JP2961491B2 - Preparation method of metal electrode material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for producing a metal electrode material which can be used for industrial electrolysis electrodes and sensor element electrodes, has a large specific surface area, can be bent, and has little deterioration over time even in an electrolytic solution containing water. Things.

[0002]

2. Description of the Related Art While the surface of a general metal electrode material is smooth, the surface of a metal electrode material used for industrial electrolysis or the like is subjected to sandblasting, chemical or electrochemical etching, or the like. A roughened metal electrode material is used. The purpose of this is to reduce the overvoltage of the electric reaction by increasing the specific surface area due to the surface roughening, and to improve the electrolysis efficiency or the electrolysis reaction speed of the metal electrode reaction.

Also, as a metal electrode material having a large specific surface area, a foamed metal, a sintered body of metal fiber or metal powder, an aluminum etched foil for an aluminum electrolytic capacitor, and the like are known. It is used for miniaturization and high performance.

[0004]

However, the surface roughening method according to the conventional method described above cannot be said to have a sufficient effect of increasing the surface area, and a method for further increasing the specific surface area is required. In addition, although the specific surface area of a sintered metal foam metal, a metal fiber or a metal powder having a large specific surface area is improved, it is difficult to reduce the thickness due to the manufacturing method thereof.
Further, there is a problem that the material itself is not suitable for bending because of its poor flexibility.

In the case of an aluminum-etched foil, it is possible to solve the problems of a metal sintered body in terms of bending workability and thickness reduction, but in an electrolytic solution containing water, Deterioration over time due to the formation of hydrated oxides and the like was inevitable.

[0006]

Means for Solving the Problems Aluminum having a purity of 99% or more is immersed in an etching solution, and is etched by applying a direct current or an alternating current to form micropits and reduce the surface area of the aluminum foil to 5 to 150 nm. Metal plating is performed on the aluminum-etched foil that has been doubled in size, and then, the metal-etched foil is dissolved and removed, and the shape of the micropit is transferred to produce a metal electrode material. I do.

As another method, aluminum having a purity of 99% or more is immersed in an etching solution, and etching is performed by applying a direct current or an alternating current to form micropits, thereby increasing the surface area of the aluminum foil by 5 to 150 times. After applying metal plating on the aluminum etched foil expanded to, the aluminum etched foil is dissolved and removed to transfer the shape of the micro pits, and the surface of the metal plating layer is coated with a substance having a catalytic action. It is characterized by producing a metal electrode material.

[0008] The metal plating is preferably a plating made of one or more metals selected from nickel, copper, platinum, palladium, rhodium, lead, tin and zinc.

[0009]

The aluminum used as a matrix is formed by immersing aluminum having a purity of 99% or more in an etching solution and applying a direct current or an alternating current to perform etching to form micropits. When etching is performed by applying an electric current, etching proceeds only in the [100] direction of the aluminum crystal structure, so that tunnel-like pits are obtained, and when an AC current is applied, tuft-like pits are obtained. be able to. Therefore, the surface area of aluminum serving as a matrix can be increased by 5 to 150 times. The metal electrode material of the present invention is obtained by immersing aluminum having a purity of 99% or more used as a matrix in an etching solution, applying a direct current or an alternating current to perform etching, forming micropits, and forming an aluminum foil. Has a surface shape obtained by transferring the shape of micro-pits of an aluminum-etched foil whose surface area is increased by 5-150 times, whereby the specific surface area can be increased. The surface area enlargement magnification can be arbitrarily selected depending on the specific surface area of the aluminum-etched foil used as the matrix.

The thickness of the metal plating layer formed on the aluminum-etched foil can be reduced by selecting the thickness of the metal plating layer, whereby a metal electrode material that can be bent can be manufactured.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preparation of the metal electrode material of the present invention is roughly divided into the following continuous processes. In other words, this is a method in which a high-magnification aluminum-etched foil obtained by electrochemical etching is subjected to a catalyst activation treatment and an electroless plating treatment after being subjected to an acid cleaning treatment, followed by heat treatment and aluminum dissolution removal.

Here, the aluminum-etched foil used is formed of aluminum having a purity of 99% or more to a thickness of about 100 μm, immersed in an etching solution mainly containing hydrochloric acid, and applying a direct current or an alternating current. By doing so, the surface area of the aluminum foil is enlarged by a factor of 5 to 150 to form an aluminum-etched foil.

[0013] This aluminum etched foil subjected to the surface enlargement is etched by applying a direct current,
Since etching proceeds only in the [100] direction of the aluminum crystal structure, etching pits are formed in a tunnel shape from the aluminum foil surface as shown in FIG.
Aluminum etched foil with tunnel pit structure.

When the aluminum foil is etched by applying an alternating current, the shape of the etching pits is as shown in FIG. Aluminum etched foil with a pit structure.

As each of the treatment baths used for producing the metal electrode material, a generally known acid, an activation treatment bath for plating, an electroless plating bath, an electrolytic plating bath and the like can be selected. For example, the metal electrode material of the present invention can be manufactured under the conditions shown in the following Example 1.

Example 1 An aluminum-etched foil having a tunnel pit structure was immersed in 30% by volume of nitric acid, and then subjected to a palladium activating treatment for plating under the following treatment conditions. Bath 1 PdCl ₂ .2H ₂ O 0.1 g / L HCl 5 mg / L Immersion at 60 ° C. for 1-5 minutes Bath 2 NaH ₂ PO ₂ .H ₂ O 50 g / L 5 minutes at 40 ° C. Immersion

Next, the aluminum etched foil after the palladium treatment was subjected to electroless nickel plating under the following conditions to fill nickel into the micropits of the aluminum etched foil. Bath 3 NiSO ₄ .6H ₂ O 20 g / L NaH ₂ PO ₂ .H ₂ O 15 g / L Na ₃ .Citrate 15 g / L NaOH 5 g / L pH = 6, immersion at 40 ° C. for 5 minutes

Further, electrolytic nickel plating was performed under the following conditions to increase the thickness of the nickel layer to improve the mechanical strength of the finally obtained brush-type nickel electrode material. Bath 4 NiSO ₄ .6H ₂ O 150 g / L NH ₄ Cl 15 g / L H ₃ BO ₃ 15 g / L Additives Appropriate amount At pH = 6, 40 ° C., plating was performed using a nickel plate as a counter electrode. Cathodic electrolysis was performed at a current density of 10 mA / cm ² for 30 minutes.

The sample treated as described above was heat-treated at 350 ° C. for 90 minutes and then immersed in a 10% sodium hydroxide solution at 60 ° C. for 30 minutes to dissolve and remove aluminum. The brush-shaped nickel electrode material obtained after dissolving aluminum had a thickness of about 50 microns.

FIG. 1 shows an SEM photograph of the surface of the obtained brush-shaped nickel electrode material. From the figure, it can be seen that the tunnel pit shape of the aluminum-etched foil used as the master was well transferred.

FIG. 2 shows a brush type nickel electrode material of 3M.
-Potassium hydroxide solution, cathode current-potential curve at 25 ° C. The cathode polarization characteristics of a rolled nickel foil electrode having a smooth surface as a comparative electrode and a rolled nickel foil electrode whose surface was roughened by AC electrolysis were also shown.
From the figure, it was found that the brush-type nickel electrode material can reduce the hydrogen overvoltage more than the two kinds of nickel electrodes in comparison.

(Example 2) By coating the brush-shaped nickel electrode prepared in Example 1 with a substance having a catalytic action in various electrode reactions, the function of the brush-type electrode material can be further enhanced. Examples of the substance having a catalytic action include metals such as platinum, lead, mercury, rhodium, and palladium, and oxides thereof. For the coating, platinum can be coated on the surface of the brush-shaped nickel electrode by the following treatment, for example. Bath _{5 H 2 PtCl 6 · 6H 2} O 20 g / L HCl 20 seconds immersed in 300 mL / L 60 ° C

FIG. 3B shows a surface SEM photograph of the brush-shaped nickel electrode material after platinum coating. Fine grain precipitation of platinum was observed, thereby further improving the specific surface area.

FIG. 2 also shows the cathode polarization characteristics of the brush-shaped nickel electrode material after platinum coating. As can be seen from the figure, it can be seen that the hydrogen overvoltage was further reduced as compared with Example 1.

Example 3 After a palladium treatment for plating in the same manner as in Example 1, a copper electrode material in which the micropit shape of an aluminum-etched foil has been transferred can be produced, for example, under the following conditions. Bath 6 CuSO ₄ .5H ₂ O 5 g / L NaOH 7 g / L Rochelle salt 25 g / L Formalin (37%) 10 mL / L Dipping treatment at 20 ° C. for 2 minutes causes copper in the micro pit After that, electrolytic copper plating was performed under the following conditions. Bath 7 CuSO ₄ .5H ₂ O 250 g / L H ₂ SO ₄ 10 mL / L Thiourea 0.75 g / L 40 ° C. Cathodic electrolysis was performed for 40 minutes at a current density of 50 mA / cm ² using a copper plate as a counter electrode. This sample was dissolved and removed in the same manner as in Example 1 to obtain a brush-type copper electrode material.

FIG. 5 shows a cathode current-potential curve using the brush type copper electrode. As in the case of Example 1, it was confirmed that the hydrogen overvoltage can be reduced as compared with the copper electrode having a smooth surface.

Further, even with the above metals other than nickel and copper, a plating layer made of one or more metals selected from platinum, palladium, rhodium, lead, tin, zinc and the like is formed on the aluminum-etched foil. Then, by dissolving and removing the aluminum-etched foil, a metal electrode material having the same surface area expanding effect as in the above embodiment can be manufactured.

Further, in the above embodiment, the case where an aluminum-etched foil having a tunnel pit structure is used has been described. However, metal plating is performed on the aluminum-etched foil having a tufted pit structure. When a metal electrode material is formed by dissolving an aluminum-etched foil into a metal electrode material, a metal electrode material in which a tuft-like pit structure is transferred is produced. Even in this case, the surface area of the produced metal electrode material has a large specific surface area as in the case of having the tunnel pit structure, and the electrical characteristics are to be improved at the same level as when aluminum etched foil having the tunnel pit structure is used. Was completed.

[0029]

Since the metal electrode material produced according to the present invention can form a large specific surface area, it can be used as an anode or a cathode in an electrolytic reaction, for example, to reduce hydrogen gas generation overvoltage due to water electrolysis, and to reduce oxygen overvoltage. Can be reduced, and the energy consumption of the electrolytic reaction can be reduced.

Further, the sensitivity and size of the element can be increased by using it as a base for functional element electrodes and sensor element electrodes to which various metals, metal oxides, catalysts, enzymes, etc. are added. The anchoring effect obtained from the fine shape of the above makes it possible to prolong the life of the device by preventing the modifier from falling off.

[Brief description of the drawings]

FIG. 1 is a surface SEM photograph of a brush-shaped nickel electrode material obtained in Example 1.

FIG. 2 is a graph showing a cathode current-potential curve of the brush-shaped nickel electrode material and the platinum-coated brush-shaped nickel electrode material obtained in Examples.

3A is a surface SEM photograph of the brush-shaped nickel electrode material obtained in Example 1, and FIG. 3B is a surface SEM photograph of the platinum-coated brush-shaped nickel electrode material obtained in Example 2. It is.

FIG. 4 is a surface SEM photograph of the brush-type copper electrode material obtained in Example 3.

FIG. 5 is a cathode current-potential curve of the brush-type copper electrode material obtained in Example 3.

FIG. 6 is an SEM photograph of an oxide replica of an aluminum-etched foil having a tunnel pit structure.

FIG. 7 is an SEM photograph of an oxide replica of an aluminum-etched foil having a tufted pit structure.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-50-141540 (JP, A) JP-A-63-171891 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C25B 11/00-11/20 C25D 1/00 C25D 1/04

Claims (3)

(57) [Claims] 1. An aluminum sheet having a purity of 99% or more is etched.
Immersion in a liquid, and apply DC or AC current
Etching to form microbits, aluminum
A metal electrode formed by applying metal plating on an aluminum-etched foil whose surface area is increased by 5-150 times, dissolving and removing the aluminum-etched foil, and transferring the shape of the micropits. How to make the material. 2. An aluminum sheet having a purity of 99% or more is etched.
Immersion in a liquid, and apply DC or AC current
Etching to form micro pits, aluminum
After metal plating is performed on an aluminum-etched foil whose surface area is increased by 5-150 times , the aluminum-etched foil is dissolved and removed to transfer the shape of the micro-pits, and the metal plating layer surface A method for producing a metal electrode material, characterized in that a material having a catalytic action is coated on a substrate. 3. The metal plating applied on the aluminum-etched foil is nickel, copper, platinum, palladium, rhodium,
3. The method for producing a metal electrode material according to claim 1, wherein the plating is performed using one or more metals selected from the group consisting of lead, tin, and zinc.