Method and apparatus for producing formic acid using conductive diamond electrodes

Abstract

To provide an efficient method and apparatus for producing formic acid. [Solution] Using activated conductive diamond electrodes, carbon dioxide is electrolytically reduced. The present invention provides a method and apparatus for producing formic acid.

Description

Technical Field

[0001] The present disclosure relates to a method and apparatus for producing formic acid by electrolytic reduction of carbon dioxide using a conductive diamond electrode.

Background Art

[0002] Formic acid is an important industrial raw material and has been produced by methods such as acid decomposition of sodium formate, oxidation of hydrocarbons, and direct hydrolysis of methyl formate. In recent years, from the viewpoints of preventing global warming, protecting oil resources, and further realizing a sustainable and viable society, the production of formic acid using carbon dioxide as a raw material has attracted attention.

[0003] Patent Document 1 describes an electrolytic reduction apparatus for carbon dioxide. In the method of Patent Document 1, carbon dioxide is saturated in an aqueous potassium carbonate solution with a concentration of about 7M and electrolytic reduction is performed. The products are described as acetic acid and formic acid.

[0004] Patent Document 2 describes an electrochemical reduction apparatus using a diamond electrode. In the method of Patent Document 2, carbon dioxide is saturated in a methanol solution under high pressure and electrolytic reduction is performed.

[0005] Patent Document 3 describes a method and apparatus for producing formic acid with high selectivity from carbon dioxide using a diamond electrode. In Patent Document 3, methods and apparatuses using potassium chloride, rubidium chloride, or cesium chloride at a relatively high current density are disclosed.

[0006] Non-Patent Document 1 describes a method and apparatus for producing formic acid with high selectivity from carbon dioxide using a diamond electrode.

[0007] ​​​​​​​​​​​An efficient method for producing formic acid is needed. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2011-174139 (Japanese Patent No. 5368340) [Patent Document 2] Japanese Patent Publication No. 2014-167151 (Japanese Patent No. 6042749) [Patent Document 3] Japanese Patent Publication No. 2018-141220 [Non-patent literature]

[0009] [Non-Patent Document 1] S. Kaneko, R. Iwao, K. IIba, K. Ohta and T. Mizuno, Energy, 23 (1998) No. 12, pp. 1107-1112 [Overview of the project] [Problems that the invention aims to solve]

[0010] Method for producing formic acid by electrolytic reduction of carbon dioxide using a diamond electrode as described in Patent Document 3 According to the method, in order to obtain a practical amount of formic acid, the potential of the working electrode should be greater than -2.2V relative to the reference electrode. It also needed to be made larger, and improvements were needed from the standpoint of power consumption. Also, Patent Document 3 The formic acid obtained by the electrolytic reduction of carbon dioxide using the diamond electrode described above is an electrolyte It contains halides derived from potassium chloride, etc. The gypsum obtained by these methods Acids are used in applications such as fuel cells and hydrogen storage because they deactivate metal catalysts due to halides. A problem was that it could not be used for applications involving contact with catalysts.

[0011] This disclosure provides a method and apparatus for producing formic acid that at least partially solves the problems of the prior art. The objective is to provide. In certain embodiments, this disclosure uses carbon dioxide as a raw material. In the production of formic acid, the present invention provides an apparatus and method for producing formic acid with low power consumption. In certain embodiments, the present disclosure describes how to produce formic acid using a halogen-free electrolyte. To provide a method. [Means for solving the problem]

[0012] In certain embodiments, the present disclosure describes how to activate a diamond electrode, thereby enabling two Apparatus and method for producing formic acid with low power consumption through electrolytic reduction of carbon oxide This provides a diamond electrode. In certain embodiments, this disclosure also provides a diamond electrode for activation. By doing so, in the electrolytic reduction of carbon dioxide, a halogen-free electrolyte can be used. This document provides a method for producing acid.

[0013] In other words, this disclosure includes the following embodiments: [1] A method for producing formic acid by electrolytically reducing carbon dioxide using an electrolytic cell equipped with an anode and a cathode. There is, The cathode is a conductive diamond electrode, In an electrolyte solution containing dissolved carbon dioxide and a supporting electrolyte, a voltage of -2.0V to -3.0V is applied relative to the reference electrode. Apply cathode potential within the specified range, and set it to -0.5 mA / cm². 2 By electrolysis at the above current density, the conductivity An activation process including activating a diamond electrode, The activated conductive diamond electrode serves as the cathode, and the system contains carbon dioxide and a supporting electrolyte. Perform electrolytic reduction in an electrolyte solution at a cathode potential of -1.5V to -2.2V relative to the reference electrode. A formic acid production process including, A method for producing formic acid containing [the specified ingredient]. [2] The supporting electrolyte used in the activation step and the supporting electrolyte used in the formic acid production step The formic acid according to Embodiment 1, characterized in that the supporting electrolyte also contains a halogenated compound. A method for manufacturing this product. [3] An embodiment characterized in that the supporting electrolyte containing the halogen is potassium chloride. A method for producing formic acid as described in Form 2. [4] A method for producing formic acid by electrolytically reducing carbon dioxide using an electrolytic cell equipped with an anode and a cathode. There is, The cathode is a conductive diamond electrode, In an electrolyte solution containing carbon dioxide and a supporting electrolyte, relative to the reference electrode Then, apply a cathode potential in the range of -2.0V to -3.0V, and -0.5 mA / cm 2 Electrolysis is performed at the above current density. An activation step including activating the conductive diamond electrode by the means thereof, An electrolyte solution obtained by dissolving the support electrolyte containing the aforementioned halogen, and a support electrolyte that does not contain halogen. A solution exchange step, which includes replacing the retained electrolyte with an electrolyte solution in which the retained electrolyte has been dissolved, Electrolytic reduction is performed using an electrolyte solution containing the aforementioned halogen-free supporting electrolyte and carbon dioxide. A formic acid production process that includes the following: A method for producing formic acid containing [the specified ingredient]. [5] The supporting electrolyte containing the halogen is potassium chloride, and the halogen contains Production of formic acid according to Embodiment 4, characterized in that the non-supporting electrolyte is potassium sulfate. method. [6] The method according to any one of embodiments 1 to 5, wherein the activation step is performed for 30 minutes or more. [7] The current density of the cathode potential applied in the activation process is -0.5 mA / cm 2 More than ~-5.0mA / cm 2The method according to any one of Embodiments 1 to 6 below. [8] A formic acid production apparatus that produces formic acid by reducing carbon dioxide at a cathode, The electrolytic cell has an anode and a cathode, The cathode is a conductive diamond electrode, The conductive diamond electrode is in an electrolyte solution containing carbon dioxide and a supporting electrolyte. A cathode potential in the range of -2.0V to -3.0V is applied to the irradiating electrode, and -0.5 mA / cm 2 The above current density It is activated by electrolyzing carbon dioxide. The aforementioned formic acid production apparatus. [9] The conductive diamond electrode is in an electrolyte solution in which carbon dioxide and a supporting electrolyte are dissolved. Then, a cathode potential in the range of -2.0V to -3.0V is applied to the reference electrode, and -0.5 mA / cm 2 The above electricity Embodiment 8, which is activated by electrolyzing carbon dioxide at a high fluid density for 30 minutes or more. The device described.

[10] The conductive diamond electrode is an electrolyte solution in which carbon dioxide and a supporting electrolyte are dissolved. Inside, a cathode potential is applied to the reference electrode in the range of -2.0V to -3.0V, and the current is -0.5 mA / cm. 2 That's all~- 5.0 mA / cm 2 Activated by electrolyzing carbon dioxide at the following current densities, The apparatus described in form 8 or 9. [Effects of the Invention]

[0014] According to this disclosure, by activating conductive diamond electrodes, low power consumption is achieved. To provide an apparatus and method for producing formic acid, and to activate a conductive diamond electrode. This provides a method for producing formic acid that does not contain halides. [Brief explanation of the drawing]

[0015] [Figure 1] An example of the apparatus of this disclosure is shown in Figure 1. [Figure 2-1] This figure shows the changes in current density and potential during the activation process. [Figure 2-2] This figure shows the change in current density during the formic acid production process. [Figure 3] Figure 3 shows the Faraday efficiency of formic acid production in the formic acid production process. [Figure 4] This figure shows the Faraday efficiency of formic acid production in the formic acid generation process for activated electrode (b) and unactivated electrode (a) after a solution exchange. The electrolyte solution after the solution exchange was 0.25 M K2SO4. [Figure 5] The graph shows the change in current density when formic acid is produced by constant potential electrolysis using activated (bottom) and unactivated (top) conductive diamond electrodes, with a cathode potential of -1.8V applied. [Figure 6] The graph shows the change in current density when formic acid is produced by constant potential electrolysis using activated (bottom) and unactivated (top) conductive diamond electrodes, with a cathode potential of -1.9V applied. [Figure 7] The graph shows the change in current density when formic acid is produced by constant potential electrolysis using activated (bottom) and unactivated (top) conductive diamond electrodes, with a cathode potential of -2.2V applied. [Modes for carrying out the invention]

[0016] Formic acid production equipment In one embodiment, the present disclosure relates to formic acid production, which involves reducing carbon dioxide at a cathode to produce formic acid. The apparatus is provided. The formic acid production apparatus of this embodiment has an electrolytic cell equipped with an anode and a cathode, and The cathode is a conductive diamond electrode. In a particular embodiment, the conductive diamond The electrode is an activated conductive diamond electrode. In one embodiment, The activated conductive diamond electrode is an electrolyte in which carbon dioxide and a supporting electrolyte are dissolved. In a quality solution, a cathode potential is applied in the range of -2.0 V to -3.0 V, for example, in the range of -2.2 V to -3.0 V, for example, in the range of -2.2 V to -2.8 V with respect to the reference electrode, and carbon dioxide is electrolyzed at a current density of -0.5 mA / cm 2 or more, for example, -1.0 mA / cm 2 or more to be activated. The conductive diamond electrode is defined as one formed as an electrode by imparting conductivity to a thin film or bulk diamond. The method of imparting conductivity to diamond is not particularly limited, but a trace amount of impurities can be doped into the diamond. Examples of

[0017] impurities include boron (B), sulfur (S), nitrogen (N), oxygen (O), silicon (Si), etc. For example, diamond on a thin film or bulk is obtained by a vapor phase synthesis method. To dope boron into a raw material gas containing a carbon source, diborane, trimethoxyborane, boron oxide can be used. To dope sulfur, sulfur oxide, hydrogen sulfide can be used. To dope oxygen, oxygen or carbon dioxide can be used. To dope nitrogen, ammonia or nitrogen can be used. To dope silicon, silane, etc. can be added. In particular, a boron-doped conductive diamond electrode is advantageous because it has the advantages of a wide potential window and a small background current compared with other electrode materials. Hereinafter, the conductive diamond electrode may be simply described as a diamond electrode, and a boron-doped diamond electrode may be described as a boron-doped diamond electrode or a BDD electrode. The method of imparting conductivity to diamond is not particularly limited, but a trace amount of impurities can be doped into the diamond. Examples of impurities include boron (B), sulfur (S), nitrogen (N), oxygen (O), silicon (Si), etc. For example, diamond on a thin film or bulk is obtained by a vapor phase synthesis method. To dope boron into a raw material gas containing a carbon source, diborane, trimethoxyborane, boron oxide can be used. To dope sulfur, sulfur oxide, hydrogen sulfide can be used. To dope oxygen, oxygen or carbon dioxide can be used. To dope nitrogen, ammonia or nitrogen can be used. To dope silicon, silane, etc. can be added. In particular, a boron-doped conductive diamond electrode is advantageous because it has the advantages of a wide potential window and a small background current compared with other electrode materials. Hereinafter, the conductive diamond electrode may be simply described as a diamond electrode, and a boron-doped diamond electrode may be described as a boron-doped diamond electrode or a BDD electrode. impurities include boron (B), sulfur (S), nitrogen (N), oxygen (O), silicon (Si), etc. For example, diamond on a thin film or bulk is obtained by a vapor phase synthesis method. To dope boron into a raw material gas containing a carbon source, diborane, trimethoxyborane, boron oxide can be used. To dope sulfur, sulfur oxide, hydrogen sulfide can be used. To dope oxygen, oxygen or carbon dioxide can be used. To dope nitrogen, ammonia or nitrogen can be used. To dope silicon, silane, etc. can be added. In particular, a boron-doped conductive diamond electrode is advantageous because it has the advantages of a wide potential window and a small background current compared with other electrode materials. Hereinafter, the conductive diamond electrode may be simply described as a diamond electrode, and a boron-doped diamond electrode may be described as a boron-doped diamond electrode or a BDD electrode. impurities include boron (B), sulfur (S), nitrogen (N), oxygen (O), silicon (Si), etc. For example, diamond on a thin film or bulk is obtained by a vapor phase synthesis method. To dope boron into a raw material gas containing a carbon source, diborane, trimethoxyborane, boron oxide can be used. To dope sulfur, sulfur oxide, hydrogen sulfide can be used. To dope oxygen, oxygen or carbon dioxide can be used. To dope nitrogen, ammonia or nitrogen can be used. To dope silicon, silane, etc. can be added. In particular, a boron-doped conductive diamond electrode is advantageous because it has the advantages of a wide potential window and a small background current compared with other electrode materials. Hereinafter, the conductive diamond electrode may be simply described as a diamond electrode, and a boron-doped diamond electrode may be described as a boron-doped diamond electrode or a BDD electrode. impurities include boron (B), sulfur (S), nitrogen (N), oxygen (O), silicon (Si), etc. For example, diamond on a thin film or bulk is obtained by a vapor phase synthesis method. To dope boron into a raw material gas containing a carbon source, diborane, trimethoxyborane, boron oxide can be used. To dope sulfur, sulfur oxide, hydrogen sulfide can be used. To dope oxygen, oxygen or carbon dioxide can be used. To dope nitrogen, ammonia or nitrogen can be used. To dope silicon, silane, etc. can be added. In particular, a boron-doped conductive diamond electrode is advantageous because it has the advantages of a wide potential window and a small background current compared with other electrode materials. Hereinafter, the conductive diamond electrode may be simply described as a diamond electrode, and a boron-doped diamond electrode may be described as a boron-doped diamond electrode or a BDD electrode. impurities include boron (B), sulfur (S), nitrogen (N), oxygen (O), silicon (Si), etc. For example, diamond on a thin film or bulk is obtained by a vapor phase synthesis method. To dope boron into a raw material gas containing a carbon source, diborane, trimethoxyborane, boron oxide can be used. To dope sulfur, sulfur oxide, hydrogen sulfide can be used. To dope oxygen, oxygen or carbon dioxide can be used. To dope nitrogen, ammonia or nitrogen can be used. To dope silicon, silane, etc. can be added. In particular, a boron-doped conductive diamond electrode is advantageous because it has the advantages of a wide potential window and a small background current compared with other electrode materials. Hereinafter, the conductive diamond electrode may be simply described as a diamond electrode, and a boron-doped diamond electrode may be described as a boron-doped diamond electrode or a BDD electrode. impurities include boron (B), sulfur (S), nitrogen (N), oxygen (O), silicon (Si), etc. For example, diamond on a thin film or bulk is obtained by a vapor phase synthesis method. To dope boron into a raw material gas containing a carbon source, diborane, trimethoxyborane, boron oxide can be used. To dope sulfur, sulfur oxide, hydrogen sulfide can be used. To dope oxygen, oxygen or carbon dioxide can be used. To dope nitrogen, ammonia or nitrogen can be used. To dope silicon, silane, etc. can be added. In particular, a boron-doped conductive diamond electrode is advantageous because it has the advantages of a wide potential window and a small background current compared with other electrode materials. Hereinafter, the conductive diamond electrode may be simply described as a diamond electrode, and a boron-doped diamond electrode may be described as a boron-doped diamond electrode or a BDD electrode. impurities include boron (B), sulfur (S), nitrogen (N), oxygen (O), silicon (Si), etc. For example, diamond on a thin film or bulk is obtained by a vapor phase synthesis method. To dope boron into a raw material gas containing a carbon source, diborane, trimethoxyborane, boron oxide can be used. To dope sulfur, sulfur oxide, hydrogen sulfide can be used. To dope oxygen, oxygen or carbon dioxide can be used. To dope nitrogen, ammonia or nitrogen can be used. To dope silicon, silane, etc. can be added. In particular, a boron-doped conductive diamond electrode is advantageous because it has the advantages of a wide potential window and a small background current compared with other electrode materials. Hereinafter, the conductive diamond electrode may be simply described as a diamond electrode, and a boron-doped diamond electrode may be described as a boron-doped diamond electrode or a BDD electrode. impurities include boron (B), sulfur (S), nitrogen (N), oxygen (O), silicon (Si), etc. For example, diamond on a thin film or bulk is obtained by a vapor phase synthesis method. To dope boron into a raw material gas containing a carbon source, diborane, trimethoxyborane, boron oxide can be used. To dope sulfur, sulfur oxide, hydrogen sulfide can be used. To dope oxygen, oxygen or carbon dioxide can be used. To dope nitrogen, ammonia or nitrogen can be used. To dope silicon, silane, etc. can be added. In particular, a boron-doped conductive diamond electrode is advantageous because it has the advantages of a wide potential window and a small background current compared with other electrode materials. Hereinafter, the conductive diamond electrode may be simply described as a diamond electrode, and a boron-doped diamond electrode may be described as a boron-doped diamond electrode or a BDD electrode. impurities include boron (B), sulfur (S), nitrogen (N), oxygen (O), silicon (Si), etc. For example, diamond on a thin film or bulk is obtained by a vapor phase synthesis method. To dope boron into a raw material gas containing a carbon source, diborane, trimethoxyborane, boron oxide can be used. To dope sulfur, sulfur oxide, hydrogen sulfide can be used. To dope oxygen, oxygen or carbon dioxide can be used. To dope nitrogen, ammonia or nitrogen can be used. To dope silicon, silane, etc. can be added. In particular, a boron-doped conductive diamond electrode is advantageous because it has the advantages of a wide potential window and a small background current compared with other electrode materials. Hereinafter, the conductive diamond electrode may be simply described as a diamond electrode, and a boron-doped diamond electrode may be described as a boron-doped diamond electrode or a BDD electrode. impurities include boron (B), sulfur (S), nitrogen (N), oxygen (O), silicon (Si), etc. For example, diamond on a thin film or bulk is obtained by a vapor phase synthesis method. To dope boron into a raw material gas containing a carbon source, diborane, trimethoxyborane, boron oxide can be used. To dope sulfur, sulfur oxide, hydrogen sulfide can be used. To dope oxygen, oxygen or carbon dioxide can be used. To dope nitrogen, ammonia or nitrogen can be used. To dope silicon, silane, etc. can be added. In particular, a boron-doped conductive diamond electrode is advantageous because it has the advantages of a wide potential window and a small background current compared with other electrode materials. Hereinafter, the conductive diamond electrode may be simply described as a diamond electrode, and a boron-doped diamond electrode may be described as a boron-doped diamond electrode or a BDD electrode. impurities include boron (B), sulfur (S), nitrogen (N), oxygen (O), silicon (Si), etc. For example, diamond on a thin film or bulk is obtained by a vapor phase synthesis method. To dope boron into a raw material gas containing a carbon source, diborane, trimethoxyborane, boron oxide can be used. To dope sulfur, sulfur oxide, hydrogen sulfide can be used. To dope oxygen, oxygen or carbon dioxide can be used. To dope nitrogen, ammonia or nitrogen can be used. To dope silicon, silane, etc. can be added. In particular, a boron-doped conductive diamond electrode is advantageous because it has the advantages of a wide potential window and a small background current compared with other electrode materials. Hereinafter, the conductive diamond electrode may be simply described as a diamond electrode, and a boron-doped diamond electrode may be described as a boron-doped diamond electrode or a BDD electrode. impurities include boron (B), sulfur (S), nitrogen (N), oxygen (O), silicon (Si), etc. For example, diamond on a thin film or bulk is obtained by a vapor phase synthesis method. To dope boron into a raw material gas containing a carbon source, diborane, trimethoxyborane, boron oxide can be used. To dope sulfur, sulfur oxide, hydrogen sulfide can be used. To dope oxygen, oxygen or carbon dioxide can be used. To dope nitrogen, ammonia or nitrogen can be used. To dope silicon, silane, etc. can be added. In particular, a boron-doped conductive diamond electrode is advantageous because it has the advantages of a wide potential window and a small background current compared with other electrode materials. Hereinafter, the conductive diamond electrode may be simply described as a diamond electrode, and a boron-doped diamond electrode may be described as a boron-doped diamond electrode or a BDD electrode.

[0018] In one embodiment, the conductive diamond electrode may be in the form of a thin film deposited on a substrate. When depositing conductive diamond onto a substrate, the substrate often becomes very hot, so the substrate and For example, semiconductors such as silicon, and high melting points such as tungsten, niobium, molybdenum, and titanium. Metals can be used. A method for depositing a thin film of conductive diamond electrode onto a substrate. For this purpose, known methods can be used, for example, as described in the examples below, for chemical gas Phase synthesis (CVD method) can be used.

[0019] In one embodiment, a metal electrode such as platinum or nickel may be used as the anode. It is possible to use common carbon electrodes such as glassy carbon and graphite, and conduction Electrolytic diamond electrodes can be used. In one embodiment, the electrolytic cell is a batch cell. It can take various forms, such as a cell type or a flow cell type. For example, in one embodiment, an electrolytic cell This could be a flow cell type electrolytic cell that can continuously produce formic acid.

[0020] The configuration of the electrolytic cell in this disclosure is not particularly limited and can be various configurations. In this context, the electrolytic cell may have a reference electrode. This allows for precise control of the potential. Examples of reference electrodes include well-known electrodes such as standard hydrogen electrodes, silver-silver chloride electrodes, and saturated calomel electrodes. The electrode potential varies depending on the type of reference electrode used in the electrolytic cell, but in this specification... Unless otherwise specified, the electrode potential is assumed to be the cathode potential relative to the silver-silver chloride electrode (vs Ag / AgCl ).

[0021] In one embodiment, the electrolytic cell may be a two-chamber electrolytic cell having a diaphragm. By separating it into an anode chamber and a cathode chamber, independent electrochemical processes can be performed in the anode chamber and the cathode chamber, respectively. The reaction can be carried out and the reaction can be easily controlled. Examples of membranes include cation exchange membranes and anion exchange membranes. Ion exchange membranes such as ion exchange membranes and bipolar membranes can be used, but are not limited to these. In certain embodiments, the diaphragm may be a cation exchange membrane.

[0022] In one embodiment, the formic acid production apparatus includes carbon dioxide, which is the raw material for formic acid, and a supporting electrolyte. An electrolyte solution in which the electrolyte is dissolved can be used. The electrolyte solution is readily available and has conductivity. It can be made into an excellent aqueous solution. Carbon dioxide can be added, for example, to an electrolyte solution. It can be dissolved by bubbling. In certain embodiments, carbon dioxide gas Before bubbling, to remove dissolved gases such as dissolved oxygen contained in the electrolyte solution The system can be bubbled with inert gases such as nitrogen or argon.

[0023] As the supporting electrolyte for the activation process, an electrolyte containing a halide, such as potassium chloride, Examples of electrolytes containing halides such as rubidium chloride and cesium chloride include, but are not limited to, those listed below. It does not work. By using an electrolyte containing a halide, the conductive diamond electrode can be converted to dioxide Electron transfer to carbon occurs actively, resulting in a high activation effect.

[0024] In one embodiment, the conductive diamond electrode of the present disclosure is composed of carbon dioxide and a supporting electrolyte. In an electrolyte solution in which the following is dissolved, the voltage range is -2.0V to -3.0V relative to the reference electrode, for example, from -2.2V to - Apply a cathode potential within the range of 3.0V, for example, from -2.2V to -2.8V, and achieve a current of -0.5 mA / cm². 2 The above is an example. -1.0 mA / cm2 It may be activated by electrolysis at the above current density. Activation involves electrolyzing carbon dioxide in an electrolyte solution containing carbon dioxide at a relatively high potential. That is, electrons from the diamond electrode, which is the cathode, to the carbon dioxide dissolved in the electrolyte solution. The electrode itself is activated by actively inducing movement. The inventors of this invention have developed a conductive da In conducting various experiments on the electrolytic reduction of carbon dioxide using diamond electrodes, we found that activation Compared to performing electrolysis using unactivated electrodes, using activated electrodes... We unexpectedly discovered that electrolysis proceeds more actively when this is the case. However, the inventors have found that carbon atoms of carbon dioxide and the surface of a conductive diamond electrode exist Bonds are formed between the carbon atoms present, and carbon dioxide originates from the conductive diamond electrode surface. The formation of carboxyl groups improves the affinity between the electrode surface and carbon dioxide molecules. This is considered to be one of the factors that activate the conductive diamond electrode. However, this disclosure does not apply The mechanism is not limited in any way.

[0025] The inventors have developed an activated conductive diamond electrode that has adsorbed molecules and functional groups on its surface. We attempted to identify the type. We will now describe our current attempt. It is not possible to definitively identify the types of adsorbed molecules and functional groups near the surface, within a few micrometers of the surface, using only text. This means that each conductive diamond electrode has a different structure and associated properties. It is impossible if illuminated. Also, the structure or properties of the activated conductive diamond electrode, Identifying this through analysis based on measurements is also not possible with the analytical techniques available at the time of filing this application. It is possible or nearly impossible. A scanning electron microscope is a technique for measuring the state of existence of a material in detail. While there are methods such as scanning electron microscopes (SEM) and X-ray photoelectron spectroscopy (XPS), these measuring devices cannot measure the object being measured. This needs to be observed in an ultra-high vacuum chamber, and in such an environment, the desorption of adsorbed molecules from the surface Because separation occurs, the conductive diamond electrode cannot maintain an activated state. Furthermore, as a measuring device that does not require vacuum conditions, there is a Fourier transform infrared spectrometer (FT-IR). Examples include Raman spectrometers, but these devices are used for spatial resolution to identify surface structures. Due to a lack of ability, it is not possible to identify the surface structure of activated conductive diamond electrodes. do not have.

[0026] In one embodiment, the potential applied to the cathode when activating the diamond electrode is, A range of -2.0V to -3.0V relative to the illumination electrode, a range of -2.1V to -3.0V, for example, -2.2V to -3.0V A range, for example, a range from -2.0V to -2.9V, for example, a range from -2.1V to -2.9V, for example, a range from -2.2V to -2. A range of 9V, for example, from -2.0V to -2.8V, for example, from -2.1V to -2.8V, for example, from -2.2V A range of -2.8V, for example, a range from -2.0V to -2.7V, for example, a range from -2.1V to -2.7V, for example, -2. A range from 2V to -2.7V, for example, a range from -2.0V to -2.6V, for example, a range from -2.1V to -2.6V, for example For example, in the range of -2.2V to -2.6V, for example, in the range of -2.0V to -2.5V, in the range of -2.1V to -2.5V, for example The voltage may be in the range of -2.2V to -2.5V. In certain embodiments, the conductive diamond electrode is The cathode potential required for activation is greater than -2.0V and less than -2.5V. The cathode potential is too low. This prevents electron transfer from the diamond electrode to carbon dioxide, thus preventing a sufficient activation effect. Sometimes it may not be obtained. Also, if the cathode potential is too high, electrons from the diamond electrode into the water will not be obtained. Movement takes priority, and hydrogen may be generated. In this case, carbon dioxide may also be released from the electrodes. Electron transfer does not occur, and a sufficient activation effect cannot be obtained.

[0027] In one embodiment, the current density when activating the diamond electrode is -0.5 mA / cm². 2 Below Top, -0.6 mA / cm 2 More than -0.7 mA / cm 2 More than -0.8 mA / cm 2 More than -0.9 mA / cm 2 For example, -1 0.0 mA / cm 2 The above is possible. If the current density is too low, carbon dioxide will be transferred from the diamond electrode. Because electron transfer does not occur, a sufficient activation effect may not be obtained. Also, the current density There is no upper limit, but as the current density increases, the cathode potential increases. Therefore, It is preferable to adjust the cathode potential appropriately within a range that does not exceed the range described above. The current density when activating the diamond electrode is -5.0 mA / cm². 2 Below -4.5 mA / cm 2 Below Below, -4.0 mA / cm 2 Below, -3.5 mA / cm 2 Less than -3.0 mA / cm 2 Below -2.5 mA / cm 2 Less than -2.0 mA / cm 2 Below -1.5 mA / cm 2 For example, -0.5 mA / cm 2 ~-5.0 mA / cm 2 -0.6 mA / cm 2 ~-4.0 mA / c m 2 -0.7 mA / cm 2 ~-3.0 mA / cm2 -0.8 mA / cm 2 ~-2.0 mA / cm 2 For example, -0.9 mA / cm 2 ~-1.5 mA / cm 2 It is possible.

[0028] In one embodiment, in the diamond electrode activation process, an external power supply mechanism is used A voltage can be applied between the cathode and the anode. The external power supply mechanism is not particularly limited, A potentiometer-galvanostat can be used. The electrochemical reaction of the working electrode in the electrolyte is controlled, and its potential and current are measured. Using a galvanostat, the cathode potential and current density relative to the reference electrode are set to the aforementioned range. To achieve this, the potential can be controlled using a constant potential electrolysis method to obtain the desired current density. Alternatively, the current value may be controlled by a constant current electrolysis method to obtain the desired current value. A potentiostat or galvanostat may be used as the power supply mechanism.

[0029] In one embodiment, the time required for the diamond electrode activation process is set as appropriate. This can be done. In one embodiment, the activation step is 30 seconds or more, 1 minute or more, 5 minutes or more, 10 minutes or less Above, 15 minutes or more, for example 30 minutes or more, 90 minutes or less, for example 60 minutes or less, for example 1 to 90 minutes, 10 to 60 minutes For example, it can be 30 to 60 minutes, but it is not limited to this. If the activation time is too short, it may not be sufficient. The activation effect may not be obtained, and if the duration is too long, it affects the productivity and power consumption of the formic acid production equipment. This can put you at a disadvantage.

[0030] Furthermore, the potential and electric current applied to the cathode in the process of activating the diamond electrode of this disclosure Regarding the fluidity, the conventional formic acid production method has a higher applied potential and current density than the applied potential and current density. The applied potential and current density may be indicated. In such cases, in the prior art... The formic acid production method involves a cathode application step in which the diamond electrode of this disclosure is instantaneously activated. Potential and current density may be crossed. However, instantaneously, the diamond of this disclosure Simply crossing the cathode applied potential and current density in the electrode activation process is not sufficient for adequate activation. It is considered that no chemical effect can be obtained. Therefore, the conventional formic acid production method is not applicable. The instantaneous cathode applied potential and current density are used in the process of activating the diamond electrode of this disclosure. This does not apply to the potential and current density applied to the cathode.

[0031] Formic Acid Production Method In one embodiment, the present disclosure describes an electrolytic cell comprising an anode and a cathode that electrolyzes carbon dioxide. The present invention provides a method for producing formic acid that can be reduced. The method for producing formic acid in this embodiment includes an activation step and The process includes a formic acid production step. In a particular embodiment, the activation step involves the conductive cathode. The diamond electrode is positioned relative to the reference electrode in a range of -2.0V to -3.0V, for example, -2.2V to -3.0V. Apply a cathode potential within a range, for example, from -2.2V to -2.8V, and achieve a current of -0.5 mA / cm². 2 For example, -1.0 mA / cm 2 This is a process of activation by electrolysis at the above current density. In a specific embodiment... In the formic acid production step, a reference electrode is subjected to an electrolyte solution containing carbon dioxide and a supporting electrolyte. The cathode potential is between -1.5V and -2.2V, between -1.5V and -2.0V, for example, between -1.8V and -2.0V. This is a process that performs electrolytic reduction using electric potential. The activation process is as described above.

[0032] In one embodiment, this disclosure describes the production of formic acid by electrolytic reduction of carbon dioxide. A method for activating a conductive diamond electrode, comprising dissolving carbon dioxide and a supporting electrolyte. In the dissolved electrolyte solution, the cathode potential is set to a conductive electrode in the range of -2.0V to -3.0V relative to the reference electrode. Applied to a diamond electrode, -0.5 mA / cm 2 To electrolyze carbon dioxide at the above current density The present invention provides an activation method that includes a step of further activating the conductive diamond electrode. Conductive diamond electrodes activated by this method can be used in the production of formic acid.

[0033] In the formic acid production step of this embodiment, the conductive diamond activated by the activation step A diamond electrode is used. An electrolytic cell equipped with an activated conductive diamond electrode is used as the cathode. When electrolytic reduction of carbon dioxide is performed using an unactivated conductive diamond electrode, Compared to the case where electron transfer to carbon dioxide occurs at a lower cathode potential, this allows for electron transfer to carbon dioxide. Furthermore, formic acid is produced at a small cathode potential range, for example, from -1.5V to -2.0V relative to the reference electrode. This makes it possible to reduce the power consumption required for electrolytic reduction.

[0034] In one embodiment, the cathode potential in the formic acid production step is, for example, -1.5V or higher and -1.6V or lower. Above -1.7V, above -1.8V, for example below -2.2V, below -2.1V, below -2.0V, for example between -1.5V and -2 It can be 0.2V, -1.6V to -2.1V, -1.7V to -2.0V, or -1.8V to -2.0V. If the electrode potential is too low... The amount of formic acid produced by the electrolytic reduction of carbon dioxide may decrease. Electrode potential If the size is too large, the amount of formic acid produced will increase, but the power consumption required for electrolysis will also increase. ru.

[0035] The current density in the formic acid production process is not particularly limited, but if it is too small or too large, This is undesirable because it may fall outside the range of the cathode potential described above. From the viewpoint of the amount of formic acid produced, It is preferable to adjust the settings to maximize the cathode potential within the range in which the aforementioned cathode potential can be obtained.

[0036] In a specific embodiment, formic acid using the activated diamond electrode of this disclosure The manufacturing method, compared to conventional formic acid production methods, changes the cathode potential in the formic acid production process. It can be made smaller. That is, with respect to the potential applied to the cathode in the formic acid production process, The prior art method for producing formic acid teaches an applied potential greater than the applied potential described in this disclosure. This may be the case. In such cases, in the conventional method for producing formic acid, applying an electric potential At the start or end of the process, particularly at the end of the operation of the apparatus, instantaneously the formic acid production process of this disclosure The cathode applied potential may be crossed instantaneously. Simply crossing the cathode applied potential during the process does not reduce the power consumption required for formic acid production. The power consumption is the same as before. Therefore, such instantaneous power consumption in the conventional formic acid production method The cathode applied potential in the formic acid production process is crossed, and the cathode in the formic acid production process of this disclosure This does not apply to the potential applied to the device.

[0037] The supporting electrolyte used in the formic acid production step of this embodiment is potassium chloride, rubidium chloride. Examples of electrolytes containing halides such as cesium chloride, etc., include, but are not limited to, halo Electrolytes containing ions promote active electron transfer from conductive diamond electrodes to carbon dioxide. Because this can occur, it can also be used in the activation process of diamond electrodes. If an electrolyte containing a halide is used in the subsequent formic acid production process, a small cathode potential will occur. This makes it possible to produce formic acid. In certain embodiments, it is used in the activation step. The same electrolyte solution is used continuously in the subsequent formic acid production process. By using it, the process can be simplified.

[0038] In the formic acid production step of this embodiment, as in the diamond electrode activation step, an external electric current is used. A voltage can be applied between the cathode and anode using a power source mechanism. The external power supply mechanism is particularly limited. Although not specified, a potentiometer-galvanostat can be used. To obtain the desired potential using a vanostat, the potential is directly controlled by a constant potential method. Alternatively, the current value can be controlled using a constant current method to provide the desired potential. A potentiostat or galvanostat may be used as the power supply mechanism.

[0039] In this embodiment, the time required for the formic acid production process can be set as appropriate. In the application method, the time spent on the formic acid manufacturing process is 10 minutes or more, 30 minutes or more, 60 minutes or more, or 2 hours or more. Above, 3 hours or more, 6 hours or more, 12 hours or more, 24 hours or more, 48 hours or more, for example, 72 hours or more It is possible, but not limited to this. The time required for the formic acid manufacturing process depends on the supply of carbon dioxide, which is a raw material, and By making the process as long as possible without reducing the rate of formic acid production, the production of formic acid can be increased. This can be increased. In a particular embodiment, the time taken for the formic acid production process is 144 It could be less than an hour, less than 72 hours, less than 48 hours, or less than 24 hours, but is not limited to these.

[0040] In one embodiment, the present disclosure describes an electrolytic cell comprising an anode and a cathode that electrolyzes carbon dioxide. The present invention provides a method for producing formic acid that can be reduced. The method for producing formic acid in this embodiment includes an activation step and The process includes a liquid exchange step and a formic acid production step. In the activation step, carbon dioxide and a halogenate are used. In an electrolyte solution containing the supporting electrolyte, the voltage range is -2.0V to -3.0V relative to the reference electrode, for example. For example, apply a cathode potential in the range of -2.2V to -3.0V, or for example, in the range of -2.2V to -2.8V, and -0.5 mA / cm 2 For example, -1.0 mA / cm 2 By electrolysis at the above current density, the conductive diamond The end electrode can be activated. In the liquid exchange process, the supporting containing the halide ions is used. Electrolyte solution containing dissolved main electrolyte, and support electrolyte containing no halide ions. It can be replaced with an electrolyte solution. In the formic acid production process, the halogen ions are contained Electrolytic reduction can be performed using an electrolyte solution in which a supporting electrolyte and carbon dioxide are dissolved. The fermentation process is as described above.

[0041] The liquid exchange step in this embodiment involves dissolving the supporting electrolyte containing the halide used in the activation step. The electrolyte solution was then used to dissolve a halogen-free supporting electrolyte used in the formic acid production process. This is the step of replacing with an electrolyte solution. The conductive diamond is activated by the activation step. Regarding the electrode, in order to exchange the electrolyte solution while maintaining the activated state, an activated conductive die It is preferable to replace the electrolyte solution without drying the surface of the Diamond electrode. If the surface dries out, the surface activation effect produced by the activation process may be lost. be.

[0042] A method for replacing the electrolyte solution without drying the electrode surface can be selected from any available options. This is possible, but in certain embodiments, for example, a support containing a halide used in the activation step. To prevent the residue of the electrolyte solution containing the dissolved electrolyte, the supporting electrolyte containing the halogenated compound is used. After replacing it with pure water, the pure water is used in the formic acid production process, and the halogen-free support electricity is used. The dissolved electrolyte solution can be replaced. For example, a flow cell type electrolytic cell can be used. In this case, a liquid transfer pump is used to transfer the electrolyte solution used in the activation process from the electrolyte solution tank. After removing the solution, fill the electrolyte solution tank with pure water, and then circulate the pure water through the electrolytic cell. The procedure involves cleaning the electrolytic cell and electrolyte solution tank, which are then used in the activation process. Dry the electrode surface with an electrolyte solution containing a supporting electrolyte that has been dissolved in it. It can be replaced with pure water without any problems. Also, using the same procedure, the pure water in the electrolyte solution tank can be replaced with pure water. The halogen-free supporting electrolyte used in the formic acid production process is replaced with an electrolyte solution containing dissolved halogens. It is possible. In one embodiment, the liquid delivery pump is an intermittent liquid delivery pump such as a peristaltic pump. It can be a pump that performs this. This can also be used in the formic acid production process. In one embodiment, The desorbent solution can be replaced without drying the electrode surface. In another embodiment, the electrolyte When changing the solution, all or part of the electrode surface may dry out temporarily.

[0043] In the formic acid production process after the liquid exchange, a support electrolyte that does not contain halogen ions and carbon dioxide are used. Electrolytic reduction can be performed with an electrolyte solution containing dissolved ions. A halogen-free support electrode. The dissolution process is not particularly limited; for example, potassium sulfate, potassium carbonate, potassium hydroxide, and hydrogen bicarbonate. Potassium, tetrabutylammonium tetrafluoroborate (TBABF4), potassium perchlorate Mu is one example, but it is not the only one.

[0044] In the formic acid production step of this embodiment, as in the diamond electrode activation step, an external electric current is used. A voltage can be applied between the cathode and anode using a power source mechanism. The external power supply mechanism is particularly limited. Although not specified, a potentiometer-galvanostat can be used. To obtain the desired potential using a vanostat, the potential is directly controlled by a constant potential method. Alternatively, the current value may be controlled by a constant current method to provide the desired potential. A potentiostat or galvanostat may be used as the power source mechanism.

[0045] In this embodiment, the time required for the formic acid production process can be set as appropriate. In the application method, the time spent on the formic acid manufacturing process is 10 minutes or more, 30 minutes or more, 60 minutes or more, or 2 hours or more. Above, 3 hours or more, 6 hours or more, 12 hours or more, 24 hours or more, 48 hours or more, for example, 72 hours or more It is possible, but not limited to this. The time required for the formic acid manufacturing process depends on the supply of carbon dioxide, which is a raw material, and By making the process as long as possible without reducing the rate of formic acid production, the production of formic acid can be increased. This can be increased. In a particular embodiment, the time taken for the formic acid production process is 144 It could be less than an hour, less than 72 hours, less than 48 hours, or less than 24 hours, but is not limited to these.

[0046] In this disclosure, electrolytic reduction is performed using a constant potential method, where the cathode potential relative to the reference electrode is kept constant. Constant voltage method, which keeps the voltage between the cathode and anode constant, and constant current density method, which keeps the current density of the cathode constant. A current-type method may also be used. In one embodiment, the current can be direct current.

[0047] In the case where a constant potential method is adopted in this disclosure, the formic acid production apparatus includes a cathode, an anode and A three-electrode configuration with a reference electrode can be used. Furthermore, a constant voltage or constant current method can be used. When adopted, the formic acid production apparatus shall have a three-electrode configuration having a cathode, an anode, and a reference electrode. Alternatively, a two-electrode configuration having a cathode and an anode but no reference electrode may be used. In the case of adopting the three-electrode configuration, the potential of the reference electrode is within the range described in this disclosure. This disclosure also includes the cathode potential relative to the reference electrode when the two-electrode configuration is adopted. Although not measured, if measured, it includes the fact that the potential of the reference electrode is within the range described in this disclosure. Hmm. In other words, regarding the method for producing formic acid of this disclosure, for example, -2.0 relative to a reference electrode The cathode potential is applied in the range of V to -3.0V, and this does not necessarily mean that the reference electrode is used as the reference in a three-electrode configuration. It does not stipulate that the cathode potential must be measured, and the two-electrode configuration is When a voltage is applied between the cathode and anode, the cathode potential is measured with reference to the reference electrode. If so, and if the potential is consequently within the range described in this disclosure, then the applied voltage is actually Qualitatively, applying a cathode potential in the range of -2.0V to -3.0V to the reference electrode in this disclosure It shall be considered to fall under the following categories.

[0048] In one embodiment, the current of the conductive diamond electrode in the formic acid production reaction is -0.1 mA to -50mA, -0.5mA to -40mA, -1mA to -30mA, -2mA to -20mA, for example -15mA, -10mA, -5mA or It can be set to -2mA.

[0049] In one embodiment, the current density of the conductive diamond electrode in the formic acid production reaction is -0.5mA / cm 2 ~-5mA / cm 2 -0.6mA / cm 2 ~-4.5mA / cm 2 -0.7mA / cm 2 ~-4.0mA / cm 2 -0.8mA / cm 2 ~-3.5mA / cm 2 -0.9mA / cm² 2 ~-3.0mA / cm 2 -1.0mA / cm 2 ~-2.5mA / cm 2 -1.5mA / cm 2 ~-2.0mA / cm 2 For example, -0.5mA / cm 2 -1.0mA / cm 2 -2.0mA / cm 2 -3mA / cm 2 -4mA / cm 2 , or -5mA / cm 2 It can be done this way.

[0050] In one embodiment, the BDD electrode has a diamond containing 0.01-8% w / w boron raw material on the substrate surface. It has a diamond layer with deposited diamond. The substrate is a Si substrate, a glass substrate such as SiO2, or a quartz substrate. Ceramic substrates such as Al2O3, silicon carbide, silicon nitride, tungsten, molybdenum, and nickel. It can be a metal such as titanium. The entire or partial surface of the substrate may be covered with a diamond layer. This is possible. In another embodiment, the electrode portion of the BDD electrode has bulk diamond obtain.

[0051] The size of the electrode portion of a conductive diamond electrode is not particularly limited, but 1 cm 2 Over 5cm 2 That's all. , 10cm 2 More than 50cm 2 The area can be as described above. The entire or partial diamond layer can be divided into two. It can be used in the formic acid production reaction by contacting it with a solution containing carbon oxide. (Electrode area and shape) The state can be determined as appropriate depending on the configuration of the device.

[0052] In one embodiment, the BDD electrode has a Si substrate surface that is mixed with high boron raw material (raw material preparation) It has a diamond layer deposited with diamond (0.01-8% w / w boron raw material). Raw material mixing rates are, for example, 0.01-5% w / w, 0.02-4% w / w, 0.03-3% w / w, 0.04-2% w / w, 0.05- This is approximately 1% w / w, for example, around 0.1 to 1.0% w / w.

[0053] The deposition process of boron-containing diamond onto a substrate is carried out, for example, at 700-900°C for 2-12 hours. It is possible to create conductive diamond thin films using chemical vapor deposition (CVD), for example, microwave It can be fabricated by plasma chemical vapor deposition (MPCVD). For example, a base such as silicon single crystal (100). The plate is placed inside the film deposition apparatus, and a film deposition gas, with high-purity hydrogen gas as the carrier gas, is flowed through it. The gas contains gaseous components including carbon and boron. When microwaves are applied inside to induce a plasma discharge, carbon is released from the carbon source in the film deposition gas. Radicals are generated, and sp is formed on the Si single crystal. 3 Deposition while maintaining the structure and incorporating boron. Thus, a thin film of diamond is formed. Unless otherwise specified, the conductive diamond of this disclosure In particular, boron-doped conductive diamond is sp3 This is the structure. In a particular embodiment, this The disclosed conductive diamond, in particular boron-doped conductive diamond, is sp 2 No structure .

[0054] The thickness of a diamond thin film can be controlled by adjusting the deposition time. The thickness of the thin film can be, for example, 100 nm to 1 mm, 1 μm to 0.1 mm, 1 μm to 10 μm, 2 μm to 20 μm, etc. It is possible.

[0055] The conditions for depositing boron-doped diamond onto the substrate surface should be determined according to the substrate material. For example, the plasma output can be 500W to 7000W, for example, 3kW to 5kW. It can be up to 5kW. If the plasma output is within this range, synthesis will proceed efficiently, and by-products A high-quality conductive diamond thin film with few impurities is formed.

[0056] Any known method can be used as the manufacturing method for BDD electrodes, including the CVD method (hot). In addition to methods using the filament method, there are also vacuum deposition methods, ion plating methods, Methods such as ion implantation can also be used.

[0057] In one embodiment, the BDD electrode may be hydrogen-terminated or cathode-reduced. In the embodiment, the BDD electrode may be oxygen-terminated or anodized. Hydrogen-terminated The specific method involves annealing (heating) a conductive diamond electrode in a hydrogen atmosphere. ) or hydrogen plasma treatment are examples of specific methods for cathode reduction. Then, hydrogen is continuously generated by applying a potential of -3V for 5 to 10 minutes in a 0.1M sodium perchlorate solution. Examples include the above. Specific methods for oxygen termination include the conductive diamond The electrode is annealed (heated) or treated with oxygen plasma in an oxygen atmosphere (air). Examples include: Specific methods of anodizing include, for example, a 0.1M sodium perchlorate solution. One example is applying a potential of +3V inside for 5 to 10 minutes to continuously generate oxygen.

[0058] The electrodes described above are described in Japanese Patent Publication No. 2006-98281 and Japanese Patent Publication No. 2007-139725. , Japanese Patent Publication No. 2011-152324, Japanese Patent Publication No. 2015-172401, or Japanese Patent Publication No. 2 It is disclosed in publication No. 018-141220, etc., and is prepared in accordance with the descriptions in these publications. It is possible.

[0059] The conductive diamond electrode of this disclosure has high thermal conductivity, high hardness, and is chemically inert. It has a wide potential window, low background current, and excellent electrochemical stability.

[0060] An example of the apparatus of this disclosure is shown in Figure 1. The apparatus comprises a cathode, an anode, Cathode tank, anode tank, solid electrolyte membrane, external power supply mechanism, carbon dioxide supply It has a supply unit, a liquid transfer pump, a first storage tank, and a second storage tank. In Figure 1, the cathode is a BDD electrode. The anode is a metal electrode, and can be made of silver, gold, platinum, carbon, stainless steel, iridium, or palladium. Platinum, osmium, rhodium, ruthenium, etc., can be used. In Figure 1, the anode is a platinum electrode. Carbon dioxide is supplied from the carbon dioxide supply unit to the first storage tank. In some cases, carbon dioxide is supplied to the first storage tank. It can be connected to a sampling bag for collecting gaseous components. The sampling bag is These could be bags made of aluminum, fluororesin, polyvinyl fluorocarbon, polyester, etc. However, this is not the only example. The solid electrolyte membrane is sandwiched between the cathode and anode baths. For example, the sulfonic acid group in Nafion® film (THE CHEMOURS COMPANY FC LLC) Fluorine-based polymer membranes, sulfo-based ion exchange resin membranes, Flemion™ ion exchange membranes This may include, but is not limited to, Aciplex™ ion exchange membranes. The solid electrolyte membrane is connected to the cathode cell. Because it is separated from the anode chamber, the formic acid produced at the cathode is not oxidized at the anode. The cathode chamber is two It contains a primary electrolyte solution that may contain carbon oxide. The primary electrolyte solution is delivered by a liquid transfer pump. It is supplied from the first storage tank. In Figure 1, the reference electrode is located in the cathode tank. The anode tank is located in the second tank. It contains the desaturation solution. The second electrolyte solution is supplied from the second storage tank by a liquid transfer pump. BD The D electrode is placed in the cathode bath so as to be in contact with the first electrolyte solution. The anode is in the second electrolyte solution. It is placed in the anode bath so as to be in contact with the first electrolyte solution and the second electrolyte solution, even if they are the same. That's fine.

[0061] In one embodiment, the apparatus of the present disclosure may optionally include means for controlling the current to a constant value (ga It may also be equipped with a rubanostat (also called an ampelostat). This allows the current to be controlled to a constant level during the formic acid production reaction. In one embodiment, The apparatus of the invention may further include a reference electrode. Examples of the reference electrode include a silver-silver chloride electrode. In this case, the apparatus of the present invention may further include a potentiostat.

[0062] In one embodiment, the electrolytic reduction of carbon dioxide can be carried out by the following procedure: (1) The working electrode is a BDD electrode, and the electrolytic cell is equipped with a BDD electrode and a counter electrode. A reference electrode is provided. (2) Inject the electrolyte solution into the reaction apparatus. The electrolyte solution for the anode and the cathode The electrolyte solution used for (D) may be the same as or different from that used for (D). (3) If necessary, nitrogen is bubbled in to remove oxygen from the aqueous solution. (4) Bubble carbon dioxide into the aqueous solution. (5) If necessary, adjust the pH of the electrolyte solution to a pH suitable for the formic acid production reaction. (6) Activate the BDD electrode (activation step). (7) Electrolytic reduction of carbon dioxide is performed (formic acid production step).

[0063] In certain embodiments, a liquid exchange step can be performed between steps (6) and (7). Reduction can be carried out at room temperature or low temperature. Electrolytic reduction can be carried out at atmospheric pressure or high pressure.

[0064] In one embodiment, the apparatus of the present disclosure may have an instruction manual. The instruction manual is conductive The activation conditions for activating the diamond electrode (e.g., applied potential, current density, etc.) are described herein. This may include a description of the conditions under which the device is described. The apparatus of this disclosure is a conductive diamond under such conditions. A program that controls the activation of electrodes and the formic acid production reaction, or an implementation of said program. It may include software that enables conductive diamonds. That is, in one embodiment, the present disclosure enables conductive diamonds. A control program that performs the activation of the electrode and the formic acid production reaction, or a software that implements said program. The software is provided. In some embodiments, the disclosure also provides conductive diamond electrodes. A control program that performs the activation and formic acid production reaction, or software that implements said program The present invention provides a formic acid production apparatus equipped with A. In one embodiment, a program or software The data may be stored on a recording medium. In one embodiment, a program or software This may be a cloud application. In another embodiment, a program or software The software is stored in the cloud and controls the formic acid production apparatus of this disclosure by appropriate implementation means. It can be controlled. In these embodiments, the program or software is used in the production of formic acid as disclosed herein. The device's hardware, for example, is temporarily stored in memory, and controls the formic acid production apparatus of this disclosure. Therefore, these embodiments also refer to the formic acid production apparatus of the present disclosure, which is said to be the program or software. This applies to cases where the wear is provided.

[0065] The method or apparatus disclosed herein can produce formic acid with high Faraday efficiency. Araday efficiency is the ratio of the amount of charge used to produce the reaction product to the total amount of reaction charge (P -Century) is: Faraday efficiency (%) = 100 × (amount of charge used to form the reaction product) / (total amount of reaction charge) In this specification, when referring to the formic acid production efficiency, unless otherwise specified, it refers to the formic acid produced. This refers to the Faraday efficiency for this purpose.

[0066] The conductive diatoms are produced by an electrolytic reduction process in an electrolyte solution containing carbon dioxide and potassium chloride. The surface of the diamond electrode can be activated. This activation process can bring the voltage down to -2.2V or below. Even with a small electrode potential, a sufficient amount of formic acid can be produced. Through a chemical process, an electrolyte solution containing carbon dioxide and potassium sulfate, but without potassium chloride, is obtained. The Faraday efficiency of formic acid production in the electrolytic reduction process is significantly improved. [Examples]

[0067] The present invention will be described in more detail below using examples. However, the technical scope of the present invention is limited. This is not limited in any way by those examples.

[0068] [Example 1] Boron-doped diamond electrodes are processed using a microwave plasma CVD system (Cornes Technology). It was manufactured using a (model AX5400) manufactured by the company. Specifically, the pretreatment was performed on a silicon substrate Si( 100) The surface is nucleated with diamond powder, and then 50 ml of acetone is used as a carbon source. Using 0.4 ml of trimethoxyborate (boron concentration 0.1%), the plasma output was set to 500. The film was deposited on the substrate under the conditions of 0W for 6 hours and a pressure of 115 Torr. The electrolytic cell shown in Figure 1 is also used. The two-chamber flow cell electrolytic cell described was used.

[0069] Activation process As an activation step, a conductive diamond electrode (electrode area 9.62 cm²) is placed on the cathode. 2 ), platinum at the anode Electrode (electrode area 9.62cm 2 ), a silver-silver chloride electrode is used as the reference electrode, and a cation exchange membrane is used as the diaphragm. An electrolytic cell equipped with a Nafion membrane was used. After bubbling nitrogen as the cathode solution for 30 minutes, two 50 0.5M potassium chloride aqueous solution saturated with carbon dioxide by bubbling carbon dioxide for 60 minutes Using ml of 1.0 M potassium hydroxide aqueous solution as the anode, electrolytic reduction of carbon dioxide was performed. During electrolytic reduction, the electrolytes for the cathode and anode were transferred using a liquid transfer pump. The solution was circulated. Electrolytic reduction involved bubbling carbon dioxide into a 0.5M potassium chloride aqueous solution, which served as the cathode solution. While continuing the process, the current density was -1.0 mA / cm². 2 Constant current electrolysis was performed for 60 minutes. After the activation process... The 0.5M potassium chloride aqueous solution, which is the cathode solution, was analyzed by high-performance liquid chromatography. The amount of acid produced was determined.

[0070] Formic acid production process As part of the formic acid production process, carbon dioxide is bubbled into a 0.5 M potassium chloride aqueous solution, which is the cathode solution. While continuing the process, a constant current electrolysis was performed by applying a cathode potential of -2.0V to the silver-silver chloride reference electrode. The process was carried out for a certain amount of time. The 0.5M potassium chloride aqueous solution, which is the cathode solution after the formic acid production process, was subjected to high-performance liquid chromatography. The amount of formic acid produced was determined by analyzing the data using graphography and comparing it to the amount of formic acid produced after the activation process.

[0071] [Example 2] The current density during the activation process is -2.0 mA / cm². 2 Except for the change, the method is the same as in Example 1 for diacidation. Formic acid was produced by the electrolytic reduction of carbon dioxide.

[0072] [Comparative Example 1] This is the same as Example 1, except that the activation step was omitted and the conductive diamond electrode was not activated. Formic acid was produced by electrolytic reduction of carbon dioxide using a similar method.

[0073] [Comparative Example 2] The current density during the activation process is -0.1 mA / cm². 2 Except for the change, the method is the same as in Example 1 for diacidation. Formic acid was produced by the electrolytic reduction of carbon dioxide.

[0074] The results are shown in Figures 2-1 and 2-2. Since electrolysis is performed using a constant potential method, the electric currents shown in the figures are... The greater the increase in fluid density, the more formic acid is generated. The active conductivity of the conductive diamond electrode in Comparative Example 1. Compared to the case where no curing was performed, the current density was increased by the activation step as shown in Examples 1 and 2. It can be seen that the degree has increased. Comparative Example 2 has undergone an activation process, but the current density has increased. Because the size is small, it can be said that the activation effect is not necessarily sufficient.

[0075] Furthermore, Figure 3 shows the Faraday efficiency of formic acid production in the formic acid production process. The ratio represents how much of the current that flowed in Examples 1 and 2 and Comparative Examples 1 and 2 was used for formic acid production. This indicates the degree of the process, and a higher Faraday efficiency suggests a higher selectivity for formic acid production.

[0076] As shown in Figure 3, compared to the case where the conductive diamond electrode in Comparative Example 1 was not activated, In contrast, as shown in Examples 1 and 2, the current density is increased by the activation process, It can be seen that the Faraday efficiency has also improved. As a result, the amount of formic acid produced by the activation process is It can be seen that has increased significantly. Note that in Comparative Example 2, although an activation process was performed, The small increase in fluid density and improvement in Faraday efficiency suggests that the activation effect is not necessarily sufficient. I determined that there wasn't one.

[0077] [Example 3] Next, we investigated the case where different electrolyte solutions were used in the activation step and the formic acid production step. A conductive diamond electrode was prepared in the same manner as in Example 1, and the same electrolytic cell as in Example 1 was used. Ta.

[0078] Activation process As an activation step, a conductive diamond electrode (electrode area 9.62 cm²) is placed on the cathode. 2 ), platinum at the anode Electrode (electrode area 9.62cm 2 ), a silver-silver chloride electrode is used as the reference electrode, and a cation exchange membrane is used as the diaphragm. An electrolytic cell equipped with a Nafion membrane was used. After bubbling nitrogen as the cathode solution for 30 minutes, two 50 0.5M potassium chloride aqueous solution saturated with carbon dioxide by bubbling carbon dioxide for 30 minutes Using ml and 50 ml of 0.5 M potassium hydroxide aqueous solution as the anode, electrolytic reduction of carbon dioxide was performed. Electrolytic reduction involves bubbling carbon dioxide into a 0.5M potassium chloride aqueous solution, which is the cathode solution. While continuing, the current density was -2.0 mA / cm². 2 Constant current electrolysis was performed for 60 minutes.

[0079] Liquid exchange process As part of the fluid exchange process, care must be taken to prevent the conductive diamond electrode, which serves as the cathode, from drying out. Then, using a liquid transfer pump, replace the 0.5M potassium chloride solution in the cathode solution tank with 50 ml of pure water. Then, pure water was circulated through the electrolytic cell. After repeating this operation three times, the cathode was treated using a liquid transfer pump. Replace the pure water in the liquid tank with 50 ml of 0.25 M potassium sulfate solution, and add 0.25 M potassium sulfate to the electrolytic cell. The aqueous solution was circulated. After repeating this operation twice, the 0.25M potassium sulfate solution in the cathode solution tank was used. For 50 ml of solution, perform nitrogen bubbling for 30 minutes, followed by carbon dioxide bubbling for 30 minutes. The carbon dioxide solution was saturated.

[0080] Formic acid production process As part of the formic acid production process, carbon dioxide is added to 50 ml of 0.25 M potassium sulfate aqueous solution, which serves as the cathode solution. While continuing bubbling, a current density of -2.0 mA / cm² was applied to the silver-silver chloride reference electrode. 2 Constant current electric The solution was analyzed for 4 hours. Cathode solution was sampled every hour, and high-performance liquid chromatography was performed. The amount of formic acid produced was determined by analyzing it using a ionograph.

[0081] [Comparative Example 3] This is the same as Example 3, except that the activation step was omitted and the conductive diamond electrode was not activated. Formic acid was produced by electrolytic reduction of carbon dioxide using a similar method.

[0082] The results are shown in Figure 4. A higher Faraday efficiency indicates higher selectivity formic acid production. In Comparative Example 3 and Comparative Example 3, a constant current method is employed, so the higher the Faraday efficiency, the higher the formic acid It can be said that the amount produced is high.

[0083] If the conductive diamond electrode in Comparative Example 3 was not activated, the formic acid Faraday The efficiency is only 10% after one hour of electrolysis. Over time, the Faraday efficiency gradually increases. However, even after 4 hours of electrolysis, the percentage is only about 20%. As shown in Example 3, conductive die Activation of the Diamond electrode resulted in a Faraday efficiency of 95% for formic acid production after 1 hour, indicating the formation of formic acid. The quantity increased dramatically.

[0084] [Example 4] Next, we investigated the applied potential in the formic acid production process. The cathode in the formic acid production process in Example 1. In this embodiment, where a potential of -2.0V is applied, constant current is applied at -1.8V, -1.9V, and -2.2V. The solution was run for 3 hours. Other conditions were the same as in Example 1.

[0085] Figure 5 shows the case when a cathode potential of -1.8V is applied, and Figure 6 shows the case when a cathode potential of -1.9V is applied. As shown above, Figure 7 shows the case when a cathode potential of -2.2V is applied. Under all application conditions, activation When the electrodes were used, formic acid was efficiently produced. Furthermore, from these results, It is thought that formic acid is also produced with high Faraday efficiency when acid generation is carried out at -1.5V. It can be done. [Industrial applicability]

[0086] The formic acid production apparatus and method of the present invention enable the efficient production of formic acid. [Explanation of symbols]

[0087] 1 cathode 2 Anode 3 Reference electrode 4 Solid electrolyte membrane 5 Cathode bath 6 Anode tank 7. Carbon Dioxide Supply Department 8. Liquid transfer pump 9 1st storage tank 10 Second storage tank 11 External power supply

Claims

1. This was a method for producing formic acid by electrolytically reducing carbon dioxide using an electrolytic cell equipped with an anode and a cathode. hand, The cathode is a conductive diamond electrode, In an electrolyte solution containing dissolved carbon dioxide and a supporting electrolyte, a voltage of -2.0V to -3.0V is applied relative to the reference electrode. Apply cathode potential within the specified range, and set it to -0.5 mA / cm². 2 By electrolysis at the above current density, the conductivity An activation process including activating a diamond electrode, The activated conductive diamond electrode serves as the cathode, and the system contains carbon dioxide and a supporting electrolyte. Perform electrolytic reduction in an electrolyte solution at a cathode potential of -1.5V to -2.2V relative to the reference electrode. A formic acid production process including, A method for producing formic acid containing [the specified ingredient].

2. Either the supporting electrolyte used in the activation step or the supporting electrolyte used in the formic acid production step The preparation of formic acid according to claim 1, characterized in that the supporting electrolyte contains a halogenated compound. Construction method.

3. The supporting electrolyte containing the halogen is potassium chloride, as described in the second characteristic. The method for producing formic acid as described above.

4. This was a method for producing formic acid by electrolytically reducing carbon dioxide using an electrolytic cell equipped with an anode and a cathode. hand, The cathode is a conductive diamond electrode, In an electrolyte solution containing carbon dioxide and a supporting electrolyte, relative to the reference electrode Then, apply a cathode potential in the range of -2.0V to -3.0V, and -0.5 mA / cm 2 Electrolysis is performed at the above current density. An activation step including activating the conductive diamond electrode by the means thereof, An electrolyte solution obtained by dissolving the support electrolyte containing the aforementioned halogen, and a support electrolyte that does not contain halogen. A solution exchange step, which includes replacing the retained electrolyte with an electrolyte solution in which the retained electrolyte has been dissolved, Electrolytic reduction is performed using an electrolyte solution containing the aforementioned halogen-free supporting electrolyte and carbon dioxide. A formic acid production process that includes the following: A method for producing formic acid containing [the specified ingredient].

5. The supporting electrolyte containing the halogen is potassium chloride, and the supporting electrolyte not containing the halogen is potassium chloride. A method for producing formic acid according to claim 4, characterized in that the supporting electrolyte is potassium sulfate.

6. The method according to any one of claims 1 to 5, wherein the activation step is performed for 30 minutes or more.

7. The current density of the cathode potential applied during the activation process is -0.5 mA / cm 2 More than -5.0mA / cm 2 The method according to any one of claims 1 to 6, which is as follows:

8. A formic acid production apparatus that produces formic acid by reducing carbon dioxide at the cathode, The electrolytic cell has an anode and a cathode, The cathode is a conductive diamond electrode, The conductive diamond electrode is in an electrolyte solution containing carbon dioxide and a supporting electrolyte. A cathode potential in the range of -2.0V to -3.0V is applied to the irradiating electrode, and -0.5 mA / cm 2 The above current density It is activated by electrolyzing carbon dioxide. The aforementioned formic acid production apparatus.

9. The conductive diamond electrode is in an electrolyte solution in which carbon dioxide and a supporting electrolyte are dissolved. A cathode potential in the range of -2.0V to -3.0V is applied to the reference electrode, and -0.5 mA / cm 2 The above current density The invention described in claim 8, which is activated by electrolyzing carbon dioxide at a temperature of 30 degrees for 30 minutes or more. Device.

10. The conductive diamond electrode is in an electrolyte solution in which carbon dioxide and a supporting electrolyte are dissolved. A cathode potential in the range of -2.0V to -3.0V is applied to the reference electrode, and -0.5 mA / cm 2 Above -5.0mA / cm 2 Activated by electrolyzing carbon dioxide at the following current densities, claim 8 or This is the device described in section 9.

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