ELECTROCHEMICAL SENSOR WITH A MEASURING CELL AND AN OXIDIZATION COMPONENT AND METHOD USING SUCH A SENSOR

Description

[0001] The invention relates to an electrochemical sensor with a measuring cell, wherein the measuring cell is capable of detecting a predetermined gas component in a gas and / or measuring the concentration of the predetermined gas component, for example, oxygen, in the gas. Furthermore, the invention relates to a method in which such a sensor is used.

[0002] An electrochemical oxygen sensor 1 is described in EP 2002251 B1. A housing 12 encloses a chamber in which a measuring cell with a measuring electrode 6, a counter electrode 5, a reference electrode 9, and an electrolyte is arranged. An impermeable insulating element 11 is arranged between the measuring electrode 6 and the counter electrode 5. A gas to be analyzed for oxygen can reach the measuring electrode 6 through a first opening 2. The gas can escape from the chamber through a second opening 3. The two openings 2 and 3 are arranged on the same side of the housing 12.

[0003] The electrochemical sensor of JP 2005083956 A comprises a channel with an inlet 32, a chamber 31, and an outlet 33, through which a gas sample to be analyzed can flow. At least a portion of the gas sample flowing through this channel reaches a measuring electrode 10 of a measuring cell through porous membranes 18, 17 and through a component 16. The measuring cell further comprises a counter electrode 5 and a reference electrode 6, as well as an electrolyte 20 between the measuring electrode 10 on one side and the two electrodes 5 and 6 on the other side. The component 16 causes H2S in the gas sample to be oxidized through a chemical reaction. Air from the environment can reach the two electrodes 5 and 6 through an opening 30.

[0004] The invention is based on the object of providing an electrochemical sensor having the features of the preamble of claim 1 and a method having the features of the preamble of claim 9, which are less sensitive to environmental influences than known electrochemical sensors and methods.

[0005] The object is achieved by an electrochemical sensor having the features of claim 1 and by a method having the features of claim 9. Advantageous embodiments of the electrochemical sensor according to the invention are, where appropriate, also advantageous embodiments of the method according to the invention and vice versa.

[0006] The electrochemical sensor according to the invention comprises a housing. This housing encloses an interior space. An inlet on the measuring cell side is capable of establishing, at least temporarily, a fluid connection between the interior space and an environment of the electrochemical sensor. Furthermore, the interior space is at least temporarily in fluid communication with the environment via a pressure equalization outlet.

[0007] The electrochemical sensor according to the invention further comprises a measuring cell. The measuring cell is arranged between the measuring cell-side inlet and the pressure equalization outlet. A gas to be analyzed can pass through the measuring cell-side inlet to the measuring cell. This gas can contain at least one predetermined gas component. This gas component is to be detected and is often referred to as the target gas.

[0008] The measuring cell includes a measuring electrode, a counter electrode and a layer between the two electrodes.

[0009] On the one hand, the layer between the two electrodes of the measuring cell is electrically insulating, preventing short circuits between the two electrodes. On the other hand, the layer is ionically conductive, allowing ions to flow from one electrode to the other.

[0010] A chemical reaction takes place on or in the measuring cell. This chemical reaction depends on the concentration of the gas component to be detected in the interior. If the gas to be analyzed contains several gas components to be detected, the chemical reaction usually depends on the combined concentrations of these gas components.

[0011] The chemical reaction influences a measurable electrical quantity, such as the current or the electrical charge (accumulated current), or the electrical voltage. An electrical measuring unit of the sensor can measure a measure of this influenced or influenceable electrical quantity. An "electrochemical sensor" is a sensor with such a measuring cell.

[0012] The electrochemical sensor further comprises an oxidation component. This oxidation component comprises at least one electrode. The oxidation component is arranged between the pressure equalization outlet and the measuring cell. A spatial distance exists between the measuring cell and the oxidation component. The oxidation component is electrically conductive and electrically insulated from the measuring cell. Preferably, at least one component of the oxidation component, for example, the electrode, is electrically conductive. Preferably, the oxidation component is connected to the measuring cell in an ionically conductive manner.

[0013] The oxidation component is capable of oxidizing at least one, preferably every, oxidizable gas component in the gas, ideally completely. This gas component flows or has flowed into the interior space through the pressure equalization outlet as part of the gas to be analyzed. Because the gas component is oxidized, it no longer reaches the measuring cell.

[0014] The method according to the invention is carried out using an electrochemical sensor according to the invention and comprises the following steps: A sample of the gas to be analyzed flows through the inlet on the measuring cell side into the interior, in particular by diffusion and / or suction, and reaches the measuring cell. A chemical reaction takes place on and / or in the measuring cell. This chemical reaction depends on the concentration of the gas component to be detected in the interior. The chemical reaction influences a measurable electrical quantity. The electrical measuring unit measures a measure of this electrical quantity. It is possible for gas to enter the interior through the pressure equalization outlet. The oxidation component oxidizes at least one, preferably every oxidizable gas component, whereby the or each oxidized gas component belongs to the gas that enters the interior through the pressure equalization outlet.

[0015] The measuring cell's measuring unit measures an electrical quantity influenced by the chemical reaction in the measuring cell. This chemical reaction is caused and / or sustained by at least one gas component to be detected, which may be present in the ambient gas under investigation. Typically, no component of the electrochemical sensor, especially no component of the electrical measuring unit, is significantly consumed during use. Therefore, it is often unnecessary to monitor the fill level of a substance and replenish it as needed.

[0016] In many cases, the measuring cell consumes less electrical energy than any other conceivable electrochemical sensor design, and than an optional signal processing evaluation unit and an optional display unit. Often, the measuring cell and the measuring unit consume no electrical energy at all as long as no target gas to be detected is present. The advantage of low energy consumption is particularly relevant when the sensor according to the invention is used as a portable device and includes its own power supply unit.

[0017] The gas to be analyzed can diffuse through the inlet on the measuring cell side into the interior and then into the measuring cell, or flow in other ways, such as being sucked in. The chemical reaction in the measuring cell can lead to excess pressure in the interior. Thanks to the pressure equalization outlet, this excess pressure can be released into the environment. Typically, no fluid delivery unit is required to relieve this excess pressure.

[0018] However, particularly when there is no overpressure in the interior, gas to be tested or other gas can also enter the interior through the pressure equalization outlet. If this gas reaches the measuring cell, i.e. from the other side, this gas can falsify a measurement made by the measuring cell. A key reason for this possible falsification is that the gas changes a reference voltage of the measuring electrode, whereby the influenced electrical quantity depends on this reference voltage. This reference voltage would be falsified in particular if the reference voltage is set by an optional reference electrode and the gas reaches the reference electrode through the pressure equalization outlet. For this reason in particular, gas to be tested should not reach the measuring cell through the pressure equalization outlet, but only through the inlet on the measuring cell side.In addition, gas that enters the interior through the pressure equalization outlet could lead to deposits on an electrode of the measuring cell.

[0019] The oxidation component according to the invention provides a solution to this problem. The oxidation component is arranged in a fluid connection between the pressure equalization outlet and the measuring cell and oxidizes all oxidizable components in a gas that flows through the pressure equalization outlet into the interior space. As a result, the oxidation component completely or at least largely prevents an oxidizable gas component from reaching the measuring cell from the pressure equalization outlet. On the other hand, the oxidation component ideally has no influence on a gas that flows through the inlet on the measuring cell side into the interior space and reaches the measuring cell.

[0020] It is possible, but not necessary thanks to the oxidation component, to close the pressure equalization outlet with a gas-impermeable cap as long as there is no excess pressure in the interior, and to only remove this cap to relieve excess pressure. Such a cap could inadvertently be left on the pressure equalization outlet even when excess pressure is present and needs to be relieved. It is possible to close the pressure equalization outlet with a gas-permeable cap, whereby excess pressure can be relieved through this cap and this cap protects the interior to a certain degree from mechanical damage from the outside. It is possible to close the pressure equalization outlet with a gas-impermeable cap when the electrochemical sensor is not in use.

[0021] According to the invention, the oxidizing component is arranged between the pressure equalization outlet and the measuring cell. Because the oxidizing component oxidizes oxidizable gas components and is arranged at a distance from the measuring cell, the risk of an oxidizable gas component altering a reference voltage of the measuring electrode and thereby distorting a measurement result is lower compared to a design without an oxidizing component and / or without a distance. This distance makes it possible to arrange at least one barrier layer between the oxidizing component and the measuring cell.

[0022] A sufficiently high electrical potential can be applied to the oxidation component. This high electrical potential increases the certainty that all oxidizable components in the chamber are actually oxidized and that no significant amount of any oxidizable component reaches the measuring cell. Because the oxidation component operates electrically, it does not wear out, or at least wears out more slowly than other possible components capable of oxidizing a gas. In particular, this allows the oxidation component to not require a chemical substance, which would be consumed over time.

[0023] Because the oxidation component is preferably connected to the measuring cell in an ionically conductive manner, the measuring cell is able to determine an electrical reference potential and / or an electrical reference voltage of the oxidation component.

[0024] The oxidizing component preferably has an electrical potential that is higher than the electrical potential of the measuring electrode. This reliably and quickly prevents an oxidizable gas component, especially organic vapors, from reaching the measuring cell through the pressure equalization outlet. Instead, this gas component is reliably oxidized by the oxidizing component.

[0025] Especially when the sensor according to the invention is used in ambient air, the measuring cell can become very hot and could even be damaged if a large amount of oxygen reaches the measuring cell. Ambient air is known to have an oxygen content of approximately 20%. InIn a preferred embodiment, a volume flow reducer is therefore arranged between the measuring cell-side inlet and the measuring cell. This volume flow reducer is preferably a mechanical filter and reduces the volume flow of a gas to the measuring cell, with this gas flowing through the measuring cell-side inlet into the interior space, very significantly compared to a state in which no volume flow reducer is arranged between the measuring cell-side inlet and the measuring cell. "Very significantly" means: by at least 95%, preferably by at least 99%, particularly preferably by at least 99.9%, in particular by at least 99.99%.

[0026] The volume flow reducer preferably comprises at least one barrier layer. This barrier layer preferably has a thickness of less than 0.1 mm, particularly preferably less than 20 µm. Thanks to the oxidation component, no such volume flow reducer needs to be arranged between the pressure equalization outlet and the measuring cell. Therefore, any excess pressure in the interior is reduced more quickly than if the volume flow through the pressure equalization outlet were also reduced by another volume flow reducer.

[0027] InIn a preferred embodiment, the electrochemical sensor comprises a reference electrode. This reference electrode can be described as a component of the measuring cell. This reference electrode has a constant electrical potential and thus determines the electrical reference voltage of the measuring electrode. The reference electrode is preferably ionically conductively connected to the measuring electrode and thus determines the electrical potential of the measuring electrode.

[0028] Preferably, the oxidation component is arranged between the reference electrode and the pressure equalization outlet. Particularly preferably, a gap is provided between the reference electrode and the oxidation component. This positioning further reduces the risk of a significant amount of a combustible gas component reaching the reference electrode through the pressure equalization outlet and undesirably altering the reference voltage. The gap allows for the provision of at least one barrier layer.

[0029] The oxidation component comprises at least one electrode, preferably two electrodes. The oxidation component is preferably connected in an ionically conductive manner not only to the measuring cell but also to the reference electrode. Thus, the reference electrode also determines the electrical potential of the electrode or at least one electrode of the oxidation component.

[0030] InIn one embodiment, the oxidation component comprises two electrodes and a layer between the two electrodes. This layer electrically insulates the two electrodes from each other and connects them in an ionically conductive manner. This layer can be constructed in the same way as the layer between the two electrodes of the measuring cell and, in particular, can comprise an electrolyte.

[0031] The pressure equalization outlet can also be used as an inlet, particularly before use of the sensor. Preferably, a liquid electrolyte can flow into the housing and from there through the pressure equalization outlet and past the oxidation component to the measuring cell. This configuration makes it possible to fill the electrochemical sensor with liquid electrolyte before use and, in particular, to ensure that the added liquid electrolyte reaches the oxidation component and the measuring cell and creates the required or desired ionically conductive connections. Preferably, the sensor is placed in a position in which the measuring cell is located vertically or diagonally below the pressure equalization outlet. Gravity causes the electrolyte in the interior to flow vertically or diagonally downwards to the measuring cell.Ideally, it is not necessary to refill liquid electrolyte after commissioning the sensor.

[0032] In In one embodiment, at least one gas-impermeable barrier layer is arranged between the pressure equalization outlet and the measuring cell. At least one gas-permeable through-opening is provided in the or each barrier layer, and optionally at least two permeable through-openings are provided in a barrier layer. The design with the barrier layer further reduces the risk of gas that has flowed into the interior through the pressure equalization outlet reaching the measuring cell. Thanks to the through-opening, pressure equalization can still occur.

[0033] According to the invention, a gas from the environment can flow through the inlet on the measuring cell side into the interior space. In one embodiment, the gas flows from a spatial area directly adjacent to the housing of the electrochemical sensor into the interior space, for example by diffusion and / or by suction. In one embodiment, an adapter can be attached to the inlet on the measuring cell side and preferably removed again. This adapter is connected in a fluid-tight manner to one end of a fluid guide unit, wherein this fluid guide unit is arranged outside the electrochemical sensor. When the adapter is attached, the inlet on the measuring cell side is only connected to the environment through the fluid guide unit. In other words: a sample of a gas to be analyzed cannot bypass the adapter to reach the interior of the sensor. The gas flows through this fluid guide unit and through the inlet on the measuring cell side into the interior space.The adapter preferably does not cover the pressure equalization outlet, so that excess pressure in the interior can be quickly relieved even with the adapter in place. The sensor can preferably be used either with or without the adapter in place. The sensor or the adapter preferably includes a fluid delivery unit capable of drawing a gas through the fluid guide unit.

[0034] A fluid guide unit is a component capable of guiding a fluid along a predetermined trajectory and ideally preventing the fluid from deviating from this trajectory. A hose and a tube are two examples of a fluid guide unit. A fluid delivery unit is capable of causing a flow of fluid. A pump, a blower, and a piston-cylinder unit are three examples of a fluid delivery unit.

[0035] The design with the attachable adapter and the fluid guide unit makes it possible to analyze a gas in a spatial region that is spatially separated from the electrochemical sensor. This separated region can, in particular, be an enclosed space, and the electrochemical sensor can be arranged outside this space. Substances in the enclosed space can only reach the interior of the sensor through the fluid guide unit and the inlet on the measuring cell side, but not through the pressure equalization outlet.

[0036] The sensor according to the invention can be designed as a portable device and have its own power supply unit. A user can carry the sensor according to the invention with them in order to examine a gas in their environment. The sensor according to the invention can also be designed as a stationary device and can be connected to a stationary power supply network. Optionally, the sensor according to the invention comprises a fluid conveying unit, e.g. a pump or a blower, which can suck in gas from the environment. The sensor according to the invention can comprise its own output unit which outputs a measurement result of the measuring cell in a manner perceptible by a human. The sensor can comprise its own alarm unit which outputs an alarm in a form perceptible by a human if a measured value lies outside a predetermined range.Preferably, the alarm is emitted in a tactile form, for example, through vibrations. It is also possible for the sensor according to the invention to comprise a communication unit capable of transmitting a measurement result or an alarm from the measuring cell to a remote receiver.

[0037] The invention is described below using an exemplary embodiment. Figure 1 schematically shows in a cross-sectional view how gas can enter the interior of the sensor; Figure 2 schematically shows in a cross-sectional view the structure of the sensor according to the invention; Figure 3 schematically shows in the cross-sectional view of Figure 1 an adapter and a hose on the measuring cell side inlet.

[0038] In the exemplary embodiment, the sensor according to the invention is used to detect whether a gas contains a predetermined gas component or not, and / or to measure the content (concentration) of this gas component in the gas. The gas component is, for example, oxygen in the form of O2 or a gas mixture which contains oxygen, for example N2O or H2O or CO, or hydrogen in the form of H2 or organic vapors. In the following description, oxygen is mentioned as an example as the gas component to be detected. In addition to the oxygen to be detected, oxidizable gas components may be present in the gas to be analyzed, for example SO2, NO2, alcohol, aldehydes and / or unsaturated hydrocarbons.

[0039] Figure 1 shows schematically in a cross-sectional view how gas G can enter the interior of an electrochemical sensor 100 according to the invention. Figure 2shows schematically a cross section through the sensor 100 according to the invention of Figure 1 .

[0040] The sensor 100 comprises a housing 10 with a cover 11, wherein the housing 10 surrounds an interior space I. In a plane perpendicular to the planes of the drawing of Figure 1 and Figure 2 The housing 10 preferably has a circular cross-sectional area.

[0041] When using the sensor 100, a gas G to be examined flows in the direction R.1 through an opening Ö into the interior space I, in Figure 1 and Figure 2 i.e., upwards. This opening is referred to below as the measuring cell-side opening and functions as the measuring cell-side inlet of the exemplary embodiment. The opening is recessed into a wall W.1 of the housing 10.

[0042] During the completion of the sensor 100 and / or before use, a liquid electrolyte E is transferred from a container 20 into the interior space I. The electrolyte E flows in the example of Figure 1 from above into the interior space I. The liquid electrolyte E is poured into the interior space I, for example, with the cover 11 removed or through an opening (not shown) in the cover 11. An aqueous solution comprising sulfuric acid, phosphoric acid, or perchloric acid with a water content of at least 5% is used as the electrolyte E, for example. The boiling point of the liquid electrolyte E is above the temperature at which the sensor 100 is used, so that the electrolyte E does not evaporate.

[0043] In the interior I, a measuring electrode (working electrode) 2 and a counter electrode 4 are arranged, cf. Figure 2In the example shown, the measuring electrode 2 is shaped like a disk, and the counter electrode 4 is shaped like a torus. In one embodiment, the following chemical reactions take place: Oxygen on the measuring electrode 2 is reduced to 2O 2-<. For example, the chemical reaction O 2 + 2H 2 O + 4e -< → 4OH -< takes place. 2O 2-<, which is contained in the electrolyte E, is oxidized to O 2 at the counter electrode 4. For example, the reverse chemical reaction 2H 2 O → O 2 + 4H +< + 4e -< takes place.

[0044] A reference electrode 5 determines the electrical potential at the measuring electrode 2. Preferably, the electrical potential of the measuring electrode 2 is several hundred mV lower than that of the reference electrode 5. This triggers the chemical reaction at the measuring electrode 2. In particular, the electrical potential of the measuring electrode 2 triggers the chemical reactions described above. Ideally, the following situation is achieved: The concentration of O2 at the measuring electrode 2 is permanently zero due to the chemical reaction. At the counter electrode 4, however, O2 is generated. One implementation of such a measuring cell can be referred to as an "oxygen pump."

[0045] The chemical reactions create an O2 concentration gradient between the two electrodes 2 and 4. This O2 gradient causes electrons to flow from the counter electrode 4 to the measuring electrode 2. Therefore, an electric current flows through a wire 14, which connects the measuring electrode 2 to the counter electrode 4 and is arranged at a distance from the electrolyte 12. The two electrodes 2 and 4, the electrolyte 12, and the wire 14 together form an electrical circuit. An electrical measuring resistor (not shown) is arranged in the wire 14. A measuring unit in the form of a current sensor 15 measures the strength or quantity (electrical charge) of the current flowing through the wire 14. The current strength or the electrical charge is a measure of the concentration or content of oxygen in the interior space I in the sensor 100.

[0046] In the exemplary embodiment, the two electrodes 2 and 4, the insulating layer 12, the wire 14 and the current sensor 15 belong to the measuring cell of the sensor 100.

[0047] The distance between the two electrodes 2 and 4 is so large, and the insulating layer 12 with the electrolyte E is designed such that the following is achieved: O2 is largely prevented from diffusing back from the counter electrode 4 to the measuring electrode 2. The electrodes 2 and 4 are made of a metal, preferably a noble metal, which is resistant to materials of the electrolyte E as well as to CO, H2S and other possible components of the gas G. The two electrodes 2, 4 are particularly preferably made of platinum or gold. With this material, the chemical reactions described above take place sufficiently quickly. On the other hand, this material is chemically resistant to the electrolyte E. It is also possible for the measuring electrode 2 and / or the counter electrode 4 to be made of gold.

[0048] The two electrodes 2, 4 are electrically insulated from each other by an insulating layer 12 with at least one layer of glass fiber or glass fleece impregnated with the electrolyte E. At the same time, the electrolyte E allows the flow of ions.

[0049] The cover 11 is placed on a support sleeve 16, which is mechanically connected to a wall W.2 of the housing 10. The area enclosed by this support sleeve 16 functions as the pressure equalization outlet of the exemplary embodiment. An elastic, gas-permeable plunger 9 is arranged inside this support sleeve 16. This plunger 9 presses the electrodes and other layers together, ensuring that the electrodes can only move relatively slightly relative to one another, thus ensuring that the wire 14 permanently and reliably contacts the two electrodes 2 and 4.

[0050] As is known, air has an oxygen content of approximately 20%. Such a large amount of oxygen would lead to a large conversion of oxygen at the measuring electrode 2 and rapidly damage the measuring electrode 2. Therefore, a volume flow reducer in the form of a thin barrier layer 1 separates the measuring electrode 2 from the environment in a nearly fluid-tight manner. "Nearly fluid-tight" in the exemplary embodiment means that less than 1%, in particular less than 1‰, preferably less than 0.1‰, of the gas G flowing from the environment in the direction R.1 through the opening Ö into the interior space I can penetrate the barrier layer 1 and reach the measuring electrode 2. This small amount is sufficient for the measured current or electrical charge through the wire 14 to correlate with the desired oxygen concentration with sufficient reliability.

[0051] In the exemplary embodiment, the barrier layer 1 has a thickness of at least 5 µm and less than 50 µm, preferably less than 20 µm, particularly preferably a thickness between 10 µm and 15 µm. The aim is to prevent a crack or hole from occurring in the barrier layer 1. In the example shown, the barrier layer 1 is arranged in the manner of a sandwich between two support membranes 7 and 13. Each support membrane 7, 13 is made of PTFE, for example. The support membrane 7 between the opening Ö and the barrier layer 1 protects the barrier layer 1 from mechanical damage due to external influences acting through the opening Ö. The support membrane 13 between the barrier layer 1 and the measuring electrode 2 protects the barrier layer 1 from possible mechanical damage caused by the wire 14.

[0052] The reference electrode 5 is arranged downstream of the counter electrode 4, as viewed in the flow direction R.1. This reference electrode 5 provides an electrical reference potential and prevents the current or electrical charge measured by the current sensor 15 from drifting or oscillating at a constant oxygen concentration. Because the reference electrode 5 is arranged a sufficiently large distance downstream of the two electrodes 2 and 4, the reference electrode 5 lies outside the area in which the O 2 concentration gradient described above occurs. Therefore, this O 2 gradient does not act on the reference electrode 5 and ideally does not influence the reference voltage determined by the reference electrode 5.

[0053] Arranged in the interior I are several parallel insulating layers 3 impregnated with the electrolyte E and comprising, for example, glass fleece. The electrolyte E passes through the insulating layer 3 to the insulating layer 12 and wets the surface of the measuring electrode 2. Because the counter electrode 4 is shaped like a circular ring, the electrolyte E can flow through the hole in the circular ring to the measuring electrode 2. The membrane 13 between the measuring electrode 2 and the barrier layer 1 prevents the electrolyte E from flowing further toward the barrier layer 1.

[0054] In one embodiment, the reference electrode 5 is surrounded on both sides in the manner of a sandwich by an insulating layer 3 containing electrolyte E. At least one insulating layer 3 is arranged between the reference electrode 5 and the counter electrode 4, and in the example shown, even two insulating layers 3. As a result, the reference electrode 5 is electrically insulated from the counter electrode 4, but is connected in an ionically conductive manner. Due to the distance described above and this electrical insulation, the reference electrode 5 is not significantly influenced by the O 2 gradient between the two electrodes 2 and 4. This undesirable effect is largely prevented because the insulating layers 3 have an electrically insulating effect and because oxygen diffuses relatively slowly.

[0055] Overpressure can arise in the interior I due to a chemical reaction, in particular due to one of the reactions in the measuring cell just described. This overpressure must be dissipated quickly, in particular because the overpressure can lead to oxygen dissolving in the electrolyte E and diffusing to the measuring electrode 2, which can result in incorrect measurement results. Therefore, in one embodiment, the optional cover 11 is gas-permeable or has a permanent opening. The plunger 9 is also gas-permeable. The cover 11 protects the plunger 9 from external mechanical damage. The overpressure in the interior I can therefore be dissipated through the plunger 9 and the cover 11. The plunger 9 and the cover 11 are arranged in or on the pressure equalization outlet 16 of the exemplary embodiment.

[0056] As explained above, oxygen in the form of O 2 is generated at the counter electrode 4. The barrier layer 12 with the electrolyte E prevents the undesired event of this oxygen reaching the measuring electrode 2. In particular, thanks to the oxygen generated at the counter electrode 4 and unable to penetrate the barrier layer 12, an overpressure occurs in the area between the counter electrode 4 and the cover 11. In the exemplary embodiment, the counter electrode 4 is designed as a ring, and a gap occurs between the reference electrode 5 and the housing 10. This implementation facilitates the desired result of this overpressure being reduced in the direction R.1 through the pressure equalization outlet 16, in Figure 1 and Figure 2 so upwards.

[0057] When the cover 11 is removed or through the cover 11 or through an opening in the cover 11 and through the elastic piston 9, gas G can flow from the environment in the direction R.2, in Figure 1 and Figure 2 i.e., downwards, and thereby enter the interior space I. This applies in particular if there is no excess pressure in the interior space I relative to the environment. This gas G can contain at least one oxidizable gas component that can shift the reference potential of the reference electrode 5 or that can lead to deposits on an electrode 2, 4, 5. Examples of such oxidizable gas components were mentioned at the beginning.

[0058] An oxidizing component 6 is arranged between the plunger 9 on the one hand and the electrodes 5, 4, 2 on the other. This oxidizing component 6 largely prevents oxidizable gas components that have flowed through the pressure equalization outlet 16 into the interior space I from reaching an electrode 5, 4, 2. The oxidizing component 6 comprises at least one electrode, in the example shown two spaced-apart electrodes 6.1 and 6.2. In one embodiment, the oxidizing component 6, just like the measuring cell, comprises two electrodes 6.1, 6.2 and an ionically conductive connection between the electrodes 6.1 and 6.2, for example a layer 3 saturated with the electrolyte E. An O2 gradient also occurs between these two electrodes 6.1 and 6.2.

[0059] Preferably, the or each electrode 6.1, 6.2 of the oxidation component 6 is made of platinum or gold. The or at least one electrode 6.1, 6.2 of the oxidation component 6 is maintained at an electrical potential that differs from the electrical potential of the reference electrode 5 and lies between 0.1 V and 0.5 V, preferably between 0.2 V and 0.4 V. The oxidation component 6 therefore oxidizes all oxidizable components of the gas G that diffuse through the cover 11 and the plunger 9 in the direction R.2 into the interior space I, ideally completely.

[0060] At least one insulating layer 3 electrically insulates the oxidizing component 6 from the reference electrode 5, in the example shown two spaced-apart insulating layers 3. The oxidizing component 6 is ionically conductively connected to the reference electrode 5, in the exemplary embodiment by the electrolyte E in the insulating layer 3. Thanks to the ionically conductive connection, the reference electrode 5 additionally determines the electrical potential of the oxidizing component 6 or at least the electrical potential of an electrode 6.1 or 6.2 of the oxidizing component 6.

[0061] Optionally, two gas-impermeable barrier films 8.1 and 8.2 are arranged between the oxidation component 6 and the counter electrode 4. The two barrier films 8.1 and 8.2 are made, for example, from a gas-impermeable plastic, such as a perfluoroalkoxy polymer (PFA) or polyvinylidene fluoride (PVDF). The barrier films 8.1 and 8.2 reduce the risk of O2 diffusing from the counter electrode 4 to the reference electrode 5 or even to the oxidation component 6, or of a gas flowing in the direction R.2 reaching an electrode 2, 4. The two barrier films 8.1 and 8.2 are resistant to the electrolyte E. To ensure that the electrolyte E can still reach the measuring electrode 2, a sufficiently large gap Sp is created between the barrier film 8.2 and the housing 10. The barrier foil 8.1 has the shape of a ring so that the electrolyte E can flow through the hole Lo in this ring to the measuring electrode 2.

[0062] In the design according to Figure 1 the gas G diffuses from a spatial area immediately adjacent to the opening Ö into the interior space I. Figure 3 shows an alternative design. An adapter 30 is placed on the opening Ö. The adapter 30 is connected in a fluid-tight manner to a hose 31. The gas G can only reach the opening Ö through the hose 31, but not past the adapter 30. Apart from the hose 31, the adapter 30 surrounds the opening Ö in a fluid-tight manner. The free end of the hose 31 is located in an area containing the gas to be examined. A schematically shown pump 32 sucks the gas G through the hose 31 and directs it further through the opening Ö into the interior I. Just like an embodiment of the Figure 1 Gas G can also reach the interior I through the pressure equalization outlet 16.

[0063] The adapter 30 can be removed from the opening Ö again, so that the gas G then reaches the interior directly through the opening Ö, as shown in Figure 1 is indicated. List of reference symbols 1 Inlet-side barrier layer, arranged between the support membranes 7 and 13, acts as a volume flow reducer for the opening Ö 2 Measuring electrode, belongs to the measuring cell 3 Insulating layer, impregnated with the electrolyte E 4 ring-shaped counter electrode, belongs to the measuring cell 5 Reference electrode (reference electrode), belongs to the measuring cell 6 Oxidation component, comprises at least one electrode, preferably the two electrodes 6.1 and 6.2, arranged between the pressure equalization outlet 16 and the measuring cell 6.1, 6.2 Electrodes of the oxidation component 6 7 gas-permeable support membrane between the barrier layer 1 and the opening Ö 8.1 annular barrier foil between the reference electrode 5 and the measuring electrode 2, has the hole Lo 8.2 disc-shaped barrier foil between the oxidation component 6 and the reference electrode 5, 5, surrounded by the annular gap Sp 9 elastic stamp between the oxidation component 6 and the cover 11 11 in the support sleeve 16 10 Housing, encloses the interior I, includes the measuring cell-side opening Ö, is mechanically connected to the support sleeve 16, accommodates, among other things, the measuring cell and the oxidation component 6 11 Cover for the housing 10 12 Electrolyte between electrodes 2 and 4 of the measuring cell 13 gas-permeable support membrane between the barrier layer 1 and the measuring electrode 2 14 Wire that electrically connects electrodes 2 and 4 15 Current sensor, measures the current or the electrical charge of the current flowing through the wire 14 16 Support sleeve around the elastic piston 9, is mechanically connected to the wall W.2 of the housing 10, accommodates the piston 9, can be closed by the cover 11, acts as a pressure equalization outlet 20 Container for filling the electrolyte E 30 Adapter that can be detachably attached to the opening Ö 31 Hose connected to adapter 30 32 Pump that sucks the gas G through the hose 31 100 Sensor, comprises the electrodes 2, 4, 5, 6, the housing 10, the barrier layers 3, the barrier foil 8.1 and 8.2, the stamp 9 and the cover 11 E liquid electrolyte is filled from the container 20 into the sensor 100 from above G The gas to be examined can flow into the interior space I in the directions R.1 and R.2 I Interior of the sensor 100, enclosed by the housing 10 Lo Hole in the annular barrier foil 8.1 Ö Opening through which gas G diffuses through the barrier layer 1 into the interior I, acts as the measuring cell-side inlet R.1 Direction in which gas G to be examined flows through the opening Ö into the interior I R.2 The direction in which the gas G to be examined flows through the support sleeve 16 into the interior I is opposite to the direction R.1 Sp Gap between the barrier film 8.2 and the housing 10 W.1 Wall of the housing 10, into which the measuring cell-side inlet Ö is embedded W.2 Wall of the housing 10, with which the support sleeve 16 is connected

Claims

1. Electrochemical sensor (100) for detecting a predetermined gas component in a gas (G) and / or for measuring the concentration of the gas component in the gas (G), wherein the electrochemical sensor (100) comprises - a housing (10) that encloses an interior space (I), - a measuring cell (2, 4, 12, 15) in the interior space (I), - an electrical measuring unit (15), - a measuring-cell-side inlet (Ö) in the housing (10) and - an oxidation component (6) in the interior space (I), wherein the measuring-cell-side inlet (Ö) is capable of establishing a fluid connection between the housing (10) and an environment of the electrochemical sensor (100), wherein the measuring cell (2, 4, 12, 15) comprises - a measuring electrode (2), - a counter electrode (4) and - an electrically insulating and ionically conductive layer (12) between the two electrodes (2, 4), wherein the measuring cell (2, 4, 12, 15) is designed in such a way that a chemical reaction takes place at the measuring cell (2, 4, 12, 15), which - depends on the concentration of the gas component in the interior space (I) and - influences a measurable electrical quantity, and wherein the electrical measuring unit (15) is designed to measure a measure of the influenced electrical quantity, characterized in that the electrochemical sensor (100) comprises a pressure equalization outlet (16) in the housing (10), wherein the pressure equalization outlet (16) is capable of establishing a fluid connection between the housing (10) and an environment of the electrochemical sensor (100), wherein the measuring cell (2, 4, 12, 15) is arranged between the measuring-cell-side inlet (Ö) and the pressure equalization outlet (16) and wherein the oxidation component (6) - is arranged between the pressure equalization outlet (16) and the measuring cell (2, 4, 12, 15) and at a distance from the measuring cell (2, 4, 12, 15), - comprises at least one electrode, preferably two electrodes (6.1, 6.2), - is electrically insulated from the measuring cell (2, 4, 12, 15), - is arranged and designed to oxidize at least one, preferably every oxidizable component in the gas (G) which passes through the pressure equalization outlet (16) into the interior space (I), and - is preferably connected to the measuring cell (2, 4, 12, 15) in an ionically conductive manner.

2. Electrochemical sensor (100) according to claim 1, characterized in that the measuring electrode (2) has an electrical potential and at least one electrode (6.1, 6.2) of the oxidation component (6) has an electrical potential which is above the electrical potential of the measuring electrode (2).

3. Electrochemical sensor (100) according to any of the preceding claims, characterized in that the electrochemical sensor (100) comprises a volume flow reducer (1) between the measuring-cell-side inlet (Ö) and the measuring cell (2, 4, 12, 15), wherein the volume flow reducer (1) is designed to reduce the volume flow from the environment through the measuring-cell-side inlet (Ö) to the measuring cell (2, 4, 12, 15) - compared to a state without the volume flow reducer (1) - by at least 95%, preferably by at least 99%, particularly preferably by at least 99.9%, in particular by at least 99.99%.

4. Electrochemical sensor (100) according to any of the preceding claims, characterized in that the electrochemical sensor (100) comprises a reference electrode (5), which has a constant electrical potential, wherein the oxidation component (6) - is arranged between the reference electrode (5) and the pressure equalization outlet (16), preferably at a distance from the reference electrode (5), and - is connected to the reference electrode (5) in an ionically conductive manner.

5. Electrochemical sensor (100) according to any of the preceding claims, characterized in that the electrochemical sensor (100) is designed so that a liquid electrolyte (E) can flow from the pressure equalization outlet (16) past the oxidation component (6) to the measuring cell (2, 4, 12, 15).

6. Electrochemical sensor (100) according to any of the preceding claims, characterized in that at least one barrier layer (8.1, 8.2) which is impermeable to gas is arranged between the pressure equalization outlet (16) and the measuring cell (2, 4, 12, 15), wherein at least one passage opening (Sp, Lo) which is permeable to gas (G) is formed in the or each barrier layer (8.1, 8.2).

7. Electrochemical sensor (100) according to any of the preceding claims, characterized in that the measuring-cell-side inlet (Ö) and the pressure equalization outlet (16) are formed in two mutually opposite walls (W.1, W.2) of the housing (10) and the measuring cell (2, 4, 12, 15) and the oxidation component (6) are arranged between these two opposite walls (W.1, W.2).

8. Assembly comprising - an electrochemical sensor (100) according to any of the preceding claims, - an adapter (30) and - a fluid guide unit (31), wherein the fluid guide unit (31) is connected to the adapter (30) in a fluid-tight manner, and wherein the adapter (30) can be detachably mounted on the housing (10) in such a way that, when the adapter (30) is mounted, the measuring-cell-side inlet (Ö) is in fluid communication with an environment of the electrochemical sensor (100) only through the fluid guide unit (31).

9. Method for detecting a predetermined gas component in a gas (G) and / or for measuring the concentration of the gas component in the gas (G), wherein the method is carried out using an electrochemical sensor (100), wherein the electrochemical sensor (100) comprises - a housing (10) that encloses an interior space (I), - a measuring cell (2, 4, 12, 15) in the interior space (I), - an electrical measuring unit (15), - a measuring-cell-side inlet (Ö) in the housing (10) and - an oxidation component (6) in the interior space (I), wherein the measuring-cell-side inlet (Ö) at least temporarily establishes a fluid connection between the housing (10) and an environment of the electrochemical sensor (100), wherein the measuring cell (2, 4, 12, 15) comprises - a measuring electrode (2), - a counter electrode (4) and - an electrically insulating and ionically conductive layer (12) between the two electrodes (2, 4) and wherein the method comprises the steps whereby - a sample of the gas (G) flows through the measuring-cell-side inlet (Ö) into the interior space (I) and reaches the measuring cell (2, 4, 12, 15), - a chemical reaction takes place at the measuring cell (2, 4, 12, 15), which depends on the concentration of the gas component in the interior space (I) and influences a measurable electrical quantity and - the electrical measuring unit (15) measures a measure of the influenced electrical quantity, characterized in that the electrochemical sensor (100) comprises a pressure equalization outlet (16) in the housing (10), wherein the pressure equalization outlet (16) at least temporarily establishes a fluid connection between the housing (10) and an environment of the electrochemical sensor (100), wherein the measuring cell (2, 4, 12, 15) is arranged between the measuring-cell-side inlet (Ö) and the pressure equalization outlet (16), wherein the oxidation component (6) - is arranged between the pressure equalization outlet (16) and the measuring cell (2, 4, 12, 15) and at a distance from the measuring cell (2, 4, 12, 15), - comprises at least one electrode, preferably two electrodes (6.1, 6.2), and - is electrically insulated from the measuring cell (2, 4, 12, 15) and is preferably connected to the measuring cell (2, 4, 12, 15) in an ionically conductive manner and wherein the method comprises the step whereby the oxidation component (6) oxidizes at least one, preferably every oxidizable component in the gas (G) which passes through the pressure equalization outlet (16) into the interior space (I).