JPH0358464B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a galvanic cell type oxygen sensor, and its object is to improve the response speed of a galvanic cell type oxygen sensor using an assembly in which a diaphragm and a catalyst electrode are integrally joined. The goal is to write faster.

A galvanic cell-type oxygen sensor usually consists of a catalytic electrode as a positive electrode, a lead electrode as a negative electrode, and a fluororesin diaphragm that allows an electrolytic solution and oxygen to pass through, but does not allow water to pass through.

The structure of galvanic cell type oxygen sensors can be roughly classified into types in which the diaphragm and catalyst electrode are simply in contact with each other, and types in which the two are integrally joined. In the former case, the catalytic electrode is composed of a metal disk or cylinder, and the oxygen in the sensing gas first permeates through the diaphragm and then dissolves in the electrolyte film formed between the diaphragm and the catalytic electrode. It participates in the reaction on the surface of the catalytic electrode. Therefore, it is important to maintain constant contact between the diaphragm and the catalyst electrode at all times so that the thickness of the liquid film does not change. However, there is a problem in that when the pressure of the atmospheric gas changes or the relative humidity changes, the contact state between the diaphragm and the catalyst electrode changes. Furthermore, if the contact state between the diaphragm and the catalyst electrode is to be maintained constant, careful attention is required, which increases the number of man-hours required to manufacture the sensor.

From this point of view, it is more advantageous to have a structure in which the diaphragm and the catalyst electrode are integrally joined. This is because even if the diaphragm swells or dents due to a change in pressure, the catalyst electrode also follows the deformation of the diaphragm. In order to join the diaphragm and the catalytic electrode together, a catalytic metal is fixed on one side of the diaphragm by vapor deposition or sputtering, and then water-repellent treatment is applied with fluororesin or catalytic metal powder is applied. It is preferable to bond a mixture of the diaphragm and the fluororesin binder to the diaphragm. However, in such a structure, all of the oxygen that permeates through the diaphragm is not electrolytically reduced at the catalyst electrode, and excess oxygen is dissolved in the electrolyte, and this dissolved oxygen is slowly electrolyzed again. Because it participates in the reduction reaction, the output of the oxygen sensor is difficult to stabilize. In other words, the problem is that the response speed is slow.

On the other hand, in the case of a structure in which the diaphragm and the catalyst electrode are integrally joined, one issue is how to form a current collection structure. Conventionally, a method has been adopted in which, for example, a spring as a current collector is pressed against a catalyst electrode, but this method is not reliable in terms of keeping the catalytic state of the spring and the catalyst electrode constant.

The present invention aims to improve the above two problems. That is, in the present invention, a paper-like, mat-like, or woven carbon fiber is arranged on the catalyst electrode side of a diaphragm-catalyst electrode assembly, and a metal mesh or perforated metal is further arranged next to it as a current collector. Plates are arranged and these are pressed. When such a structure is adopted, firstly, since carbon fibers have a certain degree of catalytic activity for oxygen reduction, oxygen that passes through the pores of the catalyst electrode without being reduced is quickly absorbed by the carbon fibers. As a result, the response speed of the oxygen sensor becomes faster. Further, since carbon fiber has elasticity and excellent conductivity, it has good current collection performance when pressed together with a metal current collector. Carbon fibers may be subjected to water repellent treatment.

An embodiment of the present invention will be described in detail below.

Embodiment FIG. 1 shows a cross-sectional structure of a galvanic cell type oxygen sensor according to an embodiment of the present invention. In the figure, 1 is a perforated plate made of polyethylene, 2 is a porous polyethylene 4
fluorinated ethylene membrane, 3 is an O-ring, 4 is a diaphragm made of a tetrafluoroethylene-hexafluorinated propylene copolymer membrane, 5 is a catalyst electrode made of gold, 6 is carbon fiber paper, and 7 is made of expanded titanium. A current collector; 8 is a lead wire made of titanium wire; 9 is a cap; 10 is an electrolytic solution made of a mixed aqueous solution of acetic acid, potassium acetate, and lead acetate; 11 is a porous lead electrode;
2 is a holder body made of polyethylene, and 13 is a holder lid made of polyethylene.

The diaphragm 4 and the catalyst electrode 5 are integrally joined. The holder body 12 and the holder lid 13 are each threaded, and include a perforated plate 1, a porous polytetrafluoroethylene membrane 2, an O-ring 3, a diaphragm 4, a catalyst electrode 5, a carbon fiber paper 6, and a current collector. The body 7 and the cover 9 are pressed together by screwing the holder main body 12 and the holder lid 13, and a good contact state is maintained. The perforated plate 1 functions as a pressing end plate,
The porous polytetrafluoroethylene membrane 2 is for preventing the surface of the diaphragm 4 from becoming dirty. O-ring 3
This ensures airtightness and liquidtightness.

The effects of the present invention will be explained below.

The galvanic cell type oxygen sensor obtained in the above example is designated as A, and the conventional product in which the carbon fiber paper 6 is not housed in the example is designated as B, and a resistor is connected between the positive and negative electrodes of each sensor. When we investigated the change over time in the output voltage of the sensor when the oxygen concentration of the atmospheric gas was changed from 20% to 0%, we found that it took 4 minutes for the output voltage of the galvanic cell type oxygen sensor A of the present invention to stabilize. In contrast, in the case of conventional product B, it took 10 minutes. This clearly shows the effect of carbon fiber paper in the present invention.

[Brief explanation of drawings]

FIG. 1 shows a cross-sectional structure of a galvanic cell type oxygen sensor according to an embodiment of the present invention. 1... Perforated plate, 2... Porous polytetrafluoroethylene membrane, 3... O-ring, 4... Diaphragm, 5... Catalyst electrode,
6... Carbon fiber paper, 7... Electrolyte, 8... Lead wire, 9
...Opening paper, 10...Electrolyte, 11...Lead electrode, 12...Holder body, 13...Holder lid.

Claims (1)

[Claims] 1. In a galvanic cell oxygen sensor composed of a catalytic electrode as a positive electrode, a lead electrode as a negative electrode, an electrolyte, and a diaphragm, the catalytic electrode is integrally bonded to one side of a diaphragm made of fluorine resin. It is characterized by disposing paper-like, mat-like, or woven carbon fibers on the side of the catalyst electrode, and further pressing against a metal current collector such as a metal net, an expanded metal plate, or a perforated metal plate. Galvanic battery type oxygen sensor.