Electrochemical oxygen sensor

Abstract

Provided is an electrochemical oxygen sensor capable of operating well even in a low-temperature environment.　This electrochemical oxygen sensor is characterized by comprising a positive electrode, a negative electrode, and an electrolytic solution, wherein: the electrolytic solution is an aqueous solution containing at least one chloride selected from among LiCl, MgCl2, and CaCl2, and an electrolyte other than the chloride; and the concentration of the chloride in the electrolytic solution is at least 1 mass%. The electrolytic solution preferably contains a chelating agent, and preferably contains ammonia.

Description

Electrochemical oxygen sensor

[0001] The present invention relates to an electrochemical oxygen sensor that can operate well even in a low-temperature environment.

[0002] Electrochemical oxygen sensors (hereafter referred to as oxygen sensors) have the advantages of being inexpensive, easy to use, and capable of operating at room temperature, and are therefore used in a wide range of applications, such as checking for oxygen deficiencies inside ship holds and manholes, and detecting oxygen concentrations in medical equipment such as anesthesia machines and ventilators.

[0003] In order to improve the properties of such electrochemical cells, various studies have been conducted not only on the positive and negative electrodes but also on the electrolyte solution.

[0004] For example, in an oxygen sensor for measuring the oxygen concentration in the blood of a patient undergoing surgery or other procedures while anesthetized, a specific anesthetic may be reduced, but the potential overlaps with the range of the reduction potential of oxygen, making it impossible to accurately measure the oxygen concentration. To solve this problem, Patent Document 1 proposes an oxygen sensor in which an electrolyte contains a selective adsorptive component that has better adsorption to the electrode than the anesthetic. In the oxygen sensor described in Patent Document 1, the selective adsorptive component acts to suppress the reduction reaction of the anesthetic, thereby preventing the occurrence of the above problem.

[0005] In the oxygen sensor of Patent Document 1, potassium iodide, sodium iodide, lithium chloride, etc. are used as selective adsorptive components, and the above-mentioned problem is solved by including these selective adsorptive components at extremely low concentrations of about 0.01 to about 0.0001 M relative to the total volume of the electrolyte.

[0006] JP 61-82736 A (claims, page 2, lower left column, line 2 to page 3, upper left column, line 2; page 3, upper right column, line 4 to lower right column, line 5; page 4, upper right column, lines 1 to 11, etc.)

[0007] Incidentally, oxygen sensors are expected to be used not only in room temperature environments but also in low temperature environments (for example, low temperature environments down to about -40°C). However, in the case of oxygen sensors that have aqueous electrolytes, there is a problem in that in such low temperature environments, it is difficult to obtain a sufficient output voltage due to the oxygen reduction reaction, making it difficult to measure the oxygen concentration.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electrochemical oxygen sensor that can operate well even in a low-temperature environment.

[0009] The electrochemical oxygen sensor of the present invention includes a positive electrode, a negative electrode, and an electrolyte, and the electrolyte contains LiCl (lithium chloride), MgCl ２ (magnesium chloride) and CaCl ２ (calcium chloride) and an electrolyte other than the chloride, and the concentration of the chloride in the electrolytic solution is 1 mass % or more.

[0010] According to the present invention, it is possible to provide an electrochemical oxygen sensor that can operate well even in a low-temperature environment.

[0011] 1 is a cross-sectional view schematically illustrating an example of an electrochemical oxygen sensor according to the present invention, and a graph showing the relationship between the lithium chloride concentration of the electrolyte and the retention rate of the output voltage at low temperatures relative to the output voltage at 25° C. in the electrochemical oxygen sensors of Examples and Comparative Examples.

[0012] The electrochemical oxygen sensor of the present invention includes a positive electrode, a negative electrode, and an electrolyte. The electrolyte contains LiCl, MgCl ２ and CaCl ２ and other electrolytes, and the concentration of the chloride in the electrolytic solution is 1 mass % or more.

[0013] In oxygen sensors that use an aqueous solution as the electrolyte, in low-temperature environments below 0°C, particularly below -20°C (for example, around -40°C), the electrolyte solidifies, reducing or losing its function as an electrolyte. This causes a decrease in output voltage due to the oxygen reduction reaction, making it difficult to detect the oxygen concentration.

[0014] Therefore, in the oxygen sensor of the present invention, an aqueous solution containing the chloride and other electrolytes, with the chloride concentration being 1% by mass or more, is used as the electrolyte. Since an aqueous solution containing the chloride at the above concentration is inhibited from solidifying even in the low-temperature environment described above, the function of the electrolyte within the oxygen sensor can be maintained satisfactorily. Therefore, the oxygen sensor of the present invention can operate satisfactorily even in a low-temperature environment.

[0015] A cross-sectional view showing a schematic example of an electrochemical oxygen sensor according to the present invention is shown in Fig. 1. The electrochemical oxygen sensor 1 shown in Fig. 1 is an example of a galvanic cell oxygen sensor, which is one embodiment of the electrochemical oxygen sensor according to the present invention.

[0016] The oxygen sensor 1 shown in Fig. 1 has a positive electrode 50, a negative electrode 80, and an electrolyte 90 in a bottomed cylindrical container 20. The container 20 is composed of a container body 21 that holds the electrolyte 90 therein, and a sealing lid 10 for fixing a protective film 40, a diaphragm 60, and the positive electrode 50 to the opening of the container body 21. The sealing lid 10 is composed of a first sealing lid (inner lid) 11 and a second sealing lid (outer lid) 12 for fixing the first sealing lid 11, and has a through-hole 120 for introducing oxygen into the oxygen sensor 1. The sealing lid 10 is attached to the container body 21 via an O-ring 30.

[0017] Inside the container body 21 that contains the electrolyte solution 90, the negative electrode 80 is disposed in a state immersed in the electrolyte solution 90, and a lead portion 81 is formed on the negative electrode 80. The positive electrode 50 is configured by laminating a catalyst layer (catalytic electrode) 51 and a positive electrode current collector 52, and a lead wire 53 is attached to the positive electrode current collector 52. A perforation 70 is provided in the lower part of the container body 21 that holds the electrolyte solution 90 in the container 20, for passing the lead wire 53 attached to the positive electrode current collector 52. Although not shown in FIG. 1 , a perforation is also provided in the lower part of the container body 21, separate from the perforation 70, for supplying the electrolyte solution to the positive electrode 50.

[0018] A compensation resistor 100 and a temperature-compensating thermistor 110 are connected in series between the lead portion 81 of the negative electrode 80 and the lead wire 53 attached to the positive electrode current collector 52, and are housed inside the container body 21. A negative electrode terminal 82 is connected to the lead portion 81 of the negative electrode 80, and a positive electrode terminal 54 is connected to the lead wire 53 attached to the positive electrode current collector 52, and each is led out of the container body 21.

[0019] A diaphragm 60 that selectively allows oxygen to pass through and limits the amount of permeation to match the battery reaction is disposed on the outer surface side of the positive electrode 50, and oxygen from a through-hole 120 provided in the sealing lid 10 is introduced into the positive electrode 50 through the diaphragm 60. In addition, a protective film 40 that prevents dirt, dust, water, and the like from adhering to the diaphragm 60 is disposed on the outer surface side of the diaphragm 60 and is fixed by a first sealing lid 11.

[0020] That is, the first sealing lid 11 functions as a pressing end plate for the protective film 40, the diaphragm 60, and the positive electrode 50. In the oxygen sensor 1 shown in FIG. 1 , a threaded portion is formed on the inner periphery of the second sealing lid 12 so as to be threadedly engaged with a threaded portion formed on the outer periphery of the opening of the container body 21. Then, by screwing the sealing lid 10, the first sealing lid 11 is pressed against the container body 21 via the O-ring 30, and the protective film 40, the diaphragm 60, and the positive electrode 50 can be fixed to the container body 21 while maintaining airtightness and liquid tightness.

[0021] The electrolyte of the oxygen sensor contains chlorides such as LiCl and MgCl ２ and CaCl ２ The compound may contain only one of the above compounds, or may contain two or more of them.

[0022] The chloride concentration in the electrolyte (when the electrolyte contains only one of the three salts as the chloride, this refers to that concentration; when two or more salts are contained, this refers to the total concentration of the salts; the same applies below) may be 1% by mass or more, preferably 2% by mass or more, and more preferably 4% by mass or more. The upper limit of the total chloride concentration in the electrolyte is not particularly limited, but it is desirable that the concentration be such that precipitation of the salt does not occur within the operating temperature range of the oxygen sensor. Since the saturation concentration of the chloride varies depending on the type and concentration of the electrolyte used in the electrolyte, the upper limit of the chloride concentration can be set depending on the composition of the electrolyte. However, since an excessively high chloride concentration tends to slightly decrease the output voltage at low temperatures, it is preferable that the chloride concentration in the electrolyte be lower than the saturation concentration. For example, since the saturation concentration at room temperature of an electrolyte containing a chelating agent such as citric acid is 18% by mass, the concentration can be lower, but is preferably 10.9% by mass or less.

[0023] The electrolytic solution also contains electrolytes other than the chlorides, and examples of such electrolytes include organic acids or salts thereof, such as carboxylic acids, such as acetic acid, acetates (potassium acetate, lead acetate, etc.), citric acid, and citrates (alkali metal salts, etc.); alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; carbonates such as cesium carbonate and cesium hydrogen carbonate; etc. The concentration of the electrolytes other than the chlorides in the electrolytic solution varies depending on the type of electrolyte, but is usually 0.1 to 10 mol / L.

[0024] From the viewpoint of extending the life of the oxygen sensor, it is preferable to use an aqueous solution containing a chelating agent as the electrolyte, and the chelating agent may be an electrolyte other than the chloride. It is presumed that the chelating agent has the effect of chelating the constituent metals of the negative electrode and dissolving them in the electrolyte (hereinafter referred to as "chelating effect"), and this is thought to contribute to extending the life of the oxygen sensor.

[0025] The term "chelating agent" as used herein refers to a molecule (including ions) having multiple coordination sites (coordinating atoms) that form coordinate bonds with metal ions, stabilizing the metal ions by forming complexes with them (complexation), and can be contained in the electrolyte in the form of an acid or its salt that generates the molecule in the solvent that constitutes the electrolyte. Therefore, substances with a single coordination site (coordinating atom), such as phosphoric acid, acetic acid, carbonic acid, and salts thereof, which have weak complexing power, are not included in the term "chelating agent" as used herein.

[0026] Chelating agents generally have a chelating effect as well as pH buffering ability (the ability to maintain the pH of a solution at a nearly constant level even when a small amount of acid or base is added). Specific examples of chelating agents include succinic acid, fumaric acid, maleic acid, citric acid, tartaric acid, glutaric acid, adipic acid, malic acid, malonic acid, aspartic acid, glutamic acid, and salts thereof, and one or more of these may be used.

[0027] In order to enhance the chelating effect, it is more preferable to use a chelating agent that has high solubility in water, specifically, citric acid, tartaric acid, glutamic acid, and their salts. Among these, citric acid and its salts have high solubility in water [citric acid: 73 g / 100 ml (25°C), trisodium citrate: 71 g / 100 ml (25°C), tripotassium citrate: 167 g / 100 ml (25°C)]. Furthermore, citric acid has a large number of dissociable hydrogen atoms, and exhibits pH buffering capacity at multiple pHs (pKa1 = 3.13, pKa2 = 4.75, pKa3 = 6.40). Therefore, when citric acid is used as a chelating agent, its high solubility in water and high pH buffering capacity result in an improved lifespan of the oxygen sensor.

[0028] In order to prevent corrosion of the negative electrode material, the pH of the electrolyte solution is preferably 3 or higher, and more preferably 4 or higher. On the other hand, in order to prevent carbon dioxide from dissolving in the electrolyte solution and deteriorating its properties, the pH of the electrolyte solution is preferably 9 or lower, and more preferably 8 or lower.

[0029] The concentration of the chelating agent in the electrolyte solution is, for example, preferably 1.0 mol / L or more, more preferably 2.3 mol / L or more, particularly preferably 2.5 mol / L or more, and most preferably 2.7 mol / L or more.

[0030] Furthermore, if the metals from the negative electrode dissolved in the electrolyte reach a saturation concentration, oxides of the metals may form, rendering the negative electrode inactive and potentially shortening the life of the oxygen sensor. The saturation concentration is the upper limit of the chelating agent concentration in the electrolyte, and only a corresponding amount of metal ions can be chelated. Therefore, adding a chelating agent in an amount exceeding the saturation concentration to the electrolyte not only does not contribute to extending the life of the oxygen sensor, but also may result in excess chelating agent precipitating and interfering with reactions at the positive or negative electrode, limiting its effectiveness. On the other hand, adding ammonia to the electrolyte together with the chelating agent can increase the saturation concentration of the chelating agent in the electrolyte, thereby increasing the amount of chelating agent in the electrolyte. This delays the saturation of the metals from the negative electrode dissolved in the electrolyte, thereby extending the life of the oxygen sensor.

[0031] The concentration of ammonia in the electrolyte is preferably 0.1 mol / L or more to facilitate the above-mentioned action of ammonia, and more preferably 0.5 mol / L or more to further enhance the above-mentioned action, particularly preferably 1 mol / L or more, and most preferably 2 mol / L or more. Although there is no particular upper limit for the concentration of ammonia in the electrolyte, since ammonia is a compound specified in Appendix 2 of Japan's "Poisonous and Deleterious Substances Control Act," from the viewpoint of safety, the concentration of ammonia in the electrolyte is preferably less than 10 mass%.

[0032] The positive electrode of the oxygen sensor is, for example, one that is composed of a catalytic electrode and a positive electrode current collector, as shown in Fig. 1. The material that makes up the catalytic electrode is not particularly limited as long as it can generate a current by electrochemically reducing oxygen on the positive electrode, but metal elements such as gold (Au), silver (Ag), platinum (Pt), and titanium (Ti) or alloys thereof are preferably used. The catalytic electrode may be composed of a single material, or may be a laminate of different materials or a functionally gradient material whose composition changes in the thickness direction.

[0033] The negative electrode of the oxygen sensor is not particularly limited, but can be made of, for example, lead (Pb), zinc (Zn), antimony (Sb), tin (Sn), or an alloy thereof.

[0034] Examples of Sn alloys include Sn—Ag alloys, Sn—Cu alloys, Sn—Ag—Cu alloys, and Sn—Sb alloys from the viewpoint of corrosion resistance, but alloys containing metal elements such as Al, Bi, Fe, Mg, Na, Zn, Ca, Ge, In, Ni, and Co may also be used.

[0035] As shown in Figure 1, it is preferable to place a diaphragm on the outer surface of the positive electrode of the oxygen sensor to control oxygen intrusion so that too much oxygen does not reach the catalytic electrode. The diaphragm is preferably one that is selectively permeable to oxygen while limiting the amount of oxygen gas that permeates. There are no particular restrictions on the material or thickness of the diaphragm, but typically, fluororesins such as polytetrafluoroethylene and tetrafluoroethylene-hexafluoropropylene copolymer; polyolefins such as polyethylene; etc. are used. The diaphragm can be a porous membrane, a non-porous membrane, or even a membrane with holes formed with capillaries, known as a capillary type.

[0036] Furthermore, in order to protect the diaphragm, it is preferable to place a protective film made of a porous resin film on the diaphragm, as shown in Figure 1. The protective film is not particularly limited in material or thickness as long as it can prevent adhesion of dirt, dust, water, etc. to the diaphragm and has the function of allowing air (including oxygen) to permeate, but typically a fluororesin such as polytetrafluoroethylene is used.

[0037] The container body 21 of the oxygen sensor 1 can be made of, for example, acrylonitrile-butadiene-styrene (ABS) resin. The sealing lid 10 (first sealing lid 11 and second sealing lid 12) placed at the opening of the container body 21 can be made of, for example, ABS resin, polypropylene, polycarbonate, fluororesin, or the like.

[0038] Furthermore, the O-ring 30 interposed between the container body 21 of the container 20 and the sealing lid 10 (first sealing lid 11) is pressed and deformed when the container body 21 and the second sealing lid 12 are screwed together, thereby maintaining the airtightness and liquid-tightness of the oxygen sensor 1. There are no particular restrictions on the material of the O-ring, but typically, nitrile rubber, silicone rubber, ethylene propylene rubber, fluororesin, etc. are used.

[0039] While the present invention has been described above using a galvanic cell oxygen sensor as an example of one embodiment of the electrochemical oxygen sensor of the present invention, the electrochemical oxygen sensor of the present invention is not limited to the above embodiment and various modifications are possible within the scope of the technical concept. Furthermore, the oxygen sensor shown in Figure 1 can also be modified in various ways as long as it has the function of an oxygen sensor and the oxygen supply path described above.

[0040] The electrochemical oxygen sensor of the present invention can also be configured as a constant-potential oxygen sensor. A constant-potential oxygen sensor is a sensor in which a constant voltage is applied between the positive and negative electrodes, and the applied voltage is set depending on the electrochemical characteristics of each electrode and the type of gas to be detected. In a constant-potential oxygen sensor, when an appropriate constant voltage is applied between the positive and negative electrodes, the current flowing between them is proportional to the oxygen gas concentration. Therefore, if the current is converted into a voltage, the oxygen gas concentration of an unknown gas can be detected by measuring the voltage, just like a galvanic cell oxygen sensor.

[0041] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0042] Example 1 Preparation of Electrolyte Solution Citric acid monohydrate, potassium acetate, and lithium chloride were dissolved in water, and ammonia water was added to prepare an electrolyte solution. The molar concentrations of the components in the electrolyte solution were citric acid: 2.5 mol / L, potassium acetate: 1.0 mol / L, ammonia: 3.1 mol / L, and lithium chloride: 1.9 mol / L. The proportion of lithium chloride in the total amount of the electrolyte solution was 6.1 mass%.

[0043] <Assembly of oxygen sensor> Using the above-described electrolyte, a galvanic cell-type oxygen sensor having the configuration shown in Fig. 1 was assembled. The sealing lids 10 (first sealing lid 11 and second sealing lid 12) were also formed of ABS resin, similar to the container body 21. A porous polytetrafluoroethylene sheet was used for the protective film 40, and a tetrafluoroethylene-hexafluoropropylene copolymer film was used for the diaphragm 60.

[0044] The catalyst layer (catalytic electrode) 51 of the positive electrode 50 was made of gold, and the positive electrode current collector 52 and lead wire 53 were made of titanium, and the positive electrode current collector 52 and lead wire 53 were welded together. The negative electrode 80 was made of a Sn—Sb alloy (Sb content: 5% by mass).

[0045] A 39 Ω fixed resistor (correction resistor) 100 and a temperature-compensating thermistor 110 having a resistance value of 500 Ω at 25° C. were connected in series to form a resistance element (combined resistance at 25° C.: 539 Ω), which was connected to the positive electrode lead wire 53 and the negative electrode lead portion 81. Furthermore, the positive electrode terminal 54 and the negative electrode terminal 81 were led out of the positive electrode lead wire 53 and the negative electrode lead portion 81, respectively, to the outside of the container body 21, thereby enabling detection of the oxygen concentration from the output voltage.

[0046] In the assembled oxygen sensor 1, the first sealing lid 11, the O-ring 30, the polytetrafluoroethylene sheet protective film 40, the tetrafluoroethylene-hexafluoropropylene copolymer diaphragm 60, the catalytic electrode 51, and the positive electrode current collector 52 were pressed by fastening the container body 21 and the second sealing lid 12 with screws, thereby maintaining a good sealing state.

[0047] Example 2 An oxygen sensor was assembled in the same manner as in Example 1, except that the concentration of lithium chloride in the electrolyte was changed to 1.5 mass %.

[0048] Example 3 An oxygen sensor was assembled in the same manner as in Example 1, except that the concentration of lithium chloride in the electrolyte was changed to 3 mass %.

[0049] Example 4 An oxygen sensor was assembled in the same manner as in Example 1, except that the concentration of lithium chloride in the electrolyte was changed to 8.7 mass %.

[0050] Example 5 An oxygen sensor was assembled in the same manner as in Example 1, except that the concentration of lithium chloride in the electrolyte was changed to 10.9 mass %.

[0051] Comparative Example 1 An electrolyte solution was prepared and an oxygen sensor was assembled in the same manner as in Example 1, except that lithium chloride was not added. The molar concentrations in the electrolyte solution were citric acid: 2.5 mol / L, potassium acetate: 1.0 mol / L, and ammonia: 3.1 mol / L.

[0052] <Evaluation of output voltage at low temperature> Each oxygen sensor of the example and comparative example was left standing in the atmosphere at a temperature of 25°C, and the output voltage at 25°C was measured. Next, the ambient temperature was lowered to -20°C, and each oxygen sensor was left standing for 3 hours, after which the output voltage at -20°C was measured. Furthermore, the ambient temperature was lowered to -25°C, and each oxygen sensor was left standing for 3 hours, after which the output voltage at -25°C was measured.

[0053] For the oxygen sensors of Example 3 and Comparative Example 1, after measurement at -25°C, the ambient temperature was further lowered to -30°C and left to stand for 3 hours, after which the output voltage was measured at -30°C.

[0054] In the oxygen sensor of Example 5, when the output voltage was measured at low temperature, it was found that a small amount of precipitate, presumably lithium chloride, had precipitated in the electrolyte.

[0055] The output voltages of each oxygen sensor at each measurement temperature are shown in Table 1. The ratio of the output voltage at low temperatures to the output voltage at 25°C (output voltage maintenance rate) was also calculated, and the relationship between the concentration of lithium chloride in the electrolyte and the maintenance rate was determined. The results are shown in Figure 2.

[0056]

[0057] As shown in Table 1, the oxygen sensors of Examples 1 to 5, which had electrolytes containing a specific chloride (lithium chloride) at an appropriate concentration, had output voltages at room temperature (25°C) equivalent to those of Comparative Example 1, which had electrolytes that did not contain the chloride. However, the output voltage of the oxygen sensor of Comparative Example 1 decreased significantly as the temperature of the measurement environment decreased, whereas the output voltage of the oxygen sensors of Examples 1 to 5 decreased only slightly even when the environmental temperature decreased, and their characteristics were well maintained. Therefore, it became clear that the oxygen sensors of Examples 1 to 5 could operate better than the oxygen sensor of Comparative Example 1, even in low-temperature environments.

[0058] Furthermore, the results shown in FIG. 2 reveal that the retention rate of the output voltage at low temperatures relative to the output characteristics at 25° C. in the oxygen sensor increases as the concentration of the specific chloride (lithium chloride) in the electrolyte increases, but once a certain concentration is reached, the effect of improving the retention rate of the output voltage saturates.

[0059] The present invention can be implemented in other forms without departing from the spirit of the present invention. The embodiments disclosed in this application are merely examples, and the present invention is not limited to these embodiments. The scope of the present invention shall be interpreted in accordance with the appended claims rather than the description in the above specification, and all modifications within the scope of the claims are included in the scope of the claims.

[0060] The electrochemical oxygen sensor of the present invention can be used in the same applications as conventionally known electrochemical oxygen sensors. Specific applications include exhaust gas measurement devices in factories; oxygen deficiency prevention systems and oxygen concentration meters in underground and other construction sites; biotechnology equipment such as oxygen incubators and anaerobic bacteria culture devices; ventilators, anesthesia machines, oxygen concentrators, and incubators in medical settings; food storage in food factories; and oxygen measurement in educational facilities. The electrochemical oxygen sensor of the present invention can also operate well in low-temperature environments, making it particularly useful for applications requiring measurements in such environments.

[0061] 1 Electrochemical oxygen sensor 10 Sealing lid 11 First sealing lid (inner lid) 12 Second sealing lid (outer lid) 20 Container 21 Container body 30 O-ring 40 Protective film 50 Positive electrode 51 Positive electrode main body (catalytic electrode) 52 Positive electrode current collector 53 Positive electrode lead wire 54 Positive electrode terminal 60 Diaphragm 70 Hole for lead wire 80 Negative electrode 81 Negative electrode lead portion 82 Negative electrode terminal 90 Electrolyte 100 Correction resistor 110 Temperature compensation thermistor 120 Through hole

Claims

1. An electrochemical oxygen sensor comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is LiCl, MgCl ２ and CaCl ２ and an electrolyte other than the chloride, wherein the concentration of the chloride in the electrolyte is 1 mass % or more.

2. The electrochemical oxygen sensor according to claim 1, wherein the concentration of the chloride in the electrolyte is 18 mass % or less.

3. The electrochemical oxygen sensor according to claim 1, wherein the electrolyte contains an organic acid or a salt thereof.

4. The electrochemical oxygen sensor according to claim 1, wherein the electrolyte contains a chelating agent.

5. The electrochemical oxygen sensor according to claim 4, wherein the content of said chelating agent in said electrolyte is 1.0 mol / L or more.

6. The electrochemical oxygen sensor according to claim 4 or 5, wherein the electrolyte contains ammonia.

7. The electrochemical oxygen sensor according to claim 6, wherein the content of said ammonia in said electrolyte is 0.1 mol / L or more.

8. The electrochemical oxygen sensor according to claim 1, wherein the pH of the electrolyte is 9 or less.

9. The electrochemical oxygen sensor according to claim 1, wherein the negative electrode contains Sn or an Sn alloy.

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