Magnesium-based hydrogen storage material and method for preparing the same

Abstract

A method for preparing a magnesium-based hydrogen storage material, includes: a Mg—Ce—Ni family amorphous alloy is prepared by a rapid cooling process; the amorphous alloy is pulverized, so as to obtain a amorphous powder; the amorphous alloy is activated, so as to obtain a MgH.sub.2—Mg.sub.2NiH.sub.4—CeH.sub.2.73 family nanocrystalline composite; the abovementioned composite is carried out a hydrogen absorption and desorption cycle, then the composite is placed in a pure Ar atmosphere for passivation, finally, the passivated composite is oxidized, so as to obtain a MgH.sub.2—Mg.sub.2NiH.sub.4—CeH.sub.2.73—CeO.sub.2 family nanocrystalline composite.

Claims

1. A method for preparing a magnesium-based hydrogen storage material, comprising the steps of: (1) a Mg—Ce—Ni family amorphous alloy is prepared by a rapid cooling process; (2) the amorphous alloy is pulverized, so as to obtain an amorphous powder; (3) the amorphous alloy is activated, so as to obtain a MgH.sub.2—Mg.sub.2NiH.sub.4—CeH.sub.2.73 family nanocrystalline composite; (4) the abovementioned composite is carried out a hydrogen absorption and desorption cycle, then the composite is placed in a pure Ar atmosphere for passivation, (5) finally, the passivated composite is oxidized, so as to obtain a MgH.sub.2—Mg.sub.2NiH.sub.4—CeH.sub.2.73—CeO.sub.2 family nanocrystalline composite.

2. A method according to claim 1, wherein the amorphous alloy prepared in step (1) is a (x+2y) Mg-2zCe-yNi amorphous alloy, wherein x+3y+2z=100, 20≦x≦80, 5≦y≦20, and 2.5≦z≦10; the composite prepared in step (3) is a xMgH.sub.2-yMg.sub.2NiH.sub.4-2zCeH.sub.2.73 nanocrystalline composite; and the composite prepared in step (5) is a xMgH.sub.2-yMg.sub.2NiH.sub.4-zCeH.sub.2.73-zCeO.sub.2 nanocrystalline composite.

3. A method according to claim 2, wherein the method for preparing a amorphous alloy in step (1) comprises a cerium ingot and a nickel ingot are mixed in a molar ratio of 1:1, carried out a melting at 2000-3000° C. by using an arc melting process, so as to obtain a rare earth-nickel intermediate alloy; then a magnesium ingot and the rare earth-nickel intermediate alloy is carried out an induction melting, wherein the molar percentage of magnesium is 60-90%, and the melting temperature is 1000-1500° C.; finally the resulting alloy is carried out a rapid cooling by using a single-roll melt-spinning process.

4. A method according to claim 3, wherein the rotating speed of the copper roller in the single-roll melt-spinning process is 30-40 m/s, and the vacuum degree in the vacuum chamber is 5×10.sup.−5 Pa.

5. A method according to claim 1, wherein the pulverization in step (2) is carried out by using a ball mill, with a milling time of 1-2 hours, a ball/powder ratio of 40:1, and a rotating speed of 250 rpm.

6. A method according to claim 1, wherein the activation conditions in step (3) comprise hydrogen absorption is carried out at 250° C. and under 10 MPa hydrogen atmosphere for 3 hours.

7. A method according to claim 1, wherein the water and oxygen contents in the Ar atmosphere in the passivation in step (4) is both less than 10 ppm.

8. A method according to claim 1, wherein the process of the hydrogen absorption and desorption circle in step (4) comprises the hydrogen absorption is carried out at 300° C. and under a hydrogen pressure of 3 MPa for 0.5 hour, then the hydrogen desorption is carried out under a vacuum of 0.002 MPa for 0.5 hour, and cycled for 15 times sequentially.

9. A method according to claim 1, wherein the oxidation of the composite in step (5) comprises the composite is placed in a sealed container, then the container is opened in air, filled with air, and placed for 5-15 hours.

10. A magnesium-based hydrogen storage material prepared by any method of claim 1, wherein the material has a formula of xMgH.sub.2-yMg.sub.2NiH.sub.4-zCeH.sub.2.73-zCeO.sub.2, wherein x+3y+2z=100, 20≦x≦80, 5≦y≦20, and 2.5≦z≦10; and the material has a crystal particle size of 10-15 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a XRD graph of a Mg—Ce—Ni amorphous alloy prepared by rapid cooling;

(2) FIG. 2 shows a XRD graph of the product obtained after the Mg—Ce—Ni amorphous alloy is carried out the first hydrogen absorption under different atmospheres, it can be seen that after the hydrogen absorption, the Mg—Ce—Ni amorphous alloys are all converted into MgH.sub.2—Mg.sub.2NiH.sub.4—CeH.sub.2.73 family nanocomposite;

(3) FIG. 3 shows kinetics curves of the hydrogen absorption and desorption cycle of the Mg—Ce—Ni amorphous alloy;

(4) FIG. 4 shows a XRD graph of the material (a) before and (b) after the oxidation;

(5) FIG. 5 shows a DSC curve of the material (a) before and (b) after the oxidation, with the commercial available pure MgH.sub.2 (c) as a control;

(6) FIG. 6 shows a TEM graph of CeO.sub.2/CeH.sub.2.73 grown in situ, it can be seen that (a) they are grown together symbiotically, (b) sometimes can also form a shell-core structure;

(7) FIG. 7 shows a hydrogen desorption kinetics curve graph of the xMgH.sub.2-yMg.sub.2NiH.sub.4-zCeH.sub.2.73-zCeO.sub.2 (x+3y+2z=100, 20≦x≦80, 5≦y≦20, 2.5≦z≦10) composite before and after the oxidation, and after 5 and 20 cycles.

DETAILED DESCRIPTION

(8) The present invention is further described in details below in combination with the examples, but the embodiments of the present invention are not limited thereto, and as for the process parameters which are not specifically noted, reference can be made to the conventional techniques.

Example 1

(9) The cerium ingot (99.9%) and the nickel ingot (99.99%) were mixed in a molar ratio of 1:1, and carried out a melting at 2500° C. by an arc-melting process, and the melting was repeated for 8 times. The cerium-nickel intermediate alloy and the magnesium ingot (99.99%) were mixed, with a magnesium content of a molar ratio of 80%, and prepared by using an induction melting process, with a melting temperature of 1300° C.; the prepared Mg.sub.80Ce.sub.10Ni.sub.10 alloy was carried out a rapid cooling, with a rotating speed of the copper roller of 30 m/s, and an vacuum degree in the vacuum chamber of 5×10.sup.−5 Pa, so as to obtain an amorphous strip, with a width of 2 mm, and a thickness of 0.04 mm. The amorphous strip was pulverized by using a ball mill, with a milling time of 1.5 h, a ball/powder ratio of 40:1, and a rotating speed of 250 rpm, then passed through a 200 mesh sieve so as to obtain an amorphous powder.

(10) The amorphous powder was activated, with an activation atmosphere of 10 MPa+250° C., and after it was activated for 3 hours, the hydrogen absorptions of the alloys were all approached to saturation. After the activation, a 60MgH.sub.2-10Mg.sub.2NiH.sub.4-10CeH.sub.2.73 composite was obtained, and the crystal particle was very small, with a crystal particle size of 10-15 nm as calculated. Then the activated samples were carried out a hydrogen absorption and desorption cycle, wherein the hydrogen absorption was carried out at 300° C. and under a hydrogen pressure of 3 MPa for 0.5 hour, then the hydrogen desorption was carried out under a vacuum of 0.002 MPa for 0.5 hour, and they were cycled sequentially for 15 times, then placed in a glove box under a pure Ar atmosphere, and placed for one week to passivate their surfaces; finally the cycled samples were placed in a sealed tube, then the tube was opened in air, filled with air, and placed for 8 hours for oxidation, so as to obtain a 60 MgH.sub.2-10Mg.sub.2NiH.sub.4-5CeH.sub.2.73-5CeO.sub.2 composite as CeH.sub.2.73 was oxidized into CeO.sub.2. FIG. 5 was a XRD graph of the oxidized sample. After the oxidation (in this case, the molar ratio between CeO.sub.2 and CeH.sub.2.73 was about 1:1), the hydrogen desorption initial temperature of the sample was reduced by about 210° C. as compared to that of the pure MgH.sub.2. As shown in FIG. 7, CeO.sub.2/CeH.sub.2.73 was symbiotic, and can also form a shell-core structure. After the oxidation, the hydrogen desorption kinetics were significantly improved and as shown in FIG. 8, after 20 hydrogen absorption and desorption cycles, the hydrogen desorption performance can also be appropriately maintained.

Example 2

(11) The cerium ingot (99.9%) and the nickel ingot (99.99%) were mixed in a molar ratio of 1:1, and carried out a melting at 2500° C. by using an arc-melting process, and the melting was repeated for 8 times. The cerium-nickel intermediate alloy and the magnesium ingot (99.99%) were mixed, with a magnesium content of a molar ratio of 60%, and prepared by using an induction melting process, with a melting temperature of 1300° C.; the prepared Mg.sub.60Ce.sub.20Ni.sub.20 alloy was carried out a rapid cooling, with a rotating speed of the copper roller of 30 m/s, and a vacuum degree in the vacuum chamber of 5×10.sup.−5 Pa, so as to obtain an amorphous strip, with a width of 2 mm, and a thickness of 0.04 mm. The amorphous strip was pulverized by using a ball mill, with a milling time of 2 h, a ball/powder ratio of 40:1, and a rotating speed of 250 rpm, then passed through a 200 mesh sieve so as to obtain an amorphous powder.

(12) The amorphous powder was activated, with an activation atmosphere of 10 MPa+250° C., and after it was activated for 3 hours, the hydrogen absorptions of the alloys were all approached to saturation. After the activation, a 20MgH.sub.2-20Mg.sub.2NiH.sub.4-20CeH.sub.2.73 composite was obtained, and the crystal particle was very small, with a crystal particle size of 10-15 nm as calculated. Then the activated samples were carried out a hydrogen absorption and desorption cycle, wherein the hydrogen absorption was carried out at 300° C. and under a hydrogen pressure of 3 MPa for 0.5 hour, then the hydrogen desorption was carried out under a vacuum of 0.002 MPa for 0.5 hour, and they were cycled sequentially for 15 times, then placed in a glove box under a pure Ar atmosphere, and placed for one week to passivate their surfaces; finally the cycled samples were placed in a sealed tube, then the tube was opened in air, filled with air, and placed for 5 hours for oxidation, so as to obtain a 20 MgH.sub.2-20Mg.sub.2NiH.sub.4-10CeH.sub.2.73-10CeO.sub.2 composite as CeH.sub.2.73 was oxidized into CeO.sub.2.

Example 3

(13) The cerium ingot (99.9%) and the nickel ingot (99.99%) were mixed in a molar ratio of 1:1, and carried out a melting at 2500° C. by using an arc-melting process, and the melting was repeated for 8 times. The cerium-nickel intermediate alloy and the magnesium ingot (99.99%) were mixed, with a magnesium content of a molar ratio of 90%, and prepared by using an induction melting process, with a melting temperature of 1300° C.; the prepared Mg.sub.90Ce.sub.5Ni.sub.5 alloy was carried out a rapid cooling, with a rotating speed of the copper roller of 30 m/s, and a vacuum degree in the vacuum chamber of 5×10.sup.−5 Pa, so as to obtain an amorphous strip, with a width of 2 mm, and a thickness of 0.04 mm. The amorphous strip was pulverized by using a ball mill, with a milling time of 2 h, a ball/powder ratio of 40:1, and a rotating speed of 250 rpm, then passed through a 200 mesh sieve so as to obtain an amorphous powder.

(14) The amorphous powder was activated, with an activation atmosphere of 10 MPa+250° C., and after it was activated for 3 hours, the hydrogen absorptions of the alloys were all approached to saturation. After the activation, a 80MgH.sub.2-5Mg.sub.2NiH.sub.4-5CeH.sub.2.73 composite was obtained, and the crystal particle was very small, with a crystal particle size of 10-15 nm as calculated. Then the activated samples were carried out a hydrogen absorption and desorption cycle, wherein the hydrogen absorption was carried out at 300° C. and under a hydrogen pressure of 3 MPa for 0.5 hour, then the hydrogen desorption was carried out under a vacuum of 0.002 MPa for 0.5 hour, and they were cycled sequentially for 15 times, then placed in a glove box under a pure Ar atmosphere, and placed for one week to passivate their surfaces; finally the cycled samples were placed in a sealed tube, then the tube was opened in air, filled with air, and placed for 5 hours for oxidation, so as to obtain a 80 MgH.sub.2-5Mg.sub.2NiH.sub.4-2.5CeH.sub.2.73-2.5CeO.sub.2 composite as CeH.sub.2.73 was oxidized into CeO.sub.2.

(15) The abovementioned particular embodiments are only the preferred examples of the present invention, and the claims of the present invention are not limited thereto, and any other changes made without departing from the technical solutions of the present invention and other equivalent replacements, are all encompassed in the scope of the present invention.