Electrode catalyst for reducing carbon dioxide, and method of reducing carbon dioxide

Abstract

To provide an electrode catalyst of high Faraday efficiency for reducing carbon dioxide at a high current density such as 200 mA / cm2, and a method of reducing carbon dioxide.SOLUTION: The electrode catalyst for reducing carbon dioxide, formed of aurum nanoparticles each having a particle diameter of 1 to 30 nm and supported by a gas diffusion electrode, electrochemically reduces carbon dioxide to carbon monoxide. The method of reducing carbon dioxide, includes allowing carbon dioxide to contact the electrode catalyst to reduce carbon dioxide to carbon monoxide while irradiating the electrode catalyst with light.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to an electrode catalyst for reducing carbon dioxide and a method for reducing carbon dioxide. [Background technology]

[0002] Carbon dioxide reduction technology has been attracting attention. Carbon dioxide reduction technology includes biological and electrochemical methods of reducing carbon dioxide. Biological methods of reducing carbon dioxide include absorbing carbon dioxide through afforestation, etc., and biochemical reduction and fixation methods using microorganisms. Electrochemical methods of reducing carbon dioxide include reduction with hydrogen using a catalyst.

[0003] In methods such as afforestation, it takes a long time to reduce carbon dioxide. In biochemical reduction and fixation methods using microorganisms, it takes a lot of energy to refine the hydrocarbons produced by the microorganisms. In methods of reducing carbon dioxide with hydrogen using a catalyst, carbon dioxide is generated when hydrogen is synthesized from fossil fuels.

[0004] To solve such problems, for example, Patent Document 1 discloses an electrode catalyst in which silver nanoparticles are supported on a gas diffusion electrode, and which electrochemically reduces carbon dioxide to carbon monoxide.

[0005] Furthermore, Patent Document 2 discloses catalyst particles for exhaust gas purification, although not for carbon dioxide reduction, and discloses that such catalyst particles are produced by sputtering a target material and depositing the material in an ionic liquid. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2020-524742 A [Patent Document 2] JP 2014-158992 A Summary of the Invention [Problem to be solved by the invention]

[0007] In the carbon dioxide reduction catalyst disclosed in Patent Document 1, an electrode catalyst having a high Faraday efficiency at a high current density has been verified for industrial use. However, the verification was limited to silver nanoparticles, and no verification was conducted for substances other than silver nanoparticles.

[0008] The present disclosure has been made to solve the above problems. 2 The object of the present invention is to provide an electrode catalyst for carbon dioxide reduction having high faradaic efficiency at such a high current density, and a method for reducing carbon dioxide. [Means for solving the problem]

[0009] In order to achieve the above object, the present inventors have conducted intensive research and have completed the presently disclosed electrode catalyst for reducing carbon dioxide and the presently disclosed method for reducing carbon dioxide. The presently disclosed electrode catalyst for reducing carbon dioxide and the presently disclosed method for reducing carbon dioxide include the following aspects. <Aspect 1> An electrode catalyst for electrochemically reducing carbon dioxide to carbon monoxide, in which gold nanoparticles having a particle size of 1 to 30 nm are supported on a gas diffusion electrode. Aspect 2: The electrode catalyst according to aspect 1, wherein the gold nanoparticles have a particle size of 10 to 30 nm. A method for producing carbon monoxide from carbon dioxide, comprising contacting carbon dioxide with the electrode catalyst according to Aspect 1 while irradiating the electrode catalyst with light, thereby reducing the carbon dioxide to carbon monoxide. A method for producing carbon monoxide from carbon dioxide, comprising contacting carbon dioxide with the electrode catalyst according to Aspect 2 while irradiating the electrode catalyst with light, thereby reducing the carbon dioxide to carbon monoxide. Effect of the Invention

[0010] According to the present disclosure, gold nanoparticles having a predetermined particle size are supported on a gas diffusion electrode, and thus a current of 200 mA / cm 2 It is possible to provide an electrode catalyst for carbon dioxide reduction having high faradaic efficiency at a high current density such as that shown in FIG. 1. In addition, according to the present disclosure, the faradaic efficiency can be further increased by reducing carbon dioxide to carbon monoxide while irradiating the electrode catalyst with light. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is an explanatory diagram that shows a schematic overview of an example of an electrochemical reduction device. [Diagram 2] FIG. 2 is a TEM image of gold nanoparticles in the electrode catalyst of Example 1. [Diagram 3] FIG. 3 is a TEM image of gold nanoparticles in the electrode catalyst of Example 2. [Figure 4] FIG. 4 is a graph showing the ultraviolet-visible absorption spectrum of the electrode catalyst of Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, embodiments of the carbon dioxide reduction electrode catalyst and carbon dioxide reduction method of the present disclosure will be described. Note that the embodiments described below do not limit the carbon dioxide reduction electrode catalyst and carbon dioxide reduction method of the present disclosure.

[0013] Without being bound by theory, it is believed that the carbon dioxide reduction electrode catalyst and carbon dioxide reduction method disclosed herein have a current density of 200 mA / cm 2 The findings obtained by the present inventors as to why a high Faraday efficiency can be obtained for the reduction of carbon dioxide at such a high current density will be described below.

[0014] 200mA / cm 2When carbon dioxide is reduced to carbon monoxide at such a high current density, the competing reaction of hydrogen generation cannot be completely avoided. However, when gold nanoparticles having a predetermined particle size are supported on a gas diffusion electrode and used as an electrode catalyst, the competing reaction of hydrogen generation can be significantly suppressed. Furthermore, when carbon dioxide is reduced while irradiating such an electrode catalyst with light, plasmon excited electrons are generated from the gold nanoparticles, and carbon dioxide is dissociatively adsorbed onto the gold nanoparticle surface, improving the activity of carbon monoxide generation. At the same time, protons are less likely to be adsorbed onto the gold nanoparticles, suppressing the generation of hydrogen. As a result, the Faraday efficiency can be further increased compared to when light is not irradiated.

[0015] The constituent elements of the carbon dioxide reduction electrode catalyst and carbon dioxide reduction method of the present disclosure, which have been completed based on the findings and the like described thus far, will be described below.

[0016] 《Electrode catalyst for carbon dioxide reduction》 The carbon dioxide reduction electrode catalyst of the present disclosure comprises gold nanoparticles having a particle size of 1 to 30 nm supported on a gas diffusion electrode. Carbon dioxide is brought into contact with this electrode catalyst to reduce the carbon dioxide to carbon monoxide. The gold nanoparticles and the gas diffusion electrode are described below.

[0017] <Gold Nanoparticles> Gold nanoparticles have a particle size of 1 to 30 nm. The particle size of gold nanoparticles is measured by observing the gold nanoparticles with a TEM. Gold nanoparticles often consist of primary particles agglomerated to form secondary particles, and the particle size of the gold nanoparticles mentioned above is the particle size of the primary particles.

[0018] If the particle size of the gold nanoparticles is 1 nm or more, when a voltage is applied to the electrode catalyst to reduce carbon dioxide, the primary particles do not significantly aggregate due to Joule heat, and the catalytic activity is not lost due to the aggregation. From this viewpoint, the particle size may be 1.3 nm or more, 1.5 nm or more, 1.7 nm or more, 2 nm or more, 4 nm or more, 6 nm or more, 8 nm or more, 10 nm or more, 12 nm or more, 14 nm or more, 16 nm or more, or 18 nm or more. On the other hand, if the gold nanoparticles are 30 nm or less, the competing reaction of hydrogen generation can be suppressed. From this viewpoint, the particle size may be 28 nm or less, 26 nm or less, 24 nm or less, 22 nm or less, or 20 nm or less.

[0019] Gold nanoparticles are based on gold but may contain small amounts of impurities. The purity of the gold nanoparticles may be 95% by mass or more, 96% by mass or more, 97% by mass or more, 98% by mass or more, or 99% by mass or more.

[0020] As long as the particle size is within the above range, the gold nanoparticles are not particularly limited, and commercially available products may be used. In particular, when the particle size is 10 nm or less, the gold nanoparticles may be sputtered and deposited in an ionic liquid. The gold nanoparticles sputtered and deposited in an ionic liquid have many crystal lattice defects on their particle surfaces. This improves the efficiency of carbon dioxide reduction.

[0021] "Sputtering deposition in an ionic liquid" means that argon ions or the like are collided with a target material to perform sputtering, and the gaseous substance obtained by the sputtering is vapor-deposited (accumulated) in the ionic liquid. As a method for sputtering deposition in an ionic liquid, a well-known method can be adopted, and a typical example is the method disclosed in Patent Document 2. The method will be outlined below.

[0022] First, the target material is placed on the cathode in the sputtering device. Then, a glass substrate or the like on which the ionic liquid is placed is placed on the anode. Next, a high voltage is applied to the cathode in a state where the chamber of the sputtering device is in a reduced pressure atmosphere containing an inert gas such as a rare gas or nitrogen, for example, argon gas. Then, a glow discharge occurs between the cathode and the anode, and argon ions and the like generated by the glow discharge collide with the target material. This collision causes atoms in the target material to be ejected, and these atoms are deposited in the ionic liquid to form catalyst particles.

[0023] As the ionic liquid, a well-known material can be used, and for example, it can be selected from the group consisting of an aliphatic ionic liquid, an imidazolium ionic liquid, a pyridinium ionic liquid, and a combination thereof.

[0024] The aliphatic ionic liquid may be selected from the group consisting of, for example, N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide, N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium tetrafluoroborate, and combinations thereof. To obtain gold nanoparticles for use in the carbon dioxide reduction method of the present disclosure, it is preferable to employ N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide.

[0025] Examples of imidazolium ionic liquids include 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methyl-imidazolium chloride, 1-ethyl-3-methylimidazolium (L)-lactate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1 -Butyl-3-methylimidazolium trifluoromethanesulfonate, 1-Butyl-3-methylimidazolium (L)-lactate, 1-Hexyl-3-methylimidazolium bromide, 1-Hexyl-3-methylimidazolium chloride, 1-Hexyl-3-methylimidazolium hexafluorophosphate, 1-Hexyl-3-methylimidazolium tetrafluoroborate, 1-Hexyl-3-methylimidazolium trifluoromethanesulfonate, 1-Octyl-3-methylimidazolium chloride, 1-Octyl-3-methylimidazolium Imidazolium hexafluorophosphate, 1-decyl-3-methylimidazolium chloride, 1-dodecyl-3-methylimidazolium chloride, 1-tetradecyl-3-methylimidazolium chloride, 1-hexadecyl-3-methylimidazolium chloride, 1-octadecyl-3-methylimidazolium chloride, 1-ethyl-2,3-dimethylimidazolium bromide, 1-ethyl-2,3-dimethylimidazolium chloride, 1-butyl-2,3-dimethylimidazolium bromide, 1-butyl-2,3-di The imidazolium salt may be selected from the group consisting of methylimidazolium chloride, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate, 1-butyl-2,3-dimethylimidazolium trifluoromethanesulfonate, 1-hexyl-2,3-dimethylimidazolium bromide, 1-hexyl-2,3-dimethylimidazolium chloride, 1-hexyl-2,3-dimethylimidazolium tetrafluoroborate, 1-hexyl-2,3-dimethylimidazolium trifluoromethanesulfonate, and combinations thereof.

[0026] The pyridinium-based ionic liquid may be selected from the group consisting of, for example, 1-ethylpyridinium bromide, 1-ethylpyridinium chloride, 1-butylpyridinium bromide, 1-butylpyridinium chloride, 1-butylpyridinium hexafluorophosphate, 1-butylpyridinium tetrafluoroborate, 1-butylpyridinium trifluoromethanesulfonate, 1-hexylpyridinium bromide, 1-hexylpyridinium chloride, 1-hexylpyridinium hexafluorophosphate, 1-hexylpyridinium tetrafluoroborate, 1-hexylpyridinium trifluoromethanesulfonate, and combinations thereof.

[0027] The target material may be a gold-containing target material. The target material may be allowed to contain unavoidable impurities to the extent that it does not interfere with the sputtering operation and the sputtering product. In other words, the target material may contain gold, with the remainder being unavoidable impurities.

[0028] The above-mentioned target materials are not particularly limited in shape as long as the desired gold nanoparticles can be obtained. Examples of the target materials include plate materials, sintered bodies, and combinations thereof.

[0029] <Gas diffusion electrode> The gold nanoparticles are supported on a gas diffusion electrode. A gas diffusion electrode is an electrode where the three states of solid, liquid, and gas are in contact with each other. The gas diffusion electrode on which the gold nanoparticles are supported constitutes an electrode catalyst. This electrode catalyst has a catalytic function for the electrochemical reaction between the liquid phase and the gas phase.

[0030] The gas diffusion electrode includes a conductive support. The conductive support is typically carbon paper, but is not limited thereto, and may be a metal porous body, an oxide porous body, a semiconductor porous body, or the like. In the case of gold nanoparticles sputter-deposited in an ionic liquid, an ionic liquid in which gold nanoparticles are dispersed is dropped onto the conductive support (carrier) described above, dried, and then washed with an organic solvent to remove the ionic liquid, and dried again to obtain an electrode catalyst (working electrode). In the case of gold nanoparticles other than those sputter-deposited in an ionic liquid, a gold nanoparticle colloid mixed in an organic solvent is dropped onto the conductive support (carrier) described above, and then dried to obtain an electrode catalyst (working electrode).

[0031] The amount of gold nanoparticles supported may be appropriately determined taking into consideration the carbon dioxide reduction conditions, etc., and may be, for example, 0.01 mg / cm 2 More than 0.05mg / cm 2 or more than 0.1 mg / cm 2 or more, and 2 Below, 0.7mg / cm 2 Below, 0.5mg / cm 2 or less than 0.3 mg / cm 2 It may be the following:

[0032] Carbon dioxide reduction method The gold nanoparticles supported on the gas diffusion electrode described above are brought into contact with carbon dioxide, which reduces the carbon dioxide to carbon monoxide, generating carbon monoxide from the carbon dioxide. The method of generating carbon monoxide will be described together with the device used for the method.

[0033] A device shown in Fig. 1 is typically used for reducing carbon dioxide, but is not limited to this. Fig. 1 is an explanatory diagram showing a schematic overview of an example of an electrochemical reduction device. This electrochemical reduction device will be described below.

[0034] The electrochemical reduction device 100 includes an anode chamber 10, a cathode chamber 20, and a gas chamber 30. The anode chamber 10 and the cathode chamber 20 are connected via a separator 50. The cathode chamber 20 and the gas chamber 30 are connected via a working electrode 60. The working electrode 60 is a gas diffusion electrode on which gold nanoparticles are supported.

[0035] The inside of the anode chamber 10 and the inside of the cathode chamber 20 are filled with an electrolyte 70. A counter electrode 80 is installed in the anode chamber 10 so that a portion of the counter electrode 80 is immersed in the electrolyte 70. A reference electrode 90 is installed in the cathode chamber 20 so that a portion of the reference electrode 90 is immersed in the electrolyte 70. The reference electrode 90 allows a desired potential to be accurately applied to the working electrode 60.

[0036] An inlet pipe 40 and an outlet pipe 42 are installed in the gas chamber 30. Carbon dioxide gas is introduced into the gas chamber 30 from the inlet pipe 40. The carbon dioxide gas introduced into the gas chamber 30 comes into contact with the working electrode 60, which functions as an electrode catalyst to promote the reduction of the carbon dioxide gas. Then, carbon monoxide gas obtained by the reduction of the carbon dioxide gas is discharged from the outlet pipe 42.

[0037] 1, a gas diffusion electrode carrying gold nanoparticles is installed as the working electrode 60. The working electrode 60, counter electrode 80, reference electrode 90, separator 50, and electrolyte 70 will be described below.

[0038] The working electrode 60 is a gas diffusion electrode (carrier) that does not allow the electrolyte 70 to pass through but allows carbon dioxide and reduction products to pass through, and on which gold nanoparticles are supported. The gas diffusion electrode (carrier) used for the working electrode 60 is as described above.

[0039] The counter electrode 80 is not particularly limited as long as it does not prevent efficient progress of carbon dioxide reduction, but typically a platinum mesh is used.

[0040] The reference electrode 90 may be any material capable of accurately measuring the potential of the working electrode 60. Examples of materials contained in the reference electrode 90 include Hg / Hg2Cl2, Ag / AgCl, and / or reversible hydrogen, with Ag / AgCl being particularly preferred.

[0041] Well-known materials can be used for the separator 50, and examples of materials contained in the separator 50 include Nafion, glass filter, Selemion, and / or Zilphon, with Nafion being particularly preferred. A typical example of the separator 50 is a Nafion membrane.

[0042] The electrolyte 70 may be any known electrolyte, such as KHCO3, HClO4, H2SO4, HCl, and / or HNO3, with KHCO3 being preferred.

[0043] The conditions for reducing carbon dioxide may be appropriately determined depending on the combination of the working electrode 60, the counter electrode 80, the reference electrode 90, the separator 50, and the electrolyte 70. The potential of the working electrode 60 may be in the range of, for example, 0 V vs. RHE to -3.5 V vs. RHE. The current density is, for example, -800 mA / cm with respect to the working electrode. 2 More than -700mA / cm 2 or above -600mA / cm 2 or more, -500mA / cm 2 Below, -400mA / cm 2 Below, -300mA / cm 2 or less than -200mA / cm 2 The amount of carbon dioxide gas supplied may be, for example, 5 cm 3 / min or more, 10cm 3 / min or more, or 50cm 3 / min or more, 200 cm 3 / min or less, 150cm 3 / min or less, or 100cm 3 / min or less.

[0044] During the reduction of carbon dioxide, the working electrode 60 (electrode catalyst) may be irradiated with light. This can further improve the Faraday efficiency. The irradiated light preferably includes light with a wavelength of 100 nm or more, 200 nm or more, 300 nm or more, or 400 nm or more, and 700 nm or less, 650 nm or less, or 600 nm or less. The output of the irradiated light is 1 mW / cm. 2 More than 10mW / cm 2 More than 100mW / cm 2 More than 500mW / cm 2 or more than 1000mW / cm 2 More than 10W / cm 2 Below, 8W / cm 2 Below, 6W / cm 2 Below, 4W / cm 2 or less than 2W / cm 2 The wavelength and output of the irradiated light may be as described above, whereby plasmon excited electrons are generated from the gold nanoparticles, carbon dioxide is dissociatively adsorbed onto the gold nanoparticle surface, and the activity of carbon monoxide generation is improved. Furthermore, protons are less likely to be adsorbed onto the gold nanoparticles, and hydrogen generation can be suppressed. As a result, the Faraday efficiency can be further increased compared to when no light is irradiated.

[0045] Transformation The carbon dioxide reduction electrode catalyst and carbon dioxide reduction method of the present disclosure may be modified as appropriate within the scope of the claims. For example, the carbon dioxide reduction electrode catalyst of the present disclosure may be such that the specified gold nanoparticles are supported on the gas diffusion electrode, and a substance other than the specified gold nanoparticles may be supported on the gas diffusion electrode as long as the effect of the carbon dioxide reduction electrode catalyst of the present disclosure is not impaired. EXAMPLES

[0046] The carbon dioxide reduction electrode catalyst and carbon dioxide reduction method of the present disclosure will be described in more detail below with reference to examples and comparative examples. Note that the carbon dioxide reduction electrode catalyst and carbon dioxide reduction method of the present disclosure are not limited to the conditions used in the following examples.

[0047] Sample preparation Each sample was prepared as follows.

[0048] Example 1 Gold nanoparticles were obtained by sputtering deposition in an ionic liquid. The ionic liquid used was N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide (TMPA-TFSA). 3 The ionic liquid was heated to 100°C while stirring and dried under reduced pressure. A gold target material was placed in a sputtering deposition apparatus (SC-701HMCII5 manufactured by Sanyu Electronics Co., Ltd.), and the chamber was replaced with argon gas, after which pre-sputtering was performed for 15 minutes under conditions of a pressure of 3.0 Pa and a deposition current of 20 mA. The thoroughly dried ionic liquid was spread evenly on a petri dish (diameter 70 mm) and placed in the chamber, and the chamber was replaced with argon gas, after which sputtering was performed for 180 minutes under conditions of a pressure of 3.0 Pa and a deposition current of 20 mA.

[0049] A working electrode (electrode catalyst) was prepared from gold nanoparticles dispersed in an ionic liquid. Specifically, the amount of gold nanoparticles supported was 0.1 mg / cm. 2 The ionic liquid in which gold nanoparticles were dispersed was dropped onto carbon paper (SIGRACET (registered trademark), 36BB, manufactured by SGL Corporation) so that the gold nanoparticles were dispersed in the ionic liquid.

[0050] Comparative Example 1 A working electrode of Comparative Example 1 was obtained in the same manner as in Example 1, except that sputtering was performed using a copper target material instead of a gold target material.

[0051] Comparative Example 2 3.4 mg of gold nanopowder (Sigma-Aldrich, particle size 100 nm), 400 μl of isopropanol, and 4.4 μl of Nafion 117 solution (Sigma-Aldrich) were mixed and dispersed using an ultrasonic cleaner. Then, 20 μl of the dispersion solution was dropped onto carbon paper and dried to obtain a working electrode.

[0052] Example 2 200 μl of gold colloid (Shinko Chemical Industry Co., Ltd., particle size 20 nm) and 30 μl of Nafion 117 solution (Sigma-Aldrich Co., Ltd.) were mixed and dispersed using an ultrasonic cleaner. Then, 20 μl of the dispersion solution was dropped onto carbon paper and dried to obtain a working electrode.

[0053] Comparative Example 3 200 μl of silver colloid (Shinko Chemical Industry Co., Ltd., particle size 30 nm) and 30 μl of Nafion 117 solution (Sigma-Aldrich Co., Ltd.) were mixed and dispersed using an ultrasonic cleaner. Then, 20 μl of the dispersion solution was dropped onto carbon paper and dried to obtain a working electrode.

[0054] 《Reduction of Carbon Dioxide》 Carbon dioxide was reduced using the electrical reduction apparatus shown in Figure 1. A platinum mesh was used as the counter electrode, an Ag / AgCl electrode (saturated KCl) as the reference electrode, and 1M KHCO3 as the electrolyte. The working electrodes of the above-mentioned samples were placed in such an electrical reduction apparatus, and the gas compartment was filled with 10 cm 3 Carbon dioxide gas was flowed at a flow rate of -200mA / cm2 per minute. 2 The constant current was 0.5 W / cm. To obtain this constant current, a potentiogalvanostat (HZ-7000, manufactured by Hokuto Denko Corporation) was used. The reduction time (electrolysis time) was 30 minutes. Light irradiation was performed using an LED (PFBR-150RD-MN, manufactured by CCS) at 0.5 W / cm. 2 The working electrode was irradiated with an output of .

[0055] "evaluation" The products obtained when carbon dioxide was reduced using the working electrode of each sample were subjected to qualitative and quantitative analysis using a gas chromatograph and an ion chromatograph. The selectivity of the reduced products was evaluated by Faraday efficiency. The electrode catalyst of each sample was observed by TEM, and the particle size distribution was measured based on the TEM image. In addition, the electrode catalyst of Example 1 was subjected to optical absorption measurement based on ultraviolet-visible spectroscopy.

[0056] The Faraday efficiency (FE) was calculated using the following formula (A): Faraday efficiency also indicates how kinetically favorable a particular reaction process is. FE = αnF / Q (A) Here, α is the number of electrons required to form one molecule of the target product, n is the amount of the target product, F is the Faraday constant, and Q is the total charge.

[0057] The results are shown in Table 1 and Figures 2 to 4. Table 1 shows the Faraday efficiencies of Examples 1 and 2 and Comparative Examples 1 to 3. In Table 1, Au stands for gold, Ag stands for silver, and the numbers in parentheses stand for the particle size of each nanoparticle. Figure 2 is a TEM image of gold nanoparticles in the electrode catalyst of Example 1. Figure 3 is a TEM image of gold nanoparticles in the electrode catalyst of Example 2. Figure 4 is a graph showing the ultraviolet-visible absorption spectrum of the electrode catalyst of Example 1.

[0058] [Table 1]

[0059] 2 and 3, it can be seen that the particle size of the gold nanoparticles is within the desired range in the electrode catalysts of Examples 1 and 2. Also, from Table 1, in both Examples 1 and 2, the current density was 200 mA / cm 2 It can be seen that at such a high current density, the faradaic efficiency for carbon monoxide production is high.

[0060] In both the cases of Example 1 and Example 2, it can be seen that the faradaic efficiency for hydrogen generation is reduced and the faradaic efficiency for carbon monoxide generation is increased by light irradiation. In addition, in the ultraviolet-visible absorption spectrum of FIG. 3, a broad plasmon absorption band is observed at a wavelength of 320 nm skin. From these, it is considered that light irradiation generates plasmon excited electrons from the gold nanoparticles, dissociatively adsorbs carbon dioxide onto the gold nanoparticle surface, improving the activity for carbon monoxide generation and making it difficult for protons to be adsorbed onto the gold nanoparticles, thereby suppressing hydrogen generation.

[0061] In Example 2, the total Faraday efficiency exceeded 100%, but this is believed to be because pressure loss occurred when the generated gas was stored in the gas bag, resulting in a decrease in the flow rate of carbon dioxide.

[0062] In contrast, in Comparative Example 1, hydrogen generation is dominant and carbon monoxide is hardly generated, and it can be seen that hydrogen generation becomes even more dominant when light is irradiated, and no carbon monoxide is generated. In Comparative Example 2, although a small amount of carbon monoxide is generated, hydrogen generation is dominant, and it can be seen that this tendency becomes even stronger when light is irradiated. This is thought to be because light irradiation locally increases the temperature of the electrode catalyst surface and reduces the amount of dissolved carbon dioxide, which causes hydrogen generation to become dominant. In Comparative Example 3, hydrogen generation is high and carbon monoxide generation is low, and although hydrogen generation decreases when light is irradiated, carbon monoxide generation does not increase but decreases. This is thought to be because, as in the case of Comparative Example 2, the temperature of the electrode catalyst surface increases, causing the amount of dissolved carbon dioxide to decrease.

[0063] From the above results, the effects of the carbon dioxide reduction electrode catalyst and carbon dioxide reduction method disclosed herein were confirmed. [Explanation of symbols]

[0064] 10 Anode chamber 20 Cathode chamber 30 Gas Chamber 40 Introductory tube 42 Discharge pipe 50 Separator 60 Working electrode 70 Electrolyte 80 Opposite 90 Reference pole 100 Electrochemical reduction device

Claims

1. An electrode catalyst for electrochemically reducing carbon dioxide to carbon monoxide, comprising gold nanoparticles having a particle size of 1 to 30 nm supported on a gas diffusion electrode.

2. 2. The electrode catalyst according to claim 1, wherein the gold nanoparticles have a particle size of 10 to 30 nm.

3. A method for producing carbon monoxide from carbon dioxide, comprising contacting carbon dioxide with the electrode catalyst according to claim 1 while irradiating the electrode catalyst with light, thereby reducing the carbon dioxide to carbon monoxide.

4. A method for producing carbon monoxide from carbon dioxide, comprising contacting carbon dioxide with the electrode catalyst according to claim 2 while irradiating the electrode catalyst with light, thereby reducing the carbon dioxide to carbon monoxide.

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