JP6955950B2 - Electrochemical oxygen sensor - Google Patents

Description

The present invention relates to an electrochemical oxygen sensor.

An electrochemical oxygen sensor (hereinafter, also referred to as an oxygen sensor) has the advantages of being inexpensive, easy, and capable of operating at room temperature. It is used in a wide range of fields such as detection of oxygen concentration in medical devices such as vessels.

As such an electrochemical oxygen sensor, Patent Document 1 describes an electrochemical oxygen sensor including a cathode, an anode, and an electrolytic solution in which the electrolytic solution contains a chelating agent and the pH of the electrolytic solution is 12. An electrochemical oxygen sensor characterized by the above is disclosed (see [Claim 1]).

Japanese Patent No. 5019141

However, the invention described in Patent Document 1 did not improve 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 an electrochemical oxygen sensor capable of improving the life of an oxygen sensor.

Electrochemical oxygen sensor according to the present invention, holder and a positive electrode housed in the holder, comprising a negative electrode and an electrolyte, wherein the negative electrode includes a main component Sn, the electrolyte, a chelating agent, a basic It contains an inorganic acid salt showing the above or an acetate showing the basicity.

According to the present invention, there is provided an electrochemical oxygen sensor capable of improving the life of the oxygen sensor.

It is a conceptual diagram which shows the cross-sectional structure of the galvanic cell type oxygen sensor which concerns on this embodiment.

Among the electrochemical oxygen sensors according to the present invention, in the present embodiment, a galvanic cell oxygen sensor will be described as a preferable example.
FIG. 1 is a conceptual diagram showing a cross-sectional structure of a galvanic cell type oxygen sensor according to the present embodiment.
The operating principle of the galvanic cell-type oxygen sensor containing a chelating agent as shown in Patent Document 1 is considered to be as follows when described with reference to FIG.
Oxygen that has passed through the diaphragm 4A that selectively permeates oxygen and limits the permeation amount to match the battery reaction is reduced by the catalyst electrode 4B and is connected to the negative electrode 8 via the electrolytic solution 7 as follows. Causes an electrochemical reaction.

Positive ^{_{reaction: O 2 + 4H + + 4e}} - → 2H 2 O
Negative electrode reaction: Sn + 2H ₂ O → SnO ₂ + 4H ⁺ + 4e ⁻
Y ^X- + SnO ₂ + 4H ⁺ → YSn ^4-x + 2H ₂ O: Y is a chelating agent

By this electrochemical reaction, a current corresponding to the oxygen concentration is generated between the catalyst electrode 4B and the negative electrode 8. The current generated by the positive electrode reaction at the catalyst electrode 4B is collected by the positive electrode current collector 5 pressed against the catalyst electrode 4B, guided to the outside by the positive electrode lead wire 6, and passed through the correction resistor 14 and the temperature compensation thermistor 15. It flows to the negative electrode 8. As a result, it is converted into a voltage signal, and a voltage is obtained as an oxygen sensor output. After that, the obtained output voltage is converted into an oxygen concentration by a well-known method and detected as an oxygen concentration.
Sn is oxidized on the surface of the negative electrode 8 _{to generate SnO 2} , and this SnO ₂ is dissolved in the electrolytic solution, whereby new Sn is exposed on the surface, and the oxidation and dissolution are repeated (the oxidation and dissolution are repeated). The electrochemical reaction is continued by a mechanism (so-called negative electrode (Sn) is consumed), and the oxygen concentration is detected.

Here, the chelating agent (Y) is considered to have an action of chelating Sn and dissolving it in the electrolytic solution (hereinafter, referred to as "chelating action").
The present inventors considered that when Sn dissolved in the electrolytic solution reaches saturation as one of the factors that shorten the life of the oxygen sensor, the negative electrode becomes inactive and reaches the life.

Therefore, as a result of diligent studies, the inventors have found that increasing the amount of Sn that can be dissolved in the electrolytic solution, that is, increasing the molar concentration of the chelating agent (Y) in the electrolytic solution, dissolves in the electrolytic solution. It has been found that the life of the oxygen sensor can be improved by delaying the reaching saturation of Sn, and as a result, the present invention has been completed.

The present embodiment will be described in detail below.
In FIG. 1, 1 is the first holder lid (inner lid), 2 is the O-ring, 3 is the protective film for preventing dust and dust from adhering to the diaphragm, or 4A is the diaphragm, and 4B is the diaphragm. Catalyst electrode 5, 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 perforation 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 compensation thermista. The catalyst electrode 4B and the positive electrode current collector 5 form a positive electrode 45. Further, the holder lid 101 is composed of the first holder lid 1 and the second holder lid 10.

As shown in FIG. 1, the galvanic battery-powered oxygen sensor according to the present embodiment is provided on the holder 9, the positive electrode 45, the negative electrode 8 and the electrolytic solution 7 housed in the holder 9, and the positive electrode 45. A through hole that is fixedly attached to or detachably provided on the protective film 4A, the protective film 3 provided on the diaphragm 4A, and the protective film 3 of the holder 9, and serves as an oxygen supply path (space) leading to the diaphragm 4A. It includes a holder lid 101 provided with 16, a correction resistor 14 connected in series with the positive electrode 45 and the negative electrode 8, and a temperature compensation thermista 15.

The electrochemical oxygen sensor according to the present invention is an example of an embodiment as 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 negative electrode 8 contains Sn as a main component, and the electrolytic solution 7 contains a chelating agent and a basic inorganic acid salt or a basic acetate .

Hereinafter, definitions of terms will be described in the present invention.
In the present invention, "containing Sn as a main component" means that the Sn content in the negative electrode 8 is preferably 50% by mass or more, more preferably 70% by mass or more, and further preferably 90% by mass or more (100% by mass). It refers to an alloy of Sn or Sn which is (including mass%) and another metal (hereinafter, the latter is referred to as Sn alloy). The "Sn content (mass%)" referred to here is the ratio of Sn to the entire metal element measured by performing EDX analysis (beam diameter: 1 mm) at an arbitrary portion of the negative electrode 8. (Mass%).
In the present invention, the "chelating agent" has a molecule having a plurality of functional groups that coordinate-bond with a metal ion, and forms (complexes) a complex with the metal ion to inactivate the metal ion. Therefore, in the present invention, those having a single functional group such as phosphoric acid, acetic acid, carbonic acid and salts thereof having weak complexing power are not included in the "chelating agent".

In the present invention, the "salt of a chelating agent" refers to a salt of the chelating agent and a metal (sodium, potassium, etc.) (for example, when the chelating agent is citric acid, tripotassium citrate, etc.).
In the present invention, the "inorganic acid" has a higher solubility (mol / L) in water at 25 ° C. than the chelating agent (preferably 10 times or more, more preferably 100 times or more), and is chlorine or sulfur. , Nitrogen, an acid formed by combining an acid group containing non-metals such as phosphorus with hydrogen.
In the present invention, the "inorganic acid salt" and the "acetate" are salts of the inorganic acid or acetic acid and a metal (sodium, potassium, etc.) (for example, when the inorganic acid is phosphoric acid, hydrogen phosphate dihydrate). (Sodium, etc.).
In the present invention, "molar concentration (mol / L, hereinafter simply referred to as" M ")" refers to the number of moles of solute dissolved in 1 L (liter) of water at 25 ° C.
In the present invention, the "initial pH" refers to the pH of the electrolytic solution immediately after the oxygen sensor is manufactured, the product (including the sample) is shipped, and the product is first used.

In the electrochemical oxygen sensor according to the present invention, the electrolytic solution 7 contains a chelating agent and a basic inorganic acid salt or a basic acetate .
With such a configuration, the molar concentration of the chelating agent can be increased, so that the life of the oxygen sensor can be improved.
The reason for this will be considered below.
Chelating agents generally have a chelating effect and can tolerate the decrease in pH buffering capacity (pKa: how much hydrogen ions are reduced from the initial pH to a sudden pH change). ), But when it is dissolved in water by itself, it often becomes a solution with a low pH (highly acidic pH). Also, depending on the chelating agent, a fairly low pH away from pKa (a pH considerably lower than a pH having a pH buffering capacity (for example, less than pKa-1.00 (pKa1 = 3.13- if the chelating agent is citric acid)). 1.00 = less than 2.13)))), and in such a case, the oxygen concentration measurement is started from the pH range that does not have a chelating effect, so that the electrical characteristics (initial characteristics) immediately after the start of measurement. May get worse.
Therefore, in order to raise the pH of the solution to a desired value, a pH adjuster is dissolved in the solution. As the pH adjuster, a salt of the chelating agent having a chelating action is dissolved. Is preferable for improving the life of the oxygen sensor.

However, since both the chelating agent and the salt of the chelating agent have low solubility in water, there is a limit to improving the molar concentration in the electrolytic solution. In addition, there is a circumstance that the chelating agent does not have a certain pH buffering ability (weak) in the salt of the chelating agent. Therefore, if a large amount of salt of the chelating agent is dissolved in water for the purpose of adjusting the pH, the solubility of the chelating agent in water decreases accordingly. Further, depending on the chelating agent used, it is necessary to dissolve a large amount of salt of the chelating agent in order to raise the pH for the above reason (suppression of deterioration of initial characteristics, etc.). Therefore, such a solution becomes an electrolytic solution having a reduced pH buffering capacity.
In general, the pH of a basic inorganic acid salt and acetate can be adjusted in a state where the chelating action is weak but the solubility of the chelating agent in water is not significantly reduced. Therefore, it is not necessary to reduce or adjust the pH of the chelating agent with a salt, which has a low solubility, greatly reduces the solubility of the chelating agent in water, and has a low pH buffering capacity. The solubility of the agent can be increased, and as a result, the Sn dissolved in the electrolytic solution can be delayed from reaching saturation and the life of the oxygen sensor can be improved.

When the pH of the electrolytic solution is set to the lowest pKa of the chelating agent (pKa1) -1.00 or higher on the acidic solution side, the electrolytic solution is provided with a pH buffering capacity of a plurality of pKa. It is preferable in terms of exerting it. Specifically, when citric acid is used as the chelating agent, the pH of the electrolytic solution is such that each pKa of citric acid at 25 ° C. is pKa1 = 3.13, pKa2 = 4.76, and pKa3 = 6.40. Is preferably 5.40 or more in terms of exerting the pH buffering capacity of pKa3, more preferably 3.76 or more in terms of exerting the pH buffering capacity of pKa2 and pKa3, and pKa1 to pKa3. It is more preferably 2.13 or more in terms of exerting the pH buffering ability of. The upper limit of these pH values is preferably pKa + 1.00. By setting this upper limit value, the pH buffering ability at each pKa can be exhibited, which is preferable.

The pH of the electrolytic solution is preferably a pKa2 value of the chelating agent of −1.00 or higher. Here, pKa2 is the second lowest value among the plurality of pKa values.
As described above, it is considered that the chelating action (complex formation) can be enhanced more than the pKa1 value by setting the pH of the electrolytic solution to the pKa2 value −1.00 or more of the chelating agent. Therefore, the life of the oxygen sensor can be further improved.
Specifically, when citric acid is used as the chelating agent, the pH of the electrolytic solution is preferably 3.76 or higher. The upper limit is the same as described above, and is preferably pKa2 + 1.00.
The pH of the electrolytic solution is a mixture of the salt of the chelating agent (tripotassium citrate if the chelating agent is citric acid) and an inorganic acid salt or acetate , or a mixture of only the inorganic acid salt or only the acetate. It can be adjusted by adjusting the amount of the salt.

The inorganic acid is not particularly limited as long as it has a higher solubility (mol / L) in water at 25 ° C. than the chelating agent and has a pH buffering ability. As the inorganic acids, particularly hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, boric periodate, carbonate, hydrofluoric acid, hydrogen peroxide, phosphoric acid, persulfate, following perchloric acid, hydrogen bromide etc., and Ru acetate may be mentioned as an acid, exemplified similarly to the inorganic acids. Among these, from the viewpoint of suppressing deterioration or the like of the holder with an acid-phosphate, acetate, preferably carbonate, more preferably pH often pH buffering ability is exhibited (often valence of hydrogen ions) phosphate It is preferable to use it.

As described above, the inorganic acid salt and the acetate can increase the solubility of the chelating agent, and as a result, delay the saturation of Sn dissolved in the electrolytic solution and improve the life of the oxygen sensor. It is not particularly limited as long as it can be done. Disodium hydrogen phosphate can be preferably used as the inorganic acid salt.

The material of the chelating agent is not limited as long as it has a chelating action and a pH buffering ability. Examples of the chelating agent include succinic acid, fumaric acid, maleic acid, citric acid, tartaric acid, glutaric acid, adipic acid, malic acid, malonic acid, aspartic acid, glutamic acid, ascorbic acid and the like.
As the chelating agent, it is preferable to use a material having high solubility in water (any of citric acid, tartaric acid and glutamic acid) from the viewpoint of enhancing the chelating action. Among these, citric acid and its salts are highly soluble in water (citric acid (73 g / 100 ml (25 ° C)), trisodium citrate (71 g / 100 ml (25 ° C))) and tripotassium citrate (167 g /). (100 ml (25 ° C)), and citric acid has multiple pHs at which the pH buffering ability is exhibited (high hydrogen ion valences: pKa1 = 3.13, pKa2 = 4.76, pKa3 = 6.40). ) More preferred.
Therefore, by using citric acid as the chelating agent, the solubility in water is high and the pH buffering capacity is also high, so that the life of the oxygen sensor is improved.

The holder 9 is configured to accommodate the positive electrode 45, the negative electrode 8, and the electrolytic solution 7 inside. The material of the holder 9 is not particularly limited, 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 an electric current is generated by the reduction of electrochemical oxygen on the positive electrode, but it can be used for redox such as gold (Au), silver (Ag), platinum (Pt) or titanium (Ti). An active catalyst is preferably used.

The negative electrode 8 is housed in the holder 9.
Although the negative electrode 8 contains Sn as a main component, it may contain a metal other than the metal containing Sn as a main component and other impurities as long as it does not deviate from the gist of the present invention. Examples of metals other than the metal containing Sn as a main component and other impurities include In, Au, Bi, Na, S, Se and Ca.
The negative electrode 8 is preferably a Sn alloy.
Examples of Sn alloys include Sn-Ag alloys, Sn-Cu alloys, Sn-Ag-Cu alloys, and Sn-Sb alloys.
These Sn alloys can suppress the generation of hydrogen during the electrochemical reduction reaction of oxygen in the oxygen sensor.

The Sn alloy is more preferably a Sn—Sb alloy.
Compared with other Sn alloys, Sn—Sb alloys have a denser Sn metal structure and can suppress transformation (phase transition) to α-Sn (also known as tin vest), so that the temperature is low (for example, 0 ° C.). ) Is considered to be possible to drive the sensor. Therefore, it is considered that the decrease in the output stability of the sensor can be suppressed even at a low temperature.

The negative electrode 8 (preferably a Sn alloy, more preferably a Sn—Sb alloy) preferably 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 a negative electrode 8, it is possible to comply with the directive regarding the regulation of the use of specific hazardous substances in the EU (European Union) [the so-called RoHS Directive (Restriction of the Use of Certain Hazardous Substations in Electrical and Electrical). An electrochemical oxygen sensor can be obtained.

The content of Sb in the Sn—Sb alloy is not particularly limited as long as it does not deviate from the gist of the present invention.
In the present invention, the content of Sb in the Sn—Sb alloy is determined by performing an EDX analysis (beam diameter: 1 mm) on an arbitrary portion of the negative electrode 8 to be measured, and measuring the mass of Sb with respect to the entire metal element. %.

More specifically, as shown in FIG. 1, the galvanic cell-type oxygen sensor according to the present embodiment includes 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. The diaphragm 4A provided on the 45, the protective film 3 provided on the diaphragm 4A, the 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 connected in series with the positive electrode 45 and the negative electrode 8, and a temperature compensation thermistor. 15 and. Further, the holder lid 101 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) leading to the protective film 3.

The holder 9 has an opening at the upper portion, and is composed of a screw thread and a screw groove on the outer periphery of the opening, and is provided with a screw portion for screwing the outer lid 10.

The positive electrode 45 is composed of a catalyst electrode 4B that electrochemically reduces oxygen and a positive electrode current collector 5 arranged on the electrolytic solution 7 side thereof. Gold (Au), silver (Ag), platinum (Pt) or the like is usually 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.

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

The diaphragm 4A in the present embodiment is arranged to control the invasion of oxygen so that the amount of oxygen reaching the catalyst electrode 4B does not become too large. The diaphragm 4A preferably allows oxygen to be selectively permeated and the amount of oxygen gas permeated to be limited. The material and thickness of the diaphragm 4A are not particularly limited, but usually, a fluororesin such as ethylene tetrafluoride resin and an ethylene hexafluoride propylene copolymer, a polyolefin such as polyethylene, and the like are used. The diaphragm 4A includes a perforated membrane, a non-porous membrane, and a pore in which a capillary tube called a capillary type is formed.

The protective film 3 in the present embodiment is a porous resin film provided on the diaphragm 4A, which prevents dust and dirt from adhering to the diaphragm 4A or water film from adhering to the diaphragm 4A and allows air (including oxygen) to permeate. Has a function. The material of the protective film 3 is not particularly limited, but a fluororesin such as a tetrafluorinated ethylene resin is usually used.

The inner lid 1 in the present embodiment functions as a pressing end plate of 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. As a result, the protective film 3 and the positive electrode 45 can be fixed to the holder 9 while maintaining airtightness and liquidtightness. The material of the inner lid 1 is not particularly limited, but ABS resin, polypropylene, polycarbonate, fluororesin and the like are usually 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 screw tightening between the holder 9 and the outer lid 10 to maintain airtightness and liquidtightness. You can do it. The material of the O-ring 2 is not particularly limited, but nitrile rubber, silicone rubber, ethylene propylene rubber, fluororesin and the like are usually used.

The outer lid 10 in the present embodiment, together with the O-ring 2 and the inner lid 1, is configured to seal the opening of the holder 9, and is screwed with a screw portion formed on the outer peripheral portion of the opening of the holder 9. As described above, a screw portion is formed on the inner peripheral portion. The material of the outer lid 1 is not particularly limited, but ABS resin, polypropylene, polycarbonate, fluororesin and the like are usually 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, symbols 1 to 16 in FIG. 1 are not limited to these, and various design changes can be made as long as they have a function as an oxygen sensor and the oxygen supply path described above.
Further, in the present embodiment, the galvanic cell type oxygen sensor has been described, but the present invention can also be applied to the 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 type of gas to be detected. In the constant potential type oxygen sensor, when an appropriate constant voltage is applied between the positive electrode and the negative electrode, the current flowing between them and the oxygen gas concentration have a proportional relationship. Similarly, the oxygen gas concentration of an unknown gas can be detected by measuring the voltage.

Next, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.
(Preliminary experiment)
Citric acid was used as the chelating agent, tripotassium citrate was used as the salt of the chelating agent, and disodium hydrogen phosphate was used as the inorganic acid salt. Made.
Further, the transparency of the electrolytic solution was visually evaluated to see if the chelating agent was precipitated in the prepared electrolytic solutions A to H. When the transparency of the electrolytic solution was at the same level as that of pure water, it was judged as "no precipitation (none)", and when it was slightly whiter than pure water, it was judged as "precipitation (presence)".
The results are also shown in Table 1.

表１からわかるように、電界液がリン酸水素二ナトリウムを含む場合、ｐＨ３．０以上で、クエン酸濃度を３．０Ｍまで上げても析出が確認されないことがわかった。なお、リン酸水素二ナトリウムを用いない場合は、クエン酸濃度が最大で１．７２までしか上げることができなかった。

As can be seen from Table 1, when the electric field solution contained disodium hydrogen phosphate, precipitation was not confirmed even if the citric acid concentration was increased to 3.0 M at pH 3.0 or higher. When disodium hydrogen phosphate was not used, the citric acid concentration could only be increased to 1.72 at the maximum.

(Example 1)
The galvanic cell-powered oxygen sensor shown in FIG. 1 was manufactured. In FIG. 1, the inner lid 1 is made of ABS resin, the protective film 3 is a porous ethylene tetrafluoride resin sheet, the diaphragm 4A is an ethylene tetrafluoride hexafluoride copolymer film, and the catalyst electrode 4B is gold and a positive electrode. The 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.

Further, the electrolytic solution 7 is an electrolytic solution H, the negative electrode 8 is made of Sn—Sb alloy (Sb content is 0.3% by mass), the holder 9 is made of ABS resin, the outer lid 10 is made of ABS resin, and the holder 9 The outer lid 10 and the outer lid 10 are each threaded.

The inner lid 1, the O-ring 2, the sheet (protective film) made of ethylene tetrafluoride resin, the diaphragm 4A of the ethylene tetrafluoride hexafluoride copolymer film, the catalyst electrode 4B, and the positive electrode current collector 5 are the holders 9. It is pressed by tightening the screw with the outer lid 10 and a good contact state is maintained. The inner lid 1 functions as a pressing end plate, and the O-ring 2 ensures airtightness and liquidtightness.
Reference numeral 11 is a hole for supplying the electrolytic solution to the positive electrode and the diaphragm, and 12 is a hole for passing the titanium lead wire portion of the positive electrode current collector.

(Comparative Example 1)
The electrolytic solution 7 was electrolytic solution C, and the other galvanic cell-type oxygen sensor shown in FIG. 1 was produced in the same manner as in Example 1.
[Characteristic comparison]
The plurality of oxygen sensors produced were subjected to an accelerated life test by aerating 100% oxygen gas at a temperature of 40 ° C. At 40 ° C., the electrochemical reaction proceeds about twice as much as at room temperature. With 100% oxygen gas aeration, the electrochemical reaction proceeds about five times as much as in the atmosphere. Therefore, with 100% oxygen gas aeration at a temperature of 40 ° C., the life can be determined at a speed about 10 times faster than when left at room temperature in the atmosphere. In this test, the pH of the electrolytic solution is measured at any time, and the time from the start of measurement to the time before the pH of the electrolytic solution suddenly rises is defined as the life (operating time). The life of Comparative Example 1 is 1.0. The life of Example 1 was evaluated as a ratio to the life of Comparative Example 1.
The results are shown in Table 1.

The following can be considered from the results in Table 2.
Example 1 containing phosphate has a 1.5-fold longer lifespan than Comparative Example 1 without phosphate. This is because in Example 1, since the electrolytic solution contains disodium hydrogen phosphate, precipitation is not confirmed even if the citric acid concentration is raised to 3.0 M at pH 3.0 or higher, and the electrolytic solution can be constructed at a high molar concentration. It is thought that it was because of it.

1 1st holder lid (inner lid)
2 O-ring 3 Protective membrane 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)
11 Perforation for electrolyte supply 12 Perforation for lead wire 13 Positive electrode current collector holding part 14 Correction resistor 15 Temperature compensation thermistor 16 Through hole 45 Positive electrode 101 Holder lid

Claims (7)

With the holder
A positive electrode, a negative electrode, and an electrolytic solution housed in the holder are provided.
The negative electrode contains Sn as a main component and contains Sn.
The electrolytic solution is an electrochemical oxygen sensor containing a chelating agent and a basic inorganic acid salt or acetate. The electrochemical oxygen sensor according to claim 1, wherein the electrolytic solution contains a metal salt of phosphoric acid, acetic acid or carbonic acid as the inorganic acid salt or the acetate salt. The electrochemical oxygen sensor according to claim 1 or 2, wherein the electrolytic solution is an acidic solution. The electrochemical oxygen sensor according to any one of claims 1 to 3, wherein the electrolytic solution contains maleic acid, citric acid, tartaric acid, glutaric acid, malic acid, malonic acid, or ascorbic acid. The electrochemical oxygen sensor according to any one of claims 1 to 4, wherein the electrolytic solution contains a salt of a chelating agent. The electrochemical oxygen sensor according to any one of claims 1 to 5, wherein the electrolytic solution has a pH buffering ability. The negative electrode is a Sn-Ag alloy, a Sn-Cu alloy, a Sn-Ag-Cu alloy, or a Sn-Sb alloy, according to any one of claims 1 to 6 in which the Sn content is 50% by mass or more. Described electrochemical oxygen sensor.

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