Porous carbon composite diatom skeleton hydrogen storage material and preparation method thereof

Abstract

The present application belongs to the technical field of inorganic functional materials, and particularly relates to a porous carbon composite diatom skeleton hydrogen storage material and a preparation method thereof. The preparation method is to polymerize furfuryl alcohol inside and on the surface of diatom skeletons, then calcine in a nitrogen atmosphere to form a carbon structure, and then activate to create and open more pores. Experiments prove that the hydrogen storage materials prepared under different concentration acid treatment and different proportion of clay and diatomite synthesis conditions all have high performance. The specific surface area of the porous carbon composite diatom skeleton hydrogen storage material treated by 0.5M sulfuric acid and 4.0M sulfuric acid is 283.7m 2 / g and 397.1m 2 / g respectively, and the hydrogen storage capacity of the porous carbon composite diatom skeleton hydrogen storage material treated by 4.0M sulfuric acid is 1.25wt% at 298K, 5MPa; and the highest hydrogen storage capacity can reach 4.33wt% at 77K, 5MPa. The technical scheme has important value for the application and development of low-cost, high-performance, easy-to-use and large-scale prepared hydrogen storage materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of inorganic functional materials, and in particular relates to a porous carbon composite diatom skeleton hydrogen storage material and a preparation method thereof. Background Art

[0002] Hydrogen storage materials are typically porous, with a high surface area and a unique microstructure to increase the amount of hydrogen adsorbed. Common adsorbents include activated carbon, metal-organic frameworks (MOFs), coordination polymers, etc. However, the synthesis methods of these materials are relatively complex, involving expensive precursors and reaction conditions. This makes large-scale preparation a challenge, thus limiting their commercial application. Diatomaceous earth is a naturally porous material with a large specific surface area. Diatomaceous earth can also be used as a hydrogen storage material. Its pore structure can accommodate hydrogen molecules, allowing it to adsorb and release hydrogen at low temperatures and appropriate pressures. As an inexpensive and abundant material, diatomaceous earth has certain potential for the development of hydrogen storage technology. Traditionally, diatomaceous earth used for hydrogen storage is generally modified by acid-heat treatment of platinum (Pt) and palladium (Pd) nanoparticles. However, this method results in a low specific surface area of ​​the final product, mediocre hydrogen storage effect, and the price of the added metal is relatively high. Summary of the Invention

[0003] One of the objectives of the present invention is to provide a method for preparing a porous carbon composite diatom skeleton hydrogen storage material. This preparation method utilizes the original pore structure of the diatom skeleton to fill the porous carbon, forming a more complex porous structure with excellent hydrogen storage performance.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a porous carbon composite diatom skeleton hydrogen storage material, comprising the following steps:

[0005] S1. Dispersing diatomaceous earth in a 0.5M-4.0M H2SO4, HCl or HNO3 solution, keeping warm at 70-90°C for 3-6 hours, repeatedly washing and filtering until the pH is neutral, and then drying to obtain acid-treated diatomaceous earth;

[0006] S2, acid-treated diatomaceous earth, clay, water-soluble polymer and deionized water are mixed in a mass ratio of (2-3): (3-4): (0.2-0.4): (4-8), stirred to obtain a mixture, placed the mixture in a mold for shaping, dried, and then subjected to high temperature treatment at 700-900° C. in an air atmosphere for 3-6 hours to obtain a shaped diatomaceous earth skeleton;

[0007] S3, take the shaped diatomaceous earth skeleton and add it to furfuryl alcohol in an amount of 0.1-0.3g / mL, let it stand for 20-40 minutes, then add 7-8wt% hydrochloric acid solution, the volume of the hydrochloric acid solution is twice the volume of furfuryl alcohol, and stir rapidly for 15-25 seconds, take out the solid mixture, and keep it at 700-900°C for 3-6 hours in a protective atmosphere to obtain a porous carbon-supported composite diatom skeleton;

[0008] S4. Add the porous carbon-loaded composite diatom skeleton to 8-10 mol / L potassium hydroxide or sodium hydroxide solution and soak it fully, then take it out, dry it, and then place it in a protective atmosphere at 700-900 ° C for 3-6 hours. After cooling to room temperature, wash it with water, and then add excess hydrochloric acid solution for neutralization. After soaking for 2-3 hours, take it out and wash it until it is neutral, and then vacuum dry it to obtain a porous carbon composite diatom skeleton hydrogen storage material.

[0009] Further improvement of the preparation method of porous carbon composite diatom skeleton hydrogen storage material:

[0010] Preferably, in step S2, the mixture is placed in a mold for shaping and then dried at 70-90° C. for 3-6 hours.

[0011] Preferably, the protective atmosphere is a nitrogen atmosphere or an inert gas atmosphere.

[0012] Preferably, in step S4, the porous carbon-supported composite diatom skeleton is immersed in the potassium hydroxide solution at a temperature of 70-90° C. for 1-3 hours.

[0013] Preferably, the drying temperature in step S4 is 70-90° C. and the drying time is 3-6 hours.

[0014] Preferably, in steps S2, S3 and S4, the temperature is heated from room temperature to 700-900°C at a rate of 5-8°C / min.

[0015] Preferably, the water-soluble polymer is one or a combination of two or more of polyacrylic acid, polyvinyl alcohol, and polyethylene glycol.

[0016] A second object of the present invention is to provide a porous carbon composite diatom skeleton hydrogen storage material prepared by any of the above preparation methods.

[0017] The beneficial effects of the present invention compared to the prior art are:

[0018] 1) The present invention provides a method for preparing a porous carbon composite diatom skeleton hydrogen storage material, which comprises the following steps: first, dispersing diatomite in a sulfuric acid / hydrochloric acid / nitric acid solution for activation treatment to remove metal oxide impurities on the surface of the diatomite; then, adding clay to shape the diatomite, using a water-soluble polymer (polyacrylic acid) as a binder, and subjecting the diatomite to high-temperature treatment at 700-900°C, causing the water-soluble polymer to react with oxygen to generate carbon dioxide, thereby forming pores and obtaining a shaped diatomite skeleton; then, furfuryl alcohol is dispersed into the shaped diatomite skeleton, and after adding hydrochloric acid, the furfuryl alcohol and the hydrochloric acid are in situ polymerized inside and on the surface of the shaped diatomite skeleton, and then calcining in a nitrogen atmosphere to form a carbon structure and obtain a porous carbon-supported composite diatom skeleton; and finally, KOH reacts with silicates in the porous carbon-supported composite diatom skeleton, partially dissolving the silicates. Under high-temperature conditioning conditions, part of the carbon is reacted to form new pores. Potassium reacts with part of the carbon, and excess potassium hydroxide is neutralized with hydrochloric acid to keep the activated porous carbon-supported composite diatom skeleton neutral.

[0019] The results showed that the specific surface area of ​​the final porous carbon composite diatom skeleton hydrogen storage material prepared by treating diatomite with 0.5M sulfuric acid was 283.7m 2 / g, the hydrogen storage capacity is 1.08wt% at 298K and 5MPa, and the specific surface area of ​​the final porous carbon composite diatom skeleton hydrogen storage material of diatomite treated with 4.0M sulfuric acid is 397.1m 2 / g, and a hydrogen storage capacity of 1.25wt% at 298K and 5MPa. Both the specific surface area and hydrogen storage performance have been greatly improved. The technical solution of the present invention is of great value to the application and development of low-cost, high-performance, and easy-to-use hydrogen storage materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 (a) is the porous carbon composite diatom skeleton hydrogen storage material prepared in Example 4 (A 4.0 B 2-3 -CH 2.0 ) and clay, diatomite XRD pattern; (b) is the porous carbon-supported composite diatom skeleton A prepared in step S3 of Example 4 4.0 B 2-3 -C, porous carbon composite diatom skeleton hydrogen storage material A prepared in step S4 4.0 B 2-4 -CH 2.0 , Raman diagram of diatomite-clay mixture.

[0021] Figure 2 (a) is the nitrogen adsorption-desorption curve of the porous carbon-supported composite diatom skeleton prepared in step S3 of Example 1-5, and (b) is the pore size and pore volume data diagram of the porous carbon-supported composite diatom skeleton prepared in step S3 of Example 1-5 of the present invention.

[0022] Figure 3 (a) is the nitrogen adsorption-desorption curve of the porous carbon composite diatom skeleton hydrogen storage material prepared in step S4 of Example 1-5, and (b) is the pore size and volume data diagram of the porous carbon composite diatom skeleton hydrogen storage material prepared in step S4 of Example 1-5.

[0023] Figure 4 (a) is the hydrogen storage curve of the porous carbon composite diatom skeleton hydrogen storage material prepared in step S4 of Example 1-5 of the present invention at 77K, (b) is the hydrogen storage curve of the porous carbon composite diatom skeleton hydrogen storage material prepared in step S4 of Example 1-5 at 195K, and (c) is the hydrogen storage curve of the porous carbon composite diatom skeleton hydrogen storage material prepared in step S4 of Example 1-5 at 298K.

[0024] Figure 5 (a) and (b) are the fitting straight line and B Arrhenius equation model of the porous carbon composite diatom skeleton hydrogen storage material prepared in Example 4 at different temperatures, respectively.

[0025] Figure 6 This is a picture of the porous carbon composite diatom skeleton hydrogen storage material prepared in Example 4 under a scanning electron microscope. DETAILED DESCRIPTION

[0026] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] Example 1

[0028] This embodiment provides a method for preparing a porous carbon composite diatom skeleton hydrogen storage material, which specifically includes the following steps:

[0029] S1. Disperse 10 g of diatomaceous earth in 100 mL of 0.5 M H2SO4 solution, keep warm at 80°C for 4 hours, then repeatedly wash and filter until the pH is neutral, and dry at 60°C for 12 hours to obtain acid-treated diatomaceous earth;

[0030] S2. Mix 2g of acid-treated diatomaceous earth, 3g of clay, and 0.2g of polyacrylic acid, then add 4mL of deionized water. After thorough mixing, place the mixture into a mold to set the shape. Then, dry it at 80°C for 4 hours. Then, heat it in a muffle furnace under air atmosphere from room temperature to 800°C at a rate of 5°C / min and hold it at 800°C for 4 hours to obtain a shaped diatomaceous earth skeleton.

[0031] S3. 2 g of the shaped diatomite skeleton was immersed in 10 ml of furfuryl alcohol and allowed to stand for 30 minutes. Then, 20 ml of 7.78 wt% hydrochloric acid solution was added and rapidly stirred for 20 seconds. The solid mixture was taken out and heated from room temperature to 800°C in a tube furnace under a nitrogen atmosphere at a heating rate of 5°C / min and maintained at 800°C for 4 hours to obtain a porous carbon-supported composite diatomite skeleton, which was recorded as A. 0.5 B 2-3 -C, where A X Indicates the concentration of acid used to treat diatomaceous earth, B X represents the mixing mass ratio of diatomite to clay, and C indicates that the sample has been carbonized;

[0032] S4. Add 2g of porous carbon-loaded composite diatom skeleton to 9mol / L potassium hydroxide solution, soak it at 80℃ for 2h, and then take it out. Put it in an oven at 80℃ and dry it for 4h, then take it out, and then place it in a tubular furnace in a nitrogen atmosphere. The temperature is raised from room temperature to 800℃ at a heating rate of 5℃ / min, and then maintained at 800℃ for 4h. After cooling to room temperature, wash with deionized water, and then add excess hydrochloric acid solution to neutralize it. After soaking for 2 hours, wash it until neutral, then take it out and place it in a vacuum drying oven at 80℃ and dry it for 12 hours to obtain a porous carbon composite diatom skeleton hydrogen storage material, recorded as A 0.5 B 2-3 -CH 2.0 , where A X Indicates the concentration of acid used to treat diatomaceous earth, B X represents the mixing mass ratio of diatomite to clay, C represents that the sample has been carbonized, and H represents that the sample has been activated and the activation time.

[0033] Example 2

[0034] This embodiment provides a method for preparing a porous carbon composite diatom skeleton hydrogen storage material. The specific steps are similar to those in Example 1, except that the concentration of the H2SO4 solution in step S1 is 1.0 M.

[0035] Obtain the porous carbon-supported composite diatom skeleton A in step S3 1.0 B 2-3 -C, and the porous carbon composite diatom skeleton hydrogen storage material A in step S4 1.0 B 2-3 -CH 2.0 .

[0036] Example 3

[0037] This embodiment provides a method for preparing a porous carbon composite diatom skeleton hydrogen storage material. The specific steps are similar to those in Example 1, except that the concentration of the H2SO4 solution in step S1 is 2.0 M.

[0038] Obtain the porous carbon-supported composite diatom skeleton A in step S3 2.0 B 2-3 -C, and the porous carbon composite diatom skeleton hydrogen storage material A in step S4 2.0 B 2-3 -CH 2.0 .

[0039] Example 4

[0040] This embodiment provides a method for preparing a porous carbon composite diatom skeleton hydrogen storage material. The specific steps are similar to those in Example 1, except that the concentration of the HNO3 solution in step S1 is 4.0M;

[0041] Obtain the porous carbon-supported composite diatom skeleton A in step S3 4.0 B 2-3 -C, and the porous carbon composite diatom skeleton hydrogen storage material A in step S4 4.0 B 2-3 -CH 2.0 .

[0042] Example 5

[0043] This embodiment provides a method for preparing a porous carbon composite diatom skeleton hydrogen storage material. The specific steps are similar to those in Example 4, except that the mass of the clay in step S2 is 4 g;

[0044] Obtain the porous carbon-supported composite diatom skeleton A in step S3 4.0 B 2-4 -C, and the porous carbon composite diatom skeleton hydrogen storage material A in step S4 4.0 B 2-4 -CH 2.0 .

[0045] Performance Testing

[0046] Figure 1 (a) is the porous carbon composite diatom skeleton hydrogen storage material A of Example 4 4.0 B 2-4 -CH 2.0 Compared with the XRD patterns of diatomite and clay without any treatment, diatomite has a typical amorphous peak at 16°-30°, with the peak center at around 21°. Porous carbon composite diatom skeleton hydrogen storage material A 4.0 B 2-4 -CH 2.0 After calcination at 800°C, a broad diffraction peak between 16° and 30° was observed, indicating that the amorphous phase remained primarily composed of the same phase as the pre-calcination sample, containing a small amount of quartz phase. In Example 4, the addition of polyacrylic acid to the sample did not affect the diatomite crystal structure after calcination. Similarly, the addition of polyacrylic acid to the sample did not affect the clay crystal structure after calcination.

[0047] 2 g of diatomaceous earth and 3 g of clay were mixed and dried to obtain a diatomaceous earth-clay mixture; Figure 1 (b) The porous carbon-supported composite diatom skeleton A prepared in step S3 of Example 4 4.0 B 2-3 -C, porous carbon composite diatom skeleton hydrogen storage material A prepared in step S4 4.0 B 2-4 -CH 2.0 The Raman spectra of the diatomite-clay mixture show that the introduction of furfuryl alcohol condensation short-chain molecules and calcination under a nitrogen atmosphere produced a new graphite phase, and the graphitization was further enhanced after activation. Furthermore, the final porous carbon composite diatom skeleton hydrogen storage material still exhibits a typical diatomite broad peak at 16°-30°, indicating the presence of the diatom structure.

[0048] Table 1 shows the specific surface area of ​​the porous carbon composite diatom skeleton hydrogen storage materials prepared in Examples 1-5 and the average pore diameter, total pore volume and micropore volume of some porous carbon composite diatom skeleton hydrogen storage materials.

[0049] Table 1: Specific surface area and average pore size of all samples

[0050]

[0051] As can be seen from Table 1, the specific surface area of ​​the porous carbon composite diatom skeleton hydrogen storage material after the introduction of the carbon skeleton was not affected after the diatomite was treated with sulfuric acid of different concentrations. This is because the polymerization of furfuryl alcohol is random and uncontrollable. After polymerization and carbonization, blocked pores will be produced. After activation, the pores are opened and new pores are also created. The data show that the specific surface area of ​​the acid-treated diatomite increases with the increase of acid concentration, and the basic micropore volume of the acid-treated diatomite with a higher acid concentration is larger, indicating that the pores of the diatom skeleton opened by the acid treatment are beneficial to the entry of furfuryl alcohol into the diatom skeleton for polymerization. The polymerization situation of the diatom skeleton after activation can be reflected in the specific surface area data. The larger the specific surface area, the better the polymerization situation in the skeleton. After calcination under a nitrogen atmosphere, a porous carbon skeleton structure is formed, which can produce a larger specific surface area and more microporous structures after activation.

[0052] Figure 2 (a) is the nitrogen adsorption-desorption curve of the porous carbon-supported composite diatom skeleton prepared in step S3 of Example 1-5, and (b) is the pore size and pore volume data diagram of the porous carbon-supported composite diatom skeleton prepared in step S3 of Example 1-5 of the present invention.

[0053] Figure 3(a) shows the nitrogen adsorption / desorption curve of the porous carbon composite diatom framework hydrogen storage material prepared in step S4 of Example 1-5, and (b) shows the pore size and volume data of the porous carbon composite diatom framework hydrogen storage material prepared in step S4 of Example 1-5. Furfuryl alcohol is polymerized and calcined on the porous carbon composite diatom framework hydrogen storage material to produce a porous structure with varying pore sizes.

[0054] Figure 4 (a) is the hydrogen storage curve of the porous carbon composite diatom skeleton hydrogen storage material obtained in step S4 of embodiment 1-5 of the present invention at 77K and a pressure of up to 5MPa, (b) is the hydrogen storage curve of the porous carbon composite diatom skeleton hydrogen storage material obtained in step S4 of embodiment 1-5 at 195K and a pressure of up to 5MPa, and (c) is the hydrogen storage curve of the porous carbon composite diatom skeleton hydrogen storage material obtained in step S4 of embodiment 1-5 at 298K and a pressure of up to 5MPa. It can be seen from the figure that the sample with high acid treatment concentration has better hydrogen storage performance. At 77K and 5MPa, the sample hydrogen storage capacity can reach up to 4.33wt%, and at 298K and 5MPa, the sample hydrogen storage capacity can reach up to 1.25wt%. The results show that the hydrogen storage performance of some samples is outstanding, and their hydrogen storage capacity increases significantly with the increase of pressure. It shows that the final product can be applied to hydrogen storage work and has a good hydrogen storage effect.

[0055] Figure 5 (a) and (b) are the fitting straight line and B Arrhenius equation model of the porous carbon composite diatom skeleton hydrogen storage material prepared in Example 4 at different temperatures, respectively. Figure 5 (a) shows sample A 4.0 B 2-3 -CH 2.0 Fitting straight lines of hydrogen absorption (mmol / g) and pressure (MPa) at different temperatures (77, 195, and 598 K). Figure 5 (b) shows the fitting straight line of InK versus 1 / T. Figure 5 The slope of the fitted line in (a) is K. Through fitting calculation, the K values ​​at 77, 195 and 298 K were 3.555, 1.678 and 1.155 respectively. According to the Arrhenius equation and Figure 5 The slope of In K versus 1 / T in (b) is used to calculate ΔH, which is 0.896 kJ / mol for the hydrogen adsorption enthalpy.

[0056] Figure 6 This is a picture of the porous carbon composite diatom skeleton hydrogen storage material prepared in Example 4 under a scanning electron microscope. Figure 6 The material's surface is covered with densely packed micropores with uneven pore size distribution. This intricate pore structure provides it with a larger specific surface area, which, to a certain extent, supports its hydrogen storage capacity.

[0057] Those skilled in the art will appreciate that the foregoing descriptions are merely specific embodiments of the present invention, and not exhaustive. It should be noted that numerous variations and modifications are possible for those skilled in the art, and all such variations and modifications that do not exceed the scope of the claims should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a porous carbon composite diatom skeleton hydrogen storage material, characterized in that: The steps include: S1. Dispersing diatomaceous earth in a 0.5M-4.0M H2SO4, HCl or HNO3 solution, keeping warm at 70-90°C for 3-6 hours, repeatedly washing and filtering until the pH is neutral, and then drying to obtain acid-treated diatomaceous earth; S2, acid-treated diatomaceous earth, clay, water-soluble polymer and deionized water are mixed in a mass ratio of (2-3): (3-4): (0.2-0.4): (4-8), stirred to obtain a mixture, placed the mixture in a mold for shaping, dried, and then subjected to high temperature treatment at 700-900° C. in an air atmosphere for 3-6 hours to obtain a shaped diatomaceous earth skeleton; S3, take the shaped diatomaceous earth skeleton and add it to furfuryl alcohol in an amount of 0.1-0.3g / mL, let it stand for 20-40 minutes, then add 7-8wt% hydrochloric acid solution, the volume of the hydrochloric acid solution is twice the volume of furfuryl alcohol, and stir rapidly for 15-25 seconds, take out the solid mixture, and keep it at 700-900°C for 3-6 hours in a protective atmosphere to obtain a porous carbon-supported composite diatom skeleton; S4. Add the porous carbon-loaded composite diatom skeleton to 8-10 mol / L potassium hydroxide or sodium hydroxide solution and soak it fully, then take it out, dry it, and then place it in a protective atmosphere at 700-900 ° C for 3-6 hours. After cooling to room temperature, wash it with water, and then add excess hydrochloric acid solution for neutralization. After soaking for 2-3 hours, take it out and wash it until it is neutral, and then vacuum dry it to obtain a porous carbon composite diatom skeleton hydrogen storage material.

2. The method for preparing the porous carbon composite diatom skeleton hydrogen storage material according to claim 1, characterized in that: In step S2, the mixture is placed in a mold to be shaped, and then dried at 70-90° C. for 3-6 hours.

3. The method for preparing the porous carbon composite diatom skeleton hydrogen storage material according to claim 1, characterized in that: The protective atmosphere is a nitrogen atmosphere or an inert gas atmosphere.

4. The method for preparing the porous carbon composite diatom skeleton hydrogen storage material according to claim 1, characterized in that: In step S4, the porous carbon-supported composite diatom skeleton is immersed in the potassium hydroxide solution at a temperature of 70-90° C. for 1-3 hours.

5. The method for preparing the porous carbon composite diatom skeleton hydrogen storage material according to claim 1, characterized in that: The drying temperature in step S4 is 70-90° C. and the drying time is 3-6 hours.

6. The method for preparing the porous carbon composite diatom skeleton hydrogen storage material according to claim 1, characterized in that: In steps S2, S3 and S4, the temperature is heated from room temperature to 700-900°C at a rate of 5-8°C / min.

7. The method for preparing the porous carbon composite diatom skeleton hydrogen storage material according to claim 1, characterized in that: The water-soluble polymer is one or a combination of two or more of polyacrylic acid, polyvinyl alcohol and polyethylene glycol.

8. A porous carbon composite diatom skeleton hydrogen storage material prepared by the method for preparing the porous carbon composite diatom skeleton hydrogen storage material according to any one of claims 1 to 7.

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