JP2020012171A - Manufacturing method of electrode, electrode, and manufacturing method of hydrogen - Google Patents

Abstract

To provide a manufacturing method of an electrode capable of manufacturing the electrode hardly generating increase of overvoltage by a simple method, the electrode, and a manufacturing method of hydrogen.SOLUTION: The manufacturing method of an electrode has a process 1 for heat treating a solution A containing a compound of a first metal M1, where the metal M1 is at least one kind selected from a group consisting of Ni, Co, Cu, Cr, Zn, Mn and Mo, at a state that an electrode substrate is immersed in the solution A, then taking the electrode substrate and burning the same, and a process 2 for conducting a pulse electrodeposition treatment in a solution B containing a compound of a second metal M1, where the metal M1 is same metal as the metal M1 in the compound of the first metal M1, and a compound of a metal M2, where M2 is at least one kind selected from a group consisting of Fe, Co, Cu, Cr, Zn, Mn and Mo.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing an electrode, an electrode, and a method for producing hydrogen.

Hydrogen is expected to be a clean energy source that replaces fossil fuels because it emits zero CO ₂ during combustion. In particular, solar, wind, and no CO ₂ production process of hydrogen because it does not discharge by electrolysis of water to power a renewable energy hydro etc., with great expectations were received as a clean process for producing hydrogen I have.

  Generally, an electrode in which a platinum particle catalyst is fixed on a carbon substrate is used as an electrode for electrolysis of water. However, since platinum is expensive and has a limited amount of resources, there is a need for a technique for reducing the amount of platinum used and for the development of a platinum-substituted catalyst and / or an electrode.

  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 as a cathode, and an electrolytic treatment is performed in dilute sulfuric acid to remove platinum ions dissolved in a small amount in dilute sulfuric acid. A technique for depositing on a carbon substrate is disclosed. As a platinum substitute electrode for electrolysis of water, 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 formed on the base metal oxide layer. A supported electrode is disclosed.

International Publication No. WO 2010/029162 WO 2013/005252

  However, in recent years, it is desired that electrodes used for electrolysis of water and the like have further improved performance than conventional electrodes, and that such electrodes are desired to be manufactured by a simple method. Was. In particular, there is a strong demand for an electrode that does not easily cause an increase in overvoltage, and it has been desired to establish a manufacturing technique capable of manufacturing such an electrode by a simple method.

  The present invention has been made in view of the above, and an object of the present invention is to provide a method for manufacturing an electrode, an electrode, and a method for manufacturing hydrogen, which can easily manufacture an electrode in which overvoltage is unlikely to increase.

  The present inventors have conducted intensive studies to achieve the above object, and found that the above object can be achieved by setting the electrode material to a specific composition, for example, by hydrothermal synthesis of a specific compound. Thus, the present invention has been completed.

That is, the present invention includes, for example, the subjects described in the following sections.
Item 1
The electrode substrate was immersed in a solution A containing a compound of the first metal M1 (where the metal M1 is at least one selected from the group consisting of Ni, Co, Cu, Cr, Zn, Mn and Mo). After heat treatment in a state, a step 1 of taking out and firing the electrode base material;
The electrode base material fired in the step 1 is combined with a compound of the second metal M1 (the metal M1 is the same metal as the metal M1 in the compound of the first metal M1) and a compound of the metal M2 (here, A metal M2 is at least one selected from the group consisting of Fe, Co, Cu, Cr, Zn, Mn and Mo), and performing a pulse electrodeposition treatment in a solution B containing:
A method for producing an electrode, comprising:
Item 2
The electrode substrate was immersed in a solution A containing a compound of the first metal M1 (where the metal M1 is at least one selected from the group consisting of Ni, Co, Cu, Cr, Zn, Mn and Mo). After heat treatment in a state, a step 1 of taking out and firing the electrode base material;
The electrode base material fired in the step 1 is combined with a compound of the second metal M1 (the metal M1 is the same metal as the metal M1 in the compound of the first metal M1) and a compound of the metal M2 (here, , A metal M2 is at least one selected from the group consisting of Fe, Co, Cu, Cr, Zn, Mn and Mo), and a heat treatment in a state of being immersed in a solution C containing
A method for producing an electrode, comprising:
Item 3
Item 3. The method for producing an electrode according to Item 2, further comprising a step 4 of immersing the electrode obtained in the step 3 in an organic solvent and irradiating the ultrasonic wave.
Item 4
The electrode has an oxide of metal M1 and a layered double hydroxide formed on an electrode substrate,
The method according to any one of Items 1 to 3, wherein the layered double hydroxide contains a metal M1 and a metal M2.
Item 5
An electrode in which an oxide of metal M1 and a layered double hydroxide containing metal M1 and metal M2 are formed on an electrode substrate.
Item 6
Item 5. A method for producing hydrogen, comprising a step of performing an electrolytic treatment in an aqueous solution using the electrode obtained by the method according to any one of Items 1 to 4 or the electrode according to Item 5.

  ADVANTAGE OF THE INVENTION According to the manufacturing method of the electrode of this invention, the electrode with which overvoltage does not increase easily can be manufactured by a simple method.

  The electrode of the present invention, for example, hardly causes an increase in overvoltage in the electrolysis of water, and can efficiently produce hydrogen.

4 shows a linear sweep voltammetry curve of the electrodes obtained in each of the examples and comparative examples. The XRD spectrum of the electrode obtained by each Example and the comparative example is shown. 3 shows an SEM image of the electrode obtained in Example 1. It is a result of the element mapping of the electrode obtained in Example 1, (a) is the element mapping of the SEM image of the electrode surface, (b) is the element mapping spectrum, (c) is the state of distribution of Ni, (d) Shows the distribution of Fe. 4 shows a linear sweep voltammetry curve of the electrodes obtained in Examples 1 and 5 to 8. (A) to (e) show SEM images of the electrodes obtained in Example 5, Example 6, Example 1, Example 7, and Example 8, respectively. 4 shows a linear sweep voltammetry curve of the electrodes obtained in each of the examples and comparative examples. 2 shows the results of chronopotentiometry when electrolysis of water was performed using the electrode obtained in Example 1. The result of having performed the linear sweep voltammetry test using the electrode after continuing a chronopotentiometry test for 30 hours is shown. (A) and (b) are SEM images of the electrode surface before the chronopotentiometry test, and (c) and (d) are chronopotentiometry tests (current density of 50 mA / cm ² ) for 30 hours. 5 shows an SEM image of the electrode surface after continuation. 9 shows a linear sweep voltammetry curve of the electrodes obtained in Examples 13 to 17 and Comparative Example 8. The Tafel slope calculated from the linear sweep voltammetry curve is shown. 13 shows XRD spectra of the electrodes obtained in Example 1, Example 14, and Comparative Example 8.

  Hereinafter, embodiments of the present invention will be described in detail. In this specification, the expressions “contain” and “contain” include the concepts of “contain”, “contain”, “consisting essentially of” and “consisting of only”.

1. Electrode manufacturing method and electrode The electrode manufacturing method of the present invention can include, for example, a first manufacturing method and a second manufacturing method. In this specification, the expression “the manufacturing method of the present invention” means a manufacturing method including both the first manufacturing method and the second manufacturing method.

The first manufacturing method includes at least the following steps 1 and 2.
Step 1: an electrode base material in a solution A containing a compound of a first metal M1 (where the metal M1 is at least one selected from the group consisting of Ni, Co, Cu, Cr, Zn, Mn and Mo) A heat treatment in a state of immersion, and then taking out and firing the electrode substrate.
Step 2: The electrode substrate fired in the step 1 is mixed with a compound of the second metal M1 (the metal M1 is the same metal as the metal M1 in the compound of the first metal M1) and a compound of the metal M2. (Where the metal M2 is at least one selected from the group consisting of Fe, Co, Cu, Cr, Zn, Mn, and Mo) in a step of performing a pulse electrodeposition treatment in a solution B containing

The second manufacturing method includes at least the following steps 1 and 3.
Step 1: an electrode base material in a solution A containing a compound of a first metal M1 (where the metal M1 is at least one selected from the group consisting of Ni, Co, Cu, Cr, Zn, Mn and Mo) A heat treatment in a state of immersion, and then taking out and firing the electrode substrate.
Step 3: The electrode base material fired in the step 1 is mixed with a compound of the second metal M1 (the metal M1 is the same metal as the metal M1 in the compound of the first metal M1) and a compound of the metal M2. (Where the metal M2 is at least one selected from the group consisting of Fe, Co, Cu, Cr, Zn, Mn and Mo) in a state of being immersed in a solution C containing a heat treatment.

  Step 1 in the first manufacturing method is the same as step 1 in the second manufacturing method.

  The production method of the present invention has simple steps and can easily produce an electrode. In addition, when the obtained electrode is used for, for example, electrolysis of water or the like, an increase in overvoltage hardly occurs, and the electrode can have excellent durability.

(Step 1)
In the first manufacturing method and the second manufacturing method, the solution A used in the step 1 includes a compound of the first metal M1 and a solvent.

  The metal M1 is at least one selected from the group consisting of Ni, Co, Cu, Cr, Zn, Mn, and Mo. That is, the metal M1 is a specific type of divalent or trivalent transition metal element. The metal M1 is preferably Ni (nickel) or Co (cobalt), and particularly preferably nickel, from the viewpoint of easily forming an electrode that easily suppresses overvoltage.

  In the production method of the present invention, the type of the compound of the first metal M1 is not particularly limited. For example, as the compound of the first metal M1, a known inorganic acid salt, a known organic acid salt, a hydroxide of the metal M1, a halide of the metal M1, and the like can be widely used.

  Examples of the inorganic acid salt of the metal M1 include at least one selected from the group consisting of nitrate, hydrochloride, sulfate, carbonate, hydrogencarbonate, phosphate, and hydrogenphosphate of the metal M1. .

  Examples of the organic acid salt of the metal M1 include one or more selected from the group consisting of acetate, oxalate, formate, succinate, and the like of the metal M1.

  In the production method of the present invention, the compound of the first metal M1 may be a nitrate of the metal M1 from the viewpoint that it is easily dissolved in water to form an aqueous solution and a nickel oxide is easily obtained in the step 1. Preferably it is the hydrochloride. The compound of the first metal M1 may be a hydrate.

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

  In the solution A, as the solvent, water or a mixture of water and a lower alcohol (for example, an alcohol having 1 to 4 carbon atoms such as methanol and ethanol) can be used, and water is particularly preferable. As the water, various types of water such as distilled water, tap water, industrial water, ion-exchanged water, deionized water, pure water, and electrolytic water can be used. The solvent may contain a pH adjuster, a viscosity adjuster, a fungicide and the like as long as the effects of the present invention are not impaired.

  In the first manufacturing method and the second manufacturing method, in step 1, a heat treatment is performed in a state where the electrode base material is immersed in the solution A containing the compound of the first metal M1, and then the electrode base material is taken out. Perform baking. In this step 1, an oxide of the metal M1 is formed on the electrode substrate.

  In the solution A, the concentration of the compound of the first metal M1 is not particularly limited. For example, in solution A, it is preferable that 8 to 15 mmol of the compound of the first metal M1 is dissolved per 100 mL of the solvent. In this case, it is easy to uniformly form the oxide of the metal M1 having a stable structure on the electrode substrate.

The solution A may also contain other additives in addition to the compound of the first metal M1. Other additives include, for example, pH adjusters. Examples of the pH adjuster include urea (CO (NH ₂ ) ₂ ), NH ₄ F, and ammonium hydroxide. The pH adjusters can be used alone or in combination of two or more.

  In the solution A, it is preferable that 20 to 30 mmol of urea is dissolved per 100 mL of the solvent. In this case, since the solution A tends to have a pH in an alkaline region, the obtained oxide tends to have a petal shape, and a hydroxide is easily formed by hydrothermal synthesis described later.

In the solution A, it is preferable that 15 to 25 mmol of NH ₄ F is dissolved per 100 mL of the solvent. In this case, since the solution A tends to have a pH in an alkaline region, the obtained oxide tends to have a petal shape, and a hydroxide is easily formed by hydrothermal synthesis described later.

  The solution A may be composed of only the compound of the first metal M1, the pH adjuster and the solvent.

  The electrode substrate immersed in the solution A is not particularly limited, and, for example, a known conductive substrate can be widely used. Examples of the electrode substrate include nickel, carbon, a nickel-phosphorus alloy, a nickel-tungsten alloy, stainless steel, titanium, iron, copper, and conductive glass.

  The electrode substrate immersed in the solution A is preferably a carbon substrate or a nickel substrate. In this case, it becomes easy to manufacture a desired electrode, and the obtained electrode is unlikely to cause an increase in overvoltage in electrolysis of water or the like, and easily has excellent durability. More specifically, when the electrode substrate is a carbon substrate, carbon fiber paper can be exemplified, and when the electrode substrate is a nickel substrate, a nickel foam can be exemplified. In particular, in the first production method, the electrode substrate is preferably carbon fiber paper, and in the second production method, the electrode substrate is preferably nickel foam.

  The electrode substrate can be obtained by a known method, or a commercially available electrode substrate can be employed.

  The shape of the electrode substrate is not particularly limited, and can be appropriately selected depending on the purpose of use and required performance. For example, a sheet-like, plate-like, rod-like, mesh-like, or other electrode base material may be used.

  Before the electrode substrate is immersed in the solution A, a cleaning treatment can be performed in advance. The method of the cleaning treatment is not particularly limited, and a known method can be widely employed. For example, a method of washing the electrode substrate with an acid such as hydrochloric acid can be mentioned. In acid cleaning, ultrasonic treatment may be combined.

  The method of immersing the electrode substrate in the solution A is not particularly limited, and usually, the electrode substrate can be immersed in the solution A. The immersion of the electrode substrate can be performed, for example, in a container capable of hydrothermal synthesis described later. An example of such a container is a pressure-resistant autoclave.

In step 1, a heat treatment is performed with the electrode substrate immersed in the solution A. Examples of the heat treatment in Step 1 include a hydrothermal synthesis method. The hydrothermal synthesis method referred to here is a method in which the container is sealed while the electrode substrate is immersed in the solution A, and the inside of the container is heated. By this hydrothermal synthesis, a hydroxide (for example, Ni (OH) ₂ ) of the metal M1 can be formed on the electrode substrate.

  The temperature in the vessel in the hydrothermal synthesis is not particularly limited as long as the conditions for forming the hydroxide of the metal M1 can be, for example, 90 to 200 ° C. The time for holding the container at this temperature is not particularly limited, and may be, for example, 30 minutes to 5 hours. The pressure in the reaction vessel in the hydrothermal synthesis is not particularly limited, either, and can be set in an appropriate range.

  In the hydrothermal synthesis, the solution A is preferably in an alkaline region, and for example, preferably has a pH of 8 to 9. In this case, in the hydrothermal synthesis, the hydroxide of the metal M1 is more easily formed, and the shape is more easily formed in a petal shape or the like.

  In the step 1, after the heat treatment (hydrothermal synthesis), the electrode substrate is taken out of the container and fired. If necessary, the electrode base material taken out of the container may be washed with water or the like before firing, and then dried. Known methods can be widely used for the drying treatment, and examples thereof include vacuum drying.

  In the step 1, the firing method is not particularly limited, and for example, a known firing method can be widely used.

  The firing temperature can be, for example, 300 to 500 ° C, preferably 400 to 500 ° C, and particularly preferably about 450 ° C. The firing time can be appropriately selected depending on the firing temperature.

  In Step 1, the rate of temperature rise during baking is not particularly limited, and can be appropriately set to such an extent that a desired oxide is formed.

  The sintering may be performed in any of the air and the inert gas atmosphere. Preferably, the firing is performed in air. For the firing, for example, a known heating device such as a commercially available heating furnace can be used.

  By the above-mentioned firing, the hydroxide of the metal M1 on the electrode substrate is changed to an oxide of the metal M1 (for example, NiO).

  After the above step 1, step 2 is performed in the first manufacturing method, and step 3 is performed in the second manufacturing method.

(Step 2)
In the first manufacturing method, in the step 2, the electrode substrate fired in the step 1, that is, the electrode substrate modified with the oxide of the metal M1, is mixed with the compound of the second metal M1 and the compound of the metal M2. This is a step of performing a pulse electrodeposition treatment in a solution B containing This step 2 is a step for forming a layered double hydroxide of the metal M1 and the metal M2.

  The solution B used in the step 2 includes a compound of the second metal M1 and a compound of the metal M2, and a solvent.

  In step 2, the type of the compound of the second metal M1 is not particularly limited. However, the metal M1 in the compound of the first metal M1 used in the step 1 and the metal M1 in the compound of the second metal M1 used in the step 2 are the same metal. Examples of the kind of the compound of the second metal M1 include the same kind as the compound of the first metal M1.

  In the step 2, as the compound of the second metal M1, a nitrate of the metal M1, from the viewpoint of easily forming an aqueous solution by dissolving in water and forming a layered double hydroxide in the step 2 and the like, Preferably it is the hydrochloride. The compound of the second metal M1 may be a hydrate.

  The compound of the second metal M1 used in step 2 may be used alone or in combination of two or more. The compound of the second metal M1 can be obtained by a known production method, or a commercially available compound of the metal M1 can be used.

  The kind of the compound of the metal M2 used in the step 2 is not particularly limited. For example, as the compound of the metal M2, a known inorganic acid salt, a known organic acid salt, a hydroxide of the metal M2, a halide of the metal M2, and the like can be widely used.

  Here, the metal M2 is at least one selected from the group consisting of Fe, Co, Cu, Cr, Zn, Mn, and Mo. That is, the metal M2 is a specific type of divalent or trivalent transition metal element. The metal M2 is preferably Fe (iron) or Co (cobalt), and particularly preferably iron, from the viewpoint of easily forming an electrode that easily suppresses overvoltage.

  Examples of the inorganic acid salt of the metal M2 include at least one selected from the group consisting of nitrate, hydrochloride, sulfate, carbonate, hydrogencarbonate, phosphate, hydrogenphosphate, and the like of the metal M2. .

  Examples of the organic acid salt of the metal M2 include one or more selected from the group consisting of acetate, oxalate, formate, succinate, and the like of the metal M2.

  In the step 2, the compound of the metal M2 is preferably a nitrate or a hydrochloride of the metal M2 from the viewpoint that it is easily dissolved in water to form an aqueous solution and an oxide is easily obtained. The compound of the metal M2 may be a hydrate.

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

  The compound of the first metal M1 used in the step 1 and the compound of the second metal M1 used in the step 2 may be the same compound or different as long as both metals M1 are the same. It can also be a compound.

  It is preferable that the second metal M1 compound and the metal M2 compound used in the step 2 have the same kind of salt (for example, a combination of nitrates or a combination of hydrochlorides is preferable).

  In the solution B, examples of the solvent include the same type as the solvent used in the solution A, and water is particularly preferable. As the water, various types of water such as distilled water, tap water, industrial water, ion-exchanged water, deionized water, pure water, and electrolytic water can be used. The solvent may contain a pH adjuster, a viscosity adjuster, a fungicide and the like as long as the effects of the present invention are not impaired.

  In the solution B, the concentrations of the compound of the second metal M1 and the compound of the metal M2 are not particularly limited. For example, in the solution B, it is preferable that 1 to 100 mmol of the compound of the second metal M1 is dissolved per 100 mL of the solvent. In this case, electrodeposition can be easily performed by pulse electrodeposition.

  In the solution B, it is preferable that 1 to 100 mmol of the compound of the metal M2 is dissolved per 100 mL of the solvent. In this case, electrodeposition can be easily performed by pulse electrodeposition.

  In the solution B, the element ratio between the metal M1 and the metal M2 can be adjusted to an arbitrary range. For example, the element ratio M1: M2 between the metal M1 and the metal M2 in the solution B can be in the range of 4: 1 to 1: 4. In this range, the bond of M2-O-M2 (for example, Fe-O-Fe) is hardly generated, and the layered double hydroxide of the metal M1 and the metal M2 is easily formed stably. Since the layered double hydroxide is formed in a shape such as a petal, the cooperative action between the metal M1 and the metal M2 is enhanced, and the performance of the electrode is easily improved. It is particularly preferable that the element ratio M1: M2 between the metal M1 and the metal M2 in the solution B is 4: 1.

  The solution B may also contain other additives in addition to the compound of the second metal M1 and the compound of the metal M2. For example, a known additive used together with the electrodeposition treatment may be contained in the solution B. The solution B may be composed of only the solvent, the compound of the second metal M1, and the compound of the metal M2.

  In step 2, pulse electrodeposition is performed with the electrode substrate obtained in step 1 immersed in solution B. By this pulse electrodeposition treatment, a layered double hydroxide is formed on the electrode substrate.

  In the pulse electrodeposition treatment, the electrode substrate obtained in Step 1 is used as an anode. On the other hand, as the cathode for performing the pulse electrodeposition treatment, for example, a known insoluble electrode can be used. As the insoluble electrode, for example, an electrode made of carbon, a 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 a state of an alloy, a 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 the shape include a metal wire, a sheet, a plate, a bar, and a 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 the metal M1 and the metal M2 can be precipitated, and is, for example, less than 6, preferably about 0 to 4 or more. Preferably it is about 0-2.

When performing the pulse electrodeposition treatment, a reference electrode, an electrolytic device, a power supply, control software, and the like can be used in addition to the anode, the cathode, and the solution B (electrolytic solution). These can be, for example, known ones depending on the purpose. For example, as a reference electrode, a silver / silver chloride electrode (Ag / AgCl electrode), a mercury / mercury chloride electrode (Hg / HgCl ₂ electrode), a standard hydrogen electrode, or the like can be used.

  In the first manufacturing method, the pulse electrodeposition treatment is an electrodeposition treatment method capable of controlling the electrodeposition speed of metal ions. A pulse current method (PGM) in which a high-end current and a low-end current are applied in a fixed cycle, and a unipolar pulse voltage method (UPED) in which application of a high-end voltage and an open circuit state are repeated in a fixed cycle.

  It is preferable to adopt a unipolar pulse voltage method (UPED) as the pulse electrodeposition treatment method. In this case, a layered double hydroxide with the metal M1 and the metal M2 having a stable structure is easily formed, and the performance of the electrode is improved. Is easy to improve. The electrode becomes a natural potential when the pulse is turned off by the ordinary pulse application method, whereas the electrode can be electrodeposited by setting the electrode to 0 V at the time of the pulse off in the unipolar pulse voltage method (UPED).

  The conditions of the unipolar pulse voltage method are not particularly limited as long as the layered double hydroxide can be formed on the conductive substrate. For example, the applied voltage of the pulse: -2 to -1 V, the pulse time : 0.5 to 3 seconds and the number of times of pulse application: 100 to 1000 times. In particular, it is preferable that the applied voltage is -1 V, the pulse time is 1 second, and the number of pulse application is 600 times. In this case, the deposition amount, thickness and density of the layered double hydroxide become particularly appropriate, The performance of the electrode is easily improved.

  The temperature of the solution B at the time of performing the pulse electrodeposition treatment is not particularly limited, and may be, for example, about 0 to 50 ° C, preferably 20 to 30 ° C.

  The electrode obtained through the above step 2 has an oxide of metal M1 and a layered double hydroxide formed on an electrode substrate. The layered double hydroxide contains metal M1 and metal M2. The layered double hydroxide may be composed of only the double hydroxides of the metal M1 and the metal M2.

(Step 3)
In the second manufacturing method, the step 3 is a step of performing a heat treatment in a state where the electrode base material fired in the step 1 is immersed in the solution C containing the compound of the second metal M1 and the compound of the metal M2. is there. Step 3 is a step for forming a layered double hydroxide of the metal M1 and the metal M2.

  The solution C used in the step 3 includes the compound of the second metal M1 and the compound of the metal M2, and a solvent.

  In step 3, the type of the compound of the second metal M1 is not particularly limited. However, the metal M1 in the compound of the first metal M1 used in the step 1 and the metal M1 in the compound of the second metal M1 used in the step 3 are the same metal. Examples of the kind of the compound of the second metal M1 include the same kind as the compound of the first metal M1.

  In the step 3, as the compound of the second metal M1, a nitrate of the metal M1, from the viewpoint of easily forming an aqueous solution by dissolving in water and forming a layered double hydroxide in the step 3 and the like, Preferably it is the hydrochloride. The compound of the second metal M1 may be a hydrate.

  The compound of the second metal M1 used in Step 3 may be used alone or in combination of two or more. The compound of the second metal M1 can be obtained by a known production method, or a commercially available compound of the metal M1 can be used.

  The type of the metal M2 compound used in Step 3 is not particularly limited. For example, as the compound of the metal M2, a known inorganic acid salt, a known organic acid salt, a hydroxide of the metal M2, a halide of the metal M2, and the like can be widely used.

  Examples of the inorganic acid salt of the metal M2 include at least one selected from the group consisting of nitrate, hydrochloride, sulfate, carbonate, hydrogencarbonate, phosphate, hydrogenphosphate, and the like of the metal M2. .

  Examples of the organic acid salt of the metal M2 include one or more selected from the group consisting of acetate, oxalate, formate, succinate, and the like of the metal M2.

  In Step 3, the compound of the metal M2 is preferably a nitrate or a hydrochloride of the metal M2 from the viewpoint that it is easily dissolved in water to form an aqueous solution and a double hydroxide is easily obtained. The compound of the metal M2 may be a hydrate.

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

  The compound of the first metal M1 used in the step 1 and the compound of the second metal M1 used in the step 3 may be the same compound or different as long as both metals M1 are the same. It can also be a compound.

  Further, it is preferable that the compound of the second metal M1 and the compound of the metal M2 used in the step 3 have the same kind of salt (for example, a combination of nitrates or a combination of hydrochlorides is preferable).

  In the solution C, examples of the solvent include the same type as the solvent used in the solution A, and water is particularly preferable. As the water, various types of water such as distilled water, tap water, industrial water, ion-exchanged water, deionized water, pure water, and electrolytic water can be used. The solvent may contain a pH adjuster, a viscosity adjuster, a fungicide and the like as long as the effects of the present invention are not impaired.

  In the solution C, the concentrations of the compound of the second metal M1 and the compound of the metal M2 are not particularly limited. For example, in the solution C, it is preferable that 1 to 100 mmol of the compound of the second metal M1 is dissolved per 100 mL of the solvent.

  In the solution C, it is preferable that 1 to 100 mmol of the compound of the metal M2 is dissolved per 100 mL of the solvent.

  In the solution C, the element ratio between the metal M1 and the metal M2 can be adjusted to an arbitrary range. For example, the element ratio M1: M2 between the metal M1 and the metal M2 in the solution C can be in the range of 4: 1 to 1: 4. In this range, the bond of M2-O-M2 (for example, Fe-O-Fe) is hardly generated, and the layered double hydroxide of the metal M1 and the metal M2 is easily formed stably. Since the layered double hydroxide is formed in a shape such as a petal, the cooperative action between the metal M1 and the metal M2 is enhanced, and the performance of the electrode is easily improved. It is particularly preferable that the element ratio M1: M2 between the metal M1 and the metal M2 in the solution C is 4: 1.

The solution C may also include other additives in addition to the second metal M1 compound and the metal M2 compound. Other additives include, for example, pH adjusters. Examples of the pH adjuster include urea (CO (NH ₂ ) ₂ ), NH ₄ F, and ammonium hydroxide. The pH adjusters can be used alone or in combination of two or more.

  In solution C, it is preferable that 20 to 30 mmol of urea is dissolved per 100 mL of the solvent. In this case, since the solution A tends to have a pH in an alkaline region, a hydroxide is easily formed by hydrothermal synthesis described later.

In the solution C, it is preferable that 20 to 30 mmol of NH ₄ F is dissolved per 100 mL of the solvent. In this case, since the solution A tends to have a pH in an alkaline region, a hydroxide is easily formed by hydrothermal synthesis described later.

  The solution C may be composed of only the second metal M1 compound, the metal M2 compound, the pH adjuster and the solvent.

  In the step 3, the method of immersing the electrode substrate obtained in the step 1 in the solution C is not particularly limited, and it can be usually performed so that the entire electrode substrate is immersed in the solution C. The immersion of the electrode substrate can be performed, for example, in a container capable of hydrothermal synthesis described later. An example of such a container is a pressure-resistant autoclave.

  In step 3, a heat treatment is performed with the electrode substrate immersed in the solution C. Examples of the heat treatment in Step 3 include a hydrothermal synthesis method. The hydrothermal synthesis method here is the same as the hydrothermal synthesis method in step 1. By this hydrothermal synthesis, a metal M1 and a metal M2 layered double hydroxide can be formed on the electrode substrate.

  The temperature in the vessel in the hydrothermal synthesis is not particularly limited as long as it is a condition for forming a layered double hydroxide containing the metal M1 and the metal M2, and may be, for example, 120 to 200 ° C. The time for holding the container at this temperature is not particularly limited, and may be, for example, 10 minutes to 2 hours. The pressure in the vessel in hydrothermal synthesis is not particularly limited, either, and can be set in an appropriate range.

  In the hydrothermal synthesis in Step 3, the solution C is preferably in an alkaline region, and for example, preferably has a pH of 8 to 9. In this case, in the hydrothermal synthesis, a double hydroxide of the metal M1 and the metal M2 is more easily formed.

  In step 3, after the heat treatment (hydrothermal synthesis), the electrode base material may be taken out of the container, and if necessary, the taken out electrode base material may be washed with water or the like, and then dried. Known methods can be widely used for the drying treatment, and examples thereof include vacuum drying.

  In the electrode obtained through the above step 3, the oxide of the metal M1 and the layered double hydroxide are formed on the electrode substrate. The layered double hydroxide contains metal M1 and metal M2. The layered double hydroxide may be composed of only the double hydroxides of the metal M1 and the metal M2.

  In the electrode obtained through the above step 2, an oxide and a layered double hydroxide are formed on the electrode substrate. The oxide is an oxide of metal M1 (for example, Ni), and the layered double hydroxide contains metal M1 (for example, Ni) and metal M2 (for example, Fe). The metal included in the oxide may be only the metal M1, or may include, for example, a metal that is unavoidably included. The metal contained in the layered double hydroxide may be only the metal M1 and the metal M2, or may include, for example, a metal inevitably contained.

(Step 4)
The second manufacturing method may further include a step 4 of immersing the electrode obtained in the step 3 in an organic solvent and applying ultrasonic waves.

  The organic solvent used in Step 4 is preferably a compound inserted between the layers of the layered double hydroxide. Such organic solvents include, for example, formamide, phthalocyanine, terephthalate, polyvinyl alcohol, aspartate, polyaspartate, carboxylic acid, alkyl sulfate, aliphatic carboxylate, benzoate, porphyrin, nucleoside Phosphoric acid, vitamins, amino acids, fatty acids, and the like. Of these, formamide is preferred.

  In step 4, the method of ultrasonic treatment is not particularly limited. For example, ultrasonic treatment can be performed using a known ultrasonic irradiation device. For example, ultrasonic treatment can be performed at 20 to 40 ° C. for 1 to 10 minutes.

  In step 4, by performing the ultrasonic treatment, an organic solvent is inserted between the layers of the layered double hydroxide, and expansion between the layers may occur. Thereby, in the obtained electrode, an increase in overvoltage in electrolysis of water or the like is further suppressed.

(electrode)
The electrode obtained by the production method of the present invention (including the first production method and the second production method) is obtained by forming an oxide of metal M1 and a layered double hydroxide on an electrode substrate. The layered double hydroxide contains metal M1 and metal M2. The layered double hydroxide may be composed of only the double hydroxides of the metal M1 and the metal M2. The oxide of the metal M1 may include other metals inevitably included other than the metal M1, and the layered double hydroxide includes other metals inevitably included other than the metal M1 and the metal M2. be able to.

  Since the electrode obtained by the production method of the present invention has an oxide of the metal M1 and a layered double hydroxide of the metal M1 and the metal M2 on the electrode substrate, it is used for, for example, electrolysis of water. In this case, an increase in overvoltage hardly occurs, and excellent durability can be obtained. In particular, when the combination of the metal M1 is nickel and the metal M2 is iron, an increase in overvoltage is particularly unlikely to occur, and more excellent durability can be obtained. Therefore, the electrode obtained by the production method of the present invention can be widely applied to various uses, and in particular, can be suitably used as an electrode for water electrolysis and an electrode for hydrogen production.

  The electrode obtained by the manufacturing method of the present invention is formed by forming a fine structure to form an oxide of metal M1 (eg, NiO) and a layered double hydroxide of metal M1 and metal M2 (eg, a layered double hydroxide of NiFe). It is presumed that close contact was obtained, and that a cooperative catalytic action between the two was developed.

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

  The electrode obtained by the production method of the present invention has, for example, a structure in which many particles are laminated on an electrode substrate. The particles provided on the electrode substrate are formed, for example, by coating the surface of oxide particles of metal M1 such as nickel oxide with a layered double hydroxide. The layered double hydroxide is, for example, an electrode containing a metal M1 such as nickel and a metal M2 such as iron and the like. Coated to form electrodes. The particles on the electrode substrate have, for example, a petal-like shape. The size of the particles is, for example, 2.5 to 5.0 μm. The particle size referred to here is a value obtained by randomly selecting 50 particles by direct observation of an electrode with a scanning electron microscope, measuring their circle equivalent diameters, and arithmetically averaging them.

  Since the electrode of the present invention is manufactured by, for example, a combination of a hydrothermal synthesis method and an electrochemical method, or a combination of a hydrothermal synthesis method and a hydrothermal synthesis method, the three layers of the electrode (electrode substrate, oxide And layered double hydroxides), which is beneficial for charge transition between the layers. In addition, when the metal M1 is included, the fine structure of the crystal of the oxide of the metal M1 as the main component is easily controlled, and the catalytic activity of the electrode is easily improved.

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

  The electrode of the present invention can be made binder-free, so that an increase in the resistance of the entire electrode, blocking of active sites and inhibition of diffusion are easily avoided.

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

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

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

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

  As a specific example of the method for producing hydrogen, a voltage is applied to the anode using the electrode obtained by the production method of the present invention as an anode, a platinum plate as a cathode, and a KOH aqueous solution as an electrolyte. Thereby, hydrogen can be generated at the cathode. In addition, the rate of hydrogen generation can be increased by increasing the voltage applied to the anode. Further, oxygen is generated at the anode.

  As another specific example of the method for producing hydrogen, a voltage is applied to the anode using the electrode obtained by the production method of the present invention as a cathode, a platinum plate as an anode, and an aqueous KOH solution as an electrolyte. Thereby, hydrogen can be generated at the cathode. In addition, the rate of hydrogen generation can be increased by increasing the voltage applied to the anode. Further, oxygen is generated at the anode.

  As still another specific example of the method for producing hydrogen, the electrodes obtained by the method of the present invention are used as a cathode and an anode, and a voltage is applied to the anode using an aqueous KOH solution as an electrolyte. Thereby, hydrogen can be generated at the cathode. In addition, the rate of hydrogen generation can be increased by increasing the voltage applied to the anode. Further, oxygen is generated at the anode.

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

  In the method for producing hydrogen of the present invention, since the electrode obtained by the method for producing an electrode is used, an increase in overvoltage is unlikely to occur and the electrode has excellent durability, so that hydrogen can be produced efficiently.

  Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the embodiments of these examples.

(Example 1)
First, a _{Ni (NO 3) 2 · 6H} 2 O in 2 mmol, and CO _{(NH 2) 2} of 5 mmol, was prepared by dissolving and NH ₄ F in 4mmol distilled water 20mL to "Solution A" Teflon ( (Registered trademark) in an inner cylinder type autoclave, and a commercially available carbon fiber paper (hereinafter abbreviated as “CFP”) was immersed in the solution A. Thereafter, the autoclave was sealed, and the temperature of the autoclave was raised to 120 ° C. and maintained for 12 hours. As a result, a CFP modified with Ni (OH) ₂ (hereinafter abbreviated as “Ni (OH) ₂ modified CFP”) was obtained. The Ni (OH) _2- modified CFP was taken out of the autoclave, washed with distilled water, and dried in a vacuum dryer at 60 ° C for 2 hours.

After the drying, a baking treatment was performed by holding the Ni (OH) ₂ -modified CFP in air at 450 ° C. for 2 hours (step 1). As a result, a CFP modified with NiO (hereinafter abbreviated as “NiO-modified CFP”) was obtained.

Next, “Solution B” containing 0.8 mmol of Ni (NO ₃ ) ₂ .6H ₂ O, 0.2 mmol of Fe (NO ₃ ) ₃ .9H ₂ O, and 20 mL of water was added to Ni / Fe (mol Ratio) was adjusted to be 4: 1. The baked NiO-modified CFP was immersed in the solution B thus adjusted, and pulsed electrodeposition was performed (step 2). This pulse electrodeposition treatment uses a platinum plate as a counter electrode, Ag / AgCl as a reference electrode, and sets the pulse potential at the time of pulse ON and OFF to 0 V, the ON and OFF times to 1 second, and the pulse application frequency to 600 times. did. By this pulse electrodeposition treatment, a layered double hydroxide of Ni and Fe is electrodeposited, and an electrode for water electrolysis in which NiO and a layered double hydroxide of Ni and Fe are formed on the electrode substrate. I got

(Example 2)
Electrolysis of water in which NiO and layered double hydroxides of Ni and Fe were formed on the electrode substrate in the same manner as in Example 1 except that the firing temperature in step 1 was changed to 350 ° C. Electrode was obtained.

(Example 3)
Electrolysis of water in which NiO and layered double hydroxides of Ni and Fe were formed on the electrode substrate in the same manner as in Example 1 except that the firing temperature in Step 1 was changed to 400 ° C. Electrode was obtained.

(Example 4)
Electrolysis of water in which NiO and layered double hydroxides of Ni and Fe were formed on the electrode substrate in the same manner as in Example 1 except that the firing temperature in Step 1 was changed to 550 ° C. Electrode was obtained.

(Example 5)
In the same manner as in Example 1, except that the number of pulse applications in step 2 was changed to 200, electricity of water in which NiO and a layered double hydroxide of Ni and Fe were formed on the electrode substrate was used. An electrode for decomposition was obtained.

(Example 6)
In the same manner as in Example 1, except that the number of pulse applications in step 2 was changed to 400, the electric power of water in which NiO and a layered double hydroxide of Ni and Fe were formed on the electrode substrate. An electrode for decomposition was obtained.

(Example 7)
In the same manner as in Example 1, except that the number of times of pulse application in Step 2 was changed to 800, electricity of water in which NiO and a layered double hydroxide of Ni and Fe were formed on the electrode substrate was used. An electrode for decomposition was obtained.

(Example 8)
In the same manner as in Example 1, except that the number of times of pulse application in Step 2 was changed to 1,000, electricity of water in which NiO and a layered double hydroxide of Ni and Fe were formed on the electrode substrate was used. An electrode for decomposition was obtained.

(Example 9)
Except that the solution B was adjusted so that Ni / Fe (molar ratio) was 2: 1, NiO and a layered double hydroxide of Ni and Fe were formed on the electrode substrate in the same manner as in Example 1. Thus, an electrode for electrolysis of water was formed.

(Example 10)
Except that the solution B was adjusted so that Ni / Fe (molar ratio) was 1: 1, NiO and a layered double hydroxide of Ni and Fe were formed on the electrode substrate in the same manner as in Example 1. Thus, an electrode for electrolysis of water was formed.

(Example 11)
Except that the solution B was adjusted so that Ni / Fe (molar ratio) was 6: 1, NiO and a layered double hydroxide of Ni and Fe were formed on the electrode substrate in the same manner as in Example 1. Thus, an electrode for electrolysis of water was formed.

(Example 12)
Except that the solution B was adjusted so that Ni / Fe (molar ratio) was 1: 2, NiO and a layered double hydroxide of Ni and Fe were formed on the electrode substrate in the same manner as in Example 1. Thus, an electrode for electrolysis of water was formed.

(Example 13)
The same as Example 1 except that the electrode substrate was changed to a commercially available nickel foam having a size of 1 cm × 1 cm and a thickness of 2 mm (hereinafter abbreviated as “NF”) instead of CFP. By the method, an electrode for water electrolysis in which NiO and a layered double hydroxide of Ni and Fe were formed on the electrode substrate was obtained.

(Example 14)
First, a _{Ni (NO 3) 2 · 6H} 2 O in 2 mmol, and CO _{(NH 2) 2} of 5 mmol, was prepared by dissolving and NH ₄ F in 4mmol distilled water 20mL to "Solution A" Teflon ( NF was immersed in the solution A. Thereafter, the autoclave was closed, and the temperature of the autoclave was raised to 100 ° C. and maintained for 12 hours. Thus, NF modified with Ni (OH) ₂ (hereinafter abbreviated as “Ni (OH) ₂ modified NF”) was obtained. The Ni (OH) _2- modified NF was taken out of the autoclave, washed with distilled water, and dried in a vacuum dryer at 60 ° C for 2 hours.

After the drying, a baking treatment was performed by holding Ni (OH) ₂ -modified NF in an atmosphere of 450 ° C. in air for 2 hours (step 1). Thus, NF modified with NiO (hereinafter abbreviated as “NiO-modified NF”) was obtained.

Next, 0.8 mmol of Ni (NO ₃ ) ₂ .6H ₂ O, 0.2 mmol of Fe (NO ₃ ) ₃ .9H ₂ O, 5 mmol of CO (NH ₂ ) ₂ , and 4 mmol of NH ₄ F And “solution C” containing water and 20 mL of water were adjusted such that Ni / Fe (molar ratio) was 4: 1. The solution C thus adjusted was housed in a Teflon (registered trademark) inner cylinder type autoclave, and the NiO-modified NF was immersed in the solution C. Thereafter, the autoclave was sealed, and the autoclave was heated to 140 ° C. and held for 6 hours (step 3). By this hydrothermal synthesis, a layered double hydroxide of Ni and Fe is deposited to obtain an electrode for water electrolysis in which NiO and a layered double hydroxide of Ni and Fe are formed on the electrode substrate. Was.

(Example 15)
Except that the solution C was adjusted so that Ni / Fe (molar ratio) was 1: 4, NiO and a layered double hydroxide of Ni and Fe were formed on the electrode substrate in the same manner as in Example 14. Thus, an electrode for electrolysis of water was formed.

(Example 16)
Except that the solution C was adjusted so that Ni / Fe (molar ratio) was 1: 1, NiO and a layered double hydroxide of Ni and Fe were formed on the electrode substrate in the same manner as in Example 14. Thus, an electrode for electrolysis of water was formed.

(Example 17)
The electrode obtained in Example 14 was immersed in 20 mL of formamide at 30 ° C., and irradiated with ultrasonic waves for 5 minutes. Thus, after the ultrasonic treatment, the electrode was washed with pure water and dried at room temperature for 24 hours to obtain an electrode.

(Comparative Example 1)
In Example 1, the electrode was CFP modified with Ni (OH) ₂ obtained before the firing treatment in Step 1.

(Comparative Example 2)
In Example 1, the Ni (OH) ₂ -modified CFP obtained before the firing treatment in Step 1 was used as a solution B containing Ni (NO ₃ ) ₂ .6H ₂ O, Fe (NO ₃ ) ₃ .9H ₂ O and water 2. (Ni: Fe (molar ratio: 1: 1)) and subjected to pulse electrodeposition under the same conditions as in Example 1. By this pulse electrodeposition treatment, layered double hydroxides of Ni and Fe are electrodeposited, and electricity of water in which Ni (OH) ₂ and layered double hydroxides of Ni and Fe are formed on the electrode substrate. An electrode for decomposition was obtained.

(Comparative Example 3)
In Example 1, the NiO-modified CFP calcined in Step 1 was obtained as an electrode for water electrolysis without performing the pulse electrodeposition treatment in Step 2.

(Comparative Example 4)
A NiO-modified CFP was obtained in the same manner as in Comparative Example 3, except that the firing temperature was changed to 350 ° C.

(Comparative Example 5)
A NiO-modified CFP was obtained in the same manner as in Comparative Example 3, except that the firing temperature was changed to 400 ° C.

(Comparative Example 6)
A NiO-modified CFP was obtained in the same manner as in Comparative Example 3, except that the firing temperature was changed to 550 ° C.

(Comparative Example 7)
An electrode was obtained in the same manner as in Example 1, except that Solution B was adjusted so that Ni / Fe (molar ratio) was 0: 1.

(Comparative Example 8)
In Example 1, the electrode substrate was changed to NF, and the NiO-modified NF calcined in Step 1 was obtained as an electrode for water electrolysis without performing the pulse electrodeposition treatment in Step 2.

(Evaluation results)
FIG. 1 shows linear sweep voltammetry curves of the electrodes obtained in each of Examples and Comparative Examples. The linear sweep voltammetry curve in FIG. 1 is obtained by using an electrode obtained in the example or the comparative example as an anode, a platinum plate as a cathode, an Ag / AgCl electrode as a reference electrode, a 1 M KOH aqueous solution as an electrolyte, and an electrode size of 1 cm It was obtained by an oxygen generation (OER) test (potential sweep rate 5 mVs ^-1 ) with a size of × 1 cm. The measurement apparatus for obtaining a linear sweep voltammetry curve was measured using a VersaSTAT4 potentiostat galvanostat electrochemical workstation with a standard three-electrode cell.

FIG. 1 shows that all of the electrodes obtained in the examples had a high current density, and were electrodes having excellent performance. In particular, from the results of FIG. 1, it was found that the performance was most excellent when the firing temperature in step 1 was 450 ° C. (Example 1). In the linear sweep voltammetry curve of the electrode of Example 1, the overvoltage when applying a current of 10 mA / cm ² was 175.2 mV, which was a particularly low value.

  From the above results, the electrode obtained by the specific manufacturing method has a fine structure, whereby intimate contact between the layered double hydroxides of NiO and NiFe can be obtained, and a cooperative catalytic action of the two appears. It is supposed to do.

In addition, from the comparison between the example of FIG. 1 and the comparative example, the electrode of the present invention has a composite structure of Ni (OH) ₂ / CFP (Comparative Example 1) and NiO / CFP (Comparative Example 3). It was found that the electrode showed remarkably high performance as compared with the electrode of No. 1.

  FIG. 2 shows XRD spectra of the electrodes obtained in each of Examples and Comparative Examples. The average particle size of the NiO crystal determined from the XRD peak line width was 7.72 nm in Example 3, 14.13 nm in Example 1, and 20.70 nm in Example 4. The higher the firing temperature, the higher the average particle size. The diameter has increased. Therefore, it is understood that the crystal growth of the NiO particles is promoted by increasing the firing temperature.

  3A, 3B, and 3C show SEM images of the electrodes obtained in Example 1 (the imaging magnification is higher in the order of a, b, and c). From these SEM images, it was found that in the obtained electrode, NiO deposited on CFP had a petal-like structure, and the surface of the NiO was covered with a layered double hydroxide of Ni and iron. Was.

  FIG. 4 shows the results of element mapping of the electrode obtained in Example 1. Specifically, FIG. 4A shows the element mapping of the SEM image of the electrode surface, FIG. 4B shows the element mapping spectrum, FIG. 4C shows the distribution of Ni, and FIG. 4D shows the distribution of Fe. I have. The element mapping of the SEM image was measured using a scanning electron microscope (SEM, Hitachi SU8010) system equipped with an energy dispersive spectrometer (EDS) manufactured by Horiba Scientific, Inc. The measurement voltage was 10 kV.

  From the results of FIG. 4, it was found that both nickel and iron were uniformly distributed on the material surface.

  FIG. 5 shows linear sweep voltammetry curves of the electrodes obtained in Examples 1 and 5 to 8. The linear sweep voltammetry curve in FIG. 5 is obtained by using the electrode obtained in the example as an anode, a platinum plate as a cathode, an Ag / AgCl electrode as a reference electrode, a 1 M KOH aqueous solution as an electrolyte, and an electrode size of 1 cm × 1 cm. Obtained by an oxygen evolution (OER) test.

  From FIG. 5, it was found that the electrodes obtained in any of the examples had a high current density regardless of the number of times of pulse application, and were electrodes having excellent performance. In particular, from the results of FIG. 5, it was found that the performance was most excellent when the number of times of pulse application was 600 (Example 1). Therefore, it is considered that the precipitation amount of the active layered double hydroxide increases as the number of pulse applications increases. The performance was better when the pulse application frequency was 600 times (Example 1) than when the pulse application frequency was 800 times and 1000 times (Examples 7 and 8). From this, although the layered double hydroxide becomes thicker and the density increases as the number of pulse applications increases (see FIG. 6), the layered double hydroxide may become too thick or the density may become too high. Rather, it can be said that a suitable thickness and density exist.

  6A to 6E show SEM images of the electrodes obtained in Example 5, Example 6, Example 1, Example 7, and Example 8, respectively. From these SEM images, all of the obtained electrodes show that NiO deposited on CFP has a petal-like structure, and that the surface of the NiO is coated with a layered double hydroxide of Ni and iron. I understood. In particular, as the number of pulse applications increases, the layered double hydroxide tends to be thicker and have a higher density.

FIG. 7 shows linear sweep voltammetry curves of the electrodes obtained in each of Examples and Comparative Examples. The linear sweep voltammetry curve in FIG. 7 is obtained by using the electrode obtained in the example as an anode, a platinum plate as a cathode, an Ag / AgCl electrode as a reference electrode, and a 1 M KOH aqueous solution as an electrolyte. Oxygen generation (OER) test (potential sweep rate 5 mVs ^-1 ).

  FIG. 7 shows that all of the electrodes obtained in the examples had a high current density, and were electrodes having excellent performance. In particular, the results in FIG. 7 revealed that the optimal Ni / Fe molar ratio in the solution C of the step 2 was 4/1 (Example 1). As a result, it was shown that even if a small amount of Fe was added, the electrode characteristics could be significantly improved. If the amount of Fe added is in the specific range, it is presumed that the formation of Fe—O—Fe bonds in the material is unlikely to occur, and the cooperative action of Ni and Fe is unlikely to be impaired.

FIG. 8 shows the results of chronopotentiometry (current density was set to 10 mA / cm ² and 50 mA / cm ² ) in the case where water electrolysis was performed using the electrode obtained in Example 1. Is shown. The chronopotentiometry is the result when the electrode obtained in Example 1 was used as a cathode. The measurement conditions were the same as in the test for obtaining a linear sweep voltammetry curve, and the measurement was performed using a VersaSTAT4 potentiostat galvanostat electrochemical workstation in the United States together with a two-electrode cell.

  From FIG. 8, no deterioration in electrode performance was observed even after 30 hours. This result indicates that the electrode obtained in Example 1 has excellent durability.

9 (a) and 9 (b) show the results of performing a linear sweep voltammetry test using the electrode after the chronopotentiometry test of FIG. 8 was continued for 30 hours (FIG. 9, “Test”). After "). As a comparison, FIGS. 9A and 9B also show the results of a linear sweep voltammetry test of the electrode before the chronopotentiometry test (shown as “before test” in FIG. 9). The linear sweep voltammetry test was performed under the same conditions as the test conditions in FIG. 7 ((a) current density was 10 mA / cm ² , (b) current density was 50 mA / cm ² ).

  9 (a) and 9 (b), the overvoltage is suppressed even after the electrode of Example 1 has been used for 30 hours, and it is confirmed that the overvoltage is lower after use than before use. Was done. This is presumably because highly active NiOOH species were formed on the surface of the layered double hydroxide.

10A and 10B are SEM images of the electrode surface before the chronopotentiometry test in FIG. 8, and FIGS. 10C and 10D are chronopotentiometry tests in FIG. It is a SEM image of the electrode surface after continuing density (50 mA / cm < ² >) for 30 hours.

  Even after the chronopotentiometry test (after the endurance test), the NiO particles coated with the layered double hydroxide are those in which the petal-like structure is only partially collapsed. It was shown that the electrode obtained in Example 1 had excellent durability.

  FIG. 11 shows the linear sweep voltammetry curves of the electrodes obtained in Examples 13 to 17 and Comparative Example 8. The linear sweep voltammetry curve in FIG. 11 is obtained by using the electrode obtained in the example or the comparative example as an anode, a platinum plate as a cathode, an Ag / AgCl electrode as a reference electrode, a 1M KOH aqueous solution as an electrolyte, and an electrode size of 1 cm. It was obtained by an oxygen evolution (OER) test with a size of × 1 cm.

FIG. 11 shows that all of the electrodes obtained in the examples had a high current density, and were electrodes having excellent performance. The overvoltage of the electrode (using NF) prepared by depositing the NiFe layered double hydroxide by the UPED method as in Example 13 was 276.5 mV at 10 mA / cm ² and 464 mV at 50 mA / cm ² . On the other hand, when CFP was used as the base material by the same UPED method, the value was 153.7 mV at 10 mA / cm ² , which was much smaller than that when NF was used as the electrode base material. In addition, in the electrode system using CFP as a base material, an oxidation current of Ni ²⁺ species on the electrode surface to Ni ³⁺ species is observed in the region of 1.35 to 1.5 V, but there is no influence of 50 mA / cm. The overvoltage when compared under the conditions of No. ² was 330 mV.

On the other hand, the electrode obtained by depositing the NiFe layered double hydroxide on the NF by hydrothermal synthesis of the solution C as in Example 14 exhibited an overvoltage of 384 mV at 50 mA / cm ² . Furthermore, when the ultrasonic treatment was performed after the hydrothermal synthesis of the solution C as in Example 17, the overvoltage was 340 mV at 50 mA / cm ² , which was lower than that without the ultrasonic treatment. .

  FIG. 12 shows the Tafel slope calculated from the linear sweep voltammetry curve shown in FIG. FIG. 12B shows the result of chronopotentiometry of the electrode obtained in Example 17. This chronopotentiometry was performed under the same conditions as the chronopotentiometry in FIG.

  FIG. 12A shows that the electrode (combination of hydrothermal synthesis and ultrasonic treatment) obtained in Example 17 exhibited the lowest Tafel slope and the lowest overvoltage. In the chronopotentiometry of this electrode (FIG. 12 (b)), an overvoltage of 192 mV was initially observed, and the overvoltage after current supply for 1000 seconds increased only slightly to 210 mV.

Table 1 shows the results of the overvoltage (two types of current densities of 10 mA / cm ² and 50 mA / cm ² ) of each electrode obtained from FIGS. 11 and 12.

FIG. 13 shows XRD spectra of the electrodes obtained in Example 1, Example 14, and Comparative Example 8. From the XRD spectrum, generation of α-Ni (OH) ₂ , β-Ni (OH) ₂ , β-NiOOH, and NiFe ₂ O ₄ was observed at the electrode of Example 14 prepared by the hydrothermal synthesis method.

Claims (6)

The electrode substrate was immersed in a solution A containing a compound of the first metal M1 (where the metal M1 is at least one selected from the group consisting of Ni, Co, Cu, Cr, Zn, Mn and Mo). After heat treatment in a state, a step 1 of taking out and firing the electrode base material;
The electrode base material fired in the step 1 is combined with a compound of the second metal M1 (the metal M1 is the same metal as the metal M1 in the compound of the first metal M1) and a compound of the metal M2 (here, A metal M2 is at least one selected from the group consisting of Fe, Co, Cu, Cr, Zn, Mn and Mo), and performing a pulse electrodeposition treatment in a solution B containing:
A method for producing an electrode, comprising: The electrode substrate was immersed in a solution A containing a compound of the first metal M1 (where the metal M1 is at least one selected from the group consisting of Ni, Co, Cu, Cr, Zn, Mn and Mo). After heat treatment in a state, a step 1 of taking out and firing the electrode base material;
The electrode base material fired in the step 1 is combined with a compound of the second metal M1 (the metal M1 is the same metal as the metal M1 in the compound of the first metal M1) and a compound of the metal M2 (here, , A metal M2 is at least one selected from the group consisting of Fe, Co, Cu, Cr, Zn, Mn and Mo), and a heat treatment in a state of being immersed in a solution C containing
A method for producing an electrode, comprising: 3. The method for manufacturing an electrode according to claim 2, further comprising a step 4 of immersing the electrode obtained in the step 3 in an organic solvent and irradiating with an ultrasonic wave. The electrode has an oxide of metal M1 and a layered double hydroxide formed on an electrode substrate,
The method according to any one of claims 1 to 3, wherein the layered double hydroxide contains a metal M1 and a metal M2. An electrode in which an oxide of metal M1 and a layered double hydroxide containing metal M1 and metal M2 are formed on an electrode substrate. A method for producing hydrogen, comprising a step of performing an electrolytic treatment in an aqueous solution using the electrode obtained by the method according to any one of claims 1 to 4 or the electrode according to claim 5.