JP2013142166A - Electrode for producing sterilized water and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly durable electrode for electrolysis that stably exerts a high chlorine generation efficiency characteristic, even under a condition wherein electrolysis of dilute salt water such as tap water is performed while repeatedly switching polarities of an anode and a cathode with a comparatively high current density, and realizes downsizing of an electrolytic cell.SOLUTION: The electrode for electrolyzing the dilute salt water to produce sterilized water comprises an electrode catalytic layer formed on an electrode substrate composed of titanium or a titanium alloy via an intermediate layer. The electrode catalytic layer comprises a complex comprising 4-11 mol% platinum, 37-60 mol% iridium oxide, 3-11 mol% rhodium oxide and 22-53 mol% tantalum oxide, calculated in terms of metal.

Description

  The present invention is useful for generating electrolyzed water having a high sterilizing ability by directly electrolyzing dilute salt water such as tap water. The present invention also relates to an electrode for electrolysis having characteristics excellent in stability, a method for producing the electrode, and a method for producing sterilized water by electrolysis at a relatively high current density using the electrode.

Directly electrolyze dilute salt water such as tap water to generate chlorine at the anode, and use the sterilization property of hypochlorous acid produced by the reaction of this chlorine and water, for example, to add functions to general household facilities. It is known to sterilize hands, humidifying water, bath water, warm water toilet seat washing nozzles and the like. In such electrolytic, because of normal tap water is used, OH calcium in tap water is produced at the cathode side during electrolysis ^- react with, adhere as hydroxide on the cathode surface, clog the narrow space between the poles May end up. In order to remove this deposit, it is generally used by switching the polarity periodically, for example, using two or more similar electrodes and repeating the use as an anode and the use as a cathode. ing.

  As an electrode used in dilute salt water such as tap water, an electrode obtained by electroplating platinum on a titanium or titanium alloy substrate is widely used. This electrode has high stability at the time of polarity switching, and platinum. However, when using electrolyzed water for sterilization, salt must be added to tap water to increase the chlorine ion concentration in order to obtain the prescribed effective chlorine concentration. However, there is a problem that the maintenance cost of the apparatus becomes high.

  In order to obtain stable and high chlorine generation efficiency characteristics in dilute saline solution, an electrode in which an electrode catalyst layer made of a composite of platinum, iridium oxide, rhodium oxide and tantalum oxide is formed on a conductive substrate has been proposed. Yes. (See Patent Document 1). Although this proposed electrode has the advantage of maintaining high chlorine generation efficiency characteristics for a long period of time compared to platinum-plated electrodes and conventional iridium oxide-based electrodes, it has a relatively high current density at the anode and cathode. When the polarity is switched and the use is repeated, there is a problem that the electrode is consumed greatly, the electrode life is shortened, and the electrolytic cell cannot be reduced.

On the other hand, as described above, in order to attach a sterilizing water generator to a general household facility, for example, a warm water toilet seat, a predetermined sterilizing water concentration can be obtained by directly electrolyzing tap water without adding salt. It is indispensable to fit in a limited space, and it is possible to reduce the size of the electrolytic cell, and to provide a highly durable electrode that enables a higher current density than the conventional current density (5 A / dm ² or less). There is a strong demand for development.

JP2009-052069A

  The object of the present invention is to provide stable and high chlorine generation efficiency characteristics even under conditions in which dilute salt water such as tap water is electrolyzed while repeating polarity switching between the anode and the cathode at a relatively high current density. A highly durable electrode for electrolysis that can be reduced in size, a method for producing the electrode, and a method for producing sterilizing water by electrolysis at a relatively high current density using the electrode for electrolysis.

According to the present invention, the above object is
1. An electrode for forming sterilized water by electrolyzing dilute salt water by providing an electrode catalyst layer through an intermediate layer on an electrode substrate made of titanium or a titanium alloy, the electrode catalyst layer being converted into metal 1. An electrode for electrolysis comprising a composite of 4 to 11 mol% of platinum, 37 to 60 mol% of iridium oxide, 3 to 11 mol% of rhodium oxide, and 22 to 53 mol% of tantalum oxide. After a titanium hydride layer formed on the surface of a substrate made of titanium or a titanium alloy is changed into an intermediate layer of titanium oxide by thermal oxidation, a platinum compound, an iridium compound, a rhodium compound and tantalum are formed on the intermediate layer of titanium oxide. After applying the solution containing the compound, heat treatment is performed in an oxidizing atmosphere, and in terms of metal, platinum is 4 to 11 mol%, iridium oxide is 37 to 60 mol%, rhodium oxide is 3 to 11 mol%, and tantalum oxide is 22 to 22%. 2. The method for producing an electrode for electrolysis according to 1 above, wherein an electrode catalyst layer composed of a 53 mol% composite is formed. In the method of electrolyzing dilute salt water to produce sterilizing water using an electrode in which an electrode catalyst layer is provided on an electrode substrate made of titanium or a titanium alloy via an intermediate layer, the electrode for electrolysis as described in 1 above This is achieved by a method for producing sterilizing water, characterized by electrolysis using an electrode and a current density of 6 to 20 A / dm ² .

The electrode of the present invention has investigated the range in which the interaction of the four components constituting the electrode catalyst layer can be enhanced under dilute salt water such as tap water under limited electrolysis conditions such as relatively high current density. Even under electrolytic conditions in which dilute salt water such as tap water is repeatedly switched between the polarity of the anode and the cathode at a relatively high current density (6 A / dm ² or more), due to the interaction of the four components constituting the electrode catalyst layer, The electrode catalyst layer does not fall off, and there is an excellent effect that consumption can be reduced and the electrode life can be significantly extended. In addition, according to the present invention, there is an excellent effect that the electrodes and the electrolytic cell can be miniaturized.

  Hereinafter, the electrode of the present invention and the production method thereof will be described in more detail.

  Examples of the material of the electrode substrate used in the present invention include titanium or a titanium-based alloy. As the titanium alloy, a conductive alloy having corrosion resistance mainly composed of titanium can be used. For example, a Ti-based alloy that is usually used as an electrode material and includes a combination of Ti—Ta—Nb, Ti—Pd, Ti—Zr, Ti—Al, and the like. These electrode materials can be processed into a desired shape such as a plate shape, a perforated plate shape, a rod shape, or a mesh plate shape and used as an electrode substrate.

  It is desirable to pre-treat the electrode base as described above in advance, as is usually done. Specific examples of such pretreatment include the following. First, the surface of an electrode substrate (hereinafter referred to as a titanium substrate) made of titanium or a titanium-based alloy described above is washed with alcohol or the like and / or degreased by electrolysis in an alkaline solution and then fluorinated. By treating with hydrofluoric acid having a hydrogen concentration of 1 to 20% by weight or mixed acid of hydrofluoric acid and other acids such as nitric acid and sulfuric acid, the oxide film on the surface of the titanium substrate is removed and titanium crystal grain boundaries Roughening the unit. The acid treatment can be performed at a temperature of from room temperature to about 40 ° C. for a few minutes to a dozen minutes depending on the surface condition of the titanium substrate. A blasting process may be used in combination for sufficient roughening.

The surface of the titanium substrate thus treated with acid is brought into contact with hot concentrated sulfuric acid to roughen the inner surface of the titanium crystal grain boundary into fine projections and to form a thin layer of titanium hydride on the surface of the titanium substrate. Let me. Concentrated sulfuric acid to be used generally has a concentration of 40 to 80% by weight, preferably 50 to 60% by weight. Concentrated sulfuric acid contains a small amount of sulfate for the purpose of stabilizing the treatment if necessary. Etc. may be added. The contact with the hot concentrated sulfuric acid can usually be carried out by immersing the titanium substrate in a bath of concentrated sulfuric acid, and the bath temperature is generally about 100 to about 150 ° C., preferably about 110 to about 130. The temperature can be in the range of 0 ° C., and the immersion time is usually about 0.5 to about 10 minutes, preferably about 1 to about 3 minutes. By this hot concentrated sulfuric acid treatment, the inner surface of the titanium crystal grain boundary can be finely roughened like a protrusion, and a very thin titanium hydride film can be formed on the surface of the titanium substrate. The titanium substrate subjected to the hot concentrated sulfuric acid treatment is taken out of the sulfuric acid tank and is preferably quenched in an atmosphere of an inert gas such as nitrogen or argon to lower the surface temperature of the titanium substrate to about 60 ° C. or lower. For this rapid cooling, it is appropriate to use a large amount of cold water also for washing.

  The titanium substrate pretreated as described above is thermally fired in the atmosphere by firing in the atmosphere, so that the titanium hydride in the layer is substantially returned to titanium metal. Titanium near the surface of the titanium substrate can be changed to titanium oxide in a low oxidation state. This calcination can be generally performed by heating at a temperature of about 300 to about 600 ° C., preferably about 300 to about 400 ° C. for about 10 minutes to 4 hours. Thereby, a very thin conductive titanium oxide layer is formed on the surface of the titanium substrate. The thickness of the titanium oxide layer is generally within the range of 100 to 1,000 angstroms, preferably 200 to 600 angstroms, and the composition of the titanium oxide is such that x is generally 1 <x <2 as TiOx. In particular, it is desirable to be in the range of 1.9 <x <2. Alternatively, the pretreated titanium substrate may be directly subjected to the next step without performing the firing treatment as described above. In this case, the titanium hydride coating layer on the surface of the titanium substrate is converted to titanium metal and titanium oxide in a low oxidation state during the thermal decomposition treatment in the next step.

  Thereafter, the titanium oxide surface on the titanium substrate fired in this manner was converted to metal in terms of 4 to 11 mol%, iridium oxide 37 to 60 mol%, rhodium oxide 3 to 11 mol%, and tantalum oxide 22 to It is coated with a composite consisting of 53 mol%.

  The platinum compound, iridium compound, rhodium compound and tantalum compound used to form the complex are decomposed under the conditions described below and converted to platinum, iridium oxide, rhodium oxide and tantalum oxide, respectively. More specifically, examples of the platinum compound include chloroplatinic acid and platinum chloride, and chloroplatinic acid is particularly preferable. Examples of the iridium compound include iridium chloride, iridium chloride, iridium nitrate, and iridium chloride is particularly preferable. Furthermore, examples of the rhodium compound include rhodium chloride and rhodium nitrate, and rhodium chloride is particularly preferable. Examples of the tantalum compound include tantalum chloride and tantalum ethoxide, and tantalum ethoxide is particularly preferable.

  These platinum compound, iridium compound, rhodium compound and tantalum compound can be dissolved in a solvent and applied in a solution to the titanium oxide layer on the titanium substrate.

  As a solvent for preparing a solution by dissolving these platinum compound, iridium compound, rhodium compound and tantalum compound, a lower alcohol is suitable. For example, methanol, ethanol, propanol, butanol and the like or a mixture thereof can be mentioned.

The total concentration of the platinum compound, iridium compound, rhodium compound and tantalum compound in the lower alcohol solution can be generally in the range of 20 to 200 g / L, preferably 40 to 150 g / L in terms of total metal concentration. . When the metal concentration is lower than 20 g / L, the catalyst supporting efficiency is deteriorated. When the metal concentration exceeds 200 g / L, problems such as catalyst activity, supporting strength, and unevenness of the supporting amount may occur. The relative use ratio of platinum compound, iridium compound, rhodium compound and tantalum compound is, in terms of metal, platinum compound is generally 4 to 11 mol%, preferably 5 to 10 mol%, and iridium compound is generally 37 to 60 mol. %, Preferably 42-50 mol%, rhodium compounds are generally in the range 3-11 mol%, preferably 4-9 mol%, and tantalum compounds are generally in the range 22-53 mol%, preferably 35-53 mol%. can do.

  A substrate on which a titanium oxide layer on a titanium substrate is coated with a solution containing a platinum compound, an iridium compound, a rhodium compound, and a tantalum compound is optionally dried at a temperature in the range of about 20 to about 150 ° C., and then oxygenated. Baking is performed in a contained gas atmosphere, for example, in air. Firing is performed by heating to a temperature generally in the range of about 450 ° C. to about 600 ° C., preferably about 500 to about 550 ° C. in a suitable heating furnace such as an electric furnace, a gas furnace, an infrared furnace or the like. be able to. The heating time can be about 5 to 30 minutes, depending on the size of the substrate to be fired. By this firing, a platinum-iridium oxide-rhodium oxide-tantalum oxide composite can be formed and supported on the surface of the titanium oxide layer. When a sufficient amount of platinum-iridium oxide-rhodium oxide-tantalum oxide composite cannot be supported by a single loading operation, the above-described solution coating-drying-baking steps are repeated a desired number of times. be able to.

  Here, the "platinum-iridium oxide-rhodium oxide-tantalum oxide composite" is a composition in which the four components of platinum, iridium oxide, rhodium oxide, and tantalum oxide are mixed or in close contact with each other so as to interact with each other. Say things.

  The ratio of each component in the platinum-iridium oxide-rhodium oxide-tantalum oxide composite supported on the titanium oxide layer is 4 to 11 mol%, preferably 5 to 10%, and iridium oxide 37 to 60 in terms of metal. It can be in the range of mol%, preferably 42-50%, rhodium oxide 3-11 mol%, preferably 4-9% and tantalum oxide 22-53 mol%, preferably 35-53%. If the proportion of platinum in the composite is less than 4 mol%, the chlorine generation efficiency decreases greatly. On the other hand, if it exceeds 11 mol%, the consumption of the catalyst increases and the electrode life is shortened. On the other hand, when the proportion of iridium oxide is less than 37 mol%, the decrease in chlorine generation efficiency increases. On the other hand, when the proportion of iridium oxide exceeds 60 mol%, the consumption of the catalyst increases and the electrode life is shortened. Furthermore, if the ratio of rhodium oxide is less than 3 mol%, the chlorine generation efficiency is greatly reduced. On the other hand, if it exceeds 11 mol%, the consumption of the catalyst is increased and the electrode life is shortened. Furthermore, when the proportion of tantalum oxide is less than 22 mol%, the exhaustion of the catalyst is increased and the electrode life is shortened. On the other hand, when the proportion exceeds 53 mol%, the chlorine generation efficiency is greatly reduced.

The electrode for electrolysis of the present invention thus produced can be used even in electrolysis conditions in which dilute salt water such as tap water is repeatedly switched between the polarity of the anode and the cathode at a relatively high current density of 6 A / dm ² or more. The consumption is small and the durability is excellent, and the electrode and the electrolytic cell can be miniaturized. As the current density is increased, the electrode life decreases in inverse proportion. Therefore, in consideration of the practical electrode life, the current density is preferably in the range of 6 A / dm ² to 20 A / dm ^2. .

  JIS class 1 titanium plate material (t0.5mm x w100mm x l100mm) is washed with alcohol, then 2 minutes in an 8 wt% hydrofluoric acid aqueous solution at 20 ° C, and 3 minutes in an aqueous 60 wt% sulfuric acid solution at 120 ° C Processed. Next, the titanium substrate was taken out of the sulfuric acid aqueous solution and sprayed with cold water for rapid cooling. Further, it was immersed in a 0.3 wt% hydrofluoric acid aqueous solution at 20 ° C. for 2 minutes and then washed with water. After washing with water, heat treatment was performed in the atmosphere at 400 ° C. for 1 hour to form a thin titanium oxide intermediate layer on the titanium substrate surface.

  Subsequently, a butanol solution of rhodium chloride adjusted to a rhodium concentration of 100 g / L, a butanol solution of iridium chloride adjusted to an iridium concentration of 200 g / L, a butanol solution of tantalum ethoxide adjusted to a tantalum concentration of 200 g / L, and a platinum concentration of 200 g / L The butanol solution of chloroplatinic acid adjusted to L is weighed so that the composition ratio of Pt—Ir—Rh—Ta is the mol% shown in Table 1 below, and then the metal equivalent concentration of Ir is 50 g / L. Thus, it diluted with butanol and prepared the coating liquid of Examples 1-5 and Comparative Examples 1-3 shown in Table-1.

  0.27 ml of this solution was weighed with a pipette, applied to the titanium oxide intermediate layer, dried at room temperature for 20 minutes, and further baked in air at 550 ° C. for 10 minutes. This coating-drying-firing process was repeated 6 times, and Examples 1 to 5 and Comparative Examples shown in Table 1 in which a platinum-iridium oxide-rhodium oxide-tantalum oxide composite was supported on the titanium oxide intermediate layer. Electrodes 1 to 3 were produced.

The electrode thus obtained was electrolyzed at 15 A / dm ² for 60 seconds at room temperature in tap water, and then subjected to electrolysis for 100 hours by switching the polarity and repeating electrolysis for 60 seconds at −15 A / dm ² , The frequency of polarity switching was increased and the coating was consumed at an accelerated rate. The chlorine generation efficiency of each electrode after electrolysis was measured using standard water (Na ²⁺ = 5.75 ppm, Ca ²⁺ = 10.02 ppm, Mg ²⁺ = 6.08 ppm, K ⁺ = 0.98 ppm, Cl ⁻ = 17.75 ppm, SO ₄ ² = 24.5 ppm, CO ₃ ⁻ = 16.5 ppm) 12 coulomb (0.5 A, 24 sec) was electrolyzed in 150 ml, and determined by the iodine method. Table 1 shows the amount of consumption after electrolysis and the chlorine generation efficiency.

  As shown in Table 1, the consumption amount of the comparative example electrode was large, and 48 to 68% of the electrode catalyst was consumed after 100 hours of electrolysis. On the other hand, the consumption amount of each example electrode is as small as 20% or less, the consumption rate is particularly low under the above electrolysis conditions where the current density is high, and it has excellent stability.

  Further, the chlorine generation efficiency of the example electrode is almost the same as that of the comparative example electrodes 1 and 2, and has a high value.

Claims (3)

  An electrode for forming sterilized water by electrolyzing dilute salt water by providing an electrode catalyst layer through an intermediate layer on an electrode substrate made of titanium or a titanium alloy, the electrode catalyst layer being converted into metal An electrode for electrolysis comprising a composite of platinum 4 to 11 mol%, iridium oxide 37 to 60 mol%, rhodium oxide 3 to 11 mol%, and tantalum oxide 22 to 53 mol%.   After a titanium hydride layer formed on the surface of a substrate made of titanium or a titanium alloy is changed into an intermediate layer of titanium oxide by thermal oxidation, a platinum compound, an iridium compound, a rhodium compound and tantalum are formed on the intermediate layer of titanium oxide. After applying the solution containing the compound, heat treatment is performed in an oxidizing atmosphere, and in terms of metal, platinum is 4 to 11 mol%, iridium oxide is 37 to 60 mol%, rhodium oxide is 3 to 11 mol%, and tantalum oxide is 22 to 22%. 2. The method for producing an electrode for electrolysis according to claim 1, wherein an electrode catalyst layer made of a 53 mol% composite is formed. 2. The method according to claim 1, wherein the electrode comprises an electrode substrate made of titanium or a titanium alloy and an electrode catalyst layer is provided via an intermediate layer to electrolyze dilute salt water to produce sterilizing water. A method for producing sterilizing water, characterized in that electrolysis is carried out at a current density of 6 to 20 A / dm ² using a working electrode.