KR20070107411A - Electrode for electrolysis with matrix-structured catalytic layer having ordered nanopore arrays and method for preparing the same - Google Patents

Abstract

An electrode and a method for preparing the same are provided, wherein the electrode has high electrolysis efficiency and is highly durable to high current application and strong acid electrolyte by uniformly forming a coating film after coating of a catalyst, preventing the generation of cracks, and improving wear resistance of the coating film. A method for preparing an electrode for electrolysis comprises the steps of: (a) mixing an alkoxide compound of a metal selected from Ir, Ru, Pt and Sn, an alkoxide compound of a metal selected from Ta, Ti and Nb, and at least one template selected from polyalkyleneglycol, a copolymer thereof and a block copolymer thereof in the presence of an organic solvent to prepare a catalytic mixed solution; (b) adding an aqueous acidic solution into the catalytic mixed solution, and performing hydrolysis and polycondensation reaction of the mixed solution to prepare a catalytic coating solution; (c) applying the prepared catalytic coating solution onto a conductive support to form a coating layer; and (d) drying and firing the coated conductive support.

Description

Electrode for electrolysis with matrix-structured catalytic layer having regular pore structure and method for preparing same Electrode for electrolysis with matrix-structured catalytic layer having ordered nanopore arrays and method for preparing the same

1 is a cross-sectional view showing a general electrolytic cell for high speed plating,

2 is an electrolytic electrode manufacturing process chart manufactured by the pyrolysis method,

3 is an electron scanning microscope (SEM) photograph of the surface-treated titanium support,

4 is an electron scanning microscope (SEM) photograph of an electrolytic electrode manufactured by a conventional pyrolysis method.

FIG. 5 is an electron transmission microscope (TEM) photograph of a cross section of a catalyst layer coated on an electrode surface.

6 is an electron scanning microscope (SEM) of the surface of the electrode formed catalyst layer according to the present invention,

7 is a durability test result of the electrode according to Example 1 of the present invention,

8 is a test result of durability of the electrode according to the second embodiment of the present invention.

The present invention relates to an electrode for electrolysis and a method for manufacturing the same, and more particularly, characterized in that the metal oxide catalyst layer having regular matrix pores is formed on the conductive support.

In general, a large number of ions are dissolved in the electrolytic solution. When electrolyzed, water in the electrolytic solution produces hydrogen and oxygen, and an acidic ionized water may be prepared at the anode and an alkaline ionic solution at the cathode. When current flows through two electrodes of (+) and (-) poles in tap water, cations such as Ca, Mg, and minerals are collected at the (-) pole, and negative ions are collected at the (+) pole to generate acidic ionized water.

OH ^- and H ⁺ is the electrolytic generation of OH by reduction at the cathode by reduction of H ₂ O H ₂ is generated, or (Scheme 1) or dissolved oxygen ^- is produced (Scheme 2).

^{_{2H 2 O + 2e - = H}} 2 + 2OH - (1)

^{_{1 / 2O 2 + 2e - +}} H 2 O + 2OH - (2)

On the other hand, in the positive electrode, O ₂ is generated by oxidation of H ₂ O (Scheme 3).

^{_{H 2 O = 2e - + 1}} / 2O 2 + H + (3)

If Cl ⁻ ions are present in the water, an additional sterilization solution of chlorine or HC1 is produced at the anode (Scheme 4).

_{^{Cl - + H 2 O = 2e}} - + HC1O + H + (4)

As such, when a small amount of Cl ⁻ is present at the anode, the acidic ionized water generated at the anode may be used for sterilizing water and washing water, and the alkaline ionized water prepared at the cathode may be used for drinking water and washing water.

On the other hand, the electrolysis process is a process that consumes a large amount of energy, it is required to lower the electrolytic voltage in order to reduce the power cost. The electrolytic voltage is the sum of the overvoltage of the positive electrode or the negative electrode, the voltage by the electrolyte, the film voltage, the contact voltage of the metal conductor, etc. together with the theoretical decomposition voltage. Among them, all other voltages except the theoretical decomposition voltage have room for improvement, and among them, it is significant to lower the overvoltage of the positive electrode or the negative electrode.

Methods of manufacturing electrodes for electrolysis include pyrolysis, arc melting, plasma melting, electroplating, and the like. Electrodes are manufactured by one or two or more of these methods. Among them, the most common and economical method is pyrolysis, and many patents have been published mainly on the application of alkaline aqueous solution to electrolysis.

Japanese Patent Application Laid-Open No. 03-131385 discloses a technique in which titanium is used as an electrode base material, and carbonitride is coated thereon by arc melting or plasma melting. However, the above method has a disadvantage in that it is difficult to manufacture the electrode because a large amount of coating material is lost, the large electrode cannot be coated uniformly, and the coating process is complicated.

Korean Patent Publication Nos. 79-3290 and 91-2101 describe a method of fabricating an electrode for producing a metal alkali, in particular chlorine and caustic soda, by coating ruthenium, iridium, titanium, and the like on titanium. However, these electrodes have a relatively high oxygen overvoltage as a method of producing an electrode for chlorine generation, and have low electrolytic efficiency and durability shortening due to the loss of the coating surface and the loss of the active point during the high current electrolytic reaction. In addition, in the method for preparing an electrode for chlorine generation of the patent, a metal chloride having a desired composition is dissolved in a solvent, coated on a titanium support having a relatively acid resistance, and then pyrolyzed to prepare an electrode plate. The catalyst active point is easy to dissolve during high current electrolytic reactions involving oxygen generation due to large catalyst particles in the surface layer, many cracks, and nonuniformity. (FIG. 4) The flow rate of the strong acid electrolyte forms vortices at a high flow rate, causing rapid wear of the catalyst layer. Is done. In particular, the strong oxidation reaction of the anode and the diffusion through the pores of the electrode catalyst layer of the electrolyte promotes corrosion of the titanium support itself to form an oxide film to become an insulator and thus lose its function as an electrode.

In addition, Korean Patent Publication No. 1998-9525 discloses a coating obtained by dissolving one or two chlorides of a noble metal consisting of Ru, Sn, Ir, Pt, and Pb in a hydrochloric acid solvent and then mixing them in a dispersion solvent. A method of manufacturing an electrode for electrolysis, which can effectively lower the chlorine overvoltage and oxygen overvoltage of the electrode and has a long lifetime by supporting it in a solution and drying it, has been proposed. However, the above method has a disadvantage in that the coating solution is not stable, so it is difficult to store it for a long time and the coating film is difficult to be formed uniformly during coating, and the coating film is easily peeled off or worn down during the electrolytic reaction.

Accordingly, an object of the present invention is to provide a stable catalyst coating solution that can effectively lower the chlorine overvoltage and oxygen overvoltage of the electrode.

In addition, another object of the present invention is to provide an electrode having a high coating efficiency and high electrolytic efficiency, high current resistance and durability against strong acid electrolyte, and a method of manufacturing the same, after which the coating film is uniformly formed and there is no crack generation after catalyst coating. More specifically, the high current 20 ~ 150 A / dm ² is applied and the flow rate of the electrolyte withstands a flow of 80m per minute to 1000m per minute, and provides a durable electrode and a method for producing a strong acid electrolyte of pH 1 ~ 2 will be.

As a result of solving the problems of the prior art and achieving the above object, the present inventors have coated a catalyst coating liquid prepared by mixing at least one metal alkoxide compound and polyalkylene glycol or a copolymer thereof or a block copolymer thereof on a conductive support. By forming the catalyst layer having a regular matrix pore structure, the crack phenomenon formed in the general pyrolysis method is eliminated, and the catalytic activity point is uniform and the nano size is small, so that the electrolytic efficiency is excellent with high current density and low oxygen overvoltage. Because of the matrix type, compact and solid catalyst coating layer, the highly durable electrode was invented even by the strong acid electrolyte.

The present invention relates to a catalyst coating solution for producing an electrode for electrolysis, a method for producing an electrode for electrolysis using the same, and an electrode for electrolysis produced by the above method.

Accordingly, the present invention provides a catalyst coating solution for forming a metal oxide catalyst layer having regular matrix pores on an electrode surface. The catalyst coating liquid according to the present invention has a stable advantage without precipitation even during long-term storage.

In addition, the present invention provides a method for producing an electrode for electrolysis comprising the step of coating the catalyst coating solution on a conductive support, drying and calcining, and thus an electrode for electrolysis prepared accordingly.

Electrolytic electrode according to the present invention is suitable for use as a high-performance electrolysis electrode for producing zinc plating, tin-plated copper foil by the electrolytic method.

1 is a schematic view of an electrolytic facility for tin or zinc plating, the applied current is high 20 ~ 150A / dm ² and the steel plate plating is made of 80 ~ 200m to 200 ~ 800m per minute. Electrolytic electrode according to the present invention has the advantage of high durability in the application of high current 20 ~ 150 A / dm ² and the flow rate of the electrolyte withstand flow of 80m per minute to 1000m per minute and pH 1-2 strong acid electrolyte. However, the electrode according to the present invention is not limited to only for high-speed plating, and may be used as a general electrolytic reaction electrode.

Hereinafter, the present invention will be described in more detail.

Method for producing a catalyst coating liquid used in the production of an electrode for electrolysis according to the invention is characterized in that it comprises the following steps.

a) an alkoxide compound (1) of a metal selected from Ir, Ru, Pt or Sn; An alkoxide compound (2) of a metal selected from Ta, Ti or Nb; And at least one template material (3) selected from polyalkylene glycol or a copolymer thereof or a block copolymer thereof; preparing a catalyst mixture by mixing an organic solvent under an organic solvent; And

b) preparing a catalyst coating solution by adding an acidic aqueous solution to the catalyst mixture and subjecting it to hydrolysis and polycondensation.

The metal alkoxide compound (1) selected from Ir, Ru, Pt, or Sn is diluted with alcohol to a metal chloride and sodium alkoxide selected from chlorides of Ir, Ru, Pt, or Sn at a nitrogen atmosphere and a reaction temperature of 80 ° C. or higher. The metal alkoxide compound (1) is prepared through a chemical reaction for at least 4 hours.

The catalyst coating liquid according to the present invention can form a catalyst layer having regular matrix micropores by using at least one mold material 3 selected from polyalkylene glycol or a copolymer thereof or a block copolymer thereof, in particular a block copolymer. As the catalyst layer has regular matrix type micropores, the crack phenomenon formed in the general pyrolysis method is eliminated, and the catalytic activity point is uniform and the nano size is small, so that the electrolytic efficiency is excellent with high current density and low oxygen overvoltage. Due to the dense and rigid catalyst coating layer of the reticulated type, it has an excellent effect of durability by controlling the penetration of the strong acid electrolyte. Particularly, the particles of the catalytically active sites on the matrix matrix having a pore structure are not only small in size but also uniform in particle distribution, thereby providing excellent electrolytic efficiency.

The casting material used in the preparation of the catalyst coating liquid according to the present invention may be used by mixing one or two or more selected from polyalkylene glycols or copolymers thereof or block copolymers thereof. It is more preferable to use a template material selected from polyethylene oxide / polypropylene oxide / polyethylene oxide block copolymer, polyethylene glycol or polypropylene glycol, and even more preferably to use polyethylene oxide / polypropylene oxide / polyethylene oxide block copolymer. Among the polyethylene oxide / polypropylene oxide / polyethylene oxide block copolymers, P123, eg BASF's Pluronic P123 product, was most suitable for producing a catalyst layer with regular nanopores, and also a marked increase in durability. It was very good. For example, when the block copolymer is used, the durability of the electrode is increased by three times or more compared with the absence of the block copolymer, which is more significant than other polyalkylene glycols. .

The template material (3) is preferably used in an amount of 0.005 to 0.1 molar ratio with respect to the total metal alkoxide compound ((1) + (2)) in the catalyst mixture, more preferably 0.01 to 0.022 molar ratio, Preferably it is 0.015 molar ratio. If the molar ratio is outside of 0.005 to 0.01, the durability of the electrode is not preferable, so it is not preferable.

In step a), the organic solvent is preferably one or more alcohols selected from ethanol, n-propanol, isopropanol or butanol.

The alkoxide group in the alkoxide compound (1) of the metal selected from Ir, Ru, Pt or Sn, the alkoxide compound (2) of the metal selected from Ta, Ti or Nb and the sodium alkoxide group is methoxide, ethoxide, n-propoxy Preferred is selected from the side, isopropoxide or butoxide.

The acidic aqueous solution in step b) is preferably a mixture of any one acid and water selected from the group consisting of hydrochloric acid, nitric acid, acetic acid.

The method for manufacturing an electrode for electrolysis according to the present invention includes coating the catalyst coating liquid prepared by the above method on a conductive support, and drying and firing the coated conductive support.

The conductive support may be iron, nickel, titanium, titanium alloys, etc. as the conductive metal material, but it is preferable to use a titanium or titanium alloy support in terms of corrosion resistance.

The coating may be made by immersion or brush or spray to the single or mixed catalyst coating liquid. The drying is preferably treated with a catalyst solution coated support at room temperature for 10 to 120 minutes or 50 to 150 ℃ for 20 to 60 minutes, the firing is 350 to 650 after drying the catalyst solution coated support It is preferable to advance for 10 to 120 minutes at the temperature of ° C, and more preferable firing temperature is 450 to 550 ° C. If the firing temperature is too low or too high, the catalytic activity may be lowered, which is not preferable. The coating, drying and firing may be repeated once to 20 times, the last firing is preferably carried out for 1 to 5 hours.

The catalyst layer formed by the electrode manufacturing method according to the present invention includes both an oxide of a first group metal selected from Ir, Ru, Pt or Sn, and an oxide of a second group metal selected from Ta, Ti, or Nb. Doing. In the case of using the first group of metal oxides and the second group of metal oxides together, the adhesion and catalyst activity of the catalyst layer are further increased compared to the case of using the metal oxide of the second group alone, thereby improving both durability and electrolytic efficiency. Particularly, the use of tantalum as the second group of metals is more preferable because of excellent durability against strong acid electrolytes, and it is preferable to form a catalyst coating layer having a complex oxide matrix in which iridium and tantalum are covalently bonded with oxygen. The physical durability is more excellent and most preferred.

In addition, the present invention may prepare a catalyst coating liquid having a different composition to form a catalyst layer in a double layer. In the case of forming a catalyst layer with a double layer, the first coating liquid prepared by the above method is first coated, dried and calcined on the conductive support to form a first coating layer, and then a second coating liquid having a different composition is prepared to produce a first coating layer. A second coating layer is formed on the formed conductive support by coating, drying and baking. In this case, it is preferable that the first coating layer (or the intermediate layer) increase the concentration of the second group of metal oxides selected from Ta, Ti, or Nb compared to the second coating layer. This is because the coating property that is strong in corrosion resistance as well as the bond force with the is implemented to control the oxidation of the support to improve the durability of the electrode. In the case of using tantalum oxide in the second group of metal oxides contained in the first coating layer (middle layer), the electrode was further improved in corrosion resistance, which was more preferable for use for high speed plating. The first coating layer (middle layer) is a fine mesh structure without cracks, and by controlling the thickness of the film within a range that does not reduce the electrolytic efficiency of the electrode can effectively control the penetration of the strong acid electrolyte to control the oxidation of the electrode base material. .

Hereinafter, the present invention will be described in more detail with reference to the following Examples, which do not limit the scope of the present invention.

Example 1 Ti electrode coated with Ir-Ta (molar ratio 60:40)

Preparation of Catalyst Coating Liquid

10 mmol of iridium chloride (IrCl ₄ x H ₂ O) is dissolved in 100 ml anhydrous ethanol. After diluting 40 mmol sodium ethoxide in 80 ml anhydrous ethanol, 10 mmol of iridium ethoxide was prepared through a chemical reaction at 80 ° C. for 6 hours under a nitrogen atmosphere. 6.67 mmol of tantalum ethoxide diluted in 30 ml anhydrous ethanol was mixed and stirred for 15 hours. BASF's pluronic P123 ((EO) ₂₀ (PO) ₇₀ (EO) ₂₀ , average molecular weight 5800) was added to this composite metal ethoxide mixed solution as shown in Table 1 and mixed, followed by mixing with 1.15 ml of water and hydrochloric acid ( Concentration 37%) 0.8ml was added to the catalyst coating solution through a hydrolysis reaction and a polycondensation reaction.

Preparation of Electrode with Catalyst Coating Layer

A titanium support etched with oxalic acid at 85 ° C. for 4 hours is immersed-coated in the catalyst coating solution prepared above. Drying is carried out at 100 ° C. for 10 minutes and firing at 500 ° C. for 30 minutes. In this manner, after 20 repeated coatings, drying and firing, the final baking was performed at 500 ° C. for 2 hours.

Electrochemical Durability Experiment

The prepared electrode was used as a positive electrode, a nickel plate was used as a negative electrode, and 2M aqueous solution of sulfuric acid was used as an electrolyte. The applied current was applied 1000 A / dm ² through the rectifier and when the 1.5V increase from the initial electrolytic voltage was cut off (off) it was determined that the life of the electrode.

60--40% of the composition of the Ir-Ta catalyst layer was coated with a Ti support in a solution to which a block copolymer (P123) was added as shown in Table 1 below to prepare an electrode having an average of 5.5 mg Ir / cm ² of the catalyst coating amount. Specific surface area, pore size and pore volume were measured by nitrogen adsorption method and obtained by BET method. The results of electrochemical durability test are shown as below.

[Table 1] Specific surface area and electrochemical durability of catalyst layer with addition of block copolymer

The specific surface area measured by the nitrogen adsorption method increases as the amount of block copolymer added increases, and then the molar ratio of block copolymer / total metal alkoxide decreases again from 0.022 or more. Particularly, when the block copolymer / total metal alkoxide mole ratio was 0.015, the specific surface area was 381 m ² / g, which was the highest value, and there was little pore volume and the specific surface area was 45m ² / g, which was the lowest.

In the electrochemical durability measurement, the surface of the electrode (Comparative Example 1) to which the additive was not added (see FIG. 4) showed a lot of cracks on the surface, and the durability was not good as 20 hours. Durability characteristics according to the amount of block copolymer added in the electrode to which the block copolymer (P123) is added are shown in Table 1 and FIG. 7. The electrode prepared by adding 0.015 molar ratio of P123 showed the best durability at 95 hours. When the amount of added block copolymer is small, when the pore size is about 6.3 nm and the amount added is more than x = 0.015, it tends to decrease slightly from 2.8 nm to 2.4 nm. As such, the regular microporous matrix catalyst coating layer formed by the block copolymer eliminates the cracks formed in the general pyrolysis method and improves the electrolytic efficiency according to the even distribution of the catalyst active points, as well as due to the dense and rigid coating layer of the matrix type. Durability increase has an excellent effect (Figs. 5 and 6).

Example 2 Durability Characteristics of Electrolytic Electrode According to Introduction of Double Layer

The first coating solution for the one-layer coating layer was prepared using P123 X = 0.015 in the same manner as in Experiment No. 1-3 coating solution of Example 1 except that the molar ratio of Ir-Ta was 10:90. The first coating solution was immersed in a support in the same manner as in Example 1 to form a first coating layer, but as shown in Table 2, the Ir amount of the coating layer was changed from 0.5 to 2.2 mg / cm ² by repeated coating. The second coating solution for the layer catalyst layer was repeatedly coated using Experiment No. 1-3 coating solution of Example 1 to prepare an electrode such that an average Ir amount of the second coating layer was 5.5 mg / cm ² . Evaluation of the durability was performed in the same manner as in Example 1.

TABLE 2

According to the results of Table 2, in the case of Experiment No. 2-3, the durability was significantly increased to 165 hours. However, the electrode coated with a small amount of the first layer (experimental number 2-1) had almost no performance difference with the electrode not coated with a single layer (experimental number 1-3). If the first layer coating is too thick, as in Experiment No. 2-4, durability tends to decrease somewhat. This may be due to the low electrical conductivity of the support and high load on application of current. As shown in Table 2 and the durability evaluation results of FIG. 8, the regular microporous matrix type 1 layer manufactured by the block copolymer fundamentally blocks the invasion of the electrolyte to control the oxidation of the titanium support due to the electrolyte, Denseness significantly increases durability. In particular, the crack-free one-layer coating is embodied in tantalum oxide properties excellent in corrosion resistance.

The electrode manufactured according to the present invention has excellent electrolytic efficiency at high current density and low oxygen overvoltage due to a uniform active point of the catalyst and a small nano size. The regular microporous matrix structure, which is a characteristic of the catalyst coating membrane, can control the penetration of the strong acid electrolyte to prevent oxidation of the titanium support, and also has good adhesion, excellent wear resistance and corrosion resistance, and excellent durability. In particular, the microporous matrix bilayer manufactured by using a block copolymer has an excellent effect of improving the durability of the electrode by absolutely controlling the oxidation of titanium as an electrode support from a sulfuric acid solution as a strong acid electrolyte.

Claims (10)

a) an alkoxide compound of a metal selected from Ir, Ru, Pt or Sn; Alkoxide compounds of metals selected from Ta, Ti or Nb; And at least one template material selected from polyalkylene glycol, a copolymer thereof, or a block copolymer thereof; preparing a catalyst mixture by mixing an organic solvent in an organic solvent; b) adding an acidic aqueous solution to the catalyst mixture to form a catalyst coating solution by hydrolysis and polycondensation; c) coating the prepared catalyst coating liquid on a conductive support to form a coating layer; And d) drying and firing the coated conductive support; Method for producing an electrode for electrolysis comprising a. The method of claim 1, Method for producing an electrode for electrolysis, characterized in that to form a coating layer by repeating the steps c) and d) two or more times. The method of claim 1, Repeating the steps a) to d) after the step d), the method for producing an electrode for electrolysis, characterized in that to form a secondary coating layer by coating a catalyst coating liquid of a different composition from the coating layer. The method of claim 1, The template material is a method for producing an electrode for electrolysis, characterized in that the polyethylene oxide / polypropylene oxide / polyethylene oxide block copolymer. The method of claim 1, The template material is a method for producing an electrode for electrolysis, characterized in that used in 0.005 to 0.1 molar ratio with respect to the total metal alkoxide compound in the catalyst mixture. The method of claim 1, The conductive support is a method for producing an electrode for electrolysis, characterized in that made of titanium or titanium alloy. The method of claim 1, The organic solvent is a method for producing an electrode for electrolysis, characterized in that at least one alcohol selected from methanol, ethanol, n-propanol, isopropanol or butanol. An electrode for electrolysis, which is prepared by the manufacturing method according to any one of claims 1 to 7, wherein a catalyst layer having regular matrix pores is formed on a conductive support. The method of claim 8, The catalyst layer is an electrode for electrolysis, characterized in that formed in a double layer with different catalyst composition. The method according to claim 8 or 9, The electrode for electrolysis, characterized in that used for high-speed plating.

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