JPH09318591A - Carbon monoxide gas detection element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high sensitivity carbon monoxide gas detection element exhibiting excellent selective sensitivity to carbon monoxide gas. SOLUTION: The carbon monoxide gas detection element comprises a substrate 1 composed of an oxygen ion conductive solid electrolyte, and a pair of electrodes 2, 3 containing a substituted perovskite type composite oxide formed on the same or different surface of the substrate 1 wherein one of the pair of electrodes is covered with an oxidizing catalyst 4. This arrangement accelerates the oxidizing reaction of carbon monoxide gas and since the electrode is formed of a substituted perovskite type composite oxide having high electron conductivity, the detection element senses carbon monoxide gas with high selectivity while simplifying the structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon monoxide gas sensing element which is selectively sensitive to carbon monoxide gas (hereinafter, simply referred to as CO or CO gas).

[0002]

2. Description of the Related Art A direct detection method using a CO sensor has been conventionally studied as a method for detecting CO gas that is toxic to a human body when a combustor such as a gas appliance causes incomplete combustion. For example, as shown in JP-B-58-4985, a pair of platinum (Pt) electrodes are formed on an oxygen ion conductive solid electrolyte, and one of the electrodes has its surface covered with an oxidation catalyst. The other exposes its surface. (Here, this detection element is referred to as a first conventional example.) Such an element is used for 300 to 4 by a heater.
When kept at an operating temperature of 00 ° C. and placed in air containing a flammable gas, a sensor output, which is an electromotive force corresponding to the potential difference between both electrodes, is generated.

Further, a CO excellent in such a CO sensor is used.
In order to have gas selectivity, JP-A-58-99747
JP-A-59-37456 and JP-A-59-37456 propose a sensing element including a solid electrolyte and a pair of Pt electrodes covered with two kinds of catalysts having different oxidizing abilities. (This is the second
This is a conventional example. ) A method of detecting highly toxic CO gas by attaching these conventionally proposed detection elements to a room or a combustion device can be considered.

On the other hand, the inventor of the present invention has found that a perovskite type complex oxide (ABO ₃ : where A is La, Ce, P
Rare earth elements such as r and Nd, and B is V, Cr, Mn and F
A CO gas sensor having a high selectivity for CO gas, which uses e, Co, Ni, Cu or other transition metal elements) as an electrode material, has already been developed (see Japanese Patent Application No. 7-048230).

[0005]

As a first conventional example, the detecting element disclosed in Japanese Patent Publication No. 58-4985 is as follows.
The CO gas selectivity is poor, that is, it is sensitive to other combustible gases such as hydrogen gas and methane gas, and there is a risk of erroneous detection.

On the other hand, as a second conventional example, JP-A-58-99
The sensing elements disclosed in Japanese Patent Publication No. 747 and Japanese Patent Publication No. 59-37456 require two kinds of catalysts having different oxidizing capacities in order to enhance the selectivity for CO gas, and as a result, they are structurally complicated. In addition, since the materials of the two catalysts deposited on the electrodes are different, the changes over time of both catalysts are different, which causes a problem that the change over time of the element characteristics is large. In addition, the operating temperature of the device is 30 because the special catalyst is used.
The temperature must be relatively low, about 0 ° C. As a result, oxygen ion conductivity in yttria-stabilized zirconia (hereinafter, simply referred to as YSZ) is lowered, so that not only the response time (rise) is slow, but also the detection characteristics are rapidly deteriorated. This is because carbon dioxide (CO ₂ ) and water (H ₂ O) that have reacted with the catalyst and adsorbed on the surface of the catalyst are less likely to be released from the surface of the catalyst due to the low temperature.

Further, in the technical field, Japanese Patent Application No.
It is desired to develop a detection element having a CO gas selectivity which is further superior to that of the CO gas sensor using the perovskite complex oxide disclosed in the specification of No. 048230 as an electrode.

Therefore, the present invention has been made to solve the above-mentioned problems in the prior art and the recent technology, and the purpose thereof is to have more excellent CO gas selectivity and to reduce CO gas. An object is to provide a CO gas detection element of simple structure, which can be sensitive with extremely high sensitivity.

[0009]

In order to achieve the above object, according to a basic aspect of the present invention, a substitutional perovskite complex oxide (A) is formed on the surface of a substrate composed of an oxygen ion conductive solid electrolyte. ' _1-x A " _x BO ₃ : However, A'
Is a rare earth element, A ″ is an alkaline earth metal element, and B is a transition metal element.), And a pair of electrodes is formed, and one of the electrodes is covered with an oxidation catalyst. A CO gas sensing element is provided.

According to another aspect of the present invention, there is provided a CO gas detecting element characterized in that the pair of electrodes in the above-mentioned basic aspect are formed on the same surface of the substrate.

According to still another aspect of the present invention, there is provided a CO gas detection element characterized in that the pair of electrodes in the above-mentioned basic aspect are formed on different surfaces of the substrate, respectively.

The oxygen ion conductive solid electrolyte in the above-mentioned basic embodiment is ZrO ₂ , C stabilized with CaO, MgO or M ₂ O ₃ (M is a rare earth element such as Y or La).
aO or M ₂ O ₃ (M is a rare earth element such as Gd or La)
And CeO ₂ , a mixture of ThO ₂ and M ₂ O ₃ (M is a rare earth element such as Y or La), Y ₂ O ₃ , Gd ₂
O ₃ , Nb ₂ O ₅ , WO ₃ , SrO, BaO or La
It is one selected from the group consisting of a mixture of ₂ O ₃ and Bi ₂ O ₃ .

Further, the substitutional perovskite type composite oxide in the above-mentioned basic embodiment is such that a rare earth element such as La, Ce, Pr, Nd is used as A of the perovskite type composite oxide (ABO ₃ ), and V is V, Cr, Mn, F
A complex oxide in which a transition metal element such as e, Co, Ni, or Cu is used, and a part of the A is substituted with an alkaline earth metal element such as Ca, Sr, or Ba, and the alkaline earth metal element is used. The substitution amount is less than 50 mol%.

Further, the oxidation catalyst in the above-mentioned basic embodiment is selected from the group consisting of Mg, Ca, V, Cr, Mn, Fe, Co, Ni or Cu oxide, Ru, Rh, Pt and Pd. A single or a combination of two or more, and the catalyst carrier is Al ₂ O ₃ , SiO ₂ ,
TiO ₂ , MgO, SnO ₂ , ZrO ₂ , La ₂ O ₃ ,
It consists of one or a combination of two or more selected from the group consisting of CeO ₂ .

[0015]

In the carbon monoxide gas detecting element of the present invention,
Of the combustible gases present in the atmosphere, instead of a pair of electrodes made of platinum, which are particularly easy to react with hydrogen gas, a substitutional perovskite-type composite that easily causes an oxidation reaction in CO gas and has high electron conductivity A pair of electrodes made of oxide is used. From this, a CO gas detection element having higher CO sensitivity and more excellent CO gas selectivity can be provided.

[0016]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below with reference to one embodiment shown in the accompanying drawings.

FIG. 1 shows a CO gas sensor using a CO gas detecting element manufactured according to the present invention in a top view ((a) of FIG. 1) and a cross-sectional view ((b) of FIG. 1).

This CO gas sensor has a substitutional perovskite complex oxide (A ' _1-x ) on the upper surface of a substrate 1 made of yttria (Y ₂ O ₃ ) stabilized zirconia (ZrO ₂ ) which is an oxygen ion conductive solid electrolyte. A " _x BO ₃ , where A'is a rare earth element, A" is an alkaline earth metal element, and B is a transition metal element.) A pair of electrodes 2 and 3 are formed at predetermined intervals. Further, a combustible gas oxidation catalyst layer 4 made of platinum (Pt) and aluminum oxide (Al ₂ O ₃ ) is formed so as to cover one electrode 2. Lead parts 5a and 6a both made of platinum (Pt) for extracting the sensor output from the pair of electrodes 2 and 3
And lead wires 5b and 6b are respectively drawn out and connected to the measuring device shown in FIG.

[0019]

EXAMPLES Next, the CO gas detection element of the above-mentioned embodiment will be described in a little more detail with its manufacturing process taken into consideration.

ZrO stabilized with 8 mol% Y ₂ O _3
On the same surface of the substrate 1 as an oxygen ion conductor made of ₂ (hereinafter simply referred to as YSZ), lead portions 5a and 6a for extracting sensor output are first formed by printing Pt paste, and at 1350 ° C. Baked. next,
The Pt lead wires 5b and 6b for taking out the sensor output were fixed and taken out from the pair of Pt print lead portions 5a and 6a with Pt paste, and baked at 1450 ° C. Subsequently, a substitutional perovskite type composite oxide (A ′ _1-x A ″ _x BO
₃ , provided that La is added to A'as an example of the present invention.
Sr was used for A ″ and Mn was used for B.) A paste-like material was printed on the substrate 1 to form a pair of electrodes 2 and 3 and baked at 1100 ° C. , The size of each electrode is 2 mm square, and the distance between both electrodes is 0.
5 mm.

Thereafter, as the catalyst layer 4 for oxidizing the combustible gas, a paste prepared by mixing alumina powder carrying platinum (Pt) at a ratio of 1.5 wt% with an organic solvent, a binder and a surfactant is used. Prepared and printing this paste with a thickness of about 50 μm to cover one electrode 2,
It was fired at a temperature of 900 ° C.

As can be understood from the above, the CO gas detection element of the present invention has an extremely simple structure.

FIG. 2 is a graph showing the measurement results of CO gas detection using the samples of the CO gas detection element obtained in the example of the present invention. In FIG. 2, (a) shows the result when the measurement temperature (operating temperature of the sensing element) was 400 ° C., and (b) shows the result when the measurement temperature was 500 ° C. The measurement results are shown in a form in which the sensor outputs (electromotive force: mV) of CO and H ₂ of 500 ppm for each Sr substitution amount are compared with each other.

As is apparent from the graphs shown in FIGS. 2A and 2B, the ratio of the respective sensor outputs to CO and H ₂ is obtained by using the CO gas detecting element of the embodiment. (CO / H ₂ ) is the measurement temperature 400 ℃
20-25 in the case of, and 4-1 in the case of the measurement temperature of 500 ° C
6, the CO gas could be remarkably and selectively detected at both the measurement temperatures of 400 ° C and 500 ° C. Furthermore, by substituting a part of La with Sr, C
The O gas detection sensitivity can be increased, and the CO gas detection sensitivity showed the maximum value when the Sr substitution amount was 30 mol%.

As can be understood from the above results,
All the examples of the present invention showed excellent selectivity with respect to the sensitivity to CO gas.

FIG. 3 is a block diagram of the measuring apparatus used for detecting the CO gas and other combustible gases, which has obtained the results shown in FIG. 2, and is the furnace chamber of the electric furnace 11 into which the test gas is introduced. 1
The CO gas detection element 10 of the present invention is placed at a proper position within the area 2. A voltmeter 13 as a sensor output measuring device is connected to the lead wires 5b and 6b drawn from the electrodes 2 and 3 of the CO gas detecting element 10, respectively.

Further, in the gas exhaust pipe line from the furnace chamber 12,
Infrared absorption Portable gas tester as CO gas concentration analyzer 14 for detecting the CO gas concentration in the test gas introduced into the furnace chamber 12, also H ₂ gas concentration analysis for detecting the H ₂ gas concentration A gas chromatography is connected as a total of 15.

The measured values of the voltmeter 13, the CO gas concentration analyzer 14 and the H ₂ gas concentration analyzer 15 are input to a recording device 16 such as a personal computer.

On the other hand, the gas introduced into the furnace chamber 12 (1%
CO / N ₂ , 1% H ₂ / N ₂ , O ₂ , N ₂ ) is supplied from each gas cylinder 17a to 17d to the test gas mixer 20.
To the furnace chamber 12 after being mixed there and mixed there.

The gas discharged from the furnace chamber 12 after the detection and measurement is discharged to the atmosphere via the poisonous gas treatment device 21.

Each gas from the gas cylinders 17a to 17d is supplied to the test gas mixer 20 via the mass flow controller 18 whose flow rate is controlled by the flow rate control unit 19.

Although a pair of electrodes 2 and 3 are formed on the same surface of the substrate 1 in the above-described embodiment, a pair of electrodes are formed on different surfaces of the substrate 1, respectively, and a carbon monoxide gas sensing element is also formed. Exhibits the same effect.

Further, in the above embodiment, Zr stabilized with Y ₂ O ₃ is used as the oxygen ion conductive solid electrolyte of the sensing element.
O ₂ was used, La _1-x Sr _x MnO ₃ was used for the electrode, and Pt with Al ₂ O ₃ as a carrier was used as the oxidation catalyst. However, the present invention can also use the materials listed below. A CO gas detection element equivalent to that in the example can be manufactured. 1. As an oxygen ion conductive solid electrolyte, (1) Ca
ZrO ₂ , (2) CaO or M ₂ stabilized with O, MgO or M ₂ O ₃ (M is a rare earth element such as Y or La)
A mixture of O ₃ (M is a rare earth element such as Gd and La) and CeO ₂ , (3) A mixture of ThO ₂ and M ₂ O ₃ (M is a rare earth element such as Y and La), (4) Y ₂ O ₃ , Gd ₂ O
₃ , Nb ₂ O ₅ , WO ₃ , SrO, BaO or La ₂
A mixture of O ₃ and Bi ₂ O ₃ . 2. The electrode is a substitutional perovskite complex oxide (A ′ _1-x A ″ _x BO ₃ ), where A ′ is a rare earth element Ce, Pr, Nd, and A ″ is an alkaline earth metal element. A complex oxide composed of Ca, Ba, and one selected from V, Cr, Fe, Co, and Cu, which are transition metal elements as B. 3. As an oxidation catalyst, Mg, Ca, V, Cr, Mn, F
e, Co, Ni or Cu oxide, Ru, Rh, P
Al ₂ O and a catalyst substance selected from the group consisting of t and Pd, which is used alone or in combination of two or more.
₃ , SiO ₂ , TiO ₂ , MgO, SnO ₂ , ZrO
_A catalyst carrier composed of one or a combination of two or more selected from the group consisting of ₂ , La ₂ O ₃ and CeO ₂ .

The above description is merely illustrative of the preferred embodiments of the present invention and the scope of the present invention is not limited thereto. Many more modifications and adaptations of the present invention will readily occur to those skilled in the art without departing from the scope of the invention.

[0035]

According to the carbon monoxide gas detecting element of the present invention, the electrode is formed of the substitutional perovskite type complex oxide which easily causes an oxidation reaction in CO gas and has a high electron conductivity. The sensitivity to CO gas in the atmosphere is significantly higher than that of the conventional element, and CO gas can be detected more selectively.

If at least one material is used for each of the electrode and the catalyst, the performance can be sufficiently exhibited and the structure can be simplified.

[Brief description of drawings]

FIG. 1 (a) is a schematic top view showing a carbon monoxide gas detector using an embodiment of the present invention, and FIG. 1 (b) is a BB sectional view thereof.

FIG. 2 is a graph showing a result of CO gas detection using an example of the present invention in comparison with a result of H ₂ gas detection,
(A) shows the result when the measurement temperature was 400 ° C, and (b) shows the result when the measurement temperature was 500 ° C.

FIG. 3 is a block diagram of a measuring device used for gas detection in the present invention.

[Explanation of symbols]

1 YSZ substrate 2 electrode 3 electrode 4 catalyst layer 5a lead part 6a lead part 5b lead wire 6b lead wire 10 CO gas detection element 11 electric furnace 12 furnace chamber 13 voltmeter 14 CO concentration analyzer 15 H ₂ concentration analyzer 16 recording device 17a Gas cylinder 17b Gas cylinder 17c Gas cylinder 17d Gas cylinder 18 Mass flow controller 19 Flow control unit 20 Test gas mixer 21 Poisonous gas treatment device

Claims (7)

[Claims] _1. A substitutional perovskite complex oxide (A ′ _1-x A ″ _x BO ₃ : where A ′ is a rare earth element and A ″ is formed on the surface of a substrate made of an oxygen ion conductive solid electrolyte. Is an alkaline earth metal element and B is a transition metal element), and a pair of electrodes is formed, and one of the pair of electrodes is covered with an oxidation catalyst. . 2. The carbon monoxide gas sensing element according to claim 1, wherein the pair of electrodes are formed on the same surface of the substrate. 3. The carbon monoxide gas detection element according to claim 1, wherein the pair of electrodes are formed on different surfaces of the substrate, respectively. 4. The oxygen ion conductive solid electrolyte is C
ZrO ₂ , CaO or M ₂ O ₃ stabilized with aO, MgO or M ₂ O ₃ (M is a rare earth element such as Y or La)
(M is a rare earth element such as Gd or La) and CeO ₂ , a mixture of Y ₂ O ₃ , Gd ₂ O ₃ , Nb ₂ O ₅ , WO ₃ and Sr.
Carbon monoxide according to any one of claims 1 to 3, characterized in that it is one selected from the group consisting of O, BaO or a mixture of La ₂ O ₃ and Bi ₂ O _3. Gas detection element. 5. The substitutional perovskite-type composite oxide is a perovskite-type composite oxide (ABO ₃ ) in which rare earth elements such as La, Ce, Pr, and Nd are used as A.
A transition metal element such as V, Cr, Mn, Fe, Co, Ni or Cu is used as B, and a part of A is Ca, Sr,
The carbon monoxide gas detection element according to any one of claims 1 to 3, which is a composite oxide substituted with an alkaline earth metal element such as Ba. 6. The substitution amount by the alkaline earth metal element is less than 50 mol%.
The carbon monoxide gas detection element described in 1. 7. The oxidation catalyst is Mg, Ca, V, C
R, Mn, Fe, Co, Ni or Cu oxide, R
u, Rh, Pt, Pd selected from the group consisting of one or a combination of two or more, and the catalyst carrier is Al ₂ O ₃ , SiO ₂ , TiO ₂ , MgO, SnO.
The carbon monoxide according to any one of claims 1 to 3, which is selected from the group consisting of ₂ , ZrO ₂ , La ₂ O ₃ and CeO ₂ and is composed of one or a combination of two or more thereof. Gas detection element.