KR20200077927A - Anode Comprising Metal Phosphide Complex and Preparation Method thereof - Google Patents

Abstract

The present invention relates to an oxidation electrode comprising: a metal substrate; and a catalyst layer which includes complex metal phosphide composed of ruthenium, iridium, and titanium, and is positioned on the metal substrate. The present invention also relates to a manufacturing method of the oxidation electrode. The oxidation electrode of the present invention is particularly suitable for the use in electrolysis due to excellent durability and low overvoltage.

Description

Anode Comprising Metal Phosphide Complex and Preparation Method thereof

The present invention relates to an oxide electrode comprising a composite metal phosphide and a method for manufacturing the same, and the electrode of the present invention has high durability and can be used in a very strong oxidizing atmosphere and exhibits low overvoltage.

Techniques for producing hydroxide, hydrogen and chlorine by electrolysis of low-priced brine such as seawater are well known. Such an electrolysis process is also commonly referred to as a chlor-alkali process, and it can be said that the performance and reliability of technology have been proven through decades of commercial operation.

The electrolysis of brine is the most widely used ion exchange membrane method, which installs an ion exchange membrane inside the electrolytic cell to divide the electrolytic cell into an anode chamber and a cathode chamber, and uses chlorine as the electrolyte to obtain chlorine gas at the anode and hydrogen and caustic soda at the cathode. This is the method used.

On the other hand, the electrolysis process of brine is made through a reaction as shown in the following electrochemical reaction formula.

Oxidation electrode (anode) _{^{reaction: 2Cl - → Cl 2 + 2e}} - (E 0 = +1.36 V)

Reduction electrode (cathode) ^{_{reaction: 2H 2 O + 2e - →}} 2OH - + H 2 (E 0 = -0.83 V)

Total _{^{reaction: 2Cl - + 2H 2 O →}} 2OH - + Cl 2 + H 2 (E 0 = -2.19 V)

In performing the electrolysis of brine, the electrolytic voltage is the voltage required for the theoretical electrolysis of brine, the overvoltage of the oxidation electrode, the overvoltage of the reduction electrode, the voltage due to the resistance of the ion exchange membrane, and the voltage due to the distance between the oxidation electrode and the reduction electrode. All of them should be considered, and among these voltages, the overvoltage caused by the electrode is an important variable.

Accordingly, a method capable of reducing the overvoltage of the electrode has been studied, and for example, a noble metal-based electrode called a dimensionally stable anode (DSA) has been developed and used as an oxidation electrode.

DSA electrodes are generally characterized by a catalyst layer comprising a complex oxide of Ru, Ir, and Ti, and are known to exhibit sufficiently good chlorine generating reaction activity and lifetime characteristics. However, in recent years, as issues related to environmental pollution and energy saving become important, development of an oxidized electrode having an improved overvoltage is required.

Therefore, in order to be applied to a commercial brine electrolysis process, it is necessary to develop an oxide electrode having excellent brine generating reaction activity, stable under electrolytic conditions in an oxidizing atmosphere, low overvoltage, and durability including lifetime.

KR 2011-0094055 A

An object of the present invention is to provide a highly stable oxidation-resistant electrode in a very strong oxidizing atmosphere and a low overvoltage, and a method for manufacturing the same.

In order to solve the above problems, the present invention is a metal substrate; And a composite metal phosphide of ruthenium, iridium and titanium, and a catalyst layer positioned on the metal substrate.

In addition, the present invention is a step for preparing a coated electrode by applying and drying a composition for forming a catalyst layer on at least one surface of a metal substrate (S1) and placing the coated electrode in a container containing a hypophosphite compound, followed by final firing. It includes a step (S2), and the composition for forming a catalyst layer provides a method of manufacturing an oxide electrode comprising a ruthenium precursor, an iridium precursor, and a titanium precursor.

The oxidation electrode of the present invention is stable even in a very strong oxidizing atmosphere, and can be used in a chlorine generating reaction process operated in an extreme oxidizing atmosphere, and can exhibit stable performance over a long period of time due to very little elution of components even after the chlorine generating reaction. . In addition, it is easy to desorb gas generated on the electrode surface during electrolysis, and thus exhibits a low overvoltage.

1 is a graph showing half-cell evaluation for Example 1 and Comparative Examples 1 to 3 of the present invention, and as a result, a potential change over time.

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

The terms or words used in the specification and claims should not be interpreted as being limited to ordinary or dictionary meanings, and the inventor can appropriately define the concept of terms in order to best describe his or her invention. Based on the principle that it should be interpreted as a meaning and a concept consistent with the technical idea of the present invention.

Oxide electrode

The present invention is a metal substrate; And

Provided is an oxide electrode comprising a composite metal phosphide of ruthenium, iridium and titanium, and a catalyst layer positioned on the metal substrate.

When the electrode containing the metal phosphide as the catalyst layer and the electrode including the catalyst layer are applied to the gas generation reaction, gas desorption on the surface becomes easier compared to the electrode containing the metal oxide as the catalyst layer, thereby obtaining an effect of reducing overvoltage. Accordingly, problems such as elution of metal components may occur due to poor stability in an oxidizing atmosphere.

Therefore, when the inventor of the present invention uses a complex metal phosphide of ruthenium, iridium, and titanium as a coating layer of an oxide electrode, elution of the metal component is minimized, durability of the electrode can be increased, stability is secured even in an extreme oxidation atmosphere, and chlorine is generated. The present invention was completed by discovering that the performance of the electrode is stable in a variety of electrolysis reactions including reaction, and that it is energy efficient when driving the electrode due to low overvoltage.

In the present invention, ruthenium in the composite metal phosphide may be included in 10 to 50 mole%, preferably 20 to 40 mole%, based on the total moles of metal components in the composite metal phosphide.

In the present invention, iridium in the composite metal phosphide may be included in 5 to 30 mole%, preferably 10 to 20 mole%, based on the total moles of metal components in the composite metal phosphide. When the above-described range is satisfied, not only can iridium increase the catalytic activity of ruthenium, but also decomposition and corrosion dissolution of complex metal phosphide particles that may occur during the reaction can be suppressed to improve durability of the oxide electrode.

In the present invention, titanium in the composite metal phosphide may be included in an amount of 20 to 85 mole%, preferably 40 to 70 mole%, based on the total moles of metal components in the composite metal phosphide.

When each component of ruthenium, iridium, and titanium satisfies the above-mentioned range, titanium, like iridium, can not only increase the catalytic activity of ruthenium, but also suppress decomposition, corrosion, dissolution, etc. of complex metal phosphide particles that may occur during the reaction. The durability of the oxide electrode can be improved.

In the present invention, the content of ruthenium in the catalyst layer may be 5 to 40 g per unit area (m ² ), preferably 5 to 30 g, and more preferably 5 to 20 g. If less than the above-mentioned range, if the ruthenium is included, the catalytic activity of the ruthenium is low, or an appropriate level of electrode life cannot be guaranteed, and if the ruthenium is included more than the above-mentioned range, the catalyst is compared to the amount of ruthenium required to increase the content. The increase in activity is insignificant and uneconomical.

In the present invention, the metal substrate may be at least one selected from the group consisting of titanium, tantalum, aluminum, hafnium, nickel, zirconium, molybdenum, tungsten, stainless steel, or alloys thereof, and titanium is particularly preferable.

The shape of the metal substrate may be a rod, sheet, or plate shape, and the thickness of the metal substrate may be 50 to 2000 μm, and is not particularly limited as long as it can be applied to an electrode applied to a chlorine alkali electrolysis process. , The shape and thickness of the metal substrate can be suggested as an example.

The metal substrate may be a pre-treated metal substrate. The pretreatment may be to form an unevenness on the surface of the metal substrate by chemical etching, blasting or thermal spraying the metal substrate.

The pre-treatment may be performed by blasting the surface of the metal substrate to form fine irregularities, and salt treatment or acid treatment. For example, the surface of the metal substrate can be blasted with alumina to form irregularities, immersed in an aqueous sulfuric acid solution, washed and dried to pretreat. The blasting may use alumina or metal powder, and sulfuric acid, hydrochloric acid, oxalic acid, caustic soda, etc. may be used for salt treatment or acid treatment.

The oxidation electrode of the present invention may be for electrolysis. In particular, it may be used in the following reaction to generate chlorine from brine.

Oxidation electrode (anode) _{^{reaction: 2Cl - → Cl 2 + 2e}} - (E 0 = +1.36 V)

Reduction electrode (cathode) ^{_{reaction: 2H 2 O + 2e - →}} 2OH - + H 2 (E 0 = -0.83 V)

Total _{^{reaction: 2Cl - + 2H 2 O →}} 2OH - + Cl 2 + H 2 (E 0 = -2.19 V)

In the oxidation electrode of the present invention, the catalyst layer may be located on at least one surface of the metal substrate.

Manufacturing method of oxide electrode

The present invention comprises the steps of coating and drying the composition for forming a catalyst layer on at least one surface of a metal substrate to prepare a coated electrode (S1); And

Including the step of final firing after placing the coated electrode in a container containing a hypophosphite compound (S2);

The composition for forming a catalyst layer provides a method of manufacturing an oxide electrode that includes a ruthenium precursor, an iridium precursor, and a titanium precursor.

In the manufacturing method of the present invention, the coating is not limited, as long as the composition for forming the catalyst layer can be applied evenly on a metal substrate, it can be performed by a method known in the art. For example, brushing, roll coating, dip coating, electrospray coating, spray coating, screen printing, comma coating ), may be performed through die casting.

The step S1 may further include heat treatment after drying. Through the heat treatment, a metal oxide coating layer is primarily formed in the step S1, and when the heat treatment is included in the step S1, the formed metal oxide is subsequently converted into phosphide through final firing in the step S2. The heat treatment may be performed at 400 to 600° C. for 1 hour or less, and preferably at 450 to 500° C. for 10 to 30 minutes. If the above-described conditions are satisfied, metal oxide generation is easy, but the strength of the metal substrate may not be affected.

Metal phosphide is formed on the coating layer formed in the step S1 through the final firing of the step S2. The firing may be performed at 200 to 400°C for 30 minutes to 3 hours, and preferably at 250 to 350°C for 1 hour to 2 hours. When the above-mentioned range is satisfied, the formation of metal phosphide is easy, and the manufactured oxide electrode exhibits a low overvoltage.

The step S2 may be performed under an inert gas atmosphere, and the inert gas may be one or more selected from the group consisting of nitrogen, helium, neon and argon. The inert gas is preferably a nitrogen gas in view of cost.

The ruthenium precursor ruthenium (Ⅲ) chloride _{(RuCl 3 · xH 2 O)} , ruthenium (Ⅲ) nitrosyl chloride (Ru (NO) (Cl) 3), ruthenium (Ⅲ) nitrosyl nitrate (Ru (NO) ( NO ₃ ) ₃ ), ruthenium(III) nitrosyl acetate (Ru(NO)(OOCCH ₃ ) ₃ ), hexaamine ruthenium(III) chloride, and may be one or more selected from the group consisting of ruthenium acetate salts, of which Ruthenium(III) chloride is preferred.

The iridium precursor may be at least one selected from the group consisting of iridium chloride (IrCl ₃ ·xH ₂ O) and hydrogen hexachloroiridate (H ₂ IrCl ₆ ·xH ₂ O), of which iridium chloride is preferred. .

The titanium precursor may be titanium chloride (TiCl ₂ , TiCl ₃ or TiCl ₄ ), or titanium alkoxide, and titanium alkoxide is titanium isopropoxide (Ti[OCH(CH ₃ ) ₂ ] ₄ ) and titanium butoxide (Ti (OCH ₂ CH ₂ CH ₂ CH ₃ ) ₄ ) may be one or more selected from the group consisting of titanium isopropoxide is preferred.

On the other hand, the coating may be carried out by repeating the coating, drying and heat treatment sequentially before the final firing so as to be 5 to 20 g based on ruthenium per unit area (m 2) of the metal substrate. That is, in the manufacturing method according to another embodiment of the present invention, after applying, drying and heat-treating the composition for forming the catalyst layer on at least one surface of the metal substrate, again on one surface of the metal substrate coated with the composition for forming the first catalyst layer The coating to be applied, dried and heat treated can be repeatedly performed.

In addition, the manufacturing method of the present invention may include a step (S0) of pre-treating the metal substrate before coating the composition for forming a catalyst layer on at least one surface of the metal substrate. The pretreatment may be to form an unevenness on the surface of the metal substrate by chemical etching, blasting or thermal spraying the metal substrate.

The pretreatment may be performed by blasting the surface of the metal substrate to form fine irregularities, and salt treatment or acid treatment. For example, the surface of the metal substrate can be blasted with alumina to form irregularities, immersed in an aqueous sulfuric acid solution, washed and dried to pretreat.

The hypophosphite compound is selected from the group consisting of NaH ₂ PO ₂ , KH ₂ PO ₂ , Ca(H ₂ PO ₂ ) ₂ , Mg(H ₂ PO ₂ ) ₂ and Al(H ₂ PO ₂ ) ₃ It may be the above, it is preferred that NaH ₂ PO ₂ . When NaH ₂ PO ₂ is used, the yield of metal phosphide may be high. The composition for forming the catalyst layer may further include an alcohol-based solvent. The alcohol-based solvent may be a lower alcohol, of which n-butanol is preferred.

The manufacturing method of the present invention may further include a step (S3) of intermediately firing the coated electrode between the steps S1 and S2. When the step S3 is included, impurities remaining in the coating layer are removed, and a sufficient time required for conversion to a thermodynamically stable phase is provided, so that the life of the resulting electrode can be improved.

The intermediate firing of the step S3 can be performed at a temperature of 400 to 600°C for 10 minutes to 5 hours, and preferably at a temperature of 450 to 550°C for 30 minutes to 2 hours. If the above-described conditions are satisfied, it is advantageous for crystal growth and durability of the electrode can be increased.

The oxidation electrode manufactured by the manufacturing method of the present invention may be for electrolysis. In particular, it may be used in the chlorine generating reaction as described above.

Hereinafter, examples and experimental examples will be described in more detail in order to specifically describe the present invention, but the present invention is not limited by these examples and experimental examples. Embodiments according to the present invention can be modified in many different forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

Example 1

The prepared titanium expansion substrate was blasted with white alumina to form irregularities on the surface primarily, and then treated with 10% oxalic acid at 90°C for 2 hours to form secondary fine irregularities. Thereafter, the substrate was washed with distilled water and dried to prepare a pretreated titanium substrate.

Apart from the above pretreatment, ruthenium chloride (RuCl ₃ xH ₂ O), iridium chloride (IrCl ₃ xH ₂ O) and titanium isopropoxide (Ti[OCH(CH ₃ ) ₂ ] ₄ ) are mixed with n-butanol Thus, a composition for forming a catalyst layer was prepared. At this time, the molar ratio of Ru, Ir, and Ti in the composition for forming the catalyst layer was about 35:20:45.

After coating the composition for forming the catalyst layer on a pre-treated titanium substrate, put it in a convection drying oven at 70°C and dry it for 10 minutes, then put it in an electric heating furnace at 480°C and heat-treat it for 10 minutes to coat the metal oxide type coating layer. Formed. At this time, the application, drying and heat treatment of the composition for forming the catalyst layer were repeated until the titanium substrate had a ruthenium content of 7 g per unit area (1 m 2 ). After that, the mixture was calcined at 480°C for 1 hour to remove impurities remaining in the coating layer.

After the electrode on which the coating layer of the metal oxide type was formed was placed in a container containing NaH ₂ PO ₂ , the container was placed in a nitrogen atmosphere firing furnace and finally fired at 300° C. for 1 hour to include the complex metal phosphide in the coating layer. Electrodes were prepared.

Example 2

An oxide electrode was manufactured in the same manner as in Example 1, except that the final firing temperature in Example 1 was 400°C.

Example 3

In Example 1, an oxidation electrode was manufactured in the same manner as in Example 1, except that the final firing was performed immediately without undergoing heat treatment and intermediate firing.

Comparative Example 1

An oxide electrode including a ruthenium oxide coating layer was prepared in the same manner as in Example 1, except that only the ruthenium chloride was used in Example 1, and electrode production was completed in the intermediate firing step without going through the final firing step. .

Comparative Example 2

An oxide electrode including a ruthenium phosphide coating layer was prepared in the same manner as in Example 1, except that only ruthenium chloride was used in preparing the composition for forming a catalyst layer in Example 1.

Comparative Example 3

An oxide electrode including a ruthenium-iridium-titanium composite metal oxide coating layer was prepared in the same manner as in Example 1, except that the electrode preparation was completed in the intermediate firing step without going through the final firing step in Example 1. .

The components and manufacturing conditions of the formed coating layers of Examples 1 to 4 and Comparative Examples 1 to 3 are summarized and shown in Table 1 below.

Coating layer Coating layer molar ratio Heat treatment With or without intermediate firing Final firing Final firing time (hr) Final firing temperature (℃) Example 1 Ru-Ir-Ti composite metal phosphide 35:20:45 O O O One 300 Example 2 Ru-Ir-Ti composite metal phosphide 35:20:45 O O O One 400 Example 3 Ru-Ir-Ti composite metal phosphide 35:20:45 X X O One 300 Comparative Example 1 Ru oxide Ru O O X - - Comparative Example 2 Ru phosphide Ru O O O One 300 Comparative Example 3 Ru-Ir-Ti composite metal oxide 35:20:45 O O X - -

Experimental Example 1. Confirmation of potential change over time by half-cell evaluation

As the working electrode, the oxidized electrode prepared in the above Examples and Comparative Examples is used, a saturated caromel electrode (SCE) is used as a reference electrode, a Pt wire is used as a counter electrode, and a concentration of 305 gpl is used as an electrolyte. Using NaCl aqueous solution of, electrode performance was measured by a constant current time potential difference method of 4.4 kA/m ² at a cell temperature of 90°C. The initial voltage measurement results are shown in Table 2 below, and the potential changes with time of the electrodes of Example 1 and Comparative Examples 1 to 3 are shown in FIG. 1.

division Voltage (V vs. SCE) Example 1 1.250 Example 2 1.255 Example 3 1.249 Comparative Example 1 1.265 Comparative Example 2 1.324 Comparative Example 3 1.282

Comparison of the electrode of the present invention comprising a composite metal phosphide of ruthenium-iridium-titanium that has undergone the final firing step from Table 2 above, is a ruthenium-only phosphide, or a ruthenium-only oxide or a ruthenium-iridium-titanium composite metal oxide It was confirmed that it exhibited an overvoltage lower than Examples 1 to 3.

In addition, as can be seen in Figure 2, in the case of Comparative Example 2 using a ruthenium-only phosphide, it was confirmed that the potential increased due to the metal elution over time, and thus it was impossible to guarantee a certain performance of the electrode. In addition, in the case of Comparative Examples 1 and 3 using a ruthenium-only oxide or a composite metal oxide of ruthenium-iridium-titanium, it was confirmed that a high initial potential was exhibited and the amplitude of the potential was large, from which the phosphide was compared to the electrode using the oxide. It can be expected that the desorption of the chlorine gas produced by the used electrode is advantageous.

Experimental Example 2. Measurement of the durability of the oxide electrode through XRF

The oxidation electrode of Examples and Comparative Examples was subjected to a constant current time potential difference method for 8 hours according to Experimental Example 1, and the change in the content of ruthenium was analyzed by XFR using Delta professional (machine name, manufacturer: Olympus), and the results are shown in Table 3 below. Organized by

In the XFR analysis, the excitation source was a 4W Rh anode X-ray tube, the detector was a silicon drift detector, and the single beam exposure time was 30 seconds.

division Ru content before reaction (% by weight) Ru content after reaction (% by weight) Rate of change Example 1 0.87 0.87 0 Example 2 0.95 0.91 -4.2% Example 3 0.84 0.84 0 Comparative Example 1 3.01 2.30 -23.6% Comparative Example 2 2.74 0.03 -98.9% Comparative Example 3 1.10 1.05 -4.5%

From Table 3, when using Ru-only oxide or phosphide, it was confirmed that the elution of ruthenium occurred in a large amount and the durability of the electrode was weak. In particular, in the case of Comparative Example 2 using Ru only phosphide, it was confirmed that almost all Ru is eluted, and thus it is virtually impossible to use it as an electrode for chlorine generation reaction.

In addition, among Examples 1 and 2 with different final firing conditions, it was confirmed that the Ru elution amount of Example 1 fired at 300° C. for 1 hour was less, and the intermediate firing step of converting a metal compound to a metal oxide was performed. Even in the case of Example 3, which was omitted and immediately converted to phosphide, it was confirmed that the elution amount of Ru was small.

From the experimental examples for the above Examples and Comparative Examples, it was confirmed that the oxidation electrode of the present invention exhibits an improved overvoltage, and the amount of Ru eluted by the reaction is also excellent in durability.

Claims (14)

Metal substrates; And
An oxide electrode comprising a composite metal phosphide of ruthenium, iridium and titanium, and a catalyst layer positioned on the metal substrate.
According to claim 1,
The composite metal phosphide, relative to the total moles of metal components in the composite metal phosphide,
10 to 50 mol% ruthenium;
Iridium 5 to 30 mol%; And
An oxide electrode comprising 20 to 85 mol% of titanium.
According to claim 1,
The ruthenium content of the catalyst layer is 5 to 40 g per unit area (m ² ) of the oxidation electrode.
According to claim 1,
The metal substrate is one or more oxide electrodes selected from the group consisting of titanium, tantalum, aluminum, hafnium, nickel, zirconium, molybdenum, tungsten, stainless steel, or alloys thereof.
According to claim 1,
The oxidation electrode is for electrolysis.
Preparing a coated electrode by applying and drying a composition for forming a catalyst layer on at least one surface of a metal substrate (S1); And
Including the step of final firing after placing the coated electrode in a container containing a hypophosphite compound (S2);
The catalyst layer forming composition is a method of manufacturing an oxide electrode comprising a ruthenium precursor, an iridium precursor and a titanium precursor.
The method of claim 6,
The step S1 is a method of manufacturing an oxide electrode further comprising a heat treatment after drying.
The method of claim 6 or 7,
The manufacturing method further comprises the step of pre-treating the metal substrate (S0) before coating the composition for forming a catalyst layer,
The pre-treatment is a method of manufacturing an oxide electrode by chemical etching, blasting or thermal spraying a metal substrate to form irregularities on the surface of the metal substrate.
The method of claim 6 or 7,
The method of manufacturing an oxide electrode further comprising the step (S3) of intermediate firing the coated electrode between the step S1 and step S2.
The method of claim 6,
The hypophosphite compound is selected from the group consisting of NaH ₂ PO ₂ , KH ₂ PO ₂ , Ca(H ₂ PO ₂ ) ₂ , Mg(H ₂ PO ₂ ) ₂ and Al(H ₂ PO ₂ ) ₃ The manufacturing method of the above-mentioned oxide electrode.
The method of claim 6,
The composition for forming a catalyst layer further comprises an alcohol-based solvent.
The method of claim 6,
The step S2 is a method of manufacturing an oxide electrode that is performed under an inert gas atmosphere.
The method of claim 6,
The step S2 is a method of manufacturing an oxide electrode that is performed at 200 to 800 ℃.
The method of claim 6,
The step S2 is a method of manufacturing an oxide electrode that is performed for 30 minutes to 3 hours.

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