KR102237529B1 - Bifunctional electrocatalyst for water electrolysis with high oxygen vacancy and nanoporous structure, a manufacturing method thereof, and battery for water electrolysis including the electrocatalyst - Google Patents

Abstract

A bifunctional electrocatalyst for water electrolysis, a method for producing the same, and a water electrolysis battery comprising the electrode catalyst are provided. The electrocatalyst for water electrolysis has a high oxygen deficiency, has a nanoporous structure, and has high oxygen generation performance and hydrogen generation performance, and thus can be used in a water electrolysis system. The electrocatalyst for water electrolysis can be prepared in a large area simply through electrochemical treatment using a solution containing a metal cation and a halogen anion.

Description

Bifunctional electrocatalyst for water electrolysis with high oxygen vacancy and nanoporous structure, a manufacturing method thereof, and battery for water electrolysis including the electrocatalyst

It relates to a bifunctional electrocatalyst for water electrolysis having a high oxygen deficiency and a nanoporous structure, and a manufacturing method thereof. Specifically, it has a nanoporous structure with a high oxygen deficiency and has a high oxygen generation and hydrogen generation performance. It relates to an electrocatalyst for water electrolysis that can be used in a system and a method of manufacturing the same.

Efforts to replace fossil fuels and find clean and sustainable energy sources have been a challenge facing the world in recent decades, and this is a bigger issue due to the danger of radiation and radioactive waste from recent nuclear power generation and global warming caused by greenhouse gases. Is emerging as. In this respect, the water electrolysis reaction using renewable energy has many advantages in that it can be used as an energy source or chemical raw material without pollutants and self-discharge by producing hydrogen, which is a clean energy source.

However, the oxygen evolution reaction (OER) of the water electrolysis reaction has a very slow reaction rate, and thus a large amount of overvoltage must be supplied for the normal operation of the water electrolysis system, resulting in a large loss in terms of energy. In addition, platinum is widely used as a catalyst for generating hydrogen, but it is a factor that increases the price of water electrolysis systems due to the problem of precious metals (Jaramillo et al., Science 355 (2017) 146). This problem acts as an obstacle to the commercialization of the system, and in order to solve the problem, it is necessary to develop a non-precious metal-based active and durable water electrolysis catalyst electrode.

In the case of a hydrogen generating catalyst, although the reaction rate is fast, since the electrode catalyst generally used is based on platinum, it is considered to be a lot of problems from the viewpoint of commercialization of the system. Recently, researches such as MoS, NiFe, and CoW as non-precious metal catalysts are actively in progress (Jaramillo et al., Journal of American Chemical Society 137 (2015) 4347), and alternative catalysts having better activity than platinum have been reported. For commercialization, a method suitable for mass production of catalysts and large electrode area is being studied.

Accordingly, in order to commercialize or increase the scale of the water electrolysis system, a large area water oxidation and hydrogen generation electrode having high activity and a method of manufacturing the same are required in a simple method using a low-cost material as an electrode material.

One aspect of the present invention is to provide a bifunctional electrocatalyst for water electrolysis having a high oxygen deficiency and a nanoporous structure.

Another aspect of the present invention is to provide a method of manufacturing the bifunctional electrocatalyst for water electrolysis.

Another aspect of the present invention is to provide a water electrolysis battery comprising the bifunctional water electrolysis electrode catalyst.

In one aspect of the present invention,

Including a nickel support,

The nickel support has a surface of a nanoporous structure including nanopores, and includes a layered double hydroxide including a nickel alloy hydroxide on the surface, an electrocatalyst for water electrolysis is provided.

In another aspect of the present invention,

Putting a nickel support in a solution containing a metal cation and a halogen anion and applying a voltage to perform an electrochemical treatment; And

Activating the electrochemically treated nickel support under basic conditions;

There is provided a method of manufacturing the electrocatalyst for water electrolysis comprising a.

In another aspect of the present invention,

An electrode comprising the electrocatalyst for water electrolysis; And a reference electrode; and a water electrolytic battery is provided.

The electrocatalyst for water electrolysis according to an embodiment has a nanoporous structure while having a high oxygen deficiency, and has high oxygen generation performance and hydrogen generation performance, and thus may be used in a water electrolysis system. The electrocatalyst for water electrolysis can be prepared in a large area simply through electrochemical treatment using a solution containing a metal cation and a halogen anion.

1 is a schematic view for explaining a method of manufacturing an electrode catalyst for water electrolysis according to an embodiment.
2A to 2F are scanning electron microscopy (SEM) photographs step-by-step in the manufacturing process of the electrocatalyst for water electrolysis according to Example 1. FIG. Surface element analysis of (a) pure nickel foam, (b) iron and chloride ion treated nickel foam, (c, d) activated nickel foam, (e, f) resulting nickel foam
3 shows an X-ray diffraction (XRD) pattern observed for the nickel foam electrocatalyst for water electrolysis prepared in Example 1. FIG.
4A and 4B show (a) water electrolysis performance and (b) scanning electron microscopy (SEM) photographs of nickel foam according to the number of times cycling voltammetry (CV) was performed in a chloride ion solution in Comparative Example 1, respectively. Is shown.
5 is a scanning electron microscope (SEM) photograph of a nickel foam electrocatalyst according to the number of times cycling voltammetry (CV) was performed in a chloride ion solution in Comparative Example 1 at low magnification.
6 shows the impedance of a nickel foam electrode according to the number of times cycling voltammetry (CV) was performed in a chloride ion solution in Comparative Example 1. FIG.
Figures 7a and 7b show a pure nickel foam in Comparative Example 1, a nickel foam activated in a basic condition, and a nickel foam subjected to electrochemical treatment (CV 100 times) in a chlorine ion solution and a nickel foam activated in the basic condition (a). Nickel XPS spectrum, (b) oxygen XPS spectrum analysis graph.
8 is a graph of chlorine XPS spectrum analysis of pure nickel foam in Comparative Example 1, nickel foam subjected to electrochemical treatment (CV 100 times) in a chlorine ion solution, and nickel foam activated under basic conditions.
9A and 9B are graphs showing (a) iron XPS spectrum analysis and (b) water electrolysis performance of nickel foam according to the number of times cycling voltammetry (CV) was performed in an iron ion solution in Comparative Example 2, respectively. .
10A and 10B show (a) nickel of a pure nickel foam in Comparative Example 2, a nickel foam activated in a basic condition, a nickel foam subjected to electrochemical treatment (CV 100 cycles) in an iron ion solution, and a nickel foam activated in a basic condition, respectively. XPS spectrum, (b) iron XPS spectrum analysis graph.
11 shows a scanning electron microscope (SEM) photograph of a nickel foam electrochemically treated in an iron ion solution in Comparative Example 2. FIG.
12A to 12C are respectively pure nickel foam, nickel foam electrochemically treated in a chlorine ion solution in Comparative Example 1, nickel foam electrochemically treated in an iron ion solution in Comparative Example 2, and electricity from chlorine and iron ions in Example 1 The chemically treated nickel foam is (a) oxygen generation performance, (b) Tafel graph for oxygen generation performance, and (c) overvoltage graph for oxygen generation performance.
13A to 13C are respectively pure nickel foam, nickel foam electrochemically treated in a chlorine ion solution in Comparative Example 1, nickel foam electrochemically treated in an iron ion solution in Comparative Example 2, and electricity from chlorine and iron ions in Example 1 The chemically treated nickel foam is (a) hydrogen generation performance, (b) Tafel graph for hydrogen generation performance, and (c) overvoltage graph for hydrogen generation performance.
14A to 14C are graphs of (a) nickel XPS spectrum (b) iron XPS spectrum (c) oxygen XPS spectrum of nickel foam activated after electrochemical treatment with chlorine and iron ions.
15A to 15D are graphs in which a water electrolysis experiment was conducted for 20 hours using pure nickel foam and iron and chlorine ion-treated nickel foam as oxygen and hydrogen generation electrodes in Evaluation Example 5, respectively, (a) 0.1 M KOH It is a graph showing the cell voltage at, (b) the anode and cathode voltage at 0.1 M KOH, (c) the cell voltage at 1 M KOH, and (d) anode and cathode voltage at 1 M KOH.

The present inventive concept described below can apply various transformations and have various embodiments. Specific embodiments are illustrated in the drawings, and detailed descriptions will be described in detail. However, this is not intended to limit the present creative idea to a specific embodiment, and it should be understood to include all transformations, equivalents, or substitutes included in the technical scope of the present creative idea.

The terms used below are only used to describe specific embodiments, and are not intended to limit the present inventive idea. Singular expressions include plural expressions unless the context clearly indicates otherwise. Hereinafter, terms such as "include" or "have" are intended to indicate the presence of features, numbers, steps, actions, components, parts, components, materials, or a combination thereof described in the specification. It is to be understood that the above other features, or the possibility of the presence or addition of numbers, steps, actions, components, parts, components, materials, or combinations thereof, are not excluded in advance.

In the drawings, the thickness is enlarged or reduced in order to clearly express various layers and regions. Like reference numerals are attached to similar parts throughout the specification. Throughout the specification, when a part such as a layer, film, region, or plate is said to be "on" or "on" another part, this includes not only the case directly above the other part, but also the case where there is another part in the middle. . Throughout the specification, terms such as first and second may be used to describe various constituent elements, but constituent elements should not be limited by terms. The terms are used only to distinguish one component from another.

Although terms such as first, second, etc. may be used to describe various elements, components, regions, layers and/or regions, these elements, components, regions, layers and/or regions It will be understood that it should not be limited by these terms.

In addition, the processes described in the present invention do not necessarily mean that they are applied in order. For example, when the first step and the second step are described, it can be understood that the first step does not necessarily have to be performed before the second step.

Hereinafter, an electrocatalyst for water electrolysis according to exemplary embodiments, a method of manufacturing the same, and a water electrolysis battery including the electrode catalyst for water electrolysis according to exemplary embodiments will be described in more detail below with reference to the drawings.

Electrocatalyst for water electrolysis according to one embodiment,

Including a nickel support,

The nickel support has a surface of a nanoporous structure including nanopores, and includes a layered double hydroxide (LDH) including a nickel alloy hydroxide on the surface.

The nickel support used in the electrocatalyst for water electrolysis is a non-precious metal catalyst and is economical due to its low cost compared to the noble metal catalyst generally used in water electrolysis systems. According to an embodiment, the nickel support may include at least one selected from nickel foam, nickel plate, nickel wire, and nickel rod. For example, a nickel foam may be used as the nickel support. Nickel support such as nickel foam has the advantage of having a large surface area and good electrical conductivity.

The size of the nickel support is not particularly limited, and may be determined according to necessity such as electrode size.

The nickel support has a surface of a nanoporous structure including nanopores, and includes a layered double hydroxide (LDH) including a nickel alloy hydroxide on the surface. The nickel alloy hydroxide may include at least one component selected from iron, cobalt, selenium, tungsten, silver, gold, platinum, iridium, tin, and strontium.

The layered double hydroxide is a layered material having a two-dimensional nanostructure that is weakly bound by an anion layer that balances charge between the positively charged Brucite-type metal hydroxide layers. ^{According to an embodiment, OH −} may be used to form an anion layer in the LDH structure. Water oxidation reaction may occur when OH ⁻ is located between the nickel alloy hydroxide layers of LDH and meets the nickel alloy hydroxide. The reason why the LDH structure is highly active is that an ^{anion such as OH-} which is a reactant is located between the layers and the reaction area is widened.

According to an embodiment, the layered double hydroxide may be formed by putting a nickel support in a solution containing a metal cation and a halogen anion and applying a voltage to perform an electrochemical treatment. Through the electrochemical treatment, a layered double hydroxide including a nickel component on the surface of the nickel support and a nickel alloy hydroxide derived from the metal component of the metal cation may grow on the surface of the nickel support.

A nanosheet array including such a layered double hydroxide may be formed on the surface of the nickel support. The nanosheet array including the layered double hydroxide may be grown in a shape substantially perpendicular to the surface of the nickel support, and the orientation of the nanosheet array may be regular or irregular.

The nanoporous structure formed on the surface of the nickel support may increase the active surface area of the electrocatalyst, thereby improving the performance of the water electrolysis system.

The nickel support may have wrinkles formed on its surface by the nano pores of the nanoporous structure. At this time, the layered double hydroxide is present in the surface of the nickel support where there are no nanopores. As shown in FIGS. 2C and 2D, it can be seen that a nanoporous structure including nanopores is formed between a series of nanosheet arrays including a layered double hydroxide on the surface of the nickel support to show a wrinkle shape.

The electrocatalyst for water electrolysis has a nanoporous structure on the surface of the nickel support, and includes a layered double hydroxide including a nickel alloy hydroxide, thereby increasing the surface area and improving the catalytic activity, thereby generating hydrogen in the water decomposition reaction. Not only the rate of the reaction (HER) but also the rate of the oxygen evolution reaction (OER) can be significantly improved.

The electrocatalyst for water electrolysis may have a higher oxygen deficiency compared to a general smooth nickel support in which such a surface is not formed. Higher oxygen deficiency can improve the performance of the water electrolysis system by increasing the rate of the oxygen evolution reaction. The degree of oxygen deficiency of the electrocatalyst for water electrolysis may be, for example, 20% to 80%.

Here, the oxygen deficiency is the ratio of the area of the oxygen vacancy peak after dividing the oxygen peak into oxide peak (530.7 eV), oxygen vacancy peak (531.8 eV), and hydroxide peak (532.9 eV) in the oxygen O s1 spectrum of XPS. Is the calculated value by dividing by the area of the total oxygen peak.

When a general nickel electrocatalyst was activated in a base, it had an oxygen deficiency of 12.3%, and when activated after electrochemical treatment using only a halogen anion, the oxygen deficiency was measured to be 35.7%. Accordingly, it was measured as 50% of the electrocatalyst for water electrolysis prepared by electrochemical treatment and then activation using a halogen anion and a metal cation. Here, the oxygen deficiency is the ratio of the area of the oxygen vacancy peak after dividing the oxygen peak into oxide peak (530.7 eV), oxygen vacancy peak (531.8 eV), and hydroxide peak (532.9 eV) in the oxygen O s1 spectrum of XPS. Is the calculated value by dividing by the area of the total oxygen peak.

Since the electrocatalyst for water electrolysis has high activity and high durability for water electrolysis, and exhibits both functions of oxygen generation and hydrogen generation, in water electrolysis, an oxygen generating electrode (anode) and a hydrogen generating electrode (cathode) It can be applied to both.

The electrocatalyst for water electrolysis can be prepared by a simple electrochemical treatment method applicable to a large area.

A method of manufacturing an electrode catalyst for water electrolysis according to one embodiment,

Putting a nickel support in a solution containing a metal cation and a halogen anion and applying a voltage to perform an electrochemical treatment; And

And subjecting the electrochemically treated nickel support to an activation treatment in a basic condition.

1 is a schematic view for explaining a method of manufacturing an electrode catalyst for water electrolysis according to an embodiment.

As shown in Fig. 1, in the method of manufacturing the electrocatalyst for water electrolysis, a halogen anion (eg, chlorine ion) and a metal cation (eg, iron ion) are added together to perform electrochemical treatment to increase the surface area of the electrode by the halogen anion. Both effects of improving performance by impregnating with metal cations can be obtained.

In the case of electrochemical treatment in the presence of halogen ions, a nanoporous structure and high oxygen deficiency may be imposed on the surface of a nickel support (e.g., nickel foam), and in the presence of metal cations, the surface of the nickel support is impregnated with metal cations and thus the nickel support The water electrolysis performance of the electrode catalyst using is increased. In the case of metal cations, iron ions are known to contribute to the highest catalytic activity, but various metal cations such as cobalt, selenium, small amounts of ruthenium, and platinum can also be applied to the method.

In the method of manufacturing an electrocatalyst for water electrolysis according to an embodiment, electrochemical treatment and activation treatment are performed in the presence of both ions to prepare an electrocatalyst for water electrolysis having the advantages of both ions.

As the nickel support used in the manufacture of the electrocatalyst for water electrolysis, at least one selected from nickel foam, nickel plate, nickel wire, and nickel rod may be used. Nickel support is a non-precious metal catalyst and is economical due to its low cost compared to noble metal catalysts generally used in water electrolysis systems. In addition, a nickel support such as a nickel foam has a large surface area and good electrical conductivity. The size of the nickel support is not particularly limited, and may be determined according to necessity such as electrode size.

In the manufacturing method of the electrocatalyst for water electrolysis, in order to improve the catalytic activity performance of the nickel support, first, electrochemical treatment is performed using a solution containing a metal cation and a halogen anion. Through such a simple electrochemical treatment, a layered double hydroxide including a nickel alloy hydroxide may be grown while forming a nanoporous structure including nanopores on the surface of the nickel support.

Metal cations such as iron ions, for example, iron ions, are impregnated on the surface of the nickel support, thereby greatly increasing the activity and durability of the catalyst. In the case of electrochemical treatment of such metal cations with halogen ions, the metal cations are more easily impregnated on the surface of the nickel support, thereby producing an electrocatalyst with nickel alloy hydroxide having high performance.

According to an embodiment, the metal cations are iron (Fe), cobalt (Co), selenium (Se), tungsten (W), silver (Ag), gold (Au), platinum (Pt), iridium (Ir), It may contain at least one selected from tin (Sn) and strontium (Sr). For example, the metal cation may include iron ions.

Examples of the precursor compound containing the metal cation include hydroxides, nitrates, sulfates, acetates, chlorides, acetylacetonates, formates, or oxides of these metals, but are not limited thereto.

According to an embodiment, the concentration of the metal cation in the solution may range from 0.001 M to 1 M. For example, the concentration of the metal cation in the solution may range from 0.01 M to 0.1 M. In the above range, the metal cations may penetrate the surface of the nickel support to form a nickel alloy hydroxide, while forming a layered double hydroxide, which is a layered material including the nickel alloy hydroxide, on the surface of the nickel support.

A layered double hydroxide containing a nickel component on the surface of the nickel support and a nickel alloy hydroxide derived from the metal component of the metal cation is obtained by putting a nickel support into a solution containing a metal cation and a halogen anion and applying a voltage to perform electrochemical treatment. It grows on the surface of the nickel support.

This means that when the nickel support is electrochemically treated using a solution containing only metal cations without halogen anions, the metal cations only form a nickel alloy by bonding with nickel on the surface of the nickel support, and the physical structure changes on the surface of the nickel support. The difference is that it does not induce. This is also confirmed in Examples to be described later.

Solutions used for electrochemical treatment contain metal cations as well as halogen anions. According to an embodiment, the halogen anion may include at least one selected from fluorine, chlorine, and iodine. For example, the halogen anion may include a chlorine ion. The halogen ions may form a nanoporous structure on the surface of the nickel support and may improve oxygen deficiency. The nanoporous structure increases the active surface area of the electrocatalyst, and the high oxygen deficiency increases the rate of the oxygen evolution reaction, thereby improving the performance of the water electrolysis system.

According to an embodiment, the concentration of the halogen anion in the solution may be in the range of 0.001 to 3 M. For example, the concentration of the halogen anion in the solution may range from 0.01 M to 1 M. Within the above range, a nanoporous structure may be formed on the surface of the nickel support to increase the electrochemical catalytic activity of the nickel support.

The metal cation and halogen anion may be obtained by dissolving different types of precursor compounds, respectively, or may be obtained by dissolving one type of precursor compound including both. For example, in the case of selecting ^{Fe 3+} as a metal cation and ^Cl- as a halogen anion _{, Fe(NO 3} ) ₃ and HCl may be dissolved in an appropriate concentration, or alternatively, a single precursor compound of _{FeCl 3 may be dissolved and used.} May be.

The solvent for dispersing the metal cation and the halogen anion is not particularly limited, but dissolution and mixing of the precursor compound may be uniformly performed, and then a solvent capable of easily removing the solvent may be used. As the usable solvent, for example, water, alcohol-based, carbonate-based, glycol-based, thiol-based, amine-based, acetone, or a mixed solvent thereof may be used. Non-limiting examples of such solvents include distilled water; Alcohols such as ethanol and methanol; Acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone, NMP ), cyclohexane, dichloromethane, dimethyl sulfoxide (DMSO), acetonitrile, pyridine, amines, or a mixture thereof.

According to an embodiment, the electrochemical treatment may be performed using at least one selected from cyclic voltammetry, constant voltage, constant current, pulse voltage, and pulse current. For example, the electrochemical treatment may be performed using a cyclic voltammetry method.

According to an embodiment, the electrochemical treatment may be performed for 10 seconds to 60 minutes at a voltage in the range of -1 V to 2 V based on the hydrogen electrode. In the above range, it is possible to form a nanoporous structure on the surface of the nickel support without destroying the structure of the nickel support, and to grow a layered double hydroxide including a nickel alloy hydroxide to an appropriate level.

In the manufacturing method of the electrocatalyst for water electrolysis, after electrochemical treatment, the nickel support is activated under basic conditions. By the activation treatment, halogen anions present on the surface of the nickel support can be more completely removed to form a more intact nanoporous structure, and the surface of the nickel support can be replaced with a nickel hydroxide electrode having a high oxygen deficiency.

According to an embodiment, the activation treatment may be performed by applying a voltage ranging from 0.5V to 3V for 10 seconds to 2 hours in a basic solution having a pH of 10 or higher. In this case, the voltage can be applied in various ways, such as using one or more selected from cyclic voltammetry, constant voltage, constant current, pulse voltage, and pulse current.

The activation treatment step may be performed by applying a voltage in a separate basic solution, but alternatively, even if the electrochemically treated nickel support is applied as an electrode of the water electrolytic battery to which the basic solution is applied, even a small amount of operation of the water electrolytic battery It can also be a natural activation process.

Through such an activation treatment, it is converted into a nickel alloy hydroxide electrocatalyst with high oxygen deficiency.

By the above-described manufacturing method, a bifunctional electrocatalyst for water electrolysis, which exhibits high water electrolysis performance due to high oxygen deficiency, a large surface area due to a nanoporous structure, and an increase in catalytic activity, can be easily prepared in a large area. It can be seen from the following examples that the thus prepared electrocatalyst for water electrolysis can be applied to an electrode of a large area and has high durability even in a large area water electrolytic battery.

Hereinafter, a battery for water electrolysis according to another embodiment will be described.

A battery for water electrolysis according to an embodiment includes: an electrode including the electrode catalyst for water electrolysis; And a reference electrode.

Since the electrocatalyst for water electrolysis is a bifunctional electrode catalyst with improved oxygen generation performance as well as hydrogen generation performance, the electrode including the electrocatalyst for water electrolysis is an electrode (anode) in which an oxygen generation reaction (OER) occurs and a hydrogen generation reaction (HER ) Can be applied to either or both of the electrodes (cathodes) to occur.

According to an embodiment, the water electrolytic battery may include an anion exchange membrane, an electrode (cathode and anode), a separator, a gasket, a current collector, and a reference electrode.

In a water electrolytic electrode, the electrode is a place where an actual electrochemical reaction occurs, and a reaction according to voltage occurs to produce oxygen and hydrogen. The anion exchange membrane acts as a mechanism to block electricity so that the reaction occurs through the movement of ions when a water electrolytic reaction occurs and electricity does not pass directly from an electrode to another electrode. The separator is electrically connected to the electrode, and at the same time, the flow path is dug so that the reactants can flow well, thereby reducing material resistance. The gasket fixes the electrode and supports it so that it can receive the proper pressure. The current collector serves to allow electricity to pass through to the electric wire and the separating plate. Finally, in the case of the reference electrode, since there are only two electrodes in the existing electrochemical cell, it is difficult to know the actual voltage at each electrode, so it is introduced and is used to measure the absolute voltage of each electrode.

Exemplary embodiments are described in more detail through the following examples and comparative examples. However, Examples and Comparative Examples are for illustrative purposes only, and the scope of the present invention is not limited thereto.

Example 1: Electrocatalyst preparation through electrochemical treatment of nickel foam in chlorine and iron ions

Before the experiment, the nickel foam was washed in ultrapure water and ethanol through ultrasonic waves. After the three-electrode system was installed with pure nickel foam as the working electrode, the platinum wire as the counter electrode, and the Ag/AgCl electrode as the reference electrode, in a 0.02 M FeCl ₃ solution using ultrapure water-0.25 ~ 0.65 V ( vs. Ag/AgCl) cyclic voltammetry was performed 100 times at a rate ^{of 100 mV s -1 with voltage.} After electrochemical treatment, the nickel foam was washed with ultrapure water and dried in air.

The electrochemically treated nickel foam was subjected to a voltage of 0.8V ~ 1.8V vs. a KOH basic solution having a pH of 13. The activation was carried out by applying 50 times between the RHEs by cyclic voltammetry to prepare an electrocatalyst for water electrolysis.

Comparative Example 1: Preparation of Electrocatalyst through Electrochemical Treatment of Nickel Foam in Chlorine Ion

In Example 1, an electrode catalyst was prepared in the same manner as in Example 1, except that a 0.06 M HCl solution was used instead of a 0.02 M FeCl _{3 solution.}

Comparative Example 2: Preparation of an electrode through electrochemical treatment of nickel foam in iron ions

In Example 2, an electrode catalyst was prepared in the same manner as in Example 2, except that a _{0.02 M Fe(NO 3} ) ₃ solution was used instead of a 0.06 M HCl solution.

Evaluation Example 1: SEM and XRD results of nickel foam treated with chlorine-iron ion

2 shows a scanning electron microscope (SEM) photograph analyzing the process and surface components of the electrocatalyst prepared according to Example 1 above.

2A shows a pure nickel foam without any treatment, and it can be seen that the surface is smooth and there are no pores. On the other hand, FIG. 2B shows a nickel foam subjected to electrochemical treatment under chlorine and iron ions, and it can be seen that many by-products such as iron and nickel chlorine hydroxide have been generated along with a high porosity surface area. 2C and 2D show that the electrochemically treated nickel foam is activated in a basic solution, and it can be seen that materials in the form of thin valves are formed on the surface along with the porous surface.

X-ray diffraction (XRD) patterns were measured to confirm the phase of the material produced on the surface of the nickel foam, and the results are shown in FIG. 3. As shown in FIG. 3, it was confirmed that the material formed on the surface of the nickel foam had a nickel-iron plate structure (NiFe-LDH) structure. It is known that such a nickel-iron valve structure exhibits high performance in an oxygen evolution reaction.

2E and 2F show the results of conducting an EDS (Energy-dispersive spectroscopy) elemental analysis on the surface to confirm the uniformity of the prepared electrocatalyst. As a result of elemental analysis of the surface, it can be confirmed that Ni-Fe hydroxide having a NiFe-LDH structure was successfully prepared on the surface because nickel, iron, and oxygen were uniformly dispersed on the porous surface.

Evaluation Example 2: Evaluation of physical properties of a nickel foam electrode according to chlorine ion treatment

In order to investigate the effect of chlorine ions, the electrode catalyst prepared by changing the number of electrochemical cycling voltammetry (CV) in the presence of chlorine ions to 10, 100, 500 cycles in Comparative Example 1 was used with pure nickel foam and water electrolysis. The performance was compared and shown in Fig. 4A.

As shown in FIG. 4A, looking at the size of the oxidation-reduction peak before water electrolysis performance, it can be seen that the oxidation-reduction peak area increases as the number of cyclic voltammetry (CV) in chlorine ions increases. This indicates that the chlorine treatment improves the active surface area of the nickel foam. This can be confirmed from the SEM results of FIG. 4B.

4B is a SEM photograph of the electrode catalyst, and it can be seen that as the number of cyclic voltammetry (CV) increases, the roughness of the surface increases, which increases the active surface area of the electrode catalyst.

However, in the case of water electrolysis performance, the optimum catalytic performance is shown when the number of cyclic voltammetry (CV) is 100, which can be confirmed through the SEM photograph of FIG. 5 and the impedance result of FIG. 6.

Looking at the low-magnification SEM results of FIG. 5, it can be seen that when the cyclic voltammetry (CV) treatment is performed 500 times, the structure of the electrode catalyst is destroyed, and the electrical resistance increases significantly in the impedance result of FIG. 6. This indicates that if too much electrochemical treatment is performed on chlorine ions, the nickel electrocatalyst may be damaged, resulting in deterioration of performance.

To confirm the chemical effect of chlorine ions, pure nickel foam (Raw NF) and nickel foam activated in basic conditions (Raw NF AO), and nickel subjected to electrochemical treatment (circulating voltammetry 100 times) in a chlorine ion solution. The XPS of the foam (Cl-NF) and the nickel foam (Cl-NF AO) that activated it in a basic condition was measured, and the spectrum was compared, and the results are shown in FIGS. 7A and 7B.

As shown in Figs. 7a-7b, in the case of pure nickel foam, nickel hydroxide (Ni(OH) ₂ ), oxide (NiO), and metal (Ni) peaks are all present, indicating that the surface of pure nickel is slightly oxidized. Show. When pure nickel foam is activated under basic conditions, it can be seen that most of the surface is converted _{to nickel hydroxide (Ni(OH) 2 ).}

On the other hand, in the chlorinated nickel foam, most of the peaks are _{shifted to the left of the hydroxide (Ni(OH) 2} ) peak, indicating that nickel has changed to the form of _{NiCl 2 combined with chlorine ions.} It can be seen that when the chlorinated nickel foam is activated under a basic condition, most of the chlorine ions are converted to hydroxide ions. At this time, in the nickel spectrum of XPS, the nickel peak of the activated nickel foam after chlorination is shifted to the right than the position known as _{the nickel hydroxide (Ni(OH) 2) peak of the reference, which is the oxygen deficiency of nickel hydroxide.} Indicates increasing. This increase in oxygen deficiency can also be confirmed in the oxygen XPS spectrum of FIG. 7B. When the pure nickel foam is activated, the hydroxide (Ni(OH) ₂ ) peak is almost close, whereas when the chlorinated nickel foam is activated, a peak appears in the middle between the hydroxide and oxygen depletion peaks. When the XPS peak of oxygen is divided into oxide peak (530.7 eV), oxygen vacancy peak (531.8 eV), and hydroxide peak (532.9 eV), the ratio of the oxygen vacancy peak area is divided by the total oxygen peak area. When a general nickel electrode was activated with a base, it had an oxygen deficiency of 12.3%, whereas when it was prepared using only a halogen anion, it was measured to be 35.7%. This indicates that in the case of the chlorinated nickel foam, oxygen deficiency is very increased upon activation. In the case of chlorine, after activation in a base solution, most of them disappear after being substituted with hydroxide ions, which can be confirmed in the chlorine XPS spectrum of FIG. 8. Such an increase in oxygen deficiency may increase the amount of electron-rich oxygen, thereby reducing reaction activation energy and increasing catalytic activity.

Evaluation Example 3: Evaluation of physical properties of a nickel foam electrode according to iron ion treatment

In order to find out the effect of positive metal ions, the number of electrochemical cycling voltammetry (CV) in Comparative Example 2 was changed to 10, 100, 500 cycles to electrochemically treat nickel foam, and The XPS spectrum was compared and shown in FIG. 9A. The addition of iron ions is related to the water electrolysis performance.As shown in FIG. 9A, 15.5% of iron was impregnated compared to nickel even when the cyclic voltammetry (CV) was performed only 10 times, and 13.6% of iron was carried out up to 100 times. Although the content of was almost constant, the iron content decreased by a small amount at 500 times. Each of the iron ion-treated nickel foams is shown in FIG. 9B by comparing the pure nickel foam with water electrolysis performance. As a result, it can be seen that the catalytic activity is improved when the iron ion treatment is performed. When the treatment is performed 500 times, the performance decreases, which is believed to be due to the decrease in the iron content.

10A and 10B show XPS spectra before and after activation of iron ion-treated nickel foam in a base solution. As shown in Fig. 10a, in the case of iron ion treatment, it can be seen that the nickel oxide (Ni(OH) ₂ ) peak and the metal (Ni) peak are measured even after activation in the base, which is because iron ions cover the nickel surface. It is presumed to prevent the nickel surface from turning into hydroxide. Looking at the iron XPS spectrum of FIG. 10B, it can be seen that the peak position is maintained at 2.5 horizontal, indicating that some of the iron is trivalent and well impregnated with nickel, but some of the iron is adsorbed on the nickel surface as a divalent oxide.

11 shows an SEM image of a nickel foam treated with iron ions. As shown in FIG. 11, when iron ions were added alone, a little particle was generated, and unlike the case where chlorine was present, no structural change was observed on the surface. This means that impregnation of iron ions induces a change in the physical surface structure of the nickel foam, which does not improve performance, but impregnation of the nickel structure with iron, thereby kineticly improving the oxygen generation catalyst performance.

Evaluation Example 4: Evaluation of physical properties of a nickel foam electrode treated with chlorine-iron ion

In order to confirm the oxygen generation performance according to the type of ions applied in the electrochemical treatment, the oxygen generation performance of the electrode catalysts prepared in Example 1 and Comparative Examples 1 and 2 was measured, and the results were compared with pure nickel foam. As shown in Figs. 12a to 12c. 12A is a graph of oxygen generation performance, FIG. 12B is a Tapel graph of oxygen generation performance, and FIG. 12C is an overvoltage graph of oxygen generation performance.

As shown in FIG. 12A, the electrochemical water oxidation performance showed the highest performance when chlorine and iron ions were applied together, because the advantages of chlorine ions and iron ions were simultaneously shown.

By comparing the Tafel graph of FIG. 12B, it can be confirmed whether each ion has a kinetic change in catalytic activity or has an effect on a physical catalytic activity area. In the case of pure nickel foam, the Tafel slope was 89 mV/dec, and in the case of iron ion treatment, the slope decreased to 53 m/dec, indicating that the catalytic activity was kineticly improved during iron ion treatment. On the other hand, in the case of chlorine ion treatment, the slope did not change significantly to 81mv/dec, and it has a high current density at a constant voltage. This means that in the case of chlorine ion treatment, the catalytic performance is improved by increasing the catalytic active surface area by forming a porous surface structure. It is believed that the slight increase in slope is due to the increased oxygen deficiency in the chlorine treatment.

Looking at the overvoltage graph for the oxygen generation performance of FIG. 12C, it was found that the electrocatalyst to which the chloride ion and iron ion of Example 1 were applied together showed the same oxygen generation ability as other electrocatalysts with less energy, and thus had high catalytic activity. I can.

In order to confirm the hydrogen generation performance according to the type of ions applied in the electrochemical treatment, the hydrogen generation performance of the electrode catalysts prepared in Example 1 and Comparative Examples 1 and 2 was measured, and the results were compared with pure nickel foam. It is shown in Figures 13a to 13c. 13A is a graph of hydrogen generation performance, FIG. 13B is a Tapel graph of hydrogen generation performance, and FIG. 13C is an overvoltage graph of hydrogen generation performance.

As shown in FIGS. 13A to 13C, the nickel foam treated with iron and chlorine ions showed the highest performance in the hydrogen generation reaction. It can be seen that the nickel foam can be used as a hydrogen generating electrode at the same time as an oxygen generating electrode, so that it can be applied as a bifunctional electrode catalyst.

14A to 14C show XPS spectra after activation of nickel foam treated with iron and chlorine ions in Example 1 in a base solution. In the case of the nickel XPS spectrum of FIG. 14A, the peak of the nickel foam treated with iron and chlorine ions is As compared to the nickel hydroxide (Ni(OH) ₂ ) position, it is moved to a lower energy level, so it can be seen that the oxygen deficiency of the corresponding electrocatalyst is greatly increased. This can also be confirmed in the oxygen XPS spectrum of FIG. 14C. It was confirmed that the area of the oxygen deficiency peak was 50%, which was higher than that of the pure nickel electrode (12.3%) and the chlorinated electrode (35.7%). . For iron XPS spectrum of Figure 14b, showing a peak of Fe ³⁺ ions there's a Fe ³⁺ ion is well impregnated with the nickel structure can be seen to show high performance.

Evaluation Example 5: Results of actual water electrolysis performance and durability evaluation for an electrode catalyst

The electrode catalyst prepared according to Example 1 was applied to an oxygen generating electrode and a hydrogen generating electrode of an actual water electrolysis battery, and the water electrolysis performance was measured for 20 hours, and the results were compared with the case of applying pure nickel foam, FIGS. 15A to 15A. It is shown in 15d.

In the water electrolytic battery, the electrode catalyst prepared according to Example 1 was applied as both cathode and anode electrodes, and an anion exchange membrane was disposed between both electrodes, and both electrodes were subjected to appropriate pressure while the electrodes were fixed through a gasket, respectively. The water electrolysis performance is measured through the cell voltage while applying a ^{constant current of 10 mA/cm -2} for 20 hours while using a pin-shaped titanium separator so that the KOH 0.1 M aqueous solution and 1 M aqueous solution flow well and current flows well. Meanwhile, a structure capable of measuring the absolute voltage of the cathode and the anode through the Ag/AgCl reference electrode inserted in the anode side was used.

15A and 15B are graphs showing cell voltages when water electrolytic cells are driven for 20 hours under 0.1 M and 1 M KOH conditions, respectively. At this time, the cell area is 10cm ² and the driving condition is 10 mA cm ^-2 . As shown in FIGS. 15A and 15B, it can be seen that the electrocatalyst treated with iron and chlorine ions irrespective of the KOH concentration has a lower cell voltage compared to the untreated nickel foam, resulting in high water electrolysis performance. This indicates that the electrode catalyst for water electrolysis according to an embodiment can be applied to an electrode having a large area. In addition, even in a water electrolysis test for 20 hours, the cell voltage hardly changes, showing excellent durability.

15C and 15D are graphs showing the results of measuring the absolute voltage applied to the anode and the cathode under the conditions of 0.1 M and 1M KOH, respectively, using a reference electrode. As shown in FIGS. 15C and 15D, most of the voltage changes exist in the hydrogen generating electrode, and the performance of the oxygen generating electrode was constant for 20 hours, and the overvoltage at this time was constant at 256 mV @ 10 mA cm ^-2 . From this, it can be seen that the oxygen generating electrode to which the electrode catalyst according to the embodiment is applied shows high performance and durability even under large capacity and actual cell conditions.

From the results of the evaluation example, it can be seen that the electrocatalyst for water electrolysis according to an embodiment exhibits high performance due to a high oxygen deficiency, a large surface area due to a nanoporous structure, and an increase in catalytic activity due to iron ions. In addition, it can be seen that the electrode catalyst of the present invention can be applied even in a large area through the application of an actual large-area water electrolytic battery and has high durability.

In the above, a preferred embodiment according to the present invention has been described with reference to the drawings and embodiments, but this is only illustrative, and various modifications and other equivalent embodiments are possible from those of ordinary skill in the art. You will be able to understand. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims (10)

Including a nickel support,
The nickel support has a surface of a nanoporous structure including nanopores, and includes a layered double hydroxide made of a nickel alloy hydroxide on the surface,
Oxygen deficiency is 50% to 80%,
The layered double hydroxide is an electrode catalyst for water electrolysis in a state in direct contact with the surface of the nickel support. The method of claim 1,
The nickel support is an electrode catalyst for water electrolysis that forms wrinkles on the surface by the nano pores. The method of claim 1,
The nickel support is an electrode catalyst for water electrolysis comprising at least one selected from a nickel foam, a nickel plate, a nickel wire, and a nickel rod. The method of claim 1,
The nickel alloy hydroxide is an electrode catalyst for water electrolysis comprising at least one selected from iron, cobalt, selenium, tungsten, silver, gold, platinum, iridium, tin, and strontium. The method of claim 1,
The layered double hydroxide is an electrode catalyst for water electrolysis that exists in the surface of the nickel support where there are no nanopores. The method of claim 1,
The electrode catalyst for water electrolysis, wherein a nanosheet array including the layered double hydroxide is formed on the surface of the nickel support. The method of claim 1,
The electrocatalyst for water electrolysis is one that exhibits both functions of oxygen generation and hydrogen generation, an electrode catalyst for water electrolysis. The method of claim 1,
The electrocatalyst for water electrolysis has a higher degree of oxygen deficiency than the nickel support without the surface. delete An electrode comprising the electrocatalyst for water electrolysis according to any one of claims 1 to 8; And
Reference electrode;
A water electrolytic battery comprising a.

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