A preparation method of a boron-doped porous carbon loaded potassium monatomic solid-state hydrogen storage material

Abstract

A method for preparing a boron-doped porous carbon-supported potassium single-atom solid hydrogen storage material involves dissolving boric acid in a polyethylene glycol solution and stirring at room temperature until completely dissolved. Porous carbon is then added and stirred thoroughly. The mixture is allowed to stand at room temperature for soaking, followed by vacuum drying to obtain a boron-doped porous carbon precursor. This precursor is placed in a tube furnace and heated at 900°C for 3 hours under a nitrogen atmosphere, followed by natural cooling to obtain the boron-doped porous carbon material. Potassium chloride and the boron-doped porous carbon material are dispersed in deionized water to obtain a potassium chloride-boron-doped porous carbon precursor dispersion. This dispersion is centrifuged and then heat-treated in a vacuum oven to obtain the boron-doped porous carbon-supported potassium single-atom solid hydrogen storage material. The advantages are: the solid hydrogen storage material prepared by this invention exhibits excellent hydrogen adsorption and desorption performance, achieving a hydrogen adsorption capacity of 4.71 wt% at a hydrogen pressure of 70 Pa, significantly improving the hydrogen storage density.

Description

Technical Field

[0001] This invention relates to a method for preparing a boron-doped porous carbon-supported potassium single-atom solid hydrogen storage material, which is mainly used in solid hydrogen storage materials. Background Technology

[0002] In the field of solid-state hydrogen storage, existing research mainly focuses on developing hydrogen storage materials with high hydrogen storage capacity, excellent cycle stability, and suitability for large-scale production. However, these materials still face several technical challenges that need to be addressed in practical applications. First, the preparation process of most current solid-state hydrogen storage materials typically involves complex steps and high production costs, significantly limiting their application in industrial production. Furthermore, many existing materials are prone to performance degradation during long-term cycling, thus reducing their cycle life and reliability in practical applications. This performance degradation mainly stems from changes in the internal structure of the material during repeated hydrogen adsorption and desorption processes, leading to a gradual decrease in its hydrogen storage efficiency. Another significant technical challenge is that during the carbonization or activation stage, certain heteroatoms can catalyze unnecessary reactions, making the carbon framework unstable and causing the porous structure to partially or completely collapse. This collapse may be due to the introduction of strain or defects into the carbon lattice, resulting in a significant reduction in surface area.

[0003] CN117088332A discloses "a nitrogen-doped graphene-supported alkaline earth metal calcium single-atom non-pyrolytic chemisorption hydrogen storage material and its preparation method." The method involves thoroughly mixing melamine and graphene, heating to 900℃ in a tube furnace under nitrogen atmosphere, maintaining this temperature for 3 hours, and then naturally cooling under nitrogen atmosphere to obtain nitrogen-doped graphene. Calcium nitrate and nitrogen-doped graphene are added to deionized water and stirred evenly at room temperature to uniformly disperse the nitrogen-doped graphene in the mixed solution. After standing at room temperature, the supernatant is removed, the precipitate is retained, and freeze-dried at -20℃ in a vacuum freeze-drying oven to obtain nitrogen-doped graphene-supported single-atom calcium material. The advantages are: graphene, as a two-dimensional material, has a surface area primarily consisting of its exposed portion, facilitating direct loading of single-atom calcium metal. The prepared non-pyrolytic chemisorption hydrogen storage material exhibits surface-induced chemisorption, possessing a moderate adsorption strength between physical adsorption and chemical reaction, resulting in a relatively good hydrogen storage density. The disadvantage is that, although the graphene substrate has a theoretical specific surface area of ​​>2000m, 2 However, this two-dimensional material has a very large surface energy, and during the loading process of metal single atoms, it is easy to stack, which greatly reduces the theoretical specific surface area. This results in a severe reduction in the number of adsorption sites, making it impossible to fully utilize the advantage of the high specific surface area of ​​the adsorption-type hydrogen storage material, and the hydrogen storage density is not ideal.

[0004] Porous carbon materials, as a typical three-dimensional structural material, exhibit great potential in hydrogen storage and metal single-atom loading due to their extremely high specific surface area and abundant pore structure. However, compared with two-dimensional graphene, although porous carbon has a significant advantage in specific surface area, its practical application faces challenges. As a two-dimensional material, graphene's exposed external specific surface area allows metal single atoms to be directly loaded onto its surface, greatly simplifying the loading process and improving hydrogen storage performance. The high specific surface area of ​​porous carbon mainly stems from its complex pore structure. While the internal specific surface area formed within these pores theoretically increases the contact area with gas, it also increases the difficulty of loading. When metal single atoms are loaded into the porous carbon, they need to overcome the limitations imposed by the pore structure on mass transport. This can lead to low loading efficiency and uneven distribution. Furthermore, the loading process can easily cause pore blockage or excessive structural stress, resulting in the collapse of the porous structure and severely damaging the overall performance and stability of the material. Therefore, this severely limits the application of porous carbon in solid-state hydrogen storage materials. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a method for preparing a boron-doped porous carbon-supported potassium single-atom solid hydrogen storage material. This solid hydrogen storage material uses three-dimensional porous carbon as the substrate material, exhibiting a stable structure where the pores do not collapse due to heteroatom doping and loading. The method is simple, efficient, and low-cost, and can improve the material's hydrogen storage capacity, cycle stability, and exhibit high consistency in hydrogen adsorption and desorption.

[0006] The technical solution of this invention is:

[0007] A boron-doped porous carbon-supported potassium single-atom solid hydrogen storage material is characterized in that: the solid hydrogen storage material is a single-atom potassium supported on a boron-doped porous carbon material, and the boron content in the solid hydrogen storage material is 3.17 at and the potassium atom content is 0.1 at.

[0008] A method for preparing a boron-doped porous carbon-supported potassium single-atom solid hydrogen storage material, the specific steps of which are as follows:

[0009] S1: Preparation of boric acid-polyethylene glycol solution

[0010] Boric acid was dissolved in polyethylene glycol solution at a mass-to-volume ratio of 4:1 g / mL, and stirred at room temperature until completely dissolved to obtain a boric acid-polyethylene glycol solution.

[0011] S2: Impregnated porous carbon

[0012] Porous carbon was added to a boric acid-polyethylene glycol solution at a mass ratio of 1:8 to boric acid (H3BO3), ensuring that the porous carbon was completely submerged in the solution. After thorough stirring, the solution was allowed to stand and soak at room temperature for 6 hours to allow the boric acid to fully penetrate the porous carbon material. The solution was then vacuum dried to remove the solvent, polyethylene glycol, and the boron-doped porous carbon was obtained as a preliminary product.

[0013] S3: High-temperature carbonization preparation of boron-doped porous carbon materials

[0014] Boron-doped porous carbon precursor was placed in a tube furnace and heated at 900°C for 3 hours under N2 atmosphere protection, followed by natural cooling to obtain boron-doped porous carbon material.

[0015] S4: Preparation of potassium chloride-boron-doped porous carbon precursor dispersion

[0016] Potassium chloride (KCl) and boron-doped porous carbon material were mixed at a mass ratio of 7:10 and dispersed in deionized water. The mixture was stirred evenly at room temperature to obtain a potassium chloride-boron-doped porous carbon precursor dispersion, which was then centrifuged.

[0017] A potassium chloride-boron doped porous carbon black slurry was obtained;

[0018] S5: Preparation of solid-state hydrogen storage materials with boron-doped three-dimensional porous carbon-supported alkali metal single-atom potassium

[0019] A black slurry of potassium chloride-boron-doped porous carbon was placed in a vacuum oven and heat-treated at 300°C for 3 hours, and then cooled to room temperature to obtain a potassium single-atom solid hydrogen storage material supported by boron-doped porous carbon.

[0020] Furthermore, the volume ratio of polyethylene glycol to water in the polyethylene glycol solution is 1:50.

[0021] Furthermore, the total mass concentration of potassium chloride (KCl) and boron-doped porous carbon material in the potassium chloride-boron-doped porous carbon precursor dispersion is 1.7%.

[0022] Furthermore, in step S2, during vacuum drying, the drying temperature is 80℃ and the drying time is 24 hours.

[0023] Furthermore, before centrifugation, allow the sediment to stand for 3 hours to settle.

[0024] This invention uses boric acid as a precursor and porous carbon as the main material. Boron-doped porous carbon material is obtained through impregnation in a solubilizer and high-temperature carbonization. Then, an appropriate amount of potassium chloride dispersion is added, followed by stirring, centrifugation, and heat treatment to obtain a potassium single-atom solid hydrogen storage material supported on boron-doped porous carbon. Its beneficial effects are:

[0025] 1) By using polyethylene glycol as a solubilizer for impregnation, heteroatom boron is doped into porous carbon, ensuring uniform boron atom doping and preventing agglomeration and stacking in the pores. Polyethylene glycol is easy to remove and does not introduce excess impurities. Furthermore, the doping of boron atoms adjusts the interface configuration of porous carbon, breaks the symmetry of the electron density of active sites, increases the lattice spacing in porous carbon, and facilitates the diffusion and loading of larger single atoms in the pores.

[0026] 2) Using potassium single-atom loading, potassium single atoms have a large radius, which can adsorb more hydrogen molecules, giving porous carbon materials better hydrogen storage performance; at the same time, potassium loading on boron-doped porous carbon has very small electrostatic Coulomb forces interacting with the pore walls of boron-doped porous carbon, i.e., a lower diffusion energy barrier, which is beneficial to the preparation of this material.

[0027] 3) When boron is doped into porous carbon, drying is performed first to remove solvent solubilizers and avoid introducing redundant impurities. Simultaneously, it avoids excessive crystallization and structural damage during high-temperature pyrolysis, maintaining the high specific surface area and microporous structure of the porous carbon and improving the material's cyclic hydrogen absorption and desorption stability. By adjusting the amount of potassium chloride added, sufficient hydrogen absorption active sites are ensured while effectively preventing pore blockage, structural damage, and material performance degradation. The solid-state hydrogen storage material prepared by this invention has a high specific surface area of ​​2224 μm. 2 g -1 The high specific surface area provides a large number of active adsorption sites for hydrogen storage, effectively improving the hydrogen storage capacity and efficiency. At a liquid nitrogen temperature of 77K, the solid hydrogen storage material prepared in this invention exhibits excellent hydrogen adsorption and desorption performance. At a hydrogen pressure of 70 Pa, its hydrogen adsorption capacity reaches 4.71 wt%, and the hydrogen storage density is greatly improved. Attached Figure Description

[0028] Figure 1 These are scanning transmission electron microscope (STEM) images of the boron-doped porous carbon-supported potassium single-atom material of the present invention (corresponding to Example 1) at different resolutions (a. 100 nm; b. 50 nm; c. 10 nm);

[0029] Figure 2 This is the scanning transmission electron microscope (STEM) energy spectrum and elemental distribution diagram of the boron-doped porous carbon-supported potassium single-atom material of the present invention (corresponding to Example 1);

[0030] Figure 3 These are scanning electron microscope (SEM) images of the boron-doped porous carbon-supported potassium single-atom material of the present invention (corresponding to Example 1) at different resolutions (a. 20 μm; b. 1 μm);

[0031] Figure 4This is the energy dispersive X-ray spectrum (EDS) of the boron-doped porous carbon-supported potassium single-atom material of the present invention (corresponding to Example 1);

[0032] Figure 5 These are the high-resolution X-ray photoelectron spectrum (a) and the high-resolution X-ray sub-spectrum (b) of the boron-doped porous carbon-supported potassium single-atom material of the present invention (corresponding to Example 1);

[0033] Figure 6 This is the X-ray diffraction pattern of the boron-doped porous carbon-supported potassium single-atom material of the present invention (corresponding to Example 1);

[0034] Figure 7 This is the nitrogen adsorption-desorption isotherm curve of the boron-doped porous carbon-supported potassium single-atom material of the present invention (corresponding to Example 1);

[0035] Figure 8 This is a pore distribution diagram of the boron-doped porous carbon-supported potassium single-atom material of the present invention (corresponding to Example 1);

[0036] Figure 9 This is the hydrogen adsorption-desorption isotherm curve of the boron-doped porous carbon-supported potassium single-atom material of the present invention (corresponding to Example 1) at liquid nitrogen temperature. Detailed Implementation

[0037] The porous carbon powder used in Examples 1 and Comparative Examples 1-8 of this invention is from the same batch.

[0038] Example 1

[0039] S1: Preparation of polyethylene glycol solution

[0040] Mix 2 mL of polyethylene glycol (PEG) with 100 mL of deionized water and stir thoroughly to prepare a polyethylene glycol solution;

[0041] S2: Preparation of boric acid-polyethylene glycol solution

[0042] Dissolve 8g of boric acid (H3BO3) in the polyethylene glycol (PEG) solution from step S1, and stir at room temperature until completely dissolved to prepare a boric acid-polyethylene glycol solution.

[0043] S3: Impregnated porous carbon

[0044] Add 1g of porous carbon to the boric acid-polyethylene glycol solution in step S2. The porous carbon material is completely immersed in the boric acid-polyethylene glycol solution. Stir thoroughly and let it stand at room temperature for 6 hours to allow the boric acid to fully penetrate into the porous carbon material, thus obtaining a boric acid-polyethylene glycol-porous carbon material mixture.

[0045] S4: Initial product for preparing boron-doped porous carbon

[0046] The boric acid-polyethylene glycol-porous carbon material mixture was placed in a vacuum oven and vacuum dried at 80°C for 24 hours to obtain boron-doped porous carbon raw material.

[0047] S5: High-temperature carbonization preparation of boron-doped porous carbon materials

[0048] Boron-doped porous carbon precursor was loaded into a ceramic boat and heated to 900°C in a tube furnace under N2 atmosphere protection at a heating rate of 10°C / min. The temperature was maintained at this temperature for 3 hours. Then, the tube furnace was cooled to room temperature to obtain boron-doped porous carbon material.

[0049] S6: Preparation of potassium chloride-boron-doped porous carbon precursor dispersion

[0050] Weigh 1g of boron-doped porous carbon material and put it into a beaker. Add 0.7g of potassium chloride (KCl) and 100mL of deionized water. Stir well at room temperature to obtain a potassium chloride-boron-doped porous carbon precursor dispersion.

[0051] S7: Centrifugal treatment

[0052] The precursor dispersion of potassium chloride-boron doped porous carbon was allowed to stand for 3 hours to allow for sufficient reaction and precipitation. Then, it was separated by centrifugation at a speed of 10,000 r / min for 10 minutes. After centrifugation, the supernatant was removed and the lower precipitate was retained. The precipitate was then washed three times with deionized water to obtain a black slurry of potassium chloride-boron doped porous carbon.

[0053] S8: Preparation of solid-state hydrogen storage materials with boron-doped three-dimensional porous carbon-supported alkali metal single-atom potassium

[0054] A black slurry of potassium chloride-boron-doped porous carbon was placed in a vacuum oven and heat-treated at 300°C for 3 hours, and then cooled to room temperature to obtain a potassium single-atom solid hydrogen storage material supported by boron-doped porous carbon.

[0055] In the structural characterization of the boron-doped porous carbon-supported potassium single-atom solid hydrogen storage material prepared in Example 1, the scanning electron microscope images at different magnifications are as follows: Figure 1 As shown, by Figure 1 (a) Figure 1 (b) Figure 1 As can be observed in (c), a large number of fine porous structures exist, indicating that doping with boron and loading with potassium atoms do not significantly change the basic morphology and size distribution of carbon. The turbine-like layered nanostructure in 1(c) further reveals that the material synthesized by this method can provide abundant sites for hydrogen intercalation into the carbon layers, which is beneficial to improving the hydrogen storage capacity of the carbon material; the scanning transmission electron microscopy (STEM) energy dispersive spectroscopy and its elemental distribution map are shown below. Figure 2 As shown, the presence and uniform distribution of C, B, and K elements are clearly demonstrated, proving that this preparation method has successfully introduced potassium single atoms onto the surface of boron-doped porous carbon materials; Figure 3 Scanning electron microscopy (SEM) images at different resolutions (a. 20 μm; b. 1 μm) reveal a bulk granular structure. Areas with high contrast represent the porous structure of carbon, while areas with low contrast represent the porous carbon walls. Furthermore, some pores are filled with boron and potassium atoms, resulting in a smooth surface in these regions. This smoothness is likely due to pore shrinkage or coverage caused by atomic filling. Simultaneously, undoped single atoms are observed on the carbon walls. These isolated atoms fail to embed uniformly within the carbon matrix, forming high-contrast isolated points in the STEM images. Figure 4 In the energy-dispersive X-ray spectroscopy (EDS) image, it can be observed that boron and potassium single atoms are uniformly dispersed on the surface and pores of the porous carbon material. The distribution positions of boron and potassium in the EDS are identical to those of the porous carbon in the EDS, indicating successful doping of boron single atoms and successful loading of potassium single atoms into the porous carbon. The high-resolution X-ray photoelectron spectrum of boron-doped three-dimensional porous carbon loaded with alkali metal single-atom potassium can also be observed. Figure 5 In (a), it is shown that boron and potassium single atoms were successfully introduced into porous carbon, with a relative content of (B: 3.17 at%); K: 0.1 at%). The main reason why the potassium single atom peak was not clearly observed is that the potassium atom loading concentration was relatively low, which inhibited the migration and aggregation of potassium atoms in the material and prevented crystal formation, thus preventing the observation of a significant characteristic peak for potassium single atoms. High-resolution X-ray photoelectron spectroscopy of boron single atoms... Figure 5 As can be seen in (b), two boron-containing compounds, BCO2 and BC3, were mainly formed in the material (excluding the precursor H3BO3 residue); in the X-ray diffraction pattern... Figure 6 Two flat and broad peaks can be observed, indicating that the boron-doped three-dimensional porous carbon-supported alkali metal single-atom potassium is a low-crystallinity material; nitrogen adsorption-desorption capacity is shown in the figure. Figure 7 As shown, by Figure 7 It can be seen that this material has a large specific surface area, reaching 2224 m². 2 g -1 The specific surface area of ​​porous carbon decreased, indicating that the doped and loaded single atoms filled part of the pores in the porous carbon, which is consistent with the STEM image results; the pore distribution diagram of the hydrogen storage material obtained in Example 1 is shown below. Figure 8 As shown, the pores in the 2-20 nanometer range account for a relatively high proportion, indicating that the material is mainly composed of mesoporous structures, with a small portion of macroporous structures.

[0056] In the hydrogen storage performance test of the boron-doped three-dimensional porous carbon-supported alkali metal single-atom potassium material obtained in Example 1, the hydrogen adsorption-desorption isotherm curve at liquid nitrogen temperature is as follows: Figure 9 As shown, when the hydrogen pressure is 70 Pa, the hydrogen adsorption and desorption capacity reaches 4.71 wt%. Furthermore, the adsorption and desorption curves essentially overlap, further demonstrating the excellent hydrogen desorption and desorption capabilities of the boron-doped three-dimensional porous carbon-supported alkali metal single-atom potassium material prepared in this invention.

[0057] Comparative Example 1: Porous carbon-supported alkali metal potassium single-atom solid hydrogen storage material

[0058] S1: Dry porous carbon material

[0059] 2g of porous carbon was placed in a beaker and heat-treated at 200℃ for 3 hours to remove excess moisture, resulting in dried porous carbon material.

[0060] S2: Preparation of a dispersion of potassium chloride and porous carbon

[0061] Weigh 1g of dried porous carbon material and put it into a beaker, pour in 0.7g of potassium chloride (KCl), add 100mL of deionized water, and stir evenly at room temperature to obtain potassium chloride-porous carbon dispersion.

[0062] S3: Centrifugation

[0063] The potassium chloride-porous carbon dispersion was allowed to stand for 3 hours to allow for sufficient reaction and precipitation. Then, it was centrifuged to separate the potassium chloride and porous carbon. The centrifugation speed was set to 10,000 r / min and the centrifugation time was 10 minutes. After centrifugation, the supernatant was removed and the lower precipitate was retained to obtain a black slurry of potassium chloride and porous carbon.

[0064] S4: Preparation of porous carbon-supported potassium single-atom solid hydrogen storage materials

[0065] A black slurry containing potassium chloride and porous carbon was placed in a vacuum oven and heat-treated at 300°C for 10 hours, then cooled to room temperature to obtain a potassium single-atom solid hydrogen storage material supported on porous carbon.

[0066] In the hydrogen storage performance test of the potassium single-atom solid hydrogen storage material supported on porous carbon in Comparative Example 1, hydrogen adsorption-desorption was carried out at liquid nitrogen temperature. When the hydrogen pressure was 70 Pa, the hydrogen adsorption-desorption amount was less than 3 wt%, indicating poor hydrogen storage performance. The reason for this result is speculated to be that the absence of boron doping promotes the formation of more porous structures on the porous carbon, resulting in a lower loading of potassium single atoms on the porous carbon support.

[0067] Comparative Example 2: Different Boron Precursor Solutions

[0068] Boric acid (H3BO3) was replaced with boron oxide (B2O3), and all other conditions were the same as in Example 1, without any other changes. A boron-doped three-dimensional porous carbon-supported alkali metal potassium single-atom solid hydrogen storage material was thus prepared.

[0069] In the hydrogen storage performance test of the boron-doped three-dimensional porous carbon-supported alkali metal potassium single-atom solid hydrogen storage material obtained in Comparative Example 2, hydrogen adsorption-desorption was performed at liquid nitrogen temperature. When the hydrogen pressure was 70 Pa, the hydrogen adsorption-desorption amount was 4.13 wt%. It can be inferred that boric acid molecules, due to their smaller size, more easily penetrate into the pores of the porous carbon material, thus achieving a uniform doping distribution. In contrast, boron oxide particles, due to their larger size, have difficulty penetrating into the fine pores of the porous carbon material, and therefore tend to aggregate in larger pores, leading to inhomogeneity in the doping process.

[0070] Comparative Example 3: Different Solubilizers

[0071] S1: Preparation of acetone solution

[0072] Mix 8 mL of acetone (C3H6O) with 100 mL of deionized water and stir thoroughly to prepare an acetone solution.

[0073] S2: Preparation of boric acid-acetone solution

[0074] Dissolve 8g of boric acid (H3BO3) in the acetone solution from step S1 and stir at room temperature until completely dissolved to prepare a boric acid-acetone solution.

[0075] S3: Impregnated porous carbon

[0076] Add 1g of porous carbon to the boric acid-acetone solution in step S2. The porous carbon material is completely immersed in the boric acid-acetone solution. Stir thoroughly and let it stand at room temperature for 6 hours to allow the boric acid to fully penetrate into the porous carbon material, thus obtaining a boric acid-acetone-porous carbon material mixture.

[0077] S4-S8: The subsequent steps are the same as in Example 1, without any other changes.

[0078] In the hydrogen storage performance test of the boron-doped three-dimensional porous carbon-supported alkali metal potassium single-atom solid hydrogen storage material obtained in Comparative Example 3, hydrogen adsorption-desorption was performed at liquid nitrogen temperature. When the hydrogen pressure was 70 Pa, the hydrogen adsorption-desorption amount was 3.87 wt%. This result demonstrates the unique effect of the solubilizer—polyethylene glycol—selected in Example 1 of this application in promoting the loading of potassium single atoms into the porous carbon structure.

[0079] Comparative Example 4: Different Boron Doping Processes

[0080] S1: Preparation of boric acid solution

[0081] Dissolve 8g of boric acid (H3BO3) in 100mL of deionized water and stir until completely dissolved to obtain a boric acid solution.

[0082] S2: Mixed porous carbon and boric acid solution

[0083] Add 1g of porous carbon to the boric acid solution prepared above, and stir thoroughly at room temperature to ensure that the boric acid and porous carbon are in full contact.

[0084] S3: Vacuum drying

[0085] The mixed porous carbon and boric acid solution were placed in a vacuum oven and dried under vacuum at 80°C for 24 hours to remove moisture and excess boric acid, thus obtaining boron-doped porous carbon primary product.

[0086] S4: High-temperature carbonization preparation of boron-doped porous carbon materials

[0087] Boron-doped porous carbon precursor was loaded into a ceramic boat and heated to 900°C in a tube furnace under N2 atmosphere protection at a heating rate of 10°C / min. The temperature was maintained at this temperature for 3 hours. Then, the tube furnace was cooled to room temperature to obtain boron-doped porous carbon material.

[0088] S5: Preparation of potassium chloride-boron-doped porous carbon precursor dispersion

[0089] Weigh 1g of boron-doped porous carbon material and put it into a beaker. Add 1g of potassium chloride (KCl) and 100mL of deionized water. Stir well at room temperature to obtain a potassium chloride-boron-doped porous carbon precursor dispersion.

[0090] S6: Centrifugation

[0091] The precursor dispersion of potassium chloride-boron doped porous carbon was allowed to stand for 3 hours to allow for sufficient reaction and precipitation. Then, it was separated by centrifugation at a speed of 10,000 r / min for 10 minutes. After centrifugation, the supernatant was removed and the lower precipitate was retained. The precipitate was then washed three times with deionized water to obtain a black slurry of potassium chloride-boron doped porous carbon.

[0092] S7: Preparation of solid-state hydrogen storage materials with boron-doped three-dimensional porous carbon-supported alkali metal single-atom potassium

[0093] A black slurry of potassium chloride-boron-doped porous carbon was placed in a vacuum oven and heat-treated at 300°C for 3 hours, and then cooled to room temperature to obtain a potassium single-atom solid hydrogen storage material supported by boron-doped porous carbon.

[0094] In the hydrogen storage performance test of the boron-doped three-dimensional porous carbon-supported alkali metal potassium single-atom solid hydrogen storage material obtained in Comparative Example 4, hydrogen adsorption-desorption was performed at liquid nitrogen temperature. At a hydrogen pressure of 70 Pa, the hydrogen adsorption-desorption amount was 3.71 wt%, which is less than that of the material obtained by boron doping via an impregnation process. This result demonstrates the importance of the solubilizer impregnation step. Doping, through the diffusion effect of the solubilizer, can more effectively and uniformly distribute the dopant into the pore structure of the porous carbon material. This uniform distribution helps improve the uniformity of the dopant in the material, thereby optimizing the overall performance of the material.

[0095] Comparative Examples 5-8: Different Amounts of Potassium Chloride Added

[0096] Comparative Example 5

[0097] The amount of potassium chloride added was 0.1g, and the rest was the same as in Example 1.

[0098] Comparative Example 6

[0099] The amount of potassium chloride added was 0.3g, and the rest was the same as in Example 1.

[0100] Comparative Example 7

[0101] The amount of potassium chloride added was 0.5g, and the rest was the same as in Example 1.

[0102] Comparative Example 8

[0103] The amount of potassium chloride added was 1g, and the rest was the same as in Example 1.

[0104] Four groups with different amounts of potassium chloride were set up, and the other preparation conditions were the same as in Example 1. The parameters of the preparation method of boron-doped three-dimensional porous carbon-supported alkali metal single-atom potassium in comparative examples 5-8 are shown in Table 1 below:

[0105] Table 1 shows the parameters for the preparation methods of boron-doped three-dimensional porous carbon-supported alkali metal single-atom potassium in comparative examples 5–8.

[0106]

[0107] The samples prepared in Comparative Examples 5–8 were subjected to nitrogen adsorption-desorption tests under isothermal conditions and hydrogen storage performance tests at liquid nitrogen (77K) temperature and 70 Pa hydrogen pressure. The specific surface area and hydrogen adsorption / desorption capacity at 77K temperature and 70 Pa hydrogen pressure obtained from the tests of Comparative Examples 5–8 are shown in Table 2 below:

[0108] Table 2 shows the detection data of boron-doped three-dimensional porous carbon-supported alkali metal single-atom potassium in comparative examples 5–8.

[0109]

[0110] I. Performance Analysis of Example 1 of the Present Invention and Comparative Examples 1 to 8 of its Parallel Tests

[0111] The fact that the performance of the solid hydrogen storage material with only potassium units in Comparative Example 1 was inferior to that of the material obtained in Example 1 indicates that boron doping is essential and crucial for improving the hydrogen storage performance of porous carbon materials. Comparative Examples 2 and 3 demonstrate the uniqueness of the selection of boron doping solution and solubilizer. Comparative Example 4 shows that the impregnation process is an essential step in promoting uniform boron doping into the porous carbon material. The performance test data shown in Table 2, compared with the test results in Example 1, show that small or excessive amounts of potassium chloride do not promote the specific surface area or hydrogen adsorption / desorption capacity of the material. Specifically, the specific surface area data in Table 2 indicates that adding too little or too much potassium chloride slightly reduces the specific surface area of ​​the material, suggesting that the 0.7g potassium chloride dosage in Example 1 is most suitable for forming an ideal pore distribution and achieving a high degree of potassium doping, thereby enhancing hydrogen storage performance. This further demonstrates that the effect of potassium chloride on the porosity and specific surface area of ​​the material is not linear; the potassium chloride dosage in Example 1 of this invention enhances these properties without causing negative effects. Excessive potassium chloride can lead to undissolved or unevenly distributed residual potassium chloride during carbonization, resulting in its accumulation in the pores and reducing the effective surface area available for adsorption and storage, thus affecting the material's hydrogen storage performance. Conversely, insufficient potassium chloride dosage cannot provide enough potassium to create the same porosity or potassium content, resulting in poor hydrogen storage performance of the material.

[0112] II. Effect Analysis of the Boron-Doped Porous Carbon-Supported Potassium Single-Atom Solid Hydrogen Storage Material in Example 1 of the Invention

[0113] The structural characterization and performance testing of the boron-doped three-dimensional porous carbon material supported on alkali metal single-atom potassium prepared in Example 1 yielded several important conclusions. SEM and STEM image analysis revealed a large number of fine pore structures on the material surface, indicating that boron doping and potassium single-atom loading did not significantly alter the basic morphology of the porous carbon material. Particularly with the manifestation of the turbine-like layered nanostructure, this material can provide abundant active sites for hydrogen adsorption, significantly enhancing its hydrogen storage capacity. STEM energy dispersive spectroscopy and its elemental distribution map further confirmed the uniform distribution of C, B, and K elements in the material, indicating that the method successfully introduced potassium single atoms onto the surface of boron-doped porous carbon. Meanwhile, EDS and XPS results showed that boron mainly exists in the form of BCO2 and BC3 compounds, and the low crystallinity single-atom doping / loading characteristics of the material were confirmed by XRD. In nitrogen adsorption-desorption tests, the material exhibited a high molecular weight distribution (MWHM) of up to 2224 μm. 2The specific surface area per g, although lower than that of pure porous carbon, indicates that the doped and potassium single-atom-loaded portion fills the pores of the porous carbon. The pore size distribution diagram shows that the material is predominantly mesoporous, with a high proportion of pores in the 2-20 nm range. This pore structure contributes to enhanced hydrogen adsorption performance. Hydrogen storage performance tests show that at liquid nitrogen temperature and a hydrogen pressure of 70 Pa, the material's hydrogen adsorption / desorption capacity reaches 4.71 wt%. Furthermore, the adsorption and desorption curves largely overlap, further demonstrating the material's excellent hydrogen storage and release capabilities. These results indicate that the boron-doped three-dimensional porous carbon-supported potassium single-atom solid-state hydrogen storage material of this invention not only has a rational structural design but also exhibits significant advantages in hydrogen storage performance, providing possibilities for future large-scale hydrogen storage applications.

Claims

1. A method for preparing a boron-doped porous carbon-supported potassium single-atom solid hydrogen storage material, characterized in that: The specific steps are as follows: S1: Preparation of boric acid-polyethylene glycol solution Boric acid was dissolved in polyethylene glycol solution at a mass-to-volume ratio of 4:1 g / mL, and stirred at room temperature until completely dissolved to obtain a boric acid-polyethylene glycol solution. S2: Impregnated porous carbon Porous carbon was added to a boric acid-polyethylene glycol solution at a mass ratio of 1:

8. After thorough stirring, the solution was allowed to stand and soak at room temperature for 6 hours to allow the boric acid to fully penetrate the porous carbon material. The solution was then vacuum dried to obtain boron-doped porous carbon precursor. S3: High-temperature carbonization preparation of boron-doped porous carbon materials Boron-doped porous carbon precursor was placed in a tube furnace and heated at 900°C for 3 hours under N2 atmosphere protection, followed by natural cooling to obtain boron-doped porous carbon material. S4: Preparation of potassium chloride-boron-doped porous carbon precursor dispersion Potassium chloride (KCl) and boron-doped porous carbon material were mixed at a mass ratio of 7:10 and dispersed in deionized water. The mixture was stirred evenly at room temperature to obtain a potassium chloride-boron-doped porous carbon precursor dispersion, which was then centrifuged. A potassium chloride-boron doped porous carbon black slurry was obtained; S5: Preparation of solid-state hydrogen storage materials with boron-doped three-dimensional porous carbon-supported alkali metal single-atom potassium A black slurry of potassium chloride-boron-doped porous carbon was placed in a vacuum oven and heat-treated at 300°C for 3 hours, and then cooled to room temperature to obtain a potassium single-atom solid hydrogen storage material supported by boron-doped porous carbon.

2. The method of claim 1, wherein the method is characterized by: The volume ratio of polyethylene glycol to water in the polyethylene glycol solution is 1:

50.

3. The method for preparing boron-doped porous carbon-supported potassium single-atom solid hydrogen storage material according to claim 1, characterized in that: The total mass concentration of potassium chloride (KCl) and boron-doped porous carbon material in the potassium chloride-boron-doped porous carbon precursor dispersion is 1.7%.

4. The method for preparing boron-doped porous carbon-supported potassium single-atom solid hydrogen storage material according to claim 1, characterized in that: In step S2, during vacuum drying, the drying temperature is 80℃ and the drying time is 24 hours.

5. The method for preparing boron-doped porous carbon-supported potassium single-atom solid hydrogen storage material according to claim 1, characterized in that: Before centrifugation, allow the sediment to settle for 3 hours.

6. A boron-doped porous carbon-supported potassium single-atom solid hydrogen storage material prepared by the preparation method as described in claim 1, characterized in that: The solid hydrogen storage material is a boron-doped porous carbon material supported on a single-atom potassium. The boron content in the solid hydrogen storage material is 3.17 at and the potassium content is 0.1 at.

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