JP7142862B2 - Electrode manufacturing method, electrode and hydrogen manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing an electrode, an electrode, and a method for manufacturing hydrogen.

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

Generally, as an electrode for electrolysis of water, a carbon substrate on which a platinum particle catalyst is fixed is used. 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.

As a method for reducing the amount of platinum used, for example, in Patent Document 1, platinum is used as an anode and a carbon substrate is used as a cathode, and an electrolytic treatment is performed in dilute sulfuric acid to remove a trace amount of platinum ions dissolved in dilute sulfuric acid. Techniques for deposition on carbon substrates have been disclosed. Further, as a platinum substitute electrode for water electrolysis, for example, in Patent Document 2, a base metal oxide layer is formed on the surface of a conductive substrate, and a noble metal such as gold or silver is added on the base metal oxide layer. Supported electrodes are disclosed.

WO2010/029162 WO2013/005252

However, in recent years, electrodes used for electrolysis of water and the like are desired to have further improved performance compared to conventional electrodes, and it is desired to manufacture such electrodes by a simple method. rice field. In particular, there is a strong demand for an electrode that is less prone to an increase in overvoltage and has high activity, and there has also been a demand for construction of a manufacturing technology that can manufacture such an electrode by a simple method.

The present invention has been made in view of the above, and aims to provide a method for producing an electrode, an electrode, and a method for producing hydrogen, which can easily produce an electrode having high activity without causing an increase in overvoltage. aim.

As a result of intensive research to achieve the above object, the present inventors have achieved the above object by, for example, combining the hydrothermal synthesis method and the pulse electrodeposition method to make the electrode material have a specific composition. I found that it can be done, and came to complete the present invention.

That is, the present invention includes, for example, the subject matter described in the following sections.
Item 1
a compound of metal M1 (here, metal M1 is at least one selected from the group consisting of Fe, Ni, Cr, Cu, Zn, Mn and Mo) and an electrode base material in solution A containing a first cobalt compound; A step 1 of taking out and baking the electrode base material after heat-treating it while immersed in the
The electrode base material fired in the step 1 is treated with a second cobalt compound and a compound of metal M2 (here, metal M2 is at least one selected from the group consisting of Fe, Ni, Cr, Cu, Zn, Mn and Mo. a step 2 of performing pulse electrodeposition treatment in a solution B containing a seed);
A method of manufacturing an electrode, comprising:
Item 2
The electrode obtained through the step 2 has a composite oxide and a layered double hydroxide formed on the electrode substrate,
Item 2. The manufacturing method according to Item 1, wherein the composite oxide is an oxide containing Co and the metal M1, and the layered double hydroxide contains cobalt and the metal M2.
Item 3
A composite oxide containing Co and metal M1 (here, metal M1 is at least one selected from the group consisting of Fe, Ni, Cr, Cu, Zn, Mn and Mo) on an electrode substrate, cobalt and An electrode in which a layered double hydroxide containing metal M2 (here, metal M2 is at least one selected from the group consisting of Fe, Ni, Cr, Cu, Zn, Mn and Mo) is formed.
Item 4
Item 3. A method for producing hydrogen, comprising the step of performing electrolytic treatment in an aqueous solution using the electrode obtained by the production method according to Item 1 or 2 or the electrode according to Item 3.
Item 5
Item 5. The manufacturing method according to Item 4, wherein the electrode is used as at least one of an anode and a cathode.

According to the method for producing an electrode of the present invention, an electrode having a high activity in which overvoltage is unlikely to occur can be produced by a simple method.

INDUSTRIAL APPLICABILITY The electrode of the present invention, for example, in the electrolysis of water, does not easily cause an increase in overvoltage and has high activity, so that hydrogen can be efficiently produced.

4 shows an SEM image of the electrode obtained in Example 1. FIG. (a) is the linear sweep voltammetry curve of the electrode obtained in Example 1, (b) is the Tafel slope of the electrode obtained in Example 1, and (c) is the electrode obtained in Example 1 used as the anode. The results of constant-current electrolysis of water when an oxygen evolution test was performed with (a) is the linear sweep voltammetry curve of the electrode obtained in Example 1, (b) is the Tafel slope of the electrode obtained in Example 1, and (c) is the electrode obtained in Example 1 used as the cathode. shows the results of constant-current electrolysis of water when a hydrogen generation test was performed with It shows the results of chronopotentiometry when water was electrolyzed using the electrode obtained in Example 1, (a) using the electrode obtained in Example 1 as an anode, and (b) shows the results when the electrode obtained in Example 1 was used as a cathode. CV curves of each electrode obtained in Examples and Comparative Examples are shown. 1 shows a linear sweep voltammetry curve of the electrode obtained in Example 1. FIG. 1 is a graph showing changes over time in the amount of gas produced when water is electrolyzed using the electrodes obtained in Example 1 as both electrodes.

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".

1. Electrode Production Method and Electrode The electrode production method of the present invention comprises at least Step 1 and Step 2 below.
Step 1: A solution A containing a compound of metal M1 (here, metal M1 is at least one selected from the group consisting of Fe, Ni, Cr, Cu, Zn, Mn and Mo) and a first cobalt compound After the electrode base material is heat-treated while being immersed, the electrode base material is taken out and baked.
Step 2: The electrode base material fired in Step 1 is treated with a second cobalt compound and a compound of metal M2 (where metal M2 is selected from the group consisting of Fe, Ni, Cr, Cu, Zn, Mn and Mo A step of performing pulse electrodeposition treatment in a solution B containing at least one of

Since the production method of the present invention includes Steps 1 and 2, the steps are simple and an electrode can be easily produced. In addition, when the obtained electrode is used for, for example, electrolysis of water, it is difficult for the overvoltage to rise and it can have high activity. Furthermore, the electrode obtained by the manufacturing method of the present invention can be applied to both an anode and a cathode when used as an electrode for water electrolysis, for example.

In step 1, the electrode base material is immersed in a solution A containing the metal M1 compound and the first cobalt compound and subjected to heat treatment, and then the electrode base material is taken out and fired. This step 1 is a step for forming a composite oxide containing metal M1 and cobalt on the electrode substrate.

Metal M1 is at least one selected from the group consisting of Fe, Ni, Cr, Cu, Zn, Mn and Mo. That is, the metal M1 is a specific kind of divalent or trivalent transition metal element. The metal M1 is preferably Fe (iron) or Ni (nickel) from the viewpoint of easily forming a composite oxide with cobalt and easily forming an electrode that easily suppresses overvoltage, and is preferably iron. Especially preferred.

The type of compound of metal M1 used in step 1 is not particularly limited. For example, as the compound of the metal M1, known inorganic acid salts, known organic acid salts, metal M1 hydroxides, metal M1 halides, and the like can be widely used.

Examples of the inorganic acid salt of the metal M1 include one or more selected from the group consisting of nitrates, hydrochlorides, sulfates, carbonates, hydrogen carbonates, phosphates, hydrogen phosphates, etc. of the metal M1. .

Examples of organic acid salts of metal M1 include one or more selected from the group consisting of metal M1 acetates, oxalates, formates, succinates, and the like.

The compound of the metal M1 used in step 1 is preferably a nitrate or hydrochloride of the metal M1 from the viewpoint that it is easily dissolved in water to form an aqueous solution and a composite oxide is easily obtained. The compound of metal M1 may be a hydrate. In particular, the compound of metal M1 is preferably a salt of the same type as the first cobalt compound described later. For example, if the first cobalt compound is a nitrate, the compound for metal M1 is preferably also a nitrate, and if the first cobalt compound is a hydrochloride, the compound for metal M1 is also a hydrochloride. preferable.

The compound of metal M1 used in step 1 may be used singly or in combination of two or more. The compound of metal M1 can be obtained by a known production method, or a commercially available compound of metal M1 can be used.

The type of the first cobalt compound used in step 1 is not particularly limited. For example, as the first cobalt compound, inorganic acid salts of cobalt, known organic acid salts, hydroxides of cobalt, halides of cobalt, and the like can be widely used.

Examples of inorganic acid salts of cobalt include one or more selected from the group consisting of cobalt nitrates, hydrochlorides, sulfates, carbonates, hydrogen carbonates, phosphates, hydrogen phosphates, and the like.

Examples of the organic acid salt of cobalt include one or more selected from the group consisting of cobalt acetate, oxalate, formate, succinate, and the like.

The first cobalt compound used in step 1 is preferably a nitrate or hydrochloride of cobalt from the viewpoint that it is easily dissolved in water to form an aqueous solution and that a composite oxide is easily obtained. The first cobalt compound may be a hydrate. In particular, as described above, the compound of the metal M1 and the first cobalt compound preferably have the same salt type (for example, a combination of nitrates or a combination of hydrochlorides is preferable).

The first cobalt compound used in step 1 may be used singly or in combination of two or more. The first cobalt compound can be obtained by a known production method, or a commercially available first cobalt compound can be used.

Solution A used in step 1 includes a compound of metal M1 and a first cobalt compound, and a solvent.

As the solvent, water or a mixture of water and a lower alcohol (eg, an alcohol having 1 to 4 carbon atoms such as methanol and ethanol) can be used, and water is particularly preferred. 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 solvent may contain pH adjusters, viscosity adjusters, fungicides and the like as long as the effects of the present invention are not impaired.

In solution A, the concentrations of the compound of metal M1 and the first cobalt compound are not particularly limited. For example, in solution A, 1 to 100 mmol of the compound of metal M1 is preferably dissolved per 100 mL of solvent. In this case, a composite oxide having a stable structure can be easily formed.

Further, in the solution A, 1 to 100 mmol of the first cobalt compound is preferably dissolved per 100 mL of the solvent. In this case, a composite oxide having a stable structure can be easily formed.

In the solution A, the elemental ratio between the metal M1 and cobalt (Co) can be adjusted within an arbitrary range. For example, the element ratio M1:Co between the metal M1 and cobalt (Co) contained in the solution A is such that the composite oxide of the metal M1 and cobalt formed in the step 1 is formed in a shape such as a petal shape, resulting in an electrode performance. From the viewpoint that the ratio is likely to be improved, the range of 1:10 to 1:0.1 is preferable. The element ratio M1:Co is more preferably in the range of 1:5 to 1:2, particularly preferably about 1:3.

Solution A may also contain other additives besides the compound of metal M1 and the first cobalt compound. 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.

In solution A, 15 to 30 mmol of urea are preferably dissolved per 100 mL of solvent. In this case, the solution A tends to have a pH in the alkaline region, whereby the composite oxide of the metal M1 and cobalt formed in step 1 is formed in a shape such as a petal shape, and the electrode performance is easily improved.

In solution A, 10 to 20 mmol of NH ₄ F are preferably dissolved per 100 mL of solvent. In this case, a composite oxide can be easily formed. In this case, the solution A tends to have a pH in the alkaline region, whereby the composite oxide of the metal M1 and cobalt formed in step 1 is formed in a shape such as a petal shape, and the electrode performance is easily improved.

Solution A may consist of only the compound of metal M1, the first nickel compound, the pH adjuster and the solvent.

The electrode base material to be immersed in the solution A is not particularly limited, and for example, a wide range of known conductive base materials can be employed. Examples of electrode substrates include nickel, carbon, nickel-phosphorus alloys, nickel-tungsten alloys, stainless steel, titanium, iron, copper, and conductive glass.

The electrode base material to be immersed in the solution A is preferably a nickel base material, a copper base material or other metal base material, and particularly preferably a nickel base material. In this case, it becomes easy to produce a desired electrode, and the obtained electrode tends to have a high activity in the electrolysis of water, etc., without causing an increase in overvoltage. More specifically, nickel foam can be exemplified as the electrode base material.

The electrode base material can be obtained by a known method, or a commercially available electrode base material can be used.

The shape of the electrode substrate is not particularly limited, and can be appropriately selected according to the purpose of use and required performance. Examples thereof include sheet-like, plate-like, rod-like, and mesh-like electrode base materials.

Before being immersed in the solution A, the electrode substrate can be washed in advance. 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 acid such as hydrochloric acid. Ultrasonic treatment can be combined with acid cleaning.

The method of immersing the electrode base material in the solution A is not particularly limited, and usually the whole electrode base material can be immersed in the solution A. 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 may be coated with, for example, fluororesin (eg, Teflon (registered trademark)).

In step 1, heat treatment is performed while the electrode base material is immersed in the solution A. As the heat treatment in step 1, a hydrothermal synthesis method can be mentioned. The hydrothermal synthesis method referred to here is a method in which the container is sealed while the electrode base material is immersed in the solution A, and the inside of the container is heated. By this hydrothermal synthesis, a composite hydroxide containing metal M1 and cobalt can be formed 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 a composite oxide containing metal M1 and cobalt is formed, and can be, for example, 110 to 150.degree. The time for which the container is held at this temperature is also not particularly limited, and can be, for example, 8 to 15 hours. The pressure inside the vessel in the hydrothermal synthesis can also be set appropriately.

In hydrothermal synthesis, the solution A 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, the hydroxide is more easily formed in the hydrothermal synthesis, and the composite oxide finally formed in step 1 is formed in a shape such as a petal shape, and the electrode performance is easily improved. .

In step 1, after the heat treatment (hydrothermal synthesis), the electrode base material is taken out from the container and baked.

In step 1, 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 step 1, the rate of temperature increase during firing is not particularly limited, either, 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 substrate changes to an oxide, and an electrode substrate modified with a composite oxide (CoM1O) containing metal M1 and cobalt can be obtained.

In step 2, the electrode substrate fired in step 1, that is, the electrode substrate modified with the composite oxide, is subjected to pulse electrodeposition treatment in solution B containing a second cobalt compound and a compound of metal M2. It is a process to do. This step 2 is a step for forming a layered double hydroxide of cobalt and metal M2.

The type of the second cobalt compound used in step 2 is not particularly limited. For example, as the second cobalt compound, a wide range of known inorganic acid salts, known organic acid salts, cobalt hydroxides, cobalt halides, and the like can be used.

Examples of inorganic acid salts of cobalt include one or more selected from the group consisting of cobalt nitrates, hydrochlorides, sulfates, carbonates, hydrogen carbonates, phosphates, hydrogen phosphates, and the like.

Examples of the organic acid salt of cobalt include one or more selected from the group consisting of cobalt acetate, oxalate, formate, succinate, and the like.

The second cobalt compound used in step 2 may be a hydrate.

The second cobalt compound used in step 2 may be used singly or in combination of two or more. The second cobalt compound can be obtained by a known production method, or a commercially available second cobalt compound can be used.

In the production method of the present invention, the first cobalt compound and the second cobalt compound used in step 1 may be the same or different.

Metal M2 is at least one selected from the group consisting of Fe, Ni, Cr, Cu, Zn, Mn and Mo. That is, the metal M2 is a specific kind of divalent or trivalent transition metal element. The metal M2 is preferably Ni (nickel) or Fe (iron) from the viewpoint of easily forming a layered double hydroxide with cobalt and easily forming an electrode that easily suppresses overvoltage, and is nickel. is particularly preferred.

The type of compound of metal M2 used in step 2 is not particularly limited. For example, as compounds of the metal M2, known inorganic acid salts, known organic acid salts, hydroxides of the metal M2, halides of the metal M2, and the like can be widely used.

Examples of the inorganic acid salt of the metal M2 include one or more selected from the group consisting of nitrates, hydrochlorides, sulfates, carbonates, hydrogencarbonates, phosphates and hydrogenphosphates of the metal M2. .

Examples of organic acid salts of metal M2 include one or more selected from the group consisting of metal M2 acetates, oxalates, formates, succinates, and the like.

The compound of metal M2 may be a hydrate.

The compound of metal M2 used in step 2 may be used singly or in combination of two or more. The compound of metal M2 can be obtained by a known production method, or a commercially available compound of metal M2 can be used.

Solution B used in step 2 includes a second cobalt compound and a compound of metal M2, and a solvent.

As the solvent, the same types as those used in solution A can be used, and water is particularly preferred. 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 solvent may contain pH adjusters, viscosity adjusters, fungicides and the like as long as the effects of the present invention are not impaired.

In the solution B, the concentrations of the second cobalt compound and the metal M2 compound are not particularly limited. For example, in solution B, the second cobalt compound is preferably dissolved in an amount of 0.1 to 100 mmol, more preferably 3 to 10 mmol, per 100 mL of the solvent. In this case, electrodeposition can be easily performed by pulse electrodeposition.

In the solution B, the compound of metal M2 is preferably dissolved in an amount of 0.1 to 100 mmol, more preferably 1 to 8 mmol per 100 mL of the solvent. In this case, electrodeposition can be easily performed by pulse electrodeposition.

In solution B, the elemental ratio of cobalt (Co) and metal M2 can be adjusted within an arbitrary range. For example, the element ratio Co:M2 between cobalt (Co) and metal M2 in solution B is preferably in the range of 1:10 to 1:0.1 from the viewpoint of easily improving the electrode performance. :5 to 1:1.5 is more preferable, and about 3:2 is particularly preferable.

Solution B may also contain other additives besides the second cobalt compound and the compound of metal M2. For example, the solution B may contain known additives that are used in conjunction with the electrodeposition treatment.

Solution B may consist of only the second cobalt compound, the compound of metal M2, and the solvent.

In step 2, the electrode base material obtained in step 1 is immersed in solution B and subjected to pulse electrodeposition. A layered double hydroxide is formed on the electrode substrate by this pulse electrodeposition treatment.

The pulse electrodeposition process uses the electrode substrate obtained by step 1 as the anode. On the other hand, as a cathode for pulse electrodeposition treatment, for example, a known insoluble electrode can be used. As the insoluble electrode, for example, an electrode made of carbon, platinum group metal, gold, or the like can be used. Platinum group metals include platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), osmium (Os), and iridium (Ir), with platinum (Pt) being preferred. The platinum group metal may be contained in the form of an alloy, metal oxide, or the like.

The shape of the cathode is not particularly limited, and can be appropriately selected depending on the purpose of use and required performance. Examples of shapes include metal wire, sheet, plate, rod, and mesh. Specifically, a spiral platinum wire, a platinum plate, and the like can be exemplified.

In the pulse electrodeposition treatment, the pH of the solution B is not particularly limited as long as the layered double hydroxide of cobalt and metal M2 can be deposited, for example less than 6, preferably about 0 to 4, more preferably is about 0 to 2.

In addition to the anode, cathode and solution B (electrolyte), a reference electrode, an electrolytic device, a power supply, control software, etc. can be used when performing the pulse electrodeposition treatment. Known ones can be used as these, for example, depending on the purpose. For example, as a reference electrode, a silver/silver chloride electrode (Ag/AgCl electrode), a mercury/mercury chloride electrode (Hg/ _HgCl2 electrode), a standard hydrogen electrode, or the like can be used.

In the present invention, the pulse electrodeposition treatment is an electrodeposition treatment method capable of controlling the electrodeposition speed of metal ions. and a low-end current are applied in a constant cycle (PGM), and a unipolar pulse voltage method (UPED) in which a high-end voltage and an open-circuit state are repeatedly applied at a constant cycle.

When a unipolar pulsed voltage method (UPED) is employed as the pulse electrodeposition treatment method, the conditions for the unipolar pulsed voltage method are those that allow formation of a layered double hydroxide on the conductive substrate. There are no particular restrictions, and for example, voltage: -2 to -0.6 V, open circuit state, pulse time: 0.5 to 3 seconds, number of pulse applications: 100 to 1000 times. In this case, the deposition amount, thickness and density of the layered double hydroxide are appropriate, and the performance of the electrode is likely to be improved.

The temperature of solution B during pulse electrodeposition is not particularly limited, and can be, for example, about 0 to 50.degree. C., preferably 20 to 30.degree.

The electrode obtained through step 2 above is formed by forming a composite oxide and a layered double hydroxide on an electrode substrate. A composite oxide is an oxide containing cobalt (Co) and a metal M1 (eg, Fe), and a layered double hydroxide contains cobalt and a metal M2 (eg, Ni). The metals contained in the composite oxide may be only cobalt (Co) and metal M1, or may contain, for example, other metals that are unavoidably contained. The metals contained in the layered double hydroxide may be only cobalt (Co) and metal M2, or may contain, for example, other metals that are unavoidably contained.

The composite oxide is formed, for example, in a petal shape on the electrode substrate and has strong adhesion to the electrode substrate. Furthermore, the layered double hydroxide formed in step 2 is formed so as to cover the surface of the composite oxide, and can have the effect of greatly increasing the electrical conductivity and active sites of the electrode.

Since the electrode obtained by the production method of the present invention has a composite oxide containing metal M1 and cobalt and a layered double hydroxide of cobalt and metal M2, for example, when used for water electrolysis etc. , the overvoltage is less likely to rise and can have high activity. Furthermore, the electrode obtained by the manufacturing method of the present invention can be applied to both an anode and a cathode when used as an electrode for water electrolysis, for example. Therefore, the electrode obtained by the production method of the present invention can be widely applied to various uses, and can be particularly suitably used as an electrode for electrolysis of water and an electrode for hydrogen production.

In the electrode, the ratio of the composite oxide containing cobalt and metal M1 and the layered double hydroxide containing cobalt and metal M2 is not particularly limited, and can be adjusted to any ratio.

The electrode obtained by the production method of the present invention has, for example, a structure in which a large number of petal-like particles are laminated on an electrode substrate. The particle size is, for example, 1-20 μm. The particle size referred to here is the arithmetic mean value obtained by measuring the equivalent circle diameters of 50 particles selected at random by direct observation of electrodes with a scanning electron microscope.

The electrode of the present invention can ensure a good interfacial connection between the three layers of the electrode (electrode substrate, composite oxide and layered composite hydroxide), which is beneficial for charge transition between each layer. In addition, by including the metal M1, the fine structure of the cobalt oxide crystal, which is the main component, is easily controlled, and the catalytic activity of the electrode is easily improved. Also, when the composite oxide is petal-shaped, it has a large surface area and can provide a large number of active sites.

The layered double hydroxide on the surface of the composite oxide can greatly increase the electrical conductivity and active sites of the electrode.

The electrodes of the present invention can be binder-free and tend to avoid increasing overall electrode resistance, blocking active sites and inhibiting diffusion.

2. Method for Producing Hydrogen The method for producing hydrogen of the present invention includes a step of performing electrolytic treatment in an aqueous solution using the electrode obtained by the above production method.

The method for producing hydrogen of the present invention can include a step of performing electrolytic treatment in an aqueous solution using the electrode obtained by the method for producing an electrode described above, for example, as an anode. Alternatively, the method for producing hydrogen of the present invention can include a step of performing electrolytic treatment in an aqueous solution using the electrode obtained by the method for producing an electrode described above, for example, as a cathode. Furthermore, the method for producing hydrogen of the present invention can include a step of performing electrolytic treatment in an aqueous solution using the electrode obtained by the method for producing the electrode described above, for example, as both the anode and the cathode. That is, in the method for producing hydrogen, the electrode obtained by the method for producing the electrode described above can be used as at least one of the anode and the cathode.

For example, when the electrode obtained by the electrode manufacturing method described above is used only as an anode, the electrode generally used as a cathode in the electrolysis of water can be used as the cathode. For example, electrodes made of noble metals such as carbon, platinum, and gold can be used as cathodes. For example, when the electrode obtained by the above electrode manufacturing method is used only as a cathode, an electrode generally used as an anode in the electrolysis of water can be used as the anode.

In the method for producing hydrogen, an aqueous solution containing components generally used in electrolysis of water can be used as the aqueous solution. 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.

To give a specific example of the method for producing hydrogen, an electrode obtained by the production method of the present invention is used as an anode, a platinum plate is used as a cathode, and a KOH aqueous solution is used as an electrolyte, and a voltage is applied to the anode. This allows hydrogen to be produced at the cathode. Also, by increasing the voltage applied to the anode, the hydrogen production rate can be increased. In addition, oxygen is produced at the anode.

As another specific example of the hydrogen production method, the electrode obtained by the production method of the present invention is used as a cathode, a platinum plate is used as an anode, and a KOH aqueous solution is used as an electrolyte, and a voltage is applied to the anode. This allows hydrogen to be produced at the cathode. Also, by increasing the voltage applied to the anode, the hydrogen production rate can be increased. In addition, oxygen is produced at the anode.

As another specific example of the hydrogen production method, the electrodes obtained by the production method of the present invention are used as a cathode and an anode, and a KOH aqueous solution is used as an electrolyte, and a voltage is applied to the anode. This allows hydrogen to be produced at the cathode. Also, by increasing the voltage applied to the anode, the hydrogen production rate can be increased. In addition, oxygen is produced at the anode.

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 obtained by the method for producing an electrode is used, the overvoltage is unlikely to increase and the electrode has high activity, so that hydrogen can be produced efficiently.

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 commercially available nickel foam (hereinafter abbreviated as “NF”) having a size of 1 cm × 1 cm and a thickness of 2 mm is prepared, and this NF is immersed in 2 M hydrochloric acid and ultrasonically cleaned, and then further The NF was washed sequentially with water and ethanol.

Then 0.375 mmol Fe( _NO3 ) _3.9H2O , 1.125 mmol Co(NO) _3.6H2O , 6.25 mmol CO _{(NH2)2 and 5 mmol NH4F} was placed in an autoclave, and the NF washed as described above was immersed in the solution A. Thereafter, the autoclave was sealed, heated to 120° C. and held for 12 hours to obtain surface-modified NF (hereinafter abbreviated as “surface-modified NF”).

The surface-modified NF obtained as described above was taken out from the autoclave, and the surface-modified NF was calcined by holding it in the air at 350° C. for 2 hours (Step 1).

Next, the baked surface-modified NF is immersed in "solution B" prepared by dissolving _{6 mmol of CoCl 2.6H 2 O and 4 mmol of NiCl 2.6H 2 O in 100} mL of water, A pulse electrodeposition treatment was performed (step 2). In this pulse electrodeposition treatment, a platinum plate is used as a counter electrode and Ag/AgCl is used as a reference electrode, the pulse potential is -1.2 V (reference electrode standard), the on and off times are both 1 second, and the number of pulse applications is 200. times. By this pulse electrodeposition treatment, a layered double hydroxide of Co and Ni is electrodeposited, and CoFeO and a layered double hydroxide of Co and Ni are formed on the electrode substrate, which is used for electrolysis of water. I got the electrode.

(Comparative example 1)
The surface-modified NF sintered in step 1 was obtained as an electrode for water electrolysis without performing the pulse electrodeposition treatment in step 2.

(Comparative example 2)
A commercially available NF having a size of 1 cm×1 cm and a thickness of 2 mm was prepared, and the NF was immersed in 2 M hydrochloric acid and ultrasonically cleaned, and then washed with water and ethanol in this order.

The NFs washed as described above were then immersed in "Solution B" prepared by dissolving 6 mmol CoCl ₂ .6H ₂ O and 4 mmol NiCl ₂ .6H ₂ O and 4 mmol NiCl 2 .6H 2 O in 100 mL water, A pulse electrodeposition treatment was performed (that is, it was assumed not to have undergone step 1). In this pulse electrodeposition treatment, a platinum plate is used as a counter electrode and Ag/AgCl is used as a reference electrode, the pulse potential is -1.2 V (reference electrode standard), the on and off times are both 1 second, and the number of pulse applications is 200. times. By this pulse electrodeposition treatment, layered double hydroxides of Co and Ni were electrodeposited, and an electrode for water electrolysis was obtained in which the layered double hydroxides of Co and Ni were formed on the electrode substrate.

(Evaluation results)
1 shows an SEM image of the electrode obtained in Example 1. FIG. Specifically, a is NF before being subjected to step 1, b, c and d are NF after baking treatment obtained in step 1, e, f, g and h are by pulse electrodeposition treatment in step 2 It is an SEM image of the obtained electrode. b is a partially enlarged photograph of c, d is a partially enlarged photograph of c, g is a partially enlarged photograph of f, and h is a partially enlarged photograph of g.

From the results of FIG. 1, it was confirmed that the electrode obtained in Example 1 had a structure in which a large number of porous petal-like particles were laminated on the electrode substrate.

Further, as a result of elemental mapping of the electrode obtained in Example 1, it was found that cobalt was 60% by weight, nickel was 16% by weight, and iron was 24% by weight. From this result, it is considered that the obtained electrode has a composite oxide (CoFeO) containing iron and cobalt and a layered double hydroxide of cobalt and nickel. Elemental mapping of SEM images was measured using a Horiba Scientific "Scanning Electron Microscope (SEM, Hitachi SU8010) system with Energy Dispersive Spectrometer (EDS)".

2(a) shows the linear sweep voltammetry curve of the electrode obtained in Example 1. FIG. The linear sweep voltammetry curve in Fig. 2(a) was obtained using the electrode obtained in Example 1 as the anode, the platinum plate as the cathode, the Ag/AgCl electrode as the reference electrode, and the 1 M KOH aqueous solution as the electrolyte (OER ) obtained by testing. For comparison, FIG. 2(a) also shows test results when the electrode obtained in Example 1 was replaced with the electrode obtained in Comparative Examples 1 and 2 and untreated NF, respectively. The measurement equipment for obtaining linear sweep voltammetry curves was performed using a US VersaSTAT4 potentiostat-galvanostat electrochemical workstation with a standard 3-electrode cell.

FIG. 2(b) shows the Tafel slope calculated from the linear sweep voltammetry curve shown in FIG. 2(a). FIG. ² (c) shows the results of constant-current electrolysis of water when the oxygen evolution test was performed using the electrode obtained in Example 1 as an anode. It is a potential-time graph in each cm ² .

Table 1 shows the results of the OER overvoltage of each electrode (current densities of 10 mA/cm ² and 100 mA/cm ² ) obtained from FIG. 2(a).

3(a) shows the linear sweep voltammetry curve of the electrode obtained in Example 1. FIG. The linear sweep voltammetry curve in Fig. 3(a) was obtained using a platinum plate as the anode, the electrode obtained in Example 1 as the cathode, an Ag/AgCl electrode as the reference electrode, and a 1 M KOH aqueous solution as the electrolyte (HER ) obtained by testing. For comparison, FIG. 3A also shows test results when the electrode obtained in Example 1 was replaced with the electrode obtained in Comparative Examples 1 and 2 and untreated NF, respectively. The measurement equipment for obtaining linear sweep voltammetry curves was performed using a US VersaSTAT4 potentiostat-galvanostat electrochemical workstation with a standard 3-electrode cell.

FIG. 3(b) shows the Tafel slope calculated from the linear sweep voltammetry curve shown in FIG. 3(a). FIG. 3(c) shows the results of constant current electrolysis of water when the hydrogen generation test was performed using the electrode obtained in Example 1 as the cathode, and the current densities were 100 mA/cm ² and 10 mA/cm 2 . It is a potential-time graph in each cm ² .

Table 2 shows the results of HER overvoltage of each electrode (current densities of 10 mA/cm ² and 100 mA/cm ² ) obtained from FIG. 3(a).

From the results in Tables 1 and 2, it was found that the overvoltage was suppressed when the electrode obtained in Example 1 was used to electrolyze water. , the overvoltage is suppressed. In particular, it was found that the electrode obtained in Example 1 had a lower value than most of the known Ni-based electrode catalysts.

FIG. 4 shows the results of chronopotentiometry when water was electrolyzed using the electrode obtained in Example 1. (a) shows the electrode obtained in Example 1 as an anode. , (b) are the results when the electrode obtained in Example 1 was used as a cathode (measurement conditions were the same as those of the oxygen evolution test and the hydrogen evolution test, respectively). The measurement conditions were the same as those of the test for obtaining the linear sweep voltammetry curve, and the measurement was performed using a US VersaSTAT4 potentiostat galvanostat electrochemical workstation with a two-electrode cell.

In FIG. 4, the potential at a current density of 10 mA/cm ² shows a constant value of 1.45 V for 500 seconds, and the same tendency is shown even if the current density is increased stepwise to 220 mA/cm ² thereafter. rice field. Therefore, the resulting electrode was found to have good mass transport properties and mechanical robustness for the oxygen evolution reaction. FIG. 4(b) shows multi-step chronopotentiometric curves for electrodes from 10 mA/cm ² to 300 mA/cm ² , again showing good voltage response even with stepwise increasing current density. I understand. Therefore, it was found that the obtained electrode has excellent mass transport properties and mechanical robustness for the hydrogen evolution test.

FIG. 5 shows the CV curve of each electrode, (a) is NF, (b) is the electrode of Comparative Example 1, (c) is the electrode of Comparative Example 2, and (d) is the electrode of Example 1. CV curve for the case. CV measurements were performed using a US VersaSTAT4 potentiostat-galvanostat electrochemical workstation with a standard 3-electrode cell. In CV measurements, the electrochemically active surface area of the resulting electrodes was evaluated by recording the electrochemical double layer capacitance with respect to the electrochemically active surface area at different scanning speeds.

In FIG. 5, the electrode of Example 1 has the highest electrochemical double layer capacitance of 6.31 mF/cm ² , the electrode of Comparative Example 1 (2.62 mF/cm ² ) and the electrode of Comparative Example 2 (1 0.12 mF/cm ² ), improved by a factor of 2.4 and nearly 5.6. This result demonstrated that the electrode of Example 1 had an improved electrochemically active surface area. It is believed that the deposition of the "layered double hydroxide of cobalt and nickel" on the surface of the petal-shaped composite oxide achieves a large exposure of the active sites. Generally, a large electrochemically active surface area is effective for adsorption of water molecules. It is believed that the electrode of Example 1 can provide abundant active sites for catalytic reactions that more reliably enhance catalytic activity, and also improve contact with the electrolyte.

6 shows a linear sweep voltammetry curve of the electrode obtained in Example 1. FIG. The linear sweep voltammetry curve in FIG. 6 was obtained by electrolyzing water using the electrodes obtained in Example 1 for both the anode and cathode using a 1 M KOH aqueous solution as the electrolyte. From FIG. 6, the voltage was 1.62 V when the current density was 10 mA/cm ² and the voltage was 1.76 V when the current density was 100 mA/cm ² . This result indicates that the electrode obtained in Example 1 can be used as both electrodes in the electrolysis of water and has excellent performance in that case.

FIG. 7 shows changes over time in the amount of gas produced when water is electrolyzed using the electrodes obtained in Example 1 as both electrodes. Plots in FIG. 7 indicate measured values, and solid lines indicate calculated values.

The electrodes obtained in Example 1 were set at both electrodes of an H-shaped cell, and electrolysis of a 1 M KOH aqueous solution was performed at a current density of 10 mA/cm ² , and oxygen and hydrogen gases generated at both electrodes were quantified. The gas yield to the amount of electricity reached 99%.

From the above, it can be said that the electrode obtained in Example 1 is a catalyst capable of efficiently producing hydrogen because the electrode obtained in Example 1 is less likely to cause an increase in overvoltage and has high activity.

Claims (4)

a compound of metal M1 (here, metal M1 is at least one selected from the group consisting of Fe, Ni, Cr, Cu, Zn, Mn and Mo) and an electrode base material in solution A containing a first cobalt compound; Step 1 of obtaining a composite oxide containing Co and the metal M1 on the electrode substrate by taking out and baking the electrode substrate after hydrothermal synthesis in a state of being immersed;
The electrode base material fired in the step 1 is treated with a second cobalt compound and a compound of metal M2 (here, metal M2 is at least one selected from the group consisting of Fe, Ni, Cr, Cu, Zn, Mn and Mo. A layered double hydroxide containing cobalt and the metal M2 is formed by performing a pulse electrodeposition treatment in a solution B containing the metal M2, provided that the metal M2 is a metal different from the metal M1. Step 2 of obtaining
and
The hydrothermal synthesis is performed at 110 to 150 ° C.,
The method for producing an electrode , wherein the layered double hydroxide is formed so as to cover the surface of the composite oxide . A composite oxide containing Co and metal M1 (here, metal M1 is at least one selected from the group consisting of Fe, Ni, Cr, Cu, Zn, Mn and Mo) on an electrode substrate, cobalt and Metal M2 (Here, the metal M2 is at least one selected from the group consisting of Fe, Ni, Cr, Cu, Zn, Mn and Mo. However, the metal M2 is a metal different from the metal M1 ) is formed , and a layered double hydroxide containing
The electrode, wherein the layered double hydroxide is formed to cover the surface of the composite oxide . A method for producing hydrogen, comprising the step of performing electrolytic treatment in an aqueous solution using the electrode according to claim 2 . 4. The manufacturing method according to claim 3 , wherein the electrode is used as at least one of an anode and a cathode.

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