Patent Application
20220220622
The present disclosure relates to an electrode capable of producing a synthetic gas containing at least carbon monoxide, a solid electrolyte electrolysis device, and a synthetic gas production method.
Fossil fuels (oil, coal, natural gas) support a modern energy consuming society. However, reserves of such fossil fuel are limited. Thus, various alternative fuels that will replace fossil fuels have been proposed. One of them is Hydrocarbon Fuel (HC). HC can be synthesized, for example, by subjecting a synthetic gas containing at least carbon monoxide (CO) and hydrogen (H2) to Fischer-Tropsch reaction (FT reaction).
Patent Literature 1 proposes a synthetic gas synthesizing instrument. Specifically, an instrument is disclosed in which carbon dioxide (CO2) is blown into seawater to lower the pH of the seawater from 8 to 5 to 6 in a tank provided separately from an electrolyzer, and the seawater after the pH adjustment is sent from the tank to the electrolyzer for electrolysis.
The method of Patent Literature 1 has a problem of poor production efficiency of a synthetic gas due to the low solubility of CO2 in water. Thus, an object of the present disclosure is to provide a technique related to an electrode having high production efficiency of a synthetic gas containing at least CO.
According to one aspect of the present disclosure, a technique including:
a catalyst that produces at least carbon monoxide by a reduction reaction;
an electrode material having the catalyst; and
a solid base additive provided at least on the electrode material can be provided.
According to the present disclosure, a technique related to an electrode having high production efficiency of a synthetic gas containing at least CO can be provided.
Hereinafter, a solid electrolyte electrolysis device in the present disclosure will be specifically described with reference to one embodiment. The invention according to the present disclosure is not limited to the embodiment described below.
<<Solid Electrolyte Electrolysis Device 100>>
The solid electrolyte electrolysis device (also referred to as an electrolysis cell, an electrolysis module) according to the present embodiment will be described with reference to
<Cathode 101>
(Reduction Reaction at Cathode 101)
The reduction reaction at the cathode 101 depends on the type of the solid electrolyte 103. When a cation exchange membrane is used as the solid electrolyte 103, reduction reactions of the following formulas (1) and (2) occur, and when an anion exchange membrane is used as the solid electrolyte, reduction reactions of the following formulas (3) and (4) occur.
Formula 1
CO2+2H++2e−→CO+H2O (1)
2H++2e−→H2 (2)
H2O±CO2+2e−→CO+2OH− (3)
2H2O+2e−→H2+2OH− (4)
(Basic Structure and Material 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 a nonwoven fabric, or a metal mesh. Examples of the electrode material of the cathode 101 include graphite carbon, glassy carbon, titanium, and SUS. The catalyst of the cathode capable of reducing CO2 to CO included in the cathode 101 contains, for example, a metal selected from silver, gold, copper, or a combination thereof. More specifically, the catalyst includes, for example, gold, a gold alloy, silver, a silver alloy, copper, a copper alloy, or a mixed metal containing any one or more of them. The type of the catalyst is not particularly limited as long as the catalyst has a function as a catalyst, and can be determined in consideration of corrosion resistance and the like. For example, when the catalyst does not contain an amphoteric metal such as Al, Sn, or Zn, corrosion resistance can be improved. The catalyst can be supported on the cathode 101 (or the electrode material) by performing a known method such as vapor deposition, deposition, adsorption, sedimentation, adhesion, welding, physical mixing, and spraying.
(Solid Base Additive 107)
As shown in
The following mechanism of action is presumed to be the reason why the efficiency is increased when the solid base additive 107 is used. For example, when a gas having a low concentration of CO2 of 10 to 20% such as an exhaust gas in a factory is supplied to the solid electrolyte electrolysis device 100, CO2 is less likely to be adsorbed on the surface of the cathode 101 because of its low concentration. Thus, as shown in
<Anode 102>
(Oxidation Reaction at Anode 102)
The oxidation reaction at the anode 102 depends on the type of the 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 formulas (6) occurs.
[Formula 2]
2H2O→O2+4H++4e− (5)
4OH−→O2+2H2O+4e− (6)
(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 with the solid electrolyte 103 being in contact with the cathode 101 and the anode 102. Though the solid electrolyte 103 is not particularly limited to a polymer membrane, a cation exchange membrane or an anion exchange membrane is suitable, and an anion exchange membrane is more suitable. As the cation exchange membrane, for example, a strongly acidic cation exchange membrane in which a sulfone group is introduced into a fluororesin base, 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 base, or NEOSEPTA CMX (manufactured by Tokuyama Soda Co., Ltd.) can be used. Examples of the anion exchange membrane include an anion exchange membrane in which a quaternary ammonium group, a primary amino group, a secondary amino group, a tertiary amino group, or two of more of these ion exchange groups are present. As specific examples, for example, NEOSEPTA (registered trademark) ASE, AHA, AMX, ACS, AFN, and AFX (manufactured by Tokuyama Corporation), SELEMION (registered trademark) AMV, AMT, DSV, AAV, ASV, AHO, AHT, and APS4 (manufactured by AGC Inc.) can be used.
<Current Collecting Plate 104>
Examples of the current collecting plate 104 include metal materials such as copper (Cu), nickel (Ni), stainless steel (SUS), nickel-plated steel, and brass, and among them, copper is preferable from the viewpoint of ease of processing and cost. When the current collecting plate 104 is a metal material, examples of the shape of the negative electrode current collecting plate include a metal foil, a metal plate, a metal thin film, an expanded metal, a punching metal, and a foamed metal.
As shown in
In addition, when the current collecting plate 104 has air permeability, the gas supply hole and the gas collecting hole are not necessarily required.
When the cathode 101 plays a role of transmitting electrons, the current collecting plate 104 is not necessarily required.
<Supporting Plate 105>
The supporting plate 105 supports the anode. Thus, the required rigidity of the supporting plate 105 changes depending on the thickness, rigidity and the like of the anode. The supporting plate 105 needs to have electrical conductivity to receive electrons from the anode. Examples of the material of the supporting plate 105 include Ti, SUS, and Ni.
As shown in
Though in the present embodiment, the anode 102 and the supporting plate 105 are described as separate structures, the anode 102 and the supporting plate 105 can be an integrated structure (that is, the anode 102 and the supporting plate 105 can be an integrated anode 102 having a support function).
<Voltage Application Part 106>
As illustrated in
<Reaction Gas Supply Part>
The solid electrolyte electrolysis device 100 in the present disclosure can be provided with a reaction gas supply part (not illustrated) outside the solid electrolyte electrolysis device 100. That is, it is sufficient that CO2, a reaction gas, is supplied to the surface 101-2, and the reaction gas can be supplied from the reaction gas supply part to the gas supply hole 104-1 via a pipe (not illustrated) or the like, or the reaction gas can be blown to the surface 104-A of the current collecting plate 104 opposite to the contact surface 104-B with the cathode 101. A factory exhaust gas exhausted from a factory is suitably used as the reaction gas from an environmental viewpoint.
<<CO Production Method>>
A method for producing CO using the solid electrolyte electrolysis device 100 will be described with reference to
<Reaction Gas Supply Step S301>
CO2, a reaction gas, as a raw material is first supplied to the solid electrolyte electrolysis device 100 in a gas phase by a reaction gas supply part (not illustrated). At this time, CO2 is supplied to the cathode 101 through the gas supply hole 104-1 provided in the current collecting plate 104 (S301).
<CO, H2 Production Step S302>
Then, the CO2 supplied to the cathode 101 undergoes reduction reactions on the surface of the cathode 101: when a cation exchange membrane is used as the solid electrolyte 103, the reduction reactions of the formulas (1) and (2) described above occur, and when an anion exchange membrane is used as the solid electrolyte, the reduction reactions of the formulas (3) and (4) described above occur. Thereby a synthetic gas containing at least CO and H2 is produced (S302).
<Produced Gas Collecting Step S303>
Then, the produced synthetic gas containing CO and H2 is sent to a gas collecting device (not illustrated) through a gas collecting hole 104-2 provided in the current collecting plate 104, and is collected for each predetermined gas (S303).
<<Use>>
As shown in
Hereinafter, specific description will be given with reference to Examples and Comparative Examples in which the present embodiments described above is used.
The solid electrolyte electrolysis device 100 shown in
Table 1 shows experimental data in the solid electrolyte electrolysis device 100 when an anion exchange membrane was used as the solid electrolyte 103, silver (Ag) was used as a cathode catalyst, and each solid base additive was added to the cathode 101.
For experimental conditions in Table 1, a platinum mesh was used as an anode material, carbon paper on which Ag was applied to form a thin film was used as a cathode material, a saturated aqueous KHCO3 solution was used as an anode electrolysis solution, and an applied voltage applied to the current collecting plate 104 and the supporting plate 105 was 3.5 V. The solid base additive was added so that the mass per unit area would be about 5.33 mg/cm2.
The evaluation of the experimental results was performed as follows: the measured value of the partial current density (mA/cm2) of CO when no solid base additive was added was used as a judgment criteria, a symbol of Δ was given to a result in which an improvement of 2% or more was observed, a symbol of ∘ was given to a result in which an improvement of 10% or more was observed, and a symbol of ⊙ was given to a result in which an improvement of 50% or more was observed compared to the measured value, and those conditions that had such results were judged to be capable of improving the production efficiency of a synthetic gas (particularly, CO). The partial current density is a physical quantity representing the amount of electrons used to produce a specific compound, and the larger the value, the larger the production amount.
In Judgment Criteria 1 in which no solid base additive was added (no addition case), the partial current density of CO was 6.05 mA/cm2. The Faraday Efficiency (FE) of H2 was 3.19%, the FE of CO was 57.62%, and the partial current density of H2 was 0.33 mA/cm2. In this experiment in which an anion exchange membrane was used, these measured values were used as reference values for judgement.
In Example 1 in which KHCO3 was added, the FE of H2 was 26.87%, the FE of CO was 54.28%, the partial current density of H2 was 3.07 mA/cm2, and the partial current density of CO was 6.2 mA/cm2. Thus, in Example 1, the partial current density of CO increased by about 2.5% compared to that of Judgment Criteria 1, and the production efficiency of CO was not significantly improved. This is presumably because KHCO3 is water-soluble and was dissolved in H2O produced by the reaction in the cathode, so that a sufficient base effect was not obtained.
Then, in Example 2 in which 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. Thus, in Example 2, the partial current density of CO increased by about 66.6% compared to that of Judgment Criteria 1, and the production efficiency of CO was successfully improved.
Then, in Example 3 in which 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 0.71 mA/cm2, and the partial current density of CO was 9.28 mA/cm2. Thus, in Example 3, the partial current density of CO increased by about 53.4% compared to that of Judgment Criteria 1, and the production efficiency of CO was successfully improved.
Then, in Example 4 in which BaCO3 was added, the FE of H2 was 26.36%, the FE of CO was 58.17%, the partial current density of H2 was 3.81 mA/cm2, and the partial current density of CO was 8.25 mA/cm2. Thus, in Example 4, the partial current density of CO increased by about 36.4% compared to that of Judgment Criteria 1, and the production efficiency of CO was successfully improved.
Then, in Example 5 in which Y2O3 was added, the FE of H2 was 23.51%, the FE of CO was 58.78%, the partial current density of H2 was 3.43 mA/cm2, and the partial current density of CO was 8.58 mA/cm2. Thus, in Example 5, the partial current density of CO increased by about 41.8% compared to that of Judgment Criteria 1, and the production efficiency of CO was successfully improved.
Then, in Example 6 in which La2O3 was added, the FE of H2 was 8.4%, the FE of CO was 64.09%, the partial current density of H2 was 0.88 mA/cm2, and the partial current density of CO was 7.57 mA/cm2. Thus, in Example 6, the partial current density of CO increased by about 25.1% compared to that of Judgment Criteria 1, and the production efficiency of CO was successfully improved.
Table 2 shows experimental data in the solid electrolyte electrolysis device 100 when a cation exchange membrane (Nafion 117) was used as the solid electrolyte 103, copper (Cu) or (Ag) was used as a cathode catalyst, and each solid base additive was added to the cathode 101.
For experimental conditions in Table 2, a platinum mesh was used as an anode material, carbon paper on which Ag was applied to form a thin film was used as a cathode material, 0.1 mol/L of sulfuric acid was used as an anode electrolysis solution, and an applied voltage applied to the current collecting plate 104 and the supporting plate 105 was 5 V. The solid base additive was added so that the mass per unit area would be about 5.33 mg/cm2.
The evaluation of the experimental results was performed as follows: the measured value of the production amount (μmol/h) of CO per hour when the cathode catalyst was Cu and no solid base additive was added was used as Judgment Criteria 2, the measured value of the production amount (μmol/h) of CO per hour when the cathode catalyst was Ag and no solid base additive was added was used as Judgment Criteria 3, and those conditions that had results of larger production of CO than the measured values were judged to be capable of improving the production efficiency of CO.
In Judgment Criteria 2 in which Cu was used as a cathode catalyst and no solid base additive was added (no addition case), the production activity of CO was 0 μmol/h.
Then, in Example 6 in which Cu was used as a cathode catalyst and KHCO3 was added, the production activity of CO was 0.2 μmol/h, and the production efficiency of CO was successfully improved.
Then, in Example 7 in which Cu was used as a cathode catalyst and NaOH was added, the production activity of CO was 1.4 μmol/h, and the production efficiency of CO was successfully improved.
Then, in Example 8 in which Cu was used as a cathode catalyst and La2O3 was added, the production activity of CO was 5.6 μmol/h, and the production efficiency of CO was successfully improved.
Then, in Judgment Criteria 3 in which Ag was used as a cathode catalyst and no solid base additive was added (no addition case), the production activity of CO was 0 μmol/h.
Then, in Example 9 in which Ag was used as a cathode catalyst and La2O3 was added, the production activity of CO was 2.7 μmol/h, and the production efficiency of CO was successfully improved.
Table 3 shows experimental data in the solid electrolyte electrolysis device when an anion exchange membrane was used as the solid electrolyte, a cathode catalyst (Cu—In) was used, and a MgO solid base additive was added to the cathode.
For experimental conditions, a platinum mesh was used as an anode material, carbon paper on which a thin film of Cu—In was formed in a surface region was used as a cathode material, a saturated aqueous KHCO3 solution was used as an anode electrolysis solution, and a voltage applied to the current collecting plate and the supporting plate were 3.5 V. The solid base additive was added in an amount of 5 mg/cm2.
For a Cu—In catalyst, when a MgO solid base additive was added, the partial current density of CO increased by 26% compared to no addition case. The effect of base addition is sufficient.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-082033 | Apr 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/017384 | 4/22/2020 | WO | 00 |
