JP6433051B2 - Gas detector with sensitivity recovery function - Google Patents

Description

  The present invention relates to a sensitivity recovery technique for an electrochemical gas sensor that takes in a gas to be detected through a breathable diaphragm and uses an electrolysis current generated between a working electrode member and a counter electrode member as a detection signal.

  Gibbs energy such as hydrogen chloride (HCl) using a working electrode as a thin film formed by co-sputtering platinum and carbon as disclosed in Patent Document 1 (amount of energy that can be extracted as work under isothermal isobaric conditions) ) For detecting a large gas, as shown in FIG. 4, about 0.5 V with respect to the reference electrode (natural potential 0.829 V), which is higher than 0.3 V when hydrogen bromide (HBr) is detected. It is necessary to apply a high potential.

For this reason, the electrochemical gas sensor for detecting hydrogen chloride (HCl) has a problem that the sensitivity is lowered in a shorter time than the case of detecting hydrogen bromide (HBr) as shown in FIG.
In addition, in Patent Document 2, it is described that a potential having a polarity that increases the electrolysis current at the time of measurement is applied to the working electrode in order to recover the sensitivity decrease due to the adhesion of an external entry-derived material to the working electrode. When applied to the present invention derived from the oxidation of the metal constituting the working electrode, the oxidation of the metal of the working electrode proceeds and the detection sensitivity further decreases.

JP 2003-121407 A JP-A-2005-127828

  The present invention has been made in view of such problems, and an object of the present invention is to provide a sensitivity recovery technique for an electrochemical gas sensor using a metal as a working electrode.

The present invention provides an electrochemical gas sensor in which a working electrode configured by simultaneously sputtering platinum and carbon on a gas-permeable diaphragm and a counter electrode formed on the gas-permeable diaphragm are provided in a cell containing an electrolyte solution. The potential applied to is changed to the base potential side more intermittently than during the detection operation, and the platinum is reduced to recover the sensitivity.

  The detection sensitivity can be recovered by a simple method in which the potential applied to the working electrode is stopped for a short time and changed to the base potential side.

The block diagram which shows one Example of the gas detector which uses a constant potential electrolytic gas sensor. The diagram which shows the time-dependent characteristic of the sensitivity of the conventional and the potentiostatic gas sensor of this invention. The block diagram which shows the other Example of the gas detector which uses a constant potential electrolytic gas sensor. The diagram which shows the electric potential characteristic which took hydrogen chloride and hydrogen bromide as an example. The diagram which shows the time-dependent characteristic of the detection sensitivity by the electric potential of a working electrode.

Therefore, details of the present invention will be described below based on the embodiment shown in FIG.
The constant potential electrolytic gas sensor 1 is provided with windows 4 and 5 in a cell 3 containing an electrolytic solution 2, and in this embodiment, a working electrode 6 is formed by forming one window 4 by simultaneous sputtering of platinum and carbon. The other window 5 is sealed with a breathable diaphragm in which a counter electrode 7 and a reference electrode 8 are formed.

  A constant potential power supply 10 and a potential changing means 11 are connected between the working electrode 6 and the reference electrode 8 via an operational amplifier 9, and a potential suitable for detecting the target gas by the constant potential power supply 10. In general, a voltage of 300 to 700 millivolts is always applied, and a voltage for changing the potential of the working electrode 7 to the base potential side for a predetermined time T is applied by the potential changing means 11 for a predetermined time, that is, when the detection sensitivity is lowered. Is done.

  An electrolytic current detection circuit 12 for detecting a current flowing through the working electrode 6 and the counter electrode 7 is connected to the output side of the operational amplifier 9 so that the gas concentration is displayed on the display means 13.

  In this embodiment, when only the potential of the constant potential power source 10 is applied, an electrolysis (oxidation) current corresponding to the concentration of hydrogen chloride flowing in from the window 4 of the constant potential electrolysis gas sensor 1 is applied to the working electrode 6 and the counter electrode. 7, and the concentration of hydrogen chloride is displayed on the display means 11.

  When the detection sensitivity is lowered to such an extent that a measurement error is generated, the potential changing means 11 is operated to change the potential of the working electrode 6 to the base potential side as compared with the detection operation. As a result, the oxidized platinum particles constituting the working electrode 6 are reduced and the detection sensitivity is restored.

  FIG. 3 shows the sensitivity (relative span output) when the potential of the working electrode 6 is continuously maintained at a potential suitable for detection of the test gas (HCl), for example, 500 millivolts, and the sensitivity recovery technique of the present invention. Application, in this example, shows a change in sensitivity when a detection potential (500 milliV) is applied for 11 minutes and is not applied for 9 minutes and the working electrode 6 is set to a lower potential than at the time of detection. From the figure, it became clear that the decrease in sensitivity can be prevented by applying the detection potential discontinuously.

  FIG. 3 shows a second embodiment of the present invention. In this embodiment, a plurality of working electrodes are divided into two regions 61 and 62 in this embodiment. Thus, the constant potential power supply 10 is alternately switched and connected.

  In this embodiment, the region 61 is connected to the constant potential power source 10 by the switch 14 and the measurement operation is performed. When the detection sensitivity decreases with the passage of time, the constant potential power source 10 has been put into a resting state by the switch 14 until now. The area 62 is switched to.

  As a result, the detection operation is performed by the region 62 having a high catalytic ability, and the region 61 in which the catalytic ability has decreased due to the oxidation is reduced due to a decrease in potential, thereby recovering the catalytic ability.

According to this embodiment, the detection potential is applied to one of the working electrode regions, and the other region is in a reduced state, so that the detection target gas can be continuously detected with high sensitivity.

  It is apparent that the time interval for changing the working electrode to the base potential can be arbitrarily changed according to the type and concentration of the gas to be detected.

In the above-described embodiment, the case of detecting hydrogen chloride has been described, but an apparatus for detecting other gas components by setting a potential at which a thin film (working electrode) formed by simultaneous sputtering of platinum and carbon is oxidized. It is clear that it can be applied to the recovery of sensitivity.

In the above-described embodiments, the thin film (working electrode) formed by co-sputtering of platinum and carbon is used as the working electrode. However, for example, platinum black and a binder are mixed and water-repellent ventilation is performed. It is clear that the sensitivity can be recovered even when applied to an electrochemical gas sensor in which platinum oxidation proceeds in a state where a measurement potential is applied using a working electrode printed in a film shape on a conductive film.

 6 Working electrode 61, 62 Working electrode area 7 Counter electrode 10 Constant potential power supply

Claims (2)

In an electrochemical gas sensor in which a working electrode configured by simultaneously sputtering platinum and carbon on a gas-permeable diaphragm and a counter electrode formed on the gas-permeable diaphragm are provided in a cell containing an electrolyte, an electric potential applied to the working electrode The gas detector is characterized in that the sensitivity is recovered by reducing the platinum by intermittently changing to the base potential side than during the detection operation. The working electrode is divided into a plurality of regions, the detecting operation is one area, in claim 1, other areas and repeating alternately the sensitivity recovery operation held in卑電position than during the detection operation The gas detector described .

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