A method of preparing a solid oxide electrolysis cell cathode for ammonia synthesis

Abstract

The application discloses a preparation method of a solid oxide electrolytic cell cathode for ammonia synthesis, and is characterized in that the preparation method comprises the following steps: (1) a solid oxide cathode slurry is brushed on one side of a proton conductor electrolyte sheet, calcination I is performed, and a porous cathode framework is obtained; and (2) an impregnation solution containing a ruthenium salt is drop-coated on the porous cathode framework, drying, calcination II, reduction are performed, and a proton-electron mixed conductive composite cathode loaded with Ru nanoparticles is obtained; the solid oxide cathode slurry is obtained through ball milling of raw materials containing a solid oxide powder, a pore-forming agent and a binder. In the application, the catalyst does not need high-temperature calcination (>1000 DEG C), serious agglomeration of Ru particles is avoided, nano-scale Ru particles will provide a large number of high-activity centers, increase the active sites of the ammonia synthesis reaction and accelerate the charge transfer process, and the ammonia synthesis catalytic activity is significantly improved.

Description

Technical Field

[0001] This application relates to a method for preparing a cathode of a solid oxide electrolytic cell for ammonia synthesis, belonging to the technical field of solid oxide electrolytic cells. Background Technology

[0002] Ammonia, an important inorganic chemical product, is a raw material or intermediate in the manufacture of fertilizers, dyes, pharmaceuticals, and other chemicals. Furthermore, the energy density per unit volume of liquid ammonia is 1.5 times that of liquid hydrogen, and its hydrogen storage capacity per unit volume is 1.7 times that of liquid hydrogen. Simultaneously, in terms of storage and transportation, ammonia liquefaction conditions are milder than hydrogen liquefaction conditions, making it an ideal carbon-free fuel and hydrogen carrier. Currently, the Haber-Bosch process is the main industrial method for ammonia production, which requires high temperature (400–500℃) and high pressure (15–25 MPa). This process results in enormous energy consumption and significant carbon dioxide emissions. With the increasingly severe energy and environmental crisis in recent years, how to achieve efficient and environmentally friendly ammonia synthesis to support the development of related industries is a critical issue.

[0003] Compared to the traditional Haber-Bosch process, the proton-conducting solid oxide electrolyzer can achieve nitrogen-to-hydrogen reduction to ammonia at intermediate temperatures. This method does not require a high-pressure environment and operates under milder conditions. Furthermore, the proton sources for electrochemical ammonia synthesis are abundant; in addition to hydrogen, water, ethanol, and natural gas can also be used, avoiding the energy consumption associated with hydrogen preparation, storage, and transportation, and effectively reducing carbon emissions throughout the ammonia synthesis process. In conclusion, it is considered an environmentally friendly preparation method. For solid oxide electrolysis ammonia synthesis technology, early cathode materials were mostly pure metals such as Pd, Ag-Pd, and Fe (Science, 1998, 282(5386): 98-100; Solid State Ionics, 2007, 178(1-2): 153-159; Journal of Solid State Electrochemistry, 2005, 9: 201-204.). Later, various perovskite oxides, such as STF and BCYR, ​​were used (Fuel Processing Technology, 2022, 235: 107380; Journal of Materials Chemistry A, 2022, 10(46): 24813-24823; Journal of The Electrochemical Society, 2017, 164(13): F1323.). Compared with pure metal electrodes, perovskite cathodes have a better match with the thermal expansion coefficients of proton-conducting electrolytes and have significant economic advantages. Furthermore, metal catalysts such as Fe and Ru can be introduced into the perovskite cathode layer, thereby exhibiting considerable catalytic activity for ammonia synthesis (Fuel Processing Technology, 2022, 235:107380; Catalysis Today, 2017, 286:41-50; Journal of Materials Science, 2017, 52:2825-2835.). In conventional preparation methods, the cathode inevitably undergoes a high-temperature calcination process of up to 1000℃, which causes severe agglomeration of catalyst particles, reduces the reaction interface, and limits the improvement of reaction activity. Therefore, optimizing the microstructure and electrocatalytic activity of the cathode material is a key condition for realizing ammonia synthesis in a solid oxide electrolysis cell.

[0004] Impregnation, as a highly efficient cathode modification method, introduces uniformly dispersed catalyst particles into the cathode layer through solution impregnation. This method avoids high-temperature calcination, allowing the catalyst particles to remain at the nanoscale (Catalysis Today, 2017, 286:41-50). These noble metal nanoparticles can optimize the microstructure of the cathode layer, providing abundant active centers for ammonia synthesis and improving the ammonia synthesis activity of the cathode. In previous ammonia synthesis research, impregnation was typically used to introduce catalyst nanoparticles onto the perovskite framework of a pure proton conductor cathode. Although these catalyst particles usually possess good electronic conductivity, the loading capacity makes it difficult to form a sufficiently conductive network in the cathode layer, thus affecting electrochemical performance and catalytic activity. Summary of the Invention

[0005] This invention utilizes an impregnation method to generate Ru nanoparticles in situ within a porous cathode framework, preparing a proton-electron hybrid conductive composite cathode loaded with Ru nanoparticles. The use of this proton-electron hybrid conductive composite cathode further improves the interfacial contact between the electrode and the electrolyte, providing more three-phase interfaces. Simultaneously, the nanoscale Ru particles provide active centers for ammonia synthesis, accelerating the charge transfer process and significantly enhancing the ammonia synthesis catalytic activity of traditional perovskite cathode materials.

[0006] The purpose of this invention is to provide a method for preparing a composite cathode loaded with Ru nanoparticles by solution impregnation, which can improve the ammonia synthesis activity of proton-conducting solid oxide electrolyzers and overcome the shortcomings of existing cathode materials.

[0007] According to one aspect of this application, a method for preparing a cathode for a solid oxide electrolytic cell used in ammonia synthesis is provided, the method comprising the following steps:

[0008] (1) A solid oxide cathode paste is brushed onto one side of a proton conductor electrolyte sheet and calcined to obtain a porous cathode skeleton.

[0009] (2) The impregnation solution containing ruthenium salt was drop-coated onto the porous cathode framework, dried, calcined, and reduced to obtain a proton-electron hybrid conductive composite cathode loaded with Ru nanoparticles.

[0010] The solid oxide powder in the solid oxide cathode slurry includes proton conductor materials and electron conductor materials.

[0011] Optionally, the mass ratio of the proton conductor material to the electron conductor material is 1:2 to 2:1.

[0012] Optionally, the mass ratio of the proton conductor material to the electron conductor material is independently selected from any value of 1:2, 1:1, 1.5:1, 2:1 or a range between any two of the above.

[0013] Optionally, the proton conductor material is selected from at least one of BZCY, BZCYYb, BZY, BCY, BCC, BCD, BCGO, LSGM, LBGM, and SCY.

[0014] Optionally, the electronic conductor material is selected from at least one of LSCF, LST, SFM, SSC, LNF, and PCF.

[0015] Optionally, the ruthenium salt is selected from at least one of ruthenium chloride, ruthenium nitrite, and ruthenium nitrate.

[0016] Optionally, the concentration of the ruthenium salt-containing impregnation solution is 0.1 to 1 mol / L.

[0017] Optionally, the concentration of the ruthenium salt-containing impregnation solution is independently selected from any value of 0.1 mol / L, 0.2 mol / L, 0.4 mol / L, 0.5 mol / L, 0.8 mol / L, 1 mol / L, or a range between any two of the above.

[0018] Optionally, the solvent in the ruthenium salt-containing impregnation solution is a mixture of water and ethanol, with a volume ratio of water to ethanol of 3:1 to 1:3.

[0019] Optionally, in the proton-electron hybrid conductive composite cathode loaded with Ru nanoparticles, the mass of Ru element accounts for 5 to 40 wt% of the total mass of the proton-electron hybrid conductive composite cathode loaded with Ru nanoparticles.

[0020] Optionally, in the proton-electron hybrid conductive composite cathode loaded with Ru nanoparticles, the mass of Ru element as a percentage of the total mass of the proton-electron hybrid conductive composite cathode loaded with Ru nanoparticles is independently selected from any value among 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, and 40wt%, or a range between any two of the above.

[0021] Optionally, the solid oxide cathode slurry is obtained by ball milling raw materials containing solid oxide powder, pore-forming agent, and binder.

[0022] Optionally, the ball mill rotates at a speed of 100 to 200 rpm and the milling time is 0.5 to 2 hours.

[0023] Optionally, the rotational speed of the ball mill is independently selected from any value among 100 rpm, 120 rpm, 150 rpm, 180 rpm, and 200 rpm, or a range between any two of the above.

[0024] Optionally, the ball milling time is independently selected from any value of 0.5h, 1h, 1.5h, 2h or a range between any two of the above.

[0025] Optionally, the pore-forming agent is selected from at least one of starch, carbon powder, and graphite.

[0026] Optionally, the adhesive is selected from at least one of terpineol, methylcellulose, dioctyl phthalate, and polyvinyl alcohol.

[0027] Optionally, the pore-forming agent accounts for 10 to 30 wt% of the total mass of the solid oxide cathode slurry.

[0028] Optionally, the pore-forming agent is independently selected from any value of 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, or a range between any two of the above in terms of the total mass of the solid oxide cathode slurry.

[0029] Optionally, the binder accounts for 40-60 wt% of the total mass of the solid oxide cathode slurry.

[0030] Optionally, the binder as a percentage of the total mass of the solid oxide cathode slurry is independently selected from any value of 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, or a range between any two of the above.

[0031] Optionally, the proton conductor electrolyte sheet is selected from anode-supported electrolyte sheets and / or electrolyte-supported electrolyte sheets.

[0032] Optionally, in step (1), the temperature of calcination I is 900-1300℃, and the calcination time is 1-2h.

[0033] Optionally, in step (1), the temperature of calcination I is independently selected from any value of 900℃, 1000℃, 1100℃, 1200℃, 1300℃ or a range between any two of the above.

[0034] Optionally, the heating rate of the calcination I is 2 to 5 °C / min.

[0035] Optionally, the heating rate of the calcination I is independently selected from any value of 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min or a range between any two of the above.

[0036] Optionally, in step (2), the temperature of calcination II is 400-700°C, and the calcination time is 1-2 hours.

[0037] Optionally, the calcination temperature II is independently selected from any value of 400°C, 500°C, 600°C, 700°C, or a range between any two of the above.

[0038] Optionally, the heating rate of the calcination II is 2 to 5 °C / min.

[0039] Optionally, in step (2), the reduction temperature is 500-700°C, the reduction time is 1-3 hours, and the reduction atmosphere is hydrogen.

[0040] Optionally, the reduction temperature is independently selected from any value of 500°C, 600°C, 700°C, or a range between any two of the above.

[0041] Optionally, the restoration time is independently selected from any value of 1h, 1.5h, 2h, 2.5h, 3h or a range between any two of the above.

[0042] Optionally, the reduction heating rate is 1–5 °C / min.

[0043] Optionally, the reduction heating rate is independently selected from any value of 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, or a range between any two of the above.

[0044] Optionally, in step (2), the drying is vacuum drying, and the drying time is 20 minutes.

[0045] As a specific implementation method, this application is achieved through the following technical solution:

[0046] Step (1): A solid oxide cathode paste is uniformly coated on one side of the proton conductor electrolyte sheet, and a porous cathode skeleton is prepared by high-temperature sintering;

[0047] Step (2): Dissolve an appropriate amount of ruthenium salt in a mixed solution of deionized water and ethanol to prepare an impregnation solution of ruthenium salt;

[0048] Step (3): The impregnation solution obtained in step (2) is drop-coated onto the porous cathode skeleton prepared in step (1) and then vacuum dried;

[0049] Step (4): Heat the cathode obtained in step (3) to generate RuO2;

[0050] Step (5): Repeat steps (3) and (4) until the mass of Ru element accounts for 5 to 40% of the total mass of the cathode layer;

[0051] Step (6): Place the cathode obtained in step (5) in a hydrogen atmosphere, raise the temperature, and reduce it to obtain a proton-electron hybrid conductive composite cathode loaded with Ru nanoparticles.

[0052] Optionally, in step (1), the high-temperature calcination process is carried out in an air atmosphere.

[0053] Optionally, in step (4), the heating process is carried out in an air atmosphere.

[0054] In this invention, a porous cathode framework was prepared in advance, and ruthenium salt was dispersed in the porous framework by impregnation. After redox treatment, uniformly dispersed ruthenium nanoparticles were generated in situ, resulting in a proton-electron hybrid conductive cathode loaded with Ru nanoparticles, which exhibited more significant ammonia synthesis catalytic activity.

[0055] This application describes a proton-electron hybrid conductive composite cathode with Ru catalyst, prepared by impregnating a porous cathode framework with a ruthenium salt solution followed by calcination and reduction to generate Ru nanoparticles in situ on the electrode surface. Unlike traditional perovskite electrodes and pure metal electrodes, the use of this proton-electron hybrid conductive composite cathode improves the interfacial contact between the electrode and the electrolyte, increasing the three-phase interface. Furthermore, this method eliminates the need for high-temperature calcination (>1000℃) of the catalyst, avoiding severe Ru particle agglomeration. The nanoscale Ru particles provide numerous highly active centers, increasing the active sites for ammonia synthesis and accelerating charge transfer, thus significantly enhancing the catalytic activity for ammonia synthesis.

[0056] In this application, "BZCY" refers to BaZr. 1-x-y Ce x Y y O 3-δ (x+y<1);

[0057] “BZCYYb” refers to BaZr 1-x-y-z Ce x Y y Yb z O 3-δ (x+y+z<1);

[0058] “BZY” refers to BaZr x Y 1-x O 3-δ (x<1);

[0059] “BCY” refers to BaCe x Y 1-x O 3-δ (x<1);

[0060] “BCC” refers to BaCe 1-x Ca x O 3-δ(x<1);

[0061] “BCD” refers to BaCe 1-x Dy x O 3-δ (x<1);

[0062] “BCGO” refers to BaCe 1-x Gd x O 3-δ (x<1);

[0063] "LSGM" refers to La 1-x Sr x Ga 1-y Mg y O 3-δ (x<1,y<1);

[0064] "LBGM" refers to La 1-x Ba x Ga 1-y Mg y O 3-δ (x<1,y<1);

[0065] “SCY” refers to SrCe 1-x Yb x O 3-δ (x<1).

[0066] "LSCF" refers to La 1-x Sr x Co 1-y Fe y O 3-δ (x<1,y<1);

[0067] "LST" refers to La 1-x Sr x TiO 3-δ (x<1);

[0068] “SFM” refers to Sr2Fe 2-x Mo x O 6-δ (x<2);

[0069] “SSC” refers to Sm 0.5 Sr 0.5 CoO 3-δ ;

[0070] "LNF" refers to LaNi 1-x Fe x O 3-δ (x<1);

[0071] "PCF" refers to Pr 1-x Cax FeO 3-δ (x<1).

[0072] The beneficial effects that this application can produce include:

[0073] 1) This application obtained a stable nanoscale noble metal catalyst by impregnation and then oxidation-reduction. This method is simple and easy to implement, and avoids the agglomeration of noble metal catalyst caused by high temperature calcination (>1000℃). The noble metal catalyst and the perovskite cathode material are in full contact, exhibiting more catalytic active sites.

[0074] 2) Compared with traditional perovskite cathodes, the proton-electron hybrid conductive composite cathode prepared by this application with Ru nanoparticles shows that the introduction of Ru nanocatalysts significantly reduces the polarization resistance of the reaction and exhibits higher electron transfer efficiency and catalytic activity.

[0075] 3) This application uses a mixed material of proton and electron conductor as the cathode framework to reduce the use of ruthenium catalyst, saving economic costs while ensuring sufficient three-phase contact interface and conductivity;

[0076] 4) The method for preparing the proton-electron hybrid conductive composite cathode loaded with Ru nanoparticles in this application adopts a solution impregnation method, which can be used to prepare cathode materials with different metal loads and has great development potential for different reactions. Attached Figure Description

[0077] Figure 1 The images shown are scanning electron microscope (SEM) images of the Ru-loaded LSCF-BZCYYb composite cathode prepared by impregnation with ruthenium nitrite nitrate in Example 1 of this application (a, cross-sectional view, scale bar 10 μm; b, cathode honeycomb structure, scale bar 1 μm; c, distribution of Ru particles on the surface of the reduced LSCF-BZCYYb framework, scale bar 100 nm; d, LSCF-BZCYYb framework, scale bar 100 nm).

[0078] Figure 2 The image shows the XRD pattern of the LSCF-BZCYYb composite cathode material loaded with Ru nanoparticles prepared by impregnation with ruthenium nitrite nitrate in Example 1 of this application.

[0079] Figure 3 The image shows the current-voltage characteristic curve (IE) of the LSCF-BZCYYb composite cathode loaded with Ru nanoparticles, prepared by impregnation with ruthenium nitrite nitrate in Example 1 of this application, under nitrogen reduction mode.

[0080] Figure 4This is the impedance diagram (EIS) of the LSCF-BZCYYb composite cathode loaded with Ru nanoparticles, prepared by impregnation with ruthenium nitrite nitrate in Example 1 of this application, under nitrogen reduction mode. Detailed Implementation

[0081] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0082] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0083] In this application, a Shanghai Chenhua CHI 760E electrochemical workstation was used for voltammetry and impedance testing, and a JEOL JMS-7800F scanning electron microscope (3kV) was used to characterize the microstructure of the battery cathode layer.

[0084] Example 1:

[0085] 1) Mix LSCF, BZCYYb, potato starch and 6 w / v% polyethyl cellulose terpineol dispersion at a mass ratio of 3:2:1:4 and ball mill at 100 rpm for 1 h to prepare cathode slurry;

[0086] 2) The cathode slurry obtained in step 1) is uniformly brushed onto one side of the BZCYYb electrolyte sheet supported by the Ni-BZCYYb anode. After drying, it is placed in an air atmosphere and heated to 1100℃ at a rate of 5℃ / min. It is then calcined for 2 hours to obtain a porous cathode skeleton.

[0087] 3) Dissolve 0.1 mol of nitrosyl ruthenium nitrate in 50 mL of deionized water, add an equal volume of anhydrous ethanol, and prepare a 1 mol / L nitrosyl ruthenium nitrate impregnation solution;

[0088] 4) Drop-coat 4.5 μL of the nitrosyl ruthenium nitrate impregnation solution prepared in step 3) onto the porous cathode skeleton obtained by sintering in step 2), vacuum dry for 20 min, and then place the obtained cathode in an air atmosphere and heat it to 500 °C at a rate of 2 °C / min, and calcine for 1 h; the mass of Ru element accounts for 10% of the cathode layer.

[0089] 5) The obtained cathode was placed in a hydrogen atmosphere and heated to 600℃ at a rate of 1℃ / min, and reduced for 2h to obtain an LSCF-BZCYYb composite cathode loaded with nano-Ru particles.

[0090] like Figure 1 As shown, the cathode framework sintered at high temperature exhibits a continuous porous structure. After being impregnated with ruthenium nitrite solution and subjected to high-temperature oxidation-reduction, the porous cathode framework of LSCF-BZCYYb remains clearly visible, and some uniformly dispersed Ru particles with a particle size of 10–20 nm appear. Figure 2 Based on the corresponding XRD results, they can be identified as LSCF, BZCYYb, and Ru.

[0091] The Ni-BZCYYb / BZCYYb / Ru-LSCF-BZCYYb electrolytic cell prepared in Example 1 was subjected to basic electrochemical tests at 300, 400, and 500 °C. During the tests, 5% hydrogen (95% argon) was introduced into the anode at a flow rate of 30 mL / min, and nitrogen was introduced into the cathode at a flow rate of 60 mL / min. Using the anode as both the counter and reference electrode, and the cathode as the working electrode, voltammetric characteristic curves were collected at a scan rate of 10 mV / s. The results are shown below. Figure 3 As shown. From Figure 3 As can be seen from this, the battery prepared by this method has a current density as high as 144 mA cm⁻¹ at 500°C. -2 Although the current density decreases with decreasing temperature, it still maintains 10 mA cm⁻¹ at 300°C. -2 Constant-voltage electrochemical impedance spectroscopy was measured at open circuit potentials in the frequency range of 0.1 Hz to 100 kHz at 300, 400, and 500 °C. The results are as follows: Figure 4 As shown, the impedance results are consistent with the current-voltage relationship. At 500℃, the ohmic resistance and polarization resistance are only 5Ω and 90Ω, respectively, increasing to 29Ω and 400Ω, respectively, when the temperature drops to 300℃. In summary, the electrochemical performance of this battery is good at high temperatures. Although it deteriorates slightly with decreasing temperature, it is still sufficient to meet the requirements of subsequent electrocatalytic ammonia synthesis.

[0092] The Ni-BZCYYb / BZCYYb / Ru-LSCF-BZCYYb electrolytic cells prepared in Example 1 were subjected to constant potential tests at -0.1 to -0.6 V under anodic atmosphere conditions of 5% hydrogen (95% argon) and cathode atmosphere conditions of 300, 400, and 500 °C. The optimal yield (400 °C, -0.2 V) is shown in Table 1.

[0093] Example 2:

[0094] 1) Mix LST, SCY, potato starch and polyvinyl alcohol in a mass ratio of 3:2:3:6 and prepare cathode paste by spherical rotation at 150 rpm for 1 hour;

[0095] 2) Take an electrolyte-supported SCY electrolyte sheet with Ni-SCY on the anode side. Brush cathode paste onto one side of the electrolyte sheet, dry it, and place it in an air atmosphere. Heat it to 1050℃ at a rate of 3℃ / min and calcine it for 1.5h to obtain a porous cathode framework.

[0096] 3) Dissolve 0.025 mol of ruthenium chloride in 25 mL of deionized water, add anhydrous ethanol and mix well to prepare a 0.25 mol / L ruthenium chloride impregnation solution. The volume ratio of deionized water to anhydrous ethanol is 1:3.

[0097] 4) Each time, 4 μL of the impregnation solution prepared in step 3) is dropped onto the porous cathode skeleton obtained by sintering in step 2), vacuum dried for 20 min, and then the obtained cathode is placed in an air atmosphere, heated to 400℃ at 5℃ / min, and calcined for 2 h.

[0098] 5) Repeat step 4) until the mass of Ru accounts for 20% of the cathode layer. Place the obtained cathode in a hydrogen atmosphere and heat it to 600℃ at a rate of 2℃ / min. Reduce it for 3h to obtain the LST-SCY composite cathode loaded with Ru nanoparticles.

[0099] The ammonia yield of the Ni-SCY / SCY / Ru-LST-SCY electrolyzer prepared according to Example 1 was measured, and the optimal yield (400℃, -0.2V) is shown in Table 1.

[0100] Example 3:

[0101] 1) A cathode slurry was prepared by mixing LNF, BZCY, potato starch, and terpineol dispersion of 10 w / v % polyethyl cellulose at a mass ratio of 3:6:3:10 and ball milling at 200 rpm for 0.5 h.

[0102] 2) The electrolyte is uniformly brushed onto one side of the BZCY electrolyte sheet supported by the Ni-BZCY anode, dried, and placed in an air atmosphere. The temperature is increased to 1000℃ at a rate of 2℃ / min and calcined for 3h to obtain a porous cathode skeleton.

[0103] 3) Dissolve 0.05 mol of ruthenium nitrate in 75 mL of deionized water, add anhydrous ethanol and mix well to prepare a 0.5 mol / L ruthenium nitrate impregnation solution. The volume ratio of deionized water to anhydrous ethanol is 3:1.

[0104] 4) Each time, 2 μL of the impregnation solution prepared in step 3) is dropped onto the porous cathode skeleton obtained by sintering in step 2), vacuum dried for 20 min, and then the obtained cathode is placed in an air atmosphere and heated to 400°C at a rate of 5°C / min, and calcined for 1 h.

[0105] 5) Repeat step 4) until the mass of Ru accounts for 40% of the cathode layer, then place the cathode layer in an air atmosphere and heat it to 600°C at a rate of 5°C / min, and calcine it for 1 hour;

[0106] 6) The cathode layer obtained in step 5) is placed in a hydrogen atmosphere and heated to 700℃ at a rate of 5℃ / min, and reduced for 3h to obtain the LNF-BZCY composite cathode loaded with Ru nanoparticles.

[0107] The ammonia yield of the Ni-BZCY / BZCY / Ru-LNF-BZCY electrolyzer prepared according to Example 1 was measured, and the optimal yield (400℃, -0.1V) is shown in Table 1.

[0108] Example 4:

[0109] 1) Mix SFM, BCGO, graphite powder and polyvinyl alcohol in a mass ratio of 3:2:2:8 and ball mill at 200 rpm for 1 hour to prepare cathode slurry;

[0110] 2) Take an electrolyte-supported BCGO electrolyte sheet with Ni-BCGO on the anode side. Brush cathode paste onto one side of the electrolyte sheet, dry it, and place it in an air atmosphere. Heat it to 1100℃ at a rate of 5℃ / min and calcine it for 2 hours to obtain a porous cathode framework.

[0111] 3) Dissolve 0.05 mol of ruthenium nitrate in 25 mL of deionized water, add anhydrous ethanol and mix well to prepare a 0.5 mol / L impregnation solution. The volume ratio of deionized water to anhydrous ethanol is 1:3.

[0112] 4) Each time, 2 μL of the impregnation solution prepared in step 3) is dropped onto the porous cathode skeleton obtained by sintering in step 2), vacuum dried for 20 min, and then the obtained cathode is placed in an air atmosphere, heated to 600℃ at 2℃ / min, and calcined for 1 h.

[0113] 5) Repeat step 4) until the mass of Ru accounts for 10% of the cathode layer. Place the obtained cathode in a hydrogen atmosphere and heat it to 600℃ at a rate of 5℃ / min. Reduce it for 2h to obtain the SFM-BCGO composite cathode loaded with Ru nanoparticles.

[0114] The ammonia yield of the Ni-BCGO / BCGO / Ru-SFM-BCGO electrolyzer prepared according to Example 1 was measured, and the optimal yield (500℃, -0.2V) is shown in Table 1.

[0115] Example 5

[0116] 1) Mix SSC, LSGM, carbon powder and dioctyl phthalate in a mass ratio of 5:5:2:8 and ball mill at 100 rpm for 2 hours to prepare cathode slurry;

[0117] 2) Take an electrolyte-supported LSGM electrolyte sheet with Ni-LSGM on the anode side. Brush cathode paste onto one side of the electrolyte sheet, dry it, and place it in an air atmosphere. Heat it to 1000℃ at a rate of 5℃ / min and calcine it for 1 hour to obtain a porous cathode framework.

[0118] 3) Dissolve 0.01 mol of ruthenium nitrate in 50 mL of deionized water, add anhydrous ethanol and mix well to prepare a 0.1 mol / L impregnation solution. The volume ratio of deionized water to anhydrous ethanol is 1:1.

[0119] 4) Each time, 2 μL of the impregnation solution prepared in step 3) is dropped onto the porous cathode skeleton obtained by sintering in step 2), vacuum dried for 20 min, and then the obtained cathode is placed in an air atmosphere, heated to 400℃ at 2℃ / min, and calcined for 2 h.

[0120] 5) Repeat step 4) until the mass of Ru accounts for 5% of the cathode layer. Place the obtained cathode in a hydrogen atmosphere and heat it to 600℃ at a rate of 2℃ / min. Reduce it for 2h to obtain the SSC-LSGM composite cathode loaded with Ru nanoparticles.

[0121] The ammonia yield of the Ni-LSGM / LSGM / Ru-SSC-LSGM electrolyzer prepared according to Example 1 was measured, and the optimal yield (500℃, -0.2V) is shown in Table 1.

[0122] Comparative Example 1

[0123] 1) Mix Ru, LSCF, BZCYYb, potato starch and terpineol dispersion of 6 w / v cellulose in a mass ratio of 1:3:2:1:4 and ball mill at 100 rpm for 1 h to prepare cathode slurry;

[0124] 2) The cathode slurry obtained in step 1) is uniformly brushed onto one side of the BZCYYb electrolyte sheet supported by the Ni-BZCYYb anode, dried, and placed in an air atmosphere. The temperature is increased to 1100℃ at a rate of 5℃ / min and calcined for 2h.

[0125] 3) The cathode layer obtained in step 2) was placed in a hydrogen atmosphere and heated to 600℃ at a rate of 1℃ / min and reduced for 2h to obtain the Ru-LSCF-BZCYYb composite cathode.

[0126] The ammonia yield of the Ni-BZCYYb / BZCYYb / Ru-LSCF-BZCYYb electrolyzer prepared according to Example 1 was measured, and the optimal yield (400℃, -0.1V) is shown in Table 1.

[0127] Comparative Example 2

[0128] 1) BZCYYb, potato starch and 6 w / v% polyethyl cellulose terpineol dispersion were mixed at a mass ratio of 5:1:4 and ball-milled at 100 rpm for 1 h to prepare cathode slurry;

[0129] 2) The cathode slurry obtained in step 1) is uniformly brushed onto one side of the BZCYYb electrolyte sheet supported by the Ni-BZCYYb anode. After drying, it is placed in an air atmosphere and heated to 1350℃ at a rate of 5℃ / min. It is then calcined for 2 hours to obtain a porous cathode skeleton.

[0130] 3) Dissolve 0.1 mol of nitrosyl ruthenium nitrate in 50 mL of deionized water, add an equal volume of anhydrous ethanol, and prepare a 1 mol / L nitrosyl ruthenium nitrate impregnation solution;

[0131] 4) Drop-coat 4.5 μL of the impregnation solution prepared in step 3) onto the porous cathode skeleton obtained by sintering in step 2), vacuum dry for 20 min, and then place the obtained cathode in an air atmosphere and heat it to 500 °C at a rate of 2 °C / min, and calcine for 1 h; the mass of Ru element accounts for 10% of the cathode layer.

[0132] 5) The obtained cathode was placed in a hydrogen atmosphere and heated to 600℃ at a rate of 1℃ / min, and reduced for 2h to obtain a BZCYYb cathode loaded with Ru nanoparticles.

[0133] The ammonia yield of the Ni-BZCYYb / BZCYYb / Ru-BZCYYb electrolyzer prepared according to Example 2 was measured, and the optimal yield (400℃, -0.2V) is shown in Table 1.

[0134] Table 1. Ammonia synthesis activity of ruthenium cathode catalysts prepared by impregnation method and comparative catalyst activities.

[0135]

[0136] As can be seen from Table 1, the proton-electron hybrid conductive composite cathodes with ruthenium nanoparticles loaded using the preparation method of this application all exhibited certain ammonia synthesis activity, which was significantly higher than that of comparative examples 1 and 2.

[0137] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing a cathode for a solid oxide electrolytic cell used in ammonia synthesis, characterized in that, The preparation method includes the following steps: (1) The solid oxide cathode paste is brushed onto one side of the proton conductor electrolyte sheet and calcined to obtain a porous cathode skeleton; (2) The impregnation solution containing ruthenium salt was drop-coated onto the porous cathode framework, dried, calcined, and reduced to obtain a proton-electron hybrid conductive composite cathode loaded with Ru nanoparticles. The solid oxide powder in the solid oxide cathode slurry includes proton conductor materials and electron conductor materials; The mass ratio of the proton conductor material to the electron conductor material is 1:2 to 2:1; The proton conductor material is selected from at least one of BZCY, BZCYYb, BZY, BCY, BCC, BCD, BCGO, LSGM, LBGM, and SCY; The electronic conductor material is selected from at least one of LSCF, LST, SFM, SSC, LNF, and PCF.

2. The preparation method according to claim 1, characterized in that, The ruthenium salt is selected from at least one of ruthenium chloride, ruthenium nitrite, and ruthenium nitrate.

3. The preparation method according to claim 1, characterized in that, The concentration of the ruthenium salt-containing impregnation solution is 0.1~1 mol / L.

4. The preparation method according to claim 1, characterized in that, The solvent in the ruthenium salt-containing impregnation solution is a mixture of water and ethanol, with a volume ratio of water to ethanol of 3:1 to 1:

3.

5. The preparation method according to claim 1, characterized in that, In the proton-electron hybrid conductive composite cathode loaded with Ru nanoparticles, the mass of Ru element accounts for 5 to 40 wt% of the total mass of the proton-electron hybrid conductive composite cathode loaded with Ru nanoparticles.

6. The preparation method according to claim 1, characterized in that, The solid oxide cathode slurry is obtained by ball milling raw materials containing solid oxide powder, pore-forming agent, and binder.

7. The preparation method according to claim 6, characterized in that, Preferably, the ball mill rotates at 100-200 rpm and the milling time is 0.5-2 h.

8. The preparation method according to claim 6, characterized in that, Preferably, the pore-forming agent is selected from at least one of starch, carbon powder, and graphite.

9. The preparation method according to claim 6, characterized in that, The binder is selected from at least one of ethyl cellulose terpineol dispersion, methyl cellulose, dioctyl phthalate, and polyvinyl alcohol.

10. The preparation method according to claim 6, characterized in that, The pore-forming agent accounts for 10-30 wt% of the total mass of the solid oxide cathode slurry.

11. The preparation method according to claim 6, characterized in that, The binder accounts for 40-60 wt% of the total mass of the solid oxide cathode slurry.

12. The preparation method according to claim 1, characterized in that, The proton conductor electrolyte sheet is selected from anode-supported electrolyte sheets and / or electrolyte-supported electrolyte sheets.

13. The preparation method according to claim 1, characterized in that, In step (1), the temperature of calcination I is 900~1300 ℃, and the calcination time is 1~2 h.

14. The preparation method according to claim 1, characterized in that, The heating rate of the calcination I is 2~5 ℃ / min.

15. The preparation method according to claim 1, characterized in that, In step (2), the temperature of calcination II is 400~700 ℃, and the calcination time of calcination II is 1~2 h.

16. The preparation method according to claim 1, characterized in that, The heating rate of the calcination II is 2 ~ 5 °C / min.

17. The preparation method according to claim 1, characterized in that, In step (2), the reduction temperature is 500~700 ℃, the reduction time is 1~3 h, and the reduction atmosphere is hydrogen.

18. The preparation method according to claim 1, characterized in that, The reduction heating rate is 1~5 °C / min.

19. The preparation method according to claim 1, characterized in that, In step (2), the drying is vacuum drying, and the drying time is 20 min.

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