A full solid-state lithium ion membrane reactor with symmetrical structure and application thereof

Abstract

The present application relates to a kind of full solid-state lithium ion membrane reactor with symmetrical structure and its application, the reactor is in situ construction on the both sides of solid-state lithium ion conductor film with Pt and / or Ni as catalyst, with single-walled carbon nanotube etc. Conductive material is used as current collector gas diffusion electrode, the reactor can work in nitrogen hydrogen mixture atmosphere, integration is high, scale is flexible.The present application changes the working mode of traditional reactor using liquid electrolyte, replaces inefficient nitrogen and proton mass transfer with efficient lithium ion mass transfer, couples lithium-mediated nitrogen reduction and hydrogen oxidation reaction to synthesize ammonia, and the maximum working current density is increased to 1000mA / cm 2 , and can work at 40mA / cm 2 Current density for a long time, with innovation and broad industrial application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of inorganic solid electrolyte materials and electrochemical catalysis, and in particular to a full-solid-state lithium ion membrane reactor with a symmetrical structure and its application. BACKGROUND

[0002] Ammonia is an irreplaceable nitrogen source and has a wide range of applications in agriculture and chemical production, playing a vital role in social development. The Haber-Bosch process is the most mature industrial technology for directly producing ammonia from nitrogen and hydrogen, but it has harsh reaction conditions (high temperature of 400-600℃, high pressure of 100-150 bar), high power consumption, and cannot be adapted to renewable power sources. Membrane reactors based on solid-state proton conductors have achieved electrochemical synthesis at atmospheric pressure. However, due to the lack of effective mechanisms for nitrogen reduction reactions (NRR), the yield of ammonia synthesis is very low.

[0003] Lithium-mediated nitrogen reduction reactions (LiNR) can effectively dissociate the strong N≡N triple bond, and in a non-aqueous liquid electrolyte system (such as lithium salts dissolved in alcohol and tetrahydrofuran), a batch electrochemical cell is used to achieve efficient ammonia synthesis at room temperature. However, in non-aqueous liquid electrolytes, the mass transfer process of nitrogen and hydrogen is limited, and must be pressurized (5-50 bar) to ensure raw material supply. In addition, this reactor needs to constantly replenish the proton source, and has a short working life. The use of stainless steel cloth as a gas diffusion electrode (GDE) in a three-chamber cell can circumvent the limitations of gas transport in liquid electrolytes and directly use hydrogen as a proton source. However, proton transport is still limited to organic solvents. And most of the ammonia produced is distributed in the electrolyte, which needs to be purified through a complex process, further increasing the preparation cost. Therefore, it is necessary to develop a new type of efficient nitrogen fixation process that can achieve high gas diffusion rates and adapt to renewable energy sources. SUMMARY

[0004] To solve the above problems, in this research, the present application proposes a reasonable design, including a reactor based on a full-solid-state lithium ion symmetrical battery, in which the electrodes are gas diffusion electrodes synthesized in situ on solid-state electrolytes. Through the hydrogen oxidation reaction, sustainable proton replenishment is achieved, and through the LiNR reaction, the N≡N triple bond is broken, allowing continuous ammonia production for 100 h at atmospheric pressure, with an ammonia production rate of 101.9 ± 7.9 nmol / s / cm 2 at a current density of 1000 mA / cm 2 .

[0005] The present application provides the following technical solutions:

[0006] A full solid-state lithium ion membrane reactor with symmetrical structure, the component structure comprises a solid-state lithium ion conductor membrane and a gas diffusion electrode, characterized in that: the gas diffusion electrode is constructed in situ on both sides of the solid-state lithium ion conductor membrane; the component of the solid-state lithium ion conductor membrane comprises a solid-state lithium ion membrane material, the solid-state lithium ion membrane material is one of inorganic solid-state lithium ion membrane material, polymer-based solid-state lithium ion membrane material; the component of the gas diffusion electrode comprises one or both of Ni, Pt catalyst, and also comprises conductive current collector material.

[0007] Preferably, the inorganic solid-state lithium ion membrane material is one of oxide type solid-state lithium ion membrane material, halide type solid-state lithium ion membrane material and sulfide type solid-state lithium ion membrane material.

[0008] Preferably, the preparation method of the solid-state lithium ion conductor membrane prepared from the oxide type solid-state lithium ion membrane material is one of high-temperature solid-phase synthesis method and tape casting method.

[0009] Preferably, the high-temperature solid-phase synthesis method for preparing the oxide type solid-state lithium ion conductor membrane can comprise the following steps:

[0010] Step 1): obtaining oxide type solid-state lithium ion membrane material precursor;

[0011] Step 2): pouring the precursor into a mold and applying pressure to obtain a green body;

[0012] Step 3): heating and sintering the green body obtained in step 2) to obtain an oxide type solid-state lithium ion conductor membrane.

[0013] Preferably, the oxide type solid-state lithium ion membrane material precursor in step 1) is one of garnet type lanthanum lithium zirconate and its element doped compound, NASICON type lithium titanium aluminum phosphate and its element doped compound, and perovskite type lithium lanthanum titanate and its element doped compound. The preparation method of the garnet type lanthanum lithium zirconate and its element doped compound is as follows: mixing lithium source, lanthanum source, zirconium source and doping source according to stoichiometric ratio, adding grinding medium for grinding and drying, and heating and sintering to obtain lithium lanthanum zirconium oxide-based powder. The grinding medium is selected from any one of isopropyl alcohol and ethanol; the grinding is selected from at least one of manual grinding, drum ball milling, planetary ball milling and high-energy ball milling, and the grinding time is 6-24h; the heating rate is 2-5℃ / min, the sintering temperature is 800-1000℃, and the sintering time is 6-20h.

[0014] Preferably, the pressure applying method in step 2) is at least one of uniaxial static pressure and cold isostatic pressing.

[0015] Preferably, the mass of the green body in step 3) is 0.1-1.0g.

[0016] Preferably, the conductive current collector material is one or more of a metal, a conductive carbon, and a conductive ceramic.

[0017] Preferably, taking the solid-state lithium ion conductor film prepared from an oxide-type solid-state lithium ion membrane material as an example, the preparation method of the gas diffusion electrode comprises the following steps:

[0018] Step 1): mixing NiO powder and an oxide-type solid-state lithium ion membrane material, and dispersing in a solvent such as ethanol to obtain a suspension;

[0019] Step 2): dissolving H2PtCl6 powder in a solvent such as ethanol to obtain an H2PtCl6 solution;

[0020] Step 3): coating one or both of the suspension obtained in Step 1 and the H2PtCl6 solution obtained in Step 2 on both sides of the solid-state lithium ion conductor film, and then baking at an elevated temperature in an argon atmosphere glove box, so that NiO and H2PtCl6 are deposited as Ni and Pt elemental metals on both sides of the solid-state lithium ion conductor film, and finally a solid-state lithium ion conductor film loaded with one or both of Ni and Pt catalysts is obtained.

[0021] Step 4): coating a dispersion of a liquid conductive current collector material or a solid conductive current collector material on both sides of the solid-state lithium ion conductor film loaded with one or both of Ni and Pt catalysts obtained in Step 3, so that a current collector conductive network structure coated with the elemental metal catalyst is formed on both sides of the solid-state lithium ion conductor film, i.e. a gas diffusion electrode is formed on both sides of the solid-state lithium ion conductor film.

[0022] Preferably, in Step 2), the concentration of the H2PtCl6 solution is 0.1-50 mol / L.

[0023] Preferably, in Step 4), the dispersion of the solid conductive current collector material is prepared by uniformly dispersing the solid conductive current collector material in a solvent at a concentration of 1-10 mol / L.

[0024] Preferably, in Step 3), the baking condition is 300-500℃ for 5-20 s.

[0025] The application further provides an ammonia synthesis method, comprising at least the following steps: introducing N2 and H2 mixed gas into the all-solid-state lithium ion membrane reactor as described above, and performing an electric current on the gas diffusion electrodes formed on both sides of the solid-state lithium ion conductor film to perform a reaction, i.e. to synthesize ammonia.

[0026] Preferably, the reaction temperature is 300-600℃.

[0027] Preferably, the current density of the reaction is 1-1000 mA / cm2.2 .

[0028] The beneficial effects of the present application are:

[0029] 1. The present application provides a full solid-state lithium ion membrane reactor with a symmetrical structure, which realizes lithium-mediated nitrogen reduction reaction based on solid-state electrolyte, and in-situ synthesis of gas diffusion electrode catalytic hydrogen oxidation to protons on the solid-state electrolyte. Nitrogen and hydrogen can directly reach the surface of the gas diffusion electrode, eliminating the mass transfer limitation of traditional liquid reactors. Nitrogen and hydrogen can serve as continuous nitrogen source and proton source for ammonia synthesis reaction.

[0030] 2. The present application also provides a new ammonia synthesis method, which uses a full solid-state lithium ion membrane reactor with a symmetrical structure to realize industrial current density (1000 mA / cm 2 ) in a lithium-mediated ammonia synthesis reactor equipped with a gas diffusion electrode, greatly improving the ammonia yield to 101.9±7.9 nmol / s / cm 2 . The reactor can be started and stopped at will without damaging the catalyst, and can be accumulated for up to 100 hours, which is very suitable for unstable renewable energy. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 Embodiment of the present application for lithium-mediated electrochemical nitrogen reduction to ammonia.

[0032] Figure 2 Li 6.5 La3Zr 1.5 Ta 0.5 O 12 X-ray diffraction spectrum of the solid-state lithium ion membrane material at room temperature.

[0033] Figure 3 Li 6.5 La3Zr 1.5 Ta 0.5 O 12 Arrhenius plot of the total conductivity of the solid-state lithium ion membrane material.

[0034] Figure 4 Scanning electron microscope picture and energy spectrum analysis of elements of the full solid-state lithium ion membrane reactor with a symmetrical structure prepared in Example 1 and Comparative Example 1 of the present application, wherein Figure A is a cross-section of the reactor, and Figure B is a surface of the reactor.

[0035] Figure 5 a is the voltage curve of the reactor during operation and the corresponding ammonia yield, Figure 5b is the UV-Vis absorption spectrum of the collected reactor tail gas absorption solution after the color reaction.

[0036] Figure 6 Ammonia synthesis performance of the full solid-state lithium ion membrane reactor prepared in Example 1 of the present application, Figure 6 a is the ammonia synthesis stability test, Figure 6 b is working at an industrial current density (1000 mA / cm 2 ), Figure 6 c is the XRD pattern of ammonium chloride prepared by the reactor (the insert is the product photo).

[0037] Figure 7 Ammonia yield and corresponding Faraday efficiency of the full solid-state ion membrane reactor prepared in Example 1 of the present application working at different temperatures.

[0038] Figure 8 Ammonia yield and corresponding Faraday efficiency of the full solid-state ion membrane reactor prepared in Example 1 of the present application working at different current densities. DETAILED DESCRIPTION

[0039] The present application will be described in detail below in combination with specific examples.

[0040] The present application does not have special restrictions on the sources of all raw materials of the following examples, and they are commercially available products.

[0041] Example 1

[0042] The solid-state lithium ion conductor film is prepared according to the following steps in this example:

[0043] Li2CO3, La2O3, ZrO2, Ta2O5 are weighed according to the stoichiometric ratio of Li 6.5 La3Zr 1.5 Ta 0.5 O 12 The purity of the above reagents is all analytical pure, and the addition amount of Li2CO3 is 10% excess by mass ratio, and La2O3 is preheated at 900℃ for 7h. The weighed powder is added to the ball mill tank, and an appropriate amount of isopropanol is added for ball milling for 12h, and then dried in a 70℃ oven for 6h. Li 6.5 La3Zr 1.5 Ta 0.5 O 12The precursor powder was put into a crucible, then raised to 900℃ at a temperature raising rate of 5℃ / min, and kept for 7h before ending, and then naturally cooled. The obtained powder was again added with a proper amount of isopropyl alcohol and ball-milled for 12h, and then dried in a 70℃ oven for 6h after ending to obtain a solid-state lithium ion membrane material. 0.2g of the powder was weighed and poured into a mold with an inner diameter of 8mm, and a small pressure was applied and maintained for 2min to obtain a green compact in the form of a round sheet with a thickness of 0.8-1mm. The green compact was put into a cold isostatic pressing machine and kept at 270MPa for 5min to obtain a compacted round sheet green compact. One piece of the green compact was obtained by means of ultrafast high-temperature sintering technology, and the green compact was kept at 1200℃ for 5-10s to obtain a solid-state lithium ion conductor film.

[0044] The full solid-state lithium ion membrane reactor was prepared according to the following steps:

[0045] The NiO powder and Li 6.5 La3Zr 1.5 Ta 0.5 O 12 The solid-state lithium ion membrane material was mixed in a mass ratio of 1:1 and dispersed in ethanol to obtain a suspension. The obtained suspension was taken out with a pipette in two times of 20μL (10μL each time) and coated on both sides of the Li 6.5 La3Zr 1.5 Ta 0.5 O 12 solid-state lithium ion conductor film, and dried at 80℃. The H2PtCl6 powder was dissolved in ethanol to obtain a H2PtCl6 solution with a concentration of 6mol / L. The obtained solution was taken out with a pipette in two times of 20μL (10μL each time) and coated on both sides of the Li 6.5 La3Zr 1.5 Ta 0.5 O 12 solid-state lithium ion conductor film, and dried at 80℃. The treated ion membrane was kept at 500℃ for 10s to obtain a Li 6.5 La3Zr 1.5 Ta 0.5 O 12 solid-state lithium ion conductor film loaded with Ni and Pt catalysts. The single-walled carbon nanotubes were dispersed in N-methyl pyrrolidone (NMP) to obtain a suspension with a concentration of 3mol / L. The obtained suspension was taken out with a pipette in two times of 40μL (20μL each time) and coated on both sides of the Li 6.5 La3Zr 1.5 Ta 0.5 O 12 solid-state lithium ion conductor film, and dried at 150℃. Finally, the full solid-state lithium ion membrane reactor was obtained, and the surface resistance of the full solid-state lithium ion membrane reactor was tested with a universal meter to be <500Ω.

[0046] The full solid-state lithium ion membrane reactor was tested for ammonia synthesis performance according to the following steps:

[0047] The synthesis ammonia performance test process of the full solid-state lithium ion membrane reactor: silver wires were led out on the two electrodes of the full solid-state lithium ion membrane reactor (for connecting the electrochemical workstation), the full solid-state lithium ion membrane reactor was sealed in a quartz glass tube equipped with a gas pipe, and the device was fixed in a tube furnace, and the temperature was raised to the test temperature (350°C, 400°C, 450°C, 500°C) at a rate of 5°C / min. A current (10 mA / cm 2 -1000 mA / cm 2 ) was applied for 0.5 h of uninterrupted testing. The flow rate of the test gas was accurately controlled by a mass flow controller. The inlet pipe was connected to a N2 / H2 mixture with a volume ratio of 2:1, and the flow rate was 120 mL / min. The exhaust gas from the outlet pipe was introduced into a dilute sulfuric acid absorption solution with a concentration of 0.05 mol / L to absorb the generated ammonia gas. The absorbance of the absorption solution was quantitatively detected using ultraviolet-visible spectrophotometry. Finally, the ammonia yield and the corresponding current method Faraday efficiency were calculated according to the standard curve of ammonia.

[0048] Comparative Example 1

[0049] The difference from Example 1 is that no current is applied for testing.

[0050] Result analysis

[0051] 1. Mechanism analysis of ammonia synthesis in a symmetrical all-solid-state lithium-ion membrane reactor:

[0052] Figure 1 The structural details and working principle of the symmetric structure full solid-state lithium ion membrane reactor are shown. In order to clarify the reaction process, the cathode and anode in the battery structure are artificially distinguished. Pt and Ni catalysts are loaded on the Li 6.5 La3Zr 1.5 Ta 0.5 O 12 The two sides of the solid-state lithium ion membrane are used as the current collector layer with a thin layer of carbon nanotubes (CNT). During the charging stage, lithium ions migrate to the cathode surface and obtain electrons from the external circuit, resulting in the formation of metallic lithium. Subsequently, nitrogen molecules rapidly react with metallic lithium to form Li3N. Hydrogen molecules can react with Li3N at high temperatures to form Li2NH, which exists briefly on the electrode surface. During the discharging process, Li + leaves the anode side Li2NH with the help of the catalyst, and hydrogen molecules are converted to H + and supplement the Li + sites in Li2NH to form NH3.

[0053] 2、 Li 6.5 La3Zr 1.5 Ta 0.5 O 12 Phase structure analysis of solid-state lithium ion membrane materials:

[0054] Li5La3Ta2O12 synthesized in Example 1 and Comparative Example 1 6.5 La3Zr 1.5 Ta 0.5 O 12 X-ray diffraction (XRD) analysis was performed, and the experimental results are shown in Figure 2 The results show diffraction peaks of good crystallinity, which are consistent with the cubic Li5La3Ta2O12 phase. 12 The standard card is one-to-one correspondence, showing pure cubic garnet phase.

[0055] 3、 Li 6.5 La3Zr 1.5 Ta 0.5 O 12 Electrochemical performance of solid-state lithium ion membrane materials:

[0056] In order to study the electrochemical performance of Li 6.5 La3Zr 1.5 Ta 0.5 O 12 The electrochemical performance of the solid-state lithium ion membrane material was studied by coating silver paste on both sides of the prepared electrolyte sheet, drying at 200°C for 30 min, and constructing an Ag / Li 6.5 La3Zr 1.5 Ta 0.5 O 12 / Ag blocking electrode symmetrical battery, and the electrochemical impedance spectrum was tested at different temperatures, and the corresponding conductivity was calculated. The Arrhenius plot of the total conductivity is shown in Figure 3 It has a small conductivity activation energy.

[0057] 4, Li 6.5 La3Zr 1.5 Ta 0.5 O 12 Morphology and elemental distribution analysis of solid-state lithium ion membrane reactors

[0058] Li 6.5 La3Zr 1.5 Ta 0.5 O 12 The cross-section and surface morphology of the solid-state lithium ion membrane reactor were characterized, and the scanning electron micrographs and element distribution are shown in Figure 4 It is shown that the Ni and Pt elements are concentrated and uniformly distributed at the interface between the gas diffusion electrode and the solid-state lithium ion membrane within the scanning range.

[0059] 5、Li 6.5 La3Zr 1.5 Ta 0.5 O 12 Study on ammonia synthesis performance of solid-state lithium ion membrane reactor

[0060] Figure 5 a is Li5La3Ta2O12 prepared in Example 1 and Comparative Example 1 of the present application 6.5 La3Zr 1.5 Ta 0.5 O 12 The voltage curve of the solid-state lithium ion membrane reactor during operation and the corresponding ammonia yield are shown in Figure b, and the ultraviolet-visible absorption spectrum of the collected reactor tail gas absorption liquid after color reaction is shown in Figure b. Under the condition of no current, the reactor can hardly synthesize ammonia, and under the driving of current, lithium-mediated synthesis of ammonia is realized.

[0061] Figure 6 a Ammonia synthesis stability test of the full solid-state lithium ion membrane reactor prepared in Example 1 of the present application (test temperature: 450℃, current density: 40mA / cm 2 ), which maintained an ammonia yield of 6.9±0.2nmol / s / cm 2 for 100h. Figure 6 b shows that the reactor can work at an industrial current density (1000mA / cm 2 ), with a corresponding ammonia yield of 101.9±7.9nmol / s / cm 2 . c As shown in Figure 6 c, since the reactor is a full solid-state, the ammonia produced is all distributed in the gas phase, which can be absorbed by dilute hydrochloric acid and quickly prepared into ammonium chloride, greatly saving the separation and purification cost.

[0062] Figure 7 Ammonia yield and corresponding Faraday efficiency of the full solid-state ion membrane reactor prepared in Example 1 of the present application at different temperatures. In the range of 350-500℃, as the temperature increases, the yield and Faraday efficiency of the reactor also increase.

[0063] Figure 8 Ammonia yield and corresponding Faraday efficiency of the full solid-state ion membrane reactor prepared in Example 1 of the present application at different current densities. In the range of 10mA / cm 2 -1000mA / cm 2 , as the current density increases, the ammonia yield increases, but the Faraday efficiency of the reactor reaches a maximum value at a current density of 100mA / cm 2 .

[0064] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent replacements to some technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A process for ammonia synthesis, characterized by, The application discloses a full-solid-state lithium ion membrane reactor with a symmetrical structure, and continuous ammonia is produced by coupling a lithium-mediated nitrogen reduction reaction with a hydrogen oxidation reaction under normal pressure by taking nitrogen and hydrogen as continuous nitrogen sources and proton sources for the ammonia synthesis reaction. N2 and H2 mixed gas is introduced into the all-solid-state lithium ion membrane reactor, and the gas diffusion electrode formed on both sides of the solid-state lithium ion conductor membrane is powered to react: the same gas diffusion electrode formed on both sides of the solid-state lithium ion conductor membrane is artificially divided into anode and cathode; in the charging stage, lithium ions migrate to the surface of the cathode and obtain electrons from the external circuit, resulting in the formation of metallic lithium; then, nitrogen molecules rapidly react with metallic lithium to form Li3N; hydrogen molecules react with Li3N at high temperature to form Li2NH, which exists on the electrode surface for a short time; in the discharging process, Li + leaves the anode side under the drive of current, while hydrogen molecules are converted into H + and supplement Li + to Li2NH to form NH3; The full-solid-state lithium ion membrane reactor with the symmetrical structure comprises a solid-state lithium ion conductor film and a gas diffusion electrode which is in-situ constructed on two sides of the solid-state lithium ion conductor film.

2. The ammonia synthesis method according to claim 1, characterized in that, The inorganic solid-state lithium ion membrane material is one of an oxide type solid-state lithium ion membrane material, a halide type solid-state lithium ion membrane material and a sulfide type solid-state lithium ion membrane material.

3. The ammonia synthesis method according to claim 2, characterized in that, The oxide type solid-state lithium ion membrane material is one of a garnet type lanthanum zirconate lithium and an element doped compound thereof, a NASICON type lithium titanium aluminum phosphate and an element doped compound thereof, and a perovskite type lanthanum titanate lithium and an element doped compound thereof.

4. The ammonia synthesis method according to claim 1, characterized in that: The conductive current collector material is one or more of a metal, conductive carbon and conductive ceramic.

5. The ammonia synthesis method according to claim 2, characterized in that, The preparation method of the gas diffusion electrode comprises the following steps: Step 1): mixing NiO powder and the oxide type solid-state lithium ion membrane material, and dispersing them in a solvent to obtain a suspension; Step 2): dissolving H2PtCl6 powder in a solvent to obtain an H2PtCl6 solution; Step 3): coating one or both of the suspension obtained in step 1 and the H2PtCl6 solution obtained in step 2 on two sides of the solid-state lithium ion conductor film, and then performing temperature baking in an argon atmosphere glove box, so that the NiO and the H2PtCl6 are precipitated as Ni metal and Pt metal on the two sides of the solid-state lithium ion conductor film, and finally a solid-state lithium ion conductor film loaded with one or both of Ni and Pt catalysts is obtained; Step 4): loading the conductive current collector material on the two sides of the solid-state lithium ion conductor film loaded with one or both of the Ni and Pt catalysts obtained in step 3, so that the conductive current collector network structure coated with the metal catalyst is formed on the two sides of the solid-state lithium ion conductor film, that is, the gas diffusion electrode is formed on the two sides of the solid-state lithium ion conductor film.

6. The ammonia synthesis method according to claim 5, characterized in that, In step 2), the concentration of the H2PtCl6 solution is 0.1-50 mol / L.

7. The ammonia synthesis method according to claim 5, characterized in that, In step 3), the temperature baking is performed at 300-500 DEG C for 5-20 s.

8. The ammonia synthesis method according to claim 1, characterized by: The temperature for the reaction of the gas diffusion electrode formed on the two sides of the solid-state lithium ion conductor film is 300-600 DEG C.

9. The ammonia synthesis method according to claim 1, characterized in that: The current density for the reaction of the power supply to the gas diffusion electrode formed on both sides of the solid-state lithium ion conductor film is 1-1000 mA / cm 2 .

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