JPH053892B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a hydrogen gas sensor that detects hydrogen gas in gas.

Conventional technology Conventionally known hydrogen gas sensors include semiconductor gas sensors and palladium gate FETs.
There are gas sensors, catalytic combustion type gas sensors, etc.

Semiconductor gas sensors utilize the phenomenon that the resistance value of oxides such as SnO ₂ and γ-Fe ₂ O ₃ changes due to reducing gases adsorbed on the surfaces thereof.

Palladium gate FET gas sensor is
It is constructed by attaching palladium on SiO ₂ at the gate of MOSFET, and the electric double layer in FET is created by utilizing the fact that the potential of the electric double layer between palladium and SiO ₂ is proportional to the hydrogen gas concentration in the atmosphere. It detects the potential of

A catalytic combustion gas sensor attaches a gas oxidation catalyst to a temperature measuring element to combust the gas, and determines the gas concentration from the temperature rise of the temperature measuring element due to the heat generated.

Problems to be Solved by the Invention In the conventional hydrogen gas sensor as described above, it is necessary to heat the gas sensing part of the sensor, which consumes a large amount of power, and there is a gap between the gas sensing part of the sensor and the circuit, case, etc. This requires an insulated space, which limits the ability to miniaturize the sensor.

In view of the above, an object of the present invention is to provide a small-sized hydrogen gas sensor that has sufficient sensitivity at room temperature.

Means for Solving the Problems The present invention measures hydrogen gas concentration by utilizing the fact that transition metal oxides react with hydrogen ions to generate intercalation compounds. , a first electrode in contact with the oxide layer, and a second electrode opposed to the oxide layer via a hydrogen ion conductive solid electrolyte layer.

Effect Many transition metal oxides that form intercalation compounds are known. These include WO ₃ , MoO ₃ , TiO ₂ , V ₂ O ₅ and Cr ₂ O ₃ . Taking WO ₃ as an example, it is known that one equation of equilibrium is established between it and hydrogen ions, and that the resistivity of the intercalation compound H _x WO ₃ is inversely proportional to the exponent of x.

WO ₃ +xH ⁺ +xeH _x WO ₃ (1) In order for hydrogen gas to adsorb onto the surface of the oxide WO ₃ and cause the reaction of equation 1, it is necessary to raise the temperature, but if the active WO ₃ is When a thin layer of platinum or the like is attached to the surface of solid WO ₃ , one type of reaction can occur at room temperature.

On the other hand, in the presence of oxygen, the reaction H _x WO ₃ +x/2·O ₂ →WO ₃ +H ₂ O (2) occurs, resulting in a decrease in x. Therefore, H _x due to a constant hydrogen gas concentration in the presence of oxygen
The x value of WO ₃ is smaller than without oxygen.

In order to increase the sensitivity to hydrogen gas in the presence of oxygen at room temperature, it is necessary to separate H _x WO ₃ and oxygen so that they do not come into direct contact. For this purpose, a hydrogen ion conductor is provided between WO ₃ and the atmosphere, but this also cuts off the contact between hydrogen gas and WO ₃ , so that the reaction (1) no longer occurs.

Basically, the hydrogen gas sensor of the present invention, as shown in FIG. This is a configuration in which electrodes 4 are provided.
In addition, 5 is a support body. The basic operation of this hydrogen gas sensor is that when the second electrode 4 is made of palladium, for example, and a voltage is applied between the electrodes 4 and 1 so that the electrode 4 becomes positive, hydrogen adsorbed to the palladium and dissociated becomes hydrogen. It reaches the transition metal oxide layer 2 via the ion conductor and reacts with the oxide to form an intercalation compound. Next, apply an AC voltage between the two electrodes,
By measuring the impedance between the two electrodes, the amount of intercalation compound produced can be determined, and therefore the hydrogen gas concentration can be determined. Conversely, electrode 1
By applying a voltage between the electrodes 1 and 4 with the voltage positive, hydrogen can be extracted from the intercalation compound, and the sensor can be regenerated. In this way, the hydrogen gas sensor of the present invention can be used repeatedly.

Example Examples of the present invention will be described below.

Example 1 Nickel-chromium alloy with a thickness of 1000Å on a glass substrate
WO ₃ was deposited on a part of it in an area of 5 mm x 5 mm.
3000 Å is deposited, platinum is further deposited at 20 Å as a catalyst, and then SiO ₂ is deposited at 3000 Å so as to completely cover WO ₃ in an area of 6 mm×6 mm. Next 5mm x 5mm
Palladium was evaporated to a thickness of 400 Å in the same position as WO ₃ with an area of . In addition, WO ₃ is 1×
It was deposited at 10 ^-5 Torr and was amorphous.

When an alternating current with an amplitude of 0.1 V and a frequency of 10 KHz was applied between the nickel-chromium alloy electrode and the palladium electrode and the impedance was measured, it was 10.2 KΩ. Next, a voltage of 1V was applied for 10 seconds with the palladium electrode negative, and the AC impedance was measured in the same way as above, and it was 17.2KΩ. Next, this sensor was placed in an atmosphere of air mixed with 1% hydrogen gas, and the nickel-chromium alloy electrode was turned negative.
After applying a voltage of 1V for 10 seconds, the AC impedance was measured and found to be 9.6KΩ. After moving the sensor into the air and applying a negative voltage of 1V to the palladium electrode for 10 seconds, the AC impedance was measured and found to be 17.1KΩ.

Figure 2 shows the results of measurements similar to those above while changing the hydrogen gas concentration.

Example 2 Take 10 g of molybdenum oxide powder (99.9%), add it to 50 c.c. of a 0.1% aqueous solution of chloroplatinic acid, and add 0.5 g of sodium borohydride while stirring. After stirring for 1 hour, the mixture is washed with water and dried. This produces platinized molybdenum oxide. This is divided into two parts, one of which is printed with a size of 5 mm x 5 mm on a platinum electrode with a size of 5 mm x 5 mm formed on an alumina substrate by mixing a binder and a solvent, and dried. Apply phosphomolybdic acid aqueous solution on top of this for 40 minutes.
Dry by keeping at 85% RH for 5 hours. Next, ink made by mixing graphite, a binder, and a solvent with the platinized molybdenum oxide above is applied to the phosphomolybtenic acid.
Print in an area of mm x 6 mm and dry at 40°C and 85% RH to make the second electrode. The second electrode has dimensions of 5 mm x 5 mm and is covered with room temperature curable epoxy resin so as to be in contact with air.

Place this sensor in the air, set the second electrode as negative, and apply 0.5V between it and the platinum electrode.
The impedance was measured at 0.1V with a frequency of 10KHz and was 2.3MΩ. Next, place this sensor in air containing 1% hydrogen, apply a voltage of 0.5V with the platinum electrode as negative for 10 seconds, and then
When the impedance was measured with alternating current of 0.1V and frequency of 10KHz, it was 125KΩ. Next, the sensor was taken out into the air, and after applying a voltage of 0.5V with the platinum electrode as positive, the impedance was measured and found to be 2.3MΩ.

Although tungsten oxide was used in the above example, any of the above-mentioned transition metal oxides can be used, and among them, molybdenum oxide is excellent.

Effects of the Invention According to the present invention, sufficient sensitivity to hydrogen gas can be obtained at room temperature without heating the sensor, so power consumption can be significantly reduced. It is also possible to integrate it with a circuit, and it is possible to configure a small gas sensor using a small dry battery or the like as a power source.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the basic configuration of the hydrogen gas sensor of the present invention, and FIG. 2 is a diagram showing its sensitivity characteristics. 1... First electrode, 2... Transition metal oxide layer,
3... Solid electrolyte layer, 4... Second electrode.

Claims (1)

[Claims] 1. A transition metal oxide layer, a first electrode in contact with the oxide layer, and a layer laminated to cover the opposite side of the oxide layer to the surface in contact with the first electrode. a hydrogen ion conductive solid electrolyte layer, a catalyst layer formed between the oxide layer and the solid electrolyte layer, and a second catalyst layer that opposes the oxide layer through the solid electrolyte layer.
A hydrogen gas sensor characterized by having an electrode. 2. The hydrogen gas sensor according to claim 1, wherein the oxide is an oxide of tungsten or molybdenum.