A hydrogen storage material based on porous carbon supported fluorine-based functional groups, its preparation method and application

Abstract

The present invention discloses a hydrogen storage material based on porous carbon loaded with fluorine-based functional groups, its preparation method and application, belonging to the fields of inorganic nanomaterial chemistry and energy technology. Fluorine atoms are introduced onto the surface of the porous carbon through C-M-F or C-N-F bonding methods to form hydrogen absorption sites. At the same time, the present invention uses a simple solution impregnation loading method to modify the surface of the porous carbon precursor by using different kinds of hexafluorosilicates, effectively avoiding the influence of heteroatoms, and obtaining fluorine-containing functional groups on the surface of the porous carbon during high-temperature reactions, enabling the target structure and surface functional groups to form efficient adsorption sites with hydrogen. The obtained hydrogen storage material has excellent low-temperature hydrogen storage capacity and a relatively high hydrogen absorption capacity.

Description

Technical Field

[0001] The present invention belongs to the technical fields of inorganic nanomaterial chemistry and energy technology, and particularly relates to a hydrogen storage material with a fluorine-based functional group structure supported on porous carbon, a preparation method thereof, and an application thereof. Background Art

[0002] Hydrogen energy is widely regarded as an important part of future renewable energy, due to its significant potential in global energy transformation, reducing greenhouse gas emissions, and addressing climate change. Hydrogen is a clean and efficient energy carrier, and its only by-product during combustion is water, without pollutant and greenhouse gas emissions, making it an ideal green energy option. There are various ways to utilize hydrogen energy, mainly including fuel cells, water electrolysis for hydrogen production, hydrogen storage and transportation, etc. Fuel cell technology is one of the cores of hydrogen energy utilization, which converts hydrogen and oxygen into electrical energy through chemical reactions and is widely used in fields such as automobiles, public transportation, and stationary power supplies.

[0003] Hydrogen storage technology is an important part of hydrogen energy utilization, and its effectiveness directly affects the production, transportation, and application of hydrogen. Currently, hydrogen storage methods can be roughly divided into three categories: physical hydrogen storage, chemical hydrogen storage, and solid-state hydrogen storage. However, common compressed hydrogen storage requires a relatively high pressure density and has certain safety hazards. Representative examples in chemical hydrogen storage are metal hydrides (such as magnesium hydride MgH2 and sodium hydride NaH), which can release hydrogen under suitable conditions. Metal hydrides have a relatively high hydrogen density, but usually require a relatively high temperature or pressure to release hydrogen. Solid-state hydrogen storage generally uses the physical adsorption of hydrogen by solid materials, and common materials include metal-organic frameworks (MOFs) and carbon-based materials. Currently, the carbon-based hydrogen storage materials studied mainly include activated carbon, graphene, etc. Carbon-based hydrogen storage materials mainly use the strongly polar dangling bonds on the surface of carbon materials to adsorb hydrogen molecules. Expanding the specific surface area and improving the surface adsorption capacity of hydrogen are the key factors to improve their hydrogen storage performance.

[0004] Biomass-based porous carbon materials have the advantage of low cost, and porous carbon materials with a high specific surface area and a porous structure can be obtained by introducing different activators. For the preparation of biomass-based porous carbon with an increased specific surface area, existing research has been very rich, but there are still certain limitations in the interaction mechanism between the carbon precursor and hydrogen, as well as in the research on the surface structure. At the same time, existing biomass-based hydrogen storage materials cannot take into account the reasonable specific surface area, pore structure, and surface functional group modification issues, and cannot specifically improve the surface. Summary of the Invention

[0005] Aiming at the problems such as low hydrogen adsorption capacity in existing hydrogen storage materials, the first object of the present invention is to provide a hydrogen storage material of porous carbon supported with fluoro-based functional groups. By uniformly introducing special fluorine-containing functional groups on the surface of this material and cooperating with the rich internal pore structure, it has excellent low-temperature hydrogen storage capacity and a relatively high hydrogen absorption capacity.

[0006] The second object of the present invention is to provide a preparation method of a hydrogen storage material of porous carbon supported with fluoro-based functional groups. This method uses the solution impregnation loading method with simple process. By using different kinds of hexafluorosilicates to modify the surface of the porous carbon precursor, the influence of heteroatoms is effectively avoided. During the high-temperature reaction, fluorine-containing functional groups are obtained on the surface of the porous carbon, enabling the target structure and surface functional groups to form efficient adsorption sites with hydrogen.

[0007] The third object of the present invention is to provide an application of a hydrogen storage material of porous carbon supported with fluoro-based functional groups. When it is applied to the adsorption and storage of hydrogen in a low-temperature environment, it has excellent directional adsorption ability and a relatively high storage capacity for hydrogen.

[0008] To achieve the above technical objects, the present invention provides a hydrogen storage material of porous carbon supported with fluoro-based functional groups. Fluorine atoms are introduced on the surface of the porous carbon through C-M-F or C-N-F bonding modes to form hydrogen absorption sites, where M is at least one of Mg, Zn, Na, and K. The preparation process of the hydrogen storage material is as follows: The biomass raw material is crushed and carbonized to obtain a porous carbon precursor; the porous carbon precursor and hexafluorosilicate are ultrasonically mixed to obtain a porous carbon material preliminarily loaded with hexafluorosilicate; the porous carbon material loaded with hexafluorosilicate is calcined at high temperature to obtain a hydrogen storage material of porous carbon supported with C-M-F functional groups or a hydrogen storage material of porous carbon supported with C-N-F functional groups. The hexafluorosilicate is a metal hexafluorosilicate or an ammonium hexafluorosilicate, and the metal in the metal hexafluorosilicate refers to at least one of Mg, Zn, Na, and K.

[0009] The principle of the high hydrogen storage performance of the hydrogen storage material of the present invention in a low-temperature environment is as follows: On the one hand, the porous carbon material modified multiple times has a suitable mesoporous structure and microporous structure, which is beneficial to the directional adsorption of hydrogen inside specific pore diameters; on the other hand, due to the influence of fluorine-containing functional groups (C-M-F and C-N-F) on the surface of the porous carbon, the electron density of hydrogen molecules shifts towards the unsaturated orbit direction in the structure, thus resulting in the physical adsorption of hydrogen and forming strong adsorption sites.

[0010] As a preferred scheme, the M is Mg and / or Na.

[0011] More preferably, they are C-Mg-F, C-Na-F, and C-N-F. When they are the more preferred functional group structures, the hydrogen storage material of the present invention has a more excellent microporous structure, which is more conducive to the improvement of hydrogen absorption performance.

[0012] As a preferred embodiment, the specific surface area of the hydrogen storage material > 2500 m 2 g -1 , and the microporosity > 50%. The hydrogen storage material of the present invention has a rich pore structure and a microporous structure conducive to the directional adsorption of hydrogen, so that the modified material has a hydrogen storage capacity > 2.5 wt% at 77K and 1 bar.

[0013] The present invention provides a preparation method of a porous carbon supported fluorine-based functional group hydrogen storage material. The biomass raw material is crushed and carbonized to obtain a porous carbon precursor; the porous carbon precursor and hexafluorosilicate are ultrasonically mixed to obtain a porous carbon material preliminarily loaded with hexafluorosilicate; the porous carbon material loaded with hexafluorosilicate is calcined at high temperature to obtain a porous carbon supported C-M-F functional group hydrogen storage material or a porous carbon supported C-N-F functional group hydrogen storage material; wherein, M is at least one of Mg, Zn, Na, and K; the hexafluorosilicate is a metal hexafluorosilicate or an ammonium hexafluorosilicate, and the metal in the metal hexafluorosilicate refers to at least one of Mg, Zn, Na, and K.

[0014] The key to the technical solution of the present invention is to react porous carbon and hexafluorosilicate at high temperature to load a new structure on the surface of the porous carbon material and obtain a surface rich in fluorine-containing functional groups. The finally obtained sample has a high specific surface area and a developed pore structure on the surface. At the same time, the present invention introduces hexafluorosilicate into the porous carbon precursor, and silicon tetrafluoride gas can be generated at high temperature to avoid the influence of heteroatoms on the surface structure. In addition, the generation of silicon tetrafluoride gas helps to transform the surface and internal pore structures of the porous carbon, further increasing the specific surface area of the material. And under high-temperature calcination, the influence of heteroelements (such as oxygen and nitrogen) in the structure of the biomass carbon itself is also excluded, ensuring the uniformity and adsorption stability of the subsequent loaded fluorine-containing functional group structure.

[0015] The principle of preparing the C-M-F functional group by introducing a fluorine-containing functional group surface structure into the hydrogen storage material of the present invention is as follows: during the high-temperature calcination process, the metal element undergoes an alkyl elimination mechanism with the surface structure of the porous carbon precursor. By using the metal source to break the carbon-carbon bond framework and re-perform new structural modification, some carbon-carbon branched chains are replaced with surface-specific C-M-F functional groups, and strong hydrogen absorption sites are formed thereby.

[0016] The principle of preparing C-N-F functional groups by introducing a fluorine-containing functional group surface structure into the hydrogen storage material of the present invention is as follows: during the high-temperature calcination process, vacancies or edge sites are generated on the surface or inside of the carbon material. At this time, the nitrogen element in the introduced N-F can replace some carbon atoms to form C-N-F functional groups, and strong hydrogen absorption sites are formed thereby.

[0017] Experiments have found that even without special activation treatment of the carbon precursor, only introducing hexafluorosilicate can still achieve a certain activation effect and surface structure modification. And the prepared sample still has a certain hydrogen storage capacity.

[0018] As a preferred solution, the biomass raw material is derived from tobacco stems, and in actual operation, reed, corn stalk, bamboo fiber, distiller's grains, etc. can be selected.

[0019] As a preferred solution, the biomass raw material is carbonized and then subjected to high-temperature activation treatment and pickling to remove impurities to obtain a porous carbon precursor. Through high-temperature activation treatment, the internal pore structure and hydrogen storage capacity of the hydrogen storage material can be further improved, and further pickling to remove impurities can remove the influence of metal heteroatoms in the biomass raw material on the material.

[0020] As a preferred solution, the temperature of the carbonization is 350-650 °C, the time is 1-4 h, and nitrogen with a flow rate of 80-100 mL / min is used as the protective atmosphere. The present invention can obtain a porous carbon precursor with a high specific surface area and a high pore structure through carbonization, which is beneficial to the subsequent loading of hexafluorosilicate. The carbonization time and temperature directly determine the carbonization degree of the biomass. Higher temperature and appropriate time will lead to further removal of volatile components in the biomass, increase the carbon content in the solid residue, and thus improve the calorific value and stability of the carbon sample. As a preferred solution, the temperature of the high-temperature activation treatment is 650-950 °C, the time is 1-4 h, and nitrogen with a flow rate of 80-100 mL / min is used as the protective atmosphere. Further preferably, the temperature of the high-temperature activation treatment is 700-800 °C.

[0021] As a preferred solution, at least one activator such as potassium hydroxide, water vapor, and zinc chloride is added during the high-temperature activation treatment.

[0022] During the high-temperature activation treatment process of the present invention, potassium hydroxide, zinc chloride and water vapor are used as activators, so that the porous carbon does not require complicated equipment and processes during the activation reaction, which is relatively economical and affordable. In addition, the environmental impact of this process is small, which makes it have advantages in the development of green materials. The amount of the activator used is 1 to 4 times that of the carbon material of the same mass. By adjusting the amount of the activator, the activation temperature and time and other parameters, the specific surface area, porosity and pore size distribution of the porous carbon precursor can be accurately controlled. However, excessive activator will cause the carbon itself to react with the activator, causing the carbon to be oxidized to generate corresponding carbon oxides or carbonates and causing the skeleton to be etched.

[0023] As a preferred embodiment, the mass ratio of the porous carbon precursor to the hexafluorosilicate is 1:(5-20). This mass ratio, selected within the present invention, ensures the introduction of the structure during the reaction while preventing excessive hexafluorosilicate from clogging the pores and collapsing the structure, which could reduce the material's specific surface area and decrease hydrogen storage efficiency. A further preferred mass ratio is 1:(5-10).

[0024] As a preferred solution, the temperature of the high-temperature calcination is 550~950℃, and the time is 0.5~3h. The temperature and time of the high-temperature calcination of the present invention have a direct impact on the amount and uniformity of the fluorine-containing functional groups introduced on the surface of the porous carbon. Too high a temperature will cause the fluorine-containing functional group structure to fall off on the side chain, and silicon tetrafluoride will be generated too quickly, making it impossible to effectively react with the porous carbon surface, so that effective directional modification cannot be achieved. Too low a temperature will reduce the reaction rate, causing the fluorine-containing functional group structure to be generated slowly, and the effect is not good. Similarly, the length of time will also affect the introduction rate of the surface group accordingly, affecting the structure and hydrogen storage performance of the final sample. In the present invention, it is further preferred that the temperature of the high-temperature calcination is 700~800℃, and the reaction time is 1~1.5h.

[0025] As a preferred solution, the ultrasonic mixing time is 10 to 60 minutes. Within the ultrasonic mixing time range of the present invention, the loading of hexafluorosilicate can be effectively achieved.

[0026] The present invention provides a method for preparing a porous carbon-supported fluorine-based functional group hydrogen storage material, which specifically comprises the following steps:

[0027] (1) The biomass raw materials are dried and crushed into powder particles, and then carbonized under a nitrogen atmosphere to obtain preliminary carbonized materials.

[0028] (2) The preliminary carbonized material is subjected to high-temperature activation treatment with an activator to obtain a porous carbon precursor.

[0029] (3) Dissolve hexafluorosilicate and porous carbon precursor in water, mix them ultrasonically, filter them, and dry them in a vacuum drying oven to obtain a mixed black powder.

[0030] (4) Calcinate the black powder under a nitrogen atmosphere to finally obtain a hydrogen storage material with C-M-F functional groups supported on porous carbon or a hydrogen storage material with C-N-F functional groups supported on porous carbon.

[0031] The present invention finally also provides an application of a hydrogen storage material with fluorine-based functional groups supported on porous carbon, and applies it to the adsorption and storage of hydrogen in a low-temperature environment.

[0032] Furthermore, use this material for hydrogen storage at 77K and a pressure of 1-50 bar. The hydrogen storage material of the present invention can achieve a hydrogen storage capacity > 2.5 wt% at 1 bar; and a hydrogen storage capacity > 5.2 wt% at 50 bar.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The hydrogen storage material of the present invention has a suitable mesoporous structure, microporous structure and high specific surface area, which is conducive to the directional adsorption of hydrogen inside specific pore diameters; at the same time, affected by the fluorine-containing functional groups (C-M-F and C-N-F) introduced on the surface of the porous carbon, it is conducive to the electron density of hydrogen molecules to shift towards the metal empty orbital direction, resulting in the physical adsorption of hydrogen, forming strong adsorption sites, and having high hydrogen storage performance and hydrogen storage capacity in a low-temperature environment.

[0035] (2) Uniform reaction sites are formed on the surface of the hydrogen storage material of the present invention, and at the same time, it has high structural stability.

[0036] (3) The technological process of the present invention is simple, using easily available biomass materials as carbon precursors, with the characteristics of low cost, environmental friendliness, and high economic benefits.

[0037] (4) The hydrogen storage material prepared by the present invention has excellent hydrogen storage capacity, achieving an increase in the hydrogen storage capacity under low-temperature conditions.

[0038] (5) Using hexafluorosilicate as a raw material, the fluorine source and metal source or nitrogen source are introduced synchronously, and during the high-temperature calcination process, the metal element undergoes an alkyl elimination mechanism with the surface structure of the porous carbon precursor. The metal source is used to break the carbon-carbon bond framework and re-perform new structural modification, replacing some carbon-carbon branches with surface-specific C-M-F and C-N-F functional groups, and thus forming strong hydrogen absorption sites. Description of the Drawings

[0039] Figure 1 Comparison chart of hydrogen adsorption amounts of porous carbon precursors C-700, C-800, and C-900 prepared in Example 1 (where Figure 1 (a) is at 50 bar, Figure 1 (b) is at 1 bar).

[0040] Figure 2 SEM images of C-800 prepared for Example 1 ( Figure 2 (a)) and Mg-F@C-1 mM prepared for Example 2 ( Figure 2 (b)).

[0041] Figure 3 SEM images of C-800 prepared for Example 1 and Example 7 ( Figure 3 (a)) and M-FΔC ( Figure 3 (b)).

[0042] Figure 4 Comparison chart of hydrogen adsorption amounts of Mg-F@C-0.5 mM, Mg-F@C-1 mM, and Mg-F@C-1.2 mM prepared for Example 2 (where Figure 4 (a) is at 50 bar, Figure 4 (b) is at 1 bar).

[0043] Figure 5 Comparison chart of hydrogen adsorption amount of M-FΔC prepared for Example 7 (where Figure 5 (a) is at 1 bar, Figure 5 (b) is at 50 bar).

[0044] Figure 6 Characterization chart of pore volume and pore diameter of Mg-F@C prepared for Example 3, N-F@C prepared for Example 4, and C material prepared for Comparative Example 1. Detailed implementation manners

[0045] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments, and all other embodiments obtained by those skilled in the art without creative efforts still fall within the protection scope of the present invention.

[0046] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchases or can be prepared by existing methods.

[0047] Example 1 (Experiment on activation temperature exploration)

[0048] The tobacco stems are dried and crushed into powdery particles, and pre-carbonized materials are obtained by carbonization at 400 °C for 1 h under a nitrogen atmosphere of 100 ml / min.

[0049] Activation process: The pre-carbonized samples were used to prepare porous carbon precursors under different activation temperatures (700 °C, 800 °C, and 900 °C), and C-700, C-800, and C-900 were obtained respectively after removing impurities by HCl pickling.

[0050] The hydrogen adsorption performance of C-700, C-800, and C-900 was tested under the conditions of 77 k, 1 bar and 77 k, 50 bar respectively (the test powder sample was 40 mg), and the results are as Figure 1 shown.

[0051] From Figure 1 the results, it can be seen that the initial carbon samples have a certain hydrogen adsorption capacity, and C-800 shows the best hydrogen storage capacity, which indicates that C-800 has a rich and reasonable pore structure and a large specific surface area. Further, the activation temperature is preferably 700 - 800 °C.

[0052] Example 2 (Experiment on the dosage of hexafluorosilicate)

[0053] 50 mg of C-800 prepared in Example 1 was used as the carbon precursor and introduced into a beaker. 0.5 mM - 2 mM of magnesium hexafluorosilicate was added and dissolved in 50 ml of deionized water. The sample was ultrasonically treated for 30 min, and then the sample was filtered and dried in a vacuum drying oven at 60 °C for 12 h. The dried sample was placed in a tube furnace and calcined at 700 °C for 1 h, and finally Mg-F@C-0.5 mM (the mass ratio of the porous carbon precursor to hexafluorosilicate is 1:20), Mg-F@C-1 mM (the mass ratio of the porous carbon precursor to hexafluorosilicate is 1:10), and Mg-F@C-1.2 mM (the mass ratio of the porous carbon precursor to hexafluorosilicate is 1:5) were obtained respectively.

[0054] The Mg-F@C-1 mM sample prepared in this example and the C-800 sample in Example 1 were respectively tested and compared by scanning electron microscopy and energy spectrum analysis, and the results are as Figure 2 (a) and Figure 2 (b) shown. From Figure 2 it can be seen that the Mg-F@C-1 mM sample after high-temperature calcination and functional group modification has a more abundant surface pore structure and the successful loading of fluorine-containing functional groups.

[0055] Example 3

[0056] (1) Preparation of porous carbon precursor:

[0057] The biomass raw material tobacco stems were dried and then crushed into powders, carbonized at 400 °C for 1 h in a nitrogen atmosphere (gas flow rate 100 mL / min) to obtain pre-carbonized materials. Subsequently, the pre-carbonized materials were mixed with potassium hydroxide in a mass ratio of 1:3 and activated at high temperature of 800 °C for 1 h. After cooling to room temperature, they were washed with HCl for impurity removal, washed with water until neutral, and dried at 60 °C to obtain carbon precursors, named C-800-3.

[0058] (2)Preparation of hydrogen storage materials:

[0059] C-800-3 and magnesium hexafluorosilicate (1 mM) were added to 50 ml of deionized water in a mass ratio of 1:10, and ultrasonic treatment was carried out for 30 min to uniformly load magnesium hexafluorosilicate onto the surface of C-800-3. Then it was placed in a vacuum drying oven and dried at 60 °C for 12 h to obtain a porous carbon material with preliminarily loaded magnesium hexafluorosilicate. Subsequently, the sample was calcined in a tubular furnace at 700 °C for 1 h to finally obtain Mg-F@C.

[0060] Example 4

[0061] The difference between this example and Example 3 is only that the hexafluorosilicate in step 2 is replaced with an equal amount of hexafluorosilicate amine, and the rest of the steps and conditions are the same, obtaining N-F@C.

[0062] Example 5

[0063] The difference between this example and Example 3 is only that the magnesium hexafluorosilicate in step 2 is replaced with an equal amount of sodium hexafluorosilicate, and the rest of the steps and conditions are the same, obtaining Na-F@C.

[0064] Example 6

[0065] The difference between this example and Example 3 is only that the magnesium hexafluorosilicate in step 2 is replaced with an equal amount of potassium hexafluorosilicate, and the rest of the steps and conditions are the same, obtaining K-F@C.

[0066] Example 7

[0067] The difference between this example and Example 3 is only that the activator potassium hydroxide is not added during the high-temperature activation process, and the rest of the steps and conditions are the same, finally obtaining M-FΔC.

[0068] The C-800 prepared in Example 1, the Mg-F@C-1 mM prepared in Example 2, and the unactivated sample of M-FΔC prepared in this example were subjected to scanning electron microscopy tests, and the results are as Figure 2 and Figure 3 shown. It can be seen from Figure 3 (a) that the surface of the carbon material is smooth and there is no large number of pore structures. From Figure 3(b) It can be seen that the surface of M-FΔC after high-temperature loading presents a large-area pore structure similar to a shell shape, indicating that hexafluorosilicate still has a certain activation effect.

[0069] Example 8

[0070] The difference between this example and Example 3 is only that the temperature of high-temperature calcination is changed to 550 °C, and the rest of the steps and conditions are the same, obtaining Mg-F@C-550.

[0071] Example 9

[0072] The difference between this example and Example 3 is only that the temperature of high-temperature calcination is changed to 950 °C, and the rest of the steps and conditions are the same, obtaining Mg-F@C-950.

[0073] Comparative Example 1

[0074] The difference between this comparative example and Example 3 is only that magnesium hexafluorosilicate is not added, and the rest of the steps and conditions are the same, obtaining C material (i.e., C-800).

[0075] Comparative Example 2

[0076] The difference between this comparative example and Example 3 is only that an equal amount of metallic magnesium is added, and the rest of the steps and conditions are the same, obtaining a carbon material loaded with magnesium, denoted as M1.

[0077] It can be seen from the result comparison in Table 1 that the hydrogen storage capacity of only the carbon material loaded with magnesium is lower than that of the pure carbon material. This is because during the process of loading magnesium, part of the metallic magnesium is oxidized to form magnesium oxide, blocking part of the pore structure of the carbon material; this also simultaneously confirms that the present invention requires the synchronous introduction of Mg and F to optimize the pore structure of the carbon material on the one hand and form strong adsorption sites of C-Mg-F on the other hand, significantly improving the hydrogen storage performance and hydrogen storage capacity at a relatively low temperature environment.

[0078] Hydrogen storage performance evaluation

[0079] The different types of hydrogen storage materials in Example 2 and Example 7 were all measured for hydrogen adsorption-desorption isotherms under the conditions of 77 K (1 bar and 50 bar). Before analysis, all samples were evacuated at 200 °C in vacuum for 8 h. The specific surface area was determined by the Brunauer-Emmet-Teller (BET) method. The DFT theory was applied to the nitrogen adsorption isotherm to determine the pore size distribution. Finally, the mass hydrogen storage capacity (wt%) of hydrogen was calculated through the Quantity Adsorbed (cm 3 / g STP) capacity.

[0080] The final hydrogen adsorption results are as Figure 4 、 Figure 5 shown.

[0081] The examples confirmed the positive effect of the hexafluorosilicate loading on hydrogen adsorption, and further preferably the mass ratio of the porous carbon precursor to hexafluorosilicate was 1:(5 - 10) as the optimal loading amount.

[0082] Meanwhile, the hydrogen storage capacities of different samples in the examples and comparative examples under different pressures were counted, and the results are listed in Table 1. According to the data analysis in Table 1, it can be seen that the biomass-based porous carbon C-800-3 after activation by the activator was significantly superior to the unactivated biomass-based porous carbon C-800 in terms of hydrogen storage performance. Benefiting from the further structural modification and surface modification of the surface by introducing hexafluorosilicate, M-F@C-1.2 mM showed a higher hydrogen adsorption capacity and achieved a total hydrogen storage capacity of 9.7 wt% at high pressure (50 bar). In addition, the pore size distribution curve of the M-F@C material was carried out, which proved the structural etching effect of introducing hexafluorosilicate on the surface of the C material, which was the structural guarantee for obtaining excellent hydrogen storage performance.

[0083]

Claims

1. A hydrogen storage material based on fluorine-based functional groups supported on porous carbon, characterized in that: Fluorine atoms are introduced onto the surface of the porous carbon through C-M-F or C-N-F bonding to form hydrogen absorption sites, where M is at least one of Mg, Zn, Na, and K. The preparation process of the hydrogen storage material is as follows: The biomass raw material is crushed and carbonized to obtain a porous carbon precursor; the porous carbon precursor and hexafluorosilicate are ultrasonically mixed to obtain a porous carbon material preliminarily loaded with hexafluorosilicate; the porous carbon material loaded with hexafluorosilicate is calcined at high temperature to obtain a porous carbon loaded with C-M-F functional group hydrogen storage material or a porous carbon loaded with C-N-F functional group hydrogen storage material. The hexafluorosilicate is a hexafluorosilicate metal salt or hexafluoroammonium silicate, where the metal in the hexafluorosilicate metal salt refers to at least one of Mg, Zn, Na, and K.

2. The hydrogen storage material with fluorine-based functional groups supported on porous carbon according to claim 1, wherein: The M is Mg and / or Na.

3. The hydrogen storage material of fluorine-based functional groups supported on porous carbon according to claim 1 or 2, characterized in that: The specific surface area of the hydrogen storage material > 2500 m 2 g -1 , and the microporosity > 50%.

4. The preparation method of a hydrogen storage material with a fluorine-based functional group supported on porous carbon according to any one of claims 1 to 3, characterized in that: The biomass raw material is crushed and carbonized to obtain a porous carbon precursor; the porous carbon precursor and hexafluorosilicate are ultrasonically mixed to obtain a porous carbon material preliminarily loaded with hexafluorosilicate; the porous carbon material loaded with hexafluorosilicate is calcined at high temperature to obtain a porous carbon loaded with C-M-F functional group hydrogen storage material or a porous carbon loaded with C-N-F functional group hydrogen storage material. Wherein, M is at least one of Mg, Zn, Na, and K. The hexafluorosilicate is a hexafluorosilicate metal salt or hexafluoroammonium silicate, where the metal in the hexafluorosilicate metal salt refers to at least one of Mg, Zn, Na, and K.

5. The preparation method of a hydrogen storage material with fluorine-based functional groups supported on porous carbon according to claim 4, characterized in that: The biomass raw material is carbonized and then subjected to high-temperature activation treatment and pickling for impurity removal to obtain a porous carbon precursor.

6. The preparation method of a porous carbon loaded with fluorine-based functional group hydrogen storage material according to claim 5, characterized in that: The temperature of the carbonization is 350-650 °C, the time is 1-4 h, and nitrogen with a flow rate of 80-100 mL / min is used as the protective atmosphere. The temperature of the high-temperature activation treatment is 650-950 °C, the time is 1-4 h, and nitrogen with a flow rate of 80-100 mL / min is used as the protective atmosphere.

7. The preparation method of a hydrogen storage material with fluorine-based functional groups supported on porous carbon according to claim 4, characterized in that: At least one activator such as potassium hydroxide, water vapor, or zinc chloride is added during the high-temperature activation treatment.

8. The preparation method of a hydrogen storage material with fluorine-based functional groups supported on porous carbon according to claim 7, characterized in that: The mass ratio of the porous carbon precursor to the hexafluorosilicate is 1:(5-20).

9. The preparation method of a hydrogen storage material with fluorine-based functional groups supported on porous carbon according to claim 8, characterized in that: The temperature of the high-temperature calcination is 550-950 °C, and the time is 0.5-3 h.

10. Use of a hydrogen storage material with fluorine-based functional groups supported on porous carbon according to any one of claims 1 to 3, characterized in that: It is applied to the adsorption and storage of hydrogen in a low-temperature environment.

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