KR102283328B1 - Method for regenerating reduction electrode - Google Patents

Abstract

The present invention provides a method for regenerating a reduction electrode applied to electrolysis, the method comprising: first coating the reduction electrode by introducing a platinum compound solution into an electrolyte solution for a reduction electrode; And it relates to a method of regenerating the reduction electrode, comprising the step of applying a ruthenium compound solution to the electrolyte solution for the reduction electrode and secondary coating the first coated reduction electrode, wherein the electrolyte is water or brine, the method of the present invention The regeneration method of the reduction electrode for electrolysis is an economical method, and it is possible to improve the continuity of the overvoltage improvement effect during electrolysis by regenerating the reduction electrode for electrolysis to have an increased life expectancy.

Description

Regeneration method of reduction electrode

The present invention relates to a method for regenerating a reduction electrode, and more particularly, to a method for regenerating a deteriorated reduction electrode for electrolysis.

Commercially pure hydrogen is produced by electrolysis of water or brine, where the negative electrode (reducing electrode) is usually a nickel electrode or a metal oxide (oxide of ruthenium, platinum, palladium, rhodium, etc.) on a nickel substrate. A coated electrode is used. The metal oxide coated on the nickel substrate deteriorates due to physical dropout, chemical elution, and adsorption of impurities (iron ions, etc.) as the electrolysis proceeds. It is known that the dissolution is accelerated due to a reverse current phenomenon.

The deteriorated cathode causes an additional voltage (overvoltage) to rise sharply beyond the voltage required for electrolysis, and the additional voltage increases the production cost, so it needs to be replaced immediately. However, the cathode contains expensive precious metals, and since the electrolysis operation must be stopped for the replacement of the electrode, it can cause enormous economic loss.

In order to compensate for this problem, a technique for inducing electrodeposition on the electrode surface by injecting a noble metal solution into the cathode (cathode) electrolyte during electrolysis and regenerating the deteriorated coating layer has been proposed. This technology is referred to as in-situ activation, and as the noble metal, a platinum-based compound that can minimize the effect on quality by showing an excellent performance in a hydrogen generation reaction and showing an effect with only a small amount of input This is mainly used.

For example, Patent Publication No. 2002-0018673 discloses a method of introducing a solution of a platinum-based compound for regeneration of the negative electrode in the brine electrolysis process, and according to the method, hexahydroxoplatinate (H ₂ Pt(OH) ₆ ) The overvoltage reduction effect of about 200 mV is shown by adding the solution.

However, the injection of the platinum-based compound shows a visible effect only in the case of an electrode with a very high negative overvoltage (eg, a nickel electrode), and the overvoltage improvement effect is not effective for an electrode containing a ruthenium oxide coating layer and a zero-gap electrolyzer. There is a problem that it is minor. This is because, compared to a nickel electrode, an electrode containing a ruthenium oxide coating layer has a very low negative overvoltage, so that even if platinum is electrodeposited, the overvoltage improvement effect is relatively low.

Therefore, in consideration of the economical cost of the platinum-based compound, development of a new technology capable of visually exhibiting an overvoltage improvement effect for an electrode including a ruthenium oxide coating layer is required.

KR 2002-0018673 A

An object to be solved by the present invention is to provide a method of regenerating the reduction electrode for improving the continuity of the overvoltage improvement effect during electrolysis by regenerating the reduction electrode for electrolysis to have an increased life expectancy in an economical way. .

In order to solve the above problems, the present invention

As a method of regenerating a reduction electrode applied to electrolysis,

First coating the reduction electrode by adding a platinum compound solution to the electrolyte solution for the reduction electrode; and

A ruthenium compound solution is added to the electrolyte solution for the reduction electrode to include a second coating of the first coated reduction electrode,

The electrolyte solution is water or brine, and provides a method of regenerating the reduction electrode.

The regeneration method of the reduction electrode for electrolysis of the present invention is an economical method, and it is possible to improve the continuity of the overvoltage improvement effect during electrolysis by regenerating the reduction electrode for electrolysis to have an increased life expectancy.

1 is a view showing the change in potential of the reduction electrode before and after the compound solution containing platinum, or the compound solution containing platinum and the compound solution containing ruthenium in Example 1 and Comparative Examples 1 and 2;
2 is a view showing the voltage change of the electrolytic cell before and after sequentially adding the compound solution containing platinum and the compound solution containing ruthenium in Example 2;
3 is a view showing the voltage change of the electrolytic cell before and after the input of the compound solution containing platinum in Comparative Example 3.

Hereinafter, the present invention will be described in more detail to help the understanding of the present invention.

The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. It should be interpreted as meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

The method for regenerating a reduction electrode of the present invention is a method for regenerating a reduction electrode applied to electrolysis, comprising the steps of: putting a platinum (Pt) compound solution into an electrolyte for a reduction electrode and first coating the reduction electrode; and adding a ruthenium compound solution to the electrolyte solution for the reduction electrode to secondary-coat the firstly coated reduction electrode.

The reduction electrode of the present invention may be a reduction electrode applied to electrolysis, that is, a hydrogen generating electrode. The electrolysis is a method of separating the oxidizing electrode (anode) and the reducing electrode (cathode) using a separator, and then applying direct current to it to decompose water or brine. For example, in the case of brine, the oxidizing electrode and the reducing electrode are The same reaction takes place.

Oxidation electrode: 2Cl ^- → Cl ₂ (g) + 2e ^-

Reduction electrode: 2H ₂ O + 2e ^- → 2OH ^- + H ₂ (g)

According to the electrolysis method, pure hydrogen can be obtained through the above reaction.

In general, the reduction electrode applied to the electrolysis is inactivated due to the deposition of impurities on the surface, physical exfoliation or chemical elution as it is used. In addition, in some cases, hydrogen is adsorbed on the electrode surface or the electrical conductivity and surface area are decreased due to changes in the surface composition and state of the materials coated on the electrode body, thereby inactivating it.

Therefore, in the method for regenerating the reduction electrode of the present invention, a step of first coating the reduction electrode by introducing a platinum compound solution into the electrolyte solution for the reduction electrode is performed for the regeneration of the reduction electrode.

The separation membrane used in the electrolysis may be a porous polymer membrane or an ion-exchange polymer membrane. The electrolyte may be water or brine, and the water may be pure water or an aqueous alkali solution such as an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution.

The reduction electrode may be a nickel electrode, an electrode in which a metal or a metal oxide is coated on a nickel base, and the metal or metal oxide is one selected from the group consisting of platinum group metals (Pt, Ru, Rh, Os, Ir, and Pd). above) or oxides thereof. Specifically, it may be an electrode in which ruthenium oxide is coated on a nickel substrate, an electrode in which platinum is coated on a nickel substrate, or an electrode in which ruthenium oxide and platinum are coated on a nickel substrate.

When a platinum compound solution is added to the electrolyte for the reduction electrode in the first coating step, platinum is electrodeposited on the surface of the reduction electrode to primarily form a platinum coating layer. The platinum is electrodeposited to form a platinum coating layer, whereby the reduction electrode is regenerated and, accordingly, an additional voltage (overvoltage) exceeding the voltage required for electrolysis is reduced. That is, as platinum is electrodeposited on the reduction electrode, the potential of the reduction electrode increases, and specifically, the potential of 20 to 30 mV may increase.

The platinum (Pt) compound is hexachloro platinum (IV) (H ₂ PtCl ₆ ㆍ6H ₂ O, hexachloroplatinate), potassium tetrachloroplatinate (II) (K ₂ PtCl ₄ , potassium tetrachloroplatinate), diaminodinitroplatinum (II)(Pt(NH ₃ ) ₂ (NO ₂ ) ₂ , diaminodinitro platinum), hexaaminoplatinum (IV) chloride (Pt(NH ₃ ) ₆ Cl ₄ , hexaaminoplatinum chloride), tetraamineplatinum (II) chloride (Pt) (NH ₃ ) ₄ Cl ₂ , tetraamine platinum chloride), hydrogenhexahydroxoplatinate (IV) (H ₂ Pt(OH) ₆ , hydrogen hexahydroxoplatinate) and sodium tetrachloro platinum (II) (Na ₂ PtCl ₄ ㆍ 6H ₂ O, sodium tetrachloroplatinate) may be at least one selected from the group consisting of.

The platinum compound may be added in an amount of 0.1 ppm to 100 ppm, specifically 0.5 ppm to 50 ppm, based on the weight of the electrolyte contained in the electrolyte for the reduction electrode.

When the platinum compound is injected in an amount of 0.1 ppm to 100 ppm compared to the electrolyte contained in the electrolyte for the reduction electrode, the platinum ions contained in the compound containing the injected platinum are appropriately electrodeposited on the surface of the reduction electrode. It is possible to secure economic feasibility by using the amount of the platinum compound in an appropriate amount.

Next, a step of secondary coating the first coated reduction electrode by adding a ruthenium compound solution to the electrolyte solution for the reduction electrode is made.

In the secondary coating step, when a ruthenium compound solution is added to the electrolyte for the reduction electrode, ruthenium is electrodeposited on the surface of the reduction electrode on which platinum is electrodeposited. As ruthenium is electrodeposited on the surface of the platinum coating layer formed on the surface of the reduction electrode to form a ruthenium coating layer, the absolute coating amount of the noble metal is increased, and further regeneration of the reduction electrode can be made.

Since the increase in the absolute coating amount of the noble metal increases the continuity of the improvement effect, the ruthenium coating layer additionally formed on the platinum coating layer can increase the lifespan of the reduction electrode, that is, the period showing the overvoltage improvement effect, and further reduction of the overvoltage can be made there is. That is, as ruthenium is electrodeposited on the reduction electrode, the potential of the reduction electrode may additionally increase, and specifically, the potential of 5 mV to 10 mV may increase.

The ruthenium compound may be at least one selected from the group consisting of ruthenium fluoride, ruthenium chloride, ruthenium bromide, ruthenium iodide, ruthenium oxide hydrate, ruthenium acetate, and sodium ruthenate.

The ruthenium compound may be injected in an amount of 0.1 ppm to 100 ppm, specifically 0.5 ppm to 50 ppm, based on the weight of the electrolyte contained in the electrolyte for the reduction electrode. At this time, the electrolyte derived from the compound containing platinum injected in the first step is excluded from the electrolyte contained in the electrolyte, which is the basis of the injection amount of the compound containing ruthenium.

When the compound containing the ruthenium is injected in an amount of 0.1 to 100 ppm compared to the electrolyte contained in the electrolyte, the ruthenium ions contained in the compound containing the injected ruthenium are on the surface of the platinum coating layer formed on the reduction electrode. It may be appropriately electrodeposited to form a ruthenium coating layer.

The second coating step may be made after the electrodeposition of platinum on the reduction electrode through the first coating step is finished to some extent, and specifically, the timing of the second coating step can be determined by observing the potential of the reduction electrode. In addition, the second coating step may be started at a time point after 10 minutes to 300 minutes immediately after the completion of the first coating, specifically, at a time point after 50 minutes to 200 minutes.

The molar ratio of the platinum compound and the ruthenium compound may be 1:0.1 to 1:10, specifically 1:1 to 1:5.

When the molar ratio of the platinum compound and the ruthenium compound satisfies the above range, it is possible to effectively form a platinum coating layer and a ruthenium coating layer on the surface of the reduction electrode.

In order to appropriately control the shape in which the platinum coating layer and the ruthenium coating layer are electrodeposited on the surface of the reduction electrode, the platinum compound and/or the ruthenium compound may be used in the form of a ligand compound. Therefore, in the method for regenerating the reduction electrode according to an example of the present invention, the platinum compound, the ruthenium compound, or the platinum compound and the ruthenium compound may be a ligand compound. In this case, the ligand may be at least one selected from the group consisting of Ammine, EDTA, Hydroxo, Chloro, and Ethylenediamine.

When the platinum compound and/or the ruthenium compound is used in the form of a ligand compound in which a ligand is coordinated to a metal, when platinum and ruthenium are coated on the reduction electrode, complex ions, not metal cations, are electrodeposited, and more uniformly reduced The surface of the electrode may be coated. Specifically, since the reduction potential of a metal cation such as platinum or ruthenium is high, it is easily electrodeposited on the electrode surface, and in this case, the electrodeposition reaction is very sensitive to the resistance of the surface. Since the surface of the reduction electrode is not completely flat, there is a difference in resistance for each region, and electrodeposition is more likely to occur where the resistance is low. However, when a ligand compound in which a ligand is coordinated to platinum or ruthenium is used, complex ions are electrodeposited rather than metal cations. It is possible to obtain a uniform surface coating on the surface by preventing

In the regeneration method of the reduction electrode according to an example of the present invention, the supply current density of the electrolysis may be 0.1 kA/m2 to 10 kA/m2, specifically 0.5 kA/m2 to 8 kA/m2.

According to an example of the present invention, after the first step process and the second step process, the electrolysis voltage of the electrolysis may drop 10 mV to 50 mV, specifically 10 mV to 40 mV may drop . The reduction width of the electrolysis voltage may vary depending on the initial state of the electrode.

The reduction electrode regeneration method of the present invention is divided into a first coating step and a secondary coating step, and by sequentially forming a platinum coating layer and a ruthenium coating layer on the surface of the reduction electrode, the reduction electrode can be reproduced more effectively and economically. That is, it is possible to effectively improve the overvoltage during electrolysis by regenerating the reduction electrode in an economical way compared to the case where the platinum coating layer is thickly formed using only the platinum compound, and an additional ruthenium coating layer is formed on the platinum coating layer to form an additional ruthenium coating layer. additional improvements can be obtained.

In addition, when a platinum compound and a ruthenium compound are added together, ruthenium forms a coating layer competitively with platinum, and a coating layer containing both platinum and ruthenium is formed. , When the platinum compound and the ruthenium compound are sequentially added through the first step process and the second step process as in the present invention, the platinum coating layer and the ruthenium coating layer are sequentially formed on the surface of the reduction electrode.

Example

Hereinafter, examples and experimental examples will be described in more detail to describe the present invention in detail, but the present invention is not limited by these examples and experimental examples. Embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art.

Example 1: Sequential introduction of a platinum compound and a ruthenium compound

The degenerated reduction electrode (hydrogen generating electrode, nickel-based electrode coated with ruthenium oxide) used for brine electrolysis for a certain period of time was placed in a 400 mL 33% sodium hydroxide half-cell device, and at -4.4 kA/m ² current density. Constant current electrolysis was performed. _{During the electrolysis, H 2} PtCl ₆ corresponding to 4 ppm of the electrolyte was dissolved in a small amount of distilled water and put into the half-cell device. It was observed that the overvoltage of the reduction electrode decreased as Pt was electrodeposited on the electrode surface with the passage of time after the input. After 200 minutes after the completion of the H ₂ PtCl _{6 addition, RuCl 3} corresponding to 10 ppm of the electrolyte was dissolved in a small amount of distilled water and put into the half-cell device. As Ru was electrodeposited on the electrode surface, an additional decrease in cathode overvoltage was observed. The results are shown in FIG. 1 .

Comparative Example 1: Single input of platinum compound

The degenerated reduction electrode (hydrogen generating electrode, nickel-based electrode coated with ruthenium oxide) used for brine electrolysis for a certain period of time was placed in a 400 mL 33% sodium hydroxide half-cell device, and at -4.4 kA/m ² current density. Constant current electrolysis was performed. _{During the electrolysis, H 2} PtCl ₆ corresponding to 4 ppm of the electrolyte was dissolved in a small amount of distilled water and put into the half-cell device. It was observed that the overvoltage of the reduction electrode decreased as Pt was electrodeposited on the electrode surface with the passage of time after the input. The results are shown together in FIG. 1 .

Referring to FIG. 1 , as Pt was electrodeposited on the electrode surface, the overvoltage of the reduction electrode decreased (the potential of the cathode was increased), but it was confirmed that the reduction width was smaller than in Example 1.

Comparative Example 2: Simultaneous input of a platinum compound and a ruthenium compound

The degenerated reduction electrode (hydrogen generating electrode, nickel-based electrode coated with ruthenium oxide) used for brine electrolysis for a certain period of time was placed in a 400 mL 33% sodium hydroxide half-cell device, and at -4.4 kA/m ² current density. Constant current electrolysis was performed. _{During the electrolysis, H 2} PtCl ₆ corresponding to 4 ppm of the _{electrolyte and RuCl 3} corresponding to 10 ppm of the electrolyte were dissolved in a small amount of distilled water and put into the half-cell device. It was observed that the overvoltage of the reduction electrode decreased as Pt and Ru were electrodeposited on the electrode surface as time passed after the input. The results are shown together in FIG. 1 . As Pt and Ru were electrodeposited on the electrode surface, the overvoltage of the reduction electrode decreased (the potential of the cathode was increased), but it was confirmed that the decrease was smaller than in Example 1 and Comparative Example 1.

Through the results of Example 1, during the electrolysis process of water or brine like the electrolysis method of the present invention, a first step process of injecting a solution of a compound containing platinum into the electrolyte solution, and ruthenium in the electrolyte solution When the second step process of sequentially injecting a solution of a compound containing On the other hand, if the results of Example 1 and Comparative Example 3 are compared, even if the reduction electrode is regenerated using the same amount of a solution of a compound containing platinum and a solution of a compound containing ruthenium, depending on the input method, the effect is higher. It was confirmed that there was a clear difference. In addition, comparing the results of Example 1 and Comparative Example 2, by using a solution of a compound containing ruthenium in addition to the solution of the compound containing platinum, it can be confirmed that an additional overvoltage reduction effect can be brought about by an increase in the amount of coating. There was, and according to Example 1, since the noble metal compound exceeding the amount corresponding to 4 ppm compared to the electrolyte is ruthenium, not platinum, it is confirmed that an additional coating amount can be secured in an economical way compared to the case of using additional platinum. could

Example 2: Sequential input of platinum compound and ruthenium compound (commercial electrolytic cell)

A commercial electrolyzer using a reducing electrode coated with ruthenium oxide on a nickel substrate was targeted, and the electrolytic cell was ^{operated at a current density of 4.4 kA/m 2} , and the average voltage of the cells was 2.97 V. H ₂ PtCl ₆ was dissolved in 33% sodium hydroxide aqueous solution to prepare a platinum compound solution, and RuCl ₃ was dissolved in distilled water to prepare a ruthenium compound solution. The prepared platinum compound solution was injected using a pump so that it became 4 ppm compared to the electrolyte contained in the electrolyte solution (33% sodium hydroxide aqueous solution) of the cathode. While the platinum compound solution was added, the voltage of the electrolyzer decreased linearly. When the addition of the platinum compound solution was stopped, the electrolyzer voltage did not decrease any more. After 30 minutes, the ruthenium compound solution was injected using a pump so as to be 4 ppm compared to the electrolyte of the cathode. No additional electrolytic cell voltage improvement effect was observed. When the electrolyzer voltage returned to the initial voltage for more than one day, the time point was determined as the end point of the overvoltage improvement effect. The results are shown in FIG. 2, and the overvoltage improvement effect lasted for 6 weeks.

Comparative Example 3: Single input of platinum compound (commercial electrolytic cell)

A commercial electrolyzer using a reducing electrode coated with ruthenium oxide on a nickel substrate was targeted, and the electrolytic cell was ^{operated at a current density of 4.4 kA/m 2} , and the average voltage of the cells was 3.07 V. H ₂ PtCl ₆ was dissolved in 33% aqueous sodium hydroxide solution to prepare a platinum compound solution. The prepared platinum compound solution was injected using a pump so that it became 4 ppm compared to the electrolyte contained in the electrolyte solution (33% sodium hydroxide aqueous solution) of the cathode. While the platinum compound solution was added, the voltage of the electrolyzer decreased linearly. When the addition of the platinum compound solution was stopped, the electrolyzer voltage did not decrease any more. When the electrolyzer voltage returned to the initial voltage for more than one day, the time point was determined as the end point of the overvoltage improvement effect. The results are shown in FIG. 3, and the overvoltage improvement effect lasted for 3 days.

Through the results of Example 2 and Comparative Example 3, in the case of Example 2, in which a ruthenium coating layer was additionally formed using a ruthenium compound solution, the continuity of the overvoltage improvement effect can be increased by increasing the coating amount on the surface of the reduction electrode. was able to confirm

Claims (12)

As a method of regenerating a reduction electrode applied to electrolysis,
First coating the reduction electrode by adding a platinum compound solution to the electrolyte solution for the reduction electrode to electrodeposit platinum on the surface of the reduction electrode; and
By injecting a ruthenium compound solution into the electrolyte solution for the reduction electrode, and electrodepositing ruthenium on the surface of the first coated reduction electrode, comprising the step of second coating the reduction electrode,
The electrolytic solution is water or brine, the regeneration method of the reduction electrode.
The method of claim 1,
The platinum compound is hydrogen hexachloro platinum (IV) hexahydrate (H ₂ PtCl ₆ .6H ₂ O, hydrogen hexachloroplatinate (IV) hexahydrate), potassium tetrachloroplatinate (II) (K ₂ PtCl ₄ , potassium tetrachloroplatinate ( II)), diaminedinitroplatinum(II)(Pt(NH ₃ ) ₂ (NO ₂ ) ₂ , diamminedinitro platinum(II)), hexaamineplatinum(IV) chloride (Pt(NH ₃ ) ₆ Cl ₄ , hexaammineplatinum( IV) chloride), tetraamine platinum(II) chloride (Pt(NH ₃ ) ₄ Cl ₂ , tetraammine platinum(II) chloride), hydrogenhexahydroxyplatinate (IV)(H ₂ Pt(OH) ₆ , hydrogen At least one selected from the group consisting of hexahydroxyplatinate (IV)) and sodium tetrachloroplatinate (II) hexahydrate (Na ₂ PtCl ₄ .6H ₂ O, sodium tetrachloroplatinate (II) hexahydrate), a method for regenerating a reducing electrode.
The method of claim 1,
The platinum compound is input in an amount of 0.1 ppm to 100 ppm based on the weight of the electrolyte contained in the electrolyte for the reduction electrode, the regeneration method of the reduction electrode.
The method of claim 1,
The ruthenium compound is at least one selected from the group consisting of ruthenium fluoride, ruthenium chloride, ruthenium bromide, ruthenium iodide, ruthenium oxide hydrate, ruthenium acetate, and sodium ruthenate, a method for regenerating a reducing electrode.
The method of claim 1,
The ruthenium compound is input in an amount of 0.1 ppm to 100 ppm based on the weight of the electrolyte contained in the electrolyte for the reduction electrode, the regeneration method of the reduction electrode.
delete The method of claim 1,
The second coating step is started at a time point after 10 minutes to 300 minutes immediately after the completion of the first coating, the regeneration method of the reduction electrode.
The method of claim 1,
The molar ratio of the platinum compound and the ruthenium compound is 1:0.1 to 1:10, the regeneration method of the reduction electrode.
The method of claim 1,
The platinum compound, the ruthenium compound, or the platinum compound and the ruthenium compound may be a ligand compound,
The ligand is at least one selected from the group consisting of Ammine, EDTA, Hydroxo, Chloro and Ethylenediamine, a method for regenerating a reduction electrode.
The method of claim 1,
The supply current density of the electrolysis is 0.1 kA / m 2 to 10 kA / m 2, the reduction electrode regeneration method.
The method of claim 1,
The reduction electrode is a hydrogen generating electrode, the regeneration method of the reduction electrode.
The method of claim 1,
The reduction electrode is a nickel electrode or an electrode coated with a metal or metal oxide on a nickel substrate,
The metal or metal oxide is one or more metals or oxides thereof selected from the group consisting of Pt, Ru, Rh, Os, Ir and Pd, the reduction electrode regeneration method.

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