ELECTROCHEMICAL GAS SENSOR

Abstract

An electrochemical gas sensor (1) having a stacked assembly of at least one first electrode (3) and a second electrode (6), which are respectively arranged on a carrier membrane (2, 5), and a separator (4) arranged between the electrodes (3, 6), including a gas conduction path (14) between the first electrode (3) and the second electrode (6). The gas conduction path (14) is constituted within the structural space defined by the electrodes (3, 6).

Claims

1. An electrochemical gas sensor (1), comprising: a stacked assembly of at least one first electrode (3) and a second electrode (6), which are arranged on respective carrier membranes (2, 5); a separator (4) arranged between the at least one first electrode and the second electrodes (3, 6); and a gas conduction path (14) constituted between the first electrode (3) and the second electrode (6); and the gas conduction path (14) is constituted within a structural space defined by the electrodes (3, 6).

2. The electrochemical gas sensor (1) as claimed in claim 1, further comprising at least one feedthrough opening (11) arranged in the separator (4), by which the gas conduction path (14) is constituted.

3. The electrochemical gas sensor (1) as claimed in claim 2, wherein the at least one feedthrough opening (11) is arranged in the carrier membrane (2) of the at least one first electrode.

4. The electrochemical gas sensor (1) as claimed in claim 3, further comprising an insert (12) inserted in at least one of the at least one feedthrough opening (11) in the separator (4) or the carrier membrane (2) of the first electrode (3).

5. The electrochemical gas sensor (1) as claimed in claim 4, wherein at least one of the separator (4) or the insert (12) comprises at least two feedthrough openings (11), and a separate gas conduction path (13) is defined by each said feedthrough opening (11) within the structural space defined by the electrodes (3, 6).

6. The electrochemical gas sensor (1) as claimed in claim 2, wherein the at least one feedthrough opening (11) is arranged at least one of essentially centrally or coaxially to the electrodes (3, 6).

7. The electrochemical gas sensor (1) as claimed in claim 1, wherein the stacked assembly is configured with a rotationally symmetrical design.

8. The electrochemical gas sensor (1) as claimed in claim 1, wherein the separator (4) is configured as a glass-fiber membrane.

9. The electrochemical gas sensor (1) as claimed in claim 1, wherein the carrier membranes (2, 5) are comprised of polytetrafluoroethylene or PTFE.

10. The electrochemical gas sensor (1) as claimed in claim 1, wherein the electrodes (3, 6) are comprised of platinum.

11. The electrochemical gas sensor (1) as claimed in claim 1, wherein the first electrode (3) is configured as a ring.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The invention is described in greater detail hereinafter on the basis of exemplary embodiments, with reference to the attached drawings.

[0022] In the drawings:

[0023] FIG. 1: shows a schematic cross-section of a sensor according to the invention, according to a first embodiment;

[0024] FIG. 2: shows a schematic cross-section of a sensor according to the invention, according to a second embodiment;

[0025] FIG. 3: shows a schematic cross-section of a sensor according to the invention, according to a third embodiment with two independent gas paths;

[0026] FIG. 4: shows an exploded diagram of a sensor according to the invention, and

[0027] FIGS. 5A-5I: show various designs for the feedthrough openings.

DETAILED DESCRIPTION

[0028] FIG. 1 shows a schematic representation of an electrochemical gas sensor 1 according to the invention, having a stacked assembly of electrodes, according to a first embodiment. In the interests of greater clarity, no housing is shown in this schematic representation.

[0029] In the example represented, the gas sensor 1 is comprised of layers arranged in the following sequence from top to bottom: a first carrier membrane 2, a first electrode 3 (sensor electrode), a first separator 4, a second carrier membrane 5, a second electrode (auxiliary electrode) 6, a second separator 7, a shielding membrane 8, a third separator 7, a third electrode (counter-electrode) 9, a fourth electrode (reference electrode) 9′, a third carrier membrane 10 and a fourth separator 7.

[0030] The carrier membranes 2, 5 and 10 are comprised, for example, of polytetrafluoroethylene or PTFE. The separators 4 and 7 are comprised, for example, of a composite glass-fiber material.

[0031] In the present example, the gas sensor is configured with a rotationally symmetrical design. The layers represented are thus configured in either a circular or an annular arrangement.

[0032] The four electrodes 3, 6, 9 and 9′ are respectively arranged directly on the associated carrier membrane 2, 5 and 10, wherein the third electrode 9 and the fourth electrode 9′ are arranged on the same carrier membrane 10 and, in each case, occupy only approximately a half-circle thereof.

[0033] The electrodes 3, 6 and 9, together with 9′, assume a mutually equal diameter which, however, is smaller than the diameter of the carrier membranes 2, 5 and 10. The diameter of the carrier membranes 2, 5 and 10, conversely, is smaller than the diameter of the separators 4 and 7 and of the shielding membrane 8.

[0034] It is critical to the invention, however, that the first separator 4 assumes a larger diameter than the respectively adjoining carrier membranes 2 and 5, and that the first separator 4 incorporates a feedthrough opening 11.

[0035] In the present example, this feedthrough opening is arranged coaxially in the center of the first separator 4, and is also configured with a circular design. By the rotationally symmetrical configuration of the stacked arrangement, a simple assembly and an error-tolerant design is possible. A more accurate calibration can be achieved accordingly.

[0036] By this arrangement of the first separator 4 according to the invention, a central and concentric gas conduction path is constituted. This means that gas diffusion from the first electrode 3 to the second electrode 6 is executed through this feedthrough opening 11 and not, as per the prior art, at the perimeter of the sensor.

[0037] The gas conduction path 14 thus requires no structural space at the perimeter of the sensor 1. As a result, the overall diameter of the sensor can be reduced, with no undershoot of the minimum dimension of the electrodes.

[0038] Alternatively, the feedthrough opening 11 can also be arranged off-center. It is important, however, that it should be arranged within the structural space defined by the electrodes 3, 6 and thus, specifically, not in the circumferential region 13 of the carrier membranes 2, 5, which projects beyond the electrodes 3, 6.

[0039] The feedthrough opening 11 can also assume a different shape, for example quadratic or elliptical. The feedthrough opening 11 permits a reliably reproducible adjustment of gas diffusion to the second electrode. In particular, this also applies to miniaturized sensors.

[0040] In the present example, moreover, an insert 12 is inserted in the feedthrough opening 11. This insert 12 is also comprised of PTFE and securely establishes the gas contact and/or gas path between the first electrode 3 and the second electrode 6, through the separator 4. The insert 12 assumes essentially the same shape as the feedthrough opening 11, and occupies the full surface area of the latter.

[0041] The third electrode 9 is employed as a reference electrode. The fourth electrode 9′ is employed as a counter-electrode. By means of the second and third separators 7 and the shielding membrane 8, it is ensured that no gas is diffused from the second electrode 6 to the third electrode 9 and the fourth electrode 9′. It is important, however, that no gas conduction path 14 is constituted as a result.

[0042] FIG. 2 shows an alternative embodiment of a gas sensor 1 according to the invention. The layout thereof, particularly the sequence of layers, is identical to FIG. 1. Accordingly, identical parts are identified by the same reference symbols, and are not described again. There is a single distinction from the embodiment according to FIG. 1, in that the first carrier membrane 2 also incorporates a feedthrough opening, which is preferably configured in an identical manner to the feedthrough opening 11 in the first separator 4.

[0043] FIG. 3 shows a further embodiment of a gas sensor 1 according to the invention, in which the sequence of layers is identical to the embodiments according to FIGS. 1 and 2. Accordingly, identical parts are identified by the same reference symbols, and are not described again. However, this embodiment comprises two independent gas paths. To this end, the first carrier membrane 2, the first electrode 3 (the sensor electrode) and the first separator 4 respectively comprise two feedthrough openings 11. Moreover, two second electrodes (auxiliary electrodes) 6 and 6′ are provided, as a result of which, effectively, two different sensors are constituted. The two second electrodes 6 and 6′ can be configured, for example, with a semicircular or semi-annular design. In this manner, a plurality of different gases can be detected within a housing.

[0044] FIG. 4 shows an exploded diagram of a gas sensor 1 according to the invention. In the present example, the gas sensor 1 comprises a quadratic tank 18. In the present example, the sensor is a carbon monoxide sensor, wherein the tank is filled with 40% sulfuric acid. Tubular projections 19 project from the tank floor, through which electrical contacts for the four electrodes are routed. The electrical contacts comprise platinum wires 20, which can be/are connected to the respective electrodes.

[0045] A bed 17 is fitted to the tubular projections 19, which carries the layered structure of the sensor. The bed 17 incorporates two approximately centrally-arranged rectangular openings 21, through which a staple-shaped wick 16 passes. Both ends of the wick 16 are immersed in the sulfuric acid which is contained in the tank, and convey the sulfuric acid to the third electrode 9 and the fourth electrode 9′.

[0046] On the bed 17, a separator 7 is firstly arranged. A carrier membrane 10 is applied to the latter, which carries the third electrode 9 and the fourth electrode 9′. A further separator 7 is then arranged on the electrodes 9 and 9′. A shielding membrane 8 is applied to this separator 7.

[0047] Above the shielding membrane 8, the following are arranged in the sequence described hereinafter, from bottom to top: a separator 7, a second electrode (auxiliary electrode) 6, a separator 4 and a first electrode 2. The separator 4 and the first electrode 2 incorporate a central feedthrough opening 11, which is closed by an insert plate 12.

[0048] The sensor assembly is closed by a cover, wherein openings 22 are arranged in the cover 15 for the permeation of gas.

[0049] FIGS. 5A-5I shows various exemplary embodiments of feedthrough openings 11 in a first separator 4 which, in the present example, is circular. The first separator 4 can also assume a different shape which, however, has no impact upon the shape of the feedthrough openings. The feedthrough openings illustrated can also be arranged in a first carrier membrane 2. FIG. 5A shows a circular feedthrough opening 11, which is arranged coaxially to the separator 4. FIG. 5B shows a quadratic feedthrough opening 11, which is arranged centrally/coaxially to the separator 4. FIG. 5C shows two approximately bracket-shaped feedthrough openings 11, which are separated by a web.

[0050] FIG. 5D shows an elliptical feedthrough opening 11, which is arranged centrally/coaxially to the separator 4. FIG. 5E shows a plus sign-shaped feedthrough opening 11, which is arranged centrally/coaxially to the separator 4. FIG. 5F shows three circular feedthrough openings 11, which are arranged symmetrically to the center of the separator 4. FIG. 5G shows a Pacman-shaped separator 4, wherein a triangular feedthrough opening 11 is arranged at the perimeter of the separator 4. FIG. 5H shows a separator 4 having two circular segment-shaped feedthrough openings 11, which are separated by a web such that, overall, a “no entry” sign-shaped separator 4 is constituted. FIG. 5I shows a separator 4 having two circular feedthrough openings 11 which, however, assume different diameters.

[0051] In all the embodiments, the arrangement, size and/or number of feedthrough openings 11 can be varied, in order to achieve a specific and defined gas diffusion rate.

[0052] According to a further embodiment, in the embodiments according to FIGS. 5C, 5F, 5h, and 5I, each feedthrough opening 11 can define a separate gas conduction path 14, as represented, for example, in FIG. 3.

LIST OF REFERENCE SYMBOLS

[0053] 1 Sensor [0054] 2 First carrier membrane [0055] 3 First electrode (sensor electrode) [0056] 4 First separator [0057] 5 Second carrier membrane [0058] 6, 6′ Second electrode (auxiliary electrode) [0059] 7 Separator [0060] 8 Shielding membrane [0061] 9 Third electrode (counter-electrode) [0062] 9′ Fourth electrode (reference electrode) [0063] 10 Third carrier membrane [0064] 11 Feedthrough opening [0065] 12 Insert [0066] 13 Perimeter region [0067] 14 Gas conduction path [0068] 15 Cover [0069] 16 Wick [0070] 17 Bed [0071] 18 Tank [0072] 19 Tubular projection [0073] 20 Platinum wire [0074] 21 Opening in bed [0075] 22 Opening in cover