Preparation method and application of an electrocatalyst for methanol vapor leakage detection

Abstract

The application discloses a preparation method and application of an electrocatalyst for methanol vapor leakage detection, and relates to the technical field of methanol gas detection. The Pt-CNTs / rGO nanocomposite is synthesized through a simple and economical one-step hydrothermal method, and the electrochemical methanol gas sensing electrocatalyst with different proportions of CNTs and rGO is prepared. Further combined with a printing technology, a flexible methanol gas sensor is constructed, and finally the high-sensitivity and high-selectivity methanol gas detection is realized. The application provides a preparation method of the electrochemical methanol gas sensing electrocatalyst, and the method is simple, controllable and practical.

Description

Technical Field

[0001] This invention relates to the field of methanol gas detection technology, specifically to a method for preparing an electrocatalyst for electrochemical gas sensing and its application in methanol leak detection. Background Technology

[0002] Methanol (CH3OH) is an important chemical, serving as a basic organic chemical raw material and a fuel substitute. M15 methanol gasoline, in particular, has the same applicability and performance as unleaded gasoline of the same octane rating, making it a novel environmentally friendly and energy-saving fuel. However, methanol is a volatile and toxic liquid. Ingestion through the digestive tract, respiratory tract, or skin can affect the nervous and circulatory systems, and methanol vapor can damage the respiratory mucosa and vision. Therefore, the detection of methanol vapor is a crucial research area for industrial safety. Compared to other detection techniques such as chromatography, fluorescence, and spectrophotometry, electrochemical detection methods offer advantages such as simple operation, high sensitivity, and rapid response. Therefore, developing sensing materials with high sensitivity, low detection limits, and high selectivity has become a top research priority.

[0003] However, to date, the most common high-performance sensing material for detecting methanol gas is the commercially available Pt / C catalyst. However, Pt / C catalysts are expensive, and Pt is susceptible to CO (an intermediate product of methanol oxidation) poisoning. Other sensing materials (conductive polymers, semiconductor oxides, etc.) suffer from poor selectivity, high operating temperatures, and narrow linear ranges. Therefore, developing a highly sensitive and selective electrochemical sensing material for the precise detection of methanol vapor remains a challenge. Summary of the Invention

[0004] To address the aforementioned shortcomings of existing technologies, this invention proposes a method for preparing an electrocatalyst for electrochemical methanol gas sensing and its application in methanol leak detection.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for preparing an electrocatalyst for electrochemical gas sensing, wherein the catalyst is prepared by the following method:

[0007] 1) Natural graphite is placed in a pre-oxidation solution and reacted for 3-5 hours. The resulting pre-oxide is then oxidized with a strong oxidizing agent. After oxidation, it is exfoliated to obtain graphene oxide (GO).

[0008] 2) Carbon nanotubes are reacted in a strong acid, refluxed, dispersed evenly, filtered and dried to obtain CNT pretreated material;

[0009] 3) Place the CNTs pretreated material, graphene oxide (GO) and chloroplatinic acid (H2PtCl6) in a reducing agent, adjust the pH to alkaline, heat the reaction, filter and dry to obtain the Pt-CNTs / rGO nanocomposite catalyst.

[0010] 4) Mix Pt-CNTs / rGO electrocatalyst, Nafion and ethanol in a mass ratio of 1:1 to 5:1 to 5 to obtain a uniform catalyst slurry and prepare Pt-CNTs / rGO working electrode; cover the Pt-CNTs / rGO working electrode with Nafion, print the counter electrode and reference electrode surface and cure it to construct a complete flexible sensor.

[0011] In the above preparation method: the pre-oxidation solution in step (1) consists of potassium persulfate, phosphorus pentoxide and concentrated sulfuric acid, and the strong oxidizing agents are concentrated sulfuric acid and potassium permanganate.

[0012] In the above preparation method: the pre-oxidation solution in step (1) is potassium persulfate, phosphorus pentoxide and concentrated sulfuric acid in a mass ratio of 1-3:1-3:3-7; the strong oxidant is concentrated sulfuric acid and potassium permanganate in a mass ratio of 20-25:1-5.

[0013] The mass ratio of natural graphite to pre-oxidation solution is 1:1 to 5; the mass ratio of pre-oxide to strong oxidant is 1:20 to 30.

[0014] The stripping agent used is a hydrogen peroxide solution; preferably, the concentration of hydrogen peroxide is 20-40%.

[0015] In the above preparation method: the strong acid in step (2) is concentrated nitric acid or a mixture of concentrated nitric acid and concentrated sulfuric acid; the reaction temperature is 90-110℃, and the reflux time is 4-6h.

[0016] In the above preparation method: the mass ratio of pretreated CNTs, graphene oxide GO and chloroplatinic acid H2PtCl6 in step (3) is 5~10:5~10:2~3.

[0017] The reducing agent is ethylene glycol, and the alkaline conditions are pH 9-11; the reaction temperature is 120-140℃, and the reaction is stirred for 2-4 hours.

[0018] In the above preparation method: the electrode paste mentioned in step (4) can be selected from conductive carbon paste, copper paste, silver paste, and composite conductive pastes such as noble metals, transition metals and their oxides and sulfides prepared by mixing method. Preferably, printed carbon paste is used as the counter electrode, and printed Ag paste is used as the reference electrode;

[0019] In step (4), carbon paste is printed as the counter electrode, and Ag paste is printed as the reference electrode;

[0020] Step (4) Apply 1-3 μL of catalyst slurry evenly to the surface of the working electrode and cure it in a drying oven at 70-90℃ for 20-40 min. Repeat 1-3 times.

[0021] Nafion was applied to the surfaces of the three electrodes and cured at 70–90°C for 20–40 min, with a coating thickness of 1–30 μm.

[0022] An electrocatalyst for electrochemical gas sensing, which is prepared by the method described above.

[0023] In the technical solution of this invention, the electrocatalyst for electrochemical gas sensing prepared by the above method is applied in methanol leakage detection.

[0024] In this invention, the detection is conducted in a closed space, and the temperature and humidity conditions are identical except for the actual sample testing experiment. A bubbling method is used to simulate the volatile gas environment of different concentrations of real samples.

[0025] The beneficial effects of this invention are:

[0026] This invention synthesizes Pt-CNTs / rGO nanocomposite materials via a simple and economical one-step hydrothermal method, and prepares electrocatalysts for electrochemical methanol gas sensing with different ratios of CNTs and rGO. Further integration with printing technology allows for the construction of flexible methanol gas sensors, ultimately achieving highly sensitive and selective methanol gas detection. This invention provides a simple, controllable, and highly practical method for preparing electrocatalysts for electrochemical methanol gas sensing. Attached Figure Description

[0027] Figure 1 Cyclic voltammetry curves of Pt-CNTs / rGO(1:2) and Pt-CNTs / rGO(2:1) sensors.

[0028] Figure 2 TEM images of CNTs and rGO at different ratios; Note: (a)-(d) are TEM images at low magnification, in order: Pt-CNTs / rGO (1:2), Pt-CNTs / rGO (1:1), Pt-CNTs / rGO (2:1), Pt-CNTs.

[0029] Figure 3 Long-term stability of CNTs and rGO at different ratios. Note: (a) shows the stability of the four sensors on day 1, and (b) shows the stability of the four sensors on day 14. Catalysts 1-4 are Pt-CNTs, Pt-CNTs / rGO (2:1), Pt-CNTs / rGO (1:1), and Pt-CNTs / rGO (1:2), respectively.

[0030] Figure 4 Dynamic test graphs of Pt-CNTs / rGO(1:2) sensor detecting different flow rates of methanol M15 gasoline, pure water, 75% ethanol, and hypochlorous acid disinfectant. Detailed Implementation

[0031] The present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited thereto:

[0032] Example 1-1

[0033] First, graphene oxide (GO) was prepared using a redox method. The specific preparation method is as follows:

[0034] 5g of natural graphite was added to a pre-oxidation solution (15g) composed of potassium persulfate, phosphorus pentoxide and concentrated sulfuric acid (mass ratio 1:1:5.6), reacted at 80℃ for 3h, cooled to room temperature, slowly diluted with water, filtered and washed until neutral, and dried to obtain graphite pre-oxide.

[0035] Weigh 1g of the above preoxide and add it to 23ml of concentrated sulfuric acid, then add 3g of potassium permanganate. After reacting for 2 hours, add 46ml of water. After 15 minutes, add 140ml of water and 2.5ml of 30% hydrogen peroxide. After the reaction is complete, wash, filter, centrifuge and freeze dry to collect GO.

[0036] The second step is CNT pretreatment, and the specific preparation method is as follows:

[0037] Add 100 ml of concentrated nitric acid (68%) to a 250 ml three-necked round-bottom flask, weigh 1 g of CNTs and add them to the flask, heat in an oil bath at 100 °C and stir, reflux for 5 h, filter and dry.

[0038] The third step involves preparing a Pt-CNTs / rGO (1:2) catalyst (with a CNTs to rGO mass ratio of 1:2) using a one-step hydrothermal method. The specific preparation method is as follows:

[0039] In a 250 ml three-necked round-bottom flask, add 50 mg of a mixture of CNTs and GO (CNTs to GO mass ratio 1:2), 10 ml of ethylene glycol (EG), and 200 μL of an aqueous dispersion of chloroplatinic acid (H₂PtCl₆). Then, slowly add 0.1 mol / L NaOH solution to adjust the pH to 11. Maintain the oil bath temperature at 130 °C, stir for 3 h, filter, and dry to obtain the sensing active material. The mass ratio of the pretreated CNTs, graphene oxide (GO), and chloroplatinic acid (H₂PtCl₆) is 5:10:3.

[0040] The fourth step is to fabricate the complete flexible sensor. The specific fabrication method is as follows:

[0041] Using PET as a substrate, patterned reference electrodes and conductive functional strips were printed using Ag paste. Then, working electrodes and counter electrodes were prepared using carbon paste printing. Copper wires were then bonded to the ends of the conductive strip areas, and insulating printing was performed on the conductive strip areas. The sensing active material was mixed uniformly with Nafion and ethanol (at a mass ratio of 1:2:5) to prepare a catalyst slurry. 2 μL of uniform catalyst slurry was drop-coated onto the surface of the working electrode each time, and the electrode was cured in an 80°C electric thermostatic drying oven for 30 min, repeated three times. Nafion was then used to cover the entire three-electrode area, and the electrode was cured at 80°C for 30 min.

[0042] The fifth step is to detect the volatile gases in the real sample and measure the sensor's response and recovery curves.

[0043] Example 2

[0044] The difference from Example 1 is that the CNTs and rGO content of the Pt-CNTs / rGO electrocatalyst are prepared by a one-step hydrothermal method in the third step. The 50mg CNTs and GO mixture (CNTs:GO = 1:2) is changed to a 50mg CNTs and GO mixture (CNTs:GO = 1:1).

[0045] Example 3

[0046] Other conditions are the same as in Example 1, except that the mass ratio of CNTs to GO is replaced by a mass ratio of CNTs to GO of 2:1 instead of 1:2.

[0047] Performance characterization:

[0048] The CV curves of the Pt-CNTs / rGO (CNTs to GO mass ratio of 1:2) sensor and the Pt-CNTs / rGO (2:1) sensor (CNTs to GO mass ratio of 2:1) in methanol gas in Examples 1 and 3 are as follows: Figure 1 As shown, the CO poisoning resistance of the electrocatalyst is roughly evaluated by the ratio of the positive scan peak current (If) to the negative scan peak current (Ib). The larger the ratio, the better the poisoning resistance. By comparison, the ratio of the Pt-CNTs / rGO (1:2) sensor is 1.80, while that of the Pt-CNTs / rGO (2:1) sensor is 1.73, indicating that the Pt-CNTs / rGO (1:2) sensor has better poisoning resistance than the Pt-CNTs / rGO (2:1) sensor.

[0049] In Examples 1-3, the electrocatalyst was characterized and its gas-sensing performance was tested. Figure 2Transmission electron microscopy (TEM) images of CNTs and rGO at different ratios. The tubular CNTs and the lamellar rGO are uniformly mixed, and the bonding is more perfect when the CNTs / rGO ratio is 1:1 and 1:2. CNTs are interspersed between the rGO layers, and the two alternate to form a mixed three-dimensional spatial network structure, which greatly increases the specific surface area and conductivity of the composite material. Figure 3 The results show the long-term stability of sensors modified with different electrocatalysts. Four sensors were placed in methanol gas at concentrations of 1000, 1500, 2000, 2500, and 3000 ppm for 14 days for stability testing. Tests were recorded on 1 day and 14 days. The results show that the sensors retained more than 85% of their original response during this period. Figure 4 The response and recovery curves of the Pt-CNTs / rGO(1:2) sensor under different gas flow rates (100–500 mL / min) were tested for methanol, M15 gasoline, pure water, 75% ethanol, and hypochlorous acid disinfectant. The images show that the sensor can quickly and accurately detect methanol gas under M15 gas flow, and the response current is significantly higher than that of other samples.

Claims

1. The application of an electrocatalyst in methanol leak detection, characterized in that: The catalyst was prepared by the following method: 1) Place natural graphite in a pre-oxidation solution and react for 3-5 hours. The resulting pre-oxide is then oxidized with a strong oxidizing agent. After oxidation, it is exfoliated to obtain graphene oxide (GO). 2) Carbon nanotubes are reacted in a strong acid, refluxed, dispersed evenly, filtered and dried to obtain carbon nanotube pretreated CNTs; 3) Pretreated CNTs, graphene oxide (GO) and chloroplatinic acid (H2PtCl6) are placed in a reducing agent, the pH is adjusted to alkaline, the reaction is heated, and then filtered and dried to obtain Pt-CNTs / rGO nanocomposite catalyst; wherein, in step (3), the mass ratio of pretreated CNTs, graphene oxide (GO) and chloroplatinic acid (H2PtCl6) is 5~10:5~10:2~3; the reducing agent is ethylene glycol, the alkaline condition is pH 9~11; the reaction temperature is 120~140℃, and the reaction is stirred for 2~4h; The method for detecting methanol leakage using Pt-CNTs / rGO nanocomposite catalyst involves mixing Pt-CNTs / rGO electrocatalyst, Nafion, and ethanol in a mass ratio of 1:1~5:1~5 to obtain a uniform catalyst slurry, which forms the Pt-CNTs / rGO working electrode. Nafion is then coated onto the Pt-CNTs / rGO working electrode, and counter and reference electrodes are printed and cured to construct a complete flexible sensor. Gas volatiles in a real sample are detected, and the sensor's response and recovery curves are measured.

2. The application of the electrocatalyst according to claim 1 in methanol leak detection, characterized in that: The pre-oxidation solution in step (1) consists of potassium persulfate, phosphorus pentoxide and concentrated sulfuric acid, and the strong oxidizing agents are concentrated sulfuric acid and potassium permanganate.

3. The application of the electrocatalyst according to claim 2 in methanol leak detection, characterized in that: In step (1), the pre-oxidation solution is potassium persulfate, phosphorus pentoxide and concentrated sulfuric acid in a mass ratio of 1~3:1~3:3~7; the strong oxidant is concentrated sulfuric acid and potassium permanganate in a mass ratio of 20~25:1~5; the mass ratio of natural graphite to pre-oxidation solution is 1:1~5; the mass ratio of pre-oxidized material to strong oxidant is 1:20~30; and the stripping agent used is a hydrogen peroxide solution with a mass fraction of 20~40%.

4. The application of the electrocatalyst according to claim 1 in methanol leak detection, characterized in that: In step (2), the strong acid is concentrated nitric acid or a mixture of concentrated nitric acid and concentrated sulfuric acid; the reaction temperature is 90~110℃, and the reflux time is 4~6h.

5. The application of the electrocatalyst according to claim 1 in methanol leak detection, characterized in that: The carbon paste is used as the counter electrode, and the Ag paste is used as the reference electrode. 1-3 μL of catalyst slurry was uniformly drop-coated onto the surface of the working electrode and cured in a drying oven at 70-90℃ for 20-40 min. This process was repeated 1-3 times. Nafion was applied to the surfaces of the three electrodes and cured at 70-90°C for 20-40 minutes, with a thickness of 1-30 μm.

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