Process for the electrochemical reduction of nitrogen to ammonia and the biphasic solid electrolyte used therein

Abstract

The application belongs to the technical field of new energy materials, and specifically discloses a dual-phase solid electrolyte for electrochemical reduction of nitrogen to synthesize ammonia, which comprises the following steps: uniformly mixing and crushing barium nitrate, cerium nitrate, zirconium nitrate and yttrium nitrate, and then pre-sintering to obtain BCZY powder; uniformly mixing and crushing ZrO2 and Y2O3, and then pre-sintering to obtain YSZ powder; uniformly mixing the BCZY powder and the YSZ powder, and then molding into a green body; and sintering the green body at 1400-1500 DEG C for 10-12 h to obtain the dual-phase solid electrolyte BCZY@YSZ. The application also discloses a method for electrochemical reduction of nitrogen to synthesize ammonia by using the dual-phase solid electrolyte as an electrolyte layer. The application can ensure long-term service life and reliability of the electrolyte.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials technology, specifically relating to a perovskite-type solid electrolyte and its method for electrochemical reduction of nitrogen to synthesize ammonia at low temperature and ambient pressure. Background Technology

[0002] The ammonia synthesis industry is of great significance to national economic and social development. Ammonia is not only an important chemical product, but also an industrial raw material for the production of almost all nitrogen-containing compounds, with wide applications in fertilizers, transportation, refrigeration, plastics, pharmaceuticals, and explosives. Currently, the industrial ammonia synthesis method still uses the Haber-Bosch ammonia synthesis process, which originated in the early 20th century. However, this process has high equipment pressure requirements, a complex process flow, low conversion rate (10%–15%), high energy consumption, and serious environmental pollution.

[0003] In recent years, the electrochemical synthesis of ammonia has received widespread attention and research from scientists. Electrochemical ammonia synthesis can break the thermodynamic energy barrier of nitrogen activation under the action of electrical energy, removing the thermodynamic equilibrium restriction, allowing the nitrogen reduction reaction to proceed under relatively mild conditions. Aqueous electrolytes are typically used under ambient temperature and pressure conditions. Zang et al. (ACSCatalysis, 2019, 9(11): 10166-10173) developed a class of Cu single-atom catalysts based on a porous nitrogen-doped carbon network structure, NC-Cu SA, and studied their catalytic performance for nitrogen reduction in alkaline and acidic solutions. In 0.1M KOH and 0.1M HCl electrolytes, the NH3 yields of NC-Cu SA were 53.3% and 53.5%, respectively. The FE values ​​were 13.8% and 11.7%, respectively. Due to the relatively low operating temperature, the kinetic reaction rate was inevitably slow at low temperatures. Using a solid electrolyte can solve the problem of slow kinetic reaction. Skodra et al. (Solid State Ionics, 2009, 180(23 / 24 / 25):1332-1336) successfully synthesized ammonia using yttrium-stabilized zirconium oxide (8 mol% YSZ) as the electrolyte and steam and nitrogen as raw materials. The reaction device operated at 500-700 °C and one atmosphere, but the conversion rates of steam and nitrogen to ammonia were very low, mainly due to the low proton flux and poor electrode conductivity.

[0004] Based on existing literature and technology, electrochemical ammonia synthesis is an environmentally friendly alternative to traditional ammonia synthesis. However, the process of directly synthesizing ammonia using nitrogen and water at room temperature and pressure is too inefficient to achieve mass production. Using high-temperature solid electrolytes can alleviate pressure conditions while maintaining a relatively fast kinetic rate. The key lies in designing and developing electrolytes with high proton transport rates, high conductivity, and thermal stability.

[0005] Currently, among existing solid electrolytes, BCZY and YSZ are only used as single-phase electrolytes, and YSZ has insufficient proton conductivity. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a two-phase solid electrolyte (perovskite type solid electrolyte) and a method for electrochemically reducing nitrogen to synthesize ammonia at relatively low temperature (200-500℃) and normal pressure.

[0007] To solve the above-mentioned technical problems, the present invention provides a two-phase solid electrolyte for the electrochemical reduction of nitrogen to synthesize ammonia, comprising the following steps:

[0008] 1) Barium nitrate, cerium nitrate, zirconium nitrate, and yttrium nitrate are uniformly mixed according to the molar ratio of Ba:Ce:Zr:Y = 1:x:y:1-xy to obtain mixture one; x = 0.1~0.9, y = 0.1~0.9;

[0009] According to the ratio of Y2O3:ZrO2 = 7-9 mol% (preferably 8 mol%), Y2O3 is incorporated into ZrO2 and mixed uniformly to obtain mixture two;

[0010] Note: Calculate the mass of each raw material based on the required stoichiometric ratio;

[0011] 2) After pulverizing and refining the mixture (to pass through a 200-mesh sieve), pre-calcine it in air at 900-1000℃ for 3-5 hours to obtain BCZY powder;

[0012] The mixture was pulverized and refined (to pass through a 200-mesh sieve) and pre-calcined in air at 900-1000°C for 3-5 hours to obtain YSZ powder;

[0013] illustrate:

[0014] After pre-calcination, the mixture can be further pulverized (to pass through a 300-mesh sieve) to obtain BCZY powder;

[0015] After pre-calcination, the mixture can be further pulverized (to pass through a 300-mesh sieve) to obtain YSZ powder.

[0016] Pre-calcination of the above mixture can eliminate volatile components (such as nitrogen oxides NO) in the raw materials. x This promotes the initial reaction to form the perovskite phase and the stable zirconium oxide phase;

[0017] 3) Mix BCZY powder and YSZ powder evenly at a mass ratio of 1-5:5-1 to form a composite material precursor;

[0018] 4) The composite material precursor is molded into a blank, and then the molded blank is sintered in air at 1400-1500℃ for 10-12h to obtain a two-phase solid electrolyte (a dense two-phase electrolyte BCZY@YSZ).

[0019] The chemical formula of BCZY is BaCe x Zr y Y 1-x-y O3- δ δ represents the percentage of oxygen vacancies in the compound, and 3-δ is the actual oxygen concentration; this is the conventional way of expressing it.

[0020] That is, the present invention yields a novel biphase electrolyte BCZY@YSZ, which incorporates the proton-conducting material BaCe. x Zr y Y 1-x-y O3- δ (BCZY) and ZrO2 (YSZ) doped with Y2O3, an oxygen ion conductive material.

[0021] As an improvement to the two-phase solid electrolyte of the present invention:

[0022] x=0.6~0.7, y=0.2~0.3;

[0023] The mass ratio of BCZY powder to YSZ powder is 1 to 2:1.

[0024] As a further improvement to the two-phase solid electrolyte of the present invention:

[0025] In step 1), the molar ratio of Ba:Ce:Zr:Y is 1:0.7:0.2:0.1; the molar ratio of Y₂O₃:ZrO₂ is 8 mol%.

[0026] In step 2): after the first mixture is pulverized and refined, it is pre-calcined in air at 900°C for 3 hours; after the second mixture is pulverized and refined, it is pre-calcined in air at 900°C for 3 hours.

[0027] As a further improvement to the two-phase solid electrolyte of the present invention:

[0028] The pressure for compression molding is 100MPa to 200MPa.

[0029] The present invention also provides a method for electrochemically reducing nitrogen to synthesize ammonia, using a planar solid oxide fuel cell. The planar solid oxide fuel cell includes a cathode layer, an anode layer, and an electrolyte layer located between the cathode layer and the anode layer; the anode layer corresponds to the anode chamber of the battery, and the cathode layer corresponds to the cathode chamber of the battery; high-purity hydrogen (H2) is introduced into the anode chamber, and high-purity nitrogen (N2) is introduced into the cathode chamber, and the generated ammonia (NH3) is collected in the cathode chamber;

[0030] The electrolyte layer is made of a two-phase solid electrolyte;

[0031] The battery is heated and kept at 200-500°C using a high-temperature furnace, and the voltage across the battery terminals is controlled to be 0-2.0V (preferably 1.2-1.5V) using a power supply.

[0032] Explanation: The gas in the cathode chamber passes through a condenser, which condenses the ammonia into liquid or gaseous ammonia for collection.

[0033] As an improvement to the electrochemical reduction of nitrogen to synthesize ammonia of the present invention:

[0034] The anode layer material is Ni / YSZ; the cathode layer material is Fe / YSZ.

[0035] As a further improvement to the electrochemical reduction of nitrogen to synthesize ammonia of the present invention:

[0036] The thickness of the anode layer (Ni / YSZ) is 18–22 μm, the thickness of the electrolyte layer is 9–11 μm, and the thickness of the cathode layer (Fe / YSZ) is 18–22 μm.

[0037] The flow rates of hydrogen and nitrogen are both 80–120 sccm, and the pressures are both 1.1–1.3 atm (preferably both 100 sccm and both 1.2 atm); by controlling the flow rates and pressures, a stable gas supply is ensured.

[0038] As a further improvement to the electrochemical reduction of nitrogen to synthesize ammonia of the present invention:

[0039] A two-phase solid electrolyte (BCZY@YSZ) was prepared into a slurry, coated onto the anode layer (Ni / YSZ), dried and sintered to form an electrolyte layer; then Fe / YSZ was prepared into a slurry, coated onto the other side of the electrolyte layer, dried and sintered to form a cathode layer.

[0040] This invention develops a perovskite-type solid electrolyte with specific properties using nitrogen and hydrogen as raw materials for the electrochemical synthesis of ammonia under normal pressure.

[0041] Compared with the prior art, the present invention has the following advantages:

[0042] 1) A novel biphase electrolyte BCZY@YSZ is provided, which has both proton conductivity and oxygen ion conductivity. It can conduct protons and oxygen ions more effectively at high temperatures, exhibiting lower resistance and higher reactivity, thereby improving the overall efficiency of ammonia synthesis reaction.

[0043] The biphase electrolyte BCZY@YSZ exhibits both proton and oxygen ion conductivity, enabling it to conduct protons and oxygen ions more effectively at high temperatures and demonstrating lower resistance (electrode polarization impedance of 0.32 Ω·cm). 2 (and higher reactivity, thereby improving the overall efficiency of ammonia synthesis reaction.)

[0044] 2) Both BCZY and YSZ have excellent high-temperature stability and are not easily decomposed or fail under high-temperature operating conditions, thus ensuring the long service life and reliability of the electrolyte.

[0045] 3) The composite electrolyte material combines the mechanical strength of BCZY and YSZ, thus possessing good thermal shock resistance (no cracks or ruptures after 30 cycles) and mechanical properties (flexural strength 160MPa, compressive strength 460MPa), enabling it to withstand high-temperature operation and repeated cycles. Attached Figure Description

[0046] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0047] Figure 1 This is a schematic diagram of the cathode layer, anode layer, and electrolyte layer of a planar solid oxide fuel cell. Detailed Implementation

[0048] The following is a detailed description of the embodiments of the present invention. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes.

[0049] Example 1, BaCe 0.7 Zr 0.2 Y 0.1 O3- δ Preparation of @YSZ:

[0050] 1) Set the molar ratio of Ba:Ce:Zr:Y to 1:0.7:0.2:0.1, and mix barium nitrate, cerium nitrate, zirconium nitrate, and yttrium nitrate to obtain mixture one;

[0051] According to the ratio of Y2O3:ZrO2 = 8 mol%, Y2O3 is doped into ZrO2 to obtain mixture two;

[0052] 2) First, the mixture is pulverized and refined using a ball mill (until it passes through a 200-mesh sieve) to ensure uniform mixing. Then, it is pre-calcined in air at 900°C for 3 hours. The pre-calcined material is then ball-milled and pulverized (until it passes through a 300-mesh sieve) to further refine the particles and improve uniformity, thus obtaining BCZY powder.

[0053] Note: The pre-calcination of the above mixture is to eliminate volatile components (such as nitrogen oxides NO) from the raw materials.x This promotes the initial reaction to form the perovskite phase and the stable zirconium oxide phase, wherein the perovskite phase (BaCe0.7Zr0.2Y0.1O3-) δ It is mainly formed by the chemical reaction of barium, cerium, zirconium and yttrium sources. In addition, yttrium is doped into the zirconium oxide lattice to form a stable cubic crystal phase structure. δ represents the amount of oxygen vacancies, and 3-δ is the proportion of actual oxygen atoms in the material. This is the conventional way of expressing it in this industry.

[0054] The mixture was first pulverized and refined using a ball mill (to pass through a 200-mesh sieve) to ensure uniform mixing, and then pre-calcined in air at 900°C for 3 hours; the pre-calcined material was then ball-milled and pulverized (to pass through a 300-mesh sieve) to further refine the particles and improve uniformity, thus obtaining YSZ powder.

[0055] 3) Mix BCZY powder and YSZ powder at a mass ratio of 1:1 and use a ball mill to mix them evenly to form a composite material precursor;

[0056] 4) The composite precursor obtained in step 3) is pressed into a preform of the desired shape (e.g., 10mm × 10mm × 10mm) by compression molding. The preform is then sintered in air at 1400℃ for 10 hours to obtain a dense biphase electrolyte BaCe. 0.7 Zr 0.2 Y 0.1 O3- δ @YSZ.

[0057] Note: The pressure for compression molding is generally 100MPa to 200MPa.

[0058] Experiment 1: Method 1 for the electrochemical reduction of nitrogen to synthesize ammonia:

[0059] A planar solid oxide fuel cell (SOFC) is employed, comprising a cathode layer (Fe / YSZ), an anode layer (Ni / YSZ), and an electrolyte layer located between the cathode and anode layers. The anode layer corresponds to the anode chamber of the battery, and the cathode layer corresponds to the cathode chamber. High-purity hydrogen (H2) is introduced into the anode chamber, and high-purity nitrogen (N2) is introduced into the cathode chamber. Hydrogen loses electrons at the anode to generate hydrogen ions, which then react with nitrogen in the cathode chamber via the electrolyte to generate NH3. The generated ammonia (NH3) is collected in the cathode chamber. In other words, the gas in the cathode chamber (including unreacted nitrogen and generated ammonia) is discharged to a condenser to condense the ammonia into liquid or gaseous ammonia for collection. On the anode side, residual hydrogen that did not participate in the electrochemical reaction can be directly discharged.

[0060] The electrolyte layer uses the biphase electrolyte BaCe obtained in Example 1. 0.7Zr 0.2 Y 0.1 O3- δ It was prepared by @YSZ.

[0061] Specifically as follows:

[0062] The mixture in Example 1 was replaced with nickel nitrate, and the rest was the same as in Example 1. The resulting mixture was named Ni / YSZ and used as the anode layer material.

[0063] The mixture in Example 1 was replaced with ferric nitrate, while the rest remained the same as in Example 1. The resulting mixture was named Fe / YSZ and used as the cathode layer material.

[0064] The BaCe obtained in Example 1 0.7 Zr 0.2 Y 0.1 O3- δ @YSZ and ethanol as a solvent are mixed at a ratio of 1g:10mL to obtain BCZY@YSZ composite electrolyte slurry.

[0065] The BCZY@YSZ composite electrolyte slurry was coated onto a 20μm thick anode layer (Ni / YSZ), dried and sintered (drying at 80℃ for 30 minutes and sintering at 800℃ for 60 minutes) to form an electrolyte layer with a thickness of 10μm; the above drying and sintering can ensure the density and uniformity of the electrolyte layer.

[0066] Fe / YSZ was mixed with ethanol as a solvent at a ratio of 1g:10mL to obtain a cathode catalyst slurry. The cathode catalyst slurry was coated on the other side of the electrolyte layer, dried and sintered (dried at 80℃ for 30 minutes and sintered at 800℃ for 60 minutes) to obtain a cathode layer with a thickness of 20μm.

[0067] High-purity hydrogen (H2) was introduced into the anode chamber of the battery, and high-purity nitrogen (N2) was introduced into the cathode chamber. The flow rate and pressure were controlled (the flow rate of hydrogen and nitrogen were approximately 100 sccm, and the pressure was approximately 1.2 atm for both) to ensure a stable gas supply. The battery was heated using a high-temperature furnace and maintained at a constant temperature of 200°C. The voltage across the battery was controlled at 1.5V using a power supply. After continuous gas supply for 2 hours, the generated ammonia (NH3) was collected in the cathode chamber. The conversion rate of the reactants was 98%, and the product yield was 200.6 μg / h. -1 .

[0068] Reactant conversion rate = Actual amount of nitrogen converted / Theoretical amount of nitrogen converted × 100%

[0069] Product yield per unit = Actual amount of ammonia produced / Reaction time.

[0070] Experiment 2: Method Two for Electrochemical Reduction of Nitrogen to Synthesize Ammonia

[0071] In Experiment 1, the voltage across the battery terminals was changed from "1.5V" to "1.2V" using a power supply; otherwise, the experiment remained the same.

[0072] The BaCe obtained in Example 1 0.7 Zr 0.2 Y 0.1 O3- δ @YSZ performed electrochemical synthesis of ammonia according to Experiment 2. The conversion rate of the reactants and the yield of the products are shown in Table 1 below.

[0073] Example 2

[0074] Compared to Example 1, the following changes are made:

[0075] With the molar ratio of Ba:Ce:Zr:Y set to 1:0.6:0.3:0.1, barium nitrate, cerium nitrate, zirconium nitrate, and yttrium nitrate were mixed.

[0076] The pre-calcination temperature of both mixture 1 and mixture 2 was changed from "900℃" to "1000℃";

[0077] The rest is the same as in Example 1.

[0078] Obtain a dense biphase electrolyte BaCe 0.6 Zr 0.3 Y 0.1 O3- δ @YSZ.

[0079] Example 3

[0080] Compared to Example 1, the following changes are made:

[0081] The mixing ratio (mass ratio) of BCZY powder and YSZ powder was changed from "1:1" to "2:1";

[0082] The rest is the same as in Example 1.

[0083] Obtain a dense biphase electrolyte BaCe 0.7 Zr 0.2 Y 0.1 O3- δ @YSZ.

[0084] Example 4

[0085] Compared to Example 1, the following changes are made:

[0086] Change "sintering at 1400℃ for 10h" in step 4) to "sintering at 1500℃ for 12h";

[0087] The rest is the same as in Example 1.

[0088] Obtain a dense biphase electrolyte BaCe 0.7 Zr 0.2 Y 0.1 O3- δ @YSZ.

[0089] The biphase electrolytes obtained in Examples 2 to 4 were used to electrochemically reduce nitrogen to synthesize ammonia according to Experiments 1 and 2, respectively. The conversion rates of the reactants and the yields of the products are shown in Table 1 below.

[0090] Table 1

[0091]

[0092]

[0093] Comparative Example 1

[0094] Compared to Example 1, the following changes are made:

[0095] Cancel the use of "Mixture 2";

[0096] In step 3), the BCZY powder is simply mixed uniformly using a ball mill; it serves as a material precursor.

[0097] Step 4) Press the material precursor obtained in Step 3) into a blank of the desired shape by compression molding, and sinter the blank in air at 1500°C for 12 hours.

[0098] The rest is the same as in Example 1;

[0099] Obtain dense electrolyte BaCe 0.7 Zr 0.2 Y 0.1 O3- δ .

[0100] The BaCe obtained from Comparative Example 1 0.7 Zr 0.2 Y 0.1 O3- δ Electrochemical synthesis of ammonia was performed according to Experiment 2; the conversion rate of the reactants was 68.5%, and the product yield was 59.4 μg / h. -1 .

[0101] Comparative Example 2

[0102] Compared to Example 1, the following changes are made:

[0103] The mixing ratio (mass ratio) of BCZY powder and YSZ powder was changed from "1:1" to "1:10";

[0104] Furthermore, change "sintering at 1400℃ for 10h" in step 4) to "sintering at 1500℃ for 12h";

[0105] The rest is the same as in Example 1.

[0106] Obtain a dense biphase electrolyte BaCe 0.7 Zr 0.2 Y 0.1 O3- δ @YSZ

[0107] The BaCe obtained from Comparative Example 2 0.7 Zr 0.2 Y 0.1 O3- δ @YSZ performed electrochemical synthesis of ammonia according to Experiment 2; the conversion rate of the reactants was 64.2%, and the product yield was 53.5 μg / h. -1 .

[0108] Finally, it should be noted that the above examples are merely some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A two-phase solid electrolyte for the electrochemical reduction of nitrogen to synthesize ammonia, characterized in that... Includes the following steps: 1) Barium nitrate, cerium nitrate, zirconium nitrate, and yttrium nitrate are uniformly mixed according to the molar ratio of Ba:Ce:Zr:Y = 1:x:y:1-xy to obtain mixture one; x = 0.6~0.7, y = 0.2~0.3; According to the ratio of Y2O3:ZrO2 = 7~9 mol%, Y2O3 is added to ZrO2 and mixed evenly to obtain mixture two; 2) After the mixture is pulverized and refined, it is pre-calcined in air at 900~1000℃ for 3~5 h to obtain BCZY powder; The mixture was pulverized and refined, and then pre-calcined in air at 900~1000℃ for 3~5 h to obtain YSZ powder; 3) Mix BCZY powder and YSZ powder evenly at a mass ratio of 1~5: 5~1 to form a composite material precursor; 4) The composite precursor is molded into a blank, and then the molded blank is sintered in air at 1400~1500℃ for 10~12 h to obtain a two-phase solid electrolyte.

2. The dual-phase solid electrolyte according to claim 1, characterized in that: The mass ratio of BCZY powder to YSZ powder is 1~2:

1.

3. The dual-phase solid electrolyte according to claim 2, characterized in that: In step 1): the molar ratio of Ba:Ce:Zr:Y is 1:0.7:0.2:0.1; Y₂O₃:ZrO₂ = 8 mol% In step 2): after the first mixture is pulverized and refined, it is pre-calcined in air at 900°C for 3 hours; after the second mixture is pulverized and refined, it is pre-calcined in air at 900°C for 3 hours.

4. The biphase solid electrolyte according to any one of claims 1 to 3, characterized in that: The pressure for compression molding is 100 MPa ~ 200 MPa.

5. A method for electrochemically reducing nitrogen to synthesize ammonia, employing a planar solid oxide fuel cell, the planar solid oxide fuel cell comprising a cathode layer, an anode layer, and an electrolyte layer located between the cathode layer and the anode layer; the anode layer corresponds to the anode chamber of the battery, and the cathode layer corresponds to the cathode chamber of the battery; high-purity hydrogen gas is introduced into the anode chamber, high-purity nitrogen gas is introduced into the cathode chamber, and the generated ammonia gas is collected in the cathode chamber; characterized in that: The electrolyte layer is made of a biphase solid electrolyte obtained according to any one of claims 1 to 4; The battery is heated and kept at 200~500℃, and the voltage range at both ends of the battery is controlled to be 0~2.0 V.

6. The method for electrochemical reduction of nitrogen to synthesize ammonia according to claim 5, characterized in that: The anode layer material is Ni / YSZ; the cathode layer material is Fe / YSZ.

7. The method for electrochemical reduction of nitrogen to synthesize ammonia according to claim 5 or 6, characterized in that: The thickness of the anode layer is 18~22μm, the thickness of the electrolyte layer is 9~11μm, and the thickness of the cathode layer is 18~22μm; The flow rates of hydrogen and nitrogen were both 80–120 sccm, and the pressures were both 1.1–1.3 atm.

8. The method for electrochemical reduction of nitrogen to synthesize ammonia according to claim 7, characterized in that: A two-phase solid electrolyte is prepared into a slurry, coated onto the anode layer, dried and sintered to form an electrolyte layer; then Fe / YSZ is prepared into a slurry, coated onto the other side of the electrolyte layer, dried and sintered to form a cathode layer.

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