JP2017125242A - Electrode for reductive reaction and reaction device prepared therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for a reductive reaction that efficiently reduces a carbon compound while preventing the generation of hydrogen due to a side reaction.SOLUTION: An electrode for a reductive reaction 100 comprises a substrate 10 comprising a metal or a semiconductor, a carbon layer 12 that covers at least partially the surface of the substrate 10 and is made of a carbon material with the size of its individual structural unit being 1 μm or less, and a complex catalyst layer 14 that covers the surface of the carbon layer 12.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a reduction reaction electrode using a carbon material and a reaction device using the same.

  Carbon dioxide reduction device in which reaction proceeds by exciton transfer from semiconductor to metal complex using semiconductor as light absorber, metal complex (including polymer film) as carbon dioxide reduction catalyst, and semiconductor catalyst to oxidize water The invention regarding the photochemical reaction device which causes the carbon dioxide reduction reaction which used water as the electron source by combining with is disclosed (patent documents 1-3).

JP 2010-64066 A JP 2011-82144 A JP 2011-94194 A

  By the way, when a reduction electrode in which a metal complex is directly bonded to a metal or semiconductor is used, generation of hydrogen as a side reaction is promoted, and a carbon dioxide reduction reaction may not be sufficiently obtained.

  One embodiment of the present invention includes a substrate containing a metal or a semiconductor, a carbon layer that covers at least a part of the surface of the substrate, and a carbon material made of a carbon material having a structure body size of 1 μm or less, and a surface of the carbon layer. An electrode for reduction reaction, comprising a covering complex catalyst layer.

  Here, it is preferable that the carbon material includes at least one of carbon nanotubes, graphene, and graphite.

The substrate preferably includes at least one of a stainless steel material, gold (Au), silver (Ag), copper (Cu), and titanium oxide (TiO ₂ ).

The complex catalyst layer may include [Ru {4,4′-di (1-H-1-pyrrolopropyl carbonate) -2,2′-bipyridine] (CO) (MeCN) FeCl ₃ · pyrrol]. Is preferred.

  Another aspect of the present invention includes the above-described reduction reaction electrode and an oxidation reaction electrode that oxidizes water to generate oxygen, and is configured by electrochemically connecting them. The reaction device is characterized in that the carbon compound is reduced using electric energy in a state where the layer is in direct contact with a liquid containing water.

  ADVANTAGE OF THE INVENTION According to this invention, the electrode for reduction reaction which reduces a carbon compound efficiently, suppressing the generation | occurrence | production of hydrogen by a side reaction, and the reaction device using the same can be provided.

It is a figure which shows the structure of the electrode for reduction reaction in embodiment of this invention. It is a figure which shows the structure of the reaction device in embodiment of this invention. 10 is a diagram illustrating a configuration of a reduction reaction electrode in Comparative Example 7. FIG.

[Reduction reaction electrode]
FIG. 1 shows a reduction reaction electrode 100 according to the embodiment. When a voltage is applied to the reduction reaction electrode 100, electrons generated on the substrate 10 are transferred to the complex catalyst layer 14 through the carbon layer 12 and used for the reduction catalyst reaction in the complex catalyst layer 14. FIG. 1 shows an embodiment in which carbon dioxide (CO ₂ ) is reduced to formic acid (HCOOH).

The substrate 10 includes a metal or a semiconductor. The metal used as the substrate 10 is not particularly limited, but silver (Ag), gold (Au), copper (Cu), zinc (Zn), indium (In), cadmium (Cd), tin (Sn) ), Palladium (Pd), and lead (Pb). The semiconductor used as the substrate 10 is not particularly limited, but titanium oxide (TiO ₂ ), silicon (Si), strontium titanate (SrTiO ₃ ), zinc oxide (ZnO), tantalum oxide (Ta ₂ O _5). ) Etc. are suitable.

  The carbon layer 12 only needs to contain the carbon material (C), but it is preferable that the size of the carbon material structure is 1 nm or more and 1 μm or less. The carbon layer 12 preferably includes, for example, at least one of carbon nanotubes, graphene, and graphite. In the case of graphene and graphite, the size is preferably 1 nm or more and 1 μm or less. If it is a carbon nanotube, it is suitable that a diameter is 1 nm or more and 40 nm or less.

  The carbon layer 12 can be formed by applying a carbon material mixed with a liquid such as ethanol onto the substrate 10 by spraying and heating. Instead of spraying, it may be applied onto the substrate 10 by spin coating. Alternatively, the solution may be dropped directly onto the substrate 10 and dried without using spin coating.

The complex catalyst layer 14 is preferably a ruthenium complex. The complex catalyst layer 14 is formed, for example, by [Ru {4,4′-di (1-H-1-pyrrolopropyl carbonate) -2,2′-bipyridine] (CO) (MeCN) Cl ₂ ], Ru {4,4 '-Di (1-H-1-pyrrolopropyl carbonate) -2,2'-bipyridine "(CO) ₂ Cl ₂ ], [Ru {4,4'-di (1-H-1-pyrrolocarbonate) -2 , 2′-bipyridine} (CO) ₂ ] _n , [Ru {4,4′-di (1-H-1-pyrrolopropyl carbonate) -2,2′-bipyridine] (CO) (CH ₃ CN) Cl ₂ ] Or the like.

The modification by the complex catalyst layer 14 can be made by applying a solution in which the complex is dissolved in the MeCN solution on the carbon layer 12. The modification with the complex catalyst layer 14 can also be performed by an electrolytic polymerization method. An electrode of the substrate 10 on which the carbon layer 12 is formed as a working electrode, a glass substrate coated with fluorine-containing tin oxide (FTO) on the counter electrode, an Ag / Ag ⁺ electrode on the reference electrode, and Ag / Ag in an electrolyte containing a complex catalyst. A cathode current is applied to the Ag ⁺ electrode so as to be a negative voltage, and then an anode current is supplied to the Ag / Ag ⁺ electrode so as to be a positive potential, whereby a complex is formed on the substrate 10 on which the carbon layer 12 is formed. The catalyst layer 14 can be modified. Acetonitrile (MeCN) can be used for the electrolyte solution, and Tetrabutylammonium perchlorate (TBAP) can be used for the electrolyte.

  By using such a method, the surface of the substrate 10 can be effectively covered with the carbon layer 12, and electrons generated on the substrate 10 are efficiently transferred to the complex catalyst layer 14 via the carbon layer 12. be able to. Thereby, generation | occurrence | production of hydrogen which is a side reaction at the time of producing a reductive reaction can be suppressed, and the electrode 100 for reductive reaction which reduces a carbon compound efficiently on the surface of the complex catalyst layer 14 is realizable. .

[Oxidation reaction electrode]
The oxidation reaction electrode 102 includes a material that causes an oxidation reaction of water. The oxidation reaction electrode 102 is, for example, a platinum electrode (Pt), an electrode obtained by modifying iridium oxide (IrOx: x = 1 to 2) on a fluorine-containing tin oxide (FTO) substrate, or a fluorine-containing tin oxide (FTO) substrate. It is preferable to use any of the electrodes on which tungsten oxide (WO ₃ ), bismuth vanadate (BiVO ₄ ), iron oxide (Fe ₂ O ₃ ), and tantalum oxynitride (TaON) are stacked.

[Reaction device]
As shown in FIG. 2, the reaction device is configured by combining a reduction reaction electrode 100, an oxidation reaction electrode 102, and a reference electrode 104. For example, the reduction reaction electrode 100, the oxidation reaction electrode 102, and the reference electrode 104 are immersed in water in which a carbon compound is dissolved, and an appropriate bias voltage is applied between the reduction reaction electrode 100 and the reference electrode 104. Works in Thereby, as described above, the carbon compound in the water is reduced by the reduction catalytic reaction in the complex catalyst layer 14 of the reduction reaction electrode 100. For example, when the carbon compound is carbon dioxide (CO ₂ ), formic acid (HCOOH) or the like is generated by the reduction reaction. In addition, by selecting the complex catalyst layer 14 and causing a catalytic reaction in an appropriate environment, it is possible to synthesize not only formic acid but also useful organic substances such as alcohol from carbon dioxide. Further, water is oxidized into oxygen gas in the oxidation reaction electrode 102.

  Thus, according to this embodiment, a carbon compound can be converted into a more useful carbon compound using electric energy. Moreover, electric energy can be stored in the newly generated carbon compound.

  In particular, carbon dioxide can be reduced using water as an electron donor, and generation of hydrogen as a side reaction can be suppressed. Therefore, the efficiency of the reduction reaction of the carbon compound can be improved. That is, due to the hydrophobicity of the carbon layer 12 in the reduction reaction electrode 100, a nonpolar carbon compound (for example, carbon dioxide) easily approaches the metal or semiconductor that is the substrate 10, and water and protons that are polar molecules approach. It can be difficult. This makes it possible to suppress the reduction of hydrogen, which is a side reaction, particularly under a low applied voltage, to facilitate the reduction reaction of the carbon compound, and to improve the reduction efficiency of the carbon compound.

[Measurement system]
The electrochemical analyzer (ALS610) was used for the photoelectrochemical measurement, and the measurement was performed by the three-electrode method. In the three-electrode system, a Pyrex (registered trademark) cell is used for the container, and the cell is filled with an electrolytic solution, and the electrolytic solution in the electrolytic solution is a reduction reaction electrode 100, an oxidation reaction electrode 102 is a platinum electrode, and a reference electrode Hg / Hg ₂ SO ₄ was arranged as 104. For the evaluation of the products accompanying the photoelectrochemical measurement, an ion chromatograph (DIONEX, with ICS-2000 autosampler AS) and a gas chromatograph (Shimadzu GC-2014) were used.

"Example 1"
Using a commercially available stainless steel (SUS) as a substrate 10 and masking the upper portion of the substrate 10, carbon nanotubes are mixed in ethanol and sprayed at a density of about 2 mg / cm ² and heated at 350 ° C. for carbon. Layer 12 was formed. Thereafter, a copper wire was connected to the masking surface, attached to a glass substrate, and the periphery was sealed with silicon rubber. Furthermore, [Ru {4,4′-di (1-H-1-pyrrolopropyl carbonate) -2,2′-bipyridine] (CO) (MeCN) Cl as a complex catalyst layer 14 on the surface coated with the carbon layer 12. ₂ ] A MeCN solution containing FeCl ₃ · pyrrol was applied, dried, and then washed with water to form a reduction reaction electrode 100. A platinum electrode was used as the oxidation reaction electrode 102, and Hg / Hg ₂ SO ₄ was used as the reference electrode 104.

A 0.1 M phosphate buffer aqueous solution (K ₂ HPO ₄ + KH ₂ PO ₄ ) was used as the electrolytic solution, and carbon dioxide (CO ₂ ) gas was circulated in the aqueous solution. In the experiment, current-time measurement was performed in a state where the applied voltage was -1.4V.

"Comparative Example 1"
In the configuration of Example 1, the same experiment was performed without forming the carbon layer 12.

"Comparative Example 2"
In the configuration of Example 1, as the complex catalyst layer 14, [Ru {4,4′-di (1-H-1-pyrrolopropyl carbonate) -2,2′-bipyridine] (CO) (MeCN) Cl ₂ ] FeCl ₃ A similar experiment was conducted without forming a pyrol.

"Example 2"
A commercially available gold (Au) foil is used as the substrate 10 and the upper portion of the substrate 10 is masked. Then, carbon nanotubes are mixed in ethanol and sprayed at a density of about 2 mg / cm ² and heated at 350 ° C. Layer 12 was formed. Thereafter, a copper wire was connected to the masking surface, attached to a glass substrate, and the periphery was sealed with silicon rubber. Furthermore, [Ru {4,4′-di (1-H-1-pyrrolopropyl carbonate) -2,2′-bipyridine] (CO) (MeCN) Cl as a complex catalyst layer 14 on the surface coated with the carbon layer 12. ₂ ] A MeCN solution containing FeCl ₃ · pyrrol was applied, dried, and then washed with water to form a reduction reaction electrode 100. A platinum electrode was used as the oxidation reaction electrode 102, and Hg / Hg ₂ SO ₄ was used as the reference electrode 104.

A 0.1 M phosphate buffer aqueous solution (K ₂ HPO ₄ + KH ₂ PO ₄ ) was used as the electrolytic solution, and carbon dioxide (CO ₂ ) gas was circulated in the aqueous solution. In the experiment, current-time measurement was performed in a state where the applied voltage was -1.4V.

“Comparative Example 3”
In the configuration of Example 2, the same experiment was performed without forming the carbon layer 12.

“Comparative Example 4”
In the structure of Example 2, [Ru {4,4′-di (1-H-1-pyrrolopropyl carbonate) -2,2′-bipyridine] (CO) (MeCN) Cl ₂ ] FeCl ₃ as the complex catalyst layer 14. A similar experiment was conducted without forming a pyrol.

"Example 3"
Using titanium oxide (TiO ₂ ) formed by sputtering on ITO as a substrate 10 and masking the upper portion of the substrate 10, carbon nanotubes are mixed in ethanol and sprayed at a density of about 2 mg / cm ² and applied. The carbon layer 12 was formed by heating at 0 ° C. Thereafter, a copper wire was connected to the masking surface, attached to a glass substrate, and the periphery was sealed with silicon rubber. Furthermore, [Ru {4,4′-di (1-H-1-pyrrolopropyl carbonate) -2,2′-bipyridine] (CO) (MeCN) Cl as a complex catalyst layer 14 on the surface coated with the carbon layer 12. ₂ ] A MeCN solution containing FeCl ₃ · pyrrol was applied, dried, and then washed with water to form a reduction reaction electrode 100. A platinum electrode was used as the oxidation reaction electrode 102, and Hg / Hg ₂ SO ₄ was used as the reference electrode 104.

A 0.1 M phosphate buffer aqueous solution (K ₂ HPO ₄ + KH ₂ PO ₄ ) was used as the electrolytic solution, and carbon dioxide (CO ₂ ) gas was circulated in the aqueous solution. In the experiment, current-time measurement was performed in a state where the applied voltage was -1.4V.

“Comparative Example 5”
In the configuration of Example 3, the same experiment was performed without forming the carbon layer 12.

“Comparative Example 6”
In the structure of Example 3, [Ru {4,4′-di (1-H-1-pyrrolopropyl carbonate) -2,2′-bipyridine] (CO) (MeCN) Cl ₂ ] FeCl ₃ as the complex catalyst layer 14. A similar experiment was conducted without forming a pyrol.

“Comparative Example 7”
In the configuration of Example 1, carbon nanotubes are not applied as the carbon layer 12, and the same carbon fiber (CC) having a thickness of 0.38 mm and a weight of 1.7 g as in Example 1 [Ru {4,4′-di. (1-H-1-pyrrolopropyl carbonate) -2,2′-bipyridine} (CO) (MeCN) Cl ₂ ] MeCN solution containing FeCl ₃ · pyrol is applied, dried, washed with water, and then washed with substrate 10 A reduction reaction electrode as shown in FIG.

Example 4
A commercially available silver foil (Ag foil) was used as the substrate 10, and the upper portion of the substrate 10 was masked, followed by spraying and applying carbon nanotubes at a density of about 2 mg / cm ² , and heating at 350 ° C. to form the carbon layer 12. . Thereafter, a copper wire was connected to the masking surface, attached to a glass substrate, and the periphery was sealed with silicon rubber. Furthermore, [Ru {4,4′-di (1-H-1-pyrrolopropyl carbonate) -2,2′-bipyridine] (CO) (MeCN) Cl as a complex catalyst layer 14 on the surface coated with the carbon layer 12. ₂ ] A MeCN solution containing FeCl ₃ · pyrrol was applied, dried, and then washed with water to form a reduction reaction electrode 100. A platinum electrode was used as the oxidation reaction electrode 102, and Hg / Hg ₂ SO ₄ was used as the reference electrode 104.

A Pyrex (registered trademark) cell was used as the reaction cell. A 0.1 M phosphate buffer aqueous solution (K ₂ HPO ₄ + KH ₂ PO ₄ ) was used as the electrolytic solution, and carbon dioxide (CO ₂ ) gas was circulated in the aqueous solution. In the experiment, current-time measurement was performed in a state where the applied voltage was -1.4V.

"Example 5"
Using a commercially available copper foil (Cu foil) as a substrate 10 and masking the upper portion of the substrate 10, a carbon nanotube is sprayed and applied at a density of about 2 mg / cm ² and heated at 350 ° C. to form a carbon layer 12. did. Thereafter, a copper wire was connected to the masking surface, attached to a glass substrate, and the periphery was sealed with silicon rubber. Furthermore, [Ru {4,4′-di (1-H-1-pyrrolopropyl carbonate) -2,2′-bipyridine] (CO) (MeCN) Cl as a complex catalyst layer 14 on the surface coated with the carbon layer 12. ₂ ] A MeCN solution containing FeCl ₃ · pyrrol was applied, dried, and then washed with water to form a reduction reaction electrode 100. A platinum electrode was used as the oxidation reaction electrode 102, and Hg / Hg ₂ SO ₄ was used as the reference electrode 104.

A Pyrex (registered trademark) cell was used as the reaction cell. A 0.1 M phosphate buffer aqueous solution (K ₂ HPO ₄ + KH ₂ PO ₄ ) was used as the electrolytic solution, and carbon dioxide (CO ₂ ) gas was circulated in the aqueous solution. In the experiment, current-time measurement was performed in a state where the applied voltage was -1.4V.

"result"
Table 1 summarizes the results of the experiments of Examples 1-5 and Comparative Examples 1-6.

In Examples 1 to 5, formic acid (HCOOH) was produced by reducing carbon dioxide (CO ₂ ). On the other hand, when the carbon layer 12 was not provided on the reduction reaction electrode 100 as in Comparative Examples 1, 3, and 5, the reduction reaction of carbon dioxide (CO ₂ ) did not proceed. Further, even when the complex catalyst layer 14 was not present as in Comparative Examples 2, 4, and 6, the reduction reaction of carbon dioxide (CO ₂ ) did not proceed.

  From the above results, in the reduction reaction electrode 100 in the present embodiment, electrons are efficiently transferred from the substrate 10 to the complex catalyst layer 14 via the carbon layer 12, and the carbon compound is efficiently reduced. . Further, in joining the substrate 10 and the carbon layer 12 and the complex catalyst layer 14, it is not necessary to have an anchor site that specifically adsorbs on the surfaces of the substrate 10 and the carbon layer 12.

Table 2 summarizes the results of the experiments of Examples 1 to 3 and Comparative Example 7.

  Even when a carbon material other than carbon nanotubes, such as carbon cloth, is used as in Comparative Example 7, it functions as a reduction catalyst by adsorbing the complex catalyst and attaching it to the substrate 10. However, if the size of a single carbon material structure such as carbon cloth exceeds 1 μm, side reactions on the substrate 10 are not sufficiently suppressed. As a result, as shown in Table 2, the amount of formic acid (HCOOH) produced in Comparative Example 7 was lower than that in Examples 1 to 3, and the Faraday efficiency was also reduced. That is, by setting the size of the carbon material structure constituting the carbon layer 12 to 1 μm or less, the side reaction of hydrogen generation can be suppressed, and the reduction reaction efficiency of the carbon compound can be improved.

10 substrate, 12 carbon layer, 14 complex catalyst layer, 100 electrode for reduction reaction, 102 electrode for oxidation reaction, 104 reference electrode.

Claims (5)

  A substrate including a metal or a semiconductor, a carbon layer that covers at least a part of the surface of the substrate and is made of a carbon material having a structure body size of 1 μm or less, and a complex catalyst layer that covers the surface of the carbon layer. An electrode for reduction reaction. The reduction reaction electrode according to claim 1,
The electrode for reduction reaction, wherein the carbon material includes at least one of carbon nanotubes, graphene, and graphite. The reduction reaction electrode according to claim 1 or 2,
The electrode for reduction reaction, wherein the substrate includes at least one of a stainless steel material, gold (Au), silver (Ag), copper (Cu), and titanium oxide (TiO ₂ ). The electrode for reduction reaction according to any one of claims 1 to 3,
The complex catalyst layer includes [Ru {4,4′-di (1-H-1-pyrrolopropyl carbonate) -2,2′-bipyridine] (CO) (MeCN) FeCl ₃ · pyrol]. Electrode for reduction reaction. The electrode for reduction reaction according to any one of claims 1 to 4,
An oxidation reaction electrode that oxidizes water to generate oxygen;
Comprising these and connecting them electrochemically,
A reaction device characterized in that the carbon compound is reduced using electric energy in a state where the complex catalyst layer is in direct contact with a liquid containing water.

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