JPS60200156A - Preparation of diaphragm-catalyst electrode unit for gas sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the pre-preparation of a diaphragm-catalyst electrode assembly used in gas sensors such as oxygen sensors or hydrogen sensors, and its purpose is
In addition to making the bonding strength of the catalyst electrode assembly more robust,
The purpose is to increase the response speed of the sensor to V.

There are six different types of gas sensors such as oxygen sensors and hydrogen sensors, but the present invention relates to galvanic cell type (fuel cell type), polarographic type gas sensors.

Whether a gas sensor is a galvanic cell type or a polar graph type, it is composed of a cathode, an anode, an electrolyte, and a diaphragm made of a polymer Il to control the diffusion of the detected gas. There is a lIj street C.

When the sensing gas is oxygen, the cathode serves as the oxygen sensing electrode, and the anode is comprised of a base metal such as a spear. On the other hand, when the detection gas is hydrogen, the anode serves as a hydrogen detection electrode, and a metal oxide such as β-type lead dioxide is used as the cathode. The oxygen sensing electrode and the hydrogen sensing electrode serve as catalyst electrodes for the electrolytic reduction of oxygen and the electrification of hydrogen.

If we look at the 1711 models of conventional gas sensors, they can be classified into two types: one in which the diaphragm and the catalyst electrode are simply in contact, and one in which they are integrally joined.
In the case of an IR type, the catalytic electrode is made of a metal piece (14), and the sensing gas first passes through the diaphragm and then dissolves into the electrolyte film formed between the diaphragm and the catalytic electrode. Participates in the reaction on the electrode surface.

Therefore, it is important to maintain a constant state of contact with the diaphragm catalyst (4λ) so that the thickness of the liquid film does not change.However, if the pressure of the atmosphere containing the detection gas changes or the relative There is a problem that the contact state between the diaphragm and the catalyst electrode changes when the humidity changes.Also, if the contact state between the diaphragm and the catalyst electrode is kept constant, extreme care is required. There is a problem that the number of manufacturing steps increases.

From this point of view, it is more advantageous to use the latter structure in which the diaphragm and the catalyst electrode are integrally joined.

Conventionally, in order to integrally bond and cover the diaphragm and the catalyst rri electrode, a method has been adopted in which a catalytic metal is vapor-deposited or sputtered on one side of the diaphragm.
In particular, when using a fluororesin such as polytetrafluoride clay, polytetrafluoride]-ethylene fluoride: 1 polymer or tetrafluoride tyrene copolymer, the diaphragm and The problem was that the bond strength with the catalytic metal was weak, and the catalytic metal easily peeled off from the diaphragm.

In the present invention, a suspension of tetrafluoroethylene-hexafluoropropylene copolymer in water or '4FJ solvent is coated on one side of a fluorine-15 fat with a smooth surface without pores, and then dried or heated. A double-layer structure consisting of a non-porous fluororesin layer and a porous 47-fluoroethylene-hexafluoropropylene copolymer layer was prepared by applying A laminate with a catalytic metal applied by vapor deposition or sputtering is immersed in a suspension of fluororesin in water or an organic solvent, or a fluororesin is applied to the surface of the laminate where the catalytic metal is coated. A suspension of water or an organic solvent is applied, and the final step is heat treatment. I-This is intended to solve the problem of separation between the diaphragm and the catalytic metal as described in (a) above.

That is, when such a method is adopted, when the catalyst metal is deposited on the polymer layer, the catalyst metal easily enters into the pores of the porous tetrafluoroethylene-hexafluoropropylene polymer layer. 4f, the adhesion strong electric current is stronger than when the tape is placed on a non-porous smooth diaphragm as in the past. The adhesion strength between the diaphragm and the catalyst metal is further increased in the next step of coating with fluororesin. This indicates that the fluororesin in the coating process enters the gaps between particles of the catalyst metal, and this fluororesin binds and fixes the catalyst metal. This is because the catalytic metal is held firmly in place as a whole because it is held even more firmly.

1. Ribbed porous layer 4 formed on the surface of the fluororesin membrane with pores 11
71 size, the extrusion using a tetrafluoroethylene-hexafluoropropylene polymer is advantageous because this polymer has particularly excellent adhesion properties.

h, Mizumoto IIJJ) No.'-(1) rLl (+':
J kl,, Air (Ait Green (1) The purpose is to make the response speed faster. In other words, the conventional catalyst type 1k tJ,) m example water repellent 1 (because it does not have 1,
The reaction proceeded by a mechanism in which the wood was dissolved into the electrolyte, and then the reactive species that reached the surface of the catalyst electrode took part in the electrode reaction. In such a reaction, the rate-limiting step was the dissolution process of the detected gas into the liquid.
In general, it takes around 15 seconds for a 90% response of a gas sensor.In contrast, in the present invention, since the catalyst electrode is given white water properties, in this case, the reaction This occurs at the three-phase interface between the sensing gas, the electrolyte, and the catalyst electrode, and because there is no dissolution process of the gas into the liquid, the reaction rate becomes faster.

According to the monthly diaphragm in the present invention, polytetrafluoroethylene, 1 dylene tetrafluoride - 6 fluoride dylene cobolima =
Fluororesins such as , tetrafluoroethylene-ethylene copolymers are suitable. Catalytic metals include platinum and rhodium, depending on the gas being detected.

Platinum group metals such as palladium, gold or silver are suitable. The fluororesin that should be coated in the final process is polycarbonate.
Tetrafluoroethylene or tetrafluoropropylene copolymers are suitable.

In addition, during the final heat treatment process, press the sea urchin into the sea urchin and insert it into the sea urchin during the heat treatment.
Shiyoi.

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

Example: Tetrafluoroethylene-ethylene with a thickness of 25μ
Prepare a diaphragm made of 1 poly 7-, and on one side of it, j) 5
% of 4-fluorinated propylene-6-fluorinated propylene:] Borin- was applied with an aqueous suspension and heat-treated at 200°C.
Forms a porous layer. Next, gold as a catalyst metal is vaporized onto the surface of this porous layer. The incense thickness is 6008. Next, this gold-deposited laminate was coated with 5% polytetrafluoride-1-7.
After being immersed in a water suspension for 1 hour, it was once dried and then heat-treated at 270°C in a nitrogen stream. In this way, a water-repellent treatment is applied and a diaphragm-catalyst electrode assembly is obtained.

Comparative Example A galvanic cell-type oxygen valve as shown in FIG. 1 was manufactured using the diaphragm-catalyst electrode assembly prepared in Example C11. In the figure, (1) is 1l
il IID! - Catalyst electrode assembly - (with -11 porous diaphragm (2) and porous tetrafluoride polydylene-hexafluoride copylene compound (3) and catalyst electrode treated with water repellent (3)
4). (5) is the fffi electrode, (6)
is an aqueous solution of acetic acid, potassium acetate, and lead acetate! ] It is an electrolyte solution that grows every day. Each of these Lenz-1M main trees is fixed or housed in a polypropylene boulder (7), the catalyst type 1N+ (4> is the 11th pole, the lead electrode (5) is the negative electrode, and the positive electrode is the n Resistance between poles (8)
When connected, the voltage across the resistor (8) is proportional to the oxygen concentration.

This carbani cell type oxygen sink is designated as △, and the above embodiment is d'3. The following comparative test was carried out using the type Senry as B and the conventional Renly as C, in which a gold plate was brought into contact with the diaphragm as a catalyst electrode.

First, we investigated the change over time in the output voltage at the resistor end when each of the above-mentioned Renlys was placed in the air for 30 minutes, and the results shown in FIG. 2 were obtained. In other words, while the product Δ of the present invention and the conventional product C had no change in output voltage, the output voltage of the conventional product B significantly decreased. Therefore, after 30 days, each sensor was disassembled and investigated, and in the case of the conventional product [3], the gold electrode was partially separated from the diaphragm by 31 cm. On the other hand, no abnormality was observed in the case of the product ΔJ3 of the present invention and the conventional product O. From this result, in the case of the present invention, compared to the conventional product, the bonding strength between the catalyst electrode and the diaphragm was J
, I learned four strong things.

Next, we compared the response speeds and found that the time required for a 9()% response was 8 seconds for product A of the present invention, 14 seconds for conventional product B, and 14 seconds for conventional product C. In this case, it was 15 seconds.

From this result, the response speed of the product of the present invention is lower than that of the conventional product.
There are four things that are fast.

As described in detail above, in the present invention, which bonding strength + a between the diaphragm and the catalyst electrode is favorable, but is it suitable? 3: It provides a high-speed gas flow, and its industrial value is determined by humans.

Note that the gas range of the present invention can also be applied to measure the amount of air dissolved in the gas.

[Brief explanation of the drawing]

Fig. 1 is a schematic cross-sectional diagram of a galvanic cell type oxygen range using a diaphragm-catalyst electrode assembly according to an embodiment of the present invention, and Fig. 2 is a diaphragm-catalyst electrode assembly according to an embodiment of the present invention. Galvanic cell type oxygen sensor Δ using , conventional product B
FIG. 3 is a diagram comparing the changes over time in the output voltage of conventional product C and conventional product C. U... Separation IQ-catalyst electrode assembly, 2... Non-porous diaphragm, 3... Porous tetrafluoroethylene-hexafluoropropylene layer, 4... Catalyst N pole, 5... Lead electrode, 6...
Electrolyte, 7... Holder, 8... Resistor

Claims (1)

[Claims] 1. Water of tetrafluoroethylene-hexafluoropropylene copolymer or fj
Soft! After applying the AI suspension and applying heat treatment or drying, the laminate in which the catalytic metal is fixed by the incense method or sputtering method is mixed with fluororesin in water or an organic solvent. ! Either immerse it in a turbid liquid or apply a water or organic solution of fluororesin to the surface of the laminate to which the catalyst metal is fixed!
lIl! 1. A method for producing a diaphragm-catalyst electrode assembly for gas hydroxide, which comprises depositing a suspension and then subjecting it to heat treatment.