Porous biomass carbon / AlF3 composite catalyst as well as preparation method and application thereof

Abstract

The invention provides a porous biomass carbon / AlF3 composite catalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: ball-milling, mixing and uniformly dispersing a biomass carbon source and a pore-forming agent, calcining and grinding to obtain porous biomass carbon; the method comprises the following steps: mixing an aluminum salt aqueous solution and a fluoride salt aqueous solution, reacting, carrying out solid-liquid separation, and drying to obtain AlF3; alF3 is fully dispersed in ethyl alcohol, the porous biomass carbon is added, and the porous biomass carbon is obtained after reaction and drying. The preparation method of the porous biomass carbon / AlF3 composite catalyst is simple, the porous biomass carbon / AlF3 composite catalyst is obtained by uniformly loading AlF3 micron sheets on the surface of porous carbon, and the porous biomass carbon / AlF3 composite catalyst has relatively high specific surface area and porosity; the porous biomass carbon / AlF3 composite catalyst disclosed by the invention is applied to hydrogen storage of a modified 2LiBH4-MgH2 system, biomass carbon and AlF3 can generate a synergistic effect, and the hydrogen storage system shows excellent solid hydrogen storage performance in combination with high specific surface area and porosity.

Description

Technical Field

[0001] The present invention belongs to the field of composite material preparation, and in particular relates to a porous biomass carbon / AlF3 composite catalyst and a preparation method and application thereof. Background Art

[0002] Magnesium hydride (MgH2) is considered one of the most promising hydrogen storage materials due to its abundant reserves, low cost, and high hydrogen storage capacity. However, it still suffers from high hydrogen absorption and desorption temperatures, poor kinetics, and high thermodynamic stability.

[0003] Lithium borohydride (LiBH4) is a light metal coordinated hydride with a high hydrogen storage capacity (18.5 wt%), but its high hydrogen absorption / desorption temperature, slow kinetic rate, and poor reversible hydrogen storage capacity hinder its practical application.

[0004] The 2LiBH4-MgH2 system has been widely studied due to its high theoretical hydrogen storage capacity of 11.5 wt% and low enthalpy change of hydrogen absorption / desorption reaction (-45 kJ / mol). However, this hydrogen storage system still has problems such as sluggish kinetics and excessive thermodynamic stability. The reaction mechanism of the system is as follows: The second-step reaction mentioned above has an incubation period of tens of hours, which seriously affects the hydrogen absorption / desorption kinetics and needs to be improved.

[0005] Chinese patent document CN106698334A discloses a composite hydrogen storage material containing calcium carbide and its preparation method. This composite hydrogen storage material is composed of lithium borohydride, magnesium hydride (or magnesium fluoride), and calcium carbide. The molar ratio of lithium borohydride to magnesium hydride (or magnesium fluoride) is 2:1, and the amount of calcium carbide added is 12-25 mol%. During preparation, calcium carbide with a purity of at least 97% is first mechanically crushed into a powder with a particle size of less than 500 μm. The lithium borohydride, magnesium hydride (or magnesium fluoride), and calcium carbide powders are then weighed and mixed according to the desired ratio. Finally, the mixed powder is ball-milled in a planetary ball mill. This invention utilizes calcium carbide to improve the material's hydrogen storage properties, lowering the hydrogen desorption temperature, increasing the hydrogen desorption rate, and improving reversibility. However, this invention still needs further improvement in terms of hydrogen absorption and desorption temperature, kinetic properties, and thermodynamic stability.

[0006] Therefore, it is of great significance to develop a catalyst to improve the hydrogen storage performance of the 2LiBH4-MgH2 system. Summary of the Invention

[0007] To address the shortcomings of the existing technology, the present invention provides a porous biomass carbon / AlF3 composite catalyst, its preparation method, and application. The composite catalyst preparation method of the present invention is simple, and the resulting porous biomass carbon / AlF3 composite catalyst comprises AlF3 micron flakes uniformly loaded on the porous carbon surface, exhibiting a high specific surface area and porosity. The porous biomass carbon / AlF3 composite catalyst of the present invention is applied to modify a 2LiBH4-MgH2 system for hydrogen storage. The biomass carbon and AlF3 produce a synergistic effect, and the high specific surface area and porosity result in the hydrogen storage system exhibiting excellent solid-state hydrogen storage performance.

[0008] The technical solutions of the present invention are as follows:

[0009] The present invention provides a porous biomass carbon / AlF3 composite catalyst, wherein the composite catalyst is AlF3 micron sheets uniformly loaded on the surface of porous carbon; the pore size of the porous carbon is 0.5-5μm; the lateral size of the AlF3 micron sheets is 1-5μm, and the thickness is 0.1-0.5μm.

[0010] The present invention also provides a method for preparing the porous biomass carbon / AlF3 composite catalyst, comprising the steps of:

[0011] (1) mixing the biomass carbon source and the pore-forming agent by ball milling to uniformly disperse the mixture, calcining, and grinding to obtain porous biomass carbon;

[0012] (2) mixing an aqueous solution of aluminum salt and an aqueous solution of fluoride salt, reacting, separating the solid and liquid, and drying to obtain AlF3;

[0013] (3) AlF3 is fully dispersed in ethanol, porous biomass carbon is added, and the porous biomass carbon / AlF3 composite catalyst is obtained after reaction and drying.

[0014] According to the present invention, preferably, in step (1), the biomass carbon source is one of corn stalks, rice husks, or loofah sponges. Corn stalks and rice husks have high yields, low prices, and high carbon content, making them easy to synthesize high-purity biomass carbon; loofah sponges have a natural pore structure, making it easy to form pores and obtain high-porosity biomass carbon.

[0015] According to the preferred embodiment of the present invention, in step (1), the biomass carbon source further comprises the steps of cleaning, drying, ball milling, and passing through a 60-mesh sieve before use; the cleaning is carried out using deionized water and anhydrous ethanol in sequence.

[0016] According to the present invention, preferably, in step (1), the pore-forming agent is one of ammonium bicarbonate, C3N4, or ammonium chloride. All three substances can generate a large amount of gas through thermal decomposition, which is conducive to the formation of pore structures inside and on the surface of the biomass material, thereby meeting the pore-forming requirements.

[0017] According to the preferred embodiment of the present invention, in step (1), the mass ratio of the biomass carbon source to the pore-forming agent is 1-2:1, preferably 1.5:1. The ratio of the carbon source to the pore-forming agent will affect the pore-forming effect. If the proportion of the pore-forming agent is too low, it is difficult to form pores inside and on the surface of the biomass material; if the proportion of the pore-forming agent is too high, an excessive number of pores will form interconnected pores, and cause the collapse of the biomass carbon pore structure.

[0018] According to the preferred embodiment of the present invention, in step (1), the ball milling speed is 400-600 r / min, and the ball milling time is 2-4 h.

[0019] Preferably, according to the present invention, in step (1), the calcination temperature is 600-1000° C., the calcination time is 2-5 hours, and the calcination atmosphere is argon or nitrogen.

[0020] According to the preferred embodiment of the present invention, in step (1), the porous biomass carbon is ground to a particle size of 4-20 μm.

[0021] According to the preferred embodiment of the present invention, in step (2), the aluminum salt is one of aluminum chloride, aluminum sulfate or aluminum nitrate; and the concentration of the aluminum salt aqueous solution is 0.1-2 mol / L.

[0022] According to the preferred embodiment of the present invention, in step (2), the fluoride salt is one of calcium fluoride, sodium fluoride or ammonium fluoride; and the mass concentration of the fluoride salt aqueous solution is 0.05-0.5 g / mL.

[0023] According to the preferred embodiment of the present invention, in step (2), the molar ratio of the fluoride salt to the aluminum salt is (1-6):1, preferably (4-6):1, and more preferably 6:1.

[0024] According to the preferred embodiment of the present invention, in step (2), the reaction temperature is room temperature; the reaction time is 4 to 18 hours; and the reaction is carried out under stirring conditions.

[0025] According to the preferred embodiment of the present invention, in step (3), the mass ratio of AlF3 to ethanol is 0.035-0.045 g / mL.

[0026] According to the preferred embodiment of the present invention, in step (3), the mass ratio of AlF3 to porous biomass carbon is 2-9:1.

[0027] According to the preferred embodiment of the present invention, in step (3), the reaction conditions are room temperature ultrasound for 10-60 min.

[0028] The present invention also provides the use of the porous biomass carbon / AlF3 composite catalyst in hydrogen storage in a 2LiBH4-MgH2 system.

[0029] According to a preferred embodiment of the present invention, the application method includes the steps of: ball-milling and uniformly mixing the porous biomass carbon / AlF3 composite catalyst with the 2LiBH4-MgH2 system to obtain a composite material for hydrogen storage in the 2LiBH4-MgH2 system.

[0030] Preferably, the mass ratio of the porous biomass carbon / AlF3 composite catalyst to the 2LiBH4-MgH2 system is 1:5-20; the ball milling speed is 400-600 r / min, and the ball milling time is 2-4 h.

[0031] According to the preferred embodiment of the present invention, the preparation method of the 2LiBH4-MgH2 system includes the steps of: mixing LiBH4 and MgH2 by ball milling to obtain a 2LiBH4-MgH2 system; wherein the molar ratio of LiBH4 to MgH2 is 2:1, the ball milling speed is 400-600 r / min, and the ball milling time is 4-12 h.

[0032] The technical features and beneficial effects of the present invention are as follows:

[0033] (1) The present invention uses biomass carbon sources to prepare carbon materials, which have a wide range of raw material sources and are low in price, and realize the recycling of waste, which is green and environmentally friendly. The present invention first ball-mills, calcines, and grinds the carbon source and the pore-forming agent to finally obtain porous biomass carbon. The porous biomass carbon has a large specific surface area, which helps to increase the reaction space and active sites, is conducive to the uniform dispersion of AlF3, and thus improves the hydrogen storage modification performance of the composite material. The fluoride salt and the aluminum salt are hydrolyzed at a certain temperature and react to generate AlF3, which is then ultrasonically mixed with the porous biomass carbon to obtain a porous biomass carbon / AlF3 composite material. The synthesis method of the porous biomass carbon / AlF3 composite material of the present invention is simple, the reaction conditions are mild, the cost is low, and it is suitable for industrial application.

[0034] (2) The porous biomass carbon / AlF3 composite catalyst obtained in the present invention is a porous biomass carbon (pore size of 0.5-5 μm) with AlF3 micron sheets (size of about 1-5 μm, thickness of about 0.1-0.5 μm) uniformly loaded on the surface. It has the characteristics of porous structure and high specific surface area. The AlF3 micron sheets are evenly distributed and have a high loading rate, which is beneficial to the improvement of catalytic performance.

[0035] (3) In the porous biomass carbon / AlF3 composite catalyst obtained by the present invention, aluminum ions can improve the reversible hydrogen storage performance, fluoride ions can improve the kinetics of hydrogen release, and the synergistic effect of fluoride ions and aluminum ions improves its catalytic ability. At the same time, the porous structure of the porous biomass carbon can increase the specific surface area of ​​the material, and can provide more active sites for the hydrogen absorption / desorption reaction of the 2LiBH4-MgH2 system. The porous biomass carbon and AlF3 synergistically enhance the catalytic effect on the hydrogen storage performance of the 2LiBH4-MgH2 system. The preparation method of the present invention is taken as a whole, and each step and each condition work together to obtain the porous biomass carbon / AlF3 composite catalyst with the structure and performance of the present invention. The porous biomass carbon / AlF3 composite catalyst of the present invention is applied to the 2LiBH4-MgH2 system. Due to the synergistic effect of the porous biomass carbon and AlF3, combined with the porous structure, micron sheet structure, etc., the hydrogen absorption / desorption performance of the 2LiBH4-MgH2 system is enhanced, and excellent catalytic performance is exhibited. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a SEM image of the porous biomass carbon / AlF3 composite material prepared in Example 1;

[0037] Figure 2 Graphs of hydrogen release under varying temperatures for the porous biomass carbon / AlF3-modified 2LiBH4-MgH2 system and the unmodified 2LiBH4-MgH2 system prepared in Example 1;

[0038] Figure 3 The isothermal hydrogen release curves of the porous biomass carbon / AlF3 modified 2LiBH4-MgH2 system and the unmodified 2LiBH4-MgH2 system prepared in Example 1;

[0039] Figure 4 The isothermal hydrogen absorption curves of the porous biomass carbon / AlF3 modified 2LiBH4-MgH2 system and the unmodified 2LiBH4-MgH2 system prepared in Example 1;

[0040] Figure 5 The isothermal hydrogen release curves of the porous biomass carbon / AlF3 modified 2LiBH4-MgH2 system and the unmodified 2LiBH4-MgH2 system prepared in Example 2;

[0041] Figure 6 The isothermal hydrogen absorption curves of the porous biomass carbon / AlF3 modified 2LiBH4-MgH2 system and the unmodified 2LiBH4-MgH2 system prepared in Example 3;

[0042] Figure 7 This is the XRD pattern of the porous biomass carbon / AlF3 composite material prepared in Example 4;

[0043] Figure 8 Temperature-dependent hydrogen release curves of the porous biomass carbon-modified 2LiBH4-MgH2 system and the unmodified 2LiBH4-MgH2 system prepared in Comparative Example 1;

[0044] Figure 9 This is the SEM image of AlF3 prepared in Comparative Example 2. DETAILED DESCRIPTION

[0045] The present invention will be further described below with reference to specific embodiments, but is not limited thereto.

[0046] Meanwhile, the experimental methods described in the following examples, unless otherwise specified, are conventional methods; the reagents and materials, unless otherwise specified, can be obtained from commercial channels.

[0047] Example 1

[0048] A method for preparing a porous biomass carbon / AlF3 composite catalyst comprises the following steps:

[0049] (1) After the sponge gourd was cut into pieces, it was cleaned with deionized water, then washed with anhydrous ethanol, dried for use, ball-milled for 3 h, and passed through a 60-mesh sieve. 0.9 g of the sponge gourd powder obtained above was taken and ball-milled with 0.6 g of C3N4 (the ball milling speed was 500 r / min, the ball milling time was 3 h, and the ball milling temperature was room temperature) until the mixture was uniform. The mixture was calcined under an argon atmosphere at a heating rate of 5 °C / min to 800 °C and kept warm for 3 h. After cooling to room temperature, the mixture was fully ground to obtain porous biomass carbon (ground to a particle size of 4-20 μm).

[0050] (2) Dissolve 4.018 g (0.0107 mol) of aluminum nitrate nonahydrate in 17 mL of deionized water, referred to as solution A. Dissolve 2.379 g (0.0643 mol) of ammonium fluoride in 17 mL of deionized water, referred to as solution B. Slowly add solution B to solution A, stir thoroughly at room temperature for 4 h, centrifuge, and dry at 70°C overnight to obtain AlF3.

[0051] (3) 0.9 g of the prepared AlF3 was dissolved in 20 mL of ethanol, 0.1 g of porous biomass carbon was added, ultrasonicated at room temperature for 30 min, and dried at 70 °C overnight to obtain a porous biomass carbon / AlF3 composite catalyst.

[0052] like Figure 1 Shown is the SEM image of the porous biomass carbon / AlF3 composite material prepared in this embodiment. It can be seen from the figure that the composite material is a porous biomass carbon surface-loaded AlF3 micron sheet structure, the pore size of the porous biomass carbon is 0.5-5μm, the size of the AlF3 micron sheet is 1-5μm, and the thickness is 0.1-0.5μm.

[0053] The application of the porous biomass carbon / AlF3 composite catalyst in the hydrogen storage of the 2LiBH4-MgH2 system is as follows:

[0054] 1.247g of LiBH4 and 0.753g of MgH2 were ball-milled at room temperature (500 rpm for 8 h) to produce a 2LiBH4-MgH2 system. 0.05g of the porous biomass carbon / AlF3 composite catalyst was ball-milled with 0.45g of the 2LiBH4-MgH2 system at room temperature at 500 rpm for 4 h to produce a composite sample.

[0055] The obtained composite sample was subjected to a hydrogen desorption performance test as follows: 150 mg of the composite sample was transferred to a hydrogen storage tester, and the temperature was raised from room temperature to 450°C at a heating rate of 5°C / min. The temperature was kept at 450°C for 3 hours, and the initial hydrogen pressure was 3.5 bar. The amount of hydrogen desorption was measured and plotted as a temperature-dependent hydrogen desorption curve. The obtained performance was compared with that of the unmodified 2LiBH4-MgH2 system (the 2LiBH4-MgH2 system was also ball-milled according to the above conditions).

[0056] According to the test, the 2LiBH4-MgH2 system modified by porous biomass carbon / AlF3 catalysis can significantly increase the hydrogen release rate. Figure 2 As shown in the figure, the unmodified 2LiBH4-MgH2 system (ball-milled 2LiBH4-MgH2) begins to release hydrogen at 280°C and releases only 0.14 wt% of hydrogen within 70 minutes, with a hydrogen release rate of 1.22%. However, after modification with porous biomass carbon / AlF3 (loofah-derived carbon / AlF3-modified 2LiBH4-MgH2 system), hydrogen release can be achieved at 200°C, with 0.64 wt% of hydrogen released within 70 minutes, and a hydrogen release rate of 5.57%.

[0057] The obtained composite sample was subjected to a hydrogen desorption performance test as follows: 150 mg of the composite sample was transferred to a hydrogen storage tester, and the temperature was raised from room temperature to 440°C at a heating rate of 5°C / min. The temperature was kept at 440°C for 3 hours, and the initial hydrogen pressure was 3.5 bar. The amount of hydrogen released during the 440°C holding process was measured and plotted into an isothermal hydrogen desorption curve. The obtained performance was compared with that of the unmodified 2LiBH4-MgH2 system (the 2LiBH4-MgH2 system was also ball-milled according to the above conditions).

[0058] According to the test, the 2LiBH4-MgH2 system modified by porous biomass carbon / AlF3 catalysis can significantly increase the hydrogen release rate and capacity. Figure 3As shown in the data, the unmodified 2LiBH4-MgH2 system (ball-milled 2LiBH4-MgH2 system) released 5.83wt% of hydrogen at 440°C within 5 minutes, with a hydrogen release rate of 50.7%; and released 7.57wt% of hydrogen at 65.8% within 10 minutes. However, after modification with porous biomass carbon / AlF3 (porous biomass carbon / AlF3-modified 2LiBH4-MgH2 system), 8.23wt% of hydrogen was released at 440°C within 5 minutes, with a hydrogen release rate of 71.6%; and 9.56wt% of hydrogen was released at 83.1% within 10 minutes, which is a significant improvement.

[0059] The obtained composite sample was subjected to a hydrogen absorption performance test as follows: 150 mg of the composite sample was transferred to a hydrogen storage tester, and the temperature was raised from room temperature to 400°C at a heating rate of 5°C / min. The sample was kept at 400°C for 3 hours under a hydrogen pressure of 40 bar. The amount of hydrogen absorbed during the 400°C holding process was measured and plotted as an isothermal hydrogen absorption curve. The obtained performance was compared with that of the unmodified 2LiBH4-MgH2 system (the 2LiBH4-MgH2 system was also ball-milled under the above conditions).

[0060] According to the test, the 2LiBH4-MgH2 system modified by porous biomass carbon / AlF3 catalysis can significantly reduce the initial hydrogen absorption temperature and increase the hydrogen absorption capacity. Figure 4 As shown in the figure, the unmodified 2LiBH4-MgH2 system (ball-milled 2LiBH4-MgH2 system) absorbed 2.67 wt% of hydrogen within 20 minutes at 400°C, and the hydrogen absorption rate was 23.2%. After modification with porous biomass carbon / AlF3 (porous biomass carbon / AlF3 modified 2LiBH4-MgH2 system), it absorbed 6.17 wt% of hydrogen within 20 minutes at 400°C, and the hydrogen absorption rate was 53.7%, which was significantly improved.

[0061] Example 2

[0062] A method for preparing a porous biomass carbon / AlF3 composite catalyst comprises the following steps:

[0063] (1) After the corn stalks were chopped, they were cleaned with deionized water, then washed with anhydrous ethanol, dried and set aside, ball-milled for 3 h, passed through a 60-mesh sieve, and 0.9 g of the above-obtained straw powder was ball-milled with 0.6 g of ammonium bicarbonate (the ball milling speed was 500 r / min, and the ball milling time was 3 h) until the mixture was uniform. The mixture was calcined under an argon atmosphere at a heating rate of 5 °C / min to 800 °C and kept warm for 3 h. After cooling to room temperature, the mixture was fully ground to obtain porous biomass carbon (ground to a particle size of 4-20 μm).

[0064] (2) Dissolve 5.167 g (0.0214 mol) of aluminum chloride hexahydrate in 20 mL of deionized water, referred to as solution A. Dissolve 2.506 g (0.0321 mol) of calcium fluoride in 20 mL of deionized water, referred to as solution B. Slowly add solution B to solution A, stir thoroughly at room temperature for 4 h, centrifuge, and dry at 70°C overnight to obtain AlF3.

[0065] (3) 0.8 g of the prepared AlF3 was dissolved in 20 mL of ethanol, 0.2 g of porous biomass carbon was added, ultrasonicated at room temperature for 30 min, and dried at 70 °C overnight to obtain a porous biomass carbon / AlF3 composite catalyst.

[0066] The application of the porous biomass carbon / AlF3 composite catalyst in the hydrogen storage of the 2LiBH4-MgH2 system is as follows:

[0067] 1.247g of LiBH4 and 0.753g of MgH2 were ball-milled at room temperature (500 rpm for 8 h) to produce a 2LiBH4-MgH2 system. 0.05g of the porous biomass carbon / AlF3 composite catalyst was ball-milled with 0.45g of the 2LiBH4-MgH2 system at room temperature at 500 rpm for 4 h to produce a composite sample.

[0068] The obtained composite sample was subjected to a hydrogen desorption performance test as follows: 150 mg of the composite sample was transferred to a hydrogen storage tester, and the temperature was raised from room temperature to 440°C at a heating rate of 5°C / min. The temperature was kept at 440°C for 3 hours, and the initial hydrogen pressure was 3.5 bar. The amount of hydrogen released during the 440°C holding process was measured and plotted into an isothermal hydrogen desorption curve. The obtained performance was compared with that of the unmodified 2LiBH4-MgH2 system (the 2LiBH4-MgH2 system was also ball-milled according to the above conditions).

[0069] According to the test, the 2LiBH4-MgH2 system modified by porous biomass carbon / AlF3 catalysis can significantly increase the hydrogen release rate and capacity. Figure 5 As shown in the data, the unmodified 2LiBH4-MgH2 system (ball-milled 2LiBH4-MgH2 system) released 5.83wt% of hydrogen in 5 minutes at 440°C, with a hydrogen release rate of 50.7%; and released 7.57wt% of hydrogen in 10 minutes, with a hydrogen release rate of 65.8%. After modification with porous biomass carbon / AlF3 (porous biomass carbon / AlF3-modified 2LiBH4-MgH2 system), 7.98wt% of hydrogen was released in 5 minutes at 440°C, with a hydrogen release rate of 69.4%; and 9.10wt% of hydrogen was released in 10 minutes, with a hydrogen release rate of 79.1%, which is a significant improvement.

[0070] The obtained composite sample was subjected to a hydrogen desorption performance test as follows: 150 mg of the composite sample was transferred to a hydrogen storage tester, and the temperature was raised from room temperature to 450°C at a heating rate of 5°C / min. The temperature was kept at 450°C for 3 hours with an initial hydrogen pressure of 3.5 bar. The amount of hydrogen desorption was measured and the obtained performance was compared with that of the unmodified 2LiBH4-MgH2 system (the 2LiBH4-MgH2 system was also ball-milled according to the above conditions).

[0071] After testing, the 2LiBH4-MgH2 system modified by porous biomass carbon / AlF3 catalysis can increase the hydrogen release rate. The unmodified 2LiBH4-MgH2 system (ball-milled 2LiBH4-MgH2) began to release hydrogen at 280°C, and only 0.14wt% of hydrogen was released within 70 minutes, with a hydrogen release rate of 1.22%. After modification with porous biomass carbon / AlF3 (porous biomass carbon / AlF3 modified 2LiBH4-MgH2 system), hydrogen release began at 215°C, and 0.58wt% of hydrogen was released within 70 minutes, with a hydrogen release rate of 5.04%, which is a significant improvement.

[0072] Example 3

[0073] A method for preparing a porous biomass carbon / AlF3 composite catalyst comprises the following steps:

[0074] (1) The rice husk was cleaned with deionized water, then washed with anhydrous ethanol, dried and set aside, ball-milled for 3 h, passed through a 60-mesh sieve, and 0.9 g of the rice husk powder obtained above was ball-milled with 0.6 g of ammonium chloride (ball milling speed of 500 r / min, ball milling time of 3 h) until mixed evenly. The mixture was calcined under an argon atmosphere at a heating rate of 5 °C / min to 800 °C and kept warm for 3 h. After cooling to room temperature, the mixture was fully ground to obtain porous biomass carbon (ground to a particle size of 4-20 μm).

[0075] (2) Dissolve 7.132 g (0.0107 mol) of aluminum sulfate 18hydrate in 25 mL of deionized water (Solution A). Dissolve 2.70 g (0.0642 mol) of sodium fluoride in 25 mL of deionized water (Solution B). Slowly add Solution B to Solution A, stir thoroughly at room temperature for 4 h, centrifuge, and dry at 70°C overnight to obtain AlF3.

[0076] (3) 0.7 g of the prepared AlF3 was dissolved in 20 mL of ethanol, 0.3 g of porous biomass carbon was added, ultrasonicated at room temperature for 30 min, and dried at 70 °C overnight to obtain a porous biomass carbon / AlF3 composite catalyst.

[0077] The application of the porous biomass carbon / AlF3 composite catalyst in the hydrogen storage of the 2LiBH4-MgH2 system is as follows:

[0078] 1.247g of LiBH4 and 0.753g of MgH2 were ball-milled at room temperature (500 rpm for 8 h) to produce a 2LiBH4-MgH2 system. 0.05g of the porous biomass carbon / AlF3 composite catalyst was ball-milled with 0.45g of the 2LiBH4-MgH2 system at room temperature at 500 rpm for 4 h to produce a composite sample.

[0079] The obtained composite sample was subjected to a hydrogen absorption performance test as follows: 150 mg of the composite sample was transferred to a hydrogen storage tester, and the temperature was raised from room temperature to 400°C at a heating rate of 5°C / min. The sample was kept at 400°C for 3 hours under a hydrogen pressure of 40 bar. The amount of hydrogen absorbed during the 400°C holding process was measured and plotted as an isothermal hydrogen absorption curve. The obtained performance was compared with that of the unmodified 2LiBH4-MgH2 system (the 2LiBH4-MgH2 system was also ball-milled under the above conditions).

[0080] According to the test, the 2LiBH4-MgH2 system modified by porous biomass carbon / AlF3 catalysis can significantly reduce the initial hydrogen absorption temperature and increase the hydrogen absorption capacity. Figure 6 As shown in the figure, the unmodified 2LiBH4-MgH2 system (ball-milled 2LiBH4-MgH2 system) absorbed 2.67 wt% of hydrogen within 20 minutes at 400°C, and the hydrogen absorption rate was 23.2%. After modification with porous biomass carbon / AlF3 (porous biomass carbon / AlF3 modified 2LiBH4-MgH2 system), it absorbed 6.00 wt% of hydrogen within 20 minutes at 400°C, and the hydrogen absorption rate was 52.2%, which was significantly improved.

[0081] The obtained composite sample was subjected to a hydrogen desorption performance test as follows: 150 mg of the composite sample was transferred to a hydrogen storage tester, and the temperature was raised from room temperature to 450°C at a heating rate of 5°C / min. The temperature was kept at 450°C for 3 hours with an initial hydrogen pressure of 3.5 bar. The amount of hydrogen desorption was measured and the obtained performance was compared with that of the unmodified 2LiBH4-MgH2 system (the 2LiBH4-MgH2 system was also ball-milled according to the above conditions).

[0082] After testing, the 2LiBH4-MgH2 system modified by porous biomass carbon / AlF3 catalysis can increase the rate of hydrogen release. The unmodified 2LiBH4-MgH2 system (ball-milled 2LiBH4-MgH2) began to release hydrogen at 280°C, and only 0.14wt% of hydrogen was released within 70 minutes, with a hydrogen release rate of 1.22%. After modification with porous biomass carbon / AlF3 (porous biomass carbon / AlF3 modified 2LiBH4-MgH2 system), hydrogen release began at 230°C, and 0.51wt% of hydrogen was released within 70 minutes, with a hydrogen release rate of 4.43%, which is a significant improvement.

[0083] Example 4

[0084] A method for preparing a porous biomass carbon / AlF3 composite catalyst comprises the following steps:

[0085] (1) After the sponge gourd was cut into pieces, it was cleaned with deionized water, then washed with anhydrous ethanol, dried for use, ball-milled for 3 h, passed through a 60-mesh sieve, 0.9 g of the sponge gourd powder obtained above was taken and ball-milled with 0.6 g of C3N4 (the ball milling speed was 500 r / min, the ball milling time was 3 h, and the ball milling temperature was room temperature) until the mixture was uniform, and calcined under an argon atmosphere, heating to 800 ° C at a heating rate of 5 ° C / min, and kept warm for 3 h. After cooling to room temperature, it was fully ground to obtain porous biomass carbon (ground to a particle size of 4-20 μm).

[0086] (2) Dissolve 7.132 g (0.0107 mol) of aluminum sulfate 18hydrate in 25 mL of deionized water (Solution A). Dissolve 2.70 g (0.0642 mol) of sodium fluoride in 25 mL of deionized water (Solution B). Slowly add Solution B to Solution A, stir thoroughly at room temperature for 4 h, centrifuge, and dry at 70°C overnight to obtain AlF3.

[0087] (3) 0.8 g of the prepared AlF3 was dissolved in 20 mL of ethanol, 0.2 g of porous biomass carbon was added, ultrasonicated at room temperature for 30 min, and dried at 70 °C overnight to obtain a porous biomass carbon / AlF3 composite catalyst.

[0088] like Figure 7 Shown is the XRD pattern of the porous biomass carbon / AlF3 composite material prepared in this example. It can be seen from the figure that the diffraction peak of the composite material is consistent with the standard card of AlF3 (PDF#43-0435), and there are no diffraction peaks of other phases, which proves that the AlF3 synthesized by this method has a high purity. Due to the low content of porous biomass carbon or the unclear diffraction peak, no diffraction peak belonging to porous biomass carbon was observed.

[0089] The obtained composite sample was subjected to a hydrogen desorption performance test as follows: 150 mg of the composite sample was transferred to a hydrogen storage tester, and the temperature was raised from room temperature to 450°C at a heating rate of 5°C / min. The temperature was kept at 450°C for 3 hours with an initial hydrogen pressure of 3.5 bar. The amount of hydrogen desorption was measured and the obtained performance was compared with that of the unmodified 2LiBH4-MgH2 system (the 2LiBH4-MgH2 system was also ball-milled according to the above conditions).

[0090] After testing, the porous biomass carbon / AlF3 catalytically modified 2LiBH4-MgH2 system can increase the hydrogen release rate. The unmodified 2LiBH4-MgH2 system (ball-milled 2LiBH4-MgH2) began to release hydrogen at 280°C, and only released 0.14wt% of hydrogen within 70 minutes, with a hydrogen release rate of 1.22%. After modification with porous biomass carbon / AlF3 (porous biomass carbon / AlF3 modified 2LiBH4-MgH2 system), hydrogen release began at 225°C, and 0.45wt% of hydrogen could be released within 70 minutes, with a hydrogen release rate of 3.91%, which can increase the hydrogen release rate.

[0091] Comparative Example 1

[0092] A method for preparing porous biomass carbon comprises the following steps:

[0093] After the sponge gourd was chopped, it was cleaned with deionized water, then washed with anhydrous ethanol, dried for use, ball milled for 3 hours, and passed through a 60-mesh sieve. 0.9g of the sponge gourd powder obtained above was taken and ball milled with 0.6g of C3N4 (ball milling speed of 500r / min, ball milling time of 3h, ball milling temperature of room temperature) until mixed uniformly, calcined under argon atmosphere, heated to 800℃ at a heating rate of 5℃ / min, and kept warm for 3h. After cooling to room temperature, it was fully ground to obtain porous biomass carbon (ground to a particle size of 4-20μm).

[0094] The application of the porous biomass carbon in the hydrogen storage of the 2LiBH4-MgH2 system is as follows:

[0095] 1.247 g of LiBH4 and 0.753 g of MgH2 were ball-milled at room temperature (500 r / min for 8 h) to produce a 2LiBH4-MgH2 system. 0.05 g of porous biomass carbon was ball-milled with 0.45 g of the 2LiBH4-MgH2 system at room temperature at 500 r / min for 4 h to produce a composite sample.

[0096] The obtained composite sample was subjected to a hydrogen desorption performance test as follows: 150 mg of the composite sample was transferred to a hydrogen storage tester, and the temperature was raised from room temperature to 450°C at a heating rate of 5°C / min. The temperature was kept at 450°C for 3 hours, and the initial hydrogen pressure was 3.5 bar. The amount of hydrogen desorption was measured and plotted as a temperature-dependent hydrogen desorption curve. The obtained performance was compared with that of the unmodified 2LiBH4-MgH2 system (the 2LiBH4-MgH2 system was also ball-milled according to the above conditions).

[0097] After testing, the 2LiBH4-MgH2 system modified by porous biomass carbon catalysis cannot reduce the hydrogen desorption temperature and increase the hydrogen desorption rate. Figure 8 As shown in the figure, the unmodified 2LiBH4-MgH2 system (ball-milled 2LiBH4-MgH2 system) begins to release hydrogen at 280°C, releasing 0.14 wt% of hydrogen within 70 minutes, with a hydrogen release rate of 1.22%. After being modified with porous biomass carbon (porous biomass carbon-modified 2LiBH4-MgH2 system), hydrogen release begins at 350°C, releasing 0.035 wt% of hydrogen within 80 minutes, with a hydrogen release rate of 0.30%.

[0098] Comparative Example 2

[0099] A method for preparing AlF3 comprises the following steps:

[0100] Dissolve 4.018 g (0.0107 mol) of aluminum nitrate nonahydrate in 17 mL of deionized water, designated Solution A. Dissolve 2.379 g (0.0643 mol) of ammonium fluoride in 17 mL of deionized water, designated Solution B. Slowly add Solution B to Solution A, stir thoroughly at room temperature for 4 hours, centrifuge, and dry overnight at 70°C to obtain AlF3.

[0101] like Figure 9 Shown is the SEM image of AlF3 prepared in this comparative example. It can be seen from the figure that the size of the AlF3 micron sheet is 2-110 μm and the thickness is 1.5-6.5 μm.

[0102] The application of AlF3 in the hydrogen storage of 2LiBH4-MgH2 system is as follows:

[0103] 1.247g of LiBH4 and 0.753g of MgH2 were ball-milled at room temperature (500 rpm for 8 hours) to produce a 2LiBH4-MgH2 system. 0.05g of AlF3 was ball-milled at room temperature with 0.45g of the 2LiBH4-MgH2 system at 500 rpm for 4 hours to produce a composite sample.

[0104] The obtained composite sample was subjected to a hydrogen desorption performance test as follows: 150 mg of the composite sample was transferred to a hydrogen storage tester, and the temperature was raised from room temperature to 440°C at a heating rate of 5°C / min. The temperature was kept at 440°C for 3 hours, and the initial hydrogen pressure was 3.5 bar. The amount of hydrogen released during the 440°C holding process was measured and plotted into an isothermal hydrogen desorption curve. The obtained performance was compared with that of the unmodified 2LiBH4-MgH2 system (the 2LiBH4-MgH2 system was also ball-milled according to the above conditions).

[0105] Tests show that the unmodified 2LiBH4-MgH2 system (ball-milled 2LiBH4-MgH2 system) released 5.83 wt% hydrogen in 5 minutes at 440°C, with a hydrogen release rate of 50.7%. However, after AlF3 modification (AlF3-modified 2LiBH4-MgH2 system), the system released 7.36 wt% hydrogen in 5 minutes at 440°C, with a hydrogen release rate of 64%.

[0106] Comparative Example 3

[0107] A method for preparing a biomass carbon / AlF3 composite catalyst comprises the following steps:

[0108] (1) After the sponge gourd was cut into pieces, it was cleaned with deionized water, then washed with anhydrous ethanol, dried for use, ball-milled for 3 h, passed through a 60-mesh sieve, and 0.9 g of the sponge gourd powder obtained above was taken and calcined under an argon atmosphere at a heating rate of 5 ° C / min to 800 ° C and kept warm for 3 h. After cooling to room temperature, it was fully ground to obtain biomass carbon (ground to a particle size of 4-20 μm).

[0109] (2) Dissolve 4.018 g (0.0107 mol) of aluminum nitrate nonahydrate in 17 mL of deionized water, referred to as solution A. Dissolve 2.379 g (0.0643 mol) of ammonium fluoride in 17 mL of deionized water, referred to as solution B. Slowly add solution B to solution A, stir thoroughly at room temperature for 4 h, centrifuge, and dry at 70°C overnight to obtain AlF3.

[0110] (3) 0.9 g of the prepared AlF3 was dissolved in 20 mL of ethanol, 0.1 g of biomass carbon was added, ultrasonicated at room temperature for 30 min, and dried at 70 °C overnight to obtain a biomass carbon / AlF3 composite catalyst.

[0111] The application of the above-mentioned biomass carbon / AlF3 composite catalyst in hydrogen storage in the 2LiBH4-MgH2 system is as follows:

[0112] 1.247g of LiBH4 and 0.753g of MgH2 were ball-milled at room temperature (500 r / min for 8 h) to produce a 2LiBH4-MgH2 system. 0.05g of biochar was ball-milled at room temperature with 0.45g of the 2LiBH4-MgH2 system at 500 r / min for 4 h to produce a composite sample.

[0113] The obtained composite sample was subjected to a hydrogen desorption performance test as follows: 150 mg of the composite sample was transferred to a hydrogen storage tester, and the temperature was raised from room temperature to 450°C at a heating rate of 5°C / min. The temperature was kept at 450°C for 3 hours with an initial hydrogen pressure of 3.5 bar. The amount of hydrogen desorption was measured and the obtained performance was compared with that of the unmodified 2LiBH4-MgH2 system (the 2LiBH4-MgH2 system was also ball-milled according to the above conditions).

[0114] Tests have shown that a 2LiBH4-MgH2 system modified with a biomass carbon / AlF3 composite catalyst can increase the rate of hydrogen release. The unmodified 2LiBH4-MgH2 system (ball-milled 2LiBH4-MgH2 system) begins releasing hydrogen at 280°C, releasing 0.14wt% of hydrogen within 70 minutes, for a hydrogen release rate of 1.22%. After modification with the biomass carbon / AlF3 composite catalyst, hydrogen release begins at 230°C, releasing 0.41wt% of hydrogen within 70 minutes, for a hydrogen release rate of 3.57%.

Claims

1. A porous biomass carbon / AlF3 composite catalyst, characterized in that: The composite catalyst is AlF3 micron sheets uniformly loaded on the surface of porous carbon; the pore size of the porous carbon is 0.5-5 μm; the lateral size of the AlF3 micron sheets is 1-5 μm, and the thickness is 0.1-0.5 μm.

2. The method for preparing the porous biomass carbon / AlF3 composite catalyst according to claim 1, comprising the steps of: (1) mixing the biomass carbon source and the pore-forming agent by ball milling to uniformly disperse the mixture, calcining, and grinding to obtain porous biomass carbon; (2) mixing an aqueous solution of aluminum salt and an aqueous solution of fluoride salt, reacting, separating the solid and liquid, and drying to obtain AlF3; (3) AlF3 is fully dispersed in ethanol, porous biomass carbon is added, and the porous biomass carbon / AlF3 composite catalyst is obtained after reaction and drying.

3. The method for preparing the porous biomass carbon / AlF3 composite catalyst according to claim 2, characterized in that: In step (1), one or more of the following conditions are included: i. The biomass carbon source is one of corn stalks, rice husks or loofah pulp; ii. The biomass carbon source also includes the steps of cleaning, drying, ball milling, and passing through a 60-mesh sieve before use; the cleaning is carried out using deionized water and anhydrous ethanol in sequence; iii. The pore-forming agent is one of ammonium bicarbonate, C3N4 or ammonium chloride; iv. The mass ratio of the biomass carbon source to the pore-forming agent is 1-2:1, preferably 1.5:

1.

4. The method for preparing the porous biomass carbon / AlF3 composite catalyst according to claim 2, characterized in that: In step (1), one or more of the following conditions are included: i. The ball milling speed is 400-600 r / min and the ball milling time is 2-4 h; ii. The calcination temperature is 600-1000°C, the calcination time is 2-5 hours, and the calcination atmosphere is argon or nitrogen; iii. Grinding the porous biomass carbon to a particle size of 4-20 μm.

5. The method for preparing the porous biomass carbon / AlF3 composite catalyst according to claim 2, characterized in that: In step (2), one or more of the following conditions are included: i. The aluminum salt is one of aluminum chloride, aluminum sulfate or aluminum nitrate; the concentration of the aluminum salt aqueous solution is 0.1-2 mol / L; ii. The fluoride salt is one of calcium fluoride, sodium fluoride or ammonium fluoride; the mass concentration of the fluoride salt aqueous solution is 0.05-0.5g / mL; iii. The molar ratio of the fluoride salt to the aluminum salt is (1-6):1, preferably (4-6):1, and more preferably 6:1; iv. The reaction temperature is room temperature; the reaction time is 4 to 18 hours; and the reaction is carried out under stirring conditions.

6. The method for preparing the porous biomass carbon / AlF3 composite catalyst according to claim 2, characterized in that: In step (3), one or more of the following conditions are included: i. The mass ratio of AlF3 to ethanol is 0.035-0.045 g / mL; ii. the mass ratio of AlF3 to porous biomass carbon is 2-9:1; iii. The reaction conditions are room temperature ultrasound for 10-60 min.

7. Use of the porous biomass carbon / AlF3 composite catalyst as claimed in claim 1 in hydrogen storage in a 2LiBH4-MgH2 system.

8. The use according to claim 7, characterized in that The application method comprises the steps of: ball-milling and uniformly mixing a porous biomass carbon / AlF3 composite catalyst with a 2LiBH4-MgH2 system to obtain a composite material for hydrogen storage in the 2LiBH4-MgH2 system.

9. The use according to claim 8, characterized in that The mass ratio of the porous biomass carbon / AlF3 composite catalyst to the 2LiBH4-MgH2 system is 1:5-20; the ball milling speed is 400-600 r / min, and the ball milling time is 2-4 h.

10. The use according to claim 7, characterized in that The preparation method of the 2LiBH4-MgH2 system comprises the following steps: mixing LiBH4 and MgH2 by ball milling to obtain the 2LiBH4-MgH2 system; wherein the molar ratio of LiBH4 to MgH2 is 2:1, the ball milling speed is 400-600 r / min, and the ball milling time is 4-12 h.

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