JP7162300B2 - Electrocatalyst and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electrode catalyst and a method for producing the same.

Hydrogen emits zero _CO2 when burned, and is expected as a clean energy source to replace fossil fuels. In particular, the method of producing hydrogen by water electrolysis, which uses renewable energy sources such as sunlight, wind power, and hydraulic power as power, does not emit any _CO2 , so it is expected to be a clean hydrogen production method. there is

As an electrode for electrolysis of water, there is known one in which a platinum particle catalyst is fixed on an electrode base material such as a carbon base material. However, platinum is expensive and its resources are limited, so there is a demand for the development of techniques for reducing the amount of platinum used and the development of platinum-alternative catalysts and/or electrodes.

From this point of view, novel materials such as sulfides or oxides of transition metals (e.g., Co, Ni, Mn, etc.) having a nano-sized fine structure are attracting attention as electrodes for water electrolysis. The research is being actively pursued (for example, Patent Document 1). Although these materials exhibit good activity, their nanostructures often collapse due to repeated use, leaving room for improvement in terms of long-term electrode stability.

Recently, non-precious metal electrocatalysts such as transition metal chalcogenides, transition metal carbides, phosphides, phosphorus sulfides, nitrides, borides, and selenides have been developed using their unique physical and chemical properties. It is being studied as a generation electrocatalyst.

JP-A-2000-000470

However, conventionally proposed electrode catalysts exhibit their performance sufficiently only when used only under specific conditions. The performance of the electrode catalyst was demonstrated. In other words, when used at a certain pH, excellent hydrogen generation efficiency and durability are exhibited, but when the pH of the electrolyte is in a different range, the hydrogen generation efficiency and durability may decrease. there were. In particular, when the electrolyte becomes near neutral, the conventional electrode catalyst tends to lower the hydrogen generation efficiency and durability. From such a point of view, the development of an electrode catalyst that can efficiently generate hydrogen over a wide pH range and is excellent in durability has been desired.

The present invention has been made in view of the above, and it is an object of the present invention to provide an electrode catalyst that can efficiently generate hydrogen in a wide pH range and has excellent durability, and a method for producing the same.

The inventors of the present invention have made intensive studies to achieve the above objects, and as a result, found that the above objects can be achieved by forming a catalyst containing at least two types of sulfides of a specific metal on an electrode substrate. I have perfected my invention.

That is, the present invention includes, for example, the subject matter described in the following sections.
Item 1
comprising a catalyst on an electrode substrate,
The catalyst is an electrode catalyst containing a sulfide of Mo and a sulfide of a transition metal M other than Mo.
Item 2
Item 2. The electrode catalyst according to Item 1, wherein the transition metal M is at least one selected from the group consisting of Co, Fe, Ni, Cu, W and Mn.
Item 3
After the electrode base material is immersed in a first raw material containing a compound containing a transition metal M other than Mo and an aqueous solvent and subjected to heat treatment, the electrode base material is taken out and fired to form an oxide of the transition metal M. a first step of obtaining the formed electrode substrate;
The electrode substrate on which the oxide of the transition metal M is formed is immersed in a second raw material containing a Mo-containing compound, a sulfur-containing compound, and an aqueous solvent and heat-treated to cause sulfurization of Mo. a second step of obtaining an electrode substrate on which a catalyst containing a sulfide of the transition metal M and a sulfide of the transition metal M is formed;
A method for producing an electrode catalyst.
Item 4
Item 4. The electrode catalyst according to Item 3, wherein the transition metal M is at least one selected from the group consisting of Co, Fe, Ni, Cu, W and Mn.
Item 5
Item 5. A method for producing hydrogen, comprising the step of performing electrolytic treatment using the electrode catalyst according to Item 1 or 2 or using the electrode catalyst obtained by the production method according to Item 3 or 4.

The electrode catalyst according to the present invention can efficiently generate hydrogen in a wide pH range (pH 0 to 14), and is also excellent in durability.

The method for producing an electrode catalyst according to the present invention can efficiently generate hydrogen in a wide pH range (pH 0 to 14), and can easily produce an electrode catalyst that is excellent in durability.

4 is an SEM image of electrodes obtained in Examples and Comparative Examples. 2 shows the results of X-ray diffraction analysis of the catalyst (MoS ₂ /CoS ₂ ) in the electrode catalyst obtained in Example 1. FIG. 1 shows a linear sweep voltammetry curve using the MoS ₂ /CoS ₂ /CP electrode obtained in Example 1; 1 shows linear sweep voltammetry curves using MoS ₂ /CoS ₂ /CP electrodes obtained in Examples 1-3. (a) is a linear sweep voltammetry curve (pH = 0, 7, 14) using the MoS ₂ /CoS ₂ /CP electrode obtained in Example 1, and (b) is a linear sweep voltammetry curve shown in (a). shows the Tafel gradient calculated from 3 shows a linear sweep voltammetry curve after 3000 cycles of a cyclic voltammetry test (CV test) of the MoS ₂ /CoS ₂ /CP electrode obtained in Example 1. FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail. In this specification, the expressions "contain" and "include" include the concepts of "contain", "include", "substantially consist of" and "consist only of".

(Electrocatalyst)
The electrode catalyst of the present invention comprises a catalyst on an electrode substrate. In particular, the catalyst comprises a sulfide of Mo and a sulfide of a transition metal M other than Mo.

The electrode catalyst can efficiently generate hydrogen over a wide pH range of pH 0 to 14 by forming a catalyst having a specific composition on an electrode substrate. In addition, the electrode catalyst does not easily deteriorate in performance even after repeated use, and is excellent in durability.

In the electrode catalyst, the type of electrode substrate is not particularly limited, and for example, a wide range of known conductive substrates can be employed.

Examples of electrode substrates include substrates used as electrodes for electrolysis of water, and specific examples thereof include carbon substrates, metal substrates, glass substrates, and the like. Examples of carbon substrates include carbon paper and carbon rods. Examples of metal substrates include substrates of simple metals such as nickel, titanium, iron, and copper, and substrates such as nickel-phosphorus alloys, nickel-tungsten alloys, and stainless alloys. Conductive glass etc. are illustrated as a glass base material. Among them, the electrode substrate is preferably a carbon substrate, and particularly preferably carbon paper, from the viewpoint that the electrode catalyst can be more easily produced.

The electrode base material can be obtained, for example, by a known production method, or can be obtained from commercial products and the like.

The shape and size of the electrode substrate are not particularly limited, and can be appropriately selected depending on the purpose of use and required performance. For example, the shape of the electrode base material can be sheet-like, plate-like, bar-like, mesh-like, or the like.

The catalyst contains Mo (molybdenum) sulfide. Sulfides of Mo are compounds that can be represented by the chemical _formula MoS2.

The catalyst contains a sulfide of a transition metal M other than Mo. For example, if the transition metal M is Co (cobalt), the sulfide of Co is a compound that can be represented by the chemical formula _CoS2 .

The transition metal M is preferably at least one selected from the group consisting of Co, Fe, Ni, Cu, W and Mn. In this case, the production of the electrode catalyst is easy, and the electrode catalyst is excellent in hydrogen generation efficiency and easily improved in durability. Co, Fe, Ni, Cu, W and Mn have common or similar properties of their sulfides and their metal sulfides contribute to the electron distribution of Mo (molybdenum) sulfides. Common or similar impacts. Therefore, even if the transition metal M is any metal of Co, Fe, Ni, Cu, W and Mn, the electrode catalyst can exhibit the characteristics of further improving hydrogen generation efficiency and durability.

The transition metal M is more preferably at least one selected from the group consisting of Co, Fe and Ni from the viewpoint that the hydrogen generation efficiency and durability of the electrode catalyst are particularly likely to be improved, and Co is particularly preferred. preferable.

Said catalyst may contain other components such as other metals or other compounds as long as it contains Mo sulfide and transition metal M sulfide. When the catalyst contains other components, the other components are preferably 10% by mass or less, more preferably 5% by mass or less, and 1% by mass or less, relative to the total mass of the catalyst. Especially preferred. The catalyst may be formed only of Mo sulfide and transition metal M sulfide.

The shape of the catalyst is not particularly limited, and examples thereof include various shapes such as particle, wire, fibrous, needle, rod, and scale. The catalyst is preferably particulate or wire-like from the viewpoints of ease of production and the ability to exhibit excellent performance. When the catalyst is particulate, for example, spherical, petal-shaped, irregularly shaped particles can be used. The surface of the particles may be smooth or may have needle-like projections.

When the catalyst is particulate, its size is not particularly limited, and for example, the average particle diameter of the catalyst can be 0.01 to 500 μm, preferably 1 to 100 μm. Here, the average particle diameter of the particles refers to the arithmetic mean value obtained by measuring the equivalent circle diameters of 50 particles selected at random by direct observation of the electrode catalyst with a scanning electron microscope.

The structure of the catalyst is not particularly limited as long as it contains Mo sulfide and transition metal M sulfide. That is, in the catalyst, there is no particular limitation on the state of existence of the sulfide of Mo and the sulfide of the transition metal M. The catalyst preferably has a structure in which a sulfide of Mo is formed on the surface of a sulfide of the transition metal M, from the viewpoint that the hydrogen generation efficiency and durability of the electrode catalyst are likely to be improved.

In particular, the catalyst is preferably formed by coating the surface of the sulfide of the transition metal M with the sulfide of Mo. A core-shell structure can be mentioned as such a structure.

When the catalyst has a core-shell structure, the hydrogen generation efficiency and durability of the electrode catalyst are particularly likely to be improved. As a core-shell structure, a core-shell particle can be mentioned specifically.

When the catalyst is formed in a core-shell structure, for example, the core of the core-shell structure may contain the sulfide of the transition metal M, and the shell may contain the sulfide of Mo. Of course, vice versa is also possible. The core can be formed of only the sulfide of the transition metal M, and the shell can be formed of only the sulfide of Mo.

In the catalyst, the molar ratio between the Mo sulfide and the transition metal M sulfide is not particularly limited. For example, the catalyst may contain 0.01 to 100 mol, preferably 0.01 to 10 mol, and 0.01 to 1 mol of sulfide of transition metal M per 1 mol of sulfide of Mo. is particularly preferred.

The electrode catalyst may contain components other than the catalyst as long as the effects of the present invention are not impaired, and the electrode catalyst may be formed only of the electrode base material and the catalyst.

The electrode catalyst can be formed directly on the electrode base material (without passing through another layer or the like), for example. In particular, in the electrode catalyst, the sulfide of the transition metal M is directly supported on the electrode substrate, and the sulfide of Mo can be formed directly on the sulfide of the transition metal M. In the electrode catalyst, it is preferred that no layer is formed on the catalyst.

The excellent performance of the electrode catalyst of the present invention is due to the co-doping effect of the transition metal M and oxygen on the sulfide of Mo, the accompanying formation of reactive defect sites, and the high conductivity of the sulfide of the transition metal M. It can be brought about by a high contact surface area to the electrolyte due to the specific three-dimensional structure, and the like.

INDUSTRIAL APPLICABILITY The electrode catalyst of the present invention is suitable for use in various electrolysis electrodes, and in particular, when used as an electrode for water electrolysis, it can bring about excellent hydrogen generation efficiency. Suitable for cathode use.

The method for producing the electrode catalyst of the present invention is not particularly limited, and various production methods can be adopted. In particular, the electrode catalyst of the present invention can be produced by a production method including steps 1 and 2, which will be described later.

(Manufacturing method of electrode catalyst)
The method for producing an electrode catalyst of the present invention includes at least the following first step and second step.
First step: after the electrode base material is immersed in a first raw material containing a compound containing a transition metal M other than Mo and an aqueous solvent and subjected to heat treatment, the electrode base material is taken out and sintered to remove the transition metal M A step of obtaining an electrode substrate on which an oxide of is formed.
Second step: the electrode substrate on which the oxide of the transition metal M is formed is immersed in a second raw material containing a compound containing Mo, a compound containing sulfur, and an aqueous solvent and subjected to heat treatment. , a step of obtaining an electrode substrate on which a catalyst containing a sulfide of Mo and the sulfide of the transition metal M is formed.

In the first step, a first raw material containing a compound containing a transition metal M and an aqueous solvent is placed in a container, and an electrode substrate is immersed in the first raw material and heat-treated. After this heat treatment, the electrode base material is taken out from the container and fired to obtain an electrode base material on which the oxide of the transition metal M is formed. Therefore, the first step is a step for forming an oxide of the transition metal M on the electrode substrate.

In the first step, the transition metal M is other than Mo as described above. The transition metal M is at least one selected from the group consisting of Co, Fe, Ni, Cu, W, and Mn from the viewpoint that the electrode catalyst is easily produced and the hydrogen generation efficiency and durability are particularly easily improved. is preferred, at least one selected from the group consisting of Co, Fe and Ni is more preferred, and Co is particularly preferred.

1st process WHEREIN: The kind of compound containing the transition metal M is not specifically limited. For example, as the compound containing the transition metal M, an inorganic acid salt of the transition metal M, an organic acid salt of the transition metal M, a hydroxide of the transition metal M, a halide of the transition metal M, and the like can be widely used.

As the inorganic acid salt of the transition metal M, a wide range of known compounds can be employed. 1 or more selected from the group consisting of and the like.

As the organic acid salt of the transition metal M, a wide range of known compounds can be employed. For example, one or more selected from the group consisting of transition metal M acetate, oxalate, formate, succinate, etc. can be mentioned.

The compound containing the transition metal M is preferably a nitrate or hydrochloride of the transition metal M from the viewpoint of being easily dissolved in an aqueous solvent to form a solution. The compound containing transition metal M may be a hydrate.

The compounds containing the transition metal M used in the first step may be used singly or in combination of two or more. The compound containing transition metal M can be obtained by a known production method, or a commercially available compound containing transition metal M can be used.

The aqueous solvent used in the first step can be water, or a mixture of water and a lower alcohol (e.g., an alcohol having 1 to 4 carbon atoms such as methanol and ethanol), particularly preferably water. . Various types of water such as distilled water, tap water, industrial water, ion-exchanged water, deionized water, pure water, and electrolyzed water can be used as the water. The aqueous solvent may contain pH adjusters, viscosity adjusters, fungicides and the like as long as the effects of the present invention are not impaired.

The first raw material used in the first step contains the compound containing the transition metal M and the aqueous solvent. For example, the first raw material is a solution of the transition metal M dissolved in the aqueous solvent.

The concentration of the compound containing the transition metal M in the first raw material is not particularly limited. For example, the first raw material preferably contains 1 to 100 mmol of the compound containing the transition metal M per 100 mL of the aqueous solvent. In this case, an oxide of the transition metal M having a stable structure can be easily formed.

The first raw material used in the first step contains the compound containing the transition metal M and the aqueous solvent, and may also contain other additives. Other additives include, for example, pH adjusters. Examples of pH adjusters include urea (CO(NH ₂ ) ₂ ), NH ₄ F, ammonium hydroxide, and the like. A pH adjuster can be used only 1 type or in combination of 2 or more types.

When the first raw material used in the first step contains urea, it is preferable that 10 to 50 mmol of urea be dissolved in 100 mL of the aqueous solvent. In this case, the first raw material tends to have a pH in the alkaline region, thereby facilitating the formation of the oxide of the transition metal M in the desired shape in the first step.

When the first raw material used in the first step contains NH ₄ F, 10 to 50 mmol of NH ₄ F are preferably dissolved in 100 mL of the aqueous solvent. In this case, the first raw material tends to have a pH in the alkaline region, thereby facilitating the formation of the oxide of the transition metal M in the desired shape in the first step.

The first raw material may consist of only the compound containing the transition metal M, the pH adjuster and the aqueous solvent.

The method of immersing the electrode base material in the first raw material is not particularly limited, and usually the whole electrode base material can be immersed in the first raw material. The immersion of the electrode base material can be performed, for example, in a vessel capable of hydrothermal synthesis, which will be described later. As such a container, a pressure-resistant autoclave can be mentioned. The inner surface of the autoclave can be coated, for example, with a fluororesin such as Teflon (registered trademark).

The electrode base material can also be washed in advance before being immersed in the first raw material. The method of cleaning treatment is not particularly limited, and a wide range of known methods can be employed. For example, there is a method of washing the electrode base material with an inorganic acid such as sulfuric acid. Ultrasonic treatment can be combined with acid cleaning. After acid washing, it may be further washed with a solvent such as alcohol and water.

In the production method of the present invention, the type of electrode substrate is not particularly limited, and is the same as the electrode substrate used in the electrode catalyst described above.

In the first step, heat treatment is performed while the electrode base material is immersed in the first raw material. A hydrothermal synthesis method can be mentioned as the heat treatment in the first step. The hydrothermal synthesis method referred to here is a method in which a container is sealed while the electrode base material is immersed in the first raw material, and the inside of the container is heated. This hydrothermal synthesis can form a hydroxide of the transition metal M on the electrode substrate.

The temperature inside the vessel in the hydrothermal synthesis is not particularly limited as long as the conditions are such that the hydroxide of the transition metal M is formed. The time for which the container is held at this temperature is also not particularly limited, and can be, for example, 8 to 24 hours. The pressure inside the vessel in the hydrothermal synthesis can also be set appropriately.

In hydrothermal synthesis, the first raw material is preferably in the alkaline region, for example, preferably has a pH of 7 to 14, more preferably 8 to 10, and particularly preferably about 9. In this case, in hydrothermal synthesis, it becomes easier to form a hydroxide, and it is easier to control the shape of the oxide finally formed in the first step into a desired shape.

In the first step, after the heat treatment (hydrothermal synthesis), the electrode base material is taken out from the container and baked.

In the first step, the firing method is not particularly limited, and for example, a wide range of known firing methods can be employed.

The firing temperature can be, for example, 300 to 400.degree. C., preferably 340 to 380.degree. The firing time may be appropriately selected depending on the firing temperature, and may be, for example, 1.5 to 5 hours. In the first step, the rate of temperature increase during firing is not particularly limited, and can be appropriately set to the extent that a desired oxide is formed.

Firing may be performed in air or in an inert gas atmosphere. Preferably, the firing is carried out in air. For calcination, for example, a known heating device such as a commercially available heating furnace can be used.

By the firing, the hydroxide on the electrode base material changes to an oxide, and an electrode base material modified with an oxide of the transition metal M (for example, cobalt oxide) can be obtained.

In the second step, the electrode substrate on which the oxide of the transition metal M obtained in the first step is formed is immersed in a second raw material containing a compound containing Mo, a compound containing sulfur, and an aqueous solvent. Heat treatment. As a result, an electrode substrate on which a catalyst containing the sulfide of Mo and the sulfide of the transition metal M is formed is obtained. Accordingly, the second step is a step for forming a catalyst comprising Mo sulfide and said transition metal M sulfide.

2nd process WHEREIN: The kind of compound containing Mo is not specifically limited. For example, as a compound containing Mo, a metal salt of molybdic acid, an inorganic acid salt of Mo, an organic acid salt of Mo, a hydroxide of Mo, a halide of Mo, and the like can be widely used.

Examples of metal salts of molybdic acid include alkali metal and ammonium salts of molybdic acid. More specifically, metal salts of molybdate include sodium molybdate (Na ₂ MoO ₄ ), potassium molybdate (K ₂ MoO ₄ ), and ammonium molybdate ((NH ₄ ) ₂ MoO ₄ ). .

As the inorganic acid salt of Mo, a wide range of known compounds can be employed, for example, the group consisting of nitrates, hydrochlorides, sulfates, carbonates, hydrogencarbonates, phosphates and hydrogenphosphates of Mo. One or more selected from can be mentioned.

As the organic acid salt of Mo, a wide range of known compounds can be employed, for example, one or more selected from the group consisting of Mo acetate, oxalate, formate, succinate, etc. can.

The compound containing Mo is preferably a metal salt of molybdic acid, or a nitrate or hydrochloride of Mo from the viewpoint of being easily dissolved in an aqueous solvent to form a solution. A compound containing Mo may be a hydrate.

The Mo-containing compounds used in the first step may be used singly or in combination of two or more. The compound containing Mo can be obtained by a known production method, or a commercially available compound containing Mo can also be used.

The sulfur-containing compound is not particularly limited, and its kind is not limited as long as it can form a sulfide of Mo and transition metal M. For example, the sulfur-containing compound may be sulfur alone, or may be either an inorganic compound or an organic compound containing sulfur. The sulfur-containing compound is preferably an organic compound containing sulfur in that sulfides of Mo and transition metal M are easily formed.

Specific examples of sulfur-containing compounds include thioacetamide (C ₂ H ₅ NS), thiourea (CH ₄ N ₂ S), sulfur and the like.

The sulfur-containing compounds used in the second step may be used singly or in combination of two or more.

The aqueous solvent used in the second step can be water, or a mixture of water and a lower alcohol (e.g., alcohol having 1 to 4 carbon atoms such as methanol and ethanol), particularly preferably water. . Various types of water such as distilled water, tap water, industrial water, ion-exchanged water, deionized water, pure water, and electrolyzed water can be used as the water. The aqueous solvent may contain pH adjusters, viscosity adjusters, fungicides and the like as long as the effects of the present invention are not impaired.

The second raw material used in the second step includes a Mo-containing compound, a sulfur-containing compound, and the aqueous solvent. For example, the second raw material is a solution of a Mo-containing compound dissolved in the aqueous solvent.

The concentration of the Mo-containing compound in the second raw material is not particularly limited. For example, the second raw material preferably contains 1 to 100 mmol of the compound containing Mo per 100 mL of the aqueous solvent. In this case, a sulfide of Mo having a stable structure can be easily formed.

The concentration of the sulfur-containing compound in the second raw material is not particularly limited. For example, the second raw material preferably contains 1 to 100 mmol of the sulfur-containing compound per 100 mL of the aqueous solvent. In this case, a sulfide of Mo having a stable structure can be easily formed.

In the second raw material, the content ratio of the compound containing Mo and the compound containing sulfur is not particularly limited. For example, the content ratio of the compound containing Mo and the compound containing sulfur can be adjusted so that 1 to 10 moles of sulfur atoms are contained per 1 mole of Mo. More preferably, the content ratio of the Mo-containing compound and the sulfur-containing compound is adjusted so that 2 to 8 mol of sulfur atoms are contained per 1 mol of Mo. Particularly preferably, the content ratio of the Mo-containing compound and the sulfur-containing compound is adjusted so that 3 to 4 mol of sulfur atoms are contained per 1 mol of Mo.

The second raw material used in the second step contains the Mo-containing compound, the sulfur-containing compound and the aqueous solvent, and may also contain other additives.

The second raw material may consist of only the compound containing Mo, the compound containing sulfur, and the aqueous solvent.

The method of immersing the electrode base material obtained in the first step in the second raw material is not particularly limited, and usually the whole electrode base material can be immersed in the second raw material. In the second step, the electrode base material can be immersed in, for example, the same type of container as used in the first step.

In the second step, heat treatment is performed while the electrode base material is immersed in the second raw material. As the heat treatment in the second step, a hydrothermal synthesis method can be mentioned as in the first step. The hydrothermal synthesis method can be performed in the same procedure as in the first step.

In the second step, the temperature inside the vessel in the hydrothermal synthesis is not particularly limited as long as the desired sulfide is formed, and can be, for example, 120 to 250°C. The time for which the container is held at this temperature is also not particularly limited, and can be, for example, 8 to 24 hours. The pressure inside the vessel in the hydrothermal synthesis can also be set appropriately.

By the heat treatment in the second step, Mo and S ions in the second raw material react with the oxide of the transition metal M to form a sulfide of the transition metal M first. This transition metal M sulfide can form nanowires. The transition metal M sulfide thus formed can serve as a structural backbone to guide the growth of Mo sulfide nanosheets.

In the second step, after the heat treatment (hydrothermal synthesis), the inside of the container can be cooled and the electrode substrate can be taken out. By this heat treatment, a catalyst containing Mo sulfide and transition metal sulfide is formed on the electrode base material, and is obtained as an electrode catalyst. The obtained electrode catalyst is washed with water, ethanol, etc., and dried, if necessary. Vacuum drying, for example, can be employed for this drying.

In the production method of the present invention, the amount of Mo sulfide and transition metal M sulfide produced can be adjusted, for example, by adjusting the amount of the compound containing Mo used in the second step.

According to the production method of the present invention, the obtained electrode catalyst contains a sulfide of Mo and a sulfide of a transition metal M other than Mo and is formed on the electrode substrate. Therefore, the electrode catalyst obtained by the production method of the present invention can efficiently generate hydrogen in a wide pH range (pH 0 to 14), and it is possible to easily produce an electrode catalyst that is excellent in durability. can.

(Method for producing hydrogen)
The method for producing hydrogen of the present invention includes the step of performing electrolytic treatment using the electrode catalyst of the present invention. Alternatively, the method for producing hydrogen of the present invention includes a step of performing electrolytic treatment using the electrode catalyst obtained by the above-described method for producing an electrode catalyst of the present invention.

The method for producing hydrogen of the present invention can use an electrode catalyst, for example, as a cathode.

On the other hand, in the method for producing hydrogen of the present invention, an electrode that is generally used as an anode in the electrolysis of water can be used as the anode. For example, electrodes made of noble metals such as carbon, platinum, and gold can be used as cathodes.

In the method for producing hydrogen of the present invention, the aqueous solution used in electrolysis may be an aqueous solution containing components generally used in electrolysis of water. The aqueous solution may also contain halogens such as iodine, bromine, sulfate ions, and the like. When using an aqueous solution containing iodine, iodate ions are generated at the anode.

In particular, the electrode catalyst used in the hydrogen production method of the present invention can provide excellent hydrogen generation efficiency even when used over a wide range of pHs as described above, so aqueous solutions with various pHs can be used. For example, aqueous solutions such as KOH and NaOH can be used in the alkaline region, aqueous solutions such as hydrochloric acid and sulfuric acid can be used in the acidic region, and PBS (phosphate buffered saline) can be used in the neutral region. etc. can be used.

To give a specific example of the method for producing hydrogen, the electrode catalyst of the present invention is used as a cathode, a platinum plate is used as an anode, and KOH, H ₂ SO ₄ or a PBS aqueous solution is used as an electrolyte, and a voltage is applied. This allows hydrogen to be produced at the cathode. Also, by increasing the applied voltage, the rate of hydrogen generation can be increased.

Hydrogen produced by the method for producing hydrogen can be preferably used as fuel for fuel cells, hydrogen engines, and the like.

In the method for producing hydrogen of the present invention, since the electrode catalyst is used as an electrode, an increase in overvoltage is unlikely to occur, hydrogen can be produced efficiently, and the durability of the electrode catalyst is excellent. Even if you use it, the performance is unlikely to deteriorate.

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the embodiments of these examples.

(Example 1)
A Teflon-lined stainless steel autoclave with a capacity of 50 mL was charged with ₂ mmol of Co(NO ₃ ) 2.6H ₂ O, 8 mmol of NH ₄ F, 10 mmol of CO(NH ₂ ) ₂ and 36 mL of deionized water. It was added and dissolved with vigorous stirring for 30 minutes to obtain the first raw material. Next, carbon paper (hereinafter abbreviated as “CP”) having a size of 2.0 cm×2.0 cm was immersed in the first raw material in the autoclave. In addition, the CP was ultrasonically cleaned in advance with sulfuric acid, ethanol, and water in this order for 20 minutes each. After the autoclave was sealed and hermetically sealed, the autoclave was held in an electric oven at 120° C. for 12 hours to carry out hydrothermal synthesis. This supported Co(OH) ₂ nanowires on the CP. Then, after cooling the autoclave to room temperature, the electrode substrate was taken out and fired in the atmosphere at 350° C. for 2 hours to change Co(OH) ₂ to Co ₃ O ₄ to form Co ₃ O ₄ on the CP. formed. Hereinafter, this is described as "Co ₃ O ₄ /CP".

Then, 1.0 mmol of Na ₂ MoO _{4.2H 2} O, 4.0 mmol of C ₂ H ₅ NS, and 30 mL of deionized water were added to a 50 mL Teflon-lined stainless steel autoclave. A second raw material was obtained by dissolving with vigorous stirring for a minute. The Co ₃ O ₄ /CP was immersed in this second raw material. After the autoclave was sealed and hermetically sealed, the autoclave was held in an electric oven at 200° C. for 18 hours to carry out hydrothermal synthesis. As a result, Co ₃ O ₄ on CP was changed to sulfide (CoS ₂ ) and MoS ₂ was formed on CoS ₂ . The obtained electrode catalyst was described as "MoS ₂ /CoS ₂ /CP electrode". The obtained MoS ₂ /CoS ₂ /CP electrode was washed several times with water and absolute ethanol, and then dried under vacuum at 60° C. to obtain an electrode catalyst.

(Example 2)
A MoS ₂ /CoS ₂ /CP electrode was obtained in the same manner as in Example 1, except that the amount of C ₂ H ₅ NS used was changed to 2.0 mmol.

(Example 3)
A MoS ₂ /CoS ₂ /CP electrode was obtained in the same manner as in Example 1, except that the amount of C ₂ H ₅ NS used was changed to 6.0 mmol.

(Comparative example 1)
4.0 mmol of C ₂ H ₅ NS and 36 mL of deionized water were added to a 50 mL Teflon-lined stainless steel autoclave to prepare a solution. ₃ O ₄ /CP” was soaked. After the autoclave was sealed and hermetically sealed, the autoclave was held in an electric oven at 200° C. for 18 hours to carry out hydrothermal synthesis. As a result, Co ₃ O ₄ on CP was changed to CoS ₂ to obtain an electrode. This electrode was described as "CoS ₂ /CP electrode".

(Comparative example 2)
1.0 mmol of Na ₂ MoO _{4.2H 2} O, 4.0 mmol of C ₂ H ₅ NS, and 30 mL of deionized water were added to a 50 mL Teflon-lined stainless steel autoclave and vigorously stirred for 30 minutes. A solution was obtained with stirring. Then, a CP with a size of 2.0 cm×2.0 cm was immersed in this solution. In addition, the CP was ultrasonically cleaned in advance with sulfuric acid, ethanol, and water in this order for 20 minutes each. After the autoclave was sealed and hermetically sealed, the autoclave was held in an electric oven at 200° C. for 18 hours to carry out hydrothermal synthesis. This caused the formation of MoS ₂ on the CP. The obtained electrode catalyst was described as "MoS ₂ /CP electrode". The obtained MoS ₂ /CP electrode was washed several times with water and absolute ethanol, and then dried at 60° C. under vacuum.

(Evaluation results)
FIG. 1 shows SEM images of the electrodes, where a is the “Co ₃ O ₄ /CP” electrode produced in the process of manufacturing the electrode catalyst of Example 1, and b is the CoS ₂ /CP electrode obtained in Comparative Example 1. CP electrode, c is an SEM image of the MoS ₂ /CoS ₂ /CP electrode obtained in Example 1;

From FIG. 1, it can be seen that the MoS ₂ /CoS ₂ /CP electrode obtained in Example 1 has a catalyst in the form of particles having acicular projections on the surface on the electrode substrate (CP). . In Example 1, it is believed that Mo and S ions in the second raw material react with oxides of the transition metal Co to first form Co sulfides (CoS ₂ ). This transition metal M sulfide can form nanowires. _The CoS thus formed is thought to serve as a structural backbone that guides the growth of Mo sulfide nanosheets, and in Example 1, the catalyst formed on CP has a core-shell structure. presumed to be formed. In particular, the core _CoS2 nanowire exhibits a large surface area and good electrical conductivity, and it can be considered that MoS2 is formed _on the surface of this _CoS2 nanowire.

2 shows the X-ray diffraction (XRD) spectrum of the catalyst (MoS ₂ /CoS ₂ ) in the electrode catalyst obtained in Example 1. FIG. FIG. 2 also shows X-ray diffraction spectra of Co ₃ O ₄ , CoS ₂ and MoS ₂ for comparison. In addition, "SmartLab" manufactured by Rigaku was used for the X-ray diffraction measurement.

By comparison with the standard CoS ₂ pattern (JCPDS no. 19-0362) shown in _FIG . It can be seen that four sharp peaks at 2θ=32.3, 36.2, 39.8 and 55.1° corresponding to the plane are clearly observed. In addition, in the electrode catalyst obtained in Example 1, the diffraction peak of MoS ₂ is only slightly recognized due to the fact that the content of MoS ₂ is lower than that of CoS ₂ , or the thickness of the lamination is small. rice field.

FIG. 3 shows linear sweep voltammetry curves using the “MoS ₂ /CoS ₂ /CP electrode” obtained in Example 1 as the anode, (a) 0.5MH ₂ SO ₄ aqueous solution as electrolyte, (b ) is the result when a 1.0M PBS aqueous solution is used as the electrolyte, and (c) is the result when a 1.0M KOH aqueous solution is used as the electrolyte. Also shown in FIG. 3 for comparison are carbon paper with no catalyst formed (denoted as “CP” in FIG. 3 ), the “CoS ₂ /CP electrode” obtained in Comparative Example 1, and the electrode catalyst obtained in Comparative Example 2. The "MoS ₂ /CP electrode", the "Co ₃ O ₄ /CP" electrode, and the conventional carbon / Pt electrode (platinum weight 20% (denoted as "20 wt% Pt / C" in FIG. 3) are used. A linear sweep voltammetry curve was obtained from a hydrogen evolution (HER) test using a platinum plate as a cathode and an Ag/AgCl electrode as a reference electrode. The measurement equipment for the acquisition used a US VersaSTAT4 potentiostat-galvanostat electrochemical workstation with a standard 3-electrode cell.

From FIG. 3, it can be seen that the "MoS ₂ /CoS ₂ /CP electrode" obtained in Example 1 exhibits excellent hydrogen generation efficiency in any of acidic, neutral and alkaline aqueous solutions. This is attributed to the synergistic effect of the co _- doping of Co and O into MoS2, presumably due to the creation of additional new active sites through the formation of structural defects.

FIG. 4 shows linear sweep voltammetry curves using the “MoS ₂ /CoS ₂ /CP electrodes” obtained in Examples 1 to 3 as anodes, (a) 0.5MH ₂ SO ₄ aqueous solution as electrolyte, (b) is the result when using 1.0M KOH as the electrolyte. This linear sweep voltammetry curve was obtained using the same equipment and conditions as in FIG. The ratio of Mo to S (Mo:S) shown in FIG. 4 indicates the molar ratio of Mo to S in the second raw material used for producing the electrode catalyst. Therefore, Mo:S=1:4 represents Example 1, Mo:S=1:2 represents Example 2, and Mo:S=1:6 represents Example 3.

From FIG. 4, it can be seen that the electrode catalysts obtained in Examples 1 to 3 exhibit excellent hydrogen generation efficiency in both acidic and alkaline aqueous solutions, regardless of the ratio of Mo to S.

FIG. 5(a) shows linear sweep voltammetry curves using the “MoS ₂ /CoS ₂ /CP electrode” obtained in Example 1 as an anode, and tests were conducted at pH=0, 7 and 14, respectively. It shows the results when A 0.5 MH ₂ SO ₄ aqueous solution was used at pH=0, a 1.0 MPBS solution was used at pH=7, and a 1.0 M KOH aqueous solution was used at pH=14. FIG. 5(b) shows the Tafel gradient calculated from the linear sweep voltammetry curve shown in FIG. 5(a).

From the results of FIG. 5, when compared at the same current density (10 mA/cm ² ), the “MoS ₂ /CoS ₂ /CP electrode” obtained in Example 1 all have low overvoltages, especially in an acidic aqueous solution. It was found to exhibit the lowest overvoltage (acidic aqueous solution: 69 mV, neutral aqueous solution: 145 mV, alkaline aqueous solution: 81 mV).

FIG. 6 shows a linear sweep voltammetry curve using this electrode as an anode after performing a cyclic voltammetry test (CV test) of the "MoS ₂ /CoS ₂ /CP electrode" obtained in Example 1 for 3000 cycles. , (a) is a 0.5 MH ₂ SO ₄ aqueous solution as an electrolyte, (b) is a 1.0 MPBS aqueous solution as an electrolyte, and (c) is a 1.0 M KOH aqueous solution as an electrolyte. For comparison, FIG. 6 shows a linear sweep voltammetry curve using the “MoS ₂ /CoS ₂ /CP electrode” immediately after obtained in Example 1 as the anode.

6(a), (b) and (c) show the results of constant current electrolysis of water when the electrode obtained in Example 1 was used as the anode, and the current density was 100 mA. /cm ² and 10 mA/cm ² respectively are shown as insets.

Note that in the measurements of FIG. 6, CV measurements were performed using a US VersaSTAT4 potentiostat-galvanostat electrochemical workstation with a standard 3-electrode cell. The conditions of the CV test were as follows.
・For 0.5MH ₂ SO ₄ aqueous solution: 0.05 to -0.3 V (vs.RHE)
・For 1.0 M KOH aqueous solution: 0.6 to -0.6 V (vs. RHE)
・For 1.0 MPBS aqueous solution: 0.05 to -0.3 V (vs. RHE)
・Scan speed: 50mV/s

From FIG. 6, it can be seen that the "MoS ₂ /CoS ₂ /CP electrode" obtained in Example 1 has the same electrode performance as the initial (before CV test) even after 3000 cycles of CV test. , "It was also shown that the MoS ₂ /CoS ₂ /CP electrode has excellent durability.

Claims (3)

comprising a catalyst on an electrode substrate,
The catalyst contains a sulfide of Mo and a sulfide of a transition metal M other than Mo ,
The transition metal M is at least one selected from the group consisting of Co, Fe, Ni, Cu, W and Mn,
The catalyst is an electrode catalyst having a structure in which the Mo sulfide is formed on the surface of the transition metal M sulfide . An electrode base material is immersed in a first raw material containing a compound containing a transition metal M other than Mo and an aqueous solvent for hydrothermal synthesis , and then the electrode base material is taken out and sintered to form an oxide of the transition metal M. A first step of obtaining an electrode substrate on which is formed;
The electrode substrate on which the oxide of the transition metal M is formed is immersed in a second raw material containing a compound containing Mo, a compound containing sulfur, and an aqueous solvent to hydrothermally synthesize Mo. a second step of obtaining an electrode substrate on which a catalyst containing a sulfide and a sulfide of the transition metal M is formed;
with
The method for producing an electrode catalyst , wherein the transition metal M is at least one selected from the group consisting of Co, Fe, Ni, Cu, W and Mn . A method for producing hydrogen, comprising the step of performing electrolytic treatment using the electrode catalyst according to claim 1 or using the electrode catalyst obtained by the production method according to claim 2 .

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