JP2019157198A - Electrode for chemical reaction, and cell for chemical reaction and chemical reactor using the same - Google Patents

Abstract

To provide an electrode for chemical reaction which allows a proton to smoothly flow and can circulate a sufficient amount of electrolyte to supply raw materials and discharge products.SOLUTION: The present invention provides an electrode for chemical reaction in which an electrode 102 for reduction reaction and an electrode 104 for oxidation reaction are alternately arranged on the same surface of a substrate 114, and a width of the electrode 102 for reduction reaction and a width of the electrode 104 for oxidation reaction along the alternate arrangement direction are different from one another.SELECTED DRAWING: Figure 16

Description

  The present invention relates to a chemical reaction electrode, a chemical reaction cell using the electrode, and a chemical reaction apparatus.

Using solar energy, water (H ₂ O) to hydrogen (H ₂ ), water (H ₂ O) and carbon dioxide (CO ₂ ) to carbon monoxide (CO), formic acid (HCOOH), methanol (CH ₃ OH) ) And the like are disclosed. In order to realize artificial photosynthesis, it is necessary to apply a potential difference of 2 to 3 V between the oxidation reaction electrode and the reduction reaction electrode. In order to realize this, photoelectrodes in which an oxidation / reduction catalyst is supported on both surfaces of an amorphous silicon-based three-junction solar cell (a-Si 3J-SC) are used (Non-Patent Documents 1 and 2). In addition, an amorphous silicon-based three-junction solar cell is used, and a reduction catalyst is supported on the back surface (opposite the light incident surface) to form a reduction reaction electrode, and includes a member having an oxidation catalyst function so as to face this In other words, an artificial photosynthesis cell in which a solar cell and an electrochemical cell are integrated, in which an oxidation reaction electrode is arranged and connected to the surface electrode of the solar cell, is used (Non-patent Document 3). In addition, there is an example in which a counter-type cell is configured using a III-V compound two-junction solar cell (III-V 2J-SC) aiming at higher efficiency (Non-Patent Document 4).

S.Y.Reece, et al., Science 334, 645 (2011) T.Arai, et al., Energy Environ. Sci. 8, 1998 (2015) J.-P. Becker, et al., J. Mater. Chem. A5, 4818 (2017) G. Peharz, et al., Int. J. Hydrogen Energy 32, 3248 (2007)

  By the way, in order to obtain high conversion efficiency, it is desired to shorten the distance between the oxidation reaction electrode and the reduction reaction electrode so that protons can smoothly flow from the oxidation reaction electrode to the reduction reaction electrode.

  However, in an integrated chemical reaction cell in which an oxidation reaction electrode is provided on one side of the solar cell and a reduction reaction electrode is provided on the other side, the end of the cell goes around the cell and protons pass through the electrolyte. There is a problem that the efficiency of the reaction decreases when the cell is enlarged. Also, in the case of a counter-type cell in which the electrode for oxidation reaction and the electrode for reduction reaction face each other, if the distance between the electrode for oxidation reaction and the electrode for reduction reaction is shortened, sufficient supply of raw materials and rapid discharge of products are prevented. Therefore, it becomes difficult to uniformly convect a sufficient amount of electrolyte.

  In one aspect of the present invention, oxidation reaction electrodes and reduction reaction electrodes are alternately arranged on the same surface of the substrate, and the width of the oxidation reaction electrode and the reduction reaction electrode along the alternate arrangement direction. It is an electrode for chemical reaction characterized by having different widths.

  Here, it is preferable that the width of the electrode having higher current density-voltage characteristics is set narrower according to the current density-voltage characteristics of the oxidation reaction electrode and the reduction reaction electrode.

  Another aspect of the present invention is a chemical reaction cell characterized by combining the oxidation reaction electrode and a solar cell connected to the reduction reaction electrode.

  Here, it is preferable that the solar cell is an integral type part of the substrate.

  Moreover, it is preferable that the said solar cell is what connected the crystalline silicon solar cell of 3 cells or more and 6 cells or less in series.

  Further, it is preferable that the chemical reaction cell is immersed in an electrolytic solution.

  Another aspect of the present invention comprises a plurality of the chemical reaction cells, wherein the oxidation reaction electrode and the reduction reaction electrode are provided on one or both surfaces of the plurality of chemical reaction cells, and the oxidation reaction electrode and The chemical reaction apparatus is characterized in that the surfaces on which the electrodes for reduction reaction are provided are arranged to face each other.

  ADVANTAGE OF THE INVENTION According to this invention, the movement of a proton is easy, the electrode for chemical reaction which can distribute | circulate the electrolyte solution of sufficient quantity for supply of a raw material and discharge | emission of a product, the cell for chemical reaction using the same, and chemical A reactor can be provided.

It is a figure which shows the structure of the chemical reaction apparatus in embodiment of this invention. It is a perspective view which shows the structure of the electrode for reduction reaction and the electrode for oxidation reaction in embodiment of this invention. It is sectional drawing which shows the structure of the electrode for reduction reaction and the electrode for oxidation reaction in embodiment of this invention. It is a figure which shows the distance dependence between the electrode for reduction reaction-the electrode for oxidation reaction of an electric current value. It is a figure which shows the example of a relationship between the current density and the potential of an electrode for oxidation reaction and an electrode for reduction reaction. It is a figure which shows the relationship between the current density and the period, distance, and diameter of an electrode in the chemical reaction cell using an interpenetrating electrode, a counter electrode, and a conventional integrated electrode. It is a figure which shows the relationship between the current density and voltage in a chemical reaction cell. The figure which shows the fluctuation | variation of electric potential (phi) (x, z) resulting from specific resistance (rho) _{H +} when the resistance component accompanying a local proton flow density and proton propagation in a chemical reaction cell using an interpenetrating type electrode is considered as ohmic resistance. is there. It is a figure which shows the structure of the integrated chemical reaction apparatus in embodiment of this invention. It is a figure which shows the example of a relationship between the current density and output voltage of a crystalline silicon solar cell and an amorphous silicon / crystalline silicon heterojunction type solar cell. It is a figure which shows the change of the output characteristic of a chemical reaction apparatus when the number of series connection of a solar cell is changed. It is a figure which shows the relationship between the serial connection number of a solar cell, and the current density in an operating point. It is a figure which shows the change of an operating current when the time change is considered, and the amount of electric charges of one day. It is a figure which shows the relationship between the number of series connection of the solar cell at the time of changing various conditions, and the current density in an operating point. It is a figure which shows the example of a relationship between the current density and the potential of an electrode for oxidation reaction and an electrode for reduction reaction. It is sectional drawing which shows the structure of the electrode for reduction reaction and the electrode for oxidation reaction in embodiment (2nd Embodiment) of this invention. It is a figure which shows the current density, overvoltage, and current density-voltage characteristic when changing the width | variety of the electrode for reduction reaction, and the electrode for oxidation reaction. It is a figure which shows the fluctuation | variation of electric potential (phi) (x, z) resulting from specific resistance (rho) _{H +} when the resistance component accompanying a local proton flow density and a proton propagation in a chemical reaction cell is considered as ohmic resistance. It is a figure which shows the relationship between the serial connection number of a solar cell, and the current density in an operating point. It is a figure which shows the change of an operating current when the time change is considered, and the amount of electric charges of one day. It is a figure which shows a structure when a some chemical reaction apparatus is connected in parallel. It is a figure which shows a structure when a some chemical reaction apparatus is connected in series and parallel.

  As shown in the schematic diagram of FIG. 1, the chemical reaction device 100 according to the embodiment of the present invention includes a reduction reaction electrode 102, an oxidation reaction electrode 104, an electrolytic solution 106, a solar battery cell 108, a window material 110, and a frame material. 112 is comprised.

  2 and 3 are a perspective view and a cross-sectional view showing configurations of the reduction reaction electrode 102 and the oxidation reaction electrode 104, respectively. 3 is a cross-sectional view taken along line AA in FIG. 2 and 3, the dimensions of the respective parts are changed from the actual dimensions in order to clearly show the structures of the reduction reaction electrode 102 and the oxidation reaction electrode 104.

  In the present embodiment, the reduction reaction electrodes 102 and the oxidation reaction electrodes 104 are alternately arranged on the same surface of the substrate 114. Specifically, as shown in FIGS. 2 and 3, strip-shaped reduction reaction electrodes 102 and oxidation reaction electrodes 104 extending along the y direction may be alternately arranged along the x direction. Good. At this time, as shown in FIG. 2, the ends of the reduction reaction electrode 102 and the oxidation reaction electrode 104 are connected to each other to combine the reduction reaction electrode 102 and the oxidation reaction electrode 104 each having a comb shape. It becomes the composition.

  Here, the arrangement of the reduction reaction electrodes 102 and the oxidation reaction electrodes 104 alternately is not limited to a configuration in which strip-shaped electrodes are arranged in a straight line as shown in FIG. For example, the reduction reaction electrode 102 is arranged in a spiral shape on the surface of the substrate 114, and the oxidation reaction electrode 104 is fitted in a spiral shape between the spiral reduction reaction electrodes 102 on the same surface of the substrate 114. It is good also as such a structure. Further, for example, if the reduction reaction electrode 102 and the oxidation reaction electrode 104 are arranged side by side on the same surface of the substrate 114, the respective shapes may be indefinite.

  The reduction reaction electrode 102 is an electrode used for reducing a substance by a reduction reaction. The reduction reaction electrode 102 is formed on the substrate 114 as shown in the cross-sectional view of FIG. The reduction reaction electrode 102 includes the conductive layer 10 and the conductor layer 12.

  The substrate 114 is a member that structurally supports the reduction reaction electrode 102. In the present embodiment, the substrate 114 is shared with the oxidation reaction electrode 104. The material of the substrate 114 is not particularly limited, but is, for example, a glass substrate. Further, the substrate 114 may include, for example, a metal or a semiconductor. The metal used as the substrate 114 is not particularly limited. The semiconductor used as the substrate 114 is not particularly limited. When the substrate 114 includes a metal or a semiconductor, an insulating layer is formed between the reduction reaction electrode 102 and the oxidation reaction electrode 104 and the substrate 114. The insulating layer is not particularly limited, and may be a semiconductor oxide, nitride, resin, or the like.

  The conductive layer 10 is provided in order to effectively collect current in the reduction reaction electrode 102. The conductive layer 10 is not particularly limited, but is preferably a transparent conductive layer such as indium tin oxide (ITO), fluorine-doped tin oxide (FTO), or zinc oxide (ZnO). In particular, it is preferable to use fluorine-doped tin oxide (FTO) in consideration of thermal and chemical stability.

  The conductor layer 12 is made of a conductor containing a material having a reduction catalyst function. The conductor can be made of a material containing a carbon material (C). The size of the carbon material structure is preferably 1 nm or more and 1 μm or less. The carbon material preferably includes, for example, at least one of carbon nanotubes (CNT), graphene, and graphite. In the case of graphene and graphite, the size is preferably 1 nm or more and 1 μm or less. If it is a carbon nanotube, it is suitable for a diameter to be 1 nm or more and 40 nm or less. The conductor can be formed by applying a carbon material mixed with a liquid such as ethanol by spraying and heating. It may be applied by spin coating instead of spraying. Alternatively, the solution may be directly dropped and dried without using spin coating. Moreover, you may use carbon paper (CP) as a material containing a carbon material. Moreover, you may use what apply | coated carbon nanotube (CNT) etc. with respect to carbon paper (CP).

The conductor layer is modified with a material having a reducing function such as a complex catalyst. The complex catalyst is preferably a ruthenium complex, for example. The complex catalyst is, for example, [Ru {4,4′-di (1-H-1-pyrrolopropyl carbonate) -2,2′-bipyridine] (CO) (MeCN) Cl ₂ ], [Ru {4,4 ′. -di (1-H-1- pyrrolypropyl carbonate) -2,2'-bipyridine} (CO) 2 Cl 2], [Ru {4,4'-di (1-H-1-pyrrolypropyl carbonate) -2, 2′-bipyridine} (CO) ₂ ] _n , [Ru {4,4′-di (1-H-1-pyrrolopropyl carbonate) -2,2′-bipyridine] (CO) (CH ₃ CN) Cl ₂ ] Etc.

The modification with the complex catalyst can be made by applying a solution obtained by dissolving the complex in an acetonitrile (MeCN) solution on the conductor of the conductor layer 12. The modification with the complex catalyst can also be performed by an electrolytic polymerization method. An electrode of the conductor of the conductor layer 12 as a working electrode, a glass substrate coated with fluorine-containing tin oxide (FTO) as a counter electrode, an Ag / Ag ⁺ electrode as a reference electrode, and Ag / Ag in an electrolyte containing a complex catalyst After flowing a cathode current so as to be a negative voltage with respect to the ⁺ electrode, an anode current is caused so as to be a positive potential with respect to the Ag / Ag ⁺ electrode, whereby a complex catalyst is used on the conductor of the conductor layer 12. Can be modified. Acetonitrile (MeCN) can be used for the electrolyte solution, and Tetrabutylammonium perchlorate (TBAP) can be used for the electrolyte.

  The conductor layer 12 formed in this way is supported, applied, or affixed on the conductive layer 10 constituting the reduction reaction electrode 102. Thereby, the reduction reaction electrode 102 including the conductive layer 10 and the conductor layer 12 is formed.

  The oxidation reaction electrode 104 is an electrode used for oxidizing a substance by an oxidation reaction. The oxidation reaction electrode 104 is formed on the substrate 114 as shown in the cross-sectional view of FIG. The oxidation reaction electrode 104 includes the conductive layer 14 and the oxidation catalyst layer 16.

  The conductive layer 14 is provided to effectively collect current in the oxidation reaction electrode 104. The conductive layer 14 is not particularly limited, but is preferably indium tin oxide (ITO), fluorine-doped tin oxide (FTO), zinc oxide (ZnO), or the like. In particular, it is preferable to use fluorine-doped tin oxide (FTO) in consideration of thermal and chemical stability.

  The conductive layer 10 and the conductive layer 14 are provided with a transparent conductive layer on the entire surface of the substrate 114 on which the reduction reaction electrode 102 and the oxidation reaction electrode 104 are provided. It can be formed by processing into a comb shape in accordance with the shape. Specifically, a gap is formed between the reduction reaction electrode 102 and the oxidation reaction electrode 104 by laser scribing the transparent conductive film, and the reduction reaction electrode 102 and the oxidation reaction electrode 104 are electrically insulated. It is preferable to process so that it will be in the state.

  The conductive layer 10 and the conductive layer 14 may be provided with a collecting electrode such as a finger electrode or a bus electrode in order to increase conductivity. For example, a current collecting function in the conductive layer 10 and the conductive layer 14 can be improved by forming a bus electrode on the substrate 114 and extending the finger electrode from the bus electrode. The current collecting electrode may be a metal layer such as silver, copper, or gold. Specifically, for example, the current collecting electrode can be formed by applying a silver paste in a desired shape on the substrate 114 by screen printing and baking it.

  The oxidation catalyst layer 16 includes a material having an oxidation catalyst function. The material having an oxidation catalyst function can be, for example, a material containing iridium oxide (IrOx). Iridium oxide can be supported on the surface of the conductive layer 14 as a nanocolloid solution (T. Arai et.al, Energy Environ. Sci 8, 1998 (2015)).

For example, a nano colloid of iridium oxide (IrOx) is synthesized. Next, a yellow solution adjusted to pH 13 by adding 10 wt% aqueous sodium hydroxide (NaOH) solution to 50 ml of 2 mM potassium chloride iridate (IV) potassium (K ₂ IrCl ₆ ) solution at 90 ° C. using a hot stirrer. Heat for 20 minutes. The blue solution thus obtained is cooled with ice water for 1 hour. Then, 3M nitric acid (HNO ₃ ) is added dropwise to the cooled solution (20 ml) to adjust to pH 1 and stirred for 80 minutes to obtain a nanocolloid aqueous solution of iridium oxide (IrOx). Further, 1.5 wt% NaOH aqueous solution (1-2 ml) is dropped into this solution to adjust to pH 12. The iridium oxide (IrOx) nanocolloid aqueous solution thus obtained is applied to the pH of 12 on the conductive layer 14, and is dried by holding at 60 ° C. for 40 minutes in a drying furnace. After drying, the deposited salt can be washed with ultrapure water to form the oxidation reaction electrode 104. Note that the application and drying of the aqueous iridium oxide (IrOx) nanocolloid solution may be repeated a plurality of times.

The chemical reaction apparatus 100 functions by introducing an electrolytic solution 106 between the reduction reaction electrode 102 and the oxidation reaction electrode 104. For example, as shown in FIG. 1, a frame material 112 is disposed so as to surround the reduction reaction electrode 102 and the oxidation reaction electrode 104, and the reactant is dissolved on the surfaces of the reduction reaction electrode 102 and the oxidation reaction electrode 104. The electrolyte solution 106 is supplied. The reactant can be a carbonized compound, for example, carbon dioxide (CO ₂ ). The electrolyte solution 106 is preferably a phosphate buffer aqueous solution or a borate buffer aqueous solution. In a specific configuration example, a carbon dioxide (CO ₂ ) saturated phosphate buffer solution supply tank is provided, and the solution is supplied to the surfaces of the reduction reaction electrode 102 and the oxidation reaction electrode 104 by a pump, thereby reducing the reaction. The formic acid (HCOOH) produced by the above is recovered in an external recovery tank.

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

  In the present embodiment, the solar battery cell 108 is employed. The solar battery cell 108 can be disposed adjacent to the reduction reaction electrode 102 and the oxidation reaction electrode 104. In the example of FIG. 1, the solar battery cell 108 is disposed on the back surface of the reduction reaction electrode 102 and the oxidation reaction electrode 104, the positive electrode of the solar battery cell 108 is connected to the oxidation reaction electrode 104, and the negative electrode is used for the reduction reaction. It is connected to the electrode 102.

When synthesizing formic acid (HCOOH) or the like from carbon dioxide (CO ₂ ), water (H ₂ O) is oxidized to supply electrons and protons to carbon dioxide (CO ₂ ). In the vicinity of pH 7, the oxidation potential of water (H ₂ O) is 0.82 V, and the reduction potential is −0.41 V (both are NHE). The reduction potentials from carbon dioxide (CO ₂ ) to carbon monoxide (CO), formic acid (HCOOH), and methyl alcohol (CH ₃ OH) are −0.53 V, −0.61 V, and −0.38 V, respectively. . Therefore, the potential difference between the oxidation potential and the reduction potential is 1.20 to 1.43V.

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

[Examination of electrode structure]
The difference between the oxidation potential of water (H ₂ O) and the reduction potential from carbon dioxide (CO ₂ ) to formic acid (HCOOH) is 1.43 eV. Since an overvoltage of the reaction is necessary to realize artificial photosynthesis, it is required to apply a voltage of about 2 V or more between the reduction reaction electrode 102 and the oxidation reaction electrode 104.

A 1 cm ² oxidation reaction electrode (anode) supporting IrO _x on a glass substrate with SnO ₂ : F (FTO) and a carbon paper supporting a multi-walled carbon nanotube and then a Ru complex polymer were used. SnO ₂ : F (FTO ) Measurement results of current value when a constant voltage of 2 V was applied by immersing the same size reduction reaction electrode (cathode) fixed on a glass substrate with an electrolyte filled in a tube container having an inner diameter of 2.5 cm. Is shown in FIG. The electrolytic solution is obtained by saturatedly dissolving carbon dioxide (CO ₂ ) in a phosphate buffer aqueous solution having a concentration of 0.4 M or 0.8 M. The horizontal axis is the distance L between the oxidation reaction electrode and the reduction reaction electrode in the tube.

  In addition, in FIG. 4, the measurement value when a 0.8 M phosphate buffer aqueous solution is applied in a circle (broken line), and the measurement value when a 0.4 M phosphate buffer aqueous solution is applied in a square mark (broken line). Show. A solid line shows the result of fitting mentioned below about each.

As shown in FIG. 4, the current value decreased as the distance L between the oxidation reaction electrode and the reduction reaction electrode increased. That is, it has been found that the resistance component associated with the propagation of protons in the electrolyte solution from the oxidation reaction electrode to the reduction reaction electrode cannot be ignored as compared with the reaction resistance at the oxidation reaction electrode and the reduction reaction electrode. Therefore, an oxidation reaction electrode and a reduction reaction electrode are connected to a photoelectric charge separation element to constitute an artificial photosynthesis cell, and in order to convert sunlight energy into chemical acid of formic acid (HCOOH) with high efficiency, oxidation is required. The distance between the electrode for reaction and the electrode for reduction reaction must be kept short. Therefore, it is difficult to obtain high reaction efficiency when an integrated cell in which an oxidation reaction electrode is formed on one surface of the photoelectric charge separation element and a reduction reaction electrode is formed on the other surface is enlarged. On the other hand, in the facing type cell in which the oxidation reaction electrode and the reduction reaction electrode are opposed to each other and the space between them is filled with the electrolyte and convection is performed, the distance between the oxidation reaction electrode and the reduction reaction electrode is limited. It becomes difficult to uniformly convect a sufficient amount of electrolyte in a large-sized cell for sufficient supply of carbon dioxide (CO ₂ ) and rapid discharge of the product formic acid (HCOOH).

<Quantitative evaluation of resistance components>
The resistance component accompanying the propagation of protons in the electrolyte was quantitatively evaluated. FIG. 5A shows the current density (j _a ) -potential (V _a ) characteristics of the oxidation reaction electrode used in the above experiment. FIG. 5B shows the current density (j _c ) -potential (V _c ) characteristics of the reduction reaction electrode used in the experiment of the comparative example. In all cases, the phosphate buffer concentration of the electrolyte was 0.4M.

When the electrode for oxidation reaction and the electrode for reduction reaction are connected, the current density (j _ac ) _-voltage (V _ac ) characteristic between the electrode for oxidation reaction and the electrode for reduction reaction has a specific resistance ρ _If it is considered as an ohmic resistance of _{H +} , it can be obtained by solving simultaneous equations of Equation (1) and Equation (2).

When the distance L between the oxidation reaction electrode and the reduction reaction electrode becomes smaller and close to the inner diameter of the tube, the influence of the shape of the tube and the electrode becomes larger, so that the resistance component deviates from the proportional relationship with the distance L. A parameter for correcting this is ρ ₀ . When the resistance r _{H +} was determined by fitting so that j _{ac at a} phosphate buffer concentration of 0.4 M and V _a = 2V coincided with the experimental value, ρ _{H +} = 28 Ω · cm and ρ ₀ = 35 Ω. However, since the expression (2) does not hold when the distance L is small as described above, the fitting was performed in the range of distance L ≧ 10 cm. As shown in FIG. 4, the fitting results agreed well with the experimental values.

Furthermore, the calculation result when the phosphate buffer concentration of the electrolytic solution is doubled to 0.8 M is compared with the experimental value. However, this time, the values of ρ _{H +} and ρ ₀ are not fitted with the experimental results of 0.8M, but are ½ values at 0.4M (ρ _{H +} = 14Ω · cm, ρ ₀ = 17. 5Ω). As shown in FIG. 4, the measurement result at 0.8 M and the fitting result showed good agreement.

  From the results of these fittings, it can be said that the resistance component associated with the propagation of protons in the electrolyte may be treated as an ohmic resistance whose resistance value is proportional to the phosphate buffer concentration.

<Electrode structure in this embodiment (Example)>
Hereinafter, an electrode structure (hereinafter referred to as an interpenetrating electrode) in which the reduction reaction electrode 102 and the oxidation reaction electrode 104 having a comb shape in this embodiment are combined will be considered.

Even when a plurality of the electrodes are arranged side by side, the distance between the electrodes does not directly affect the propagation of protons, and therefore, the electrode may be designed in consideration of only the influence of convection of the electrolyte. Hereinafter, the current density (j _ac ) _-voltage (V _ac ) characteristic between the reduction reaction electrode 102 and the oxidation reaction electrode 104 of the interpenetrating electrode is obtained, and the widths of the reduction reaction electrode 102 and the oxidation reaction electrode 104 are obtained. Investigate the effects of

  For simplification, a case is considered where the length (y direction) is sufficiently longer than the period 2d (x direction) of the strip-shaped reduction reaction electrode 102 and the oxidation reaction electrode 104. In this case, since the influence of the end in the length direction can be ignored, the potential in the y direction is constant and the current is zero, which can be a two-dimensional problem in the xz plane.

First, consider the case where the strip-shaped reduction reaction electrode 102 and the oxidation reaction electrode 104 have the same width. Here, a gap between the reduction reaction electrode 102 and the oxidation reaction electrode 104 is w, and a width is a period d−a gap w / 2. As described above, when the resistance component accompanying propagation of protons in the electrolyte solution (phosphate buffer concentration 0.4 M) is treated as an ohmic resistance having a specific resistance ρ _{H +} = 28 Ω · cm, the formula (3) and the formula ( 4) The Poisson equation and the diffusion equation hold.

Here, φ (x, z), j _{(b) H +} (x, z) are a local potential (relative value) and a proton flow density vector at position (x, z), respectively. In the present specification, the vector is shown in bold in the mathematical expression, and is added with a subscript (b) in the text.

The origin of x is an intermediate point between the oxidation reaction electrode 104 and the reduction reaction electrode 102, and the origin of z is the surface of the reduction reaction electrode 102 and the oxidation reaction electrode 104. In the following, a hypothetical electrode configuration in which the thickness of the conductor layer 12 and the oxidation catalyst layer 16 is assumed to be 0, the interface between the conductive layer 10 and the conductor layer 12, and the conductive layer 14 and the oxidation catalyst layer 16 are assumed. And z = 0, and the surfaces of the conductor layer 12 and the oxidation catalyst layer 16 are represented by z = 0 ⁺ .

A voltage drop due to the reaction at the oxidation reaction electrode 104 is expressed by Equation (5) when linearly approximating the relationship of current density j _a -voltage V _a .

Equation (5) represents the y component of the proton flow density vector j _{(b) H +} . φ (x, 0) is the potential of the conductive material (FTO) on which the catalyst of the oxidation reaction electrode 104 is carried, and φ (x, 0 ⁺ ) is the potential of the catalyst surface. The reduction reaction electrode 102 can be handled in the same manner.

Here, V _a0 −V _c0 = 1.4969 V is a threshold voltage at which a reaction occurs.

The current density j _ac matches the proton flow density j _{H + a} flowing out from the oxidation reaction electrode 104 and the proton flow density j _{H + c} flowing into the reduction reaction electrode 102.

FIG. 6A shows a current density between the reduction reaction electrode 102 and the oxidation reaction electrode 104 when a constant voltage V _ac = 2V between the reduction reaction electrode 102 and the oxidation reaction electrode 104 is applied. The result of calculating the value of j _ac as a function of period d is shown. At this time, the gap w between the reduction reaction electrode 102 and the oxidation reaction electrode 104 was 0.1 cm, and the phosphate buffer concentration was 0.4 M. FIG. 6B shows, as a comparative example, a calculation result on the assumption that there is no adverse effect due to an insufficient flow of the electrolyte in a counter-type cell in which a reduction reaction electrode and an oxidation reaction electrode face each other. Indicates. FIG. 6 (c) shows a calculation result assuming that there is no adverse effect due to the insufficient flow of the electrolyte in the conventional integrated cell as a comparative example. However, in order to reduce the calculation load, calculation was performed using cylindrical coordinates for a disk-shaped cell.

When the period d is small, the influence is slight, and the current density j _ac between the reduction reaction electrode 102 and the oxidation reaction electrode 104 when the interpenetrating electrode is used is a counter-type in the range of the period d ≦ 1.0 cm. In this case, the value was 3.5 mA / cm ² or more when the electrode spacing L was 1 cm. If the period d ≦ 3 cm, the current density j _ac between the reduction reaction electrode 102 and the oxidation reaction electrode 104 when the interpenetrating electrode is used is the same as that when the electrode interval L is 2 cm in the counter type. It became more than a value (2.9 mA / cm < ² >). On the other hand, in the case of the conventional large integrated cell, when the diameter D is 20 cm, the current density j _ac is reduced to 1.3 mA / cm ² . On the other hand, when the interpenetrating electrode was used, it exceeded the value even if the period d was 10 cm.

In addition, the current value per unit area of the reduction reaction electrode 102 and the oxidation reaction electrode 104 increases as the period d decreases. However, since the ratio of the gap w occupying the whole becomes larger, the current density j _ac is smaller when the period d = 0.5 cm than when the period d = 1 cm.

  From the above results, it can be said that high conversion efficiency can be obtained if the period d is set to approximately 3 cm or less, and the flow of the electrolyte is ensured by sufficiently securing the interval between the adjacent electrodes or partition walls. In fact, if the opposing type is made larger, it becomes difficult to retain a sufficient amount of electrolyte uniformly as described above, so it is assumed that the interpenetrating electrode as in this embodiment is more advantageous. Is done.

7 (a) is the current density _{j ac} when the period d = 1 cm the current density _{j ac} is maximum - shows the voltage _{V ac} characteristics. FIG. 7 also shows the current density j _ac (D = 20) in the case of the conventional integrated type as a result of the current density j _ac (L = 1) in the case of the conventional opposed type when the interelectrode distance L = 1 cm. . Since the current density j _ac of the interpenetrating electrode does not depend on the outer shape of the electrode, a high value that substantially matches the conventional counter-type current density j _ac (L = 1) can be obtained even when the electrode is enlarged. On the other hand, when the diameter of the conventional integrated electrode is 20 cm, the current density j _ac (D = 20) is extremely low. It is clear from the result of FIG. 6C that the current density j _ac (D) is further reduced when the diameter of the conventional integrated electrode is increased for practical use. Further, when the counter electrode is enlarged, a problem of convection of the electrolytic solution occurs.

Figure 8 is a reduced local proton current density of the reaction electrode 102 and the oxidation electrode ^{_{104 j H + (x, 0}} +) when a voltage is applied to V = 3.2584V, due to ρ _{H +} φ (x, z) is a variation (relative value). The local proton flow density j _{H +} (x, 0 ⁺ ) was approximately constant between the reduction reaction electrode 102 and the oxidation reaction electrode 104. As the local proton flow density j _{H +} (x, 0 ⁺ ) increases, the reaction resistance increases, so that a voltage drop occurs and the increase in the local proton flow density j _{H +} (x, 0 ⁺ ) is suppressed. phi If (x, ^{0 +)} see the change of the end of the reduction reaction electrode 102 and the oxidation electrode 104 (x = ± 0.5cm) in the vicinity of the center than in the vicinity of φ (x, ^{0 +)} is Approaching zero. As a result, if the reaction resistance is zero, φ (x, 0 ⁺ ) in the reduction reaction electrode 102 and the oxidation reaction electrode 104 is constant, and as a result, the local proton flow density j _{H +} (x , 0 ⁺ ) is in contrast to the fact that the distance between the two is short and the resistance is concentrated near the center.

When the phosphate buffer concentration is increased, ρ _{H +} is decreased, so that the current density j _{ac -voltage} V _ac characteristic is affected. When the concentration is doubled to 0.8 M, ρ _{H +} is ½, 14 Ω · cm. However, since the counter electrode and the interpenetrating electrode both use the electrode distance L and the period d so that the influence of ρ _{H +} is small, as shown in FIG. 7B, the current density j _ac ( L = 1) and current density j _ac (d = 1) were only slightly increased. On the other hand, the current density j _ac (D = 20) increases because the influence of ρ _{H +} on the conventional large cell is reduced, but the current density j _ac (L = 1) and the current density j _ac (d = 1) It stayed at about 1/2 of that.

As the catalytic performance of the reduction reaction electrode 102 and the oxidation reaction electrode 104 is improved, or the surface area is increased by using a porous substrate, the reduction reaction electrode 102 is provided. Assuming that the oxidation reaction electrode 104 is doubled, as shown in FIG. 7C, the current density j _ac has increased to nearly double. However, due to the influence of ρ _{H +} , it was not completely doubled. On the other hand, although the current density j _ac (D = 20) also increases, the effect of ρ _{H +} is more significant, so that only a slight improvement is achieved. As a result, superior characteristics were obtained with the interpenetrating electrode.

<Integrated chemical reactor>
As shown in FIG. 9, an integrated chemical reaction apparatus 100 can be configured by combining an interpenetrating electrode and a photocharge separation element (solar cell). In such an integrated chemical reaction apparatus 100, the electrode area is halved compared to the case where the oxidation reaction electrode and the reduction reaction electrode are formed on both sides of the photoelectric charge separation element (solar cell), respectively. Nevertheless, a high operating current j _op , i.e. a high reaction yield, is obtained. Here, the operating current j _op is influenced by the widths of the reduction reaction electrode 102 and the oxidation reaction electrode 104, but does not depend on the outer shape of the chemical reaction apparatus 100. Therefore, if the supply of the electrolyte is sufficient, it is possible to prevent a decrease in efficiency due to an increase in size.

  As described above, since it is necessary to apply a voltage of 2 V or more between the reduction reaction electrode 102 and the oxidation reaction electrode 104 for the operation of artificial photosynthesis, a plurality of crystalline silicon solar cells are used. It is assumed that elements connected in series are used.

The current density (j _pv ) _−voltage (V _pv ) of the crystalline silicon solar cell can be expressed by Equation (10). Here, q, k _B and T are the elementary charge amount, Boltzmann constant, temperature (300K), j _ph is the photocurrent density, and j ₀ and n are the reverse saturation current and ideal factor of the diode, respectively.

When these values were obtained so that typical characteristics of a commercial product were obtained when irradiated with light of AM1.5G spectrum, which is a standard condition of sunlight, and 1 sun (intensity 100 mW / cm ² ), j _ph = 40 mA / cm ² , j ₀ = 2 × 10 ⁻⁸ , n = 1.1. At this time, the conversion efficiency was 19.9%, the open-circuit voltage was 0.61 V, and the shape factor was 0.82. FIG. 10A shows the current density j _{pv -voltage} V _pv characteristic at this time.

On the other hand, the silicon solar cell having the highest conversion efficiency currently uses an amorphous silicon / crystalline silicon heterojunction, and the conversion efficiency is 26%. Although the manufacturing cost is currently high, it is expected to gradually spread in the future. Therefore, the case where this is used is also considered. When the parameters of Equation (10) are determined so as to be close to the current density (j _pv ) -voltage (V _pv ) characteristics reported in the literature, j _ph = 42 mA / cm ² , j ₀ = 2 × 10 ⁻¹⁰ , n = 1.1. At this time, the conversion efficiency was 26.2%, the open end voltage was 0.74 V, and the shape factor was 0.84. FIG. 10B shows the current density j _{pv -voltage} V _pv characteristic at this time. Compared with FIG. 10A, this is characterized by a higher open-circuit voltage.

In order to obtain the voltage required for the artificial photosynthesis reaction, the current density j _pv ^(m) _−voltage V _pv characteristic when m crystalline silicon solar cells are connected in series can be expressed by Equation (11).

By solving simultaneous equations consisting of the current density j _{pv -voltage} V _pv characteristic of the crystalline silicon solar cell and the current density j _{ac -voltage} V _ac characteristic of the chemical reaction device 100 shown in FIG. can get. The case of the integrated chemical reaction apparatus 100 using the interpenetrating electrodes of FIG. 9 can be considered in the same way, and the areas of the reduction reaction electrode 102 and the oxidation reaction electrode 104 are each ½ of the area of the solar cell. _Therefore , a characteristic in which the current density j _ac is replaced with the current density j _ac / 2 may be used.

FIG. 11 shows the current density j _ac / 2 calculated from the current density j _{ac -voltage} V _ac characteristic when the period d = 1 cm when the interelectrode distance L = 1 cm in the conventional facing type as a comparative example. The current density j _ac (L = 1), the current density j _ac (D = 20) in the case of a conventional integrated type as a comparative example, and the current density j _{pv -voltage} V _pv characteristics of the solar cell are shown. FIG. 11A shows the characteristics when four crystalline silicon solar cells are connected in series. Similarly, FIG. 11 (b) to FIG. 11 (e) show characteristics when five to eight crystalline silicon solar cells are connected in series, respectively. FIG. 12A shows the current density at the operating point, which is the intersection of the current density j _{ac -voltage} V _ac characteristics of the chemical reaction device 100 and the solar cell current density j _{pv -voltage} V _pv characteristics in FIG. (Per unit area of solar cell).

The optimum value of the number (number) m of series connection of the crystalline silicon solar cells depends on the characteristics of the reduction reaction electrode 102 and the oxidation reaction electrode 104 and ρ _{H +} . The lower the rising (threshold) voltage of the current density j _{ac and} the steeper the subsequent slope, the smaller the number m of serial connection of crystalline silicon solar cells, so that a larger operating current density can be obtained. The operating current density depends on the current density j _ac when the number of serial connections m of the crystalline silicon solar cells is small, and is defined by the current density j _pv when the number of serial connections m of the crystalline silicon solar cells is large. The operating point is the intersection of the voltage _{V pv} characteristic maximum output point of the solar cell _{(j pv'V} pv maximum - current density of the chemical reactor 100 _{j ac} - voltage _{V ac} characteristics the solar cell of the current density _{j pv} The operating current is maximized when it is close to a point, that is, a point where j _pv starts to decrease. In the case of a conventional chemical reaction apparatus using a small counter-type electrode, the operating current is maximized when the number m of serial connection of crystalline silicon solar cells is 5, and the operating current at that time is 7. It was 7 mA / cm ² . On the other hand, in the case of chemical reaction apparatus 100 using an interpenetrating electrode in the present embodiment, the current density is low when the number m of series connections of crystalline silicon solar cells is 5, and when the number m of series connections is six. The operating current reached a maximum at that time, and the operating current at that time was 6.0 mA / cm ² . The value of this operating current was close to the maximum value in the case of a chemical reaction apparatus using a conventional small electrode. On the other hand, in the case of a chemical reaction apparatus using a conventional integrated electrode (diameter D = 20 cm), the operating current is 5.5 mA / cm ² when the number of serial connections m is 7, and an interpenetrating electrode is used. It was a value that did not reach the value in the case of the integrated chemical reaction apparatus 100. Furthermore, in a chemical reaction apparatus using a conventional integrated electrode, since the light absorption of the oxidation reaction electrode 104 that is normally formed on the light incident surface side of the solar cell cannot be ignored, the operating current j _op is further reduced. Become. Also, while the operating current j _op becomes smaller the greater diameter D Gayori, when the chemical reactor 100 integral with interpenetrating electrodes in this embodiment the operating current j _op is a cell Since it is a feature that does not depend on the outer shape, it is a suitable structure for constructing a large cell. As described above, when the counter electrode is enlarged, it is difficult to uniformly retain a sufficient amount of electrolyte, and thus the operating current j _op may be reduced.

When the irradiation light intensity decreases, the short-circuit current value of the solar cell decreases, so the operating point changes to a lower current and constant voltage side. Therefore, the value of the optimum number m of serial connection of crystalline silicon solar cells is reduced. As shown in FIG. 12 (b), in the case of 0.5 sun irradiation, it was optimum (the maximum value was 3.7 mA / cm ² ) when the number m of serial connection of crystalline silicon solar cells was 5. In this case, there was almost no difference between the chemical reaction apparatus using the conventional counter electrode and the chemical reaction apparatus 100 using the interpenetrating electrode in the present embodiment.

As described above, the characteristics and superiority of the cells of each configuration vary depending on the irradiation light intensity. Therefore, the amount of charge generated per day is compared. The fluctuation I _sun (t) of the solar radiation amount is expressed by a simple cosine curve as shown in the equation (12), ignoring the fluctuation of the spectrum in one day and considering only the change of the solar altitude.

FIG. 13A shows the result of _obtaining the operating current j _op corresponding to the solar radiation intensity at each time. However, the value of the number m in series connection is the optimum value for each chemical reaction device. For a chemical reaction device using a conventional counter electrode (interelectrode distance L = 1 cm), the number m in series connection is five. The number of series connection of a chemical reaction apparatus using an integrated electrode (diameter D = 20 cm) and an integrated chemical reaction apparatus 100 using an interpenetrating electrode (period d = 1 cm, gap w = 0.1 cm) 6 were used. Further, the same calculation was performed for a chemical reaction apparatus using a conventional integrated electrode having a diameter D = 50 cm, and it was optimum when the number m of series connections was eight. If the operating current j _op obtained in this way is integrated at time t, the daily charge amount can be obtained as shown in FIG. By using the interpenetrating electrode, a charge amount exceeding about 10% of the value of the conventional integrated electrode (diameter D = 20 cm) was obtained. In the case of the conventional integrated electrode (diameter D = 50 cm), the value remained even lower.

14 (a) and 14 (b) show the phosphate buffer concentration of 0.8M, which shows the current density j _{ac -voltage} V _ac characteristics in FIGS. 7 (b) and 7 (c). The calculation result of the operating current j _op when the current density of the electrode 102 and the electrode for oxidation reaction 104 is double is shown. In the case of the integrated chemical reaction apparatus 100 using the interpenetrating electrode and the chemical reaction apparatus using the counter electrode, the operating current j _op becomes 0. 0 when the phosphate buffer concentration becomes 0.8M compared to 0.4M. Although the increase was about ² mA / cm ² , the tendency of dependence on the number m of series connections did not change. On the other hand, in the chemical reaction apparatus using the conventional integrated electrode, the increase in the current density j _ac is large, so the maximum value of the operating current j _op (6.4 mA / cm ² , the number of series connections m = 6) is mutually penetrating. It slightly exceeded the value (6.2 mA / cm ² , the number of series connections m = 6) in the chemical reaction apparatus 100 using a mold electrode. However, as described above, the disadvantage is that the dependence on the diameter D and the influence of light absorption of the reduction reaction electrode 102 cannot be avoided.

In contrast, when the current density of the reduction reaction electrode 102 and the oxidation reaction electrode 104 is doubled, in the case of the integrated chemical reaction apparatus 100 using the interpenetrating electrodes, the number m of series connections is 5 The operating current j _op increased to 7.3 mA / cm ² at this time. On the other hand, in the case of the chemical reaction apparatus using the conventional integrated electrode, as shown in FIG. 7 (c), it was only slightly increased from the value of FIG. 12 (a). That is, when the reduction reaction electrode 102 and the oxidation reaction electrode 104 having higher activity are realized, the superiority of the integrated chemical reaction apparatus 100 using the interpenetrating electrode is more significant than the conventional integrated electrode. Became prominent.

The characteristics also changed depending on the characteristics of the photocharge separation element. FIG. 14 (c) shows the results when using a heterojunction silicon solar cell. For the integrated chemical reaction apparatus 100 using interpenetrating electrodes, the optimum value is obtained when the number m of series connections is 6, but unlike FIG. 12A, when the number m of series connections is 5. It was not much different from the value of. Even in the case where the same number m of series connections is 6, in the case of a crystalline silicon element, as shown in FIG. 12A, the current density is slightly lower than the short-circuit current density of the solar cell at the operating point. On the other hand, in the case of the heterojunction silicon element, a value close to the short-circuit current density is maintained up to a higher voltage, and thus a high operating current j _op (6.9 mA / cm ² ) was obtained.

As described above, in the chemical reaction apparatus 100 using the interpenetrating electrodes, the appropriate number m of series connections depends on the characteristics of the reduction reaction electrode 102 and the oxidation reaction electrode 104, the concentration of the electrolytic solution, and the characteristics of the combined solar cells. By selecting, the size can be made larger than that of a chemical reaction device using a conventional integrated electrode, and an operating current j _op close to that of a chemical reaction device using a counter electrode can be obtained.

Further, according to the chemical reaction apparatus 100 in the present embodiment, a smooth flow of protons from the oxidation reaction electrode 104 to the reduction reaction electrode 102, a sufficient supply of raw materials (CO _{2 and the} like), and a product (HCOOH) Etc.) can be made compatible with a sufficient amount of convection for rapid discharge.

[Second Embodiment]
In the present embodiment, it is assumed equal the period d _a period d _c and oxidation electrode 104 of the reduction electrode 102, the characteristics of the chemical activity of the reduction reaction electrode 102 and the oxidation reaction electrode 104 It may be different depending on the situation. Specifically, by reducing the width of the reduction reaction electrode 102 and the oxidation reaction electrode 104 having the lower chemical activity per unit area and narrowing the width of the higher activity electrode, the balance between the two is achieved. Is preferable.

  As mentioned earlier, the catalytic function can vary greatly depending on the material, support and manufacturing process. The characteristics of the electrode for reduction reaction and the electrode for oxidation reaction shown in FIG. 5 and the characteristics shown in the literature (T.Arai, S.Sato, and T.Morikawa, Energy Envision. Sci 8, 1998 (2015)) were compared. . Although the characteristics of the electrode for reduction reaction were approximately the same, the threshold for the oxidation reaction electrode did not change, but the current density at a predetermined applied voltage equal to or higher than the threshold was about three times that in the literature. Therefore, as shown in FIG. 15, the case where only the current density of the oxidation reaction electrode is three times the current density shown in FIG.

In this case, the differential resistance of each reaction of the oxidation reaction electrode and the reduction reaction electrode is dV _a / dj _a = 14 Ω · cm, dV _c / dj _c = 73 Ω · cm (absolute value). That is, the differential resistance of the reduction reaction electrode is much larger than that of the oxidation reaction electrode. Therefore, when the total area of the reduction reaction electrode and the oxidation reaction electrode is limited as in the interpenetrating electrode, if the area of the reduction reaction electrode is relatively large, the current value per total area may be increased. it can.

As shown in FIG. 16, the width of the oxidation reaction electrode 104 is d _a −w / 2, and the width of the reduction reaction electrode 102 is d _c −w / 2. Expressions (5) to (9) are changed to Expressions (13) to (17).

FIG. 17 (a), the period _{d a} + reduction period of the reaction electrode 102 _d c = 2 cm period _{d a} under constraint of the oxidation reaction electrode 104, by changing the period _{d c,} the voltage _V ac = 2V The result of calculating the current density j _ac when a constant voltage is applied is shown. Compared with the case where the period d _a = the period d _c = 1 cm, the current density j _ac is increased by about 10% when the optimum value of the period d _a = 0.7 cm and the period d _c = 1.3 cm is used. To do. In addition, it is thought that there is no particular fault of making it asymmetric.

When the overvoltage of the reduction reaction electrode 102 and the oxidation reaction electrode 104 (difference between the operating potential and the threshold potential at which the reaction occurs) increases, the catalyst may deteriorate, and the selectivity of the reaction may be impaired. . When the reduction reaction electrode 102 is intended for the reduction reaction from carbon dioxide (CO ₂ ) to formic acid (HCOOH), when the overvoltage increases, other substances such as carbon monoxide (CO) are generated or in an aqueous solution In some cases, water (H ₂ O) may be reduced to produce hydrogen (H ₂ ).

The average overvoltages V _op-a and V _op-c of each of the oxidation reaction electrode 104 and the reduction reaction electrode 102 can be expressed by Expression (18) and Expression (19).

FIG. 17B shows overvoltages V _op-a and V _op-c when the voltage V _ac = 2V corresponds to FIG. While the overvoltage V _op-c is reduced by widening the width of the reduction reaction electrode 102 having a large differential resistance of the reaction, the increase in the overvoltage V _op-a is slight. The problem is reduced. FIG. 17C shows the current density j _{ac -voltage} V _ac characteristic when the period d = 1 cm which is a symmetric type and the period d _a = 0.7 cm and the period d _c = 1.3 cm which are optimum values of an asymmetric type. (Respectively j _ac (d = 1), j _ac (d _a = 0.7, d _c = 1.3)).

FIG. 18 shows a symmetric type (period d = 1 cm, gap w = 0.1 cm) and asymmetric type (period d _a = 0.7 cm, period d _c = 1.3 cm, gap w = 0.1 cm). and electrode voltage _V ac = 2V local proton current density of oxidation electrodes 104 and reduction electrodes 102 upon application of a ^{_{j H + (y) (x}} , 0 +), caused by ρ _{H +} φ (x, The result of having compared the fluctuation | variation (relative value) of z) is shown. The average value of local proton flow density j _{H +} ^(y) (x, 0 ⁺ ), j _{H + a} , j _{H + c} is j _{H + a} = j _{H + c} = 4.4 mA / cm ² in the case of symmetric type and j _H in the asymmetric type. ^{_{H + a = 7.0mA / cm 2}} , were j H + c = 3.8mA / cm 2. In either case, the oxidation reaction electrode 104 is more active (the absolute value of the reaction differential resistance dV _a / dj _a is smaller), and therefore the influence of ρ _{H +} is relatively greater. The value closer to 102 (the side closer to x = 0) is larger, and the value closer to 102 is smaller. Conversely, since dV _a / dj _a is dominant for the reduction reaction electrode 102, the local proton flow density j _{H +} (x, 0 ⁺ ) hardly depends on the distance from the oxidation reaction electrode 104.

Next, the characteristics of the integrated chemical reaction apparatus 100 using an asymmetrical interpenetrating electrode are obtained. For the reduction reaction electrode 102 and the oxidation reaction electrode 104, assuming that the oxidation reaction electrode 104 has a significantly higher activity as shown in FIG. 15, the current shown in FIG. Density j _{ac -voltage} V _ac characteristics were used.

FIG. 19 shows the current density j _op (per unit area of the solar cell) at the operating point of an integrated chemical reaction apparatus in which m crystalline silicon solar cells are combined in series. When the irradiation light intensity is 1 sun, the current density j _op is maximized when the number m of series connections is 6, whereas when the intensity is 0.5 sun, the optimum value is obtained when the number m of series connections is 5. became. However, in the case of the asymmetric type, the difference between when the number of series connections m at the time of 1 sun irradiation was 5 and 6 was small.

Reflecting these, the amount of charge generated per day was maximized when the number m of series connections was five. As shown in FIG. 20, there is almost no difference between the current densities j _op when the irradiation light is weak, but as the irradiation light intensity increases, the asymmetric type (period d _a = 0.7 cm, period d _c = 1. 3 cm, gap w = 0.1 cm) was dominant. As a result, a charge amount that is approximately 5% higher than the symmetrical value (period d = 1 cm, gap w = 0.1 cm) was obtained. In addition to this, it is possible to reduce problems of deterioration and reaction selectivity.

[Modification]
FIG. 21 shows a configuration in which a plurality of chemical reaction apparatuses 100 are connected in parallel. In this case, it is preferable to immerse a plurality of chemical reaction devices 100 connected in parallel in an electrolytic solution and apply a voltage from a power source (solar cell or the like). In addition, the connection structure of the some chemical reaction apparatus 100 is not limited to this. For example, a plurality of chemical reaction devices 100 may be connected in series or in series and parallel, and a voltage corresponding to the number of series connections may be applied. When a solar cell is used as the power source, as shown in FIG. 22, a plurality of solar cells 108 may be connected in combination in series or in parallel depending on conditions such as a grounding location.

  In addition, in the said embodiment and modification, although it was set as the structure which forms an interpenetrating electrode in the single side | surface of the chemical reaction apparatus 100, it is good also as a structure formed in both surfaces.

DESCRIPTION OF SYMBOLS 10 Conductive layer, 12 Conductor layer, 14 Conductive layer, 16 Oxidation catalyst layer, 100 Chemical reaction device, 102 Reduction reaction electrode, 104 Oxidation reaction electrode, 106 Electrolyte, 108 Solar cell, 110 Window material, 112 Frame Material, 114 substrate.

Claims (7)

  The oxidation reaction electrode and the reduction reaction electrode are alternately arranged on the same surface of the substrate, and the width of the oxidation reaction electrode and the width of the reduction reaction electrode along the alternate arrangement direction are different. Electrode for chemical reaction. The chemical reaction electrode according to claim 1,
The electrode for chemical reaction, wherein the width of the electrode having higher current density-voltage characteristics is set narrower according to the current density-voltage characteristics of the oxidation reaction electrode and the reduction reaction electrode . The electrode for chemical reaction according to claim 1 or 2,
A solar cell connected to the oxidation reaction electrode and the reduction reaction electrode;
A chemical reaction cell characterized by combining the above. A chemical reaction cell according to claim 3,
A chemical reaction cell, wherein the solar cell is an integral type having a part of the substrate. A chemical reaction cell according to claim 3 or 4,
The solar cell is a chemical reaction cell characterized in that 3 to 6 cells of crystalline silicon solar cells are connected in series.   A chemical reaction cell according to any one of claims 3 to 5, wherein the chemical reaction cell is immersed in an electrolytic solution. A plurality of chemical reaction cells according to claim 6,
In the plurality of chemical reaction cells, the oxidation reaction electrode and the reduction reaction electrode are provided on one surface or both surfaces, and the surfaces on which the oxidation reaction electrode and the reduction reaction electrode are provided are arranged to face each other. A chemical reaction device characterized by