Reference electrode

Abstract

To provide a reference electrode that can be regenerated in situ when its performance deteriorates. [Solution] A reference electrode that is buried in concrete and used to measure the electric potential of metals in the concrete, comprising a cylindrical resin container 40 that contains an electrode body 10 in contact with a solid electrolyte 30, and a regenerative electrolysis counter electrode 20 in contact with at least one of the solid electrolyte 30 and the concrete, wherein the electrode body 10 has, on at least a portion of its surface 10a, at least one of an oxide layer formed by oxidizing the metal that constitutes the electrode body 10 and a first coating layer 11.

Description

[Technical field]

[0001] The present invention relates to a reference electrode. [Background technology]

[0002] Steel materials such as reinforcing bars and pipes embedded in concrete structures can corrode due to neutralization of the concrete. In addition, in concrete structures built in coastal areas in particular, chloride ions penetrate from the surface, and if the allowable concentration is exceeded, corrosion of the steel material will occur. To prevent corrosion of steel materials, for example, cathodic protection is implemented. In this case, it is necessary to bury a reference electrode in the concrete to measure the potential of the steel material and monitor the corrosion of the steel material. The potential of a metal is expressed as the difference (potential difference) with the potential of a reference electrode.

[0003] The electrode that serves as the standard when measuring the potential of steel materials is called a reference electrode. Known examples of reference electrodes include TOA-DKK's HS-205C (saturated silver-silver chloride electrode), MCMiller's RE-5 type (saturated copper sulfate electrode), and Nippon Bosoku Co., Ltd.'s AC-2 type (artificial seawater-silver chloride electrode).

[0004] Furthermore, as a reference electrode used when measuring the potential of steel materials in concrete structures, for example, a silver-silver oxide reference electrode in which silver particles and silver oxide particles are mixed in a specific ratio is known (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 6-317553 Summary of the Invention [Problem to be solved by the invention]

[0006] However, commercially available saturated silver-silver chloride electrodes and saturated copper sulfate electrodes cannot be regenerated when they no longer show the normal potential, so they must be discarded, which is uneconomical. Also, although it is possible to regenerate an artificial seawater silver chloride electrode when it no longer shows the normal potential, it is necessary to disassemble the electrode, prepare molten salt, and set up an electrolysis system in a beaker, so it cannot be regenerated on the spot.

[0007] Furthermore, the invention of Patent Document 1 has a problem that the electrode potential changes in an environment containing chloride ions, such as seawater. In addition, the invention of Patent Document 1 may reduce silver oxide depending on the constituent components. Also, there is a possibility that the electrode potential becomes unstable due to the reduction of silver oxide particles on the electrode surface by a weak current flowing during potential measurement.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a reference electrode that can be regenerated on the spot when its performance deteriorates. [Means for solving the problem]

[0009] The present invention has the following aspects. [1] A reference electrode that is embedded in concrete and used to measure the electric potential of a metal in the concrete, a cylindrical resin container that accommodates the electrode body in contact with the solid electrolyte; a counter electrode for regenerative electrolysis in contact with at least one of the solid electrolyte and the concrete; The electrode body has, on at least a portion of its surface, at least one of an oxide layer formed by oxidizing a metal constituting the electrode body and a coating layer. [2] The reference electrode according to [1], wherein the electrode body and the counter electrode for regenerative electrolysis are embedded in the same solid electrolyte. [3] The reference electrode according to [1], wherein the electrode body and the counter electrode for regenerative electrolysis are embedded in different solid electrolytes. [4] The reference electrode according to [1], wherein the metal constituting the electrode body is silver. [5] The reference electrode according to [1], wherein the counter electrode for regenerative electrolysis has a second coating layer covering at least a portion of its surface. [6] The reference electrode according to [1], having a liquid junction that seals the solid electrolyte. [7] The reference electrode according to [1], wherein the counter electrode for regenerative electrolysis is a metal buried in concrete. Effect of the Invention

[0010] According to the present invention, it is possible to provide a reference electrode that can be regenerated in situ when its performance deteriorates. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a cross-sectional view illustrating a reference electrode according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view illustrating a reference electrode according to an embodiment of the present invention. [Diagram 3] FIG. 2 is a cross-sectional view illustrating a reference electrode according to an embodiment of the present invention. [Figure 4] FIG. 2 is a cross-sectional view illustrating a reference electrode according to an embodiment of the present invention. [Diagram 5] FIG. 2 is a cross-sectional view illustrating a reference electrode according to an embodiment of the present invention. [Figure 6] FIG. 2 is a cross-sectional view illustrating a reference electrode according to an embodiment of the present invention. [Figure 7] FIG. 4 is a graph showing the results of measuring the change over time in the potential of a reference electrode in Example 1. [Figure 8] FIG. 13 is a diagram showing the results of evaluating the amount of silver oxide produced by electrolytic oxidation using a constant current reduction method in Example 2. [Figure 9] FIG. 13 is a diagram showing the results of measuring the potential of a reference electrode in a saturated calcium hydroxide solution in Example 3. [Figure 10] FIG. 13 is a diagram showing the results of measuring the potential of an electrode when the electrode was immersed in a saturated calcium hydroxide solution in Example 4. [Figure 11]FIG. 13 is a diagram showing the results of measuring the potential of an electrode when the electrode was immersed in a saturated calcium hydroxide solution in Example 5. [Figure 12] FIG. 13 is a diagram showing the results of measuring the potential of a reference electrode when the reference electrode was immersed in a saturated calcium hydroxide solution in Example 6. [Figure 13] FIG. 13 is a diagram showing the results of measuring the potential of a reference electrode in a concrete specimen during exposure in Example 7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, a reference electrode according to an embodiment of the present invention will be described with reference to the drawings. Note that the drawings used in the following description show characteristic parts in an enlarged scale for convenience, and the dimensional ratios of each component may differ from the actual ones. Furthermore, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited to them, and can be appropriately changed without departing from the spirit and scope of the present invention.

[0013] [Reference electrode] (First embodiment) FIG. 1 is a cross-sectional view showing a schematic diagram of a reference electrode according to one embodiment of the present invention. 1, the reference electrode 1 of this embodiment includes an electrode body 10, a counter electrode for regenerative electrolysis 20, a solid electrolyte 30, and a resin container 40. The electrode body 10 has a coating layer (hereinafter referred to as a "first coating layer") 11 that covers at least a portion of its surface 10a.

[0014] The resin container 40 has a hollow cylindrical shape, and the electrode body 10, the counter electrode for regenerative electrolysis 20, and the solid electrolyte 30 are accommodated in the internal space 40a. The resin container 40 is open at both ends in the axial direction (longitudinal direction). One end 40A of the resin container 40 is sealed by the solid electrolyte 30. The other end 40B of the resin container 40 is sealed by the filled resin 50. The solid electrolyte 30 and the filled resin 50 are in contact with each other in the resin container 40. The end 40B of the resin container 40 is provided with a lead wire 70 connected to the electrode body 10 by a crimp terminal 60, and a lead wire 71 connected to the counter electrode for regenerative electrolysis 20 by a crimp terminal 61. The crimp terminal 60 and the crimp terminal 61 are embedded in the filled resin 50. The electrode body 10 and the lead wire 70, and the counter electrode for regenerative electrolysis 20 and the lead wire 71 may be connected by soldering, or any known connection method may be used.

[0015] "Electrode body" The electrode body 10 is embedded in the solid electrolyte 30. Although the electrode body 10 is embedded in the solid electrolyte 30 in FIG. 1, the electrode body 10 may be in contact with the solid electrolyte 30. The electrode body 10 may be a metal that generates an oxidant (also called an active material) on the surface of the metal when electrolytically oxidized, and examples of the metal include silver, lead, copper, zinc, and tin. Oxidants of these metals have excellent chemical stability and are preferable as metals constituting the electrode body 10. However, platinum, titanium, and manganese are excluded because their electric potential changes depending on the oxygen concentration.

[0016] The electrode body 10 may have an oxide layer (not shown) formed by oxidizing the metal constituting the electrode body 10 on at least a part of its surface 10a. When the electrode body 10 is made of silver, the oxide layer is made of silver oxide. When the electrode body 10 is made of lead, the oxide layer is made of lead oxide. When the electrode body 10 is made of copper, the oxide layer is made of copper oxide. When the electrode body 10 is made of zinc, the oxide layer is made of zinc oxide. When the electrode body 10 is made of tin, the oxide layer is made of tin oxide. The oxide layer is an active material formed by oxidizing the metal constituting the electrode body 10, and an electrode potential is generated by an electrode reaction between the metal and the active material. In addition, FIG. 1 illustrates a case where the electrode body 10 is embedded in the solid electrolyte 30, but the electrode body 10 may be in contact with the solid electrolyte 30. As long as the electrode body 10 is in contact with the solid electrolyte 30, regenerative electrolysis, which will be described later, is possible.

[0017] The thickness of the oxide layer is preferably 50 nm or more. If the thickness of the oxide layer is less than 50 nm, the potential becomes unstable.

[0018] The shape of the electrode body 10 is not particularly limited, but examples thereof include a linear shape, a mesh shape, a sphere, a square shape, a cylindrical shape, an elliptical cylindrical shape, a prismatic shape, etc. Among these, the linear shape and the mesh shape are preferred because they are easily available.

[0019] "First coating layer" The first coating layer 11 covers the surface 10a of the electrode body 10 and at least a part of the oxide layer. The thickness of the first covering layer 11 is preferably 0.005 mm or more and 50 mm or less, more preferably 0.01 mm or more and 10 mm or less, and even more preferably 0.02 mm or more and 3 mm or less. When the thickness of the first covering layer 11 is equal to or more than the lower limit, the electrode potential is more likely to be stabilized. When the thickness of the first covering layer 11 is equal to or less than the upper limit, the potential stabilizer is easily prevented from peeling off from the surface of the electrode body 10. In addition, when the thickness of the first covering layer 11 is equal to or less than the upper limit, it is advantageous in terms of cost. The thickness of the first covering layer 11 can be determined, for example, by observing a cross section of the first covering layer 11 in the thickness direction with a microscope or the like.

[0020] The potential stabilizer is preferably one that contains an alkaline solid in addition to the active material obtained by oxidizing the metal constituting the electrode body 10, since it is easy to harden and form the first coating layer 11. Examples of the alkaline solid include calcium hydroxide powder, calcined gypsum powder, and cement. The alkaline solid may be used alone or in combination of two or more kinds.

[0021] The potential stabilizer is more preferably a composition containing the active material, calcium hydroxide powder, calcined gypsum powder and water, or cement and water (hereinafter also referred to as a "stabilizer composition"). When the potential stabilizer is a stabilizer composition, it is easier to form the first coating layer 11 on the surface 10a of the electrode body 10 and the surface of the oxide layer.

[0022] When the active material is silver oxide, the content of silver oxide powder contained in the stabilizer composition is preferably 10% by mass or more and 95% by mass or less, and more preferably 35% by mass or more and 85% by mass or less, based on the total mass (100% by mass) of the stabilizer composition. When the content of silver oxide powder is equal to or more than the lower limit, the electrode potential is more likely to be stabilized. When the content of silver oxide powder is equal to or less than the upper limit, the workability is good and an appropriate first coating layer 11 can be formed.

[0023] The content of the potential stabilizer can be appropriately set according to the service life of the reference electrode 1. For example, if the service life of the reference electrode 1 is set to 20 years or less in accordance with the service life of the lead wire, the content of the potential stabilizer is set to 0.01 g / cm 3 on the surface 10a of the electrode body 10. 2 More than 10g / cm 2 Less than 0.1 g / cm is preferable. 2 More than 5g / cm 2 The following is more preferred: When the content of the potential stabilizer is equal to or more than the lower limit, the electrode potential is more likely to be stabilized. When the content of the potential stabilizer is equal to or less than the upper limit, it is advantageous in terms of cost. When the stabilizer composition contains an active material, the active material constituting the oxide layer can be prevented from being reduced by diffusion. On the other hand, even if the stabilizer composition does not contain an active material, an electrode potential is generated by an electrode reaction between the electrode body 10 and the oxide layer, in other words, between a metal and an active material. That is, if there is a first coating layer 11 that covers at least a part of the surface 10a of the electrode body 10 and the oxide layer, the electrode potential is likely to be stable, but the reference electrode 1 does not need to have the first coating layer 11. Therefore, if there is the electrode body 10 and at least one of the oxide layer and the first coating layer 11, an electrode potential is generated and the reference electrode 1 functions. In addition, Figure 1 illustrates an example in which the electrode body 10 has a first coating layer 11 on at least a portion of its surface 10a, but in the reference electrode of the present invention, the electrode body may have both an oxide layer formed by oxidizing the metal constituting the electrode body and the first coating layer 11 on at least a portion of its surface, or may have only an oxide layer formed by oxidizing the metal constituting the electrode body 10, or may even have only the first coating layer 11.

[0024] "Counter electrode for regenerative electrolysis" The counter electrode 20 for regenerative electrolysis may be any material that is electronically conductive, such as stainless steel, platinum, titanium, gold, silver, copper, and graphite. In addition, while Fig. 1 illustrates a case in which the counter electrode 20 for regenerative electrolysis is embedded in the solid electrolyte 30, the counter electrode 20 for regenerative electrolysis may simply be in contact with the solid electrolyte 30. In addition, the counter electrode 20 for regenerative electrolysis may be a steel material (metal) embedded in concrete, as long as it is in contact with concrete. The shape of the counter electrode 20 for regenerative electrolysis is not particularly limited, but examples thereof include linear, mesh, spherical, rectangular, cylindrical, elliptical cylindrical, rectangular, and coiled shapes. Among these, coil and mesh shapes are preferred because they can increase the surface area. In addition, if the counter electrode 20 for regenerative electrolysis is a steel material embedded in concrete, the surface area is significantly large. If the surface area of ​​the counter electrode 20 for regenerative electrolysis is large, the power consumption during regenerative electrolysis can be reduced.

[0025] On the other hand, when the electrode body 10 is made of silver, the silver oxide particles contained in the first coating layer 11 are reduced by the weak current flowing during potential measurement, and a part of them becomes silver. The same thing can happen during regeneration electrolysis. When the shape of the counter electrode for regeneration electrolysis 20 is, for example, linear, the silver oxide particles on the path of the current flowing from the electrode body 10 to the counter electrode for regeneration electrolysis 20 during regeneration electrolysis are partially reduced to silver, so that if the silver parts become conductive with each other, there is a concern that the electrode body 10 and the counter electrode for regeneration electrolysis 20 will eventually become conductive via silver, in which case regeneration electrolysis will not be possible and will have an adverse effect on potential measurement.

[0026] "Second coating layer" Although not shown in FIG. 1, the counter electrode for regenerative electrolysis 20 constituting the reference electrode 1 of this embodiment may have a coating layer (hereinafter referred to as a "second coating layer") that covers its surface. The second coating layer covers at least a portion of the surface of the counter electrode for regenerative electrolysis 20 . The thickness of the second coating layer can be determined, for example, by observing a cross section of the second coating layer in the thickness direction with a microscope or the like.

[0027] The second covering layer may have a configuration similar to that of the solid electrolyte 30 described below. The second coating layer may be a solid electrolyte containing a deliquescent salt or a hygroscopic salt. Examples of the deliquescent salt include potassium carbonate, calcium nitrate, sodium hydroxide, magnesium chloride, and calcium chloride. By containing the deliquescent salt, an increase in the surface resistance of the regenerative electrolysis counter electrode 20 can be suppressed. The content of the deliquescent salt or the hygroscopic salt is preferably 1 mass % or more with respect to the total mass of the second coating layer. Furthermore, the second coating layer may be a solid electrolyte containing an oxidizing agent. Examples of the oxidizing agent include silver oxide, copper oxide, zinc oxide, iron oxide, manganese oxide, copper sulfate, iron sulfate, nickel sulfate, cobalt sulfate, cobalt chloride, and tin chloride. By containing an oxidizing agent, it is possible to promote the reduction reaction on the counter electrode for regeneration electrolysis during regeneration electrolysis, and to suppress the voltage. The content of the oxidizing agent is preferably 1 mass% or more with respect to the total mass of the second coating layer. Furthermore, the second coating layer may be a solid electrolyte containing an electronically conductive material. Examples of the electronically conductive material include metal powders such as zinc powder, silver powder, and copper powder, and graphite powder. By including the electronically conductive material, the apparent surface area of ​​the counter electrode 20 for regenerative electrolysis can be increased, and the voltage during electrolysis can be suppressed. The content of the electronically conductive material is preferably 1% by mass or more with respect to the total mass of the second coating layer. In addition, the second covering layer may be an electrolyte containing a gelling agent. Examples of gelling agents include sodium polyacrylate and carboxymethyl cellulose. By including a gelling agent, an increase in the surface resistance of the regenerative electrolysis counter electrode 20 can be suppressed. The content of the gelling agent is preferably 1% by mass or more with respect to the total mass of the covering layer 21. However, when a gelling agent is used, it is necessary to provide a liquid junction, which will be described later.

[0028] "Solid electrolyte" The solid electrolyte 30 is a solid electrolyte. The solid electrolyte 30 may be completely solidified or may be in a gel state. The solid electrolyte 30 may be, for example, a hardened composition containing calcium hydroxide powder, gypsum powder, and water.

[0029] The thickness of the solid electrolyte 30 (the length in the axial direction in the resin container 40) is preferably 10 mm or more, more preferably 50 mm or more, and even more preferably 100 mm or more. When the thickness of the solid electrolyte 30 is equal to or more than the lower limit, substances that may react with the metal constituting the electrode body 10 are less likely to reach the electrode body 10, and the electrode potential is more likely to be stable. In other words, the solid electrolyte 30 functions as a diffusion suppression layer that suppresses the diffusion of substances that may react with the metal constituting the electrode body 10. The upper limit of the thickness of the solid electrolyte 30 is not particularly limited, but from the viewpoint of making the reference electrode 1 compact, for example, 200 mm or less is preferable.

[0030] The solid electrolyte 30 functions as a diffusion suppression layer, making it difficult for substances that may react with the ions of the metal that constitutes the electrode body 10 to reach the electrode body 10. Therefore, the oxide layer does not undergo chemical changes, and changes in the electrode potential can be suppressed. As a result, the electrode potential is more likely to be stable.

[0031] The thickness of the solid electrolyte 30 can be appropriately set according to the service life of the reference electrode 1. For example, if the service life of the reference electrode 1 is set to 20 years or less, the thickness of the solid electrolyte 30 is preferably 180 mm or more.

[0032] The solid electrolyte 30 may be a hardened cement body. When the solid electrolyte 30 is a hardened cement body, substances that may react with ions of the metal that constitutes the electrode body 10 are less likely to reach the electrode body 10. Therefore, the oxide layer does not undergo chemical changes, and changes in the electrode potential can be more effectively suppressed. As a result, the electrode potential is more likely to be stable. An example of the hardened cement product is a hardened product of a cement composition containing cement and water. Examples of cement include various Portland cements such as ordinary Portland cement, moderate heat Portland cement, and sulfate-resistant Portland cement, and various mixed cements (blast furnace cement, fly ash cement, silica cement) obtained by mixing these Portland cements with blast furnace slag, fly ash, or silica. These cements may be used alone or in combination of two or more.

[0033] The cement composition may contain fine aggregate other than cement and water. Examples of fine aggregate include river sand, mountain sand, land sand, crushed sand, silica sand, and mixtures thereof. The content of the fine aggregate is preferably 20% by mass or more and 75% by mass or less, based on 100% by mass of the cement composition. When the content of the fine aggregate is equal to or more than the lower limit, the strength of the solid electrolyte 30 can be further increased. When the content of the fine aggregate is equal to or less than the upper limit, the fluidity of the cement composition is excellent, and the moldability of the solid electrolyte 30 can be further increased.

[0034] The solid electrolyte 30 preferably contains an active material. Examples of the active material include silver oxide, lead oxide, copper oxide, zinc oxide, and tin oxide, depending on the metal constituting the electrode body 10. The content of the active material contained in the solid electrolyte 30 is preferably 1 mass % or more relative to the total mass (100 mass %) of the solid electrolyte 30, so that the potential of the reference electrode 1 becomes stable.

[0035] The solid electrolyte 30 may contain, for example, an ion-exchangeable substance capable of removing anions bonded to the metal constituting the electrode body 10 or the active material thereof in an alkaline environment. By containing an ion-exchangeable substance in the solid electrolyte 30, anions penetrating from the environment can be removed, so that the oxide layer does not undergo chemical changes and the electrode potential can be prevented from changing. As a result, the electrode potential is more likely to be stabilized. Examples of the anion include a halide ion, a chlorate ion, a chlorite ion, a hypochlorite ion, a cyanide ion, a nitrate ion, a sulfide ion, a hydrogen sulfide ion, a thiocyanate ion, a sulfate ion, a hydrogen carbonate ion, a carbonate ion, a sulfite ion, and a thiosulfate ion.

[0036] Examples of ion-exchangeable substances include clay minerals, diatomaceous earth, calcium silicate hydrate, etc. These substances have hydroxide ions in their structures. Examples of clay minerals include kaolinite, smectite, allophane, imogolite, etc. These clay minerals may be used alone or in combination of two or more.

[0037] "Resin container" The resin container 40 forms the outer shape of the reference electrode 1 and has a hollow cylindrical shape. The cross-sectional shape of the resin container 40 may be a circle or an ellipse, or may be a polygon, etc. The material of the resin container 40 may be any material that can accommodate the electrode body 10, the counter electrode for regenerative electrolysis 20, and the solid electrolyte 30 and has electrical insulation properties, and examples of such materials include polyvinyl chloride, polystyrene, polyethylene, polypropylene, acrylic resin, polytetrafluoroethylene resin (PTFE), polyvinylidene fluoride resin (PVDF), polyether ether ketone resin (PEEK), polycarbonate resin (PC), and fiber reinforced plastic. As the material of the resin container 40, polyvinyl chloride, PC, and fiber reinforced plastic are preferable from the viewpoint of excellent durability.

[0038] The length (length in the axial direction) of the resin container 40 is not particularly limited, but is preferably 50 mm or more and 250 mm or less, more preferably 60 mm or more and 200 mm or less, and even more preferably 70 mm or more and 150 mm or less. When the length of the resin container 40 is equal to or more than the lower limit, the thickness of the solid electrolyte 30 can be made sufficiently thick, and substances that can react with the ions of the metal constituting the electrode body 10 are less likely to reach the electrode body 10. Therefore, the oxidation layer does not undergo chemical changes, and changes in the electrode potential can be suppressed. As a result, the electrode potential is more likely to be stable. When the length of the resin container 40 is equal to or less than the upper limit, the reference electrode 1 can be made compact, which is also excellent in terms of cost.

[0039] The inner diameter of the resin container 40 (the inner diameter of the opening of the resin container 40) is not particularly limited, but is preferably, for example, 3 mm to 30 mm, more preferably 5 mm to 25 mm, and even more preferably 7 mm to 20 mm. When the inner diameter of the resin container 40 is equal to or greater than the lower limit, the measurement accuracy of the reference electrode 1 can be further improved. When the inner diameter of the resin container 40 is equal to or less than the upper limit, the reference electrode 1 can be made compact, which is also advantageous in terms of cost. The thickness of the resin container 40 is not particularly limited, but is preferably 1 mm or more and 5 mm or less, and more preferably 2 mm or more and 4 mm or less. When the thickness of the resin container 40 is equal to or more than the lower limit, the strength of the reference electrode 1 can be increased, and the electrode potential is more likely to be stabilized. When the thickness of the resin container 40 is equal to or less than the upper limit, the reference electrode 1 can be made compact, which is also advantageous in terms of cost.

[0040] "Liquid junction" Although not shown in Fig. 1, the reference electrode 1 of this embodiment may have a liquid junction. The liquid junction seals the solid electrolyte 30 and allows ions to move. Examples of materials that form the liquid junction include cement, mortar, and gypsum. The reference electrode 1 does not have to have a liquid junction, but it is preferable that the reference electrode 1 has a liquid junction, since this increases durability and makes the electrode potential more stable.

[0041] The axial length of the liquid junction is preferably 5 mm or more, more preferably 10 mm or more, and even more preferably 15 mm or more. If the axial length of the liquid junction is equal to or more than the lower limit, substances that may react with the ions of the metal constituting the electrode body 10 are less likely to reach the electrode body 10. Therefore, the oxide layer does not undergo chemical changes, and changes in the electrode potential can be suppressed. As a result, the electrode potential is more likely to be stable. The upper limit of the axial length of the liquid junction is not particularly limited, but is preferably 180 mm, for example. If the axial length of the liquid junction is equal to or less than the upper limit, the reference electrode 1 can be made more compact. Furthermore, from the viewpoint of making the electrode potential more stable and making the reference electrode 1 more compact, the liquid junction may have a meandering liquid junction path (not shown). The liquid junction path is a path through which ions move inside the liquid junction. By providing a liquid junction, the thickness of the solid electrolyte 30 can be made thin, but in the present invention, the function of the liquid junction is imparted to the solid electrolyte 30, and the same effect is achieved.

[0042] The total length of the reference electrode 1 (the length in the axial direction of the resin container 40) is preferably 300 mm or less, more preferably 275 mm or less, and even more preferably 250 mm or less. When the total length of the reference electrode 1 is equal to or less than the upper limit, the reference electrode 1 can be made more compact. There is no particular limit to the lower limit of the total length of the reference electrode 1, but for example, 100 mm is preferable. When the total length of the reference electrode 1 is equal to or more than the lower limit, it is easy to install it in a concrete structure or the like.

[0043] "Filling resin" The filling resin 50 is a resin that seals the end of the resin container 40 opposite to the end where the solid electrolyte 30 is accommodated. The filling resin 50 is not particularly limited, and examples thereof include epoxy resin, acrylic resin, silicone resin, urethane resin, etc. Epoxy resin is preferable as the filling resin 50 because of its excellent filling property.

[0044] "Lead wire" The lead wires 70 and 71 are conductors for extracting the current flowing during potential measurement to the outside. Any material having electronic conductivity may be used as the lead wires, and copper wires are usually used. In this specification, the lengths of the lead wires 70 and 71 are not included in the overall length of the reference electrode 1 .

[0045] In the reference electrode 1, it is preferable to dispose the portion of the electrode body 10 covered with the first covering layer 11 away from the counter electrode for regenerative electrolysis 20. This makes it possible to eliminate the possibility that the active material constituting the first covering layer 11 is partially reduced during regenerative electrolysis, resulting in electrical conduction between the electrode body 10 and the counter electrode for regenerative electrolysis 20 via the partially reduced active material.

[0046] Second embodiment Fig. 2 is a cross-sectional view showing a schematic diagram of a reference electrode according to one embodiment of the present invention, in which the same components as those shown in Fig. 1 are denoted by the same reference symbols and their description will be omitted. As shown in FIG. 2, the reference electrode 100 of this embodiment includes an electrode body 10, a counter electrode for regenerative electrolysis 20, a solid electrolyte 30, and a resin container 40.

[0047] In the reference electrode 100 of this embodiment, the counter electrode 20 for regeneration electrolysis is coiled. By forming the counter electrode 20 for regeneration electrolysis in a coiled shape, the current flowing from the electrode body 10 to the counter electrode 20 for regeneration electrolysis during regeneration electrolysis can be dispersed, so that silver oxide particles are partially reduced to silver, and the electrical conduction between silver portions can be delayed. The same effect can also be achieved by forming the electrode body 10 in a coiled shape, for example.

[0048] (Third embodiment) Fig. 3 is a cross-sectional view showing a schematic diagram of a reference electrode according to one embodiment of the present invention, in which the same components as those shown in Fig. 1 are denoted by the same reference symbols and their description will be omitted. As shown in FIG. 3, the reference electrode 200 of this embodiment includes an electrode body 10, a counter electrode for regenerative electrolysis 210, a solid electrolyte 30, and a resin container 40.

[0049] In the reference electrode 200 of this embodiment, a ring-shaped counter electrode for regenerative electrolysis 210 is embedded in the filled resin 50. Furthermore, the ring-shaped counter electrode for regenerative electrolysis 210 is arranged in the filled resin 50 so as to contact the end face 30a of the solid electrolyte 30 on the filled resin 50 side (the interface between the solid electrolyte 30 and the filled resin 50). By making the counter electrode for regenerative electrolysis 210 ring-shaped and arranging it so as to contact the end face 30a of the solid electrolyte 30 on the filled resin 50 side, it is possible to disperse the current flowing from the electrode body 10 to the counter electrode for regenerative electrolysis 210 during regenerative electrolysis, so that the silver oxide particles are partially reduced to silver, and it is possible to delay the electrical conduction between the silver parts.

[0050] (Fourth embodiment) Fig. 4 is a cross-sectional view showing a schematic diagram of a reference electrode according to one embodiment of the present invention, in which the same components as those shown in Fig. 1 are denoted by the same reference symbols and their description will be omitted. As shown in FIG. 4, the reference electrode 300 of this embodiment includes an electrode body 10, a counter electrode for regenerative electrolysis 20, a solid electrolyte 30, and a resin container 40.

[0051] One end 40A of the resin container 40 is sealed with a solid electrolyte 30 (30A). The other end 40B of the resin container 40 is sealed with a filled resin 50. Furthermore, a solid electrolyte 30 (30B) is disposed so as to contact an end face 40b of the resin container 40 on the other end 40B side.

[0052] In the reference electrode 300 of this embodiment, the counter electrode 20 for regenerative electrolysis has a coiled shape similar to that of the second embodiment. The counter electrode 20 for regenerative electrolysis is embedded in a solid electrolyte 30. By forming the counter electrode 20 for regenerative electrolysis in a coiled shape, the current flowing from the electrode body 10 to the counter electrode 20 for regenerative electrolysis during regenerative electrolysis can be dispersed, so that silver oxide particles are partially reduced to silver, and the electrical conduction between the silver portions can be delayed.

[0053] In the reference electrode 300 of this embodiment, the counter electrode 20 for regenerative electrolysis is embedded in a solid electrolyte 30 (30B) different from the solid electrolyte 30 (30A) in which the electrode body 10 is embedded. By embedding the counter electrode 20 for regenerative electrolysis in a solid electrolyte 30 (30B) different from the solid electrolyte 30 (30A) in which the electrode body 10 is embedded, it is possible to suppress electrical conduction between the electrode body 10 and the counter electrode 20 for regenerative electrolysis via the metal (e.g., silver) constituting the electrode body 10. The same applies when the counter electrode 20 for regenerative electrolysis is in contact with concrete and when the counter electrode 20 for regenerative electrolysis is a steel material embedded in concrete. In this way, when electrolytic oxidation is performed through concrete, there is no electrical conduction between the electrode body 10 and the counter electrode 20 for regenerative electrolysis because there is no active material in the concrete. In this embodiment, the solid electrolyte 30 (30B) in which the regenerative electrolysis counter electrode 20 is embedded is arranged so as to contact the end face 40b on the end 40B side of the resin container 40, but the solid electrolyte 30 (30B) may be accommodated inside the resin container 40 in which the end 40B side of the resin container 40 is extended in the axial direction (longitudinal direction).

[0054] Fifth embodiment Fig. 5 is a cross-sectional view showing a schematic diagram of a reference electrode according to one embodiment of the present invention, in which the same components as those shown in Fig. 1 are denoted by the same reference symbols, and description thereof will be omitted. 5, the reference electrode 400 of this embodiment includes an electrode body 10, a counter electrode for regenerative electrolysis 20, a solid electrolyte 30, and resin containers 410, 411. In the reference electrode 400 of this embodiment, the resin containers 410 and 411 are disposed adjacent to each other so as to be in contact with each other on their outer surfaces, the electrode body 10 and the solid electrolyte 30 are contained in the resin container 410, and the counter electrode for regenerative electrolysis 20 and the solid electrolyte 30 are contained in the resin container 411. The counter electrode for regenerative electrolysis 20 is embedded in a solid electrolyte 30 that is different from the solid electrolyte 30 in which the electrode body 10 is embedded.

[0055] One end 410A of the resin container 410 is sealed with the solid electrolyte 30. The other end 410B of the resin container 410 is sealed with the filled resin 50. One end 411A of the resin container 411 is sealed with the solid electrolyte 30. The other end 411B of the resin container 411 is sealed with the filled resin 50. By embedding the counter electrode 20 for regeneration electrolysis in a solid electrolyte 30 different from the solid electrolyte 30 in which the electrode body 10 is embedded, there is no conduction between the electrode body 10 and the counter electrode 20 for regeneration electrolysis since there is no active material in the concrete during regeneration electrolysis.

[0056] Sixth embodiment Fig. 64 is a cross-sectional view showing a schematic diagram of a reference electrode according to one embodiment of the present invention. In Fig. 6, the same components as those shown in Fig. 1 are denoted by the same reference symbols, and the description thereof will be omitted. As shown in FIG. 6, the reference electrode 500 of this embodiment includes an electrode body 10, a counter electrode for regenerative electrolysis 310, a solid electrolyte 30, and a resin container 40.

[0057] In the reference electrode 500 of this embodiment, a hollow cylindrical counter electrode for regenerative electrolysis 510 is disposed so as to contact the end face 40b on the other end 40B side of the resin container 40. One end 40A side of the resin container 40 is sealed with the solid electrolyte 30. The other end 40B of the resin container 40 and the counter electrode for regenerative electrolysis 510 are sealed with a filled resin 50.

[0058] The counter electrode 510 for regenerative electrolysis and the counter electrode 20 for regenerative electrolysis are made of the same material. The counter electrode 510 for regenerative electrolysis is connected to a lead wire 71 at its inner surface 510a by a crimp terminal 61. The counter electrode 310 for regenerative electrolysis is placed in contact with concrete. The counter electrode 510 for regenerative electrolysis is made to have a hollow cylindrical shape and is placed in contact with concrete, so that there is no active material in the concrete during regenerative electrolysis, and therefore no electrical conduction occurs between the electrode body 10 and the counter electrode 20 for regenerative electrolysis.

[0059] [Manufacturing method of reference electrode] The manufacturing method of the reference electrode of this embodiment includes a polishing step of polishing the surface 10a of the electrode body 10, a formation step of electrolytically oxidizing the polished surface 10a of the electrode body 10 in an alkaline solution to form an oxide layer on at least a part of the surface 10a of the electrode body 10 by oxidizing the metal constituting the electrode body 10, a coating step of applying a potential stabilizer to the electrode body 10 having the oxide layer, a polishing step of polishing the surface of the counter electrode 20 for regenerative electrolysis, and a coating step of applying a solid electrolyte or the like to the polished surface of the counter electrode 20 for regenerative electrolysis.

[0060] A method for manufacturing the reference electrode 1 shown in FIG. 1 will now be described.

[0061] First, a cylindrical resin container 40 of a predetermined material and dimensions, the electrode body 10, the counter electrode for regenerative electrolysis 20, and a composition serving as raw materials for the solid electrolyte 30 (hereinafter also referred to as "electrolyte composition") are prepared. A commercially available product or a cast product formed using a mold of any shape may be used as the electrode body 10. A lead wire 70 is attached to one end of the electrode body 10 in the axial direction. The counter electrode for regenerative electrolysis 20 may be a commercially available product or a product molded into any shape. A lead wire 71 is attached to one end in the axial direction of the counter electrode for regenerative electrolysis 20. However, when a steel material buried in a concrete structure is used as the counter electrode for regenerative electrolysis 20, the lead wire 71 may be attached to any part of the steel material or to an existing terminal rising from the steel material.

[0062] Next, the surface 10a of the electrode body 10 and the surface of the counter electrode 20 for regenerative electrolysis are polished (polishing step). By polishing the surface 10a of the electrode body 10 and the surface of the counter electrode 20 for regenerative electrolysis, impurities (dirt and inclusions in the metal) and inactive films on the surface 10a of the electrode body 10 and the surface of the counter electrode 20 for regenerative electrolysis can be removed, and the surface 10a of the electrode body 10 and the surface of the counter electrode 20 for regenerative electrolysis can be made active. As a result, the efficiency of the electrode body 10 during electrolytic oxidation can be increased, and the surface resistance of the counter electrode 20 for regenerative electrolysis can be reduced. The polishing step may involve, for example, mechanical polishing, chemical polishing (wet etching or dry etching), or electrolytic polishing.

[0063] When mechanically polishing the surface 10a of the electrode body 10 and the surface of the regenerative electrolysis counter electrode 20, for example, abrasive paper may be used, and the grit size of the abrasive paper is preferably, for example, about medium grit size #120 to #240. When wet etching the surface 10a of the electrode body 10, it is necessary to use a polishing liquid suitable for the material of the electrode body 10. For example, when the electrode body 10 is made of silver, it is preferable to immerse the electrode body 10 in a polishing liquid consisting of 10 mass % ferric chloride and 90 mass % distilled water for about 3 seconds to 1800 seconds. When dry etching the surface 10a of the electrode body 10 and the surface of the counter electrode for regenerative electrolysis 20, the etching can be performed using plasma of a gas reactive with the material of the electrode body 10 or the counter electrode for regenerative electrolysis 20 or an inert gas. When electrolytically polishing the surface 10a of the electrode body 10, it is necessary to use a polishing liquid suitable for the material of the electrode body 10. For example, when the electrode body 10 is made of silver, it is preferable to adjust the polishing liquid, which is made of 40% by volume of concentrated phosphoric acid, 40% by volume of ethanol, and 20% by volume of distilled water, to 40°C, use silver (electrode body 10) as the anode and aluminum as the cathode, and apply a voltage of 25V to 30V for about 4 to 6 minutes. As described above, various types of polishing methods have been exemplified, and only one of them may be performed, or two or more of them may be performed in the polishing step.

[0064] After the polishing step, the polished surface 10a of the electrode body 10 is electrolytically oxidized in an alkaline solution to form an oxide layer (forming step). As the alkaline solution, a saturated calcium hydroxide solution is preferable. The current density during electrolytic oxidation was 0.005mA / cm 2 More than 20mA / cm 2 Less than 0.01mA / cm is preferable. 2 More than 15mA / cm 2 Less than 0.05 mA / cm is more preferable. 2 More than 10mA / cm 2 The following is even more preferable: When the current density during electrolytic oxidation is within the above-mentioned numerical range, an oxide layer of sufficient thickness can be formed on the surface 10a of the electrode body 10, and the electrode potential is likely to be stable. In the electrolytic oxidation of the electrode body 10, the amount of electrolysis electricity is 30 mC / cm 2 More than 500mC / cm 2 Less than 50mC / cm is preferable. 2 More than 400mC / cm 2 Less than 70mC / cm is more preferable. 2 More than 300mC / cm 2 When the amount of electricity for electrolysis is equal to or greater than the lower limit, an oxide layer of sufficient thickness can be formed. When the amount of electricity for electrolysis is equal to or less than the upper limit, it is advantageous in terms of cost. The electrolytic oxidation time is adjusted so that the above-mentioned amount of electricity for electrolysis is obtained at the above-mentioned current density, but it is preferable to carry out electrolysis for at least about 30 seconds regardless of the current density, so that the electrode potential becomes stable.

[0065] When applying the potential stabilizer to the surface 10a of the electrode body 10, a stabilizer composition made into a paste by adding water may be applied to the surface 10a of the electrode body 10 and the surface of the oxide layer, and solidified to form the first coating layer 11. The oxide layer is present between the electrode body 10 and the first coating layer 11.

[0066] After the forming step, with the electrode body 10 and the counter electrode for regenerative electrolysis 20 held in appropriate positions in the resin container 40, the inside of the resin container 40 is filled with the solid electrolyte 30 and allowed to solidify. Next, a composition serving as the raw material for filled resin 50 (hereinafter also referred to as "filled resin composition") is filled into the opening of resin container 40 on the side where lead wire 70 and lead wire 71 are attached, and allowed to solidify. The solid electrolyte 30 and the filled resin composition may be filled first, or the filled resin composition may be filled first, or both may be filled at the same time. When forming a liquid junction, for example, a cylindrical frame made of paper is provided in the resin container 40 on the side of the solid electrolyte 30 so that a liquid junction of desired dimensions is formed on the side of the solid electrolyte 30, and a raw material composition (hereinafter also referred to as "liquid junction composition") is filled into the frame to obtain the desired dimensions, and then solidified. When the liquid junction is made to be tortuous, the liquid junction composition is filled into a flexible container, and the container is made to be tortuous to allow the liquid junction composition to solidify, resulting in a liquid junction having a tortuous liquid junction path. As shown in FIG. 1, the formation of a solid electrolyte in which a counter electrode for regenerative electrolysis 20 is embedded in the end of a resin container 40 filled with a filling resin 50 may be performed by the same method as that used for forming the liquid junction described above.

[0067] Through the above steps, the reference electrode 1 is obtained.

[0068] The reference electrode 1 of this embodiment includes an electrode body 10 and a counter electrode for regenerative electrolysis 20. Therefore, when the oxide layer on the surface 10a of the electrode body 10 is reduced and the electrode potential fluctuates significantly, the oxide layer can be regenerated by applying a voltage to the counter electrode for regenerative electrolysis 20 to perform regenerative electrolysis on the electrode body 10. Therefore, the reference electrode 1 can be regenerated on the spot when its performance is degraded.

[0069] In the regenerative electrolysis of the electrode body 10, the current density is 0.005 mA / cm 2 More than 20mA / cm 2 Less than 0.01mA / cm is preferable. 2 More than 15mA / cm 2 Less than 0.05 mA / cm is more preferable. 2 More than 10mA / cm 2 When the current density is equal to or higher than the lower limit, the oxide layer can be regenerated. When the current density is equal to or lower than the upper limit, it is advantageous in terms of cost.

[0070] In the regeneration electrolysis of the electrode body 10, the amount of electricity in the regeneration electrolysis is 30 mC / cm 2 More than 500mC / cm 2 Less than 50mC / cm is preferable. 2 More than 400mC / cm 2 Less than 70mC / cm is more preferable. 2 More than 300mC / cm 2 When the amount of regenerated electrolytic electricity is equal to or more than the lower limit, the oxide layer can be regenerated. When the amount of regenerated electrolytic electricity is equal to or less than the upper limit, it is advantageous in terms of cost.

[0071] In the regeneration electrolysis of the electrode body 10, the time for performing the regeneration electrolysis is adjusted so that the above-mentioned amount of electrolysis electricity is obtained at the above-mentioned current density, but it is preferable to perform the electrolysis for at least about 30 seconds regardless of the current density. As a result, the electrode potential becomes stable.

[0072] The reference electrode 1 of the present embodiment uses the solid electrolyte 30, which makes it difficult for substances that may react with the active material to reach the electrode body 10. Therefore, for example, when the active material is silver oxide, the reference electrode 1 exhibits a more stable electrode potential even in an environment with a high concentration of chloride ions. The reference electrode 1 of this embodiment can be made compact by minimizing its length, making it easy to install in an actual structure. The reference electrode 1 of this embodiment is excellent in terms of cost because the content of the potential stabilizer is kept to a necessary minimum.

[0073] Although the reference electrode of this embodiment has been described above, the present invention is not limited to the above embodiment and can be modified as appropriate without departing from the spirit of the present invention. In the above-described embodiment, the reference electrode has a cylindrical shape extending in the axial direction, but the reference electrode may have a curved or branched shape. EXAMPLES

[0074] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0075] [Example 1] (Restoring silver oxide electrode potential through regenerative electrolysis) A reference electrode was fabricated with the same configuration as that shown in Figure 1. Silver was used as the metal constituting the electrode body. The electrode potential of the obtained reference electrode was measured in a saturated calcium hydroxide solution. The potential measurement was performed with a saturated silver-silver chloride reference electrode (SSE). The electrode potential of the reference electrode in other examples was also measured with the SSE as the reference. After confirming the deterioration of performance, regeneration electrolysis was performed in a saturated calcium hydroxide solution. Regeneration electrolysis was performed twice in total, on the 38th and 90th test days. The results of measuring the change in the potential of the reference electrode over time are shown in Figure 7. The results shown in Figure 7 confirm that the potential of the reference electrode can be restored to the normal potential (220 ± 20 mV vs. SSE) by generating silver oxide on the surface of the silver that constitutes the electrode body through regenerative electrolysis, and that the potential of the reference electrode after regenerative electrolysis is reproducible.

[0076] [Example 2] A pure silver wire is immersed in a saturated calcium hydroxide solution and a current of 0.1 mA / cm 2 ~0.6mA / cm 2 The amount of silver oxide produced by electrolytic oxidation was evaluated using a constant current reduction method. The results are shown in Figure 8. From the results shown in Figure 8, when silver oxide is generated on a silver surface by electrolytic oxidation, if the electrolytic oxidation is performed at an excessive current density, active dissolution of silver and oxygen generation also occur at the same time, reducing the efficiency of silver oxide generation. Conversely, it was found that silver oxide is not generated when the current density is low. In other words, the current density at which silver oxide is efficiently generated is 0.2 mA / cm 2 0.4mA / cm or less 2 It was found that the following was true.

[0077] [Example 3] The structure is the same as that shown in FIG. 1, and the amount of electrolysis electricity is 20 mC / cm 2 ~100mC / cm 2 The reference electrode was made of silver. The potential of the resulting reference electrode was measured in a saturated calcium hydroxide solution, and the results are shown in Figure 9. From the results shown in Figure 9, the electrochemical reaction was carried out under conditions with a small amount of electrochemical electricity (20 mC / cm 2 ~40mC / cm 2 ), the reference electrode showed a change in potential from the beginning. 2 ) showed a stable potential for over 60 days. This shows that the greater the amount of electrolysis, the more stable the potential becomes.

[0078] [Example 4] Electrolytic oxidation (100mC / cm 2We fabricated an electrode by solidifying the electrolytically oxidized silver wire with cement, and an electrode consisting of only the electrolytically oxidized silver wire. Each electrode was immersed in a saturated calcium hydroxide solution, and the potential of each electrode was measured. The results are shown in Figure 10. From the results shown in Figure 10, the electrode that was left electrolytically oxidized (liquid electrolyte in the figure) showed a stable potential for about four days, after which it showed a sudden change in potential. On the other hand, the electrode solidified with cement (solid electrolyte in the figure) showed an initial change in potential, but then showed a stable potential for a long time. From this, it is believed that a reference electrode made using a solid electrolyte can have a longer life.

[0079] [Example 5] A reference electrode was fabricated with the same structure as that shown in Figure 1. Silver was used as the metal constituting the electrode body. An electrode containing a solid electrolyte with silver oxide powder added as an active material, and an electrode containing a solid electrolyte without silver oxide powder added were fabricated. Each electrode was immersed in a saturated calcium hydroxide solution, and the potential of each electrode was measured. The results are shown in Figure 11. From the results shown in Figure 11, the electrode containing a solid electrolyte without the addition of silver oxide powder experienced a change in potential from the early stages of the test. In contrast, the electrode containing a solid electrolyte with the addition of silver oxide powder showed little change in potential, and showed a relatively stable potential. This shows that adding an active material (silver oxide powder) to a solid electrolyte leads to improved potential stability.

[0080] [Example 6] A reference electrode was fabricated with the same structure as that shown in Figure 1. Silver was used as the metal constituting the electrode body. An arbitrary amount of active material (silver oxide powder) was added to the solid electrolyte. The obtained reference electrode was immersed in a saturated calcium hydroxide solution, and the potential of the reference electrode was measured. The results are shown in FIG. From the results shown in FIG. 12, from the initial stage of the test until the 100th day, all of the reference electrodes in which the amount of active material added was 1% by mass to 30% by mass relative to the total mass of the solid electrolyte (100% by mass) showed a stable potential (220±20 mV vs. SSE). After 100 days, the electrode in which the amount of active material added was 1% by mass showed a significant change in potential. The electrode in which the amount of active material added was 5% by mass also showed a slight change in potential. The electrodes in which the amount of active material added was 10% by mass to 30% by mass showed a stable potential. From this, it was found that the amount of active material added to the solid electrolyte needs to be at least 1% by mass. Furthermore, if long-term potential stability is expected, it is considered that the amount of active material added needs to be 10% by mass or more.

[0081] [Example 7] A concrete specimen with a reference electrode embedded therein, having the same structure as that shown in Figure 2, was exposed outdoors. The potential of the reference electrode inside the concrete specimen was measured during exposure. The results are shown in Figure 13. From the results shown in Fig. 13, a decrease in performance was observed from about the 200th test day. 0.1mA / cm on the 230th test day 2 The reference electrode was regenerated at a constant current density of 1000 mC / cm for 1,000 seconds. 2 As a result, it was confirmed that performance was restored through regenerative electrolysis. [Industrial Applicability]

[0082] The reference electrode of the present invention can be used in environments with high chloride ion concentrations, such as for measuring the potential of steel materials in concrete bridges, steel materials in reinforced concrete in seawater, piping in air mortar-filled sheath pipes, steel materials in concrete structures that use seawater, steel materials in improved soil, and steel materials in submerged tunnels. It can also be used to measure the potential of steel materials in soil. For this reason, it has extremely high industrial applicability. [Explanation of symbols]

[0083] 1,100,200,300,400,500 Reference electrode 10 Electrode body 11 First covering layer 20,210,510 Regenerative electrolytic counter electrodes 30 Solid electrolyte 40,410,411 Resin containers 50, Filled resin 60,61 Crimp terminal 70,71 Lead wire

Claims

1. A reference electrode that is embedded in concrete and is used to measure the electric potential of a metal in the concrete, comprising: a cylindrical resin container that accommodates the electrode body in contact with the solid electrolyte; a counter electrode for regenerative electrolysis in contact with at least one of the solid electrolyte and the concrete; The electrode body has, on at least a portion of its surface, at least one of an oxide layer formed by oxidizing a metal constituting the electrode body and a coating layer.

2. 2. The reference electrode according to claim 1, wherein said electrode body and said counter electrode for regenerative electrolysis are embedded in the same solid electrolyte.

3. 2. The reference electrode according to claim 1, wherein the electrode body and the counter electrode for regenerative electrolysis are embedded in different solid electrolytes.

4. 2. The reference electrode according to claim 1, wherein the metal constituting the electrode body is silver.

5. 2. The reference electrode according to claim 1, wherein the counter electrode for regeneration electrolysis has a second coating layer covering at least a part of its surface.

6. 2. The reference electrode according to claim 1, further comprising a liquid junction sealing said solid electrolyte.

7. 2. The reference electrode according to claim 1, wherein the counter electrode for regenerative electrolysis is a metal buried in concrete.

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