JPS60210757A - Galvanic battery type oxygen sensor - Google Patents

Abstract

PURPOSE:To obtain an oxygen sensor of which the response speed is accelerated by the perfect reduction of O2, by integrally connecting a catalytic electrode to the single surface of a diaphragm made of a fluorocarbon resin and pressing a carbon fiber having a paper like form and a metal collector having a reticulated structure to the opposite side of the connected surface of the catalytic electrode. CONSTITUTION:A drilled plate 1 made of polyethylene, a porous polytetrafuloroethylene membrane 2 and an integrally connected body consisting of a diaphragm 4 made of a copolymer of F2C=CF2 and F2C=CF-CF3 and a catalytic electrode 5 comprising gold are successively stacked and, next, a carbon fiber 6 having a paper or mat like shape, a metal collector 7 made of Ti having a reticulated or expanded structure and filter paper 9 are superposed thereon while a holder main body and a lid 3, both of which are made of polyethylene are threaded and pressed, in such a state that an O- ring 3 is arranged between the drilled plate 1 and the main body 12, to fabricate an oxygen sensor. The delamination of the diaphragm 2 and the electrode 5 is prevented by the carbon fiber 6 and the collector 7 and the perfect reduction of O2 transmitting through the diaphragm 2 by the O2-reducing catalytic action of the carbon fiber 6 is performed to accelerate a speed for making output constant. Therefore, the sensor having an accelerated reaction speed to the concn. of circumferential O2 is obtained.

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. It helps you feel refreshed faster.

A galvanic cell type oxygen sensor is usually composed of a catalyst electrode as a positive electrode, a lead electrode as a negative electrode, and a fluororesin fit membrane that permeates an electrolytic solution and oxygen but hardly permeates water.

The structure of galvanic cell type oxygen sensors can be roughly divided 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 consists of a metal disk or cylinder, and the oxygen in the sensing gas first passes through the diaphragm;
Next, it dissolves into the electrolytic solution formed between the diaphragm and the catalyst electrode and participates in a reaction on the surface of the catalyst electrode. Therefore, the state of contact between the diaphragm and the catalyst electrode is kept constant at all times.
It is important that the thickness of the liquid film remains unchanged. 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 catalytic type/flea is to be maintained constant, careful attention is required, which poses the problem of increasing 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 catalyst electrode together, the 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 catalyst metal powder and fluororesin are bonded together. Advantageously, a mixture with a binder is bonded 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 dissolves in the electrolyte.
Since this dissolved oxygen again and slowly participates in the electrolytic reduction reaction, the output of the oxygen sensor is difficult to stabilize, or in other words, 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 what to do with the 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 one
In terms of keeping the contact state constant (ii), it is not reliable.

The present invention aims to improve the above two problems. That is, in the present invention, a vapor mat or fabric made of carbon fiber is provided on the catalyst electrode side of the diaphragm-catalyst electrode assembly, and a metal net or screen as a current collector is provided next to it. , to press these. If such a structure is adopted, firstly, since carbon fibers have a certain degree of catalytic activity against oxygen reduction, oxygen that passes through the pores of the catalyst electrode without being reduced is
Electrolytic reduction occurs sufficiently quickly on the carbon fibers, and 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 properties 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 polytetrafluoroethylene membrane, (3) is an O-ring, (4) is a diaphragm made of a tetrafluoroethylene-67fluoropropylene copolymer membrane, (5) (6) is carbon fiber paper, (7) is a current collector made of expanded titanium,
(8) is a lead wire made of titanium wire, (9) is a cover, (
10) is an electrolytic solution consisting of a mixed aqueous solution of acetic acid, potassium acetate, and lead acetate, (11) is a porous lead electrode, (12) is a polyethylene holder body, and (13) is a polyethylene holder lid. .

The diaphragm (4) and the catalyst electrode (5) are integrally joined. The holder body (12) and the holder lid (13) are each threaded, and have a perforated plate (1) and a porous polytetrafluoroethylene membrane (2).

O-ring (3), diaphragm (4), catalyst electrode (5).

The carbon fiber paper (6), the current collector (7) and the opening paper (9) are
The holder main body (12) and the holder lid (13) are pressed together by screwing, and a good contact state is maintained. The perforated plate (1) functions as a pressing end plate, and the porous polytetrafluoroethylene plate (2) is for preventing the surface of the diaphragm (4) from becoming dirty. Airtight with O-ring (3),
Liquid tightness is ensured.

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 resistance is placed between the positive and negative electrodes of each sensor. Connect and set the oxygen concentration of the atmosphere gas to 20
When we investigated the change over time in the output voltage of the sensor when changing it from % 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, whereas that of the conventional sensor In the case of product B, it was 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. DESCRIPTION OF SYMBOLS 1... Perforated plate, 2... Porous poly 4-fluorinated ethylene base, 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...Boulder body, 13...Holder lid 1 8

Claims (1)

[Claims] 1. In a galvanic cell type 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 fluororesin. A galvanic device characterized in that paper-like, mat-like, or woven carbon fibers are arranged on the side of a catalyst electrode, and a metal current collector in the form of a net, an expanded metal, or a screen is pressed. Battery operated oxygen sensor.