JP2008266690A - Hydrogen storage body, hydrogen storage device and hydrogen sensor using the same, nickel nanoparticles, and manufacturing method thereof - Google Patents

Abstract

An object of the present invention is to provide a hydrogen storage body that can efficiently store hydrogen even at a relatively low temperature and low pressure and can be obtained at low cost.
[MEANS FOR SOLVING PROBLEMS] The hydrogen storage body of the present invention is made of Ni nanoparticles, or Ni nanoparticles are formed into a thin film using a binder. For example, this Ni nanoparticle has at least one crystal structure selected from an fcc structure and an hcp structure.
[Selection figure] None

Description

  The present invention relates to a hydrogen storage body, a hydrogen storage device using the same, and a hydrogen sensor.

  Hydrogen has a low environmental impact because the product after fuel is water, and is expected as a future main fuel. Hydrogen storage requires a hydrogen storage material that reversibly absorbs / releases hydrogen.

Currently, various hydrogen storage alloys such as palladium (Pd) and alloys of nickel (Ni) and rare earth elements have been proposed as materials capable of efficiently storing hydrogen (see, for example, Patent Document 1).
JP 2004-27346 A

  However, platinum group metals such as Pd, alloys of Ni and rare earth elements, and the like are expensive, and it has been difficult to obtain an inexpensive hydrogen storage material. Ni is an inexpensive metal, but Ni in the bulk state does not exhibit hydrogen storage characteristics unless the hydrogen pressure is very high.

  Accordingly, an object of the present invention is to provide a hydrogen storage body that can efficiently store hydrogen even at a relatively low temperature and low pressure and can be obtained at low cost. It is another object of the present invention to provide a hydrogen storage device and a hydrogen sensor using such a hydrogen storage body. Furthermore, it aims also at providing the Ni nanoparticle which can be used for a hydrogen storage body, and its manufacturing method.

  The present inventor has found that Ni exhibits a property of occluding hydrogen at a relatively low temperature or low pressure in the form of nanoparticles.

  The present invention provides a hydrogen storage body comprising Ni nanoparticles. Moreover, this invention provides the hydrogen storage body by which Ni nanoparticle is formed in thin film form using a binder.

  From another aspect, the present invention provides a method for using Ni nanoparticles as a hydrogen storage material.

  The present invention provides a hydrogen storage device comprising the above-described hydrogen storage body of the present invention and a container for storing the hydrogen storage body.

  The present invention provides a hydrogen sensor comprising the above-described hydrogen storage material of the present invention and a magnetic susceptibility detecting means for detecting a change in magnetic susceptibility accompanying a change in the crystal structure of Ni nanoparticles.

  The present invention provides Ni nanoparticles having an hcp structure, wherein at least a part of the surface is coated with a water-soluble organic polymer. Further, the present invention heats a solution containing a Ni salt, a water-soluble organic polymer, and a polyhydric alcohol, and reduces Ni ions contained in the Ni salt, so that at least a part of the surface is obtained. Provided is a method for producing Ni nanoparticles, which obtains Ni nanoparticles having an hcp structure coated with the organic polymer.

  For example, Ni nanoparticles can occlude hydrogen at a relatively low temperature of about 200 ° C. under a hydrogen pressure of about 1 atmosphere (about 0.1 MPa). Ni is an inexpensive metal. Thus, according to the present invention, it is possible to efficiently store hydrogen even at a relatively low temperature and low pressure, and to provide an inexpensive hydrogen storage body. Moreover, by using such a hydrogen storage body, according to the present invention, an inexpensive hydrogen storage device and hydrogen sensor can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description does not limit the present invention.

(Hydrogen storage)
The present invention provides a hydrogen storage body composed of Ni nanoparticles and a hydrogen storage body in which Ni nanoparticles are formed into a thin film using a binder. In addition, in this specification, a nanoparticle means a particle | grain with a particle size of 100 nm or less.

  The particle size of the Ni nanoparticles constituting the hydrogen storage body of the present invention is not particularly limited, but for example, the particle size is preferably in the range of 2.5 to 50 nm in order to store hydrogen efficiently.

  The crystal structure of the Ni nanoparticles constituting the hydrogen storage body of the present invention is not particularly limited. For example, Ni nanoparticles having an fcc (face-centered cubic) structure and / or Ni nanoparticles having an hcp (hexagonal close-packed) structure are used. Particles can be used.

  The hydrogen storage body made of Ni nanoparticles can be used in the form of a powder, for example, or in the form of a thin film.

  The method for producing Ni nanoparticles used in the hydrogen storage material of the present invention is not particularly limited. For example, a method of reducing Ni ions in a solution containing an alcohol such as ethanol as a solvent, or a solution containing phosphine or the like as a protective agent. Various methods currently reported, such as a method for reducing Ni ions, can be applied.

  In the case of a hydrogen storage material in which Ni nanoparticles are formed into a thin film with a binder, a solution containing Ni nanoparticles, a binder, and a solvent is formed on a substrate with a predetermined thickness using, for example, a spin coat method. It can apply | coat so that it may become, and can obtain by drying a coating film after that. The binder used here is not particularly limited, and for example, polyvinyl pyrrolidone (Poly (N-vinyl-2-pirrolidone)), polyvinyl alcohol, alkanethiol, oleic acid, phosphine, and the like can be used. Moreover, alcohol, hexane, ether, acetone, water etc. can be used for a solvent, for example.

  According to the hydrogen storage body of the present invention, for example, hydrogen can be stored at a hydrogen pressure of 1 atm (about 0.1 MPa) or less and a temperature of about 200 ° C.

(Hydrogen storage device)
The hydrogen storage device of the present invention includes the above-described hydrogen storage body of the present invention and a container that accommodates the hydrogen storage body. An example of the hydrogen storage device of the present invention is shown in FIG. The hydrogen storage device 1 shown in FIG. 1 is configured by filling a pressure-resistant container 11 provided with a hydrogen inlet / outlet 13 with a powdered hydrogen storage body 12 made of Ni nanoparticles.

(Hydrogen sensor)
The hydrogen sensor of the present invention includes the above-described hydrogen storage body of the present invention and magnetic susceptibility detection means for detecting a change in magnetic susceptibility associated with a change in the crystal structure of Ni nanoparticles.

  The present inventor has found that the crystal structure of Ni nanoparticles changes before and after storing hydrogen. Specifically, it has been found that, for example, when hydrogen pressure is applied to Ni nanoparticles having an hcp structure to occlude hydrogen, the crystal structure is changed to become Ni nanoparticles having an fcc structure. On the other hand, Ni nanoparticles are known to change in magnetic susceptibility depending on the crystal structure. Specifically, at room temperature, Ni nanoparticles having an hcp structure are antiferromagnetic and exhibit a low magnetic susceptibility, whereas Ni nanoparticles having an fcc structure exhibit ferromagnetism.

  Hydrogen can be detected by utilizing the above-described characteristics of Ni nanoparticles, that is, by utilizing a phenomenon in which a hydrogen occlusion body made of Ni nanoparticles occludes hydrogen and changes its magnetic susceptibility.

  FIG. 2 shows an example of the hydrogen sensor of the present invention. The hydrogen sensor 2 of this example includes a hydrogen storage body 21 made of Ni nanoparticles filled in a container and a magnetic susceptibility detection device 22 that detects a change in magnetic susceptibility of the hydrogen storage body 21. The hydrogen detection determination unit 23 determines that hydrogen is present according to the amount of change in magnetic susceptibility obtained from the rate detection device 22.

(Ni nanoparticles and production method thereof)
An example of the Ni nanoparticles of the present invention and a method for producing the same will be described.

  The Ni nanoparticles of the present invention are at least partially covered with a water-soluble organic polymer (for example, polyvinylpyrrolidone), and have an hcp structure as a crystal structure. The entire surface of the Ni nanoparticles of the present invention may be coated with a water-soluble organic polymer.

  Such Ni nanoparticles of the present invention are produced, for example, by heating a solution containing a Ni salt, a water-soluble organic polymer, and a polyhydric alcohol, and reducing Ni ions contained in the Ni salt. it can. In order to efficiently obtain Ni nanoparticles having an hcp structure, the heating temperature of the solution is preferably set to 150 ° C. or higher. In this method, for example, polyvinyl pyrrolidone can be used as the organic polymer, and, for example, ethylene glycol and / or triethylene glycol can be used as the polyhydric alcohol. For example, when ethylene glycol is used as the polyhydric alcohol, the heating time is desirably 8 hours or more when the heating temperature is 150 ° C., and desirably 3 hours or more when refluxing (about 194 ° C.). When triethylene glycol is used as the polyhydric alcohol, when refluxing (284 ° C.), it is possible to obtain Ni nanoparticles having an hcp structure by heating for about 30 minutes.

  Ni nanoparticles can be obtained in a higher yield in a shorter time as the alcohol having a higher valence is heated at a higher temperature. In particular, when a water-soluble organic polymer is used as a protective agent (protective polymer that protects the surface of Ni nanoparticles), particle aggregation can be prevented, so that Ni nanoparticles can be synthesized at a high temperature in a short time. It becomes possible.

  Hereinafter, the present invention will be described more specifically with reference to examples. In addition, the Example shown below is only the illustration of this invention, and does not limit this invention.

Example 1
In this example, the hydrogen storage characteristics of Ni nanoparticles were confirmed.

<Synthesis of Ni nanoparticles>
(A) Ni nanoparticle having fcc structure Ni chloride hexahydrate (NiCl ₂ · 6H ₂ O) (made by Kishida Chemical Co., Ltd./special grade reagent) 237.5 mg ethylene glycol (made by Kishida Chemical Co., Ltd./special grade reagent) 150 mL And dissolved in ethylene chloride solution (6.7 × 10 ⁻² mol / L). In addition, 1.0 mL of hydrazine monohydrate (N ₂ H ₄ · H ₂ O) (made by Kishida Chemical Co., Ltd., reagent grade) as a reducing agent, and polyvinylpyrrolidone (Poly (N-vinyl-2-pirrolidone) as a protective agent )) (Hereinafter abbreviated as PVP) (made by Wako Pure Chemical Industries, reagent grade) 11.10 g, sodium hydroxide (NaOH) (made by Kishida Chemical, reagent grade) previously dissolved in 50 mL of ethylene glycol as a reduction accelerator 185. 4 mg was added in this order and stirred well. The molar ratio of PVP: Ni ions at this time was set to 100: 1.

  The solution prepared as described above was heated to 150 ° C. using an oil bath and subjected to a reduction reaction for 1 hour with vigorous stirring to obtain nanoparticles as a black precipitate / brown solution (dispersion).

  A mechanical stirrer was used for the above stirring.

(B) Ni nanoparticles with hcp structure The preparation of the solution was performed in the same manner as in the synthesis of Ni nanoparticles with an fcc structure.

  The obtained solution was heated to 150 ° C. with vigorous stirring using an oil bath, heated for 8 hours, and subjected to a reduction reaction to obtain nanoparticles as a black precipitate / black brown solution (dispersion).

  A mechanical stirrer was used for the above stirring.

<Measurement of particle size dispersion by transmission electron microscope (TEM)>
On a carbon-coated copper grid for an electron microscope, about 3 drops of the Ni nanoparticle dispersion solution obtained by the above method was dropped with a Pasteur pipette and dried to prepare a transmission electron microscope (JEOL). Manufactured, JEM-200CX, acceleration voltage: 200 kV, magnification: 100,000 times, Kyushu University long-term high-voltage electron microscope room), and observation and photography were performed. About 200 particles were selected from an arbitrary area in the TEM photograph, the particle size was measured, and the particle size dispersion (average particle size and standard deviation) was determined. The TEM photograph obtained by such a method and the results of particle size dispersion are shown in FIGS.

  FIG. 3 is a TEM photograph of fcc-structured Ni nanoparticles, and FIG. 4 is a histogram of fcc-structured Ni nanoparticles. The average particle diameter of the fcc structure Ni nanoparticles was 10.5 nm, and the standard deviation was 2.9 nm.

  FIG. 5 is a TEM photograph of hcp structured Ni nanoparticles, and FIG. 6 shows an enlarged view thereof. The average particle diameter of the obtained hcp structure Ni nanoparticles was about 6 nm. In addition, about hcp structure Ni nanoparticle, since the number of particle | grains sufficient for calculating | requiring a standard deviation in a photograph was not obtained, the standard deviation and a histogram are not calculated | required.

<Analysis by X-ray diffraction>
A black powder sample (fcc structure Ni nanoparticle, hcp structure Ni nanoparticle) obtained by the above method was dried under reduced pressure and then ground well using an agate mortar, and then a glass capillary (0.5 mmφ, W. Muller) was packed with about 5 to 6 mm of particles from the bottom. The sealing was performed after deaeration in a vacuum. In this way, a 1.5 to 2 cm capsule-shaped sample tube was produced. In addition, for the sample whose temperature was changed, the temperature was changed by putting the sample portion of the capillary in an oil bath when degassing in vacuum.

  Using the sample tube manufactured as described above, synchrotron radiation (SPring-8 BL02B2 (λ = 0.054294 (1) nm), KEK-PF BL-1B (λ = 0.068818 (1) nm)) X-ray powder diffraction (XRD) structural analysis was performed.

  FIG. 7 shows an XRD pattern of fcc-structured Ni nanoparticles measured at a wavelength λ = 0.054294 (1) nm, and FIG. 8 shows an hcp-structured Ni nanoparticle measured at a wavelength λ = 0.068818 (1) nm. The XRD pattern of is shown. For comparison, FIG. 7 shows an XRD pattern for bulk Ni, and FIG. 8 also shows an XRD pattern for fcc-structured Ni nanoparticles.

<Confirmation of hydrogen storage capacity>
A PCT (Hydrogen Pressure-Composition-Isotherms) curve was measured for the fcc-structure Ni nanoparticles and hcp-structure Ni nanoparticles obtained from the above. For the measurement, a PCT automatic characteristic measuring device (manufactured by Suzuki Shokan) was used. The maximum pressure in the hydrogen atmosphere was 0.1 MPa (760 Torr), and the measurement temperature was 473K.

  FIG. 9 shows the PCT curve of the fcc structure Ni nanoparticles, and FIG. 10 shows the PCT curve of the hcp structure Ni nanoparticles. For comparison, FIG. 11 shows a PCT curve of bulk Ni. From these PCT curves, it was confirmed that both the fcc structure Ni nanoparticles and the hcp structure Ni nanoparticles occlude hydrogen at a hydrogen pressure of 1 atm or less at 473K. On the other hand, for bulk Ni, it can be seen from the PCT curve shown in FIG. 11 that hydrogen is not occluded under the same conditions (hydrogen is not occluded only under high pressure).

(Example 2)
In this example, the change in crystal structure due to hydrogen occlusion of Ni nanoparticles was confirmed.

  The hcp structure Ni nanoparticles obtained by the same method as in Example 1 were subjected to hydrogen pressurization at 473 K and 0.087 MPa (650 Torr), and structural changes before and after hydrogen pressurization were examined. The structural change was confirmed by powder X-ray diffraction structural analysis. A specific method of X-ray diffraction is the same as that in the first embodiment. The results are as shown in FIG. Further, X-ray diffraction was performed in the same manner on the hydrogen-pressurized hcp-structure Ni nanoparticles placed under vacuum to reduce the hydrogen pressure. The result is also shown in FIG.

  It was confirmed that when a hydrogen pressure was applied to the hcp structure Ni nanoparticles, the peak attributed to the hcp structure disappeared and the peak intensity attributed to the fcc structure increased. Moreover, when the Ni nanoparticles after application of hydrogen were placed under vacuum and hydrogen decompression was performed, the disappeared hcp structure peak appeared and the fcc structure peak decreased. From this result, it is inferred that at 473 K, the hcp-structure Ni nanoparticles are performing hydride formation accompanied by structural changes.

  The present invention is a hydrogen storage body that can be obtained at a lower cost than before, and has great utility value in this technical field. Moreover, it may be applicable not only to a hydrogen storage device and a hydrogen sensor but also to any application product that requires storage of hydrogen, such as a fuel cell electrode catalyst and a hydrogenation catalyst.

It is sectional drawing which shows roughly the example of 1 structure of the hydrogen storage apparatus of this invention. It is a block diagram which shows roughly the example of 1 structure of the hydrogen sensor of this invention. It is a TEM photograph of Ni nanoparticles of fcc structure produced in an example. It is a histogram of Ni nanoparticle of fcc structure produced in the Example. It is a TEM photograph of Ni nanoparticles of the hcp structure produced in the example. It is an enlarged photograph of the TEM photograph shown in FIG. It is a figure which shows the X-ray-diffraction pattern of Ni nanoparticle of fcc structure measured in the Example, and bulk Ni. It is a figure which shows the X-ray-diffraction pattern of Ni nanoparticle of the hcp structure and Ni nanoparticle of the fcc structure which were measured in the Example. It is a figure which shows the PCT curve of the Ni nanoparticle of fcc structure produced in the Example. It is a figure which shows the PCT curve of Ni nanoparticle of the hcp structure produced in the Example. It is a figure which shows the PCT curve of bulk Ni. It is a figure which shows the X-ray-diffraction pattern about the Ni nanoparticle of the hcp structure produced in the Example before hydrogen pressure application, after hydrogen pressure application, and after hydrogen pressure reduction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hydrogen storage apparatus 2 Hydrogen sensor 11 Pressure-resistant container 12 Hydrogen storage body 13 Hydrogen inlet / outlet 21 Hydrogen storage body 22 Magnetic susceptibility detection apparatus 23 Hydrogen detection judgment part

Claims (12)

  Hydrogen storage material consisting of nickel nanoparticles.   A hydrogen storage material in which nickel nanoparticles are formed into a thin film using a binder.   The hydrogen storage body according to claim 1, wherein the nickel nanoparticles have at least one crystal structure selected from an fcc structure and an hcp structure.   Use of nickel nanoparticles as a hydrogen storage material.   A hydrogen storage device comprising the hydrogen storage body according to claim 1 or 2 and a container for storing the hydrogen storage body.   A hydrogen sensor comprising: the hydrogen storage material according to claim 1; and a magnetic susceptibility detecting unit that detects a change in magnetic susceptibility associated with a change in the crystal structure of the nickel nanoparticles.   Nickel nanoparticles having an hcp structure, wherein at least a part of the surface is coated with a water-soluble organic polymer.   The nickel nanoparticle according to claim 7, wherein the organic polymer is polyvinylpyrrolidone.   By heating a solution containing a nickel salt, a water-soluble organic polymer, and a polyhydric alcohol and reducing nickel ions contained in the nickel salt, at least a part of the surface is covered with the organic polymer. The nickel nanoparticle manufacturing method which obtains the nickel nanoparticle which has the hcp structure made.   The manufacturing method of the nickel nanoparticle of Claim 9 whose heating temperature of the said solution is 150 degreeC or more.   The method for producing nickel nanoparticles according to claim 9, wherein the organic polymer is polyvinylpyrrolidone.   The method for producing nickel nanoparticles according to claim 9, wherein the polyhydric alcohol is at least one selected from ethylene glycol and triethylene glycol.