KR102628316B1 - Catalyst, electrode and electrochemical reaction system - Google Patents

Abstract

The present invention relates to a catalyst, an electrode and an electrochemical reaction system, wherein the catalyst contains a trivalent transition metal and has a non-stoichiometric reaction represented by A _{1- δ} O (A is a transition metal, 0 < δ < 0.5). It is characterized by containing (non-stoichiometric) transition metal oxide nanoparticles.

Description

Catalyst, electrode and electrochemical reaction system {CATALYST, ELECTRODE AND ELECTROCHEMICAL REACTION SYSTEM}

The present invention relates to catalysts, electrodes and electrochemical reaction systems. More specifically, it relates to catalysts, electrodes, and electrochemical reactions applicable to various electrochemical catalytic reactions such as water splitting oxidation/reduction reaction, hydrogen production reaction, and CO ₂ reduction reaction.

Recently, as a measure to solve environmental problems caused by depletion of carbon-based energy and fuel gas emissions, research has been actively conducted on ways to store energy by producing hydrogen and oxygen through water decomposition or to obtain energy through fuel cells. It's going on. In these methods, an electrochemical reaction is used, and in the case of the oxygen generation reaction in water decomposition and the oxygen reduction reaction in a fuel cell, the reaction rate is slow and thus acts as a rate determining step. Therefore, an electrocatalyst is required to increase the oxygen generation rate or oxygen reduction rate.
Reference Prior Literature 1: Jin, K. et al. Partially Oxidized Sub-10 nm MnO Nanocrystals with High Activity for Water Oxidation Catalysis. Scientific Reports, 5, 10279, pages 1 to 11, Supporting Information pages 1 to 15, published on May 22, 2015
Reference Prior Document 2: Japanese Patent Publication No. 2017-016895 (2017.01.19.)

Currently, the industry uses catalysts based on precious metals such as Ru, Pt, and Ir. Precious metal-based oxide catalysts have good properties, but are expensive due to their scarcity. Therefore, in order to compete on price and dominate the market, it is necessary to develop a catalyst manufactured using relatively inexpensive raw materials.

In the case of molecular catalysts, a representative example is the molecule called mononuclear ruthenium complex [Ru(bda)(isoq) ₂ ] (H2bda = 2,2′-bipyridine-6,6′-dicarboxylic acid; isoq = isoquinoline) reported by the Sun group. Catalysts include catalysts. In the case of these molecular-level catalysts, they have the advantage of high characteristics and a high degree of freedom in synthesis, but their recyclability is low, they are mostly limited to precious metal-based catalysts, so they are expensive, and the stability of the catalyst is critically low. It has disadvantages.

In the case of heterogenous catalysts, Co-Pi reported by the Nocera group is a representative example. This catalyst has the advantages of high stability and high applicability in various chemical reactions, but its selectivity as a catalyst is significantly lower than that of molecular-based catalysts, and TOF It has the disadvantage of relatively low catalytic efficiency.

Additionally, the industry is currently using catalysts based on noble metals such as Ru, Pt, and Ir. Precious metal-based oxide catalysts have good properties, but are expensive due to their scarcity. Therefore, in order to compete on price and dominate the market, it is necessary to develop a catalyst manufactured using relatively inexpensive raw materials.

The present invention is intended to solve various problems including the above-mentioned problems. The purpose of the present invention is to provide a catalyst and a catalyst preparation method that have high stability, can be used in various chemical reactions, have high catalytic efficiency, and are highly economical. do.

However, these tasks are illustrative and do not limit the scope of the present invention.

According to one aspect of the present invention for solving the above problem, a non-stoichiometric metal containing a trivalent transition metal and expressed as A _{1- δ} O (A is a transition metal, 0 < δ < 0.5) ) A catalyst comprising transition metal oxide nanoparticles is provided.

Additionally, according to an embodiment of the present invention, the transition metal may be any one of Co, Ni, Cu, and Fe.

Additionally, according to an embodiment of the present invention, the trivalent transition metal and the divalent transition metal may be located on the surface of the transition metal oxide.

Additionally, according to one embodiment of the present invention, the transition metal oxide nanoparticles may have a size of 100 nm or less.

Additionally, according to an embodiment of the present invention, the transition metal oxide may be in the form of a thin film.

And, according to one aspect of the present invention for solving the above problem, a nano core containing the transition metal oxide; And a catalyst comprising metal nanoparticles adsorbed on the surface of the nanocore is provided.

In addition, according to an embodiment of the present invention, the metal nanoparticles include iridium (Ir), cobalt (Co), copper (Cu), nickel (Ni), iron (Fe), chromium (Cr), and ruthenium (Ru). , it may include at least one of gold (Au), platinum (Pt), palladium (Pd), and rhodium (Rh).

Additionally, according to one embodiment of the present invention, the nanocore may have a size of 100 nm or less, and the metal nanoparticle may have a size of 3 nm or less.

And, according to one aspect of the present invention for solving the above problems, an electrode containing the catalyst is provided.

And, according to one aspect of the present invention for solving the above problems, an electrochemical reaction system including the catalyst is provided.

According to one embodiment of the present invention as described above, it has high stability, can be used in various chemical reactions, has high catalytic efficiency, and is highly economical. Of course, the scope of the present invention is not limited by this effect.

1 is a flowchart showing a catalyst production process according to an embodiment of the present invention.
2 to 5 are TEM images of transition metal oxides according to various embodiments of the present invention.
Figure 6 is a graph showing the results of X-Ray Diffraction (XRD) analysis of cobalt oxide according to an embodiment of the present invention.
Figure 7 is a flowchart showing the catalyst production process according to another embodiment of the present invention.
Figure 8 is a schematic perspective view of a nanostructure containing a transition metal oxide according to an embodiment of the present invention.
Figure 9 is a TEM photo of a nanostructure containing cobalt oxide according to an embodiment of the present invention.
Figure 10 is a graph showing the catalytic properties of transition metal oxides according to various embodiments of the present invention.
Figure 11 is a graph showing the catalytic properties of a nanostructure containing a transition metal oxide according to an embodiment of the present invention.
Figure 12 is a schematic diagram of a water splitting system including a catalyst according to an embodiment of the present invention.
Figure 13 is a schematic diagram of a fuel cell system including a catalyst according to an embodiment of the present invention.

The detailed description of the invention described below refers to the accompanying drawings, which show by way of example specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It should be understood that the various embodiments of the invention are different from one another but are not necessarily mutually exclusive. For example, specific shapes, structures and characteristics described herein with respect to one embodiment may be implemented in other embodiments without departing from the spirit and scope of the invention. Additionally, it should be understood that the location or arrangement of individual components within each disclosed embodiment may be changed without departing from the spirit and scope of the invention. Accordingly, the detailed description that follows is not intended to be taken in a limiting sense, and the scope of the invention is limited only by the appended claims, together with all equivalents to what those claims assert, if properly described. Similar reference numbers in the drawings refer to identical or similar functions across various aspects, and the length, area, thickness, etc. may be exaggerated for convenience.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings in order to enable those skilled in the art to easily practice the present invention.

Preparation of transition metal oxides and transition metal oxide nanoparticles

1 is a flowchart showing a catalyst production process according to an embodiment of the present invention.

Referring to Figure 1, the method for producing transition metal oxide nanoparticles according to an embodiment of the present invention includes preparing a first solution containing a transition metal ion supply material and a fatty acid surfactant (S110), an alcohol surfactant Preparing a second solution containing (S120), maturing the first and second solutions respectively at a predetermined temperature (S130), adding the second solution to the first solution to form transition metal oxide nanoparticles. It may include a step (S140) and a step (S150) of maturing the transition metal oxide nanoparticles at a predetermined temperature. Additionally, the method for producing transition metal oxide nanoparticles according to an embodiment may further include a step (S160) of surface treating the transition metal oxide nanoparticles.

The method for producing transition metal oxide nanoparticles includes preparing a first solution containing a transition metal ion supply material and a fatty acid surfactant (S110), preparing a second solution containing an alcohol surfactant (S120), Aging the first and second solutions at a predetermined temperature (S130), adding the second solution to the first solution to form transition metal oxide nanoparticles (S140), and forming the transition metal oxide nanoparticles It may include a step of maturing at a predetermined temperature (S150). In addition, the method for producing transition metal oxide nanoparticles according to an embodiment may further include a step (S160) of surface treating the transition metal oxide nanoparticles.

The transition metal may be any one of Co, Ni, Cu, and Fe.

In the step of preparing a first solution including a transition metal ion supply material and a fatty acid surfactant (S110), the transition metal ion supply material and the fatty acid surfactant may be mixed in an organic solvent to prepare the first solution. Fatty acid surfactants help dissolve the transition metal ion supply material and can be used to disperse the transition metal oxide nanoparticles formed in the subsequent S140 step.

The fatty acid surfactant may be, for example, myristic acid, stearic acid, oleic acid, etc., and may be in a solution state with a concentration of 0.1 M to 0.5 M. The transition metal ion supply material is transition metal acetate. For example, cobalt ions can be supplied using cobalt acetate. The first solution may be a cationic solution, and the concentration of the cation may be 0.5mM to 2mM.

In the step of preparing a second solution containing an alcohol surfactant (S120), the alcohol surfactant may be, for example, decanol, myristyl alcohol, stearyl alcohol, etc. and a second solution can be prepared by mixing with an organic solvent. Alcohol surfactants may be involved in nucleation and growth. In steps S110 and S120, the organic solvent may be, for example, octadecene or hexadecylamine.

The step (S130) of maturing the first and second solutions at a predetermined temperature may be performed at a temperature of 250° C. to 300° C., and the temperature may be maintained constant during the aging period. The maturation time may be, for example, about 1 hour each.

In the step of forming transition metal oxide nanoparticles by adding the second solution to the first solution (S140), transition metal oxide nanoparticles may be formed by hot injection and thermal decomposition. This step can be performed at a temperature of 250°C to 300°C.

The step (S150) of maturing the transition metal oxide nanoparticles at a predetermined temperature may be performed for 1 minute to 24 hours after the addition of the second solution, and the size of the transition metal oxide nanoparticles produced through adjustment of the aging time may vary. It can be controlled. The size of the transition metal oxide nanoparticles may be, for example, 1 nm to 100 nm. In one embodiment, the size of the transition metal oxide nanoparticles may be determined depending on the ratio of the transition metal ion supply material and the fatty acid surfactant, and the ratio may range from 1:2 to 1:6, for example. The lower the ratio of fatty acid surfactant, the smaller the size of the transition metal oxide nanoparticles can be.

The step of surface treating the transition metal oxide nanoparticles (S160) may be a step for removing the ligand on the surface of the transition metal oxide nanoparticles. Ligands are formed when fatty acid surfactants are adsorbed on the surface of transition metal oxide nanoparticles and have low conductivity, so they need to be removed in order to use transition metal oxide nanoparticles as a catalyst. This step can be performed, for example, by immersing the prepared transition metal oxide nanoparticles in a basic solution such as ammonia water (NH ₄ OH), sodium hydroxide (NaOH), etc. Alternatively, this step may be performed by heat treatment. In particular, the surface of the transition metal oxide nanoparticles is partially oxidized by this step, and the transition metal oxide nanoparticles may contain trivalent transition metals (Co ^Ⅲ , Ni ^Ⅲ , Cu ^Ⅲ , Fe ^Ⅲ ).

The transition metal oxide prepared according to this example may have a non-stoichiometric composition and may be represented by the following formula (1).

[Formula 1]

A _1-δ O

In Formula 1, A is a transition metal and is any one of Co, Ni, Cu, and Fe, δ satisfies 0 < δ < 0.5, and the ratio of transition metal A to oxygen O is the atomic ratio, or δ is the atomic ratio. am.

In this specification, a non-stoichiometric composition can be understood to mean excluding the thermodynamically stable quantitative relationship between a transition metal and oxygen in a compound composed of a transition metal and oxygen. For example, in the case of cobalt oxide, the stoichiometric cobalt oxide may include CoO, Co ₃ O ₄ , Co ₂ O ₃ and CoO ₂ . Therefore, specifically, the cobalt oxide may have a composition excluding the case where δ is 0.25 and 1/3. That is, δ may satisfy the ranges of 0 < δ < 0.25, 0.25 < δ < 1/3, and 1/3 < δ < 0.5.

The transition metal oxide may include a trivalent transition metal (for example, trivalent cobalt (Co ^III )), and the trivalent transition metal may be located on the surface of the transition metal oxide. The trivalent transition metal located on the surface of the transition metal oxide may be thermodynamically unstable. Additionally, the trivalent transition metal located on the surface of the transition metal oxide may be in the form of a type of defect that is not located within the lattice structure. Both trivalent and divalent transition metals can be located on the surface of the transition metal oxide.

In the example of FIG. 1, a method of manufacturing transition metal oxides into nanoparticles is shown, but the present invention is not limited thereto. For example, transition metal oxides may be manufactured in the form of thin films. In this case, the transition metal oxide can be produced using a method of coating transition metal oxide nanoparticles as described above, or a deposition method such as electrodeposition or sputtering.

Structure of transition metal oxide nanoparticles

2 to 5 are TEM images of transition metal oxides according to various embodiments of the present invention. Figure 2 shows a picture of cobalt oxide (Co-Oxide), Figure 3 shows a picture of nickel oxide (Ni-Oxide), Figure 4 shows a picture of copper oxide (Cu-Oxide), and Figure 5 shows a picture of iron oxide (Fe-Oxide).

Referring to FIGS. 2 to 5, transition metal oxide nanoparticles prepared according to steps S110 to S160 of the example of FIG. 1 were analyzed by TEM. Specifically, the transition metal oxide nanoparticles used in the analysis were treated with aqueous ammonia (NH ₄ OH) for 1 hour in step S160. According to Figures 2 to 5, transition metal oxide nanoparticles have a size of about 100 nm or less, for example, cobalt oxide nanoparticles have a size of about 20 nm or less, nickel oxide nanoparticles and iron oxide nanoparticles have a size of about 10 nm or less, Copper oxide nanoparticles may have a size of about 100 nm or less. In addition, in the diffraction pattern analysis, the crystal plane of the transition metal oxide with a composition of A ₃ O ₄ (A is a transition metal, one of Co, Ni, Cu, and Fe) and the crystal plane of the transition metal oxide with the composition of AO are indexed together. It can be. Therefore, the surface of the prepared transition metal oxide nanoparticles may be partially oxidized by step S160.

Figure 6 is a graph showing the results of X-Ray Diffraction (XRD) analysis of cobalt oxide according to an embodiment of the present invention.

Referring to Figure 6, the crystal structure analysis results of cobalt oxide nanoparticles prepared according to steps S110 to S160 of the example of Figure 1 are shown. Cobalt oxide nanoparticles have a composition of CoO, and accordingly, can exhibit signals of the (111) plane (36°), (200) plane (42°), and (220) plane (62°) of CoO.

Preparation of nanostructures containing transition metal oxides

Figure 7 is a flowchart showing the catalyst production process according to another embodiment of the present invention. Figure 8 is a schematic perspective view of a nanostructure 100 containing a transition metal oxide according to an embodiment of the present invention.

Referring to FIG. 7, the method of manufacturing a nanostructure 100 containing a transition gold oxide according to an embodiment of the present invention includes the step of coating the transition metal oxide nanoparticles according to the embodiment of FIG. 1 on a substrate ( It may include steps S210), immersing the substrate in a metal ion solution (S220), and maturing the metal ion solution in which the substrate is immersed at a predetermined temperature (S230).

The step of coating transition metal oxide nanoparticles on a substrate (S210) may use methods such as spin-coating or drop-casting. The substrate may be, for example, glassy carbon, but is not limited thereto.

In the step of immersing the substrate in the metal ion solution (S220), the metal ion solution includes iridium (Ir), cobalt (Co), copper (Cu), nickel (Ni), iron (Fe), chromium (Cr), and ruthenium ( It may contain at least one cation selected from Ru), gold (Au), platinum (Pt), palladium (Pd), and rhodium (Rh). The metal ion solution may include at least one of acetate, nitrate, and chloride. The concentration of metal cations in the metal ion solution may be 1mM to 50mM.

Metal nanoparticles 120 may be formed on the surface of the transition metal oxide nanoparticles 110 by maturing the metal ion solution in which the substrate is immersed at a predetermined temperature (S230). Ripening can be performed at a temperature of 60°C to 100°C. Additionally, the aging time may be 30 minutes to 24 hours. Depending on the aging time, the size of the metal nanoparticles formed on the surface of the transition metal oxide nanoparticles 110 can be controlled.

In one embodiment, the transition metal oxide nanoparticles 110 in the step of coating the transition metal oxide nanoparticles 110 on the substrate (S210) are the transition metal oxide nanoparticles 110 without performing step S160 of FIG. 1. ) can be. In this case, step S160 may be performed immediately after step S210 of coating the transition metal oxide nanoparticles 110 on the substrate.

Referring to FIG. 8, according to the above embodiment, a nano core 110 that is a transition metal oxide nanoparticle containing a trivalent transition metal and a metal nanoparticle 120 adsorbed on the surface of the nano core 110 are included. Nanostructure 100 can be manufactured.

The nanocore 110 may have a non-stoichiometric composition and may be represented by [Formula 1] above. As an example, the nano core 110 may include trivalent cobalt (Co ^III ) on its surface. In particular, the nanocore 110 may be a transition metal oxide having a structure corresponding to the embodiments of FIGS. 2 to 5.

Metal nanoparticles 120 include iridium (Ir), cobalt (Co), copper (Cu), nickel (Ni), iron (Fe), chromium (Cr), ruthenium (Ru), gold (Au), and platinum. It may be at least one of (Pt), palladium (Pd), rhodium (Rh), and alloys thereof.

A plurality of metal nanoparticles 120 may be formed on the surface of one nanocore 110. The size (D1) of the nanocore 110 may be 20 nm or less (cobalt oxide nanoparticles), 10 nm or less (nickel oxide nanoparticles, iron oxide nanoparticles), or 100 nm or less (copper oxide nanoparticles), depending on the transition metal. The size (D2) of the metal nanoparticle 120 may be 1 nm to 10 nm, particularly 3 nm or less.

Figure 9 is a TEM image of a nanostructure 100 containing cobalt oxide according to an embodiment of the present invention.

Referring to FIG. 9, the nanostructure 100 containing cobalt oxide 110 manufactured according to the example of FIG. 7 was analyzed by TEM. The nanostructure 100 may include a nanocore 110 of cobalt oxide and metal nanoparticles 120 adsorbed on the nanocore 110. The metal nanoparticles 120 may be adsorbed substantially uniformly on the surface of the nano core 110. In particular, in this embodiment, the metal nanoparticles 120 may include iridium (Ir). Metal nanoparticles 120 appearing as black dots can be seen on the nano core 110 appearing in gray.

Catalytic properties of transition metal oxides and nanostructures

Figure 10 is a graph showing the catalytic properties of transition metal oxides according to various embodiments of the present invention. Figure 11 is a graph showing the catalytic properties of a nanostructure containing a transition metal oxide according to an embodiment of the present invention.

Hereinafter, the catalytic properties are examined by mixing the transition metal oxide prepared according to the embodiments of the present invention with a carbon additive, drying it to form a powder, and then coating the powder on a conductive substrate to prepare an electrode. This was done by measuring the characteristics.

The powder may be coated on the conductive substrate by, for example, spin coating, in which case the rotation speed may range from 2000 rpm to 4000 rpm. Additionally, the coating time may range from 10 seconds to 60 seconds. Electrochemical properties can be measured using a 3-electrode cell or 2-electrode cell filled with an aqueous buffer electrolyte solution. Specifically, in the case of a three-electrode cell, a catalyst-coated working electrode, a counter electrode consisting of a platinum (Pt) wire or a platinum (Pt) plate, and a reference of silver/silver chloride (Ag/AgCl) It may consist of a reference electrode, and a two-electrode cell may consist of a working electrode and a counter electrode without a reference electrode. The aqueous buffer electrolyte solution may be a sodium phosphate or potassium phosphate solution with a pH of 5 to 8, or a sodium hydroxide (NaOH) or potassium hydroxide solution (KOH) with a pH of 11 to 14.

Referring to FIG. 10, a cyclic current-voltage curve (cyclic voltammogram) when using a transition metal oxide catalyst according to various embodiments of the present invention is shown compared to a standard hydrogen electrode (Normal Hydrogen Electrode, NHE).

Catalyst properties are shown in FIG. 8 using cobalt oxide, nickel oxide, copper oxide, and iron oxide among transition metal oxides as examples, and manganese oxide as a comparative example.

In the case of cobalt oxide, it showed the best catalytic properties and showed better properties than manganese oxide.

Referring to FIG. 11, the circulating current when using a catalyst of the nanostructure 100 including the cobalt oxide and iron oxide nanocores 110 formed with iridium (Ir) 120 according to various embodiments of the present invention - A cyclic voltammogram is shown compared to a normal hydrogen electrode (NHE).

In particular, the nano core 110 (or nano structure 100) with metal nanoparticles 120 formed on the surface showed better catalytic properties. This may be because a trivalent transition metal (eg, cobalt (Co ^III )) in an unstable state on the surface of the transition metal oxide nanoparticle is involved in the catalytic action. In addition, when calculating the overpotential value, which is the value obtained by subtracting the equilibrium potential of the reaction from the electrode potential during the electrochemical reaction, in the case of cobalt oxide nanoparticles formed with metal nanoparticles, it is about 300 mV at an electrode current density of 10 mA/cm ² or more. The following values are shown. As another example, values below 600mV were shown for Mn, Co, and Ni, and values below 800mV were shown for Cu and Fe. It shows high activity compared to cobalt (Co), nickel (Ni), copper (Cu), and iron (Fe)-based solid phase catalysts. Compared to the nanostructure 100, the transition metal oxide nanoparticles showed relatively low catalytic properties, which can be interpreted as being due to low conductivity due to the ligand surrounding the transition metal oxide nanoparticles.

And, in step S160 of FIG. 1, the example treated with ammonia water (NH ₄ OH) for 1 hour showed relatively higher catalytic properties than the example treated with ammonia water (NH 4 OH) for 24 hours. The longer the surface treatment, the more the surface of the transition metal oxide is completely oxidized and can be viewed as being in a stable state, which can be interpreted as being a stoichiometric transition metal oxide or a state close to it. As a result of additional experiments, the best catalytic properties were shown when the treatment time with ammonia water (NH ₄ OH) was about 1 hour, and lower catalytic properties were shown when the treatment time was 30 minutes and 2 hours. It showed a characteristic of gradually decreasing as time increased. However, this optimized processing time may change depending on the size of the transition metal oxide nanoparticles, process conditions, etc.

Application example of electrochemical reaction system

Figure 12 is a schematic diagram of a water splitting system including a catalyst according to an embodiment of the present invention.

Referring to FIG. 12, the water splitting system 200 may include an electrolyzer 210, an aqueous buffer electrolyte solution 220, a first electrode (anode) 230, and a second electrode (cathode) 240. . The first and second electrodes 230 and 240 may be connected by a power source. In one embodiment, the water splitting system 200 may further include an ion exchange unit disposed between the first and second electrodes 230 and 240.

The first and second electrodes 230 and 240 may each be made of a semiconductor or conductive material. An oxygen generation catalyst 260 may be disposed on at least one surface of the first electrode 230, and the oxygen generation catalyst 260 is a transition metal oxide according to the embodiment of the present invention described above with reference to FIGS. 1 to 11. (110) or a nanostructure 100 including it.

The electrolyzer 210 may further be formed with an inlet and outlet, such as an intake pipe and a drain pipe.

The aqueous buffer electrolyte solution 220 may serve as a source of water used in the water decomposition reaction and as a receptor for protons generated during the water decomposition reaction. The aqueous buffer electrolyte solution 220 may include at least one of potassium phosphate and sodium phosphate, such as KH ₂ PO ₄ , K ₂ HPO ₄ , K ₃ PO ₄ , or mixtures thereof. The pH of the buffer electrolyte aqueous solution 220 may be 2 to 14. In particular, when using the oxygen generating catalyst 260 of the present invention, the aqueous buffer electrolyte solution 220 may have neutral conditions. To serve as a proton acceptor, the buffer electrolyte aqueous solution 220 may contain a proton-accepting anion. Accordingly, even if the amount of protons (H ⁺ ) produced increases as the water decomposition reaction progresses, the proton-soluble anion can accommodate at least a portion of these protons, thereby lowering the pH reduction rate of the aqueous buffer electrolyte solution 220. The proton-accepting anion may include at least one of phosphate ion, acetate ion, borate ion, and fluoride ion.

When a voltage is applied between the first and second electrodes 230 and 240 in the water splitting system 200, a reaction in which oxygen is generated from the first electrode 230 and hydrogen is generated from the second electrode 240. This happens. Each half reaction is represented by Schemes 1 and 2 below.

[Scheme 1] 2H ₂ O → O ₂ + 4H ⁺ + 4e ^-

[Scheme 2] 4H ⁺ + 4e ^- → 2H ₂

The oxygen generation catalyst 260 according to an embodiment of the present invention may participate in the reaction at the first electrode 230 represented by Scheme 1 above. Thereby, the water decomposition reaction can be achieved with low overpotential even under neutral conditions.

Figure 13 is a schematic diagram of a fuel cell system including a catalyst according to an embodiment of the present invention.

Referring to FIG. 13 , the fuel cell system 300 may include an electrolyte membrane 320, a first electrode (anode) 330, and a second electrode (cathode) 340. In addition, the fuel cell system 300 has first to third inlet/outlet portions 352, 354, and 356, and a cover portion on which first and second electrodes 330 and 340 and an electrolyte membrane 320 are disposed. It may include (310).

The fuel cell system 300 of this embodiment may be a solid oxide fuel cell (SOFC), but is not limited thereto. The first and second electrodes 330 and 340 and the electrolyte membrane 320 can form one unit cell, and a fuel cell can be formed by stacking a plurality of unit cells.

In the fuel cell system 300, the electrochemical reaction may proceed in a reverse direction to the water decomposition system 200 of FIG. 12.

Cations may be generated through an oxidation reaction of hydrogen at the first electrode 330, and water may be generated through a reduction reaction of oxygen at the second electrode 340. At this time, electrons are generated in the first electrode 330 and electrons are consumed in the second electrode 340, so when the two electrodes are connected to each other, electricity flows.

The first and second electrodes 330 and 340 may each be made of a semiconductor or conductive material. At least one surface of the second electrode 340 is an oxygen reduction reaction catalyst 360, and a transition metal oxide 110 or a nanostructure containing the same according to an embodiment of the present invention described above with reference to FIGS. 1 to 10 ( 100) may be coated. The oxygen reduction reaction catalyst 360 of this embodiment may be the same material as the oxygen generation catalyst 260 of the embodiment of FIG. 12, but may be referred to differently since it is involved in the reverse direction. Therefore, the oxygen evolution catalyst of the present invention can act as a catalyst for both the oxygen evolution reaction and the reverse reaction.

The electrolyte membrane 320 may be in the form of a proton or negative conductive polymer membrane depending on the type of target reaction, and simultaneously separates the first electrode 330 side from the second electrode 330 side and generates proton or negative electrons between them. It can enable the flow of electrons. For example, the proton conductive polymer membrane may be Nafion (NAFION ^® ), and the negative electron conductive polymer membrane may be an anion exchange membrane (AEM).

In the fuel cell system 300, the oxidation and reduction reactions occur at useful rates, and the oxygen reduction reaction catalyst 360 according to an embodiment of the present invention can be used to ensure that the reactions occur at a reduced potential.

As a system including an oxygen generating catalyst according to an embodiment of the present invention, a water splitting system and a fuel cell system have been described as examples, but the present invention is not limited thereto, and the oxygen generating catalyst or oxygen generating catalyst according to an embodiment of the present invention The reduction reaction catalyst may be used in various electrochemical reaction systems.

Although the present invention has been shown and described with reference to preferred embodiments as described above, it is not limited to the above embodiments and may be modified in various ways by those skilled in the art without departing from the spirit of the invention. Transformation and change are possible. Such modifications and variations should be considered to fall within the scope of the present invention and the appended claims.

100: Nanostructure
110: Nano core, transition metal oxide
120: Metal nanoparticles
200: Water splitting system
260: Oxygen generation catalyst
300: Fuel cell system
360: Oxygen reduction reaction catalyst

Claims (10)

Contains trivalent transition metals,
[Chemical formula]
A _1-δ O (A is a transition metal selected from Co, Ni, Cu, or Fe, 0 < δ < 0.5, the ratio of transition metal A to oxygen O is the atomic ratio)
A catalyst for electrochemical reactions, comprising non-stoichiometric transition metal oxide nanoparticles represented by . According to paragraph 1,
In the above formula, any one of 0 < δ < 0.25, 0.25 < δ < 1/3, and 1/3 < δ < 0.5. According to paragraph 1,
A catalyst for electrochemical reaction in which the trivalent transition metal and the divalent transition metal are located on the surface of the transition metal oxide. According to paragraph 1,
A catalyst for electrochemical reaction, wherein the transition metal oxide nanoparticles have a size of 100 nm or less. delete A nano core containing the transition metal oxide of claim 1; and
A catalyst for electrochemical reaction, comprising metal nanoparticles adsorbed on the surface of the nanocore. According to clause 6,
The metal nanoparticles include iridium (Ir), cobalt (Co), copper (Cu), nickel (Ni), iron (Fe), chromium (Cr), ruthenium (Ru), gold (Au), platinum (Pt), A catalyst for electrochemical reaction, comprising at least one of palladium (Pd) and rhodium (Rh). According to clause 6,
A catalyst for electrochemical reaction, wherein the nanocore has a size of 100 nm or less, and the metal nanoparticles have a size of 3 nm or less. An electrode for an electrochemical reaction comprising the electrochemical reaction catalyst of any one of claims 1 to 4 and 6 to 8. An electrochemical reaction system comprising the electrochemical reaction catalyst of any one of claims 1 to 4 and 6 to 8.

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