Electrochemical gas sensor and electrochemical gas measurement method

Abstract

To provide an electrochemical gas sensor which exhibits stable and highly responsive output characteristics over a prolonged period of time.SOLUTION: An electrochemical gas sensor 10 is provided, comprising a casing 11 containing an electrolyte, and an anode 30 and cathode 35 arranged with the electrolyte interposed therebetween. The anode 30 contains iron or an iron alloy, and the electrolyte contains at least either of chloride and sulfate.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electrochemical gas sensor and the like. [Background technology]

[0002] In electrochemical gas sensors such as a galvanic cell gas sensor, for example, an anode and a cathode are arranged with an electrolyte stored in a casing, and when the gas to be measured is reduced at the cathode, a current flowing between the electrodes is detected via lead members connected to the anode and the cathode. This type of electrochemical gas sensor has the advantages of being simple in configuration and operable at room temperature, and is therefore used, for example, in oxygen sensors for checking oxygen deficiency conditions.

[0003] Lead (Pb) has been used as an anode material for many years. On the other hand, in order to avoid the use of harmful substances such as lead (Pb), electrochemical sensors using anodes other than lead (Pb), for example, electrochemical gas sensors using tin or tin alloy as the anode, have also been proposed (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6985533 Summary of the Invention [Problem to be solved by the invention]

[0005] In this type of electrochemical gas sensor, the metal of the anode dissolves into the electrolyte while the target gas is reduced at the cathode, so that the concentration of the metal salt or metal hydroxide of the anode in the electrolyte increases over time. According to unpublished research by the present inventors, for example, when tin (Sn) is used for the anode, if the concentration of tin ions (tin salt or tin hydroxide) in the electrolyte increases, the indicated value (output value) of the gas concentration in the electrochemical gas sensor decreases, and the output response speed of the electrochemical gas sensor to changes in gas concentration decreases.

[0006] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide an electrochemical gas sensor and the like which is capable of obtaining stable and highly responsive output characteristics over a long period of time without using lead (Pb) or tin (Sn) as the main component of the anode surface. [Means for solving the problem]

[0007] The present invention, which achieves the above-mentioned object, is an electrochemical gas sensor comprising a casing that contains an electrolyte, and an anode and a cathode that are arranged so that the electrolyte is interposed therebetween, wherein the anode contains iron or an iron alloy, and the electrolyte contains at least one of a chloride and a sulfate.

[0008] In the electrochemical gas sensor described above, the electrolyte may contain at least one of a carbonate and a hydrogen carbonate.

[0009] In the electrochemical gas sensor described above, the electrolyte may contain at least one of potassium chloride and potassium sulfate.

[0010] In the above electrochemical gas sensor, the electrolyte may contain potassium bicarbonate.

[0011] In the electrochemical gas sensor described above, at least one of the chloride and the sulfate contained in the electrolyte may be set to a concentration at which no precipitation occurs at 0°C.

[0012] The present invention, which achieves the above-mentioned object, provides an electrochemical gas measurement method, comprising: accommodating an electrolyte in a casing; arranging an anode and a cathode with the electrolyte between them; making the anode contain iron or an iron alloy; making the electrolyte contain at least one of a chloride and a sulfate; reducing a target gas at the cathode; detecting the target gas by a current flowing between the anode and the cathode; and removing the iron-containing coating formed on the surface of the anode with at least one of the chloride and the sulfate in the electrolyte. Effect of the Invention

[0013] According to the electrochemical gas sensor of the present invention, stable and highly responsive output characteristics can be obtained for a long period of time even though iron or an iron alloy, which is a general-purpose material, is used for the anode. [Brief description of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view showing an example of the configuration of an electrochemical gas sensor according to an embodiment of the present invention. [Diagram 2] 1 is a graph showing daily changes in oxygen indication, which is a first verification result using the electrochemical gas sensors of Examples 1 to 4 and Comparative Examples 1 and 2. [Diagram 3] 13 is a graph showing the change over time in oxygen indication value due to carbon dioxide, which is a second verification result using the electrochemical gas sensors of Examples 5 and 6. [Figure 4] 13 is a table and a graph showing the oxygen indication output corresponding to the change in atmospheric oxygen concentration, which is a third verification result using the electrochemical gas sensor of Example 7. [Diagram 5] 13 is a graph showing response characteristics corresponding to changes in atmospheric oxygen concentration, which is a fourth verification result using the electrochemical gas sensor of Example 7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 shows the overall configuration of a galvanic cell type gas sensor which is an electrochemical gas sensor 10 according to an embodiment of the present invention.

[0016] The electrochemical gas sensor 10 detects, for example, oxygen as a gas to be detected, and includes a casing 11 which is a generally cylindrical container, an electrolyte held within the casing 11, a cathode 35 disposed at a gas inlet 22 formed in the casing 11, an anode 30 disposed within the casing 11, and a current / voltage conversion circuit board 90. For ease of explanation, the side of the gas introduction hole 12B in the central axial direction of the casing 11 is defined as the "front side," and the opposite side as the "rear side."

[0017] (Casing) The casing 11 includes a main body 12 having a generally cylindrical shape with a bottom, and a front cap 13 attached to the front side of the main body 12. The main body 12 and the front cap 13 are made of a resin material, for example, ABS resin.

[0018] The main body 12 integrally has a cylindrical peripheral wall 12C, a rear surface 12G covering the rear side of the peripheral wall 12C, and a front surface 12A covering the front side of the peripheral wall 12C. These form an electrolyte storage space S in which an electrolyte is stored within the main body 12. An electrolyte filling hole 12F is formed in the rear surface 12G. The electrolyte filling hole 12F is sealed by a bolt plug 110 after the electrolyte is filled into the electrolyte storage space S. A pressure adjustment hole 12E is formed in the peripheral wall 12C, and this pressure adjustment hole 12E is blocked by a water-repellent pressure air membrane (pressure adjustment membrane) 57. The front cap 13 is fixed to the front surface 12A of the main body 12 by a screw 120. A gas introduction hole 12B is formed in the center of the front surface 12A. This pressure air membrane 57 is made of, for example, soft polyvinyl chloride resin, and its peripheral portion is fixed to the peripheral wall 12C by, for example, ultrasonic welding.

[0019] A ring-shaped step is formed on the front side of the gas inlet hole 12B, and the cathode 35 is arranged in a position covering the gas inlet hole 12B by utilizing this step. In addition, a water-repellent gas-permeable diaphragm 55 is arranged on the front side of the cathode 35. The gas-permeable diaphragm 55 liquid-tightly seals the gas inlet hole 12B, thereby preventing leakage of the electrolyte, and at the same time, only the gas can reach the cathode 35. Specifically, the gas-permeable diaphragm 55 covers a wider area than the gas inlet hole 12B on the further front side of the front surface 12A, and is sandwiched between the front cap 13 and the front surface 12A of the main body 12. At this time, the gas-permeable diaphragm 55 is pressed against the periphery of the gas inlet hole 12B by the ring-shaped seal member 16. Gas-permeable membrane 55 selectively allows oxygen to pass through, and limits the amount of oxygen passing through to match the cell reaction, and is made of a fluororesin such as FEP (tetrafluoroethylene-hexafluoropropylene copolymer) or PTFE (polytetrafluoroethylene). The thickness of gas-permeable membrane 55 is, for example, 13 to 25 μm.

[0020] The front cap 13 has a lid-side gas introduction through hole 13B formed in the center, which is connected to the gas introduction hole 12B of the casing 11 to form the gas inlet 22. Here, the front cap 13 is fixed to the main body 12 by a screw 120, but it may be fixed by other means such as engagement by crimping. The gas permeable diaphragm 55 and the cathode 35 of the front cap 13 are pressed against the front surface 12A of the main body 12 via the ring-shaped seal member 16. As a result, liquid-tightness on the front side of the electrolyte storage space S is ensured.

[0021] A concave sealed space 12H is formed on the outside of the rear surface 12G of the main body 12. This sealed space 12H is filled with resin (including adhesive) and sealed during the assembly process. This sealing structure makes the rear side of the electrolyte containing space S a liquid-tight environment.

[0022] (cathode) The cathode 35 is a disk-shaped metal member whose front side is in contact with the gas to be measured and whose back side is in contact with the electrolyte. The cathode 35 is not particularly limited as long as at least the electrode surface has a structure that can generate a current by reducing oxygen. For example, metals such as gold, silver, platinum, and titanium are preferably used for the electrode surface.

[0023] In this embodiment, cathode 35 is made of a metal base material made of stainless steel with gold attached (plated) on the surface. Cathode 35 is formed to have a convex shape toward the outside (front side), thereby suppressing the amount of deformation due to internal pressure fluctuation. One end of cathode lead member 42, which serves as a cathode wiring, is connected to cathode 35. Cathode lead member 42 passes through electrolyte storage space S and reaches rear surface 12G of main body 12. Cathode lead member 42 is further disposed so as to penetrate rear surface 12G and pass through sealed space 12H, and terminal 90B is provided at its end. The vicinity of terminal 90B of cathode lead member 42 is connected to a cathode-side input terminal (not shown) of current-voltage conversion circuit board 90 disposed in sealed space 12H. As a result, the vicinity of the end of cathode lead member 42 is embedded in the resin filled in sealed space 12H, but terminal 90B at the end is exposed to the outside. The cathode lead member 42 is made of a material that does not react when it comes into contact with the electrolyte, for example, a metal wire having at least a surface made of a precious metal such as gold, silver, platinum, etc. In this embodiment, a stainless steel wire having a gold (Au) plated surface is used.

[0024] (anode) The anode 30 disposed in the electrolyte storage space S is a columnar metal member. At least the surface of the anode 30 that comes into contact with the electrolyte is made of iron (Fe) or an iron alloy. In particular, in this embodiment, pure iron with a purity of 99.9% is used. When an iron alloy is used, for example, an Fe-C-Cu-Ni alloy is exemplified.

[0025] An anode support part 28 is formed on the rear surface 12G of the main body 12. The anode support part 28 is, for example, a through hole that penetrates the rear surface 12G and communicates with the sealed space 12H. A columnar anode 30 fits into this through hole, causing a part of the anode 30 (the rear surface side) to protrude into the sealed space 12H. The sealed space 12H is filled with resin, whereby the anode 30 is fixed to the anode support part 28.

[0026] An anode lead member 48 serving as an anode wire is provided on a portion (rear side) of the anode 30 that protrudes into the sealed space 12H. When the anode 30 is held by the anode support portion 28, one end of the anode lead member 48 and the anode 30 are welded to each other, thereby electrically connecting the two. The anode lead member 48 is disposed so as to pass through the sealed space 12H, and a terminal 90A is provided at its end. The vicinity of the terminal 90A of the anode lead member 48 is connected to an anode-side input terminal (not shown) of a current / voltage conversion circuit board 90 disposed in the sealed space 12H. As a result, the vicinity of the end of the anode lead member 48 is embedded in the resin filled in the sealed space 12H, but the terminal 90A at the end is exposed to the outside. The anode lead member 48 is a metal wire made of, for example, stainless steel. When the anode lead member 48 has a wiring structure that comes into contact with the electrolyte, for example, a metal wire having at least a surface made of a precious metal such as gold, silver, or platinum is used.

[0027] (Current / voltage conversion circuit board) The current / voltage conversion circuit board 90 includes a conversion circuit that converts the current flowing between the cathode 35 and the anode 30 into a voltage. The conversion circuit has a structure in which, for example, a resistor and a temperature compensation thermistor are arranged in series between the cathode 35 and the anode 30. The voltage output is output from a pair of terminals 90A and 90B formed on the current / voltage conversion circuit board 90. Note that, as long as the voltage output can be detected, either the terminal 90A or the terminal 90B may be the cathode lead member 42 or the anode lead member 48 itself.

[0028] The current / voltage conversion circuit board 90 is disposed within the sealed space 12H between the cathode lead member 42 and the anode lead member 48. Therefore, when the sealed space 12H is filled with resin, the anode lead member 48, parts of the cathode lead member 42, and the current / voltage conversion circuit board 90 are embedded in the resin.

[0029] Although not specifically shown here, the casing 11 and the current / voltage conversion circuit board 90 can be housed in a metallic exterior body. This exterior body is divided into a first exterior body and a second exterior body that are electrically insulated from each other, and one terminal 90A is connected to the first exterior body and the other terminal 90B is connected to the second exterior body, so that the exterior body itself can be used as an electrode terminal.

[0030] (electrolyte) The electrolyte is an aqueous solution containing at least one of chlorides and sulfates (hereinafter, these will be referred to as "film-forming inhibitors"). Examples of chlorides that can be used include potassium chloride (KCl), sodium chloride (NaCl), calcium chloride, cesium chloride, strontium chloride, iron chloride, barium chloride, and magnesium chloride. Examples of sulfates that can be used include potassium sulfate (K2SO4) and sodium sulfate. In this embodiment, potassium chloride (KCl) or potassium sulfate (K2SO4) is used as the film-forming inhibitor.

[0031] The concentration of the coating-inhibiting substance contained in the aqueous solution is preferably set to a concentration at which the coating-inhibiting substance does not precipitate at 0°C. In other words, the electrolyte preferably contains an amount of the coating-inhibiting substance that does not reach the solubility at 0°C. Since the solubility of potassium chloride (KCl) at 0°C is 3.728 mol / L, the concentration may be set to less than this. As will be described in detail later, it is preferable that the electrolyte does not contain an antifreeze agent, and therefore if the temperature falls below 0°C, the electrolyte freezes and becomes impossible to measure. As a result, the lower limit of the recommended temperature band for use of the electrochemical gas sensor 10 is set to 0°C or higher, and the reference temperature that defines the upper limit of the content concentration is set to 0°C to be on the safe side.

[0032] The film inhibitor is a chloride ion (Cl - ), sulfate ion (SO4 2- ), and the high reactivity of these substances suppresses the formation of a coating on the surface of the anode 30. This "suppression" also includes the concept of destroying the coating formed on the surface of the anode 30. The coating that can be formed on the surface of the anode 30 is, for example, a passive coating (passive thin film) made of iron oxide (black rust) or hydroxide, and is often insoluble and insulating. As a result, if this coating is left as it is, the function of the anode 30 as an anode will deteriorate. Therefore, in the electrochemical gas sensor 10, in order to stably exert the coating suppression effect of the coating suppression substance over a long period of time, it is preferable that the concentration of the coating suppression substance is set to 0.1 mol / L or more.

[0033] The electrolyte preferably further contains at least one of a carbonate and a bicarbonate. As the carbonate, for example, potassium carbonate, sodium carbonate, etc. can be used. As the bicarbonate, for example, potassium bicarbonate (KHCO3), sodium bicarbonate (NaHCO3), etc. can be used. By including a carbonate or a bicarbonate in the electrolyte, even if carbon dioxide in the atmosphere is dissolved in the electrolyte, the fluctuation of the sensor output can be mitigated.

[0034] Furthermore, it is preferable that the electrolyte does not contain an antifreeze agent (e.g., ethylene glycol). The inventors of the present invention have found that the inclusion of an antifreeze agent reduces the film-suppressing effect of the film-suppressing substance. As a result of not including an antifreeze agent, it is preferable that the lower limit of the recommended temperature range for use of the electrochemical gas sensor 10 is set to 0°C or higher. It is preferable that the upper limit of the recommended temperature range for use of the electrochemical gas sensor 10 is set to, for example, 40°C or lower.

[0035] <Estimated effect> In the electrochemical gas sensor 10 of this embodiment, oxygen that has passed through the gas inlet 22 and the gas permeable diaphragm 55 is reduced at the cathode 35 and undergoes the following electrochemical reaction with the anode 30 via the electrolyte: Cathode reaction: O2+2H2O+4e - →4OH - Anode reaction: 2Fe → 2Fe 2+ +4e -

[0036] This electrochemical reaction generates a current corresponding to the oxygen concentration between the anode 30 and the cathode 35. This current (electrons) is guided from the anode 30 through the anode lead member 48 to the outside of the electrolyte containing space S, and flows through a resistor and a temperature compensating thermistor in the current-voltage conversion circuit board 90 to the cathode lead member 42 and the cathode 35. In the current-voltage conversion circuit board 90, the current is converted into a voltage signal, and a voltage signal serving as a sensor output is output between terminals 90A and 90B. This voltage signal is converted into an oxygen concentration by a well-known method to provide an oxygen concentration indication value (%).

[0037] In this case, if an insoluble insulating coating such as black rust (Fe3O4) or iron hydroxide is formed on the surface of the anode 30, the coating may inhibit the above-mentioned anode reaction, causing deterioration of the voltage signal. Therefore, in this embodiment, a coating inhibitor is added to the electrolyte to inhibit (destroy) the formation of the coating, thereby reducing the deterioration of the voltage signal over a long period of time (for example, one year or more).

[0038] <Example 1> The electrochemical gas sensor 10 of this embodiment was prepared in which the cathode 35 was gold-plated, the anode 30 was made of pure iron, and the electrolyte was an aqueous solution containing potassium chloride (KCl) at a concentration of 3 mol / L.

[0039] <Example 2> The electrochemical gas sensor 10 of this embodiment was prepared in which the cathode 35 was gold-plated, the anode 30 was made of pure iron, and the electrolyte was an aqueous solution containing potassium sulfate (K2SO4) at a concentration of 0.5 mol / L.

[0040] <Example 3> The electrochemical gas sensor 10 of this embodiment was prepared in which the cathode 35 was gold-plated, the anode 30 was made of pure iron, and the electrolyte was an aqueous solution containing potassium chloride (KCl) with a concentration of 3 mol / L and potassium bicarbonate (KHCO3) with a concentration of 0.5 mol / L.

[0041] <Example 4> The electrochemical gas sensor 10 of this embodiment was prepared in which the cathode 35 was gold-plated, the anode 30 was an iron alloy (SMF5030) containing carbon, copper, and nickel, and the electrolyte was an aqueous solution containing potassium chloride (KCl) with a concentration of 3 mol / L and potassium bicarbonate (KHCO3) with a concentration of 0.5 mol / L.

[0042] <Comparative Example 1> An electrochemical gas sensor 10 was prepared in which the cathode 35 was gold-plated, the anode 30 was made of pure iron, and the electrolyte was an aqueous solution containing potassium iodide (KI) at a concentration of 5 mol / L. The electrochemical gas sensor 10 used had the same structure as in Example 1, except for the electrolyte.

[0043] <Comparative Example 2> An electrochemical gas sensor 10 was prepared in which the cathode 35 was gold-plated, the anode 30 was made of pure iron, and the electrolyte was an aqueous solution containing potassium nitrate (KNO3) at a concentration of 1 mol / L. The electrochemical gas sensor 10 used had the same structure as in Example 1, except for the electrolyte.

[0044] (First Verification) For the electrochemical gas sensors of Examples 1 to 4 and Comparative Examples 1 and 2, the change in oxygen concentration (oxygen reading) in the air atmosphere over time was measured. The results are shown in FIG. 2. The electrochemical gas sensors 10 of Examples 1 to 4 maintained stable oxygen readings over time. On the other hand, the electrochemical gas sensor of Comparative Example 1 showed an oxygen reading that increased by several percent from the initial value between about 5 days and about 30 days, and after about 30 days, the oxygen reading began to decrease from the initial value, decreasing by about 5% after about 60 days. The electrochemical gas sensor of Comparative Example 2 showed an oxygen reading that began to decrease immediately after the start of the test, decreasing by about 3% after about 30 days.

[0045] <Example 5> The electrochemical gas sensor 10 of this embodiment was prepared in which the cathode 35 was gold-plated, the anode 30 was made of pure iron, and the electrolyte was an aqueous solution containing potassium chloride (KCl) at a concentration of 1 mol / L.

[0046] <Example 6> The electrochemical gas sensor 10 of this embodiment was prepared in which the cathode 35 was gold-plated, the anode 30 was made of pure iron, and the electrolyte was an aqueous solution containing potassium chloride (KCl) with a concentration of 1 mol / L and potassium bicarbonate (KHCO3) with a concentration of 0.5 mol / L.

[0047] (Second Verification) The electrochemical gas sensors of Examples 5 and 6 were placed in an air atmosphere (oxygen reading of about 21%), and then pure carbon dioxide (CO2) was continuously supplied to the gas inlet 22 of the electrochemical gas sensor, and the change in the oxygen reading over time was measured. The results are shown in FIG. 3. The electrochemical gas sensor 10 of Example 5 showed an oxygen reading that started to rise from about 0% after about 5 hours. After about 10 hours, the oxygen reading reached 4%, and then gradually dropped to about 0% after about 30 hours. On the other hand, the electrochemical gas sensor of Example 6 showed an oxygen reading that was stable at about 0% until 60 hours had passed from the start of measurement. In other words, it can be seen that if the electrolyte contains carbonate or hydrogen carbonate that generates carbonate ions in advance, as in Example 6, the output fluctuation of the oxygen reading can be suppressed even if carbon dioxide in the atmosphere dissolves in the electrolyte during measurement.

[0048] <Example 7 and Third Verification> Five electrochemical gas sensors 10 (management numbers A to E) of this embodiment were prepared, each having a gold-plated cathode 35, a pure iron anode 30, and an aqueous solution containing potassium chloride (KCl) at a concentration of 3 mol / L and potassium bicarbonate (KHCO3) at a concentration of 0.2 mol / L. These electrochemical gas sensors 10 were placed in various atmospheric environments with oxygen concentrations of 20.9%, 16.7%, 12.4%, 8.3%, 4.1%, and 0.0%, and the oxygen indication output was measured. The results are shown in FIG. 4. All the electrochemical gas sensors 10 output oxygen indication values ​​corresponding to the atmospheric oxygen concentrations almost accurately. Furthermore, the variation in the output values ​​of the five electrochemical gas sensors 10 was also extremely small.

[0049] <Fourth Verification> Five electrochemical gas sensors 10 (manufacturer numbers A to E) of Example 7 were used, and placed in an air atmosphere (oxygen reading of approximately 21%). After 3 minutes had elapsed since the start of the measurement, the atmosphere was switched to a nitrogen atmosphere (100% nitrogen, 0% oxygen), and after 6 minutes had elapsed since the start of the measurement, the atmosphere was switched back to an air atmosphere (oxygen reading of approximately 21%). The output change in the oxygen reading was measured. The results are shown in FIG. 5. For all five electrochemical gas sensors 10 (manufacturer numbers A to E), the response speed when switching from an air atmosphere to a nitrogen atmosphere was extremely fast, and the response speed when switching from a nitrogen atmosphere to an air atmosphere was also fast. Furthermore, the variation in the response waveforms between all five electrochemical gas sensors 10 (manufacturer numbers A to E) was extremely small.

[0050] As can be seen from the above verification, the electrochemical gas sensor 10 of this embodiment can maintain good accuracy and response characteristics of the oxygen indication.

[0051] The structure of the electrochemical gas sensor shown in this embodiment is merely an example, and other structures may be used in the present invention. Furthermore, the electrochemical gas sensor of the present invention is not limited to a structure having two electrodes (two-electrode type), and may be a structure having three or four electrodes (three-electrode type, four-electrode type).

[0052] In the present embodiment, the anode support portion 28 is formed by forming a through hole in the main body 12, but the present invention is not limited thereto. For example, the anode support portion 28 may be formed by forming a recess inside the main body 12, and the anode 30 may be fitted into the recess. Furthermore, the anode support portion 28 may be fixed to the main body 12 using a resin such as an adhesive. Furthermore, in the present modified example, the anode 30 is fixed to the molded main body 12 afterwards, but the present invention is not limited thereto. For example, the anode 30 may be insert-molded when manufacturing the main body 12, and the anode 30 may be held by the main body 12 by this insert-molded structure.

[0053] The present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0054] 10 Electrochemical gas sensors 11 Casing 12 Main unit 12A front 12B Gas inlet 12C Peripheral wall 12G rear 13 Front cap 13B Gas inlet hole on the lid side 16 Sealing material 22 Gas inlet 28 Anode support part 30 Anode 35 Cathode 42 Cathode lead material 48 Anode lead material 55 Gas-permeable membrane 57 Air pressure membrane 90 Current-voltage conversion circuit board 90A Terminal 90B Terminal S Electrolyte storage space

Claims

1. An electrochemical gas sensor comprising a casing for accommodating an electrolyte, and an anode and a cathode disposed with the electrolyte interposed therebetween, the anode contains iron or an iron alloy; The electrolyte contains at least one of a chloride and a sulfate. Electrochemical gas sensor.

2. 2. The electrochemical gas sensor according to claim 1, wherein the electrolyte contains at least one of a carbonate and a hydrogen carbonate.

3. 2. The electrochemical gas sensor according to claim 1, wherein the electrolyte contains at least one of potassium chloride and potassium sulfate.

4. 3. The electrochemical gas sensor according to claim 2, wherein the electrolyte contains potassium bicarbonate.

5. At least one of the chloride and the sulfate contained in the electrolytic solution is set to a concentration at which it does not precipitate at 0 ° C.

2. The electrochemical gas sensor according to claim 1.

6. The casing contains an electrolyte; An anode and a cathode are disposed so as to sandwich the electrolytic solution therebetween; The anode contains iron or an iron alloy, and the electrolyte contains at least one of a chloride and a sulfate; The target gas is detected by a current flowing between the anode and the cathode by reducing the target gas at the cathode; The iron-containing coating formed on the surface of the anode is removed by at least one of the chloride and the sulfate in the electrolyte. Electrochemical gas measurement method.

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