JPH0641639B2 - Water electrolysis device for space life support device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a water electrolysis device for a space life support device, which can obtain high-purity oxygen and hydrogen.

[Conventional technology and its problems]

An electrolytic device in which an anode and a cathode are provided in contact with both sides of a diaphragm made of a solid polymer electrolyte (hereinafter, abbreviated as SPE) is
It is known as an excellent energy-saving electrolysis system because of its advantages such as reduction of electrolysis voltage and downsizing of equipment, and it is applied to various aqueous solution electrolysis.

In such an electrolysis device, the method of joining the SPE, the electrode catalyst, and the current collector is technically important, and can be roughly classified into two types depending on the joining method.

The first type is one in which an electrode catalyst is directly supported on SPE to be integrated, and a current collector is pressed against this. For example US
The method described in P3, 432, 355 and USP 3,297, 484 is a method in which a metal such as platinum, iridium, rhodium, ruthenium or an oxide thereof is formed in advance using polytetrafluoroethylene or the like as a binder, and this film is used as an electrode. This is a bonding method generally called a dry method, in which the catalyst layer is bonded to the SPE film by thermocompression bonding. In addition, Japanese Patent Publication Nos. 42-5014 and 58-47471 describe a method generally called a wet method in which a metal is chemically deposited directly on an SPE surface using a reducing agent and a metal salt solution.

The second type is one in which an electrode catalyst is integrally supported on a current collector, and this is pressed against an SPE membrane to form an electrolysis device, which is known as, for example, JP-A-56-93883.

In these conventional techniques, the first type cannot separately replace or repair or recover the SPE and the electrode catalyst, which have different lifespans, during or after the use for electrolysis. Since the collector is brought into contact with the extremely thin electrode catalyst layer above, the SPE and the electrode catalyst layer are easily damaged.

On the other hand, the second type does not have the above-mentioned drawbacks because the current collector carries the catalyst, so that the desired electrode catalyst and S
Can be freely joined to PE. Therefore, it has been considered to be applied as a high performance water electrolysis device for space life support devices, etc., but part of the gas generated at the anode and cathode permeates the SPE and mixes with the gas generated at the counter electrode. The purity of oxygen and hydrogen obtained so far has not been sufficient.

[Object of the Invention]

The present invention has been made to solve the above problems,
It is an object of the present invention to provide a water electrolysis device that can obtain oxygen and hydrogen of high purity that can be used as a space water electrolysis device.

[Means for solving problems]

The present invention is a water electrolysis apparatus for space such as a solid electrolyte membrane composed of a cation exchange membrane, on both sides of which a gas permeable anode current collector and a cathode current collector carrying an electrode catalyst are in close contact with each other. A platinum group metal layer having a surface resistance value of 10 to 1000 Ω / cm is provided on the side surface of the anode.

According to the present invention, the platinum group metal layer provided on the SPE allows the S
Oxygen and hydrogen that have permeated PE are catalytically treated to obtain high-purity oxygen and hydrogen, and water electrolysis is possible at a low electrolysis voltage.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a partially exploded cross-sectional view for explaining the basic configuration of the water electrolysis device of the present invention.

In the electrolytic device of the present invention, the solid polymer electrolyte (SP
E) As the diaphragm 1, a conventionally known cation exchange membrane can be widely used, but a perfluorosulfonic acid cation exchange membrane having a sulfonic acid group is particularly preferable. The diaphragm 1
A platinum group metal layer 2 described later is provided on the anode side surface of
The anode current collector 3 and the cathode current collector 4 supporting the electrode catalyst are arranged in close contact with each other from both side surfaces. These form an electrolysis apparatus unit using the anode frame 5, the cathode frame 6 and the gasket 7, and a plurality of the units are connected as required to form an electrolysis apparatus. The connection method may be either a double-pole type in which they are electrically connected in series or a single-pole type in which they are connected in parallel, but the former double-pole type is preferable in terms of downsizing of the device.

The anode current collector 3 and the cathode current collector 4 may have any conductivity and corrosion resistance, and may have an air-permeable structure capable of sufficiently releasing the generated gas and allowing the electrolyte solution to flow therethrough. Any of the materials and structures can be applied. As such a porous anode current collector 3, for example, a porous body based on titanium, tantalum, zirconium or the like, a net-like body, or a mat-like fibrous body can be preferably used, and as the cathode current collector 4, nickel, Similar porous materials such as stainless steel and carbon are used. As the anode catalyst 8 and the cathode catalyst 9 carried on these air-permeable current collectors, any known ones for oxygen generation and hydrogen generation can be used, but iridium having a low oxygen overvoltage and oxides thereof, or these Is preferable as the anode catalyst 8, and as the cathode catalyst 9, platinum, platinum black or the like having a low hydrogen overvoltage is preferable. As a method for supporting the electrode catalyst on the current collector, various known methods can be appropriately applied, and for example, a thermal decomposition method, a plating method, a hot pressing method, or the like can be used.

As described above, the present invention provides the platinum group metal layer 2 on the anode side surface of the SPE diaphragm 1 of such an electrolysis apparatus so that the surface resistance value thereof is 10 to 1000 Ω / cm.
This is based on the finding that high-purity oxygen and hydrogen gases can be obtained without increasing the electrolysis cell voltage. Although the reason is not clear, the hydrogen gas diffused from the cathode is consumed by reacting with the oxygen gas on the platinum group metal layer as shown in the following equation, and at the same time, the diffusion of oxygen gas to the cathode side is prevented. It is considered that this is because the contamination with the produced gas as an impure gas is reduced.

2H ₂ + O ₂ → 2H ₂ O The platinum group metal layer 2 is provided in such an amount that the surface resistance value is within the above-mentioned range. In the present invention, the surface resistance value is S
A resistance value between two points on the surface of the platinum group metal layer 2 provided on the PE membrane 1. When the resistance value is less than 10 Ω / cm, the electrolysis voltage increases, and when it exceeds 1000 Ω / cm, the gas purity is improved. The effect becomes low, which is not preferable.

As the platinum group metal layer, platinum, palladium, rhodium, osmium and the like are used, but platinum and palladium are particularly preferable in terms of hydrogen reaction catalytic activity.

The method for forming the platinum group metal layer 2 on the diaphragm 1 is not particularly limited, but the chemical plating method as described in JP-B-58-47471 is preferable. By the method,
A platinum group metal layer is deposited and formed on the surface of the diaphragm and in the inside of the diaphragm, and the above effect can be sufficiently achieved.

〔Example〕

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.

Example 1 A commercially available cation exchange membrane (trade name Nafion 117, manufactured by DuPont) was used as SPE, and a platinum layer was formed on one side surface by a chemical plating method.

The method is as follows: Cylindrical cell 2 with inner diameter of 76 mm and volume of 300 ml.
Assemble the plating cell by using the individual pieces, aligning the flange parts, packing Teflon and sandwiching SPE with a diameter of about 100 mm, and first adsorb the platinum ion in the ammine complex ion form on the SPE using the following adsorption bath. A platinum layer was deposited on the inner surface of the SPE by using the reducing bath of.

(Adsorption bath) Chloroplatinic acid 0.5 g Ammonia water (25%) 39 ml Water 261 ml pH approx. 11 Note) For adsorption, put 300 ml of the above bath in one cell and 300 ml of 3.3% ammonia water in the other cell. , 25 ℃
It was held for 2 hours.

(Reduction bath) Sodium borohydride 0.5 g Ammonia water (25%) 39 ml Water 261 ml pH approx. 11 Note) For reduction, put 300 ml of the above bath in one cell and 300 ml of 3.3% ammonia water in the other cell. Put, 25 ℃
Held for 16 hours.

The platinum layer of the SPE film thus obtained had a surface resistance value of about 100 Ω / cm.

Separately, IrO ₂ powder and Nafion liquid (manufactured by Aldrich Chemical Co.) as a binder and Teflon liquid (Mitsui
DuPont Fluorochemical Co., Ltd. 30-J) was slurried, applied to an aluminum foil, dried, and then hot pressed (2.2 tonnes) on a 1 mm thick titanium bibli fiber (Tokyo Steel Co., Ltd.) as an anode current collector. / Cm ² , 200 ° C) and then 5
to remove the aluminum foil by molNaOH solution, to prepare a positive electrode current collector carrying Ir0 ₂ as an anode catalyst.

Further, Pt powder was used as a cathode catalyst, and a 0.5 mm-thick stainless steel fiber (manufactured by Nippon Seisen Co., Ltd., as a cathode current collector,
P using the same method as above except using the product name Naslon)
A cathode current collector carrying t was produced.

The obtained SPE diaphragm provided with a platinum layer on the anode side, the anode and cathode current collectors carrying the electrode catalyst were constituted as an electrolyzer as shown in FIG. 1, and the current density was 100 A / dm ² , 60
Water with a specific resistance of 1 × 10 ⁶ Ωcm (25 ° C) is applied to the anode side at 5 ℃.
Electrolysis was performed while supplying at a rate of / min, and the purity of the generated gas and the electrolysis voltage were measured. The gas purity was measured by gas chromatography. A molecular sieve 5A (60 to 80 mesh) was used as a column packing material, and He gas was used as a carrier gas for measuring hydrogen purity and Ar gas was used as a carrier gas for measuring oxygen purity.

As a comparative example, the same cation exchange membrane as in Example 1 was used at 25 ° C.
In the same electrolysis apparatus as in Example 1 except that an SPE diaphragm without a platinum layer was used, which was simply immersed in a 0.1 mo1H ₂ SO ₄ aqueous solution for 16 hours and washed with water, water electrolysis was performed in the same manner.

The results are summarized in Table-1.

As is clear from the results in Table 1, it is found that the water electrolysis apparatus of the present invention can obtain oxygen and hydrogen of extremely high purity while maintaining a low electrolysis voltage.

Example 2 The same cation exchange membrane as in Example 1 was held at 70 ° C. for 2 hours using a liquid having the following liquid composition to adsorb palladium ions.

Palladium chloride 0.5 g Ammonia water (25%) 39 ml Water 261 ml pH about 11 Then, using the same reducing bath as in Example 1, a palladium layer was similarly deposited on one side.

The surface resistance value of the palladium layer of the obtained SPE film is about 50.
It was 0 Ω / cm.

Using this SPE diaphragm, an electrolytic cell was constructed in the same manner as in Example 1 and a water electrolysis test was conducted. The purity of oxygen gas was 99.9.
A high-purity gas having a hydrogen gas purity of 6% and 99.88% was obtained, and the electrolysis voltage was 2.01V.

〔The invention's effect〕

According to the present invention, a platinum group metal layer having a surface resistance value of 10 to 1000 Ω / cm is provided on the surface of an anode of an SPE diaphragm made of a cation exchange membrane, and an anode and a cathode current collector carrying an electrode catalyst are brought into close contact with each other to form an electrolysis device. Since it is configured, oxygen and hydrogen of extremely high purity can be obtained, and water electrolysis can be performed at a low electrolysis voltage, which is useful for a life support device for space and the like.

[Brief description of drawings]

FIG. 1 is an exploded sectional view showing an example of a water electrolysis apparatus according to the present invention. 1. SPE diaphragm 2. Platinum group metal layer 3. Anode current collector 4. Cathode current collector 5. Anode frame 6. Cathode frame 7. Gasket 8. Anode catalyst 9. Cathode catalyst

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-56-93883 (JP, A) JP-B-61-36074 (JP, B2)

Claims (3)

[Claims] 1. A water electrolysis apparatus comprising a solid polymer electrolyte membrane comprising a cation exchange membrane and a gas permeable positive electrode current collector carrying an electrode catalyst and a negative electrode current collector in contact with both sides of the solid polymer electrolyte membrane. A water electrolysis device for a space life support device, characterized in that a platinum group metal layer having a surface resistance value of 10 to 1000 Ω / cm is provided on the side surface. 2. The water electrolysis apparatus according to claim 1, wherein platinum is used as the platinum group metal. 3. The water electrolysis device according to claim 1, wherein palladium is used as the platinum group metal.