JPH05251114A - Hydrogen ion concentration detecting element and lead-acid battery provided with element thereof - Google Patents

Abstract

PURPOSE:To stably detect hydrogen ion concentration in a wide range. CONSTITUTION:A hydrogen ion detecting element is composed of a first electrode and a second electrode wherein the first electrode is an ion electrode which corresponds to the hydrogen ion concentration or is composed of an ion selective field effect type transistor and the second electrode is prepared by coating the surface of a silver 1 with silver chloride 2 to give an electrode, coating the electrode with a first film 3 composed of a mixture of a water soluble polymer compound and a salt which dissociate in water and produces chlorine ion, and coating the first film with a mixture of a water insoluble polymer compound and a proton sensitive material and a lead-acid storage battery is provided with the hydrogen ion cocentration detecting element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen ion concentration detecting element for measuring the hydrogen ion concentration in an aqueous solution and a lead storage battery equipped with this element.

[0002]

2. Description of the Related Art As a method for measuring the hydrogen ion concentration in an aqueous solution, an ion-selective electrode whose potential changes according to the target ion concentration and a reference electrode whose potential does not change even when the target ion concentration changes A general method is to combine the above and obtain the concentration from the potential difference between both electrodes.

A pH meter using a glass electrode is widely known as an ion-selective electrode for measuring hydrogen ion concentration, and molybdophosphoric acid << Old Carpenter, Murata, Ikeda,
Proceedings of the 34th Annual Meeting of the Analytical Chemistry Society of Japan, 2D05, P489 (1985)》
And dodecylamine << D. Ammann et.al., Anal. Chem., 53,
2267 (1981) >> and the like, a solid film type hydrogen ion electrode in which an ion-sensitive substance is immobilized by, for example, a polymer has also been proposed.
Furthermore, as a hydrogen ion sensitive substance, SiO ₂ , Al ₂ O
₃ , oxides such as Ta ₂ O ₅ and Si ₃ N ₄ 《Matsuo, Esashi,
Electrochemical, 50, 64 (1982) ", or titanium nitride (TiN
) Wakida, Makabe, Mochizuki, Yamane, East, Proposal of 58th Spring Annual Meeting of the Chemical Society of Japan 1,3IG17, P360 (1989) >> has been proposed for an ion selective field effect transistor (ISFET). ..

Standard hydrogen electrodes, calomel electrodes, silver chloride electrodes and the like are well known as reference electrodes, all of which are prepared by incorporating an aqueous electrolyte into the reference electrode.

On the other hand, in a lead storage battery, the charge / discharge reaction of the battery follows the following equation.

[Chemical 1]

That is, as the battery discharges, the sulfuric acid (H ₂ SO ₄ ) in the electrolytic solution is consumed and its concentration decreases,
On the contrary, as the charge progresses, sulfuric acid is produced and its concentration increases. In other words, since the consumption amount or production amount of sulfuric acid is proportional to the discharge electricity amount or the charge electricity amount, the charge / discharge state or the remaining capacity of the lead storage battery can be known by measuring the sulfuric acid concentration.

On the basis of such a principle, a float type hydrometer and a photorefractive hydrometer have been put to practical use in order to know the charge / discharge state of a lead storage battery. However, these pycnometers are generally large in size, and are not used by being integrally attached to a lead acid battery, but the method of pumping a part of the electrolyte solution out of the lead acid battery and then measuring its specific gravity is Has been adopted. Therefore, such a hydrometer cannot be used especially when the lead acid battery is a sealed type.

As a method for measuring the concentration of the electrolytic solution even in the sealed lead-acid battery, for example, West German Patent 2,254,2
As shown in No. 07 (1973), focusing on the fact that the water vapor pressure in the space above the sulfuric acid solution in vapor-liquid equilibrium with the sulfuric acid solution depends on the concentration of the sulfuric acid solution, the humidity sensor Method for measuring the concentration of sulfuric acid aqueous solution by measuring, and further developing this principle, the humidity sensor measures the partial pressure of water vapor diffused through the pores of the porous polypropylene membrane with the humidity sensor. Method 《JLWe
ininger et.al., J. Electrochem. Soc. , 129 , 2409 (1982)
], And an electrode-type hydrometer based on the principle that the potential difference between a lead dioxide electrode and a lead electrode depends on the concentration of sulfuric acid (for example, JP-A-60-62066).

[0009]

Regarding the reference electrode which has been used so far when the ion concentration is measured by the ion selective electrode, for example, the standard hydrogen electrode has excellent potential stability, but the system is not stable. It has a drawback that it is complicated and cannot be used easily, and that the calomel electrode and the silver chloride electrode are usually double-junction type and have a complicated shape and cannot be miniaturized.

Conventionally, hydrogen ion electrodes such as a pH meter have generally been drastically changed from a Nernst's straight line to a so-called acid error or alkali error in a region beyond the so-called pH measurement region (2 to 12). Since it shifts, it cannot be used in a strong acid or strong alkaline aqueous solution.
The concentration of sulfuric acid aqueous solution used in lead-acid batteries is usually in the range of specific gravity of about 1.28 to 1.05 (concentration of about 5.2 mol / l to 0.8 mol / l)
Therefore, there has been no proposal to use a hydrogen ion electrode as a sulfuric acid concentration sensor for a lead storage battery.
As an exception, in the case of the solid film type hydrogen ion sensor in which molybdophosphoric acid is bound with a binder as described above, it is reported that the Nernst equation is obeyed in the concentration range of the sulfuric acid aqueous solution used in this lead acid battery. .. Among the methods for measuring the hydrogen ion concentration using a field effect transistor with an oxide or nitride film attached, tantalum oxide (Ta
₂ O ₅ ) has been reported to show the most excellent properties << Matsuo, Esashi, Applied Physics 49 596 (1980) >>. In addition, there is also an example of using zirconium phosphate, which is a proton conductive solid electrolyte, as an ion sensitive substance <JP-A-3-165252>.

Further, in the method of measuring the sulfuric acid concentration using the conventional humidity sensor, the response is generally slow and there is a problem that sulfuric acid vapor corrodes the humidity sensor. In the case of the above-mentioned electrode type specific gravity sensor, self-discharge of the electrodes occurs,
Since it is necessary to apply an electric current from the outside to carry out electrolytic redox from time to time, there is a drawback that it is extremely troublesome in operation. Moreover, in the case of a sealed lead-acid battery, generally, a very small amount of sulfuric acid aqueous solution is held in the glass mat which is the electrolytic solution holding agent at the same time as the separator, and there is almost no free electrolytic solution. It is necessary to miniaturize the ion detecting element so that the concentration of sulfuric acid in the glass mat portion can be measured.

[0012]

According to the present invention, an ion-selective electrode or an ion-selective field-effect transistor is used as a first electrode, and an electrode having a silver surface coated with silver chloride is dissolved in a water-soluble polymer compound and water. A first film consisting of a mixture with a salt that dissociates to produce chlorine ions is coated, and this first film is further covered with a second film consisting of a mixture of a water-insoluble polymer compound and a proton-sensitive substance. The above-mentioned problem is solved by using the coated solid electrode as a second electrode and combining these two electrodes to form a hydrogen ion concentration detecting element.

Further, by mounting this hydrogen ion detecting element on a lead storage battery, it is possible to detect the concentration of sulfuric acid which is an electrolytic solution and to constantly know the charging / discharging state of the lead storage battery through it. is there

[0014]

[Function] A solid film type hydrogen ion electrode using molybdophosphoric acid or zirconium phosphate used as the first electrode, and an ion concentration measuring electrode such as an ion selective field effect transistor using tantalum oxide or titanium nitride for the sensitive film. To
When placed in a sample solution containing hydrogen ions, the following Nernst equation holds between the potential E and the hydrogen ion concentration [H ⁺ ] mol / l. E = E ° + 2.303 × (RT / nF) log [a _H ⁺ ] Therefore, when the voltage between the electrode and a suitable reference electrode whose potential is constant in the concentration range of the measurement solution is measured, hydrogen is measured. The relationship between the logarithm of the ion concentration or activity and the voltage is a straight line rising to the right as shown in Fig. 2, and its slope (voltage change when the concentration or activity changes 10 times, this is called sensitivity) is at room temperature. It is about 60 mV.

The solid electrode as the second electrode has a structure in which a silver / silver chloride electrode is coated with two kinds of films. The first membrane is composed of a mixture of a water-soluble polymer compound and a salt which dissociates in water to generate chloride ions, and the second membrane is composed of a mixture of a water-insoluble polymer compound and a proton-sensitive substance.
In the first film that is in direct contact with silver chloride, there is an equilibrium between chloride ions and silver chloride, and since this first film is covered with the second film, it does not come into direct contact with the sample solution. Therefore, the concentration of ions in the first film is always kept constant. Therefore, the potential at the silver chloride / first film interface is always constant. The salt that produces chlorine ions used for the first film is
It is soluble in water with a few exceptions, but its solubility in organic solvents is extremely low. Therefore, when mixing these salts and a high molecular compound, an organic solvent cannot be used in many cases.
Therefore, when these salts are mixed with the polymer compound, if the polymer compound is water-soluble, the polymer compound and the salt can be dissolved in water together and mixed, and the resulting film has a uniform composition.
It is very convenient. The second film is composed of a proton-sensitive substance and a polymer compound, and is in contact with the first film on the inside and with the sample solution on the outside. Therefore, the polymer compound forming the second membrane must be insoluble in water. It is considered that the ion-sensitive substance in the second film dissolves in the sample solution and changes its composition. However, this composition change is considered to be gradual. It can be considered that the electric potential of the interface is constant. Since the second membrane contains a proton-sensitive substance, the potential of the interface of the second membrane / sample solution changes according to the hydrogen ion concentration in the sample solution.

When this second electrode and an appropriate reference electrode whose potential is constant within the concentration range of the measurement solution are immersed in a sample solution containing hydrogen ions and the voltage between both electrodes is measured, the hydrogen ion concentration or The relationship between activity and voltage is a straight line descending to the right as shown in Fig. 3, and its slope (sensitivity) is about -80 mV at room temperature. However, at present, the theoretical elucidation of this relationship has not been possible.

Therefore, when the first electrode and the second electrode are combined to form a hydrogen ion concentration detecting element and this is immersed in the sample solution, the logarithm of the hydrogen ion concentration or activity and the logarithm between the first electrode and the second electrode are obtained. The voltage relationship is a straight line as shown in FIG. 4, and its slope (sensitivity) is about 140 mV.

As described above, the potential difference corresponding to a certain concentration change is about 60 mV in the case of using the reference electrode in which the potential is constant even when the concentration of the sample solution changes in the related art, compared to about 60 mV. When the element is used, it is about 140 mV, which is more than doubled, and the resolution is increased accordingly.

Further, the second electrode according to the present invention has not only the usual thin concentration range of 10 ⁻⁵ mol / l to 1 mol / l of hydrogen ion concentration, but also the concentration range of sulfuric acid which is an electrolytic solution of a lead storage battery. It shows stable and reproducible potential characteristics even in a wide range of 0.8 mol / l to 5.2 mol / l. Moreover, even if it is soaked in sulfuric acid having such a concentration for a long period of more than half a year, its potential characteristics do not change. Further, the solid-state electrode according to the present invention is an all-solid-state type, its structure is extremely simple, and its shape can be made into a thin linear shape. Therefore, a hydrogen ion electrode of the same size and a proton-sensitive electric field effect can be obtained. When combined with a transistor, it is easy to install in a lead-acid battery, especially a sealed lead-acid battery containing a very small amount of electrolyte. As a specific mounting place, a space between the electrode of the lead storage battery and the separator is suitable, but not limited to this. Further, as a lead-acid battery, the effect of the present invention is more remarkable in the case of the sealed type, but the effect can of course be exhibited even in the non-sealed type.

[0020]

EXAMPLES The present invention will be described below with reference to preferred examples.

Example 1 The second electrode was manufactured in the following order. The tip of a silver wire with a length of about 5 cm and a diameter of 0.2 mm, 1 cm, is placed in about 0.5 mol / l hydrochloric acid, and a platinum electrode is used as a counter electrode to conduct electricity, and silver chloride is attached to the silver surface to obtain a silver / silver chloride electrode. Next, tetra-n-butylammonium chloride 40% was added to 4 cc of a 1% aqueous solution of polyethylene oxide having a molecular weight of about 4 million.
mg is dissolved, the silver chloride part of the silver / silver chloride electrode is immersed in this solution, a polyethylene oxide solution containing tetra-n-butylammonium chloride is applied to the surface of silver chloride, and dried. This dipping / drying was repeated 5 times, followed by drying in air for 2 days to attach the first membrane. Next, 120 mg of polyvinyl chloride and 40 mg of zirconium phosphate were dissolved in 4 cc of tetrahydrofuran, and the silver / silver chloride electrode with the first film attached was immersed in this solution, and the polyzirconium phosphate containing zirconium phosphate was placed on the first film. Apply the vinyl chloride solution. This dipping and drying were repeated 7 times, and then the film was dried in air for 2 days to attach the second film to obtain the second electrode. Figure 1
Shows the structure of the prepared second electrode. In the figure, 1 is silver, 2 is silver chloride, 3 is a first film made of polyethylene oxide containing tetra-n-butylammonium chloride, and 4 is phosphoric acid. A second film made of polyvinyl chloride containing zirconium, and 5 is an insulating seal tape.

Next, this second electrode was combined with a double-junction type silver-silver chloride reference electrode and immersed in sulfuric acid aqueous solutions having different concentrations to determine the relationship between the sulfuric acid activity in the solution and the voltage. Figure 3 shows the results. The relationship between the logarithm of sulfuric acid activity and the voltage is that the voltage decreases as the sulfuric acid activity increases, showing a linear relationship in a wide activity range, and the sensitivity (activity changes 10 times). Voltage change) was about -80 mV.
It takes about 1 time for the potential of the second electrode to stabilize.
It was shown that the response time was very short, being very short within minutes.

[Example 2] A hydrogen ion electrode obtained by forming a titanium nitride (TiN) thin film having a thickness of about 3000 angstroms on the surface of a titanium disk by a plasma CVD method was used as a first electrode, and was prepared in Example 1. A hydrogen ion concentration detecting element was obtained by combining the above-mentioned second electrode. This device was immersed in aqueous sulfuric acid solutions having different concentrations, and the relationship between the sulfuric acid activity in the solution and the voltage was determined. FIG. 4 shows the results, and the logarithm of sulfuric acid activity and the voltage show a linear relationship in a wide activity range,
The sensitivity was about 140 mV.

[Example 3] A titanium nitride thin film having a thickness of about 3000 angstrom was formed on the gate insulating film of a field effect transistor by a plasma CVD method to obtain an ion selective field effect transistor. Next, using this ion-selective field-effect transistor as the first electrode, Example 1
A hydrogen ion concentration detection element was obtained by combining with the second electrode prepared in. The device was immersed in sulfuric acid aqueous solutions having different concentrations, and the relationship between the sulfuric acid activity in the solution and the voltage was determined. The measurement conditions of the ion-selective field-effect transistor were drain-source voltage = 5.0 V and drain current = 200 μA. The logarithm of the sulfuric acid activity in the solution and the voltage between the source and the second electrode show a linear relationship in a wide activity range, and the sensitivity is shown in Example 2.
It became about 140mV as well.

[Embodiment 4] A hydrogen ion concentration detecting element obtained by combining the ion selective field effect transistor having the titanium nitride film described in Embodiment 3 and the second electrode prepared in Embodiment 1 is used for an automobile. It was immersed in an electrolyte solution of a lead storage battery, and the voltage between the source and the second electrode of the ion selective field effect transistor was measured according to the charge / discharge state of the battery.
FIG. 5 shows a state in which a hydrogen ion concentration detection element is attached to a lead storage battery. In FIG. 5, 6 is an ion selective field effect transistor as a first electrode, 7 is a second electrode, and 8 is a positive electrode. Plate, 9 is a negative electrode plate, 10 is a separator, 11 is an ion selective field effect transistor and an insulating film for preventing contact between the second electrode and the positive electrode plate, 1
2 is an electrolytic solution. The measurement conditions of the ion-selective field effect transistor were the same as in the case of Example 3. At the same time, the specific gravity of the electrolytic solution was measured with a float type hydrometer. Fig. 6 shows the relationship between the voltage and the specific gravity of the electrolytic solution. The voltage when the specific gravity of the electrolytic solution is 1.28 (fully charged state) is about 390 mV, and the voltage when the specific gravity of electrolytic solution is 1.05 (fully discharged state). Indicates about 300 mV,
In this concentration range, the voltage and the logarithmic value of sulfuric acid activity showed a linear relationship. As can be seen from FIG. 6, the specific gravity of the electrolytic solution can be known from the voltage between the source and the second electrode of the ion selective field effect transistor. In lead acid batteries, it is known that the specific gravity of the electrolyte directly indicates the charge / discharge state of the battery, so it is necessary to know the charge / discharge state of the battery from the voltage between the source and the second electrode of the ion-selective field effect transistor. You can

[0026]

EFFECTS OF THE INVENTION A first electrode comprising a hydrogen ion electrode or a hydrogen ion sensitive field effect transistor according to the present invention and a second electrode obtained by coating a silver / silver chloride electrode with a double film are combined. The hydrogen ion concentration detection element can display a wide range of hydrogen ion concentration in the form of voltage,
It has excellent sensitivity due to its high sensitivity, and exhibits stable characteristics in high-concentration sulfuric acid. It can also be used to measure the concentration of any acid solution other than sulfuric acid. Moreover, its handling is simple, its response speed is fast, continuous measurement is possible while it is immersed in the solution to be measured, it can be used for a long time, and its reliability is extremely high. Further, since the voltage characteristic of the second electrode is irrelevant to its size, it is possible to miniaturize it by devising the manufacturing method, and an ultra-compact hydrogen ion concentration detecting element can be obtained.

Therefore, the hydrogen ion detecting element according to the present invention is not only effective for measuring the thin hydrogen ion concentration, which has been conventionally measured by using a glass electrode, but is also attached to a lead acid battery. The advantage is that the charge / discharge state of the lead storage battery can always be known.

The materials used for the first film and the second film of the second electrode used in the hydrogen ion concentration detecting element according to the present invention are not limited to those described in the embodiments. That is, the water-soluble polymer compound of the first film is polyvinyl alcohol, polymethacrylic acid, etc., and the salt contained in the first film is potassium chloride / sodium chloride.
Quaternary ammonium chloride, polystyrene, polyacrylonitrile, natural lacquer, etc. as the water-insoluble polymer compound of the second membrane, and molybdophosphoric acid and tungstoline as the hydrogen ion sensitive substance contained in the second membrane. Proton conductive solid electrolyte such as acid, quinone compound,
Needless to say, the same effect can be obtained by using a perfluorocarbon sulfonic acid resin or a quaternary ammonium chloride.

Further, by using the lead-acid battery equipped with the hydrogen ion concentration detecting element according to the present invention, the charge / discharge state can be detected more reliably and easily.

As described above, the hydrogen ion concentration detecting element according to the present invention and the lead storage battery provided with the element have extremely high industrial and practical values.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a second electrode of a hydrogen ion concentration detection element according to the present invention.

FIG. 2 is a diagram showing a relationship between a voltage between a conventional hydrogen ion electrode and a silver / silver chloride reference electrode and a logarithm of sulfuric acid activity in a sulfuric acid aqueous solution.

FIG. 3 is a diagram showing the relationship between the voltage between the second electrode and the silver / silver chloride reference electrode of the hydrogen ion concentration detection element according to the present invention and the logarithm of sulfuric acid activity in an aqueous sulfuric acid solution.

FIG. 4 is a diagram showing the relationship between the voltage of the hydrogen ion concentration detection element of the present invention and the logarithm of sulfuric acid activity in an aqueous sulfuric acid solution.

FIG. 5 is a view showing a state in which the hydrogen ion concentration detecting element according to the present invention is attached to a lead storage battery.

FIG. 6 is a diagram showing the relationship between the voltage of the hydrogen ion concentration detection element according to the present invention, the electrolytic solution specific gravity of the lead storage battery, and the charge / discharge state of the battery.

[Explanation of symbols]

 1 silver 2 silver chloride 3 first film 4 second film

Claims (2)

[Claims] 1. A water-soluble polymer compound comprising a first electrode composed of an ion electrode or an ion-selective field effect transistor responsive to hydrogen ion concentration, and an electrode having a silver surface (1) coated with silver chloride (2). And a second membrane (3) made of a mixture of water and a salt which dissociates in water to generate chlorine ions, and the first membrane is made of a mixture of a water-insoluble polymer compound and a proton-sensitive substance. A hydrogen ion concentration detecting element comprising: a second electrode coated with a film (4); 2. A lead storage battery provided with the hydrogen ion concentration detection element according to claim 1.