Process for the lithium-mediated synthesis of ammonia and electrolyte used

Abstract

The present application relates to the field of electrochemical synthesis of ammonia, in particular to a lithium-mediated method for synthesizing ammonia and the electrolyte used, and discloses a preparation method of a lithium-titanium oxide electrolyte for depositing noble metal films, comprising the following steps: mixing lithium carbonate and ammonium titanate for solid-phase reaction, placing the obtained lithium-titanium oxide (LiTiO2) as a substrate on a sample table of a vacuum cavity of a PVD device, starting a vacuum pump and a sputtering source, and depositing a noble metal film. The present application also discloses a lithium-mediated method for electrochemically synthesizing ammonia, which uses the above-mentioned lithium-titanium oxide electrolyte for depositing noble metal films; thereby strengthening nitrogen mass transfer, and using water as a hydrogen source to improve the safety and stability of the system.

Description

Technical Field

[0001] This invention relates to the field of electrochemical ammonia synthesis, and more specifically to a lithium-mediated ammonia synthesis method and the electrolyte used therein. Background Technology

[0002] Ammonia (NH3), as an important chemical raw material and energy carrier, has wide applications in agriculture, chemical industry, energy, and other fields. Currently, the ammonia produced globally each year is mainly used to manufacture fertilizers to increase crop yields. In addition, ammonia is also used to produce various chemicals, clean fuels, and as a potential hydrogen carrier due to its ease of liquefaction, storage, and transportation, as well as its high energy density and carbon-free characteristics. However, the traditional ammonia synthesis method, namely the Haber-Bosch process, poses significant challenges to the environment and energy consumption due to its high energy consumption and high-temperature, high-pressure operating environment. Therefore, developing a low-energy, environmentally friendly ammonia synthesis method has become a current research hotspot.

[0003] Lithium-mediated ammonia synthesis is an emerging ammonia synthesis technology with the potential to achieve ammonia synthesis at ambient temperature and pressure. This method mainly relies on the high activity of lithium metal to reduce nitrogen (N2) to ammonia through an electrochemical reaction. Jens K. et al. (Energy & Environmental Science, 2017, 10(7): 1621-1630.) reported a novel ammonia production strategy, taking the electrochemical lithium cycle process as an example. This process provides a green ammonia synthesis route by directly coupling with renewable electricity. Compared with the traditional aqueous phase electrochemical method, this method bypasses the hydrogen evolution reaction by using a step-by-step synthesis method. The ammonia synthesis process of this method is divided into the electrolysis of LiOH, direct nitridation of Li, and hydrolysis of Li3N to release ammonia and re-form LiOH, thus achieving a cyclic ammonia production. However, in non-aqueous liquid electrolytes, the mass transfer process of nitrogen and hydrogen is limited, and pressurization must be applied to ensure the supply of raw materials. In response, Wang et al. from the University of Science and Technology of China (CN202410103839.1) proposed a reasonable design, including a reactor based on an all-solid-state lithium-ion symmetric battery, the use of solid-state lithium-ion membrane materials, and a gas diffusion electrode synthesized in situ on a solid electrolyte. Sustainable proton replenishment is achieved through hydrogen oxidation, and the N≡N triple bond is broken through the LiNR reaction, enabling continuous ammonia production for 100 hours at atmospheric pressure and a current density of 1000 mA / cm². 2 The highest ammonia production was 101.9 ± 7.9 nmol / s / cm. 2 However, this method uses hydrogen gas as its hydrogen source, and hydrogen gas mostly comes from fossil fuels, so it still faces energy and environmental problems. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a lithium-mediated synthesis of ammonia and the electrolyte used therein.

[0005] To address the aforementioned technical problems, this invention provides an electrolyte for lithium-mediated ammonia synthesis: a lithium titanium oxide electrolyte with deposited noble metal films.

[0006] This invention also provides a method for preparing lithium titanium oxide electrolyte with deposited noble metal films, comprising the following steps:

[0007] 1) Mix lithium carbonate and ammonium titanate in a molar ratio of 1 to 5:1, heat the resulting mixture to 700 to 1000℃ (preferably 800 to 900℃) and hold for solid-phase reaction for 4 ± 0.5 h, and then cool (naturally cool to room temperature) to obtain lithium titanium oxide (LiTiO2).

[0008] 2) Place lithium titanium oxide (LiTiO2) as a substrate on the sample stage of the vacuum chamber of the PVD equipment, start the vacuum pump and sputtering source, and deposit a noble metal thin film. During the deposition process, control the deposition rate at (0.1±0.01) nm / s and the time at 1000±50s.

[0009] An improvement to the preparation method of the lithium oxide titanium electrolyte for depositing noble metal films according to the present invention:

[0010] The precious metals are Pd and Pt (i.e., pure Pd and Pt are selected as the target material);

[0011] The sputtering gas is Ar.

[0012] As a further improvement to the preparation method of the lithium oxide titanium electrolyte for depositing noble metal films according to the present invention, in step 2):

[0013] The temperature was 200±20℃ and the sputtering power was 200±20W.

[0014] As a further improvement to the preparation method of the lithium oxide titanium electrolyte for depositing noble metal films according to the present invention, in step 2):

[0015] The target-to-substrate distance was set to 80 mm; the vacuum pump and sputtering source were started, and the initial pressure in the vacuum chamber was 5 × 10⁻⁶ mm. -4 Pa, the working pressure in the vacuum chamber is maintained at 0.5 Pa during sputtering to deposit a noble metal thin film. The substrate temperature is maintained at 200±20℃ during the deposition process, the sputtering power is 200±20W, and the deposition rate is (0.1±0.01)nm / s.

[0016] This invention also provides a method for lithium-dielectric electrochemical synthesis of ammonia, utilizing a lithium titanium oxide electrolyte with a deposited noble metal film obtained by any of the above methods.

[0017] The lithium titanium oxide electrolyte (using precious metal-modified lithium titanium oxide ore as the electrolyte) with deposited noble metal film was placed in an electrolytic cell (with water flowing through it) and connected to a potentiostat. High-purity nitrogen gas (purity ≥99.999%) was introduced into the electrolytic cell at a flow rate of 100±10 sccm. A voltage was applied to initiate ion transport in the electrolyte. The current-time (It) curve was recorded to monitor the electrolysis process. The separated ammonia gas was collected, and the ammonia yield was analyzed using ion chromatography.

[0018] As an improvement to the lithium-dielectric electrochemical synthesis method of ammonia of the present invention: the applied voltage range is -1.0 to 0V.

[0019] The technical solution of this invention improves the safety and stability of the system by using a solid lithium-containing electrolyte, enhancing nitrogen mass transfer, and using water as a hydrogen source.

[0020] This invention provides an electrolyte for lithium-mediated ammonia synthesis, namely, a novel electrolyte material and its preparation method. By optimizing the material composition and structural design, efficient lithium-ion conduction and good chemical stability are achieved, thereby improving the efficiency and stability of lithium-mediated ammonia synthesis.

[0021] This invention has the following technical advantages:

[0022] 1) Lithium oxide titanium ore has excellent ionic conductivity and good chemical stability, and can resist the corrosive effects of reaction products such as water and nitrogen, thereby maintaining its performance and long-term stability.

[0023] 2) After modifying the electrolyte surface with noble metal catalysts (electrodes) such as platinum or palladium, lithium titanium oxide can effectively enhance the electrochemical synthesis reaction rate and selectivity of ammonia, and achieve a more efficient catalytic effect by optimizing the interface between the metal electrode and the electrolyte.

[0024] Note: The platinum metal on the surface of the solid electrolyte is equivalent to a catalyst, therefore the electrolyte is considered to have catalytic function.

[0025] 3) The solid-state reaction process for preparing lithium titanium oxide is relatively mature, which can efficiently control the crystal structure and micromorphology, improve the density and conductivity of the material, and reduce energy consumption and preparation time.

[0026] In summary, this invention provides an electrolyte for lithium-mediated ammonia synthesis; specifically, it provides a lithium titanium oxide electrolyte with deposited noble metal films for lithium-mediated ammonia synthesis. The lithium titanium oxide of this invention exhibits excellent ionic conductivity and good chemical stability. After modifying the electrode surface with noble metal catalysts such as platinum or palladium, the electrochemical synthesis reaction rate and selectivity of ammonia can be effectively enhanced. The solid-state reaction process is relatively mature, enabling efficient control of crystal structure and microstructure, improving material density and conductivity, while reducing energy consumption and preparation time. Detailed Implementation

[0027] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto:

[0028] Example 1: A method for preparing a lithium oxide titanium electrolyte with deposited noble metal Pd film:

[0029] 1) Mix an appropriate amount of lithium carbonate and ammonium titanate in a 1:1 molar ratio. Take 5g of the mixture and transfer it to a ceramic crucible. Place the crucible in a tube furnace and heat it to 800℃ (heating rate of 10℃ / min). Keep it for 4h to carry out solid-phase reaction. After the heat preservation is completed, let the furnace cool naturally to room temperature. The resulting product is named lithium titanium oxide (LiTiO2).

[0030] 2) Place the lithium titanium oxide (LiTiO2) obtained in step 1) on the sample stage of the vacuum chamber of the PVD equipment, using pure Pd as the target material and Ar gas as the sputtering gas; set the target-substrate distance to 80 mm; start the vacuum pump and sputtering source, and the initial pressure in the vacuum chamber is approximately 5 × 10⁻⁶ mm. -4 During sputtering, the working pressure inside the vacuum chamber is maintained at 0.5 Pa to deposit a noble metal Pd thin film. The substrate temperature is maintained at 200℃, the sputtering power is 200W, and the deposition rate is 0.1nm / s until the target (Pd thin film) thickness is 100nm, that is, the sputtering time is about 1000s. The result is named noble metal Pd modified lithium titanium oxide (Pd / LiTiO2), that is, lithium titanium oxide electrolyte with deposited noble metal film.

[0031] Target-substrate distance refers to the distance between the target and the substrate during magnetron sputtering.

[0032] Experiment 1: The Pd / LiTiO2 modified with noble metal Pd obtained in Example 1 was placed in an electrolytic cell (with water flowing through it) and connected to a potentiostat. High-purity nitrogen gas (purity ≥99.999%) was introduced into the electrolytic cell at a flow rate of 100 sccm, and a voltage of -0.5V was applied to initiate ion transport in the electrolyte. The current-time (It) curve was recorded to monitor the electrolysis process. The separated ammonia gas was collected, and the ammonia yield was analyzed using ion chromatography. The ammonia yield was 200.5 nmol / s / cm. 2 .

[0033] Ammonia production (nmol s) -1 cm -2 ) = n NH3 / (t×A).

[0034] In the above formula, n NH3 The measured number of moles of ammonia produced is given by t, where t is the electrolysis time (2 h) and A is the contact area between the electrolyte sample and the electrode (5 cm²). 2 ).

[0035] Experiment 2, Conductivity Test: The Pd / LiTiO2 obtained in Example 1 was fabricated into a thin sheet. Electrodes were clamped to both sides of the sample, and impedance spectroscopy was performed with a frequency range of 10 Hz to 1 MHz. The impedance values ​​of the sample at different frequencies were recorded. The measured conductivity was 1.3 × 10⁻⁶. -3 S / cm.

[0036] Electrical conductivity:

[0037] In the above formula, L is the sample thickness (1.5 mm), R is the measured resistance value, and A is the contact area between the electrolyte sample and the electrode (5 cm²). 2 ).

[0038] Experiment 3, Stability Test: In the electrochemical test, the stability of the electrolyte is evaluated by the degree of current decay over a long period of time.

[0039] The Pd / LiTiO2 modified with noble metal Pd obtained in Example 1 was placed in an electrolytic cell and connected to a potentiostat. High-purity nitrogen gas (purity ≥99.999%) was introduced into the electrolytic cell at a flow rate of 100 sccm, and a voltage of -0.5 V was applied. The current-time (It) curve under long-term (200 h) electrolysis conditions was recorded. The obtained current decay rate was 2.5%.

[0040] Current attenuation level = (I 初始 -I 最终 ) / I 初始 ×100%.

[0041] Example 2-1: Compared to Example 1, the molar ratio of lithium carbonate and ammonium titanate was changed from "1:1" to "2:1", while the total amount remained unchanged at 5g; the rest was the same as in Example 1.

[0042] The Pd-modified lithium titanium oxide ore obtained in Example 2-1 was tested according to the method described in Experiment 1, and the ammonia yield was 180.4 nmol / s / cm. 2 .

[0043] The Pd-modified lithium titanium oxide obtained in Example 2-1 was tested according to the method described in Experiment 2, and the conductivity was found to be 1.6 × 10⁻⁶. -3 S / cm.

[0044] The Pd-modified lithium titanium oxide obtained in Example 2-1 was tested according to the method described in Experiment 3, and the current decay rate was 3.6%.

[0045] Example 2-2: Compared to Example 1, the molar ratio of lithium carbonate and ammonium titanate was changed from "1:1" to "5:1", while the total amount remained unchanged at 5g; the rest was the same as in Example 1.

[0046] The Pd-modified lithium titanium oxide ore obtained in Examples 2-2 was tested according to the method described in Experiment 1, and the ammonia yield was 176.2 nmol / s / cm. 2 .

[0047] The Pd-modified lithium titanium oxide obtained in Examples 2-2 was tested according to the method described in Experiment 2, and the conductivity was found to be 1.7 × 10⁻⁶. -3 S / cm.

[0048] The Pd-modified lithium titanium oxide obtained in Examples 2-2 was tested according to the method described in Experiment 3, and the current attenuation was 3.8%.

[0049] Example 3: Compared with Example 1, the temperature in step 1) is changed from "800℃" to "900℃"; the rest is the same as Example 1.

[0050] The Pd-modified lithium titanium oxide ore obtained in Example 3 was tested according to the method described in Experiment 1, and the ammonia yield was 194.1 nmol / s / cm. 2 .

[0051] The Pd-modified lithium titanium oxide obtained in Example 3 was tested according to the method described in Experiment 2, and the conductivity was found to be 2.1 × 10⁻⁶. -3 S / cm.

[0052] The Pd-modified lithium titanium oxide obtained in Example 3 was tested according to the method described in Experiment 3, and the current attenuation was 4.1%.

[0053] Example 4: Compared with Example 1, the "deposit of noble metal Pd thin film" in step 2) is changed to "deposit of noble metal Pt thin film". That is, step 2) is specifically changed as follows: "selecting pure Pd as target material" is changed to "selecting pure Pt as target material", and the rest is the same as Example 1.

[0054] The Pt-modified lithium titanium oxide ore obtained in Example 4 was tested according to the method described in Experiment 1, and the ammonia yield was 169.8 nmol / s / cm. 2 .

[0055] The Pt-modified lithium titanium oxide obtained in Experiment 4 was tested according to the method described in Experiment 2, and the conductivity was found to be 1.7 × 10⁻⁶. -3 S / cm.

[0056] The Pt-modified lithium titanium oxide obtained in Example 4 was tested according to the method described in Experiment 3, and the current decay rate was 3.2%.

[0057] Comparative Example 1: Compared to Example 1, the temperature in step 1) is changed from "800°C" to "500°C"; the rest is the same as in Example 1.

[0058] The Pd-modified lithium titanium oxide ore obtained in Comparative Example 1 was tested according to the method described in Experiment 1, and the ammonia yield was 69.2 nmol / s / cm. 2 .

[0059] The Pd-modified lithium titanium oxide obtained in Comparative Example 1 was tested according to the method described in Experiment 2, and the conductivity was found to be 9.6 × 10⁻⁶. -3 S / cm.

[0060] The Pd-modified lithium titanium oxide obtained in Comparative Example 1 was tested according to the method described in Experiment 3, and the current decay rate was 18.2%.

[0061] Comparative Example 2: Compared to Example 1, the molar ratio of lithium carbonate and ammonium titanate was changed from "1:1" to "20:1", while the total amount remained unchanged at 5g; the rest was the same as in Example 1.

[0062] The Pd-modified lithium titanium oxide obtained in Comparative Example 2 was tested according to the method described in Experiment 1, and the ammonia yield was 90.4 nmol / s / cm. 2 .

[0063] The Pd-modified lithium titanium oxide obtained in Comparative Example 2 was tested according to the method described in Experiment 2, and the conductivity was found to be 5.6 × 10⁻⁶. -4 S / cm.

[0064] The Pd-modified lithium titanium oxide obtained in Comparative Example 2 was tested according to the method described in Experiment 3, and the current attenuation was 21.3%.

[0065] Comparative Example 3: Compared to Example 1, “depositing a noble metal Pd thin film” is changed to “depositing a metal Cu thin film”, that is, step 2) is specifically changed as follows: “using pure Pd as the target material” is changed to “using pure Cu as the target material”, and the rest is the same as Example 1.

[0066] The Cu-modified lithium titanium oxide ore obtained in Comparative Example 3 was tested according to the method described in Experiment 1, and the ammonia yield was 90.4 nmol / s / cm. 2 .

[0067] The Cu-modified lithium titanium oxide obtained in Comparative Example 3 was tested according to the method described in Experiment 2, and the conductivity was found to be 9.5 × 10⁻⁶. -4 S / cm.

[0068] The Cu-modified lithium titanium oxide obtained in Comparative Example 3 was tested according to the method described in Experiment 3, and the current decay rate was 26.4%.

[0069] 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 method for preparing lithium oxide titanium electrolyte with deposited noble metal film, characterized in that... Includes the following steps: 1) Mix lithium carbonate and ammonium titanate in a molar ratio of 1 to 5:1, heat the resulting mixture to 700 to 1000°C and hold for solid-phase reaction for 4 ± 0.5 h, then cool to obtain lithium titanium oxide ore. 2) Place the lithium titanium oxide as a substrate on the sample stage of the vacuum chamber of the PVD equipment, start the vacuum pump and sputtering source, and deposit a noble metal thin film. During the deposition process, control the deposition rate to (0.1±0.01) nm / s and the time to 1000±50s.

2. The method for preparing lithium titanium oxide electrolyte with deposited noble metal film according to claim 1, characterized in that: The precious metals are Pd and Pt; The sputtering gas is Ar.

3. The method for preparing lithium titanium oxide electrolyte with deposited noble metal film according to claim 2, characterized in that... In step 2): The temperature was 200±20℃ and the sputtering power was 200±20W.

4. The method for preparing lithium titanium oxide electrolyte with deposited noble metal film according to claim 3, characterized in that... In step 2): The target-to-substrate distance was set to 80 mm; the vacuum pump and sputtering source were started, and the initial pressure in the vacuum chamber was 5 × 10⁻⁶ mm. -4 Pa, maintaining the working pressure in the vacuum chamber at 0.5 Pa during sputtering, depositing noble metal thin films, maintaining the substrate temperature at 200±20℃ during deposition, sputtering power at 200±20W, and deposition rate at (0.1±0.01) nm / s.

5. A method for lithium-dielectric electrochemical synthesis of ammonia, characterized in that: Lithium titanium oxide electrolyte with deposited noble metal film obtained by any of claims 1 to 4 The lithium oxide titanium electrolyte with deposited noble metal film was placed in an electrolytic cell and connected to a potentiostat; high-purity nitrogen gas was introduced into the electrolytic cell at a flow rate of 100±10 sccm, and a voltage was applied to initiate ion transport in the electrolyte, and the separated ammonia gas was collected.

6. The method for lithium-dielectric electrochemical synthesis of ammonia according to claim 5, characterized in that: The applied voltage range is -1.0 to 0 V.