Method for modifying electrodes for electrochemical reactions

Abstract

The present invention relates to a method for modifying an electrode for an electrochemical reaction, wherein the method sequentially applies an electro-dissolution process and an electro-deposition process to the electrode to be modified, thereby minimizing impurities on the electrode surface and optimizing the composition of the electrode surface to make it meet the purpose of the reaction.

Description

Technical Field

[0001] The present invention relates to a method for modifying an electrode for electrochemical reaction, and more specifically, to a method for modifying an electrode for electrochemical reaction, wherein the electrode is subjected to an electrodissolution process and an electrodeposition process in sequence to minimize impurities on the electrode surface and optimize the composition of the electrode surface to meet the purpose of the reaction.

[0002] [Explanation on national support for R&D]

[0003] This research was completed under the supervision of the Korea Advanced Institute of Science and Technology with support from the Ministry of Environment. The research project name is the Global Top Environmental Technology Development Project (R&D), and the research topic name is Development of Electrochemical-Based High-Concentration Organic Matter and Total Nitrogen Control Technology (Topic Unique Number: 1485016103). Background Art

[0004] It is known that electrochemical reaction is a heterogeneous charge transfer process that occurs at the interface between the electrode and the solution. Compared with the interior of the solution, the electrochemical reaction is greatly affected by slight changes in the double layer or diffusion layer at the electrode-solution interface. Properly adjusting the reactivity of the electrode-solution interface is an important part of electrochemical research.

[0005] Chemically modified electrode means an electrode that has been modified in a manner consistent with the purpose of the reaction. Chemically modified electrodes (CME) can be manufactured by a variety of methods. For example, it can be manufactured by methods based on chemisorption, covalent bonding, polymer (organic), multi-core (inorganic) or composite membrane coating, mixing the electrode matrix material with the modifier, etc. Chemically modified electrodes (CME) can also be distinguished based on the coating method. For example, cross-linking, dip coating, electrochemical deposition, electrochemical polymerization, solvent evaporation, spin coating (spin casting), etc. are known. The above-mentioned modified electrodes themselves play the role of repelling or attracting electrons in the reaction. It is particularly noteworthy that the electrocatalytic properties can be applied to various electrochemical fields.

[0006] In addition, the stability of the electrode is more important than anything else in the electrochemical reaction. The main problems that occur in the electrochemical reaction are the dissolution of electrode components, the increase of resistance on the electrode surface, and the side reaction with the electrolyte, which are mainly caused by the change of reactivity on the electrode surface.

[0007] In order to maintain the reactivity of the electrode surface, it is necessary to minimize the impurities on the electrode surface and optimize the composition of the electrode surface to make it meet the reaction purpose. However, the existing technology has limitations in controlling the impurities on the electrode surface or optimizing the composition of the electrode surface. Summary of the invention

[0008] The present invention has been developed to solve the above-mentioned problems, and its purpose is to provide a method for modifying electrodes for electrochemical reactions. This method minimizes impurities on the electrode surface and optimizes the composition of the electrode surface to make it meet the reaction purpose by sequentially applying an electro-dissolution process and an electro-deposition process to the electrode to be modified.

[0009] The modification method of the electrode for electrochemical reaction according to the present invention for achieving the above-mentioned purpose is characterized in that it comprises the following steps: a step of preparing an electrode to be modified; an electro-dissolution step of immersing the electrode to be modified as an anode in an electrochemical reaction tank filled with an electrolyte, applying a first potential to the electrode to be modified to oxidize the surface of the electrode to be modified; and an electro-deposition step of immersing the electrode to be modified after the above-mentioned electro-dissolution step as a cathode in an electrochemical reaction tank filled with an electrolyte in which a deposition metal is dissolved, applying a second potential to the electrode to be modified to induce deposition metal to be deposited on the electrode to be modified by a reduction reaction.

[0010] The first potential is a potential greater than the standard electrode potential of a metal having the largest standard electrode potential among metals included in the electrode to be modified and less than or equal to an oxygen evolution potential.

[0011] The second potential is a potential that is greater than or equal to the hydrogen evolution potential and less than or equal to the standard electrode potential of the metal with the smallest standard electrode potential among the metals included in the electrode to be modified.

[0012] The metal contained in the electrode to be modified is any one of Pd, Ag, Rh, Cu, Bi, Pb, Sn, Ni, Co, Tl, In, Fe, Zn, B, Cr, Mn, Ti and Al, or a combination thereof. The metal with the largest standard electrode potential among the metals contained in the electrode to be modified is the metal with 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 with the largest standard electrode potential in a combination of any one or more of Pd, Ag, Rh, Cu, Bi, Pb, Sn, Ni, Co, Tl, In, Fe, Zn, B, Cr, Mn, Ti and Al.

[0013] In addition, in the electrodeposition step, the deposition metal can be any one of Au, Pt, Pd, Ir, Ag, Rh, Cu, Bi, Pb, Sn, Ni, Co, Tl, In, Fe, Zn, B, Cr or a combination thereof.

[0014] The electrolyte in the above-mentioned electrodeposition step is an electrolyte with a pH of 2 to 8.

[0015] The material of the electrode to be modified is stainless steel (SUS) or titanium (Ti), and the electrolyte in the electrolysis step can be an alkaline electrolyte.

[0016] The concentration of the deposition metal dissolved in the electrolyte during the electrodeposition step is preferably greater than 500 mM.

[0017] The method further includes a pretreatment step for pretreating the electrode to be modified before the electrodissolution step. The pretreatment step includes: a process of increasing the specific surface area of ​​the electrode to be modified by sandpapering the surface of the electrode to be modified; a process of removing one or more of the organic solvent and oil remaining on the surface of the electrode to be modified; and a process of removing the natural oxide film and inorganic impurities present in the electrode to be modified.

[0018] When the electrode to be modified is an oxidation electrode of an electrochemical water treatment device and the oxidation electrode is composed of a metal oxide, the deposition metal suitable for the electrodeposition step is any one of Pb, Ni, Pt, Mn, Ir, Ru, Co and Fe or a combination thereof. After the electrodeposition step, in order to oxidize the deposited metal, a process of heat treating the electrode to be modified at a temperature of 300 to 500°C in an oxygen atmosphere is carried out.

[0019] The above-mentioned modified electrode is an electrode made of stainless steel (SUS) or titanium (Ti) suitable as the cathode of an electrochemical water treatment device that reduces nitrate nitrogen to ammonia nitrogen. The impurity metal contained on the surface of the modified electrode is removed by the above-mentioned electrodissolution step, and Fe or Zn metal can be deposited on the surface of the modified electrode by the above-mentioned electrodeposition step.

[0020] The method for modifying an electrode for electrochemical reaction according to the present invention has the following effects.

[0021] By sequentially applying the electrodissolution process and the electrodeposition process, impurity metals contained in the electrode to be modified can be effectively removed, and the composition of the electrode to be modified can be controlled and optimized in a manner suitable for the purpose of the reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram showing the electrodissolution process and the electrodeposition process.

[0023] Figure 2 This is a reference diagram for explaining the range of potential applied to the electrode to be modified (anode) during the electrolysis process.

[0024] Figure 3 This is a reference diagram for explaining the range of potential applied to the electrode to be modified (cathode) during the electrodeposition process.

[0025] Figure 4 These are the experimental results showing the nitrate nitrogen reduction characteristics of SUS electrodes.

[0026] Figure 5 The experimental results show the nitrate nitrogen reduction characteristics of the target electrode according to the modification of the electrolyte during the electrolysis process.

[0027] Figure 6 These are experimental results showing the nitrate nitrogen reduction characteristics depending on the type of metal.

[0028] Figure 7 The experimental results show the nitrate nitrogen reduction characteristics of the electrode to be modified according to the type of metal used for deposition during the electrodeposition process.

[0029] Figure 8 A reference diagram representing a Pourbaix diagram. DETAILED DESCRIPTION

[0030] The present invention provides a method for modifying an electrode used for electrochemical reaction.

[0031] As mentioned in the above “Background Art”, the electrode used for electrochemical reaction will experience the phenomenon of electrode component dissolution or electrode surface resistance increase after a certain period of time. The main reason is that part of the electrode falls off during the repeated electrochemical reaction and the initial composition of the electrode changes.

[0032] Electrodes used for electrochemical reactions are made of substances of specific composition, such as specific pure metals or alloys of specific composition, so as to meet the purpose of the reaction, but undesirable impurity metals may be contained in the electrodes during the manufacturing process of the electrodes. As an example, it is known that in the case of cathode electrodes used in electrochemical water treatment devices for removing nitrate nitrogen, they are generally made of Fe material, and the Ni component hinders the nitrate nitrogen reduction reaction.

[0033] Thus, undesirable trace amounts of impurity metals may be included in the electrode during the manufacturing process of the electrode, but such impurity metals do not participate in the electrochemical reaction or hinder the electrochemical reaction, and may accelerate the dissolution of normal electrode components during repeated electrochemical reactions. That is, the more undesirable impurity metals there are on the electrode surface, the more electrode dissolution may occur on the electrode surface.

[0034] Undesirable impurity metals contained in the electrode are dissolved together with normal electrode components, so that the composition of the electrode deviates from the initial state, causing changes such as an increase in resistance on the electrode surface and a side reaction with the electrolyte as described above.

[0035] The present invention proposes the following technology, namely, taking an electrode prepared with a specific composition as the object, removing impurities from the electrode, especially those existing on the surface of the electrode, through an electro-dissolution process, and depositing specific metal elements through an electro-deposition process, thereby optimizing the composition of the electrode to make it meet the purpose of the reaction.

[0036] Electro-dissolution is a process that causes the metal components on the electrode surface to oxidize and fall off (see Figure 1 ), during the electro-dissolution process, not only the impurity metal on the electrode surface, but also the normal metal components on the electrode surface may be oxidized and fall off. The normal metal components other than the impurity metal are also partially oxidized and fall off, so that the composition of the electrode may be different from the initial state. When the composition of the electrode is different from the initial state, it may cause the problems mentioned above, that is, the resistance of the electrode surface increases, side reactions with the electrolyte, etc. 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.

[0037] Electrodeposition is a process in which a specific metal is deposited on the surface of an electrode through a reduction reaction after an electrodissolution process (see Figure 1 ). When the electrodeposition process is carried out after the specific metal is pre-dissolved in the electrolytic cell for the electrodeposition process, 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 reaction purpose through this process.

[0038] In order to optimize the oxidation reaction based on the electro-dissolution process, the reduction reaction based on the electro-deposition process, the removal characteristics of impurity metals through the oxidation reaction in the electro-dissolution process, and the deposition characteristics of specific metals through the reduction reaction in the electro-deposition process, it is necessary to control the potential applied to the modification object electrode during the electro-dissolution process and the potential applied to the modification object electrode during the electro-deposition process.

[0039] That is, depending on the potential applied to the electrode to be modified during the electrodissolution process, the oxidation reaction and the removal characteristics of the impurity metal based on the oxidation reaction change, and depending on the potential applied to the electrode to be modified during the electrodeposition process, the reduction reaction and the deposition characteristics of the specific metal based on the reduction reaction are different.

[0040] In order to optimize the removal characteristics of impurity metals based on the electrodissolution process and the deposition characteristics of specific metals based on the electrodeposition process, the present invention sets the following potential conditions and pH conditions for the electrodissolution process and the electrodeposition process, respectively.

[0041] In order to optimize the removal characteristics of impurity metals based on the electro-dissolution process, the conditions of applying a potential higher than the standard electrode potential of the metal with the largest standard electrode potential among the metals contained in the modified object electrode and applying a potential less than or equal to the oxygen evolution potential are met during the electro-dissolution process. In other words, the potential applied to the modified object electrode during the electro-dissolution process is greater than the standard electrode potential of the metal with the largest standard electrode potential among the metals contained in the modified object electrode and is less than or equal to the oxygen evolution potential. Here, the metal with the largest standard electrode potential among the metals contained in the modified object electrode means the metal where the oxidation reaction occurs last. Reference Figure 2 When the electrode to be modified (SUS electrode) is used as an anode during the electrodissolution process, a potential of 0.6 V greater than the standard electrode potential of Fe (-0.036 V) is applied, and 0.6 V corresponds to the oxygen evolution potential under alkaline conditions.

[0042] When the potential applied to the electrode to be modified during the electrolysis process is lower than the standard electrode potential, no oxidation reaction will occur. However, when the potential is higher than the oxygen evolution potential, the entire electrode to be modified will be rapidly oxidized.

[0043] In addition, in order to optimize the removal characteristics of impurity metals based on the electrolysis process, the pH of the electrolyte during the electrolysis process is not limited, but it is preferably an alkaline state of pH 8 to 12. At the same time, the premise is that the electrode to be modified is used as an anode during the electrolysis process. The use of an alkaline electrolyte during the electrolysis process may be more effective when the electrode to be modified is used for a nitrate nitrogen reduction reaction.

[0044] When the above potential is applied to the electrode to be modified in the alkaline electrolyte of the electrochemical reaction cell, the metal on the surface of the electrode to be modified is dissolved and OH is reacted. - The ions are adsorbed to the electrode to be modified, and the OH - The ions accelerate the conversion of nitrate nitrogen to ammonia nitrogen.

[0045] On the other hand, in order to optimize the deposition characteristics of a specific metal during the electro-deposition process, a potential greater than or equal to the hydrogen evolution potential and less than the standard electrode potential of the metal with the smallest standard electrode potential among the metals included in the modified electrode is applied to the modified electrode. Here, the metal with the smallest standard electrode potential among the metals included in the modified electrode means the metal in which the reduction reaction occurs the latest. Figure 3 In the electrodissolution process, the electrode to be modified (SUS electrode) is used as a cathode, and a potential of about -0.3 V, which is lower than the standard electrode potential of Fe (-0.036 V), is applied.

[0046] When the potential applied to the electrode to be modified during electrodeposition is less than the hydrogen evolution potential, the reduction reaction proceeds rapidly, and the efficiency is reduced due to the hydrogen generated on the surface. When it is greater than the standard electrode potential, the oxidation reaction proceeds.

[0047] In addition, in order to optimize the deposition characteristics of a specific metal during the electrodeposition process, the prerequisite is that the electrolyte during the electrodeposition process is suitable for the electrode to be modified during the electrodeposition process as a cathode. When the electrodeposition process is carried out under alkaline electrolyte conditions, metal ions combine with oxygen and are precipitated, making it impossible to effectively deposit the metal on the surface of the electrode to be modified. This can also be achieved by Figure 8 This can be confirmed by using the Pourbaix diagram.

[0048] 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.

[0049] First, prepare the electrode to be modified. The electrode to be modified is an electrode that requires surface modification for electrochemical reaction, and can be applied to the cathode or anode of the electrochemical reaction. The constituent material of the electrode to be modified is not limited according to the cathode or anode that can be applied to the electrochemical reaction. That is, as long as the electro-dissolution process (electro-dissolution) and electro-deposition process (electro-deposition) described later can be applied in sequence to remove the impurity metal on the electrode surface while achieving the control of the electrode composition, the constituent material of the electrode to be modified is not particularly limited. However, the electrode to be modified has a desired specific composition depending on the purpose of the electrochemical reaction, whether it is used for the anode or for the cathode. In addition, the electrode to be modified is composed of a specific composition to make it meet the purpose of the reaction, but may contain some impurity metals during the manufacturing process of the electrode.

[0050] As an example, in the case of an electrochemical water treatment device, stainless steel or Ti can be used as the cathode of the reduction electrode.

[0051] In a state where the electrode to be modified is prepared, an electro-dissolution process and an electro-deposition process are sequentially applied to the electrode to be modified.

[0052] Before the electrodissolution process and the electrodeposition process are carried out, in order to improve the efficiency of the electrodissolution process and the electrodeposition process, the electrode to be modified needs to be pretreated. Specifically, the surface of the electrode to be modified is treated with sandpaper to increase the specific surface area of ​​the surface of the electrode to be modified. Increasing the specific surface area of ​​the surface of the electrode to be modified by sandpaper treatment is to promote the oxidation reaction of the electrodissolution process and the reduction reaction of the electrodeposition process. When the sandpaper treatment is completed, acetone or the like is used to remove the organic solvent, oil, etc. remaining on the surface of the electrode to be modified. Then, oxalic acid or the like is used to remove the native oxide film (native oxide) and inorganic impurities present in the electrode to be modified, and the pretreatment of the electrode to be modified is completed.

[0053] The electro-dissolution process was performed as follows.

[0054] The modified electrode is immersed in an electrochemical reaction tank filled with an electrolyte as an anode, so that the electrochemical reaction tank has a cathode. In this state, a potential of a specific condition is applied to the modified electrode suitable as an anode. Here, the potential of a specific condition means a potential greater than the standard electrode potential of the metal with the largest standard electrode potential among the metals contained in the modified electrode and less than or equal to the oxygen evolution potential. When the potential applied to the modified electrode during the electrodissolution process is less than the standard electrode potential, no oxidation reaction will occur, and when it is greater than the oxygen evolution potential, the modified electrode as a whole will be rapidly oxidized. There are many kinds of metals contained in the modified electrode, but considering that the elements shown in Table 1 are usually included, the metal with the largest standard electrode potential among the metals contained in the modified electrode in the present invention can be specifically Pd.

[0055]

Table 1

[0056] <Metallic Elements of Electrodes for Electrochemical Reaction>

[0057] element 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

[0058] Since the potential under the above-mentioned specific conditions is applied to the electrode to be modified (anode), the surface of the electrode to be modified is oxidized, and due to the oxidation, metal components are dissolved from the surface of the electrode to be modified. At this time, the metal components dissolved from the surface of the electrode to be modified include normal electrode components of the electrode to be modified and undesirable impurity metal components. That is, as described above, the electrode to be modified is manufactured to a desired specific composition, but the electrode to be modified may contain undesirable impurity metals during the manufacturing process of the electrode, and the undesirable impurity metal components are dissolved together with the normal metal components, that is, the desired metal components, during the above-mentioned electrodissolution process. As an example, in the case where the electrode to be modified is desired to be 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 dissolved together with Fe or Ti as normal metal components during the above-mentioned electrodissolution process.

[0059] The pH of the electrolyte filled in the electrochemical reaction tank during the electrolysis process is not limited, but when the electrode to be modified is used as an electrode for the nitrate nitrogen reduction reaction, an alkaline electrolyte with a pH of 8 to 12 is preferably used. When the electrode to be modified is used as an anode in the alkaline electrolyte of the electrochemical reaction tank, when the potential under the above conditions is applied to the electrode to be modified, the metal on the surface of the electrode to be modified is dissolved, and OH is - The ions are adsorbed to the electrode to be modified, and the OH - The ions play a role in accelerating the conversion of nitrate nitrogen to ammonia nitrogen.

[0060] On the other hand, dissolving impurity metals from the metal to be modified means that the problems caused by the impurity metals can be solved, but the initial composition state of the electrode to be modified changes as normal metal components other than the impurity metals are dissolved together. The change in the initial composition state of the electrode to be modified means that it is not optimized for the reaction purpose, which may cause changes such as an increase in resistance on the electrode surface and side reactions with the electrolyte.

[0061] When the electrolysis process is completed, the electrode to be modified after the electrolysis process is subjected to an electro-deposition process. The electro-deposition process is performed as follows.

[0062] The electrochemical reaction tank is filled with an electrolyte in which a deposition metal is dissolved. The deposition metal is a material that is deposited on the electrode to be modified by the electrodeposition process, and can be selected according to the reaction purpose of the electrode to be modified, whether it is used as an anode or a cathode. As an embodiment, when the electrode to be modified is used as a cathode of an electrochemical water treatment device that reduces nitrate nitrogen in water to ammonia nitrogen, Fe or Zn can be used as the metal dissolved in the electrolyte.

[0063] In an electrochemical reaction tank having an electrolyte dissolved with a metal for deposition, an anode is immersed, and at the same time, the modified object electrode that has undergone an electrodissolution process is immersed as a cathode. In this state, a potential of a specific condition is applied to the modified object electrode that is applicable as a cathode. Here, the potential of the specific condition means a potential that is greater than or equal to the hydrogen evolution potential and less than the standard electrode potential of the metal with the smallest standard electrode potential among the metals included in the modified object electrode. When the potential applied to the modified object electrode during the electrodeposition process is less than the hydrogen evolution potential, a reduction reaction is rapidly carried out or the deposition efficiency may be reduced due to competition with hydrogen evolution, and a reduction reaction is not carried out when it is greater than the standard electrode potential.

[0064] Since the potential under the above-mentioned specific conditions is applied to the electrode to be modified (cathode), the deposition metal dissolved in the electrolyte is deposited on the surface of the electrode to be modified.

[0065] In this way, the deposition metal, that is, 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 and optimized to meet the purpose of the reaction.

[0066] In the above-mentioned electrodeposition process, in addition to the potential conditions and electrolyte pH conditions as described above, the concentration of the deposition metal dissolved in the electrolyte should also be considered. Due to the metal dissolved in the electrolyte by the surface deposition of the modified object electrode during the electrodeposition process, the potential of the modified object electrode applicable as the cathode is applied to generate hydrogen, and hydrogen deposition and electrodeposition constitute a competitive reaction relationship. Thus, in order to improve the selectivity of electrodeposition relative to hydrogen deposition, the concentration of the deposition metal dissolved in the electrolyte should be applied with a numerical value above a fixed value. In addition, hydrogen deposition in the electrodeposition process works as a factor to improve the pH of the electrolyte. For this reason, the concentration of the deposition metal dissolved in the electrolyte should also be applied with a numerical value above a fixed value. Therefore, the concentration of the deposition metal dissolved in the electrolyte is preferably set to be greater than 0.5M.

[0067] During the electrodeposition process, the deposited metal can be 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, depending on the reaction purpose of the modified metal.

[0068] On the other hand, when the electrode to be modified is an oxidation electrode of an electrochemical water treatment device and the oxidation electrode is composed of a metal oxide, the deposition metal suitable for the electrodeposition process can be any one of Pb, Ni, Pt, Mn, Ir, Ru, Co and Fe or a combination thereof. After the electrodeposition process, in order to oxidize the deposited metal, an additional process is added to heat treat the electrode to be modified at a temperature of 300 to 500°C in an oxygen atmosphere.

[0069] As described above, the unwanted impurity metal can be dissolved from the electrode to be modified by the electrodissolution process. The problem of the initial composition of the electrode to be modified being destroyed by dissolving the normal metal components of the electrode to be modified during the electrodissolution process can be solved by the subsequent deposition of the deposition metal based on the electrodeposition process. At the same time, the composition of the electrode to be modified can be controlled so that it can be optimized to meet the reaction purpose.

[0070] The above is a description of a method for modifying an electrode for electrochemical reaction according to an embodiment of the present invention. Next, the present invention will be described in more detail by means of experimental examples.

[0071] <Experimental Example 1: Nitrate Nitrogen Reduction Characteristics of SUS Electrodes>

[0072] SUS 310, SUS 316, and SUS 420 having the compositions shown in Table 2 below were used as cathodes for the electrochemical nitrate nitrogen reduction reaction. Referring to Table 2, it is shown that when the Fe content increases in the order of SUS 310, SUS 316, and SUS 420, the Ni and Cr contents increase in the reverse order. As the anode, Ir 0.7 Ta 0.3 O x The electrolyte used was a mixture of 16 mM NaNO3 (224 mg / L [N-NO3 - ]) and 50mM Na2SO4 solution, the distance between the electrodes was 1cm, and the current was applied at 30mA / cm 2 .

[0073]

Table 2

[0074] <Composition of each SUS type>

[0075]

[0076] Experimental results, such as Figure 4 As shown, when SUS420, which has the highest Fe content and the lowest Ni and Cr contents, is used as a reduction electrode for the electrochemical nitrate nitrogen reduction reaction, the nitrate nitrogen reduction efficiency is the best.

[0077] <Experimental Example 2: Electrode modification and nitrate reduction efficiency using electrolysis>

[0078] After the electrode surface is modified by electro-dissolution, the modified electrode is applied to an electrochemical water treatment device to observe the removal efficiency of nitrate nitrogen. The modified electrode is SUS 420, which has been judged to have relatively excellent nitrate nitrogen reduction efficiency by Experimental Example 1. During electro-dissolution, the pH conditions of the electrolyte are set to acidic, neutral, and alkaline, respectively, and the modified electrode is modified under each condition. The acidic electrolyte uses 500mM H2SO4, the neutral electrolyte uses 2mM NaNO3 and 50mM Na2SO4, and the alkaline electrolyte uses 500mM NaOH to constitute alkaline conditions. The experimental conditions for the nitrate nitrogen reduction reaction are the same as those in Experimental Example 1.

[0079] Experimental results, see Figure 5 When the electrode was electrolyzed using an alkaline electrolyte (500 mM NaOH), the nitrate nitrogen reduction current efficiency was 40% or more. On the contrary, when the electrode was electrolyzed using an acidic or neutral electrolyte, the nitrate nitrogen reduction current efficiency was 30% or less.

[0080] XPS analysis results show that the modified electrode contains 16.6% Fe in the case of electrolysis using an alkaline electrolyte, 9.1% Fe in the case of a neutral electrolyte, and 3.8% Fe in the case of an acidic electrolyte. In addition, the results of electrolysis regardless of the pH of the electrolyte show that Ni and Cr components are completely removed in all cases.

[0081] Based on this result, it is inferred that when an alkaline electrolyte is used, Ni and Cr components are completely removed from the electrode to be modified, while Fe loss is minimized and acts favorably on the nitrate nitrogen reduction reaction.

[0082] <Experimental Example 3: Nitrate Nitrogen Reduction Characteristics of Various Metals>

[0083] Electrodes composed of Ni, Zn, Cu, and Fe, respectively, were used as cathodes in the electrochemical nitrate nitrogen reduction reaction and the nitrate nitrogen reduction characteristics were observed.

[0084] Experimental results, such as Figure 6 As shown, the nitrate nitrogen reduction current efficiency of the Zn electrode is the best, followed by the nitrate nitrogen reduction current efficiency of the Fe electrode.

[0085] <Experimental Example 4: Electrode modification and nitrate reduction efficiency using electrodissolution and electrodeposition>

[0086] After the electroplating process was carried out on the SUS electrode that had undergone the electrodissolution process in Experimental Example 2, the modified electrode was applied to an electrochemical water treatment device and the nitrate nitrogen reduction efficiency was observed. During the electroplating process, 500 mM of Zn(NO3)2, Fe(NO3)2, and Ni(NO3)2 were dissolved respectively. Under alkaline conditions, the SUS electrode that had undergone the electrodissolution process was applied as a cathode in the electroplating process.

[0087] Experimental results, see Figure 7 When the electrodeposition process was carried out using an electrolyte in which Fe ions were dissolved and an electrolyte in which Zn ions were dissolved, it was confirmed that the nitrate nitrogen reduction current efficiency increased to more than 50%. On the contrary, when using an electrolyte in which Ni ions were dissolved, it was confirmed that the nitrate nitrogen reduction current efficiency decreased to less than 5%. This is a result that can confirm that the metal dissolved in the electrolyte is deposited on the electrode through the electrodeposition process, and it is a result that proves that Fe and Zn play a role in improving the nitrate nitrogen reduction efficiency when the electrode is made of SUS material and is suitable for the nitrate nitrogen reduction process.

[0088] On the other hand, the electrodissolution process and the electrodeposition process of Experimental Examples 1 to 4 are performed at room temperature, and can be preferably performed at a temperature of 10 to 60° C. depending on the experimental environment.

Claims

1. A method for modifying an electrode for an electrochemical reaction, characterized in that: The method comprises the following steps: Steps for preparing electrodes for modification; an electrolysis 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; as well as an electrodeposition step, wherein the electrode to be modified after the electrodissolution step is immersed as a cathode in an electrochemical reaction tank filled with an electrolyte in which a deposition metal is dissolved, and a second potential is applied to the electrode to be modified to induce the deposition metal to be deposited on the electrode to be modified by a reduction reaction, The metal contained in the electrode to be modified is any one of Pd, Ag, Rh, Cu, Bi, Pb, Sn, Ni, Co, Tl, In, Fe, Zn, Cr, Mn, Ti and Al, or a combination thereof; the metal with the largest standard electrode potential among the metals contained in the electrode to be modified is the metal with the largest standard electrode potential among Pd, Ag, Rh, Cu, Bi, Pb, Sn, Ni, Co, Tl, In, Fe, Zn, Cr, Mn, Ti and Al, or the metal with the largest standard electrode potential among a combination of any one or more of Pd, Ag, Rh, Cu, Bi, Pb, Sn, Ni, Co, Tl, In, Fe, Zn, Cr, Mn, Ti and Al; wherein in the electrodeposition step, the deposition metal is any one of Au, Pt, Pd, Ir, Ag, Rh, Cu, Bi, Pb, Sn, Ni, Co, Tl, In, Fe, Zn and Cr or a combination thereof, wherein the undesired impurity metal on the surface of the electrode to be modified is removed by the electrodissolution step, The electrolyte in the electrodissolution step is an alkaline electrolyte.

2. The method for modifying an electrode for electrochemical reaction according to claim 1, characterized in that: The first potential is a potential greater than the standard electrode potential of a metal having the largest standard electrode potential among metals included in the electrode to be modified and less than or equal to an oxygen evolution potential.

3. The method for modifying an electrode for electrochemical reaction according to claim 1, characterized in that: The second potential is a potential that is equal to or greater than the hydrogen evolution potential and is less than the standard electrode potential of a metal with the smallest standard electrode potential among the metals included in the electrode to be modified.

4. The method for modifying an electrode for electrochemical reaction according to claim 1, characterized in that: The electrolyte in the electrodeposition step is an electrolyte with a pH of 2 to 8.

5. The method for modifying an electrode for electrochemical reaction according to claim 1, characterized in that: The material of the electrode to be modified is SUS or Ti.

6. The method for modifying an electrode for electrochemical reaction according to claim 1, characterized in that: The concentration of the deposition metal dissolved in the electrolyte during the electrodeposition step is greater than 500 mM.

7. The method for modifying an electrode for electrochemical reaction according to claim 1, characterized in that: The method further comprises a pretreatment step of pretreating the electrode to be modified before the electrolysis step, wherein the pretreatment step comprises: The process of increasing the specific surface area of ​​the modified electrode surface by sandpapering the surface of the modified electrode. A process of removing one or more of the organic solvent and oil remaining on the surface of the electrode to be modified, and The process of removing the natural oxide film and inorganic impurities present in the electrode to be modified.

8. The method for modifying an electrode for electrochemical reaction according to claim 1, characterized in that: When the electrode to be modified is an oxidation electrode of an electrochemical water treatment device and the oxidation electrode is composed of a metal oxide, the deposition metal suitable for the electrodeposition step is any one of Pb, Ni, Pt, Mn, Ir, Ru, Co and Fe or a combination thereof, After the electrodeposition step, a step of heat treating the electrode to be modified at a temperature of 300 to 500° C. in an oxygen atmosphere is performed in order to oxidize the deposited metal.

9. The method for modifying an electrode for electrochemical reaction according to claim 1, characterized in that: The electrode to be modified is an electrode made of stainless steel or Ti and is suitable as a cathode of an electrochemical water treatment device for reducing nitrate nitrogen to ammonia nitrogen. The impurity metal contained in the surface of the electrode to be modified is removed by the electrodissolution step, and the Fe or Zn metal is deposited on the surface of the electrode to be modified by the electrodeposition step.

Images