JP2017053689A - Electrochemical type oxygen sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrochemical type oxygen sensor capable of suppressing occurrence of output fluctuation or output abnormality caused by an electrochemical reaction itself easily affected by a measured value of a detected oxygen concentration.SOLUTION: An electrochemical type oxygen sensor includes a holder 9, and an electrode 8 and electrolytic solution 7 stored in the holder 9. The electrode 8 is constituted of a Pb-Sb alloy.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrochemical oxygen sensor that contains Pb (lead) in an electrode and measures the concentration of gas or liquid by the electrochemical reaction of the electrode.

  Oxygen sensors are used in a wide range of fields, such as checking for oxygen deficiency in ship holds and manholes, and detecting oxygen concentrations in medical devices such as anesthesia machines and ventilators.

  Various types of oxygen sensors such as an electrochemical type, a magnetic type, and a zirconia type are used. Among these oxygen sensors, electrochemical methods are widely used because they are inexpensive and easy to operate and operate at room temperature.

  The operation principle of the electrochemical oxygen sensor is as follows. Oxygen that has passed through a diaphragm (equivalent to 4A in FIG. 1) that selectively allows oxygen to permeate and limits the amount of permeation to match the cell reaction, is a catalyst electrode that can electrochemically reduce oxygen (see FIG. 1). 1) (corresponding to 4B in FIG. 1), and undergoes the following electrochemical reaction with the electrode (corresponding to negative electrode 8 in FIG. 1) via the electrolytic solution (corresponding to 7 in FIG. 1).

When electrolyte is acidic, positive electrode reaction: O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O
Negative electrode reaction: 2Pb + 2H ₂ O → 2PbO + 4H ⁺ + 4e ⁻
Total reaction: 2Pb + O ₂ → 2PbO
When electrolyte is alkaline, positive electrode reaction: O ₂ + 2H ₂ O + 4e ⁻ → 4OH ⁻
Negative electrode reaction: 2Pb + 4OH ⁻ → 2PbO + 2H ₂ O + 4e ⁻
Total reaction: 2Pb + O ₂ → 2PbO

  In the case where the electrolyte (7) is acidic and the case where it is alkaline, the charge bearer is different. In either case, a current corresponding to the oxygen concentration is generated between the catalyst electrode (4B) and the electrode (8). To do. The current generated by the positive electrode reaction at the catalyst electrode (4B) is collected by a positive electrode current collector (corresponding to 5 in FIG. 1) in pressure contact with the catalyst electrode (4B), and the positive electrode lead wire (in FIG. 1 at 6) Equivalent) and is converted into a voltage signal by flowing into the electrode (8) through a drive circuit (described later), and a voltage is obtained as an oxygen sensor output. Thereafter, the obtained output voltage is converted into an oxygen concentration by a known method and detected as an oxygen concentration. The PbO generated on the surface of the negative electrode is dissolved in the electrolytic solution, whereby new Pb is exposed on the surface, and the electrochemical reaction is continued by a mechanism in which it is further oxidized.

Such an electrochemical oxygen sensor is required to have less output fluctuation and output abnormality, and a technology that can solve these problems even when heat, impact, or the like is applied is disclosed.
For example, Patent Document 1 describes an aspect in which an electrolyte solution holding member is provided in the positive electrode current collector and the negative electrode chamber opening so that an air layer is not formed between the positive electrode and the negative electrode due to application of vibration, impact, heat, or the like. ing. Further, in Patent Document 2, in order to make it difficult to change the contact state between the positive electrode current collector and the positive electrode lead wire when vibration or impact is applied, these are made of metal and integrated by welding or the like. Furthermore, the aspect provided with an electrolyte solution holding material in contact with the positive electrode current collector is described.
In addition, in order to extend the life and prevent the formation of an oxygen reduction inhibiting layer on the anode surface, an aspect is described in which a thin layer containing a synthetic component of at least one metal of copper, lead, antimony or germanium is held on the anode surface. ing.

JP 2002-350384 A JP 2001-296268 A JP-A-6-88268

However, the techniques described in Patent Documents 1 to 3 do not suppress the occurrence of output fluctuations and output abnormalities caused by the above-described electrochemical reaction itself that is easily influenced by the measured value of the detected oxygen concentration.
The present invention has been made to solve such problems, and suppresses the occurrence of output fluctuations and output abnormalities caused by the electrochemical reaction itself that is easily affected by the measured value of the detected oxygen concentration. It is an object of the present invention to provide an electrochemical oxygen sensor capable of performing

  The electrochemical oxygen sensor according to the present invention includes a holder, an electrode accommodated in the holder, and an electrolytic solution, and the electrode is a Pb—Sb alloy.

The Pb—Sb alloy preferably has a metal structure having Pb-based crystal grains containing Sb.
The Pb-Sb alloy preferably has a metal structure in which Pb-based crystal grains containing Sb and a Pb-Sb-based eutectic structure are mixed.
It is preferable that the Pb—Sb alloy has a metal structure having only a Pb—Sb eutectic structure.
The Pb-Sb alloy preferably has a metal structure in which Pb-based crystal grains containing Sb, a Pb-Sb eutectic structure, and a solid solution of Sb are mixed.
The Pb-Sb alloy is one or more selected from the group consisting of Al, Ag, As, Bi, Cd, Cu, Fe, Mg, Na, Hg, Sn, Zn, S, Se, and Ca. It is preferable that an element is contained.
In the electrochemical oxygen sensor, the electrode is a negative electrode, and is preferably a constant potential electrochemical oxygen sensor (hereinafter referred to as a constant potential oxygen sensor).

  ADVANTAGE OF THE INVENTION According to this invention, the electrochemical oxygen sensor which can suppress generation | occurrence | production of the output fluctuation and output abnormality resulting from the electrochemical reaction itself which is easy to be influenced by the measured value of the detected oxygen concentration can be provided.

It is a conceptual diagram which shows the cross-section of the cell of the cell part of the constant potential type oxygen sensor which concerns on this embodiment. It is a conceptual diagram showing the metal structure in the arbitrary surfaces of the electrode used for the constant potential type oxygen sensor which concerns on this embodiment. It is a conceptual diagram showing the other metal structure | tissue in the arbitrary surfaces of the electrode used for the constant potential type oxygen sensor which concerns on this embodiment. It is a conceptual diagram showing the other metal structure | tissue in the arbitrary surfaces of the electrode used for the constant potential type oxygen sensor which concerns on this embodiment. It is a conceptual diagram showing the other metal structure | tissue in the arbitrary surfaces of the electrode used for the constant potential type oxygen sensor which concerns on this embodiment. It is an equilibrium diagram of a general Pb-Sb binary alloy. It is a conceptual diagram for demonstrating that an output voltage is stabilized. It is a conceptual diagram showing the metal structure in the arbitrary surfaces of the conventional electrode. It is a schematic diagram which shows an example of the relationship between the electric potential of a constant potential type oxygen sensor and an electric current. It is an example of the cell part and drive circuit of a constant potential type oxygen sensor. It is another example of the circuit of the cell part of the constant potential type oxygen sensor which concerns on this embodiment. It is another example of the circuit of the cell part of the constant potential type oxygen sensor which concerns on this embodiment.

The present inventor has found that there is a problem in which output fluctuations and output abnormalities are caused by the above-described electrochemical reaction itself, and further has found a means for solving the problem.
Such an electrochemical oxygen sensor performs measurement by the above-described electrochemical reaction, that is, a mechanism that consumes the electrode (Pb). This consumption usually occurs on the surface of the electrode (Pb), but depending on the degree, it has become clear that it also occurs inside the electrode (Pb). In this case, since the mechanical strength of the portion where the wear has occurred inside the electrode is reduced, the electrode is chipped from the portion, and the chipped piece is further perforated for supplying the electrolyte from the electrolyte (7) ( 11) and lead wire perforations (12) and contacted with the positive electrode current collector (5) and the catalyst electrode (4B), which revealed that output fluctuations and output abnormalities occurred.
For this reason, the present inventor has studied to increase the hardness of the electrode (Pb). However, when the hardness is simply increased to suppress the electrochemical reaction, the electrode activity of the electrode is deteriorated. For this reason, it is difficult to detect an accurate oxygen concentration, and the sensor may not function. Therefore, it has been necessary to solve the conflicting problem of suppressing the electrode cracking while suppressing the suppression of the reaction.

  Therefore, as a result of intensive studies, the present inventors have found that the electrode (Pb) is made of a Pb—Sb alloy, thereby functioning as a sensor and suppressing the chipping of the electrode. As a result, it has been found that output fluctuations and output abnormalities caused by the electrochemical reaction itself can be suppressed, and that the life of the sensor can be extended, and the present invention has been completed.

Hereinafter, embodiments of the present invention will be described.
In this embodiment, a description will be given using a constant potential oxygen sensor as a preferred example of the electrochemical oxygen sensor according to the present invention.
A constant potential oxygen sensor, which is a kind of electrochemical oxygen sensor, includes a cell portion in which an electrochemical reaction as described above occurs, and a drive circuit for keeping a voltage between a positive electrode and a negative electrode of the cell portion constant.

FIG. 1 is a conceptual diagram showing a cross-sectional structure of a cell (“Sensor Cell” in FIG. 10) of a cell portion of a constant potential oxygen sensor according to the present embodiment.
In FIG. 1, 1 is a first holder lid (inner lid), 2 is an O-ring, 3 is a protective film for preventing dirt, dust or water film from adhering to the diaphragm, 4A is a diaphragm, and 4B is a diaphragm. Catalyst electrode, 5 positive electrode current collector, 6 positive electrode lead wire, 7 electrolyte, 8 negative electrode, 9 holder, 10 second holder lid (outer lid), 11 perforation for electrolyte supply, 12 Is a lead wire perforation, 13 is a positive electrode current collector holding portion, and 14 is a negative electrode lead wire. The catalyst electrode 4B and the positive electrode current collector 5 constitute a positive electrode 45. The first holder lid 1 and the second holder lid 10 constitute a holder lid 101.

  As shown in FIG. 1, the constant potential oxygen sensor according to the present embodiment is provided on a holder 9, a positive electrode 45, a negative electrode 8, an electrolyte solution 7 accommodated in the holder 9, and the positive electrode 45. A diaphragm 4A, a protective film 3 provided on the diaphragm 4A, and a through-hole that is fixedly or detachably provided on the protective film 3 of the holder 9 and serves as an oxygen supply path (space) leading to the diaphragm 4A 16 is provided with a holder lid 101 provided with 16 and a drive circuit shown in FIG. 10 connected to the positive electrode 45 and the negative electrode 8.

FIG. 9 is a schematic diagram illustrating an example of the relationship between the potential and current of the constant potential oxygen sensor.
In FIG. 9, the horizontal axis represents the current flowing between the positive electrode and the negative electrode, and the vertical axis represents the positive electrode potential with respect to the negative electrode potential (hereinafter simply referred to as “voltage”). In FIG. 9, I ₀ indicates a limit current value in 0% oxygen gas, I ₂₁ indicates a limit current value in 21% oxygen gas, and I ₁₀₀ indicates a limit current value in 100% oxygen gas. . The voltage is low areas and voltage E ₁ is higher than E ₂ region, the current varies greatly depending on the voltage, between the voltage of the E ₁ and E _2, the current value reaches passes through the oxygen permeable membrane to the positive electrode When the voltage is set to an appropriate value E ₀ between E ₁ and E ₂ in accordance with the amount of oxygen, that is, oxygen concentration, the current is proportional to the oxygen concentration at that time, I ₀ , I ₂₁ , I ₁₀₀ It becomes.
Since the values of E ₁ and E ₂ vary depending on the measurement conditions such as the material of the positive electrode and the negative electrode, the type of the electrolyte, the area of the positive electrode, and the temperature, it is necessary to select an E ₀ value suitable for these conditions. There is.

By applying an appropriate voltage E ₀ between E ₁ and E ₂ from the outside, the current value can be operated as a constant potential type in which the current value falls within the limiting current region of oxygen gas.

  As the positive electrode of the electrochemical oxygen sensor of the present invention, a metal effective for electrochemical reduction of oxygen is used. When these metals are operated as a constant potential type, a catalyst electrode such as gold (Au) or platinum (Pt) can be used.

  An example of a cell portion and a driving circuit of the constant potential oxygen sensor is shown in FIG. In FIG. 10, a portion surrounded by a dotted line is a cell portion, and the rest is a drive circuit. In the cell portion shown in FIG. 10, Sa is a negative electrode, Sc is a positive electrode, St is a thermistor terminal, IC1, IC2, and IC3 are all differential amplifiers, IC4 is a shunt regulator, TH is a thermistor element for temperature compensation, RY1, RY2 is an optical relay.

  Due to the characteristics of the differential amplifier / shunt regulator, the potential # 3 is maintained at the potential set by the shunt regulator IC4 and the resistors R8 and R9 with respect to the ground potential (GND) of the drive circuit. The potential of # 4 is the same as the ground potential (GND) of the drive circuit. Therefore, the positive electrode potential of the cell portion of the oxygen sensor is held at a constant value with respect to the negative electrode potential.

On the other hand, all of the sensor current generated by the reduction of oxygen in the cell portion flows into the output of the differential amplifier IC2 through the temperature compensation thermistor element TH, but the voltage generated at both ends of the thermistor element TH at that time is different. The signal is input to the dynamic amplifier IC3, amplified according to the amplification set by the resistors R2, R3, R4, and R5, output to the output terminal of the differential amplifier IC3, and taken out as the output of the drive circuit.
With the above electric circuit operation, the positive electrode potential of the cell portion of the oxygen sensor is held at a constant value with respect to the negative electrode potential, and at the same time, a voltage proportional to the sensor current is output.
In the example circuit diagram shown in FIG. 10, the positive terminal and the negative terminal are in an open state.

  In the electrochemical oxygen sensor of the present invention, the potential to be maintained between the positive electrode and the negative electrode during measurement depends on the current-potential characteristics of the sensor, and the positive electrode and negative electrode materials used in the cell portion, the type of electrolyte, and the area of the positive electrode Therefore, it is necessary to select the resistance and thermistor constants according to the type and structure of the sensor.

11 and 12 are other examples of the circuit of the cell portion of the constant potential oxygen sensor according to the present embodiment. 11 and 12, a resistor and a thermistor are provided in series between the positive terminal (Sc) and the negative terminal (Sa).
In the circuit of the cell portion shown in FIGS. 11 and 12, it is necessary to select the resistance and the thermistor constant according to the configuration of the cell portion (positive electrode, negative electrode, electrolyte, surface area of the positive electrode, etc.).

The electrochemical oxygen sensor according to the present invention is exemplified by an embodiment as shown in FIG. 1, and includes a holder 9, an electrode (a negative electrode 8 in FIG. 1) accommodated in the holder 9, and an electrolytic solution. 7 and the electrode is a Pb—Sb alloy.
The “Pb—Sb alloy” in the present invention is an alloy mainly composed of Pb and Sb, but does not depart from the gist of the present invention (the metal structure shown in FIGS. 2 to 5 described later). As far as it is concerned, metals other than Pb and Sb and other impurities may be contained. Examples of metals and other impurities other than Pb and Sb include Al, Ag, As, Bi, Cd, Cu, Fe, Mg, Na, Hg, Sn, Zn, S, Se, and Ca.

Thus, the electrochemical oxygen sensor according to the present invention has a Pb—Sb alloy as the electrode (the negative electrode 8 in FIG. 1), so that it functions as a sensor and can suppress chipping of the electrode. This is because even when a Pb—Sb alloy is used, Pb is present in the alloy, so that an electrochemical reaction of Pb occurs on the electrode surface, while Sb is present inside the electrode. Is considered to be suppressed. In addition, since the surface area which contributes to the reaction is smaller than the reaction on the electrode surface, the reaction inside the electrode is considered to be small in reaction scale.
From the above, by using a Pb—Sb alloy for the electrode (the negative electrode 8 in FIG. 1), the suppression of the electrochemical reaction can be suppressed, that is, it can function as a sensor and the chipping of the electrode can also be suppressed. As a result, the occurrence of output fluctuations and output abnormalities can be suppressed, and the sensor life can be extended.

FIG. 2 is a conceptual diagram showing a metal structure on an arbitrary surface of an electrode used in the constant potential oxygen sensor according to the present embodiment, and FIG. 6 is an equilibrium diagram of a general Pb—Sb binary alloy. FIG. 8 is a conceptual diagram showing a metal structure on an arbitrary surface of a conventional electrode.
As shown in FIG. 2, the Pb—Sb alloy preferably has a metal structure having Pb-based crystal grains (α phase in FIG. 6, hereinafter the same) 18 containing Sb30 therein. A crystal grain boundary 20 is provided between the Pb crystal grains 18.

The metal structure in FIG. 2 is when the Sb content in the Pb—Sb alloy is 0.5 wt% or more and less than 3.5 wt% (more preferably 0.5 wt% or more and 3.0 wt% or less). is there.
In the present invention, the Sb content in the Pb—Sb alloy is determined by performing EDX analysis (beam diameter: 1 mm) on an arbitrary portion of the alloy to be measured, It is a value calculated by mass% (Pb + Sb + “metal and other impurities other than Pb and Sb” = 100%).

Since the negative electrode 8 of the conventional electrochemical oxygen sensor is Pb, as shown in FIG. 8, the metal structure thereof is a grain boundary between the Pb crystal grains 18A not containing Sb30 and the Pb crystal grains 18A. 20A.
On the other hand, in the present invention, since the negative electrode 8 has a metal structure as shown in FIG. 2, it functions as a sensor and can suppress chipping of the electrode (negative electrode 8). This is because an electrochemical reaction of Pb occurs on the surface of the Pb-based crystal grains 18, but Sb exists inside the electrodes, so that the metal bonds at the crystal grain boundaries 20 between the Pb-based crystal grains 18 are strengthened, and the inside of the electrodes ( In particular, it is considered that the reaction at the grain boundary 20) is suppressed.

  As described above, the reaction inside the electrode is considered to be small in scale. Therefore, by making the negative electrode 8 have a metal structure as shown in FIG. 2, the suppression of the electrochemical reaction can be suppressed, that is, it can function as a sensor and the chipping of the electrode can also be suppressed. As a result, it is possible to suppress the occurrence of output fluctuations and output abnormalities, and further to extend the life of the sensor.

FIG. 3 is a conceptual diagram showing another metal structure on an arbitrary surface of the electrode used in the constant potential oxygen sensor according to the present embodiment.
As shown in FIG. 3, the Pb—Sb alloy preferably has a metal structure in which Pb-based crystal grains 18 containing Sb 30 and Pb—Sb-based eutectic structure 50 are mixed.
The metal structure in FIG. 3 is when the Sb content in the Pb—Sb alloy is 3.5 wt% or more and less than 11.1 wt% (more preferably 4.0 wt% or more and 10.0 wt% or less). is there.

Thus, since the Pb—Sb alloy has a metal structure as shown in FIG. 3, the Pb—Sb alloy functions as a sensor, and chipping of the electrode (negative electrode 8) can be suppressed.
This is presumably because the electrochemical reaction of Pb occurs on the surface of the Pb-based crystal grain 18, while Sb is present inside the electrode, so that the metal bond at the crystal grain boundary 20 is strengthened. Therefore, it is considered that the reaction inside the electrode (particularly, the grain boundary 20) is suppressed. Since the crystal width of the Pb—Sb eutectic structure 50 is finer than that of the Pb crystal grains 18, the grain interface area in contact with the electrolytic solution increases. Therefore, it is considered that the dissolution of the Pb—Sb eutectic structure 50 inside the electrode is reduced.

  Therefore, by making the negative electrode 8 have a metal structure as shown in FIG. 3, the suppression of the electrochemical reaction can be suppressed, that is, it can function as a sensor and the chipping of the electrode can also be suppressed. As a result, it is possible to suppress the occurrence of output fluctuations and output abnormalities, and further to extend the life of the sensor.

FIG. 4 is a conceptual diagram showing another metal structure on an arbitrary surface of an electrode used in the constant potential oxygen sensor according to the present embodiment.
As shown in FIG. 4, the Pb—Sb alloy preferably has a metal structure having only a Pb—Sb eutectic structure.
The metal structure in FIG. 4 is obtained when the Sb content in the Pb—Sb alloy is 11.1 wt%.

Thus, since the Pb—Sb alloy has a metal structure as shown in FIG. 4, the Pb—Sb alloy functions as a sensor and can suppress chipping of the electrode (negative electrode 8).
This is because the above-described reaction is suppressed inside the electrode by the refined Pb—Sb-based eutectic structure 50, but the interfacial area in contact with the electrolytic solution increases on the surface, but the electrochemical reaction of Pb has been conventional. This is considered to be the same as that of the Pb negative electrode.
Therefore, by making the negative electrode 8 have a metal structure as shown in FIG. 4, the suppression of the electrochemical reaction can be suppressed, that is, it can function as a sensor and the chipping of the electrode can also be suppressed. As a result, it is possible to suppress the occurrence of output fluctuations and output abnormalities, and further to extend the life of the sensor.

FIG. 5 is a conceptual diagram illustrating another metal structure on an arbitrary surface of an electrode used in the constant potential oxygen sensor according to the present embodiment.
As shown in FIG. 5, the Pb—Sb alloy has a Pb-based crystal grain containing Sb30 therein, a Pb—Sb-based eutectic structure 50, and a solid solution 60 of Sb (β phase in FIG. 6, the same applies hereinafter). It is preferable to have a metal structure in which is mixed.
The metal structure in FIG. 5 is when the Sb content in the Pb—Sb alloy exceeds 11.1 wt%.

Thus, since the Pb—Sb alloy has a metal structure as shown in FIG. 5, the Pb—Sb alloy functions as a sensor and can suppress chipping of the electrode (negative electrode 8).
This is because an electrochemical reaction of Pb occurs on the surface of the Pb-based crystal grain 18, but Sb exists inside the electrode, so that the metal bond of the crystal grain boundary 20 is strengthened and the inside of the electrode (particularly, the crystal grain boundary 20). In addition, the reaction does not occur on the surface of the solid solution 60 of Sb, but the reaction proceeds on the surface of the Pb—Sb eutectic structure 50 as in the case of the conventional Pb negative electrode. It is thought to do.

  Therefore, by making the negative electrode 8 have a metal structure as shown in FIG. 5, it is possible to suppress the electrochemical reaction, that is, to function as a sensor and to suppress the chipping of the electrode. As a result, it is possible to suppress the occurrence of output fluctuations and output abnormalities, and further to extend the life of the sensor.

  In addition, the workability at the time of manufacturing an electrode falls, so that content of Sb in a Pb-Sb alloy is high. Therefore, when considering this viewpoint, the Sb content in the metal structure shown in FIG. 5 is preferably more than 11.1 wt% and not more than 40.0 wt%, more preferably more than 11.1 wt%. The metal structure shown in FIGS. 3 and 4 (Sb content is not less than 3.5 wt% and not more than 11.1 wt% (more preferably not less than 4.0 wt% and not more than 11.1 wt%)) More preferably, the metal structure shown in FIG. 3 (the Sb content is 3.5 wt% or more and less than 11.1 wt% (more preferably 4.0 wt% or more and 10.0 wt% or less)), more preferably, FIG. 2 (Sb content is 0.5 wt% or more and less than 3.5 wt% (more preferably 0.5 wt% or more and 3.0 wt% or less)).

The “Pb—Sb alloy” is one or two selected from the group consisting of Al, Ag, As, Bi, Cd, Cu, Fe, Mg, Na, Hg, Sn, Zn, S, Se, and Ca. It is preferable that the above elements are contained.
Thus, by including the above elements, it can function as a sensor and can further suppress chipping of the electrode (negative electrode 8).
Moreover, the deterioration of workability due to the inclusion of Sb in Pb can be suppressed by including the above elements.
The element contained in the “Pb—Sb alloy” is preferably As, more preferably As and S.

The electrochemical oxygen sensor is preferably a constant potential oxygen sensor.
A suitable effect can be obtained by using the electrochemical oxygen sensor according to the present invention for such an application.

  The electrolytic solution 7 is not particularly limited as long as it dissolves the electrode and causes the electrochemical reaction. When the electrolytic solution 7 is acidic, a mixed aqueous solution of acetic acid and potassium acetate is preferably used. Further, when the electrolytic solution 7 is alkaline, an aqueous potassium hydroxide solution or an aqueous sodium hydroxide solution is used, and an aqueous potassium hydroxide solution is particularly preferably used.

The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the technical idea.
For example, the symbols 1 to 14 and 16 in FIG. 1 are not limited thereto, and various design changes can be made as long as they have a function as an electrochemical oxygen sensor and the oxygen supply path described above.

Further, the Pb—Sb alloy does not have to have a single type of metal structure in each of the electrodes shown in FIGS. 2 to 5, and may be a mixture of these metal structures.
Furthermore, although the present invention has been described by taking a constant potential oxygen sensor as an example, it can be applied to other applications as long as the sensor has an electrochemical reaction that consumes electrodes.

Next, the present invention will be described more specifically based on examples, but the present invention is not limited thereto.
(Examples 1 to 4)
A constant potential oxygen sensor having a one-year life shown in FIG. 1 was produced. In FIG. 1, the inner lid 1 is made of ABS resin, the protective film 3 is a porous tetrafluoroethylene resin sheet, the diaphragm 4A is a tetrafluoroethylene hexafluoropropylene copolymer film, the catalyst electrode 4B is gold, and the positive electrode The current collector 5 is made of titanium, the positive electrode lead wire 6 and the negative electrode lead wire 14 are made of titanium, and the positive electrode current collector 5 and the positive electrode lead wire 6 and the negative electrode 8 and the negative electrode lead wire 14 are integrated by welding.

  The electrolyte solution 7 is a mixed aqueous solution of acetic acid and potassium acetate (acetic acid: 6 mol / L, potassium acetate: 3 mol / L, pH: 5.05 (25.5 ° C.)), and the negative electrode 8 is made of a Pb—Sb alloy ( The Sb content will be described later), the holder body 9 is made of ABS resin, the outer lid 10 is made of ABS resin, and the holder body 9 and the outer lid 10 are each screwed.

Inner lid 1, O-ring 2, tetrafluoroethylene resin sheet (protective membrane) 3, tetrafluoroethylene hexafluoropropylene copolymer membrane 4A, catalyst electrode 4B, positive electrode current collector 5 are holder main body 9 And the outer lid 10 are pressed by screw tightening to maintain a good contact state. The inner lid 1 functions as a pressing end plate, and air-tightness and liquid-tightness are secured by the O-ring 2.
11 is a perforation for supplying an electrolyte solution to the positive electrode and the diaphragm, and 12 is a perforation for passing the titanium lead wire portion of the positive electrode current collector.

The negative electrode 8 made of the Pb—Sb alloy was produced by the following method.
The content of Sb (antimony) in the Pb—Sb alloy is 0.5 wt% (Example 1), 1.0 wt% (Example 2), 2.0 wt% (Example 3), 3.0 wt% ( Example 4) Each of the Pb raw material and the Sb raw material was adjusted so as to be the same, and after melting at a temperature of 630 ° C. or higher, it was cooled to room temperature to produce a negative electrode 8 having a metal structure as shown in FIG. .

(Examples 5 to 9)
The content of Sb in the Pb—Sb alloy is 4.0 wt% (Example 5), 5.0 wt% (Example 6), 10.0 wt% (Example 7), 11.1 wt% (Example 8). 14.0 wt% (Example 9), the metal Sb raw material is adjusted and melted at a temperature of 630 ° C. or higher, and then cooled to room temperature, and has a metal structure as shown in FIGS. Each of the negative electrodes 8 was produced.
Thereafter, similarly to Example 1, a constant potential oxygen sensor having a one-year life shown in FIG.

(Comparative Example 1)
The negative electrode 8 is not a Pb—Sb alloy, but a Pb metal (metal having a metal structure as shown in FIG. 8), and then the constant potential oxygen sensor having a one-year life shown in FIG. Produced.

[Characteristic comparison]
With respect to each of the produced oxygen sensors (Examples 1 to 9, Comparative Example 1), current-voltage curves in the case of flowing 21% oxygen gas at 25 ° C. were measured and obtained in comparison with FIG. Further, E ₀ was fixed so as to be a constant voltage within the range of E ₁ and E ₂ .
Next, the produced oxygen sensors (Examples 1 to 9, Comparative Example 1) were left at room temperature (25 ° C.) for 360 days, then disassembled, and electrode fragments (lumps) in the electrolytic solution. ) (The value obtained by measuring and averaging the length of the longest side and the length of the shortest side of the lump: the same shall apply hereinafter) was visually confirmed to be present.

In addition, it was evaluated whether the output voltage was stable when the oxygen sensor was left standing and air was passed.
Here, the output voltage is stable as shown in FIG. 7 when the horizontal axis is the measurement time and the vertical axis is the output voltage, and the tendency of the output voltage in the measurement time is plotted as shown in FIG. When drawing a straight line (hereinafter the same).
Table 1 shows the results.

  As can be seen from Table 1, except for Comparative Example 1, it is possible to prevent a part of the electrode from being applied in a lump state. Further, it can be seen that the output voltage is stable in any metal structure shown in FIGS.

(Examples 10 to 13)
The Sb content in the Pb—Sb alloy was 0.5 wt% (Example 10), 1.0 wt% (Example 11), 2.0 wt% (Example 12), 3.0 wt% (Example 13). 2), the Pb raw material and the Sb raw material were prepared, respectively, melted at a temperature of 630 ° C. or higher, and then cooled to room temperature, to prepare a negative electrode 8 having a metal structure as shown in FIG.

(Examples 14 to 18)
The content of Sb in the Pb—Sb alloy is 4.0 wt% (Example 14), 5.0 wt% (Example 15), 10.0 wt% (Example 16), 11.1 wt% (Example 17). 14.0 wt% (Example 18), the metal Sb raw material was adjusted and melted at a temperature of 630 ° C. or higher, and then cooled to room temperature to have a metal structure as shown in FIGS. Each of the negative electrodes 8 was produced.
Thereafter, the electrolytic solution 7 was a potassium hydroxide aqueous solution (9.24 mol / L, pH 15 (26.0 ° C.)), and other than that, in the same manner as in Example 1, each negative electrode 8 had a one-year life shown in FIG. A constant potential oxygen sensor was fabricated.

(Comparative Example 2)
The negative electrode 8 is not a Pb—Sb alloy, but a Pb metal (metal having a metal structure as shown in FIG. 8), and then the electrolytic solution 7 is an aqueous potassium hydroxide solution (9.24 mol / L, pH 15 (26.0 ° C.)). 1) Other than that, a constant potential oxygen sensor having a one-year life shown in FIG.

[Characteristic comparison]
The produced oxygen sensors (Examples 10 to 18 and Comparative Example 2) are allowed to stand at room temperature (25 ° C.) for 360 days, and then disassembled in an electrolytic solution having the same size as that of Example 1. The presence or absence of broken pieces (lumps) of the electrode was visually confirmed. In addition, it was evaluated whether the output voltage was stable when the oxygen sensor was left standing and air was passed.
Table 2 shows the results.

  As can be seen from Table 2, except for Comparative Example 2, it is possible to prevent a part of the electrode from being applied in a lump state. Further, it can be seen that the output voltage is stable in any metal structure shown in FIGS.

(Examples 19 and 20)
A negative electrode 8 containing a small amount of As (less than 0.5 wt%) in the Pb—Sb alloy and the others being the same as in Example 5 was produced (Example 19).
A negative electrode 8 containing a small amount (total: less than 0.5 wt%) of two elements of As and S (sulfur) in the Pb—Sb alloy was the same as in Example 6 (Example 20).
Thereafter, similarly to Examples 5 and 6, a constant potential oxygen sensor having a one-year life shown in FIG. 1 was produced.

The produced oxygen sensors (Examples 19 and 20) were allowed to stand at room temperature (25 ° C.) for 360 days, then disassembled, and electrode fragments in an electrolyte solution having the same size as in Example 1. The presence or absence of (lumps) was confirmed visually. In addition, it was evaluated whether the output voltage was stable when the oxygen sensor was left standing and air was passed.
Table 3 shows the results.

As can be seen from Table 3, in Examples 19 and 20, it is possible to prevent a part of the electrodes from being applied in a lump state. It can also be seen that the output voltage is stable.
Moreover, regarding Examples 5, 6, 19, and 20, the presence or absence of an electrode fragment (lumb) in the electrolyte solution having a size of less than 0.1 mm (hereinafter referred to as a powdery chunk) was visually confirmed.
As a result, Examples 5 and 6 were at the same level, and it was confirmed that the occurrence of powdery lumps was suppressed in the order of Examples 5 (or 6), 19 and 20.
This tendency was the same even when the Sb content in the Pb—Sb alloy was changed and / or the electrolytic solution 7 was an aqueous potassium hydroxide solution.

1 First holder lid (inner lid)
2 O-ring 3 Protective film 4A Diaphragm 4B Catalyst electrode 5 Positive electrode current collector 6 Positive electrode lead wire 7 Electrolyte
8 Negative electrode 9 Holder 10 Second holder lid (outer lid)
DESCRIPTION OF SYMBOLS 11 Electrolyte supply perforation 12 Lead wire perforation 13 Positive electrode collector holding part 14 Negative electrode lead wire 16 Through hole 18 Pb crystal grain 18A Pb crystal grain 20 Crystal grain boundary 20A Crystal grain boundary 30 Sb
45 Positive electrode 50 Pb and Sb eutectic 60 Sb
101 Holder lid

Claims (7)

With a holder,
Comprising an electrode and an electrolyte contained in the holder,
The electrochemical oxygen sensor, wherein the electrode is a Pb-Sb alloy.   2. The electrochemical oxygen sensor according to claim 1, wherein the Pb—Sb alloy has a metal structure having a Pb-based crystal grain containing Sb.   2. The electrochemical oxygen sensor according to claim 1, wherein the Pb—Sb alloy has a metal structure in which a Pb crystal grain containing Sb and a Pb—Sb eutectic structure are mixed.   2. The electrochemical oxygen sensor according to claim 1, wherein the Pb—Sb alloy has a metal structure including only a Pb—Sb eutectic structure.   2. The electrochemical oxygen sensor according to claim 1, wherein the Pb—Sb alloy has a metal structure in which a Pb crystal grain containing Sb, a Pb—Sb eutectic structure, and a solid solution of Sb are mixed.   The Pb-Sb alloy is one or more selected from the group consisting of Al, Ag, As, Bi, Cd, Cu, Fe, Mg, Na, Hg, Sn, Zn, S, Se, and Ca. The electrochemical oxygen sensor according to any one of claims 1 to 5, wherein an element is contained. The electrode is a negative electrode;
The electrochemical oxygen sensor according to claim 1, wherein the electrochemical oxygen sensor is a constant potential oxygen sensor.

Images