JPS6353273B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for aqueous electrolysis of alkali metal halides, alkali metal hydroxides, etc. More specifically, the present invention provides an electrolysis method using a new cathode that can significantly reduce hydrogen overvoltage compared to conventional electrolysis. When electrolyzing an aqueous sodium chloride solution to produce hydrogen, chlorine, and caustic soda, or electrolyzing an alkali metal hydroxide aqueous solution to produce hydrogen and oxygen using an electrolytic cell, the power efficiency caused by hydrogen overvoltage at the cathode The loss of
This is a serious problem. It is known that the hydrogen overvoltage at the cathode varies significantly depending on the material, surface material, surface condition, etc. of the cathode. Based on these findings, a cathode for aqueous electrolysis of alkali metal halides or alkali metal hydroxides has been proposed in which the surface of the cathode substrate is treated with a metal having a low hydrogen overvoltage or a compound thereof. For example, a cathode in which the cathode base material is coated with an alloy of sacrificial metal and nickel etc. (Japanese Patent Laid-Open No. 51-54877), a cathode in which rhenium is coated (Japanese Patent Laid-Open No. 51-55782, 51-83083),
A cathode in which powdered metals such as nickel, cobalt, platinum, and iron are adhered to the cathode base material using a metal powder spraying method (Japanese Patent Application Laid-open No. 52-32832), and a mixture of cobalt and zirconia powders is coated using a metal powder spraying method. (Japanese Unexamined Patent Publication No. 52-36582), and a cathode whose cathode base material is coated with nickel or cobalt powder or a mixture of these and aluminum powder using the same method (Japanese Unexamined Patent Publication No. 52-36582).
36583), a cathode in which the cathode base material is coated with nickel using a chemical plating method (Japanese Patent Laid-Open No. 52-110282), a cathode in which a nickel, cobalt, and tungsten alloy is also chemically plated (Japanese Patent Laid-Open No. 52-133100), Alternatively, an alloy of nickel, vanadium, or molybdenum may be coated using an electroplating method (Japanese Patent Application Laid-open No. 102888/1988), or a cathode base material may be coated with an alloy of nickel, molybdenum, or vanadium in the coexistence of hydrosulfite (patented patent application). No. 203635) A cathode in which ground steel powder is coated on a base material using a sintering method.
147479) etc. have been disclosed. However, these cathodes each have weak coatings, low hydrogen overvoltage reduction effects, expensive metals or powders, and difficulty in homogeneous application to cathode substrates with complex shapes (e.g., mesh bodies). There are many drawbacks such as difficulty. Therefore, the present inventor electroplated an iron-cobalt alloy on a specific substrate under various conditions and used it as a cathode, and as a result of studying a method for electrolyzing aqueous solutions of alkali metal halides, alkali metal hydroxides, etc. The present invention was completed based on the discovery that it is effective to use an iron-cobalt alloy plating obtained under these conditions as a cathode. That is, the gist of the present invention is that one selected from the group consisting of starch, dextrin, poly-2-diethylaminoethyl methacrylate, and polyaluminum chloride is added to at least one surface of a substrate made of titanium or a titanium alloy with ferrous ions and cobalt. Total ion concentration is 0.1-2mol/l, 2.5PH6.0
This is an aqueous solution electrolysis method in which an iron-cobalt alloy is electroplated by adding it to an iron-cobalt alloy plating bath, and this is used as a cathode. Next, the method for manufacturing the cathode used in the present invention will be explained in detail. The specific substrate in the present invention is titanium or a titanium alloy, which has electrical conductivity, mechanical properties, chemical resistance to electrolytes, plating layer, coating layer, etc., as well as iron, nickel, stainless steel, platinum group metals, etc. Although it is suitable in terms of adhesive properties, it is equally suitable as a material for electrolytic cells and a substrate for anodes, and can be used for both anodes and cathodes by applying appropriate plating or coating. This shows that it is promising not only as a substrate for monopolar electrodes but also as a substrate for bipolar electrodes. In addition to titanium, titanium alloys may also be used, but alloys of titanium with zirconium, tantalum, niobium, molybdenum, chromium, iron, vanadium, manganese, etc. are particularly suitable. In general, a suitable composition contains components other than titanium in an amount of several percent by weight. When titanium or titanium alloy is used as a cathode, it is generally in the form of a flat plate, a box, or a mesh. In addition to chemical roughening such as surface roughening and etching, it is preferable to carry out appropriate treatments such as metal coating, alone or in combination, from the viewpoint of adhesion of the plating layer that has been subjected to the plating treatment, which is a component of the present invention. . It has been found that additives to the electroplating bath are those that are generally used as flocculants for suspended substances in water in so-called water treatment technology, and include starch, dextrin, poly-2-diethylaminoethyl methacrylate, or polyester. Aluminum chloride can be used. Usually one type of these additives is sufficient, but there is no adverse effect when two or more types are used in combination. On the other hand, there is no particular limitation on the amount of these additives, but if too large, it will have a negative effect on the peeling resistance of the plating layer and the mechanical strength of the plating surface, so the amount added should be determined depending on the conditions of use as a cathode. must be decided. Next, in the present invention, an iron-cobalt alloy is selected as the component to be plated, and the plating bath consists of a ferrous salt such as ferrous chloride or ferrous sulfate, and a cobalt salt such as cobalt chloride or cobalt sulfate. A bath consisting of a mixed solution of The pH of the plating bath has a significant effect on the plating film. The preferred pH range of the plating bath is 2.5 to 6.0, although it is influenced by the strength of bath agitation. If the stirring is weak, it is possible to use a lower pH, but this will cause problems with the uniformity of the plated surface. The concentration of ferrous ions and cobalt ions in the plating bath is preferably such that the total amount of both is 0.1 mol/l to 2 mol/l, more preferably 0.4 mol/l to 1.7 mol/l.
is good. The ratio of ferrous ions and cobalt ions is not particularly limited, but in practice Co/Fe=
0.01-0.5 is preferred. If the total concentration of ferrous ions and cobalt ions exceeds the above range, an inactive plated surface is likely to be formed, and the effect of reducing hydrogen overvoltage as a cathode is significantly reduced. If the concentration is lower than this range, problems will occur in terms of peeling resistance of the plating film, current efficiency, etc. In addition, in Patent No. 206743, the presence of ferric salt in the plating bath is an essential condition, and iron oxide is intended to be contained in the plating layer formed, but in the present invention, the above-mentioned addition to the iron-cobalt alloy plating bath One of the constituent requirements is the coexistence of ferric salts and iron oxides, and on the other hand, PH
Depending on the conditions, ferric salts and iron oxides can easily be produced, but even if they are produced, they will not cause any harm even if they are separated by precipitation, so there is a great advantage in being able to set a wide range of PH conditions. In order to increase the electrical conductivity of the plating bath, an inorganic salt such as calcium chloride, which is conventionally added, may be added as necessary. However, salts containing ammonium ions must be avoided because they interfere with the formation of the plating. In the case of a plating bath having a relatively low concentration of metal ions, the electrical conductivity of the plating solution is low, so the addition of the above-mentioned inorganic salt is useful. However, if a large amount is added, the effect of reducing the hydrogen overvoltage of the plating cathode will be reduced. The temperature of the plating bath is the customary plating temperature (approximately 20~
(90°C) may be employed, and although not particularly limited, 70°C or higher is preferred. The current density during plating is set under the conventional conditions (1 to
5A/dm ² ) is appropriate. Even higher current densities are possible, but the surface condition becomes rough and the peeling resistance deteriorates. Although it is possible to use a current density lower than the above, the peeling resistance of the plating film deteriorates. Further, it is preferable that the plating bath be stirred to the extent that it is used in conventional electroplating operations. However, air agitation tends to oxidize ferrous ions and turn them into unnecessary ferric iron, which must be avoided. For this purpose, non-oxidizing gas stirring such as nitrogen gas stirring is preferred from the above point of view. The present invention will be explained in detail below using Examples. Examples 1 to 5 A cathode plate plated under the conditions shown in Table 1 was placed opposite an anode made of a titanium plate coated with ruthenium oxide, and sodium chlorate 100g/l, sodium chloride 240g/l, and sodium hydroxide 4g/l were applied. Electrolysis is carried out at a temperature of 45℃ by immersing it in an aqueous solution of
The lower column of the same table shows the reduction in hydrogen overvoltage compared to a conventional mild steel plate cathode (polished with abrasive paper) under each condition of 10 A/dm ² , 20 A/dm ² , and 30 A/dm ² . The cathode potential was measured using a saturated calomel electrode through a Luggin capillary. Examples 6 to 14 The lower column of the table shows the results of measuring the decrease in hydrogen overvoltage of the cathodes prepared under the conditions shown in Table 2 relative to the mild steel plate cathode in water electrolysis in response to current density. The cathode potential was set at 45℃ for the plated mild steel plate.
A pure nickel plate was placed opposite an anode and immersed in a 10% by weight aqueous sodium hydroxide solution, and measured using a saturated calomel electrode through a Luggin capillary tube. Further, as the mild steel plate cathode, a mild steel plate polished with #80 abrasive paper was used. Example 15 Asbestos was deposited on a cathode wire mesh plated under the conditions shown in Table 3 to serve as a cathode for an asbestos diaphragm.The cathode was placed opposite an anode made of a titanium wire mesh coated with ruthenium oxide at a temperature of 70°C and a current density. 20A/d
Asbestos diaphragm electrolysis of saturated brine for the production of sodium hydroxide was carried out at ^m2 . Conventional mild steel wire mesh cathode (polished with a wire brush)
The lower column of the same table shows the effect of reducing the electrolytic voltage of the plating-treated cathode. Example 16 A cathode plate prepared under the conditions shown in Table 4 was heated at 65°C.
Pure nickel anodes were immersed oppositely in a 30% by weight aqueous potassium hydroxide solution, and water electrolysis was performed at a current density of 20 A/dm ² . As a result of electrolysis, the electrolytic voltage decreased considerably as shown in the same table. Comparative Examples 1 to 5 Comparisons were made with Examples 1 to 5 using cathode plates plated under the conditions shown in Table 5. Comparative Examples 6 to 11 The lower column of the table shows the results of measuring the reduction in hydrogen overvoltage against mild steel plates in water electrolysis using cathodes prepared under the plating bath conditions shown in Table 6, corresponding to each current density condition. . The cathode potential measuring method, the mild steel plate cathode, and its surface treatment were the same as in Examples 6-14.

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Claims (1)

[Claims] 1 Starch, dextrin, poly-2-
one selected from the group consisting of diethylaminoethyl methacrylate and polyaluminum chloride with a total ferrous ion and cobalt ion concentration of 0.1
An aqueous solution electrolysis method in which an iron-cobalt alloy is electroplated by adding it to an iron-cobalt alloy plating bath with ~2 mol/l and 2.5 PH6.0, and this is used as a cathode.