JP7081226B2 - Electrodes for chemical reactions, cells for chemical reactions using them, and chemical reaction equipment - Google Patents

Description

The present invention relates to an electrode for a chemical reaction, a cell for a chemical reaction 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) ) Etc. are disclosed. In order to realize artificial photosynthesis, it is necessary to apply a potential difference of 2 to 3 V between the electrode for oxidation reaction and the electrode for reduction reaction. In order to realize this, optical electrodes in which oxidation / reduction catalysts are supported on both sides of an amorphous silicon-based 3-junction solar cell (a-Si 3J-SC) are used (Non-Patent Documents 1 and 2). Further, using an amorphous silicon-based 3-junction solar cell, a reduction catalyst is supported on the back surface (opposite the light incident surface) to form a reduction reaction electrode, and a member having an oxidation catalyst function is included so as to face the electrode. However, an artificial photosynthetic cell in which a solar cell and an electrochemical cell are integrated is used, in which an electrode for an oxidation reaction is arranged and connected to a surface electrode of the solar cell (Non-Patent Document 3). In addition, there is also an example in which a facing cell is configured by using a III-V group compound 2-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 flow smoothly from the oxidation reaction electrode to the reduction reaction electrode.

However, in an integrated chemical reaction cell in which an oxidation reaction electrode and a reduction reaction electrode are provided on one surface of the solar cell, the cells wrap around the end of the cell and protonate in the electrolytic solution. There is a problem that the efficiency of the reaction decreases when the cell is enlarged. Further, in the case of a facing 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 performed. Therefore, it becomes difficult to uniformly convection a sufficient amount of the electrolytic solution.

In one aspect of the present invention, 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 reduction reaction electrode along the alternating arrangement direction are provided. It is an electrode for a chemical reaction characterized by having different widths.

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

Another aspect of the present invention is a chemical reaction cell comprising a combination of the oxidation reaction electrode and a solar cell connected to the reduction reaction electrode.

Here, it is preferable that the solar cell is an integrated type as a part of the substrate.

Further, it is preferable that the solar cell is a series of crystalline silicon solar cells having 3 cells or more and 6 cells or less connected in series.

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

In another aspect of the present invention, a plurality of the chemical reaction cells are provided, and in the plurality of chemical reaction cells, the oxidation reaction electrode and the reduction reaction electrode are provided on one side or both sides, and the oxidation reaction electrode and the oxidation reaction electrode are provided. It is a chemical reaction apparatus characterized in that the surfaces provided with the reduction reaction electrodes are arranged so as to face each other.

According to the present invention, an electrode for a chemical reaction, an electrode for a chemical reaction using the electrode, a cell for a chemical reaction, and chemistry, in which protons can be easily transferred and a sufficient amount of an electrolytic solution can be circulated for supplying a raw material and discharging a product. 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 and the electrode for oxidation reaction of a current value. It is a figure which shows the example of the relationship between the current density and the potential of the electrode for an oxidation reaction and the electrode for a 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 which used the mutual penetration type electrode, the opposed type electrode, and the conventional integrated type electrode. It is a figure which shows the relationship between the current density and voltage in a chemical reaction cell. The figure shows the fluctuation of the potential φ (x, z) due to the specific resistance ρ _{H +} when the local proton flow density and the resistance component associated with the proton propagation are regarded as the ohmic resistance in the chemical reaction cell using the mutual penetration type electrode. be. 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 the relationship between the current density and the 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 number of series connection of a solar cell, and the current density at an operating point. It is a figure which shows the change of the operating current and the electric charge amount in one day when the time change is taken into consideration. It is a figure which shows the relationship between the number of series connection of a solar cell, and the current density at an operating point when various conditions are changed. It is a figure which shows the example of the relationship between the current density and the potential of the electrode for an oxidation reaction and the electrode for a reduction reaction. 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 (second embodiment). It is a figure which shows the current density, the overvoltage and the current density-voltage characteristic when the width of the electrode for a reduction reaction and the electrode for an oxidation reaction is changed. It is a figure which shows the fluctuation of the potential φ (x, z) caused by the specific resistance ρ _{H +} when the local proton flow density in a chemical reaction cell and the resistance component accompanying the proton propagation are regarded as the ohmic resistance. It is a figure which shows the relationship between the number of series connection of a solar cell, and the current density at an operating point. It is a figure which shows the change of the operating current and the electric charge amount in one day when the time change is taken into consideration. It is a figure which shows the structure when a plurality of chemical reaction apparatus are connected in parallel. It is a figure which shows the structure when a plurality of chemical reaction apparatus are connected in series-parallel.

As shown in the schematic diagram of FIG. 1, the chemical reaction apparatus 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 cell 108, a window material 110, and a frame material. Consists of including 112.

2 and 3 are perspective views and cross-sectional views showing the configurations of the reduction reaction electrode 102 and the oxidation reaction electrode 104. FIG. 3 is a cross-sectional view taken along the line AA in FIG. In addition, in FIGS. 2 and 3, the dimensions of each part are changed from the actual ones 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 electrode 102 and the oxidation reaction electrode 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 extending along the y direction and oxidation reaction electrodes 104 may be alternately arranged along the x direction. good. At this time, as shown in FIG. 2, by connecting the ends of the reduction reaction electrode 102 and the oxidation reaction electrode 104, the reduction reaction electrode 102 and the oxidation reaction electrode 104 having a comb shape are combined. It will be configured.

Here, the arrangement of the reduction reaction electrode 102 and the oxidation reaction electrode 104 alternately is not limited to the configuration in which the 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 may be configured as such. 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 shapes of the respective electrodes may be irregular.

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 a conductive layer 10 and a conductive 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 or the like. 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 contains 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, but may be a semiconductor oxide, a nitride, a 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), and zinc oxide (ZnO). In particular, considering thermal and chemical stability, it is preferable to use fluorine-doped tin oxide (FTO).

The conductor layer 12 is composed of a conductor containing a material having a reduction catalytic function. The conductor can be made of a material including the carbon material (C). It is preferable that the size of the single structure of the carbon material is 1 nm or more and 1 μm or less. The carbon material preferably contains, for example, at least one of carbon nanotubes (CNTs), graphene and graphite. For graphene and graphite, the size is preferably 1 nm or more and 1 μm or less. If it is a carbon nanotube, it is preferable that the diameter is 1 nm or more and 40 nm or less. The conductor can be formed by applying a carbon material mixed with a liquid such as ethanol by spraying and heating the conductor. Instead of spraying, it may be applied by spin coating. Further, instead of using spin coating, the solution may be directly dropped, dried and applied. Further, carbon paper (CP) may be used as the material containing the carbon material. Further, carbon paper (CP) coated with carbon nanotubes (CNT) or the like may be used.

The conductor layer is modified with a material having a reducing function, such as a complex catalyst. The complex catalyst is preferably, for example, a ruthenium complex. The complex catalyst may be, for example, [Ru {4,4'-di (1-H-1-pyrrolipropyl carbononate) -2,2'-bipyridine} (CO) (MeCN) Cl ₂ ], [Ru {4,4'. -Di (1-H-1-pyridriplopyl carbononate) -2,2'-bipyridine} (CO) ₂ Cl ₂ ], [Ru {4,4'-di (1-H-1-pyridopely carbonate) -2, 2'-bipyridine} (CO) ₂ ] _n , [Ru {4,4'-di (1-H-1-pyridopyl carbonate) -2,2'-bipyridine} (CO) (CH ₃ CN) Cl ₂ ] And so on.

Modification with a complex catalyst can be made by applying a solution prepared by dissolving the complex in an acetonitrile (MeCN) solution onto the conductor of the conductor layer 12. Further, the modification with a complex catalyst can also be performed by an electrolytic polymerization method. Using the conductor electrode of the conductor layer 12 as the working electrode, the glass substrate coated with fluorine-containing tin oxide (FTO) as the counter electrode, and the Ag / Ag ⁺ electrode as the reference electrode, Ag / Ag in the electrolytic solution containing the complex catalyst. After a cathode current is passed through the ⁺ electrode so that it becomes a negative voltage, an anode current is passed through the Ag / Ag ⁺ electrode so that it becomes a positive potential, so that the conductor of the conductor layer 12 is covered with a complex catalyst. Can be modified. Acetonitrile (MeCN) can be used as the electrolyte solution, and Tetrabutylammoniumperchlate (TBAP) can be used as the electrolyte.

The conductor layer 12 thus formed is supported, coated or affixed on the conductive layer 10 constituting the reduction reaction electrode 102. As a result, the reduction reaction electrode 102 including the conductive layer 10 and the conductive 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 a conductive layer 14 and an 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, considering thermal and chemical stability, it is preferable to use fluorine-doped tin oxide (FTO).

The conductive layer 10 and the conductive layer 14 are provided with a transparent conductive layer on the entire surface of the surface of the substrate 114 on which the reduction reaction electrode 102 and the oxidation reaction electrode 104 are provided, and the transparent conductive layer is provided on the entire surface of the reduction reaction electrode 102 and the oxidation reaction electrode 104. It can be formed by processing it into a comb shape that matches 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 from each other. It is preferable to process it so that it is in a state of being free.

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

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

For example, iridium oxide (IrOx) nanocolloids are synthesized. Next, a yellow solution adjusted to pH 13 by adding a 10 wt% sodium hydroxide (NaOH) aqueous solution to 50 ml of a 2 mM potassium (IV) chloride (K ₂ IrCl ₆ ) aqueous solution was prepared at 90 ° C. using a hot stirrer. Heat for 20 minutes. The resulting blue solution 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 the pH to 1, and the mixture is stirred for 80 minutes to obtain a nanocolloidal aqueous solution of iridium oxide (IrOx). Further, a 1.5 wt% NaOH aqueous solution (1-2 ml) is added dropwise to this solution to adjust the pH to 12. The nano-colloidal aqueous solution of iridium oxide (IrOx) thus obtained is applied onto the conductive layer 14 at pH 12, and kept at 60 ° C. for 40 minutes in a drying oven to dry. After drying, the precipitated salt can be washed with ultrapure water to form the oxidation reaction electrode 104. The application and drying of the nanocolloidal aqueous solution of iridium oxide (IrOx) 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 arranged 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 electrolytic solution 106 is supplied. The reaction product can be a carbide compound, for example, carbon dioxide (CO ₂ ). Further, it is preferable that the electrolytic solution 106 is a phosphate buffered aqueous solution or a boric acid buffered aqueous solution. In a specific configuration example, a tank for supplying a carbon dioxide (CO ₂ ) saturated phosphate buffer is provided, and the liquid is supplied to the surfaces of the reduction reaction electrode 102 and the oxidation reaction electrode 104 by a pump to perform a reduction 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 to each other, and an appropriate bias voltage is applied. The means for applying the bias voltage is not particularly limited, and examples thereof include chemical batteries (including primary batteries, secondary batteries, etc.), constant voltage sources, solar cells, and the like. At this time, the positive electrode is connected to the oxidation reaction electrode 104, and the negative electrode is connected to the reduction reaction electrode 102.

In this embodiment, the solar cell 108 is adopted. The solar cell 108 can be arranged adjacent to the reduction reaction electrode 102 and the oxidation reaction electrode 104. In the example of FIG. 1, the solar cell 108 is arranged on the back surface of the reduction reaction electrode 102 and the oxidation reaction electrode 104, the positive electrode of the solar 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 ). At around pH 7, the oxidation potential of water (H ₂ O) is 0.82 V, and the reduction potential is −0.41 V (both are NHE). The reduction potentials of carbon dioxide (CO ₂ ) to carbon monoxide (CO), formic acid (HCOOH), and methyl alcohol (CH ₃ OH) are -0.53V, -0.61V, and -0.38V, respectively. .. Therefore, the potential difference between the oxidation potential and the reduction potential is 1.20 to 1.43 V.

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

[Examination of electrode structure]
The difference between the oxidation potential of water (H ₂ O) and the reduction potential of carbon dioxide (CO ₂ ) to formic acid (HCOOH) is 1.43 eV. Since an overvoltage of the reaction is required 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.

SnO ₂ : F (FTO) -equipped glass substrate with IrO _x for 1 cm ² oxidation reaction electrode (anode), carbon paper with multilayer carbon nanotubes, and Ru complex polymer supported with SnO ₂ : F (FTO) ) Attached A measurement result of the current value when a reduction reaction electrode (cathode) of the same size fixed on a glass substrate is immersed in an electrolytic solution filled in a tubular container with an inner diameter of 2.5 cm and a constant voltage of 2 V is applied. Is shown in FIG. The electrolytic solution is a saturated solution of carbon dioxide (CO ₂ ) in a phosphoric acid buffer aqueous solution having a concentration of 0.4 M or 0.8 M. The horizontal axis is the distance L between the electrode for oxidation reaction and the electrode for reduction reaction in the tube.

In FIG. 4, the circle (broken line) shows the measured value when a 0.8 M phosphate buffer aqueous solution is applied, and the square mark (broken line) shows the measured value when a 0.4 M phosphate buffer aqueous solution is applied. show. The solid line shows the result of fitting described later for each.

As shown in FIG. 4, the current value decreased as the distance L between the electrode for the oxidation reaction and the electrode for the reduction reaction increased. That is, it was found that the resistance component associated with the propagation of protons in the electrolytic solution from the oxidation reaction electrode to the reduction reaction electrode cannot be ignored as compared with the reaction resistance of the oxidation reaction electrode and the reduction reaction electrode. Therefore, in order to connect the electrode for oxidation reaction and the electrode for reduction reaction to the photocharge separation element to form an artificial photosynthetic cell, and to convert solar energy into chemical energy of formic acid (HCOOH) with high efficiency, oxidation is performed. The reaction electrode-reduction reaction electrode distance must be kept short. Therefore, it is difficult to obtain high reaction efficiency when the integrated cell in which the electrode for oxidation reaction is formed on one surface of the photocharge separation element and the electrode for reduction reaction is formed on the other surface is enlarged. On the other hand, in a facing type cell in which the electrode for oxidation reaction and the electrode for reduction reaction are opposed to each other and the space between them is filled with an electrolytic solution to cause convection, the distance between the electrode for oxidation reaction and the electrode for reduction reaction is limited, so that it is a raw material. Due to the sufficient supply of carbon dioxide (CO ₂ ) and the rapid discharge of the product, formic acid (HCOOH), it becomes difficult to uniformly convection a sufficient amount of electrolyte into the enlarged cell.

<Quantitative evaluation of resistance component>
The resistance component associated with the propagation of protons in the electrolytic solution was quantitatively evaluated. FIG. 5A shows the current density (ja) _-potential ( _Va ) characteristics of the oxidation reaction electrode used in the above experiment. FIG. 5 (b) shows the current density (j _c ) -potential (V _c ) characteristics of the reduction reaction electrode used in the experiment of the above comparative example. In each case, the phosphate buffer concentration of the electrolytic solution was 0.4 M.

The current density (jac) _{-voltage (Vac )} characteristics between the oxidation reaction electrode and the reduction reaction electrode when the oxidation reaction electrode and the reduction reaction electrode are connected are the specific resistance ρ of the resistance component associated with proton propagation. Considering the ohmic resistance of _{H +} , it can be obtained by solving the simultaneous equations of the equations (1) and (2).

When the distance L between the electrode for oxidation reaction and the electrode for reduction reaction becomes small and approaches the inner diameter of the tube, the influence of the shape of the tube and the electrode becomes large, so that the resistance component deviates from the proportional relationship with respect to the distance L. The parameter for correcting this is ρ ₀ . When the resistance r _{H +} was determined by fitting so that the _jac at the phosphoric acid buffer concentration of 0.4 M and _Va = 2 V matched the experimental value, it was ρ _{H +} = 28 Ω · cm and ρ ₀ = 35 Ω. However, as described above, if the distance L is small, the mathematical formula (2) does not hold, so the fitting was performed in the range of the distance L ≧ 10 cm. As shown in FIG. 4, the fitting results were in good agreement with the experimental values.

Further, 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 halved of the values of 0.4M (ρ _{H +} = 14Ω · cm, ρ ₀ = 17. 5Ω) was used for calculation. As shown in FIG. 4, the measurement result and the fitting result at 0.8 M showed a good agreement.

From the results of these fittings, it can be said that the resistance component associated with the propagation of protons in the electrolytic solution 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 a mutual penetration type electrode) in which a reduction reaction electrode 102 and an oxidation reaction electrode 104 having a comb shape in the present embodiment are combined will be examined.

Since the distance between the electrodes does not directly affect the propagation of protons even when a plurality of the electrodes are arranged side by side, it is sufficient to design the electrodes only in consideration of the influence of convection of the electrolytic solution. Hereinafter, the current density (jac) _{-voltage (Vac )} characteristics between the reduction reaction electrode 102 and the oxidation reaction electrode 104 of the mutual penetration type electrode are obtained, and the widths of the reduction reaction electrode 102 and the oxidation reaction electrode 104 are obtained. Investigate the effect of.

For simplification, consider a case where the length (y direction) of the strip-shaped reduction reaction electrode 102 and the oxidation reaction electrode 104 is sufficiently longer than the period 2d (x direction). 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 becomes zero, which can be a two-dimensional problem in the xz plane.

First, a case where the widths of the strip-shaped reduction reaction electrode 102 and the oxidation reaction electrode 104 are the same will be examined. Here, the gap between the reduction reaction electrode 102 and the oxidation reaction electrode 104 is w, and the width is the period d-gap w / 2. As described above, if the resistance component associated with the propagation of protons in the electrolytic solution (phosphate buffer concentration 0.4 M) is treated as an ohmic resistance with a specific resistance ρ _{H +} = 28 Ω · cm, equations (3) and equations (3) and equations ( The Poisson equation and the diffusion equation in 4) hold.

Here, φ (x, z) and j _{(b) H +} (x, z) are the local potential (relative value) and the proton flow density vector at the position (x, z), respectively. In the present specification, the vector is shown in bold in the mathematical formula and is indicated by the 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. Further, in the following, assuming a virtual electrode configuration in which the thickness of the conductor layer 12 and the oxidation catalyst layer 16 is 0, the interface between the conductor layer 10 and the conductor layer 12 and the conductive layer 14 and the oxidation catalyst layer 16 are assumed. The interface with and is indicated by z = 0, and the surfaces of the conductor layer 12 and the oxidation catalyst layer 16 are indicated by z = 0 ⁺ .

The voltage drop accompanying the reaction at the oxidation reaction electrode 104 is expressed by the equation (5) when the relationship between the current density _ja and the voltage _Va is linearly approximated.

Equation (5) shows the y component of the proton flow density vector j _{(b) H +} . φ (x, 0) is the potential of the conductive material (FTO) carrying the catalyst of the oxidation reaction electrode 104, 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 = 1.4969V is the threshold voltage at which the reaction occurs.

The current density _jac coincides with 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 the current density between the reduction reaction electrode 102 and the oxidation reaction electrode 104 when a constant voltage of _Vac = 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 the 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 phosphoric acid buffer concentration was 0.4 M. FIG. 6B shows, as a comparative example, a calculation result assuming that there is no adverse effect due to insufficient flow of the electrolytic solution in the opposed cell in which the electrode for the reduction reaction and the electrode for the oxidation reaction face each other. Is shown. FIG. 6C shows, as a comparative example, a calculation result assuming that there is no adverse effect due to insufficient flow of the electrolytic solution in the conventional integrated cell. However, in order to reduce the calculation load, the disk-shaped cells were calculated using cylindrical coordinates.

When the period d is small, the effect is small, and the current density _jac of the reduction reaction electrode 102-oxidation reaction electrode 104 when the mutual penetration type electrode is used is the opposite type in the range of the period d ≦ 1.0 cm. 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 _jac between the reduction reaction electrode 102 and the oxidation reaction electrode 104 when the mutual penetration type electrode is used is the case where the electrode spacing L is 2 cm in the opposed type. The value was (2.9 mA / cm ² ) or higher. On the other hand, in the case of the conventional integrated large cell, the current density _jac decreased to 1.3 mA / cm ² when the diameter D was 20 cm. On the other hand, when the mutual penetration type electrode was used, the value was exceeded even if the period d was 10 cm.

Further, the smaller the period d, the larger the current value per unit area of the reduction reaction electrode 102 and the oxidation reaction electrode 104. However, since the ratio of the gap w to the whole becomes large, the current density _jac becomes smaller when the period d = 0.5 cm as compared with the period d = 1 cm.

From the above results, it can be said that high conversion efficiency can be obtained by setting the period d to about 3 cm or less and ensuring a sufficient distance from the adjacent electrode or partition wall to secure the flow of the electrolytic solution. Actually, if the facing type is made large, it becomes difficult to uniformly retain a sufficient amount of the electrolytic solution as described above, so it is presumed that the mutual penetration type electrode as in the present embodiment becomes more dominant. Will be done.

FIG. 7A shows the current density j _ac -voltage V _ac characteristic when the period d = 1 cm at which the current density j _ac is maximized. FIG. 7 also shows the current density j _ac (L = 1) in the case of the conventional opposed type and the distance between electrodes L = 1 cm, and the current density j _ac (D = 20) in the case of the conventional integrated type. .. Since the current density _jac of the mutual penetration type electrode does not depend on the outer shape of the electrode, a high value that almost matches the conventional opposed type current density _jac (L = 1) can be obtained even if the size is increased. On the other hand, when the diameter of the conventional integrated electrode is 20 cm, the current density _jac (D = 20) is extremely low. It is clear from the results of FIG. 6 (c) that the current density _jac (D) becomes even smaller when the diameter of the conventional integrated electrode is increased for practical use. Further, when the size of the opposed electrode is increased, the problem of convection of the electrolytic solution arises.

FIG. 8 shows the local proton flow densities j _{H +} (x, 0 ⁺ ) of the reduction reaction electrode 102 and the oxidation reaction electrode 104 when the voltage V = 3.2584V is applied, and φ (x, 0 +) due to ρ _{H +} . It is a fluctuation (relative value) of z). The local proton flow density j _{H +} (x, 0 ⁺ ) was almost 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. Looking at the change in φ (x, 0 ⁺ ), φ (x, 0 ⁺ ) is larger near the center than near the ends (x = ± 0.5 cm) of the reduction reaction electrode 102 and the oxidation reaction electrode 104. It approaches 0. This result shows that 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 small and concentrated near the center.

As the phosphate buffer concentration increases, ρ _{H +} decreases, so that the current density j _ac -voltage V _ac characteristics are affected. When the concentration is doubled to 0.8 M, ρ _{H +} becomes 1/2 of 14 Ω · cm. However, since the inter-electrode distance L and the period d are used so that the influence of ρ _{H +} is small in both the opposed type electrode and the mutual penetration type electrode, the current density _jac (as shown in FIG. 7 (b)). L = 1) and the current density _jac (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 becomes smaller, but the current density j _ac (L = 1) and the current density j _ac (d = 1) are still present. It stayed at about 1/2 of.

As the catalytic performance of the reduction reaction electrode 102 and the oxidation reaction electrode 104 is improved, or the surface is provided with an uneven shape, or the effective surface area is increased by using a porous base material, the reduction reaction electrode 102 Assuming that the electrode 104 for the oxidation reaction is doubled, the current density _jac has almost doubled as shown in FIG. 7 (c). However, due to the influence of ρ _{H +} , it did not completely double. On the other hand, although the current density _jac (D = 20) also increased, the effect of ρ _{H +} was more remarkable, so that the improvement was only slight. As a result, the mutual penetration type electrode obtained excellent characteristics.

<Integrated chemical reaction device>
As shown in FIG. 9, a mutual penetration type electrode and a photocharge separation element (solar cell) can be combined to form an integrated chemical reaction apparatus 100. In such an integrated chemical reaction apparatus 100, the electrode area is halved as compared with the case where the oxidation reaction electrode and the reduction reaction electrode are formed on both sides of the photocharge separation element (solar cell), respectively. Nevertheless, a high operating current _hop , that is, a high reaction yield can be obtained. Here, the operating current _hop is affected 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 electrolytic solution is sufficient, it is possible to prevent a decrease in efficiency due to an increase in size.

As described above, in order to operate artificial photosynthesis, it is necessary to apply a voltage of 2 V or more between the reduction reaction electrode 102 and the oxidation reaction electrode 104, so that 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 the mathematical formula (10). Here, q, k _B , and T are charge elements, Boltzmann's constant, and temperature (300K), respectively, j _ph is the photocurrent density, and j ₀ , n are the inverse saturation current of the diode and ideal factors, respectively.

When these values were obtained so that the typical characteristics of commercial products could be obtained when irradiated with light of AM1.5G spectrum, which is the 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, and at this time, the conversion efficiency was 19.9%, the open end 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-based solar cell having the highest conversion efficiency at present uses an amorphous silicon / crystalline silicon heterojunction, and the conversion efficiency is 26%. Although the manufacturing cost is high so far, it is expected that it will gradually spread in the future. Therefore, the case of using this is also considered. When the parameters of the equation (10) were set so that the values were 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, and 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 characteristics at this time. Compared with FIG. 10A, this is characterized by a higher open end voltage.

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

By solving a simultaneous equation 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 reactor 100 shown in FIG. 7, the current density at the operating point can be obtained. can get. The same applies to the case of the integrated chemical reaction apparatus 100 using the mutual penetration electrode of FIG. 9, and the areas of the reduction reaction electrode 102 and the oxidation reaction electrode 104 are 1/2 of the area of the solar cell, respectively. Therefore, the 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 in the case of the conventional opposed type as a comparative example and the distance L = 1 cm between the electrodes. The current density j _ac (L = 1), the current density j _ac (D = 20) in the case of the conventional integrated type as a comparative example, and the current density j _pv -voltage V _pv characteristics of the solar cell are shown together. FIG. 11A shows the characteristics when four crystalline silicon solar cells are connected in series. Similarly, FIGS. 11 (b) to 11 (e) show the characteristics when 5 to 8 crystalline silicon solar cells are connected in series, respectively. Further, FIG. 12A shows the current density at the operating point, which is the intersection of the graphs of the current density _{jac-voltage V ac characteristic} of the chemical reaction apparatus 100 and the current density j _pv -voltage V _pv characteristic of the solar cell in FIG. (Per unit area of solar cell) is shown.

The optimum value of the number (number) m of connected series of 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 _jac and the steeper the slope thereafter, the smaller the number of series connections m of the crystalline silicon solar cell may be, and therefore a larger operating current density can be obtained. The operating current density depends on the current density _jac when the number of series connections of the crystalline silicon solar cell is small, and is defined by the current density _jpv when the number of series connections of the crystalline silicon solar cell is large. The operating point, which is the intersection of the current density j _ac -voltage V _ac characteristic of the chemical reactor 100 and the current density j _pv -voltage V _pv characteristic of the solar cell, is the maximum output point of the solar cell (j _{pv'V pv is} the maximum. The operating current becomes maximum when it is close to the point, roughly the point where _jpv starts to decrease). The maximum operating current is when the number of connected series m of crystalline silicon solar cells is 5 in the case of a conventional chemical reaction device using a small opposed electrode, and the operating current at that time is 7. It was 7 mA / cm ² . On the other hand, in the case of the chemical reaction apparatus 100 using the mutual penetration type electrode in the present embodiment, the current density is low when the number of series connections m of the crystalline silicon solar cell is 5, and when the number of series connections m is 6. The operating current became maximum, 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 device using a conventional small electrode. On the other hand, in the case of a chemical reaction device using a conventional integrated electrode (diameter D = 20 cm), the operating current is 5.5 mA / cm ² when the number of series connections is 7, and a mutual penetration type electrode is used. The value did not reach the value in the case of the integrated chemical reaction apparatus 100. Further, in the conventional chemical reaction apparatus using the integrated electrode, the light absorption of the oxidation reaction electrode 104 normally formed on the light incident surface side of the solar cell cannot be ignored, so that the operating current _hop is further reduced. Become. Further, while the operating current _hop becomes smaller as the diameter D becomes larger, in the case of the integrated chemical reaction apparatus 100 using the mutual penetration type electrode in the present embodiment, the operating current _hop is the cell. Since it does not depend on the outer shape, it has a structure suitable for constructing a large cell. As described above, if the opposed electrode is made large, it becomes difficult to uniformly retain a sufficient amount of the electrolytic solution, so that the operating current _jop may decrease.

When the irradiation light intensity becomes weak, the short-circuit current value of the solar cell becomes small, so that the operating point changes to a lower current and a constant voltage side. Therefore, the value of the number of connected series m of the optimum crystalline silicon solar cell becomes small. As shown in FIG. 12 (b), in the case of 0.5 sun irradiation, the optimum value (maximum value 3.7 mA / cm ² ) was when the number of series connections m of the crystalline silicon solar cells was 5. In this case, there was almost no difference between the conventional chemical reaction device using the opposed electrode and the chemical reaction device 100 using the mutual penetration type electrode in the present embodiment.

In this way, the characteristics and superiority of the cells of each configuration change depending on the irradiation light intensity. Therefore, the amount of electric charge generated in one day is compared. The fluctuation of the amount of solar radiation _Isun (t) is expressed by a simple cosine curve as in the formula (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 _hop corresponding to the illuminance intensity at each time. However, the value of the number of series connections m is the optimum value for each chemical reaction device, and for the chemical reaction device using the conventional opposed electrodes (distance between electrodes L = 1 cm), the number of series connections m is five, conventional. For the chemical reaction device using the integrated electrode (diameter D = 20 cm) and the integrated chemical reaction device 100 using the mutual penetration type electrode (period d = 1 cm, gap w = 0.1 cm), the number of series connections is m. Was set to 6. Further, when the same calculation was performed for a chemical reaction apparatus using a conventional integrated electrode having a diameter of D = 50 cm, it was optimal when the number of series connections m was eight. By integrating the operating current _jop thus obtained at time t, the amount of electric charge per day can be obtained as shown in FIG. 13 (b). By using the mutual penetration type electrode, an amount of charge exceeding the value of the conventional integrated electrode (diameter D = 20 cm) by about 10% was obtained. In the case of the conventional integrated electrode (diameter D = 50 cm), the value remained even lower.

14 (a) and 14 (b) are phosphate buffer concentrations of 0.8 M showing current density j _ac -voltage V _ac characteristics in FIGS. 7 (b) and 7 (c), and are used for the reduction reaction. The calculation result of the operating current _hop when the current densities of the electrode 102 and the oxidation reaction electrode 104 are doubled is shown. In the case of the integrated chemical reaction device 100 using the mutual penetration type electrode and the chemical reaction device using the opposed type electrode, the operating current _jump is 0. Although it increased by about 2 mA / cm ² , the tendency of dependence on the number of series connections m did not change. On the other hand, in the conventional chemical reaction device using an integrated electrode, the current density jac increases _{significantly} , so the maximum value of the operating current _jop (6.4 mA / cm ² , number of series connections m = 6) penetrates into each other. It slightly exceeded the value (6.2 mA / cm ² , number of series connections m = 6) in the chemical reaction apparatus 100 using the mold electrode. However, as described above, there are drawbacks that the dependence on the diameter D and the influence of the light absorption of the reduction reaction electrode 102 cannot be avoided.

In contrast, when the current densities of the reduction reaction electrode 102 and the oxidation reaction electrode 104 are doubled, the number of series connections m is 5 in the case of the integrated chemical reaction apparatus 100 using the mutual penetration type electrode. At this time, the operating current jump increased to _7.3 mA / cm ² . On the other hand, in the case of the conventional chemical reaction apparatus using the integrated electrode, as shown in FIG. 7 (c), the value was only slightly increased from the value in FIG. 12 (a). That is, if a more active reduction reaction electrode 102 and an oxidation reaction electrode 104 are realized, the advantage of the integrated chemical reaction apparatus 100 using the mutual penetration type electrode will be higher than that of the conventional integrated electrode. It became remarkable.

In addition, the characteristics also changed depending on the characteristics of the light charge separation element. FIG. 14 (c) shows the results when a heterojunction silicon solar cell is used. For the integrated chemical reaction apparatus 100 using the mutual penetration type electrode, the optimum value is obtained when the number of series connections m is 6, but unlike FIG. 12 (a), when the number of series connections m is 5. It was not much different from the value of. Further, even if the same number of series connections is 6, in the case of a crystalline silicon element, the current density at the operating point is slightly lower than the short-circuit current density of the solar cell, as shown in FIG. 12 (a). On the other hand, in the case of the heterojunction silicon element, the value close to the short-circuit current density is maintained up to a higher voltage, so that a high operating current _jop (6.9 mA / cm ² ) is obtained.

As described above, in the chemical reaction apparatus 100 using the mutual penetration type electrode, the appropriate number of series connections m is determined according to 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 solar cell to be combined. By selecting, it is possible to increase the size of the chemical reaction device using the conventional integrated electrode, and it is possible to obtain an operating current _hop close to that of the chemical reaction device using the opposed electrode.

Further, according to the chemical reaction apparatus 100 in the present embodiment, the smooth flow of protons from the oxidation reaction electrode 104 to the reduction reaction electrode 102, the sufficient supply of raw materials (CO ₂ and the like), and the product (HCOOH). Etc.), it is possible to achieve both convection of a sufficient amount of electrolytic solution for rapid discharge.

[Second Embodiment]
In the present embodiment, the period _{d c} of the reduction reaction electrode 102 and the period da of the oxidation reaction electrode 104 are equal to each other, but the chemical activity characteristics of the reduction reaction electrode 102 and the oxidation reaction electrode 104. It may be different depending on the situation. Specifically, the width of the electrode 102 for the reduction reaction and the electrode 104 for the oxidation reaction, whichever has the lower chemical activity per unit area, is made wider, and the width of the one, which has the higher activity, is made narrower to balance the two. It is preferable because it can be removed.

As mentioned earlier, catalytic function can vary widely depending on the material, carrier and manufacturing process. The characteristics of the reduction reaction electrode and the oxidation reaction electrode 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. .. The characteristics of the electrode for reduction reaction were almost the same, but the current density at a predetermined applied voltage above the threshold was about three times higher in the literature, although the threshold value did not change in the electrode for oxidation reaction. Therefore, as shown in FIG. 15, a case where only the current density of the electrode for oxidation reaction is three times the current density shown in FIG. 5A was examined.

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 electrode for reduction reaction is much larger than the differential resistance of the electrode for oxidation reaction. Therefore, when the total area of the reduction reaction electrode and the oxidation reaction electrode is limited as in the case of the mutual penetration type electrode, the current value per total area can be increased by increasing the area of the reduction reaction electrode relatively. 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. The formulas (5) to (9) are changed to the formulas (13) to (17).

In _FIG . 17 (a), the period _{da a and the period dc are changed under the constraint of the period da a of the oxidation reaction electrode 104 + the period dc of the reduction reaction electrode 102 = 2 cm, and the voltage V ac = 2 V.} The result of calculating the current density _jac when a constant voltage is applied is shown. Compared to the case where the period da _a = period d _c = 1 cm, the current density j _ac increases by about 10% when the asymmetric type with the optimum period d _a = 0.7 cm and the period d _c = 1.3 cm is used. do. It is considered that there is no particular drawback in making it asymmetric.

If the overvoltage (difference between the action potential and the threshold potential at which the reaction occurs) of the reduction reaction electrode 102 and the oxidation reaction electrode 104 becomes large, the deterioration of the catalyst may progress and the selectivity of the reaction may be impaired. .. When the purpose of the reduction reaction from carbon dioxide (CO ₂ ) to formic acid (HCOOH) at the reduction reaction electrode 102 is to increase the overvoltage, other substances such as carbon monoxide (CO) are generated, or in an aqueous solution. Water (H ₂ O) may be reduced to generate hydrogen (H ₂ ).

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

FIG. 17B shows the overvoltages V _op-a and V _op-c when the voltage V _ac = 2 V corresponding to FIG. 17 (a). By widening the width of the reduction reaction electrode 102, which has a large differential resistance of the reaction, the overvoltage V _op-c becomes smaller, while the increase in the overvoltage V _op-a is slight. The problem is reduced. FIG. 17 (c) shows the current density j _ac -voltage V _ac characteristics when the period d = 1 cm, which is the symmetric type, the period _{d a} = 0.7 cm, which is the optimum value of the asymmetric type, and the period dc = 1.3 cm. ( _Jac (d = 1) and _jac ( _{d a} = 0.7, dc = 1.3), respectively) are shown.

FIG. 18 shows a mutual penetration type of a symmetrical type (period _d = 1 cm, gap w = 0.1 cm) and an asymmetric type (period da _a = 0.7 cm, period dc = 1.3 cm, gap w = 0.1 cm). Local proton flow densities j _{H +} ^(y) (x, 0 ⁺ ) of the oxidation reaction electrode 104 and the reduction reaction electrode 102 when a voltage V _ac = 2 V is applied to the electrodes, and φ (x, x, due to ρ _{H +} ). The result of comparing the fluctuation (relative value) of z) is shown. The average values of the local proton flow densities j _{H +} ^(y) (x, 0 ⁺ ), j _{H + a} and j _{H + c} , are j _{H + a} = j _{H + c} = 4.4 mA / cm ² for the symmetrical type and j for the asymmetric type. _{H + a} = 7.0 mA / cm ² and j _{H + c} = 3.8 mA / cm ² . In either case, the oxidation reaction electrode 104 has higher activity (the absolute value of the differential resistance dV _a / dj _a of the reaction is smaller), and therefore the influence of ρ _{H +} is relatively large. Therefore, the reduction reaction electrode The value on the side closer to 102 (the side closer to x = 0) is large, and the value on the far side is smaller. On the contrary, 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 the asymmetrical mutual penetration type electrode are determined. Regarding the reduction reaction electrode 102 and the oxidation reaction electrode 104, it is assumed that the oxidation reaction electrode 104 has significantly higher activity as shown in FIG. 15, and the current shown in FIG. 17 (c) is assumed. The density j _ac -voltage V _ac characteristic was used.

FIG. 19 shows the current density _pop (per unit area of the solar cell) at the operating point of the 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 _jop becomes maximum when the number of series connections m is 6, whereas when the irradiation light intensity is 0.5 sun, the optimum value is obtained when the number of series connections m is 5. became. However, in the case of the asymmetric type, the difference between the case where the number of series connections m at the time of 1 sun irradiation was 5 and the case where the number m was 6 became small.

Reflecting these, the amount of electric charge generated in one day was the maximum when the number of series connections m was five. As shown in FIG. 20, there is almost no difference between the two in the current density _jop when the irradiation light is weak, but when the irradiation light intensity increases, the asymmetric type (period da _a = 0.7 cm, period _dc = 1. 3 cm, gap w = 0.1 cm) became dominant. As a result, an amount of charge exceeding the symmetric type (period d = 1 cm, gap w = 0.1 cm) value by about 5% was obtained. In addition to this, problems of deterioration and deterioration of reaction selectivity can be reduced.

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

In the above-described embodiment and modification, the mutual penetration type electrode is formed on one side of the chemical reaction apparatus 100, but it may be formed on both sides.

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 substrates.

Claims (7)

Oxidation reaction electrodes and reduction reaction electrodes are alternately arranged on the same surface of the substrate, and the ratio d of the width _{da of the oxidation reaction electrode and the width d c} of _the reduction reaction electrode dc along the alternating arrangement direction. An electrode for a chemical reaction, characterized in that _c / da _is 1.2 or more and 2.3 or less . The electrode for chemical reaction according to claim 1.
A chemical reaction electrode characterized in that the width of the electrode having a higher current density-voltage characteristic is set narrower according to the current density-voltage characteristic of the oxidation reaction electrode and the reduction reaction electrode. .. The electrode for chemical reaction according to claim 1 or 2,
The solar cell connected to the oxidation reaction electrode and the reduction reaction electrode,
A cell for chemical reaction characterized by the combination of. The chemical reaction cell according to claim 3.
A cell for a chemical reaction, which is an integral type in which the solar cell is a part of the substrate. The chemical reaction cell according to claim 3 or 4.
The solar cell is a chemical reaction cell in which crystalline silicon solar cells of 3 cells or more and 6 cells or less are connected in series. The 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 are provided.
In the plurality of chemical reaction cells, the oxidation reaction electrode and the reduction reaction electrode are provided on one side or both sides, and the surfaces provided with the oxidation reaction electrode and the reduction reaction electrode are arranged so as to face each other. A chemical reaction device characterized by.

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