JPH0773875A - Hydrogen or its isotope storage method - Google Patents

Abstract

PURPOSE:To provide a high deuterium storage ratio with excellent reproducibility by using an electrode obtained by partially covering the surface of a hydrogen storage metal with a material whose hydrogen overpotential is higher than that of the hydrogen storage metal. CONSTITUTION:The surface of an electrode 1 made of a hydrogen storage metal such as Pd is covered by about 80% by forming in the form of stripe a thin film 2 of metal such as gold whose hydrogen overpotential is higher than that of Pd. Hydrogen or its isotope is electrolytically stored in the electrode 1. Current is concentrated on the surface 3, where is exposed without being covered with the film 2, of the hydrogen storage metal, and current density on the surface 3 is heightened compared with the average current density on the whole surface of the electrode. Deuterium ions are efficiently stored in the hydrogen storage metal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for storing hydrogen or its isotopes capable of increasing the storage rate of hydrogen or its isotopes by electrolysis of hydrogen storage metals. The hydrogen-storing cathode thus densely filled with hydrogen or its isotope can be applied to nickel hydride batteries, cold fusion and the like.

[0002]

2. Description of the Related Art Conventionally, a hydrogen storage metal material such as palladium is used as a cathode and platinum is used as an anode to supply a direct current to electrolyze heavy water D ₂ O containing lithium deuterium oxide LiOD. It is known that a high output energy with respect to the input energy was obtained by continuing to store the deuterium atoms generated in 1. in the cathode. In order to cause such a phenomenon, it is necessary to occlude the deuterium element D in the palladium electrode, which is the cathode, as much as possible. Generally, the deuterium occlusion ratio is the atomic ratio (D
It is said that / Pd) must be 0.9 or more.

Further, in a method in which a hydrogen storage metal immersed in an electrolytic solution, for example, a palladium electrode is used to store deuterium in the palladium electrode by electrolysis, 1M Li
When OD is used, the deuterium storage rate in palladium is D
/Pd≦0.88, and it is difficult to achieve 0.88 or more by the usual method. Under the above electrolysis conditions, 60% thiourea (NH ₂ ) ₂ CS was added to the electrolytic solution.
It is known that the maximum D / Pd = 0.94 is obtained when 0 μM is added.

[0004]

The deuterium storage rate in palladium increases when the current density during electrolysis is increased to increase the hydrogen overvoltage, but when electrolysis is performed at a large current density of 0.5 A / cm ² or more. , The temperature of the electrolyte rises due to the input power, so the deuterium release phenomenon that was stored in the palladium occurs, and the deuterium storage rate decreases on the contrary.
It is difficult to set D / Pd to 0.88 or more. When heavy water is electrolyzed on the entire surface of palladium, a current distribution is generated, and deuterium that has been occluded is released on the surface of palladium, so deuterium starts to be released and it is difficult to increase the deuterium storage rate.

On the other hand, the method of increasing the deuterium storage rate by adding thiourea to the electrolytic solution has a problem that thiourea is adsorbed on the gas diffusion electrode to deteriorate the performance as an anode.

Therefore, the present invention solves the above-mentioned problems in a method of occluding hydrogen or its isotope (for example, deuterium) in a hydrogen occluding metal by an electrolytic method, and deuterium occluding rate D / Pd ≧ 0. It is an object of the present invention to provide a method of occluding hydrogen or its isotope capable of obtaining 88 with high reproducibility.

[0007]

In order to solve the above-mentioned problems, the present invention allows hydrogen storage metal immersed in an electrolytic solution to store hydrogen or its isotope (for example, deuterium) by an electrolytic method. In the method, a material having a hydrogen overvoltage higher than that of the hydrogen storage metal (that is, a material more inert than the hydrogen storage metal) is used to partially cover the surface of the hydrogen storage metal or use an electrode in which the entire surface of the hydrogen storage metal is covered. Alternatively, the method for storing hydrogen or its isotope is characterized by storing the isotope thereof.

In the present invention, "partially covering" means
A state in which a film such as a thin film or a thick film is formed and covered while leaving a part of the surface of the hydrogen storage metal, or "covering the entire surface" means a state in which there is no exposed portion of the hydrogen storage metal and it is 100% covered. Say.

As a material of the film for covering the surface of the hydrogen storage metal, it is necessary to use a material having a hydrogen overvoltage larger than that of the hydrogen storage metal (in the electrolytic solution, gold has a larger hydrogen overvoltage than palladium). ). It is important that the membrane used in the present invention is a membrane that does not permeate hydrogen or a membrane that does not easily permeate hydrogen, and that the membrane does not dissolve in the electrolyte. When the hydrogen storage metal is palladium, the material of the film for covering the surface of the hydrogen storage metal is Au, Ag, or Cu that can be used in an acid or alkaline electrolyte, and Ni or Cd can be used in an alkaline electrolyte. . Further, it is more effective to form an oxide as an insulating film on the metal thin film. PH for oxide materials
Al ₂ O ₃ (AlO ₂ ) with an electrolyte solution of ≧ 12, TiO ₂ (Ti ₂ O ₃ ) with an electrolyte solution of pH ≧ 6, ZrO ₃ with an electrolyte solution of pH = 4 to 13 and an electrolyte solution of pH ≦ 10 SiO ₂ can be used.

By covering the surface of the hydrogen storage metal with a material having a hydrogen overvoltage higher than that of the hydrogen storage metal, the formed film becomes more inactive in the electrolytic solution in the hydrogen electrode reaction than the hydrogen storage metal. The thickness of the film can be 10 Å to 100 μm when it is a thin film.
For forming this thin film, vacuum deposition, electrolytic plating, electroless plating, powder sintering, bulk, thin film bonding, etc. can be applied. Further, in order to form the film covering the surface of the hydrogen storage metal in the present invention, means such as thick film and laminating can be applied in addition to the thin film.

In the deuterium storage method for hydrogen storage metals by the electrolysis method of heavy water, it is conventionally known that the deuterium storage rate increases when the current density is increased and the hydrogen overvoltage is increased. The liquid heat is generated and the temperature of the electrolytic solution rises. As a result, deuterium stored in the hydrogen storage metal is released by the desorption reaction, and the deuterium storage rate becomes small.

On the other hand, according to the present invention, by using an electrode in which the surface of the hydrogen storage metal is partially covered with a material having a hydrogen overvoltage larger than that of the hydrogen storage metal, deuterium is stored by an electrolytic method. The current is concentrated on the surface of the hydrogen storage metal that is not covered with the film and is partially exposed, and the current density on the surface is higher than the average current density of the entire electrode surface, so that deuterium ions are efficiently stored in hydrogen. It is possible to make the metal occlude.

Further, in the present invention, although it is not a membrane that does not allow hydrogen to permeate at all, it is a membrane of a material having a low hydrogen permeability and a hydrogen charge voltage higher than that of the hydrogen occluding metal, and the entire surface (100 %), The hydrogen charge voltage is consequently increased, and deuterium ions can be occluded efficiently.

As described above, in the present invention, the deuterium storage is efficiently performed, so that the temperature rise of the electrolytic solution can be suppressed and the deuterium storage rate can be increased. Although the above description mainly describes deuterium storage by the electrolysis method of heavy water, hydrogen storage by the electrolysis method of water is also similarly described.

[0015]

【Example】

[Embodiment 1] FIG. 1 is a plan view and a side view of an electrode used in this embodiment in which a hydrogen storage metal is partially covered with a material having a hydrogen overvoltage larger than that of the hydrogen storage metal. 2 is shown in FIG.
It is an enlarged view of the portion A of the side view of FIG. Reference numeral 1 in FIG. 1 denotes an electrode, and a thin gold film 2 is partially formed in a stripe shape on the surface of palladium.
%. Therefore, the exposed surface 3 of palladium is 20%. Reference numeral 4 in FIG. 1 denotes the upper surface or the lower surface of the electrode 1. The thickness of the gold thin film 2 on the palladium surface is 2000Å
Is.

Pd rod (φ4 × 21 mm, made by Tanaka Kikinzoku)
The surface of the mirror is mirror-polished, and the sputtering equipment (ULVA
Film thickness of 2000Å by sputtering using C)
Au thin film of 80% of the total palladium surface in a stripe pattern
Was formed so as to cover. Next, Au lead wire (φ0.5
(* 15 mm) was spot-welded, etched with nitric acid for 5 minutes to remove Ag adhering at the time of welding, and degassed in vacuum at 200 ° C. for 3 hours to obtain an electrode made of the hydrogen storage metal of Example 1. did. On the other hand, an electrode was manufactured in the same manner as the above-described electrode manufacturing method except that sputtering was not performed, and the electrode was used as a comparative example.

Next, deuterium was occluded by an electrolysis method using the electrode made of the hydrogen storage metal of Example 1 and the electrode made of the hydrogen storage metal of the comparative example. FIG. 3 shows the electrolytic cell used in this Example 1. In FIG. 3, 11 is a pressure vessel of the electrolytic cell. The pressure vessel 11 is made of SUS, but its inner wall is coated with ceramics to prevent corrosion (Cerashield: trade name, Yoshida SKT Co., Ltd.).
Manufactured), and the electrolytic solution 12 is contained in the pressure vessel 11. Near the center of the pressure vessel 11, a cathode 13 made of a hydrogen storage metal is held by a holding member 20 and immersed in the electrolytic solution 12 to be arranged. An anode 14 composed of a gas diffusion electrode is arranged around the cathode 13 with a space. A gas supply device 15 composed of a Teflon membrane filter containing 100 × 60 mm carbon paper 21 is attached to the anode 14. Electrolyte 1
2, a reference electrode (RHE) 16 is fixed laterally 3 mm from the upper end surface of the cathode 13. An electrolytic solution thermometer 17 for detecting the temperature of the electrolytic solution 12 is provided in the electrolytic solution 12, and a gas phase thermometer 18 for detecting the temperature of the gas phase is provided in an upper portion of the pressure vessel 11. 19 are arranged respectively.

1 M LiOD / D ₂ O was used as the electrolytic solution 12, and 50 ml was put in the pressure vessel 11. Pressure vessel 11
The gas phase temperature and the electrolytic solution temperature inside were measured at each location. The temperature of the electrolytic solution in the pressure vessel 11 was kept constant at 10 ° C. Heavy water was electrolyzed at an initial current density of 30 mA / cm ² .

FIG. 4 shows changes in the deuterium occlusion rate of Pd, which is a hydrogen occlusion metal, with respect to the elapsed time of electrolysis at the initial stage of electrolysis. In the line A in FIG. 4, the H ⁺ generated at the gas diffusion electrode of the counter electrode is not covered with the Au thin film, and the Pd content is 20%.
A line in an ideal state (current density 100%) is assumed when the surface is occluded.

In FIG. 4, line B represents 20% of D ⁺ generated in the counter gas diffusion electrode, which corresponds to the Pd surface area ratio.
It shows a line with a current efficiency of 20% assuming that only Pd is occluded.

In FIG. 4, line C shows the line when the current efficiency is 70%.

In FIG. 4, a line D is formed by using an electrode, which is used in the first embodiment, in which the surface of Pd is partially covered with Au which is a material having a hydrogen overvoltage larger than Pd which is a hydrogen storage metal. It is a line determined based on the data actually measured by the experiment in which deuterium was stored. A straight line obtained by drawing a tangent line to the curve of the line D represents the current consumed by the deuterium storage in Pd among the currents flowing through the entire electrode, and the slope of the line with a current efficiency of 100% ( 2.2
From the ratio of the slope (1.59) of the tangent to 7),
The current efficiency of the electrode at was calculated to be 70%, which coincides with the line C having a current efficiency of 70%.

According to FIG. 4, the current efficiency for a surface area of 20% Pd is 20% (for line B), whereas
The film-treated Pd of the present invention was found to have a current efficiency of 70%. This means that according to the deuterium storage method of the present invention, which uses an electrode partially (80%) covered on the surface, a current efficiency of 70% is achieved although a current efficiency of 20% is predicted. Better than expected 3.5
It can be seen that a twice higher current efficiency has been achieved. Such results indicate that Au is more inactive than Pd (hydrogen overvoltage is large).
Since it is difficult for the current to flow, it can be said that the current is concentrated on Pd.

FIG. 5 shows changes in the hydrogen storage rate with respect to the magnitude of the current density applied to the entire electrode made of the hydrogen storage metal.
It is shown based on the data obtained by electrolysis for 6 days. In FIG. 5, white circles are Pd that do not cover the conventional surface at all.
The case of the electrode (the electrode of the comparative example) is shown, and the black circle shows the case of the Pd electrode in which 80% of the entire palladium surface of this example is covered with the material Au having a hydrogen overvoltage larger than that of the hydrogen storage metal. According to FIG. 5, as for the deuterium storage rate at the same current density, the electrode of which the surface of Pd was partially covered with Au of Example 1 had a higher deuterium storage rate than the Pd electrode which did not cover anything. It is 2 to 3% larger, and it can be seen that the current density of the electrode of Example 1 is higher with respect to the current density to Pd.

Further, according to FIG. 5, the current density is 0.1 A.
/ Cm ² or more, deuterium storage ratio D / Pd is 0.8
You can see that you have achieved 8 or more. Further, it can be seen that the deuterium storage ratio does not decrease even at a small current density (0.01 A / cm ² ) or less. The reason is that A covering the surface of Pd
It seems that u suppresses the release of absorbed deuterium.

[Embodiment 2] In this embodiment 2, a cathode made of a hydrogen storage metal in which the adhesion property with Pd is improved by further subjecting the Au thin film formed on the Pd surface to thermal diffusion treatment. In the point that hydrogen storage was performed using this hydrogen storage cathode, and that the storage performance of hydrogen or its isotope was confirmed for the case where the Pd surface was covered with 100% hydrogen storage cathode, The implementation conditions differ greatly from Example 1.

Tanaka Kikinzoku Pd was cut into φ4 × 20 mm and its surface was mirror-polished. Au lead wire (φ
0.5 × 120 mm) was spot-welded using Cu as a contact. Then, an Au thin film having a film thickness of 0.7 μm was 100% coated on the entire palladium surface by sputtering using a sputtering device (manufactured by ULVAC),
Those coated with 97% and those coated with 80% were prepared. Then, degassing treatment is performed in vacuum at 200 ° C. for 3 hours, and heat treatment is further performed at 250 ° C. for 1 hour to diffuse a part of the components of the Au thin film to the Pd electrode to enhance the adhesion strength and to absorb hydrogen. As a negative electrode.

Under the same conditions as in Example 1, 1M LiOD was prepared by using three kinds of hydrogen storage cathodes having different coverages obtained by the above method and an electrode made of only palladium which was not coated for comparison. Deuterium was occluded with an electrolyte solution of / D ₂ O.

FIG. 6 shows the relationship of the deuterium storage rate in the cathode with respect to the lapse of time from the start of electrolysis to the 1.2th day. In FIG. 6, line 1 represents the hydrogen storage rate line in the ideal state when the current efficiency is 100%. Line 2
Shows a line based on the actual measurement value in the case of a Pd electrode not covered with anything. Line 3 is a line based on the measured value in the case of a Pd electrode in which 80% of the palladium surface is covered with an Au thin film. Line 4 is a line based on the measured value in the case of a Pd electrode in which 97% of the palladium surface was covered with an Au thin film. Line 5 is a line based on the actual measurement value in the case of a Pd electrode in which 100% of the palladium surface is covered with an Au thin film. From FIG. 6, it is understood that deuterium can be occluded even when electrolysis is performed using a Pd electrode in which the surface of palladium is 100% covered with an Au thin film.

FIG. 7 shows changes in the deuterium storage rate with respect to the current density based on data obtained by long-term electrolysis. In FIG. 7, the X mark indicates P that does not cover the palladium surface at all.
d electrode, a triangular mark is a Pd electrode whose palladium surface is covered with an Au thin film by 80%, and a square mark is a palladium surface which is an Au thin film.
7 shows a Pd electrode with 7% coverage. As shown in FIG. 7, the higher the ratio of covering the palladium surface with the Au thin film, the higher (up to 0.98) the deuterium storage ratio (D / Pd) obtained.

[0031]

According to the present invention, deuterium is absorbed by using an electrode in which the surface of the hydrogen storage metal is partially or entirely covered with a material having a hydrogen overvoltage larger than that of the hydrogen storage metal. The storage ratio D / Pd ≧ 0.88 can be obtained with good reproducibility.

In the present invention, hydrogen or its isotope (for example, deuterium) is efficiently occluded, so that the temperature rise of the electrolytic solution can be suppressed and the occluding rate of hydrogen or its isotope can be increased. You can

According to the present invention, an electrode of a hydrogen storage metal is used in which a film is formed on the surface of the hydrogen storage metal with a material having a large hydrogen overvoltage, and then a diffusion process by heat is performed so that the film is not peeled off. Therefore, the deuterium storage rate can be further increased.

[Brief description of drawings]

1A and 1B are a plan view and a side view of an electrode used in Example 1 in which a hydrogen storage metal is partially covered with a material having a hydrogen overvoltage larger than that of the hydrogen storage metal.

FIG. 2 is an enlarged view of a portion A of the side view of FIG.

FIG. 3 shows the electrolytic cell used in Example 1.

FIG. 4 shows changes in the deuterium storage rate of Pd, which is a hydrogen storage metal, with respect to the electrolysis elapsed time in the initial stage of electrolysis in Example 1.

FIG. 5 shows changes in the hydrogen storage rate with respect to the magnitude of the current density applied to the entire electrode made of the hydrogen storage metal of Example 1.

FIG. 6 shows the relationship of the deuterium storage rate in the cathode with respect to the elapsed time from the start of electrolysis to Day 1.2 in Example 2.

FIG. 7 shows changes in deuterium storage rate with respect to current density.

[Explanation of symbols]

 1 Electrode 2 Gold Thin Film 3 Palladium Exposed Surface 4 Top or Bottom of Electrode 11 Pressure Vessel 12 Electrolyte 13 Cathode 14 Anode 15 Gas Supply Device 16 Reference Electrode (RHE) 17 Electrolyte Thermometer 18, 19 Gas Phase Temperature Total 20 Holding member 21 Carbon paper

Claims (3)

[Claims] 1. A method of storing hydrogen or its isotope in a hydrogen storage metal immersed in an electrolytic solution by an electrolytic method,
A method for storing hydrogen or its isotope, which comprises performing electrolysis using an electrode in which the surface of the hydrogen storage metal is partially covered with a material having a hydrogen overvoltage higher than that of the hydrogen storage metal. 2. A method for storing hydrogen or its isotope in a hydrogen storage metal immersed in an electrolytic solution by an electrolytic method,
A method for storing hydrogen or its isotope, which comprises electrolyzing using an electrode in which the surface of the hydrogen storage metal is entirely covered with a material having a hydrogen overvoltage higher than that of the hydrogen storage metal. 3. A method of partially or entirely covering the surface of a hydrogen storage metal with a material having a hydrogen overvoltage higher than that of the hydrogen storage metal, comprising: forming a film on the surface of the hydrogen storage metal by a material having a high hydrogen overvoltage; The method for occluding hydrogen or its isotope according to claim 1 or 2, which has been subjected to a diffusion treatment by heat.