CN109972010B - Nano magnesium-based composite hydrogen storage material and preparation method thereof - Google Patents

Abstract

The invention relates to a nano-magnesium-based composite hydrogen storage material and a preparation method thereof. The main component of the material is magnesium, and it also contains various catalysts such as mixed rare earth, carbonyl nickel powder and graphite to improve its low-temperature hydrogen absorption performance. The material has a nanocrystalline structure, the grain size is 20-50 nanometers, and has excellent low-temperature hydrogen absorption kinetic properties. In the preparation method, vacuum induction smelting is used to first vacuum smelt pure magnesium and a certain amount of mixed rare earth to prepare a brittle magnesium-rare earth alloy ingot in which magnesium is in-situ doped with rare earth elements; then the obtained alloy is mixed with carbonyl nickel powder, Graphite powder and inert organic grinding aid are mixed, and a high-capacity magnesium-based composite hydrogen storage material is further prepared by mechanical ball milling. The material preparation method overcomes the wall sticking phenomenon during the mechanical ball milling of the magnesium-based hydrogen storage alloy, improves the material recovery rate, and obtains a high-capacity magnesium-based composite hydrogen storage material with excellent low-temperature hydrogen absorption performance.

Description

A kind of nanometer magnesium-based composite hydrogen storage material and preparation method thereof

technical field

The invention belongs to the technical field of hydrogen storage materials, and particularly relates to a high-capacity magnesium-based hydrogen storage material with excellent low-temperature hydrogen absorption kinetic performance and a preparation method.

Background technique

As a clean, efficient, abundant and sustainable ideal secondary energy, hydrogen energy is regarded as an energy material with the most development potential, and has received extensive attention worldwide. Safe and efficient hydrogen storage technology is one of the key links in the process of hydrogen energy utilization. The metal hydride method for hydrogen storage has the advantages of high bulk density, good reversibility, and high safety, and is considered to be the most promising hydrogen storage material. The reversible hydrogen storage capacity of magnesium is as high as 7.6 wt.%. In addition, magnesium has the advantages of abundant resources, low price, and environmental friendliness, and has great application prospects. Although magnesium satisfies many practical conditions as a hydrogen storage material, it cannot be applied to mobile hydrogen storage systems, especially in-vehicle fuel cell hydrogen supply devices. This is mainly due to the poor thermodynamic properties of pure magnesium for hydrogen storage, and the hydrogenation and dehydrogenation processes need to be carried out at temperatures above 300 °C. In addition, the hydrogen absorption and desorption reaction rate of pure magnesium is extremely slow, which cannot meet the requirements.

Mechanical ball milling is one of the effective methods to improve the hydrogen storage performance of magnesium-based materials. The particle size of the material obtained by the ball milling method is significantly reduced, and the surface activity is increased. The shearing, grinding and squeezing in the ball milling process produce a large number of defects inside the material, and even change the phase composition and crystal structure of the material, thereby affecting the physical and chemical properties of the material. Patent CN100358624 discloses a method for preparing magnesium/graphite composite hydrogen storage material by high-energy ball milling in a hydrogen atmosphere. The obtained magnesium-based material has a grain size of 70-100 nm, although the hydrogen storage performance of magnesium is greatly improved, But the reaction temperature is still high. Patent CN102418018 also discloses a preparation method of magnesium/carbon-supported nickel hydrogen storage alloy powder, which has better hydrogen absorption kinetic characteristics at 100°C. However, the preparation process of this material is extremely complicated, and there are difficulties in the production process.

Another unique advantage of mechanical ball milling is that it can compound materials in almost any state, including solids and solids, solids and liquids, and solids and gases with different physical properties. However, magnesium has a certain plasticity and toughness, and will adhere to the grinding ball and the tank wall during the mechanical ball milling process, resulting in uneven material composition. Therefore, it is of great significance to improve the sticking phenomenon during the ball milling of magnesium-based alloys.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a high-capacity magnesium-based composite hydrogen storage material and a preparation method for the synergistic catalysis of mechanical ball milling and multiple catalysts in view of the deficiencies of the current technology. The material takes magnesium as the main hydrogen-absorbing phase, the catalyst contained is mixed rare earth, carbonyl nickel powder and graphite, and the auxiliary agent in the preparation process is a volatile inert organic solvent. The preparation method is as follows: first, pure magnesium and a certain amount of mixed rare earth are vacuum smelted by a vacuum induction melting method to prepare a brittle magnesium-rare earth alloy ingot in which magnesium is in-situ doped with rare earth elements; then the obtained alloy is mixed with a certain proportion of carbonyl Nickel powder, graphite powder, and inert organic grinding aid are mixed, and the composite material is further prepared by mechanical ball milling; finally, the organic liquid grinding aid is removed under vacuum conditions to obtain a high-capacity magnesium-based composite hydrogen storage material. The above-mentioned method successfully overcomes the material sticking phenomenon in the process of mechanical ball milling, and can obtain a magnesium-based composite hydrogen storage material with a nanocrystalline structure of multiphase synergistic catalysis, thereby greatly improving the hydrogen absorption kinetics of the magnesium-based hydrogen storage material. characteristic. The composite hydrogen storage material provided by the invention can rapidly absorb hydrogen at 100° C. to meet practical requirements.

The technical scheme of the present invention is as follows:

A nano-magnesium-based composite hydrogen storage material, the main component of which is magnesium, and is prepared by synergistic catalysis of mixed rare earth, carbonyl nickel powder and graphite, and has a nano-crystalline structure and a grain size of 20-50 nanometers; and It has excellent low temperature hydrogen absorption kinetic properties; among them, mixed rare earths account for 10-15% of the mass of pure magnesium, carbonyl nickel powder accounts for 3-10% of the total mass of magnesium-rare earths, and graphite accounts for 3-5% of the total mass of magnesium-rare earths. %.

The excellent low-temperature hydrogen absorption kinetic performance of the magnesium-based composite hydrogen storage material is specifically that it can absorb 5-6.5 wt % of hydrogen within 30 seconds under the conditions of 100° C. and 3 MPa hydrogen pressure.

The preparation method of the magnesium-based composite hydrogen storage material comprises the following main steps:

a. Using magnesium and mixed rare earth metals as raw materials, vacuum induction melting method is used to prepare brittle magnesium-rare earth alloy ingots; wherein, the vacuum at the back of the melting furnace is 2.0×10 ^-2 Pa, and the protective gas is high-purity high-purity 0.04-0.06MPa pressure. Argon, the induction coil power during vacuum smelting is 8-10kW, and the melt holding time is 10-15 minutes; after the smelting is completed, it is poured into an ingot; the quality of the mixed rare earth is 10-10-10% of the mass fraction of the magnesium-rare earth alloy. 15%;

b. The obtained magnesium-rare earth alloy ingot is mechanically crushed into alloy powder below 100 mesh, then mixed with carbonyl nickel powder, graphite powder and organic liquid grinding aid, and ground with a planetary mechanical ball mill for 5-10 hours;

Wherein, the mass of the carbonyl nickel powder is 3-10% of the mass of the magnesium-rare earth alloy powder; the mass of the graphite powder is 3-5% of the mass of the magnesium-rare earth alloy powder; the organic liquid grinding aid The mass of the agent is 50-100% of the mass of the magnesium-rare earth alloy powder;

c. Vacuum-drying the ball-milled mixed material at room temperature to obtain a magnesium-based composite hydrogen storage material.

The mixed rare earth contains lanthanum, cerium, praseodymium, neodymium, samarium and other small amounts of rare earth elements and a very small amount of impurity elements, and the total content of rare earth elements is greater than 99.5%.

The carbonyl nickel powder refers to ultrafine nickel powder obtained by reducing carbonyl nickel, and the particle size range is 0.5-1 micron.

The organic liquid grinding aid can be one or more of ethanol, cyclohexane, hexane, n-heptane, benzene, toluene and tetrahydrofuran.

The purity of the high-purity argon is 99.999 Vol.%.

In the method for preparing the magnesium-based composite hydrogen storage material, there is basically no sticking phenomenon of the material in the process of mechanical ball milling.

The essential features of the present invention are:

The invention uses mixed rare earths in the preparation of high-capacity magnesium-based hydrogen storage materials, which not only improves the ball milling efficiency and overcomes the wall sticking phenomenon by smelting it with magnesium to form a brittle alloy, but also plays an important role in the process of hydrogen absorption and desorption. The nano-phase catalysis improves the low-temperature hydrogen absorption performance of the material.

The beneficial effects of the present invention are:

1) Mechanical ball milling is carried out with brittle magnesium-rare earth alloy as raw material, and graphite powder is added in the ball milling process, which improves the ball milling efficiency, overcomes the sticking effect during the ball milling process, and makes the sample recovery rate basically higher than 90%, up to 99%; 2) The synergistic catalysis of rare earth elements, graphite, and carbonyl nickel powder greatly improves the reversible hydrogen storage properties of magnesium, making the material rapidly absorb hydrogen at 100 °C, and its performance is better than the existing published literature. Metal hydride hydrogen storage systems for automobiles have shown good application prospects.

Description of drawings

FIG. 1 is a SEM microscopic topography diagram of the hydrogen storage material obtained in Example 1 of the present invention.

FIG. 2 is a SEM microscopic topography diagram of the hydrogen storage material obtained in Example 3 of the present invention.

3 is a TEM microscopic topography diagram of the hydrogen storage material obtained in Example 4 of the present invention after hydrogen absorption.

FIG. 4 is a SEM microscopic topography diagram of the hydrogen storage material obtained in Example 5 of the present invention.

FIG. 5 is the hydrogen absorption kinetic curve of the hydrogen storage material obtained in Example 1 of the present invention at different temperatures.

FIG. 6 is the hydrogen absorption kinetic curve of the hydrogen storage material obtained in Example 2 of the present invention at different temperatures.

FIG. 7 is the hydrogen absorption kinetic curve of the hydrogen storage material obtained in Example 3 of the present invention at different temperatures.

FIG. 8 is the hydrogen absorption kinetic curve of the hydrogen storage material obtained in Example 4 of the present invention at different temperatures.

FIG. 9 is the hydrogen absorption kinetic curve of the hydrogen storage material obtained in Example 5 of the present invention at different temperatures.

Detailed ways

The present invention will be further described in detail below in conjunction with the examples.

The carbonyl nickel powder is a well-known material, and refers to the ultrafine nickel powder obtained by reducing the carbonyl nickel powder. The carbonyl nickel powder used in the embodiment of the present invention has a particle size range of 0.5-1 micron.

The mixed rare earth is a well-known material, which refers to the rare earth metal mixture obtained after purification and smelting of natural rare earth ore in nature, including lanthanum, cerium, praseodymium, neodymium, samarium and other small amounts of rare earth elements and impurity elements, and the total content of rare earth elements. More than 99.5%, the proportion of each rare earth element is slightly different with the place of origin and batch, but it does not affect the use effect of the present invention; the mixed rare earth metals involved in the following examples were purchased from Baotou Rare Earth Research Institute (CAS: 62379-61-7), but The present invention is not limited to this.

Example 1

Put 1kg of pure magnesium ingot (purity greater than 99%) and 0.15kg (15wt%) of mixed rare earth metal into the magnesia crucible of vacuum induction melting furnace, evacuate to below 2.0×10 ^-2 Pa, and then fill with 0.04 -High-purity argon gas at a pressure of 0.06 MPa (purity of 99.999 Vol.%). Adjust the power of the intermediate frequency induction coil to 8-10kW, and heat the metal raw materials. After all the metal blocks are completely melted, continue to keep the temperature for 10-15 minutes to homogenize the alloy composition. After the smelting is completed, the alloy melt is poured into a circular ingot with a diameter of 30 mm in a cast iron mold, and the magnesium-rare earth alloy ingot is obtained after cooling to room temperature. The alloy ingot was mechanically pulverized and passed through a 100-mesh standard sieve, and then 5 g of magnesium-rare earth alloy powder, 0.25 g (5 wt %) of carbonyl nickel powder, 0.15 g (3 wt %) of graphite powder, and 5 g (100 wt %) of organic liquid grinding aid tetrahydrofuran were taken. ) was placed in a 300ml stainless steel vacuum ball mill jar, then put in agate grinding balls, and filled with 0.15MPa high-purity argon as protective gas after vacuuming. The ball-to-material ratio adopted in the embodiment of the present invention is 20:1, the rotational speed of the ball mill is 350 r/min, and the ball milling time is 10 hours. The ball-milled material is placed in a vacuum drying oven, and vacuum-dried at room temperature for more than 2 hours to obtain a magnesium-based hydrogen storage material. The degree of adhesion of the material is measured by the sample recovery rate, that is, the percentage of the mass of the recovered solid sample to the mass of the input solid raw material. The size of the recovery rate can reflect the sticking phenomenon of the material during the ball milling process. The lower the sample recovery rate, the more significant the sticking effect of the material during the ball milling process, and the less conducive to the material preparation. The material recovery rate in this example is about 88%.

The microstructure of the composite material was observed by SEM, and it was found that the material was composed of large particles formed by agglomeration of small particles, and the large particle size was 10-50 microns, as shown in Figure 1. The added nickel carbonyl powder and graphite are uniformly dispersed inside the material matrix under the action of mechanical ball milling to form a composite material. The material was activated and desorbed for 5 times at 300 °C with Sieverts equipment. After the kinetic properties were stabilized, the isothermal hydrogen absorption curve of the material was tested. The initial hydrogen pressure was 3MPa, and the test temperature was 300, 200, and 100 °C. The results As shown in Figure 5. It can be seen that the saturated hydrogen absorption of the material after 5 minutes at 300°C is 5.9 wt%. Lowering the temperature greatly improves the hydrogen absorption kinetics of the material. At 100 °C, the hydrogen absorption of the material can reach 5.7 wt% within 30 seconds, showing excellent low-temperature hydrogen absorption kinetics.

Example 2

The other steps of the material preparation method in this example are the same as those in Example 1, except that the ball milling time is 5 hours, the carbonyl nickel powder in the ball milling process is 0.5g (10wt%), and the graphite powder is 0.25g (5wt%) , the grinding aid is ethanol, and the added amount of the grinding aid is 2.5g (50wt%).

No obvious sticking phenomenon was found in the ball-milled material, and the material recovery rate was about 94%. The hydrogen absorption kinetic curve of the composite material after 5 times of hydrogen absorption and desorption activation is shown in FIG. 6 . It can be seen that the saturated hydrogen absorption of the material after 5 minutes at 300° C. is about 5.2 wt %, which is slightly lower than that of Example 1. The material also has good hydrogen absorption kinetics at 100 °C, and the hydrogen absorption amount can reach more than 5 wt% within 30 seconds.

Example 3

The other steps of the material preparation method in this example are the same as those in Example 1, except that the amount of rare earth added in the alloy smelting process is 0.1kg (10wt%), and the mass of carbonyl nickel powder in the ball milling process is 0.15g (3wt%) , the mass of graphite powder is 0.05g (1wt%), and the grinding aid is n-heptane.

The material after ball milling has obvious sticking phenomenon, and the sample recovery rate is about 68%. The SEM microstructure of the composite material of this embodiment is shown in FIG. 2 , and the material is also formed by clusters of fine particles, and the size of the large particles is 10-70 μm. The hydrogen absorption kinetic curve of the material after 5 times of hydrogen absorption and desorption activation is shown in Figure 7. It can be seen that the saturated hydrogen absorption of the material after 5 minutes at 300 °C is about 6.3 wt%, but the kinetic performance of hydrogen absorption of the material is not significantly improved at 100 °C, and the hydrogen absorption rate is much lower than that of Example 1 and Example 1. Example 2, this is because the graphite powder content in this example is low, the material composition after ball milling is not uniform enough, the carbonyl nickel powder cannot be uniformly dispersed in the alloy, and its catalytic effect is limited.

Example 4

The other steps of the material preparation method in this example are the same as those in Example 1, except that the amount of rare earth added during the alloy smelting process is 0.1 kg (10 wt%), and the grinding aid is cyclohexane.

No obvious sticking phenomenon was found in the ball-milled material, and the material recovery rate was about 93%. Figure 3 shows the TEM microstructure of the material of this example after 5 activation cycles of hydrogen absorption and desorption. It can be seen that the material is composed of crystal grains of 20-50 nanometers, and the overall appearance is nanocrystalline structure. The hydrogen absorption kinetic curve of the material after 5 times of hydrogen absorption and desorption activation is shown in Figure 8. It can be seen that the saturated hydrogen absorption of the material after 5 minutes at 300 °C is about 6.1 wt%. At 100°C, the magnesium-based composite material obtained in this example also has excellent hydrogen absorption kinetic properties, and the hydrogen absorption amount within 30 seconds can reach more than 6 wt%.

Example 5

The other steps of the material preparation method in this example are the same as those in Example 1, except that the amount of rare earth added during the alloy smelting process is 0.1kg (10wt%), the mass of graphite powder is 0.5g (10wt%), and the grinding aid is Cyclohexane.

The material after ball milling has no sticking phenomenon at all, and the material recovery rate is 99%. The SEM microstructure of the composite material of this example is shown in FIG. 4 , it can be seen that the material is composed of coarse particles, and the graphite powder is distributed among the alloy particles. The excessive lubrication produced by the higher graphite powder content resulted in a sharp drop in the ball milling efficiency, with little added nickel entering the interior of the alloy. The hydrogen absorption kinetic curve of the composite material after 5 times of hydrogen absorption and desorption activation is shown in FIG. 9 . It can be seen that the saturated hydrogen absorption of the material after 10 minutes at 300 °C is about 5.6 wt%. At lower temperature, the magnesium-based composite material in this example has poor kinetic properties, and the hydrogen absorption after 10 minutes at 100° C. is only 2.8 wt %. It can be seen that a higher amount of graphite is not conducive to improving the hydrogen absorption kinetics of the material.

The invention selects mixed rare earth elements and magnesium for alloy smelting. On the one hand, magnesium and rare earth elements form intermetallic compounds after vacuum induction melting, which improves the brittleness of magnesium-based alloys, and can improve the crushing efficiency and sticking of materials in the ball milling process. phenomenon; on the other hand, the rare earth elements in the composites precipitated nano-rare earth hydride secondary phases in situ during the hydrogenation process, which can be used as catalysts to improve the hydrogen storage performance of magnesium. A small amount of rare earth elements cannot make the alloy form a brittle phase, and too much rare earth elements will reduce the reversible hydrogen storage capacity of the material. After many experiments, it has been found that 10-15wt% of misch metal alloyed with magnesium has the best comprehensive performance. The lubricating effect of graphite can not only improve the sticking phenomenon in the ball milling process, but also improve the contact effect between the carbonyl nickel powder and the alloy matrix, promote the dispersion of nickel in the alloy matrix, and then improve the effect of nickel in the hydrogen absorption and desorption reaction of the material. catalytic efficiency. However, too much graphite produces excessive lubrication in the ball milling process. For example, the graphite content in Example 5 is 10wt%, which reduces the ball milling efficiency, which is not conducive to improving the hydrogen absorption rate and reversible hydrogen storage capacity of the material. By comparing the results of the above examples, it is considered that the material ratio provided in Example 4 has the best comprehensive hydrogen absorption performance.

Matters not addressed in the present invention are known in the art.

Claims (6)

1. A nanometer magnesium-based composite hydrogen storage material is characterized in that the main component of the material is magnesium, the material comprises multiple catalysts of mixed rare earth, carbonyl nickel powder and graphite, the material has a nanocrystal structure, the grain size of the material is 20-50 nanometers, and the material has excellent low-temperature hydrogen absorption dynamic performance; wherein, the mixed rare earth accounts for 10-15% of the pure magnesium, the carbonyl nickel powder accounts for 3-10% of the total mass of the magnesium-rare earth, and the graphite accounts for 3-5% of the total mass of the magnesium-rare earth;

the preparation method of the magnesium-based composite hydrogen storage material comprises the following main steps:

a. magnesium and mixed rare earth metal are used as raw materials, and vacuum induction melting is adoptedPreparing a brittle magnesium-rare earth alloy ingot by a smelting method; wherein the back bottom vacuum of the smelting furnace is 2.0 multiplied by 10⁻²Pa, the protective gas is high-purity argon with the pressure of 0.04-0.06MPa, the power of an induction coil during vacuum melting is 8-10kW, and the heat preservation time of a melt is 10-15 minutes; casting into cast ingots after smelting is finished; the mass of the mixed rare earth is 10-15% of the mass fraction of the magnesium-rare earth alloy;

b. mechanically crushing the magnesium-rare earth alloy ingot into alloy powder with the granularity of less than 100 meshes, uniformly mixing the alloy powder with carbonyl nickel powder, graphite powder and an organic liquid grinding aid, and grinding for 5-10 hours by using a planetary mechanical ball mill;

wherein, the mass of the carbonyl nickel powder is 3-10% of that of the magnesium-rare earth alloy powder; the mass of the graphite powder is 3-5% of that of the magnesium-rare earth alloy powder; the mass of the organic liquid grinding aid is 50-100% of that of the magnesium-rare earth alloy powder;

c. and (3) drying the mixed material subjected to mechanical ball milling in vacuum at room temperature to obtain the magnesium-based composite hydrogen storage material.

2. The nano magnesium-based composite hydrogen storage material as claimed in claim 1, wherein the magnesium-based composite hydrogen storage material has excellent low temperature hydrogen absorption kinetics of 5-6.5wt% hydrogen absorption within 30 seconds at 100 ℃ and 3MPa hydrogen pressure.

3. The nano magnesium-based composite hydrogen storage material of claim 1, wherein the mixed rare earth comprises lanthanum, cerium, praseodymium, neodymium, samarium and other minor rare earth elements and a very small amount of impurity elements, and the total content of the rare earth elements is more than 99.5%.

4. The magnesium-based composite hydrogen storage material as claimed in claim 1, wherein in the preparation method, the particle size of said nickel carbonyl powder is in the range of 0.5-1 μm.

5. The Mg-based composite hydrogen storage material as claimed in claim 4, wherein in the preparation method, the organic liquid grinding aid is one or more of ethanol, hexane, n-heptane, benzene, toluene and tetrahydrofuran.

6. The magnesium-based composite hydrogen storage material as claimed in claim 4, wherein in the preparation method, the purity of the high purity argon gas is 99.999 Vol.%.

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