JPH112616A - Humidity sensor using high polymer electrolyte composite membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a humidity sensor capable of detecting changes in the humidity of an environment being monitored with high responsiveness from changes in electric resistance which changes due to moisture content adsorbed to an electrolyte composite membrane. SOLUTION: A humidity sensor 10 is constituted by providing platinum electrodes 12 and 12 at both sides of a high polymer electrolyte composite membrane 14 and connecting a resistance measuring part 16 between the electrodes. A major component of the high polymer electrolyte composite membrane 14 is a perfluorocarbon sulfonic acid, a water-absorbing polymer is mixed into it, and the crosslinking reaction of the water-absorbing polymer has taken place. As electric resistance changes with high responsiveness due to moisture content adsorbed to the electrolyte composite membrane 14, changes in the humidity of an environment being monitored are speedily detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a humidity sensor using a polymer electrolyte composite membrane, and more particularly, to a humidity sensor for detecting humidity from an electric resistance value which varies depending on the amount of moisture adsorbed on a solid polymer electrolyte. It concerns a sensor.

[0002]

2. Description of the Related Art Conventionally, this type of humidity sensor is classified into a swelling type, an electric resistance type, an electric capacity type and the like according to the classification based on the measurement principle. Among them, a humidity sensor using a polymer electrolyte membrane is an electric resistance type that detects a change in electric resistance due to humidity, or a sensor that forcibly electrolyzes absorbed water and matches the current value flowing at that time with the humidity. A technique for detecting the odor has already been proposed.

[0003] For example, Japanese Patent Application Laid-Open No. 60-36947 and Technical Report GS News vol. 46, No. 42 JUN, 1
What is disclosed in 987 is the trade name "Nafion"
An organic solid electrolyte membrane such as perfluorocarbon sulfonic acid represented by (Dupont Corporation) is used as a moisture-sensitive element, and electrodes of a platinum group metal or alloy such as rhodium are provided on both surfaces thereof, and a platinum wire is used as a terminal. Connected.
When this is used as a humidity sensor, a direct current voltage is applied between both electrodes to forcibly electrolyze moisture adsorbed in equilibrium with the humidity in the atmosphere gas, and the humidity is detected from a current value flowing at that time. I have to. Incidentally, the basic molecular structure of this perfluorocarbon sulfonic acid type “Nafion” is shown in Chemical formula 1 (in this case, m ≧ 1, n =
2).

[0004]

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On the other hand, in a fuel cell system, for example, Japanese Patent Application Laid-Open No. 8-138691, the end of an ion exchange membrane of a battery cell and a catalyst carrier are provided in a reaction gas passage.
They are arranged at an appropriate distance, and are contacted / cut by swelling and shrinking depending on the degree of water absorption of the ion exchange membrane. A technique is disclosed in which the contact / disconnection is used as a switch to measure a voltage and used as a humidity sensor.

[0006]

However, the technology disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 60-36947 and the technical report GS News Vol. 46, No. 42 JUN, 1987 discloses that the humidity sensor is used in a wide humidity range. Although it can be applied, it is pointed out that the response speed is slow (several minutes) because the adsorbed water is forcibly electrolyzed once.

Further, according to the technique disclosed in Japanese Patent Application Laid-Open No. 8-138691, the swelling of the electrolyte membrane due to a change in humidity is caused.
There is a problem that it is difficult to monitor a quick response and a change process because of a switch type sensor using contraction.

An object of the present invention is to provide a polymer capable of detecting a change in the humidity of a monitoring environment with good responsiveness from a change in electric resistance which varies depending on the amount of water adsorbed on the solid polymer electrolyte membrane. An object of the present invention is to provide a humidity sensor using an electrolyte composite membrane.

[0009]

To solve this problem, a humidity sensor according to the present invention uses, as a moisture-sensitive layer, a polymer electrolyte composite membrane obtained by blending a water-absorbing polymer with an organic polymer electrolyte. The gist is that.

In this case, the organic polymer electrolyte constituting the polymer electrolyte composite membrane serving as a moisture-sensitive layer includes perfluorocarbon sulfonic acid represented by the trade name “Nafion” (registered trademark) manufactured by DuPont. Examples include a phenolsulfonic acid film, a polystyrenesulfonic acid film, and a polytrifluorostyrenesulfonic acid film. Examples of other suitable organic polymer electrolytes include a polymer skeleton in which all or a part thereof is a fluorinated carbon or hydrocarbon, and an ion exchange group is a cation exchange type. Examples thereof include sulfonic acid, carboxylic acid, phosphonic acid, phosphonous acid and phenol, and in the case of anion exchange type, 1,2,3, quaternary amine and the like.

The water-absorbing polymer is desirably a cross-linkable polymer having compatibility with the above-mentioned polymer electrolyte. Preferable examples thereof include a crosslinked polyethylene oxide (PEO) -based water-absorbent resin “Aquaprene WS-105” and “Aquaprene WS-10” manufactured by Meisei Chemical Industry Co., Ltd. And acrylic-based crosslinked sodium polyacrylate, starch-based, cellulose-based, and hyaluronic acid-based resins. Further as the water-absorbing polymer particles, for example, a crosslinked polyacrylate, a neutralized product of a starch-acrylic acid graft polymer, a crosslinked polyvinyl alcohol modified product,
Crosslinked isobutylene-maleic anhydride copolymers, polyethylene oxide crosslinked products, acrylamide-acrylic acid crosslinked polymers, and the like are also included.

The ratio of the organic polymer electrolyte to the water-absorbing polymer can take a wide range of a mixed composition of 1 to 99% of the water-absorbing polymer with respect to 99 to 1% by weight of the polymer electrolyte. In this case, as the electrode attached to the moisture-sensitive layer, a simple substance or alloy of a platinum group element, gold, or silver is used.

The humidity sensor according to the present invention is manufactured, for example, as follows. That is, for the organic solid electrolyte composite membrane, first, the organic polymer electrolyte and the water-absorbing polymer are blended while applying ultrasonic waves at an appropriate mixing ratio. The blended mixture is then left to evaporate off the solvent. Thereafter, under an environment of a predetermined temperature (120 ° C.) and pressure (50 kg / cm ² ), for several minutes to several tens minutes,
Heating is performed using a hot press machine, and an electrolyte composite membrane is obtained by a crosslinking reaction. Examples of the blending method include stirring, ultrasonic vibration, and kneading. Examples of the method for removing the solvent include evaporation, heating, and reduced pressure. Examples of the curing method include heating and a curing method using a crosslinking agent. The electrodes are attached to the polymer electrolyte composite membrane by plating, crimping, thermocompression, or the like.

According to the humidity sensor having the above-described structure, the water-absorbing polymer is blended with the organic polymer electrolyte containing the organic sulfonic acid-based polymer as a main component, so that the moisture-absorbing material has a fast response due to a change in humidity in the use environment, or Changes in drying occur. Therefore, the change in electrical resistance with respect to the change in humidity of the electrolyte membrane is faster than in the case of using only the polymer electrolyte. The changed humidity is instantaneously measured as an electric resistance value via the metal electrode. As a result, the responsiveness of the humidity sensor is increased, and the drying of the electrolyte membrane is quickly detected.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of a humidity sensor using a polymer electrolyte composite membrane according to an embodiment of the present invention. In FIG. 1, the humidity sensor 10 measures humidity by measuring an electric resistance value, which varies depending on the amount of moisture adsorbed on the polymer electrolyte composite membrane 14 to which the electrodes 12 and 12 made of platinum are attached, by a resistance measuring unit 16. It is to detect. This polymer electrolyte composite membrane 14 has a function as a moisture-sensitive layer,
It is formed by blending a water-absorbing polymer with an organic polymer electrolyte containing an organic sulfonic acid-based polymer as a main component and causing a crosslinking reaction. This promotes a change in electric resistance with respect to a change in moisture adsorbed on the polymer electrolyte composite membrane 14, that is, a change in humidity.

In this embodiment, various types of humidity sensors were manufactured using a polymer electrolyte composite membrane manufactured under several conditions. Hereinafter, Examples and Comparative Examples will be described.

Example 1 Crosslinked polyethylene oxide (PEO) manufactured by Meisei Chemical Industry Co., Ltd. as a water-absorbing polymer
Water-absorbent resin “Aquaprene WS-105” (absorption ratio about 5 times) and a 5% solution of a perfluorocarbon sulfonic acid resin “Nafion” manufactured by DuPont as an organic polymer electrolyte were mixed with “Aquaprene WS-105”. Was mixed so that the weight percentage of the mixture was 12.5 wt%, and mixed for 10 minutes while applying ultrasonic waves. Then, the solvent was evaporated and removed by leaving the glass substrate in a 25 ° C. temperature environment for two nights. This was dried under a temperature environment of 70 ° C. for 2 hours, and then 13 minutes under a condition of a temperature of 120 ° C. and a pressing pressure of 50 kg / cm ² using a hot press machine (heating for 3 minutes.
Holding 10 minutes), a heat curing treatment was performed to obtain a polymer electrolyte composite membrane having a film thickness of about 60 μm. Then, platinum electrodes were joined to the opposite end surfaces of the polymer electrolyte composite membrane, and the resistance measuring section and the electrodes were connected to prepare a humidity sensor as "Product 1 of the present invention".

(Example 2) A crosslinked PEO-based water-absorbing resin "Aquaprene WS-10" manufactured by Meisei Chemical Industry Co., Ltd. (absorption capacity: about 10 times) was used as a water-absorbing polymer, and a DuPont polymer was used as an organic polymer electrolyte. A 5% solution of a fluorocarbon sulfonic acid resin "Nafion" was blended so that the weight percentage of "Aquaprene WS-10" was 12.5 wt%, and mixed for 10 minutes while applying ultrasonic waves. Then, the solvent was evaporated and removed by leaving the glass substrate in a 25 ° C. temperature environment for two nights. This was dried under a temperature environment of 70 ° C. for 2 hours, and then heated and cured using a hot press machine at a temperature of 120 ° C. and a pressing pressure of 50 kg / cm ² for 13 minutes (heating 3 minutes, holding 10 minutes). By performing the treatment, a polymer electrolyte composite membrane having a thickness of about 60 μm was obtained. Then, platinum electrodes were joined to both opposing end surfaces of the polymer electrolyte composite membrane, and the resistance measuring section and the electrodes were connected to prepare a humidity sensor as "Product 2 of the present invention". Further, a humidity sensor of "Product 3 of the present invention" was produced in the same process as in Example 2, using a polymer electrolyte composite film having a thickness of 30 μm.

(Comparative Example) A 5% solution of a perfluorocarbon sulfonic acid resin "Nafion" manufactured by DuPont as an organic polymer electrolyte was left on a glass substrate under a temperature environment of 25 ° C. for 2 nights, and this was carried out. A heat treatment was carried out under the same conditions as in Example 1 to obtain a Nafion recast film having a thickness of about 60 μm. Then, platinum electrodes were joined to both opposing end faces of the single film, and the resistance measurement part and the electrodes were connected to prepare a humidity sensor as a “comparative product”.

Next, the change with time of the film resistance of the product of the present invention and the comparative product was measured. This is because the product of the present invention and the comparative product are arranged inside a battery cell which is a flow path of a reaction gas of a polymer electrolyte fuel cell, and are in a wet state (95.3% relative humidity).
The change with time of the film resistance when the humidity was changed from 0 to a dry state (0% relative humidity) was obtained by measuring the impedance by applying an alternating current under a temperature environment of 25 ° C. 2 and 3 are graphs showing the results of these measurements, in which the horizontal axis represents time (seconds) and the vertical axis represents the common logarithm of the resistance value (Ω). Hereinafter, comparison and evaluation of the product of the present invention and the comparative product will be performed with reference to these drawings.

FIG. 2 shows a comparison of the change over time in the membrane resistance of the polymer electrolyte composite membrane containing the water-absorbing polymer (Product 1 of the present invention) and the Nafion recast membrane (Comparative product). A humidity sensor was placed in a reaction gas of a fuel cell having a relative humidity of 95.3%, measurement of electric resistance was started, and time measurement was started after the operation state was stabilized. And about 60
When 0 seconds have elapsed (indicated by an arrow A in the figure), the relative humidity of the reaction gas is set to 0%, and the measurement of the electrical resistance is continued until approximately 3600 seconds (50 minutes from the start of the change) have elapsed from the start of the time measurement. did.

The product 1 of the present invention exhibited a log (electrical resistance value) of about 4.4 at the start of timekeeping, and showed a value which was almost flat although a slight decrease was observed until the relative humidity was changed.
When the relative humidity of the reaction gas is set to 0%, the electric resistance value starts to increase linearly rapidly immediately after that, and about 1000 seconds have elapsed since the time measurement was started, and about 400 seconds have elapsed since the relative humidity was set to 0%. The value showed a maximum value (6.2) when the measurement was performed, and thereafter showed a gradual decrease, and reached approximately 6.0 when about 2000 seconds had elapsed since the start of the timing. Until the measurement was completed, the value remained almost flat (about 6.0) stably.

On the other hand, the comparison product has a log
(Electric resistance value) was about 3.5, and remained almost unchanged until the relative humidity was changed. When the relative humidity of the reaction gas was set to 0%, an increase in the electrical resistance was observed immediately after that, but the increase was much more gradual than that of the product 1 of the present invention. And about 1600 seconds after starting the timing,
When 1000 seconds have passed since the relative humidity was reduced to 0%, l
og (electrical resistance value) was about 5.5, and after this, the degree of the increase became more gradual, and the electric resistance value continued to increase until the measurement was completed.

According to the product 1 of the present invention, the relative humidity is 93.5.
It takes only about 400 seconds for the electrical resistance to reach its maximum value even when the resistance is suddenly changed from 0% to 0%. it can. Therefore, a change in humidity from a wet state to a dry state can be detected quickly and accurately.

According to the comparative product, it takes about 1000 seconds or more until it is detected that the electric resistance value has changed when the relative humidity is changed from 93.5% to 0%. It is not very responsive and lacks accuracy and speed.

FIG. 3 shows a polymer electrolyte composite membrane containing the water-absorbing polymer (Product 2 of the present invention), a polymer electrolyte composite membrane having a thickness of 1/2 (Product 3 of the present invention), and a Nafion recast membrane (Comparison product). 2) shows the change with time of the film resistance in comparison. The electric resistance was measured in the same manner as the product 1 of the present invention. When about 600 seconds had elapsed (indicated by an arrow B in the figure), the relative humidity of the reaction gas was set to 0%, and the relative humidity was kept at about 36%.
The measurement of the electrical resistance was continued until 00 seconds had elapsed.

The product 2 of the present invention had a log (electric resistance value) at the start of aging of about 4.2, and remained almost unchanged until the relative humidity was changed. Set the relative humidity of the reaction gas to 0
%, The electric resistance value starts to increase linearly rapidly immediately after that, and when about 400 seconds have elapsed after the start of timekeeping and about 400 seconds after the relative humidity was set to 0%, the maximum value was 6.2. , And then gradually decreased to about 5.9 at about 2000 seconds from the start of timing. Then, a value almost leveling out was stably shown until the measurement was completed.

The product 2 of the present invention was thinned (60 μm → 30
μm) In the case of the product 3 of the present invention, the log (electric resistance value) at the start of aging showed about 4.5, and remained almost unchanged until the relative humidity was changed. When the relative humidity of the reaction gas is set to 0%, the electric resistance value rises sharply for about 100 seconds immediately after that, reaches the maximum value (6.2), and then decreases rapidly toward a stable value. Then, within about 100 seconds after that, a stable state of about 6.0 was obtained, and the value remained almost unchanged until the measurement was completed.

According to the product 2 of the present invention, the relative humidity was 93.5.
Even when the ratio was rapidly changed from 0% to 0%, the same excellent response as the product 1 of the present invention was exhibited for about 400 seconds until the electric resistance value reached the maximum value. Further, according to the product 3 of the present invention, it takes about 100 seconds (about 1 to 1) for the electrical resistance to reach the maximum value when the relative humidity is reduced from 93.5% to 0% by thinning the composite film. 2 minutes) and the film thickness is 2
It is extremely excellent in responsiveness even when the present invention products 1 and 2 are doubled, and can quickly reach a high resistance value. Therefore, the change in humidity from the wet state to the dry state can be detected more quickly and accurately.

FIG. 4 shows a schematic configuration of a state in which the above-described humidity sensor of the present invention is used for monitoring the dry / wet state of a solid electrolyte membrane of a polymer electrolyte fuel cell. As shown in FIG. 4, the polymer electrolyte fuel cell supplies hydrogen (fuel) to the anode side of the cell and oxygen (oxidant) to the cathode side.
, Hydrogen ions (H ⁺ ) generated on the anode side move to the cathode side via ion exchange groups in the solid polymer electrolyte membrane, and react with oxygen on the cathode side to form water (H ₂ O) is generated, and at this time, electric energy is extracted to the outside.

In this polymer electrolyte fuel cell, it is necessary that the electrolyte membrane be kept in an appropriate water-containing state and exhibit high proton conductivity. If water is insufficient, the resistance of the electrolyte increases, and conversely, water becomes insufficient. Becomes excessive, the electrodes become flooded, and the supply of the reaction gas is hindered. In any case, a stable voltage cannot be obtained.

Therefore, as shown in FIG. 4, if the humidity sensor 10 of the present invention is provided on the solid polymer electrolyte membrane of the polymer electrolyte fuel cell, when the electrolyte membrane of the fuel cell becomes dry, Polymer electrolyte composite membrane 1 of humidity sensor 10
4, the electrolyte membrane of the fuel cell needs to be appropriately wetted in order to show a rapid change in electric resistance faster than the electrolyte membrane itself, as described with reference to FIGS. 2 and 3. Is quickly detected.

Although not shown, the humidity sensor 1
If the reaction gas (hydrogen, air) used in the fuel cell is automatically humidified by the humidifier based on the detection signal of the resistance measuring unit 16 of 0, the solid polymer electrolyte membrane of the fuel cell is always The desired wet state is maintained, and a stable power generation state is maintained.

If the humidity sensor according to the present invention is incorporated in a solid polymer electrolyte fuel cell, the humidification state of the solid polymer electrolyte membrane for which moisture management is important is continuously monitored, and the solid polymer electrolyte membrane may be damaged for some reason. When it becomes dry, the abnormality is quickly detected, and humidification control is performed. As a result, the fuel cell can be operated in an optimum humidity state, and the performance of the polymer electrolyte fuel cell is expected to be improved.

The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, an example in which the present invention is applied to monitoring (monitoring) of a solid electrolyte membrane of a polymer electrolyte fuel cell is described. However, in addition to the above, air conditioning equipment, therapeutic equipment (respiratory system), food and plants, etc. It can be used for the management of culture, the management of culture atmosphere, the management of artistic objects such as paintings and lacquerware, and the like, especially for the humidity control of those that do not like drying.

[0036]

As described above, the humidity sensor according to the present invention is obtained by blending a water-absorbing polymer with an organic polymer electrolyte such as Nafion, and changes in the amount of water adsorbed on the electrolyte composite membrane. That is, it is possible to quickly and accurately detect a change in the film resistance value that changes due to a change in humidity. Therefore, if this humidity sensor is applied for monitoring the humidified state of the electrolyte membrane of a polymer electrolyte fuel cell, further improvement in the performance of the fuel cell is expected, and it can be applied to other uses.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a humidity sensor according to an embodiment of the present invention.

FIG. 2 is a diagram showing a change over time of electric resistance in a change in a humidification state of the humidity sensor of the present invention.

FIG. 3 is a diagram showing a change over time of an electric resistance of a humidity sensor according to another embodiment of the present invention.

FIG. 4 is a diagram showing an example in which the humidity sensor of the present invention is applied to monitoring of a humidified state of an electrolyte membrane of a polymer electrolyte fuel cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Humidity sensor 12 Electrode 14 Polymer electrolyte composite film 16 Resistance measurement part

Claims (1)

[Claims] 1. A humidity sensor using a polymer electrolyte composite membrane, comprising a water absorbing polymer mixed with an organic polymer electrolyte.