Carbon material manufacturing method

Abstract

The present disclosure provides a method for producing a carbon material, wherein a carbon material is obtained by electrolytically reducing carbon dioxide in an electrolytic reduction apparatus that comprises an anode electrode, a cathode electrode and an electrolyte solution that contains carbon dioxide. With respect to this method for producing a carbon material, the electrolyte solution contains an ionic liquid.

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing a carbon material, specifically, a method for producing a carbon material by electrolytic reduction of carbon dioxide. [Background technology]

[0002] As one of the countermeasures against global warming in recent years, there is a demand for the development of carbon recycling technology, which regards carbon dioxide as a carbon resource, captures it, and reuses it as various carbon compounds.

[0003] As such a technique, a method has been proposed in which carbon dioxide is decomposed to fix the carbon in the carbon dioxide, for example, a method in which diamond is deposited on a cathode by electrolyzing carbon dioxide using a high-temperature molten salt (see Patent Document 1). Furthermore, when a mixture of two ionic liquids, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide (DEME-TFSI) and 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4), is used to electrolyze carbon dioxide using a Ni electrode as the cathode and a Pt electrode as the anode, it has been suggested that a carbon material will be produced on the cathode (see Non-Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-89230 [Non-patent literature]

[0005] [Non-Patent Document 1] 49th International Conference on Environmental Systems ICES-2019-141 2019, Boston Summary of the Invention [Problem to be solved by the invention]

[0006] The former method, which uses high-temperature molten salt, poses cost challenges due to the energy required for heating and the need for expensive heat-resistant equipment. Furthermore, the need for high-temperature operation poses safety challenges. The latter method, on the other hand, examined various mixture ratios and electrolysis potentials of two ionic liquids, DEME-TFSI and BMIM-BF4. Electrolysis was performed at a DEME-TFSI / BMIM-BF4 mixture ratio of 25:75 (mol%) at -1.0 V (vs. a silver pseudo-reference electrode). SEM / EDS analysis of the cathode product suggested carbon formation. However, Raman spectra and other data were not obtained, so details, including whether carbon actually precipitated, are unknown. Furthermore, the use of a pseudo-reference electrode poses challenges, making the exact electrolysis potential unclear.

[0007] An object of the present disclosure is to provide a method for producing a carbon material by simply reducing carbon dioxide with low energy. [Means for solving the problem]

[0008] The present disclosure includes the following aspects. [1] A method for producing a carbon material, in which a carbon material is obtained by electrolytic reduction of carbon dioxide in an electrolytic reduction device having an anode electrode, a cathode electrode, and an electrolyte solution containing carbon dioxide, wherein the electrolyte solution contains an ionic liquid. [2] The method for producing a carbon material according to the above [1], wherein the anode electrode is a Pt electrode and the cathode electrode is an Ag electrode. [3] The method for producing a carbon material according to [1] or [2] above, wherein the ionic liquid is an imidazolium-based ionic liquid, an aromatic ionic liquid, a pyrrolidinium-based ionic liquid, an ammonium-based ionic liquid, a piperidinium-based ionic liquid, or a quaternary phosphonium-based ionic liquid. [4] The ionic liquid is N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium tetrafluoroborate (DEME-BF4), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide (DEME-TFSI), N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP 13 -TFSI), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMIM-TFSI), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4), triethylpentylphosphonium bis(trifluoromethanesulfonyl)imide (P 2225 -TFSI), triethyloctylphosphonium bis(trifluoromethanesulfonyl)imide (P 2228 -TFSI), or tributylmethylphosphonium bis(trifluoromethanesulfonyl)imide (P 4441 -TFSI). [5] The method for producing a carbon material according to any one of the above [1] to [4], wherein the electrolytic solution contains a supporting electrolyte. [6] A method for electrolytically reducing carbon dioxide in an electrolytic reduction device having an anode electrode, a cathode electrode, and an electrolyte containing carbon dioxide, wherein the method selectively electrolytically reduces carbon dioxide to a carbon material selected from the group consisting of diamond, graphite, glassy carbon, amorphous carbon, carbon nanotubes, carbon nanohorns, and graphene by applying a potential between the anode electrode and the cathode electrode. [7] The electrolytic reduction method according to [6] above, wherein the electrolytic solution contains an ionic liquid. [8] A method for electrolytic reduction of carbon dioxide in an electrolytic reduction device having an anode electrode, a cathode electrode, and an electrolyte solution containing carbon dioxide, wherein the electrolyte solution contains an ionic liquid. [9] The anode electrode is a Pt electrode, and the cathode electrode is an Ag electrode. The electrolytic reduction method according to any one of the above [6] to [8].

[10] The electrolytic reduction method according to any one of the above [7] to [9], wherein the ionic liquid is an imidazolium-based ionic liquid, an aromatic ionic liquid, a pyrrolidinium-based ionic liquid, an ammonium-based ionic liquid, a piperidinium-based ionic liquid, or a quaternary phosphonium-based ionic liquid.

[11] The ionic liquid is N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium tetrafluoroborate (DEME-BF4), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide (DEME-TFSI), N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP 13 -TFSI), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMIM-TFSI), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4), triethylpentylphosphonium bis(trifluoromethanesulfonyl)imide (P 2225 -TFSI), triethyloctylphosphonium bis(trifluoromethanesulfonyl)imide (P 2228 -TFSI), or tributylmethylphosphonium bis(trifluoromethanesulfonyl)imide (P 4441 -TFSI).

[12] The electrolytic reduction method according to any one of the above [6] to

[11] , wherein the electrolytic solution contains a supporting electrolyte.

[13] The electrolytic reduction method according to

[12] above, wherein the supporting electrolyte is KHCO3, KHPO4, LiBF4, LiPF6, LiClO4, LiAsF6, LiTf, LiTFSI, LiFSI, K2CO3, Li2CO3, Na2CO3, or NaHCO3.

[14] The electrolytic reduction method according to the above

[12] to

[13] , wherein the supporting electrolyte is LiBF4, LiPF6, LiTFSI, or LiFSI.

[15] The electrolytic reduction method according to any one of the above

[12] to

[14] , wherein the concentration of the supporting electrolyte contained in the ionic liquid is from 0.01 mol / L to a saturated concentration.

[16] The electrolytic reduction device further includes a reference electrode, and the reference electrode is Ag + The electrolytic reduction method according to any one of the above [6] to

[15] , wherein the cathode electrode is a Ag / Ag electrode, and the potential of the cathode electrode is −5.0V to −0.5V.

[17] The electrolytic reduction method according to any one of the above [6] to

[16] , wherein the temperature of the electrolytic solution is 0 to 100°C.

[18] The electrolytic reduction method according to any one of the above [6] to

[17] , wherein the carbon dioxide is reduced to diamond.

[19] An electrolytic reduction device having an anode electrode, a cathode electrode, and an electrolyte solution containing carbon dioxide, wherein the electrolyte solution contains an ionic liquid.

[20] The anode electrode is a Pt electrode, The cathode electrode is an Ag electrode. The electrolytic reduction device according to the above

[19]

[21] The electrolytic reduction apparatus according to the above

[19] to

[20] , wherein the ionic liquid is an imidazolium-based ionic liquid, an aromatic ionic liquid, a pyrrolidinium-based ionic liquid, an ammonium-based ionic liquid, a piperidinium-based ionic liquid, or a quaternary phosphonium-based ionic liquid.

[22] The ionic liquid is N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium tetrafluoroborate (DEME-BF4), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide (DEME-TFSI), triethylpentylphosphonium bis(trifluoromethanesulfonyl)imide (P 2225 -TFSI), triethyloctylphosphonium bis(trifluoromethanesulfonyl)imide (P 2228 -TFSI), or tributylmethylphosphonium bis(trifluoromethanesulfonyl)imide (P 4441The electrolytic reduction device according to any one of the above

[19] to

[21] , wherein the catalyst is a TFSI.

[23] The electrolytic reduction device according to any one of the above

[19] to

[21] , wherein the electrolytic solution contains a supporting electrolyte.

[24] The electrolytic reduction device according to

[23] above, wherein the supporting electrolyte is KHCO3, KHPO4, LiBF4, LiPF6, LiClO4, LiAsF6, LiTf, LiTFSI, LiFSI, K2CO3, Li2CO3, Na2CO3, or NaHCO3.

[25] The electrolytic reduction apparatus according to the above

[23] to

[24] , wherein the supporting electrolyte is LiBF4, LiPF6, LiTFSI, or LiFSI.

[26] The electrolytic reduction device according to any one of the above

[18] to

[20] , wherein the concentration of the supporting electrolyte contained in the ionic liquid is from 0.01 mol / L to a saturated concentration.

[27] The electrolytic reduction apparatus according to any one of the above

[19] to

[26] , wherein the carbon dioxide is reduced to diamond. [Effects of the Invention]

[0009] According to the present disclosure, a carbon material can be produced by reducing carbon dioxide efficiently at low cost. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram schematically illustrating an experimental device used in an experiment. [Figure 2] 1 is a cyclic voltammogram illustrating the reduction behavior of carbon dioxide during electrolytic reduction carried out using electrolyte A. [Figure 3] 1 is a graph showing the change in current over time during constant-potential electrolytic reduction carried out using electrolytic solution A. [Figure 4] 1 is a graph showing the results of measuring the Raman spectrum of the Ag electrode surface after constant-potential electrolytic reduction carried out using electrolytic solution A. [Figure 5] 1 is a cyclic voltammogram illustrating the reduction behavior of carbon dioxide during electrolytic reduction carried out using electrolyte B. [Figure 6] 1 is a graph showing the change in current over time during constant-potential electrolytic reduction at −2.60 V carried out using electrolytic solution B. [Figure 7] 1 is a graph showing the change in current over time during constant-potential electrolytic reduction at −3.00 V carried out using electrolytic solution B. [Figure 8] 1 is a graph showing the change in current over time during constant-potential electrolytic reduction at −3.15 V carried out using electrolytic solution B. [Figure 9] 1 is a graph showing the change in current over time during constant-potential electrolytic reduction at −3.25 V carried out using electrolytic solution B. [Figure 10] 1 is a graph showing the change in current over time during constant-potential electrolytic reduction at −3.70 V carried out using electrolytic solution B. [Figure 11] 1 is a graph showing the results of measuring the Raman spectrum of the Ag electrode surface after electrolytic reduction at a constant potential of −2.60 V using electrolytic solution B. [Figure 12] 1 is a graph showing the results of measuring the Raman spectrum of the Ag electrode surface after electrolytic reduction at a constant potential of −3.00 V using electrolytic solution B. [Figure 13] 1 is a graph showing the results of measuring the Raman spectrum of the Ag electrode surface after electrolytic reduction at a constant potential of −3.15 V using electrolytic solution B. [Figure 14] 1 is a graph showing the results of measuring the Raman spectrum of the Ag electrode surface after electrolytic reduction at a constant potential of −3.25 V using electrolytic solution B. [Figure 15] 1 is a graph showing the results of measuring the Raman spectrum of the Ag electrode surface after electrolytic reduction at a constant potential of −3.70 V using electrolytic solution B. [Figure 16] 1 is a cyclic voltammogram illustrating the reduction behavior of carbon dioxide during electrolytic reduction in Example 12 and Comparative Example 3. [Figure 17] 1 is a cyclic voltammogram illustrating the reduction behavior of carbon dioxide during electrolytic reduction in Example 13 and Comparative Example 4. [Figure 18]1 is a cyclic voltammogram illustrating the reduction behavior of carbon dioxide during electrolytic reduction in Example 14 and Comparative Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present disclosure will be described in detail below.

[0012] The present disclosure provides a method for producing a carbon material by electrolytically reducing carbon dioxide in an electrolytic reduction device having an anode electrode, a cathode electrode, and an electrolyte solution containing carbon dioxide, and also provides such an electrolytic reduction device.

[0013] The method for producing the carbon material of the present disclosure utilizes electrolytic reduction.

[0014] Thus, the present disclosure also provides a method for electrolytically reducing carbon dioxide in an electrolytic reduction device having an anode electrode, a cathode electrode, and an electrolyte solution containing carbon dioxide.

[0015] The electrolytic reduction is usually carried out in an electrolytic cell, which may be any of a single-chamber type, a two-chamber type, a PEM (solid polymer membrane) type, a flow type, and a bipolar type.

[0016] The electrolytic reduction device used in the electrolytic reduction method includes an anode electrode, a cathode electrode, and an electrolyte solution containing carbon dioxide. The anode electrode and the cathode electrode are arranged so that at least a portion of them is in contact with the electrolyte solution. In such a device, by applying a potential between the anode electrode and the cathode electrode, carbon dioxide is reduced to a carbon material at the cathode electrode, causing a current to flow.

[0017] The anode electrode is not particularly limited, but examples thereof include electrodes of Pt, conductive metal oxides, glassy carbon, boron-doped diamond, etc. Examples of conductive metal oxide electrodes that can be used include transparent conductive electrodes called ITO electrodes, in which a mixed oxide of indium and tin is formed on glass, and DSA electrodes (trademark of De Nora Permelec Electrodes, Inc.), in which an oxide of a platinum group metal such as ruthenium or iridium is formed on a substrate such as titanium.

[0018] In a preferred embodiment, the anode electrode may be a Pt electrode. Using a Pt electrode as the anode electrode enables stable electrolytic reduction over a long period of time at a lower cell voltage. A lower cell voltage reduces the power required for electrolytic reduction, resulting in a lower environmental impact.

[0019] The cathode electrode is not particularly limited, but examples include electrodes of Ag, Cu, Ni, Pb, Hg, Tl, Bi, In, Sn, Cd, Au, Zn, Pd, Ga, Ge, Ni, Fe, Pt, Pd, Ru, Ti, Cr, Mo, W, V, Nb, Ta, and Zr, and alloys thereof, as well as electrodes of carbon materials such as glassy carbon, pyrolytic graphite, plastic-formed carbon, and conductive diamond.

[0020] In a preferred embodiment, the cathode electrode may be an Ag electrode. Use of an Ag electrode as the cathode electrode enables stable electrolytic reduction over a long period of time at a lower cell voltage.

[0021] In a more preferred embodiment, the anode electrode may be a Pt electrode and the cathode electrode may be an Ag electrode. Using a Pt electrode as the anode electrode and an Ag electrode as the cathode electrode enables stable electroreduction over a long period of time at a lower cell voltage, and also allows the electroreduction to proceed more efficiently.

[0022] In a preferred embodiment, the anode electrode and / or the cathode electrode is a plate electrode. Preferably, the cathode electrode is a plate electrode, and more preferably, both the anode electrode and the cathode electrode are plate electrodes.

[0023] The electrolyte preferably contains at least an ionic liquid. By including an ionic liquid in the electrolyte, electrolytic reduction proceeds efficiently at a lower temperature. Here, the ionic liquid refers to an ionic substance that is in a molten state at least at 40°C, preferably at 25°C, and that is composed of a cation moiety and an anion moiety.

[0024] The ionic liquid may preferably be an ionic liquid having a melting point of room temperature or lower, specifically 25° C. or lower, preferably 20° C. or lower. Use of an ionic liquid having a melting point of room temperature or lower enables efficient electrolytic reduction at room temperature, and eliminates the need to heat the electrolyte during electrolytic reduction.

[0025] The ionic liquid preferably has a wide potential window, i.e., high oxidation-reduction resistance. By using an ionic liquid that is stable against the oxygen evolution reaction at the anode and the carbon dioxide reduction reaction at the cathode in this production method, electrolytic reduction can be carried out efficiently for a long period of time.

[0026] The ionic liquid preferably has a high solubility of carbon dioxide. By using an ionic liquid with a high solubility of carbon dioxide, electrolytic reduction can be carried out more efficiently.

[0027] Examples of the ionic liquid include imidazolium-based ionic liquids, aromatic-based ionic liquids, pyrrolidinium-based ionic liquids, ammonium-based ionic liquids, piperidinium-based ionic liquids, and quaternary phosphonium-based ionic liquids.

[0028] The imidazolium-based ionic liquid is not particularly limited, but examples thereof include hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (C1C6Im-NTf2), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMIM-TFSI, C1C4Im-NTf2), 1-hexyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide (C1C1Im-NTf2), 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide (C1C1Im-NTf2), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (C1C2Im-NTf2), 1-nonyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (C1 C8Im-NTf2), 1-nonyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide (C1C1C8Im-NTf2), 1-propyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide (C1C1C3Im-NTf2), 1-ethyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide (EVIm-NTf2), 1,2-dimethyl-1-propylimidazolium bis(trifluoromethanesulfonyl)imide (DMPI-TFSI), 1,2-dimethyl-1-propylimidazolium tris(trifluoromethylsulfonyl)imide (DMPI-Me), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4), 1-ethyl-3-methylimidazolium chloride (EMI-C l ), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI), 1-ethyl-3-methylimidazolium bis((perfluoroethyl)sulfonyl)imide (EMI-BETI), 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-TfO), 1-ethyl-3-methylimidazolium trifluoroacetate (EMI-TA), 1-ethyl-3-methylimidazolium 2.3 hydrogen fluoride (EMI-F(HF) 2.3), 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMI-FSI), 1-ethyl-3-methylimidazolium hexafluorophosphate (EMI-PF6), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4), 1-butyl-3-methylimidazolium trifluoroacetate (BMIM-TA), 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6), 1-butyl-3-methylimidazolium bis(trifluoromethyl)imide 1-octyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMIM-TFSI), 1-octyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (C8MI-TFSI), 1-decyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (C8MI-TFSI), 1,2-dimethyl-3-propylimidazolium bis(trifluoromethanesulfonyl)imide (DMPI-TFSI), 1,2-dimethyl-3-propylimidazolium bismethide (DMPI-Me), and the like.

[0029] The aromatic ionic liquid is not particularly limited, but examples thereof include diphenylmethane diisocyanate bis(trifluoromethanesulfonyl)imide (MDI-TFSI).

[0030] The ammonium-based ionic liquid is not particularly limited, but examples thereof include N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium tetrafluoroborate (DEME-BF), trimethylpropylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI), tetraethylammonium 2,2,2-trifluoro-N-(trifluoromethylsulfonyl)acetamide (TEA-(CFCO)(CFSO)N), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide (DEME-TFSI), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide (DEME-NTF), and N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(fluorosulfonyl)imide (DEME-FSI).

[0031] The pyrrolidinium-based ionic liquid is not particularly limited, but examples thereof include N-methyl-N-propylpyrrolidinium hexafluorophosphate (P 13 -PF6), N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (P 13 -TFSI), N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (P 13 -FSI), N-methyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (P 14 -FSI) etc.

[0032] The piperidinium-based ionic liquid is not particularly limited, but examples thereof include N-propyl-N-methylpiperidinium bis(trifluoromethanesulfonyl)imide (PMPip-CFSO)N), N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP 13 -TFSI) etc.

[0033] The quaternary phosphonium ionic liquid is not particularly limited, but for example, triethylpentylphosphonium bis(trifluoromethanesulfonyl)imide (P 2225 -TFSI), triethyloctylphosphonium bis(trifluoromethanesulfonyl)imide (P 2228 -TFSI), tributylmethylphosphonium bis(trifluoromethanesulfonyl)imide (P 4441 -TFSI), triethylmethoxymethylphosphonium bis(trifluoromethanesulfonyl)imide (P 222 ( 1O1 )-TFSI) etc.

[0034] In a preferred embodiment, the ionic liquid is N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium tetrafluoroborate (DEME-BF), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide (DEME-TFSI), N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP 13 The ionic liquid may be DEME-BF4, DEME-TFSI, PP 13 By using -TFSI, BMIM-TFSI, or BMIM-BF4, the electrolytic reduction proceeds at a lower temperature and efficiently.

[0035] The above ionic liquids may be used alone or in combination of two or more.

[0036] In one embodiment, the electrolyte comprises an ionic liquid.

[0037] In another embodiment, the electrolytic solution may contain, in addition to the ionic liquid, a supporting electrolyte and other additives that can increase the efficiency of electrolytic reduction.

[0038] In one embodiment, the electrolyte solution comprises an ionic liquid and a supporting electrolyte. By using an electrolyte solution comprising an ionic liquid and a supporting electrolyte, electrolytic reduction can proceed efficiently at a lower temperature.

[0039] The supporting electrolyte is not particularly limited, but preferably contains a cation having a standard electrode potential that is so base as not to interfere with the electrolytic reduction of carbon dioxide or the electrolytic reduction of H2O, or is equivalent to the base.

[0040] The supporting electrolyte is not particularly limited, but examples thereof include KHCO3, KHPO4, LiBF4, LiPF6, and LiClO 4、 LiAsF 6、 LiTf, LiTFSI, LiFSI, K2CO 3、 Li2CO 3、 NaCO 3、 Examples include NaHCO3.

[0041] In a preferred embodiment, the supporting electrolyte may be LiBF, LiPF, LiTFSI, or LiFSI. By using LiBF, LiPF, LiTFSI, or LiFSI as the supporting electrolyte, the electrolytic reduction proceeds efficiently at a lower temperature.

[0042] The above supporting electrolytes may be used alone or in combination of two or more.

[0043] In a preferred embodiment, the combination of the ionic liquid and supporting electrolyte may be DEME-BF4, or a combination of DEME-TFSI and LiBF4, more preferably a combination of DEME-BF4 and LiBF4.

[0044] The concentration of the supporting electrolyte added to the ionic liquid in the electrolytic solution may be preferably 0.01 mol / L to the saturated concentration, more preferably 0.02 to 1.00 mol / L, even more preferably 0.05 to 0.75 mol / L, and even more preferably 0.10 to 0.50 mol / L. By adjusting the concentration of the supporting electrolyte added to the ionic liquid to be within the above range, electrolytic reduction proceeds more efficiently.

[0045] In a preferred embodiment, the electrolyte solution is substantially free of protic solvents such as water. Since the electrolyte solution does not contain a protic solvent such as water, the electrolytic reduction proceeds efficiently without hydrogen generation due to electrolysis of water. Examples of protic solvents include alcohols, formic acid, and hydrogen fluoride.

[0046] The concentration of carbon dioxide in the electrolytic solution is not particularly limited, but is preferably a high concentration, and may be, for example, a saturated concentration.

[0047] The method for dissolving carbon dioxide in the electrolytic solution is not particularly limited, but examples thereof include bubbling carbon dioxide into the electrolytic solution, saturating the carbon dioxide in an electrolytic cell containing the electrolytic solution, stirring with a stirring device, stirring by ultrasonic irradiation, and using a flow electrolytic cell.

[0048] In the electrolytic reduction method of the present disclosure, carbon dioxide may be used in combination with other gases, such as argon, nitrogen, hydrogen, and water vapor.

[0049] The temperature of the electrolytic solution during electrolytic reduction may be preferably 0 to 100° C., more preferably 0 to 80° C., even more preferably 10 to 50° C., and even more preferably 20 to 40° C. In the electrolytic reduction method of the present disclosure, even when the temperature of the electrolytic solution is set to a relatively low temperature such as described above, the electrolytic reduction proceeds efficiently, and energy costs can be reduced.

[0050] The pressure during electrolytic reduction may be preferably atmospheric pressure to 0.5 MPa, for example, 0.1 MPa to 0.5 MPa, more preferably 0.1 MPa to 0.3 MPa, and even more preferably 0.1 MPa to 0.2 MPa. In the electrolytic reduction method of the present disclosure, even without pressurization or with only a small pressurization, electrolytic reduction proceeds efficiently and energy costs can be reduced.

[0051] In a preferred embodiment, the electrolytic reduction is carried out preferably at 20 to 40° C. and at 0.09 to 0.11 MPa, more preferably at room temperature and normal pressure.

[0052] The potential of the cathode electrode during electrolytic reduction may be preferably −5.0 V to −0.5 V, more preferably −3.5 V to −0.5 V. In addition, such a potential may be + The potential is measured when a silver electrode is used as the reference electrode. By setting the potential of the cathode electrode within the above range, electrolytic reduction proceeds more efficiently.

[0053] Carbon materials obtainable by the carbon material production method of the present disclosure include diamond, graphite, glassy carbon, amorphous carbon, carbon nanotubes, carbon nanohorns, and graphene.

[0054] The carbon material is preferably diamond or glassy carbon, and more preferably diamond.

[0055] In the method for producing a carbon material according to the present disclosure, carbon dioxide can be selectively electrolytically reduced to a carbon material by adjusting the potential applied between the anode electrode and the cathode electrode.

[0056] Therefore, the present disclosure also provides a method for electrolytically reducing carbon dioxide in an electrolytic reduction device having an anode electrode, a cathode electrode, and an electrolyte solution containing carbon dioxide, which selectively electrolytically reduces carbon dioxide to a carbon material selected from the group consisting of diamond, graphite, glassy carbon, amorphous carbon, carbon nanotubes, carbon nanohorns, and graphene by applying a potential between the anode electrode and the cathode electrode.

[0057] For example, when the ionic liquid is DEME-BF4 and LiBF4 is added as a supporting electrolyte at a concentration of 0.2 mol / L, diamond is generated at room temperature by setting the potential between -5.0 V and -2.4 V. In addition, when the ionic liquid is P 2225 When the solution is -TFSI and does not contain a supporting electrolyte, diamond is produced at room temperature by setting the potential to -3.7V to -2.6V.

[0058] As described above, the method for producing a carbon material from carbon dioxide disclosed herein allows for efficient electrolytic reduction of carbon dioxide at a relatively low temperature. In particular, by including an ionic liquid in the electrolyte, the potential window is widened, and by controlling the applied potential, the electrolytic reduction of carbon dioxide to a carbon material can be performed more efficiently. Furthermore, since the melting temperature of the ionic liquid is low and the liquid is highly stable, safe and stable electrolytic reduction can be performed at low temperatures, reducing energy costs. Furthermore, by controlling the applied potential, a desired carbon material can be obtained.

[0059] Although the present invention has been described above, the present invention is not limited to the above and various modifications are possible within the scope of the present invention. [Example]

[0060] The present invention will be described in more detail below with reference to the following examples, but the present invention is not limited to these examples.

[0061] Figure 1 shows an outline of the experimental equipment used in this example. The experimental equipment includes an electrolytic cell 1, a carbon dioxide supply pipe 2, a working electrode WE as a cathode electrode, a counter electrode CE as an anode electrode, a reference electrode RE, and an exhaust pipe 3. The electrolytic cell 1 includes a cell body 11 and a lid 12 that closes the top opening of the cell body 11. The working electrode WE is an Ag plate electrode and is connected to a Ni conductor 4. The counter electrode CE is a Pt plate electrode and is connected to a Ni conductor 4. The reference electrode RE is an Ag + The working electrode WE is a Ag / Ag electrode, and is connected to a Ni lead wire 4. An electrolyte 7 is present in the electrolytic cell 1, and the working electrode WE, counter electrode CE, and reference electrode RE are fixed in a state of being immersed in the electrolyte 7. The working electrode WE, reference electrode RE, and counter electrode CE were connected to a potentiostat / galvanostat device (manufactured by Biologic) through the lead wire 4.

[0062] Example 1 DEME-BF4 as an ionic liquid was mixed with LiBF4 as a supporting electrolyte at a ratio of 0.2 mol / L to obtain electrolyte A. The obtained electrolyte A was added to electrolytic cell 1 in an amount such that each electrode was immersed in electrolyte A and the gas supply pipe 2 and exhaust pipe 3 were not in contact with electrolyte A. In this state, carbon dioxide was supplied from gas supply pipe 2 to electrolytic cell 1 at a gas pressure of 0.1 MPa, creating a carbon dioxide-saturated atmosphere in electrolytic cell 1. Next, the reduction behavior of carbon dioxide was observed by cyclic voltammetry, where a potential was applied between the working electrode WE and the counter electrode CE at a scan rate of 10 mV / s and the current density was measured.

[0063] (Comparative Example 1) The same procedure as in Example 1 was carried out except that Ar was used instead of carbon dioxide.

[0064] The results of Example 1 and Comparative Example 1 are shown in the graph of Figure 2. In the graph, the solid line shows the results of Example 1, and the dashed line shows the results of Comparative Example 1. From the results of Figure 2, it was confirmed that the reduction current in the carbon dioxide atmosphere of Example 1 began to rise from -2.5 V. That is, it was confirmed that in electrolyte A, the electrolytic reduction of carbon dioxide proceeds at potentials less noble than -2.5 V.

[0065] Examples 2 and 3 The change in current density was measured in the same manner as in Example 1, except that the potentials of the Ag electrodes serving as cathodes were cathodically polarized to constant potentials of −2.45 V and −4.86 V. The results are shown in FIG.

[0066] From the results shown in Figure 3, it was confirmed that the reduction current value remained constant regardless of whether the Ag electrode potential was negatively polarized to -2.45 V or -4.86 V, and furthermore, it was confirmed that the reduction reaction of carbon dioxide proceeded stably at either potential.

[0067] In Examples 2 and 3, the surface state of each Ag electrode was analyzed by Raman spectroscopy after electrolytic reduction for 1 hour. The results are shown in FIG.

[0068] As shown in Figure 4, the 1332 cm -1 The Raman peak at 1580 cm is attributed to the G-band of carbon. -1 Raman bands around 1360 cm and the D-band of carbon -1 A Raman band was observed around 1000 kJ / cm. This means that it was confirmed that carbon dioxide was reduced by electrolytic reduction and that a carbon material containing diamond was precipitated.

[0069] Example 4 The electrolytic cell 1 of the electrolysis device is charged with an ionic liquid, P 2225 The change in current density was measured in the same manner as in Example 1 above, except that electrolyte B consisting only of -TFSI was added.

[0070] (Comparative Example 2) The same procedure as in Example 4 was carried out except that Ar was used instead of carbon dioxide.

[0071] The results of Example 4 and Comparative Example 2 are shown in Figure 5. In the graph, the solid line shows the results of Example 4, and the dashed line shows the results of Comparative Example 2. From the results of Figure 5, it is clear that the electrolytic reduction of carbon dioxide was achieved using ionic liquid P 2225It was confirmed that the reaction proceeds within the potential window of the TFSI. 2225 The reduction current using TFSI in an inert Ar atmosphere started at around -3.4 V, whereas in a carbon dioxide atmosphere, the reduction current started at a more noble potential of around -2.8 V. These results suggest that the reduction of carbon dioxide is 2225 -This indicates that this occurs without being affected by the reductive decomposition of TFSI itself.

[0072] (Examples 5 to 9) The change in current density was measured in the same manner as in Example 4, except that the potential of the Ag electrode serving as the cathode was cathodically polarized at constant potentials of −2.60 V, −3.00 V, −3.15 V, −3.25 V, and −3.70 V. The results are shown in Figures 6 to 10.

[0073] From the results shown in Figures 6 to 10, it was confirmed that the reduction current value remained constant regardless of whether the Ag electrode potential was negatively polarized to -2.60 V, -3.00 V, -3.15 V, -3.25 V, or -3.70 V, and furthermore, it was confirmed that the reduction reaction of carbon dioxide proceeded stably at any potential.

[0074] In Examples 5 to 9, the surface state of each Ag electrode was analyzed by Raman spectroscopy after electrolytic reduction for 1 hour. The results are shown in Figures 11 to 15.

[0075] As shown in Figures 11 to 16, Raman bands derived from diamond and the G-band and D-band of carbon were confirmed at all electrolysis potentials, confirming that carbon materials including diamond were precipitated by reduction of carbon dioxide at least in the range of -3.7V to -2.6V.

[0076] Example 10 P 2225 -TFSI instead of triethyloctylphosphonium bis(trifluoromethanesulfonyl)imide (P 2228The same operations as in Examples 4 to 9 were carried out, except that electrolyte H consisting of TFSI was added.

[0077] The results confirmed that when electrolyte H was used, CO2 was reduced in the range of -3.2V to -0.7V.

[0078] Example 11 P 2225 -TFSI instead of tributylmethylphosphonium bis(trifluoromethanesulfonyl)imide (P 4441 The same operations as in Examples 4 to 9 were carried out, except that electrolyte I consisting of TFSI was added.

[0079] The results confirmed that when electrolyte I was used, CO2 was reduced in the range of -3.2V to -0.5V.

[0080] (Example 12 and Comparative Example 3) Instead of DEME-BF4, N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP 13 The operations were the same as in Example 1 and Comparative Example 1, respectively, except that a 12-TFSI (-TFSI) was used. The results are shown in the graph of Figure 16. The solid line shows the results of Example 12, and the dashed line shows the results of Comparative Example 3.

[0081] (Example 13 and Comparative Example 4) The same operations as in Example 1 and Comparative Example 1 were carried out, respectively, except that 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMIM-TFSI) was used instead of DEME-BF4. The results are shown in the graph in Figure 17. The solid line shows the results of Example 13, and the dashed line shows the results of Comparative Example 4.

[0082] (Example 14 and Comparative Example 5) The same operations as in Example 1 and Comparative Example 1 were carried out, except that 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF) was used instead of DEME-BF. The results are shown in the graph in Figure 18. The solid line shows the results of Example 14, and the dashed line shows the results of Comparative Example 5.

[0083] 16 to 18, it was confirmed that the reduction current rose in a carbon dioxide atmosphere in all of Examples 12 to 14. That is, it was confirmed that the electrolytic reduction of carbon dioxide proceeds at a potential less noble than a predetermined potential.

[0084] Example 15 DEME-BF4 as an ionic liquid was mixed with LiBF4, LiPF6, LiTFSI, and LiFSI as supporting electrolytes at a ratio of 0.2 mol / L to obtain electrolytes A1 to A4. Except for using the obtained electrolytes A1 to A4, the change in current density for each electrolyte was measured in the same manner as in Example 1. The results confirmed that when electrolytes A1 to A4 were used, CO2 was reduced in the range of -3.5 V to -0.8 V.

[0085] Example 16 Except for changing the concentration of the supporting electrolyte to 0.4 mol / L, electrolyte solutions B1 to B4 were prepared in the same manner as in Example 15, and the change in current density was measured for each electrolyte solution. The results confirmed that when electrolyte solutions B1 to B4 were used, CO2 was reduced in the range of -3.5 V to -0.6 V.

[0086] Example 17 Except for changing the concentration of the supporting electrolyte to 0.6 mol / L, electrolyte solutions C1 to C4 were prepared in the same manner as in Example 15, and the change in current density was measured for each electrolyte solution. The results confirmed that when electrolyte solutions C1 to C4 were used, CO2 was reduced in the range of -3.5 V to -0.6 V.

[0087] Example 18 Except for changing the concentration of the supporting electrolyte to 0.8 mol / L, electrolyte solutions D1 to D4 were prepared in the same manner as in Example 15, and the change in current density was measured for each electrolyte solution. The results confirmed that when electrolyte solutions D1 to D4 were used, CO2 was reduced in the range of -3.6 V to -1.0 V.

[0088] Example 19 Except for changing the concentration of the supporting electrolyte to 1.0 mol / L, electrolyte solutions E1 to E4 were prepared in the same manner as in Example 15, and the change in current density was measured for each electrolyte solution. The results confirmed that when electrolyte solutions D1 to D4 were used, CO2 was reduced in the range of -3.6 V to -1.0 V.

[0089] Example 20 Except for changing the concentration of the supporting electrolyte to 1.2 mol / L, electrolyte solutions F1 to F4 were prepared in the same manner as in Example 15, and the change in current density was measured for each electrolyte solution. The results confirmed that when electrolyte solutions F1 to F4 were used, CO2 was reduced in the range of -3.6 V to -0.8 V.

[0090] Example 21 Except for changing the concentration of the supporting electrolyte to 1.4 mol / L, electrolyte solutions G1 to G4 were prepared in the same manner as in Example 15, and the change in current density was measured for each electrolyte solution. The results confirmed that when electrolyte solutions G1 to G4 were used, CO2 was reduced in the range of -3.6 V to -1.0 V. [Industrial Applicability]

[0091] The electrolytic reduction method of the present disclosure is capable of converting carbon dioxide, which causes global warming and other problems, into useful carbon materials, and is therefore useful in various fields, particularly in the environmental field. [Explanation of symbols]

[0092] 1...Electrolytic cell 2...Gas supply pipe 3...Exhaust pipe 4…Conducting wire 7… Electrolyte 11…Slot body 12…cover

Claims

1. A method for producing a carbon material, comprising: obtaining a carbon material by electrolytically reducing carbon dioxide to a carbon material in an electrolytic reduction device having an anode electrode, a cathode electrode, and an electrolyte solution containing carbon dioxide, wherein the electrolyte solution contains an ionic liquid, and the ionic liquid is an imidazolium-based ionic liquid, an aromatic-based ionic liquid, a pyrrolidinium-based ionic liquid, an ammonium-based ionic liquid, a piperidinium-based ionic liquid, or a quaternary phosphonium-based ionic liquid, and the temperature of the electrolyte solution is 0 to 100°C.

2. the anode electrode is a Pt electrode, The cathode electrode is an Ag electrode. The method for producing the carbon material according to claim 1 .

3. 3. The method for producing a carbon material according to claim 1 or 2, wherein the ionic liquid is N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium tetrafluoroborate, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide, N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium tetrafluoroborate, triethylpentylphosphonium bis(trifluoromethanesulfonyl)imide, triethyloctylphosphonium bis(trifluoromethanesulfonyl)imide, or tributylmethylphosphonium bis(trifluoromethanesulfonyl)imide.

4. The method for producing a carbon material according to any one of claims 1 to 3, wherein the electrolytic solution contains a supporting electrolyte.

5. The supporting electrolyte is KHCO ３ , KHPO ４ , LiBF ４ , LiPF ６ , LiClO ４ , LiAsF ６ , LiTf, LiTFSI, LiFSI, K ２ CO ３ , Li ２ CO ３ , Na ２ CO ３ , or NaHCO ３ The electrolytic reduction method according to claim 4, wherein

6. The supporting electrolyte is LiBF ４ , LiPF ６ 6. The electrolytic reduction method according to claim 4 or 5, wherein the catalyst is LiTFSI, LiTFSI, or LiFSI.

7. 7. The electrolytic reduction method according to claim 4, wherein the concentration of the supporting electrolyte contained in the ionic liquid is from 0.01 mol / L to a saturated concentration.

8. The electrolytic reduction device further includes a reference electrode, and the reference electrode is Ag ＋ 8. The electrolytic reduction method according to claim 1, wherein the cathode electrode is a Ag / Ag electrode, and the potential of the cathode electrode is −5.0 V to −0.5 V.

9. The electrolytic reduction method according to any one of claims 1 to 8, wherein the electrolytic reduction is carried out at room temperature and atmospheric pressure.

10. 10. The electrolytic reduction method according to claim 1, wherein the carbon material is diamond, graphite, glassy carbon, amorphous carbon, carbon nanotube, carbon nanohorn, or graphene.

11. 11. The electrolytic reduction method according to claim 1, wherein the carbon material is diamond.

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