JPS60227161A - Multigas sensor - Google Patents

Abstract

PURPOSE:To enable simple and accurate measurement of the concn. of plural kinds of gases with one sensor by using a photoelectrochemical cell consisting of plural porous photoelectrodes consisting of two kinds of semiconductor compds. having different band gaps at changed compounding ratios and a sheet of common counter electrode. CONSTITUTION:The plural electrodes consisting of the porous photoelectrodes 1'1-1'n made of, for example, CdS and CdSe having different band gaps or CdTe alone or plural changed compounding ratios in such a way as to consist the electrodes of the CdS alone, 3/1, 1/1, 1/3 CdS/CdSe, 1/1 CdSe/CdTe and CdTe alone are provided on a conductive film which is a Cd<2+> impermeable polypyrrole film by sputtering. Hexafluoropolypropylene is electrostatically painted and baked on the electrodes 1'1-1'n to form an ion conductor film 2 having impermeability to the photoelectrode material ion. The counter electrode 5' common with the film 3 is formed of a platinum plate and an electrolyte (30% aq. sulfuric acid soln.) 4 is inserted between the film 3 and the counter electrode 5', by which a multigas sensor is obtd. 11-1n, 5 are lead wires. The simultaneous measurement of, for example, CH4, CH3OH, C2H5OH, HCO, HCOOH, CO, etc. is thus made possible with one cell.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a multi-gas sensor that utilizes photoelectrode reactions.

Conventional configurations and their problems Conventional gas sensors include semiconductor type, which utilizes the change in resistance of oxide semiconductor ceramics, and catalytic combustion, which utilizes the change in resistance of a platinum wire embedded in a catalyst carrier due to catalytic combustion. Many formulas have been put into practical use.

Although it is possible to select the gases that can be detected to some extent depending on the type of semiconductor, catalyst, and set temperature, there are a considerable number of interfering gases.

In response, sensors that combine the permselectivity of organic polymer membranes and solid electrolytes with electrochemical measurement methods have been developed, and the selectivity has been considerably improved, but it is still difficult to expect perfection. It was true.

Furthermore, these sensors are discrete sensors intended for single measurement, and are not intended to simultaneously detect the types and concentrations of many gases with a single sensor.

OBJECTS OF THE INVENTION The present invention provides a new type of sensor based on this principle, which simultaneously detects the type and concentration of a photoreacting gas based on the difference in band gap.

Structure of the Invention The present invention is a sensor with excellent selectivity that can detect the identification and concentration of multiple types of substances with a single element. This is a multi-gas sensor that prepares a porous photoelectrode, identifies the type of gas by utilizing the fact that the potential for photoelectrode reactions to occur differs depending on the type of gas, and detects the concentration using the diffusion limit current.

DESCRIPTION OF THE EMBODIMENTS FIG. 1 shows the basic structure of a multi-gas sensor according to an embodiment of the present invention, in which A is a front view, the opening is a side view, and C is a rear view. In the figure, 11 to 1n are leads from the porous photoelectrode. Usually PT foil is used. 11-1n are photoelectrodes with slightly different band gaps, Examples 1-2
So Cd5on1. y.

CdS/CdSe = 3/1.1/j, 1/3, C
d5eon only.

02 was made by sputtering CdSe/Cd5=7/1 and CdTeonly or a mixture thereof to a thickness of approximately 5000 mm on a conductor film 3 consisting of a polypyrrole film that is impermeable to Cd2+4 ions, and the photoelectrode current was It is a porous film made of a transparent material that is controlled by the diffusion of the detection gas from the atmosphere. In the example, it is made by electrostatically coating hexafluoride polypropylene on the photoelectrode 11~1゜ and baking it at 200~250°C. Ta. 3 is an ion conductor film impermeable to ions of the photoelectrode material to prevent corrosion of the photoelectrode. 4 is an electrolytic solution, and in the example, a 30% H2S4 aqueous solution was used. 5 is the opposite lead. 5' is a counter electrode, in which a single smooth platinum plate was used in the example; 6 is a cell container made of electrolyte-resistant resin; 7 is photoelectrode elements 1'1 to 1'n, 2.3, and Epoxy resin was used as the adhesive material for fixing the counter electrode 5' to the cell container 6.

After irradiating the photoelectrode with a 500 WX e-lamp, CH4, CH30H,, C2H3O style HCH○, HCO
Oh.

The short-circuit current flowing between each photoelectrode and the counter electrode was measured when exposed to an atmosphere of 10'ppm Co (remaining air).

The currents are shown in numbers 1 to 6 in FIG. 2, respectively.

From this, the photocurrent flows from the electrode where the valence band of the photoelectrode is about 150 mV higher than the oxidation/reduction potential of the gas, and the oxidation/reduction potential (CH40, 169v1CH
30HQ, o44v1C2H5oH0,028v1HC
HO-0,050V, HCOOH-o, 1ssV, C0
-0.103V).

In other words, if we take a preliminary look at the correspondence relationship, we can determine the type of debris by looking at which electrode the photocurrent begins to flow from. From this example, it was confirmed that a photoelectrode with a large band gap exhibits a saturation current value for any gas type.

In order to see whether this saturation current value is due to the diffusion limit current, in other words, whether the gas concentration can be determined from the saturation current value iλ, CH30)'i concentration is set to 1.
The current value flowing through the CdS photoelectrode which showed a sufficient saturation current value was measured by changing the current value in the range of 0 to 200 ppm.

As shown in FIG. 3, this value is completely proportional to the gas concentration, and it was found from this that the gas concentration can be determined for a single gas.

CH4, CH to see the effect of photocurrent due to mixed gas
The photocurrent was measured in an atmosphere containing 60 and 1100 pp of 30H, HCOoH. In this case, in order to increase the detection accuracy of the gas type, the solid solution ratio of the photoelectrode is changed to CdTe/
Cd5e=3/1.1/3 and CdSe/Cd5=7/1
And so.

The photocurrents in each gas atmosphere are shown at A and A in Figure 4.

When this result is viewed together with the results for single gases in FIGS. 2 and 3, it is recognized that the photocurrent in FIG. 46 shows the sum of the photocurrents for single gases. It is constituted by several photocurrent plateaus.

The band gap at which the photocurrent rises from the flat region corresponds to the gap at which the photocurrent of a single gas flows, so the type of gas can be fixed by this.

Furthermore, since the flat current is the sum of the saturation currents of multiple gas species, the concentration of a single gas in the mixed gas can be determined by comparing them.

In the above embodiment, the porous photoelectrode forms a solid-liquid three-phase region with respect to the electrolytic solution and gas, so that the photoelectrode reaction is diffusion-controlled.

Effects of the Invention As described above, by attaching a photoelectrode to one sensor and measuring the photocurrent of each, an unprecedented effect can be expected in which a plurality of gases and their concentrations can be easily known.

[Brief explanation of the drawing]

Figures 1-I are a front view, side view, and rear view of a multi-sensor according to an embodiment of the present invention, and Figure 2 shows the current flowing through each photoelectrode when the multi-sensor is exposed to a single gas atmosphere. Figure 3 shows the relationship between the CdS photoelectrode current and CH30H concentration when the multi-sensor is exposed to a CH30H atmosphere, and Figure 4 shows the relationship between the CdS photoelectrode current and CH30H concentration when the multi-sensor is exposed to a mixed gas. FIG. 3 is a diagram showing a current flowing through a photoelectrode. 11-1n... Porous photoelectrode, 2... Transparent porous membrane, 3... Conductor film, 4... Electrolyte, 6... ... Counter electrode lead, 6 ... Cell container, 7 ... Adhesive material. Name of agent: Patent attorney Toshio Nakao (1st person)
Figure (Ino (Rono (7\) Figure 2. ” t, 4 /, 6 L, S z, o 2.2 2.4
Figure 3 θ 4Q 80 120/60 2θθQH30/-1
Inn- (Inn-) Figure 4

Claims (2)

[Claims] (1) A plurality of porous photoelectrodes made of two types of semiconductor compounds with different 1 band gaps or raw materials obtained by solid solutioning them with different blending ratios are connected in parallel, and a counter electrode common to the plurality of porous electrodes is connected in parallel. A photoelectrochemical cell is constructed between
coating the gas side of the porous photoelectrode with a porous transparent material;
A multi-gas sensor characterized in that the electrolyte side of the porous body is coated with an ion-conductive 11C film that is impermeable to ions of an electrode material. (2) The porous electrode is made of CdS and CdSe or CdTe.
2. The multi-gas sensor according to claim 1, wherein the multi-gas sensor is a solid solution in which the mixing ratio of one or more of these is varied, and the counter electrode is made of PT or Pd metal.