A TiN-based electrochemical NO2 gas sensor and its preparation method

Abstract

The present invention provides a TiN-based electrochemical NO2 gas sensor and a method for preparing the same. The electrochemical NO2 gas sensor comprises a membrane electrode assembly, a working electrode sheet, a counter electrode sheet, and a cathode sealed gas chamber; wherein the membrane electrode assembly contains TiN. The electrochemical NO2 gas sensor of the present invention utilizes TiN material with a high specific surface area and NVs sites, significantly enhancing properties such as gas diffusion, adsorption, and catalytic reactions. Compared to conventional gas sensors that enhance gas response by loading Pt onto sensitive materials, this not only significantly reduces the cost of the gas sensor but also solves the long-term stability issue caused by the shedding and aggregation of Pt nanoparticles during prolonged operation. Furthermore, the sensor exhibits excellent gas selectivity.

Description

Technical Field

[0001] The present invention relates to the technical field of gas sensors, and in particular to a TiN-based electrochemical NO2 gas sensor and a preparation method thereof. Background Art

[0002] With the rapid development of industrialization and urbanization, air pollution is becoming increasingly serious. Nitrogen dioxide (NO2) emissions, in particular, not only damage the respiratory system but are also closely linked to the development of chronic diseases such as asthma. It is listed as one of the six major air pollutants by the U.S. Clean Air Act and the World Health Organization. Currently, approximately 99% of the global population is exposed to air that does not meet WHO standards. Therefore, monitoring NO2 pollution in the air is crucial for protecting public health. The U.S. Environmental Protection Agency has set the annual average safe concentration of NO2 in ambient air at 53 ppb. Over 117 countries worldwide are actively using various gas sensors for air quality monitoring. The performance of gas sensors depends on the gas-sensing material. Such materials enhance sensitivity by increasing their surface area and number of reactive sites. However, current metal oxide semiconductors (MOS) such as SnO2 and ZnO suffer from poor selectivity. High-performance electrochemical sensors based on Pt / C are expensive and lack long-term stability.

[0003] Recent studies have explored new materials for high-performance gas sensors, such as: 1) Quantum dots (QDs) dispersed in gels can increase the specific surface area and gas active sites, but the stability is poor. For example, the effect of PdCdSe QDs decays by 10% after 75 hours; 2) Single-atom catalysts (SACs) improve electron transport by exposing the surface and dispersing active sites at the atomic level, but face the challenges of low synthesis efficiency and poor stability; 3) Transition metal nitrides (TMNs), such as titanium nitride (TiN), have attracted much attention due to their high electronic conductivity and excellent chemical stability. However, due to the significant activation energy barriers during nucleation and crystallization, the development of TMNs with high specific surface area and catalytic activity is highly challenging, and the resulting gas sensors are not highly selective and have poor long-term stability. Summary of the Invention

[0004] (1) Technical problems solved

[0005] In response to the deficiencies in the prior art, the present invention provides a TiN-based electrochemical NO2 gas sensor and a preparation method thereof. By using specific TiN materials, the selectivity and long-term stability of the gas sensor are improved, solving the problems raised in the above-mentioned background technology.

[0006] (2) Technical solution

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0008] According to a first aspect of the present invention, there is provided a TiN-based electrochemical NO2 gas sensor comprising a membrane electrode assembly, a working electrode sheet, a counter electrode sheet, and a cathode sealed gas chamber;

[0009] Wherein, the membrane electrode assembly contains TiN.

[0010] Preferably, the metal sites of the TiN are surrounded by abundant nitrogen vacancies, and the specific surface area of ​​the TiN is 34 to 222 m 2 / g.

[0011] According to a second aspect of the present invention, a method for preparing a TiN-based electrochemical NO2 gas sensor is provided, comprising the following steps:

[0012] (1) Preparation of MIL-125(Ti)

[0013] Adding H2BDC and TTIP to a mixed solution containing N,N-dimethylformamide and methanol, heating the mixture at 150-160° C. for 16-24 hours, filtering, washing with N,N-dimethylformamide and methanol alternately 3-5 times, and drying to obtain the MIL-125(Ti);

[0014] (2) Preparation of TiN

[0015] The MIL-125 (Ti) powder is placed in a ceramic boat, which is then sealed in a tube furnace, and high-purity ammonia gas is introduced to perform an ammonolysis reaction, followed by cooling to room temperature to obtain the TiN;

[0016] (3) Preparation of electrochemical NO2 gas sensor

[0017] The TiN is dissolved in a mixed solution containing a Nafion solution and isopropyl alcohol and subjected to ultrasonic treatment to obtain a catalyst ink; the catalyst ink is then drop-cast onto a carbon paper surface at 80-100° C., a Nafion N-115 membrane is sandwiched between two carbon papers, and two polytetrafluoroethylene membranes are attached to the surface of the carbon paper, and hot pressing is performed at 80-100° C. and 1-3 MPa for 60-180 seconds, and the polytetrafluoroethylene membranes are peeled off to obtain the membrane electrode assembly;

[0018] The membrane electrode assembly is bonded to a working electrode sheet and a counter electrode sheet to form a small fuel cell, and the cathode of the small fuel cell is sealed with a cathode sealing gas chamber to obtain the electrochemical NO2 gas sensor.

[0019] Preferably, in step (1), the molar ratio of H2BDC to TTIP is 1.5 to 3:1;

[0020] The volume ratio of N,N-dimethylformamide to methanol in the mixed solution containing N,N-dimethylformamide and methanol is 0.5-1.5:1.

[0021] Preferably, in step (2), the heating rate of the ammonolysis is 3 to 8°C / min, the temperature of the ammonolysis is 500 to 900°C, and the time of the ammonolysis is 3 to 5 hours.

[0022] Preferably, in step (2), the flow rate of the ammonia gas is 50 to 150 cm 3 / min.

[0023] Preferably, in step (3), the mass of the TiN is 0.5 to 1.5 mg.

[0024] Preferably, in step (3), the volume ratio of Nafion solution to isopropanol in the mixed solution containing Nafion solution and isopropanol is 1:11.5;

[0025] The concentration of the Nafion solution is 5-20 wt %.

[0026] Preferably, after obtaining the membrane electrode assembly, the process further includes cutting the membrane electrode assembly into sizes that match the working electrode sheet and the counter electrode sheet, and bonding the membrane electrode assembly to the stainless steel electrode by hot melt adhesive.

[0027] (3) Beneficial effects

[0028] The present invention provides a TiN-based electrochemical NO2 gas sensor and a method for preparing the same. It has the following beneficial effects:

[0029] (1) This solution provides a TiN-based electrochemical NO2 gas sensor that uses TiN material with a high specific surface area and NVs sites, significantly enhancing the properties of gas diffusion, adsorption, and catalytic reactions. Compared with traditional gas sensors that enhance gas response by loading Pt on sensitive materials, this solution not only significantly reduces the cost of gas sensors, but also solves the problem of poor long-term stability caused by the shedding and aggregation of Pt nanoparticles during long-term operation.

[0030] (2) This scheme provides a TiN-based electrochemical NO2 gas sensor. Due to the use of TiN material with a high specific surface area and NVs sites, it has high stability in low temperature and humid environments and is less affected by low temperature and humid environments.

[0031] (3) This proposal provides a method for preparing a TiN-based electrochemical NO2 gas sensor. By ammoniolysis of MOF-MIL-125(Ti), the synthesized TiN material has an ultra-high specific surface area, up to 221.9 m2 / g, and has abundant NVs sites, which solves the problem of significant activation energy barriers in the nucleation and crystallization processes of traditional TMNs. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the preparation process of TiN of the present invention;

[0033] Figure 2 X-ray diffraction patterns of MIL-125(Ti) powder and TiN prepared in Examples 1 to 5, wherein a) is the XRD pattern of MIL-125(Ti) powder; b) is the XRD pattern of TiN-600; c) is the XRD pattern of TiN-500, TiN-700, TiN-800, and TiN-900;

[0034] Figure 3 N2 adsorption-desorption isotherms were performed for the TiN prepared in Examples 1 to 5 and commercially available TiN;

[0035] Figure 4 Transmission electron micrographs of the MIL-125(Ti) powder and TiN prepared in Example 1, wherein a) is an HRTEM image of TiN-600; b) is an HRTEM image of MIL-125(Ti); and c) is a filtered image of the boxed area in a).

[0036] Figure 5 Selectivity diagram of the electrochemical NO2 gas sensor prepared in Example 1, Comparative Example 1 and Comparative Example 2 to different analytical gases;

[0037] Figure 6 Response transient curves of the electrochemical NO2 gas sensors prepared in Examples 1 to 4 to 50 ppm NO2;

[0038] Figure 7 This is the response recovery transient curve of the electrochemical NO2 gas sensor prepared in Example 1 to a NO2 concentration of 50 ppm;

[0039] Figure 8 Response changes of the electrochemical NO2 gas sensor prepared in Example 1 to 50 ppm NO2 within 130 days. DETAILED DESCRIPTION

[0040] The following is a clear and complete description of the technical solution of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0041] Example 1

[0042] The preparation process of TiN in this embodiment is as follows Figure 1 As shown:

[0043] Preparation of MIL-125(Ti): 1000 mg of H2BDC and 864 mg of TTIP were added to a mixed solution of 25 mL of DMF and 25 mL of methanol, stirred thoroughly at room temperature, and then transferred to a 100 mL Teflon-lined autoclave and heated at 150°C for 16 h. The residue was collected by filtration, washed alternately with DMF and methanol three times, and dried to obtain a white solid MIL-125(Ti) powder.

[0044] Preparation of TiN: 100 mg of MIL-125 (Ti) powder was placed in a ceramic boat in a tube furnace. 3 Ammonia was continuously introduced at a flow rate of 1 / min, and then the temperature was raised to 600°C at a rate of 5°C / min and maintained for 3 hours for aminolysis. After the end, ammonia was continuously introduced until the tube furnace cooled to room temperature to obtain TiN, which was recorded as TiN-600.

[0045] Preparation of an electrochemical NO2 gas sensor: 5 mg of TiN-600 powder, 40 μL of a 5 wt% Nafion solution, and 460 μL of isopropyl alcohol were ultrasonically treated to obtain a catalyst ink. The catalyst ink was then drop-cast onto a 90°C carbon paper surface. A Nafion N-115 membrane was then sandwiched between two sheets of carbon paper, and two polytetrafluoroethylene membranes were attached to the carbon paper surfaces. The membrane electrode assembly was obtained by hot pressing at 90°C and 1 MPa for 120 seconds, and then the polytetrafluoroethylene membranes were peeled off.

[0046] The obtained membrane electrode assembly was cut into a size suitable for the working electrode sheet and the counter electrode sheet, and bonded to the stainless steel electrode with hot melt adhesive to form a small fuel cell. The cathode of the small fuel cell was sealed with a cathode sealing gas chamber to obtain an electrochemical NO2 gas sensor, which was recorded as a TiN-600 sensor.

[0047] Example 2

[0048] The preparation method of this embodiment is the same as that of embodiment 1, except that the temperature of the ammonolysis in step (2) is 500°C, the obtained TiN is recorded as TiN-500, and the obtained electrochemical NO2 gas sensor is recorded as TiN-500 sensor.

[0049] Example 3

[0050] The preparation method of this embodiment is the same as that of embodiment 1, except that the temperature of the ammonolysis in step (2) is 700°C, the obtained TiN is recorded as TiN-700, and the obtained electrochemical NO2 gas sensor is recorded as TiN-700 sensor.

[0051] Example 4

[0052] The preparation method of this embodiment is the same as that of embodiment 1, except that the temperature of the ammonolysis in step (2) is 800°C, the obtained TiN is recorded as TiN-800, and the obtained electrochemical NO2 gas sensor is recorded as TiN-800 sensor.

[0053] Example 5

[0054] The preparation method of this embodiment is the same as that of embodiment 1, except that the temperature of the ammonolysis in step (2) is 900°C, the obtained TiN is recorded as TiN-900, and the obtained electrochemical NO2 gas sensor is recorded as TiN-900 sensor.

[0055] Comparative Example 1

[0056] The preparation method of this embodiment is the same as that of embodiment 1, except that the sensitive material used in step (3) is commercially purchased TiN-CM material.

[0057] Comparative Example 2

[0058] The preparation method of this embodiment is the same as that of Example 1, except that the sensitive material used in step (3) is the traditional Pt / C material.

[0059] Performance measurement of TiN prepared in Examples 1 to 5:

[0060] X-ray diffraction was performed on the MIL-125 (Ti) powder and TiN prepared in Example 1 of the present invention, as well as the TiN prepared in Examples 2 to 5. Figure 2 As shown, the present invention successfully prepared MIL-125 (Ti) powder and TiN, and used MOF as a sacrificial template to synthesize TiN by precisely controlling the temperature of the ammonolysis process, while retaining the high specific surface area structure of MOF, forming rich NVs sites around the metal sites.

[0061] The TiN prepared in Examples 1 to 5 of the present invention and the directly purchased TiNTiN-CM were subjected to N2 adsorption-desorption tests. Figure 3 As shown, according to Figure 3 It can be seen that TiN derived from MOF has a high specific surface area, and the specific surface area of ​​TiN-600 reaches 221.9m 2 / g, which is 90 times that of TiN-CM.

[0062] according to Figure 4 As can be seen from the transmission electron microscopy images, Figure a) shows a series of lattice fringes associated with the (331) and (400) crystal planes of TiN-600, showing randomly oriented grains. The boxed area in Figure a) shows the scanning electron microscopy image of TiN-600, which presents a uniform square morphology, which is consistent with the morphology of the precursor MIL-125(Ti) shown in Figure b), indicating that MIL-125(Ti) still maintains its morphology after low-temperature ammonolysis and obtains abundant surface active sites. According to Figure c), the discontinuity of the lattice fringes and the blurring or missing of some lattice sites indicate the presence of vacancy defects, which can serve as active centers, thereby increasing catalytic activity.

[0063] Performance comparison of the gas sensors prepared in Examples 1 to 5 and Comparative Examples 1 to 2:

[0064] The selectivity of the gas sensors of Example 1 and Comparative Examples 1-2 to different analytical gases was analyzed. Figure 5 As shown in the figure, the response of the TiN-600 sensor to NO2 is significantly higher than that of the TiN-CM sensor and the Pt / C material sensor. The responses to various interfering gases (including 300 ppm of NO, acetone, methanol, trimethylamine, ammonia, hydrogen and ethanol) are low and can be ignored, indicating that the TiN-600 sensor has high selectivity for NO2.

[0065] By monitoring the response of the NO2 gas sensors of Examples 1 to 4 to NO2, as Figure 6 As shown, the sensor using TiN-600 exhibits the highest response. Figure 7 As shown in the figure, the response and recovery time of the TiN-600 sensor to 50ppm NO2 are 7.4s and 5.2s respectively, which shows a fast response.

[0066] according to Figure 8 As shown in Figure 3, the sensing response of the TiN-600 sensor was tested for up to 130 days, and it was found that the response at 130 days only decreased by 3.3% compared with the first day, showing excellent long-term stability.

[0067] According to the above test results, the present invention optimizes the preparation process of TiN material to obtain an electrochemical NO2 gas sensor with excellent NO2 gas selectivity and stability.

[0068] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a TiN-based electrochemical NO2 gas sensor, characterized in that: The following steps are involved: (1) Preparation of MIL-125 (Ti) Adding H2BDC and TTIP to a mixed solution containing N,N-dimethylformamide and methanol, heating the mixture at 150-160°C for 16-24 hours, filtering, washing with N,N-dimethylformamide and methanol alternately 3-5 times, and drying to obtain the MIL-125 (Ti); (2) Preparation of TiN The MIL-125 (Ti) powder is placed in a ceramic boat, which is then sealed in a tube furnace, high-purity ammonia is introduced to perform an ammonolysis reaction, and then cooled to room temperature to obtain the TiN; (3) Preparation of electrochemical NO2 gas sensor The TiN is dissolved in a mixed solution containing a Nafion solution and isopropyl alcohol and ultrasonically treated to obtain a catalyst ink; the catalyst ink is then drop-cast onto a carbon paper surface at 80-100° C., a Nafion N-115 membrane is sandwiched between two carbon papers, and two polytetrafluoroethylene membranes are attached to the surface of the carbon paper, and hot pressing is performed at 80-100° C. and 1-3 MPa for 60-180 seconds, and the polytetrafluoroethylene membranes are peeled off to obtain a membrane electrode assembly; The membrane electrode assembly is bonded to a working electrode sheet and a counter electrode sheet to form a small fuel cell, and the cathode of the small fuel cell is sealed with a cathode sealing gas chamber to obtain the electrochemical NO2 gas sensor.

2. The method for preparing a TiN-based electrochemical NO2 gas sensor according to claim 1, wherein: In step (1), the molar ratio of H2BDC to TTIP is 1.5-3:1; The volume ratio of N,N-dimethylformamide to methanol in the mixed solution containing N,N-dimethylformamide and methanol is 0.5-1.5:

1.

3. The method for preparing a TiN-based electrochemical NO2 gas sensor according to claim 1, wherein: In step (2), the heating rate of the ammonolysis is 3-8°C / min, the temperature of the ammonolysis is 500-900°C, and the time of the ammonolysis is 3-5h.

4. The method for preparing a TiN-based electrochemical NO2 gas sensor according to claim 1, wherein: In step (2), the flow rate of the ammonia gas is 50~150cm 3 / min.

5. The method for preparing a TiN-based electrochemical NO2 gas sensor according to claim 1, wherein: In step (3), the mass of the TiN is 0.5-1.5 mg.

6. The method for preparing a TiN-based electrochemical NO2 gas sensor according to claim 1, wherein: In step (3), the volume ratio of the Nafion solution to the isopropanol in the mixed solution containing the Nafion solution and isopropanol is 0.5-1.5:11.5; The concentration of the Nafion solution is 5-20 wt %.

7. The method for preparing a TiN-based electrochemical NO2 gas sensor according to claim 1, wherein: After obtaining the membrane electrode assembly, the process also includes cutting the membrane electrode assembly into sizes that match the working electrode sheet and the counter electrode sheet, and bonding the membrane electrode assembly to the stainless steel electrode by hot melt adhesive.

8. A TiN-based electrochemical NO2 gas sensor prepared according to the preparation method according to any one of claims 1 to 7, characterized in that: It includes a membrane electrode assembly, a working electrode sheet, a counter electrode sheet and a cathode sealing gas chamber; Wherein, the membrane electrode assembly contains TiN.

9. The TiN-based electrochemical NO2 gas sensor according to claim 8, characterized in that: The TiN has abundant nitrogen vacancies around the metal sites, and the specific surface area of ​​the TiN is 34~222m 2 / g.

Images