JPS6022077B2 - How to attach metal fine particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for attaching fine metal particles of rhodium, palladium, or platinum to the surface of a hydrogen-absorbing metal (meaning a metal capable of absorbing hydrogen, hereinafter the same).

In the method of electrolyzing water to generate hydrogen and passing this hydrogen through a metal hydrogen-permeable membrane to produce extremely high-purity hydrogen, it is possible to use the metal hydrogen-permeable membrane as an electrode for water electrolysis. It is being done.

Palladium metal is widely used as such metal hydrogen permeable membranes and electrodes for water electrolysis, but if fine particles of metal such as rhodium, palladium, or platinum are attached to this palladium metal, hydrogen permeability can be improved. It is known. On the other hand, as a method for attaching fine particles of metal such as palladium to the surface of a metal to be adhered to, there are two methods: 1) immerse the metal to be adhered in an aqueous solution of a salt of a metal such as palladium, and conduct electrolysis using the wave-attached metal as a cathode. There are two methods: (2) a method of immersing the metal to be deposited in a solution of a salt of a metal such as palladium in the coexistence of a reducing agent, and depositing fine particles of a metal such as palladium on the surface thereof. However, method (2) cannot be applied to objects with complex shapes because the current density varies depending on the distance to the anode, and is limited to objects with simple shapes, such as flat objects and rod-like objects. Even if the current density is large at acute angles and points, not only the amount of metal fine particles attached becomes uneven, but also the light weight of the fine particles becomes coarse and non-uniform. There was a drawback. On the other hand, in the case of method (■), it can be applied to objects with relatively complex shapes, but the amount and particle size of the metal particles may vary slightly depending on the concentration of palladium, etc., temperature, and concentration of the reducing agent. However, not only is it impossible to obtain the desired adhesion amount and grain size, but there is also the drawback that the adhesion is generally weak and will fall off even when a slight mechanical force is applied. Furthermore, when a metal with fine particles such as palladium adhered to it obtained by such a conventional method is used as a hydrogen permeable membrane and an electrode for water electrolysis, the hydrogen permeability is low due to the above-mentioned drawbacks of the conventional method. The price was not high enough to be practically satisfactory, and the lifespan was too short to put it into practical use.

The present inventors have discovered that the above-mentioned drawbacks of conventional methods should be overcome.As a result of intensive research, the present inventors have discovered that metal fine particles such as palladium can be deposited in a uniform amount without being limited by the shape of the object. The method of the present invention has been achieved in which the metal fine particles do not become coarse, have a uniform particle size, and have a strong adhesion force.

That is, the present invention provides a method for attaching fine metal particles of rhodium, palladium, or platinum to the surface of a hydrogen-absorbing metal that has been occluded by water electrolysis by bringing it into contact with an aqueous solution containing rhodium, palladium, or platinum. It is.

The hydrogen storage metal used in the present invention is not particularly limited, but includes titanium, zirconium, cesium, palladium, nickel,
Iron and copper are each preferred.

Among these, titanium, zirconium, cesium, palladium, and nickel are particularly preferred because they have a large hydrogen storage capacity, and a sufficient amount of metal fine particles can be attached with great adhesion by just one electrolysis and attachment of water. In order to store hydrogen in a hydrogen-absorbing metal, water is electrolyzed in the usual manner using a hydrogen-absorbing land metal (hereinafter also referred to as a deposited metal) to which fine metal particles are attached as a cathode.

The electrolyte is usually preferably an alkaline aqueous solution. As this aqueous alkali solution, an aqueous solution of an alkali metal hydroxide is usually used, preferably an aqueous solution of sodium hydroxide or potassium hydroxide. The concentration of the alkali metal hydroxide in the alkaline aqueous solution is the same as in the commonly practiced electrolysis of water to generate hydrogen, but in practice it is 1 to 30 wt%, preferably 5 to 13 wt%. It is. The temperature of the electrolytic solution during electrolysis varies depending on the type of metal to be deposited, but is usually 0 to 100 qo, preferably 20 to 80 qo.

In addition, in practice, it is usually carried out at room temperature or room temperature, but heating and cooling are not prohibited as long as the temperature is within the above range. There is no particular limit to the current density during electrolysis, but if the current density is too low, it will take a long time to absorb hydrogen and the equilibrium hydrogen storage amount of the deposited metal will decrease, so it should be 0.001 to 5 A/
, preferably 0.1 to 0.4 A/.

The electrolysis time varies depending on the hydrogen absorption rate of the metal to be deposited, but it is preferable to electrolyze until the entire surface of the part of the metal to be deposited immersed in the electrolyte is uniformly adsorbed, and under the above electrolytic conditions, it may take 30 minutes or less. , usually about 10 to 20 minutes.

After electrolysis, the deposited metal is brought into contact with an aqueous solution containing rhodium, palladium, or platinum.

There are no particular restrictions on the means of contact, and examples of methods that can be used include flowing down, counterfeiting, and immersion, but immersion is most preferred from a practical standpoint. The aqueous solution containing rhodium, palladium, or platinum is an aqueous solution of a rhodium compound, a palladium compound, and a platinum compound, respectively. Compounds of these metals are not particularly limited as long as they are water-repellent and may be organic acid salts, inorganic acid salts, rust salts or double salts, but chlorides, hydrochlorides and sulfates are preferred. Typical examples of these metal compounds include platinous chloroplatinic acid (PtC14), diplatinic acid chloride (4PtC16/mother LO), potassium chloride platinum (K2PtC14), and ammonium chloride platinum (K2PtC14).
NH4)2PtC14), sodium diplatinate chloride (
N is also PtC16/mother LO), platinum tetraaminonitrite (
Pt(NH3)4(N02)2), potassium tetracyanoplatinate (balanced Pt(CN)4・20, palladium chloride (PdC12・2), palladium nitrate (Pb
(N03)2), palladium sulfate (PdS04・2LO
), palladium diaminonitrite (Pd(NH3)2(N
Q) 2), sodium palladium ethylenediaminetetraacetate (C, oH, 2N208Na2Pd), rhodium chloride (RhC13/Misaki 20), sodium sulfate (Rh2(S0
4) 3・12LO) and sodium chloride rhodate (
Examples include Na3RhC16 and insect LO). There is no particular limitation on the concentration of these metal compounds in this aqueous solution, but if it is too low, the adhesion will not occur quickly, and if the concentration is too high, the adhered metal particles will become coarse, so the concentration should be 0.02~ 1 skin t%, preferably 0.1~
It is a fine t%. In addition, aqueous solutions containing these metals include
It is preferable to contain stannic acid containing an anion or a halogen atom contained in the metal compound used in preparing this aqueous solution. For example, hydrochloric acid is used for chloroplatinic acid, and sulfuric acid is used for rhodium sulfate. The temperature of this aqueous solution at the time of counterfeiting may be a temperature at which the metal compound does not precipitate, but if the temperature of the solution is too high, the particles tend to become coarse, so it is usually 0 to 150°C,
Preferably it is 10-8000.

In addition, in practice, it is usually carried out at room temperature or room temperature, but heating and cooling are not prohibited as long as the temperature is within the above range. The time required for dipping varies depending on the type of metal to be adhered to, the type of metal compound, the concentration of the metal compound in the aqueous solution of the metal compound, and the temperature of the liquid at the time of dipping, and cannot be definitively stated, but usually it takes less than 10 minutes. Preferably it is about 1 to 5 minutes. If this time is too long, the attached metal particles will become coarse. Further, it is preferable to keep the ion concentration of the liquid uniform by washing the liquid.

According to the present invention, each fine particle of rhodium, palladium, or platinum can be deposited with a uniform amount of metal fine particles without being restricted by the shape of the object to be adhered,
Furthermore, there are advantages in that Z does not occur if the metal fine particles are coarse, the particle size is uniform, and the adhesion force of the metal fine particles is large.

According to the present invention, the hydrogen-absorbing metal to which metal fine particles are attached can be suitably used as a hydrogen permeable membrane and an electrode for water electrolysis, as well as an electrode for an electrical conductivity meter, an electrode for water electrolysis using a Z caustic alkali aqueous solution, etc. It can also be suitably used as

The present invention will be explained in more detail with reference to Examples.

Example 1 After degreasing and cleaning a palladium-silver alloy tube with an outer diameter of 2, a thickness of 0.1 and a length of 150, this was used as a cathode, and a tube with an inner diameter of 28 and a thickness of 1 was placed on the outside as an anode. 5M by placing nickel tube
% caustic soda aqueous solution was used as the electrolyte, and the temperature was 50q.
Each powder was electrolyzed by passing a direct current 2 of 2 amperes at 100 mA to occlude hydrogen.

After washing the tube used as a cathode with water, it was heated with palladium chloride (PdC12/Pan 20) at 36% HC1 for 7.2 nights.
The skin was soaked in an aqueous solution consisting of 20 skin and pure water for 2 minutes. Note that the liquid temperature at this time was maintained at 50 qo.
3 Palladium black with a particle diameter of 1.8 was adhered to the tube obtained in this way, and when observed with an electron microscope, the size of the palladium fine particles on both the inner and outer surfaces was 0.2~
It was lAm. In addition, the thickness of the deposited metal fine particle layer is 5 to 5.
It was 7 mm. 16 tubes obtained in this way
As a set, this was used as a hydrogen permeable membrane and an electrode for water electrolysis, and extremely high purity hydrogen was produced by water electrolysis.

The electrolysis conditions were: DC voltage 2.7V, DC current 5 peaks L current density 0.33A/ground, electrolyte 1% aqueous caustic soda solution, and electrolysis temperature 80qo. The hydrogen pressure generated is 4k9/
It was the enemy G.

The hydrogen permeation amount and hydrogen permeation efficiency at the initial stage of production are respectively 28 side C. C. and 80.3%, and 25
After 25 months each. C. minutes and 74.0
%Met. The purity of the obtained hydrogen is 99.999.
It was 99%.

Example 2 After degreasing and cleaning a smooth nickel plate with #400 polishing and measuring 10 mm in height and 1 rib in height, this was used as a cathode.
Two nickel plates were placed as anodes, one on each side of the nickel plate as a cathode, and a 1 K% caustic potassium aqueous solution was used as the electrolyte, and a direct current of 6 amperes was applied at a temperature of 7.0°C for 18 minutes to electrolyze the hydrogen. was absorbed.

After washing the nickel plate used as a cathode with water, dichloroplatinic acid (day 2PtC16/mother LO) was added at 17.5pm, 3pm.
It was immersed for 3 minutes in an aqueous solution consisting of 10 parts of 6% HCI and 1 to 5 parts of pure water. Note that the liquid temperature at this time was maintained at 70°C. The plate obtained in this way has 9/9 of 3.9.
Platinum black was attached to the surface, and when observed with an electron microscope, the size of the fine particles was 0.5 to 1.5 r.

Furthermore, the thickness of the deposited metal particle layer was 5 to 10 mounds.

The plate thus obtained was used as an anode, one stainless steel plate was placed on each side of the anode as a cathode, and a 2 t% caustic soda aqueous solution was electrolyzed.

The current density was set to IA/, and the electrolyte temperature was maintained at 70°C.
After 6 months of electrolysis, the surface of the electrolyte was observed, but no change was observed. In addition, there was almost no change in the voltage and power efficiency from immediately after the start. 0 Comparative Example 1 A tube similar to that used as a cathode during hydrogen storage by water electrolysis in Example 1 was prepared using a 10% aqueous solution of palladium chloride (palladium concentration 1%), 20% formic acid as a reducing agent, and 20% of formic acid as a reducing agent. The tube was immersed in an aqueous solution consisting of 400 ml of pure water, and the temperature of the liquid was maintained at 80 ℃ to allow black fine particles of palladium to adhere to the surface of the tube.

Note that the bond immersion time was 15 minutes. Palladium black with an o/base of 1.2 is adhered to the tube thus obtained, and according to electron microscopic observation, the size of palladium black fine particles on both the inner and outer surfaces is 5 to 20 F. It was a desk.

The thickness of the deposited metal particle layer was 0 to 30 mm. Using the tube thus obtained, water was electrolyzed in the same manner as in Example 1 to produce highly pure hydrogen.

As a result, the hydrogen permeation amount and hydrogen permeation efficiency at the initial stage of production were determined by C.23, respectively. C. /min and 61.8%, and 13 respectively after 2 weeks. C. /min and decreased to 38.2%. The purity of the obtained hydrogen was 9
It was 9.99999%.

Comparative Example 2 A smooth nickel plate similar to that used in Example 2 was used as a cathode, and a platinum plate was used as an anode.
An aqueous solution consisting of C12 secretion and 500% pure water was used as an electrolyte, and a direct current was passed for 5 minutes at a current density of 0.0 pine/earth to deposit platinum black on a smooth nickel plate.

In addition, the liquid temperature at this time was maintained at 5.0 psi. On this plate, 3-year-old platinum black was adhered, and when observed with an electron microscope, the size of the fine particles was 2 to 10'', so the thickness of the adhered metal particle layer was 3 to 15 mm. Using the thus obtained plate, electrolysis of a 2% t% caustic soda aqueous solution was carried out in the same manner as in Example 2.

After 10 days, the platinum black flaked off, the voltage increased, and the power efficiency decreased.

Claims (1)

[Claims] 1. A method in which a hydrogen-absorbing metal that has occluded hydrogen by electrolysis of water is brought into contact with an aqueous solution containing rhodium, palladium, or platinum, and fine metal particles of rhodium, palladium, or platinum are attached to the surface of the metal.