JP2012042222A - Solid electrolyte-based co sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a solid electrolyte-based CO sensor for installation in or near gas equipment that directly measures CO concentration in combustion exhaust gas or other gas and improves performance of gas equipment and gas atmosphere safety.SOLUTION: The CO sensor comprises an electrode which is inactive in oxidation of CO and an electrode which is active in the oxidation of the CO with an oxygen ion conductive solid electrolyte inbetween. The solid electrolyte-shaped CO sensor is constituted of a solid electrolyte material obtained by adding a Fe group element to LSGM8282 (La.Sr.Ga.Mg.O) as the oxygen ion conductive solid electrolyte.

Description

  The present invention is a solid electrolyte type CO sensor for directly measuring the concentration of CO (carbon monoxide) in combustion exhaust gas and other gases, and is built in or near a gas instrument to improve the performance of the gas instrument The present invention relates to a solid electrolyte CO sensor that can improve the safety of the atmosphere.

  Conventionally, when a combustor such as a gas appliance causes incomplete combustion, CO is generated, the temperature is lowered, the size of the flame is changed, and the oxygen concentration is lowered. Therefore, paying attention to these phenomena, a method for detecting incomplete combustion using a CO sensor, a thermocouple, a frame rod, an oxygen sensor, or the like is known. Among them, detection of incomplete combustion by a thermocouple, oxygen sensor, and frame rod is effective for a combustor having a small fluctuation in combustion load such as a small water heater.

  However, for a combustor with a large load fluctuation such as a large water heater, the shape of the flame and the oxygen concentration in the flame change greatly with the load fluctuation. For this reason, there is a possibility that incomplete combustion may be erroneously recognized by the method using a sensor that detects a change in the shape of the flame and the oxygen concentration in the flame. On the other hand, the method of directly detecting CO using a CO sensor does not have such a problem.

  By the way, as a CO sensor for measuring CO which is a combustible gas in exhaust gas from a combustor, a semiconductor type, a catalytic combustion type, or a solid electrolyte type is known. Among these, the solid electrolyte CO sensor does not generate an electromotive force because there is no difference between the adsorbed substances on the electrodes provided on both sides of the solid electrolyte when there is no CO. This utilizes the principle that an electromotive force is generated by causing an electrochemical reaction between CO and oxygen on the electrode on the side where (= CO oxidation catalyst) is present.

When this CO sensor is installed in the exhaust gas discharged from the combustor, even if the combustion load fluctuates, electromotive force is generated because there is no difference in the adsorbed material of both electrodes unless CO, which is a flammable gas, is generated. Absent.
In contrast, when CO gas, which is a flammable gas, is generated in the exhaust gas due to incomplete combustion, there is no difference in the adsorbed material of both electrodes, but the reaction of CO and oxygen on the electrode on the side where the oxidation catalyst is present. Therefore, an electromotive force, that is, a sensor output is generated. Therefore, it can be used as an incomplete combustion detection sensor for exhaust gas.

FIG. 12 is a diagram for explaining a combustible gas detecting element such as a solid electrolyte type CO (that is, a CO sensor when the combustible gas is CO) (Japanese Patent Publication No. 58-4985). The oxygen ion conductive solid electrolyte 11 is made of ZrO ₂ —Y ₂ O ₃ , and platinum electrodes 12 and 13 are deposited on both upper and lower surfaces thereof, and one of the electrodes 12 is a catalyst for oxidizing a combustible gas. It is covered with a certain platinum alumina catalyst 14. This element is kept at 200 to 700 ° C. by the heater 15, and air containing combustible gas flows in the direction of the arrow 17, and the electromotive force generated between the electrodes 12 and 13 is indicated on the indicator 16.

Japanese Patent Publication No.58-4985

  When the element is brought into contact with air containing a small amount of combustible gas, the electrode 13 is in direct contact with air containing the combustible gas. Since one electrode 12 is covered with the oxidation catalyst 14, the combustible gas contained in the air is oxidized by the oxidation catalyst 14. For this reason, combustible gas contained in the air does not reach the electrode 12, and as a result, an electromotive force is generated between the electrodes 12 and 13.

  That is, as shown in FIG. 12B, for example, flammable gas CO is better adsorbed to the three-phase interface 23 composed of the solid electrolyte 21, the electrode 22, and the gas than nitrogen and oxygen. Therefore, the electrochemical reaction represented by the following formula (1) occurs simultaneously with the inhibition of oxygen adsorption. On the other hand, in the oxidation catalyst 25 covering the electrode 24, a small amount of CO contained in the air is oxidized by the oxidation catalyst 25 and therefore does not reach the electrode 24, and the three-phase interface 26 contains a combustible gas. A gas having almost an air composition arrives and only the reaction shown in the reaction formula (2) proceeds.

  An object of the present invention is to provide a solid electrolyte type CO sensor for directly measuring the CO (carbon monoxide) concentration in combustion exhaust gas and other gases. An object of the present invention is to provide a solid electrolyte type CO sensor capable of improving performance and improving safety of a gas atmosphere.

The present invention (1) is a CO sensor comprising an electrode inert to CO oxidation and an electrode active to CO oxidation across an oxygen ion conductive solid electrolyte, wherein the oxygen ion conductive solid electrolyte is LSGM 8282 ( la _{0. 8} Sr _0. a ₂ Ga _{0. 8} Mg _0. solid oxide CO sensors, wherein ₂ O ₃₎ of a material consisting be configured.

The present invention (2) is a CO sensor comprising an electrode inactive to CO oxidation and an electrode active in CO oxidation across an oxygen ion conductive solid electrolyte, wherein the oxygen ion conductive solid electrolyte is LSGM 8282 ( la _{0. 8} Sr _0. a ₂ Ga _{0. 8} Mg _0. solid oxide CO sensors, characterized in that formed by a material obtained by adding Fe group element ₂ O _3).

The present invention (3) is added to the solid oxide CO sensor according to claim 2, wherein an oxygen ion conductive solid electrolyte _{LSGM8282 (La 0. 8 Sr 0} . 2 Ga 0. 8 Mg 0. 2 O 3) The solid electrolyte type CO sensor is characterized in that the Fe group element is Fe.

The present invention (4) is a CO sensor comprising an electrode inert to CO oxidation and an electrode active to CO oxidation across an oxygen ion conductive solid electrolyte, wherein the oxygen ion conductive solid electrolyte has the chemical formula: la _0. a _{8 Sr 0. 2 Ga 1-} X Fe X O 3 (x = 0.1~0.3) solid oxide CO sensors, characterized in that formed by a material represented by.

The present invention (5) is a CO sensor comprising an electrode inert to CO oxidation and an electrode active to CO oxidation across an oxygen ion conductive solid electrolyte, wherein the oxygen ion conductive solid electrolyte is LSGFe8282 ( It is a solid electrolyte type CO sensor characterized by comprising a material made of La _0.8 Sr _0.2 Ga _0.8 Fe _0.2 O ₃ ).

The present invention (6) is a CO sensor comprising an electrode inert to CO oxidation and an electrode active to CO oxidation across an oxygen ion conductive solid electrolyte, wherein the oxygen ion conductive solid electrolyte is LSGFe 8273 ( _{la 0.8 Sr 0.2 Ga 0.7 Fe 0.3} O 3) of a material consisting be configured is a solid electrolyte CO sensor according to claim.

The present invention (7) is a CO sensor comprising an electrode inert to CO oxidation and an electrode active to CO oxidation across an oxygen ion conductive solid electrolyte, wherein the oxygen ion conductive solid electrolyte is LSGFe828515 ( It is a solid electrolyte type CO sensor characterized by comprising a material made of La _0.8 Sr _0.2 Ga _0.85 Fe _0.15 O ₃ ).

The present invention (8) is a CO sensor comprising an electrode inert to CO oxidation and an electrode active to CO oxidation with an oxygen ion conductive solid electrolyte interposed therebetween, wherein the oxygen ion conductive solid electrolyte is LSGFe 8291 ( _{la 0.8 Sr 0.2 Ga 0.9 Fe 0.1} O 3) of a material consisting be configured is a solid electrolyte CO sensor according to claim.

  The present invention (9) is characterized in that, in the solid electrolyte CO sensor according to any one of the present invention (1) to (7), the electrode inactive to the oxidation of CO is made of a material composed of ITO + Au 10 wt%. This is a solid electrolyte type CO sensor.

  ITO + Au 10 wt% is a preferred example, but the constituent material of the “electrode inactive to CO oxidation” in the solid electrolyte CO sensor according to the present invention is not limited thereto.

The present invention (10), in either solid electrolyte CO sensor of the present invention (1) to (8), active electrodes for the oxidation of the CO is _{RuO 2 + LSC64 (La 0.} 6 Sr 0. 4 Co 0 A solid electrolyte type CO sensor characterized in that it is made of a material comprising ₂ O ₃ ).

The present invention (11), in either solid electrolyte CO sensor of the present invention (1) to (9), wherein the active electrode for the oxidation of CO is _{"RuO 2 + LSC64 (La 0.} 6 Sr 0. 4 Co _{0. 2} O ₃₎ "to a solid oxide CO sensors, characterized in that formed by a material obtained by adding Pt and / or Pd.

They _{"RuO 2 + LSC64 (La 0.} 6 Sr 0. 4 Co 0. 2 O 3) composed of material from the" and _{"RuO 2 + LSC64 (La 0.} 6 Sr 0. 4 Co 0. 2 O 3) to Pt and / “A material added with Pd” is a preferred example, but the constituent material of “an electrode active in oxidation of CO” in the solid electrolyte CO sensor according to the present invention is not limited to these materials.

  According to the solid electrolyte type CO sensor of the present invention, a solid electrolyte type CO sensor that directly measures the CO concentration in combustion exhaust gas and other gases to improve the performance of gas equipment and the safety of gas atmosphere is obtained. According to the solid electrolyte CO sensor of the present invention, the performance of the gas equipment is improved and the safety of the gas atmosphere is improved by directly measuring the concentration of CO in the combustion exhaust gas and other gases. Can be achieved.

FIG. 1 corresponds to Table 1 and shows a sample in which Cu, Ru, Ni, Co, or Fe is added to the constituent material LSGM8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ) of the oxygen ion conductive film, respectively. It is the figure which made the graph the change of the measured current value by the CO density | concentration in test gas. FIG. 2 is a diagram showing the results of <measurement of CO sensitivity depending on the CO concentration in the test gas>, and is a graph showing changes in measured current values corresponding to the respective CO concentrations in the test gas. FIG. 3 shows (2) CO sensor produced using a sample of LSGMFe828515 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.05 Fe _0.15 O ₃ ): Measurement of CO sensitivity depending on CO concentration in test gas: 300 to 500 ° C. It is a figure which shows the result of>, and is the figure which graphed the change of the measured current value corresponding to each CO density | concentration in test gas. FIG. 4 shows ((3) CO sensor manufactured using a sample of LSGFe8282 (La _0.8 Sr _0.2 Ga _0.8 Fe _0.2 O ₃ ): measurement of CO sensitivity depending on CO concentration in test gas: 300 to 500 ° C.). It is a figure which shows a result, and is the figure which graphed the change of the measured current value corresponding to each CO density | concentration in test gas. Figure 5 is <(Part _{4) LSGM8282 (La 0.8 Sr 0.2} Ga 0.8 Mg 0.2 O 3) CO sensitivity by adding content whether the Fe to: 400 ° C.> is a diagram showing the test results. FIG. 6 is a diagram showing the relationship between measured temperature and CO sensitivity for a CO sensor manufactured using four types of LSGFe having different composition ratios of Ga and Fe measured in the above test. FIG. 7 shows a CO sensor manufactured using La _0.8 Sr _0.2 Ga _1-X Fe _X O ₃ (x = 0.1, 0.15, _0.2, 0.3) at a temperature of 400 ° C. It is the figure which showed the sensitivity. FIG. 8 shows a CO sensor manufactured using “LSC64 + RuO ₂ ” as an electrode active for CO and an electrode added with Pd, Pt, and Ag as additive metals, or a combination thereof in a test gas. It is the figure which showed the relationship between CO density | concentration and CO sensitivity. FIG. 9 is a diagram showing the relationship between the temperature of 400 to 500 ° C. and the CO sensitivity of a CO sensor manufactured using electrodes in which Pt, Pd, and Ni are added to “LSC64 + RuO ₂ ” as an electrode active for CO. is there. FIG. 10 shows a CO sensor manufactured using “LSC64 + RuO ₂ ” without adding Pt as an active electrode to CO at temperatures of 500 ° C. and 400 ° C., and an electrode obtained by adding Pt to “LSC 64 + RuO ₂ ”. It is the figure which showed the relationship of CO sensitivity about the CO sensor produced in this way. FIG. 11 shows the response characteristics of CO sensors made of LSGFe828515 (La _0.8 Sr _0.2 Ga _0.85 Fe _0.15 O ₃ ) as an electrolyte at 400 ° C. with respect to CO, H ₂ , CH ₄ , and CO ₂ . It is the figure which graphed the change of the measured current value corresponding to CO concentration. FIG. 12 is a diagram for explaining a combustible gas detection element such as CO of solid electrolyte type (that is, a CO sensor when the combustible gas is CO) (Japanese Patent Publication No. 58-4985). FIG. 13 shows the principle of CO sensitivity measurement for the sensor element (test CO sensor) used up to the present invention, and a method of detecting a change in hybrid potential or electrode overvoltage as a change in current value, etc. FIG. FIG. 14 is a diagram for explaining a mode in which a measuring instrument is arranged in the power supply for the test CO sensor.

<Search for CO active electrode, oxygen ion conducting film, and CO inactive electrode capable of detecting trace amounts of CO>
The solid-electrolyte type combustible gas detection element such as CO described in Patent Document 1 is an example, but the present inventors have a CO active electrode capable of detecting a minute amount of CO in a gas such as combustion exhaust gas, oxygen ion conduction In pursuit of a conductive solid electrolyte membrane and a CO inert electrode, a material having a good characteristic, that is, a material having a good characteristic was found. Hereinafter, the process will be described in order including the progress.

(1) Combination of CO active electrode, oxygen ion conductive film, and CO inactive electrode, which are the basis of the study As shown in FIG. 13, the solid electrolyte type CO sensor according to the present invention is an oxygen ion conductive solid electrolyte film. “Electrode active for CO oxidation (= CO active electrode)” and “electrode inactive for CO oxidation (= CO inactive electrode)” are provided on both surfaces, respectively. Then, oxygen ions (O ²⁻ ) are pumped by an oxygen ion conductive solid electrolyte membrane, that is, an oxygen ion conductor, and CO is oxidized by the pumped oxygen ions (O ²⁻ ). Alternatively, the difference between the electrode overvoltages) is output as a change in current value and a change in voltage value, and is detected.

  FIG. 14 is a diagram showing a mode in which a measuring instrument is arranged in a power source for a test CO sensor or the like. 14A shows a mode in which a measuring instrument (voltmeter or ammeter) is arranged in the power source, and FIG. 14B shows a mode in which the ammeter A is arranged in the power source among the measuring instruments shown in FIG. 14A. It shows.

LSGM 9182 (La _0.9 Sr _0.1 Ga _0.8 Mg _0.2 O ₃ ) which is a high oxygen ion conductor was used as a solid electrolyte which was an oxygen ion conductor, gold was used as a CO inactive electrode, and RuO ₂ was used as a CO active electrode. However, a CO inert electrode is obtained by adding an ITO-based oxide to gold [In ₂ O ₃ (stannic oxide) 95 mol%, SnO ₂ (stannic oxide) 5 mol% and Au (gold) 10 wt%. added], those in the CO active electrode with the addition of LSC based oxide RuO _{2 [LSC64 (= La 0.6 Sr 0.4 Co} 0.2 O 3) to that added RuO ₂ (ruthenium dioxide)] has been improved CO sensitivity .

Here, with respect to the oxygen ion conductive film, the CO sensitivity of LSGM8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ) was improved compared to LSGM 9182 (La _0.9 Sr _0.1 Ga _0.8 Mg _0.2 O ₃ ). Therefore, the CO inactive electrode is ITO955 + Au 10 wt%, the CO active electrode is LSC64 + RuO ₂ , and the oxygen ion conductive film is based on the composition of LSGM8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ), and more sensitive oxygen ions We searched for conductive films.

(2) Study on metal addition to LSGM 8282 LSGM 8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ) and the LSGM 8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ) with Fe, Co, Ni, Ru, Cu A sample to which was added was prepared, and the CO sensitivity was tested and investigated. As a result, the addition of Fe was most effective. Table 1 shows the results.

  Table 1 shows the results. Table 1 shows the measured values at a temperature of 400 ° C. In Table 1, the constituent materials of the CO inert electrode, the oxygen ion conductive membrane, and the CO active electrode are as follows.

As the CO inert electrode, “ITO955 + Ag 10 wt% [In ₂ O ₃ (second indium oxide) 95 mol%, SnO ₂ (stannic oxide) 5 mol%, Au (gold) added 10 wt%]] was used. The inert electrode is an electrode that does not have a function (catalytic action) of reacting with CO in the gas and changing to CO ₂ .

The constituent materials of the oxygen ion conductive film are “LSGM 8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ )”, “LSGMCu 828155 (= La _0.8 Sr _0.2 Ga _0.8 Mg _0.15 Cu _0.05 O ₃ )”, “LSGMru 828155 (= La _0.8 Sr _0.2). Ga _0.8 Mg _0.15 Ru _0.05 O ₃ ) ”,“ LSGMCo 828155 (= La _0.8 Sr _0.2 Ga _0.8 Mg _0.15 Co _0.05 O ₃ ) ”,“ LSGMNi 828155 (= La _0.8 Sr _0.2 Ga _0.8 Mg _0.15 Ni _0.05 O ₃ ) ”,“ _{LSGMFe828155 (= La 0.8 Sr 0.2 Ga} 0.8 Mg 0.15 Fe 0.05 O 3) "is.

In these formulas, the suffix attached to each element is the composition ratio (molar ratio). For example, when La _0.8 Sr _0.2 Ga _0.8 Mg _0.15 Fe _0.05 O ₃ is taken as an example, the molar ratio of La: Sr: Ga: Mg: Fe: O is 0.8: 0.2: 0.8: 0.15. : 0.05: 3, which is abbreviated as “LSGMFe828155”.

The CO active electrode is RuO ₂ -LSC 64, that is, [LSC 64 (= La _0.6 Sr _0.4 Co _0.2 O ₃ ) with RuO ₂ added]. The CO active electrode is an electrode having a function (catalysis) that reacts with CO in the gas and changes to CO ₂ .

In Table 1, as shown in (1), “ITO955 + Au 10 wt% [In ₂ O ₃ (second indium oxide) 95 mol%, SnO ₂ (stannic oxide) 5 mol%, Au (gold) 10 wt% as the CO inactive electrode] Is added, LSGM8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ) as a high oxygen ion conductor is used as a solid electrolyte that is an oxygen ion conductor, and “RuO ₂ + LSC64” system as a CO active electrode A CO sensor manufactured using an oxide added has CO sensitivity = 90 μA (μA = current value per unit concentration change), and shows a good current value.

Similarly, for the CO inactive electrode and the CO active electrode, LSGM8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ), which is a high oxygen ion conductor, is used as a solid electrolyte that is an oxygen ion conductor. , Ni, Co, and Fe were added to produce a CO sensor, and a CO sensitivity test was performed. The following (2) to (6) are the results.

<(2) CO sensor using LSGMCu828155>
High oxygen ion conductor: LSGM8282 in CO sensitivity = 0 .mu.A of CO sensor using LSGMCu828155 which Cu is added to _{(La 0.8 Sr 0.2 Ga 0.8 Mg} 0.2 O 3) (La 0.8 Sr 0.2 Ga 0.8 Mg 0.15 Cu 0.05 O 3) Yes, indicating that it is not suitable as a CO sensor.

<(3) CO sensor using LSGMRu 828155>
High oxygen ion conductor: LSGM8282 produced using _{(La 0.8 Sr 0.2 Ga 0.8 Mg} 0.2 O 3) in the addition of _{Ru LSGMRu828155 (La 0.8 Sr 0.2 Ga} 0.8 Mg 0.15 Ru 0.05 O 3), implementing the CO sensitivity test did. The CO sensitivity of the CO sensor is 17 μA, which is lower than the sensitivity of the CO sensor using LSGM8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ).

<(4) CO sensor using LSGMNi828185>
High oxygen ion conductor: LSGM8282 CO sensitivity of the CO sensor using _{(La 0.8 Sr 0.2 Ga 0.8 Mg} 0.2 O 3) to the addition of _{Ni LSGMNi828155 (La 0.8 Sr 0.2 Ga} 0.8 Mg 0.15 Ni 0.05 O 3) is 88μA In other words, the sensitivity is almost the same as that of the CO sensor using LSGM8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ).

<(5) CO sensor using LSGMCo828155>
High oxygen ion conductor: LSGM8282 CO sensitivity of the CO sensor using _{(La 0.8 Sr 0.2 Ga 0.8 Mg} 0.2 O 3) to the addition of _{Co LSGMCo828155 (La 0.8 Sr 0.2 Ga} 0.8 Mg 0.15 Co 0.05 O 3) is 189μA Yes, the sensitivity is twice that of the CO sensor using LSGM8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ).

<(6) CO sensor using LSGMFe828155>
The CO sensitivity of the CO sensor using LSGMFe828155 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.15 Fe _0.05 O ₃ ) obtained by adding Fe to the high oxygen ion conductor: LSGM 8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ) is 672 μA. In addition, the sensitivity is remarkably superior to the sensitivity of the CO sensor using LSGM8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ).

FIG. 1 corresponds to Table 1 and shows a sample in which Cu, Ru, Ni, Co, or Fe is added to the constituent material LSGM8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ) of the oxygen ion conductive film, respectively. It is the figure which made the graph the change of the measured current value by the CO density | concentration in test gas. In FIG. 1, the horizontal axis represents the CO concentration (ppm) in the test gas, and the vertical axis represents the current value (μA) measured for each sample.
Here, in FIG. 1, the horizontal axis indicates a logarithmic scale, and the description “decade” as a unit of current value means “per unit concentration”. This also applies to the description in other drawings.

  As shown in FIG. 1, the current value of the sample obtained by adding Fe to the constituent material LSGM8282 greatly increases as the CO concentration in the test gas increases. This means that the current value is sensitively measured as the CO concentration in the test gas increases. That is, the sample in which Fe is added to the constituent material LSGM8282 exhibits particularly good measurement sensitivity corresponding to the CO concentration in the test gas, which means that the CO concentration in the test gas can be measured more accurately.

<Measurement of CO sensitivity depending on CO concentration in test gas>
For a CO sensor manufactured using a sample of LSGMFe828155 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.15 Fe _0.05 O ₃ ), the change in the measured current value depending on the CO concentration in the test gas was measured. That is, a CO sensor manufactured using a sample of LSGMFe828155 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.15 Fe _0.05 O ₃ ), which has the highest CO sensitivity in Table 1, with respect to the constituent material of the oxygen ion conductive membrane, is being tested. The CO concentration in the test gas was changed to 50 ppm, 100 ppm, 500 ppm, and 1030 ppm every predetermined time, the test gas atmosphere at each CO concentration was maintained for a predetermined time, and the change in the current value was measured. The test gas atmosphere temperature was 400 ° C.

FIG. 2 is a graph showing changes in the measured current value corresponding to each CO concentration in the test gas. Each test CO sensor is placed in an atmosphere of each test gas at 400 ° C., and the amount of current corresponding to the CO concentration in the atmosphere is measured. As shown in FIG. 2, the CO sensor produced using a sample of LSGMFe 828155 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.15 Fe _0.05 O ₃ ) has a current value measured corresponding to the stepwise CO concentration in the test gas. It becomes larger in steps, showing good CO measurement sensitivity, and showing that the CO concentration in the test gas can be measured more accurately according to the current value.

<Optimization of Fe addition to LSGM>
The optimization of the addition amount of Fe to LSGM was examined. Regarding the composition of the oxygen ion conductive membrane, a CO sensor was fabricated using a sample in which Mg was reduced and the amount of Fe added was increased, and the CO sensitivity was investigated. Table 2 shows the results.

From Table 2, the following facts are clear. (A) 0.05 mol of Mg in LSGM 8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ) was replaced with Fe (that is, 0.05 mol of Mg was reduced and 0.05 mol of Fe was added) The current value of LSGMFe 828155 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.15 Fe _0.05 O ₃ ) (proportional to CO sensitivity) is 2 μA at a temperature of 300 ° C. and 18 μA at a temperature of 400 ° C., but is improved to 176 μA at a temperature of 500 ° C. ing.

(B) 0.1 mol of Mg in LSGM 8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ) was replaced with Fe (that is, 0.1 mol of 0.2 mol of Mg was replaced with 0.1 mol of Fe). The current value of LSGMFe82811 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.1 Fe _0.1 O ₃ ) added at 1 mol was 47 μA at a temperature of 300 ° C. and 90 μA at a temperature of 400 ° C., but improved to 183 μA at a temperature of 500 ° C. .

(C) 0.15 mol of Mg in LSGM 8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ) was replaced with Fe (that is, Fe was changed to 0.15 mol out of 0.2 mol of Mg and Fe was changed to 0 The current value of LSGMFe828515 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.05 Fe _0.15 O ₃ ) added at .15 mol is improved to 136 μA at a temperature of 300 ° C., 138 μA at a temperature of 400 ° C., and 658 μA at a temperature of 500 ° C.

(D) 0.2 mol of Mg in LSGM8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ) was replaced with Fe (that is, 0.2 mol of Fe was added instead of all 0.2 mol of Mg) The current value of LSGFe 8282 (La _0.8 Sr _0.2 Ga _0.8 Fe _0.2 O ₃ ) has been improved to 556 μA at a temperature of 300 ° C., 2342 μA at a temperature of 400 ° C., and 4681 μA at a temperature of 500 ° C.

  From these results (a) to (d), the value of the flowing current increases as the amount of Fe added increases, and the CO sensitivity improves. Among them, (d), that is, the one in which Mg is completely substituted with Fe has the highest CO sensitivity.

<(Part 1) LSGMFe828515 CO sensor sample was prepared using the _{(La 0.8 Sr 0.2 Ga 0.8 Mg} 0.05 Fe 0.15 O 3): Measurement of the CO sensitivity by CO concentration whether in the test gas: 300 to 500 ° C.>
With respect to a CO sensor manufactured using a sample of LSGMFe828515 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.05 Fe _0.15 O ₃ ), the change in the measured current value depending on the CO concentration in the test gas was measured. That is, a CO sensor manufactured using the materials shown in Tables (10) to (12) for the CO inactive electrode material, the constituent material of the oxygen ion conductive membrane, and the CO active electrode material were used, and the temperature was 300 to 500. At 0 ° C., during the test, the CO concentration in the test gas was changed to 50 ppm, 100 ppm, 500 ppm, and 1030 ppm every predetermined time, the test gas atmosphere of each CO concentration was maintained for a predetermined time, and the CO concentration was measured.

  FIG. 3 is a graph showing the change in the measured current value corresponding to each CO concentration in the test gas. Each test CO sensor is placed in an atmosphere of a test gas at each temperature of 300 ° C., 400 ° C., and 500 ° C., and the amount of current corresponding to the CO concentration in the atmosphere is measured.

As shown in FIG. 3, the CO sensor produced using the sample of LSGMFe828515 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.05 Fe _0.15 O ₃ ) shows a good current value at each temperature of 300 ° C., 400 ° C., and 500 ° C. In particular, a very good current value is shown at a temperature of 500 ° C., and the current value increases as the CO concentration in the test gas increases.

<(Part 2) LSGFe8282 CO sensor sample was prepared using the _{(La 0.8 Sr 0.2 Ga 0.8 Fe} 0.2 O 3): Measurement of the CO sensitivity by CO concentration whether in the test gas: 300 to 500 ° C.>
With respect to a CO sensor manufactured using a sample of LSGFe8282 (La _0.8 Sr _0.2 Ga _0.8 Fe _0.2 O ₃ ), the change in the measured current value depending on the CO concentration in the test gas was measured. That is, a CO sensor produced using the materials shown in (13) to (15) in Table 2 with respect to the CO inactive electrode material, the constituent material of the oxygen ion conductive membrane, and the CO active electrode material, and the temperature was 300 to 500. At ℃, during the test, the CO concentration in the test gas was changed to 10 ³ ppm, 10 ^3.3 ppm, 10 ^3.46 ppm, 10 ^3.6 ppm, 10 ^3.6 ppm, 10 ^3.7 ppm every predetermined time, and the test gas atmosphere at each CO concentration was maintained for a predetermined time. Then, the current value was measured.

  FIG. 4 is a graph showing changes in the measured current value corresponding to each CO concentration in the test gas. Each test CO sensor is placed in an atmosphere of a test gas at each temperature of 300 ° C., 400 ° C., and 500 ° C., and the amount of current corresponding to the CO concentration in the atmosphere is measured.

As shown in FIG. 4, the CO sensor produced using a sample of LSGFe8282 (La _0.8 Sr _0.2 Ga _0.8 Fe _0.2 O ₃ ) exhibits a good current value at a temperature of 300 to 500 ° C., particularly 400 to 500 ° C. It shows a very good current value at temperature, and the current value increases with an increase in the CO concentration in the test gas.

<(Part _{3) LSGM8282 (La 0.8 Sr 0.2} Ga 0.8 Mg 0.2 O 3) CO sensitivity by adding content whether the Fe to: 400 ° C.>
The CO sensitivity depending on the amount of Fe added to LSGM 8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ) was tested. FIG. 5 shows the test results at a temperature of 400 ° C.

Looking at the CO sensitivity, as shown in FIG. 5, LSGMFe828155 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.15 Fe _0.05 O ₃ ) has almost no CO sensitivity, and LSGMFe82811 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.1 Fe _0.1 O ₃ ) The CO sensitivity is 100 μA. In contrast, the CO sensitivity of LSGMFe828515 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.05 Fe _0.15 O ₃ ) is 200 μA, and the CO sensitivity of LSGFe 8282 (La _0.8 Sr _0.2 Ga _0.8 Fe _0.2 O ₃ ) is 1750 μA.

Thus, a CO sensor having excellent CO sensitivity can be configured by replacing the entire amount of Mg in LSGM8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ) with Fe.

From the examination results in the above (Part 1) to (Part 3), a composite oxide obtained by substituting part or all of Mg in LSGM8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ) with Fe Is clearly useful as a solid electrolyte which is an oxygen ion conductor in a solid electrolyte CO sensor. Among them, in particular, a composite oxide obtained by substituting all of Mg with Fe has excellent characteristics in terms of CO sensitivity.

In the following (Part 4), the test results on the CO sensitivity depending on the CO concentration in the test gas are shown for the composite oxide in which all of Mg in LSGM8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ) is substituted with Fe. explain.

With respect to the CO sensor manufactured using the sample in which the proportion of Fe was changed with respect to the composition of the oxygen ion conductive film, the change in the measured current value depending on the CO concentration in the test gas was measured. Table 3 shows the results. As shown in Table _{3, <LSGFe8282 (La 0.8 Sr} 0.2 Ga 0.8 Fe 0.2 O 3)>, <LSGFe8273 (La 0.8 Sr 0.2 Ga 0.7 Fe 0.3 O 3)>, <LSGFe828515 (La 0.8 Sr 0.2 Ga 0.85 Fe 0.15 O 3 )> And <LSGFe 8291 (La _0.8 Sr _0.2 Ga _0.9 Fe _0.1 O ₃ )>, a CO sensor using any oxygen ion conductor can provide good CO sensitivity, but in Table 3, (7) to (9) As shown in the section, the improvement of the CO sensitivity was most observed when the added amount of Fe was 15% (mol%).

<(Part _{5) LSGFe8282 (La 0.8 Sr 0.2} Ga 0.8 Fe 0.2 O 3) or the like, the measurement of the CO sensitivity by CO concentration whether the test gas by CO sensor using a composite oxide was replaced with Fe all the Mg>

<Test related to measurement temperature and CO sensitivity for LSGFe having different composition ratios of Ga and Fe>
FIG. 6 is a diagram showing the relationship between measured temperature and CO sensitivity for a CO sensor manufactured using four types of LSGFe having different composition ratios of Ga and Fe measured in the above test. As shown in FIG. 6, LSGFe82815 (La _0.8 Sr _0.2 Ga _0.85 Fe _0.15 O ₃ ) shows the best CO sensitivity at 300 ° C., 400 ° C. and 500 ° C., and LSGFe 8282 (La _0.8 Sr _0.2 Ga _0.8 Fe _0.2 O ₃ ) Is based on that.

_{<La 0.8 Sr 0.2 Ga 1-} X Fe X O 3 (x = 0.1,0.15,0.2,0.3) CO sensor CO sensitivity produced using: 400 ° C.>
Tested CO sensitivity in CO sensors manufactured using the additive amount i.e. _{La 0.8 Sr 0.2 Ga 1-X} Fe X O 3 of Fe (x = 0.1,0.15,0.2,0.3) in LSGFe did. FIG. 7 shows the test results at a temperature of 400 ° C.

Looking at the CO sensitivity, as shown in FIG. 7, the CO sensitivity of the CO sensor using LSGFe 8291 (La _0.8 Sr _0.2 Ga _0.9 Fe _0.1 O ₃ ) is 6.9 mA, but LSGFe 828515 (La _0.8 Sr _0.2 Ga _0.85 Fe _0.15 The CO sensitivity of the CO sensor using O ₃ ) is 12.9 mA, and the CO sensitivity of the CO sensor using LSGFe 8273 (La _0.8 Sr _0.2 Ga _0.7 Fe _0.3 O ₃ ) is 7.0 mA.

Based on the facts of Fig. 7, indicating the oxygen-ion conductive solid electrolyte LSGFe the composition ranges for obtaining a CO sensitivity over longitudinal 7mA by the chemical formula _{La 0. 8 Sr 0. 2} Ga 1-X Fe X O 3 (X = 0.1 to 0.3).

Thus, among the LSGM8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ) and other complex oxides containing La, Sr, Ga, and Mg, a CO sensor with excellent CO sensitivity by replacing the entire amount of Mg with Fe Can be configured.

<Optimization of CO active electrode>
The CO sensor according to the present invention includes an electrode that is active in oxidizing CO and an electrode that is inactive in oxidizing CO with an oxygen ion conductive solid electrolyte interposed therebetween.
In the above, by using the ITO + Au10wt% as an inactive electrode for the oxidation of CO, it has been described embodiments using _{RuO 2 + LSC64 (La 0.} 6 Sr 0. 4 Co 0. 2 O 3) as an active electrode in CO However, in the following, the optimization of CO active electrodes will be described.

A sample in which a noble metal was added to a CO active electrode: LSC64 + RuO ₂ in an electrode inactive to CO: ITO + Au 10 wt%, an oxygen ion conductive solid electrolyte: LSGMFe828155 was prepared, and the CO sensitivity was investigated. In Table 4, a CO sensor configured by selecting various constituent materials of an electrode active in CO in a combination of an electrode inactive to CO: ITO + Au 10 wt%, an oxygen ion conductive solid electrolyte: LSGMFe828155 and an electrode active in CO The test results are shown.

As shown in Tables (1) to (3), the CO sensitivity of the CO sensor using LSC64 + RuO ₂ as an active electrode for CO is ₂ μA at 300 ° C., 18 μA at 400 ° C., and 176 μA at 500 ° C. On the other hand, as shown in Table 4 (4), the CO sensitivity of the CO sensor using LSC64 + RuO ₂ with Pd and Pt added as an active electrode for CO is 56 μA at 400 ° C., which is better. .

As shown in Table 5 (5) to (7), the CO sensitivity of the CO sensor using LSC64 + RuO ₂ with Pt added as an active electrode for CO is 5 μA at 300 ° C., 50 μA at 400 ° C., and 98 μA at 500 ° C. And better. As shown in Tables (8) to (10), the CO sensitivity of the CO sensor using LSC64 + RuO ₂ with Ag added as an active electrode for CO is ₂ μA at 300 ° C., 14 μA at 400 ° C., and 27 μA at 500 ° C. Therefore, it is understood that there is no improvement effect for the CO sensor using LSC64 + RuO ₂ .

RuO <for CO sensor using the electrode obtained by adding Pt to LSC64 + RuO ₂ as active electrode (Part 1) CO, measurement of CO sensitivity by CO concentration whether in the test gas> as active electrodes in (a) CO _{2 -Pt1wt% / LSC64 (La 0} . 6 Sr 0. 4 Co 0. 2 O 3) with respect to that used to <a (Part II) CO to active electrode as LSC64 + electrode with the addition of Ag to the RuO ₂ for CO sensor _{using, RuO 2 -Ag1wt% / LSC64 (} La 0 as the active electrode to the CO concentration in the measurement of the CO sensitivity> by whether (a) CO in the test _{gas. 6 Sr 0. 4 Co 0} . 2 O ₃ ) is different in that it is used.

The measured current value is as follows. (Part 1) For a CO sensor using an electrode in which Pt is added to LSC64 + RuO ₂ as an electrode active to CO (= electrode active to CO oxidation), CO depending on the CO concentration in the test gas. (A) CO sensor using “RuO ₂ —Pt ₁ wt%” as an active electrode for CO is larger, but “RuO ₂ —Ag ₁ wt%” is used (Part 2) As for a CO sensor using an electrode obtained by adding Ag to LSC64 + RuO ₂ as an active electrode, “RuO ₂ -Pt ₁ wt%” was also used for the CO sensor of “Measurement of CO sensitivity depending on CO concentration in test gas> Although it is lower than the CO sensor, it shows a good measured current value.

FIG. 8 shows the measurement using the above test, measured at 400 ° C., using “LSC64 + RuO ₂ ” as an active electrode for CO, and an electrode added with Pt, Pd, and Ag as additive metals. It is the figure which showed the relationship between CO density | concentration in test gas, and CO sensitivity about the produced CO sensor. This CO sensor uses LSGMFe828155 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.15 Fe _0.05 O ₃ ) as an oxygen ion conductive solid electrolyte, and ITO + Au 10 wt% as an electrode inert to CO (= an electrode inert to oxidation of CO). Is used.

As shown in FIG. 8, the CO sensor using “RuO ₂ — (Pt1 wt%) LSC64” shows a good measured current value at any CO concentration in the test gas. “RuO ₂ − (Pd 10 wt% + Pt 5 wt%) LSC64”, “RuO ₂ − (Ag 1 wt%) LSC64” and “RuO ₂ −LSC64” are almost the same in the low concentration CO region, but in the high concentration CO region The CO sensor using “RuO ₂ − (Pd 10 wt% + Pt 5 wt%) LSC64” shows a good measured current value.

FIG. 9 is a diagram showing the relationship between the temperature of 400 to 500 ° C. and the CO sensitivity of a CO sensor manufactured using electrodes in which Pt, Pd, and Ni are added to “LSC64 + RuO ₂ ” as an electrode active for CO. is there. Each of these CO sensors uses LSGM8282 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ) as an oxygen ion conductive solid electrolyte, and ITO + Au 10 wt% as an electrode inactive to CO (= an electrode inactive in oxidation of CO). I use it.

As shown in FIG. 9, at a temperature of 400 to 500 ° C., the CO sensitivity of the CO sensor manufactured using the electrode added with Pt is the largest, and the CO sensor manufactured using the electrode added with Pd and Ni is also added. This is an improvement over a CO sensor fabricated with no “RuO ₂ -LSC 64”.

FIG. 10 shows a CO sensor manufactured using “LSC64 + RuO ₂ ” without adding Pt as an active electrode to CO at temperatures of 500 ° C. and 400 ° C., and an electrode obtained by adding Pt to “LSC 64 + RuO ₂ ”. It is the figure which showed the relationship of CO sensitivity measured about the CO sensor produced in this way. Each CO sensor uses LSGMFe828155 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.15 Fe _0.05 O ₃ ) as an oxygen ion conductive solid electrolyte, and ITO + Au 10 wt% as an electrode inactive to CO (= an electrode inactive in oxidation of CO). Is used.

As shown in FIG. 10, at each temperature of 500 ° C. and 400 ° C., the CO sensor produced using the electrode added with Pt has a large CO sensitivity, and is an electrode made of “LSC64 + RuO ₂ ” as an electrode active in CO. The effect of addition of Pt to is observed.

<Response characteristics of CO sensor produced using LSGMFe828155 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.15 Fe _0.05 O ₃ ) as an electrolyte to CO, H ₂ , CH ₄ and CO ₂ at 400 ° C.>
Response characteristics with respect to CO, H ₂ , CH ₄ , and CO ₂ at 400 ° C. of a CO sensor manufactured using LSGMFe 828155 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.15 Fe _0.05 O ₃ ) as an electrolyte were measured. An electrode obtained by adding Pt to “LSC64 + RuO ₂ ” is used as an electrode active in CO, and ITO + Au 10 wt% is used as an electrode inactive to CO (= an electrode inactive in oxidation of CO).

FIG. 11 is a graph showing the change in the measured current value corresponding to each Gas concentration in the test gas. The test CO sensor is placed in each test gas atmosphere at 400 ° C., and the amount of current corresponding to the CO concentration in each atmosphere is measured. As shown in FIG. 11, the CO sensor produced using LSGMFe828155 (La _0.8 Sr _0.2 Ga _0.8 Mg _0.15 Fe _0.05 O ₃ ) as an electrolyte has high selective response to CO in the test gas. On the other hand, H ₂ , CH ₄ , and CO ₂ are only slightly responsive to H ₂ , and hardly respond to CH ₄ and CO ₂ . Thus, the solid electrolyte type CO sensor according to the present invention has high selectivity for CO in gas and has good CO measurement sensitivity.

11 Oxygen ion conductive solid electrolyte 12, 13 Platinum electrode 14 Platinum alumina catalyst 15 Heater 16 Electromotive force indicator 17 Direction of air containing flammable gas 21 Solid electrolyte 22, 24 Electrode 23 Three-phase interface 25 Oxidation covering electrode 24 catalyst

Claims (11)

A CO sensor consisting of active electrodes for the oxidation of across the oxygen ion conductive solid electrolyte for oxidation of CO inert electrode and CO, the oxygen ion conductive solid electrolyte _{LSGM8282 (La 0. 8 Sr 0} . _{2 Ga 0. 8 Mg 0.} 2 O 3) solid electrolyte CO sensor characterized by comprising formed of a composed material from the. A CO sensor consisting of active electrodes for the oxidation of across the oxygen ion conductive solid electrolyte for oxidation of CO inert electrode and CO, the oxygen ion conductive solid electrolyte _{LSGM8282 (La 0. 8 Sr 0} . _{2 Ga 0. 8 Mg 0.} 2 O 3) to be constructed of a material obtained by adding Fe group elements solid oxide CO sensors, characterized by comprising. In the solid electrolyte CO sensor according to claim 2, wherein the oxygen-ion conductive solid electrolyte in which _{LSGM8282 (La 0. 8 Sr 0} . 2 Ga 0. 8 Mg 0. 2 O 3) in the added Fe group element A solid electrolyte type CO sensor characterized by being Fe. A CO sensor consisting of active electrodes for the oxidation of across the oxygen ion conductive solid electrolyte for oxidation of CO inert electrode and CO, the oxygen ion conductive solid electrolyte formula:. La _{0 8} Sr _{0. 2 Ga 1-X Fe X O} 3 (x = 0.1~0.3) solid oxide CO sensors, characterized in that formed by a material represented by. A CO sensor comprising an electrode inactive for CO oxidation and an electrode active for CO oxidation across an oxygen ion conductive solid electrolyte, wherein the oxygen ion conductive solid electrolyte is LSGFe8282 (La _0.8 Sr _0.2 Ga _0.8 Fe A solid electrolyte type CO sensor characterized by comprising a material made of _0.2 O ₃ ). A CO sensor comprising an electrode inactive for CO oxidation and an electrode active for CO oxidation across an oxygen ion conductive solid electrolyte, wherein the oxygen ion conductive solid electrolyte is LSGFe8273 (La _0.8 Sr _0.2 Ga _0.7 Fe A solid electrolyte type CO sensor comprising a material comprising _0.3 O ₃ ). A CO sensor comprising an electrode inactive for CO oxidation and an electrode active for CO oxidation across an oxygen ion conductive solid electrolyte, wherein the oxygen ion conductive solid electrolyte is LSGFe828515 (La _0.8 Sr _0.2 Ga _0.85 Fe A solid electrolyte type CO sensor comprising a material comprising _0.15 O ₃ ). A CO sensor comprising an electrode inactive for CO oxidation and an electrode active for CO oxidation across an oxygen ion conductive solid electrolyte, wherein the oxygen ion conductive solid electrolyte is LSGFe 8291 (La _0.8 Sr _0.2 Ga _0.9 Fe A solid electrolyte type CO sensor comprising a material made of _0.1 O ₃ ).   8. The solid electrolyte type CO sensor according to claim 1, wherein the electrode inactive to the oxidation of CO is made of a material made of ITO + Au 10 wt%. . In the solid electrolyte CO sensor according to any one of claims 1-9, active electrodes for the oxidation of the CO consists of _{RuO 2 + LSC64 (La 0.} 6 Sr 0. 4 Co 0. 2 O 3) A solid electrolyte type CO sensor comprising a material. In the solid electrolyte CO sensor according to any one of claims 1 to 10, active electrodes for the oxidation of the CO is _{"RuO 2 + LSC64 (La 0.} 6 Sr 0. 4 Co 0. 2 O 3) " A solid electrolyte type CO sensor characterized by comprising a material obtained by adding Pt and / or Pd to.

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