Electrochemical gas sensor

Abstract

The utility model provides a kind of electrochemical gas sensor for detecting target gas, the electrochemical gas sensor includes the substrate with upside, three electrodes are arranged on the upside and are configured to be connected to constant potential device, electrolyte is in contact with the electrode surface on the upside, cover is installed on the electrolyte on the reference electrode, wherein the cover covers at least half of the surface of the reference electrode, and the average extension dimension of the electrolyte perpendicular to the upside is less than the average extension dimension of the electrolyte parallel to upside.

Description

Technical Field

[0001] This utility model relates to an electrochemical gas sensor. Background Technology

[0002] Electrochemical gas sensors can be used to measure the concentration of target gases in ambient air. Miniaturization and low-cost manufacturing are absolutely essential for developing as many applications as possible. However, stringent requirements exist regarding accuracy, specificity, power consumption, and lifespan. Furthermore, miniaturizing stable reference electrodes such as silver / silver chloride is not easy.

[0003] Patent application WO2015200755A1 discloses an electrochemical gas sensor with a porous platinum electrode, wherein the porous platinum electrode is applied to a porous substrate by screen printing.

[0004] Patent document US9,213,013B2 discloses an electrochemical sensor comprising a substrate having three electrodes on its upper side. An ionic liquid membrane is disposed as an electrolyte covering surface and the three electrodes are arranged accordingly. The three electrodes are spaced apart from each other to enable electrochemical measurement of a target gas absorbed in the ionic liquid membrane. The three electrodes are configured as a reference electrode, a working electrode, and a corresponding electrode in the electrochemical sensor for connection to a potentiostat. A bias voltage is applied via the reference electrode and the working electrode, and the current generated by the applied voltage is measured via the working electrode and the corresponding electrode.

[0005] An electrochemical pH sensor is described in a scientific publication accessible via the permanent link https: / / doi.org / 10.3390 / s17092036. This sensor has a working electrode and a reference electrode both made of ruthenium oxide, which is coated with a mixture of polyvinyl butyral and silica powder. In use, both electrodes are coated with an electrolyte solution. Utility Model Content

[0006] In this context, an electrochemical gas sensor is proposed here according to the present invention.

[0007] An electrochemical gas sensor for detecting a target gas includes a substrate having an upper side. Three electrodes are disposed on the upper side and configured to be connected to a potentiostat, each electrode serving as a working electrode, a corresponding electrode, and a reference electrode. Each electrode has an electrode surface and an electrolyte on the upper side, the electrolyte covering the electrodes such that the target gas diffuses primarily to the electrodes through the electrolyte. A cap is mounted on the electrolyte above the reference electrode, the cap being composed of a solidified liquid phase and hermetically mounted on the electrolyte, the diffusion coefficient of the target gas in the cap being less than the diffusion coefficient of the target gas in the electrolyte, the cap covering at least half of the electrode surface of the reference electrode, and the average extension dimension of the electrolyte perpendicular to the upper side being less than, advantageously at least twice, and advantageously at least five times, the average extension dimension of the electrolyte parallel to the upper side.

[0008] The electrochemical gas sensor according to this invention has a simple structure, which facilitates low-cost mass production. Conventional amperometric electrochemical sensors require diffusion restriction of the target gas relative to the working electrode / electrolyte interface, typically in the form of a capillary or porous membrane, which is covered except for a small opening. The sensor according to this invention is implemented in embodiments without such diffusion restriction relative to the working electrode structure, which simplifies manufacturing and reduces costs while potentially improving sensitivity and detection limits. A substrate (e.g., silicon wafer or glass sheet, circuit board, liquid crystal polymer (LCP) or polyimide film) having an upper side and an opposite lower side constitutes the base. Three electrodes are constructed on the upper side of the substrate, and an electrolyte is applied covering the electrodes. The electrodes are constructed such that they can be connected to a potentiostat as a working electrode, a reference electrode, and a corresponding electrode. The target gas can diffuse from above through the electrolyte, and when there is a target gas concentration gradient between the working electrode and the reference electrode, a potential difference is formed between the two electrodes, thereby allowing the current through the corresponding electrode to be measured, for example, in the amperometric measurement principle, or the potential difference itself to be measured in the potential measurement principle.

[0009] In the prior art, this potential difference is actively adjusted as a bias voltage via the potentiostat. Applying this bias voltage has the disadvantage that the electrochemical sensor becomes sensitive to analytes different from the target gas. In particular, water molecules may affect the sensor's performance. In the sensor according to this invention, a concentration gradient is created by combining a thin, defined electrolyte layer with a cap hermetically mounted on the electrolyte over the reference electrode. The average diffusion path of the target gas through the electrolyte to the working electrode can be constructed to be shorter than the average diffusion path to the reference electrode. Here, the average value is taken on the surface of the electrode connected to the electrolyte. Because the target gas is used on the electrode, the equilibrium concentration at the corresponding electrode depends on how much target gas is replenished by diffusion. If the diffusion paths are different, a concentration gradient is then created. The diffusion coefficient of the target gas in the cap should be less than the diffusion coefficient of the target gas in the electrolyte. Furthermore, the cap is advantageously hermetically mounted on the electrolyte. The aim is to prevent the target gas from reaching the underside of the cap via a diffusion process having the diffusion coefficient of the target gas in air. The electrolyte is thin or flat, meaning that its vertical extension dimension to the upper side is smaller than its lateral extension dimension. The diffusion path of the target gas from above to the working electrode via the electrolyte is then shorter than the lateral diffusion path of the target gas to the covered reference electrode. In an embodiment, the cover does not cover the entire reference electrode (covering means that the normal projection of the cover on the upper side includes the normal projection of the reference electrode surface on the upper side); the cover, for example, covers half of the surface of the reference electrode. Therefore, it is ensured that the average diffusion path through the electrolyte to the reference electrode is sufficiently longer than the average diffusion path through the electrolyte to the working electrode, which is significant for generating a potential difference. Advantageously, the working electrode is not covered, but it is also conceivable that the cover may cover the working electrode relative to the reference electrode, for example, if the target gas passes through the working electrode via the shortest diffusion path from the electrolyte to the reference electrode, for example, if the working electrode is circumferentially surrounding the reference electrode.

[0010] Depending on the target gas, a non-zero bias voltage may be advantageous.

[0011] The reference electrode and the working electrode can be made of the same material. This has the advantage that fluctuations in environmental conditions, such as humidity fluctuations, do not affect the working electrode and the reference electrode in the same or similar manner as fluctuations in the target gas's environment. Particularly advantageous for this is that the cap is permeable to water vapor. Using the same material also simplifies the manufacturing process and prevents different aging behaviors of the reference electrode and the working electrode.

[0012] The electrolyte may include an ionic liquid. This has the advantages that the vapor pressure is negligible at ambient temperature and prevents the sensor from aging due to dryness. Ionic liquids also have other advantages, such as high electrochemical and thermal stability. Here and below, ionic liquid can be understood to refer to a salt that is liquid at room temperature. This name is retained even if the ionic liquid solidifies, for example, into a gel.

[0013] The electrode may comprise metal nanoparticles. This can have the advantage that, compared to an electrode made of solid metal, the porous nanostructure significantly increases the surface area in contact with the electrolyte. The increased electrode-electrolyte interface of the working electrode can improve the sensitivity of the electrochemical sensor. The increased surface area of ​​the corresponding electrode enables the extraction of electrons in the corresponding reaction, with the aim of preventing the formation of excessively high potentials on the corresponding electrode. As previously mentioned, the reference electrode is made of the same material as the working electrode, and advantageously, the reference electrode also contains nanoparticles if the working electrode is also made of nanoparticles. Catalytically active metals (e.g., platinum, palladium, ruthenium, gold, or silver) are particularly suitable.

[0014] In each of the electrodes, the metal nanoparticles can be applied onto a metal thin film. This has the advantage of minimizing the contact resistance between the electrode and the lead, and ensuring that the potential remains as constant as possible across the entire nanosurface. The metal of the thin film can be the same as or different from the metal of the nanoparticles.

[0015] The electrolyte can have a viscosity greater than 1 Pascal-second. Advantageously, the electrolyte is gelled, making the orientation of the sensor in space irrelevant because the electrolyte does not flow. Furthermore, the gelled electrolyte facilitates the use of a liquid phase for subsequent solidification to achieve the cap, since the electrolyte constitutes a solid substrate for the application.

[0016] In manufacturing the sensor, methods from the semiconductor industry are advantageously used, enabling low-cost, large-scale production. For example, a silicon wafer can be used as a substrate on which metal electrodes are structured using standard processes such as sputtering and etching. Additional metal nanoparticles and electrolytes can be applied at the wafer level with high precision, e.g., by coating. The processed wafer is then divided into individual sensors, e.g., by dicing.

[0017] A particularly advantageous aspect of manufacturing the electrochemical sensor is the hermetic application of the cap to the electrolyte. The cap is advantageously applied to the electrolyte in a sealed manner because otherwise the target gas might diffuse beneath the cap during diffusion, a diffusion process having a diffusion coefficient in air that is several times greater than the diffusion coefficient of the target gas in the electrolyte or the cap. This sealing application is particularly well achieved if the cap is applied to the electrolyte in a liquid phase (e.g., by coating) and then cured (e.g., in the case of a dissolved polymer, by solvent evaporation or by chemically or physically mediated crosslinking). Attached Figure Description

[0018] Figure 1 A top view of an electrochemical gas sensor is shown.

[0019] Figure 2 A top view of an electrochemical gas sensor with a modified electrode layout is shown.

[0020] Figure 3 A cross-sectional view of an electrochemical gas sensor is shown.

[0021] Figure 4 A cross-sectional view of an electrochemical gas sensor is shown, showing only the substrate and electrodes.

[0022] Figure 5 A flowchart illustrating a method for manufacturing an electrochemical gas sensor is shown. Detailed Implementation

[0023] exist Figure 1The diagram shows a top view of an electrochemical gas sensor according to the present invention. Platinum electrodes 21 to 23 with leads 4 are structured on a silicon substrate 1. These leads can be connected to a potentiostat and used in operation as a working electrode 21, a corresponding electrode 22, and a reference electrode 23. The target gas (e.g., formaldehyde) is used on the working electrode 21. The same process occurs on the reference electrode 23, but to a lesser extent due to the cap. The potentiostat maintains the potential difference between the working electrode 21 and the reference electrode 23 at zero volts by regulating the current through the corresponding electrode 22. Electrode 2 includes a thin-film electrode 41, which is, for example, composed of platinum, gold, silver, ruthenium, or palladium as a substrate and combined with a porous layer composed of nanoparticles 42 (e.g., composed of platinum, gold, silver, ruthenium, or palladium), see [see section 1]. Figure 4 The substrate 1 has dimensions of 5 mm × 5 mm. An electrolyte membrane 2, made of an ionic liquid (e.g., 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, or 1-butyl-3-methylimidazolium trifluoromethanesulfonate) and gelled from silica by pyrolysis, is present on the substrate 1, covering electrodes 21 to 23. The electrolyte membrane 2 has a thickness of 30 micrometers to 300 micrometers and covers the three electrodes 21 to 23. A cap 3, made of silicone (e.g., cross-linked polydimethylsiloxane with silica or alumina particles, or ethyl cyanoacrylate), is sealed onto the reference electrode 23 on the electrolyte membrane 2. The cap has a thickness of 20 micrometers to 500 micrometers.

[0024] exist Figure 2 An alternative electrode layout is shown, where the working electrode 21 essentially includes the reference electrode 23. The remaining dimensions are the same as in... Figure 1 The same applies. In this configuration, the working electrode is traversed via a lateral diffusion path from the electrolyte to the reference electrode covered by the cap.

[0025] exist Figure 3 The middle shows Figure 1 A cross-sectional view of the electrochemical gas sensor in the image, but only the portion including the reference electrode 23 is shown.

[0026] exist Figure 4 A preferred electrode structure is schematically illustrated. A thin-film electrode 41 is structured on a silicon substrate by sputtering and etching. Platinum black is applied to and electrically connected to the thin-film electrode 41. The thin-film electrode 41 has a thickness of 10 nanometers to 200 nanometers, and the thickness of the platinum black layer is 0.2 micrometers to 20 micrometers.

[0027] exist Figure 5The diagram schematically illustrates a manufacturing process for an electrochemical sensor according to the present invention. In step 1, a substrate, such as silicon, is provided. In step 2, electrodes 21 to 23 are structured on the substrate 1 (e.g., by sputtering and etching). To increase the catalytically active surface area of ​​electrodes 21 to 23, in an optional step 3, platinum black may be coated onto the electrodes in a solvent, and optionally as a binder, and then sintered at a temperature step of 150°C to 300°C. In step 4, an electrolyte 2 is coated onto the substrate covering electrodes 21 to 23. Exemplarily, the electrolyte 2 comprises a mixture of water, an ionic liquid (e.g., 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, or 1-butyl-3-methylimidazolium trifluoromethanesulfonate), and pyrolytic silica, which is cured in a temperature step of 60°C to 120°C after the coating. In step 5, the cap 3 is sealed over the reference electrode and applied to the electrolyte, advantageously in liquid form, such as a silicone adhesive (e.g., an adhesive consisting of polydimethylsiloxane and silica particles, octamethylcyclotetrasiloxane with crosslinking agent and alumina particles, or ethyl cyanoacrylate), and then the silicone adhesive is cured in a temperature step at 60°C to 120°C.

[0028] List of reference numerals

[0029] 1 base

[0030] 2 electrolytes

[0031] 21 Working electrode

[0032] 22 Corresponding Electrode

[0033] 23 Reference Electrode

[0034] 211 working electrode surface

[0035] 221 Corresponding electrode surface

[0036] 231 Reference Electrode Surface

[0037] 3 caps

[0038] 4 leads

[0039] 41 Metal Thin Film Electrode

[0040] 42 Metal Nanoparticles

Claims

1. An electrochemical gas sensor for detecting a target gas in air, the electrochemical gas sensor comprising: A base (1) having an upper side (11). Three electrodes are disposed on the upper side (11) and configured to be connected to a constant potential device. Each of the electrodes serves as a working electrode (21), a corresponding electrode (22), and a reference electrode (23), respectively. The electrodes have electrode surfaces. The electrolyte (2) on the upper side (11) and the electrolyte covering the electrode are arranged such that the target gas diffuses to the electrode through the electrolyte. A cover (3) is mounted on the electrolyte (2) above the reference electrode (23). The cover (3) is made of a solidified liquid phase and is hermetically mounted on the electrolyte (2). The characteristic is that the diffusion coefficient of the target gas in the cover (3) is less than the diffusion coefficient of the target gas in the electrolyte (2). The cover (3) covers at least half of the electrode surface (231) of the reference electrode (23), and The average extension dimension of the electrolyte (2) perpendicular to the upper side (11) is smaller than the average extension dimension of the electrolyte (2) parallel to the upper side (11).

2. The electrochemical gas sensor according to claim 1, characterized in that The average extension dimension of the electrolyte (2) perpendicular to the upper side (11) is at least twice as small as the average extension dimension of the electrolyte (2) parallel to the upper side (11).

3. The electrochemical gas sensor according to claim 1, characterized in that The average extension dimension of the electrolyte (2) perpendicular to the upper side (11) is at least five times smaller than the average extension dimension of the electrolyte (2) parallel to the upper side (11).

4. The electrochemical gas sensor according to any one of claims 1 to 3, characterized in that The reference electrode (23) and the working electrode (21) are made of the same material.

5. The electrochemical gas sensor according to any one of claims 1 to 3, characterized in that The electrolyte (2) includes an ionic liquid.

6. The electrochemical gas sensor according to any one of claims 1 to 3, characterized in that The electrode comprises metal nanoparticles.

7. The electrochemical gas sensor according to claim 6, characterized in that The metal nanoparticles (42) are applied onto the metal film (41).

8. The electrochemical gas sensor according to any one of claims 1 to 3, characterized in that The electrolyte (2) has a viscosity greater than 1 Pascal second.

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