JP2023073500A - Electrochemical measurement device and electrochemical measurement method for metal material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrochemical measurement device that is used for evaluating the corrosion resistance (corrosion characteristic) of metal material in a solution including fluoride ions (F^-), the electrochemical measurement device capable of appropriately reducing the occurrence of contamination in the solution.

SOLUTION: An electrochemical measurement device performs electrochemical measurement of metal material in a solution including fluoride ions (F^-), and comprises: a cell 1 that stores the solution; and a reference electrode 2 and a counter electrode 3 that are immersed in the solution in the cell 1, and in the device, the cell 1 is formed of fluorine resin. Preferably, the reference electrode 2 is formed of a double junction type reference electrode, and its external cylinder has a configuration in which the outside of a glass cylinder being a base material is covered with fluorine resin. In the electrochemical measurement of the metal material in the solution including fluoride ions (F^-), contamination derived from glass (for example, boron (B), aluminum (Al), and silicon (Si)) in the solution can be reduced.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2023,JPO&INPIT

Description

The present invention is an electrochemical measurement device used to evaluate the corrosion resistance (corrosion characteristics) of a metal material in a solution containing fluoride ions (F ⁻ ), and in particular, the metal used in polymer electrolyte fuel cells The present invention relates to an electrochemical measurement apparatus suitable for evaluating corrosion resistance of separator materials.

In recent years, a polymer electrolyte fuel cell (PEFC) has attracted attention as a clean next-generation power source for automobiles and the like. The PEFC operates at a lower temperature than other fuel cells (for example, a phosphoric acid fuel cell and a solid oxide fuel cell) and exhibits high power generation efficiency, and is therefore becoming more and more popular.
The PEFC constitutes a single cell by sandwiching one membrane electrode assembly (MEA) between two separators. Since the voltage output from a single cell is about 0.7 V, a stack of stacked single cells is actually used. Since the separator occupies a large proportion of the total weight and volume of the stack, from the standpoint of thinning the separator and reducing the cost, the separator should be made of press-workable and inexpensive stainless steel (SUS304, SUS316L, etc.). A metal material that has been subjected to surface treatment with excellent electrical conductivity is adopted.

In a PEFC power generation environment, sulfate ions (SO ₄ ²⁻ ) and fluoride ions (F ⁻ ) liberated due to the deterioration of the perfluorosulfonic acid polymer membrane used as the proton-conducting membrane of the MEA are released into the separator/gas. Since it is concentrated in the diffusion layer and becomes an acidic environment containing fluoride ions (F ⁻ ), the metal material for the separator is required to have corrosion resistance under such an environment. For this reason, electrochemical measurements are performed to evaluate the corrosion resistance (corrosion characteristics) of metal materials for separators in a simulated PEFC environment, that is, in an acidic aqueous solution containing fluoride ions (F ⁻ ).
In general, electrochemical measurements of metallic materials are performed with a device in which three electrodes consisting of a working electrode of a sample to be tested, a counter electrode for passing current, and a reference electrode are immersed in a test solution placed in a cell ( For example, in Patent Document 1), in the electrochemical measurement of the metal material for the separator described above, an acidic aqueous solution containing a predetermined concentration of fluoride ions (F ⁻ ), which simulates a PEFC environment, is used as a test liquid.

JP 2011-196737 A

However, as a result of repeated tests and studies by the present inventors, contamination occurred in the test solution (acidic aqueous solution containing fluoride ions (F ⁻ )) in the electrochemical measurement of the metal material for the separator described above, and this caused contamination. It was found that this affects the accuracy of corrosion resistance evaluation. Specifically, (i) for the test liquid subjected to electrochemical measurement, from the sample (metal material for separator) by inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma atomic emission spectrometry (ICP-AES) Quantitative analysis of eluted metals is performed, but contamination has an adverse effect on the analysis results. (iii) some of the contaminants accelerate the corrosion of the sample (working electrode) during electrochemical measurements, lowering the measurement accuracy of the corrosion current. bottom.

Therefore, an object of the present invention is to provide an electrochemical measurement ^apparatus used for evaluating the corrosion resistance (corrosion characteristics) of a metal material in a solution containing fluoride ions (F ⁻ ). It is an object of the present invention to provide an electrochemical measuring apparatus which is suitable for evaluating the corrosion resistance of metal separator materials used in polymer electrolyte fuel cells because the generation of contamination inside is appropriately suppressed.

In order to solve the above-described problems, the inventors of the present invention have obtained the following findings as a result of examining sources of contamination and countermeasures against them.
In the electrochemical measurement of the metal separator material described above, when the components of contamination generated in the test solution (solution containing fluoride ions (F ⁻ )) were examined, the main component was a part of the glass component (boron (B), aluminum (Al), silicon (Si), etc.), and was found to be a component derived from the glass constituting the cell and reference electrode of the electrochemical measurement device. That is, a glass cell is used in a conventional electrochemical measurement device, but in the electrochemical measurement of a metal separator material, the temperature of the test solution is relatively high, about 80°C. It was found that the glass was contaminated with fluoride ions (F ⁻ ) inside, and part of the glass component was eluted into the test liquid as contamination. In addition, glass was also used for the outer cylinder of the double-junction reference electrode used as the reference electrode, and it was found that part of the glass component was eluted as contaminants from this outer cylinder into the test solution.

Contaminants in the test solution also contained chloride ions ( ^Cl.sup.- ), which accelerated the corrosion of the test sample (working electrode). As described above, in the electrochemical measurement of the metal separator material, the temperature of the test solution is relatively high at about 80°C, so the chloride ions (Cl ⁻ ) in the internal solution of the double-junction reference electrode (outer cylinder) are Excessive exudation from the liquid junction was found to mix into the test liquid and cause contamination.

Therefore, as a result of examining the above contamination countermeasures, it was found that by configuring the cell with fluororesin, more preferably by coating the outer cylinder of the double-junction reference electrode with fluororesin, it is contained in the test solution It was found that glass-derived contamination (boron (B), aluminum (Al), silicon (Si), etc.) can be effectively reduced.
Furthermore, by configuring the liquid junction of the outer cylinder of the double-junction reference electrode with a ceramic porous material having a predetermined wire diameter or less, excessive exudation of chloride ions (Cl ⁻ ) from the internal liquid into the test liquid・It was found that contamination can be properly prevented and the chloride ion (Cl ⁻ ) concentration in the test solution can be reduced.

The present invention was made based on such findings, and has the following gist.
[1] A device for electrochemical measurement of a metal material in a solution containing fluoride ions (F ⁻ ),
It comprises a cell (1) containing a solution, a reference electrode (2) and a counter electrode (3) immersed in the solution in the cell (1), and the cell (1) is made of fluororesin. electrochemical measurement device.
[2] In the electrochemical measurement device of [1] above, the reference electrode (2) consists of a double-junction reference electrode, and the outer cylinder of the outer cylinder is coated with a fluororesin on the outside of the glass cylinder that is the base material. An electrochemical measurement device characterized by comprising:

[3] In the electrochemical measurement device of [1] or [2] above, the reference electrode (2) is a double-junction reference electrode, and the liquid junction at the tip of the outer cylinder is made of a ceramic porous body. . An electrochemical measurement device, wherein the wire diameter of the ceramic porous body is 0.7 mm or less.
[4] In the electrochemical measurement device according to any one of [1] to [3] above, the lid (4) and connector (5) attached to the cell (1) are made of fluororesin. Electrochemical measurement device.
[5] Electrochemical measurement of a metal material, characterized in that electrochemical measurement of a metal separator material used in a polymer electrolyte fuel cell is performed using the electrochemical measurement device according to any one of [1] to [4] above. Method.

The electrochemical measurement device of the present invention contains fluoride ions (F ⁻ ) by configuring the cell with a fluororesin, preferably by coating the outer cylinder of the double-junction reference electrode with a fluororesin. In electrochemical measurements performed to evaluate the corrosion resistance (corrosion properties) of metal materials in solution, glass-derived contaminants (boron (B), aluminum (Al), silicon (Si), etc.) in the solution should be kept low. can be done. In addition to this, by forming the liquid junction of the outer cylinder of the double-junction reference electrode with a ceramic porous material having a predetermined wire diameter or less, chloride ions (Cl ⁻ ) of the internal liquid are released into the solution. It is possible to prevent excessive exudation and contamination, and to suppress contamination (chloride ions (Cl ⁻ )) derived from the reference electrode internal liquid in the solution. As a result, the analysis accuracy of eluted metals in solution, the measurement accuracy of sample contact resistance, the measurement accuracy of corrosion current, etc. are improved, and the corrosion resistance (corrosion characteristics) of metal materials can be accurately evaluated. Therefore, the electrochemical measurement apparatus of the present invention is particularly suitable as an electrochemical measurement apparatus for evaluating the corrosion resistance of metal separator materials used in polymer electrolyte fuel cells.

BRIEF DESCRIPTION OF THE DRAWINGS An explanatory diagram schematically showing one embodiment of the electrochemical measurement device of the present invention. Drawing showing an embodiment of a double-junction reference electrode provided in the electrochemical measurement device of the present invention in a state in which the outer cylinder is longitudinally sectioned. Partially enlarged view of part A in FIG. Partially enlarged view of B part in FIG. FIG. 2 shows another embodiment of the double-junction reference electrode provided in the electrochemical measurement apparatus of the present invention, and is a partially enlarged vertical cross-sectional view of the tip of the outer cylinder. Drawing showing another embodiment of the double-junction reference electrode provided in the electrochemical measurement apparatus of the present invention in a state in which the outer cylinder and the cooling cylinder are longitudinally sectioned. Sectional view along line VII-VII in Fig. 6 Explanatory diagram showing how the reference electrodes shown in FIGS. 6 and 7 are used

The electrochemical measuring device of the present invention is a device used to evaluate the corrosion resistance (corrosion characteristics) of a metal material in a solution containing fluoride ions (F ⁻ ), and this electrochemical measuring device is basically is used to apply a potential to a sample under test in solution in a cell and measure its electrical response (corrosion current, etc.). etc., and the corrosion resistance (corrosion characteristics) of metal materials can be evaluated based on the results of these measurements and analyses.

FIG. 1 schematically shows one embodiment of the electrochemical measurement device of the present invention, and is an explanatory view (explanatory view of a state in which the cell is longitudinally sectioned) showing how the device is used.
This electrochemical measurement apparatus includes a cell 1 (test tank) containing a solution y (acidic aqueous solution) containing fluoride ions (F ⁻ ), a reference electrode 2 and a counter electrode 3 which are immersed in the solution y in the cell 1. When using the apparatus, a sample x (working electrode), which is a metal material to be tested, is also immersed in the solution y as shown. These configurations are similar to those of conventionally used known measuring devices.

The cell 1 is a beaker-like container with an open top, and a lid 4 is attached to the top opening. A plurality of mounting holes 40 for mounting the reference electrode 2 and the counter electrode 3 are formed through the cover 4 . The reference electrode 2 , the counter electrode 3 and the sample x are each inserted into the cell 1 through the mounting holes 40 and supported by the lid 4 via the connector 5 . That is, the connector 5 serves to support the reference electrode 2 , the counter electrode 3 and the sample x on the lid 4 . The connector 5 also serves to block the upper end of the mounting hole 40 in order to prevent evaporation of the solution y.
Further, the cover 4 may be provided with a mounting hole (not shown) for mounting a thermometer. A thermometer is inserted into the cell 1 through its mounting hole. By inserting a thermometer, the liquid temperature can be accurately assessed, for example, when trying to control the liquid temperature.

In the device of the present invention, the cell 1 is made of fluororesin. The cell of the conventional device is made of glass. As mentioned earlier, when a solution containing fluoride ions (F ⁻ ) is put into the cell made of glass, the glass components (boron (B), aluminum (Al), silicon ( Si), etc.) was found to be eluted and become contaminants. On the other hand, the fluororesin cell 1 provided in the apparatus of the present invention is stable against a solution containing fluoride ions (F ⁻ ) and does not cause contamination such as eluted components derived from glass.
Although the lid 4 and the connector 5 attached to the cell 1 are not members that the solution y comes into direct contact with, the evaporated solution y adheres to them, so these members may also be made of fluororesin. preferable.

The reference electrode 2 may be of either a single-junction type or a double-junction type. In the double-junction reference electrode, chloride ions (Cl ⁻ ) in the internal solution of the inner cylinder pass through the internal solution of the outer cylinder to the test solution. Since a very small amount leaks inside, there is an advantage that the acceleration of corrosion due to the leaked chloride ions (Cl ⁻ ) can be suppressed by lowering the chloride ion (Cl ⁻ ) concentration of the inner liquid of the outer cylinder. Therefore, the reference electrode 2 is preferably a double-junction reference electrode.
In the device of the present invention, in order to prevent contamination by eluted components derived from glass, the outer cylinder of the double-junction reference electrode is coated with a fluororesin on the outer side of the glass cylindrical body that is the base material. is preferred. Although it has been considered to construct the outer cylinder of the double-junction reference electrode itself with fluororesin, the difference in thermal expansion between the outer cylinder made of fluororesin and the ceramic porous material that constitutes the liquid junction is large. A large amount of the liquid inside the outer cylinder leaked into the test liquid, and it was found that it could not withstand use. On the other hand, a cylinder made of glass, which is the base material of the outer cylinder, has a coefficient of thermal expansion close to that of a ceramic porous body, and does not cause such a problem.

2 to 4 show an embodiment of a double-junction reference electrode provided as the reference electrode 2 in the device of the present invention, FIG. 2, and FIG. 4 is a partially enlarged view of B portion (tip of the inner cylinder) in FIG.
This double-junction reference electrode comprises an outer cylinder 20, an inner cylinder 21 disposed inside the outer cylinder 20, an Ag/AgCl electrode 22 disposed inside the inner cylinder 21, and a liquid at the tip of the outer cylinder 20. A ceramic porous body 23 forming a junction, a ceramic porous body 24 forming a liquid junction at the tip of the inner cylinder 21, and an internal liquid 25 (solution y ), an internal liquid 26 (KCl) filled in the inner cylinder 21, and the like.

The outer cylinder 20 has a fluororesin coating layer 28 formed on the outside of a glass cylinder 27 that is a base material. From the viewpoint of minimizing the surface of the glass substrate (cylindrical body 27) in contact with the solution y, the fluororesin coating layer 28 is provided at least on the surface of the outer cylinder 20 (the outer cylinder to which the evaporated solution y adheres) in contact with the solution y. 20 surface).
In this embodiment, the entire peripheral surface (shown in FIG. 2) except for the distal end surface of the cylindrical body is applied to a considerable length portion (a portion having a length of half or more of the total length of the cylindrical body) on the lower side (tip side) of the cylindrical body 27. A fluororesin coating layer 28 is formed in the area). The fluororesin coating layer 28 is formed by covering the cylinder 27 with a heat-shrinkable tube made of fluororesin and then thermally shrinking it. There is no layer 28, and the glass base material contacts the solution y at this portion, but within this extent of contact, the elution of the glass component is negligible, and there is no problem.
The inner cylinder 21 is also usually made of glass, but since it does not come into contact with the solution y, it is not necessary to provide a fluororesin coating layer.

The fluororesin coating layer 28 can be formed by covering the cylindrical body 27 with a fluororesin heat-shrinkable tube as described above, and then heat-shrinking it with a heat gun or the like, or by coating with fluororesin (spray coating of liquid paint, powder coating, etc.). etc.).
In the method of coating the fluororesin, the fluororesin coating layer 28 can also be formed on the tip surface of the cylinder 27 . FIG. 5 shows an embodiment in that case, and is a partially enlarged vertical cross-sectional view of the distal end portion of the outer cylinder 20. As shown in FIG. The fluororesin coating layer 28 is formed not only on the peripheral surface of the cylinder 27 but also on the tip surface of the cylinder 27 .

There is no particular limitation on the type of fluororesin forming the cell 1 and the fluororesin coating layer 28 (furthermore, the lid 4, the connector 5, etc.). Usable fluororesins include, for example, polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE, CTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), tetrafluoroethylene/perfluoro Alkyl vinyl ether copolymer (PFA), ethylene tetrafluoride/propylene hexafluoride copolymer (FEP), ethylene/tetrafluoroethylene copolymer (ETFE), ethylene/chlorotrifluoroethylene copolymer (ECTFE) etc., and one or more of these can be used.

As described above, in the device of the present invention, the cell 1 is made of a fluororesin, and preferably, as the reference electrode 2, the double cell is provided with the outer cylinder 20 of which the outer surface of the glass cylinder as the base material is coated with a fluororesin. By using the junction-type reference electrode, glass-derived contaminants (boron (B), aluminum (Al), silicon (Si), etc.) in the solution y can be kept low. That is, in the quantitative analysis of boron (B), aluminum (Al), and silicon (Si) contained in solution y, each quantitative analysis value of boron (B), aluminum (Al), and silicon (Si) in solution y can be less than 0.4 mgL ⁻¹ , preferably less than 0.1 mgL ⁻¹ .

The liquid junction of the double-junction reference electrode is usually composed of a ceramic porous material. Chloride ions (Cl ⁻ ) exude excessively from the liquid junction and mix into the solution y, resulting in contamination. To address this problem, the wire diameter _d1 of the ceramic porous body 23 forming the liquid junction at the tip of the outer cylinder 20 is preferably 0.7 mm or less, more preferably 0.5 mm or less. . As a result, the chloride ions (Cl ⁻ ) in the internal liquid of the outer cylinder 20 are prevented from being excessively exuded and mixed into the solution y through the liquid junction, and the chloride ions (Cl ⁻ ) in the solution y are prevented from Concentration can be kept low. Specifically, the concentration of chloride ions (Cl ⁻ ) derived from the reference electrode internal solution in solution y can be less than 2.0 mgL ⁻¹ . On the other hand, although there is no particular lower limit for the wire diameter _d1 of the ceramic porous body 23, if the wire diameter _d1 is too small, the resistance of the ceramic porous body 23 increases and liquid clogging may occur. A lower limit is preferred.

Contaminant chloride ions (Cl ⁻ ) leak from the inner liquid 26 of the inner cylinder 21 into the test ^liquid via the inner liquid 25 of the outer cylinder 20 in a very small amount. Therefore, if the wire diameter _d2 of the porous ceramic body 24 constituting the liquid junction at the tip of the inner cylinder 21 is large, the concentration of chloride ions (Cl ⁻ ) in the internal liquid 25 of the outer cylinder 20 increases. Chloride ions (Cl ⁻ ) tend to exude excessively from the liquid junction of the outer cylinder 20 . Therefore, the wire diameter _d2 of the ceramic porous body 24 is preferably 2.0 mm or less. On the other hand, there is no particular lower limit for the wire diameter _d2 , but if the wire diameter is too small, the resistance of the ceramic porous body 24 increases and liquid clogging may occur, so the lower limit is preferably about 0.1 mm. .
Also, if the porosity of the ceramic porous body 23 is too large, chloride ion ( ^Cl.sup.- ) leakage tends to accelerate corrosion of the material. Therefore, the porosity is preferably 34% or less, more preferably 31% or less.

6 and 7 show another embodiment of the double-junction reference electrode provided as the reference electrode 2 in the device of the present invention, and FIG. 7 is a cross-sectional view taken along line VII-VII in FIG.
It is known that the electrode potential of reference electrodes such as Ag/AgCl and calomel electrodes generally used in electrochemical measurements depends on the temperature according to the Nernst equation. should be controlled. The temperature of the internal liquid 26 of the inner cylinder 21 is a standard specification temperature of 25° C., and generally the temperature is converted to the standard hydrogen electrode standard of 25° C. and the data is organized. Therefore, from the viewpoint of versatility, it is preferable to control the temperature of the reference electrode (internal liquid 26) to 25°C.

The embodiments of FIGS. 6 and 7 enable such temperature control by providing the reference electrode 2 with a temperature adjustment function (cooling function). A cooling cylinder 29 (cooling pipe) is provided to surround the cooling cylinder 29, and a cooling water inlet 290 and a cooling water outlet 291 for flowing cooling water are provided in the cooling cylinder 29. As shown in FIG.
That is, a cooling cylinder 29 is provided along the longitudinal direction of the outer cylinder 20 outside the upper portion (base end side) of the outer cylinder 20 where the fluororesin coating layer 28 is not formed. The cooling cylinder 29 surrounds a predetermined length of the outer cylinder 20 , and both longitudinal ends thereof are joined to the outer surface of the outer cylinder 20 . A cooling water inlet 290 is provided on the upper side (position near the upper end) of the cooling cylinder 29, and a cooling water outlet 291 is provided on the lower side (position near the lower end). supply to and discharge from the cooling cylinder 29 can be performed.

Here, if a cooling water inlet is provided on the lower side (position closer to the lower end) of the cooling cylinder 29 and a cooling water outlet is provided on the upper side (position closer to the upper end), the inside of the inner cylinder 21 The internal liquid 25 (solution y) of the outer cylinder 20 cooled together with the liquid 26 is supercooled, and as a result, the test liquid (solution y) in the cell 1 is also supercooled, and the test liquid (solution y) in the cell 1 is supercooled. temperature drops. In order to suppress the temperature drop of the test solution (solution y) in the cell 1, it is necessary to increase the temperature of the pure water in the constant temperature water bath in which the cell 1 is placed. There is a risk that water vapor will be generated and the temperature of the peripheral member will exceed the heat-resistant temperature, and dew condensation will occur in the electrical system of the peripheral member, causing a short circuit in the electrical system. Therefore, it is preferable to provide the cooling water inlet 290 on the upper side of the cooling cylinder 29 and provide the cooling water outlet 291 on the lower side as in the present embodiment.

It is preferable that the cooling water flowing through the cooling cylinder 29 is circulated through a chiller (cold water circulation device) to control the temperature of the cooling water. Further, it is preferable to provide a thermocouple (not shown) for measuring the temperature of the internal liquid 26 and to control the temperature of the internal liquid 26 by controlling the temperature of the cooling water based on the temperature measurement by this thermocouple.
FIG. 8 shows a state in which the reference electrode 2 of this embodiment is installed in the cell 1, and FIG.
Similarly, the reference electrode 2 is supported by the cover 4 via the connector 5 and its tip end portion is inserted into the cell 1 through the mounting hole 40 .

As shown in [Example 3] described later, when the temperature of the test solution (solution y) in the cell 1 is maintained at about 80°C in the constant temperature water bath, the reference electrode 2 has a temperature adjustment function (cooling function). Without a measuring device, it is difficult to control the temperature of the internal liquid 26 of the inner cylinder 21 to be constant, and the temperature is around 50.degree. On the other hand, in the measuring device in which the reference electrode 2 has a temperature adjusting function (cooling function) as in the present embodiment, the temperature of the internal liquid 26 in the inner cylinder 21 can be controlled to be constant. The temperature variation range is reduced, and the accurate temperature of the internal liquid 26 can be known. As a result, the accuracy of the potential obtained from the temperature of the internal liquid 26 is enhanced, and the measurement accuracy of the device of the present invention can be further enhanced. Furthermore, since the internal liquid 26 can be maintained at about 25° C., which is the standard specification temperature, conversion to the standard hydrogen electrode standard of the reference electrode 2 is facilitated.

The apparatus of the present invention can be used for electrochemical measurements for evaluating the corrosion resistance (corrosion properties) of various metal materials. It is suitable as an electrochemical measuring device for evaluating. In this case, the solution y is a PEFC-simulated environment, that is, an acidic aqueous solution containing a predetermined concentration of fluoride ions (F ⁻ ), and an electrochemical measurement is performed using a metal separator material (candidate material) as a sample x. Corrosion resistance (corrosion characteristics) of the metal material to be tested in the PEFC environment is evaluated based on the corrosion current, analysis results of the eluted metals of the solution y, and the like.

[Example 1]
Elution tests of constituent components of a cell and a reference electrode were performed using the electrochemical measurement apparatus of the present invention example and the comparative example (conventional example) having the structure shown in FIG. The apparatus configurations of Invention Examples 1 and 2 and Comparative Example are as follows.
・Invention example 1
The cell 1 was made of fluororesin (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer; PFA), and the lid 4 and connector 5 were also made of fluororesin (polytetrafluoroethylene; PTFE). Further, the external cylinder 20 of the double-junction reference electrode, which is the reference electrode 2, was provided with a fluororesin coating layer 28 as shown in FIGS. The fluororesin coating layer 28 is formed by covering the cylindrical member 27 made of glass with a heat-shrinkable tube of fluororesin (PTFE) and heat shrinking it.

・Invention Example 2
The cell 1 was made of fluororesin (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer; PFA), and the lid 4 and connector 5 were also made of fluororesin (polytetrafluoroethylene; PTFE). On the other hand, the outer cylinder of the double-junction reference electrode, which is the reference electrode 2, was not provided with the fluororesin coating layer as in Example 1, but was made of glass only.
・Comparative example (conventional device)
The cell and its cover are made of glass, and the outer cylinder of the double-junction reference electrode is also made of glass.

In both the present invention example and the comparative example, the double-junction reference electrode has a wire diameter of 0.4 mm in the ceramic porous material that forms the liquid junction at the tip of the outer cylinder, and a ceramic material that forms the liquid junction at the tip of the inner cylinder. The wire diameter of the porous body was set to 0.9 mm.
In this elution test, NaF powder was added as a reagent to sulfuric acid so that the fluoride ion (F ⁻ ) was 2 ppm, and a test solution adjusted to pH 3 was used. After pouring 400 mL of this test solution into the cell, , the temperature of the test solution was raised to 80°C in a constant temperature water bath, and the dissolution test was carried out at that temperature for one week.

After the test, the test solution was subjected to quantitative analysis of eluted components (boron (B), aluminum (Al), silicon (Si)) from the cell and the double-junction reference electrode (outer cylinder) by ICP-AES. For comparison, the same analysis was performed on the test solution before the dissolution test. Those results are shown in Table 1.
In this test, the reference value for each content of boron (B), aluminum (Al), and silicon (Si) in the solution was set to 0.4 mgL ^-1 , and as a comprehensive evaluation, boron (B), aluminum (Al), Each content of silicon (Si) is all less than the standard value "pass", one or more of each content of boron (B), aluminum (Al), silicon (Si) is more than the standard value "pass"Failed."

According to Table 1, in the comparative example (conventional device), the content of silicon (Si), which is an elution component from the glass cell and the double-junction reference electrode (outer cylinder), etc., greatly exceeds the standard value. Also, the contents of boron (B) and aluminum (Al), which are similarly eluted components, are higher than those of the present invention example, and it can be seen that contamination derived from glass occurs. On the other hand, in the present invention example, each content of boron (B), aluminum (Al), and silicon (Si) is less than the reference value, and contamination derived from glass is not detected. Comparing Invention Example 1 and Invention Example 2, in Invention Example 1, in which the outer cylinder 20 of the double-junction reference electrode is provided with a fluororesin coating layer 28 on the outer side of the glass cylinder 27 that is the base material, It can be seen that the silicon (Si) content is significantly reduced as compared with Invention Example 2.

[Example 2]
In the apparatus of Invention Example 1 of [Example 1] above, as the double-junction reference electrode, a ceramic porous wire constituting each liquid junction at the tip of the outer cylinder and the tip of the inner cylinder as shown in Table 2 Using different diameters, the effect of the wire diameter of the ceramic porous body on contamination (chloride ion (Cl ⁻ ) concentration) derived from the reference electrode internal solution in the test solution was investigated.

The test conditions were the same as in [Example 1] above, and the chloride ion (Cl ⁻ ) concentration in the test solution after the test was quantitatively analyzed by ion chromatography (IC). For comparison, the same analysis was performed on the solution before the test.
The chloride ion (Cl ⁻ ) concentration analysis results in the test solution were analyzed using the ceramic porous body of the double-junction reference electrode provided in each device (the ceramic It is shown in Table 2 together with the wire diameter of the porous body).

In this test, the preferable range of chloride ion (Cl ⁻ ) concentration derived from the reference electrode internal solution in the test solution was <2.0 mgL ⁻¹ . According to Table 2, the concentration of chloride ions (Cl ⁻ ) can be kept low by setting the wire diameter d ₁ of the ceramic porous body forming the liquid junction at the tip of the outer cylinder to 0.7 mm or less. It turns out.

[Example 3]
6 and 7, the reference electrode has a temperature adjustment function (cooling function), and the reference electrode as shown in FIGS. 2 and 3 has a temperature adjustment function (cooling function). The same electrochemical measurement (dissolution test) as in Example 1 was performed using a measuring device (the device of the present invention) that does not have a sample, and the test solution was kept at 80° C. in a constant temperature water bath. In the measurement device in which the reference electrode has a temperature control function (cooling function), the cooling water was flowed into the cooling cylinder 29 while controlling the temperature of the cooling water at 20.5° C. with a chiller.

During the test, the temperature of the reference electrode (internal liquid) was measured with a thermocouple. As a result, the temperature of the reference electrode (internal liquid) changed in the range of 48 to 53°C in the case of the measuring device in which the reference electrode did not have a temperature control function (cooling function). On the other hand, in the case of a measuring device in which the reference electrode has a temperature adjusting function (cooling function), the temperature of the reference electrode (internal liquid) could be kept constant at 25°C.
In the dissolution test using an electrochemical measurement device, the measurement results are obtained after conversion to the reference electrode potential based on the temperature of the reference electrode (internal solution). When using a measuring device (device of the present invention) in which the reference electrode has a temperature adjustment function (cooling function) as shown in FIGS. Therefore, variations in measurement results are suppressed, and measurement accuracy can be further improved.

REFERENCE SIGNS LIST 1 cell 2 reference electrode 3 counter electrode 4 lid 5 connector 20 outer cylinder 21 inner cylinder 22 Ag/AgCl electrode 23, 24 ceramic porous body 25 inner liquid of outer cylinder 26 inner liquid of inner cylinder 27 cylinder 28 fluororesin coating layer 29 cooling cylinder 40 mounting hole 290 cooling water inlet 291 cooling water outlet x sample y solution

Claims (5)

A device for electrochemical measurement of a metal material in a solution containing fluoride ions (F ⁻ ),
It comprises a cell (1) containing a solution, a reference electrode (2) and a counter electrode (3) immersed in the solution in the cell (1), and the cell (1) is made of fluororesin. electrochemical measurement device. 2. An electric electrode according to claim 1, characterized in that the reference electrode (2) is a double-junction reference electrode, the outer cylinder of which is a base material made of glass and the outer surface of which is coated with a fluororesin. Chemical measurement device. The reference electrode (2) is a double-junction reference electrode, the liquid junction at the tip of the outer cylinder is made of a ceramic porous body, and the wire diameter of the ceramic porous body is 0.7 mm or less. 3. The electrochemical measurement device according to claim 1 or 2. 4. The electrochemical measuring apparatus according to any one of claims 1 to 3, wherein the lid (4) and the connector (5) attached to the cell (1) are made of fluororesin. 5. A method for electrochemical measurement of a metal material, comprising performing an electrochemical measurement of a metal separator material used in a polymer electrolyte fuel cell, using the electrochemical measurement device according to any one of claims 1 to 4.

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