JPH08201336A - Electrochemical gas sensor and driving method thereof - Google Patents

Abstract

PURPOSE: To provide an electrochemical gas sensor and its driving method capable of shortening the time until the output current becomes the stable operation state after an excitation start and having an initial stabilization time. CONSTITUTION: This gas sensor is provided with an action electrode 20, a counter electrode 30, and a reference electrode 40 on the surface of a silicon substrate 10 applied with oxidation and insulation treatment, and the electrodes 20, 30, 40 are electrically connected via a polymer solid electrolyte film 50. The electrodes 20, 30, 40 are connected to a power circuit section 60 at one end. The power circuit section 60 is provided with a sensor drive section applying a voltage different in magnitude from the applied voltage in the gas detection state between the action electrode 20 and the reference electrode 40 for the prescribed time at the time of the excitation start and setting the voltage to the applied voltage in the gas detection state after the prescribed time elapses and a circuit for detecting and amplifying the output current of the gas sensor element 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrochemical gas sensor and its driving method.

[0002]

2. Description of the Related Art Conventionally, various gases in the atmosphere such as carbon monoxide, hydrogen,
Various electrochemical gas sensors for detecting nitrogen compounds and the like have been proposed (for example, JP-A-1-156657). For example, in the electrochemical gas sensor shown in FIG.
Working electrode 20, counter electrode 30, and reference electrode 4 on the insulating substrate 10.
0 is provided and these electrodes 20, 30, 40 are electrically connected via the solid polymer electrolyte membrane 50. In this electrochemical gas sensor, when a certain constant voltage is applied between the working electrode 20 as a gas reaction electrode and the reference electrode 40, an electrochemical reaction occurs with the gas to be sensed in the working electrode 20, Carriers generated by the reaction flow in the solid polymer electrolyte membrane 50, and a sensor current having a current value corresponding to the gas concentration of the reaction gas flows. The voltage value applied between the working electrode 20 and the reference electrode 40 is determined by the gas species to be detected,
For example, about 0.4 V is suitable for detecting carbon monoxide gas, and about -0.6 V is suitable for detecting oxygen.

[0003]

When the above-mentioned electrochemical gas sensor is made to function as a carbon monoxide gas sensor, for example, it is necessary to apply a voltage of 0.4 V between the working electrode 20 and the reference electrode 40. Simultaneously with the start of energization, 0.4 V was applied between the working electrode 20 and the reference electrode 40.

However, in such a voltage applying method, as shown in FIG. 5, immediately after the start of energization, an output current of 100 nA or more flows even though there is no gas to be detected, and then the output is gradually output. The current decreases and stabilizes at a current value of 0 to several nA which is a steady state, but it took 4 hours or more for the current value to stabilize. The time required for the output current to stabilize after the start of energization depends on the length of the non-energized state before the start of energization, but normally it is a period of several hours to one day. Was needed.

Until the output current stabilizes, the zero level of the output current shifts, and accurate gas detection and gas concentration measurement cannot be performed. The fact that the stabilization time takes several hours or more has been a practical problem. In order to solve the above problems, the present invention provides an electrochemical gas sensor having a short initial stabilization time and a method of driving the same, which can shorten the time until the output current reaches a stable operation state after the start of energization. The purpose is to do.

[0006]

In order to achieve the above object, in the invention of claim 1, a working electrode, a counter electrode and a reference electrode are provided on the same surface of an insulating substrate, and each electrode and each electrode In the electrochemical gas sensor provided with a solid electrolyte membrane covering the above, a voltage having a magnitude different from the applied voltage in the gas detection state is applied for a predetermined time between the working electrode and the reference electrode at the start of energization. A circuit for setting the applied voltage in the gas detection state after the lapse of the predetermined time is provided.

According to a second aspect of the present invention, there is provided an electrochemical gas sensor in which a working electrode, a counter electrode, and a reference electrode are provided on the same surface of an insulating substrate, and a solid electrolyte membrane is provided so as to cover each electrode and each electrode. In the driving method, a voltage having a magnitude different from the applied voltage in the gas detection state is applied between the working electrode and the reference electrode for a predetermined time at the start of energization, and after the predetermined time has elapsed, the gas detection state is reached. It is characterized in that the gas detection operation is started by setting the applied voltage of.

[0008]

According to the first and second aspects of the present invention, at the start of energization of the electrochemical gas sensor, a voltage having a magnitude different from the applied voltage in the normal detection state is applied between the working electrode and the reference electrode, and then gas detection is performed. Since the applied voltage of the state is set, the initial stabilization time of the electrochemical gas sensor can be shortened.

[0009]

The present invention will be described below with reference to examples. FIG.
FIG. 3 is a configuration diagram of an electrochemical gas sensor according to an example of the present invention. The gas sensor element 1 of this embodiment has a size of 10 mm × 10.
A platinum film was formed as the working electrode 20 and the counter electrode 30 and a gold film was formed as the reference electrode 40 by the sputtering method on the surface of the silicon substrate 10 that was subjected to the oxidation insulation treatment of 10 mm, and the electrodes 20, 30, 40 and the space between the electrodes were formed. As a polymer solid electrolyte membrane 50, a perfluorosulfonate polymer (trade name: Nafion: manufactured by DuPont) is formed by a solution casting method so as to cover the. Each electrode 20, 30, 4
One end of 0 is extended and exposed to the outside of the solid polymer electrolyte membrane 50, and the terminal portions 21, 31, 4 formed by the exposed portions are exposed.
1 is connected to the power supply circuit section 60 via the power supply lead wires 22, 32, 42. A voltage having a magnitude different from the applied voltage in the gas detection state is applied to the power supply circuit unit 60 between the working electrode 20 and the reference electrode 40 for a predetermined time at the start of energization, and after the predetermined time has elapsed, the gas detection is performed. It is provided with a circuit for detecting and amplifying the output current of the gas sensor element 1 and the sensor drive unit for setting the applied voltage of the state.

A case where a voltage of 0.4 V is applied between the working electrode 20 and the reference electrode 40 to be used as an electrochemical gas sensor for detecting carbon monoxide gas will be described below. First, when the power supply circuit unit 60 starts energization,
As shown in (a), after applying a voltage of 0.7 V between the working electrode 20 and the reference electrode 40 for 30 seconds and then switching to 0.4 V, which is the applied voltage in the gas detection state, the figure immediately after the start of energization As in the case of the conventional example shown in FIG. 4, a very large sensor current flows as shown in FIG. 2 (b), but when the applied voltage is switched from 0.7V to 0.4V, the output current temporarily decreases to the negative side. Immediately after being touched, it turns to the positive side again and the output current stabilizes in about 20 minutes. As described above, in this embodiment, the time required for the output current to stabilize can be greatly shortened.

3 (a) and 3 (b), a voltage of 0.6 V is applied between the working electrode 20 and the reference electrode 40 for 60 seconds at the start of energization, and then the applied voltage is 0.4 V in the gas detection state. The applied voltage waveform and the output voltage waveform when switched are shown. The output current shown in FIG. 3B changes similarly to the case of the above-described embodiment, and the output current is stable in 10 to 15 minutes.

If the magnitude of the voltage applied at the start of energization is smaller in absolute value than the applied voltage in the gas detection state, there is no effect of accelerating the stabilization of the output current.
On the contrary, if the absolute value of the applied voltage at the start of energization is too large, the sensor performance, particularly the polymer solid electrolyte membrane 50 and the electrode portion may be adversely affected. Specifically, the applied voltage is 0.
At 8 V or higher, the electrolysis of water contained in the solid polymer electrolyte membrane 50 becomes the main reaction at the working electrode 20, so that it becomes difficult to quantitatively detect the gas to be detected.

Therefore, it is appropriate that the absolute value of the magnitude of the voltage applied at the start of energization is larger than the applied voltage in the gas detection state and 0.8 V or less. As long as the voltage is within this range, the voltage does not have to be a constant value as shown in the above embodiment, and it is also possible to apply a sinusoidal or triangular wave voltage or a plurality of voltage values in steps. .

In the above embodiment, the applied voltage between the working electrode 20 and the reference electrode 40 in the gas detection state is 0.4V.
As an example, the case of detecting carbon monoxide gas has been described as an example, but the present invention is not limited to this, and can be used for detecting various gases other than carbon monoxide gas or for measuring concentration.

[0015]

According to the invention of claim 1, a voltage having a magnitude different from the applied voltage in the gas detection state is applied between the working electrode and the reference electrode for a predetermined time at the start of energization, and after a predetermined time, A circuit for setting the applied voltage in the gas detection state is provided, and the invention of claim 2 supplies a voltage having a magnitude different from the applied voltage in the gas detection state between the working electrode and the reference electrode. At the start, the voltage is applied for a predetermined time, and after a predetermined time, the applied voltage in the gas detection state is set, and the gas detection operation is started, so the initial stabilization time of the electrochemical gas sensor can be shortened and accurate gas concentration measurement can be performed in a short time. There is an effect that can be done in.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2A is an explanatory diagram of an operation of an applied voltage in the above.
(B) is an operation explanatory view of the output current of the above.

FIG. 3A is an operation explanatory diagram of an applied voltage according to another embodiment of the present invention. (B) is an operation explanatory view of the output current of the above.

FIG. 4A is a sectional view showing an example of a conventional electrochemical gas sensor. (B) is a top view same as the above.

FIG. 5 is a diagram illustrating a conventional output current operation.

[Explanation of symbols]

 1 Gas Sensor Element 10 Insulating Substrate 20 Working Electrode 30 Counter Electrode 40 Reference Electrode 50 Polymer Solid Electrolyte 21, 31, 41 Terminal Section 22, 32, 42 Lead Wire 60 Power Circuit Section

Claims (2)

[Claims] 1. An electrochemical gas sensor in which a working electrode, a counter electrode, and a reference electrode are provided on the same surface of an insulating substrate, and a solid electrolyte membrane is provided so as to cover each electrode and each electrode. Between the reference electrode, a voltage having a magnitude different from the applied voltage in the gas detection state is applied for a predetermined time at the start of energization, and after the elapse of the predetermined time,
An electrochemical gas sensor comprising a circuit for setting an applied voltage in a gas detection state. 2. A method of driving an electrochemical gas sensor, wherein a working electrode, a counter electrode, and a reference electrode are provided on the same surface of an insulating substrate, and a solid electrolyte membrane is provided so as to cover each electrode and each electrode. A voltage having a magnitude different from the applied voltage in the gas detection state is applied between the working electrode and the reference electrode for a predetermined time at the start of energization, and after the elapse of the predetermined time, the applied voltage in the gas detection state is set. Then, a method for driving an electrochemical gas sensor, characterized by starting a gas detection operation.