KR102158638B1 - Method for preparing two-dimensional vanadium carbide for hydrogen-generating catalyst electrode - Google Patents

Abstract

The present invention relates to a method for producing a two-dimensional vanadium carbide for an electrochemical catalyst electrode used to generate hydrogen, and to a catalyst electrode including the two-dimensional vanadium carbide.

Description

Method for preparing two-dimensional vanadium carbide for hydrogen-generating catalyst electrode

The present invention relates to a method for producing a two-dimensional vanadium carbide for an electrochemical catalyst electrode used to generate hydrogen, and to a catalyst electrode including the two-dimensional vanadium carbide.

As a two-dimensional material similar to graphene, MXene is formed from a layered MAX phase material. The MAX phase material is a crystalline substance in which MX of semi-ceramic properties and M and other metal elements A are combined, M is a transition metal, A is a group 13 or 14 element, and X is carbon and/or nitrogen.

Mexine has excellent physical properties such as electrical conductivity, chemical resistance, and processability, and thus is applied to the electrode field, but has a limitation in terms of electrical properties along with thinning.

Meanwhile, technologies for producing hydrogen energy as alternative energy for fossil fuels are actively researched and developed in various ways. As an example, there is an electrolysis method using water. However, in the process for generating hydrogen, high temperatures and voltages are required or energy efficiency is poor, making it difficult to commercialize them. Among them, an organic or inorganic catalyst is used as an electrochemical catalyst electrode applied to an electrode for generating hydrogen, but the efficiency is poor and it is insufficient to achieve stable performance for a long time.

Accordingly, there is a need for research on a material that can be applied to an electrochemical catalyst for hydrogen generation that has improved efficiency and can secure durability and stability.

An object of the present invention is to provide a method for producing phosphorus-doped vanadium carbide having a two-dimensional layered structure.

Another object of the present invention is to provide a catalyst electrode having excellent hydrogen generation efficiency and improved durability by applying phosphorus-doped two-dimensional vanadium carbide to a hydrogen generation catalyst.

In order to achieve the above object, one aspect of the present invention,

V ₂ C mexin production step from V ₂ AlC,

Heat-treating the mixture of the V ₂ C mexine and triphenylphosphine, and

Acid treatment of the heat-treated product

It is to provide a method for producing a two-dimensional vanadium carbide doped with phosphorus containing.

In the method for producing phosphorus-doped vanadium carbide according to an embodiment of the present invention, the heat treatment may be performed at 300°C to 800°C.

In the method for producing phosphorus-doped vanadium carbide according to an embodiment of the present invention, the step of heat-treating may include raising the temperature to a heat treatment temperature range of 2° C./min to 20° C./min.

In the method for producing phosphorus-doped vanadium carbide according to an embodiment of the present invention, the mixture may include 1 to 100 parts by weight of triphenylphosphine based on 100 parts by weight of V ₂ C mexine.

In the method for producing phosphorus-doped vanadium carbide according to an embodiment of the present invention, the V ₂ C mexine production step may include removing Al with a strong acid containing a fluorine atom and then reducing it using a reducing agent. have.

In the method for producing phosphorus-doped vanadium carbide according to an embodiment of the present invention, the reducing agent may include an alkali metal and an amine or ammonia.

In the method for producing phosphorus-doped vanadium carbide according to an embodiment of the present invention, the acid treatment step is carried out using at least one selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and chloride sulfonic acid. Can be.

Another aspect of the present invention is prepared by the above-described manufacturing method and includes a two-dimensional layered vanadium carbide doped with 3 to 15 at.% phosphorus, and an overvoltage of 50 mV to 300 mV based on a current density of 10 mA/cm ² It is to provide a catalytic electrode including vanadium carbide doped with phosphorus having a power consumption of 3W or less.

The catalyst electrode according to an embodiment of the present invention may be for a hydrogen generating electrode.

The present invention implements excellent performance as an electrochemical catalyst electrode, and has an effect of producing a vanadium carbide of a two-dimensional structure doped with phosphorus, which realizes improved electrical properties including high capacitance due to excellent phosphorus doping efficiency.

In addition, the present invention has the advantage of providing a hydrogen generation electrochemical catalyst electrode that has low power consumption, can maximize efficiency, has excellent durability, and can secure long-term performance stability.

1 shows the XRD analysis results of vanadium carbide doped with phosphorus (P) according to Example 1.
FIG. 2 shows a TEM photograph of vanadium carbide doped with phosphorus (P) according to Example 1. FIG.
Figure 3 shows the Tafel slope according to the hydrogen generation reaction of the catalyst electrode made of vanadium carbide of Examples 1 to 2 and Comparative Example 1.
Figure 4 shows the results of the durability test according to the hydrogen generation reaction of the catalyst electrode made of vanadium carbide of Example 1.

Hereinafter, a method for producing phosphorus-doped vanadium carbide having a two-dimensional structure and a catalyst electrode including phosphorus-doped vanadium carbide having a two-dimensional structure of the present invention will be described in detail with reference to the accompanying drawings. The present invention can be better understood by the following examples. The following examples are for illustrative purposes of the present invention, and are not intended to limit the scope of protection defined by the appended claims. In this case, the technical terms and scientific terms used have meanings commonly understood by those of ordinary skill in the technical field to which this invention belongs, unless otherwise defined.

The inventors of the present invention to prepare a meksin (MXene) of V ₂ C from among, V ₂ AlC of the MAX phase (phase) was conducted research on the possible materials applied as a hydrogen-producing electrochemical catalyst, it triphenylphosphine In spite of low power consumption when applied to the catalytic electrode by maintaining a two-dimensional layered structure on the MAX, while enabling efficient phosphorus doping through a simple process by using the ignition reaction, it not only shows high reaction efficiency, but also has improved electrical characteristics and excellent durability. The present invention was completed by finding that stable performance for a long period of time can be implemented.

Specifically, the method for producing vanadium carbide of a two-dimensional structure doped with phosphorus according to an aspect of the present invention,

V ₂ C mexin production step from V ₂ AlC,

Heat-treating the mixture of the V ₂ C mexine and triphenylphosphine, and

Acid treatment of the heat-treated product

Includes.

According to an aspect of the present invention, the V ₂ C mexine production step is a step of selectively removing Al from V ₂ AlC in the MAX phase.

The MAX phase is a crystalline structure that is a combination of M, a transition metal, and A of X and Group 13 or 14 elements of carbon or nitrogen.Unlike two-dimensional materials such as graphite, there is a weak chemical between the A element and the transition metal M between the transition metal carbide layers. It is laminated with metal bonds.

In the present invention, a vanadium carbide having a target phosphorus-doped two-dimensional structure is prepared by using V ₂ C mexine (MAXene) prepared by selectively removing Al using V ₂ AlC on MAX. V ₂ C Mexine is characterized by having a layered structure on a plane like graphene.

According to an aspect of the present invention, the method of removing Al from V ₂ AlC on the MAX may be used without limitation as long as vanadium carbide (V ₂ C) can maintain a two-dimensional structure after the process.

In one aspect, the V ₂ AlC on MAX may be treated with an acid capable of reacting with Al to remove the aluminum atomic layer from the V ₂ AlC by etching. At this time, the acid may be an organic acid or an inorganic acid. Specifically, a strong acid containing a fluorine atom, for example, hydrofluoric acid (HF) may be used, but is not limited thereto. In addition, it may be used as an etching solution for removing aluminum by mixing hydrochloric acid, sulfuric acid, nitric acid, or a mixture thereof.

The process of removing Al from the V ₂ AlC may be performed at 20° C. to 400° C., specifically 25 to 200° C., and more specifically 30 to 100° C., but is not limited thereto.

When the removal of aluminum using an acid from V ₂ AlC is completed, vanadium carbide (V ₂ C) having a two-dimensional structure from which aluminum is removed through centrifugation or filtration and drying is obtained. At this time, the obtained vanadium carbide (V ₂ C) may contain functional groups such as oxide, epoxide, hydroxide, and fluoride on the surface of the vanadium due to the acid treatment performed in the aluminum removal step. Accordingly, a reduction process for removing a functional group may be additionally performed, and the reduction process may be performed as a chemical or thermal reduction process.

One aspect of the reduction process may be performed using a reducing agent. The reducing agent may be a mixture of an alkali metal and an amine or ammonia, but is not limited thereto. At this time, the alkali metal may be any one or more selected from lithium, sodium, and potassium, and the amine may be ethylenediamine, methylamine, diisopropylamine, or the like, but is limited thereto. It is not.

The product obtained by the reduction process may be neutralized using hydrochloric acid or the like, and washed, filtered and dried using ethanol.

From V ₂ AlC Al it is selectively removed by the vanadium carbide of V ₂ C MEC worn obtained may be a single crystal layer of the two-dimensional layered structure stacked with a plurality of interlayer bonding can be bonded to the van der Waals forces.

The particle size of the V ₂ C mexin is not limited, but may be 0.1 μm to 100 μm, specifically 0.2 μm to 50 μm, and more specifically 0.5 μm to 20 μm. It has an advantageous effect in achieving the objective within the above range, but this is only a non-limiting example and is not limited to the above numerical range.

Next, a step of preparing a solid mixture of the V ₂ C mexine and triphenylphosphine is performed.

The step of preparing the solid mixture is a step of preparing a solid mixture by mixing with triphenylphosphine capable of inducing a phosphorylation reaction in order to dope phosphorus into V ₂ C mexine.

The triphenylphosphine is decomposed into hydrogen phosphide (PH ₃ ) at a high temperature, which induces a phosphorylation reaction at a certain reaction temperature, thereby having an advantageous effect in doping V ₂ C mexin with phosphorus. V ₂ C Mexine vanadium carbide formed by the combination of vanadium and phosphorus on the surface of mexine is doped with phosphorus while maintaining a two-dimensional layered structure, so it is an electrochemical catalyst that can secure high efficiency, excellent electrical properties, as well as durability and long-term performance stability. It is more effective in terms of.

According to one aspect of the present invention, the content of triphenylphosphine is not significantly limited within a range that does not impair the object of the present invention, but 1 to 100 parts by weight based on 100 parts by weight of V ₂ C mexin in the solid mixture Parts, specifically 5 to 90 parts by weight, more specifically 10 to 80 parts by weight may be included. It is effective in that the phosphorus induction reaction is performed efficiently in the above range, and phosphorus doping efficiency can be increased.

Next, a step of heat-treating the prepared solid mixture is performed.

The heat treatment step is a process of controlling the heating temperature range of the mixture for phosphorus doping and inducing a phosphorylation reaction through it, and may be performed at 300°C to 800°C, specifically 400°C to 700°C. In the above range, it is effective in terms of decomposition of triphenylphosphine and the efficiency of phosphorus doping V ₂ C mexine.

In addition, the heat treatment process may be performed within a temperature increase rate range of 2° C./min to 20° C./min, specifically 5° C./min to 15° C./min. In the above range, phosphorus-doped vanadium carbide capable of securing high-efficiency phosphorus doping and structural stability at the same time can be obtained, which is effective, but this is only a non-limiting example and is not limited to the numerical range.

After the heat treatment step, a step of acid treatment is performed on the heat treated product.

The acid treatment step is a step of removing unreacted substances or foreign substances contained in the product obtained in the heat treatment step.

According to an aspect of the present invention, the acid treatment material used for the acid treatment may be used without limitation as long as it removes unreacted substances or foreign substances including triphenylphosphine. Specifically, any one or more selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and chlorinated sulfonic acid may be mentioned. More specifically, hydrochloric acid may be used, and in this case, hydrochloric acid having a concentration of 1 to 10% by weight may be used, but is not limited thereto.

Thereafter, filtration, washing and drying are performed using a solvent to obtain a vanadium carbide having a final phosphorus-doped two-dimensional structure.

Ethanol may be used as the solvent, but is not limited thereto. Further, drying may be carried out under vacuum using a vacuum oven.

Another aspect of the present invention is to provide a catalytic electrode including vanadium carbide having a two-dimensional structure doped with phosphorus prepared by the above-described manufacturing method.

The catalyst electrode according to an aspect of the present invention may have an overvoltage of 50 mV to 300 mV based on a current density of 10 mA/cm 2. In addition, the power consumption may be 3 W or less, specifically 0.5W to 3W. This has the effect of realizing excellent catalytic efficiency even at a low voltage and maximizing hydrogen generation efficiency despite low power consumption.

According to an aspect of the present invention, the catalytic electrode may be manufactured by a known method using a composition for forming an electrode layer including phosphorus-doped two-dimensional vanadium carbide and an organic solvent. In one embodiment, after adding phosphorus-doped vanadium carbide to Nafion-dispersed ethanol, dispersing it using an ultrasonic disperser, and coating a mixture of the dispersed vanadium carbide and Nafion on the graphite electrode, It may be manufactured by drying, but is not necessarily limited thereto.

According to an aspect of the present invention, the vanadium carbide of a two-dimensional structure doped with phosphorus in the catalyst electrode may have a total phosphorus content of 3 to 15 at.%, specifically 4 to 12 at.%. In the above range, although it is more preferred because it has characteristics that can maximize the efficiency of the catalyst electrode and secure durability and stability, it is not necessarily limited thereto.

In addition, the vanadium carbide may have a 0002 peak ( c- lattice parameter; c-LP) according to XRD analysis of 18Å to 22Å, specifically 19Å to 21Å, and more specifically 20Å to 21Å.

The catalytic electrode may be used as an electrode for generating hydrogen, but is not limited thereto.

In another aspect of the present invention, an electrode material including vanadium carbide having a two-dimensional structure doped with phosphorus is provided. This is highly utilized for various materials such as electrochemical energy devices, and may be specifically used for fuel cells or secondary cells, but is not limited thereto.

Hereinafter, a method for producing a phosphorus-doped two-dimensional vanadium carbide according to the present invention, a phosphorus-doped two-dimensional vanadium carbide produced therefrom, and a catalyst electrode including the same will be described in more detail through the following examples. However, the following examples are only one reference for describing the present invention in detail, and the present invention is not limited thereto, and may be implemented in various forms.

(Example 1)

2 g of vanadium metal powder (V, ALFA ASEAR), 1.1 g of aluminum metal powder (Al, ALFA ASEAR), and 1 g of graphite (Graphite, 325 mesh, BAY CARBON) were mixed for 24 hours using a ball mill. The mixture was put in an alumina boat, heated to 1600° C. at 10° C./min under an argon (Ar) gas atmosphere, sintered at 1600° C. for 5 hours, and then powdered by ball milling. 100 ml of 50 wt% HF was added to ₂ g of the synthesized MAX phase V ₂ AlC and stirred at room temperature for 72 hours, and then the obtained product was put in distilled water, centrifuged, filtered, and dried. Thereafter, 1 g of the dried product was mixed with 0.1 g of lithium (Li) metal and 10 ml of ethylenediamine, followed by reaction under a nitrogen atmosphere at 80° C., and the obtained product was neutralized with 500 ml of 5 wt% HCl. Next, the resulting product was washed and filtered using ethanol, and then dried in a vacuum oven at 100° C. for 48 hours to obtain V ₂ C mexine (FIG. 1).

200 mg of the obtained V ₂ C mexin was directly mixed with 200 mg of triphenylphosphine in a nitrogen atmosphere to prepare a solid mixture, which was heated to 500° C. over 1 hour at a heating rate of 8° C./min and reacted at 500° C. for 1 hour Made it.

After the reaction was completed, the solid powder was filtered using ethanol, treated with 1wt% hydrochloric acid (HCl), washed with ethanol, and dried under vacuum at 80°C to prepare phosphorus-doped vanadium carbide. The prepared phosphorus-doped vanadium carbide had a phosphorus doping content of 3.83 at.% as measured by photoelectron spectroscopy (XPS).

In order to confirm the crystallinity of the prepared phosphorus-doped vanadium carbide, an XRD (X-Ray Diffractometer) analysis was performed using a smart lab of RIGAKU using an X-ray diffraction pattern. Analysis conditions were driven at 40 kV and 200 mA, each of which was measured by 0.02° at a rate of 2°/min in the range of 3 to 50°, and data was extracted with the PDXL program. As a result, the c -lattice parameter ( c -LP) was 20.88 Å. This corresponds to the diffraction peak at 8.48°, and it was confirmed that the vanadium carbide (V ₂ C) due to phosphorus doping had a wider interlayer distance while maintaining a two-dimensional layered structure.

In addition, as shown in FIG. 2, a structure in which plate-like structures are stacked in layers was confirmed, and it was confirmed that the layered structure of the two-dimensional structure was maintained even after phosphorus was doped.

(Example 2)

In Example 1, it was carried out in the same manner as in Example 1, except that the heat treatment temperature and the heating rate of the obtained solid mixture of V ₂ C mexine and triphenylphosphine were changed to 400°C and 6°C/min, respectively. Phosphorus-doped vanadium carbide was prepared. The prepared phosphorus-doped vanadium carbide had a phosphorus doping content of 4.05 at.% as measured by photoelectron spectroscopy (XPS).

(Comparative Example 1)

100 ml of 50 wt% HF was added to ₂ g of MAX phase V ₂ AlC synthesized in Example 1 and stirred at room temperature for 72 hours, and the obtained product was put in distilled water, centrifuged, filtered, and dried. Thereafter, 1 g of the dried product was mixed with 0.1 g of lithium (Li) metal and 10 ml of ethylenediamine, followed by reaction under a nitrogen atmosphere at 80° C., and the obtained product was neutralized with 500 ml of 5 wt% HCl. Next, the resultant was washed and filtered using ethanol, and then dried in a vacuum oven at 100° C. for 48 hours to obtain V ₂ C mexine. The obtained V ₂ C mexine was used as it was without any separate treatment.

(evaluation)

(1) electrode characteristics

The efficiency of the hydrogen generation catalyst electrode was tested through water electrolysis. To this end, a CHI 660c electrochemical analysis device was used, and as an electrode attachment device, a rotating disk electrode device was used to perform the analysis at 1600 rpm. As a working electrode, vanadium carbide prepared in Examples and Comparative Examples was added to ethanol (1 mL) containing 5% by weight of Nafion to prepare an electrode slurry, and then the electrode slurry was coated on glass carbon. What formed the catalyst layer (thickness 10 micrometers) was used. Ag/AgCl in 3M KCl was used as a reference electrode. A graphite plate was used as a counter electrode. In addition, 0.5 MH ₂ SO ₄ was used as an electrolyte in the case of the hydrogen generation catalyst characteristic analysis. The analysis was conducted after activation of the electrode by performing the cyclic current method 20 or more times.

(2) Characterization of catalyst electrode

Using the above prepared hydrogen generation catalyst electrode, the electrode characteristics were analyzed using a linear scan voltammetry (LSV) for water electrolysis in a 0.5 M aqueous sulfuric acid solution. As a result, the overvoltage under the condition that the current density according to the voltage of the hydrogen generation catalyst electrode is 10 mA·cm 2 is shown in Table 1 below. As shown in Table 1 below, the examples showed a lower overvoltage than the comparative examples, and it was confirmed that hydrogen generation efficiency can be remarkably improved through excellent catalytic efficiency even at a low voltage.

division Example 1 Example 2 Comparative Example 1 Overvoltage (mV) of the hydrogen generation catalyst electrode 157 250 779

3 shows the Tafel slope according to the hydrogen generation reaction, and it was found that the examples require a lower voltage for hydrogen production compared to the comparative example. In the case of Example 1, the voltage required to reach the hydrogen production was 74 mV/dec, and in the case of Example 2, it was 85 mV/dec, and in the case of Comparative Example 1, it could be reduced by up to 60.4% compared to 187 mV/dec. . This shows that efficiency can be maximized with low power consumption.

In addition, Figure 4 is a durability test of the catalyst electrode according to Example 1 according to the hydrogen generation reaction, it was confirmed that the performance did not change even after 1400 cycles.

As can be seen from the above, it was confirmed that the hydrogen generation catalyst electrode according to an aspect of the present invention exhibited excellent efficiency in terms of hydrogen generation, and also exhibited excellent durability characteristics. In addition, since the phosphorus doping efficiency is about 2 to 15 at.%, it is possible to secure a capacitance of 70 mF/cm ² or more, so that it can be applied to various fields including energy storage electrodes.

Although a preferred embodiment of the present invention has been described above, it is clear that the present invention can use various changes, modifications, and equivalents, and that the above embodiment can be appropriately modified and applied in the same manner. Therefore, the above description does not limit the scope of the present invention determined by the limits of the following claims.

Claims (10)

V ₂ C mexin production step from V ₂ AlC,
Heat-treating the mixture of the V ₂ C mexine and triphenylphosphine, and
Acid treatment of the heat-treated product
Phosphorus-doped two-dimensional vanadium carbide manufacturing method comprising a. The method of claim 1,
The heat treatment step is carried out at 300 ℃ to 800 ℃ method for producing a two-dimensional vanadium carbide doped with phosphorus. The method of claim 1,
The step of heat-treating comprises raising the temperature at a heating rate of 2° C./min to 20° C./min up to a heat treatment temperature range, and a method for producing phosphorus-doped vanadium carbide having a two-dimensional structure. The method of claim 1,
The mixture comprises 1 to 100 parts by weight of triphenylphosphine based on 100 parts by weight of V ₂ C mexine. A method for producing a two-dimensional vanadium carbide doped with phosphorus. The method of claim 1,
The V ₂ C mexine production step is a method for producing phosphorus-doped two-dimensional vanadium carbide comprising removing Al with a strong acid containing a fluorine atom and then reducing it using a reducing agent. The method of claim 5,
The reducing agent is a method of producing a two-dimensional vanadium carbide doped with phosphorus containing an alkali metal and an amine or ammonia. The method of claim 1,
The acid treatment step is carried out using at least one selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid and chlorinated sulfonic acid. The method for producing phosphorus-doped two-dimensional vanadium carbide. A catalyst electrode having a two-dimensional layered structure, containing vanadium carbide doped with 3 to 15 at.% phosphorus, and having an overvoltage of 50 mV to 300 mV and power consumption of 3 W or less based on a current density of 10 mA/cm ² . The method of claim 8,
The phosphorus-doped two-dimensional vanadium carbide has a 0002 peak (c-LP) according to XRD analysis of 18 Å to 22 Å. The method of claim 8,
The catalyst electrode is a catalyst electrode for a hydrogen generating electrode.

Images