JP3199340B2 - Catalytic electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst electrode used in an electrolytic cell for producing a gas such as hydrogen or chlorine by a diaphragm electrolysis method.

[0002]

2. Description of the Related Art Heretofore, as one type of such an electrolytic cell, there has been used an electrolytic cell in which a plate-like electrode made of carbon fiber having a space through which an electrolytic solution can flow is closely attached to both surfaces of a thin film-like diaphragm. However, in order to reduce power consumption during electrolysis, an activation overvoltage is reduced by carrying a catalyst on an electrode. Examples of such a supporting form include a method in which a catalyst is directly supported on the plate-like electrode through which an electrolyte can flow, and a method in which the catalyst is supported on a thin carbon sheet. Method of sandwiching the catalyst electrode between the diaphragm and the plate electrode
No. 50490) is known.

[0003]

However, in the conventional electrode, when the catalyst is directly supported on the plate-like electrode, the catalyst penetrates to the inside of the felt-like electrode, so that the gas generated by the reaction is in the electrode. The apparent gas conductivity decreased due to the generated gas, and the voltage drop in the electrolyte increased. This voltage drop increases in the thickness direction of the plate-like electrode as the distance from the counter electrode (that is, the diaphragm) increases, and the electrode reaction occurs intensively near the diaphragm,
The catalyst was not effectively used in the portion far from the diaphragm.

When an expensive catalyst such as a platinum group metal is used as a catalyst, it is a major problem that the catalyst is not effectively used. However, it is complicated to selectively support the catalyst in the vicinity of the surface of the electrode in contact with the diaphragm. There is a problem that a process is required and the production cost increases.

A method of sandwiching a carbon sheet carrying a catalyst between a diaphragm and a plate-like electrode also involves a method in which a gas generated inside a carbon sheet composed of carbon fibers stays and a voltage generated by an electrolytic solution is similarly increased. There has been a problem that the drop increases, that is, the electrolytic voltage increases and the power consumption increases. Accordingly, an object of the present invention is to provide a catalyst electrode capable of reducing an electrolytic voltage by reducing gas retention in the electrode and effectively using an expensive catalyst to reduce the amount of catalyst used.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, a catalyst electrode according to the present invention is an electrode comprising a carbon fiber and having a catalyst carried on a carbon sheet having fine voids. Characterized by having a slit-shaped notch. As a carbon sheet composed of carbon fibers and having fine voids, carbon felt, carbon cloth, and the like can also be used. Further, as the slit, a linear, downward dendritic, or other shape is used. The effect of the catalyst electrode of the present invention can be exerted by interposing it between the ion exchange membrane and the electrode and bringing the electrode into close contact therewith.

[0007]

In the above means, the carbon sheet functions as a reaction layer, and the gas generated by the electrolysis is released through the slit, so that the electrolysis voltage can be reduced, and all the supported catalysts are effectively used. can do.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. As the electrolytic cell used for the performance evaluation of the catalyst electrode of the present invention, the electrolytic cell was partitioned by an ion-exchange membrane, and an anode electrode made of carbon felt was placed on one side of the ion-exchange membrane in close contact with the ion-exchange membrane. On one surface, a cathode sheet made of carbon felt was placed in close contact with a carbon sheet (having a large number of slits in this embodiment) supporting a catalyst.

[0009] Here, as shown in FIG.
0.3mm thick carbon sheet 1 with 16 slits 2 of width 2mm and length 230mm at equal intervals in the area excluding the peripheral 10mm 9mm horizontal 9mm of 200mm carbon sheet 2
(Example) and 0.56 mg / cm ² of platinum (Pt) as a catalyst were supported on each of a carbon sheet (comparative example 1) having a thickness of 250 mm and a width of 200 mm without slits and a thickness of 0.3 mm (Comparative Example 1). A catalyst-attached carbon sheet for Example 1 was produced. The catalyst is supported by diluting an organic solvent with a chloroplatinic acid solution.
(In this embodiment, 2-propanol is diluted with pure water)
Each of the carbon sheets was impregnated and supported with the chloroplatinic acid diluted solution to which was added, and then subjected to hydrogen reduction.

[0010] A carbon sheet with a catalyst and a carbon sheet without a slit (both 0.56 mg / cm ²
(Pt supported) was used in the above-mentioned electrolytic cell, and an electrolysis experiment was conducted simultaneously under the following conditions. As a result, the change with time of the electrolytic voltage was as shown in FIG. (Electrolysis conditions) Temperature: 60 ° C Anolyte: 1.0 mol / l FeSO ₄ , 0.5 mol / l H ₂ SO
₄ aqueous solution Catholyte: 0.5 mol / l H ₂ SO ₄ aqueous solution Electrolysis method: constant current electrolysis 50, 100 A (100, 200 mA / cm ²
Anode and cathode: 5mm thick carbon felt

FIG. 3 shows that when electrolysis was carried out at 100 mA / cm ² , there was almost no difference in the electrolysis voltage.
^At the current density of ^2, the electrolysis voltage of the carbon sheet with slits is about 0.07 V lower than that of the carbon sheet without slits. This is because the gas staying in the vicinity of the catalyst electrode is effectively exhausted from the slit, and the effect is apparent at a high current density where gas generation is large.

Further, the same carbon sheet with a slit having a catalyst as described above (supporting 0.56 mg / cm ² Pt) (Example) and 0.56 m
g / cm ² Pt-supported (Comparative Example 2) and 1.5 mg / cm ² Pt-supported (Comparative Example 3) carbon felts with catalyst were used for the electrolytic cell under the same conditions as above (except that the current density was 100 A (200 mA / c).
(equivalent to m ² )), and the change with time in the electrolysis voltage was as shown in FIG.

FIG. 4 shows that the performance of the catalyst-carrying carbon sheet with slits is equivalent to that of the catalyst-carrying carbon felt with a platinum amount of 1/3 of that of the catalyst-carrying carbon felt, and that the platinum catalyst is effectively used. .

Next, as shown in FIG.
5mm in diameter excluding 20mm around carbon sheet 2mm
Of holes (punches) 5 at intervals of 10 mm in 17 rows and 22 rows total 374
A holed carbon sheet 4 having the same catalytic effective area as that of the slitted carbon sheet of the example was prepared, and 0.56 mg / cm ² of platinum (Pt) was prepared in the same manner as described above.
The supported catalyst electrode was prepared as an electrode of Comparative Example 4. A carbon sheet with a slit with a catalyst (supporting 0.56 mg / cm ² Pt) (Example) and a carbon sheet with a pore with a catalyst supporting 0.56 mg / cm ² Pt and having a thickness of 0.3 mm (Comparative Example 4) were used as electrolytic cells. Use the same conditions as above (except that the current density is 100A
(200mA / cm ² equivalent) only)
The change with time of the electrolysis voltage was as shown in FIG. FIG.
This indicates that the electrolysis voltage of the slit is 0.04 to 0.07 V lower than that of the hole, and that the slit can obtain a more efficient reaction. This is presumably because the gas easily escapes upward through the slits, but the holes are difficult to escape due to gas trapping above the respective holes.

From the above, it can be seen that the carbon sheet electrode with slits of the present invention is more effective in reducing the amount of supported catalyst and the power consumption.

In the above embodiment, the case where platinum is used as the catalyst has been described. However, the present invention is not limited to this case. For example, a simple substance such as gold, silver, palladium or rhodium, an alloy, an oxide or the like may be used. It may be used as a catalyst. Further, the slit is not limited to a linear shape in the up-down direction, but may be a tree-like shape facing downward, or a shape in which gas can easily escape.

[0017]

As described above, according to the catalyst electrode of the present invention, the carbon sheet functions as a reaction layer, and the gas generated by electrolysis is released through the slit. The retention can be reduced, the amount of the catalyst can be significantly reduced as compared with the related art, and the electrolysis can be performed at a low electrolytic voltage, and the power consumption can be reduced.

[Brief description of the drawings]

FIG. 1 is a front view of a slit-equipped carbon sheet with a catalyst used in an embodiment of the present invention.

FIG. 2 is a front view of a carbon sheet with holes used in Comparative Example 4.

FIG. 3 is an explanatory view showing a change over time of an electrolysis voltage in an electrolysis experiment using a carbon sheet with and without a slit with a catalyst.

FIG. 4 is an explanatory diagram showing a change over time of an electrolysis voltage in an electrolysis experiment using a carbon sheet with a slit with a catalyst and a conventional carbon felt with a catalyst.

FIG. 5 is an explanatory diagram showing a change over time of an electrolysis voltage in an electrolysis experiment using a carbon sheet with a slit with a catalyst and a carbon sheet with a hole with a catalyst.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Carbon sheet with a slit with a catalyst 2 Carbon sheet 3 Slit 4 Carbon sheet with a hole with a catalyst 5 Hole

Continuation of front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C25B 1/00-15/08

Claims (1)

(57) [Claims] 1. An electrode comprising a carbon sheet made of carbon fibers and having a catalyst carried on a carbon sheet having fine voids, wherein the carbon sheet has a large number of slit-shaped cuts.