JP7356704B2 - Electrochemical measuring device - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act (1) Publication Department of Applied Molecular Chemistry, College of Industrial Science, Nihon University 2018 Graduation Thesis Presentation Lecture Preliminary Research Abstract ``Potential application method aimed at improving the precision of electrochemical chromatography'' Nakagama, Saito, and Yamane Laboratory Publication date: February 4, 2019 (2) Meeting name: Department of Applied Molecular Chemistry, College of Industrial Engineering, Nihon University 2018 Graduation Thesis Presentation Time Zone P2 Presentation Number 20 Date Heisei February 5, 2019 (3) Publication Nihon University College of Industrial Science and Technology Department of Applied Molecular Chemistry 2018 Graduation Thesis Presentation Lecture Preliminary Research Abstract “Construction of High-Precision Electrochemical Chromatography Column” Nakagama-Saito-Yamane Laboratory Publication date: February 4, 2019 (4) Meeting name: Department of Applied Molecular Chemistry, College of Industrial Science, Nihon University 2018 Graduation Thesis Presentation Time slot: P3 Presentation number: 18 Date: February 5, 2019

The present invention relates to an electrochemical measuring device.

Research on electrochemical measurements is not only important for the development of electrochemistry as a basic science, but is also considered extremely important because it can be applied to industrial fields such as batteries, displays, and sensors. .

An example of a technique related to electrochemical measurement is the electrochemical measurement section related to Patent Document 1, for example. This electrochemical measurement section is for flow measurement, and is an electrochemical measurement section for flow measurement in which a cell having a pair of reference electrode and a working electrode is connected to one or more cells having another working electrode. A pair of electrodes made of a conductive material are provided on the upstream and downstream sides of the electrochemical measuring section, and the pair of electrodes made of the conductive material are kept at the same potential and used as counter electrodes.

Japanese Patent Application Publication No. 07-103936

However, since this electrochemical measurement section requires the reference electrode to be immersed in the sample, it can only be used under measurement conditions that allow the use of a special reference electrode or under measurement conditions that allow the reference electrode to be used normally. Unable to perform electrochemical measurements. In addition, if a reference electrode is inserted into a tank, etc. other than the connected cells, and the cell and the tank, etc. are connected with a salt bridge, liquid junction, etc., these salt bridges, liquid junctions, etc. should be used normally. Electrochemical measurements can only be carried out under measurement conditions that allow

Therefore, an object of the present invention is to provide an electrochemical measurement device that can perform electrochemical measurements under more diverse measurement conditions.

One aspect of the present invention includes: a first holding part holding a first solution in which the concentration of the substance to be measured is equal to or higher than a first threshold; a first working electrode immersed in the first solution; a first counter electrode immersed in a solution; and a second holding section different from the first holding section, holding a second solution in which the concentration of the substance to be measured is less than or equal to a second threshold value, which is smaller than the first threshold value; a second working electrode electrically connected to the first working electrode and immersed in the second solution; and a second working electrode electrically connected to the first counter electrode and immersed in the second solution. two counter electrodes, a reference electrode immersed in the second solution, electrically connected to the first working electrode, the first counter electrode, the second working electrode, the second counter electrode and the reference electrode; a potential control unit that sweeps the potential of the first working electrode by sweeping the potential difference between the second working electrode and the reference electrode , the first working electrode passing the first solution through the first working electrode; The present invention is an electrochemical measurement device that measures the total current of a first current flowing through one counter electrode and a second current flowing from the second working electrode through the second solution to the second counter electrode.

According to the present invention, electrochemical measurements can be performed under more diverse measurement conditions.

1 is a diagram showing an example of the configuration of an electrochemical measuring device according to an embodiment of the present invention. FIG. 3 is a diagram showing an example of the results of cyclic voltammetry performed by the electrochemical measuring device according to the embodiment of the present invention. FIG. 2 is a diagram showing an example of the results of cyclic voltammetry performed by an electrochemical measuring device that employs a general three-electrode method.

An electrochemical measuring device according to an embodiment will be described with reference to FIG. FIG. 1 is a diagram showing an example of the configuration of an electrochemical measuring device according to an embodiment of the present invention. As shown in FIG. 1, the electrochemical measuring device 1 includes a first holding part 11, a first working electrode 12, a first counter electrode 13, a second holding part 21, a second working electrode 22, and a second holding part 11, a first working electrode 12, a first counter electrode 13, a second holding part 21, a second working electrode It includes a counter electrode 23, a reference electrode 30, and a potential control section 40.

The first holding unit 11 is an electrolytic cell that holds a first solution L1 in which the concentration of the substance to be measured is equal to or higher than a first threshold value. The first solution L1 is an aqueous sodium sulfate solution with a concentration of 0.1 M (molar), in which potassium ferrocyanide (K ₄ [Fe(CN) ₆ ]) of 12.5 mM (molar) is dissolved as an example of the measurement substance. It is an electrolyte solution. Further, the first threshold referred to herein is, for example, from 2.5 mM to 1.25 mM, and is preferably a threshold that is larger than a second threshold, which will be described later, and is sufficiently larger than the second threshold. Furthermore, since the reference electrode 30 is not present in the first holding part 11, the first solution L1 may be under conditions such as high temperature and high pressure, and even if the first holding part 11 is a minute electrolytic bath. good.

The first working electrode 12 is an electrode immersed in the first solution L1. For example, the first working electrode 12 is a cylindrical platinum electrode, and the side surface is covered with a cylindrical coating 12C. The coating 12C is made of, for example, polyether ether ketone (PEEK), and is designed to prevent the first solution L1 from penetrating between the side surface of the first working electrode 12 and the coating 12C. It is in close contact with the side surface of the electrode 12. Moreover, the end surface of the first working electrode 12 is polished before electrochemical measurement using the electrochemical measuring device 1 is performed, and is in contact with the first solution L1.

The first counter electrode 13 is an electrode immersed in the first solution L1. For example, the first counter electrode 13 is a cylindrical platinum electrode.

The second holding unit 21 is an electrolytic cell that holds a second solution L2 in which the concentration of the substance to be measured is equal to or lower than a second threshold value. The second solution L2 is an aqueous sodium sulfate solution with a concentration of 0.1 M (Molar), and potassium ferrocyanide, which is an example of the substance to be measured, is not dissolved therein. That is, the second solution L2 is an electrolyte solution containing sodium sulfate as an electrolyte. Further, the second threshold referred to here is a threshold smaller than the first threshold described above, preferably a threshold sufficiently smaller than the first threshold, and may be zero.

The second working electrode 22 is an electrode immersed in the second solution L2. For example, the second working electrode 22 is a cylindrical platinum electrode, and the side surface is covered with a cylindrical coating 22C. The coating 22C is made of polyetheretherketone, for example, and is tightly attached to the side surface of the second working electrode 22 to prevent the second solution L2 from penetrating between the side surface of the second working electrode 22 and the coating 22C. There is. Moreover, the end surface of the second working electrode 22 is polished before electrochemical measurement using the electrochemical measuring device 1 is performed, and is in contact with the second solution L2. Further, the second working electrode 22 is electrically connected to the first working electrode 12. For example, as shown in FIG. 1, the second working electrode 22 is electrically connected to the first working electrode 12 by a conducting wire 50. Further, the shape, material, arrangement, etc. of the conducting wire 50 are arbitrary and may be freely designed.

The second counter electrode 23 is an electrode immersed in the second solution L2. For example, the second counter electrode 23 is a cylindrical platinum electrode. Further, the second counter electrode 23 is electrically connected to the first counter electrode 13. For example, the second counter electrode 23 is electrically connected to the first counter electrode 13 by a conductive wire 60. Further, the shape, material, arrangement, etc. of the conducting wire 60 are arbitrary and may be freely designed.

Reference electrode 30 is a reference electrode immersed in the second solution. For example, the reference electrode 30 is a silver-silver chloride electrode, and has a structure in which a member whose surface is coated with silver chloride is immersed in an aqueous chloride solution held in a glass tube.

The potential control unit 40 is, for example, a potentiostat, and is electrically connected to the first working electrode 12 , the first counter electrode 13 , the second working electrode 22 , the second counter electrode 23 and the reference electrode 30 , and is electrically connected to the second working electrode 22 . The potential difference between the reference electrode 30 and the reference electrode 30 is swept. As a result, the first working electrode 12 is electrically connected to the second working electrode 22 by the conducting wire 50, so the potential control section 40 can sweep the potential of the first working electrode 12. Thereby, the potential control unit 40 performs electrochemical measurement using the electrochemical measuring device 1, for example, cyclic voltammetry (CV).

FIG. 2 is a diagram showing an example of the results of cyclic voltammetry performed by the electrochemical measuring device according to the embodiment of the present invention. The horizontal axis in FIG. 2 indicates the potential of the first working electrode 12. In FIG. 2, the vertical axis indicates the current flowing through the first working electrode. That is, FIG. 2 shows a cyclic voltammogram obtained by the electrochemical measuring device 1.

In the experimental example shown in FIG. 2, the potential control unit 40 increases the potential of the first working electrode 12 from the starting potential of -0.2V to the maximum potential of +0.4V, and then increases the potential of the first working electrode 12 from the maximum potential of +0.4V to the minimum potential of -0.4V. The process of decreasing the potential of the first working electrode 12 to 0.4V and increasing the potential of the first working electrode 12 from a minimum potential of -0.4V to a starting potential of -0.2V is repeated three times. Further, in this case, the potential control unit 40 always sweeps the potential of the first working electrode 12 at a constant sweep rate of 20 mV/s. Note that the starting potential is a potential at which no electrode reaction occurs.

In FIG. 2, when the potential of the first working electrode 12 is increasing, an oxidation reaction of divalent iron ions (Fe ²⁺ ) occurs at the end face of the first working electrode 12, and trivalent iron ions (Fe ³⁺ ) and electrons (e ⁻ ) are generated.

Electrons (e ⁻ ) generated by this oxidation reaction flow into the first working electrode 12 . Then, when the potential of the first working electrode 12 is reaching +0.12V, the reaction rate of the oxidation reaction increases rapidly, and the electrons (e ^- ) flowing into the end face of the first working electrode 12 rapidly increase. As a result, the positive current increases rapidly.

Trivalent iron ions (Fe ³⁺ ) generated by this oxidation reaction remain near the end surface of the first working electrode 12 . When the potential of the first working electrode 12 exceeds +0.12V and begins to deviate from +0.12V, most of the chemical species present near the end surface of the first working electrode 12 become trivalent iron ions (Fe ³⁺ ). As a result, the number of electrons (e ⁻ ) flowing into the first working electrode 12 decreases rapidly, and the current in the positive direction decreases rapidly.

Therefore, it is considered that an upward peak appears near +0.12V in the cyclic voltammogram shown in FIG. Note that when the potential of the first working electrode 12 is increasing in FIG. 2, some kind of reduction reaction occurs on the surface of the first counter electrode 13 due to the electrons (e ⁻ ) flowing into the first working electrode 12. For example, a reduction reaction of water (H ₂ O) occurs to generate hydrogen (H ₂ ) and hydroxide ions (OH ⁻ ).

In FIG. 2, when the potential of the first working electrode 12 is decreasing, a reduction reaction of trivalent iron ions (Fe ³⁺ ) occurs at the end face of the first working electrode 12, and divalent iron ions (Fe ²⁺ ) is occurring.

Electrons (e ⁻ ) acquired by trivalent iron ions (Fe ³⁺ ) in this reduction reaction are supplied from the end surface of the first working electrode 12 . When the potential of the first working electrode 12 is reaching +0.05V, the reaction rate of the reduction reaction increases rapidly, and the electrons (e ^- ) supplied from the end face of the first working electrode 12 are Since the current increases rapidly, the current in the negative direction increases rapidly.

Divalent iron ions (Fe ²⁺ ) generated by this reduction reaction remain near the end surface of the first working electrode 12 . When the potential of the first working electrode 12 falls below +0.05V and begins to deviate from +0.05V, most of the chemical species present near the end surface of the first working electrode 12 become divalent iron ions (Fe ²⁺ ). As a result, the number of trivalent iron ions (Fe ³⁺ ) that acquire electrons (e ⁻ ) from the end face of the first working electrode 12 is reduced, so that the current in the negative direction rapidly decreases.

Therefore, it is considered that a downward peak appears near +0.05V in the cyclic voltammogram shown in FIG. Note that when ^the potential of the first working electrode 12 is decreasing in FIG. The reversible reaction of water electrolysis progresses in the direction of

Furthermore, the intermediate potential between the upward peak near +0.12V and the downward peak near + ^0.05V in the cyclic voltammogram shown in FIG. It can be approximated to the reversible half-wave potential of Fe ³⁺ ). Furthermore, this potential can be approximated to a standard redox potential.

FIG. 3 is a diagram showing an example of the results of cyclic voltammetry performed by an electrochemical measuring device employing a general three-electrode method. When the cyclic voltammogram shown in FIG. 3 is obtained, the solution held in the electrolytic cell is a sodium sulfate aqueous solution with a concentration of 0.1M (molar), and an example of the measurement substance is 2.5mM (molar). This is an electrolyte solution in which potassium ferrocyanide (K ₄ [Fe(CN) ₆ ]) is dissolved. Further, when the cyclic voltammogram shown in FIG. 3 is obtained, the starting potential, maximum potential, minimum potential, and sweep speed are −0.1 V, +0.8 V, −0.4 V, and 20 mV/s, respectively. The cyclic voltammogram shown in FIG. 3 has an upward peak near +0.12V and a downward peak near +0.08V.

The cyclic voltammogram shown in FIG. 2 is similar to the cyclic voltammogram shown in FIG. Therefore, it is considered that the electrochemical measurement device 1 performs cyclic voltammetry that is relatively similar to the cyclic voltammetry performed by an electrochemical measurement device that employs a general three-electrode method.

In addition, in FIG. 2, when the surface charge of the first working electrode 12 is a positive potential, that is, when the surface charge of the second working electrode 22 is a positive potential, a negative charge is generated near the end surface of the second working electrode 22. Sulfate ions (SO ₄ ²⁻ ), hydroxide ions (OH ⁻ ), etc. with a positive charge gather near the surface of the second counter electrode 23, and sodium ions (Na ⁺ ) and oxium ions (H ₃ O ^＋ ) etc. are collected. On the other hand, in FIG. 2, when the surface charge of the first working electrode 12 is a negative potential, that is, when the surface charge of the second working electrode 22 is a negative potential, sodium ions ( Na ⁺ ), oxoium ions (H ₃ O ⁺ ), and the like gather, and hydroxide ions (OH ⁻ ) and the like gather near the surface of the second counter electrode 23 . Note that these two types of states of the second solution L2 are called an electric double layer.

The electrochemical measuring device 1 according to the embodiment has been described above. The electrochemical measuring device 1 sweeps the potential difference between the second working electrode 22 and the reference electrode 30, and sweeps the potential of the first working electrode 12, which is electrically connected to the second working electrode 22 through the conductor 50. do. Further, in the electrochemical measuring device 1, there is no need to immerse the reference electrode 30 in the first holding part 11 holding the first solution L1 in which the first working electrode 12 is immersed.

Therefore, the electrochemical measurement device 1 can perform electrochemical measurement of the substance to be measured even under conditions where the reference electrode 30 cannot be used normally. The conditions under which the reference electrode 30 cannot be used normally include, for example, conditions where the concentration of the substance to be measured is higher than the first threshold value and the first solution L1 is at high temperature or pressure; The condition is that the holding portion 11 is minute. Furthermore, because the electrochemical measuring device 1 has such effects, it is useful for research on the mechanism of chemical reactions that occur in solutions under ultra-high pressure, and for research on the behavior of batteries installed in robots used at ultra-high temperatures. It can be said that it is useful in various research fields and industrial fields.

In addition, in the embodiment described above, the case where the electrochemical measurement device 1 performs electrochemical measurement when the first solution L1 and the second solution L2 are not stirred has been described as an example, but the present invention is not limited to this. . For example, the electrochemical measurement device 1 may perform electrochemical measurement when at least one of the first solution L1 and the second solution L2 is stirred.

Further, in the above-described embodiment, the case where the first holding part 11 and the second holding part 21 are tanks has been described as an example, but the present invention is not limited to this. For example, the first holding part 11 may be a tubular member through which the first solution L1 flows. Similarly, the second holding part 21 may be a tubular member through which the second solution L2 flows. Furthermore, in these cases, it may be necessary to pressurize the first solution L1 to flow into the tube, so it is assumed that electrochemical measurement using the same principle as electrochemical measurement device 1 will be effective. be done.

Further, in the above-described embodiment, the first solution L1 and the second solution L2 are electrolyte solutions, but the present invention is not limited thereto. For example, at least one of the first solution L1 and the second solution L2 may be an ionic liquid.

Further, in the above-described embodiment, the case where the measurement substance is not dissolved in the second solution L2 has been described as an example, but the present invention is not limited to this. For example, the substance to be measured may be dissolved in the second solution L2.

The embodiments of the present invention have been described above in detail with reference to the drawings, but the specific configuration is not limited to these embodiments, and various modifications, substitutions, and designs can be made without departing from the gist of the present invention. At least one of the changes can be made. The configurations described in each of the embodiments described above may be combined.

DESCRIPTION OF SYMBOLS 1... Electrochemical measuring device, 11... First holding part, L1... First solution, 12... First working electrode, 13... First counter electrode, 21... Second holding part, L2... Second solution, 22... Second Working electrode, 23... Second counter electrode, 30... Reference electrode, 40... Potential control unit, 50, 60... Leading wire

Claims (1)

a first holding part holding a first solution in which the concentration of the substance to be measured is equal to or higher than a first threshold;
a first working electrode immersed in the first solution;
a first counter electrode immersed in the first solution;
a second holding section different from the first holding section, holding a second solution in which the concentration of the measurement substance is equal to or less than a second threshold smaller than the first threshold;
a second working electrode electrically connected to the first working electrode and immersed in the second solution;
a second counter electrode electrically connected to the first counter electrode and immersed in the second solution;
a reference electrode immersed in the second solution;
electrically connected to the first working electrode, the first counter electrode, the second working electrode, the second counter electrode, and the reference electrode, and sweeping a potential difference between the second working electrode and the reference electrode; a potential control unit that sweeps the potential of the first working electrode;
Equipped with
The sum of a first current flowing from the first working electrode through the first solution to the first counter electrode and a second current flowing from the second working electrode through the second solution to the second counter electrode. An electrochemical measurement device that measures the current of .

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