JPH042958A - Electrode for gas sensor using electrode reaction - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Purpose of the Invention) (Industrial Application Field) The present invention is directed to the treatment of sulfur dioxide, -acid, and This invention relates to electrodes for gas sensors that utilize electrode reactions for detecting gas components such as carbon, exhaust gases emitted from cars, and combustion gases in general households.

(Prior Art) To detect a specific gas component, a semiconductor gas sensor or an electrical resistance sensor is generally used, and tin dioxide or zinc oxide is used as an electrode.

Furthermore, the operating temperature is relatively high at 100° C. to 500° C., and it is necessary to control the operating temperature to the optimum temperature depending on the type of gas.

Furthermore, the manufacturing process for the sintered element was complicated and required high-temperature treatment.

In order to increase gas sensing sensitivity and selectivity, expensive noble metal catalysts such as platinum and palladium were used, making them expensive and requiring a power source for heating.

On the other hand, a gas sensor that utilizes an electrode reaction electrochemically oxidizes or reduces a gas to be detected, and extracts the electricity flowing through an external circuit as a sensor output.

This method is generally called a potentiostatic electrolysis type or galvanic cell type gas sensor, and the electrode material is limited to gold or platinum black, and the sensor structure is formed on a Teflon membrane or a Teflon porous membrane. It is difficult to use, has short gas selectivity and electrolyte life, is prone to liquid leakage, and has disadvantages such as decreased stability and accuracy.

A general galvanic cell type gas sensor is simple and has no power source, but has the disadvantage that the positive electrode wears out after several months of use.

In addition, electrodes for gas sensors that utilize electrode reactions are thick, porous, and extremely hard and brittle.

(Problem to be solved by the invention/device) The present inventor has developed an aromatic compound and/or a heterocyclic compound that can be electropolymerized or chemically oxidized without using a catalyst such as gold or platinum. We discovered that by using a conductive polymer formed by oxidative polymerization, it has excellent acid resistance, alkali resistance, and heat resistance, and can improve various drawbacks of gas sensor electrodes that utilize conventional electrode reactions. This led to an invention.

An example of the fact that conductive polymers such as polythiophene and polypyrrole can be used as electrodes for gas sensors for N08 was reported by Katsumi Yoshino et al.
, 26, 103 (1,985), a single conductive polymer film on an electrode is susceptible to peeling and cracking, making it unsuitable for long-term use.

The present invention has a long electrode life, is flexible because it is in the form of a thin film or film with no catalyst loss, and can be processed into any shape, making it lightweight and making the sensor compact. The present invention provides an inexpensive and highly reliable electrode for a gas sensor that utilizes electrode reactions to detect various gases.

[Structure of the invention]

(Means for Solving the Problems) An electrode for a gas sensor that utilizes electrode reaction and is characterized by being composed of a composite material of a resin compound and a conductive resin compound, and a method for manufacturing the same, and/or a resin compound and a conductive resin. This is a gas sensor electrode that utilizes an electrode reaction composed of a composite material of compounds and organometallic complexes.

The resins used in the present invention include fluorocarbon resins such as polytetrafluoroethylene, silicone resins,
Sulfur-based resin 1 such as polyreelphone, vinyl-based resin,
Examples of resins include olefin resins, phenol resins, polyester resins, polyamide resins, and polyimide resins.

Examples of organometallic complexes used as catalysts for gas sensors using electrode reactions in the present invention include phthalocyanine, naphthalocyanine, porphyrin, phenatoborphyrin, biscyclopentadiphenyl, carbonyl, hydride, carchene, carbine, acetylacetone complex, and salicylamine chelate. , salicylaldehyde complex salt, ethylenediaminetetraacetate, glycine chelate-1-, ferrocene, etc., or to these, a halogen atom, a nitro group,
Platinum, iron, cobalt, nisogel, copper, derivatives into which atoms or substituents such as sulfone groups, sulfonic acid groups, alkyl groups, hydroxyl groups, carboxyl groups, and amino groups have been introduced;
It is a complex of a metal such as palladium or molybdenum, and two or more types of organometallic complexes can also be used depending on the necessity of the detection gas.

In addition, in order to improve the effective utilization rate of the catalyst,
It is desirable to use organic metal complexes that are soluble in the same solvent as the resin member used.For example, as for the combination of organic metal complexes, solvents, and resins, for acetylacetone complexes, acetone solvent, libinyl A combination of a halogen compound and/or a polystyrene resin, a dimethylformamide and/or pyridine) vehicle, a combination of a halogen compound and/or a polyacetylene and/or a polyvinyl halide resin, a salicylamine Aldehyde nails with salt, chloroform? Medium, polyvinyl acetate
1- and (or) a combination of polyvinyl sulfoxide resins, for ferrocene, a benzene solvent, a combination of polyvinyl acetate and (or) polystyrene resins, for sulfonate derivatives such as porphyrins, phthalocyanines, dimethylpolamide or dimethyl sulfoxide. ? Examples include, but are not limited to, carriers, polyvinyl alcohol and/or polyvinyl halogen compounds, and/or polyacrylonitrile butadiene styrene and/or polyacrylonitrile and/or polyacetylene resins.

A resin member made of the above-mentioned organometallic complex and resin or (
or) The resin-only member must have the property of permeating the gas used in the gas sensor electrode utilizing electrode reaction according to the present invention.

For example, when the gas is oxygen, the oxygen permeability coefficient of the resin member is I x 10'' (cm3 (STP) cm
-cm-2S-'(cmHg)-' or more, preferably l
Xl0-" or more.

Not identified as a detected gas. For example, sulfur dioxide gas,
- Including flammable and harmful gases such as carbon oxide, carbon dioxide, hydrogen sulfide, nitrogen oxide, nitrogen dioxide, hydrochloric acid gas, chlorine gas, etc. Any gas that causes a redox reaction can be detected as a detection gas. It can be used.

In the present invention, conductive substrates used as electrodes for electrolytic polymerization include metal materials such as platinum, nickel, copper, silver, gold, palladium, carbonaceous materials such as grady carbon, and indium trioxide. It is possible to use a transparent electrode (such as ITo glass) on which a material such as ITO glass is vapor-deposited.

The shape of the conductive base material is not particularly limited, and linear, plate-like, rod-like, spherical, mesh-like, paper-like, cross-like, hollow, and other shapes can be used.

As a chemical oxidation polymerization method, it is also possible to form a composite film by dispersing ferric chloride or the like in a resin and immersing the resin in a solution of a monomer that undergoes chemical oxidation polymerization such as a heterocyclic compound to polymerize it.

In particular, it is preferable to manufacture the electrode for a gas sensor with high precision by an electrolytic polymerization method, but there is no need to limit it to this method.

In the present invention, a composite material as an electrode for a gas sensor that utilizes an electrode reaction is composed of the above-mentioned resin member and a conductive base material, or (or) a resin-only resin member and a conductive base material.

The composite material is prepared by: (1) The above organometallic complex and resin are treated in an ether solvent such as tetrahydrofuran, an amine solvent such as diaminodiphenylmethane, a ketone solvent such as acetone, methyl ethyl ketone, or an aromatic solvent such as phenol, toluene, or xylene. A coating material dissolved (including melting) or dispersed in an appropriate organic solvent such as an aliphatic solvent such as cyclohexene is applied onto the conductive substrate and dried.

(2) The mixture of the organometallic complex and resin is molded by an appropriate method such as extrusion molding, injection molding, or pressure molding, and the resulting molded product and the conductive base material are bonded by thermocompression or conductive adhesive. Glue using material.

(3) Powder coating or extrusion coating a mixture of the organometallic complex and resin onto the conductive substrate.

(4) Molding the mixture of the organometallic complex and resin by an appropriate method such as extrusion molding, injection molding, or pressure molding,
Providing a conductive base material on the obtained molded product by vapor deposition,
Alternatively, it can be produced by a method in which the organometallic complex is excluded from the methods (11 to (4)) above.

In the chemical oxidation polymerization method, there is no need to provide a conductive base material, and the resin alone or a composition containing an organometallic complex can be manufactured using an appropriate method such as the above-mentioned manufacturing method, coating method, extrusion molding, injection molding, or pressure molding. can. Further, the catalyst in the chemical oxidative polymerization method can also be produced by mixing with the above-mentioned organometallic complex and applying the coating method, extrusion molding, injection molding, or pressure molding.

Among these methods, in particular: (1) A coating agent obtained by dissolving (including melting) or dispersing, more preferably dissolving (including melting) the above-mentioned organometallic complex and resin in an appropriate organic solvent, is used in the above-mentioned method. Preferably, the composite material is made by coating it on a conductive substrate and drying it.

An electrolytically polymerizable aromatic compound and/or a heterocyclic compound is electrolytically polymerized on the conductive base material of the composite material thus obtained.

In the case of chemical oxidative polymerization, oxidative polymerization is carried out in a solution of an oxidatively polymerizable aromatic compound or a heterocyclic compound or in monomer vapor.

Examples of aromatic compounds or heterocyclic compounds that can be electrolytically polymerized or chemically oxidized polymerized include azulene, pyrene, 1-lihuenylene, aniline, pyrrole, thiophene, 3-methylthiophene, furan, piperazine, isothianaphthene, or halogens of these compounds. Examples include derivatives into which atoms or substituents such as atoms, nitro groups, sulfone groups, sulfonic acid groups, alkyl groups, allyl groups, hydroxyl groups, carboxyl groups, and amino groups are introduced.

Catalysts for chemical oxidative polymerization include ferric chloride, ruthenium trichloride, molybdenum trichloride, molybdenum pentachloride, aluminum chloride, titanium tetrachloride, ferric chloride, hydrochloric acid, sulfuric acid, hydrofluoric acid, perchloric acid, trichloroacetic acid, and trichloroacetic acid. Examples include fluoroacetic acid and phosphoric acid.

Electrolytic polymerization only needs to occur at least on the part of the conductive base material covered with the resin member, and from the viewpoint of the efficiency of forming a polymer by electrolytic polymerization, it is not necessary to use the resin member for profiteering. Preferably, the uncovered parts are covered with an insulating material, which may or may not be peelable, prior to electropolymerization.

As the electrolyte used for electrolytic polymerization, as a cation,
There are alkali metal ions, alkaline earth metal ions, quaternary alkylammonium ions, quaternary alkyl phosbonium ions, quaternary alkyl arsenium ions, quaternary sulfonium ions, and substituted products of these. , sulfonate ion, nitrate ion, perchlorate ion, carboxylate ion, tetrafluoroacetate ion, hexafluorophosphate ion, or substituted products thereof. Among the electrolytes composed of these cations and anions, from the viewpoint of solubility in organic solvents, in particular, te1-rhabdelammonium verchlorate, tetraethylammonium perchlorate 1-, and teI
・Butylammonium tetrafluorobaltate, TeI
- As for lafluoro, it is preferable to use thorium oxalate or the like.

Organic solvents used during electrolytic polymerization include nitriles such as acetonitrile and hendinitrile, amides such as dimethylformamide, dimethylace1-amide, and N-methylacetamide, ethylenediamine, hexamethylbosporamide, and pyridine. , amines such as tetrahydrofuran, dioxane, ethers of j82-dimethoxyethannat, carboxylic acids such as acetic acid and acetic anhydride, alcohols such as methanol and ethanol, sulfur compounds such as dimethyl sulfoxide, sulporan, and dimethyl sulfone, Propylene caponate, nitromethane, methylene chloride, acetone, etc. can be used. Among these organic solvents, it is particularly preferable to use methanol, ethanol, acetonitrile, dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, propylene carbonate, nitromethane, and the like.

The amount of current applied during electrolytic polymerization is usually 0.1 to 100 C/cm.
2, if the amount of current is set to 1 to 10 C/cm2, the surface of the polymer deposited (grown) by electrolytic polymerization can be smoothed, and a highly sensitive electrode reaction with high conductivity can be used. A conductive resin compound for gas sensor electrodes is obtained.

In the case of chemical oxidation polymerization, an oxidation catalyst is kneaded into the resin, or a resin film is impregnated in a solution of the oxidation catalyst, and then impregnated in the vapor of an oxidation-polymerizable monomer or a solution of an oxidation-polymerizable monomer for polymerization. By doing so, a conductive resin compound for gas sensor electrodes utilizing the desired electrode reaction can be obtained.

In the electrolytic polymerization method, a conductive resin compound for a gas sensor electrode using an electrode reaction is obtained from which the porous conductive base material is removed, if necessary.

If the conductive substrate is not removed, the conductive substrate is preferably porous.

The electrolyte used in a gas sensor that utilizes an electrode reaction can be a solution type or a solid electrolyte. As the solution electrolyte, inorganic electrolytes such as potassium hydroxide, sodium hydroxide, potassium sulfite, potassium sulfate, mono-lithium sulfite, and sodium sulfate can be used, and the optimal electrolyte can be selected depending on the type of gas to be detected. desirable.

As the solid electrolyte, a conductive electrolyte obtained by impregnating paper or resin with the above electrolyte can be used.

The electrode for a gas sensor that utilizes the electrode reaction obtained by this method can be made lighter and thinner, resulting in a gas sensor electrode with higher sensitivity, and can be processed such as molding more easily.

(Function) In the present invention, the conductive base material acts as an electrode during electrolytic polymerization.

In the gas sensor electrode that utilizes the electrode reaction obtained in the present invention, the polymer deposited (grown) in the electrode by electrolytic polymerization or chemical oxidation polymerization is used as a gas detector as well as a conductor in the sensor electrode body. act.

In addition, organometallic complexes act as catalysts for gas detection,
It works to increase sensitivity.

In addition, if the conductive base material is not removed, the conductive base material also acts as a conductor in the electrode body for a gas sensor using electrode reaction.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples. Note that in the film, parts represent parts by weight.

Example 1 A dispersion obtained by dispersing 50 parts of cobalt phthalocyanine in 250 parts of a solution consisting of 50 parts of polyvinyl chloride and 200 parts of dimethylbormamide was mixed with ITO.
It was applied onto glass and dried at 120°C for 2 hours to obtain a composite material. Using the obtained composite material as an electrode and a platinum plate as a counter electrode, the amount of current was 3
Electrolytic polymerization is performed until C/Cm2 is reached, then 1,
Peel off the TO glass, wash thoroughly with acetonitrile,
It was dried at 80° C. for 5 hours to obtain a thin film electrode with a thickness of 20 μm. The obtained electrode contained 3% by weight of polypyrrole.

Using the electrodes obtained in this way, a gas sensor using electrode reactions was fabricated using a 1N aqueous solution of potassium hydroxide as an electrolyte and a platinum plate as a counter electrode, and the mixing ratio of sulfur dioxide gas and oxygen was The change in potential difference was measured by changing the voltage. Measurements were carried out at 25°C using Ag/Ag as the reference electrode.
An Agc+ electrode was used. Repeat test of mixed gas 1
Although the test was carried out for more than 1,000 hours, the reproducibility was excellent and no liquid leakage occurred. Table 1 shows the results of measuring the potential (mV) of each mixture ratio gas. Current density 0.05mA/cm
Measurements were made with the setting set to 2.

(Left below) Example 2 Using a gas sensor electrode that utilized the electrode reaction obtained according to Example 1, the ratio of various mixed gases was changed and the change in potential was set to a current density of 0.05 mA/cm2. and measured. The results are shown in Table 2.

Table 2 Potential (mV) changes when using various mixed gases I was born.

Example 3 Under the same conditions as Example 1, polyvinyl chloride resin that does not contain the organometallic complex cobalt phthalocyanine was treated with ITO.
Painted on glass. Polypyrrole was fixed in the membrane by electrolytic polymerization under the same conditions as in Example 1. A composite material containing 3% by weight of polypyrrole in the electrode was obtained. This was carried out in the same manner as in Example 1, using a normal aqueous solution of potassium hydroxide as the electrolyte.
Table 3 shows the results of fabricating a gas sensor that utilizes electrode reactions and measuring changes in potential by changing the mixing ratio of sulfur dioxide gas and oxygen gas.
It was shown to.

These results indicate that the device has a function as a gas sensor that utilizes electrode reactions. For carbon dioxide, the redox potential is reversed and the inflection point is set at 2 points, the current density is -0.0.
5m A/cm 2. Reference electrode Ag/AgCl electrode, measurement temperature -25°C Example 4 Using the electrode of Example 1, the electrolytic aqueous solution was treated in the same manner as in Example 1 using 0.5N potassium carbonate, potassium sulfite J., and potassium sulfate. 0.05mV/cm” using mixed gas
As a result of measuring the gas detection characteristics at a current density of 1%, a large change in potential difference was observed even in 1% wetness of sulfur dioxide gas, and it was found that the electrode can be used as a useful sulfur dioxide gas sensor electrode.

Example 5 A dispersion obtained by dispersing 25 parts of cobalt phthalocyanine in 250 parts of a solution consisting of 50 parts of polyvinyl chloride and 200 parts of dimethylbormamide was applied onto a glass plate and dried at 120°C for 2 hours to form a composite. I got a body. The obtained film was peeled off from the glass plate, impregnated with 20% ferric chloride in an aqueous solution for 2 hours, and dried at 100° C. for 1 hour.

This film was impregnated in an ethanol solution of pyrrole at a concentration of 3%, and a conductive film was obtained by a chemical oxidation polymerization method.

The conductivity of the obtained conductive film was 3×10 −2 S/cm. Using this film, the gas detection characteristics of sulfur dioxide gas were measured in the same manner as in Example 1, and as a result, almost the same results as in Example 3 were obtained.

(Effects of the Invention) According to the present invention, it is possible to obtain a gas sensor electrode that has a long gas sensor life and utilizes an electrode reaction without catalyst loss.

Further, according to the present invention, by changing the amount and type of organometallic t (1) depending on the type of detection gas, it becomes possible to obtain more excellent selectivity and detection sensitivity.

By making the film thinner, it is possible to manufacture gas sensor electrodes using electrode reactions that are lightweight and have excellent moldability, and by using solid polymer electrolytes, it is possible to make compact gas sensors.

In addition, processing, molding, and weight reduction can be easily performed.

Claims (1)

[Scope of Claims] 1. An electrode for a gas sensor that utilizes an electrode reaction, characterized by being composed of a composite material of a resin compound and a conductive resin compound. 2. An electrode for a gas sensor that utilizes an electrode reaction and is characterized by being composed of a composite material of a resin compound, a conductive resin compound, and an organometallic complex compound. 3. The electrode for a gas sensor utilizing an electrode reaction according to claim 1 or 2, characterized in that a conductive resin compound produced by a chemical oxidative polymerization method or an electrolytic polymerization method is used.