阅读说明：本技术 电化学反应用电极的修饰方法 (Method for modifying electrode for electrochemical reaction ) 是由 洪锡垣 崔在佑 李知镐 埃文迪·拉赫曼 于 2019-12-20 设计创作，主要内容包括：本发明涉及一种电化学反应用电极的修饰方法,该方法通过对修饰对象电极依次适用电溶解过程(electro-dissolution)和电沉积过程(electro-deposition),从而使电极表面的杂质最小化的同时优化电极表面的组成以使其符合反应目的。(The present invention relates to a method for modifying an electrode for electrochemical reaction, which optimizes the composition of the electrode surface to meet the reaction purpose while minimizing impurities on the electrode surface by applying an electro-dissolution process and an electro-deposition process to an electrode to be modified in this order.)

1. A method for modifying an electrode for electrochemical reaction, comprising the steps of:

preparing a modification target electrode;

an electrodissolution step of immersing the electrode to be modified as an anode in an electrochemical reaction tank filled with an electrolyte, and applying a first potential to the electrode to be modified to oxidize the surface of the electrode to be modified; and

and an electrodeposition step of immersing the electrode to be modified, which has been subjected to the electrodissolution step, as a cathode in an electrochemical reaction tank filled with an electrolyte in which a deposition metal is dissolved, and inducing the electrode to be modified to deposit the deposition metal on the electrode to be modified by a reduction reaction by applying a second potential to the electrode to be modified.

2. The method of claim 1, wherein the first potential is a potential which is higher than a standard electrode potential of a metal having a maximum standard electrode potential among metals contained in the electrode to be modified and is equal to or lower than an oxygen evolution potential.

3. The method of claim 1, wherein the second potential is a potential which is equal to or higher than a hydrogen evolution potential and lower than a standard electrode potential of a metal having a minimum standard electrode potential among metals included in the electrode to be modified.

4. The method of claim 2, wherein the metal contained In the electrode to be modified is any one or a combination of Pd, Ag, Rh, Cu, Bi, Pb, Sn, Ni, Co, Tl, In, Fe, Zn, B, Cr, Mn, Ti and Al,

the metal having the largest standard electrode potential among the metals contained In the electrode to be modified is a metal having the largest standard electrode potential among Pd, Ag, Rh, Cu, Bi, Pb, Sn, Ni, Co, Tl, In, Fe, Zn, B, Cr, Mn, Ti and Al, or a metal having the largest standard electrode potential among any one or more of Pd, Ag, Rh, Cu, Bi, Pb, Sn, Ni, Co, Tl, In, Fe, Zn, B, Cr, Mn, Ti and Al In combination.

5. The method for modifying an electrode for electrochemical reaction according to claim 1, wherein In the electrodeposition step, the metal for deposition is any one of Au, Pt, Pd, Ir, Ag, Rh, Cu, Bi, Pb, Sn, Ni, Co, Tl, In, Fe, Zn, B and Cr, or a combination thereof.

6. The method for modifying an electrode for electrochemical reaction according to claim 1, wherein the electrolyte in the electrodeposition step is an electrolyte having a pH of 2 to 8.

7. The method of claim 1, wherein the electrode to be modified is made of SUS or Ti, and the electrolyte in the electrodissolution step is an alkaline electrolyte.

8. The method of modifying an electrode for electrochemical reaction according to claim 1, wherein the concentration of the metal for deposition dissolved in the electrolyte in the electrodeposition step is more than 500 mM.

9. The method of claim 1, further comprising a pretreatment step of pretreating the electrode to be modified before the electrodissolution step, wherein the pretreatment step comprises:

a process of increasing the specific surface area of the surface of the electrode to be modified by sand paper treatment of the surface of the electrode to be modified,

a process for removing at least one of an organic solvent and an oil remaining on the surface of the electrode to be modified, and

and a process for removing a natural oxide film and inorganic impurities present in the electrode to be modified.

10. The method of claim 1, wherein when the electrode to be modified is an oxidation electrode of an electrochemical water treatment apparatus and the oxidation electrode is made of a metal oxide, the metal for deposition suitable for the electrodeposition step is any one or a combination of Pb, Ni, Pt, Mn, Ir, Ru, Co and Fe,

after the electrodeposition step, a step of heat-treating the electrode to be modified at a temperature of 300 to 500 ℃ in an oxygen atmosphere is performed in order to oxidize the deposited metal.

11. The method of claim 1, wherein the electrode to be modified is a stainless steel or Ti electrode suitable as a cathode of an electrochemical water treatment apparatus for reducing nitrate nitrogen to ammonia nitrogen,

removing impurity metal contained in the surface of the electrode to be modified by the electro-dissolution step, and depositing Fe or Zn metal on the surface of the electrode to be modified by the electro-deposition step.

Technical Field

The present invention relates to a method for modifying an electrode for electrochemical reaction, and more particularly, to a method for modifying an electrode for electrochemical reaction, which can minimize impurities on the surface of the electrode and optimize the composition of the surface of the electrode to meet the purpose of reaction by applying an electro-dissolution process and an electro-deposition process to the electrode to be modified in this order.

[ statement regarding national support for research & development ]

The present study was completed under the supervision of the korea institute of science and technology, with the title of the research project being top-level environmental technology development (R & D) worldwide, and the title of the research project being electrochemical-based development of high-concentration organic substances and total nitrogen control technology (project inherent number: 1485016103).

Background

It is known that an electrochemical reaction is a non-uniform charge transfer process (hetereogenous charge transfer) occurring at an interface between an electrode and a solution, and the electrochemical reaction is greatly influenced according to a fine change of an electric double layer or a diffusion layer (diffusion layer) of an electrode-solution interface (electrode-solution interface) compared to the inside of the solution. Proper adjustment of the reactivity of the electrode-solution interface is an important part of electrochemical research.

The Chemically Modified Electrode (CME) means an electrode modified in a manner suitable for the purpose of reaction, and can be produced by various methods. For example, the electrode can be produced by a method based on chemical adsorption (chemisorption), covalent bonding, coating with a polymer (organic), polynuclear (inorganic) or composite film, or mixing an electrode matrix substance with a modifying agent. Chemically Modified Electrodes (CME) can also be distinguished by the manner of coating. For example, crosslinking (cross-linking), dip coating (dip coating), electrochemical deposition (electrochemical deposition), electrochemical polymerization (electrochemical polymerization), solvent evaporation (solvent evaporation), spin coating (spin casting), and the like are known. The modified electrode itself plays a role of a reactant repelling or attracting electrons in the reaction, and particularly, the electrocatalytic property can be applied to various electrochemical fields.

In addition, the stability of the electrode in the electrochemical reaction is important. Elution of electrode components, an increase in the resistance of the electrode surface, a side reaction with the electrolyte solution, and the like are problems mainly generated in the electrochemical reaction, and are mainly caused by a change in the reactivity of the electrode surface.

In order to maintain the reactivity of the electrode surface, it is necessary to minimize impurities of the electrode surface and optimize the composition of the electrode surface to meet the purpose of the reaction. However, the prior art has limitations in controlling impurities on the surface of the electrode or optimizing the composition of the surface of the electrode.

Disclosure of Invention

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method for modifying an electrode for electrochemical reaction, which is capable of optimizing the composition of the electrode surface to meet the reaction purpose while minimizing impurities on the electrode surface by applying an electro-dissolution process (electro-dissolution) and an electro-deposition process (electro-deposition) to the electrode to be modified in this order.

The method for modifying an electrode for electrochemical reaction according to the present invention for achieving the above object is characterized by comprising the steps of: preparing a modification target electrode; an electrodissolution step of immersing the electrode to be modified as an anode in an electrochemical reaction tank filled with an electrolyte, and applying a first potential to the electrode to be modified to oxidize the surface of the electrode to be modified; and an electrodeposition step of immersing the electrode to be modified having undergone the above-described electrodissolution step as a cathode in an electrochemical reaction tank filled with an electrolyte in which a deposition metal is dissolved, and inducing the electrode to be modified to deposit the deposition metal on the electrode to be modified by a reduction reaction by applying a second potential to the electrode to be modified.

The first potential is a potential which is higher than a standard electrode potential of a metal having a maximum standard electrode potential among metals included in the electrode to be modified and is equal to or lower than an oxygen evolution potential.

The second potential is a potential equal to or higher than the hydrogen evolution potential and equal to or lower than the standard electrode potential of the metal having the smallest standard electrode potential among the metals included in the electrode to be modified.

The metal contained In the electrode to be modified is any one or a combination of Pd, Ag, Rh, Cu, Bi, Pb, Sn, Ni, Co, Tl, In, Fe, Zn, B, Cr, Mn, Ti and Al, and the metal having the largest standard electrode potential among the metals contained In the electrode to be modified is the metal having the largest standard electrode potential among Pd, Ag, Rh, Cu, Bi, Pb, Sn, Ni, Co, Tl, In, Fe, Zn, B, Cr, Mn, Ti and Al, or the metal having the largest standard electrode potential among Pd, Ag, Rh, Cu, Bi, Pb, Sn, Ni, Co, Tl, In, Fe, Zn, B, Cr, Mn, Ti and Al.

In the electrodeposition step, any one of Au, Pt, Pd, Ir, Ag, Rh, Cu, Bi, Pb, Sn, Ni, Co, Tl, In, Fe, Zn, B, and Cr, or a combination thereof may be used as the deposition metal.

The electrolyte in the electrodeposition step is an electrolyte with pH of 2-8.

The material of the electrode to be modified is Stainless Steel (SUS) or titanium (Ti), and an alkaline electrolyte can be used as the electrolyte in the electrolytic dissolution step.

The concentration of the deposition metal dissolved in the electrolyte in the electrodeposition step is preferably more than 500 mM.

The method further comprises a pretreatment step of pretreating the electrode to be modified before the electrodissolution step, wherein the pretreatment step comprises: a process of increasing the specific surface area of the surface of the electrode to be modified by performing sand paper treatment on the surface of the electrode to be modified; a process of removing one or more of an organic solvent and oil remaining on the surface of the electrode to be modified; and a process for removing a natural oxide film and inorganic impurities present in the electrode to be modified.

When the electrode to be modified is an oxidation electrode of an electrochemical water treatment apparatus and the oxidation electrode is made of a metal oxide, the metal for deposition suitable for the electrodeposition step is any one or a combination of Pb, Ni, Pt, Mn, Ir, Ru, Co and Fe, and after the electrodeposition step is performed, a step of heat-treating the electrode to be modified at a temperature of 300 to 500 ℃ in an oxygen atmosphere is performed in order to oxidize the deposited metal.

The electrode to be modified is made of Stainless Steel (SUS) or titanium (Ti) material and is used as a cathode of an electrochemical water treatment apparatus for reducing nitrate nitrogen to ammonia nitrogen, and the impurity metal contained in the surface of the electrode to be modified is removed by the electro-dissolution step, and Fe or Zn metal can be deposited on the surface of the electrode to be modified by the electro-deposition step.

The method for modifying an electrode for electrochemical reaction according to the present invention has the following effects.

By applying the electro-dissolution process and the electro-deposition process in this order, the impurity metal contained in the electrode to be modified can be effectively removed, and the composition of the electrode to be modified can be controlled to optimize in a manner that meets the purpose of the reaction.

Drawings

Fig. 1 is a schematic view showing an electrodissolution process and an electrodeposition process.

Fig. 2 is a reference diagram for explaining a range of a potential applied to an electrode (anode) to be modified in an electrodissolution process.

Fig. 3 is a reference diagram for explaining a range of the potential applied to the modification target electrode (cathode) in the electrodeposition process.

FIG. 4 shows the results of experiments on the nitrate nitrogen reduction characteristics of SUS electrodes.

Fig. 5 shows the results of experiments showing the nitrate nitrogen reduction characteristics of the electrode to be modified by the electrolyte during the electrodissolution process.

FIG. 6 shows the results of experiments showing the reduction characteristics of nitrate nitrogen depending on the type of metal.

Fig. 7 shows the results of experiments showing the nitrate nitrogen reduction characteristics of the electrode to be modified depending on the type of the metal for deposition during the electrodeposition process.

FIG. 8 is a reference diagram showing a Pourbaix diagram (Pourbaix diagram).

Detailed Description

The present invention provides a method for modifying an electrode for electrochemical reactions.

As mentioned in the above "background art", the electrode used for the electrochemical reaction causes elution of the electrode components or an increase in the resistance of the electrode surface when a certain time elapses. The main reason for this is that a part of the electrode falls off and the initial composition of the electrode changes during the electrochemical reaction repeatedly proceeds.

The electrode for electrochemical reaction is composed of a substance of a specific composition, such as a specific pure metal or an alloy of a specific composition, so as to be suitable for the purpose of the reaction, but there may be an undesirable impurity metal contained in the electrode during the manufacturing process of the electrode. As an example, it is known that when a cathode electrode is applied to an electrochemical water treatment apparatus for removing nitrate nitrogen, the cathode electrode is generally made of an Fe material, and the Ni component inhibits the reduction reaction of nitrate nitrogen.

As described above, an undesirable trace amount of impurity metal may be contained in the electrode during the manufacturing process of the electrode, but the impurity metal does not participate in or inhibit the electrochemical reaction, and the elution of normal electrode components may be accelerated during the repeated electrochemical reaction. That is, the more the impurity metal is undesirably present on the electrode surface, the more the electrode elution phenomenon on the electrode surface may increase.

Since the undesired impurity metal contained in the electrode is eluted together with the normal electrode components, the composition of the electrode is deviated from the initial state, and the resistance of the electrode surface is increased, and the side reaction with the electrolyte solution and the like are changed as described above.

The present invention proposes a technique of removing impurities present on an electrode, particularly on the surface of the electrode, by an electro-dissolution process (electro-dissolution) and simultaneously depositing a specific metal element by an electro-deposition process (electro-deposition) with respect to the electrode prepared with a specific composition, thereby optimizing the composition of the electrode to meet the reaction purpose.

The electro-dissolution process (electro-dissolution) is a process of oxidizing and removing metal components on the surface of an electrode (see fig. 1), and not only impurity metals on the surface of the electrode but also normal metal components on the surface of the electrode may be oxidized and removed in the electro-dissolution process. The composition of the electrode may be different from the initial state due to the oxidation and exfoliation of a part of the normal metal components other than the impurity metal. When the composition of the electrode is different from the initial state, problems such as an increase in the resistance of the electrode surface, side reactions with the electrolyte, and the like may be caused as described above. The phenomenon that the electrode composition is different from the initial state due to the electro-dissolution process is solved by the electro-deposition process (electro-deposition).

The electro-deposition process (electro-deposition) is a process of depositing a specific metal on the surface of an electrode by a reduction reaction with respect to the electrode subjected to an electro-dissolution process (see fig. 1). When the electrodeposition process is carried out after the specific metal is dissolved in advance in the electrolytic bath in which the electrodeposition process is carried out, the specific metal can be deposited on the surface of the electrode, and the composition of the electrode can be optimized or controlled to meet the purpose of the reaction by this process.

In order to optimize the oxidation reaction based on the electro-dissolution process (electro-dissolution), the reduction reaction based on the electro-deposition process (electro-deposition), and the removal characteristics of impurity metals by the oxidation reaction of the electro-dissolution process, the deposition characteristics of specific metals by the reduction reaction of the electro-deposition process, it is necessary to control the potential (potential) applied to the modification object electrode in the electro-dissolution process and the potential applied to the modification object electrode in the electro-deposition process.

That is, the oxidation reaction and the removal characteristic of the impurity metal by the oxidation reaction change according to the potential applied to the electrode to be modified in the electrodissolution process, and the deposition characteristic of the specific metal by the reduction reaction and the reduction reaction differ according to the potential applied to the electrode to be modified in the electrodeposition process.

In order to optimize the removal characteristics of impurity metals based on an electro-dissolution process and the deposition characteristics of specific metals based on an electro-deposition process, the following potential conditions and pH conditions are respectively set for the electro-dissolution process and the electro-deposition process.

In order to optimize the removal characteristics of impurity metals by an electro-dissolution process (electro-dissolution), the conditions are satisfied in which a potential higher than a standard electrode potential of a metal having the highest standard electrode potential among metals included in a modification target electrode is applied in the electro-dissolution process, and a potential equal to or lower than an oxygen evolution potential is applied. In other words, the potential applied to the electrode to be modified during the electrodissolution is greater than the standard electrode potential of the metal having the highest standard electrode potential among the metals included in the electrode to be modified and equal to or less than the oxygen evolution potential. Here, the term "the maximum standard electrode potential among the metals contained in the electrode to be modified" means the metal in which the oxidation reaction occurs at the latest. Referring to fig. 2, the electrode to be modified (SUS electrode) was applied as an anode during the electrodissolution, and a potential of 0.6V, which is greater than the standard electrode potential of Fe (-0.036V), was applied, with 0.6V corresponding to the oxygen evolution potential under alkaline conditions.

When the potential applied to the electrode to be modified in the electrodissolution process is lower than the standard electrode potential, the oxidation reaction does not proceed, and when the potential is higher than the oxygen evolution potential, the whole electrode to be modified is rapidly oxidized.

In addition, in order to optimize the removal characteristics of the impurity metals by the electro-dissolution process, the pH of the electrolyte during the electro-dissolution process is not limited, but it is preferably in an alkaline state having a pH of 8 to 12. Meanwhile, it is a precondition that the modification target electrode is applied as an anode in the electro-dissolution process. The application of an alkaline electrolyte in the electrodissolution process may be more effective in the case where the modification target electrode is applied for the purpose of nitrate nitrogen reduction reaction.

When the potential under the above-described conditions is applied to the electrode to be modified in the state where the electrode to be modified is applied as an anode in the alkaline electrolyte of the electrochemical reaction cell, the metal on the surface of the electrode to be modified is eluted and OH is simultaneously eluted^-Ions are adsorbed to the electrode to be modified, and OH adsorbed to the electrode to be modified^-The ions play a role in accelerating the conversion of nitrate nitrogen into ammonia nitrogen.

On the other hand, in order to optimize the deposition characteristics of a specific metal in the electro-deposition process (electro-deposition), a potential equal to or higher than the hydrogen evolution potential and lower than the standard electrode potential of the metal having the smallest standard electrode potential among the metals contained in the modification target electrode is applied to the modification target electrode. Here, the term "the smallest standard electrode potential among the metals contained in the electrode to be modified" means the metal in which the reduction reaction occurs at the latest. Referring to fig. 3, a modification object electrode (SUS electrode) was applied as a cathode during electro-dissolution, and a potential of about-0.3V, which is less than the standard electrode potential (-0.036V) of Fe, was applied.

When the potential applied to the electrode to be modified in the electrodeposition process is less than the hydrogen evolution potential, the reduction reaction rapidly proceeds, the efficiency decreases due to the hydrogen gas generated on the surface, and the oxidation reaction proceeds when the potential is greater than the standard electrode potential.

In addition, in the electrodeposition process, in order to optimize the deposition characteristics of a specific metal, it is a prerequisite that the electrolyte in the electrodeposition process is adapted as a cathode to the modification target electrode in the electrodeposition process. When the electrodeposition process is performed under alkaline electrolyte conditions, metal ions are bonded to oxygen and precipitated, and thus metal deposition on the surface of the electrode to be modified cannot be efficiently performed. This can also be confirmed by the Pourbaix diagram (Pourbaix diagram) of FIG. 8.

Hereinafter, a method for modifying an electrode for electrochemical reaction according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

First, a modification target electrode is prepared. The electrode to be modified is an electrode for electrochemical reaction requiring surface modification, and can be applied to a cathode or an anode for electrochemical reaction. The material constituting the electrode to be modified is not limited, depending on the cathode or anode that can be applied to the electrochemical reaction. That is, the constituent material of the electrode to be modified is not particularly limited as long as the control of the electrode composition can be achieved while removing the impurity metal on the surface of the electrode by applying the later-described electro-dissolution process (electro-dissolution) and electro-deposition process (electro-deposition) in this order. However, the modification target electrode has a desired specific composition depending on the purpose of the electrochemical reaction, use for the anode, or use for the cathode. In addition, the electrode to be modified is composed of a specific composition so as to meet the purpose of reaction, but may contain some impurity metals in the manufacturing process of the electrode.

For example, in the case of an electrochemical water treatment apparatus, stainless steel or Ti can be used as the cathode of the reduction electrode.

In a state where the modification target electrode is prepared, an electro-dissolution process (electro-dissolution) and an electro-deposition process (electro-deposition) are sequentially applied to the modification target electrode.

In order to improve the efficiency of the electrodissolution process and the electrodeposition process before the electrodissolution process and the electrodeposition process are performed, the electrode to be modified needs to be pretreated. Specifically, the surface of the electrode to be modified is sandpaper-treated to increase the specific surface area of the surface of the electrode to be modified. The specific surface area of the electrode surface to be modified is increased by sand paper treatment in order to promote the oxidation reaction in the electrodissolution process and the reduction reaction in the electrodeposition process. After the sand paper treatment is completed, the organic solvent, oil, or the like remaining on the surface of the electrode to be modified is removed with acetone or the like. Then, natural oxide (native oxide) and inorganic impurities present in the electrode to be modified are removed by oxalic acid (oxalic acid) or the like, and the pretreatment of the electrode to be modified is completed.

The electro-dissolution process (electro-dissolution) is performed as follows.

The electrode to be modified is immersed as an anode in an electrochemical reaction vessel filled with an electrolyte, and the electrochemical reaction vessel is provided with a cathode. In this state, a potential under a specific condition is applied to the electrode to be modified, which is applied as an anode. Here, the potential under the specific condition means a potential which is greater than the standard electrode potential of the metal having the maximum standard electrode potential among the metals included in the electrode to be modified and is equal to or less than the oxygen evolution potential. When the potential applied to the electrode to be modified in the electrodissolution process is lower than the standard electrode potential, the oxidation reaction does not proceed, and when the potential is higher than the oxygen evolution potential, the whole electrode to be modified is rapidly oxidized. The metal included in the electrode to be modified may be in various forms, but the metal having the highest standard electrode potential among the metals included in the electrode to be modified in the present invention may be specifically Pd, considering that the metal generally includes the elements shown in table 1 below.

[ TABLE 1 ]

< Metal element of electrode for electrochemical reaction >

Element(s)	Standard electrode potential (V vs NHE)
		Pd(s)	0.915
Ag(s)	0.799
		Rh(s)	0.76
C(s)	0.52
		Cu(s)	0.518
Bi(s)	0.308
		Pb(s)	-0.126
Sn(s)	-0.141
		Ni(s)	-0.236
Co(s)	-0.282
		Tl(s)	-0.336
In(s)	-0.338
		Fe(s)	-0.44
Zn(s)	-0.762
		B(s)	-0.792
Cr(s)	-0.7
		Mn(s)	-1.18
Ti(s)	-1.6
		Al(s)	-1.677

Since the electric potential under the above-described specific condition is applied to the electrode to be modified (anode), the surface of the electrode to be modified is oxidized, and the metal component is eluted from the surface of the electrode to be modified due to the oxidation. In this case, the metal component eluted from the surface of the electrode to be modified includes a normal electrode component of the electrode to be modified and an undesired impurity metal component. That is, although the electrode to be modified is manufactured to have a desired specific composition as described above, an undesired impurity metal may be contained in the electrode to be modified in the manufacturing process of the electrode, and an undesired impurity metal component may be eluted together with a desired metal component, which is a normal metal component, in the above-described electrolytic dissolution process. As an example, when the electrode to be modified is made of stainless steel or Ti, the electrode to be modified may contain undesirable Ni and Cr, and Ni and Cr as impurity metals may be eluted together with Fe or Ti as a normal metal component in the above-described electrolytic dissolution process.

The pH of the electrolyte filled in the electrochemical reaction cell during the electrodissolution is not limited, but when the electrode to be modified is applied as an electrode for nitrate nitrogen reduction reaction, an alkaline electrolyte having a pH of 8 to 12 is preferably applied. When the potential under the above-described conditions is applied to the electrode to be modified in the state where the electrode to be modified is applied as an anode in the alkaline electrolyte of the electrochemical reaction cell, the metal on the surface of the electrode to be modified is eluted, and OH is simultaneously eluted^-Ions are adsorbed to the electrode to be modified, and OH adsorbed to the electrode to be modified^-The ions play a role in accelerating the conversion of nitrate nitrogen into ammonia nitrogen.

On the other hand, elution of the impurity metal from the modification target metal means that the problem caused by the impurity metal can be solved, but the initial composition state of the modification target electrode changes as normal metal components other than the impurity metal are eluted together. The change in the initial composition state of the electrode to be modified means that the electrode is not optimized for the purpose of the reaction, and may cause a change such as an increase in the resistance of the electrode surface or a side reaction with the electrolyte.

In a state where the electro-dissolution process is completed, an electro-deposition process (electro-deposition) is performed on the modification target electrode subjected to the electro-dissolution process. The electrodeposition process (electro-deposition) is carried out as follows.

An electrolyte in which a metal for deposition is dissolved is filled in the electrochemical reaction tank. The deposition metal is a material to be deposited on the modification target electrode by an electrodeposition process, and may be selected depending on the purpose of reaction of the modification target electrode, use for the anode, or use for the cathode. As an example, when the electrode to be modified is used as a cathode of an electrochemical water treatment apparatus for reducing nitrate nitrogen in water to ammonia nitrogen, Fe or Zn can be applied as a metal dissolved in an electrolyte.

An anode is immersed in an electrochemical reaction tank having an electrolyte in which a metal for deposition is dissolved, and an electrode to be modified which has undergone an electrodissolution process is immersed as a cathode. In this state, a potential under a specific condition is applied to the electrode to be modified, which is applied as a cathode. Here, the potential under the specific condition means a potential equal to or higher than a hydrogen evolution potential and lower than a standard electrode potential of a metal having the smallest standard electrode potential among metals included in the electrode to be modified. When the potential applied to the electrode to be modified during electrodeposition is less than the hydrogen evolution potential, the reduction reaction proceeds rapidly, or the deposition efficiency may decrease due to competition with hydrogen evolution, and when the potential is greater than the standard electrode potential, the reduction reaction does not proceed.

Since the electric potential under the above-described specific condition is applied to the modification target electrode (cathode), the deposition metal dissolved in the electrolyte is deposited on the surface of the modification target electrode.

In this way, the deposition metal, i.e., the specific metal, can be deposited on the surface of the electrode to be modified by the electrodeposition process, and the composition of the electrode to be modified can be controlled by the electrodeposition process, so that optimization can be performed to meet the purpose of the reaction.

In carrying out the above electrodeposition, the concentration of the deposition metal dissolved in the electrolyte is considered in addition to the potential conditions and the electrolyte pH conditions as described above. In the electrodeposition process, the surface of the electrode to be modified is deposited with a metal dissolved in an electrolyte, and at the same time, a potential under the above-described conditions is applied to the electrode to be modified which is suitable as a cathode to generate hydrogen, so that hydrogen evolution and electrodeposition form a competitive reaction relationship. Therefore, in order to increase the selectivity of electrodeposition with respect to hydrogen evolution, the concentration of the deposition metal dissolved in the electrolyte should be applied at a fixed value or more. Further, hydrogen evolution during electrodeposition acts as a factor for increasing the pH of the electrolyte, and for this reason, the concentration of the deposition metal dissolved in the electrolyte should be applied at a fixed value or more. Therefore, the concentration of the deposition metal dissolved in the electrolyte is preferably set to be greater than 0.5M.

In the electrodeposition process, the metal for deposition may be any one of Au, Pt, Pd, Ir, Ag, Rh, Cu, Bi, Pb, Sn, Ni, Co, Tl, In, Fe, Zn, B and Cr or selected from combinations thereof, depending on the purpose of reaction of the modification target metal.

On the other hand, when the electrode to be modified is an oxidation electrode of an electrochemical water treatment apparatus and the oxidation electrode is made of a metal oxide, the metal for deposition suitable for the electrodeposition step may be any one or a combination of Pb, Ni, Pt, Mn, Ir, Ru, Co and Fe, and after the electrodeposition step, a step of heat-treating the electrode to be modified at a temperature of 300 to 500 ℃ in an oxygen atmosphere is added to oxidize the deposited metal.

As described above, the problem that the initial composition of the electrode to be modified is destroyed by eluting the normal metal component of the electrode to be modified in the electrodissolution process is solved by the subsequent deposition of the metal for deposition by the electrodeposition process, and the composition of the electrode to be modified is controlled so as to be optimized to meet the reaction object.

The method for modifying an electrode for electrochemical reaction according to an embodiment of the present invention is described above. The present invention will be described more specifically with reference to the following experimental examples.

< experimental example 1: nitrate nitrogen reduction characteristics of SUS electrode >

SUS 310, SUS316, and SUS420 having the compositions shown in table 2 below were used as cathodes for electrochemical nitrate nitrogen reduction reactions. Referring to table 2, it is shown that the contents of Ni and Cr increase in the reverse order when the Fe content increases in the order of SUS 310, SUS316, and SUS 420. As the anode, Ir is utilized_0.7Ta_0.3O_xThe electrolyte utilizes NaNO mixed with 16mM₃(224mg/L[N-NO₃ ^-]) And 50mM Na₂SO₄With an inter-electrode distance of 1cm and a current of 30mA/cm²。

[ TABLE 2 ]

< composition of respective SUS species >

As a result of the experiment, as shown in fig. 4, when SUS420 having the highest Fe content and the lowest Ni and Cr contents was applied as a reduction electrode for an electrochemical nitrate nitrogen reduction reaction, the nitrate nitrogen reduction efficiency was the most excellent.

< experimental example 2: electrode modification and nitrate nitrogen reduction efficiency by electrodissolution >

After the surface of the electrode was modified by electro-dissolution (electro-dissolution), the modified electrode was applied to an electrochemical water treatment apparatus, and the removal efficiency of nitrate nitrogen was observed. The electrode to be modified was SUS420 which was judged to have relatively excellent nitrate nitrogen reduction efficiency in experimental example 1. The pH conditions of the electrolyte during electrodissolution were set to acidic, neutral, and alkaline, respectively, and the electrode to be modified was modified under each condition. Acid electrolyte utilization 500mM H₂SO₄Neutral electrolyte utilizes 2mM NaNO₃And 50mM Na₂SO₄Alkaline electrolyte alkaline conditions were established with 500mM NaOH. The experimental conditions for the nitrate nitrogen reduction reaction were the same as in experimental example 1.

As a result of the experiment, referring to fig. 5, the nitrate nitrogen reduction current efficiency was 40% or more in the case of the electrode in which the electrodissolution was performed using the alkaline electrolyte (500mM NaOH), and was 30% or less in the case of the electrode using the acidic and neutral electrolytes.

The XPS analysis results showed that the electrode to be modified contained 16.6% of Fe when electrodissolution was performed using an alkaline electrolyte, 9.1% of Fe when a neutral electrolyte was used, and 3.8% of Fe when an acidic electrolyte was used. Further, the results of performing the electro-dissolution regardless of the pH of the electrolyte showed that the Ni and Cr components were completely removed in all cases.

Based on such results, it was concluded that, in the case of using an alkaline electrolyte, Ni and Cr components were completely removed from the modification object electrode while minimizing the loss of Fe to favorably act on the nitrate nitrogen reduction reaction.

< experimental example 3: nitrate nitrogen reduction characteristics of respective metals >

Electrodes each composed of Ni, Zn, Cu, and Fe were applied as cathodes for electrochemical nitrate nitrogen reduction reaction, and nitrate nitrogen reduction characteristics were observed.

As a result of the experiment, as shown in fig. 6, it was revealed that the nitrate nitrogen reduction current efficiency of Zn is the most excellent, and secondly the nitrate nitrogen reduction current efficiency of the Fe electrode is excellent.

< experimental example 4: electrode modification and nitrate nitrogen reduction efficiency by electrodissolution and electrodeposition >

After the electrodeposition process was performed on the SUS electrode subjected to the electrodissolution process of experimental example 2, the modified electrode was applied to an electrochemical water treatment apparatus and the nitrate nitrogen reduction efficiency was observed. 500mM of Zn (NO) were dissolved in each case during electrodeposition₃)₂、Fe(NO₃)₂、Ni(NO₃)₂. Under alkaline conditions, an SUS electrode subjected to an electro-dissolution treatment is suitable as a cathode in the electrodeposition process.

As a result of the experiment, referring to fig. 7, it was confirmed that the nitrate nitrogen reduction current efficiency increased to 50% or more when the electrodeposition process was performed using the electrolyte in which Fe ions were dissolved and the electrolyte in which Zn ions were dissolved. On the contrary, when an electrolyte in which Ni ions are dissolved is used, it is confirmed that the nitrate nitrogen reduction current efficiency is reduced to 5% or less. This is a result of confirming that the metal dissolved in the electrolyte by the electrodeposition process is deposited on the electrode, and also a result of confirming that Fe and Zn play a role in improving the reduction efficiency of nitrate nitrogen in the case where the SUS-made electrode is applied to the nitrate nitrogen reduction process.

On the other hand, the electro-dissolution process and the electro-deposition process with respect to the above experimental examples 1 to 4 are performed at a normal temperature, and may be preferably performed under a temperature condition of 10 to 60 ℃ depending on experimental environments.