JP6707431B2 - Galvanic battery oxygen sensor - Google Patents

Description

The present invention relates to a galvanic battery type oxygen sensor.

The galvanic battery oxygen sensor (hereinafter also referred to as the oxygen sensor) has the advantages of being inexpensive, convenient, and capable of operating at room temperature. It is used in a wide range of fields such as the detection of oxygen concentration in medical devices such as respiratory organs.

As an electrochemical oxygen sensor including such a galvanic cell type oxygen sensor, Patent Document 1 discloses that in an electrochemical oxygen sensor including a cathode, an anode, and an electrolytic solution, the electrolytic solution contains a chelating agent. An electrochemical oxygen sensor" (claim [1]) is disclosed. Further, Patent Document 1 discloses that, as an effect of the invention, "the present invention can provide an electrochemical oxygen sensor having a fast response speed." (paragraph [0015]).

WO2009/069749

However, when the chelating agent described in Patent Document 1 is used in the electrolytic solution, there is a limit to the improvement of the life of the oxygen sensor.
The present invention has been made to solve the above problems, and an object of the present invention is to provide a galvanic battery type oxygen sensor that has a high response speed and can also have a long life as an oxygen sensor.

The galvanic cell oxygen sensor according to the present invention includes a holder, a positive electrode, a negative electrode, and an electrolytic solution housed in the holder, and the electrolytic solution contains citric acid.

According to the present invention, there is provided a galvanic battery type oxygen sensor which has a high response speed and can also have a long life as an oxygen sensor.

It is a conceptual diagram which shows the cross-section of the galvanic cell type oxygen sensor which is one suitable embodiment of this invention. It is a conceptual diagram for demonstrating that output voltage stabilizes.

The configuration and operational effects of the present invention will be described with a technical idea. However, the action mechanism includes estimation, and the correctness thereof does not limit the present invention. Further, among the constituent elements in the following embodiments, the constituent elements that are not described in the independent claims showing the highest concept are described as arbitrary constituent elements.

The present inventor has found that the life as an oxygen sensor matches the content (concentration) of the chelating agent contained in the electrolytic solution.
Therefore, in order to extend the life of the oxygen sensor containing the chelating agent in the electrolytic solution, the present inventor should dissolve the chelating agent in the electrolytic solution as much as possible (that is, use a chelating agent having high solubility). ) Is important, and the present invention has been completed.

Hereinafter, as a preferred embodiment of the present invention (hereinafter referred to as “the present embodiment”), a galvanic cell type oxygen sensor will be specifically described.
The galvanic cell oxygen sensor is an electrochemical oxygen sensor having a resistor connected between a positive electrode and a negative electrode. Specifically, in the galvanic cell type oxygen sensor, a current generated by electrochemical reduction of oxygen on the positive electrode is converted into a voltage at the resistance, and the current converted into the voltage and the oxygen concentration have a proportional relationship. Therefore, the oxygen concentration in the unknown gas can be detected by measuring the voltage.

FIG. 1 is a conceptual diagram showing a cross-sectional structure of a galvanic cell type oxygen sensor according to the present embodiment.
In FIG. 1, 1 is a first holder lid (interior lid), 2 is an O-ring, 3 is a protective film for preventing dust and dust from adhering to a diaphragm, or a water film is attached, 4A is a diaphragm, and 4B is a diaphragm. A catalyst electrode, 5 is a positive electrode current collector, 6 is a positive electrode lead wire, 7 is an electrolytic solution, 8 is a negative electrode, 9 is a holder, 10 is a second holder lid (outer lid), 11 is a hole for supplying an electrolytic solution, 12 Is a hole for a lead wire, 13 is a positive electrode current collector holding portion, 14 is a correction resistor, and 15 is a temperature compensating thermistor. The positive electrode 45 is composed of the catalyst electrode 4B and the positive electrode current collector 5. The first holder lid 1 and the second holder lid 10 form a holder lid 101.

The galvanic cell oxygen sensor according to the present invention is, for example, an embodiment shown in FIG. 1, and includes a holder 9, a positive electrode 45, a negative electrode 8 and an electrolytic solution 7 housed in the holder 9. The electrolytic solution 7 contains citric acid.

The holder 9 is configured to accommodate the positive electrode 45, the negative electrode 8 and the electrolytic solution 7 therein. The material of the holder 9 is not particularly limited as long as there is no problem such as corrosion by the electrolytic solution 7 described later, but ABS resin is preferably used.
The positive electrode 45 is housed in the holder 9. The material of the positive electrode 45 is not particularly limited as long as a current is generated by electrochemical reduction of oxygen on the positive electrode, but gold (Au), silver (Ag), platinum (Pt) or titanium (Ti) is preferably used. Be done.

The electrolytic solution 7 is contained in the holder 9. Further, the electrolytic solution 7 contains citric acid.
The term “citric acid” as used in the present invention does not depart from the gist of the present invention (providing a galvanic cell type oxygen sensor which has a fast response speed and can also have a long life as an oxygen sensor, the same applies hereinafter). In addition to citric acid (the chemical formula C(OH)(CH ₂ COOH) ₂ COOH, an organic compound contained in citrus fruits and one of the hydroxy acids), its hydrate (citric acid monohydrate) Etc.) and salts of citric acid or hydrates thereof (sodium citrate, sodium citrate dihydrate, etc.).
In addition, the term “electrolytic solution contains citric acid” in the present invention means that the electrolytic solution 7 may contain citric acid without departing from the gist of the present invention. The type and concentration of citric acid in the electrolytic solution 7 are not particularly limited. Further, the electrolytic solution 7 may contain a component other than citric acid as long as it does not depart from the gist of the present invention.

Since the galvanic cell type oxygen sensor according to the present invention contains citric acid in the electrolytic solution, the response speed becomes faster due to the chelating agent effect, and the life as an oxygen sensor can be improved. That is, citric acid has higher solubility in water than other chelating agents described in Patent Document 1 (citric acid: 73 g/100 ml (20° C.), citric acid monohydrate: 163 g/100 ml (20° C.). , Sodium citrate: 42.5 g/100 ml (25° C.), sodium citrate dihydrate: 77 g/100 ml (20° C.), etc., so that the chelating agent can be dissolved in the electrolytic solution as much as possible. .. Therefore, since the content (concentration) of the chelating agent contained in the electrolytic solution can be made higher than that of other chelating agents (for example, EDTA/tetrasodium salt: 60 g/100 ml (22°C)), it can be used as an oxygen sensor. The life can be improved.

The concentration of citric acid contained in the electrolytic solution is preferably 0.001 mol/L or more, and more preferably 0.005 mol/L or more, from the viewpoint of increasing the response speed.
When strict requirements are required, such as when the galvanic cell oxygen sensor according to the present invention is applied to a medical device, the concentration of citric acid is preferably 0.1 mol/L or more, and 1.0 mol/L. It is more preferably L or more.
On the other hand, the upper limit value of the concentration of citric acid contained in the electrolytic solution is such that the higher the concentration of citric acid is, the longer the life as an oxygen sensor can be. (Concentration).

The citric acid preferably includes citric acid monohydrate.
Since citric acid monohydrate has higher solubility in water than other types of citric acid, it can be more dissolved in the electrolytic solution. Therefore, the life of the oxygen sensor can be further improved.

The negative electrode 8 is housed in the holder 9.
The material of the negative electrode 8 is not particularly limited without departing from the gist of the present invention. For the negative electrode 8, Cu, Fe, Ag, Ti, Al, Mg, Zn, Ni, Sn, and alloys thereof (hereinafter referred to as negative electrode metal) can be used.
Further, the material of the negative electrode 8 may contain a metal other than the negative electrode metal or other impurities, without departing from the scope of the present invention. Examples of metals and other impurities other than the negative electrode metal include In, Au, Bi, Na, S, Se and Ca.

The negative electrode 8 is preferably a Sn alloy, more preferably a Sn-Sb alloy.
The Sn alloy can suppress the generation of hydrogen during the electrochemical oxygen reduction reaction in the oxygen sensor.
Further, the Sn-Sb alloy is considered to have a higher metal binding force between metal crystals than other Sn alloys, and therefore the response speed is increased by the effect of citric acid contained in the electrolytic solution 7, and Even if the life of the oxygen sensor is improved, it is possible to suppress the decrease in output stability due to the negative electrode 8.

It is preferable that the negative electrode or the Sn—Sb alloy contains substantially no lead.
The term “substantially free of lead” as used herein means that the content of Pb contained in the negative electrode 8 is less than 1000 ppm. By using such an Sn-Sb alloy, the EU (European Union) directive on the use of specific hazardous substances [also known as the RoHS directive (Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic)]. A possible electrochemical oxygen sensor can be obtained.

The content of the metal (Sb) other than Sn in the Sn—Sb alloy is not particularly limited as long as it does not depart from the gist of the present invention.
In the present invention, the content of the metal (Sb) other than Sn in the Sn-Sb alloy is measured by performing EDX analysis (beam diameter: 1 mm) on an arbitrary position of Sn-Sb to be measured. It is the weight% of Sb with respect to the whole metal element (Sn+Sb+“metals other than Sn and Sb and other impurities”=100%).

More specifically, the galvanic cell type oxygen sensor according to the present embodiment is, as shown in FIG. 1, a holder 9, a positive electrode 45, a negative electrode 8 and an electrolytic solution 7 housed in the holder 9, and the positive electrode. 45A, a diaphragm 4A, a protective film 3 provided on the diaphragm 4A, a first holder lid (inner lid) 1 for fixing the protective film 3, the holder 9 and the inner lid 1. An O-ring 2 arranged between the two, a second holder lid (outer lid) 10 for fixing the inner lid 1, a correction resistor 14 and a temperature compensating thermistor serially connected to the positive electrode 45 and the negative electrode 8. 15 and. Further, the holder lid 101, which is composed of the outer lid 10 and the inner lid 1, is provided with a through hole 16 serving as an oxygen supply path (space) communicating with the protective film 3.

The holder 9 has an opening in the upper part, and a screw portion for screwing the outer lid 10 is provided on the outer periphery of the opening, the screw thread and the screw groove being formed.

The positive electrode 45 is composed of a catalyst electrode 4B that electrochemically reduces oxygen and a positive electrode current collector 5 that is arranged on the electrolyte 7 side. Usually, gold (Au), silver (Ag), platinum (Pt), or the like is used as the catalyst electrode 4B, and titanium (Ti) is usually used as the positive electrode current collector 5. The material is not limited to these.

Below the positive electrode current collector 5, a positive electrode current collector holding portion 13 that holds the positive electrode current collector 5 is provided.
The positive electrode collector holding portion 13 is provided with a hole 11 for supplying an electrolytic solution to the positive electrode 45 and a hole 12 for passing the positive electrode lead wire 6.
The material of the positive electrode collector holding portion 13 is not particularly limited, but usually ABS resin is used.

The diaphragm 4A in the present embodiment is arranged to control the invasion of oxygen so that the oxygen reaching the catalyst electrode 4B does not become too large. It is preferable that the diaphragm 4A be capable of selectively permeating oxygen and limiting the amount of oxygen gas permeation. The material of the diaphragm 4A is not particularly limited, but usually, a fluororesin such as tetrafluoroethylene resin or tetrafluoroethylene hexafluoropropylene copolymer, or a polyolefin such as polyethylene is used.

The protective film 3 in the present embodiment is a porous resin film provided on the diaphragm 4A and has a function of preventing dust, dust, or water film from adhering to the diaphragm 4A. The material of the protective film 3 is not particularly limited, but a fluororesin such as tetrafluoroethylene resin is usually used.

The inner lid 1 in this embodiment functions as a pressing end plate for the protective film 3 and the positive electrode 45, and is pressed against the holder 9 via the O-ring 2 by screwing the holder 9 and the outer lid 10. Thus, the protective film 3 and the positive electrode 45 can be fixed to the holder 9 while maintaining the airtightness and the liquidtightness. The material of the inner lid 1 is not particularly limited, but normally ABS resin, polypropylene, polycarbonate, fluororesin or the like is used.

The O-ring 2 in the present embodiment is arranged between the holder 9 and the inner lid 1, and is pressed and deformed by screwing the holder 9 and the outer lid 10 to maintain airtightness and liquid tightness. You can do it. The material of the O-ring 2 is not particularly limited, but normally, nitrile rubber, silicone rubber, ethylene propylene rubber, fluororesin or the like is used.

The outer lid 10 in the present embodiment is configured to seal the opening of the holder 9 together with the O-ring 2 and the inner lid 1, and is screwed with the screw portion formed on the outer peripheral portion of the opening of the holder 9. Thus, the threaded portion is formed on the inner peripheral portion. The material of the outer lid 1 is not particularly limited, but normally ABS resin, polypropylene, polycarbonate, fluororesin or the like is used.

The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of its technical idea.
For example, the symbols 1 to 15 in FIG. 1 are not limited to this, and various designs can be changed as long as the function as an oxygen sensor and the oxygen supply path described above are provided.
Further, although the present embodiment has been described using the galvanic cell type oxygen sensor, the present invention can also be applied to a constant potential type oxygen sensor.
The constant potential oxygen sensor is a sensor that applies a constant voltage between the positive electrode and the negative electrode, and the applied voltage is set according to the electrochemical characteristics of each electrode and the gas species to be detected. In a constant-potential oxygen sensor, when an appropriate constant voltage is applied between the positive electrode and the negative electrode, the current flowing between them has a proportional relationship with the oxygen gas concentration. Similarly, the oxygen gas concentration of an unknown gas can be detected by measuring the voltage.

Next, the present invention will be described more specifically based on examples, but the present invention is not limited thereto.
(Examples 1 to 4)
The galvanic cell type oxygen sensor 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, and the catalyst electrode 4B is gold (Au). ), the positive electrode current collector 5 is made of titanium, the positive electrode lead wire 6 is made of titanium, and the positive electrode current collector 5 and the positive electrode lead wire 6 are welded and integrated.

In addition, the negative electrode 8 is a Sn-5.0Sb alloy (the left number is, as described above, the weight% of Sb in the Sn alloy (Sn + other metal + "metal other than Sn and other metal and other impurities" = 100). %), and the electrolyte solution 7 is (Example 1) citric acid, (Example 2) citric acid monohydrate, or (Example 3) a mixture of citric acid and citric acid monohydrate (mixing ratio= 1:1), the holder body 9 is made of ABS resin, and the outer lid 10 is made of ABS resin, and the holder body 9 and the outer lid 10 are respectively threaded.
Each of the electrolytic solutions ((Example 1) citric acid, (Example 2) citric acid monohydrate, (Example 3) mixture of citric acid and citric acid monohydrate) was used in the electrolytic solution. Was the saturation concentration.

The inner lid 1, the O-ring 2, the tetrafluoroethylene resin sheet (protective film) 3, the diaphragm 4A of a tetrafluoroethylene hexafluoropropylene copolymer film, the catalyst electrode 4B, and the positive electrode current collector 5 are the holder body 9 The outer cover 10 and the outer lid 10 are screwed to be pressed to maintain a good contact state. The inner lid 1 functions as a pressing end plate, and the O-ring 2 ensures air tightness and liquid tightness.
Reference numeral 11 is a hole for supplying an electrolytic solution to the positive electrode and the diaphragm, and 12 is a hole for passing a titanium lead wire portion of the positive electrode current collector.

(Comparative Example 1)
A 1-year-old galvanic cell type oxygen sensor shown in FIG. 1 was manufactured as in Example 1 except that EDTA.4 sodium salt was used as the chelating agent, and the concentration was saturated in the electrolyte solution.

[Characteristic comparison]
With respect to the plurality of galvanic battery type oxygen sensors thus produced, "90% response speed" was evaluated two months after the production. The 90% response speed is obtained by stabilizing the output of each sensor in the air (oxygen concentration 21%), and then aeration of 100% oxygen is passed to the sensor whose output is stable. The time required for the output to change by 90% was measured by setting the output (saturated output) that can be generated by aeration of oxygen of 100% as 100%. In this evaluation test, the output after 30 minutes of ventilation was taken as the saturated output. The results obtained by the above evaluation test are shown in Table 1. In Table 1, ◯ means that the 90% response speed is less than 15 seconds, Δ means that the response speed is 15 seconds or more and less than 60 seconds, and x means that the response speed is 60 seconds or more. means.

Further, the plurality of galvanic battery type oxygen sensors prepared above were left for 360 days in the same environment at room temperature (25° C.), and it was evaluated whether or not the output voltage of the oxygen sensor was stable. Note that the output voltage is stable here as shown in FIG. 2 when the tendency of the output voltage at the measurement time is plotted with the horizontal axis as the measurement time and the vertical axis as the output voltage as shown in FIG. When drawing a straight line.

Further, an accelerated life test was conducted by passing 100% oxygen gas at a temperature of 40°C. At 40°C, the electrochemical reaction progresses about twice as much as at room temperature and about 5 times as much as 100% oxygen gas in the atmosphere, so it is possible to judge the life at about 10 times the speed when left at room temperature in the atmosphere. .. In the accelerated life test, the life of Comparative Example 1 was set to 1.0, and the Example was evaluated by the multiple thereof.
The results are shown in Table 1.

As can be seen from Table 1, in the galvanic cell type oxygen sensors of Examples 1 to 3, the response speed is fast and the output voltage is stable, and further, in the life, Example 1 is more than 1. It was confirmed that the life was improved twice, that in Example 3 was 1.8 times, and that in Example 2 was 2.5 times.

1 1st holder lid (middle lid)
2 O-ring 3 protective film 4A diaphragm 4B catalyst electrode 5 positive electrode current collector 6 positive electrode lead wire 7 electrolytic solution
8 Negative electrode 9 Holder 10 Second holder lid (outer lid)
11 Perforation for Electrolyte Supply 12 Perforation for Lead Wire 13 Positive Electrode Current Collector Holding Section 14 Correction Resistor 15 Temperature Compensating Thermistor 16 Through Hole 45 Positive Electrode 101 Holder Lid

Claims (5)

With a holder,
Comprises a positive electrode, a negative electrode and an electrolytic solution housed in the holder,
The negative electrode is a Sn-Sb alloy,
A galvanic cell type oxygen sensor in which the electrolytic solution contains citric acid. The galvanic battery type oxygen sensor according to claim 1, wherein the citric acid includes citric acid monohydrate. The galvanic cell type oxygen sensor according to claim 1, wherein the concentration of citric acid contained in the electrolytic solution is 0.001 mol /L or more. The galvanic cell type oxygen sensor according to claim 1, wherein the Sn—Sb alloy does not substantially contain lead. The positive electrode has a catalytic electrode for electrochemically reducing oxygen,
The galvanic cell type oxygen sensor according to claim 1, wherein the catalyst electrode contains gold, silver, or platinum.

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