A perovskite mixed conductor film that surface evolves metal, a method of electrically driving in situ evolution of metal nanoparticles, and uses thereof

Abstract

The application discloses a perovskite mixed conductor film with metal precipitated on the surface, a method for electrically driving in-situ precipitation of metal nanoparticles and application, the surface of the mixed conductor film has metal nanoparticles precipitated in-situ by electric driving, and a preparation method of the mixed conductor film comprises the following steps: building an electrically driven reduction device with the perovskite mixed conductor film as a cathode, applying a negative voltage to the cathode at normal temperature, performing a reduction reaction, and precipitating metal nanoparticles. The application uses the perovskite mixed conductor film as the cathode, utilizes the redox characteristics of the metal at the B position, designs defects at the A position to provide auxiliary reduction, applies a potential to the cathode at normal temperature, makes the surface of the perovskite film restructure, and then precipitates metal nanoparticles.

Description

Technical Field

[0001] This invention belongs to the field of functional ceramics technology, specifically relating to a perovskite-type hybrid conductor film with surface metal precipitation, a method for electrically driven in-situ precipitation of metal nanoparticles, and their applications. Background Technology

[0002] Dense hybrid conductor membranes, due to their high oxygen ion-electron conductivity, are widely used in green chemical industries such as air separation, oxygen-enriched combustion, and catalytic membrane reactors. Among them, perovskite materials (with the general formula ABO3) possess flexible and adjustable crystal structures and elemental compositions. Their variable oxygen ion mobility and high structural stability at high temperatures make them one of the most commonly used hybrid conductor oxygen-permeable membrane materials. However, during oxygen permeation, perovskite membranes are constrained by the relationship between oxygen transport performance and stability, failing to meet industrial requirements. Improving the oxygen permeation flux of perovskite membranes and solving their operational stability issues during high-temperature oxygen permeation are key to advancing their industrial application.

[0003] Loading metal particles onto the membrane surface is an effective way to improve membrane transport properties, but particle sintering and agglomeration are inevitable during the preparation process, leading to performance degradation. Numerous studies have shown that B-site metals in perovskites can be precipitated onto the perovskite surface through heat treatment in a reducing atmosphere. The precipitated metal particles are anchored on the surface, exhibiting good dispersibility, stability, and anti-coking properties, making it a promising strategy for preparing high-efficiency functional perovskite materials. Patent CN113332992B discloses a perovskite catalyst and its preparation method, employing a combination of oxidation followed by reduction, followed by calcination at high temperature and in an air atmosphere to precipitate one or more water-absorbing oxide nanoparticles in situ. The calcination temperature is 700–800℃, and the calcination time is 4–6 h. Patent CN108654592B discloses a perovskite catalyst and its preparation and in-situ testing methods. The perovskite precursor powder is reduced at 800 °C in a 5% H₂-N₂ atmosphere for 4–12 h, causing B-site catalytic metal to precipitate in situ into B-site metal nanoparticles that coat the surface of the perovskite precursor powder. Patent CN115548356B discloses a method for preparing and applying a perovskite-type solid oxide battery electrode catalyst. This involves doping the B-site of perovskite with transition elements, resulting in the in-situ precipitation of alloy particles under a high-temperature reducing atmosphere. The reduction temperature is 850 °C, and the reduction time is 1–3 h. Therefore, currently used methods require high reduction temperatures (typically greater than 600 °C) and long reduction times (including heating / cooling time and holding time, typically greater than 10 h), and most research focuses on the modification of perovskite powder catalysts rather than film preparation. Therefore, developing a method for metal particle precipitation on the surface of perovskite membranes at room temperature is expected to quickly and easily obtain high-flux and stable oxygen-permeable membranes. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a perovskite-type hybrid conductor film with surface metal deposition, a method for electrically driven in-situ deposition of metal nanoparticles, and its applications. The perovskite-type hybrid conductor film is used as the cathode. The redox properties of the metal at the B site are utilized, and defects at the A site 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, thereby depositing metal nanoparticles.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for in-situ precipitation of metal nanoparticles from an electrically driven perovskite-type hybrid conductor film includes the following steps: (1) Construction of the electrically driven reduction device: A pre-prepared perovskite-type mixed conductor film is fixed as the cathode using electrode clamps. A material with stable electrochemical performance is selected as the anode. A certain concentration of electrolyte solution is added to ensure electron transport. The cathode is connected to the negative terminal of the power supply, and the anode is connected to the positive terminal of the power supply using wires to ensure circuit continuity. See details. Figure 1 .

[0006] (2) Preparation of perovskite-type hybrid conductor films with electrically driven reduction precipitation of metal nanoparticles: A negative voltage is applied to the cathode of the electrically 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 hybrid conductor film is 0.1~5 mm, it has the general formula of perovskite metal oxide ABO3, and the A-site element is a 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 photographs of the aforementioned perovskite hybrid conductor film obtained at magnifications of 50,000 to 100,000, the number of surface metal particles ranges from 20 to 500, and the particle size ranges from 30 to 200 nm.

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

[0011] Preferably, the precipitated metal nanoparticles consist of one or more of the B-site elements of the perovskite-type hybrid conductor film.

[0012] Preferably, the chemical formula of the aforementioned perovskite-type hybrid conductor film is (La 0.6 Sr 0.4 ) 0.9 Co 0.2 Fe 0.8 O 3-δ The precipitated metal particles are composed of elemental Co.

[0013] Preferably, the electrolyte solution of the aforementioned electrically driven reduction device is any conductive alkaline or neutral solution such as NaOH, KOH, or H2O with a molar concentration of 0-1 mol / L. The anode material is a graphite rod or other material that will not dissolve into the electrolyte during the application of voltage. The power source is a dry cell, a storage battery, an electrochemical workstation, or other device that can maintain a stable voltage and current in the circuit.

[0014] The aforementioned perovskite-type hybrid conductor membrane with precipitated metal nanoparticles is used in oxygen separation.

[0015] The reaction mechanism of this invention: During electroreduction, under the combined effects of the negative cathode 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, leading to local reconstruction and the generation of new phases. The precipitation and anchoring of metal particles on the membrane surface significantly improves the oxygen flux of perovskite oxygen-permeable membranes. This is mainly because the presence of metal nanoparticles increases the number of active sites on the membrane surface, alters the local electronic structure of the membrane surface, thereby promoting oxygen adsorption / desorption and electron transfer. Compared to traditional impregnation methods for supporting metal catalysts, in-situ precipitated nanoparticles exhibit stronger bonding with the substrate and possess higher anti-coking performance and stability.

[0016] The advantages of this invention are: (1) The present invention uses an electro-driven reduction method at room temperature to precipitate metal nanoparticles on the surface of a perovskite-type hybrid conductor film, which can be coupled with renewable energy systems such as solar and wind power. This method not only avoids the potential safety risks caused 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 hybrid conductor film, with higher precipitation efficiency and faster precipitation speed; (3) The precipitation device of the present invention is simple to operate, easy to use, and the process conditions are easy to control. It has the advantages of simple process conditions and low cost. It can be applied to a variety of fields such as pure oxygen separation and catalytic membrane reactor, and has positive social benefits and significant economic benefits. Attached Figure Description

[0017] Figure 1 A schematic diagram of an apparatus for electrically driven reduction of perovskite-type hybrid conductor films; Figure 2 The XRD diffraction patterns of the LSCF perovskite hybrid conductor films obtained before and after electroreduction in Examples 1 and 4 are shown. Figure 3 SEM images of the LSCF perovskite hybrid conductor film surface obtained before and after electroreduction in Examples 1-4 are shown below (a: no electro-driven reduction treatment was performed in Example 4; b: the electro-driven reduction time was 1 h in Example 2; c: the electro-driven reduction time was 5 h in Example 1; d: the electro-driven reduction time was 24 h in Example 3). Figure 4 The graph shows a comparison of the oxygen permeation performance of the LSCF perovskite hybrid conductor membranes obtained before and after electroreduction in Examples 1 and 4. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0019] To improve the oxygen permeability and operational stability of perovskite-type hybrid conductor membranes, this method utilizes the potential effect of the negative cathode potential during electrolysis, along with the combined effects of adsorption and migration of molecules, ions, and reaction intermediates in the electrolyte or cathode material, to achieve the deposition of B-site metals as nanoparticles on the membrane surface at room temperature. This method is not only simple to operate and low in cost, but also effectively saves energy, achieving a simultaneous improvement in oxygen permeability and stability.

[0020] A method for in-situ precipitation of metal nanoparticles from an electrically driven perovskite-type hybrid conductor film, the method comprising: (1) According to the designed stoichiometric ratio, the metal oxide raw material and the ball milling media are fully mixed by ball milling. After drying and sieving, the mixture is placed in a muffle furnace to sinter into a phase, thus preparing perovskite powder with A-site defects.

[0021] (2) Take 1 g of sintered perovskite powder material and add a small amount of polyvinyl alcohol binder. After grinding and mixing evenly, pour it into a mold. Press the powder into shape using a tablet press by applying a certain pressure using the isostatic pressing method. After pressing, take it out to obtain a perovskite sheet film preform with A-site defects. A certain pressure refers to the pressure range that can press the perovskite powder into a regular sheet film preform shape and prevent it from scattering due to force during handling.

[0022] (3) The obtained green body is placed in a muffle furnace for sintering to remove organic matter and transform it into a dense membrane structure, thus obtaining a perovskite sheet membrane with A-site defects.

[0023] (4) The perovskite sheet film with the A-site defect is fixed with an electrode clamp and used as a cathode. Then, the power supply and anode, and the power supply and cathode are connected by wires respectively, forming a circuit under the action of the electrolyte. By applying a certain voltage, the current flows through the circuit. After maintaining a constant voltage for a period of time, the cathode is polarized and reconstructed, and finally a perovskite-type hybrid conductor film with metal nanoparticles deposited on the surface is obtained. Wherein: the anode is a graphite rod electrode, and the electrolyte is a 0.1 M KOH solution.

[0024] The fourth step was performed under different parameter conditions to obtain perovskite-type hybrid conductor films with different surface morphologies. The surface microstructure of the films was obtained by SEM. Among the SEM images of the samples under different electroreduction conditions, the parameter conditions corresponding to the sample with a dense perovskite film surface and uniform distribution of precipitated metal particles were taken as the optimal values ​​for electroreduction.

[0025] Metal nanoparticles are formed when the valence of transition metal cations at the B site in the perovskite phase decreases after electron transfer. Under the influence of the concentration gradient, they migrate to the film surface, nucleate and grow on the surface, and eventually anchor to the metal element on the film surface.

[0026] Example 1: The method for electrically driven reduction of perovskite to precipitate metal nanoparticles at room temperature is implemented according to the following steps: (1) Preparation of A-site defects (La) by solid-state sintering process 0.6 Sr 0.4 ) 0.9 Co 0.2 Fe 0.8 O 3-δ Perovskite powder La₂O₃ (99.0%), SrCO₃ (99.0%), Co₂O₃ (99.0%), and Fe₂O₃ (99.0%) were mixed according to stoichiometric ratios and ball-milled in ethanol for 24 h. The resulting slurry was dried at 70 °C for 24 h and then sieved through a 100-mesh sieve. The sieved powder was then calcined at 900 °C for 5 h, with the heating and cooling rates controlled at 2 °C / min, to form A-site defects in (La₂O₃). 0.6 Sr 0.4 ) 0.9 Co 0.2 Fe 0.8 O 3-δ Perovskite powder (LSCF).

[0027] (2) Preparation of perovskite hybrid conductor film by isostatic pressing To obtain a dense perovskite hybrid conductor oxygen-permeable membrane, a die from a tablet press was used for the forming process, including powder loading, pressing, and removal. A pressure of 10 MPa was applied to the die by the press, and after holding the pressure for 1 min, the pressure was released, and the die was removed from the press to obtain a perovskite hybrid conductor membrane preform. The LSCF preform was then sintered in a muffle furnace at 1200 °C for 10 h, with the heating and cooling rates controlled at 2 °C / min, to obtain a dense LSCF perovskite hybrid conductor oxygen-permeable membrane.

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

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

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

[0031] Example 4: The specific difference between this example and Example 1 is that the electric drive reduction process is not adopted in step (3).

[0032] Performance testing: (1) XRD pattern 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 both before and after electro-driven reduction. After reduction, the XRD pattern of the sample obtained in Example 1 showed a slight left shift compared to the sample in Example 4, indicating lattice expansion. The sample obtained in Example 1 showed characteristic peaks of elemental Co, proving that Co metal can be successfully deposited on the membrane surface by this electro-reduction method. During the reduction process, due to the high applied negative potential, when the electron supply exceeds the amount required for the reduction of H2O in the electrolyte to generate H2, the excess electrons begin to reduce B-site Co and Fe ions in the LSCF membrane, as well as lattice oxygen in the perovskite. At this time, atomic migration will occur near the surface of the perovskite membrane. 2+ The required deposition potential of ions compared to Co 2 +With higher ion concentrations, Co is preferentially deposited onto the membrane surface. After the metal nanoparticles are deposited, continuous cathodic polarization will prevent the deposited particles from being oxidized again.

[0034] (2) The samples obtained in Examples 1 to 4 were subjected to scanning electron microscopy (SEM) tests.

[0035] pass Figure 3 It can be seen that the surface of the untreated LSCF membrane is smooth. Figure 3 (a); after 1 h of electroreduction treatment, there was still no significant change on the membrane surface ( Figure 3 (b) When the electroreduction treatment time reached 5 h, a large number of uniformly distributed nanoparticles were observed on the surface of the LSCF film. Figure 3 Based on the XRD results, it can be confirmed that it is Co metal nanoparticles. However, when the electroreduction treatment time is extended to 24 h, the dense structure on the surface of the perovskite film is destroyed. Figure 3 (d) The grains disintegrate and fall into the water, making it unusable for oxygen permeability testing. Therefore, it can be seen that using the electro-driven reduction process of this invention, metal nanoparticles were successfully precipitated on the surface of the perovskite-type hybrid conductor membrane, and the morphology of the membrane surface changed with the extension of the constant voltage holding time. This is because the prolonged application of a high negative potential and the ion leaching effect caused by the surrounding water environment lead to the perovskite structure being in a metastable state. Simultaneously with the precipitation of Co metal, Sr... 2+ Ions may also leach into the electrolyte, causing the membrane to lose its original airtightness. Therefore, the LSCF perovskite oxygen permeation membrane treated for 5 h exhibits the best surface microstructure.

[0036] (3) The oxygen permeability of the samples obtained in Examples 1 and 4 was tested using the following methods: Step a: Setting up the high-temperature oxygen permeation apparatus. Place an alumina tube of appropriate length vertically. Use silver glue as a sealant to seal the perovskite-type mixed conductor membrane at the upper end of the alumina tube with a suitable inner diameter. Connect the lower end of the alumina tube to the assembly with white glue. The assembly has one inlet and one outlet, allowing gas to enter the alumina tube to purge the membrane and analyze the gas composition.

[0037] Step b: Introduce purge gas (He, 60 mL / min) into 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 containing the membrane in the high-temperature oxygen permeation device into a tube furnace for temperature control and testing. During the oxygen permeation test, the temperature is controlled at 700~900 ℃, and the heating and cooling rate is 5 ℃ / min.

[0039] Step d: Online gas chromatography with a thermal conductivity detector and a 5A molecular sieve column was used to analyze the permeate-side outlet gas content. During oxygen measurement, the gas leakage on the feed side was less than 0.5%.

[0040] like Figure 4 As shown, at the same operating temperature, Example 1 exhibits a higher oxygen permeation flux than Example 4. This is because the precipitation of Co nanoparticles increases the specific surface area of ​​the membrane and the number of O2 adsorption sites, effectively enhancing the surface exchange rate of the membrane. This demonstrates the beneficial effect of electro-driven reduction method on perovskite oxygen permeable membranes at room temperature.

[0041] This invention successfully precipitated uniformly distributed metal nanoparticles on the surface of a perovskite hybrid conductor membrane via electroreduction treatment at room temperature. The surface morphology of the prepared membrane was characterized using XRD and SEM, and the performance of the oxygen-permeable membranes was compared using oxygen permeation testing. The perovskite oxygen-permeable membrane with precipitated metal nanoparticles obtained by this method exhibited a higher oxygen permeation flux.

[0042] The foregoing has shown and described 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 way, and all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. The application of a perovskite-type hybrid conductor membrane with surface-deposited metal in oxygen separation, characterized in that, The perovskite-type hybrid conductor film has a thickness of 0.1-5 mm and is prepared by the following steps: (1) Perovskite powder with A-site defects was prepared by solid-state sintering process; (2) Perovskite-type hybrid conductor film was prepared by isostatic pressing of perovskite powder; (3) At room temperature, metal nanoparticles are precipitated in situ on a perovskite-type mixed conductor film by electro-drive in an electrolyte solution; The chemical formula of the perovskite powder is (La 0.6 Sr 0.4 ) 0.9 Co 0.2 Fe 0.8 O 3-δ The metal nanoparticles are elemental Co; in the photographs of the perovskite hybrid conductor film obtained at magnification of 50,000 to 100,000, the number of surface metal nanoparticles is 20 to 500, and the particle size is 30 to 200 nm.

2. The application according to claim 1, characterized in that, The specific method of step (3) is as follows: an electro-driven reduction device with a perovskite-type mixed conductor film as the cathode is constructed, a negative voltage is applied to the cathode at room temperature to carry out the reduction reaction, and metal nanoparticles are precipitated on the surface of the perovskite-type mixed conductor film; the negative voltage applied to the cathode is greater than -2 V, and the reduction time is 5 h; the electrolyte solution of the electro-driven reduction device is an alkaline or neutral solution with a molar concentration of 0~1 mol / L.

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