Mixed potential type ammonia gas sensor and preparation method thereof
By using a layered nickel silicate sensitive electrode and a solid electrolyte made of NASICON powder, a hybrid potential type ammonia sensor was constructed, which solved the problem of insufficient response at low temperatures and achieved high sensitivity and high response for ammonia, making it suitable for mass production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ANHUI UNIV OF SCI & TECH
- Filing Date
- 2025-12-30
- Publication Date
- 2026-05-01
Smart Images
Figure CN121955151A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of gas sensor detection, specifically a hybrid potential type ammonia sensor and its preparation method. Background Technology
[0002] Gaseous ammonia (NH3) is a colorless, alkaline gas with a strong, pungent odor. It is a toxic gas that has a significant impact on human health. Parts per million (ppm) of NH3 can irritate the nose, eyes, and throat; higher levels of NH3 can lead to dizziness, respiratory failure, and even death.
[0003] According to OSHA standards, the workplace ammonia exposure threshold is 50 ppm. Exposure to ammonia levels below 35 ppm for 15 minutes or below 25 ppm for 8 hours in ambient air may impair human health. The Toxic Substances and Disease Registry (ATSDR) has summarized serious problems caused by acute ammonia (500 ppm) exposure in its reports, including permanent lung damage, chemical burns to the skin, and pulmonary effusion.
[0004] Solid electrolyte-based hybrid potential ammonia gas sensors have advantages such as being all-solid-state, simple in structure, low in cost, and resistant to high temperatures, making them one of the most widely studied gas sensors. However, existing hybrid potential ammonia gas sensors still suffer from low response at low temperatures and low concentrations, and cannot effectively detect ammonia gas concentrations at room temperature. Summary of the Invention
[0005] The purpose of this invention is to provide a hybrid potential type ammonia sensor to solve the problems mentioned in the background art.
[0006] To achieve the above objectives, the present invention provides the following technical solution: A hybrid potential type ammonia sensor includes: a layered nickel silicate sensitive electrode, a reference electrode, and a solid electrolyte; the layered nickel silicate sensitive electrode and the reference electrode are located on the surface of the solid electrolyte; the layered nickel silicate sensitive electrode is made of three different morphologies of layered nickel silicate electrode slurries. The solid electrolyte is disposed on top of a heating element, and a ceramic plate is disposed on the heating element, with the ceramic plate positioned between the solid electrolyte and the heating element. A platinum point is disposed on the sensitive electrode, and a platinum point is disposed on the reference electrode.
[0007] To achieve the above objectives, the present invention provides another technical solution as follows: A method for preparing a hybrid potential type ammonia sensor includes the following steps: Step S21: Prepare the reference electrode; Step S22: Prepare layered nickel silicate electrode paste; Step S23: Prepare a layered nickel silicate sensitive electrode; Step S24: Attach two Pt wires to the middle of the layered nickel silicate sensitive electrode with dotted Ag paste to serve as electrode leads; place the heating element on the ceramic plate and place the solid electrolyte prepared above on the heating element; Step S25: Solder and package the obtained device to obtain a hybrid potential type ammonia gas sensor.
[0008] As a further aspect of the present invention: before step S21, the method further includes: preparing a solid electrolyte, specifically including: NASICON powder was synthesized via the sol-gel method. PVA solution was added to the prepared NASICON powder and the mixture was ground to obtain powder. The powder was then pressed into shape and sintered to obtain solid electrolyte NASICON.
[0009] As a further aspect of the present invention: a method for preparing layered nickel silicate electrode paste, comprising the following steps: Step S1: Synthesize layered nickel silicate; Step S12: Calcine layered nickel silicate in air to obtain layered nickel silicate electrode slurry.
[0010] As a further aspect of the present invention: synthesizing nanotube-shaped layered nickel silicate, which includes the following steps: Step S121: Dissolve nickel chloride hexahydrate, sodium silicate nonahydrate, and sodium hydroxide in deionized water according to a preset ratio, and stir until completely dissolved to obtain the first solution; Step S123: Transfer the first solution to a reaction vessel for underwater thermal reaction. After the reaction is completed, cool to room temperature, and then centrifuge, wash and dry the reaction product to obtain nanotube-shaped layered nickel silicate.
[0011] As a further aspect of the present invention: the synthesis of layered nickel silicate includes the following steps: Prepare dry MOF powder; Dry MOF powder and sodium silicate nonahydrate were magnetically dispersed in 120 mL of anhydrous ethanol / water solution of equal volume concentration according to the ratio. Then, sodium hydroxide solution was added dropwise and ultrasonic stirring was performed continuously. After the suspension was reacted underwater for a period of time, it was washed several times by centrifugation with deionized water and anhydrous ethanol, and then vacuum dried to obtain light green lamellar nickel silicate.
[0012] As a further aspect of the present invention: the synthesis of layered nickel silicate includes the following steps: Silicon dioxide, nickel nitrate hexahydrate, and urea were added to the flask in sequence according to the preset molar ratio. Then, dilute nitric acid solution was added and stirred until the solute was completely dissolved to obtain the second solution. The second solution was heated to obtain a green suspension. After the reaction was completed, the green suspension was cooled for a period of time, then centrifuged, washed with deionized water and dried to obtain light green powder nano-flower-shaped layered nickel silicate.
[0013] As a further aspect of the present invention: the preparation of the reference electrode includes the following steps: The first raw material slurry is coated onto the solid electrolyte and kept at 120-180℃ for 20-40 minutes to allow the organic solvent in the Pt slurry to evaporate completely. The electrolyte substrate is then calcined at 800-1200℃ for 20-40 minutes. Platinum dots are then applied to the reference electrode and connected with a Pt wire of about 5 cm to form the reference electrode.
[0014] As a further aspect of the present invention: the preparation of the layered nickel silicate sensitive electrode includes the following steps: The prepared layered nickel silicate electrode slurry is coated on a solid electrolyte, with the reference electrode on the same side of the solid electrolyte. Then, it is placed at 120-180℃ for 20-40 minutes to allow the organic solvent in the electrode material to evaporate completely. Then, the solid electrolyte is applied, and platinum dots are applied to the sensitive electrode. Finally, a Pt wire of about 5 cm is connected to form a layered nickel silicate sensitive electrode.
[0015] As a further aspect of the present invention: the preparation of the layered nickel silicate electrode paste includes the following steps: Terpineol and ethyl cellulose were mixed at a mass ratio of 9:1 to obtain modified terpineol; layered nickel silicate electrode slurry was weighed, and the modified terpineol was added dropwise at a mass ratio of 3:1 between terpineol and layered nickel silicate material, and then the mixture was thoroughly ground for 0.6-1.4 hours to obtain layered nickel silicate electrode slurry.
[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention uses layered nickel silicate as the sensitive electrode, which significantly improves the response value to ammonia gas at room temperature, with a response value of approximately -38mV at 50ppm ammonia. Compared with the most advanced existing mixed potential type ammonia gas sensors, this invention can also significantly improve the response to low concentrations of ammonia at room temperature compared with other high-temperature mixed potential type ammonia sensors.
[0017] 2. The morphology of the layered nickel silicate sensitive electrode in this invention is highly adjustable. By changing the manufacturing method, the morphology of the three sensitive electrodes can be controlled, thereby improving the sensitivity characteristics to ammonia gas. This invention achieves high response and high sensitivity detection of ammonia gas in a simple and effective way.
[0018] 3. The hybrid potential type ammonia gas sensor involved in this invention has a hybrid potential type structure. Its main components include a sensitive electrode, a reference electrode, and a solid electrolyte. It has a simple structure, low manufacturing difficulty, and is easy to miniaturize and integrate, which is beneficial for mass production and practical application. The sensor components involved in this invention include a heating element and a ceramic plate. Adjusting the temperature of the monitored ammonia gas is simple and safe. Attached Figure Description
[0019] Figure 1 This invention provides XRD images and FTIR results of a layered nickel silicate sensor in a hybrid potential ammonia gas sensor.
[0020] Figure 2 This invention provides scanning electron microscope (SEM) images of (a) T-NIPS, (b) L-NIPS, (c) F-NIPS and (de) T-NIPS of a layered nickel silicate sensor in a hybrid potential type ammonia sensor.
[0021] Figure 3 This invention presents the dynamic response curves of a layered nickel silicate sensor in a hybrid potential type ammonia sensor as a function of ammonia concentrations ranging from 5 to 200 ppm at (a) 25°C and (b) 50°C; and the response values of three sensors as a function of the logarithm of ammonia concentration at (c) 25°C and (d) 50°C.
[0022] Figure 4 The present invention relates to a hybrid potential type ammonia sensor in which a layered nickel silicate sensor with a nanotube-shaped sensor detects ammonia at room temperature, and the following properties are described: (a) consistency, (b) long-term stability, (c) repeatability, and (d) moisture resistance.
[0023] Figure 5. A two-dimensional graph comparing the performance of a layered nickel silicate sensor and a state-of-the-art ammonia sensor in a hybrid potential type ammonia sensor according to an embodiment of the present invention.
[0024] Figure 6 is a schematic diagram of a hybrid potential type ammonia sensor according to an embodiment of the present invention.
[0025] In the diagram: Solid electrolyte-1, Sensitive electrode-2, Reference electrode-3, Sensitive electrode Pt point-4, Reference electrode Pt point-5, Ceramic plate-6, Heating element-7. Detailed Implementation
[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0027] Based on the response mechanism of mixed potential ammonia gas sensors, the electrocatalytic activity, ammonia adsorption capacity, and pore structure of the SE material are key factors in manufacturing high-performance sensors, significantly influencing the ammonia sensitivity. Layered nickel silicate is a two-dimensional, infinitely extending layered compound composed of continuous silicon-oxygen tetrahedral layers and nickel-oxygen octahedral layers sharing apical oxygen atoms. Depending on the composition of the silicon-oxygen tetrahedrons and the nickel cation, layered nickel silicate can also curl into flower-like or tubular morphologies under appropriate conditions. The exposed, coordinatingly unsaturated transition metal Ni at the edges of the nickel-oxygen octahedrons in layered nickel silicate materials... 2+ Layered nickel silicate possesses abundant Lewis acid sites. In the field of gas sensors, Lewis acid sites, as active sites, have been widely proven to effectively promote gas adsorption. According to acid-base coordination theory, these Lewis acid sites exhibit strong adsorption and catalytic capabilities for typical Lewis base ammonia molecules. Furthermore, the synthesis route of layered nickel silicate is simple and its microstructure is highly tunable, allowing for the easy synthesis of materials with large pore sizes and high porosity, which is beneficial for the rapid diffusion of ammonia. Therefore, developing porous layered nickel silicate with special morphologies to further improve the sensitivity of mixed-potential ammonia gas sensors is of great significance. This invention provides a mixed-potential ammonia gas sensor. The three special layered structures of the layered nickel silicate sensitive material, higher density and highly exposed acid sites, and high porosity and large pore size microstructure improve the transport and diffusion of ammonia within the sensitive electrode, as well as the electrochemical reaction rate, enhancing interfacial electrochemical activity and thus improving the sensor's sensitivity to ammonia gas.
[0028] This invention also provides a hybrid potential type ammonia gas sensor, comprising: a layered nickel silicate sensitive electrode 2, a reference electrode 3, and a solid electrolyte 1; the layered nickel silicate sensitive electrode 2 and the reference electrode 3 are located on the surface of the solid electrolyte 1; the layered nickel silicate sensitive electrode 2 is made of three different morphologies of layered nickel silicate electrode slurries. The solid electrolyte 1 is disposed on top of a heating element 7, and a ceramic plate 6 is disposed on the heating element 7, with the ceramic plate 6 positioned between the solid electrolyte 1 and the heating element 7. A sensitive electrode Pt point 4 is disposed on the sensitive electrode 2, and a reference electrode Pt point 5 is disposed on the reference electrode 3.
[0029] This invention enables real-time response to ammonia gas by collecting the potential difference change between the layered nickel silicate sensitive electrode 2 and the reference electrode 3 in an ammonia atmosphere, thereby obtaining ammonia gas concentration data in the environment.
[0030] The reference electrode 3 can be made of the noble metal Pt; the solid electrolyte 1 is made of NASICON.
[0031] The reference electrode 3 is provided with a Pt wire.
[0032] The layered nickel silicate sensitive electrode 2 and the reference electrode 3 are separate from each other and symmetrically arranged at both ends of the upper surface of the solid electrolyte 1.
[0033] This invention also provides a method for preparing a hybrid potential type ammonia sensor, comprising the following steps: Step S21: Prepare reference electrode 3; In this embodiment of the invention, before step S21 and the preparation of the reference electrode 3, the method further includes: preparing a solid electrolyte 1, which specifically includes: NASICON powder was synthesized via the sol-gel method. PVA solution was added to the prepared NASICON powder and the mixture was ground to obtain powder. The powder was then pressed into shape and sintered to obtain solid electrolyte NASICON.
[0034] Specifically, in some embodiments: an appropriate amount of PVA solution is added to NASICON powder and the mixture is ground for 1.5-2.2 hours. Finally, a quantitative amount of powder is taken, pressed into shape under a pressure of 160-200 MPa, and sintered at 1000-1200℃ for 10-14 hours to obtain solid electrolyte NASICON.
[0035] In some embodiments: an appropriate amount of PVA solution is added to NASICON powder and the mixture is ground for 2.2 hours. Finally, a quantitative amount of powder is pressed into shape under a pressure of 200 MPa and sintered at 1200 °C for 14 hours to obtain solid electrolyte NASICON.
[0036] In some embodiments: an appropriate amount of PVA solution is added to NASICON powder and the mixture is ground for 1.5 h. Finally, a quantitative amount of powder is pressed into shape under a pressure of 1600 MPa and sintered at 1000 °C for 10 h to obtain solid electrolyte NASICON.
[0037] In some embodiments: an appropriate amount of PVA solution is added to NASICON powder and the mixture is ground for 1.7 h. Finally, a quantitative amount of powder is pressed into shape under a pressure of 170 MPa and sintered at 1050 °C for 1 h to obtain solid electrolyte NASICON.
[0038] In some embodiments: an appropriate amount of PVA solution is added to NASICON powder and the mixture is ground for 2.0 h. Finally, a quantitative amount of powder is pressed into shape under a pressure of 190 MPa and sintered at 150 °C for 13 h to obtain solid electrolyte NASICON.
[0039] In some embodiments: an appropriate amount of PVA solution is added to NASICON powder and the mixture is ground for 1.8 hours. Finally, a quantitative amount of powder is pressed into shape under a pressure of 180 MPa and sintered at 100°C for 12 hours to obtain solid electrolyte NASICON.
[0040] The mass of the solid electrolyte NASICON is approximately 0.4g.
[0041] In this embodiment of the invention, the preparation of the reference electrode 3 includes the following steps: The first raw material slurry is coated onto the solid electrolyte 1 and kept at 120-180℃ for 20-40 minutes to allow the organic solvent in the Pt slurry to evaporate completely. The electrolyte substrate 1 is then calcined at 800-1200℃ for 20-40 minutes. Pt points 5 are then applied to the reference electrode and connected with a platinum wire of about 5 cm to form the reference electrode 3.
[0042] In some embodiments, the preparation of the reference electrode 3 includes the following steps: The first raw material slurry is coated onto the solid electrolyte 1 and kept at 120°C for 20 minutes to allow the organic solvent in the Pt slurry to evaporate completely. Then, the electrolyte substrate 1 is calcined at 800°C for 20 minutes to form the reference electrode 3.
[0043] In some embodiments, the preparation of the reference electrode 3 includes the following steps: The first raw material slurry is coated onto the solid electrolyte 1 and kept at 180°C for 40 minutes to allow the organic solvent in the Pt slurry to evaporate completely. Then, the electrolyte substrate 1 is calcined at 1200°C for 40 minutes to form the reference electrode 3.
[0044] In some embodiments, the preparation of the reference electrode 3 includes the following steps: The first raw material slurry is coated onto the solid electrolyte 1 and kept at 170°C for 35 minutes to allow the organic solvent in the Pt slurry to evaporate completely. Then, the electrolyte substrate 1 is calcined at 100°C for 35 minutes to form the reference electrode 3.
[0045] In some embodiments, the preparation of the reference electrode 3 includes the following steps: The first raw material slurry is coated onto the solid electrolyte 1 and kept at 130°C for 25 minutes to allow the organic solvent in the Pt slurry to evaporate completely. Then, the electrolyte substrate 1 is calcined at 900°C for 25 minutes to form the reference electrode 3.
[0046] In some embodiments, the preparation of the reference electrode 3 includes the following steps: The first raw material slurry is coated onto the solid electrolyte 1 and kept at 150°C for 30 minutes to allow the organic solvent in the Pt slurry to evaporate completely. Then, the electrolyte substrate 1 is calcined at 1000°C for 30 minutes to form the reference electrode 3.
[0047] In this embodiment of the invention, the preparation of the layered nickel silicate electrode slurry includes the following steps: Terpineol and ethyl cellulose were mixed at a mass ratio of 9:1 to obtain modified terpineol; layered nickel silicate electrode slurry was weighed, and the modified terpineol was added dropwise at a mass ratio of 3:1 between terpineol and layered nickel silicate material, and then the mixture was thoroughly ground for 0.6-1.4 hours to obtain layered nickel silicate electrode slurry.
[0048] In some embodiments, the preparation of the layered nickel silicate electrode slurry includes the following steps: Terpineol and ethyl cellulose were mixed at a mass ratio of 1:1 to obtain modified terpineol; layered nickel silicate electrode slurry was weighed, and the modified terpineol was added dropwise at a mass ratio of 4:1 between terpineol and layered nickel silicate material, and then the mixture was ground thoroughly for 1.4 hours to obtain layered nickel silicate electrode slurry.
[0049] In some embodiments, the preparation of the layered nickel silicate electrode slurry includes the following steps: Terpineol and ethyl cellulose were mixed at a mass ratio of 7:1 to obtain modified terpineol; layered nickel silicate electrode slurry was weighed, and the modified terpineol was added dropwise at a mass ratio of 2:1 between terpineol and layered nickel silicate material, and then the mixture was ground thoroughly for 0.6 hours to obtain layered nickel silicate electrode slurry.
[0050] In some embodiments, the preparation of the layered nickel silicate electrode slurry includes the following steps: Terpineol and ethyl cellulose were mixed at a mass ratio of 10:1 to obtain modified terpineol; layered nickel silicate electrode slurry was weighed, and the modified terpineol was added dropwise at a mass ratio of terpineol to layered nickel silicate material of 3.5:1, and then the mixture was ground thoroughly for 1.2 hours to obtain layered nickel silicate electrode slurry.
[0051] In some embodiments, the preparation of the layered nickel silicate electrode slurry includes the following steps: Terpineol and ethyl cellulose were mixed at a mass ratio of 8:1 to obtain modified terpineol; layered nickel silicate electrode slurry was weighed, and the modified terpineol was added dropwise at a mass ratio of 2.5:1 between terpineol and layered nickel silicate material, and then the mixture was ground thoroughly for 0.8 hours to obtain layered nickel silicate electrode slurry.
[0052] Step S22: Prepare layered nickel silicate electrode paste; In this embodiment of the invention, step S22, preparing the layered nickel silicate electrode paste, includes the following steps: Step S221: Synthesize layered nickel silicate; In one embodiment of the present invention, step S221, synthesizing nanotube-shaped layered nickel silicate, includes the following steps: Step S221a1: Dissolve nickel chloride hexahydrate, sodium silicate nonahydrate, and sodium hydroxide in deionized water according to a preset ratio, and stir until completely dissolved to obtain the first solution.
[0053] Specifically, in some embodiments, nickel chloride hexahydrate, sodium silicate nonahydrate, and sodium hydroxide are dissolved in 200 mL of deionized water in a molar ratio of 6:4:5, and stirred for 40 min until both are completely dissolved, which is denoted as solution A.
[0054] In some embodiments, nickel chloride hexahydrate, sodium silicate nonahydrate, and sodium hydroxide are dissolved in 200 mL of deionized water in a molar ratio of 6:4:5, and stirred for 20 min until both are completely dissolved. This solution is denoted as solution A.
[0055] In some embodiments, nickel chloride hexahydrate, sodium silicate nonahydrate, and sodium hydroxide are dissolved in 200 mL of deionized water in a molar ratio of 6:4:5, and stirred for 30 min until both are completely dissolved. This solution is denoted as solution A.
[0056] Step S221a2: The first solution is transferred to a reaction vessel for underwater thermal reaction. After the reaction is completed, it is cooled to room temperature. The reaction product is then centrifuged, washed, and dried to obtain nanotube-shaped layered nickel silicate.
[0057] Specifically, in some embodiments, solution A was transferred to the inner liner of a 400 mL polytetrafluoroethylene high-pressure reactor and hydrothermally reacted at 220°C for 12 h. After the reaction was completed, the mixture was cooled to room temperature, and then the product was centrifuged, washed, and dried to obtain nanotube-shaped layered nickel silicate.
[0058] In some embodiments, solution A was transferred to the inner liner of a 400 mL polytetrafluoroethylene high-pressure reactor and hydrothermally reacted at 180 °C for 90 h. After the reaction was completed, the mixture was cooled to room temperature, and then the product was centrifuged, washed, and dried to obtain nanotubular layered nickel silicate.
[0059] In some embodiments, solution A was transferred to the inner liner of a 400 mL polytetrafluoroethylene high-pressure reactor and hydrothermally reacted at 200 °C for 96 h. After the reaction was completed, the mixture was cooled to room temperature, and then the product was centrifuged, washed, and dried to obtain nanotubular layered nickel silicate.
[0060] Step S222: Calcine layered nickel silicate in air to obtain layered nickel silicate electrode slurry.
[0061] In another embodiment of the present invention, step S221, synthesizing layered nickel silicate, includes the following steps: Step S221b1: Prepare dry MOF powder; In some embodiments, step S221b1, preparing dry MOF powder, includes: Nickel nitrate hexahydrate and terephthalic acid were dissolved in 10 mL of N,N-dimethylformamide at a molar ratio of 1:1 and stirred vigorously to form a homogeneous solution. Then, 2 mL of 0.2 mol / L sodium hydroxide solution was added, and the mixture was stirred vigorously for another 1 h. The mixture was carefully transferred to an autoclave lined with polytetrafluoroethylene and reacted at 100 °C for 15 h. After repeated centrifugation, the mixture was washed with N,N-dimethylformamide and methanol, respectively, and the light green MOF powder was collected. Subsequently, it was vacuum dried at 60 °C to constant weight. The molar ratio of nickel nitrate hexahydrate to N,N-dimethylformamide can be set as needed. In some embodiments, the molar ratio of nickel nitrate hexahydrate to N,N-dimethylformamide is 1:128.
[0062] Step S221b2: Disperse the dry MOF powder and sodium silicate nonahydrate magnetically in an equal volume of anhydrous ethanol / water solution according to the ratio. Then add sodium hydroxide solution dropwise and continuously stir with ultrasound. After reacting the suspension underwater for a period of time, wash it several times with deionized water and anhydrous ethanol by centrifugation and vacuum drying to obtain light green lamellar nickel silicate.
[0063] Specifically, 0.8 g of MOF powder and 1.14 g of sodium silicate nonahydrate were magnetically dispersed in 120 mL of anhydrous ethanol / water solution of equal volume concentration. Then, 6 mL of 1 mol / L sodium hydroxide solution was added dropwise, and the mixture was ultrasonically stirred continuously for at least 30 min to avoid clumping and precipitation. The suspension was then subjected to hydrothermal reaction at 170 °C for 15 h, washed several times by centrifugation with deionized water and anhydrous ethanol, and vacuum dried overnight at 60 °C. Finally, the target product, a pale green lamellar nickel silicate, was obtained.
[0064] In another embodiment of the present invention, step S221, synthesizing layered nickel silicate, includes the following steps: Step S221c1: Add silicon dioxide, nickel nitrate hexahydrate and urea to the flask in sequence according to the preset molar ratio, then add dilute nitric acid solution and stir until the solute is completely dissolved to obtain the second solution.
[0065] Specifically, nickel nitrate hexahydrate, urea, and a specific surface area of 280 g / m² are weighed according to the preset ratio. 2The silica was added sequentially to the flask, followed by approximately 50 mL of a 0.02 mol / L dilute nitric acid solution, which was then added to the flask and stirred continuously until the solute was completely dissolved to obtain the second solution.
[0066] In some embodiments, the specific surface area is taken as 280 g / m². 2 The molar ratios of silicon dioxide (0.38 g), nickel nitrate hexahydrate (2.03 g), and urea (1.26 g) were 2:2:7, and the molar ratio of dilute nitric acid to nickel nitrate hexahydrate was 1:6.
[0067] The flask can be a three-necked flask.
[0068] In step S221c2, the second solution is heated to obtain a green suspension. After the reaction is completed, the green suspension is cooled for a period of time, then centrifuged, washed with deionized water and dried to obtain light green powder nano-flower-like layered nickel silicate.
[0069] Specifically, in some embodiments, the second solution is heated to 95°C and the reaction time is within the range of 50 hours. After the reaction is completed, the flask is transferred from the oil bath, and after the green suspension cools for 12 hours, it is centrifuged, washed with deionized water, and dried in an oven at 80°C for 28 hours. The resulting light green powder is nano-flower-like layered nickel silicate.
[0070] In some embodiments, the reaction time is 50 min after the second solution is heated to 85°C. After the reaction is complete, the flask is removed from the oil bath, and after the green suspension has cooled for 8 h, it is centrifuged, washed with deionized water, and dried in an oven at 60°C for 20 h. The resulting light green powder is nano-flower-like layered nickel silicate.
[0071] In some embodiments, the second solution is heated to 92°C and the reaction time is within the range of 40 h. After the reaction is completed, the flask is transferred from the oil bath, and after the green suspension cools for 1 h, it is centrifuged, washed with deionized water, and dried in an oven at 75°C for 26 h. The resulting light green powder is nano-flower-like layered nickel silicate.
[0072] In some embodiments, the second solution is heated to 88°C and the reaction time is within the range of 10 hours. After the reaction is completed, the flask is transferred from the oil bath, and after the green suspension is cooled for 9 hours, it is centrifuged, washed with deionized water, and dried in an oven at 65°C for 22 hours. The resulting light green powder is nano-flower-like layered nickel silicate.
[0073] In some embodiments, the reaction time is 25 hours after the second solution is heated to 90°C. After the reaction is completed, the flask is removed from the oil bath, and the green suspension is cooled for 10 hours. After centrifugation, washing with deionized water, and drying in an oven at 70°C for 248 hours, the resulting light green powder is nano-flower-like layered nickel silicate.
[0074] Step S23: Prepare layered nickel silicate sensitive electrode 2; In this embodiment of the invention, step S23, preparing the layered nickel silicate sensitive electrode 2, includes: The prepared layered nickel silicate electrode slurry is coated on the solid electrolyte 1, and the reference electrode 3 is on the same side of the solid electrolyte 1. Then, it is placed at 120-180℃ for 20-40 minutes to allow the organic solvent in the electrode material to evaporate completely. Then, the solid electrolyte 1 is coated, and platinum dots 4 are applied to the sensitive electrode and connected with a platinum wire of about 5 cm to form the layered nickel silicate sensitive electrode 2.
[0075] In some embodiments, step S23, preparing the layered nickel silicate sensitive electrode 2, includes: The prepared layered nickel silicate electrode slurry is coated on the solid electrolyte 1, with the reference electrode 3 on the same side of the solid electrolyte 1. Then, it is placed at 120°C for 20 minutes to allow the organic solvent in the electrode material to evaporate completely. The solid electrolyte 1 is then calcined at 300°C for 1.5 hours to form the layered nickel silicate sensitive electrode 2.
[0076] In some embodiments, step S23, preparing the layered nickel silicate sensitive electrode 2, includes: The prepared layered nickel silicate electrode slurry was coated on the solid electrolyte 1, with the reference electrode 3 on the same side of the solid electrolyte 1. Then, it was placed at 180°C for 40 minutes to allow the organic solvent in the electrode material to evaporate completely. The solid electrolyte 1 was then calcined at 400°C for 2.5 hours to form the layered nickel silicate sensitive electrode 2.
[0077] In some embodiments, step S23, preparing the layered nickel silicate sensitive electrode 2, includes: The prepared layered nickel silicate electrode slurry was coated on the solid electrolyte 1, with the reference electrode 3 on the same side of the solid electrolyte 1. Then, it was placed at 140°C for 25 minutes to allow the organic solvent in the electrode material to evaporate completely. The solid electrolyte 1 was then calcined at 320°C for 1.8 hours to form the layered nickel silicate sensitive electrode 2.
[0078] In some embodiments, step S23, preparing the layered nickel silicate sensitive electrode 2, includes: The prepared layered nickel silicate electrode slurry was coated on the solid electrolyte 1, with the reference electrode 3 on the same side of the solid electrolyte 1. Then, it was placed at 160°C for 35 minutes to allow the organic solvent in the electrode material to evaporate completely. The solid electrolyte 1 was then calcined at 380°C for 2.2 hours to form the layered nickel silicate sensitive electrode 2.
[0079] In some embodiments, step S23, preparing the layered nickel silicate sensitive electrode 2, includes: The prepared layered nickel silicate electrode slurry was coated on the solid electrolyte 1, with the reference electrode 3 on the same side of the solid electrolyte 1. Then, it was placed at 150°C for 30 minutes to allow the organic solvent in the electrode material to evaporate completely. The solid electrolyte 1 was then calcined at 350°C for 2.0 hours to form the layered nickel silicate sensitive electrode 2.
[0080] In this embodiment of the invention, the preparation of the layered nickel silicate electrode slurry includes the following steps: Terpineol and ethyl cellulose were mixed at a mass ratio of 9:1 to obtain modified terpineol; layered nickel silicate electrode slurry was weighed, and the modified terpineol was added dropwise at a mass ratio of 3:1 between terpineol and layered nickel silicate material, and then the mixture was ground thoroughly for 1 hour to obtain layered nickel silicate electrode slurry.
[0081] In some embodiments, the preparation of the layered nickel silicate electrode paste includes the following steps: Terpineol and ethyl cellulose were mixed at a mass ratio of 7:1 to obtain modified terpineol; layered nickel silicate electrode slurry was weighed, and the modified terpineol was added dropwise at a mass ratio of 2:1 between terpineol and layered nickel silicate material, and then the mixture was ground thoroughly for 0.6 hours to obtain layered nickel silicate electrode slurry.
[0082] In some embodiments, the preparation of the layered nickel silicate electrode paste includes the following steps: Terpineol and ethyl cellulose were mixed at a mass ratio of 1:1 to obtain modified terpineol; layered nickel silicate electrode slurry was weighed, and the modified terpineol was added dropwise at a mass ratio of 4:1 between terpineol and layered nickel silicate material, and then the mixture was ground thoroughly for 1.4 hours to obtain layered nickel silicate electrode slurry.
[0083] In some embodiments, the preparation of the layered nickel silicate electrode paste includes the following steps: Terpineol and ethyl cellulose were mixed at a mass ratio of 8:1 to obtain modified terpineol; layered nickel silicate electrode slurry was weighed, and the modified terpineol was added dropwise at a mass ratio of 2.5:1 between terpineol and layered nickel silicate material, and then the mixture was ground thoroughly for 0.8 hours to obtain layered nickel silicate electrode slurry.
[0084] In some embodiments, the preparation of the layered nickel silicate electrode paste includes the following steps: Terpineol and ethyl cellulose were mixed at a mass ratio of 10:1 to obtain modified terpineol; layered nickel silicate electrode slurry was weighed, and the modified terpineol was added dropwise at a mass ratio of terpineol to layered nickel silicate material of 3.5:1, and then the mixture was ground thoroughly for 1.2 hours to obtain layered nickel silicate electrode slurry.
[0085] Step S24: Attach two Pt wires to the middle position of the layered nickel silicate sensitive electrode 2 with dotted Ag paste to serve as electrode leads; place the heating element 6 on the ceramic plate 7 and place the solid electrolyte prepared above on the heating element 6.
[0086] Step S25: Solder and package the obtained device to obtain a hybrid potential type ammonia gas sensor.
[0087] Performance testing: The performance of the fabricated sensor was tested using traditional static testing methods. A data acquisition instrument was used to measure the electromotive force between the sensor's sensitive electrode 2 and reference electrode 3. The sensor's output potential was synchronously recorded via a connection between the data acquisition instrument and a computer. The layered nickel silicate sensitive electrode 2 was connected to the positive terminal of the data acquisition instrument, and the Pt reference electrode 3 was connected to the negative terminal. A constant voltage was applied across the heating element using a DC power supply (Wanptrk GPS3010D). By adjusting the power supply voltage, the temperature of the heating element was changed, thus placing the gas sensor at different operating temperatures. The actual temperature of the sensor was measured by multiple thermocouples.
[0088] Specific test results are as follows: Figures 1-5 .
[0089] Lamellar layered nickel silicate is designated as L-NIPS, nanotube layered nickel silicate as T-NIPS, and nanoflower-like layered nickel silicate as F-NIPS.
[0090] According to XRD patterns ( Figure 1a) For T-NIPS, characteristic diffraction peaks appeared at 11.90°, 19.88°, 24.9°, 34.10°, 36.84°, and 60.62°, corresponding to the (002), (110), (004), (200), (202), and (060) crystal planes, respectively. The (002) peak at 11.90° corresponds to an interlayer spacing of approximately 0.74 nm, indicating that its complete interlayer spacing is approximately 0.74 nm. Meanwhile, the (060) peak at 60.62° (d≈1.53 Å) confirms its trioctahedral structure, indicating that the synthesized T-NIPS is a well-crystallized 1:1 type monoclinic nickel serpentine with a trioctahedral structure. In contrast, the peak intensities of L-NIPS and F-NIPS are weaker, which is related to their lower synthesis temperature and shorter synthesis time, resulting in poorer crystallinity. Furthermore, it is worth noting that the low-angle interlayer peaks of L-NIPS and F-NIPS are significantly broadened and exhibit a certain shift, mainly due to the distortion caused by the disordered nature of the monoclinic phase interlayer spacing. Based on the (002) peak, the interlayer spacings of L-NIPS and F-NIPS were calculated to be 1.24 nm and 1.32 nm, respectively. Meanwhile, the (060) peak at 60.6° (d≈1.53 Å) confirms that both exhibit trioctahedral structural characteristics.
[0091] FT-IR spectroscopy is an effective method for verifying the formation of layered nickel silicate structures. Figure 1 Figure b shows the FT-IR spectra of three Ni-PS structures. In the Ni-PS structure, Ni coordinates with O or -OH to form nickel-oxygen octahedra, Si coordinates with O to form silicon-oxygen tetrahedra, and Ni and Si are bonded through oxygen bridges to form Ni-O-Si. Figure 1 As can be seen in b, for the three types of Ni-PS, at 472 cm⁻¹ -1 The characteristic peak observed at 3642 cm⁻¹ is attributed to the Si-O bond stretching vibration. -1 The characteristic peak is attributed to the stretching vibration of the structural hydroxyl group -OH. Additionally, at 1028 cm⁻¹... -1 and 670 cm -1 The characteristic peaks observed at 3446 cm⁻¹ are attributed to the stretching vibrations of the Si-O-Ni bond and Ni-O, respectively. These structures collectively confirm that the three synthesized Ni-PS are all layered nickel silicates. Furthermore, at 3446 cm⁻¹... -1 and 1632 cm -1 Characteristic peaks at 3446 cm⁻¹ were observed, attributed to the stretching vibration of OH and the bending vibration of HOH in physically adsorbed water molecules, respectively. The synergistic appearance of these two characteristic peaks confirms the presence of physically adsorbed water on the material surface. Compared to L-NIPS and F-NIPS, T-NIPS is located at 3446 cm⁻¹. -1 1632 cm-1 and 3642 cm -1 The significant increase in characteristic bands indicates that T-NIPS has more physically adsorbed water and structural hydroxyl groups.
[0092] SEM and TEM images confirmed the successful synthesis of layered nickel silicate with different morphologies. Figure 2 a shows that L-NIPS exhibits a rough, layered, sheet-like structure. In contrast, Figure 2 b, d, and e SEM and TEM images show that T-NIPS exhibits a nanotube morphology, characterized by being hollow and open at both ends. The nanotubes are approximately 60-80 nm in length and 10-20 nm in diameter, with the tube walls composed of several stacked layers, approximately 12-17 layers in total. Figure 2 c. F-NIPS exhibits a typical three-dimensional flower-like structure. SEM images show that its surface displays an interlaced, flower-like structure, with the "flowers" approximately 300 nm in diameter and the "petals" approximately 50 nm in diameter. The formation of T-NIPS may be attributed to the addition of a high concentration of NaOH during the reaction, which provides sufficient chemical potential to cause the sheet-like layered nickel silicate to release surface strain through self-rolling, forming a hollow tubular structure. This structure possesses a complex pore structure formed by the special pore size of nanotubes. In contrast, the nanoflower-like morphology is a typical flower-like structure formed by the tight adhesion of layered nickel silicate sheets, interlaced on a self-sacrificing spherical template. This structure also has an interlaced and complex pore structure.
[0093] Figure 3 Figures a and b show the dynamic response curves of the three sensors at ammonia concentrations ranging from 5 ppm to 200 ppm at room temperature (25°C) and 50°C, respectively. When the three sensors were exposed to an ammonia atmosphere, the open-circuit voltage signals shifted towards negative values, then reached a minimum. The open-circuit voltage shift of the three sensors increased with increasing temperature. Furthermore, when the sensors were re-exposed to air, the open-circuit voltage signals recovered to their initial values. The reaction behavior conforms to the mixed potential theory. A decreasing trend in the baseline open-circuit voltage of the three sensors was observed with increasing ammonia concentration. To further understand the performance of the three sensors, Figure 3c and d show the responses of the three sensors as a function of the logarithm of ammonia concentration at room temperature and 50°C, respectively. It clearly shows that the absolute values of the responses of the three sensors monotonically increase with increasing ammonia concentration. Regardless of the temperature, the response values and sensitivities of the three sensors follow the pattern: nanotube sensor > nanoflower sensor > sheet sensor. At room temperature, the response values of the three sensors to 50 ppm are -2 mV, -23 mV, and -38 mV, respectively, with the nanotube sensor's response being 19 times that of the sheet sensor. Compared to the most advanced hybrid potential ammonia sensor reported to date, the nanotube sensor achieves the same or even higher response values at room temperature as high-temperature ammonia sensors. Figure 4 ).
[0094] Based on the above test results, a nanotube sensor was selected to further study its other performance characteristics. Figure 5 Figures a and c show the consistency of the test results of the two nanotube sensors at room temperature, and the results of six repeated tests of the nanotube sensor at room temperature on 50 ppm ammonia, respectively. This indicates that the nanotube sensor exhibits good consistency and repeatability. Figure 5 b shows the response value of the nanotube sensor to ammonia gas during continuous testing from day 1 to day 50. It can be seen that during the 50-day measurement period, the response value of the nanotube sensor to ammonia gas fluctuated little, with no significant decrease and no significant change in the volatility, indicating that the nanotube sensor has good long-term stability. Figure 5 The data shows that as humidity gradually increases, the sensitivity of the nanotube sensor to ammonia gradually decreases at room temperature.
[0095] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.
[0096] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.
Claims
1. A hybrid potential type ammonia gas sensor, characterized in that, include: A layered nickel silicate sensitive electrode, a reference electrode, and a solid electrolyte; the layered nickel silicate sensitive electrode and the reference electrode are located on the surface of the solid electrolyte; the layered nickel silicate sensitive electrode is made of three different morphologies of layered nickel silicate electrode slurries.
2. A method for preparing a hybrid potential type ammonia sensor as described in claim 1, characterized in that, Includes the following steps: Preparation of reference electrode; Preparation of layered nickel silicate electrode paste; Fabrication of layered nickel silicate sensitive electrodes; Two Pt wires were attached to the middle of the layered nickel silicate sensitive electrode with dotted Ag paste to serve as electrode leads; the heating element was placed on a ceramic plate, and the solid electrolyte prepared above was placed on the heating element; The obtained device is welded and packaged to obtain a hybrid potential type ammonia gas sensor.
3. The method for preparing a hybrid potential type ammonia sensor according to claim 2, characterized in that, Before step S21, the method further includes: preparing a solid electrolyte, specifically including: NASICON powder was synthesized via the sol-gel method. PVA solution was added to the prepared NASICON powder and the mixture was ground to obtain powder. The powder was then pressed into shape and sintered to obtain solid electrolyte NASICON.
4. The method for preparing a hybrid potential type ammonia sensor according to claim 2, characterized in that, A method for preparing layered nickel silicate electrode paste includes the following steps: Synthetic layered nickel silicate; Layered nickel silicate is calcined in air to obtain layered nickel silicate electrode paste.
5. The method for preparing a hybrid potential type ammonia sensor according to claim 4, characterized in that, The synthesis of nanotube-shaped layered nickel silicate includes the following steps: Nickel chloride hexahydrate, sodium silicate nonahydrate, and sodium hydroxide are dissolved in deionized water according to a preset ratio and stirred until completely dissolved to obtain the first solution. The first solution was transferred to a reaction vessel for underwater thermal reaction. After the reaction was completed, it was cooled to room temperature. The reaction product was then centrifuged, washed, and dried to obtain nanotube-shaped layered nickel silicate.
6. The method for preparing a hybrid potential type ammonia sensor according to claim 4, characterized in that, The synthesis of layered nickel silicate includes the following steps: Prepare dry MOF powder; Dry MOF powder and sodium silicate nonahydrate were magnetically dispersed in an equal volume of anhydrous ethanol / water solution according to a certain ratio. Then, sodium hydroxide solution was added dropwise and ultrasonic stirring was performed continuously. After the suspension was reacted underwater for a period of time, it was washed several times by centrifugation with deionized water and anhydrous ethanol, and then vacuum dried to obtain light green lamellar nickel silicate.
7. The method for preparing a hybrid potential type ammonia sensor according to claim 4, characterized in that, The synthesis of layered nickel silicate includes the following steps: Silicon dioxide, nickel nitrate hexahydrate, and urea were added to the flask in sequence according to the preset molar ratio. Then, dilute nitric acid solution was added and stirred until the solute was completely dissolved to obtain the second solution. The second solution was heated to obtain a green suspension. After the reaction was completed, the green suspension was cooled for a period of time, then centrifuged, washed with deionized water and dried to obtain light green powder nano-flower-shaped layered nickel silicate.
8. The method for preparing a hybrid potential type ammonia sensor according to claim 2, characterized in that, The preparation of the reference electrode includes the following steps: The first raw material slurry is coated onto the solid electrolyte and kept at 120-180℃ for 20-40 minutes to allow the organic solvent in the Pt slurry to evaporate completely. The electrolyte substrate 1 is then calcined at 800-1200℃ for 20-40 minutes. Pt dots are then applied to the reference electrode and connected with Pt wires to form the reference electrode.
9. The method for preparing a hybrid potential type ammonia sensor according to claim 2, characterized in that, The preparation of the layered nickel silicate sensitive electrode includes the following steps: The prepared layered nickel silicate electrode slurry is coated on a solid electrolyte, with the reference electrode on the same side of the solid electrolyte. Then, it is placed at 120-180℃ for 20-40 minutes to allow the organic solvent in the electrode material to evaporate completely. Then, the solid electrolyte is applied, and Pt dots are applied to the sensitive electrode and connected with Pt wires to form a layered nickel silicate sensitive electrode.
10. The method for preparing a hybrid potential type ammonia sensor according to claim 9, characterized in that, The preparation of the layered nickel silicate electrode paste includes the following steps: Terpineol and ethyl cellulose were mixed at a mass ratio of 9:1 to obtain modified terpineol; layered nickel silicate electrode slurry was weighed, and the modified terpineol was added dropwise at a mass ratio of 3:1 between terpineol and layered nickel silicate material, and then the mixture was thoroughly ground for 0.6-1.4 hours to obtain layered nickel silicate electrode slurry.