Electrochemical hydrogen sulfide sensor and preparation method thereof

Abstract

An electrochemical hydrogen sulfide sensor of the present invention comprises a shell with a detachable top cover, an air inlet for gas to enter is provided on the top cover of the shell, a liquid reservoir is provided at the bottom of the shell, a support plate covering the liquid reservoir is provided on the top of the liquid reservoir, the support plate has a porous structure, a working electrode, a reference electrode and a counter electrode are stacked in sequence from the air inlet to the liquid reservoir in the shell, an electrolyte is stored in the liquid reservoir, a liquid absorbing material three is provided in the liquid reservoir, the liquid absorbing material three is a roll-shaped structure, a liquid absorbing material one is provided between the working electrode and the reference electrode, a liquid absorbing material two is provided between the reference electrode and the counter electrode, pins connected to the working electrode, the reference electrode and the counter electrode are provided at the bottom of the shell, and an O-ring is provided between the working electrode and the top cover of the shell. The sensor is not interfered by impurity gases, has good selectivity, and has a simple structure, low manufacturing difficulty and low cost. The present invention also proposes a method for preparing an electrochemical hydrogen sulfide sensor.

Description

Technical Field

[0001] The invention relates to an electrochemical hydrogen sulfide sensor, belonging to the technical field of electrochemical sensors. Background Art

[0002] Hydrogen sulfide (chemical formula H2S) is a colorless, toxic gas with the smell of rotten eggs. High concentrations of hydrogen sulfide often exist in the closed environment of factories, oil fields, and sewers, which seriously threatens people's survival and health, so hydrogen sulfide gas must be strictly monitored. There are many types of sensors used to detect hydrogen sulfide, such as electrochemical, semiconductor, catalytic combustion, and optical fiber. Among them, electrochemical hydrogen sulfide sensors have become the mainstream sensors for detecting hydrogen sulfide gas due to their fast response time, high sensitivity, stable output signal, good reproducibility, no need for heating, low power consumption, and good linear characteristics. They are widely used in related monitoring devices and equipment, and are mainly used to detect hydrogen sulfide gas at a concentration level of one part per million (ppm).

[0003] In the environment where hydrogen sulfide sensors are used for monitoring, other interfering gases often exist, such as carbon monoxide (CO), hydrogen (H2), sulfur dioxide (SO2), nitric oxide (NO), nitrogen dioxide (NO2), chlorine (Cl2), ammonia (NH3), hydrogen cyanide (HCN), vinyl chloride, etc. These gases can react at the working electrode of the electrochemical hydrogen sulfide sensor, causing the instrument to have false alarms or delayed alarms, seriously threatening people's lives and safety.

[0004] In order to reduce false alarms or delayed alarms, the following four technical approaches are usually adopted to enhance the selectivity of electrochemical gas sensors:

[0005] 1. Use a suitable working electrode catalyst, but the catalyst material generally responds to a certain type of gas substance, so this method has limitations;

[0006] 2. Place a physical or chemical filter inside the sensor to filter out interfering gases. When the physical filter is saturated with adsorption or the chemical filter reacts completely, the filter becomes ineffective, and the selection range of filters is limited, so this method has certain limitations;

[0007] 3. Select an intermediate electrolyte system, in which the relevant components in the electrolyte only react with the target gas, thereby improving the selectivity of the sensor. However, this method is usually more complicated, and the electrolyte has a capacity limit and is a consumable electrolyte, which limits the effective service life of the sensor;

[0008] 4. Select the potential of the sensor. The activation energy of the electrochemical reaction is mainly affected by the electric field strength at the "electrode / solution" interface. Different gases have different optimal reaction potentials. Selecting the potential can improve the selectivity of the sensor. Usually, the sensor will respond to a certain type of gas substance at a certain potential.

[0009] In addition, sensor electrodes generally use precious metal catalysts, which are expensive and have limited reserves. On the other hand, the production process of sensor electrodes is cumbersome, including the preparation of catalysts, mixing slurries, coating, sintering, etc. The electrochemical hydrogen sulfide sensor includes three types of electrode sheets: working electrode, reference electrode and counter electrode. Each electrode sheet needs to be manufactured according to the process flow, and there are scraps in the process of manufacturing electrode sheets, which consumes a lot of manpower and financial resources. Therefore, in order to reduce the manufacturing cost of sensors, new technologies must be found to reduce the use of precious metals from every aspect.

[0010] Therefore, there is a need for an electrochemical hydrogen sulfide sensor that is resistant to interference from multiple gases such as CO, H2, SO2, NO, NO2, and has low manufacturing cost and low difficulty. Summary of the invention

[0011] In order to overcome the deficiencies of the prior art, the present invention proposes an electrochemical hydrogen sulfide sensor, which is not interfered by impurity gases, has good selectivity, and has a simple structure, low manufacturing difficulty and low cost.

[0012] To achieve the above-mentioned purpose, an electrochemical hydrogen sulfide sensor of the present invention comprises a shell with a detachable top cover, an air inlet hole for gas to enter is opened on the top cover of the shell, a liquid storage tank is provided at the bottom of the shell, a support plate covering it is provided on the top of the liquid storage tank, and the support plate has a porous structure. A working electrode, a reference electrode and a counter electrode are stacked in sequence from the air inlet hole to the liquid storage tank in the shell, an electrolyte is stored in the liquid storage tank, a liquid absorbing material three is provided in the liquid storage tank, and the liquid absorbing material three is a roll-shaped structure, a liquid absorbing material one is provided between the working electrode and the reference electrode, a liquid absorbing material two is provided between the reference electrode and the counter electrode, pins respectively connected to the working electrode, the reference electrode and the counter electrode are provided at the bottom of the shell, and an O-ring is provided between the working electrode and the top cover of the shell.

[0013] Furthermore, the shell is a hollow cylindrical structure, the working electrode is a disc-shaped structure, the counter electrode is a ring-shaped structure with an outer diameter the same as the working electrode, and the reference electrode is a disc-shaped structure with a diameter the same as the inner diameter of the counter electrode.

[0014] Furthermore, the working electrode, the reference electrode and the counter electrode are gas diffusion electrodes made of the same material, and the working electrode, the reference electrode and the counter electrode are electrodes produced from the same batch.

[0015] Furthermore, the reference electrode and the counter electrode are discs and rings cut from the same disc-shaped electrode in a concentric circle manner.

[0016] Furthermore, the gas diffusion electrode comprises a diffusion layer and a catalyst layer coated thereon, the diffusion layer adopts a porous polymer membrane, and the catalyst layer comprises a catalyst material and a binder mixture coated on the diffusion layer.

[0017] Furthermore, the catalyst material is one or any combination of platinum, ruthenium, iridium, gold, rhodium and palladium, and the binder is polytetrafluoroethylene emulsion.

[0018] Furthermore, the catalyst material is a platinum ruthenium black catalyst, and the molar ratio of platinum to ruthenium in the platinum ruthenium black catalyst is 1:1-1:3.

[0019] Furthermore, the catalyst material is a carbon-loaded / blended platinum-ruthenium black catalyst, and the platinum-ruthenium black loading / blending amount in the carbon-loaded / blended platinum-ruthenium black catalyst is 5%-40%.

[0020] Furthermore, the electrolyte is a sulfuric acid solution with a concentration of 3M to 12M.

[0021] The present invention also provides a method for preparing an electrochemical hydrogen sulfide sensor, comprising the following steps:

[0022] S1: Take the catalyst material and add activated carbon powder, mix well, then add binder, and stir magnetically for 40h-60h to prepare electrode slurry;

[0023] S2: Apply the electrode slurry on the diffusion layer by screen printing, spraying, dripping or scraping, and dry it at 55°C-65°C for 24h to obtain the electrode;

[0024] S3: Use a punch to punch out two disc-shaped electrodes, one of which is used as a working electrode, and a small disc-shaped electrode is cut from the center of the other disc-shaped electrode using a punch as a reference electrode, and the cut concentric ring electrodes are used as counter electrodes;

[0025] S4: Assemble, fill the liquid absorbing material 3 in the liquid storage tank, install the support plate, sequentially load the counter electrode, liquid absorbing material 2, reference electrode, liquid absorbing material 1 and working electrode into the shell, inject electrolyte, install O-ring, and complete the assembly after sealing the shell with the top cover;

[0026] S5: Test the sensitivity and anti-interference of the sensor.

[0027] The electrochemical hydrogen sulfide sensor of the present invention is not interfered by impurity gases, has good selectivity, and has a simple structure, low manufacturing difficulty and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be further described and explained below in conjunction with the accompanying drawings.

[0029] Figure 1 It is a cross-sectional view of an electrochemical hydrogen sulfide sensor according to a preferred embodiment of the present invention.

[0030] Figure numerals: 1. Shell; 2. Working electrode; 3. Reference electrode; 4. Counter electrode; 5. Liquid absorbent material one; 6. Liquid absorbent material two; 7. Liquid absorbent material three; 8. Support plate; 9. Air inlet; 10. Liquid storage tank; 11. Pin; 12. O-ring. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be more clearly and completely explained below through description of preferred embodiments of the present invention in combination with the accompanying drawings.

[0032] like Figure 1 As shown, an electrochemical hydrogen sulfide sensor of the preferred embodiment of the present invention includes a housing 1 with a detachable top cover, the housing 1 is a hollow cylindrical structure, and the housing 1 can be a standard part, such as a 4-series electrochemical gas sensor, whose inner diameter is 20 mm. The housing 1 is made of an engineering plastic material that is inert to the target gas and the electrolyte, and can be formed of, but not limited to, ABS, PE, PPO, PP, or any combination or blend thereof. In this embodiment, ABS plastic is used.

[0033] like Figure 1 As shown, an air inlet hole 9 for gas to enter is opened on the top cover of the shell 1. The aperture of the air inlet hole 9 is determined by the measurement sensitivity of the electrochemical hydrogen sulfide sensor. The aperture of the air inlet hole 9 can be 1mm-6mm, preferably 2mm-3mm. The aperture of the air inlet hole 9 in this embodiment is 3mm.

[0034] like Figure 1 As shown, the bottom of the shell 1 has a liquid storage tank 10, and the liquid storage tank 10 stores an electrolyte. The electrolyte can be any conventional aqueous acidic electrolyte, such as sulfuric acid, phosphoric acid or a neutral ion solution or any combination thereof. A sulfuric acid solution with a concentration of 3M to 12M is preferably selected. In this embodiment, a 9M sulfuric acid solution is used.

[0035] like Figure 1As shown, a support plate 8 covering the top of the liquid storage tank 10 is provided, and a working electrode 2, a reference electrode 3 and a counter electrode 4 are stacked in sequence in the shell 1 from the air inlet 9 to the liquid storage tank 10. The support plate 8 has a porous structure, and the porous support plate 8 can facilitate the movement of the electrolyte in the shell 1, so that it can contact the working electrode 2, the reference electrode 3 and the counter electrode 4, thereby providing sufficient electrolyte for the electrochemical reaction of the gas. For cost considerations, the support plate 8 is made of the same material as the shell 1, and is molded together with the shell 1. The support plate 8 provides support for the working electrode 2, the reference electrode 3 and the counter electrode 4 to ensure consistent stress in the sensor.

[0036] like Figure 1 As shown, the bottom of the housing 1 is provided with three pins 11 respectively connected to the working electrode 2, the reference electrode 3 and the counter electrode 4, for communicating with an external circuit, so as to output the sensor signal to the external circuit.

[0037] like Figure 1 As shown, a liquid absorbing material 1 5 is provided between the working electrode 2 and the reference electrode 3, a liquid absorbing material 2 6 is provided between the reference electrode 3 and the counter electrode 4, and a liquid absorbing material 3 7 is provided in the liquid storage tank 10. The liquid absorbing material 3 7 is a roll-shaped structure. The liquid absorbing material 1 5, the liquid absorbing material 2 6 and the liquid absorbing material 3 7 are made of glass fiber cotton or viscose fiber non-woven fabric, or any suitable material known in the art. The liquid absorbing material 1 5 and the liquid absorbing material 2 6 can effectively avoid short circuit caused by physical contact between the working electrode 2, the reference electrode 3 and the counter electrode 4, and have a strong liquid absorbing ability, thereby providing sufficient electrolyte for the electrochemical reaction. In addition, it also serves as an electrolyte retention layer, which can effectively extend the service life of the sensor. The liquid absorbing material 3 7 in the liquid storage tank 10 can limit the fluidity of the electrolyte, avoid the leakage of the electrolyte to a certain extent, and is conducive to the use and transportation of the sensor. In addition, electrochemical hydrogen sulfide sensors usually use acidic electrolytes, such as 9M sulfuric acid in this embodiment. In a high humidity environment, the electrolyte will absorb water from the environment and cause the volume to increase, which is easy to cause electrolyte leakage. The liquid absorbing material 37 is placed in the liquid storage tank 10. When the ambient humidity is high, the liquid absorbing material 37 can absorb excess water and store the water in the liquid storage tank 10, and the pressure formed by the water absorption will not cause the electrolyte to leak out of the sensor.

[0038] like Figure 1 As shown, an O-ring 12 is provided between the working electrode 2 and the top cover of the housing 1. The O-ring 12 has two functions: on the one hand, the O-ring 12 provides environmental sealing for the internal electrodes of the electrochemical hydrogen sulfide sensor; on the other hand, when there is pressure, the O-ring 12 deforms to provide buffer protection for the internal components of the electrochemical hydrogen sulfide sensor.

[0039] like Figure 1As shown, the working electrode 2 is a disc-shaped structure, the counter electrode 4 is a ring-shaped structure with an outer diameter the same as the diameter of the working electrode 2, and the reference electrode 3 is a disc-shaped structure with a diameter the same as the inner diameter of the counter electrode 4. The working electrode 2, the reference electrode 3 and the counter electrode 4 are gas diffusion electrodes made of the same material, and the working electrode 2, the reference electrode 3 and the counter electrode 4 are electrodes made from the same batch, which can reduce the difference between the electrodes and improve the stability of the sensor. In order to reduce manufacturing costs, the reference electrode 3 and the counter electrode 4 are discs and rings cut from the same disc-shaped electrode in a concentric circle manner. The diameter of the working electrode 2 in the present embodiment is 18mm, the diameter of the reference electrode 3 is 6mm, and the size of the counter electrode 4 is 18mm*6mm.

[0040] The gas diffusion electrode includes a diffusion layer and a catalyst layer coated thereon. The diffusion layer uses a porous polymer membrane. In this embodiment, a polytetrafluoroethylene membrane produced by ZITEX is used, and the thickness is 0.02 mm. The catalyst layer includes a catalyst material and a binder mixture coated on the diffusion layer. The binder uses a polytetrafluoroethylene emulsion produced by DuPont.

[0041] The catalyst material is one or more of platinum, ruthenium, iridium, gold, rhodium, and palladium in any combination. The catalyst material in this embodiment is a platinum ruthenium black catalyst, and the molar ratio of platinum to ruthenium in the platinum ruthenium black catalyst is 1:1. Platinum has a good adsorption effect on hydrogen sulfide gas and high catalytic activity, so platinum is usually used as an electrochemical hydrogen sulfide sensor catalyst. Ruthenium, as an additional catalyst, can suppress the sensitivity of gases such as carbon monoxide. Adding a catalyst that has no catalytic activity or has lower catalytic activity than the target gas to the gas diffusion electrode can effectively improve the selectivity of the electrochemical hydrogen sulfide sensor. Ruthenium is added to the Pt catalyst according to a molar ratio of platinum to ruthenium of 1:1, which greatly improves the selectivity of the sensor to hydrogen sulfide gas and is almost not interfered by other gases. In addition, the platinum ruthenium black catalyst can be loaded / blended on the carbon material, and the platinum ruthenium black loading / blending amount is 25%. The addition of carbon material can further suppress the response of the gas diffusion electrode to the interfering gas, reduce the material cost of the gas diffusion electrode, and increase the conductivity of the gas diffusion electrode. The carbon material can be Vulcan XC-72 activated carbon, Vulcan XC-72R activated carbon, R330, etc. In this embodiment, Vulcan XC-72 activated carbon powder is specifically used.

[0042] The working principle of the electrochemical hydrogen sulfide sensor of the present invention is:

[0043] When the target hydrogen sulfide gas enters the sensor through the air inlet 9, it is adsorbed at the working electrode 2 and generates the following electrochemical reaction:

[0044] Working electrode 2: H2S+4H2O→H2SO4+8H + +8e (1)

[0045] On the other side, at the counter electrode 4, O2 undergoes the following chemical reaction:

[0046] Counter electrode 4: O2+8H + +8e→4H2O (2)

[0047] The reference electrode 3 does not participate in the electrochemical reaction, is combined with an external electronic voltage stabilization circuit, and serves as an electrical reference point to maintain the potential of the working electrode 2 .

[0048] Overall, under the action of the electrolyte solution, reactions (1) and (2) occur simultaneously, which is equivalent to the following overall reaction occurring inside the sensor:

[0049] Overall reaction: H2S+2O2→H2SO4 (3).

[0050] A method for preparing an electrochemical hydrogen sulfide sensor according to a preferred embodiment of the present invention comprises the following steps:

[0051] S1: Take 0.5g of platinum ruthenium black, add 2g of activated carbon powder, mix well, add polytetrafluoroethylene emulsion, and stir magnetically for 48h to prepare electrode slurry;

[0052] S2: The electrode slurry was coated on a polytetrafluoroethylene membrane using a wire rod and dried at 60°C for 24 h to obtain an electrode;

[0053] S3: Use a punch to punch out two disc-shaped electrodes with a diameter of 18 mm, one of which is used as the working electrode 2, and a small disc-shaped electrode is cut from the center of the other disc-shaped electrode using a 6 mm circular hollow cutting head as the reference electrode 3, and the cut concentric ring electrodes are used as the counter electrode 4;

[0054] S4: Assemble, fill the liquid absorbing material three 7 in the liquid storage tank 10, install the support plate 8, sequentially load the counter electrode 4, the liquid absorbing material two 6, the reference electrode 3, the liquid absorbing material one 5 and the working electrode 2 into the housing 1, inject 9M sulfuric acid solution, install the O-ring 12, and use the top cover to close the housing 1 to complete the assembly;

[0055] S5: Test the sensitivity and anti-interference of the sensor.

[0056] In step S5, the test method of the electrochemical hydrogen sulfide sensor is: 50ppmH2S gas is introduced, and the response time T90 is measured to be 25 seconds, the baseline is 0.00uA, and the sensitivity is 1uA / ppm. Then the electrochemical hydrogen sulfide sensor is exposed to air for 5 minutes, and then exposed to other gases for 5 minutes. Table 1 shows the interference values ​​of CO, H2, SO2, NO, NO2 and other gases in this embodiment.

[0057] Table 1:

[0058]

[0059]

[0060] It can be seen from Table 1 that gases such as CO, SO2, NO, NO2, and Cl2 have no cross-interference with the electrochemical H2S sensor of the embodiment. In addition, the electrochemical H2S sensor has a service life of 2 to 3 years.

[0061] The electrochemical hydrogen sulfide sensor of the present invention has not only fast response time, stable baseline, high sensitivity, but also simple structure, low manufacturing difficulty, low manufacturing cost, excellent sensitivity and accuracy, no interference from gases such as CO, SO2, NO, NO2, Cl2, etc., and good selectivity for hydrogen sulfide gas. It is suitable for production process control, safety detection and environmental monitoring in industries such as chemical plants, sewage treatment, fertilizer production, pharmaceuticals, paper mills, oil gas production, electroplating treatment, etc.

[0062] The above specific implementations are only descriptions of the preferred implementations of the present invention, and do not limit the protection scope of the present invention. Without departing from the design concept and spirit of the present invention, various modifications, substitutions and improvements made by ordinary technicians in this field to the technical solution of the present invention based on the text description and drawings provided by the present invention should all fall within the protection scope of the present invention. The protection scope of the present invention is determined by the claims.

Claims

1. An electrochemical hydrogen sulfide sensor, characterized in that: The invention comprises a shell with a detachable top cover, wherein the top cover of the shell is provided with an air inlet hole for gas to enter, the bottom of the shell is provided with a liquid storage tank, the top of the liquid storage tank is provided with a support plate covering it, the support plate has a porous structure, a working electrode, a reference electrode and a counter electrode are sequentially stacked in the shell from the air inlet hole to the liquid storage tank, an electrolyte is stored in the liquid storage tank, a liquid absorbing material three is provided in the liquid storage tank, the liquid absorbing material three is a roll-shaped structure, a liquid absorbing material one is provided between the working electrode and the reference electrode, a liquid absorbing material two is provided between the reference electrode and the counter electrode, the bottom of the shell is provided with pins respectively connected to the working electrode, the reference electrode and the counter electrode, and an O-ring is provided between the working electrode and the top cover of the shell; The shell is a hollow cylindrical structure, the working electrode is a disc-shaped structure, the counter electrode is a ring-shaped structure with the same outer diameter as the working electrode, and the reference electrode is a disc-shaped structure with the same diameter as the inner diameter of the counter electrode; The working electrode, the reference electrode and the counter electrode are gas diffusion electrodes made of the same material, and the working electrode, the reference electrode and the counter electrode are electrodes made from the same batch; the reference electrode and the counter electrode are discs and rings cut from the same disc-shaped electrode in a concentric circle manner; The gas diffusion electrode comprises a diffusion layer and a catalyst layer coated thereon, wherein the diffusion layer adopts a porous polymer membrane, and the catalyst layer comprises a catalyst material and a binder mixture coated on the diffusion layer.

2. An electrochemical hydrogen sulfide sensor as claimed in claim 1, characterized in that: The catalyst material is one or any combination of platinum, ruthenium, iridium, gold, rhodium and palladium, and the binder is polytetrafluoroethylene emulsion.

3. An electrochemical hydrogen sulfide sensor as claimed in claim 2, characterized in that: The catalyst material is a platinum ruthenium black catalyst, and the molar ratio of platinum to ruthenium in the platinum ruthenium black catalyst is 1:1-1:

3.

4. An electrochemical hydrogen sulfide sensor as claimed in claim 3, characterized in that: The catalyst material adopts a carbon-loaded / blended platinum-ruthenium black catalyst, and the platinum-ruthenium black loading / blending amount in the carbon-loaded / blended platinum-ruthenium black catalyst is 5%-40%.

5. An electrochemical hydrogen sulfide sensor as claimed in claim 1, characterized in that: The electrolyte is a sulfuric acid solution with a concentration of 3M to 12M.

6. A method for preparing an electrochemical hydrogen sulfide sensor as claimed in any one of claims 1 to 5, characterized in that: The following steps are involved: S1: Take the catalyst material and add activated carbon powder, mix well, then add binder, and stir magnetically for 40h-60h to prepare electrode slurry; S2: Apply the electrode slurry on the diffusion layer by screen printing, spraying, dripping or scraping, and dry it at 55°C-65°C for 24h to obtain the electrode; S3: Use a punch to punch out two disc-shaped electrodes, one of which is used as a working electrode, and a small disc-shaped electrode is cut from the center of the other disc-shaped electrode using a punch as a reference electrode, and the cut concentric ring electrodes are used as counter electrodes; S4: Assemble, fill the liquid absorbing material 3 in the liquid storage tank, install the support plate, sequentially load the counter electrode, liquid absorbing material 2, reference electrode, liquid absorbing material 1 and working electrode into the shell, inject electrolyte, install O-ring, and complete the assembly after sealing the shell with the top cover; S5: Test the sensitivity and anti-interference of the sensor.

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