Proton conductor and electrochemical device

Abstract

This proton conductor comprises a two-dimensional covalent organic framework (30) in which at least two linkers different from each other form a cyclic repeating unit in the two-dimensional direction by means of a covalent bond. In the repeating unit, a pore (31) is formed on the inside of the cyclic shape. A plurality of two-dimensional covalent organic frameworks are stacked in a stacking direction so that pores communicate with each other, to form a single crystal (32). The single crystal of the two-dimensional covalent organic frameworks has a plurality of communicating pores (33) in which pores communicate with each other. The plurality of communicating pores are oriented in the same direction.

Description

Proton conductors and electrochemical devices

[0001] This disclosure relates to proton conductors and electrochemical devices.

[0002] Proton conductors are solid materials through which protons can move, and are used in fuel cells, hydrogen sensors, hydrogen pumps, and other applications. Examples of proton conductors include proton-conducting polymers such as Nafion (registered trademark) and metal oxides with a perovskite structure.

[0003] In recent years, the use of covalent organic frames (COFs) as proton conductors has been investigated. COFs are a group of crystalline porous organic solid materials composed of organic structural units linked by covalent bonds in two-dimensional or three-dimensional space. For example, as disclosed in Patent Document 1, COFs formed in the form of a two-dimensional planar sheet are called two-dimensional covalent organic frames (2D-COFs).

[0004] Chinese Patent Application Publication No. 114456339 Specification

[0005] Therefore, in order to improve the performance of electrochemical devices such as fuel cells, there is a need to search for proton conductors that can exhibit sufficient proton conductivity. Even with the 2D-COF mentioned above, there is still room for improvement in terms of proton conductivity.

[0006] In view of the above, this disclosure aims to provide a proton conductor capable of improving proton conductivity and an electrochemical device using the same.

[0007] To achieve the above objective, a proton conductor according to one aspect of the present disclosure comprises a two-dimensional covalent organic structure in which two or more different linkers form a two-dimensional repeating cyclic unit by covalent bonds, wherein pores are formed inside the annular shape of the repeating unit, and the multiple two-dimensional covalent organic structures are stacked in a stacking direction such that the pores communicate with each other to form a single crystal, and the single crystal of the two-dimensional covalent organic structure has multiple communicating pores, and the multiple communicating pores are oriented in the same direction.

[0008] According to this, in single crystals of two-dimensional covalent organic structures, the proton conductivity in the pore-through direction, which is the direction in which the pores extend, can be increased. As a result, it becomes possible to improve the proton conductivity of proton conductors.

[0009] This is a conceptual diagram of a fuel cell cell according to one embodiment. This is an explanatory diagram showing a single crystal of 2D-COF in one embodiment. This is an explanatory diagram for explaining the stacking state of 2D-COF in one embodiment. This is an explanatory diagram for explaining the orientation state of 2D-COF in the electrolyte in one embodiment. This is an explanatory diagram showing a single particle of unoriented COF. This is an explanatory diagram for explaining the orientation state of 2D-COF in the electrolyte in an unoriented COF electrolyte. This is a diagram showing the PXRD measurement results in Experimental Example 1. This is a diagram showing the PXRD measurement results in Experimental Example 2. This is a diagram showing the PXRD measurement results in a comparative experimental example. This is a diagram showing the GI-WAXS image in Experimental Example 1. This is a diagram showing the GI-WAXS image in Experimental Example 2. This is a diagram showing the GI-WAXS image in a comparative experimental example. This is a diagram showing the proton conductivity measurement results in Experimental Example 1. This is a diagram showing the proton conductivity measurement results in Experimental Example 2. This is a diagram showing the proton conductivity measurement results in a comparative experimental example. This is a diagram showing the TEM and TEM-ED measurement results in Experimental Example 1. This is a diagram showing the TEM and TEM-ED measurement results in Experimental Example 2. This figure shows the results of TEM and TEM-ED measurements in comparative experimental examples. This figure shows the MD simulation results for proton mobility in an oriented COF electrolyte according to one embodiment. This is an explanatory diagram for explaining the orientation state of 2D-COF in the electrolyte of the comparative example. This figure shows the MD simulation results for proton mobility in the COF electrolyte of the comparative example.

[0010] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. Note that at least one of the members or parts described with reference numerals is provided, unless otherwise specified as "one" or similar.

[0011] In this embodiment, the proton conductor of the present disclosure is applied to a fuel cell cell 100 of a fuel cell. The fuel cell cell 100 is an electrochemical device that transports protons in a predetermined proton transport direction.

[0012] As shown in FIG. 1, the fuel cell 100 includes a membrane electrode assembly (MEA) composed of an electrolyte membrane 110 and a pair of electrodes 120 and 130 that sandwich the electrolyte membrane 110. The pair of electrodes 120 and 130 consists of an anode electrode 120 and a cathode electrode 130. Note that the anode electrode 120 is also referred to as a hydrogen electrode, and the cathode electrode 130 is also referred to as an air electrode.

[0013] The fuel cell 100 outputs electrical energy by utilizing the electrochemical reaction between hydrogen and oxygen in the air. It can be used in a stack structure in which a plurality of fuel cells 100 are stacked as basic units. Hydrogen is the fuel gas, and oxygen in the air is the oxidant gas.

[0014] When hydrogen is supplied to the anode electrode 120 and air is supplied to the cathode electrode 130, hydrogen and oxygen undergo an electrochemical reaction to output electrical energy as follows.

[0015] (Anode electrode side) H ２ → 2H ＋ + 2e － (Cathode electrode side) 2H ＋ + 1 / 2O ２ + 2e － → H ２ O At this time, on the anode electrode 120, hydrogen is ionized into electrons (e － ) and protons (H ＋ ) by a catalytic reaction, and the protons (H ＋ ) move through the electrolyte membrane 110. On the other hand, on the cathode electrode 130, the protons (H ＋ ) that have moved from the anode electrode 120 side, the electrons that have flowed in from the outside, and the oxygen (O ２ ) in the air react to generate water (H ２ O).

[0016] The anode electrode 120 comprises an anode-side catalyst layer 121 positioned in close contact with the anode-side surface of the electrolyte membrane 110, and an anode-side diffusion layer 122 positioned outside the anode-side catalyst layer 121. The cathode electrode 130 comprises a cathode-side catalyst layer 131 positioned in close contact with the cathode-side surface of the electrolyte membrane 110, and a cathode-side diffusion layer 132 positioned outside the cathode-side catalyst layer 131. The diffusion layers 122 and 132 are formed of carbon cloth or the like.

[0017] The catalyst layers 121 and 131 contain catalysts 121a and 131a, and ionomers 121b and 131b that coat the catalysts 121a and 131a. As an example, in this embodiment, catalyst-supported carbon is used as the catalysts 121a and 131a, in which a platinum catalyst that promotes an electrochemical reaction is supported on a carbon support. The platinum catalyst only needs to contain platinum; for example, elemental platinum or a platinum-cobalt alloy consisting of platinum and cobalt can be used.

[0018] Ionomers 121b and 131b contain a proton conductor and a polymer as a binder. For example, polytetrafluoroethylene (PTFE) can be used as the binder.

[0019] The electrolyte membrane 110 is a proton conductor. The proton conductor constituting the electrolyte membrane 110 contains a polymer as a binder and a proton carrier, which is a proton conducting material.

[0020] The proton conductor of this embodiment comprises a two-dimensional covalent organic structure (hereinafter referred to as 2D-COF) formed in the shape of a two-dimensional sheet. The 2D-COF is a crystalline porous material in which two or more different linkers form repeating cyclic units in the two-dimensional direction by covalent bonds. In the repeating units of the 2D-COF, pores are formed on the inside of the annular structure. Hereinafter, in the repeating units of the 2D-COF, the annular portion that forms the pores will be referred to as the annular portion.

[0021] The two-dimensional covalently linked organic structure has a side chain containing a proton-conductive functional group in the skeleton which is a repeating unit. In this embodiment, as an example, at least one selected from a sulfonic acid group, a phosphonic acid group, a carboxylic acid group, a hydroxy group, and an amino group is used as the proton-conductive functional group.

[0022] Also, the linker constituting the 2D-COF may be at least one selected from an aromatic compound having two amino groups located at the para position, a heterocyclic compound containing a nitrogen atom, and an aromatic compound having three aldehyde groups.

[0023] In this embodiment, as an example, a compound represented by the following formula (1) is used as the 2D-COF.

[0024]

[0025] However, in formula (1), R represents at least one selected from the compounds represented by the following formulas (2) to (78). In formulas (2) to (78), m represents an integer of 0 to 4.

[0026]

[0027]

[0028]

[0029]

[0030]

[0031]

[0032]

[0033]

[0034] In the proton conductor of this embodiment, as shown in FIG. 2, in the 2D-COF 30, pores 31 are formed inside the annular portion 34. In other words, in the 2D-COF 30, the pores 31 are partitioned by the annular portion 34. That is, the annular portion 34 is a pore-forming portion that forms the pores 31. In the chemical formula in FIG. 2, n represents an integer of 1 or more.

[0035] 2D-COF 30 is formed by stacking in a predetermined stacking direction so that the pores 31 communicate with each other, and then forming a single crystal. The single crystal 32 of 2D-COF 30 has multiple communicating pores 33 in which the pores 31 communicate with each other. The multiple communicating pores 33 are oriented in the same direction to each other. In other words, an annular portion 34 is provided in the single crystal 32 of 2D-COF 30 so that the multiple communicating pores 33 are oriented in the same direction to each other.

[0036] In Figure 2, a single crystal 32 of 2D-COF 30 is shown, formed such that the dimension in the direction in which the interconnected pores 33 extend is longer than the dimensions in other directions. However, the aspect ratio of the single crystal 32 of 2D-COF 30 is not limited to a specific aspect ratio.

[0037] Here, in this disclosure, "oriented in the same direction" does not mean that they are not perfectly oriented in the same direction. In other words, "multiple communicating pores 33 are oriented in the same direction to one another" also includes a state in which the angle between the direction in which one of the multiple communicating pores 33 extends and the direction in which another communicating pore 33 extends is less than 90°.

[0038] As an example, in this embodiment, the 2D-COF may have an orientation state determined from the positions of the diffraction spots of the (100) plane and the (001) plane in the two-dimensional diffraction pattern obtained by micro-angle incident wide-angle X-ray scattering measurement.

[0039] As an example, in this embodiment, as shown in Figure 3, the single crystal 32 of 2D-COF 30 has an AA stacking structure. An AA stacking structure refers to a state in which multiple two-dimensional sheet-like 2D-COF 30 are stacked such that the constituent atoms of adjacent 2D-COF 30 in the stacking direction are in the same position.

[0040] As shown in Figure 4, the proton conductor of this embodiment comprises a plurality of single crystals 32. The plurality of single crystals 32 are arranged within the electrolyte membrane 110 such that the interconnected pores 33 of each single crystal 32 are oriented in the same direction.

[0041] Here, "the interconnected pores 33 of each single crystal 32 are oriented in the same direction" also includes a state in which the angle between the direction in which the interconnected pores 33 extend in one single crystal 32 and the direction in which the interconnected pores 33 extend in another single crystal 32 is less than 90°.

[0042] As an example, in this embodiment, the multiple single crystals 32 may be arranged such that the degree of orientation F of the interconnected pores 33 of each single crystal 32 within the electrolyte membrane 110 is 51% or more. The degree of orientation F is calculated using the following formula (F1).

[0043] F = (360° - ΣW) / 360° ... (F1) where, in formula (F1), W is the full width at half maximum of the intensity-azimuth angular spectrum output from the θ-direction integral of the (100) plane peak of the annular spectrum in the Grazing Incidence Wide Angle X-ray Scattering (GI-WAXS) image.

[0044] Furthermore, as an example, the proton conductor of this embodiment may have a proton conductivity of 90% or more after the water resistance test. In this embodiment, the water resistance test is a test in which the proton conductor is immersed in pure water at 25°C for 24 hours and the proton conductivity is measured before and after the test.

[0045] Furthermore, in the fuel cell cell 100 of this embodiment, the proton conductors are arranged such that the direction in which the pores 31 extend is the same as the direction of proton transport.

[0046] The following sections will explain this disclosure in more detail using experimental examples, but this disclosure is not limited to the experimental examples described later.

[0047] In the following, a 2D-COF 30 in which multiple interconnected pores in a single crystal 32 are oriented in the same direction, and the interconnected pores 33 of each single crystal 32 are oriented in the same direction, will be referred to as an oriented COF.

[0048] Furthermore, a 2D-COF 30 in which multiple interconnected pores in a single particle are not oriented in the same direction, or in which the interconnected pores 33 of each single crystal 32 are not oriented in the same direction, is called an unoriented COF.

[0049] In other words, as shown in Figure 5, the unoriented COF may be arranged such that the directions in which multiple interconnected pores 33 extend are different from each other within a single particle of 2D-COF. Alternatively, as shown in Figure 6, the unoriented COF may consist of multiple single crystals 32, each with multiple interconnected pores 33 oriented in the same direction, and the directions in which the interconnected pores 33 extend are different from each other within each single crystal 32.

[0050] (Experimental Example 1) In Experimental Example 1, the oriented COF is TpPa-COF-SO, which is represented by the following formula (79). ３ H was used.

[0051]

[0052] However, in equation (79), n represents an integer greater than or equal to 1.

[0053] In Experimental Example 1, an electrolyte containing oriented COF (hereinafter referred to as oriented COF electrolyte) was synthesized by the following water-oil interface method. Specifically, 0.1 mmol of 1,3,5-triformyl phloroglucinol was dissolved in 20 mL of octanoic acid. 0.15 mmol of 2,5-diaminobenzenesulfonic acid was dissolved in 30 mL of pure water.

[0054] Next, an amine monomer solution was injected into a 50 mm diameter vial, and then an aldehyde monomer solution was gently injected to form an octanoic acid / water interface. The vial with the octanoic acid / water interface was left to stand in a 16°C incubator for 7 days to synthesize oriented COF.

[0055] After synthesis was complete, only the lower layer (i.e., the aqueous layer) in the vial was collected using a pipette, filled into cellulose tubing for dialysis (MWCO: 12,000-14,000), and dialyzed in a large volume of pure water for three days. This produced an oriented COF dispersion from which unreacted components and minute-sized COF particles had been removed.

[0056] Oriented COF was collected by vacuum suction filtration of the oriented COF dispersion to obtain an oriented COF electrolyte. A PX series filter (Synder Filtration, manufactured by Sterlitech) was used, and the vacuum was controlled at -0.08 MPa. After filtration, the filter containing the oriented COF electrolyte was immersed in N,N-dimethylformamide to remove the oriented COF electrolyte from the filter.

[0057] The oriented COF electrolyte, detached from the filter, was washed again with N,N-dimethylformamide and then treated with 2 mol / L sulfuric acid at 60°C for 3 days. The treated oriented COF electrolyte film was thoroughly washed with water until the wash water reached pH 7. Thus, an oriented COF electrolyte film was obtained.

[0058] (Experimental Example 2) In Experimental Example 2, the oriented COF is TpBd-COF-SO, which is shown in the following formula (80). ３ H was used.

[0059]

[0060] However, in equation (80), n represents an integer of 1 or greater.

[0061] In Experimental Example 2, the oriented COF electrolyte was synthesized by the following water-oil interface method. Specifically, 0.1 mmol of 1,3,5-triformyl phloroglucinol was dissolved in 20 mL of octanoic acid. 0.15 mmol of 4,4'-diamino-[1,1'-biphenyl]-3,3'-disulfonic acid was dissolved in 60 mL of pure water.

[0062] Next, an amine monomer solution was injected into a 50 mm diameter vial, and then an aldehyde monomer solution was gently injected to form an octanoic acid / water interface. The vial with the octanoic acid / water interface was left to stand in a 60°C incubator for 14 days to synthesize oriented COF.

[0063] After the synthesis was complete, a membrane of oriented COF electrolyte was obtained by performing the same procedure as in Example 1 (i.e., dialysis, vacuum suction filtration, DMF peeling, 2M sulfuric acid treatment, and water washing).

[0064] (Comparative Experiment Example) In the comparative experiment example, the unoriented COF used is TpPa-COF-SO4, which is the same type of 2D-COF as in Experiment Example 1. ３ H was used. In other words, while experimental example 1 and the comparative experimental example use the same type of 2D-COF, they differ in whether or not the interconnected pores in each are oriented in the same direction.

[0065] In a comparative experiment, an electrolyte containing unoriented COF (hereinafter referred to as unoriented COF electrolyte) was synthesized by the following hydrothermal synthesis method. Specifically, a Schlenk tube was filled with 0.4 mmol of 1,3,5-triformyl phloroglucinol, 0.6 mmol of 2,5-diaminobenzenesulfonic acid, 0.8 mL of acetic acid (6 mol / L), 4.5 mL of mesitylene, and 1.5 mL of dioxane. After sonication for 15 minutes, the Schlenk tube was flash-frozen in a liquid nitrogen bath, degassed by three freeze-thaw cycles, and then sealed. Subsequently, it was treated at 120°C for 96 hours to produce a powder.

[0066] Subsequently, the generated powder was collected, washed with dimethylformamide (DMF), water, and methanol, and dried under vacuum at 80°C for 48 hours to obtain a powder of unoriented COF electrolyte. The obtained powder was press-molded at 40 MPa to obtain an unoriented COF electrolyte.

[0067] (PXRD Measurement) Powder X-ray diffraction (PXRD) measurements were performed on the oriented COF electrolytes of Experimental Examples 1 and 2 and the unoriented COF electrolyte of the comparative experiment. Specifically, PXRD measurements were performed using a powder X-ray diffractometer to obtain PXRD spectra for the oriented COF electrolytes of Experimental Examples 1 and 2 and the unoriented COF electrolyte of the comparative experiment. A MiniFlex 600 powder X-ray diffractometer (manufactured by Rigaku Corporation) was used. The results are shown in Figures 7 to 9.

[0068] In Experimental Examples 1 and 2 and the Comparative Experiment, peaks are formed in the (100) and (001) planes in the PXRD spectra, as shown in Figures 7 to 9. This indicates that the constituent atoms are regularly arranged in the oriented COF single crystals of Experimental Examples 1 and 2 and the unoriented COF single crystal of the Comparative Experiment.

[0069] (GI-WAXS) Grazing Incidence Wide Angle X-ray Scattering (GI-WAXS) measurements were performed on the oriented COF electrolytes of Experimental Examples 1 and 2 and the unoriented COF electrolyte of the comparative experiment. Specifically, the oriented COF electrolyte and the unoriented COF electrolyte were placed as samples on a non-reflective Si substrate. X-rays were incident on the surface of each sample, and two-dimensional diffraction patterns (GI-WAXS patterns) were acquired using an R-AXIS detector. The X-ray wavelength was 0.92 Å and the incident angle was 0.3 degrees. The results are shown in Figures 10 to 12.

[0070] In the oriented COF electrolytes of Experimental Examples 1 and 2, scattered X-rays from the (100) plane in the Qz direction and the (001) plane in the Qxy direction are observed anisotropically in the GI-WAXS images, as shown in Figures 10 and 11. This indicates that, as a whole, the interconnected COF pores in the oriented COF of Experimental Examples 1 and 2 are oriented in the same direction.

[0071] On the other hand, in the unoriented COF electrolyte of the comparative experiment, as shown in Figure 12, anisotropic scattered X-rays from the (100) and (001) planes were not observed in the GI-WAXS image, but isotropic scattered X-rays were observed. This indicates that the unoriented COF of the comparative experiment is unoriented, as the interconnected COF pores are not oriented in the same direction.

[0072] (Proton Conductivity Measurement) Proton conductivity measurements were performed for the oriented COF electrolytes in Experimental Examples 1 and 2, and the unoriented COF electrolyte in the comparative experiment. For the oriented COF electrolytes in Experimental Examples 1 and 2, proton conductivity measurements were performed in the direction of penetration through the pores and the direction of transverse pores.

[0073] Note that the pore penetration direction is the direction in which the interconnected pores extend. The pore transverse direction is the direction perpendicular to the pore penetration direction. For the unoriented COF electrolyte in the comparative experiment, proton conductivity measurements were performed in a predetermined direction 1 and in direction 2, which is perpendicular to direction 1.

[0074] Specifically, the proton conductivity σ (S / cm) of the oriented COF electrolytes in Experimental Examples 1 and 2 and the unoriented COF electrolyte in the comparative experiment was calculated using the following formula (F2) after obtaining the resistance value R (Ω) from the Cole-Cole plot obtained by the AC impedance method.

[0075] σ = l / (R × A) ... (F2) where l is the distance between electrodes (cm) and A is the electrode area (cm²) ２ Specifically, measurements were taken in an environment of 80°C and 90% relative humidity, using Pt electrodes, with an oscillation voltage of 30mV and a frequency range of 1MHz to 1Hz. The results are shown in Figures 13 to 15.

[0076] The sample density for Experimental Example 1 was 1.38 g / cm³. ３ The sample density in Experimental Example 2 was 1.20 g / cm³. ３ The sample density in the comparative experiment was 1.13 g / cm³. ３ That was the case.

[0077] In the oriented COF of Experimental Example 1, as shown in Figure 13, the proton conductivity in the transverse direction of the pore was 0.006 S / cm, while the proton conductivity in the penetrating direction of the pore was 0.086 S / cm. In other words, in the oriented COF of Experimental Example 1, the proton conductivity in the penetrating direction of the pore was approximately 14 times that of the proton conductivity in the transverse direction of the pore. Therefore, in the oriented COF of Experimental Example 1, high proton conductivity in the penetrating direction of the pore can be ensured.

[0078] Similarly, in the oriented COF of Experimental Example 2, as shown in Figure 14, the proton conductivity in the transverse direction of the pore was 0.002 S / cm, while the proton conductivity in the penetrating direction of the pore was 0.338 S / cm. In other words, in the oriented COF of Experimental Example 2, the proton conductivity in the penetrating direction of the pore was approximately 169 times that of the proton conductivity in the transverse direction of the pore. Therefore, in the oriented COF of Experimental Example 2, higher proton conductivity can be ensured in the penetrating direction of the pore.

[0079] On the other hand, in the unoriented COF used in the comparative experiment, as shown in Figure 15, the proton conductivity in direction 1 was 0.0003 S / cm, while the proton conductivity in direction 2 was 0.0002 S / cm. In other words, in the unoriented COF used in the comparative experiment, there was no significant difference between the proton conductivity in direction 1 and the proton conductivity in direction 2.

[0080] (TEM and TEM-ED Measurements) Transmission electron microscopy (TEM) was performed on the oriented COF electrolytes of Experimental Examples 1 and 2 and the unoriented COF of the comparative experiment. Furthermore, electron diffraction (TEM-ED) using a transmission electron microscope was performed on the oriented COF electrolytes of Experimental Examples 1 and 2 and the unoriented COF of the comparative experiment.

[0081] Specifically, dispersions of the oriented COF electrolytes in Experimental Examples 1 and 2 were dropped onto a TEM observation grid with a carbon support membrane (UHR-C10, manufactured by JEOL Ltd.), dried, and then COF nanosheets were placed on the grid. In addition, the unoriented COF electrolyte in Comparative Experimental Example 1 was ultrasonically dispersed in pure water as a powder and then dropped onto the grid.

[0082] TEM and TEM-ED images were acquired using a JEM-ARM300F (JEOL Ltd.). The acceleration voltage was set to 300 kV and the camera length to 80 cm, and selected-field electron diffraction images were acquired. The obtained electron diffraction images were used to identify the crystal orientation of the COF single crystal using electron diffraction simulation software (ReciPro). The results are shown in Figures 16 to 18.

[0083] In the oriented COF electrolytes of Experimental Examples 1 and 2, as shown in Figures 16 and 17, electron diffraction patterns of the COF single crystals observed in TEM images were obtained, showing a regular pattern of diffraction spots. Since this diffraction pattern matches the structural simulation of COF having an AA stacking structure, it was found that in the oriented COF single crystals of Examples 1 and 2, the interconnected pores are oriented in the same direction.

[0084] On the other hand, in the unoriented COF electrolyte of the comparative experiment, a concentric pattern was formed, as shown in Figure 18. This revealed that in the unoriented COF of the comparative experiment, the interconnected pores of each particle were arranged randomly and without regularity. In other words, it was found that the unoriented COF of the comparative experiment was a polycrystalline material formed in such a way that the directions in which the interconnected pores extend differ from one another.

[0085] As described above, the proton conductor of this embodiment has a 2D-COF that is stacked and single-crystallized so that the pores are in communication with each other. The 2D-COF single crystal 32 has a plurality of communicating pores 33 in which the pores 31 are in communication with each other. In the 2D-COF single crystal 32, the plurality of communicating pores 33 are oriented in the same direction to each other.

[0086] According to this, the proton conductivity in the pore-penetrating direction can be increased in the 2D-COF single crystal 32. As a result, it becomes possible to improve the proton conductivity of the proton conductor.

[0087] Furthermore, the proton conductor of this embodiment comprises a plurality of 2D-COF single crystals 32. The plurality of single crystals 32 are arranged so that the interconnected pores 33 of the single crystals 32 are oriented in the same direction within the electrolyte membrane 110. This makes it possible to increase the proton conductivity in the direction in which the interconnected pores 33 extend throughout the entire electrolyte membrane 110. As a result, it becomes possible to further improve the proton conductivity of the proton conductor.

[0088] Here, Figure 19 shows the results of molecular dynamics (MD) simulations using machine learning force fields for the proton motion (i.e., mobility) in an oriented COF electrolyte oriented to have an AA stacking structure. In Figure 19, the solid line a represents the proton mobility in the direction of penetration of the pores, and the dashed line b represents the proton mobility in the direction of transverse pores.

[0089] As is clear from Figure 19, in an oriented COF electrolyte oriented to have an AA stacking structure, protons move easily in the direction of pore penetration. Therefore, the proton conductivity in the direction of pore penetration is increased.

[0090] In contrast, as a comparative example, a COF electrolyte oriented to have an AB stacking structure can be cited, as shown in Figure 20. An AB stacking structure refers to a state in which adjacent two-dimensional sheet-like 2D-COF 30 are stacked with their positions shifted by 1 / 2 the pore diameter in the x and y directions, and these adjacent two-dimensional sheets are repeatedly stacked in the stacking direction.

[0091] Figure 21 shows the results of MD simulations using a machine learning force field for the proton mobility in an oriented COF electrolyte oriented to have an AB stacking structure. In Figure 21, the dashed line c represents the proton mobility in the sheet-like plane of the 2D-COF, and the solid line d represents the proton mobility in the direction perpendicular to the sheet-like plane of the 2D-COF.

[0092] As is clear from Figure 21, in COF electrolytes oriented to have an AB stacking structure, the effect of orientation on the mobility of protons is small, and the absolute value of mobility is also small.

[0093] Therefore, as in this embodiment, by using an AA stacking structure for the 2D-COF single crystal 32 in the proton conductor, the proton conductivity in the pore-penetrating direction is increased. As a result, the proton conductivity in the proton conductor can be improved.

[0094] Furthermore, in the fuel cell cell 100 of this embodiment, the proton conductors are arranged such that the direction in which the pores 31 extend, which is the direction of penetration of the pores, is the same as the direction of proton transport. This allows for efficient transport of protons in the direction of penetration of the pores, thereby increasing the proton conductivity in the proton transport direction, which is the same direction as the direction of penetration of the pores. As a result, it becomes possible to more reliably improve the proton conductivity of the fuel cell cell 100.

[0095] This disclosure is not limited to the embodiments described above, and can be modified in various ways without departing from the spirit of this disclosure, as follows.

[0096] In the above embodiment, an example was described in which a proton conductor was applied to a fuel cell cell of a fuel cell, but the application of the proton conductor is not limited to this embodiment. For example, the proton conductor may be applied to the electrolyte membrane of a water electrolysis device, which is an electrochemical device.

[0097] The technical features of the proton conductor and electrochemical device disclosed herein are as follows: (Item 1) A proton conductor comprising a two-dimensional covalent organic structure (30) in which two or more different linkers form a two-dimensional repeating cyclic unit by covalent bonds, wherein pores (31) are formed on the inside of the cyclic in the repeating unit, a plurality of the two-dimensional covalent organic structures are stacked in a stacking direction such that the pores communicate with each other to form a single crystal (32), the single crystal of the two-dimensional covalent organic structure has a plurality of communicating pores (33) in which the pores communicate with each other, and the plurality of communicating pores are oriented in the same direction to each other. (Item 2) The proton conductor according to Item 1, comprising a plurality of the single crystals, wherein the plurality of single crystals are arranged such that the communicating pores of each single crystal are oriented in the same direction to each other. (Item 3) The proton conductor according to Item 1 or 2, wherein the two-dimensional covalent organic structure has an orientation determined from the positions of scattering spots on the (100) plane and the (001) plane in a two-dimensional diffraction pattern obtained by micro-angle incident wide-angle X-ray scattering measurement. (Item 4) The proton conductor according to any one of Items 1 to 3, wherein the single crystal has an AA stacking structure such that all constituent atoms of the two-dimensional covalent organic structure adjacent to each other in the stacking direction are in the same position. (Item 5) The proton conductor according to any one of Items 1 to 4, wherein the proton conductivity after a water resistance test in which the protons are 90% or more after being immersed in pure water for 24 hours. (Item 6) The proton conductor according to any one of Items 1 to 5, wherein the two-dimensional covalent organic structure has a side chain containing a proton-conducting functional group. (Item 7) The proton conductor according to Item 6, wherein the proton-conducting functional group is at least one selected from a sulfonic acid group, a phosphonic acid group, a carboxylic acid group, a hydroxyl group, and an amino group. (Item 8) The proton conductor according to any one of items 1 to 7, wherein the linker is at least one selected from an aromatic compound having two amino groups located in the para position, a heterocyclic compound containing a nitrogen atom, or an aromatic compound having three aldehyde groups.(Item 9) An electrochemical device that transports protons in a predetermined proton transport direction, comprising a proton conductor as described in any one of Items 1 to 8. (Item 10) The electrochemical device as described in Item 9, wherein the direction in which the pores in the proton conductor extend is the same as the direction of proton transport.

[0098] This disclosure is described in accordance with the embodiments, but it is understood that this disclosure is not limited to such embodiments or structures. This disclosure also includes various modifications and variations within the equivalence. In addition, various combinations and forms, as well as other combinations and forms that include only one, more, or fewer of those elements, fall within the scope and concept of this disclosure.

Claims

1. A proton conductor comprising a two-dimensional covalent organic structure (30) in which two or more different linkers form a repeating annular unit in a two-dimensional direction by covalent bonds, wherein a pore (31) is formed inside the annular part of the repeating unit, and a plurality of the two-dimensional covalent organic structures are stacked in a stacking direction such that the pores communicate with each other to form a single crystal (32), and the single crystal of the two-dimensional covalent organic structure has a plurality of communicating pores (33) in which the pores communicate with each other, and the plurality of communicating pores are oriented in the same direction with respect to each other.

2. The proton conductor according to claim 1, comprising a plurality of single crystals, wherein the plurality of single crystals are arranged such that the communicating pores of each single crystal are oriented toward the same direction.

3. The proton conductor according to claim 1, wherein the two-dimensional covalent organic structure has an orientation state determined from the positions of scattering spots in the (100) plane and the (001) plane in a two-dimensional diffraction pattern obtained by micro-angle incident wide-angle X-ray scattering measurement.

4. The proton conductor according to claim 1, wherein the single crystal has an AA stacking structure such that all constituent atoms of the two-dimensional covalent organic structure adjacent to each other in the stacking direction are in the same position.

5. The proton conductor according to claim 1, wherein the proton conductivity after a water resistance test in which the conductor is immersed in pure water for 24 hours is 90% or more.

6. The proton conductor according to claim 1, wherein the two-dimensional covalent organic structure has a side chain containing a proton-conducting functional group.

7. The proton conductor according to claim 6, wherein the proton-conducting functional group is at least one selected from a sulfonic acid group, a phosphonic acid group, a carboxylic acid group, a hydroxyl group, and an amino group.

8. The proton conductor according to claim 1, wherein the linker is at least one selected from an aromatic compound having two amino groups located in the para position, a heterocyclic compound containing a nitrogen atom, and an aromatic compound having three aldehyde groups.

9. An electrochemical device for transporting protons in a predetermined proton transport direction, comprising a proton conductor according to any one of claims 1 to 8.

10. The electrochemical device according to claim 9, wherein the direction in which the pores in the proton conductor extend is the same as the direction of proton transport.

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