JP2021021095A - Electrode for reductive reaction, and device of reducing carbon compound - Google Patents

Abstract

To provide an electrode for a reductive reaction, capable of at least controlling a production ratio of hydrogen resulting from a side reaction or enhancing the production ratio of a reduction product resulting from a reductive reaction of a carbon compound, in a reductive reaction of a carbon compound.SOLUTION: The electrode for a reductive reaction according to the present invention is an electrode for a reductive reduction to be used in a reductive reaction of a carbon compound and comprises an electrode body modified with a hydrophobic polymer.SELECTED DRAWING: None

Description

The present invention relates to an electrode for a reduction reaction and a carbon compound reducing device.

Research on reduction reaction electrodes used in the reduction reaction of carbon compounds such as carbon dioxide to solve problems such as global warming due to an increase in the concentration of carbon dioxide (CO ₂ ) in the atmosphere and depletion of energy resources and carbon resources. Is done all over the world.

For example, Patent Document 1 has a conductive member and an adsorbent on the surface of the conductive member, and the adsorbent has conductivity and pores and is porosity capable of adsorbing carbon dioxide. An electrode for carbon dioxide reduction having a base material and a metal complex having a central metal capable of reducing carbon dioxide in the pores is disclosed.

Further, Patent Document 2 discloses a carbon dioxide reducing electrode having a metal-containing member capable of reducing carbon dioxide and an adsorbent capable of adsorbing carbon dioxide on the surface of the metal-containing member.

Further, Patent Document 3 discloses a reduction reaction electrode including an electrode modified with a silane coupling agent.

Further, Non-Patent Document 1 discloses a carbon dioxide reduction technique using a metal electrode.

Further, Non-Patent Document 2 discloses a copper metal electrode modified with a hydrophilic polymer.

JP-A-2017-125234 JP-A-2017-78190 JP-A-2017-101285

Yoshio Hori, "Electrolytic Reduction of Carbon Dioxide with Steel Electrodes", Electrochemistry, 1990, 11, p996-1002 Aya K. Buckley et al. , J. Am. Chem. Soc. , 2019, 141, p7355-7364, "Electrocatalyst at Organic-Metal Interfaces: Electrocatalyst of Structure-Reactivity Reaction Surfaces for CO2 Redox Surfaces"

By the way, in the reduction reaction of a carbon compound such as carbon dioxide, an electrode for a reduction reaction capable of suppressing hydrogen production by a side reaction and enhancing the production of a reduction product by the reduction reaction of a carbon compound is desired.

Therefore, an object of the present invention is at least one of suppressing the production ratio of hydrogen by a side reaction and improving the production ratio of a reduction product by the reduction reaction of a carbon compound in the reduction reaction of a carbon compound. It is an object of the present invention to provide an electrode for a reduction reaction and a carbon compound reduction apparatus capable of the above.

The present invention is a reduction reaction electrode used for a reduction reaction of a carbon compound, and is a reduction reaction electrode including an electrode body modified with a hydrophobic polymer.

Further, in the electrode for reduction reaction, the water contact angle of the electrode body modified with the hydrophobic polymer is preferably 89 degrees or more.

Further, in the electrode for reduction reaction, the carbon compound preferably contains carbon dioxide.

The present invention also comprises the reduction reaction electrode, an oxidation reaction electrode that is electrically connected to the reduction reaction electrode and causes an oxidation reaction, and an electrolyte solution that is a solution containing an electrolyte. It is a carbon compound reducing apparatus in which the electrode for a reduction reaction and the electrode for an oxidation reaction are immersed in the electrolyte solution.

According to the present invention, in the reduction reaction of a carbon compound, at least one of suppressing the production ratio of hydrogen by a side reaction and improving the production ratio of a reduction product by the reduction reaction of a carbon compound is possible. It is possible to provide an electrode for a reduction reaction and a carbon compound reducing device.

It is a schematic block diagram of an example of the electrode for reduction reaction which concerns on this embodiment. It is a schematic block diagram of an example of the carbon compound reduction apparatus which concerns on this embodiment. It is an infrared absorption spectrum of electrodes A to D for a reduction reaction. It is an SEM image of electrodes A to D for a reduction reaction. It is a figure which shows the water contact angle measurement of the reduction reaction electrode A to D. It is a schematic block diagram of the electrochemical cell used in an Example and a comparative example. It is an infrared absorption spectrum of electrodes E to H for a reduction reaction. It is an SEM image of electrodes E to H for a reduction reaction.

An example of the electrode for reduction reaction and the carbon compound reduction apparatus according to the present embodiment will be described below.

[Electrodes for reduction reaction]
FIG. 1 shows a schematic configuration diagram of an example of a reduction reaction electrode according to the present embodiment. The reduction reaction electrode 1 shown in FIG. 1 has a metal electrode body 10 and a modification layer 12 that modifies the surface of the metal electrode body 10. In the reduction reaction electrode 1 shown in FIG. 1, the lead wire 16 is connected to the metal electrode body 10 by the contact member 14.

The metal electrode body 10 is not particularly limited, but silver (Ag), gold (Au), copper (Cu), zinc (Zn), indium (In), cadmium (Cd), tin (Sn), and the like. A metal containing palladium (Pd), lead (Pd), iron (Fe), and tantalum (Ta) is preferable. Further, the metal electrode body 10 may have, for example, a configuration in which a metal layer is formed on a base material containing a carbon material. Examples of the carbon material include carbon nanotubes, graphene, carbon black, carbon cloth, carbon paper, glassy carbon, graphite and the like. Further, a P-type semiconductor having a potential at the lower end of the conductor on the negative side of the reduction potential of the carbon compound may be contained. Examples of the P-type semiconductor include oxides such as silicon (Si), copper oxide (Cu ₂ O) and zinc-doped iron oxide (Fe ₂ O ₃ ), indium phosphide (InP), gallium phosphide (GaP), and gallium phosphide. phosphorus compounds such as phosphorus (InGaP), gallium nitride _(GaN), nitrogen compounds such as C 3 _{N 4,} CIGS, selenium compounds such as CZTSSe like.

The modified layer 12 contains a hydrophobic polymer. The hydrophobic polymer is a polymer that is poorly soluble or insoluble in water, and has a solubility of less than 1 g in 100 g of pure water at 20 ° C. Examples of the hydrophobic polymer include polystyrene (PS), polymethylmethacrylate (PMMA), polycarbonate (PC), polypropylene (PP), polyethylene terephthalate (PET), polyethylene (PE), polyvinylidene fluoride (PVDF), and poly. Examples thereof include methylpentene (PMP), polylactic acid (PLA), cyclic olefin copolymer (COC) and cyclic olefin polymer (COP).

The modified layer 12 is formed, for example, by applying a solution of a hydrophobic polymer in an organic solvent to the metal electrode body 10 or immersing the metal electrode body 10 in the solution. By such a method, for example, a reduction reaction electrode having a sea-island structure having a region (island) in which the modified hydrophobic polymer is aggregated on the metal electrode body 10 and a region (sea) in which the metal electrode body is exposed can be obtained. can get. The organic solvent may be one in which a hydrophobic polymer is dissolved, and examples thereof include tetrahydrofuran, acetone, 2-propanol, ethanol and the like.

Also. For the modified layer 12, for example, a liquid obtained by developing a solution of a hydrophobic polymer in an organic solvent on water such as pure water or ultra-pure water is applied to the metal electrode body 10, or the metal electrode body 10 is used. May be formed by immersing the water in the liquid. By using a liquid obtained by developing a solution of a hydrophobic polymer in an organic solvent on water, the hydrophobic polymer self-assembles, so that the hydrophobic polymer microparticles are placed on the metal electrode body 10. (Particle size of about several μm) can be formed. That is, a reduction reaction electrode in which microparticles of a hydrophobic polymer are dispersed on the metal electrode body 10 can be obtained. The liquid obtained by developing a solution of a hydrophobic polymer in an organic solvent on water may be used immediately after preparation, or may be used after being left for several hours to several days.

The hydrophobic polymer may be modified so as to cover the entire surface of the metal electrode body 10, but the sea-island structure and microparticles as described above are dispersed in terms of the reduction reactivity of the carbon compound and the like. Better.

The contact member 14 may be a member capable of connecting the lead wire 16 to the metal electrode body 10, and is not particularly limited, and examples thereof include copper tape, indium, carbon tape, lead, tin, and tantalum.

The lead wire 16 may be any member as long as it can be energized, and is not particularly limited, and examples thereof include a copper wire and an aluminum wire.

When a voltage is applied to the reduction reaction electrode 1, the electrons generated in the metal electrode body 10 are used for the reduction reaction of the carbon compound. When the carbon compound is carbon dioxide, due to the reduction reaction of carbon dioxide, for example, 2-electron reduction products such as CO and HCOOH, CH ₄ (8-electron reduction products), C ₂ H ₄ (12-electron reduction products), A reduction product such as a multi-electron reduction product having more than two electrons such as C ₂ H ₅ OH (12-electron reduction product) is produced. The carbon compound preferably contains carbon dioxide from the viewpoint of suppressing global warming due to an increase in the concentration of carbon dioxide (CO ₂ ) in the atmosphere, but is not limited to carbon dioxide, for example, CO or the like. Any carbon compound that causes a reduction reaction at the reduction reaction electrode 1 may be used.

Here, in the reduction reaction electrode 1, hydrogen generation also occurs due to a side reaction such as water decomposition. However, according to the reduction reaction electrode 1, the hydrophobic polymer (modifying layer 12) that modifies the surface of the metal electrode body 10 suppresses the contact of water molecules with the surface of the metal electrode body 10, and the carbon compound is formed. It is easy to contact. As a result, as compared with the metal electrode body in which the hydrophobic polymer is not modified, the production ratio of hydrogen due to the side reaction is suppressed, the production ratio of the reduction product due to the reduction reaction of the carbon compound is improved, or both. Can be achieved.

In the reduction reaction electrode 1, the water contact angle of the metal electrode body 10 modified with the hydrophobic polymer suppresses the production rate of hydrogen by the side reaction and improves the production rate of the reduction product by the reduction reaction of the carbon compound. It is preferably 89 degrees or higher, and more preferably 95 degrees or higher, in terms of allowing the temperature to rise.

For the water contact angle, 0.5 μL of water droplet was dropped on the sample surface (the surface of the electrode body modified by the hydrophobic polymer) using a contact angle meter (Kyowa Surface Chemistry, DM-501), and the water droplet immediately after the drop was dropped. It is obtained by photographing the shape and measuring from the obtained image using the θ / 2 method. Here, for example, in the case of a porous metal electrode body in which a metal layer is formed on a base material such as carbon cloth or carbon paper, even if water droplets are dropped on the surface of the porous electrode body modified by a hydrophobic polymer. , Water droplets penetrate inside and the water contact angle cannot be measured. In this case, a metal layer is formed on a smooth substrate (for example, a glass substrate) under the same conditions, and a hydrophobic polymer is further modified on the metal layer under the same conditions as a sample. The water contact angle measured in 1 is defined as the water contact angle on the surface of the electrode body modified with the hydrophobic polymer.

"Carbon compound reduction device"
FIG. 2 shows a schematic configuration diagram of an example of the carbon compound reducing device according to the present embodiment. The carbon compound reducing device 3 shown in FIG. 2 is an electrode for an oxidation reaction that is electrically connected to the first electrode (cathode) 1 which is the electrode for the reduction reaction described above and the first electrode 1 to cause an oxidation reaction. It has a second electrode (anode) 20 of the above, and an electrolyte solution containing a cathode chamber electrolyte solution 30 and an anode chamber electrolyte solution 32.

In the carbon compound reducing device 3 shown in FIG. 2, for example, the inside of the storage container 26 is separated into a cathode chamber 22 and an anode chamber 24 by a diaphragm 28, and the cathode chamber 22 is a cathode chamber electrolyte which is a solution containing a cathode chamber electrolyte. The solution 30 is contained, and the anode chamber electrolyte solution 32, which is a solution containing the anode chamber electrolyte, is contained in the anode chamber 24. Then, the first electrode 1 which is the electrode for the reduction reaction described above is immersed in the cathode chamber electrolyte solution 30, and the second electrode 20 is immersed in the anode chamber electrolyte solution 32. The cathode chamber electrolyte solution 30 contains a carbon compound such as carbon dioxide.

By electrically connecting the first electrode 1 and the second electrode 20 and applying an appropriate bias voltage, an oxidation reaction occurs and a potential is obtained in the second electrode 20. Be done. In the first electrode 1, the reduction reaction of a carbon compound such as carbon dioxide proceeds by obtaining an electric potential from an electrode that causes an oxidation reaction.

The means for applying the bias voltage is not particularly limited, and examples thereof include a chemical battery (including a primary battery, a secondary battery, etc.), a constant voltage source, a solar cell, and the like.

By using a solar cell as a means for applying a bias voltage, the carbon compound reducing device 3 shown in FIG. 2 and a solar cell that generates electric power supplied to the first electrode 1 and the second electrode 20 are provided. It can be an artificial photosynthesis device. In the artificial photosynthesis apparatus according to the present embodiment, the first electrode 1 and the second electrode 20 of the carbon compound reducing apparatus 3 are connected via a solar cell, and are driven by using sunlight as an energy source.

Potassium chloride chamber electrolytes include potassium chloride (KCl), potassium hydrogen carbonate (KHCO ₃ ), potassium sulfate (K ₂ SO ₄ ), potassium carbonate (K ₂ CO ₃ ), potassium tetraborate (K ₂ B ₄ O ₇ ). , Potassium hydrogen phosphate (K ₂ HPO ₄ ), Potassium dihydrogen phosphate (KH ₂ PO ₄ ), etc., and the more basic the vicinity of the electrode surface, the more the side reaction H ₂ production can be suppressed. From this point of view, potassium chloride (KCl), potassium hydrogen carbonate (KHCO ₃ ) and the like are preferable.

As the anode chamber electrolyte, sodium hydrogen carbonate (NaHCO ₃ ), potassium hydrogen carbonate (KHCO ₃ ), potassium carbonate (K ₂ CO ₃ ), potassium sulfate (K ₂ SO ₄ ), potassium tetraborate (K ₂ B ₄ O) ₇ ), dipotassium hydrogen phosphate (K ₂ HPO ₄ ), potassium dihydrogen phosphate (KH ₂ PO ₄ ), potassium hydroxide (KOH), etc., and water is used to make the vicinity of the electrode surface more basic. Potassium hydrogen carbonate (KHCO ₃ ), potassium tetraborate (K ₂ B ₄ O ₇ ), potassium hydroxide (KOH) and the like are preferable from the viewpoint that O ₂ production by the oxidation reaction facilitates.

Examples of the solvent for the cathode chamber electrolyte solution 30 and the anode chamber electrolyte solution 32 include organic solvents such as acetonitrile and N, N-dimethylformamide (DMF) in addition to water.

The concentration of the electrolyte in the cathode chamber electrolyte solution 30 is, for example, in the range of 0.01 mol / L to 3 mol / L, and preferably in the range of 0.1 mol / L to 1.0 mol / L.

The concentration of the electrolyte in the anode chamber electrolyte solution 32 is, for example, in the range of 0.01 mol / L to 3 mol / L, and preferably in the range of 0.1 mol / L to 1.0 mol / L.

The second electrode 20 is an electrode used to oxidize a substance by an oxidation reaction. The second electrode 20 includes platinum, gold, carbon, mercury, fluorine-containing tin oxide (FTO), tin-doped indium oxide (ITO), iridium oxide (IrOx: x = 1-2) or a cobalt compound on a semiconductor substrate. An electrode modified from the above can be used. Examples of the semiconductor substrate include tungsten oxide (WO ₃ ), bismuth vanadate (BiVO ₄ ), iron oxide (Fe ₂ O ₃ ), silicon (Si), and tantalum nitride (TaON).

Examples of the diaphragm 28 include a proton exchange membrane, an anion exchange membrane, a bipolar membrane, a porous glass membrane, and the like, and Nafion (registered trademark), which is a proton exchange membrane, can be preferably used. It is preferable to provide the diaphragm 28 from the viewpoint of efficiently advancing the reduction reaction of the carbon compound at the first electrode 1 (reduction reaction electrode), but the diaphragm 28 may not be provided.

As the storage container 26, for example, a closed container made of metal, plastic, glass, or the like, a reaction container having a mechanism for circulating gas, or the like can be used.

The carbon compound reducing device 3 shown in FIG. 2 is a two-electrode type using a reduction reaction electrode and an oxidation reaction electrode, but is not limited to this, and may be a three-electrode type in which reference electrodes are combined. As shown in FIG. 2, in the carbon compound reducing device provided with a diaphragm, the reference electrode is installed on the cathode chamber side.

Hereinafter, the present invention will be further described with reference to Examples, but the present invention is not limited to these Examples.

<Electrode A for reduction reaction>
Develop 100 μL of a tetrahydrofuran (Fuji Film Wako Pure Chemical Industries, Ltd., ultra-dehydration) solution in which 1 mg / L polystyrene (Mw: 2.7 × 103, PDI: 1.16) is dissolved on the water surface of 40 mL of ultrapure water (MiLLIQ). After immersing the silver foil in the liquid, it was dried. Then, a tantalum foil (contact member) was connected to the silver foil. This was used as the electrode A for the reduction reaction.

<Electrode B for reduction reaction>
Develop 1 mL of a tetrahydrofuran (Fuji Film Wako Pure Chemical Industries, Ltd., ultra-dehydrated) solution in which 1 mg / L polystyrene (Mw: 2.7 × 103, PDI: 1.16) is dissolved on the water surface of 1 mL of ultrapure water (MiLLIQ). The liquid was left at room temperature for 2 days to prepare polystyrene microparticles (Self-ORganized Prescription: SORP method). 100 μL of the prepared liquid containing the microparticles was applied to the silver foil by the drop casting method, and then dried. Then, the tantalum foil was connected to the silver foil. This was used as the electrode B for the reduction reaction.

<Electrode C for reduction reaction>
100 μL of a tetrahydrofuran (Fuji Film Wako Pure Chemical Industries, Ltd., ultra-dehydration) solution in which 1 mg / L polystyrene (Mw: 2.7 × 103, PDI: 1.16) is dissolved is applied to silver foil by the drop cast method and then dried. did. Then, the tantalum foil was connected to the silver foil. This was used as the electrode C for the reduction reaction.

<Electrode D for reduction reaction>
A tantalum foil was connected to the silver foil. This was used as the electrode D for the reduction reaction.

FIG. 3 is an infrared absorption spectrum of the reduction reaction electrodes A to D. The infrared absorption spectra of the reduction reaction electrodes A to D were measured by mounting an ATR unit on a Ge substrate on a Fourier transform infrared spectroscopic analyzer (Thermo Fisher Scientific: iS50 FT-IR). (Measurement wavelength: 4000-800 cm ^-1 , total number of times: 32). As shown in FIG. 3, polystyrene has a peak due to the characteristic CH ₂ C—H variable angle vibration and the C = C expansion and contraction vibration of the aromatic ring near 1500 cm ^-1 , and the peak is a reduction reaction. It was observed on the electrodes A to C, but not on the reduction reaction electrodes D. Therefore, it was suggested that polystyrene was modified on the silver foil in the electrodes A to C for the reduction reaction.

FIG. 4 is an SEM image of the reduction reaction electrodes A to D. Using a scanning electron microscope SU3500 (manufactured by Hitachi High-Technologies Corporation), SEM images of reduction reaction electrodes A to D were taken. As shown in FIG. 4, it was confirmed that polystyrene was aggregated on the silver foil in the reduction reaction electrode C, and polystyrene microparticles were formed on the silver foil in the reduction reaction electrodes A and B. It was confirmed that. In the reduction reaction electrode A, some of the polystyrene microparticles were agglomerated, but in the reduction reaction electrode B, the aggregation of the polystyrene microparticles was hardly observed, and the microparticle structure was maintained. ..

FIG. 5 is a diagram showing water contact angle measurement of the reduction reaction electrodes A to D. For the water contact angle, 0.5 μL of water droplet was dropped on the sample surface using a contact angle meter (Kyowa Surface Chemistry, DM-501), the contact angle was measured at 10 points (n = 10), and the average value was adopted. did. The water contact angle of the reduction reaction electrode A is 90.2 ± 1.5 degrees, the water contact angle of the reduction reaction electrode B is 98.6 ± 1.7 degrees, and the water contact of the reduction reaction electrode C is 98.6 ± 1.7 degrees. The angle was 89.2 ± 0.9 degrees, and the water contact angle of the reduction reaction electrode D was 78.6 ± 1.5 degrees. That is, the reduction reaction electrodes A to C in which polystyrene was modified on the silver foil had a higher water contact angle than the reduction reaction electrodes D, which are silver foils. Among the reduction reaction electrodes A to C, the reduction reaction electrode B on which polystyrene microparticles were formed had the highest water contact angle. It is presumed that this is because the uneven structure formed by the polystyrene microparticles has a structure that improves water repellency such as the Lotus effect.

<CO ₂ electrolysis using electrodes A to D for reduction reaction>
(Example 1)
For the electrochemical measurement, the electrochemical cell (two-chamber cell) shown in FIG. 6 was used. Using an electrochemical measurement system 42 (Bio-Logic Science Instruments, SP-50), the working electrode 44 is the reduction reaction electrode A, the counter electrode 46 is the platinum foil (Niraco), and the reference electrode 48 is the Ag / AgCl electrode (EC). The three-electrode method using Frontier) was used. The two chambers of the electrochemical cell are separated by a diaphragm 50 (proton exchange membrane (manufactured by Aldrich, Nafion® 117)), and the working electrode 44 (reduction reaction electrode A) and the reference electrode 48 are placed in the cathode chamber 54. A counter electrode 46 was installed in the anode chamber 56. A 0.5 mol / L potassium hydrogen carbonate aqueous solution was placed in the cathode chamber 54 and the anode chamber 56 as the electrolyte solution 58. Measurements after the CO ₂ gas 20 minutes circulation in the cathode chamber 54, the current still flows through the CO ₂ gas - performs voltage measurement, then, under a stream of CO ₂ gas at 20mL / min, -1.6V vsAg / AgCl After applying the potential of No. 3 for 3 hours, the gas phase in the cell was measured by gas chromatography (manufactured by Shimadzu Corporation, GC-2014) to identify and quantify the reduction product.

(Example 2)
The measurement was carried out in the same manner as in Example 1 except that the reduction reaction electrode B was used instead of the reduction reaction electrode A as the working electrode 44.

(Example 3)
The measurement was carried out in the same manner as in Example 1 except that the reduction reaction electrode C was used instead of the reduction reaction electrode A as the working electrode 44.

(Comparative Example 1)
The measurement was carried out in the same manner as in Example 1 except that the reduction reaction electrode D was used instead of the reduction reaction electrode A as the working electrode 44.

Table 1 shows the Faraday efficiency and the amount of H ₂ and CO produced by the CO ₂ electrolysis of Examples 1 to 3 and Comparative Example 1.

As shown in Table 1, in Examples 1 to 3, the current efficiency of H ₂ was lower than that in Comparative Example 1. Further, in Examples 1 to 3 as compared with Comparative Example 1, the CO current efficiency was about the same or higher, and the amount of CO produced was also increased. Therefore, by using a silver foil (metal electrode body) modified with polystyrene, which is a hydrophobic polymer, as an electrode for a reduction reaction, the rate of H ₂ production could be reduced and the rate of CO production could be increased.

<Electrode E for reduction reaction>
An electrode body in which silver was formed on carbon paper (Toray Industries, Inc., TGP-H-060) was modified with polystyrene to obtain an electrode E for a reduction reaction. The RF magnetron sputtering method was used to form silver on carbon paper. Argon (Ar) gas is introduced at a flow rate of 50 sccm and a pressure of 0.5 Pa in a sputtering device with a movable mask mechanism (Canon Tokki, SPK-404L) to produce silver with a film thickness of about 200 nm under the condition of an output of 100 W. Filmed. Polystyrene modification of the obtained electrode body was carried out in the same manner as in the reduction reaction electrode A.

<Electrode F for reduction reaction>
Polystyrene was modified on an electrode body in which silver was formed on carbon paper, which was produced in the same manner as above, in the same manner as in the reduction reaction electrode B. This was used as the electrode F for the reduction reaction.

<Electrode G for reduction reaction>
Polystyrene was modified on an electrode body in which silver was formed on carbon paper, which was produced in the same manner as above, in the same manner as in the reduction reaction electrode C. This was used as the electrode G for the reduction reaction.

<Electrode H for reduction reaction>
An electrode body in which silver was formed on carbon paper produced in the same manner as described above was used as the electrode H for the reduction reaction.

FIG. 7 is an infrared absorption spectrum of the reduction reaction electrodes E to H. As shown in FIG. 7, polystyrene-derived peaks (peaks caused by CH ₂ C—H variable angle vibration and aromatic ring C = C expansion / contraction vibration) near 1500 cm ^-1 are found in the reduction reaction electrodes E to G. It was observed, but not on the reduction reaction electrode H. Therefore, in the reduction reaction electrodes E to G, it was suggested that polystyrene was modified on the electrode body in which silver was formed on carbon paper.

FIG. 8 is an SEM image of the reduction reaction electrodes E to H. As shown in FIG. 8, in the reduction reaction electrode G, it was confirmed that polystyrene was aggregated on the carbon paper on which silver was formed. In the reduction reaction electrode E, self-assembly of polystyrene occurs on the electrode body (carbon paper on which silver is formed) in the manufacturing process. In such a reduction reaction electrode E, the figure is shown. As shown in No. 8, it was confirmed that polystyrene microparticles were formed on the electrode body. The reduction reaction electrode F is obtained by applying a liquid on which polystyrene microparticles of about several μm are formed in advance on the electrode body in the manufacturing process. In such a reduction reaction electrode F, FIG. As shown, some of the polystyrene microparticles retained their microparticle structure, but many microparticles were agglomerated.

<CO ₂ electrolysis using reduction reaction electrodes E to H>
(Example 4)
For the electrochemical measurement, the electrochemical cell (two-chamber cell) shown in FIG. 6 was used. Then, the measurement was carried out in the same manner as in Example 1 except that the reduction reaction electrode E was used instead of the reduction reaction electrode A as the working electrode 44.

(Example 5)
The measurement was carried out in the same manner as in Example 1 except that the reduction reaction electrode F was used instead of the reduction reaction electrode A as the working electrode 44.

(Example 6)
The measurement was carried out in the same manner as in Example 1 except that the reduction reaction electrode G was used instead of the reduction reaction electrode A as the working electrode 44.

(Comparative Example 2)
The measurement was carried out in the same manner as in Example 1 except that the reduction reaction electrode H was used instead of the reduction reaction electrode A as the working electrode 44.

Table 2 shows the Faraday efficiency and the amount of H ₂ and CO produced by the CO ₂ electrolysis of Examples 4 to 6 and Comparative Example 2.

As shown in Table 2, in Examples 4 to 6, the current efficiency of H ₂ decreased and the current efficiency of CO increased as compared with Comparative Example 2. Among Examples 4-6, is the fourth embodiment using the reduction electrode E, the current efficiency and the amount of H ₂ is suppressed, also was able to increase the current efficiency and the generation amount of CO .. As described above, in the process of producing the reduction reaction electrode E, polystyrene self-assembly occurs on the electrode body (carbon paper on which silver is formed), and polystyrene microparticles are formed on the electrode body. However, in this case, the electrode body is not completely covered with polystyrene, and the uneven structure of the microparticles has a structure that improves water repellency such as the lotus effect, so CO ₂ is placed on the electrode. It can be selectively adsorbed, and it is presumed that the CO production rate has increased.

1 Electrode for reduction reaction (1st electrode), 3 Carbon compound reducing device, 10 Metal electrode body, 12 Modified layer, 14 Contact member, 16 Lead wire, 20 2nd electrode, 22,54 Cathode chamber, 24,56 Anode chamber, 26 Containment vessel, 28,50 diaphragm, 30 cathode chamber electrolyte solution, 32 anode chamber electrolyte solution, 42 electrochemical measurement system, 44 working electrode, 46 counter electrode, 48 reference electrode, 58 electrolyte solution.

Claims (4)

An electrode for reduction reaction used in the reduction reaction of carbon compounds.
An electrode for a reduction reaction, which comprises an electrode body modified with a hydrophobic polymer. The electrode for a reduction reaction according to claim 1, wherein the electrode body modified with the hydrophobic polymer has a water contact angle of 89 degrees or more. The electrode for a reduction reaction according to claim 1 or 2, wherein the carbon compound contains carbon dioxide. The electrode for reduction reaction according to any one of claims 1 to 3 and
An oxidation reaction electrode that is electrically connected to the reduction reaction electrode and causes an oxidation reaction,
With an electrolyte solution, which is a solution containing an electrolyte,
A carbon compound reducing apparatus, wherein the reduction reaction electrode and the oxidation reaction electrode are immersed in the electrolyte solution.