KR101692852B1 - Catalyst for oxygen reduction reaction based cobalt and the preparation method thereof - Google Patents

Abstract

The present invention provides a catalyst for an oxygen reduction reaction, comprising nitrogen-doped graphene in which a complex represented by chemical formula 1 of cobalt is coordinated. The catalyst for an oxygen reduction reaction according to the present invention has an effect of exhibiting excellent oxygen reduction reaction activity. In particular, the catalyst of the present invention has effects of securing more low price and fairness by being synthesized through a solution process at room temperature in comparison with conventional iron and cobalt-based catalyst systems which undergo heat treatment at a high temperature as well as being inexpensive compared to a precious metal catalyst such as conventional platinum.

Description

TECHNICAL FIELD The present invention relates to a catalyst for cobalt-based oxygen reduction reaction and a process for producing the same,

The present invention relates to a catalyst for cobalt-based oxygen reduction reaction and a method for producing the same, and more particularly, to a catalyst for oxygen reduction reaction in which cobalt-based organometallic molecules are coordinated to a graphene material doped with nitrogen.

A catalyst for oxygen reduction reaction (ORR) at the anode when driving a fuel cell or a lithium-air bettery device is needed. These catalysts have been mainly used as platinum (Pt) catalysts, but they are very expensive and have problems in stability against moisture and methanol. New catalyst systems have been studied to overcome these problems.

Catalyst systems consisting of metal and nano-carbon of noble metal, non-noble metal (iron, cobalt, etc.), metal-free noble metal system (MNC ).

Although a lot of research is still being conducted on the above catalyst systems, the development of a new catalyst system with high activity, low cost and high stability is very important for practical application in industry. In particular, a catalyst system using a platinum-based alloy or a platinum-based noble metal catalyst still has a disadvantage in that the cost of the catalyst is still high, and the nano-carbon system without the metal has a problem in that the catalyst is inexpensive.

On the other hand, iron (Fe) and cobalt (Co), which are inexpensive transition metals, and a catalyst system (MNC) using nanocarbon are relatively inexpensive and can exhibit good activity. However, in the case of the MNC catalyst system described above, a heat treatment process at a temperature higher than several hundreds is essential, which is another problem of increasing the production cost. In addition, it is difficult to control the active species of the catalyst in such a heat treatment process, which is a problem in practical catalyst applications.

On the other hand, graphene has a thickness of one carbon atom and has a two-dimensional plate-like structure. In addition, because of its excellent sp2 carbon structure, it has excellent electrical, thermal and mechanical properties and has a large surface area. Therefore, it can be used as a transistor, a transparent electrode, an energy storage material (fuel cell catalyst, ultra high capacity capacitor, Polymer complexes and the like.

One way to control the physical properties of graphene is by chemical doping. For example, when one more electron than carbon is introduced chemically into the structure of graphene, more free electrons can change the overall electronic structure.

The present inventors have studied a catalyst for oxygen reduction using cobalt as a non-noble metal, and have developed a catalyst for oxygen reduction reaction containing graphene doped with nitrogen in which cobalt organometallic molecules are coordinated. And that the catalyst can be produced at room temperature, thereby completing the present invention.

It is an object of the present invention to provide a cobalt-based catalyst for oxygen reduction reaction which exhibits excellent oxygen reduction activity and a method for producing a catalyst for oxygen reduction reaction which can achieve low cost and fairness.

In order to achieve the above object,

There is provided a catalyst for an oxygen reduction reaction comprising graphene doped with nitrogen in which a complex represented by the following Chemical Formula 1 is coordinated with cobalt.

≪ Formula 1 >

(Wherein R _1, R ₂ and R ₃ are each independently a C ₁ to C ₂ alkyl substituted by hydrogen or C ₁ to C ₂ alkyl, or one or more F.)

In addition,

Preparing nitrogen-doped graphene (step 1); And

(Step 2) of mixing the graphene doped with nitrogen prepared in the step 1 and the complex represented by the formula (1) of cobalt (step 2).

Further,

A negative electrode material composition of a fuel cell or a lithium air cell in which cobalt is graphene doped with a nitrogen coordinated complex represented by the above formula (1).

The catalyst for oxygen reduction reaction according to the present invention has an effect of exhibiting excellent oxygen reduction reaction activity. In particular, since the conventional iron and cobalt-based catalyst systems undergo heat treatment at a high temperature as well as conventional noble metal catalysts such as platinum, the catalyst of the present invention can be synthesized through a solution process at room temperature It is possible to secure low price and fairness.

FIG. 1 is a photograph of a catalyst for oxygen reduction reaction prepared in Examples 1 and 2 according to the present invention and a graphene doped with nitrogen prepared in Comparative Example 1 by a scanning electron microscope (SEM). FIG.
FIG. 2 is a photograph of a catalyst for oxygen reduction reaction prepared in Example 1 and Example 2 according to the present invention and a graphene doped with nitrogen prepared in Comparative Example 1 by transmission electron microscopy (TEM). FIG.
3 is a graph showing X-ray diffraction analysis of the catalyst for oxygen reduction reaction prepared in Examples 1 and 2 and the graphene doped with nitrogen prepared in Comparative Example 1 according to the present invention;
4 is a graph of a linear moving voltage curve (LSV) analysis using the catalysts prepared in Example 1, Example 2 and Comparative Examples 1 to 3 according to the present invention.

The present invention

There is provided a catalyst for an oxygen reduction reaction comprising graphene doped with nitrogen in which a complex represented by the following Chemical Formula 1 is coordinated with cobalt.

≪ Formula 1 >

(Wherein R _1, R ₂ and R ₃ are each independently a C ₁ to C ₂ alkyl substituted by hydrogen or C ₁ to C ₂ alkyl, or one or more F.)

Hereinafter, the oxygen reduction reaction catalyst according to the present invention will be described in detail.

Although a noble metal catalyst system such as platinum has been mainly used, it has a disadvantage in that the price is very high. Therefore, a catalyst system using metals such as iron (Fe) or cobalt (Co) and nano carbon is being studied, but most of the manufacturing processes require a heat treatment process of several hundreds or more, There is a problem that the performance is inferior to that of the platinum catalyst.

Here, the catalyst for oxygen reduction reaction according to the present invention is characterized in that a complex of cobalt is coordinated to graphene doped with nitrogen.

The catalyst for an oxygen reduction reaction according to the present invention is preferably prepared at a temperature of 10 ° C to 35 ° C in the form of coordination of a cobalt-based organometallic molecule on a graphene material doped with nitrogen. Since it can be produced through a solution phase process at room temperature, it is economically advantageous in comparison with a high temperature process used for preparing catalysts including conventional transition metals and nano-carbon. In addition, since the structure of the organometallic molecules is maintained in the complex of cobalt, it is easy to predict and control the catalytically active species.

As described above, it is preferable that the catalyst for oxygen reduction reaction according to the present invention does not contain cobalt particles. It does not contain cobalt particles and can exhibit excellent catalytic activity.

When metal particles or nanoparticles are adsorbed on the graphenes, it is very important to control the uniform dispersion and also it is very difficult to control the structure and composition of the nanoparticles during manufacturing. On the other hand, since the catalyst of the present invention has a composite material prepared by bonding with nitrogen-doped graphene without breaking the structure of the organometallic molecule by using the solution phase reaction at room temperature, the catalytic active site can be predicted and controlled It is very easy to follow. In addition, the dispersion is also superior to the non-uniformity of the nanoparticles due to the bonding at the molecular level.

In the catalyst for oxygen reduction reaction according to the present invention, the complex of cobalt may be cobalt (II) acetylacetonate or cobalt (III) acetylacetonate as a specific example, and preferably cobalt (II) It can be Nate.

In addition,

Preparing nitrogen-doped graphene (step 1); And

And a step (step 2) of mixing the graphene doped with nitrogen prepared in the step 1 and the complex represented by the following formula (1) of cobalt (step 2).

≪ Formula 1 >

(Wherein R _1, R ₂ and R ₃ are each independently a C ₁ to C ₂ alkyl substituted by hydrogen or C ₁ to C ₂ alkyl, or one or more F.)

Hereinafter, the method for producing the catalyst according to the present invention will be described in detail for each step.

First, in the method for producing a catalyst according to the present invention, step 1 is a step of preparing graphene doped with nitrogen.

Graphene has a thickness of one carbon atom and has a two-dimensional plate-like morphology. In addition, because of its excellent sp2 carbon structure, it has excellent electrical, thermal and mechanical properties and has a large surface area. Therefore, it can be used as a transistor, a transparent electrode, an energy storage material (fuel cell catalyst, ultra high capacity capacitor, Polymer complexes and the like.

One way to control the physical properties of graphene is by chemical doping. For example, when one more electron than carbon is introduced chemically into the structure of graphene, more free electrons can change the overall electronic structure.

As a typical example of a method of producing graphene, there is a chemical stripping method. The chemical stripping method is easy to mass-produce, and since graphite is used as a starting material, not only the unit price is low, but also a uniform colloid form It can be applied in various forms. In addition, various chemical modifications can be used to introduce desired properties to suit the purpose. Therefore, it is preferable that the step 1 is performed by a chemical stripping method.

The preparation of the nitrogen-doped graphene in the step 1 is, as a specific example,

Mixing graphene oxide, distilled water and ammonium hydroxide (step a); And

And refluxing the mixture of step a) (step b).

First, step (a) is a step of mixing graphene oxide, distilled water and ammonium hydroxide.

Specifically, in step (a), graphene oxide and distilled water are preferably mixed and dispersed in advance to prepare a dispersion solution.

At this time, it is preferable that 0.1 mg to 10 mg of the graphene oxide is mixed with 1 mL of distilled water, more preferably 1 mg to 5 mg.

Ammonia water is added to the dispersion solution, and the amount of ammonia water to be added is preferably 1 to 100 μl, preferably 5 μl to 25 μl, per 1 ml of the dispersion solution.

If the content of graphene oxide, distilled water and ammonia water mixed in the step a is out of the above range, it is difficult to uniformly disperse graphene oxide, and graphene oxide is not reduced and nitrogen doping is not performed.

Next, step (b) is a step of refluxing the mixture of step (a).

Specifically, the reflux of step b may be carried out at a temperature of 100 ° C to 200 ° C for 4 hours to 48 hours.

The process of doping nitrogen through reflux of the graphene oxide dispersion solution containing ammonia water is easy to mass-produce nitrogen-doped graphene.

Next, in the method for producing a catalyst according to the present invention, Step 2 is a step of mixing the nitrogen-doped graphene prepared in Step 1 and the complex represented by the formula 1 of cobalt.

Although a noble metal catalyst system such as platinum has been mainly used, it has a disadvantage in that the price is very high. Therefore, a catalyst system using metals such as iron (Fe) or cobalt (Co) and nano carbon is being studied, but most of the manufacturing processes require a heat treatment process of several hundreds or more, There is a problem that the performance is inferior to that of the platinum catalyst.

At this time, the step 2 of the production method according to the present invention enables the production of the catalyst through a solution process at a low temperature.

Concretely, it is preferable that the mixing of step 2 is carried out at a temperature of 10 ° C to 35 ° C. Since the process for preparing the catalyst according to the present invention can be produced through a solution phase process at room temperature, it has an economical advantage over the conventional process used for preparing catalysts containing transition metals and nano-carbon. In addition, since the structure of the organometallic molecules is maintained in the complex of cobalt, it is easy to predict and control the catalytically active species. The mixing of the step 2 may be performed for 3 to 48 hours and may be performed for 6 to 24 hours, but the mixing time of the step 2 is not limited thereto.

The mixing of the step 2 may be carried out using N, N-dimethylformamide (DMF), acetone, N-methylpyrrolidone (NMP), diethylether, ), And ethanol.

Further, the complex of step 2 is preferably mixed with 0.01 mmol to 10 mmol, preferably 0.1 mmol to 5 mmol, based on 30 mg of graphene doped with nitrogen. If the complex of step 2 is mixed with less than 0.01 mmol of the graphene doped with nitrogen in a concentration of less than 0.01 mmol, there is a problem in that the catalyst performance is deteriorated due to insufficient cobalt organometallic molecules coordinated to graphene. There is a problem that the catalyst performance is deteriorated.

The cobalt complex in step 2 may be, for example, cobalt (II) acetylacetonate or cobalt (III) acetylacetonate, preferably cobalt (II) acetylacetonate.

Further,

There is provided a negative electrode material composition for a fuel cell or a lithium air cell in which cobalt represented by the following Chemical Formula 1 is included and graphene doped with nitrogen is coordinated.

≪ Formula 1 >

(Wherein R _1, R ₂ and R ₃ are each independently a C ₁ to C ₂ alkyl substituted by hydrogen or C ₁ to C ₂ alkyl, or one or more F.)

A catalyst for an oxygen reduction reaction (ORR) at the anode when driving a fuel cell or a lithium-air bettery device is required.

However, conventional high performance catalysts are not economical because they are based on expensive noble metals, and they are vulnerable to moisture and methanol. In addition, low-cost transition metal-based catalysts are difficult to exhibit high performance and require a high heat treatment process, which is not economical.

However, the negative electrode material composition comprising nitrogen-doped graphene complexed with a complex represented by the formula (1) of the present invention represented by the general formula (1) of the present invention is a composition in which a cobalt-based organometallic molecule is coordinated on a graphene material doped with nitrogen Lt; 0 > C to 35 < 0 > C. Since it can be produced through a solution phase process at room temperature, it is economically advantageous in comparison with a high temperature process used for preparing catalysts including conventional transition metals and nano-carbon. In addition, since the structure of the organometallic molecules is maintained in the complex of cobalt, it is easy to predict and control the catalytically active species. In addition, it exhibits high oxygen reduction activity.

Hereinafter, the present invention will be described in detail with reference to the following examples and experimental examples.

It should be noted, however, that the following examples and experimental examples are illustrative of the present invention, but the scope of the invention is not limited by the examples and the experimental examples.

≪ Example 1 > Preparation of catalyst for oxygen reduction reaction 1

Step 1: Graphite oxide and deionized water (18.2 M) were added at a ratio of 3 mg to 1 mL and dispersed for 200 minutes in an ultrasonic cleaner. To a dispersed graphene oxide suspension, 1 mL to 10 μL of ammonium hydroxide was added with stirring.

The mixture was placed in a preheated oil bath at a temperature of 130 < 0 > C and refluxed for 12 hours. After 12 hours, the product was filtered using a glass filter and washed 10 times with deionized water. The product was again dried in a vacuum oven for 12 hours to prepare nitrogen-doped graphene.

Step 2: The nitrogen-doped graphene prepared in Step 1 and N, N-dimethylformamide (DMF) were mixed at a ratio of 3 mg to 1 mL and stirred.

Cobalt (II) acetylacetonate, Co (II) (acac) 2) was added to a solution containing graphene doped with nitrogen in an amount of 1 mmol per 30 mg of graphene doped with nitrogen And stirred.

The mixture was stirred at room temperature for 12 hours, and after 12 hours, the product was filtered using a glass filter and washed with DMF and deionized water each at least 10 times. The product was dried again in a vacuum oven for 12 hours to prepare a catalyst for an oxygen reduction reaction.

≪ Example 2 > Preparation of catalyst for oxygen reduction reaction 2

Except that 1 mmol of cobalt (III) acetylacetonate, Co (III) (acac) 3) was added in the amount of 30 mg of graphene doped with nitrogen in Step 2 of Example 1 And a catalyst for an oxygen reduction reaction was prepared in the same manner as in Example 1.

≪ Comparative Example 1 > Preparation of graphene doped with nitrogen

Graphite oxide and deionized water (18.2 M) were added at a ratio of 3 mg to 1 mL and dispersed for 200 minutes in an ultrasonic cleaner. To a dispersed graphene oxide suspension, 1 mL to 10 μL of ammonium hydroxide was added with stirring.

The mixture was placed in a preheated oil bath at a temperature of 130 < 0 > C and refluxed for 12 hours. After 12 hours, the product was filtered using a glass filter and washed 10 times with deionized water. The product was again dried in a vacuum oven for 12 hours to prepare nitrogen-doped graphene.

≪ Comparative Example 2 > Preparation of reduced graphene

Graphite oxide and deionized water (18.2 M) were added at a ratio of 3 mg to 1 mL and dispersed for 200 minutes in an ultrasonic cleaner. The mixture was placed in a preheated oil bath at a temperature of 130 < 0 > C and refluxed for 5 days. After 12 hours, the product was filtered using a glass filter and washed 10 times with deionized water. The product was again dried in a vacuum oven for 12 hours to prepare a simple reduced graphene.

≪ Comparative Example 3 &

Step 1: Reduced graphene of Comparative Example 2 was prepared.

Step 2: The reduced graphene prepared in Step 1 and N, N-dimethylformamide (DMF) were mixed at a ratio of 3 mg to 1 mL and stirred.

Cobalt (II) acetylacetonate, Co (II) (acac) 2) was added to a solution containing the reduced graphene in an amount of 1 mmol per 30 mg of reduced graphene and stirred .

The mixture was stirred at room temperature for 12 hours, and after 12 hours, the product was filtered using a glass filter and washed with DMF and deionized water each at least 10 times. The product was dried again in a vacuum oven for 12 hours to prepare a catalyst for an oxygen reduction reaction.

<Experimental Example 1> Scanning electron microscope and transmission electron microscope analysis

In order to confirm the morphology of the oxygen reduction catalyst according to the present invention, the catalyst for oxygen reduction reaction prepared in Examples 1 and 2 and the graphene doped with nitrogen prepared in Comparative Example 1 were observed under a scanning electron microscope SEM) and a transmission electron microscope (TEM). The results are shown in FIGS. 1 and 2.

As shown in FIG. 1, the surface morphologies of the catalysts prepared in Examples 1 and 2 were not observed even after introducing the metal onto the surface of the corrugated graphene.

Further, as shown in FIG. 2, the graphene doped with nitrogen prepared in Comparative Example 1 was able to observe the surface of graphene having many holes and defects, and no metal particles were observed .

Further, no metal particles were observed on the surface of the catalyst for oxygen reduction reaction containing graphene doped with nitrogen in which cobalt (II) acetylacetonate prepared in Example 1 was coordinated. It was confirmed that the cobalt metal was coordinated with graphene at the molecular level rather than the nanoparticle form.

Experimental Example 2 X-ray diffraction analysis

In order to confirm the morphology of the oxygen reduction catalyst according to the present invention, the catalyst for oxygen reduction reaction prepared in Examples 1 and 2 and the graphene doped with nitrogen prepared in Comparative Example 1 were subjected to X-ray diffraction Analysis (XRD), and the results are shown in FIG.

XRD analysis is an analytical method that traditionally identifies the structure of intrinsic metal particles, and a very sharp peak is observed even with small amounts of uniform nanoparticles.

As shown in FIG. 3, not only the graphene doped with nitrogen prepared in Comparative Example 1 but also the catalysts for oxygen reduction reaction prepared in Examples 1 and 2 were found to have broad broad peak And it can be confirmed that no cobalt nanoparticles are present.

Example 3 Analysis of Linear Moving Voltage Curve (LSV)

In order to confirm the performance of the catalyst for oxygen reduction reaction according to the present invention, a linear movement voltage curve (LSV) analysis and stability experiment were performed using the catalysts prepared in Examples 1 and 2 and Comparative Examples 1 to 3 The results are shown in FIGS. 4 and 5. FIG.

As shown in FIG. 4, it can be confirmed that the performance of the oxygen reduction catalyst according to the present invention is very excellent.

Although the performance may be slightly lower than that of the Pt / C catalyst, which is a commercially available catalyst, it exhibits the highest performance among the cobalt-based catalyst systems.

Further, as shown in FIG. 5, it was confirmed that the stability of the catalyst for oxygen reduction reaction according to the present invention was also excellent.

As described above, the catalyst for oxygen reduction reaction according to the present invention has an effect of exhibiting excellent oxygen reduction reaction activity. In particular, since the conventional iron and cobalt-based catalyst systems undergo heat treatment at a high temperature as well as conventional noble metal catalysts such as platinum, the catalyst of the present invention can be synthesized through a solution process at room temperature, It is possible to secure low price and fairness.

Claims (8)

1. A catalyst for oxygen reduction reaction comprising cobalt-doped graphene complexed with a complex represented by the following formula (1) and not containing cobalt nano-particles:

&Lt; Formula 1 >

(Wherein R _1, R ₂ and R ₃ are each independently a C ₁ to C ₂ alkyl substituted by hydrogen or C ₁ to C ₂ alkyl, or one or more F.).
delete delete Preparing nitrogen-doped graphene (step 1); And
A method for preparing a catalyst according to claim 1, comprising mixing graphene and cobalt doped with nitrogen prepared in step 1 above at a room temperature (step 2) with a complex represented by the following formula 1:

&Lt; Formula 1 >

(Wherein R _1, R ₂ and R ₃ are each independently a C ₁ to C ₂ alkyl substituted by hydrogen or C ₁ to C ₂ alkyl, or one or more F.).
5. The method of claim 4,
Wherein the complex of step 2 is mixed with 0.01 mmol to 10 mmol based on 30 mg of graphene doped with nitrogen.
5. The method of claim 4,
Wherein the mixing of step 2 is carried out at a temperature of from 10 캜 to 35 캜 for from 3 hours to 48 hours.
5. The method of claim 4,
The mixing of step 2 may be carried out in a solvent such as N, N-dimethylformamide (DMF), acetone, N-methylpyrrolidone (NMP), diethylether, Wherein at least one organic solvent selected from the group consisting of ethanol and ethanol is used.
1. A negative electrode material composition for a fuel cell or a lithium air cell which contains cobalt-doped graphene complexed with a complex represented by the following Chemical Formula 1 and does not contain cobalt nano-particles:

&Lt; Formula 1 >

(Wherein R _1, R ₂ and R ₃ are each independently a C ₁ to C ₂ alkyl substituted by hydrogen or C ₁ to C ₂ alkyl, or one or more F.).

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