A cathode material for B-site high-entropy solid oxide electrolysis cells, its preparation method and application

Abstract

The present invention discloses a cathode material for a B-site high-entropy solid oxide electrolytic cell, its preparation method and application, wherein the cathode material has a high-entropy perovskite structure of the A2B2O6 type, and the chemical formula is Sr2FeTi 0.2 Cr 0.2 Mn 0.2 Mo 0.2 Co 0.2 O6. This cathode material is an electron-ion mixed conductor, has good conductivity, and the ionic radii of the B-site elements are close, with small ionic size differences, which is conducive to the formation of a stable single-phase structure. Sr2FeTi 0.2 Cr 0.2 Mn 0.2 Mo 0.2 Co 0.2 O6 high-entropy perovskite material can simultaneously transport oxygen ions and electrons, can effectively reduce the polarization resistance of the cathode of the oxygen ion conduction type solid oxide electrolytic cell, improve the electrolysis current density of the electrolytic cell, and can maintain good structural stability in a pure carbon dioxide atmosphere, which can effectively enhance the output stability of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid oxide electrolysis cells, and particularly relates to a cathode material for a B-site high-entropy solid oxide electrolysis cell, a preparation method thereof, and an application thereof. Background Art

[0002] Among the existing carbon dioxide conversion methods, electrochemical reduction of carbon dioxide has the main advantages such as adjustable output with an applied voltage and consumption and utilization of renewable energy. Under high-temperature (>700 °C) operating conditions, using a solid oxide electrolysis cell (SOEC) for carbon dioxide electrolysis has good thermodynamic efficiency and fast electrokinetic rate, thereby obtaining excellent current density and energy efficiency.

[0003] The electrode material of the cathode of the SOEC has always been the electrode material of the anode of a solid oxide fuel cell (SOFC). Traditional SOFC cermet anodes such as Ni / YSZ are prone to problems such as nickel agglomeration, redox instability, carbon deposition, and sulfur poisoning when using hydrocarbon fuels. Perovskite-structured oxides have excellent anti-carbon deposition ability, strong impurity tolerance, high redox stability, and high ionic and electronic conductivity. However, such materials have problems of low conductivity and low fuel catalytic activity, which bring great difficulties to their commercial applications. The high-entropy effect in thermodynamics, lattice distortion effect in structure, slow diffusion effect in kinetics, and "cocktail" effect in electrical properties of high-configurational entropy perovskite oxides make such materials have great application prospects. Therefore, developing high-performance SOEC cathode materials is of great significance. Summary of the Invention

[0004] The purpose of the present invention is to provide a cathode material for a B-site high-entropy solid oxide electrolysis cell, a preparation method thereof, and an application thereof. This material can simultaneously transport oxygen ions and electrons, effectively reduce the polarization resistance of the cathode of an oxygen ion-conducting solid oxide electrolysis cell, improve the electrolysis current density of the electrolysis cell, and maintain good structural stability in a pure carbon dioxide atmosphere, effectively enhancing the output stability of the battery.

[0005] To achieve the above purpose, a cathode material for a B-site high-entropy solid oxide electrolysis cell of the present invention has a high-entropy perovskite structure of A2B2O6 type, wherein the A-site element is Sr element, and the B-site element is composed of six transition metal elements Fe, Ti, Cr, Mn, Mo, and Co mixed in a molar ratio of 5:1:1:1:1:1.

[0006] As a further scheme of the present invention: the chemical formula of the A2B2O6 is Sr2FeTi 0.2 Cr 0.2 Mn 0.2 Mo0.2 Co 0.2 O6。

[0007] A preparation method of a cathode material for a B-site high-entropy solid oxide electrolyzer, comprising the following steps:

[0008] S1, dissolving the precursors corresponding to the respective constituent elements of the cathode material of the solid oxide electrolyzer in water according to the stoichiometric ratio to obtain an aqueous metal ion solution;

[0009] S2, adding a complexing agent to the aqueous metal ion solution obtained in step S1 and adjusting the pH value to obtain a complexing sol;

[0010] S3, heating and stirring the complexing sol obtained in step S2 at 80 °C to evaporate and form a gel, and then self-propagating combustion occurs to obtain primary powder;

[0011] S4, transferring the primary powder obtained in step S3 to a high-temperature furnace for drying and calcination to obtain a cathode material powder for a B-site high-entropy solid oxide electrolyzer.

[0012] As a further scheme of the present invention: the precursors of the constituent elements Sr, Fe, Cr, Mn, and Co in step S1 are nitrates, the precursor of Ti is titanium dioxide, and the precursor of Mo is ammonium molybdate.

[0013] As a further scheme of the present invention: the complexing agent in step S2 is one or two of citric acid and ethylenediaminetetraacetic acid, the molar ratio of the complexing agent to the total molar amount of metal ions is 1:1 - 3:1, and ammonia water is added to adjust the pH value to 7.

[0014] As a further scheme of the present invention: the drying in step S4 is carried out in a high-temperature drying oven at a temperature of 300 °C for 10 h, and the calcination is carried out in a muffle furnace at 1200 °C for 10 h..

[0015] An application of the cathode material for a B-site high-entropy solid oxide electrolyzer as described above is applied to the cathode of a solid oxide fuel cell.

[0016] Compared with the prior art, the present invention dopes transition metal elements Fe, Ti, Cr, Mn, Mo, and Co at the B-site. This cathode material is an electron-ion mixed conductor with good electrical conductivity, and the ionic radii of the above 6 B-site elements are close, and the ionic size difference is small, which is conducive to the formation of a stable single-phase structure. Sr2FeTi in the present invention 0.2 Cr 0.2 Mn 0.2 Mo 0.2 Co 0.2The O6 high-entropy perovskite material can simultaneously transport oxygen ions and electrons, effectively reduce the polarization resistance of the cathode of an oxygen ion-conducting solid oxide electrolyzer, increase the electrolysis current density of the electrolyzer, and maintain good structural stability in a pure carbon dioxide atmosphere, effectively enhancing the output stability of the cell. Its preparation method is simple and can be applied to solid oxide fuel cells. Description of the Drawings

[0017] Figure 1 is the XRD pattern of the SFTCMMC high-entropy perovskite material synthesized by the sol-gel method.

[0018] Figure 2 is the XRD pattern of the high-entropy perovskite material SFTCMMC after reduction in a CO2 atmosphere.

[0019] Figure 3 is the I-V diagram of the SOEC assembled in the example for electrolyzing CO2 under different temperature conditions.

[0020] Figure 4 is the EIS diagram of the SOEC assembled in the example for electrolyzing CO2 under different temperature conditions. Detailed Embodiments

[0021] The present invention will be further described below with reference to the accompanying drawings.

[0022] A cathode material for a B-site high-entropy solid oxide electrolyzer has a high-entropy perovskite structure of the A2B2O6 type, where the A-site element is the Sr element, and the B-site element is composed of six transition metal elements, Fe, Ti, Cr, Mn, Mo, and Co, mixed in a molar ratio of 5:1:1:1:1:1. This cathode material is an electron-ion mixed conductor with good conductivity, and the ionic radii of the above six B-site elements are close, with small ionic size differences, which is conducive to the formation of a stable single-phase structure. The specific chemical formula is: Sr2FeTi 0.2 Cr 0.2 Mn 0.2 Mo 0.2 Co 0.2 O6.

[0023] A preparation method for a cathode material for a B-site high-entropy solid oxide electrolyzer includes the following steps:

[0024] S1, dissolving the precursors corresponding to the respective constituent elements of the cathode material of the solid oxide electrolyzer in water according to the stoichiometric ratio to obtain an aqueous metal ion solution;

[0025] S2, adding a complexing agent to the aqueous metal ion solution obtained in step S1 and adjusting the pH value to obtain a complexing sol;

[0026] S3. Heat and stir the complex sol obtained in step S2 at 80 °C to evaporate and form a gel, which then undergoes self-propagating combustion to obtain the primary powder.

[0027] S4. Transfer the primary powder obtained in step S3 to a high-temperature furnace for drying and calcination to obtain the cathode material powder of the B-site high-entropy solid oxide electrolytic cell.

[0028] Among them, the precursors of the constituent elements Sr, Fe, Cr, Mn, and Co in step S1 are nitrates, the precursor of Ti is titanium dioxide, and the precursor of Mo is ammonium molybdate.

[0029] The complexing agent in step S2 is one or more of citric acid, ethylenediaminetetraacetic acid, and glycine. The molar ratio of the complexing agent to the total molar number of metal ions is 1:1 - 3:1, and ammonia water is added to adjust the pH value to 7.

[0030] In step S4, drying is carried out in a high-temperature drying oven at a temperature of 300 °C for 10 h, and calcination is carried out in a muffle furnace at 1200 °C for 10 h.

[0031] The purpose of drying is to discharge ammonia gas in the nitrate and moisture in the raw materials to prevent the appearance of pores and cracking during the later sintering process, and to obtain a crystallized precursor powder.

[0032] The purpose of calcination is to remove organic substances and improve the density, and to refine the grains in a high-temperature environment to obtain a high-entropy perovskite ceramic material with regular grain shape and size.

[0033] An application of the B-site high-entropy solid oxide fuel cell cathode material as described above, used for the cathode of a solid oxide cell. The preparation method of the solid oxide cell is as follows:

[0034] A. Mix the above-mentioned B-site high-entropy solid oxide fuel cell cathode material powder with a binder, transfer it to a ball mill, and ball mill and mix evenly to obtain the cathode slurry.

[0035] B. Uniformly coat the cathode slurry on the surface of the barrier layer by screen printing or brushing method, and sinter at 1000 - 1200 °C for 1 - 3 h to obtain the cathode of the solid oxide cell.

[0036] In step A, the applicable electrolyte is scandia-stabilized zirconia or lanthanum strontium gallium magnesium. The binder is one or more of terpineol, ethyl cellulose, dibutyl phthalate, and butyl carbitol, and the mass fraction of ethyl cellulose is 3 - 7 wt%.

[0037] In step b, the barrier layer slurry is gadolinium-doped ceria or samarium-doped ceria.

[0038] Example:

[0039] Sr2FeTi 0.2 Cr 0.2 Mn 0.2 Mo 0.2 Co 0.2 Preparation of O6 high-entropy perovskite materials

[0040] S1. According to the chemical formula Sr2FeTi 0.2 Cr 0.2 Mn 0.2 Mo 0.2 Co 0.2 O6, weigh Sr(NO3)2, Fe(NO3)3·9H2O, TiO2, Cr(NO3)3·9H2O, H8MnN2O 10 , (NH4)6Mo7O 24 ·4H2O, Co(NO3)2·6H2O respectively in stoichiometric ratio and dissolve them in 300 ml of deionized water in turn. After the nitrates are completely dissolved, add complexing agents, including citric acid and ethylenediaminetetraacetic acid. Add citric acid and stir to dissolve it according to the molar ratio of total metal ions to citric acid of 1:1. Add ethylenediaminetetraacetic acid to the solution at a ratio of 1.5:1 to total metal ions, and add ammonia water to adjust the pH value to 7 to obtain a complex solution.

[0041] S2. Heat and stir the complex sol obtained in step S1 on a heating table at 80 °C to evaporate and form a gel, and then self-propagating combustion occurs to obtain primary powder;

[0042] S3. Transfer the primary powder obtained in step S2 to a high-temperature drying oven and dry it at 300 °C for 10 h to obtain a crystallized precursor powder.

[0043] S4. Put the powder obtained in step S3 into a crucible and transfer it to a high-temperature furnace for drying and calcination. Raise the temperature to 1200 °C at a heating rate of 2 °C / min, keep it at 1200 °C for 10 h, and then cool it to room temperature at a cooling rate of 3 °C / min to obtain the electrode material powder. Perform XRD analysis on the obtained powder, and the results are as Figure 1 shown.

[0044] S5. Take out the electrode material powder calcined in step S4 and put it into a test furnace, and calcine it at 850 °C for 10 h in a carbon dioxide atmosphere. Perform XRD analysis on the powder after reduction of the above powder in a carbon dioxide atmosphere, and the results are as Figure 2 shown.

[0045] By Figure 1-2It can be seen that the SFTCMMC fuel electrode material can be successfully prepared by the sol-gel method, and the material forms a uniform single-phase perovskite structure. The powder after reduction in a carbon dioxide atmosphere can maintain a good perovskite structure and no other impurity peaks appear, indicating that the fuel electrode material does not decompose in a carbon dioxide atmosphere and has good stability.

[0046] Application Example: Preparation Method of Solid Oxide Electrolytic Cell

[0047] A. Weigh an appropriate amount of the above-mentioned Sr2FeTi 0.2 Cr 0.2 Mn 0.2 Mo 0.2 Co 0.2 O6 solid oxide cell fuel electrode powder material in a mortar, and then add an appropriate amount of binder (the binder is terpineol and ethyl cellulose), plasticizer (dibutyl phthalate) and dispersant (butyl carbitol), and grind evenly to obtain the fuel electrode slurry.

[0048] B. Weigh an appropriate amount of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 o 3-δ and Ce 0.9 Gd 0.1 O 2-δ powders in a mortar according to a mass ratio of 6:4, add an appropriate amount of binder, and mix evenly to obtain the LSGF-GDC air electrode composite material.

[0049] C. Weigh an appropriate amount of Ce 0.9 Gd 0.1 O 2-δ barrier layer powder in a mortar, add a certain amount of binder and grind evenly to make the barrier layer slurry;

[0050] D. Uniformly coat the barrier layer slurry in step B above on both sides of a 0.3 mm thick (Sc2O3) 0.1 (CeO2) 0.01 (ZrO2) 0.89 electrolyte by screen printing, place it in an oven and dry for 30 min. The electrolyte is prepared by the tape casting method. The green body is placed in an oven and dried for 10 h, and then transferred to a muffle furnace and sintered at 1450 °C for 3 h.

[0051] E. Put the dried electrolyte above into a muffle furnace and sinter at 1250 °C for 3 h to obtain a multi-layer electrolyte material.

[0052] F. Coat the fuel electrode slurry and air electrode composite material prepared in steps A and B evenly on both sides of the above-mentioned multi-layer electrolyte material respectively. After drying, a full cell is obtained, which is transferred into a high-temperature sintering furnace for sintering to obtain a solid oxide electrolytic cell with Sr2FeTi 0.2 Cr 0. 2Mn 0.2 Mo 0.2 Co 0.2 O6 as the cathode material, where the fuel electrode material Sr2FeTi 0.2 Cr 0.2 Mn 0.2 Mo 0.2 Co 0.2 O6 is sintered in a high-temperature sintering furnace at 1100 °C for 2 h, and the air electrode material LSGF-GDC is sintered in a high-temperature sintering furnace at 1050 °C for 3 h.

[0053] After collecting the current of the solid oxide electrolytic cell prepared in step F with silver-palladium paste and silver wire, seal the single cell at one end of the ceramic tube with ceramic glue, with the fuel electrode facing inwards, and fix it in the test furnace. The fuel electrode and air electrode of the electrolytic cell are connected to an electrochemical workstation through silver wires. During the SOEC performance test of the prepared electrolytic cell (SFTCMMC|GDC|SSZ|GDC|LSCF-GDC), control the atmosphere on the fuel electrode side to be carbon dioxide and the air electrode side to be air. Figure 3 This is the I-V curve of the electrolytic cell at 700 °C - 800 °C with different applied voltages. At an applied voltage of 1.5 V, the electrolysis current densities of the single cell at 800 °C, 750 °C, and 700 °C are 0.76 A / cm -2 , 0.35 A / cm -2 , 0.19 A / cm -2 .

[0054] To further understand the electrochemical performance of the battery, electrochemical impedance spectroscopy tests are carried out under the condition of an applied voltage of 1.5 V. As Figure 4 shown, the Rp values at 700 °C, 750 °C, and 850 °C are 5.64 Ω·cm -2 , 2.17 Ω·cm -2 , 1.55 Ω·cm -2 .

Claims

1. A cathode material for B-site high-entropy solid oxide electrolysis cells, characterized in that, The cathode material has a high-entropy perovskite structure of the A2B2O6 type, where the A-site element is the Sr element, and the B-site element is composed of six transition metal elements, namely Fe, Ti, Cr, Mn, Mo, and Co, mixed in a molar ratio of 5:1:1:1:1:

1. The chemical formula of the A2B2O6 is Sr2FeTi 0.2 Cr 0.2 Mn 0.2 Mo 0.2 Co 0.2 O6.

2. The preparation method of a cathode material for a B-site high-entropy solid oxide electrolytic cell according to claim 1, characterized in that Including the following steps: S1. Dissolve the precursors corresponding to the constituent elements of the solid oxide electrolytic cell cathode material in water according to the stoichiometric ratio to obtain an aqueous metal ion solution; S2. Add a complexing agent to the aqueous metal ion solution obtained in step S1 and adjust the pH value to obtain a complexing sol; S3. Heat and stir the complexing sol obtained in step S2 at 80 °C to evaporate and form a gel, and then self-propagating combustion occurs to obtain primary powder; S4. Transfer the primary powder obtained in step S3 to a high-temperature furnace for drying and calcination to obtain a B-site high-entropy solid oxide electrolytic cell cathode material powder.

3. The preparation method according to claim 2, characterized in that, In step S1, the precursors of the constituent elements Sr, Fe, Cr, Mn, and Co are nitrates, the precursor of Ti is titanium dioxide, and the precursor of Mo is ammonium molybdate.

4. The preparation method according to claim 2, wherein The complexing agent in step S2 is one or both of citric acid and ethylenediaminetetraacetic acid. The molar ratio of the complexing agent to the total molar number of metal ions is 1:1 - 1.5:1, and ammonia water is added to adjust the pH value to 7.

5. The preparation method according to claim 2, characterized in that, In step S4, drying is carried out in a high-temperature drying oven at a temperature of 300 °C for 10 h, and calcination is carried out in a muffle furnace at 1200 °C for 10 h.

6. Use of the cathode material of the B-site high-entropy solid oxide electrolysis cell as described in claim 1, characterized in that, Applied to the cathode of a solid oxide fuel cell.

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