JP3264534B2 - Gas electrode structure and electrolysis method using the structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power-saving gas electrode structure used in an electrochemical process and an electrolysis method using the structure.

[0002]

2. Description of the Related Art Conventionally, as an electrode for an electrochemical process, a conductive material having sufficient durability when used as an electrode has been used. That is, iron or nickel which is stable and easily available at the time of negative polarization is used as a cathode, and graphite carbon is used as an anode instead of a usual metal which dissolves. In addition, a valve metal such as titanium is passivated as it is, but is extremely stable against anodic polarization, and is used on the valve metal as an electrode substrate to prevent passivation of the valve metal and as an electrode material. Electrodes prepared by coating a functional platinum group metal or its oxide have been used. In addition, lead oxide and manganese oxide, which are conductive oxides, themselves have insufficient physical strength and conductivity, but have been put into practical use as electrodes by coating the above substance on a substrate such as titanium. I have.

[0003] In these electrodes, a current is caused to flow in an electrolytic solution while generating hydrogen at the cathode and oxygen and halogen are generated at the anode, and a desired electrolytic reaction proceeds or electrolytic salt separation is performed. In these anodes and cathodes, the generated gas is often not a target product, and there is a problem in that the energy required for generating the gas is extremely large, resulting in energy loss. In order to solve this drawback, for example, an oxygen-containing gas is supplied to the cathode chamber and reacted with hydrogen generated in the cathode chamber to avoid wasting energy required for hydrogen gas generation, thereby reducing energy consumption or recovering energy. There is known a so-called gas electrode for performing electrolysis while performing hydrogenation, or circulating hydrogen generated in a cathode chamber to react with oxygen generated in the anode chamber to similarly perform electrolysis while reducing energy consumption.

The gas electrode has a porous structure which is usually made of a conductive material mainly composed of carbon, and has one surface made hydrophobic (water repellent) to prevent the permeation of the electrolytic solution and to effectively supply the gas over the entire surface. The other surface is a hydrophilic layer carrying an electrode catalyst, and the gas infiltrating the hydrophobicity and the electrolyte in the electrolyte react on the surface of the hydrophilic layer to depolarize, and the electrolysis is performed with a small amount of power. To do. This electrode has no problem under ideal electrolysis conditions with few impurities as in electrolysis experiments, but when it is used industrially, impurities are usually contained in the electrolytic solution and these impurities form the electrode catalyst. If the electrolyte used is poisoned or corrosive, the electrode catalyst is consumed. Conventionally, there has been proposed a method of obtaining salt and caustic soda without generating hydrogen by industrial salt electrolysis, that is, chloralkali electrolysis, to lower the electrolysis voltage, but it has not been put to practical use. This is thought to be due to the fact that the electrode catalyst does not have sufficient durability in the conditions of the current ion exchange membrane method in the cathode chamber, that is, in 30 to 35% caustic soda at 90 ° C or higher. It has to be said that it is extremely difficult to produce an electrode having both the activity as a catalyst and the performance that can be maintained for several years or more even with the current technology.

[0005]

An object of the present invention is to provide a gas electrode structure which solves the above-mentioned problems and which can sufficiently withstand long-term industrial use even if the electrolyte is corrosive, and an electrolysis method using the structure. The purpose is to provide.

[0006]

A gas electrode structure according to the present invention comprises a corrosion-resistant porous substrate, a thin layer containing an ion exchange resin formed on one surface of the porous substrate, and a thin layer formed on the surface of the thin layer. A gaseous electrode structure comprising a carbonaceous layer supporting a catalyst, wherein the gaseous electrode structure is used as an anode or a cathode or as both an anode and a cathode. is there. Hereinafter, the present invention will be described in detail.

A feature of the gas electrode according to the present invention is that, unlike the above-mentioned conventional gas electrode, the liquid electrode is substantially impermeable and conductive between the electrode surface in contact with the electrolyte and the carbonaceous layer having the electrode catalyst. In that a thin layer of ion exchange resin having If the thin layer of the ion exchange resin is not provided, the electrolytic solution reaches the carbonaceous layer having the electrode catalyst as in the related art, causing the corrosiveness of the electrolytic solution and the consumption and deterioration of the electrode catalyst due to impurities contained in the electrolytic solution. I do. However, in the electrolytic reaction using a gas electrode, the electrolytic solution does not need to contact the electrode catalyst, and the electrolyte in the electrolytic solution and the gas supplied separately from the electrolyte contact the electrode catalyst to form predetermined ions. All you need is enough. In other words, in the anode chamber, H ₂ → 2H ⁺ + 2e ⁻
Hydrogen ions are generated according to the following equation, and O ₂ + 2H is generated in the cathode chamber.
It is sufficient that hydroxyl ions are respectively generated according to the formula ^: ₂₀ + 4e ⁻ → 4OH ⁻ .

In the gas electrode of the present invention, since the ion exchange resin thin layer is provided between the porous substrate and the carbonaceous layer supporting the electrode catalyst, the anode chamber and / or the cathode chamber are formed by the gas electrode. Only a desired electrolyte that is divided into a chamber and a gas chamber and that can permeate the thin layer of the ion exchange resin in the electrolyte on the electrolyte chamber side reaches the carbonaceous layer through the thin layer and reacts with the gas by the electrode catalyst. The desired electrolytic reaction takes place, and the product is again returned by the electric field through the thin layer to the electrolyte chamber. Therefore, corrosive substances and impurities in the electrolytic solution hardly permeate the ion exchange resin thin layer and reach the carbonaceous layer to deteriorate the electrode catalyst. It is possible to provide a gas electrode which can be used and has a long life.

The gas electrode according to the present invention can be used as either an anode or a cathode, and the material of the porous substrate, which is a constituent member of the gas electrode according to the present invention, depends on the characteristics of the pole used. For example, in the case of use as an anode, in the case of a strongly acidic electrolyte, a porous ceramic body such as a filter cloth and a glass filter, a polytetrafluoroethylene (PTFE) -based nonwoven fabric subjected to a hydrophilic treatment, or the like may be used. It is preferable to use a PTFE sheet or the like. In the case of alkaline, it is preferable not to use the ceramics such as the above-mentioned filter cloth and glass filter because the ceramic itself is easily corroded. Corrosion resistance such as a hydrophilicized PTFE-based nonwoven fabric, a PTFE sheet or polyethylene Is preferred. In particular, considering use at a temperature of 70 ° C. or more, it is preferable to use a fluororesin. When used as a cathode, it is desirable to use a fluororesin-based porous material because the electrolyte is almost strongly alkaline.

The ion exchange resin thin layer formed on the porous substrate is a cation exchange resin when the gas electrode is used as an anode and an anion exchange resin when the gas electrode is used as a cathode. It is desirable. As the cation exchange resin, there is, for example, a cation exchange resin liquid called Nafion (trade name) liquid.
An ion-exchange resin thin layer can be formed by applying it to a porous substrate such as FE and drying or baking it, and this thin layer can impart an ion-exchange effect while maintaining the hydrophilicity of the electrode. Become. Further, as an anion exchange resin, there is a triammonium or tetraammonium salt ion exchange resin, and this fine powder can be coated on the porous substrate together with a fluororesin suspension by coating and baking to coat the substrate. it can. As described above, when used as an anode, it is preferable to use a cation exchange resin, and in particular, even if a cation exchange resin is used, the cations can form a thin layer of the ion exchange resin because the potential is more noble than the electrolytic solution. Although there is almost no possibility of poisoning the electrode catalyst and causing no problem, it is also possible to use an anion exchange resin at the anode and a cation exchange resin at the cathode.

The carbonaceous layer coated on the ion exchange resin thin layer is formed of any conductive carbonaceous material, and the material is desirably graphite carbon.
Fine powder of graphite, preferably fine powder containing submicron size or pitch-based carbon fiber is kneaded with a fluororesin, and the graphite fine powder is attached to the thin layer of the ion exchange resin by baking or chemical vapor deposition or spray coating. A carbonaceous layer is formed by fixing a fluororesin as a binder.

Next, an electrode catalyst is supported on the carbonaceous layer. As the electrode catalyst, a platinum group metal or its oxide is preferably used, and platinum black or ruthenium black is particularly effective.
Further, ruthenium oxide and iridium oxide are also particularly effective as anode materials. These electrocatalyst components may be selected in consideration of the type of reaction, economy, and ease of preparation. For example, in order to carry platinum, after activating the surface of the carbonaceous layer, an aqueous solution of a platinum group metal compound such as chloroplatinic acid, an alcohol solution or a diluted hydrochloric acid aqueous solution is applied,
Decompose by heating at 200 to 300 ° C, or apply the aqueous solution of the platinum group metal compound on the carbonaceous layer, dry, apply an aqueous solution of a reducing agent such as hydrazine, heat to about 100 ° C, and then wash with water and dry as appropriate. Just do it.

The gas electrode carrying the electrode catalyst prepared in this manner may be used as it is, but as a result of being exposed to a humid gas, it is entirely covered with an aqueous layer and thus comes into contact with the supply gas. May not be perfect and durability may be insufficient. For this purpose, it is preferable to impart a certain degree of hydrophobicity to the surface of the gas electrode. The surface of the gas electrode is coated with the above-mentioned Nafion liquid, which is a water-soluble fluororesin liquid or a fluororesin-based ion exchange resin liquid, and dried. By removing excess liquid, the electrode surface can be made hydrophobic. In particular, Nafion liquid is particularly desirable because it has a hydrophilic surface and a large protective effect. Although the surface area is reduced due to the coating of the Nafion solution, the reactant is a gas, becomes an ion upon contact with the catalyst, passes through the thin layer of the ion exchange resin, and is quickly removed together with the electrolytic solution, so that there is almost no problem in the reaction. .

The gas electrode thus prepared is used as it is or after being heat-treated at 100 to 250 ° C., connected to a current collector and used as a predetermined electrode. As the current collector, a material having the same material and shape as the conventional one, for example, a mesh having metal fine holes or a perforated plate may be used. This gas electrode can be used as either an anode or a cathode, and the above-mentioned preparation step can be performed by the same process except that a catalyst is appropriately selected.

Next, the gas electrode of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic longitudinal sectional view showing a state in which a gas electrode according to the present invention is incorporated in an electrolytic cell as an anode.
The box-shaped electrolytic cell 1 is divided into an anode chamber 3 and a cathode chamber 4 by an ion exchange membrane 2, and the anode chamber 3 is further divided by a gas electrode 5 into an electrolyte chamber 6 and a gas chamber 7. The gas electrode 5
Is a porous substrate 9 formed from a fluororesin or the like having a lower end in contact with the electrolytic cell bottom plate 8 from the side of the ion exchange membrane 2-a cation exchange material comprising a sulfonic acid type fluororesin or the like having a lower end in contact with the electrolytic bath bottom plate 8 Ion exchange resin thin layer 10 composed of a resin and an appropriate binder; carbonaceous layer 11 composed of graphite or the like carrying an electrode catalyst composed of a platinum group metal or an oxide thereof.
The porous body 9 and the thin ion-exchange resin layer 10 prevent the electrolyte in the electrolyte chamber 6 from migrating into the gas chamber 7. In the cathode chamber 4, a cathode 13 made of a nickel plate or the like immersed in an electrolytic solution is provided.
Are arranged.

When the electrolytic cell 1 having the gas electrode 5 is used for sodium sulfate electrolysis, an aqueous solution of sodium sulfate is used in the electrolytic solution chamber 6 of the anode chamber 3, a dilute aqueous solution of caustic soda is used in the cathode chamber 4, and an aqueous solution of the anode chamber 3 is used. Power is supplied through the current collector 12 while supplying hydrogen gas to the gas chamber 7. Water in the electrolyte chamber 6 permeates the porous substrate 9 and the ion exchange resin thin layer 10 to reach the carbonaceous layer 11 on which the electrode catalyst is supported, and is electrolyzed to generate oxygen ions. Since the oxygen ions react with the supplied hydrogen gas and are converted into water, the electrolysis can be advanced with energy lower than that required for gas generation, that is, at a low electrolysis voltage. In this electrolysis, the permeation of sulfate ions and other impurities contained in the electrolytic solution in the electrolytic solution chamber 6 is suppressed by the ion exchange resin thin layer 10, and these substances which may deteriorate the electrode catalyst have the electrode catalyst. Since the electrode catalyst does not reach the carbonaceous layer 11, deterioration of the electrode catalyst is suppressed, and the life of the electrode catalyst can be extended.

[0017]

EXAMPLES Next, examples in which the gas electrode of the present invention is applied to Glauber's salt electrolysis will be described, but the gas electrode of the present invention and the electrolytic method of the present invention are not limited thereto.

Example 1 A non-woven fabric of PTFE fiber was used as a porous substrate, the surface of which was treated with a sodium-reducing agent (trade name: tetra-etch), and a liquid obtained by diluting Nafion liquid with water was applied to the surface of the porous substrate. It was applied to the entire surface and dried. Further, a Nafion solution was applied to one surface to a thickness of about 10 μm, and heated and baked at 150 ° C. to form a substantially thin ion-exchange resin layer.

Nafion and water were added as binders to the fine graphite powder and kneaded to form a paste. This paste is applied to the surface of the ion-exchange resin thin layer and air-dried.
It was baked at 150 ° C. to form a carbonaceous layer. An aqueous chloroplatinic acid solution containing 5 g / liter of platinum was applied to the surface of the carbonaceous layer and dried. A commercially available 1: 3 aqueous solution of hydrazine is applied to the surface of the carbonaceous layer and heated at 120 ° C. for 10 minutes. This coating and heating operation of hydrazine is repeated three times, and further maintained at 120 ° C. for 1 hour and washed with water. After drying, a gas electrode was prepared. The platinum loading calculated from the weight increase is 18 ~
It was 20 g / m ² . As shown in FIG. 1, this gas electrode was incorporated as an anode in a two-chamber electrolytic cell having a cation exchange membrane as Nafion 324 manufactured by DuPont as a diaphragm.
A nickel expanded mesh coated with Raney nickel was used as a cathode.

A 20% by weight aqueous solution of sodium sulfate (Glauber's salt) is introduced into the anode compartment and deionized water is introduced into the cathode compartment. The hydrogen gas generated in the cathode compartment is sent to the anode compartment and corresponds to 20% of the theoretical amount. Hydrogen is supplied to the anode chamber after passing through the water layer from another electrolytic cell, and the electrolysis is performed while maintaining the current density at 20 A / dm ² and adjusting the concentration of caustic soda generated in the cathode chamber to 15%. Was. Excess hydrogen is released to the outside through a water trap, and the pressure of hydrogen on the anode chamber side is set to +200 Aq with respect to the atmospheric pressure using the water trap. The voltage at a temperature of 70 ° C. was 2.2 V.

[0020]

COMPARATIVE EXAMPLE 1 A dimensionally stable electrode having an iridium oxide coating on a titanium mesh was used in place of the gas electrode of Example 1 except that the hydrogen generated in the cathode chamber was released to the atmosphere. When the Glauber's salt electrolysis was performed under the same conditions as in Example 1, the cell voltage was 3.6 V, which was 1.4 V higher than in Example 1.
it was high. That is, in the electrolysis of the first embodiment, the electrolysis can be performed at about two-thirds of the voltage of the conventional electrolysis using no gas electrode.

[0021]

Example 2 PTF was used as a porous substrate in the same manner as in Example 1.
A non-woven fabric made of E-based fiber was used, and the above-mentioned Nafion solution was applied to make it semi-hydrophilic. On one side of this porous substrate, 3
A suspension prepared by mixing a powder of a highly amine-based strongly acidic anion exchange resin in an aqueous suspension of PTFE was applied, dried, and baked at 120 ° C. for 1 hour. Repeat this operation twice to obtain about 30 μm
To form a thin layer of an ion exchange resin. A carbonaceous layer of about 50 μm graphite-based carbon was formed on the surface of the ion exchange resin thin layer by a chemical vapor deposition method, and isopropyl alcohol in which ruthenium black was dispersed was applied. Further, apply a thin suspension of PTFE in water on this surface, and
After baking for a minute, the ruthenium black was fixed and the surface was made semihydrophobic.

The thus prepared gas electrode is used as a cathode and attached to the cathode compartment of an electrolytic cell partitioned into an anode compartment and a cathode compartment by a cation exchange membrane.
Oxygen after passing through the aqueous layer was supplied in a% excess.
As the anode, a dimensionally stable electrode in which iridium oxide was coated on a titanium mesh was used, and Nafion 324 manufactured by DuPont was used as a cation exchange membrane. 20 on the anode compartment side
Weight% sodium sulfate aqueous solution and deionized water into the cathode compartment. The concentration of caustic soda generated in the cathode compartment is 15%.
The electrolysis was performed while adjusting so that The voltage at a temperature of 70 ° C. was 2.7 V, and the voltage in the case of a normal gas generating cathode was 3.4 V, and a voltage drop of 0.7 V was observed. It is presumed that the voltage drop was smaller than that of the anode of Example 1 because the electric resistance of the anion exchange resin portion was large.

[0023]

The gas electrode structure according to the present invention carries a corrosion-resistant porous substrate, a thin layer containing an ion exchange resin formed on one surface of the porous substrate, and a catalyst formed on the surface of the thin layer. A gas electrode structure comprising a carbonaceous layer formed as described above. In the gas electrode structure of the present invention having such a configuration, since the ion exchange resin thin layer is provided between the porous substrate and the carbonaceous layer supporting the electrode catalyst, the gas electrode forms an anode chamber and / or a cathode. The chamber is divided into an electrolyte chamber and a gas chamber, and only the desired electrolyte that can permeate the thin layer of the ion exchange resin in the electrolyte on the electrolyte chamber side penetrates the thin layer to reach the carbonaceous layer, and the gas is generated by the electrode catalyst. And the desired electrolytic reaction takes place, and the product returns to the electrolyte chamber through the thin layer again by the electric field. Therefore, corrosive substances and impurities in the electrolytic solution hardly permeate the ion exchange resin thin layer and reach the carbonaceous layer to deteriorate the electrode catalyst. It is possible to provide a gas electrode that can be used and has a long life.

The gas electrode of the present invention can be used both as an anode and a cathode. The preparation is the same except that the type of the electrode catalyst and, if necessary, the ion exchange resin of the ion exchange resin thin layer are appropriately selected. Can be prepared in the process. The method of the present invention is an electrolysis method using the gas electrode as an anode and / or a cathode. In the electrolysis method, a desired electrolysis reaction can be performed at a low electrolysis voltage while suppressing the advantage of the gas electrode, that is, the deterioration of the electrode catalyst. The advantage of being able to do so can be achieved as it is.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view showing a state where a gas electrode according to the present invention is incorporated in an electrolytic cell as an anode.

[Description of Signs] 1 ... Electrolyzer 2 ... Ion exchange membrane 3 ... Anode chamber 4 ... Cathode chamber 5 ... Gas electrode 6 ... Electrolyte chamber 7 ... Gas chamber 8・ ・ ・ Bottom plate 9 ・ ・ ・ Porous substrate 10 ・ ・ ・ Ion exchange resin thin layer 11 ・ ・ ・ Carbon layer 12 ・ ・ ・ Current collector 13
···cathode

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C25B 1/00-15/08

Claims (3)

(57) [Claims] 1. A porous substrate comprising a corrosion-resistant porous substrate, a thin layer containing an ion exchange resin formed on one surface of the porous substrate, and a carbonaceous layer carrying a catalyst formed on the surface of the thin layer. Characteristic gas electrode structure. 2. A thin layer containing a cation exchange resin is formed on one side of a corrosion-resistant porous substrate in the anode chamber of an electrolytic cell partitioned into an anode chamber and a cathode chamber by an ion exchange membrane. A gas electrode structure formed by forming a carbonaceous layer supporting a catalyst is disposed so that only the porous substrate side is in contact with the electrolytic solution, and wet hydrogen is supplied from the carbonaceous layer side of the gas electrode structure. An electrolysis method characterized by performing electrolysis while performing. 3. A thin layer containing an anion exchange resin is formed on one surface of a corrosion-resistant porous substrate in the cathode chamber of an electrolytic cell partitioned into an anode chamber and a cathode chamber by an ion exchange membrane. A gas electrode structure formed by forming a carbonaceous layer supporting a catalyst is disposed so that only the porous substrate side is in contact with an electrolytic solution, and the gas electrode structure is wetted with oxygen from the carbonaceous layer side of the gas electrode structure. An electrolysis method characterized by performing electrolysis while supplying gas.