Electrochemical formaldehyde sensor electrode, preparation method thereof and electrochemical formaldehyde sensor

Abstract

The invention relates to the technical field of gas sensors, and particularly discloses an electrochemical formaldehyde sensor electrode, a preparation method thereof and an electrochemical formaldehyde sensor. The electrochemical formaldehyde sensor comprises an electrochemical formaldehyde sensor electrode and a binary electrolyte, the electrochemical formaldehyde sensor electrode comprises a polytetrafluoroethylene film, the polytetrafluoroethylene film is coated with slurry for an electrochemical formaldehyde sensor electrode; and the slurry is formed by mixing nano manganese dioxide, platinum carbon and a Nafion solution. According to the electrochemical formaldehyde sensor, the electrode prepared from the slurry formed by mixing the nano manganese dioxide, the platinum carbon and the Nafion solution has relatively high catalytic activity, so that the sensor shows extremely high sensitivity and extremely good linearity on formaldehyde, and the electrochemical formaldehyde sensor has relatively high catalytic activity by regulating and controlling the proportion of the binary electrolyte. The electrochemical formaldehyde sensor has the advantages of high sensitivity, low cost, fast response, high detection precision and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas sensors, and more particularly to an electrochemical formaldehyde sensor electrode, a preparation method thereof and an electrochemical formaldehyde sensor. BACKGROUND

[0002] Formaldehyde (HCHO) is not only a colorless and soluble irritating gas, but also a toxic substance with a long incubation period. It is listed as one of the carcinogenic substances by the International Cancer Research Agency. The main sources of formaldehyde in outdoor air are the combustion of petroleum, coal and natural gas, atmospheric photochemical reactions, and the emissions of some factories producing organic resins, chemical fibers, dyes and coatings. The main sources in indoor air are building materials, furniture, various adhesives, coatings, synthetic fabrics, etc. When the human body is exposed to high-concentration formaldehyde gas, symptoms of discomfort will appear in a short time. Long-term exposure to high-concentration formaldehyde gas environment can cause serious harm to the human body. Therefore, it is of great significance to test and monitor formaldehyde accurately and quickly for human health and environmental protection.

[0003] As one of the most commonly used detection methods, electrochemical formaldehyde sensors have the advantages of convenient use, low cost, and can detect formaldehyde gas concentration online in real time. However, the existing electrochemical formaldehyde gas sensors have low sensitivity, high cross-response to alcohol gas, etc. Moreover, the synthesis of the electrode of the electrochemical formaldehyde gas sensor currently uses expensive noble metals (such as iridium, gold, etc.), and the synthesis method and path are complex, which is difficult to realize large-scale batch production and application. SUMMARY

[0004] In order to improve the sensitivity, selectivity, high linearity within the measurement range, low cost and easy batch production of the sensor, the present application provides an electrochemical formaldehyde sensor electrode, a preparation method thereof and an electrochemical formaldehyde sensor.

[0005] In a first aspect, the present application provides a preparation method of an electrochemical formaldehyde sensor electrode, which adopts the following technical scheme: The preparation method of the electrochemical formaldehyde sensor electrode comprises the following steps: (1) After stirring and mixing potassium permanganate, deionized water and anhydrous ethanol, stirring and reaction are carried out at 130-150℃ for 6-8h to obtain a reaction solution; the reaction solution is centrifuged, the lower precipitate is collected, and washed with water to obtain a precursor; The precursor is dried at 60-80℃ for 4-6h to obtain a solid powder of the precursor; The solid powder of the precursor is calcined at 400-500℃ for 1-3h to obtain nano manganese dioxide; (2) mixing the nano-manganese dioxide, platinum carbon and Nafion solution, and grinding at a speed of 300-400 r / min for 0.5-1 h to obtain a ground slurry; (3) coating the ground slurry on a polytetrafluoroethylene film and drying at 60-80℃ for 0.5-1 h to obtain an electrochemical formaldehyde sensor electrode.

[0006] By using the above technical solution, the nano-manganese dioxide, platinum carbon and Nafion solution are compounded into a slurry according to the above weight ratio, and then coated on the electrochemical formaldehyde sensor electrode. The slurry has high decomposition catalytic effect on formaldehyde, the platinum carbon has high catalytic activity, and the perfluoro ion sulfonic acid resin can effectively promote the flow of ions and the transfer of electric charges. Therefore, the sensor assembled by coating the above slurry has high response sensitivity to formaldehyde.

[0007] Meanwhile, the nano-manganese dioxide prepared by the hydrothermal method is in the form of spherical or near-spherical morphology with a particle size distribution of 30-50 nm, and has a large specific surface area, which is beneficial to the aggregation and transmission of electric charges on the surface of the spherical powder. Therefore, the electrode coated with the slurry has high catalytic activity for gas reaction, and the sensor assembled by using the electrode has higher response sensitivity to formaldehyde.

[0008] Preferably, in the step (1), the mass ratio of potassium permanganate, deionized water and anhydrous ethanol is 1:(20-30):(30-50).

[0009] Preferably, in the step (1), the speed of centrifugation is 8000-10000 r / min, and the time is 4-8 min.

[0010] Preferably, the particle size of the platinum carbon is 100-400 nm. The platinum carbon is composed of platinum and carbon in a mass ratio of 4:1.

[0011] Preferably, the mass ratio of the nano-manganese dioxide, platinum carbon and Nafion solution is (0.1-0.3):1:(0.1-0.25).

[0012] Preferably, the grinding is ball milling, and the speed of the ball milling is 300-400 r / min.

[0013] Preferably, the coating method of the slurry includes any one of rolling, spraying, screen printing and die pressing.

[0014] In the second aspect, the application provides an electrochemical formaldehyde sensor, which uses the following technical solution: An electrochemical formaldehyde sensor includes the above electrochemical formaldehyde sensor electrode and a binary electrolyte.

[0015] Preferably, the binary electrolyte comprises any two of sulfuric acid, phosphoric acid, hydrochloric acid, lithium chloride and trisodium citrate.

[0016] Preferably, the molar concentration of the sulfuric acid is 3-6 mol / L, the molar concentration of the phosphoric acid is 2-7 mol / L, the molar concentration of the hydrochloric acid is 0.5-8 mol / L, the molar concentration of the lithium chloride is 0.5-9 mol / L, and the molar concentration of the trisodium citrate is 0.2-4 mol / L.

[0017] Preferably, the binary electrolyte is composed of lithium chloride and trisodium citrate.

[0018] By adopting the above technical solution, since the electrochemical formaldehyde sensor electrode has high catalytic reaction activity to formaldehyde, the electrochemical formaldehyde sensor assembled by using the electrode and the binary electrolyte has high sensitivity to formaldehyde gas and excellent linearity within the measurement range.

[0019] Meanwhile, by regulating the composition of the binary electrolyte of the electrochemical formaldehyde sensor, high selectivity of the electrochemical formaldehyde sensor is achieved, and the influence of environmental interference gas on the formaldehyde sensor is greatly reduced, thereby improving the detection accuracy. In particular, the lithium chloride and the trisodium citrate are selected as the binary electrode liquid, which does not affect the response sensitivity of the formaldehyde gas entering the sensor, and at the same time, the transmission rate of cross interference gas such as alcohol is inhibited, thereby improving the selectivity of the sensor.

[0020] In summary, the present application has the following beneficial effects: 1. Since the present application adopts nanometer manganese dioxide mixed and dispersed with platinum carbon and Nafion solution to prepare a slurry coated on an electrode, the electrode has high catalytic activity to formaldehyde, and therefore the electrochemical formaldehyde gas sensor electrode assembled by using the electrode has high sensitivity to formaldehyde and excellent linearity within the measurement range; 2. The nanometer manganese dioxide prepared by the simple hydrothermal method has a spherical or near-spherical morphology and a particle size distribution of 30-50 nm, and has a large specific surface area, which is beneficial to the aggregation and transmission of electric charges on the surface of the spherical powder, thereby improving the catalytic activity of the electrode coated with the slurry to the formaldehyde gas; 3. The electrochemical formaldehyde sensor of the present application regulates the composition of the binary electrolyte to achieve high selectivity of the electrochemical formaldehyde sensor, greatly reduces the influence of environmental interference gas on the formaldehyde sensor, and improves the detection accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The scanning electron microscope photograph of the nanometer manganese dioxide prepared for Preparation Example 1; Figure 2Response recovery curves of Examples 1 to 5 in 0 to 1 ppm formaldehyde gas; Figure 3 The step ventilation and linear fitting curves of Example 5 in 0-10 ppm formaldehyde gas are shown; Figure 4 This is the cyclic adsorption-desorption curve of Example 5 in 0-10 ppm formaldehyde gas. DETAILED DESCRIPTION

[0022] The present application is further described in detail below with reference to the accompanying drawings and examples.

[0023] Preparation Example 1 A nano manganese dioxide method comprises the following steps: S1: 15 g of potassium permanganate, 100 mL of deionized water, and 18 g of anhydrous ethanol were stirred and reacted at 150° C. for 6 h to obtain a reaction solution; the reaction solution was centrifuged at 900 r / min for 6 min, the lower precipitate was collected, and washed with water to obtain a precursor; S2: drying the precursor at 80°C for 6 h to obtain a solid powder of the precursor; S3: calcining the solid powder of the precursor at 450° C. for 1.5 h to obtain 4.06 g of nano manganese dioxide.

[0024] Depend on Figure 1 It can be seen that the nano manganese dioxide prepared in Preparation Example 1 has a spherical or nearly spherical morphology with a particle size distribution of 30 to 50 nm and a large specific surface area, which is conducive to the aggregation and transmission of charges on the surface of the spherical powder, and is beneficial to improving the catalytic activity of the reaction with formaldehyde gas.

[0025] Performance Testing The electrochemical formaldehyde sensor prepared in the embodiment was subjected to a gas ventilation test in 1 ppm formaldehyde gas and a cross-response test in different gases. The test steps are as follows: (1) Gas ventilation test in 1 ppm formaldehyde gas: Under room temperature, the electrochemical formaldehyde sensor that has been aged in the embodiment is subjected to a gas ventilation test in 1 ppm formaldehyde gas. The output current of the test circuit board is measured before and after ventilation, thereby obtaining the gas sensitivity performance of the sensor; (2) Cross-response test in different gases: Under room temperature, the electrochemical formaldehyde sensor that has been aged in the embodiment is subjected to ventilation test in different cross-gases, and the output current of the test circuit board is tested before and after ventilation, thereby obtaining the gas sensitivity performance of the sensor; The cross-gas tested by the formaldehyde sensor in the present invention is: 50ppm ethanol gas, 50ppm carbon monoxide gas, 50ppm hydrogen gas, and 50ppm methane gas.

[0026] Example 1 An electrochemical formaldehyde sensor comprises a plastic shell, a working electrode, a reference electrode and a counter electrode are assembled in the plastic shell. The electrodes are filled with absorbent cotton between the electrodes and electrolyte is filled in as the medium for electron flow. The working electrode, the reference electrode and the counter electrode are connected with the test circuit board through platinum wire and pin to realize output of current signal.

[0027] An upper cover for air inlet is arranged on the plastic shell. After the working electrode, the reference electrode and the counter electrode are installed in the shell, 300 μL of 4M sulfuric acid electrolyte is added, the shell is sealed after the air inlet upper cover is assembled. Finally, the working electrode and the counter electrode are short-circuited for aging for 5 days, and the aged electrochemical formaldehyde sensor is obtained.

[0028] In the embodiment of the application, the materials of the working electrode, the reference electrode and the counter electrode are all electrochemical formaldehyde sensor electrodes, wherein the working electrode and the reference electrode are both φ16 mm round sheets, and the counter electrode is a φ16*6 mm round ring.

[0029] The electrochemical formaldehyde sensor electrode comprises a polytetrafluoroethylene film, and the polytetrafluoroethylene film is coated with a slurry for electrochemical formaldehyde sensor electrodes.

[0030] The slurry for electrochemical formaldehyde sensor electrodes is composed of 1.0 g of nanometer manganese dioxide, 5.0 g of platinum carbon and 1.0 g of Nafion solution.

[0031] In the embodiment of the application, the nanometer manganese dioxide is commercial nanometer manganese dioxide, and the particle size is 30-60 nm. The platinum carbon is composed of platinum and carbon at a mass ratio of 4:1, and the particle size is 300 nm. The mass percentage of perfluorosulfonic acid resin in the Nafion solution is 10%.

[0032] The preparation method of the electrochemical formaldehyde sensor electrode comprises the following steps: (1) The nanometer manganese dioxide, the platinum carbon and the Nafion solution are mixed to obtain a slurry for electrochemical formaldehyde sensor electrodes. The slurry is mixed and ball milled at a speed of 300 r / min for 0.5 h to obtain a ground slurry.

[0033] (2) The ground slurry is screen printed on the polytetrafluoroethylene film and dried at 60°C for 0.5 h to obtain the electrochemical formaldehyde sensor electrode.

[0034] Comparative Example 1 An electrochemical formaldehyde sensor, which is different from the electrochemical formaldehyde sensor of Example 1 in that the slurry for electrochemical formaldehyde sensor electrodes is composed of 5.0 g of platinum carbon and 0.9 g of Nafion solution.

[0035] Platinum carbon is composed of platinum and carbon with a mass ratio of 4:1, and the particle size is 300 nm; The mass percentage of perfluorosulfonic acid resin in the Nafion solution is 10%.

[0036] Comparative Example 2 An electrochemical formaldehyde sensor, which is different from Example 1 in that the slurry for the electrode of the electrochemical formaldehyde sensor is composed of 1.6 g of commercial nanometer manganese dioxide, 5.0 g of platinum carbon and 1.2 g of Nafion solution.

[0037] Comparative Example 3 An electrochemical formaldehyde sensor, which is different from Example 1 in that the slurry for the electrode of the electrochemical formaldehyde sensor is composed of 1.1 g of commercial nanometer manganese dioxide, 5.0 g of platinum carbon and 0.4 g of Nafion solution.

[0038] Comparative Example 4 An electrochemical formaldehyde sensor, which is different from Example 1 in that the slurry for the electrode of the electrochemical formaldehyde sensor is composed of 1.0 g of commercial nanometer manganese dioxide, 5.0 g of platinum carbon and 1.4 g of Nafion solution.

[0039] The electrochemical formaldehyde sensors prepared in Example 1 and Comparative Examples 1-4 are subjected to gas aeration test in 1 ppm formaldehyde gas, and the test results are shown in Table 1.

[0040] Table 1: Comparison table of response sensitivity of electrochemical formaldehyde sensors of Examples 1-5 to 1 ppm formaldehyde gas

[0041] According to the data analysis of Table 1, the sensitivity of Comparative Example 1 without adding nanometer manganese dioxide in the sensor electrode to formaldehyde is low, and the sensitivity of Example 1 with the addition of commercial nanometer manganese dioxide in the sensor electrode to formaldehyde is greatly improved. However, with the further increase of the amount of nanometer manganese dioxide added in the sensor electrode, the response sensitivity of the sensor of Comparative Example 2 to formaldehyde gas is slightly reduced. The possible reason is that the introduction of excessive nanometer manganese dioxide inhibits the catalytic activity of platinum carbon, resulting in the reduction of response sensitivity.

[0042] As can be seen from Table 1, the response sensitivity of the sensor of Comparative Example 3 to formaldehyde gas decreases with the decrease of the amount of perfluoro ion sulfonic acid resin, and the possible reason is that the oxidation-reduction reaction of formaldehyde gas after entering the sensor requires perfluoro ion sulfonic acid resin to promote the flow of ions and the transfer of electric charges. When the amount of perfluoro sulfonic acid resin loaded on the electrode of the sensor is insufficient to meet the normal output of the signal, the response sensitivity is reduced. Similarly, when the amount of perfluoro ion sulfonic acid resin of the sensor of Comparative Example 4 is large, the response sensitivity of the sensor to formaldehyde gas is not further improved, and at this time the main factor affecting the response sensitivity of the sensor is the catalytic activity of the catalyst, and the effect of perfluoro sulfonic acid resin is low.

[0043] Therefore, in the electrochemical formaldehyde sensor of the present application, when the slurry coated on the surface of the electrode of the electrochemical formaldehyde sensor is composed of manganese dioxide nanoparticles, platinum carbon and Nafion solution mixed in a weight ratio of (0.1-0.3):1:(0.1-0.25), the response sensitivity of the electrochemical formaldehyde sensor can be improved.

[0044] Example 2 An electrochemical formaldehyde sensor, different from Example 1, wherein the manganese dioxide nanoparticles in the electrode of the electrochemical formaldehyde sensor are spherical or near-spherical in morphology with a particle size distribution of 30-50 nm, which are prepared according to Preparation Example 1; and the platinum carbon is composed of platinum and carbon in a mass ratio of 4:1, and the particle size thereof is 350 nm.

[0045] Example 3 An electrochemical formaldehyde sensor, different from Example 2, wherein the electrolyte is composed of 150 μL of 4M sulfuric acid and 150 μL of 1.1M lithium chloride.

[0046] Example 4 An electrochemical formaldehyde sensor, different from Example 2, wherein the electrolyte is composed of 150 μL of 4M sulfuric acid and 150 μL of 2.7M phosphoric acid.

[0047] Example 5 An electrochemical formaldehyde sensor, different from Example 2, wherein the electrolyte is composed of 150 μL of 1.1M lithium chloride and 150 μL of 2.8M trisodium citrate.

[0048] The response recovery curves of the electrochemical formaldehyde sensors prepared in Example 1 and Examples 2-5 in 1 ppm formaldehyde gas are shown in Figure 2 Figure 2 ​It can be seen that the sensor prepared in Example 1 has a low response signal to formaldehyde gas, and the desorption of formaldehyde gas is also slow after the aeration is finished. The sensor prepared in Example 2 has an improved response sensitivity to formaldehyde gas by adding self-made nano manganese dioxide in the sensor electrode, which meets the requirements of signal output, but still has the problem of long response and desorption time.

[0049] However, from the response recovery curves of Examples 3-5, it can be seen that when the sensor electrode is maintained as the same component, by adjusting the electrolyte to a binary component, the response signal of the sensor to formaldehyde is further improved, and the response and recovery rates are also improved accordingly.

[0050] The reason may be that the electrolyte solution has a decisive influence on ion conduction during the reaction of the gas entering the electrochemical sensor. Different gases entering the sensor have different unit sensitivity signals, and the conduction rate is also greatly different under different electrolyte solutions. Therefore, the selection of binary lithium chloride and trisodium citrate as the electrolyte does not affect the response sensitivity of formaldehyde gas entering the sensor, while suppressing the transmission rate of cross-interference gases such as alcohols, thereby improving the selectivity of the sensor.

[0051] The electrochemical formaldehyde sensors prepared in Examples 1-5 were tested for cross-response in different gases, and the test results are shown in Table 2.

[0052] Table 2: Cross-response test control table of electrochemical formaldehyde sensors of Examples 1-5

[0053] From Figure 3 It can be seen that the formaldehyde sensor of Example 5 has a response and recovery time maintained within a relatively short time as the formaldehyde gas concentration increases within 0-10 ppm, which reflects excellent response and recovery characteristics. There is still a stable current output of 1500 nA when testing 0.5 ppm formaldehyde gas, which reflects an excellent lower detection limit. At the same time, Figure 3 The inset in FIG. 6 is a linear fitting curve of the response sensitivity of the formaldehyde sensor of Example 5 under different formaldehyde gas concentrations: y = 2993.52X - 21.42, where X is the formaldehyde gas concentration, and y is the response sensitivity corresponding to the gas concentration; from Figure 3 As can be seen from the inset in FIG. 6, the sensor has a good linear relationship with the output sensitivity value under different formaldehyde gas concentrations. R 2 is the linear fitting coefficient, which is a statistical quantity for measuring the goodness of the linear regression model fitting data, and R 2= regression sum of squares / total sum of squares, the value of R² is between 0 and 1, and the closer the value is to 1, the better the model fits the data; the linear fitting coefficient R of Example 5 of the present application is 2 It is 0.997, indicating that the formaldehyde sensor has an extremely low detection limit and excellent linearity within the measurement range.

[0054] Figure 4 This is the cyclic adsorption-desorption curve of the formaldehyde sensor prepared in Example 5 in 10ppm formaldehyde gas. It can be seen from the figure that the sensor shows good response sensitivity to formaldehyde gas in each cyclic test period, and the response and desorption performance is maintained in a stable state, reflecting the characteristic of not being easily poisoned at high concentrations, and the consistency is excellent.

[0055] In summary, combined with the data of each embodiment, it can be seen that: The sensor prepared in Example 1 using platinum carbon as an electrode has a low response sensitivity to formaldehyde gas and cannot output an effective signal to achieve the purpose of detecting formaldehyde gas; The sensor prepared by adding nano-manganese dioxide powder to the catalyst electrode of Example 2 greatly improved the sensor's response sensitivity to formaldehyde gas, but also had a large cross-response sensitivity to gases such as ethanol and carbon monoxide, which could easily cause false alarms in actual application environments. The binary electrolyte components used in the sensors in Examples 3 and 4 further improve the sensor's response sensitivity to formaldehyde gas, while also reducing the cross-response sensitivity to ethanol and carbon monoxide. However, this still cannot meet the needs of actual use and there is also a risk of false alarms.

[0056] Example 5 adjusts the binary electrolyte composition of the sensor, achieving maximum sensitivity to formaldehyde gas and improving signal output strength. Therefore, using a molar concentration of 0.5-9 mol / L sodium chloride and a molar concentration of 0.2-4 mol / L trisodium citrate significantly reduces crosstalk with common gases like ethanol and carbon monoxide, resulting in a high-performance electrochemical formaldehyde sensor.

[0057] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. An electrochemical formaldehyde sensor, characterized in that: including an electrochemical formaldehyde sensor electrode and a binary electrolyte; The electrochemical formaldehyde sensor electrode comprises a polytetrafluoroethylene film; the polytetrafluoroethylene film is coated with the electrochemical formaldehyde sensor electrode slurry; The electrochemical formaldehyde sensor electrode slurry is composed of nano-manganese dioxide, platinum carbon and Nafion solution mixed in a weight ratio of (0.1-0.3):1:(0.1-0.25); The binary electrolyte is composed of a mixture of lithium chloride and trisodium citrate; The molar concentration of the lithium chloride is 0.5-9 mol / L, and the molar concentration of trisodium citrate is 0.2-4 mol / L.

2. A method for preparing an electrochemical formaldehyde sensor electrode, characterized in that: The following steps are involved: (1) Potassium permanganate, deionized water, and anhydrous ethanol are stirred and mixed, and the mixture is stirred and reacted at 130-150° C. for 6-8 hours to obtain a reaction solution; the reaction solution is centrifuged, the lower precipitate is collected, and the precipitate is washed with water to obtain a precursor; Drying the precursor at 60-80° C. for 4-6 hours to obtain a solid powder of the precursor; calcining the solid powder of the precursor at 400-500°C for 1-3 hours to obtain nano manganese dioxide; The nano manganese dioxide has a spherical or nearly spherical shape with a particle size distribution of 30 to 50 nm; (2) Mixing nano-manganese dioxide, platinum carbon, and Nafion solution in a weight ratio of (0.1-0.3):1:(0.1-0.25) to obtain a slurry for an electrochemical formaldehyde sensor electrode; mixing and grinding the slurry at a speed of 300-400 r / min for 0.5-1 h to obtain a ground slurry; (3) The ground slurry is coated on a polytetrafluoroethylene film and dried at 60-80°C for 0.5-1h to obtain an electrochemical formaldehyde sensor electrode.

3. The method for preparing the electrochemical formaldehyde sensor electrode according to claim 2, wherein: In the step (1), the mass ratio of potassium permanganate, deionized water and anhydrous ethanol is 1:(20-30):(30-50).

4. The method for preparing the electrochemical formaldehyde sensor electrode according to claim 2, wherein: In the step (1), the centrifugal speed is 8000-10000 r / min and the time is 4-8 min.

5. The method for preparing the electrochemical formaldehyde sensor electrode according to claim 2, characterized in that: The particle size of the platinum carbon is 100 to 400 nm; The platinum carbon is composed of platinum and carbon in a mass ratio of 4:

1.

6. The method for preparing an electrochemical formaldehyde sensor electrode according to claim 2, wherein: The grinding is ball milling, and the ball milling speed is 300-400 r / min.

7. An electrochemical formaldehyde sensor electrode, characterized in that: The electrochemical formaldehyde sensor electrode is prepared by the preparation method of any one of claims 2 to 6.

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