Method for manufacturing porous magnesium, porous magnesium manufactured by the method, and hydrogen storage material containing hydrogen supported in the porous magnesium

Abstract

The present invention provides a method for producing porous magnesium through a simple solution process in which a magnesium precursor is added to a reducing agent solution and reacted therewith, porous magnesium produced by the method, and a hydrogen storage material including hydrogen supported on the porous magnesium.

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing porous magnesium that can be used as a hydrogen storage material, porous magnesium manufactured by the manufacturing method, and a hydrogen storage material containing hydrogen supported in the porous magnesium. [Background technology]

[0002] Fossil fuels, which are currently the most widely used energy source, produce greenhouse gases such as carbon dioxide and air pollutants such as fine dust, so it is essential to develop new renewable energy sources in order to reduce dependence on fossil fuels in the future.

[0003] Hydrogen, one of the new renewable energy resources, is an environmentally friendly energy resource that does not produce air pollutants when burned, and can be applied in a wide range of areas to almost all sectors of the energy system, including household and industrial fuel cells.

[0004] However, conventional methods of storing hydrogen in the form of compressed gas using high-pressure hydrogen storage tanks are difficult to store safely, as there is always a risk of explosion. Recently, research has been conducted into solid-state material-based storage methods that can replace conventional high-pressure hydrogen storage tanks.

[0005] Metal hydrides are known as hydrogen storage materials that have a high hydrogen storage capacity and, unlike conventional physical hydrogen storage methods, can store hydrogen at relatively low hydrogen partial pressures of 100 bar or less.

[0006] In order to improve the hydrogen storage performance of the metal hydride, there have been attempts to infiltrate a lightweight carbon-based porous matrix into the metal hydride to form a composite, but the conventional carbon porous matrix has a problem of low hydrogen storage capacity.In addition, carbon nanotubes, which have been extensively studied as a carbon-based porous matrix material, require a separate separation process to increase purity in order to maintain a constant pore size, which makes them less cost-competitive. Summary of the Invention [Problem to be solved by the invention]

[0007] One embodiment is to provide a method for producing porous structured magnesium that is solution-based and allows for a facile one-pot synthesis.

[0008] Another embodiment provides porous structure magnesium produced by the method for producing porous structure magnesium.

[0009] Another embodiment utilizes the porous structure of magnesium to provide a hydrogen storage material that allows for improved kinetics of hydrogen absorption and release processes and hydrogen storage at relatively low pressures. [Means for solving the problem]

[0010] According to one embodiment, a method for producing porous structured magnesium is provided, comprising the step of adding a magnesium precursor to a reducing agent solution.

[0011] The magnesium precursor may include a compound prepared by dissolving a salt containing magnesium.

[0012] The magnesium-containing salt may include MgCl2.

[0013] The reducing agent solution may be a lithium-based reducing agent solution.

[0014] The magnesium precursor may include a mixture prepared by dissolving together a magnesium-containing salt and a transition metal compound.

[0015] The transition metal compounds may include salts containing Ni, Co, Ti or combinations thereof.

[0016] According to another embodiment, there is provided porous structure magnesium produced by the above-mentioned production method.

[0017] The porous magnesium is 10 2 / g or less.

[0018] The porous magnesium may have a large number of voids, and the average width of the voids may be 50 nm or less.

[0019] The porous magnesium may be doped with a transition metal.

[0020] The transition metal may include Co, Ni, Ti or a combination thereof.

[0021] Another embodiment provides a hydrogen storage material comprising hydrogen supported on the porous structure of magnesium. Effect of the Invention

[0022] According to one embodiment, unlike conventional porous structure synthesis methods such as template method, dealloying method, PVD method, etc., a method is provided that can easily obtain porous structure magnesium by a simple process of adding a magnesium precursor to a strong reducing agent solution, and the magnesium produced by the method has an excellent hydrogen storage capacity unlike conventional porous structure metals, and can be very usefully used as a new hydrogen storage medium. In addition, unlike conventional manufacturing methods, the manufacturing method according to one embodiment is very simple and very easy to apply to mass production processes at an industrial level, not at a laboratory level. [Brief description of the drawings]

[0023] [Figure 1] FIG. 2 is a diagram showing how hydrogen gas is adsorbed into bulk magnesium with a non-porous structure.

[0024] [Diagram 2] FIG. 2 is a diagram showing hydrogen gas being adsorbed into porous magnesium according to one embodiment.

[0025] [Diagram 3] FIG. 1 is a diagram showing how MgCl2, a magnesium precursor, is added to lithium naphthalenide, a strong reducing agent solution, and the MgCl2 is reduced to porous magnesium.

[0026] [Figure 4] This is a photo showing the reduction reaction proceeding when magnesium precursor MgCl2 is added to lithium naphthalenide, a strong reducing agent solution.

[0027] [Diagram 5] This is a TEM image of porous magnesium produced after the reduction reaction was completed.

[0028] [Figure 6-7] These are TEM and SEM images of porous magnesium produced after the reduction reaction was completed.

[0029] [Figure 8] This is a comparison of how hydrogen gas is adsorbed onto magnesium with a non-porous structure (left) and a porous structure (right).

[0030] [Figure 9] 1A to 1C are diagrams sequentially illustrating how hydrogen gas is adsorbed into porous magnesium according to one embodiment.

[0031] [Figure 10-11] 11A-11C are graphs showing hydrogen adsorption performance for magnesium of a porous structure according to one embodiment, respectively.

[0032] [Figure 12-13] 10A-10C are graphs showing hydrogen desorption performance for magnesium of a porous structure according to one embodiment, respectively.

[0033] [Figure 14] 1 is an XRD graph showing the as-synthesized structure (before hydrogen adsorption) of a porous magnesium structure according to one embodiment.

[0034] [Figure 15] 1 is an XRD graph showing the structure of porous magnesium according to one embodiment after hydrogen desorption.

[0035] [Figure 16] 1 is a TEM photograph showing the structure of a porous magnesium structure according to one embodiment after hydrogen has been desorbed.

[0036] [Figure 17-18] 11A-11C are graphs showing hydrogen adsorption performance of Ni-doped porous structures versus magnesium according to one embodiment, respectively.

[0037] [Figure 19-20] 10A-10C are graphs showing hydrogen desorption performance for magnesium of Ni-doped porous structures according to one embodiment, respectively;

[0038] [Figure 21-22] 11A-11C are graphs showing hydrogen adsorption performance versus magnesium for a Co-doped porous structure according to one embodiment.

[0039] [Figure 23-24] 10A-10C are graphs showing hydrogen desorption performance for Co-doped porous structure magnesium according to one embodiment, respectively; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings, in which: FIG. 1 is a schematic diagram of a method for manufacturing a semiconductor device according to the present invention; This specification does not describe all elements of the embodiments, and omits general content in the technical field to which the present invention pertains or content that overlaps between the embodiments.

[0041] In addition, when a part is said to "comprise" a certain component, this does not mean that other components are excluded, but that other components may be further included, unless otherwise specified to the contrary. The singular expression includes the plural expression, unless there is a clear exception in the context.

[0042] In this specification, when a part such as a layer, film, region, or plate is said to be "on" another part, this includes not only the case where the part is "directly on" the other part, but also the case where there is another part between them. Conversely, when a part is said to be "directly on" another part, it means that there is no other part between them.

[0043] A method for producing porous magnesium according to one embodiment will now be described.

[0044] Hydrogen has the highest weight-specific energy density of all substances. (Hydrogen's lower heating value (LHV) is 120 kJ / g or less.) Hydrogen is extremely abundant on Earth, and is a next-generation, environmentally friendly energy source that can replace petroleum energy sources. Currently, multiple attempts are being made simultaneously around the world to use hydrogen to produce electricity and to promote desalinization. (From recent attempts to use hydrogen as a means of transportation to develop commercial vehicles such as taxis and buses, to more distant attempts to desalinate seawater, hydrogen is attracting the most attention as a next-generation energy source, and this is an unarguable point.)

[0045] However, to use hydrogen as an energy source, a hydrogen storage system capable of storing hydrogen is first required, but conventional physical hydrogen storage systems require high pressure (350-700bar) and an extremely low temperature extreme environment of -252.8℃ or less, which results in low energy density per volume. In addition, there is a risk of explosion, and there are always concerns about stability, and hydrogen stored in this way is expensive, making it uneconomical.

[0046] For this reason, various attempts have been made to develop new systems for storing hydrogen, but a satisfactory hydrogen storage medium has yet to be developed.

[0047] The inventors of the present invention, after accurately recognizing the above-mentioned background and the problems and limitations to date, conducted extensive research while searching for materials from all over the world for many years, and ultimately discovered that by modifying magnesium to a porous structure, specifically a nanoporous structure, it is possible to easily store hydrogen even at low pressures and to construct a safe and efficient hydrogen storage system, thereby completing the present invention.

[0048] Theoretically, magnesium has a high hydrogen storage capacity of 7.6% by weight, but because it is a light metal, it has a high weight energy density. In addition, because it is an element that is abundant on Earth, it is advantageous in terms of price, has a moderate equilibrium pressure for hydrogen, and hydrogen can be stored even at a relatively low hydrogen pressure of 100 bar or less. In addition, it has a high reversible energy density of 9 MJ / kg, and has many other advantages.

[0049] However, the hydrogen absorption / desorption rate is too slow, which is disadvantageous in terms of kinetics, and the hydrogen release process requires high temperatures of over 330℃, and above all, magnesium has the fatal drawback of being difficult to completely hydrogenate inside. Furthermore, magnesium is a highly reactive element and is easily oxidized in air. Despite the advantages mentioned above, magnesium has not been able to be used as a hydrogen storage medium due to these fatal drawbacks.

[0050] However, according to one embodiment, the magnesium (bulk Mg) is modified to a nanoporous structure, more specifically a transition metal doped nanoporous structure, thereby overcoming all of the above mentioned shortcomings and providing a hydrogen storage medium with a level of excellence not previously available.

[0051] More precisely, one embodiment provides a method for synthesizing nanoporous magnesium in a one-pot solution process using a magnesium precursor from the beginning, rather than modifying the bulk Mg.

[0052] That is, one embodiment provides a method for producing porous structured magnesium by adding a magnesium precursor to a reducing agent solution.

[0053] Magnesium produced by the production method according to one embodiment has a nanoporous structure, which can significantly improve hydrogen adsorption / desorption performance.

[0054] Specifically, the magnesium may structurally collapse due to the volume expansion that occurs every time hydrogen is absorbed / released repeatedly. However, the magnesium produced by the production method according to one embodiment has a nanoporous structure, which i) significantly reduces the risk of such structural collapse, ii) reduces the Mg ligament size, which is advantageous in terms of kinetics by reducing the distance that hydrogen travels to react with magnesium, and iii) increases the surface area that can react with hydrogen, which reduces the equilibrium pressure (P eq ) is reduced, iv) the amount of magnesium that cannot react inside can be reduced, and the level of hydrogenation can be significantly increased, and v) high temperatures are not required when releasing hydrogen.

[0055] Thus, by using a manufacturing method according to one embodiment, magnesium with a nanoporous structure can be easily obtained, which can facilitate hydrogen storage even at low pressures and can be an important medium for constructing a safe and efficient hydrogen storage system.

[0056] That is, in one embodiment, a new solid hydrogen storage material is provided by making magnesium, which has a porous structure that has hardly been studied so far, have a nanoporous structure, and this allows easy mass production by solution-based one-pot synthesis, thereby providing a new method for manufacturing a new solid hydrogen storage material. (Conventional porous structure synthesis methods include a template method and a dealloying method, but since neither of these are solution-based synthesis methods, one-pot synthesis is impossible, and the quality of the finally manufactured porous structure is not suitable for storing solid hydrogen safely and efficiently at low pressure.)

[0057] For example, the magnesium precursor may include a compound prepared by dissolving a magnesium-containing salt.

[0058] For example, the magnesium-containing salt may include MgCl2.

[0059] When the magnesium-containing salt MgCl2 is added to a reducing agent solution, the following reaction occurs as shown in Reaction Scheme 1. [Reaction Scheme 1] MgCl2+2e- →Mg+2Cl-

[0060] In other words, when MgCl2 is added to the reducing agent solution, the volume change per mole between MgCl2 and pure magnesium can be exploited to easily synthesize porous structures via chemical reduction.

[0061] For example, the reducing agent solution may be a lithium-based reducing agent solution.

[0062] When a lithium-based reducing agent solution is used as the reducing agent solution, MgCl2 may be easily reduced to Mg due to a reduction potential difference.

[0063] For example, lithium naphthalenide may be used as the lithium-based reducing agent solution, and lithium naphthalenide is a strong reducing agent, and lithium ions generated by the reduction reaction may be easily dissolved in the THF solution used during the reaction. However, the type of the lithium-based reducing agent solution is not necessarily limited thereto, and any combination of metals and radical anions may be used as the reducing agent solution.

[0064] Adding the magnesium precursor to a reducing agent solution to produce porous magnesium is a very simple method for synthesizing porous magnesium that has been attempted for the first time, and the porous structure produced by this synthesis method has pores with a width of about 50 nm or less, which is very advantageous for safely and effectively storing and releasing solid hydrogen at low pressure.

[0065] For example, the magnesium precursor may include a mixture prepared by dissolving together a magnesium-containing salt and a transition metal compound.

[0066] That is, according to one embodiment of the method, a magnesium precursor including a mixture prepared by dissolving the magnesium-containing salt and the transition metal compound together may be added to the reducing agent solution, in which case bimetallic magnesium having a porous structure can be synthesized by doping with the transition metal, and the hydrogen adsorption / desorption rate can be further improved compared to before doping with the transition metal (kinetic improvement). In other words, the doping with the transition metal can act as a catalyst for the hydrogen adsorption / desorption performance of magnesium having a nanoporous structure.

[0067] For example, the transition metal may include, but is not necessarily limited to, Ni, Co, Ti, or combinations thereof.

[0068] On the other hand, in one embodiment, a method for producing porous magnesium using a magnesium precursor is claimed, but in the case of highly reactive metals other than magnesium, the same method as in one embodiment can be applied to produce porous metals.

[0069] According to another embodiment, there is provided porous structure magnesium produced by the above-mentioned production method.

[0070] For example, due to the advantage of its porous structure, the porous magnesium according to one embodiment can react with a significant amount of hydrogen and exhibits improved kinetics in the process of absorbing and releasing hydrogen, so that the porous magnesium manufactured by the manufacturing method according to one embodiment can be found to be very effective as a storage medium that can store and reuse hydrogen.

[0071] For example, the porous magnesium may have a large number of voids, and the average width of the voids may be 50 nm or less (see FIG. 5).

[0072] For example, the porous magnesium structure may be doped with a transition metal.

[0073] For example, the transition metal may include, but is not necessarily limited to, Co, Ni, Ti, or combinations thereof.

[0074] Another embodiment provides a hydrogen storage material comprising hydrogen supported on the porous structure of magnesium.

[0075] The above-mentioned embodiments of the present invention will be described in more detail with reference to the following examples. However, the following examples are merely for illustrative purposes and are not intended to limit the scope of the present invention.

[0076] Fabrication of nanoporous magnesium structures As shown in FIG. 8, magnesium having a nanoporous structure was synthesized by adding a magnesium precursor containing MgCl2 to a lithium naphthalenide reducing agent solution and then removing the lithium salt (dissolution).

[0077] Rating 1 SEM and TEM images of the synthesized nanoporous magnesium were taken, and the results are shown in Figures 5 to 7. As can be seen from Figures 5 to 7, the synthesized nanoporous magnesium contains pores having a width of 50 nm or less.

[0078] Hydrogen adsorption on nanoporous magnesium structures As shown in Figure 10, hydrogen gas was adsorbed into the nanoporous magnesium synthesized above. Specifically, (1) hydrogen gas was adsorbed (transported) onto the surface of the nanoporous magnesium, (2) hydrogen gas (H2) was separated (dissociated) into two hydrogen atoms from the surface of the nanoporous magnesium, and (3) chemical adsorption of hydrogen atoms was performed. Then, (4) hydrogen atoms were transferred (diffusion) from the surface of the nanoporous magnesium to its center, and (5) finally, nucleation and growth into MgH2 (hydride formation) were performed, and the nanoporous magnesium was used as a hydrogen storage material.

[0079] -Analysis of hydrogen adsorption / desorption performance of nanoporous Mg 11 to 14, it can be seen that as the hydrogen adsorption / desorption cycle progresses, the rate becomes faster and the storage capacity increases, indicating that the nanoporous magnesium according to one embodiment has a much lower energy barrier than non-porous magnesium.

[0080] -Analysis of structure before and after hydrogen adsorption / desorption cycling (XRD, TEM analysis) 15 to 18 show that the (002) peak before hydrogen storage was very high, whereas the (002) peak after cycling became significantly lower. From this, it can be inferred that the Mg crystalline state gradually recovered to an equilibrium state during the hydrogen cycling process, improving the hydrogen storage performance.

[0081] -Hydrogen storage performance and activation energy of Mg / Ni Bimetal and Mg / Co Bimetal From Figures 19 to 26, it can be seen that the introduction of small amounts of transition metals Ni and Co significantly accelerates the hydrogen absorption / desorption kinetics and shortens the activation process required. (This is consistent with the XRD results of Mg / Ni and Mg / Co, which show a low (002) peak even before cycling.) Furthermore, as a result of activation energy calculation, it can be seen that the energy barrier in hydrogen absorption / desorption was measured to be lower than that of porous magnesium not doped with transition metals. (In particular, the energy barrier in hydrogen desorption is very low.) Generally, the introduction of transition metals into magnesium reduces the hydrogen storage capacity, but it can be seen that the introduction (doping) of transition metals into the nanoporous magnesium can further improve the kinetics while maintaining a high hydrogen storage capacity (without reducing the hydrogen storage capacity).

[0082] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also belong to the scope of the present invention.

Claims

1. A method for producing porous structured magnesium comprising the step of adding a magnesium precursor to a reducing agent solution.

2. 2. The method for producing porous magnesium according to claim 1, wherein the magnesium precursor comprises a compound produced by dissolving a salt containing magnesium.

3. The magnesium-containing salt is MgCl 2 3. The method for producing porous magnesium according to claim 2, comprising:

4. 2. The method for producing porous magnesium according to claim 1, wherein the reducing agent solution is a lithium-based reducing agent solution.

5. 2. The method for producing porous magnesium according to claim 1, wherein the magnesium precursor comprises a mixture prepared by dissolving a magnesium-containing salt and a transition metal compound together.

6. 6. The method for producing porous magnesium according to claim 5, wherein the transition metal compound comprises a salt containing Ni, Co, Ti or a combination thereof.

7. 2. Magnesium having a porous structure produced by the method of claim 1.

8. The porous magnesium is 10 2 8. Porous structure magnesium according to claim 7, characterized in that it has a BET surface area of ​​less than or equal to 1.0 g / g.

9. The porous magnesium according to claim 7, characterized in that the porous magnesium has a large number of voids, and the average width of the voids is 50 nm or less.

10. The porous magnesium according to claim 7, wherein the porous magnesium is doped with a transition metal.

11. 11. The porous structure magnesium of claim 10, characterized in that the transition metal comprises Co, Ni, Ti or a combination thereof.

12. A hydrogen storage material comprising hydrogen supported on the porous magnesium according to any one of claims 7 to 11.

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