiment of the present invention. FIG. 15 is a graph illustrating the mass activity of the catalyst at a cell voltage of 1.8 V_cell in comparison with the Prior Literature.

From FIG. 14, it can be confirmed that at a cell voltage of 1.8 V_cell, the RuAu10Mo30/Ti PTL reduction electrode (cathode) achieved a current density of 1.39 A/cm², exhibiting better PEMWE performance than the Ru/Ti PTL (0.93 A/cm²) and RuAu10/Ti PTL (1.20 A/cm²). Furthermore, from FIG. 15, it can be seen that the performance of trimetallic RuAuMo is competitive when compared to the values reported in the Prior Literature using Ru-based bimetallic catalysts.

PRIOR LITERATURE

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Although the exemplary embodiments of the present invention have been described above in conjunction with the preferred embodiments mentioned above, various modifications or variations can be made without departing from the spirit and scope of the invention. Therefore, it is intended that the appended claims cover all such modifications and variations as falling within the true spirit and scope of the present invention.