JP7492953B2 - Electrode, solid electrolyte electrolysis device, and synthesis gas generation method - Google Patents

Description

The present disclosure relates to an electrode capable of producing a synthesis gas containing at least carbon monoxide, a solid electrolyte electrolysis device, and a synthesis gas production method.

Fossil fuels (oil, coal, natural gas) support the modern energy-consuming society. However, the reserves of such fossil fuels are limited. Therefore, various alternative fuels have been proposed to replace fossil fuels. One of them is hydrocarbon fuels (HC). HC can be synthesized, for example, by subjecting a synthesis gas containing at least carbon monoxide (CO) and hydrogen (H ₂ ) to the Fischer-Tropsch reaction (FT reaction).

Patent Document 1 proposes a synthetic gas synthesis apparatus. Specifically, the apparatus discloses a tank provided separately from an electrolytic cell in which carbon dioxide (CO ₂ ) is blown into seawater to lower the pH of the seawater from 8 to 5-6, and the seawater after the pH adjustment is sent from the tank to the electrolytic cell for electrolysis.

Japanese Patent Application Laid-Open No. 61-73893

Here, the method of Patent Document 1 has a problem that the solubility of _CO2 in water is low, so the production efficiency of synthesis gas is low. Therefore, an object of the present disclosure is to provide a technology related to an electrode that has high production efficiency of synthesis gas containing at least CO.

According to one aspect of the present disclosure,
A catalyst that produces at least carbon monoxide by a reduction reaction;
an electrode material having the catalyst;
A solid base provided on at least the electrode material;
It is possible to provide a technique having the above-mentioned features.

The present disclosure makes it possible to provide technology relating to electrodes that have high production efficiency for synthetic gas containing at least CO.

1 is a solid electrolyte electrolysis device preferably used in an embodiment of the present disclosure. FIG. 1 is a conceptual diagram showing how CO ₂ can be locally and efficiently adsorbed by adding a solid base to the cathode surface in a solid electrolyte electrolysis device suitably used in an embodiment of the present disclosure. 1 is a flowchart showing a method for producing synthetic gas using a solid electrolyte electrolysis device preferably used in an embodiment of the present disclosure. 1 is an example of an application of a solid electrolyte electrolysis device preferably used in an embodiment of the present disclosure.

The solid electrolyte electrolysis device according to the present disclosure will be specifically described below with reference to one embodiment. Note that the invention according to the present disclosure is not limited to the embodiment described below.

<Solid electrolyte electrolysis device 100>
First, a solid electrolyte electrolysis device (also referred to as an electrolysis cell or electrolysis module) according to this embodiment will be described with reference to Fig. 1. As shown in Fig. 1, the solid electrolyte electrolysis device 100 according to this embodiment includes a cathode 101, an anode 102 forming a pair of electrodes with the cathode 101, a solid electrolyte 103 interposed between the cathode 101 and the anode 102 in a state in which at least a part of the solid electrolyte 103 is in contact with the cathode 101, a current collector 104 in contact with the cathode 101 at a surface 101-2 opposite to a contact surface 101-1 with the solid electrolyte 103, a support plate 105 in contact with the anode 102 at a surface 102-1 opposite to a contact surface 102-2 with the solid electrolyte 103, and a voltage application unit 106 that applies a voltage between the current collector 104 and the support plate 105 (i.e., between the cathode and the anode). In addition, _CO2 in a gas phase and supporting electrolyte _H2O are supplied by a supply source and a supply device (not shown). For the sake of explanation, the solid electrolyte electrolysis device 100 shown in FIG. 1 is illustrated with each component, such as the cathode 101 and the anode 102, separated. In reality, the current collector 104, the cathode 101, the solid electrolyte 103, the anode 102, and the support plate 105 are bonded together by a predetermined method and integrated together. Each component may be detachably configured to constitute one solid electrolyte electrolysis device 100. Each component will be described in detail below.

<Cathode 101>
(Reduction reaction at cathode 101)
The reduction reaction in the cathode 101 depends on the type of solid electrolyte 103. When a cation exchange membrane is used as the solid electrolyte 103, the reduction reactions of the following formulas (1) and (2) occur, and when an anion exchange membrane is used as the solid electrolyte, the reduction reactions of the following formulas (3) and (4) occur.

(Basic structure and materials of cathode 101)
The cathode 101 is a gas diffusion electrode including a gas diffusion layer. The gas diffusion layer includes, for example, carbon paper or nonwoven fabric, or a metal mesh. Examples of the electrode material of the cathode 101 include graphite carbon, glassy carbon, titanium, and SUS. The cathode catalyst capable of reducing CO ₂ to CO, which the cathode 101 has, includes, for example, a metal selected from silver, gold, copper, or a combination thereof. More specifically, the catalyst includes, for example, gold, gold alloy, silver, silver alloy, copper, copper alloy, or a mixed metal including any one or more of them. The type of catalyst is not particularly limited as long as it has a catalytic function, and can be determined in consideration of corrosion resistance and the like. For example, the catalyst does not include amphoteric metals such as Al, Sn, and Zn, thereby improving corrosion resistance. The catalyst can be supported on the cathode 101 (or electrode material) by carrying out a known method such as vapor deposition, deposition, adsorption, deposition, adhesion, welding, physical mixing, spraying, etc.

(Solid Base 107)
Here, as shown in FIG. 2, the cathode 101 has a solid base 107 . The solid base 107 is not particularly limited as long as it is a base that is solid at room temperature (25° C.), and examples thereof include potassium bicarbonate (KHCO ₃ ), sodium hydroxide (NaOH), an oxide of an alkaline earth metal, a hydroxide of an alkaline earth metal, or a carbonate of an alkaline earth metal {e.g., magnesium oxide (MgO), magnesium hydroxide (Mg(OH) ₂ ), magnesium carbonate (MgCO ₃ ), calcium oxide (CaO), calcium hydroxide (Ca(OH) ₂ ), calcium carbonate (CaCO ₃ ), strontium oxide (SrO), strontium hydroxide (Sr(OH) ₂ ), strontium carbonate (SrCO ₃ ), barium oxide (BaO), barium hydroxide (Ba(OH) ₂ ), barium carbonate (BaCO ₃ ), etc.}, an oxide of a rare earth metal, a hydroxide of a rare earth metal, or a carbonate of a rare earth metal {e.g., yttrium oxide (Y ₂ O ₃ ), lanthanum oxide (La ₂ O 3 ), etc.}. ₃ ) and the like}, hydrotalcite (e.g., metal complex hydroxide, carbonate, LDH, HT-CO ₃ , HT-OH, etc.), surface-basified zeolite, base-treated molecular sieve, surface-basified porous alumina (KF-Al ₂ O ₃ ), and the like are preferably used. In particular, as described in the examples below, a weakly basic solid base having a small atomic number is more preferable. In addition, it is even more preferable to use an alkaline earth metal oxide, an alkaline earth metal hydroxide, or an alkaline earth metal carbonate, an alkaline earth metal oxide, a rare earth metal hydroxide, or a rare earth metal carbonate, which are water-insoluble solid bases, because they are not washed away by water in the gas or water generated by the reaction, and the durability of the cathode having the solid base 107 is not reduced. Here, "water-insoluble" refers to a substance that does not dissolve 10 mg in 100 mL of water at 20°C. It is preferable that the solid base 107 is present on the contact surface 101-1 side of the cathode 101 with the solid electrolyte 103. The reason for this configuration is that the interface between the cathode 101 and the solid electrolyte 103 is a reaction site. The solid base 107 may be present as a mixture with the material of the cathode 101, or may be present in an integrated state as a compound. The solid base 107 can be supported on the cathode 101 (or the electrode material) by carrying out a known method such as coating, vapor deposition, precipitation, physical mixing, etc. The mass per unit area of the solid base is not particularly limited, but is, for example, 0.1 to 10 mg/cm ² , preferably 0.1 to 6 mg/cm ² .

Here, the reason why the efficiency is improved by using the solid base 107 is presumed to be the following mechanism of action. First, when a low-concentration CO ₂ gas with a content concentration of 10 to 20%, such as exhaust gas from a factory, is supplied to the solid electrolyte electrolysis device 100, the CO ₂ is not easily adsorbed on the surface of the cathode 101 due to its low concentration. Therefore, as shown in FIG. 2, it is understood that by adding the solid base 107 to the surface of the cathode 101, CO ₂ can be locally and efficiently adsorbed to the area where the solid base exists, and CO ₂ reduction can be promoted. In addition, when a cation exchange membrane is adopted as the solid electrolyte 103, it is understood that if there is a lot of H ⁺ on the surface of the cathode 101, CO ₂ cannot be sufficiently adsorbed. In this case, it is considered that the reaction proceeds when the solid base 107 is present (for example, it is preferable to control the pH so that pH>2). On the other hand, when an anion exchange membrane is adopted as the solid electrolyte, OH ^- exists on the cathode surface, so that CO ₂ is adsorbed and is suitable for CO ₂ reduction. However, if there is too much ^OH- , it is adsorbed as stable _CO3 ^2- , and it is understood that the _CO2 reduction reaction does not proceed sufficiently. In this case, if a weakly basic solid base 107 is present, it is considered that the _CO2 reduction reaction proceeds more (for example, it is preferable to control the pH so that the pH is less than 12). In the present invention, an electrode having such a solid base and catalyst can be expressed as "an electrode having a catalyst, an electrode material having a catalyst, and at least a solid base provided on the electrode material" (in other words, an electrode having an electrode material having a catalyst and a solid base), or "a cathode having a catalyst and further having a solid base", etc.

<Anode 102>
(Oxidation Reaction at the Anode 102)
The oxidation reaction at the anode 102 depends on the type of solid electrolyte 103. When a cation exchange membrane is used as the solid electrolyte 103, the oxidation reaction of the following formula (5) occurs, and when an anion exchange membrane is used as the solid electrolyte 103, the oxidation reaction of the following formula (6) occurs.

(Basic structure and material of anode 102)
The anode 102 is a gas diffusion electrode including a gas diffusion layer. The gas diffusion layer includes, for example, a metal mesh. Examples of the electrode material of the anode 102 include Ir, _IrO2 , Ru, _RuO2 , Co, CoOx, Cu, CuOx, Fe, FeOx, FeOOH, FeMn, Ni, NiOx, NiOOH, NiCo, NiCe, NiC, NiFe, NiCeCoCe, NiLa, NiMoFe, NiSn, NiZn, SUS, Au, and Pt.

<Solid Electrolyte 103>
The solid electrolyte 103 is interposed between the cathode 101 and the anode 102 in contact with each other. Here, the solid electrolyte 103 is not particularly limited to a polymer membrane, but is preferably a cation exchange membrane or an anion exchange membrane, and more preferably an anion exchange membrane. As the cation exchange membrane, for example, a strongly acidic cation exchange membrane in which a sulfone group is introduced into a fluororesin matrix, such as Nafion 117, Nafion 115, Nafion 212, or Nafion 350 (manufactured by DuPont), a strongly acidic cation exchange membrane in which a sulfone group is introduced into a styrene-divinylbenzene copolymer matrix, or Neocepta CMX (manufactured by Tokuyama Soda Co., Ltd.), can be used. As the anion exchange membrane, for example, a quaternary ammonium group, a primary amino group, a secondary amino group, a tertiary amino group, or an anion exchange membrane in which a plurality of these ion exchange groups are mixed can be used. Specific examples include Neocepta (registered trademark) ASE, AHA, AMX, ACS, AFN, AFX (manufactured by Tokuyama Corporation), Selemion (registered trademark) AMV, AMT, DSV, AAV, ASV, AHO, AHT, APS4 (manufactured by Asahi Glass Co., Ltd.), etc.

<Current collector plate 104>
Examples of the current collector 104 include metal materials such as copper (Cu), nickel (Ni), stainless steel (SUS), nickel-plated steel, and brass, and among these, copper is preferred from the viewpoints of ease of processing and cost. When the current collector 104 is made of a metal material, examples of the shape of the negative electrode current collector include metal foil, metal plate, metal thin film, expanded metal, punched metal, and foamed metal.

As shown in FIG. 1, the current collector 104 is provided with a gas supply hole 104-1 and a gas recovery hole 104-2 for supplying and recovering gas (raw material gas and generated gas) to the cathode 101. The gas supply hole 104-1 and the gas recovery hole 104-2 make it possible to uniformly and efficiently feed raw material gas to the cathode 101 and discharge generated gas (including unreacted raw material gas). Note that, although one gas supply hole and one gas recovery hole are provided in the figure, the number, location, and size are not limited and are set appropriately. In addition, if the current collector 104 is breathable, the gas supply hole and the gas recovery hole are not necessarily required.

Furthermore, if the cathode 101 has the role of transmitting electrons, the collector plate 104 is not necessarily required.

<Support Plate 105>
The support plate 105 plays a role of supporting the anode. Therefore, the required rigidity of the support plate 105 varies depending on the thickness and rigidity of the anode. The support plate 105 must also have electrical conductivity in order to receive electrons from the anode. Examples of materials for the support plate 105 include Ti, SUS, and Ni.

1, the support plate 105 is provided with a gas flow path 105-1 for feeding a source gas (H ₂ O, etc.) to the anode 102. The gas flow path makes it possible to feed the source gas uniformly and efficiently to the anode 102. In the figure, eight gas flow paths are provided, but the number, location, and size of the gas flow paths are not limited and may be set appropriately.

In this embodiment, the anode 102 and the support plate 105 are described as separate entities, but the anode 102 and the support plate 105 may be of an integral structure (i.e., they may be configured as an integrated anode 102 with a support function).

<Voltage application unit 106>
1, the voltage application unit 106 applies a voltage between the cathode 101 and the anode 102 by applying a voltage to the current collector 104 and the support plate 105. As described above, the current collector 104 is a conductor and therefore supplies electrons to the cathode 101, while the support plate 105 is also a conductor and therefore receives electrons from the anode 102. In addition, in the case where the current collector 104 is not required as described above, a voltage is applied between the cathode 101 and the support plate 105. In addition, a control unit (not shown) may be electrically connected to the voltage application unit 106 in order to apply an appropriate voltage.

<Reaction gas supply unit>
The solid electrolyte electrolysis device 100 in the present disclosure may be provided with a reaction gas supply unit (not shown) on the outside of the solid electrolyte electrolysis device 100. That is, it is sufficient that CO ₂ , which is a reaction gas, is supplied to the surface 101-2, and the reaction gas may be supplied from the reaction gas supply unit to the gas supply hole 104-1 via a pipe (not shown) or the like, or the reaction gas may be sprayed onto the surface 104-A of the current collector 104 opposite to the contact surface 104-B with the cathode 101. From an environmental perspective, it is preferable to use factory exhaust gas discharged from a factory as the reaction gas.

<CO generation method>
Next, a method for producing CO using the above-mentioned solid electrolyte electrolysis device 100 will be described with reference to FIG.

<Reaction gas supply process S301>
First, _CO2 , which is a reactant gas serving as a raw material, is supplied in a gas phase state by a reactant gas supply unit (not shown) to the solid electrolyte electrolysis device 100. At this time, _CO2 is supplied to the cathode 101 through the gas supply hole 104-1 provided in the current collector plate 104 (S301).

<CO, _H2 production process S302>
Next, the _CO2 supplied to the cathode 101 undergoes a reduction reaction on the surface of the cathode 101. When a cation exchange membrane is used as the solid electrolyte 103, the reduction reactions of the above-mentioned formulas (1) and (2) occur. When an anion exchange membrane is used as the solid electrolyte, the reduction reactions of the above-mentioned formulas (3) and (4) occur, thereby generating a synthesis gas containing at least CO and _H2 (S302).

<Produced gas recovery step S303>
Next, the synthesis gas containing the generated CO and _H2 is sent to a gas recovery device (not shown) through gas recovery holes 104-2 provided in the current collector 104, and is recovered in predetermined gas fractions (S303).

<Application>
As shown in Fig. 4, for the solid electrolyte electrolysis device according to the present disclosure as described above, it is possible to generate a synthesis gas containing at least CO and _H2 in a desired production ratio by using, for example, _CO2 gas discharged from a factory as a raw material and utilizing renewable energy such as a solar cell for the voltage application unit 106. The synthesis gas thus generated can be used to generate a fuel base material or a chemical raw material by a method such as FT synthesis or methanation.

Below, we will provide specific examples and comparative examples of the use of the above-mentioned embodiment.

The solid electrolyte electrolysis device 100 shown in Figure 1 was assembled (support plate = 3 mm Ti plate), and the synthesis gas production results for each cathode catalyst and solid base material used are shown in Table 1-3.

Table 1 shows experimental data for a solid electrolyte electrolysis device 100 in which an anion exchange membrane is used as the solid electrolyte 103, silver (Ag) is used as the cathode catalyst, and each solid base is added to the cathode 101.

The experimental conditions in Table 1 were as follows: platinum mesh was used as the anode material, carbon paper coated with Ag to form a thin film was used as the cathode material, a saturated _KHCO3 aqueous solution was used as the anode electrolyte, and the voltage applied to the current collector 104 and the support plate 105 was 3.5 V. The solid base was added so that the mass per unit area was about 5.33 mg/ ^cm2 .

The experimental results were evaluated using the measured value of the partial current density (mA/ ^cm2 ) of CO when no solid base was added as the judgment criterion, with results showing an improvement of 2% or more from the measured value being given the symbol △, results showing an improvement of 10% or more being given the symbol ○, and results showing an improvement of 50% or more being given the symbol ◎, and it was judged that the production efficiency of synthetic gas (particularly CO) could be improved. Note that the partial current density is a physical quantity that indicates the amount of electrons used to produce a specific compound, and the larger the value, the greater the amount produced.

First, as judgment criterion 1, when no solid base was added (no addition), the partial current density of CO was 6.05 mA/cm ^2. In addition, the Faraday efficiency (FE) of H ₂ was 3.19%, the FE of CO was 57.62%, and the partial current density of H ₂ was 0.33 mA/cm ^2. In this experiment using an anion exchange membrane, these measured values are judged as standard values.

In Example 1, when KHCO ₃ was added, the FE of H ₂ was 26.87%, the FE of CO was 54.28%, the partial current density of H ₂ was 3.07 mA/cm ² , and the partial current density of CO was 6.2 mA/cm ^2. Therefore, in Example 1, the partial current density of CO in Criterion 1 was improved by about 2.5%, and the CO generation efficiency could not be significantly improved. This is thought to be because KHCO ₃ is water-soluble and dissolves in H ₂ O generated by the reaction at the cathode, and the base effect was not sufficiently obtained.

Next, in Example 2, when MgO was added, the FE of _H2 was 20.85%, the FE of CO was 77.19%, the partial current density of _H2 was 2.72 mA/ ^cm2 , and the partial current density of CO was 10.08 mA/ ^cm2 . Therefore, in Example 2, the partial current density of CO in the judgment criterion 1 was improved by about 66.6%, and the generation efficiency of CO could be improved.

Next, in Example 3, when Sr(OH) ₂ was added, the FE of _H2 was 4.15%, the FE of CO was 54.61%, the partial current density of _H2 was 0.71mA/ ^cm2 , and the partial current density of CO was 9.28mA/ ^cm2 . Therefore, in Example 3, the partial current density of CO in the judgment criterion 1 was improved by about 53.4%, and the generation efficiency of CO could be improved.

Next, in Example 4, when _BaCO3 was added, the FE of _H2 was 26.36%, the FE of CO was 58.17%, the partial current density of _H2 was 3.81mA/ ^cm2 , and the partial current density of CO was 8.25mA/ ^cm2 . Therefore, in Example 4, the partial current density of CO in the judgment criterion 1 was improved by about 36.4%, and the generation efficiency of CO was improved.

Next _, in Example 5, when _Y2O3 was added, the FE of _H2 was 23.51%, the FE of CO was 58.78%, the partial current density of _H2 was 3.43mA/ ^cm2 , and the partial current density of CO was 8.58mA/ ^cm2 . Therefore, in Example 5, the partial current density of CO in the judgment criterion 1 was improved by about 41.8%, and the generation efficiency of CO could be improved.

Next _, in Example 6, when _La2O3 was added, the FE of _H2 was 8.4%, the FE of CO was 64.09%, the partial current density of _H2 was 0.88mA/ ^cm2 , and the partial current density of CO was 7.57mA/ ^cm2 . Therefore, in Example 6, the partial current density of CO in the judgment criterion 1 was improved by about 25.1%, and the generation efficiency of CO could be improved.

Table 2 shows experimental data for a solid electrolyte electrolysis device 100 using a cation exchange membrane (Nafion 117) as the solid electrolyte 103, copper (Cu) or (Ag) as the cathode catalyst, and adding each solid base to the cathode 101.

The experimental conditions in Table 2 were as follows: platinum mesh was used as the anode material, carbon paper coated with Ag to form a thin film as the cathode material, 0.1 mol/L sulfuric acid was used as the anode electrolyte, and the voltage applied to the current collector 104 and the support plate 105 was 5 V. At this time, the solid base was added so that the mass per unit area was about 5.33 mg/ ^cm2 .

The experimental results were evaluated as follows: the measured amount of CO produced per hour (μmol/h) when the cathode catalyst was Cu and no solid base was added was used as judgment criterion 2; the measured amount of CO produced per hour (μmol/h) when the cathode catalyst was Ag and no solid base was added was used as judgment criterion 3; and it was determined that the CO production efficiency could be improved when more CO was produced than the measured values.

First, as judgment criterion 2, when Cu was used as the cathode catalyst and no solid base was added (no addition), the CO production activity was 0 μmol/h.

Next, in Example 6, when Cu was used as the cathode catalyst and KHCO ₃ was added, the CO production activity was 0.2 μmol/h, and the CO production efficiency was improved.

Next, in Example 7, when Cu was used as the cathode catalyst and NaOH was added, the CO production activity was 1.4 μmol/h, and the CO production efficiency was improved.

Next, in Example 8, when Cu was used as the cathode catalyst and La ₂ O ₃ was added, the CO production activity was 5.6 μmol/h, and the CO production efficiency was improved.

Next, as judgment criterion 3, when Ag was used as the cathode catalyst and no solid base was added (no addition), the CO production activity was 0 μmol/h.

Next, in Example 9, when Ag was used as the cathode catalyst and La ₂ O ₃ was added, the CO production activity was 2.7 μmol/h, and the CO production efficiency was improved.

Table 3 shows experimental data for a solid electrolyte electrolysis device using an anion exchange membrane as the solid electrolyte, a cathode catalyst (Cu-In), and adding MgO solid base to the cathode.

The experimental conditions were as follows: platinum mesh was used as the anode material, carbon paper with a thin film of Cu-In formed on the surface region was used as the cathode material, a saturated _KHCO3 aqueous solution was used as the anode electrolyte, and the voltage applied to the current collector and support plate was 3.5 V. The amount of solid base added was 5 mg/ ^cm2 .

In the case of the Cu-In catalyst, when the MgO solid base was added, the partial current density of CO was improved by 26% compared to when no base was added. It is considered that the effect of adding the base is sufficient.

Claims (7)

A catalyst for generating at least carbon monoxide by a reduction reaction of a reaction gas;
An electrode material supporting the catalyst;
a solid base present locally on at least the surface of the electrode material;
having
The catalyst is formed in a thin film on a surface of the electrode material,
The electrode, wherein the solid base is at least one selected from the group consisting of KHCO ₃ , an oxide of an alkaline earth metal, Sr(OH) ₂ , BaCO ₃ , an oxide of a rare earth metal, and NaOH. The electrode of claim 1, wherein the electrode is a cathode. a cathode having a catalyst that generates at least carbon monoxide by a reduction reaction of a raw material gas and an electrode material that supports the catalyst;
an anode forming a pair of electrodes with the cathode;
a solid electrolyte interposed between the cathode and the cathode in contact therewith;
a voltage application unit that applies a voltage between the cathode and the anode;
The catalyst is formed in a thin film on a surface of the electrode material,
the cathode further comprises a solid base, which is at least one selected from the group consisting of KHCO ₃ , an oxide of an alkaline earth metal, Sr(OH) ₂ , BaCO ₃ , an oxide of a rare earth metal, and NaOH;
A solid electrolyte electrolysis device in which the solid base is present locally on the surface of the electrode material. The solid electrolyte electrolysis device according to claim 3, wherein the solid base is present on the contact surface side of the cathode with the solid electrolyte. The solid electrolyte electrolysis device according to claim 3 or 4, wherein the solid electrolyte is an anion exchange membrane. The solid electrolyte electrolysis device according to claim 3 or 4, wherein the solid electrolyte is a cation exchange membrane. supplying a reactant gas to a solid electrolyte electrolysis device comprising: a cathode having a catalyst and an electrode material supporting the catalyst; an anode forming a pair of electrodes with the cathode; a solid electrolyte interposed between the cathode and the anode in contact with each other; and a voltage application unit applying a voltage between the cathode and the anode, the catalyst being formed in a thin film on a surface of the electrode material; the cathode further comprising a solid base which is at least one selected from the group consisting of KHCO ₃ , an oxide of an alkaline earth metal, Sr(OH) ₂ , BaCO ₃ , an oxide of a rare earth metal, and NaOH, the solid base being locally present on the surface of the electrode material;
a step of contacting the reaction gas with the cathode to cause a reduction reaction, thereby producing a synthesis gas containing at least carbon monoxide;
recovering the synthesis gas;
A method for producing synthesis gas comprising:

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