Patent Application
20250236973
This application claims priority to and the benefit of Korean Patent Application No. 2024-0009961, filed on Jan. 23, 2024, and Korean Patent Application No. 2024-0185131, filed on Dec. 12, 2024, the disclosure of which are incorporated herein by reference in their entirety.
The present inventive concept relates to a water treatment cell, and more specifically, to an oxygen evolution electrode used in an alkaline water electrolysis cell.
In alkaline water electrolysis, the stack accounts for 50% of the total cost, and since the electrode cost is half of the stack cost, reducing the electrode cost is one of the ways to lower the unit cost of hydrogen production. Therefore, the development of electrodes with high energy efficiency and economic feasibility is very important for the commercialization of alkaline water electrolysis.
Currently, for electrode research for commercialization of alkaline water electrolysis, the focus is on a method of depositing a catalyst on a conductive electrode (substrate) for use, and in this case, there are difficulties such as 1) limitations in material selection for different deposition methods for each material, 2) difficulties in the deposition process in large-area/mass production technology for commercialization, and 3) enormous facility and equipment investment costs depending on the deposition method.
Accordingly, a new electrode manufacturing method is required for the development of a commercializable water electrolysis electrode.
The problem to be solved by the present inventive concept is to improve the shortcomings and problems of the related art as described above, and to provide a method of manufacturing a highly active oxygen evolution electrode for water electrolysis.
The technical problems to be solved by the present inventive concept are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present inventive concept belongs from the description below.
In order to solve the above problems, one aspect of the present inventive concept provides a method of manufacturing a highly active oxygen evolution electrode for water electrolysis. The method of manufacturing a highly active oxygen evolution electrode for water electrolysis includes exposing a surface of a nickel electrode to water vapor; and heat-treating the electrode exposed to water vapor.
The exposure to water vapor may be exposure to a mixture of a carrier gas with the water vapor.
The carrier gas may be hydrogen gas.
The water vapor concentration may be 40% or more.
The exposure to water vapor may be performed at 250 to 350° C.
The exposure to water vapor may form a hydroxide layer on a surface of a nickel electrode.
The hydroxide layer may include NiOOH and Ni(OH)2.
In the hydroxide layer, a surface area of NiOOH is characterized as being greater than a surface area of Ni(OH)2.
The NiOOH may occupy 60 to 90% of a surface area of the hydroxide layer.
The nickel electrode may be a porous nickel electrode.
The porosity of the porous nickel electrode may be 90% or more.
The method may further include removing impurities on the surface of the nickel electrode prior to the exposure to water vapor.
In addition, the method may further include depositing a catalyst on the electrode after the heat-treating of the electrode exposed to the water vapor.
The catalyst may be a double layer hydroxide (LDH)-based catalyst.
In addition, another aspect of the present inventive concept provides a highly active oxygen evolution electrode for water electrolysis. The highly active oxygen evolution electrode for water electrolysis includes a nickel electrode; and a hydroxide layer formed on a surface of the nickel electrode by exposure to water vapor.
The nickel electrode may be a porous nickel electrode.
The porosity of the porous nickel electrode may be 90% or more.
The hydroxide layer may include NiOOH and Ni(OH)2.
In the hydroxide layer, a surface area of NiOOH is characterized as being greater than a surface area of Ni(OH)2.
The NiOOH may occupy 60 to 90% of a surface area of the hydroxide layer.
The highly active oxygen evolution electrode for water electrolysis may further include a catalyst formed on the hydroxide layer.
The catalyst may be a double layer hydroxide (LDH)-based catalyst.
The above and other objects, features and advantages of the present inventive concept will become more apparent to those of ordinary skill in the art by describing exemplary embodiments thereof in detail with reference to the accompanying drawings, in which:
Since the present inventive concept can undergo various changes and have various embodiments, specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the present inventive concept to specific embodiments, and it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present inventive concept.
The terms used in the present inventive concept are only used to describe specific embodiments, and are not intended to limit the present inventive concept. Singular expressions include plural expressions unless the context clearly dictates otherwise.
In the present inventive concept, it is to be understood that the terms “include(s)” or “have (has)” and the like are intended to specify the presence of stated features, numbers, steps, operations, components, parts, or combinations thereof, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.
In the present inventive concept, terms such as first, second, and the like may be used to describe various components, but the components may not be limited by the terms. The terms may be used only for the purpose of distinguishing one component from another.
In the present inventive concept, when it is mentioned that a component is “connected” or “coupled” to another component, it can be understood that it may be directly connected or coupled to the other component, but there may also be other components present therebetween. On the other hand, when a component is said to be “directly connected” or “directly coupled” to another component, it can be understood that there are no other components therebetween.
In the present inventive concept, when a part such as a layer, film, region, plate, etc. is described as being “on” another part, it includes not only the case where the part is “directly on” the other part, but also the case when there is another part therebetween. Conversely, when a part is said to be “directly on” another part, it means that there are no other parts therebetween.
Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present inventive concept belongs. Terms such as those defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application.
One aspect of the present inventive concept provides a method of manufacturing a highly active oxygen evolution electrode for water electrolysis.
Referring to
Hereinafter, the method of manufacturing a highly active oxygen evolution electrode for water electrolysis according to the present inventive concept will be described in detail for each step.
First, a nickel electrode is exposed to water vapor. However, since water vapor has a low vapor pressure of about 20 Torr at room temperature, and the vapor pressure changes greatly depending on the temperature, it is one of the gases that is difficult to control and flow in large quantities. Accordingly, it is preferable that the water vapor is introduced into a vacuum chamber 30 after being mixed with a carrier gas, and it is also preferable that the nickel electrode is disposed on a support member 20 within the vacuum chamber 30 so that the nickel electrode is exposed to the water vapor within the vacuum chamber.
Specifically, the supply of water vapor may be performed by inputting a carrier gas into water and bubbling it to input the carrier gas and water vapor together into the vacuum chamber. In this method, the amount of water vapor that can actually be introduced is only the partial pressure of the carrier gas and water vapor of the mixed gas. Accordingly, the concentration of water vapor that can be introduced may be controlled by controlling the partial pressure of the carrier gas and water vapor.
At this time, hydrogen gas may be used as the carrier gas. The hydrogen gas may prevent oxidation of the electrode at high temperatures. As described above, the concentration of the water vapor may be adjusted by controlling the partial pressure of the carrier gas and the water vapor. As shown in
It is preferable that the water vapor exposure is performed at a temperature of 250 to 350° C. The above temperature may be maintained through a heating means 40 outside the vacuum chamber 30. When the nickel electrode is exposed to water vapor at the above temperature, a reaction as shown in the following Reaction Scheme 1 occurs between the water vapor and the surface of the nickel electrode, thereby forming a hydroxide layer on the surface of the nickel electrode.
Ni+2H2O(g)→NiOOH+3/2H2(g)
Ni+2H2O(g)→Ni(OH)2+H2(g) [Reaction Scheme 1]
The hydroxide layer may include NiOOH and Ni(OH)2, and in one embodiment of the present inventive concept, the formation of the hydroxide layer including NiOOH and Ni(OH)2 can be confirmed through a transmission electron microscope (see
The thickness of the hydroxide layer may be 1 to 15 nm, but is not limited thereto, and the hydroxide layer may be formed to a thickness at which oxygen evolution reaction performance is effectively improved.
The nickel electrode may be a porous nickel electrode. In the case of porous nickel bodies, since the surface area increases, the surface area of an NiOOH-containing hydroxide layer, which exhibits excellent oxygen evolution reaction catalytic activity and is formed by exposure to water vapor, can also increase, so that the oxygen evolution reaction performance can be further improved compared to non-porous bodies. At this time, the higher the porosity of the porous nickel electrode, the better it is. For example, it is preferable to have a porosity of 90% or more, but is not limited thereto.
The method may further include removing impurities on the surface of the nickel electrode prior to exposure to water vapor. The impurity removal process may use a method known in the art, and as an example, impurities may be removed through acid treatment, but the method is not limited thereto.
The nickel electrode may be heat-treated after exposure to water vapor. This heat treatment may be performed by a first heat treatment at 250 to 350° C. and then a second heat treatment at 30 to 60° C., but is not limited thereto.
In addition, the method may further include depositing a catalyst on the electrode after the heat-treating of the electrode exposed to the water vapor.
The catalyst may be a double layer hydroxide (LDH)-based catalyst, and may be, for example, an NiFe LDH catalyst, but is not limited thereto, and any catalyst used in the OER reaction may be used without limitation.
In addition, another aspect of the present inventive concept provides a highly active oxygen evolution electrode for water electrolysis.
The highly active oxygen evolution electrode for water electrolysis is manufactured by the manufacturing method according to the present inventive concept, and is characterized by including the nickel electrode; and a hydroxide layer formed on the surface of the nickel electrode by exposure to water vapor.
In addition, the highly active oxygen evolution electrode for water electrolysis may further include a catalyst formed on the hydroxide layer.
At this time, the composition and characteristics of the nickel electrode, the hydroxide layer, and the catalyst are as described above, so they are omitted to avoid redundant description.
According to the present inventive concept, a simple method of exposing the surface of a nickel electrode to water vapor induced the formation of a hydroxide layer including NiOOH and Ni(OH)2 on the surface of the nickel electrode, and in the formed hydroxide layer, especially NiOOH improved OER activity, lowered the overpotential, and improved charge transfer dynamics, thereby significantly improving the oxygen evolution reaction performance and long-term stability of the nickel electrode. Therefore, the nickel electrode on which the hydroxide layer is formed can be usefully used as a water electrolysis oxygen evolution electrode.
Hereinafter, preferred manufacturing examples and experimental examples are presented to help understand the present inventive concept. However, the following manufacturing examples and experimental examples are only for helping to understand the present inventive concept, and the present inventive concept is not limited by the following manufacturing examples and experimental examples.
A porous nickel electrode (porosity>93%, thickness: 1.6 mm) was sonicated with 3 M HCl for 30 minutes before use, and then washed several times with distilled water and ethanol to remove surface impurities.
Thereafter, using the device of
The porous nickel electrode exposed to wet hydrogen was sequentially heat-treated at 300° C. for 10 hours and at 30° C. for 5 hours in a reducing atmosphere to manufacture a highly active oxygen evolution electrode for water electrolysis.
A highly active oxygen evolution electrode for water electrolysis was manufactured in the same manner as in Manufacturing Example 1, except that the porous nickel electrode was exposed to wet hydrogen having a water vapor concentration of 30% instead of 10%.
A highly active oxygen evolution electrode for water electrolysis was manufactured in the same manner as in Manufacturing Example 1, except that the porous nickel electrode was exposed to wet hydrogen having a water vapor concentration of 40% instead of 10%.
NiFe double layer hydroxide (LDH) was deposited as a catalyst on the highly active oxygen evolution electrode for water electrolysis manufactured in Manufacturing Example 3.
A porous nickel electrode was used as an electrode without surface treatment (pristine Ni foam).
NiFe double layer hydroxide (LDH) was deposited as a catalyst on the porous nickel electrode of Comparative Example 1.
The surfaces of the porous nickel electrodes of Manufacturing Examples 1 to 3 and Comparative Example 1 were subjected to X-ray diffraction (XRD) analysis, and the results are shown in
As shown in
In addition, as shown in
The surfaces of the porous nickel electrodes of Manufacturing Examples 1 to 3 and Comparative Example 1 were observed using a scanning electron microscope (SEM), and are shown in
As shown in
As shown in
Next, the surfaces of the porous nickel electrodes of Example 2 and Comparative Example 1 were observed using a transmission electron microscope (TEM), and the results are shown in
As shown in
As a result of analyzing the composition by observing the hydroxide layer using a high-resolution TEM, the hydroxide layer showed three different lattice crystals with sizes of 0.26 nm, 0.24 nm, and 0.14 nm, respectively, aligned with the (100) plane, (110) plane, and (300) plane of NiOOH, and the (101) plane of Ni(OH)2 of about 0.233 nm was also confirmed. Therefore, it was confirmed that a hydroxide layer, presumed to be Ni(OH)2 and NiOOH, was formed on the surface of the porous nickel electrode after the porous nickel electrode was treated with water vapor. It was confirmed that the thickness of the hydroxide layer increases as the concentration of water vapor being treated increases.
To further investigate the chemical composition and oxidation state of the porous nickel electrode surface before and after water vapor treatment, X-ray photoelectron spectroscopy (XPS) was performed, and the results are shown in
As shown in
The O 1s XPS spectrum in
To determine the effect of water vapor treatment of a porous nickel electrode according to the present inventive concept on the OER, the following experiments were performed.
Specifically, before performing the OER measurement, the Ni2+ content and Ni3+ content were measured for the porous nickel electrode of Comparative Example 1 before water vapor treatment and the porous nickel electrodes of Examples 1 to 3 after water vapor treatment, and the results are shown in
Next, for the four porous nickel electrodes, after the porous nickel electrodes were pre-activated through cyclic voltammetry (CV) at a scan rate of 100 mV/s, the Ni2+ content and Ni3+ content were measured and are shown in
Next, for the four nickel porous electrodes, the overvoltage was measured through the OER polarization curve with iR compensation with reference to the reversible hydrogen electrode (RHE), and the results are shown in
It was confirmed that as shown in
In the Nyquist plot, the semicircle corresponds to the polarization resistance (Rp) including the charge transfer resistance (Rct).
As shown in
This is thought to be because the hydroxide layer (NiOOH) formed on the porous nickel electrode surface after water vapor treatment exhibits high activity for the oxygen evolution reaction, and through this, it can be seen that the NiOOH layer induces high activity for the oxygen evolution reaction.
Thereafter, a more comprehensive analysis of the catalytic dynamics occurring at the electrode-electrolyte interface was performed by applying the distribution of relaxation time (DRT) plots derived from the Nyquist diagram using a Gaussian basis function.
Specifically, an oxygen evolution reaction was performed on the porous nickel electrode of Manufacturing Example 3 treated with water vapor having a water vapor concentration of 40%, and a three-dimensional DRT plot and a contour plot according to overvoltage were measured and presented in
As shown in
As shown in
As shown in
In order to determine the mechanism by which the reaction activity is enhanced when performing the OER using a water vapor-treated nickel electrode according to the present inventive concept, the following experiment was performed.
First, the Gibbs energy change in the step-by-step reaction path of the OER on Ni, NiOOH, and Ni(OH)2 present on the nickel electrode surface was calculated and the results are shown in
As shown in
However, since the reaction of NiOOH+½H2(g)→Ni(OH)2 is generally a spontaneous reaction, it is important to maintain the state of NiOOH by suppressing the reaction of NiOOH to Ni(OH)2 to increase the OER activity of the nickel electrode.
Meanwhile, when a nickel electrode is treated with water vapor according to the present inventive concept, the porous nickel electrode is exposed to wet hydrogen (wet H2) including water vapor. At this time, the reaction energy according to the reaction path when the hydrogen ion (H+) source provided to NiOOH is water vapor and when it is hydrogen was calculated, and the results are shown in
As shown in
In addition, when a nickel electrode is treated with water vapor according to the present inventive concept, the surface movement trajectories of H2 and H2O were calculated according to the concentration of the treated water vapor, and the results are shown in
As shown in
As shown in
As shown in
In this way, the water vapor treatment according to the present inventive concept showed a great influence on the electrocatalytic properties of the material, especially the oxygen evolution reaction properties, in a simple manner, and this can be usefully used in the fields of energy conversion and storage.
As shown in
Therefore, the porous nickel electrode treated with water vapor according to the present inventive concept may secure long-term stability of the catalyst.
Although preferred embodiments of the present inventive concept have been described above, it will be understood by those skilled in the art that various changes and modifications of the present inventive concept may be made by addition, alteration, deletion, or the like of the components without departing from the spirit of the present inventive concept as set forth in the claims, and that these changes are also included within the scope of the present inventive concept. For example, each component described as a single type may be implemented in a distributed form, and likewise components described as distributed may be implemented in a combined form. The scope of the present inventive concept is indicated by the following claims rather than by the above description, and all changes or modifications that come from the meaning and range of the claims and their equivalents should be construed to be included within the scope of the present inventive concept.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2024-0009961 | Jan 2024 | KR | national |
| 10-2024-0185131 | Dec 2024 | KR | national |
