JP7588580B2 - Oxygen sensor and micromechanical electrical device having the same - Google Patents

Description

The present invention relates to an oxygen sensor and a micromechanical electrical element having the same.

There are various known oxygen sensors that use oxide ion-permeable solid electrolytes. These types of oxygen sensors are broadly divided into electromotive force type and limiting current type. For example, Patent Document 1 describes an electromotive force type oxygen sensor that is composed of an electrochemical oxygen pump section, a sealed space, and an electrochemical sensor section. In this oxygen sensor, an external voltage is applied between the two electrodes of the electrochemical oxygen pump section, and oxygen gas present in the sealed space is forcibly discharged to the outside according to the principle of the electrochemical oxygen pump, and the reference gas chamber is controlled to a predetermined low oxygen partial pressure.

Patent Document 2 describes an oxygen sensor in which a current is applied between an outer electrode and an inner electrode to introduce oxygen in a detection gas into the vicinity of the inner electrode, and the introduced oxygen is used as a reference gas. In this oxygen sensor, in order to introduce oxygen in a detection gas into the vicinity of the inner electrode, a buffer layer having a porous structure containing zirconia and aluminum is provided on the outer surface of the inner electrode, allowing oxygen to enter the buffer layer.

Japanese Patent Application Publication No. 05-240833 JP 2006-112918 A

The oxygen sensor in Patent Document 1 attempts to accurately measure the oxygen concentration in the test gas by controlling the oxygen partial pressure in the reference gas chamber to a low reference. However, because the oxygen partial pressure in the reference gas chamber is controlled to a low value, even a slight change in the oxygen partial pressure has a large effect on the electromotive force, making it difficult to improve detection accuracy.

The oxygen sensor described in Patent Document 2 uses oxygen as a reference gas by increasing the partial pressure of oxygen introduced near the inner electrode to be higher than the partial pressure of oxygen in the atmosphere, and forms a cylindrical element. For this reason, it is necessary to make the relaxation layer porous and strong. However, making the relaxation layer porous and strong is disadvantageous in terms of miniaturizing the oxygen sensor. It is not easy to apply the formation of such a porous layer or the manufacture of a cylindrical element to, for example, a micromechanical electrical element called MEMS (MicroElectroMechanical Systems).

The objective of the present invention is to provide an oxygen sensor that can eliminate the various drawbacks of the conventional technology described above.

The present invention provides a first membrane electrode assembly including a first solid electrolyte membrane having oxide ion conductivity and a first electrode disposed on one surface of the solid electrolyte membrane;
a second membrane electrode assembly including a second solid electrolyte membrane having oxide ion conductivity and a second electrode disposed on one surface of the solid electrolyte membrane;
the first membrane electrode assembly and the second membrane electrode assembly are arranged such that the first solid electrolyte membrane in the first membrane electrode assembly and the second solid electrolyte membrane in the second membrane electrode assembly face each other with a gap therebetween;
an intermediate electrode is disposed between the first solid electrolyte membrane of the first membrane electrode assembly and the second solid electrolyte membrane of the second membrane electrode assembly so as to be in contact with both solid electrolyte membranes, and a reference oxygen concentration space is defined by an oxygen-permeable wall portion provided so as to surround the intermediate electrode;
The present invention provides an oxygen sensor configured to measure the oxygen concentration in the atmosphere to be measured that faces the first electrode by positioning a first electrode so that the first electrode faces the atmosphere to be measured, connecting the intermediate electrode to the positive terminal of a power source and connecting the second electrode to the negative terminal of the power source to create a state in which the oxygen concentration in the reference oxygen concentration space is increased, and measuring the electromotive force generated between the first electrode and the intermediate electrode.

The present invention also provides a membrane electrode assembly including a solid electrolyte membrane having oxide ion conductivity, and a first electrode and a second electrode disposed on either side of the solid electrolyte membrane,
an electrode opposing member is disposed to face the second electrode;
a reference oxygen concentration space is defined between the solid electrolyte membrane and the member by a wall portion provided so as to surround a second electrode,
At least one of the member and the wall portion is made of a material that is permeable to oxygen,
The present invention provides an oxygen sensor that measures the oxygen concentration in the atmosphere to be measured that the first electrode faces by positioning a first electrode so that the first electrode faces the atmosphere to be measured, connecting a second electrode to the positive terminal of a power source and connecting the first electrode to the negative terminal of the power source to create a state in which the oxygen concentration in the reference oxygen concentration space is increased, disconnecting the first electrode and the second electrode from the power source, and further measuring the electromotive force generated between the first electrode and the second electrode.

The present invention further provides a membrane electrode assembly including a solid electrolyte membrane having oxide ion conductivity, a first electrode and a second electrode disposed on one side of the solid electrolyte membrane, and an intermediate electrode disposed on the other side of the solid electrolyte membrane,
an electrode opposing member is disposed to face the intermediate electrode,
a reference oxygen concentration space is defined between the solid electrolyte membrane and the member by a wall portion provided so as to surround the intermediate electrode,
At least one of the member and the wall portion is made of a material that is permeable to oxygen,
The present invention provides an oxygen sensor that measures the oxygen concentration in a measurement atmosphere facing the first electrode by arranging a first electrode and a second electrode so that the first electrode faces the measurement atmosphere and the second electrode faces the measurement atmosphere or the outside air, connecting the intermediate electrode to the positive terminal of a power source and the second electrode to the negative terminal of the power source to create a state in which the oxygen concentration in the reference oxygen concentration space is increased, and measuring the electromotive force generated between the first electrode and the intermediate electrode.

FIG. 1 is a schematic diagram showing the structure of an embodiment of an oxygen sensor of the present invention. FIG. 2 is a graph showing how the relationship between the concentration of oxygen gas in a test gas and the electromotive force of a concentration cell depends on the concentration of oxygen gas contained in a reference gas. FIG. 3 is a schematic diagram showing the structure of another embodiment of the oxygen sensor of the present invention. FIG. 4 is a schematic diagram showing the structure of a further embodiment of the oxygen sensor of the present invention. FIG. 5 is a schematic diagram showing the structure of a further embodiment of the oxygen sensor of the present invention. FIG. 6 is a graph showing the change in voltage over time when the concentration of oxygen gas is measured using the oxygen sensor of the embodiment shown in FIG. FIG. 7 is a schematic diagram showing the structure of still another embodiment of the oxygen sensor of the present invention. FIG. 8 is a schematic diagram showing the structure of still another embodiment of the oxygen sensor of the present invention.

The present invention will now be described based on preferred embodiments thereof with reference to the drawings. FIG. 1 shows an embodiment of an oxygen sensor of the present invention. The oxygen sensor 1 shown in the figure comprises a first membrane electrode assembly 10 and a second membrane electrode assembly 20.

The first membrane electrode assembly 10 comprises a first solid electrolyte membrane 100 having oxide ion conductivity and a first electrode 101 arranged on one side of the solid electrolyte membrane 100. On the other hand, the second membrane electrode assembly 20 comprises a second solid electrolyte membrane 200 having oxide ion conductivity and a second electrode 102 arranged on one side of the solid electrolyte membrane 200.

The first solid electrolyte membrane 100 and the second solid electrolyte membrane 200 may be made of the same material or different materials as long as they have oxide ion conductivity. The first electrode 101 and the second electrode 102 may be made of the same material or different materials as long as they are conductive.

In the oxygen sensor 1, the first membrane electrode assembly 10 and the second membrane electrode assembly 20 are arranged so that the other side of the first solid electrolyte membrane 100 in the first membrane electrode assembly 10 (i.e., the side on which the first electrode 101 is not arranged) and the other side of the second solid electrolyte membrane 200 in the second membrane electrode assembly 20 (i.e., the side on which the second electrode 102 is not arranged) face each other with a gap therebetween. In FIG. 1, the first solid electrolyte membrane 100 and the second solid electrolyte membrane 200, both of which are flat, are shown arranged approximately parallel to each other at a certain distance. The gap between the first solid electrolyte membrane 100 and the second solid electrolyte membrane 200 is not critical in the present invention, and may be set to an appropriate value depending on the size of the oxygen sensor 1, the situation of use, etc. In general, if the gap between the first solid electrolyte membrane 100 and the second solid electrolyte membrane 200 is set to 0.05 mm or more and 10 mm or less, the concentration of oxygen gas can be measured with high accuracy.

An intermediate electrode 120 is disposed between the other surface of the first solid electrolyte membrane 100 in the first membrane electrode assembly 10 and the other surface of the second solid electrolyte membrane 200 in the second membrane electrode assembly 20 so as to be in contact with both solid electrolyte membranes 100, 200. The intermediate electrode 120 may be made of the same material as the first electrode 101 and the second electrode 102 described above, or may be made of a different material, so long as it is conductive.

In the oxygen sensor 1, an annular wall portion 30 through which oxygen can pass is provided between the first solid electrolyte membrane 100 in the first membrane electrode assembly 10 and the second solid electrolyte membrane 200 in the second membrane electrode assembly 20. The annular wall portion 30 is structured to allow oxygen gas to flow between the inside and outside of the wall portion. The annular wall portion 30 is provided to surround the intermediate electrode 120. As a result, in the oxygen sensor 1, a reference oxygen concentration space S is defined between the first solid electrolyte membrane 100 and the second solid electrolyte membrane 200 by the annular wall portion 30. In FIG. 1, the reference oxygen concentration space S is defined by the annular wall portion 30, the first solid electrolyte membrane 100, the second solid electrolyte membrane 200, and the intermediate electrode 120. The reference oxygen concentration space S is connected to the outside world through the annular wall portion 30 made of an oxygen-permeable material, for example, a porous material.

The volume of the reference oxygen concentration space S is not critical in the present invention, and may be set to an appropriate value depending on the size of the oxygen sensor 1, the situation of use, etc. Generally, if the volume of the reference oxygen concentration space S is set to 0.01 ^mm3 or more and 1000 ^mm3 or less, the concentration of oxygen gas can be measured with high accuracy. Note that if the intermediate electrode 120 is made of a porous material or the like and has a void, the void can also be used as the reference oxygen concentration space S. Therefore, it is not necessary to provide a complete space between the intermediate electrode 120 and the annular wall portion 30.

There are no particular limitations on the cross-sectional shape of the annular wall portion 30, so long as it is annular. For example, a cylindrical annular wall portion having a circular or rectangular cross-section can be used. The shape of the annular wall portion 30 to be used can be appropriately selected depending on the shape of each solid electrolyte membrane 100, 200, the size of the oxygen sensor 1, etc.

In the oxygen sensor 1, the first solid electrolyte membrane 100 and the first electrode 101 and intermediate electrode 120 arranged on each side thereof constitute the first unit cell. Similarly, the second solid electrolyte membrane 200 and the second electrode 102 and intermediate electrode 120 arranged on each side thereof constitute the second unit cell. The intermediate electrode 120 serves as both the electrode of the first unit cell and the electrode of the second unit cell. The first unit cell acts as a concentration cell. On the other hand, the second unit cell acts as an oxygen pump. In detail, as shown in FIG. 1, a voltmeter 60 is connected between the first electrode 101 and the intermediate electrode 120 in the first unit cell, so that the electromotive force generated between both electrodes of the concentration cell can be measured. In the second unit cell, a DC power source 40 is connected between the second electrode 102 and the intermediate electrode 120, so that a voltage is applied between the two electrodes. In this case, the intermediate electrode 120 is connected to the positive electrode of the DC power supply 40 , and the second electrode 102 is connected to the negative electrode of the DC power supply 40 .

The method of measuring the oxygen concentration in the test gas using the oxygen sensor 1 having the above configuration is as follows. First, the first electrode 101 is arranged so that it faces the atmosphere to be measured and the second electrode 102 faces the outside air (generally the atmosphere). In this state, the entire oxygen sensor 1 is heated so that the first and second solid electrolyte films 100, 200 exhibit oxide ion conductivity. The heating temperature varies depending on the constituent materials of the first and second solid electrolyte films 100, 200, but when the first and second solid electrolyte films 100, 200 are composed of materials described below, for example, practical oxide ion conductivity is exhibited even at temperatures below about 600°C. The heating temperature is preferably 200°C or higher, more preferably 300°C or higher, and even more preferably 400°C or higher. By heating the entire oxygen sensor 1 to make the first and second solid electrolyte films 100, 200 reach the above temperature or higher, sufficient measurement accuracy can be obtained. It should be noted that this temperature is not a set temperature but the actual temperature of the first and second solid electrolyte membranes 100 and 200 .

When the oxide ion conductivity is manifested in the first and second solid electrolyte membranes 100, 200, the intermediate electrode 120 is connected to the positive electrode of the DC power source 40 and the second electrode 102 is connected to the negative electrode of the DC power source 40. This causes the oxygen pumping action of the second single cell to be manifested, and the oxygen gas contained in the outside air is reduced to oxide ions. The oxide ions move through the second solid electrolyte membrane 200 and reach the intermediate electrode 120. The oxide ions that reach the intermediate electrode 120 release electrons and change to oxygen gas. The oxygen gas thus generated is accumulated in the reference oxygen concentration space S. However, the reference oxygen concentration space S is partially defined by the annular wall portion 30 made of a material that is permeable to oxygen, and the reference oxygen concentration space S is connected to the outside, so that the pressure in the reference oxygen concentration space S does not rise excessively. As a result, the reference oxygen concentration space S maintains a certain pressure while the partial pressure of oxygen gas is high. The oxygen concentration in this state is called the reference oxygen concentration. It is preferable to set the reference oxygen concentration to 100 vol% oxygen in order to perform highly accurate measurements. Whether the oxygen concentration in the space S is 100 vol% or not can be determined by measuring the electromotive force between the electrodes in an atmosphere with a known concentration of the gas to be detected, such as an oxygen concentration of 20.9% in normal air.

When the reference oxygen concentration is reached in space S, the electromotive force generated between first electrode 101 and intermediate electrode 120 in the first unit cell is measured by voltmeter 60. During the measurement, a DC voltage is continuously applied between second electrode 102 and intermediate electrode 120 in the second unit cell to maintain the oxygen concentration in reference oxygen concentration space S at a certain high level. Based on the measured electromotive force, the concentration of oxygen gas in the measurement target atmosphere is calculated using the Nernst equation shown below.
E=(RT/4F)ln(P _O2 ^A /P _O2 ^B )
In the formula, E represents the electromotive force (V) generated between the first electrode 101 and the intermediate electrode 120, R represents the gas constant, T represents the absolute temperature (K), F represents the Faraday constant, P _O2 ^A represents the concentration of oxygen gas in the atmosphere to be measured, and P _O2 ^B represents the concentration of oxygen gas in the reference oxygen concentration space S. In the above formula, since E, R, T, F, and P _O2 ^B are known, P _O2 ^A , i.e., the concentration of oxygen gas in the atmosphere to be measured, can be calculated.

The advantage of using the second single cell as an oxygen pump in the oxygen sensor 1 to increase the concentration of the reference oxygen concentration space S will be explained with reference to FIG. 2. The figure is a graph showing the relationship between oxygen gas concentration and electromotive force according to the Nernst equation for the oxygen sensor 1 of this embodiment. In the figure, lines A and B are simulation results when T = 600 ° C and the reference oxygen concentration is set to 0.010 vol% and 0.020 vol%. As is clear from the comparison between lines A and B, even when the reference oxygen concentration differs only slightly by 0.010 vol%, the electromotive force differs by several tens of mV, which results in a large difference in the calculated oxygen gas concentration. In contrast to this, lines C to E are simulation results when T = 600 ° C and the reference oxygen concentration is set to 80 vol%, 90 vol%, and 100 vol%. As is clear from a comparison of lines C and E, even when the reference oxygen concentration differs by as much as 20 vol%, it can be seen that there is almost no difference in the electromotive force. As a result, there is almost no difference in the calculated oxygen gas concentration. Thus, according to the present invention, by measuring the oxygen gas concentration with a high reference oxygen concentration, the advantageous effect of improving the measurement accuracy is achieved.

In particular, as is clear from Figure 2, with the oxygen sensor 1 of this embodiment, the absolute value of the electromotive force becomes larger as the concentration of oxygen gas in the test gas decreases, which is the concentration range in which measurement errors are likely to occur, and therefore there is also the advantage that measurement errors are less likely to occur even when the concentration of oxygen gas is low.

Moreover, unlike conventional oxygen sensors, the oxygen sensor 1 of this embodiment does not use air as the reference gas for the concentration cell, so it is less susceptible to the effects of impurities contained in the air. This also allows the concentration of oxygen gas to be measured with high accuracy.

In order to make the above advantages even more pronounced, it is advantageous to measure the oxygen gas concentration in the reference oxygen concentration space S under conditions in which the oxygen gas concentration is set to preferably 60 vol% or more and 100 vol% or less, more preferably 80 vol% or more and 100 vol% or less, and even more preferably 90 vol% or more and 100 vol% or less. The oxygen gas concentration in the reference oxygen concentration space S is measured by measuring the electromotive force between the electrodes in an atmosphere of a known test gas concentration, such as an oxygen concentration of 20.9% in normal air.

In order to set the concentration of oxygen gas in the reference oxygen concentration space S within the above range, for example, the voltage of the DC power supply may be set preferably to 0.05 V or more and 3 V or less, the volume of the reference oxygen concentration space S may be set to 0.01 ^mm3 or more and 800 mm3 ^or less, or the amount of oxygen permeating through the annular wall portion 30 may be reduced.

In addition to the concentration of oxygen gas in the reference oxygen concentration space S, it is advantageous to maintain the pressure of the reference oxygen concentration space S within a specific range in order to perform stable measurements. From this perspective, it is advantageous to measure the concentration of oxygen gas under conditions in which the pressure (Pa) of the reference oxygen concentration space S is set to a value, preferably 1.0 to 3.0, more preferably 1.0 to 2.0, and even more preferably 1.0 to 1.5, relative to the atmospheric pressure (Pa) in the atmosphere to be measured (i.e., the value of the pressure (Pa) of the reference oxygen concentration space S/the atmospheric pressure (Pa) in the atmosphere to be measured).

In order to set the pressure of the reference oxygen concentration space S within the above range, for example, the voltage of the DC power supply may be set preferably to 1.0 V or more and 3.0 V or less, the volume of the reference oxygen concentration space S may be set to 0.01 ^mm3 or more and 1000 mm3 or ^less , or the amount of oxygen permeating through the annular wall portion 30 may be adjusted. These methods of adjusting the oxygen gas concentration and pressure of the reference oxygen concentration space S can also be applied to other embodiments of the oxygen sensor described later.

Figure 3 shows another embodiment of the oxygen sensor shown in Figure 1. The oxygen sensor 1 shown in Figure 3 differs from the oxygen sensor 1 shown in Figure 1 in that the intermediate electrode 120 of the oxygen sensor shown in Figure 1 is divided into a third electrode 103 that is in contact only with the first solid electrolyte membrane 100 and a fourth electrode 104 that is in contact only with the second solid electrolyte membrane 200, and these electrodes are independent of each other. By separating the electrodes, deterioration of the electrodes is less likely to occur, and an improvement in the sensor life can be expected.

3, the first membrane electrode assembly 10 includes a first solid electrolyte membrane 100, and a first electrode 101 and a third electrode 103 arranged on each side of the solid electrolyte membrane 100. On the other hand, the second membrane electrode assembly 20 includes a second solid electrolyte membrane 200, and a second electrode 102 and a fourth electrode 104 arranged on each side of the solid electrolyte membrane 200. The first electrode 101 to the fourth electrode 104 may be made of the same material or different materials as long as they are conductive.

In the oxygen sensor 1, the first membrane electrode assembly 10 and the second membrane electrode assembly 20 are arranged so that the third electrode 103 in the first membrane electrode assembly 10 and the fourth electrode 104 in the second membrane electrode assembly 20 face each other with a gap between them. In FIG. 1, the third electrode 103 and the fourth electrode 104, both of which are flat, are shown arranged approximately parallel to each other at a certain distance. The gap between the third electrode 103 and the fourth electrode 104 is not critical in the present invention, and may be set to an appropriate value depending on the size of the oxygen sensor 1, the situation of use, etc. In general, if the gap between the third electrode 103 and the fourth electrode 104 is set to 0.05 mm or more and 10 mm or less, the concentration of oxygen gas can be measured with high accuracy.

In the oxygen sensor 1 shown in FIG. 3, the annular wall portion 30 is provided to surround the third electrode 103 and the fourth electrode 104. As a result, in the oxygen sensor 1, the annular wall portion 30 defines a reference oxygen concentration space S between the first solid electrolyte membrane 100 and the second solid electrolyte membrane 200. In FIG. 3, the reference oxygen concentration space S is defined by the annular wall portion 30, the first solid electrolyte membrane 100, the second solid electrolyte membrane 200, the third electrode 103, and the fourth electrode 104. The reference oxygen concentration space S is in communication with the outside world through the annular wall portion 30 made of a material that is permeable to oxygen gas.

In the oxygen sensor 1 shown in FIG. 3, the first membrane electrode assembly 10 constitutes a single cell. Similarly, the second membrane electrode assembly 20 also constitutes a single cell. The first membrane electrode assembly 10 acts as a concentration cell. On the other hand, the second membrane electrode assembly 20 acts as an oxygen pump. In detail, as shown in FIG. 3, a voltmeter 60 is connected between the first electrode 101 and the third electrode 103 in the first membrane electrode assembly 10, so that the electromotive force generated between the two electrodes of the concentration cell can be measured. In the second membrane electrode assembly 20, a DC power source 40 is connected between the second electrode 102 and the fourth electrode 104, so that a voltage is applied between the two electrodes. In this case, the fourth electrode 104 is connected to the positive electrode of the DC power source 40, and the second electrode 102 is connected to the negative electrode of the DC power source 40.

The method of measuring the oxygen concentration in a test gas using the oxygen sensor 1 shown in FIG. 3 is as follows. First, the first electrode 101 is arranged so that it faces the atmosphere to be measured and the second electrode 102 faces the outside air (generally the atmosphere). In this state, the entire oxygen sensor 1 is heated so that oxide ion conductivity is developed in the first and second solid electrolyte membranes 100, 200. Next, the fourth electrode 104 is connected to the positive electrode of the DC power source 40 and the second electrode 102 is connected to the negative electrode of the DC power source 40. This develops the oxygen pumping action of the second membrane electrode assembly 20, and the oxygen gas contained in the outside air is reduced to oxide ions. The oxide ions move through the second solid electrolyte membrane 200 to reach the fourth electrode 104 and are converted into oxygen gas. The oxygen gas thus generated is accumulated in the reference oxygen concentration space S. As a result, the reference oxygen concentration space S is in a state where the partial pressure of oxygen gas is high while maintaining a certain pressure.

When the reference oxygen concentration is reached in space S, the electromotive force generated between the first electrode 101 and the third electrode 103 in the first membrane electrode assembly 10 is measured by a voltmeter 60, and the concentration of oxygen gas in the atmosphere being measured is calculated according to the Nernst equation described above.

Figure 4 shows yet another embodiment of the oxygen sensor shown in Figure 1. The oxygen sensor 1 shown in Figure 4 comprises a first membrane electrode assembly 10 and a second membrane electrode assembly 20, similar to the oxygen sensor shown in Figure 1. The first membrane electrode assembly 10 comprises a first solid electrolyte membrane 100 and a first electrode 101 arranged on one side of the solid electrolyte membrane 100. The second membrane electrode assembly 20 comprises a second solid electrolyte membrane 200 and a second electrode 102 arranged on one side of the solid electrolyte membrane 200.

In the oxygen sensor of this embodiment, the first membrane electrode assembly 10 and the second membrane electrode assembly 20 are arranged differently from the embodiment shown in FIG. 1. In detail, the first membrane electrode assembly 10 and the second membrane electrode assembly 20 are arranged so that the surface of the first solid electrolyte membrane 100 on which the first electrode 101 is arranged and the surface of the second solid electrolyte membrane 200 on which the second electrode 102 is arranged face each other with a gap therebetween. The intermediate electrode 120 is arranged so as to contact both the surface of the first solid electrolyte membrane 100 on which the first electrode 101 is arranged and the surface of the second solid electrolyte membrane 200 on which the second electrode 102 is arranged. However, the first electrode 101 is not in contact with the second solid electrolyte membrane 200, and the second electrode 102 is not in contact with the first solid electrolyte membrane 100. Therefore, with respect to the first solid electrolyte membrane 100, the first electrode 101 and the intermediate electrode 120 are disposed on the same surface of the first solid electrolyte membrane 100, and with respect to the second solid electrolyte membrane 200, the second electrode 102 and the intermediate electrode 120 are disposed on the same surface of the second solid electrolyte membrane 200. Note that in Fig. 4, the first electrode 101 and the second electrode 102 are not disposed so as to overlap when viewed in the thickness direction of the oxygen sensor 1, i.e., in the vertical direction of the paper in the figure, but instead, both electrodes 101, 102 may be disposed so as to overlap.

In the oxygen sensor 1 shown in FIG. 4, the first solid electrolyte membrane 100, the first electrode 101, and the intermediate electrode 120 constitute the first unit cell. The second solid electrolyte membrane 200, the second electrode 102, and the intermediate electrode 120 constitute the second unit cell. The first unit cell acts as a concentration cell. On the other hand, the second unit cell acts as an oxygen pump. In detail, as shown in FIG. 4, a voltmeter 60 is connected between the first electrode 101 and the intermediate electrode 120 in the first unit cell, so that the electromotive force generated between the two electrodes of the concentration cell can be measured. In the second unit cell, a DC power source 40 is connected between the second electrode 102 and the intermediate electrode 120, so that a voltage is applied between the two electrodes. In this case, the intermediate electrode 120 is connected to the positive electrode of the DC power source 40, and the second electrode 102 is connected to the negative electrode of the DC power source 40.

The method of measuring the oxygen concentration in the test gas using the oxygen sensor 1 shown in FIG. 4 is as follows. First, the first electrode 101 is arranged so as to face the atmosphere to be measured, and the second electrode 102 is arranged so as to face the atmosphere to be measured or the outside air (generally the atmosphere). In this state, the entire oxygen sensor 1 is heated so that the first and second solid electrolyte membranes 100, 200 exhibit oxide ion conductivity. Next, the intermediate electrode 120 is connected to the positive electrode of the DC power source 40, and the second electrode 102 is connected to the negative electrode of the DC power source 40. This causes the oxygen pumping action of the second single cell to be exhibited, and oxygen gas is accumulated in the reference oxygen concentration space S. When the reference oxygen concentration is reached in the space S, the electromotive force generated between the first electrode 101 and the intermediate electrode 120 is measured by the voltmeter 60, and the concentration of oxygen gas in the measurement atmosphere is calculated according to the Nernst equation described above.

The oxygen sensor 1 of this embodiment also measures the concentration of oxygen gas in the measurement target atmosphere with a high reference oxygen concentration, which has the advantageous effect of improving measurement accuracy. Moreover, according to the oxygen sensor 1 of this embodiment, the first electrode 101 and the intermediate electrode 120 are arranged on the same surface of the first solid electrolyte membrane 100, and the second electrode 102 and the intermediate electrode 120 are arranged on the same surface of the second solid electrolyte membrane 200, which has the advantage of simplifying the manufacturing process of the oxygen sensor 1.

In the oxygen sensor 1 shown in Figures 1, 3, and 4, the first solid electrolyte membrane 100 and the second solid electrolyte membrane 200 can be made of any material having oxide ion conductivity without any particular restrictions. For example, it is preferable that at least one of the first solid electrolyte membrane 100 and the second solid electrolyte membrane 200 is made of a compound containing A, M, and O (A is one or more elements selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Be, Mg, Ca, Sr, and Ba. M is one or more elements selected from the group consisting of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Y, Zr, Ta, Nb, B, Si, Ge, Zn, Sn, W, and Mo). In particular, when the first solid electrolyte membrane 100 is made of a compound containing A, M and O, the transport number of the oxide ions can be increased, and a stable electromotive force can be obtained, which is preferable.

At least one of the first solid electrolyte membrane 100 and the second solid electrolyte membrane 200 has a general formula: _A9.33+x [ _{T6.00-yMy ] O26.0+z} (wherein A is one or more elements selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Be, Mg, Ca, Sr, and Ba. T is an element containing Si or Ge, or both. M is Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Y, Zr, Ta, Nb, B, G and x is a number equal to or greater than -1.33 and equal to or less than 1.50, y is a number equal to or greater than 0.00 and equal to or less than 3.00, and z is a number equal to or greater than -5.00 and equal to or less than 5.20, and the ratio of the number of moles of A to the number of moles of T is 1.33 or greater and 3.61 or less. In particular, when the second solid electrolyte membrane 200 used in the second membrane electrode assembly 20 acting as an oxygen pump is made of a compound containing a complex oxide represented by the general formula: A9.33 _+x [ _{T6.00-yMy ] O26.0+z} , the oxygen pumping action is more pronounced at a lower temperature, which is preferable.

The compound represented by the general formula A9.33 _+x [ _{T6.00-yMy ] O26.0+z} is an oriented apatite-type oxide ion conductor, and from the viewpoint of increasing the oxide ion conductivity, it is preferable that the degree of orientation measured by the Lotgering method is 0.6 or more.

The thickness of the first solid electrolyte membrane 100 and the second solid electrolyte membrane 200 is not critical in the present invention, and they only need to have a strength sufficient to withstand the use of the oxygen sensor 1. The thickness of these electrolyte membranes can generally be 0.1 μm or more and 1.0 mm or less. The thicknesses of these electrolyte membranes may be the same or different.

The first electrode 101 to the fourth electrode 104 and the intermediate electrode 120 may be made of a metal material, but it is preferable that at least one of them is made of a conductive oxide from the viewpoint of improving the conductivity of oxide ions. In particular, it is preferable that the oxide has a perovskite structure represented by MNO ₃ (M is one or more elements selected from the group consisting of Ca, Sr, Ba, La, Pr, and Y. N is one or more elements selected from the group consisting of Ni, Ti, V, Zr, Cr, Mn, Fe, Co, Mo, Ru, Pd, and Re) from the viewpoint of further improving the oxide ion conductivity between the solid electrolyte membrane and the electrode. An intermediate layer such as CeO ₂ doped with Sm may be provided between the solid electrolyte membrane and the electrode.

The planar shapes of the first electrode 101 to the fourth electrode 104 and the intermediate electrode 120 can be various shapes, such as circular or polygonal. If necessary, processing to increase the surface area can be performed using a known method. For example, the surface area can be increased by making the surface of the electrode uneven. This processing can further promote the movement of oxygen.

Like the thickness of the solid electrolyte membrane, the thickness of the first electrode 101 to the fourth electrode 104 and the intermediate electrode 120 is not critical in the present invention, and it is sufficient that they have a strength sufficient to withstand the use of the oxygen sensor 1. The thickness of these electrodes can generally be 0.01 μm or more and 100 μm or less. The thickness of these electrodes may be the same or different.

The annular wall portion 30, which is permeable to oxygen, can be made of a material that is stable at the operating temperature of the oxygen sensor 1, such as a ceramic material. Examples of ceramic materials that can be used include alumina, zirconia, silica, and zeolite. To incorporate the annular wall portion 30 into the oxygen sensor 1, for example, an adhesive may be applied to the upper and lower end surfaces of the annular wall portion 30, and then the annular wall portion 30 may be joined to the first membrane electrode assembly 10 and the second membrane electrode assembly 20. For example, a zirconia-based adhesive may be used as the adhesive.

Next, other embodiments of the oxygen sensor of the present invention will be described with reference to Figures 5 to 8. Regarding these embodiments, differences from the embodiment shown in Figures 1 to 4 described above will be described, and the description of the embodiment shown in Figures 1 to 4 will be applied as appropriate to points not specifically described. Also, in Figures 5 to 8, the same reference numerals are used for the same members as in Figures 1 to 4.

The oxygen sensor 1a shown in Figure 5 includes a membrane electrode assembly 10a. The membrane electrode assembly 10a includes a solid electrolyte membrane 100a having oxide ion conductivity, and a first electrode 101a and a second electrode 102a arranged on each side of the solid electrolyte membrane 100a. The membrane electrode assembly 10a functions as a concentration cell and an oxygen pump depending on the switching of the switch 70.

As the solid electrolyte membrane 100a, the same material as that constituting the first solid electrolyte membrane 100 or the second solid electrolyte membrane 200 in the oxygen sensor 1 of the embodiment shown in Figures 1 and 3 can be used. As for the first electrode 101a and the second electrode 102a, the same material as that constituting the first electrode 101 to the fourth electrode 104 and the intermediate electrode 120 in the oxygen sensor 1 of the embodiment shown in Figures 1 and 3 can be used. In addition, the material constituting the first electrode 101a and the material constituting the second electrode 102a may be the same or different.

In the oxygen sensor 1a, an electrode opposing member 50 is disposed so as to face the second electrode 102a. In Fig. 5, the electrode opposing member 50 is depicted as a flat plate-shaped member. In Fig. 5, the electrode opposing member 50 and the second electrode 102a are shown in close contact with each other without any gaps, but this is not limited thereto, and the electrode opposing member 50 and the second electrode 102a may be disposed with a gap therebetween.

An annular wall portion 31 is provided between the solid electrolyte membrane 100a and the electrode opposing member 50. The annular wall portion 31 is provided so as to surround the second electrode 102a. As a result, in the oxygen sensor 1a, a reference oxygen concentration space S is defined between the solid electrolyte membrane 100a and the electrode opposing member 50 by the annular wall portion 31. In FIG. 5, the reference oxygen concentration space S is defined by the annular wall portion 31, the solid electrolyte membrane 100a, the electrode opposing member 50, and the second electrode 102a.

At least one of the electrode opposing member 50 and the annular wall portion 31 is made of a material that is permeable to oxygen. For example, a porous material can be used as such a material. Therefore, the reference oxygen concentration space S is in communication with the outside via at least one of the electrode opposing member 50 and the annular wall portion 31. From the viewpoint of ease of manufacturing when miniaturizing the oxygen sensor 1a, it is preferable that only the annular wall portion 31 is made of a material that is permeable to oxygen.

1, 3 and 4, the annular wall portion 31 in the oxygen sensor 1a of this embodiment does not necessarily need to be permeable to oxygen, as described above. The annular wall portion 31 may be made of any material that can withstand the operating temperature of the oxygen sensor 1a.

The method for measuring the oxygen concentration in a test gas using the oxygen sensor 1a having the above configuration is as follows. First, the first electrode 101a is arranged so that it faces the atmosphere to be measured, and the electrode opposing member 50 faces the outside air (generally the atmosphere). In this state, the entire oxygen sensor 1a is heated so that oxide ion conductivity is expressed in the solid electrolyte membrane 100a. The heating temperature can be the same as in the embodiments shown in Figures 1, 3, and 4.

When oxide ion conductivity is manifested in the solid electrolyte membrane 100a, the second electrode 102a is connected to the positive electrode of the DC power source 40 and the first electrode 101a is connected to the negative electrode of the DC power source 40. This manifests an oxygen pumping action, and the oxygen gas contained in the atmosphere to be measured is reduced to oxide ions. The oxide ions move through the solid electrolyte membrane 100a and reach the second electrode 102a. The oxide ions that reach the second electrode 102a release electrons and change to oxygen gas. The oxygen gas thus produced is accumulated in the reference oxygen concentration space S. However, since a part of the reference oxygen concentration space S is defined by a material that allows oxygen to pass through, and the reference oxygen concentration space S is connected to the outside, the pressure in the reference oxygen concentration space S does not increase excessively. As a result, the reference oxygen concentration space S maintains a certain pressure and becomes a reference oxygen concentration in which the partial pressure of oxygen gas is high. It is preferable to set the reference oxygen concentration to 100 vol% oxygen in terms of being able to perform highly accurate measurements. The determination as to whether the oxygen concentration in the space S is 100 vol % or not is as described above.

When the oxygen concentration in the reference oxygen concentration space S increases and reaches the reference oxygen concentration in the space S, the switch 70 disconnects the first electrode 101a and the second electrode 102a from the DC power supply 40. At the same time, the electromotive force generated between the first electrode 101a and the second electrode 102a is measured by the voltmeter 60. Thereafter, the oxygen concentration in the measurement target atmosphere facing the first electrode 101a is calculated according to the Nernst equation using the same procedure as in the embodiment shown in FIG.

This embodiment also measures the concentration of oxygen gas in the measurement target atmosphere with a high reference oxygen concentration, which has the advantageous effect of improving measurement accuracy. Moreover, unlike the oxygen sensor 1a described in Patent Document 2 mentioned above, the oxygen sensor 1a of this embodiment does not require the electrode opposing member 50 to have high strength because it is sufficient to have high-concentration oxygen gas present in the reference oxygen concentration space S.

6 shows an example of the result of measuring the voltage between the first electrode 101a and the second electrode 102a using the oxygen sensor 1a. As shown in the figure, when the switch 70 is turned on and the voltage of the DC power supply 40 is applied between the first electrode 101a and the second electrode 102a, the voltage _E1 of the DC power supply 40 is observed between the two electrodes. While the voltage _E1 is being applied, oxygen gas is accumulated in the reference oxygen concentration space S by the oxygen pump action, and the concentration of oxygen gas increases. During this period, the oxygen sensor 1a does not measure the concentration of oxygen gas in the atmosphere to be measured.

When oxygen gas is sufficiently accumulated in the reference oxygen concentration space S and the concentration of oxygen gas is sufficiently increased, the switch 70 is turned off. From this point, the oxygen sensor 1a starts measuring the concentration of oxygen gas in the measurement target atmosphere. At this time, the voltage between the first electrode 101a and the second electrode 102a, that is, the electromotive force generated by the principle of a concentration cell, is lower than _E1 as shown in FIG. 6, and shows a value corresponding to the concentration of oxygen gas in the measurement target atmosphere. The electromotive force shown in FIG. 6 is an example when the concentration of oxygen gas in the measurement target atmosphere is constant. The duration of measurement of the concentration of oxygen gas by the oxygen sensor 1a, that is, the time during which the switch 70 is turned off, depends on the change in the concentration of oxygen gas in the reference oxygen concentration space S. In detail, as long as the concentration of oxygen gas in the reference oxygen concentration space S is constant, highly accurate measurement can be continued. When the concentration of oxygen gas in the reference oxygen concentration space S decreases (the oxygen gas dissipates to the outside through at least one of the electrode opposing member 50 and the annular wall portion 31), the switch 70 is turned on again as shown in Fig. 6 to accumulate oxygen gas in the reference oxygen concentration space S. Thereafter, the concentration of oxygen gas in the measurement target atmosphere is measured by the above-mentioned procedure.

In this way, the oxygen sensor 1a of this embodiment alternates between supplying oxygen to the reference oxygen concentration space S and measuring the electromotive force by applying a pulsed voltage between the first electrode 101a and the second electrode 102a. By switching the switch 70 to suitably use the concentration cell and the oxygen pump function, it is possible to achieve power saving in the sensor, so the oxygen sensor 1a of this embodiment is suitable for application to portable devices.

Although it depends on the dimensions of the oxygen sensor 1a and the degree of porosity of the electrode opposing member 50, it is preferable that the time for which the switch 70 is turned on is 0.5 seconds or more and 10 seconds or less. On the other hand, the duration for which the concentration of oxygen gas in the measurement target atmosphere can be measured with the switch 70 turned off is generally 3 seconds or more and 200 seconds or less.

The oxygen sensor 1b shown in Figure 7 includes a membrane electrode assembly 10b. The membrane electrode assembly 10b includes a solid electrolyte membrane 100b having oxide ion conductivity, a first electrode 101b and a second electrode 102b arranged on one side of the solid electrolyte membrane 100b, and an intermediate electrode 120b arranged on the other side of the solid electrolyte membrane 100b. The membrane electrode assembly 10b includes a concentration cell and an oxygen pump within its structure.

As the solid electrolyte membrane 100b, a material similar to that constituting the first solid electrolyte membrane 100 or the second solid electrolyte membrane 200 in the oxygen sensor 1 of the embodiment shown in Figures 1 and 3 can be used. As for the first electrode 101b, the second electrode 102b, and the intermediate electrode 120b, a material similar to that constituting the first electrode 101 to the fourth electrode 104 and the intermediate electrode 120 in the oxygen sensor 1 of the embodiment shown in Figures 1 and 3 can be used. In addition, the materials constituting the first electrode 101b, the second electrode 102b, and the intermediate electrode 120b may be the same or different.

In the oxygen sensor 1b, an electrode opposing member 50 is disposed to face the intermediate electrode 120b. In Fig. 7, the electrode opposing member 50 is depicted as a flat plate-shaped member. In Fig. 7, the electrode opposing member 50 and the intermediate electrode 120b are shown in close contact with each other without any gaps, but this is not limited thereto, and the electrode opposing member 50 and the intermediate electrode 120b may be disposed with a gap therebetween.

Between the solid electrolyte membrane 100b and the electrode opposing member 50, an annular wall portion 31 is provided. The annular wall portion 31 is provided so as to surround the intermediate electrode 120b. As a result, in the oxygen sensor 1b, the annular wall portion 31 defines a reference oxygen concentration space S between the solid electrolyte membrane 100b and the electrode opposing member 50. In FIG. 7, the reference oxygen concentration space S is defined by the annular wall portion 31, the solid electrolyte membrane 100b, the electrode opposing member 50, and the intermediate electrode 120.

The method of measuring the oxygen concentration in the test gas using the oxygen sensor 1b having the above configuration is as follows. First, the first electrode 101b and the second electrode 102b are arranged so that they face the atmosphere to be measured and the electrode opposing member 50 faces the outside air (generally the atmosphere). In this state, the entire oxygen sensor 1b is heated so that oxide ion conductivity is expressed in the solid electrolyte membrane 100b. As an alternative method, these members may be arranged so that the first electrode 101b faces the atmosphere to be measured and the second electrode 102b and the electrode opposing member 50 face the outside air (generally the atmosphere).

Next, the intermediate electrode 120b is connected to the positive electrode of the DC power supply 40, and the second electrode 102b is connected to the negative electrode of the DC power supply 40. This causes an oxygen pumping action, and oxygen gas is accumulated in the reference oxygen concentration space S. The reference oxygen concentration space S is maintained at a certain pressure, and the reference oxygen concentration is reached, where the partial pressure of oxygen gas is high. Under this condition, the electromotive force generated between the first electrode 101b and the intermediate electrode 120b is measured by the voltmeter 60. Thereafter, the oxygen concentration in the measurement target atmosphere facing the first electrode 101b is calculated according to the Nernst equation, using the same procedure as in the embodiment shown in FIG. 1.

This embodiment also has the advantageous effect of improving measurement accuracy by measuring the concentration of oxygen gas in the measurement target atmosphere with a high reference oxygen concentration. Moreover, the oxygen sensor 1b of this embodiment has the advantage of improving measurement accuracy and shortening the oxygen pumping time.

Figure 8 shows another embodiment of the oxygen sensor shown in Figure 7. The oxygen sensor 1b shown in Figure 8 differs from the oxygen sensor 1 shown in Figure 7 in that the intermediate electrode 120b of the oxygen sensor shown in Figure 7 is divided into a third electrode 103b and a fourth electrode 104b, which are independent of each other. The materials constituting the third electrode 103b and the fourth electrode 104b may be the same or different. The third electrode 103b and the fourth electrode 104b are surrounded by an annular wall portion 31. As a result, in the oxygen sensor 1b, as shown in Figure 8, a reference oxygen concentration space S is defined by the annular wall portion 31, the solid electrolyte membrane 100b, the electrode opposing member 50, the third electrode 103b, and the fourth electrode 104b.

The method for measuring the oxygen concentration in a test gas using the oxygen sensor 1b having the above configuration is as follows. First, the first electrode 101b and the second electrode 102b are arranged so that they face the atmosphere to be measured and the electrode opposing member 50 faces the outside air. In this state, the entire oxygen sensor 1b is heated so that oxide ion conductivity is developed in the solid electrolyte membrane 100b.

Next, the fourth electrode 104b is connected to the positive electrode of the DC power supply 40, and the second electrode 102b is connected to the negative electrode of the DC power supply 40. This causes an oxygen pumping action, and oxygen gas is accumulated in the reference oxygen concentration space S. Under this condition, the electromotive force generated between the first electrode 101b and the third electrode 103b is measured by the voltmeter 60. Thereafter, the oxygen concentration in the measurement target atmosphere facing the first electrode 101b is calculated according to the Nernst equation in the same procedure as in the embodiment shown in FIG. This embodiment also has the advantageous effect of improving the measurement accuracy by measuring the concentration of oxygen gas in the measurement target atmosphere with the reference oxygen concentration increased.

The oxygen sensors 1, 1a, and 1b of the above-described embodiments can be made smaller and more compact due to their structure, allowing for a significant reduction in power consumption. Therefore, the oxygen sensors 1, 1a, and 1b can be equipped with a micro-mechanical electrical device (MEMS). This makes it possible to measure the concentration of oxygen gas in a small space by mounting the oxygen sensor on a mobile device such as a personal computer or a mobile terminal.

According to the present invention, an oxygen sensor capable of measuring the oxygen concentration in a test gas with high accuracy is provided. Also, according to the present invention, an oxygen sensor capable of being miniaturized is provided.

Claims (10)

a first membrane electrode assembly including a first solid electrolyte membrane having oxide ion conductivity and a first electrode disposed on one surface of the solid electrolyte membrane;
a second membrane electrode assembly including a second solid electrolyte membrane having oxide ion conductivity and a second electrode disposed on one surface of the solid electrolyte membrane;
the first membrane electrode assembly and the second membrane electrode assembly are arranged such that the one surface of the first solid electrolyte membrane in the first membrane electrode assembly and the one surface of the second solid electrolyte membrane in the second membrane electrode assembly face each other with a gap therebetween;
an intermediate electrode is disposed so as to be in contact with both the one surface of the first solid electrolyte membrane in the first membrane electrode assembly and the one surface of the second solid electrolyte membrane in the second membrane electrode assembly, and a reference oxygen concentration space is defined by an oxygen-permeable wall portion provided so as to surround the intermediate electrode,
An oxygen sensor configured to measure the oxygen concentration in the atmosphere to be measured facing the first electrode by arranging the first electrode facing the atmosphere to be measured and the second electrode facing the atmosphere to be measured or the outside air, connecting the intermediate electrode to the positive terminal of a power source and connecting the second electrode to the negative terminal of a power source to create a state in which the oxygen concentration in the reference oxygen concentration space is increased, and measuring the electromotive force generated between the first electrode and the intermediate electrode. The oxygen sensor according to claim 1, wherein at least one of the first solid electrolyte film and the second solid electrolyte film is made of a compound containing A, M, and O (A is one or more elements selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Be, Mg, Ca, Sr, and Ba. M is one or more elements selected from the group consisting of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Y, Zr, Ta, Nb, B, Si, Ge, Zn, Sn, W, and Mo.) At least one of the first solid electrolyte membrane and the second solid electrolyte membrane has a general formula: _A9.33+x [ _{T6.00- yMy} ] _O26.0+z (wherein A is one or more elements selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Be, Mg, Ca, Sr, and Ba. T is an element containing Si or Ge, or both. M is Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Y, Zr, Ta, Nb, B, Ge, Zn, and x in the formula is a number that is equal to or greater than -1.33 and equal to or less than 1.50, y in the formula is a number that is equal to or greater than 0.00 and equal to or less than 3.00, and z in the formula is a number that is equal to or greater than -5.00 and equal to or less than 5.20, and the ratio of the number of moles of A to the number of moles of T is 1.33 or greater and 3.61 or less. The oxygen sensor according to claim 1, 2 or 3, wherein at least one of the first electrode, the second electrode and the intermediate electrode is made of an oxide. The oxygen sensor according to claim 3, wherein the compound represented by the general formula: A _9.33+x [T _6.00-y M _y ]O _26.0+z is an oriented apatite-type oxide ion conductor, and has a degree of orientation of 0.6 or more as measured by the Lotgering method. The oxygen sensor according to claim ₄ , wherein the oxide has a perovskite structure represented by MNO3 (M is one or more elements selected from the group consisting of Ca, Sr, Ba, La, Pr and Y, and N is one or more elements selected from the group consisting of Ni, Ti, Zr, V, Cr, Mn, Fe, Cu, Co, Mo, Ta, Nb, Ru, Pd and Re). An oxygen sensor according to any one of claims 1 to 6, which measures oxygen concentration under conditions in which the pressure (Pa) of the reference oxygen concentration space is set to 1.0 to 3.0 Pa compared to the atmospheric pressure (Pa) in the measurement target atmosphere. An oxygen sensor according to any one of claims 1 to 7, in which the oxygen concentration in the reference oxygen concentration space is set to 60% or more and 100% or less, and the oxygen concentration is measured. A micromechanical electrical element comprising an oxygen sensor according to any one of claims 1 to 8. A method for measuring oxygen concentration using an oxygen sensor according to any one of claims 1 to 8.

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