Pretreatment method for cathode used for carbon dioxide electrolysis, carbon dioxide electrolytic reduction method, cathode for solid electrolyte type electrolysis device, manufacturing method for ion exchange membrane-electrode assembly, and manufacturing method for solid electrolyte type electrolysis device

Abstract

Provided is a pretreatment method for a cathode which is used for carbon dioxide electrolysis, a carbon dioxide electrolytic reduction method, a cathode for a solid electrolyte type electrolysis device, a manufacturing method for an ion exchange membrane-electrode assembly, and a manufacturing method for a solid electrolyte type electrolysis device, each of which is capable of suppressing salt deposition at the cathode of a carbon dioxide electrolytic reduction cell, enabling long-term operation of the carbon dioxide reduction cell, and enabling improvement of electrolysis performance in the initial period after the start of operation.　This pretreatment method for a cathode used for carbon dioxide electrolysis comprises a treatment step for causing the cathode to hold a solution containing one or more cations from among alkali metal ions, alkaline earth metal ions, quaternary ammonium ions, quaternary phosphonium ions, imidazolium ions, pyridinium ions, piperidinium ions, and pyrrolidinium ions.

Description

Method for pretreatment of cathodes used in carbon dioxide electrolysis, method for carbon dioxide electrolysis reduction, cathode for solid electrolyte electrolytic apparatus, method for manufacturing ion exchange membrane-electrode junctions, and method for manufacturing solid electrolyte electrolytic apparatus

[0001] The present invention relates to a method for pretreatment of a cathode used in carbon dioxide electrolysis, a method for reducing carbon dioxide through electrolysis, a cathode for a solid electrolyte electrolytic apparatus, a method for manufacturing an ion exchange membrane-electrode assembly, and a method for manufacturing a solid electrolyte electrolytic apparatus.

[0002] Carbon dioxide is emitted when energy is extracted from fossil fuels and other sources. The rise in atmospheric carbon dioxide concentration is considered one of the causes of global warming. Because carbon dioxide is an extremely stable substance, there have been very few established technologies for its effective utilization until now. However, given the current situation of worsening global warming, new technologies are needed to convert carbon dioxide into other substances and recycle it.

[0003] Research on carbon dioxide reduction using electrical energy is being conducted widely worldwide. Among these, the solid electrolyte type electrolytic device (also called a polymer electrolyte type electrolytic cell or carbon dioxide electrolytic reduction cell) equipped with an ion exchange membrane-electrode assembly (MEA) with the structure described in Patent Document 1 (Figure 1) has advantages in that it can directly reduce gaseous carbon dioxide and reduces ion transport resistance by using a thin film polymer electrolyte.

[0004] The cathode for carbon dioxide reduction in an ion exchange membrane-electrode junction generally comprises a catalyst layer containing a mixture of catalyst nanoparticles, a conductive carrier, and a binder. The binder is used to improve the adhesion of the catalyst nanoparticles to the electrode surface. Ion exchange resins can also be used as the binder, in which case the binder also functions to transport ions consumed or generated by the reduction reaction. These ion exchange resins are generally referred to as ionomers.

[0005] In an ion exchange membrane-electrode junction, the ion exchange membrane, due to its structure, contains ions (e.g., H) that contribute to the electrolytic reaction. ＋ , OH － ) In addition to the electrolytes contained in the electrolyte solution (for example, K＋ It has the property of permeating even ions. As a result, the electrolyte supplied to the anode often penetrates the ion exchange membrane and precipitates as salt inside the cathode. This salt precipitation phenomenon hinders the supply of carbon dioxide to the cathode catalyst and causes a decrease in electrolytic performance, such as CO generation current density and CO selectivity. The adverse effects of this salt precipitation become more pronounced as the electrolyte concentration of the anode electrolyte increases.

[0006] On the other hand, it has been reported that when pure water without dissolved electrolyte is used as the electrolyte for the anode in an ion-exchange membrane-electrode junction, the rate and selectivity of the carbon dioxide reduction reaction decrease significantly (see, for example, Non-Patent Documents 1 and 2). Therefore, the presence of an electrolyte (especially alkali metal ions as cationic species) is necessary to drive the carbon dioxide reduction reaction with high selectivity. This is due, firstly, to the effect of the electrolyte (alkali metal ions) stabilizing the intermediate by temporarily bonding with it in the carbon dioxide reduction reaction, and secondly, to the effect of reducing the resistance of the electrolyte.

[0007] From the above, there are conflicting requirements: one to reduce the electrolyte concentration in the anodic electrolyte to suppress salt deposition at the cathode, and another to increase the electrolyte concentration to improve the selectivity of the carbon dioxide reduction reaction.

[0008] Several methods have been proposed to resolve these conflicting technical challenges. For example, Non-Patent Document 3 reports a method in which an ion exchange membrane is pre-substituted with alkali metal ions. However, this method cannot supply sufficient alkali metal ions near the cathode catalyst, resulting in a selectivity of less than 1% for the carbon dioxide reduction reaction.

[0009] International Publication No. 2024 / 101045

[0010] MCO Monteiro, F. Dattila, B. Hagedoorn, R. Garcia-Muelas, N. Lopez, MTM Koper, Nature catalysis, 2021, 4, 654-662.JA Rebstock, Q. Zhu, LR Baker, Chemical Science, 2022, 13, 7634-7643.W. Liao, D. Tsai, W. Hong, Y. Huang, L. Lin, Y. Pan, Chemical Engineering Journal, 2022, 434, 134765.

[0011] As described above, a major challenge in conventional carbon dioxide electrolytic reduction cells has been to appropriately control the alkali metal ion concentration near the cathode while simultaneously reducing the concentration of the anodic electrolyte to prevent salt deposition.

[0012] Furthermore, as the operating time of the carbon dioxide electrolytic reduction cell increases, the amount of salt precipitated increases, further degrading the electrolytic performance. Therefore, establishing a carbon dioxide electrolytic reduction technology that can operate for extended periods is a crucial challenge.

[0013] Furthermore, there is a need for carbon dioxide electrolysis reduction technology that can improve the electrolysis performance of carbon dioxide electrolysis reduction cells during the initial stages of operation.

[0014] Therefore, the object of the present invention is to provide a method for pretreatment of a cathode used in carbon dioxide electrolysis, a carbon dioxide electrolysis reduction method, a cathode for a solid electrolyte type electrolytic apparatus, a method for manufacturing an ion exchange membrane-electrode assembly, and a method for manufacturing a solid electrolyte type electrolytic apparatus, which suppress salt deposition at the cathode of a carbon dioxide electrolytic reduction cell, enable long-term operation of the carbon dioxide reduction cell, and improve electrolytic performance in the initial stages of operation.

[0015] To achieve the above objectives, the present invention provides a method for pre-treating a cathode used in carbon dioxide electrolysis, a method for reducing carbon dioxide through electrolysis, a cathode for a solid electrolyte electrolytic apparatus, a method for manufacturing an ion exchange membrane-electrode assembly, and a method for manufacturing a solid electrolyte electrolytic apparatus.

[0016] [1] A method for pretreatment of a cathode used in carbon dioxide electrolysis, comprising a processing step of holding a solution containing one or more cations selected from alkali metal ions, alkaline earth metal ions, quaternary ammonium ions, quaternary phosphonium ions, imidazolium ions, pyridinium ions, piperidinium ions, and pyrrolidinium ions on the cathode. [2] The pretreatment method according to [1], wherein the processing step comprises impregnating the cathode with the processing solution containing the cations. [3] The pretreatment method according to [2], wherein the impregnation step is performed under a reduced pressure environment of 0 to 90 kPa. [4] The pretreatment method according to [2] or [3], wherein the processing solution is a solution containing the cations at a total concentration of 0.01 to 5 mol / L. [5] The pretreatment method according to [3], wherein the impregnation step comprises immersing the cathode in the processing solution for 10 to 120 minutes. [6] The pretreatment method according to [1], wherein the processing step includes applying a voltage to a solid electrolyte electrolytic apparatus equipped with a cathode, an ion exchange membrane, an anode, and an anode electrolyte tank, so that the cations in the processing solution containing the cations placed in the anode electrolyte tank permeate the ion exchange membrane, and the solution containing the permeated cations is held in the cathode. [7] The pretreatment method according to [6], wherein the processing solution is a solution containing the cations at a total concentration of 0.03 to 2 mol / L. [8] The pretreatment method according to [6] or [7], wherein the voltage application time is 0.1 to 24 hours. [9] The pretreatment method according to any one of [6] to [8], wherein the voltage is such that the applied potential of the cathode to a silver / silver chloride reference electrode (having a saturated potassium chloride solution in its internal solution) is -1.1 to -1.8 V.

[10] The processing step is performed so that the total amount of cations held in the cathode is 0.3 to 170 μmol / cm³. ２A pretreatment method according to any one of [1] to [9], comprising a step performed to achieve the above.

[11] A pretreatment method according to any one of [1] to

[10] , wherein the alkali metal ion is one or more of lithium ions, sodium ions, potassium ions, cesium ions, and rubidium ions.

[12] A pretreatment method according to any one of [1] to

[11] , wherein the alkaline earth metal ion is one or more of beryllium ions, magnesium ions, calcium ions, strontium ions, and barium ions.

[13] A pretreatment method according to any one of [1] to

[12] , wherein the quaternary ammonium ion is one or more of benzyltrimethylammonium ions, trimethylphenylammonium ions, tetramethylammonium ions, tetraethylammonium ions, and tetrapropylammonium ions.

[14] The pretreatment method according to any one of [1] to

[13] , wherein the quaternary phosphonium ion is one or more of tetrabutylphosphonium ion, tributylmethylphosphonium ion, tributylethylphosphonium ion, and tributylhexylphosphonium ion.

[15] The pretreatment method according to any one of [1] to

[14] , wherein the imidazolium ion is one or more of 1-methylimidazolium ion, 1,3-dimethylimidazolium ion, and 1-ethyl-3-methylimidazolium ion.

[16] The pretreatment method according to any one of [1] to

[15] , wherein the pyridinium ion is one or more of 1-methylpyridinium ion, 1-ethylpyridinium ion, and 1-propylpyridinium ion.

[17] The pretreatment method according to any one of [1] to

[16] , wherein the piperidinium ion is one or more of 1-butyl-1-methylpiperidinium ions and 1-methyl-1-propylpiperidinium ions.

[18] A carbon dioxide electrolytic reduction method comprising the step of electrolyzing carbon dioxide using a solid electrolyte electrolytic apparatus equipped with a cathode, an ion exchange membrane, an anode, and an anode electrolyte cell that have been pretreated by the pretreatment method according to any one of [1] to

[17] .

[19] The method for electrolytic reduction of carbon dioxide according to

[18] , wherein in the step of electrolyzing carbon dioxide, the electrolytic solution in the anode electrolytic solution tank is a solution containing the cations at a total concentration of 0.01 to 0.5 mol / L.

[20] A cathode for a solid electrolyte type electrolysis apparatus, wherein a solution containing one or more cations selected from the group consisting of alkali metal ions, alkaline earth metal ions, quaternary ammonium ions, quaternary phosphonium ions, imidazolium ions, pyridinium ions, piperidinium ions and pyrrolidinium ions at a total concentration of 0.01 to 5 mol / L is retained in the cathode.

[21] A method for producing a solid electrolyte type electrolysis apparatus, comprising a step of providing a cathode pretreated by the pretreatment method according to any one of [1] to

[17] .

[22] A method for producing an ion exchange membrane-electrode assembly, comprising a step of providing a cathode pretreated by the pretreatment method according to any one of [1] to

[17] .

[23] The method for producing an ion exchange membrane-electrode assembly according to

[22] , wherein the ion exchange membrane comprises an anion exchange membrane.

[24] A method for producing a solid electrolyte type electrolysis apparatus, comprising a step of providing the ion exchange membrane-electrode assembly according to

[22] or

[23] .

[0017] According to the present invention, there can be provided a pretreatment method for a cathode used in carbon dioxide electrolysis, a method for electrolytic reduction of carbon dioxide, a cathode for a solid electrolyte type electrolysis apparatus, a method for producing an ion exchange membrane-electrode assembly, and a method for producing a solid electrolyte type electrolysis apparatus, which suppress salt precipitation at the cathode of a carbon dioxide electrolytic reduction cell, enable long-term operation of the carbon dioxide reduction cell, and improve electrolytic performance in the initial stage of operation start.

[0018] The reason why the present invention achieves the above effects is presumed to be as follows. In the production of carbon monoxide using a carbon dioxide electrolytic reduction cell, the cationic species in the cathode are presumed to promote the carbon dioxide electrolytic reduction reaction by exhibiting the effect of lowering the ohmic resistance as an electrolyte, locally increasing the carbon dioxide concentration on the electrode surface by adsorbing carbon dioxide, and stabilizing the intermediate by temporarily binding with the intermediate in the carbon dioxide reduction reaction by functioning as a Lewis acid. Furthermore, if the cationic species in the cathode are present in a solution state, it is presumed that under negative voltage application conditions, the effects of the cationic species are further promoted by the accumulation of cationic species on the electrode surface. Herein, the cathode pretreatment method, carbon dioxide electrolytic reduction method, cathode for solid electrolyte type electrolytic apparatus, method for manufacturing ion exchange membrane-electrode junction, and method for manufacturing solid electrolyte type electrolytic apparatus according to the embodiments of this disclosure are presumed to exhibit the above effects and promote the carbon dioxide electrolytic reduction reaction by pre-maintaining specific cationic species in a solution state in the cathode, thereby resulting in a carbon monoxide production method with high electrolytic performance from the initial stages of operation. Furthermore, the carbon dioxide electrolytic reduction method described herein allows for a lower concentration of the anodic electrolyte due to the aforementioned effects. This suppresses the phenomenon of electrolytes in the anodic electrolyte permeating the ion exchange membrane and causing salt deposition inside the cathode, which is expected to enable long-term operation of the carbon dioxide reduction cell.

[0019] This is a schematic diagram of an apparatus for pre-treating cathodes by vacuum impregnation. The XRF spectra of each electrode (each comparative example) after electrolysis are shown. The XRF spectra of each electrode (each example) after electrolysis are shown. The XRF spectra of each electrode (each example) after electrolysis are shown. The XRF spectra of each electrode (each example) after electrolysis are shown. The GC chart of Example 1 is shown. The GC chart of Example 2 is shown. The GC chart of Example 3 is shown. The GC chart of Example 4 is shown.

[0020] The embodiments of the present invention (hereinafter referred to as "these embodiments") will be described in detail below, but the present invention is not limited thereto, and various modifications are possible without departing from the spirit of the invention.

[0021] In the present specification, unless otherwise specified, the description of the numerical range "X (lower limit value) to Y (upper limit value)" means "not less than X and not more than Y". Further, when a plurality of numerical ranges are described, the lower limit values and upper limit values of each numerical range can be arbitrarily combined.

[0022] [Pretreatment method for cathode used in carbon dioxide electrolysis] The pretreatment method for a cathode used in carbon dioxide electrolysis according to the present embodiment includes a treatment step of retaining a solution containing one or more cations selected from any one of alkali metal ions, alkaline earth metal ions, quaternary ammonium ions, quaternary phosphonium ions, imidazolium ions, pyridinium ions, piperidinium ions and pyrrolidinium ions on the cathode. Retaining the solution on the cathode means keeping the solution on the cathode.

[0023] The alkali metal ions in the present embodiment are preferably one or more selected from any one of lithium ions, sodium ions, potassium ions, cesium ions and rubidium ions, more preferably one or more selected from any one of sodium ions, potassium ions and cesium ions, and even more preferably potassium ions.

[0024] The alkaline earth metal ions in the present embodiment are preferably one or more selected from any one of beryllium ions, magnesium ions, calcium ions, strontium ions and barium ions, more preferably one or more selected from any one of magnesium ions, calcium ions and strontium ions, and even more preferably magnesium ions.

[0025] As the cations in the present embodiment, in addition to alkali metal ions and alkaline earth metal ions, organic cations, particularly onium cations, are preferable, and any cations may be used as long as they hydrate in water and can form a coordination interaction with the oxygen atom of adsorbed carbon dioxide during the carbon dioxide electrolytic reduction reaction.

[0026] Among onium cations, coordination bond formation requires an organic cation to accept an electron pair from an oxygen atom, and thus electrophilicity is required. Quaternary ammonium ions and quaternary phosphonium ions that exhibit electrophilicity in an environment using water as a solvent are preferred. When all substituents are bulky, coordination bond formation is presumed to be difficult, so a substituent structure that is sterically small to some extent is required; therefore, it is desirable that two out of the four substituents are substituents with relatively small steric hindrance. Relatively bulky substituents can be used for the remaining two. For example, preferred examples include quaternary ammonium ions and quaternary phosphonium ions having the following structures.

[0027] Here, R １ and R ２ : a linear or branched alkyl group (C≦6), or a hydrogen atom; R ３ and R ４ : a linear or branched alkyl group (C≦20), a phenyl group, a cycloalkyl group (C≦20), a phenylalkyl group (C≦6), or an adamantyl group; R ３ and R ４ may have a substituent. Examples of the substituent include a hydroxyl group, an amino group, an alkoxy group (the alkyl group therein has C≦6), and a linear or branched alkyl group (C≦6).

[0028] In this embodiment, the quaternary ammonium ions include tetramethylammonium ion, tetraethylammonium ion, triethylmethylammonium ion, tetrapropylammonium ion, tetrabutylammonium ion, tributylmethylammonium ion, tetrahexylammonium ion, and hexadecyltrimethylammonium ion. Preferably, the ion is one or more of the following: benzyltrimethylammonium ion, benzyltriethylammonium ion, N,N,N-trimethyl-1-adamantylammonium ion, trimethylphenylammonium ion, or cyclohexyltrimethylammonium ion. More preferably, it is one or more of the following: benzyltrimethylammonium ion, trimethylphenylammonium ion, tetramethylammonium ion, tetraethylammonium ion, or tetrapropylammonium ion. Even more preferably, it is benzyltrimethylammonium ion. These ions have counterions such as OH. － , Br － TFSI － You can use those.

[0029] In this embodiment, the quaternary phosphonium ions include tetramethylphosphonium ion, tributylmethylphosphonium ion, tetraethylphosphonium ion, tributylethylphosphonium ion, tetrapropylphosphonium ion, tributylpropylphosphonium ion, and tetrabutylphosphonium ion. Ion), tetrahexylphosphonium ion, hexadecyltrimethylphosphonium ion, benzyltrimethylphosphonium ion, benzyltriethylphosphonium ion, N,N,N-trimethyl-1-adamantylphosphonium ion, trimethylphenylphosphonium ion It is preferable that there be one or more of the following ions: tetrabutylphosphonium ion, tributylmethylphosphonium ion, tributylethylphosphonium ion, and tributylhexylphosphonium ion, and more preferably that there be one or more of the following ions: tetrabutylphosphonium ion. These ions have counterions such as OH － , Br － TFSI － You can use those.

[0030] Other preferred onium cations include imidazolium ions, pyridinium ions, piperidinium ions, and pyrrolidinium ions.

[0031] In this embodiment, the imidazolium ions include 1-methylimidazolium ion, 1,3-dimethylimidazolium ion, 1-ethyl-3-methylimidazolium ion, 1-methyl-3-propylimidazolium ion, and 1-butyl-3-methylimidazolium ion. Preferably, it is one or more of the following: 1-methylimidazolium ion, 1,3-dimethylimidazolium ion, and 1,1-ethyl-3-methylimidazolium ion.

[0032] In this embodiment, the pyridinium ions include 1-methylpyridinium ion, 1-ethylpyridinium ion, 1-propylpyridinium ion, 1-ethyl-2-methylpyridinium ion, 1-ethyl-3-methylpyridinium ion, 1-ethyl-4-methylpyridinium ion, and 1-butylpyridinium ion. Preferably, it is one or more of the following: 1-methylpyridinium ion, 1-butyl-3-methylpyridinium ion, and 1-butyl-4-methylpyridinium ion, and more preferably, it is one or more of the following: 1-methylpyridinium ion, 1-ethylpyridinium ion, and 1-propylpyridinium ion.

[0033] In this embodiment, the piperidinium ion is preferably one or more of the following: 1-methyl-1-propylpiperidinium ion, 1-butyl-1-methylpiperidinium ion, or 1-butyl-1-methylpiperidinium ion.

[0034] In this embodiment, the pyrrolidinium ion is preferably one or more of the following: 1-ethyl-1-methylpyrrolidinium ion, 1-methyl-1-propylpyrrolidinium ion, 1-butyl-1-methylpyrrolidinium ion, 1-methyl-1-pentylpyrrolidinium ion, or 1-hexyl-1-methylpyrrolidinium ion.

[0035] As the cathode to which the above processing step of the pretreatment method according to this embodiment is performed, a known cathode used in carbon dioxide electrolysis can be used. The known cathode has at least a catalyst layer and a gas diffusion layer. As the gas diffusion layer, for example, carbon paper, nonwoven fabric, metal mesh, etc., can be used. Examples of these materials include graphite carbon, glassy carbon, titanium, SUS steel, etc.

[0036] In the pretreatment method according to this embodiment, the step of holding a solution containing one or more cations from alkali metal ions, alkaline earth metal ions, quaternary ammonium ions, quaternary phosphonium ions, imidazolium ions, pyridinium ions, piperidinium ions, and pyrrolidinium ions on the cathode is not particularly limited and can be carried out by various methods. For example, preferred embodiments include the "pretreatment by impregnation" and the "pretreatment by voltage application" described below.

[0037] [Pretreatment by impregnation] As a specific example of the above treatment steps in this embodiment, one can be cited as the step of impregnating the cathode with a treatment solution containing one or more cations from among alkali metal ions, alkaline earth metal ions, quaternary ammonium ions, quaternary phosphonium ions, imidazolium ions, pyridinium ions, piperidinium ions, and pyrrolidinium ions and retaining it. Impregnating the cathode with the treatment solution and retaining it means keeping the treatment solution in the cathode. In other words, in this embodiment, after impregnation with the treatment solution, the cathode contains the treatment solution. If the cathode is water-repellent, even if the treatment solution is impregnated into the cathode, the treatment solution will be released from inside the cathode to outside the cathode over time, making it difficult to retain the treatment solution inside the cathode. In this embodiment, there are no particular restrictions on the method of impregnating the cathode with the treatment solution and retaining it. When a water-repellent cathode is used, for example, after impregnating the cathode with the treatment solution, the cathode and the ion exchange membrane may be joined in a short time to confine and retain the treatment solution inside the cathode. The time from impregnating the cathode with the treatment solution to joining the cathode with the ion exchange membrane is not particularly limited as long as the treatment solution can be retained on the cathode. For example, it may be 0.5 seconds to 10 hours, 0.7 seconds to 1 hour, 1.0 second to 20 minutes, or 1.0 second to 5 minutes. When a water-repellent cathode is used, the time from impregnating the cathode with the treatment solution to joining the cathode with the ion exchange membrane is preferably 0.5 seconds to 60 minutes, preferably 0.7 seconds to 40 minutes, more preferably 1.0 second to 20 minutes, and even more preferably 1.0 second to 5 minutes. Here, a water-repellent cathode is a cathode with a static contact angle of 90° or more on the electrode surface, including superhydrophobic (150° to 180°) cathodes. In this embodiment, a water-repellent cathode with a static contact angle in the range of, for example, 100-175°, 105-170°, 110-165°, 115-165°, 120-170°, 125-165°, 130-160°, 135-155°, or 140-150° can be used. The static contact angle can be measured, for example, by the static droplet method (also called the liquid droplet method).

[0038] The impregnation process described above is preferably carried out under reduced pressure. The reduced pressure environment is preferably 0 to 90 kPa (absolute pressure), more preferably 0.1 to 50 kPa (absolute pressure), even more preferably 0.5 to 40 kPa (absolute pressure), and particularly preferably 1 to 20 kPa (absolute pressure), from the viewpoint of sufficiently degassing the air inside the cathode and encapsulating the treatment solution. This embodiment will be described with reference to Figure 1. A container 2 containing a treatment solution 4 containing one or more cations from alkali metal ions, alkaline earth metal ions, quaternary ammonium ions, quaternary phosphonium ions, imidazolium ions, pyridinium ions, piperidinium ions, and pyrrolidinium ions, and a cathode 3 immersed in the treatment solution 4 is placed in a reduced pressure desiccator 1, and then the desiccator is evacuated to create a reduced pressure state. To ensure sufficient degassing of the air inside the cathode and to prevent physical damage to the cathode under reduced pressure conditions, this immersion state is maintained for a predetermined time, preferably 10 to 120 minutes, more preferably 15 to 90 minutes, and even more preferably 30 to 60 minutes, allowing the treatment solution to impregnate the cathode.

[0039] The above-mentioned treatment solution 4 is preferably a solution containing one or more cations from among alkali metal ions, alkaline earth metal ions, quaternary ammonium ions, quaternary phosphonium ions, imidazolium ions, pyridinium ions, piperidinium ions, and pyrrolidinium ions in a total concentration of 0.01 to 5 mol / L. From the viewpoint of supplying a sufficient amount of cations to exhibit the reaction-promoting effect of cations in the electrolytic reduction reaction of carbon dioxide, particularly the stabilizing effect of the reaction intermediate, the lower limit of the total concentration is more preferably 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, or 0.09 mol / L, even more preferably 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9 mol / L, and most preferably 1.0, 1.1, 1.2, 1.3, 1.4, or 1.5 mol / L. Furthermore, from the viewpoint of suppressing salt precipitation due to exceeding the saturation concentration, the upper limit of the total concentration is more preferably 4.9, 4.8, 4.7, 4.6, 4.5, 4.4, 4.3, 4.2, or 4.1 mol / L, even more preferably 4.0, 3.9, 3.8, 3.7, or 3.6 mol / L, and most preferably 3.5 mol / L.

[0040] If the above-mentioned processing solution 4 contains potassium ions, from the viewpoint of ion membrane permeation rate, it is preferable to use a solution containing the same alkaline cations as the electrolyte in the anode electrolyte tank of a solid electrolyte electrolytic apparatus equipped with a cathode, ion exchange membrane, anode, and anode electrolyte tank that has been pre-treated by the pre-treatment method according to the above embodiment.

[0041] To prevent the discharge of the treatment solution, it is preferable to keep the cathode pretreated by the above pretreatment method immersed in the same solution as the treatment solution until the ion exchange membrane-electrode assembly is manufactured.

[0042] [Pretreatment by voltage application] As another specific example of the processing steps in this embodiment, a voltage is applied to a solid electrolyte electrolytic apparatus equipped with a cathode, an ion exchange membrane, an anode, and an anode electrolyte tank, thereby causing one or more cations from among alkali metal ions, alkaline earth metal ions, quaternary ammonium ions, quaternary phosphonium ions, imidazolium ions, pyridinium ions, piperidinium ions, and pyrrolidinium ions in a processing solution placed in the anode electrolyte tank to permeate the ion exchange membrane, and the solution containing the permeated cations is held in the cathode.

[0043] The above-mentioned treatment solution is preferably a solution containing 0.03 to 2.0 mol / L of one or more cations from among alkali metal ions, alkaline earth metal ions, quaternary ammonium ions, quaternary phosphonium ions, imidazolium ions, pyridinium ions, piperidinium ions, and pyrrolidinium ions in a total concentration of 0.03 to 2.0 mol / L, more preferably 0.1 to 1.0 mol / L, and even more preferably 0.2 to 0.5 mol / L, from the viewpoint of supplying a sufficient amount of cations to exhibit the reaction-promoting effect of cations in the electrolytic reduction reaction of carbon dioxide, while suppressing salt deposition due to the supply of excess ions.

[0044] The voltage application time may be 0.01 to 36 hours, 0.1 to 24 hours, 0.1 to 12 hours, 0.1 to 6.0 hours, preferably 0.1 to 3.0 hours, more preferably 0.2 to 2.0 hours, and even more preferably 0.5 to 1.0 hours, from the viewpoint of supplying a sufficient amount of cations to exhibit the reaction-promoting effect of cations in the electrolytic reduction reaction of carbon dioxide, while suppressing salt deposition due to the supply of excess ions.

[0045] From the viewpoint of supplying a sufficient amount of cations by ion transport to exhibit the reaction-promoting effect of cations in the electrolytic reduction reaction of carbon dioxide, while suppressing salt deposition due to excess ion transport, the voltage applied to the cathode relative to the silver / silver chloride reference electrode (which has a saturated potassium chloride solution in its internal solution) is preferably -1.1 to -1.8 V, more preferably -1.3 to -1.8 V, and even more preferably -1.5 to -1.8 V.

[0046] If the above-mentioned treatment solution contains potassium ions, from the viewpoint of ion membrane permeation rate, it is preferable to use a solution containing the same alkaline cations as the electrolyte in the anode electrolyte tank of a solid electrolyte electrolytic apparatus equipped with a cathode, ion exchange membrane, anode, and anode electrolyte tank that has been pre-treated by the pre-treatment method according to the above embodiment.

[0047] The cathode pretreated by the above pretreatment method is preferably stored in the solid electrolyte electrolytic apparatus until carbon dioxide electrolysis is performed using the solid electrolyte electrolytic apparatus, in order to prevent the discharge of the treatment solution. Alternatively, the cathode may be removed from the electrolytic apparatus and immersed in the same solution as the treatment solution.

[0048] The above-mentioned "pretreatment by impregnation" and "pretreatment by voltage application" may be performed individually or in combination.

[0049] In the pretreatment method according to this embodiment, the treatment step of holding a solution containing one or more cations from among alkali metal ions, alkaline earth metal ions, quaternary ammonium ions, quaternary phosphonium ions, imidazolium ions, pyridinium ions, piperidinium ions, and pyrrolidinium ions on the cathode is such that the total amount of one or more cations from among alkali metal ions, alkaline earth metal ions, quaternary ammonium ions, quaternary phosphonium ions, imidazolium ions, pyridinium ions, piperidinium ions, and pyrrolidinium ions held on the cathode is 0.3 to 175 μmol / cm³. ２It is preferable that the process be carried out in such a manner. From the viewpoint of supplying a sufficient amount of cations to exhibit the reaction-promoting effect of cations in the carbon dioxide electrolytic reduction reaction, particularly the stabilizing effect of the reaction intermediate, the lower limit of the total retention amount is 0.5 to 1.9 μmol / cm³. ２ It is more preferably any value within the range of 2 to 19 μmol / cm³. ２ It is even more preferable that the value be any number within the range of 20 to 30 μmol / cm³. ２ It is most preferable that the value be any value within the specified range. Furthermore, from the viewpoint of suppressing salt precipitation due to exceeding the saturation concentration, the upper limit of the total retention amount should be 110 μmol / cm³. ２ More than 175μmol / cm ２ It is more preferable that the concentration be any number within the range less than (for example, 170, 165, 160, 155, 150, 145, 140, 135, 130, 125, 120, 115, 110, etc.), and the concentration is 94 to 109 μmol / cm³. ２ It is even more preferable that the value be any number within the range (for example, 105, 100, 95, etc.), and 93 μmol / cm³. ２ It is most preferable that this be the case.

[0050] [Method for electrolytic reduction of carbon dioxide] The method for electrolytic reduction of carbon dioxide according to this embodiment includes the step of electrolyzing carbon dioxide using a solid electrolyte type electrolytic apparatus equipped with a cathode, an ion exchange membrane, an anode, and an anode electrolyte tank that have been pretreated by the pretreatment method according to this embodiment.

[0051] In the process of electrolyzing carbon dioxide as described above, the electrolyte in the anodic electrolyte tank is preferably a solution containing one or more cations from among alkali metal ions, alkaline earth metal ions, quaternary ammonium ions, quaternary phosphonium ions, imidazolium ions, pyridinium ions, piperidinium ions, and pyrrolidinium ions in a total concentration of 0.01 to 0.5 mol / L, more preferably 0.01 to 0.3 mol / L, and even more preferably 0.01 to 0.2 mol / L, from the viewpoint of sufficiently lowering the ohmic resistance of the anodic electrolyte while preventing excessive ion movement and salt deposition due to ion transport that occurs when a negative voltage is applied.

[0052] Aside from using a cathode pretreated by the pretreatment method according to this embodiment and using the electrolyte described above, the procedure can be carried out by known technology.

[0053] [Cathode for Solid Electrolyte Type Electrolyzer] The cathode for the solid electrolyte type electrolyzer according to this embodiment holds a solution containing a total concentration of 0.01 to 5 mol / L of one or more cations selected from alkali metal ions, alkaline earth metal ions, quaternary ammonium ions, quaternary phosphonium ions, imidazolium ions, pyridinium ions, piperidinium ions, and pyrrolidinium ions. From the viewpoint of supplying a sufficient amount of cations to exhibit the reaction-promoting effect of cations in the electrolytic reduction reaction of carbon dioxide, particularly the stabilizing effect of reaction intermediates, the lower limit of the total concentration is more preferably 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, or 0.09 mol / L, even more preferably 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9 mol / L, and most preferably 1.0, 1.1, 1.2, 1.3, 1.4, or 1.5 mol / L. Furthermore, from the viewpoint of suppressing salt precipitation due to exceeding the saturation concentration, the upper limit of the total concentration is more preferably 4.9, 4.8, 4.7, 4.6, 4.5, 4.4, 4.3, 4.2, or 4.1 mol / L, even more preferably 4.0, 3.9, 3.8, 3.7, or 3.6 mol / L, and most preferably 3.5 mol / L.

[0054] The cathode according to this embodiment can be manufactured, for example, by pre-treating a known cathode for a solid electrolyte electrolytic device using the pre-treatment method according to this embodiment.

[0055] [Method for manufacturing an ion exchange membrane-electrode assembly] The method for manufacturing an ion exchange membrane-electrode assembly according to this embodiment includes the step of providing a cathode that has been pre-treated by the pre-treatment method according to this embodiment. The ion exchange membrane may be a commercially available product such as a cation exchange membrane or an anion exchange membrane. It is preferable that the ion exchange membrane includes an anion exchange membrane.

[0056] From the viewpoint of reducing ion resistance, the average thickness of the ion exchange membrane in a dry state is preferably 60 μm or less. Furthermore, from the viewpoint of preventing pinhole formation, the average thickness in a dry state is preferably 10 μm or more. From the viewpoint of balancing ion resistance and pinhole prevention, the average thickness of the ion exchange membrane in a dry state is more preferably 15 to 50 μm, and even more preferably 20 to 40 μm.

[0057] When an anion exchange membrane is used as the ion exchange membrane, the base point density is 0.5 to 5.0 mmol / cm³ in a dry state. ３ Preferably, the concentration is 2.5 mmol / cm ３ Above, 4.5 mmol / cm ３ It is more preferable to be less than 2.9 mmol / cm³. ３ Above, 4.5 mmol / cm ３ It is even more preferable that it be less than [amount].

[0058] Examples of cation exchange membranes that can be used include strongly acidic cation exchange membranes such as Nafion 117, Nafion 115, Nafion 212, and Nafion 350 (manufactured by Chemours), which are formed by introducing sulfone groups into a fluororesin matrix, and Neosepta CSE (manufactured by Astom), which are formed by introducing sulfone groups into a styrene-divinylbenzene copolymer matrix.

[0059] Examples of anion exchange membranes include those having one or more ion exchange groups selected from the group consisting of quaternary ammonium groups, primary amino groups, secondary amino groups, and tertiary amino groups. Specifically, examples include Neosepta® ASE, AHA, ACS, AFX (manufactured by Astom Co., Ltd.), Celemion® AMVN, DSVN, AAV, ASVN, AHO (manufactured by Asahi Glass Co., Ltd.), and others.

[0060] The ion exchange membrane-electrode assembly according to this embodiment can be manufactured according to known manufacturing methods, except that the cathode according to this embodiment is used.

[0061] [Method for Manufacturing a Solid Electrolyte Type Electrolyte] The method for manufacturing a solid electrolyte type electrolyte according to this embodiment includes the step of providing a cathode that has been pre-treated by the pre-treatment method according to this embodiment. Another method for manufacturing a solid electrolyte type electrolyte according to this embodiment includes the step of providing an ion exchange membrane-electrode assembly according to this embodiment.

[0062] The electrolytic apparatus according to this embodiment can be manufactured according to known manufacturing methods, except that the cathode or ion exchange membrane-electrode assembly according to this embodiment is used.

[0063] The present invention will now be described with reference to examples, but the present invention is not limited to these examples.

[0064] [Examples 1-23, Comparative Examples 1-5] [Synthesis Process of Ni Monoatom Catalyst] In a beaker, 8.0 mmol of pentaethylenehexamine and 1.3 mmol of nickel(II) chloride hexahydrate were mixed in ethanol solvent to form a nickel-pentaethylenehexamine complex. Next, 3.0 g of carbon black support (conductive support: VULCAN® XC-72 manufactured by Cabot) was mixed in, and the resulting ethanol dispersion was irradiated with ultrasound for 10 minutes. After that, the ethanol was evaporated by heating and drying the ethanol dispersion, and the resulting mixture was calcined in a calcination furnace in an inert gas at 890-900°C for 10 seconds or more. After that, the product was washed with an aqueous sulfuric acid solution, the solid was recovered using a suction filter, and the solid was dried under reduced pressure at 60°C overnight to obtain a catalyst powder on which the nickel complex was supported.

[0065] [Cathode (Reduction Electrode) Fabrication Process] The obtained catalyst powder was dispersed in ethanol, and a cation exchange resin (Nafion® dispersion solution DE521, manufactured by Chemours) was mixed with the dispersion as a binder. After mixing, sonication was performed for 10 minutes, and the mixture was exposed for 10 minutes in a desiccator under a reduced pressure of 10 kPa (absolute pressure). Using a spray coater, the mixture was loaded onto microporous carbon paper (SIGRACET® 39BB, manufactured by SGL Carbon) with a dry load of 1.5-2 mg / cm². ２The material was applied in this manner to obtain a cathode (reduction electrode). In the comparative example, the obtained cathode was used as is without any pretreatment. The static contact angle of the obtained cathode was measured and was found to be in the range of 140 to 150°. The static contact angle was measured using a contact angle meter with the droplet method. 2 to 4 μL of pure water was dropped onto the catalyst layer surface of the cathode, and the change in contact angle using the θ / 2 method was measured for 5 seconds, and the average value over 5 seconds was calculated. Furthermore, the measurement was repeated 5 times per sample while changing the measurement location within the catalyst layer surface, and the average value was taken as the static contact angle.

[0066] [Cathode Pretreatment by Vacuum Impregnation] In Examples 1-2 and 5-23, the obtained cathodes were immersed in a potassium bicarbonate aqueous solution of 2 mol / L (Examples 1-2) or the concentration listed in Table 2 (Examples 5-23). ​​With the electrodes immersed, they were left standing in a desiccator under a reduced pressure of 2 kPa (absolute pressure) for 30 minutes to impregnate the electrode voids of the cathode with the potassium bicarbonate aqueous solution. In Example 12, the cathode was immersed in a 2 mol / L cesium bicarbonate aqueous solution, and the same procedure was carried out under the above conditions to impregnate the electrode voids of the cathode with the cesium bicarbonate aqueous solution. The pretreated cathodes remained immersed in the above aqueous solution until the film-electrode assembly was manufactured.

[0067] [Cathode Pretreatment by Voltage Application] In Examples 3 and 4, after manufacturing a solid electrolyte electrolytic device by the following manufacturing method (however, cathode pretreatment by vacuum impregnation was not performed), the cathode was subjected to a voltage of -1.8 V for 1 hour relative to the silver / silver chloride reference electrode (which has a saturated potassium chloride solution in its internal solution) under conditions where the cell was heated to 40°C, thereby reducing the electrolyte of the oxidation electrode electrolyte bath (0.3 mol / L KHCO3). ３ A film crossover was performed using an aqueous solution, and the electrode void of the cathode was filled with an aqueous potassium bicarbonate solution.

[0068] [Manufacturing of Solid Electrolyte Type Electrolyte] An anion exchange membrane with a thickness of approximately 30 μm (ion exchange capacity 1.5 meq / g), a cathode (reduction electrode) obtained by pretreatment of the cathode by vacuum impregnation, and an oxide electrode (commercial product) made by supporting iridium oxide on a titanium mesh (Taiyo Kanami Co., Ltd., aperture ratio 56%) were bonded together within 60 seconds after the above pretreatment to form a membrane-electrode assembly. The anode (oxide electrode) was made of electrolyte (KHCO3 at concentrations listed in Tables 1-2). ３ The structure was designed to be in contact with an aqueous solution tank (Cesium bicarbonate aqueous solution in Example 13, and sodium bicarbonate aqueous solution in Example 14).

[0069] [Implementation and evaluation of the electrolysis process] Using the manufactured solid electrolyte electrolytic device, pure CO ２ CO is supplied to the cathode, and under conditions where the cell is heated to 40°C, the applied potential of the cathode is set to -1.8V relative to the silver / silver chloride reference electrode (which has a saturated potassium chloride solution in its internal solution), ２ The current density for CO production when electrolyzing to produce CO [mA / cm²] ２ The CO selectivity [%] was measured. The electrolysis time in each example and comparative example is shown in Tables 1 and 2. The carbon dioxide electrolysis reduction cell had an effective area of ​​2.25 cm². ２ A serpentine channel shape was used, and the cathode gas supply rate was set to 60 mL / min. The electrolysis test was performed using an electrochemical measurement system (SI1287; Solartron Analytical), and the cathode-side generated gas during electrolysis was analyzed using a gas chromatograph (Nexis GC-2030; Shimadzu Corporation). The gas chromatograph charts are shown in Figures 6 to 9. In addition, the presence or absence of salt deposition at the cathode at the end of electrolysis was confirmed by visual inspection or optical microscope observation. Furthermore, the fluorescent X-ray spectrum at the Kα-ray energy position (approximately 3.31 keV) of K (potassium) at the cathode at the end of electrolysis was measured using fluorescent X-ray analysis (NEX DE; Rigaku). The fluorescent X-ray spectrum charts are shown in Figures 2 to 5. In Figures 2 to 5, the region with a spectral intensity of 0.12 or higher is shown in gray, with the fluorescent X-ray spectrum of Comparative Example 2, in which salt deposition was observed, as the reference. The results are shown in Tables 1 and 2.

[0070] The following describes the various indicators of electrolysis performance. The CO selectivity (Faraday efficiency of carbon monoxide) of the cathode-side generated gas is the percentage of the amount of carbon monoxide actually observed relative to the amount of carbon monoxide generated per unit time if all the current applied to the electrolytic cell were used for carbon monoxide generation. The current value applied to the electrolytic cell was measured using an electrochemical measuring device, and the amount of carbon monoxide actually generated was calculated by measuring the gas discharged from the cathode-side gas discharge channel using a gas chromatograph. The current density was calculated by measuring the current value applied to the electrolytic cell using an electrochemical measuring device and dividing the current value by the electrode area. The CO generation current density (CO partial current density) was calculated by multiplying the current density by the CO selectivity.

[0071] Potassium ion content of the cathode after pretreatment in Examples 1-11, cesium ion content of the cathode after pretreatment in Example 12, sodium ion content of the cathode after pretreatment in Examples 13-14, magnesium ion content of the cathode after pretreatment in Example 15, benzyltrimethylammonium ion content of the cathode after pretreatment in Examples 16-19 (NR ４ ＋ ) Content and the tetrabutylphosphonium ion (PR) of the cathode after pretreatment in Examples 20-23 ４ ＋ The content was calculated using the following method and is shown in Tables 1 and 2. In Table 2, the content of each ion (μmol / cm³) is shown in the "Cation Content" column. ２ ) was shown.

[0072] <Method for calculating potassium ion content in Examples 3-4 (pretreatment: voltage application)> Under conditions where the cell is heated to 40°C, the applied potential of the cathode is -1.8V for 1 hour relative to the silver / silver chloride reference electrode (which has a saturated potassium chloride solution in its internal solution), thereby calculating the electrolyte (0.3 mol / L KHCO3) in the anode electrolyte cell. ３Potassium ions and water in an aqueous solution were crossovered as a membrane at the cathode, and the electrolyte was packed into the electrode cavity of the reducing electrode. After packing, the reducing electrode was subjected to X-ray fluorescence analysis (NEX DE; Rigaku), and the X-ray fluorescence spectrum at the Kα-ray energy position of K was measured. The potassium ion content was calculated from the X-ray fluorescence spectrum using a calibration curve of samples with known concentrations.

[0073] <Method for calculating potassium ion content in Examples 1-2 and 5-11 (Pretreatment: Vacuum impregnation)> The reducing electrode is impregnated with electrolyte (0.01-4.7 mol / L KHCO3 ３ The electrodes were immersed in an aqueous solution. With the electrodes immersed, they were left standing in a desiccator under a reduced pressure of 2 kPa (absolute pressure) for 30 minutes, and KHCO3 was applied to the electrode gap. ３ The electrode was impregnated with an aqueous solution. The weight of the electrode before and after impregnation was used to determine the amount of KHCO impregnated into the electrode void. ３ The weight of the aqueous solution was calculated, and the potassium ion content was determined from the electrolyte concentration and weight.

[0074] <Method for calculating the cesium ion content in Example 12 (Pretreatment: Vacuum impregnation)> The reducing electrode was impregnated with electrolyte (2.0 mol / L CsHCO3) ３ The electrodes were immersed in an aqueous solution. With the electrodes immersed, they were left standing in a desiccator under a reduced pressure of 2 kPa (absolute pressure) for 30 minutes, and CsHCO3 was applied to the electrode gap. ３ The electrode was impregnated with an aqueous solution. The weight of the electrode before and after impregnation was used to determine the amount of CsHCO impregnated into the electrode void. ３ The weight of the aqueous solution was calculated, and the cesium ion content was determined from the electrolyte concentration and weight.

[0075] <Method for calculating sodium ion content in Examples 13-14 (Pretreatment: Vacuum impregnation)> The reducing electrode was placed in the electrolyte (1.0 mol / L NaHCO3 ３ The electrodes were immersed in an aqueous solution. With the electrodes immersed, they were left standing in a desiccator under a reduced pressure of 2 kPa (absolute pressure) for 30 minutes, and NaHCO3 was applied to the electrode gap. ３ The electrode was impregnated with an aqueous solution. The weight of the electrode before and after impregnation was used to determine the amount of NaHCO impregnated into the electrode void. ３ The weight of the aqueous solution was calculated, and the sodium ion content was determined from the electrolyte concentration and weight.

[0076] <Method for calculating magnesium ion content in Example 15 (Pretreatment: Vacuum impregnation)> The reducing electrode is placed in the electrolyte (0.2 mol / L MgSO ４ The electrodes were immersed in an aqueous solution. With the electrodes immersed, they were left standing for 30 minutes in a desiccator under a reduced pressure of 2 kPa (absolute pressure), and MgSO4 was placed in the electrode gap. ４ The electrode was impregnated with an aqueous solution. The amount of MgSO impregnated into the electrode void was determined from the electrode weight before and after impregnation. ４ The weight of the aqueous solution was calculated, and the magnesium ion content was determined from the electrolyte concentration and weight.

[0077] <Method for calculating the benzyltrimethylammonium ion content in Examples 16-19 (Pretreatment: Vacuum impregnation)> The reducing electrode was immersed in an electrolyte (0.2 mol / L benzyltrimethylammonium hydroxide aqueous solution). With the electrode immersed, it was left standing in a desiccator under a reduced pressure of 2 kPa (absolute pressure) for 30 minutes, impregnating the electrode void with the benzyltrimethylammonium hydroxide aqueous solution. The weight of the benzyltrimethylammonium hydroxide aqueous solution impregnated into the electrode void was calculated from the electrode weight before and after impregnation, and the benzyltrimethylammonium ion content was calculated from the electrolyte concentration and weight.

[0078] <Method for calculating tetrabutylphosphonium ion content in Examples 20-23 (Pretreatment: Vacuum impregnation)> The reducing electrode was immersed in an electrolyte (0.2 mol / L aqueous solution of tetrabutylphosphonium hydroxide). With the electrode immersed, it was left standing in a desiccator under a reduced pressure of 2 kPa (absolute pressure) for 30 minutes, impregnating the electrode void with the aqueous solution of tetrabutylphosphonium hydroxide. The weight of the aqueous solution of tetrabutylphosphonium hydroxide impregnated into the electrode void was calculated from the electrode weight before and after impregnation, and the tetrabutylphosphonium ion content was calculated from the electrolyte concentration and weight.

[0079]

[0080]

[0081] As shown in Tables 1 and 2, the examples using the pretreatment method of this embodiment were able to suppress salt deposition at the cathode of the carbon dioxide electrolytic reduction cell. Furthermore, Examples 1-4, 12, 13, 17, 19, 21, and 23, with electrolysis times of 20 to 50 hours, were able to suppress salt deposition and exhibit high electrolysis performance, allowing the carbon dioxide reduction cell to be operated for a long period of time. In addition, Examples 5-11, 14-16, 18, 20, and 22, with an electrolysis time of 1 hour, showed superior CO generation current density compared to Comparative Examples 3-5, which also had an electrolysis time of 1 hour. Therefore, Examples 5-11, 14-16, 18, 20, and 22 showed improved electrolysis performance in the initial stages of operation. On the other hand, in the comparative examples using a method that did not include the treatment step of this embodiment, Comparative Examples 1 and 2, with an electrolysis time of 20 hours, were unable to suppress salt deposition. Furthermore, Comparative Examples 1 and 2 exhibited inferior electrolysis performance compared to Examples 1-4, 12, 13, 17, 19, 21, and 23, and the carbon dioxide reduction cell could not be operated for an extended period. This is presumed to be because salt precipitation occurred, causing blockage of the gas flow path and making gas supply difficult, thus hindering operation.

[0082] 1: Reduced pressure desiccator, 2: Container, 3: Cathode, 4: Processing liquid

Claims

1. A method for pretreatment of a cathode used in carbon dioxide electrolysis, comprising a step of holding a solution containing one or more cations selected from alkali metal ions, alkaline earth metal ions, quaternary ammonium ions, quaternary phosphonium ions, imidazolium ions, pyridinium ions, piperidinium ions, and pyrrolidinium ions on the cathode.

2. The pretreatment method according to claim 1, wherein the processing step includes impregnating the cathode with a processing solution containing the cations.

3. The pretreatment method according to claim 2, wherein the impregnation step is carried out under a reduced pressure environment of 0 to 90 kPa.

4. The pretreatment method according to claim 2 or 3, wherein the treatment solution is a solution containing the cations in a total concentration of 0.01 to 5 mol / L.

5. The pretreatment method according to claim 3, wherein the impregnation step includes immersing the cathode in the treatment solution for 10 to 120 minutes.

6. The pretreatment method according to claim 1, wherein the processing step includes applying a voltage to a solid electrolyte electrolytic apparatus comprising a cathode, an ion exchange membrane, an anode, and an anode electrolyte tank, thereby causing the cations in the processing solution containing the cations placed in the anode electrolyte tank to permeate the ion exchange membrane, and the solution containing the permeated cations to be held in the cathode.

7. The pretreatment method according to claim 6, wherein the treatment solution is a solution containing the cations in a total concentration of 0.03 to 2 mol / L.

8. The pretreatment method according to claim 6 or 7, wherein the voltage application time is 0.1 to 24 hours.

9. The pretreatment method according to any one of claims 6 to 8, wherein the voltage is such that the applied potential of the cathode to a silver / silver chloride reference electrode (having a saturated potassium chloride solution in its internal solution) is -1.1 to -1.8 V.

10. The processing step is performed so that the total amount of cations held in the cathode is 0.3 to 170 μmol / cm³. ２ A pretreatment method according to any one of claims 1 to 9, comprising a step performed to such an extent.

11. The pretreatment method according to any one of claims 1 to 10, wherein the alkali metal ion is one or more of lithium ions, sodium ions, potassium ions, cesium ions, and rubidium ions.

12. The pretreatment method according to any one of claims 1 to 11, wherein the alkaline earth metal ion is one or more of beryllium ions, magnesium ions, calcium ions, strontium ions, and barium ions.

13. The pretreatment method according to any one of claims 1 to 12, wherein the quaternary ammonium ion is one or more of benzyltrimethylammonium ion, trimethylphenylammonium ion, tetramethylammonium ion, tetraethylammonium ion, and tetrapropylammonium ion.

14. The pretreatment method according to any one of claims 1 to 13, wherein the quaternary phosphonium ion is one or more of tetrabutylphosphonium ion, tributylmethylphosphonium ion, tributylethylphosphonium ion, and tributylhexylphosphonium ion.

15. The pretreatment method according to any one of claims 1 to 14, wherein the imidazolium ion is one or more of 1-methylimidazolium ions, 1,3-dimethylimidazolium ions, and 1-ethyl-3-methylimidazolium ions.

16. The pretreatment method according to any one of claims 1 to 15, wherein the pyridinium ion is one or more of 1-methylpyridinium ion, 1-ethylpyridinium ion, and 1-propylpyridinium ion.

17. The pretreatment method according to any one of claims 1 to 16, wherein the piperidinium ion is one or more of 1-butyl-1-methylpiperidinium ions and 1-methyl-1-propylpiperidinium ions.

18. A method for electrolytic reduction of carbon dioxide, comprising the step of electrolyzing carbon dioxide using a solid electrolyte electrolytic apparatus equipped with a cathode, an ion exchange membrane, an anode, and an anode electrolyte tank, which have been pretreated by the pretreatment method described in any one of claims 1 to 17.

19. The carbon dioxide electrolytic reduction method according to claim 18, wherein in the step of electrolyzing carbon dioxide, the electrolyte in the anodic electrolyte tank is a solution containing the cations at a total concentration of 0.01 to 0.5 mol / L.

20. A cathode for a solid electrolyte electrolytic device, which holds a solution containing a total concentration of 0.01 to 5 mol / L of one or more cations from among alkali metal ions, alkaline earth metal ions, quaternary ammonium ions, quaternary phosphonium ions, imidazolium ions, pyridinium ions, piperidinium ions, and pyrrolidinium ions.

21. A method for manufacturing a solid electrolyte electrolytic apparatus, comprising the step of providing a cathode that has been pretreated by the pretreatment method described in any one of claims 1 to 17.

22. A method for manufacturing an ion exchange membrane-electrode assembly, comprising the step of providing a cathode that has been pretreated by the pretreatment method described in any one of claims 1 to 17.

23. The method for manufacturing an ion exchange membrane-electrode assembly according to claim 22, wherein the ion exchange membrane includes an anion exchange membrane.

24. A method for manufacturing a solid electrolyte electrolytic device, comprising the step of providing an ion exchange membrane-electrode assembly according to claim 22 or 23.

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