Manganese oxide catalyst substituted with transition metal, method for manufacturing same, and oxygen evolution reaction using same

Abstract

The present invention relates to a manganese oxide catalyst substituted with a transition metal, a method for manufacturing same, and an oxygen evolution reaction using same and, more particularly, to a manganese oxide catalyst in which four transition metal elements of Co, V, Fe, and Ni are simultaneously substituted into a manganese oxide (MnO2) lattice, thereby exhibiting excellent oxygen evolution reaction catalytic performance sufficient to replace commercialized ruthenium / iridium-based noble metal materials.

Description

Transition metal-substituted manganese oxide catalyst, method for preparing the same, and oxygen evolution reaction using the same

[0001] The present invention relates to a transition metal-substituted manganese oxide catalyst, a method for manufacturing the same, and an oxygen evolution reaction using the same. More specifically, the invention relates to a transition metal-substituted manganese oxide catalyst that exhibits excellent oxygen evolution catalytic performance capable of replacing commercially available ruthenium / iridium-based precious metal materials by simultaneously substituting small amounts of four types of transition metal elements, Co, V, Fe, and Ni, into a manganese oxide (MnO2) lattice, a method for manufacturing the same, and an oxygen evolution reaction using the same.

[0002] As the depletion of fossil fuel resources and environmental pollution become increasingly severe, research in the energy sector to address these issues is actively underway. In particular, new energy production devices are being developed globally to replace greenhouse gas-emitting fossil fuels with the goal of carbon neutrality. To solve these problems, the development of hydrogen energy as an alternative energy source is emerging as a key objective. Among the various hydrogen production devices currently available, green hydrogen production technology based on water splitting using electrochemical catalysts is receiving significant attention as it is closest to commercialization. However, in hydrogen production via water splitting, the development of oxygen evolution catalyst materials is just as important as that of hydrogen evolution catalysts. This is because the oxygen evolution reaction is a major factor limiting the overall efficiency of water splitting. Without an effective oxygen evolution catalyst, more energy is required, leading to increased production costs and making commercialization difficult. Therefore, the development of high-efficiency, low-cost oxygen evolution catalysts is essential for enhancing the economic viability of hydrogen production and ultimately accelerating the commercialization of green hydrogen technology.

[0003] When electrical energy is applied to water molecules through water electrolysis, hydrogen and oxygen molecules are produced, and the overall reaction equation is expressed as follows.

[0004] 2H2O ↔ 2H2 + O2, E=1.23V

[0005] The water electrolysis reaction for generating hydrogen energy consists of two half-reactions: the Hydrogen Evolution Reaction (HER) and the Oxygen Evolution Reaction (OER). During the water electrolysis process, water molecules introduced into the anode, which is the oxidation electrode, are oxidized to produce protons, electrons, and oxygen molecules. The protons move from the anode through the electrolyte, and the cathode, which is the reduction electrode, accepts electrons moving through the external circuit to release hydrogen molecules.

[0006] To reduce the total overpotential required for water electrolysis, it is necessary to reduce the overpotentials applied during both the hydrogen and oxygen evolution reactions. In the case of the hydrogen evolution reaction, since the reaction mechanism is simpler than that of the oxygen evolution reaction, 100 mA / cm² 2 Numerous excellent hydrogen evolution catalysts exist with low overpotentials at the standard level of 100 mV. On the other hand, the oxygen evolution reaction requires a high overpotential due to its slower reaction rate and more complex process compared to the hydrogen evolution reaction. In other words, because the reaction mechanism is complex and various intermediates are formed during the reaction, oxygen evolution catalysts generally have an overpotential of 100 mA / cm². 2 It has a high overpotential of approximately 400 mV. For example, in the case of platinum (Pt), a representative hydrogen generation catalyst, it is 100 mA / cm². 2 While it exhibits a standard characteristic of 60 mV, iridium (Ir), a representative catalyst for the oxygen evolution reaction, shows 100 mA / cm². 2It exhibits characteristics of 330 mV (Y. Li, et al., 2 Sim, U. et al.). Therefore, while the electrolysis of water in an acidic electrolyte generates hydrogen more efficiently compared to an alkaline medium, there is a problem in that large quantities of expensive precious metals such as ruthenium (Ru) and iridium (Ir) are required due to the dissolution of metals caused by rapid oxidation under acidic media and harsh corrosive conditions. Since these precious metal materials are expensive and resources are limited, the development of new materials to replace them is essential.

[0007] Meanwhile, although research on manganese oxide (MnO2) is actively underway due to its low cost and abundant resources, it has limitations in that its oxygen evolution catalytic performance is significantly lower than that of Ir / Ru-based materials.

[0008] Therefore, the development and research of oxygen evolution catalysts with low overpotential comparable to hydrogen evolution catalysts remains a major challenge to be overcome for high-efficiency water electrolysis devices.

[0009]

[0010] Accordingly, the inventors made diligent efforts to solve the above problems and produce a material with excellent oxygen evolution catalytic performance at a low cost. As a result, they confirmed that when a small amount of four types of transition metal elements, Co, V, Fe, and Ni, are simultaneously substituted into a manganese oxide (MnO₂) lattice, the oxygen evolution catalytic performance is excellently improved, and thus completed the present invention.

[0011] The objective of the present invention is to provide a transition metal-substituted manganese oxide catalyst that exhibits excellent oxygen evolution reaction catalyst performance capable of replacing commercially available ruthenium / iridium-based precious metal materials while being inexpensive, a method for manufacturing the same, and an oxygen evolution reaction using the same.

[0012] To achieve the above objective, the present invention provides a manganese oxide catalyst characterized by being represented by General Formula 1:

[0013] [General Formula 1]

[0014] Mn a V b Co c Ni d Fe e O2

[0015] In general formula 1

[0016] a, b, c, d, and e are 0.4 ≤ a ≤ 0.99, 0.01 ≤ b ≤ 0.4, 0.01 ≤ c ≤ 0.4, 0.01 ≤ d ≤ 0.4, and 0.01 ≤ e ≤ 0.4, respectively.

[0017] The present invention also provides a method for producing the manganese oxide catalyst, comprising the step of hydrothermally synthesizing a solution containing a manganese precursor, a vanadium precursor, a cobalt precursor, an iron precursor, and a nickel precursor.

[0018] The present invention also provides an electrode for water electrolysis comprising the manganese oxide catalyst.

[0019] The present invention also provides a water electrolysis cell comprising the manganese oxide catalyst.

[0020] According to the present invention, the MnO2 catalyst substituted with V, Co, Ni, and Fe can be applied in various energy and environment-related fields. Major application areas include green hydrogen production, fuel cells, electrochemical energy storage devices, and environmental purification technologies, thereby contributing to the advancement of renewable energy and environmental technologies.

[0021] The catalyst material synthesized in this invention exhibits excellent performance when used as a water splitting catalyst, sufficient to replace commercially available ruthenium / iridium-based precious metal materials.

[0022] In addition, it offers excellent economic efficiency as it is very inexpensive compared to precious metals.

[0023] The catalytic material according to the present invention has high market potential due to its excellent performance and economic efficiency. In particular, it has the potential to replace existing expensive precious metal catalysts in the hydrogen production process through water splitting, thereby contributing significantly to the commercialization of the hydrogen energy industry. This catalytic material, which provides high performance at a low cost, is applicable in various fields such as green hydrogen production, fuel cells, and energy storage systems; furthermore, as the transition to a hydrogen economy accelerates, the demand for this material is expected to increase.

[0024] FIG. 1 is a powder X-ray diffraction pattern (X-ray diffraction - Company: Rigaku / MiniFlex) of a material synthesized according to one embodiment of the present invention.

[0025] FIG. 2 is a field emission-scanning electron microscopy image (Field Emission-Scanning Electron Microscopy - Company: JEOL JSM-7001F) of a material synthesized according to one embodiment of the present invention.

[0026] FIG. 3 shows (a) a transmission electron microscopy (company: JEOL F200) image and (b) an elemental mapping image of a material synthesized according to one embodiment of the present invention.

[0027] Figure 4 is Raman data of a material synthesized according to one embodiment of the present invention.

[0028] Figure 5 is oxygen evolution reaction (OER) activity data of materials synthesized according to one embodiment of the present invention.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by a skilled expert in the art to which this invention pertains. In general, the nomenclature used herein is well known and commonly used in the art.

[0030]

[0031] In the present invention, performance was improved by simultaneously substituting small amounts of four types of transition metal elements—Co, V, Fe, and Ni—into the MnO₂ lattice. As a result, it was confirmed that the oxygen evolution catalytic performance was significantly enhanced after substitution. While there have been many studies on substituting a single element into manganese oxide, the present invention is the first to provide an oxygen evolution catalytic material in which four elements are substituted simultaneously. In order to develop a material with excellent oxygen evolution catalytic performance that is economical and affordable, the present invention provides a transition metal-substituted manganese oxide material and, to manufacture it, provides a synthesis method in which Co, V, Fe, and Ni are substituted into manganese oxide using a hydrothermal synthesis method.

[0032]

[0033] In the present invention, it was confirmed that VCNF-MnO2, which is substituted with four types of transition metals simultaneously, exhibits superior oxygen evolution catalytic performance compared to V-MnO2, Fe-MnO2, Co-MnO2, and Ni-MnO2, which are substituted with only a single element. Accordingly, it was confirmed that substituting four types of elements simultaneously is very effective in improving the performance of the catalyst.

[0034] Accordingly, the present invention relates to a manganese oxide catalyst characterized by being represented by General Formula 1 in one aspect:

[0035] [General Formula 1]

[0036] Mn a V b Co c Ni d Fe e O2

[0037] In general formula 1

[0038] a, b, c, d, and e are 0.4 ≤ a ≤ 0.99, 0.01 ≤ b ≤ 0.4, 0.01 ≤ c ≤ 0.4, 0.01 ≤ d ≤ 0.4, and 0.01 ≤ e ≤ 0.4, respectively.

[0039] In addition, the present invention relates to a method for producing the manganese oxide catalyst comprising the step of hydrothermally synthesizing a solution containing a manganese precursor, a vanadium precursor, a cobalt precursor, an iron precursor, and a nickel precursor, in another aspect.

[0040] In the present invention, a preferred embodiment is Mn 0.8 V 0.05 Co 0.05 Ni 0.05 Fe 0.05 It could be O2.

[0041] In the present invention, the manganese oxide catalyst may be a one-dimensional nanostructure, and the manganese oxide nanostructure may include a nanowire, nanorod, nanoparticle, nanotube, nanosheet, nanofiber, or a combination thereof, and the shape of the manganese oxide nanostructure produced may change depending on the molar ratio of the manganese and other substituted transition metals, but is not limited thereto.

[0042] In the present invention, the structure may have an α-MnO2 structure. In this case, vanadium (V), cobalt (Co), nickel (Ni) and iron (Fe) are partially substituted for the manganese ion sites.

[0043] The present invention can also produce the manganese oxide catalyst by hydrothermally synthesizing a solution containing a manganese precursor, a vanadium precursor, a cobalt precursor, an iron precursor, and a nickel precursor.

[0044] In the manufacturing method of the present invention, the manganese precursor may be selected from the group consisting of permanganate, manganese acetate hydrate (Mn(CH3COO)2·4H2O), manganese chloride (MnCl2), manganese nitrate tetrahydrate (Mn(NO3)2·4H2O), manganese sulfate tetrahydrate (MnSO4·4H2O), manganese iodide (MnI2), and manganese fluoride (MnF2). For example, the permanganate may have potassium, sodium, or lithium cations to form permanganate anions in water, but is not limited thereto.

[0045] In the manufacturing method of the present invention, the vanadium precursor is vanadium chloride (VCl3), vanadium (III) acetylacetonate (C 15 H 21 It can be selected from the group consisting of O6V) and vanadium nitrate (VO(NO3)3), preferably vanadium chloride, but is not limited thereto.

[0046] In the manufacturing method of the present invention, the cobalt precursor may be selected from the group consisting of cobalt nitrate hexahydrate (Co(NO3)2·6H2O), cobalt chloride hexahydrate (CoCl2·6H2O), cobalt sulfate heptahydrate (CoSO4·7H2O), cobalt bromide (CoBr2) cobalt fluoride tetrahydrate (CoF2·4H2O), and cobalt acetate hydrate (Co(CH3COO)2·4H2O), preferably cobalt nitrate, but is not limited thereto.

[0047] In the manufacturing method of the present invention, the iron precursor may be selected from the group consisting of iron nitrate nonhydrate (Fe(NO3)3·9H2O), iron chloride (FeCl3), iron phosphate dihydrate (FePO4·2H2O), and iron fluoride (FeF3), preferably iron nitrate nonhydrate is used, but is not limited thereto.

[0048] In the manufacturing method of the present invention, the nickel precursor may be selected from the group consisting of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), nickel chloride hexahydrate (NiCl2·6H2O), nickel sulfate hexahydrate (NiSO4·6H2O) and nickel acetic acid tetrahydrate (Ni(CH3COO)2·4H2O), preferably nickel nitrate hexahydrate is used, but is not limited thereto.

[0049] In the manufacturing method of the present invention, the hydrothermal synthesis can be carried out at a temperature of 100 to 200°C for 10 to 20 hours, and preferably at a temperature of 120 to 160°C for 10 to 14 hours.

[0050] In the manufacturing method of the present invention, a step of washing and drying after hydrothermal synthesis may be additionally included.

[0051]

[0052] In addition, as a result of measuring the Oxygen Evolution Reaction (OER) performance using the above manganese oxide catalyst as an electrochemical catalyst, it was confirmed that it exhibited significantly superior oxygen evolution catalytic activity compared to MnO2 without transition metal substitution.

[0053] Accordingly, the present invention relates, in another aspect, to an electrode for water electrolysis comprising the manganese oxide catalyst and a water electrolysis cell comprising the manganese oxide catalyst.

[0054] In addition, the present invention relates to an oxygen evolution reaction (OER) that generates oxygen from water using the manganese oxide catalyst in another aspect.

[0055] Furthermore, the manganese oxide catalyst according to the present invention can be utilized as an oxygen electrode catalyst for reversible fuel cells and is widely applicable in the fields of fuel cells and water electrolysis. Moreover, it can be useful for hydrogen energy source devices, such as electrodes for water electrolysis and water electrolysis cells, that require hydrogen production through the electrolysis of water.

[0056]

[0057] The present invention will be described in more detail below through examples. These examples are solely for illustrating the present invention, and it will be obvious to those skilled in the art that the scope of the present invention is not to be interpreted as being limited by these examples.

[0058]

[0059] [Example]

[0060] Example 1: Synthesis of Transition Metal-Substituted Manganese Oxide

[0061] Mn, a manganese oxide substituted with transition metals 0.8 V 0.05 Co 0.05 Ni 0.05 Fe 0.05 O2 nanowires were synthesized using the following method.

[0062] 0.00248 mol KMnO4, 0.0000155 mol VCl3, 0.0000155 mol Co(NO3)2·6H2O, 0.0000155 mol Fe(NO3)3·9H2O, 0.0000155 mol Ni(NO3)2·6H2O, and 0.02 mol Na2S2O8 were added to 50 mL of distilled water and stirred for 20 minutes. The resulting solution was placed in a hydrothermal synthesizer vessel and reacted at 140°C for 12 hours. The obtained precipitate was thoroughly washed with water and dried in an oven. Manganese oxide nanowires without transition metal substitution were synthesized using the same method as above by adding 0.0031 mol KMnO4 and 0.02 mol Na2S2O8. The synthesized manganese oxide nanowires were MnO2 with Mn 0.8 V0.05 Co 0.05 Ni 0.05 Fe 0.05 O2 nanowires are named VCNF-MnO2.

[0063]

[0064] Example 2: Measurement of Oxygen Evolution Reaction (OER) Performance

[0065] 7 mg of the synthesized material and 3 mg of conductive carbon (Vulcan-XC72R) were mixed with 4 ml of triple-distilled water, 1 ml of isopropanol solution, and 40 µl of 5 wt% Nafion solution, and dispersed using ultrasound for one hour. 10 µl of the dispersed solution was sampled onto a 3 mm diameter Glassy Carbon (GC) (Company: ALS) and used as the working electrode. A saturated calomel electrode (SCE) was used as the reference electrode, and a Pt wire was used as the counter electrode. Oxygen evolution reaction catalytic activity was tested using an RRDE-3A Rotating Ring Disk Electrode Apparatus (Company: ALS) and IVIUMSTAT.

[0066]

[0067] Figure 1 shows the powder X-ray diffraction patterns of transition metal-substituted MnO2 and unsubstituted MnO2. In the case of unsubstituted MnO2, it exhibits a typical α-MnO2 crystal structure, and it was confirmed that VCNF-MnO2 substituted with V, Co, Fe, and Ni was also synthesized purely without impurities.

[0068] Figure 2 is a field-effect scanning electron microscope (FE-SEM) image. It was confirmed that MnO2 without transition metal substitution has a one-dimensional nanowire structure. It can be seen that VCNF-MnO2 with transition metal substitution also has a one-dimensional nanowire structure, but compared to MnO2, the nanowire length is shorter and the thickness is slightly thicker.

[0069] Figure 3 is a transmission electron microscope image. As can be seen from the transmission electron microscope, both materials have a one-dimensional structure, and through elemental mapping analysis of VCNF-MnO2, it can be seen that transition metal substitution was very well achieved, as Mn, O, Ni, Fe, V, and Co elements are evenly dispersed.

[0070] Figure 4 shows the micro-Raman data of the synthesized materials. The Raman data also indicates that MnO2 and VCNF-MnO2 have the structure of typical α-MnO2. The v2 / v1 peak ratio decreased after transition metal substitution, which means that the oxidation state of Mn in MnO2 was lowered after transition metal substitution.

[0071] Figure 5 shows the Oxygen Evolution Reaction (OER) catalytic activity results. The synthesized materials were measured in a 1M KOH solution, and the scan rate was set to 5mV / s. As a result of the measurements, VCNF-MnO2 substituted with transition metals exhibited significantly superior oxygen evolution catalytic activity compared to MnO2 without transition metal substitution. Furthermore, VCNF-MnO2 also showed superior catalytic activity when compared to V-MnO2, Fe-MnO2, Ni-MnO2, and Co-MnO2, which were substituted with only a single transition metal. This suggests that substituting four elements simultaneously is more effective in improving the oxygen evolution catalytic performance of MnO2.

[0072]

[0073] Foregoing, specific parts of the present invention have been described in detail. It will be apparent to those skilled in the art that such specific descriptions are merely preferred embodiments and do not limit the scope of the invention. Accordingly, the actual scope of the invention is defined by the claims and their equivalents.

Claims

1. Manganese oxide catalyst characterized by being represented by general formula 1: [General Formula 1] Mr a V b Co c Ni d Feb e O2 In general formula 1 a, b, c, d, and e are 0.4 ≤ a ≤ 0.99, 0.01 ≤ b ≤ 0.4, 0.01 ≤ c ≤ 0.4, 0.01 ≤ d ≤ 0.4, and 0.01 ≤ e ≤ 0.4, respectively.

2. In paragraph 1, Mn 0.8 V 0.05 Co 0.05 Ni 0.05 Fe 0.05 Manganese oxide catalyst characterized by being O2.

3. A manganese oxide catalyst according to claim 1, characterized as being a one-dimensional nanostructure.

4. A manganese oxide catalyst according to claim 1, characterized by having an α-MnO2 structure.

5. In Paragraph 1, A manganese oxide catalyst characterized by vanadium (V), cobalt (Co), nickel (Ni), and iron (F) partially substituting for manganese ion sites.

6. A method for manufacturing a manganese oxide catalyst of claim 1, comprising the step of hydrothermally synthesizing a solution containing a manganese precursor, a vanadium precursor, a cobalt precursor, an iron precursor, and a nickel precursor.

7. In Paragraph 6, A method for preparing a manganese oxide catalyst, characterized in that the above manganese precursor is selected from the group consisting of permanganate, manganese acetate hydrate (Mn(CH3COO)2·4H2O), manganese chloride (MnCl2), manganese nitrate tetrahydrate (Mn(NO3)2·4H2O), manganese sulfate tetrahydrate (MnSO4·4H2O), manganese iodide (MnI2), and manganese fluoride (MnF2).

8. In Paragraph 6, The above vanadium precursors are vanadium chloride (VCl3) and vanadium(III) acetylacetonate (C 15 H 21 Selected from the group consisting of O6V) and vanadium nitrate (VO(NO3)3), A method for preparing a manganese oxide catalyst, characterized in that the above-mentioned cobalt precursor is selected from the group consisting of cobalt nitrate hexahydrate (Co(NO3)2·6H2O), cobalt chloride hexahydrate (CoCl2·6H2O), cobalt sulfate heptahydrate (CoSO4·7H2O), cobalt bromide (CoBr2) cobalt fluoride tetrahydrate (CoF2·4H2O), and cobalt acetate hydrate (Co(CH3COO)2·4H2O).

9. In claim 6, the iron precursor is selected from the group consisting of iron nitrate nonahydrate (Fe(NO3)3·9H2O), iron chloride (FeCl3), iron phosphate dihydrate (FePO4·2H2O), and iron fluoride (FeF3), and A method for preparing a manganese oxide catalyst, characterized in that the nickel precursor is selected from the group consisting of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), nickel chloride hexahydrate (NiCl2·6H2O), nickel sulfate hexahydrate (NiSO4·6H2O), and nickel acetic acid tetrahydrate (Ni(CH3COO)2·4H2O).

10. Electrode for water electrolysis comprising the manganese oxide catalyst of claim 1.

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