JP7464315B2 - Oxygen electrode, measuring device, and method for manufacturing oxygen electrode - Google Patents

Description

The present invention relates to an oxygen electrode and a measuring device.

Conventionally, oxygen electrodes used to measure the concentration of dissolved oxygen in liquids have been known (see, for example, Patent Document 1). With this oxygen electrode, when a voltage is applied between a cathode and an anode in contact with an electrolyte, a current corresponding to the dissolved oxygen concentration flows through the electrolyte, making it possible to measure the dissolved oxygen concentration.

However, in the oxygen electrode of Patent Document 1, the water content of the electrolyte is evaporated during manufacturing, resulting in a state in which the electrolyte is devoid of water and the dissolved oxygen concentration cannot be measured. Therefore, in order to make this oxygen electrode function, water is supplied to the electrolyte through an oxygen-permeable membrane by a method such as immersing it in water at room temperature overnight or more, thereby activating the electrolyte.

Japanese Patent Application Laid-Open No. 10-78407

However, the oxygen electrode of Patent Document 1 had the problem that after the electrolyte was activated, at least a portion of the water in the electrolyte evaporated, resulting in an unstable response to the applied voltage.

The present invention has been made in consideration of the above, and aims to provide an oxygen electrode and measurement device that have a stable response to an applied voltage.

In order to solve the above-mentioned problems and achieve the object, an oxygen electrode according to one aspect of the present invention is characterized by comprising a cathode formed on a substrate, an anode formed on the substrate, an electrolyte layer that is disposed on the cathode and the anode and contains an electrolyte and a moisturizing agent, and an oxygen-permeable membrane that covers the electrolyte layer.

In one aspect of the oxygen electrode of the present invention, the electrolyte layer is a sheet member that is placed on at least a portion of the cathode and the anode and is impregnated with an electrolyte and a moisturizing agent.

Another aspect of the oxygen electrode of the present invention is that the sheet member is made of paper.

The oxygen electrode according to one aspect of the present invention is characterized in that it includes a spacer that is approximately the same thickness as the sheet member and is arranged to surround the edge of the sheet member.

In one aspect of the present invention, the oxygen electrode is characterized in that the moisturizer contains at least one of sucrose, glucose, or sorbitol.

The measurement device according to one aspect of the present invention is characterized by having an oxygen electrode and a sample injection section that is placed on the oxygen permeable membrane and into which a sample can be injected.

The measurement device according to one aspect of the present invention is characterized in that multiple pairs of the cathode and the anode are formed.

The present invention makes it possible to realize an oxygen electrode and measurement device that has a stable response to an applied voltage.

FIG. 1 is an exploded perspective view showing the structure of an oxygen electrode according to an embodiment of the present invention. FIG. 2 is a view of the oxygen electrode shown in FIG. FIG. 3 is a cross-sectional view corresponding to the line BB in FIG. FIG. 4 is a diagram showing the change in current over time when the time of immersion in water is changed. FIG. 5 is a diagram showing the change in current over time when the potential applied between the electrodes is changed. FIG. 6 is a graph showing the change in current over time when a moisturizer is included and when it is not included. FIG. 7 is a cross-sectional view of an oxygen electrode according to a modified example.

The following describes in detail the form (embodiment) for carrying out the present invention with reference to the drawings. The present invention is not limited to the contents described in the following embodiment. Furthermore, the components described below include those that a person skilled in the art would easily imagine and those that are substantially the same. Furthermore, the components described below can be combined as appropriate.

In addition, in the drawings, the same or corresponding elements are appropriately labeled with the same reference numerals. It should be noted that the drawings are schematic, and the dimensional relationships and ratios of each element may differ from reality. There may also be parts in which the dimensional relationships and ratios differ between the drawings.

(Embodiment)
[Configuration of oxygen electrode]
Fig. 1 is an exploded perspective view showing the configuration of an oxygen electrode according to an embodiment of the present invention. Fig. 2 is a view seen from an arrow A of the oxygen electrode shown in Fig. 1. Fig. 3 is a cross-sectional view corresponding to the line B-B in Fig. 2. As shown in Figs. 1 to 3, an oxygen electrode 1 according to the present embodiment includes a substrate 2, a cathode 3, a wiring 4, an electrode pad 5, an anode 6, a wiring 7, an electrode pad 8, an insulating layer 9, a sheet member 10, and an oxygen permeable membrane 11.

Substrate 2 is a flat substrate made of glass.

The cathode 3 is formed on the substrate 2 and is, for example, circular, but the shape is not particularly limited. The cathode 3 is made of platinum (Pt), but may also be made of gold (Au) or silver (Ag).

The wiring 4 electrically connects the cathode 3 and the electrode pad 5.

The electrode pad 5 is electrically connected to the outside. The electrode pad 5 is used, for example, when applying a voltage between the cathode 3 and the anode 6.

The anode 6 is formed on the substrate 2 and is arranged concentrically around the cathode 3, but the shape is not particularly limited. The anode 6 is made of silver (Ag) but may be made of lead (Pb). When the anode 6 is made of silver, chlorine ions in the electrolyte react with the anode 6 when a current is passed through it to form silver chloride (AgCl).

The wiring 7 electrically connects the anode 6 and the electrode pad 8.

The electrode pad 8 is electrically connected to the outside. The electrode pad 8 is used, for example, when applying a voltage between the cathode 3 and the anode 6.

The insulating layer 9 should expose the cathode 3, anode 6, and electrode pads 5, 8, and cover the remaining parts including the wiring 4, 7, but may also cover only a small portion of the ends of the cathode 3 and anode 6. Also, if most of the anode 6 is covered with this insulating layer 9 and only the end on the cathode 3 side is partially exposed, silver chloride is formed quickly, stabilizing the current value and achieving a long life. The insulating layer 9 is made of polyimide, for example, but any material having insulating properties will do.

The sheet member 10 (electrolyte layer) is disposed on the cathode 3 and the anode 6, and contains an electrolyte and a moisturizing agent. Specifically, the sheet member 10 is a paper placed on at least a part of the cathode 3 and the anode 6. Since the sheet member 10 is in contact with both the cathode 3 and the anode 6, when a voltage is applied between the cathode 3 and the anode 6, a current flows according to conditions such as the dissolved oxygen concentration. In addition, as the electrolyte layer, a liquid containing an electrolyte and a moisturizing agent may be injected into the lower layer of the oxygen permeable membrane 11. In addition, as the electrolyte layer, a paste containing an electrolyte and a moisturizing agent may be applied onto the cathode 3 and the anode 6. By including a moisturizing agent in the electrolyte layer, evaporation of water from the electrolyte layer is suppressed, and the response of the oxygen electrode 1 is stabilized.

The sheet member 10 is, for example, a circular piece of paper with a diameter of 7.0 mm and a thickness of 20 μm. The sheet member 10 may be made of any material that is uniform in thickness and can be impregnated with a liquid containing an electrolyte and a moisturizing agent, and may be made of cloth or nonwoven fabric. The uniform thickness of the sheet member 10 forms a homogeneous electrolyte layer, stabilizing the response of the oxygen electrode 1. Furthermore, the use of the sheet member 10 improves the mechanical strength, stabilizing the response of the oxygen electrode 1. The thickness of the sheet member 10 can be selected appropriately depending on the material, and may be, for example, 10 μm to several hundreds of μm, so long as it has a sufficient strength. The shape of the sheet member 10 can be changed depending on the shapes of the cathode 3 and the anode 6, and may be such that at least a portion of the sheet member 10 is in contact with the cathode 3 and the anode 6.

The sheet member 10 is impregnated with these components by immersing the paper in a solution containing 2.0 M KCl as an electrolyte, 2.0 M Tris-HCl as a buffer component for adjusting the pH, 5.0 wt % sorbitol as a moisturizer, and 4.0 wt % polyvinylpyrrolidone as an adhesive for the substrate 2. By immersing the paper sheet member 10 in this solution, the electrolyte is uniformly absorbed into the sheet member 10, stabilizing the response of the oxygen electrode 1. The moisturizer is not limited to sucrose, and may be, for example, glucose or sorbitol. The electrolyte, buffer component, and adhesive are just examples, and the materials and amounts can be changed as appropriate.

The oxygen-permeable membrane 11 is formed to cover the sheet member 10. The oxygen-permeable membrane 11 is made of, for example, silicone.

[Method for producing oxygen electrode]
Next, a method for producing the oxygen electrode 1 will be described.

1. Cleaning of the Substrate First, the glass substrate, which is the substrate 2, is cleaned. Specifically, the substrate 2 is immersed for 5 minutes in a boiled aqueous solution of 25 wt % ammonia water, 30 wt % hydrogen peroxide water, and pure water mixed in a ratio of 1:1:4. Thereafter, the substrate 2 is immersed in boiled pure water for 5 minutes and rinsed. The substrate 2 is further immersed in another boiled pure water for 5 minutes and rinsed, and then naturally dried.

2. Formation of the Cathode Next, a platinum electrode is formed as the cathode 3. First, a positive photoresist is formed on the cleaned substrate 2 by spin coating at 500 rpm for 5 seconds and at 2000 rpm for 10 seconds. Then, the substrate is baked in a dry oven at 80° C. for 30 minutes. Then, the substrate is naturally cooled in a dark place for 15 minutes or more.

Using a mask, expose the film to the G-line (wavelength 436 nm) of a mask aligner for 40 seconds. Then, immerse the film in toluene at 30°C for 40 seconds, bake in a dry oven at 80°C for 15 minutes, and allow to cool naturally in the dark for at least 15 minutes. Then, develop the film using a developer for 60 seconds (with stirring), rinse with distilled water, and dry with nitrogen gas.

After performing dry etching for 5 minutes using a sputtering device with a power of 200 W and an argon atmosphere of approximately 0.55 Pa, chromium, which will become an adhesive layer for the platinum layer, is sputtered for 5 minutes (approximately 30 nm) at a power of 100 W and an argon atmosphere of approximately 0.35 Pa. Next, platinum is sputtered twice for 15 minutes at a power of 100 W and an argon atmosphere of approximately 0.35 Pa, for a total of 30 minutes (approximately 300 nm).

Then, the substrate 2 on which the platinum has been sputtered is immersed in acetone for one hour. Furthermore, unnecessary parts other than the platinum layer are peeled off using a cotton swab. The substrate is then rinsed with distilled water and dried with nitrogen gas to form the cathode 3.

3. Formation of the Anode Next, a silver electrode is formed as the anode 6. First, a positive photoresist is formed on the cleaned substrate 2 by spin coating at 500 rpm for 5 seconds and at 2000 rpm for 10 seconds. Then, the substrate is baked in a dry oven at 80° C. for 30 minutes. Then, the substrate is naturally cooled in a dark place for 15 minutes or more.

Using a mask, expose the film to the G-line (wavelength 436 nm) of a mask aligner for 40 seconds. Then, immerse the film in toluene at 30°C for 40 seconds, bake in a dry oven at 80°C for 15 minutes, and allow to cool naturally in the dark for at least 15 minutes. Then, develop the film using a developer for 60 seconds (with stirring), rinse with distilled water, and dry with nitrogen gas.

After performing dry etching for 5 minutes using a sputtering device with a power of 200 W and an argon atmosphere of approximately 0.55 Pa, silver is sputtered twice for 15 minutes each at a power of 100 W and an argon atmosphere of approximately 0.35 Pa for a total of 30 minutes (approximately 550 nm).

Then, the substrate 2 on which the platinum and silver have been sputtered is immersed in acetone for one hour, and then unnecessary parts other than the silver are peeled off using a cotton swab. The substrate is then rinsed with distilled water and dried with nitrogen gas to form the anode 6.

4. Formation of Insulating Layer Next, a polyimide layer is formed as the insulating layer 9. First, a polyimide prepolymer is formed on the substrate 2 by spin coating at 500 rpm for 10 seconds and at 2000 rpm for 5 seconds. Then, the substrate is baked in a dry oven at 80° C. for 30 minutes.

A positive photoresist is formed on the substrate 2 on which the polyimide layer has been formed by spin coating at 500 rpm for 5 seconds and 2000 rpm for 10 seconds. Then, the substrate is baked in a dry oven at 80°C for 30 minutes.

After baking, cool in a dark place for about 10 minutes, then use a mask to expose to the G line of a mask aligner for 40 seconds.

After exposure, the substrate 2 is immersed in the developer for 120 seconds (with stirring, about 3 rotations per second, and the temperature of the developer adjusted to about 25°C), and immediately thereafter, it is cleaned in an ultrasonic cleaner for 10 seconds. The surface is then rinsed with distilled water, and the size of the holes is checked under a microscope.

The substrate 2 is immersed in ethanol and stirred for 5 minutes to remove the resist layer. It is then rinsed with ethanol and dried with nitrogen gas. It is then heated on a hot plate at 150°C for 15 minutes, 250°C for 15 minutes, and 280°C for 30 minutes to denature the polyimide and form an insulating layer 9. Light is blocked during heating.

5. Formation of Sheet Member Next, the sheet member 10 is formed. First, a solution containing 2.0 M KCl, 2.0 M Tris-HCl, 5.0 wt % sorbitol, and 4.0 wt % polyvinylpyrrolidone is prepared. Then, this solution is impregnated into a 20 μm thick piece of paper cut into a circle with a diameter of 7.0 mm. Furthermore, this paper is placed on the cathode 3 and anode 6, and naturally dried to form the sheet member 10.

6. Formation of Oxygen-Permeable Film Next, the oxygen-permeable film 11 is formed. Specifically, the oxygen-permeable film 11 is formed by spin-coating silicone at 1500 rpm for 10 seconds.

[Activation of the electrolyte of the oxygen electrode]
Next, the time for immersion in water to activate the electrolyte of the oxygen electrode 1 will be described. Since the oxygen permeable membrane 11 only allows gas to pass through, when the oxygen electrode 1 is immersed in water, water vapor passes through the oxygen permeable membrane 11, and moisture is supplied to the sheet member 10, activating the electrolyte. After immersing the oxygen electrode 1 in water for 29 hours, 24 hours, and 5 hours, a voltage of -0.8 V was applied between the cathode 3 and the anode 6, and the change in current over time was measured.

FIG. 4 is a diagram showing the change in current over time when the time of immersion in water is changed. In FIG. 4, the vertical axis represents current, and the horizontal axis represents time. Line L1 represents the measurement results when the immersion time is 29 hours, line L2 represents the measurement results when the immersion time is 24 hours, and line L3 represents the measurement results when the immersion time is 5 hours. As shown in FIG. 4, the longer the immersion time in water, the greater the power generated for the applied voltage. At the time zero, the oxygen electrode 1 was taken out of the water and sodium sulfite (Na ₂ SO ₃ ), which can be used as an oxygen scavenger, was allowed to act on it. Then, as time passed from zero, the dissolved oxygen concentration decreased due to the oxygen scavenger, and the current decreased, indicating that a current corresponding to the dissolved oxygen concentration flows through the oxygen electrode 1.

The above shows that the longer the oxygen electrode 1 is immersed in water, the better the response to the applied voltage. However, if the oxygen electrode 1 is left immersed in water for a long period of time, the sheet member 10 may be damaged, so an immersion time of about 24 hours is appropriate. When the oxygen electrode 1 is immersed in water for about 24 hours, the electrolyte impregnated in the sheet member 10 is sufficiently activated and the oxygen electrode 1 becomes functional.

[Voltage applied to oxygen electrode]
Next, a description will be given of the voltage applied between the cathode 3 and the anode 6 of the oxygen electrode 1. Voltages of -0.7 V, -0.8 V, and -0.9 V were applied between the cathode 3 and the anode 6, and the change in current over time was measured.

Figure 5 shows the change in current over time when the potential applied between the electrodes is changed. The vertical axis of Figure 5 shows current, and the horizontal axis shows time. Line L11 shows the measurement results when the applied voltage is -0.7 V, line L12 shows the measurement results when the applied voltage is -0.8 V, and line L13 shows the measurement results when the applied voltage is -0.9 V. As shown in Figure 5, in line L13, the current does not approach zero even after sufficient time has passed since the oxygen scavenger was applied. This is due to the effect of residual power associated with the reduction of protons. On the other hand, in lines L11 and L12, the effect of residual power is small enough to be ignored.

From the above, the optimal voltage to be applied between the cathode 3 and the anode 6 is -0.8V.

[Response of oxygen electrode to applied voltage]
Next, a description will be given of the response of the oxygen electrode 1 to an applied voltage. A voltage of −0.8 V was applied between the cathode 3 and the anode 6 in both cases where the sheet member 10 contained a moisturizing agent and where the sheet member 10 did not contain a moisturizing agent, and the change in current over time was measured.

Figure 6 is a diagram showing the change in current over time when a moisturizer is included and when it is not included. The vertical axis of Figure 6 represents current, and the horizontal axis represents time. Line L21 represents the measurement result when the sheet member 10 includes sorbitol as a moisturizer, and line L22 represents the measurement result when the sheet member 10 does not include a moisturizer. As shown in Figure 6, line L21 provides a stable response to the applied voltage over a long period of time. On the other hand, line L22 provides an electrolyte that becomes inactive as the water in the electrolyte evaporates over time, causing the electrolyte to become inactive, resulting in an unstable response to the applied voltage.

According to the embodiment described above, the sheet member 10 is impregnated with a moisturizing agent, thereby realizing an oxygen electrode 1 that has a stable response to an applied voltage for a long period of time.

In addition, according to the embodiment, since the sheet member 10 is impregnated with the electrolyte, the electrolyte layer can be formed uniformly. As a result, not only is the response stable during measurement, but the rate at which oxygen electrodes 1 that operate stably can be manufactured increases, and assembly during manufacturing is also easy. In contrast, when a liquid or paste-like electrolyte is placed on the cathode 3 and anode 6, the electrolyte under the oxygen permeable membrane 11 is in a soft state during measurement, so the thickness of the electrolyte is likely to be non-uniform, and the response is not stable.

(Modification)
Fig. 7 is a cross-sectional view of an oxygen electrode according to a modified example. As shown in Fig. 7, the oxygen electrode 1A has a spacer 12A that has approximately the same thickness as the sheet member 10 and is arranged so as to surround the edge of the sheet member 10. The spacer 12A is made of a resin such as polyimide, but the material is not particularly limited. In this case, no step is formed in the oxygen permeable membrane 11, so that it is possible to prevent a break or the like from being formed in the oxygen permeable membrane 11 during manufacturing, which would cause the operation to become unstable.

〔measuring device〕
A measuring device may be produced that includes the oxygen electrode 1. Specifically, by placing a sample injection section having a chamber into which a sample can be injected on the oxygen permeable membrane 11, a measuring device capable of measuring the dissolved oxygen concentration in a sample can be realized.

It is also possible to fabricate a measurement device in which multiple pairs of the above-mentioned cathode 3 and anode 6 are formed. By providing multiple pairs of cathode 3 and anode 6, it is possible to perform measurements on multiple samples simultaneously.

REFERENCE SIGNS LIST 1, 1A oxygen electrode 2 substrate 3 cathode 4, 7 wiring 5, 8 electrode pad 6 anode 9 insulating layer 10 sheet member 11 oxygen permeable membrane 12A spacer

Claims (5)

a cathode formed on the substrate;
an anode formed on the substrate;
a spacer disposed so as to surround the outer periphery of the anode;
an oxygen permeable membrane covering the cathode, the anode and an inner periphery of the spacer ;
an electrolyte layer, which is a liquid containing an electrolyte and a moisturizing agent and is injected into a lower layer of the oxygen-permeable membrane and is in contact with the cathode and the anode;
Equipped with
The oxygen electrode , wherein the moisturizer includes at least one of sucrose, glucose, and sorbitol . The oxygen electrode of claim 1, characterized in that the electrolyte contains potassium chloride (KCl). The oxygen electrode according to claim 1 ;
a sample injection part that is placed on the oxygen permeable membrane and into which a sample can be injected;
A measuring device comprising: forming a cathode and an anode on a substrate;
A spacer is disposed so as to surround the outer periphery of the anode;
forming an oxygen permeable membrane covering the cathode, the anode and the inner periphery of the spacer ;
A method for manufacturing an oxygen electrode, comprising: injecting a liquid containing an electrolyte and a moisturizer containing at least one of sucrose, glucose, and sorbitol into a lower layer of the oxygen-permeable membrane so as to contact the cathode and the anode, thereby forming an electrolyte layer. 5. The method for producing an oxygen electrode according to claim 4 , wherein the electrolyte contains potassium chloride (KCl).

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