Perovskite cathode catalytic material for hydrogen production through solid oxide ammonia electrolysis and preparation of perovskite cathode catalytic material

Abstract

The invention discloses a perovskite cathode catalytic material for hydrogen production through solid oxide ammonia electrolysis and preparation and application of the perovskite cathode catalytic material. And the cathode catalytic material is double perovskite Sr2Fe < 1.5-x > CoxMo < 0.5 > O6 (x is greater than or equal to 0 and less than or equal to 0.3). The cathode prepared from the material can operate under the working condition of medium and high temperature, hydrogen reduction can occur in the ammonia electrolysis process to generate ferrocobalt and the ferrocobalt is anchored on the surface of layered perovskite Sr3Fe2-x-yCoxMoyO7 (x is greater than or equal to 0 and less than or equal to 0.3, and y is greater than or equal to 0 and less than or equal to 0.3), so that the cathode interface has more low-valence ions, acceptor electrons can be provided for water dissociation, and the service life of the cathode is prolonged. And the alloy on the surface also provides more active sites for water dissociation, so that the cathode can be used for hydrogen production through solid oxide ammonia electrolysis.

Description

Technical Field

[0001] The invention belongs to the field of preparation of cathode catalysts for solid oxide ammonia electrolysis cells, and specifically relates to a perovskite cathode catalytic material for solid oxide ammonia electrolysis hydrogen production and a preparation and application thereof. Background Art

[0002] In the context of global energy transformation, with the increasing depletion of non-renewable energy such as coal, oil and natural gas, the development of clean and efficient renewable energy has become the key. Hydrogen has attracted much attention due to its advantages of being renewable, high calorific value and clean. Traditional hydrogen production methods rely on coal, oil and natural gas. Although they are mainstream, they have greenhouse gas emissions; and renewable energy sources such as wind power generation and hydropower generation have low efficiency in producing hydrogen by electrolysis of water. Common water electrolysis methods include solid oxide water electrolysis (SOEC), proton exchange membrane water electrolysis and low-temperature alkaline membrane water electrolysis. Among them, SOEC has unique advantages. Its reverse process can efficiently convert electrical energy into chemical energy, and its sandwich structure composed of electrolyte, cathode and anode effectively avoids the risk of leakage of liquid batteries. However, the energy consumption of SOEC water electrolysis to produce hydrogen is limited by the large difference in oxygen partial pressure between the positive and negative electrodes caused by the oxygen absorption reaction of the anode. For this reason, auxiliary fuel electrolysis strategies have emerged, among which ammonia electrolysis stands out. Compared with 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 has become a relatively promising technical route.

[0003] Solid oxide ammonia electrolysis is the reverse process of solid oxide ammonia fuel cells. Its cathode undergoes hydrogen evolution reaction. Therefore, cathode materials play a key role in the ammonia electrolysis process. Traditional nickel-based metals as cathode materials are easily oxidized at high temperatures, and the particles will coarsen, resulting in reduced catalytic activity and shortened service life, thus affecting the efficiency and stability of water electrolysis. Precious metals have good catalytic activity and stability, but their high cost limits their large-scale application. Single perovskite materials show certain catalytic performance. Their advantage is that they have relatively good oxygen ion conductivity and can promote the reaction. However, their catalytic active sites are limited, and structural changes may also occur during long-term use, affecting performance. Double perovskite materials show more potential on this basis. For example, through strategies such as doping, active particles can be precipitated in a reducing atmosphere. These active particles can serve as higher active sites, effectively adsorb reaction intermediates, and accelerate the electron transfer process, thereby significantly improving the catalytic activity of water electrolysis, reducing the overpotential required for the reaction, and improving energy utilization efficiency. This further lays the foundation for efficient ammonia electrolysis to produce hydrogen, thereby promoting the sustainable development of energy. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a perovskite cathode catalytic material for solid oxide ammonia electrolysis to produce hydrogen, as well as its preparation and application. The cathode prepared with the perovskite cathode catalytic material can achieve higher catalytic activity, hydrogen production rate and good stability in hydrogen production by water vapor dissociation.

[0005] To achieve the above object, the present invention adopts the following technical solution: A perovskite cathode catalytic material for solid oxide ammonia electrolysis to produce hydrogen, which is a double perovskite Sr2Fe 1.5- x Co x Mo 0.5 O6 (0≤x≤0.3), which is reduced during ammonia electrolysis to form a cobalt-iron alloy and anchored in the layer perovskite Sr3Fe 2-x-y Co x Mo y O7 (0≤x≤0.3, 0≤y≤0.3) to improve the catalytic activity.

[0006] The preparation method of the perovskite cathode catalyst material comprises the following steps: (1) Add strontium nitrate, cobalt nitrate hexahydrate, iron nitrate nonahydrate and ammonium molybdate to deionized water and mix well. Then add citric acid and continue stirring for 2-4 hours until the solution is completely clear and transparent to ensure that the metal ions are fully complexed with citric acid. (2) Add ethylenediaminetetraacetic acid (EDTA) to the above solution and continue stirring until uniform; (3) adding aqueous ammonia to the solution obtained in step (2) to adjust the pH of the solution to 5-7; (4) The pH-adjusted solution is transferred to an oil bath and heated in the oil bath under continuous stirring to allow the solution to further react and concentrate to form a precursor gel with a certain viscosity; (5) The obtained precursor gel is dried, ground, and calcined to obtain Sr2Fe 1.5- x Co x Mo 0.5 O6 (0≤x≤0.3) powder.

[0007] 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.

[0008] Furthermore, the amount of citric acid used in step (1) is 1-2 times the total molar amount of metal ions in the solution.

[0009] Furthermore, the amount of EDTA used in step (2) is 1-2 times the total molar amount of metal ions in the solution.

[0010] Furthermore, in step (4), the temperature of the oil bath heating is 80-110° C. and the time is 2-5 h.

[0011] Furthermore, the drying temperature in step (5) is 120-200°C and the drying time is 8-20 h.

[0012] Furthermore, the calcination in step (5) is performed by heating the precursor to 400°C at a rate of 2°C / min and pre-calcining the precursor for 2-8 h to initially decompose and crystallize the precursor, remove organic matter and part of the water therein, and reduce cracks and defects that may be generated during the subsequent high-temperature calcination process; then, the temperature is further increased to 900-1200°C at a rate of 2-5°C / min and calcined at this temperature for 5-8 h to fully crystallize the powder.

[0013] The above-mentioned perovskite cathode catalyst material can be made into cathode slurry and further used in solid oxide ammonia electrolysis to produce hydrogen.

[0014] Furthermore, the method for preparing cathode slurry using the cathode catalyst material is to first mix the thickener and the viscous agent in a mass ratio of 4:96, then heat the mixture in a water bath, stop the water bath after the solution becomes clear and transparent, and put the mixture in a refrigerator after cooling; then, mix the perovskite cathode catalyst material and cerium-doped gadolinium (GDC) in a mass ratio of 6:4 and grind for 20-40 min, then slowly add 4-8 drops of the prepared solution, and continue grinding for 30 min to obtain a cathode slurry.

[0015] Furthermore, the thickener is one of ethyl cellulose, hydroxyethyl cellulose, methyl cellulose, guar gum, hydroxypropyl methyl cellulose and polyacrylamide.

[0016] Furthermore, the viscous agent is one or more of turpentine alcohol, terpineol, neroli oil, orange leaf oil, camphor oil, and lemon oil.

[0017] Furthermore, the water bath heating temperature is 50-90°C.

[0018] Furthermore, the refrigerated temperature is maintained at 0-5°C.

[0019] The present invention adopts a sol-gel complexation method to introduce an appropriate amount of cobalt into the B position of the double perovskite material. Under hydrogen reduction, it can be converted into a three-layer perovskite with a cobalt-iron alloy anchored on the surface. Compared with the double-layer perovskite, its crystal structure is more complex and has more crystal faces. The combination of ions at the A and B positions is diverse, which provides more active sites, optimizes the electronic structure, and greatly improves the catalytic activity; the ions are tightly stacked, the interlayer effect is strong, and the thermal stability is excellent. It can maintain the integrity of the structure under complex working conditions and reduce performance degradation; it can also generate more ordered oxygen vacancies, optimize the electron delocalization state, improve the ion and electron conductivity, reduce the polarization resistance, and make the charge transfer more efficient.

[0020] The significant advantages of the present invention are: (1) The present invention changes the proportion of low-valent elements by cobalt doping to provide acceptor electrons to facilitate water dissociation and improve the overall reaction efficiency.

[0021] (2) With the doping of cobalt, the oxygen vacancies in the resulting perovskite material gradually increase, enhancing its water adsorption capacity and promoting the water electrolysis reaction.

[0022] (3) Compared with double-layer perovskite, the triple-layer perovskite generated by the catalytic material of the present invention has significant advantages. Its crystal structure is more complex, with more crystal faces, and the combination of A and B ions is diverse, which can provide more active sites, optimize the electronic structure, greatly improve the catalytic activity, and reduce performance degradation.

[0023] (4) The precipitation 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 reaction activation energy, improve the catalytic activity and electrolysis current density, accelerate the water electrolysis rate, and optimize the water electrolysis effect.

[0024] (5) The preparation method of the present invention is simple and has low energy consumption. The prepared double perovskite precursor Sr2Fe 1.5-x Co x Mo 0.5 O6 (0≤x≤0.3) cathode material can achieve cobalt iron precipitation under reducing atmosphere, thereby improving catalytic activity. When used as the cathode for solid oxide ammonia electrolysis to produce hydrogen, it can show high electrolysis performance when ammonia is introduced into the anode, which is 4 times higher than the electrolysis performance of the undoped Co matrix SFM and much higher than commercial cathode materials. It is a cathode hydrogen evolution catalyst suitable for large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Sr2Fe prepared in Example 1-4 1.5-x Co x Mo 0.5 XRD spectra of O6 (0≤x≤0.3) samples before (a, b) and after (c, d) reduction.

[0026] 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.

[0027] Figure 3 Sr2Fe prepared in Example 1-4 1.5-x Co x Mo 0.5 IV curves of O6 (0≤x≤0.3) sample and LSM and LSCF as cathode at 750 ℃ ​​(NH3 is used as fuel gas at the anode and argon is used as water vapor at the cathode).

[0028] Figure 4 Sr2Fe prepared in Example 3 1.3 Co 0.2 Mo 0.5 IV diagram of O6 as cathode at 750-650 ℃ (hydrogen or ammonia is passed through the anode). DETAILED DESCRIPTION

[0029] A perovskite cathode catalytic material for solid oxide ammonia electrolysis to produce hydrogen, the preparation of which comprises the following steps: a) Solution preparation: Weigh 6.34 g strontium nitrate, 0.4-1.5 g cobalt nitrate hexahydrate, 7-10 g ferric nitrate nonahydrate and 1.32 g ammonium molybdate respectively, add to 50-100 ml deionized water and mix well, add 1-2 times the total molar amount of metal ions of citric acid, stir at 400-800 r / min for 2-4 h until the solution is completely clear and transparent; b) Oil bath heating: Add 1-2 times the total molar amount of metal ions of ethylenediaminetetraacetic acid (EDTA) to the above solution, continue to stir evenly, 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 solution with adjusted pH value to an oil bath pot, and heat at a constant temperature of 80-110 ° C for 2-5 h under continuous stirring to form a precursor gel with a certain viscosity; c) Calcination: The obtained precursor gel is taken out from the oil bath, placed in an oven, and dried at 120-200 °C for 8-20 h to obtain a dry solid precursor; the dried precursor is then ground into fine powder and placed in a muffle furnace, first heated to 400 °C at a rate of 2 °C / min, pre-baked for 2-8 h, and then continued to heat to 900-1200 °C at a rate of 2-5 °C / min, and calcined for 5-8 h to obtain Sr2Fe 1.5-x Co x Mo 0.5 O6 powder (0≤x≤0.3).

[0030] In order to make the contents of the present invention easier to understand, the technical solution of the present invention is further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0031] Example 1 1) Sr2Fe 1.5 Mo 0.5 Synthesis of O6 oxide a) Weigh 6.34 g strontium nitrate, 9.09 g ferric nitrate nonahydrate and 1.32 g ammonium molybdate into a 250 ml beaker, then add 50 ml deionized water and 18.7 g citric acid. Stir at 500 r / min for 3 h until the solution is completely clear and transparent.

[0032] b) Add 26.4 g of ethylenediaminetetraacetic acid (EDTA) to the above solution, continue to stir evenly, slowly add ammonia water to accurately adjust the pH value of the solution to 6, and then transfer the solution with adjusted pH value to an oil bath pot, and heat it at 110 ° C for 3 h under continuous stirring to form a precursor gel with a certain viscosity.

[0033] c) Calcination: The obtained precursor gel was taken out of the oil bath, placed in an oven, and dried at 150 °C for 12 h to obtain a black block-shaped dry solid precursor; the dried precursor was then ground into fine powder and placed in a muffle furnace, first heated to 400 °C at a rate of 2 °C / min, pre-baked for 2 h, and then continued to heat to 1100 °C at a rate of 2 °C / min, and calcined at this high temperature for 5 h to form Sr2Fe 1.5 Mo 0.5 O6 oxide powder.

[0034] Example 2 In step 1), 6.34 g strontium nitrate, 8.484 g ferric nitrate nonahydrate, 0.437 g cobalt nitrate hexahydrate and 1.32 g ammonium molybdate were weighed to prepare double perovskite Sr2Fe 1.4 Co 0.1 Mo 0.5 O6 oxide, other operations are the same as in Example 1.

[0035] Example 3 In step 1), 6.34 g strontium nitrate, 7.878 g ferric nitrate nonahydrate, 0.8731 g cobalt nitrate hexahydrate and 1.32 g 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.

[0036] Example 4 In step 1), 6.34 g strontium nitrate, 7.272 g ferric nitrate nonahydrate, 1.3097 g cobalt nitrate hexahydrate and 1.32 g 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.

[0037] Comparative Example 1 Commercial LSCF powder.

[0038] Comparative Example 2 Commercial LSM powder.

[0039] Figure 1 Sr2Fe prepared in Example 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 50 Sccm hydrogen environment. 1.5-x Co x Mo 0.5 The precursor of O6 (0≤x≤0.3) is a pure double perovskite structure (a), and its main peak gradually shifts to the right as the amount of cobalt doped at the b position increases (b), indicating that cobalt is successfully doped into the perovskite. After hydrogen reduction, a cobalt-iron alloy phase is precipitated, converting it into a layered perovskite structure Sr3Fe 2-x-y Co x Mo y O7 (0≤x≤0.3, 0≤y≤0.3) oxide (c), among which Sr2Fe 1.3 Co 0.2 Mo 0.5 O6 produced the largest amount of cobalt-iron alloy (d).

[0040] Figure 2 Sr2Fe prepared in Example 3 1.3 Co 0.2 Mo 0.5 TEM images of O6 before reduction and after reduction at 750℃ for 5 h in 50 Sccm hydrogen environment. 1.3 Co 0.2 Mo 0.5 The surface of O6 oxide is clear, and the precipitated cobalt-iron alloy particles are numerous and uniform, which indicates that the prepared catalyst has good uniformity.

[0041] Product performance test: The cathode slurry was prepared using the obtained perovskite oxide powder, and the specific steps were as follows: first, ethyl cellulose and turpentine alcohol were weighed in a mass ratio of 4:96 and placed in a beaker, and heated in a water bath at 80 °C. When the thickened solution became clear and transparent, the water bath could be stopped, and the solution was placed in a refrigerator after cooling, and the refrigeration temperature was maintained at 0 °C. Then, the perovskite oxide powder and GDC were poured into an agate mortar in a mass ratio of 6:4 for preliminary mixing, and then the agate pestle was used to repeatedly mix and grind for 15 min, and the grinding could be stopped when there was no obvious granularity during the grinding process. Four drops of thickening solution were slowly added to the ground powder using a 1 ml dropper, and grinding was continued for 30 min to promote the full mixing of the solution and the mixed powder to obtain SFM-GDC cathode slurry.

[0042] The obtained cathode slurry was further used to prepare button cells for solid oxide ammonia electrolysis to produce hydrogen for performance testing. The cell was an anode support with a diameter of 15 mm, and its structure included YSZ / NiO-YSZ, which was specifically prepared by screen printing commercial GDC slurry on the YSZ side of the anode support (effective area 0.785 cm 2 ), calcined at 1200 °C for 2 h, and SFM-GDC cathode slurry (effective area 0.196 cm) was prepared by screen printing on the isolation layer side. 2 ), dried and calcined at 1000℃ for 2 h, and cooled to obtain the required SFM-GDC / GDC / YSZ single cell. Before assembling the cells, a thin layer of silver paste is evenly screen-printed on the cathode of the single cell to play a current collecting role in the test, ensuring that the test data can accurately reflect the performance of the cell under actual working conditions.

[0043] The assembly of the battery first places the platinum wire (0.5 mm in diameter, 50 mm in length) and the nickel mesh (15 mm in diameter) on the corundum tube of the test device, and then places the anode side of the single cell to be tested on the nickel mesh to ensure that the anode is in contact with the fuel gas, and the cathode is in contact with the water vapor carried by the argon gas. The middle part is sealed with a high-temperature ceramic adhesive. Finally, add a silver mesh and platinum wire to the cathode, and use platinum slurry to tightly connect the platinum wire to the electrode material. Then use Kraft glue to seal the cathode gas inlet and outlet pipes of the reactor. After the ceramic adhesive is sealed, high-purity (99.999%) ammonia is used as the anode gas for testing. This time, the Gamary5000 electrochemical workstation was used for electrolysis current density and impedance testing.

[0044] Table 1 Electrolysis current density of solid oxide cell at 750 ℃ ​​and 0.6 V

[0045] Figure 3 For Sr2Fe prepared by Example 1-41.5-x Co x Mo 0.5 The performance of hydrogen production by electrolysis of ammonia using O6 (0≤x≤0.3) as cathode precursor and comparative commercial cathodes LSCF and LSM at 750℃ and 0.6V is compared. The 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 of hydrogen production by ammonia electrolysis of O6, LSM, and LSCF at 750 ℃ ​​and 0.6 V are 257, 924, 1450, 515, 573, and 825 mA / cm, respectively. 2 It can be seen that Sr2Fe 1.3 Co 0.2 Mo 0.5 The current density of O6 as cathode is based on Sr2Fe 1.5 Mo 0.5 O6 as a cathode is 5.64 times higher than that of the commonly used commercial cathode materials LSM and LSCF. This indicates that the appropriate amount of Co is introduced into Sr2Fe 1.5 Mo 0.5 Under reducing conditions, O6 forms a three-layer perovskite cathode catalyst anchored by cobalt-iron alloy, which helps to improve the electrolysis performance.

[0046] Figure 4 The Sr2Fe prepared in Example 3 1.3 Co 0.2 Mo 0.5 Comparison of the electrolytic performance of ammonia with O6 as cathode precursor at 750-650 ℃. As can be seen from the figure, in the range of 650-750 ℃, the electrolytic performance of ammonia and hydrogen fuels in the anode is I- V , the electrolysis current density is very close, which illustrates the applicability of the cathode catalyst to ammonia electrolysis. The electrolysis of ammonia as the anode gas can achieve an electrolysis effect close to that of hydrogen as the anode, which can further reflect the feasibility of ammonia electrolysis.

[0047] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A perovskite cathode catalytic material for solid oxide ammonia electrolysis to produce hydrogen, characterized in that: The perovskite cathode catalytic material is double perovskite Sr2Fe 1.5-x Co x Mo 0.5 O6, where 0≤x≤0.3; It is reduced during ammonia electrolysis to form a cobalt-iron alloy and anchored on the surface of the layered perovskite.

2. A method for preparing a perovskite cathode catalyst material as claimed in claim 1, characterized in that: The following steps are involved: (1) Add strontium nitrate, cobalt nitrate hexahydrate, ferric nitrate nonahydrate and ammonium molybdate into 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 uniform; (3) adding aqueous ammonia to the solution obtained in step (2) to adjust the pH of the solution to 5-7; (4) transferring the solution whose pH value has been adjusted in step (3) into an oil bath, and heating the solution in the oil bath under continuous stirring to form a precursor gel having 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.

3. The method for preparing the perovskite cathode catalyst material according to claim 2, 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.

4. The method for preparing the perovskite cathode catalyst material according to claim 2, 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.

5. The method for preparing the perovskite cathode catalyst material according to claim 2, characterized in that: The amount of EDTA used in step (2) is 1-2 times the total molar amount of metal ions in the solution.

6. The method for preparing the perovskite cathode catalyst material according to claim 2, characterized in that: The temperature of the oil bath heating in step (4) is 80-110°C and the time is 2-5 h.

7. The method for preparing the perovskite cathode catalyst material according to claim 2, characterized in that: The drying temperature in step (5) is 120-200°C and the drying time is 8-20 h.

8. The method for preparing the perovskite cathode catalyst material according to claim 2, characterized in that: The calcination in step (5) is performed by heating the temperature to 400°C at a rate of 2°C / min, pre-calcining for 2-8 h, then continuing to heat the temperature to 900-1200°C at a rate of 2-5°C / min, and calcining at this temperature for 5-8 h.

9. Use of the perovskite cathode catalyst material as claimed in claim 1 in hydrogen production by solid oxide ammonia electrolysis.

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