JP4115014B2 - Hydrogen gas sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydrogen gas sensor that measures the hydrogen concentration in a gas based on the concentration of hydrogen gas.
[0002]
[Prior art]
The measurement principle of the hydrogen gas concentration cell type hydrogen gas sensor is described in “New Ceramics (1996) No. 11”. That is, in this document, two gas chambers are provided using a solid electrolyte CaZr _0.9 In _0.1 O ₃ -α exhibiting proton conductivity as a partition, a gas with a high hydrogen partial pressure is provided in one gas chamber, and the other gas is provided. By introducing a low hydrogen partial pressure gas to be measured into the chamber, a reaction occurs in which hydrogen is separated into protons and electrons on the high hydrogen gas partial pressure side, and an opposite reaction occurs on the low hydrogen gas partial pressure side. The electromotive force at this time is given by Nernst's equation: E = (RT / 2F) ln [P _H2 (1) / P _H2 (2)]. Where E is the electromotive force (V), R is the gas constant, F is the Faraday constant, T is the absolute temperature (K), P _H2 (1) is the high hydrogen partial pressure on the negative electrode side, and P _H2 (2) is the positive electrode The low hydrogen partial pressure on the side.
[0003]
Therefore, when the electromotive force E is measured, the ratio of the hydrogen partial pressures of the two gas chambers separated by the solid electrolyte is obtained, and if the hydrogen partial pressure of one of the gas chambers is kept known, the other is obtained from the electromotive force and the temperature. The hydrogen partial pressure in the measurement gas in contact with the measurement gas introduced into the gas chamber is determined. Using this measurement principle, a hydrogen sensor for molten metal has already been put into practical use.
[0004]
[Problems to be solved by the invention]
However, when a hydrogen gas sensor is configured by the method described in the above document, it is necessary to prepare a reference hydrogen gas with a known hydrogen partial pressure in a tank or the like in advance and supply it to one gas chamber, which complicates the sensor configuration. There was a fault to become.
An object of the present invention is to provide a hydrogen gas sensor that does not require reference hydrogen gas.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, the inventors of the present invention have made various studies and considered that the hydrogen concentration can be measured from the hydrogen partial pressure of the measurement gas by generating the reference hydrogen gas from the measurement gas, thereby completing the present invention. It came to.
That is, the hydrogen gas sensor of the present invention is a solid having proton conductivity formed between the first electrode and the second electrode, and the first electrode and the second electrode, which are in contact with the measurement gas containing hydrogen to be measured. An electrolyte part for a hydrogen pump comprising an electrolyte and a DC voltage source connected between the first electrode and the second electrode; a third electrode and a fourth electrode in contact with a measurement gas containing hydrogen to be measured; and A hydrogen partial pressure pumped by the hydrogen pump unit comprising a solid electrolyte having proton conductivity formed between the third electrode and the fourth electrode, and a hydrogen partial pressure of the measurement gas in contact with the third electrode; A measurement electrolyte portion that generates a difference between the third electrode and the fourth electrode as an electromotive force, and an electromotive force measurement unit connected between the third electrode and the fourth electrode, and the hydrogen pump electrolyte. Front of solid electrolyte The solid electrolyte of the electrolyte part for measurement is formed into an integral rod shape by embedding a wire material in which the second electrode and the fourth electrode are formed as one electrode along the length direction, and the outer periphery of both ends thereof Wherein the first electrode and the third electrode are formed .
[0006]
[Action]
In the hydrogen gas sensor of the present invention, hydrogen in the measurement gas is pumped by the hydrogen pump electrolyte unit, and the pumped hydrogen is collected near the third electrode of the measurement electrolyte unit as a reference gas having a known hydrogen partial pressure. Since the measurement gas is in contact with the third electrode of the measurement electrolyte part, an electromotive force corresponding to the difference between the hydrogen partial pressure of the generated reference gas gathered and contacted in the vicinity of the fourth electrode and the hydrogen partial pressure in the measurement gas Is measured by the electromotive force measuring means, and the hydrogen concentration in the measurement gas can be measured.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The solid electrolyte of the electrolyte part for hydrogen pump and the solid electrolyte of the electrolyte part for measurement are perovskite protons having a composition such as SrCeYb _0.95 O ₃ -α, BaCe _0.9 Nd _0.1 O ₃ -α, CaZr _0.9 In _0.1 O ₃ -α, etc. It is preferable to use a conductive solid electrolyte.
[0008]
Each electrode is preferably a metal having excellent electrical conductivity such as Pt, Au, Fe, Cu, Zn, Cn, and Mo. The same metal is used for the lead wire connecting the DC voltage source between the first electrode and the second electrode and the lead wire connecting the electromotive force measuring means between the third electrode and the fourth electrode.
The formation of the first electrode and the second electrode on the electrolyte part for the hydrogen pump and the formation of the third electrode and the fourth electrode on the solid electrolyte part for measurement are each made of a solid electrolyte of about 15 mm in diameter and about 0.5 mm in thickness. What is necessary is just to press-form into a disk shape, apply | coat and sinter a paste-form electrode material about 8 mm in diameter on the front and back of this disk-shaped solid electrolyte.
[0009]
As the DC voltage source, a DC stabilized power supply device such as a potentiostat can be used. The positive electrode of the DC voltage source is connected to the first electrode of the hydrogen pump electrolyte part, and the negative electrode of the DC voltage source is connected to the second electrode of the hydrogen pump electrolyte part. As a result, a hydrogen pumping action is generated in the solid electrolyte of the electrolyte part for the hydrogen pump.
A reference gas chamber for storing hydrogen gas pumped by the hydrogen pump electrolyte unit may be provided between the hydrogen pump electrolyte unit and the measurement electrolyte unit. By accumulating the hydrogen gas pumped in the reference gas chamber in this way, there is an advantage that the hydrogen partial pressure of the reference gas is stabilized. However, the reference gas chamber for storing the pumped hydrogen gas needs to be provided with a predetermined ventilation means so that the gas is vented when a certain hydrogen partial pressure is accumulated.
[0010]
The second electrode and the fourth electrode can be formed as one electrode. That is, it has a five-layer structure in which one electrode that functions as the second electrode and the fourth electrode is sandwiched between the solid electrolyte in the hydrogen pump electrolyte part and the solid electrolyte in the measurement electrolyte part.
The solid electrolyte of the electrolyte part for the hydrogen pump and the solid electrolyte of the measurement electrolyte part are formed in a rod shape in which the second electrode and the fourth electrode are integrally formed along the length direction, You may form a 1st electrode and a 3rd electrode in the outer periphery of the both ends.
[0011]
The rod-shaped solid electrolyte composed of the solid electrolyte in the hydrogen pump electrolyte part and the measurement electrolyte part may have a diameter of about 5 mm and a length of about 30 mm. The integrated second electrode and fourth electrode are wires having a diameter of about 0.3 mm.
In a hydrogen gas sensor with a solid electrolyte as a rod, the portion of the solid electrolyte where the pumped hydrogen moves away from the portion of the solid electrolyte where the measurement hydrogen moves, so the applied voltage affects the electromotive force measurement. Difficult to measure accuracy.
[0012]
As the electromotive force measuring means, a voltmeter such as an electrometer is used.
[0013]
【Example】
Reference examples and examples of the present invention will be shown to describe the present invention more specifically.
(First reference example)
As shown in the cross-sectional view of FIG. 1, the hydrogen gas sensor of the first reference example has a ring-shaped housing 1 made of alumina, and a disc-shaped disk having proton conductivity respectively fitted in a through hole of the housing 1. A solid electrolyte 2, 3, an alumina spacing ring 4 interposed on the outer edge side of the solid electrolyte 2 and the solid electrolyte 3 so that the solid electrolyte 2 and the solid electrolyte 3 overlap with each other at a distance; A first electrode 5 formed on the surface where the middle upper solid electrolyte 2 is in contact with the outside; a second electrode 6 formed on the back surface of the solid electrolyte 2 facing away from the first electrode 5; The third electrode 7 formed on the surface in contact with the outside of the solid electrolyte 3, the fourth electrode 8 formed on the back surface of the solid electrolyte 3 facing away from the third electrode 7, the first electrode 5 and the second electrode A DC voltage source 10 connected between the electrodes 6 via a lead wire 9; 7 and the fourth electrode 8 are connected to the electromotive force measuring means 12 via the lead wire 11, the spacing ring 4, the solid electrolyte 2 and the solid electrolyte 3, and the housing 1. An inorganic adhesive 13 to be fixed and a glass seal 14 attached to the surface of the inorganic adhesive 13 by means of coating, application, or the like are provided.
[0014]
The first electrode 5, the second electrode 6, the solid electrolyte 2 and the DC voltage source 10 constitute the hydrogen pump electrolyte section 15 of the present invention, and the third electrode 7, the fourth electrode 8, the solid electrolyte 3 and the electromotive force measurement. The means 3 constitutes the measurement electrolyte part 16. Further, a reference gas chamber 17 having the wall surface of the solid electrolyte 2, the solid electrolyte 3 and the spacing ring 4 is formed by the spacing ring 4 interposed between the solid electrolyte 2 and the solid electrolyte 3. The reference gas chamber 17 communicates with the outside through a vent hole 17 a penetrating the inorganic adhesive 13 from the spacing ring 4 and penetrating the housing 1.
[0015]
The DC voltage source 10 used a potentiostat, and the electromotive force measuring means 12 used an electrometer. The DC voltage source 10 has a positive electrode connected to the first electrode 5 and a negative electrode connected to the second electrode 6. The positive electrode of the electromotive force measuring means 12 is connected to the third electrode 7 and the negative electrode is connected to the fourth electrode 8.
As the solid electrolytes 2 and 3, SrCeYb _0.95 O ₃₋ α, which is a perovskite type proton conductive solid electrolyte, was press-molded into a disk shape having a diameter of 15 mm and a thickness of 0.5 mm. Each of the electrodes 5 to 8 was formed by baking Pt at a central portion of the solid electrolytes 2 and 3 to a diameter of 8 mm. As the lead wires 9 and 11, Pt wires having a diameter of 0.3 mm were used.
[0016]
The hydrogen gas sensor of the first reference example having the above configuration measures the hydrogen concentration in the measurement gas by exposing the whole to the measurement gas. When the hydrogen gas sensor is exposed to the measurement gas, the first electrode 5 surface side of the solid electrolyte 2 and the third electrode 7 surface side of the solid electrolyte 3 come into contact with the measurement gas. Since the positive voltage of the DC voltage source 10 is applied to the first electrode 5, when the measurement gas comes into contact with the first electrode 5, hydrogen in the measurement gas becomes protons near the first electrode 5 of the solid electrolyte 2. And generate electrons. The proton moves through the solid electrolyte 2 and reaches the second electrode 6 facing away from the first electrode 5. On the other hand, the electrons pass through the lead wire 9 connecting the first electrode 5 and the second electrode 6, and reach the second electrode 6 through the DC voltage source 10. Then, protons and electrons that reach the second electrode 6 react to generate hydrogen having a known hydrogen partial pressure proportional to the voltage value generated by the DC voltage source 10. The generated hydrogen is accumulated in the reference gas chamber 17. The hydrogen accumulated in the reference gas chamber 17 escapes to the outside through the vent hole 17a so as not to exceed a certain pressure after a certain period of time has elapsed since the start of energization. Thereby, the hydrogen partial pressure in the reference gas chamber 17 is kept constant.
[0017]
The production reference gas having the hydrogen partial pressure is in contact with the fourth electrode 8, and the fourth electrode 8 on the high hydrogen partial pressure side is caused by the difference from the hydrogen partial pressure in the measurement gas in contact with the third electrode 7. An electromotive force represented by the Nernst equation is generated between the third electrode 7 and the negative electrode. Therefore, by measuring this electromotive force by the electromotive force measuring means 12, the hydrogen concentration in the measurement gas can be known.
[0018]
FIG. 2 is a characteristic diagram of electromotive force when the voltage value of the DC voltage source 10 is changed to 2 V, 3 V, and 5 V, and the hydrogen partial pressure of the measurement gas is changed at each voltage value. The vertical axis represents the electromotive force (mV), and the horizontal axis represents the logarithm of the hydrogen partial pressure of the measurement gas. This characteristic diagram shows that the slope of the electromotive force characteristic with respect to the logarithmic change of the hydrogen partial pressure increases as the voltage value increases. The closer the slope is to the slope of the theoretical electromotive force characteristic indicated by the Nernst equation indicated by the dotted line, the more accurate measurement is possible.
[0019]
According to the experimental results shown in FIG. 2, the difference in the hydrogen partial pressure of the generated reference gas with respect to the hydrogen partial pressure of the measurement gas is increased by increasing the voltage value of the DC voltage source 10 from 2V to 3V and 3V to 5. It can be seen that a change in the hydrogen partial pressure of the measurement gas can be considered as a larger change in electromotive force.
However, the voltage value of the DC voltage source 10 is not necessarily high in all cases, and is set to a voltage value in a range where a clear electromotive force change appears according to the hydrogen concentration of the measurement gas.
[0020]
(Second reference example)
As shown in FIG. 3, the hydrogen gas sensor of the second reference example has one disk-shaped solid electrolyte 21, a first electrode 5 formed on one surface of the solid electrolyte 21, and the first electrode 5 is opposite to the first gas electrode 5. The solid electrolyte 21 is divided into a solid electrolyte portion 18 for hydrogen pump and a solid electrolyte portion 19 for measurement at the center position in the thickness direction of the solid electrolyte 21 and the third electrode 7 formed on the surface of the solid electrolyte 21. A disc-shaped porous Pt intermediate electrode 20 embedded in the manner described above, a DC voltage source 10 connected between the first electrode 5 and the intermediate electrode 20 via a Pt lead wire 9, An electromotive force measuring means 12 connected between the third electrode 7 and the intermediate electrode 20 via a lead wire 11 made of Pt is provided.
[0021]
The intermediate electrode 20 is formed by integrating the second electrode 6 and the fourth electrode 8 of the first reference example. That is, in the hydrogen gas sensor of the second reference example, the solid electrolyte 2 of the hydrogen pump electrolyte part 15 and the solid electrolyte 3 of the measurement electrolyte part 16 in the first reference example are formed in a disk shape as one solid electrolyte 21, The intermediate electrode 20 is sandwiched at the center position in the thickness direction of the solid electrolyte 21 and is integrally sintered.
[0022]
In the present embodiment a slight gap corresponding to the reference gas chamber 17 of the first reference example is formed in the interface between the intermediate electrode 20 and the solid electrolyte 21 for example in the manufacturing process, the gap is the same solid and first reference example The electrolyte 21 communicates with each other through a vent 21a.
The hydrogen gas sensor was manufactured as follows. The material of the solid electrolyte 21 was a perovskite type proton conductive solid electrolyte SrCeYb _0.95 O _3-α as in the first reference example, and had a diameter of 15 mm and a thickness of 3 mm. The intermediate electrode 20 had a diameter of 8 mm and was embedded in the solid electrolyte 21 when the solid electrolyte 21 was press-molded. Thereafter, the first electrode 5 and the third electrode 7 were attached to the solid electrolyte 21 by sintering. When the entire hydrogen gas sensor cools after sintering, a gap corresponding to the reference gas chamber 17 is formed due to the difference in thermal expansion coefficient between the Pt intermediate electrode 20 and the solid electrolyte 21.
[0023]
In the hydrogen gas sensor of the second reference example, the hydrogen pumped by the DC voltage source 9 moves through the solid electrolyte part 18 and collects as a reference gas having a known hydrogen partial pressure in the vicinity of the intermediate electrode 20. An electromotive force using the intermediate electrode 20 as a negative electrode is generated by a gas partial pressure difference between hydrogen in the vicinity of the intermediate electrode 20 and hydrogen in the measurement gas in contact with the third electrode 7. Also in the hydrogen gas sensor having such a configuration, an electromotive force characteristic similar to that in FIG. 2 was obtained.
[0024]
( Example )
As shown in FIG. 4, the hydrogen gas sensor of the embodiment is formed on a rod-shaped solid electrolyte 22, a linear intermediate electrode 23 embedded in the axial center position of the solid electrolyte 22, and both ends of the solid electrolyte 22. The first electrode 24 and the third electrode 25, the DC voltage source 10 connected between the first electrode 24 and the intermediate electrode 23 via the lead wire 9 made of Pt, and the third electrode 25 and the intermediate electrode 23 And an electromotive force measuring means 12 connected via a lead wire 11 made of Pt.
[0025]
As the rod-shaped solid electrolyte 22, SrCeYb _0.95 O _3- α having a diameter of 5 mm and a length of 30 mm was used. The intermediate electrode 23 is a porous Pt wire, and is inserted into the axial center position of the rod-shaped solid electrolyte 22. The first electrode 24 and the third electrode 25 were each wound around the outer periphery of both ends of the solid electrolyte 22 in a band shape having a width of 5 mm and sintered. Also in the hydrogen gas sensor of this embodiment, a gap corresponding to the reference gas chamber 17 is formed at the interface between the intermediate electrode 23 and the solid electrolyte 22 during the manufacturing process, and the gap communicates with the outside through the vent hole 22a.
[0026]
Also in the hydrogen gas sensor having such a configuration, hydrogen is pumped in the vicinity of the intermediate electrode 23 by the voltage applied between the intermediate electrode 23 and the first electrode 24 as in the second reference example. It was found that an electromotive force was generated due to a gas partial pressure difference with hydrogen in the measurement gas in contact with the three electrodes 25.
FIG. 5 shows the electromotive force characteristics measured by the hydrogen gas sensor of the example . According to FIG. 5, when the voltage value of the DC voltage source 10 is set to 0.25 V, 0.50 V, and 0.75 V, the theoretical electromotive force characteristic indicated by the dotted line overlaps very well and the hydrogen concentration can be measured accurately. I understand.
[0027]
FIG. 6 shows the result of measuring the responsiveness by changing the hydrogen concentration of the measurement gas with the hydrogen gas sensor of the example . The hydrogen concentration of the measurement gas was changed to 1.2%, 4.9%, 10.3%, 49.9%, and 100%. An applied voltage of 0.5 mV was applied with the intermediate electrode 20 side being negative. The vertical axis represents electromotive force (unit: mV), and the horizontal axis represents time (unit: sec). It shows that the interface between the electrode 20 and the solid electrolyte 21 is in the same state as the measurement gas before voltage application. When voltage application was started with a hydrogen concentration of 1.2%, the electromotive force changed rapidly and stabilized at approximately 160 mV. When the hydrogen gas concentration of the measurement gas was increased to 4.9%, the electromotive force decreased to 120 mV and stabilized. Similarly, when the hydrogen concentration is increased, the electromotive force also decreases according to the hydrogen concentration, which coincides with the tendency calculated from the electromotive force equation, suggesting that the sensor functions as a sensor.
[0028]
In particular embodiments, compared with the first reference example and the second reference example, since the sites of the solid electrolyte 22 pumping hydrogen is moved, a portion of the solid electrolyte in which hydrogen is moved for measurement are separated, applied The voltage hardly influences the electromotive force measurement, and the measurement accuracy becomes accurate.
[0029]
【The invention's effect】
With the hydrogen gas sensor of the present invention, it is not necessary to use a reference gas whose hydrogen partial pressure is known, and when a constant voltage is applied, the hydrogen partial pressure can be measured in quick response to changes in the hydrogen concentration in the measurement gas. I understood.
In addition, since it is not necessary to use a reference gas with a known hydrogen partial pressure, the supply means is unnecessary, and the configuration is extremely simple, and the portion of the solid electrolyte where the hydrogen for measurement moves is separated from the applied voltage. Is less affected by electromotive force measurement and the measurement accuracy is accurate .
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a hydrogen gas sensor of a first reference example.
FIG. 2 is a characteristic diagram showing electromotive force characteristics of the hydrogen gas sensor of the first reference example.
FIG. 3 is a cross-sectional view showing a hydrogen gas sensor of a second reference example.
FIG. 4 is a cross-sectional view showing a hydrogen gas sensor of an example .
FIG. 5 is a characteristic diagram showing electromotive force characteristics of an example .
FIG. 6 shows the results of measuring the responsiveness by changing the hydrogen concentration of the measurement gas.

Claims (2)

A solid electrolyte having proton conductivity formed between the first electrode and the second electrode, the first electrode, and the second electrode that are in contact with the measurement gas containing hydrogen to be measured, the first electrode, and the first electrode An electrolyte part for a hydrogen pump comprising a DC voltage source connected between two electrodes;
The hydrogen pump electrolyte comprising a third electrode and a fourth electrode that are in contact with a measurement gas containing hydrogen to be measured, and a solid electrolyte having proton conductivity formed between the third electrode and the fourth electrode. An electrolyte part for measurement that generates a difference between a hydrogen partial pressure pumped by the part and a hydrogen partial pressure of a measurement gas contacting the third electrode as an electromotive force between the third electrode and the fourth electrode;
Electromotive force measuring means connected between the third electrode and the fourth electrode ,
In the solid electrolyte of the hydrogen pump electrolyte part and the solid electrolyte of the measurement electrolyte part, a wire material in which the second electrode and the fourth electrode are formed as one electrode is embedded inside along the length direction. The hydrogen gas sensor is characterized in that the first electrode and the third electrode are formed on the outer periphery of both ends .   The hydrogen gas sensor according to claim 1, further comprising a reference gas chamber that stores hydrogen pumped by the hydrogen pump electrolyte.

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