KR20240010241A - Fabrication of porous carbonized wood framworks for electrocatalytic water splitting - Google Patents

Abstract

The water electrolysis catalyst according to the present invention includes carbonized wood; Nickel particles distributed on the carbonized wood; And a graphene layer electrically connecting the nickel particles.

Description

Water electrolysis catalyst containing porous carbonized wood and method for manufacturing the same {Fabrication of porous carbonized wood framworks for electrocatalytic water splitting}

The present invention relates to a water electrolysis catalyst comprising porous carbonized wood and a method for manufacturing the same.

As energy demand increases, there is a need to develop low-cost, high-efficiency alternative energy. Hydrogen has recently received the most attention as an alternative energy, and in order to continuously supply this hydrogen, the development of catalyst materials that generate hydrogen and oxygen by decomposing water through water electrolysis is being actively conducted.

Water electrolysis can be divided into a hydrogen evolution reaction (HER) that occurs at the cathode and an oxygen evolution reaction (OER) that occurs at the oxidation electrode.

In theory, water decomposition occurs when a voltage of 1.23 V is applied, but in actual decomposition reactions, decomposition occurs only when a voltage higher than 1.23 V is applied due to various factors. In this case, the additional voltage required for water decomposition is called overvoltage (overvoltage). It is called overpotential.

Currently known water electrolysis catalysts with the highest efficiency and lowest overvoltage are platinum or platinum group elements at the cathode and iridium oxide or ruthenium oxide at the oxygen electrode. Using these materials as a catalyst has the advantage of low overvoltage. However, since platinum or platinum group elements and noble metal oxides have very high unit costs, they have limitations that make them difficult to apply to mass production and commercialization of water electrolysis devices.

Accordingly, there is a need to develop a non-precious metal-based water electrolysis catalyst that has low production costs and high catalytic efficiency.

U.S. Patent Publication No. 2022-0002887 US Patent Publication No. 10815580

The purpose of the present invention is to provide a water electrolysis catalyst that is environmentally friendly, including wood, and has a low production cost.

The water electrolysis catalyst according to the present invention includes carbonized wood; Nickel particles distributed on the carbonized wood; And a graphene layer electrically connecting the nickel particles.

In the water electrolysis catalyst according to an embodiment of the present invention, the carbonized wood may be characterized by carbonizing plate-shaped wood cut perpendicular to the longitudinal direction.

The water electrolysis catalyst according to an embodiment of the present invention may be characterized in that the carbonized wood is heat-treated at 800 to 1200 ° C. for 30 to 300 minutes.

In the water electrolysis catalyst according to an embodiment of the present invention, the nickel particles may be manufactured through plating.

In the water electrolysis catalyst according to an embodiment of the present invention, the plating may be characterized as a step of applying a voltage of -0.9 to -1.2 V in a plating solution containing a nickel precursor.

In the water electrolysis catalyst according to an embodiment of the present invention, the nickel particles may have an average particle diameter of 120 to 300 nm.

In the water electrolysis catalyst according to an embodiment of the present invention, the water electrolysis catalyst may be characterized as having an overvoltage of 0.4 V or less based on 10 mA/cm2 in the hydrogen generation reaction.

The water electrolysis catalyst according to an embodiment of the present invention may be characterized by an overvoltage of 2 V or less based on 10 mA/cm2 in the oxygen generation reaction.

The present invention also provides a method for producing a water electrolysis catalyst, which includes a first step of carbonizing wood to produce carbonized wood;

A second step of forming a nickel particle layer on the carbonized wood by plating; and

It includes a third step of forming a graphene layer by deposition on the nickel particle layer.

In the water electrolysis catalyst manufacturing method according to an embodiment of the present invention, the first step may be characterized as a step of heat treatment at 800 to 1200 ° C. for 30 to 300 minutes.

In the water electrolysis catalyst manufacturing method according to an embodiment of the present invention, the second step may be characterized as applying a voltage of -0.9 to -1.2 V.

In the water electrolysis catalyst manufacturing method according to an embodiment of the present invention, the second step may be performed for 5 to 20 minutes.

In the water electrolysis catalyst manufacturing method according to an embodiment of the present invention, the metal particles may have an average particle diameter of 150 to 400 nm.

In the method for producing a water electrolysis catalyst according to an embodiment of the present invention, the third step may include the step of injecting methane at a rate of 20 to 80 sccm at a temperature of 800 to 1200 °C.

In the method for producing a water electrolysis catalyst according to an embodiment of the present invention, the water electrolysis catalyst may be used for a hydrogen production reaction or an oxygen production reaction.

The water electrolysis catalyst according to the present invention includes carbonized wood; Nickel particles distributed on the carbonized wood; And a graphene layer that electrically connects the nickel particles; it is environmentally friendly and has the advantage of low production cost.

Figures 1 to 3 show the results of nickel plating on carbonized wood observed at different voltages using an SEM.
Figure 4 shows graphene formed on nickel-plated carbide wood and observed with an SEM.
Figure 5 shows the results of XRD analysis performed on samples prepared in Examples and Comparative Examples of the present invention.
Figure 6 shows the results of Raman spectrum analysis performed on samples prepared in Examples and Comparative Examples of the present invention.
Figure 7 shows the analysis of electrochemical activity of samples of Examples and Comparative Examples using cyclic voltammetry.

Advantages and features of the embodiments of the present invention and methods for achieving them will become clear by referring to the embodiments described in detail below along with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and may be implemented in various different forms. The present embodiments are merely provided to ensure that the disclosure of the present invention is complete and to be understood by those skilled in the art. It is provided to fully inform those who have the scope of the invention, and the present invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

In describing embodiments of the present invention, if a detailed description of a known function or configuration is judged to unnecessarily obscure the gist of the present invention, the detailed description will be omitted. The terms described below are terms defined in consideration of functions in the embodiments of the present invention, and may vary depending on the intention or custom of the user or operator. Therefore, the definition should be made based on the contents throughout this specification.

The water electrolysis catalyst according to the present invention includes carbonized wood;

Nickel particles distributed on the carbonized wood; and

A water electrolysis catalyst comprising a graphene layer electrically connecting the nickel particles.

Conventionally known water electrolysis catalysts contain precious metals, so their production costs are significantly high, and their reserves are limited, which limits their commercialization. Accordingly, there is a need to develop a water electrolysis catalyst containing non-precious metal elements.

The water electrolysis catalyst according to the present invention uses the natural structure of carbonized wood and does not contain precious metals, so the production cost is low and it can be easily mass-produced. In addition, there is an advantage in preventing a decrease in catalytic activity due to a decrease in conductivity by supplementing the limitations of nickel particles, which have catalytic activity but low electrical conductivity, by forming a graphene layer.

Specifically, the carbonized wood may be carbonized plate-shaped wood cut perpendicular to the longitudinal direction, and by using wood cut perpendicular to the longitudinal direction, the cross section of the tubular structure naturally formed in the wood is exposed, creating a porous structure. It has the advantage of forming more pores on the surface compared to wood cut lengthwise.

The carbonized wood may have a thickness of 0.4 to 1.5 mm. If the thickness is too thick, it may cause a decrease in catalytic activity due to a decrease in conductivity, and if the thickness is too thin, sufficient support may be difficult and catalyst durability may be reduced.

The carbonization of wood may be carried out at 800 to 1200°C for 30 to 300 minutes, specifically at 900 to 1150°C for 40 to 90 minutes, and may be carried out in an inert gas atmosphere such as argon.

The nickel particles may have an average particle diameter of 150 to 400 ㎚, preferably 180 to 350 ㎚. If the average particle diameter of the nickel particles is small, agglomeration of nickel particles may occur, and if the average particle diameter of the nickel particles is large, the surface area decreases. It may cause a decrease in catalytic activity.

The nickel particles may be manufactured through plating, and the plating may be performed by applying a voltage of -0.9 to -1.2 V in a plating solution containing the nickel precursor, and in this range, the excellent catalytic activity of the nickel particles can be secured.

The water electrolysis catalyst may contain 5 to 20% by weight of nickel particles, specifically 7 to 15% by weight, and more specifically 8 to 12.5% by weight, and within this range, the catalytic activity of nickel is secured while the conductivity by the graphene layer is maintained. The improvement effect can be maximized.

The water electrolysis catalyst according to an embodiment of the present invention can be applied to both hydrogen generation reaction and oxygen generation reaction in water electrolysis. Specifically, the water electrolysis catalyst has an overvoltage of 10 mA/cm2 in the hydrogen generation reaction. It may be characterized as being 0.4 V or less, specifically 0.39 V or less, and the overvoltage based on 10 mA/cm2 in the oxygen evolution reaction may be characterized as being 2 V or less, specifically 1.8 V or less.

The present invention also provides a method for producing a water electrolysis catalyst, which includes a first step of carbonizing wood to produce carbonized wood;

A second step of forming a nickel particle layer on the carbonized wood by plating; and

It includes a third step of forming a graphene layer by deposition on the nickel particle layer.

The method for producing a water electrolysis catalyst according to the present invention has the advantage of producing an environmentally friendly water electrolysis catalyst in a simple method by including the first to third steps described above.

Specifically, the wood may be processed into a plate shape by cutting the wood perpendicular to the longitudinal direction, and by cutting perpendicular to the longitudinal direction, the cross section of the tubular structure of the wood may be exposed to increase porosity.

In the water electrolysis catalyst manufacturing method according to the present invention, in the first step, unnecessary components can be removed from wood through carbonization, only the carbon skeleton can remain, and electrical conductivity can be secured by carbon arrangement.

The first step may be performed at 800 to 1200°C for 30 to 300 minutes, specifically at 900 to 1150°C for 40 to 90 minutes. When the temperature is low or the heat treatment time is short, it is difficult to secure sufficient conductivity, and the temperature If the heat treatment time is high or the heat treatment time is long, energy consumption may increase compared to the increase in conductivity, which may cause a problem of extremely low efficiency. Additionally, the first step may be performed under an inert gas atmosphere such as argon.

The metal plating layer may preferably contain nickel, and water electrolysis catalyst activity can be secured by nickel plating. Specifically, the plating may be performed by installing carbonized wood as a working electrode in a plating solution containing a nickel precursor, installing a counter electrode, and then applying a voltage. At this time, the applied voltage is 0.9 to 1.2 V, specifically. It may be 0.95 to 1.15 V. If the applied voltage is low, it is difficult to sufficiently form a nickel plating layer, and if the voltage is high, the nickel particles may become too large and catalytic activity may decrease.

At this time, the counter electrode can be used without limitation if it is a counter electrode normally used for plating. As a specific and non-limiting example, the counter electrode may be Ag/AgCl.

The nickel precursor contained in the plating solution may include one or two or more selected from nickel acetate, nickel sulfate, nickel chloride, nickel carbonate, nickel nitrate, and hydrates thereof. Preferably, the nickel precursor is nickel chloride or nickel chloride. It may be nickel hydrate. In addition, the plating solution may further include salts such as sodium chloride and potassium chloride to ensure conductivity in addition to the nickel precursor.

Specifically, the plating solution may include the nickel precursor at a concentration of 0.05 to 2 M and the salt at a concentration of 0.05 to 2 M. If the concentration of the nickel precursor is low, plating efficiency may decrease and formation of a nickel plating layer may become difficult, and if the nickel precursor concentration is high, the size of the nickel particles generated may become excessively large.

Additionally, the second step may be performed for 5 to 20 minutes. If the plating time is short, it is difficult to sufficiently form a nickel plating layer, and if the plating time is long, the size of the nickel particles may become excessively large, which may lead to a decrease in catalytic activity.

The water electrolysis catalyst prepared by the water electrolysis catalyst manufacturing method according to an embodiment of the present invention may contain 5 to 20% by weight, specifically 7 to 15% by weight, and more specifically 8 to 12.5% by weight, nickel. If it contains a small amount, a decrease in catalytic activity may occur, and if it contains a large amount of nickel, there is a problem in that it is difficult to demonstrate the electrical connection effect by graphene.

In the third step, the graphene layer may be formed through deposition, specifically chemical vapor deposition. At this time, chemical vapor deposition may be performed under conditions commonly used to form a graphene layer, and the present invention is not limited thereto. As a specific and non-limiting example, the third step may be performed including heating to a temperature of 800 to 1200 ° C, specifically 900 to 1100 ° C, then injecting hydrogen, and then injecting methane. At this time, hydrogen may be injected at an injection rate of 10 to 40 sccm, and methane may be injected at a rate of 20 to 80 sccm, preferably 24 to 55 sccm, for 15 to 25 minutes.

After completing the third step, the water electrolysis catalyst is characterized by the formation of carbonized wood, nickel particles distributed on the carbonized wood, and a graphene layer that electrically connects these nickel particles.

The metal particles may have an average particle diameter of 150 to 400 nm, preferably 180 to 350 nm, and within this range, excellent catalytic activity can be secured and nickel may not be easily separated from the graphene layer.

The water electrolysis catalyst prepared by the manufacturing method according to an embodiment of the present invention can be applied to both hydrogen generation reaction and oxygen generation reaction, and both can secure high hydrogen production efficiency with high catalytic activity and low overvoltage.

Hereinafter, the present invention will be described in detail by examples and comparative examples. The examples below are only intended to aid understanding of the present invention, and the scope of the present invention is not limited by the examples below.

[Example]

1. Carbonized wood manufacturing

Wood was cut perpendicular to the growth direction to produce plate-shaped wood. The plate-shaped wood was heat-treated for 1 hour under an argon atmosphere. The conductivity was measured according to the heat treatment temperature, and the results are shown in Table 1.

Heat treatment temperature (℃) 500 or less 600 700 800 900 1000 conductivity - 3.627μS 3.639 mS 29.76mS 58.82mS 67.57mS

Referring to Table 1, it can be seen that conductivity is almost non-existent when the heat treatment temperature is less than 600 ℃, and the conductivity is highest at 1000 ℃.

In addition, plate-shaped wood with a thickness of 3 mm was carbonized at 1000°C, and the thickness of the wood shrunk after carbonization was around 2 mm. The wood that shrank after carbonization was ground and processed to a thickness of 1 mm, and then used in the experiment.

2. Nickel plating

Carbonized wood produced by carbonization at 1000°C was used for nickel plating. Specifically, Ag/AgCl is used as the reference electrode, carbonized wood is used as the working electrode, a solution satisfying 0.1 M NiCl ₂ and 0.1 M NaCl is used as the plating solution, and voltages of -0.8 V, -0.9 V, and -1.1 V are used. was applied to each to perform nickel plating.

Figures 1 to 3 show the nickel plating results observed by SEM. Referring to Figures 1 to 3, it can be seen that nickel particles are filled in the pores of the carbonized wood after nickel plating. In addition, it can be seen that when a voltage of -1.1 V is applied, a uniform and high-density nickel plating layer is formed.

In addition, by comparing the weight of the initial carbonized wood and the weight of the nickel-plated carbonized wood, it was confirmed that nickel was about 10% by weight of the total weight.

3. Graphene layer formation

A graphene layer was formed using chemical vapor deposition on carbonized wood plated with nickel at -1.1 V. Specifically, nickel-plated carbonized wood was placed in a quartz tube and heated to 1000°C at a temperature increase rate of 20°C per minute while hydrogen was injected at a rate of 20 sccm. After maintaining the temperature at 1000°C for 30 minutes, methane was injected at a rate of 40 sccm for 20 minutes to form a graphene layer on the nickel-plated carbonized wood.

Figure 4 shows the water electrolysis catalyst finally prepared by forming a graphene layer observed by SEM. Referring to Figure 4, it can be seen that nickel particles with an average particle diameter of 275 nm are evenly distributed on the carbonized wood.

[Comparative Example 1]

The tree was cut perpendicular to the growth direction, carbonized at 1000°C, and used in the experiment.

[Comparative Example 2]

Nickel was plated on the carbonized wood prepared in Comparative Example 1 by applying a voltage of -1.1 V in the same manner as in Example 1, and used in the experiment.

XRD analysis

XRD (X-ray Diffraction) analysis was performed on the samples of Examples and Preparation Examples, and the results are shown in Figure 5.

Referring to FIG. 5, the diffraction peaks located at ~22° and ~43° shown in the sample prepared according to the example correspond to the (002) and (100) crystal planes of carbon, respectively, and the characteristic peaks of metallic nickel and carbon A weak and broad peak can be confirmed, and the sensitivity of the typical peak of graphene and the nickel peak obtained at about 26° after chemical vapor deposition increased.

Raman spectral analysis

Raman spectrum analysis was performed on the samples of Examples and Preparation Examples, and the results are shown in FIG. 6.

Referring to Figure 6, the peaks at 506 cm ^-1 , 688 cm ^-1 , and 1064 cm ^-1 correspond to Ni-O bonding, Ni(OH) ₂ , and OO stretching modes in NiOOH, respectively, and the 2D peak after chemical vapor deposition treatment is 2691.8 cm. It appeared at position ^-1 .

Check double layer capacitance

The samples prepared in Examples and Comparative Examples were scanned using cyclic voltammetry (CV) at a scan rate of 5 to 100 mV/s, and the results are shown in FIG. 7.

In Figure 7, a is Comparative Example 1, b is Comparative Example 2, c is an example, and d shows the calculated current density difference according to the scan speed difference. Referring to FIG. 7, it can be seen that the catalyst according to the example has a double layer capacitance that is more than 1.5 times higher than the nickel-only plated case of Comparative Example 2 and more than 17 times higher than the carbonized wood of Comparative Example 1.

Electrochemical activity analysis

The electrochemical activities of the samples according to Comparative Example 1 and Examples were analyzed in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), and the results are shown in FIG. 8. At this time, electrochemical activity was performed using 1M KOH electrolyte and a reversible hydrogen electrode.

Referring to FIG. 8, it can be seen that the carbonized wood of Comparative Example 1 does not exhibit electrochemical activity, and the catalyst according to the example shows catalytic activity in both the hydrogen evolution reaction and the oxygen evolution reaction.

Specifically, in the case of the catalyst according to the example, the overvoltage based on 10 mA/cm2 in the hydrogen evolution reaction is about 0.32 V, which represents an overvoltage of 0.4 V or less, and in the oxygen evolution reaction, the overvoltage based on 10 mA/cm2 is about 1.66 V, which is 2 V. Below, it can be confirmed that the overvoltage is specifically 1.8 V or less, and based on this, it can be confirmed that the catalyst according to the embodiment of the present invention can be used in both oxygen evolution reaction and hydrogen evolution reaction.

Claims (15)

carbonized wood;
Nickel particles distributed on the carbonized wood; and
A water electrolysis catalyst comprising a graphene layer electrically connecting the nickel particles. According to clause 1,
The carbonized wood is a water electrolysis catalyst characterized in that it is carbonized plate-shaped wood cut perpendicular to the longitudinal direction. According to clause 2,
The carbonized wood is a water electrolysis catalyst characterized in that wood is heat-treated at 800 to 1200 ° C. for 30 to 300 minutes. According to clause 1,
A water electrolysis catalyst, wherein the nickel particles are manufactured through plating. According to clause 4,
The water electrolysis catalyst is characterized in that the plating is a step of applying a voltage of -0.9 to -1.2 V in a plating solution containing a nickel precursor. According to clause 1,
A water electrolysis catalyst wherein the nickel particles have an average particle diameter of 150 to 400 nm. According to clause 1,
The water electrolysis catalyst is characterized in that the overvoltage is 0.4 V or less based on 10 mA/cm2 in the hydrogen generation reaction. According to clause 1,
The water electrolysis catalyst is characterized in that the overvoltage is 2 V or less based on 10 mA/cm2 in the oxygen generation reaction. A first step of carbonizing wood to produce carbonized wood;
A second step of forming a nickel particle layer on the carbonized wood by plating; and
A water electrolysis catalyst manufacturing method comprising a third step of forming a graphene layer by deposition on the nickel particle layer. According to clause 9,
The first step is a method of producing a water electrolysis catalyst, characterized in that heat treatment at 800 to 1200 ° C. for 30 to 300 minutes. According to clause 9,
The second step is a method of producing a water electrolysis catalyst, characterized in that the step of applying a voltage of -0.9 to -1.2 V. According to claim 11,
A method for producing a water electrolysis catalyst, wherein the second step is performed for 5 to 20 minutes. According to clause 13,
A method for producing a water electrolysis catalyst, wherein the nickel particles have an average particle diameter of 150 to 400 nm. According to clause 1,
The third step is a water electrolysis catalyst manufacturing method comprising the step of injecting methane at 20 to 80 sccm at a temperature of 800 to 1200 ° C. According to clause 9,
A method of producing a water electrolysis catalyst, characterized in that the water electrolysis catalyst is for a hydrogen production reaction or an oxygen production reaction.