JPH0244243A - Galvanic battery type oxygen sensor - Google Patents

Abstract

PURPOSE:To obtain a galvanic battery type oxygen sensor excellent in performance such as output stability and response speed by setting an amount of a catalyst electrode joined integrally with a diaphragm to be 400-1,000Angstrom in thickness. CONSTITUTION:A catalyst electrode 2 is formed at a specified thickness by a sputtering or vacuum evaporation on one side of a diaphragm 1 comprising a fluorine based high polymer thin film. Then, parts, that is, a negative pole 4, a current collector 8 comprising porous carbon or the like to collect current evenly from the entire surface of the catalyst electrode, a thermistor 6 for temperature compensation of a sensor output and a resistor 7, are mounted in a container body 5. A junction body of the electrode 2 and the diaphragm 1 is mounted at the tip of the body 5 to obtain a galvani battery type oxygen sensor. Here, when the catalyst electrode is formed at a specified thickness, time of the sputtering or vacuum evaporation, the temperature of a substrate, voltage temperature and the like are controlled to make the thickness of a porous metal layer as catalyst electrode range from 400 to 1,000Angstrom thereby enabling the obtaining of a sensor excellent in performance such as output stability, response speed and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention provides a catalyst electrode that functions as a positive electrode and a lead tf! electrode that functions as a negative electrode. and a diaphragm to which an electrolytic solution and the catalyst electrode are integrally joined.

Galvanic cell-type oxygen sensors are small, lightweight, operate at room temperature and pressure, and are inexpensive, so they can be used to check oxygen deficiency conditions inside ships, manholes, tunnels, or rooms where heaters are used. It is used in a wide range of fields such as monitoring oxygen concentration in medical equipment such as anesthesia machines and ventilators. Additionally, sensors housed in waterproof containers that can be used underwater are used as dissolved oxygen sensors for aqueous solutions to monitor dissolved oxygen concentrations in fish farming and hydroponic vegetable cultivation.

Conventional galvanic cell type oxygen sensors generally have the structure shown in FIG. In other words, in principle, oxygen passing through the barrier [1] that has selective oxygen permeability is
It is reduced on the catalytic electrode 2 as a positive electrode, and causes an electrochemical reaction with the negative electrode 4 via the electrolytic solution 3, resulting in a catalytic charge [i2 and a negative f! 4, a current is generated depending on the oxygen concentration. The current is obtained as a sensor output voltage through a thermistor 6 for temperature compensation.

In such a galvanic cell type oxygen sensor, the structure of the parts where oxygen reacts, that is, the diaphragm and the catalyst electrode, is very important in obtaining a sensor with good performance. Galvanic cell type oxygen sensors can be broadly classified based on the structure of the diaphragm and catalyst electrode.
187846), and a type in which both are integrally joined by means such as vapor deposition or pressure bonding (for example, British Patent No. 1).
No. 200595). In the former case, the catalytic electrode is composed of a metal disk or cylinder, and oxygen in the gas to be detected, most likely in the aqueous solution to be detected, first permeates through the diaphragm and then forms between the diaphragm and the catalytic electrode. It dissolves in the electrolyte film and takes part in the reaction on the catalyst electrode. In this case, it is important to always maintain a constant state of contact between the diaphragm and the catalyst electrode so that the thickness of the electrolyte film does not change. If this is not done, changes in the pressure or relative humidity of the environment in which the sensor is placed will change the contact status between the diaphragm and the catalyst electrode, making the sensor output unstable. be.

On the other hand, in the latter case, the oxygen that has permeated through the diaphragm participates in a reaction at the interface between the electrolytic solution that has soaked into the pores of the porous catalyst electrode and the catalyst electrode. In this case, since the diaphragm and the catalyst electrode are integrated, even if the diaphragm swells or dents due to changes in external pressure, the sensor output will not become unstable.

Problems to be Solved by the Invention In the case of a galvanic cell type oxygen sensor that has a structure in which a diaphragm and a catalytic electrode are integrally joined, the amount of catalyst is a problem, but until now, little has been done about the amount of catalyst. It wasn't taken into account. This is because the amount of oxygen that permeates through the diaphragm is minute, so it is thought that more or less catalyst is sufficient, and there was no suitable method to maintain the amount of catalyst at a certain value. .

However, as tests were repeated with the aim of improving sensor response speed and ensuring long-term output stability, it became clear that the amount of catalyst was an important issue. In other words, if the amount of catalyst is too small, the entire amount of oxygen that has passed through the diaphragm cannot be reacted quickly and remains near the diaphragm, resulting in poor sensor response and unstable output. . In addition, if the amount of catalyst is too large, the porosity of the catalyst electrode is inhibited, and the amount of the interface where oxygen reacts is reduced, resulting in a decrease in output or instability.

Means for Solving the Problems The present invention provides a galvanic cell type oxygen sensor in which a diaphragm and a catalyst electrode are integrally bonded, and the thickness of the porous metal layer that is formed on the diaphragm by vapor deposition or the like and becomes the catalytic electrode is determined. 400～
By controlling the thickness to 1000 angstroms, the above-mentioned problems are solved.

Function As described above, oxygen that has permeated through the diaphragm from the gas to be detected or the aqueous solution to be detected reacts within the porous metal layer formed to an appropriate thickness and serving as the catalyst electrode. At this time, since an appropriate amount of catalyst is present, the entire amount of oxygen that has permeated reacts quickly. Therefore, the response speed of the sensor is sufficiently fast. Furthermore, since there is a sufficient interface between the electrolyte and the catalyst electrode where oxygen reacts, stable sensor output can be obtained even if the sensor is placed in a high-concentration oxygen atmosphere for a long time.

Preferably, the metal material for the catalyst electrode is a noble metal such as gold or platinum from the viewpoint of reactive corrosion resistance.

In this way, the amount of catalyst in the catalyst electrode that is integrally joined to the diaphragm is set to 4.
By setting the thickness to 00 to 1000 angstroms, it is possible to obtain a galvanic cell type oxygen sensor with excellent performance such as output stability and response speed.

Example The thickness of the catalyst metal formed by vapor deposition on the diaphragm was 50~
We prototyped oxygen sensors with various thicknesses between 3000 angstroms and investigated their performance.

The basic structure of the prototype galvanic cell type oxygen sensor is shown in FIG. 1, and the prototype was made as described below.

First, a catalyst electrode 2 is formed to a predetermined thickness on one side of the partition 1111 made of a fluoropolymer thin film by sputtering or vacuum deposition.Next, a current is uniformly collected from the entire surface of the negative electrode 4 and the contact electrode. A current collector 8 made of porous carbon or the like for temperature compensation, a thermistor 6 and a resistor 7 for temperature compensation of the sensor output are mounted inside the container body 5.

A galvanic cell type oxygen sensor was obtained by attaching the above-mentioned catalytic electrode 2 and diaphragm 1 assembly to the tip of the container body.Although gold was used as the material for the catalytic electrode, precious metals such as platinum and iridium could also be used. The effect is the same no matter how you use it. Further, as a method for forming the catalyst electrode to a predetermined thickness, the deposition time of sputtering or vacuum evaporation, the substrate temperature, the voltage and current value, etc. are controlled.

For each sample of the galvanic cell type oxygen sensor obtained, the response speed, the output change ΔV (ratio of change to the initial sensor output) when the sensor is held in a 100% oxygen atmosphere for 2 hours, and the oxygen concentration of the sensor output Linearity for ■＾/V100 (however, VA indicates the sensor output value in the atmosphere, Vloo indicates the sensor output value in the 100% oxygen atmosphere, VA /'V100 = 20.9/1
00 = 0.209 (perfectly linear) was measured. The results are shown in Table 1.

From Table 1, sample No. 3.4.5 showed good values in various properties, and it was found that the appropriate thickness of the catalyst electrode was in the range of 400 to 1000 angstroms. That is, the thickness of the catalyst electrode is 40
Samples No. 1 and 2 that are thinner than 0 angstroms have a slow response speed, unstable output in a high oxygen concentration atmosphere, and poor linearity. In addition, No. 6, in which the thickness of the catalyst electrode is thicker than 1000 angstroms,
In samples 7 and 7, the output becomes unstable and the linearity also deteriorates.

Effects of the Invention Samples No. 4 in Table 1 were held in atmospheres with various oxygen concentrations for long periods of time to examine the stability of the sensor output. That is, in 0% oxygen for 1 hour and in the atmosphere (20% oxygen).
Changes in sensor output were examined by repeating the test 10,000 times in which the sample was held in 100% oxygen for 1 hour and 1 hour in 100% oxygen. As a result, the values shown in Table 1 hardly changed, and the output was very stable.

As described in detail above, the present invention makes it possible to obtain a galvanic cell type oxygen sensor with excellent performance such as output stability and response speed.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the galvanic cell type oxygen sensor of the present invention, and FIG. 2 is a sectional view of a general galvanic cell type oxygen sensor.

Claims (1)

[Claims] In a galvanic cell type oxygen sensor composed of a catalytic electrode functioning as a positive electrode, a lead electrode functioning as a negative electrode, an electrolyte and a diaphragm, the catalytic electrode is integrally joined to one side of the diaphragm, and the amount of the catalytic electrode is That is, a galvanic cell type oxygen sensor characterized in that the thickness of the catalyst electrode is 400 to 1000 angstroms.