JPH06240485A - Electrolytic cell - Google Patents

Abstract

PURPOSE: To form an electrolytic cell having sufficiently electrical conductivity and corrosion resistance at a low cost by constituting the anode chamber component members of the electrolytic cell for oxidizing hydrogen to proton by an anode of specific materials.

CONSTITUTION: The inside wall surface of the box type electrolytic cell 1 used for an electrolytic process for forming an acid in the anode chamber by oxidizing the hydrogen to the proton, for example, recovery of the acid and alkali from a neutral salt is formed of a mixed coating layer composed of conductive carbon powder and water-repellent resin. The electrolytic cell is segmented to the anode chamber 3 and a cathode chamber 4 by an ion exchange membrane 2. A gas electrode 5 is arranged in the part in tight contact with the ion exchange membrane 2 in the anode chamber 3 and a meshed current collector 6 is disposed on the cathode chamber 3 side thereof and a current collecting rod 7 is connected thereto. The electrolytic cell side wall on the cathode chamber 4 side functions as the cathode 8 and is energized by a power feeding rod 9. The inside wall of the electrolytic cell 1 and the current collector 6 are coated with the mixed layers stable under electrolytic conditions and, therefore, the electrolytic cell, which has resistance to the corrosion by an electrolyte, does not contaminate the electrolyte by dissolving therein and is low in cost and excellent in performance without using costly Pt or An is formed.

COPYRIGHT: (C)1994,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic cell in which an anode chamber constituent member excluding an anode such as an anode current collector and an anode chamber inner wall is made of a specific material, and more specifically, hydrogen is oxidized into protons. The present invention relates to an electrolytic cell for producing an acid in an anode chamber, for example, an anode chamber constituent member made of a specific material for use in recovering an acid and an alkali from a neutral salt.

[0002]

2. Description of the Related Art Conventionally, various materials have been proposed and used as electrodes for various electrochemical processes.
These electrodes must have activity for a predetermined electrolytic reaction, and need not dissolve in an electrolytic solution to contaminate electrolytic products. On the other hand, the electrolytic cell constituent members that come into contact with the electrolytic solution other than the electrodes, such as the electrode current collector and the inner wall of the electrolytic cell, are not required to have activity for the electrolytic reaction, but when dissolved in the electrolytic solution, they contaminate the electrolytic product, so Durability is required to be equivalent to that of electrodes. However, unlike the electrodes, the above-mentioned components of the electrolytic cell do not participate in the electrolytic reaction, and the amount of material used is much larger than that of the electrodes, so it is not possible to use so expensive materials.

For example, US Pat. No. 4,561,945 discloses tantalum or graphite as an anode interior wall material, and gold, platinum, graphite, niobium, titanium-palladium alloy, titanium-nickel-molybdenum alloy, etc. as an anode current collector. There is.
Among these anode chamber constituent materials, tantalum has excellent corrosion resistance, but is very expensive and not easily available. Since graphite is fragile and heavy, it is difficult to handle and process, and the total weight of the electrolytic cell becomes considerable.

Further, gold and platinum as an anode current collector have sufficient corrosion resistance and conductivity, but are extremely expensive and cannot be used as a material as they are. Even when it is used as gold plating or platinum plating, it is still expensive because it needs a sufficient thickness to eliminate pinholes. As described above, graphite has the drawback that it is fragile and heavy. Niobium is insufficient in terms of corrosion resistance, and various titanium alloys such as titanium-palladium are stable in an oxidizing atmosphere, but do not show sufficient corrosion resistance under electrolytic conditions in which hydrogen is oxidized in the process in the anode, It is speculated that this is because a sufficient corrosion-resistant oxide film of titanium does not grow under hydrogen atmosphere or is destroyed even if grown. The present inventors have found that zirconium, molybdenum and silver can be used as a material for forming the anode chamber (Japanese Patent Application No.
No. 352633), but it has not been put to practical use because of its price and difficulty of availability.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to provide an electrolytic cell constituting member made of an inexpensive material which has sufficient conductivity and sufficient corrosion resistance under the electrolytic conditions of oxidizing hydrogen into protons in the anode chamber. It aims at providing the electrolytic cell which has.

[0006]

The electrolytic cell according to the present invention comprises an anode for supplying hydrogen to oxidize protons.
At least a part of the anode chamber constituent members other than the anode that comes into contact with the electrolytic solution comprises a metal base material coated with a mixture of conductive carbon powder and a water-repellent resin, which is an electrolytic cell. The anode chamber constituent members are mainly the anode current collector and the anode chamber inner wall. The present invention will be described in detail below.

The electrolytic cell in the present invention is limited to an electrolytic cell which oxidizes hydrogen into protons at the anode, which is usually a gas electrode. The gas electrode is composed of a hydrophilic layer formed on the side in contact with the solution and a water-repellent layer formed on the side in contact with the gas, and is installed in the electrolytic cell so that an electrode chamber such as an anode chamber is provided with a solution chamber and a gas chamber. Partition into In the anode chamber, there are a current collector for supplying a current to the anode and an inner wall of the electrolytic cell as members that come into contact with the electrolytic solution, in addition to the anode. As described above, it is desirable that these anode chamber constituent members are made of a material that is as inexpensive as possible so long as they are insoluble in the electrolytic solution. The present invention has been completed by finding that a metal base material coated with a mixture of a hydrophilic carbon powder and a water-repellent resin meets the above conditions.

In order to function as an anode chamber constituent member of the electrolytic cell according to the present invention, it is necessary to have sufficient conductivity and corrosion resistance. Sufficient conductivity means conductivity equivalent to that of a metal. For example, a graphite material that has sufficient corrosion resistance other than a metal has an electrical resistance that is 1 order (10 times) or more larger than that of a metal in order to flow the same electricity. Double thickness is required, and therefore, among conventional materials, metallic materials have sufficient conductivity or insufficient corrosion resistance, while materials other than metals have satisfactory corrosion resistance. The conductivity of the material was not such that it could be used as an electrode material.

In the present invention, by coating the surface of the metallic base material with a water-repellent resin, the corrosion resistance of the metallic base material is improved, and carbon powder having sufficient conductivity and corrosion resistance is added to the resin. Thus, there is provided an electrolytic cell which is composed of an anode chamber constituent member whose conductivity is ensured and whose corrosion resistance is further improved. When the anode chamber constituent member is a current collector, the metal base material has a porous plate shape, and when it is an inner wall of the electrolytic cell, it has a plate shape. The perforated plate is an expanded mesh,
It may have any shape such as a punch plate. The metal constituting the metal base material is not particularly limited because it is protected by the mixed coating of the water-repellent resin and carbon powder, but it is preferable that the metal has high corrosion resistance to acid, such as titanium alloy, nickel-chromium-molybdenum alloy, titanium , Stainless steel, etc. can be used.

The coating formed on the surface of the metallic substrate is a mixture containing the water repellent resin and the conductive carbon powder as described above. The thicker this coating layer is, the more advantageous it is in terms of corrosion resistance, but the thicker it is, the more electrical resistance increases.
It is desirable to form it to a thickness in the range of 50 μm. As the conductive carbon powder, specifically, a commercially available carbon simple substance can be used as it is, or a chemically stable and excellent conductive metal component or metal oxide is supported on the surface of the carbon simple substance. The conductivity can be adjusted depending on the degree of treatment or the amount supported. The treatment or supporting may be performed after the coating layer is formed. The smaller the particle size of the carbon powder, the better, and the optimum range is 0.01 to 10 μm. The water repellent resin is not particularly limited, but it is desirable to use a perfluorocarbon resin such as Teflon (trade name, manufactured by DuPont, USA), which is a highly water repellent resin. The coating layer in which the electrically conductive carbon powder and the water-repellent resin are mixed is an inexpensive material, and is very inexpensive especially compared with noble metals such as gold and platinum. The anode chamber constituent member made of a metal base material on which the mixture coating layer is formed exhibits sufficient conductivity and corrosion resistance even under the condition of oxidizing hydrogen into protons in a hydrogen atmosphere.

The method for forming the mixed coating layer containing both materials is not particularly limited, but the carbon powder and the water-repellent resin powder are sufficiently mixed in a liquid to form a suspension, and this suspension is placed on the anode chamber constituent member. Then, a suitable coating layer can be formed by applying it to the above and further heat treating. When the anode chamber constituent member is the inner wall of the electrolytic cell, the suspension is applied and pyrolyzed on the entire inner wall before assembling the electrolytic cell to form a coating layer preferably having a uniform thickness. When is a current collector, a coating layer is formed when the current collector is installed. The anode current collector on which the coating layer is formed is installed in the anode chamber in a state of being connected to the anode, and is usually located on the gas chamber side of the anode, and further on either the solution chamber side or the gas chamber side of the anode. Alternatively, it may be embedded in the anode. Power may be supplied to the anode current collector directly, but in the case of a large current, power is usually supplied from the anode chamber frame of the electrolytic cell. Therefore, in order to facilitate welding, it is desirable that the anode current collector and the anode chamber frame including the anode chamber inner wall be made of the same material. Further, the electrolytic cell of the present invention can be applied to other electrochemical cells such as fuel cells.

Next, an example of the electrolytic cell of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic vertical sectional view showing an example of the electrolytic cell according to the present invention. Box type electrolytic cell 1 having a mixed coating layer of conductive carbon powder and water repellent resin formed on the inner wall surface
Is divided into an anode chamber 3 and a cathode chamber 4 by an ion exchange membrane 2 which is a diaphragm, and a portion of the anode chamber 3 that is in close contact with the ion exchange membrane 2 is made of, for example, a fluorocarbon resin or a catalyst-supported graphite or the like as a substrate. A gas electrode 5 formed by coating is disposed on the anode chamber 3 side of the gas electrode 5, and a mesh-shaped current collector 6 on which the mixed coating layer is formed is located. It is connected to the rod 7.

The ion exchange membrane 2-gas electrode 5-current collector 6 are not adhered to each other, but are pressed against the power supply rod 7 by the water pressure on the cathode chamber 4 side and are in close contact with each other. The side wall of the electrolytic cell 1 on the cathode chamber 4 side functions as a cathode 8, and electricity is supplied to the cathode 8 from a power supply rod 9. In addition, 10 and 11 are hydrogen gas supply ports and hydrogen and drain water discharge ports installed on the upper and lower electrolytic cell walls of the anode chamber 3, and 12 is a hydrogen discharge port installed on the upper wall of the cathode chamber 4. In the electrolytic cell shown,
Since the inner wall of the electrolytic cell and the current collector 6 are coated with a mixed coating layer that is stable under electrolysis conditions, they are resistant to corrosion by the electrolytic solution, hardly dissolve and contaminate the electrolytic solution, and the electrolytic voltage is high. Is stable at a low value, the same effect as when expensive gold or platinum is used can be obtained.

[0014]

EXAMPLES Next, examples of corrosion resistance test of a metal porous plate usable as an anode chamber constituent member of the electrolytic cell of the present invention and electrolysis by the electrolytic cell of the present invention will be described. It is not limited to.

Example 1 Graphitized carbon powder having an average particle diameter of 2 μm (manufactured by Tokai Carbon Co., Ltd.) was added to an aqueous polytetrafluoroethylene (hereinafter referred to as “PTFE”) aqueous dispersion to give a weight ratio of carbon to PTFE of 1: 0.2. And mixed ultrasonically to prepare a coating liquid.

As a metal perforated plate, the diameter is 49 mm and the plate thickness is 0.2.
Using a disc-shaped titanium micromesh material of mm, etching was performed for 5 to 10 minutes in 20% boiling hydrochloric acid as a pretreatment for expanding the surface area and roughening the surface. About 10 mg of the above coating solution was applied to the entire surface of this porous plate, pre-dried at 50-60 ° C for 30 minutes, and then baked at 370 ° C for 90 minutes, and this step was repeated to prepare a water-repellent resin-coated current collector. . This current collector was installed in the Pyrex electrolytic cell shown in Fig. 1, hydrogen gas was supplied from the rear side, and 70 ° C as the electrolyte on the front side.
15% by weight of sulfuric acid was supplied, and the electrode potential was measured when the current density was 25 and 30 A / dm ^{2 using the} mercuric sulfate electrode as a reference electrode, and at 25 A / dm ² , −0.212 V, 30 A / dm 2. -0.193 V at ²
The result was obtained.

Further, an electrolytic test was conducted at a current density of 30 A / dm ² in the electrolytic cell of FIG. 1 using the above current collector, and the initial cell voltage was 0.
After long-term electrolysis at 868 V for 1 month, the current collector had no change and the surface water repellency was as good as before electrolysis.
Further, during the long-term electrolysis test, the titanium concentration in the metal porous plate of the current collector dissolved in the electrolytic solution in the anode chamber where the current collector was present in about 7 days was extremely low, 1.3 ppm.

[0017]

Example 2 A water-repellent resin-coated current collector prepared by the same method as in Example 1 was used, except that a stainless micromesh was used as the metal perforated plate. The water-repellent resin-coated current collector of the same performance was obtained, and the elution of the metal porous plate was extremely small.

[0018]

Comparative Example 1 An experiment was conducted under the same conditions as in Example 1 using the same current collector as in Example 1 except that the coating of the water repellent resin and the carbon powder was not applied. The electrode potential at a density of 25 A / dm ² was −0.248 V. When an electrolytic test was conducted with a current density of 30 A / dm ² , the initial cell voltage was 1.68 V, but electrolysis became impossible about 5 days after the start of electrolysis. Also, the titanium concentration in the metal perforated plate of the current collector, which was dissolved in the electrolyte in the anode chamber where the current collector was present in about 1 day, was 80.3.
It was ppm, and it was found that a large amount of titanium was dissolved.

[0019]

The electrolytic cell according to the present invention comprises an anode for supplying hydrogen to oxidize into protons, and at least a part of the anode chamber constituent members other than the anode in contact with the electrolytic solution is made of conductive carbon powder. And an electrolyzer comprising a metal base material coated with a mixture of a water-repellent resin. When electrolysis was performed using this electrolytic cell, a mixed coating layer of conductive carbon powder and a water-repellent resin, which is a constituent member of the anode chamber such as the anode current collector and the anode chamber inner wall, was formed under the electrolysis conditions in the anode chamber. Corrosion by the metal base material, for example, sulfuric acid under a hydrogen atmosphere, which is a particularly corrosive environment, hardly dissolves and hardly contaminates the electrolyte solution,
Moreover, since the electrolysis voltage is stable at a low value, it is possible to obtain the same effect as when using expensive gold or platinum, and it is possible to perform economical electrolysis using an inexpensive material,
This is more advantageous than using expensive gold or platinum.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view showing an example of an electrolytic cell according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electrolyte tank 2 ... Ion exchange membrane 3 ... Anode chamber 4 ... Cathode chamber 5 ... Gas electrode 6 ... Current collector 7 ... Feed rod 8 ... Cathode 9 ... Power supply rods

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shuji Nakamatsu 5568-4 Ooba, Fujisawa-shi, Kanagawa Papillon Grace II 102 (72) Inventor Yoshinori Nishiki 1-1-1, Fujisawa, Kanagawa Prefecture (72) Invention Takahiro Ashida 66 Nodai, Zama City, Kanagawa Prefecture

Claims (1)

[Claims] 1. An anode chamber for supplying hydrogen to oxidize to protons is provided, and at least a part of the anode chamber constituent member excluding the anode in contact with an electrolytic solution is coated with a mixture of conductive carbon powder and a water repellent resin. An electrolytic cell comprising a metal base material as described above.