JP4819239B2 - Solid electrolyte type hydrogen / water vapor measuring method and measuring apparatus using hydrogen pump - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method and an apparatus for measuring hydrogen and water vapor using a solid electrolyte having proton conductivity.
[0002]
[Prior art]
As a method for measuring hydrogen using a solid electrolyte having proton conductivity, a method using a hydrogen concentration cell is conventionally known. For example, a conventional hydrogen concentration cell type hydrogen gas measuring apparatus is provided with a reference electrode on one side of a solid electrolyte having proton conductivity, a measurement electrode on the other side facing away, and a hydrogen cylinder on the reference electrode side. It was necessary to supply hydrogen from an external hydrogen source to keep the hydrogen partial pressure on the reference electrode side constant. In other words, the main part of the hydrogen gas measuring device can be miniaturized using a solid electrolyte, but since an external hydrogen source is required, the entire device becomes large and lacks portability or is easy to install in a narrow space. There was a problem of lacking.
[0003]
Recently, a water vapor sensor that does not require an external hydrogen source using a hydrogen pump action as shown in FIG. 6 was reported in Sensors and Actuators, B67, pp189-193 (2000). This is because a cell in which electrodes 22, 23 and 24, 25 are provided on opposite surfaces of two proton conductive solid electrolytes 20, 24 is stacked via a spacer 26, and the region is defined by the spacer 26 and the two cells. 31 has a structure connected to the outside through a hole 27. A DC power supply 28 is connected to the electrodes 22 and 23 via a lead wire 30, and an electrometer 29 is connected to the electrodes 24 and 25 via a lead wire 30. When this water vapor sensor is arranged in air containing water vapor, the electrode 22 (anode) of the upper cell is H ₂ O (in air) → 2H ⁺ +. ^{_{O 2/2 + 2e - (}} 1)
The following reaction occurs. The generated protons pass through the solid electrolyte 20 and reach the electrode 23. In the electrode 23 (cathode), 2H ⁺ + 2e ⁻ → H ₂ (2)
Then, the generated hydrogen is stored in the partition region 31. That is, hydrogen is pumped from the air, the hydrogen partial pressure in the partition region 31 is increased, and since the partition region 31 is connected to the outside through the hole 27, it is saturated with 1 atmosphere of hydrogen. At this point, the lower cell functions as a hydrogen-air fuel cell with the electrode 24 as a reference electrode and the electrode 25 as a measurement electrode, and an electromotive force E represented by the Nernst equation (3) is generated in the electrometer 29. To do.
[0004]
E = (RT / 2F) lnK + (RT / 2F) ln [[PH ₂ (1) PO ₂ (2) 1/2] / PH ₂ O (2)] (3)
Here, R is a gas constant, T is a temperature, K is an equilibrium constant, F is a Faraday constant, PH ₂ (1) is a hydrogen partial pressure on the reference electrode 24 side, and PO ₂ (2) is an oxygen content on the measuring electrode 25 side. The pressure, PH ₂ O (2) is the water vapor partial pressure on the measurement electrode 25 side. In formula (3), PH ₂ (1) is constant at 1 atm, and the solid electrolyte 24 does not allow oxygen ions to pass therethrough. Therefore, the electromotive force E changes only at the water vapor partial pressure PH ₂ O (2) on the measurement electrode 25 side. As a result, water vapor can be measured. However, this conventional water vapor sensor requires a cell composed of two solid electrolytes and two circuits (a DC application circuit and an electromotive force measurement circuit), is complicated, has a problem that it cannot be downsized and is expensive. ing.
[0005]
[Problems to be solved by the present invention]
The present invention does not require an external hydrogen source and two solid electrolyte cells and two circuits, that is, a single cell and one circuit, and a hydrogen / water vapor measuring method suitable for miniaturization and cost reduction, and It aims at providing a measuring device.
[0006]
[Means for Solving the Problems]
In the hydrogen / water vapor measuring method according to the present invention, which solves the above problem, a battery is connected between a solid electrolyte having proton conductivity, a reference electrode provided on one surface thereof, and a measuring electrode provided on the other surface thereof. A method for forming and measuring hydrogen or water vapor, the first step of pumping hydrogen by applying a direct current between the reference electrode and the measurement electrode, and an electromotive force between the reference electrode and the measurement electrode And a step of pumping hydrogen from the measurement electrode side to the reference electrode side so that the hydrogen partial pressure on the reference electrode side is a constant value larger than zero. It is characterized by being.
[0007]
A hydrogen / water vapor measuring apparatus according to the present invention that has solved the above problems includes a solid electrolyte having proton conductivity, a reference electrode provided on one surface of the solid electrolyte and having a shield that is isolated from the atmosphere to be measured, A measuring electrode provided on the other surface of the solid electrolyte facing the reference electrode and in contact with the atmosphere to be measured; a voltage applying means and an electromotive force measuring means connected to the reference electrode and the measuring electrode; Ri, the reference electrode is characterized that you have connected to the measuring atmosphere hole.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The solid electrolyte having proton conductivity is a perovskite type based on SrCeO ₃ or CaZrO ₃ , and a part of Ce and Zr is a rare earth element (Sc, Y, La, Nd, Sm, Eu, Gd, Dy, Ho, 1 to 30 mol% substituted solid solution with one or more elements selected from the group consisting of Yb).
[0009]
The reference electrode and the measurement electrode can be formed by a normal PVD method or CVD method. However, a paste of Ni, Pt, Au or the like is applied to the surface of the solid electrolyte and baked at 800 ° C. or higher in a reducing atmosphere (paste application) Is preferable because it forms a porous film and facilitates the entry of hydrogen gas. In the case of a metal that is difficult to oxidize, such as Pt or Au, it may be baked in the air.
[0010]
The reference electrode has a shield and is isolated from the measured atmosphere. A shield in which the entire outer surface of the reference electrode formed on the solid electrolyte is covered with glass or the like may be used, but a shield in which the reference electrode is sandwiched with a dielectric substrate and the outer peripheral end is fused with glass or the like may be used. The latter is more advantageous in that cracks due to thermal shock can be avoided by using a material having the same thermal expansion coefficient as the solid electrolyte for the substrate.
[0011]
In the case of the hydrogen / water vapor measuring method in which the first step of pumping hydrogen is a step of pumping hydrogen from the measuring electrode in contact with the measured atmosphere to make the hydrogen partial pressure of the reference electrode isolated from the measured atmosphere constant. A current is applied by applying a DC voltage so that the measurement electrode in contact with the measured atmosphere is an anode and the reference electrode isolated from the measured atmosphere is a cathode. The applied voltage is 1 V or higher, preferably 2 V or higher. This is because the hydrogen partial pressure pumped to the reference electrode side becomes constant at 2 V or more.
[0012]
In the case of the hydrogen / water vapor measurement method in which the first step of pumping hydrogen is a step of pumping hydrogen from a reference electrode isolated from the measurement atmosphere to make the hydrogen partial pressure of the reference electrode constant, A direct current is applied and a current is applied so that the measurement electrode in contact is a cathode and the reference electrode isolated from the measurement atmosphere is an anode.
[0013]
In the second step of measuring the electromotive force, a battery is formed between the reference electrode and the measurement electrode, and the electromotive force is measured with an electrometer connected to both electrodes.
[0014]
The battery functions as a hydrogen concentration cell when the hydrogen gas partial pressure on the measurement electrode side and the hydrogen gas partial pressure on the reference electrode side are different, and an electromotive force proportional to the hydrogen gas partial pressure of the measurement atmosphere in contact with the measurement electrode Is generated. In addition, the battery functions as a hydrogen-air fuel cell when the measurement atmosphere in contact with the measurement electrode is wet air, that is, air containing water vapor, and generates an electromotive force proportional to the water vapor partial pressure.
[0015]
The first step of pumping hydrogen and the second step of measuring electromotive force may be performed alternately or simultaneously. When alternately performed, the DC voltage application time in the first step is linked to the electromotive force measurement time in the second step, and if the application time is long, the measurement time can be extended. For example, when the application time is 2 seconds, the measurement time is 10 seconds. By repeating voltage application and electromotive force measurement for a certain period of time, hydrogen and water vapor can be measured continuously.
[0016]
A solid electrolyte having proton conductivity, a reference electrode provided on one side of the solid electrolyte and having a shield isolated from the atmosphere to be measured, and provided on the other side of the solid electrolyte facing the reference electrode And a solid electrolyte type hydrogen measuring apparatus using a hydrogen pump, characterized by comprising: a measuring electrode in contact with an atmosphere to be measured; a reference electrode; a voltage applying means connected to the measuring electrode; and an electromotive force measuring means. In this case, the voltage applying means only needs to be able to supply a current by applying a DC voltage, and a normal DC power supply or battery can be used. The electromotive force measuring means may be a commercially available electrometer. The reference electrode having a shield may be connected to the measured atmosphere through a hole.
[0017]
[Action]
The solid electrolyte type hydrogen / water vapor measuring method and measuring apparatus using a hydrogen pump according to the present invention comprises a hydrogen pump action in a first step and an electromotive force generation action in a second step.
[0018]
The hydrogen pump action in the first step functions by applying a direct current between a measurement electrode that is in contact with the measurement atmosphere and a reference electrode that is isolated from the measurement atmosphere. When applying DC voltage so that the measurement electrode in contact with the measurement atmosphere is an anode and the reference electrode isolated from the measurement atmosphere is a cathode, the measurement electrode is wet air and the measurement electrode is expressed by equation (1). When the atmosphere to be measured is a gas containing hydrogen, H ₂ → 2H ⁺ + 2e ⁻ (4)
The following reaction occurs and protons are generated. The generated protons pass through the solid electrolyte and reach the reference electrode, and the reaction of the formula (2) occurs to generate hydrogen. That is, hydrogen is pumped from the measurement electrode side to the reference electrode side, and the hydrogen partial pressure on the reference electrode side is increased and saturated. When a DC voltage is applied so that the measurement electrode in contact with the atmosphere to be measured is a cathode and the reference electrode isolated from the atmosphere to be measured is an anode, a reaction represented by the equation (4) occurs at the reference electrode, and protons Is generated. The generated proton passes through the solid electrolyte and reaches the measurement electrode, and the reaction of the formula (2) occurs to generate hydrogen. That is, hydrogen is pumped from the reference electrode side to the measurement electrode side, and the hydrogen partial pressure on the reference electrode side is reduced to a constant value.
[0019]
The electromotive force generation action of the second step is to function as a battery by connecting an electrometer between the reference electrode and the measurement electrode when the hydrogen partial pressure on the reference electrode side increases or decreases, and generates an electromotive force. . That is, when the atmosphere to be measured is wet air, it functions as a hydrogen-air fuel cell, and an electromotive force expressed by the equation (3) is generated. When the measurement atmosphere is a gas containing hydrogen, it functions as a hydrogen concentration cell, and the electromotive force is proportional to the hydrogen gas partial pressure PH ₂ (2) of the measurement atmosphere in contact with the measurement electrode.
E = (RT / 2F) ln [PH ₂ (1) / PH ₂ (2)] (5)
Is generated.
[0020]
【Example】
Hereinafter, the present invention will be described specifically by way of examples.
[0021]
Example 1
Example 1 is a hydrogen gas measuring device, the device configuration is shown in FIG. 1, the change in terminal voltage is shown in FIG. 3, and the relationship between hydrogen gas partial pressure and electromotive force is shown in FIG.
[0022]
This hydrogen gas measuring apparatus has a measurement electrode 2 formed on the upper surface of a solid electrolyte 1 having proton conductivity, a reference electrode 3 formed on the lower surface, the reference electrode 3 sandwiched by a substrate 4a, and a glass 4b having a peripheral edge as a shielding material. It is welded with. That is, the substrate 4a and the shield material 4b constitute the shield 4 to isolate the reference electrode 3 from the outside. The measurement electrode 2 is connected to the minus of a DC power source 5 as a voltage applying means via a switch 7, and the reference electrode 3 is connected to the plus through a lead wire 8. Further, an electrometer 6 as electromotive force measuring means is connected to the measurement electrode 2 and the reference electrode 3 in parallel with the DC power source 5.
[0023]
The solid electrolyte 1 is a dense ceramic disk having a composition of SrCe _0.95 Yb _0.05 O ₃₋ α, a diameter of 14.5 mm, and a thickness of 0.5 mm. Since the measurement electrode 2 and the reference electrode 3 are porous electrodes, porous Pt is bonded to the upper and lower surfaces of the solid electrolyte 1. Both electrodes have an area of 0.6 cm ² . The substrate 4a is made of the same material as that of the solid electrolyte 1 and has the same thermal expansion coefficient. This is to prevent damage due to thermal shock. The lead wire 8 is a Pt wire, and is connected to the measurement electrode 2 and the reference electrode 3 with a solder paste.
[0024]
While supplying a voltage of 2 mA from the DC power source 5 between the measuring electrode 2 and the reference electrode 3 and pumping hydrogen, the electromotive force response and the terminal voltage are changed with the electrometer 6 by changing the hydrogen concentration in the atmosphere to be measured at 700 ° C. The change of was measured. It can be seen that the present hydrogen gas measuring device responds quickly to changes in the hydrogen concentration (response speed ˜50 sec). FIG. 4 is a rewrite of FIG. 3 with the electromotive force on the vertical axis and the hydrogen concentration on the horizontal axis. It can be seen that the electromotive force is proportional to the logarithm of the hydrogen partial pressure and hydrogen gas can be measured.
[0025]
Example 2
Example 2 is a water vapor measuring apparatus operating in wet air. FIG. 2 shows the apparatus configuration, and FIG. 5 shows the relationship between electromotive force and water vapor partial pressure.
[0026]
In the water vapor measuring apparatus of this embodiment, the shield 4 is connected to the atmosphere to be measured through the hole 9 having a diameter of 20 μm, the plus of the DC power source 5 as the voltage applying means is applied to the measuring electrode 2, and the minus is applied to the reference electrode 3. Are the same as those of the first embodiment except that they are connected by lead wires 7 (the same components as those of the first embodiment are denoted by the same reference numerals and the description thereof is omitted).
[0027]
Turning on the switch 7 and applying a voltage of 2 V from the DC power source 5 between the measuring electrode 2 and the reference electrode 3 to start the hydrogen pump, and measuring the electromotive force with the electrometer 6 after 3 min. The measurement was repeated while changing the water vapor concentration in the atmosphere to be measured. FIG. 5 shows that the electromotive force is proportional to the logarithm of the water vapor partial pressure, so that water vapor can be measured.
[0028]
【effect】
The solid electrolyte gas measuring method and measuring apparatus using the hydrogen pump of the present invention uses the hydrogen pump to make the hydrogen partial pressure on the reference electrode side constant, so that no external hydrogen source is required and the measuring apparatus is compact. Improved portability and portability. In addition, a single solid electrolyte (one cell) with an electrode formed on the back surface measures the electromotive force in proportion to the concentration of the hydrogen pump and the gas to be measured, thereby reducing the size and cost. .
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a hydrogen gas measuring apparatus according to a first embodiment.
2 is a cross-sectional view of a water vapor measuring device according to Embodiment 2. FIG.
FIG. 3 is a graph showing an electromotive force response and a change in terminal voltage of the hydrogen gas measuring device.
4 is a graph showing the relationship between the electromotive force and the hydrogen partial pressure of the hydrogen gas measurement device of Example 1. FIG.
FIG. 5 is a graph showing the relationship between the electromotive force and the water vapor partial pressure of the water vapor measuring device of Example 2.
FIG. 6 is a cross-sectional view of a conventional water vapor sensor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Solid electrolyte which has proton conductivity, 2 ... Measuring electrode, 3 ... Reference electrode, 4 ... Shield, 4a ... Substrate, 4b ... Shield material, 5 ... Voltage application means, 6 ... Electromotive force measuring means, 7 ... Switch, 8 ... Lead wire, 9 ... Hole

Claims (4)

A battery is connected between a solid electrolyte having proton conductivity, a reference electrode provided on one side of the solid electrolyte and isolated from the measurement atmosphere, and a measurement electrode provided on the other side and in contact with the measurement atmosphere. A method of forming and measuring gas,
A first step of pumping hydrogen by applying a direct current between the reference electrode and the measurement electrode;
A second step of measuring an electromotive force between the reference electrode and the measurement electrode;
And the first step is a step of pumping hydrogen from the measurement electrode side to the reference electrode side so that the hydrogen partial pressure on the reference electrode side is a constant value larger than zero. Solid electrolyte type hydrogen / water vapor measurement method using a pump. 2. The method for measuring solid electrolyte hydrogen / water vapor using a hydrogen pump according to claim 1, wherein the battery is a hydrogen concentration battery. 2. The solid electrolyte hydrogen / water vapor measuring method using a hydrogen pump according to claim 1, wherein the battery is a hydrogen-air fuel cell. A solid electrolyte having proton conductivity, a reference electrode provided on one side of the solid electrolyte and having a shield isolated from the atmosphere to be measured, and provided on the other side of the solid electrolyte facing the reference electrode and a measuring electrode in contact with the atmosphere to be measured, and the direct current applying unit and the electromotive force measuring means connected to the reference electrode and the measuring electrode, Ri Tona, Rukoto said reference electrode is not connected to the measuring atmosphere hole Solid electrolyte type hydrogen / water vapor measuring device using a hydrogen pump characterized by

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