JP2006118023A - Method for manufacturing electrode for generating hydrogen - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for generating hydrogen, which is used in the electrolysis of water or an aqueous solution of an chloride of an alkali metal, has sufficiently low hydrogen overvoltage and is superior in durability because of hardly being poisoned by ferrous ions and having a catalytic layer with excellent adhesiveness to a substrate, and to provide a manufacturing method therefor. <P>SOLUTION: The electrode for generating hydrogen includes a platinum alloy containing platinum and one metal selected from the group of nickel, cobalt, copper, silver and iron, carried on an electroconductive substrate, wherein the platinum alloy contains platinum in a range of 0.40 to 0.99 by mole ratio. The electrode is obtained by the steps of: applying a solution of a platinum compound which forms an ammine complex with a compound of one metal selected from the group consisting of nickel, cobalt, copper, silver and iron, onto the electroconductive substrate; drying the film; thermally decomposing the component of the film at 200 to 700°C; and then reducing the product. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing an electrode for hydrogen generation used for electrolysis of water or electrolysis of an aqueous solution of an alkali metal chloride such as salt.

  The water or alkali metal chloride aqueous solution electrolysis industry is a power intensive industry, and various technological developments have been made to save energy. The energy saving means is to substantially reduce the electrolysis voltage composed of theoretical decomposition voltage, liquid resistance, diaphragm resistance, anode overvoltage, cathode overvoltage, and the like. In particular, regarding the reduction of the overvoltage, since the overvoltage value depends on the electrode catalyst material and the morphology of the electrode surface, many researches and developments have been conducted on the improvement thereof. As a result of extensive research and development for reducing anode overvoltage in salt exchange electrolysis using an ion exchange membrane method, a dimensional stability electrode having a low anode overvoltage and excellent durability [for example, a DSE electrode manufactured by Permerek Electrode Co., Ltd. ( Registered trademark)] has been completed and has already been used in a wide range of fields including the salt electrolysis industry.

  On the other hand, regarding hydrogen generating electrodes for reducing cathode overvoltage, so-called active cathodes, various proposals have heretofore been made mainly of nickel having high corrosion resistance in a caustic solution and relatively high catalytic activity. The main production methods include electroplating, in which the catalyst component is electrodeposited from a bath in which the active ingredient and metal salt are dissolved, and dispersion plating, in which the catalyst component is electrophoretically deposited from a bath in which the active substance is dispersed in a metal salt solution. And a thermal spraying method in which a molten catalyst material is directly sprayed onto a substrate, and a thermal decomposition method in which a solution of a metal salt is applied and fired.

  For example, a method is disclosed in which a conductive substrate surface is coated with a substance containing an organic compound such as amino acid, carboxylic acid, or amine in addition to a combination of nickel, iron, cobalt, and indium by electroplating ( Patent Document 1). Also disclosed is a method of coating an alloy layer made of nickel and molybdenum by an arc ion plating method (Patent Document 2).

  On the other hand, it has long been known that hydrogen overvoltage can be reduced by using platinum, which is a highly active catalyst, and as a method of coating platinum, a solution containing platinum and cerium as a base is applied, dried and fired, so-called A method of coating a catalyst composed of platinum and cerium oxide by a thermal decomposition method has been disclosed (Patent Document 3), but further improvement has been studied for use in an electrolysis industry or the like of an aqueous alkali metal chloride solution. Yes.

Further, as a method with high coating efficiency, a method of efficiently covering platinum by electroplating using a plating bath made of an alkali metal solution of dinitrodiammine platinum and an organic acid or an inorganic acid is disclosed (Patent Document 4).
In addition, as a method for coating a platinum alloy, as a method for producing an insoluble anode for electrolysis such as chlorine generation, electroplating using a ternary alloy composed of platinum-molybdenum-iron group metal on a copper substrate using induced eutectoid phenomenon. A method of coating by a method (Patent Document 5) and a method of coating an alloy of platinum and iridium on brass by an electroplating method are disclosed (Patent Document 6).

  In view of the above, various methods for producing electrodes for hydrogen generation have been proposed for the purpose of reducing the power consumption of water or alkali metal chloride aqueous solution electrolysis industry. No manufacturing method has been known for the hydrogen generating electrode.

Japanese Patent No. 3319370 (Example) Japanese Patent No. 3358465 (Example) JP 2000-239882 A (Example) Japanese Examined Patent Publication No. 61-58557 (Example) JP-A-10-212592 (Example) Japanese Patent No. 3117656 (Example)

  An object of the present invention is to provide a method for producing a hydrogen generating electrode having a sufficiently low hydrogen overvoltage that can be used in water or an alkali metal chloride aqueous solution electrolysis industry.

  As a result of intensive studies to solve the above problems, the present inventors have found that a transition metal compound and a platinum compound whose immersion potential at pH = 5 to 8 is lower than 0.5 V on the basis of SCE are formed on a conductive substrate. When a dissolved plating bath is used, it has been found that a platinum alloy can be coated by an electroplating method, and the present invention has been completed.

  Hereinafter, the present invention will be described in detail.

  The platinum alloy used in the electrode for hydrogen generation of the present invention does not exist as a mixture of metal platinum and transition metal, a mixed oxide or composite oxide of transition metal oxide and platinum, or the like. Using a plating bath in which a transition metal compound and a platinum compound having an immersion potential at pH = 5 to 8 lower than 0.5 V on the basis of SCE are dissolved on a conductive substrate. Obtained by co-deposition of platinum alloy by plating.

  First, regarding a platinum alloy, platinum forms an alloy phase such as a solid solution or an intermetallic compound with many metal elements, and the alloy phase changes variously depending on its composition ratio and temperature. These are disclosed in alloy phase diagrams such as a full solid solution type, a precipitation type, a peritectic reaction type, a eutectic reaction type, and a monotectic reaction type.

  For example, in the case of an alloy combining platinum and cobalt, the alloy phase diagram belongs to a precipitation type, and platinum and cobalt form a solid solution alloy at any composition ratio. In addition to platinum and cobalt, platinum and many other elements such as nickel, copper, silver, iron, morbden, and manganese form a solid solution alloy at any composition ratio (edited by Seizo Nagasaki and Satoshi Hirabayashi, “2 Original Alloy Phase Diagrams ", Agne Technical Center Publishing, 2nd edition, 13, 112, 136, 152, 230).

  The platinum alloy used in the electrode for hydrogen generation of the present invention is a solution in which transition metal and platinum are solid-solved and alloyed. For example, the (111) plane spacing is the X-ray main diffraction peak of CuKα rays of metal platinum. It can be identified from changes in

  Specifically, the crystal structure of metallic platinum is ASTM card, No. As disclosed in Japanese Patent No. 4-0802, it is a face-centered cubic lattice, and the (111) plane spacing, which is the main diffraction peak due to CuKα rays, is 2.265 angstroms. When the metals having different atomic radii are dissolved and alloyed with the metal platinum, the lattice of the metal platinum expands and contracts. Therefore, the presence or absence of alloying can be confirmed from the change in (111) plane spacing.

  Next, the production method of the present invention will be described in detail.

  First, examples of the conductive substrate to be used include nickel, iron, copper, titanium, and stainless steel alloy, and nickel having excellent corrosion resistance against an alkaline solution is particularly preferable. The shape of the conductive substrate is not particularly limited, and generally may be a shape that matches the electrode of the electrolytic cell. For example, a flat plate, a curved plate, etc. can be used, and an expanded metal, a punch metal, a net, etc. are used. it can.

  The conductive substrate is preferably roughened in advance. This is because the surface area of contact can be increased by roughening, and the adhesion between the substrate and the deposit is improved. The surface roughening means is not particularly limited and can be used by a known method such as sand blasting, etching with oxalic acid or hydrochloric acid solution, washing with water and drying. Moreover, in order to improve the adhesiveness between the base and the electrodeposit, it is preferable to perform base plating in advance.

  Next, a platinum alloy is co-deposited from a plating bath containing a transition metal compound and a platinum compound. In order to co-deposit, it is essential that the standard electrode potential or precipitation equilibrium potential of the transition metal and platinum be close. . However, as can be seen from the standard electrode potential ("Electrochemical Handbook" 5th edition, Maruzen Publishing, pages 92-95), platinum is a noble standard electrode and easy to deposit, whereas many transition metals are standard electrodes. Since the potential is base and the potentials are too far from each other, it is difficult to co-deposit them.

  However, by complexing platinum in the plating bath and lowering the platinum precipitation equilibrium potential from the standard electrode potential, ie, lower than 0.5 V on a SCE basis at pH = 5-8, nickel, cobalt, iron Therefore, co-deposition is possible. In particular, it is effective to make the precipitation equilibrium potential of the complex platinum and the precipitation equilibrium potential of the transition metal close to each other, that is, to reduce the difference between the precipitation equilibrium potentials to 0.5 V or less at pH = 5-8. It is preferable to do.

  In the present invention, the deposition equilibrium potential is measured by the potential when the electrode is immersed in the plating bath, that is, the immersion potential, and the deposition equilibrium potential of the transition metal and platinum is replaced with the immersion potential.

  When the immersion potential of platinum at pH = 5 to 8 is nobler than 0.5 V on the basis of SCE, platinum is preferentially electrodeposited because it is too far from the immersion potential of the transition metal, so that co-deposition is difficult. The platinum alloy cannot be coated.

  The transition metal compound may be a transition metal such as nitrate, sulfate, chloride, carbonate, acetate, sulfamate, etc. For example, noble metals such as gold, silver, copper palladium, iridium, and ruthenium are complexed by adding complex salts such as glycine, citric acid, malonic acid, and succinate, and the immersion potential at pH = 5 to 8 is based on SCE. What is necessary is just to make it lower than 0.5V.

  The pH of the plating bath is preferably pH = 3 or more in order to prevent dissolution of the conductive substrate. The pH may be adjusted using a pH buffer such as ammonia, borate, phosphate, etc., but when the pH is neutral to alkaline and precipitates such as hydroxide are generated, as shown above A complex complex may be formed by adding a complex salt.

  Moreover, in order to stabilize electroconductivity, you may add electrolytes, such as potassium chloride, and the density | concentration of each component in a plating bath is not specifically limited, The range of 0.001-1 mol / liter can be illustrated.

  Regarding plating conditions, conditions such as plating bath temperature, plating time, current density are not limited, and by changing these conditions, the composition of platinum and transition metal co-deposits, the loading amount, etc. should be controlled according to the purpose. The electrode after plating may be cleaned using pure water or ion exchange water.

  As described above, the hydrogen generating electrode coated with the platinum alloy can be efficiently and easily manufactured by the manufacturing method of the present invention.

  By this invention, the electrode for hydrogen generation which coat | covered the platinum alloy with low hydrogen overvoltage which can be used in water or an alkali metal chloride aqueous solution electrolysis industry etc. can be manufactured efficiently.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  In addition, each evaluation was implemented by the method shown below.

(Crystal structure)
About the obtained electrode surface, using an X-ray diffractometer with CuKα ray (model MXP3 manufactured by Mac Science), acceleration voltage 40 kV, acceleration current 30 mA, step interval 0.04 deg, sampling time 3 sec, measurement range 2θ = 20˜ A range of 60 ° was measured. From the diffraction pattern, the (111) plane spacing, which is the main diffraction peak, was calculated from the Bragg equation.
(Supported amount and platinum content)
The obtained electrode was dissolved in the aqua regia with an ICP emission analyzer (Perkin Elmer, model optima3000). For the electrode to which nickel was added, EPMA (Horiba, model EMAX-5770W) was used. Was used to measure the content of platinum and transition metal elements, and the platinum content in the electrodeposits was calculated by the following formula.

Platinum content = platinum / (platinum + transition metal) molar ratio (measurement of immersion potential)
Adjust the plating solution to 200 mL, immerse two ² cm ² platinum electrodes, conduct pre-electrolysis at a current density of 1 mA / cm ² for 1 hour, and then immerse the plating solution at 25 ° C. while bubbling nitrogen. Was measured.

Example 1
A nickel expanded mesh (2 × 5 cm) was used as the conductive substrate, dinitrodiammine platinum nitrate solution (Tanaka Kikinzoku, platinum concentration: 4.5 wt%, solvent: 8 wt% nitric acid solution) and cobalt nitrate 6 water. After adjusting the concentration of each of the following plating baths using a Japanese product, trisodium citrate, glycine, and ammonium dihydrogen phosphate, the pH of the plating bath was adjusted to 8 using a 10% aqueous ammonia solution.
Dinitrodiammine platinum 0.005 mol / liter cobalt nitrate hexahydrate 0.005 mol / liter trisodium citrate 0.01 mol / liter glycine 0.01 mol / liter ammonium dihydrogen phosphate 0.01 mol / liter separately As a result of measuring the immersion potential of a dinitroammine platinum solution and a cobalt nitrate hexahydrate solution with a concentration of 0.005 mol / liter prepared with an aqueous ammonia solution at pH = 8, pH = 8, SCE standard 0.21V and − 0.08V, and both immersion potentials were lower than 0.50V on the basis of SCE.

Next, the plating bath was heated to 65 ° C., and was plated for 30 minutes at a current density of 50 mA / cm ² using a platinum plate as a counter electrode. The obtained electrodeposits were washed with water, the platinum content determined by the above method is shown in Table 1, and the XRD pattern of the platinum alloy is shown in FIG.

Examples 2-3
Except for changing the current density during plating, the same procedure as in Example 1 was performed. The platinum content determined by the above method is shown in Table 1, and the XRD pattern of the platinum alloy is shown in FIG.

The immersion potentials were pH = 8, respectively, SCE standard 0.21V and −0.08V, and both immersion potentials were lower than 0.50V based on SCE.
Example 4
Except that the cobalt nitrate hexahydrate in the plating bath was changed to nickel nitrate hexahydrate, the same procedure as in Example 1 was carried out. The platinum content determined by the above method is shown in Table 1, and the XRD pattern of the platinum alloy Is shown in FIG.

  The immersion potential is 0.210V with SCE standard at pH = 8 in dinitroammine platinum solution, and 0.053V with SCE standard at pH = 8 in nickel nitrate solution. Both immersion potentials are lower than 0.50V on SCE standard. The difference was also 0.50 V or less.

Comparative Example 1
Using a nickel expanded mesh (2 × 5 cm) as the conductive substrate, a chloroplatinic acid solution (Tanaka Kikinzoku, Pt concentration 15 wt%, cobalt nitrate hexahydrate, ammonium dihydrogen phosphate, After adjusting each concentration in the plating bath, the pH of the plating bath was adjusted to 5 using a 10% aqueous ammonia solution.
Chloroplatinic acid 0.005 mol / liter Cobalt nitrate hexahydrate 0.005 mol / liter Ammonium dihydrogen phosphate 0.01 mol / liter Next, the plating bath was heated to 65 ° C., and a platinum plate was placed on the counter electrode. And plated for 30 minutes at a current density of 25 mA / cm ² . The obtained electrodeposits were washed with water, the platinum content determined by the above method was shown in Table 1, and the XRD pattern was shown in FIG.

  In the chloroplatinic acid solution, the immersion potential is pH = 5, SCE standard 1.10V, and the cobalt nitrate solution is 0.11V, and the immersion potential of chloroplatinic acid is nobler than 0.50V in SCE standard. The difference was 0.5V or more.

In the examples and comparative examples of the present invention, the supported amount after the reduction treatment was in the range of 10 g / m ^{2 to} 15 g / m ² . In addition, in the X-ray diffractograms of Examples 1 to 4, the metal or oxide state of platinum and transition metal was not detected, the (111) plane spacing, which is the main diffraction peak of metal platinum, changed, and the transition metal and metal It was confirmed that a platinum alloy in which platinum was dissolved was obtained.

The X-ray diffraction diagram of the electrode for hydrogen generation obtained in Examples 1, 2, 3, 4 and Comparative Example 1 is shown, in which the X axis (horizontal axis) is the diffraction angle (2θ, the unit is “°”). Y axis (vertical axis) is count (unit is arbitrary).

Explanation of symbols

1: Peak of base nickel 2: Peak of metallic platinum (111) 3: Peak of platinum alloy

Claims (3)

It is supported by electroplating on a conductive substrate using a plating bath in which a transition metal compound and a platinum compound in which the immersion potential at pH = 5 to 8 is lower than 0.5 V on the basis of SCE is dissolved. A method for producing a hydrogen generating electrode. The method for producing an electrode for hydrogen generation according to claim 1, wherein the platinum compound is an ammine complex salt. The method for producing an electrode for hydrogen generation according to claim 1 or 2, wherein the difference in immersion potential between the platinum compound and the transition metal compound at pH = 5 to 8 is 0.5 V or less.

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