JP2000087279A - Gas diffusion electrode using bonded body of gas supply layer and porous metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bonded body of a gas supply layer in which a porous metal body and a fibrillated PTFE porous sheet are firmly bonded to a porous metal body, and a long-life and high-performance gas diffusion electrode using the same. I will provide a. SOLUTION: A metal porous body and carbon black are added in an amount of 0 to 5;
A fibrillated PTFE water-repellent porous sheet containing 5% and a temperature equal to or higher than the melting point of PTFE;
A porous metal-water-repellent porous sheet assembly for a gas diffusion electrode, wherein the porous metal and the water-repellent porous sheet are strongly bonded by hot pressing at a pressure of at least kg / cm ² . A gas diffusion electrode produced by filling a reaction layer material from the porous metal side of the joined body of claim 1 and hot-pressing the reaction layer material under optimum conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal porous body for a gas diffusion electrode, particularly for a gas diffusion electrode used for salt electrolysis and the like.
The present invention relates to a water-repellent porous sheet assembly and a gas diffusion electrode obtained therefrom, and particularly to a gas diffusion electrode having a long life.

[0002]

2. Description of the Related Art Conventionally, in a gas diffusion electrode, a reaction layer is formed of carbon black carrying silver fine particles and a resin binder such as PTFE, and a gas supply layer is formed of a resin binder porous body such as PTFE. There was a diffusion electrode. However, when such a gas diffusion electrode is used as an oxygen electrode, the carbon black carrying the catalyst is gradually oxidized, and the fine particles of the catalyst fall off due to disappearance of the carbon black of the carrier, the conductivity is reduced, and the hydrophilicity is reduced. As a result, the electrode performance deteriorates due to the decrease of the interface of the three-phase zone due to the increase of the thickness, and there is a problem that the electrode life of two years or more cannot be achieved. When used in a salt electrolyzer, durability of 5 years or more is required. Therefore, an electrode having such a short electrode life cannot be used in this type of electrolyzer. In view of this, a gas diffusion electrode having a reaction layer consisting of only silver fine particles and PTFE, which does not have to worry about carbon corrosion, has been proposed. As a device expected to have a long life, the reaction layer is composed of silver fine particles, PTFE, and a gas supply layer. There was a non-carbon black-based gas diffusion electrode made of PTFE porous material.

[0003]

A conventional gas diffusion electrode having a catalyst supported on carbon black requires 20 kg / cm at a temperature not lower than the melting point of PTFE as a binder in order to increase strength.
Pressing at ² or more high pressure. However, silver fine particles and P
In a gas diffusion electrode consisting only of TFE, PTFE and silver fine particles are soft and easily deformed under such pressing conditions, so that pores between particles serving as an electrolyte and a gas passage are blocked, and silver particles of an oxygen reduction catalyst are used. Surface area is drastically reduced. Therefore, compared with the case of using PTFE and carbon black carrying silver fine particles, the pressing temperature is lower than the melting point of 250 ° C.
The required electrode performance cannot be obtained unless pressed at a low pressure of 10 kg / cm ² or less at a temperature of 10 ° C. An electrode manufactured under such manufacturing conditions has a problem that mechanical strength is small, it is easily broken, and careful handling is required. In particular, separation of the reaction layer and the gas supply layer easily occurs, which causes liquid leakage and performance degradation. For this reason, it has been difficult for the silver-based gas diffusion electrode to achieve durability of two years or more with good reproducibility.

The present invention has been made in view of such conventional problems, and has been made in consideration of the above-mentioned problems, and is intended to provide a bonding between a gas supply layer in which at least a porous metal body and a fibrillated PTFE porous sheet are firmly bonded, and a porous metal body. It is an object of the present invention to provide a body and a long-life, high-performance gas diffusion electrode using the same.

[0005]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that a gas comprising a fibrillated PTFE water-repellent porous sheet which does not lose its pores even when heated above the melting point of PTFE. By hot-pressing the supply layer sheet to the porous metal body at a temperature higher than the melting point of PTFE and a pressure of 5 kg / cm ² or higher, the porous metal body and the gas supply layer are firmly joined at a contact actual pressure of 20 kg / cm ² or higher. If the reaction body is filled with the raw material of the reaction layer and hot-pressed under the optimum conditions of the reaction layer, high strength of the electrode can be obtained, and sintering of silver fine particles in the reaction layer does not occur. The inventors have found that an electrode having a high layer peel strength can be obtained, and have completed the present invention. The water-repellent porous sheet may be simply referred to as a “porous sheet” below.

That is, the present invention has solved the above-mentioned problems by the following constitution. (1) A porous metal body and a fibrillated PTFE water-repellent porous sheet containing 0 to 55% of carbon black are heated at a temperature equal to or higher than the melting point of PTFE and at a pressure of 20 kg / cm.
^A bonded metal / water-repellent porous sheet for a gas diffusion electrode, wherein the porous metal and the water-repellent porous sheet are strongly bonded by hot pressing with ^two or more. (2) A gas diffusion electrode prepared by filling the reaction layer material from the porous metal side of the joined body of (1) and hot-pressing the reaction layer material under optimum conditions. (3) The gas diffusion electrode according to the above (2), wherein the reaction layer is formed in a state in which a part of the water-repellent porous sheet of the joined body of the above (1) has a missing portion without any part. (4) The gas diffusion according to claim 3, wherein a thin silver plate or silver powder is adhered to the missing portion and hot pressing is performed to reduce liquid permeability and improve conductivity to the gas chamber side. electrode.

[0007] With this configuration, the metal porous body of the reaction layer and the gas supply layer sheet are not peeled off. In addition, the life of the electrode is dramatically increased. And conventionally,
The electrode was manufactured by one hot press, but the strength and performance were both achieved by performing the press twice.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION As a porous metal body, a silver net, a silver-plated nickel net, a silver expanded metal, and a silver-plated nickel foam are preferably used. The thickness is 10 for silver mesh
0 to 300 microns, a wire diameter of 100 to 300 microns, and a pitch of 0.5 to 3 mm are preferably used. Next, a silver mesh and a fibrillated PTFE porous sheet (pore size 1
(Micron) at 350 ° C. and 20 kg / cm ² , and the silver mesh is firmly bonded to the porous PTFE sheet to obtain a bonded body of the silver mesh and the fibrillated PTFE porous sheet. Here, the term “fibrillated PTFE porous body” refers to a uniaxial or biaxial stretching of an unfired or fired PTFE sheet formed from a mixture of PTFE powder and a liquid lubricant under heating. It is a porous body made of fine nodules and fibers. The fibrillated PTFE porous body sheet may contain carbon black, and the content thereof is determined by the amount of the fibrillated PTFE.
Up to 55% by weight based on E. Since carbon black may not be contained in some cases, its content is from 0 to 55
Weight percent. The preferred content is 40 to 50% by weight.

From the silver mesh side of the joined body, for example, silver fine particles having an average particle diameter of 100 nm (Ag-30, manufactured by Mitsui Kinzoku Mining Co., Ltd.)
To 10), a surfactant is added, PTFE dispersion D-1 (manufactured by Daikin Industries, Ltd.) is added and dispersed. Alcohol is added to this dispersion, self-assembled, and the slurry obtained by filtration is reacted. Fill as layer material. After drying, the surfactant is removed with an extraction device using alcohol. After drying, hot pressing is performed at, for example, 260 ° C. and 20 kg / cm ² to obtain a gas diffusion electrode. The optimum conditions for hot pressing differ depending on the material, composition, and dispersion state.

The technical features of the present invention under the above press conditions will be described in detail with reference to the drawings. FIG. 1 is an explanatory cross-sectional view showing a bonded state of a bonded body 1 of a porous metal body (for example, a silver mesh) 2 and a fibrillated PTFE porous sheet 3.
In joining the silver mesh 2 and the PTFE sheet 3, the fibrillated PTFE does not lose its pores at a pressure higher than the melting point and lower than 10 kg / cm ² . However, 20 kg / cm ²
With the above pressure, the silver mesh 1 and the PTFE sheet 3 are fused at the contact portion a. Of course, the silver meshes 2 and the PTFE sheets 3 can also be joined. FIG. 2 is an explanatory cross-sectional view showing a gas diffusion electrode 4 produced by filling the reaction layer material 5 from the metal porous body 2 side of the above-mentioned joined body 1 and hot-pressing it under optimum conditions. The contact part b between the reaction layer material 5 and the PTFE sheet 3 is
When pressed at a temperature below the melting point of PTFE, 50 kg /
Even if pressed at ² cm ² , the pores of PTFE do not disappear, and the bonding strength with the reaction layer is to some extent. The overall strength is provided at the contact portion a between the silver mesh 2 and the porous PTFE 3.

[0011]

The present invention will be described in detail with reference to the following examples. However, the present invention is not limited to only these examples. Throughout the examples, all parts mean parts by weight.

Example 1 A fibrillated PTFE porous sheet (pore diameter 1 micron, thickness 25 micron) was laminated on a silver expanded metal having a size of 12 cm × 12 cm, a thickness of 100 μm, a wire diameter of 100 μm, and a pitch of 2 mm. , 350 ° C, 20k
g / cm ² , hot press for 10 seconds, quench,
The silver mesh wire and the PTFE porous body were firmly joined. A state was obtained in which a PTFE porous body was stretched over the opening. This is similar to the state in which paper is stuck to the crosspiece of the shoji. Silver fine particles (Ag-3010, manufactured by Mitsui Kinzoku Mining Co., Ltd., average particle size 0.1
One part of Triton surfactant and 9 parts of water were added to 5 parts (1 micron) (weight, the same applies hereinafter) and dispersed by an ultrasonic dispersing machine. To this, 1 part of PTFE dispersion D-1 (manufactured by Daikin Industries, Ltd.) was added, and the mixture was stirred and mixed. Then, 20 parts of ethanol was added, followed by stirring to form a self-assembly. The precipitate was filtered through 0.8 micron filter paper to obtain a slurry. The above-mentioned conjugate was uniformly applied so that the silver mesh was hidden from the silver mesh side, dried at 80 ° C. for 3 hours, and the surfactant was removed with an ethanol extraction device. After drying, 260 kg at 20 kg / cm ²
Hot pressing was performed at 60 ° C. for 60 seconds to obtain a gas diffusion electrode. When the oxygen reduction performance of this electrode was measured, 32% NaO
H, 0.81 V (v) at 30 A / dm ² under the conditions of 80 ° C.
s. RHE). Peel strength is PTF
Part 1 compared to the case where the porous E body and the silver mesh are joined at 260 ° C
It became 0 to 15 times.

EXAMPLE 2 A silver-plated nickel foam body (50 ppi, 2 mm thick, porosity 96%, 12 × 28 cm square) was thinned to 0.5 mm with a roll. A fibrillated PTFE porous sheet (pore diameter 1 micron, thickness 25 micron) was added to this foam.
Hot pressing was performed at 50 ° C. and 20 kg / cm ² for 10 seconds, followed by rapid cooling, so that the silver-plated foamed nickel and the PTFE porous body were firmly joined. Silver fine particles (Mitsui Metal Mining Co., Ltd., Ag
(5 parts of −3010, average particle size: 0.11 μm), 1 part of surfactant Triton and 9 parts of water were added and dispersed by an ultrasonic dispersing machine. One part of PTFE dispersion D-1 (manufactured by Daikin Industries, Ltd.) was added thereto, and the mixture was stirred and mixed.
Was added and stirred to form a self-organized mixture. The precipitate was filtered with a 0.8 micron filter paper, and the slurry was applied from the foamed nickel body side of the above-mentioned joined body, and was uniformly filled therein. Dry at 80 ° C. for 3 hours, place 1 mm silicone rubber on the foam side, press pressure at 230 ° C. 40 kg
/ Cm ² for 60 seconds to obtain a gas diffusion electrode. When the oxygen reduction performance of this electrode was measured, 30 A
A high performance of 0.78 V (vsRHE) was obtained at / dm ² .

Example 3 Three silver expanded metals each having a size of 12 cm × 12 cm, a thickness of 100 μm, a wire diameter of 100 μm, and a pitch of 2 mm were arranged in three rows and three columns, and 5 mm of each was superposed. A fibrillated PTFE porous sheet (pore diameter 1 micron, thickness 25 micron) having a width of 33 cm is placed on top of this, hot-pressed at 350 ° C., 20 kg / cm ² for 10 seconds, and quenched to obtain a silver mesh line and PTFE. The porous body was firmly joined. Each silver mesh and the porous PTFE sheet were firmly joined to form a single sheet.

Silver fine particles (Ag-30, manufactured by Mitsui Kinzoku Mining Co., Ltd.)
(10, average particle size 0.11 micron) 1 part of surfactant Triton and 9 parts of water were added to 5 parts and dispersed by an ultrasonic dispersing machine. To this, 1 part of PTFE dispersion D-1 (manufactured by Daikin Industries, Ltd.) was added, and the mixture was stirred and mixed. Then, 20 parts of ethanol was added, followed by stirring to form a self-assembly. The precipitate was filtered through 0.8 micron filter paper to obtain a slurry. The slurry was uniformly applied to such an extent that the silver mesh was hidden from the silver mesh side of the above-mentioned joined body, dried at 80 ° C. for 3 hours, and the surfactant was removed with an ethanol extraction device. After drying, 20kg /
Hot pressing was performed at 260 ° C. for 60 seconds at cm ² to obtain a gas diffusion electrode. When the oxygen reduction performance of this electrode was measured, a high performance of 0.8 V (vs. RHE) was obtained at 30 A / dm ² .

Example 4 Hydrophobic carbon black (No. 6, average particle size 500)
(Prototype, manufactured by Denki Kagaku Kogyo) 2 parts of surfactant 20
20% Triton and PTFE dispersion D-
1 part (manufactured by Daikin Industries) is dispersed. 50 parts of isopropyl alcohol is added to this dispersion to allow self-organization. Solvent naphtha is added to this raw material and rolled to form a 0.1 mm sheet, and the sheet is used to remove the surfactant by an extractor using ethyl alcohol.
After drying at 100 ° C., hot pressing is performed at 380 ° C. and a pressure of 50 kg / cm ² for 60 seconds. This sheet was stretched by 200% at 150 ° C. to obtain a carbon black PTFE porous sheet.

The porous carbon black PTFE sheet (pore diameter 0.9 micron, thickness 56 micron) is placed on a silver expanded metal having a size of 12 × 24 cm, a thickness of 100 μm, a wire diameter of 100 μm, and a pitch of 2 mm. , 350 ° C., 40 kg / cm ² , hot-press for 10 seconds, quenched, silver wire and carbon black PT
The porous FE sheet was firmly joined. Each silver mesh and the carbon black PTFE porous sheet were firmly joined to form a single sheet. Silver fine particles (Tanaka precious metal prototype,
5 parts of specific surface area (8.7 m ² / g), 1 part of Triton and 9 parts of water are added and dispersed by an ultrasonic dispersing machine. This is PTFE
One part of Dispersion D-1 (manufactured by Daikin Industries, Ltd.) is added, and the mixture is stirred and mixed. Then, 20 parts of ethanol is added, and the mixture is stirred to be self-organized. The precipitate is filtered through a filter paper having a pore size of 0.2 micron to obtain a slurry. The mixture is uniformly applied to the extent that the silver mesh is hidden from the silver mesh side, dried at 80 ° C. for 3 hours, and the surfactant is removed with an ethanol extraction device. After drying, an electrode was obtained by hot pressing at 260 ° C. for 60 seconds at 20 kg / cm ² . When the oxygen reduction performance of this electrode was measured, 32% NaOH, 80 ° C.
At 30 A / dm ² , 0.81 V (vs. RH
High performance E) was obtained.

[0018]

According to the present invention, porous metal and PTFE
Bonding of porous body is 10 kg / cm above the melting point of PTFE
Since hot pressing was performed at a high temperature and a high pressure of ² or more, the adhesive strength between the metal porous body and the PTFE porous body was significantly increased as compared with the case where the melting point was equal to or lower than the melting point. A large sheet can be produced by stacking a small silver mesh and a small porous PTFE sheet.
As for the pressing conditions of the reaction layer, the sintering of the catalytic metal fine particles does not proceed so much, but hot pressing can be performed under the optimum conditions for bonding with the porous metal and maximizing the performance. As a result, the gas supply layer does not peel off from the gas diffusion electrode and has a long life,
A high performance gas diffusion electrode was obtained. Since the gas supply layer is firmly joined to the porous metal body, the mechanical strength of the gas diffusion electrode is improved, and handling is easy.

[Brief description of the drawings]

FIG. 1 is an explanatory cross-sectional view showing one embodiment of a bonded body of a porous metal body and a fibrillated PTFE porous sheet according to the present invention.

FIG. 2 is an explanatory sectional view showing one embodiment of the gas diffusion electrode of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Joined body 2 Metal porous body (silver net) 3 Fibrillated PTFE porous sheet 4 Gas diffusion electrode 5 Reaction layer material a Contact part b Contact part

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[Procedure amendment]

[Submission date] August 2, 1999 (1999.8.2)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Name of invention

[Correction method] Change

[Correction contents]

[Title of the Invention] A joined body of a gas supply layer and a porous metal body
Gas diffusion electrodes had use

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

Wherein said water-repellent porous body according to claim 1 gas diffusion electrode, wherein the configuring the reaction layer with a partially with no missing portion of the sheet.

3. A silver sheet to the missing part, by adhering silver powder, to reduce the liquid permeability by hot pressing, according to claim 2, characterized in that to improve the conductivity of the gas chamber side Gas diffusion electrode.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0001

[Correction method] Change

[Correction contents]

[0001]

BACKGROUND OF THE INVENTION The present invention is Rukin genus porous body is used in particular gas diffusion electrode brine electrolysis, etc. - relates repellent porous body sheet assembly or we obtained gas diffusion electrode, in particular a long life gas diffusion Electrodes.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0002

[Correction method] Change

[Correction contents]

[0002]

2. Description of the Related Art Conventionally, in a gas diffusion electrode, a reaction layer has a carbon black carrying silver fine particles and a polytetrafluoride.
There has been a gas diffusion electrode made of a resin binder such as ethylene (hereinafter referred to as "PTFE") and a gas supply layer made of a porous resin binder such as PTFE. However,
When such a gas diffusion electrode is used as an oxygen electrode, the carbon black carrying the catalyst is gradually oxidized, and the fine particles of the catalyst fall off due to disappearance of the carbon black on the carrier,
Electrode performance is reduced due to a decrease in conductivity and a decrease in a three-phase band interface due to an increase in hydrophilicity, and there has been a problem that an electrode life of two years or more cannot be achieved. When used in a salt electrolyzer, durability of 5 years or more is required. Therefore, an electrode having such a short electrode life cannot be used in this type of electrolyzer. In view of this, a gas diffusion electrode having a reaction layer consisting of only silver fine particles and PTFE, which does not have to worry about carbon corrosion, has been proposed. As a device expected to have a long life, the reaction layer is composed of silver fine particles, PTFE, and a gas supply layer. PT
There was a non-carbon black gas diffusion electrode made of a porous FE.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0004

[Correction method] Change

[Correction contents]

The present invention has been made in view of such conventional problems, and has been made in consideration of the above-mentioned problems, and is intended to provide a bonding between a gas supply layer in which at least a porous metal body and a fibrillated PTFE porous sheet are firmly bonded, and a porous metal body. It is an object of the present invention to provide a long-life, high-performance gas diffusion electrode using a body .

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction contents]

That is, the present invention has solved the above-mentioned problems by the following constitution. (1) A porous metal body and a fibrillated polytetrafluoroethylene water-repellent porous sheet containing 0 to 55% of carbon black are heated at a temperature equal to or higher than the melting point of polytetrafluoroethylene and at a contact pressure of 20 kg / cm ^2. The reaction layer material is applied from the metal porous body side of the joined body in which the porous metal body and the water repellent porous sheet are firmly joined by hot pressing as described above.
Filled, below the melting point of polytetrafluoroethylene of the reaction layer material
That it was made by hot pressing under the conditions
Characterized gas diffusion electrode. (2) above, wherein in that constitutes the reaction layer in a state with a missing portion part is not the repellent porous sheet (1)
The gas diffusion electrode as described in the above. ( 3 ) The gas according to ( 2 ), wherein a thin silver plate or silver powder is adhered to the missing portion and hot pressing is performed to reduce liquid permeability and improve conductivity to the gas chamber side. Diffusion electrode.

 ──────────────────────────────────────────────────続 き Continued on the front page (71) Applicant 000000941 Kanebuchi Chemical Industry Co., Ltd. 3-4-2 Nakanoshima, Kita-ku, Osaka-shi, Osaka (72) Inventor Choichi Furiya 2-14F, Nakamuracho, Kofu-shi, Yamanashi Prefecture Terms (reference) 4K011 AA10 AA11 AA68 BA03 BA04 BA06 CA04 DA02 5H018 AA01 AS01 BB01 BB03 BB05 BB06 BB08 BB09 BB11 BB12 CC06 DD01 DD03 DD08 EE02 EE05 EE16 EE19

Claims (4)

[Claims] 1. The method of claim 1, wherein the porous metal and carbon black are mixed in an amount of 0 to 5
A fibrillated PTFE water-repellent porous sheet containing 5% and a temperature equal to or higher than the melting point of PTFE;
A porous metal-water-repellent porous sheet assembly for a gas diffusion electrode, wherein the porous metal body and the water-repellent porous sheet are strongly bonded by hot pressing at a pressure of at least kg / cm ² . 2. A gas diffusion electrode prepared by filling a reaction layer material from the metal porous body side of the joined body of claim 1 and hot-pressing the reaction layer material under optimum conditions. 3. The gas diffusion electrode according to claim 2, wherein the reaction layer is formed in a state in which a part of the water-repellent porous sheet of the joined body of the bonded body has a missing portion. 4. The method according to claim 3, wherein a thin silver plate or silver powder is adhered to said missing portion and hot pressing is performed to reduce liquid permeability and improve conductivity to the gas chamber side. Gas diffusion electrode.