A method for producing porous magnesium, porous magnesium produced by the above method, and a hydrogen storage material containing hydrogen supported on 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 producing magnesium having a porous structure that can be utilized as a hydrogen storage material, magnesium having a porous structure produced by the production method, and a hydrogen storage material containing hydrogen supported on the magnesium having a porous structure.

Background Art

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

[0003] Hydrogen, which is one of the new renewable energy resources, is an environmentally friendly energy resource that does not generate air pollutants during combustion and can be applied in various fields of almost all energy systems, including household and industrial fuel cells.

[0004] However, the conventional hydrogen storage method in the form of compressed gas using a high-pressure hydrogen storage tank is difficult to store hydrogen safely, such as the constant risk of explosion. Recently, a solid-state material-based storage method that can replace the conventional high-pressure hydrogen storage tank has been studied.

[0005] As hydrogen storage materials, metal hydrides are known that have a high hydrogen storage capacity and can be stored even at a relatively low hydrogen partial pressure of 100 bar or less, unlike conventional physical hydrogen storage methods.

[0006] To improve the hydrogen storage performance of the aforementioned metal hydrides, there have been attempts to composite them by impregnating them into a lightweight carbon-based porous matrix. However, conventional carbon porous matrices have the problem of low hydrogen storage capacity. Furthermore, carbon nanotubes, which have been the subject of much research as a carbon-based porous matrix material, require a separate separation process to increase purity in order to maintain a constant pore size, resulting in a lack of price competitiveness. [Overview of the project] [Problems that the invention aims to solve]

[0007] One embodiment provides a method for producing porous magnesium that can be easily synthesized in a solution-based, one-pot method.

[0008] Another embodiment is to provide porous magnesium produced by the method for producing porous magnesium described above.

[0009] Another embodiment involves utilizing the porous structure of magnesium to provide a hydrogen storage material that enables kinetic improvements in 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 magnesium is provided, which includes the step of adding a magnesium precursor to a reducing agent solution.

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

[0012] The aforementioned magnesium-containing salt may also contain 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 a magnesium-containing salt and a transition metal compound together.

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

[0016] According to another embodiment, a porous magnesium structure produced by the above-described manufacturing method is provided.

[0017] The aforementioned porous magnesium is 10m 2 It may have a BET surface area of ​​less than or equal to / g.

[0018] The porous magnesium structure has numerous voids, and the average width of these voids may be 50 nm or less.

[0019] The porous magnesium structure 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 containing hydrogen supported on the porous magnesium structure. [Effects of the Invention]

[0022] According to one embodiment, different from the conventional synthetic methods of porous structures such as the template method, the dealloying method, and the PVD method, a method is provided that can easily obtain porous magnesium by simply adding a magnesium precursor to a strong reducing agent solution. The magnesium produced by this method, different from the conventional metals with porous structures, has excellent hydrogen storage capacity and can be very usefully used as a new hydrogen storage medium. Also, the manufacturing method according to one embodiment is very simple, different from the conventional manufacturing methods, and is very easy to apply to mass production processes at the industrial level rather than the laboratory level.

Brief Description of the Drawings

[0023] [Figure 1] It is a diagram showing the state in which hydrogen gas is adsorbed on bulk magnesium with a non-porous structure.

[0024] [Figure 2] It is a diagram showing the state in which hydrogen gas is adsorbed on magnesium with a porous structure according to one embodiment.

[0025] [Figure 3] It is a diagram showing the state in which MgCl2, which is a magnesium precursor, is added to lithium naphthalenide, which is a strong reducing agent solution, and the MgCl2 is reduced to porous magnesium.

[0026] [Figure 4] It is a photograph showing that the reduction reaction is proceeding by adding MgCl2, which is a magnesium precursor, to lithium naphthalenide, which is a strong reducing agent solution.

[0027] [Figure 5] It is a TEM photograph of the porous magnesium produced after the reduction reaction.

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

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

[0030] [Figure 9] This figure sequentially illustrates the process by which hydrogen gas is adsorbed onto a porous magnesium structure according to one embodiment.

[0031] [Figure 10-11] These graphs independently show the hydrogen adsorption performance of a porous structure on magnesium according to one embodiment.

[0032] [Figure 12-13] These graphs independently show the hydrogen desorption performance of a porous structure on magnesium according to one embodiment.

[0033] [Figure 14] This is an XRD graph showing the structure of magnesium immediately after synthesis (structure before hydrogen adsorption) of a porous structure according to one embodiment.

[0034] [Figure 15] This is an XRD graph showing the structure of magnesium after hydrogen has been desorbed from a porous structure according to one embodiment.

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

[0036] [Figure 17-18] These graphs independently show the hydrogen adsorption performance of a Ni-doped porous magnesium structure according to one embodiment.

[0037] [Figure 19-20] These graphs independently show the hydrogen desorption performance of a Ni-doped porous structure on magnesium according to one embodiment.

[0038] [Figure 21-22] These graphs independently show the hydrogen adsorption performance of a Co-doped porous magnesium structure according to one embodiment.

[0039] [Figure 23-24] These graphs independently show the hydrogen desorption performance of a Co-doped porous magnesium structure according to one embodiment. [Modes for carrying out the invention]

[0040] The embodiments of the present invention will be described in detail below so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be implemented in a variety of different forms and is not limited to the embodiments described herein. This specification does not describe all elements of the examples, and general content in the art to which the present invention pertains, or overlapping content between examples, is omitted.

[0041] Furthermore, when a part is said to "include" a certain component, unless otherwise stated, this means that it can include other components rather than excluding other constituent elements. Unless there is an obvious exception in the context, singular expressions include plural expressions.

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

[0043] The following describes a method for producing porous magnesium according to one embodiment.

[0044] Hydrogen has the highest specific energy density by weight of all substances. (Its lower heating value (LHV) is less than 120 kJ / g). Despite being extremely abundant on Earth, it is a next-generation, environmentally friendly energy source that can replace petroleum energy sources, and attempts to produce electricity using hydrogen and to advance desalination are currently underway simultaneously all over the world. (From recent attempts to apply hydrogen to transportation and develop commercial vehicles such as taxis and buses, to more distant attempts to desalinate seawater, hydrogen is currently the most talked-about next-generation energy source, and there is no room for argument.)

[0045] However, in order to use hydrogen as an energy source, a hydrogen storage system capable of storing hydrogen is first necessary. Conventional physical hydrogen storage systems require high pressure (350-700 bar) and an extremely low temperature environment of -252.8°C or below, resulting in a problem of low energy density relative to volume. Furthermore, there is a risk of explosion, concerns about stability always exist, and hydrogen stored in this way is expensive, making it economically unfeasible.

[0046] For this reason, various attempts have been made to develop new systems for storing hydrogen, but a hydrogen storage medium that meets satisfactory standards has not yet been developed.

[0047] After accurately recognizing the aforementioned background, problems to date, and limitations, the inventors of this invention conducted extensive research over many years, searching for materials from around the world. As a result, they finally discovered that by modifying magnesium into a porous structure, specifically a nanoporous structure, hydrogen storage can be facilitated even at low pressure, enabling the construction of a safe and efficient hydrogen storage system, thus completing the present invention.

[0048] Theoretically, magnesium has a high hydrogen storage capacity of 7.6% by weight, and as a light metal, it also has a high gravimetric energy density. Furthermore, because it is an abundant element on Earth, it is cost-effective, has a suitable equilibrium pressure for hydrogen, and can store hydrogen even at relatively low hydrogen pressures of less than 100 bar. In addition, it has a high reversible energy density of 9 MJ / kg, among other advantages.

[0049] However, magnesium has several fatal drawbacks: its hydrogen absorption / desorption rate is too slow, making it kinetically undesirable; it requires high temperatures of over 330°C for the hydrogen release process; and, most importantly, it is difficult to completely hydrogenate the interior of the magnesium. Furthermore, because magnesium is a highly reactive element, it is easily oxidized in air. Despite the advantages mentioned above, magnesium has not been usable as a hydrogen storage medium until now due to these fatal drawbacks.

[0050] However, according to one embodiment, by modifying the magnesium (bulk Mg) into a nanoporous structure, more specifically a nanoporous structure doped with a transition metal, all of the aforementioned drawbacks are overcome, and a hydrogen storage medium of an unprecedentedly superior level is provided.

[0051] More precisely, one embodiment provides a method for very easily synthesizing nanoporous magnesium in a one-pot step in solution, using a magnesium precursor from the outset, rather than modifying the aforementioned bulk magnesium (bulk Mg).

[0052] In other words, one embodiment provides a method for producing porous magnesium by adding a magnesium precursor to a reducing agent solution.

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

[0054] Specifically, while the volume expansion that occurs with each repeated absorption / release of hydrogen can potentially cause structural collapse of magnesium, magnesium produced by the manufacturing method according to one embodiment has a nanoporous structure, which means that i) the risk of such structural collapse can be significantly reduced, ii) the Mg ligament size can be reduced, reducing the distance hydrogen has to travel to react with magnesium, which is advantageous from a kinetic standpoint, and iii) the surface area that can react with hydrogen is increased, and the equilibrium pressure (P) can be increased. eq iv) reduces the amount of magnesium that cannot react internally, significantly increasing the level of hydrogenation, and v) does not require high temperatures when releasing hydrogen.

[0055] Therefore, 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 pressure and serve as an important medium for constructing a safe and efficient hydrogen storage system.

[0056] In other words, one embodiment provides a novel solid hydrogen storage material by giving porous magnesium, which has been largely unstudied until now, a nanoporous structure, enabling easy mass production by solution-based one-pot synthesis and providing a new method for producing this new solid hydrogen storage material. (Conventional methods for synthesizing porous structures include template methods and dealloying methods, but none of these are solution-based synthesis methods, making one-pot synthesis impossible, and the quality of the porous structure ultimately produced is not suitable for safely and efficiently storing solid hydrogen at low pressure.)

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

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

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

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

[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 the reduction potential difference.

[0063] For example, lithium naphthalenide can be used as the lithium-based reducing agent solution. Lithium naphthalenide is a strong reducing agent, and lithium ions generated by the reduction reaction are likely to dissolve well into the THF solution used during the reaction. However, the type of lithium-based reducing agent solution is not necessarily limited to this, and various combinations of metals and radical anions can be used as the reducing agent solution.

[0064] Adding the aforementioned magnesium precursor to a reducing agent solution to produce porous magnesium is a first attempt at a very simple method for synthesizing porous magnesium. The porous structure produced by this synthesis method has voids with a width of approximately 50 nm or less, making it 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 a magnesium-containing salt and a transition metal compound together.

[0066] In other words, according to one embodiment of the manufacturing method, a magnesium precursor containing a mixture produced by dissolving a magnesium-containing salt and a transition metal compound together may be added to the reducing agent solution. In this case, the transition metal doping allows for the synthesis of bimetallic magnesium having a porous structure, and the hydrogen adsorption / desorption rate can be further improved compared to before the transition metal doping (kinetic improvement). That is, the transition metal doping 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 limited to, Ni, Co, Ti, or combinations thereof.

[0068] On the other hand, while one embodiment claims a method for producing porous magnesium using a magnesium precursor, the same method can be applied to other highly reactive metals to produce porous metals as well.

[0069] According to another embodiment, a porous magnesium structure produced by the above-described manufacturing method is provided.

[0070] For example, due to the advantages of its porous structure, a porous magnesium material produced by one embodiment can react with a considerable amount of hydrogen and exhibits improved kinetics in the process of hydrogen absorption and release. Therefore, a porous magnesium material produced by the manufacturing method of one embodiment is found to be very effective as a storage medium for storing and reusing hydrogen.

[0071] For example, the porous magnesium structure may have numerous voids, and the average width of these voids may be 50 nm or less. (See Figure 5)

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

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

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

[0075] The embodiments of the present invention described above will be explained in more detail below through the examples. However, the following examples are for illustrative purposes only and do not limit the scope of the present invention.

[0076] Manufacturing of magnesium with nanoporous structures As shown in Figure 8, a magnesium precursor containing MgCl2 was added to a lithium naphthalenide reducing agent solution, and then the lithium salt was removed (dissolved) to synthesize nanoporous magnesium.

[0077] Rating 1 SEM and TEM images of the nanoporous magnesium synthesized as described above were taken, and the results are shown in Figures 5 to 7. As can be seen from Figures 5 to 7, it can be confirmed that the synthesized nanoporous magnesium contains voids with a width of 50 nm or less.

[0078] Hydrogen adsorption onto magnesium with nanoporous structures Figure 9As shown above, hydrogen gas was adsorbed onto 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 occurred. Subsequently, (4) hydrogen atoms migrated (diffusion) from the surface of the nanoporous magnesium to its center, and (5) finally nucleation and growth into MgH2 (hydride formation) occurred, making the nanoporous magnesium a hydrogen storage material.

[0079] - Analysis of the hydrogen adsorption / desorption performance of nanoporous Mg Figures 10-13 From this, it can be confirmed that as the hydrogen adsorption / desorption cycle progresses, the rate becomes even faster, and the storage capacity increases. From this, it can be seen that nanoporous magnesium according to one embodiment has a much lower energy barrier than nonporous magnesium.

[0080] - Analysis of the structure before and after hydrogen adsorption / desorption cycling (XRD, TEM analysis) Figures 14-16 From this, it can be seen that the (002) peak before hydrogen storage was very high, while the (002) peak after cycling was significantly lower. From this, it can be inferred that the Mg crystalline state gradually recovered to an equilibrium state during the hydrogen cycling process, and the hydrogen storage performance improved.

[0081] - Hydrogen storage performance and activation energy of Mg / Ni bimetal and Mg / Co bimetal. Figure 17Figure 24 shows that introducing small amounts of the transition metals Ni and Co significantly accelerates hydrogen absorption / release kinetics and shortens the required activation process. (This is consistent with the XRD results for Mg / Ni and Mg / Co, which also show low (002) peaks before cycling.) Furthermore, activation energy calculations show that the energy barriers in hydrogen adsorption / desorption are lower than those of porous magnesium that is not doped with transition metals. (In particular, the energy barrier in hydrogen desorption is extremely low.) Generally, introducing transition metals into magnesium reduces its hydrogen storage capacity, whereas introducing (doping) transition metals into the aforementioned nanoporous magnesium allows for further improvement of kinetics while maintaining a high hydrogen storage capacity (without reducing hydrogen storage capacity).

[0082] Although 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 by those skilled in the art that utilize the basic concepts of the present invention as defined in the following claims also fall within the scope of the present invention.

Claims

1. A method for producing porous magnesium, comprising the step of adding a magnesium precursor to a reducing agent solution, The method for producing the porous magnesium structure, wherein the porous magnesium has numerous voids, and the average width of the voids is greater than 0 nm and less than or equal to 50 nm.

2. The method for producing porous magnesium according to claim 1, characterized in that the magnesium precursor includes a compound produced by dissolving a salt containing magnesium.

3. The aforementioned magnesium-containing salt is MgCl 2 A method for producing a porous magnesium structure according to claim 2, characterized by including the following:

4. The method for producing a porous magnesium structure according to claim 1, characterized in that the reducing agent solution is a lithium-based reducing agent solution.

5. The method for producing porous magnesium according to claim 1, characterized in that the magnesium precursor includes a mixture produced by dissolving a magnesium-containing salt and a transition metal compound together.

6. The method for producing a porous magnesium structure according to claim 5, characterized in that the transition metal compound includes a salt containing Ni, Co, or Ti, or a combination thereof.

7. A porous magnesium, The porous magnesium structure has numerous voids, and the average width of these voids is greater than 0 nm and less than or equal to 50 nm. The porous magnesium is a porous magnesium that is doped with a transition metal.

8. The aforementioned porous magnesium is 10m 2 A porous magnesium structure according to claim 7, characterized by having a BET surface area of ​​less than or equal to / g.

9. The porous magnesium structure according to claim 7, characterized in that the transition metal includes Co, Ni, Ti, or a combination thereof.

10. A hydrogen storage material containing hydrogen supported on a porous magnesium structure according to any one of claims 7 to 9.

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