KR20220101460A - Oxygen Evolution Reaction catalyst comprising Copper-Iridium core-shell structure and Manufacturing method of the Same - Google Patents

Abstract

The present invention relates to a catalyst for oxygen generation reaction comprising copper-iridium having a core-shell structure and a preparation method thereof, and more particularly, to a catalyst which forms a thin iridium layer with a thickness of 2 to 3 nanometers in the form of a core-shell on copper nanowires to reduce the use of precious metals and exhibit excellent activity and durability and a preparation method thereof. The catalyst according to the present invention can be applied to a cation-exchange electrolyte membrane water electrolytic cell and the like. In addition, the preparation method according to the present invention can be applied to the reduction of other precious metals such as platinum and can be usefully used in the development of a fuel cell catalyst.

Description

Oxygen Evolution Reaction Catalyst comprising Copper-Iridium core-shell structure and Manufacturing method of the Same

The present invention relates to a catalyst for oxygen evolution comprising copper-iridium having a core-shell structure and a method for preparing the same, and more particularly, to a core-shell It relates to a catalyst that not only reduces the amount of precious metal used by forming it in a shape but also exhibits excellent activity and durability, and a method for preparing the same.

In various energy conversion and storage systems such as next-generation lithium-air batteries, cation-exchange membrane fuel cells, and anion-exchange membrane fuel cells, electrochemical catalysts are an important factor in determining the efficiency of reactions. In the case of technologies such as polymer electrolyte membrane fuel cells and polymer electrolyte membrane water electrolysis, platinum and iridium are used in excess in oxygen electrodes, respectively, so it is important to reduce the amount of the noble metals used.

Therefore, it is important to develop an oxygen evolution reaction (OER) catalyst that uses the same amount of noble metal and has high activity, that is, high activity per mass of noble metal. Methods to increase the basic catalytic activity by changing the electronic structure of Among them, the alloy being studied is a copper-iridium alloy, and it is reported that the alloy with copper reduces the bonding energy between iridium and oxygen and consequently contributes to lowering the activation energy of the oxygen evolution reaction.

On the other hand, nanowire structures are being studied as fuel cells and water electrolysis catalysts due to their high conductivity, which is helpful as an electrochemical catalyst, and structural specificity to prevent aggregation between particles.

Many studies have also been reported on core-shell catalysts having a dislocation metal core and a noble metal shell for reducing the amount of noble metal used. The thinner the shell, the more advantageous it is to reduce the amount of precious metal used. When the thickness of the precious metal shell is 5 nanometers or more, it is disadvantageous in terms of reducing precious metals compared to iridium nanoparticles, which are catalysts generally used for oxygen evolution. it can be said that

Therefore, there is a need to develop a technology capable of economically synthesizing a core-shell catalyst having a nanometer-scale noble metal shell for use in an oxygen evolution reaction.

Korean Patent No. 2183156

An object of the present invention is to form a thin iridium shell with a thickness of 2 to 3 nanometers on the surface of the copper nanowire core by separating the synthesis steps of the copper nanowire as the core and iridium as the shell, thereby generating oxygen showing excellent electrochemical activity and stability. An object of the present invention is to provide a catalyst for reaction and a method for preparing the same.

On the one hand, the present invention

copper nanowires; and

Iridium formed on the copper nanowire; consists of,

The copper nanowire constitutes a core, and the iridium forms a shell structure in which the iridium is synthesized on the core,

The iridium is formed on the copper nanowire to a thickness of 2 to 3 nm to reduce the content of the iridium, and provides a catalyst for oxygen generation reaction including a core-shell structure copper-iridium.

On the other hand, the present invention

(i) preparing a copper nanowire core;

(ii) preparing a mixture in which the copper nanowire core and iridium acetylacetonate are mixed;

(iii) dispersing the mixture in a solvent whose ratio is adjusted to be 1 to 2 ml per 1 mg of the copper nanowire core, and reacting at a stirring speed of 350 to 450 rpm; and

(iv) forming an iridium shell so as to surround the core while reducing iridium on the surface of the nanowire core through the reaction process; including, a core-shell structure of a copper-iridium-containing catalyst for oxygen generation reaction A manufacturing method is provided.

The catalyst for oxygen generation reaction comprising copper-iridium having a core-shell structure according to the present invention synthesizes an iridium shell with a thin thickness of 2 to 3 nanometers on a copper nanowire, thereby significantly reducing the amount of expensive precious metal and at the same time , can exhibit excellent activity and durability corresponding to the existing iridium catalyst even with a very small amount of iridium.

The catalyst according to the present invention is applicable to a cation-exchange electrolyte membrane water electrolytic cell and the like. In addition, the manufacturing method according to the present invention is applied to the reduction of other noble metals such as platinum, and can be usefully used in the development of a fuel cell catalyst.

1 is a scanning electron microscope (SEM) analysis result of the copper nanowire of Example 1 according to the present invention.
2 is a transmission electron microscope (TEM) analysis result of the copper nanowire of Example 1 according to the present invention.
3 is an energy dispersive X-ray spectroscopy (EDS) analysis result of the copper nanowire of Example 1 according to the present invention.
4 is an energy dispersive X-ray spectroscopy (EDS) analysis result of the catalyst of Example 2 according to the present invention.
5 is a scanning electron microscope (SEM) analysis result of the catalyst of Example 2 according to the present invention.
6 is a transmission electron microscope (TEM) analysis result of the catalyst of Example 2 according to the present invention.
7 is a scanning transmission electron microscope (STEM) analysis result of the catalyst of Example 2 according to the present invention.
8 is a scanning electron microscope (SEM) analysis result of the copper nanowire and nanoparticles of Comparative Example 1 according to the present invention.
9 is a transmission electron microscope (TEM) analysis result of the catalyst of Comparative Example 2 according to the present invention.
10 is an energy dispersive X-ray spectroscopy (EDS) analysis result of the catalyst of Comparative Example 3 according to the present invention.
11 is a transmission electron microscope (TEM) analysis result of the catalyst of Comparative Example 4 according to the present invention.
12 is a graph showing linear sweep voltammetry (LSV) polarization curves for oxygen evolution reaction in an acidic electrolyte environment of the catalysts of Examples and Comparative Examples according to the present invention as a voltage versus current density.
13 is a graph showing a voltage versus time measurement of a change in voltage while applying a constant current in an acidic electrolyte environment of the catalysts of Examples and Comparative Examples according to the present invention.

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

One embodiment of the present invention relates to a catalyst for oxygen evolution comprising a core-shell structure copper-iridium,

copper nanowires; and

Iridium formed on the copper nanowire; consists of,

The copper nanowire constitutes a core, and the iridium forms a shell structure in which the iridium is synthesized on the core,

The iridium is formed on the copper nanowire to a thickness of 2 to 3 nm to reduce the content of the iridium.

The catalyst according to the present invention is characterized in that it is formed by synthesizing a noble metal layer having a thin thickness of 2 to 3 nm on a copper nanowire having a length of micrometers in order to exhibit excellent stability.

In one embodiment of the present invention, the length of the copper nanowire is 10 to 20 μm, it is preferable that the thickness is 4 to 50 nm. If the above range is not satisfied, a sufficient surface area to form an iridium shell may not be secured.

In one embodiment of the present invention, the noble metal layer is composed of iridium, and the iridium is preferably composed of a shell shape surrounding the copper nanowire, which is a core. In this case, the thinner the shell, the less the amount of noble metal used, so it is more preferable to have a thickness of 2 to 3 nm in consideration of structural stability.

One embodiment of the present invention relates to a method for preparing a catalyst for oxygen evolution comprising copper-iridium having a core-shell structure,

(i) preparing a copper nanowire core;

(ii) preparing a mixture in which the copper nanowire core and iridium acetylacetonate are mixed;

(iii) dispersing the mixture in a solvent whose ratio is adjusted to be 1 to 2 ml per 1 mg of the copper nanowire core, and reacting at a stirring speed of 350 to 450 rpm; and

(iv) forming an iridium shell to surround the core while reducing iridium on the surface of the nanowire core through the reaction process;

Hereinafter, a method for preparing a catalyst for oxygen evolution including copper-iridium having a core-shell structure of the present invention will be described in detail.

The manufacturing method according to the present invention is characterized in that by separating the synthesis of the copper nanowire core and the synthesis of the iridium shell, a thin iridium shell having a thickness of 2 to 3 nanometers is formed on the surface of the copper nanowire.

(a) Preparation of copper nanowire cores

The copper nanowire core may be prepared by dispersing the copper precursor mixture in a solvent and reacting it at a temperature of 160 to 170° C. under an argon atmosphere for 7 to 8 hours.

Specifically, the copper precursor mixture contains copper acetyleacetonate, ruthenium chloride hydrate, ferrous chloride tetrahydrate, and L-ascorbic acid in a molar ratio. It is preferable that the reaction proceeds in a high-purity argon atmosphere while mixing at a ratio of 2:1:2:12, dispersing in a solvent, and stirring the solution at 600 to 800 rpm.

At this time, if oxygen or water is introduced more than a certain amount during the reaction process, since most nanoparticles, not copper nanowires, can be synthesized, it is essential to remove excess moisture and oxygen in the reaction vessel. Therefore, it is preferable to repeat the vessel vacuum and argon gas atmosphere replacement for 3 minutes at 100° C. for 3 minutes before the reaction so that oxygen and water do not flow in the reaction process, and maintain it under an argon gas atmosphere at 120° C. for 15 to 20 minutes.

As the copper precursor, copper acetylacetonate, copper(I) chloride (Cu(I) chloride), copper(II) chloride (Cu(II) chloride), etc. may be used, but the present invention is not limited thereto. , it is preferable to use copper acetylacetonate.

(b) Preparation of copper-iridium catalyst

The present invention is characterized in that the catalyst is synthesized by an easy method using a solution process at atmospheric pressure.

The copper nanowire core and iridium acetylacetonate are mixed in a molar ratio of 12:1 to 8:1, dispersed in a solvent whose ratio is adjusted to be 1 to 2 ml per 1 mg of the copper nanowire core, and the stirring speed is increased. It is preferable to proceed with the reaction at 350 to 450 rpm.

When iridium is reduced on the surface of the nanowire core through the reaction process, an iridium shell may be formed to surround the core through heterogenous nucleation.

At this time, in order to uniformly synthesize the iridium shell on the copper nanowire core, the reaction is performed at a temperature of 245 to 255 ° C. It is preferable to reach the temperature from room temperature to the temperature within 7 to 8 minutes.

In the catalyst preparation step of the method according to the present invention, an iridium shell having a uniform thickness of 2 to 3 nm on the copper nanowire core only when all of the conditions of reaction temperature, stirring speed, and solvent content compared to the copper nanowire core are satisfied is formed, and if even one of the above conditions is not met, an iridium shell having a desired thickness may not be synthesized.

In one embodiment of the present invention, the solvent may be an oleylamine solution, dimethylformamide, or the like, but is not limited thereto.

Hereinafter, the present invention will be described in more detail by way of Examples. These examples are only for illustrating the present invention, and it will be apparent to those skilled in the art that the scope of the present invention is not limited to these examples.

Example 1: Preparation of copper nanowires

The precursors copper acetylacetonate, ruthenium chloride hydrate, ferrous chloride tetrahydrate and L-ascorbic acid in a molar ratio of 2:1:2: 12, dispersed in the oleylamine solution, and the reaction was carried out in a high purity argon atmosphere while stirring the solution at 700 rpm. At this time, the synthesis temperature was 170 °C and the reaction was maintained for 7 hours.

If oxygen or water is introduced during the reaction process, the majority of nanoparticles, not copper nanowires, can be synthesized. Excess moisture was removed and the oxygen ratio in the vessel was minimized by maintaining it in a high-purity argon atmosphere for -20 minutes.

Upon completion of the reaction, the mixture was cooled to room temperature, and then, using a centrifuge, excess oleylamine was removed with a solution of hexane and ethanol. Then, copper nanowires were manufactured through a drying process in a vacuum oven.

1 relates to a scanning electron microscope (SEM) analysis result of the copper nanowire prepared in Example 1. 1, it was confirmed that a copper nanowire having a length of 2-3 micrometers (㎛) was manufactured.

FIG. 2 relates to a transmission electron microscope (TEM) analysis result of the copper nanowire prepared in Example 1. FIG. 2 , it was confirmed that copper nanowires having a thickness of 3 to 40 nanometers (nm) were manufactured.

Table 1 and FIG. 3 show the results of energy dispersive X-ray spectroscopy (EDS) analysis of the copper nanowires prepared in Example 1, confirming that the reduction of elements other than Cu was not performed.

element(%) copper nanowire Copper 99.26 steel 0.40 ruthenium 0.34

Example 2: Preparation of a catalyst in which a nanometer-thick iridium shell is synthesized on a copper nanowire

An oleylamine solution in which the copper nanowires prepared in Example 1 and iridium acetylacetonate were mixed at a molar ratio of 10:1, and the ratio was adjusted to 1 to 2 ml per 1 mg of the copper nanowires After dispersion, the reaction was carried out by setting the stirring speed to 400 rpm in a 50 ml vial. At this time, the synthesis temperature was set to 250 °C and the reaction was maintained for 5 hours. In order to uniformly form the iridium shell, it was allowed to reach the synthesis temperature within 7 to 8 minutes.

When the reaction was completed, the reaction was cooled to room temperature, and then, using a centrifuge, excess oleylamine was removed with a solution of hexane and ethanol. Then, through a drying process in a vacuum oven, a copper-iridium catalyst having a core-shell structure was obtained.

Table 2 and FIG. 4 show the results of energy dispersive X-ray spectroscopy (EDS) analysis of the catalyst prepared in Example 2, and it was confirmed that iridium was present in a ratio of about 9 to 10%.

element(%) catalyst Copper 90.80 iridium 9.20

5 is a scanning electron microscope (SEM) analysis result of the catalyst prepared in Example 2, it was confirmed that the nanowire structure is maintained even after iridium reduction.

6 and 7 show transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) analysis results of the catalyst prepared in Example 2, confirming that an iridium shell having a thickness of 2-3 nanometers was synthesized.

Comparative Example 1: Preparation of copper nanowires

In the copper nanowire manufacturing method of Example 1, copper nanowires were prepared by changing the oxygen concentration to 0.001%.

8 shows the results of scanning electron microscope (SEM) analysis of the copper nanowires and nanoparticles prepared in Comparative Example 1. Referring to FIG.

Referring to FIG. 8 , the existence of numerous copper nanoparticles was confirmed. Through this, if oxygen and humidity cannot be controlled during the copper nanowire synthesis process and the synthesis is not performed under a high-purity argon environment, copper nanoparticles are synthesized simultaneously with the formation of copper nanowires, thereby reducing iridium on the pure nanowires. can't This is because it is difficult to separate copper nanowires and copper nanoparticles.

Comparative Example 2: Preparation of catalyst

The catalyst was prepared in the same manner as in the catalyst preparation method of Example 2, but by changing the stirring speed to 300 rpm and 500 rpm and proceeding with the synthesis.

9 shows the results of transmission electron microscopy (TEM) analysis of the catalyst prepared in Comparative Example 2.

Referring to FIG. 9 , it was confirmed that the iridium shell was not evenly formed on the surface of the copper nanowire when the stirring speed was not within the range according to the present invention during catalyst preparation.

Comparative Example 3: Preparation of catalyst

The catalyst was prepared in the same manner as in the catalyst preparation method of Example 2, except that the ratio of oleylamine was changed to 0.1 to 0.2 ml instead of 1 to 2 ml per 1 mg of copper nanowire, and the synthesis was carried out to prepare a catalyst.

Table 3 and FIG. 10 show the results of energy dispersive X-ray spectroscopy (EDS) analysis of the catalyst prepared in Comparative Example 3.

element(%) catalyst Copper 98.44 iridium 1.56

Referring to Table 3 and FIG. 10, the catalyst prepared in Comparative Example 3 had a very low reduction rate of iridium itself, and it was found that the iridium was present in a remarkably small proportion of about 1 to 2%.

Comparative Example 4: Preparation of catalyst

The catalyst was prepared in the same manner as in Example 2, except that the synthesis temperature was changed to 240° C. or 260° C. and the synthesis was performed.

11 shows the results of transmission electron microscopy (TEM) analysis of the catalyst prepared in Comparative Example 4.

Referring to FIG. 11 , when the synthesis temperature of the catalyst is lower than the temperature range according to the present invention, the reduction of iridium does not occur, and when it is higher than the temperature range, the iridium nano is due to homogenous nucleation of iridium. It was confirmed that the particles were not formed only on the copper nano, but were formed separately.

Comparative Example 5: Commercial Iridium Catalyst

A commercial catalyst (Premetek) having an iridium content of 20 wt% was prepared and compared with the catalyst prepared in the above example.

Experimental Example 1: Evaluation of half-cell activity and durability of the catalyst

The half-cell activity of the catalysts prepared in Example 2 and Comparative Example 5 in the acidic electrolyte was evaluated. To evaluate the activity, the current was measured by applying a voltage of 1.2-1.8 V _RHE in the oxidation direction at a rate of 5 mV/s in an argon gas saturated electrolyte environment. In addition, the voltage was corrected by measuring the resistance by impedance spectroscopy (EIS) at 1.50 V _RHE . The results are presented as voltage versus current density. The amount of iridium mounted on the electrode during measurement was fixed at 30 μg _Ir / cm ² .

In addition, the half-cell durability of the catalysts prepared in Example 2 and Comparative Example 5 in the acidic electrolyte was evaluated. The durability evaluation was conducted in an argon gas saturated electrolyte environment, and the evaluation was performed using a constant current method. A change in voltage was measured by applying a constant current density of 10 mA/cm ² .

The activity and durability evaluation results are shown in FIGS. 12 and 13, and the activity and durability indicators are numerically summarized in Table 4 below.

division activity per mass
(A/g _Ir @1.55V _RHE ) Time to reach 2 V _RHE
(minute) Example 2 380 208 Comparative Example 5 208 137

The activity of the oxygen evolution catalyst is expressed as activity per mass of iridium, and with reference to Table 4, the catalyst of Example 2 showed an activity increase of 1.5 times or more compared to the catalyst of Comparative Example 5.

In addition, durability evaluation was evaluated based on the time to reach 2 V _RHE , and the catalyst of Example 2 showed 1.5 times or more durability compared to the catalyst of Comparative Example 5.

Therefore, it was confirmed that the catalyst of Example 2 showed higher performance than the catalyst of Comparative Example 5 and showed good durability when both activity and durability were considered.

As the specific part of the present invention has been described in detail above, for those of ordinary skill in the art to which the present invention pertains, it is clear that these specific techniques are only preferred embodiments, and the scope of the present invention is not limited thereto. do. Those of ordinary skill in the art to which the present invention pertains will be able to make various applications and modifications within the scope of the present invention based on the above contents.

Accordingly, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Claims (9)

copper nanowires; and
Iridium formed on the copper nanowire; consists of,
The copper nanowire constitutes a core, and the iridium forms a shell structure in which the iridium is synthesized on the core,
The iridium is formed on the copper nanowire to a thickness of 2 to 3 nm to reduce the content of the iridium, a core-shell structure copper-catalyst for oxygen generation reaction comprising iridium. According to claim 1, wherein the length of the copper nanowire is 2 to 3 ㎛, characterized in that the thickness of 3 to 40 ㎚, core-shell structure copper-Iridium-containing catalyst for oxygen evolution reaction. (i) preparing a copper nanowire core;
(ii) preparing a mixture of the copper nanowire core and iridium acetylacetonate;
(iii) dispersing the mixture in a solvent whose ratio is adjusted to be 1 to 2 ml per 1 mg of the copper nanowire core, and reacting at a stirring speed of 350 to 450 rpm; and
(iv) forming an iridium shell to surround the core while reducing iridium on the surface of the nanowire core through the reaction process; A method for preparing a catalyst for reaction. The core of claim 3, wherein the copper nanowire core in step (i) is prepared by dispersing a copper precursor mixture in a solvent and reacting in an argon atmosphere at a temperature of 160 to 170° C. for 7 to 8 hours. - A method for producing a catalyst for oxygen evolution containing copper-iridium of a shell structure. 5. The method of claim 4, wherein in the reaction process, the vessel vacuum and argon gas atmosphere replacement are repeated three times at 100°C for 3 minutes before the reaction so that oxygen and water are not introduced, and maintained under an argon gas atmosphere at 120°C for 15 to 20 minutes. A method for producing a catalyst for oxygen evolution reaction comprising a core-shell structure copper-iridium, characterized in that performing the step of removing excess moisture and oxygen in the reaction vessel by doing so. According to claim 3, wherein in step (ii), the copper nanowire core and iridium acetylacetonate are mixed in a molar ratio of 12:1 to 8:1, core-shell structure copper- containing iridium A method for preparing a catalyst for an oxygen evolution reaction. According to claim 3, wherein the reaction of step (iii) is carried out at a temperature of 245 to 255 ℃, characterized in that the control so as to reach the temperature from room temperature to the temperature within 7 to 8 minutes, core-shell structure copper- A method for producing a catalyst for oxygen evolution containing iridium. [4] The method of claim 3, wherein the solvent in step (iii) is an oleylamine solution. According to claim 3, wherein the thickness of the iridium shell in step (iv) is 2 to 3 nm, it characterized in that the use of iridium is reduced by forming the thickness of the shell thin, the core-shell structure copper-iridium A method for producing a catalyst for an oxygen evolution reaction comprising a.

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