JP2013253269A - Carbon dioxide reduction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon dioxide reduction device that can increase an amount of a generated fuel material.SOLUTION: A carbon dioxide reduction device includes: a photoelectric conversion layer having a light-receiving surface and a rear surface; an electrolytic solution tank; first and second electrodes for electrolysis, disposed in the electrolytic solution tank to pinch an electrolytic solution; and a COsupply part that supplies carbon dioxide in the electrolytic solution tank, wherein the photoelectric conversion layer and the first and second electrodes for electrolysis are connected so that photoelectromotive force of the photoelectric conversion layer may be output to the first and second electrodes for electrolysis, the first electrode for electrolysis includes a catalyst for carbon dioxide reduction, the second electrode for electrolysis includes a catalyst for oxygen generation, and the first and second electrodes for electrolysis are disposed so that bubbles can be moved between the first and second electrodes for electrolysis.

Description

  The present invention relates to a carbon dioxide reduction device.

Carbon dioxide gas emitted by burning fossil fuel is one of the causes of global warming. For this reason, various research and development have been conducted to reduce the amount of carbon dioxide gas emitted.
In particular, a technique for reducing the carbon dioxide gas to produce a fuel material is attracting attention because it can reduce the amount of carbon dioxide gas discharged and can produce a fuel material. As a method of reducing carbon dioxide gas, a method of reacting carbon dioxide gas and water at a high temperature (for example, Patent Document 1), a method of electrolytic reduction of carbon dioxide in an aqueous solution (for example, Patent Document 2), etc. are proposed. Has been.

JP 2010-163678 A JP 2011-140719 A

However, the conventional technique for reducing the carbon dioxide gas to generate the fuel material has a problem that the amount of the generated fuel material is small and it is difficult to use the fuel material as the fuel.
This invention is made | formed in view of such a situation, and provides the carbon dioxide reduction apparatus which can increase the quantity of the fuel substance produced | generated.

The present invention includes a photoelectric conversion layer having a light-receiving surface and a back surface, an electrolytic solution tank, first and second electrolysis electrodes provided with an electrolytic solution sandwiched in the electrolytic solution tank, and the electrolytic solution tank. A CO ₂ supply section for supplying carbon dioxide, and the photoelectric conversion layer and the first and second electrolysis electrodes output the photovoltaic power of the photoelectric conversion layer to the first and second electrolysis electrodes. The first electrolysis electrode has a carbon dioxide reduction catalyst, the second electrolysis electrode has an oxygen generation catalyst, and the first and second electrolysis electrodes have the first and second electrolysis electrodes. Provided is a carbon dioxide reduction device characterized in that bubbles are provided so as to be movable between two electrolysis electrodes.

According to the present invention, a photoelectric conversion layer, an electrolytic solution tank, first and second electrolysis electrodes provided in the electrolytic solution tank, and a CO ₂ supply unit that supplies carbon dioxide into the electrolytic solution tank And the photoelectric conversion layer and the first and second electrolysis electrodes are connected so that the photovoltaic power of the photoelectric conversion layer is output to the first and second electrolysis electrodes. A potential difference can be generated between the first electrolysis electrode and the second electrolysis electrode by the photovoltaic power of the layer, and water and carbonic acid contained in the electrolytic solution can be reacted electrochemically.
According to the present invention, since the first electrolysis electrode has the carbon dioxide reduction catalyst, the electrolytic reduction reaction of carbonic acid contained in the electrolytic solution can be advanced. As a result, fuel substances such as methanol, ethanol, formaldehyde, acetaldehyde, formic acid or acetic acid can be produced.
According to the present invention, since the second electrolysis electrode has the oxygen generation catalyst, the reaction for generating oxygen from the electrolytic solution can proceed in the second electrolysis electrode.
According to the present invention, the first and second electrolysis electrodes are arranged with the electrolytic solution interposed therebetween, and the bubbles are movably provided between the first and second electrolysis electrodes. A partition wall is not provided between the two electrolysis electrodes, and the interval between the first and second electrolysis electrodes can be narrowed. As a result, the first and second electrolysis electrodes can be provided in the electrolytic solution tank so that the surface area thereof is increased, and the contact area between the first and second electrolysis electrodes and the electrolytic solution can be increased. it can. As a result, the surface area of the carbon dioxide reduction catalyst in which the carbonic acid electroreduction reaction proceeds can be increased, and the amount of fuel material produced by reduction of carbonic acid can be increased. In addition, the carbon dioxide reduction device can be reduced in size. Furthermore, since the distance between the first and second electrolysis electrodes can be narrowed, there is an imbalance in ion concentration between the electrolyte solution near the first electrolysis electrode and the electrolyte solution near the second electrolysis electrode. Generation | occurrence | production can be suppressed and it can suppress that progress of the electrolytic reduction reaction of carbonic acid becomes slow.

It is a schematic plan view which shows the structure of the carbon dioxide reduction apparatus of one Embodiment of this invention. It is a schematic sectional drawing of the carbon dioxide reduction apparatus in the dotted line XX of FIG. It is a schematic sectional drawing of the carbon dioxide reduction apparatus in the broken line YY of FIG. It is a schematic plan view which shows the structure of the carbon dioxide reduction apparatus of one Embodiment of this invention. It is a schematic sectional drawing of the carbon dioxide reduction apparatus in dotted line AA of FIG. It is a schematic sectional drawing of the carbon dioxide reduction apparatus in the broken line BB of FIG. It is a schematic sectional drawing of the carbon dioxide reduction apparatus in the dashed-dotted line CC of FIG. It is a schematic sectional drawing of the carbon dioxide reduction apparatus in the dashed-dotted line DD of FIG. It is a schematic sectional drawing which shows the structure of the carbon dioxide reduction apparatus of one Embodiment of this invention. It is a schematic sectional drawing which shows the structure of the carbon dioxide reduction apparatus of one Embodiment of this invention. It is a schematic sectional drawing which shows the structure of the carbon dioxide reduction apparatus of one Embodiment of this invention. It is a schematic sectional drawing which shows the structure of the carbon dioxide reduction apparatus of one Embodiment of this invention. It is a schematic sectional drawing which shows the structure of the carbon dioxide reduction apparatus of one Embodiment of this invention. It is a schematic sectional drawing which shows the structure of the carbon dioxide reduction apparatus of one Embodiment of this invention. It is a schematic sectional drawing which shows the structure of the carbon dioxide reduction apparatus of one Embodiment of this invention. It is a schematic sectional drawing which shows the structure of the carbon dioxide reduction apparatus of one Embodiment of this invention.

The carbon dioxide reduction device of the present invention includes a photoelectric conversion layer having a light receiving surface and a back surface, an electrolytic solution tank, first and second electrolysis electrodes provided with an electrolytic solution sandwiched in the electrolytic solution tank, A CO ₂ supply unit for supplying carbon dioxide into the electrolytic solution tank, and the photoelectric conversion layer and the first and second electrolysis electrodes have a photovoltaic power of the photoelectric conversion layer for the first and second electrolysis. The first electrolysis electrode has a carbon dioxide reduction catalyst, the second electrolysis electrode has an oxygen generation catalyst, and the first and second electrolysis electrodes are connected to be output to the electrode. Further, the present invention is characterized in that air bubbles are provided between the first and second electrolysis electrodes.
In the present specification, carbon dioxide and carbonic acid (H ₂ CO ₃ ) are used with substantially the same meaning, but in particular, carbon dioxide dissolved in an electrolytic solution is described as carbonic acid.

In the carbon dioxide reduction device of the present invention, it is preferable that the photoelectric conversion layer is provided with the first and second electrolysis electrodes and the electrolytic solution tank on the back side of the photoelectric conversion layer.
According to such a structure, a photoelectric converting layer and the 1st and 2nd electrode for electrolysis can be installed in the same space, and an apparatus can be reduced in size. Moreover, the wiring distance between the photoelectric conversion layer and the first and second electrolysis electrodes can be shortened, and the carbon dioxide reducing substance can be efficiently generated using the photovoltaic power of the photoelectric conversion layer.
In the carbon dioxide reduction device of the present invention, it is preferable that the first and second electrolysis electrodes each have a main surface and are provided so that the main surfaces face each other.
According to such a configuration, the surface areas of the first and second electrolysis electrodes can be increased, and the amount of carbon dioxide reducing substance generated can be increased. Further, the ion concentration imbalance between the electrolytic solution in the vicinity of the first electrolysis electrode and the electrolytic solution in the vicinity of the second electrolysis electrode can be easily eliminated, and the progress of the electroreduction reaction of carbon dioxide can be reduced. The decrease can be suppressed.

In the carbon dioxide reduction device of the present invention, it is preferable that the first and second electrolysis electrodes are arranged so as to be substantially perpendicular to the back surface of the photoelectric conversion layer.
According to such a configuration, the surface areas of the first and second electrolysis electrodes can be increased, and the amount of carbon dioxide reducing substance generated can be increased.
In the carbon dioxide reduction device of the present invention, it is preferable that the first and second electrolysis electrodes are provided so as to be alternately arranged.
According to such a configuration, the surface areas of the first and second electrolysis electrodes can be increased, and the amount of carbon dioxide reducing substance generated can be increased.

In the carbon dioxide reduction device of the present invention, it is preferable that one of the first and second electrolysis electrodes is surrounded by the other.
According to such a configuration, the surface areas of the first and second electrolysis electrodes can be increased, and the amount of carbon dioxide reducing substance generated can be increased.

In the carbon dioxide reduction device of the present invention, each of the first and second electrolysis electrodes has a comb-like structure having a trunk and a plurality of branches extending from the trunk, and the branches of the first electrolysis electrode are second electrolysis. Preferably, the second electrolysis electrode support is disposed between the two support portions of the first electrolysis electrode, and is disposed between the two support portions of the first electrolysis electrode.
According to such a configuration, the surface areas of the first and second electrolysis electrodes can be increased, and the amount of carbon dioxide reducing substance generated can be increased.
In the carbon dioxide reduction device of the present invention, it is preferable that the first and second electrolysis electrodes each have a wound structure.
According to such a configuration, the surface areas of the first and second electrolysis electrodes can be increased, and the amount of carbon dioxide reducing substance generated can be increased.

In the carbon dioxide reduction device of the present invention, the photoelectric conversion layer is provided so that a photovoltaic force is generated between the light receiving surface and the back surface, and one of the first and second electrolysis electrodes is the light receiving device. It is preferable that it is provided so as to be electrically connected to the surface, and the other is provided so as to be electrically connected to the back surface.
According to such a configuration, a stacked solar cell can be used for the photoelectric conversion layer, and the manufacturing cost can be reduced.
In the carbon dioxide reduction device of the present invention, the photoelectric conversion layer is provided so that a photovoltaic force is generated between the first and second areas on the back surface of the photoelectric conversion layer, and the first and second electrolysis electrodes Preferably, one is provided so as to be electrically connected to the first area, and the other is provided so as to be electrically connected to the second area.
According to such a configuration, it is not necessary to provide an electrode on the light receiving surface side of the photoelectric conversion layer, and the photoelectric conversion efficiency of the photoelectric conversion layer can be improved.

In the carbon dioxide reduction apparatus of the present invention, the CO ₂ supply unit includes a CO ₂ flow path and a first gas diffusion unit having water repellency and porosity, and the first gas diffusion unit is introduced into the electrolyte bath. It is preferable to supply carbon dioxide gas.
According to such a configuration, carbon dioxide gas can be supplied to the electrolytic solution stored in the electrolytic solution tank while suppressing the electrolytic solution from flowing into the CO ₂ flow path.

In the carbon dioxide reduction device of the present invention, the CO ₂ supply unit preferably supplies an electrolytic solution in which carbon dioxide is dissolved into the electrolytic solution tank.
According to such a configuration, carbon dioxide gas can be supplied to the electrolytic solution stored in the electrolytic solution tank without providing a gas diffusion portion.
In the carbon dioxide reduction device of the present invention, it is preferable that the apparatus further includes a gas discharge part, and the gas discharge part has a discharge flow path and a second gas diffusion part having water repellency and porosity.
According to such a configuration, the generated gas in the electrolytic solution tank can be discharged from the gas discharge unit, the generated gas stays on the surfaces of the first and second electrolysis electrodes, and the amount of carbon dioxide reducing substance generated Can be reduced. Moreover, it can suppress that electrolyte solution flows in into a discharge flow path.

In the carbon dioxide reduction apparatus of the present invention, it is preferable that a translucent substrate is further provided, and the photoelectric conversion layer is provided on the translucent substrate.
According to such a configuration, the photoelectric conversion layer can be formed on the translucent substrate.
In the carbon dioxide reduction device of the present invention, it is preferable that the apparatus further includes a back substrate, and the electrolyte bath is provided between the translucent substrate and the back substrate.
According to such a structure, an electrolyte solution tank can be provided in the back surface side of a photoelectric converting layer.

In the carbon dioxide reduction device of the present invention, it is preferable that the photoelectric conversion layer includes a plurality of photoelectric conversion units connected in series.
According to such a configuration, the output voltage of the photoelectric conversion layer can be increased, and the electrolytic reduction reaction of carbon dioxide easily proceeds.
In the carbon dioxide reduction apparatus of the present invention, the carbon dioxide reduction catalyst is preferably a catalyst that reduces carbon dioxide to produce methanol, ethanol, propanol, formaldehyde, acetaldehyde, formic acid, or acetic acid.
According to such a configuration, since the carbon dioxide reducing substance is mixed with the electrolytic solution, mixing of the carbon dioxide reducing substance and oxygen gas can be suppressed.

In the carbon dioxide reduction apparatus of the present invention, the carbon dioxide reduction catalyst is a solid metal, an alloy, a metal oxide, or a metal complex, and the solid metal, the alloy, or the metal oxide is Cu, Ag, Fe, or Ni is included, and the metal complex preferably includes Co, Fe, Ni, or Ru.
According to such a structure, the electrolytic reduction reaction of carbon dioxide can be advanced in the first electrode for electrolysis.
In the carbon dioxide reduction apparatus of the present invention, the oxygen generation catalyst preferably contains Mn, Ca, Zn, Co, Pt, Ni, or Ir.
According to such a configuration, oxygen gas can be generated in the second electrolysis electrode.
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The configurations shown in the drawings and the following description are merely examples, and the scope of the present invention is not limited to those shown in the drawings and the following description.

Configuration of Carbon Dioxide Reduction Device FIG. 1 is a schematic plan view showing the configuration of the carbon dioxide reduction device of this embodiment, and FIG. 2 is a schematic cross-sectional view of the carbon dioxide reduction device taken along the dotted line XX in FIGS. FIG. 3 is a schematic cross-sectional view of the carbon dioxide reduction device taken along the broken line YY in FIG.
FIG. 4 is a schematic plan view showing the configuration of the carbon dioxide reduction device of the present embodiment, FIG. 5 is a schematic cross-sectional view of the carbon dioxide reduction device taken along the dotted line AA in FIGS. 8 is a schematic cross-sectional view of the carbon dioxide reduction device taken along the broken line BB in FIGS. 5, 7, and 8. FIG. 7 is a schematic cross-sectional view of the carbon dioxide reduction device taken along the alternate long and short dash line CC in FIGS. FIG. 7 is a schematic cross-sectional view of the carbon dioxide reduction device taken along one-dot chain line DD in FIGS.
9 to 16 are schematic cross-sectional views showing the configuration of the carbon dioxide reduction device of the present embodiment. FIGS. 9 to 12 correspond to the cross-sectional view of FIG. 6, and FIGS. 15 corresponds to the cross-sectional view, FIG. 15 corresponds to the cross-sectional view of the carbon dioxide reduction device taken along the dotted line EE in FIG. 9, and FIG. 16 corresponds to the cross-sectional view of the carbon dioxide reduction device taken along the dotted line FF in FIG. .

The carbon dioxide reduction device 35 of the present embodiment includes a photoelectric conversion layer 3 having a light receiving surface and a back surface, an electrolytic solution tank 10, and first and second electrolysis units provided with an electrolytic solution in the electrolytic solution tank 10. The electrodes 8 and 9 and the CO ₂ supply part 22 for supplying carbon dioxide into the electrolytic solution tank 10 are provided, and the photoelectric conversion layer 3 and the first and second electrodes for electrolysis 8 and 9 are formed of the photoelectric conversion layer 3. Photoelectromotive force is connected to be output to the first and second electrolysis electrodes 8, 9. The first electrolysis electrode 8 has a carbon dioxide reduction catalyst, and the second electrolysis electrode 9 is oxygen It has a production catalyst, and the first and second electrolysis electrodes 8 and 9 are characterized in that bubbles are provided between the first and second electrolysis electrodes 8 and 9.
Hereinafter, the carbon dioxide reduction device 35 of the present embodiment will be described. The carbon dioxide reduction device 35 of this embodiment is an electrolysis in which the photoelectric conversion layer 3 and the first and second electrolysis electrodes 8 and 9 as shown in FIGS. 1 to 3 or 4 to 8 are provided. A carbon dioxide reduction device 35 (hereinafter referred to as a photoelectric conversion-carbon dioxide reduction integrated device) integrated with the liquid tank 10 may be used, and the photoelectric conversion layer 3 and the first and second electrolysis electrodes 8, 9 may be provided. The carbon dioxide reduction apparatus 35 provided separately from the electrolytic solution tank 10 provided therein may be used.
Moreover, the photoelectric conversion / carbon dioxide reduction integrated apparatus may have a flat shape. Here, the flat shape is a shape having a relatively thin thickness, for example, a shape whose thickness is 10% or less of the length in the main surface direction.

1. First Electrolysis Electrode, Second Electrolysis Electrode, Electrolytic Solution The first electrolysis electrode 8 and the second electrolysis electrode 9 are provided in an electrolytic solution tank 10 that stores an electrolytic solution. As a result, the photoelectromotive force of the photoelectric conversion layer 3 is output between the first and second electrolysis electrodes 8 and 9, so that the surface of the first and second electrolysis electrodes 8 and 9 is electrochemical. The reaction can proceed. The electrolytic solution may be an electrolytic solution (aqueous electrolyte solution) using water as a solvent, or an organic electrolytic solution. The electrolytic solution is not particularly limited as long as it is an electrolytic solution using water as a solvent. For example, carbonates (including normal salts, bicarbonates, carbonates) such as sodium bicarbonate aqueous solution and potassium bicarbonate aqueous solution. Is an electrolyte solution. Further, the electrolytic solution may include a plurality of types of electrolytes.
The electrolyte bath 10 is not particularly limited as long as the first electrolysis electrode 8 and the second electrolysis electrode 9 can be disposed therein and the electrolyte can be stored. Moreover, the electrolyte solution tank 10 can have a temperature control part which controls the temperature of electrolyte solution. For example, a heater or a cooling unit. Thus, the temperature of the electrolytic solution can be controlled to an optimum temperature at which the electrolytic reduction reaction of carbonic acid proceeds. The temperature of the electrolytic solution can be controlled, for example, in the range of 10 ° C to 80 ° C.
The electrolytic solution tank 10 in the case where the carbon dioxide reducing device as shown in FIGS. 1 to 3 or 4 to 8 is an integrated photoelectric conversion / carbon dioxide reducing device will be described later.

The first electrolysis electrode 8 and the second electrolysis electrode 9 are connected to the photoelectric conversion layer 3 so that the photovoltaic power of the photoelectric conversion layer 3 is output to the first and second electrolysis electrodes 8 and 9. . Thereby, the electrolytic reduction reaction of carbonic acid can be advanced using the photovoltaic power of the photoelectric conversion layer 3, and carbon dioxide can be reduced without discharging carbon dioxide.
The first electrolysis electrode 8 and the second electrolysis electrode 9 and the photoelectric conversion layer 3 are electrically connected so that the photoelectromotive force of the photoelectric conversion layer 3 is always output to the first and second electrolysis electrodes 8 and 9. The photovoltaic power of the photoelectric conversion layer 3 may be connected to the first and second electrolysis electrodes 8 and 9 via a switch.
When the photoelectric conversion layer 3 and the electrolyte bath 10 in which the first and second electrolysis electrodes 8 and 9 are provided are provided separately, the photoelectric conversion layer 3 and the first and second electrolysis electrodes 8 and 8 9 may be connected by a conducting wire or the like. Further, in the case of the photoelectric conversion-carbon dioxide reduction integrated device, the photoelectric conversion layer 3 and the first and second electrolysis electrodes 8 and 9 are the translucent electrode 5 provided on the light receiving surface side of the photoelectric conversion layer 3, You may connect via the back surface electrode 6 provided in the back surface side of the photoelectric converting layer 3, and the electroconductive part 20a.

The first and second electrodes for electrolysis 8 and 9 and the electrolytic solution tank 10 may be provided on the back side of the photoelectric conversion layer 3. Thus, the photoelectric conversion layer 3, the first and second electrolysis electrodes 8 and 9, and the electrolytic solution tank 10 can be arranged in the same space. As a result, the wiring distance between the photoelectric conversion layer 3 and the first and second electrolysis electrodes 8 and 9 can be shortened, and the photovoltaic power of the photoelectric conversion layer 3 can be efficiently used to generate carbon dioxide. Can be reduced. Further, since the wiring distance between the photoelectric conversion layer 3 and the first and second electrolysis electrodes 8 and 9 is shortened, the carbon dioxide reduction device 35 can be further simplified, and the carbon dioxide reduction device 35 is installed. Costs and maintenance costs can be reduced.
Moreover, the electrolytic solution tank 10 may be provided over substantially the entire back surface side of the photoelectric conversion layer 3.
The photoelectric conversion layer 3, the first and second electrolysis electrodes 8, 9 and the electrolytic solution tank 10 are configured as separate devices, and on the back side of the photoelectric conversion layer 3 of the device including the photoelectric conversion layer 3, An apparatus including the first and second electrolysis electrodes 8 and 9 and the electrolytic solution tank 10 may be provided. Further, the photoelectric conversion layer 3, the first and second electrolysis electrodes 8, 9 and the electrolytic solution tank 10 are the photoelectric conversion / carbon dioxide reduction integrated apparatus as shown in FIGS. Thus, it may be configured as an integrated device.

  The first electrolysis electrode 8 has a carbon dioxide reduction catalyst, and the second electrolysis electrode 9 has an oxygen generation catalyst that generates oxygen gas as bubbles. Further, the first and second electrolysis electrodes 8 and 9 are arranged with the electrolytic solution interposed therebetween. Accordingly, the electrolytic reduction reaction of carbonic acid can proceed in the first electrolysis electrode 8, and the reaction in which water is electrolyzed and oxygen gas is generated can proceed in the second electrolysis electrode.

The catalyst for reducing carbon dioxide may be a catalyst that reduces carbon dioxide to produce methanol, ethanol, propanol, formaldehyde, acetaldehyde, formic acid or acetic acid (hereinafter referred to as carbon dioxide reducing substance). Further, the carbon dioxide reduction catalyst may be a catalyst that selectively generates these substances. As a result, carbon dioxide reducing substances can be produced, and these substances can be used as fuel or the like. Further, since these carbon dioxide reducing substances are mixed with the electrolytic solution, the carbon dioxide reducing substances are recovered by recovering the electrolytic solution from the electrolytic solution tank 10 and separating it from the electrolytic solution. For example, the electrolytic solution mixed with the carbon dioxide reducing substance can be recovered by discharging the electrolytic solution from the electrolytic solution discharge port 29 while injecting the electrolytic solution into the electrolytic solution tank 10 from the electrolytic solution injection port 30. . The carbon dioxide reducing substance can be separated and recovered from the recovered electrolytic solution, and the separated electrolytic solution can be injected again into the electrolytic solution tank 10 from the electrolytic solution inlet 30. In this way, the carbon dioxide reducing substance can be recovered.
In addition, since the carbon dioxide reducing substance is mainly mixed in the electrolyte, it is possible to suppress the oxidation of the carbon dioxide reducing substance caused by mixing the oxygen gas generated in the second electrolysis electrode 9 and the carbon dioxide reducing substance. The amount of carbon dioxide reducing substance recovered can be increased. Further, since the carbon dioxide reducing substance is mainly mixed in the electrolytic solution, it is not necessary to provide a partition wall for separating the generated gas between the first electrolysis electrode 8 and the second electrolysis electrode 9. Accordingly, the first and second electrolysis electrodes 8 and 9 are provided between the first and second electrolysis electrodes 8 and 9 so that the bubbles of oxygen gas generated in the second electrolysis electrode 9 can move. . As a result, the distance between the first and second electrolysis electrodes 8 and 9 can be reduced. Accordingly, the first and second electrolysis electrodes 8 and 9 can be provided in the electrolytic solution tank 10 so that the surfaces thereof are widened, and the contact area between the first and second electrolysis electrodes 8 and 9 and the electrolytic solution can be increased. Can be widened. Thus, the surface area of the carbon dioxide reduction catalyst in which the electrolytic reduction reaction of carbonic acid proceeds can be increased, and the amount of carbon dioxide reducing substance produced by reduction of carbonic acid can be increased. Further, the carbon dioxide reduction device 35 can be reduced in size. Further, since the distance between the first and second electrolysis electrodes 8 and 9 can be narrowed, ions are present between the electrolyte near the first electrolysis electrode 8 and the electrolyte near the second electrolysis electrode 9. The occurrence of concentration imbalance can be suppressed, and the progress of the electrolytic reduction reaction of carbonic acid can be suppressed.
Note that the carbon dioxide reduction device 35 may include a partition as long as bubbles can move between the first and second electrolysis electrodes 8 and 9.

  The carbon dioxide reduction catalyst may be one that reduces carbon dioxide to produce methane, ethane, carbon monoxide, or ethylene, or may produce hydrogen from water. In this case, the produced gas such as methane and hydrogen is recovered by being separated from the mixed gas with the oxygen gas generated in the second electrolysis electrode 9.

Examples of the carbon dioxide reduction catalyst include solid metals, alloys, metal oxides, and metal complexes. The solid metal, the alloy, or the metal oxide contains, for example, Cu, Ag, Fe, or Ni. The solid metal, the alloy, or the metal oxide may contain a group V element (vanadium, niobium, tantalum), Pb, In, Sn, Cd, Zn, Au, or Ag.
The metal complex includes, for example, Co, Fe, Ni, or Ru. Further, the metal complex is a metal complex containing at least one element selected from Group VII and Group VIII elements, for example, at least one selected from ruthenium, rhenium, manganese, osmium, rhodium, iridium, nickel, palladium, platinum and the like. It may be a metal complex containing these elements.
When the carbon dioxide reduction catalyst is a conductive material such as a solid metal or an alloy, the first electrolysis electrode 8 and the carbon dioxide reduction catalyst may be the same. For example, when the first electrolysis electrode 8 and the carbon dioxide reduction catalyst are made of a copper plate, the surface of the copper plate that is the first electrolysis electrode 8 is the carbon dioxide reduction catalyst.
The first electrolysis electrode 8 and the carbon dioxide reduction catalyst are supported on, for example, a metal plate, a porous layer made of porous carbon or porous metal formed thereon, and the porous layer. You may comprise from metals, such as Cu, Ag, and Ni, or metal oxides, such as CuO, AgO, and NiO. As a result, the surface area of the carbon dioxide reduction catalyst can be increased, and the amount of carbon dioxide reducing substance produced can be increased. The first electrolysis electrode 8 and the carbon dioxide reduction catalyst may have a structure in which a metal that becomes a carbon dioxide reduction catalyst is deposited on the surface of the metal plate by electrolytic deposition. Furthermore, you may have the structure which formed the film containing carbon dioxide reduction catalysts, such as a metal complex.
The carbon dioxide reduction catalyst may be any catalyst that can reduce carbon dioxide, and is not limited to the example shown here.

The catalyst for generating oxygen is, for example, a catalyst containing Mn, Ca, Zn, Co, or Ir. When the oxygen generation catalyst is a conductive material such as a solid metal or an alloy, the second electrolysis electrode 9 and the oxygen generation catalyst may be the same. For example, when the second electrolysis electrode 9 and the oxygen generation catalyst are made of a copper plate, the surface of the copper plate that is the second electrolysis electrode 9 is the oxygen generation catalyst. The second electrolysis electrode 9 and the oxygen generation catalyst include, for example, a metal plate, a porous layer made of porous carbon or porous metal formed thereon, and Mn supported on the porous layer. , Ca, Zn, Co, Ir, and the like, or a metal oxide thereof. As a result, the surface area of the oxygen generation catalyst can be increased, and a reduction in the reaction rate of the electrolytic reaction can be suppressed.
The oxygen generation catalyst may be any catalyst that can generate oxygen, and is not limited to the example shown here.

For example, as in the carbon dioxide reduction apparatus shown in FIGS. 1 to 3, the first and second electrolysis electrodes 8 and 9 are provided so that their main surfaces are substantially parallel to the back surface of the photoelectric conversion layer 3. be able to. Thus, the first and second electrolysis electrodes 8 and 9 can be easily provided, and the manufacturing cost can be reduced.
For example, like the carbon dioxide reduction apparatus shown in FIGS. 4 to 8, the first and second electrolysis electrodes 8 and 9 each have a main surface and are provided so that the main surfaces face each other. Also good. As a result, the surface areas of the first and second electrolysis electrodes 8 and 9 can be increased, and the amount of carbon dioxide reducing substance generated can be increased. Further, the ion concentration imbalance between the electrolytic solution in the vicinity of the first electrolysis electrode 8 and the electrolytic solution in the vicinity of the second electrolysis electrode 9 can be easily eliminated, and the progress rate of the electrolytic reduction reaction of carbonic acid can be reduced. The decrease can be suppressed.
Moreover, for example, like the carbon dioxide reduction apparatus shown in FIGS. 4 to 8, the first and second electrolysis electrodes 8 and 9 each have a main surface and are provided on the back surface side of the photoelectric conversion layer 3. You may arrange | position so that it may become substantially perpendicular | vertical with respect to the back surface of the photoelectric converting layer 3. FIG. Accordingly, the photoelectric conversion layer 3 and the first and second electrolysis electrodes 8 and 9 can be arranged in the same space, and the surface area of the first and second electrolysis electrodes 8 and 9 can be increased. Can do. As a result, the amount of carbon dioxide reducing substance produced can be increased.
In this case, the photoelectric conversion-carbon dioxide reduction integrated device may be used, and the photoelectric conversion layer 3, the first and second electrolysis electrodes 8, 9 and the electrolyte bath 10 may be configured as separate devices. Good.

  Further, the first and second electrolysis electrodes 8 and 9 may be provided so as to be alternately arranged. As a result, the surface areas of the first and second electrolysis electrodes 8 and 9 can be increased, and the amount of the carbon dioxide reducing substance produced can be increased. The first and second electrolysis electrodes 8 and 9 may be arranged at an interval of 0.5 cm to 10 cm, for example.

  The first and second electrolysis electrodes 8 and 9 can be provided so that the first electrolysis electrodes 8 and the second electrolysis electrodes 9 are alternately arranged, for example, as shown in FIGS. Further, the first and second electrolysis electrodes 8 and 9 can be provided so that one of the first electrolysis electrode 8 and the second electrolysis electrode 9 is surrounded by the other, as shown in FIGS. . Further, the first and second electrolysis electrodes 8 and 9 have, for example, a comb structure having a trunk and a plurality of branches extending from the trunk as shown in FIG. May be disposed between the two branches of the second electrolysis electrode 9, and the branch of the second electrolysis electrode 9 may be disposed between the two branches of the first electrolysis electrode 8. The first and second electrolysis electrodes 8 and 9 may each have a wound structure as shown in FIGS.

In addition, the first and second electrolysis electrodes 8 and 9 can have gas discharge paths. As a result, it is possible to suppress the generation gas from staying on the surface of the first electrolysis electrode 8 and inhibiting the progress of the electrolytic reduction reaction of carbonic acid, and the generation gas stays on the surface of the second electrolysis electrode 9. It is possible to suppress the progress of the oxygen gas generation reaction. The gas discharge path is not limited as long as it is for discharging the generated gas. For example, the gas discharge path may be an opening formed in the first electrolysis electrode 8 or the second electrolysis electrode 9. There may be.
For example, when the carbon dioxide reduction device 35 has the configuration as shown in FIGS. 1 to 3 or FIGS. 4 to 8, bubbles of oxygen gas generated in the second electrolysis electrode 9 are discharged from the gas discharge unit 26. The carbon dioxide reduction device 35 is installed so that the gas discharge unit 26 is at the top. Thereby, oxygen gas can be moved to the gas discharge part 26 by the buoyancy of bubbles. 7 and 8, the first electrolysis electrode 8 has a cut portion serving as a gas exhaust path in a portion adjacent to the gas exhaust portion 26, so that bubbles are formed on the surface of the first electrolysis electrode 8. The gas is discharged from the gas discharge unit 26 without stagnation.

Even when the carbon dioxide reduction device 35 has a cross section as shown in FIG. 9, the first electrolysis electrode 8 can have a cut portion similar to the cut portion as shown in FIGS. 7 and 8.
When the carbon dioxide reduction device 35 has a cross section as shown in FIGS. 10 to 12, the first electrolysis electrode 8 and the second electrolysis electrode 9 are formed with a discharge path composed of an opening and a cut portion, whereby the first electrolysis It can suppress that a bubble stays on the surface of the electrode 8 and the electrode 9 for 2nd electrolysis.

2. Photoelectric Conversion Layer, Translucent Substrate The photoelectric conversion layer 3 is not particularly limited as long as it can output photovoltaic power to the first and second electrolysis electrodes 8, 9. For example, photoelectric conversion layers using a silicon-based semiconductor can be used. A conversion layer, a photoelectric conversion layer using a compound semiconductor, a photoelectric conversion layer using a dye sensitizer, a photoelectric conversion layer using an organic thin film, and the like.
The carbon dioxide reduction device may have a translucent electrode on the light receiving surface side of the photoelectric conversion layer, and has a translucent electrode and a back electrode for outputting the photovoltaic power of the photoelectric conversion layer. Also good. When the carbon dioxide reducing device is a photoelectric conversion-carbon dioxide reducing integrated device, the carbon dioxide reducing device may have an insulating layer between the photoelectric conversion layer and the first and second electrolysis electrodes.

2-1. Translucent substrate The translucent substrate 1 may be provided in the carbon dioxide reduction device 35 of the present embodiment. Moreover, the photoelectric conversion layer 3 may be provided on the translucent substrate 1 so that the light receiving surface is on the translucent substrate 1 side. The translucent substrate 1 is a member that serves as a base for forming the photoelectric conversion layer 3, and is a member for protecting the photoelectric conversion layer 3. In addition, when the photoelectric converting layer 3 consists of a semiconductor substrate etc. and has fixed intensity | strength, the translucent board | substrate 1 can be abbreviate | omitted. Further, when the photoelectric conversion layer 3 can be formed on a flexible material such as a resin film, the translucent substrate 1 can be omitted.
When the carbon dioxide reducing device 35 is a photoelectric conversion-carbon dioxide reducing integrated device, the translucent substrate 1 can be an outer wall portion of the electrolytic solution tank 10.

In addition, the translucent substrate 1 is preferably transparent and has high light transmittance, but the light transmittance is not limited as long as the light can be efficiently incident on the photoelectric conversion layer 3.
As a substrate material having a high light transmittance, for example, a transparent rigid material such as soda glass, quartz glass, Pyrex (registered trademark), or a synthetic quartz plate, or a transparent resin plate or film material is preferably used. In view of chemical and physical stability, it is preferable to use a glass substrate.
On the surface of the translucent substrate 1 on the photoelectric conversion layer 3 side, a fine uneven structure can be formed so that incident light is effectively irregularly reflected on the surface of the photoelectric conversion layer 3. This fine concavo-convex structure can be formed by a known method such as reactive ion etching (RIE) treatment or blast treatment.

2-2. Translucent Electrode The translucent electrode 5 can be provided on the translucent substrate 1, and can be provided in contact with the light receiving surface of the photoelectric conversion layer 3. Further, the translucent electrode 5 may be provided directly on the light receiving surface of the photoelectric conversion layer 3 when the translucent substrate 1 can be omitted. The translucent electrode 5 can be electrically connected to one of the first electrolysis electrode 8 and the second electrolysis electrode 9. By providing the translucent electrode 5, the current flowing between the light receiving surface of the photoelectric conversion layer 3 and the first electrolysis electrode 8 or the second electrolysis electrode 9 can be increased. Further, when the photoelectric conversion layer 3 generates an electromotive force between the first area and the second area on the back surface of the photoelectric conversion layer 3 as shown in FIGS. 15 and 16, the translucent electrode 5 is unnecessary. .
The translucent electrode 5 may be electrically connected to the first electrolysis electrode 8 or the second electrolysis electrode 9 via a conductive wire or the like, and the first translucent electrode 5 via the conductive portion 20a as shown in FIGS. The electrode 8 for electrolysis or the electrode 9 for second electrolysis may be electrically connected.
The translucent electrode 5 may be made of a transparent conductive film such as ITO or SnO ₂ or may be made of a metal finger electrode such as Ag or Au.

Here, a case where the carbon dioxide reduction device is a photoelectric conversion-carbon dioxide reduction integrated device and the translucent electrode 5 is a transparent conductive film will be described.
The transparent conductive film is used to facilitate contact between the light receiving surface of the photoelectric conversion layer 3 and the first electrolysis electrode 8 or the second electrolysis electrode 9.
What is generally used as a transparent electrode can be used. Specifically, In—Zn—O (IZO), In—Sn—O (ITO), ZnO—Al, Zn—Sn—O, SnO _{2 and the} like can be given. The transparent conductive film preferably has a sunlight transmittance of 85% or more, particularly 90% or more, and particularly 92% or more. This is because the photoelectric conversion layer 3 can absorb light efficiently.
As a method for producing the transparent conductive film, a known method can be used, and examples thereof include sputtering, vacuum deposition, sol-gel method, cluster beam deposition method, and PLD (Pulse Laser Deposition) method.

The conductive portion 20a can be provided so as to be in contact with the translucent electrode 5 and the first electrolysis electrode 8 or the second electrolysis electrode 9 respectively. By providing the conductive portion 20a, the translucent electrode 5 in contact with the light receiving surface of the photoelectric conversion layer 3 and the first electrolysis electrode 8 or the second electrolysis electrode 9 can be easily electrically connected.
In addition, the conductive part 20 a may be provided in a contact hole that penetrates the photoelectric conversion layer 3. As a result, the current path between the light receiving surface of the photoelectric conversion layer 3 and the first electrolysis electrode 8 or the second electrolysis electrode 9 can be shortened, and the carbon dioxide can be electrolytically reduced more efficiently. . Further, the contact hole provided with the conductive portion 20a may be one or plural, and may have a circular cross section.
Moreover, the electroconductive part 20a may be provided on the side surface of the photoelectric converting layer 3 like FIG.

  The material of the electroconductive part 20 will not be restrict | limited especially if it has electroconductivity. A paste containing conductive particles, for example, a carbon paste, an Ag paste or the like applied by screen printing, an inkjet method, etc., dried or baked, a method of forming a film by a CVD method using a raw material gas, a PVD method, Examples thereof include a vapor deposition method, a sputtering method, a sol-gel method, and a method using an electrochemical redox reaction. Note that the material and manufacturing method of the conductive portion 20 are applicable to other conductive portions 20 included in the carbon dioxide reduction device 35 as long as there is no contradiction.

2-3. Photoelectric Conversion Layer The photoelectric conversion layer 3 has a light receiving surface and a back surface thereof. The light receiving surface is a surface that receives light for photoelectric conversion, and the back surface is the back surface of the light receiving surface. In addition, the photoelectric conversion layer 3 can be provided on the translucent substrate 1 on which the translucent electrode 5 is provided with the light receiving surface facing down. For example, the photoelectric conversion layer 3 may be one in which an electromotive force is generated between the light receiving surface and the back surface as illustrated in FIGS. 2, 5, 7, and 8. An electromotive force may be generated between the first area and the second area on the back surface. The photoelectric conversion layer 3 as shown in FIG. 15 can be formed by a semiconductor substrate on which the n-type semiconductor portion 40 and the p-type semiconductor portion 39 are formed.
Although the shape of the photoelectric converting layer 3 is not specifically limited, For example, it can be made into a square shape.
The photoelectric conversion layer 3 is not particularly limited as long as it can separate charges by incident light and generates an electromotive force. For example, the photoelectric conversion layer using a silicon-based semiconductor or the photoelectric conversion layer using a compound semiconductor And a photoelectric conversion layer using a dye sensitizer and a photoelectric conversion layer using an organic thin film.

  When the photoelectric conversion layer 3 receives light, an electromotive force necessary for advancing the electrolytic reduction reaction of carbonic acid in the first electrolysis electrode 8 and advancing the oxygen generation reaction in the second electrolysis electrode 9 is generated. It is necessary to use materials. Therefore, the photoelectric conversion layer 3 can connect two or more junctions in series such as a pn junction to generate an electromotive force. For example, in the case of the photoelectric conversion layer 3 in which an electromotive force is generated between the light receiving surface and the back surface as shown in FIGS. 7 and 8, the photoelectric conversion layer 3 has a structure in which a plurality of photoelectric conversion portions having a pn junction are stacked. Can do. 15 and 16, in the case of the photoelectric conversion layer 3 in which an electromotive force is generated between the first area and the second area on the back surface, the photoelectric conversion layer 3 includes the n-type semiconductor portion 40 and the p-type semiconductor portion, respectively. The photoelectric conversion part in which 39 is formed can have a structure in which the conductive part 20d is connected in series.

  Examples of the material that performs photoelectric conversion include silicon-based semiconductors, compound semiconductors, and materials based on organic materials, and any photoelectric conversion material can be used. In order to increase the electromotive force, these photoelectric conversion materials can be stacked. In the case of stacking, it is possible to form a multi-junction structure with the same material, but stacking multiple photoelectric converters with different optical band gaps and complementing the low sensitivity wavelength regions of each photoelectric converter By doing so, incident light can be efficiently absorbed over a wide wavelength region. The plurality of photoelectric conversion units preferably have different band gaps. According to such a configuration, the electromotive force generated in the photoelectric conversion layer 3 can be further increased, and the electrolytic reduction reaction of carbonic acid can be efficiently advanced.

Moreover, it is possible to interpose a conductor such as a transparent conductive film between the photoelectric conversion units in order to improve the serial connection characteristics between the photoelectric conversion units and to match the photocurrent generated in the photoelectric conversion layer 3. Thereby, deterioration of the photoelectric conversion layer 3 can be suppressed.
An example of the photoelectric conversion layer 3 will be specifically described below. The photoelectric conversion layer 3 may be a combination of these. Moreover, the following examples of the photoelectric conversion layer 3 can be used as a photoelectric conversion part as long as there is no contradiction.

2-3-1. Photoelectric conversion layer using a silicon-based semiconductor Examples of the photoelectric conversion layer 3 using a silicon-based semiconductor include a single crystal type, a polycrystalline type, an amorphous type, a spherical silicon type, and a combination thereof. Any of them can have a pn junction in which a p-type semiconductor and an n-type semiconductor are joined. Further, a pin junction in which an i-type semiconductor is provided between a p-type semiconductor and an n-type semiconductor may be provided. Further, it may have a plurality of pn junctions, a plurality of pin junctions, or a pn junction and a pin junction.
The silicon-based semiconductor is a semiconductor containing silicon, such as silicon, silicon carbide, or silicon germanium. In addition, silicon or the like in which n-type impurities or p-type impurities are added is included, and crystalline, amorphous, or microcrystalline silicon is also included.
Further, the photoelectric conversion layer 3 using a silicon-based semiconductor may be a thin film or a thick film photoelectric conversion layer formed on the translucent substrate 1, or a pn junction or a wafer such as a silicon wafer. A pin junction may be formed, or a thin film photoelectric conversion layer may be formed on a wafer having a pn junction or a pin junction.

An example of forming the photoelectric conversion layer 3 using a silicon-based semiconductor is shown below.
On the translucent electrode 5 laminated on the translucent substrate 1, a first conductivity type semiconductor layer is formed by a method such as plasma CVD. As the first conductive type semiconductor layer, a p ⁺ type or n ⁺ type amorphous Si thin film doped with a conductivity type determining impurity atom concentration of about 1 × 10 ^{18 to} 5 × 10 ²¹ / cm ³ , or many A crystalline or microcrystalline Si thin film is used. The material of the first conductivity type semiconductor layer is not limited to Si, and it is also possible to use a compound such as SiC, SiGe, or Si _x O _1-x .

On the first conductivity type semiconductor layer thus formed, a polycrystalline or microcrystalline crystalline Si thin film is formed as a crystalline Si photoactive layer by a method such as plasma CVD. The conductivity type is the first conductivity type having a lower doping concentration than the first conductivity type semiconductor, or the i conductivity type. The material for the crystalline Si-based photoactive layer is not limited to Si, and it is also possible to use a compound such as SiC, SiGe, or Si _x O _1-x .

Next, in order to form a semiconductor junction on the crystalline Si-based photoactive layer, a second conductivity type semiconductor layer having a conductivity type opposite to the first conductivity type semiconductor layer is formed by a method such as plasma CVD. As the second conductive type semiconductor layer, an n ⁺ type or p ⁺ type amorphous Si thin film doped with about 1 × 10 ^{18 to} 5 × 10 ²¹ / cm ³ of a conductivity type determining impurity atom, or polycrystalline Alternatively, a microcrystalline Si thin film is used. The material of the second conductivity type semiconductor layer is not limited to Si, and it is also possible to use a compound such as SiC, SiGe, or Si _x O _1-x . In order to further improve the bonding characteristics, it is possible to insert a substantially i-type non-single-crystal Si-based thin film between the crystalline Si-based photoactive layer and the second conductive type semiconductor layer. In this manner, one photoelectric conversion portion closest to the light receiving surface can be stacked.

  Subsequently, a second layer photoelectric conversion portion is formed. The photoelectric conversion part of the second layer is composed of a first conductive type semiconductor layer, a crystalline Si-based photoactive layer, and a second conductive type semiconductor layer, and each layer corresponds to the first photoelectric conversion part. The first conductive type semiconductor layer, the crystalline Si-based photoactive layer, and the second conductive type semiconductor layer are formed. When a potential sufficient for water splitting cannot be obtained with a two-layer tandem, it is preferable to take a three-layer structure or more. However, it is preferable that the volume crystallization fraction of the crystalline Si-based photoactive layer of the photoelectric conversion part of the second layer is higher than that of the crystalline Si-based photoactive layer of the first layer. Similarly, when three or more layers are laminated, it is preferable to increase the volume crystallization fraction as compared with the lower layer. This increases the absorption in the long wavelength region, shifts the spectral sensitivity to the long wavelength side, and can improve the sensitivity in a wide wavelength region even when the photoactive layer is configured using the same Si material. It is because it becomes. That is, by using a tandem structure with Si having different crystallization rates, the spectral sensitivity is widened, and light can be used with high efficiency. At this time, if the low crystallization rate material is not on the light receiving surface side, high efficiency cannot be achieved. Further, when the crystallization rate is lowered to 40% or less, the amorphous component increases and deterioration occurs.

Next, an example of forming the photoelectric conversion layer 3 using a silicon substrate is shown below.
As the silicon substrate, a single crystal silicon substrate, a polycrystalline silicon substrate, or the like can be used, and may be p-type, n-type, or i-type. An n-type semiconductor portion 40 is formed by doping an n-type impurity such as P into a part of this silicon substrate by thermal diffusion or ion implantation, and a p-type impurity such as B is heated on the other part of the silicon substrate. The p-type semiconductor portion 39 can be formed by doping by diffusion or ion implantation. Thus, pn junction in the silicon substrate, pin junction can be formed and npp ⁺ junction or pnn ⁺ junction, it is possible to form a photoelectric conversion layer 3.
In such a photoelectric conversion layer 3, the surface of the silicon substrate on which the n-type semiconductor portion 40 and the p-type semiconductor portion 39 are formed is the back surface of the photoelectric conversion layer 3, and the opposite surface is the light receiving surface. In addition, one of the areas where the n-type semiconductor part 40 and the p-type semiconductor part 39 are formed on the back surface of the photoelectric conversion layer 3 is a first area, and the other is a second area. Between the first and second areas. One of the first area and the second area can be electrically connected to the first electrolysis electrode 8 and the other can be electrically connected to the second electrolysis electrode 9. This electrical connection may be connected by a conductive wire, may be connected by direct contact, or may be connected by conductive portions 20b and 20c as shown in FIGS.

Each of the n-type semiconductor unit 40 and the p-type semiconductor unit 39 can form one region on the silicon substrate, and a plurality of either one of the n-type semiconductor unit 40 and the p-type semiconductor unit 39 can be formed. . 15 and 16, the photoelectric conversion layer 3 can also be formed by arranging and arranging silicon substrates on which the n-type semiconductor portion 40 and the p-type semiconductor portion 39 are formed and connecting them in series by the conductive portion 20d.
Note that, although described with reference to a silicon substrate, pn junction, pin junction, may use other semiconductor substrate or the like can be formed npp ⁺ junction or pnn ⁺ junction. Moreover, as long as the n-type semiconductor part 40 and the p-type semiconductor part 39 can be formed, the semiconductor layer is not limited to the semiconductor substrate, and may be a semiconductor layer formed on the substrate.

2-3-2. Photoelectric Conversion Layer Using Compound Semiconductor Photoelectric conversion layer 3 using a compound semiconductor is, for example, CdTe / CdS composed of GaP, GaAs, InP, InAs, and II-VI group elements composed of III-V group elements. And CIGS (Copper Indium Gallium DiSelenide) composed of I-III-VI group and the like, and a pn junction formed.

An example of a manufacturing method of the photoelectric conversion layer 3 using a compound semiconductor is shown below. In this manufacturing method, all the film forming processes are performed using a metal organic chemical vapor deposition (MOCVD) apparatus. It is done continuously. As a group III element material, for example, an organic metal such as trimethylgallium, trimethylaluminum, or trimethylindium is supplied to the growth apparatus using hydrogen as a carrier gas. For example, a gas such as arsine (AsH ₃ ), phosphine (PH ₃ ), and stibine (SbH ₃ ) is used as the material of the group V element. As a dopant of p-type impurities or n-type impurities, for example, diethyl zinc for p-type conversion, monosilane (SiH ₄ ), disilane (Si ₂ H ₆ ), hydrogen selenide (H ₂ Se) for n-type conversion. Etc. are used. These source gases can be thermally decomposed by supplying them onto a substrate heated to, for example, 700 ° C., and a desired compound semiconductor material film can be epitaxially grown. The composition of these growth layers can be controlled by the gas composition to be introduced, and the film thickness can be controlled by the gas introduction time. When multi-junction laminating these photoelectric conversion parts, it is possible to form a growth layer with excellent crystallinity by adjusting the lattice constant between layers as much as possible, and to improve the photoelectric conversion efficiency. Become.

  In addition to the portion where the pn junction is formed, for example, a known window layer on the light receiving surface side or a known electric field layer on the non-light receiving surface side may be provided to improve carrier collection efficiency. Further, a buffer layer for preventing diffusion of impurities may be provided.

2-3-3. Photoelectric Conversion Layer Using Dye Sensitizer The photoelectric conversion layer 3 using a dye sensitizer is mainly composed of, for example, a porous semiconductor, a dye sensitizer, an electrolyte, a solvent, and the like.
As a material constituting the porous semiconductor, for example, one or more kinds of known semiconductors such as titanium oxide, tungsten oxide, zinc oxide, barium titanate, strontium titanate, cadmium sulfide can be selected. As a method for forming a porous semiconductor on a substrate, a paste containing semiconductor particles is applied by a screen printing method, an ink jet method and the like, dried or baked, a method of forming a film by a CVD method using a raw material gas, etc. , PVD method, vapor deposition method, sputtering method, sol-gel method, method using electrochemical oxidation-reduction reaction, and the like.

  As the dye sensitizer adsorbed on the porous semiconductor, various dyes having absorption in the visible light region and the infrared light region can be used. Here, in order to firmly adsorb the dye to the porous semiconductor, the carboxylic acid group, carboxylic anhydride group, alkoxy group, sulfonic acid group, hydroxyl group, hydroxylalkyl group, ester group, mercapto group, phosphonyl in the dye molecule It is preferable that a group or the like is present. These functional groups provide an electrical bond that facilitates electron transfer between the excited state dye and the conduction band of the porous semiconductor.

  Examples of dyes containing these functional groups include ruthenium bipyridine dyes, quinone dyes, quinone imine dyes, azo dyes, quinacridone dyes, squarylium dyes, cyanine dyes, merocyanine dyes, and triphenylmethane dyes. Xanthene dyes, porphyrin dyes, phthalocyanine dyes, berylene dyes, indigo dyes, naphthalocyanine dyes, and the like.

  Examples of the method for adsorbing the dye to the porous semiconductor include a method in which the porous semiconductor is immersed in a solution in which the dye is dissolved (dye adsorption solution). The solvent used in the dye adsorption solution is not particularly limited as long as it dissolves the dye, and specifically, alcohols such as ethanol and methanol, ketones such as acetone, ethers such as diethyl ether and tetrahydrofuran. Nitrogen compounds such as acetonitrile, aliphatic hydrocarbons such as hexane, aromatic hydrocarbons such as benzene, esters such as ethyl acetate, water, and the like.

The electrolyte is composed of a redox pair and a solid medium such as a liquid or polymer gel holding the redox pair.
In general, iron- and cobalt-based metals and halogen substances such as chlorine, bromine, and iodine are preferably used as the redox pair, and metal iodides such as lithium iodide, sodium iodide, and potassium iodide and iodine are used. The combination of is preferably used. Furthermore, imidazole salts such as dimethylpropylimidazole iodide can also be mixed.

  As the solvent, carbonate compounds such as propylene carbonate, nitrile compounds such as acetonitrile, alcohols such as ethanol and methanol, water, aprotic polar substances, and the like are used. Of these, carbonate compounds and nitrile compounds are preferred. Used.

2-3-4. Photoelectric conversion layer using organic thin film Photoelectric conversion layer 3 using an organic thin film is an electron hole transport layer composed of an organic semiconductor material having electron donating properties and electron accepting properties, or an electron transport layer having electron accepting properties. And a hole transport layer having an electron donating property may be laminated.
The electron-donating organic semiconductor material is not particularly limited as long as it has a function as an electron donor, but it is preferable that a film can be formed by a coating method, and among them, an electron-donating conductive polymer is preferably used. The

  Here, the conductive polymer means a π-conjugated polymer, which is composed of a π-conjugated system in which double bonds or triple bonds containing carbon-carbon or hetero atoms are alternately linked to single bonds, and exhibits semiconducting properties. Point.

  Examples of the electron-donating conductive polymer material include polyphenylene, polyphenylene vinylene, polythiophene, polycarbazole, polyvinyl carbazole, polysilane, polyacetylene, polypyrrole, polyaniline, polyfluorene, polyvinyl pyrene, polyvinyl anthracene, and derivatives, Examples thereof include a polymer, a phthalocyanine-containing polymer, a carbazole-containing polymer, and an organometallic polymer. Among these, thiophene-fluorene copolymer, polyalkylthiophene, phenyleneethynylene-phenylene vinylene copolymer, fluorene-phenylene vinylene copolymer, thiophene-phenylene vinylene copolymer, and the like are preferably used.

The electron-accepting organic semiconductor material is not particularly limited as long as it has a function as an electron acceptor. However, it is preferable that a film can be formed by a coating method, and among them, an electron-donating conductive polymer is preferably used. The
Examples of the electron-accepting conductive polymer include polyphenylene vinylene, polyfluorene, and derivatives and copolymers thereof, or carbon nanotubes, fullerene and derivatives thereof, CN group or CF ₃ group-containing polymers, and -CF thereof. Examples thereof include _3- substituted polymers.

In addition, an electron-accepting organic semiconductor material doped with an electron-donating compound, an electron-donating organic semiconductor material doped with an electron-accepting compound, or the like can be used. Examples of the electron-accepting conductive polymer material doped with the electron-donating compound include the above-described electron-accepting conductive polymer material. As the electron-donating compound to be doped, for example, a Lewis base such as an alkali metal such as Li, K, Ca, or Cs or an alkaline earth metal can be used. The Lewis base acts as an electron donor. Examples of the electron-donating conductive polymer material doped with the electron-accepting compound include the above-described electron-donating conductive polymer material. As the electron-accepting compound to be doped, for example, a Lewis acid such as FeCl ₃ , AlCl ₃ , AlBr ₃ , AsF ₆ or a halogen compound can be used. In addition, Lewis acid acts as an electron acceptor.

  In the photoelectric conversion layer 3 shown above, it is primarily assumed that sunlight is received and photoelectric conversion is performed. However, the photoelectric conversion layer 3 emits light from a fluorescent lamp, an incandescent lamp, an LED, or a specific heat source depending on the application. It is also possible to perform photoelectric conversion by irradiating artificial light such as light.

2-4. Back Electrode The back electrode 6 can be provided on the back surface of the photoelectric conversion layer 3. The back electrode 6 can be electrically connected to one of the first electrolysis electrode 8 and the second electrolysis electrode 9. By providing the back electrode 6, ohmic cross between the back surface of the photoelectric conversion layer 3 and the first electrolysis electrode 8 or the second electrolysis electrode 9 can be reduced. The back electrode 6 and the first electrolysis electrode 8 or the second electrolysis electrode 9 may be connected by a conductive wire, may be connected by direct contact, or may be connected by a conductive portion 20.
When the carbon dioxide reducing device 35 is an integrated photoelectric conversion / carbon dioxide reducing device, the back electrode 6 preferably has corrosion resistance to the electrolytic solution and liquid shielding properties to the electrolytic solution. Thereby, corrosion of the photoelectric conversion layer 3 by the electrolytic solution can be prevented.
Although it will not specifically limit if the back surface electrode 6 has electroconductivity, For example, it is a metal thin film, for example, is thin films, such as Al, Ag, Au. These can be formed by, for example, sputtering. Further, for example, a transparent conductive film such as In—Zn—O (IZO), In—Sn—O (ITO), ZnO—Al, Zn—Sn—O, and SnO ₂ is used.

2-5. Insulating Layer When the carbon dioxide reducing device 35 is an integrated photoelectric conversion-carbon dioxide reducing device, the insulating layer 13 can be provided to prevent the occurrence of leakage current. For example, when the conductive portion 20 is provided in the contact hole that penetrates the photoelectric conversion layer 3, the insulating layer 13 can be provided on the side wall of the contact hole. 7 and 8, when the conductive portion 20a is provided on the side portion of the photoelectric conversion layer 3, the insulating layer 13b can be provided between the conductive portion 20a and the side portion of the photoelectric conversion layer 3.
The insulating layer 13a can be provided between the back electrode 6 and the first electrolysis electrode 8 or the second electrolysis electrode 9. For example, as shown in FIGS. 5, 7, and 8, the first electrolysis electrode 8 and the light receiving surface of the photoelectric conversion layer 3 are electrically connected, and the second electrolysis electrode 9 and the back surface of the photoelectric conversion layer 3 are electrically connected. In this case, an insulating layer 13a can be provided between the back electrode 6 and the first electrolysis electrode 8. As a result, the occurrence of leakage current can be prevented.

In addition, when the photoelectric conversion layer 3 receives a light as shown in FIGS. 15 and 16 to generate a potential difference between the first area and the second area on the back surface of the photoelectric conversion layer 3, the insulating layer 13c The insulating layer 13 c is provided between the first electrolysis electrode 8 and the back surface of the photoelectric conversion layer 3 and between the second electrolysis electrode 9 and the back surface of the photoelectric conversion layer 3. You may have an opening on it. Thereby, the electrons and holes formed by the photoelectric conversion layer 3 receiving light can be efficiently separated, and the photoelectric conversion efficiency can be further increased.
The insulating layer 13 preferably has corrosion resistance to the electrolytic solution and liquid shielding properties to the electrolytic solution. Thereby, generation | occurrence | production of a leakage current can be prevented and corrosion of the photoelectric converting layer 3 by electrolyte solution can be prevented.

As the insulating layer 13, any organic material or inorganic material can be used. For example, polyamide, polyimide, polyarylene, aromatic vinyl compound, fluorine polymer, acrylic polymer, vinylamide polymer, etc. Examples of organic polymers and inorganic materials include metal oxides such as Al ₂ O ₃ , SiO ₂ such as porous silica films, fluorine-added silicon oxide films (FSG), SiOC, HSQ (Hydrogen Silsesquioxane) films, SiN _x , It is possible to use a method of forming a film by dissolving silanol (Si (OH) ₄ ) in a solvent such as alcohol and applying and heating.

  As a method for forming the insulating layer 13, a paste containing an insulating material is applied by a screen printing method, an ink jet method, a spin coating method, etc. and dried or baked, or a film is formed by a CVD method using a raw material gas. And a method using a PVD method, a vapor deposition method, a sputtering method, a sol-gel method, and the like.

3. Electrolyte Tank The electrolyte tank 10 is not particularly limited as long as the first electrolysis electrode 8 and the second electrolysis electrode 9 can be disposed therein and can store the electrolyte, but here, FIG. -3 or FIGS. 4-8 is demonstrated about the electrolytic solution tank 10 in case a carbon dioxide reduction apparatus is a photoelectric conversion-carbon dioxide reduction integrated apparatus.
The electrolytic solution tank 10 can be provided in a space between the translucent substrate 1 and the back substrate 15. Further, the electrolyte bath 10 can be formed by joining the end of the translucent substrate 1 and the end of the back substrate 15 with the seal member 17 or the like.
In the electrolytic solution tank 10, for example, a pump, a fan, a convection generator using heat, or the like that circulates the electrolytic solution so that the bubbles of the product gas are efficiently separated from the first electrolysis electrode 8 or the second electrolysis electrode 9. It is also possible to provide a simple device.

3-1. Back substrate The back substrate 15 can be provided so as to face the translucent substrate 1 and provide a space therebetween. This space can be used as the electrolytic solution tank 10, and by introducing the electrolytic solution into the electrolytic solution tank 10, the first electrolytic electrode 8 and the second electrolytic electrode 7 can be brought into contact with the electrolytic solution. Moreover, when using a box-shaped thing for the back substrate 15, the back substrate 15 may be the bottom part of a box.

  Further, the back substrate 15 is a material that constitutes the electrolytic solution tank 10 and confines the generated gas and the electrolytic solution, and a highly confidential substance is required. It is not particularly limited whether it is transparent or opaque, but a transparent material is preferable in that it can be visually confirmed that the generated gas is generated. The transparent back substrate 15 is not particularly limited, and examples thereof include a transparent rigid material such as quartz glass, Pyrex (registered trademark), and a synthetic quartz plate, a transparent resin plate, and a transparent resin film. Among them, it is preferable to use a glass material because it is a gas that is not chemically permeable and is chemically and physically stable.

3-2. Seal member The seal member 17 is a material for adhering the translucent substrate 1 and the back substrate 15 to seal the electrolyte solution in the electrolyte bath 10 and the like. When a box-shaped substrate is used for the back substrate 15, a seal member 17 is used to bond the box and the translucent substrate 1. For example, an ultraviolet curable adhesive, a thermosetting adhesive, or the like is preferably used as the seal member 17, but the type thereof is not limited. The UV curable adhesive is a resin that undergoes polymerization upon irradiation with light having a wavelength of 200 to 400 nm and undergoes a curing reaction within a few seconds after light irradiation, and is divided into a radical polymerization type and a cationic polymerization type. Examples of the polymerization type resin include acrylates, unsaturated polyesters, and examples of the cationic polymerization type include epoxy, oxetane, and vinyl ether. Examples of the thermosetting polymer adhesive include organic resins such as phenol resin, epoxy resin, melamine resin, urea resin, and thermosetting polyimide. The thermosetting polymer adhesive is heated and polymerized in a state where pressure is applied at the time of thermocompression bonding, and then cooled to room temperature while being pressurized. I don't need it. In addition to the organic resin, a hybrid material having high adhesion to the glass substrate can be used. By using a hybrid material, mechanical properties such as elastic modulus and hardness are improved, and heat resistance and chemical resistance are dramatically improved. The hybrid material is composed of inorganic colloidal particles and an organic binder resin. For example, what is comprised from inorganic colloidal particles, such as a silica, and organic binder resin, such as an epoxy resin, a polyurethane acrylate resin, and a polyester acrylate resin, is mentioned.

  Here, the seal member 17 is described. However, the seal member 17 is not limited as long as it has a function of adhering the translucent substrate 1 and the back substrate 15, and a member such as a screw is externally used using a resin or metal gasket. It is also possible to appropriately use a method of applying pressure physically to increase confidentiality.

4). CO ₂ Supply Unit, Gas Exhaust Unit The carbon dioxide reduction device 35 can include a CO ₂ supply unit 22 that supplies carbon dioxide into the electrolytic solution stored in the electrolytic solution tank 10. Thus, carbon dioxide consumed by the electrolytic reduction reaction of carbonic acid in the first electrolysis electrode 8 can be supplied into the electrolytic solution, and a decrease in the carbonic acid concentration of the electrolytic solution can be suppressed.
The CO ₂ supply unit 22 may be a part that supplies carbon dioxide gas to the electrolytic solution stored in the electrolytic solution tank 10 or a part that supplies an electrolytic solution containing carbonic acid to the electrolytic solution stored in the electrolytic solution tank 10. Also good.

The CO ₂ supply part 22 has a CO ₂ flow path 23 and a first gas diffusion part 24a having water repellency and porosity, and supplies carbon dioxide gas from the first gas diffusion part 24a into the electrolyte bath 10. Can be provided. By providing the first gas diffusion part 24 a, it is possible to suppress the electrolyte from flowing into the CO ₂ flow path 23. In addition, by providing the first gas diffusion portion 24a, carbon dioxide gas can be supplied uniformly to the electrolytic solution stored in the electrolytic solution tank 10, and the occurrence of a portion where the carbonic acid concentration decreases in the electrolytic solution is suppressed. can do.

The CO ₂ supply unit 22 is provided so as to supply carbon dioxide from the side of the electrolytic solution tank 10, for example, like the carbon dioxide reduction device 35 shown in FIGS. 1 to 3, 4 to 12, 15, and 16. May be. By providing the CO ₂ supply unit 22 in this manner and installing the carbon dioxide reduction device 35 so that the CO ₂ supply unit 22 is at the lower side, carbon dioxide can be efficiently supplied into the electrolyte solution.
Moreover, the CO ₂ supply unit 22 may be provided so as to supply carbon dioxide from the back substrate 15 side of the electrolyte layer 10, for example, like the carbon dioxide reduction device 35 shown in FIGS. By providing the CO ₂ supply unit 22 in this manner, carbon dioxide can be efficiently supplied into the electrolytic solution even when the carbon dioxide reduction device 35 is installed without being inclined.

The carbon dioxide reduction device 35 can include a gas discharge unit 26 that discharges the generated gas in the electrolytic solution tank 10 and the carbon dioxide gas that has not dissolved in the electrolytic solution. As a result, it is possible to suppress the product gas from staying on the surfaces of the first electrolysis electrode 8 and the second electrolysis electrode 9 and reducing the amount of carbon dioxide reducing substance produced.
The gas discharge part 26 can have the discharge flow path 27 and the 2nd gas diffusion part 24b which has water repellency and porosity. As a result, the electrolyte can be prevented from flowing into the discharge channel 27.

The gas discharge part 26 is provided so that produced gas may be discharged from the side part of the electrolytic solution tank 10 like the carbon dioxide reduction apparatus 35 shown in FIGS. 1-3, FIGS. 4-12, 15, 16 for example. May be. By providing the gas discharge part 26 in this way and installing the carbon dioxide reduction device 35 at an angle so that the gas discharge part 26 is at the top, the generated gas can be discharged efficiently.
Moreover, the gas discharge part 26 may be provided in the photoelectric conversion layer 3 side of the electrolyte tank 10, for example like the carbon dioxide reduction apparatus 35 shown in FIG. By providing the gas discharge part 26 in this manner, the generated gas can be efficiently discharged from the electrolytic solution tank even when the carbon dioxide reduction device 35 is installed without being inclined. In this case, the gas diffusion part 24b can be omitted.

1: Translucent substrate 3: Photoelectric conversion layer 5: Translucent electrode 6: Back electrode 8: Electrode for first electrolysis 9: Electrode for second electrolysis 10: Electrolyte bath 13: Insulating layer 15: Back substrate 17: Seal member 20: Conductive part 22: CO ₂ supply part 23: CO ₂ flow path 24: Gas diffusion part 26: Gas discharge part 27: Discharge flow path 29: Electrolyte waste outlet 30: Electrolyte injection inlet 31: Valve 35: Carbon dioxide reduction device 38: semiconductor part 39: p-type semiconductor part 40: n-type semiconductor part 41: isolation

Claims (19)

A photoelectric conversion layer having a light receiving surface and a back surface, an electrolytic solution tank, first and second electrodes for electrolysis provided with the electrolytic solution sandwiched in the electrolytic solution tank, and supplying carbon dioxide into the electrolytic solution tank A CO ₂ supply unit
The photoelectric conversion layer and the first and second electrolysis electrodes are connected such that the photovoltaic power of the photoelectric conversion layer is output to the first and second electrolysis electrodes,
The first electrolysis electrode has a carbon dioxide reduction catalyst,
The second electrolysis electrode has an oxygen generation catalyst,
The carbon dioxide reducing device, wherein the first and second electrolysis electrodes are provided so that bubbles can move between the first and second electrolysis electrodes.   2. The carbon dioxide reduction device according to claim 1, wherein the first and second electrodes for electrolysis and the electrolytic solution tank are provided on a back surface side of the photoelectric conversion layer.   The carbon dioxide reduction device according to claim 2, wherein each of the first and second electrodes for electrolysis has a main surface and is provided so that the main surfaces face each other.   The carbon dioxide reduction device according to claim 3, wherein the first and second electrolysis electrodes are disposed so as to be substantially perpendicular to the back surface of the photoelectric conversion layer.   5. The carbon dioxide reduction device according to claim 1, wherein the first and second electrolysis electrodes are provided so as to be alternately arranged.   The carbon dioxide reduction device according to any one of claims 1 to 5, wherein one of the first and second electrolysis electrodes is surrounded by the other. The first and second electrolysis electrodes each have a comb structure having a trunk and a plurality of branches extending from the trunk,
The branch of the first electrolysis electrode is disposed between the two branches of the second electrolysis electrode,
The carbon dioxide reduction device according to any one of claims 1 to 5, wherein the branch portion of the second electrolysis electrode is disposed between the two branch portions of the first electrolysis electrode.   The carbon dioxide reduction device according to any one of claims 1 to 5, wherein each of the first and second electrolysis electrodes has a wound structure. The photoelectric conversion layer is provided so that a photovoltaic force is generated between the light receiving surface and the back surface,
One of the first and second electrolysis electrodes is provided so as to be electrically connected to the light receiving surface, and the other is provided to be electrically connected to the back surface. The carbon dioxide reduction device according to one. The photoelectric conversion layer is provided so that a photovoltaic force is generated between the first and second areas on the back surface of the photoelectric conversion layer,
9. The electrode according to claim 1, wherein one of the first and second electrolysis electrodes is provided so as to be electrically connected to the first area, and the other is provided so as to be electrically connected to the second area. The carbon dioxide reduction apparatus as described in any one. The CO ₂ supply section has a CO ₂ flow path and a first gas diffusion section having water repellency and porosity, and supplies carbon dioxide gas from the first gas diffusion section into the electrolyte bath. The carbon dioxide reducing apparatus according to any one of 1 to 10. The CO ₂ supply unit carbon dioxide reduction device according to any one of claims 1 to 10 for supplying the electrolytic solution of carbon dioxide is dissolved into the electrolyte bath. A gas exhaust part,
The carbon dioxide reduction device according to any one of claims 1 to 12, wherein the gas discharge unit includes a discharge channel and a second gas diffusion unit having water repellency and porosity. A translucent substrate;
The said photoelectric conversion layer is a carbon dioxide reduction apparatus as described in any one of Claims 1-13 provided on the said translucent board | substrate. A back substrate,
The carbon dioxide reducing apparatus according to claim 14, wherein the electrolytic bath is provided between the translucent substrate and the back substrate.   The carbon dioxide reduction device according to claim 1, wherein the photoelectric conversion layer includes a plurality of photoelectric conversion units connected in series.   The carbon dioxide reduction device according to any one of claims 1 to 16, wherein the carbon dioxide reduction catalyst is a catalyst that reduces carbon dioxide to produce methanol, ethanol, propanol, formaldehyde, acetaldehyde, formic acid, or acetic acid. The carbon dioxide reduction catalyst is a solid metal, an alloy, a metal oxide or a metal complex,
The solid metal, the alloy or the metal oxide includes Cu, Ag, Fe or Ni,
The carbon dioxide reduction device according to any one of claims 1 to 17, wherein the metal complex contains Co, Fe, Ni, or Ru.   The carbon dioxide reduction device according to any one of claims 1 to 18, wherein the oxygen generation catalyst contains Mn, Ca, Zn, Co, Pt, Ni, or Ir.