JPS62163261A - Manufacture of electrode of high electric conductivity - Google Patents

Abstract

PURPOSE:To enhance electric conductivity without losing original useful properties, by using an electroless plating method to deposit an electroconductive metal layer on the surface of an active carbon fiber. CONSTITUTION:A phosphite, hydrazine, a hydrogenated boron compound, amine borane or the like is used as a chemical reducing agent for an electroless plating solution. Nickel, cobalt, copper, silver, gold, platinum, rhodium or the like is used as a plated metal. The ratio of the weight of a deposited electroconductive metal layer to that of an active carbon fiber is 3-100%. An electrode of high electric conductivity is thus manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a highly conductive electrode in which a conductive metal layer is supported on the surface of activated carbon fibers.

[Conventional technology]

In recent years, electrodes using activated carbon fibers with a large specific surface area have been actively developed. Applications of these electrodes include electrode plates for fuel cells (JP-A-59-46762, JP-A-58-
100364), Polarizable electrode for electric double layer capacitor (JP-A-5B-206116, JP-A-59-4114)
), electrodes for secondary batteries (JP-A-59-157974, JP-A-S9-163765), opposing W for electrochemical display devices (JP-A-59-143130), etc. have been proposed.

Activated carbon fibers having a large specific surface area such as 100 to 40 Q Om2/g are extremely useful as various electrode materials because of their large contact area with solutions. For example, in the case of electric double layer capacitors using activated carbon fibers as polarizable II poles, a large amount of doping is possible due to their large specific surface area, making it possible to create capacitors with high energy output. Has characteristics.

However, electrodes using such useful activated carbon fibers have a drawback of high resistance. Therefore, when used in various types of batteries, the resistance of the II pole is large, resulting in a disadvantage that the internal resistance of the various types of batteries increases.

Attempts to lower the resistance of W poles made of activated carbon fibers are actively being made by those in the industry. As the best method, JP-A-59-67617 proposes a method in which activated carbon fibers are supported with a conductive modification layer.

In the above invention, there are two methods: (1) an immersion pyrolysis method using a thermally decomposable salt such as ruthenium chloride, (2) a method of applying or impregnating a conductive paint such as a carbon colloid liquid, and (2) a method of applying a conductive oxide such as tin oxide. Examples include methods of forming by vacuum evaporation or sputtering.

[Problem that the invention seeks to solve]

However, depending on the immersion pyrolysis method (2) or the coating or impregnation method (2), the effect of improving conductivity may not be sufficient, or the fiber surface may be coated, resulting in a problem that the specific surface area is significantly reduced. . Furthermore, according to the vacuum evaporation or sputtering method (2), since the metal layer is supported only on the subatomic fibers on the surface, the effect of improving conductivity is not sufficient, especially in the form of a sheet. Therefore, no matter which conventional method is adopted, the usefulness of activated carbon fibers is maintained.
It has been extremely difficult to improve conductivity.

The object of the present invention is to obtain an electrode made of activated carbon fibers which has significantly improved conductivity without losing these useful properties.

[Means for solving problems]

The present inventors conducted extensive studies in view of the above objectives, and found that an electrode using a gold conductive layer deposited on the surface of activated carbon fibers using an electroless plating method was found to be useful. The present invention was achieved by recognizing that the conductivity of the electrode itself can be significantly improved without losing its properties.

That is, the present invention relates to a method for producing a highly conductive electrode characterized by plating activated carbon fibers by electroless plating. This highly conductive electrode is extremely useful as an electrode for various batteries.

The activated carbon fibers used in the present invention are recycled fibers with particularly excellent adsorption ability, and generally have a specific surface area of 10 Om/1 or more. The preferred specific surface area is 700I
/y or more, particularly in the range of 1400 Qη or more. Such activated carbon fibers include cotton, linen, cellulose regenerated fiber,
It can be obtained from raw material fibers such as polyvinyl alcohol fibers, acrylic R fibers, aromatic polyamide fibers, crosslinked formaldehyde fibers, lignin fibers, phenol fibers, and petroleum pitch fibers according to conventional methods. As a raw material fiber, polyvinyl is used because not only the obtained activated carbon fiber has a large specific surface area and excellent adsorption ability, but also the performance of the activated carbon fiber hardly deteriorates even when subjected to electroless plating. It is preferable to use alcohol-based fibers or phenol-based fibers.

The activated carbon fibers can be electrolessly plated in any form. That is, when a sheet-like electrode is preferred, the activated carbon fiber sheet obtained by using the raw material fiber as a fabric such as a woven fabric or a non-woven fabric can be directly plated.

In the present invention, a normal electroless plating method is directly adopted. That is, degreasing, etching, etc. are performed to remove dirt on the surface of the material, a surface conditioning process to improve the adhesion of the plating film, and/or gold or platinum is applied to the surface of the material to start the electroless plating reaction. This can be done by immersing activated carbon fibers that have undergone a catalytic process of providing noble metal catalyst nuclei such as palladium, silver, etc. in an electroless plating solution containing a chemical reducing agent.

The catalytic process is subdivided into a sensitization process and an activation process. The sensitization process is a process in which metals with reducing power are adsorbed onto the surface of the material. This step is carried out by immersing the material in a sensitizing solution. Examples of the sensitizing solution include chlorides of tin and noble metals, and among these, a solution of stannous chloride in hydrochloric acid is preferable because it produces metal ions with strong reducing power. The activation treatment step is a step of imparting noble metal catalyst nuclei to the surface of the material. This step is carried out by immersing the sensitized material in an activation treatment solution. As the activation treatment liquid, an acidic solution of noble metal ions is exemplified, but it is preferable to use a hydrochloric acid solution of palladium chloride because the resulting metal film has high conductivity.

As the chemical reducing agent used in the electroless plating solution, hypophosphite is best, but hydrazino, borohydride compounds, amineborane, etc. can also be used. Examples of metals that can be plated include nickel, cobalt, copper, silver, gold, platinum, and rhodium, but nickel is the most suitable because it provides good conductivity of the resulting electrode and is inexpensive. Are better. Plating conditions are greatly influenced by bath composition, plating time, temperature or pH.
It is necessary to adequately manage it in accordance with conventional laws.

The temperature is usually raised to 40 to 70°C, particularly preferably 50 to 60°C, for 30 seconds to 10 hours, particularly preferably 5 minutes to 3 hours, and the pH is 3.5 to 12, particularly preferably 4 to 5 or 7 to 1.
This is done within the range of 1.

The amount of conductive metal layer supported is based on the weight of activated carbon fiber.
The range is preferably 3% by weight or more and 100% by weight, particularly preferably 5% by weight or more and 50% by weight or less. If the supported amount is too small, the conductivity effect will not be sufficient, and if the supported amount is too large, the specific surface area may decrease more.

According to the above electroless plating method, activated carbon fiber can be produced.

In addition, according to this electroless plating method, when plating a sheet, the metal layer is uniformly supported on the surface of the activated carbon fibers inside the sheet, so the conductivity of the sheet is significantly improved. As a result, an electrode with excellent adsorption performance and electrical conductivity can be obtained.

The highly conductive electrode of the present invention is industrially very important as an electrode plate for fuel cells, a polarizable electrode for electric double layer capacitors, an electrode for secondary batteries, and a counter electrode for electrochemical display devices.

〔Example〕

The present invention will be explained in more detail below using examples.

Example 1 [Nickel electroless plating on activated carbon fiber sheet] Sheet made of phenolic activated carbon fiber [specific surface area: 2500-r? L/f], and nickel electroless plating was performed on this. Prior to plating, the following three solutions were prepared.

■ 5nC12 in distilled water] OVl, HCJ 0
．． Sensitization treatment solution dissolved at a concentration of 5 CC/1.

■ Pd ring at 2 f/l and Hα at 10 in distilled water.
Activation treatment solution dissolved at a concentration of cc/l.

■ In distilled water, add 201/l of NiSO4/6H20, 20 f/l of sodium hypophosphite, 10 f/l of trisodium citrate, and 5 cc/l of lactic acid (50 wt%).
l.

A tamping solution in which NH4OH (25wt%) is dissolved at a concentration of 40 CC/l.

An activated carbon fiber sheet (5 cm x 10 cts) was sensitized by immersing it in 100 cc of the above sensitizing solution at 20° C. for 5 minutes. Thereafter, the sheet was taken out of the liquid, thoroughly washed with water, and dehydrated by suction. The dehydrated sheet was immersed in 100 cc of the above activation treatment solution for 5 minutes to perform activation treatment. Thereafter, the sheet was taken out of the liquid and thoroughly washed with water, followed by suction dehydration. Above plating solution 5
The temperature of the oocc was raised to 55° C. in a water path, and the activated sheet was placed therein and lightly stirred. After about 3 minutes, bubbles were generated from the sheet surface and plating started at the same time.

After the plating reaction started, let it react for 10 minutes, then remove the sheet from the solution, wash it thoroughly with water, and heat it at 150°C.
Vacuum drying was performed for 4 hours.

The weight of the sheet before plating was 13 mg/z, but after plating it increased to 21 mg, an increase of about 60% by weight.

The resistance of the sheet is spaced between two stainless steel wires of CLL (
The evaluation was made by pressing an electrode having a thickness of l + m from a direction perpendicular to the sheet and measuring the resistance between the electrodes.

While the resistance before plating was 540, it decreased to 6Ω/cm after plating. The specific surface area before and after plating was measured using the BET method.
y, but after plating it was 2100.717g, which was a decrease of about 16%.

When the surface of the activated carbon fiber was observed using a scanning electron microscope, many micropores were observed in the metal layer.

Comparative Example 1 [Effects of immersion pyrolysis of ruthenium chloride] The same activated carbon fiber sheet used in Example was dipped in a 0.5 mol/l ruthenium chloride aqueous solution for 5 minutes.
The activated carbon fibers were kept in a furnace at 0° C. and their surfaces were coated with a ruthenium oxide layer.

The resistance of this sheet was measured in the same manner as in Example 1. The resistance of the sheet before treatment was 54Ω/αM, which decreased to 20Ω/α after treatment, but the degree of reduction was extremely small compared to when the nickel electroless plating method was used. The specific surface area after treatment was measured, but before treatment it was 2500.
m/f, but after treatment it was 1300 m/f.
l, a decrease of about 48%.

In any case, this method of forming a conductive layer by immersion pyrolysis of a pyrolyzable salt not only does not have a sufficient effect of improving conductivity but also significantly reduces the specific surface area because the fiber surface is covered. There was a drawback.

Comparative Example 2 [Effects of Metal Conductive Layer Deposited in Vacuum] The same activated carbon fiber sheet used in Example was placed in a Pel jar of a pure nitrogen evaporator, and the system was evacuated to 1 x 10 Torr. Vacuum deposition was performed.

Vacuum deposition was performed a total of six times, three times on each side of the sheet.

The resistance of this sheet was measured in the same manner as in Example 1. The resistance of the sheet before treatment was 54 Ω/C, but it decreased to 460 Ai after gold deposition. The specific surface area after the treatment was measured and was found to be 2200 cm/f. According to observation using a stereoscopic microscope, it was confirmed that the conductive layer was not applied to the fibers inside the activated carbon fiber sheet. For this reason, it was not possible to significantly reduce the resistance of the sheet.

Example of use as an electric double layer capacitor The activated carbon fiber sheet coated with nickel electroless plated in Example 1 was cut into a size of 1 cx x 1 cm. An electric double layer capacitor was fabricated using these two samples as polarizable electrodes. A sheet Hachiflon membrane filter (pore size: 3 μm) was installed at both electrodes, and 20 ml of propylene carbonate dissolved in lithium perchlorate at a total concentration of 1 mol/l was used as the electrolyte.

The capacitance and internal resistance of this electric double layer capacitor at 256C were measured and the results are shown in Table 1.

Furthermore, a capacitor was produced using an untreated activated carbon fiber sheet (used in Example 1) and the sample obtained in Comparative Example 1.2. The same method as in the case of using the sample of Example 1 was used except that a platinum mesh was used as the current collecting electrode. Table 1 shows the characteristics of this capacitor.

Comparing the results in Table 1, it was found that a capacitor using an activated carbon fiber sheet subjected to electroless plating provided significantly superior performance.

〔Effect of the invention〕

As explained above, according to the present invention, a highly conductive electrode can be obtained, and by using this electrode, various devices such as batteries with reduced internal resistance can be manufactured.

Claims (1)

[Claims] 1. A method for producing a highly conductive electrode, characterized in that an electroless plating method is used to support a conductive metal layer on the surface of activated carbon fibers. 2. Claim 1, wherein the activated carbon fiber is an activated carbon fiber having a specific surface area of 700 to 4000 m^2/g.
Method for manufacturing electrodes described in Section 1.