KR20190063290A - Method of core-shell catalyst production including liquid phase nitriding - Google Patents

Abstract

The present invention relates to a core-shell catalyst producing method treated with liquid vaporization and, more specifically, to a liquid nitridation-treated core-shell catalyst producing method which includes a step of irradiating ultrasonic waves to solution including a liquid nitrogen source, a reducing solvent, a precious metal precursor, a transition metal precursor, and a carbon support, forming a cavity due to the irradiation of ultrasonic waves, forming a transition metal precursor core and precious metal precursor shell particles due to a difference in a vapor pressure, and performing nitridation by combining the nitrogen source with the transition metal precursor simultaneously in one reactor. The core-shell catalyst producing method treated with liquid nitridation is suitable for fuel battery fields by: enabling a high level of nitrification and the easiness of the control of a nitrogen content in a core through an easy and single process; and having high degree of dispersion and uniformity with a small average particle size while the produced catalyst has excellent durability.

Description

[0001] The present invention relates to a method for producing a core-shell catalyst,

The present invention relates to a method for producing a core-shell catalyst which is nitrided in a liquid environment, and more particularly to a method for producing a core-shell catalyst in which the durability and the electrochemical performance of the catalyst are improved by including a nitrogen element in the core in a liquid phase It is about.

Fuel cell, which is generally regarded as a next generation energy source, is a device that directly converts chemical energy generated by oxidation / reduction of fuel into electric energy. Recently, fuel cell (fuel cell) It is expected to be the future electric power for the future. The electrode reaction in the fuel cell consists of the hydrogen oxidation reaction in the anode and the oxygen reduction reaction in the anode. In a fuel cell system driven at low temperature, such as a polymer electrolyte membrane fuel cell, The reaction rate must be effectively increased in order to occur smoothly.

For the above reasons, platinum (Pt), which is a noble metal catalyst, has been inevitably used in the conventional fuel cell system. However, although the platinum catalyst exhibits excellent energy conversion efficiency, the fuel cell is problematic because it is very expensive and has a limited amount of reserves. In particular, the need for a new, high-efficiency, yet low-cost, electrical catalyst has been among the most urgent issues associated with PEMFC (Polymer electrolyte membrane fuel cell). In order to solve the above-mentioned failure factors and to promote the commercialization of fuel cells, in order to replace the platinum electrode supported on the present carbon support in recent years, it has been proposed to use nano-particles including a plurality of components such as alloy nanoparticles and core- Particles (multi-component nanoparticles) have been studied. This method has the disadvantage that synthesis is cumbersome and not economical, inevitably increases the particle size, and disappears of the surface area having catalytic activity. In particular, a technology has been developed that minimizes the deterioration of the catalyst performance compared with the platinum catalyst, which is composed of a transition metal-based core and a platinum-based shell. However, in this case, the durability of the catalyst is limited, . Particularly, in the prior art, nitrogen has been injected to improve the above. However, after the core is manufactured, nitrogen is added to the core and the shell is coated in order to manufacture the core and shell, The thickness is not uniform, and the catalyst manufacturing step and the nitrogen treating step constituting the core and the shell are separately carried out. Therefore, the manufacturing process is complicated and takes a long time.

Korean Patent No. 1468113 Korean Patent Publication No. 2013-0039456 U.S. Published Patent Application No. 2015-0147682

Accordingly, it is an object of the present invention to provide a simple and efficient method for manufacturing a core-shell catalyst having a non-noble metal-based core and a platinum shell and improved durability of the catalyst.

It is an object of the present invention to provide a core-shell catalyst production method in which a catalyst preparation step constituting the core and the shell and a nitriding step of including nitrogen in the core are simultaneously carried out.

It is another object of the present invention to provide a method for producing a core-shell catalyst in which the average particle diameter of the catalyst is increased while nitrogen is contained in the core and the uniformity of the core and the shell can be improved Respectively.

The method for producing a core-shell catalyst according to the present invention comprises irradiating a solution containing a liquid nitrogen source, a reducing solvent, a noble metal precursor, a transition metal precursor to the noble metal precursor, and a carbon support to generate ultraviolet light, And forming a transition metal precursor core and noble metal precursor shell particles due to the difference in vapor pressure while nitriding the nitrogen source at the same time by bonding the transition metal precursor with the transition metal precursor.

Here, the liquid-phase nitridation-treated core-shell catalyst is characterized in that the nitrogen source is maintained at a ratio of 10 to 50 mol per 50 to 90 mol.

In the method for producing a core-shell catalyst according to the present invention, the nitrogen source of the liquid phase is urea, and the average particle diameter of the core-shell catalyst subjected to the liquid-phase nitration treatment is 4.0 nm or less.

In the method for producing a core-shell catalyst according to the present invention, the reducing solvent is a solvent having a reducing power at a temperature of 130 ° C or higher.

Further, in the method for producing a core-shell catalyst according to the present invention, the carbon support is a porous carbon support, and the core-shell catalyst is a cobalt core and a platinum shell.

The core-shell catalyst produced by the nitriding treatment under the liquid phase condition according to the present invention can easily perform the nitriding treatment on the core-shell particles by a single process.

In addition, the core-shell catalyst produced by the nitriding treatment under the liquid phase condition according to the present invention has a high nitrogen content in the core, so that the prepared catalyst has excellent durability, small average particle size, high dispersibility and uniformity.

In addition, the core-shell catalyst produced by the nitriding treatment under the liquid phase condition according to the present invention has an effect that the production process is easy and can be obtained in a large amount.

Therefore, it is expected that the core-shell catalyst of the present invention contributes to the commercialization of the fuel cell when applied as an electrode catalyst having an oxygen reduction reaction efficiency.

1 is a STEM-EDS photograph of the core-shell catalyst prepared in Examples 1 to 3 according to the present invention,
2 is an XRD photograph of the core-shell catalyst prepared in Examples 1 to 3 and Comparative Example 1 according to the present invention,
FIG. 3 shows the size, particle uniformity and dispersion of the core-shell catalyst prepared in Examples 1 to 3 and Comparative Example 2 according to the present invention,
4 shows activity per unit area and activity per mass of the core-shell catalyst prepared in Examples 1 to 3 and Comparative Example 2 according to the present invention,
FIG. 5 shows the electrochemically active surface area (ECSA) of the core-shell catalyst prepared in Examples 1 to 3 and Comparative Example 2 according to the present invention.

The present invention relates to a method for producing a core-shell catalyst having improved durability and electrochemical performance by liquid-phase nitrification treatment.

Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor should appropriately interpret the concepts of the terms appropriately It should be interpreted in accordance with the meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined.

Therefore, the embodiments described in the present specification and the configurations shown in the drawings are only the most preferred embodiments of the present invention, and not all of the technical ideas of the present invention are described. Therefore, It should be understood that various equivalents and modifications are possible.

Hereinafter, the method for producing the core-shell catalyst according to the present invention will be described in detail.

First, ultrasonic waves are irradiated to a solution containing a liquid nitrogen source, a reducing solvent, a noble metal precursor, a transition metal precursor, and a carbon support. The high frequency oscillation of the ultrasonic waves causes bubbles in the cavity, which causes oscillatory growth, and finally the cavity explodes after reaching a certain scale. This series of processes caused by ultrasonic irradiation is also called 'acoustics cavitation mechanism'. The joint explosion occurring in the last stage of the acoustic cavitation mechanism can cause a huge heat energy reaching about 5000K, and its extinction is achieved within a very short time of about 10 ^-6 seconds. When two or more reactants in a chemical reaction to which ultrasonic irradiation is applied are two or more substances having different vapor pressures, the speed at which the two or more reactants are evaporated into bubbles due to the high frequency vibration of ultrasonic waves are different, The structural and electrochemical characteristics of the result can be controlled. For example, when two or more metal precursors are used as a reactant and ultrasound is irradiated to produce nanoparticles containing two or more metals, the two or more metal precursors may have a difference in vapor pressure, The distribution of the metal element can be controlled. For example, a metal precursor having a low vapor pressure in the nanoparticle may be positioned in a shell portion, and a metal precursor having a high vapor pressure may be positioned in a core portion to obtain a core / shell structure nanoparticle having an adjusted element distribution. have. The nitrogen source of the liquid phase is generally used in the art and is not particularly limited. For example, urea may be used. By the nitridation treatment using such a liquid nitrogen source, the nitrogen source is placed in the transition metal core, and the durability of the catalyst is improved. The nitrogen source of the liquid phase is pyrolyzed or hydrolyzed while being irradiated with ultrasonic waves to generate ammonia. The ammonia reacts with the transition metal seeds formed at the beginning of the reaction and is nitrided, and then the nitrided transition metal forms a core.

The reducing solvent may be an organic solvent which is generally used in the art and has no moisture and oxygen source. Specifically, the reducing solvent may be a solvent having a reducing power at a temperature of 70 ° C or higher. Specifically, Examples of the reducing agent include ethylene glycol, ethylene glycol, tri-ethylene glycol, and poly-ethylene glycol. The reducing solvent serves to reduce the metal precursor, which is a reactant, in the cavity formed by the ultrasonic treatment.

The noble metal precursor may have a vapor pressure lower than the vapor pressure of the transition metal precursor and contribute to a galvanic substitution reaction after formation of transition metal seed particles and increase in size. Specifically, the noble metal precursor is not particularly limited, and is generally used in the art. However, the noble metal precursor is not limited to the precursor of the noble metal such as an acetylacetonate precursor, a noble metal hexafluoroacetylacetonate precursor, and a noble metal pentafluoroacetylacetonate precursor It may be at least one selected.

The transition metal precursor may be at least one selected from the group consisting of precursors of nickel, cobalt, iron and manganese, although the transition metal precursor is generally used in the art and is not particularly limited. The transition metal precursor may be, for example, at least one selected from the group consisting of an acetyl acetonate precursor of a transition metal and a hexafluoroacetylacetonate precursor of a transition metal. Such transition metal precursors are rapidly volatilized by high vapor pressures and are quickly trapped in cavities by ultrasonic waves, so that in the core-shell structure of the reaction product, the transition metal can be located in the core portion.

The carbon support is not particularly limited as long as it is commonly used in the art as a support for a core-shell catalyst. For example, a porous carbon support may be used. When a porous carbon support is used, a large amount of core / shell structure nanoparticles can be efficiently supported by a large surface area.

In addition, a metal oxide capable of supporting nanoparticles of a core / shell structure may be used.

The reaction may be maintained at a reaction temperature of 70 to 220 DEG C by heat generated by ultrasonic irradiation. That is, it is formed naturally by the heat generated by the ultrasonic irradiation without additional heating.

According to the present invention, when the ultrasonic wave is irradiated, a cavity is formed, and the transition metal precursor is trapped in the cavity before the noble metal precursor due to the difference in vapor pressure to form a core. Specifically, the transition metal precursor is first volatilized relative to the noble metal precursor and is first captured in a cavity formed by the irradiation of the ultrasonic wave. The noble metal precursor is then deposited on the core to form a shell.

The core-shell catalyst according to the present invention can reduce the unit cost of the electrode catalyst by positioning the transition metal in the core portion, and the noble metals such as platinum and palladium located in the shell portion are located, . For example, the core-shell catalyst may be a cobalt core and a platinum shell, a nickel core and a platinum shell.

In addition, the core-shell catalyst subjected to the liquid phase nitridation treatment according to the present invention maintains a nitrogen atom ratio of 10 to 50 mol per 50 to 90 mol of the transition metal.

In addition, according to the present invention, the average particle diameter of the liquid-phase nitrided core-shell catalyst is 4.0 nm or less and is improved compared to the specific activity platinum single metal electrode catalyst per unit area, and mass activity is equivalent to that of the platinum single metal electrode catalyst Level.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. , And it is natural that such variations and modifications fall within the scope of the appended claims.

Example 1

Nitrogen-derived urea, platinum acetylacetonate (Aldrich) solution, cobalt acetylacetonate (Aldrich) solution, and porous carbon support (Vulcan XC72) were added to ethylene glycol which is a reducing solvent. In this state, a high-strength ultrasonic probe , model VC-500, amplitude 30%, 13 mm solid probe, 20 kHz) under an argon atmosphere at a high temperature of 150 ° C for 3 hours. At this time, the urea was used in an amount of 0.01% by weight based on ethylene glycol. The reaction temperature was naturally controlled by a balance between the heat generated by ultrasonic waves and the heat dissipation rate. The solid product obtained as a result of ultrasonic irradiation was purified and washed with ethanol, and dried in a vacuum atmosphere to prepare a core-shell catalyst (CoN _x @ Pt / C).

Example 2

(CoN _x @ Pt / C) was prepared in the same manner as in Example 1, except that urea was used in an amount of 0.03% by weight based on ethylene glycol.

Example 3

The procedure of Example 1 was repeated except that urea was used in an amount of 0.05 wt% based on ethylene glycol to prepare a core-shell catalyst (CoN _x @ Pt / C).

Comparative Example 1

Pt / C commercial catalyst (Johnson Matthey, HiSpec 4000)

Comparative Example 2

Platinum acetylacetonate (Aldrich) solution, cobalt acetylacetonate (Aldrich) solution, and porous carbon support (Vulcan XC72) were added to ethylene glycol, which is a reducing solvent, and a high-strength ultrasonic probe (Sonic and Materials, model VC- 500, amplitude 30%, 13 mm solid probe, 20 kHz) under an argon atmosphere at a high temperature of 150 ° C for 3 hours. The reaction temperature was naturally controlled by a balance between the heat generated by ultrasonic waves and the heat dissipation rate. The solid product obtained as a result of ultrasonic irradiation was purified and washed with ethanol and dried in a vacuum atmosphere to prepare a core-shell catalyst (Co @ Pt / C).

FIG. 1 is a STEM-EDS photograph of the core-shell catalyst prepared in Examples 1 to 3 according to the present invention. The catalysts of Examples 1 to 3 clearly show a platinum shell (0.3 to 0.5 nm) Respectively.

The following Table 1 and FIG. 2 show the structural analysis results of the catalysts prepared in Examples 1 to 3 and Comparative Examples 1 and 2.

division
Mole ratio Distance between Pt and Pt
N content (% by weight)
Co N Example 1 78.5 21.5 0.2731 0.37 Example 2 62.7 37.3 0.2730 0.76 Example 3 63.3 36.7 0.2730 1.00 Comparative Example 1 - - 0.2780 - Comparative Example 2 - - 0.2713 -

FIG. 3 shows the size, particle uniformity, and dispersion of the core-shell catalyst prepared in Examples 1 to 3 and Comparative Example 2. The average particle size of the catalyst particles prepared in Examples 1 to 3 was 4.0 nm or less Uniform, and uniformly dispersed on the carbon support.

FIGS. 4 and 5 show the electrochemical performance of the core-shell catalyst prepared in Examples 1 to 3 and Comparative Example 2, wherein FIG. 4 shows activity per unit area and activity per mass, and FIG. 5 shows an accelerated endurance evaluation 0.6 V to 1.0 V, 30,000 cycles).

The basic electrochemical activity can be confirmed through the nitriding process. In the evaluation of the same acceleration durability, the half-wave potential variation of the electrochemical surface area and the oxygen reduction reaction is 37.8% and 25 mV, respectively. In Example 3, the electrochemical surface area value was increased by about 1.4% after the acceleration endurance evaluation, and the half-wave potential of the oxygen reduction reaction was also increased by about 4 mV.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. The scope of protection of the present invention should be construed under the following claims, and all technical ideas within the scope of equivalents thereof should be construed as being included in the scope of the present invention.

Claims (8)

A solution containing a nitrogen source in a liquid phase, a reducing solvent, a noble metal precursor, a transition metal precursor, and a carbon support is irradiated with ultrasonic waves,
Forming a transition metal precursor core and noble metal precursor shell particles due to the difference in vapor pressure between the irradiation of the ultrasonic waves and nitriding the nitrogen source at the same time by bonding with the transition metal precursor A process for producing a liquid phase nitrided core-shell catalyst.
The method according to claim 1, wherein the liquid-phase nitridation-treated core-shell catalyst maintains a nitrogen atom ratio of 10 to 50 mol per 50 to 90 mol of the transition metal.
The method for producing a core-shell catalyst according to claim 1, wherein the liquid nitrogen source is a urea or ammonia solution and a mixture thereof.
The method for producing a core-shell catalyst according to claim 1, wherein the average particle diameter of the core-shell catalyst subjected to the liquid phase nitridation treatment is 4.0 nm or less.
The method for producing a core-shell catalyst according to claim 1, wherein the reducing solvent is a solvent having a reducing power at a temperature of 70 ° C or higher.
The method of claim 1, wherein the carbon support is a porous carbon support.
The method of claim 1, wherein the core-shell catalyst is a cobalt core and a platinum shell.
The method of claim 1, wherein the core-shell catalyst is a nickel core and a platinum shell.

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