KR102569309B1 - Fe-N-C TYPE ELECTRODE CATALYST USING RADICAL SCAVENGER AND METHOD FOR MANUFACTURING THE SAME - Google Patents

Abstract

The present invention is a Fe-NC-based electrocatalyst using a radical scavenger capable of mitigating the performance degradation of the catalyst by removing active oxygen species in the form of radicals generated as by-products during an oxygen reduction reaction (ORR), and a method for manufacturing the same start about
An Fe—NC-based electrocatalyst using a radical scavenger according to the present invention includes a carbon-based catalyst structure; and a radical scavenger coupled to the surface of the carbon-based catalyst structure, wherein the carbon-based catalyst structure includes a carbon support layer; It is characterized in that it comprises; Fe—N _x active sites dispersed on the carbon support layer.

Description

Fe-N-C-based electrode catalyst using a radical scavenger and its manufacturing method

The present invention relates to a Fe—N—C based electrocatalyst using a radical scavenger and a method for preparing the same.

A polymer electrolyte fuel cell (PEMFC) is a next-generation high-efficiency energy conversion device. In the polymer electrolyte fuel cell, an oxidation of fuel and hydrogen occurs at the anode electrode and a reduction reaction of oxygen occurs at the cathode electrode, resulting in a voltage difference between the two electrodes, thereby generating electricity. At the center of such fuel cell technology, development of a catalyst capable of overcoming a high activation barrier of an oxygen reduction reaction (ORR) remains a major challenge. A polymer electrolyte fuel cell typically uses platinum (Pt) for a cathode electrode. However, since platinum reserves are small and expensive, it acts as a major obstacle to popularization of fuel cells.

The Me(Fe, Co)-N-C catalyst, emerging as a next-generation catalyst to replace platinum, is reported to have relatively good performance in the oxygen reduction reaction in fuel cells.

In this regard, Korean Patent Publication No. 10-2018-0013499 (published on February 7, 2018) discloses a carbon support and a porphyrin-based Fe-N-C electrocatalyst including a carbon layer.

Recently, prior to market entry and popularization of these non-noble metal catalysts, stability as well as performance of the catalysts is a very important part. In an acid electrolyte condition of a general polymer electrolyte fuel cell, the stability of the Fe—NC catalyst is lower than that in a basic electrolyte condition. Dissolution of iron and oxidation of carbon layer have been suggested as causes of deterioration of non-noble metal catalysts under acid electrolyte conditions. In addition, hydroxyl radicals generated when hydrogen peroxide, a by-product generated during the oxygen reduction reaction (ORR), reacts with iron (Fe ²⁺ ) of the Fe-NC catalyst may also act as a cause of deterioration. Hydroxyl radicals are generated in close proximity to the catalyst surface. Accordingly, the hydroxyl radical directly attacks the carbon layer of the catalyst, resulting in oxidation of the carbon layer.

As such, hydroxyl radicals act as a cause of catastrophic catalyst deterioration. Therefore, the hydroxyl radical is a factor to be overcome in improving the stability of Fe—N—C catalysts.

An object of the present invention is to provide a Fe-N-C-based electrocatalyst in which a radical scavenger is coupled to an Fe-N-C-based catalyst structure in order to secure catalyst stability.

In addition, an object of the present invention is to provide a method for preparing an Fe—N—C based electrocatalyst that removes active oxygen species generated in an oxygen reduction reaction (ORR).

In the present invention, an Fe—NC-based electrocatalyst including a carbon-based catalyst structure is provided. To this end, the carbon-based catalyst structure includes a carbon support layer and Fe—N _x active sites dispersed on the carbon support layer.

In addition, the present invention provides an Fe-N-C based electrocatalyst including a radical scavenger bonded to the surface of a carbon-based catalyst structure. For this purpose, the radical scavenger is an aromatic compound containing a condensed ring. In addition, the condensed ring is substituted with at least one functional group selected from a ketone group and a hydroxyl group.

In the present invention, (a) preparing a carbon-based catalyst structure so that the Fe—N _x active sites on the carbon support layer are dispersed; (b) mixing a first solution in which the carbon-based catalyst structure is dispersed in an organic solvent and a second solution in which a radical scavenger is dissolved in an organic solvent, and performing ultrasonic treatment; (c) washing after filtering the sonicated solution; and (d) drying the washed product to prepare an Fe-NC-based electrocatalyst, wherein in step (b), a radical scavenger is bonded to the surface of the carbon-based catalyst structure. A method for preparing a based electrocatalyst is provided.

The Fe-N-C electrocatalyst according to the present invention is a tandem catalyst in which a radical scavenger, an antioxidant, is bonded to a carbon-based catalyst structure through a π-π bond.

Through the radical scavenger, the Fe-N-C-based electrocatalyst can remove radical-type active oxygen species generated as by-products during an oxygen reduction reaction (ORR).

Therefore, the Fe—N—C based electrocatalyst can improve catalyst stability by minimizing degradation of catalyst performance. In addition, the Fe—N—C based electrode catalyst can exhibit excellent durability when applied to a fuel cell. In addition, the Fe-N-C-based electrocatalyst can be used as a high-performance non-noble metal-based catalyst that can replace the platinum catalyst.

1 is a two-dimensional schematic diagram of an Fe-NC-based electrocatalyst in which anthraquinone is bonded in a π-π bond to a Fe-NC catalyst structure according to the present invention.
2 is a flow chart showing a method for preparing an Fe—NC-based electrocatalyst according to the present invention.
Figure 3 shows the Fe-NC electrocatalyst to which the radical scavenger is applied in the present invention (parts by weight of the aromatic compound: parts by weight of the Fe-NC electrocatalyst = 3: 100) and the original without combining the radical scavenger It is a graph showing the amount of activity reduction of Fe-NC catalysts before and after water treatment.
Figure 4 shows the Fe-NC electrocatalyst to which the radical scavenger is applied in the present invention (parts by weight of the aromatic compound: parts by weight of the Fe-NC catalyst = 10: 100) and the original Fe without the radical scavenger - This is a graph showing the amount of activity reduction before and after overwater treatment of the NC catalyst.

Advantages and features of the present invention, and methods of achieving them, will become clear with reference to the detailed description of the following embodiments taken in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various different forms, only these embodiments make the disclosure of the present invention complete, and common knowledge in the art to which the present invention belongs. It is provided to fully inform the holder of the scope of the invention, and the present invention is only defined by the scope of the claims. Like reference numbers designate like elements throughout the specification.

Hereinafter, an Fe—N—C based electrocatalyst using a radical scavenger according to a preferred embodiment of the present invention and a manufacturing method thereof will be described in detail with reference to the accompanying drawings.

The Fe-N-C-based electrode catalyst using a radical scavenger according to the present invention is a tandem catalyst in which an organic radical scavenger is coupled to a Fe-N-C-based catalyst structure. Here, the tandem catalyst is a catalyst in which two or more different catalysts are combined in a one-pot reaction. The tandem catalyst is characterized in that several types of catalysts can be used in a single molecule.

The Fe-N-C-based electrocatalyst can remove active oxygen species in the form of radicals generated as by-products during the oxygen reduction reaction through a radical scavenger. Therefore, it is possible to mitigate performance degradation of the Fe-N-C-based electrode catalyst and secure stability of the electrode catalyst.

The Fe—N—C based electrocatalyst using a radical scavenger according to the present invention includes a carbon-based catalyst structure and a radical scavenger.

The carbon-based catalyst structure includes a carbon support layer. The carbon support layer includes at least one of carbon black, graphene, carbon nanotubes, carbon nanofibers, reduced graphene oxide (rGO), and a metal organic framework (MOF). Here, the metal-organic framework forms a highly crystalline porous network in which metals are bridged through organic ligands. In addition, since the metal-organic framework has a nano-sized pore structure, it has a large surface area.

The carbon-based catalyst structure includes Fe—N _x active sites dispersed on the carbon support layer. The active site formed by the transition metal (M)-N _x coordination provides stability to the catalyst and serves to increase the activity of the catalyst. Here, x is the coordination number and means the number of coordination bonds between the metal cation and the ligand. The ligand is a substance that provides a pair of electrons to the central metal ion to form a coordination bond.

The radical scavenger is bound to the surface of the carbon-based catalyst structure. The radical scavenger serves to stabilize the catalyst by removing active oxygen species generated from the reaction of iron and hydrogen peroxide during the oxygen reduction reaction.

The radical scavenger is an aromatic compound containing a condensed ring. The condensed ring has a ring-shaped structure in which two or more rings share two or more atoms. A radical scavenger having such a structure can form a π-π bond with the catalyst structure. Although the strength of π-π bonds is relatively weak, considerable strength can be achieved by forming sufficient amounts of π-π bonds. The π-π bond forms a structure in which planar aromatic groups are stacked flat, facing each other. The radical scavenger reacts with radicals to remove the radicals and at the same time stabilize the radicals. To this end, the condensed ring is preferably substituted with at least one functional group selected from a ketone group and a hydroxyl group. Specifically, the condensed ring has a ketone group at the C9 or/and C10 position. And, the phenyl group is substituted with an additional functional group capable of reacting with a radical. The hydroxy group may react with the radical to stabilize the radical through electron and H ⁺ transfer (electron transfer-proton transfer) or donation of hydrogen atom from the hydroxy group to the radical. This means that the activity of the radical scavenger may vary depending on the position of the hydroxyl group and the number of functional groups.

Aromatic compounds containing the condensed ring include, for example, Alizarin, Purpurin, Quinalizarin, anthraflavic acid, anthraquinone, (+)-catechin ((+)-catechin), 1,8-dihydroxyanthraquinone, 1-hydroxyanthra-9,10-quinone, hydroquinone ( It may be anthraquinone derivatives including hydroquinone), pyrocatechol, and the like. In addition, the aromatic compound including the condensed ring may be, for example, a flavonoid-based material including baicalein and quercetin. Some of the aromatic compounds containing the condensed ring are shown in [Compounds].

[compound]

The reactive oxygen species include hydroxyl radicals, superoxide radicals, hydroperoxyl radicals, and the like.

The content of the radical scavenger according to the present invention is preferably 1 to 10 parts by weight based on 100 parts by weight of the catalyst structure. When the content is less than 1 part by weight, it may be difficult to secure the stability of the electrode catalyst. Conversely, when the content exceeds 10 parts by weight, the additional effect of improving stability may not be seen, and rather, the activity of the catalyst may be reduced.

As such, the radical scavenger may be bound to the surface of the catalyst structure in an amount ranging from 1 to 10 parts by weight to exhibit an effect of removing active oxygen species.

As shown in FIG. 1, an organic radical scavenger such as anthraquinone may be bonded to a portion of the surface of the catalyst structure in a π-π bond method.

2 is a flow chart showing a manufacturing method of an Fe-N-C-based electrocatalyst.

Referring to FIG. 2, the method for manufacturing an Fe-N-C-based electrocatalyst using a radical scavenger according to the present invention includes the step of preparing a carbon-based catalyst structure (S110), a first step in which the carbon-based catalyst structure is dispersed Mixing the solution and the second solution in which the radical scavenger is dispersed are treated with ultrasonic waves (S120), filtered and washed (S130), and dried to prepare an Fe—N—C-based electrocatalyst (S140). do.

Preparing a carbon-based catalyst structure (S110)

First, a carbon-based catalyst structure is prepared so that Fe—N _x active sites on the carbon support layer are dispersed.

A carbon (C) precursor, an iron (Fe) precursor, and a nitrogen (N) precursor are mixed.

The carbon precursor includes at least one of carbon black, graphene, carbon nanotube, carbon nanofiber, reduced graphene oxide (rGO), and metal organic framework (MOF). The iron precursor may include iron salts such as Iron(II) acetate, Iron(II) chloride, and Iron(II) sulfate. The nitrogen precursor may include at least one of a nitrogen-containing monomer and a nitrogen-containing polymer so as to form an iron-nitrogen ligand. For example, the nitrogen precursor may include 1,10-phenanthroline, polyaniline, polypyrrole, melamine, and the like.

Subsequently, the mixed product is heat treated at 800 to 1100 ° C. The mixed product is formed into a catalyst structure through heat treatment. The temperature of heat treatment is 800℃ If it is less than or exceeds 1100 °C, the formation of Fe-N _x active sites may not occur smoothly.

Mixing and ultrasonicating the first solution in which the carbon-based catalyst structure is dispersed and the second solution in which the radical scavenger is dispersed (S120)

Subsequently, a first solution in which the carbon-based catalyst structure is dispersed in an organic solvent is prepared. As the organic solvent, it is preferable to use a solvent having dispersibility with respect to the catalyst structure, such as ethanol or methanol. In addition, as the organic solvent, a solvent having low solubility in the catalyst structure is used.

Then, a second solution in which the radical scavenger is dissolved in an organic solvent is prepared. The organic solvent may be a solvent having solubility and dispersibility with respect to radical scavengers, such as ethanol and methanol.

The first solution and the second solution are mixed and ultrasonicated. Sonication is performed to exert a good dispersing effect. During the sonication process, the first solution and the second solution are sufficiently stirred. In this process, the radical scavenger is bonded to the surface of the catalyst structure in a π-π bond method.

Ultrasonic treatment may have a frequency greater than 1 kHz. Ultrasonic power may be 100 W or more. In the mixing process of the first solution and the second solution, it is preferable to mix 1 to 10 parts by weight of the radical scavenger with respect to 100 parts by weight of the catalyst structure. When the content of the radical scavenger is less than 1 part by weight, it may be difficult to secure the stability of the electrode catalyst. Conversely, when the content exceeds 10 parts by weight, the additional effect of improving stability may not be seen, and rather, the activity of the catalyst may be reduced.

Step of washing after filtering (S130)

Then, the sonicated solution is filtered and then washed. The filtering may be performed using a vacuum pump. The product remaining after filtering is a catalyst structure to which the radical scavenger is bound, and remains in the form of a powder.

The powdered product is washed 1 to 3 times with washing water such as ethanol, methanol, and distilled water.

Drying to prepare an Fe-N-C-based electrode catalyst (S140)

Subsequently, the washed product is dried to prepare an Fe—N—C based electrocatalyst.

As such, the Fe-N-C-based electrocatalyst using the radical scavenger according to the present invention has a structure in which the radical scavenger is bonded to the surface of the carbon-based catalyst structure in a π-π bond method. By using the radical scavenger, active oxygen species in the form of radicals that hinder the performance of the electrocatalyst can be removed. In addition, by using the radical scavenger, there is an effect of stabilizing the electrode catalyst. In addition, the Fe—N—C based electrode catalyst can secure excellent durability when applied to a fuel cell for a long period of time. Accordingly, the expensive platinum catalyst can be replaced with the Fe-N-C-based electrode catalyst.

As described above, a specific example of the Fe—N—C based electrode catalyst using a radical scavenger is as follows.

1. Preparation of Fe-N-C-based Electrocatalyst

Example

MOF-based Fe-NC catalyst structure samples were prepared. Iron(II) acetate (0.5wt%), 1,10-phenanthroline (19.9wt%), and zeolitic imidazolate framework (specified as Basolite Z1200-ZIF8) (79.6wt%) precursors were placed in a ZrO ₂ crucible, and 5 mm diameter zirconium Add 100 oxide balls. The container is sealed and pulverized by repeating a total of 4 cycles for 30 minutes at 400 rpm in a ball mill. After pulverization, the precursor mixture is heat-treated at 1050° C. for 1 hour in a nitrogen atmosphere in a furnace. The catalyst precursor contained 0.5 wt% of iron and the ratio of phenanthroline:ZIF-8 was 2:8. Then, the synthesized Fe-NC catalyst structure (denoted as FeNC-dry-0.5) was dispersed in methanol.

The method of combining the radical scavenger to be applied to the Fe-N-C catalyst structure in a π-π bond method is as follows.

The corresponding aromatic compound, acting as a radical scavenger, is dissolved in methanol. Methanol in which the radical scavenger is dissolved is mixed with the solution in which the Fe—N—C catalyst structure was previously dispersed. Depending on the radical scavenger content (3 parts by weight, 10 parts by weight), the weight part of the aromatic compound: the weight part of the Fe-N-C catalyst is 3: 100 or 10: 100, respectively. After sufficiently stirring the mixed solution, ultrasonic treatment is performed for about 30 minutes under conditions of a frequency of 40 kHz and an ultrasonic power of 300 W.

After that, the resultant was filtered using a vacuum pump and washed twice with methanol. One final wash was performed with DI water. The resulting catalyst powder was dried in an oven at 70° C. for 6 hours. Subsequently, the dried product was transferred to a vacuum oven and stored for 24 hours at 70° C. temperature condition.

In the same way, the radical scavenger was performed by type.

2. Physical property evaluation method and result

The activity of the catalyst for the oxygen reduction reaction was measured under the following conditions. 800μgcm ^-2 of catalyst was loaded on RDE (Rotating Disk Electrode) under 0.1M HClO ₄ conditions and adjusted to 900rpm and 10mV/s, and then LSV (Linear Sweep Voltammetry) graph was obtained to measure the amount of decrease in activity (change in activity) of the catalyst. .

For the purpose of measuring the antioxidant effect of the catalyst (including a radical scavenger), hydrogen peroxide, a source of radicals, was injected into 1 wt% of 0.1M HClO ₄ electrolyte. At this time, the temperature was maintained at 50 °C. The hydrogen peroxide treatment was performed for 2 hours. 3 and 4 are results showing all LSV graphs for the oxygen reduction reaction before and after hydrogen peroxide treatment. For comparison of the antioxidant effect, LSV graphs of the original Fe-NC catalyst (FeNC-dry-0.5) not bound to the radical scavenger before and after overwater treatment were obtained and the amount of reduction in activity of the catalyst was compared. The amount of decrease in activity (change in activity) was expressed as a ratio (percentage, %) of the current density at a specific potential (0.8V _RHE ) before and after the overwater treatment of the catalyst.

Figure 3 shows the Fe-N-C electrocatalyst to which the radical scavenger is applied in the present invention (parts by weight of the aromatic compound: parts by weight of the Fe-N-C electrocatalyst = 3:100) and the original without combining the radical scavenger It is a graph showing the decrease in activity of Fe-N-C catalyst (FeNC-dry-0.5) before and after overwater treatment.

A total of five radical scavengers were applied: anthraquinone, alizarin, purpurin, baicalin, and quercetin. When comparing the electrocatalyst with 3 parts by weight of radical scavenger and the existing FeNC-dry-0.5 catalyst, the electrocatalyst with radical scavenger showed a much smaller decrease in activity. This seems to mitigate the performance degradation of the catalyst because the radical scavenger removed the radicals generated on the catalyst surface and stabilized the radicals.

Figure 4 shows the Fe-N-C electrode catalyst to which the radical scavenger is applied in the present invention (parts by weight of the aromatic compound: parts by weight of the Fe-N-C catalyst = 10: 100) and the original Fe without the radical scavenger - This is a graph showing the amount of activity reduction before and after overwater treatment of the N-C catalyst (FeNC-dry-0.5).

A total of two radical scavengers, such as anthraquinone and alizarin, were applied. When comparing the electrocatalyst with 10 parts by weight of radical scavenger and the existing FeNC-dry-0.5 catalyst, the electrocatalyst with radical scavenger showed a much smaller decrease in activity. This seems to mitigate the performance degradation of the catalyst because the radical scavenger removed the radicals generated on the catalyst surface and stabilized the radicals.

The results of FIGS. 3 and 4 show that aromatic compounds, known as radical scavengers in the biological field, act as scavengers even when bound to the Fe-N-C catalyst surface, which is not a unit material, in an acidic electrolyte environment other than neutral pH. means to do

Therefore, through the Fe-NC-based electrocatalyst to which the radical scavenger of the present invention is applied, fruit trees generated as by-products during the oxygen reduction reaction and iron (Fe ²⁺ ) of the catalyst structure react with hydroxyl radicals, In addition, reactive oxygen species that may be additionally induced may be removed and the electrocatalyst may be stabilized. Accordingly, it is possible to overcome the performance degradation of the electrode catalyst. When the electrode catalyst is applied to a fuel cell for a long period of time, it seems that durability can be secured.

Although the embodiments of the present invention have been described with reference to the accompanying drawings, the present invention is not limited to the above embodiments and can be manufactured in various different forms, and those skilled in the art in the art to which the present invention belongs A person will understand that the present invention may be embodied in other specific forms without changing the technical spirit or essential features. Therefore, the embodiments described above should be understood as illustrative in all respects and not limiting.

Claims (7)

a carbon-based catalyst structure; and
A radical scavenger bonded to the surface of the carbon-based catalyst structure;
The carbon-based catalyst structure
a carbon support layer;
It includes; Fe—N _x active sites dispersed on the carbon support layer,
The radical scavenger is an aromatic compound containing a condensed ring,
The condensed ring is substituted with at least one functional group selected from a ketone group and a hydroxyl group.
Fe-NC-based electrode catalyst.
According to claim 1,
The carbon support layer includes at least one of carbon black, graphene, carbon nanotubes, carbon nanofibers, reduced graphene oxide (rGO), and a metal organic framework (MOF).
Fe-NC-based electrode catalyst.
(a) preparing a carbon-based catalyst structure so that Fe—N _x active sites on the carbon support layer are dispersed;
(b) mixing a first solution in which the carbon-based catalyst structure is dispersed in an organic solvent and a second solution in which a radical scavenger is dissolved in an organic solvent, and performing ultrasonic treatment;
(c) washing after filtering the sonicated solution; and
(d) preparing an Fe-NC-based electrocatalyst by drying the washed product;
In the step (b), a radical scavenger is bound to the surface of the carbon-based catalyst structure,
The radical scavenger is an aromatic compound containing a condensed ring,
The condensed ring is substituted with at least one functional group selected from a ketone group and a hydroxyl group.
Manufacturing method of Fe-NC-based electrocatalyst.
According to claim 3,
The (a) step of preparing a carbon-based catalyst structure so that the Fe—N _x active sites on the carbon support layer are dispersed,
(a1) mixing a carbon (C) precursor, an iron (Fe) precursor, and a nitrogen (N) precursor; and
(a2) heat-treating the mixed result at 800 to 1100 ° C; including,
Manufacturing method of Fe-NC-based electrocatalyst.
According to claim 4,
The carbon (C) precursor includes at least one of carbon black, graphene, carbon nanotubes, carbon nanofibers, rGO, and metal-organic frameworks (MOFs).
Manufacturing method of Fe-NC-based electrocatalyst.
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