KR20210017265A - Electrode structures for electrochemical reaction, and systems including the same - Google Patents

Abstract

According to an embodiment of the present invention, provided is an electrode structure for an electrochemical reaction which can secure catalytic properties regardless of an electrode material. The electrode structure for an electrochemical reaction comprises: an electrode for an oxidation reaction; a catalyst layer coated on a surface of the electrode; and an intermediate layer disposed between the electrode and the catalyst layer, wherein the electrode is a first work function, and the intermediate layer has a second work function greater than the first work function.

Description

Electrochemical reaction electrode structure and electrochemical reaction system including the same {ELECTRODE STRUCTURES FOR ELECTROCHEMICAL REACTION, AND SYSTEMS INCLUDING THE SAME}

The present invention relates to an electrode structure for an electrochemical reaction and an electrochemical reaction system including the same, and more particularly, to an electrode structure including a catalyst layer used for a water oxidation reaction and an electrochemical reaction system including the same.

Recently, as a measure to solve environmental problems caused by depletion of carbon-based energy and emission of fuel gas, research on a method of storing energy by producing hydrogen and oxygen by water decomposition or obtaining energy through fuel cells has been actively conducted. It is going on. In these methods, an electrochemical reaction is used, and in order to increase the reaction rate, it is required to secure the performance of the catalyst. However, since the performance of the catalyst varies depending on the material of the electrode, it has been difficult to select an electrode material that does not degrade the performance of the catalyst while satisfying the durability, corrosion resistance, heat resistance, light weight, and cost of the electrode.

One of the technical problems to be achieved by the technical idea of the present invention is to provide an electrode structure for an electrochemical reaction and an electrochemical reaction system including the same, in which catalytic properties can be secured regardless of the electrode material.

An electrode structure for an electrochemical reaction according to an embodiment of the present invention includes an electrode for an oxidation reaction, a catalyst layer coated on a surface of the electrode, and an intermediate layer disposed between the electrode and the catalyst layer, wherein the electrode is It has one work function, and the intermediate layer has a second work function that is greater than the first work function.

An electrochemical reaction system according to an embodiment of the present invention includes a reactor including an electrolyte containing water, first and second electrodes in which at least a portion is immersed in the electrolyte, and coated on the surface of the first electrode, and A catalyst layer containing an oxide, an intermediate layer disposed between the first electrode and the catalyst layer and having a work function greater than that of the first electrode, and an electrical signal to the first and second electrodes so that water is oxidized to generate hydrogen It includes a power supply for applying.

By introducing an intermediate layer between the electrode and the catalyst layer, an electrode structure for an electrochemical reaction and an electrochemical reaction system including the same can be provided in which catalytic properties can be secured regardless of the electrode material.

Various and beneficial advantages and effects of the present invention are not limited to the above-described contents, and may be more easily understood in the course of describing specific embodiments of the present invention.

1 is a schematic diagram of a water decomposition system including an electrode structure for an electrochemical reaction according to an embodiment of the present invention.
2 is a schematic diagram showing an electrode structure for an electrochemical reaction according to an embodiment of the present invention.
3A and 3B are graphs showing catalyst characteristics of a catalyst layer according to an electrode material.
4A and 4B are energy band diagrams for an electrode structure.
5 is a current-voltage graph showing catalyst characteristics of a catalyst layer according to an intermediate layer material in an electrode structure according to an embodiment of the present invention.
6 is a current-voltage graph showing catalyst characteristics of a catalyst layer according to an intermediate layer thickness in an electrode structure according to an embodiment of the present invention.
7A to 7C are diagrams showing catalytic properties of a catalyst layer according to an intermediate layer material in an electrode structure according to an exemplary embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

The embodiments of the present invention may be modified into various different forms or a combination of various embodiments, and the scope of the present invention is not limited to the embodiments described below. In addition, embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the art. Accordingly, the shapes and sizes of elements in the drawings may be exaggerated for clearer explanation, and elements indicated by the same reference numerals in the drawings are the same elements.

Electrochemical reaction system and electrode structure for electrochemical reaction

1 is a schematic diagram of a water decomposition system including an electrode structure for an electrochemical reaction according to an embodiment of the present invention.

Referring to FIG. 1, the water decomposition system 100 may include an electrolytic cell 110, an aqueous electrolyte solution 120, a first electrode structure ES, and a second electrode 140. . The first electrode structure ES and the second electrode 140 may be connected by the power supply unit 180. According to embodiments, the water decomposition system 100 may further include a membrane made of an ion-permeable material by dividing the first electrode structure ES and the second electrode 140. In addition, according to embodiments, the water cracking system 100 may further include a product collecting unit. The water decomposition system 100 may be a system for generating oxygen and hydrogen by decomposing water in the aqueous electrolyte solution 120.

The first electrode structure ES includes a first electrode 130, a catalyst layer 150 coated on at least one surface of the first electrode 130, and between the first electrode 130 and the catalyst layer 150. It may include an intermediate layer 160 disposed in the. The first electrode 130 may be an oxidation electrode, and the second electrode 140 may be a reduction electrode. Each of the first and second electrodes 130 and 140 may be made of a conductive material such as a semiconductor or a metal. The first and second electrodes 130 and 140 are, for example, fluorine-doped tin oxide (FTO), cobalt (Co), copper (Cu), nickel (Ni), iron (Fe), iridium (Ir), At least one of ruthenium (Ru), palladium (Pd), gold (Au), platinum (Pt), titanium (Ti), zirconium (Zr), rhodium (Rh), chromium (Cr), and stainless steel It may include.

The catalyst layer 150 may include a catalyst material that promotes the water oxidation reaction, for example, a metal oxide, and in particular, a p-type metal oxide. In particular, the catalyst layer 150 may include a transition metal oxide, for example, at least one oxide of cobalt (Co), copper (Cu), nickel (Ni), iron (Fe), and manganese (Mn). It may include. The catalyst layer 150 may include spherical or hexahedral metal oxide nanoparticles, and in this case, each of the nanoparticles may have a diameter of 60 nm or less. For example, the catalyst layer 150 may include manganese oxide (Mn ₃ O ₄ ) nanoparticles. However, the shape of the catalyst layer 150 is not limited to nanoparticles.

The intermediate layer 160 may be interposed between the first electrode 130 and the catalyst layer 150 in order to secure a function of a catalyst in an oxygen evolution reaction (OER). Specifically, the intermediate layer 160 may be involved in a charge transport process in an electrochemical reaction, so that the catalyst layer 150 may function as a catalyst without being influenced by the material of the first electrode 130. . This will be described in more detail below with reference to FIGS. 5 to 7C. The intermediate layer 160 is a coating layer coated on the surface of the first electrode 130 and may be a kind of electrode surface treatment layer, and may be a layer irrelevant to the improvement of catalytic activity. Since the intermediate layer 160 is a layer for improving charge transfer in relation to the catalyst layer 150, the intermediate layer 160 has lower catalytic performance than the catalyst layer 150, or unlike the catalyst layer 150, according to embodiments. It may be a layer that does not participate in the electrochemical reaction. The intermediate layer 160 may include a metallic material, for example, cobalt (Co), copper (Cu), nickel (Ni), iron (Fe), iridium (Ir), ruthenium (Ru), palladium (Pd). ), gold (Au), platinum (Pt), titanium (Ti), zirconium (Zr), and at least one of stainless steel. In particular, the intermediate layer 160 may be made of a material having a work function greater than that of the first electrode 130, and for example, the work function may be 4.8 eV or more.

The electrolyzer 110 accommodates the aqueous electrolyte solution 120, and may further include an inlet and an outlet such as an inlet pipe and a drain pipe.

The aqueous electrolyte solution 120 may serve as a source of water used for a water decomposition reaction and a receptor for protons generated during a water decomposition reaction. The aqueous electrolyte solution 120 may include at least one of potassium phosphate and sodium phosphate such as, for example, NaH ₂ PO ₄ , Na ₂ HPO ₄ , Na ₃ PO _4, or a mixture thereof. The pH of the aqueous electrolyte solution 120 may range from 2 to 14. In order to serve as a receptor for the proton, the aqueous electrolyte solution 120 may include a proton-accepting anion. Accordingly, even if the amount of protons (H ⁺ ) is increased as the water decomposition reaction proceeds, the proton-soluble anion accommodates at least some of these protons, thereby lowering the rate of decrease in pH of the aqueous electrolyte solution 120. The proton-soluble anion may include at least one of a phosphate ion, an acetate ion, a borate ion, and a fluoride ion.

When a voltage is applied between the first and second electrodes 130 and 140 by the power supply unit 180 in the water decomposition system 100, oxygen is generated in the first electrode 130 and the second electrode 140 Hydrogen is generated in the reaction. Each half reaction is represented by Schemes 1 and 2 as follows.

[Reaction Scheme _{1] 2H 2 O → O 2} + 4H + + 4e -

[Reaction Scheme ^{2] 4H + + 4e - →} 2H 2

The first electrode structure ES according to an embodiment of the present invention may be involved in an oxygen generation reaction (OER), which is an oxidation reaction in the first electrode 130 represented by Reaction Formula 1 above. Accordingly, the OER can be performed with a relatively low overpotential under the function of the stable catalyst layer 150.

As an electrochemical reaction system according to an embodiment of the present invention, a water decomposition system has been exemplarily described, but the present invention is not limited thereto, and the electrode structure according to an embodiment of the present invention is an oxidation reaction in various electrochemical reaction systems. It could be used for a dragon electrode.

Method of manufacturing electrode structure for electrochemical reaction

In the electrode structure for electrochemical reaction as shown in FIG. 1, cleaning the surface of the first electrode 130, coating the intermediate layer 160 on the surface of the first electrode 130, and on the intermediate layer 160 It may include the step of coating the catalyst layer 150.

The step of cleaning the surface of the first electrode 130 includes washing the surface of the first electrode 130 twice in the order of acetone, ethanol, and distilled water (DI water), and 0.5 M sulfuric acid (H ₂ SO _{4 ).} ) It may include the step of heat-treating for 1 hour at a temperature of 60 ℃ in the solution.

The step of coating the intermediate layer 160 on the surface of the first electrode 130 is, for example, a physical vapor deposition method such as thermal evaporation, electron beam evaporation, and sputtering. Vapor Deposition (PVD) or chemical vapor deposition (Chemical Vapor Deposition, CVD) can be used to form.

The coating of the catalyst layer 150 on the intermediate layer 160 includes synthesizing a material of the catalyst layer 150 and spin-coating the material of the catalyst layer 150, drop-casting, etc. It may include the step of coating by the method of, or preparing and applying in the form of a paste or ink.

In the step of synthesizing the material of the catalyst layer 150, when the catalyst layer 150 is a transition metal oxide in the form of nanoparticles, for example, preparing a first solution containing a transition metal ion supply material and a fatty acid surfactant , Preparing a second solution containing an alcohol surfactant, annealing the first and second solutions at a predetermined temperature, respectively, and adding the second solution to the first solution to obtain a transition metal oxide nanoparticle. It may be prepared by forming particles, and heat-treating the transition metal oxide nanoparticles at a predetermined temperature.

When the material of the catalyst layer 150 is prepared and applied in the form of a paste or ink, a paste or ink to be prepared may be prepared by adding a carbon conductor, and in this case, the mass ratio of carbon/transition metal oxide is 0.1 to 1.0. It can be a range.

Examples of electrode structures for electrochemical reactions

In the electrode structure (ES) of the embodiment, the intermediate layer 160 was deposited on the first electrode 130 by sputtering, and the catalyst layer 150 was synthesized by the above-described manufacturing method through a thermal decomposition method. After preparing nm manganese oxide (Mn ₃ O ₄ ) nanoparticles, they were washed twice with toluene and acetone. The nanoparticles were spin-coated on the intermediate layer 160 together with n-hexane. The spin coating was performed for a coating time of 10 seconds to 30 seconds at a rotation speed in the range of 1000 rpm to 4000 rpm, and the catalyst layer 150 was coated to a thickness of about 150 nm. The electrode structure was prepared by spin coating and heat treatment at a temperature of about 200 °C for 1 hour.

Catalytic properties in electrode structures for electrochemical reactions

2 is a schematic diagram showing an electrode structure for an electrochemical reaction according to an embodiment of the present invention.

Referring to FIG. 2, the first electrode structure ES may include a first electrode 130, an intermediate layer 160, and a catalyst layer 150 sequentially stacked. For example, the first electrode 130 has a thickness in the range of 0.1 mm to 4 mm, the intermediate layer 160 has a thickness in the range of 10 nm to 1 mm, and the catalyst layer 150 has a thickness of 50 nm to 500 nm. It may have a thickness in a range, but is not limited thereto.

Even when the oxidation reaction described above with reference to Figure 1, an electron (e ^-), generated as H ₂ O is oxidized to O ₂ at the surface of the catalyst layer 150, the interface between the electrolyte solution 120 and the catalyst layer 150 (① ), the inside of the catalyst layer 150 (②), and the charge transfer path along the interface (③) between the catalyst layer 150 and the first electrode 130. While studies on the catalyst properties of the catalyst layer 150 are focused on ① and ② above, studies on the interface of ③, which is an interface that is not exposed to the outside, have not been studied in terms of charge transfer.

According to an embodiment of the present invention, by inserting the intermediate layer 160 in consideration of the work function at the interface of ③, that is, the interface between the catalyst layer 150 and the first electrode 130, the mechanism of charge transfer at the interface is controlled. Thus, the function of the catalyst layer 150 can be secured, and accordingly, OER performance can be improved.

Hereinafter, with reference to the introduction of the intermediate layer according to an embodiment of the present invention, with reference to Figures 3a to 4b will be described the analysis of the catalyst characteristics according to the electrode material and the mechanism of charge transfer at the electrode structure interface.

3A and 3B are graphs showing catalyst characteristics of a catalyst layer according to an electrode material.

In FIGS. 3A and 3B, in order to examine the effect of the catalyst characteristics due to the interface of ③ of FIG. 2, the catalyst characteristics of the comparative example without the intermediate layer 160 in the first electrode structure ES of the present invention are shown. In the electrode structure of the comparative example, the catalyst layer 150 was prepared in the same manner as in the above-described embodiment, and was prepared by spin coating on the first electrode 130 instead of the intermediate layer 160. As the first electrode 130, FTO, nickel (Ni), stainless steel, copper (Cu), titanium (Ti), and zirconium (Zr) were used, respectively.

Referring to FIG. 3A, a current-voltage graph for the electrode structure of the comparative example is shown compared to a standard hydrogen electrode (NHE). As the potential reaching a specific current density is smaller, it can be determined that the catalyst properties are excellent, and as shown, the material of the first electrode 130 is FTO, nickel (Ni), stainless steel, copper (Cu), and titanium. In the case of (Ti) and zirconium (Zr), it was found that the catalyst properties were excellent in the above order.

Referring to FIG. 3B, an overpotential value for reaching an OER current density of 1 mA/cm ² in the electrode structure of the comparative example is shown together with the work function of the material of the first electrode 130. In the case of titanium (Ti), copper (Cu), and FTO having a work function of 4.8 eV or less, the overpotential tends to decrease as the work function increases. In the case of FTO, stainless steel, and nickel (Ni) having a work function of 4.8 eV or more, the overpotential did not decrease even when the work function increased, and a tendency to be almost constant, that is, saturated, was observed. From these results, it can be seen that when the work function of the material of the first electrode 130 is greater than or equal to a specific range, that is, greater than or equal to 4.8 eV, the catalyst properties are not affected by the material of the first electrode 130. This means that when the work function of the material of the first electrode 130 is 4.8 eV or more, the catalyst characteristics are not affected by the interface between the catalyst layer 150 and the first electrode 130, which is the interface of ③ described above with reference to FIG. 2 do.

The material of the electrode such as the first electrode 130 is determined in consideration of various conditions such as durability, corrosion resistance, heat resistance, light weight, and price. As shown above, the properties of the catalyst are also affected by the electrode material. Must be considered together. Therefore, there is a limitation in the selection of the electrode material.

4A and 4B are energy band diagrams for an electrode structure.

4A and 4B, E _FM and E _FS denote the Fermi level of the first electrode 130 and the catalyst layer 150, respectively, and E _C and E _V denote the conduction band levels of the catalyst layer 150, respectively ( conduction band level) and valence band level, Φ _B indicates Schottky barrier height, and V indicates the magnitude of the applied voltage.

Referring to FIG. 4A, a band diagram of the electrode structure of the comparative example without the intermediate layer 160 as described above with reference to FIGS. 3A and 3B is shown for a state before a voltage is applied and a state where a voltage is applied, respectively. do. The size of the work function of the first electrode 130 corresponds to the size between E _FM and the vacuum level, and according to the size of the work function, the Schottky barrier in the Schottky contact between the p-type catalyst layer 150 The height is determined. When a voltage is applied, the barrier of a hole is further increased by the applied potential. Therefore, when the work function is less than 4.8 eV as in FIG. 3B, the height of the Schottky barrier decreases as the work function increases, thereby moving holes from the first electrode 130 to the catalyst layer 150 It can be interpreted that as is increased, the overpotential is decreased. In addition, when the work function is 4.8 eV or more, the movement of holes is sufficiently increased, and it can be interpreted that the overpotential reaches saturation as the rate determining step in the electrochemical reaction is switched to another step. In this way, by controlling the work function of the first electrode 130, it is possible to control the flow of holes.

Referring to FIG. 4B, a band diagram of the electrode structure of the embodiment of the present invention in which the intermediate layer 160 is inserted is shown in a state in which a voltage is applied. As the intermediate layer 160 is inserted, the height of the Schottky barrier is determined by the work function of the intermediate layer 160 regardless of the material of the first electrode 130. Accordingly, the overpotential in the electrochemical reaction can be controlled by the intermediate layer 160 and the OER performance can be controlled.

According to this result, in the embodiment of the present invention, a material having a work function of 4.8 eV or more was introduced as the intermediate layer 160 between the catalyst layer 150 and the first electrode 130. Accordingly, it is possible to expect a certain catalytic property regardless of the material of the first electrode 130. Accordingly, the material of the first electrode 130 may be selected without limitation in consideration of durability, corrosion resistance, heat resistance, light weight, and productivity, and the performance of the catalyst layer 150 may be secured by the intermediate layer 160.

5 is a current-voltage graph showing catalyst characteristics of a catalyst layer according to an intermediate layer material in an electrode structure according to an embodiment of the present invention.

In FIG. 5, the first electrode 130 is made of titanium (Ti), and gold (Au), platinum (Pt), nickel (Ni), and copper (Cu) are used as the intermediate layer 160. The result is shown. In addition, as a comparative example, the case of using FTO and titanium (Ti) as the first electrode 130 without using the intermediate layer 160 is shown together. The catalyst layer 150 was prepared by spin coating on the intermediate layer 160 as in the above-described embodiment.

Referring to FIG. 5, a current-voltage graph for the electrode structure of the embodiment is shown compared to a standard hydrogen electrode (NHE). As shown, compared to the case where the first electrode 130 is titanium (Ti) and there is no intermediate layer 160, when the intermediate layer 160 is used, the catalyst properties are gold (Au), platinum (Pt), nickel ( Ni), and copper (Cu) in that order was found to be excellent. In addition, when gold (Au) was used as the intermediate layer 160, it was found that the catalytic properties were superior to that of the case where FTO was used as the first electrode 130, which is the case in which the graph of FIG. That is, by introducing the intermediate layer 160 of gold (Au) while using titanium (Ti) as the first electrode 130, the catalyst characteristics are improved compared to the case where the first electrode 130 of FTO is used without the intermediate layer 160. You can see that it is.

Gold (Au) has a work function of 5.1 eV, platinum (Pt) is 5.65 eV, nickel (Ni) is 5.15 eV, titanium (Ti) is 4.33 eV, and copper (Cu) is 4.65 eV. Therefore, compared with copper (Cu) having a work function of 4.8 eV or less, it can be seen that gold (Au), platinum (Pt), and nickel (Ni) having a work function of 4.8 eV or more have relatively excellent catalytic properties. Accordingly, in the electrode structure of the present invention, the material of the intermediate layer 160 is particularly cobalt (Co) (5.0 eV), nickel (Ni) (5.15 eV), and iridium (Ir) (5.27 eV) having a work function of 4.8 eV or more, and Palladium (Pd) (5.12 eV), gold (Au) (5.1 eV), stainless steel (4.83 eV), and platinum (Pt) (5.65 eV) could be used.

6 is a current-voltage graph showing catalyst characteristics of a catalyst layer according to an intermediate layer thickness in an electrode structure according to an embodiment of the present invention.

Referring to FIG. 6, for an electrode structure including a first electrode 130 made of titanium (Ti) and an intermediate layer 160 made of gold (Au), the thickness of the intermediate layer 160 is 10 nm, 50 nm, And the catalyst properties were measured while changing to 75 nm. As shown in FIG. 6, the change in the thickness of the intermediate layer 160 did not affect the catalyst characteristics. This may be interpreted as because the intermediate layer 160 does not participate in the electrochemical reaction.

7A to 7C are diagrams showing catalytic properties of a catalyst layer according to an intermediate layer material in an electrode structure according to an exemplary embodiment of the present invention.

7A and 7B show Nyquist diagrams measured at different voltages (1.30 V and 1.35 V vs. NHE) by electrochemical impedance spectroscopy (EIS), and an impedance equivalent circuit. The model is shown in Figure 7c. In FIGS. 7A and 7B, the measured results are shown when the first electrode 130 is made of FTO and titanium (Ti), respectively, and gold (Au) is used as the intermediate layer 160. In addition, as a comparative example, the case of using FTO and titanium (Ti) as the first electrode 130 without using the intermediate layer 160 is shown together. The catalyst layer 150 was prepared by spin coating on the intermediate layer 160 as in the above-described embodiment. In FIG. 7C, Rs represents the resistance of the aqueous electrolyte solution 120, R1 represents the total OER charge transfer resistance, and R2 represents the resistance between the catalyst layer 150 and the aqueous electrolyte solution 120.

In FIGS. 7A and 7B, the diameter of the semicircle of the graphs is proportional to the resistance R1, and the graphs represent the total OER charge transfer resistance, which is charge transfer depending on the catalytic properties of the electrode structure. Thus, a small semicircle means a small impedance in the catalyst of the electrode structure. As shown, when the intermediate layer 160 of gold (Au) is used on the first electrode 130 of the FTO, the smallest impedance is displayed, and gold (Au) is used on the first electrode 130 of titanium (Ti). In the case of using the intermediate layer 160 of ), the second smallest impedance was shown. When the intermediate layer 160 was not used, it exhibited a relatively large impedance. In particular, as shown in FIG. 6B, when titanium (Ti) is used as the first electrode 130 and there is no intermediate layer 160, the impedance is very large, but when the intermediate layer 160 is used, the impedance is significantly reduced. Was observed.

As such, it can be seen that a difference occurs in actual charge transfer by the intermediate layer 160, and it can be seen that the impedance of such an electrode structure can be optimized according to an embodiment of the present invention.

The present invention is not limited by the above-described embodiments and the accompanying drawings, but is intended to be limited by the appended claims. Therefore, various types of substitutions, modifications and changes will be possible by those of ordinary skill in the art within the scope not departing from the technical spirit of the present invention described in the claims, and this also belongs to the scope of the present invention. something to do.

100: water cracking system
110: electrolyzer
120: aqueous buffer electrolyte solution
130: first electrode
140: second electrode
150: catalyst layer
160: middle floor

Claims (10)

An electrode for oxidation reaction;
A catalyst layer coated on the surface of the electrode; And
Including an intermediate layer disposed between the electrode and the catalyst layer,
The electrode structure for electrochemical reactions has a first work function, and the intermediate layer has a second work function greater than the first work function.
The method of claim 1,
The second work function is equal to or greater than 4.8 eV electrode structure for electrochemical reaction.
The method of claim 1,
The electrode and the intermediate layer is an electrode structure for an electrochemical reaction made of a metallic material.
The method of claim 3,
The electrode includes titanium (Ti), and the intermediate layer includes at least one of gold (Au), platinum (Pt), and nickel (Ni), cobalt (Co), iridium (Ir), stainless steel, and palladium (Pd). Electrochemical reaction electrode structure comprising one.
The method of claim 1,
The catalyst layer is an electrode structure for an electrochemical reaction comprising a transition metal oxide.
The method of claim 5,
The catalyst layer is an electrode structure for an electrochemical reaction comprising manganese oxide nanoparticles.
A reactor containing an electrolyte containing water;
First and second electrodes at least partially immersed in the electrolyte;
A catalyst layer coated on the surface of the first electrode and including a transition metal oxide;
An intermediate layer disposed between the first electrode and the catalyst layer and having a work function greater than that of the first electrode; And
An electrochemical reaction system comprising a power supply for applying an electrical signal to the first and second electrodes so that water is oxidized to generate hydrogen.
The method of claim 7,
The first electrode is an electrochemical reaction system in which an oxidation reaction occurs.
The method of claim 7,
The work function of the intermediate layer is equal to or greater than 4.8 eV electrochemical reaction system.
The method of claim 7,
The first electrode includes FTO or titanium (Ti), and the catalyst layer includes gold (Au), platinum (Pt), and nickel (Ni), cobalt (Co), iridium (Ir), stainless steel, and palladium ( An electrochemical reaction system comprising at least one of Pd).

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