JP2007240462A - Gas detecting element, hydrogen sensor, and manufacturing method for gas detecting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas detecting element capable of manufacturing a sensor of simple sensor structure, simple in a manufacturing process, and having a high response speed and high sensitivity, and hydrogen sensor provided with the gas detecting element. <P>SOLUTION: A metal layer containing two kinds or more of metals different in hydrogen storage abilities and hydrogen releasing abilities is provided on a thin film comprising a conductor or a semiconductor provided on a substrate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a gas detection element, and more particularly to a gas detection element for a hydrogen sensor that detects hydrogen gas, a hydrogen sensor including the gas detection element, and a method for manufacturing the gas detection element.

Various gases and humidity sensors using oxide semiconductors such as SnO ₂ , ZnO, TiO ₂ , Fe ₂ O ₃ , and Cr ₂ O ₃ have been put into practical use. Recently, a low-sensitivity, high-sensitivity and high-selectivity sensor in the range of several ppm to ppb has been developed especially for atmospheric environment measurement and odor sensors. On the other hand, technologies for utilizing hydrogen energy sources such as fuel cells are attracting attention, and hydrogen sensors having high sensitivity and high-speed response are required as important components.
A conventional oxide semiconductor hydrogen sensor needs to raise the temperature of a bulk semiconductor sensor to several hundred degrees Celsius at the time of detection, and there are many problems in terms of response speed, safety, and power consumption. In addition, the catalytic combustion type hydrogen sensor using platinum wire and fine particles needs to raise the temperature of the sensor to several hundred degrees Celsius like the oxide semiconductor type hydrogen sensor, which is problematic in terms of response speed, safety and power consumption. In addition, the amount of precious metals such as platinum used is also large. Recently, the combination of hydrogen oxidation / combustion heat and thermoelectric conversion elements on platinum, electrochromism by oxidation / reduction of tungstate, and volume expansion associated with hydrogen absorption of palladium such as metal palladium thin films and palladium nanoparticles. Various new sensors have been reported such as materials that detect hydrogen concentration from changes in electrical conductivity by using the method (see Patent Documents 1 and 2).

Patent Document 1 discloses a hydrogen sensor including a hydrogen detection unit including a non-oxide semiconductor and a hydrogen absorber attached to at least a part of the surface of the semiconductor. This hydrogen sensor detects hydrogen from a resistance value change corresponding to the presence or absence of hydrogen absorption in the hydrogen absorber. By using a non-oxide semiconductor as a semiconductor, it can be used even at room temperature.
Patent Document 2 discloses a hydrogen sensor including a semiconductor mainly composed of titanium oxide having predetermined electrical characteristics. Similar to the hydrogen sensor disclosed in Patent Document 1, this hydrogen sensor can be used even at room temperature.
JP 2005-315700 A JP 2006-003153 A

  However, there are many problems to be solved, such as the complexity and durability of the sensor structure and high sensitivity. The hydrogen sensor disclosed in Patent Document 1 has a low response speed and is not practical. Further, although the hydrogen sensor disclosed in Patent Document 2 can be used at room temperature, the response speed and sensitivity are low. In order to improve these, it is necessary to irradiate ultraviolet rays at a high temperature of 100 ° C. or higher. is there. Therefore, it becomes a complicated structure to make a practical sensor.

  In view of the above problems, the present invention provides a gas detection element capable of manufacturing a sensor having a simple sensor structure and a manufacturing process, and having a high response speed and sensitivity, and a hydrogen sensor including the gas detection element. The purpose is to provide.

  The present inventors improve response speed and sensitivity by providing a metal layer containing two or more kinds of metals having different hydrogen storage capabilities and / or hydrogen release capabilities on a thin film made of a conductor or semiconductor provided on a substrate. As a result, the present invention has been completed. Specifically, the present invention provides the following.

  (1) A gas detection element in which a metal layer containing two or more kinds of metals having different hydrogen storage capabilities and / or hydrogen release capabilities is provided on a thin film made of a conductor or semiconductor provided on a substrate.

  In the conventional gas detection element, a reducing gas such as hydrogen gas peels off oxygen from the semiconductor layer, thereby changing the region where electrons trapped in oxygen remain in the semiconductor layer and charge carriers exist. The operating principle is to change the resistance value of the semiconductor layer. However, the resistance value of the semiconductor layer can be changed by its own temperature change, and the operation principle based on the resistance value change due to the temperature change may operate with higher sensitivity than the conventional operation principle. it can.

  Therefore, according to the invention described in (1), the gas detection element contains a thin film made of a conductor or a semiconductor. By using a conductor or semiconductor as a thin film, the heat of combustion of the metal layer occluded with hydrogen can be transmitted uniformly and at high speed. This makes it possible to operate with higher sensitivity than the conventional operating principle. In addition, by using a thin film, the sensor structure and manufacturing process of the gas detection element can be simplified.

  In addition, the gas detection element further includes a metal layer containing two or more kinds of metals having different hydrogen storage capabilities and / or hydrogen release capabilities. By containing a plurality of kinds of metals having different properties in this way, it becomes possible to easily cause a temperature change of the thin film.

The two or more kinds of metals are preferably a combination of a metal having a high hydrogen storage rate and a metal having a high hydrogen release rate.
By containing a metal with a high hydrogen storage rate, hydrogen in the detection gas can be adsorbed and stored in a short time, so that the temperature of the semiconductor layer can be increased by facilitating combustion with oxygen in the atmosphere on the surface of the semiconductor layer. Can be easily raised. This makes it possible to operate with higher sensitivity than the conventional operating principle.
Moreover, when a metal having a high hydrogen release rate is contained, hydrogen can be released at a relatively early stage when the hydrogen concentration is low. As a result, the response speed can be increased and a quantitative resistance change due to a change in hydrogen concentration can be realized. Therefore, by using these in combination, it is possible to operate with high sensitivity, to increase the response speed, and to develop a change in resistance value having concentration dependency.

  The above two or more kinds of metals are a combination of a metal having a high hydrogen storage rate and a metal having a high hydrogen release rate, but at least one kind of metal is in contact with a combustible gas such as hydrogen gas. It is preferable to cause a combustion reaction (or oxidation exothermic reaction).

The “metal having a high hydrogen storage rate” and the “metal having a high hydrogen release rate” in the present invention are based on the difference in entropy of heat of dissolution and dissolution (ΔS) with respect to the solid solution of hydrogen in the metal. For example, the heat of dissolution and the entropy of dissolution of palladium and platinum are as follows.
Pd: ΔH ₀ = −10 kJ / molH, ΔS ₀ / R = −7 molH
Pt: ΔH ₀ = + 46 kJ / molH, ΔS ₀ / R = −7 molH
(ΔH is the difference in enthalpy, and the above value is a value per mole of hydrogen atoms)
From this, hydrogenation (hydrogen solid solution) is much more likely to occur in palladium.

  (2) The gas detection element according to (1), wherein the two or more kinds of metals are a combination of platinum or an alloy thereof and palladium or an alloy thereof.

  Palladium absorbs hydrogen relatively quickly, and platinum releases hydrogen relatively quickly. Therefore, according to the invention described in (2), palladium or a palladium alloy is used as the metal having hydrogen storage properties, platinum or an alloy thereof is used as the metal having hydrogen releasing properties, and these are used in combination. Thus, it is possible to manufacture a gas detection element with higher sensitivity and higher response speed.

  (3) The element for gas detection according to (1) or (2), wherein the platinum or an alloy thereof is mainly supported on the palladium or an alloy thereof.

  According to the invention of (3), by supporting platinum or an alloy thereof on palladium or an alloy thereof, it is possible to use palladium which is a metal having a high hydrogen storage rate as a reduction active point. As a result, platinum or an alloy thereof can be easily supported on palladium. By supporting the metals in this order, it is possible to manufacture a gas detection element with higher response speed and sensitivity.

  Here, “mainly” means that 50% or more of the total amount of platinum or its alloy is supported on palladium or its alloy. The loading ratio of palladium and platinum is preferably 10: 1 to 1: 5, more preferably 5: 1 to 1: 1 by mass ratio.

  (4) The gas detection element according to any one of (1) to (3), wherein the thin film has a photocatalytic effect.

  According to the invention of (4), since the thin film is a thin film having a photocatalytic action, a metal having a high hydrogen storage rate can be easily supported on the thin film. This makes it possible to simplify the manufacturing process. Here, the “photocatalytic action” refers to an action that causes a catalytic reaction by absorption of light.

  (5) The gas detection element according to any one of (1) to (4), wherein the thin film is a titanium oxide thin film.

  According to the invention of (5), it is possible to promote the photocatalytic reaction by making the thin film a titanium oxide thin film. As a result, it is possible to further promote the loading of the metal having a high hydrogen storage rate, and it is possible to further simplify the manufacturing process.

  (6) The gas detection element according to any one of (1) to (5), a pair of electrodes provided in the gas detection element, a resistance measurement unit that measures a change in resistance value between the electrodes, A hydrogen sensor comprising:

(7) heat capacity of the substrate constituting the gas sensing element is in a 1.8J ^{· K -1 · g} -1 from 0.4J ^{· K -1 · g} -1 at a constant pressure specific heat capacity (6) The hydrogen sensor described.

  (8) The hydrogen sensor according to (6) or (7), wherein the substrate has a heat capacity adjusting means for adjusting a heat capacity on a surface opposite to a surface in contact with the thin film.

  (9) A method for producing an element for gas detection, comprising a step of supporting platinum or an alloy thereof and palladium or an alloy thereof on a thin film made of a conductor or a semiconductor provided on a substrate.

  (10) The gas detection element according to (9), wherein the thin film is a thin film having a photocatalytic action that promotes supporting of the metal.

According to the present invention, for providing a gas detection with improved response speed and sensitivity by providing a metal layer containing two or more kinds of metals having different hydrogen storage capabilities and / or hydrogen release capabilities on a thin film made of a conductor or semiconductor. An element can be provided.
In addition, since the thin film is a thin film having a photocatalytic action, the two or more kinds of metals can be easily supported. This makes it possible to simplify the manufacturing process.

  Hereinafter, embodiments of the present invention will be described.

  The gas detection element according to the present invention includes a substrate, a thin film made of a conductor or a semiconductor provided on the substrate, and a metal layer containing a predetermined metal.

[Gas detection element]
FIG. 1 is a view showing a gas detection element according to this embodiment. In this gas detection element 1, a thin film 20 made of a conductor or a semiconductor is provided on the surface of a substrate 10, and a metal layer 30 containing a predetermined metal is further formed on the thin film 20.

In the present embodiment, a glass substrate having a size of 25 mm × 10 mm × 1 mm was used as the substrate 10. The substrate 10 is not particularly limited as long as it is a flat plate having insulating properties. Specifically, an insulating material such as a glass substrate such as SiO ₂ or a quartz substrate, a ceramic substrate such as Al ₂ O _3, or an Si substrate as an insulating substrate not doped with ions can be used. Further, the heat capacity of the substrate 10 is preferably from 0.4J ^{· K -1 · g} -1 is 1.8J ^{· K -1 · g} -1 at a constant pressure specific heat capacity, 0.5 J · K at constant pressure specific heat capacity More preferably, it is from ⁻¹ · g ⁻¹ to 1.0 J · K ⁻¹ · g ⁻¹ .
The size of the substrate 10 is not particularly limited, but is preferably 10 mm × 5 mm × 1 mm.

In the present embodiment, TiO ₂ is used for the thin film 20. The material of the thin film 20 is not limited as long as it is a conductor or a semiconductor, but is preferably an oxide semiconductor having a photocatalytic action. The oxide semiconductor is made of TiO ₂ , ZnO, SnO, SnO ₂ , Fe ₂ O ₃ , Fe ₃ O ₄ , CeO, Ce ₂ O ₃ , ZrO ₂ , CdS, SiC, rare earth doped alkaline earth titanate. It is preferable to contain at least one selected from the group. Among these, TiO ₂ is preferably used because it has a high reducing action by the photocatalytic reaction.
The thickness of the thin film 20 is preferably thinner than the substrate 10. Specifically, the thickness is preferably 10 nm to 10,000 nm, and more preferably 100 nm to 1000 nm.

In the present embodiment, palladium and platinum are used for the metal layer 30. The metal layer 30 contains a metal having a high hydrogen storage rate and a metal having a high hydrogen release rate. An example of the metal having a high hydrogen storage rate is palladium or an alloy thereof. Examples of the palladium alloy include a co-support with a metal such as Ru, Rh, Au, La, Ti, Zr, Mg, rare earth metal, Ca, and V. Of these, palladium is preferable because it has a high hydrogen storage rate and a large amount of hydrogen storage.
On the other hand, platinum or its alloy is mentioned as a metal with a high hydrogen discharge | release rate. Examples of platinum alloys include co-supports with metals such as Ru, Rh, Au, La, Ti, Zr, Mg, rare earth metals, Ca, and V, as with palladium alloys. Of these, platinum is preferred because of its high hydrogen release rate and high catalytic combustion action.

[Method for manufacturing element for gas detection]
As a method for manufacturing the gas detection element 1 according to this embodiment, first, a semiconductor layer forming composition is applied to the surface of the substrate 10. Examples of the coating method include known methods such as sputtering, vacuum deposition, and dipping. Next, this is fired at 300 to 500 ° C. for 1 to 24 hours to obtain the thin film 20. The thin film 20 may be formed so as to cover the entire surface of the substrate 10 or may be formed so as to cover a part of the surface.
Note that the composition for forming a semiconductor layer refers to a solution obtained by dissolving a metal salt capable of forming an oxide semiconductor in an organic solvent.

Subsequently, a metal layer 30 containing a predetermined metal is formed on the surface of the thin film 20. The metal layer 30 is formed by immersing the substrate 10 in an electrodeposition solution in which a metal salt having a high hydrogen storage rate and a metal salt or organometallic compound having a high hydrogen release rate are dissolved in an organic solvent. Examples thereof include a method in which a predetermined metal is carried on the surface of the thin film 20 by irradiating light, a method in which an electrodeposition solution is applied to the surface of the thin film 20 by a sputtering method, and ultraviolet light is irradiated.
As the electrodeposition solution, an electrodeposition solution containing a metal having a high hydrogen storage rate and a metal having a high hydrogen release rate may be used, or an electrodeposition solution obtained by mixing them may be used.

  As a method of supporting a predetermined metal on the surface of the thin film 20, (1) a method of first supporting a metal having a high hydrogen storage rate and subsequently supporting a metal having a high hydrogen release rate, Examples include a method of supporting a high metal and subsequently a metal having a high hydrogen storage rate, and (3) a method of simultaneously supporting these metals. Among these, the method described in (1) is preferable from the viewpoint of further improving response speed and sensitivity.

  As the ultraviolet light source, a known light source such as a light emitting diode, a laser, a xenon lamp, a mercury lamp, or a black light can be used.

[Hydrogen sensor]
A hydrogen sensor according to the present embodiment includes the above-described gas detection element, electrodes provided on the gas detection element, and resistance measurement means for measuring a change in resistance value between the electrodes. The gas detection element is usually housed in a case in order to avoid the influence of the ambient wind flow and ambient temperature change.
In this embodiment, in order to improve the sensitivity of the gas detection element, it is preferable to use an electric furnace capable of raising the temperature up to 400 ° C. as a case. The temperature in the electric furnace at the time of detection is preferably 100 ° C. to 400 ° C., more preferably 200 ° C. to 300 ° C. This case also has a gas inlet for introducing the gas to be measured into the case. A gas net or the like is usually provided at the gas inlet to prevent foreign matter from entering the case.
Further, a gas discharge port for leading the gas out of the case is provided on the diagonal line of the gas intake port. Similar to the gas suction port, the gas discharge port is also provided with a wire mesh or the like.

  The pair of electrodes are formed apart from each other at both ends in the longitudinal direction of the gas detection element. These electrodes are preferably formed on the surface of the metal layer. In addition, examples of the material of the electrode include highly conductive metals such as gold, silver, aluminum, and alloys thereof.

  An electrode lead wire is connected to the element electrode of the gas detection element and is pulled out of the case, and a resistance value signal of the semiconductor layer is detected by an external resistance measuring means. When the gas comes into contact with the gas detection element, the temperature rises and the resistance value changes, and the resistance measurement unit converts the resistance value into a hydrogen gas concentration. Examples of the resistance measuring means include known resistance measuring means such as a combination of a constant voltage source and an ammeter, a combination of a constant voltage source / potentiometer and a bridge circuit, a digital multimeter, and an impedance meter.

  When hydrogen gas is detected using this hydrogen sensor, the gas detection element is housed in the case so as not to be affected by external temperature changes as described above, but higher measurement accuracy can be stably obtained. For this purpose, it is preferable to control the gas detection element to a constant temperature by overheating. Therefore, it is preferable that the case is provided with a heating device. Examples of the heating device include an electric furnace, an infrared lamp, a metal containing a resistance heating element, ceramics, plastics, a rubber block / thick film, and the like.

  The substrate further has a heat capacity adjusting means for adjusting the heat capacity of the substrate on the surface opposite to the surface in contact with the thin film. The heat capacity adjusting means is a thin film that is adjusted so that the thermal equilibrium of the substrate is performed smoothly, and preferably has a certain degree of thermal conductivity. Specific examples include brass, aluminum and alloys thereof, metals such as copper, and high thermal conductive ceramics such as aluminum nitride.

  According to this embodiment, by using a semiconductor layer having a photocatalytic action as a gas detection element, a metal (palladium) having a high hydrogen storage rate is easily supported on the surface of the semiconductor layer by a photocatalytic reaction. It became possible. In addition, the supported metal having a high hydrogen storage rate can be used as the reduction active site. As a result, it became possible to easily carry a metal (platinum) having a high hydrogen release rate on a metal having a high hydrogen storage rate. By supporting the metals in this order, it is possible to manufacture a gas detection element with higher response speed and sensitivity.

  In the hydrogen sensor according to the present embodiment, the gas detection element is housed in an electric furnace capable of raising the temperature to a predetermined temperature, thereby detecting the gas without being affected by an external temperature change. It became possible. Further, it is possible to adjust the thermal balance of the substrate by further providing a heat capacity adjusting means for adjusting the heat capacity of the substrate on the surface opposite to the surface in contact with the thin film of the substrate. This makes it possible to manufacture a hydrogen sensor with higher response speed and sensitivity.

[Examples 1 and 2]
A substrate was prepared using a slide glass having an area of 2.5 cm × 1.0 cm for the substrate body. Titanium isopropoxy acetylacetonate {[CH ₃ COCH═C (O—) CH ₃ ] ₂ Ti [OCH (CH ₃ ) ₂ ] -2 propanol solution (TIPAA)} was used as the semiconductor layer forming composition. This was diluted with 2-isopropanol to prepare a Ti concentration of 1.0% by mass.
First, the glass slide was washed with a neutral detergent, rinsed with distilled water, and ultrasonically washed with acetone for 10 minutes to clean the surface. Thereafter, acetone was sufficiently volatilized and removed by drying at room temperature. Next, the slide glass was immersed in the above composition for forming a semiconductor layer (dip coating), pulled up at 5 mm / second, dried at room temperature for 3 minutes, and calcined at 400 ° C. for 10 minutes. This was repeated 5 times. Further, this was baked at 500 ° C. for 8 hours to form a TiO ₂ semiconductor layer to obtain a substrate for the gas detection element according to the present invention. In addition, although the film | membrane was produced on both surfaces of the slide glass at the time of a dip coating, one side was wiped off with ethanol and the semiconductor layer was produced only on one side.

Subsequently, a metal layer is formed by an electrodeposition method. Ethanol was used as a sacrifice for oxidation in a palladium chloride solution diluted with water to obtain a predetermined concentration (20 ppm or 40 ppm) as a metal electrodeposition solution having hydrogen storage properties. Moreover, ethanol was used as an oxidation sacrificial solution in which chloroplatinic acid (H ₂ PtCl ₆ ) was diluted with water to a predetermined concentration (20 ppm or 40 ppm) as a metal electrodeposition solution having hydrogen releasing properties. These electrodeposition solutions were electrodeposited by the following three methods.
(1) A method in which palladium is first supported on a palladium-containing electrodeposition solution and then platinum is supported on a platinum-containing electrodeposition solution (sample 1).
(2) A method of supporting these metals simultaneously (Sample 2).
Further, by using black light as an ultraviolet light source and adjusting the height, irradiation was performed for a predetermined time (15 minutes in total for 30 minutes or 30 minutes) with an ultraviolet light intensity of 3.0 W / m ² .

[Comparative Examples 1 and 2]
A sample was prepared in the same manner as in Examples 1 and 2 except that only palladium was supported by a palladium-containing electrodeposition solution. This was designated as Sample 3. A sample was prepared in the same manner as in Examples 1 and 2, except that only platinum was supported by the platinum-containing electrodeposition solution. This was designated as Sample 4.

The gas responsiveness of the sample obtained by the above method was evaluated.
The electrodes were formed by directly applying silver paste to both ends of the samples 1 to 4 in the longitudinal direction. The gas contact area at this time was 1.5 cm × 1.0 cm as shown below.

  These samples were held in an electric furnace at a set temperature, and hydrogen and air were allowed to flow alternately, or the sensor characteristics were evaluated by varying the hydrogen concentration. The gas flow rate is 100 ml / min in total flow rate. Selection and mixing of the flow gas and adjustment of the flow rate were performed using a gas mixer. Since the gas circulation cycle was set variously depending on the sample, it will be shown each time the result is shown. The resistance value was measured using a digital multimeter. The inflow and outflow ports of the gas in the electric furnace are located on the diagonal line of the electric furnace, and the inflowing gas flows through the entire electric furnace.

  FIG. 2 shows the measurement results of the sensor characteristics (resistance value change due to air dilution hydrogen gas flow) of samples 1 to 4. Both sample 1 (in the figure: triangle data) and sample 2 (in the figure: square data) were more stable than sample 3 (in the figure: diamond data) and sample 4 (in the figure: circle data). Resistance value change was shown. Moreover, it was saturated at a hydrogen concentration of 50%, and thereafter the lower limit value of the resistance value coincided. After the hydrogen concentration of 30%, both samples show almost the same change in resistance value. However, it was shown that the responsiveness of sample 1 was improved over that of sample 2 at a concentration of 10%.

  Moreover, the result of having evaluated the sensor characteristic of the samples 1 and 2 by changing hydrogen concentration is shown in FIG. The resistance of the sample 1 (in the figure: white circle data) in which palladium and platinum are sequentially supported and the sample 2 in which palladium and platinum are simultaneously supported (in the figure: black circle data) are more stable than the thin film alone. Change in value was shown. In addition, the hydrogen concentration was saturated at 50% as before, and thereafter the lower limit value of the resistance value coincided. After the hydrogen concentration of 30%, both samples show almost the same change in resistance value. However, at the concentration of 10%, the response of the sample 1 was improved compared to the sample 2.

  Furthermore, the results of evaluating the sensor characteristics of Samples 1 and 2 in the hydrogen concentration range of 3% to 15% are shown in FIG. Good sensor characteristics were obtained in both samples. The resistance value decreased in proportion to the hydrogen concentration, and thereafter the resistance value became constant at a certain constant value. In addition, the resistance value recovered to the initial resistance value even during air circulation, and it was observed that the resistance value was constant there. In particular, at the low concentration, the resistance value of Sample 2 (black circle data in the figure) did not fall completely in 5 minutes, and the recovery of the resistance value during air circulation started before reaching a constant value, whereas Sample 1 In the figure (white circle data), the resistance value was constant even at a hydrogen concentration of 3%. Since the change in the resistance value of both samples is almost the same after the concentration of 8%, the result of improving the sensor characteristics on the low concentration side by supporting platinum was obtained.

  The results of evaluating the sensor characteristics of Sample 1 and Sample 3 are shown in FIG. From this result, particularly at low concentrations of 3% and 5%, Sample 1 (in the figure: white circle data) has a quick response to hydrogen and a large resistance value variation range, and shows good sensor characteristics. From this, it was shown that the sensor characteristics on the low concentration side were improved by supporting platinum on palladium.

[Reference Examples 1 and 2]
Sensor characteristics of a sample in which palladium and platinum are supported alone are shown in FIGS.
FIG. 6 is a diagram showing the results of evaluating the sensor characteristics by preparing samples by changing the concentration of the palladium-containing electrodeposition solution and the ultraviolet irradiation time (electrodeposition time). From this, the resistance value decreased during the flow of air diluted hydrogen gas, but the resistance value change of any sample was the same at a hydrogen concentration of 50% or more. It was also shown that it took a considerable time for the resistance value to stabilize.

FIG. 7 is a view showing the results of evaluating the sensor characteristics by preparing a sample by changing the concentration of the platinum-containing electrodeposition solution (40 ppm) and changing the ultraviolet irradiation time (electrodeposition time). Ultraviolet light irradiation time (loading time) 15 minutes and 30 minutes, both in the case of Pd, the resistance value decreases with air diluted hydrogen gas flow, and then recovers to the initial resistance value by circulating air did. Moreover, the concentration dependence of the resistance value change was confirmed up to 30% in the irradiation 15 minutes and up to 50% in the irradiation 30 minutes. Since the change in the resistance value is relatively stable as in the case of carrying Pd, it can be said that the sensor characteristics are improved by carrying platinum as compared with the TiO ₂ thin film alone. Moreover, it was observed that the lower limit value of the resistance value after 50% of the hydrogen concentration gradually increased in both irradiation time data.

It is a figure which shows sectional drawing of the element for gas detection which concerns on this invention. It is a figure which shows the gas responsiveness of the sample of an Example and a comparative example. It is a figure which shows the gas responsiveness of the sample of an Example and a comparative example. It is a figure which shows the gas responsiveness of the sample of an Example and a comparative example. It is a figure which shows the gas responsiveness of the sample of an Example and a comparative example. It is a figure which shows the gas responsiveness of the sample of a reference example. It is a figure which shows the gas responsiveness of the sample of a reference example.

Explanation of symbols

1 Gas detection element 10 Substrate 20 Thin film 30 Metal layer

Claims (10)

  A gas detection element in which a metal layer containing two or more kinds of metals having different hydrogen storage capabilities and / or hydrogen release capabilities is provided on a thin film made of a conductor or a semiconductor provided on a substrate.   The element for gas detection according to claim 1, wherein the two or more kinds of metals are a combination of platinum or an alloy thereof and palladium or an alloy thereof.   The gas detection element according to claim 1, wherein the platinum or an alloy thereof is supported mainly on the palladium or an alloy thereof.   The gas detection element according to claim 1, wherein the thin film is a thin film having a photocatalytic action.   The gas detection element according to claim 1, wherein the thin film is a titanium oxide thin film. A gas detection element according to any one of claims 1 to 5,
A pair of electrodes provided in the gas detection element;
A hydrogen sensor comprising: a resistance measuring unit that measures a change in resistance value between the electrodes. Heat capacity of the substrate constituting the gas sensing element, hydrogen according to claim 6 at a constant pressure specific heat capacity from 0.4J ^{· K -1 · g} -1 is 1.8J ^{· K -1 · g} -1 Sensor.   The hydrogen sensor according to claim 6 or 7, wherein the substrate has a heat capacity adjusting means for adjusting a heat capacity on a surface opposite to a surface in contact with the thin film.   A method for producing an element for gas detection, comprising a step of supporting platinum or an alloy thereof and palladium or an alloy thereof on a thin film made of a conductor or a semiconductor provided on a substrate. The gas detection element according to claim 9, wherein the thin film is a thin film having a photocatalytic action that promotes the loading of the metal.

Images