JPS60211347A - Gaseous hydrogen sensor - Google Patents

Abstract

PURPOSE:To increase the sensitivity of a hydrogen sensor by making use of the decrease in the resistance value of tungsten oxide when gaseous hydrogen is absorbed to the tungsten oxide. CONSTITUTION:The 1st electrode 2 and the 2nd electrode 4 are provided on a substrate 1. The 1st electrode 2 is made of Pt, Pd, Ti, etc. and the 2nd electrode 4 of Pd, etc. A WO3 film 3 is formed on the electrode 2 and under the electrode 4 to 4.0-6.0g/cm<3> packing density and 100-10,000Angstrom film thickness, thereby constituting a hydrogen sensor. When hydrogen is brought into contact with the sensor, the hydrogen is absorbed by the film 3 by the catalytic effect of Pt, etc. of the electrode 4, by which the resistance value thereof is decreased and the resistance 7 between the 1st electrode 2 and the 2nd electrode 4 is decreased. The hydrogen is consequently more absorbed by the WO3 film and the resistance is lower as the concn. of the hydrogen is higher. The hydrogen is thus detected with high sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a hydrogen gas sensor that detects the amount of hydrogen gas contained in the gas as an electrical signal.

Conventional configurations and their problems Recently, due to the increase in energy demand and the desire for clean energy due to environmental pollution, there has been an increasing demand for using hydrogen gas as an energy source.

On the other hand, since hydrogen gas is a highly dangerous gas with a low flash point, there is an increasing demand for gas sensors that detect gas wetness of hydrogen gas.

Conventionally, commonly used hydrogen gas sensors utilize changes in the electrical resistance of a platinum wire caused by burning hydrogen gas in a heated platinum wire. Such a sensor had the following drawbacks. That is,
Even if flammable gases other than hydrogen gas, such as isobutane and propane, coexist, they will be detected in the same way as hydrogen gas and will malfunction. Therefore, there was a need for a highly reliable sensor that could only detect hydrogen gas.

It has been known that tungsten oxide (WO2) reacts with hydrogen using a catalyst such as platinum.

The reaction mechanism is that hydrogen gas enters tungsten oxide at the contact interface between tungsten oxide and platinum or palladium.
As a result, the electrical resistance of the produced tungsten bronze becomes extremely low.

For example, Japanese Patent Application Laid-open No. 5 (1973)
7-74648, WO3 by sputter deposition
Gas sensors using membranes have been described. but,
The WO3 film was polycrystalline and had low sensitivity to hydrogen gas.

OBJECTS OF THE INVENTION The present invention aims to improve the hydrogen gas sensor that utilizes this WO3 film to make it more sensitive.

Structure of the Invention The present invention is based on the discovery that an amorphous WO3 film with a low packing density is highly sensitive to hydrogen gas. A thin film of platinum or palladium is provided as the second electrode.

In the present invention, as mentioned above, the catalyst metal platinum or palladium also serves as the second electrode, and the packing density of WO2 is 4.0 to 6 Oy/mA, and the film thickness is 10
Preferably 0 to 10,000 people.

Description of examples Example 1 Pt on an insulating substrate such as ceramic or glass.

A first electrode made of a metal such as Pd, Ni, Ti, Ta, A(1, Aq, AI, etc.) or a semiconductor such as In2o3.5no2 is provided, and an amorphous WO3 film is formed thereon by a vacuum evaporation method. Palladium was laminated thereon by vapor deposition, and a second electrode was provided.

FIG. 1 shows a hydrogen gas sensor constructed as described above, in which 1 is a substrate, 2 is a first electrode, 3 is a WO3 film, and 4 is a second electrode. The packing density of WO2 is 5,4
p/ctli, its thickness is 3000 mm, and the thickness of the second electrode is 500 mm.

Note that 6 and 6 are leads for the first and second electrodes, respectively, and 7 is an electrical resistance detector.

When a certain concentration of hydrogen gas is blown onto the sensor section, the resistance between the first electrode and the second electrode changes significantly. FIG. 2 shows the relationship between the hydrogen gas concentration and the resistance value between the electrodes.

The electrical resistance value is measured at ±50 mV, 60Hz.
I did it. The measured value is the value 3 seconds after spraying hydrogen gas. After this, when air is blown onto the sensor part, 5~
It recovered to its original state within 10 seconds.

Example 2 In Example 1, the degree of vacuum during the deposition of the amorphous WO3 film was changed, and films with different packing densities were deposited to a thickness of 3000 mm, and the same sensor as in Example 1 was constructed and tested.

As a result, membranes with lower packing densities were more sensitive to hydrogen gas. However, when the packing density becomes low, Wo
It was found that the 3 films themselves became brittle and lacked stability.

A stable and highly sensitive VVO3 film has a packing density of 4.
Those in the range of o to 6t Of/c, a were favorable.

Furthermore, the packing density of the WO3 film is 5.4y/c? l! As a result of examining the deposition film thickness while keeping it constant, the thinner film showed the highest sensitivity. The preferred film thickness is 100-1
It was in the range of 0,000 people.

Example 3 In Example 1, a sensor was made using platinum instead of palladium for the second electrode, and the sensitivity to hydrogen gas was measured. As a result, almost the same sensitivity as in Example 1 was obtained.

Example 4 In Example 1, sensors were created in which the thickness of the palladium vapor deposition film of the second electrode was different. The thinner the palladium film is, the
Although the intercalation reaction of hydrogen gas to o3 becomes faster, the electrical resistance of the electrode itself becomes higher. The thickness of the palladium film was preferably 100 to 1,000. The same was true for platinum.

Effects of the Invention As described above, according to the present invention, a highly sensitive and stable hydrogen gas sensor with a simple structure can be obtained.

Additionally, this sensor is highly reliable as it does not respond to other flammable gases.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the main part of a hydrogen gas sensor according to an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between the hydrogen gas concentration and the electrical resistance value of the sensor. 1...Substrate, 2...First electrode, 3...
... wO3 film, 4... second electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2He JLjll tpprn)

Claims (3)

[Claims] (1) A hydrogen gas sensor characterized in that an amorphous tungsten oxide layer is provided on a first electrode, and a platinum or palladium thin film layer is further laminated thereon as a second electrode. (2) The tungsten oxide layer has a packing density of 4.0 to 6.
, Of/ctA, and a film thickness of 100 to 10,000. The hydrogen gas sensor according to claim 1. (3) The thickness of the platinum or palladium film is 100 to 1
The hydrogen gas sensor according to claim 2, which is an ooO person.