Systems and methods for improved baseline stability for electrochemical sensors

Abstract

Embodiments generally relate to systems and methods for operating an electrochemical oxygen sensor at low relative humidity (i.e., 15% RH or less). The methods can include: operating an electrochemical sensor to detect oxygen in a field, wherein the electrochemical sensor includes an electrolyte and one or more electrodes, the electrolyte configured to electrically connect the one or more electrodes and having a sulfuric acid with an initial concentration of approximately 8M; and maintaining sensor accuracy to detect oxygen in the field during operation of the sensor without recalibrating the sensor using a nitrogen source, wherein the relative humidity of the environment is approximately 15% or less.

Description

[0001] Cross-references to related applications not applicable.

[0002] Statement regarding federally funded research or development not applicable.

[0003] References to microfilm attachments not applicable. Background Technology

[0004] Electrochemical gas sensors typically include electrodes in contact with an electrolyte for detecting gas concentration. The electrodes are electrically coupled to external circuitry via contact lines (or leads) coupled to connector pins. When a gas comes into contact with the electrolyte and the electrodes, a reaction occurs that can create a potential difference between the electrodes and / or cause a current to flow between them. The resulting signal can then be correlated with the gas concentration in the environment.

[0005] When monitoring the presence of various gases, other gases that can react within the sensor may also be present. For example, the working electrode may contain a catalyst that catalyzes the reaction between the target gas and the interfering gas. Therefore, the presence of the interfering gas can create cross-sensitivity in the sensor, leading to the illusion that the level of the target gas present in the ambient gas is greater than its actual level. Due to the danger posed by the presence of various target gases, the threshold level used to trigger an alarm can be relatively low, and the cross-sensitivity caused by the presence of interfering gases can be high enough to produce a false alarm (e.g., a false positive) for the target gas sensor. This is especially true when the interfering gas is harmless (meaning that the sensor can trigger an alarm even when exposed to low levels (or even the absence of) actually harmful gases). Summary of the Invention

[0006] In an implementation, a method for operating an electrochemical oxygen sensor may include: operating the electrochemical sensor to detect oxygen in a field, wherein the electrochemical sensor includes an electrolyte and one or more electrodes, the electrolyte being configured to electrically connect the one or more electrodes and having an initial concentration of sulfuric acid of approximately 8 M; and maintaining sensor accuracy for detecting oxygen in a field during sensor operation, wherein the relative humidity of the environment is approximately 15% or lower, without requiring recalibration of the sensor using a nitrogen source.

[0007] In an embodiment, the electrochemical sensor may include: a housing; one or more electrodes located within the housing; and an electrolyte deposited within the housing and configured to electrically connect the one or more electrodes, wherein the electrolyte contains sulfuric acid at an initial concentration of approximately 8 M, and wherein the sensor is configured to detect oxygen in an environment with a relative humidity of approximately 15% or lower without requiring recalibration of the sensor using a nitrogen source.

[0008] In an implementation, a method for retrofitting an existing electrochemical sensor may include: providing an electrochemical sensor comprising a housing and one or more electrodes; and depositing an electrolyte within the housing, wherein the electrolyte is configured to electrically connect the one or more electrodes, and wherein the electrolyte contains sulfuric acid at an initial concentration of approximately 8 M. Attached Figure Description

[0009] To gain a more complete understanding of this disclosure, reference is now made to the following brief description in conjunction with the accompanying drawings and detailed embodiments, wherein similar reference numerals denote similar components.

[0010] Figure 1 A cross-sectional view of an electrochemical sensor according to an embodiment of the present disclosure is shown. Detailed Implementation

[0011] First, it should be understood that although exemplary embodiments of one or more implementations are shown below, the disclosed systems and methods can be implemented using any number of techniques, whether currently known or not yet available. This disclosure should in no way be limited to the exemplary embodiments, drawings, and techniques shown below, but modifications can be made within the scope of the appended claims and their equivalents.

[0012] The following brief terminology definitions should apply throughout the application: The term "comprising" means including but not limited to, and should be interpreted in the manner commonly used in the patent context; The phrases “in one embodiment”, “according to one embodiment”, etc., generally mean that the specific feature, structure or characteristic following the phrase may be included in at least one embodiment of the invention, and may be included in more than one embodiment of the invention (importantly, such phrases do not necessarily refer to the same embodiment). If the instruction manual describes something as "exemplary" or "example," it should be understood as referring to a non-exclusive example; The terms “about” or “approximately”, when used with numbers, may refer to a specific number, or alternatively, a range close to that specific number as understood by those skilled in the art; and If the specification states that a component or feature "may," "can," "should," "will," "preferably," "possibly," "usually," "optionally," "for example," "often," or "may" (or other such language) be included or have that characteristic, then that particular component or feature is not required to be included or have that characteristic. Such components or features may be optionally included in some embodiments or may be excluded.

[0013] Embodiments of this disclosure include systems and methods for improving the operation of electrochemical sensors, particularly in low-humidity environments. Typical gas detectors employing one or more chemical sensors may require calibration to obtain accurate sensor readings. As an example, an oxygen (O2) sensor may require calibration if the observed O2 reading is not 20.9%. Calibration can be performed manually or using an automated test and calibration system. Generally, calibration involves calibration with pure nitrogen (N2) (i.e., an O2 reading of zero) and calibration with 20.9% oxygen. N2 calibration will typically require the gas detector to be attached to a nitrogen source, such as a gas cylinder. 20.9% O2 calibration can be performed using ambient (e.g., fresh) air.

[0014] These calibration steps (especially with N2) can be difficult and expensive for users to perform after they have already adopted the gas detector. To prevent the need for calibration after the user has adopted the gas detector, the disclosed embodiments provide a gas detector with a stable signal independent of temperature and / or humidity changes. When ambient humidity changes, especially at low humidity levels, typical oxygen sensors can experience baseline drift, thus requiring recalibration of the gas detector (and oxygen sensor). Low humidity environments can include approximately 15% relative humidity (RH) or lower.

[0015] In operation, at the working (or sensing) electrode of the electrochemical sensor, O2 is reduced according to the following formula: O 2 + 4H + + 4e - → 2H 2 O (1) .

[0016] At the counter electrode of the electrochemical sensor, an anti-equilibrium oxidation occurs according to the following formula: 2H 2 O → 4H + + O 2 + 4e - (2) .

[0017] The sensor signal can be generated by the reaction of O2 at the working electrode. O2 can contact the working electrode through the sensor inlet, and in some cases, O2 can contact the working electrode via back diffusion from the sensor's counter electrode and / or outlet. The electrolyte of the electrochemical sensor can be configured to prevent O2 back diffusion from the counter electrode and outlet.

[0018] In some typical electrochemical sensors, the electrolyte is equilibrated to typical ambient conditions (e.g., approximately 25°C and approximately 50% RH). As an example, 6 mol (M) sulfuric acid (H₂SO₄) can be used as the electrolyte. Under normal operating conditions, the electrolyte can adsorb water when ambient humidity increases and lose water when ambient humidity decreases. When the sensor is exposed to low humidity, the electrolyte volume will decrease due to water evaporation, resulting in a change in the electrolyte distribution within the sensor. Additionally, the resistance of the electrolyte to O₂ back diffusion (from the sensor's counter electrode and / or outlet) can decrease with decreasing volume, leading to baseline signal drift in the sensor (requiring recalibration). Due to this O₂ back diffusion, typical electrochemical sensors can be affected by a drifting baseline signal during and after operation at low relative humidity (such as 15% RH or lower).

[0019] Embodiments of this disclosure include systems and methods for improving the resistance of an electrolyte to O2 backdiffusion. In one exemplary embodiment, the electrolyte volume at low humidity can be increased by increasing the initial concentration of sulfuric acid from about 6M to about 8M. This corresponds to a 33% volume increase compared to a typical 6M sulfuric acid electrolyte, which represents a 33% increase in the electrolyte's resistance to O2 backdiffusion. The electrolyte containing the increased concentration of sulfuric acid (i.e., 8M sulfuric acid) can operate successfully within a range of humidity conditions, such as 10% RH to 95% RH. The signal of an oxygen sensor containing the electrolyte is stable within this range of humidity conditions. The oxygen sensor signal is particularly resistant to drift under low humidity conditions (e.g., 15% RH or lower).

[0020] The described implementation provides improved oxygen sensing in low-humidity environments. Historically, the increase in electrolyte volume due to increased electrolyte concentration (e.g., from 6M sulfuric acid to 8M sulfuric acid) may not have been desirable when the oxygen sensor only needs to operate in normal humidity environments (i.e., above 15% RH), because gas detectors and electrochemical sensors have one or more finite internal volumes (e.g., due to the miniature size of the detector and / or sensor). However, when using the sensor in low-humidity environments (even temporarily), an increase in volume may be necessary to prevent O2 backdiffusion. Furthermore, at humidity levels above 15% RH, the volume increase may not negatively impact sensor operation.

[0021] Figure 1A cross-sectional view of an electrochemical sensor 10 is shown. The sensor 10 typically includes a housing 12 that defines a cavity or reservoir 14 designed to contain an electrolyte solution 34. A working (or sensing) electrode 24 may be positioned within the reservoir 14 and adjacent to an opening 28 in the housing 12 (where one or more walls of the housing 12 may define the reservoir 14). The opening 28 may include a capillary opening. A counter electrode 16 and a reference electrode 20 may be positioned within the reservoir 14. When a gas (e.g., oxygen) reacts within the reservoir 14 (e.g., at the interface between the working electrode 24 and the electrolyte 34), a current and / or potential may be generated between the electrodes to provide an indication of the gas concentration. The reference electrode 20 may also be positioned within the reservoir 14 to provide a reference for the current and potential detected between the working electrode 24 and the counter electrode 16. The reference electrode 20 may also be configured to provide a reference for the potential of the working electrode 24 relative to a standard reference electrode (such as a reversible hydrogen electrode).

[0022] Figure 1 An example of a "stacked" configuration of the electrochemical sensor 10 is shown. The embodiments disclosed herein can also be applied to other sensor configurations, such as planar configurations and / or other stacked configurations.

[0023] The housing 12 defines an internal reservoir 14, and one or more openings 28 may be provided in the housing 12 to allow the target gas to enter the gas space through the housing 12. The housing 12 can generally be formed of any material that is substantially inert to the electrolyte and the target gas being measured. In embodiments, the housing 12 may be formed of a polymeric material, metal, or ceramic. For example, the housing 12 may be formed of materials including, but not limited to, acrylonitrile butadiene styrene (ABS), polyphenylene ether (PPO), polystyrene (PS), polypropylene (PP), polyethylene (PE) (e.g., high-density polyethylene (HDPE)), polyphenylene ether (PPE), or any combination or blend thereof.

[0024] One or more openings 28 and 30 may be formed through the housing 12 to allow ambient gases to enter the reservoir 14 and / or to allow any gases generated within the housing 12 to escape. Figure 1 In the illustrated embodiments, one or more openings may include an inlet 28 and an outlet 30. One or more openings 28 and 30 may be disposed in a cover (e.g., when a cover is present) and / or in the wall of the housing 12. In some embodiments, one or more openings 28 and 30 may include diffusion barriers to restrict the flow of gases (e.g., oxygen, nitrogen, etc.) to the working electrode 24. Diffusion barriers can be created by forming the opening 28 as a capillary, and / or a thin film or membrane can be used to control the mass flow rate through the one or more openings 28 and 30.

[0025] In one embodiment, inlet 28 may serve as a capillary opening to provide rate-limited gas exchange between the interior and exterior of housing 12. In another embodiment, one or more openings 28 and / or 30 may have a diameter between about 10 µm and about 1.5 mm, wherein larger openings may be formed using conventional drilling, while smaller openings may be formed using laser drilling. In yet another embodiment, one or more openings 28 and / or 30 may be larger, comprising any diameter up to the total diameter of housing 12. One or more openings 28 and / or 30 may have a length between about 0.5 mm and about 5 mm, depending on the thickness of the cap or housing 12. When the membrane is used to control the flow of gas into and / or out of the housing, the opening diameter may be larger than the dimensions listed above, as the membrane may help and / or may be responsible for controlling the flow rate of gas into and out of housing 12.

[0026] exist Figure 1 In this embodiment, the reservoir 14 may include (or contain) a counter electrode 16, a reference electrode 20, and a working electrode 24. In some embodiments, an electrolyte 34 may be contained within the reservoir 14, and the counter electrode 16, the reference electrode 20, and the working electrode 24 may be electrically contacted through the electrolyte 34. In some embodiments, one or more porous separators or other porous structures may be used to retain the electrolyte 34 in contact with the electrodes.

[0027] Electrolyte 34 can be any conventional aqueous acidic electrolyte, such as sulfuric acid (H2SO4), phosphoric acid, or any combination thereof. For example, electrolyte 34 may contain sulfuric acid with a molar concentration of about 8M. Since sulfuric acid is hygroscopic, the concentration can vary from about 10% by weight to about 70% by weight (1 mole to 11.5 moles) in the range of about 3% to about 95% of ambient relative humidity (RH).

[0028] In some embodiments, electrolyte 34 may be in the form of a solid polymeric electrolyte comprising an ion-exchange membrane. In some embodiments, electrolyte 34 may be in the form of a free liquid disposed in a matrix or slurry, such as glass fiber, or disposed in the form of a semi-solid or solid gel.

[0029] The working electrode 24 may be disposed within the housing 12. Gas entering the sensor 10 may contact one side of the working electrode 24 and pass through the working electrode 24 to reach the interface between the working electrode 24 and the electrolyte 34. The gas may then react to generate a current indicating the concentration of a target gas. As discussed herein, the working electrode 24 may comprise multiple layers. The base layer or substrate layer may comprise a hydrophobic material or a hydrophobically treated material. A catalytic material may be formed as an electrode on one side of the working electrode 24 and positioned to contact the electrolyte 34.

[0030] In some embodiments, the working electrode 24 may include a porous substrate or membrane as a base layer. The substrate may be permeable to a gas of interest (which may include oxygen). In some embodiments, the substrate may include carbon paper formed from carbon fibers or graphite fibers. In some embodiments, the substrate may be made conductive by adding a conductive material such as carbon. The use of carbon provides sufficient conductivity to allow detection of current generated by the reaction of a gas at the surface of the working electrode 24 with the electrolyte 34 via contacts coupled to the working electrode 24 (e.g., where the contacts may contain a platinum material). Other conductive substrates may also be used, such as carbon felt, porous carbon plates, and / or conductive polymers (e.g., polyacetylene), each of which may be made hydrophobic as described below. Alternatively, conductive contacts (e.g., the conductive contacts may contain a platinum material) may be coupled to a catalyst layer to electrically couple the catalyst material to an external circuit, as described in more detail herein. In some embodiments, the substrate may be about 5 mils to about 20 mils thick.

[0031] The porous substrate may be hydrophobic to prevent the electrolyte 34 from passing through the working electrode 24. The substrate may be formed from a hydrophobic material, or the substrate may be treated with a hydrophobic material. In embodiments, the substrate may be made hydrophobic by impregnating it with a hydrophobic material such as a fluoropolymer (e.g., PTFE). In some embodiments, the substrate or membrane may contain GEFC-IES (e.g., a copolymer of perfluorosulfonic acid and PTFE, commercially available from GoldenEnergy Fuel Cell Co., Ltd.), Nafion... ® (A copolymer of polytetrafluoroethylene and perfluoro-3,6-dioxa-4-methyl-7-octene-sulfonic acid, which is available from DuPont) ™ The material is commercially available or pure or nearly pure polytetrafluoroethylene (PTFE). The impregnation process may include applying a solution or slurry containing the hydrophobic material onto the substrate using a dip-coating, coating, or rolling process. Alternatively, a dry composition, such as a powder, may be applied to the substrate. In some embodiments, an optional sintering process may be used to inject the hydrophobic material into the substrate to create a hydrophobic base layer for the working electrode 24, wherein both sides of the hydrophobic base layer are hydrophobic. The sintering process may result in the hydrophobic polymer bonding or fusing with the carbon of the substrate to firmly bond the hydrophobic material to the substrate.

[0032] The resulting substrate may contain about 30% to about 50% by weight of a hydrophobic polymer. The amount of hydrophobic material added to the substrate can affect the conductivity of the substrate, wherein the conductivity tends to decrease with increasing amount of hydrophobic material. The amount of hydrophobic polymer used with the substrate may depend on the desired degree of hydrophobicity, oxygen porosity, and conductivity of the resulting working electrode.

[0033] A catalyst layer can be formed by mixing the desired catalyst with a binder and depositing the mixture onto a substrate material. The binder may include a perfluorinated ionic electrolyte solution (e.g., GEFC-IES, Nafion). ® Hydrophobic materials (such as PTFE), mixtures thereof, etc. When used as adhesives, GEFC-IES, Nafion, etc. ® And / or PTFE can influence gas diffusion parameters, while simultaneously loading electrocatalysts and maximizing the interface between the catalyst, gas, and electrolyte at the site of the electrochemical process. Ethylene glycol or other similar chemicals can be used as diluents to form catalyst slurries, formulations, or catalyst systems, which can be printed onto a substrate using a printer.

[0034] The catalyst layer can be deposited onto the substrate, for example by screen printing, filtration from a suspension placed on the substrate in selected areas, spraying, or any other method suitable for producing a patterned deposition of a solid material. Deposition can be the deposition of a single material or the sequential deposition of more than one material in the layer to, for example, alter the properties of the electrode material by its thickness, or to add a second layer with increased conductivity on or under the layer where the gas reaction is predominant. Once deposited, the printed element can be sintered at high temperature to form an electrode.

[0035] In the working electrode 24, the catalyst layer may comprise carbon (e.g., graphite) and / or one or more metals, such as palladium, platinum, ruthenium, and / or iridium. In embodiments of the sensor 10, the working electrode 24 may comprise platinum. The catalyst used may be pure metal powder, metal powder mixed with carbon, or metal powder supported on a conductive medium (such as carbon), or a combination of two or more metal powders as a blend or as an alloy. The materials used for the various electrodes may be the same or different.

[0036] The counter electrode 16 may include a substrate or membrane on which a catalytic material is disposed, such as a PTFE membrane, a GEFC-IES membrane, or a Nafion membrane. ® Membranes, etc. In an embodiment, the catalytic material can be mixed and placed on the membrane using any suitable process, such as rolling, coating, screen printing, etc., to apply the catalytic material onto the membrane, as described in more detail herein. The catalyst layer can then be bonded to the membrane by a sintering process as described herein.

[0037] In embodiments, the catalytic material for the counter electrode 16 may include noble metals such as platinum (Pt), ruthenium (Ru), rhodium (Rh), iridium (Ir), or any combination thereof. The catalyst loading of the counter electrode 16 may be within any range described herein with respect to the working electrode 24. In embodiments, the catalyst loading of the counter electrode 16 may be the same as or substantially the same as the catalyst loading of the working electrode 24, or it may be greater than or less than the catalyst loading of the working electrode 24.

[0038] Similarly, the reference electrode 20 may include a substrate or film on which a catalytic material is disposed, such as a PTFE film, a GEFC-IES film, or a Nafion film. ® Membranes, etc. In embodiments, the catalytic material may be mixed with a hydrophobic material (e.g., PTFE, etc.) and disposed on a PTFE membrane. Any method used to form a working electrode or counter electrode may also be used to prepare the reference electrode 20. In embodiments, the catalytic material used with the reference electrode 20 may include noble metals such as platinum (Pt), ruthenium (Ru), rhodium (Rh), iridium (Ir), or any combination thereof. The catalyst loading of the reference electrode 20 may be within any range described herein with respect to the working electrode 24. In embodiments, the catalyst loading of the reference electrode 20 may be the same as or substantially the same as the catalyst loading of the working electrode 24, or it may be greater than or less than the catalyst loading of the working electrode 24. Although in Figure 1 The diagram shows a reference electrode 20, but some embodiments of the electrochemical sensor 10 may not include a reference electrode 20.

[0039] To detect the transelectrode current and / or potential difference generated in response to the presence of oxygen, one or more electrical contacts (or leads) can be electrically coupled to the working electrode 24, the reference electrode 20, and / or the reverse electrode 16. The contacts contacting the working electrode 24 can contact either side of the working electrode 24 because the substrate comprises a conductive material. Similarly, the contacts can be electrically coupled to the reverse electrode 16 and the reference electrode 20. The contacts can also be electrically coupled to external connection pins to provide electrical connection to external processing circuitry. The external circuitry can detect the current between the electrodes and convert the current into a corresponding oxygen concentration (e.g., by comparison with a pre-existing table / database that correlates current and / or potential difference with gas levels, e.g., based on previous testing).

[0040] In use, ambient gas can flow into or diffuse into sensor 10 through opening 28, which serves as the gas inlet port of sensor 10. Ambient gas may include oxygen. The gas can contact the working electrode and pass through the pores of the porous substrate layer to reach the surface of the working electrode 24, which has been treated with a catalyst layer. An electrolyte can contact the surface of the working electrode 24, and the oxygen can react, resulting in an electrolytic current formed between the working electrode 24 and the counter electrode 16, corresponding to the concentration of oxygen in the ambient gas. By measuring the current, the oxygen concentration can be determined using, for example, an external detection circuit.

[0041] Some embodiments of this disclosure may include methods for operating an electrochemical oxygen sensor, wherein the sensor may include an initial electrolyte concentration of approximately 8 M. Exemplary methods may include providing a sensor comprising one or more electrodes and an 8 M sulfuric acid electrolyte configured to electrically connect the one or more electrodes. A nitrogen source (i.e., oxygen-free) may be used to initially calibrate the sensor to establish a zero baseline for the oxygen sensor. In some embodiments, fresh (or ambient) air containing approximately 20.9% oxygen may also be used to calibrate the sensor (before use in the field).

[0042] The method may also include operating the sensor to detect oxygen in a field where the relative humidity of the environment is approximately 15% or lower. The method may also include maintaining sensor accuracy for detecting oxygen in a field during sensor operation, where the relative humidity of the environment is approximately 15% or lower, without requiring recalibration of the sensor using a nitrogen source (i.e., the sensor can operate in low humidity environments without recalibration). In some embodiments, the sensor is operable to detect oxygen in a field where the relative humidity of the environment is approximately 10% or lower. In some embodiments, the sensor is operable to detect oxygen even when operating at approximately 15% or lower relative humidity, with an accuracy within ±0.1% of O2. In some embodiments, although the sensor is operated in an environment with approximately 15% or lower relative humidity, recalibration of the sensor using a nitrogen source may not be required during the sensor's lifetime.

[0043] The implementation may also include a method for retrofitting an existing electrochemical sensor with an electrolyte containing sulfuric acid at an initial concentration of approximately 8 M (where the existing sensor may typically contain less than 8 M sulfuric acid). In the retrofitting method, providing the electrochemical sensor may include applying an electrolyte to the existing sensor, wherein the electrolyte contains sulfuric acid at a concentration of approximately 8 M.

[0044] In some cases, existing sensor structures can be used in conjunction with changes in electrolyte concentration. Changes can be made without requiring reconfiguration of pre-existing sensor designs (including size, materials, layout, etc.).

[0045] Various devices and methods have been described herein, and exemplary embodiments or aspects may include, but are not limited to: In a first embodiment, a method for operating an electrochemical oxygen sensor may include: operating the electrochemical sensor to detect oxygen in a field, wherein the electrochemical sensor includes an electrolyte and one or more electrodes, the electrolyte being configured to electrically connect the one or more electrodes and having an initial concentration of sulfuric acid of approximately 8 M; and maintaining sensor accuracy for detecting oxygen in a field during sensor operation, wherein the relative humidity of the environment is approximately 15% or lower, without requiring recalibration of the sensor using a nitrogen source.

[0046] The second embodiment may include the method according to the first embodiment, and further include operating a sensor to detect oxygen in the field, wherein the relative humidity of the environment is about 10% or lower.

[0047] The third embodiment may include the method according to the first and second embodiments, and further includes operating a sensor to detect oxygen, although operating at a relative humidity of about 15% or lower, the sensor having an accuracy within ±0.1% oxygen.

[0048] The fourth embodiment may include the method according to any one of the first to third embodiments, wherein although the sensor is operated in an environment with a relative humidity of about 15% or lower, the sensor does not need to be recalibrated with a nitrogen source during the life of the sensor.

[0049] The fifth embodiment may include the method according to any one of the first to fourth embodiments, and further includes providing an electrochemical sensor comprising an electrolyte and one or more electrodes, the electrolyte comprising sulfuric acid at an initial concentration of approximately 8M.

[0050] A sixth embodiment may include the method according to the fifth embodiment, wherein providing an electrochemical sensor includes modifying an existing electrochemical sensor with an electrolyte containing sulfuric acid at an initial concentration of approximately 8 M.

[0051] The seventh embodiment may include the method according to the fifth or sixth embodiment, wherein modifying an existing electrochemical sensor includes: providing an electrochemical sensor comprising a housing and one or more electrodes; applying an electrolyte within the housing, wherein the electrolyte is configured to electrically connect the one or more electrodes, and wherein the electrolyte contains sulfuric acid at an initial concentration of approximately 8 M.

[0052] The eighth embodiment may include the method according to any one of the first to seventh embodiments, and further includes using a nitrogen source free of any oxygen to initially calibrate the electrochemical sensor to set a zero baseline for the electrochemical sensor.

[0053] The ninth embodiment may include the method according to any one of the first to eighth embodiments, and further includes using air containing approximately 20.9% oxygen to initially calibrate the electrochemical sensor.

[0054] The tenth embodiment may include the method according to any one of the first to ninth embodiments, and further includes maintaining sensor accuracy after the sensor has been operated in an environment with a relative humidity of about 15% or lower.

[0055] In an eleventh embodiment, the electrochemical sensor may include: a housing; one or more electrodes located within the housing; and an electrolyte deposited within the housing and configured to electrically connect the one or more electrodes, wherein the electrolyte contains sulfuric acid at an initial concentration of approximately 8 M, and wherein the sensor is configured to detect oxygen in an environment with a relative humidity of approximately 15% or lower without requiring recalibration of the sensor using a nitrogen source.

[0056] The twelfth embodiment may include the electrochemical sensor according to the eleventh embodiment, wherein one or more electrodes include a working electrode configured to reduce oxygen entering the sensor via an opening in the housing.

[0057] The thirteenth embodiment may include the electrochemical sensor according to the twelfth embodiment, wherein one or more electrodes include a counter electrode configured to provide chemical equilibrium to the working electrode and oxidize water to produce oxygen.

[0058] The fourteenth embodiment may include the electrochemical sensor according to the thirteenth embodiment, wherein the electrolyte is configured to prevent oxygen generated at the counter electrode from reacting at the working electrode.

[0059] The fifteenth embodiment may include an electrochemical sensor according to any one of the eleventh to fourteenth embodiments, wherein the electrochemical sensor is configured to be initially calibrated with nitrogen before use in the field.

[0060] In a sixteenth embodiment, a method for retrofitting an existing electrochemical sensor may include: providing an electrochemical sensor comprising a housing and one or more electrodes; and depositing an electrolyte within the housing, wherein the electrolyte is configured to electrically connect the one or more electrodes, and wherein the electrolyte contains sulfuric acid at an initial concentration of approximately 8 M.

[0061] The seventeenth embodiment may include the method according to the sixteenth embodiment, and further includes operating the electrochemical sensor to detect oxygen in an environment with a relative humidity of 15% or lower without recalibrating the electrochemical sensor using a nitrogen source.

[0062] The eighteenth embodiment may include the method according to the seventeenth embodiment, and further includes maintaining the accuracy of the sensor during and after operation of the electrochemical sensor to detect oxygen in an environment with a relative humidity of 15% or lower.

[0063] The nineteenth embodiment may include the method according to any one of the sixteenth to eighteenth embodiments, and further includes operating an electrochemical sensor to detect oxygen without changing the specifications of the existing sensor.

[0064] The twentieth embodiment may include the method according to any one of the sixteenth to nineteenth embodiments, and further includes initially calibrating the sensor using nitrogen gas to establish a zero baseline for the sensor before operating the electrochemical sensor.

[0065] Although various embodiments based on the principles disclosed herein have been shown and described above, modifications can be made by those skilled in the art without departing from the spirit and teachings of this disclosure. The embodiments described herein are representative only and not intended to be limiting. Many variations, combinations, and modifications are possible and are within the scope of this disclosure. Alternative embodiments resulting from combining, integrating, and / or omitting features of one or more embodiments are also within the scope of this disclosure. Therefore, the scope of protection is not limited by the description given above, but is defined by the following claims, which include all equivalents of the subject matter of the claims. Each claim is incorporated into the specification as further disclosure, and the claims are for one or more embodiments of the invention. Furthermore, any of the foregoing advantages and features may relate to specific embodiments, but the application of such published claims should not be limited to methods and structures that achieve any or all of the above advantages or have any or all of the above features.

[0066] Furthermore, the section headings used herein are intended to align with the recommendations of 37 CFR 1.77 or otherwise provide organizational clues. These headings should not limit or characterize one or more inventions that can be set forth in any of the claims published in this disclosure. Specifically, and by way of example, although a heading may refer to “technical field,” the claims should not be limited by the language chosen under that heading to describe the so-called technical field. Moreover, the description of the technology in the “Background Art” section should not be construed as an admission that a particular technology is prior art to any one or more inventions of this disclosure. “Summary of the Invention” should also not be considered a limiting characterization of one or more inventions set forth in the published claims. Furthermore, any reference to the singular form “invention” in this disclosure should not be used to prove that there is only one novel point in this disclosure. Multiple inventions may be set forth according to the limitations of the multiple claims published in this disclosure, and such claims accordingly define one or more inventions protected by them, as well as their equivalents. In all cases, the scope of these claims should be considered in accordance with the advantages of the claims themselves, and should not be limited by the headings set forth herein.

[0067] It should be understood that the use of broad terms such as “comprising,” “including,” and “having” provides support for narrower terms such as “consisting of,” “substantially composed of,” and “substantially constituted by.” The use of terms such as “optionally,” “may,” “possibly,” etc., with respect to any element of an embodiment indicates that the element is not required, or alternatively, that the element is required, both of which are within the scope of one or more embodiments. Furthermore, references to examples are for illustrative purposes only and are not intended to be exclusive.

[0068] While several embodiments have been provided in this disclosure, it should be understood that the disclosed systems and methods may be embodied in many other specific forms without departing from the spirit or scope of this disclosure. The examples of the invention should be considered illustrative rather than restrictive, and are not intended to be limited to the details given herein. For example, various elements or components may be combined or integrated into another system, or certain features may be omitted or not implemented.

[0069] Furthermore, without departing from the scope of this disclosure, technologies, systems, subsystems, and methods described and illustrated as separate or independent in the various embodiments may be combined or integrated with other systems, modules, technologies, or methods. Other items shown or discussed as directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component, whether such coupling or communication is carried out electrically, mechanically, or otherwise. Other examples of variations, substitutions, and modifications that can be identified by those skilled in the art without departing from the spirit and scope of the disclosure herein will also be provided.

Claims

1. A method for operating an electrochemical oxygen sensor, the method comprising: The electrochemical oxygen sensor is operated to detect oxygen in a field, wherein the electrochemical oxygen sensor includes an electrolyte and one or more electrodes, the electrolyte being configured to electrically connect the one or more electrodes, the one or more electrodes including a working electrode and a counter electrode, the working electrode being configured to reduce oxygen entering the electrochemical oxygen sensor through an opening in the housing, and the counter electrode being configured to provide chemical equilibrium with the working electrode and oxidize water to produce oxygen; The initial concentration of the electrolyte was increased from 6M sulfuric acid to 8M sulfuric acid, wherein the increase in the concentration of the electrolyte improved the resistance to the back diffusion of oxygen within the electrochemical oxygen sensor and maintained a stable sensor signal. as well as When the humidity level of the field is 15% or lower relative humidity, the electrochemical oxygen sensor maintains its accuracy in detecting oxygen in the field during operation without the need to use a nitrogen source or ambient air to recalibrate the electrochemical oxygen sensor.

2. The method of claim 1, further comprising using the nitrogen source, which contains no oxygen, to initially calibrate the electrochemical oxygen sensor to set a zero baseline for the electrochemical oxygen sensor.

3. The method of claim 1, further comprising using air containing 20.9% oxygen to initially calibrate the electrochemical oxygen sensor.

4. A method for providing, calibrating, and operating an electrochemical oxygen sensor, the method comprising: An electrochemical oxygen sensor is provided, the electrochemical oxygen sensor comprising two or more electrodes and an electrolyte, wherein the electrolyte is configured to electrically connect the two or more electrodes to sulfuric acid with an initial concentration of 8M; The electrochemical oxygen sensor can be initially calibrated using an oxygen-free nitrogen source to establish a zero baseline, or using ambient air with known oxygen levels to initially calibrate the electrochemical oxygen sensor. The electrochemical oxygen sensor was operated to detect oxygen concentration, including an electrolyte with an initial concentration of 8M sulfuric acid, in an environment with a relative humidity of 15% or lower, without any recalibration after the initial calibration.

5. The method of claim 4, further comprising operating the electrochemical oxygen sensor to detect oxygen in the field, wherein the relative humidity of the environment is 10% or lower.

6. The method of claim 4, wherein, although operating at a relative humidity of 15% or lower, operating the electrochemical oxygen sensor includes detecting oxygen with an accuracy within ±0.1% of oxygen.

7. The method of claim 4, wherein providing the electrochemical oxygen sensor comprises retrofitting an existing electrochemical oxygen sensor with the electrolyte comprising sulfuric acid at an initial concentration of 8M.

8. The method of claim 7, wherein modifying the existing electrochemical oxygen sensor comprises: Provides a powered chemical oxygen sensor including a housing and two or more electrodes; An electrolyte is applied within the housing, wherein the electrolyte is configured to electrically connect the two or more electrodes, and wherein the electrolyte contains sulfuric acid with an initial concentration of 8M.

9. An electrochemical oxygen sensor, comprising: shell: Two or more electrodes located within the housing; and An electrolyte deposited within the housing, configured to electrically connect the two or more electrodes, wherein the electrolyte comprises sulfuric acid at an initial concentration of 8M at 15% or lower relative humidity, without requiring recalibration of the sensor using a nitrogen source. The housing includes an opening through which ambient gas reaches the electrochemical oxygen sensor, and the two or more electrodes include a working electrode comprising a porous substrate layer and a surface treated with a catalyst layer, arranged such that ambient gas that has passed through the opening passes through the porous substrate layer to the catalyst-treated surface of the working electrode.

10. The electrochemical oxygen sensor of claim 9, wherein the two or more electrodes include counter electrodes.

11. The electrochemical oxygen sensor according to claim 10, wherein the electrolyte is in the form of a free liquid.

12. The electrochemical oxygen sensor of claim 10, wherein the working electrode further comprises a base layer or substrate layer, the base layer or substrate layer comprising a hydrophobic material or a hydrophobically treated material.

13. An electrochemical sensor, comprising: shell; One or more electrodes located within the housing; and An electrolyte deposited within the housing, the electrolyte being configured to electrically connect the one or more electrodes, wherein the electrolyte comprises sulfuric acid at an initial concentration of 8M in an environment with a relative humidity of 15% or lower, and The electrochemical sensor is configured to detect oxygen in an environment with a relative humidity of 15% or lower without recalibrating the electrochemical sensor using a nitrogen source. The housing forms one or more openings, the one or more openings including diffusion barriers that restrict the flow of oxygen or nitrogen to the working electrode, wherein the counter electrode is located between the working electrode and the reference electrode.

14. The electrochemical sensor of claim 13, wherein the one or more electrodes include a working electrode configured to reduce oxygen entering the electrochemical sensor via an opening in the housing.

15. The electrochemical sensor of claim 14, wherein the one or more electrodes comprise a counter electrode configured to provide chemical equilibrium to the working electrode and oxidize water to produce oxygen.

16. The electrochemical sensor of claim 15, wherein the electrolyte is configured to prevent oxygen generated at the counter electrode from reacting at the working electrode.

17. The electrochemical sensor of claim 13, wherein the electrochemical sensor is configured to be initially calibrated with nitrogen gas prior to on-site use.

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