Hydrolysis catalyst for borohydride metal salts, method for hydrolysis of borohydride metal salts, method for producing hydrogen, and copper / oxidation-resistant green rust composite.

Abstract

This invention provides a hydrolysis catalyst that exhibits excellent catalytic activity for hydrolysis reactions that produce hydrogen from metal borohydride salts and is chemically stable, a hydrolysis method for producing hydrolysis of metal borohydride salts in the presence of this hydrolysis catalyst, a method for producing hydrogen, and a catalyst material suitable for this hydrolysis catalyst. [Solution] A hydrolysis catalyst for a borohydride metal salt containing oxidation-resistant green rust, a hydrolysis method for producing hydrolysis of a borohydride metal salt in the presence of this hydrolysis catalyst, and a method for producing hydrogen, as well as a copper / oxidation-resistant green rust composite containing oxidation-resistant green rust and copper.

Description

[Technical Field]

[0001] This invention relates to a hydrolysis catalyst for borohydride metal salts, a method for hydrolyzing borohydride metal salts, a method for producing hydrogen, and a copper / oxidation-resistant green rust composite. [Background technology]

[0002] Green Rust (GR) is a divalent iron atom (ferrous iron: Fe II ) and trivalent iron atoms (ferric iron: Fe III It is a mixed-valence iron hydroxide mineral containing ). As its name suggests, GR is green in color and structurally is classified as a layered double hydroxide (LDH). The metal atoms that make up GR are iron (Fe II / Fe III ) is the only material available, and its application as an inexpensive functional material has been eagerly sought after. However, GR is highly susceptible to oxidation and is thought to be an intermediate produced during the corrosion process of iron. For example, at room temperature (25°C) in air, GR (green) is easily oxidized and changes into a more stable phase (black) containing magnetite in just a few minutes.

[0003] Recently, techniques for imparting oxidation resistance to GR have been reported. Patent Document 1 describes that a trivalent iron salt, a nucleating agent, and a reducing solvent are mixed, the mixture is heat-treated, and then the reducing solvent is removed and washed to obtain GR with excellent oxidation resistance. Regarding specific embodiments, Patent Document 1 states that 0.0167 mol of anhydrous FeCl3 is prepared as the trivalent iron salt, 0.05 mol of sodium acetate trihydrate is prepared as the nucleating agent, and these are dissolved in 100 mL of glycerol, which is a reducing solvent. The resulting solution is sealed and subjected to autoclave treatment (solvothermal reaction at 200 °C for 24 hours). It is described that the obtained green wet powder is washed with a mixture of ultrapure water and ethanol and then dried to obtain GR powder. Patent Document 1 also describes that this GR powder does not change in properties even when held in air at room temperature for 90 days, and its X-ray diffraction pattern does not change even when immersed in an aqueous solution containing dissolved oxygen, indicating excellent oxidation resistance. Patent Document 1 describes that for the oxidation-resistant GR obtained by the above solvothermal reaction, the atomic ratio of Fe III and Fe II (Fe III / [Fe III + Fe II ) is 0.80 or more and 0.99 or less, and the full width at half maximum (FWHM) of the signal waveform of the basic spacing d(003) in X-ray diffraction measurement is 0.06° or more and 0.5° or less.

[0004] Non-Patent Document 1 also describes obtaining oxidation-resistant GR by the same solvothermal reaction as above. Non-Patent Document 1 uses FeCl2 in addition to FeCl3 as the raw material iron salt for the atomic ratio of Fe III and Fe II (Fe III / [Fe III + Fe IIThe report describes how various GRs were obtained by solvothermal reactions using ]), that all of the obtained GRs were stable in air for at least 3 months, that these oxidation-resistant GRs functioned as hydrolysis catalysts (hydrogen generation catalysts) for ammonia borane (AB), a hydrogen storage material, under light irradiation, but that their catalytic activity was significantly inferior to that of existing platinum-supported catalysts.

[0005] In recent years, global population growth and rapid economic development have led to increased energy demand worldwide. Hydrogen is attracting attention as a clean energy source to address this growing energy demand. In addition to the above-mentioned AB, metal borohydride salts, such as sodium borohydride (SBH), are known as solid hydrogen storage materials. SBH undergoes hydrolysis when brought into contact with water in the presence of a suitable solid catalyst, producing hydrogen as described below. NaBH4 + 2H2O → 4H2 + NaBO2 This hydrolysis is highly reactive and proceeds even at room temperature. A photocatalyst made of titanium oxide supported with a precious metal such as platinum has been conventionally known as a catalyst for this reaction. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2022-80364 [Non-patent literature]

[0007] [Non-Patent Document 1] ACS Sustainable Chemistry & Engineering, 2023, Vol. 11, pp. 2295-2302 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Conventional hydrolysis catalysts for obtaining hydrogen from borohydride metal salts use expensive precious metals, as mentioned above, and the price of titanium dioxide itself is also on the rise. However, there are no reports of precious metal-free hydrolysis catalysts that can efficiently carry out the above hydrolysis reaction.

[0009] The present invention aims to provide a hydrolysis catalyst that exhibits excellent catalytic activity for hydrolysis reactions that produce hydrogen from metal borohydride salts and is chemically stable. Furthermore, the present invention aims to provide a hydrolysis method for producing hydrolysis of metal borohydride salts in the presence of the above-mentioned hydrolysis catalyst, and a method for producing hydrogen. Finally, the present invention aims to provide a catalyst material suitable as the above-mentioned hydrolysis catalyst.

[0010] In view of the above problems, the inventors conducted extensive research and found that the oxidation-resistant GR exhibits excellent catalytic activity as a hydrolysis catalyst that generates hydrogen from borohydride metal salts. Furthermore, they discovered that the catalytic activity is further enhanced when the oxidation-resistant GR is immersed in a copper salt solution to create a composite with copper on its surface. The present invention was completed based on these findings and further research.

[0011] The above-mentioned problems of the present invention are solved by the following means. [1] A hydrolysis catalyst for metal borohydride salts, containing oxidation-resistant green rust. [2] The Fe possessed by the aforementioned oxidation-resistant green rust III and Fe II Atomic ratio (Fe III / [Fe III +Fe II The hydrolysis catalyst described in [1], wherein ]) is 0.10 or more and 0.99 or less. [3] Fe in the aforementioned oxidation-resistant green rust II Fe content III The ratio of the content is, on a mass basis, Fe III / Fe IIA hydrolysis catalyst as described in [1] or [2], wherein the ratio is 50 / 1 to 1 / 10. [4] The hydrolysis catalyst according to any one of [1] to [3], wherein the oxidation-resistant green rust has lactate ions between the crystalline layers. [5] The hydrolysis catalyst according to any one of [1] to [4], wherein the hydrolysis catalyst contains the oxidation-resistant green rust and copper. [6] The hydrolysis catalyst according to [5], wherein the proportion of copper in the total content of the copper and the oxidation-resistant green rust constituting the hydrolysis catalyst is 0.10 to 2.00% by mass. [7] The copper is Cu + A hydrolysis catalyst as described in [5] or [6]. [8] The hydrolysis catalyst according to any one of [1] to [7], wherein the hydrolysis reaction of the borohydride metal salt in the presence of the hydrolysis catalyst is a hydrolysis reaction under light irradiation. [9] A method for hydrolyzing a metal borohydride salt, comprising contacting the metal borohydride salt with water in the presence of a hydrolysis catalyst described in any one of items (1) to (8).

[10] The hydrolysis method according to [9], wherein the contact between the borohydride metal salt and water is carried out under light irradiation.

[11] The hydrolysis method according to [9] or

[10] , wherein the contact between the borohydride metal salt and water is carried out in the presence of glycerol and / or methanol.

[12] A method for producing hydrogen, comprising generating hydrogen by contacting a metal borohydride salt with water in the presence of a hydrolysis catalyst described in any of [1] to [8].

[13] The method for producing hydrogen according to

[12] , wherein the contact between the borohydride metal salt and water is carried out under light irradiation.

[14] A method for producing hydrogen according to

[12] or

[13] , wherein the contact between the borohydride metal salt and water is carried out in the presence of glycerol and / or methanol.

[15] A copper / oxidation-resistant green rust composite containing oxidation-resistant green rust and copper.

[16] A method for producing a copper / oxidation-resistant green rust composite according to

[15] , comprising impregnating the oxidation-resistant green rust in a copper salt solution to make copper present on the surface of the oxidation-resistant green rust. [Effects of the Invention]

[0012] The hydrolysis catalyst of the present invention exhibits excellent catalytic activity for hydrolysis reactions that produce hydrogen from borohydride metal salts, and is also chemically stable. The hydrolysis method of the present invention allows for highly efficient hydrolysis of metal borohydride salts. Furthermore, the hydrogen production method of the present invention allows for highly efficient hydrolysis of metal borohydride salts, thereby increasing the hydrogen production efficiency. The copper / oxidation-resistant green rust composite of the present invention is suitable as a hydrolysis catalyst of the present invention. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 shows the 57Fe Mössbauer spectra of the oxidation-resistant GR and copper / oxidation-resistant GR composite prepared in the examples. [Figure 2] Figure 2 shows the results of X-ray diffraction analysis (XRD patterns) of the oxidation-resistant GR and copper / oxidation-resistant GR composite prepared in the examples. [Figure 3] Figure 3 shows the results of X-ray photoelectron spectroscopy analysis of the oxidation-resistant GR and copper / oxidation-resistant GR composite prepared in the examples. [Figure 4] Figure 4 shows the diffuse reflectance spectra of the oxidation-resistant GR and copper / oxidation-resistant GR composite prepared in the examples. [Figure 5]Figure 5 shows scanning electron microscope images of the oxidation-resistant GR and copper / oxidation-resistant GR composite prepared in the examples. [Figure 6] Figure 6 shows scanning transmission electron microscope images and elemental mapping results of the copper / oxidation-resistant GR composites prepared in the examples. [Figure 7] Figure 7 shows the fast Fourier transform patterns of the copper / oxidation-resistant GR composites prepared in the examples. [Figure 8] Figure 8 is a graph showing the time course of hydrogen (H2) generation from the hydrolysis reaction of SBH using the various catalysts prepared in the [Examples] section. [Figure 9] Figure 9 is a graph showing the time course of hydrogen (H2) generation from the hydrolysis reaction of SBH using the oxidation-resistant GR and copper / oxidation-resistant GR composite prepared in the examples as catalysts. [Figure 10] Figure 10 is a graph showing the turnover frequency (catalyst turnover frequency) when the copper / oxidation-resistant GR composite prepared in the examples was used as a catalyst for the hydrolysis reaction (hydrogen production reaction) of SBH. [Figure 11] Figure 11 shows the XRD patterns of the copper / oxidation-resistant GR composite prepared in the examples, before and after use as a catalyst for the hydrolysis reaction of SBH. [Figure 12] Figure 12 is a graph showing the time course of hydrogen (H2) generation from the hydrolysis reaction of SBH under light irradiation and without light irradiation, using the oxidation-resistant GR and copper / oxidation-resistant GR composite prepared in the examples as catalysts. [Figure 13] Figure 13 is a graph showing the effect of glycerol addition on the hydrogen production efficiency when the copper / oxidation-resistant GR composite prepared in the examples was used as a catalyst for the hydrolysis reaction of SBH. [Figure 14] Figure 14 shows the effect of glycerol addition on the XRD pattern (structural stability) of the catalyst when the copper / oxidation-resistant GR composite prepared in the examples was used as a catalyst for the hydrolysis reaction of SBH. [Figure 15]Figure 15 is a graph showing the relationship between the copper content (copper loading) in the copper / oxidation-resistant GR composite and the catalytic activity of the SBH hydrolysis reaction (hydrogen production reaction). [Modes for carrying out the invention]

[0014] [Hydrolysis catalyst for metal borohydride salts] The hydrolysis catalyst for borohydride metal salts of the present invention (hereinafter also referred to as "the catalyst of the present invention") contains oxidation-resistant GR. The catalyst of the present invention may be oxidation-resistant GR itself, or it may contain other components in addition to oxidation-resistant GR. For example, it is also preferable to have a form that contains oxidation-resistant GR and a metal (for example, a composite in which oxidation-resistant GR and a metal are integrated, typically a form in which the metal is present on the surface of the oxidation-resistant GR). This metal may be a noble metal, but it is preferable from a cost standpoint that it is not a noble metal. As an example of a form in which the metal is present on the surface of the oxidation-resistant GR, there is a form in which metal-containing nanoparticles such as metal oxides are supported on the surface of the oxidation-resistant GR. A preferred specific example is a form in which copper is present on the surface of the oxidation-resistant GR, and as an example of this form, there is a form in which copper-containing nanoparticles are supported on the surface of the oxidation-resistant GR. Furthermore, the catalyst of the present invention may contain a binder for binding GR particles together, a solvent such as water (residual solvent), etc. When the catalyst of the present invention is subjected to a catalytic reaction while supported on a substrate (typically a porous substrate, which usually does not have catalytic activity; for example, honeycomb structures, foamed ceramics, etc.), this "substrate" (support) is positioned as a structure different from the catalyst of the present invention. If the catalyst of the present invention contains components other than oxidation-resistant GR, the content of oxidation-resistant GR in the catalyst of the present invention is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and also preferably 90% by mass or more. The catalyst of the present invention may be in powder form (particulate form), or it may be formed into a desired shape by binding the particles together. For example, by solidifying the components of the catalyst of the present invention with a binder (such as an organic polymer) as needed, and then removing part or all of the binder by heating, a porous material can be obtained that increases the specific surface area, thereby further enhancing catalytic efficiency and improving handling properties. As described above, the catalyst of the present invention can also be used in a state in which the catalyst is supported on a substrate (preferably a porous substrate).

[0015] The oxidation-resistant GR component of the catalyst of this invention will be described below.

[0016] <Oxidation-resistant Green Rust> The oxidation-resistant GR used in the catalyst of the present invention has iron (Fe) as its constituent metal element. II and / or Fe III ) is the only such material, and due to its structural characteristics, it is classified as a layered double hydroxide. The oxidation-resistant GR used in this invention is a chemically stable layered double hydroxide, despite being a GR. In the present invention, "oxidation-resistant GR" means GR that does not change color (maintains its green color without changing to black) even after 1 hour in an atmosphere of air (relative humidity 40%), 25°C, and 0.1 MPa. This color change can be judged by visual observation. Preferably, the "oxidation-resistant GR" used in the present invention does not change color even after 4 hours in an atmosphere of air (relative humidity 40%), 25°C, and 0.1 MPa, preferably after 12 hours, preferably after 24 hours, more preferably after 48 hours, even more preferably after 96 hours, even more preferably after 192 hours, even more preferably after 384 hours, even more preferably after 768 hours, even more preferably after 1536 hours, and particularly preferably after 3072 hours. In this specification, when referring to "oxidation-resistant GR used in the catalyst of the present invention" or "oxidation-resistant GR used in the present invention," it means the oxidation-resistant GR itself if the catalyst of the present invention is the oxidation-resistant GR itself, and if the catalyst of the present invention contains components other than oxidation-resistant GR (for example, metals such as copper), it means the oxidation-resistant GR in the state in which the catalyst of the present invention is composed, unless otherwise specified.

[0017] The oxidation-resistant GR used in this invention is Fe III and Fe II Atomic ratio (Fe III / [Fe III +Fe II The ratio of atoms is preferably 0.10 to 0.99. This atomic ratio is more preferably 0.20 to 0.95, even more preferably 0.25 to 0.90, even more preferably 0.25 to 0.87, even more preferably 0.30 to 0.85, even more preferably 0.40 to 0.80, even more preferably 0.40 to 0.75, and even more preferably 0.40 to 0.70. The above atomic ratio can be determined by Mössbauer spectroscopy.

[0018] The oxidation-resistant GR used in this invention is Fe II Fe content III The ratio of the content is, on a mass basis (mass ratio), Fe III / Fe II It is preferable that the ratio is 50 / 1 to 1 / 10. The value of this ratio is Fe III / Fe II =40 / 1~1 / 8 is more preferable, Fe III / Fe II =30 / 1~1 / 6 is more preferable, Fe III / Fe II =20 / 1~1 / 4 is more preferable, Fe III / Fe II =18 / 1~1 / 3 is even more preferable, Fe III / Fe II =15 / 1~1 / 2 is even more preferable, Fe III / Fe II =15 / 1~2 / 3 is even more preferable. Also, the value of this ratio is Fe III / Fe II=10 / 1 to 1 / 2 is also acceptable, Fe III / Fe II =8 / 1 to 1 / 2 is also acceptable, Fe III / Fe II =7 / 1 to 2 / 3 is also acceptable, Fe III / Fe II =6 / 1 to 2 / 3 is also acceptable, Fe III / Fe II =5 / 1 to 2 / 3 is also acceptable, Fe III / Fe II It is also preferable that there are values ​​ranging from 4 / 1 to 2 / 3.

[0019] The oxidation-resistant GR used in the present invention preferably has lactate ions between its crystalline layers. When GR is produced by a solvothermal reaction using a reducing solvent (e.g., an alcohol, more preferably a polyhydric alcohol (such as glycerol)), lactate ions are generated from the reducing solvent during this reaction and incorporated into the interlayers of the GR as interlayer anions. These lactate ions are thought to function as electron donors and exert an inhibitory effect against the oxidation of GR.

[0020] In the present invention, the oxidation-resistant GR preferably has a Full Width Half Maximum (FWHM) of the signal waveform at the basic interval d(003) in X-ray diffraction (XRD) measurements of 0.06° or more and 0.50° or less. Preferably, this FWHM is 0.10° or more and 0.40° or less. The lower limit of FWHM at (003), 0.06°, is a theoretical value derived from the GR structure based on structural calculations. The XRD measurement conditions are 40kV and 40mA using a Smart-lab Rigaku X-ray diffractometer and a Cu target.

[0021] The method for producing oxidation-resistant GR used in the present invention is publicly known, and for example, one can refer to the descriptions in Japanese Patent Application Publication No. 2022-80364, ACS Sustainable Chemistry & Engineering, 2023, Vol. 11, pp. 2295-2302, etc., as appropriate. For example, a divalent iron salt and a trivalent iron salt are used in a desired ratio and mixed with a nucleating agent and a reducing solvent. This mixture is subjected to high temperature and high pressure treatment (solvothermal reaction), and then the solvent is washed off and dried to obtain oxidation-resistant GR (powder). Examples of the nucleating agent include sodium acetate and potassium acetate. These may be in hydrate form. Examples of the reducing solvent include alcohols. The alcohol preferably has 1 to 10 carbon atoms, more preferably 1 to 8, even more preferably 1 to 6, and even more preferably 1 to 3. Furthermore, polyhydric alcohols (preferably 2 to 6-valent, more preferably 2 to 4-valent, and even more preferably 2 or 3-valent alcohols) are preferred. Specific examples of preferred alcohols include glycerol, ethylene glycol, cellulose, cellulose, glucose, and the like.

[0022] A preferred embodiment of the catalyst of the present invention is one containing the above-mentioned oxidation-resistant GR and copper. This copper is preferably in the form of finer particles than the oxidation-resistant GR and is present (adhered) to the surface of the oxidation-resistant GR. This copper is usually supported on the surface of the oxidation-resistant GR in the form of copper-containing nanoparticles (in the present invention, the state in which copper-containing nanoparticles are supported may be simply expressed as "copper is supported"). Copper-containing nanoparticles are usually particles made of an inorganic compound containing copper, and are typically copper oxide. A catalyst in which copper-containing nanoparticles are supported on the surface of oxidation-resistant GR can be obtained, for example, by impregnating the oxidation-resistant GR in a copper salt solution and then drying it. The details will be explained later in the method for producing the copper / oxidation-resistant GR composite. In the present invention, a composite containing oxidation-resistant GR and copper as described above (typically a composite containing oxidation-resistant GR and copper-containing nanoparticles supported on its surface) is referred to as a "copper / oxidation-resistant GR composite." In the present invention, nanoparticles refer to particles whose equivalent circle diameter in planar observation (for example, planar observation by a scanning electron microscope) is in the range of 1 to 100 nm, and this equivalent circle diameter is preferably 1 to 50 nm, more preferably 1 to 30 nm, and also preferably 1 to 10 nm. By compounding the above oxidation-resistant GR with copper, the hydrolysis reaction of borohydride metal salts can be made more efficient.

[0023] The above copper / oxidation-resistant GR composite preferably has a copper atom content (also simply called "copper content" or "copper ratio") of 0.10 to 2.00 mass%, more preferably 0.12 to 1.90 mass%, even more preferably 0.15 to 1.85 mass%, and still more preferably 0.20 to 1.80 mass%. The copper atom content in the above copper / oxidation-resistant GR composite can be determined by subjecting a sample of the copper / oxidation-resistant GR composite, which has been completely dissolved in sulfuric acid and nitric acid, to inductively coupled plasma atomic emission spectroscopy (ICP-OES analysis).

[0024] The above copper / oxidation-resistant GR composite consists of copper (copper atoms) constituting the copper-containing nanoparticles. + It is preferable that it exists as such. That is, in the copper / oxidation-resistant GR composite, the copper constituting the copper-containing nanoparticles supported on the surface of the oxidation-resistant GR is elemental Cu or Cu 2+ (For example, not in the state of CuO) + It is preferable that the copper constituting the copper-containing nanoparticles is Cu + "Existing as" means that the copper that makes up the copper-containing nanoparticles is Cu + This means that there are substances in this state, and some of the copper constituting the copper-containing nanoparticles is carrier Cu, or Cu 2+ It may also be the case that the copper (Cu) is in the state of the copper that makes up the copper-containing nanoparticles. + Cu 2+ The element (or elemental Cu) can be determined by the various analytical methods described in the examples below.

[0025] The method for producing the above copper / oxidation-resistant GR composite is not particularly limited. For example, copper-containing nanoparticles can be supported on the surface of oxidation-resistant GR by impregnating it in a copper salt solution. This immersion is preferably carried out at a temperature of 10 to 40°C, and more preferably at 15 to 30°C. It is also preferable to stir while immersing. The immersion time can be, for example, 1 hour or more, preferably 2 hours or more, more preferably 4 hours or more, even more preferably 8 hours or more, and even more preferably 16 hours or more. There is no particular upper limit to this immersion time. For example, it can be 72 hours or less, may be 48 hours or less, or 36 hours or less. After that, the copper / oxidation-resistant GR composite powder can be obtained by heating and drying to a desired temperature as needed. The copper salt constituting the copper salt solution is not particularly limited. Examples include copper chloride (preferably CuCl2), Cu(NO3)2, Cu(CH3COO)2, Cu(C5H7O2)2 (copper(II) acetylacetonate), etc. The copper salt may be anhydrous or hydrated. As the solvent constituting the copper salt solution, for example, various organic solvents capable of dissolving copper salts can be used. The ratio of the amount of copper atoms in the copper salt solution to the amount of oxidation-resistant GR immersed in the copper salt solution roughly correlates with the ratio of the amount of copper atoms to the amount of oxidation-resistant GR in the resulting copper / GR composite.

[0026] The catalyst of the present invention is a catalyst for use in the hydrolysis of borohydride metal salts. Examples of borohydride metal salts include sodium borohydride (NaBH4), lithium borohydride (LiBH4), and magnesium borohydride (MgBH2), among which sodium borohydride is preferred from the viewpoint of high hydrogen storage capacity and ease of handling.

[0027] [Hydrolysis reaction] In one embodiment, the present invention provides a method for hydrolyzing a metal borohydride salt (referred to as "the hydrolysis method of the present invention"), which includes contacting the metal borohydride salt with water in the presence of the catalyst of the present invention. The contact between the metal borohydride salt and water may be carried out under light-shielding conditions or under light irradiation. From the viewpoint of further improving the efficiency of the hydrolysis reaction, it is preferable to carry out the hydrolysis reaction of the metal borohydride salt by contacting the metal borohydride salt with water under light irradiation in the presence of the catalyst of the present invention. When the hydrolysis reaction is carried out under light irradiation, the wavelength of the irradiated light may be ultraviolet light, visible light, or infrared light. That is, the catalyst of the present invention has an absorption spectrum that covers a wide wavelength range including the visible light range. For example, the form of irradiation using simulated sunlight is preferred as the hydrolysis reaction of the present invention. Furthermore, various light irradiation conditions such as white light irradiation, light irradiation using LED lamps of a specific wavelength, or mercury lamps can be adopted without particular limitation. When the hydrolysis reaction is carried out under light irradiation, the amount of light irradiation may be appropriately adjusted according to the purpose.

[0028] The hydrolysis reaction of the present invention (contact between a borohydride metal salt and water) is also preferably carried out in the presence of glycerol and / or methanol. Glycerol and / or methanol function as electron donors and are inexpensive compounds that contribute to the stabilization (inhibition of oxidation) of the catalyst of the present invention.

[0029] The reaction temperature for the hydrolysis reaction of the present invention is preferably 0 to 100°C, and more preferably 5 to 95°C. The reaction time can be set appropriately considering the amount of raw materials used. This reaction may be carried out in a batch or flow manner. In a flow manner, for example, the catalyst may be immobilized in a flow channel and an aqueous SBH solution may be circulated through it.

[0030] [Hydrogen production method] In another embodiment, the present invention provides a method for producing hydrogen (referred to as "the hydrogen production method of the present invention") which includes generating hydrogen by contacting a borohydride metal salt with water in the presence of the catalyst of the present invention. In the hydrogen production method of the present invention, the generation of hydrogen by contacting a borohydride metal salt with water is a result of the hydrolysis reaction of the borohydride metal salt. Therefore, the reaction conditions described in the hydrolysis reaction of the present invention can be preferably adopted as the reaction conditions in the hydrogen production method of the present invention.

[0031] [Copper / oxidation-resistant Green Rust composite] The copper / oxidation-resistant GR composite of the present invention is a composite containing oxidation-resistant green rust and copper present on the surface of this oxidation-resistant green rust, as described above. More preferably, it is a composite comprising copper-containing nanoparticles and oxidation-resistant GR on which these copper-containing nanoparticles are supported on the surface. The copper / oxidation-resistant GR composite of the present invention is suitable as a constituent material for the catalyst of the present invention. [Examples]

[0032] The present invention will be described in more detail below based on examples, but the present invention is not limited thereto.

[0033] [Preparation of oxidation-resistant GR - 1] 7.2 g of sodium acetate trihydrate and 100 mL of glycerol were placed in a 250 mL beaker and vigorously stirred at 80°C for 30 minutes to obtain a solution. 2.7 g each of FeCl3 and FeCl2 were added to this solution (FeCl3 / FeCl2 = 35 / 65 (molar ratio)), and the mixture was stirred at 100°C for 60 minutes. The resulting mixture was transferred to a 200 mL Teflon-lined stainless-steel autoclave and subjected to treatment at 200°C for 24 hours (solvothermal reaction). The green wet powder (wet oxidation-resistant GR) obtained by the solvothermal reaction was collected and washed twice with 140 mL of ethanol / water mixture (volume ratio 1 / 1), followed by one wash with 100 mL of ethanol. Finally, it was dried at 80°C for 24 hours to obtain oxidation-resistant GR powder (simply referred to as "GR" in the table and figure below). The obtained oxidation-resistant GR powder remained stable in air (relative humidity 40%), at 25°C and 0.1 MPa for at least one year without changing color (not oxidizing). Furthermore, using this oxidation-resistant GR powder, Fe III and Fe II The content was determined by ICP-OES (total Fe content) and Mössbauer spectroscopy (Fe III and Fe II When measured using the ratio of Fe, III The content is 20.4% by mass, Fe II The content was 20.9% by mass. Furthermore, analysis was performed in the same manner as the FTIR evaluation described in Japanese Patent Publication No. 2022-80364, and it was confirmed that this oxidation-resistant GR has lactate ions between the crystalline layers.

[0034] [Preparation of oxidation-resistant GR - 2] In the above [Preparation of oxidation-resistant GR-1], the amounts of FeCl3 and FeCl2 used are changed, and the resulting oxidation-resistant GR contains Fe III The content of is 32.1% by mass, Fe IIExcept for setting the content of 2.4% by mass, an oxidation-resistant GR powder (referred to as "LGR" in the table and figure below) was obtained in the same manner as in [Preparation of Oxidation-Resistant GR-1] above. The obtained oxidation-resistant GR powder was able to exist stably in air (relative humidity 40%), at 25°C and 0.1 MPa for at least one year without changing color (not oxidizing) while remaining green. Furthermore, analysis by FTIR, as described above, confirmed that this oxidation-resistant GR has lactate ions between the crystalline layers.

[0035] [Preparation of oxidation-resistant GR - 3] The oxidation-resistant GR powder obtained in [Preparation of Oxidation-Resistant GR-1] above was further pulverized in a planetary ball mill to create a fine powder. Note that this fine powdering process increases the surface area, so in [Preparation of Copper / Oxidation-Resistant GR Composite-3] described below, while the finely powdered oxidation-resistant GR was immersed in the CuCl2·2H2O solution, Cu II Reduction and the resulting Fe II The oxidation of Fe is accelerated, III The proportion of Fe increases. II It is expected that the proportion will decrease.

[0036] [Preparation of copper / oxidation-resistant GR composite - 1] CuCl2·2H2O was dissolved in 100 mL of ethanol / hexane mixture (volume ratio 3 / 17). 0.2 g of the oxidation-resistant GR powder prepared in [Preparation of Oxidation-Resistant GR-1] above was added to this solution and stirred at room temperature (25°C) for 24 hours. The precipitate obtained by centrifugation (3500 rpm, 15 minutes) was then washed with the ethanol / hexane mixture and dried at 80°C for 20 hours to obtain an oxidation-resistant GR (copper / oxidation-resistant GR composite) powder with supported copper nanoparticles. The amount of CuCl2·2H2O used was adjusted so that the copper content (supported amount) in the copper / oxidation-resistant GR composite (powder) was as shown in the table below (0.18~1.79 mass%), thereby obtaining seven types of copper / oxidation-resistant GR composites with different copper support amounts. In this context, the copper / oxidation-resistant GR composite powder with a copper loading of 0.50% by mass is simply labeled "Cu-GR" in the figure, while the copper / oxidation-resistant GR composite powder with a copper loading of 0.22% by mass is labeled "Cu-GR(0.2wt%)" in the figure. In this invention, the copper atom content in the copper / oxidation-resistant GR composite was determined as follows. Approximately 5 mg of the powdered sample was placed in a quartz beaker, 5 mL of sulfuric acid (1+1) and a few drops of nitric acid were added, and the mixture was heated until white fumes were produced to dissolve the powdered sample. After cooling, the solution was transferred to a 100 mL glass volumetric flask, and the solution, diluted to the mark with Mili-Q water, was subjected to ICP-OES analysis to determine the copper atom content.

[0037] [Preparation of copper / oxidation-resistant GR composite - 2] In the above [Preparation of Copper / Oxidation-Resistant GR Composite - 1], the copper / oxidation-resistant GR composite powder was obtained in the same manner as in the above [Preparation of Copper / Oxidation-Resistant GR Composite - 1], except that the oxidation-resistant GR (LGR) powder prepared in the above [Preparation of Oxidation-Resistant GR - 2] was used instead of the oxidation-resistant GR powder prepared in the above [Preparation of Oxidation-Resistant GR - 1], and the amount of CuCl2·2H2O dissolved in the ethanol / hexane mixture was adjusted so that the copper loading amount was 0.13% by mass. This copper / oxidation-resistant GR composite will be referred to as "Cu-LGR" in the table and figure below.

[0038] [Preparation of copper / oxidation-resistant GR composite - 3] In the above [Preparation of Copper / Oxidation-Resistant GR Composite - 1], the copper / oxidation-resistant GR composite powder was obtained in the same manner as in the above [Preparation of Copper / Oxidation-Resistant GR Composite - 1], except that the oxidation-resistant GR (bGR) powder prepared in the above [Preparation of Oxidation-Resistant GR - 3] was used instead of the oxidation-resistant GR powder prepared in the above [Preparation of Oxidation-Resistant GR Composite - 1], and the amount of CuCl2·2H2O dissolved in the ethanol / hexane mixture was adjusted so that the copper loading amount was 0.48% by mass. This copper / oxidation-resistant GR composite will be referred to as "Cu-bGR" in the table and figure below.

[0039] [Preparation of Pt-TiO2 and Cu-TiO2] A TiO2 powder supported with Pt nanoparticles was prepared according to ACS Appl. Mater. Interfaces, 2017, Vol. 9, pp. 24538-24544, and named "Pt-TiO2". In addition, Cu was prepared according to [Preparation of copper / oxidation-resistant GR composite - 1]. 2+ Ion-modified TiO2 powder was prepared and named "Cu-TiO2". The Pt content in the Pt-TiO2 powder was 0.20% by mass, and the Cu content in the Cu-TiO2 powder was 0.25% by mass.

[0040] [Table 1]

[0041] [analysis] <Mössbauer spectral measurement> Using the oxidation-resistant GR powder prepared in [Preparation of oxidation-resistant GR-1] above, and the copper / oxidation-resistant GR composite powder (copper content 0.50% by mass) prepared in [Preparation of copper / oxidation-resistant GR composite-1] above, the method described in Japanese Patent Application Publication No. 2022-80364 is used. 57 The Fe Mössbauer spectrum was measured. The results are shown in Figure 1. The spectrum shown in Figure 1 was in good agreement with the previously known green rust spectrum. From the results of Fig. 1, it was found that the powder of oxidation-resistant GR obtained above (「GR」 in Fig. 1) is a green last, and even when copper is supported on this oxidation-resistant GR to form a copper / oxidation-resistant GR composite (「Cu-GR」 in Fig. 1), the 57 Fe Mössbauer spectrum characteristics hardly changed.

[0042] <X-ray diffraction analysis> Using the powder of oxidation-resistant GR prepared in the above [Preparation of oxidation-resistant GR-1] and the powder of copper / oxidation-resistant GR composite prepared in the above [Preparation of copper / oxidation-resistant GR composite-1] (copper content 0.50% by mass), X-ray diffraction (XRD) analysis was performed by the method described in JP-A-2022-80364. The analysis results are shown in Fig. 2. This XRD pattern also well matched the XRD pattern of the conventional green last. That is, from the XRD pattern as well, it was found that the powder of oxidation-resistant GR obtained above (「GR」 in Fig. 2) is a green last, and even when copper is supported on this oxidation-resistant GR to form a copper / oxidation-resistant GR composite (「Cu-GR」 in Fig. 2), the XRD characteristics of the green last hardly changed. Also, since no diffraction peaks due to Cu species (Cu, CuO, Cu2O, etc.) were observed in the XRD analysis of Cu-GR, it was suggested that the supported Cu species are very small or have low crystallinity. In the above XRD pattern, the full width at half maximum (FWHM) of the signal waveform at the basic spacing d(003) was approximately 0.28 to 0.39°.

[0043] <X-ray photoelectron spectroscopy analysis> By performing X-ray photoelectron spectroscopy analysis using the powder of oxidation-resistant GR prepared in the above [Preparation of oxidation-resistant GR-1] and the powder of copper / oxidation-resistant GR composite prepared in the above [Preparation of copper / oxidation-resistant GR composite-1] (copper content 0.50% by mass), the state of Cu in the copper / oxidation-resistant GR composite was examined. The results are shown in Fig. 3. In the Cu2 p region XPS spectrum, peaks were observed at 931.7 eV and 951.4 eV. These peaks are respectively, Cu2p3 / 2 and Cu2 p1 / 2 resulting from the release from the level, and the oxidation state is Cu 0 and / or Cu + suggesting that it is. Considering the data in FIGS. 4 and 6 described later, it can be determined that it is Cu +

[0044] <UV-Vis Spectroscopic Analysis> Using the powder of antioxidant GR prepared in the above [Preparation of antioxidant GR-1] and the powder of copper / antioxidant GR composite prepared in the above [Preparation of copper / antioxidant GR composite-1] (copper content 0.50% by mass), UV-Vis spectroscopic analysis was performed to examine the state of Cu in the copper / antioxidant GR composite. FIG. 4 shows the diffuse reflection spectra of antioxidant GR ("GR" in FIG. 4) and copper / antioxidant GR composite ("Cu-GR" in FIG. 4). Cu in or on the titanium nanosheet due to localized surface plasmon resonance centered around 680 nm 0 such as Cu nanoparticles (3 - 40 nm) 0 Almost no absorption bands characteristic of such species were observed. Also, absorption bands characteristic of highly dispersed Cu ions and CuO clusters on different carriers (absorption at wavelengths of 400 - 450 nm and >650 nm) were not observed. On the other hand, for TiO2 doped with Cu ions, spectral characteristics showing slight absorption at wavelengths >400 nm have been reported. Therefore, it is considered that the copper / antioxidant GR composite contains highly dispersed Cu ions and clusters 2+ ions + ions + ions and clusters

[0045] <Scanning Electron Microscopy Analysis, Scanning Transmission Electron Microscopy Analysis> Figure 5 shows scanning electron microscope (SEM) images of the oxidation-resistant GR powder prepared in [Preparation of Oxidation-Resistant GR-1] above, and the copper / oxidation-resistant GR composite powder (copper content 0.50 mass%) prepared in [Preparation of Copper / Oxidation-Resistant GR Composite-1] above. Both the oxidation-resistant GR powder ("GR" in Figure 5) and the copper / oxidation-resistant GR composite powder ("Cu-GR" in Figure 5) were composed of plate-like particles and belt-like particles with a length of 1-2 μm. Furthermore, upon closer observation, it can be seen that the copper / oxidation-resistant GR composite particles have extremely fine irregularities on their edges, while the GR particles have smooth edges. Figure 6 shows the scanning transmission electron microscope (STEM) image and elemental mapping results of the copper / oxidation-resistant GR composite. The scanning transmission electron microscope image (bright-field image) is shown on the left side of Figure 6, and the HAADF image is shown in the upper left of the four-part right-hand region of Figure 6. Furthermore, as a result of elemental mapping, the Cu mapping image is shown in the upper right of the right-hand four-part region of Figure 6, the Fe mapping image is shown in the lower left of the right-hand four-part region of Figure 6, and the Cu and Fe mapping images are shown in the lower right of the right-hand four-part region of Figure 6. The Cu and Fe mapping images in Figure 6 are shown in grayscale, and the areas shown in brighter light indicate the presence of each element. From the results in Figure 6, it can be seen that extremely fine irregularities are formed by the deposition of Cu. It can also be seen that Cu is distributed not only at the particle edges of the copper / oxidation-resistant GR composite, but also throughout the entire particle plate. Furthermore, the Fast Fourier Transform (FFT) pattern of the selected region is shown in Figure 7. From Figure 7, it can be seen that the d value of Cu on the particle edge is in the range of 0.25 to 0.27 nm and exists as Cu2O such as cubic Cu2O (Cu + It became clear that it exists as such.

[0046] [Hydrolysis reaction of SBH (hydrogen production reaction)] A Pyrex® glass tube (34 mL tube) containing 1.0 mg of SBH crystals and 11.3 mg of the powder sample prepared above (oxidation-resistant GR, copper / oxidation-resistant GR composite, Pt-TiO2, or Cu-TiO2) was purged with Ar gas for 1 minute and sealed with a rubber diaphragm. Next, 3.75 mL of Ar-purged Milli-Q water (containing 20% ​​glycerol by volume) was injected into the tube through the rubber diaphragm using a syringe. The mixture in the tube was continuously stirred at room temperature (25°C) and immediately irradiated with simulated sunlight using a solar power simulator (manufactured by Sanei Electric Works, Ltd.) (wavelength > 300 nm, 1000 Wm). -2 The headspace gas was collected using an airtight syringe, and the generated gas (hydrogen gas) was quantified using a Shimadzu GC-2010 gas chromatograph equipped with a barrier discharge ionization detector.

[0047] <Hydrogen generation amount> Figure 8 shows the time course of hydrogen (H2) generation from the hydrolysis reaction of SBH described above. The horizontal axis represents reaction time, and the vertical axis represents the amount of hydrogen generated (cumulative amount, μmol). 1.0 mg of SBH is approximately 26 μmol, and from the reaction equation NaBH4 + 2H2O → 4H2 + NaBO2, the ideal amount of hydrogen generated is 26 × 4 = 104 μmol. The copper / oxidation-resistant GR composite powder with a copper content of 0.50 mass% (labeled "Cu-GR" in Figure 8) showed a significantly faster rate of SBH hydrolysis and a remarkably higher hydrogen generation rate compared to the Cu-TiO2 and Pt-TiO2 powders. The copper / oxidation-resistant GR composite powder with a copper content of 0.22 mass% (labeled "Cu-GR (0.2 wt%)" in Figure 8) also showed a clearly faster rate of SBH hydrolysis and higher hydrogen generation efficiency compared to the Cu-TiO2 (containing 0.25 mass% Cu) and Pt-TiO2 (containing 0.20 mass% Pt) powders, even with approximately the same loading amount. Furthermore, it was found that using a copper / oxidation-resistant GR composite powder ("Cu-bGR" in Figure 8), in which copper is supported on finely milled oxidation-resistant GR (bGR), as a catalyst for hydrolysis of SBH dramatically increased the reaction rate of the hydrolysis.

[0048] Moreover, the powder of oxidation-resistant GR without copper loading (denoted as "GR" in Figure 8) itself achieved a higher hydrogen generation efficiency than the Cu-TiO₂ powder and was comparable to the Pt-TiO₂ powder in terms of hydrogen generation efficiency. In previous reports, oxidation-resistant GR itself functioned as a hydrolysis catalyst for ammonia borane (AB), but its catalytic activity was reported to be much inferior compared to platinum-supported catalysts. That is, when the reaction substrate was changed from AB to SBH, it was revealed that hydrolysis proceeded efficiently even with oxidation-resistant GR itself, which can be produced at a lower cost, and it exhibited catalytic activity (hydrogen generation efficiency) equal to or higher than that of existing expensive SBH hydrolysis catalysts.

[0049] Thus, it became clear that oxidation-resistant GR itself also exhibited unexpectedly excellent catalytic activity as a hydrolysis reaction catalyst for SBH, contrary to previous knowledge. Furthermore, by loading inexpensive copper, which is a non-noble metal, onto oxidation-resistant GR, it was found that the catalytic activity was significantly enhanced compared to that without loading.

[0050] Regarding the enhancement of catalytic activity by loading copper onto oxidation-resistant GR, it was also verified for the case of using the oxidation-resistant GR obtained in the above [Preparation of oxidation-resistant GR - 2]. The results are shown in Figure 9. As shown in Figure 9, oxidation-resistant GR with a higher content of Fe in oxidation-resistant GR (denoted as "LGR" in Figure 9) itself also exhibited catalytic activity for the hydrolysis reaction of SBH, and it was found that this catalytic activity was significantly enhanced by loading copper to form a copper / oxidation-resistant GR composite. III Regarding the enhancement of catalytic activity by loading copper onto oxidation-resistant GR, it was also verified for the case of using the oxidation-resistant GR obtained in the above [Preparation of oxidation-resistant GR - 2]. The results are shown in Figure 9. As shown in Figure 9, oxidation-resistant GR with a higher content of Fe in oxidation-resistant GR (denoted as "LGR" in Figure 9) itself also exhibited catalytic activity for the hydrolysis reaction of SBH, and it was found that this catalytic activity was significantly enhanced by loading copper to form a copper / oxidation-resistant GR composite.

[0051] <Turnover frequency> The turnover frequency (TOF) is calculated by dividing the number of moles of hydrogen generated within 5 minutes by the total number of moles of Cu. The TOF of the powder of the copper / oxidation-resistant GR composite with a copper content of 0.50 mass% ("Cu-GR") was 1603 min -1 as shown as "1st" in Figure 10. This TOF value is considerably higher than that of many known SBH hydrolysis catalysts (for the TOF of known SBH hydrolysis catalysts, for example, Ru / C: 57.08 min-1 Co-Ru / C: 117 min -1 Ni-nanogel: 6.3 min -1 , Ni-Co / Hierarchical porous ZIF-8:588min -1 Pd / ZnO: 57 min -1 etc.).

[0052] <Reusability of copper / oxidation-resistant GR composites> The reusability of the copper / oxidation-resistant GR composite was investigated. The first SBH hydrolysis reaction was performed using a copper / oxidation-resistant GR composite powder with a copper content of 0.50 mass% as a catalyst. The mixture in the tube was then purged with Ar gas to remove residual gas. Next, SBH was added, and then, through the rubber septum of the tube to be reused, Milli-Q water (containing 20 volume% glycerol), purged with Ar in the same manner as the first SBH hydrolysis reaction, was added to perform a second SBH hydrolysis reaction. As shown in Figure 10, the second hydrolysis reaction (2nd) and even the third hydrolysis reaction (3rd) achieved the same excellent hydrogen production efficiency as the first hydrolysis reaction (1st). The XRD pattern of the copper / oxidation-resistant GR composite recovered after the first hydrolysis reaction is shown in Figure 11 as "After". It can be seen that there was almost no structural change compared to the unused copper / oxidation-resistant GR composite ("Before" in Figure 11). These results indicate that the Cu supported on the oxidation-resistant GR is sufficiently stabilized to function as a catalyst (photocatalyst) for SBH hydrolysis.

[0053] <Catalytic activity under non-photoirradiation conditions> The catalytic activity of the oxidation-resistant GR prepared in [Preparation of Oxidation-Resistant GR-1] above, and the copper / oxidation-resistant GR composite with a copper content of 0.50 mass% prepared in [Preparation of Copper / Oxidation-Resistant GR Composite-1] above, for the hydrolysis reaction of SBH was investigated under conditions without irradiation of simulated sunlight (darkness). The results are shown in Figure 12. While catalytic activity tends to increase with light irradiation, it can be seen that excellent catalytic activity for the hydrolysis reaction of SBH is observed even without light irradiation.

[0054] <Stabilization of copper / oxidation-resistant GR complex by glycerol> The hydrolysis reaction of SBH described above involved mixing glycerol with water, then mixing this with SBH, and reacting in the presence of oxidation-resistant GR or a copper / oxidation-resistant GR complex as a catalyst. This is because alcohols such as glycerol function as electron donors, increasing the stability of the catalyst. When glycerol is not added to the water, as shown in Figure 13, the catalytic activity decreases sequentially in the second and third hydrolysis reactions compared to the first SBH hydrolysis reaction. In Figure 13, under "1st," "2nd," and "3rd," the left bar represents the result without glycerol, and the right bar represents the result with glycerol (same as Figure 10). The XRD pattern of the copper / oxidation-resistant GR complex recovered after the third hydrolysis reaction without glycerol is shown in Figure 14 as "After, without glycerol." Without the addition of glycerol, the pattern of the unused copper / oxidation-resistant GR complex ("Before" in Figure 13) could not be maintained, suggesting that a structural change occurred and catalytic activity decreased. Furthermore, even when catalytic activity decreased, it maintained a high TOF value compared to known SBH hydrolysis catalysts.

[0055] <Effect of copper load on catalytic activity> The catalytic activity of various copper / oxidation-resistant GR composite powders with different copper content (copper loading amounts), prepared in the above [Preparation of Copper / Oxidation-Resistant GR Composite - 1], was compared in the SBH hydrolysis reaction. The results are shown in Figure 15. In Figure 15, the number in parentheses to the right of "Cu-GR" (wt%) represents the copper content (mass%). It can be seen that by supporting copper, the catalytic activity of the SBH hydrolysis reaction can be greatly enhanced, regardless of the amount of copper supported.

[0056] As supported by the experimental results described above, the present invention provides a hydrolysis catalyst or a method for producing the same that exhibits excellent catalytic activity for hydrolysis reactions that produce hydrogen from borohydride metal salts and is chemically stable. Furthermore, the present invention provides a hydrolysis method for producing hydrolysis of borohydride metal salts in the presence of the above hydrolysis catalyst and a method for producing hydrogen. Furthermore, the present invention provides a copper / oxidation-resistant GR composite suitable as the above hydrolysis catalyst.

Claims

1. A hydrolysis catalyst for metal borohydride salts, containing oxidation-resistant green rust.

2. The Fe possessed by the aforementioned oxidation-resistant green rust III and Fe II The atomic ratio (Fe III / [Fe III +Fe II The hydrolysis catalyst according to claim 1, wherein the ratio of ) is 0.10 or more and 0.99 or less.

3. Fe in the oxidation-resistant green last II The ratio of the content of Fe III to the content of Fe III is, on a mass basis, Fe II / Fe = 50 / 1 to 1 / 10, the hydrolysis catalyst according to claim 1.

4. The hydrolysis catalyst according to claim 3, wherein the oxidation-resistant green rust has lactate ions between the crystalline layers.

5. The hydrolysis catalyst according to claim 4, wherein the hydrolysis catalyst contains the oxidation-resistant green rust and copper.

6. The hydrolysis catalyst according to claim 5, wherein the proportion of copper in the total content of the copper and the oxidation-resistant green rust constituting the hydrolysis catalyst is 0.10 to 2.00% by mass.

7. The copper is Cu ＋ The hydrolysis catalyst according to claim 6, which exists as such.

8. The hydrolysis catalyst according to claim 7, wherein the hydrolysis reaction of the borohydride metal salt in the presence of the hydrolysis catalyst is a hydrolysis reaction under light irradiation.

9. A method for hydrolyzing a metal borohydride salt, comprising contacting the metal borohydride salt with water in the presence of a hydrolysis catalyst according to any one of claims 1 to 8.

10. The hydrolysis method according to claim 9, wherein the contact between the borohydride metal salt and water is carried out under light irradiation.

11. The hydrolysis method according to claim 9, wherein the contact between the borohydride metal salt and water is carried out in the presence of glycerol and / or methanol.

12. A method for producing hydrogen, comprising generating hydrogen by contacting a metal borohydride salt with water in the presence of a hydrolysis catalyst according to any one of claims 1 to 8.

13. The method for producing hydrogen according to claim 12, wherein the contact between the borohydride metal salt and water is carried out under light irradiation.

14. The method for producing hydrogen according to claim 12, wherein the contact between the borohydride metal salt and water is carried out in the presence of glycerol and / or methanol.

15. A copper / oxidation-resistant green rust composite containing oxidation-resistant green rust and copper.

16. A method for producing a copper / oxidation-resistant green rust composite according to claim 15, comprising impregnating the oxidation-resistant green rust in a copper salt solution to provide copper on the surface of the oxidation-resistant green rust.

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