JP6950384B2 - Electrode for reduction reaction - Google Patents

Description

The present invention relates to electrodes for reduction reactions.

An artificial photosynthesis device is disclosed in which a semiconductor is used as a photoabsorber and a metal complex is used as a carbon dioxide reduction catalyst, and the reaction proceeds by moving excited electrons from the semiconductor to the metal complex. In order to put this into practical use, it is necessary to realize an electrode for a reduction reaction that causes a reaction with high efficiency.

For example, silicone rubber is applied and dried on the central part of the surface of the stainless steel plate, the ruthenium complex polymer / porous carbon / carbon cloth is connected to the periphery of the stainless steel plate with silver (Ag) paste, and the connection part is covered with silicone rubber. A reducing electrode having an insulated structure is disclosed (Non-Patent Document 1).

Takeo Arai et al, "A monolithic device for CO2 photoreduction to generate liquid organic substances in a single-compartment reactor", Energy Environ. Sci., 2015, 8, 1998-2002

By the way, in the reducing electrode described in Non-Patent Document 1, only the peripheral region connected by the silver (Ag) paste acting as a current collecting electrode contributes to the reaction. That is, the potentials are different between the peripheral portion and the central portion of the electrode, and the contribution to the reaction in the central portion far from the electrode is insufficient. In addition, it is not suitable for increasing the current, and it is difficult to increase the area.

One aspect of the present invention is a reduction reaction electrode comprising a substrate and a conductor layer having a reducing function adhered to the substrate using a conductive adhesive.

Here, it is preferable that it is used for a reduction reaction of a carbon compound or a proton.

Further, it is preferable that the conductive adhesive partially adheres the substrate and the conductor layer.

Further, it is preferable that the occupied area of the conductive adhesive with respect to the area facing the substrate and the conductor layer is 5% or more and 40% or less.

Further, it is preferable that the substrate is conductive, and a conductive current collecting wiring is provided on the surface of the substrate on the side where the conductor layer is adhered with the conductive adhesive. ..

Further, it is preferable that at least a part of the periphery of the current collector wiring is covered with an insulating sealing material.

Further, it is preferable that at least a part of the current collecting wiring is covered with the conductive adhesive.

Further, the conductive adhesive preferably contains a carbon-based adhesive.

Further, the conductor layer is preferably made of carbon containing a substance having a reducing function.

According to the present invention, it is possible to provide an electrode for a reduction reaction in which the operating voltage can be lowered and high current efficiency can be realized.

It is a figure which shows the structure of the photosynthesis apparatus in 1st Embodiment. It is sectional drawing which shows the structure of the electrode for reduction reaction in 1st Embodiment. It is a plane schematic diagram which shows the structure of the electrode for reduction reaction in 1st Embodiment. It is sectional drawing which shows another example of the structure of the electrode for reduction reaction in 1st Embodiment. It is sectional drawing which shows the structure of the electrode for oxidation reaction in 1st Embodiment. It is a figure which shows the result of the characteristic measurement in Example 1 and Comparative Example 1. It is sectional drawing which shows the structure of the electrode for reduction reaction in 2nd Embodiment. It is sectional drawing which shows another example of the structure of the electrode for reduction reaction in 2nd Embodiment. It is a figure which shows the result of the characteristic measurement in Example 2 and Comparative Example 1. It is a figure explaining the method of measuring the resistance value of a conductive adhesive.

<First Embodiment>
As shown in the schematic diagram of FIG. 1, the photosynthetic apparatus 100 according to the first embodiment includes a reduction reaction electrode 102, an oxidation reaction electrode 104, an electrolytic solution 106, a solar cell 108, a window material 110, and a frame material 112. Consists of including. The photosynthetic apparatus 100 can be used for a reduction reaction of a carbide compound such as _{carbon dioxide (CO 2) or a proton.}

The reduction reaction electrode 102 is an electrode used for reducing a substance by a reduction reaction. The reduction reaction electrode 102 includes a substrate 10, a conductive adhesive 12, a conductor layer 14, an external wiring 16, and a support seal portion 18, as shown in a schematic cross-sectional view of FIG. 2 and a schematic plan view of FIG. It is composed. Note that FIGS. 2 and 3 are schematic views, and the film thickness, width, and the like of each layer are different from the actual ones.

The substrate 10 is a member that structurally supports the reduction reaction electrode 102, and the material is not particularly limited, but is, for example, a glass substrate or the like. Further, the substrate 10 may include, for example, 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), lead (Pb). The semiconductor used as the substrate 10 is not particularly limited, but is limited to titanium oxide (TiO ₂ ), silicon (Si), strontium titanate (SrTiO ₃ ), zinc oxide (ZnO), and tantalum oxide (Ta ₂ O _5). ) Etc. are preferable.

A conductive layer may be provided on the surface of the substrate 10. The conductive layer is provided in order to effectively collect current in the reduction reaction electrode 102. The conductive layer is not particularly limited, but is preferably indium tin oxide (ITO), fluorine-doped tin oxide (FTO), zinc oxide (ZnO), or the like. In particular, considering thermal and chemical stability, it is preferable to use fluorine-doped tin oxide (FTO).

The conductive adhesive 12 is a member that connects the substrate 10 and the conductor layer 14. The conductive adhesive 12 is preferably a carbon-based adhesive containing graphite, carbon black, or the like, or a metal-based adhesive containing fine metal particles such as silver (Ag) and copper (Cu). For example, as shown in FIG. 1, a conductive adhesive 12 is applied to the entire surface of the substrate 10 to bond the substrate 10 and the conductor layer 14. The conductive adhesive 12 preferably has a curing temperature of 60 ° C. or lower.

The conductor layer 14 is composed of a conductor containing a material having a reduction catalyst function. The conductor layer 14 can be formed by supporting a reduction catalyst on the conductor. The conductor can be made of a material including the carbon material (C). It is preferable that the size of the carbon material structure alone is 1 nm or more and 1 μm or less. The carbon material preferably contains at least one of a porous material such as carbon nanotubes, graphene and graphite. For graphene and graphite, the size is preferably 1 nm or more and 1 μm or less. If it is a carbon nanotube, it is preferable that the diameter is 1 nm or more and 40 nm or less. The conductor can be formed by applying a carbon material mixed with a liquid such as ethanol by spraying and heating. Instead of spraying, it may be applied by spin coating. Alternatively, the solution may be directly dropped, dried and applied without using spin coating.

The material having a reduction catalyst function is preferably a complex catalyst. The complex catalyst is preferably, for example, a ruthenium complex. Complex catalysts include, for example, [Ru {4,4'-di (1-H-1-pyrypropyl carbonate) -2,2'-bipyridine} (CO) (MeCN) Cl ₂ ], [Ru {4,4'. -Di (1-H-1-pyridypropyl carbonate) -2,2'-bipyridine} (CO) ₂ Cl ₂ ], [Ru {4,4'-di (1-H-1-pyridyl carbonate) -2, 2'-bipyridine} (CO) ₂ ] _n , [Ru {4,4'-di (1-H-1-pyridine) -2,2'-bipyridine} (CO) (CH ₃ CN) Cl ₂ ] And so on.

Modification with a complex catalyst can be made by applying a solution of the complex in an acetonitrile (MeCN) solution onto the conductor of the conductor layer 14. Further, the modification with a complex catalyst can also be performed by an electrolytic polymerization method.

The external wiring 16 is provided to apply a bias voltage to the reduction reaction electrode 102 and allow a current generated by the reaction to flow. The external wiring 16 can be made of, for example, a wiring material of silver (Ag) or copper (Cu), and is connected to a part of the conductive adhesive 12.

The support seal portion 18 is a member that mechanically supports the members constituting the reduction reaction electrode 102. The support seal portion 18 is not particularly limited, but can be made of, for example, a resin such as silicone. The support seal portion 18 is provided so as to cover the back surface of the reduction reaction electrode 102, that is, the surface on which the conductor layer 14 is not provided and the end surface.

As shown in FIG. 4, the reduction reaction electrode 102 may be provided with a current collecting electrode. The reduction reaction electrode 102 includes a substrate 10, a transparent conductive layer 10a, a current collecting wiring 20, a first sealing portion 22, a second sealing portion 24, a conductive adhesive 12, a conductive layer 14, an external wiring 16, and a supporting sealing portion. 18 is included. Note that FIG. 4 is a schematic view, and the film thickness, width, and the like of each layer are different from the actual ones.

The transparent conductive layer 10a is provided on the surface of the substrate 10. The transparent conductive layer 10a is provided in order to effectively collect electricity in the reduction reaction electrode 102. The transparent conductive layer 10a is not particularly limited, but is preferably indium tin oxide (ITO), fluorine-doped tin oxide (FTO), zinc oxide (ZnO), or the like. In particular, considering thermal and chemical stability, it is preferable to use fluorine-doped tin oxide (FTO). The external wiring 16 is connected to the transparent conductive layer 10a or the conductive adhesive 12.

The current collecting wiring 20 is provided to enhance the effect of current collecting on the reduction reaction electrode 102. That is, when the area of the reduction reaction electrode 102 is increased, the transparency for promoting the reaction cannot be ensured on the entire surface of the reduction reaction electrode 102 only with the transparent conductive layer 10a. Therefore, the reduction reaction electrode 102 It is provided to increase conductivity. The current collecting wiring 20 may have, for example, a configuration in which linear finger electrodes arranged in a comb shape at intervals and a bus electrode for further collecting current from the finger electrodes are combined. The current collecting wiring 20 is made of a highly conductive material, and is preferably made of a material containing metal. For example, it is preferably composed of a material containing silver (Ag), copper (Cu) and the like. The current collector wiring 20 can be formed by a method such as screen printing.

Further, the current collecting wiring 20 is covered with the first seal portion 22 and the second seal portion 24. The first seal portion 22 and the second seal portion 24 are provided so as to cover at least a part of the current collector wiring 20 in order to chemically and mechanically protect the current collector wiring 20. The first sealing portion 22 can be a glass coating material having a low melting point. The first seal portion 22 can be formed by applying low melting point glass so as to cover the region where the current collecting wiring 20 is formed by using a method such as screen printing. The second seal portion 24 is made of silicone rubber (deoxidized type, low molecular weight siloxane reducing material, oil resistant / solvent resistant fluorosilicone, etc.), polyisobutylene, polypropylene, methacryl (acrylic), polycarbonate, fluororesin (teflon), epoxy. It can be a resin such as a resin. The second seal portion 24 can be formed by applying a resin so as to cover the region where the first seal portion 22 is formed by using a coating device such as screen printing or a dispenser.

The conductive adhesive 12 is a member that connects the substrate 10 provided with the transparent conductive layer 10a and the current collecting wiring 20 to the conductive layer 14. As shown in FIG. 4, the conductive adhesive 12 is applied so as to cover the surface of the transparent conductive layer 10a including the current collecting wiring 20, the first sealing portion 22, and the second sealing portion 24, and is conductive with the substrate 10. Adheres to the body layer 14. The conductive adhesive 12 is preferably a carbon-based adhesive containing graphite, carbon black, or the like, or a metal-based adhesive containing fine metal particles such as silver (Ag) and copper (Cu).

In the reduction reaction electrode 102 of the present embodiment, since the conductive adhesive 12 is provided on the entire surface, the conductor layer 14 has substantially the same potential not only in the peripheral portion but also in the central portion, and the reduction reaction occurs on almost the entire surface. Contribute to. Therefore, the current density can be increased, the operating voltage can be lowered, and high current efficiency can be realized. In addition, it is easy to increase the area. It is also excellent in running cost.

Further, by joining the substrate 10 and the conductor layer 14 with the conductive adhesive 12, the conductivity of the conductor layer 14 and the external wiring 16 that contribute to the reduction reaction is ensured, and the conductivity of glass or the like is increased. A non-existent substrate 10 and a low conductive substrate 10 can also be used. This makes it possible to use the substrate 10 which is inexpensive and has excellent chemical stability, can reduce the cost, and can maintain stable performance for a long period of time.

The oxidation reaction electrode 104 is an electrode used for oxidizing a substance by an oxidation reaction. As shown in the schematic cross-sectional view of FIG. 5, the oxidation reaction electrode 104 includes a substrate 30, a transparent conductive layer 32, a current collecting wiring 34, and an oxidation catalyst 36. Note that FIG. 5 is a schematic view, and the film thickness, width, and the like of each layer are different from the actual ones.

The material that structurally supports the oxidation reaction electrode 104 is not particularly limited, but is, for example, a glass substrate or the like.

The transparent conductive layer 32 is provided in order to effectively collect current in the oxidation reaction electrode 104. The transparent conductive layer 32 is not particularly limited, but is preferably indium tin oxide (ITO), fluorine-doped tin oxide (FTO), zinc oxide (ZnO), or the like. In particular, considering thermal and chemical stability, it is preferable to use fluorine-doped tin oxide (FTO).

The current collecting wiring 34 is provided to enhance the effect of current collecting on the oxidation reaction electrode 104. That is, when the area of the oxidation reaction electrode 104 is increased, the transparent conductive layer 32 alone cannot ensure sufficient conductivity on the entire surface of the oxidation reaction electrode 104, so that the oxidation reaction electrode 104 cannot be secured. It is provided to increase conductivity. The current collecting wiring 34 may have, for example, a configuration in which linear finger electrodes arranged in a comb shape at intervals and a bus electrode for further collecting current from the finger electrodes are combined. The current collecting wiring 34 is preferably composed of a conductive portion 34a, a first seal portion 34b, and a second seal portion 34c. The conductive portion 34a is made of a highly conductive material, and is preferably made of a material containing a metal. For example, it is preferably composed of a material containing silver (Ag), copper (Cu) and the like. Further, the first seal portion 34b and the second seal portion 34c are provided so as to cover at least a part of the conductive portion 34a in order to chemically and mechanically protect the conductive portion 34a. The first sealing portion 34b can be a glass coating material having a low melting point. The second seal portion 34c is made of silicone rubber (deoxime type, low molecular weight siloxane reducing material, oil resistant / solvent resistant fluorosilicone, etc.), polyisobutylene, polypropylene, methacryl (acrylic), polycarbonate, fluororesin (teflon), epoxy. It can be a resin such as a resin.

The oxidation catalyst 36 is composed of a material having an oxidation catalyst function. The material having an oxidation catalyst function can be, for example, a material containing iridium oxide (IrOx). Iridium oxide can be supported as a nanocolloidal solution on the surface of the transparent conductive layer 32 on which the current collecting wiring 34 is formed (T. Arai et.al, Energy Environ. Sci 8, 1998 (2015)).

The photosynthetic apparatus 100 according to the present embodiment is configured by combining a reduction reaction electrode 102 and an oxidation reaction electrode 104. For example, as shown in FIG. 1, the reduction reaction electrode 102 and the oxidation reaction electrode 104 are arranged so that the conductor layer 14 and the oxidation catalyst 36 face each other, and the electrolytic solution 106 in which the reactant is dissolved is introduced between them. Let me. The reaction product can be a carbonized compound, for example, carbon dioxide (CO ₂ ). Further, the electrolytic solution 106 is preferably a phosphate buffered aqueous solution or a boric acid buffered aqueous solution. In a specific configuration example, _{a tank of carbon dioxide (CO 2} ) saturated phosphate buffer solution is provided, and the solution is supplied to the gap provided between the reduction reaction electrode 102 and the oxidation reaction electrode 104 by a pump. , Formic acid (HCOOH) and oxygen (O ₂ ) generated by the reduction reaction are recovered in an external fuel tank.

The reduction reaction electrode 102 and the oxidation reaction electrode 104 are electrically connected to each other, and an appropriate bias voltage is applied. The means for applying the bias voltage is not particularly limited, and examples thereof include a chemical battery (including a primary battery, a secondary battery, etc.), a constant voltage source, a solar cell, and the like. At this time, the positive electrode is connected to the oxidation reaction electrode 104, and the negative electrode is connected to the reduction reaction electrode 102.

In this embodiment, the solar cell 108 is adopted. The solar cell 108 can be arranged adjacent to the reduction reaction electrode 102 and the oxidation reaction electrode 104. In the example of FIG. 1, the solar cell 108 is arranged on the back surface of the reduction reaction electrode 102 of the electrochemical cell in which the reduction reaction electrode 102 and the oxidation reaction electrode 104 face each other, and the positive electrode of the solar cell 108 is oxidized. It is connected to the reaction electrode 104, and the negative electrode is connected to the reduction reaction electrode 102.

When synthesizing formic acid (HCOOH) or the like from carbon dioxide (CO _{2 ), water (H 2} O) is oxidized to supply electrons and protons to _{carbon dioxide (CO 2).} At around pH 7, _{the oxidation potential of water (H 2} O) is 0.82 V, and the reduction potential is −0.41 V (both are NHE). The reduction potentials of carbon dioxide (CO ₂ ) to carbon monoxide (CO), formic acid (HCOOH), and methyl alcohol (CH ₃ OH) are -0.53V, -0.61V, and -0.38V, respectively. .. Therefore, the potential difference between the oxidation potential and the reduction potential is 1.20 to 1.43 V. _{Therefore, when reducing carbon dioxide (CO 2} ), which is a carbonized compound, the solar cell 108 is a crystalline silicon 4-junction solar cell or three amorphous silicon solar cells in which four crystalline silicon solar cells are directly connected. It is preferable to use an amorphous silicon-based 3-junction solar cell in which the above are connected in series.

For the solar cell 108, it is preferable to provide the window material 110 on the light receiving surface side. The window material 110 is a member that protects the solar cell 108. The window material 110 is a member that transmits light having a wavelength that contributes to power generation in the solar cell 108, and may be, for example, glass, plastic, or the like. The reduction reaction electrode 102, the oxidation reaction electrode 104, the solar cell 108, and the window material 110 are structurally supported by the frame material 112.

[Example 1]
(Method of manufacturing electrodes for reduction reaction)
As the substrate 10, a glass substrate coated with a transparent conductive layer 10a which is fluorine-containing tin oxide (FTO) was used. A silver (Ag) paste was applied onto the transparent conductive layer 10a by screen printing, and heat treatment was performed at 450 ° C. in the air to form a current collecting wiring 20 having a desired pattern. Further, using screen printing, glass having a low melting point was applied so as to cover the current collector wiring 20, and heat treatment (400 ° C.) was performed in the air to form the first seal portion 22. Further, a silicone resin (rubber) was applied so as to cover the first seal portion 22 using a dispenser, and dried at room temperature to form the second seal portion 24. On the other hand, the conductor layer 14 was formed by modifying a carbon cloth with a ruthenium complex polymer. Specifically, on the carbon cloth, as a complex catalyst layer, a ruthenium complex polymer [Ru {4,4'-di (1-H-1-pyridropyl carbonate) -2,2'-bipyridine} (CO) (MeCN) Cl ₂ ] _{A MeCN solution containing FeCl 3} · pyrrol was applied, dried, and then modified by washing with water. Then, using a carbon-based conductive adhesive as the conductive adhesive 12, the transparent conductive layer 10a and the conductive layer 14 were adhered to the entire surface. Further, the peripheral portion of the reduction reaction electrode 102 was sealed with a silicone resin to form the support seal portion 18. In this way, a reduction reaction electrode 102 having a size of 10 cm × 10 cm was obtained.

(Method of manufacturing electrodes for oxidation reaction)
First, nanocolloids of iridium oxide (IrOx) were synthesized (T. Arai, S. Sato, and T. Morikawa, Energy Environ. Sci 8, 1998 (2015)). A yellow solution adjusted to pH 13 by adding a 10 wt% sodium hydroxide (NaOH) aqueous solution to 50 ml of a 2 mM potassium (IV) chloride (K ₂ IrCl _{6) aqueous solution is heated at 90 ° C. for 20 minutes using a hot stirrer.} bottom. The resulting blue solution was cooled with ice water for 1 hour. _{Further, 3M nitric acid (HNO 3} ) was added dropwise to the cooled solution (20 ml) to adjust the pH to 1, and the mixture was stirred for 80 minutes to obtain a nanocolloidal aqueous solution of iridium oxide (IrOx). A 1.5 wt% NaOH aqueous solution (1-2 ml) was added dropwise to this solution to adjust the pH to 12.

In this embodiment, the substrate 30 and the transparent conductive layer 32 are made of glass with a fluorine-doped tin oxide (FTO) transparent conductive film (SA-25 manufactured by Nippon Sheet Glass), which is more chemically and thermally stable than ITO. .. Screen printing is applied on the transparent conductive layer 32 which is an FTO, a paste of silver (Ag) is applied to a desired pattern, and heat treatment at 450 ° C. is performed in the air to sinter silver (Ag). The conductive portion 34a was formed. Further, a screen printing method is applied on the silver (Ag) wiring, the cover glass is applied using a low melting point glass paste, and the cover glass is first sealed by heat treatment (400 ° C.) in the air. It was formed as part 34b. A silicone resin (rubber) was applied onto the silicone resin (rubber) using a dispenser and dried at room temperature to form a second seal portion 34c. As a result, the current collecting wiring 34 having a three-layer structure was produced. In this way, a nanocolloidal aqueous solution of iridium oxide (IrOx) adjusted to pH 12 was applied onto the transparent conductive layer 32 on which the current collecting wiring 34 was formed, and the mixture was kept in a drying furnace at 60 ° C. for 40 minutes for drying. .. After drying, the precipitated salt was washed with ultrapure water to form an oxidation catalyst 36. In this way, an electrode 104 for an oxidation reaction having a size of 10 cm × 10 cm was obtained.

[Comparative Example 1]
In addition, as a comparative example, an electrochemical cell using a reduction reaction electrode and an oxidation reaction electrode prepared according to Reference 1 (T. Arai et al., Energy Environ. Sci., 2015, 8, 1998-2002) is used. Made. At this time, the electrode for the reduction reaction and the electrode for the oxidation reaction were produced in an area of 10 cm × 10 cm.

(Electrochemical characterization)
_{Hg / HgSO 4} was used as the reference electrode (RE). The reduction reaction electrode 102 and the oxidation reaction electrode 104 were connected to a constant current power source, ^{energized at a current density of 2.0 mA / cm 2} for 30 minutes, and then the voltage value was measured. As the electrolytic solution 106, a 0.1 mol phosphoric acid buffer aqueous solution (K ₂ HPO ₄ + KH ₂ PO ₄ ) was used, and carbon dioxide (CO ₂ ) gas was circulated in the aqueous solution.

FIG. 6 shows the current efficiency (%) and the voltage (V) in Example 1 and Comparative Example 1. The current efficiency is derived by the ratio of current efficiency = amount of current consumed for the production of formic acid (HCOOH) / amount of current flowing × 100 (%).

In Example 1, as a result of irradiating light in the photosynthesis apparatus 100 for 1 hour, the formation of formic acid (HCOOH) was confirmed. Compared with Comparative Example 1 which was evaluated in the same manner as in Example 1, the current efficiency was significantly improved in Example 1. Further, in Example 1, the voltage at the time of reaction was lower than that in Comparative Example 1, and the power consumption could be reduced. That is, by using the reduction reaction electrode 102 of Example 1, the operating voltage can be lowered and high current efficiency can be realized, so that the photosynthesis apparatus 100 having excellent running cost can be realized.

<Second Embodiment>
As shown in the schematic cross-sectional view of FIG. 7, the reduction reaction electrode 102 in the second embodiment includes a substrate 10, a transparent conductive layer 10a, a conductive adhesive 12, a current collecting wiring 20, a conductor layer 14, and an external surface. It includes a wiring 16 and a support seal portion 18. Note that FIG. 7 is a schematic view, and the film thickness, width, and the like of each layer are different from the actual ones.

The substrate 10, the transparent conductive layer 10a, the conductive layer 14, the external wiring 16, and the support seal portion 18 are the same as those in the first embodiment. Therefore, the conductive adhesive 12 and the current collecting wiring 20 are mainly described below. explain.

The current collecting wiring 20 may have a configuration in which linear finger electrodes arranged in a comb shape at intervals and a bus electrode for further collecting current from the finger electrodes are combined. The current collecting wiring 20 is made of a highly conductive material, and is preferably made of a material containing metal. For example, it is preferably composed of a material containing silver (Ag), copper (Cu) and the like. The current collector wiring 20 can be formed by a method such as screen printing.

In the configuration of FIG. 7, the first seal portion 22 and the second seal portion 24 that cover the current collector wiring 20 are not provided, but as shown in FIG. 8, the first seal portion 22 and the first seal portion 22 and the second seal portion 24 that cover the current collector wiring 20 are not provided. The configuration may be such that the two seal portions 24 are provided.

The conductive adhesive 12 adheres the substrate 10 (transparent conductive layer 10a) and the conductor layer 14. In the present embodiment, the conductive adhesive 12 does not bond the conductor layer 14 on the entire surface of the substrate 10, but partially adheres the substrate 10 and the conductor layer 14.

Here, it is preferable that the occupied area of the conductive adhesive 12 with respect to the facing area between the substrate 10 and the conductor layer 14 is 5% or more and 40% or less. In this way, by adhering the substrate 10 and the conductor layer 14 partially with the conductive adhesive 12 instead of the entire surface, it is possible to realize the reduction reaction electrode 102 exhibiting good characteristics even at a high current density. Therefore, the efficiency of the reduction reaction can be increased, and the photosynthesis apparatus 100 can be miniaturized.

Specifically, for example, as shown in FIG. 7, it is preferable to apply the conductive adhesive 12 to both side surfaces of the current collecting wiring 20 to bond the substrate 10 and the conductor layer 14. That is, the conductive adhesive 12 is applied to both side surfaces of the current collecting wiring 20 with a thickness similar to the thickness of the current collecting wiring 20, and the substrate 10 and the conductor layer 14 are adhered to each other.

[Example 2]
(Method of manufacturing electrodes for reduction reaction)
As the substrate 10, a glass substrate coated with a transparent conductive layer 10a which is fluorine-containing tin oxide (FTO) was used. A silver (Ag) paste was applied onto the transparent conductive layer 10a by screen printing, and heat treatment was performed at 450 ° C. in the air to form a current collecting wiring 20 having a desired pattern. Further, using screen printing, glass having a low melting point was applied so as to cover the current collector wiring 20, and heat treatment (400 ° C.) was performed in the air to form the first seal portion 22. Further, a silicone resin (rubber) was applied so as to cover the first seal portion 22 using a dispenser, and dried at room temperature to form the second seal portion 24. On the other hand, the conductor layer 14 was formed by modifying a carbon cloth with a ruthenium complex polymer. Specifically, on the carbon cloth, as a complex catalyst layer, a ruthenium complex polymer [Ru {4,4'-di (1-H-1-pyridropyl carbonate) -2,2'-bipyridine} (CO) (MeCN) Cl ₂ ] _{A MeCN solution containing FeCl 3} · pyrrol was applied, dried, and then modified by washing with water. Then, the substrate 10 (transparent conductive layer 10a) and the conductive layer 14 are partially adhered using a carbon-based conductive adhesive only in the vicinity of the current collecting wiring 20, the first sealing portion 22, and the second sealing portion 24. bottom. Further, the peripheral portion of the reduction reaction electrode 102 was sealed with a silicone resin to form the support seal portion 18. In this way, a reduction reaction electrode 102 having a size of 10 cm × 10 cm was obtained.

(Method of manufacturing electrodes for oxidation reaction)
The electrode 104 for the oxidation reaction was formed in the same manner as in Example 1.

(Electrochemical characterization)
_{Hg / HgSO 4} was used as the reference electrode (RE). The reduction reaction electrode 102 and the oxidation reaction electrode 104 are connected to a constant current power source and ^{energized at a current density of 2.0 mA / cm 2} for 60 minutes, then energized at a current density of 3.0 mA / cm ² for another 60 minutes, and then the voltage is applied. The value was measured. As the electrolytic solution 106, a 0.1 mol phosphoric acid buffer aqueous solution (K ₂ HPO ₄ + KH ₂ PO ₄ ) was used, and carbon dioxide (CO ₂ ) gas was circulated in the aqueous solution.

FIG. 9 shows the current efficiency (%) and the voltage (V) in Example 2 and Comparative Example 1.

In Example 2, as a result of irradiating light in the photosynthetic apparatus 100 for 1 hour, the formation of formic acid (HCOOH) was confirmed. Compared with Comparative Example 1 which was evaluated in the same manner as in Example 2, the current efficiency was significantly improved in Example 2. Further, in Example 2, the voltage at the time of reaction was lower than that in Comparative Example 1, and the power consumption could be reduced. That is, by using the reduction reaction electrode 102 of Example 2, good characteristics can be obtained even at a high current density, the reaction efficiency can be improved, and the photosynthesis apparatus 100 can be miniaturized.

<Measurement of conductive adhesive characteristics>
FIG. 10 is a diagram showing a method for evaluating the electrical resistance of the conductive adhesive 12 used in the first embodiment and the second embodiment. The conductive adhesive 12 is applied onto the substrate 10 provided with the transparent conductive layer 10a (for example, FTO), and the carbon paper 40 is attached via the conductive adhesive 12. Then, the resistance value between the central portion of the carbon paper 40 and the portion on the transparent conductive layer 10a separated by 30 mm is measured by the measuring instrument 42.

The resistance value of the conductive adhesive 12 when the method for evaluating the electric resistance is used is preferably 50 Ω or less. The resistance value of the conductive adhesive 12 used in Examples 1 and 2 was 11.21Ω.

10 Substrate, 10a Transparent conductive layer, 12 Conductive adhesive, 14 Conductive layer, 16 External wiring, 18 Support seal part, 20 Current collection wiring, 22 1st seal part, 24 2nd seal part, 30 Substrate, 32 Transparent Conductive layer, 34 current collecting wiring, 34a conductive part, 34b first seal part, 34c second seal part, 36 oxidation catalyst, 40 carbon paper, 42 measuring instrument, 100 photosynthesis device, 102 reduction reaction electrode, 104 oxidation reaction Electrodes, 106 electrolytes, 108 solar cells, 110 window materials, 112 frame materials, 450 heat treatment.

Claims (7)

A substrate and a conductor layer having a reducing function adhered to the substrate using a conductive adhesive are provided .
The conductive adhesive partially adheres the substrate and the conductor layer, and the occupied area of the conductive adhesive with respect to the facing area between the substrate and the conductor layer is 5% or more and 40% or less. reduction electrode, characterized in that. The reduction reaction electrode according to claim 1.
An electrode for a reduction reaction, which is used for a reduction reaction of a carbon compound or a proton. The reduction reaction electrode according to claim 1 or 2.
An electrode for a reduction reaction , wherein the conductive layer and the conductive current collecting wiring are provided on the surface of the substrate on the side where the conductive layer is adhered with the conductive adhesive. The reduction reaction electrode according to claim 3.
An electrode for a reduction reaction, characterized in that at least a part around the current collecting wiring is covered with an insulating sealing material. The reduction reaction electrode according to claim 3 or 4.
An electrode for a reduction reaction, wherein at least a part of the current collecting wiring is covered with the conductive adhesive. The electrode for reduction reaction according to any one of claims 1 to 5.
The conductive adhesive is an electrode for a reduction reaction, which comprises a carbon-based adhesive. The electrode for reduction reaction according to any one of claims 1 to 6.
The conductor layer is an electrode for a reduction reaction, which is made of carbon containing a substance having a reducing function.

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