KR20230029087A - Nickel oxide/three dimensional-nickel structure catalyst, a method for manufacturing the same and a electrode for water decomposition comprising the nickel oxide/three dimensional-nickel structure catalyst - Google Patents

Abstract

The present invention relates to a nickel oxide/3D-nickel structure catalyst, a method for manufacturing the same, and an electrode for water splitting comprising the nickel oxide/3D-nickel structure catalyst. More specifically, a flower-shaped three-dimensional nickel structure is formed on a nickel film, and a nickel oxide layer is formed on the surface of the three-dimensional nickel structure to prepare a nickel oxide/three-dimensional nickel structure catalyst, which has a large number of active sites and provides various catalysts, thereby having excellent hydrogen generation reaction performance in the electrolyte that is equivalent to or better than existing platinum-based catalysts. In addition, by forming a nickel oxide layer on the three-dimensional nickel structure, structural collapse of the catalyst can be suppressed and long-term reaction stability can be significantly improved. The same can be usefully used not only as a platinum replacement catalyst but also as a water splitting device and electronic device.

Description

Nickel oxide/three dimensional-nickel structure catalyst, a method for manufacturing the same, and an electrode for water decomposition comprising the nickel oxide/three dimensional-nickel structure catalyst {Nickel oxide/three dimensional-nickel structure catalyst, a method for manufacturing the same and a electrode for water decomposition comprising the nickel oxide/three dimensional-nickel structure catalyst}

The present invention suppresses structural collapse of the catalyst by coating a nickel oxide layer on a flower-shaped three-dimensional nickel structure, and a nickel oxide / three-dimensional-nickel structure catalyst with improved hydrogen generation reaction performance and long-term reaction stability, a method for preparing the same, and It relates to an electrode for water splitting comprising the nickel oxide/three-dimensional nickel structure catalyst.

As energy demand increases, hydrogen, an eco-friendly energy source, is attracting attention as a future alternative energy source in that it can minimize environmental pollution and is an abundant resource. Hydrogen production through water electrolysis is the easiest and most effective hydrogen production method, but it is not suitable for an effective large-capacity hydrogen production method in terms of energy, so a catalyst must be used to maximize energy efficiency.

So far, platinum (Pt) has been used as a hydrogen evolution reaction (HER) catalyst due to its high reactivity, but most Pt-based novel metals have been used. There was also a problem with poor stability.

Therefore, for large-capacity hydrogen production, research is needed to develop a platinum-replacement catalyst with high reactivity and stability. In addition, since the pH of the electrolyte is unavoidable during the HER reaction, a catalyst that effectively exhibits HER efficiency even in various pH electrolytes is required.

Candidates for replacing Pt-based catalysts include W, Mo, Co, and Ni-based catalysts. Among them, Ni is very cheap and has advantages such as high chemical stability in alkaline solutions and excellent electrical conductivity, so it can be used as a substitute for Pt. There are advantages to being suitable for However, Ni-based HER catalysts have a disadvantage in that it is difficult to show high-efficiency HER performance because a high overvoltage of about 0.3 V is applied.

In order to reduce this high overpotential, previous studies have conducted studies on various Ni compounds such as Ni sulfides, Ni selenides, and Ni oxides, but still high efficiency stability at various pH Since research on Ni-based catalysts is insufficient, research on this is required.

Korean Patent Registration No. 10-1932575

In order to solve the above problems, the present invention suppresses structural collapse of the catalyst by coating a nickel oxide layer on a flower-shaped three-dimensional nickel structure, and nickel oxide / three-dimensional-nickel with improved hydrogen generation reaction performance and long-term reaction stability It aims at providing a structured catalyst.

In addition, an object of the present invention is to provide an electrode for water splitting comprising the nickel oxide/three-dimensional nickel structure catalyst.

In addition, an object of the present invention is to provide an electrochemical water splitting device including the electrode.

In addition, an object of the present invention is to provide a method for preparing a nickel oxide/three-dimensional nickel structure catalyst.

The present invention is a nickel film; a three-dimensional flower-shaped nickel structure formed on the nickel film; and a nickel oxide layer coated on all or part of the surface of the three-dimensional nickel structure, wherein the nickel oxide layer has a thickness of 0.1 to 20 nm.

In addition, the present invention provides a water splitting electrode including the nickel oxide/three-dimensional nickel structure catalyst.

In addition, the present invention provides an electrochemical water splitting device including the electrode, a counter electrode, and an electrolyte or an ionized liquid.

In addition, the present invention comprises the steps of applying a nickel precursor solution on a nickel film and subjecting it to a hot water reaction to form a nickel hydroxide layer; reducing the nickel hydroxide layer formed on the nickel film to form a three-dimensional flower-shaped nickel structure; and preparing a nickel oxide/three-dimensional-nickel structure catalyst in which a nickel oxide layer is formed on all or part of the surface of the three-dimensional nickel structure by heat-treating the three-dimensional nickel structure in air. A method for preparing a dimensional-nickel structure catalyst is provided.

The nickel oxide/3D-nickel structure catalyst according to the present invention forms a flower-shaped 3D-nickel structure on a nickel film and coats a nickel oxide layer on the surface of the 3D-nickel structure, thereby forming a plurality of active sites. Therefore, in various electrolytes, it can have excellent hydrogen generation reaction performance equal to or better than existing platinum-based catalysts.

In addition, the nickel oxide/3-dimensional nickel structure catalyst according to the present invention can suppress structural collapse of the catalyst and significantly improve long-term reaction stability due to the formation of a nickel oxide layer on the 3-dimensional nickel structure. As a result, it can be usefully used not only as a platinum replacement catalyst but also as a water splitting device and an electronic device.

Figure 1a is (a) a schematic diagram schematically showing a manufacturing method of a three-dimensional nickel structure (3D-Ni) prepared in Example 1 according to the present invention, (b) a SEM image of a general nickel foam (Ni foam), (c) SEM image of 3-dimensional nickel structure (3D-Ni), (d) XRD pattern graph of nickel foam and 3D-Ni.
1B is a cross-sectional SEM image of a 3D-nickel structure (3D-Ni) prepared in Example 1 according to the present invention.
1c is a BET analysis graph of a three-dimensional nickel structure (3D-Ni) prepared in Example 1 according to the present invention.
Figure 2 (a ~ c) platinum mesh (Pt mesh), nickel foam (Ni foam) and photocurrent density for 3D-Ni of Example 1 according to the present invention in various electrolytes, (d) K-borate buffer electrolyte HER reaction stability graph of 3D-Ni (10 mA/cm ² reference overpotential), (e) SEM image of 3D-Ni after 10 hours of reaction.
Figure 3 is a SEM image of NiO / 3D-Ni prepared in Example 1 of the present invention before (a) and after 10 hours of reaction (b), Pt mesh in K-borate buffer solution, 3D-Ni charge and discharge reaction and photocurrent density (c) and stability graph (d) for NiO/3D-Ni.
Figure 4 is a TEM according to the heat treatment temperature of 200 ℃ and 250 ℃ and the heat treatment time of 5 to 30 minutes for the nickel oxide / three-dimensional-nickel structure (NiO / 3D-Ni) catalyst prepared in Example 1 according to the present invention It is an image.
Figure 5 is a TEM according to the heat treatment temperature of 300 ℃ and 350 ℃ and the heat treatment time of 5 to 30 minutes for the nickel oxide / three-dimensional-nickel structure (NiO / 3D-Ni) catalyst prepared in Example 1 according to the present invention It is an image.
Figure 6 is a three-dimensional nickel structure (3D-Ni) and nickel oxide / three-dimensional nickel structure (NiO / 3D-Ni) catalyst and Pt mesh prepared in Example 1 according to the present invention (a) 200 ℃ , (b) 250 ℃, (c) 300 ℃ and (d) 350 ℃ (electrolyte: K-borate buffer) is a graph showing the current density for the NiO / 3D-Ni catalyst at various temperature conditions.
7 shows (a) XRD pattern results and (b) of a 3D-nickel structure (3D-Ni) and a nickel oxide/3D-nickel structure (NiO/3D-Ni) catalyst prepared in Example 1 according to the present invention. ) O 1s and (c) Ni 2p XPS spectrum results are shown.
8 shows (a) a schematic diagram of a BiVO ₄ dual electrode and a reflector and (b) a photocurrent density of the working electrode BiVO ₄ when Pt mesh and NiO/3D-Ni of Example 1 were used as counter electrodes in a three-electrode photochemical system. This is a graph of the measured results.

Hereinafter, the present invention will be described in more detail as an embodiment.

The present invention relates to a nickel oxide/three-dimensional-nickel structure catalyst, a manufacturing method thereof, and a water splitting electrode including the nickel oxide/three-dimensional-nickel structure catalyst.

As described above, the conventional Pt-based catalyst has a high-efficiency hydrogen generation reaction, but has disadvantages of high cost and poor stability. Accordingly, in the present invention, in order to replace such a Pt-based catalyst, a flower-shaped three-dimensional nickel structure is formed on a nickel film, and a nickel oxide layer is coated on the surface of the three-dimensional nickel structure to form nickel oxide / three-dimensional nickel oxide. By preparing a structured catalyst, it can have a plurality of active sites and have excellent hydrogen generation reaction performance equivalent to or better than conventional platinum-based catalysts in various electrolytes. In addition, by forming the nickel oxide layer on the three-dimensional nickel structure, structural collapse of the catalyst can be suppressed and long-term reaction stability can be remarkably improved. By using this, it can be usefully used as a platinum replacement catalyst as well as a water splitting device and an electronic device.

Specifically, the present invention is a nickel film; a three-dimensional flower-shaped nickel structure formed on the nickel film; and a nickel oxide layer coated on all or part of the surface of the three-dimensional nickel structure, wherein the nickel oxide layer has a thickness of 0.1 to 20 nm.

The three-dimensional nickel structure may be formed by reducing a flower-shaped nickel hydroxide layer formed by hydrothermal reaction on the nickel film. Since the three-dimensional nickel structure is composed of a flower-shaped three-dimensional structure, the hydrogen generation reaction performance can be remarkably improved by increasing the number of catalytically active sites compared to general nickel foam.

The 3D-nickel structure may have a thickness of 0.01 to 1 mm and a surface area of 12 to 30 m ² /g. It preferably has a thickness of 0.015 to 0.5 mm and a surface area of 14 to 25 m ² /g, most preferably a thickness of 0.025 to 0.04 mm and a surface area of 16 to 19 m ² /g. At this time, if the thickness of the 3D-nickel structure is less than 0.01 mm or the surface area is less than 12 m ² /g, the catalytically active site may decrease and hydrogen generation reaction performance may deteriorate. Conversely, when the thickness of the 3D-nickel structure is greater than 1 mm, structural stability is excellent, but catalytic activity may decrease.

The nickel oxide layer is formed by heating the 3D-nickel structure in air to suppress structural collapse of the 3D-nickel structure and to improve reaction stability during charging and discharging for a long time. It may be formed by oxidizing. Since the nickel oxide layer is hydrophobic, the hydrogen generation reaction performance may be lower than that of pure nickel. Therefore, when coated on the 3D-nickel structure, the hydrogen generation reaction performance is maximized while improving structural stability. Coating is important.

An optimized thickness of the nickel oxide layer may be 0.1 to 20 nm, preferably 1 to 10 nm, more preferably 1.5 to 7 nm, and most preferably 2 to 4 nm. At this time, when the thickness of the nickel oxide layer is less than 0.1 nm, the structural stability of the 3D-nickel structure is lowered, so that the 3D structure collapses during a long-term reaction, and thus the catalytic activity may be lowered. Conversely, if the thickness exceeds 20 nm, the three-dimensional structural stability of the nickel structure is excellent, but the hydrogen generation reaction performance may be relatively deteriorated due to excessive thickness.

The nickel oxide/three-dimensional nickel structure catalyst may be a catalyst for hydrogen generation reaction, and an overvoltage of -0.240 to -0.230 V at a K-borate buffer electrolyte and a photocurrent density of 10 mA/cm ² can have

Meanwhile, the present invention provides a water splitting electrode including the nickel oxide/three-dimensional nickel structure catalyst.

In addition, the present invention provides an electrochemical water splitting device including the electrode, a counter electrode, and an electrolyte or an ionized liquid.

In addition, the present invention comprises the steps of applying a nickel precursor solution on a nickel film and subjecting it to a hot water reaction to form a nickel hydroxide layer; reducing the nickel hydroxide layer formed on the nickel film to form a three-dimensional flower-shaped nickel structure; and preparing a nickel oxide/three-dimensional-nickel structure catalyst in which a nickel oxide layer is formed on all or part of the surface of the three-dimensional nickel structure by heat-treating the three-dimensional nickel structure in air. A method for preparing a dimensional-nickel structure catalyst is provided.

The nickel film may additionally perform a step of physically polishing using sandpaper before the hot water reaction, through which an oxide layer on the nickel film and impurities such as dust may be removed, and the nickel hydroxide layer and the nickel film may be removed. It can improve the binding force between the liver.

The nickel precursor solution is nickel chloride (NiCl ₂ ), nickel chloride hydrate (NiCl ₂ 6H ₂ O), nickel acetate hydrate (Ni(OCOCH ₃ ) ₂ 4H ₂ O), nickel nitrate hydrate (Ni(NO ₃ ) ₂ 6H ₂ O), nickel acetylacetonate (Ni(C ₅ HO ₂ ) ₂ ), nickel hydroxide (Ni(OH) ₂ ), nickel phthalocyanine (C ₃₂ H ₁₆ N ₈ Ni) and nickel carbonate hydrate (NiCO ₃ 2Ni(OH) ₂ ·6H ₂ O) may include one or more types of nickel precursors selected from the group consisting of. Preferably, it may be nickel nitrate hydrate (Ni(NO ₃ ) ₂ 6H ₂ O), nickel acetate hydrate (Ni(OCOCH ₃ ) ₂ 4H ₂ O) or a mixture thereof, and most preferably nickel nitrate hydrate ( Ni(NO ₃ ) ₂ ·6H ₂ O) may include a nickel precursor.

The step of forming the nickel hydroxide layer may be performed by applying a nickel precursor solution on a nickel film and performing a hydrothermal reaction. The hydrothermal reaction is carried out at a temperature of 70 to 130 ° C. It may be carried out at 120 ° C for 3 to 5 hours, most preferably at 95 to 105 ° C for 3.5 to 4.5 hours.

In the step of forming the 3D-nickel structure, the nickel hydroxide layer formed on the nickel film is reduced to form a flower-shaped 3D-nickel structure as the water molecules in the nickel hydroxide layer evaporate and the inside is structured in a 3D manner. can form At this time, the reduction is performed at 300 to 500 ° C. for 30 minutes to 2 hours, preferably at 320 to 410 ° C. for 40 minutes to 90 minutes, and most preferably at 340 to 360 ° C. for 50 minutes to 2 hours while flowing hydrogen gas under vacuum conditions. It can be done in 80 minutes.

In the preparing of the nickel oxide/3D-nickel structure catalyst, a nickel oxide layer (NiO) may be formed on all or part of the surface of the 3D-nickel structure by heat-treating the 3D-nickel structure in air. The nickel oxide layer (NiO) may be formed by oxidizing nickel present on the surface of the 3D-nickel structure through heat treatment in air. In particular, by optimizing the thickness of the nickel oxide layer (NiO) through heat treatment temperature and time control, structural collapse of the 3D-nickel structure can be prevented and stability can be improved during long-term reaction.

The heat treatment may be performed in air at a temperature of 150 to 350 ° C for 5 minutes to 30 minutes, preferably at 180 to 300 ° C for 7 minutes to 20 minutes, and most preferably at 200 to 250 ° C for 8 to 12 minutes. . At this time, if the heat treatment temperature is less than 150 ° C. or the heat treatment temperature is less than 5 minutes, the nickel oxide layer is not uniformly and evenly formed on the surface of the 3D-nickel structure, so structural collapse may occur during long-term reaction, and reaction stability is remarkably can be significantly lowered. Conversely, if the temperature exceeds 350 ° C. or exceeds 30 minutes, the nickel oxide layer is thickly coated due to the long-term heat treatment at high temperature, which may hinder the hydrogen generation reaction.

In particular, although not explicitly described in the following Examples or Comparative Examples, in the method for preparing a nickel oxide/three-dimensional-nickel structure catalyst according to the present invention, the following 7 conditions are varied to obtain nickel oxide/three-dimensional-nickel A structure catalyst was prepared, and an electrochemical water splitting device was formed using it as an electrode. Using this, the hydrogen generation amount and hydrogen generation rate were measured in a neutral solution (potassium borate buffer solution of pH 9.7) by a conventional method, respectively, and the durability of the electrode, electrochemical thermal stability, and long-term life characteristics according to 500 repeated experiments were evaluated. evaluated.

As a result, unlike under other conditions and other numerical ranges, durability, electrochemical thermal stability, and long-life characteristics were uniformly superior to those of conventional platinum-based catalysts when all of the following conditions were satisfied, and hydrogen generation amount and generation rate were improved over a long period of time. It was confirmed that it was maintained at a high level.

① the nickel precursor solution includes a nickel precursor of nickel nitrate hydrate (Ni(NO ₃ ) ₂ 6H ₂ O), ② the hydrothermal reaction is carried out at 95 to 105 ° C. for 3.5 to 4.5 hours, ③ the above 3 In the step of forming a dimensional-nickel structure, reduction is performed at 340 to 360 ° C. for 50 minutes to 80 minutes while flowing hydrogen gas in a vacuum condition, ④ the heat treatment is performed in air at 200 to 250 ° C. for 8 to 12 minutes ⑤ the three-dimensional nickel structure has a thickness of 0.025 to 0.04 mm and a surface area of 16 to 19 m ² /g, ⑥ the nickel oxide layer has a thickness of 2 to 4 nm, ⑦ the nickel oxide / The three-dimensional nickel structure catalyst may have an overvoltage of -0.240 to -0.230 V at a K-borate buffer electrolyte and a photocurrent density of 10 mA/cm ² .

However, when any one of the above 7 conditions is not satisfied, structural collapse of the electrode occurs over time, electrochemical thermal stability is lowered, and the amount and rate of hydrogen generation is lower than that of conventional platinum-based catalysts. showed a lower level than that of In addition, after charging and discharging more than 200 times, the long-term life characteristics rapidly deteriorated.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited by the following examples.

Example 1: Preparation of NiCoP-WOx/NF nanocomposites

(1) Synthesis of nickel hydroxide structure (Ni(OH) ₂ )

First, a nickel film used as a substrate of a three-dimensional nickel structure (3D-Ni) was prepared. Since the nickel film was coated with an oxide film, the oxide film was removed through acid treatment after pretreatment with sandpaper to remove it. Then, a precursor solution was prepared by mixing 12.5 mL of a 200 mM nickel nitrate hexahydrate (Ni(NO) ₃ 6H ₂ O) aqueous solution and 12.5 mL of a 200 mM hexamethylenetetramine (HMTA, C ₆ H ₁₂ N ₄ ) aqueous solution. . Thereafter, the precursor solution was applied on the nickel film and heated for 4 hours at a temperature of 100 ° C. by a hydrothermal reaction in an autoclave to prepare a hierarchical nickel hydroxide (hierarchical Ni(OH) ₂ ) product. . After the synthesized product was completely filtered with deionized water and ethanol, the collected powder was dried at 120 °C for 12 hours under vacuum conditions to obtain a nickel hydroxide structure (Ni(OH) ₂ ) powder.

(2) Synthesis of flower-shaped three-dimensional nickel structure (3D-Ni)

The dried Ni(OH) ₂ structure powder was put into a tube furnace, and after a vacuum condition was made, 100 sccm H ₂ gas was flowed. Then, after undergoing a reduction process at 350 °C for 1 hour using chemical vapor deposition, the furnace was removed and quickly cooled using a fan. After being taken out of the pipe while being cooled to room temperature, nickel hydroxide was reduced to pure nickel to obtain a flower-shaped three-dimensional structure (3D-Ni).

(3) Synthesis of nickel oxide/3D-nickel structure (NiO/3D-Ni) catalyst

The obtained 3D-Ni was heat-treated in air at 200° C. for 10 minutes to prepare a NiO/3D-Ni catalyst having a NiO layer having a thickness of 2 to 4 nm formed on the surface of the 3D-Ni.

Experimental Example 1: SEM, XRD, BET analysis of 3D-nickel structure (3D-Ni)

In order to confirm the shape and crystallinity of the three-dimensional nickel structure (3D-Ni) prepared in Example 1, scanning electron microscopy (SEM), X-ray-diffraction (XRD) and specific surface area (BET) analysis were used to analyzed. The results are shown in Figures 1a to 1c.

Figure 1a is (a) a schematic diagram schematically showing the manufacturing method of the three-dimensional nickel structure (3D-Ni) prepared in Example 1, (b) a SEM image of a general nickel foam (Ni foam), (c) SEM image of three-dimensional nickel structure (3D-Ni), (d) XRD pattern graph of nickel foam and 3D-Ni.

Referring to (a) of FIG. 1A, a general Ni film was used as a substrate for a 3D-nickel structure (3D-Ni) to form flower-shaped 3D-nickel hydroxide by hydrothermal reaction. It shows the process of manufacturing a 3D-nickel structure (3D-Ni) by reducing 3D-nickel hydroxide to pure nickel through chemical vapor deposition under hydrogen gas on the formed 3D-nickel hydroxide.

Referring to (b) and (c) of FIG. 1a , in the case of 3D-Ni prepared through a reduction reaction of nickel hydroxide, it was confirmed that it had a flower-shaped three-dimensional structure, unlike a general nickel foam image. Also, referring to (d) of FIG. 1A, it was confirmed that the 3D-Ni showed the same crystal pattern of Ni (111), Ni (200), and Ni (220) as the nickel foam, which indicates that 3D-Ni It meant that it was made of pure Ni without any other impurities.

1B is a cross-sectional SEM image of a 3D-nickel structure (3D-Ni) prepared in Example 1 above.

Figure 1c is a BET analysis graph of the three-dimensional nickel structure (3D-Ni) prepared in Example 1 above.

Referring to FIGS. 1b and 1c, the thickness of the formed 3D-Ni was adjustable according to the reaction time and temperature of the hydrothermal reaction of nickel hydroxide. The 3D-Ni of Example 1 had a thickness of 0.025 to 0.03 mm and a surface area of 17.4 mm. It was confirmed that m ² /g. In addition, it was found that the surface area of 3D-Ni was very wide compared to general Ni foam through the nano-sized three-dimensional structure, and it was possible to guess that the increased surface area could have a great effect on increasing the HER efficiency.

Experimental Example 2: HER Performance and HER Reaction Stability Analysis of 3-D Nickel Structure (3D-Ni)

In order to confirm HER performance and HER reaction stability for the three-dimensional nickel structure (3D-Ni) prepared in Example 1, charging and discharging were performed and analyzed by a conventional method. In the HER performance test, platinum mesh, nickel foam, and 3D-Ni electrode were used for comparison as the working electrode, platinum mesh as the counter electrode, and Ag/AgCl electrode as the reference electrode. used In addition, as the electrolyte, (a) 0.5MH ₂ SO ₄ (pH 0.5), (b) K-borate buffer (pH 9.7) and (c) 1M KOH (pH 13.6) were used, respectively, at 10 mA/cm ² according to the voltage. The photocurrent density was measured at baseline, and the HER performance of each working electrode was tested. The results are shown in Figure 2.

2 shows (a to c) photocurrent densities for Pt mesh, Ni foam, and 3D-Ni of Example 1 in various electrolytes; (d) 3D-Ni in K-borate buffer electrolyte; HER reaction stability graph of Ni (10 mA/cm ² standard overpotential), (e) SEM image of 3D-Ni after 10 hours of reaction.

Referring to (a to c) of FIG. 2, in all electrolytes, the 3D-Ni is compared to general Ni foam (a) 0.5M H2 _S O ₄ : -0.18 V, (b) K-borate buffer: -0.2 V and (c) 1M KOH: -0.08 V, respectively, showing very improved performance. In particular, in 1M KOH, 3D-Ni exhibits an overvoltage of -0.08 V, which is 0.04 V higher than that of Pt mesh, at a photocurrent density of 10 mA/cm ² . knew that it was

On the other hand, referring to (d) of FIG. 2, as can be seen in the overvoltage versus time stability graph (10 mA/cm ² standard overvoltage, electrolyte K-borate buffer), 3D-Ni reacts at -0.27 V at the initial reaction time for a long time. It showed a tendency to decrease continuously to -0.39 V after 10 hours at . As a result of checking the SEM image to find the cause of the decrease in stability, in the SEM image (e) of FIG. 2, it was confirmed that the three-dimensional structure of 3D-Ni collapsed after 10 hours of charging and discharging reaction. That is, the HER performance of the 3D-Ni was improved compared to the general Ni foam due to its structural characteristics, but it was found that the stability decreased in the long-term reaction through the stability graph and SEM image of FIG. 2. In order to compensate for this structural instability, in Example 1, it was found that it is preferable to form NiO/3D-Ni by coating an oxide film of a nickel oxide layer on the surface of 3D-Ni.

Experimental Example 3: Analysis of HER Performance and HER Reaction Stability of Nickel Oxide/3D-Nickel Structure (NiO/3D-Ni) Catalyst

In order to confirm the HER performance, photocurrent density and HER reaction stability for the three-dimensional nickel structure (3D-Ni) and nickel oxide / three-dimensional-nickel structure (NiO / 3D-Ni) catalysts prepared in Example 1, the above It was analyzed by performing charging and discharging in the same manner as in Experimental Example 2. The results are shown in Figure 3.

Figure 3 is a SEM image before (a) and after 10 hours of reaction (b) of NiO / 3D-Ni prepared in Example 1, Pt mesh, 3D-Ni and NiO in K-borate buffer solution Photocurrent density (c) and stability graph (d) for 3D-Ni.

Referring to (a, b) of FIG. 3, the NiO/3D-Ni shows the same image as the 3D-Ni of FIG. but. After charging and discharging for 10 hours, NiO / 3D-Ni with the same three-dimensional structure as the image before reaction was shown without collapse of the three-dimensional structure, unlike the 3D-Ni of FIG. It was found that it could be prevented.

In addition, referring to (c) of FIG. 3, the HER reactivity of the NiO / 3D-Ni was increased through the NiO coating, showing an overvoltage reduction of -0.045 V at a photocurrent density of 10 mA / cm ² compared to the 3D-Ni electrode confirmed that

In addition, referring to (d) of FIG. 3, as can be seen in the overvoltage versus time stability graph (10 mA/cm ² standard overvoltage, electrolyte K-borate buffer), the 3D-Ni whose overvoltage continuously rises in the long-term reaction Unlike NiO/3D-Ni, the NiO/3D-Ni exhibited a constant overpotential even after a 10-hour charge/discharge reaction, which showed that the HER reaction stability was improved.

Experimental Example 4: Analysis of the thickness and current density of the nickel oxide layer according to the heat treatment temperature of the nickel oxide/3-dimensional-nickel structure (NiO/3D-Ni) catalyst

Confirm current density and overvoltage at various temperature conditions for the three-dimensional nickel structure (3D-Ni) and nickel oxide / three-dimensional-nickel structure (NiO / 3D-Ni) catalyst and Pt mesh prepared in Example 1 did In order to compare and optimize the current density according to the thickness of NiO coated on the 3D-Ni surface, the test method was performed at each heat treatment temperature condition of 200 ° C, 250 ° C, 300 ° C, and 350 ° C and a minimum of 5 minutes and a maximum of 30 minutes. The overvoltage according to the current density was evaluated under the time conditions up to (5, 10, 20, 30 minutes). The overvoltage efficiency of each electrode was analyzed by performing charging and discharging under the conditions of the counter electrode Pt, reference electrode Ag/AgCl, working electrode NiO/3D-Ni and K-borate buffer electrolyte in the same manner as in Experimental Example 2 above. The results are shown in Figures 4 to 6.

4 is a TEM image of the nickel oxide/three-dimensional-nickel structure (NiO/3D-Ni) catalyst prepared in Example 1 according to heat treatment temperatures of 200 °C and 250 °C and heat treatment time of 5 to 30 minutes. Referring to FIG. 4, as the heat treatment time increases to 5 minutes, 10 minutes, 20 minutes, and 30 minutes at temperatures of 200 ° C. and 250 ° C., the average thickness of the nickel oxide layer is 1 to 2 nm and 2 to 4 nm, respectively. , 4 to 7 nm and 7 to 10 nm were formed.

5 is a TEM image of the nickel oxide/three-dimensional-nickel structure (NiO/3D-Ni) catalyst prepared in Example 1 according to heat treatment temperatures of 300 °C and 350 °C and heat treatment time of 5 to 30 minutes. Referring to FIG. 5, as the heat treatment time increases to 5 minutes, 10 minutes, 20 minutes, and 30 minutes at temperatures of 300 ° C. and 350 ° C., the average thickness of the nickel oxide layer is 4 to 7 nm and 7 to 10 nm, respectively. , 10 to 15 nm and 15 to 20 nm.

6 shows the 3D-nickel structure (3D-Ni) and nickel oxide/3D-nickel structure (NiO/3D-Ni) catalyst and Pt mesh prepared in Example 1 (a) at 200 °C, (b) ) 250 ℃, (c) 300 ℃ and (d) 350 ℃ (electrolyte: K-borate buffer) is a graph showing the current density for the NiO / 3D-Ni catalyst at various temperature conditions.

Referring to FIG. 6, each current density showed the best current density at a heat treatment time of 10 minutes in common under all temperature conditions, and the hydrogen generation reaction efficiency tended to decrease due to an increase in overvoltage at a heat treatment time longer than that. Among them, it was confirmed that the most optimal condition was NiO / 3D-Ni heat-treated at 200 to 250 ° C. for 10 minutes, as shown in (a) and (b) of FIG. 6.

In addition, in the case of (c) and (d) of FIG. 6, the hydrogen generation reaction efficiency is rather reduced under the temperature condition of 300 ℃ or more, which means that the NiO layer thickly coated on the surface at high temperature and long time heat treatment promotes the hydrogen generation reaction. I knew it was because it was interfering.

Through this, when heat treatment is performed at a temperature of 200 to 250 ° C. for 10 minutes to improve current density and stability while maximizing the hydrogen generation reaction, a nickel oxide layer having a thickness of 2 to 4 nm can be most optimally formed. confirmed.

Experimental Example 5: XRD and XPS analysis of nickel oxide/3-dimensional-nickel structure (NiO/3D-Ni) catalyst

XRD and XPS (x- ray photoelectron spectroscopy) analysis was performed, and the results are shown in FIG. 7 .

7 shows (a) XRD pattern results and (b) O 1s of the 3D-nickel structure (3D-Ni) and nickel oxide/3D-nickel structure (NiO/3D-Ni) catalyst prepared in Example 1. and (c) XPS spectrum results of Ni 2p.

Referring to (a) of FIG. 7, as a result of confirming the crystal patterns of the 3D-Ni and NiO / 3D-Ni by XRD pattern analysis, the same peaks were shown in (111), (200), and (220) planes. It was found that this is the same XRD crystal pattern as that of Ni foam, as in (d) of FIG. 1a. In addition, in the case of NiO, since it is coated on the surface of 3D-Ni with a very thin thickness of 2 to 4 nm, it was found that the amount occupied in the entire electrode was relatively very small and was not confirmed in the XRD pattern.

In addition, (b) and (c) of FIG. 7 are the results of XPS analysis to further confirm the presence of NiO, and the 3D-Ni also has a partially oxidized part in air, so that the O 1s peak at 532 eV However, unlike the 3D-Ni, the NiO/3D-Ni exhibited a stronger peak at 532 eV due to the presence of a NiO oxide film on the entire surface.

In addition, in (c) of FIG. 7, NiO/3D-Ni is compared to Ni 2p _3/2 (852.5eV) and Ni 2p _1/2 (869.8eV) of 3D-Ni. A shift occurred with binding energies of Ni 2p _3/2 (852.7 eV) and Ni 2p _1/2 (867.0 eV) as high as 0.2 eV, respectively, indicating that Ni was oxidized. Finally, through the above analysis, it was confirmed that NiO was formed on the surface.

Experimental Example 6: Analysis of water decomposition performance of nickel oxide/3-dimensional-nickel structure (NiO/3D-Ni) catalyst

In order to confirm the water decomposition performance of the nickel oxide/3-dimensional-nickel structure (NiO/3D-Ni) catalyst and the Pt mesh prepared in Example 1, an experiment was conducted as follows. Specifically, for the water decomposition performance test, 1 sun (AM 1.5G) light was used, BiVO ₄ was used as the working electrode, Pt mesh and NiO/3D-Ni were used as the counter electrode, and Ag/AgCl was used as the reference electrode. K-borate buffer and 0.2M Na2SO3 solution (pH 9.63) were used as the electrolyte. 0.2M Na ₂ SO ₃ serves as a hole scavenger to prevent surface charge-hole recombination and was added to K-borate buffer to optimize water decomposition performance. The experimental results for this are shown in FIG. 8 .

8 shows (a) a schematic diagram of a BiVO ₄ dual electrode and a reflector and (b) a photocurrent density of the working electrode BiVO ₄ when Pt mesh and NiO/3D-Ni of Example 1 were used as counter electrodes in a three-electrode photochemical system. This is a graph of the measured results.

8(a) is a schematic diagram showing BiVO ₄ used as a photoanode. In order to maximize water decomposition performance, two BiVO ₄ electrodes are overlapped to form a dual BiVO ₄ electrode, and solar It shows the use of a common mirror as a reflector on the bottom of the dual BiVO ₄ to maximize light usage.

Also, referring to (b) of FIG. 8, when a Pt mesh is used as a counter electrode, a typical dual BiVO ₄ electrode has a water decomposition standard of 1.23V vs. RHE showed a photocurrent density of about 8 mA/cm ² , and when NiO/3D-Ni was used as a counter electrode, a photocurrent density of 7.79 mA/cm ² 97% of that of Pt mesh was shown. These results indicate that the NiO/3D-Ni exhibits high HER performance comparable to that of the Pt mesh, and secures long-term stability as shown in FIG. 3(d), thereby being an electrode to replace the Pt mesh.

As described above, the nickel oxide / 3D-nickel structure catalyst of the present invention grows a Ni (OH) ₂ layer, which is a 3D flower-shaped structure, on a nickel film, and then forms a 3D-nanostructure (3D-nanostructure) through a reduction process. Ni) and form a nickel oxide (NiO) layer on the surface of the 3D-nanostructure (3D-Ni) through heat treatment in air to improve reaction stability, and finally the nickel oxide / 3D-nickel structure ( NiO/3D-Ni) catalyst was prepared.

The nickel oxide/three-dimensional nickel structure catalyst has excellent hydrogen generation reaction performance compared to conventional Ni foam in electrolytes having various pHs, and showed good HER performance comparable to Pt mesh. In particular, it showed high stability for a long time in K-borate buffer electrolyte, and in the water decomposition performance test in which BiVO ₄ was used as a working electrode and Pt mesh as a counter electrode, the NiO/3D-Ni was tested when the Pt mesh was used as a counter electrode. It was confirmed that it can be used very usefully as a Pt replacement catalyst by showing an efficiency close to 97% compared to the BiVO ₄ efficiency of Pt mesh and showing good performance compared to Pt mesh.

Claims (14)

nickel film;
a three-dimensional flower-shaped nickel structure formed on the nickel film; and
A nickel oxide layer coated on all or part of the surface of the three-dimensional nickel structure; includes,
The nickel oxide layer is a nickel oxide / three-dimensional-nickel structure catalyst having a thickness of 0.1 to 20 nm.
According to claim 1,
The three-dimensional nickel structure has a thickness of 0.01 to 1 mm and a surface area of 12 to 30 m ² /g. Nickel oxide / three-dimensional nickel structure catalyst.
According to claim 1,
The three-dimensional nickel structure is a nickel oxide / three-dimensional-nickel structure catalyst formed by reducing a flower-shaped nickel hydroxide layer formed by a hydrothermal reaction on the nickel film.
According to claim 1,
The nickel oxide layer is formed by heat-treating the three-dimensional nickel structure in air to oxidize nickel present on the surface of the three-dimensional nickel structure.
According to claim 1,
The nickel oxide / three-dimensional-nickel structure catalyst is a catalyst for hydrogen generation reaction.
According to claim 1,
The nickel oxide/three-dimensional-nickel structure catalyst has an overvoltage of -0.240 to -0.230 V at a K-borate buffer electrolyte and a photocurrent density of 10 mA/cm ² Nickel oxide/three-dimensional- Nickel structure catalyst.
An electrode for water splitting comprising the nickel oxide/three-dimensional nickel structure catalyst of any one selected from claims 1 to 6.
An electrochemical water splitting device comprising the electrode of claim 7, a counter electrode, and an electrolyte or an ionized liquid.
forming a nickel hydroxide layer by applying a nickel precursor solution on a nickel film and performing a hot water reaction;
reducing the nickel hydroxide layer formed on the nickel film to form a three-dimensional flower-shaped nickel structure; and
Heat-treating the 3D-nickel structure in air to prepare a nickel oxide/3D-nickel structure catalyst in which a nickel oxide layer is formed on all or part of the surface of the 3D-nickel structure;
Method for producing a nickel oxide / three-dimensional-nickel structure catalyst comprising a.
According to claim 9,
The nickel precursor solution is nickel chloride (NiCl ₂ ), nickel chloride hydrate (NiCl ₂ 6H ₂ O), nickel acetate hydrate (Ni(OCOCH ₃ ) ₂ 4H ₂ O), nickel nitrate hydrate (Ni(NO ₃ ) ₂ 6H ₂ O), nickel acetylacetonate (Ni(C ₅ HO ₂ ) ₂ ), nickel hydroxide (Ni(OH) ₂ ), nickel phthalocyanine (C ₃₂ H ₁₆ N ₈ Ni) and nickel carbonate hydrate (NiCO ₃ 2Ni (OH) ₂ · 6H ₂ O) method for producing a nickel oxide / three-dimensional nickel structure catalyst comprising at least one nickel precursor selected from the group consisting of.
According to claim 9,
The hydrothermal reaction is a method for producing a nickel oxide / three-dimensional-nickel structure catalyst that is carried out at a temperature of 70 to 130 ° C. for 2 to 6 hours.
According to claim 9,
In the step of forming the three-dimensional nickel structure, the reduction is carried out at 300 to 500 ° C. for 30 minutes to 2 hours while flowing hydrogen gas in a vacuum condition. Method for producing a nickel oxide / three-dimensional nickel structure catalyst.
According to claim 9,
The heat treatment is a method for producing a nickel oxide / three-dimensional-nickel structure catalyst that is performed for 5 minutes to 30 minutes at a temperature of 150 to 350 ° C. in air.
According to claim 9,
The nickel precursor solution includes a nickel precursor of nickel nitrate hydrate (Ni(NO ₃ ) ₂ 6H ₂ O),
The hydrothermal reaction is carried out at 95 to 105 ° C. for 3.5 to 4.5 hours,
In the step of forming the three-dimensional nickel structure, the reduction is performed at 340 to 360 ° C. for 50 to 80 minutes while flowing hydrogen gas in a vacuum condition,
The heat treatment is performed in air at 200 to 250 ° C. for 8 to 12 minutes,
The three-dimensional nickel structure has a thickness of 0.025 to 0.04 mm and a surface area of 16 to 19 m ² /g,
The nickel oxide layer has a thickness of 2 to 4 nm,
The nickel oxide/three-dimensional-nickel structure catalyst has an overvoltage of -0.240 to -0.230 V at a K-borate buffer electrolyte and a photocurrent density of 10 mA/cm ² Nickel oxide/three-dimensional- A method for producing a nickel structure catalyst.

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