JP2013152090A - Working pole structure of galvanic cell type oxygen sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sensor which can discharge carbonate from between a working pole and a diaphragm, with forced flow of an electrolyte even for a working pole with a closed circumference.SOLUTION: A working pole of a galvanic cell type oxygen sensor includes a plurality of through holes 2 at a central region, and recesses 4 radially extending from the through holes 2 toward periphery on a face in contact with a gas permeable diaphragm.

Description

  The present invention relates to a structure of a working electrode of a galvanic cell type oxygen sensor.

In the galvanic cell type oxygen sensor, a working electrode made of a noble metal such as Au, Pt, or Ag and a counter electrode made of Pb are immersed in an electrolytic solution tank, and a breathable diaphragm is in close contact with the outer surface of the working electrode. Oxygen passes through the diaphragm and is reduced at the working electrode. At the same time, Pb oxidation proceeds at the counter electrode.
Thus, when the working electrode and the counter electrode are connected by a resistor, a voltage proportional to the oxygen concentration is generated in the resistor.

However, the carbon dioxide in the air is the electrolyte and CO2 + 2KOH → K2CO3 + H2O.
As a result of this reaction, carbonate (K2CO3) is generated and deposited between the working electrode and the diaphragm, which reduces the sensitivity.
In order to solve such a problem, as seen in Patent Document 1, radial ridges or ridges are formed on one surface of the working electrode and the diaphragm, and the electrolyte solution between the working electrode and the diaphragm is removed. It is conceivable to improve the fluidity.

  However, although the above-described sensor has a working electrode whose periphery is open to the electrolyte, a sensor having a structure in which the periphery of the working electrode is closed, such as the sensor described in Patent Document 2, has a somewhat convex shape. Even if strips or recesses are formed, the carbonate between the working electrode and the diaphragm cannot be discharged into the electrolyte tank because the working electrode and the diaphragm are not in communication with the electrolyte tank. It is.

Japanese Utility Model Publication No.59-21758 JP 2002-55077 A

  The present invention has been made in view of such circumstances, and the object of the present invention is to promote the flow of the electrolytic solution even if the working electrode has a closed peripheral edge, so that carbon dioxide is introduced from between the working electrode and the diaphragm. It is to provide a sensor capable of discharging salt into an electrolyte bath.

  In order to achieve such a problem, in the present invention, in the working electrode of the galvanic oxygen sensor, a plurality of through holes are formed in the central region, and the peripheral portion from the through hole is formed on the surface in contact with the breathable diaphragm. A cathode of a galvanic oxygen sensor in which a radial recess extending in the direction is formed.

  The generated carbonate crystals are quickly discharged from the opening through the radial recesses to the electrolyte bath, and the detection sensitivity is maintained regardless of the presence of CO2.

FIGS. 2A and 2B are plan views showing an embodiment of the working electrode of the galvanic oxygen sensor of the present invention. Diagram showing the cross-sectional structure when the working electrode is installed as a sensor The diagram which shows the time passage of the sensitivity recovery | restoration by the cathode of this invention, and the conventional cathode.

  FIGS. 1A and 1B show one embodiment of the working electrode (cathode) of the galvanic oxygen sensor of the present invention, respectively, and FIG. 2 shows a sectional structure when the working electrode is incorporated as a sensor. (In this figure, in order to clarify the structure of the working electrode, the diaphragm is shown slightly lifted from the working electrode.) The working electrode 1 is described in Patent Document 2. Similar to the sensor, a plurality of through holes 2 are formed at equal intervals in the central region of the metal having an oxidizing action, and each of these through holes 2 is in contact with the breathable diaphragm 3 so as to start from here. Concave portions 4 extending radially in the outer circumferential direction are formed on the side surface by etching or the like.

  In the figure, reference numeral 5 denotes a through hole formed in the center, and reference numeral 6 denotes a base part of a sensor constituent member that supports the working electrode 1 at its peripheral edge 1a.

  According to this embodiment, the carbonate produced between the diaphragm 3 and the working electrode 1 by the CO2 that has passed through the diaphragm 3 moves to the through-hole 2 via the recess 4 and is discharged to the electrolytic solution tank and is discharged into the electrolytic solution. Spreads in.

  As a result, even if the peripheral edge 1a of the working electrode 1 is pressed or the peripheral edge 1a is embedded in a resin and the peripheral edge 1a of the working electrode 1 is not in communication with the electrolytic solution tank, The target gas can be accurately measured over a long period of time regardless of the CO2 concentration.

  FIG. 3 shows the progress of detection sensitivity of the target gas after leaving for a predetermined time in an environment containing a constant concentration of CO 2. In FIG. 3, reference symbols A and C indicate the case of contact with the atmosphere, and reference symbol B indicates the concentration. The sensor of the present invention (solid line in the figure) in the case of continuous contact with a mixed gas of 5% CO2, 20% concentration O2 and 75% concentration N2 for 7 days, and the conventional sensor (in the figure) , Dotted line) indicates a change in the indicated value.

From this figure, when the oxygen sensor is configured using the working electrode of the present invention, the indicated value corresponding to the oxygen concentration is presented in a short time, whereas in the oxygen sensor configured by the conventional working electrode, The indicator value gradually changes over a long period of time due to the effect of CO2 and presents a concentration lower than the actual O2 concentration.
This shows that the present invention is useful.

  In the above-described embodiment, the working electrode with the peripheral edge portion closed is described as an example. However, it is obvious that the embodiment is more effective when applied to a type in which the peripheral edge portion is open.

1 Working electrode 2, 4 Through hole 3 Diaphragm 4 Recess

Claims (1)

In the working electrode of the galvanic oxygen sensor, a galvanic oxygen in which a plurality of through holes are formed in the central region, and a radial recess extending from the through hole toward the peripheral portion is formed on the surface in contact with the breathable diaphragm. The working electrode of the sensor.

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