Gas storage material, and producing method thereof, as well as, gas storage method

Abstract

To provide a gas storage material capable of storing a gas even around room temperature.SOLUTION: This disclosure provides a gas storage material that has a part of a graphite structure, wherein the density measured by a gas pycnometer method using He gas at 25°C is 1 g / cm3 or less, and when the intensity of the G band observed in the Raman spectrum measured with a measurement light source of 532 nm in the range of 1550 to 1750 cm-1 is defined as IG, and the intensity of the 2D band observed in the range of 2550 to 2850 cm-1 is defined as I2D, the ratio of I2D to IG is 0.2 or more and less than 1.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a gas storage material, a method for manufacturing the same, and a gas storage method, and more particularly to a gas storage material having a graphite structure in part, etc.

Background Art

[0002] Graphite and graphene oxide have been studied as adsorbents with excellent adsorption performance and selectivity. For example, in Patent Document 1, an aromatic compound containing at least one atom selected from the group consisting of carbon atoms and hydrogen, nitrogen, sulfur, and oxygen atoms is thermally polymerized and deposited in pores of 2 nm or less in activated carbon fibers, and a molecular sieve activated carbon fiber having selective adsorption ability is disclosed.

[0003] Application to a gas storage material using the adsorption performance of graphite or graphene oxide has been studied. For example, Patent Document 2 discloses a hydrogen storage product containing a single-layer structure or a multi-layer structure of reduced graphene oxide functionalized with boron species and modified with an alkali metal or an alkaline earth metal, and each layer of the structure further contains a boron-oxygen functional group of an oxygen atom bonded to a boron atom. The hydrogen storage product enables hydrogen storage by functionalized boron species, modified alkali metal, alkaline earth metal chemical species, etc.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Although graphite or graphene as described above is excellent in the adsorption performance of gas molecules to be adsorbed, it is not easy to maintain the adsorption of the adsorbed gas molecules and apply them to storage. For example, even if gases such as hydrogen and methane can be adsorbed, adjustments such as storing them in a container that can withstand high pressure for maintenance or controlling the temperature to low temperature to suppress the desorption of the adsorbed molecules are required.

[0006] An object of the present disclosure is to provide a gas storage material capable of storing a gas even near room temperature and a method for manufacturing the same. Another object of the present disclosure is to provide a gas storage method using the above-described gas storage material.

Means for Solving the Problems

[0007] The present disclosure provides the following [1] to [6].

[0008] [1] A gas storage material having a graphite structure in part, the density measured by the gas pycnometer method at 25 ° C using He gas is 1 g / cm 3 or less, in the Raman spectrum measured using a measurement light source of 532 nm, the intensity of the G band observed in the range of 1550 to 1750 cm -1 is defined as I G , and the intensity of the 2D band observed in the range of 2550 to 2850 cm -1 is defined as I 2D , when the ratio of I G to I 2D is 0.2 or more and less than 1, the gas storage material. [2] The BET specific surface area measured at -196 ° C is 300 m 2 / g or less, the gas storage material according to [1]. [3] A raw material having a graphite structure is heated to 800 °C or higher under an argon stream, methane gas is added to the argon stream so that the methane concentration becomes 5 to 30% by volume, and a plurality of single-layer graphene sheets are provided on the raw material having the graphite structure by chemical vapor deposition under conditions of holding for 0.5 hours or longer. A method for producing a gas storage material comprising the above steps. [4] Further comprising preparing the raw material by activating graphite. The production method according to [3]. [5] Heating the gas storage material according to [1] or [2] to 140 °C or higher under a gas atmosphere to be stored and under a pressure condition of 10 MPa or higher. A gas storage method comprising cooling the gas storage material to 130 °C or lower while maintaining the gas atmosphere and the pressurized state. [6] The gas storage method according to [5], wherein the gas to be stored contains at least one selected from the group consisting of hydrogen, oxygen, methane, and ethane.

Advantages of the Invention

[0009] According to the present disclosure, a gas storage material capable of storing gas even near room temperature and a method for producing the same can be provided. According to the present disclosure, a gas storage method using the above gas storage material can also be provided.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

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Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings in some cases. However, the following embodiments are examples for explaining the present disclosure and are not intended to limit the present disclosure to the following contents. The positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. The dimensional ratios of the respective elements are not limited to the ratios illustrated in the drawings.

[0012] Unless otherwise specified, the materials exemplified in this specification can be used alone or in combination of two or more. The content of each component in the composition means the total amount of the plurality of substances present in the composition when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified.

[0013] FIG. 1 is a schematic diagram showing an example of a gas storage material. The gas storage material 60 includes a main body portion 20 having a graphite structure and a graphene sheet portion 40 composed of a plurality of graphene sheets 4 provided on at least a part of the outer periphery of the main body portion 20. The main body portion 20 has a plurality of pores 3.

[0014] The gas storage material according to the present disclosure includes a main body having a graphite structure, and a graphene sheet portion composed of a plurality of graphene sheets provided on at least a part of the outer periphery of the main body (excluding those forming a graphite structure). The main body is porous with a plurality of pores, and the plurality of graphene sheets constituting the graphene sheet portion have portions that partially overlap each other and are positioned to cover the pores in this way. The overlapping portions of the graphene sheets with each other may be fixed by intermolecular forces, and by having such a configuration, it is possible to suppress the gas stored inside the graphite structure from flowing out to the outside of the gas storage material near room temperature. Further, the graphene sheet portion fixed by intermolecular forces can be made to freely move each of the graphene sheets constituting the graphene sheet portion by supplying energy (for example, heating) that exceeds the intermolecular forces, and in this situation, it is possible to fill the main body with gas.

[0015] As a substance having a graphite structure, for example, activated carbon can be considered. However, as shown in FIG. 9, although the activated carbon 2 can adsorb or fill gas inside the pores 3, it does not have a configuration corresponding to a graphene sheet portion, and since the gas can easily enter and exit, the gas storage performance is low and it is difficult to use as a gas storage material.

[0016] The graphite structure in this specification means the same or a similar structure to graphite, and means a stacked structure of a plurality of graphenes like graphite and a structure in which the relative positions of the graphenes are fixed. On the other hand, in the graphene sheet portion in this specification, the relative positions between the graphene sheets are not fixed and can vary with each other. For example, by supplying kinetic energy by heating to a certain extent and this energy exceeding the intermolecular forces between the graphene sheets, each graphene sheet can move, and by utilizing this, it is possible to make the behavior like that of a lid of a gas storage material.

[0017] In one embodiment of the gas storage material, at least a part of the pores of the main body is covered by the graphene sheet portion, so that at around room temperature, the intrusion of gas into the pores and the outflow of the gas filled in the pores to the outside are suppressed. Therefore, the density measured by the gas pycnometer method using the gas is lower than the density of general graphite. For example, activated carbon composed of graphite generally has a density measured by the gas pycnometer method at 25 °C using He gas of about 2 g / cm 3 or so. On the other hand, the density of the gas storage material according to the present disclosure measured by the gas pycnometer method at 25 °C using He gas is 1 g / cm 3 or less, showing a small value.

[0018] The upper limit value of the density of the above gas storage material measured by the gas pycnometer method at 25 °C using He gas is, for example, 1.00 g / cm 3 or less, 0.95 g / cm 3 or less, 0.90 g / cm 3 or less, or 0.85 g / cm 3 or less. The upper limit value of the density being within the above range means that the volume for filling the gas in the graphite structure is large, and more gas can be filled. The lower limit value of the density is, for example, 0.50 g / cm 3 or more, 0.60 g / cm 3 or more, 0.65 g / cm 3 or more, 0.70 g / cm 3 or more, or 0.80 g / cm 3 or more. By the lower limit value of the density being within the above range, the decrease in the mechanical strength of the gas storage material itself can be more sufficiently suppressed. The density of the gas storage material according to the present disclosure measured by the gas pycnometer method at 25 °C using He gas can be adjusted within the above range, for example, 0.65 - 0.95 g / cm 3 , or 0.70 - 0.85 g / cm 3 or so.

[0019] The density in this specification means the skeletal density measured at 25°C in accordance with the description in JIS Z 8837:2018, "Measurement of density by volume displacement - Skeletal density by gas pycnometer method", using He gas. For the measurement, for example, a density measuring device "BELPYCNO" (trade name) of MicrotracBEL Co., Ltd. can be used. Since the above density measurement is affected by moisture, gas, etc. adhering to the sample to be measured, when measuring, the above sample shall be heated at 110°C for 1 hour, weighed promptly after the heat treatment, and incorporated into the measuring device. The measurement shall be performed at least 10 times. If the difference between the measurement values of the 9th and 10th times is within 2%, the measurement result of the 10th time shall be adopted as the density value of the target sample. When the above difference exceeds 2%, the measurement shall be repeated further, and the measurement result after the measurement value at which the difference between consecutive measurement values is within 2% shall be adopted as the density value of the target sample.

[0020] The above gas storage material has a graphene sheet part, and this part forms bonds with each other by intermolecular force near room temperature and becomes a state with high crystallinity. Therefore, in the gas storage material of the present disclosure, in the Raman spectrum, the intensity on the lower wavenumber side in the region of the so-called 2D band (peaks observed in the wavenumber range of 2550~2850 cm -1 , also referred to as the G' band) increases. The Raman spectrum for the gas storage material according to the present disclosure, in addition to the above 2D band, has peaks in the D band (peaks peculiar to single-layer graphene observed in the wavenumber range near 1350 cm -1 ) and the G band (peaks peculiar to single-layer graphene observed in the wavenumber range near 1590 cm -1 ) derived from the graphene sheet part. In the Raman spectrum for the gas storage material according to the present disclosure, the intensity of the G band tends to decrease compared with conventional activated carbon, etc.

[0021] In the Raman spectrum measured using a measurement light source of 532 nm, for the above gas storage material, the intensity of the G band observed in the range of 1550~1750 cm -1 is defined as I G , and for 2550~2850 cm -1When the intensity of the 2D band observed in the range is I 2D and the ratio of I G to I 2D (the value of I 2D / I G ) is 0.2 or more and less than 1.

[0022] The above gas storage material has a density measured by the gas pycnometer method at 25 °C within the above range, and the value of I 2D / I G is within the above range. Having such a configuration corresponds to the gas storage material having a graphene sheet portion and having a portion crystallized between the graphene sheets near room temperature. By having such a configuration, gas filling can be made possible by heat treatment, and the once-filled gas can be stored at a temperature from low temperature to near room temperature (for example, a temperature exceeding 0 °C and not exceeding 35 °C). Since the kinetic energy of the gas is small, the gas storage material according to the present disclosure can store and maintain the gas filled near room temperature, and can also be regarded as a container by itself. Near room temperature, since the intrusion of gas into the gas storage material is suppressed, it is also possible to suppress the decrease in the purity of the stored gas due to the mixing of outside air into the stored gas. The gas storage material according to the present disclosure does not require a special pressure-resistant container or the like during gas storage, and does not require cooling to a low temperature, and is extremely useful in practice. By increasing the formation amount of the graphene sheet portion, it is also possible to maintain the gas storage state even at a certain high temperature. For example, up to about 130 °C, the gas can be stably maintained in a stored state.

[0023] The upper limit value of the value of the above I 2D / I G may be, for example, 0.9 or less, or 0.8 or less. When the upper limit value of the value of the above I 2D / I G is within the above range, the graphene sheet portion composed of two or more single-layer graphene is multilayered, and after storing the gas, the gas can be more reliably retained in the pores inside the gas storage material. The above I 2D / I GThe lower limit value of the value of 2D / I G may be, for example, 0.2 or more, 0.3 or more, or 0.4 or more. By the lower limit value of the value of 2D / I G being within the above range, it is possible to achieve a higher level of compatibility between the stability of the graphene sheet portion near room temperature and the mobility of each graphene sheet during heating, and it is possible to further improve the role as a lid of the gas storage material. The value of

[0024] in this specification 2D / I G is a value measured at 25 °C using a measurement light source of 532 nm. More specifically, using a laser Raman spectrophotometer, the laser intensity is set to 0.9 mW and attenuated to 5% with a neutral density filter. The exposure time in the measurement is 10 seconds, and the Raman spectrum is obtained by integrating 10 measurements. As the laser Raman spectrophotometer, for example, "NSR-4100" (trade name) manufactured by JASCO Corporation can be used.

[0025] Since at least a part of the pores of the main body portion is covered by the graphene sheet portion in the above gas storage material, the entry of gas into the pores is suppressed in the region below room temperature. Therefore, the specific surface area can be smaller than that of general graphite. The BET specific surface area of the gas storage material according to the present disclosure measured at -196 °C 2 / g or less may be sufficient. A lid is formed on the pores of the main body portion by the graphene sheet portion, and near room temperature, it can be said that the pores behave like so-called closed pores.

[0026] The upper limit value of the above BET specific surface area is, for example, 250 m 2 / g or less, 200 m 2 / g or less, or 100 m 2It may be below / g. By the upper limit value of the BET specific surface area being within the above range, the storage capacity of the stored gas can be further improved. The lower limit value of the BET specific surface area is not particularly limited. For example, it may be 0.01 m 2 / g or more, 0.05 m 2 / g or more, or 0.1 m 2 / g or more. The BET specific surface area may be adjusted within the above range. For example, it may be 0.01 - 300 m 2 / g, or 0.1 - 100 m 2 / g.

[0027] The BET specific surface area in this specification means a value measured in accordance with JIS Z 8830:2013 "Method for Measuring Specific Surface Area of Powder (Solid) by Gas Adsorption". More specifically, nitrogen adsorption measurement is performed at 77K, and the obtained result is analyzed by the BET multipoint method to determine the above BET specific surface area.

[0028] The above gas storage material is suitable for gas storage. In an atmosphere containing the gas to be stored in the above gas storage material, it is heated, and the pressure of the surrounding atmosphere is increased according to the intended storage quantity, so that the gas is filled into the gas storage material. By cooling the gas storage material while maintaining the pressure, at least a part of the graphene sheets constituting the graphene sheet part form an overlap with each other, thereby suppressing the outflow of gas from the inside of the gas storage material, and the gas can be stored. Also, the extraction of the stored gas to the outside can be performed by heating the gas storage material. Note that the heating temperature is set to be equal to or higher than the temperature at which kinetic energy exceeding the intermolecular force between the graphene sheets can be supplied to the graphene sheets based on the degree of overlap in the graphene sheet part. The gas storage material according to the present disclosure is also useful in that the storage and release of gas can be repeated as described above.

[0029] The gas storage capacity in the above gas storage material can be adjusted by adjusting the length and overlap of the graphene sheets in the graphene sheet portion. The lower limit value of the storage capacity can be, for example, 50 times or more, 60 times or more, 70 times or more, 80 times or more, 100 times or more, 120 times or more, or 140 times or more based on the volume of the gas storage material. By setting the lower limit value of the storage capacity within the above range, the storage capacity of the gas storage material can be further improved. The upper limit value of the storage capacity can be, for example, 220 times or less, 200 times or less, 180 times or less, 170 times or less, or 150 times or less based on the volume of the gas storage material. By setting the upper limit value of the storage capacity within the above range, leakage of the gas stored in the gas storage material can be more sufficiently suppressed. The storage capacity may be adjusted within the above range and may be, for example, 100 to 220 times, 100 to 170 times, or 140 to 220 times based on the volume of the gas storage material.

[0030] Figure 2 is a schematic diagram for explaining a gas storage method and a gas extraction method using the above gas storage material. First, at a relatively low temperature t L1 (for example, room temperature), the gas storage material 60 is prepared in a gas atmosphere to be filled (Fig. 2(a)), heated while maintaining the ambient pressure, and the temperature t at which the graphene sheet portion of the gas storage material 60 can break the intermolecular force and move H is raised (Fig. 2(b)). Then, while maintaining the ambient pressure, it is cooled, and the temperature t at which the graphene sheet portion of the gas storage material 60 recombines again by the intermolecular force L2 is cooled down to or below (Fig. 2(c)). By doing so, the gas can be filled and stored inside the gas storage material. In Fig. 2, an example is shown where t L1 and t L2 are the same temperature t L . Once the stored gas is taken out, it can be done by heating to a temperature above the above temperature t H (Fig. 2(d)).

[0031] One embodiment of the gas storage method includes heating the above-described gas storage material under a gas atmosphere to be stored and under a pressurization condition of 10 MPa or more, and cooling the gas storage material while maintaining the gas atmosphere and the pressurized state. A more specific example of the gas storage method includes heating the above-described gas storage material to 140°C or higher or 150°C or higher under a gas atmosphere to be stored and under a pressurization condition of 25 MPa or more, and cooling the gas storage material to 130°C or lower or 100°C or lower while maintaining the gas atmosphere and the pressurized state.

[0032] The pressure in the gas storage method may be adjusted according to the target amount of the gas filling amount into the gas storage material and the like. The lower limit value of the pressure under the pressurization condition may be, for example, 10 MPa or more, 15 MPa or more, 20 MPa or more, or 25 MPa or more. By setting the lower limit value of the pressure within the above range, the storage capacity of the gas storage material can be further improved. The upper limit value of the pressure under the pressurization condition may be, for example, 35 MPa or less, 30 MPa or less, or 27 MPa or less. By setting the lower limit value of the pressure within the above range, leakage of the gas stored in the gas storage material can be more sufficiently suppressed. The pressure under the pressurization condition may be adjusted within the above range, and may be, for example, 15 to 35 MPa, 15 to 30 MPa, or 25 to 30 MPa. The pressure in this specification means absolute pressure.

[0033] The heating temperature in the gas storage method can be adjusted according to the structure of the graphene sheet part constituting the gas storage material, that is, the degree of overlap between the graphene sheets. The lower limit value of the heating temperature may be, for example, 140 °C or higher, 145 °C or higher, or 150 °C or higher. By setting the lower limit value of the heating temperature within the above range, the gas to be stored can more easily permeate through the graphene sheet part, and gas filling into the pores in the graphite structure part becomes easier. The upper limit value of the heating temperature may be, for example, 300 °C or lower, 280 °C or lower, 250 °C or lower, 220 °C or lower, or 200 °C or lower. By setting the upper limit value of the heating temperature within the above range, the gas to be stored can be introduced into the pores in the graphite structure part at a higher density. The heating temperature may be adjusted within the above range, for example, 140 - 300 °C, 140 - 200 °C, or 150 - 300 °C.

[0034] The temperature reached during cooling in the gas storage method can be adjusted according to the structure of the graphene sheet part constituting the gas storage material, that is, the degree of overlap between the graphene sheets. The upper limit value of the temperature reached during the cooling may be 130 °C or lower, 100 °C or lower, 80 °C or lower, 60 °C or lower, or 40 °C or lower. When the upper limit value of the reached temperature is within the above range, permeation of the stored gas through the graphene sheet part can be more sufficiently suppressed, and the storage stability of the gas storage material can be further improved. The lower limit of the temperature reached during the cooling is not particularly limited and may even be absolute zero, but it may be 0 °C or higher, or 30 °C or higher. The reached temperature may be adjusted within the above range, for example, 0 - 130 °C, 30 - 130 °C, or 0 - 60 °C.

[0035] The type of gas to be stored in the above gas storage material is not particularly limited. The filling of gas into the gas storage material according to the present disclosure is achieved by the kinetic energy of gas molecules exceeding the repulsive force (energy barrier) formed between the carbon atoms of the graphene sheet and the gas molecules. The above repulsive force means the total value of the repulsive forces received between the carbon atoms constituting each graphene sheet when the gas molecules are located in the region sandwiched between two graphene sheets. When there is a supply of heat such that the graphene sheets constituting the graphene sheet portion can freely perform thermal motion beyond the intermolecular forces exerted on each other, the graphene sheet portion itself vibrates, and the distance between each single-layer graphene (each graphene sheet) changes periodically. When the distance between the gas molecules and the graphene sheet becomes the largest, the repulsive force between the gas molecules and the carbon atoms constituting the graphene sheet, that is, the energy barrier, becomes the smallest value. The energy barrier becomes smaller when the amplitude of the graphene sheet with reference to the position of the gas atoms becomes the largest, but since the above amplitude increases as the temperature increases, the above energy barrier tends to become smaller as the temperature is higher. And the average kinetic energy E of gas molecules is determined by a function of the Boltzmann constant k and the absolute temperature T (E = (3 / 2)kT), is proportional to the temperature at which the gas molecules are placed, and does not depend on the type of molecules.

[0036] When the thermal motion of each graphene sheet constituting the graphene sheet portion is a harmonic vibration from a reference position (the position where the white circle shown in FIG. 3(a) is located) as shown in FIG. 3(a), the energy barrier b that the gas molecule g receives from the graphene sheet becomes the minimum when the distance x between the atoms constituting the graphene sheet and the gas molecule g becomes the largest, and when x coincides with the maximum value of the amplitude L of the harmonic vibration. At this time, the repulsive force b that the gas molecule g receives from the graphene sheet is proportional to the -12th power of the distance L. Assuming the proportionality constant is C1, the repulsive force b is b = C1 × L -12 obtained by. Considering that the gas storage material is composed of at least two graphene sheets (hypothetically graphene sheet A and graphene sheet B), the minimum value B of the energy barrier b felt by the gas molecule g is the repulsive force b received from the graphene sheet AA (=C1 A ×L A -12 ) and the repulsive force b received from the graphene sheet B B (=C1 B ×L B -12 ) is the sum of them. Therefore, the repulsive force acting between the gas molecule and the graphene sheet is proportional to the -12th power of the temperature. On the other hand, since the amplitude changes with temperature, L can be said to be a function of temperature. Here, since the energy is proportional to the square of the amplitude, assuming that the frequencies and amplitudes of the two graphene sheets A and graphene sheet B are the same, let the proportionality constants be C 2 , C 3 , and when the frequency is T, the minimum value B of the energy barrier b received by the gas molecule g is B = (C1 A + C1 B )×L A -12 = (C1 A + C1 B )×C 2 ×T -6 = C 3 ×T -6 and can be obtained. That is, it can be seen that the minimum value B of the energy barrier b received by the gas molecule g is a value proportional to the -6th power of the temperature. Then, the relationship between the average kinetic energy E of the gas molecule g and the minimum value B of the energy barrier b felt by the gas molecule g is the relationship shown in Fig. 3(b). In the graph shown in Fig. 3(b), if it is the region where E > B, the gas molecule g is filled or released into the gas storage material, and if it is the region where E < B, it means that the gas molecule g cannot enter the inside of the gas storage material or the gas molecule g cannot come out from the inside of the gas storage material to the outside.

[0037] The gas to be stored may include at least one selected from the group consisting of, for example, hydrogen, oxygen, methane, and ethane, may be at least one selected from the group consisting of hydrogen, oxygen, methane, and ethane, and may be any one of hydrogen, oxygen, methane, and ethane.

[0038] The method for manufacturing a gas storage material is performed by supplying a carbon source to a raw material having a graphite structure using chemical vapor deposition (CVD method) and providing a graphene sheet.

[0039] FIG. 4 is a schematic diagram for explaining an example of the method for manufacturing a gas storage material. FIG. 4 shows an example in which a carbon material having pores is prepared (schematic diagram of activated carbon fiber (ACF) in FIG. 4(a)), and a raw material having a graphite structure with an expanded pore diameter is prepared by an activation treatment (schematic diagram of activated activated carbon fiber (a-ACF) in FIG. 4(b)), and then a graphene sheet portion is provided by the CVD method to prepare a gas storage material (schematic diagram of an example of a gas storage material in FIG. 4(c)). Here, the activation of the carbon material is an arbitrary treatment, and if the raw material having a graphite structure has pores and the like suitable for the target gas storage material, the gas storage material can also be manufactured by forming a graphene sheet portion by the CVD method on this raw material. Further, since it is only necessary to prepare the above raw material by an activation treatment, the carbon material does not necessarily have to have pores.

[0040] One embodiment of the method for manufacturing a gas storage material is to heat a raw material having a graphite structure to 800 ° C or higher under an argon stream, add methane gas to the argon stream so that the methane concentration becomes 5 to 30% by volume, and hold for 0.5 hours or more. Providing a plurality of single-layer graphene to the raw material having the graphite structure by chemical vapor deposition under the conditions. Instead of the argon stream, nitrogen gas can also be used. The methane concentration is a value calculated based on the volume of the gas under standard conditions. The heating temperature is 800 ° C or higher, but preferably 900 ° C or lower, and may be 800 to 900 ° C, or 840 to 860 ° C. The chemical vapor deposition method may be performed at 0.09 to 0.13 MPa, or may be performed under a pressure of about 0.10 MPa (under normal pressure). The chemical vapor deposition method performed under the same pressure environment as the surrounding environment without controlling the pressure is sometimes called an atmospheric pressure chemical vapor deposition method, and the chemical vapor deposition method used in the method for manufacturing a gas storage material according to the present disclosure may be an atmospheric pressure chemical vapor deposition method.

[0041] Examples of the raw material having a graphite structure include activated carbon, graphene oxide, etc. The shape of the above raw material is not particularly limited, and may be, for example, powdery, fibrous, plate-shaped, film, etc. Activated carbon having a fibrous structure is also called activated carbon fiber. As long as the raw material has a graphite structure, commercially available products may be used, or those prepared separately may be used.

[0042] The carbon source used in the chemical vapor deposition method may contain, for example, methane, ethane, methanol, etc., preferably contains methane, and more preferably is methane. Providing the graphene sheet portion provided by the chemical vapor deposition method can also mean grafting the graphene sheet onto the main body portion derived from the raw material having a graphite structure. When forming single-layer graphene by chemical vapor deposition, additives may be used. Examples of the additive include hydrogen gas.

[0043] The chemical vapor deposition method is a technique for forming layers of various substances. A raw material gas containing the constituent components of the target thin film is supplied to a substrate, and a film is formed by a reaction with the substrate surface or a chemical reaction in the vicinity of the substrate surface. In the present disclosure, by applying a chemical vapor deposition method utilizing thermal decomposition of a carbon source (for example, methane), a raw material gas containing carbon is supplied to a raw material having a graphite structure, and a single-layer graphene (graphene sheet) is grown around the opening of the pores provided in the graphite structure. The raw material having a graphite structure has high activity at the end of the graphene sheet forming the graphite structure, and a new graphene sheet preferentially grows at the end forming the pores. In this way, a gas storage material having a main body portion having a graphite structure and a graphene sheet portion composed of a plurality of graphene sheets provided on at least a part of the outer periphery of the main body portion can be formed.

[0044] As specific conditions for performing the chemical vapor deposition method, 100 mg of a raw material (for example, activated carbon fiber) is placed in a tubular furnace and heated to a target temperature (for example, 840 to 860 °C) under an argon gas flow. Then, pure methane gas is added to the argon gas flow so that the methane concentration becomes 12.5% by volume and held for a predetermined time (for example, 0.5 to 3 hours, or 2 hours). After the lapse of the predetermined time, the addition of methane is stopped and natural cooling is performed in the argon gas flow. This method is preferable.

[0045] The above manufacturing method may further include activating a carbon material to prepare the above raw material (a raw material having a graphite structure). The carbon material may be, for example, graphite, coconut shell activated carbon, pitch-based activated carbon, graphene oxide, or the like. The activation treatment refers to a treatment for generating pores in the carbon material. By performing the activation treatment, pores of the obtained raw material can be generated or increased, and the volume capable of filling gas can be further increased. In addition, the pore diameter of the pores of the raw material can also be adjusted by the activation treatment.

[0046] The activation treatment may be, for example, gas activation or chemical activation. Gas activation is a heat treatment of a carbon material in an atmosphere containing at least one of water vapor and oxygen, or an atmosphere containing at least one of water vapor and carbon dioxide. In this process, pores are formed by the desorption of a part of the carbon constituting the carbon material as carbon dioxide gas or carbon monoxide gas. Chemical activation is a heat treatment of a carbon material together with an activator (for example, zinc chloride, phosphoric acid, potassium hydroxide, sodium hydroxide, etc.). The activation treatment may be, for example, setting 1 g of activated carbon fiber (for example, manufactured by Adol Co., Ltd., product name: A20) in a quartz reaction tube, installing it in a tubular furnace, flowing pure argon gas (for example, G1 grade) at a flow rate of 240 mL / min, and heating to 950 °C at a heating rate of 20 °C per minute. After reaching 950 °C, pure carbon dioxide gas (for example, G1 grade) is added to the flow of pure argon gas at a flow rate of 60 mL / min and reacted for 4 hours. After 4 hours have elapsed, the carbon dioxide gas flow is stopped, the tubular furnace is turned off, and it is left to cool naturally until it reaches a temperature of 30 °C and then taken out.

[0047] Although several embodiments have been described above, the present disclosure is not limited to the above embodiments in any way. Also, the description contents of the above-described embodiments can be applied to each other.

Example

[0048] Hereinafter, the content of the present disclosure will be described in more detail with reference to examples and comparative examples. However, the present disclosure is not limited to the following examples.

[0049] (Example 1) [Preparation of Raw Material Having Graphite Structure] Activated carbon fibers (manufactured by Adol Co., Ltd., product name: A20) prepared by baking petroleum pitch were prepared. The activated carbon fibers were placed in a quartz reaction tube and heated to 950 °C at a heating rate of 20 °C / min under an argon stream with a flow rate of 240 mL / min. When 950 °C was reached, the argon stream was changed to a carbon dioxide stream with a flow rate of 60 mL / min. After changing to the carbon dioxide stream and maintaining the temperature at 950 °C, the reaction was carried out for 4 hours. Then, the heating was terminated, the gas stream was changed back to an argon stream with a flow rate of 240 mL / min, and it was cooled to room temperature. Through such treatment, the activated carbon fibers were activated, and activated activated carbon fibers (raw materials having a graphite structure) were prepared. By this treatment, it was confirmed that the BET specific surface area and pore volume of the activated carbon fibers increased from 1620 m 2 / g and 1.02 cm 3 / g to 2460 m 2 / g and 1.66 cm 3 / g, respectively, and it was confirmed that they were activated.

[0050] [Preparation of Gas Storage Material] The activated activated carbon fibers prepared as described above were placed in a quartz reaction tube and heated to 840 °C at a heating rate of 20 °C / min under an argon stream with a flow rate of 350 mL / min. When the temperature reached 840 °C, a methane stream with a flow rate of 50 mL / min was added to the argon stream to make a mixed gas flow of 400 mL / min, and the temperature was maintained at 840 °C and reacted for 2 hours by chemical vapor deposition using methane as a carbon source. Then, the heating was terminated, the gas flow was changed back to an argon stream with a flow rate of 350 mL / min, and it was cooled to room temperature. By such treatment, a gas storage material having a graphene sheet part and a main body part having a graphite structure was prepared by extending the graphene sheet on the activated activated carbon fibers.

[0051] <Character Evaluation of Gas Storage Material> For the obtained gas storage material, based on the method described later, density, appearance observation by scanning electron microscope, and Raman spectrum measurement were performed. The results are shown in Table 1, Figures 5 and 6. For reference, the activated carbon fibers before activation (denoted as ACF) and the activated carbon fibers after activation (denoted as a-ACF) are also shown in Table 1, Figures 5 and 6.

[0052] [Density] Using He gas, the skeletal density at 25 °C was measured in accordance with the description of JIS Z 8837:2018 "Measurement of Density by Volume Displacement - Skeletal Density by Gas Pycnometer Method".

[0053] [Appearance Observation by Scanning Microscope] For the obtained gas storage material, external appearance observation was carried out using a scanning electron microscope and a transmission electron microscope. For the scanning electron microscope observation, a scanning electron microscope "SU8000" (trade name) manufactured by Hitachi High-Tech Corporation was used. First, a carbon double-sided tape was attached to a φ1-inch aluminum sample stage, and the gas storage material to be measured was attached and fixed thereon to prepare a measurement sample. The observation was carried out at an acceleration voltage of 2 kV. Next, for the transmission electron microscope observation, a field emission transmission electron microscope "JEM-2100F" (trade name) manufactured by JEOL Ltd. was used. First, the gas storage material to be measured was placed on a copper grid with a carbon film to obtain a measurement sample. Since the graphene sheet part is vulnerable to the electron beam and is destroyed at a high acceleration voltage, low-voltage measurement at 80 kV was performed.

[0054] [Raman Spectrum Measurement] For the obtained gas storage material, a Raman spectrum was acquired, and the value of I 2D / I G was determined according to the method described below. The Raman spectrum was obtained using a laser Raman spectrophotometer (manufactured by JASCO Corporation, product name: NSR-4100). First, a slide glass with an aluminum foil attached to its surface was prepared, and the gas storage material to be measured was pressed and fixed on the aluminum foil to prepare a measurement sample. The wavelength of the laser light source was set to 532 nm. The laser intensity was set to 0.9 mW and attenuated to 5% using a neutral density filter. The exposure time was set to 10 seconds, and the Raman spectrum was acquired by integrating 10 measurements. From the obtained Raman spectrum, the peak intensities I D 、I G 、and I 2D corresponding to the D band, G band, and 2D band were determined, and the value of I 2D / I G was determined. In FIG. 6, the solid line corresponds to the result of Reference Example 1.

[0055] [Evaluation of Gas Storage Performance of Gas Storage Material] For the obtained gas storage material, the gas storage performance was evaluated based on the method described below. Specifically, a measuring device as shown in Fig. 7 was assembled, 20 mg of the gas storage material was placed in a U-shaped stainless steel sample cell, and it was incorporated into the measuring device. Pure methane of G1 grade was introduced into the sample cell at a flow rate of 50 mL / min for 10 minutes. Then, the sample cell was heated at a heating rate of 5 °C / min to a storage temperature of 200 °C. While adjusting the pressure of methane in the sample cell to 25 MPa when the storage temperature was reached, it was held for 1 hour to fill methane into the pores inside the gas storage material. Next, while maintaining the pressure of methane, the sample cell was gradually cooled to about 30 °C, and then the methane in the sample cell was released to return to normal pressure. In this way, a gas storage material storing methane was prepared and taken out from the sample cell. The taken-out gas storage material was stored in a desiccator at room temperature for 1 day. After 1 day passed, the storage capacity of the gas storage material was determined by measuring the volume of methane stored in the gas storage material (methane storage amount). The measurement of the methane storage amount was performed using a thermogravimetric analyzer (Thermo Plus TG8120 (trade name) manufactured by Rigaku Corporation). The measurement was carried out by heating at a heating rate of 1 °C per minute while flowing pure nitrogen at 100 mL / min. The weight loss from the start temperature of the thermogravimetric analysis to 600 °C was taken as the methane storage amount. For reference, the results of the thermogravimetric analysis are shown in Fig. 8.

[0056] (Example 2, Example 3) As shown in Table 1, a gas storage material was produced in the same manner as in Example 1 except that the temperature of the CVD treatment was changed.

[0057] (Reference Example 1) The properties of the activated carbon fiber prepared in Example 1 were evaluated in the same manner as in Example 1. The evaluation results are described in Table 1 as Reference Example 1 for reference.

[0058]

Table 1

Industrial Applicability

[0059] According to the present disclosure, a gas storage material capable of storing a gas even near room temperature and a method for producing the same can be provided. According to the present disclosure, a gas storage method using the above-described gas storage material can also be provided.

Description of Signs

[0060] 2... activated carbon, 3... pores, 4... graphene sheet, 20... main body portion, 40... graphene sheet portion, 60... gas storage material.

Claims

1. A gas storage material having a graphite structure in part, The density measured by the gas pycnometer method at 25 °C using He gas is 1 g / cm ３ or less, In the Raman spectrum measured using a measurement light source of 532 nm, the intensity of the G band observed in the range of 1550 to 1750 cm －１ is defined as I Ｇ , and the intensity of the 2D band observed in the range of 2550 to 2850 cm －１ is defined as I ２Ｄ . When the ratio of I Ｇ to I ２Ｄ is 0.2 or more and less than 1, a gas storage material.

2. - The BET specific surface area measured at -196 °C is 300 m ２ / g or less, the gas storage material according to claim 1.

3. A method for producing a gas storage material, comprising: heating a raw material having a graphite structure to 800 °C or higher under an argon stream, adding methane gas to the argon stream so that the methane concentration becomes 5 to 30% by volume, and providing a plurality of single-layer graphene to the raw material having the graphite structure by chemical vapor deposition under conditions of holding for 0.5 hours or longer.

4. The production method according to claim 3, further comprising preparing the raw material by activating graphite.

5. Heating the gas storage material according to claim 1 or 2 to 140 °C or higher under a gas atmosphere to be stored and a pressurization condition of 10 MPa or higher; A gas storage method, comprising: cooling the gas storage material to 130 °C or lower while maintaining the gas atmosphere and the pressurized state.

6. The gas storage method according to claim 5, wherein the gas to be stored contains at least one selected from the group consisting of hydrogen, oxygen, methane, and ethane.

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