Electrochemical oxygen sensor and manufacturing method of counter electrode of oxygen sensor

Abstract

The invention belongs to the field of electrochemical sensors, and relates to an electrochemical oxygen sensor which comprises a working electrode, a counter electrode and an electrolyte, the counter electrode comprises a substrate and a slurry layer, the substrate adopts a polytetrafluoroethylene film, and the slurry layer comprises a metal catalyst, nano hollow carbon spheres and a hydrophobic polymer material; and the electrolyte is an acidic electrolyte with the concentration of 0.01 wt%-5 wt%. In addition, the invention further relates to a manufacturing method of the oxygen sensor counter electrode. In the embodiment of the invention, the nano hollow carbon spheres and the hydrophobic polymer material are added into the material of the counter electrode of the oxygen sensor, so that the adsorption rate of O2 on the surface of the counter electrode is improved, the retention time of O2 bubbles is prolonged, and the selectivity of 2e-WOR and the generation rate of H2O2 in a water oxidation reaction on the surface of the counter electrode are greatly improved; the electrochemical sensor with the design can work under weak acid electrolyte, and the defect that an existing oxygen pump type oxygen sensor adopts strong acid electrolyte is overcome.

Description

Technical Field

[0001] The present application relates to the technical field of electrochemical sensors, and in particular to an electrochemical oxygen sensor and a method for manufacturing an oxygen sensor counter electrode. Background Art

[0002] Oxygen pump sensors are currently one of the main product categories of electrochemical oxygen sensors. The electrochemical process of their internal working principle is as follows:

[0003] Working electrode: O2+4H + +4e - =2H2O

[0004] Counter electrode: 2H2O=O2+4H + +4e -

[0005] This type of sensor reaction process does not consume any material, has a long service life (generally greater than 5 years), and has more stable performance. It is currently widely used in the industrial field.

[0006] To improve sensor performance, the electrolyte of oxygen pump-type oxygen sensors mainly uses high-concentration sulfuric acid or phosphoric acid, with a concentration generally ranging from 20% to 60%. Once this strong acid electrolyte leaks during use, it can corrode surrounding objects at the very least, and pollute the environment or cause accidents at worst. Therefore, the application of sensors using strong acids or strong bases as electrolytes will be limited in some high-end precision equipment. Therefore, reducing the corrosiveness of the electrolyte is also an important indicator that researchers need to consider.

[0007] Therefore, how to design an oxygen sensor that can work in a weak acid electrolyte environment and minimize the impact on the performance of the oxygen sensor is a technical problem that needs to be solved. Summary of the Invention

[0008] The purpose of the embodiments of the present application is to provide an electrochemical oxygen sensor and a method for manufacturing an oxygen sensor counter electrode. By adding nano-hollow carbon spheres and hydrophobic polymer materials to the material of the oxygen sensor counter electrode, the adsorption rate of O2 on the electrode surface is improved, the residence time of O2 bubbles is prolonged, and the selectivity of 2e-WOR and the H2O2 generation rate in the water oxidation reaction on the electrode surface are greatly improved. The electrochemical sensor designed in this way can operate in a weak acid electrolyte environment, avoiding the defects of existing oxygen pump-type oxygen sensors that use strong acid electrolytes.

[0009] In order to solve the above technical problems, the present invention provides an electrochemical oxygen sensor, which adopts the following technical solution:

[0010] Working electrode, counter electrode and electrolyte;

[0011] The counter electrode comprises a substrate and a slurry layer, wherein the substrate is a polytetrafluoroethylene membrane, and the slurry layer comprises a metal catalyst, nano hollow carbon spheres and a hydrophobic polymer material;

[0012] The electrolyte is an acidic electrolyte with a concentration of 0.01 wt% to 5 wt%.

[0013] Furthermore, in the slurry layer, the metal catalyst accounts for 25%-70% by mass, the nano hollow carbon spheres account for 5%-70% by mass, and the hydrophobic polymer material accounts for 2%-25% by mass.

[0014] Furthermore, the hydrophobic polymer material includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, fluorinated epoxy resin, and ethylene vinyl acetate.

[0015] Furthermore, the electrochemical oxygen sensor further includes a breathable membrane arranged at the air inlet.

[0016] In order to solve the above technical problems, the present invention further provides a method for manufacturing an oxygen sensor counter electrode, comprising the following steps:

[0017] Preparing a mother solution containing a hydrophobic polymer material;

[0018] adding a metal catalyst and nano hollow carbon spheres to the mother solution and stirring for a preset time to obtain a counter electrode slurry;

[0019] The counter electrode slurry is coated on a polytetrafluoroethylene film and dried to obtain a counter electrode for an oxygen sensor.

[0020] Furthermore, the hydrophobic polymer material includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, fluorinated epoxy resin, and ethylene vinyl acetate.

[0021] Furthermore, the mass proportion of the hydrophobic polymer material in the mother liquor is 2%-25%.

[0022] Furthermore, the solvent of the mother liquor is dimethyl sulfoxide or N,N-dimethylformamide.

[0023] Furthermore, before the step of scraping the counter electrode slurry onto a polytetrafluoroethylene film and drying it to obtain the counter electrode of the oxygen sensor, the manufacturing method further includes:

[0024] The polytetrafluoroethylene film is plasma-treated with a fluorine-containing gas.

[0025] Furthermore, the fluorine-containing gas includes CF4, SF6 or F2.

[0026] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0027] In an embodiment of the present application, by adding nano-hollow carbon spheres and a hydrophobic polymer material to the slurry layer of the counter electrode of an electrochemical oxygen sensor, the gas affinity and hydrophobicity of the counter electrode surface can be significantly enhanced, the adsorption rate of O2 on the counter electrode surface is increased, the residence time of O2 bubbles is prolonged, and the selectivity of 2e-WOR and the rate of H2O2 generation are significantly improved, thereby increasing the speed of oxygen reduction at the counter electrode. Because this reaction can occur in an electrolyte with a relatively low acid concentration, the oxygen sensor designed in this manner can use a weak acid electrolyte, thus realizing the design of an oxygen pump oxygen sensor for a weak acid electrolyte environment, avoiding the drawbacks of existing oxygen pump oxygen sensors that use a strong acid electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the solutions in this application, a brief introduction will be given below to the drawings required for use in the description of the embodiments of this application. Obviously, the drawings described below are some embodiments of this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0029] Figure 1 Schematic diagram of the process for manufacturing the oxygen sensor counter electrode provided in the embodiment of the present application. DETAILED DESCRIPTION

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which this application belongs. The terms used in the specification of the application are for the purpose of describing specific embodiments only and are not intended to limit this application. The terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned drawings are intended to cover non-exclusive inclusions. The terms "first", "second", etc. in the specification and claims of this application or the above-mentioned drawings are used to distinguish different objects, not to describe a specific order.

[0031] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0032] The embodiments of the present application are described in detail below.

[0033] From the electrochemical process described above regarding the internal working principle of an oxygen pump oxygen sensor, it can be seen that the oxygen evolution reaction (OER) occurs at the counter electrode of the oxygen pump oxygen sensor. It is generally believed that bubbles generated on the electrode surface by the oxygen evolution reaction are harmful. However, some literature has shown that by examining the water oxidation performance of the electrode surface under different bubble states and the impact of bubbles on the water oxidation pathway, it was found that bubbles on the electrode surface can significantly promote the two-electron water oxidation reaction (2e-WOR) to synthesize H2O2. Under certain acidic conditions, when H2O2 accumulates to a certain level, it will continue to decompose into water and oxygen. However, in a strongly acidic electrolyte environment, because the theoretical potential of the oxygen evolution reaction is lower than that of the 2e-WOR, the water oxidation reaction tends to directly produce O2 rather than H2O2.

[0034] The inventors have discovered that a novel electrochemical oxygen sensor can be designed using the 2e-WOR reaction mechanism. If this 2e-WOR reaction mechanism is followed, the following reactions will occur within the novel electrochemical oxygen sensor:

[0035] Working electrode: O2+4H + +4e - =2H2O

[0036] Counter electrode: 2H2O=H2O2+2H + +2e - =O2+4H + +4e -

[0037] As can be seen from the above, if the oxygen sensor reacts according to this 2e-WOR reaction mechanism, in order to make the water oxidation reaction of the counter electrode more inclined to produce H2O2 rather than directly produce O2, the new electrochemical oxygen sensor needs to use a weak acid electrolyte, thereby avoiding the disadvantages of conventional oxygen pump type oxygen sensors using strong acid electrolytes. However, the inventors further discovered that the oxygen sensor using the 2e-WOR reaction mechanism requires high selectivity while the counter electrode undergoes the 2e-WOR reaction, that is, it is necessary to make the water oxidation reaction on the counter electrode surface tend to go through the 2e-WOR reaction mechanism as much as possible. Otherwise, the overall response signal of the sensor is low and the response time is very long. Based on this, the present application discloses an electrochemical sensor and a method for manufacturing an oxygen sensor counter electrode, respectively. By increasing the hydrophobicity and aerophilicity of the counter electrode surface, it can quickly adsorb and accumulate bubbles, improve the 2e-WOR selectivity, and thus improve the performance of the new electrochemical oxygen sensor. As a result, a high-precision electrochemical oxygen sensor using a weak acid electrolyte can be designed, and the specific description is as follows.

[0038] The present application discloses an electrochemical oxygen sensor, wherein the electrochemical sensor comprises:

[0039] Working electrode, counter electrode and electrolyte;

[0040] The counter electrode includes a substrate and a slurry layer, wherein the substrate adopts a polytetrafluoroethylene membrane, and the slurry layer includes a metal catalyst, nano hollow carbon spheres and a hydrophobic polymer material;

[0041] The electrolyte is an acidic electrolyte with a concentration of 0.01 wt% to 5 wt%.

[0042] In this embodiment, both the working electrode and the counter electrode include a substrate layer and a slurry layer, and the substrates can be made of a hydrophobic and breathable polytetrafluoroethylene (PTFE) membrane.

[0043] The slurry layer of the working electrode includes a metal catalyst, graphite, and perfluorosulfonic acid resin (Nafion-H). The metal catalyst has a certain degree of catalytic activity for the oxidation-reduction reaction (ORR) and can be a precious metal catalyst such as platinum, palladium, or iridium with a purity greater than 99%. The relative weight proportion of the precious metal catalyst is 10%-90%, the relative weight proportion of graphite is 10%-50%, and the relative weight proportion of perfluorosulfonic acid resin is 0.1%-30%.

[0044] The slurry layer of the counter electrode includes a metal catalyst, nano hollow carbon spheres and a hydrophobic polymer material. The material selection of the metal catalyst is consistent with that of the working electrode.

[0045] Among them, hollow carbon spheres have a unique cavity structure compared to ordinary graphite or other nanocarbon materials, have natural hydrophobicity, and have a larger specific surface area and large pore volume. This structure can provide a place for the storage and transportation of substances, and can be used to load various functional molecules, such as gases, drugs, catalysts, etc. It has obvious advantages in improving gas adsorption capacity and mass transfer efficiency, and has high efficiency in fields such as adsorption and catalytic reactions.

[0046] Hydrophobic polymer materials refer to polymer compounds that are insoluble in water or other polar solvents and are water-repellent. They can adsorb oxygen generated on the surface of the electrode through van der Waals forces, thereby further increasing the oxygen adsorption rate on the electrode surface.

[0047] The electrolyte may be an acidic electrolyte with a concentration of 0.01 wt% to 5 wt%, specifically an inorganic acid such as sulfuric acid or phosphoric acid.

[0048] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0049] In the embodiments of the present application, by adding nano-hollow carbon spheres and a hydrophobic polymer material to the slurry layer of the counter electrode of an electrochemical oxygen sensor, the gas affinity and hydrophobicity of the counter electrode surface can be significantly enhanced, the adsorption rate of O2 on the counter electrode surface is increased, the residence time of O2 bubbles is prolonged, and the selectivity of 2e-WOR and the H2O2 generation rate in the water oxidation reaction on the counter electrode surface are significantly improved. Because this reaction can occur in electrolytes with relatively low acid concentrations, the oxygen sensor designed in this manner can use weak acid electrolytes, thus realizing the design of an oxygen pump oxygen sensor for weak acid electrolyte environments, avoiding the drawbacks of existing oxygen pump oxygen sensors that use strong acid electrolytes.

[0050] In some possible implementations, the mass proportion of the metal catalyst in the slurry layer of the counter electrode is 25%-70%, the mass proportion of the nano hollow carbon spheres is 5%-70%, and the mass proportion of the hydrophobic polymer material is 2%-25%. Among them, the sum of the mass proportions of the metal catalyst, nano hollow carbon spheres and hydrophobic polymer material does not exceed 100%. In a specific embodiment, the mass proportions of the metal catalyst, nano hollow carbon spheres and hydrophobic polymer material can be set to 35%, 45% and 20% respectively.

[0051] In some possible implementations, the hydrophobic polymer material includes one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated epoxy resin, and ethylene vinyl acetate resin.

[0052] In some possible implementations, the electrochemical oxygen sensor further includes a gas permeable membrane disposed at the gas inlet.

[0053] In this embodiment, the working electrode and counter electrode are spaced apart within the sensor housing. An air inlet is provided on the wall of the housing directly opposite the working electrode, allowing the gas to enter the sensor through this inlet and initiate an electrochemical reaction on the surface of the working electrode. This inlet is equipped with a breathable membrane with a thickness of 10-200 μm, made of either FEP polytetrafluoroethylene (PTFE) or polytetrafluoroethylene (FEP). This membrane prevents dust, dirt, and liquids from invading the sensor head, controls gas diffusion permeability, and allows gas to pass through the membrane immediately, thereby ensuring a constant sensor response speed and preventing errors and delays in measurement results.

[0054] The following combination Figure 1 The present application also discloses a method for manufacturing an oxygen sensor counter electrode, comprising the following steps:

[0055] S11, preparing a mother solution containing a hydrophobic polymer material.

[0056] The hydrophobic polymer material may include one or more of polyvinylidene fluoride, polytetrafluoroethylene, fluorinated epoxy resin, and ethylene vinyl acetate. The weight percentage of the hydrophobic polymer in the mother liquor is 2% to 25%. The solvent of the mother liquor may be dimethyl sulfoxide (DMSO) or N,N-dimethylformamide (DMF).

[0057] S12, adding the metal catalyst and the nano hollow carbon spheres into the mother liquor and stirring for a preset time to obtain a counter electrode slurry.

[0058] The metal catalyst has a certain ORR catalytic activity, and can be a noble metal catalyst such as platinum, palladium, or iridium, with a purity greater than 99%. The stirring time of the process can be controlled between 2 and 24 hours.

[0059] S13, coating the counter electrode slurry on a polytetrafluoroethylene film and drying the film to obtain a counter electrode for the oxygen sensor.

[0060] The process can be dried in an oven at 40-150° C. to remove the DMSO or DMF solvent in the electrode slurry. After drying, the electrode slurry forms a slurry layer.

[0061] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0062] In an embodiment of the present application, by adding nano-hollow carbon spheres and a hydrophobic polymer material to the slurry layer of the counter electrode of the oxygen sensor, the gas affinity and hydrophobicity of the counter electrode surface can be significantly enhanced, the adsorption rate of O2 on the counter electrode surface can be increased, the residence time of O2 bubbles can be prolonged, and the selectivity of its 2e-WOR and the rate of H2O2 generation can be greatly improved, thereby increasing the speed of oxygen reduction at the counter electrode. Because this reaction can occur under the conditions of an electrolyte with a relatively low acid concentration, the oxygen sensor using this counter electrode can use a weak acid electrolyte, thereby realizing the design of an oxygen pump oxygen sensor for a weak acid electrolyte environment, avoiding the defects of the existing oxygen pump oxygen sensor design that uses a strong acid electrolyte.

[0063] In some possible implementations, refer to Figure 1 Before the step of coating the counter electrode slurry on a polytetrafluoroethylene film and drying it to obtain the counter electrode of the oxygen sensor, the manufacturing method further includes:

[0064] S14, plasma-treating the polytetrafluoroethylene film with a fluorine-containing gas.

[0065] The fluorine-containing gas may include CF4, SF6 or F2, etc. Through ion treatment, the hydrophobicity and aerophilicity of the electrode substrate PTFE membrane can be enhanced, and the adhesion after slurry coating can be enhanced.

[0066] In addition, the third embodiment of the present application discloses a method for manufacturing a working electrode of an oxygen sensor, comprising the following steps:

[0067] S21. Prepare 5 wt% PFSA perfluorosulfonic acid resin mother solution, using DMSO or ethylene glycol as the solvent.

[0068] S22. Weigh a certain mass of precious metal catalyst and graphite.

[0069] The metal catalyst has a certain ORR catalytic activity, such as platinum, palladium, iridium and other precious metal catalysts, with a purity greater than 99%. The graphite sheet diameter ranges from 1 μm to 300 μm.

[0070] S23. Add the metal catalyst and graphite together into 5 wt% PFSA mother liquor and stir for 2-24 h.

[0071] S24. The slurry prepared in step (3) is coated on a hydrophobic and breathable PTFE membrane, and then dried in an oven at 40-150° C. to remove the solvent DMSO or ethylene glycol in the working electrode slurry to obtain a working electrode sheet.

[0072] Here is a specific example:

[0073] 1. Preparation of working electrode

[0074] Prepare a 5wt% PFSA mother liquor (using ethylene glycol as the solvent) and weigh 0.7g of platinum black (99% purity) and 0.2g of graphite. Then, slowly add 2g of the 5wt% PFSA mother liquor while stirring for 12 hours to prepare a working electrode slurry. This slurry is then coated onto a PTFE membrane and dried to obtain a working electrode sheet.

[0075] 2. Preparation of counter electrode

[0076] Prepare a 5wt% PVDF mother liquor (DMF solvent) and add 0.5g of platinum black (99% purity) and 0.4g of hollow carbon nanospheres to a beaker. Then, slowly add 2g of the 5wt% PVDF mother liquor while stirring for 12 hours to create a counter electrode slurry. This slurry is then applied by doctor blade to a plasma-hydrophobicized PTFE membrane and dried to obtain the counter electrode.

[0077] 3. Sensor assembly

[0078] The working electrode and counter electrode prepared above were used to assemble an oxygen sensor: the cathode electrode sheet and the 25 μm PTFE breathable membrane were assembled in sequence, and then 0.1 mol / L (0.97 wt%) sulfuric acid solution was added as the electrolyte to assemble the oxygen sensor.

[0079] 4. Testing

[0080] The sensor prepared above was exposed to different oxygen concentrations to detect current changes. The test results showed that the response time and linearity of this low-acid concentration oxygen pump sensor were good, basically meeting the requirements of use, indicating that this sensor has potential for application in the market in the future.

[0081] Among them, the test performance parameters of the sensor are as follows:

[0082] Sensitivity Linearity R2 Response time 0.12uA / % 0.9999 10s

[0083] It should be understood that although the steps in the flowcharts of the accompanying drawings are shown in sequence as indicated by the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some of the steps in the flowcharts of the accompanying drawings may include multiple sub-steps or multiple stages, and these sub-steps or stages are not necessarily executed at the same time, but can be executed at different times, and their execution order is not necessarily sequential, but can be executed in turn or alternately with other steps or at least a portion of the sub-steps or stages of other steps.

[0084] Obviously, the embodiments described above are only some of the embodiments of the present application, rather than all of the embodiments. The preferred embodiments of the present application are given in the accompanying drawings, but they do not limit the patent scope of the present application. The present application can be implemented in many different forms. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive. Although the present application has been described in detail with reference to the aforementioned embodiments, for those skilled in the art, it is still possible to modify the technical solutions described in the aforementioned specific embodiments, or to make equivalent replacements for some of the technical features therein. Any equivalent structure made using the contents of the present application specification and the accompanying drawings, directly or indirectly used in other related technical fields, is also within the scope of patent protection of the present application.

Claims

1. An electrochemical oxygen sensor comprising a working electrode, a counter electrode, and an electrolyte, characterized in that: The counter electrode comprises a substrate and a slurry layer, wherein the substrate is a polytetrafluoroethylene membrane, and the slurry layer comprises a metal catalyst, nano hollow carbon spheres and a hydrophobic polymer material; The electrolyte is an acidic electrolyte with a concentration of 0.01 wt% to 5 wt%.

2. The electrochemical oxygen sensor according to claim 1, characterized in that In the slurry layer, the metal catalyst accounts for 25%-70% by mass, the nano hollow carbon spheres account for 5%-70% by mass, and the hydrophobic polymer material accounts for 2%-25% by mass.

3. The electrochemical oxygen sensor according to claim 2, characterized in that The hydrophobic polymer material includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, fluorinated epoxy resin, and ethylene vinyl acetate.

4. The electrochemical oxygen sensor according to any one of claims 1 to 3, characterized in that The electrochemical oxygen sensor further includes a gas permeable membrane arranged at the gas inlet.

5. A method for manufacturing an oxygen sensor counter electrode, characterized in that: The steps include: Preparing a mother solution containing a hydrophobic polymer material; adding a metal catalyst and nano hollow carbon spheres to the mother solution and stirring for a preset time to obtain a counter electrode slurry; The counter electrode slurry is coated on a polytetrafluoroethylene film and dried to obtain a counter electrode for an oxygen sensor.

6. The manufacturing method according to claim 5, characterized in that The hydrophobic polymer material includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, fluorinated epoxy resin, and ethylene vinyl acetate.

7. The manufacturing method according to claim 6, characterized in that The mass proportion of the hydrophobic polymer material in the mother liquor is 2%-25%.

8. The manufacturing method according to claim 7, characterized in that The solvent of the mother liquor is dimethyl sulfoxide or N,N-dimethylformamide.

9. The manufacturing method according to any one of claims 5 to 8, characterized in that: Before the step of scraping the counter electrode slurry onto a polytetrafluoroethylene film and drying it to obtain the counter electrode of the oxygen sensor, the manufacturing method further comprises: The polytetrafluoroethylene film is plasma-treated with a fluorine-containing gas.

10. The manufacturing method according to claim 9, characterized in that: The fluorine-containing gas includes CF4, SF6 or F2.

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