METHOD FOR PRODUCE POROUS MAGNESIUM, POROUS MAGNESIUM PRODUCED BY METHOD AND HYDROGEN STORAGE MATERIAL COMBINATES POROUS MAGNESIUM WITH INCREASE INHALED HYDROGEN

Abstract

Provided are: a process for the production of porous magnesium, comprising a simple solution-based process in which a magnesium precursor is added to a reduction solution and reacted; porous magnesium produced by the process; and a hydrogen storage material comprising porous magnesium with hydrogen incorporated.

Description

[Technical field]

[0001] The present invention relates to a process for producing porous magnesium which can be used as a hydrogen storage material, porous magnesium produced thereby, and a hydrogen storage material comprising porous magnesium with hydrogen incorporated therein. [State of the art]

[0002] Fossil fuels, currently the most widely used energy source, produce greenhouse gases such as carbon dioxide and air pollutants such as particulate matter. Therefore, it is important to develop renewable energy to reduce dependence on fossil fuels in the future.

[0003] Hydrogen, one of the renewable energy sources, is an environmentally friendly energy source that does not produce air pollutants when burned and can be used in almost all areas of the energy system, including household 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 systems due to the constant risk of explosion. Therefore, in recent years, solid hydrogen storage has been investigated as a possible replacement for conventional high-pressure hydrogen storage systems.

[0005] Metal hydrides are known as hydrogen storage materials because they have a high hydrogen storage capacity and, unlike conventional physical hydrogen storage methods, can be stored at relatively low hydrogen partial pressures below 100 bar.

[0006] There have been attempts to improve the hydrogen storage performance of these metal hydrides by embedding them in a lightweight, carbon-based porous matrix, but previous porous carbon matrices suffered from low hydrogen storage capacity. Furthermore, carbon nanotubes, a carbon-based porous matrix material that has been extensively studied in the past, require a separate separation process to increase purity and maintain constant pore size, making them price-uncompetitive. [Detailed description of the invention][Technical problem]

[0007] An embodiment of the invention provides a process for producing porous magnesium that can be easily carried out by a one-pot solution-based synthesis.

[0008] Another example is porous magnesium produced by this manufacturing process.

[0009] Another embodiment provides a hydrogen storage material that uses porous magnesium to improve the kinetics of hydrogen absorption and desorption and enable hydrogen storage at relatively low pressures. [Technical solution]

[0010] 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 solution.

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

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

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

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

[0015] The transition metal compound may comprise a salt containing Ni, Co and Ti or a combination thereof.

[0016] According to a further embodiment, the present invention provides porous magnesium produced by the method described above.

[0017] The porous magnesium can have a BET surface area of ​​10 m 2 / g or less.

[0018] The porous magnesium can have a large number of pores, with the average pore width being 50 nm or less.

[0019] The porous magnesium can 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 porous magnesium with stored hydrogen. [Beneficial effect]

[0022] According to one embodiment, the present invention provides a method for easily obtaining porous magnesium through a simple process of adding a magnesium precursor to a strong reduction solution, in contrast to conventional synthesis methods for porous structures such as template, dealloying, and PVD processes. The magnesium produced by the present method has a very high hydrogen storage capacity, unlike conventional porous metals, and can be very useful as a new hydrogen storage medium. Furthermore, in contrast to conventional production methods, the production method according to one embodiment is very simple and can be easily applied to mass production processes at the industrial level, rather than at the laboratory level. [Brief description of the drawings] Fig. shows the absorption of hydrogen gas on bulk magnesium with a non-porous structure. Fig. shows the absorption of hydrogen gas on porous magnesium, according to one embodiment. Fig. shows the addition of a magnesium precursor, MgCl2, to a strong reducing solution, lithium naphthalenide, whereby the MgCl2 is reduced to porous magnesium. Fig. shows a photograph of an ongoing reduction reaction in which a magnesium precursor, MgCl2, is added to a strong reducing solution, lithium naphthalenide. Fig. is a TEM image of the prepared porous magnesium after completion of the reduction reaction. Fig. and Fig. are TEM and SEM images of prepared porous magnesium after completion of the reduction reaction. Fig. shows a comparison of hydrogen gas absorption on magnesium with a non-porous structure (left) and a porous structure (right). Fig. is a sequential representation of hydrogen gas absorption on a porous magnesium, according to one embodiment. Fig. and Fig. are graphs illustrating hydrogen absorption performance on porous magnesium according to one embodiment. Fig. and Fig. are graphs illustrating the hydrogen desorption performance of porous magnesium according to one embodiment. Fig. is an XRD diagram showing the structure immediately after synthesis of porous magnesium (before hydrogen absorption), according to one embodiment. Fig. is an XRD diagram showing the structure after hydrogen desorption from porous magnesium according to one embodiment. Fig. is a TEM image of the structure after hydrogen desorption from porous magnesium, according to one embodiment. Fig. and Fig. are graphs illustrating the hydrogen absorption performance of magnesium with Ni-doped porous structure according to an embodiment, each independently of each other. Fig. and Fig. are diagrams illustrating the hydrogen desorption performance of magnesium with Ni-doped porous structure according to an embodiment, each independently of each other. Fig. and Fig. are graphs illustrating the hydrogen absorption performance of magnesium with Co-doped porous structure according to an embodiment, each independently of each other. Fig. and Fig. are graphs illustrating the hydrogen desorption performance of magnesium in a co-doped porous structure according to one embodiment, each independently of the other. [Detailed description of the invention]

[0023] Embodiments of the present invention will now be described in detail to facilitate the practice of the invention by those skilled in the art. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein.

[0024] This description does not describe all elements of the embodiments and omits common or redundant information known to those skilled in the art.

[0025] When a part “includes” a component, it means that it may include more other components, not that it excludes other components, unless explicitly stated otherwise.

[0026] Terms in the singular include the plural unless the context clearly indicates otherwise.

[0027] When a layer, film, region, plate, or the like is described herein as being "on top of another," this implies not only that it is "directly on top of" it, but also that another part may be in between. Conversely, the statement that a part is "directly on top of" another part means that there is nothing in between.

[0028] In the following, a method for producing porous magnesium according to an embodiment is described.

[0029] Hydrogen has the highest energy-to-weight density of any substance (hydrogen has a lower heating value (LHV) of 120 kJ / g or less). Hydrogen is one of the most abundant and environmentally friendly energy sources on Earth, and there are currently efforts around the world to use hydrogen to generate electricity or desalinate water (from applications of hydrogen in transportation, such as the development of commercial vehicles like taxis and buses, to seawater desalination, hydrogen is arguably the next big thing in energy).

[0030] However, to use hydrogen as an energy source, a hydrogen storage system is necessary to store the hydrogen. Existing physical hydrogen storage systems, however, require high pressure (350 to 700 bar), extreme cryogenic environments of minus 252.8 °C or below, and low energy density relative to volume. Furthermore, safety concerns remain due to the risk of explosion, and hydrogen stored in this way is expensive, making it uneconomical.

[0031] Therefore, various attempts have been made to develop new hydrogen storage systems, but no satisfactory hydrogen storage medium has been developed so far.

[0032] After fully acknowledging the above-mentioned background as well as the current problems and limitations, the inventors of the present invention researched and studied for many years by acquiring data available worldwide, and finally found that modifying magnesium into a porous structure, especially into a nanoporous structure, facilitates the storage of hydrogen even at low pressure and can construct a safe and efficient hydrogen storage system; and finally completed this invention.

[0033] Theoretically, magnesium has a high hydrogen storage capacity of 7.6 wt% and a high gravimetric density for a light metal. It is also an earth-abundant element, making it cost-effective. It has a moderate equilibrium pressure for hydrogen, allowing hydrogen storage at relatively low pressures below 100 bar. It also has a high reversible energy density of 9 MJ / kg.

[0034] However, hydrogen has disadvantages in terms of its kinetics, as the absorption and desorption rate is too slow, the hydrogen release process requires high temperatures of at least 330 °C, and, most importantly, the complete hydrogenation of the magnesium within is difficult. Furthermore, magnesium is a highly reactive element that is easily oxidized in air. Despite the advantages of magnesium, these critical disadvantages have so far prevented its use as a hydrogen storage medium.

[0035] However, according to one embodiment, by modifying the magnesium (bulk Mg) into a nanoporous structure, more specifically into a nanoporous structure doped with a transition metal, all these disadvantages can be overcome and a very superior hydrogen storage medium can be provided that was not previously available.

[0036] More specifically, one embodiment provides a very simple way to synthesize nanoporous magnesium in a one-pot process in solution by using a magnesium precursor from the beginning instead of modifying the magnesium (bulk Mg).

[0037] In other words, one embodiment provides a method for producing porous magnesium by adding a magnesium precursor to a reducing solution.

[0038] Magnesium produced by the method according to one embodiment has a nanoporous structure, which can significantly improve hydrogen absorption / desorption performance.

[0039] In particular, structural collapse of the magnesium may occur due to the volume expansion associated with each repeated absorption / desorption of hydrogen, and the magnesium produced by the process according to one embodiment has a nanoporous structure, which i) can significantly reduce the risk of structural collapse described above, ii) can reduce the size of the magnesium ligaments, which is advantageous in terms of kinetics because the path that the hydrogen has to travel to react with the magnesium is shortened, iii) can increase the available surface area for reaction with hydrogen, which leads to a reduction in the equilibrium pressure (P eq), iv) can reduce the amount of unreacted magnesium inside, which can significantly improve the hydrogenation progress, and v) can potentially eliminate the need for high temperatures during hydrogen release.

[0040] Finally, the processes according to one embodiment allow for easy extraction of nanoporous magnesium, which enables the storage of hydrogen even at low pressures, making it an important medium for the construction of safe and efficient hydrogen storage systems.

[0041] In other words, one embodiment provides a novel solid hydrogen storage material by preparing porous magnesium, which has been little studied so far, with a nanoporous structure, and provides a novel method for preparing a novel solid hydrogen storage material that enables easy mass production through a solution-based one-pot synthesis (existing methods for synthesizing porous structures include template methods and dealloying methods, which, however, are not solution-based synthesis methods and therefore cannot be used for one-pot synthesis, and the quality of the resulting porous structures is not suitable for safe and efficient storage of solid hydrogen at low pressure).

[0042] The magnesium precursor may, for example, comprise a compound prepared by dissolving a magnesium-containing salt.

[0043] The magnesium-containing salt may, for example, include MgCl2.

[0044] When MgCl2, a magnesium-containing salt, is added to the reducing solution, the reaction shown in reaction equation 1 takes place. MgCl2 + 2 e - → Mg + 2 Cl - [Reaction equation 1]

[0045] This means that when MgCl2 is added to a reducing solution, a porous structure can be easily synthesized by chemical reduction, taking advantage of the volume change per mole between MgCl2 and pure magnesium.

[0046] The reduction solution can, for example, be a lithium-based reduction solution.

[0047] If a lithium-based reducing solution is used as the reducing solution, MgCl2 can be easily reduced to Mg due to the reduction potential difference.

[0048] For example, lithium naphthalenide can be used as a lithium-based reducing solution. Lithium naphthalenide is a strong reducing agent, and the lithium ions generated by the reduction reaction are highly soluble in the THF solution used during the reaction. However, the type of lithium-based reducing solution is not necessarily limited to those mentioned above, and various combinations of metals and radical anions can be used as the reducing solution.

[0049] This is the first attempt to produce porous magnesium by adding a magnesium precursor to a reducing solution, which is a very simple method for synthesizing porous magnesium, and the porous structure prepared by the synthesis method described above has pores with a width of about 50 nm or less, which is very advantageous for safe and effective storage and release of solid hydrogen at low pressure.

[0050] The magnesium precursor may, for example, comprise a mixture prepared by co-dissolving a magnesium-containing salt and a transition metal compound.

[0051] In other words, according to a manufacturing method according to one embodiment, a magnesium precursor comprising a mixture of a magnesium-containing salt and a transition metal compound can be added to the reduction solution. In this case, doping with transition metals can synthesize a bimetallic magnesium with a porous structure, which further improves the hydrogen absorption / desorption rate compared to before the transition metal doping (kinetic improvement). In other words, the transition metal doping described above can act as a catalyst for the hydrogen absorption / desorption performance of nanoporous magnesium.

[0052] For example, the transition metal may include, but is not necessarily limited to, Ni, Co, Ti, or combinations thereof.

[0053] While one embodiment claims a method for producing porous magnesium using a magnesium precursor, it is possible that the same method can be applied to produce porous metals using highly reactive metals other than magnesium.

[0054] According to a further embodiment, the present invention provides porous magnesium produced by the method described above.

[0055] For example, the porous magnesium according to one embodiment can react with significant amounts of hydrogen due to its advantageous porous structure and it shows improved kinetics in the process of hydrogen absorption and release, which makes the porous magnesium produced by the method according to one embodiment an effective storage medium for the storage of hydrogen and its subsequent reuse.

[0056] For example, the porous magnesium may have a large number of pores, with the pores having an average width of 50 nm or less (see Fig. ).

[0057] The porous magnesium can, for example, be doped with a transition metal.

[0058] The transition metal may include, for example, Co, Ni, Ti or combinations thereof, but is not necessarily limited to them.

[0059] Another embodiment provides a hydrogen storage material containing hydrogen in a porous magnesium support. [Mode for carrying out the invention]

[0060] The above examples of the present invention are described in more detail in the following embodiments. However, the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Production of nanoporous magnesium

[0061] As in Fig. As shown, a magnesium precursor comprising MgCl2 was added to a lithium naphthalenide reduction solution, and then the lithium salt was removed (dissolved) to synthesize nanoporous magnesium. Rating 1

[0062] SEM and TEM images of the nanoporous magnesium synthesized above were taken, and the results are shown in Fig. until Fig. As shown in Fig. until Fig. As can be seen, the synthesized nanoporous magnesium has pores with a width of 50 nm or less. Hydrogen absorption on nanoporous magnesium

[0063] As in Fig. As shown, hydrogen gas was absorbed by the nanoporous magnesium synthesized above. Specifically, (1) hydrogen gas was adsorbed and transported on the surface of the nanoporous magnesium, (2) hydrogen gas (H2) was dissociated into two hydrogen atoms on the surface of the nanoporous magnesium, and (3) chemisorption of hydrogen atoms occurred. Then, (4) hydrogen atoms were transferred from the surface of the nanoporous magnesium to its center (diffusion), and (5) finally, nucleation and growth of MgH2 (hydride formation) occurred, transforming the nanoporous magnesium into a hydrogen storage material. - Analysis of hydrogen absorption / desorption performance of nanoporous Mg

[0064] In Fig. until Fig. It can be seen that as the hydrogen absorption / desorption cycles progress, the rate increases and the storage capacity increases.

[0065] This means that nanoporous magnesium, according to one embodiment, has a significantly lower energy barrier than non-porous magnesium. - Structural analysis before and after hydrogen absorption / desorption cycles (XRD, TEM analysis)

[0066] In Fig. until Fig. It can be seen that the (002) peak before hydrogen storage is very high, while the (002) peak after cycling is significantly lower, which suggests that the crystalline state of Mg is gradually restored to equilibrium during hydrogen cycling and the hydrogen storage performance is improved. - Hydrogen storage capacity and activation energy for Mg / Ni bimetal and Mg / Co bimetal

[0067] In Fig. until Fig.It can be seen that the introduction of small amounts of the transition metals Ni and Co significantly accelerated the hydrogen absorption / release kinetics and shortened the required activation process (this is consistent with the XRD results of Mg / Ni and Mg / Co, which show a low (002) peak even before cycling). Furthermore, activation energy calculations show that the energy barrier for hydrogen absorption / desorption is also lower than that of porous magnesium not doped with a transition metal (in particular, the energy barrier for hydrogen desorption is significantly lower).It is found that the introduction of a transition metal into magnesium generally leads to a lower hydrogen storage capacity, while the introduction (doping) of a transition metal into the above-mentioned nanoporous magnesium can further improve the kinetics while maintaining a higher hydrogen storage capacity (instead of decreasing the hydrogen storage capacity).

[0068] Although preferred embodiments of the present invention have been described in detail above, the scope of the invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concepts of the invention as defined in the following claims are also included within the scope of the invention.

Claims

[1] A process for producing porous magnesium comprising adding a magnesium precursor to a reducing solution. [2] The process for producing porous magnesium according to claim 1, wherein the magnesium precursor comprises a compound prepared by dissolving a magnesium-containing salt. [3] A process for producing porous magnesium according to claim 2, wherein the magnesium-containing salt comprises MgCl2. [4] The method for producing porous magnesium according to claim 1, wherein the reducing solution is a lithium-based reducing solution. [5] A process for producing porous magnesium according to claim 1, wherein the magnesium precursor comprises a mixture prepared by co-dissolving a magnesium-containing salt and a transition metal compound. [6] A process for producing porous magnesium according to claim 5, wherein the transition metal compound comprises a salt comprising Ni, Co, Ti or a combination thereof. [7] Porous magnesium produced by the process of claim 1. [8] Porous magnesium according to claim 7, wherein the porous magnesium has a BET surface area of ​​10 m 2 / g or less. [9] Porous magnesium according to claim 7, wherein the porous magnesium has a plurality of pores and the average width of the pores is 50 nm or less. [10] Porous magnesium according to claim 7, wherein the porous magnesium is doped with a transition metal. [11] Porous magnesium according to claim 10, wherein the transition metal comprises Co, Ni, Ti or a combination thereof. [12] A hydrogen storage material comprising porous magnesium according to any one of claims 7 to 11 with stored hydrogen.

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