Platinum-rhodium-based electrode slurry and preparation method and application thereof

Abstract

The invention relates to the technical field of sensors, and discloses platinum-rhodium-based electrode slurry as well as a preparation method and application thereof. The platinum-rhodium-based electrode slurry comprises the following raw materials in percentage by weight: 34%-49% of platinum powder, 10%-14% of rhodium powder, 7.1%-10% of a zinc oxide-nickel oxide compound, 5.2%-6.4% of yttria-stabilized zirconia, 23%-38% of an organic binder and 0.5%-1.2% of an inorganic binder, wherein the organic binder is prepared from the following raw materials: terpilenol, dibutyl phthalate, ethyl cellulose and polyaniline modified polyethylene glycol. The electrode slurry provided by the invention has relatively good rheological property and stability, and is not easy to generate a slurry phase separation phenomenon after long-time storage, the printing property of the slurry is improved, and the electrode morphology and the three-phase interface length of a formed sensitive electrode can be improved, so that the sensitive electrode has relatively high catalytic activity.

Description

Technical Field

[0001] The present invention relates to the technical field of sensors, and particularly relates to a platinum-rhodium-based electrode paste, a preparation method thereof, and an application thereof. Background Art

[0002] With the continuous growth of the automobile ownership, the environmental pollution caused by automobile exhaust is also deteriorating, and the emission of atmospheric pollutant NOx (nitrogen oxides) is particularly prominent. The selective catalytic reduction system (SCR) is one of the main emission treatment technologies for NOx at present. The SCR requires a sensor that can quickly respond to the change in the concentration of nitrogen oxides, that is, a nitrogen oxide sensor (NOx sensor), and the NOx sensor is installed upstream and downstream of the SCR.

[0003] Currently, the most commonly used is the current-type NOx sensor. The detection component of this sensor is a ceramic chip, which is co-fired by six layers of YSZ (yttria-stabilized zirconia) and includes two internal cavities, three oxygen pump cells, and a heater. Its basic principle is that the exhaust gas enters the first chamber (oxygen pump layer) at a certain rate after passing through the diffusion channel. The oxygen pump cell in the chamber controls the oxygen concentration at a preset level through feedback control, and the following reaction occurs: NO2→2NO2+O2.

[0004] After the exhaust gas is treated in the first chamber, the exhaust gas containing low-concentration oxygen enters the second chamber at a certain diffusion rate through the second diffusion channel. This chamber contains an oxygen pump cell and a sensitive electrode, and the oxygen pump cell further controls the oxygen concentration in the chamber to be close to 0 (about 10 -3 ppm). The sensitive electrode is actually also a pump cell, which is specifically used to measure the oxygen concentration after the decomposition of NOx. Since the oxygen in the second chamber is further pumped out, the balance of the reaction between O2 and NO is broken, resulting in the decomposition of NO on the sensitive electrode, and the following reaction mainly occurs: 2NO→N2+O2. After the decomposed oxygen is pumped away by the oxygen pump cell, by measuring the corresponding pump oxygen current, the finally decomposed oxygen concentration can be obtained, and the effect of measuring NOx can be achieved through conversion.

[0005] From the structural principle, it can be seen that the sensitive electrode is an important component in the NOx sensor and is the key activation electrode. When preparing the sensitive electrode, the sensitive electrode paste is printed on the surface of the solid electrolyte and forms the sensitive electrode after high-temperature sintering. The components of the sensitive electrode paste include platinum powder (Pt powder), rhodium powder (Rh powder), inorganic binder, and organic binder. Among them, the organic binder is prepared from ethyl cellulose and organic solvent. The existing organic binder can disperse the powder materials. However, it has poor thixotropy, which affects the rheology and storage stability of the paste. Especially during long-time printing, phase separation of the paste easily occurs, and the printability of the paste is poor, which affects the length of the three-phase interface of the prepared sensitive electrode and the morphology of the sensitive electrode. Although the sensitive electrode is active for the decomposition of NOx at temperatures above 800 °C, the corresponding sensor cannot detect low-concentration (<100 ppm) NOx well, and there is also a problem of slow response speed for the detection of NOx. Summary of the Invention

[0006] The main object of the present invention is to provide a platinum-rhodium-based electrode paste, its preparation method and application, aiming to solve the problems of poor rheology and poor storage stability of the sensitive electrode paste in the prior art.

[0007] To achieve the above object, the present invention provides a platinum-rhodium-based electrode paste, which comprises the following raw materials in parts by weight: 34-49% of platinum powder; 10-14% of rhodium powder; 7.1-10% of zinc oxide-nickel oxide composite; 5.2-6.4% of yttria-stabilized zirconia; 23-38% of organic binder; 0.5-1.2% of inorganic binder; wherein, the preparation raw materials of the organic binder include terpineol, dibutyl phthalate, ethyl cellulose, and polyaniline-modified polyethylene glycol.

[0008] Optionally, the preparation method of the polyaniline-modified polyethylene glycol comprises the following steps: S1. Mix polyethylene glycol and N,N-dimethylformamide, heat, drop in thionyl chloride, carry out the reaction, collect the crude product of the reaction, adjust the pH of the crude product to neutral, vacuum dry, filter to remove impurities, and obtain polyethylene glycol chloride; S2. Mix p-aminophenol, sodium hydroxide, and tetrabutylammonium bromide, stir, add the polyethylene glycol chloride obtained in the step S1, heat and react, carry out solid-liquid separation on the reactant, distill the separated liquid, and vacuum dry the distillation product to obtain polyethylene glycol amino compound; S3. Mix the polyethylene glycol amino compound obtained in the step S2, ammonium persulfate, and hydrochloric acid, control the temperature of the mixture to be lower than 3 °C, under the condition of a protective atmosphere, stir and react, dropwise add a mixed solution of aniline and hydrochloric acid, react at 0 °C, filter, wash, and dry the reaction product to obtain the polyaniline-modified polyethylene glycol.

[0009] Optionally, in the step S1, the molar ratio of polyethylene glycol, N,N-dimethylformamide, and thionyl chloride is (0.08~0.11):(0.05~0.07):(0.2~0.4); and / or, in the step S2, the molar ratio of p-aminophenol, sodium hydroxide, tetrabutylammonium bromide, and polyethylene glycol chloride is (0.19~0.21):(0.75~0.89):(0.003~0.004):(0.09~0.11); and / or, in the step S3, the molar ratio of the polyethylene glycol amino compound, ammonium persulfate, and aniline is (0.01~0.03):(0.10~0.15):(0.1~0.2).

[0010] Optionally, the weight ratio of terpineol, dibutyl phthalate, ethyl cellulose, and polyaniline-modified polyethylene glycol is (65~73):(9~20):(5~10):(7~15).

[0011] Preferably, the weight ratio of terpineol, dibutyl phthalate, ethyl cellulose, and polyaniline-modified polyethylene glycol is (68~70):13:7:(10~12).

[0012] More preferably, the weight ratio of terpineol, dibutyl phthalate, ethyl cellulose, and polyaniline-modified polyethylene glycol is 68:13:7:12.

[0013] Optionally, the zinc oxide-nickel oxide composite is prepared by a hydrothermal method; the raw materials for preparing the zinc oxide-nickel oxide composite include a zinc salt, a nickel salt, and sodium hydroxide, and the mass ratio of the zinc salt, the nickel salt, and the sodium hydroxide is (0.28~0.32):(0.26~0.30):(0.30~0.35).

[0014] Preferably, the zinc salt includes zinc nitrate hexahydrate, and the nickel salt includes nickel nitrate hexahydrate.

[0015] Optionally, the platinum-rhodium-based electrode paste includes the following raw materials in weight percentages: 39~44% of platinum powder, 12.5% of rhodium powder, 8.5% of zinc oxide-nickel oxide composite, 6% of yttria-stabilized zirconia, 28~33% of organic binder, and 1% of inorganic binder.

[0016] Optionally, the inorganic binder includes at least one of SiO2, B2O3, Bi2O3, Al2O3, MgO, CaO, ZrO2, and TiO2.

[0017] Preferably, the inorganic binder comprises: 13-15 wt% SiO2, 5-7 wt% B2O3, 62-68 wt% Bi2O3, 8-12 wt% Al2O3, 0.8-1.3 wt% MgO, 1-2 wt% CaO, 1-2 wt% ZrO2, and 0.5-1.5 wt% TiO2.

[0018] The present invention also provides a method for preparing a platinum-rhodium based electrode paste, comprising the following steps: Providing platinum powder, rhodium powder, zinc oxide-nickel oxide composite, yttria-stabilized zirconia, an inorganic binder, and an organic binder, adding the platinum powder, the rhodium powder, the zinc oxide-nickel oxide composite, the yttria-stabilized zirconia, and the inorganic binder into the organic binder, and fully stirring to obtain the platinum-rhodium based electrode paste.

[0019] The present invention also provides an application of the platinum-rhodium based electrode paste as described in any one of the above in a nitrogen oxide sensor. Specifically, the nitrogen oxide sensor comprises a ceramic chip, and the platinum-rhodium based electrode paste is used to prepare a sensitive electrode on the ceramic chip.

[0020] In the technical solution of the present invention, dibutyl phthalate has strong polar groups and is easy to combine with the hydroxyl groups on ethyl cellulose to form a multi-dimensional network structure; there are differences in the solubility of polyaniline and polyethylene glycol in the solvent in polyaniline-modified polyethylene glycol, so that polyaniline-modified polyethylene glycol has an aggregation property and can form a strip structure. The polyaniline-modified polyethylene glycol aggregates to form a strip structure, and dibutyl phthalate forms a multi-dimensional network structure with ethyl cellulose. The formed strip structure and network structure cooperate with each other, which can effectively improve the rheology and stability of the electrode paste, ensure the dispersibility of the electrode paste, and even after long-term storage, the phenomenon of paste phase separation is not likely to occur, improving the printability of the paste. Even after long-term printing, the printability of the paste can be better ensured, and further, the electrode morphology of the formed sensitive electrode and the length of the three-phase interface can be improved, so that the sensitive electrode has high catalytic activity, the corresponding sensor has a fast response speed, and can better detect low-concentration NOx.

[0021] Platinum powder (Pt powder) and rhodium powder (Rh powder) are used as functional phase powders and have the functions of catalysis and conductivity. Zinc oxide-nickel oxide (ZnO-NiO) composite and yttria-stabilized zirconia are used as additives, which can improve the length of the three-phase interface and the electrode morphology of the electrode to further improve the catalytic activity of the sensitive electrode. The inorganic binder can improve the adhesion between the electrode and the YSZ substrate, so that the formed electrode film is stably attached to the YSZ substrate, ensuring the conductivity and catalytic activity of the electrode. The corresponding sensor has a fast response speed and can better detect low-concentration NOx. Description of the Drawings

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art.

[0023] Figure 1 For the NOx sensors of Application Example 1 and Application Comparative Examples 1 to 4 of the present invention, the pump current I was measured under different concentrations of NO P2 The relationship diagram of the change with the NO concentration.

[0024] The realization of the object of the present invention, functional features and advantages will be further described with reference to the accompanying drawings in combination with the embodiments. Specific embodiments

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0026] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, such descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In addition, the meaning of "and / or" appearing throughout the text includes three parallel solutions. Taking "A and / or B" as an example, it includes Solution A, or Solution B, or the solution where A and B are satisfied simultaneously. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the fact that those of ordinary skill in the art can implement it. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present invention.

[0027] The electrode paste is a material for preparing sensitive electrodes, which includes platinum powder (Pt powder), rhodium powder (Rh powder), inorganic binder, and organic binder; when preparing sensitive electrodes, the electrode paste is printed on the surface of a solid electrolyte and sintered at high temperature. The organic binder is prepared from ethyl cellulose and organic solvents. Existing organic binders can disperse the powder materials. However, they have poor thixotropy, which affects the rheology and storage stability of the paste. Especially during long-term printing, phase separation of the paste easily occurs, resulting in poor printability of the paste, affecting the effective length of the three-phase interface of the prepared sensitive electrode and the morphology of the sensitive electrode. Although the sensitive electrode has activity for the decomposition of NOx at temperatures above 800 °C, it cannot detect low-concentration (<100 ppm) NOx well, and the response speed of the corresponding sensor is slow.

[0028] In view of this, the present invention provides a platinum-rhodium-based electrode paste, its preparation method and application to solve the problems of poor rheology and poor storage stability of the existing sensitive electrode paste.

[0029] In the present invention, a platinum-rhodium-based electrode paste comprises raw materials in the following weight percentages: 34-49% of platinum powder, 10-14% of rhodium powder, 7.1-10% of zinc oxide-nickel oxide composite, 5.2-6.4% of yttria-stabilized zirconia, 23-38% of organic binder, and 0.5-1.2% of inorganic binder; wherein, the preparation raw materials of the organic binder include terpineol, dibutyl phthalate, ethyl cellulose, and polyaniline-modified polyethylene glycol.

[0030] In the technical solution of the present invention, dibutyl phthalate has strong polar groups and can easily combine with the hydroxyl groups on ethyl cellulose to form a multi-dimensional network structure; there are differences in the solubility of polyaniline and polyethylene glycol in the solvent in polyaniline-modified polyethylene glycol, and polyaniline-modified polyethylene glycol has an aggregation property and can form a strip structure. The strip structure formed by the aggregation of polyaniline-modified polyethylene glycol and the multi-dimensional network structure formed by dibutyl phthalate and ethyl cellulose cooperate with each other, which can effectively improve the rheology and stability of the electrode paste, ensure the dispersibility of the electrode paste, and phase separation of the paste is not likely to occur even after long-term storage, improving the printability of the paste. Even during long-term printing, the printability of the paste can be well ensured, thereby improving the electrode morphology and the length of the three-phase interface of the formed sensitive electrode, enabling the sensitive electrode to have high catalytic activity, the corresponding sensor to have a fast response speed, and being able to detect low-concentration NOx well.

[0031] Platinum powder (Pt powder) and rhodium powder (Rh powder), as functional phase powders, have the functions of catalysis and conductivity. Zinc oxide-nickel oxide (ZnO-NiO) composite and yttria-stabilized zirconia as additives can improve the length of the three-phase interface of the electrode and the electrode morphology, so as to further improve the catalytic activity of the sensitive electrode. The inorganic binder can improve the adhesion between the electrode and the YSZ substrate, making the formed electrode film stably adhere to the YSZ substrate, ensuring the conductivity and catalytic activity of the electrode. The corresponding sensor has a fast response speed and can better detect low-concentration NOx.

[0032] It should be noted that if the dosage of the organic binder is too low, the effect of dispersion stability is lacking, and the phenomenon of slurry phase separation is likely to occur. The printability of the slurry is poor, which affects the length of the three-phase interface of the sensitive electrode and the electrode morphology, and cannot well ensure the catalytic activity of the prepared sensitive electrode, affecting the response speed of the prepared sensor and the detection of low-concentration NOx; if the dosage of the organic binder is too high, it is easy to affect the rheology of the slurry, and to a certain extent, dilute the functional phase powder, which will also affect the catalytic activity of the prepared sensitive electrode, affecting the response speed of the prepared sensor and the detection of low-concentration NOx. If the dosage of the inorganic binder is too low, the adhesion of the sensitive electrode is affected. If the dosage of the inorganic binder is too high, it is easy to affect the conductivity of the sensitive electrode.

[0033] The average particle size of Pt powder is 0.5 - 1 μm, and the average particle size of Rh powder is 0.5 - 0.8 μm; the yttria-stabilized zirconia is 5 mol% yttria-stabilized zirconia (5YSZ); the particle size of the inorganic binder is 400 mesh.

[0034] Furthermore, the preparation method of the polyaniline-modified polyethylene glycol includes the following steps: S1. Provide polyethylene glycol and N,N-dimethylformamide, mix polyethylene glycol and N,N-dimethylformamide, heat, drop in thionyl chloride, carry out the reaction, collect the crude product of the reaction, adjust the pH of the crude product to neutral, vacuum dry, filter to remove impurities, and obtain polyethylene glycol chloride; S2. Mix p-aminophenol, sodium hydroxide and tetrabutylammonium bromide, stir, add the polyethylene glycol chloride prepared in step S1, heat and react, carry out solid-liquid separation on the reactant, distill the separated liquid, and vacuum dry the distillation product to obtain polyethylene glycol amino compound; S3. Mix the polyethylene glycol amino compound prepared in step S2, ammonium persulfate and hydrochloric acid, control the temperature of the mixture to be lower than 3°C, stir and react under the condition of a protective atmosphere, dropwise add the mixed solution of aniline and hydrochloric acid, react under the condition of 0°C, filter, wash and dry the reaction product to obtain the polyaniline-modified polyethylene glycol.

[0035] By adopting the above technical solution, through specific raw materials and preparation processes, polyaniline-modified polyethylene glycol with better performance can be prepared. It should be noted that in step S1, adjusting the pH of the washed product to neutral means adjusting the pH value of the washed product to 7; in step S3, the protective atmosphere can be nitrogen. Of course, according to actual needs, it can also be other single gases or mixed gases.

[0036] Furthermore, in the said step S1, the molar ratio of polyethylene glycol, N,N-dimethylformamide, and thionyl chloride is (0.08~0.11):(0.05~0.07):(0.2~0.4); and / or, In the said step S2, the molar ratio of p-aminophenol, sodium hydroxide, tetrabutylammonium bromide, and polyethylene glycol chloride is (0.19~0.21):(0.75~0.89):(0.003~0.004):(0.09~0.11); and / or, In the said step S3, the molar ratio of the polyethylene glycol amino compound, ammonium persulfate, and aniline is (0.01~0.03):(0.10~0.15):(0.1~0.2).

[0037] By adopting the above technical solution, through specific ratios among the raw materials, polyaniline-modified polyethylene glycol can be preferably prepared. It should be noted that the molecular weight of the polyethylene glycol (PEG) in step S1 is 400, that is, the polyethylene glycol is PEG-400.

[0038] Furthermore, the weight ratio of the terpineol, the dibutyl phthalate, the ethyl cellulose, and the polyaniline-modified polyethylene glycol is (65~73):(9~20):(5~10):(7~15).

[0039] By adopting the above technical solution, by compounding terpineol, dibutyl phthalate, ethyl cellulose, and polyaniline-modified polyethylene glycol according to a specific ratio to form an organic binder, the dispersion stability of the slurry can be preferably improved.

[0040] Furthermore, the weight ratio of the terpineol, the dibutyl phthalate, the ethyl cellulose, and the polyaniline-modified polyethylene glycol is (68~70):13:7:(10~12).

[0041] By adopting the above technical solution, by further optimizing the dosage ratios of terpineol, dibutyl phthalate, ethyl cellulose, and polyaniline-modified polyethylene glycol, the dispersion stability of the slurry can be improved to a large extent.

[0042] Further, the zinc oxide-nickel oxide composite is prepared by a hydrothermal method. The raw materials for preparing the zinc oxide-nickel oxide composite include a zinc salt, a nickel salt, and sodium hydroxide, and the mass ratio of the zinc salt, the nickel salt, and the sodium hydroxide is (0.28-0.32):(0.26-0.30):(0.30-0.35).

[0043] By adopting the above technical solution, the prepared ZnO-NiO composite presents a multi-layer flaky structure, which can be well matched with YSZ to improve the effective length of the three-phase interface and the electrode morphology of the Pt-Rh based electrode. It should be noted that the average particle size of YSZ is 0.2-0.4 μm.

[0044] Further, the Pt-Rh based electrode paste includes the following raw materials in weight percentages: 39-44% of platinum powder, 12.5% of rhodium powder, 8.5% of zinc oxide-nickel oxide composite, 6% of yttria-stabilized zirconia, 28-33% of organic binder, and 1% of inorganic binder.

[0045] Further, the inorganic binder includes at least one of SiO2, B2O3, Bi2O3, Al2O3, MgO, CaO, ZrO2, and TiO2.

[0046] By adopting the above technical solution, the inorganic binder melts during sintering and has good flow wettability, so that the electrode is stably attached to the surface of the YSZ substrate.

[0047] The present invention also provides a preparation method of a Pt-Rh based electrode paste, including the following steps: Providing platinum powder, rhodium powder, zinc oxide-nickel oxide composite, yttria-stabilized zirconia, inorganic binder, and organic binder, adding the platinum powder, the rhodium powder, the zinc oxide-nickel oxide composite, the yttria-stabilized zirconia, and the inorganic binder into the organic binder, and fully stirring to obtain the Pt-Rh based electrode paste.

[0048] In the technical solution of the present invention, platinum powder (Pt powder) and rhodium powder (Rh powder) are used as the functional phase powders, and zinc oxide-nickel oxide (ZnO-NiO) composite and yttria-stabilized zirconia (YSZ) are used as additives, which can improve the length of the three-phase interface of the electrode and the electrode morphology, so as to further improve the catalytic activity of the sensitive electrode. The inorganic binder can improve the adhesion between the electrode and the YSZ substrate, so that the formed electrode film is stably attached to the YSZ substrate, ensuring the electrical conductivity and catalytic activity of the electrode. The corresponding sensor has a fast response speed and can better detect low concentrations of NOx. The organic binder can effectively improve the rheology and stability of the electrode paste, ensure the dispersibility of the electrode paste, and is not prone to paste phase separation even after long-term storage, improving the printability of the paste. Even after long-term printing, the printability of the paste can be well ensured, and then the electrode morphology and the length of the three-phase interface of the formed sensitive electrode can be improved, so that the sensitive electrode has high catalytic activity. The corresponding sensor has a fast response speed and can better detect low concentrations of NOx.

[0049] The present invention also provides an application of any of the above platinum-rhodium-based electrode pastes in a nitrogen oxide sensor. Specifically, the nitrogen oxide sensor includes a ceramic chip, and the platinum-rhodium-based electrode paste is used to prepare a sensitive electrode on the ceramic chip.

[0050] The technical solution of the present invention will be further described in detail below in conjunction with specific embodiments and the accompanying drawings. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention. Example 1

[0051] A method for preparing a platinum-rhodium-based electrode paste includes the following steps: (1) Preparation of an inorganic binder After grinding and mixing 14wt% SiO2, 6wt% B2O3, 65wt% Bi2O3, 10wt% Al2O3, 1wt% MgO, 1.5wt% CaO, 1.5wt% ZrO2, and 1wt% TiO2, it is placed in a crucible and heated in a high-temperature furnace to 1400°C for 30 minutes. The molten glass water is quenched in deionized water to obtain particulate matter. The particulate matter is dried and then ground and pulverized in a ball mill and passed through a 400-mesh sieve. The material passing through the sieve is the inorganic binder. Among them, SiO2, B2O3, Bi2O3, Al2O3, MgO, CaO, ZrO2, and TiO2 are all of analytical purity.

[0052] (2) Preparation of an organic binder 70wt% terpineol, 13wt% dibutyl phthalate, 7wt% ethyl cellulose, and 10wt% polyaniline-modified polyethylene glycol were mixed, heated at 90°C, stirred with a magnetic stirrer, and fully mixed to obtain an organic binder, wherein the terpineol was analytically pure, the ethyl cellulose was chemically pure, and the purity of dibutyl phthalate was 99%.

[0053] (3) Preparation of platinum-rhodium electrode slurry 44wt% of Pt powder with an average particle size of 0.7μm, 12.5wt% of Rh powder with an average particle size of 0.6μm, 8.5wt% of ZnO-NiO composite, 6wt% of 5mol% yttria-stabilized zirconia (5YSZ) with an average particle size of 0.3μm, and 1wt% of inorganic binder were added to 28wt% of organic binder, stirred and mixed thoroughly to prepare platinum-rhodium based electrode slurry.

[0054] Wherein, in step (2), the preparation method of polyaniline-modified polyethylene glycol comprises the following steps: S1. Prepare materials according to the molar ratio of PEG-400, N,N-dimethylformamide and thionyl chloride of 0.1:0.06:0.3; add PEG-400 and N,N-dimethylformamide into a reaction container, heat to 50°C, drop thionyl chloride into the reaction container, react at 60°C under reflux conditions for 6 hours, cool the reaction solution, wash with saturated brine, collect the crude product, adjust the pH value to 7.0 with anhydrous potassium carbonate, vacuum dry to remove moisture, filter to remove sodium chloride, and obtain the product polyethylene glycol chloride.

[0055] S2. Prepare materials according to the molar ratio of p-aminophenol, sodium hydroxide, tetrabutylammonium bromide, polyethylene glycol chloride, and dichloromethane of 0.205:0.82:0.004:0.1:1.56; add p-aminophenol, sodium hydroxide and tetrabutylammonium bromide into a reaction vessel, stir at room temperature (25°C) at a stirring rate of 100 rpm for 10 minutes, add dry polyethylene glycol chloride, and after the reaction is naturally exothermic, heat the mixture to 60°C, and stir at a constant temperature at a stirring rate of 100 rpm for 24 hours; after the reaction liquid is cooled, add dichloromethane into the reaction vessel to dissolve the crude product, separate the solid insoluble matter by centrifuge, distill the upper liquid at atmospheric pressure to remove dichloromethane, place the distillation product in a vacuum drying oven at 60°C for vacuum drying for 24 hours to obtain polyethylene glycol amino product.

[0056] S3. Dissolve polyethylene glycol amino compound in HCl solution to obtain mixture A. In mixture A, the concentration of polyethylene glycol amino compound is 0.01 mol / L, and the concentration of HCl is 0.99 mol / L. Dissolve ammonium persulfate in HCl solution to obtain mixture B. In mixture B, the concentration of ammonium persulfate is 0.11 mol / L, and the concentration of HCl is 0.89 mol / L. Dissolve aniline in HCl solution to obtain mixture C. In mixture C, the concentration of aniline is 0.1 mol / L, and the concentration of HCl is 0.9 mol / L.

[0057] S4. Add mixture A into a reaction vessel, place it in an ice-water bath, keep the temperature of mixture A below 3°C, add mixture B with a temperature below 3°C, evacuate and refill the reaction vessel with nitrogen, stir at a stirring rate of 100 rpm. When the solution in the reaction vessel turns purple, slowly add mixture C, and then react at 0°C for 24 h. Filter the reaction product with a Buchner funnel, wash it with deionized water until the filtrate is colorless. Wash the obtained product three times with 1 mol / L HCl solution and then vacuum dry it at 60°C for 24 h to obtain polyaniline-modified polyethylene glycol. Among them, the volume ratio of mixture A, mixture B, and mixture C is 1:1:1.

[0058] In step (3), the preparation method of the ZnO-NiO composite includes the following steps: Prepare materials according to the mass ratio of Zn(NO3)2·6H2O, Ni(NO3)2·6H2O, deionized water, and NaOH of 1:0.30:40:0.29; Add Zn(NO3)2·6H2O and Ni(NO3)2·6H2O into deionized water, stir magnetically, mix well, add NaOH, stir magnetically at room temperature (25°C) until a light green solution appears, transfer the reaction solution to a reaction kettle, keep it warm in a constant temperature air blast drying oven at 120°C for 7 h, naturally cool to room temperature, take out the reaction kettle, collect the precipitate by a centrifuge. During centrifugation, wash it 5 times with deionized water, dry the precipitate in a vacuum drying oven at 60°C, place the dried reactant in a muffle furnace, heat it to 500°C at a heating rate of 2°C / min, and keep it warm for 2 h to obtain the zinc oxide-nickel oxide composite.

[0059] Examples 2 - 9 Examples 2 - 4 are based on Example 1, the difference is that: in step (3), the dosage of the organic binder changes, and Pt powder is used to balance the change amount, specifically as shown in Table 1 below.

[0060] Examples 5 - 6 are based on Example 3, the difference is that: in step (3), the dosages of the raw materials other than the organic binder change, specifically as shown in Table 1 below.

[0061] Examples 7 to 9 are based on Example 3, with the difference that: in step (2), the dosage of polyaniline-modified polyethylene glycol changes, and terpineol is used to balance the change amount, as specifically shown in Table 2 below.

[0062] Table 1 Dosage of each raw material of the electrode paste (unit: wt%)

[0063] Table 2 Dosage of each raw material of the organic binder (unit: wt%)

[0064] Comparative Example 1 This comparative example is based on Example 1, with the difference that: in step (2), terpineol with an equal weight fraction is used to replace polyaniline-modified polyethylene glycol.

[0065] Comparative Example 2 This comparative example is based on Example 1, with the difference that: in step (2), terpineol with an equal weight fraction is used to replace dibutyl phthalate.

[0066] Comparative Example 3 This comparative example is based on Example 1, with the difference that: in step (3), Pt powder with an equal weight fraction is used to replace the ZnO-NiO composite.

[0067] Comparative Example 4 This comparative example is based on Example 1, with the difference that: in step (3), Pt powder with an equal weight fraction is used to replace 5YSZ.

[0068] Application Examples 1 to 9 and Application Comparative Examples 1 to 4 The current-type NOx sensors are respectively prepared from the platinum-rhodium-based electrode pastes prepared in Examples 1 to 9 and Comparative Examples 1 to 4, corresponding to Application Examples 1 to 9 and Application Comparative Examples 1 to 4 in sequence. The preparation method of the current-type NOx sensors in Application Examples 1 to 9 and Application Comparative Examples 1 to 4 includes the following steps: The green body of 5 mol% YSZ is prepared by the tape casting process. Various electrode pastes (including the pumping oxygen electrode paste, the sensitive electrode paste, and the reference electrode paste), the cavity filler, the insulating layer, the gas diffusion layer, and the protective layer are printed on the YSZ green body by screen printing. Among them, the sensitive electrode paste uses the platinum-rhodium-based electrode paste prepared in the corresponding Examples 1-9 and Comparative Examples 1-4, and the pumping oxygen electrode paste and the reference electrode paste use commercial Pt-based electrode pastes. The YSZ green body carrying each functional layer is placed in a drying oven and dried at 80 °C for 2 h, then subjected to warm pressing, lamination, and cutting to form individual ceramic chip green bodies, which are placed in a high-temperature furnace and co-fired at 1400 °C for 2 h to obtain ceramic chips. Among them, the thickness of the formed sensitive electrode is 10 μm. The obtained ceramic chips are connected to the control unit through connecting wires to obtain a current-type NOx sensor.

[0069] Performance test 1. Operating temperature test The operating temperatures of the sensors prepared in Examples 1-9 and Comparative Examples 1-4 are detected. Test gas: 21 vol% O2 + 0 vol% NO + the balance N2, and the oxygen content in the test gas is relatively close to that in the air. By changing the operating temperature of each sensor, the influence relationship of the corresponding operating temperature on the oxygen pumping ability of the main oxygen pump is obtained. From the relationship between the main oxygen pump current I p0 and the main oxygen pump voltage V p0 it can be concluded that the operating temperatures of the sensors prepared in Examples 1-9 and Comparative Examples 1-4 are about 800 °C.

[0070] 2. Single pump operation test The single-pump gas-sensing performance of the sensors prepared in Examples 1-9 and Comparative Examples 1-4 is tested.

[0071] (1) Separate operation test of the main oxygen pump Operating temperature: 800 °C; Test gas: 21 vol% O2 + 0 vol% NO + the balance N2; The auxiliary pump voltage V p1 and the measurement pump voltage V p2 are both 0 V. The main oxygen pump voltage V p0 is increased from 0.0 V to 1.2 V at a rate of 0.01 V / s, and the relationship between the main oxygen pump current I p0 and the main oxygen pump voltage V p0 is obtained. From this, it can be concluded that the main oxygen pump of the sensors prepared in Examples 1-9 and Comparative Examples 1-4 shows a limiting current plateau at 300-500 mV.

[0072] (2) Separate operation test of the auxiliary pump The operating temperature and the test gas are the same as those in the separate operation test of the main oxygen pump. The main oxygen pump voltage V p0With the measurement of the pump voltage V p2 Both are 0V, and the auxiliary pump voltage V p1 Increases from 0.0V to 1.2V at a rate of 0.01V / s to obtain the auxiliary pump current I p1 And the auxiliary pump voltage V p1 The relationship between them shows that the auxiliary pumps of the sensors prepared in Application Examples 1 to 9 and Application Comparative Examples 1 to 4 have a limiting current plateau at 750 - 900 mV.

[0073] (3)Measurement pump single - working test The working temperature and test gas are the same as those in the main oxygen pump single - working test. The main oxygen pump voltage V p0 And the auxiliary pump voltage V p1 Both are 0V, and the measurement pump voltage V p2 Increases from 0.0V to 1.2V at a rate of 0.01V / s to obtain the measurement pump current I p2 And the measurement pump voltage V p2 There is no limiting current plateau for each measurement pump voltage, and the current and voltage show a linear relationship.

[0074] 3. Joint test and response time test under an atmosphere environment Test conditions: The main oxygen pump voltage V p0 = 300 mV, the auxiliary pump voltage V p1 = 750 mV, the measurement pump voltage V p2 = 900 mV, the working temperature is 800 °C; Test gas: 15 vol% O2 + x vol% NO + the remaining nitrogen. The change in the NO gas concentration is obtained by adjusting the volume ratio of N2. Among them, the volume percentage of O2 is controlled at 15%.

[0075] (1)Make the NO concentration range from 0 to 2000 ppm to test the relationship curve between the NO concentration and the measurement pump current I p2 In the current - type NOx sensors of Application Example 1 and Application Comparative Examples 1 to 4, as shown in Figure 1 Shown.

[0076] From Figure 1 It can be seen that the nitrogen - oxygen sensor corresponding to Application Example 1 can better detect NOx with a concentration below 2000 ppm, and the output current signal of the nitrogen - oxygen sensor corresponding to Application Example 1 is significantly stronger than that of the nitrogen - oxygen sensors corresponding to Application Comparative Examples 1 to 4, indicating that the sensitive electrode corresponding to Application Example 1 has strong catalytic activity.

[0077] (2)Test of the response time. The response time refers to the measurement pump current I p2Time required for change with the change in gas volume fraction. The concentration of the NO standard gas is 300 ppm. During the process of testing the change in NO concentration from 0 ppm to 300 ppm, the time required for the change from 33% to 66%, and during the process of the change in NO concentration from 300 ppm to 0 ppm, the time required for the change from 66% to 33%, where 33% in 33% - 66% refers to 33% of the concentration of the NO standard gas (300 ppm), and 66% refers to 66% of the concentration of the NO standard gas (300 ppm). Then 33% - 66% refers to the rising response time corresponding to the process in which the concentration of NO rises from 33% of its standard gas concentration (300 ppm) to 66% of its standard gas concentration (300 ppm). Similarly, 66% - 33% corresponds to the falling response time. For Application Examples 1 - 9 and Application Comparative Examples 1 - 4, 33% - 66% and 66% - 33% are shown in Table 3 below.

[0078] Table 3 Rising response time and falling response time of NOX sensors

[0079] From the results in Table 3, it can be seen that the nitrogen oxide sensors corresponding to Application Examples 1 - 9 have relatively fast response times (rising response times) and recovery times (falling response times), indicating that the electrode paste prepared in the embodiments of the present invention has strong catalytic activity.

[0080] The response times and recovery times of the nitrogen oxide sensors corresponding to Application Comparative Example 1 and Application Comparative Example 2 are relatively slow. The reason may be that one of polyaniline - modified polyethylene glycol and dibutyl phthalate is missing in the raw materials for preparing the organic binder, which affects the dispersion stability of the paste, and further affects the effective length of the electrode triple phase interface and the electrode morphology, resulting in relatively slow response times and recovery times of the corresponding NOx sensors.

[0081] The response times and recovery times of the nitrogen oxide sensors corresponding to Application Comparative Example 3 and Application Comparative Example 4 are on the slow side. The reason may be that one of the ZnO - NiO composite and 5YSZ is missing in the raw materials for preparing the paste, which affects the effective length of the electrode triple phase interface and the electrode morphology, resulting in relatively slow response times and recovery times of the corresponding NOx sensors.

[0082] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the patent protection scope of the present invention.

Claims

1. A platinum-rhodium based electrode paste, characterized in that, It includes raw materials in the following weight percentages: 34 - 49% of platinum powder; 10 - 14% of rhodium powder; 7.1 - 10% of zinc oxide - nickel oxide composite; 5.2 - 6.4% of yttria - stabilized zirconia; 23 - 38% of organic binder; 0.5 - 1.2% of inorganic binder; Among them, the raw materials for preparing the organic binder include terpineol, dibutyl phthalate, ethyl cellulose, and polyaniline - modified polyethylene glycol.

2. The platinum-rhodium-based electrode paste according to claim 1, characterized in that, The preparation method of the polyaniline - modified polyethylene glycol includes the following steps: S1. Mix polyethylene glycol and N,N - dimethylformamide, heat, drop in thionyl chloride, carry out the reaction, collect the crude product of the reaction, adjust the pH of the crude product to neutral, carry out vacuum drying, filter to remove impurities, and obtain polyethylene glycol chloride; S2. Mix p - aminophenol, sodium hydroxide, and tetrabutylammonium bromide, stir, add the polyethylene glycol chloride obtained in step S1, carry out a heating reaction, carry out solid - liquid separation on the reactant, distill the separated liquid, and carry out vacuum drying on the distillation product to obtain polyethylene glycol amino compound; S3. Mix the polyethylene glycol amino compound, ammonium persulfate, and hydrochloric acid obtained in step S2, control the temperature of the mixture to be lower than 3°C, under the condition of a protective atmosphere, stir and react, dropwise add a mixed solution of aniline and hydrochloric acid, react under the condition of 0°C, filter, wash, and dry the reaction product to obtain the polyaniline - modified polyethylene glycol.

3. The platinum-rhodium-based electrode paste according to claim 2, wherein In step S1, the molar ratio of polyethylene glycol, N,N - dimethylformamide, and thionyl chloride is (0.08 - 0.11):(0.05 - 0.07):(0.2 - 0.4); and / or, In step S2, the molar ratio of p - aminophenol, sodium hydroxide, tetrabutylammonium bromide, and polyethylene glycol chloride is (0.19 - 0.21):(0.75 - 0.89):(0.003 - 0.004):(0.09 - 0.11); and / or, In step S3, the molar ratio of the polyethylene glycol amino compound, ammonium persulfate, and aniline is (0.01 - 0.03):(0.10 - 0.15):(0.1 - 0.2).

4. The platinum-rhodium-based electrode paste according to claim 1, wherein The weight ratio of terpineol, dibutyl phthalate, ethyl cellulose, and polyaniline - modified polyethylene glycol is (65 - 73):(9 - 20):(5 - 10):(7 - 15).

5. The platinum-rhodium based electrode paste according to claim 4, wherein The weight ratio of terpineol, dibutyl phthalate, ethyl cellulose, and polyaniline - modified polyethylene glycol is (68 - 70):13:7:(10 - 12).

6. The platinum-rhodium-based electrode paste according to claim 1, wherein The zinc oxide - nickel oxide composite is prepared by a hydrothermal method; The raw materials for preparing the zinc oxide - nickel oxide composite include zinc salt, nickel salt, and sodium hydroxide, and the mass ratio of the zinc salt, the nickel salt, and the sodium hydroxide is (0.28 - 0.32):(0.26 - 0.30):(0.30 - 0.35).

7. The platinum-rhodium-based electrode paste according to claim 1, wherein It includes raw materials in the following weight percentages: 39 - 44% of platinum powder, 12.5% of rhodium powder, 8.5% of zinc oxide - nickel oxide composite, 6% of yttria - stabilized zirconia, 28 - 33% of organic binder, 1% of inorganic binder.

8. The platinum-rhodium-based electrode paste according to claim 1, characterized in that, The inorganic binder includes at least one of SiO2, B2O3, Bi2O3, Al2O3, MgO, CaO, ZrO2, and TiO2.

9. A method for preparing a platinum-rhodium-based electrode paste, characterized in that, It includes the following steps: Providing platinum powder, rhodium powder, zinc oxide-nickel oxide composite, yttria-stabilized zirconia, an inorganic binder, and an organic binder, adding the platinum powder, the rhodium powder, the zinc oxide-nickel oxide composite, the yttria-stabilized zirconia, and the inorganic binder into the organic binder, and fully stirring to obtain the platinum-rhodium-based electrode paste.

10. A nitrogen oxide sensor, characterized in that, It includes a sensitive electrode, and the sensitive electrode is prepared from the platinum-rhodium-based electrode paste according to any one of claims 1 to 8.

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