Carbon dioxide adsorbent and carbon dioxide absorption / release device

Abstract

To provide an adsorbent capable of realizing a carbon dioxide adsorption-desorption device that can efficiently adsorb and desorb carbon dioxide, as well as a carbon dioxide adsorption-desorption device that includes the adsorbent.SOLUTION: According to one embodiment, a carbon dioxide adsorbent is provided. The carbon dioxide adsorbent is capable of adsorbing and desorbing carbon dioxide and has a fused heteroaromatic ring structure that includes one or more quinone structures.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Embodiments of the present invention relate to carbon dioxide adsorbents and carbon dioxide absorption / release devices. [Background technology]

[0002] The technology of absorbing carbon dioxide (CO2) with absorbents such as amines is used in CCS (Carbon dioxide Capture and Storage) plants such as thermal power plants and is considered a leading candidate for preventing global warming. The absorbent material that has absorbed carbon dioxide is generally heated in a regeneration tower and regenerated by releasing carbon dioxide, allowing it to be reused repeatedly. The typical temperature at this time is around 140°C, which consumes a large amount of energy. The heat and energy required for regeneration are also called the heat duty or energy penalty. If this heating temperature can be lowered and the release of carbon dioxide can be made more efficient, energy can be reduced, and the widespread adoption of this technology as a global warming prevention technology can be promoted.

[0003] One energy-saving regeneration method involves replacing adsorbed carbon dioxide with water vapor. Through a replacement reaction between adsorbed carbon dioxide and water vapor, the carbon dioxide is released from the adsorbent. While this method allows the heating temperature to be lowered to below 100°C, the released gas contains water vapor in addition to carbon dioxide. Therefore, a subsequent step is required to cool the released gas and condense the water vapor to separate it from the carbon dioxide. Consequently, while this method may be more energy-efficient than thermal desorption, it is not considered the optimal method for regenerating absorbents.

[0004] On the other hand, technologies are being investigated that use molecules or polymers containing electrically responsive active groups to separate carbon dioxide by switching the electrical potential instead of heating. This method is expected to have energy-saving effects because it allows for the release of carbon dioxide without heating. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] U.S. Patent Application Publication No. 2014 / 0271434 [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2022 - 25699 [Patent Document 3] Japanese Patent Publication for International Application No. 2022 - 546697 [Non - Patent Document]

[0006] [Non - Patent Document 1] J. Am. Chem. Soc., 2013, 135, 16821 - 16824 [Summary of the Invention] [Problems to be Solved by the Invention]

[0007] An embodiment aims to provide an adsorbent that can realize a carbon dioxide absorption - release device capable of efficiently absorbing and releasing carbon dioxide, and a carbon dioxide absorption - release device containing the adsorbent. [Means for Solving the Problems]

[0008] According to an embodiment, a carbon dioxide adsorbent is provided. The carbon dioxide adsorbent can adsorb and release carbon dioxide and has a condensed heteroaromatic ring structure. The condensed heteroaromatic ring structure contains one or more quinone structures. [Brief Description of the Drawings]

[0009] [Figure 1] CO2 adsorption - desorption scheme by a redox molecule having a condensed heteroaromatic ring structure containing an example of a quinone structure. [Figure 2] CO2 adsorption - desorption scheme by a redox molecule having a condensed heteroaromatic ring structure containing another example of a quinone structure. [Figure 3] Diagram showing the structural formula of a redox molecule having a condensed heteroaromatic ring structure containing an example of a quinone structure. [Figure 4] A diagram showing the structural formulas of redox molecules having condensed heteroaromatic ring structures, including quinone structures, as in other examples. [Figure 5] A diagram showing the structural formulas of redox molecules having condensed heteroaromatic ring structures, including quinone structures, as in other examples. [Figure 6] A distribution diagram showing the CO2 binding energy at the reaction site and the superiority of CO2 adsorption to the reaction site compared to reactive oxygen species formation for an example of a redox molecule. [Figure 7] A schematic cross-sectional view showing an example of a carbon dioxide absorption and release device according to the embodiment. [Figure 8] A schematic cross-sectional view of an electrochemical cell, which may be included in other examples of the carbon dioxide absorption and release device according to the embodiment. [Figure 9] A graph showing the cyclic voltammetry curve measured in Example 1. [Modes for carrying out the invention]

[0010] The embodiments will be described below with reference to the drawings as appropriate. Common components throughout the embodiments will be denoted by the same reference numerals, and redundant explanations will be omitted. Furthermore, each figure is a schematic diagram intended to illustrate the embodiments and facilitate understanding; their shapes, dimensions, ratios, etc., may differ from those of the actual device. These can be appropriately modified in accordance with the following description and known technology.

[0011] The following embodiments relate to an adsorbent and device for separating carbon dioxide (CO2) from a gas containing carbon dioxide by an electrochemical process. The adsorbent described herein is one that enables the realization of an electrically responsive device that efficiently absorbs and releases carbon dioxide.

[0012] (Carbon dioxide adsorbent) The carbon dioxide adsorbent according to this embodiment has a condensed heteroaromatic ring structure when it is electrically neutral. This condensed heteroaromatic ring structure contains one or more quinone structures. Because this carbon dioxide adsorbent contains quinone structures, it can adsorb and release carbon dioxide. Hereafter, this carbon dioxide adsorbent may be simply referred to as "adsorbent." Compounds and materials having a condensed heteroaromatic ring structure containing quinone structures can be manufactured by appropriately applying known methods.

[0013] According to one embodiment, an adsorbent is provided for a device that performs electro-swing adsorption. The electrochemical swing process is a process that repeatedly maintains a specific potential in the forward direction and a different potential in the reverse direction. In this method, the affinity for the target adsorbent can be adjusted by using redox active groups that can be reduced at one potential and oxidized at a different potential. According to such an embodiment, energy is efficiently delivered to act on an electrochemical reaction that results in the capture of the target substance (e.g., CO2).

[0014] In such adsorbents, the quinone structure exhibits a redox response. That is, the quinone structure functions as a redox active site. In the adsorbent, carbon dioxide is adsorbed and released by the redox response of the quinone structure. Specifically, carbon dioxide can be adsorbed onto the quinone structure in the reduced state, and the carbon dioxide adsorbed onto the quinone structure can be released in the oxidized state.

[0015] It has been reported that typical adsorbents that exhibit redox responses may compete with the redox reaction of oxygen depending on the environment in which they are used. In environments where oxygen is present, reactive oxygen species may be generated by the redox reaction of oxygen, and it is known that these reactive oxygen species degrade the adsorbent. Therefore, it is desirable that the adsorbent preferentially transfers electrons even in the presence of oxygen, that is, that the adsorbent exhibits a redox potential that is nobler than that of oxygen.

[0016] After extensive research, we found that the redox potential of molecules containing condensed heteroaromatic ring structures, including quinone structures, tends to be nobler than that of oxygen. Figures 1 and 2 show examples of carbon dioxide adsorption / desorption schemes using molecules with such structures. Figure 1 shows the scheme using 4,7-phenanthroline-5,6-dione (CAS No. 84-12-8). Figure 2 shows the scheme using benzo[1,2-b:4,5-b']bisthiophene-4,8-dione (CAS No. 32281-36-0). Figures 1 and 2 show examples using redox molecules containing ortho-quinone and para-quinone structures, respectively. The quinone structure (diketone structure) takes up two electrons when a reduction potential is applied, and the negatively charged ketone oxygen, due to electron localization, binds to CO2. Conversely, applying an oxidation potential breaks the bond with CO2, allowing the quinone structure to be formed again. The above chemical reaction proceeds reversibly.

[0017] In systems for electrochemically separating gases such as CO2, unsubstituted quinone compounds such as 1,4-benzoquinone and substituted quinone compounds with substituents such as halogens have been reported as electrochemically active species that can bind to the gas. Molecules having a condensed heteroaromatic ring structure containing a quinone structure exhibit superior oxygen-to-oxygen dominance during reduction and CO2 adsorption compared to conventionally used unsubstituted and substituted quinone compounds. Therefore, adsorbents containing a condensed heteroaromatic ring quinone structure can provide an electroresponsive carbon dioxide absorption and release device that can efficiently absorb and release carbon dioxide.

[0018] It is desirable that the condensed heteroaromatic ring structure has one or more selected from the group consisting of benzene-based heteroaromatic ring structures, naphthalene-based heteroaromatic ring structures, anthracene-based heteroaromatic ring structures, and phenanthrene-based heteroaromatic ring structures. That is, it is desirable that the condensed heteroaromatic ring structure has a skeletal structure similar to a benzene ring, naphthalene ring, anthracene ring, or phenanthrene ring. The condensed heteroaromatic ring structure may be a derivative of a benzene ring, naphthalene ring, anthracene ring, or phenanthrene ring. The heteroatoms contained in the condensed heteroaromatic ring structure may be one or more selected from the group consisting of nitrogen, oxygen, and sulfur, for example. In addition to nitrogen (N), oxygen (O), and sulfur (S), other examples of heteroatoms include phosphorus (P), selenium (Se), and boron (B). Molecules containing condensed heteroaromatic ring structures may also have functional groups such as halogen groups, amino groups, nitro groups, imide groups, imine bonds, and aldehyde groups. An example is shown in Figures 3 to 5.

[0019] Figures 3 to 5 are diagrams showing the structural formulas of molecules having a condensed heteroaromatic ring structure containing an example of a quinone structure. Figure 3 shows a condensed heteroaromatic ring structure containing sulfur as a heteroatom, such as thiophene molecules. Figure 4 shows a condensed heteroaromatic ring structure containing oxygen as a heteroatom, such as furan molecules. Figure 5 shows examples of molecules having a condensed heteroaromatic ring structure containing nitrogen as a heteroatom, such as pyridine and pyrrole molecules. The condensed heteroaromatic ring quinone molecules that can function as adsorbents are not limited to the examples shown. Furthermore, the condensed heteroaromatic ring structures containing quinone structures that adsorbents may contain are not limited to the structures of the molecules shown.

[0020] Figure 3 shows examples of thiophene molecules with a naphthalene heteroaromatic ring structure in the left column. Similarly, Figure 4 shows examples of furan molecules with a naphthalene heteroaromatic ring structure in the left column. Figure 5 shows four pyridine molecules with a naphthalene heteroaromatic ring structure in the top two rows of the two left columns, and three pyrrole molecules with a naphthalene heteroaromatic ring structure in the bottom two rows of the right column and the bottom row of the center right column. These molecules with a naphthalene heteroaromatic ring structure can also be described as molecules with a naphthoquinone-based condensed heteroaromatic ring structure.

[0021] The central column of Figure 3 shows examples of thiophene molecules having an anthracene heteroaromatic ring structure, the central column of Figure 4 shows examples of furan molecules having an anthracene heteroaromatic ring structure, and the upper right section of Figure 5 shows examples of pyrrole molecules having an anthracene heteroaromatic ring structure, and the upper right section to its left shows examples of pyridine molecules having an anthracene heteroaromatic ring structure. These molecules having anthracene heteroaromatic ring structures can also be described as molecules having anthraquinone-based condensed heteroaromatic ring structures.

[0022] The right column of Figure 3 shows examples of thiophene-based molecules having a phenanthrene-based heteroaromatic ring structure, the right column of Figure 4 shows examples of furan-based molecules having a phenanthrene-based heteroaromatic ring structure, and the lower section of the two left columns of Figure 5 shows two examples of pyridine-based molecules having a phenanthrene-based heteroaromatic ring structure, while the middle section of the center right column shows one example of a pyrrole-based molecule having a phenanthrene-based heteroaromatic ring structure. These molecules having a phenanthrene-based heteroaromatic ring structure can also be described as molecules having a condensed heteroaromatic ring structure based on phenanthrenequinone.

[0023] It is preferable that the redox active site contained in the adsorbent is reduced preferentially over oxygen even in the presence of oxygen, thereby adsorbing CO2. This avoids not only competition with the redox reaction of oxygen but also degradation of the adsorbent by reactive oxygen species, making it possible to select the application environment and the gas to be treated for the adsorbent without worrying about the presence or absence of oxygen. If the material has a high binding energy with CO2 and the highest occupied molecular orbital (HOMO) of the molecule in the reduced state is lower than that of oxygen, it can be preferentially reduced and adsorb CO2 in the presence of oxygen. Therefore, by evaluating two evaluation parameters, superiority over reactive oxygen species generation and CO2 binding energy, using first-principles calculations, it is possible to estimate molecules that are advantageous as redox active sites in the presence of oxygen.

[0024] The quinone structure (diketone structure) is formed when the oxygen atoms of two ketones (R2C=O) are anionized by two-electron reduction (R2C-O - ), each -O - CO2 is bonded to the base to form two R2C-O-CO2 - This is the result. On the other hand, when an oxygen molecule O2 is reduced by one electron, it becomes a reactive oxygen species O2. - (Superoxide) is formed from two molecules of O2. - The difference between the stabilization energy during the formation of the quinone structure and the stabilization energy during the localization of electrons in the quinone structure and the ionization of oxygen is defined as the superiority parameter for reactive oxygen species generation. Furthermore, the stabilization energy due to the formation of a bond with CO2 in the ionized state of the quinone structure is defined as the CO2 bond energy, which is the other parameter. An example is shown below.

[0025] The structure and energy of various redox-responsive molecules, and their interaction and adsorption reaction systems with CO2, were calculated using density functional theory (DFT) with B3LYP functional. The basis set used was 6-31++G(d,p). The molecular structure was optimized using the energy gradient method in a dielectric field of acetonitrile, and the structure obtained by normal vibration analysis was confirmed to be the equilibrium structure. For calculations in a dielectric field, a dielectric model (PCM (polarization continuum) model) that considers solvent effects was used. All calculations were performed using the molecular orbital calculation program Gaussian 16 (Hewlinks Co., Ltd.).

[0026] When the CO2 bond energy is low, it is equivalent to CO2 floating around the molecule. Therefore, the higher this energy, the more stably the bond between the molecule and CO2 can be maintained. Also, the smaller the advantage parameter, the more ambiguous the difference becomes between achieving the reduced state of the molecule and generating reactive oxygen species. Therefore, a larger energy difference is preferable.

[0027] Tables 1 to 4 show the calculation results for examples of molecules having condensed heteroaromatic ring structures, including quinone structures. Table 1 shows the results for thiophene molecules, Table 2 for furan molecules, Table 3 for pyridine molecules, and Table 4 for pyrrole molecules.

[0028] [Table 1]

[0029] [Table 2]

[0030] [Table 3]

[0031] [Table 4]

[0032] Some of the results shown in Tables 1 to 4 are summarized in Figure 6. Figure 6 is a distribution map plotting the superiority in generating reactive oxygen species on the horizontal axis and the binding energy between the molecule and CO2 on the vertical axis. Molecules with higher CO2 adsorption capacity compared to reactive oxygen species are more likely to bind with CO2 even in the presence of oxygen, and molecules with higher binding energy to CO2 are more likely to bind with CO2.

[0033] Heteroatoms introduced into heteroaromatic rings are electron-donating. Therefore, depending on the positional relationship between the heteroatom and the quinone, the resonance effect may vary to some extent, but it is expected that in quinone compounds containing heteroaromatic rings, the electron density of the quinone's oxygen atom will increase slightly, reducing its advantage in reactive oxygen species formation. However, the calculation results above show a high advantage in reactive oxygen species formation, suggesting that in molecules with a condensed heteroaromatic ring structure containing a quinone structure, electrons are pulled by the heteroatom, reducing the number of oxygen atoms in the quinone. In other words, contrary to the expectation that electron-donating heteroatoms would be detrimental to the oxidation-reduction of quinone, the introduction of heteroatoms is advantageous.

[0034] In condensed heteroaromatic quinones, compared to non-heterocyclic quinones where a diketone is attached to the aromatic ring of the carbon skeleton, electrons are somewhat attracted to the introduced heteroatom, thereby reducing the degree of electron localization of the quinone to the oxygen atom. On the one hand, the attraction of electrons by the heteroatom reduces the binding energy to CO2. On the other hand, because the electron localization of the quinone to the oxygen atom is reduced, the binding of the quinone to CO2 becomes more dominant than the reactive oxygen species reaction of the ambient oxygen. In more detail, as the electron density decreases, the oxidation-reduction potential shifts to a noble potential, so the reaction proceeds preferentially over the reactive oxygen species reaction. As a result, the heteroaromatic ring ultimately becomes dominant.

[0035] Furthermore, even when halogen substituents are introduced, electrons are withdrawn due to the inductive effect (I effect) of the halogen, thus reducing the electron density of the oxygen atom in the quinone. This reduces the binding energy with CO2, but it is more advantageous than reactive oxygen species formation. Since the I effect is not included in the conjugated system of the aromatic ring, the effect of halogen introduction is solely that of the I effect. Condensed heteroaromatic ring quinones exhibit better oxygen superiority and CO2 adsorption than non-heterocyclic quinones substituted with halogens, etc. Therefore, condensed heteroaromatic ring structures containing quinone structures are suitable as carbon dioxide adsorbents.

[0036] The adsorbent may be a porous material containing a condensed heteroaromatic ring structure including a quinone structure as an oxidation-reduction active site. Alternatively, the adsorbent may be an oligomer or polymer containing a molecule containing the condensed heteroaromatic ring structure as a unit structure.

[0037] One possible form of the carbon dioxide adsorbent is a porous body, which includes a porous material having a large number of pores. The pore diameter is preferably 5 nm or less. Specifically, the porous body is preferably a sub-nanoporous material or a nanoporous material having pores ranging from angstrom size (1 nm or less) to nanometer size, and more specifically, 0.5 nm to 5 nm.

[0038] The porous material contains a redox active moiety, i.e., the quinone structure described above, which reduces the diketone structure by electrical response to bond with carbon dioxide, and then oxidizes it by electrical response to break the bond with carbon dioxide and reform the diketone structure. The redox active moiety may be included as a functional group in the molecular structure constituting the porous material. The redox active moiety is not limited to the molecules and compounds of the example described above, but can also be their derivatives or other molecules and compounds having a condensed heteroaromatic ring structure containing a quinone structure.

[0039] The content of molecules having a condensed heteroaromatic ring structure containing a quinone structure that exhibits redox activity through electrical response, contained in the porous material, is preferably 10% to 80% by mass, and more preferably 20% to 75% by mass, based on the total mass of the porous material.

[0040] Generally, a higher amount of active groups in an adsorbent results in greater absorption and desorption of carbon dioxide per unit volume of the adsorbent. Therefore, from the perspective of energy consumption, plant equipment size, and processing efficiency, a higher amount of active groups is desirable.

[0041] The content of molecules having a condensed heteroaromatic ring structure containing a quinone structure that exhibits redox activity by electrical response is preferably 90% by mass or less based on the total mass of the porous material. At this content, the amount of redox active sites per unit volume of the porous material can be appropriately controlled, so that the redox active groups are not too close together and the pore size can be maintained. In addition, carbon dioxide can easily access the active groups, so the active groups can be fully utilized. The content of molecules having a condensed heteroaromatic ring structure containing a quinone structure is more preferably 75% by mass or less.

[0042] By ensuring that the content of redox active sites is 10% by mass or more, sufficient carbon dioxide adsorption amount and adsorption rate can be obtained, resulting in excellent processing efficiency. Therefore, porous materials with a content of redox active sites within the above range are advantageous in carbon dioxide recovery applications not only because of their high carbon dioxide absorption amount and rate, but also because they exhibit high carbon dioxide desorption from the porous material and a high carbon dioxide desorption rate (reaction rate), enabling efficient carbon dioxide recovery.

[0043] Specific examples of molecules having a condensed heterocyclic aromatic ring structure containing a quinone structure that can function as a redox active site in a porous body include those having an amino group or an aldehyde group as functional groups R and R’ as shown in FIGS. 3 to 5. As shown in the drawing, molecules having an amino group or an aldehyde group as functional groups R and R’ present at opposite positions of the ring can be suitably incorporated into the molecular structure of the porous body.

[0044] As in the above example, the quinone structure which is an active site in the porous body absorbs CO2 and then releases CO2 to be regenerated and used repeatedly. Therefore, it is preferable that the chemical stability of the condensed heterocyclic aromatic ring structure containing the quinone structure is high.

[0045] The porous body preferably contains one or more porous materials selected from the group consisting of a covalent organic framework (COF) having electrical response activity, a metal organic framework (MOF), a porous carbon material, zeolite, porous silica, and porous alumina. For example, the porous body may contain a COF having electrical responsiveness. Alternatively, the porous body may contain a MOF having electrical responsiveness.

[0046] The presence or absence of the quinone structure 1 can be estimated based on H NMR (Nuclear Magnetic Resonance) and 13 13C NMR measurements to form a structure of a condensed heterocyclic aromatic ring structure containing a quinone structure. Also, when absorption derived from the stretching vibration of carbonyl is observed at 1600 cm -1 - 1800 cm -1 , it can be determined that a ketone structure is included. Regarding the heterocyclic aromatic ring structure, for example, when a sulfur atom is included, based on Raman spectroscopy, at 1060 cm -1 - 1100 cm -1The presence of a heteroaromatic ring structure can be determined by observing strong luminescence originating from the stretching vibrations of aromatic SC bonds. The same applies to heteroaromatic rings containing nitrogen or oxygen. In this way, by combining infrared spectroscopy, Raman spectroscopy, and NMR measurements, it is confirmed that the carbon dioxide adsorbent has a condensed heteroaromatic ring structure containing a quinone structure.

[0047] The carbon dioxide adsorbent described above contains a condensed heteroaromatic ring structure that includes one or more quinone structures. This adsorbent can efficiently adsorb and release carbon dioxide even in the presence of oxygen.

[0048] (Carbon dioxide absorption and release device) The carbon dioxide absorption and release device according to the embodiment includes the carbon dioxide adsorbent according to the embodiment described above.

[0049] As explained earlier, the adsorbent in question can exhibit redox activity through electrical response. Therefore, the carbon dioxide absorption and release device can adsorb and release carbon dioxide at the redox active sites (quinone structures; ketone groups) of the adsorbent by changing the potential applied to the device. A device using such an adsorbent that absorbs and releases carbon dioxide at its electrically responsive redox active sites can absorb and release carbon dioxide at room temperature. As a result, the device can absorb and release carbon dioxide with low energy.

[0050] As described above, the device can suitably absorb carbon dioxide and can be suitably applied to carbon dioxide recovery equipment for factory exhaust gases and atmospheric carbon dioxide. For example, a carbon dioxide recovery system can be constructed using this carbon dioxide absorption and release device.

[0051] The device may include an electrode for applying a charge to the redox active site of an adsorbent having a condensed heteroaromatic ring structure containing the quinone structure described above. In the device, the adsorbent may be contained in the electrode (working electrode). The electrode is preferably porous, such as in a mesh shape, so that more of the adsorbent can transfer electrons. The adsorbent can also be dispersed within the porous electrode. The adsorbent may also be dispersed in a solution within the device. The solution containing the adsorbent and the electrode may be arranged in a way that the solution and the electrode are in electrical contact within the device.

[0052] The electrode may further include a current collector. For example, the adsorbent may be included in the electrode by being supported on the current collector in the form of a porous body as described above, dispersed within another porous structure, or modified into a conductive member. For example, a porous body may be formed on the surface of the current collector.

[0053] The current collector can function as a conductor to transfer electric charge to the adsorbent, causing the redox active sites to respond electrically. By changing the potential of the current collector, the redox active sites contained in the adsorbent can be oxidized and reduced, causing carbon dioxide to be adsorbed and released from those sites.

[0054] A porous composite can also be constructed by combining a porous material with a conductive member. This combination is achieved, for example, by mixing the porous material and the conductive member, or by modifying (coating) the surface of the conductive member with the porous material.

[0055] In a porous composite, it is preferable that the redox active sites contained in the adsorbent are close to or in contact with a nearby conductive member. Therefore, it is preferable that the adsorbent covers at least a portion of the surface of the conductive member or that the adsorbent adheres to the conductive member. For example, the COF and MOF mentioned above can be included in the porous composite in such a way as to cover the conductive member.

[0056] The electrode may further contain a binder. The binder may or may not be included. The binder can, for example, bond a current collector to a porous material and a conductive member, or a current collector to a porous composite. Examples of binders that can be used include polyvinylidene fluoride (PVdF), polymethyl methacrylate (PMMA), and polyimide (PI).

[0057] The carbon dioxide absorption and release device may further comprise an electrolyte (e.g., an electrolyte solution). An adsorbent may be dispersed in the electrolyte solution. Alternatively, the electrolyte may be held in a porous body in an electrode comprising a porous body or porous composite. The electrolyte may be contained, for example, in the pores of the porous body. By including an electrolyte, conductivity is improved, and the ability to absorb and release CO2 is enhanced.

[0058] The device uses an electrode containing the above-mentioned adsorbent or an electrode electrically in contact with a solution in which the adsorbent is dispersed as the working electrode. By applying a potential to this working electrode, a charge is applied to the redox active site contained in the adsorbent. In other words, by controlling the potential of the electrode, the redox state of the adsorbent is switched between an oxidized state and a reduced state. The adsorbent can adsorb carbon dioxide in the reduced state and release carbon dioxide in the oxidized state.

[0059] For example, by using a counter electrode for the working electrode and applying a voltage between the two electrodes, a potential can be added to the working electrode. For example, a carbon dioxide absorption and release device may include a counter electrode for the electrodes included in the device. In other words, an electrochemical cell using the working electrode and counter electrode may be constructed as a carbon dioxide absorption and release device. The device configuration is not limited to an electrochemical cell. As a specific example of an electrochemical cell, a trielectrode cell can be given that further includes a reference electrode in addition to the working electrode and counter electrode.

[0060] Specific examples of carbon dioxide absorption and release devices according to the embodiment will be described with reference to Figures 7 and 8. Figure 7 is a schematic cross-sectional view showing an example of a carbon dioxide absorption and release device according to the embodiment. Figure 8 is a schematic cross-sectional view showing an electrochemical cell that may be included in other example devices.

[0061] The carbon dioxide absorption and release device 100 shown in Figure 7 comprises an electrochemical cell 110 and a potentiostat 10. The electrochemical cell 110 includes an electrolytic cell 1 containing cells 1a and 1b, a working electrode 2, a counter electrode 3, a reference electrode 4, a separator 6, a nozzle 8 for introducing gas, a nozzle 18 for recovering released carbon dioxide, and a lid 9. Cell 1a houses an electrolyte 5a and a rotor 7 for stirring the electrolyte 5a. Carbon dioxide adsorbent may be included in the electrochemical cell 110 in a dispersed state within the electrolyte 5a. Cell 1b houses the electrolyte 5b. In one example, the electrolyte 5b does not contain carbon dioxide adsorbent. Lids 9 are provided at the openings of each cell to prevent outside air from entering cells 1a and 1b, and a gas containing carbon dioxide can be introduced into the electrolyte 5a through a nozzle 8 that penetrates the lids 9. In the illustrated example, the working electrode 2 and the counter electrode 3 are located separately in cell 1a and cell 1b, respectively. The electrode arrangement is not limited to this example; for example, the counter electrode and the working electrode may be integrated with a separator in between. A specific example is the electrochemical cell 120 shown in Figure 8.

[0062] The electrochemical cell 120 shown in Figure 8 includes a cell 121, a working electrode 122, a counter electrode 123, and a separator 126. The cell 121 is divided into upper and lower chambers with the separator 126 in between, and the working electrode 122 and the counter electrode 123 are provided on the upper and lower main surfaces of the separator 126, respectively. The lower chamber of the cell 121 contains an electrolyte 125, and the counter electrode 123 is in contact with the electrolyte 125. The counter electrode 123 may be immersed in the electrolyte 125. The working electrode 122 is located in the upper chamber of the cell 121. The working electrode 122 contains a carbon dioxide adsorbent and may, for example, be the porous composite described above. The electrolyte 125 contained in the lower chamber does not contain an adsorbent. The upper chamber where the working electrode 122 is located can function as a gas flow path 128, and by passing a gas containing carbon dioxide through it, the contained carbon dioxide can be adsorbed onto the adsorbent in the working electrode 122.

[0063] To improve current flow to the working electrode 122, a porous collector electrode 124 can be laminated on the outside of the working electrode 122, and a porous support 127 can be laminated further outside to fix the entire working electrode 122 and porous collector electrode 124. A porous support 127 can also be laminated on the outside of the counter electrode 123 in a similar manner. The ends of the laminate of the porous collector electrode 124, working electrode 122, separator 126, and counter electrode 123, sandwiched between the supports 127 thus constructed, can be fixed with a fixing device 129. Since the working electrode 122 is porous, the porous collector electrode 124 can be omitted if necessary. Also, if the mechanical strength of the working electrode 122 and counter electrode 123 is sufficient, the porous support 127 can be omitted.

[0064] The current collector, conductive member, and electrolyte will be described in detail below.

[0065] Current collector Components made of carbon or metal can be used as current collectors. The better the conductivity and the larger the surface area of ​​the current collector, the more charge can be transferred to oxidation-reduction active sites. Examples of carbon components include glassy carbon, graphite sheets, carbon felt, carbon cloth, carbon mesh, carbon paper, and carbon sheets with a gas diffusion layer. Examples of metal components include copper plates, copper sheets, copper mesh, aluminum plates, aluminum sheets, aluminum mesh, nickel plates, nickel sheets, and nickel mesh. The carbon components and metal components are not limited to those listed above.

[0066] conductive material For example, a carbon material with good conductivity can be used as the conductive member. The conductive member includes, for example, one or more selected from the group consisting of carbon nanotubes, graphite, graphene, carbon nanofibers, and Ketjenblack. The shape of the conductive member is preferably linear or flat to increase the probability of contact, and is preferably rod-shaped, tubular, fiber-shaped, sheet-shaped, or flake-shaped.

[0067] electrolyte The electrolyte may be, for example, a liquid electrolyte (electrolyte solution). The electrolyte may include, for example, an ionic salt. Specifically, one or more ionic salts selected from the group consisting of alkali metal salts, alkaline earth metal salts, transition metal salts, amphoteric metal salts, ammonium salts, imidazolium salts, pyridinium salts, and phosphonium salts are preferred. The form of the ionic salt may be solid or liquid, and an example of a liquid is, for example, an ionic liquid.

[0068] The cations of ionic salts include alkali metals such as Li, Na, K, Rb, and Cs; alkaline earth metals such as Mg, Ca, Sr, and Ba; transition metals such as Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Pd, and Ag; amphoteric metals such as Al, Ga, and Sn; ammonium ions and ammonium ions substituted with lower hydrocarbons of C1-C5 (N(C) n H2n+1 )4 + , n=1~5); imidazolium ion or imidazolium ion with 1 to 3 substituents; pyridinium ion or pyridinium ion with 1 to 3 substituents; piperidinium ion or piperidinium ion with 1 to 3 substituents; pyrrolidinium ion or pyrrolidinium ion with 1 to 3 substituents; and phosphonium ion PR4 with 4 substituents + You may use one or more selected from the group consisting of (R: hydrocarbon group), and you may use one of the above alone or a combination of several.

[0069] The anion of the ionic salt is Cl - , Br - , and I - Halogens such as nitrate ions (NO3) - ), PF6 - BF4 - CF3SO3 - , N(SO2F2)2 - , N(SO2CF3)2 - CH3COO - CF3COO - , and ClO4 - You may use one or more selected from the group consisting of the above, and you may use one of the above alone or a combination of several of them.

[0070] As the ion-conducting polymer, it is preferable to use one or more selected from the group consisting of polyethylene oxide (PEO), polypropyl oxide (PPO), polyacrylonitrile (PAN), polyvinyl chloride (PVC), ionic liquid polymer, polyaniline, and polythiophene (PEDOT).

[0071] The electrolyte may contain a solvent. The solvent of the electrolyte may be, for example, water or an organic solvent. If the electrolyte is an ionic liquid, a solvent may or may not be used. As the organic solvent, it is desirable to use one or more selected from the group consisting of acetonitrile, propylene carbonate, ethylene carbonate, vinylene carbonate, vinylethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, succinic anhydride, cyclohexylbenzene, thiophene, toluene, fluorobenzene, and hexafluorobenzene.

[0072] <Manufacturing method> Such carbon dioxide absorption and release devices can be manufactured, for example, as follows:

[0073] First, prepare the carbon dioxide adsorbent. For example, the adsorbent can be obtained through synthesis.

[0074] To obtain a device containing an adsorbent in solution, the prepared adsorbent is added to the electrolyte, and the electrodes are set up so that they come into contact with the resulting solution.

[0075] When integrating an adsorbent with an electrode, for example, a porous body containing the adsorbent is synthesized, and a paste containing the resulting porous body is applied to a current collector to obtain an electrode containing the adsorbent. Specifically, the synthesized porous body is mixed with a conductive material, binder, solvent, etc., as appropriate to prepare a paste. By applying this paste to a current collector, an electrode is obtained.

[0076] The above is merely an example, and the paste does not necessarily have to contain a binder. Furthermore, depending on the properties of the conductive material, it is possible to create a self-supporting electrode by heating and drying the paste. In other words, an electrode can be obtained that includes, for example, a porous body containing an adsorbent, without using a current collector.

[0077] To incorporate an electrolyte into the electrode, for example, an electrolyte solution can be prepared, cast onto the electrode surface, and then vacuum impregnation can be performed to incorporate the electrolyte into the electrode.

[0078] The carbon dioxide absorption and release device described above comprises a carbon dioxide adsorbent having a condensed heteroaromatic ring structure. The condensed heteroaromatic ring structure contains one or more quinone structures. Such a device is a carbon dioxide absorption and release device that can efficiently absorb and release carbon dioxide with low energy.

[0079] (Carbon dioxide separation method) The carbon dioxide separation method according to the embodiment includes removing carbon dioxide from a gas containing carbon dioxide by adsorbing carbon dioxide onto an adsorbent using the carbon dioxide absorption and release device described above, and regenerating the adsorbent by desorbing carbon dioxide from it. Adsorbing carbon dioxide onto the adsorbent includes passing an electric current through the adsorbent at the reduction potential of the adsorbent, and bringing the gas containing carbon dioxide into contact with the adsorbent while maintaining the potential flowing through the adsorbent at the reduction potential. Regenerating the adsorbent by desorbing carbon dioxide from it includes switching the potential flowing through the adsorbent that has adsorbed carbon dioxide to the oxidation potential of the adsorbent. The regenerated adsorbent can be reused.

[0080] By setting the device back to the reduction potential after carbon dioxide has been separated from the adsorbent, the carbon dioxide adsorption process can be repeated. In this way, by switching the potential of the current flowing through the adsorbent between the reduction potential and the oxidation potential, the device can be used repeatedly.

[0081] The method for bringing a carbon dioxide-containing gas into contact with the adsorbent is not particularly limited. For example, in a carbon dioxide absorption / release device containing an electrolyte, one method is to bubble a carbon dioxide-containing gas into the electrolyte to adsorb the carbon dioxide in the electrolyte. Another example is to configure the carbon dioxide absorption / release device so that the adsorbent is exposed to a gas stream containing carbon dioxide.

[0082] The concentration of carbon dioxide brought into contact with the adsorbent is not particularly limited, but it can handle a wide range of CO2 concentrations, from atmospheric levels to concentrations emitted from thermal power plants and the like. Specifically, a carbon dioxide concentration of 0.01 vol% or higher is preferred, and 0.04 vol% to 50 vol% is more preferred.

[0083] The ambient temperature during carbon dioxide absorption and release processing is generally preferred to be between 0°C and 60°C. A more preferred temperature is below 50°C, and a particularly preferred temperature is between 10°C and 45°C. The lower the absorption temperature, the greater the amount of carbon dioxide adsorbed. The lower limit of the processing temperature can be determined by the gas temperature in the process, the heat recovery target, etc. The adsorption pressure of carbon dioxide is usually approximately equal to atmospheric pressure. To improve absorption performance, it is possible to pressurize to a higher pressure.

[0084] A method for absorbing and releasing carbon dioxide using such a carbon dioxide absorption and release device may include, for example, the following steps: A process of applying an electric current at the reduction potential to a part containing an adsorbent; The process by which carbon dioxide is adsorbed onto an adsorbent material; A process of changing the electrical potential to the oxidation potential and passing an electric current through it; The process by which carbon dioxide is desorbed from the adsorbent.

[0085] The carbon dioxide separation method described above includes adsorbing carbon dioxide onto an adsorbent contained in a carbon dioxide absorption / release device, separating the carbon dioxide by desorption from the adsorbent, and regenerating the adsorbent. Carbon dioxide is adsorbed onto the adsorbent while the current flowing through the adsorbent is maintained at the reduction potential. The current flowing through the adsorbent is switched to the oxidation potential, and carbon dioxide is desorbed while the oxidation potential is maintained. According to this separation method, carbon dioxide can be absorbed and released efficiently. [Examples]

[0086] The following describes an example of a carbon dioxide absorption and release device using a carbon dioxide adsorbent.

[0087] (Example 1) <Synthesis of Phenanthrene-dithiophene (PDT)> Commercially available phenanthrene-dithiophene (PDT) was prepared and used as it was.

[0088] <Fabrication of the device> The PDT obtained above and tetrabutylammonium tetrafluoroborate (TBABF4) as an electrolyte were added to propylene carbonate (PC) to be 0.2 mol / L and 0.75 mol / L respectively, and heated and mixed (about 80 °C) to obtain a pale yellow transparent solution. The obtained solution was set as an electrolyte in an electrolytic cell to obtain the device of Example 1. Other details of the device will be described later.

[0089] (Example 2) <Synthesis of 2,6-diaminobenzo[1,2-b:4,5-b']dithiophene-4,8-dione (2NH2-BDTD)> Commercially available 2,6-diaminobenzo[1,2-b:4,5-b']dithiophene-4,8-dione (2NH2-BDTD) was prepared and used as it was.

[0090] <Fabrication of the device> The 2NH2-BDTD and TBABF4 obtained above were added into PC and adjusted to be 0.2 mol / L and 0.75 mol / L respectively to obtain an electrolyte. The obtained electrolyte was set in an electrolytic cell to obtain the device of Example 2. Other details of the device will be described later.

[0091] (Example 3) <Synthesis of 2NH2-BDTD-TFP-COF composite electrode> Referring to Non-Patent Document 1 (J. Am. Chem. Soc., 2013, 135, 16821-16824), 2NH2-BDTD and 1,3,5-triformylphloroglucinol (TFP) were placed in a heat-resistant container in a molar ratio of 1:3 and heated at 120 °C for 2 days in a dioxane solvent. The obtained crude crystals were washed and filtered with a dimethylacetamide (DMA) solvent and dried under reduced pressure to obtain 2NH2-BDD-TFP-COF. The obtained 2NH2-BDTD-TFP-COF was mixed with carbon nanofibers (CNF) and polyvinylidene fluoride (PVdF) in a mass ratio of 6:3:1 under an N-methylformamide solvent (NMF solvent), and coated on a carbon felt to obtain an electrode as a composite containing a porous body.

[0092] <Fabrication of Device> The composite electrode obtained above was set in an electrolytic cell, and a device of Example 3 was obtained using an electrolytic solution prepared by dissolving 0.75 mol / L of TBABF4 in PC. Other details of the device will be described later.

[0093] (Example 4) <Synthesis of 5,8-Quinolinediol (QD)> Commercially available 5,8-quinolinediol (QD) was prepared and used as it was.

[0094] <Fabrication of Device> QD and TBABF4 obtained above were added to PC and adjusted to 0.2 mol / L and 0.75 mol / L respectively to obtain an electrolytic solution. The obtained electrolytic solution was set in an electrolytic cell to obtain a device of Example 4.

[0095] (Example 5) <Synthesis of Benzo[1,2-b:4,5-b']difuran-4,8-dione (BDFD)> Commercially available benzo[1,2-b:4,5-b']difuran-4,8-dione (BDFD) was prepared and used as it was.

[0096] <Fabrication of the Device> BDFD and TBABF4 obtained above were added into PC and adjusted to 0.2 mol / L and 0.75 mol / L respectively to obtain an electrolyte solution. The obtained electrolyte solution was set in an electrolytic cell to obtain the device of Example 5.

[0097] (Example 6) <Synthesis of 1H-Indole-4,5-dione (ID)> Commercially available 1H-indole-4,5-dione (ID) was prepared and used as it was.

[0098] <Fabrication of the Device> ID and TBABF4 obtained above were added into PC and adjusted to 0.2 mol / L and 0.75 mol / L respectively to obtain an electrolyte solution. The obtained electrolyte solution was set in an electrolytic cell to obtain the device of Example 6.

[0099] (Example 7) <Synthesis of Benzo[b]selenophene-4,7-dione (BSD)> Commercially available benzo[b]selenophene-4,7-dione (BSD) was prepared and used as it was.

[0100] <Fabrication of the Device> BSD and TBABF4 obtained above were added into PC and adjusted to 0.2 mol / L and 0.75 mol / L respectively to obtain an electrolyte solution. The obtained electrolyte solution was set in an electrolytic cell to obtain the device of Example 7.

[0101] (Comparative Example 1) <Preparation of 1,8-diaminoanthraquinone (2NH2-AQ)> Commercially available 1,8-diaminoanthraquinone (1,8-diaminoanthraquinone; 2NH2-AQ) was prepared and used as it was.

[0102] <Device Fabrication> A device of Comparative Example 1 was obtained in the same manner as in Example 1, except that 2NH2-AQ was used instead of PDT.

[0103] (Comparative Example 2) <Synthesis of Naphthazarin (NZ)> Naphthazarin (NZ) was obtained.

[0104] <Device Fabrication> A device of Comparative Example 2 was obtained in the same manner as in Example 1, except that NZ was used instead of PDT.

[0105] (Evaluation) <Infrared Spectroscopy> Infrared spectroscopy was performed on the PDT prepared in Example 1. The infrared spectroscopy was carried out as follows. Using an infrared spectrometer (FT-IR6100 manufactured by JASCO Corporation), the measurement range was 400 cm -1 - 4000 cm -1 and the measurement speed was 40 cm -1 / sec. Absorption derived from the stretching vibration of the aromatic S-C bond was observed near 1100 cm -1 and absorption derived from the stretching vibration of the aromatic ring was observed at 1400 cm -1 - 1600 cm -1 . A strong absorption derived from the stretching vibration of the C=O bond was observed near 1600 cm -1 - 1850 cm -1 . It was confirmed that it is a heteroaromatic ring structure containing S having a quinone structure. <Raman Spectroscopy> Raman spectroscopy was performed on the PDT prepared in Example 1.

[0106] Raman spectroscopic measurement was carried out as follows. Using a Raman spectrometer (LabRAM Evolution manufactured by HORIBA), the excitation laser wavelength was 532 nm and the measurement range was 200 cm -1 - 3300 cm -1 for measurement. From the presence of strong emissions at 1060 cm -1 - 1100 cm -1 derived from the stretching vibration of the aromatic S-C bond, and strong emissions at 1400 cm -1 - 1600 cm -1 derived from the stretching vibration of the aromatic ring, it was confirmed that there is a heteroaromatic ring structure containing S in the molecular structure.

[0107] <NMR Measurement> For the PDT prepared in Example 1, 1 1H and 13 13C NMR measurements were performed. The peaks confirmed by the measurement conditions and measurement spectra were as follows.

[0108] 1 1H NMR (CD2Cl2, 400 MHz, δ in ppm): 7.62 (dd, 2H), 7.44 (dd, 2H). 13 13C NMR (DMSO, 一百MHz, δ in ppm): 127.0, 135.0, 138.2, 149.5, 177.0. <Electrochemical Measurement> For each device fabricated in Examples 1 to 6 and Comparative Examples 1 and 2, the electrochemical performance was evaluated. Specifically, test devices using the fabricated devices were constructed and cyclic voltammetry (CV) measurements were performed.

[0109] For Examples 1, 2, and 4-6, and Comparative Examples 1-2, the test device employed a three-electrode electrochemical cell configuration similar to the carbon dioxide absorption / release device 100 shown in Figure 7. The test device consisted of a φ3mm glassy carbon rod for working electrode 2, an electrolyte (5a) containing the adsorbents prepared in Examples 1, 2, 4-6, and Comparative Examples 1-2, a platinum mesh electrode for counter electrode 3, a 0.75 mol / L TBABF4 electrolyte (5b) containing 0.01 mol / L ferrocene, and an Ag / Ag electrode for reference electrode 4. + An electrode (acetonitrile / 0.1M (M:mol / L) tetrabutylammonium perchlorate solution / 0.01M AgNO3) was used.

[0110] Before measurement, argon (Ar) gas was passed through nozzle 8 into the electrolyte 5a in cell 1a for about 30 minutes, and CV measurement was performed using potentiostat 10. Subsequently, 100% carbon dioxide gas was passed through nozzle 8 for about 30 minutes, and CV measurement was performed again.

[0111] For Example 3, since the adsorbent was integrated with the electrode, measurements were carried out using a test device with an electrochemical cell having the configuration shown in Fig. 8. The fabricated composite electrode was used as the working electrode 122 and laminated with a platinum mesh electrode as the counter electrode 123 via a separator 126. A porous current collector 124 was laminated outside the working electrode 122 to improve the energization of the composite electrode, and a support 127 of a porous material for fixing the entire electrode was further laminated outside thereof. A support 127 of a porous material was similarly laminated outside the counter electrode 123, and the ends were fixed with a fixture 129. An electrolytic solution 125 (a 0.75 mol / L TBABF4 solution containing 0.01 mol / L ferrocene without an adsorbent) was placed in one chamber of the cell 121 having two communicating chambers, the communication between the two chambers was blocked, and a laminate including the working electrode 122 and the counter electrode 123 was set in the cell 121 such that the counter electrode 123 was immersed in the electrolytic solution 125. The chamber without the electrolytic solution 125 was used as a gas flow path 128 for ventilating Ar gas and carbon dioxide gas. The separator 126 used had a structure that allowed the electrolytic solution 125 to penetrate to the working electrode 122 across the separator 126. CV measurements were carried out in the same manner as in Example 1, etc., except that such an electrochemical cell 120 was used.

[0112] As an example, the CV measurement results of PDT obtained by the device of Example 1 are shown in Fig. 9. In the graph shown in Fig. 9, the curve during the CV measurement under a CO2 atmosphere is indicated by a solid line. As shown in the graph, a reduction peak was observed around -0.8V (vs. Ag / Ag + ) and an oxidation peak was observed around -0.66V (vs. Ag / Ag + ). Therefore, as predicted by the calculation, it was confirmed that the redox reaction was carried out at a potential nobler than the redox potential of oxygen.

[0113] <CO2 Absorption and Release Test> Carbon dioxide absorption and release tests were conducted using the devices fabricated in Examples 1-6 and Comparative Examples 1-2. The basic procedure for these tests was the same as for CV evaluation. First, an inert gas was introduced into the electrolyte and bubbling was performed for about 30 minutes. Argon gas was used as the inert gas. Then, while bubbling carbon dioxide gas, a potential slightly exceeding the reduction potential of each adsorbent was applied for a certain period of time to adsorb carbon dioxide onto the adsorbent. After that, the space above the electrolyte was replaced with an inert gas, and a tube for recovering CO2 was connected to the cell. With everything except the CO2 recovery tube sealed, a potential slightly exceeding the oxidation potential of each adsorbent was applied for a certain period of time to desorb carbon dioxide from the adsorbent. The desorbed carbon dioxide accumulated in the space above the electrolyte. After stopping the application of the potential for carbon dioxide desorption, sampling was performed on the space above the electrolyte. The amount of carbon dioxide adsorbed and recovered by the adsorbent was determined by quantitative analysis using gas chromatography (GC) with the collected gas. The amount of CO2 recovered by each adsorbent is shown in Table 5 below. Table 5 also shows the abbreviations and chemical structures of each adsorbent. However, for Example 3, the chemical structure is shown below Table 5 due to its size.

[0114] [Table 5]

[0115] [ka]

[0116] The results from Examples 1-6 and Comparative Examples 1-2 shown in Table 5 indicate that it is advantageous not only to introduce substituents on the outer circumference of the condensed ring, but also to replace some of the carbon atoms constituting the ring to form a heterocycle. Furthermore, Examples 1, 2, and 3 show that there is no significant difference in the performance of adsorbents having a condensed heteroaromatic ring structure depending on the heteroatoms introduced into the ring. In addition, Examples 2 and 3 show that because the COF is on the electrode, electron transfer is easier than in the solution type, resulting in a slightly higher CO2 content.

[0117] According to the one or more embodiments and examples described above, a carbon dioxide adsorbent and a carbon dioxide absorption / release device using the same are provided. The adsorbent has a condensed heteroaromatic ring structure containing one or more quinone structures and can efficiently absorb and release carbon dioxide. As a result, the device can efficiently absorb and release carbon dioxide and efficiently recover carbon dioxide.

[0118] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents.

[0119] Several embodiments of the present invention are described below. [1] A carbon dioxide adsorbent capable of adsorbing and releasing carbon dioxide, having a condensed heteroaromatic ring structure containing one or more quinone structures. [2] The carbon dioxide adsorbent according to [1], which is capable of adsorbing carbon dioxide on the quinone structure in a reduced state and releasing carbon dioxide from the quinone structure in an oxidized state. [3] The carbon dioxide adsorbent according to [1] or [2], which can undergo oxidation-reduction by an electrical response. [4] The carbon dioxide adsorbent according to any one of [1] to [3], wherein the condensed heteroaromatic ring structure is one or more selected from the group consisting of a benzene-based heteroaromatic ring structure, a naphthalene-based heteroaromatic ring structure, anthracene-based heteroaromatic ring structure, and a phenanthrene-based heteroaromatic ring structure. [5] The carbon dioxide adsorbent according to any one of [1] to [4], wherein the condensed heteroaromatic ring structure comprises one or more selected from the group consisting of nitrogen, oxygen, and sulfur. [6] A porous metal-organic structure, the carbon dioxide adsorbent described in any one of [1] to [5]. [7] A porous covalent organic structure, the carbon dioxide adsorbent according to any one of [1] to [5]. [8] The carbon dioxide adsorbent according to any one of [1] to [5], wherein the oligomer or polymer contains a molecule containing the condensed heteroaromatic ring structure as a unit structure. [9] A carbon dioxide adsorbent according to any one of [1] to [8], which exhibits a redox potential that is nobler than that of oxygen. A carbon dioxide absorption and release device comprising a carbon dioxide adsorbent described in any one of [1] to [9]. [Explanation of Symbols]

[0120] 1...Electrolytic cell, 1a...Cell, 1b...Cell, 2...Working electrode, 3...Counter electrode, 4...Reference electrode, 5a...Electrolyte, 5b...Electrolyte, 6...Separator, 7...Rotor, 8...Nozzle, 9...Lid, 10...Potenstiostat, 18...Nozzle, 100...Carbon dioxide absorption / release device, 110...Electrochemical cell, 120...Electrochemical cell, 121...Cell, 122...Working electrode, 123...Counter electrode, 125...Electrolyte, 126...Separator, 128...Gas flow path.

Claims

1. A carbon dioxide adsorbent capable of adsorbing and releasing carbon dioxide, having a condensed heteroaromatic ring structure containing one or more quinone structures.

2. The carbon dioxide adsorbent according to claim 1, which is capable of adsorbing carbon dioxide on the quinone structure in a reduced state and releasing carbon dioxide from the quinone structure in an oxidized state.

3. A carbon dioxide adsorbent according to claim 1 or 2, which can undergo oxidation-reduction by an electrical response.

4. The carbon dioxide adsorbent according to claim 3, wherein the condensed heteroaromatic ring structure comprises one or more selected from the group consisting of a benzene-based heteroaromatic ring structure, a naphthalene-based heteroaromatic ring structure, anthracene-based heteroaromatic ring structure, and a phenanthrene-based heteroaromatic ring structure.

5. The carbon dioxide adsorbent according to claim 3, wherein the condensed heteroaromatic ring structure comprises one or more selected from the group consisting of nitrogen, oxygen, and sulfur.

6. A carbon dioxide adsorbent according to claim 1 or 2, wherein the adsorbent is a porous metal-organic structure.

7. A carbon dioxide adsorbent according to claim 1 or 2, which is a porous covalent organic structure.

8. The carbon dioxide adsorbent according to claim 1 or 2, which is an oligomer or polymer containing a molecule containing the aforementioned condensed heteroaromatic ring structure as a unit structure.

9. A carbon dioxide adsorbent according to claim 1 or 2, which exhibits a redox potential nobler than that of oxygen.

10. A carbon dioxide absorption and release device comprising the carbon dioxide adsorbent described in claim 1.

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