Carbon-based fuel micro-nano structure gradient heat sequence construction reinforced hydrogen storage method

Abstract

A method for enhancing hydrogen storage through the hierarchical thermal sequence construction of carbon-based fuel micro / nano structures belongs to the field of carbon-based hydrogen storage material preparation technology. The purpose of this invention is to address the difficulty in achieving precise control over the pore structure and oxygen-containing functional groups of carbon-based materials using existing technologies, thus hindering the realization of their hydrogen storage potential at low and room temperatures. This method utilizes potassium-containing compounds to activate and prepare a carbon substrate with a specific physicochemical structure. Then, it employs low-temperature H2O to enhance the generation of micro / nano channels. Finally, it uses low-temperature air oxidation to construct a hierarchical thermal sequence micro / nano structure with oxygen-containing functional groups. On the one hand, the synergistic effect of oxygen-containing groups and micro / nano pores significantly improves the hydrogen adsorption capacity of carbon-based fuels. On the other hand, the use of H2O and air post-treatment greatly reduces the amount of chemical activation reagents required, making the overall technology more environmentally friendly and cleaner. Simultaneously, it achieves quantitative control over the micro-meso-hierarchical pore structure and ultra-micropore sequence / oxygen content, efficiently utilizing carbon-based fuels and providing a new approach for the preparation of hydrogen storage materials.

Description

Technical Field

[0001] This invention belongs to the field of carbon-based hydrogen storage material preparation technology, and specifically relates to a biomass / coal-based carbon material preparation technology with excellent hydrogen adsorption performance. Background Technology

[0002] Carbon-based materials possess advantages such as large specific surface area, high chemical stability, and fast hydrogen adsorption / desorption kinetics, making them a key research focus in solid-state hydrogen storage technology. For hydrogen storage at liquid nitrogen temperatures, specific surface area is the primary influencing factor, while at room temperature, the role of oxygen-containing functional groups cannot be ignored. Current single activation techniques struggle to achieve precise control over the pore structure and oxygen-containing functional groups of carbon-based materials, hindering the full realization of their hydrogen storage potential at both low and room temperatures.

[0003] Chinese invention patent CN119735164 A discloses a method for preparing hydrogen storage carbon material based on bamboo, which uses liquid-phase microwave pretreatment technology to achieve a hydrogen storage capacity of 3.01 wt% at atmospheric pressure and 77K. However, this method is highly dependent on the microwave pretreatment step with specific power and time, has a narrow process window, and requires high precision in equipment control, raising questions about the stability and repeatability of large-scale industrial production.

[0004] Chinese invention patent CN120191889 B discloses a porous carbon-supported fluorine-based functional group hydrogen storage material. This material introduces strong CMF / CNF hydrogen absorption sites on the porous carbon surface through high-temperature calcination of hexafluorosilicate, achieving a hydrogen storage capacity as high as 9.7 wt% (77K / 50bar). Its functional group design concept is novel. However, the hexafluorosilicate raw material used in this method may decompose at high temperatures to produce toxic silicon tetrafluoride gas, posing a serious challenge to the safety and environmental protection of production equipment. The process does not mention the optimization effect on the pore structure of biochar, nor does it describe the hydrogen storage capacity at room temperature.

[0005] Chinese invention patent CN119263209 A discloses a method for preparing ZIF-8@pine wood chips composite carbon-based hydrogen storage material. This method constructs a three-dimensional interconnected hierarchical porous structure by in-situ growing metal-organic frameworks (MOFs) on a biomass carbon support, achieving a hydrogen storage capacity of up to 5.76 wt% at 77 K / 60 bar, demonstrating excellent performance. However, this method relies on ZIF-8 crystal growth, requires the use of organic solvents such as methanol and a long reaction time, and the key reagent used, 2-methylimidazole, is a Group 2B carcinogen. The experimental operation carries significant risks, the overall process is complex, and there are environmental pollution risks.

[0006] In summary, existing carbon-based hydrogen storage materials still suffer from insufficient optimization of pore structure. No suitable technology has yet been developed to achieve a proper match between pore structure and functional groups, thereby maximizing the hydrogen storage performance of carbon-based materials. Furthermore, some carbon-based hydrogen storage material activation technologies are highly polluting and require sophisticated techniques. Summary of the Invention

[0007] The purpose of this invention is to address the difficulty in achieving precise control over the pore structure and oxygen-containing functional groups of carbon-based materials in existing technologies, thus hindering the realization of their hydrogen storage potential at low and room temperatures. This invention provides a method for enhancing hydrogen storage through the hierarchical thermal sequence construction of micro / nano structures for carbon-based fuels. This method utilizes potassium-containing compounds to activate and prepare a carbon substrate with a specific physicochemical structure. Then, it employs low-temperature H2O to enhance the generation of micro / nano channels. Finally, it uses low-temperature air oxidation to construct the hierarchical thermal sequence of the micro / nano structure loaded with oxygen-containing functional groups. On one hand, the synergistic effect of oxygen-containing functional groups and micro / nano pores significantly improves the hydrogen adsorption capacity of carbon-based fuels. On the other hand, the use of H2O and air post-treatment greatly reduces the amount of chemical activation reagents required, making the overall technology more environmentally friendly and cleaner. Simultaneously, it achieves quantitative control over the micro-to-meta-hierarchical pore structure and ultra-micropore sequence / oxygen content, efficiently utilizing carbon-based fuels and providing a new approach for the preparation of hydrogen storage materials.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for enhancing hydrogen storage through the cascaded thermal sequence construction of carbon-based fuel micro / nano structures, the method comprising:

[0010] Step 1: After being crushed and dried, the carbon-based fuel is placed in a fixed bed and pyrolyzed in an inert gas atmosphere. After pyrolysis, the carbon-based fuel is quickly pushed out of the reaction zone for cooling. The raw material is crushed to a size of 53-125 micrometers.

[0011] Step 2: Acid wash the carbon-based fuel from Step 1 with an acidic reagent, then filter and dry it for later use.

[0012] Step 3: Mix the carbon-based fuel from Step 2 with the potassium-containing compound and grind it carefully in a mortar at room temperature until it is uniformly mixed; collect the sample obtained after mixing into a nickel crucible, place it in a fixed bed, and activate it under an inert gas atmosphere. After activation, the sample is cooled to room temperature according to the reaction temperature program.

[0013] Step 4: Remove the nickel crucible from the fixed bed after the reaction in Step 3 has ended and cooled. Take out the carbon-containing precursor from the nickel crucible, wash it with an acidic reagent, filter it, and dry it for later use.

[0014] Step 5: Collect the sample obtained in Step 4 into a quartz reactor, place it in a fixed bed and heat it to the target temperature, introduce water vapor, stop the supply of water vapor after the reaction is completed, and cool it down with inert gas according to the reaction temperature program.

[0015] Step Six: After the sample from Step Five has cooled to a certain temperature, introduce air into the reactor for low-temperature oxidation. After the oxidation is complete, switch to an inert gas and allow the temperature to drop to room temperature as programmed. Then, collect the sample.

[0016] Furthermore, the method specifically includes:

[0017] Step 1: The dried carbon-based fuel is pyrolyzed in a constant temperature tube furnace at a temperature of 400~600 ℃, with a nitrogen or argon atmosphere and a heating rate of 5~10 ℃ / min. When the temperature reaches 400~600 ℃, it is held for 30~60 min. The reacted sample is then quickly pushed into the cooling jacket on the right. The sample is taken out after cooling to room temperature.

[0018] Step 2: Mix the carbon material prepared in Step 1 with the acidic solution at a mass ratio of 40:1, stir in a magnetic stirrer at room temperature in an air atmosphere for 24 h, filter the mixture and wash it repeatedly with deionized water until the pH value of the washing solution is constant and neutral, and dry the sample in a constant temperature drying oven for 24 h to obtain carbon-based acid washing raw material.

[0019] Step 3: Replace the quartz tube of the tube furnace with a corundum tube. After mixing the carbon-based pickling raw material from Step 2 with the potassium-containing compound, grind it thoroughly in a crucible. Place the mixture in a nickel crucible and heat it at a rate of 5~10 ℃ / min. When the temperature reaches 700~900 ℃, hold it for 30 min, and then cool it to room temperature at a rate of 5 ℃ / min before removing it.

[0020] Step 4: Mix the sample collected in Step 3 with the acidic solution at a mass ratio of 40:1, stir at room temperature for 4 hours in an air atmosphere using a magnetic stirrer, filter the mixture and wash it repeatedly with deionized water until the pH of the washing solution is constant and neutral, and dry the sample in a constant temperature drying oven for 24 hours to obtain the carbon-based acid-washed raw material.

[0021] Step 5: Load the sample from Step 4 into a quartz reactor and place it in the center of a tube furnace. The heating rate is 5-10℃ / min. When the temperature reaches 700-800℃, introduce the vaporized water vapor. The water vapor volume concentration ratio is 10vol%-50vol% (the rest is inert gas). Maintain the reaction for 30-90 min, then stop the water vapor supply and cool down at 5℃ / min.

[0022] Step Six: After the sample from Step Five has cooled to 200~400℃, introduce air for low-temperature oxidation for 10~60min. After that, switch to inert gas and then cool to room temperature at a cooling rate of 5℃ / min. Remove the sample.

[0023] It is worth noting that those skilled in the art can make reasonable adjustments to parameters such as temperature and time based on actual equipment or environmental differences, and can make reasonable selections of raw materials based on their own existing materials. As long as the modified carbon-based fuel prepared based on the scheme proposed in this invention has an increased adsorption capacity for hydrogen, it falls within the equivalent implementation scope of this invention.

[0024] Furthermore, in step one, the carbon-based fuel is one or more of straw, rice husks, sawdust, and bituminous coal.

[0025] Furthermore, in step two, the acidic solution is a low-concentration acidic solution of less than or equal to 0.2 mol / L, such as dilute sulfuric acid or dilute hydrochloric acid, which can remove metals such as K and Ca from biomass but does not damage the biomass.

[0026] Furthermore, in step three, the potassium-containing compound is one or more of potassium hydroxide, potassium carbonate, and potassium bicarbonate; the mass ratio of the carbon-based pickling raw material to the potassium-containing compound is 1:1~4.

[0027] Furthermore, in step four, the acidic solution is a low-concentration acidic solution of less than or equal to 0.2 mol / L, such as dilute sulfuric acid or dilute hydrochloric acid, which can remove metals such as K and Ca from biomass but does not damage the biomass.

[0028] Furthermore, in step five, water vapor is generated by injecting ultrapure water into a 180°C water vapor generator via an injection pump.

[0029] Furthermore, in step six, the reaction atmosphere is air.

[0030] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0031] Carbon-based fuels have complex compositions and structures, and existing single activation techniques are insufficient to effectively enhance the construction of specific pores and quantitatively control oxygen-containing groups, resulting in limited hydrogen molecule adsorption. The technical solution of this invention uses a combination of potassium-containing compound activation, H2O etching, and low-temperature air oxidation to load oxygen-containing groups. This achieves quantitative control of the micro-meta-hierarchical pore structure and ultramicro-pore order / oxygen content, further enhancing the specific surface area, reducing the amount of activation reagent used, and improving the hydrogen storage performance of carbon-based materials. Specifically, it includes the following advantages:

[0032] (1) This invention employs a method of first activating with potassium-containing compounds, then etching carbon-based fuels with H2O, and finally oxidizing with air at low temperature to load oxygen-containing groups. This achieves a synergistic hydrogen storage effect between oxygen-containing groups and micro / nanopores of different scales. Specifically, a carbon substrate with a certain specific surface area and distinct mesoporous-microporous layers is first prepared using potassium-containing compounds. Then, H2O etching is used to enhance the formation of micropores and ultramicropores. Finally, oxygen-containing groups are loaded with air at low temperature. The first two activation methods work synergistically to create a large number of ultramicropores and micropores. The third modification method loads oxygen-containing groups onto the material, enhancing the material's adsorption energy for hydrogen. Ultimately, these three methods achieve a synergistic hydrogen storage effect between oxygen-containing groups and micro / nanopores, enhancing the adsorption of hydrogen.

[0033] (2) The present invention utilizes water vapor and air to activate and enhance the adsorption of carbon-based fuel gases, which can greatly reduce the amount of chemical activation reagents used.

[0034] (3) The cascaded thermal sequencing technology showed universality in enhancing the low-temperature hydrogen storage performance of different types of biomass and bituminous coal. The low-temperature hydrogen storage capacity at 5 MPa of rice husk, sawdust, straw and bituminous coal reached 6.41 wt.%, 6.28 wt.%, 5.72 wt.% and 4.68 wt.%, respectively, which were 11.02%, 16.50%, 30.87% and 8.84% higher than that of pure KOH activated samples.

[0035] (4) The cascaded thermal sequencing technology showed universality in enhancing the room temperature hydrogen storage performance of different types of biomass and bituminous coal. The room temperature hydrogen storage capacity of rice husk, sawdust, straw and bituminous coal at 5 MPa was 0.53 wt.%, 0.50 wt.%, 0.51 wt.% and 0.36 wt.%, respectively, which were 33.40%, 108.78%, 38.43% and 28.57% higher than that of pure KOH activated samples.

[0036] (5) This technology optimizes the hydrogen storage performance of different carbon materials in the low-pressure section (≤5 MPa) by using a low activator dosage of potassium compound / biochar 2:1 (saving 50% compared to the traditional 4:1 process), providing theoretical support and technical path for subsequent large-scale application. Attached Figure Description

[0037] Figure 1 The oxygen content distribution diagram of the carbon-based hydrogen storage material prepared according to an embodiment of the preparation method of the present invention. Detailed Implementation

[0038] The specific embodiments of the present invention will be described in more detail below with reference to examples, so as to fully and clearly convey the implementation of the present invention to those skilled in the art. The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention should be covered within the protection scope of the present invention.

[0039] Carbon-based hydrogen storage materials rely on specific pore sizes and oxygen-containing functional groups to enhance their hydrogen storage capacity. However, in existing preparation technologies, the oxygen-containing functional groups exhibit a dynamic "generation-consumption" process during the activation of carbon-based hydrogen storage materials. To address this, this invention proposes a stepwise thermal activation approach and develops a technology for modifying carbon-based fuels by coupling low-temperature gasification etching with potassium compounds and H2O with low-temperature air oxidation. This enables the orderly control of the pore size and oxygen content of carbon-based fuels, overcoming the problem in existing carbon-based adsorbent preparation technologies that struggle to guarantee a large specific surface area and precise construction of ultramicropores while simultaneously possessing a high oxygen content. This effectively improves the hydrogen storage capacity of carbon-based materials.

[0040] This invention relates to a technique for low-temperature vaporization etching coupled with low-temperature air oxidation modification using potassium-containing compounds and H2O. By utilizing potassium-containing compound activation and H2O etching, it prepares carbon-based materials with high specific surface area and enhances the formation of ultra-micropores. Simultaneously, the introduction of low-temperature air oxidation effectively controls the oxygen content of the carbon-based materials. Compared to existing technologies, this method has the following breakthrough potential: it allows for precise control of the thermal reaction process of H2O and air at different temperatures, enabling precise regulation of the pore structure and oxygen-containing groups in the carbon-based materials. The overall process is green and stable, facilitating large-scale applications. It provides new material support for the high-value utilization of carbon-based fuels such as agricultural and forestry waste and coal, as well as for enhanced hydrogen storage.

[0041] Combination Figure 1 Tables 1 and 2 show that the carbon-based hydrogen storage material prepared by this technical solution has increased specific surface area, fully developed micropores, and better controlled oxygen content compared with the material obtained by simply activating potassium-containing compounds. Ultimately, the hydrogen storage capacity at low temperature and room temperature under different pressures is significantly increased.

[0042] Comparative Example 1:

[0043] This comparative example is based on corn stalks. The preparation process of CS-KBC using only potassium salt is as follows:

[0044] (1) The dried corn stalk raw material was pyrolyzed in a constant temperature tube furnace at a temperature of 600 ℃ and an atmosphere of N2. The sample was loaded in a quartz boat and placed in the center of the tube furnace. The heating rate was 10 ℃ / min. When the temperature reached 600 ℃, it was held for 30 min. The reacted sample was then quickly pushed into the cooling jacket on the right. The sample was taken out after cooling to room temperature.

[0045] (2) The prepared biochar was mixed with 0.2 mol / L H2SO4 at a mass ratio of 40:1 and stirred in a magnetic stirrer at room temperature under air atmosphere for 24 h. The mixture was filtered and washed repeatedly with deionized water until the pH of the washing solution was constant and neutral. The sample was dried in a constant temperature drying oven for 24 h to obtain the biochar acid-washed raw material.

[0046] (3) Replace the quartz tube of the tube furnace with a corundum tube. Mix the biochar pickling raw material with KOH at a mass ratio of 1:2 and grind them thoroughly in the crucible. Place the nickel crucible containing the sample in the center of the tube furnace and heat it at a rate of 5 °C / min. When the temperature reaches 900 °C, hold it for 30 min, and then cool it to room temperature at a rate of 5 °C / min before taking it out.

[0047] (4) The activated biochar was mixed with 0.2 mol / L H2SO4 at a mass ratio of 40:1 and stirred in a magnetic stirrer at room temperature under air atmosphere for 4 h. The mixture was filtered and washed repeatedly with deionized water until the pH of the washing solution was constant and neutral. The sample was dried in a constant temperature drying oven for 24 h to obtain CS-KBC.

[0048] (5) The CS-KBC was used in the BSD-PM high-performance specific surface area analyzer to conduct nitrogen adsorption and desorption experiments at -196 ℃. The PSD-PH device was used to record the hydrogen physical adsorption isotherms at temperatures of -196 ℃ and 25 ℃, and pressure ranges of 0.1~5 MPa. The oxygen content was tested using an elemental analyzer.

[0049] Comparative Example 2:

[0050] This comparative example is based on rice husks and uses a method for preparing RH-KBC using only K salt. The difference between this and Comparative Example 1 is that the object is rice husks.

[0051] Comparative Example 3:

[0052] This comparative example is based on sawdust and uses a method for preparing SD-KBC using only K salt. The difference between this and Comparative Example 1 is that the object is sawdust.

[0053] Comparative Example 4:

[0054] This comparative example is based on Shenhua bituminous coal and uses a method for preparing SH-KBC using only K salt. The difference between this and Comparative Example 1 is that the target is Shenhua bituminous coal.

[0055] Comparative Example 5:

[0056] This comparative example is based on corn stalks. The preparation process of CS-KSBC using K salt and H2O etching is as follows:

[0057] (1) Perform the procedure in the same way as step (1) in Comparative Example 1.

[0058] (2) Perform the procedure in the same way as step (2) in Comparative Example 1.

[0059] (3) Perform the procedure in the same way as step (3) in Comparative Example 1.

[0060] (4) Perform the procedure in the same way as step (4) in Comparative Example 1.

[0061] (5) In an argon atmosphere, CS-KBC was heated to 700 ℃ (heating rate of 5 ℃ / min), and ultrapure water was introduced into a steam generator. The vaporization temperature was set to 180 ℃, the H2O volume concentration was controlled to 30 vol%, and the etching time was 60 min. After the reaction was completed, the water supply was stopped, and then the mixture was cooled to room temperature at a cooling rate of 5 ℃ / min before being taken out to obtain CS-KSBC.

[0062] (6) The CS-KSBC was used in a BSD-PM high-performance surface area analyzer to conduct nitrogen adsorption and desorption experiments at -196 °C. The PSD-PH device was used to record the hydrogen physical adsorption isotherms at temperatures of -196 °C and 25 °C, and pressure ranges of 0.1~5 MPa. The oxygen content was tested using an elemental analyzer.

[0063] Comparative Example 6:

[0064] This comparative example is based on rice husks and uses a method for preparing RH-KSBCs by etching with K salt and H2O. The difference between this and Comparative Example 5 is that the object is rice husks.

[0065] Comparative Example 7:

[0066] This comparative example is based on a method for preparing SD-KSBCs using wood chips and etching with K salt and H2O. The difference between this and Comparative Example 5 is that the object is wood chips.

[0067] Comparative Example 8:

[0068] This comparative example is based on Shenhua bituminous coal and uses the method of preparing SH-KSBC by etching with K salt and H2O. The difference between this and Comparative Example 5 is that the target is Shenhua bituminous coal.

[0069] Example 1:

[0070] The preparation process of CS-KSBC-350-30 based on corn stalks using K salt, H2O etching, and low-temperature air oxidation is as follows:

[0071] (1) Same as step (1) in Comparative Example 5.

[0072] (2) Same as step (2) in Comparative Example 5.

[0073] (3) Same as step (3) in Comparative Example 5.

[0074] (4) is the same as step (4) in Comparative Example 5.

[0075] (5) In an argon atmosphere, CS-KBC was heated to 700 ℃ (heating rate of 5 ℃ / min), ultrapure water was introduced into the steam generator, the vaporization temperature was set to 180 ℃, the H2O volume concentration was controlled to 30 vol%, the etching time was 60 min, the water supply was stopped after the reaction was completed, and then the temperature was cooled to 350 ℃ at a cooling rate of 5 ℃ / min. The argon gas was switched to air and the reaction was carried out for 30 min. After the reaction was completed, the argon gas was switched back to air and cooled to room temperature before being taken out to obtain CS-KSBC-350-30.

[0076] (6) The CS-KSBC-350-30 was used in the BSD-PM high-performance specific surface area analyzer to conduct nitrogen adsorption and desorption experiments at -196 ℃. The PSD-PH device was used to record the hydrogen physical adsorption isotherms at temperatures of -196 ℃ and 25 ℃, and pressure ranges of 0.1~5 MPa. The oxygen content was tested using an elemental analyzer.

[0077] Example 2:

[0078] This embodiment uses corn stalks and a method to prepare RH-KSBC-200-30 by etching with K salt and H2O and low-temperature oxidation in air. The difference from Example 1 is that the low-temperature oxidation temperature is 200℃.

[0079] Example 3:

[0080] This embodiment uses corn stalks and a method to prepare RH-KSBC-250-30 by etching with K salt and H2O and low-temperature oxidation in air. The difference from Example 1 is that the low-temperature oxidation temperature is 250℃.

[0081] Example 4:

[0082] This embodiment uses corn stalks and a method to prepare RH-KSBC-350-30 by etching with K salt and H2O and low-temperature oxidation in air. The difference from Example 1 is that the low-temperature oxidation temperature is 350℃.

[0083] Example 5:

[0084] This embodiment uses corn stalks and a method to prepare RH-KSBC-400-30 by etching with K salt and H2O and low-temperature oxidation in air. The difference from Example 1 is that the low-temperature oxidation temperature is 400℃.

[0085] Example 6:

[0086] This embodiment uses corn stalks and a method to prepare RH-KSBC-350-10 by etching with K salt and H2O and low-temperature oxidation in air. The difference from Example 1 is that the low-temperature oxidation time is 10 minutes.

[0087] Example 7:

[0088] This embodiment uses corn stalks and a method to prepare RH-KSBC-350-60 by etching with K salt and H2O and low-temperature oxidation in air. The difference from Example 1 is that the low-temperature oxidation time is 60 minutes.

[0089] Example 8:

[0090] This embodiment uses corn stalks and a method to prepare RH-KSBC-350-90 by etching with K salt and H2O and low-temperature oxidation in air. The difference from Example 1 is that the low-temperature oxidation time is 90 minutes.

[0091] Example 9:

[0092] This embodiment is based on rice husks and uses a method to prepare RH-KSBC-350-30 by K salt, H2O etching and low-temperature air oxidation. The difference between this embodiment and Example 1 is that the target is rice husks.

[0093] Example 10:

[0094] This embodiment is based on wood chips and uses a method to prepare SD-KSBC-350-30 by K salt, H2O etching and low-temperature air oxidation. The difference between this embodiment and Example 1 is that the target is wood chips.

[0095] Example 11:

[0096] This embodiment is based on Shenhua bituminous coal and uses a method to prepare SH-KSBC-350-30 by K salt, H2O etching and low-temperature air oxidation. The difference between this embodiment and Embodiment 1 is that the target material is Shenhua bituminous coal.

[0097] Table 1 shows the specific pore structure parameters of the carbon-based hydrogen storage materials prepared by the preparation method of the present invention.

[0098]

[0099] Among them, a) the Brunauer, Emmett and Teller (BET) method; b) the t-plot method; c) the calculation of P / P0 = 0.99; and d) the HK method.

[0100] Table 2 Hydrogen adsorption capacity of carbon-based hydrogen storage materials under different pressures

[0101]

[0102] The above are merely exemplary embodiments of the present invention and do not constitute any limitation on the scope of protection of the present invention. All technical solutions formed by equivalent exchange or substitution fall within the scope of protection of the present invention. Finally, it should be noted that the above specific embodiments are merely embodiments of the present invention, used to illustrate the preparation process of the biochar, and are not intended to limit it. Any person skilled in the art can still modify the aforementioned specific embodiments within the technical scope described in the present invention, and the essence of these modifications does not depart from the effective scope of the embodiments of the present invention, and all should be covered within the scope of protection of the present invention.

Claims

1. A method for enhancing hydrogen storage by constructing a cascaded thermal sequence structure for carbon-based fuel micro / nano structures, characterized in that: The method is as follows: Step 1: Pyrolyze the carbon-based fuel in an inert gas atmosphere, and then cool it after pyrolysis. Step 2: Acid wash the carbon-based fuel from Step 1 with an acidic reagent, then filter and dry it for later use. Step 3: Mix the carbon-based fuel from Step 2 with the potassium-containing compound and grind until uniformly mixed; collect the sample obtained after mixing into a nickel crucible, place it in a fixed bed, and activate it under an inert gas atmosphere. After activation, the sample is cooled to room temperature according to the reaction temperature program. Step 4: Remove the nickel crucible, take out the carbon-containing precursor from the nickel crucible, acid wash it with an acidic reagent, filter it after acid washing, and dry it for later use. Step 5: Heat the sample obtained in Step 4 to the target temperature, introduce water vapor, stop the supply of water vapor after the reaction is completed, and cool down in an inert gas according to the reaction temperature program. Step Six: After the sample from Step Five has cooled to a certain temperature, introduce air for low-temperature oxidation. After the oxidation is complete, switch to an inert gas and allow the temperature to drop to room temperature according to the reaction program. Then, collect the sample.

2. The method for enhancing hydrogen storage by constructing a cascaded thermal sequence structure for carbon-based fuel micro / nano structures according to claim 1, characterized in that: The method is specifically as follows: Step 1: The dried carbon-based fuel is pyrolyzed in a tube furnace at a temperature of 400-600 ℃ in a nitrogen or argon atmosphere at a heating rate of 5-10 ℃ / min. When the temperature reaches 400-600 ℃, it is held for 30-60 min. The reacted sample is then quickly pushed into the cooling jacket on the right. The sample is removed after cooling to room temperature. Step 2: Mix the carbon material prepared in Step 1 with the acidic solution at a mass ratio of 40:1, stir in a magnetic stirrer at room temperature in an air atmosphere for 24 h, filter the mixture and wash it repeatedly with deionized water until the pH value of the washing solution is constant and neutral, and dry the sample for 24 h to obtain carbon-based acid washing raw material. Step 3: Replace the quartz tube of the tube furnace with a corundum tube. After mixing the carbon-based pickling raw material from Step 2 with the potassium-containing compound, grind it thoroughly in a crucible. Place the mixture in a nickel crucible and heat it at a rate of 5~10 ℃ / min. When the temperature reaches 700~900 ℃, hold it for 30 min, and then cool it to room temperature at a rate of 5 ℃ / min before removing it. Step 4: Mix the sample collected in Step 3 with the acidic solution at a mass ratio of 40:1, stir at room temperature in an air atmosphere for 4 hours in a magnetic stirrer, filter the mixture and wash it repeatedly with deionized water until the pH of the washing solution is constant and neutral, and dry the sample for 24 hours to obtain the carbon-based acid washing raw material. Step 5: Load the sample from Step 4 into a quartz reactor and place it in the center of a tube furnace. The heating rate is 5-10℃ / min. When the temperature reaches 700-800℃, introduce the vaporized water vapor. The water vapor volume concentration is 10 vol%-50 vol%. Maintain the reaction for 30-90 min, then stop the water vapor supply and cool down at 5℃ / min. Step Six: After the sample from Step Five has cooled to 200~400℃, introduce air for low-temperature oxidation for 10~60min. After that, switch to inert gas and then cool to room temperature at a cooling rate of 5℃ / min. Remove the sample.

3. A method for enhancing hydrogen storage by constructing a cascaded thermal sequence structure for carbon-based fuel micro / nano structures according to claim 1 or 2, characterized in that: In step one, the carbon-based fuel is one or more of straw, rice husks, wood chips, and bituminous coal.

4. A method for enhancing hydrogen storage by constructing a cascaded thermal sequence structure for carbon-based fuel micro / nano structures according to claim 1 or 2, characterized in that: In step two, the acidic solution is dilute sulfuric acid or dilute hydrochloric acid with a concentration of less than or equal to 0.2 mol / L.

5. A method for enhancing hydrogen storage by constructing a cascaded thermal sequence structure for carbon-based fuel micro / nano structures according to claim 1 or 2, characterized in that: In step three, the potassium-containing compound is one or more of potassium hydroxide, potassium carbonate, and potassium bicarbonate; the mass ratio of the carbon-based pickling raw material to the potassium-containing compound is 1:1~4.

6. A method for enhancing hydrogen storage by constructing a cascaded thermal sequence structure for carbon-based fuel micro / nanostructures according to claim 1 or 2, characterized in that: In step four, the acidic solution is dilute sulfuric acid or dilute hydrochloric acid with a concentration of less than or equal to 0.2 mol / L.

7. A method for enhancing hydrogen storage by constructing a cascaded thermal sequence structure for carbon-based fuel micro / nano structures according to claim 1 or 2, characterized in that: In step five, water vapor is generated by injecting ultrapure water into a 180°C water vapor generator via an injection pump.

8. A method for enhancing hydrogen storage by constructing a cascaded thermal sequence structure for carbon-based fuel micro / nano structures according to claim 1 or 2, characterized in that: In step six, the reaction atmosphere is air.

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