JPH0417383B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrochemical cell and device that is simple in structure, has excellent low temperature operability and durability.

Oxygen sensors using electrochemical devices, such as zirconia solid electrolyte concentration cells, cannot sufficiently detect superpower in gases at temperatures below about 350°C, so in order to operate at low temperatures, a heating resistor must be attached to the sensor element. I'm letting you do it. At this time, if the resistor was in contact with the solid electrolyte, electrolysis of the solid electrolyte would occur due to the resistor current, resulting in deterioration of the solid electrolyte. Furthermore, a structure in which an insulating material such as alumina porcelain is interposed between the resistor and the solid electrolyte has been proposed, as disclosed in Japanese Patent Laid-Open No. 55-116248. Due to the difference in coefficient of thermal expansion between

The purpose of the electrochemical cell and device of the present invention is to solve the above-mentioned conventional drawbacks, and to obtain an electrochemical device that can be heated from room temperature to show excellent low-temperature operation characteristics and that is less prone to deterioration. That is.

The electrochemical cell and device of the present invention include a solid electrolyte, a pair of electrodes attached to the solid electrolyte, and a porous structure embedded in the solid electrolyte and made of the same main component as the solid electrolyte. an electrochemical cell consisting of a porous body, a refractory resistor embedded in the porous body, and a power source connected to both ends of the resistor, which is heated as a voltage is applied to the resistor. An electrochemical cell is an electrochemical device that detects or controls the concentration of components involved in electrode reactions in a fluid.

That is, the present invention applies an alternating voltage or current voltage to both ends of a resistor that is in contact with an electrochemical cell through a porous solid electrolyte, and heats the solid electrolyte by the heat generated by the resistor. This is based on the discovery that no electrolysis occurs, and therefore there is no deterioration of the solid electrolyte.

A more detailed configuration of the present invention will be explained with reference to FIG. 1, which shows an oxygen concentration detector as a specific example, and FIG. 2, which is a developed view of the cell portion of FIG. 1.

Platinum electrodes 2 and 3 are provided on both sides of a solid electrolyte 1 made of zirconia porcelain doped with ittria, and a resistor 5 made of platinum is provided on one side of one electrode 3 via a porous body 4 made of zirconia porcelain doped with ittria.
is provided, and the resistor 5 is connected to a power source 20. The porous body 4 is covered with an airtight layer 6 made of the same material as the solid electrolyte 1.

The electrode 3 is a reference electrode of the oxygen concentration battery, and its surface is exposed to the porous layer 4 interposed between the airtight layer 6 and the solid electrolyte 1. An electrode 2 made of platinum is provided on the other side of the solid electrolyte 1 as a gas electrode to be measured, and the solid electrolyte 1 and electrodes 2 and 3 constitute an oxygen concentration cell.

The gas to be measured reaches the surface of the electrode 2 through the opening 8 of the housing 7 and the opening 10 of the heat-insulating cylinder 9. On the other hand, the air serving as the reference gas passes through the vent hole 12 of the cap 11 and the hole 14 of the insulator 13 made of alumina porcelain to reach the surface of the electrode 3 serving as the reference electrode. The gas to be measured and air are hermetically sealed off by a glass 16 and a sealing part 17 that fill the gap between the support flange 15 and the solid electrolyte 1. In this case, the sealing portion 17 is held airtight by the spring 18 with the flange 15 of the supporting member being pressed against the housing 7 via the insulator 13 and the metal washer 19.

When a power source 20 is connected to both ends of the resistor 5, the resistor generates heat due to the Joule heat of the current flowing through the resistor 5, and heats the porous body 4 and the solid electrolyte 1 that are in close contact with the resistor.

The porous body 4 comes to exhibit oxygen ion conductivity as the temperature rises. Then, part of the current applied to both ends of the resistor 5 also flows into the porous body 4. However, oxygen, which is a product of electrolysis caused by the current flowing into the porous body 4, circulates through the porous layer, and no deterioration of the solid electrolyte occurs.

For example, in the case of zirconia porcelain, the porous material preferably has a Cubic phase;
It is preferable to add Ta, Na, etc. to reduce the conductivity.

Note that the porous body of the present invention has the same main components as the solid electrolyte means that, for example, when a zirconia solid electrolyte is used, a zirconia porous body is used, and stabilizers, sintering aids, etc. The additive components are not concerned.

In addition to zirconia porcelain, solid electrolytes that can be used in the present invention include β-alimina, aluminum titanide, NASICON, SrCeO ₃ , Bi ₂
O ₃ − rare earth oxide solid solution, La _1-X Ca _X YO _3- 〓, etc. Also, as a resistor, nickel, silver,
gold, platinum, rhodium, palladium, iridium,
Metals such as ruthenium, tungsten, and molybdenum or alloys thereof are preferred because of their excellent durability, but other compounds such as zinc oxide, LaCrO ₃ , LaB ₆ , and SiC may also be used.

In addition, methods for applying the resistor to the solid electrolyte include vacuum evaporation, sputtering, electroless plating,
It can be applied by any known method conventionally used for applying electrodes to ceramics, such as thermal decomposition or reduction of a metal salt solution, baking of a paste, cermet or thermal spraying.

In order to prevent the resistor from evaporating or becoming contaminated during use, the resistor may be protected with a fire-resistant layer such as spinel or alumina, or it may be embedded in a porous solid electrolyte.

It is also desirable to mix fine powder of zirconia, alumina, etc. into the resistor in order to prevent the resistor from peeling or disconnection due to sintering during use, and to adjust the resistance value of the resistor.

Example 1 Powder 100 consisting of 97 mol% ZrO ₂ and ₃ mol% Y ₂ O
1 part by weight of alumina as a sintering aid per part by weight;
In addition, 8 parts by weight of polyvinyl butyral and 4 parts by weight of dioctyl phthalate were added and mixed as molding aids, and a plate-shaped body having a thickness of 0.5 mm was formed from this mixture.

Then, a paste containing 95% platinum powder and 5% zirconia powder is printed on both sides of this plate-shaped body to form a gas electrode 2 to be measured and a reference electrode 3.
A paste consisting of 92 mol% ZrO ₂ and 8 mol% Y ₂ O ₃ which will become the porous body 4 is packed into the hollow part of this plate-shaped body, and one side of this plate-shaped body is filled with a paste that will become the porous body 4.
A paste consisting of 92 mol% ZrO ₂ and 8 mol% Y ₂ O ₃ was printed, and on top of that, 80% platinum and 20% rhodium were printed.
% alloy powder paste was printed to form a resistor 5, and a plate-shaped body alone was prepared, and as shown in FIG. 2, they were sequentially laminated to obtain an electrochemical cell.

This was sintered at 1400℃ to create an oxygen concentration detector. At that time, the solid electrolyte 1 was in the tetragonal phase, and the porous body 4 was in the Cubic phase. As a result of connecting a 12V DC power supply 20 to this oxygen concentration detector and applying electricity, the temperature of the resistor 5 rises to 600°C in about 40 seconds after the start of electricity supply, the current flowing at that time is 0.3A, and the temperature of the resistor 5 increases to 600°C.
The impedance between and 3 was 1KΩ, and it worked well as an oxygen concentration detector, and there was no effect on superpower due to the DC power supply.

As mentioned above, although the electrochemical cell and device of the present invention have a simple structure, they can quickly heat the solid electrolyte with a low voltage even at low temperatures, so they have extremely excellent low-temperature operability. Moreover, the solid electrolyte exhibits almost no deterioration due to heating and has excellent durability. It can be used as a detector or controller for components involved in reactions, and especially when used as a detector for oxygen concentration in exhaust gas discharged from an internal combustion engine, it can be used immediately after startup or in low-temperature exhaust gas during low-speed rotation. It also has the advantage of being able to accurately detect oxygen concentration, and is extremely useful from an industrial and pollution prevention perspective.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a specific example of using the electrochemical device of the present invention as an oxygen concentration detector;
FIG. 2 is an explanatory diagram showing the expanded structure and electrical connection method of the main parts of the electrochemical device shown in FIG. 1. 1... Solid electrolyte, 2, 2', 3... Electrode, 7
... Housing, 8, 10 ... Opening, 9 ... Heat insulation tube, 11 ... Cap, 12 ... Ventilation hole, 13
... Insulator, 14 ... Hole, 15 ... Flange, 1
6...Glass, 17...Sealing part, 18...Spring,
19... Washer, 20... Power source, 21... Potentiometer, 4... Porous body, 5... Resistor, 6... Airtight layer, 22... Ammeter.

Claims (1)

[Claims] 1. A solid electrolyte, a pair of electrodes attached to the solid electrolyte, and a porous body made of the same main component as the solid electrolyte and airtightly embedded in the solid electrolyte. and a refractory resistor embedded in the porous body. 2. A solid electrolyte, a pair of electrodes attached to the solid electrolyte, a porous body made of the same main component as the solid electrolyte and airtightly embedded in the solid electrolyte, and the porous body An electrochemical cell consisting of a refractory resistor embedded therein, and a power supply connected to both ends of the resistor, the fluid being heated in the electrochemical cell by applying a voltage to the resistor. An electrochemical device that detects or controls the concentration of components involved in an electrode reaction.