EP4012073A1

EP4012073A1 - Electrode structures for electrochemical reaction, and electrochemical reaction systems including same

Info

Publication number: EP4012073A1
Application number: EP20849318.9A
Authority: EP
Inventors: Ki-Tae NAM; Heon-Jin HA; Moo-Young Lee
Original assignee: Seoul National University R&DB Foundation; Global Frontier Center For Multiscale Energy Systems
Current assignee: SNU R&DB Foundation
Priority date: 2019-08-07
Filing date: 2020-08-04
Publication date: 2022-06-15
Also published as: KR20210017265A; KR102305658B1; EP4012073A4; WO2021025438A1

Abstract

Electrode structures for an electrochemical reaction, according to one embodiment of the present invention, each comprise: an electrode for an oxidation reaction; a catalyst layer coated on the surface of the electrode; and an intermediate layer disposed between the electrode and the catalyst layer, wherein the electrode has a first work function, and the intermediate layer has a second work function which is greater than the first work function.

Description

[Technical Field]

The present disclosure relates to electrode structures for electrochemical reaction, and electrochemical reaction systems including same, and more particularly, to electrode structures including a catalyst layer used for a water oxidation reaction and electrochemical reaction systems including the same.

[Background Art]

Recently, as a measure for solving environmental problems caused by the depletion of carbon-based energy and emissions of fuel gas, studies into a method of storing energy by producing hydrogen and oxygen by water splitting or obtaining energy through a fuel cell have been actively conducted. In these methods, an electrochemical reaction may be used, and to increase a reaction rate, it may be necessary to secure performance of a catalyst. However, there may be a phenomenon in which performance of a catalyst may vary, depending on a material of an electrode, such that it may be difficult to select an electrode material which may satisfy durability, corrosion resistance, thermal resistance, lightness, costs, and the like, of an electrode and which may also not degrade performance of a catalyst.

[Disclosure]

[Technical Problem]

An aspect of the present disclosure is to provide an electrode structure for an electrochemical reaction which may secure catalytic properties regardless of an electrode material, and an electrochemical reaction system including the same.

[Technical Solution]

According to an aspect of the present disclosure, an electrode structure for an electrochemical reaction includes an electrode for 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 has a first work function, and the intermediate layer has a second work function greater than the first work function.
According to an aspect of the present disclosure, an electrochemical reaction system includes a reactor including an electrolyte containing water, first and second electrodes at least partially immersed in the electrolyte, a catalyst layer coated on a 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 a power unit for applying an electrical signal to the first and second electrodes such that water is oxidized to generate hydrogen.

[Advantageous Effects]

By including an intermediate layer between an electrode and a catalyst layer, an electrode structure for an electrochemical reaction which may secure catalytic properties regardless of an electrode material and an electrochemical reaction system including the same may be provided.
Various advantages and effects of the present disclosure are not limited to the above, and will be more easily understood while describing specific embodiments of the present disclosure.

[Brief Description of Drawings]

FIG. 1 is a schematic diagram illustrating a water splitting system including an electrode structure for an electrochemical reaction according to an embodiment of the present disclosure;
FIG. 2 is a schematic diagram illustrating an electrode structure for an electrochemical reaction according to an embodiment of the present disclosure;
FIGS. 3a and 3b are graphs illustrating catalytic properties of a catalyst layer depending on an electrode material;
FIGS. 4a and 4b are energy band diagrams for an electrode structure;
FIG. 5 is a current-voltage graph illustrating catalytic properties of a catalyst layer depending on a material of an intermediate layer in an electrode structure according to an embodiment of the present disclosure;
FIG. 6 is a current-voltage graph illustrating catalytic properties of a catalyst layer depending on a thickness of an intermediate layer in an electrode structure according to an embodiment of the present disclosure; and
FIGS. 7a to 7c are diagrams illustrating catalytic properties of a catalyst layer according to a material of an intermediate layer in an electrode structure according to an embodiment of the present disclosure.

[Best Mode for Invention]

Hereinafter, preferable embodiments of the present disclosure will be described with reference to the accompanying drawings.
However, the embodiments of the present disclosure may be modified in various other forms and various embodiments may be combined, and the scope of the present disclosure is not limited to the embodiments described below. Also, the embodiments of the present disclosure are provided to more completely describe the present disclosure to a person having ordinary skill in the art. The shapes and sizes of the elements in the drawings may be exaggerated for clearer description, and the elements indicated by the same reference numerals in the drawings are the same elements.

Electrochemical reaction system and electrode structure for electrochemical reaction

FIG. 1 is a schematic diagram illustrating a water splitting system including an electrode structure for an electrochemical reaction according to an embodiment of the present disclosure.
Referring to FIG. 1, a water splitting system 100 may include an electrolytic cell 110, an aqueous electrolyte solution 120, a first electrode (anode) structure ES and a second electrode (cathode) 140. The first electrode structure ES and the second electrode 140 may be connected to each other by a power supply unit 180. In embodiments, the water splitting system 100 may further include a membrane formed of an ion-permeable material, which may divide the first electrode structure ES and the second electrode 140. Also, in embodiments, the water splitting system 100 may further include a product collecting unit. The water splitting system 100 may be a system decomposing water in the aqueous electrolyte solution 120 and generating oxygen and hydrogen.
The first electrode structure ES may include a first electrode (anode) 130, a catalyst layer 150 coated on at least one surface of the first electrode 130, and an intermediate layer 160 disposed between the first electrode 130 and the catalyst layer 150. 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 formed of a conductive material such as a semiconductor or a metal. The first and second electrodes 130 and 140 may include at least one of fluorine-doped tin oxide (FTO), cobalt (Co), copper (Cu), nickel (Ni), iron (Fe), iridium (Ir), ruthenium (Ru), palladium (Pd), gold (Au), platinum (Pt), titanium (Ti), zirconium (Zr), rhodium (Rh), chromium (Cr), and stainless steel, for example.
The catalyst layer 150 may include a catalyst material promoting a water oxidation reaction, such as, for example, a metal oxide, and particularly, the catalyst layer 150 may include a p-type metal oxide. In particular, the catalyst layer 150 may include a transition metal oxide, and may include, for example, an oxide of at least one of cobalt (Co), copper (Cu), nickel (Ni), iron (Fe), and manganese (Mn). 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 (Mn₃O₄) nanoparticles. However, the form 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 to secure the function of a catalyst in an oxygen evolution reaction (OER). Specifically, the intermediate layer 160 may be involved in a charge transport process in the electrochemical reaction, such that the catalyst layer 150 may function as a catalyst without being affected by the material of the first electrode 130, which will be described in greater detail with reference to FIGS. 5 to 7c below. The intermediate layer 160 may be a coating layer coated on the surface of the first electrode 130 and may be an electrode surface treatment layer, and may be independent of the improvement of catalytic activity. Since the intermediate layer 160 is for improving charge transfer in relation to the catalyst layer 150, the intermediate layer 160 may have catalytic performance lower than that of the catalyst layer 150, or may not participate in the electrochemical reaction unlike the catalyst layer 150 in embodiments. The intermediate layer 160 may include a metal material, such as, for example, at least one of cobalt (Co), copper (Cu), nickel (Ni), iron (Fe), iridium (Ir), ruthenium (Ru), palladium (Pd), gold (Au), platinum (Pt), titanium (Ti), zirconium (Zr), and stainless steel. In particular, the intermediate layer 160 may be formed of a material having a work function greater than that of the first electrode 130, and a work function thereof may be 4.8 eV or more.
The electrolytic cell 110 may accommodate the aqueous electrolyte solution 120, and may further include an inlet portion and an outlet portion, such as an inlet pipe and a drain pipe.
The aqueous electrolyte solution 120 may work as a source of water used in the water splitting reaction and as an acceptor of protons formed during the water splitting reaction. The aqueous electrolyte solution 120 may include, for example, at least one of potassium phosphate and sodium phosphate such as NaH₂PO₄, Na₂HPO₄, and Na₃PO₄, or a mixture thereof. The pH of the aqueous electrolyte solution 120 may be in the range of 2 to 14. To work as an acceptor of the protons, the aqueous electrolyte solution 120 may include a proton-accepting anion. Accordingly, even when the amount of protons (H⁺) increases as the water splitting reaction is performed, the proton-accepting anion may accommodate at least a portion of the protons, such that the pH decrease rate of the aqueous electrolyte solution 120 may be reduced. The proton-accepting 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 splitting system 100, the reaction in which oxygen is created in the first electrode 130 and hydrogen is created in the second electrode 140 may occur. Each half-reaction may be represented by chemical equations 1 and 2 as below:

[Chemical equation 1] 2H₂O → O₂ + 4H⁺+ 4e^-

[Chemical equation 2] 4H⁺+ 4e^- → 2H₂
The first electrode structure ES according to an embodiment of the present disclosure may participate in an oxygen evolution reaction (OER), which is an oxidation reaction in the first electrode 130 represented by chemical equation 1 above. Accordingly, OER may 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 disclosure, a water splitting system may be used, but the present disclosure is not limited thereto, and the electrode structure according to an embodiment of the present disclosure may be used for an electrode for oxidation reaction in various electrochemical reaction systems.

Method of manufacturing electrode structure for electrochemical reaction

The method of manufacturing the electrode structure for an electrochemical reaction as illustrated in FIG. 1 may include washing the surface of the first electrode 130, coating the intermediate layer 160 on the surface of the first electrode 130, and coating the catalyst layer 150 on the intermediate layer 160.
The washing the surface of the first electrode 130 may include washing the surface of the first electrode 130 twice using acetone, ethanol, and distilled (DI) water in order and performing a heat treatment thereon in sulfuric acid (H₂SO₄) solution of 0.5 M at 60°C for 1 hour.
The coating the intermediate layer 160 on the surface of the first electrode 130 may be performed using, for example, physical vapor deposition (PVD) such as thermal evaporation, electron beam evaporation, or sputtering, or chemical vapor deposition (CVD).
The coating the catalyst layer 150 on the intermediate layer 160 may include synthesizing the material of the catalyst layer 150 and coating the material of the catalyst layer 150 by methods such as spin-coating or drop-casting or coating the material by preparing the material in the form of paste or ink.
The synthesizing the material of the catalyst layer 150 may include, when the catalyst layer 150 is a transition metal oxide in the form of nanoparticles, 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, forming transition metal oxide nanoparticles by adding the second solution to the first solution, and annealing the transition metal oxide nanoparticles at a predetermined temperature.
When the material of the catalyst layer 150 is prepared in the form of a paste or ink and applied, 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 may be 0.1 to 1.0.

Embodiment of electrode structure for electrochemical reaction

In the electrode structure (ES) in the embodiment, the intermediate layer 160 may be deposited on the first electrode 130 by sputtering, and as for the catalyst layer 150, manganese oxide (Mn₃O₄) nanoparticles of about 4 nm synthesized by the above-described preparing method was prepared, and was washed twice using 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 have a thickness of about 150 nm. The electrode structure was prepared by annealing at a temperature of about 200°C for 1 hour after the spin-coating.

Catalytic properties in electrode structure for electrochemical reaction

FIG. 2 is a schematic diagram illustrating an electrode structure for an electrochemical reaction according to an embodiment of the present disclosure.
Referring to FIG. 2, the first electrode structure ES may include a first electrode 130, an intermediate layer 160, and a catalyst layer 150 stacked in order. For example, the first electrode 130 may have a thickness in the range of 0.1 mm to 4 mm, the intermediate layer 160 may have a thickness in the range of 10 nm to 1 mm, and the catalyst layer 150 may have a thickness in the range of 50 nm to 500 nm, but an example embodiment thereof is not limited thereto.
During the water oxidation reaction described above with reference to FIG. 1, electrons (e^-) created while H₂O is oxidized to O₂ on the surface of the catalyst layer 150 may move along the charge transfer path including the interfacial surface (①) of the aqueous electrolyte solution 120 and the catalyst layer 150, the internal portion of the catalyst layer 150 (②), and the interfacial surface (③) between the catalyst layer 150 and the first electrode 130. The studies on the catalytic properties of the catalyst layer 150 are focused on ① and ②, whereas studies on the interfacial surface ③ which is not externally exposed in terms of charge transfer has not be conducted.
According to an embodiment of the present disclosure, by inserting the intermediate layer 160 to the interfacial surface, that is, the interfacial surface ③, between the catalyst layer 150 and the first electrode 130 in consideration of the work function, the function of the catalyst layer 150 may be secured by controlling the mechanism of the charge transfer on the interfacial surface, and accordingly, OER performance may improve.
Hereinafter, in relation to including the intermediate layer according to an embodiment of the present disclosure, the catalytic properties depending on the electrode material and the charge transfer mechanism on the interfacial surface of the electrode structure will be described with reference to FIGS. 3a to 4b.
FIGS. 3a and 3b are graphs illustrating catalytic properties of a catalyst layer depending on an electrode material.
FIGS. 3a and 3b illustrate catalytic properties of a comparative example in which the first electrode structure ES in the embodiment does not include the intermediate layer 160 to examine the influence of the catalytic properties by the interfacial surface ③ in FIG. 2. In the electrode structure in the comparative example, the catalyst layer 150 was prepared in the same manner as in the above-described embodiment, and was coated on the first electrode 130 instead of the intermediate layer 160 by spin-coating. As the first electrode 130, each of FTO, nickel (Ni), stainless steel, copper (Cu), titanium (Ti), and zirconium (Zr) was used.
Referring to FIG. 3a, a current-voltage graph for the electrode structure in the comparative example is illustrated in comparison to a normal hydrogen electrode (NHE). It may be determined that the catalytic properties may be excellent as the potential reaching a specific current density is smaller, and as illustrated, it is indicated that, when the material of the first electrode 130 was FTO, nickel (Ni), stainless steel, copper (Cu), titanium (Ti) and zirconium (Zr) in order, the catalyst properties were excellent in the above order.
FIG. 3b illustrates an overpotential value for reaching an OER current density of 1 mA/cm² in the electrode structure in the comparative example along 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, there was the tendency that the overpotential decreased as the work function increased. 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 and was constant, that is, a saturated state, even when the work function increased. According to these results, it is indicated that, when the work function of the material of the first electrode 130 is equal to or greater than a specific range, that is, equal to or greater than 4.8 eV, the catalytic properties may not be affected by the material of the first electrode 130, which may indicate that, when the work function of the material of the first electrode 130 is 4.8 eV or more, the catalyst properties may not be affected by the interfacial surface between the catalyst layer 150 and the first electrode 130, which is the interfacial surface ③ described above with reference to FIG. 2.
The material of the electrode such as the first electrode 130 may be determined in consideration of various conditions such as durability, corrosion resistance, thermal resistance, lightness, and price, and as indicated in the above results, since the properties of the catalyst are also affected by the electrode material, this should be considered as well. Therefore, there may be a limitation in selecting the electrode material.
FIGS. 4a and 4b are energy band diagrams for an electrode structure.
In FIGS. 4a and 4b, E_FM and E_FS represent the Fermi level of the first electrode 130 and the catalyst layer 150, respectively, E_C and E_V represent the conduction band level and the valence band level of the catalyst layer 150, respectively, Φ_B represents a Schottky barrier height, and V represents the magnitude of an applied voltage.
FIG. 4a are band diagrams of an electrode structure of a comparative example in which the intermediate layer 160 described above with reference to FIGS. 3a and 3b is not provided with respect to a state before a voltage is applied and a state in which a voltage is applied. The size of the work function of the first electrode 130 corresponds to the size between the E_FM and the vacuum level, and the Schottky barrier height in the Schottky contact with the p-type catalyst layer 150 may be determined according to the size of the work function. When a voltage is applied, the barrier of the hole may further increase by the applied potential. Accordingly, it is indicated that, when the work function is 4.8 eV or less as illustrated in FIG. 3b, the Schottky barrier height may decrease as the work function increases, and accordingly, the holes from the first electrode 130 may increasingly move to the catalyst layer 150 such that the overpotential may decrease. Also, it is indicated that, when the work function is 4.8 eV or more, the movement of holes may sufficiently increase, and the step of determining the rate in the electrochemical reaction may be switched to another step, such that the overpotential may reach a saturation state. By controlling the work function of the first electrode 130 as described above, the flow of holes may be controlled.
FIG. 4b is a band diagram of an electrode structure in an embodiment of the present disclosure in which the intermediate layer 160 is inserted with respect a state in which a voltage is applied. As the intermediate layer 160 is inserted, the Schottky barrier height may be determined by the work function of the intermediate layer 160 irrespective of the material of the first electrode 130. Accordingly, the overpotential in the electrochemical reaction may be controlled by the intermediate layer 160 and the OER performance may be controlled.
According to these results, in the embodiment of the present disclosure, a material having a work function of 4.8 eV or more was provided as the intermediate layer 160 between the catalyst layer 150 and the first electrode 130. Accordingly, constant catalytic properties may be expected regardless of the material of the first electrode 130. Accordingly, the material of the first electrode 130 may be selected without a limitation in consideration of durability, corrosion resistance, thermal resistance, lightness, and productivity, and the performance of the catalyst layer 150 may be secured by the intermediate layer 160 as well.
FIG. 5 is a current-voltage graph illustrating catalytic properties of a catalyst layer depending on a material of an intermediate layer in an electrode structure according to an embodiment of the present disclosure.
FIG. 5 illustrates the results of the measurement in the example in which the first electrode 130 was formed of titanium (Ti), and gold (Au), platinum (Pt), nickel (Ni), and copper (Cu) were used as the intermediate layer 160. Also, as a comparative example, the example in which FTO and titanium (Ti) were used as the first electrode 130 without using the intermediate layer 160 is also illustrated. The catalyst layer 150 was prepared by spin-coating the catalyst layer 150 on the intermediate layer 160 as in the aforementioned embodiment.
Referring to FIG. 5, a current-voltage graph for the electrode structure in an embodiment is illustrated in comparison to a standard hydrogen electrode (NHE). As illustrated, as compared to the example in which the first electrode 130 was titanium (Ti) and the intermediate layer 160 was not provided, when the intermediate layer 160 is used, the catalytic properties were excellent in the order of gold (Au), platinum (Pt), nickel (Ni), and copper (Cu). Also, when gold (Au) was used as the intermediate layer 160, the catalytic properties were more excellent than the example in which FTO was used as the first electrode 130, which is the example in which the most excellent catalytic properties were exhibited in the graph in FIG. 3a. That is, by including the intermediate layer 160 of gold (Au) while using titanium (Ti) as the first electrode 130, catalyst properties improved as compared to the example in which the first electrode 130 of FTO is used without the intermediate layer 160.
Gold (Au) may have a work function of 5.1 eV, platinum (Pt) may have a work function of 5.65 eV, nickel (Ni) may have a work function of 5.15 eV, titanium (Ti) may have a work function of 4.33 eV, and copper (Cu) may have a work function of 4.65 eV. Accordingly, it is indicated that, as compared to copper (Cu) having a work function of 4.8 eV or less, gold (Au), platinum (Pt), and nickel (Ni) having a work function of 4.8 eV or more may have relatively superior catalytic properties. Accordingly, in the electrode structure in the present disclosure, as the material of the intermediate layer 160, particularly, cobalt (Co) (5.0 eV), nickel (Ni) (5.15 eV), iridium (Ir) (5.27 eV), palladium (Pd) (5.12 eV), gold (Au) (5.1 eV), stainless steel (4.83 eV), and platinum (Pt) (5.65 eV), which may have a work function of 4.8 eV or more, may be used.
FIG. 6 is a current-voltage graph illustrating catalytic properties of a catalyst layer depending on a thickness of an intermediate layer in an electrode structure according to an embodiment of the present disclosure.
Referring to FIG. 6, catalyst properties were measured while changing the thickness of the intermediate layer 160 to be 10 nm, 50 nm, and 75 nm with respect to the electrode structure including the first electrode 130 formed of titanium (Ti) and the intermediate layer 160 formed of gold (Au). As illustrated in FIG. 6, the changes in the thickness of the intermediate layer 160 did not affect the catalyst properties, which may be because the intermediate layer 160 did not participate in the electrochemical reaction.
FIGS. 7a to 7c are diagrams illustrating catalytic properties of a catalyst layer according to a material of an intermediate layer in an electrode structure according to an embodiment of the present disclosure
FIGS. 7a and 7b illustrate the Nyquist diagram measured at different voltages (1.30 V and 1.35 V vs. NHE) by electrochemical impedance spectroscopy (EIS), and an impedance equivalent circuit model is illustrated in FIG. 7c. FIGS. 7a and 7b illustrate the results of measurement in the example in which the first electrode 130 was formed of FTO and titanium (Ti), respectively, and gold (Au) was used as the intermediate layer 160. Also, as a comparative example, the example in which FTO and titanium (Ti) were used as the first electrode 130 without using the intermediate layer 160 is illustrated as well. The catalyst layer 150 was prepared by spin-coating the catalyst layer 150 on the intermediate layer 160 as in the aforementioned embodiment. In FIG. 7c, Rs is the resistance of the aqueous electrolyte solution 120, R1 is the total OER charge transfer resistance, and R2 is the resistance between the catalyst layer 150 and the aqueous electrolyte solution 120.
The diameter of the semicircle in the graphs in FIGS. 7a and 7b is proportional to the resistance R1, and the graphs illustrate the total OER charge transfer resistance, which may be the charge transfer dependent on the catalytic properties, in the electrode structure. Accordingly, the small semicircle may refer to low impedance in the catalyst of the electrode structure. As illustrated, when the intermediate layer 160 of gold (Au) was used on the first electrode 130 of FTO, the smallest impedance was exhibited, and when the intermediate layer 160 of gold (Au) was used on the first electrode 130 formed of titanium (Ti), the second lowest impedance was exhibited. When the intermediate layer 160 was not used, high impedance was exhibited. In particular, as illustrated in FIG. 6b, when titanium (Ti) is used as the first electrode 130 and the intermediate layer 160 is not provided, the extremely high impedance was exhibited, whereas, when the intermediate layer 160 was used, impedance significantly decreased.
As such, it is indicated that, by the intermediate layer 160, there may be a difference in actual charge transfer, and that the impedance of the electrode structure may be optimized according to an embodiment of the present disclosure.
While the embodiments have been illustrated and described above, it will be apparent to those skilled in the art that modifications and variations could be made without departing from the scope in the embodiment as defined by the appended claims.

[Industrial Applicability]

The electrode structure for an electrochemical reaction and an electrochemical reaction system including the same according to an embodiment of the present disclosure may be widely used in the field of nanotechnology and energy technology in which catalyst performance should be secured. Specifically, the electrode structure and the electrochemical reaction system for an electrochemical reaction according to an embodiment of the present disclosure may be used for environmentally friendly energy production including hydrogen energy production.

Claims

An electrode structure for an electrochemical reaction, comprising:
an electrode for 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 has a first work function, and the intermediate layer has a second work function greater than the first work function.
The electrode structure of claim 1, wherein the second work function is equal to or greater than 4.8 eV.
The electrode structure of claim 1, wherein the electrode and the intermediate layer are formed of a metal material.
The electrode structure of claim 3, wherein the electrode includes titanium (Ti), and the intermediate layer includes at least one of gold (Au), platinum (Pt), nickel (Ni), cobalt (Co), iridium (Ir), stainless steel, and palladium (Pd).
The electrode structure of claim 1, wherein the catalyst layer includes a transition metal oxide.
The electrode structure of claim 5, wherein the catalyst layer includes manganese oxide nanoparticles.
An electrochemical reaction system, comprising:
a reactor including an electrolyte containing water;

first and second electrodes at least partially immersed in the electrolyte;

a catalyst layer coated on a 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 a work function of the first electrode; and

a power unit for applying an electrical signal to the first and second electrodes such that water is oxidized to generate hydrogen.
The electrochemical reaction system of claim 7, wherein the first electrode is an oxidizing electrode in which an oxidation reaction occurs.
The electrochemical reaction system of claim 7, wherein the work function of the intermediate layer is equal to or greater than 4.8 eV.
The electrochemical reaction system of claim 7, wherein the first electrode includes FTO or titanium (Ti), and the catalyst layer includes at least one of gold (Au), platinum (Pt), nickel (Ni), cobalt (Co), iridium (Ir), stainless steel, and palladium (Pd).