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

Abstract

The present invention relates to the field of sensor technology, and discloses a platinum-rhodium-based electrode slurry and its preparation method and application. The platinum-rhodium-based electrode slurry includes the following raw materials in percentage by weight: 34-49% platinum powder, 10-14% rhodium powder, 7.1-10% zinc oxide-nickel oxide composite, 5.2-6.4% yttria-stabilized zirconia, 23-38% organic binder, and 0.5-1.2% inorganic binder; wherein, the raw materials for preparing the organic binder include terpineol, dibutyl phthalate, ethyl cellulose, and polyaniline-modified polyethylene glycol. The electrode slurry provided by the present invention has better rheology and stability, and is not prone to slurry phase separation phenomenon after long-term storage, thereby improving the printability of the slurry, and improving the electrode morphology of the formed sensitive electrode and the length of the three-phase interface so that the sensitive electrode has higher catalytic activity.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology, and in particular to a platinum-rhodium based electrode slurry and a preparation method and application thereof. Background Art

[0002] As the number of vehicles continues to grow, environmental pollution caused by vehicle exhaust is also worsening. NOx (nitrogen oxides) emissions are particularly prominent. Selective catalytic reduction (SCR) systems are currently one of the primary technologies for treating NOx emissions. SCR requires a sensor that can quickly respond to changes in nitrogen oxide concentrations—a nitrogen oxide sensor (NOx sensor). NOx sensors are installed upstream and downstream of the SCR.

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

[0004] After the exhaust gas is treated in the first chamber, the exhaust gas containing low concentration of oxygen enters the second chamber at a certain diffusion rate through the second diffusion channel. The chamber contains an oxygen pump battery and a sensitive electrode. The oxygen pump battery further controls the oxygen concentration in the chamber to a level close to 0 (10 -3 The sensitive electrode is actually a pump cell, specifically designed to measure the oxygen concentration after NOx decomposition. As oxygen in the second chamber is further pumped out, the equilibrium between O2 and NO is disrupted, leading to NO decomposition at the sensitive electrode through the following reaction: 2NO → N2 + O2. After the decomposed oxygen is pumped away by the oxygen pump cell, the corresponding oxygen pumping current is measured to determine the final decomposed oxygen concentration, which can then be converted to measure NOx.

[0005] From the structural principle, it can be seen that the sensitive electrode is a key component of the NOx sensor and a key activation electrode. During the preparation of the sensitive electrode, the sensitive electrode slurry is printed onto the surface of the solid electrolyte and then sintered at high temperature to form the sensitive electrode. The components of the sensitive electrode slurry include platinum powder (Pt powder), rhodium powder (Rh powder), an inorganic binder, and an organic binder. The organic binder is prepared from ethyl cellulose and an organic solvent. Existing organic binders can disperse the powders, but they have poor thixotropy, which affects the rheological and storage properties of the slurry. In particular, phase separation of the slurry is prone to occur during long printing periods. Poor printability of the slurry affects the length of the three-phase interface and the morphology of the resulting sensitive electrode. Although the sensitive electrode is active in NOx decomposition at temperatures above 800°C, the corresponding sensor cannot effectively detect low NOx concentrations (<100 ppm) and suffers from slow response speed. Summary of the Invention

[0006] The main purpose of the present invention is to provide a platinum-rhodium based electrode slurry and its preparation method and application, aiming to solve the problems of poor rheological properties and poor storage properties of sensitive electrode slurries in the prior art.

[0007] To achieve the above objectives, the present invention proposes a platinum-rhodium-based electrode slurry, comprising the following raw materials in parts by weight: 34-49% platinum powder; 10-14% rhodium powder; 7.1-10% zinc oxide-nickel oxide composite; 5.2-6.4% yttria-stabilized zirconia; 23-38% organic binder; and 0.5-1.2% inorganic binder. The raw materials for preparing 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:

[0009] S1. Mix polyethylene glycol and N,N-dimethylformamide, heat them, add thionyl chloride dropwise, react, collect the crude product, adjust the pH of the crude product to neutral, dry it in vacuo, filter and remove impurities, and obtain polyethylene glycol chloride;

[0010] S2, p-aminophenol, sodium hydroxide and tetrabutylammonium bromide are mixed and stirred, and the polyethylene glycol chloride prepared in step S1 is added, and the mixture is heated to react, the reactants are subjected to solid-liquid separation, the separated liquid is distilled, and the distilled product is vacuum-dried to obtain polyethylene glycol amino;

[0011] S3. Mixing the polyethylene glycol amino product obtained in step S2, ammonium persulfate and hydrochloric acid, controlling the temperature of the mixture to be lower than 3° C., stirring and reacting under a protective atmosphere, adding dropwise a mixture of aniline and hydrochloric acid, reacting at 0° C., filtering the reaction product, washing and drying to obtain the polyaniline-modified polyethylene glycol.

[0012] Optionally, 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,

[0013] 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,

[0014] 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).

[0015] Optionally, 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).

[0016] Preferably, 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).

[0017] Further preferably, the weight ratio of the terpineol, the dibutyl phthalate, the ethyl cellulose, and the polyaniline-modified polyethylene glycol is 68:13:7:12.

[0018] 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 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).

[0019] Preferably, the zinc salt comprises zinc nitrate hexahydrate, and the nickel salt comprises nickel nitrate hexahydrate.

[0020] Optionally, the platinum-rhodium based electrode slurry comprises the following raw materials in the following weight percentages: 39-44% platinum powder, 12.5% ​​rhodium powder, 8.5% zinc oxide-nickel oxide composite, 6% yttria-stabilized zirconia, 28-33% organic binder, and 1% inorganic binder.

[0021] Optionally, the inorganic binder includes at least one of SiO2, B2O3, Bi2O3, Al2O3, MgO, CaO, ZrO2, and TiO2.

[0022] 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.

[0023] The present invention also provides a method for preparing a platinum-rhodium based electrode slurry, comprising the following steps:

[0024] Platinum powder, rhodium powder, zinc oxide-nickel oxide composite, yttria-stabilized zirconia, an inorganic binder, and an organic binder are provided. The platinum powder, rhodium powder, zinc oxide-nickel oxide composite, yttria-stabilized zirconia, and the inorganic binder are added to the organic binder and stirred thoroughly to obtain the platinum-rhodium-based electrode slurry.

[0025] The present invention also provides the use of any of the above-mentioned platinum-rhodium-based electrode slurries in a nitrogen oxide sensor. Specifically, the nitrogen oxide sensor includes a ceramic chip, and the platinum-rhodium-based electrode slurry is used to prepare a sensitive electrode on the ceramic chip.

[0026] In the technical solution of the present invention, dibutyl phthalate has a strong polar group that easily combines with the hydroxyl groups on ethyl cellulose to form a multidimensional network structure. The polyaniline and polyethylene glycol in the polyaniline-modified polyethylene glycol have different solubility in solvents, which makes the polyaniline-modified polyethylene glycol have aggregation characteristics and can form a strip structure. The polyaniline-modified polyethylene glycol aggregates to form a strip structure, and the dibutyl phthalate forms a multidimensional network structure on the ethyl cellulose. The formed strip structure cooperates with the network structure to effectively improve the rheological properties and stability of the electrode slurry, ensure the dispersibility of the electrode slurry, and is not prone to slurry phase separation during long-term storage, thereby improving the printability of the slurry. Even if printed for a long time, the printability of the slurry can be well guaranteed. Furthermore, 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 higher catalytic activity, and the corresponding sensor has a faster response speed and can better detect low concentrations of NOx.

[0027] Platinum powder (Pt powder) and rhodium powder (Rh powder) serve as functional phase powders, possessing catalytic and conductive properties. Zinc oxide-nickel oxide (ZnO-NiO) composites and yttria-stabilized zirconia serve as additives to improve the length of the electrode's three-phase interface and electrode morphology, further enhancing the catalytic activity of the sensitive electrode. An inorganic binder improves the adhesion between the electrode and the YSZ substrate, ensuring stable adhesion of the resulting electrode film to the YSZ substrate. This ensures the electrode's conductivity and catalytic activity, resulting in a faster response speed and excellent detection of low-concentration NOx. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments or the prior art.

[0029] Figure 1 The pump current I is measured for the NOx sensors of Application Example 1 and Comparative Examples 1 to 4 of the present invention under conditions of different NO concentrations. P2 Relationship diagram with changes in NO concentration.

[0030] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0031] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0032] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of such features. In addition, the meaning of "and / or" appearing throughout the text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme in which A and B are satisfied at the same time. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0033] Electrode slurry is the material used to prepare sensitive electrodes. It includes platinum powder (Pt powder), rhodium powder (Rh powder), an inorganic binder, and an organic binder. To prepare the sensitive electrode, the electrode slurry is printed onto the surface of a solid electrolyte and sintered at high temperature. Organic binders are made from ethyl cellulose and organic solvents. Existing organic binders can disperse the powders, but they have poor thixotropy, which affects the slurry's rheological properties and storage properties. Especially when printed for long periods, the slurry is prone to phase separation. This poor printability affects the effective length of the three-phase interface and the morphology of the resulting sensitive electrode. While the sensitive electrode is active in NOx decomposition at temperatures above 800°C, it cannot effectively detect low NOx concentrations (less than 100 ppm), and the corresponding sensor has a slow response speed.

[0034] In view of this, the present invention proposes a platinum-rhodium based electrode slurry and a preparation method and application thereof, in order to solve the problems of poor rheological properties and poor storage properties of existing sensitive electrode slurries.

[0035] In the present invention, a platinum-rhodium-based electrode slurry includes the following raw materials in weight percentage: 34-49% platinum powder, 10-14% rhodium powder, 7.1-10% zinc oxide-nickel oxide composite, 5.2-6.4% yttria-stabilized zirconia, 23-38% organic binder, and 0.5-1.2% inorganic binder; wherein the raw materials for preparing the organic binder include terpineol, dibutyl phthalate, ethyl cellulose, and polyaniline-modified polyethylene glycol.

[0036] In the technical solution of the present invention, dibutyl phthalate has a strong polar group and is easily combined with the hydroxyl groups on ethyl cellulose to form a multidimensional network structure. The polyaniline and polyethylene glycol in the polyaniline-modified polyethylene glycol have different solubility in solvents, and the polyaniline-modified polyethylene glycol has aggregation characteristics and can form a strip structure. The polyaniline-modified polyethylene glycol aggregates to form a strip structure, and the dibutyl phthalate forms a multidimensional network structure on the ethyl cellulose. The formed strip structure cooperates with the network structure to effectively improve the rheological properties and stability of the electrode slurry, ensure the dispersibility of the electrode slurry, and is not prone to phase separation during long-term storage, thereby improving the printability of the slurry. Even if printed for a long time, the printability of the slurry can be well guaranteed. Furthermore, 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 higher catalytic activity, and the corresponding sensor has a faster response speed and can better detect low-concentration NOx.

[0037] Platinum powder (Pt powder) and rhodium powder (Rh powder) serve as functional phase powders, possessing catalytic and conductive properties. Zinc oxide-nickel oxide (ZnO-NiO) composites and yttria-stabilized zirconia serve as additives to improve the length of the electrode's three-phase interface and electrode morphology, further enhancing the catalytic activity of the sensitive electrode. An inorganic binder improves the adhesion between the electrode and the YSZ substrate, ensuring stable adhesion of the resulting electrode film to the YSZ substrate. This ensures the electrode's conductivity and catalytic activity, resulting in a faster response speed and excellent detection of low-concentration NOx.

[0038] It should be noted that if the amount of organic binder is too low, the dispersion stability effect is insufficient, slurry phase separation is likely to occur, the slurry printability is poor, the three-phase interface length and electrode morphology of the sensitive electrode are affected, the catalytic activity of the prepared sensitive electrode cannot be well guaranteed, and the response speed of the prepared sensor and the detection of low-concentration NOx are affected. If the amount of organic binder is too high, it is easy to affect the rheological properties of the slurry and dilute the functional phase powder to a certain extent, which will also affect the catalytic activity of the prepared sensitive electrode, the response speed of the prepared sensor and the detection of low-concentration NOx. If the amount of inorganic binder is too low, the adhesion of the sensitive electrode is affected. If the amount of inorganic binder is too high, it is easy to affect the conductive properties of the sensitive electrode.

[0039] The average particle size of the Pt powder is 0.5-1 μm, and the average particle size of the Rh powder is 0.5-0.8 μm; the yttria-stabilized zirconia is 5 mol % yttria-stabilized zirconia (5YSZ); and the particle size of the inorganic binder is 400 mesh.

[0040] Furthermore, the preparation method of the polyaniline-modified polyethylene glycol comprises the following steps:

[0041] S1. Providing polyethylene glycol and N,N-dimethylformamide, mixing the polyethylene glycol and N,N-dimethylformamide, heating, adding thionyl chloride dropwise, reacting, collecting a crude product of the reaction, adjusting the pH of the crude product to neutral, vacuum drying, filtering and removing impurities, and obtaining polyethylene glycol chloride;

[0042] S2, p-aminophenol, sodium hydroxide and tetrabutylammonium bromide are mixed and stirred, and the polyethylene glycol chloride prepared in step S1 is added, and the mixture is heated to react, the reactants are subjected to solid-liquid separation, the separated liquid is distilled, and the distilled product is vacuum-dried to obtain polyethylene glycol amino;

[0043] S3, mixing the polyethylene glycol amino product obtained in step S2, ammonium persulfate and hydrochloric acid, controlling the temperature of the mixture to be lower than 3° C., stirring and reacting under a protective atmosphere, adding dropwise a mixture of aniline and hydrochloric acid, reacting at 0° C., filtering the reaction product, washing, and drying to obtain the polyaniline-modified polyethylene glycol.

[0044] By adopting the above technical solution, using specific raw materials and preparation processes, polyaniline-modified polyethylene glycol with excellent performance can be produced. It should be noted that in step S1, adjusting the pH of the washed product to neutral means adjusting the pH of the washed product to 7; in step S3, the protective atmosphere can be nitrogen, of course, or other single gases or mixed gases according to actual needs.

[0045] Furthermore, 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,

[0046] 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,

[0047] 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).

[0048] By adopting the above technical solution and using a specific ratio between 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.

[0049] 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).

[0050] By adopting the above technical solution, terpineol, dibutyl phthalate, ethyl cellulose, and polyaniline-modified polyethylene glycol are compounded in a specific ratio to form an organic binder, which can effectively improve the dispersion stability of the slurry.

[0051] 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).

[0052] By adopting the above technical solution and further optimizing the dosage ratio of terpineol, dibutyl phthalate, ethyl cellulose, and polyaniline-modified polyethylene glycol, the dispersion stability of the slurry can be greatly improved.

[0053] Furthermore, the zinc oxide-nickel oxide composite is prepared by a hydrothermal method, and 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).

[0054] The resulting ZnO-NiO composite exhibits a multilayered, flake-like structure, which works well with YSZ to improve the effective length of the three-phase interface and the electrode morphology of Pt-Rh-based electrodes. It should be noted that the average particle size of YSZ is 0.2-0.4 μm.

[0055] Furthermore, the platinum-rhodium-based electrode slurry comprises the following raw materials in weight percentage: 39-44% platinum powder, 12.5% ​​rhodium powder, 8.5% zinc oxide-nickel oxide composite, 6% yttria-stabilized zirconia, 28-33% organic binder, and 1% inorganic binder.

[0056] Furthermore, the inorganic binder includes at least one of SiO2, B2O3, Bi2O3, Al2O3, MgO, CaO, ZrO2, and TiO2.

[0057] By adopting the above technical solution, the inorganic binder melts during sintering and has good flow and wettability, so that the electrode is stably attached to the surface of the YSZ substrate.

[0058] The present invention also provides a method for preparing a platinum-rhodium based electrode slurry, comprising the following steps:

[0059] Platinum powder, rhodium powder, zinc oxide-nickel oxide composite, yttria-stabilized zirconia, an inorganic binder, and an organic binder are provided. The platinum powder, rhodium powder, zinc oxide-nickel oxide composite, yttria-stabilized zirconia, and the inorganic binder are added to the organic binder and stirred thoroughly to obtain the platinum-rhodium-based electrode slurry.

[0060] The technical solution of this invention utilizes platinum powder (Pt powder) and rhodium powder (Rh powder) as functional phase powders, along with a zinc oxide-nickel oxide (ZnO-NiO) composite and yttria-stabilized zirconia (YSZ) as additives. This improves the length of the electrode's three-phase interface and electrode morphology, further enhancing the catalytic activity of the sensitive electrode. The inorganic binder improves the adhesion between the electrode and the YSZ substrate, ensuring that the resulting electrode film adheres more stably to the YSZ substrate, ensuring the electrode's electrical conductivity and catalytic activity. The resulting sensor exhibits a faster response and is highly capable of detecting low concentrations of NOx. Organic binders can effectively improve the rheological properties and stability of the electrode slurry, ensure the dispersibility of the electrode slurry, and are less likely to cause slurry phase separation even after long-term storage, thereby improving the printability of the slurry. Even if printed for a long time, the printability of the slurry can be well guaranteed, thereby improving the electrode morphology and the length of the three-phase interface of the formed sensitive electrode, so that the sensitive electrode has higher catalytic activity, the corresponding sensor has a faster response speed, and can better detect low concentrations of NOx.

[0061] The present invention also proposes the use of any of the above-mentioned platinum-rhodium-based electrode slurries in a nitrogen oxide sensor. Specifically, the nitrogen oxide sensor includes a ceramic chip, and the platinum-rhodium-based electrode slurry is used to prepare a sensitive electrode on the ceramic chip.

[0062] The technical solutions of the present invention are further described in detail below in conjunction with specific embodiments and 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

[0063] A method for preparing a platinum-rhodium based electrode slurry comprises the following steps:

[0064] (1) Preparation of inorganic binder

[0065] 14wt% SiO2, 6wt% B2O3, 65wt% Bi2O3, 10wt% Al2O3, 1wt% MgO, 1.5wt% CaO, 1.5wt% ZrO2, and 1wt% TiO2 were ground and mixed, placed in a crucible, and heated to 1400°C in a high-temperature furnace for 30 minutes. The molten glass was then quenched in deionized water to produce a pellet. The pellet was then dried and ground in a ball mill. The pellet was then passed through a 400-mesh sieve, and the residue below the sieve was the inorganic binder. SiO2, B2O3, Bi2O3, Al2O3, MgO, CaO, ZrO2, and TiO2 were all analytical grade.

[0066] (2) Preparation of organic binder

[0067] An organic binder was prepared by mixing 70 wt% terpineol, 13 wt% dibutyl phthalate, 7 wt% ethyl cellulose, and 10 wt% polyaniline-modified polyethylene glycol, heating them at 90°C, stirring them with a magnetic stirrer, and thoroughly mixing them. The terpineol was analytically pure, the ethyl cellulose was chemically pure, and the dibutyl phthalate had a purity of 99%.

[0068] (3) Preparation of platinum-rhodium electrode slurry

[0069] 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 a platinum-rhodium based electrode slurry.

[0070] Wherein, in step (2), the preparation method of polyaniline-modified polyethylene glycol comprises the following steps:

[0071] 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 vessel, raise the temperature to 50°C, add thionyl chloride dropwise, react under reflux condition of 60°C 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.

[0072] S2. Prepare the 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, then 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, and place the distilled product in a vacuum drying oven at 60°C for vacuum drying for 24 hours to obtain polyethylene glycol amino product.

[0073] S3. Polyethylene glycol amide was dissolved in HCl solution to obtain mixture A, in which the concentration of polyethylene glycol amide was 0.01 mol / L and the concentration of HCl was 0.99 mol / L; ammonium persulfate was dissolved in HCl solution to obtain mixture B, in which the concentration of ammonium persulfate was 0.11 mol / L and the concentration of HCl was 0.89 mol / L; aniline was dissolved in HCl solution to obtain mixture C, in which the concentration of aniline was 0.1 mol / L and the concentration of HCl was 0.9 mol / L.

[0074] S4. Add mixture A to 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 the reaction vessel and fill it with nitrogen, stir at a stirring rate of 100 rpm. When the solution in the reaction vessel turns purple, slowly add mixture C dropwise, and then react at 0°C for 24 hours. Filter the reaction product with a Buchner funnel and wash it with deionized water until the filtrate is colorless; wash the resulting product three times with 1 mol / L HCl solution and then vacuum dry it at 60°C for 24 hours to obtain polyaniline-modified polyethylene glycol; wherein the volume ratio of mixture A, mixture B and mixture C is 1:1:1.

[0075] In step (3), the preparation method of the ZnO-NiO composite comprises the following steps:

[0076] Prepare the 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;

[0077] Zn(NO3)2·6H2O and Ni(NO3)2·6H2O were added to deionized water, magnetically stirred, and fully mixed. NaOH was added and magnetically stirred at room temperature (25°C) until a light green solution appeared. The reaction solution was transferred to a reactor and kept in a constant temperature forced air drying oven at 120°C for 7 hours. The mixture was naturally cooled to room temperature, the reactor was taken out, and the precipitate was collected by a centrifuge. During the centrifugation process, the precipitate was washed with deionized water 5 times. The precipitate was dried in a vacuum drying oven at 60°C. The dried reactants were placed in a muffle furnace and heated to 500°C at a heating rate of 2°C / min and kept for 2 hours to obtain a zinc oxide-nickel oxide complex.

[0078] Examples 2 to 9

[0079] Examples 2 to 4 are based on Example 1, with the difference that in step (3), the amount of the organic binder is changed, and the amount of the change is balanced by using Pt powder, as shown in Table 1 below.

[0080] Examples 5 and 6 are based on Example 3, with the difference that in step (3), the amount of raw materials other than the organic binder is changed, as shown in Table 1 below.

[0081] Examples 7 to 9 are based on Example 3, with the difference that in step (2), the amount of polyaniline-modified polyethylene glycol is changed, and the amount of terpineol is used to balance the change, as shown in Table 2 below.

[0082] Table 1 Amount of each raw material in electrode slurry (unit: wt%)

[0083]

[0084] Table 2 Amount of each raw material of organic binder (unit: wt%)

[0085]

[0086] Comparative Example 1

[0087] This comparative example is based on Example 1, with the difference that in step (2), an equal weight fraction of terpineol is used to replace the polyaniline-modified polyethylene glycol.

[0088] Comparative Example 2

[0089] This comparative example is based on Example 1, with the difference that in step (2), terpineol is used in an equal weight fraction to replace dibutyl phthalate.

[0090] Comparative Example 3

[0091] This comparative example is based on Example 1, with the difference that in step (3), an equal weight fraction of Pt powder is used to replace the ZnO-NiO composite.

[0092] Comparative Example 4

[0093] This comparative example is based on Example 1, with the difference that in step (3), an equal weight fraction of Pt powder is used to replace 5YSZ.

[0094] Application Examples 1 to 9 and Comparative Application Examples 1 to 4

[0095] The platinum-rhodium-based electrode slurries prepared in Examples 1-9 and Comparative Examples 1-4 were used to prepare amperometric NOx sensors, corresponding to Application Examples 1-9 and Comparative Examples 1-4, respectively. The preparation methods of the amperometric NOx sensors in Application Examples 1-9 and Comparative Examples 1-4 include the following steps:

[0096] A 5 mol % YSZ green body was prepared by a tape casting process, and various electrode slurries (including an oxygen pumping electrode slurry, a sensitive electrode slurry, and a reference electrode slurry), cavity fillers, insulating layers, gas diffusion layers, and protective layers were printed on the YSZ green body by screen printing, wherein the sensitive electrode slurry used the platinum-rhodium-based electrode slurry prepared in the corresponding Examples 1-9 and Comparative Examples 1-4, and the oxygen pumping electrode slurry and the reference electrode slurry used commercial Pt-based electrode slurry; the YSZ green body carrying the various functional layers was placed in a drying furnace and dried at 80° C. for 2 h, then warm-pressed and laminated, and cut to form a single ceramic chip green body, which was placed in a high-temperature furnace and co-fired at 1400° C. for 2 h to obtain a ceramic chip, wherein the thickness of the formed sensitive electrode was 10 μm; the obtained ceramic chip was connected to a control unit via a connecting wire to obtain a current-type NOx sensor.

[0097] Performance Testing

[0098] 1. Working temperature test

[0099] The working temperature of the sensors made in Examples 1 to 9 and Comparative Examples 1 to 4 was tested. The test gas was 21 vol% O2 + 0 vol% NO + residual nitrogen. The oxygen content of the test gas was close to that in the air. By changing the working temperature of each sensor, the relationship between the corresponding working temperature and the oxygen pumping capacity of the main oxygen pump was obtained. The main oxygen pump current I p0 and the main oxygen pump voltage V p0 It can be concluded from the relationship between and that the operating temperature of the sensors prepared in Application Examples 1 to 9 and Comparative Examples 1 to 4 is approximately 800°C.

[0100] 2. Single pump working test

[0101] The single-pump gas-sensing performance test was performed on the sensors prepared according to the corresponding use cases 1 to 9 and the comparative examples 1 to 4.

[0102] (1) Main oxygen pump single working test

[0103] Working temperature: 800℃; Test gas: 21 vol% O2+0 vol% NO+ residual nitrogen; Auxiliary pump voltage V p1 and measuring the pump voltage V p2 are all 0V, and the main oxygen pump voltage V p0 The main oxygen pump current I is obtained by increasing the voltage from 0.0V to 1.2V at a rate of 0.01V / s. p0 and the main oxygen pump voltage V p0 From the relationship between , it can be concluded that the main oxygen pump of the sensors prepared in Application Examples 1 to 9 and Comparative Examples 1 to 4 has a limiting current platform at 300 to 500 mV.

[0104] (2) Auxiliary pump single working test

[0105] The working temperature and test gas are the same as those of the main oxygen pump working alone. The main oxygen pump voltage V p0 and measuring the pump voltage V p2 are all 0V, the auxiliary pump voltage V p1 The auxiliary pump current I is increased from 0.0V to 1.2V at a rate of 0.01V / s. p1 and the auxiliary pump voltage V p1 From the relationship between , it can be concluded that the auxiliary pumps of the sensors prepared in Application Examples 1 to 9 and Comparative Examples 1 to 4 have a limiting current platform at 750 to 900 mV.

[0106] (3) Measuring pump single working test

[0107] The working temperature and test gas are the same as those of the main oxygen pump working alone. The main oxygen pump voltage V p0 and the auxiliary pump voltage V p1 are all 0V, measure the pump voltage V p2 The pump current I is measured by increasing the voltage from 0.0V to 1.2V at a rate of 0.01V / s. p2 and measuring the pump voltage V p2 There is no limiting current platform for each measuring pump voltage, and the current and voltage are in a linear relationship.

[0108] 3. Joint test and response time test under atmospheric environment

[0109] Test conditions: Main oxygen pump voltage V p0 =300mV, auxiliary pump voltage V p1 =750mV, measure the pump voltage V p2 =900mV, operating temperature is 800℃; test gas: 15 vol%O2+x vol%NO+residual nitrogen, the change of NO gas concentration is obtained by adjusting the volume ratio of N2, among which the volume percentage of O2 is controlled to be 15%.

[0110] (1) The NO concentration is kept between 0 and 2000 ppm to test the NO concentration and the pump current I in the current-type NOx sensor of Application Example 1 and Comparative Examples 1 to 4. p2 The relationship curve, such as Figure 1 shown.

[0111] Depend on Figure 1 It can be seen that the nitrogen oxide sensor corresponding to Application Example 1 can better detect NOx with a concentration below 2000 ppm, and the output current signal of the nitrogen oxide sensor corresponding to Application Example 1 is significantly stronger than that of the nitrogen oxide sensors corresponding to Application Comparative Examples 1 to 4, indicating that the sensitive electrode corresponding to Application Example 1 has strong catalytic activity.

[0112] (2) Response time test. Response time refers to the measurement pump current I output by the NOX sensor when the gas concentration changes. p2 The time required to change with the change of gas volume fraction. The NO standard gas concentration is 300ppm. When the NO concentration changes from 0ppm to 300ppm, The time required for NO concentration to increase from 33% to 66% and the time required for NO concentration to change from 300ppm to 0ppm, 66%~33% of the time required, of which, 33% in 33%~66% refers to 33% of the NO standard gas concentration (300ppm), and 66% refers to 66% of the NO standard gas concentration (300ppm). 33%~66% refers to the rising response time corresponding to the process in which the NO concentration rises from 33% of its standard gas concentration (300ppm) to 66% of its standard gas concentration (300ppm). Similarly, 66%~33% corresponds to the falling response time. 33%~66% and 66%~33% are shown in Table 3 below.

[0113] Table 3 Rising and falling response times of NOX sensors

[0114]

[0115] From the results in Table 3, it can be seen that the nitrogen oxide sensors corresponding to Application Examples 1 to 9 have faster response times (rising response times) and recovery times (falling response times), indicating that the electrode slurries prepared in the embodiments of the present invention have strong catalytic activity.

[0116] The response time and recovery time of the nitrogen oxide sensors corresponding to Comparative Example 1 and Comparative Example 2 are both slow. The reason may be that the raw materials for preparing the organic binder lack one of polyaniline-modified polyethylene glycol and dibutyl phthalate, which affects the dispersion stability of the slurry and further affects the effective length of the electrode three-phase interface and the electrode morphology, resulting in the corresponding NOx sensor having a slow response time and recovery time.

[0117] The response time and recovery time of the nitrogen oxide sensors corresponding to Comparative Example 3 and Comparative Example 4 are slow. The reason may be that the raw materials for preparing the slurry lack one of the ZnO-NiO composite and 5YSZ, which affects the effective length of the electrode three-phase interface and the electrode morphology, resulting in the corresponding NOx sensor having a slower response time and recovery time.

[0118] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of the present invention.

Claims

1. A platinum-rhodium based electrode slurry, characterized in that The invention comprises the following raw materials in weight percentage: platinum powder 34-49%; rhodium powder 10-14%; zinc oxide-nickel oxide composite 7.1-10%; yttria-stabilized zirconia 5.2-6.4%; organic binder 23-38%; inorganic binder 0.5-1.2%; 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 slurry according to claim 1, wherein The preparation method of the polyaniline-modified polyethylene glycol comprises the following steps: S1. Mixing polyethylene glycol and N,N-dimethylformamide, heating, adding thionyl chloride dropwise, reacting, collecting the crude product of the reaction, adjusting the pH of the crude product to neutral, vacuum drying, filtering and removing impurities, to obtain polyethylene glycol chloride; S2, p-aminophenol, sodium hydroxide and tetrabutylammonium bromide are mixed and stirred, and the polyethylene glycol chloride prepared in step S1 is added, and the mixture is heated to react, the reactants are subjected to solid-liquid separation, the separated liquid is distilled, and the distilled product is vacuum-dried to obtain polyethylene glycol amino; S3. Mixing the polyethylene glycol amino product obtained in step S2, ammonium persulfate and hydrochloric acid, controlling the temperature of the mixture to be lower than 3° C., stirring and reacting under a protective atmosphere, adding dropwise a mixture of aniline and hydrochloric acid, reacting at 0° C., filtering the reaction product, washing and drying to obtain the polyaniline-modified polyethylene glycol.

3. The platinum-rhodium based electrode slurry according to claim 2, characterized in that 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 slurry according to claim 1, wherein 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).

5. The platinum-rhodium based electrode slurry according to claim 4, characterized in that 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).

6. The platinum-rhodium based electrode slurry according to claim 1, characterized in that 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 slurry according to claim 1, characterized in that The invention comprises the following raw materials in percentage by weight: 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.

8. The platinum-rhodium based electrode slurry 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 slurry, characterized in that: The following steps are involved: Platinum powder, rhodium powder, zinc oxide-nickel oxide composite, yttria-stabilized zirconia, an inorganic binder, and an organic binder are provided. The platinum powder, rhodium powder, zinc oxide-nickel oxide composite, yttria-stabilized zirconia, and the inorganic binder are added to the organic binder and stirred thoroughly to prepare the platinum-rhodium-based electrode slurry.

10. A nitrogen oxygen sensor, characterized in that: The invention comprises a sensitive electrode, wherein the sensitive electrode is made of the platinum-rhodium based electrode slurry according to any one of claims 1 to 8.

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