JPH11172484A - Gas diffusion electrode structural body and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To exhaust an electrolytic product via a hydrophilic porous layer, to make the supply of a gas to a gas diffusion electrode smooth and to enable electrolysis under low voltage by forming a gas-permeable electrode substance layer on one side of a hydrophilic porous layer and adhesively forming an ion exchange membrane on the other side. SOLUTION: Paste contg. an electrode substance is applied and backed on at least a part of one side of a hydrophilic porous layer 16 provided with a core material according to necessary to form a liq. and gas-permeable gaseous oxygen diffusion cathode 17, and an ion exchange membrane 12 is adhesively formed on the other side of the hydrophilic porous layer 16. The obtd. gas diffusion electrode structural body is arranged in the main body 11 of an electrolytic cell and is divided into an anode chamber 13 and a cathode chamber 14 by the ion exchange membrane 12. Moreover, the side of the anode chamber 13 in the ion exchange membrane 12 is provided with an insoluble anode 15, and saturated brine is supplied to the anode chamber 13, humidificated gaseous oxygen is supplied to the cathode 14, and electrolysis is executed. In this way, an aq. soln. of NaOH electrolytically formed diffuses into the porous layer 16, is flowed down, is flowed out from the periphery thereof and is recovered, and the supply of the gas to the gas diffusion cathode 17 is not checked.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas diffusion electrode structure capable of smoothly supplying a gas and a method for producing the same, and more particularly, to a gas diffusion electrode structure capable of smoothly supplying a gas and an electrolytic solution for producing sodium hydroxide and hydrogen peroxide. The present invention relates to a gas diffusion electrode structure capable of achieving a large energy saving effect and a method of manufacturing the same.

[0002]

2. Description of the Related Art Electrolysis is a process in the chemical industry in which good product selectivity, extremely few co-produced substances, relatively simple process and easy handling, and high product quality It is a technology widely used for the reasons described above, and is also attracting attention in terms of environmental problems because it often leads to environmental purification rather than environmental pollution. Furthermore, it has the characteristics that the operating conditions are relatively mild, the utilization rate of raw materials is high, and the amount of waste is extremely small.
Therefore, the electrolysis plays an important role in the material industry represented by chloralkali electrolysis. Although it has such an important role, energy consumption required for chloralkali electrolysis is large, and energy saving is a major problem in countries with high energy costs such as Japan. For example, in chlor-alkali electrolysis, in order to solve environmental problems and achieve energy saving, the mercury method was switched to the ion exchange membrane method via the membrane method, and in about 25 years, about 40% energy saving has been achieved. However, this energy saving is not enough, and the power cost, which is energy, accounts for 50% of the total manufacturing cost. No further power savings are possible using current methods. In order to achieve further energy savings, drastic changes have to be made, such as using an electrode reaction different from the conventional one. As an example, the use of a gas diffusion electrode employed in a polymer solid electrolyte fuel cell or the like that can be operated under almost the same conditions as ordinary aqueous electrolysis is the most likely currently possible,
This is a means of saving power.

[0003] Gas diffusion electrodes are characterized by having a property of easily supplying a gas as a reactant to the electrode surface, and have been developed in consideration of applications such as fuel cells. Recently, the use of gas diffusion electrodes for industrial electrolysis has begun to be considered. For example, an on-site hydrogen peroxide production apparatus uses a hydrophobic cathode for performing an oxygen reduction reaction (In
dustrial Electrochemistry (2nd Edit.) p279 ~, 199
1) In addition, in the production of alkalis and various recovery processes, as an alternative to the generation of oxygen at the anode or the generation of hydrogen at the cathode as a counter electrode, hydrogen oxidation at the anode or oxygen reduction at the cathode is performed using a gas diffusion electrode to reduce power consumption. Is being planned. It has also been reported that depolarization by a hydrogen anode is possible as a counter electrode for recovering metals such as collecting zinc or for galvanizing. However, in these industrial electrolysis systems,
Since the composition and operating conditions of the solution and gas are not as simple as those of a fuel cell, there is a problem that the life and performance of the electrode cannot be sufficiently obtained.

An example of a process for producing sodium hydroxide by salt electrolysis will be described. Sodium hydroxide and chlorine, which are important as industrial raw materials, are mainly produced by salt electrolysis. This electrolysis process has undergone the above-mentioned changes, and has shifted to an ion exchange membrane method using an ion exchange membrane as a diaphragm and an activated cathode with a small overvoltage. During this time, the power consumption per unit of production of 1 ton of sodium hydroxide is about 20
It decreased to 00 kWh. Furthermore, if the oxygen reduction reaction without hydrogen generation is performed instead of the hydrogen generation at the cathode as in the conventional method, the theoretical decomposition voltage is increased from the conventional 2.19V.
It becomes 0.96V, and the reduction of 1.23V becomes possible, and significant energy saving can be expected. As an application technique of the salt electrolysis, there is a use of a gas diffusion electrode for electrolytic separation of sodium sulfate, which is a neutralized salt, into acid and alkali. Conventionally, an oxygen-generating electrode was used as an anode and a hydrogen-generating electrode was used as a cathode.However, a hydrogen gas-diffusion electrode was used as an anode and hydrogen generated at the cathode was used as hydrogen supplied to the gas-diffusion electrode. Voltage drop.

The conventional electrolytic reaction is as follows: anode: H ₂ O → 1 / 2O ₂ + 2H ⁺ + 2e ⁻ E ₀ = 1.23 V Cathode: 2H ₂ O + 2e ⁻ → H ₂ + 2OH ⁻ E ₀ ′ = −0.83 V E ₀ −E ₀ ′ = 2.06 V, and the electrolytic reaction using the gas diffusion electrode is as follows: anode: H ₂ → 2H ⁺ + 2e ⁻ E ₀ = 0.0 V Cathode: 2H ₂ O + 2e ⁻ → H ₂ + 2OH ⁻ E ₀ ′ = −0.83 V E ₀ −E ₀ ′ = 0.83 V, a theoretical difference of about 1.2 V, and a difference of about 1.5 V due to the application of the electrode overvoltage.
The above voltage reduction is possible. In order to industrially realize these new processes, an oxygen gas diffusion cathode (gas diffusion cathode using oxygen as a supply gas) or a hydrogen gas diffusion anode (hydrogen supply The development of a gas diffusion anode, which becomes a gas, becomes indispensable.
FIG. 1 is a schematic view of a salt electrolysis cell using an oxygen gas diffusion cathode which is currently most commonly used.

In this electrolytic cell 1, the electrolytic cell 1 is partitioned by a cation exchange membrane 2 into an anode chamber 3 and a cathode chamber 4, and the cathode chamber 4 is further separated by a solution chamber 6 and a gas chamber 7 by an oxygen gas diffusion cathode 5. Is divided into Oxygen gas as a raw material is supplied to the gas phase surface of the oxygen gas diffusion cathode 5 from the gas chamber 7 side, diffuses inside the oxygen gas diffusion cathode 5 and reacts with water in the catalyst layer inside the cathode 5 to convert sodium hydroxide. Generate. Therefore, the cathode used in this electrolysis method must be a so-called gas-liquid separation type gas diffusion electrode that sufficiently permeates only oxygen and prevents permeation of sodium hydroxide from the solution chamber to the gas chamber. Oxygen gas diffusion cathodes currently proposed for salt electrolysis as electrodes satisfying such requirements include carbon powder and P
The center is a gas diffusion electrode in which a catalyst such as silver or platinum is supported on an electrode substrate formed by mixing TFE and forming a sheet. The anodic reaction and the cathodic reaction in the conventional salt electrolysis are as follows, respectively, and the theoretical decomposition voltage is 2.19V. Anode reaction: 2Cl ⁻ → Cl ₂ + 2e (1.36V) Cathodic reaction: 2H ₂ O + 2e → 4OH ⁻ + H ₂ (−0.83V)

Here, when electrolysis is performed while supplying oxygen to the cathode, hydrogen is consumed by the supplied oxygen, and the cathode reaction is as follows. Cathode reaction: 2H ₂ O + O ₂ + 4e → 4OH ⁻ (0.40 V) Therefore, theoretically 1.23 V, 0.8 in the practical current density range
V power consumption can be reduced, saving 700 kWh per tonne of sodium hydroxide. From the viewpoint of energy saving, practical application of salt electrolysis using a gas diffusion electrode has been studied since the 1980s, but this type of electrode has the following disadvantages.

[0008] Carbon used as an electrode material is easily degraded at high temperatures in the presence of sodium hydroxide and oxygen, and significantly lowers electrode performance. It is difficult to prevent the leakage of sodium hydroxide to the gas chamber side, which is caused by the rise of the liquid pressure and the deterioration of the electrode. It is difficult to produce an electrode of a required size (1 m ² or more) at a practical level. The pressure in the tank varies with the height, and it is difficult to provide a supply oxygen gas pressure distribution that compensates for this. There is a solution resistance loss of the catholyte and power for stirring the solution is required. For practical use, it is necessary to significantly improve existing electrolytic equipment. When air is used as oxygen gas, carbon dioxide gas in the air reacts with sodium hydroxide and precipitates as sodium carbonate in the pores of the gas diffusion electrode, so that the gas diffusion ability is reduced.

An electrolysis method which solves these problems is a cellogap type electrolysis method using an electrolytic cell shown in FIG. In this electrolysis method, the solution chamber shown in FIG. 1 is eliminated by bringing the oxygen gas diffusion cathode 9 of the electrolytic cell 8 into close contact with the ion exchange membrane 10.
It is characterized by supplying oxygen gas and water as raw materials and recovering sodium hydroxide as a product from the same side. When this electrolysis method is used, gas leakage between the solution chamber and the gas chamber is eliminated, so that the above-mentioned problem is solved. Further, since the electrode and the ion exchange membrane are in close contact with each other, the electrolytic equipment of the conventional ion exchange membrane method is used. Can be used without much improvement, so the above problem is also solved. The performance required of an oxygen gas diffusion cathode suitable for this electrolytic process is as follows:
High gas permeability, high hydrophobicity required to avoid wetting by sodium hydroxide, and high permeability required for sodium hydroxide to move through the electrode. For such a purpose, the oxygen gas diffusion cathode is made of a durable metal such as nickel or silver, so that the above-mentioned problems are solved and long-term electrolysis can be expected.

In this electrolysis process, since sodium hydroxide permeated to the oxygen supply side is recovered, it is not necessary to partition the solution chamber and the gas chamber by the cathode as in the conventional case. Therefore, the electrode has no problem even if the liquid is permeable,
It is considered that upsizing is relatively easy, and the problem is solved. Since there is no solution chamber, and therefore there is no change in the liquid pressure in the height direction, no problem can naturally occur.
In addition, since the generated sodium hydroxide necessarily moves to the oxygen supply side through the inside of the electrode, the problem hardly occurs. As described above, attempts to adapt the gas diffusion electrode to an industrial electrolysis system have been continuously made, and various improvements have been made and results have been obtained. However, when an existing electrolytic cell having a height of 1 m is used, the original electrolytic performance cannot be sufficiently obtained even with the gas diffusion electrode having the above structure. The reason is that, in addition to the alkali solution that moves to the oxygen supply side, the liquid that has moved in the height direction due to gravity stays inside the electrode, which hinders gas supply.
In order to solve this drawback, attempts have been made to make the gas diffusion electrode uneven or to attach an eaves-like guide plate at a certain height to promote separation of the electrolytic solution from the electrolytic surface. In particular, in the case of a large electrolytic cell, there is a tendency that sufficient liquid separation cannot be achieved and the voltage tends to increase, and a problem that a complete solution has not been proposed remains.

[0011]

An object of the present invention is to solve the above-mentioned problems of the prior art, namely, gas diffusion electrode type electrolysis, for example, zero gap type salt electrolysis in which an oxygen gas diffusion electrode is brought into close contact with an ion exchange membrane, and hydrogen gas. It solves the problem that gas supply to the gas diffusion electrode surface is not smooth in salt separation and hydrogen peroxide generation electrolysis using a three-chamber electrolytic cell having a diffusion electrode. An object of the present invention is to provide a gas diffusion electrode structure capable of producing hydrogen or the like and a method for producing the same.

[0012]

The gas diffusion electrode structure according to the present invention comprises a hydrophilic porous layer, a liquid and gas permeable electrode material layer formed on one surface of the hydrophilic porous layer, and the hydrophilic porous layer. A gas diffusion electrode structure comprising an ion-exchange membrane in close contact with the other surface of the porous layer, wherein the method for producing a gas diffusion electrode structure according to the present invention comprises the steps of: A paste containing an electrode substance is partially applied, and a liquid and gas-permeable electrode substance layer is formed on one surface of the hydrophilic porous layer by heating and baking, and on the other surface of the hydrophilic porous layer. A method for producing a gas diffusion electrode structure, characterized in that an ion exchange membrane is adhered, and the sintering or baking of the hydrophilic porous layer may be performed simultaneously with the baking of the electrode material layer.

Hereinafter, the present invention will be described in detail. Conventionally, application of gas diffusion electrodes to industrial electrolysis such as salt electrolysis has been studied and reported. For example, in an electrolytic cell of a type in which a cathode chamber is divided into a solution chamber and a gas chamber by an oxygen gas diffusion cathode, the liquid resistance due to the liquid between the ion exchange membrane and the cathode is not negligible. The zero-gap type in which the ion exchange membrane and the cathode are in close contact with each other is a technique developed to reduce the liquid resistance. For example, in the case of salt electrolysis, the above-described cathodic reaction: 2H ₂ O + 2e → 4OH ⁻ + H ₂ occurs at the interface between the ion exchange membrane and the cathode, and the generated sodium hydroxide permeates through the oxygen gas diffusion cathode as a solution to form the cathode. It is taken out from the gas phase side. In this case, since the flow direction of the sodium hydroxide and the flow direction of the oxygen-containing gas are opposite to each other, the solution stays in the oxygen electrode or the gas supply speed becomes slow.

For example, when the oxygen gas diffusion cathode is used for salt electrolysis and when the gas generating electrode is used for salt electrolysis, the increase in the electrolysis voltage with respect to the increase in current density is about 1.5 to 2 times that of the latter. It is known that there is. This is regarded as the characteristic of the oxygen gas diffusion cathode, and it has been found that the main factor is not the type of reaction but the overvoltage other than the electrode reaction. One of the causes of the overvoltage rise is a shortage of supply gas to the oxygen gas diffusion cathode,
For example, in the case of salt electrolysis, it is known that when the gas source is air or pure oxygen, the former has a higher overvoltage of about 200 mV. In addition, the overvoltage becomes lower when the supply amount is increased, but there is a problem in taking out the product, and as a result, the gas cannot be supplied smoothly.

[0015] The present invention is not limited to the case where the oxygen gas diffusion cathode is used for salt electrolysis, the case where the hydrogen gas diffusion anode is used for salt separation in a three-chamber method, and the case where the gas diffusion electrode is used for electrolytic production of hydrogen peroxide. Another object of the present invention is to provide a gas diffusion electrode structure used in an electrolytic cell and a method for producing the gas diffusion electrode, which can smoothly carry out both the removal of a solution containing an electrolytic product and the supply of a raw material gas in the case where the gas is used, and the like. The possibility of realizing an industrial electrolytic cell using a diffusion electrode is increased. In the present invention, a hydrophilic porous layer is provided between the ion exchange membrane and the electrode substance layer of the zero-gap type electrolytic cell in which the ion exchange membrane and the electrode substance layer of the gas diffusion electrode are placed in close contact with each other. The gas diffusion electrode structure is constituted by the porous layer and the electrode material layer. This hydrophilic porous layer extracts all or a part of the solution in which sodium hydroxide or hydrogen peroxide generated in the ion exchange membrane is dissolved through the hydrophilic porous layer to the periphery of the electrode chamber, particularly to the lower portion, and the solution is removed. The residence time between the ion-exchange membrane and the electrode material layer is shortened, so that the supply of a source gas such as an oxygen-containing gas or a hydrogen-containing gas from the back surface of the electrode material layer is performed smoothly. Therefore, according to the present invention, the operations in different directions such as the smooth extraction of the solution in which the product is dissolved and the smooth supply of the raw material gas are performed at the maximum efficiency, the electrolysis voltage is reduced more than before, and the gas diffusion electrode is applied to industrial electrolysis. To widen the path of doing things. This gas diffusion electrode structure can also be used as an oxygen gas diffusion cathode for salt electrolysis, as a hydrogen gas diffusion anode for salt separation, or as a gas diffusion electrode for hydrogen peroxide production,
It is useful as a gas diffusion electrode for various electrolysis.

From the viewpoint of the liquid resistance, it is preferable that nothing exists between the ion exchange membrane and the electrode material layer. Therefore, it is better not to insert the hydrophilic porous layer of the present invention between them. If inserted, the electrolytic voltage rises. However, there is no necessity that the ion exchange membrane and the electrode have to be in close contact with each other except when the ion exchange membrane such as pure water electrolysis is used as a solid electrolyte, and the insertion of the hydrophilic porous layer causes the increase in the electrolytic voltage or more. If the effect appears, energy saving as a whole can be achieved. The present invention aims exactly at this effect, and achieves smooth gas supply by taking out the above-mentioned solution through the hydrophilic porous layer, thereby increasing the electrolytic voltage by the amount of increase due to the insertion of the hydrophilic porous layer. And to save energy as a whole.

Further, when the hydrophilic porous layer is a continuous liquid layer,
A difference in pressure applied to the electrode material layer occurs in the height direction of the liquid layer, which may be a bottleneck for upsizing. As described above, the gas diffusion electrode structure according to the present invention is composed of an ion exchange membrane, a hydrophilic porous layer, and an electrode material layer. For example, this structure is used as an oxygen gas diffusion cathode of a salt electrolytic cell and is in close contact with the ion exchange membrane. When accommodated in a cathode chamber consisting of only a gas chamber, there is no solution chamber in the cathode chamber, the gas pressure is equally applied on the back side of the oxygen gas diffusion cathode, and the solution is substantially separated from the hydrophilic porous layer. It is appropriately extracted as a droplet, and it is appropriate to think that a continuous liquid layer is not generated in the hydrophilic porous layer but a liquid film that is interrupted in the middle, The oxygen gas diffusion cathode does not receive a pressure change in the height direction. The same applies to the case where the gas diffusion electrode structure of the present invention is applied to a hydrogen gas diffusion anode of a three-chamber electrolytic cell or a gas diffusion electrode for producing hydrogen peroxide.

The electrode material layer used in the present invention can be used while utilizing the characteristics of the conventional gas diffusion electrode. For example, a wire mesh made of a corrosion-resistant material such as titanium, niobium, tantalum, stainless steel, nickel, zirconium, carbon, silver,
A material such as a powdered sintered body, a metal fiber sintered body, or a foamed body may be pretreated and washed as necessary to form an electrode material layer, or may be formed of platinum, palladium, ruthenium, iridium,
Copper, silver, cobalt, conductive graphite or carbon black powder carrying a metal such as lead or oxides thereof,
Alternatively, a metal silver powder alone or a ceramic such as titanium oxide carrying platinum or a platinum group metal alloy is kneaded with a fluororesin as a binder to form a paste.
It is baked by heating or hot pressing at ~ 300 ° C to form an electrode material layer. The kneaded material may be applied to the surface of the wire net or the like and baked. In order to further increase the porosity of the electrode material layer, a compound which is decomposed or volatilized by heating, such as alcohol or ethylene glycol, may be added to the paste. Of course, a foaming agent may be added instead of such a decomposable or volatile substance.

In order to quickly carry out the mass transfer of the reaction gas, it is preferable to disperse and carry a hydrophobic material on the electrode material layer and the current collector. Preferable examples of the hydrophobic material include pitch fluoride, graphite fluoride, and fluororesin. Particularly, fluororesin is preferably 200 to 400 to obtain uniform and good performance.
Firing at a temperature of ° C. is also preferred. The particle diameter of the fluorine component powder is preferably 0.005 to 100 μm. It is desirable that the hydrophobic and hydrophilic portions are respectively continuous along the electrode cross-sectional direction. From the viewpoint of corrosion resistance and economy, it is desirable to apply a noble metal plating, particularly silver plating, to the electrode material layer. The hydrophobic silver plating bath is, for example, a solution of PTFE particles in an aqueous solution of 10 to 50 g / l of silver thiocyanate and 200 to 400 g / l of potassium thiocyanate.
10-200 g / liter and surfactant 10-200 g /
(G / PTFE), and electrodeposited at room temperature with a current density of 0.2 to ^{2 A} / dm ² while stirring appropriately. Good hydrophobicity and corrosion resistance are exhibited when the plating thickness is 1 to 300 μm. After plating, it is preferable to sufficiently wash with acetone or the like.

In the present invention, since the hydrophilic porous layer located between the ion exchange membrane and the gas diffusion electrode does not contribute to the transfer of electrons, it does not have to have conductivity. Although the material is not particularly limited, for example, in the case of salt electrolysis, it needs to have sufficient resistance because it comes into contact with high concentration sodium hydroxide at about 100 ° C. When used as an anode for salt separation, the potential is almost the same, but since the electrolyte often becomes a strong acid, it is necessary to use an acid-resistant material. Further, since the ion exchange membrane installed in the electrolytic cell is not necessarily a perfect plane, it is desirable that the electrode material layer also has a flexibility to some extent along it, in other words, the electrode material layer is deformed when pressure unevenness occurs. Preferably, the material absorbs the pressure. Examples of the material of the hydrophilic porous layer include metal oxides such as zirconium oxide, silicon oxide and titanium oxide, ceramics such as carbon and silicon carbide, resins such as PTFE and EEP which have been made hydrophilic, nickel, stainless steel, silver and the like. There are metals and alloys, etc., in the case of materials other than the above-mentioned resin is a binder
It is baked together with 30% or less of a fluororesin and, if necessary, is subjected to pretreatment washing to obtain a hydrophilic porous layer.

The hydrophilic porous layer has a thickness of 0.01 to 10
mm, preferably 0.1 to 1 mm, and more preferably a material and a structure that can always hold the electrolytic solution.
There are non-woven fabrics and foams, and particularly preferably a sintered plate obtained by forming a sheet from a powder as a raw material with a pore-forming agent and various binders and removing pore-forming particles with a solvent, or a laminate thereof. The average porosity of the powder constituting the hydrophilic porous layer is not limited to this, but is 50 to 90%, preferably 70 to 90%.
90%. If the porosity exceeds 90%, the physical strength is weakened and handling problems occur. If the porosity is less than 50%, the water retention and water permeability decrease, and the electric resistance during electrolysis increases.
Although depending on other conditions, the average particle size of the hydrophilic porous layer material for setting the porosity to 50 to 90% is about 5 to 10 μm, and the particle size distribution is preferably as small as possible.

The thickness of the hydrophilic porous layer is adjusted according to the amount of the electrolyte flowing from the ion exchange membrane toward the electrode material layer, that is, the amount of the electrolyte to be removed by the hydrophilic porous layer. However, when the thickness is increased to 500 to 1000 μm, it is preferable to increase the average particle size of the particles used accordingly. When the hydrophilic porous layer is thick, the electrolysis voltage is increased, and the power consumption may deteriorate. If the hydrophilic porous layer is composed of only the above-mentioned particles of metal oxide and the like and a binder, the strength becomes insufficient and the handling may be inconvenient. In this case, a metal foam, a metal mesh, carbon fiber, a fluororesin, or the like may be used as a core material, and a porous layer of the particles and the binder may be formed on both surfaces of the core material. However, this core material also needs the characteristics described with respect to the material of the hydrophilic porous layer described above. For example, when used as an oxygen gas diffusion cathode for salt electrolysis, copper or nickel plated with metallic silver or silver is used. When used as a hydrogen gas diffusion anode for salt separation, it is desirable to use acid-resistant titanium, zirconium or Hastelloy. Since this core material does not contribute to the transfer of electrons similarly to the hydrophilic porous layer, it may be conductive or non-conductive, but it is preferable that the function as an electrode is as small as possible.

In order to produce a hydrophilic porous layer having such a core material, a kneaded material of the above-described raw material powder and fluororesin is applied to both surfaces of the core material and, for example, 20
It can be molded by hot pressing at a temperature of about 0 to 350 ° C. In order to arrange the hydrophilic porous layer between the ion exchange membrane and the electrode material layer, the hydrophilic porous layer is sandwiched between the ion exchange membrane and the electrode material layer, and a water pressure difference of 0.1 to 30 kgf / cm ² depending on the height of the electrolytic solution.
It can be integrated with a moderate pressure. Further, the hydrophilic porous layer may be formed in advance on the surface of the electrode material layer on the membrane side or on the surface of the ion exchange membrane on the electrode material layer, and the ion exchange membrane and the electrode material layer may be placed in a predetermined position in close contact with each other. good.
However, the electrode material layer having liquid and gas permeability is applied to at least a part of one surface of the hydrophilic porous layer with a paste containing a kneaded material of an electrode material which is a component constituting the electrode material layer, and heated. It is desirable to form by performing baking. This heating is performed, for example, in air at 200 to 350 ° C.
Can be done with Heat baking is possible even at a temperature lower than 200 ° C, but in that case, the compound to be added should be more easily decomposed or volatilized. If the heating temperature exceeds 350 ° C., decomposition of the fluororesin as a binder begins to occur, so that a short time treatment is required. At a high temperature, sintering and inactivation of the catalyst particles are liable to proceed. As described above, the conditions for forming the electrode material layer by applying the paste need to be appropriately set according to the type of the electrode material and the type of the binder.

Further, the hydrophilic porous layer is used as a precursor of the hydrophilic porous layer before heating and sintering composed of the particles for forming the porous layer and the fluorine resin as a binder, and at least a part of one surface of the precursor is provided as described above. A paste containing a kneaded material of the electrode material, which is a component of the electrode material layer, is applied, and then heated and sintered, whereby the hydrophilic porous layer and the electrode material layer are sintered in a single heat treatment operation. To improve the workability. The electrode material layer with the hydrophilic porous layer thus configured is installed so as to be always in contact with the ion exchange membrane when housed in the electrolytic cell.
A gas diffusion electrode structure composed of a hydrophilic porous layer and an electrode material layer is obtained.

When the gas diffusion electrode structure of the present invention is used for salt electrolysis, a fluorine resin-based cation exchange membrane is preferable as the ion exchange membrane from the viewpoint of corrosion resistance. As the anode, it is desirable to use a titanium insoluble electrode called ordinary DSA, and other electrodes can be used. The electrolysis conditions are preferably, for example, a temperature of 60 to 90 ° C. and a current density of 10 to 100 A / dm ^{2. The} supplied oxygen-containing gas is humidified if necessary. As a humidification method, a humidification device humidified at 70 to 95 ° C. is provided at the inlet of the electrolytic cell, and the humidification is controlled by passing the oxygen-containing gas. In the performance of currently commercially available membranes, if the anolyte concentration is kept below 200 g / l, especially around 170 g / l, humidification of the oxygen-containing gas becomes unnecessary. The obtained sodium hydroxide concentration is suitably about 25 to 40%, but is basically determined by the performance of the ion exchange membrane.

When salt electrolysis is performed using an electrolytic cell provided with the gas diffusion electrode structure of the present invention, sodium hydroxide mainly generated near the surface of the oxygen gas diffusion cathode on the side of the ion exchange membrane is converted to the hydrophilic porous layer. Through, ie, without passing through the oxygen gas diffusion cathode. At this time, if the hydrophilic porous layer has a seed shape, the sodium hydroxide is not extracted unless it reaches the periphery, and a relatively long time may be required until the sodium hydroxide is extracted. In order to solve this problem, in the present invention, for example, a sheet is divided into a plurality of sheets, and one end of each divided sheet is formed, for example, from these gaps of an oxygen gas diffusion cathode formed with a slit or guide having a width of 1 to 5 mm. If it is arranged so as to reach the back surface, the produced sodium hydroxide is extracted from between the ion exchange membrane and the oxygen gas diffusion cathode in a short time before reaching the periphery.

FIG. 3 is a longitudinal sectional view showing an example of an electrolytic cell for salt electrolysis using an oxygen gas diffusion cathode according to the present invention. The electrolytic cell body 11 is divided into an anode chamber 13 and a cathode chamber 14 by an ion exchange membrane 12, and a mesh-shaped insoluble anode 15 is in close contact with the ion exchange membrane 12 on the anode chamber 13 side. A sheet-shaped hydrophilic porous layer 16 is in close contact with the cathode chamber 14 side, and a liquid-permeable oxygen gas diffusion cathode 17 is in close contact with the cathode chamber side of the hydrophilic porous layer 16. A mesh-shaped cathode current collector 18 is connected and is supplied with power by the current collector 18. Reference numeral 19 denotes an anolyte (saturated saline) inlet formed on the side wall near the bottom of the anode chamber, and 20 denotes an anolyte (unreacted saline) formed on the side wall near the top of the anode chamber.
And a chlorine gas outlet, 21 is a (humidified) oxygen-containing gas inlet formed on the side wall near the top of the cathode chamber, and 22 is an outlet for sodium hydroxide and excess oxygen formed on the side wall near the bottom of the cathode chamber. .

When a saturated saline solution as an anolyte is supplied to the anode chamber 13 of the electrolytic cell 11 and a humidified oxygen-containing gas such as pure oxygen or air is supplied to the cathode chamber 14, electricity is supplied between the electrodes 15 and 17. Then, sodium hydroxide is generated on the surface of the ion exchange membrane 12 on the cathode chamber 14 side. In a normal electrolytic cell, this sodium hydroxide permeates the oxygen gas diffusion cathode as an aqueous solution and reaches the cathode chamber side surface. However, in the illustrated electrolytic cell 11, a hydrophilic porous layer 16 is provided between the ion exchange membrane 12 and the oxygen gas diffusion cathode 17.
Due to the presence of the sodium hydroxide aqueous solution, the resistance is smaller than that passing through the inside of the cathode 17, the inside of the hydrophilic porous layer 16 is dispersed, and the lower end of the hydrophilic porous layer 16 is particularly lowered by gravity. , And falls as a droplet at the bottom of the cathode chamber 14 and is stored. When this electrolytic cell is compared with the conventional electrolytic cell shown in FIG. 2 and the like, in the conventional electrolytic cell shown in FIG. 2, the generated sodium hydroxide aqueous solution must pass through the dense oxygen gas diffusion cathode, and therefore The residence time in the inside becomes long, impeding the smooth permeation of the supplied oxygen-containing gas,
Since the gas supply for controlling the reaction is insufficient, the apparent cathode overvoltage increases, and the cell voltage increases. In contrast, in the electrolytic cell shown in FIG. 3, the generated sodium hydroxide aqueous solution is taken out from the reaction site by dispersion in the hydrophilic porous layer having relatively small resistance, and hardly stays in the cathode. Is smoothly performed, and thus a low voltage is maintained.

FIG. 4 is a perspective view of the main part of a part of the electrolytic cell of FIG. 3 in which a generated aqueous sodium hydroxide solution can be taken out more smoothly. FIG. 4A is an example in which a cathode is divided into a plurality of parts. 4b shows an example in which a slit is formed in the cathode. In FIG. 4a, the oxygen gas diffusion cathode 17a is divided into a plurality of cathode pieces 17b, and the hydrophilic porous layer 16a is also divided into a corresponding number of hydrophilic porous layer pieces 16b. The lower end of each hydrophilic porous layer piece b is bent in the direction of the cathode 17b, passes between vertically adjacent cathodes 17b, reaches the back of the cathode 17b, and is bent.
c is formed.

When electrolysis is carried out using this electrolytic cell, an aqueous solution of sodium hydroxide generated on the surface of the ion exchange membrane on the side of the cathode compartment is converted into a hydrophilic porous layer piece in the same manner as in the electrolytic cell of FIG. Transmit through 16b. Since the hydrophilic porous layer 16b is divided, the aqueous solution of sodium hydroxide does not move to the peripheral portion but moves within each hydrophilic porous layer piece 16b a relatively short distance to the lower end thereof, so that the cathode 17b Drops fall from the bent piece 16c bent in the direction. Therefore, the liquid can be drained more smoothly than the electrolytic cell shown in FIG.
FIG. 4B shows an example in which the cathode 17c is not divided into a plurality of parts and the slit 17 is formed in the cathode 17c in a horizontally long rectangular shape. When the cathode is divided into a plurality of parts as shown in FIG. 4A, it is necessary to supply power to each divided piece, which is complicated. However, as shown in FIG. 4B, a slit 23 is formed in the cathode 17c, and the cathode 16b is bent through the slit 23. If the piece 16c is located on the back surface of the cathode, it is more convenient since the power supply to the cathode can be performed by a single current collector.

[0031]

EXAMPLES Next, a method for manufacturing a gas diffusion electrode structure according to the present invention and examples of salt electrolysis and salt separation using the gas diffusion electrode structure will be described, but the examples limit the present invention. Not something.

[0032]

EXAMPLE 1 A core material made of a woven fabric of carbon fiber having an apparent thickness of 0.2 mm, zirconium oxide powder having an average particle diameter of 7 μm, and a fluororesin equivalent to 30% by weight of the zirconium oxide as a solid content on both surfaces of the core material A 30 K (binder) kneaded product of DuPont, which is an aqueous dispersion of a fluororesin containing, is applied to form a plate having an apparent thickness of 0.5 mm, and a pressure of 1 kg / cm ² is applied to the plate. While hot pressing at 250 ° C. for 15 minutes, sintering was performed to obtain a hydrophilic porous layer. On one surface of this hydrophilic porous layer, a dispersion of a catalyst substance obtained by baking platinum on the surface of silver particles having an average particle diameter of 1 μm was applied, and then the average particle diameter was 3 μm.
Silver particles having an apparent thickness of 0.1
mm (the amount of platinum carried was 3 g / m ² ).
This was hot-pressed at 200 ° C. for 15 minutes while applying a pressure of 1 kg / cm ² to form an electrode material layer on one surface of the hydrophilic porous layer.

The hydrophilic porous layer of the electrode material layer having the hydrophilic porous layer was placed in a cathode chamber of a small-sized two-chamber ion exchange membrane electrolytic cell having an electrolysis area of 100 cm ² (10 cm × 10 cm) manufactured by DuPont. The cathode was set up so as to be in close contact with the ion exchange membrane, Nafion 961. The current collector in the cathode chamber used was a copper perforated plate having a thickness of 1 mm, the surface of which was plated with silver. An insoluble metal electrode made of a titanium expanded mesh substrate coated with a ruthenium oxide-based electrode material was used as an anode, and the ion exchange membrane was sandwiched together with the cathode so as to be in close contact with each other. A drain is provided in the cathode compartment,
All generated catholyte was drained downward. A 180 g / liter saline solution is circulated in the anode compartment, and PS is supplied in the cathode compartment.
A 90% oxygen concentration gas enriched in oxygen by Method A
When sodium hydroxide was produced by salt electrolysis while supplying 1.2 times, the current density was 30 A / dm ² and the electrolysis voltage was
2.01 V, and stable electrolysis was possible even after continuous operation for 100 hours or more.

[0034]

Comparative Example 1 A dispersion of a catalyst substance obtained by baking platinum on the surface of silver particles having an average particle diameter of 1 μm was applied to the surface of the carbon fiber fabric used in Example 1, and then the silver particles having an average particle diameter of 3 μm were coated on the surface. An electrode material layer was formed by applying 30 J as a binder so as to have an apparent thickness of 0.1 mm (the amount of platinum carried was 3 g /
m ² ). Electrolysis was performed under the same conditions as in Example 1 except that this electrode material layer was used as a cathode and was directly adhered to the ion exchange membrane. The initial voltage was 2.0 V, but the voltage gradually increased. After an hour, it increased by 100 mV. When the electrolysis was interrupted and resumed 30 minutes later, the voltage returned to 2.0 V, and the voltage gradually increased again with the passage of the voltage time. This can be presumed to be because the electrolyte that has permeated to the back surface of the electrode material layer hinders the supply of oxygen.

[0035]

[Embodiment 2] The plate-like body having an apparent thickness of 0.5 mm of
It dried at ° C and became a hydrophilic porous layer. On one surface of this hydrophilic porous layer, a paste made of ultrafine silver powder having an average particle diameter of 0.3 μm, dextrin and ethylene glycol was applied by a doctor blade method so as to have an apparent thickness of 3 μm, dried, and then further dried. A kneaded mixture of 7 μm silver particles and a fluororesin dispersion liquid 30J manufactured by DuPont was applied and hot-pressed at 300 ° C. for 30 minutes while applying a pressure of 1 kg / cm ² , and an electrode material was applied to one surface of the hydrophilic porous layer. The layer was prepared to form an electrode material layer with a hydrophilic porous layer. The hydrophilic porous layer of the electrode material layer having the hydrophilic porous layer was placed in the cathode chamber of a two-chamber ion exchange membrane electrolytic cell so as to be in close contact with an ion exchange membrane, Nafion 961 manufactured by DuPont, to form a cathode. . An insoluble metal electrode coated with a ruthenium oxide-based electrode material was used as an anode, and the ion exchange membrane was sandwiched together with the cathode so as to be in close contact with each other. Electrolysis was performed at a temperature of 90 ° C. and a current density of 30 A / dm ² while circulating a 180 g / liter saline solution in the anode chamber and sending oxygen gas saturated with water vapor to the cathode chamber. V, and stable electrolysis could be continued.

[0036]

Example 3 The electrode material layer of 10 cm × 10 cm used in Example 1 was left as it is, and the length of the hydrophilic porous layer in close contact with the electrode material layer was extended downward by 1 cm to 11 cm, and the lower end was left. The length was drawn out to the opposite side of the ion exchange membrane to form a liquid conducting portion, and was guided to the back side through the gap between the current collectors. Ten electrode material layers each having a hydrophilic porous layer were prepared, connected in the longitudinal direction, and incorporated into a two-chamber ion exchange membrane electrolytic cell having a height of 100 cm.
Electrolysis was performed under the same conditions as in Example 1 except that the electrode material layer with a hydrophilic porous layer having such a configuration was used. The electrolysis voltage was 2.00 V at a current density of 30 A / dm ² , and the electrolytic solution was as described above. It is observed that the liquid has been dripped to the outside of the electrode material layer through the liquid guide part, and almost no seepage to the back side of the electrode material layer that directly penetrates the electrode material layer is observed, and the amount thereof is equal to the entire liquid. It was estimated that it was less than 20%. No voltage change was observed even after 100 hours of continuous electrolysis, and when the current density was increased to 40 A / dm ^{2, the} electrolysis voltage increased to 2.15 V, but no time-dependent voltage change was observed.

[0037]

Example 4 A mesh prepared by weaving titanium wires having a wire diameter of 0.1 mm was used as a core material, and the average particle size was 10 μm over the entire surface.
A paste obtained by kneading the titanium oxide powder and a fluororesin dispersion liquid 30J was applied and baked at 300 ° C. to form a hydrophilic porous layer. The porosity of the hydrophilic porous layer was about 80%. An ethylene glycol solution of chloroplatinic acid was applied to one surface of the hydrophilic porous layer, and kept at 300 ° C. for 30 minutes in a hydrogen stream to precipitate platinum metal to form an electrode material layer.

This electrode material layer with a hydrophilic porous layer was used as an anode of a salt separation apparatus by a three-chamber method as follows. In other words, the gas diffusion electrode structure is formed of a hydrophilic porous layer formed of the anion exchange membrane, wherein the anode chamber and the intermediate chamber are formed by an anion exchange membrane, and the intermediate chamber and the cathode chamber are formed by the cation exchange membrane. And a nickel mesh was used as a cathode as a counter electrode. An aqueous solution of sodium nitrate is supplied to the intermediate chamber, hydrogen generated in the cathode chamber and hydrogen equivalent to 10% by weight of the aqueous solution are supplied from a cylinder to the anode chamber, and deionized water is dropped into the cathode chamber to form a hydroxide. Electrolysis was performed at a temperature of 45 ° C. and a current density of 20 A / dm ² while adjusting the sodium concentration to be maintained at 15% (adjusted to adjust the nitric acid concentration to 10% by adding steam to the anode chamber). ). By this electrolysis, stable salt separation proceeded at an electrolysis voltage of 2.4 V, and nitric acid was obtained in the anode chamber and sodium hydroxide was obtained in the cathode chamber at a current efficiency of 80%.

[0039]

Comparative Example 2 Electrolysis was performed under the same conditions as in Example 4 except that an oxygen-generating insoluble metal electrode was used as the anode. As a result, the electrolysis voltage was 3.9 V.

[0040]

Comparative Example 3 Electrolysis was carried out under the same conditions as in Example 4 except that an electrode material layer without a hydrophilic porous layer was used. It was unstable and the maximum current density was limited to 10 A / dm ² , above which electrolysis was not possible.

[0041]

Example 5 A mesh prepared by weaving a titanium wire having a wire diameter of 0.1 mm was used as a core material, and a material obtained by kneading silica powder having an average particle size of 5 μm, a silicon-based foaming material, and a fluororesin aqueous dispersant was applied to both surfaces thereof. And dried to obtain a hydrophilic porous layer. A kneaded product of hydrophilic carbon black and a fluororesin aqueous dispersant 30J is molded into a flat shape, and an ethylene glycol solution of chloroplatinic acid is applied to one surface of the molded product, and the mixture is heated to 300 ° C. in a hydrogen stream.
For 30 minutes to deposit platinum metal to form an electrode material layer. The hydrophilic porous layer and the platinum deposition side of the electrode material layer are brought into close contact with each other, and hot-pressed at 250 ° C. while applying a pressure of 1 kg / cm ² to form an electrode material layer on one surface of the hydrophilic porous layer. An electrode material layer with a porous layer was formed. The porosity of this hydrophilic porous layer was about 85%.

This electrode material layer with a hydrophilic porous layer was used as an anode of a three-chamber salt separation electrolysis apparatus, and the same apparatus as in Example 4 was constructed. 200 g / l of sodium sulfate was supplied to the intermediate chamber, and deionized water was supplied to the cathode chamber so that the catholyte (sodium hydroxide) concentration was 100 g / l. As the anode supply gas, a gas obtained by resaturating water with hydrogen generated by the cathode was used. Temperature 45 ° C, current density 10A / dm
^When electrolysis was performed at ² , the electrolysis voltage was 2.75 V and the current efficiency was 85
%, And stable operation could be continued even after 100 hours of continuous electrolysis.

[0043]

The gas diffusion electrode structure of the present invention comprises a hydrophilic porous layer, a liquid and gas permeable electrode material layer formed on one surface of the hydrophilic porous layer and the other surface of the hydrophilic porous layer. A gas diffusion electrode structure comprising an ion-exchange membrane in close contact. In a conventional electrolytic cell using a gas diffusion electrode, particularly in a zero-gap type electrolytic cell in which the gas diffusion electrode is in close contact with the ion exchange membrane, the target product generated on the surface of the ion exchange membrane permeates through the relatively high density gas diffusion electrode. In other words, the gas must pass through the gas diffusion electrode in a direction opposite to the supply direction of the supplied reaction gas, in other words, while inhibiting the supply of the reaction gas, and the more the products increase, the more the reaction gas reaches the reaction site. There is a problem in that the supply of oxygen is hindered and the electrolytic voltage rises.

On the other hand, in the gas diffusion electrode structure of the present invention, since the hydrophilic porous layer is disposed between the electrode material layer and the ion exchange membrane, almost all of the structure is conventionally extracted through the gas diffusion electrode. Products such as aqueous sodium hydroxide solution that had to be passed through the hydrophilic porous layer without passing through the gas diffusion electrode (electrode material layer) and the reaction gas was supplied from the surface of the ion exchange membrane without being opposed to each other. Can be taken out. Therefore, even if the amount of the product increases, the supply of the reaction gas is hardly affected, and the predetermined electrolytic reaction can be continued while the voltage is kept low. The hydrophilic porous layer can be produced by baking a kneaded paste of the porous layer constituting particles and a binder, but sometimes the strength alone is not sufficient.In this case, the paste is applied to both sides of the core using a core. By coating and heating, a gas diffusion electrode structure having high mechanical strength can be obtained.

According to the method of the present invention, a paste containing an electrode substance is applied to at least a part of one surface of a hydrophilic porous layer, and heated and baked to form a liquid and gas permeable electrode on one surface of the hydrophilic porous layer. A method for producing a gas diffusion electrode structure, comprising forming a material layer and adhering an ion exchange membrane to the other surface of the hydrophilic porous layer. The gas diffusion electrode structure according to the present invention described above may be constituted by mechanically bringing a separately produced hydrophilic porous layer and an electrode material layer into close contact with each other by applying pressure. When an electrode substance-containing paste is applied to the surface of the porous porous layer and heated, the two are strongly bonded to each other to increase the mechanical strength. Further, since the hydrophilic porous layer and the electrode material layer are integrated, transportation and the like are simplified, and handling is facilitated. Further, by sintering the hydrophilic porous layer and the electrode material layer by applying a paste to at least a part of one surface of the hydrophilic porous layer precursor before sintering in the same manner as described above, and then sintering the electrode material layer. It can be performed by a heat treatment operation, whereby the workability can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a conventional salt electrolysis tank.

FIG. 2 is a schematic diagram showing another example of a conventional salt electrolysis tank.

FIG. 3 is a longitudinal sectional view showing an example of an electrolytic cell for salt electrolysis using a gas diffusion electrode structure according to the present invention.

4 is a longitudinal sectional view showing another example of the electrolytic cell for salt electrolysis using the gas diffusion electrode structure according to the present invention, FIG. 4a shows an example in which a plurality of cathodes are disassembled, and FIG. Is formed and an example is shown.

[Explanation of symbols]

11 ・ ・ ・ Electrolyzer main body 12 ・ ・ ・ Ion exchange membrane 13 ・ ・ ・
Anode compartment 14 ・ ・ ・ Cathode compartment 15 ・ ・ ・ Insoluble anode 16 ・ ・
・ Hydrophilic porous layer 17 ・ ・ ・ Oxygen gas diffusion cathode 18 ・ ・ ・ Current collector

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Takayuki Shimamune, Inventor 3006-30, Honmachida, Machida-shi, Tokyo (72) Inventor Masashi Tanaka 3-12-9, Terao-Honcho, Ayase-shi, Kanagawa Prefecture Shalman I-401 (72) Invention Person Yoshinori Nishiki 1-3-1304-1, Fujisawa, Fujisawa City, Kanagawa Prefecture (72) Inventor Takahiro Ashida 2-7-6, Nodai, Zama City, Kanagawa Prefecture (72) Inventor Shuhei Wakita 5-5 Tsujido Motomachi, Fujisawa City, Kanagawa Prefecture -9, II-3

Claims (4)

[Claims] 1. A device comprising a hydrophilic porous layer, a liquid and gas permeable electrode material layer formed on one surface of the hydrophilic porous layer, and an ion exchange membrane in close contact with the other surface of the hydrophilic porous layer. A gas diffusion electrode structure characterized by the above-mentioned. 2. The gas diffusion electrode structure according to claim 1, wherein the hydrophilic porous layer has a core material. 3. A paste containing an electrode material is applied to at least a part of one surface of the hydrophilic porous layer, and heated and baked to form a liquid and gas permeable electrode material layer on one surface of the hydrophilic porous layer. A method for manufacturing a gas diffusion electrode structure, comprising forming an ion exchange membrane in close contact with the other surface of the hydrophilic porous layer. 4. A sintering or baking of the hydrophilic porous layer and a baking of the electrode material layer are performed simultaneously by applying and heating a paste containing an electrode material on at least a part of one surface of the hydrophilic porous layer precursor. Producing a liquid and gas permeable electrode material layer on one surface of the hydrophilic porous layer, and adhering an ion exchange membrane to the other surface of the hydrophilic porous layer. Method.