Technology for surface modification of LaNi5 rare earth hydrogen storage material through CeO2

Abstract

The invention discloses a method for improving the cycling stability and the dynamic performance of a LaNi5 rare earth hydrogen storage material through a CeO2 surface modification LaNi5 rare earth hydrogen storage material technology. By coating or doping the CeO2 protective layer on the surface of the LaNimaterial, a plurality of problems faced by the traditional rare earth hydrogen storage material are effectively solved. After modification, the hydrogen dissociation energy barrier is remarkably reduced, for example, the hydrogen dissociation energy barrier is reduced from 120 kJ / mol to 80-90 kJ / mol, and the hydrogen diffusion speed is greatly increased. Experimental data show that the cycle life of the modified material can reach more than 1000 times, and the modified material shows excellent tolerance in an impurity gas environment containing HS or CO. The technology is suitable for a fuel cell hydrogen storage tank, a vehicle-mounted hydrogen energy system and industrial hydrogen purification equipment, and has a wide application prospect.

Description

Technical Field

[0001] The present invention focuses on the technical field of hydrogen storage materials and is committed to solving the key problems in the practical application of rare earth hydrogen storage materials. Specifically, the present invention proposes an innovative method, namely a method of surface modification of LaNi by CeO 2 on rare earth hydrogen storage materials to form a nanoscale protective layer, thereby significantly improving the cycle stability and kinetic performance of the materials and opening up a new path for the development of hydrogen storage materials. 5 Background Art

[0002] In the context of the global energy transition, hydrogen energy, as a clean and efficient energy carrier, has received extensive attention. Hydrogen storage materials are a key link in the large-scale application of hydrogen energy. Among them, LaNi 5 as a typical AB 5 type rare earth hydrogen storage alloy exhibits many advantages. Its theoretical hydrogen storage capacity can reach 1.4 wt%, with great hydrogen storage potential; at the same time, at room temperature, it has good reversibility and can maintain relatively stable performance during the hydrogen absorption and desorption processes, providing convenience for practical applications. However, LaNi 5 faces a series of severe technical challenges in practical applications. First, the hydrogen dissociation energy barrier on the material surface is as high as 120 kJ / mol. This relatively high energy barrier makes the dissociation process of hydrogen atoms on the material surface difficult, directly resulting in slow hydrogen absorption and desorption kinetics. For example, in an actual hydrogen storage application scenario, when rapid hydrogen release is required to meet energy demands, due to the slow hydrogen dissociation rate, sufficient hydrogen cannot be provided in time, seriously affecting the efficiency of energy supply. Secondly, in an actual hydrogen environment, there are often impurity gases such as H 2 S and CO. LaNi 5 is extremely prone to chemical poisoning in such an environment. The impurity gases react with the active sites on the material surface, resulting in the inactivation of the active sites. Taking a hydrogen environment containing 0.1% H 2 S as an example, the hydrogen storage capacity retention rate of unprocessed LaNi 5 is only 28% after 200 cycles in this environment, greatly reducing the service life and performance of the material. In addition, LaNi 5 will exhibit volume expansion during repeated hydrogen absorption and desorption processes, with an expansion rate of about 20%. This large volume change will generate stress inside the material, and as the number of cycles increases, the material gradually pulverizes. Generally, its cycle life is less than 300 times, which greatly limits the long-term stable application of LaNi 5 ​​At present, although the physical coating method in the prior art can block the entry of external impurities into the material to a certain extent, due to the lack of catalytic activity, it cannot increase the diffusion rate of hydrogen inside the material, and has limited effect on improving the hydrogen absorption and desorption kinetic performance of the material. Although the alloying method can improve the material performance in some aspects, such as improving the strength of the material, etc., it is difficult to balance catalytic activity and interface stability, and it is difficult to fundamentally solve the problems of high hydrogen dissociation energy barrier, chemical poisoning, and pulverization mentioned above. Therefore, it is urgent to develop a surface modification technology that is efficient, low-cost and can significantly improve the performance of LaNi 5 materials. SUMMARY OF THE INVENTION

[0003] The present invention provides a surface protection method for CeO 2 modified LaNi 5 hydrogen storage materials, including the following steps, as shown in the appendix Figure 1 :[[]] 1. Preparation of precursor solution: Dissolve cerium nitrate [Ce(NO 3 ) 3 ·6H 2 O] in deionized water to prepare a solution with a concentration in the range of 0.05 - 0.2 mol / L. In this process, in order to ensure that a stable complex structure can be formed among the components in the solution, citric acid is added as a complexing agent, and the molar ratio of Ce³ + to citric acid is strictly controlled between 1:1.5 - 1:2.5; 2. Sol-gel process: Adjust the pH of the solution to between 3.5 - 4.5 by adding a suitable alkaline substance (such as ammonia water). This pH range is conducive to the formation reaction of the sol-gel. Subsequently, place the solution in a water bath environment at 60 - 80 °C and continuously stir for 2 - 4 hours. In this process, the solution gradually undergoes hydrolysis and polymerization reactions, and finally forms a uniform and transparent sol. Under the condition of stirring in a 70 °C water bath for 3 hours, a sol with better quality can be obtained, and its internal structure is stable, which is conducive to the subsequent loading process; 3. Surface pretreatment of LaNi 5 : Select LaNi 5 alloy powder with a particle size in the range of 50 - 100 μm. This particle size range can not only ensure that the material has a large specific surface area, which is conducive to the hydrogen storage reaction, but also avoid problems such as agglomeration caused by too small particle size. The selected LaNi 5 alloy powder is ultrasonically cleaned successively with 0.1 mol / L dilute hydrochloric acid, absolute ethanol and deionized water. Dilute hydrochloric acid can effectively remove the oxides on the material surface, absolute ethanol can further remove the residual acid solution and other organic substances on the surface, and deionized water is used to thoroughly clean the material surface to ensure that the material surface is clean; 4. CeO 2 Loading: Immerse the surface-pretreated LaNi 5 powder into the above-prepared sol. To enable the sol to fully penetrate into the pores and surface of the LaNi 5 powder, the vacuum impregnation method is adopted, and the impregnation time is controlled within 1 - 2 hours. After the vacuum impregnation is completed, take out the sample and dry it at 80°C for 12 hours to cure the sol on the surface of the LaNi 5 powder, forming a film layer containing CeO 2 precursor; 5. Heat treatment: Place the dried sample in an argon-protected environment for roasting treatment. The roasting temperature is controlled at 350 - 450°C, and the time is 2 - 4 hours. Under argon protection, the sample can be prevented from being oxidized at high temperatures, ensuring the smooth progress of the heat treatment process. After roasting, the CeO 2 precursor in the sol is transformed into CeO 2 nanoparticles, which are uniformly loaded on the surface of the LaNi 5 material, forming a nanoscale protective layer. In the finally obtained LaNi 2 composite material with a nanoscale CeO 5 protective layer, the CeO 2 loading amount is 1 - 5% of the total mass of the material, and the particle size of the CeO 2 particles is 5 - 15 nm. Description of the Drawings

[0004] Figure 1 This is a flow chart of implementing the technology of surface-modifying LaNi5 rare earth hydrogen storage material by CeO2 in the present invention. Detailed Embodiment Embodiment

[0005] In this embodiment, by using a medium CeO 2 loading amount (3.5%) and optimized impregnation time (1.2 hours), the hydrogen dissociation activation energy is significantly reduced on the premise of ensuring interface stability, and at the same time, the anti-poisoning ability of the material in an environment containing CO is improved. The specific steps are as follows: (1) Preparation of precursor solution: Weigh 3.91 g of Ce(NO 3 ) 3 ·6H 2 O and dissolve it in 45 mL of deionized water to prepare a 0.12 mol / L solution, and add 2.52 g of citric acid (the molar ratio of Ce³ + to citric acid is 1:2.0); (2) Sol-gel process: Adjust the pH to 3.7 with ammonia water, heat and stir in a water bath at 68°C for 2.8 hours to form a uniform and transparent sol; (3)LaNi 5 Surface pretreatment: 15 g of LaNi 5 alloy powder (particle size 55 - 75 μm) was ultrasonically cleaned with 0.12 mol / L dilute hydrochloric acid, absolute ethanol, and deionized water for 25 minutes each to thoroughly remove surface oxides; (4)CeO 2 Loading: The pretreated LaNi 5 powder was immersed in the sol, vacuum impregnated for 1.2 hours, and then dried at 90 °C for 11 hours; (5)Heat treatment: Under argon protection, it was calcined at 410 °C for 3 hours to obtain a composite material with a CeO 2 loading of 3.5% of the total mass of the material and a particle size of 9 - 13 nm. Performance test: For this composite material, at 28 °C and a hydrogen pressure of 1.5 MPa, the hydrogen dissociation activation energy of the modified material decreased to 85 kJ / mol (120 kJ / mol for the unmodified material), and the hydrogen absorption rate increased by 2.8 times; after cycling 400 times in hydrogen containing 0.06% CO, the capacity retention rate was 87%. XRD analysis showed that the CeO 2 grain size was stable at 11 nm. After cycling 1100 times at room temperature and normal pressure, the capacity retention rate was 91%, and the pulverization rate was less than 1.5%. Example

[0006] In this example, through the combination of a higher precursor concentration (0.18 mol / L) and low-temperature short-time calcination (370 °C), the efficient loading of CeO 2 nanoparticles (7 - 10 nm) was achieved, significantly improving the corrosion resistance of the material in an H 2 S environment. The specific steps are as follows: (1)Preparation of precursor solution: Weigh 6.08 g of Ce(NO 3 ) 3 ·6H 2 O and dissolve it in 55 mL of deionized water to prepare a 0.18 mol / L solution, and add 4.21 g of citric acid (the molar ratio of Ce³ + to citric acid is 1:2.3); (2)Sol - gel process: Adjust the pH to 4.4 with nitric acid, heat and stir in a water bath at 72 °C for 3.2 hours to form a uniform and transparent sol; (3)LaNi 5 Surface pretreatment: 20 g of LaNi 5 alloy powder (particle size 80 - 100 μm) was ultrasonically cleaned with 0.08 mol / L dilute hydrochloric acid, absolute ethanol, and deionized water for 18 minutes each; (4) CeO 2 Loading: Immerse the pretreated LaNi 5 powder into the sol, impregnate it under vacuum for 1.6 hours, and then dry it at 88 °C for 13 hours; (5) Heat treatment: Calcinate it at 370 °C for 2.8 hours under argon protection to obtain CeO 2 composite material with a CeO loading of 4.5% of the total mass of the material and a particle size of 7 - 10 nm. Performance test: For this composite material, at 35 °C and a hydrogen pressure of 1.8 MPa, the hydrogen diffusion coefficient is increased to 2.5×10 - ⁻¹¹ m² / s (for the unmodified material it is 9.0×10 - ⁻¹² m² / s), and the hydrogen absorption time is shortened to 2.2 minutes; after cycling 150 times in hydrogen containing 0.15% H 2 ₂S, the capacity retention rate reaches 78% (for the unmodified material it is 18%), and after cycling 1300 times at normal temperature and pressure, the capacity retention rate is 89%. SEM shows that the coating is intact without peeling. Example

[0007] In this example, by increasing the CeO 2 loading (5%) and prolonging the calcination time, the hydrogen storage stability of the material under high - pressure conditions is optimized, and at the same time, the tolerance to complex impurity gases (such as mixed H 2 ₂S and CO) is enhanced. The specific steps are as follows: (1) Preparation of precursor solution: Weigh 7.83 g of Ce(NO 3 ) 3 ₃·6H 2 ₂O and dissolve it in 65 mL of deionized water to prepare a 0.2 mol / L solution, and add 5.76 g of citric acid (the molar ratio of Ce³ + ⁺ to citric acid is 1:2.5); (2) Sol - gel process: Adjust the pH to 4.5 with ammonia water, heat and stir in a water bath at 78 °C for 4 hours to form a high - viscosity transparent sol; (3) Surface pretreatment of LaNi 5 : Ultrasonically clean 18 g of LaNi 5 alloy powder (particle size 90 - 110 μm) with 0.2 mol / L dilute hydrochloric acid, absolute ethanol, and deionized water for 30 minutes each to ensure the surface is completely clean; (4) CeO 2 loading: Immerse the pretreated LaNi 5 powder into the sol, impregnate it under vacuum for 2 hours, and then dry it at 95 °C for 15 hours; (5) Heat treatment: Calcined at 430 °C for 4 hours under argon protection to obtain CeO 2 composite material with a loading of 5% of the total mass of the material and a particle size of 10 - 15 nm. Performance test: For this composite material, at 40 °C and a hydrogen pressure of 2.5 MPa, the hydrogen dissociation activation energy is reduced to 78 kJ / mol (120 kJ / mol for the unmodified material), and the hydrogen absorption rate is increased by 3.5 times; after cycling 300 times in a mixed gas containing 0.1% H 2 S and 0.05% CO, the capacity retention rate is 83% (18% for the unmodified material), and after cycling 800 times under high pressure (3 MPa) conditions, the capacity retention rate is 88%. SEM shows that the material structure is intact and there is no obvious volume expansion. Example

[0008] This example uses a low CeO 2 loading amount (1.5%) and a low-temperature short-time calcination process to focus on improving the hydrogen absorption and desorption kinetic performance of the material in a low-temperature environment (such as -10 °C). The specific steps are as follows: (1) Preparation of precursor solution: Weigh 2.17 g of Ce(NO 3 ) 3 ·6H 2 O and dissolve it in 30 mL of deionized water to prepare a 0.05 mol / L solution, and add 1.44 g of citric acid (the molar ratio of Ce³ + to citric acid is 1:1.5); (2) Sol-gel process: Adjust the pH to 3.5 with nitric acid, heat and stir in a water bath at 62 °C for 2 hours to form a low-viscosity transparent sol; (3) Surface pretreatment of LaNi 5 : Ultrasonically clean 5 g of LaNi 5 alloy powder (particle size 30 - 50 μm) with 0.05 mol / L dilute hydrochloric acid, absolute ethanol, and deionized water for 10 minutes each to remove surface impurities; (4) CeO 2 loading: Immerse the pretreated LaNi 5 powder into the sol, vacuum impregnate for 1 hour, and then dry at 70 °C for 8 hours; (5) Heat treatment: Calcined at 350 °C for 2 hours under argon protection to obtain CeO 2 composite material with a loading of 1.5% of the total mass of the material and a particle size of 4 - 8 nm. Performance test: For this composite material, at -10 °C and a hydrogen pressure of 0.5 MPa, the hydrogen diffusion coefficient is increased to 1.2×10 -¹¹ m² / s (the unmodified material is 5.0×10 - ¹² m² / s), and the hydrogen absorption time is shortened to 4 minutes; after cycling 500 times in low-temperature hydrogen containing 0.03% H 2 S, the capacity retention rate is 89%, and after cycling 2000 times at a low temperature (-20 °C), the capacity retention rate is 94%. XRD analysis shows that the CeO 2 grain size is stable at 6 nm.

[0009] In the field of fuel cells, the performance of the hydrogen storage tank directly affects the endurance and stability of the fuel cell. When the CeO 2 modified LaNi 5 hydrogen storage material is applied to the hydrogen storage tank of the fuel cell, due to its excellent hydrogen storage performance and cycle stability, it can increase the hydrogen storage capacity of the hydrogen storage tank, and maintain stable performance during multiple charge and discharge cycles, thereby effectively improving the endurance of the fuel cell, enhancing its working stability at the same time, and reducing fuel cell failures caused by hydrogen storage problems; In the on-vehicle hydrogen energy system, the storage and release efficiency of hydrogen is a key factor affecting vehicle performance. The hydrogen storage material prepared by this technology can improve the storage and release efficiency of hydrogen, enabling the vehicle to obtain the required hydrogen more quickly during operation, thereby enhancing the power performance and acceleration performance of the vehicle and improving the overall usage experience of the vehicle; In industrial production, strict requirements are imposed on the purity of hydrogen. When the hydrogen storage material of the present invention is applied to industrial hydrogen purification equipment, it can effectively remove impurity gases in hydrogen, such as H 2 S, CO, etc., by using the CeO 2 modification layer on its surface, improve the purity of hydrogen, meet the requirements of industrial production for high-quality hydrogen, and ensure the smooth progress of the industrial production process and the stability of product quality.

Claims

1. A method for improving the performance of LaNi5 rare earth hydrogen storage materials by modifying the surface of LaNi5 rare earth hydrogen storage materials with CeO2, characterized in that: The following steps are involved: (1) Prepare cerium nitrate precursor solution, add citric acid as a complexing agent, Ce³ + The molar ratio with citric acid is 1:1.5-1:2.5; (2) adjusting the pH to 3.5-4.5, heating and stirring to form a uniform and transparent sol; (3) performing surface pretreatment on the LaNi5 alloy powder to remove surface oxides; (4) immersing the pretreated LaNi5 powder into the sol, vacuum impregnating and then drying; (5) calcining under argon protection to obtain a LaNi5 composite material with a CeO2 nanoscale protective layer.

2. The method according to claim 1, characterized in that The concentration of the cerium nitrate precursor solution is 0.05-0.2 mol / L.

3. The method according to claim 1, characterized in that The calcination temperature is 350-450° C., and the calcination time is 2-4 hours.

4. The method according to claim 1, characterized in that The CeO2 loading amount is 1-5% of the total mass of the material, and the particle size of CeO2 particles is 5-15nm.

5. The method according to claim 1, characterized in that The particle size of the LaNi5 alloy powder is 50-100 μm.

6. A LaNi5 hydrogen storage material having a CeO2 nanoscale protective layer prepared by any method of claims 1-5, characterized in that: The hydrogen dissociation activation energy of the material is 80-90 kJ / mol, the hydrogen absorption rate at room temperature is increased by 2-3 times, and the hydrogen diffusion coefficient is increased by 1 order of magnitude.

7. The hydrogen storage material according to claim 6, characterized in that After 1000 cycles at room temperature and pressure, the capacity retention rate is ≥90%.

8. The hydrogen storage material according to claim 6, characterized in that After circulating 200 times in hydrogen containing 0.1% H2S, the capacity retention rate is ≥80%; after circulating 500 times in hydrogen containing 0.05% CO, the capacity retention rate is ≥85%.

9. Use of the hydrogen storage material according to any one of claims 6 to 8 in a fuel cell hydrogen storage tank, a vehicle-mounted hydrogen energy system or an industrial hydrogen purification device.

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