JP2001033425A - Hydrogen gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure the durability of platinum electrodes by providing a hydrogen oxidizing catalyst to the region, where gas to be inspected flows in one platinum electrode dominantly, being a part of the ceramic porous member with a specific pore size or less provided in close contact with platinum electrodes. SOLUTION: A heating means 1, an oxygen ion conductive solid electrolyte 2 and a pair of the platinum electrodes 3 on the same plane as the solid electrolyte 2 are provided and a ceramic porous member 4 with a mean pore size of about 100 Åis arranged in close contact with the platinum electrodes 4. Further, a hydrogen oxidizing catalyst 5 is provided to the region, where gas to be inspected flows in one platinum electrode 3 dominantly, being a part of the ceramic porous member 4. The porous ceramic member is held to a temp. of about 400-500 deg.C necessary for driving the solid electrolyte 2 by the heating means 1. When hydrogen-containing air comes into contact with the ceramic porous member, hydrogen passed through the hydrogen oxidizing catalyst 5 of one platinum electrode 3 is oxidized and oxygen adsorbed by hydrogen in air is reduced by the other platinum electrode 3 and the electromotive force caused by the oxygen concn. difference between the platinum electrodes 3 is generated and the concn. of hydrogen gas can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen gas sensor for detecting hydrogen gas, and more particularly to a hydrogen gas sensor having excellent characteristics in terms of durability.

[0002]

2. Description of the Related Art Hydrogen gas is expected to become the most important energy in the 21st century. However, if hydrogen gas leaks, there is a possibility of causing an explosion accident, and a stable hydrogen gas sensor that detects the leak of hydrogen gas with high sensitivity is required.

[0003] Hydrogen is a colorless, tasteless and odorless gas, and has a specific gravity of 0.09 g / cm ³ and is the lightest. There is no information on the harmfulness and toxicity of hydrogen itself, but if leaked, the concentration of oxygen in the air would be reduced, causing oxygen deficiency. The ignition point of hydrogen is 572 ° C.
However, the diffusion rate in air is about 3 times faster than that of methane, the burning rate is about 7 times faster than that of methane, and the concentration in air is 4%.
Exceeds the risk of fire and explosion, 4 to 74.5 Wt
Risk of fire and explosion over a wide range of concentrations. It is also said that the flame when burning is almost colorless and is difficult to see especially in bright places.

[0004] As hydrogen is applied to fuel cells, automobiles, and household generators (cogeneration) in the future, it is highly reliable and highly reliable in order to cope with the risk of gas leakage. There is a need for a sensitive hydrogen gas sensor.

[0005] As the conventionally proposed hydrogen gas sensors, if they are classified into chemical sensors and physical sensors, only chemical sensors have been studied as practical objects. As a representative of this type of chemical sensor, an N-type semiconductor oxide sensitized by adding a trace amount of a metal element such as a noble metal, for example, a sintered body such as tin oxide is used to make these semiconductor oxides flammable. Gas detection method (semiconductor gas sensor) that utilizes the property that electrical conductivity changes when it comes in contact with gas, 20μ
Alumina is attached to a thin platinum wire of about m and heated to a certain temperature using a pair of comparison elements, one carrying a noble metal and the other carrying noble metal, and the combustible gas comes into contact with this element to carry out the catalytic oxidation reaction. There is known a method of detecting a difference in heat generated at the time of the operation (contact combustion type gas sensor).

For example, supervised by Toyoaki Omori: “Sensor Practical Encyclopedia”: Fuji Techno System [Refer to Chapter 14, Basics of Gas Sensors (in charge of Masatake Haruta), pp. 112-130 (1986)].

[0007]

The biggest problem with a hydrogen gas sensor has been that it is impossible to construct a fail-safe system in spite of the fact that it is a decisive sensor relating to safety. It is an out detection system. That is, there is a concern that the sensor characteristic cannot be output when the sensor output is reduced and the sensor output is reduced. Specifically, when the signal as the sensor does not detect hydrogen gas, it is zero, and since the sensor basically has a characteristic of outputting a signal by detecting hydrogen gas, the output signal is reduced due to deterioration of the sensor. There is a factor in doing so. However, this is an unavoidable task because it is an essential property.

In particular, when a hydrogen gas sensor is mounted on a fuel cell applied system device and used for the purpose of detecting hydrogen gas leakage, the danger of hydrogen gas leakage increases only after the fuel cell applied system device has been considerably used. In many cases, the hydrogen gas sensor may be deteriorating at that time.If the output signal decreases due to the deterioration of the hydrogen gas sensor, even if there is hydrogen gas leakage, the detection Risk of becoming useless.

The reason why the output of the hydrogen gas sensor is reduced, that is, deteriorated, is that the electrode and the catalyst, which are responsible for the central function of the hydrogen gas sensor, deteriorate with time as the reaction progresses. , The catalyst is reduced by reducing gas such as hydrocarbons coexisting in the detection gas,
This is because a silicon compound or a sulfur-based compound is strongly adsorbed on the electrode surface, thereby hindering the hydrogen detection reaction. In these chemical sensor-type hydrogen gas sensors, noble metals are often used for electrodes or catalysts that play a central role in the sensor function, but these noble metals are weak to sulfur-based compounds and silicone-based compounds and are susceptible to deterioration, and are durable. There is a problem that it becomes very difficult to secure the information.

The hydrogen gas sensor of the present invention uses a solid electrolyte type. For the solid electrolyte type, generally with a few exceptions, in the case of an oxygen ion conductive solid electrolyte such as yttria-stabilized zirconia, etc., in order to secure a necessary temperature for driving the solid electrolyte. Heat source is required. The solid electrolyte type hydrogen gas sensor, which is hardly known in the past, exhibits an operation very similar to that of a carbon monoxide sensor having a similar operation behavior.
The operating principle is such that one of a pair of platinum electrodes formed on the surface of the solid electrolyte is covered with a porous hydrogen oxidation catalyst layer.

Thus, the coated electrode side is a reference electrode, and the uncoated bare electrode side is a hydrogen detection electrode.
When hydrogen gas is present in the air, hydrogen is detected by using an electromotive force output related to the hydrogen concentration obtained between the two electrodes. This is due to the fact that a kind of oxygen concentration cell is formed between the platinum electrode on the hydrogen oxidation catalyst layer side and the bare platinum electrode, and the oxygen in the air reaches the electrode on the hydrogen oxidation catalyst layer side, that is, the reference electrode side as it is. Is in a state of high oxygen adsorption because hydrogen cannot be reached, whereas on the bare side, that is, on the detection side electrode, both oxygen and hydrogen reach the electrode surface, this hydrogen reduces oxygen, and low oxygen on the electrode surface It becomes an adsorption state. This utilizes the fact that an oxygen concentration cell is formed between both electrodes and an electromotive force output appears.

However, when the platinum electrode is brought into contact with a gas having a higher adsorptivity than hydrogen, for example, air containing sulfurous acid gas, the diffusion resistance of the porous hydrogen oxidation catalyst layer or the adsorption trap causes Since the levels of sulfur dioxide reaching the two platinum electrodes are different, the sensor output first increases as the adsorption starts from the bare electrode side, but after a while, the electrode on the porous hydrogen oxidation catalyst side also As the sulfurous acid gas arrives, the sensor output gradually decreases, and no output is eventually obtained. Sulfurous acid gas is contained in a trace amount in the atmospheric gas, and its concentration level varies depending on the type of fuel of the fuel cell, but has a bad influence on the life of the hydrogen gas sensor.

Further, even in a general living environment, various cosmetics, household products such as waxes and hair styling products contain a silicone compound, and when the silicone compound reaches the electrode surface, it is strongly adsorbed to the electrode and, like the sulfurous acid gas, Causes deterioration. The degradation behavior of chemical sensors has been described using the solid electrolyte type as an example.However, in the semiconductor type where the operating temperature is lower than that of the solid electrolyte type, and in the catalytic combustion type, the effect of poisoning deterioration of silicone compounds etc. is more serious. It becomes something.
The operating temperature of the solid electrolyte type is about 300 to 450 ° C., whereas that of the catalytic combustion type is about 200 to 300 ° C. and that of the semiconductor type is about 100 to 200 ° C.

Further, as described above, since the sensor system is not essentially fail-safe, a highly reliable sensor having extremely high durability is required in order to be able to use the sensor system with high reliability. However, there has been a problem that a sensor system that has been properly established at the ideological level without guaranteeing durability has not been realized.

[0015]

In order to solve the above-mentioned problems, a gas sensor according to the present invention comprises a heating means, an oxygen ion conductive solid electrolyte, and a pair of platinum ions formed on the same surface of an oxygen ion conductive solid electrolyte. An electrode is provided, and a ceramic porous body having an average pore diameter of 100 ° or less is disposed in close contact with the platinum electrode, and further in a part of the porous body, a region where the gas to be detected flows into one platinum electrode dominantly. It has a configuration equipped with a hydrogen oxidation catalyst.

With this configuration, it is possible to regulate the inflow of an adverse gas such as sulfurous acid gas that deteriorates the electrode through a pair of ceramic porous bodies having an average pore diameter of 100 ° or less, and even if sulfurous acid gas or the like partially flows into the electrode, Since a similar progression of deterioration occurs between the pair of electrodes, the balance of the zero point is hardly changed, so that the gas sensor can operate stably for a long time. A ceramic porous body having an average pore diameter of 100 ° or less has different gas permeation characteristics depending on the size of the average pore diameter. When the average pore diameter is in the range from 100 ° or less to 10 °, the property that the permeation rate is inversely proportional to the square root of the molecular weight of the gas, that is, the property of Knudsen diffusion is exhibited. Permeation of sulfur dioxide gas and gas of high molecular weight such as low molecular silicone compound is suppressed. Further, in a porous body whose average pore diameter is controlled to 10 ° or less, gas molecules exhibit molecular sieve type or surface diffusion type permeability, and the inflow is regulated by the size of the gas molecules, or the gas molecules and the inner wall of the pores. It has the property that the diffusivity into the porous body is determined by its affinity with Particularly, in the case of a porous body in which the average pore diameter is controlled to 10 ° or less by a film containing at least one of silica and zirconia, the pore wall has strong hydrophobicity. It is possible to inhibit the diffusion of water vapor in the pores, which may cause capillary condensation inside the pores and block the pores, thereby preventing water vapor condensation. Similarly, it also inhibits the hydrophilic surface diffusion of sulfur dioxide and can block the inflow of sulfurous acid gas. By the above, in the operation of the hydrogen gas sensor,
The poisoning effect on the most important electrodes can be reduced and equalized.

In addition, since the ceramic porous body is in close contact with the electrode, when the average pore diameter is in the range of 100 ° or less to 10 °, deterioration occurs due to the effect of restricting the inflow of sulfurous acid gas as described above. Not only is the time extended, but even when the average pore diameter is, for example, 50 °, the entire pores include a portion having a pore size of 10 ° or less, and in that portion, the sulfur dioxide gas is completely blocked. As a result, some electrodes with large pores can survive completely and even if they are deteriorated by sulfur dioxide, some electrodes with small pores can survive completely and continuously exhibit sensor characteristics. it can. If a pair of ceramics are manufactured by the same process, they have similar pore characteristics, so that the above-described effects can be achieved.

The ceramic porous substrate will be described below. The ceramic porous substrate is used by coating the pores of a porous ceramic prepared by a sintering method and controlling the pores to have appropriate pore characteristics. The ceramic porous substrate has a configuration in which it is in close contact with a typical oxygen ion conductor, a yttria-stabilized zirconia solid electrolyte.From the viewpoint of thermal shock resistance of the sensor element, alumina or a thermal expansion coefficient close to zirconia is used. It is desirable to use zirconia.

It is well known that porous ceramics are used for various applications as ceramic filters, for example, for separating yeast from beer. Although the pore diameter is about 0.1 μm to several μm, it is not possible to obtain gas selective permeability in this state, and it is necessary to fill the pores and control the pore diameter.

The method for controlling the pore diameter is to form a sol-gel film on the surface of the pores. Alternatively, a CVD method or the like for controlling the pores by forming a film in the pores by thermal decomposition is known. As the pore controlling method of the porous body of the present invention, various known film forming methods are known. The law is applicable. CVD in which a sol-gel film is formed or a film is formed in the pores by thermal decomposition to control the pores
Regardless of which method is selected, the ceramic porous body whose pores are controlled in the same manner and under the same control conditions has similar pore characteristics, so by using these in combination,
A pair of ceramics with similar pore properties can be obtained.

The heat source required for driving the hydrogen gas sensor element is achieved by heating means provided in the gas sensor, and if necessary, temperature control is performed by using temperature detecting means such as a thermistor and a thermocouple. . As the heating means, various means such as a heating wire and a resistance heater film can be applied.As a material used for the resistance heater film, a noble metal-based material such as platinum is desirable in terms of durability, and when a heating wire is used, Iron-chromium type and nickel-chromium type can be used. Further, the temperature control of the sensor element may be performed using the resistance-temperature characteristics of the heater.

Regarding the operation of the hydrogen gas sensor of the present invention,
This will be described below. That is, the gas leaking from the combustion battery system into the general atmosphere is oxidized in the porous layer containing the hydrogen oxidation catalyst on one platinum electrode side, that is, on the reference electrode side. , The inflow amount is regulated, but air containing no hydrogen reaches the reference electrode surface. On the other detection electrode side, the amount is similarly regulated, but air containing hydrogen arrives. While the oxygen concentration on the reference electrode side remains at the high oxygen concentration, on the detection electrode side, hydrogen reduces oxygen to a low oxygen concentration. As a result, a difference in oxygen concentration occurs between the pair of platinum electrodes, and an electromotive force related to the hydrogen concentration is generated between the electrodes via the oxygen ion conductor. Various organic vapors, silicone oligomers, and the like that are adsorbed on the electrode and adversely affect the operation of the gas sensor can hardly reach the electrode portion due to the ceramic porous body whose pores are controlled to 100 ° or less. The inflow of sulfurous acid gas is also significantly restricted. Also, sulfurous acid gas may enter preferentially from the pores having a large pore diameter and degrade some electrodes, but most electrodes having a small pore diameter are in an operable state,
Since the output characteristics are related to the oxygen concentration ratio of the pair of platinum electrodes, the oxygen concentration ratio hardly changes, and as a result, the zero point can be stabilized over time. By stabilizing the characteristics in this manner, a decrease in output due to deterioration over time can be avoided, and a highly reliable hydrogen gas sensor can be obtained.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention comprises a heating means, an oxygen ion conductive solid electrolyte, and a pair of platinum electrodes formed on the same surface of the oxygen ion conductive solid electrolyte. The average pore diameter is 10
A ceramic porous body of 0 ° or less is provided, and a hydrogen oxidation catalyst is provided in a part of the porous body in which a gas to be detected predominantly flows into one platinum electrode. Due to the heating means provided in the hydrogen gas sensor, the hydrogen gas sensor
The temperature is maintained at about 400 to 500 ° C. necessary for driving the solid electrolyte element.

Therefore, in the case of air containing no hydrogen, when the air comes into contact with the present hydrogen gas sensor, the oxygen concentration level of the pair of platinum electrodes is the same, so that no electromotive force output is generated. Then, on the side of the pair of platinum electrodes, on the side where air passes through exclusively through the hydrogen oxidation catalyst, the hydrogen is oxidized by the hydrogen oxidation catalyst, and air containing no hydrogen arrives, whereas the other electrode reaches the other electrode. Since the air containing hydrogen arrives, oxygen adsorbed on the electrodes is reduced by the hydrogen, an electromotive force output is generated between the electrodes due to a difference in oxygen concentration, and the hydrogen gas concentration is detected.

Also, a gas such as a low molecular weight silicone or a sulfurous acid gas which deteriorates the electrode and adsorbs on the electrode and hinders the adsorption of oxygen is restricted or blocked by a pair of ceramic porous bodies having an average pore diameter of 100 ° or less. . Thereby, a longer life is achieved. Even if a part of the gas flows, it flows into the pair of electrodes at the same time, so that the oxygen concentration balance between the electrodes is not lost and the instability of the movement of the zero point is released, and the life of the sensor is expected to be prolonged. It is.

A second embodiment of the present invention comprises a heating means, an oxygen ion conductive solid electrolyte, and a pair of platinum electrodes formed on the same surface of the oxygen ion conductive solid electrolyte. A ceramic porous body having an average pore diameter of 100 ° or less was arranged, and a porous body containing a hydrogen oxidation catalyst was arranged in a portion where the gas to be detected predominantly flowed into one platinum electrode on the surface side of the ceramic porous body. Things. This embodiment is different from the first embodiment in the arrangement of the hydrogen oxidation catalyst. That is, in the case of the first embodiment, the hydrogen oxidation catalyst is applied to a part of the ceramic porous body having an average pore diameter of 100 ° or less, more specifically, to the inside and the surface of the pores of the ceramic porous body. In the present embodiment, the porous body containing the hydrogen oxidation catalyst has an average pore diameter of 10
The ceramic porous body is independently disposed on a part of the surface side of the ceramic porous body of 0 ° or less. Therefore, the operation as the hydrogen gas sensor and the effect of extending the life thereof are the same as those in the first embodiment.

A third embodiment of the present invention is directed to a heating means, a pair of platinum electrodes formed on opposing surfaces of an oxygen ion conductive solid electrolyte and an oxygen ion conductive solid electrolyte, and hydrogen oxidation on one surface thereof. A ceramic porous body having a catalyst and having an average pore diameter of 100 ° or less is provided, and a ceramic porous body having an average pore diameter of 100 ° or less and containing no hydrogen oxidation catalyst is provided on the other surface. . This embodiment is different from the first embodiment in that a pair of platinum electrodes is arranged to face the oxygen ion conductive solid electrolyte like a capacitor. The operation as a hydrogen gas sensor is not particularly different, only that the electrode is arranged to face the solid electrolyte. Since the detection gas flowing into the electrode flows through the ceramic porous body having an average pore diameter of 100 ° or less, the protection effect of the electrode is the same as in the first and second embodiments. The effect of the hydrogen gas sensor on durability and zero point stability is the same as in the previous section.

The fourth embodiment of the present invention comprises a heating means, a pair of platinum electrodes formed on the same surface of an oxygen ion conductive solid electrolyte and an oxygen ion conductive solid electrolyte, and one of the electrodes is hydrogen oxidized. An element formed by coating with a porous body containing a catalyst is housed in a ceramic porous body container having an average pore diameter of 100 ° or less. An element comprising a heating means and a pair of platinum electrodes formed on the same surface of an oxygen ion conductive solid electrolyte and an oxygen ion conductive solid electrolyte, and one electrode covered with a porous material containing a hydrogen oxidation catalyst. Operates as a hydrogen gas sensor as described in the first embodiment. Since the present hydrogen gas sensor element is housed in a ceramic porous body container having an average pore diameter of 100 ° or less, all air flows into and out of the hydrogen gas sensor element through a ceramic porous body having an average pore diameter of 100 ° or less. Average pore size is 1
Since the ceramic porous body having a diameter of not more than 00 ° has a gas selective permeation characteristic, the inflow of a gas having a large gas molecule size affecting the electrode of the hydrogen gas sensor element and the hydrogen oxidation catalyst is regulated. Therefore, similarly to the first to third embodiments, the hydrogen gas sensor of the present embodiment has excellent stability of the zero point and stability of the sensor output.

The fifth embodiment of the present invention comprises an oxygen ion conductive solid electrolyte and a pair of platinum electrodes formed on the same surface of the oxygen ion conductive solid electrolyte, and one of the electrodes contains a hydrogen oxidation catalyst. The element formed by coating with the porous body is placed in a ceramic porous body provided with a heating means having an average pore diameter of 100 ° or less. In the present embodiment, in the case of the fourth embodiment, the hydrogen gas sensor element has heating means, whereas the hydrogen gas sensor element does not have heating means, and the hydrogen gas sensor element has an average hydrogen gas sensor element inside. The difference is that a ceramic porous body having a pore diameter of 100 ° or less has a heating means. Providing the heating means in the ceramic porous body having an average pore diameter of 100 ° or less is disadvantageous from the viewpoint of energy saving, but has a feature that the sensor can be easily manufactured from the viewpoint of manufacturing the sensor. The operation as a hydrogen gas sensor and the effects of durability and the like are the same as in the previous embodiment.

According to a sixth embodiment of the present invention, an oxygen ion conductive solid electrolyte layer and a pair of patterned platinum electrode layers are further laminated on an insulating substrate provided with a heater film therein, and one of them is laminated. A region is formed by laminating ceramic porous bodies having a hydrogen oxidation catalyst and having an average pore diameter of 100 ° or less in a region where the electrodes dominantly flow into the electrodes. In the present embodiment,
A specific configuration of the heating means is realized by using an insulating substrate having a heater film therein. The sensor has an oxygen ion conductive solid electrolyte layer, a pair of patterned platinum electrode layers, and a hydrogen oxidation catalyst in a region where one of the electrodes flows dominantly.
積 層 It is constructed by laminating the following ceramic porous bodies. As the heater film inside the insulating substrate, a resistive film such as a noble metal is used. The temperature of 400 to 500 ° C. required for the operation of the oxygen ion conductive solid electrolyte is obtained by applying electric current to the resistance film. Operation as hydrogen gas sensor and average pore diameter of 1
Protecting the electrodes by using a ceramic porous body of not more than 00 ° can realize a stable sensor operation and expect high durability, as in the previous embodiment.

The seventh embodiment of the present invention is the same as the first to sixth embodiments, except that magnesium, silver, zinc, indium, tin,
It has a structure in which oxides or composite oxides of one or more elements selected from the group consisting of germanium and silicon are used as main components. A commonly used noble metal or transition metal oxide-based oxidation catalyst has the ability to oxidize a reducing gas such as hydrogen, but also has the ability to oxidize gases other than hydrogen. That is, there is a problem that the selectivity to hydrogen gas is inferior. Oxides and composite oxides of one or more elements selected from the group consisting of magnesium, silver, zinc, indium, tin, germanium, and silicon have the ability to adsorb oxygen and hydrogen, while reducing gases other than hydrogen For example, since a reducing gas such as carbon monoxide has no adsorptivity, it has an ability to oxidize only a hydrogen gas. Among these compounds, silver, zinc, indium and tin are particularly excellent in activity as a catalyst.

Magnesium, silver, zinc, indium,
Since the catalyst mainly composed of an oxide of one or more elements selected from the group of tin, germanium and silicon and a composite oxide has the capability of a hydrogen oxidation catalyst, it is used in the first to seventh implementations. When applied to the embodiment, the function as a hydrogen gas sensor is expected, and stable operation and high durability as the sensor are expected as in the previous embodiment. The method of forming the hydrogen oxidation catalyst includes a method in which the hydrogen oxidation catalyst is dispersed or supported in an enamel or an inorganic coating, a method in which the hydrogen oxidation catalyst is dispersed or supported in a nonwoven fabric of ceramic fibers, and a method such as plasma spraying. Performed by

The eighth embodiment of the present invention comprises the first to seventh embodiments using a thin film having an oxygen ion conductive solid electrolyte of 10 μm or less.
Even if the oxygen ion conductive solid electrolyte is a thin film having a thickness of 10 μm or less, there is no difference in terms of function, so that stable operation and high durability as a sensor can be expected. By forming the oxygen ion conductive solid electrolyte into a thin film having a thickness of 10 μm or less, particularly in a flat sensor, a ceramic porous body having an average pore diameter of 100 ° or less and an electrode can be formed as compared with the case of using a bulk sintered product. There is an advantage that it is not necessary to provide a seal with the oxygen ion conductive solid electrolyte in which is formed. As a method for forming the oxygen ion conductive solid electrolyte into a thin film having a thickness of 10 μm or less, a vacuum thin film forming process such as sputtering is used. This is disadvantageous in terms of productivity of the sensor because batch processing is performed by forming a vacuum system with a thin film, but it is advantageous in terms of downsizing of the sensor, particularly in terms of energy saving operation. As a method for forming the platinum electrode, thick film printing may be used. However, from the viewpoint of reducing the size of the entire sensor element, it is preferable to form the platinum electrode using a thin film such as sputtering as in the case of the oxygen ion conductive solid electrolyte.

In the ninth embodiment of the present invention, the ceramic porous body having an average pore diameter of 100 ° or less is formed by using a porous body selected from the group consisting of an alumina compound and a zirconia compound. To the eighth embodiment. The alumina compound and the zirconia compound have a thermal expansion coefficient close to that of the oxygen ion conductor, and the respective elements are stacked and joined to form a hydrogen gas sensor having high heat stability. The porous body selected from the group consisting of the alumina compound and the zirconia compound is prepared by uniformly dispersing the raw material powder, molding the sheet into a sheet shape with a doctor blade or the like, sintering this, and cutting it to a required size. By optimizing the composition, particle size and sintering temperature of the raw material powder,
A porous body having an average pore diameter of about 0.1 to 1 μm is obtained. A fine porous body having an average pore diameter of about 0.05 μm can be obtained by mixing the organic resin powder and molding in the same manner. This porous material is sol-gel method or CVD
By controlling the pores by the method, a desired porous body having an average pore diameter of 100 ° or less can be obtained. The sensor configured as described above has a stable operation as a hydrogen gas sensor and excellent durability as in the previous embodiment.

In a tenth embodiment of the present invention, a ceramic porous body having an average pore diameter of 100 ° or less is formed on a surface of the ceramic porous body by using a porous body selected from the group of alumina compounds or zirconia compounds. The first to ninth embodiments are constituted by using a porous body on which one or more films selected from the group of silica compounds or zirconia compounds are formed. In this configuration, a silica compound or one or more films selected from the group of zirconia compounds are formed on the surface of the porous ceramic body for the purpose of controlling the pores, thereby simultaneously controlling the pores and simultaneously waterproofing the surface of the porous body. Properties and acid resistance can be improved.

In particular, when the pore diameter becomes 10 mm or less, when the surface is made of a hydrophilic material, water vapor or sulfurous acid gas is condensed in the pores by capillary condensation and becomes liquid by the capillary condensation. There is a concern that the pores will be closed and gas permeability will be impaired. One or more films selected from the group consisting of silica compounds and zirconia compounds have high water resistance and acid resistance and do not have the risk of the above-mentioned capillary condensation. Therefore, in the present embodiment, in particular, the durability and the stability of the zero point for a long time are further improved. The overall operation and effect are the same as described above.

[0037]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

(Embodiment 1) FIG. 1 is a schematic sectional view of a hydrogen gas sensor according to Embodiment 1 of the present invention. In FIG. 1, reference numeral 1 denotes a heating means. For example, various resistance films are formed by thick-film printing on an insulating base material such as alumina and used.
The heating means 1 allows the hydrogen gas sensor to operate in a 3
It is heated to a temperature range of 00 to 500 ° C. Reference numeral 2 denotes an oxygen ion conductive solid electrolyte to which yttria-stabilized zirconia (YSZ) or ceria-stabilized zirconia (CSZ) can be applied. Two pairs of platinum electrodes are formed on the same surface of the two oxygen ion conductive solid electrolytes.

Further, a pair of ceramic porous bodies 4 having an average pore diameter of 100 ° or less are arranged in close contact with the platinum electrode, and a hydrogen oxidation catalyst 5 is formed in a partial region of the porous bodies. The ceramic porous body 4 is a layer having air permeability and allows oxygen and hydrogen gas to easily pass therethrough. Hydrogen is completely oxidized, especially when passing through a region provided with a hydrogen oxidation catalyst. A gas containing almost no hydrogen reaches one electrode by the hydrogen oxidation catalyst. That is, while the gas containing hydrogen reaches the other electrode, an oxygen concentration cell is formed between the electrodes and the hydrogen gas can be detected.

As the oxygen ion conductive solid electrolyte, a bulk ceramic sintered body or a film formed by a thin film forming method such as sputtering may be used. In the case of the thin film method, bonding is not required, but when a ceramic bulk product is used, bonding between the oxygen ion conductive solid electrolyte 2 and the porous ceramic body 4 is required. In that case, bonding is performed using glass or an inorganic adhesive. The platinum electrode 3 is formed of a ceramic bulk of the oxygen ion conductive solid electrolyte 2, that is, an oxygen ion conductive solid obtained by molding a raw material composition of the oxygen ion conductor by a press molding method, a doctor blade, or the like, and then firing and cutting to a predetermined size. The electrolyte 2 may be formed by a thin film method such as a sputtering method or an electron beam evaporation method in a state where the surface is masked in a predetermined pattern. Alternatively, a thick film printing method may be used. That is, it may be formed by screen-printing a predetermined pattern using a platinum-based paste and then firing. This does not change even when the oxygen ion conductive solid electrolyte is formed by the sputtering method. However, in the case of the sputtering method, it is desirable that the platinum electrode 3 is also formed by the thin film method. When the oxygen ion conductive solid electrolyte is formed as a thin film, the heat capacity is small and the sensor can be downsized.
There is also an advantage that a structure such as a seal is not required when configuring the laminated structure as described above.

In particular, when a solid electrolyte is formed as a thin film, it is necessary that the thickness of the solid electrolyte layer be 10 μm or less in order to construct a sensor that is stable with respect to heat.
The ceramic porous body 4 is arranged for the purpose of restricting the flow of various gases into the electrode. The sintered body of the ceramic porous body is used as a base material so that the average pore diameter is reduced to 100 ° or less by coating treatment. It is produced by controlling.

The ceramic porous body 4 has a pore diameter of 0.1 produced by a sintering method using alumina or zirconia.
A pore control film is formed by a sol-gel method or a CVD method using a ceramic porous substrate of 1 to 1 μm, and the pores are controlled to an average pore diameter of 100 ° or less.
In this case, the thermal expansion coefficient is close to that of the oxygen ion conductive solid electrolyte, so that it becomes stable against thermal shock and the like. The base material of the ceramic porous body is produced by molding a ceramic powder as it is or by mixing it with an organic substance such as a resin to form a predetermined shape, and then sintering at a temperature lower than the temperature for complete sintering. The average pore diameter of the porous body produced by the sintering method is 0.1
μm is the limit.

Therefore, in order to use it for the purpose of the present invention, it is necessary to use a porous substrate produced by a sintering method and treat its pores with a coating film. Since the porous body produced by the sintering method is generally commercially available as a microfiltration membrane, the commercially available ceramic porous substrate can be used in the present invention.

Next, a method of controlling pores by the sol-gel method will be described below. After hydrolyzing a metal alkoxide such as zirconium isopropoxide or tetraethoxysilane, it is subjected to polycondensation under catalytic conditions such as hydrochloric acid to prepare a desired sol solution. When the porous ceramic is contacted with a porous ceramic having pores penetrating the sol solution, for example, when the porous ceramic is immersed in the sol, the sol solution is sucked by capillary force, and when the sol is dried, the sol solution is dried in the pores of the porous ceramic. Concentration of the sol and further gelation occur.

Further, when heating is further advanced, sintering proceeds from gelation to form a coating film. If necessary, a method of filtering the sol solution using a porous ceramic can also be adopted. By utilizing this phenomenon, the pore diameter can be controlled. By adjusting the wettability of the pore surface of the porous ceramic, the solvent of the sol, the concentration of the sol, the immersion time, and the pulling speed of the ceramic, a porous body having a relatively uniform pore diameter of 100 ° or less can be obtained.

The pores produced in this way have different characteristics depending on the level of the average pore diameter in the gas flow in the pores of the porous body. It shows properties and shows gas permeation properties that are inversely proportional to the square root of the molecular weight. The average pore size is 10
When the pore size is less than Å, an effective molecular sieving effect that does not allow passage of high molecular weight gas is exhibited. In addition, the interaction with the gel film formed inside the pores increases the gas permeability.

That is, the intermolecular force between the gas molecule and the gel molecule is determined by the orientation force due to the interaction between the permanent hyperboloids, the induced force between the permanent hyperboloid and the induced hyperboloid, and the dispersion force based on the van der Waals interaction. Gas permeation, ie, surface diffusion. In particular, when the pore size is 10
Å When the water content is less than or equal to the above, since the problem of capillary condensation also occurs with moisture, the film needs to be a hydrophobic film. The above problems can be overcome by using silica or zirconia as a treatment film for controlling pores. In that case, it is in the region of molecular sieves, and a high degree of gas quality separation is possible. Even if the average pore diameter is not particularly reduced to 10 ° or less, for example, 100 °
However, since a pore portion of 10 ° or less is also generated from the pore diameter distribution, the above-mentioned hydrophobic treatment becomes important.

The region 5 containing the hydrogen oxidation catalyst is formed by using a ceramic porous body having an average pore diameter controlled to 100 ° or less, and supporting the catalyst in the pores and on the surface. Here, as the hydrogen oxidation catalyst, an oxide or a composite oxide of a transition metal such as platinum, palladium, or another such white metal or iron, manganese, copper, nickel, chromium, or cobalt can also be used. in case of,
It has the property of detecting reducing gases other than hydrogen as well. Desirably, magnesium, silver, zinc, indium, tin,
An oxide or a composite oxide of one or more elements selected from the group consisting of germanium and silicon is used.

These not only adsorb oxygen, but also do not adsorb other reducing gas molecules, adsorb only hydrogen molecules,
This is because they have an ability to oxidize, and by using them as a catalyst, excellent hydrogen selectivity can be obtained. The supporting method is such that a ceramic porous body whose average pore diameter is controlled to 100 ° or less using an acid aqueous solution or a complex compound aqueous solution of each metal element is immersed or coated in the aqueous solution, dried, fired, and reduced to form. .

As a hydrogen gas sensor, the components formed as described above are laminated as necessary using a binder as shown in FIG. 1 to complete a laminated structure. As the bonding agent, for example, bonding is performed using a system inorganic adhesive such as glass frit, metal phosphate, or alkali metal silicate. The lamination of the electrode and a ceramic porous body having an average pore diameter of 100 ° or less prevents or regulates the invasion of a gas such as a low-molecular-weight silicone compound into the electrode, which is likely to be adsorbed and poisoned on the platinum electrode in the general atmosphere. You.

According to the structure of the present embodiment, in the solid electrolyte type hydrogen gas sensor, an electrode, which is the most problematic in terms of durability characteristics, is sufficiently protected, and a highly reliable gas sensor with very little zero point drift with time is obtained. Can be In this configuration, since the catalyst is also protected in the pores, it is hardly affected by poisoning, and high durability is expected.

(Embodiment 2) FIG. 2 is a schematic sectional view of a hydrogen gas sensor according to Embodiment 2 of the present invention. The basic configuration is similar to that of Example 1. However, in Example 1, the function of the hydrogen oxidation catalyst was formed in a partial region of the ceramic porous body having an average pore diameter of 100 ° or less. The difference is that a porous body 6 containing a hydrogen oxidation catalyst is provided outside a ceramic porous body 4 having an average pore diameter of 100 ° or less. As the porous body 6 containing the hydrogen oxidation catalyst, various porous bodies such as a heat-resistant metal, ceramic, and glass are used, and a metal oxide, a composite metal oxide, or
A precious metal is formed and used together with the bonding porous binder.
Naturally, the basic operation and effect of the hydrogen gas sensor of the second embodiment are the same as those of the first embodiment.

(Embodiment 3) FIG. 3 is a conceptual sectional view of a hydrogen gas sensor according to Embodiment 3 of the present invention. In FIG. 3, reference numeral 1 denotes a heating unit. Unlike the first and second embodiments, the first heating unit is formed on the lower ceramic porous body surface 4 that does not include the hydrogen oxidation catalyst.

In the third embodiment, a pair of platinum electrodes 3 are formed on two opposite surfaces of two oxygen ion conductive solid electrolytes. The ceramic porous body 4 is laminated on each of platinum electrodes formed on both surfaces of the oxygen ion conductive solid electrolyte, and the lower side is a ceramic porous body containing no hydrogen oxidation catalyst and the upper side is a ceramic containing the hydrogen oxidation catalyst 5. It has a porous body. The only difference is the layer configuration of the hydrogen gas sensor, and the method of forming each element is substantially the same. In the hydrogen gas sensor of the present embodiment, the upper electrode of the ceramic porous body provided with the hydrogen oxidation catalyst serves as the standard electrode, and the lower electrode opposed via the oxygen ion conductive solid electrolyte serves as the hydrogen gas detection electrode. , Operates as a hydrogen gas sensor. The effect of the present embodiment is the same as that of the previous embodiment, and stabilization of characteristics and prolongation of life are achieved.

(Embodiment 4) FIG. 4 is a conceptual view of a cross section of a hydrogen gas sensor according to Embodiment 4 of the present invention. FIG.
In the above, a hydrogen gas sensor similar to the hydrogen gas sensor element described in the first embodiment (however, in this embodiment,
The difference is that the ceramic porous body does not use a controlled pore.) However, the ceramic porous body is housed in a cylindrical container 7 formed of a controlled ceramic porous body having an average pore diameter of 100 ° or less. In FIG. 4, the storage container has a cylindrical shape. However, the storage container does not necessarily have to be cylindrical.

The air circulating portion of the storage container does not necessarily have to be the entire surface of the storage container. For example, only a part of the cylindrical portion may be used.

In the same manner as in the hydrogen gas element of Example 1, the prepared hydrogen gas sensor element was used and stored in a cylindrical storage container 7 formed of a ceramic porous body having a controlled average pore diameter of 100 ° or less. Thus, a hydrogen gas sensor is formed. The cylindrical storage container 7 formed of a ceramic porous body having a controlled average pore diameter of 100 ° or less is produced by subjecting a sintered product of the ceramic porous body to a pore control coating treatment. The hydrogen gas sensor element can operate as a hydrogen gas sensor as in the first embodiment. With the configuration of the present embodiment,
Gases such as low-molecular-weight silicone that reach the electrode portion or the hydrogen oxidation catalyst portion of the hydrogen gas sensor element and cause deterioration are protected by a cylindrical housing formed of a controlled ceramic porous body having an average pore diameter of 100 mm or less. Since it does not reach the inside, stable operation and long life as a hydrogen gas sensor are expected.

(Embodiment 5) FIG. 5 shows a conceptual diagram of a cross section of a hydrogen gas sensor according to Embodiment 5 of the present invention.

The fifth embodiment is similar to the fourth embodiment, except that the heating means provided in the hydrogen gas sensor element of the fourth embodiment is omitted, and the heating means is arranged outside the storage container 7. is there. In FIG. 5, reference numeral 8 denotes a heating unit arranged outside the storage container 7. The heating means of No. 8 secures the temperature required for the operation of the oxygen ion conductive solid electrolyte and the hydrogen oxidation catalyst. The method of forming the storage container and the like are the same as in the fourth embodiment. According to the configuration of the present embodiment, similarly to the case of the fourth embodiment, a gas such as low molecular weight silicone which reaches the electrode portion or the hydrogen oxidation catalyst portion of the hydrogen gas sensor element and causes deterioration has an average pore diameter of 100 ° or less. Since it is protected by the cylindrical housing formed of the controlled ceramic porous body and does not reach the inside of the element, stable operation and long life as a hydrogen gas sensor are expected.

(Embodiment 6) FIG. 6 is a conceptual diagram showing a cross section of a hydrogen gas sensor according to Embodiment 6 of the present invention. FIG.
In the hydrogen gas sensor of the sixth embodiment, the oxygen ion conductive solid electrolyte layer 2 and a pair of patterned platinum electrode layers 3 are further laminated on an insulating substrate 10 having a heater film 9 therein, and It has a configuration in which a ceramic porous body 4 having a hydrogen oxidation catalyst and having an average pore diameter of 100 ° or less is laminated in a region where the dominant flow into the electrode is provided. Arranging an insulating substrate having a heater film therein is one of the specific heating means described in the first and second embodiments.

An insulating substrate having a heater film inside is formed by forming a ceramic green sheet of alumina or the like in a state of a pair of green sheets on one of the sheet bases by pattern printing or the like, and then bonding and firing. It is formed by tying. Since the heater circuit is formed inside the ceramic, the heat dissipation loss and the heat resistance are small, so that the heating means can be a low power consumption type heating device with good heating start-up characteristics. In the hydrogen gas sensor configured as described above, the most important electrode in terms of its durability characteristics is sufficiently protected, and a highly reliable hydrogen gas sensor with very little zero-point drift over time can be obtained. The same as in the case of 1.

The results of experiments relating to the effects of the present invention will be described below.

As the oxygen ion conductor, a commercially available sintered product of yttria-stabilized zirconia (8% yttria product) (dimensions: 10 mm × 10 mm × 0.35 mm) was used. A pair of platinum electrode patterns having a dimension of 3 × 8 mm was formed on one surface of the pair by sputtering at a substrate temperature of 250 ° C. with a thickness of 0.5 μm using a masking jig. Using a commercially available platinum paste, a platinum lead wire having a diameter of 0.1 mm was taken out from the end of the electrode.

As a heating means, a device in which a platinum resistance film was formed on an alumina substrate and lead wires were joined was used.

A ceramic porous substrate having an average pore diameter of 100 ° or less is a zirconia porous substrate (average pore diameter of 0.1 μm and dimensions of 10 mm × 10 mm × 0.5 mm) prepared by adjusting the particle size distribution and firing temperature. Was cut into an alkoxide solution containing zirconia isopropoxide as a main component to control pores. The fine pores were controlled by applying a 20 Wt% solution of alkoxide and applying the same again.

Incidentally, the average pore diameter was evaluated by a wet method according to a molecular weight cutoff method. The average pore diameter is 3 times
It was found that the average pore diameter was formed at about 80 °. Further, using a porous base material, platinum, palladium, silver oxide, zinc oxide, tin oxide, and indium oxide were supported in half the area. Although the surface was colored, it was not clear how far inside the pores it had penetrated, so it was analyzed, but in most cases it penetrated only up to about 20 μm from the surface. Each element produced as described above was laminated to experimentally produce a hydrogen gas sensor element having the structure shown in FIG. The bonding agent for laminating the gas sensor elements was performed using a commercially available inorganic adhesive “Sumiceram” (trade name). As an object, a sample in which pore control was not performed was also prototyped.

The output of each of the above hydrogen gas sensor elements with respect to 500 ppm hydrogen gas at 350 ° C. and 1000 ppm
The results of evaluating the operation with respect to carbon monoxide are shown below.

(1) Platinum catalyst: hydrogen (55 mV), carbon monoxide (30 mV) (2) Palladium catalyst: hydrogen (44 mV), carbon monoxide (27 mV) (3) Silver oxide catalyst: hydrogen (30 mV) Carbon oxide (5m
V) (4) Zinc oxide catalyst: hydrogen (50 mV), carbon monoxide (0
mV) (5) Tin oxide catalyst: hydrogen (52 mV), carbon monoxide (0 m
V) (6) Indium oxide catalyst: (48 mV), carbon monoxide (0 mV) As described above, it was confirmed that platinum and palladium had poor selectivity to hydrogen gas, but other prototype catalysts had good selectivity. .

Further, using a distribution type test apparatus, 50 pp
The durability of this prototype sensor was evaluated by an acceleration test through silicone vapor of m. Untreated product, ie 0.1μ
In the element having an average pore diameter of m, the zero point was shifted by 100 mV or more, and no output was obtained in about 2 hours. On the other hand, when the average pore diameter was 100 ° or less, the sensor output did not change even after 50 hours.

As described above, an effective effect regarding durability was confirmed.

[0071]

The hydrogen gas sensor of the present invention is embodied in the form described above, and has the following effects.

(1) Regarding the detection of hydrogen gas, the weak point of fail-out can be covered, and the reliability of the element configuration is high and a wide range of applications can be considered.

(2) In terms of the practical use of chemical sensors, with regard to durability, which has been the greatest problem in the past, a ceramic porous body having a controlled pore diameter for restricting the arrival of an interfering gas to the hydrogen gas sensor element is used. An extremely reliable hydrogen gas sensor that can control various gases that have a poisoning effect on the hydrogen gas sensor by protecting the electrode, which is a weak point of the sensor, or can dramatically increase the life by the effect of completely blocking it. A system can be built.

(3) It is possible to provide an inexpensive hydrogen gas sensor which has a simple structure, is excellent in process productivity, and is inexpensive.

[Brief description of the drawings]

FIG. 1 is a conceptual cross-sectional view of a hydrogen gas sensor according to a first embodiment of the present invention.

FIG. 2 is a conceptual cross-sectional view of a hydrogen gas sensor according to a second embodiment of the present invention.

FIG. 3 is a conceptual sectional view of a hydrogen gas sensor according to a third embodiment of the present invention.

FIG. 4 is a conceptual sectional view of a hydrogen gas sensor according to a fourth embodiment of the present invention.

FIG. 5 is a conceptual sectional view of a hydrogen gas sensor according to a fifth embodiment of the present invention.

FIG. 6 is a conceptual sectional view of a hydrogen gas sensor according to a sixth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating means 2 Oxygen ion conductive solid electrolyte 3 Platinum electrode 4 Porous ceramic having an average pore diameter of 100 mm or less 5 Hydrogen oxidation catalyst

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Takashi Niwa, Inventor 1006 Kadoma, Kazuma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Kunihiro Tsuruta 1006, Kadoma, Kazuma, Kadoma City, Osaka Matsushita Electric Industrial Co. 72) Inventor Takahiro Umeda 1006 Kadoma, Kazuma, Osaka Prefecture F-term (reference) 2G004 BB04 BD04 BE12 BE22 BF12 BF14 BG09 BG13 BJ02 BK01 BK03 BL08

Claims (10)

[Claims] 1. A ceramic having a heating means, an oxygen ion conductive solid electrolyte, and a pair of platinum electrodes formed on the same surface of the oxygen ion conductive solid electrolyte, the ceramic having an average pore diameter of 100 ° or less in close contact with the platinum electrode. A hydrogen gas sensor comprising a porous body, and further comprising a hydrogen oxidation catalyst in a region where the gas to be detected predominantly flows into one platinum electrode in a partial region of the ceramic porous body. 2. A ceramic having a heating means, a pair of platinum electrodes formed on the same surface of an oxygen ion conductive solid electrolyte and an oxygen ion conductive solid electrolyte, and having a mean pore diameter of 100 ° or less in close contact with said platinum electrode. A hydrogen gas sensor comprising a porous body, and a porous body containing a hydrogen oxidation catalyst at a portion of the surface of the ceramic porous body into which a gas to be detected flows into one platinum electrode. 3. A heating means, a pair of platinum electrodes formed on opposite surfaces of the oxygen ion conductive solid electrolyte and the oxygen ion conductive solid electrolyte, and a hydrogen oxidation catalyst disposed on one surface of the pair of platinum electrodes has an average pore diameter of 100 °. It has a ceramic porous body having the following characteristics, and the other surface has an average pore diameter of 1
A hydrogen gas sensor comprising a ceramic porous body having a characteristic of not more than 00 ° and containing no hydrogen oxidation catalyst. 4. A heating means and a pair of platinum electrodes formed on the same surface of an oxygen ion conductive solid electrolyte and an oxygen ion conductive solid electrolyte, and one of the electrodes is covered with a porous material containing a hydrogen oxidation catalyst. A hydrogen gas sensor in which the element formed as described above is housed in a container of a ceramic porous body having an average pore diameter of 100 ° or less. 5. An oxygen ion conductive solid electrolyte and a pair of platinum electrodes formed on the same surface of the oxygen ion conductive solid electrolyte, one of the electrodes being covered with a porous material containing a hydrogen oxidation catalyst. A hydrogen gas sensor comprising the element thus prepared and housed in a porous ceramic container provided with a heating means having an average pore diameter of 100 ° or less. 6. An oxygen ion conductive solid electrolyte layer and a pair of patterned platinum electrode layers are further laminated on an insulating substrate provided with a heater film therein, and are formed in a region which flows predominantly into one electrode. Average pore size with hydrogen oxidation catalyst is 1
A hydrogen gas sensor laminated with a ceramic porous body of not more than 00 °. 7. As a hydrogen oxidation catalyst, magnesium, silver,
The hydrogen gas sensor according to any one of claims 1 to 6, wherein an oxide or a composite oxide of one or more elements selected from the group consisting of zinc, indium, tin, germanium, and silicon is used as a main component. 8. The hydrogen gas sensor according to claim 1, wherein the oxygen ion conductive solid electrolyte uses a thin film having a thickness of 10 μm or less. 9. The hydrogen gas sensor according to claim 1, wherein the ceramic porous body is a porous body selected from the group consisting of an alumina compound and a zirconia compound. 10. A ceramic porous body comprising a porous body selected from the group consisting of an alumina compound and a zirconia compound, and forming at least one film formed on the surface thereof from a silica compound or a zirconia compound. The hydrogen gas sensor according to claim 1, wherein the hydrogen gas sensor is a porous body.