Method for producing porous magnesium, porous magnesium produced thereby, and hydrogen storage material comprising hydrogen supported by porous magnesium

Abstract

Provided are: a method for producing porous magnesium having a simple solution process of adding a magnesium precursor to a reducing agent solution; porous magnesium produced by the process; and a hydrogen storage material comprising hydrogen supported in the porous magnesium.

Description

Technical Field

[0001] The present invention relates to a method for producing porous magnesium, porous magnesium produced by the method, and a hydrogen storage material comprising hydrogen supported by the porous magnesium. Background Art

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

[0003] As a renewable energy source, hydrogen is a clean energy source that produces no air pollutants when burned and can be used in nearly every area of ​​the energy system, including domestic and industrial fuel cells.

[0004] However, it is difficult to safely store hydrogen in the form of compressed gas using conventional high-pressure hydrogen storage tanks because there is always a risk of explosion, so solid-state, material-based storage methods that can replace conventional high-pressure hydrogen storage tanks have been studied in recent years.

[0005] As hydrogen storage materials, metal hydrides are known to have high hydrogen storage capacity and, unlike conventional physical hydrogen storage methods, can be stored at relatively low hydrogen partial pressures below 100 bar.

[0006] To improve the hydrogen storage performance of metal hydrides, attempts have been made to composite them by infiltrating them into lightweight carbon-based porous matrices, but previous carbon-based porous matrices have low hydrogen storage capacity. In addition, carbon nanotubes, a carbon-based porous matrix material that has been widely studied in the past, require a separate separation process to increase purity to keep the pore size consistent, which makes it uncompetitive in price. Summary of the invention

[0007] Technical issues

[0008] One example provides a method for preparing porous magnesium that can be easily synthesized in a one-pot solution-based manner.

[0009] Another example provides porous magnesium prepared by the above method for preparing porous magnesium.

[0010] Another example provides a hydrogen storage material that utilizes porous magnesium to improve the kinetics of the hydrogen absorption and release process and is capable of storing hydrogen at relatively low pressures.

[0011] Technical Solution

[0012] According to one embodiment, the present invention provides a method for producing porous magnesium, comprising the step of adding a magnesium precursor to a reducing agent solution.

[0013] The magnesium precursor may include a compound prepared by dissolving a salt including magnesium.

[0014] The salt comprising magnesium may include MgCl2.

[0015] The reducing agent solution may be a lithium-based reducing agent solution.

[0016] The magnesium precursor may include a mixture prepared by dissolving a magnesium-containing salt and a transition metal compound together.

[0017] The transition metal compound may include a salt including Ni, Co, and Ti, or a combination thereof.

[0018] According to another embodiment, the present invention provides porous magnesium prepared by the above method.

[0019] The porous magnesium structure has a 10m 2 / g or less BET surface area.

[0020] The porous magnesium has a plurality of pores, wherein an average width of the pores may be 50 nm or less.

[0021] The porous magnesium may be doped with a transition metal.

[0022] The transition metal may include Co, Ni, Ti, or a combination thereof.

[0023] Another example provides a hydrogen storage material comprising hydrogen supported in porous magnesium.

[0024] Beneficial Effects

[0025] According to one example, the present invention provides a method for easily obtaining porous magnesium by a simple process of adding a magnesium precursor to a strong reducing agent solution, which is different from conventional porous structure synthesis methods (such as template, dealloying and PVD methods), and the magnesium prepared by the present method is different from conventional porous metals, which has a very high hydrogen storage capacity and can be very useful as a new hydrogen storage medium. In addition, unlike conventional manufacturing methods, the manufacturing method according to one example is very simple and can be easily applied to large-scale production processes at the industrial rather than laboratory level. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The diagram shows the adsorption of hydrogen onto bulk magnesium with a non-porous structure.

[0027] Figure 2 is a diagram illustrating the adsorption of hydrogen onto porous magnesium according to one example.

[0028] Figure 3The addition of a magnesium precursor MgCl2 to a strong reducing agent solution lithium naphthalenide is shown, wherein the MgCl2 is reduced to porous magnesium.

[0029] Figure 4 A photograph of an ongoing reduction reaction is shown, in which the magnesium precursor MgCl2 is added to the strong reducing agent solution lithium naphthalene.

[0030] Figure 5 This is a TEM image of porous magnesium produced after the reduction reaction is completed.

[0031] Figure 6 and Figure 7 The following are TEM and SEM images of porous magnesium produced after the reduction reaction is completed.

[0032] Figure 8 A comparison of hydrogen adsorption on magnesium with a non-porous structure (left) and magnesium with a porous structure (right) is shown.

[0033] Fig. 9 is a schematic diagram of the sequence of hydrogen adsorption onto porous magnesium according to one example.

[0034] Fig.10 and Fig.11 Independently is a graph depicting hydrogen adsorption performance on porous magnesium according to one example.

[0035] Fig.12 and Fig.13 Independently is a graph depicting hydrogen desorption performance on porous magnesium according to one example.

[0036] Fig.14 is an XRD diagram showing the structure of porous magnesium after synthesis (before hydrogen adsorption) according to one example.

[0037] Fig.15 is an XRD graph showing a structure after hydrogen is desorbed from porous magnesium according to an example.

[0038] Fig.16 is a TEM image of a structure after hydrogen desorption from porous magnesium according to one example.

[0039] Fig.17 and Fig.18 Each independently is a graph depicting hydrogen adsorption performance on magnesium having a Ni-doped porous structure according to an example.

[0040] Fig.19 and Fig. 20 Each independently is a graph depicting hydrogen desorption performance on magnesium having a Ni-doped porous structure according to an example.

[0041] Fig.21 and Fig. 22 Each independently is a graph depicting hydrogen adsorption performance on magnesium having a Co-doped porous structure according to an example.

[0042] Fig.23 and Fig.24 Each independently is a graph depicting hydrogen desorption performance on magnesium having a Co-doped porous structure according to an example. DETAILED DESCRIPTION

[0043] Now, examples of the present invention will be described in detail to facilitate practice by those skilled in the art. However, the present invention can be implemented in many different forms and is not limited to the examples described herein.

[0044] This specification does not describe all components of the examples, and omits components that are common in the art or redundant between examples.

[0045] In addition, unless explicitly stated otherwise, when a part “includes” components, it means that it can include more other components, rather than excluding other components.

[0046] Unless the context clearly indicates otherwise, a singular expression includes a plural expression.

[0047] When a layer, film, region, plate, etc. is referred to as being "on" another in this article, this includes not only when it is "directly on" another, but also when there is another part between them. On the contrary, when it is said that a part is "on" another component, it means that there is nothing between them.

[0048] A method for producing porous magnesium according to one example is described below.

[0049] Hydrogen has the highest energy density by weight of all substances. (The lower heating value (LHV) of hydrogen is 120kJ / g or less.) Hydrogen is one of the most abundant and environmentally friendly energy sources on Earth, and attempts are being made around the world to use it to generate electricity or desalinate water. (From applying hydrogen to transportation, to developing commercial vehicles (such as taxis and buses), to desalinating seawater, hydrogen can be said to be the next big thing in the energy field.)

[0050] However, in order to utilize hydrogen as an energy source, a hydrogen storage system is needed to store hydrogen, but existing physical hydrogen storage systems require high pressure (350 to 700 bar), an extremely low temperature environment of minus 252.8°C or lower, and a low energy density volume ratio. In addition, there are always safety issues due to the risk of explosion, and hydrogen stored in this way is expensive, making it uneconomical.

[0051] Therefore, various attempts have been made to develop new systems for storing hydrogen, but no satisfactory hydrogen storage medium has been developed.

[0052] After fully recognizing the above background and current problems and limitations, the inventors of the present invention conducted many years of investigation and research, looking for data from all over the world, and finally realized that by modifying magnesium into a porous structure, especially a nanoporous structure, hydrogen storage can be promoted even at low pressures, and a safe and efficient hydrogen storage system can be constructed; and finally completed the present invention.

[0053] Theoretically, magnesium has a high hydrogen storage capacity of 7.6% by weight and a high gravimetric energy density for a light metal. It is also an abundant element on Earth, which makes it cost-effective, has a moderate hydrogen equilibrium pressure, allowing hydrogen storage at relatively low hydrogen pressures below 100 bar, and has a high reversible energy density of 9 MJ / kg.

[0054] However, the kinetics of hydrogen are unfavorable because the absorption / desorption rates are too slow, the hydrogen release process requires a high temperature of at least 330°C, and most importantly, it is difficult to fully hydride into the magnesium interior. Moreover, magnesium is a highly reactive element, meaning that it is easily oxidized in air. Despite magnesium's advantages, these key drawbacks have prevented it from being used as a hydrogen storage medium to date.

[0055] However, according to one embodiment, by modifying magnesium (bulk magnesium) into a nanoporous structure, more specifically, a nanoporous structure doped with transition metals, all of the above disadvantages are overcome and a highly superior hydrogen storage medium not previously available is provided.

[0056] More specifically, one example provides a very simple method to synthesize nanoporous magnesium in a one-pot process in solution by using magnesium precursors from scratch rather than by modifying magnesium (bulk magnesium).

[0057] In other words, one example provides a method for preparing porous magnesium by adding a magnesium precursor to a reducing agent solution.

[0058] The magnesium prepared by the method according to one example has a nanoporous structure, which can significantly improve hydrogen adsorption / desorption performance.

[0059] Specifically, the structural collapse of magnesium may be caused by the volume expansion that occurs each time hydrogen is repeatedly absorbed / released, and the magnesium prepared by the method according to one example has a nanoporous structure, which can i) greatly reduce the risk of the above-mentioned structural collapse, ii) reduce the size of the Mg ligaments, which is kinetically advantageous and reduces the travel distance required for hydrogen to react with magnesium iii) increase the surface area available for reaction with hydrogen, resulting in a lower equilibrium pressure (Peq), iv) reduce the amount of unreacted magnesium inside, which can significantly improve the hydrogenation process, and v) potentially eliminate the need for high temperatures during hydrogen release.

[0060] Finally, using the method according to one example, nanoporous magnesium can be easily obtained, which facilitates hydrogen storage even at low pressures, making it an important medium for building safe and efficient hydrogen storage systems.

[0061] In other words, one example provides a new solid hydrogen storage material by making porous magnesium, which has been less studied so far, have a nanoporous structure, and provides a new method for preparing a new solid hydrogen storage material by achieving easy large-scale production through a solution-based one-pot synthesis. (Existing methods for synthesizing porous structures include template methods and dealloying methods, all of which are not solution-based synthesis methods and therefore cannot be used for one-pot synthesis, and the quality of the resulting porous structure is not suitable for safe and efficient storage of solid hydrogen at low pressure.)

[0062] For example, the magnesium precursor may include a compound prepared by dissolving a salt including magnesium.

[0063] For example, the salt comprising magnesium may include MgCl2.

[0064] When MgCl 2 (a salt containing magnesium) is added to a reducing agent solution, a reaction shown in the following reaction formula 1 occurs.

[0065] [Reaction 1]

[0066] MgCl2+2e - →Mg+2Cl -

[0067] This means that when MgCl2 is added to a reducing agent solution, the volume / mole change between MgCl2 and pure magnesium can be exploited to easily synthesize porous structures via chemical reduction.

[0068] The reducing agent solution may be a lithium-based reducing agent solution.

[0069] If a lithium-based reducing agent solution is used as the reducing agent solution, MgCl2 can be easily reduced to Mg due to the reduction potential difference.

[0070] For example, naphthalene lithium can be used as the lithium-based reducing agent solution, wherein naphthalene lithium is a strong reducing agent, and lithium ions generated by the reduction reaction can be well dissolved in the THF solution used during the reaction. However, the type of lithium-based reducing agent solution is not necessarily limited to the above-mentioned type, and various combinations of metals and radical anions can be used as the reducing agent solution.

[0071] This is the first attempt to prepare porous magnesium by adding the above-mentioned magnesium precursor to a reducing agent solution, which is a very simple method for synthesizing porous magnesium, and the porous structure prepared by the above-mentioned synthesis method has pores with a width of about 50 nm or less, which is very beneficial for safely and efficiently storing and releasing solid hydrogen at low pressure.

[0072] For example, the magnesium precursor may include a mixture prepared by melting together a salt including magnesium and a transition metal compound.

[0073] In other words, according to an example preparation method, a magnesium precursor including a mixture prepared by melting a salt containing magnesium and a transition metal compound together can be added to a reducing agent solution, in which case bimetallic magnesium having a porous structure can be synthesized by transition metal doping, and the hydrogen adsorption / desorption rate can be further improved compared to before transition metal doping. (Kinetic improvement) In other words, the above-mentioned transition metal doping can act as a catalyst for the hydrogen adsorption / desorption performance of nanoporous magnesium.

[0074] For example, the transition metal may include, but is not necessarily limited to, Ni, Co, Ti, or combinations thereof.

[0075] Although one example claims a method of producing porous magnesium using a magnesium precursor, the same method can also be applied to produce porous metals using highly reactive metals other than magnesium.

[0076] According to another embodiment, the present invention provides porous magnesium prepared by the above method.

[0077] For example, due to the advantages of its porous structure, the porous magnesium according to one example can react with a large amount of hydrogen and exhibit enhanced kinetics during hydrogen absorption and release, making the porous magnesium prepared by the method according to one example very effective as a storage medium for storing hydrogen and then reusing it.

[0078] For example, porous magnesium can have a plurality of pores, wherein the pores have an average width of 50 nm or less. (See Figure 5 )

[0079] For example, porous magnesium can be doped with transition metals.

[0080] For example, the transition metal may include, but is not necessarily limited to, Co, Ni, Ti, or combinations thereof.

[0081] Another example provides a hydrogen storage material comprising hydrogen supported in porous magnesium.

[0082] Modes for carrying out the invention

[0083] The above examples of the present invention will be described in more detail in the following examples. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0084] Making nanoporous magnesium

[0085] like Figure 8 As shown, a magnesium precursor including MgCl2 is added to a naphthalene lithium reducing agent solution, and then the lithium salt is removed (dissolved) to synthesize nanoporous magnesium.

[0086] Rating 1

[0087] SEM and TEM images of the synthesized nanoporous magnesium were taken. Figures 5 to 7 As shown. Figures 5 to 7 As shown, it can be seen that the synthesized nanoporous magnesium has pores with a width of 50 nm or less.

[0088] Hydrogen adsorption on nanoporous magnesium

[0089] like Fig.10 As shown, hydrogen is adsorbed on the nanoporous magnesium synthesized above. Specifically, (1) hydrogen is adsorbed and transported on the surface of the nanoporous magnesium, (2) hydrogen (H2) dissociates into two hydrogen atoms on the surface of the nanoporous magnesium, and (3) chemical adsorption of hydrogen atoms occurs. Then, (4) hydrogen atoms are transferred from the surface of the nanoporous magnesium to the center thereof (diffusion), and (5) finally, nucleation and growth of MgH2 (hydride formation) occur, making the nanoporous magnesium a hydrogen storage material.

[0090] -Analysis of hydrogen adsorption / desorption performance of nanoporous Mg

[0091] from Figures 11 to 14 It can be seen that as the adsorption / desorption cycle of hydrogen progresses, the rate becomes faster and the storage capacity increases. It can be seen that the nanoporous magnesium according to an example has a much lower energy barrier than non-porous magnesium.

[0092] -Structural analysis before and after hydrogen adsorption / desorption cycles (XRD, TEM analysis)

[0093] from Figures 15 to 18 It can be seen that the (002) peak before hydrogen storage is very high, while the (002) peak after cycling is significantly lower, which can be inferred that the Mg crystal state gradually returns to equilibrium during hydrogen cycling and the hydrogen storage performance is improved.

[0094] -Hydrogen storage properties and activation energy of Mg / Ni bimetallic and Mg / Co bimetallic

[0095] from Figure 19 to Figure 2 6 It can be seen that the introduction of a small amount of transition metals Ni and Co significantly accelerates the absorption / release kinetics of hydrogen and shortens the required activation process. (This is consistent with the XRD results of Mg / Ni and Mg / Co, which show lower (002) peaks even before cycling.) In addition, activation energy calculations show that the energy barrier for hydrogen adsorption / desorption is also lower than that of porous magnesium not doped with transition metals (especially the energy barrier for hydrogen desorption is much lower). It can be seen that the introduction of transition metals into magnesium generally leads to lower hydrogen storage capacity, while the introduction of transition metals (doping) into the above-mentioned nanoporous magnesium can further improve the kinetics while maintaining a higher hydrogen storage capacity (rather than reducing the hydrogen storage capacity).

[0096] 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 concepts of the present invention defined by the following claims are also within the protection scope of the present invention.

Claims

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

2. The method for producing porous magnesium according to claim 1, wherein: The magnesium precursor includes a compound prepared by dissolving a salt including magnesium.

3. The method for producing porous magnesium according to claim 2, wherein: The magnesium-containing salt includes MgCl2.

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

5. The method for producing porous magnesium according to claim 1, wherein: The magnesium precursor includes a mixture prepared by dissolving a salt including magnesium and a transition metal compound together.

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

7. Porous magnesium prepared by the method according to claim 1.

8. The porous magnesium according to claim 7, wherein: The porous magnesium has 10m 2 / g or less BET surface area.

9. The porous magnesium according to claim 7, wherein: The porous magnesium structure has a plurality of pores, and an average width of the pores is 50 nm or less.

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

11. The porous magnesium according to claim 10, wherein: The transition metal compound includes Ni, Co, Ti or a combination thereof.

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

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