Perovskite type mixed conductor film with metal precipitated on surface, method for electrically driving in-situ precipitation of metal nanoparticles and application of perovskite type mixed conductor film

Abstract

The invention discloses a perovskite type mixed conductor film with metal precipitated on the surface, a method for electrically driving in-situ precipitation of metal nanoparticles and application, and the surface of the mixed conductor film is provided with the metal nanoparticles which are electrically driven in-situ precipitation. The preparation method comprises the following steps: constructing an electrically driven reduction device taking a perovskite type mixed conductor film as a cathode, applying negative voltage to the cathode at normal temperature, carrying out reduction reaction, and separating out the metal nanoparticles. According to the invention, a perovskite type mixed conductor film is used as a cathode, an A-site defect is designed by using the oxidation-reduction characteristic of B-site metal of the perovskite type mixed conductor film so as to provide auxiliary reduction, and potential is applied to the cathode at normal temperature, so that the surface of the perovskite film is reconstructed, and then metal nanoparticles are separated out.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional ceramics, and particularly relates to a perovskite-type mixed conductor film with surface-precipitated metal, a method for electro-driven in-situ precipitation of metal nanoparticles, and uses thereof. Background Art

[0002] Dense mixed conductor films are widely used in green chemical industries such as air separation, oxy-fuel combustion, and catalytic membrane reactors due to their high oxygen ion-electron conductivity characteristics. Among them, perovskite materials (with the general formula ABO 3 ) have a flexible and adjustable crystal structure and elemental composition. Their variable oxygen ion mobility and high structural stability at high temperatures make them one of the most commonly used mixed conductor oxygen permeable membrane materials. During the oxygen permeation process, the perovskite membrane is affected by the restrictive relationship between oxygen transport performance and stability, and cannot meet the industrial requirements. Improving the oxygen permeation flux of the perovskite oxygen permeable membrane and solving its operational stability problem during high-temperature oxygen permeation are the keys to promoting its industrialization.

[0003] Loading metal particles on the membrane surface is an effective means to improve the membrane transport characteristics, but particle sintering and agglomeration will inevitably occur during the preparation process, resulting in performance degradation. A large number of studies have shown that the B-site metal in perovskite can be precipitated onto the perovskite surface by heat treatment in a reducing atmosphere. The precipitated metal particles are anchored on the surface, with good dispersibility, stability, and anti-coking properties, which is a promising strategy for preparing highly efficient functional perovskite materials. Patent CN113332992B discloses a perovskite catalyst and its preparation method. By first oxidizing and then reducing, calcination in a high-temperature and air atmosphere can in-situ precipitate one or several oxide nanoparticles with water absorption properties. The calcination temperature is 700~800 °C, and the calcination time is 4~6 h. Patent CN108654592B discloses a perovskite catalyst, its preparation method, and an in-situ testing method. The perovskite precursor powder is reduced in a 5% H 2 -N 2 atmosphere at 800 °C for 4~12 h to in-situ precipitate B-site catalytic metal B-site metal nanoparticles and cover the surface of the perovskite precursor powder. Patent CN115548356B discloses a preparation method and application of a perovskite-type solid oxide battery electrode catalyst. By doping transition elements in the B-site of perovskite, alloy particles are in-situ precipitated under a high-temperature reducing atmosphere. The reduction temperature is 850 °C, and the reduction time is 1~3 h. It can be seen that the currently commonly used methods require a relatively high reduction temperature (usually greater than 600 °C) and a relatively long reduction time (plus the heating and cooling time and the holding time, usually greater than 10 h), and most of the research focuses on the modification of perovskite powder catalysts rather than the preparation of membranes. Therefore, developing a method for precipitating metal particles on the surface of perovskite membranes at room temperature is expected to obtain a high-throughput and stable oxygen permeable membrane quickly and simply. Summary of the Invention

[0004] To solve the deficiencies of the prior art, the object of the present invention is to provide a perovskite-type mixed conductor film with surface-precipitated metal, a method and use for electro-driven in-situ precipitation of metal nanoparticles. Using the perovskite-type mixed conductor film as the cathode, and utilizing the redox characteristics of the B-site metal, A-site defects are designed to provide auxiliary reduction. A potential is applied to the cathode at room temperature, causing the surface of the perovskite film to be reconstructed, and then metal nanoparticles are precipitated.

[0005] To achieve the above object, the present invention adopts the following technical solutions: A method for electro-driven in-situ precipitation of metal nanoparticles on a perovskite-type mixed conductor film, comprising the following steps: (1) Setup of the electro-driven reduction device: Fix a pre-prepared perovskite-type mixed conductor film as the cathode with an electrode clip, select a material with stable electrochemical performance as the anode, add an electrolyte solution with a certain concentration to ensure electron transfer, connect the cathode to the negative terminal of the power supply with a wire, and connect the anode to the positive terminal of the power supply to ensure the circuit is connected. See Figure 1 .

[0006] (2) Preparation of the perovskite-type mixed conductor film for electro-driven reduction and precipitation of metal nanoparticles: Apply a negative voltage to the cathode of the electro-driven reduction device at room temperature to carry out a reduction reaction and precipitate metal nanoparticles.

[0007] Preferably, the thickness of the aforementioned perovskite-type mixed conductor film is 0.1 - 5 mm, having a perovskite metal oxide general formula of ABO 3 , and the A-site element is the defect amount.

[0008] Preferably, the applied negative voltage is greater than -2 V, and the reduction time is 1 - 24 h.

[0009] Preferably, in the photograph obtained with a magnification of 50,000 - 100,000 times of the aforementioned perovskite-type mixed conductor film, the number range of surface metal particles is 20 - 500, and the particle size range is 30 - 200 nm.

[0010] Preferably, the A-site element of the aforementioned perovskite-type mixed conductor film is selected from rare earth or alkali metal elements, and is one of Be, Mg, Ca, Sr, Ba, La, Ce, Cd, Pb or Bi; the B-site element of the perovskite-type mixed conductor film is selected from transition metal elements, and is one of Fe, Ni, Ti, Ta, Nb, Co, Mn, Al, Mo, Cu, Sc or Cr.

[0011] Preferably, the precipitated metal nanoparticles are composed of one or more of the B-site elements of the perovskite-type mixed conductor membrane.

[0012] Preferably, the chemical formula of the aforementioned perovskite-type mixed conductor membrane is (La 0.6 Sr 0.4 ) 0.9 Co 0.2 Fe 0.8 O 3-δ ; the material of the precipitated metal particles is elemental Co.

[0013] Preferably, the electrolyte solution of the aforementioned electro-driven reduction device is any conductive alkaline or neutral solution such as NaOH, KOH, H 2 O with a molar concentration of 0 - 1 mol / L, the anode material is a material such as a graphite rod that will not dissolve into the electrolyte during the application of voltage, and the power supply is a device such as a dry battery, storage battery, or electrochemical workstation that can maintain a steady voltage and current in the circuit.

[0014] Application of the obtained perovskite-type mixed conductor membrane of precipitated metal nanoparticles in oxygen separation.

[0015] Reaction mechanism of the present invention: During the electroreduction process, under the combined action of the potential effect of the cathode negative potential and the adsorption and migration of molecules, ions, and reaction intermediates in the electrolyte or cathode material, atomic migration, leaching, and rearrangement can occur on the cathode, resulting in local reconstruction and the formation of a new phase. The precipitation and anchoring of metal particles on the membrane surface significantly improve the oxygen flux of the perovskite oxygen permeable membrane. This is mainly because the presence of metal nanoparticles increases the number of active centers on the membrane surface, changes the local electronic structure of the membrane surface, thereby promoting oxygen adsorption / desorption and promoting electron transfer. Compared with the traditional impregnation method for loading metal catalysts, the in-situ precipitated nanoparticles have a stronger binding force with the substrate and higher anti-coking performance and stability.

[0016] Advantages of the present invention: (1) By using the electro-driven reduction method at room temperature to precipitate metal nanoparticles on the surface of the perovskite-type mixed conductor membrane, the present invention can be coupled with renewable energy systems such as solar energy and wind energy. This method not only avoids the potential safety risks brought by long-term high-temperature operation but also effectively reduces energy consumption and improves energy utilization efficiency; (2) Compared with the traditional thermal reduction method, the metal nanoparticles obtained by the electro-driven reduction method are more uniformly and densely distributed on the surface of the perovskite-type mixed conductor membrane, with a higher precipitation efficiency and a faster precipitation speed; (3) The precipitation device of the present invention is simple to operate, convenient to use, and the process conditions are easy to control. It has the advantages of simple process conditions and low cost, and can be applied to various fields such as pure oxygen separation and catalytic membrane reactors, with positive social benefits and significant economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the device for electro-driven reduction of perovskite-type mixed conductor membrane; Figure 2 It is the XRD diffraction pattern of the surface of the LSCF perovskite-type mixed conductor membrane obtained before and after electro-reduction in Examples 1 and 4; Figure 3 It is the SEM images of the surface of the LSCF perovskite-type mixed conductor membrane obtained before and after electro-reduction in Examples 1-4 (a: no electro-driven reduction treatment in Example 4, b: electro-driven reduction duration of 1 h in Example 2; c: electro-driven reduction duration of 5 h in Example 1, d: electro-driven reduction duration of 24 h in Example 3); Figure 4 It is the comparison chart of the oxygen permeation performance test of the LSCF perovskite-type mixed conductor membrane obtained before and after electro-reduction in Examples 1 and 4. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be specifically introduced below in conjunction with the drawings and specific embodiments.

[0019] In order to improve the oxygen permeation performance and operation stability of the perovskite-type mixed conductor membrane, by utilizing the potential effect of the negative cathode potential during electrolysis and the combined action of the adsorption and migration of molecules, ions and reaction intermediates in the electrolyte or cathode material, the goal of precipitating the B-site metal in the form of nanoparticles on the membrane surface at room temperature is achieved. This method is not only simple to operate and low in cost, but also effectively saves energy and realizes the simultaneous improvement of oxygen permeation amount and stability.

[0020] A method for in-situ precipitating metal nanoparticles on a perovskite-type mixed conductor membrane by electro-driving, the method comprising: (1) According to the designed stoichiometric ratio, the metal oxide raw material and the ball milling medium are fully mixed by ball milling. After drying and sieving, it is put into a muffle furnace for sintering into a phase to prepare a perovskite powder with A-site defects.

[0021] (2) Take 1 g of the sintered perovskite powder material and add a small amount of polyvinyl alcohol binder. After grinding and mixing evenly, pour it into a mold, and use a tablet press to apply a certain pressure by isostatic pressing to press the powder into a shape and then take it out to obtain a green body of the perovskite sheet membrane with A-site defects. A certain pressure refers to the pressure range that can press the perovskite powder into a regular sheet membrane blank shape and will not scatter due to force during the taking process.

[0022] (3) Put the obtained green body into a muffle furnace for sintering to remove organic substances and convert it into a dense membrane structure, obtaining a perovskite sheet membrane with A-site defects.

[0023] (4) Fix the perovskite sheet membrane with A-site defects using electrode clamps as the cathode, and then use wires to connect the power supply to the anode and the power supply to the cathode respectively to form a circuit under the action of the electrolyte. By applying a certain voltage to make the current flow through the circuit, after maintaining a constant voltage for a period of time, the cathode undergoes polarization and reconstruction, and finally a perovskite-type mixed conductor membrane with metal nanoparticles precipitated on the surface is obtained. Among them: the anode is a graphite rod electrode, and the electrolyte is 0.1 M KOH solution.

[0024] Perform the fourth step under different parameter conditions to obtain perovskite-type mixed conductor membranes with different surface morphologies, and obtain the surface micrographs of the membranes by SEM method; in the SEM spectra of the samples under different electroreduction conditions, take the parameter conditions corresponding to the samples with a dense perovskite membrane surface and evenly distributed precipitated metal particles as the optimal values of electroreduction.

[0025] The metal nanoparticles are metal simple substances that are reduced in valence after receiving electrons from the B-site transition metal cations in the perovskite bulk phase, migrate to the membrane surface under the influence of the concentration gradient, nucleate and grow on the surface, and finally anchor on the membrane surface.

[0026] Example 1. The method for electro-driven reduction of perovskite to precipitate metal nanoparticles at room temperature is realized according to the following steps: (1) Prepare perovskite powder with A-site defects of (La 0.6 Sr 0.4 ) 0.9 Co 0.2 Fe 0.8 O 3-δ by solid-phase sintering process. Mix La 2 O 3 (99.0%), SrCO 3 (99.0%), Co 2 O 3 (99.0%), Fe 2 O 3 (99.0%) according to the stoichiometric ratio, ball-mill in ethanol for 24 h, dry the obtained slurry at 70 °C for 24 h and then pass through a 100-mesh sieve, and calcine the sieved powder at 900 °C for 5 h, controlling the heating and cooling rates at 2 °C / min to form perovskite powder with A-site defects of (La 0.6 Sr 0.4 ) 0.9 Co 0.2 Fe 0.8 O 3-δ (LSCF).

[0027] (2) Preparation of perovskite mixed conductor film by isostatic pressing In order to obtain a dense perovskite mixed conductor oxygen permeable membrane, the mold of a tablet press is used for the forming process, including loading, pressing and removing the powder; the press applies a pressure of 10 MPa on the mold, and after holding the pressure for 1 min, the pressure is released and the mold is removed from the press to obtain a perovskite mixed conductor membrane green body. The LSCF green body is sintered at 1200 °C in a muffle furnace for 10 h, and the heating and cooling rates are controlled at 2 °C / min to obtain a dense LSCF perovskite mixed conductor oxygen permeable membrane.

[0028] (3) Electrically driven reduction of perovskite-type mixed conductor films The dense LSCF perovskite mixed conductor oxygen permeable membrane was fixed with a clamp and used as a cathode. It was connected to the graphite rod anode and an external power supply with a wire to form a path. The electrolyte was 0.1 M KOH solution. A negative potential of -3 V was applied to the cathode at room temperature to polarize the cathode, causing the membrane surface to be reduced and atomic rearrangement to occur. After maintaining a constant voltage for 5 h, the membrane was taken out, washed with ethanol solution and dried to obtain a LSCF perovskite mixed conductor oxygen permeable membrane with Co metal element precipitated on the surface.

[0029] Example 2. The specific difference between this example and Example 1 is that the constant voltage time in step (3) is 1 h.

[0030] Example 3. The specific difference between this example and Example 1 is that the constant voltage time in step (3) is maintained for 24 h.

[0031] Embodiment 4: The specific difference between this embodiment and embodiment 1 is that the electric driven reduction treatment is not adopted in step (3).

[0032] Performance testing: (1) XRD analysis was performed on the samples obtained in Example 1 and Example 4.

[0033] pass Figure 2 It can be seen that the membrane surface exhibits a cubic perovskite structure before and after the electric-driven reduction. After reduction, the XRD spectrum of the sample obtained in Example 1 shows a slight left shift compared with the sample in Example 4, indicating that lattice expansion has occurred. The sample obtained in Example 1 shows a characteristic peak of Co metal element, proving that Co metal can be successfully precipitated on the membrane surface by this electric reduction method. During the reduction process, due to the high negative potential applied, when the electron supply exceeds the supply to H in the electrolyte, the electrons in the electrolyte will be precipitated. 2 O is reduced to generate H 2 When the required number of electrons is reached, the excess electrons begin to reduce the B-site Co and Fe ions in the LSCF film and the lattice oxygen in the perovskite. At this time, atomic migration will occur near the surface of the perovskite film.2+ The precipitation potential required for the ions is higher than that of Co 2 + ions, and the Co element is preferentially precipitated onto the membrane surface. After the metal nanoparticles are precipitated, continuous cathodic polarization will maintain the precipitated particles from being re-oxidized.

[0034] (2)Perform scanning electron microscopy (SEM) tests on the samples obtained in Examples 1 to 4.

[0035] Through Figure 3 it can be seen that the surface of the untreated LSCF membrane is flat ( Figure 3 a); after 1 h of electroreduction treatment, there is still no obvious change on the membrane surface ( Figure 3 b); when the electroreduction treatment time reaches 5 h, a large number of uniformly distributed nanoparticles are observed on the LSCF membrane surface ( Figure 3 c). Combining with the XRD results, it can be confirmed that they are Co metal nanoparticles. When the electroreduction treatment time is extended to 24 h, the dense structure on the surface of the perovskite membrane is damaged ( Figure 3 d), and the crystal grains collapse and fall off into the water, making it impossible to be used for oxygen permeation performance testing. It can be seen that by using the electro-driven reduction treatment process of the present invention, metal nanoparticles are successfully precipitated on the surface of the perovskite-type mixed conductor membrane, and the morphology of the membrane surface changes with the extension of the constant voltage holding time. This is because the long-term application of a high negative potential and the ion leaching effect brought about by the surrounding water environment cause the perovskite structure to be in a metastable state. While Co metal is precipitated, Sr 2+ ions may also leach into the electrolyte, resulting in the membrane being unable to maintain its original airtightness. It can be seen that the surface micro-morphology of the LSCF perovskite oxygen permeation membrane treated for 5 h is the best.

[0036] (3)Perform oxygen permeation performance tests on the samples obtained in Example 1 and Example 4. The test method is as follows: Step a: Set up a high-temperature oxygen permeation device. Take a corundum tube of appropriate length and place it vertically. Use silver glue as a sealant to seal the perovskite-type mixed conductor membrane at the upper end of the corundum tube with a suitable inner diameter. The lower end of the corundum tube is connected to the component with white glue. The component has an air inlet and an air outlet respectively, and gas can be introduced into the corundum tube to purge the membrane and then analyze the gas components.

[0037] Step b: Introduce a purge gas (He, 60 mL / min) on the permeation side (inside the corundum tube), while the feed side (outside the corundum tube) is in a static air atmosphere, and the gas flow rate is controlled by a mass flow meter.

[0038] Step c: Place the upper end of the corundum tube where the membrane is located in the high-temperature oxygen permeation device into the tubular furnace for temperature control and detection. During the oxygen permeation test, the temperature is controlled at 700-900 °C, and the heating and cooling rate is 5 °C / min.

[0039] Step d: Use an on-line gas chromatography equipped with a thermal conductivity detector and a 5A molecular sieve column to analyze the gas content at the outlet of the permeate side. During the oxygen measurement process, the gas leakage rate on the feed side is less than 0.5%.

[0040] As Figure 4 shown, at the same operating temperature, the oxygen permeation flux of Example 1 is greater than that of Example 4. This is because the precipitation of Co nanoparticles increases the specific surface area of the membrane and the 2 adsorption sites for O, effectively improving the surface exchange rate of the membrane, which proves the beneficial effect of the metal nanoparticles precipitated by the electro-driven reduction method at room temperature on the perovskite oxygen permeable membrane.

[0041] The present invention has successfully precipitated uniformly distributed metal nanoparticles on the surface of the perovskite-type mixed conductor membrane through electro-reduction treatment at room temperature. The surface morphology of the prepared membrane was characterized by XRD and SEM, and the performance of the prepared oxygen permeable membrane was compared in combination with the oxygen permeation test. The perovskite oxygen permeable membrane with precipitated metal nanoparticles obtained by this method exhibits a higher oxygen permeation flux.

[0042] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any form. Any technical solutions obtained by using equivalent replacements or equivalent transformations fall within the protection scope of the present invention.

Claims

1. A perovskite-type mixed conductor film with metal precipitated on the surface, characterized in that: The perovskite mixed conductor film has a thickness of 0.1 to 5 mm, has a general formula of perovskite metal oxide of ABO3, and the A-site element is a defect amount; the surface of the perovskite mixed conductor film has nano-metal particles precipitated by an electrically driven reduction method; in a photograph of the perovskite mixed conductor film obtained at a magnification of 50,000 to 100,000, the number of surface metal particles is 20 to 500, and the particle size is 30 to 200 nm.

2. The perovskite type mixed conductor film with metal deposited on the surface according to claim 1, characterized in that: The A-site element of the perovskite-type mixed conductor film is selected from rare earth or alkali metal elements, which is one of Be, Mg, Ca, Sr, Ba, La, Ce, Cd, Pb or Bi; the B-site element is selected from transition metal elements, which is one of Fe, Ni, Ti, Ta, Nb, Co, Mn, Al, Mo, Cu, Sc or Cr.

3. The perovskite type mixed conductor film with metal deposited on the surface according to claim 1, characterized in that: The precipitated metal nanoparticles are composed of one or more of the B-site elements of the perovskite-type mixed conductor film.

4. The method for preparing a perovskite-type mixed conductor film with metal precipitated on the surface according to claim 1, characterized in that: Metal nanoparticles are deposited in situ on a perovskite mixed conductor film by electric drive, comprising the following steps: constructing an electric drive reduction device with the perovskite mixed conductor film as a cathode, applying a negative voltage to the cathode at room temperature to carry out a reduction reaction, and depositing metal nanoparticles on the surface of the perovskite mixed conductor film.

5. The method for preparing a perovskite-type mixed conductor film with metal precipitation on the surface according to claim 4, characterized in that: The negative voltage applied to the cathode is greater than -2 V, and the reduction time is 1 to 24 h.

6. The method for preparing a perovskite-type mixed conductor film with metal precipitated on the surface according to claim 4, characterized in that: The electrolyte solution of the electrically driven reduction device is an alkaline or neutral solution with a molar concentration of 0-1 mol / L.

7. Use of the perovskite mixed conductor membrane according to claim 1 in oxygen separation.

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