An aluminum-based chemical hydrogen storage composite material, its preparation method, and its application in hydrogen production via water electrolysis.

Abstract

This invention discloses an aluminum-based chemical hydrogen storage composite material, its preparation method, and its application in hydrogen production via water electrolysis. The method includes the following steps: an aluminum-calcium alloy is placed in a ball mill jar and evacuated; then hydrogen is introduced into the ball mill jar for ball milling, thereby obtaining the aluminum-based chemical hydrogen storage composite material for hydrogen production via water electrolysis. In this composite material, aluminum and calcium hydride are bonded at the grain level. This invention employs a gas-solid reaction and room-temperature ball milling method, which is simple and low-cost. This composite method not only avoids the direct use of expensive calcium hydride but also overcomes the disadvantage of reduced theoretical hydrogen release capacity in other composite systems. The in-situ formed calcium hydride releases heat through hydrolysis, exposes fresh aluminum, and generates CaO around the aluminum. 2+ and OH ¯ Local concentration fields play a crucial role in improving the kinetics of aluminum hydrolysis.

Description

Technical Field

[0001] This invention belongs to the field of high-capacity controllable hydrogen release technology, specifically relating to an aluminum-based chemical hydrogen storage composite material, its preparation method, and its application in hydrogen production via water electrolysis. Background Technology

[0002] Hydrogen is a high-density, pollution-free synthetic fuel that can replace traditional fossil fuels. Unlike hydrocarbon fossil fuels, hydrogen cannot be obtained naturally in large quantities, so it must be produced on a large scale through economical and efficient methods, ideally using renewable energy to produce hydrogen by splitting water. Although water electrolysis technology is becoming increasingly mature, the lack of hydrogen storage and transportation facilities severely hinders the development of the hydrogen economy. In the early stages of a hydrogen society, on-demand hydrogen production via water electrolysis has attracted much attention due to its advantages such as integrated production, storage, and transportation, high hydrogen purity, environmental friendliness, simple operation, and suitability for portable fuel cells. Current water electrolysis hydrogen production materials, i.e., chemical hydrogen storage materials, include metals (such as aluminum and magnesium), metal hydrides (such as magnesium hydride), and metal borohydrides (such as sodium borohydride and lithium borohydride). Aluminum, as a typical light metal, has been widely used for on-site hydrogen production due to its abundant resources, low cost, high hydrogen release density (11.1 wt% excluding water), and pollution-free byproducts. In addition, aluminum can be regenerated through the Hall-Heroult process using Al(OH)3 or AlOOH byproducts.

[0003] From a thermodynamic perspective, the hydrolysis reaction of aluminum (Equation (1)) is spontaneous. However, the dense Al2O3 and Al(OH)3 layers generated on the aluminum surface in the air and during the hydrolysis process respectively hinder the contact and diffusion mass transfer between aluminum and water, resulting in slow hydrolysis kinetics and low hydrogen production yield. The following strategies can be used to solve the problem of Al2O3 and Al(OH)3 passivation layers: (1) Controlling the composition of the hydrolysis solution, alloying, and combining with other compounds. (2) Using alkaline solutions instead of pure water for hydrolysis, which can effectively and continuously corrode and destroy the Al2O3 and Al(OH)3 passivation layers, ensuring that the hydrolysis reaction continues. Previous studies have shown that only when the alkali concentration is higher than 10 wt% can the continuous reaction between aluminum and water be achieved, thereby obtaining a higher hydrogen production yield and hydrogen production rate. However, the addition of a large amount of alkali will corrode the reactor and reduce the system's hydrogen release capacity. Alloying aluminum with low melting point metals such as Ga, In, Sn, and Bi can improve the reactivity of aluminum in water. However, the high cost of low-melting-point metals and their weight, which contributes nothing to hydrogen production, make this strategy uncompetitive.

[0004] Al + 6H2O → 2Al(OH)3+ 3H2(20-280 ℃)(1) Ball milling mixtures of aluminum with neutral salts, metal oxides, or metal hydrides can also effectively promote aluminum hydrolysis. Salts such as NaCl and KCl, due to their hard and brittle properties, can help break aluminum into fine particles during ball milling and can also destroy the Al2O3 passivation layer on the aluminum surface, thereby promoting aluminum hydrolysis. For example, Alinejad et al. (Int. J. Hydrogen Energy, 34(2009) 7934-7938) ball-milled aluminum with NaCl at a 1:1.5 molar ratio for 20 h, achieving a hydrolysis conversion rate close to 100%. Modification effects remain effective when aluminum is ball-milled with metal oxides such as Al2O3, TiO2, ZrO2, and Co3O4. For example, a 30% Al + 70% γ-Al2O3 composite material requires 20 h of hydrolysis at 22℃ to achieve complete hydrolysis, with an average hydrogen production rate of only 1.32 mL / min. -1 (J. Am. Ceram. Soc., 88 (2005) 977-979, Int. J. Hydrogen Energy, 35 (2010) 9561-9568). It is worth noting that the above method improves hydrogen production conversion by adding large amounts of additives that do not contribute to hydrogen production (neutral salts such as NaCl and KCl, or metal oxides such as Al2O3, TiO2, ZrO2, and Co3O4), but significantly reduces the amount of hydrogen produced per unit mass, i.e., the system's hydrogen release capacity. To overcome these problems, the advantages of each component's hydrolysis reaction can be integrated by combining it with metal borohydrides (such as NaBH4) or simple metal hydrides (such as LiH). However, due to the high cost of NaBH4 and LiH, these additives are not recommended for hydrogen production via hydrolysis.

[0005] In summary, current methods for improving the hydrolysis performance of aluminum hydrolysis still suffer from drawbacks such as low hydrogen production rates and yields, high costs, and poor reaction controllability. Therefore, the commercial application of aluminum hydrolysis hydrogen production technology is limited. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides an aluminum-based chemical hydrogen storage composite material and its preparation method. This invention employs a strategy of ball milling an aluminum-calcium alloy reaction under a hydrogen atmosphere, where the in-situ generated calcium hydride forms a tightly bonded composite material with the remaining aluminum. The preparation conditions are mild and the process is simple. This invention also provides the application of the prepared grain-level bonded aluminum-calcium hydride composite material in water electrolysis hydrogen production, exhibiting high rates and yields of hydrogen production.

[0007] This invention provides a method for preparing an aluminum-based chemical hydrogen storage composite material, comprising the following steps: An aluminum-calcium alloy is placed in a ball mill jar and evacuated. Then, hydrogen is introduced into the ball mill jar for ball milling to obtain the aluminum-based chemical hydrogen storage composite material, namely, an aluminum-calcium hydride composite hydrolysis hydrogen production material. The calcium hydride in this composite material is formed in situ, and aluminum and calcium hydride form a tight composite structure at the grain level.

[0008] The aluminum-calcium alloy is obtained by melting aluminum and calcium in a molar ratio of Al:Ca = 2:1 or 4:1. The melting temperature is controlled at 80-100 ℃ above the corresponding alloy liquidus temperature, and the melting time is 4-6 min.

[0009] Preferably, the aluminum-calcium alloy is Al2Ca or Al4Ca.

[0010] More preferably, the aluminum-calcium alloy is Al2Ca, which yields the aluminum-calcium hydride composite material with the highest hydrolysis hydrogen production rate and the best overall hydrolysis performance.

[0011] Preferably, the hydrogen filling pressure is 0.5-2.5 MPa.

[0012] All ball milling processes proposed in this invention are performed at room temperature.

[0013] Preferably, the ball milling process is a solid-phase ball milling method, the ball-to-material ratio is 30-50:1, and the milling time is 2.5-12.5 hours. To prevent overheating, the ball milling process can be paused for 30 minutes after 30 minutes before continuing.

[0014] Preferably, the ball milling process is performed using a planetary ball mill with a rotational speed of 250-400 r / min.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) Compared with the prior art, the present invention adopts a gas-solid reaction and ball milling at room temperature, which is simple and safe to operate, does not require special equipment or additives that do not contribute to hydrogen production, has good reaction controllability, low cost, and avoids the direct use of expensive calcium hydride.

[0016] (2) Calcium hydride formed in situ has high hydrolysis reactivity. Calcium hydride, which is tightly bound to aluminum, preferentially hydrolyzes to form Ca(OH)2, releasing a large amount of heat (Δ). H r o = -228.23 kJ mol -1 This opens the "gate," exposing fresh aluminum to react with water, thus promoting the hydrolysis of aluminum. More importantly, because Ca(OH)₂ is slightly soluble in water (K₂O₂), it... sp =4.6×10 -6), calcium hydride hydrolyzes to produce Ca around aluminum. 2+ and OH ¯ Local concentration field. In Ca 2+ and OH ¯ Under localized concentration conditions, the Al(OH)3 passivation layer formed on the aluminum surface will primarily further form Al2Ca3(OH). 12 It is destroyed by Ca2Al(OH)7·3H2O, leading to the rapid hydrolysis of fresh aluminum to produce hydrogen gas. Al2Ca3(OH)2 is another example. 12 For example, Al2Ca3(OH) 12 The formation occurs via the following reactions (Equations (2) and (3)). It is noteworthy that this occurs during the formation of Al₂Ca₃(OH)₃. 12 At the same time, OH ¯ The release can retain OH ¯ Ion concentration is favorable for the progress of reaction (2).

[0017] Al(OH)3+ OH ¯ [Al(OH)4] ¯ (2) 2[Al(OH)4] ¯ + 3Ca(OH)2 Al2Ca3(OH) 12 + 2OH ¯ (3) (3) In this invention, calcium hydride is generated in situ by reacting hydrogen with aluminum-calcium alloy. The reaction equation is Al2Ca+H2→2Al+CaH2 or Al4Ca+H2→4Al+CaH2. This can break the Al2O3 passivation layer, expose more fresh aluminum surface, and form a tightly bonded composite structure, maximizing the coupling effect and thus improving the hydrolysis of aluminum.

[0018] (4) The aluminum-calcium hydride hydrolysis hydrogen production material synthesized in this invention overcomes the disadvantage of reduced theoretical hydrogen release capacity in other composite systems. The hydrolysis performance of the aluminum-calcium hydride hydrolysis hydrogen production material prepared in this invention is superior to that of currently reported aluminum-based hydrolysis materials: it undergoes hydrolysis reaction at room temperature (35℃) and atmospheric pressure in pure water, with fast hydrolysis kinetics, and a hydrolysis rate of 1075.6 mL g in the first minute. -1 min -1 Hydrogen production from H2 via hydrolysis within 15 min yielded 1263.0 mL g. -1 H2. Attached Figure Description

[0019] Figure 1The XRD patterns of the products obtained after ball milling raw aluminum, raw Al2Ca and Al2Ca in an argon atmosphere or 2.5 MPa H2 for 10 h are shown. The examples corresponding to each spectral line in the figure are: 3) Comparative Example 1; 4) Example 1.

[0020] Figure 2 Hydrolysis hydrogen production curves of the products were obtained by ball milling raw aluminum, raw Al2Ca, and Al2Ca in an argon atmosphere or at 2.5 MPa H2 for 10 h.

[0021] Figure 3 XRD patterns (a) of the products obtained by ball milling raw aluminum, raw Al4Ca and Al4Ca in an argon atmosphere or 2.5 MPa H2 for 10 h are shown. The examples corresponding to each spectral line in the figure are: 3) Comparative Example 2; 4) Example 2; and the energy spectrum of raw Al4Ca (b).

[0022] Figure 4 Hydrolysis hydrogen production curves of raw aluminum, raw Al4Ca, and Al4Ca obtained by ball milling in an argon atmosphere or at 2.5 MPa H2 for 10 h are shown.

[0023] Figure 5 The XRD patterns of the products obtained after ball milling Al2Ca under different hydrogen pressures for 10 h are shown. The examples corresponding to each spectral line in the figure are: 2) Example 3; 3) Example 4; 4) Example 5.

[0024] Figure 6 Hydrogen production curves of Al2Ca obtained after ball milling for 10 h under different hydrogen pressures.

[0025] Figure 7 Hydrogen production curves of the product obtained by ball milling raw aluminum and Al2Ca at 1.0 MPa H2 and aluminum and calcium hydride at a molar ratio of 2:1 for 10 h were obtained.

[0026] Figure 8 The hydrogen production curves (a) of the product obtained by ball milling Al2Ca with H2 at 1.0 MPa for 10 h at different temperatures and its Arrhenius equation diagram (b) are shown.

[0027] Figure 9 XPS Al 2p spectrum of Al2Ca obtained after ball milling in argon atmosphere or 1.0 MPa H2 for 10 h.

[0028] Figure 10SEM images of the hydrolysis products of Al2Ca obtained by ball milling in an argon atmosphere for 10 h and (b) Al2Ca obtained by ball milling in 1.0 MPa H2 for 10 h; TEM image (c), selected electron diffraction pattern (d), high-resolution TEM image (e), and EDS surface scan image (f) of the product obtained by ball milling Al2Ca in 1.0 MPa H2 for 10 h.

[0029] Figure 11 XRD patterns of the hydrolysis products obtained by ball milling Al2Ca in an argon atmosphere for 10 h and Al2Ca in a 1.0 MPa H2 atmosphere for 10 h are shown.

[0030] Figure 12 The XRD patterns of the products obtained after Al2Ca was ball-milled at 1.0 MPa H2 for different times are shown. The examples corresponding to each spectral line in the figure are: 1) Example 6; 2) Example 7; 3) Example 8; 4) Example 4; 5) Example 9.

[0031] Figure 13 Hydrolysis hydrogen production curves of Al2Ca obtained after ball milling at 1.0 MPa H2 for different times. Detailed Implementation

[0032] The following embodiments are further illustrations of the present invention, but not limitations thereof.

[0033] Unless otherwise specified, the experimental materials and reagents used in this invention are all commercially available products commonly used in this technical field.

[0034] The following examples illustrate the preparation methods of Al2Ca and Al4Ca alloy powders: Al2Ca and Al4Ca intermetallic compound ingots were prepared by vacuum induction melting using pure aluminum (purity ≥99%) and pure calcium (purity ≥99%) at molar ratios of 2:1 and 4:1, respectively. The melting temperature was controlled at 80-100 °C above the corresponding alloy liquidus temperature, and the melting time was 4-6 min. Then, the obtained aluminum-calcium alloy ingots were polished with a grinding wheel to remove the contamination layer from the casting mold and the surface oxide layer. Finally, the ingots were crushed and passed through a 100-mesh sieve.

[0035] A typical hydrolysis experiment in the examples: First, approximately 0.1 g of powdered sample was placed into a Schlenk reaction flask in an argon-filled glove box, and the flask opening was sealed with a rubber stopper. Then, the Schlenk reaction flask was connected to the hydrolysis apparatus. Next, 10 mL of deionized water was injected into the hydrolysis reaction flask through the rubber stopper using a syringe. The sample then came into contact with the water to undergo the hydrolysis reaction, which was carried out using magnetic stirring (800-1000 r / min). The hydrogen production was continuously measured using the water displacement method. The precipitated hydrogen was collected in a Mendelssohn wash flask containing water, and the water was displaced into a beaker. The mass of the water discharged into the beaker was weighed using an electronic balance connected to a computer. The hydrogen conversion yield (Y) was calculated. hc The calculation formula for ) is as follows: Y hc =( V e / V t )×100%(4) Among them, V e and V t These represent the actual and theoretical hydrogen production rates, respectively. To obtain the activation energy, the Schlenk reaction flask was immersed in water baths at different temperatures (0, 25, and 35°C), and hydrolysis was performed using water at the corresponding temperatures. After hydrolysis, the hydrolysis byproducts were collected by freeze-drying.

[0036] Hydrolysis byproducts and aluminum-based composite hydrolyzed materials were characterized using powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Sample preparation was performed in a glove box. For XRD characterization, samples were covered with liquid paraffin to isolate them from airborne water and oxygen. Prepared SEM and TEM samples were rapidly transferred into the SEM and TEM sample chambers, where they were only briefly exposed to air.

[0037] In the following examples, ball milling was performed at room temperature.

[0038] Comparative Example 1 First, 1 g of Al₂Ca was weighed into a ball mill jar in a glove box under a 1 atm argon atmosphere, with a ball-to-material ratio of 50:1. The jar was then placed directly into a planetary ball mill (Pulverisette 5) and milled at 350 r / min for 10 h. To prevent overheating, milling was continued for 30 min followed by a 30 min pause. The resulting Al₂Ca hydrolysis hydrogen production material was then obtained.

[0039] Figure 1 Curve 3) in a) is the XRD pattern of the ball-milled product. Apart from diffraction peaks for Al₂Ca and a small amount of iron sloughed off during ball milling, no other phases show diffraction peaks. The ball-milled product was then hydrolyzed in pure water at 25°C to produce hydrogen. Figure 2As shown, due to the initial Al2O3 passivation layer, the original aluminum hydrolysis reaction hardly proceeds. When alloyed with Ca and ball-milled under an argon atmosphere, the hydrolysis performance of aluminum improves, with an average hydrolysis rate of 307.7 mL in the first 1 minute. g -1 min -1 Hydrogen gas was released, with only 312.1 mL released within 15 minutes. g -1 Hydrogen is produced, but the rate and yield of hydrogen production remain low.

[0040] Example 1 An aluminum-calcium hydride composite hydrolysis hydrogen production material, the preparation method of which includes the following steps: In a glove box under a 1 atm argon atmosphere, 1 g of Al₂Ca was weighed, mixed, and placed into a ball mill jar at a ball-to-material ratio of 50:1. The ball mill jar was then evacuated. Subsequently, hydrogen gas at 2.5 MPa was introduced into the ball mill jar. Finally, the ball mill jar was placed in a planetary ball mill (Pulverisette 5) at a milling speed of 350 r / min for 10 h, with a 30 min interval between milling cycles to prevent overheating. This resulted in a grain-level bonded aluminum-calcium hydride hydrolysis hydrogen production material.

[0041] Figure 1 Curve 4) in the figure is the XRD pattern of the ball-milled product. Only diffraction peaks of the Al and CaH2 phases are observed, indicating the successful preparation of the aluminum-calcium hydride composite hydrolysis hydrogen production material. Notably, the large half-width at half-maximum (FWHM) of the Al and CaH2 diffraction peaks indicate numerous defects and fine grains in the composite material. Hydrolysis of the prepared aluminum-calcium hydride composite hydrogen production material in pure water at 25°C showed a significantly improved hydrogen production rate and yield compared to Al2Ca after argon ball milling, with an average hydrolysis rate of 805.7 mL in the first minute. g -1 min -1 Hydrogen gas was released, with 1228.7 mL released within 15 minutes. g -1 Hydrogen (with a hydrogen conversion yield of 97%) exhibits rapid hydrolysis kinetics, high hydrogen production yield, and excellent hydrolysis hydrogen production performance. Figure 2 As shown, the hydrogen production rate and hydrogen production efficiency have been significantly improved, which is due to the synergistic effect of abundant defects, fine grains, and in-situ generated CaH2.

[0042] Comparative Example 2 First, 1 g of Al₄Ca was weighed into a ball mill jar in a glove box under a 1 atm argon atmosphere, with a ball-to-material ratio of 50:1. The jar was then placed directly into a planetary ball mill (Pulverisette 5) and milled at 350 r / min for 10 h. To prevent overheating, milling was continued for 30 min followed by a 30 min pause. The resulting Al₄Ca hydrolysis hydrogen production material was thus obtained.

[0043] Figure 3 Curve 2) in a is the XRD pattern of the prepared Al4Ca alloy, which shows a two-phase mixture of Al4Ca and Al2Ca, but from... Figure 3 The energy spectrum results in b show that the atomic ratio of Al to Ca is close to 4:1. Therefore, this invention still refers to this alloy material as Al4Ca. Figure 3 Curve 3) in section a is the XRD pattern of the ball-milled Al4Ca alloy product. The ball-milled product was then hydrolyzed in pure water at 25°C to produce hydrogen. (The remaining text appears to be incomplete and requires further context.) Figure 4 As shown, due to the initial Al2O3 passivation layer, the original aluminum hydrolysis reaction hardly proceeds. When alloyed with Ca and ball-milled under an argon atmosphere, the hydrolysis performance of aluminum improves, with an average hydrolysis rate of 97.5 mL in the first 1 minute. g -1 min -1 Hydrogen gas was released, with only 124.4 mL released within 15 minutes. g -1 Hydrogen is produced, but the rate and yield of hydrogen production remain low.

[0044] Example 2 A hydrogen production material by hydrolysis of an aluminum-calcium hydride composite is prepared in a manner that is basically the same as that in Example 1, except that the aluminum-calcium alloy is Al4Ca.

[0045] Figure 3 Curve 4) in section a is the XRD pattern of the ball-milled product. Only diffraction peaks of the Al and CaH2 phases are observed, indicating the successful preparation of the aluminum-calcium hydride composite hydrolysis hydrogen production material. Notably, the large half-width at half-maximum (FWHM) of the Al and CaH2 diffraction peaks indicate numerous defects and fine grains in the composite material. Hydrolysis of the prepared aluminum-calcium hydride composite hydrogen production material in pure water at 25°C showed a significantly improved hydrogen production rate and yield compared to Al4Ca after argon ball milling, with an average hydrolysis rate of 538.6 mL in the first minute. g -1 min -1 Hydrogen gas was released, with 1176.2 mL released within 15 minutes. g -1Hydrogen (with a 90% hydrogen conversion yield) exhibits rapid hydrolysis kinetics, high hydrogen production yield, and excellent hydrolysis hydrogen production performance. Figure 4 As shown, the hydrogen production rate and hydrogen production efficiency have been significantly improved, which is due to the synergistic effect of abundant defects, fine grains, and in-situ generated CaH2.

[0046] Example 3 An aluminum-calcium hydride composite hydrolysis hydrogen production material is prepared by a method that is basically the same as that in Example 1, except that the pressure of hydrogen gas introduced is 0.5 MPa.

[0047] Figure 5 Curve 2) in the figure is the XRD pattern of the ball-milled product. It is observed that the diffraction peak of Al₂Ca disappears, accompanied by the appearance of diffraction peaks of Al and CaH₂. Furthermore, Figure 5 The diffraction peak intensities of Al and CaH2 show that they hardly increase with increasing hydrogen pressure. This structural analysis indicates that Al2Ca is almost entirely converted to Al and CaH2, successfully realizing the preparation of an aluminum-calcium hydride composite hydrolysis hydrogen production material. Figure 6 As shown, the prepared aluminum-calcium hydride composite hydrolysis hydrogen production material exhibited excellent hydrolysis hydrogen production performance when hydrolyzed in pure water at 25℃, with an average hydrolysis rate of 884.5 mL in the first 1 minute. g -1 min -1 Hydrogen gas was released, with 1227.6 mL released within 15 minutes. g -1 Hydrogen gas. Even using only low hydrogen pressure can significantly promote the hydrolysis of Al.

[0048] Comparative Example 3 First, aluminum and calcium hydride were weighed at a molar ratio of 2:1 in a 1 atm argon atmosphere glove box. 1 g of the mixture, with a ball-to-material ratio of 50:1, was loaded into a ball mill jar, and the jar was sealed tightly. Next, the ball mill jar was placed directly into a planetary ball mill (Pulverisette 5) and milled at 350 r / min for 10 h. To prevent overheating, milling was continued for 30 min, followed by a 30 min pause. The final product was an aluminum-calcium hydride hydrolysis hydrogen production material. Figure 7 As shown, the hydrolysis hydrogen production rate and yield of this aluminum-calcium hydride hydrolysis hydrogen production material are also significantly improved, proving that calcium hydride can significantly promote the hydrolysis of aluminum.

[0049] Example 4 An aluminum-calcium hydride composite hydrolysis hydrogen production material is prepared by a method that is basically the same as that in Example 1, except that the pressure of hydrogen gas introduced is 1.0 MPa.

[0050] Figure 5Curve 3) in the figure is the XRD pattern of the ball-milled product. Only diffraction peaks of Al and CaH2 were observed, indicating that the preparation of the aluminum-calcium hydride composite hydrolysis hydrogen production material was successfully achieved. Figure 6 As shown, the hydrogen production yield further increased within 15 minutes, reaching a maximum of 1246.9 mL g, as the hydrogen pressure increased from 0.5 MPa to 1.0 MPa. -1 The hydrogen conversion yield was 98%. The average hydrolysis rate in the first minute was 832.4 mL. g -1 min -1 hydrogen.

[0051] The aluminum-calcium hydride hydrolysis hydrogen production material with grain-level bonding was hydrolyzed in water at different temperatures (0, 25, 35°C), and the reaction flasks were placed in constant temperature water baths at the corresponding temperatures. Figure 8 As shown in Figure a, the hydrogen production yield and rate of the aluminum-calcium hydride hydrolysis hydrogen production material significantly increased with increasing temperature. At 35℃, the aluminum-calcium hydride hydrolysis hydrogen production material achieved the fastest hydrolysis rate and the highest hydrogen production yield, with an average hydrolysis rate of 1075.6 mL in the first minute. g -1 min -1 Hydrogen gas was released, with 1263.0 mL released within 15 minutes. g -1 Hydrogen (hydrogen conversion yield 99.2%). The activation energy (E0) of the hydrolysis reaction of this aluminum-calcium hydride hydrolysis hydrogen production material was calculated through fitting. a The value is 52.29 kJ / mol. -1 The pre-exponential factor (A) is 6.21 × 10⁻⁶. 9 ( Figure 8 (b). The extremely large pre-exponential factor (A) is an important reason why this aluminum-calcium hydride hydrolysis hydrogen production material has a fast hydrolysis hydrogen production rate.

[0052] It is worth noting that the hydrolysis performance of this aluminum-calcium hydride hydrolysis hydrogen production material (Example 4) is superior to that of Comparative Example 3, which may be due to the different microstructures. To understand the mechanism by which in-situ calcium hydride formation improves Al hydrolysis performance, XPS (… Figure 9 ) and TEM ( Figure 10 Further investigation was conducted on the phase composition, structure, and morphology of the in-situ formed calcium hydride-aluminum composite material using XRD (cf), and the results were analyzed. Figure 11 ) and SEM ( Figure 10 The hydrolysis byproducts of (a) and (b) were studied and compared with those of ball-milled Al2Ca. Figure 9The two XPS peaks at ~73.8 and 71.5 eV correspond to Al in Al2O3, respectively. 3+ And Al 0 Al₂O₃ is formed by the slight oxidation of Al. From Figure 9 It can be seen from the aluminum-calcium hydride composite material that Al 0 The XPS peak of Al in Al2Ca was higher than that of Al in Al2Ca argon balloon milling. 0 The stronger peak indicates that the in-situ formation of calcium hydride exposes more fresh aluminum, thereby promoting the hydrolysis of aluminum. Figure 10 A series of diffraction rings corresponding to aluminum and calcium hydride appeared in the selected area electron diffraction pattern of d, consistent with the XRD results. This is shown in the high-resolution TEM image. Figure 10 The lattice fringes with an interplanar spacing of 0.299 nm (e) belong to the (111) plane of aluminum, while the lattice fringes of 0.278 nm and 0.272 nm belong to the (111) and (113) planes of calcium hydride, respectively. High-resolution TEM results show that the aluminum-calcium hydride composite material has many defects consistent with the XRD results, indicating that the composite material has high hydrolytic activity. Furthermore, as indicated by the dashed lines, aluminum and calcium hydride form a tight composite structure at the grain level, maximizing their coupling effect. Figure 10 As shown in f, aluminum and calcium elements are uniformly distributed, indicating that aluminum and calcium hydride are uniformly distributed in the complex. From Figure 11 It can be seen that the hydrolysis products of Al2Ca ball-milled under argon atmosphere consist of unreacted Al2Ca and CaAl2((OH)8(H2O)2)(H2O) 1.84 The composition changed, and the aluminum and calcium hydride in the hydrolysis products of the in-situ formed calcium hydride-aluminum complex disappeared, replaced by Ca2Al(OH)7·3H2O, Ca4Al2O7·9H2O, and Al2Ca3(OH). 12 And Al(OH)3. Among them, Al2Ca3(OH)3... 12 Al(OH)3 is the main hydrolysis product. Al2Ca3(OH)2 is another product. 12 The formation of Ca2Al(OH)7·3H2O can suppress the formation of a secondary Al(OH)3 passivation layer, which is beneficial to diffusion mass transfer and hydrolysis kinetics. Therefore, the hydrolysis products of the in-situ formed calcium-aluminum hydride complex exhibit high porosity and sponge-like aggregate morphology, while Al2Ca ball-milled under argon atmosphere exhibits an irregular bulk morphology with a porous structure. Figure 10 (a, b). Based on the above analysis, in-situ formed calcium hydride exhibits higher hydrolysis reactivity. Calcium hydride, tightly bound to aluminum, preferentially hydrolyzes to form Ca(OH)₂, releasing a large amount of heat (Δ). H r o = -228.23 kJ mol -1This opens the "gate," exposing fresh aluminum to react with water, thus promoting the hydrolysis of aluminum. More importantly, because Ca(OH)₂ is slightly soluble in water (K₂O₂), it... sp =4.6×10 -6 ), calcium hydride hydrolyzes to produce Ca around aluminum. 2+ and OH ¯ Local concentration field. In Ca 2+ and OH ¯ Under localized concentration conditions, the Al(OH)3 passivation layer formed on the aluminum surface will primarily consist of Al2Ca3(OH). 12 It is destroyed by Ca2Al(OH)7·3H2O, and the freshly exposed aluminum then rapidly hydrolyzes to produce hydrogen gas. Al2Ca3(OH) 12 For example, Al2Ca3(OH) 12 The formation occurs via the following reactions (Equations (2) and (3)). It is noteworthy that this occurs during the formation of Al₂Ca₃(OH)₃. 12 At the same time, OH ¯ Released to retain OH ¯ Ion concentration is favorable for the progress of reaction (2).

[0053] Al(OH)3+ OH ¯ [Al(OH)4] ¯ (2) 2[Al(OH)4] ¯ + 3Ca(OH)2 Al2Ca3(OH) 12 + 2OH ¯ (3) Example 5 An aluminum-calcium hydride composite hydrolysis hydrogen production material is prepared by a method that is basically the same as that in Example 1, except that the pressure of hydrogen gas introduced is 1.5 MPa.

[0054] Figure 5 Curve 4) in the figure is the XRD pattern of the ball-milled product. Only diffraction peaks for Al and CaH2 were observed, indicating that the preparation of the aluminum-calcium hydride composite hydrolysis hydrogen production material was successfully achieved. Figure 6 As shown, the rate and yield of hydrogen production from hydrolysis decreased slightly as the hydrogen pressure increased from 1.0 MPa to 1.5 MPa, with an average hydrolysis rate of 737.9 mL in the first minute. g -1 min -1 Hydrogen gas was released, with 1225.6 mL released within 15 minutes. g -1 hydrogen.

[0055] Example 6 An aluminum-calcium hydride composite hydrolysis hydrogen production material is prepared by a method that is basically the same as that in Example 4, except that the ball milling time is 2.5 h.

[0056] Figure 12 Curve 1) in the figure is the XRD pattern of the ball-milled product. It is observed that the XRD diffraction peaks of Al₂Ca almost disappear, while strong diffraction peaks of aluminum and calcium hydride appear, indicating that the preparation of the aluminum-calcium hydride composite hydrolysis hydrogen production material was successfully achieved after only a short ball milling time of 2.5 h. Figure 13 As shown, the prepared aluminum-calcium hydride composite hydrolysis hydrogen production material exhibited excellent hydrolysis hydrogen production performance when hydrolyzed in pure water at 25℃, with an average hydrolysis rate of 559.2 mL in the first 1 minute. g -1 min -1 Hydrogen gas was released, with 1137.7 mL released within 15 minutes. g -1 hydrogen.

[0057] Example 7 An aluminum-calcium hydride composite hydrolysis hydrogen production material is prepared by a method that is basically the same as that in Example 4, except that the ball milling time is 5.0 h.

[0058] Figure 12 Curve 2) in the figure is the XRD pattern of the ball-milled product. When the ball milling time increased from 2.5 h to 5.0 h, the XRD diffraction peaks of Al₂Ca completely disappeared, indicating an increase in the calcium hydride content in the aluminum-calcium hydride composite hydrolysis hydrogen production material. Figure 13 As shown, the hydrogen production rate and yield increased with increasing ball milling time from 2.5 h to 5.0 h, with an average hydrolysis rate of 872.8 mL in the first minute. g -1 min -1 Hydrogen gas was produced at a yield of 1194.1 mL within 15 minutes. g -1 hydrogen.

[0059] Example 8 An aluminum-calcium hydride composite hydrolysis hydrogen production material is prepared by a method that is basically the same as that in Example 4, except that the ball milling time is 7.5 h.

[0060] Figure 12 Curve 3) in the figure is the XRD pattern of the ball-milled product. After the ball-milling time exceeded 5.0 h, further increasing the ball-milling time did not significantly change the intensity of the diffraction peaks for aluminum and calcium hydride. Figure 13As shown, the prepared aluminum-calcium hydride composite hydrolysis hydrogen production material exhibited excellent hydrolysis hydrogen production performance when hydrolyzed in pure water at 25℃, with an average hydrolysis rate of 842.7 mL in the first 1 minute. g -1 min -1 Hydrogen gas was released, with 1186.0 mL released within 15 minutes. g -1 hydrogen.

[0061] Example 9 An aluminum-calcium hydride composite hydrolysis hydrogen production material is prepared by a method that is basically the same as that in Example 4, except that the ball milling time is 12.5 h.

[0062] Figure 12 Curve 5) in the figure is the XRD pattern of the ball-milled product. Only diffraction peaks of Al and CaH2 were observed, indicating that the preparation of the aluminum-calcium hydride composite hydrolysis hydrogen production material was successfully achieved. After increasing the ball milling time by 12.5 h, as shown... Figure 13 As shown, the prepared aluminum-calcium hydride composite hydrolysis hydrogen production material exhibited excellent hydrolysis hydrogen production performance when subjected to hydrolysis in pure water at 25℃, with an average hydrolysis rate of 778.9 mL in the first 1 minute. g -1 min -1 Hydrogen gas was released, with 1261.6 mL released within 15 minutes. g -1 Hydrogen. The slight decrease in the hydrogen production rate due to hydrolysis was caused by particle agglomeration resulting from prolonged ball milling.

[0063] The above description of the embodiments is only for the purpose of helping to understand the technical solution and core idea of ​​the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing an aluminum-based chemical hydrogen storage composite material, characterized in that, Includes the following steps: An aluminum-calcium alloy is placed in a ball mill jar and evacuated. Then, hydrogen is introduced into the ball mill jar for ball milling to obtain an aluminum-calcium hydride composite, which is the aluminum-based chemical hydrogen storage composite material.

2. The preparation method according to claim 1, characterized in that, The aluminum-calcium alloy is one or more of Al2Ca and Al4Ca.

3. The preparation method according to claim 1, characterized in that, The aluminum-calcium alloy is obtained by melting aluminum and calcium in a molar ratio of Al:Ca = 2:1 or 4:

1. The melting temperature is controlled at 80-100 °C above the corresponding alloy liquidus temperature, and the melting time is 4-6 min.

4. The preparation method according to claim 1, characterized in that, The hydrogen filling pressure is 0.5-2.5 MPa.

5. The preparation method according to claim 1, characterized in that, The ball milling process described is a solid-phase ball milling method.

6. The preparation method according to claim 1, characterized in that, The ball milling process is performed using a planetary ball mill with a rotation speed of 250-400 r / min and a ball-to-material ratio of 30-50:

1.

7. The preparation method according to claim 1, characterized in that, The ball milling process is carried out at room temperature for 2.5-12.5 hours.

8. The aluminum-based chemical hydrogen storage composite material prepared by the preparation method according to any one of claims 1-7.

9. The aluminum-based chemical hydrogen storage composite material according to claim 8, characterized in that, The calcium hydride in this composite material is formed in situ, and aluminum and calcium hydride form a tight composite structure at the grain level.

10. The application of the aluminum-based chemical hydrogen storage composite material according to claim 8 or 9 in hydrogen production by water electrolysis.

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