ELECTRODE FOR CHLORINE EVOLUTION AND MANUFACTURING METHOD THEREFOR

Description

TECHNICAL FIELD

The present disclosure claims priority to and the benefit of filing date of Korean Patent Application No. 10-2022-0113002 filed in the Korean Intellectual Property Office on Sep. 6, 2022, and the entire contents thereof are included in the present disclosure.

The present disclosure relates to an electrode for chlorine evolution including a niobium-ruthenium-titanium composite oxide particle layer formed on a porous titanium metal substrate and a method for manufacturing the same.

BACKGROUND ART

Recently, RuO₂ has been known as one of the most common catalysts for chlorine evolution reaction (CER). However, ruthenium-based catalysts have excellent catalytic properties but there is a problem in that they are very expensive.

Therefore, a dimensionally stable anode (DSA) composed of 30 mol % of RuO₂, and 70 mol % of TiO₂ with rutile structure of which performance is degraded to the minimum while minimizing the use of RuO₂, is used as a commercial catalyst electrode.

The catalyst electrode is an insoluble electrode, and since the electrode does not dissolve during electrochemical reaction, the catalyst electrode is widely applied and utilized in the field of water treatment due to the advantages in that lifespan of the electrode is semi-permanent and it has excellent durability. However, the DSA has a structure with a small specific surface area, so it has a disadvantage of having a large use amount of catalyst. In addition, when performing a chlorine evolution reaction using DSA, there is a problem in that RuO₂ dissolves in DSA.

Therefore, a technology capable of manufacturing an electrode for chlorine evolution that is price competitive while having excellent stability by solving the problem of RuO₂ dissolving in the chlorine evolution reaction is needed.

DISCLOSURE

Technical Problem

The technical problem that the present disclosure seeks to solve is to provide an electrode for chlorine evolution having excellent stability and electrochemical properties and a method for easily manufacturing the same.

However, the problem to be solved by the present disclosure is not limited to the problem mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description.

Technical Solution

According to one aspect of the present disclosure, there is provided an electrode for chlorine evolution including: a porous titanium metal substrate; and a niobium-ruthenium-titanium composite oxide particle layer formed on the porous titanium metal substrate, wherein the porous titanium metal substrate has a microstructure on the surface and includes a titanium dioxide layer doped with niobium, and the niobium-ruthenium-titanium composite oxide particle layer contains niobium-ruthenium-titanium composite oxide particles composed of: a core represented by Chemical Formula 1 below; and a titanium dioxide shell.

In the above formula, 0<x<1, 0<y<1, and 0<x+y<1.

One embodiment of the present disclosure provides a method for manufacturing an electrode for chlorine evolution, the method including steps of: forming a titanium dioxide layer on the surface by oxidizing a porous titanium metal substrate; coating a niobium precursor solution on the porous titanium metal substrate having the titanium dioxide layer formed thereon and then manufacturing a porous titanium metal substrate having a niobium-doped titanium dioxide layer formed thereon through a first hydrothermal reaction; coating a ruthenium precursor solution on the porous titanium metal substrate having the niobium-doped titanium dioxide layer formed thereon and then depositing ruthenium on the niobium-doped titanium dioxide layer by performing a second hydrothermal reaction; and heat-treating the porous titanium metal substrate having the ruthenium-deposited niobium-doped titanium dioxide layer formed thereon.

In the above formula, 0<x<1, 0<y<1, and 0<x+y<1.

Advantageous Effects

The electrode for chlorine evolution including a niobium-ruthenium-titanium composite oxide particle layer formed on a porous titanium metal substrate according to one embodiment of the present disclosure has excellent electrochemical properties and can exhibit excellent stability and chlorine evolution efficiency.

In addition, the method for manufacturing an electrode for chlorine evolution including a niobium-ruthenium-titanium composite oxide particle layer formed on a porous titanium metal substrate according to one embodiment of the present disclosure can easily manufacture an electrode for chlorine evolution having excellent stability and electrochemical properties.

However, the effects of the present disclosure are not limited to the effects described above, and may be variously expanded within a scope that does not depart from the idea and scope of the present disclosure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an electrode for chlorine evolution according to one embodiment of the present disclosure.

FIG. 2 is an SEM image of the surface of an electrode for chlorine evolution manufactured in Example 1 of the present disclosure.

FIG. 3 is SEM images taken from the side surfaces of the electrode for chlorine evolution manufactured in Example 1 of the present disclosure.

FIG. 4 is element mapping images of the electrode for chlorine evolution manufactured in Example 1 of the present disclosure.

FIG. 5 is an image showing the distribution of titanium and ruthenium particles on the surface of the electrode for chlorine evolution manufactured in Example 1.

FIG. 6 is a graph showing surface areas of electrodes for chlorine evolution manufactured in Example 1 and Comparative Example 1 and a conventional DSA participating in the electrochemical reactions.

FIG. 7 is a graph showing CV curves of the electrodes for chlorine evolution manufactured in Example 1 and Comparative Example 1 and the conventional DSA.

FIG. 8 is a graph showing Tafel slopes of the electrodes for chlorine evolution manufactured in Example 1 and Comparative Example 1 and the conventional DSA.

FIG. 9 is a graph showing faradaic efficiencies in a 5.0 M NaCl solution of the electrode for chlorine evolution manufactured in Example 1 and the conventional DSA.

FIG. 10 is a graph showing stability of the electrode for chlorine evolution manufactured in Example 1 according to the operating time at 400 mA cm², which is a commercial process condition.

FIG. 11 is a graph comparing an overpotential of the electrode for chlorine evolution manufactured in Example 1 with those of electrodes using conventional commercial catalysts.

FIG. 12 is graphs comparing resistance values that impede charge transfer on the surfaces of the electrodes for chlorine evolution manufactured in Example 1 and Comparative Example 1 with that of the conventional DSA.

FIG. 13A is a graph showing diffusion resistances of the electrodes for chlorine evolution manufactured in Example 1 and Comparative Example 1 in a convective environment, and FIG. 13B is a graph comparing diffusion resistances by blocking the side surfaces of the electrode for chlorine evolution manufactured in Example 1.

FIG. 14 is CV graphs showing results of measuring chlorine and hydrogen evolution performances of the electrode for chlorine evolution manufactured in Example 1 under industrial conditions.

FIG. 15 is a graph showing results of measuring stability over time of the electrode for chlorine evolution manufactured in Example 1 under industrial conditions.

BEST MODE FOR CARRYING OUT THE INVENTION

Throughout this specification, when a part “includes” a certain element, this means that it may further include other elements rather than excluding other elements, unless specifically stated to the contrary.

Throughout this specification, when a member is said to be located “on” another member, this includes not only cases where a member is in contact with another member, but also cases where another member exists between the two members.

Throughout this specification, at % may represent atomic percentage, wt % may represent weight percentage or weight part, and mol % may represent mole percentage.

Hereinafter, specific details for implementing the present disclosure will be described in detail with reference to the attached drawings.

According to one aspect of the present disclosure, there is provided an electrode for chlorine evolution including: a porous titanium metal substrate; and a niobium-ruthenium-titanium composite oxide particle layer formed on the porous titanium metal substrate, wherein the porous titanium metal substrate includes a titanium dioxide layer which has a microstructure on the surface thereof and is doped with niobium, and the niobium-ruthenium-titanium composite oxide particle layer includes ruthenium-niobium-titanium composite oxide particles (Ru—Nb—Ti mixed oxide) composed of: a core represented by Chemical Formula 1 below; and a titanium dioxide shell.

In the above formula, 0<x<1, 0<y<1 and 0<x+y<1.

FIG. 1 is a schematic diagram showing an electrode for chlorine evolution according to one embodiment of the present disclosure. Referring to FIG. 1, a titanium dioxide layer which has a microstructure and is doped with niobium is formed on the surface of a porous titanium metal substrate. In addition, the niobium-ruthenium-titanium composite oxide particle layer is composed of niobium-ruthenium-titanium composite oxide particles having a core of Ru_xNb_yTi_1-x-yO₂ and a shell of TiO₂.

The electrode for chlorine evolution according to one embodiment of the present disclosure is excellent in stability and may have excellent electrochemical properties. Specifically, when the electrode for chlorine evolution is utilized, the electrode for chlorine evolution may have excellent chlorine evolution efficiency. In addition, the niobium-ruthenium-titanium composite oxide particles may have excellent resistance to anodic corrosion. Specifically, a shell including titanium dioxide particles is formed in the core represented by Chemical Formula 1 above so that the ruthenium particles may be effectively suppressed from dissolving when applied as an electrode for chlorine evolution.

In addition, the electronic conductivity of the electrode for chlorine evolution may be improved by doping niobium into titanium dioxide on the surface of a porous titanium metal substrate, and more excellent electrochemical properties may be maintained for a long period of time by effectively suppressing titanium dioxide from being hydroxylated. In addition, the electrode for chlorine evolution may have excellent price competitiveness since it includes a very small amount of high-priced ruthenium.

According to one embodiment of the present disclosure, in Chemical Formula 1 above, x may be 0.30 or more to 0.50 or less. Specifically, it may be 0.32 or more to 0.48 or less, 0.34 or more to 0.46 or less, 0.36 or more to 0.44 or less, 0.38 or more to 0.42 or less, 0.38 or more to 0.44 or less, or 0.36 or more to 0.42 or less. In addition, the content of the niobium atom may be based on a total of 100 at % of ruthenium atom, titanium atom, and niobium atom. The electrochemical properties of the niobium-ruthenium-titanium composite oxide particle layer may be effectively improved by satisfying the above range.

According to one embodiment of the present disclosure, in Chemical Formula 1 above, y may be 0.05 or more to 0.15 or less. Specifically, it may be 0.06 or more to 0.14 or less, 0.07 or more to 0.13 or less, 0.08 or more to 0.12 or less, 0.08 or more to 0.11 or less, 0.07 or more to 0.12 or less, or 0.07 or more to 0.10 or less. In addition, the content of the ruthenium atom may be based on a total of 100 at % of ruthenium atom, titanium atom, and niobium atom. The electrochemical properties of the niobium-ruthenium-titanium composite oxide particle layer may be effectively improved by satisfying the above range.

According to one embodiment of the present disclosure, the niobium-ruthenium-titanium composite oxide particles having a core-shell structure included in the niobium-ruthenium-titanium composite oxide particle layer may exist discontinuously. That is, the composite oxide particle layer may include a portion where the niobium-ruthenium-titanium composite oxide particles having a core-shell structure exist and a portion where the composite oxide particles do not exist, and the portion where the composite oxide particles do not exist may include a ruthenium element.

According to one embodiment of the present disclosure, the niobium-ruthenium-titanium composite oxide particle layer may contain 0.0001 g or more to 0.0003 g or less of ruthenium per 1 cm² of the porous titanium metal substrate unit surface area. Specifically, it may contain 0.00011 g or more to 0.00028 g or less, 0.00012 g or more to 0.00026 g or less, 0.00011 g or more to 0.0024 g or less, 0.00013 g or more to 0.00022 g or less, 0.00014 g or more to 0.00020 g or less, 0.00013 g or more to 0.00018 g or less, 0.00014 g or more to 0.00016 g or less, or 0.000013 g or more to 0.00016 g or less of ruthenium per 1 cm² of the porous titanium metal substrate unit surface area. The electrochemical properties may be effectively improved by satisfying the above range. In addition, the cost of the process may be reduced by containing a smaller amount of ruthenium compared to the conventional DSA commercial catalyst electrode.

According to one embodiment of the present disclosure, the shell is a single layer, and the shell may have a thickness of 1 Å or more to 8 Å or less. Specifically, it may have a thickness of 2 Å or more to 7 Å or less, 2 Å or more to 6 Å or less, or 1 Å or more to 6 Å or less. The niobium-ruthenium-titanium composite oxide particles provided with a titanium dioxide shell having the thickness in the above-described range may implement excellent resistance to anodic corrosion and excellent electrochemical properties.

According to one embodiment of the present disclosure, the niobium-ruthenium-titanium composite oxide particles of the niobium-ruthenium-titanium composite oxide particle layer formed on the porous titanium metal substrate may have an average particle diameter of 1.0 nm or more to 3.0 nm or less. Specifically, it may have an average particle diameter of 1.1 nm or more to 2.9 nm or less, 1.2 nm or more to 2.8 nm or less, 1.3 nm or more to 2.7 nm or less, 1.4 nm or more to 2.8 nm or less, 1.5 nm or more to 2.5 nm or less, 1.5 nm or more to 2.7 nm or less, or 1.4 nm or more to 2.6 nm or less. The niobium-ruthenium-titanium composite particle layer formed on the porous titanium metal substrate having the average particle diameter in the above-described range may implement excellent resistance to anodic corrosion and excellent electrochemical properties.

According to one embodiment of the present disclosure, the niobium-doped titanium dioxide layer and the niobium-ruthenium-titanium composite oxide particle layer formed on the surface of the porous titanium metal substrate may have a total thickness of 30 nm or more to 50 nm or less. Specifically, it may have a total thickness of 32 nm or more to 48 nm or less, 34 nm or more to 46 nm or less, 36 nm or more to 44 nm or less, 38 nm or more to 42 nm or less, 36 nm or more to 42 nm or less, 38 nm or more to 46 nm or less, or 38 nm or more to 40 nm or less. Excellent resistance to anodic corrosion and excellent electrochemical properties may be implemented by satisfying the above thickness range.

According to one embodiment of the present disclosure, there is provided a method for manufacturing an electrode for chlorine evolution, the method including steps of: forming a titanium dioxide layer on the surface by oxidizing a porous titanium metal substrate; coating a niobium precursor solution on the porous titanium metal substrate having the titanium dioxide layer formed thereon and then manufacturing a porous titanium metal substrate having a niobium-doped titanium dioxide layer formed thereon through a first hydrothermal reaction; coating a ruthenium precursor solution on the porous titanium metal substrate having the niobium-doped titanium dioxide layer formed thereon and then depositing ruthenium on the niobium-doped titanium dioxide layer by performing a second hydrothermal reaction; and heat-treating the porous titanium metal substrate having the ruthenium-deposited niobium-doped titanium dioxide layer formed thereon.

A method for manufacturing an electrode for chlorine evolution including a niobium-ruthenium-titanium composite oxide particle layer formed on the porous titanium metal substrate according to one embodiment of the present disclosure may easily manufacture an electrode for chlorine evolution having excellent stability and electrochemical properties.

Hereinafter, a method for manufacturing an electrode for chlorine evolution according to one embodiment of the present disclosure will be specifically described step by step.

According to one embodiment of the present disclosure, a titanium dioxide layer having a microstructure may be formed on the surface of the substrate by oxidizing the porous titanium metal substrate. The surface area may be increased by having a microstructured surface roughness on the surface of the substrate.

According to one embodiment of the present disclosure, a titanium metal substrate may be oxidized using hydrogen peroxide (H₂O₂) to form a titanium dioxide layer on the surface of the titanium metal substrate. When hydrogen peroxide is used, titanium metal is easily ionized and forms a concave surface shape on the surface of the titanium metal substrate to form a microstructure, thereby imparting high roughness. When the surface of the titanium metal substrate has high roughness, a larger amount of niobium may be doped during niobium doping, and further, a larger amount of ruthenium may be deposited during ruthenium deposition.

According to one embodiment of the present disclosure, the hydrogen peroxide may have a concentration of 40 wt % or more to 60 wt % or less. Specifically, it may have a concentration of 42 wt % or more to 58 wt % or less, 46 wt % or more to 56 wt % or less, 48 wt % or more to 54 wt % or less, 48 wt % or more to 52 wt % or less, 46 wt % or more to 52 wt % or less, or 46 wt % or more to 50 wt % or less. When the concentration range of hydrogen peroxide is satisfied, titanium metal is more easily ionized and may more easily form a concave surface shape on the surface of the titanium metal substrate to form a microstructure, thereby imparting high roughness.

According to one embodiment of the present disclosure, the step of forming a titanium dioxide layer on the surface by oxidizing a porous titanium metal substrate may be performed, for example, by immersing the substrate in hydrogen peroxide at a temperature of 50° C. or more to 90° C. or less for 20 minutes or more to 40 minutes or less. Specifically, it may be performed at a temperature of 55° C. or more to 85° C. or less, 60° C. or more to 80° C. or less, 65° C. or more to 75° C. or less, 60° C. or more to 70° C. or less, or 65° C. or more to 80° C. or less for 23 minutes or more to 37 minutes or less, 26 minutes or more to 34 minutes or less, 29 minutes or more to 31 minutes or less, 26 minutes or more to 31 minutes or less, or 29 minutes or more to 34 minutes or less. When the temperature and time ranges at which a titanium dioxide layer is formed on the surface of the porous metal substrate by oxidizing the porous metal substrate are satisfied, a concave surface shape may be more easily formed to form a microstructure.

According to one embodiment of the present disclosure, the porous titanium metal substrate may be in the form of a foam. The porous titanium metal substrate in the form of a foam may facilitate niobium doping and ruthenium deposition, and may have excellent compatibility with the niobium precursor and the ruthenium precursor. The pores of the porous titanium metal substrate may have an average particle diameter of 10 μm or more to 50 μm or less. When the porous titanium metal substrate having pores with an average particle diameter in the above-described range is used, niobium doping and ruthenium deposition may be performed more easily, and the electrochemical properties of the electrode for chlorine evolution may be further improved.

Next, a niobium precursor solution is coated on a porous titanium metal substrate having a titanium dioxide layer formed on the surface thereof, and then a porous titanium metal substrate having a niobium-doped titanium dioxide layer formed thereon is manufactured by a first hydrothermal reaction. Niobium is doped into the titanium metal substrate having a microstructure formed on the surface thereof by oxidation and a titanium dioxide layer formed thereon so that the heat treatment temperature for forming niobium-ruthenium-titanium composite oxide particles may be lowered afterwards, and the niobium-ruthenium-titanium composite oxide particle layer may be effectively suppressed from dissolving when the electrode for chlorine evolution is used. In addition, niobium is doped into the porous titanium metal substrate to form a niobium-doped titanium dioxide layer on the surface of the substrate so that the electronic conductivity of the electrode for chlorine evolution may be improved, and titanium dioxide is effectively suppressed from being hydroxylated so that more excellent electrochemical properties may be maintained for a long period of time.

According to one embodiment of the present disclosure, a material capable of doping niobium into a titanium dioxide layer on the surface of a porous titanium metal substrate having a titanium dioxide layer formed on the surface thereof may be used as a precursor. Specifically, the niobium precursor may include a niobium halide. For example, the niobium halide may include at least one of NbF₅, NbCl₅, NbBr₅, and NbI₅. More specifically, the niobium halide may include NbCl₅ in terms of solubility and thermal stability. The titanium dioxide layer formed on the surface of the porous titanium metal substrate may be more stably and effectively doped with niobium by using the niobium precursor including a niobium halide.

According to one embodiment of the present disclosure, the niobium precursor solution may have a niobium precursor content of 0.005 mol % or more to 0.015 mol % or less. Specifically, the content of the niobium precursor contained in the first mixture may be 0.006 mol % or more to 0.014 mol %, 0.007 mol % or more to 0.013 mol %, 0.008 mol % or more to 0.012 mol %, 0.009 mol % or more to 0.011 mol %, 0.008 mol % or more to 0.011 mol %, or 0.010 mol % or more to 0.012 mol % or less. When the content of the niobium precursor contained in the first mixture is within the above-described range, the titanium dioxide layer formed on the surface of the titanium metal substrate may be stably doped with niobium. In addition, the content of the niobium precursor contained in the niobium precursor solution is adjusted within the above-described range so that the niobium content of the electrode for chlorine evolution may be appropriately adjusted as described later, thereby further improving the stability and electrochemical properties of the electrode.

According to one embodiment of the present disclosure, a porous titanium metal substrate on which a niobium-doped titanium dioxide layer is formed may be manufactured more easily through the first hydrothermal reaction, thereby effectively reducing the cost required for the entire process of manufacturing the electrode for chlorine evolution. That is, an electrode for chlorine evolution including a niobium-ruthenium-titanium composite oxide particle layer formed on a porous titanium metal substrate having excellent price competitiveness may be manufactured through the method according to one embodiment of the present disclosure.

According to one embodiment of the present disclosure, the first hydrothermal reaction may be performed at a temperature of 150° C. or more to 200° C. or less for a time of 5 hours or more to 8 hours or less. Specifically, the temperature at which the first hydrothermal reaction is performed may be 160° C. or more to 190° C. or less, 170° C. or more to 180° C. or less, 150° C. or more to 180° C. or less, or 160° C. or more to 200° C. or less. In addition, the time for which the first hydrothermal reaction is performed may be 6 hours or more to 7 hours or less, 5 hours or more to 7 hours or less, or 6 hours or more to 8 hours or less. The temperature and time at which the first hydrothermal reaction is performed are adjusted within the above-described ranges so that niobium may be more stably and efficiently doped onto the porous titanium metal substrate on which the titanium dioxide layer is formed.

According to one embodiment of the present disclosure, the first hydrothermal reaction may be performed at a temperature increasing rate of 5° C./min or more to 15° C./min or less, 7° C./min or more to 13° C./min or less, 5° C./min or more to 10° C./min or less, or 10° C./min or more to 15° C./min or less up to the temperature range described above. When the temperature increasing rate of the first mixture is within the range described above, a thermal shock may be prevented from being applied to reaction products, thereby allowing niobium to be more stably and efficiently doped onto the surface of the porous titanium metal substrate on which the titanium dioxide layer is formed.

According to one embodiment of the present disclosure, fluorine-doped tin oxide (FTO) is additionally made and used in the form of a roof on the porous titanium metal substrate during the first hydrothermal reaction so that niobium particles may be uniformly doped on the surface of the porous titanium metal substrate on which the titanium dioxide layer is formed during the first hydrothermal reaction.

That is, the FTO roof exists, thereby preventing niobium particles that are heterogeneously generated during the hydrothermal synthesis process from falling on the substrate so that only homogeneous niobium particles may be allowed to be deposited.

Before depositing ruthenium on the porous titanium substrate on which the niobium-doped titanium dioxide layer is formed, a step of drying it in a vacuum oven may be additionally included. For example, the porous titanium substrate on which the niobium-doped titanium dioxide layer is formed may be dried in a vacuum oven for about 24 hours.

In the next step, a ruthenium precursor solution is coated on the porous titanium metal substrate on which the niobium-doped titanium dioxide layer is formed, and then ruthenium is deposited through a second hydrothermal reaction.

According to one embodiment of the present disclosure, the ruthenium precursor solution may include a ruthenium halide. For example, the ruthenium halide may include at least one of RuF₃, RuCl₃, RuBr₃, and RuI₃. Specifically, the ruthenium halide may include RuCl₃ in terms of solubility and thermal stability. Ruthenium may be effectively deposited by using the ruthenium precursor including the ruthenium halide. Through this, an electrode for chlorine evolution including a niobium-ruthenium-titanium composite oxide particle layer formed on a porous titanium metal substrate may be stably manufactured. In addition, the ruthenium precursor may be a hydrate. Compatibility with the porous titanium metal substrate doped with niobium may be improved by using the ruthenium precursor in the form of a hydrate.

According to one embodiment of the present disclosure, the ruthenium precursor solution may have a ruthenium precursor content of 0.01 mol % or more to 0.02 mol % or less. Specifically, the content of the ruthenium precursor contained in the ruthenium precursor solution may be 0.011 mol % or more to 0.019 mol %, 0.012 mol % or more to 0.018 mol %, 0.013 mol % or more to 0.017 mol %, 0.014 mol % or more to 0.016 mol %, 0.015 mol % or more to 0.017 mol %, or 0.014 mol % or more to 0.017 mol % or less. When the content of the ruthenium precursor contained in the ruthenium precursor solution is within the above-described range, ruthenium may be stably deposited on the surface of the titanium metal substrate. In addition, the content of the ruthenium precursor contained in the ruthenium precursor solution may be adjusted within the above-described range to appropriately adjust the ruthenium content of the electrode for chlorine evolution as described later, thereby further improving the stability and electrochemical properties of the electrode.

When the content of the ruthenium precursor is within the above-described range, an electrode for chlorine evolution including a niobium-ruthenium-titanium composite oxide particle layer on a porous titanium metal substrate may be stably manufactured through the second hydrothermal reaction. In addition, the content of the ruthenium precursor may be adjusted within the above-described range, thereby manufacturing an electrode for chlorine evolution which minimizes the content of ruthenium particles and has excellent electrochemical properties at the same time as described later.

The cost required for the entire process of manufacturing an electrode for chlorine evolution including a niobium-ruthenium-titanium composite oxide particle layer on a porous titanium metal substrate may be effectively reduced through the second hydrothermal reaction. That is, an electrode for chlorine evolution having excellent price competitiveness may be manufactured through the method according to one embodiment of the present disclosure.

According to one embodiment of the present disclosure, the second hydrothermal reaction may be performed at a temperature of 130° C. or more to 180° C. or less for a time of 8 hours or more to 15 hours or less. Specifically, the temperature at which the second hydrothermal reaction is performed may be 140° C. or more to 170° C. or less, 150° C. or more to 160° C. or less, 130° C. or more to 160° C. or less, 140° C. or more to 150° C. or less, 140° C. or more to 180° C. or less, or 150° C. or more to 170° C. or less. In addition, the time for which the second hydrothermal reaction is performed may be 9 hours or more to 13 hours or less, 10 hours or more to 12 hours or less, 8 hours or more to 11 hours or less, 10 hours or more to 15 hours or less, or 10 hours or more to 13 hours or less. The temperature and time at which the second hydrothermal reaction is performed may be adjusted within the above-described ranges, thereby more stably and efficiently forming an electrode for chlorine evolution including a niobium-ruthenium-titanium composite oxide particle layer on a porous titanium metal substrate.

According to one embodiment of the present disclosure, the second hydrothermal reaction may heat the second mixture at a temperature increasing rate of 5° C./min or more to 15° C./min or less, 7° C./min or more to 13° C./min or less, 5° C./min or more to 10° C./min or less, or 10° C./min or more to 15° C./min or less up to the temperature range described above. When the temperature increasing rate is within the above-described range, the electrode for chlorine evolution may be manufactured more stably by preventing a rapid thermal shock from being applied to the reaction products.

According to one embodiment of the present disclosure, fluorine-doped tin oxide (FTO) is additionally made and used in the form of a roof on the porous titanium metal substrate during the second hydrothermal reaction as in the first hydrothermal reaction so that ruthenium particles may be uniformly doped on the surface of the porous titanium metal substrate during the first hydrothermal reaction.

According to one embodiment of the present disclosure, the temperature at which the first hydrothermal reaction is performed may be higher than the temperature at which the second hydrothermal reaction is performed, and the time for which the first hydrothermal reaction is performed may be shorter than the time for which the second hydrothermal reaction is performed. Through this, there are process advantages in that the efficiency of the entire manufacturing process of the electrode for chlorine evolution may be improved, and the manufacturing cost and time may be effectively reduced.

Next, the porous titanium metal substrate on which the niobium-doped titanium dioxide layer on which ruthenium is deposited is formed is heat-treated.

Through the heat treatment, titanium of the porous substrate may be diffused into deposited ruthenium to form a niobium-ruthenium-titanium composite oxide particle layer.

According to one embodiment of the present disclosure, the heat treatment may be performed at a temperature of 150° C. or more to 250° C. or less. Specifically, the temperature at which heat treatment is performed may be 165° C. or more to 235° C. or less, 180° C. or more to 220° C. or less, 190° C. or more to 210° C. or less, 150° C. or more to 220° C. or less, 170° C. or more to 210° C. or less, 180° C. or more to 200° C. or less, 180° C. or more to 250° C. or less, 190° C. or more to 230° C. or less, or 200° C. or more to 220° C. or less. The stability and electrochemical properties of the electrode for chlorine evolution including the niobium-ruthenium-titanium composite oxide particle layer formed on the porous titanium metal substrate may be effectively improved by adjusting the heat treatment temperature within the above-described range. Specifically, when the heat treatment temperature is within the above-described range, a composite particle layer in which a titanium dioxide shell is formed on the surface of the niobium-ruthenium-titanium oxide core as described later may be effectively formed. Through this, the electrochemical properties may be improved when it is used as an electrode for chlorine evolution, and ruthenium particles may be effectively suppressed from dissolving.

According to one embodiment of the present disclosure, the heat treatment step may be performed for 0.5 hours or more to 2 hours or less. Specifically, the heat treatment step may be performed for a time of 1 hour or more to 2 hours or less. The time for which the heat treatment step is performed is adjusted within the above-described range, thereby effectively forming the niobium-ruthenium-titanium composite oxide particle layer having the core-shell structure.

According to one embodiment of the present disclosure, ruthenium may remain in a portion where the composite oxide particles are not formed in the process of forming a composite oxide particle layer containing core-shell structured niobium-ruthenium-titanium composite oxide particles through the heat treatment. The electrochemical properties of the electrode may be improved by including residual ruthenium.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present disclosure will be described in detail by way of Examples in order to specifically explain the present disclosure. However, the Examples according to the present disclosure may be modified in various different forms, and the scope of the present disclosure is not interpreted as being limited to the Examples described below. The Examples in this specification are provided to more completely explain the present disclosure to those skilled in the art.

Example 1

A porous titanium metal substrate (MTIKOREA, EQ-TiF-1106, porosity: 40%) was prepared, NbCl₅ (Aldrich, purity 99%) was prepared as a niobium precursor, RuCl₃·3H₂O (Aldrich, purity 99.98%) was prepared as a ruthenium precursor, and hydrogen peroxide (Aldrich, 50%) was prepared.

A porous titanium metal substrate (MTIKOREA, EQ-TiF-1106, porosity: 40%) was prepared as a specimen in the form of a disk with a diameter of 1 cm and a thickness of 1 mm. After ultrasonically washing the porous titanium metal substrate with acetone, ethanol, and distilled water for 5 minutes each, it was washed again with ethanol, and then finally washed with third distilled water and dried to prepare a porous titanium metal substrate. After that, a porous titanium metal substrate having a titanium dioxide layer formed on the surface thereof was prepared through a process of immersing the porous titanium metal substrate in 50 wt % hydrogen peroxide heated to 70° C. for 30 minutes.

A niobium precursor solution with a NbCl₅ content of 0.001 mol % was prepared and coated on the titanium metal substrate having the titanium dioxide layer formed thereon. After that, it was transferred to a Teflon container and placed in an autoclave to perform a hydrothermal reaction in a furnace for hydrothermal synthesis (CBF-S010M, Thermotek Co., Ltd.). At this time, the hydrothermal reaction was performed at a temperature of 180° C. for 6 hours by adjusting a first hydrothermal reaction at a temperature increasing rate of 10° C./min. At this time, a roof shape was formed on the metal substrate using FTO so that the doping of niobium occurred uniformly. Thereafter, the metal substrate on which the hydrothermal reaction was completed was cooled to room temperature and washed with distilled water. The washed metal substrate was dried in a vacuum oven maintained at 70° C. for 24 hours, thereby obtaining a porous titanium metal substrate on which a niobium-doped titanium dioxide layer was formed.

The manufactured porous titanium metal substrate having the niobium-doped titanium dioxide layer formed thereon was coated using a ruthenium precursor solution having a RuCl₃ content of 0.016 mol %. Thereafter, the porous titanium metal substrate having the niobium-doped titanium dioxide layer formed thereon, which was coated with the ruthenium precursor solution, was transferred to a Teflon container and placed in an autoclave to perform a hydrothermal reaction in a furnace for hydrothermal synthesis. At this time, the hydrothermal reaction was performed at a temperature of 150° C. for 10 hours by adjusting the hydrothermal reaction at a temperature increasing rate of 10° C./min. At this time, a roof shape was formed on the metal substrate using FTO to allow deposition of ruthenium to be uniformly performed. Thereafter, the metal substrate on which the hydrothermal reaction was completed was washed with distilled water. The washed metal substrate was dried in a vacuum oven maintained at 70° C. for 24 hours. An electrode for chlorine evolution including a niobium-ruthenium-titanium composite oxide particle layer formed on a porous titanium metal substrate was manufactured.

Comparative Example 1

An electrode for chlorine evolution including a niobium-ruthenium-titanium composite oxide particle layer formed on a titanium metal substrate was manufactured in the same manner as in Example 1 except that a nonporous titanium metal substrate was used and a titanium dioxide layer was not formed on the surface thereof through an oxidation process.

Experimental Example

The physical properties of the manufactured electrode for chlorine evolution were observed and evaluated using the experimental equipment as follows.

1. TEM: JEM-2100F, JEOL Ltd./200 kV acceleration voltage conditions

2. Cs-TEM: Cs-corrected monochromated TEM (Themis Z, Thermo Fisher)/300 kV acceleration voltage conditions

3. XRD: New D8 ADVANCE, Bruker/Cu Kα radiation (λ=0.1542 nm) used

4. FESEM: Field-emission scanning electron microscopy (Model: SU70, Hitachi)

5. ICP-MS: Inductively coupled plasma-mass spectrometry (Model: NwxION 350D, Perkin-Elmer)

Morphological Analysis

FIG. 2 is an SEM image of an electrode for chlorine evolution manufactured in Example 1. Specifically, it was confirmed that the surface roughness increased through anodic oxidation. It was confirmed that the porous titanium metal substrate had a pore diameter of about 10 μm to 50 μm and a porosity of 40%.

FIG. 3 is an SEM image taken from the side surfaces of the electrode for chlorine evolution manufactured in Example 1. Referring to FIG. 3A, the titanium metal substrate is at the very bottom and a titanium dioxide layer doped with niobium may be confirmed above it. The particle size of deposited ruthenium is so small that it cannot be confirmed in this image. Additionally, it was confirmed that the titanium dioxide layer doped with niobium had a thickness of 40 nm. Referring to FIG. 3B, the elemental distribution of FIG. 3A can be confirmed. Specifically, referring to FIG. 3B, it can be confirmed that the average atomic distribution throughout the niobium-doped titanium dioxide layer and the niobium-ruthenium-titanium composite oxide particle layer is composed of 70 at % of titanium, 20 at % of niobium, and 10 at % of ruthenium.

FIG. 4 is a drawing showing element mapping images of the electrode for chlorine evolution manufactured in Example 1 of the present disclosure. Specifically, FIG. 4A shows element mapping images of niobium-ruthenium-titanium composite oxide particles formed on a porous titanium metal substrate, showing a high ruthenium content as 52.7 at % of titanium, 38.5 at % of ruthenium, and 8.8 at % of niobium. In contrast, referring to FIG. 4B, it can be seen that a small amount of ruthenium remains in a place where niobium-ruthenium-titanium composite oxide particles are not formed, with 72.2 at % of titanium, 7.6 at % of ruthenium, and 20.2 at % of niobium.

FIG. 5 shows a particle distribution in a niobium-ruthenium-titanium composite oxide particle layer of the electrode for chlorine evolution manufactured in Example 1. Specifically, it was confirmed that a titanium dioxide shell of about 2 Å to 6 Å was formed on a complex oxide particle core of about 2 nm in size.

Analysis of Electrochemical Physical Properties

FIG. 6 is a graph showing surface areas of electrodes for chlorine evolution manufactured in Example 1 and Comparative Example 1 and a conventional DSA participating in the electrochemical reactions. Specifically, it was confirmed that the surface area of Example 1 participating in the electrochemical reaction was twice or more larger than that of DSA that is an electrode commercialized using a porous substrate.

FIG. 7 is a graph showing CV curves of the electrodes for chlorine evolution manufactured in Example 1 and Comparative Example 1 and the conventional DSA. Referring to FIG. 7A, it was confirmed that the current densities of Comparative Example 1 and DSA gradually decreased, while the electrode for chlorine evolution manufactured in Example 1 maintained a stable electrocatalytic activity, and at the same time has the current density gradually increasing as the CV cycle was repeated. Through this, it can be seen that the electrode for chlorine evolution manufactured in Example 1 has excellent durability against anodic corrosion.

FIG. 8 is a graph showing Tafel slopes of the electrodes for chlorine evolution manufactured in Example 1 and Comparative Example 1 and the conventional DSA. Specifically, the Tafel slope means the amount of change in voltage required to increase the current by 10 times, and it can be confirmed that the smaller the Tafel slope, the more current flows even at a low voltage, thereby indicating excellent electrical conductivity. Referring to FIG. 8, it was confirmed that the electrical conductivities of Example 1 and Comparative Example 1 were higher than that of the conventional DSA, and that the electrical conductivity of Example 1 in the form of a foam was higher than that of Comparative Example 1 in the form of a general substrate.

FIG. 9 is a graph showing faradaic efficiencies in a 5.0 M NaCl solution of the electrode for chlorine evolution manufactured in Example 1 and the conventional DSA. Specifically, Example 1 maintained a value 20% higher on average than DSA and showed an efficiency of 85% or more in the entire range.

FIG. 10 is a graph showing stability of the electrode for chlorine evolution manufactured in Example 1 at 400 mA cm⁻², which is a commercial process condition. Specifically, it was confirmed that the electrode for chlorine evolution manufactured in Example 1 had high electrode stability by showing a very low voltage change rate of 33 mV for 24 hours.

FIG. 11 is a graph comparing an overpotential of the electrode for chlorine evolution manufactured in Example 1 with those of electrodes for chlorine evolution using conventional commercial catalysts. Specifically, referring to FIG. 11 and Table 1 below, it was confirmed that the electrode for chlorine evolution manufactured in Example 1 had excellent performance compared to catalysts that had been known even in terms of overpotential.

TABLE 1
		Faradaic
		Efficiency	Evaluation
Material	Overpotential (mV)	(%)	condition

ALD TiO2/IrO2	120@1 mAcm−2	99	5.0M NaCl
			pH = 2
RuO2/FTO	140@10 mAcm−2	90	5.0M NaCl
			pH = 2
RuO2 NPs@TiO2	66@10 mAcm−2	90.3	Saturated NaCl
NBs			pH = 2
Pt1/CNT	50@10 mAcm−2	97.1	1.0M NaCl
			pH = 1
IrO2/TiO2	104@10 mAcm−2	84.6	Saturated NaCl
flat			pH = 2
IrO2/TiO2	40@10 mAcm−2	95.8	Saturated NaCl
NSAs			pH = 2
Ru/Ir/TiO2	385@10 mAcm−2	—	4.0M NaCl
			pH = 3
RuO2@TiO2	58@10 mAcm−2	90	Saturated NaCl
			pH = 2
CoSb2Ox	570@10 mAcm−2	97.4	4.0M NaCl
			pH = 3
RuO2/b-TiO2	72@1 mAcm−2	95.3	5.0M NaCl
NTAs	109@100 mAcm−2		pH = 2
Ru0.3Ti0.7O2	150@100 mAcm−2	—	4.0M NaCl
			pH = 3
Ti—Ru—Ir	431@100 mAcm−2	90	4.0M NaCl
			pH = 3
RuO2/Nb:TiO2	22@10 mAcm−2	97.3	0.6M NaCl
	55@100 mAcm−2		pH = 6
Comparative	66@10 mAcm−2	—	5.0M NaCl
Example 1	179@100 mAcm−2		pH = 2
Example 1	9@10 mAcm−2	98.7	5.0M NaCl
	42@500 mAcm−2		pH = 2

That is, it can be seen that the electrode for chlorine evolution including the niobium-ruthenium-titanium composite oxide particle layer formed on the porous titanium metal substrate according to one embodiment of the present disclosure is superior to commercialized catalysts in terms of catalytic activity, product selectivity, cost efficiency, etc.

FIG. 12 is a graph showing resistance values on the surfaces of the electrodes for chlorine evolution manufactured in Example 1 and Comparative Example 1 and that on the surface of the conventional DSA. Referring to FIG. 12A, it was confirmed that Example 1 showed a lower resistance value than Comparative Example 1 and DSA, and had a fast reaction speed in a low current density region. Referring to FIG. 12B, it was confirmed that Example 1 in the form of a foam showed a very low diffusion resistance compared to Comparative Example 1 in the form of a general substrate, and had a high voltage value at a high current density.

Performance Analysis

FIG. 13 is graphs showing diffusion resistances of the electrodes for chlorine evolution manufactured in Example 1 and Comparative Example 1 in a convective environment. Through FIG. 13A, it can be confirmed that Example 1 having a porous structure has much lower diffusion resistance than Comparative Example 1 in the form of a general substrate even in a convective environment. FIG. 13B is data measuring diffusion resistances after blocking other surfaces except the reaction surface of Example 1 that is in the form of a foam through taping. Even when a convective environment was not created, a lower diffusion resistance was confirmed when it was not blocked, and the difference in diffusion resistance increased in a convective environment. Through this, it was confirmed that a porous structure may reduce diffusion resistance.

FIG. 14 is CV graphs showing results of measuring chlorine and hydrogen evolution performances of the electrode for chlorine evolution manufactured in Example 1 under industrial conditions. FIG. 14A is a graph showing results of measuring the chlorine evolution reaction performance in saturated NaCl at 90° C., FIG. 14B is a graph showing results of measuring the hydrogen generation reaction performance in a 3.0 M NaOH+3.0 M NaCl solution at 90° C., and FIG. 14C is a graph showing results of measuring the performance of a reaction in which chlorine and hydrogen are simultaneously generated under actual industrial conditions. In addition, when the potential is read based on a specific current density on the CV graph, the lower the potential, the more excellent the catalytic properties are evaluated. Specifically, referring to FIG. 14 and Table 2 below, it was confirmed that the electrode for chlorine evolution manufactured in Example 1 had excellent performance compared to known catalysts even in terms of overpotential.

TABLE 2
		Temperature	Evaluation
Material	Overpotential (mV)	(° C.)	condition

NiCoZn/Copper	140@100 mAcm−2	25	1M KOH
Fe82B18	430@300 mAcm−2	25	1M KOH
NiMn/graphite	141@100 mAcm−2	25	NaOH 30%
Ni—Sn/copper	—	25	1M KOH
Ni—CeO2/mild	—	25	1M KOH
steel
Ni—P/mild	340@250 mAcm−2	30	NaOH 32%
steel
Ni—Fe—C/steel	70@250 mAcm−2	90	NaCl 3.5%
Co90W10	326@100 mAcm−2	25	1M NaOH
Pt	460@50 mAcm−2	85	8M KOH
Nano-Zr67Ni33	1530@100 mAcm−2	25	6M KOH
Ru/WNO@C	108@500 mAcm−2	90	3M NaOH +
			3.0M NaCl
Ru/Ni/WC@NPC	10@10 mAcm−2	90	3M NaOH +
	99@100 mAcm−2		3.0M NaCl
Example 1	11@10 mAcm−2	90	3M NaOH +
RNTO/Ti Foam	64@100 mAcm−2		3.0M NaCl
	64@100 mAcm−2

FIG. 15 is a graph showing results of measuring stability over time of the electrode for chlorine evolution manufactured in Example 1 under industrial conditions. Specifically, it was confirmed that the electrode for chlorine evolution manufactured in Example 1 had stability by maintaining a constant voltage even when the reaction was performed for 10 hours in a 3.0 M NaOH+3.0 M NaCl solution at 90° C.

The above detailed description is intended to illustrate and explain the present disclosure. In addition, the above-described contents merely illustrate and explain preferred embodiments of the present disclosure, and as described above, the present disclosure can be used in various other combinations, modifications, and environments, and changes or modifications are possible within the scope of the concept of the invention disclosed in this specification, the scope equivalent to the above-described disclosure, and/or the scope of technology or knowledge in the art. Therefore, the above detailed description of the invention is not intended to limit the present disclosure to the disclosed embodiments. In addition, the appended claims should be interpreted to include other embodiments.