Fuel cells and water electrolysis devices

Abstract

To provide a highly durable Schottky-conjunction-based electrochemical catalyst for selective redox reactions.SOLUTION: The present invention relates to a Schottky-conjunction-based electrochemical catalyst for selective redox reactions, specifically, to a Schottky-conjunction-based electrochemical catalyst for selective redox reactions, which has effects of preventing catalyst deterioration and increasing durability by controlling a Schottky barrier such that an interface between a metal and a metal oxide that acts as a semiconductor material forms a Schottky contact to selectively induce an oxidation-reduction reaction, thereby causing only the oxidation reaction to occur in an anode that constitutes a fuel cell or water electrolyzer, and only a reduction reaction to occur in cathode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a Schottky junction electrochemical catalyst for selective oxidation-reduction reactions, and more specifically, to a Schottky junction electrochemical catalyst for selective oxidation-reduction reactions, which has the effect of preventing catalyst degradation and increasing durability by controlling the Schottky barrier so that the interface between a metal and a metal oxide acting as a semiconductor material forms a Schottky contact to selectively induce oxidation-reduction reactions, thereby causing substantially only oxidation reactions to occur at the anode constituting a fuel cell or water electrolyzer, and substantially only reduction reactions to occur at the cathode. [Background technology]

[0002] Electrocatalysis is utilized in many fields, including water electrolysis, which produces green hydrogen, the foundation of a hydrogen economy; fuel cells, which generate electricity based on electrolysis; and CO2 reduction technology, which directly reduces CO2 emissions through CO2 reduction. While research efforts on electrocatalysis are also active, most of the research focuses primarily on catalyst activity, durability, or economics. For example, there is already a vast amount of literature on modifying catalyst structures to increase the active surface area and thereby improve performance, exploring alloy materials for more stable conditions, reducing the amount of precious metals, or developing non-precious metal catalysts to reduce costs.

[0003] However, research into catalyst selectivity has been quite limited, despite the need for further research given its significant impact on the durability of fuel cells and water electrolyzers. In fuel cells, the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) proceed at the anode and cathode, respectively. In water electrolyzers, the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) proceed simultaneously at the anode and cathode, respectively. However, the characteristic of electrochemical catalysts that allow oxidation / reduction reactions to occur in pairs can sometimes cause problems by unintentionally reversed reactions, resulting in the reversed reduction / oxidation reactions.

[0004] Typically, during start-up / shutdown (SU / SD) of a fuel cell, external air leaks into the anode, causing unwanted ORR, which raises the potential of the cathode (opposite electrode) above 1.4 V. This causes a carbon oxidation reaction (COR) in which carbon is oxidized at the cathode, resulting in catalyst degradation. Furthermore, during shutdown of a water electrolyzer, residual voltage crosses over to the cathode, causing dissolved oxygen to oxidize the cathode. Thus, a reduction reaction at the anode and an oxidation reaction at the cathode, opposite to the designed reaction configuration, cause catalyst degradation.

[0005] Research on selective catalysts has generally been focused on photocatalysis and other gas sensor systems. In electrocatalysis, selectivity has been limited to competing reactions, such as the conversion rate of CO2 to CO or the production rate of H2O2 using a two-electron reaction in the oxygen reduction reaction (ORR). Since the introduction of research on selective HOR by the Markovic group, the term has increasingly been used to refer to the selectivity of the reaction itself. This research aimed to improve catalyst durability under SU / SD conditions in fuel cells. By controlling the active area by adsorbing an organic compound called calix[4]arene onto the platinum (Pt) surface using a self-assembled monolayer (SAM) technique, we were able to selectively suppress ORR activity while maintaining HOR activity.

[0006] Previously, researchers had succeeded in achieving HOR selectivity using dodecanethiol. However, organic materials have a fatal drawback: their thermal and electrochemical stability cannot be guaranteed. This made their practical application difficult. Subsequently, drawing inspiration from the control of electrical properties using the rectification effect of heterojunctions, often used in semiconductor research, researchers attempted to overcome the limitations of organic materials by utilizing the metal-insulator transition (MIT) phenomenon, which occurs when a metal catalyst is bonded to an oxide support. Using platinum as the metal catalyst and tungsten oxide as the oxide support, researchers successfully achieved selectivity by promoting the oxidation reaction in fuel cells while simultaneously suppressing the reduction reaction. This research was recognized as an outstanding achievement when it was selected as the main cover article of the British scientific journal Nature Catalysis in 2020, and is considered to be the highest level of research on electrocatalytic selectivity. On the other hand, the issue of catalyst durability under shut-down conditions of water electrolyzers has only recently been addressed compared to research on SU / SD of fuel cells, so it is currently difficult to find solutions, including related research.

[0007] Similar research using bifunctional alloy catalysts based on iridium has been reported, but they are not comparable to commercial catalysts in terms of performance retention, and the high cost of iridium (Ir) makes them somewhat unsatisfactory from an economic standpoint.

[0008] From this perspective, the inventors of the present invention recognized the need to research selective catalysts that can solve the problem of catalyst durability in fuel cells and water electrolyzers. In particular, they discovered the interesting fact that, by interpreting metal oxides as semiconductors and controlling the Schottky barrier, which is a more generalized method than the MIT phenomenon, electrochemical redox reactions can be selectively promoted. They established this as the mechanism of selectivity of metal-oxide catalysts and realized the need to develop Schottky junction-type electrochemical catalysts for selective redox reactions based on this.

[0009] In this regard, Prior Patents 1 and 2 disclose a method for manufacturing a three-dimensional metal catalyst electrode coated with a crude catalyst that can be used for electrochemical carbon dioxide reduction, but they fail to specifically present an electrochemical catalyst for Schottky junction-type selective oxidation-reduction reactions or a method for manufacturing the same. As such, the catalysts are not applicable to fuel cells or water electrolyzers, and thus there remains a limitation in that they cannot meet the aforementioned development needs. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Korean Patent No. 10-1784626 (registered on September 27, 2017) [Patent Document 2] Korean Patent No. 10-1771368 (registered on August 18, 2017) Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been devised to overcome the problems and limitations of the conventional inventions described above, and an object of the present invention is to provide a Schottky junction electrochemical catalyst for selective oxidation-reduction reactions, which prevents catalyst degradation due to side reactions during shutdown and startup, thereby increasing durability, by providing a Schottky junction electrochemical catalyst so that the cathode and anode catalysts in fuel cells and water electrolyzers selectively induce electrochemical oxidation-reduction reactions at each electrode.

[0012] The technical problems that the present invention aims to solve are not limited to the problems described above, and other problems not mentioned will be clearly understood by those skilled in the art to which the present invention pertains from the following description. [Means for solving the problem]

[0013] The Schottky junction electrochemical catalyst for selective oxidation-reduction reactions according to the present invention is composed of a support layer made of a semiconductor material and a catalyst layer made of a metal formed on the surface of the support, and is formed so that the support layer and the catalyst layer form a Schottky junction. When the semiconductor material is n-type, the catalyst functions only as a reduction reaction catalyst, and when the semiconductor material is p-type, the catalyst functions only as an oxidation reaction catalyst.

[0014] In this case, when the semiconductor material forming the support is p-type, it has a work function value greater than that of the metal forming the catalyst layer, and when the semiconductor material forming the support is n-type, it has a work function value smaller than that of the metal forming the catalyst layer.

[0015] Generally, when a metal catalyst is supported on a metal oxide support, an interface identical to that between a metal and a semiconductor is formed. This interface is classified as a Schottky contact or an Ohmic contact depending on the relationship between the work functions of the two materials and the type of n-type or p-type semiconductor. The work function value Φ of the metal M is the semiconductor work function value Φ S is larger than the work function value Φ of the metal, M is the semiconductor work function value Φ S If the semiconductor is p-type, a Schottky contact is made, otherwise an ohmic contact is made.

[0016] If we consider only the Schottky contact condition, excluding ohmic contacts where electrons do not move, we can see that there is a specific current direction depending on whether the semiconductor is n-type or p-type. When we analyze this current direction in terms of electron movement in catalytic reactions, if the semiconductor is n-type, electrons are transferred only from the support to the catalyst, allowing only a reduction reaction to occur. If the semiconductor is p-type, electrons are transferred only from the catalyst to the support, allowing only an oxidation reaction to occur. Therefore, by utilizing this phenomenon, it is possible to manufacture a selective electrochemical redox catalyst that selectively induces only the desired type of oxidation or reduction reaction.

[0017] On the other hand, the Schottky junction selective oxidation-reduction catalyst of the present invention is constructed in a form in which a metal acting as a catalyst is simply supported on the surface of a semiconductor acting as a support. The material forming the catalyst layer is platinum, because platinum is a catalyst used in both HOR and ORR in fuel cells. Furthermore, in consideration of the quantum size effect, a nano-sized material must be used to have the same properties as a conventional bulky material, and the particle size of the platinum particles is preferably 1.2 nm or more.

[0018] Meanwhile, the semiconductor material used as the support must be stable under strongly acidic conditions of pH 1, considering that it will be exposed to a strongly acidic electrolyte when used in a fuel cell. A p-type semiconductor material must be selected as the support to induce only an oxidation reaction for HOR, and an n-type semiconductor material must be selected as the support to induce only a reduction reaction for ORR. However, to meet the Schottky contact conditions, a p-type semiconductor material with a work function higher than that of platinum (Pt), which is 5.65 eV, and an n-type semiconductor material with a work function lower than that of platinum must be selected as the support.

[0019] Semiconductor materials that satisfy these conditions have been found, and it is preferable that the n-type semiconductor material is tin oxide (SnO2) and the p-type semiconductor material is cobalt oxide (Co3O4). Cobalt oxide was selected as a p-type semiconductor material to selectively support the hydrogen oxidation reaction (HOR), an oxidation reaction at the anode of a fuel cell, because it is stable at pH 1 and has a work function of 6.3 eV, which is larger than the work function of platinum, 5.65 eV. In addition, tin oxide was selected as an n-type semiconductor material to selectively support the hydrogen evolution reaction (HER), a reduction reaction at the cathode of water electrolysis, because it is stable at pH 1 and has a work function of 4.9 eV, which is smaller than the work function of platinum, 5.65 eV.

[0020] In this case, when constructing the Schottky junction electrochemical catalyst for selective oxidation-reduction reaction according to the present invention, it is preferable that the thickness of the platinum catalyst layer in the selective oxidation reaction catalyst is 5 nm, and the thickness of the cobalt oxide, which is a p-type semiconductor material forming the support layer, is 15 to 30 nm.

[0021] On the other hand, in constructing the Schottky junction electrochemical catalyst for selective oxidation-reduction reaction according to the present invention, it is preferable that the thickness of the platinum catalyst layer in the selective reduction reaction catalyst is 3 to 7 nm, and the thickness of the tin oxide, which is an n-type semiconductor material forming the support layer, is 50 nm.

[0022] Specific details of other embodiments are included in the detailed description and drawings. [Effects of the Invention]

[0023] Therefore, according to the present invention, a Schottky contact occurs at the interface between the platinum catalyst and the semiconductor material, allowing electrons to flow in only one direction, thereby selectively inducing either an oxidation reaction or a reduction reaction. This significantly reduces side reactions that may occur at each electrode of the fuel cell or water electrolyzer, thereby solving the problem of deterioration in durability that may occur during start-up and shutdown of the fuel cell or water electrolyzer.

[0024] The effects of the present invention are not limited to the effects described above, and other effects not mentioned will be clearly understood by those skilled in the art to which the present invention pertains from the description of the following specification. [Brief explanation of the drawings]

[0025] [Figure 1] 1 illustrates the operation mechanism of a Schottky junction-type electrochemical catalyst for selective oxidation-reduction reactions according to an embodiment of the present invention. [Figure 2] 1 is a graph showing the degree to which the effectiveness of a Schottky junction selective oxidation catalyst made of platinum and cobalt oxide is realized in a catalyst for a fuel cell according to an embodiment of the present invention; [Figure 3] 1 is a graph showing a comparison of the degree to which the efficacy of a Schottky junction-type selective reduction catalyst made of platinum and tin oxide is realized in a catalyst for a water electrolysis cell according to an embodiment of the present invention. [Figure 4] 1 is a graph showing constant voltage measurements performed under conditions simulating hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) conditions for Pt, Co3O4, and P / Co3O4 according to an embodiment of the present invention. [Figure 5] 1 shows data obtained by measuring the work function of Pt / Co3O4 in various reactions according to an embodiment of the present invention. [Figure 6] 1 shows data obtained by measuring the work function of Pt / SnO2 in various reactions according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, embodiments of the present application will be described in more detail with reference to the accompanying drawings. However, the technology disclosed in the present application is not limited to the embodiments described herein and may be embodied in other forms. The embodiments introduced herein are provided solely to ensure that the disclosed content is thorough and complete and to fully convey the concept of the present application to those skilled in the art. In the drawings, the dimensions of the widths and thicknesses of the components of each device are slightly exaggerated to clearly show the components.

[0027] In addition, for ease of explanation, only some of the components may be shown, but those skilled in the art should be able to easily grasp the remaining components. Throughout this specification, when describing the drawings from the viewpoint of an observer, when an element is referred to as being located above or below another element, this includes both the meaning that the element may be located immediately above or below the other element and the meaning that there may be additional elements interposed between these elements.

[0028] Furthermore, a person having ordinary skill in the art should be able to realize the concept of the present application in various other forms without departing from the technical concept of the present application.

[0029] Furthermore, singular expressions should be understood to include plural terms unless the context clearly dictates otherwise, and terms such as "comprises," "having," or "having" should be understood to specify only the presence of features, numbers, steps, operations, components, parts, or combinations thereof set forth in the specification, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0030] Additionally, in performing a method or process, the steps of the method may be performed in an order other than that stated, unless the context clearly dictates a particular order, i.e., the steps may be performed in the same order as stated, or substantially simultaneously, or in reverse order.

[0031] FIG. 1 illustrates the mechanism of operation of the Schottky junction electrochemical catalyst for selective oxidation-reduction reactions according to the present invention.

[0032] The electrochemical catalyst according to the present invention has a structure in which a metal acting as a catalyst is simply supported on the surface of a semiconductor material acting as a support.

[0033] As shown in the diagram on the right, in a catalyst for selective oxidation reaction, electrons must be transferred from the metal to the semiconductor material, so the semiconductor material must be a p-type semiconductor material and must have a work function value greater than that of the metal catalyst.

[0034] As shown in the diagram on the left, in a catalyst for selective reduction reaction, an n-type semiconductor material must be used because electrons must move from a semiconductor material to a metal, and the work function value of the metal catalyst must be greater than that of the n-type semiconductor material.

[0035] In one embodiment of the present invention, platinum (Pt), which is commonly used in both HOR and ORR, is selected as the metal catalyst. A p-type semiconductor material must be used as the support to induce only the oxidation reaction in the HOR, which is the oxidation reaction of a fuel cell. An n-type semiconductor material must be used as the support to induce only the reduction reaction in the ORR, which is the reduction reaction. Considering that the semiconductor material used as the support will be exposed to a strongly acidic electrolyte, it must be stable under strongly acidic conditions (pH 1). Furthermore, to create Schottky contact conditions, a p-type semiconductor material with a work function higher than the work function of platinum (Pt), which is 5.65 eV, must be selected as the support. Additionally, an n-type semiconductor material with a work function lower than the work function of platinum (Pt), which is 5.65 eV, must be selected as the support.

[0036] Meanwhile, such a Schottky junction-type electrochemical catalyst for selective oxidation-reduction reactions was fabricated by depositing semiconductor materials on a glassy carbon rod using physical vapor deposition (PVD), and then sequentially depositing platinum (Pt) on the surface of the semiconductor materials.

[0037] In Example 1, selective oxidation catalysts that only cause oxidation reactions at the anode were fabricated as catalysts for fuel cells. Cobalt oxide (Co3O4), a p-type semiconductor material, was deposited on glassy carbon rods by PVD to thicknesses of 50, 30, and 15 nm, and platinum (Pt), a metal material, was then deposited on the surface to a thickness of 5 nm.

[0038] As a control, a catalyst prepared by depositing only platinum (Pt) on a glassy carbon rod to a thickness of 5 nm was used.

[0039] This is to confirm the structural conditions of the catalyst that are effective as a Schottky junction type selective oxidation reaction catalyst.

[0040] In Example 2, a selective reduction catalyst that only causes a reduction reaction at the reduction electrode (cathode) was prepared as a catalyst for a water electrolysis cell. The catalyst was prepared by depositing tin oxide (SnO), an n-type semiconductor material, to a thickness of 50 nm on a glassy carbon rod using a PVD method, and then depositing platinum (Pt) to a thickness of 7 nm.

[0041] As a control, platinum (Pt) alone was deposited on a glassy carbon rod to a thickness of 7 nm to form a catalyst.

[0042] This is to confirm the structural conditions of the catalyst that are effective as a Schottky junction type selective reduction reaction catalyst.

[0043] FIG. 2 is a graph showing the degree to which the action of a Schottky junction selective oxidation catalyst made of platinum and cobalt oxide is realized as a catalyst for a fuel cell.

[0044] The graphs of HOR activity and ORR activity of the Pt / Co3O4 catalyst realized by the selective oxidation catalyst prepared in Example 1 show that the thinner the Co3O4 deposited, the better the performance, based on the HOR activity. However, samples deposited with Co3O4 thicknesses of 30 nm or more exhibited excessively low conductivity, failing to demonstrate meaningful activity. This can be interpreted as the excessively thick Co3O4 layer being dominated by the non-conductive properties of metal oxides, making it difficult for electrons to pass through the band barrier formed during Schottky contact. Samples deposited to a thickness of 15 nm, considered appropriate, exhibited performance similar to that of a pure platinum (bare Pt) catalyst. In contrast, ORR evaluation revealed that samples deposited with Co3O4 thicknesses of 30 nm or more also exhibited low conductivity, but even the sample deposited to a thickness of 15 nm exhibited a sharp decline in activity compared to pure Pt. From these different results for the oxidation and reduction reactions of Pt / Co3O4, it was confirmed that selective oxidation reaction catalytic action was realized under actual experimental conditions.

[0045] FIG. 3 is a graph showing the degree to which the action of a Schottky junction type selective reduction catalyst made of platinum and tin oxide is realized as a catalyst for a water electrolysis cell.

[0046] An example was prepared by depositing SnO2 as an n-type semiconductor material to a thickness of 50 nm on a glassy carbon rod, and then platinum (Pt), a metal catalyst material, was deposited on the surface to a thickness of 7 nm. As a control group, a catalyst (Pt / GC) was prepared by depositing only platinum catalyst to a thickness of 7 nm on glassy carbon. These were used as catalysts for water electrolysis cells, and the conditions before and after the shutdown test were compared.

[0047] As can be seen from the CV graph on the left, the hydrogen adsorption (underpotential adsorption hydrogen (H UPD ) are formed in almost the same way regardless of the SnO2 deposition layer, but the oxidation peak is formed only in the catalyst (Pt / GC) that uses only platinum catalyst without the n-type semiconductor material SnO2. Therefore, it was confirmed that the oxidation reaction is suppressed and the reduction reaction occurs selectively only in the catalyst (Pt / SnO2 on GC) that uses tin oxide as the n-type semiconductor material.

[0048] As can be seen from the HER graph shown on the right, before the shutdown test of the water electrolysis cell, despite the presence of SnO2, the initial activity (before data) was almost the same as that of Pt / GC, which indicates that there is no problem with the supply of reducing current.

[0049] In contrast, when examining the results (after data) after a shutdown test in a water electrolysis cell, 2 Based on this, the HER overpotential for the control Pt / GC increased by 2.4 times (32 to 78 mV), while for the Pt / SnO2 selective reduction catalyst of Example 2, it only increased by about 1.1 times (39 to 43 mV), showing no significant change. Therefore, from these experimental results, it was confirmed that under shutdown conditions of a water electrolyzer employing the selective reduction catalyst of Example 2 employing tin oxide (SnO2) as an n-type semiconductor, the supply of oxidation current was suppressed, thereby improving the durability of the catalyst.

[0050] The results of various experiments conducted to examine the effects of the present invention will be described below.

[0051] Figure 4 shows constant voltage measurements of Pt, Co3O4, and Pt / Co3O4 under conditions that mimic the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) conditions. Under HOR conditions of 0.05 V and H2 saturation, Pt and Pt / Co3O4, except for Co3O4, which is close to being a nonconductor (insulator), show high currents.

[0052] Under ORR conditions of 0.8 V and O2 saturation, Co3O4 exhibited extremely low current, while Pt still exhibited high current, whereas Pt / Co3O4 exhibited low current close to that of Co3O4. This confirmed the selective behavior of Pt / Co3O4, in which reduction current was suppressed and only oxidation current was actively transmitted.

[0053] Figure 5 shows data obtained by measuring the work function for each reaction. The initial sample, which is in the state immediately after deposition, and the sample after HOR showed roughly the same work function, while the sample after ORR showed an increased work function. This confirms that the Schottky barrier increases significantly only through ORR, a reduction reaction, thereby hindering current flow.

[0054] When the conductivity between these surfaces was checked, it was as shown in Table 1 below.

[0055] [Table 1]

[0056] When the interfacial conductivity measured using a Hall Measurement System was examined, it was found that when Pt / Co3O4 was exposed to an oxidation reaction as a selective oxidation catalyst, the conductivity was almost the same as that of Pt. However, when exposed to a reduction reaction, the conductivity was 10 5 You can see that it doubles.

[0057] 6 shows data on the work function of Pt / SnO2 in various reactions according to an embodiment of the present invention. Compared to Pt / Co3O4, Pt / SnO2 is formed such that the work functions of each sample are relatively similar.

[0058] However, the work function increases in the order of HER < initial < stop, and the work function decreases slightly when the HER, which is a reduction reaction, is passed through compared to the initial state immediately after deposition. However, conversely, after stop, which is an oxidation reaction, the Schottky barrier increases, which confirms that current is impeded.

[0059] Therefore, according to the present invention, a Schottky contact occurs at the interface between the platinum catalyst and the semiconductor material, allowing electrons to flow in only one direction, thereby selectively inducing either an oxidation reaction or a reduction reaction. This significantly reduces side reactions that may occur at each electrode of the fuel cell or water electrolyzer, thereby solving the problem of deterioration in durability that may occur during start-up and shutdown of the fuel cell or water electrolyzer.

[0060] While the present invention has been described with reference to limited embodiments and drawings, the present invention is not limited to the above embodiments, and various modifications and variations can be made by those skilled in the art based on such descriptions. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the scope of the appended claims.

Claims

1. A fuel cell having an anode and a cathode, The fuel cell accommodates an electrolyte between the anode and the cathode, the anode electrode is formed by a support layer made of a semiconductor material and a catalyst layer made of a metal formed on a surface of the support layer, and the support layer and the catalyst layer are formed in a Schottky junction state; The semiconductor material is a p-type semiconductor material that serves as a catalyst for selective oxidation reaction and selectively supports only hydrogen oxidation reaction (HOR) at the anode electrode, the material forming the catalyst layer is platinum, and the p-type semiconductor material is cobalt oxide (Co 3 O 4 ). fuel cell.

2. 2. The fuel cell according to claim 1, wherein the p-type semiconductor material contained in the support layer has a work function value greater than that of the metal contained in the catalyst layer.

3. 2. The fuel cell according to claim 1, wherein the platinum particles forming the catalyst layer have a particle size of 1.2 nm or more.

4. The platinum catalyst layer has a thickness of 5 nm, 2. The fuel cell according to claim 1, wherein the thickness of the p-type semiconductor material, cobalt oxide, forming the support layer is 15 to 30 nm.

5. A fuel cell having an anode and a cathode, The fuel cell accommodates an electrolyte between the anode and the cathode, the cathode electrode is formed by a support layer made of a semiconductor material and a catalyst layer made of a metal formed on a surface of the support layer, and the support layer and the catalyst layer are formed in a Schottky junction state; The semiconductor material is an n-type semiconductor material that selectively supports only the oxygen reduction reaction (ORR) at the cathode as a catalyst for the selective reduction reaction, the material forming the catalyst layer is platinum, and the n-type semiconductor material is tin oxide (SnO 2 ). fuel cell.

6. the catalyst layer made of platinum has a layer thickness of 7 nm; The thickness of the n-type semiconductor material, tin oxide, forming the support layer is 50 nm. The fuel cell according to claim 5 .

7. A water electrolysis device having an anode and a cathode, the water electrolysis device accommodates an electrolyte between the anode and the cathode; the cathode electrode is formed by a support layer made of a semiconductor material and a catalyst layer made of a metal formed on a surface of the support layer, and the support layer and the catalyst layer are formed in a Schottky junction state; The semiconductor material is an n-type semiconductor material that selectively supports only the hydrogen evolution reaction (HER) at the cathode as a catalyst for the selective reduction reaction, the material forming the catalyst layer is platinum, and the n-type semiconductor material is tin oxide (SnO 2 ). Water electrolysis equipment.

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