A doped perovskite catalyst, its preparation method and application

Abstract

The present invention relates to a doped perovskite catalyst, a preparation method thereof and an application thereof, belonging to the technical field of catalysts. The doped perovskite catalyst of the present invention comprises a catalytic substrate, and SrMoO4 dispersed in the catalytic substrate; the chemical formula of the catalytic substrate is A a Sr (1‑a) Co b B (1‑b) O3, 0.6 ≤ a < 1, 0.1 ≤ b < 1, A is selected from Pr, La or Nd, and B is selected from Fe, Ni or Cu. By introducing SrMoO4, it is partially converted into conductive SrMoO3 under CO2 reduction conditions, and SMO4 and SMO4-derived SMO3 form a "conductive Sr 2+ cation trap". By using the "conductive Sr 2+ cation trap", the segregation of Sr 2+ to the electrochemically inert phase can be effectively prevented, and the electrode conductivity and CO2 reduction activity can be synchronously improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and particularly relates to a doped perovskite catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] The high-temperature CO2 reduction reaction (HT-CO2RR) based on a solid oxide electrolyzer (SOEC) is a feasible path for achieving net-zero emission chemical synthesis. ABO3-type perovskite oxides have been widely used as HT-CO2RR catalysts due to their high ionic / electronic conductivity, redox cycle stability, and abundant active sites. However, currently, mainstream catalysts (such as La x Sr 1-x MnO3, La 0.8 Sr 0.2 CoO3, La 1-x Sr x Co 0.2 Fe 0.8 O3) generally face the problem of chemical instability caused by the segregation of Sr 2+ cations on the material surface to form SrCO3 after initial high activity. These electrochemically inert products will block the contact between the active center and the reactants, leading to a serious attenuation of the ionic oxygen surface exchange coefficient, electronic conductivity, and catalytic stability, and resulting in poor stability and low efficiency of the solid oxide CO2 electrolysis device.

[0003] Sr 2+ The driving force for segregation mainly comes from two aspects: one is the cation redistribution caused by the free energy difference between the surface and the bulk phase (which can overcome the phase separation barrier at high temperatures); the other is the electrostatic interaction between the A-site cation and the oxygen vacancy (Ov). Existing studies have found that the segregation can be inhibited by doping difficult-to-reduce cations (Ti, Nb, Zr, Hf, Al, etc.) to reduce the surface Ov concentration, or by using the "reverse cation trapping" method to prepare Sr 2+ depleted surfaces to avoid precipitation. However, the more negative potential required for HT-CO2RR (about 1V lower than the ORR cathode of SOEC) will generate additional Ov through the B-site cation desolvation path, exacerbating Sr 2+ segregation. In addition, when HT-CO2RR operates above the thermoneutral potential (~1.47V), the exothermic mode will be initiated, and the cathode temperature rise will further deteriorate the segregation process.

[0004] Therefore, it is still extremely challenging to develop a catalytic material with excellent performance to improve its stability in HT-CO2RR, etc. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a doped perovskite catalyst, its preparation method and application. By introducing SrMoO4, it is partially converted into conductive SrMoO3 under CO2 reduction conditions. SMO4 and SMO3 derived from SMO4 form a "conductive Sr 2+ cation trap". In this trap, SMO4 is used to capture the desorbed Sr 2+ , while SMO3 formed by (electro)chemical reduction of SMO4 provides high electronic conductivity. Using the "conductive Sr 2+ cation trap", the segregation of Sr 2+ to the electrochemically inert phase can be effectively prevented, and the electrode conductivity and CO2 reduction activity can be simultaneously improved.

[0006] The first object of the present invention is to provide a doped perovskite catalyst, including a catalytic substrate, and SrMoO4 dispersed in the catalytic substrate;

[0007] The chemical formula of the catalytic substrate is A a Sr (1-a) Co b B (1-b) O3, 0.6 ≤ a < 1, 0.1 ≤ b < 1, A is selected from Pr, La or Nd, and B is selected from Fe, Ni or Cu.

[0008] In an embodiment of the present invention, the mass percentage of SrMoO4 is 10% - 50%.

[0009] The second object of the present invention is to provide a preparation method of the doped perovskite catalyst, including the following steps: adding a complexing agent and an auxiliary complexing agent to an aqueous solution containing A salt, Sr salt, Co salt, B salt and Mo salt, adjusting the pH to 5 - 9, and obtaining the doped perovskite catalyst through stirring, heating, drying and calcination.

[0010] In an embodiment of the present invention, the A salt is selected from one or more of Pr(NO3)2, La(NO3)3 and C4H4NNbO9;

[0011] and / or, the Sr salt is selected from one or more of Sr(NO3)2, SrO, SrCO3 and Sr(OH)2;

[0012] and / or, the Co salt is selected from Co(NO3)2 and / or (CH3COO)2Co;

[0013] and / or, the B salt is selected from one or more of Cu(NO3)2, (CH3COO)2Cu, Fe(NO3)3 and Ni(NO3)2;

[0014] and / or, the Mo salt is selected from H24 Mo7N6O 24 and / or (NH4)3[PMo 12 O 40 .

[0015] In one embodiment of the present invention, the complexing agent is citric acid;

[0016] and / or, the auxiliary complexing agent is ethylenediaminetetraacetic acid.

[0017] In one embodiment of the present invention, the molar ratio of the total metal ions, the complexing agent and the auxiliary complexing agent is 1:(1 - 2):(1 - 2).

[0018] In one embodiment of the present invention, the temperature of the stirring and heating is 190°C - 210°C.

[0019] In one embodiment of the present invention, the temperature of the calcination is 940°C - 960°C, and the time is 5h - 7h.

[0020] The third object of the present invention is to provide a solid oxide electrolyzer, and the solid oxide electrolyzer includes the doped perovskite catalyst described above.

[0021] The fourth object of the present invention is to provide an application of the solid oxide electrolyzer described above in reducing CO2 to produce CO.

[0022] The technical solution of the present invention has the following advantages compared with the prior art:

[0023] (1) The doped perovskite catalyst of the present invention utilizes the "conductive Sr 2+ cation trap" strategy to introduce a substance with higher Sr 2+ chemical stability than SrCO3, and blocks the migration of Sr 2+ to the inert phase through a thermodynamic mechanism. This trap can continuously capture Sr 2+ and stably form a Sr-deficient perovskite surface, breaking the contradiction between high performance and long-term stability. The specific method is to chemically fix Sr 2+ in SrMoO4 (SMO4), which can be in-situ converted into highly conductive SrMoO3 (SMO3) during the reaction.

[0024] (2) The doped perovskite catalyst of the present invention doubles the current density while increasing the stability by an order of magnitude. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to make the content of the present invention be more clearly understood, the following further describes the present invention in detail according to the specific embodiments of the present invention in conjunction with the drawings, wherein:

[0026] Figure 1 This is the structure and morphology of the material before the catalytic reaction in the test examples of the present invention; among them, a is the X-ray diffraction pattern of SPG-19, SPG-3 and PG, and b-d are the scanning electron microscopy energy spectrum analysis results of PSCC, 3wt% SMO4 / PSCC and 19wt% SMO4 / PSCC, respectively;

[0027] Figure 2 This is the comparison result of the HT-CO2RR stability of SPG-19, SPG-3 and PG at an inlet CO partial pressure of 1.3V and 0.1atm in the test examples of the present invention;

[0028] Figure 3 This is the morphology of the material after the catalytic reaction in the test examples of the present invention; among them, a is the scanning electron microscopy image of PG, and b is the scanning electron microscopy image of SPG-19;

[0029] Figure 4 This is the photoelectron spectrum of the material after the catalytic reaction in the test examples of the present invention; among them, a is the deconvoluted Sr 3d X-ray photoelectron spectrum result of the untested material, b is the deconvoluted Sr 3d X-ray photoelectron spectrum result of the tested material, and c is the proportion of the corresponding Sr species in a and b;

[0030] Figure 5 This is the phase change of the SMO4 electrolytic cell after electrolysis testing in the test examples of the present invention; among them, a is the electrolyte conductivity of the SMO4 electrolytic cell at different potentials relative to the open circuit voltage (OCV) at 0.1atm and 0.3atm CO partial pressure, b is the comparison of the X-ray structure maps of the SMO4 electrolytic cell before and after the test in a, and c is the transmission electron microscopy image of the SMO4 sample after the test in b after focused ion beam cutting of the sample;

[0031] Figure 6 This is the X-ray diffraction pattern of SrO and SMO4 with a molar ratio of 1:1 after calcination at 400 °C, 600 °C, 800 °C and 1000 °C for 3h in the test examples of the present invention compared with the original SrO;

[0032] Figure 7 This is the in-situ Raman study result of PSCC and 19wt% SMO4 / PSCC in a pure CO2 atmosphere in the test examples of the present invention;

[0033] Figure 8 This is the comparison of the thermodynamic stability of SrMoO4 and SrCO3 with changes in temperature and CO partial pressure in the test examples of the present invention;

[0034] Figure 9 This is the stability test result of a single electrolytic cell with an SPG-19 cathode at a constant current of 1.3A / cm 2 under the present invention. Specific Embodiments

[0035] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the specific embodiments cited do not limit the present invention.

[0036] In the present invention, unless otherwise specified, the raw materials in the preparation process of the doped perovskite catalyst are all purchased from Aladdin Reagents.

[0037] In the present invention, unless otherwise specified, the LSCF and GDC powders are purchased from Ningbo SOFCMAN Energy Technology Co., Ltd. Example 1

[0038] The doped perovskite catalyst of the present invention and its preparation method specifically include the following steps:

[0039] Dissolve 6 g of Pr(NO3)2·6H2O, 1.458 g of Sr(NO3)2, 4.51 g of Co(NO3)2·6H2O, 0.32 g of Cu(NO3)2·xH2O and 2.13 g of H 24 Mo7N6O 24 ·4H2O in deionized water, and sequentially add 14.41 g of citric acid and 14.61 g of ethylenediaminetetraacetic acid (EDTA). The molar ratio of the total metal ions, citric acid and ethylenediaminetetraacetic acid is about 1:1.5:1; then adjust the pH to 7 with ammonia water, continuously stir and heat to 200 °C to form a gel and then dry; finally, calcine in an air atmosphere at 950 °C for 6 h to obtain the doped perovskite catalyst; among them, the chemical formula of the catalytic substrate is Pr 0.8 Sr 0.2 Co 0.9 Cu 0.1 O3 (PSCC), and the mass percentage of SrMoO4 (SMO4) is 19%, denoted as 19 wt% SMO4 / PSCC. Comparative Example 1

[0040] Basically the same as Example 1, the difference is: adjust the dosage of Sr(NO3)2 to 0.911 g, and the dosage of H 24 Mo7N6O 24 ·4H2O to 0.532 g to obtain a doped perovskite catalyst with a mass percentage of SrMoO4 of 3%, denoted as 3 wt% SMO4 / PSCC. Comparative Example 2

[0041] Basically the same as Example 1, the difference is: adjust the dosage of Sr(NO3)2 to 0.729 g, and adjust H 24 Mo7N6O 24· The amount of 4H2O is 0, and a perovskite catalyst without SrMoO4 is obtained, denoted as PSCC.

[0042] Test Example

[0043] Preparation of solid oxide electrolytic cell:

[0044] S1. Prepare an SSZ substrate with a thickness of about 0.2 mm and a diameter of about 40 mm by tape casting method, and sinter it at 1500 °C for 5 h;

[0045] S2. Screen-print a GDC barrier layer on both sides of the SSZ substrate and calcine it at 1350 °C for 3 h to obtain a GDC|SSZ|GDC component;

[0046] S2. Ball-mill LSCF powder and GDC powder in a mass ratio of 60:40 for 12 h, then add 20 wt% terpineol and 10 wt% PMMA binder, and stir evenly to obtain an anode slurry;

[0047] The materials prepared in Example 1 and Comparative Examples 1-2 were respectively ball-milled with gadolinium-doped cerium oxide (GDC) in a mass ratio of 60:40 for 12 h to obtain mixed materials (labeled as SPG-19, SPG-3, and PG respectively); then 20 wt% terpineol and 10 wt% PMMA binder were added and stirred evenly to obtain a cathode slurry.

[0048] S3. Screen-print the anode slurry on the GDC|SSZ|GDC component to form an anode layer (effective area 0.2 cm 2 ), and calcine it at 1150 °C for 2 h; screen-print the cathode slurry on the other side of the GDC|SSZ|GDC component to form a cathode layer (effective area 0.5 cm 2 ), and calcine it at 1050 °C for 2 h. Use silver paste as the current collector to obtain a solid oxide electrolytic cell (SOEC).

[0049] Performance test:

[0050] Before the catalytic reaction, XRD characterization of SPG-19, SPG-3, and PG was carried out using a PANalytical Empyrean diffractometer (Cu Kα radiation, λ = 1.54 Å), and the results are as Figure 1 shown in a. It can be seen from Figure 1 a that PSCC adopts the orthorhombic Pnma phase, while SMO4 presents the tetragonal I41 / a phase, with obvious reflection peaks of (112), (004), and (204).

[0051] Before the catalytic reaction, SEM and EDS characterizations of PSCC, 3wt% SMO4 / PSCC, and 19wt% SMO4 / PSCC were carried out using TALOS 200X and JEOL JEM-2100F equipped with Oxford X-Max 80T energy spectrometer, and the results are as Figure 1 shown in b-d of Figure 1 . It can be seen from b-d of

[0052] that SMO4 is uniformly distributed on the surface of PSCC, and the SMO4 coverage increases from 0% of PSCC to about 50% of 19wt% SMO4 / PSCC. Figure 2 The degradation rates of SPG-19, SPG-3, and PG were tested by the constant current chronoamperometry method, where the flow rate of the CO2 reactant was 50 sccm / min, the working temperature was 800 °C, and the working potential was 1.3 V, and the results are as Figure 2 shown. It can be seen from -1 Figure 2 that the decay rate of SPG-19 is 0.1% h -1 , one order of magnitude lower than that of PG (1.17% h -1

[0053] and SPG-3 (1.63% h Figure 3 ), indicating that SPG-19 has excellent stability. Figure 3 After the catalytic reaction, SPG-19 and PG were characterized by Zeiss G500 scanning electron microscope, and the results are as

[0054] shown. It can be seen from Figure 4 Figure 4 that cobalt-copper nanoparticles and lamellar strontium element aggregation layers are precipitated on the surface of PG, while there is no strontium element enrichment phenomenon on the surface of SPG-19 except for the precipitated cobalt-copper nanoparticles, indicating the inhibitory effect of SMO4 on Sr segregation. 2+

[0055] 2+

[0055] 2+

[0055] 2+

[0055] 2+

[0055] 2+

[0055]

[0055] In order to explore other possibilities for improving HT-CO2RR in the presence of SMO4, a cell using only SMO4 as a catalyst (i.e., SMO4 electrolyzer) was prepared for HT-CO2RR. Electrochemical impedance spectroscopy was used to test the structure of SMO4 after the test using a PANalytical Empyrean diffractometer and TALOS 200X. The results are shown in Figure 2. Figure 5 As shown. Figure 5 As can be seen in Figure a, the conductivity of the SMO4 electrolyzer increases by about two orders of magnitude when the applied voltage is swept from 0 to 900 mV vs OCV. Specifically, the conductivity under OCV is ~3.1×10 -6 Scm -1 , 4.5×10 at 0.3atm PCO - 6 Scm -1 , and then increased to 5.1±1.4×10 at 900mV -4 Scm -1 .from Figure 5 As can be seen in b, SrMoO3 (SMO3) does exist, and this perovskite oxide has 10 4 Scm -1 The high electronic conductivity of the material is indicated by the cubic phase diffraction peaks at (110), (200), and (211). Figure 5 As can be seen in Figure c, the SMO3 phase was identified within a depth of about 3 nm on the surface of the bulk SMO4 by combining focused ion beam (FIB) and TEM. In summary, the conductivity of SMO4 increased significantly under applied potential, and the surface was covered with an in-situ generated SMO3 nanoshell, proving that SMO3 increased the conductivity of the catalyst and that SMO3 was easily oxidized to SMO4, confirming that the conductive Sr 2+ The TRAP consists of SMO4 and the SMO4-derived SMO3.

[0056] The crystal structures of SrO and SMO4 with a molar ratio of 1:1 after calcination at 400℃, 600℃, 800℃ and 1000℃ for 3h were analyzed by PANalytical Empyrean diffractometer. Figure 6 As shown. Figure 6 It can be seen that the disappearance of the SrO (100) reflection peak during the sintering process indicates that SrO and SMO4 undergo a solid phase reaction, and SMO4 can react with the Sr element enriched on the surface. When SrO and SMO4 are calcined at a molar ratio of 1:1, the product is Sr 11 Mo4O 23 and Sr2MoO4. This further confirms that SMO4 has a wide range of Sr 2+ The ability to capture continuously at segregation levels.

[0057] In-situ Raman spectroscopy was used to characterize the surface states of PG and SPG-19 under working conditions, and the results are as Figure 7 shown. It can be seen from Figure 7 that during the reaction of PG, segregation of Sr element occurred and it existed in the form of SrCO3 on the surface of PG, while no Sr segregation occurred in SPG-19 during the reaction.

[0058] Density functional theory was used to calculate the relationship between the formation energies of SrMoO4 and SrCO3 and the CO partial pressure, and the results are as Figure 8 shown. It can be seen from Figure 8 that at 800 °C and 0.3 atm CO atmosphere, the energy difference between SrCO3 and SrMoO4 is 0.46 eV atom -1 . This indicates that the formation of SrMoO4 is more favorable than that of SrCO3, and it has no obvious relationship with the concentration of the reactant CO, confirming the priority of SrMoO4 in reacting with free Sr ions.

[0059] The constant current chronopotentiometry was used to test the stability of a 0.2 cm 2 button battery with an SPG-19 cathode at a high current density (a constant current of 1.3 A / cm 2 ), and the results are as Figure 9 shown. It can be seen from Figure 9 that SPG-19 operates stably without obvious decay phenomenon, demonstrating the positive effect of SMO4 on improving the stability of the catalyst.

[0060] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A doped perovskite catalyst, characterized in that: It includes a catalytic substrate, and SrMoO4 ​​dispersed in the catalytic substrate; The chemical formula of the catalytic substrate is A a Sr (1-a) Co b B (1-b) O3, 0.6≤a<1, 0.1≤b<1, A is selected from Pr, La or Nd, B is selected from Fe, Ni or Cu; The mass percentage of SrMoO4 ​​is 10%-50%.

2. The method for preparing the doped perovskite catalyst according to claim 1, characterized in that: The following steps are involved: A complexing agent and an auxiliary complexing agent are added to an aqueous solution containing A salt, Sr precursor, Co salt, B salt and Mo salt, the pH is adjusted to 5-9, and the doped perovskite catalyst is obtained by stirring, heating, drying and calcining.

3. The method for preparing a doped perovskite catalyst according to claim 2, characterized in that: The A salt is selected from one or more of Pr(NO3)2, La(NO3)3 and C4H4NNbO9; and / or, the Sr precursor is selected from one or more of Sr(NO3)2, SrO, SrCO3 and Sr(OH)2; and / or, the Co salt is selected from Co(NO3)2 and / or (CH3COO)2Co; and / or, the B salt is selected from one or more of Cu(NO3)2, (CH3COO)2Cu, Fe(NO3)3 and Ni(NO3)2; And / or, the Mo salt is selected from H 24 Mo7N6O 24 and / or (NH4)3[PMo 12 O 40 ].

4. The method for preparing a doped perovskite catalyst according to claim 2, characterized in that: The complexing agent is citric acid; And / or, auxiliary complexing agent ethylenediaminetetraacetic acid.

5. The method for preparing a doped perovskite catalyst according to claim 2, characterized in that: The molar ratio of the total metal ions, the complexing agent and the auxiliary complexing agent is 1:(1-2):(1-2).

6. The method for preparing a doped perovskite catalyst according to claim 2, characterized in that: The stirring and heating temperature is 190°C-210°C.

7. The method for preparing a doped perovskite catalyst according to claim 2, characterized in that: The calcination temperature is 940° C.-960° C., and the calcination time is 5 h-7 h.

8. A solid oxide electrolytic cell, characterized in that: The solid oxide electrolytic cell comprises the doped perovskite catalyst of claim 1.

9. Use of the solid oxide electrolytic cell according to claim 8 in reducing CO2 to produce CO.

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