Perovskite cathode catalyst material for solid oxide ammonia electrolysis hydrogen production and preparation thereof

Abstract

The application discloses a perovskite cathode catalytic material for hydrogen production by solid oxide ammonia electrolysis and preparation and application thereof. 1.5‑x Co x Mo 0.5 O6 (0≤x≤0.3). The cathode prepared by the material can operate under medium-high temperature working conditions, and hydrogen reduction occurs in the ammonia electrolysis process, cobalt-iron alloy is generated and anchored in the layer perovskite Sr3Fe 2‑x‑ y Co x Mo y O7 (0≤x≤0.3, 0≤y≤0.3) surface, which makes the cathode interface have more content of low-valence state ions, can provide acceptor electrons for water dissociation, enhances the adsorption and desorption capacity of the cathode interface to water vapor, and the surface alloy also provides more active sites for water dissociation, and thus can be used for hydrogen production by solid oxide ammonia electrolysis.

Description

Technical Field

[0001] This invention belongs to the field of cathode catalyst preparation for solid oxide ammonia electrolysis cells, specifically relating to a perovskite cathode catalyst material for hydrogen production by solid oxide ammonia electrolysis and its preparation and application. Background Technology

[0002] Against the backdrop of global energy transition, with the increasing depletion of non-renewable energy sources such as coal, oil, and natural gas, the development of clean and efficient renewable energy has become crucial. Hydrogen has attracted much attention due to its advantages such as being renewable, having a high calorific value, and being clean. Traditional hydrogen production methods rely on coal, oil, and natural gas, which, although mainstream, pose greenhouse gas emission problems; while renewable energy sources such as wind power and hydropower have low efficiency in water electrolysis for hydrogen production. Common water electrolysis methods include solid oxide electrolysis (SOEC), proton exchange membrane electrolysis, and low-temperature alkaline membrane electrolysis. Among them, SOEC has unique advantages. Its reverse process can efficiently convert electrical energy into chemical energy, and its sandwich structure consisting of electrolyte, cathode, and anode effectively avoids the leakage risk of liquid batteries. However, the energy consumption of SOEC water electrolysis for hydrogen production is limited by the large difference in oxygen partial pressure between the anode and cathode caused by the oxygen absorption reaction at the anode. Therefore, auxiliary fuel electrolysis strategies have emerged, among which ammonia electrolysis has stood out. Compared to fuels such as methane and ethanol, ammonia has the characteristics of high-energy negative hydrogen, easy transportation and storage, and does not have the disadvantage of producing greenhouse gases like carbon-containing fuels. Therefore, using solid oxide ammonia electrolysis to produce hydrogen is a promising technical route.

[0003] Solid oxide ammonia electrolysis is the reverse process of a solid oxide ammonia fuel cell, with hydrogen evolution occurring at the cathode. Therefore, the cathode material plays a crucial role in ammonia electrolysis. Traditional nickel-based metals, when used as cathode materials, are easily oxidized at high temperatures and exhibit particle coarsening, leading to reduced catalytic activity and shortened lifespan, thus affecting the efficiency and stability of water electrolysis. Noble metals possess good catalytic activity and stability, but their high cost limits their large-scale application. Single perovskite materials exhibit certain catalytic performance, with the advantage of relatively good oxygen ion conductivity, which promotes the reaction. However, their catalytic active sites are limited, and structural changes may occur during long-term use, affecting performance. Dual perovskite materials show greater potential. For example, through doping strategies, they can precipitate active particles under a reducing atmosphere. These active particles can serve as higher active sites, effectively adsorbing reaction intermediates and accelerating electron transfer processes, thereby significantly improving the catalytic activity of water electrolysis, reducing the overpotential required for the reaction, and improving energy utilization efficiency. This lays a further foundation for efficient ammonia electrolysis to produce hydrogen, thus promoting sustainable energy development. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a perovskite cathode catalytic material for hydrogen production by solid oxide ammonia electrolysis, its preparation and application, and the cathode prepared therefrom can achieve high catalytic activity, hydrogen production rate and good stability in hydrogen production by water vapor dissociation.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A perovskite cathode catalyst material for hydrogen production by solid oxide ammonia electrolysis, which is a double perovskite Sr2Fe 1.5- x Co x Mo 0.5 O6 (0≤x≤0.3) undergoes reduction during ammonia electrolysis to form a cobalt-iron alloy that is anchored to the perovskite Sr3Fe layer. 2-x-y Co x Mo y O7 (0≤x≤0.3, 0≤y≤0.3) is used to improve catalytic activity.

[0007] The preparation method of the perovskite cathode catalytic material includes the following steps:

[0008] (1) Add strontium nitrate, cobalt nitrate hexahydrate, ferric nitrate nonahydrate and ammonium molybdate to deionized water and mix well. Add citric acid and stir continuously for 2-4 hours until the solution is completely clear and transparent to ensure that the metal ions are fully complexed with citric acid.

[0009] (2) Add ethylenediaminetetraacetic acid (EDTA) to the above solution and continue stirring until homogeneous;

[0010] (3) Add ammonia to the solution obtained in step (2) to adjust the pH of the solution to 5-7;

[0011] (4) Transfer the pH-adjusted solution to an oil bath and heat it in the oil bath under continuous stirring to allow the solution to react and concentrate further, forming a precursor gel with a certain viscosity.

[0012] (5) The obtained precursor gel was dried, ground, and calcined to obtain Sr2Fe with a perovskite structure. 1.5- x Co x Mo 0.5 O6 (0≤x≤0.3) powder.

[0013] Furthermore, the mass ratio of strontium nitrate, cobalt nitrate hexahydrate, ferric nitrate nonahydrate and ammonium molybdate used in step (1) is 6.34:(0.4-1.5):(7-10):1.32.

[0014] Furthermore, the amount of citric acid used in step (1) is 1-2 times the total molar amount of metal ions in the solution.

[0015] Furthermore, the amount of ethylenediaminetetraacetic acid used in step (2) is 1-2 times the total molar amount of metal ions in the solution.

[0016] Furthermore, the oil bath heating temperature in step (4) is 80-110 ℃, and the time is 2-5 h.

[0017] Furthermore, the drying temperature in step (5) is 120-200 °C and the time is 8-20 h.

[0018] Further, in step (5), the calcination is carried out by heating to 400 ℃ at a rate of 2 ℃ / min and pre-calcining for 2-8 h to allow the precursor to decompose and crystallize initially, remove organic matter and some moisture, and reduce cracks and defects that may be generated during subsequent high-temperature calcination; then the temperature is further increased to 900-1200 ℃ at a rate of 2-5 ℃ / min and calcined for 5-8 h to allow the powder to fully crystallize.

[0019] The aforementioned perovskite cathode catalyst material can be made into cathode slurry and further used for hydrogen production by solid oxide ammonia electrolysis.

[0020] Furthermore, the method for preparing cathode slurry using the aforementioned cathode catalytic material is as follows: First, a thickener and a viscous agent are mixed at a mass ratio of 4:96, and then heated in a water bath. After the solution becomes clear and transparent, the water bath is stopped, and the mixture is cooled and refrigerated. Then, the perovskite cathode catalytic material and gadolinium oxide (GDC) are mixed at a mass ratio of 6:4 and ground for 20-40 minutes. Next, 4-8 drops of the prepared solution are slowly added, and the mixture is ground for another 30 minutes to obtain the cathode slurry.

[0021] Furthermore, the thickener is one of ethyl cellulose, hydroxyethyl cellulose, methyl cellulose, guar gum, hydroxypropyl methyl cellulose, and polyacrylamide.

[0022] Furthermore, the thickener is one or more of turpentine percolate, terpineol, neroli oil, orange leaf oil, camphor oil, and lemon oil.

[0023] Furthermore, the water bath heating temperature is 50-90 ℃.

[0024] Furthermore, the refrigeration temperature is maintained at 0-5 °C.

[0025] This invention employs a sol-gel complexation method, introducing an appropriate amount of cobalt at the B-site of a bilayer perovskite material. Under hydrogen reduction, it can be converted into a trilayer perovskite with a cobalt-iron alloy anchored on the surface. Compared with bilayer perovskite, its crystal structure is more complex, with more crystal faces and diverse A- and B-site ion combinations, providing more active sites, optimizing the electronic structure, and greatly enhancing catalytic activity. The ions are densely packed, with strong interlayer interactions, and excellent thermal stability, maintaining structural integrity under complex operating conditions and reducing performance degradation. It can also generate more ordered oxygen vacancies, optimize the electron delocalization state, improve ionic and electronic conductivity, reduce polarization resistance, and make charge transfer more efficient.

[0026] The significant advantages of this invention are:

[0027] (1) The present invention changes the proportion of low-valence elements by cobalt doping to provide acceptor electrons to facilitate water dissociation and improve the overall reaction efficiency.

[0028] (2) With the doping of cobalt, the oxygen vacancies in the resulting perovskite material gradually increase, which enhances its water adsorption capacity and can promote the electrolysis of water reaction.

[0029] (3) Compared with bilayer perovskite, the trilayer perovskite generated by the catalytic material of the present invention has significant advantages. Its crystal structure is more complex, with more crystal faces and diverse combinations of A and B site ions, which can provide more active sites, optimize the electronic structure, greatly improve catalytic activity, and reduce performance degradation.

[0030] (4) The deposition of cobalt-iron alloy is applied to the cathode reaction interface of water electrolysis, which can provide more active sites for water dissociation, reduce the activation energy of the reaction, improve the catalytic activity and electrolysis current density, accelerate the water electrolysis rate, and optimize the water electrolysis effect.

[0031] (5) The preparation method of the present invention is simple and has low energy consumption. The precursor prepared is double perovskite Sr2Fe 1.5-x Co x Mo 0.5 O6 (0≤x≤0.3) cathode materials can achieve cobalt-iron deposition under a reducing atmosphere, thereby enhancing catalytic activity. When used as a cathode for hydrogen production via solid oxide ammonia electrolysis, it exhibits high electrolysis performance when ammonia gas is introduced at the anode. Its electrolysis performance is four times higher than that of undoped Co-based SFM and far exceeds that of commercial cathode materials, making it a suitable cathode hydrogen evolution catalyst for large-scale promotion and application. Attached Figure Description

[0032] Figure 1 Sr2Fe prepared in Examples 1-4 1.5-x Co x Mo 0.5 XRD patterns of O6 (0≤x≤0.3) samples before (a, b) and after (c, d) reduction.

[0033] Figure 2 Sr2Fe prepared in Example 3 1.3 Co 0.2 Mo 0.5 TEM spectra of O6 before (a) and after (b) reduction.

[0034] Figure 3 Sr2Fe prepared in Examples 1-4 1.5-x Co x Mo 0.5 IV curves of O6 (0≤x≤0.3) sample and LSM and LSCF as cathodes at 750 °C (NH3 is used as fuel gas for anode and argon carries water vapor for cathode).

[0035] Figure 4 Sr2Fe prepared in Example 3 1.3 Co 0.2 Mo 0.5 O6 is used as the cathode in the IV diagram at 750-650 ℃ (hydrogen or ammonia is passed through the anode). Detailed Implementation

[0036] A perovskite cathode catalyst material for hydrogen production by solid oxide ammonia electrolysis is prepared by the following steps:

[0037] a) Solution preparation: Weigh 6.34 g of strontium nitrate, 0.4-1.5 g of cobalt nitrate hexahydrate, 7-10 g of ferric nitrate nonahydrate and 1.32 g of ammonium molybdate respectively, add them to 50-100 ml of deionized water and mix well. Add citric acid with a total molar amount of metal ions of 1-2 times, and stir continuously at 400-800 r / min for 2-4 h until the solution is completely clear and transparent.

[0038] b) Oil bath heating: Add 1-2 times the total molar amount of metal ions in ethylenediaminetetraacetic acid (EDTA) to the above solution, continue stirring until homogeneous, then slowly add 20-30 ml of ammonia water as a pH adjuster to adjust the pH of the solution to 5-7. Then transfer the pH-adjusted solution to an oil bath and heat at 80-110 ℃ for 2-5 h under continuous stirring to form a precursor gel with a certain viscosity.

[0039] c) Calcination: The obtained precursor gel was removed from the oil bath and placed in an oven to dry at 120-200 °C for 8-20 h to obtain a dry solid precursor. The dried precursor was then ground into a fine powder and placed in a muffle furnace. The temperature was first increased to 400 °C at a rate of 2 °C / min for pre-calcination for 2-8 h, and then increased to 900-1200 °C at a rate of 2-5 °C / min for calcination for 5-8 h to obtain Sr2Fe. 1.5-x Cox Mo 0.5 O6 powder (0≤x≤0.3).

[0040] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0041] Example 1

[0042] 1) Sr2Fe 1.5 Mo 0.5 Synthesis of O6 oxides

[0043] a) Weigh 6.34 g of strontium nitrate, 9.09 g of ferric nitrate nonahydrate and 1.32 g of ammonium molybdate into a 250 ml beaker, then add 50 ml of deionized water and 18.7 g of citric acid. Stir continuously at 500 r / min for 3 h until the solution is completely clear and transparent.

[0044] b) Add 26.4 g of ethylenediaminetetraacetic acid (EDTA) to the above solution, continue stirring until homogeneous, then slowly add ammonia water to precisely adjust the pH value of the solution to 6. Then transfer the pH-adjusted solution to an oil bath and heat at 110 °C for 3 h under continuous stirring to form a precursor gel with a certain viscosity.

[0045] c) Calcination: The obtained precursor gel was removed from the oil bath and placed in an oven to dry at 150 °C for 12 h, yielding a black, blocky, dry solid precursor. The dried precursor was then ground into a fine powder and placed in a muffle furnace. The temperature was first increased to 400 °C at a rate of 2 °C / min for pre-calcination for 2 h, and then increased to 1100 °C at a rate of 2 °C / min for calcination at this high temperature for 5 h, forming Sr2Fe with a perovskite structure. 1.5 Mo 0.5 O6 oxide powder.

[0046] Example 2

[0047] In step 1), 6.34 g of strontium nitrate, 8.484 g of ferric nitrate nonahydrate, 0.437 g of cobalt nitrate hexahydrate, and 1.32 g of ammonium molybdate were weighed out to prepare double perovskite Sr₂Fe. 1.4 Co 0.1 Mo 0.5 O6 oxide, other operations are the same as in Example 1.

[0048] Example 3

[0049] In step 1), 6.34 g of strontium nitrate, 7.878 g of ferric nitrate nonahydrate, 0.8731 g of cobalt nitrate hexahydrate, and 1.32 g of ammonium molybdate were weighed to prepare double perovskite Sr₂Fe. 1.3 Co 0.2 Mo 0.5 O6 oxide, other operations are the same as in Example 1.

[0050] Example 4

[0051] In step 1), 6.34 g of strontium nitrate, 7.272 g of ferric nitrate nonahydrate, 1.3097 g of cobalt nitrate hexahydrate, and 1.32 g of ammonium molybdate were weighed to prepare double perovskite Sr₂Fe. 1.2 Co 0.3 Mo 0.5 O6 oxide, other operations are the same as in Example 1.

[0052] Comparative Example 1

[0053] Commercial LSCF powder.

[0054] Comparative Example 2

[0055] Commercial LSM powder.

[0056] Figure 1 Sr2Fe prepared in Examples 1-4 1.5-x Co x Mo 0.5 XRD patterns of O6 (0≤x≤0.3) samples before reduction and after reduction at 750 ℃ ​​for 5 h in a 50 Sccm hydrogen atmosphere. From the figure, it can be seen that before reduction, the obtained Sr2Fe... 1.5-x Co x Mo 0.5 The O6 (0≤x≤0.3) precursor exhibits a pure-phase double perovskite structure (a), with its main peak gradually shifting to the right as the cobalt doping concentration at site b increases (b), indicating successful cobalt doping into the perovskite. Hydrogen reduction precipitates a cobalt-iron alloy phase, transforming it into a layered perovskite structure, Sr3Fe. 2-x-y Co x Mo y O7 (0≤x≤0.3, 0≤y≤0.3) oxides (c), of which Sr2Fe 1.3 Co 0.2 Mo 0.5 O6 produces the largest amount of cobalt-iron alloy (d).

[0057] Figure 2 Sr2Fe prepared in Example 3 1.3 Co 0.2 Mo 0.5TEM images of O6 before reduction and after reduction at 750℃ for 5 h in a 50 sccm hydrogen atmosphere. These images show that the cobalt-iron alloy particles are anchored to Sr₂Fe. 1.3 Co 0.2 Mo 0.5 The surface of the O6 oxide and the presence of numerous and uniform cobalt-iron alloy particles indicate that the prepared catalyst has good uniformity.

[0058] Product performance testing:

[0059] The cathode slurry was prepared using the obtained perovskite oxide powder. The specific steps are as follows: First, ethyl cellulose and turpentine percolate were weighed at a mass ratio of 4:96 and placed in a beaker. The mixture was heated in a water bath at 80 °C until the thickened solution became clear and transparent. The water bath was then stopped, and the mixture was cooled and refrigerated at 0 °C. Next, the perovskite oxide powder and GDC were poured into an agate mortar at a mass ratio of 6:4 for initial mixing. Then, the mixture was repeatedly ground with an agate mortar for 15 minutes until no obvious particles were felt during grinding. Four drops of thickening solution were slowly added to the ground powder using a 1 ml dropper, and grinding continued for 30 minutes to promote thorough mixing of the solution and the powder, thus obtaining the SFM-GDC cathode slurry.

[0060] The obtained cathode paste was further used to prepare a button cell for solid oxide ammonia electrolysis hydrogen production for performance testing. This cell has an anode support with a diameter of 15 mm and a structure comprising YSZ / NiO-YSZ. Specifically, a commercial GDC paste was screen-printed onto the YSZ side of the anode support (effective area 0.785 cm²). 2 The cathode paste (effective area 0.196 cm²) was prepared by screen printing on the isolation layer side after calcination at 1200 ℃ for 2 h. 2 After drying, the cells are calcined at 1000℃ for 2 hours and then cooled to obtain the desired SFM-GDC / GDC / YSZ single-cell solar cells. Before cell assembly, a thin layer of silver paste is uniformly screen-printed on the cathode of each cell to act as a current collector during testing, ensuring that the test data accurately reflects the performance of the cell under actual operating conditions.

[0061] The battery assembly process began with placing a platinum wire (0.5 mm in diameter, 50 mm in length) and a nickel mesh (15 mm in diameter) on the corundum tube of the testing apparatus. Then, the anode side of the single cell to be tested was placed on the nickel mesh, ensuring contact between the anode and the fuel gas. The cathode was in contact with water vapor carried by argon gas, and the middle section was sealed with a high-temperature ceramic adhesive. Finally, a silver mesh and platinum wire were added to the cathode, and platinum paste was used to tightly connect the platinum wire to the electrode material. Kaft glue was then used to seal the cathode gas inlet and outlet pipes of the reactor. After the ceramic adhesive was fully sealed, high-purity (99.999%) ammonia was used as the anode gas for testing. A Gamary 5000 electrochemical workstation was used for electrolytic current density and impedance testing.

[0062] Table 1 Electrolytic current density of solid oxide batteries at 750 °C and 0.6 V

[0063]

[0064] Figure 3 Sr2Fe prepared using Examples 1-4 1.5-x Co x Mo 0.5 The performance of O6 (0≤x≤0.3) as a cathode precursor and comparative commercial cathodes LSCF and LSM in ammonia electrolysis for hydrogen production at 750 °C and 0.6 V is compared in Table 1. Specific data are shown in Table 1. Figure 3 As can be seen from Table 1, the cathode material Sr2Fe 1.5, Mo 0.5 O6, Sr2Fe 1.4 Co 0.1 Mo 0.5 O6, Sr2Fe 1.3 Co 0.2 Mo 0.5 O6, Sr2Fe 1.2 Co 0.3 Mo 0.5 The current densities for hydrogen production by ammonia electrolysis using O6, LSM, and LSCF at 750 °C and 0.6 V were 257, 924, 1450, 515, 573, and 825 mA / cm², respectively. 2 It can be seen that, with Sr2Fe 1.3 Co 0.2 Mo 0.5 The current density when O6 is used as the cathode is based on Sr2Fe 1.5 Mo 0.5 O6 was 5.64 times more abundant than the cathode material, and significantly higher than commonly used commercial cathode materials LSM and LSCF. This indicates that an appropriate amount of Co was introduced into Sr2Fe. 1.5 Mo 0.5O6 forms a three-layer perovskite cathode catalyst anchored by a cobalt-iron alloy under reducing conditions, which helps to improve electrolysis performance.

[0065] Figure 4 To utilize the Sr2Fe prepared in Example 3 1.3 Co 0.2 Mo 0.5 The figure compares the performance of O6 as a cathode precursor in ammonia electrolysis at 750-650 °C. It shows the differences in performance between ammonia and hydrogen fuel at the anode within the 650-750 °C range. I- V The electrolysis current densities are very close, which indicates the applicability of the cathode catalyst to ammonia electrolysis. Ammonia as the anode gas can achieve an electrolysis effect close to that of hydrogen as the anode, which further demonstrates the feasibility of ammonia electrolysis.

[0066] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. The application of a perovskite cathode catalyst in solid oxide ammonia electrolysis for hydrogen production, characterized in that: The perovskite cathode catalyst material is a double perovskite Sr2Fe. 1.5-x Co x Mo 0.5 O6, where 0 < x ≤ 0.3; During ammonia electrolysis, it undergoes reduction to generate a cobalt-iron alloy, which is then anchored on the surface of the perovskite layer. The preparation method of the perovskite cathode catalytic material includes the following steps: (1) Add strontium nitrate, cobalt nitrate hexahydrate, ferric nitrate nonahydrate and ammonium molybdate to deionized water and mix well. Then add citric acid and continue stirring until the solution is completely clear and transparent. (2) Add ethylenediaminetetraacetic acid to the solution obtained in step (1) and continue stirring until homogeneous; (3) Add ammonia to the solution obtained in step (2) to adjust the pH of the solution to 5-7; (4) Transfer the solution with pH value adjusted in step (3) to an oil bath and heat it in the oil bath under continuous stirring to form a precursor gel with a certain viscosity. (5) The precursor gel obtained in step (4) is dried, ground, and calcined to obtain Sr2Fe 1.5-x Co x Mo 0.5 O6 powder.

2. The application according to claim 1, characterized in that: The mass ratio of strontium nitrate, cobalt nitrate hexahydrate, ferric nitrate nonahydrate and ammonium molybdate used in step (1) is 6.34:(0.4-1.5):(7-10):1.

32.

3. The application according to claim 1, characterized in that: The amount of citric acid used in step (1) is 1-2 times the total molar amount of metal ions in the solution.

4. The application according to claim 1, characterized in that: The amount of ethylenediaminetetraacetic acid used in step (2) is 1-2 times the total molar amount of metal ions in the solution.

5. The application according to claim 1, characterized in that: The oil bath heating in step (4) is at a temperature of 80-110℃ for 2-5 hours.

6. The application according to claim 1, characterized in that: The drying temperature in step (5) is 120-200℃ and the time is 8-20 h.

7. The application according to claim 1, characterized in that: The calcination in step (5) involves heating to 400 ℃ at a rate of 2 ℃ / min, pre-calcining for 2-8 h, and then continuing to heat to 900-1200 ℃ at a rate of 2-5 ℃ / min, and holding for calcination for 5-8 h.

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