KR20150124467A - Electrochemical sensor divice for measurement of carbon dioxide - Google Patents

Abstract

An object of the present invention is to provide an electrochemical carbon dioxide sensor element having a fast response characteristic and a long-term stability even in a humid environment, wherein a first protective film is formed on the side surface of the alkali metal ion conductor, a second protective film is formed on the upper surface, By fixing the reference voltage on the reference electrode side with the reference gas having the oxygen ion conductor and the oxygen partial pressure fixed by using the platinum (Pt) instead of the conventional unstable alkali metal electrode as the reference electrode by preventing the penetration of the moisture, , The response characteristics and the long-term stability of the conventional electrochemical carbon dioxide sensor device are significantly improved.

Description

ELECTROCHEMICAL SENSOR DIVICE FOR MEASUREMENT OF CARBON DIOXIDE BACKGROUND OF THE INVENTION [0001]

The present invention relates to an electrochemical carbon dioxide sensor element for sensing carbon dioxide.

Since carbon dioxide is a chemically stable gas in the atmosphere and is the main cause of global warming, it is necessary to monitor from the environmental point of view, and it is also necessary to control the concentration of carbon dioxide in the indoor space such as a building room and a greenhouse for gardening .

Non-dispersive infrared absorption (NDIR) is the most widely used method for measuring the concentration of carbon dioxide gas present in the atmosphere. This is because the principle of absorption of only infrared rays of a specific wavelength Is used to measure the degree of absorption of infrared rays to measure the concentration of carbon dioxide. Although this method has the advantage of being excellent in selectivity, quantitative and reproducibility, there is a disadvantage in that a sealed space is required for measurement and the volume is large and very heavy due to the physical size of the components. In addition, the driving unit and the measuring station are very expensive, and the configuration of the processing unit for control is also complicated, so that the overall cost of the measuring equipment is high and the system is not widely used. In particular, when the optical system is exposed to a harsh environment, the optical system is likely to be contaminated.

A comparatively inexpensive carbon dioxide sensing device compared to the NDIR type carbon dioxide sensing device is an electrochemical carbon dioxide sensor device using a solid electrolyte. Electrolytic carbon dioxide sensor devices using solid electrolytes have been developed since the research of carbon sensor devices of galvanic cell structure using potassium carbonate salt by Gauthier and Chamberland in the 1970s and have developed into NASICON and LISICON, , And beta-alumina (NBA) have been actively studied and developed.

The structure of a conventional electrochemical carbon dioxide sensor element is shown in Fig. Referring to FIG. 1, a conventional electrochemical carbon dioxide sensor device 100 has a structure in which a sensing electrode 120 and a reference electrode 130 are formed on an alkali metal ion conductor 110. Sodium ion (Na ^+), for the case of using jeondocheeul example, an alkali metal ion conductor (110) includes and uses a material such as a tank top cone, the sense electrode 120 is sodium carbonate are carbon dioxide gas and the thermodynamic equilibrium reaction that occurs in the air ( Na ₂ CO ₃₎ is used a material, such as, the reference electrode 130 as a metal oxide / oxide mixed-phase so as to secure a steady stream of activity (activity) of Na ₂ O at the interface between the sodium ion conductor 110 Is used. Since the electromotive force between the sensing electrode 120 and the reference electrode 130 changes according to the concentration of carbon dioxide gas in the atmosphere in the carbon dioxide sensor device 100 having such a structure, The concentration of carbon dioxide gas in the atmosphere can be calculated by measuring the electromotive force between the electrodes 130. [ Metal electrodes such as platinum (Pt) are formed on the sensing electrode 120 and the reference electrode 130 at the interface between the electrodes 120 and 130 and the ion conductor 110 or between the electrodes 120, and 130, and a heater for heating the sensor to a measurement temperature may be attached.

However, the conventional electrochemical carbon dioxide sensor device 100 having such a structure has an advantage that it is simple in structure and relatively inexpensive, but has a problem that the response speed is slow and the long-term stability is poor. Especially, since it is sensitive to humidity, when it is allowed to stand in a humid environment for a long time, the characteristic change is severe and it is not widely commercialized. FIG. 2 is a result of measuring the sensing characteristics of a conventional electrochemical carbon dioxide sensor element. As a result, it is a result of measuring characteristics after standing for a predetermined time in a dry environment and a high humidity environment. The concentration of carbon dioxide is 500 ppm, Lt; 0 > C. According to Fig. 2, although the response speed is somewhat slowed depending on the settling time even in a dry environment, the response speed is very slow in a humid environment and the measured electromotive force value is also different when the settling time is long .

FIG. 3 shows the time required for stabilizing the electromotive force (EMF) value in a humid environment. It can be seen that it takes a long time to stabilize the output value of the sensor element when used in a humid environment. The device is becoming a decisive cause of not being widely used.

Further, since the conventional electrochemical carbon dioxide sensor element can not be directly mounted on the circuit board, a separate plastic package having a circuit connecting pin is provided to connect the sensing electrode and the reference electrode to the circuit connecting pin, There is a problem in that it is not only inconvenient to be mounted on the vehicle but also has a large size.

Korean Patent Publication No. 2010-0012536

An object of the present invention is to provide an electrochemical carbon dioxide sensor element having a high response speed even in a humid environment, a small change in characteristics, and an excellent long-term stability.

Another object of the present invention is to provide an electrochemical carbon dioxide sensor element that is easy to mount directly on a circuit board and can be manufactured in a relatively small size.

According to an aspect of the present invention, there is provided an electrochemical carbon dioxide sensor element comprising: an alkali metal ion conductor; a first protective film having a first opening formed therein to surround the periphery of the alkali metal ion conductor; A second protective layer formed on the upper surface of the alkali metal ion conductor and having a second opening formed therein so as to form the sensing electrode, an oxygen ion conductor laminated on the lower surface of the alkali metal ion conductor, And a reference electrode formed on the lower surface of the oxygen ion conductor and exposed to the reference gas.

Here, a third protective layer may be further formed on the upper surface of the sensing electrode to suppress the penetration of foreign matter or moisture, and the heater may further include a heater for heating the sensor element to an operating temperature. At this time, the heater may be stacked on the lower portion of the oxygen ion conductor, and a third opening may be formed to expose the reference electrode to the outside air as a reference gas.

In addition, the sensing electrode may be composed of a mixture of an alkali metal carbonate and gold (Au).

At least one of the alkali metal ion conductor, the first protective film, the second protective film, and the oxygen ion conductor may have a thickness between 1 and 1000 micrometers.

The heater may include an upper heater substrate, a lower heater substrate, and a heater pattern interposed therebetween. The lower heater substrate may be electrically connected to the reference electrode, the sensing electrode, and the heater pattern, Terminals can be formed.

The electrochemical carbon dioxide sensor element according to the present invention is characterized in that a protective film is laminated on the side and top surface of an alkali metal ion conductor and an oxygen ion conductor is laminated on the bottom surface to prevent penetration of moisture, and platinum Pt is used instead of the unstable metal oxide reference electrode. By using the reference electrode, the response speed is quick, the change in characteristics is small, and the long-term stability is excellent even in a humid environment.

Further, by forming all of the electrode terminals on the lower surface of the sensor element, it is easy to mount directly on the circuit board, and there is an effect that it can be downsized.

FIG. 1 shows a structure of a conventional electrochemical carbon dioxide sensor element.
FIG. 2 is a result of measuring the sensing characteristics of a conventional electrochemical carbon dioxide sensor element.
FIG. 3 is a graph showing the time taken for the electromotive force (EMF) value of a conventional electrochemical carbon dioxide sensor element to stabilize in a humid environment.
4 is a schematic cross-sectional view of an electrochemical carbon dioxide sensor device according to the present invention.
5 is an exploded perspective view of the electrochemical carbon dioxide sensor element according to the present invention as viewed from the lower side.
6 is a conceptual diagram for explaining the measurement principle of the electrochemical carbon dioxide sensor element according to the present invention.
7 is a graph showing response characteristics of the electrochemical carbon dioxide sensor according to the present invention.
8 is a graph showing long-term stability characteristics of an electrochemical carbon dioxide sensor according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, but the present invention is not limited to or limited by the embodiments. In describing the various embodiments of the present invention, corresponding elements are denoted by the same names and the same reference numerals.

FIG. 4 is a cross-sectional view of an electrochemical carbon dioxide sensor device 400 according to the present invention, and FIG. 5 is an exploded perspective view of an electrochemical carbon dioxide sensor device 400 according to the present invention.

4 and 5, an electrochemical carbon dioxide sensor device 400 according to the present invention includes an alkali metal ion conductor 410 and a first A sensing electrode 420 formed on the upper surface of the alkali metal ion conductor 410, a sensing electrode 420 formed on the upper surface of the alkali metal ion conductor 410, A second protective film 460 having a second opening 461 formed therein so as to be formed with an oxygen ion conductor 430 stacked on the lower surface of the alkali metal ion conductor 410, And a reference electrode 440 formed on the bottom surface and exposed to the reference gas.

The alkali metal ion conductor 410 is formed of a solid electrolyte conductivity is large to alkali metal ions such as lithium ion, sodium ion, potassium ion, for example, NBA (Na ₂ O and 11Al ₂ O _3), tank top cone _{(NASICON: Na 1 + x Zr} 2 Si x P 3 - x O 12), beta-alumina (β-alumina: Na ₂ O and _{χAl 2 O 3), Na 2} CO 3, Li 2 CO 3, K 2 CO 3 , Li ₃ PO ₄ or LIPON (Lithium Phosphorous Oxy Nitride), LISICON (Li _{1 + y} Zr ₂ Si _y P _{3 - y} O ₁₂ ), or a mixture thereof.

The alkali metal ion conductor 410 is formed in the first opening 451 of the first protection film 450 and is surrounded by the first protection film 450. The first protection film 450 is formed of an alkali metal ion conductor 410 from moisture and can be formed of a dense ceramic material such as alumina (Al ₂ O ₃ ), zirconia (Zr ₂ O ₃ ), YSZ (Yttria stabilized zirconia) and the like. The size of the first opening 451 should be at least larger than the size of the alkali metal ion conductor 410, but it is preferable that the size of the first alkali metal ion conductor 410 is similar to that of the alkali metal ion conductor 410.

The sensing electrode 420 is formed on the upper surface of the alkali metal ion conductor 410. The sensing electrode 420 may be formed of a carbonate material having a thermodynamic equilibrium reaction with the carbon dioxide gas in the atmosphere depending on the material of the alkali metal ion conductor 410, Or a mixture of a carbonate and a noble metal such as platinum (Pt), gold (Au) and silver (Ag) may be used, and it is preferable to form the mixture of carbonate and gold (Au). Examples of the carbonate material include Na ₂ CO ₃ , BaCO ₃ , Li ₂ CO ₃ , SrCO ₃ , CaCO ₃ , Cs ₂ CO ₃ , MnCO ₃ , MgCO ₃ , K ₂ CO ₃ , Rb ₂ CO ₃ , CuCO ₃ , Can be used.

The second protective film 460 is laminated on the upper surfaces of the alkali metal ion conductor 410 and the first protective film 450. The second protective film 460 protects the upper surface of the alkali metal ion conductor 410 from moisture Role. When the second protective film 460 covers the upper surface of the alkali metal ion conductor 410 completely, a space for forming the sensing electrode 420 is not secured. Therefore, the sensing electrode 420 may be formed on the second protective film 460 The second opening 461 is provided. The second protective film 460 is preferably formed of a ceramic material such as alumina (Al ₂ O ₃ ).

The oxygen ion conductor 430 is laminated on the lower surface of the alkali metal ion conductor 410. The oxygen ion conductor 430 may include stabilized zirconia made by adding various materials to zirconia (ZrO ₂ ), for example, Yttria stabilized zirconia ), CSZ (calcium stabilized zirconia), MSZ (Magnesium stabilized zirconia) or CeO ₂ compound added with Gd ₂ O ₃ or the like can be used. The oxygen ion conductor 430 forms a heterojunction solid electrolyte structure together with the alkali metal ion conductor 410 to function as a sensing part for measuring the carbon dioxide concentration according to a principle to be described later, To prevent external moisture from penetrating.

A reference electrode 440 is formed on the lower surface of the oxygen ion conductor 430. The reference electrode 440 is preferably formed of a noble metal electrode such as platinum Pt. Since the reference carbon electrode sensor 400 according to the present invention exposes the reference electrode 440 to the reference gas with fixed oxygen partial pressure to fix the reference voltage on the reference electrode 440 side, Exposed to gas. Wherein the reference gas is preferably outside air.

At least the third protective layer 470 may be formed on the upper surface of the sensing electrode 420 to suppress foreign matter such as dust and moisture. In order to sense the external carbon dioxide gas concentration, the sensing electrode 420 may include carbon dioxide Since the gas may permeate, the third protective layer 470 may be formed of a porous material such as porous ceramic or porous graphite including a gas permeable polymer or a plurality of pores, and particularly preferably formed of porous alumina Do. The third protective layer 470 may be formed to cover the entire upper surface of the second protective layer 460 and the sensing electrode 420 as shown in FIGS.

Since the electrochemical carbon dioxide sensor element 400 operates at a high temperature of 500 ° C, it is preferable that the sensor element 400 is provided with a heater 480 for heating together. For example, the heater 480 may be stacked on the lower surface of the oxygen ion conductor 430 as shown in FIGS. 4 and 5. When external air is used as the reference gas, the reference electrode 440 May be formed in the third opening 485 to expose the first opening 482 to the outside air.

5, the heater 480 includes a heater substrate 481 and a lower heater substrate 482 stacked with a heater pattern 483 interposed therebetween. . The heater pattern 483 may be a platinum (Pt) pattern formed on the upper heater substrate 481 or the lower heater substrate 482 by a printing technique or the like and may be formed so as to surround the third opening 485 have.

It is preferable that all the electrode terminals are formed on one surface of the sensor element 400 so that the sensor element 400 according to the present invention can be directly mounted on the circuit board, . 5, a reference electrode terminal 491 electrically connected to the reference electrode 440, a sensing electrode 420, and a reference electrode 440 are formed on the lower surface of the lower heater substrate 482, which is the lowermost surface of the sensor element 400, A sensing electrode terminal 492 electrically connected thereto, and two or more heater terminals 493 electrically connected to the heater pattern 483 are formed. In this case, a reference electrode via hole 441 is formed in the upper heater substrate 481 and the lower heater substrate 482 to electrically connect the reference electrode 440 and the reference electrode terminal 491, The reference electrode 440 may be electrically connected to the reference electrode terminal 491 through the upper heater substrate 481 and the lower heater substrate 482 as shown in FIG. The sensing electrode 420 and the sensing electrode terminal 492 and the heater pattern 483 and the heater terminal 493 may be connected in the same manner. That is, the second protective film 460, the first protective film 450, A via hole 421 for a sensing electrode is formed on the ion conductor 430, the upper heater substrate 481 and the lower heater substrate 482 and the inside thereof is filled with a conductive material and a via hole for a heater terminal The inside of which is filled with a conductive material so as to be connected to the heater terminal 493. Of course, the connection with the terminals 491, 492, 493 is not limited to the above-described method. Instead of forming the via hole, another method such as forming a connection line with the terminal along the side surface of the sensor element 400 Of course.

The electrochemical carbon dioxide sensor device 400 according to the present invention may be configured such that an alkali metal ion conductor 410, an oxygen ion conductor 430, a first protective film 450, a second protective film 460, , Which can be manufactured simply by making each configuration into a thin ceramic tape form about 1 to 1000 micrometers thick and then using a tape casting technique. The sensing electrode 420 may be formed by a method such as printing through a second opening 461 formed in the second protective film 460 after the second protective film 460 and the alkali metal ion conductor 410 are bonded to each other And the reference electrode 440 may be formed by a method such as printing through the third opening 485 formed in the heater 480. [

The principle of measuring the carbon dioxide gas concentration by the electrochemical carbon dioxide sensor device 400 according to the present invention will be described with reference to FIG. 6, the heater 480 and the third protective film 470 are not shown.

6, since the sensing electrode 420 is reactive with the external carbon dioxide gas and the reference electrode 440 is exposed to the reference gas to which the oxygen partial pressure is fixed, the alkali metal ion conductor 410 is a sodium ion conductor Assuming that the sensing electrode 420 is a mixture of sodium carbonate (Na ₂ CO ₃ ) and gold (Au) and the reference electrode 440 is platinum (Pt), the structure of the sensor element 400 is as follows Can be expressed by equation (1). Here, Na ⁺ and O ^{2 -} refer to sodium ion conductors and oxygen ion conductors, respectively.

CO ₂ , O ₂ , Au, Na ₂ CO ₃ | Na ⁺ || O ^{2 -} | Pt, O ₂ ------------ (1)

In this case, the total reaction formula of the sensor is as shown in Formula (2), and the electromotive force E between the reference electrode 440 and the sensing electrode 420 is calculated by assuming that the oxygen partial pressure in the reference gas is 0.21 atm. ) Is expressed by the equation (3).

Na ₂ CO ₃ = Na ₂ O + CO _{2 -} (2)

E = E _o + 2.303 (RT / 2F) log [CO ₂ ] - (3)

In equation (3), R is the gas constant, F is the Faraday constant, and [CO ₂ ] is the carbon dioxide gas concentration. It can be seen that the concentration of carbon dioxide gas can be determined by measuring the electromotive force E between the reference electrode 440 and the sensing electrode 420.

The electrochemical carbon dioxide sensor device 400 according to the present invention has a structure in which the side surface and the upper surface of the alkali metal ion conductor 410 sensitive to moisture are formed as the first protective film 450 and the second protective film 460, And the third protective film 470 is formed on the sensing electrode 460, the change of the sensor characteristic due to humidity is suppressed as much as possible, and even when the device is left in a humid environment for a long time, The effect is maintained. In the case of a conventional electrochemical carbon dioxide sensor element, a mixture of Na ₂ Ti ₆ O ₁₃ and TiO ₂ is used as a reference electrode, or Na ₂ ZrO ₃ -ZrO ₂ , Na ₂ MoO ₄ -MoO ₃ , Na ₂ WO ₄ -WO ₃ , Na ₂ SnO ₃ -SnO ₂ , Na ₂ Ti ₆ O ₁₃ -Na ₂ Ti ₃ O ₇ , Na ₂ Si ₂ O ₅ -SiO ₂ , Na ₂ Si ₂ O ₅ -Na ₂ Si ₁ O ₃ , Na ₂ Since a mixture of Ge ₄ O ₃ -GeO ₂ , Li ₂ TiO ₃ -TiO ₂ , and LiCoO ₂ -Co ₃ O ₄ is used, it reacts with carbon dioxide or moisture in the air to form a compound such as NaHCO ₃ to exhibit unstable behavior However, the sensor element 400 according to the present invention uses a reference electrode 440 made of platinum (Pt) and a reference voltage on the side of the reference electrode 440 by means of the oxygen ion conductor 430 and the reference gas to which the oxygen partial pressure is fixed It is possible to fundamentally solve the problems of the conventional electrochemical carbon dioxide sensor element, thereby securing fast response characteristics and long-term stability.

Also, by forming the sensing electrodes 420 and the reference electrodes 440 and the terminals 491, 492, 493 connected to the heater pattern 483 at the lowermost end face of the sensor element 400, It is possible to directly mount the sensor element 400 on the substrate 400 and to dramatically reduce the size of the sensor element and to manufacture a plurality of layers in a stacked form so that a plurality of sensor elements are formed into a single wafer process, It is also possible to mass-produce by using the method of

Hereinafter, the characteristics of the electrochemical carbon dioxide sensor device 400 according to the present invention will be described with reference to the characteristics of the electrochemical carbon dioxide sensor device 100 of the related art.

< Example >

The sensor element 400 was fabricated as shown in FIGS. 4 and 5, and its characteristics were measured. Yttria stabilized zirconia (YSZ) was used as the alkali metal ion conductor 410 and oxygen ion conductor 430. The reference electrode 440 was formed of platinum Pt and the sensing electrode 420 was formed of sodium A mixture of carbonate (Na ₂ CO ₃ ) and gold (Au) was used. Alumina (Al ₂ O ₃ ) is used as the first protective film 450 and the second protective film 460 and porous alumina is used as the third protective film 470. The heater 480 is formed of the upper and lower alumina substrates 481, A platinum heater pattern 483 was printed and formed.

7 is a graph showing the response characteristics of the sensor element 400 having such a structure. In this case, the operating temperature of the sensor element 400 was 500 DEG C and the carbon dioxide gas concentration was 500 ppm. The characteristics of the conventional electrochemical carbon dioxide sensor element 100 (see FIG. 1), which were left for a day or two days in a relative humidity of 85% or 95% environment for comparison, are also shown.

It can be seen from FIG. 7 that the sensor element 400 according to the present invention exhibits a very fast response characteristic unlike the conventional sensor elements 100, and the sensor signal is stabilized at an accurate concentration of 500 ppm within about 10 minutes .

8 shows the long-term stability characteristics of the sensor device 400 according to the present invention. It shows that even when the sensor device 400 is kept in a humid environment for 180 days or longer, it exhibits excellent long-term stability characteristics without changing the sensor signal.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. Accordingly, the scope of protection of the present invention should be determined by the description of the claims and their equivalents.

100, 400: electrochemical carbon dioxide sensor element
110, 410: Alkali metal ion conductor
120, 420: sensing electrode
430: oxygen ion conductor
130, 440: reference electrode
450: first protective film, 451: first opening
460: second protective film, 461: second opening
470: Third protective film
480: Heater
481: upper heater substrate
482: Lower heater substrate
483: Heater pattern
485: third opening
491, 492, 493: terminal

Claims (7)

Alkali metal ion conductors;
A first protective layer having a first opening formed therein to surround the periphery of the alkali metal ion conductor;
A sensing electrode formed on an upper surface of the alkali metal ion conductor;
A second protective layer stacked on the alkali metal ion conductor and having a second opening formed therein so that the sensing electrode can be formed;
An oxygen ion conductor laminated on a lower surface of the alkali metal ion conductor;
A reference electrode formed on a bottom surface of the oxygen ion conductor and exposed to a reference gas;
Wherein the carbon dioxide sensor element is a carbon dioxide sensor element. The method according to claim 1,
Wherein a third protective film is formed on an upper surface of the sensing electrode to suppress penetration of foreign matter or moisture. The method according to claim 1,
Further comprising a heater for heating the sensor element to an operating temperature. The method of claim 3,
Wherein the heater is laminated on the lower portion of the oxygen ion conductor and a third opening is formed to expose the reference electrode to the outside air as a reference gas. The method according to claim 1,
Wherein the sensing electrode is composed of a mixture of an alkali metal carbonate and gold (Au). 6. The method according to any one of claims 1 to 5,
Wherein at least one of the alkali metal ion conductor, the first protective film, the second protective film, and the oxygen ion conductor has a thickness between 1 and 1000 micrometers. The method of claim 3,
The heater includes an upper heater substrate, a lower heater substrate, and a heater pattern interposed therebetween,
And a terminal electrically connected to the reference electrode, the sensing electrode, and the heater pattern are formed on the lower surface of the lower heater substrate.

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