JPS5846441B2 - Hydrogen storage structure with electrode part - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a structure for storing hydrogen generated by electrolysis in the form of a metal hydride and its use.

The structure of the present invention can also be used when hydrogen generated by a method other than electrolysis is stored and utilized in the form of a metal hydride.

The method of storing, transporting, and using electrical energy in the form of hydrogen through electrolysis has no resource constraints on raw materials, and since the final oxidizing product is water, it does not disturb the natural environment and is a clean fuel. Because it has many advantages, such as being able to be used as a

When hydrogen is used as secondary energy,
The most important issue is energy conversion efficiency, and research and improvement have been conducted at each stage of hydrogen generation through electrolysis, storage and transportation of the generated hydrogen, and final usage.

The purpose of the present invention also coincides with the purpose of the above-mentioned research and improvement, but it is characterized by having a form that has higher overall energy efficiency, including the final usage form, and is extremely easy to use compared to conventional ones. That is.

First of all, if we consider under what circumstances it would be necessary to convert electrical energy into hydrogen through electrolysis in our country, the first would be when hydrogen is used as a substitute for fossil fuels.

In this case, hydrogen gas itself has sufficient properties as a substitute for fossil fuels, but the problem is the storage form.

Gaseous hydrogen is difficult to handle, and liquid hydrogen has storage, handling, and other problems.A storage form that can be handled almost in the same way as fossil fuels is metal hydride as the metal material for hydrogen storage used in the present invention. This is a method of occluding in the form of

Second, it may be used as a means of storing surplus electricity at night.

Currently, pumped storage power generation is addressing this problem, and the same will likely be the case in the future.

However, in the future when there is a shortage of fossil fuels and electricity is supplied by nuclear power generation or other methods other than thermal power generation, it will be sufficient to use surplus electricity at night to generate hydrogen gas to compensate for the shortage of fossil fuels. Conceivable.

Thirdly, it is a method of storing electricity obtained by solar cells.

Energy such as solar energy, which has a small amount of energy per unit area and unit time (thin energy), has extremely limited uses unless it is concentrated in some way.

If it is converted to hydrogen, it can be used in various ways.

The most energy efficient method must be used for thin energy accumulation.

Even if hydrogen gas were to be generated, it would be impractical to compress it into cylinders, cool it, and liquefy it, as the energy loss required for these tasks would be extremely large.

In this case as well, it is preferable to form a metal hydride, and moreover, rather than collecting the generated hydrogen once and then storing it in the metal,
From the point of view of energy efficiency, it is also preferable to occlude the metal immediately on the spot.

Fourth, it can be considered as a fuel source when hydrogen fuel cells with performance that can replace lead batteries are created in the future.

In this case as well, it is preferable to use the form of a metal hydride from the viewpoint of handling.

In summary, in the future, at least in Japan, the best way to store hydrogen obtained through electrolysis is to use metal hydrides, which are easier to handle and have less energy loss up to the final form of use. It can be said that a sweet potato is preferable.

The disadvantages of using the conventional technology and the advantages of using the structure according to the present invention in order to achieve the above object are as follows.

In addition, these drawbacks are basically that the conventional technology pursues only one of hydrogen generation by electrolysis, hydrogen storage, transportation, and hydrogen utilization, and does not give much consideration to overall efficiency. This may also be due to the fact that it is not.

Next, a hydrogen storage structure having an electrode portion according to the present invention will be described.

In other words, the structure of the present invention is characterized by integrating a hydrogen-permeable electrode with a metal body that forms a compound with hydrogen, that is, a metal body that can store hydrogen, and using an electrically insulating material to cover the entire structure except for the hydrogen-permeable electrode part. It is at the point where the surface is covered.

Its functional feature is that the hydrogen generated by electrolysis does not bubble out into the electrolyte, and almost all of it passes through the hydrogen-permeable electrode and immediately reacts with the hydrogen storage metal body, producing metallic hydrogen. hydrogen gas can be stored by simply placing it in an atmosphere higher than the equilibrium hydrogen pressure of the metal material for hydrogen storage without using it as a cathode part of electrolysis, and conversely, the equilibrium hydrogen pressure The two advantages are that it releases highly pure hydrogen gas by placing it in an atmosphere with a lower hydrogen partial pressure, and that it can be used as a hydrogen electrode with a hydrogen storage section in a hydrogen fuel cell.

Furthermore, when used in fuel cells or electrolyzers, the structural features of hydrogen can be utilized to reduce the heat generated by hydrogen storage and release.
Another feature is that it is possible to utilize endothermic heat in a way that reduces energy loss.

This point will be discussed in detail later in the description of the electrolyzer and fuel cell.

The hydrogen-permeable electrode in the present invention is described in "Electrochemistry and Industrial Physics J VOl, 40. NO, 2, 127 et seq., in Japanese Patent Publications No. 5561-1982, No. 418-416, and No. 25423-1982. An electrode using a membrane having a hydrogen permeability of metal palladium, palladium-silver alloy, palladium-gold alloy, palladium-
A film of silver-gold alloy or the like is used.

Further, membranes whose surfaces are coated with palladium black or palladium-platinum black can also be used as hydrogen-permeable electrode membranes.

In addition, metal materials for hydrogen storage have a large hydrogen storage capacity,
The phase equilibrium conditions of hydrogen gas are suitable for hydrogen storage, for example, Japanese Patent Publication No. 49-34315,
6-23479, etc., and in addition, iron-titanium, magnesium-nickel alloy, metallic niobium,
Although metal vanadium and others are known, the present invention is not limited to these materials.

Hydrogen storage metals generally generate heat when storing hydrogen, and absorb heat when releasing hydrogen.

Figure 1 is an explanatory diagram showing a conventional method of occluding hydrogen by electrolysis into a metal material for hydrogen storage, and the method using a hydrogen-permeable electrode is the most conventional technique for achieving the above purpose. Since it is considered to be superior, the hydrogen gas generating section is modeled after that described in Japanese Patent Publication No. 46-5561.

1 is a counter electrode, 2 is a hydrogen permeable electrode membrane, 3 is an electrode support, 4
is a hydrogen gas chamber.

Further, 5 is an electrolytic solution (E), 6 is an electrolytic tank, I is a power source, 8 is a hydrogen storage metal, 16 is a container thereof, and 10 is a cock.

If the conditions are suitable, almost 100% of the hydrogen generated by electrolysis of the electrolytic solution (e) passes through the hydrogen-permeable electrode membrane 2.
Hydrogen collects in the gas chamber 4 with a current efficiency of , and does not bubble out to the electrolyte (water) side.

For example, Fig. 2 is an explanatory diagram of an electrode, and as a hydrogen permeable membrane, a palladium plate a (purity 9
9.9%), one side is coated with palladium black at a rate of 20 mm/-, and the other side is coated with palladium-platinum mixed black (palladium black io onyi 7 cyi, platinum black 1 mm/g) (b).
C) Use a metal plate with the palladium black side facing the gas chamber,
When electrolysis is performed at 25°C using 5N potassium hydroxide as an electrolyte, the hydrogen trapping efficiency (electrical efficiency) is 92 to 120 rmA/crA at an electrical density of 30 to 120 rmA/crA.
It is known that it is 100%.

The generated hydrogen gas is led into a hydrogen storage metal container as shown in Japanese Patent Publication No. 49-34315, for example.
There, it comes into contact with the hydrogen storage metal and is absorbed.

Hydrogen storage metal generates heat when storing hydrogen, so when using such a conventional electrolyzer, the metal body must be cooled in order to increase the amount of hydrogen stored, and the hydrogen storage The disadvantage is that the heat generated during this process ends up being completely unused as energy loss.

The situation is exactly the same in ordinary electrolyzers that do not use hydrogen permeable electrodes.

On the other hand, the hydrogen storage structure having an electrode part of the present invention has a hydrogen permeable membrane 2 provided on the surface of a hydrogen storage metal material 8, as shown in the explanatory diagram of FIG. As a method for providing on the surface of the metal material 8, physical/chemical means such as electroplating, electroless plating, and vapor deposition are used.

To explain the hydrogen permeable electrode membrane 2 in more detail, in the explanatory diagram of FIG. 3, A is a palladium-gold-silver alloy membrane, B is
It is best when C is a palladium black film and C is a platinum black film.

9 is an electrical insulation seal.

Although the structure looks similar to that shown in FIG. 3 in appearance, the hydrogen permeable electrode film 2 is not formed on the hydrogen storage metal body 8 but is formed separately. The body 8 is only in close contact with the body 8 mechanically, and
Instead of being covered with an electrically insulating seal 9, it may be an electrically insulating container or a container 9' provided with an electrically insulating seal.

When the hydrogen storage metal body 8 occludes hydrogen, this structure
It is suitable for use in cases where the material tends to become powdery.

Furthermore, in this case, if the electrode film has the structure shown in Figure 3, even if the hydrogen storage metal body absorbs hydrogen and becomes powder, reducing its adhesion to the electrode film 2, the hydrogen storage metal body absorbs hydrogen and becomes powder. It is possible to reduce the decrease in storage and release capabilities.

Such a container-type structure is used when it is necessary to use a pressure-resistant container 9' in which the equilibrium hydrogen pressure of the hydrogen storage metal material is considerably higher than 1 atm.

When the structure of the present invention thus obtained is attached as shown in the explanatory diagram of Fig. 4 and electrolysis is performed as a cathode with only the electrode film in contact with the electrolyte, some of the hydrogen generated becomes hydrogen gas. The hydrogen bubbles out from the surface of the electrode membrane, but the other part passes through the hydrogen-permeable electrode and is bonded to the hydrogen storage metal as a hydride and occluded without passing through the gas state.

If a suitable electrolyte (e.g. alkaline water) and an electrode membrane surface treated (e.g. coated with palladium-platinum black) are used, the amount of hydrogen gas bubbling from the electrode surface will be extremely small, and the electrolysis conditions can be adjusted appropriately. If this is done, almost no bubbling phenomenon will be observed, and the efficiency of energy conversion into hydrogen will remain the same as in the conventional method.

This electrolyzer shown in FIG. 4 is much more energy efficient than the conventional device shown in FIG. 1 in the following respects.

It is known that the permeation efficiency of hydrogen-permeable electrode membranes increases as the temperature rises, while hydrogen storage metals generate heat when storing hydrogen.

Therefore, the electrode membrane and electrolyte are heated, and the permeation efficiency is increased.

Furthermore, power efficiency improves as the temperature of the electrolyte increases.

Furthermore, since the hydrogen storage metal is cooled, the amount of hydrogen stored increases.

Therefore, overall energy efficiency is significantly improved.

In the conventional method, electrical energy conversion efficiency can be improved by heating the electrolyte and cooling the hydrogen storage metal, but if the energy for this heating and cooling is obtained externally, the overall energy efficiency can be improved. I couldn't do that.

Hydrogen storage metals can be broadly classified into those with an equilibrium hydrogen pressure of 1 atm or higher near room temperature, and those with an equilibrium hydrogen pressure of 1 atm or less, and those with an equilibrium hydrogen pressure of less than 1 atm. Conventionally, in order to store hydrogen gas, it is necessary to store hydrogen gas above the equilibrium hydrogen pressure. It was necessary to pressurize.

If the structure according to the present invention is used, the efficiency will decrease somewhat (about 10 factors) when the pressure is up to about 10 atm, but hydrogen storage metal with an equilibrium hydrogen pressure of 1 atm or more can store hydrogen without the need for a pressurizing device. It is possible to occlude it in the material.

The electrolyzer using the structure of the present invention is particularly good when a solar cell is used as the power source for electrolysis.

In other words, the electrolyzer of the present invention has better energy conversion efficiency than conventional ones as described above, but the reaction between hydrogen and hydrogen storage metal material tends to be rate-limiting, so the current density is low. This is because good results are obtained when the value is low.

Next, the use of the hydrogen storage structure having the electrode portion of the present invention in a fuel cell will be described.

FIG. 5 is an explanatory diagram showing the concept of a conventional hydrogen-oxygen fuel cell, where 11 is an oxygen electrode, 12 is a hydrogen electrode, and 5 is an electrolyte.

13 is an oxygen or air introduction section, and 14 is a hydrogen introduction section.

The generated electricity is used in the power consumer 15.

When using the hydrogen storage structure having the electrode part of the present invention in a fuel cell, a type of fuel cell that uses air (airborne oxygen) has the greatest utility value.

FIG. 6 is an explanatory diagram schematically showing a fuel cell using a hydrogen storage structure having an electrode portion of the present invention, and is different from FIG. 5 showing a conventional example only in the hydrogen donor mechanism. .

That is, the hydrogen storage structure having the electrode portion of the present invention that occludes hydrogen is used as a hydrogen donor with a hydrogen electrode.

In this way, the following advantages can be obtained in terms of energy efficiency compared to the conventional method.

That is, in the conventional method, it was necessary to cool the fuel cell to some extent to prevent the temperature from rising too much during operation.

Furthermore, when hydrogen gas is supplied from a cylinder, energy is required to fill the cylinder.

On the other hand, in the fuel cell according to the present invention, the heat generated during operation is used to dissociate hydrogen from the hydrogen storage metal body.

That is, when hydrogen is dissociated from the hydrogen storage metal, an endothermic reaction occurs, and the heat generated by the exothermic reaction when the fuel cell operates is utilized.

Therefore, the energy efficiency is significantly improved compared to the conventional one.

Furthermore, the hydrogen storage structure having the electrode portion of the present invention can be used not only for storing hydrogen by electrolysis, but also for storing and utilizing hydrogen by other methods.

That is, if the structure of the present invention is placed in an atmosphere where the hydrogen partial pressure is higher than the equilibrium hydrogen pressure of the hydrogen storage metal material, only hydrogen will pass through the hydrogen permeable electrode membrane and be stored.

Hydrogen storage metals alone have this effect, but components other than hydrogen in the atmosphere, such as carbon monoxide,
Hydrogen storage capacity deteriorates due to oxygen of more than p, p, or m.

In the structure of the present invention, such deterioration does not occur because the hydrogen permeable electrode permeates only hydrogen.

As described above, the present invention provides a hydrogen permeable electrode on a part of the surface of a hydrogen storage body made of a metal material that chemically bonds with hydrogen, and seals the entire surface except for this hydrogen permeable electrode part with an electrically insulating material. or a hydrogen storage structure sealed with an electrically insulating container, which can be used as a cathode with a hydrogen storage part in an electrolyzer or as a hydrogen donor in a hydrogen-oxygen fuel cell. It is.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a conventional method of electrolyzing an electrolyte to store hydrogen, Fig. 2 is an explanatory diagram of an electrode in the conventional method, and Fig. 3 is a hydrogen storage structure having an electrode part according to the present invention. FIG. 4 is an explanatory diagram showing a hydrogen storage method by electrolysis using the structure of the present invention, FIG. 5 is an explanatory diagram showing the operation of a conventional fuel cell, and FIG. 6 is an explanatory diagram showing the structure of the present invention. FIG. 2 is an explanatory diagram when the body is used in a fuel cell. DESCRIPTION OF SYMBOLS 1... Counter electrode, 2... Hydrogen permeable electrode membrane, 5... Electrolyte solution, 6... Electrolytic cell, 7.
...Power supply, 8...For hydrogen absorption (storage)
Metal, 9...Electrical insulation seal, 9'...
・Electrically insulating sealed container, 10... Cook, 11
...Oxygen electrode, 12...Hydrogen electrode, 13.
...Oxygen introduction part, 14...Hydrogen introduction part,
15... Power consumption body, 16... Hydrogen storage container, A... Palladium-gold-silver alloy membrane,
B... Palladium black (coating layer, C...
...Platinum black coating layer.

Claims (1)

[Scope of Claims] 1. A hydrogen permeable electrode is provided in a part of the hydrogen storage body, and the entire surface of the hydrogen storage body except for the hydrogen permeable electrode is sealed with an electrically insulating material, or an electrically insulating container is provided. A hydrogen storage structure having an electrode portion, wherein the hydrogen storage body is made of a metal material that chemically bonds with hydrogen, and the hydrogen permeable electrode is made of palladium or a palladium alloy. Storage structure. 2. The hydrogen storage structure according to claim 1, which is used as a cathode with a hydrogen storage section in an electrolyzer. 3. The hydrogen storage structure according to claim 1, which is used as a hydrogen donor in a hydrogen-oxygen fuel cell.