JP6774165B2 - Photochemical reaction device, electrode for oxidation reaction and electrode for reduction reaction used for it - Google Patents

Description

The present invention relates to a photochemical reaction device for synthesizing a carbon compound by reducing carbon dioxide using water as an electron source, and an electrode for an oxidation reaction and an electrode for a reduction reaction used therein.

In Patent Documents 1 to 4 and Non-Patent Documents 1 and ₂ , as a photocatalyst for a reduction reaction exhibiting a reduction reaction of carbon dioxide, powder of a semiconductor catalyst such as TiO ₂ and zirconium oxide is suspended in water and carbon dioxide is passed through. However, a technique for producing formaldehyde, formic acid, methane, methanol, etc. when irradiated with light from an artificial light source such as a xenon lamp or a high-pressure mercury lamp is disclosed.

Further, Non-Patent Document 3 discloses a technique of modifying a metal electrode with a metal complex catalyst polymer by an electrolytic polymerization method to selectively reduce carbon dioxide in water. Specifically, Faraday efficiency under the condition that an electrochemical bias of -0.8 V (against Ag / AgCl) was applied using a catalyst in which an electrochemically Ru complex was polymerized on a carbon or platinum electrode. A technique for producing formic acid at 85% is disclosed.

Further, Non-Patent Document 4 discloses a technique relating to water splitting using a three-junction amorphous silicon laminate in which amorphous silicon (a-Si) and amorphous silicon germanium (a-SiGe) are laminated in three layers. .. Further, Patent Documents 16 and 17 disclose techniques relating to a carbon dioxide photoreduction reaction using a three-junction amorphous silicon laminate as a light absorber and a metal catalyst as a reduction catalyst. Carbon monoxide is produced by reducing carbon dioxide using a two-chamber cell structure using an ion exchange membrane. The solar conversion efficiency in the carbon dioxide reduction reaction is 1.5%.

Further, Patent Documents 4 to 11 disclose techniques for photoreducing carbon dioxide in water using a metal electrode or a metal compound electrode.

Further, Patent Documents 12 to 15 disclose techniques for decomposing hydrocarbon compounds using semiconductor particles modified with a complex catalyst or semiconductor electrodes modified with a complex catalyst.

Further, Non-Patent Document 5 discloses a wireless device that functions in a one-chamber cell by applying an SrTiO3 photoelectrode as an electrode that oxidizes water with respect to the structure of a complex catalyst / semiconductor electrode. The solar conversion efficiency in the carbon dioxide reduction reaction in the two-chamber cell is 0.14%, and the solar conversion efficiency in the one-chamber wireless device is 0.08%.

Japanese Patent No. 2526396 Japanese Unexamined Patent Publication No. 6-158374 Japanese Patent No. 3590837 Japanese Unexamined Patent Publication No. 2011-140719 Japanese Unexamined Patent Publication No. 2013-129883 Japanese Unexamined Patent Publication No. 2013-147676 International Publication No. 11/067873 Pamphlet International Publication No. 11/132375 Pamphlet International Publication No. 11/135782 Pamphlet International Publication No. 11/135783 Pamphlet Special Table 2012-516392 JP-A-2010-64066 Japanese Unexamined Patent Publication No. 2011-82144 Japanese Unexamined Patent Publication No. 2011-94194 International Publication No. 12/091045 Pamphlet Japanese Unexamined Patent Publication No. 2014-101550 Japanese Unexamined Patent Publication No. 2014-101551

Fujishima et al., Nature 277 (1979) 637 Fujishima et al., The Journal of Physical Chemistry 102 (1998) 9834 Deronzier et al., The Journal of Electroanalytical Chemistry 444 (1998) 253 S.Y.Reece et al., Science 334 (2011) 645 T. Arai et al., Energy & Environmental Science 6 (2013) 1274

However, the conventional technique has a problem that carbon dioxide cannot be reduced by using water as an electron source, and even if it can be reduced, the solar conversion efficiency (0.04% or the like) is low. Further, in order to suppress the decomposition of the reduction product of carbon dioxide, it is necessary to form a two-chamber type cell in which a proton exchange membrane is provided between the electrode for the oxidation reaction and the electrode for the reduction reaction, and the apparatus configuration is complicated. There is a problem of becoming.

Further, there is a problem that the product produced by reducing carbon dioxide is decomposed at the electrode for oxidation reaction, and oxygen generated by the decomposition of water inhibits the reaction on the electrode for reduction reaction.

One aspect of the present invention is an oxidation reaction electrode that selectively oxidizes water to generate oxygen in the presence of a first carbon compound, and the first carbon compound selectively in the presence of oxygen. Contains a reduction reaction electrode that reduces a different second carbon compound, and is configured by electrically connecting these, and the reduction reaction electrode is a liquid containing water by utilizing the irradiated light energy. Among them, it is a photochemical reaction device characterized by reducing the second carbon compound.

Here, it is preferable that the electrode for the oxidation reaction contains a transparent conductor modified with an iridium compound, a cobalt compound, and bismuth vanadate. Since the oxidizing selectively H _{2 O} in the presence of CO ₂ reduction product, it is possible to suppress the decomposition of the CO ₂ reduction products. Therefore, for example, it is not necessary to adopt a two-chamber reaction cell structure in which a proton exchange film is provided between the oxidation reaction electrode and the reduction reaction electrode to separate them, and the oxidation reaction electrode and the reduction reaction electrode can be separated from each other. It can be applied to a one-chamber reaction cell without a proton exchange film between them and a wireless device integrated with a reduction reaction electrode.

Further, it is preferable that the electrode for the oxidation reaction contains IrOx (x = 1 to 2) or WO ₃ / BiVO ₄ .

Further, the electrode for the reduction reaction is preferably a bonded body having an arrangement of a light absorber / carbon layer / metal complex. For example, the electrode for the reduction reaction is preferably a multi-junction amorphous silicon laminate / carbon layer / ruthenium metal complex conjugate. It is preferable that the multi-junction amorphous silicon laminate has a higher output voltage than the silicon alone, the carbon layer has a high hydrogen overvoltage, and the ruthenium metal complex has a CO ₂ reducing ability even in water.

Further, it is preferable that the one-chamber type is not provided with a proton exchange membrane between the oxidation reaction electrode and the reduction reaction electrode.

Further, the oxidation reaction electrode and the reduction reaction electrode are electrically connected to each other by being integrated with each other, and the oxidation reaction electrode has light transmission and is transparent to light. , It is preferable that the electrode is arranged on the incident side of the light from the electrode for the reduction reaction. Such a configuration is known as a so-called wireless device structure, and the device configuration can be simplified. The reasons for the wireless device structure are as follows. As the material of the electrode for the oxidation reaction, a material containing FTO / IrOx or WO ₃ / BiVO ₄ having high light transmission is adopted, and the electrode for the oxidation reaction has light transmission. Therefore, the oxidation reaction electrode and the reduction reaction electrode are integrated, and the oxidation reaction electrode is arranged on the incident side of the light from the reduction reaction electrode, so that the light transmitted through the oxidation reaction electrode is used for the reduction reaction. It enters the electrode and the photochemical reaction according to the present invention proceeds. In addition, water can be selectively oxidized even in the presence of a product without proceeding with a reverse reaction.

Moreover, it is preferable that the second carbon compound is carbon dioxide. Moreover, it is preferable that the first carbon compound is at least one of an alcohol and a carboxylic acid.

Another aspect of the present invention is an electrode for an oxidation reaction of a photochemical reaction device for reducing a carbon compound, which comprises an iridium compound, a cobalt compound, and a transparent conductor modified with bismuth vanadate. It is a reaction electrode. The oxidation reaction for electrodes, since the oxidizing selectively H _{2 O} in the presence of CO ₂ reduction product, it is possible to suppress the decomposition of the CO ₂ reduction products. Therefore, for example, it is not necessary to adopt a two-chamber reaction cell structure in which a proton exchange film is provided between the oxidation reaction electrode and the reduction reaction electrode to separate them, and the oxidation reaction electrode and the reduction reaction electrode can be separated from each other. It can be applied to a one-chamber reaction cell without a proton exchange film between them and a wireless device integrated with a reduction reaction electrode.

Here, it is preferable to include IrOx (x = 1 to 2) or WO ₃ / BiVO ₄ .

Another aspect of the present invention is preferably an electrode for a reduction reaction of a photochemical reaction device for reducing a carbon compound, and preferably includes a conjugate having an arrangement of a light absorber / carbon layer / metal complex. For example, it is an electrode for a reduction reaction, which comprises a three-junction amorphous silicon laminate / carbon layer / ruthenium metal complex conjugate. It is preferable that the multi-junction amorphous silicon laminate has a higher output voltage than the silicon alone, the carbon layer has a high hydrogen overvoltage, and the ruthenium metal complex has a CO ₂ reducing ability even in water.

According to the present invention, carbon dioxide can be reduced by using light energy to synthesize a useful carbon compound with high efficiency.

It is a figure which shows the structure of the photochemical reaction device in Embodiment (Examples 1 and 2) of this invention. It is a figure which shows another structure of the photochemical reaction device in embodiment of this invention. It is a figure which shows another structure of the photochemical reaction device in embodiment of this invention. It is a figure which shows the structure of the photochemical reaction device in Embodiment (Example 3) of this invention. It is a figure which shows the structure of the photochemical reaction device in Embodiment (Examples 4 and 5) of this invention. It is a figure which shows the structure of the photochemical reaction device in the comparative example 1. FIG. It is a figure which shows the structure of the photochemical reaction device in the comparative example 2. It is a figure which shows the structure of the photochemical reaction device in the comparative examples 3 and 4. It is a figure which shows the structure of the photochemical reaction device in Embodiment (Example 6) of this invention. It is a figure which shows the experimental result of the photolysis of formic acid in the potassium phosphate aqueous solution in Example 7. It is a figure which shows the experimental result of the photodecomposition of methanol in the potassium phosphate aqueous solution in Example 8. It is a figure which shows the experimental result of the photodecomposition of ethanol in the potassium phosphate aqueous solution in Example 9. It is a figure which shows the experimental result of the photolysis of formic acid in the potassium phosphate aqueous solution in Example 11.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of the photochemical reaction device according to the embodiment. The reduction reaction electrode 10 which is a semiconductor electrode and the oxidation reaction electrode 12 which is the opposite electrode thereof and is a semiconductor electrode are electrically connected.

Then, the catalyst 16 comes into contact with the reduction reaction electrode 10 in a state where electrons e ⁻ can be exchanged. In the illustrated example, a metal complex (ruthenium complex polymer) is used as the catalyst 16.

In such a system, when light is irradiated to the reduction electrode 10, wherein the photo-excited electrons e ^- are generated, the photo-excited electrons e ^- are utilized in the reduction catalytic reaction of the catalyst 16. In this example, carbon dioxide (CO ₂ ) is reduced to formic acid (HCOOH).

On the other hand, in the oxidation reaction electrode 12, a reaction occurs in which water (H ₂ O) is oxidized to oxygen ((1/2) O ₂ ) or hydrogen peroxide, and the electron e ⁻ generated here is the electrode for reduction reaction. It moves to 10 and combines with holes generated as a pair of photoexcited electrons inside the reduction reaction electrode 10. When conductive glass (FTO / IrOx, etc .: x = 1 to 2) carrying a cocatalyst is used, light irradiation may or may not be performed, and the oxidation reaction electrode 12 may be a semiconductor electrode (WO ₃ /). When BiVO ₄ or the like is used, the oxidation reaction electrode 12 also needs to be irradiated with light.

As described above, in the present embodiment, the photoexcited electrons e ⁻ generated inside the reduction reaction electrode 10 by light irradiation move to the catalyst 16 that exhibits the reducing action of the carbon compound, so that the reduction reaction of the carbon compound is carried out. In particular, since carbon compounds (carbon dioxide and the like) can be reduced without applying a bias voltage to utilize photoexcited electrons, useful organic compounds can be synthesized with high efficiency and high reaction product selectivity. In addition, water can be oxidized by the oxidation reaction electrode 12 to extract electrons. Then, the electrons generated here are efficiently bonded to the holes generated in the reduction reaction electrode 10. Therefore, water can be used as an electron donor for the carbon dioxide reduction reaction without applying a bias power source from the outside. As shown in FIG. 2, a bias power supply 14 is arranged between the reduction reaction electrode 10 and the oxidation reaction electrode 12, and a bias voltage is applied between the two electrodes to make the reaction more efficient. You can also proceed in a targeted manner.

"Reduction reaction electrode"
Here, the semiconductor used for the reduction reaction electrode 10 subtracts the value of the lowest energy level among the molecular orbitals not occupied by the electrons of the catalyst 16 from the value of the energy level at the lowermost end of the conduction band. The material shall have a value of 0.2 electron volt or less.

In the present embodiment, as shown in FIG. 3, the reduction reaction electrode 10 has a three-junction amorphous silicon (3jn-a-Si) laminated film (multi-junction amorphous silicon laminate) 20 serving as a photoabsorbing layer. A photoelectrode which is a combination of carbon cloth (CC) 22 modified with a ruthenium complex polymer (RuCP) 24 as a catalyst 16 is used.

The three-junction amorphous silicon laminated film 20 includes a metal substrate 30, a metal reflective layer 31, a transparent conductive film 32, a first amorphous silicon germanium (a-SiGe) laminated body 33, and a second amorphous silicon germanium (a-SiGe) laminated body. 34, an amorphous silicon (a—Si) laminate 35, and a transparent conductive film 36 are included.

The metal substrate 30 is a member that serves as a base material for the three-junction amorphous silicon laminated film 20, and for example, stainless steel or the like is applied. The metal reflective layer 31 is a layer for reflecting the light incident from the transparent conductive film 36 side and re-incidentizing it on the first a-SiGe laminate 33, the second a-SiGe laminate 34, and the a-Si laminate 35. Is. For example, a silver thin film or the like can be applied to the metal reflective layer 31. The transparent conductive film 32 is a seed layer for laminating the first a-SiGe laminate 33, the second a-SiGe laminate 34, and the a-Si laminate 35. As the transparent conductive film 32, zinc oxide (ZnO), indium-containing tin oxide (ITO), or the like can be used. The first a-SiGe laminate 33 is a first photovoltaic body, and has an n-type amorphous silicon layer (n1: a-Si) 33a, an i-type amorphous silicon germanium layer (i1: a-SiGe) 33b, and the like. A p-type microcrystalline silicon layer (p1: nc-Si) 33c is laminated. The i-type amorphous silicon germanium layer (i1: a-SiGe) may have a band gap of, for example, about 1.4 eV. The second a-SiGe laminate 34 is a second photovoltaic body, and has an n-type amorphous silicon layer (n2: a-Si) 34a, an i-type amorphous silicon germanium layer (i2: a-SiGe) 34b, and the like. It is formed by laminating a p-type microcrystalline silicon layer (p2: nc-Si) 34c. The i-type amorphous silicon germanium layer (i2: a-SiGe) may have a band gap of, for example, about 1.6 eV. The a-Si laminate 35 is a third photovoltaic element, and is an n-type amorphous silicon layer (n3: a-Si) 35a, an i-type amorphous silicon layer (i3: a-Si) 35b, and a p-type. The microcrystalline silicon layer (p3: nc-Si) 35c is laminated. The i-type amorphous silicon layer (i3: a-Si) may have a band gap of, for example, about 1.8 eV. The transparent conductive film 36 is an electrode layer on the light incident side of the reduction reaction electrode 10. As the transparent conductive film 36, indium-containing tin oxide (ITO), zinc oxide (ZnO) and the like can be used.

The three-junction amorphous silicon laminated film 20 can be formed by forming each of the above layers on a metal substrate 30 by a sputtering method, a chemical vapor deposition method, or the like. Existing methods can be applied to the method for forming these three-junction amorphous silicon laminated films 20. Further, a commercially available three-junction amorphous silicon laminated film 20 may be used.

The reduction reaction electrode 10 has a structure in which a ruthenium complex polymer 24 serving as a catalyst 16 is laminated on a three-junction amorphous silicon laminated film 20 via a carbon cloth 22.

The catalyst 16 is obtained by subtracting the value of the lowest energy level among the molecular orbitals not occupied by the electrons of the catalyst 16 from the value of the energy level at the lowermost end of the conduction band of the semiconductor of the reduction reaction electrode 10. The material is 0.2 electron volt or less.

Modification with the ruthenium complex polymer 24 can be performed by an electrolytic polymerization method. Electrodes of carbon cloth 22 as a working electrode, a glass substrate coated with fluorine-containing tin oxide counter electrode (FTO), using the Ag / Ag ⁺ electrode a reference electrode, with respect to Ag / Ag ⁺ electrode in an electrolytic solution containing ruthenium complex The ruthenium complex polymer 24 can be modified on the carbon cloth 22 by passing a cathode current so as to have a negative voltage and then passing an anode current so as to have a positive potential with respect to the Ag / Ag ⁺ electrode. Acetonitrile (MeCN) can be used as the electrolyte solution, and Tetrabutylamoneiumperchlate (TBAP) can be used as the electrolyte. A ruthenium complex [Ru {4,4'-di (1-H-1-pyrrolipropyl carbonate) -2,2'-bipyridine} (CO) (MeCN) Cl ₂ ] is dissolved in this electrolyte solution and used.

The ruthenium complex is not limited to this, and is a polymerized Ru complex or a Ru complex in which a ligand is partially exchanged, Ru {4,4'-di (1-H-1-pyrrolipolytropyl carbonate). -2,2'-bipyridine} (CO) ₂ Cl ₂ ], [Ru {4,4'-di (1-H-1-pyrrolipropyl carbonate) -2,2'-bipyridine} (CO) ₂ ] _n , It may be [Ru {4,4'-di (1-H-1-pyrrolipropyl carbonate) -2,2'-bipyridine} (CO) (CH ₃ CN) Cl ₂ ].

In the reduction reaction electrode 10, the three-junction amorphous silicon laminated film 20 and the catalyst 16 (ruthenium complex polymer 24) may coexist so as to allow electrons to be exchanged. For example, the catalyst 16 may be suspended in an electrolytic solution provided with the three-junction amorphous silicon laminated film 20, or the catalyst 16 may be bonded to the three-junction amorphous silicon laminated film 20. When joining, it is preferable to join the three-bonded amorphous silicon laminated film 20 and the catalyst 16 via the carbon cloth 22.

"Electrode for oxidation reaction"
As the oxidation reaction electrode 12, one that exerts a photocatalytic function and causes an oxidation reaction of water by irradiation with light is used. In the present embodiment, the electrode 12 for oxidation reaction contains a transparent conductor modified with an iridium compound, a cobalt compound, and bismuth vanadate. For example, the oxidation reaction electrode 12 is an electrode in which iridium oxide (IrOx: x = 1-2) is modified on a fluorine-containing tin oxide (FTO) substrate, or tungsten oxide is formed on a fluorine-containing tin oxide (FTO) substrate. It is preferable to use an electrode in which (WO ₃ ) and bismuth vanadate (BiVO ₄ ) are laminated. Such an oxidation reaction electrode 12 has light transmission.

Fluorine-containing tin oxide (FTO) can be formed by doping tin oxide with fluorine to impart conductivity by contacting tin oxide with a fluorine gas in an inert gas atmosphere. However, the method for forming fluorine-containing tin oxide (FTO) is not limited to this.

Iridium oxide (IrOx) can be modified by sputtering iridium oxide (IrOx) on fluorine-containing tin oxide (FTO). Reactive RF sputtering can be used for sputtering. However, the method of modifying with iridium oxide (IrOx) is not limited to this.

Tungsten oxide (WO ₃ ) and bismuth vanadate (BiVO ₄ ) are fired after applying a precursor solution of tungsten oxide (WO ₃ ) and bismuth vanadate (BiVO ₄ ) on fluorine-containing tin oxide (FTO). It can be synthesized by. However, the method of modification with tungsten oxide (WO ₃ ) and bismuth vanadate (BiVO ₄ ) is not limited to this.

[Photochemical reaction device]
The photochemical reaction device functions by immersing the reduction reaction electrode 10 and the oxidation reaction electrode 12 in water in which a carbon compound is dissolved, and irradiating the reduction reaction electrode 10 or both electrodes 10 and 12 with light. As a result, as described above, the carbon compound in water is reduced by the reduction catalytic reaction in the catalyst 16. For example, when the carbon compound is carbon dioxide (CO ₂ ), formic acid (HCOOH) is produced by the reduction reaction. By selecting the catalyst 16 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, in the oxidation reaction electrode 12, water is oxidized to oxygen gas.

As described above, according to the present embodiment, the carbon compound can be converted into a more useful carbon compound by utilizing the light energy. In addition, light energy can be stored in newly generated carbon compounds.

In particular, since carbon dioxide can be reduced using water as an electron donor, there is an advantage that the cost of the entire system can be reduced. Further, by using a complex catalyst exhibiting a carbon dioxide reducing action, a carbon compound can be synthesized with high reaction product selectivity.

[Measurement system]
An electrochemical analyzer (ALS, 2323) was used for the photoelectrochemical measurement, and the measurement was performed by the two-electrode method. In the two-electrode method, a quartz disk-shaped glass cell was used as the container, the cell was filled with an electrolytic solution, and the reduction reaction electrode 10 and the oxidation reaction electrode 12 were arranged in the electrolytic solution. Further, a two-chamber cell in which a proton exchange membrane (Nafion 117) was provided between the reduction reaction electrode 10 and the oxidation reaction electrode 12 to separate them, and a one-chamber cell in which no proton exchange membrane was provided were used.

A solar simulator (Asahi Spectrometer, HAL-320) was used as the light source. An ion chromatograph (DIONEX, with ICS-2000 autosampler AS) was used to evaluate the product associated with the photoelectrochemical measurement. "IonPac AS15" was used as the column of this ion chromatograph, KOH eluent was used as the eluent, and an electric conductivity detector was used as the detector.

"Example 1"
The reduction reaction electrode 10 (working electrode) is a photoelectrode (3jn-a-Si / CC / RuCP) in which a commercially available three-junction amorphous silicon laminated film 20 and a carbon cloth 22 modified with a ruthenium complex polymer 24 are combined. Using. The reduction reaction electrode 10 is a transparent conductive film 36 of a three-junction amorphous silicon laminated film 20 (a copper tape and a copper wire are connected to the ITO side, the transparent conductive film 36 side is attached to a glass substrate, and the periphery is made of silicon rubber. Sealed.

Modification with the ruthenium complex polymer 24 was performed by an electrolytic polymerization method. At this time, using a carbon cloth 22 as the working electrode, a glass substrate coated with fluorine-containing tin oxide (FTO) as the counter electrode, and an Ag / Ag ⁺ electrode as the reference electrode, −1.45 V (-1.45 V) in an electrolytic solution containing a ruthenium complex. after passing a cathodic current against Ag / Ag ⁺ electrode) and flushed with anode current at 0.95 V (vs. Ag / Ag ⁺ electrode). As a result, the ruthenium complex polymer 24 was modified on the carbon cloth 22. Acetonitrile (MeCN) was used as the solvent of the electrolytic solution, and Tetrabutylammiumperchlate (TBAP) was used as the electrolyte. A ruthenium complex [Ru {4,4'-di (1-H-1-pyrrolipropyl carbonate) -2,2'-bipyridine} (CO) (MeCN) Cl ₂ ] was dissolved in this electrolyte solution and used.

An FTO / IrOx electrode modified with iridium oxide (IrOx) on a fluorine-containing tin oxide (FTO) substrate was applied to the oxidation reaction electrode 12 (counter electrode). Iridium oxide (IrOx) was modified on a fluorine-containing tin oxide (FTO) substrate by reactive RF sputtering. Specifically, an Ar / O ₂ mixed gas was circulated in the vacuum chamber, and the metal iridium (Ir) was sputtered as a target. The film thickness of iridium oxide (IrOx) was about 10 nm.

The reaction cell is a two-chamber cell in which a photoelectrode (3jn-a-Si / CC / RuCP), which is an electrode 10 for a reduction reaction, and an FTO / IrOx electrode, which is an electrode 12 for an oxidation reaction, are separated by a proton exchange membrane (Nafion 117). And said. As the electrolytic solution, 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.

A solar simulator (Asahi Spectrometer, HAL-320) was used as the light source. As shown in FIG. 1, 1 SUN (equivalent to AM1.5) of light was directly irradiated from the reduction reaction electrode 10 side through a 10 mm square slit from the solar simulator. At this time, no bias power supply was provided between the reduction reaction electrode 10 and the oxidation reaction electrode 12, and the bias voltage between the electrodes was set to 0V.

Here, the solar conversion efficiency is derived by the following equation.

Solar conversion efficiency = heat of combustion of generated formic acid / energy of irradiated pseudo-sunlight
× 100 (%)

"Example 2"
In the configuration of Example 1, light of 1 SUN (equivalent to AM1.5) was directly irradiated from the reduction reaction electrode 10 side through a slit of 5 mm square.

"Example 3"
In the configuration of Example 1, the proton exchange membrane of the reaction cell was removed to form a one-chamber cell. Further, a solar simulator was used as a light source, and 1SUN (equivalent to AM1.5) light was irradiated from the FTO / IrOx electrode side, which is the oxidation reaction electrode 12, through a 5 mm square slit. At this time, the light was arranged so as to be incident on the photoelectrode (3jn-a-Si / CC / RuCP) which is the reduction reaction electrode 10 through the FTO / IrOx electrode (FIG. 4).

"Example 4"
In the configuration of Example 3, the electrode 12 for oxidation reaction is used as an FTO / WO ₃ / BiVO ₄ electrode in which tungsten oxide (WO ₃ ) and bismuth vanadate (BiVO ₄ ) are modified on a fluorine-containing tin oxide (FTO) substrate. changed. Tungsten oxide (WO ₃ ) and bismuth vanadate (BiVO ₄ ) are fired after applying a precursor solution of tungsten oxide (WO ₃ ) and bismuth vanadate (BiVO ₄ ) on fluorine-containing tin oxide (FTO). It was synthesized by. Reference 1 (K. Sayama et al., International Journal of Hydrogen Energy, Volume 39, Issue 6) describes the preparation method, coating method and firing temperature of the precursor solution of tungsten oxide (WO ₃ ) and bismuth vanadate (BiVO ₄ ). , 14 Feb. 2014, pages 2454-2461).

As a light source, a solar simulator was used, and 1SUN (equivalent to AM1.5) light was directly irradiated from the FTO / WO ₃ / BiVO ₄ electrode side, which is the electrode 12 for oxidation reaction, through a 5 mm square slit. At this time, the light was arranged so as to be incident on the photoelectrode (3jn-a-Si / CC / RuCP) which is the reduction reaction electrode 10 through the FTO / WO ₃ / BiVO ₄ electrode (FIG. 5). At this time, no bias power supply was provided between the reduction reaction electrode 10 and the oxidation reaction electrode 12, and the bias voltage between the electrodes was set to 0V.

"Example 5"
In the configuration of Example 4, the electrolytic solution was changed to a 0.1 mol sodium hydrogen carbonate aqueous solution.

"Comparative Example 1"
As the electrode 10 for the reduction reaction, an InP / RuCP electrode which is a zinc-containing indium phosphide (InP) single crystal substrate modified with a ruthenium complex polymer (RuCP) was used. The reduction reaction electrode 10 was formed by connecting a copper wire to an InP (100-sided) single crystal wafer with indium solder, fixing the copper wire on a glass substrate, and then sealing the periphery with silicon rubber. Modification with RuCP was performed by a chemical polymerization method. Specifically, the ruthenium complex [Ru {4,4'-di (1-H-1-pyrrolipropyl carbonate) -2,2'-bipyridine} (CO) (MeCN) Cl ₂ ] and [Ru {4,4 '-Diphosphate ruthenium-2,2'-bipyridine} (CO) ₂ Cl ₂ ] is mixed 1: 1 and a MeCN solution containing FeCl ₃ · pyrrol is applied and dried on an InP optical electrode to form a polymer film. After that, it was washed with water.

As the electrode 12 for the oxidation reaction, a commercially available titanium oxide (TiO ₂ , P25) was coated on a fluorine-containing tin oxide (FTO) substrate by the squeegee method and fired. A paste was prepared by kneading 0.2 g of P25 particles with 30 μl of acetylacetone, 400 μl of water, and 1 drop of Triton X-100. This paste was dropped onto a fluorine-containing tin oxide (FTO) substrate, spread over with a glass rod, dried, and then fired at 550 ° C. Then, as a necking treatment between the titanium oxide particles, a 100 mM TiCl4 aqueous solution was added dropwise, dried, and fired at 550 ° C. A copper wire was connected to a fluorine-containing tin oxide (FTO) portion not coated with titanium oxide with indium solder, and the connection portion was sealed with silicon rubber to obtain a titanium oxide photoelectrode.

As the reaction cell, a glass cell made of quartz was used, and the reduction reaction electrode 10 and the oxidation reaction electrode 12 were separated by a proton exchange membrane (Nafion 117). A 10-mole aqueous solution of sodium hydrogen carbonate (NaHCO ₃ ) was used as the electrolytic solution, and carbon dioxide (CO ₂ ) gas was circulated in the aqueous solution.

A solar simulator was used as a light source, and 1 SUN (equivalent to AM1.5) of light was directly irradiated from the oxidation reaction electrode 12 side through a 10 mm square slit from the solar simulator. At this time, light was also incident on the InP / RuCP electrode, which is the reduction reaction electrode 10, through the oxidation reaction electrode 12 (FIG. 6). Further, no bias power supply was provided between the reduction reaction electrode 10 and the oxidation reaction electrode 12, and the bias voltage between the electrodes was set to 0V.

The composition of Comparative Example 1 was in accordance with Reference 2 (S. Sato et al., Journal of the American Chemical Society, 2011, 133 (39), pp 15240-15243).

"Comparative Example 2"
In the configuration of Comparative Example 1, the electrode 12 for the oxidation reaction was changed to a photoelectrode obtained by hydrogen-reducing a commercially available strontium titanate (SrTiO ₃ ) single crystal. Strontium titanate (SrTIO ₃ ) single crystal is a (100) plane single crystal strontium titanate (SrTIO ₃ ) (manufactured by Shinko Co., Ltd.) in N ₂ / H ₂ mixed gas (N ₂ : 97%, H ₂ : 3%) ) After heating at 800 ° C. for 2 hours in an air stream, the mixture was left at room temperature for 1 day for hydrogen reduction treatment. By the hydrogen reduction treatment, the strontium titanate (SrTIO ₃ ) single crystal changed from colorless to dark blue. A Ga-In alloy was applied to the upper end of the strontium titanate (r-SrTiO ₃ ) single crystal thus hydrogen-reduced, and a copper wire was connected with a silver paste. The joint was sealed with silicone rubber.

As the reaction cell, a glass cell made of quartz was used, and the reduction reaction electrode 10 and the oxidation reaction electrode 12 were separated by a proton exchange membrane (Nafion 117). Phosphoric acid was added to a 0.1 mol aqueous solution of sodium hydrogen carbonate (NaHCO ₃ ) to adjust the pH to 7.7, and carbon dioxide (CO ₂ ) gas was circulated in the aqueous solution.

A solar simulator is used as the light source, the light source is branched into two by a branched fiber, 1SUN (equivalent to AM1.5) light is passed through the reduction reaction electrode 10 through a 5 mm square slit, and 1SUM (1SUM) is applied to the oxidation reaction electrode 12. Light (corresponding to AM1.5) was irradiated through a visible light filter (FIG. 7). As a result, the oxidation reaction electrode 12 was irradiated with only visible light (wavelength λ> 400 nm). At this time, no bias power supply was provided between the reduction reaction electrode 10 and the oxidation reaction electrode 12, and the bias voltage between the electrodes was set to 0V.

The composition of Comparative Example 2 was in accordance with Reference 3 (T. Arai et al., Energy & Environmental Science, 2013, 6, 1274-1282).

"Comparative Example 3"
In the configuration of Comparative Example 1, the reduction reaction electrode 10 and the oxidation reaction electrode 12 were directly bonded to form a wireless photochemical reaction device. The reaction cell was a quartz glass cell and a one-chamber cell without a proton exchange membrane (FIG. 8).

The configuration of Comparative Example 3 was in accordance with Reference 3 (T. Arai et al., Energy & Environmental Science, 2013, 6, 1274-1282).

"Comparative Example 4"
In the configuration of Comparative Example 2, the reduction reaction electrode 10 and the oxidation reaction electrode 12 were directly bonded to form a wireless photochemical reaction device. The reaction cell was a quartz glass cell and a one-chamber cell without a proton exchange membrane (FIG. 8).

The composition of Comparative Example 4 was in accordance with Reference 3 (T. Arai et al., Energy & Environmental Science, 2013, 6, 1274-1282).

"result"
Table 1 summarizes the configurations of Examples 1 to 5 and Comparative Examples 1 to 4 and the results of the experiment.

In Example 1, as a result of irradiating the reaction cell with light having an irradiation area of 1 cm ² for 1 hour, it was confirmed that formic acid was produced at 12.57 μmol / h / cm ² . Compared with Comparative Examples 1 and 2 in which the reaction was carried out in the two-chamber cell in the same manner as in Example 1, the solar conversion efficiency in Example 1 was improved to about 27 times that of Comparative Example 1 and about 8 times that of Comparative Example 2. ..

In Example 2, was changed light irradiation area 0.25 cm ^2, 23.95Myu mol / h / cm ² of formic acid generated was confirmed. This is because the surface area of the region where ruthenium complex polymer 24 (RuCP), which catalyzes the reduction reaction of carbon dioxide (CO ₂ ), and iridium oxide (IrOx), which catalyzes the oxidation reaction of water, is modified is small. It is considered that the cause is that the photocurrent generated when the irradiation area is 1 cm ² cannot be effectively used for the reaction. Therefore, it is considered that the solar conversion efficiency can be increased to 1% or more under the conditions of Example 1 by increasing the area density of the region modified by these catalysts.

In Example 3, as a result of irradiating the reaction cell with light having a light irradiation area of 0.25 cm ² for 1 hour, formic acid production of 16.4 μmol / h / cm ² was confirmed. This corresponds to 1.16% in solar conversion efficiency. In Example 3, formic acid was confirmed to be produced in a one-chamber cell without a proton exchange film. Therefore, formic acid generated in the reduction reaction of carbon dioxide (CO ₂ ) in the reduction reaction electrode 10 is the oxidation reaction electrode. It is presumed that it was not oxidized by the oxidation reaction at 12. That is, in the FTO / IrOx electrode an oxidation reaction electrode 12 water (H 2 _O) is selectively oxidized, reaction products of carbon compounds suggests that it is not oxidized.

On the other hand, in Comparative Example 3, the experiment was similarly carried out in a one-chamber cell without a proton exchange membrane, but formic acid was not detected because titanium oxide (TiO ₂ ) has a property of decomposing organic substances.

On the other hand, in Comparative Example 4, the hydrogen reduction treatment monocrystalline strontium titanate _{(SrTiO) 3} has a property of selectively oxidizing the water _(H 2 O), formic acid 1.17μ mol / h / cm ² Generation confirmed. This corresponds to a solar conversion efficiency of 0.08%.

Here, from the results of the two-chamber cell in Comparative Example 2 and the one-chamber cell of the wireless photochemical reaction device in Comparative Example 4, the sun was changed by changing the reaction cell from the two-chamber cell to the one-chamber cell by setting the photochemical reaction device to wireless. The light conversion efficiency is expected to drop to 60%. Applying this assumption, the solar conversion efficiency is expected to be about 1% when the configuration of Example 2 is a one-chamber cell of a wireless photochemical reaction device. This suggests that it is possible to achieve a solar conversion efficiency about 12 times that of Comparative Example 4.

In Example 4, the electrode 12 for the oxidation reaction is an FTO / WO ₃ / BiVO ₄ electrode, and as a result of irradiating the reaction cell with light having a light irradiation area of 0.25 cm ² for 1 hour, 11.88 μmol / h / cm. ^The formation of formic acid of ² was confirmed. This corresponds to a solar conversion efficiency of 0.84%. This result suggests that in the same manner as in Comparative Example 4, and selectively oxidizing the water (H 2 _O).

In Example 5, the electrolytic solution of Example 4 was changed to an aqueous solution of NaHCO ₃ , and as a result of irradiating with light having a light irradiation area of 0.25 cm ² for 1 hour, 12.54 μmol / h / cm ² of formic acid was produced. Was confirmed. This corresponds to a solar conversion efficiency of 0.89%. This result suggests that even electrolytic solution is changed is selectively oxidizing the water (H 2 _O).

As described above, according to the embodiment of the present invention, the solar conversion efficiency of the photochemical reaction device can be improved as compared with the conventional case. Further, the carbon compound can be reduced in a simpler one-chamber cell structure instead of the conventional two-chamber cell structure.

Further, since the light transmission of the oxidation reaction electrode 12 is high, the structure can be such that light is transmitted through the oxidation reaction electrode 12 and then incident on the reduction reaction electrode 10. Therefore, it is possible to construct a wireless device in which the oxidation reaction electrode 12 and the reduction reaction electrode 10 are integrated.

"Example 6"
A wireless device (IrOx /) that combines a commercially available three-junction amorphous silicon laminate 20 as a light absorber, iridium oxide (IrOx) as an oxidation catalyst for water, and carbon cloth 22 modified with ruthenium complex polymer 24 as a reduction catalyst for a carbon compound (IrOx /). 3jn-a-Si / CC / RuCP) was used. As iridium oxide (IrOx), IrOx nanocolloid was used. According to Reference 4 (Y. Zhao et al., Journal of Physical Chemistry Letters, 2011, 2, 402-406), an IrOx nanocolloidal solution was synthesized and applied to the ITO layer of the trijunction amorphous silicon laminated film 20. A solution obtained by mixing a ruthenium complex and a polymer material was applied onto the carbon cloth 22 and modified with the ruthenium complex by a chemical polymerization method. The carbon cloth 22 modified with the ruthenium complex polymer 24 was bonded to the metal substrate 30 (stainless steel) side of the three-bonded amorphous silicon laminated film 20, and the periphery was sealed with silicon rubber.

As the reaction cell, a one-chamber type quartz glass cell was used. As the electrolytic solution, 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. A solar simulator (Asahi Spectrometer, HAL-320) was used as the light source. As shown in FIG. 9, 1 SUN (equivalent to AM1.5) of light was directly irradiated from the solar simulator through a 5 mm square slit.

"result"
Table 2 shows the experimental results of Example 6 and Comparative Example 4.

In Example 6, as a result of irradiating the wireless device with light having a light irradiation area of 0.25 cm ² for 6 hours in a single chamber cell, formic acid of 61.3 μmol / h / cm ² was generated, and the solar conversion efficiency was 4.34. %Met. On the other hand, in Comparative Example 4, as a result of irradiating the wireless device with light having a light irradiation area of 0.25 cm ² for 3 hours in the same chamber cell, 1.17 μmol / h / cm ² of formic acid was generated, and the sun. The light conversion efficiency was 0.08%. That is, in Example 6, the solar conversion efficiency was improved by 50 times or more as compared with Comparative Example 4.

"Example 7"
As the oxidation reaction electrode 12 (working electrode), a commercially available three-junction amorphous silicon laminated film 20 modified with iridium oxide (IrOx) as an oxidation catalyst (IrOx / 3jn-a-Si) was used. In the three-junction amorphous silicon laminated film 20, a copper wire was connected to the metal substrate 30 (stainless steel) side, covered with a glass substrate, and then the periphery was sealed with silicon rubber. For modification with iridium oxide (IrOx), an IrOx nanocolloidal solution was synthesized according to Reference 4 above and applied to the ITO layer of the trijunction amorphous silicon laminated film 20. A Pt wire was used for the reduction reaction electrode 10 (counter electrode). Ag / AgCl was used as the reference electrode.

As the reaction cell, a glass cell made of quartz was used. As the electrolytic solution, a 0.1 mol phosphoric acid buffer aqueous solution (K ₂ HPO ₄ + KH ₂ PO ₄ ) containing about 6 μ mol of formic acid was used, and carbon dioxide (CO ₂ ) gas was circulated in the aqueous solution. The light source was irradiated with 1 SUN (equivalent to AM1.5) light using a solar simulator (Asahi Spectroscopy, HAL-320). At this time, a bias voltage of 0 V (vs. Ag / AgCl) is applied to the oxidation reaction electrode 12, current-time measurement is performed while irradiating light, and the amount of formic acid in the aqueous solution before and after light irradiation is ion chromatographed. Measured at.

"Example 8"
Under the experimental conditions of Example 7, the electrolytic solution was changed to a 0.1 mol phosphate buffer aqueous solution (K ₂ HPO ₄ + KH ₂ PO ₄ ) containing about 21 μ mol methanol. A bias voltage of 0 V (vs. Ag / AgCl) was applied to the oxidation reaction electrode 12, current-time measurement was performed while irradiating light, and the amount of methanol in the aqueous solution before and after light irradiation was measured by a gas chromatograph.

"Example 9"
Under the experimental conditions of Example 7, the electrolytic solution was changed to a 0.1 mol phosphate buffer aqueous solution (K ₂ HPO ₄ + KH ₂ PO ₄ ) containing about 11 μmol ethanol. A bias voltage of 0 V (vs. Ag / AgCl) was applied to the oxidation reaction electrode 12, current-time measurement was performed while irradiating light, and the amount of ethanol in the aqueous solution before and after light irradiation was measured by a gas chromatograph. ..

"result"
10 to 12 show the experimental results of Examples 7 to 9. In Example 7, as a result of current-time measurement, a photocurrent of about 1C was observed. When the oxidative decomposition reaction of formic acid occurs, the amount of formic acid in the solution is predicted to decrease to about 1.2 μmol after the current-time measurement from the observed charge amount, but before and after the current-time measurement of formic acid There was no change in the amount. From this, it was confirmed that formic acid was not decomposed in the oxidation reaction on iridium oxide (IrOx).

In Reference 5 (S. Fierro et al., Electrochimica Acta, 2009, 54, 2053-2061), it is reported that formic acid is decomposed in the oxidation reaction on iridium oxide (IrOx) in hydrogen peroxide solution. There is. Further, in Reference 6 (L-E. Owe et al., Electrochimica Acta, 2011, 58, 231-237), it is reported that phosphate ions are strongly adsorbed on iridium oxide (IrOx). From these reports, it is inferred that phosphate ions are adsorbed on the surface of iridium oxide (IrOx) to prevent contact with formic acid and suppress its decomposition.

In Example 8, as a result of current-time measurement, a photocurrent of about 5C was observed. When the oxidative decomposition reaction of methanol occurs, the amount of methanol in the solution is predicted to decrease to about 9 μmol after the current-time measurement from the observed charge amount, but the amount of methanol before and after the current-time measurement Did not change. From this, it was confirmed that methanol was not decomposed in the oxidation reaction on iridium oxide (IrOx).

In Example 9, as a result of current-time measurement, a photocurrent of about 6C was observed. When the oxidative decomposition reaction of ethanol occurs, the amount of ethanol in the solution is predicted to decrease to about 0 μmol after the current-time measurement from the observed charge amount, but the amount of ethanol before and after the current-time measurement Did not change. From this, it was confirmed that ethanol was not decomposed in the oxidation reaction on iridium oxide (IrOx).

As described above, from the results of Examples 7 to 9, it was confirmed that the carbon compound was not decomposed in the oxidation reaction on iridium oxide (IrOx).

"Example 10"
The reduction reaction electrode 10 (working electrode) is a photoelectrode (3jn-a-Si / CC / RuCP) in which a commercially available three-junction amorphous silicon laminated film 20 and a carbon cloth 22 modified with a ruthenium complex polymer 24 are combined. Using. The ruthenium complex was modified by applying a solution of the ruthenium complex and the polymerization agent on the carbon cloth 22 and applying a chemical polymerization method. A Pt wire was used for the oxidation reaction electrode 12 (counter electrode). Hg / HgSO ₄ was used as the reference electrode.

As the reaction cell, a glass cell made of quartz was used. As the electrolytic solution, 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. The light source was irradiated with 1 SUN of light using a xenon lamp. At this time, a bias voltage of +0.38 V (vs. Hg / HgSO ₄ ) was applied to the reduction reaction electrode 10, and current-time measurement was performed while irradiating light to determine the amount of formic acid in the aqueous solution before and after light irradiation. It was measured by an ion chromatograph.

"Comparative Example 5"
In Example 10, as the reduction reaction electrode 10 (working electrode), the metal substrate 30 (stainless steel) side of a commercially available three-junction amorphous silicon laminated film 20 was directly modified with a ruthenium complex polymer 24 by a chemical polymerization method. A photoelectrode (3jn-a-Si / RuCP) was used.

"result"
Table 3 shows the experimental results of Example 10 and Comparative Example 5.

In Example 10, as a result of current-time measurement, a photocurrent of 18.4C was observed, and the current efficiency of formic acid production was 94%. On the other hand, in Comparative Example 5, as a result of current-time measurement, a photocurrent of 13.3 C was observed, and the current efficiency of formic acid production was 0.3%. In Comparative Example 5, since the ruthenium complex polymer 24 is directly modified on the metal substrate 30 of the three-junction amorphous silicon laminated film 20, the hydrogen generation reaction proceeds on the metal substrate 30, and as a result, formic acid is produced. It is considered that the current efficiency of On the other hand, in Example 10, since the ruthenium complex polymer 24 is modified on the three-junction amorphous silicon laminated film 20 via the carbon cloth 22, a hydrogen generation reaction occurs on the metal substrate 30. It is presumed that there is no such condition. Further, since the overvoltage in the hydrogen generation reaction of the carbon cloth 22 is high, the electrons received by the carbon cloth 22 from the trijunction amorphous silicon laminated film 20 preferentially move to the ruthenium complex polymer 24, resulting in the formation of formic acid. It is considered that the current efficiency has improved.

"Example 11"
The reduction reaction electrode 10 (working electrode) is a photoelectrode (3jn-a-Si / CC / RuCP) in which a commercially available three-junction amorphous silicon laminated film 20 and a carbon cloth 22 modified with a ruthenium complex polymer 24 are combined. Using. A Pt wire was used for the oxidation reaction electrode 12 (counter electrode). Hg / HgSO ₄ was used as the reference electrode.

As the reaction cell, a glass cell made of quartz was used. As the electrolytic solution, 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. At this time, oxygen (O ₂ ) gas was mixed with carbon dioxide (CO ₂ ) gas, and the concentration was changed from 0 to 7.2%. The light source was irradiated with 1 SUN of light using a xenon lamp. A bias voltage of −0.82 V (vs. Hg / HgSO ₄ ) is applied to the reduction reaction electrode 10, current-time measurement is performed while irradiating light, and the amount of formic acid in the aqueous solution before and after light irradiation is ion chromatographed. Measured with a graph.

"Comparative Example 6"
In Example 11, a zinc (Zn) -doped indium phosphide (InP) single crystal substrate (InP / RuCP) modified with ruthenium complex polymer 24 was used as the electrode 10 (working electrode) for the reduction reaction.

"result"
FIG. 13 shows the results of measuring the current efficiency with respect to the oxygen concentration in Example 11 and Comparative Example 6. The circles indicate the measurement results in Example 11, and the triangles indicate the measurement results in Comparative Example 6.

In Example 11, the current efficiency of formic acid production was about 94% when oxygen (O ₂ ) gas was not mixed with carbon dioxide (CO ₂ ) gas. The current efficiency of formic acid production gradually decreased as the concentration of oxygen (O ₂ ) gas increased, and the current efficiency of formic acid production was about 72% when the concentration of oxygen (O ₂ ) gas was 7.2%. .. In Comparative Example 6, the current efficiency of formic acid production when oxygen (O ₂ ) gas was not mixed with carbon dioxide (CO ₂ ) gas was about 93%, which was almost the same as that of Example 11. As the concentration of oxygen (O ₂ ) gas increases, the current efficiency of formic acid production decreases significantly, and when the concentration of oxygen (O ₂ ) gas is 7.2%, the current efficiency of formic acid production is about 6.2%. there were. From this, it was found that the reduction reaction of carbon dioxide (CO ₂ ) by the ruthenium complex polymer 24 modified on the carbon cloth 22 is not easily affected by oxygen.

"Summary"
The reason why the solar conversion efficiency is low in the photoreduction reaction of carbon dioxide (CO ₂ ) is that the amount of light absorption is small, the excited electron-hole pair is recombined before the reaction, and the product is decomposed by the reverse reaction. And so on. According to the present invention, it is possible to increase the amount of light absorption and promote the separation of excited electron / hole pairs by using the three-junction amorphous silicon laminated film. Further, by modifying the electrode for oxidation reaction with an iridium oxide (IrOx) cocatalyst, water can be selectively oxidized even in the presence of a product without proceeding with the reverse reaction. Further, by using the carbon layer as a carrier of the metal complex catalyst, carbon dioxide (CO ₂ ) can be selectively reduced even in the presence of oxygen. As a result, the solar conversion efficiency could be improved to 4.35% in the photoreduction reaction of carbon dioxide (CO ₂ ).

Further, in the prior art, a two-chamber cell in which the reducing side and the oxidizing side are separated by a proton exchange membrane is used in order to prevent decomposition due to a reverse reaction to the product and inhibition of the reaction by the product, but in the present invention, an organic substance is used. The electrode for oxidation reaction has selectivity for the oxidation reaction of water even in the presence, and by supporting the metal complex catalyst by the carbon layer, it is also resistant to the reduction reaction of carbon dioxide (CO ₂ ) even in the presence of oxygen. Since it has selectivity, it can be used as a single-chamber cell by applying a wireless device structure.

10 Reduction reaction electrode, 12 Oxidation reaction electrode, 14 Bias power supply, 16 Catalyst, 20 Three-junction amorphous silicon laminated film, 22 Carbon cloth, 24 Ruthenium complex polymer, 30 Metal substrate, 31 Metal reflective layer, 32 Transparent conductive film , 33 First Amorphous Silicon Germanium Laminate, 34 Second Amorphous Silicon Germanium Laminate, 35 Amorphous Silicon Laminate, 36 Transparent Conductive.

Claims (6)

And oxidation electrode for generating oxygen by oxidizing water to selection択的,
An electrode for reduction reaction containing a metal complex catalyst supported on a carbon layer and selectively reducing carbon dioxide (CO ₂ ) in the presence of oxygen.
Is housed in a one-chamber cell without a proton exchange membrane , including an electrolytic cell constructed by electrically connecting them.
A photochemical reaction device characterized in that the electrolytic cell is connected to a light absorber and carbon dioxide (CO ₂ ) is reduced in a liquid containing water by utilizing the light energy applied to the light absorber . The photochemical reaction device according to claim 1 .
The oxidation reaction electrode is seen containing iridium oxide IrOx (x = 1~2), photochemical reaction device, characterized in that to generate oxygen by selectively oxidizing the water in the presence of carbon compounds. The photochemical reaction device according to claim 2 .
A photochemical reaction device , wherein the carbon compound is at least one of carbon monoxide, an alcohol and a carboxylic acid . The photochemical reaction device according to claim 1.
The reduction reaction electrode is a photochemical reaction device, characterized in that a conjugate having a sequence of the light absorber / the carbon layer / the metal complex catalyst. The photochemical reaction device according to claim 4.
The reduction reaction electrode is a photochemical reaction device, which is a conjugate of multi-junction amorphous silicon laminate / the carbon layer / ruthenium metal complex catalyst. The photochemical reaction device according to any one of claims 1 to 5 .
The oxidation reaction electrode and the reduction reaction electrode are electrically connected to each other by being integrated with each other, and the oxidation reaction electrode has light transmission and is described above. A photochemical reaction device characterized in that it is arranged on the incident side of the light from the electrode for reduction reaction.

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