Electrocatalytic ammonia synthesis system and method

Abstract

The invention relates to a system and method for electrocatalytic synthesis of ammonia, and the method comprises the following steps: enabling a catholyte to enter a micro-nano bubble generation device to be in contact with nitrogen to obtain a catholyte mixed solution containing micro-nano N2 bubbles; enabling the cathode electrolytic mixed solution to enter a synthetic ammonia reaction electric pile through a cathode electrolyte inlet to be in contact with a nitrogen reduction catalyst of a membrane electrode, and carrying out nitrogen reduction reaction to obtain a cathode product; enabling the anolyte to enter the synthesis ammonia reaction galvanic pile through the anolyte inlet to be in contact with the electrocatalytic oxidation catalyst of the membrane electrode, and carrying out electrocatalytic oxidation reaction to obtain an anode product. According to the method, the solubility and mass transfer area of nitrogen in the electrolyte can be effectively increased, the mass transfer resistance of a nitrogen reduction reaction is reduced, the nitrogen reduction reaction efficiency is improved, the Faraday efficiency and the ammonia production rate of an ammonia synthesis reaction are improved, synthesis ammonia in the electrolyte can be effectively separated, a high-quality product is obtained, and meanwhile the production cost is reduced. And continuous production and separation of synthetic ammonia are realized.

Description

Technical Field

[0001] The present disclosure belongs to the field of synthetic ammonia, and in particular relates to a system and method for catalytically synthesizing ammonia. Background Art

[0002] Ammonia, as a hydrogen storage medium and a clean fuel with zero carbon emissions, is widely used in agriculture, medicine, fine chemicals and other fields. The traditional Haber-Bosch synthetic ammonia process uses a homogeneous iron / ruthenium-based catalyst to combine N2 and H2 in the air and convert them into NH3 under high temperature (300-500°C) and high pressure (150-300atm). The process is mature and the total conversion rate can reach 97%. It is the mainstream production process in the field of industrial synthetic ammonia, with a global market share of more than 90%. However, the process is highly dependent on fossil energy, consumes a large amount of fossil fuels and has high carbon emissions. The emission of a large amount of CO2 exacerbates the global greenhouse effect and damages the ecological environment.

[0003] With the development of green ammonia, new synthetic ammonia technology has become a hot topic of research at home and abroad. Among them, electrocatalytic technology has the characteristics of energy saving, low consumption, green and environmental protection, and has great development potential. It is considered to be a very promising alternative technology to the HB process. The current electrocatalytic synthesis of ammonia technology has the following technical problems: First, the use of aqueous electrolyte in a single-chamber or double-chamber electrolyzer, N2 is introduced into the cathode, H2O participates in the reaction as a proton source, ammonia is generated on the cathode surface, and oxygen is generated by oxygen evolution reaction at the anode. In this system, N2 is very stable and has extremely low solubility in aqueous solution, which makes N2 difficult to adsorb and activate, and the ammonia production rate and Faraday efficiency are very low; second, the produced ammonia has extremely high solubility in the electrolyte and exists in the form of ammonium ions, and high-quality products cannot be obtained; third, the system is still being studied in an H-type electrolytic cell, and the reaction is an intermittent process, which cannot achieve sustainable and continuous production. Summary of the invention

[0004] The object of the present invention is to provide a system and method for catalytic synthesis of ammonia. The method provided by the present invention can effectively promote the efficiency of nitrogen reduction reaction, improve the Faraday efficiency and ammonia production rate of the synthesis ammonia reaction, and can effectively separate the synthetic ammonia in the electrolyte to obtain high-quality products while realizing the continuous production and separation of synthetic ammonia.

[0005] In order to achieve the above-mentioned object, the first aspect of the present invention provides an electrocatalytic ammonia synthesis system, wherein the system comprises a micro-nano bubble generator and an ammonia synthesis reaction stack; the micro-nano bubble generator comprises a nitrogen inlet, a cathode electrolyte inlet and a mixed liquid outlet; the ammonia synthesis reaction stack comprises a cathode electrolyte inlet, an anode electrolyte inlet and a plurality of membrane electrode electrolyzers; the cathode electrolyte inlet of the ammonia synthesis reaction stack is connected to the mixed liquid outlet of the micro-nano bubble generator;

[0006] The membrane electrode electrolyzer includes a membrane electrode, which includes a diaphragm and a cathode mesoporous catalytic material layer and an anode mesoporous catalytic material layer arranged on both sides of the diaphragm; the cathode mesoporous catalytic material layer includes a nitrogen reduction catalyst; the anode mesoporous catalytic material layer includes an electrocatalytic oxidation catalyst.

[0007] Optionally, the system further comprises an ammonia separation device and / or an anolyte separation device; the ammonia separation device comprises a rectification separation unit; the anolyte separation device comprises a gas-liquid separator;

[0008] The anode product outlet of the synthetic ammonia reactor is connected to the inlet of the anolyte separation device; the circulating anolyte outlet of the anolyte separation device is connected to the anolyte inlet of the synthetic ammonia reactor via an optional anode reflux pump; and / or,

[0009] The cathode product outlet of the synthetic ammonia reactor is connected to the inlet of the ammonia separation device; the circulating cathode electrolyte outlet of the ammonia separation device is connected to the cathode electrolyte inlet of the micro-nano bubble generating device via an optional cathode reflux pump;

[0010] Optionally, a cathode electrolyte delivery pump is provided on the pipeline connecting the mixed liquid outlet of the micro-nano bubble generating device and the cathode electrolyte inlet of the synthetic ammonia reactor.

[0011] Optionally, the system further comprises a cathode electrolyte buffer device and / or an anode electrolyte buffer device;

[0012] The cathode electrolyte buffer device is arranged on the cathode electrolyte inlet pipeline of the micro-nano bubble generating device; optionally, a cathode gas-liquid mixed flow pump is arranged on the cathode electrolyte inlet pipeline; and / or,

[0013] The anolyte buffer device is arranged on the anolyte inlet pipeline of the synthetic ammonia reactor. Optionally, an anolyte delivery pump is arranged on the anolyte inlet pipeline.

[0014] Optionally, the number of stages of the synthetic ammonia reactor is 1 to 100; the diaphragm includes one or more of a perfluorosulfonic acid proton exchange membrane, a Nafion recast membrane, a non-fluorinated polymer proton exchange membrane and a novel composite proton exchange membrane; and the thickness of the diaphragm is 10-200 μm.

[0015] Optionally, the average pore size of the cathode mesoporous catalytic material layer is 2-50 nm, and the porosity is 50-90%; the pore size of the anode mesoporous catalytic material layer is 2-50 nm, and the porosity is 50-90%;

[0016] The thickness of the cathode mesoporous catalytic material layer is 50-400 μm; the thickness of the anode mesoporous catalytic material layer is 50-400 μm;

[0017] Optionally, the nitrogen reduction catalyst comprises one or more of a metal catalyst supported by a two-dimensional material, a metal catalyst supported by an oxide, and an alloy catalyst; the active metal in the nitrogen reduction catalyst comprises a transition metal, preferably, the active metal comprises one or more of Fe, V, Mo, and Cu; the two-dimensional material comprises one or more of a metal organic framework, a two-dimensional carbon material, a polymer, graphene, a transition metal sulfide, and a nitrogen-doped carbon nanotube, and the transition metal sulfide comprises molybdenum disulfide; the oxide comprises one or more of SiO2, WO3, TiO2, and Al2O3;

[0018] The electrocatalytic oxidation catalyst comprises a metal active component and an optional oxide carrier, wherein the metal active component exists in the form of a metal or an alloy; the metal active component comprises a noble metal and / or a transition metal, and preferably, the metal active component comprises one or more of Au, Pt, Co, Ni and Cu;

[0019] Optionally, the micro-nano bubble generating device includes a micro-nano bubble generator.

[0020] The second aspect of the present invention provides a method for electrocatalytically synthesizing ammonia using the system according to the first aspect of the present invention, wherein the method comprises:

[0021] The cathode electrolyte is allowed to enter the micro-nano bubble generating device to contact with nitrogen to obtain a cathode electrolyte mixed solution containing micro-nano N2 bubbles;

[0022] The cathode electrolyte mixture is allowed to enter the ammonia synthesis reaction stack through the cathode electrolyte inlet and contact with the nitrogen reduction catalyst of the membrane electrode to perform a nitrogen reduction reaction to obtain a cathode product; the anode electrolyte is allowed to enter the ammonia synthesis reaction stack through the anode electrolyte inlet and contact with the electrocatalytic oxidation catalyst of the membrane electrode to perform an electrocatalytic oxidation reaction to obtain an anode product;

[0023] The average diameter of the micro-nano N2 bubbles is 0.01-10 μm, and the number of the micro-nano N2 bubbles in the cathode electrolyte mixture is 10 5 -10 7 Pieces / ml.

[0024] Optionally, the anolyte and the catholyte each independently include one or more of an ionic liquid electrolyte, a salt-like electrolyte, an amino acid electrolyte and an organic solvent electrolyte;

[0025] The anolyte and the catholyte are of the same or different types;

[0026] Preferably, the anolyte includes one or more of NaSO4, KOH, H2SO4, K3PO4, tetrahydrofuran and dimethyl sulfoxide; the catholyte includes one or more of NaSO4, KOH, H2SO4, K3PO4, tetrahydrofuran, dimethyl sulfoxide, propylene carbonate, ethylene carbonate and 1-ethyl-3-methylimidazole chloride.

[0027] Optionally, the method further comprises: allowing the cathode product to enter an ammonia separation device for separation to obtain a circulating cathode electrolyte and synthetic ammonia; allowing the circulating cathode electrolyte to return to the cathode electrolyte inlet of the micro-nano bubble generating device via an optional cathode reflux pump;

[0028] and / or, allowing the anode product to enter an anode electrolyte separation device for separation to obtain a circulating anode electrolyte and an anode by-product; allowing the circulating anode electrolyte to return to the anode electrolyte inlet of the synthetic ammonia reactor stack via an optional anode reflux pump;

[0029] Optionally, the electrolyte entering through the cathode electrolyte inlet of the synthetic ammonia reactor stack continuously passes through each stage of the membrane electrode and is finally discharged from the cathode outlet of the stack; the electrolyte entering through the anode electrolyte inlet of the synthetic ammonia reactor stack enters the stack from the anode side of each stage of the membrane electrode, and after the reaction, it is collected from the anode side of each stage and discharged from the circulating anode electrolyte outlet.

[0030] Optionally, the loading amount of the electrocatalytic oxidation catalyst in the anode mesoporous catalytic material layer is 0.1-1 mg·cm -2 The loading amount of the nitrogen reduction catalyst in the cathode mesoporous catalytic material layer is 0.1-1 mg·cm -2 .

[0031] Optionally, the gas flow rate of the nitrogen entering the micro-nano bubble generating device is 500-2500 ml·min -1 ;

[0032] The flow rate of the cathode electrolyte is 100-30000 ml·min -1 The flow rate of the cathode electrolyte mixture entering the ammonia synthesis reactor is 100-500ml min -1 ; The flow rate of the anolyte is 100-1000ml·min -1 ;

[0033] The reaction conditions of the ammonia synthesis reactor include: a current density of 0.1-10A / cm 2 .

[0034] Through the above technical scheme, the present invention makes the cathode electrolyte contact with nitrogen in the micro-nano bubble generating device to obtain a cathode electrolyte mixture containing micro-nano N2 bubbles, and then makes the cathode electrolyte mixture contact with the nitrogen reduction catalyst of the membrane electrode in the synthetic ammonia reactor to carry out a nitrogen reduction reaction, and makes the anode electrolyte contact with the electrocatalytic oxidation catalyst of the membrane electrode in the synthetic ammonia reactor to carry out an electrocatalytic oxidation reaction. The method provided by the present invention can effectively increase the solubility and mass transfer area of ​​nitrogen in the electrolyte, reduce the mass transfer resistance of the nitrogen reduction reaction, effectively promote the efficiency of the nitrogen reduction reaction, and improve the Faraday efficiency and ammonia production rate of the synthetic ammonia reaction; on the other hand, the synthetic ammonia reactor provided by the present invention adopts a multi-stage membrane electrode electrolyzer, wherein the membrane electrode of the membrane electrode electrolyzer includes a diaphragm and a cathode mesoporous catalytic material layer and an anode mesoporous catalytic material layer arranged on both sides of the diaphragm, and no gas diffusion layer is required. The membrane electrode provided by the present invention can efficiently adsorb micro-nano N2 bubbles, regulate the synergistic relationship between reactants and catalysts, effectively improve reaction efficiency, and enable rapid discharge of products, thereby achieving efficient separation and continuous production of synthetic ammonia.

[0035] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings:

[0037] Figure 1 This is a schematic diagram of the process flow of Example 1 of the present invention.

[0038] Figure 2 This is a schematic diagram of the structure of the synthetic ammonia reactor provided in Example 1 of the present invention.

[0039] Figure 3 This is a schematic diagram of the structure of the membrane electrode provided in Example 1 of the present invention.

[0040] Description of Reference Numerals

[0041] 1. Cathode electrolyte buffer device; 2. Cathode gas-liquid mixed flow pump; 3. Bubble generating device; 4. Cathode electrolyte delivery pump; 5. DC power supply; 6. Synthetic ammonia reaction stack; 7. Ammonia separation device; 8. Cathode reflux pump; 9. Anode electrolyte buffer device; 10. Anode electrolyte delivery pump; 11. Anode electrolyte separation device; 12. Anode reflux pump; 13. Raw gas pump.

[0042] S1, bipolar plate; S2, gasket; S3, membrane electrode; S31, diaphragm; S32, cathode mesoporous catalytic material layer; S33, anode mesoporous catalytic material layer. DETAILED DESCRIPTION

[0043] The specific implementation of the present disclosure is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described herein is only used to illustrate and explain the present disclosure, and is not used to limit the present disclosure.

[0044] The first aspect of the present disclosure provides an electrocatalytic ammonia synthesis system, wherein the system comprises a micro-nano bubble generator and an ammonia synthesis reactor; the micro-nano bubble generator comprises a nitrogen inlet, a cathode electrolyte inlet and a mixed liquid outlet; the ammonia synthesis reactor comprises a cathode electrolyte inlet, an anode electrolyte inlet and a plurality of membrane electrode electrolyzers; the cathode electrolyte inlet of the ammonia synthesis reactor is connected to the mixed liquid outlet of the micro-nano bubble generator;

[0045] The membrane electrode electrolyzer includes a membrane electrode, which includes a diaphragm and a cathode mesoporous catalytic material layer and an anode mesoporous catalytic material layer arranged on both sides of the diaphragm; the cathode mesoporous catalytic material layer includes a nitrogen reduction catalyst; the anode mesoporous catalytic material layer includes an electrocatalytic oxidation catalyst.

[0046] The synthetic ammonia reaction stack in the system provided by the present disclosure adopts a multi-stage membrane electrode electrolyzer, wherein the membrane electrode of the membrane electrode electrolyzer includes a diaphragm and a cathode mesoporous catalytic material layer and an anode mesoporous catalytic material layer arranged on both sides of the diaphragm. The membrane electrode provided by the present invention can efficiently adsorb micro-nano N2 bubbles, regulate the synergistic relationship between reactants and catalysts, effectively improve the reaction efficiency, and can quickly discharge the products, thereby realizing efficient separation and continuous production of synthetic ammonia.

[0047] In a specific embodiment, the system further includes an ammonia separation device and / or an anolyte separation device; the ammonia separation device includes a distillation separation unit; the anolyte separation device includes a gas-liquid separator; the anode product outlet of the synthetic ammonia reactor is connected to the inlet of the anode electrolyte separation device; the circulating anode electrolyte outlet of the anode electrolyte separation device is connected to the anode electrolyte inlet of the synthetic ammonia reactor via an optional anode reflux pump; and / or, the cathode product outlet of the synthetic ammonia reactor is connected to the inlet of the ammonia separation device; the circulating cathode electrolyte outlet of the ammonia separation device is connected to the cathode electrolyte inlet of the micro-nano bubble generator via an optional cathode reflux pump. In the above embodiment, the ammonia separation device provided by the present disclosure uses a distillation separation method to effectively separate the cathode product, so that the separated cathode electrolyte and the unreacted nitrogen micro-nano bubble generator are recycled; at the same time, the anode electrolysis separation device is used to effectively separate the anode product, so that the separated anode electrolyte is returned to the synthetic ammonia reactor for recycling, so as to achieve efficient separation and continuous production of synthetic ammonia. In addition, the ammonia separation device provided by the present disclosure can produce ammonia of different grades as needed.

[0048] In a specific implementation manner, a cathode electrolyte delivery pump is provided on the pipeline connecting the mixed liquid outlet of the micro-nano bubble generating device and the cathode electrolyte inlet of the synthetic ammonia reaction stack.

[0049] In a specific embodiment, the system further includes a cathode electrolyte buffer device and / or an anolyte buffer device; the cathode electrolyte buffer device is arranged on the cathode electrolyte inlet pipeline of the micro-nano bubble generating device; optionally, a cathode gas-liquid mixed flow pump is provided on the cathode electrolyte inlet pipeline; and / or, the anolyte buffer device is arranged on the anolyte inlet pipeline of the synthetic ammonia reactor stack, and optionally, an anolyte delivery pump is provided on the anolyte inlet pipeline.

[0050] The system provided by the present disclosure also includes a DC power supply, which is selected from a constant voltage power supply, wherein the operating voltage is 0.1-20V (vsRHE).

[0051] In a specific embodiment, the level of the synthetic ammonia reactor is 1-100, preferably 5-20; the diaphragm includes one or more of a perfluorosulfonic acid proton exchange membrane, a Nafion recast membrane, a non-fluorinated polymer proton exchange membrane and a new composite proton exchange membrane, preferably a perfluorosulfonic acid proton exchange membrane; the thickness of the diaphragm is 10-200 μm, preferably 50-183 μm.

[0052] The synthetic ammonia reactor stack disclosed in the present invention adopts the method of cathode series connection and anode parallel connection. The cathode series connection can effectively improve the reaction efficiency, while the anode parallel connection can effectively reduce the total internal resistance of the reactor stack and improve the current efficiency, thereby effectively improving the yield of synthetic ammonia.

[0053] In a specific embodiment, the membrane electrode electrolyzer also includes a distributor flow channel, a seal and a bipolar plate; the seal includes one or more of polytetrafluoroethylene, fluorinated rubber and polyurethane; the side of the bipolar plate is provided with an electrolyte inlet and an electrolyte outlet, and the inner surface is provided with an electrolyte flow channel, and the electrolyte flow channel can be at least one of a serpentine flow channel, a rectangular flow channel and a straight flow channel.

[0054] In a specific embodiment, the average pore size of the cathode mesoporous catalytic material layer is 2-50nm, preferably 20-50nm, and the porosity is 50-90%, preferably 70-90%; the pore size of the anode mesoporous catalytic material layer is 2-50nm, preferably 20-50nm, and the porosity is 50-90%, preferably 70-90%. In the above embodiment, the average pore size and porosity of the cathode mesoporous catalytic material layer and the anode mesoporous catalytic material layer are controlled within the preferred range, which can further efficiently adsorb micro-nano N2 bubbles, regulate the synergistic relationship between reactants and catalysts, provide a material transmission channel for reactants and products, effectively improve the reaction efficiency, and enable the product to be quickly discharged.

[0055] In a specific embodiment, the thickness of the cathode mesoporous catalytic material layer is 50-400 μm, preferably 50-200 μm; the thickness of the anode mesoporous catalytic material layer is 50-400 μm, preferably 50-200 μm.

[0056] In a specific embodiment, the nitrogen reduction catalyst includes one or more of a metal catalyst supported by a two-dimensional material, a metal catalyst supported by an oxide, and an alloy catalyst; the active metal in the nitrogen reduction catalyst includes a transition metal, preferably, the active metal includes one or more of Fe, V, Mo, and Cu; the two-dimensional material includes one or more of a metal organic framework, a two-dimensional carbon material, a polymer, graphene, a transition metal sulfide, and a nitrogen-doped carbon nanotube; the transition metal sulfide includes molybdenum disulfide; the oxide includes one or more of SiO2, WO3, TiO2, and Al2O3. In the above embodiment, the type of nitrogen reduction catalyst is limited within the scope of this application, which can provide more active sites for the reaction system, improve the catalytic activity, and promote the nitrogen reduction reaction, thereby further improving the ammonia yield and Faraday efficiency of the synthetic ammonia reaction.

[0057] In a specific embodiment, the electrocatalytic oxidation catalyst includes a metal active component and an optional oxide carrier, wherein the metal active component exists in the form of a metal or an alloy; the metal active component includes a noble metal and / or a transition metal, and preferably, the metal active component includes one or more of Au, Pt, Co, Ni and Cu. In the above embodiment, limiting the type of electrocatalytic oxidation catalyst within the scope of this application can effectively improve the catalytic efficiency, thereby further improving the ammonia yield and Faraday efficiency of the synthetic ammonia reaction.

[0058] In a specific embodiment, the micro-nano bubble generating device includes a micro-nano bubble generator.

[0059] The second aspect of the present disclosure provides a method for electrocatalytically synthesizing ammonia using the system described in the first aspect of the present disclosure, wherein the method comprises:

[0060] The cathode electrolyte is allowed to enter the micro-nano bubble generating device to contact with nitrogen to obtain a cathode electrolyte mixed solution containing micro-nano N2 bubbles;

[0061] The cathode electrolyte mixture is allowed to enter the ammonia synthesis reaction stack through the cathode electrolyte inlet and contact with the nitrogen reduction catalyst of the membrane electrode to perform a nitrogen reduction reaction to obtain a cathode product; the anode electrolyte is allowed to enter the ammonia synthesis reaction stack through the anode electrolyte inlet and contact with the electrocatalytic oxidation catalyst of the membrane electrode to perform an electrocatalytic oxidation reaction to obtain an anode product;

[0062] The average diameter of the micro-nano N2 bubbles is 0.01-10 μm, and the number of the micro-nano N2 bubbles in the cathode electrolyte mixture is 10 5 -10 7 Pieces / ml.

[0063] The present disclosure allows the cathode electrolyte to contact with nitrogen in a micro-nano bubble generator to obtain a cathode electrolyte mixture containing micro-nano N2 bubbles, and then allows the cathode electrolyte mixture to contact with the nitrogen reduction catalyst of the membrane electrode in the synthetic ammonia reactor to perform a nitrogen reduction reaction, and allows the anode electrolyte to contact with the electrocatalytic oxidation catalyst of the membrane electrode in the synthetic ammonia reactor to perform an electrocatalytic oxidation reaction. The method provided by the present disclosure can effectively increase the solubility and mass transfer area of ​​nitrogen in the electrolyte, reduce the mass transfer resistance of the nitrogen reduction reaction, effectively promote the efficiency of the nitrogen reduction reaction, and improve the Faraday efficiency and ammonia production rate of the synthetic ammonia reaction. In addition, the present disclosure can effectively increase the solubility and mass transfer area of ​​nitrogen in the electrolyte, reduce the mass transfer resistance of the nitrogen reduction reaction, effectively promote the efficiency of the nitrogen reduction reaction, and improve the Faraday efficiency and ammonia production rate of the synthetic ammonia reaction by controlling the average diameter and number of micro-nano N2 bubbles in the preferred range of the present application.

[0064] In a specific embodiment, the anolyte and the catholyte each independently include one or more of an ionic liquid electrolyte, a salt-like electrolyte, an amino acid electrolyte, and an organic solvent electrolyte; the anolyte and the catholyte are of the same or different types; preferably, the anolyte includes one or more of NaSO4, KOH, H2SO4, K3PO4, tetrahydrofuran, and dimethyl sulfoxide, preferably one or more of NaSO4, K3PO4, and KOH; the catholyte includes one or more of NaSO4, KOH, H2SO4, K3PO4, tetrahydrofuran, dimethyl sulfoxide, propylene carbonate, ethylene carbonate, and 1-ethyl-3-methylimidazole chloride, preferably NaSO4 and / or KOH. In the above embodiment, the catholyte and the anolyte use a preferred type combination, which can further increase the solubility and mass transfer area of ​​nitrogen in the electrolyte, reduce the mass transfer resistance of the nitrogen reduction reaction, effectively promote the efficiency of the nitrogen reduction reaction, and further improve the ammonia yield and Faraday efficiency of the synthetic ammonia reaction.

[0065] In the present disclosure, the electrocatalytic oxidation reaction may be one of oxygen evolution reaction, glycerol oxidation and methanol oxidation.

[0066] In a preferred embodiment, the number of micro-nano N2 bubbles in the cathode electrolyte mixture is 10 6 ~10 7 Pieces / mL.

[0067] In a specific embodiment, the method further includes: allowing the cathode product to enter an ammonia separation device for separation to obtain a circulating cathode electrolyte and synthetic ammonia; allowing the circulating cathode electrolyte to return to the cathode electrolyte inlet of the micro-nano bubble generating device via an optional cathode reflux pump; and / or allowing the anode product to enter an anode electrolyte separation device for separation to obtain a circulating anode electrolyte and an anode by-product; allowing the circulating anode electrolyte to return to the anode electrolyte inlet of the synthetic ammonia reactor stack via an optional anode reflux pump; optionally, the electrolyte entering through the cathode electrolyte inlet of the synthetic ammonia reactor stack continuously passes through each stage of membrane electrode and is finally discharged from the cathode outlet of the reactor stack; the electrolyte entering through the anode electrolyte inlet of the synthetic ammonia reactor stack enters the reactor stack from the anode side of each stage of membrane electrode, and after the reaction, it is collected from the anode side of each stage to the circulating anode electrolyte outlet for discharge.

[0068] In a specific embodiment, the loading amount of the electrocatalytic oxidation catalyst in the anode mesoporous catalyst material layer is 0.1-1 mg·cm -2 , preferably 0.1-0.5 mg·cm -2 The loading amount of the nitrogen reduction catalyst in the cathode mesoporous catalytic material layer is 0.1-1 mg·cm -2 , preferably 0.1-0.5 mg·cm-2 .

[0069] In a specific embodiment, the gas flow rate of the nitrogen entering the micro-nano bubble generating device is 500-2500 ml·min -1 , preferably 500-1500ml·min -1 ; The flow rate of the cathode electrolyte is 100-30000ml·min -1 , preferably 1000-10000ml·min -1 The flow rate of the cathode electrolyte mixture entering the ammonia synthesis reactor is 100-500ml min -1 , preferably 200-400ml·min -1 ; The flow rate of the anolyte is 100-5000ml·min -1 , preferably 500-2000ml·min -1 .

[0070] In a specific embodiment, the reaction conditions of the ammonia synthesis reactor include: a reaction current density of 0.1-10A / cm 2 , preferably 0.5-5A / cm 2 In the present disclosure, the reaction time of the synthetic ammonia reactor is determined according to the actual required ammonia production, and the reaction voltage is determined by the overall resistance value of the system.

[0071] The present invention is further described below by way of examples, but the present invention is not limited thereby. The raw materials used in the examples and comparative examples disclosed herein can be obtained through commercial channels.

[0072] Test Example 1

[0073] The average diameter of micro-nano N2 bubbles was measured using a laser particle size analyzer (equipment model PartAn SIPRO);

[0074] The number of micro-nano N2 bubbles in the cathode electrolyte mixture was measured using a nanoparticle tracking analyzer (equipment model ZetaView);

[0075] The average pore size and porosity of the cathode mesoporous catalytic material layer and the anode mesoporous catalytic material layer were measured using a gas adsorption and micropore analyzer (equipment model BSD-660M).

[0076] Example 1

[0077] This embodiment provides an electrocatalytic ammonia synthesis system, such as Figure 1As shown, the system includes: a DC power supply 5, a cathode electrolyte buffer device 1, an anode electrolyte buffer device 9, a micro-nano bubble generating device 3, an ammonia synthesis reactor 6, an ammonia separation device 7 and an anode electrolyte separation device 11.

[0078] The ammonia synthesis reactor 6 includes a membrane electrode electrolyzer, and the series number of the ammonia synthesis reactor is 5; the membrane electrode electrolyzer includes a membrane electrode S3, and the membrane electrode includes a diaphragm S31 and a cathode mesoporous catalytic material layer S32 and an anode mesoporous catalytic material layer S33 arranged on both sides of the diaphragm; the cathode mesoporous catalytic material layer S32 includes a nitrogen reduction catalyst; the anode mesoporous catalytic material layer S33 includes an electrocatalytic oxidation catalyst; the diaphragm S31 is a perfluorosulfonic acid type proton exchange membrane with a thickness of 183μm; the nitrogen reduction catalyst is a FeV alloy catalyst; the electrocatalytic oxidation catalyst is a Raney nickel catalyst; the average pore size of the cathode mesoporous catalytic material layer is 20nm, the thickness is 100μm, and the porosity is 80%; the average pore size of the anode mesoporous catalytic material layer is 20nm, the thickness is 100μm, and the porosity is 75%; the loading amount of the nitrogen reduction catalyst in the cathode mesoporous catalytic material layer is 0.3mg·cm -2 The loading amount of active metal in the electrocatalytic oxidation catalyst in the anode mesoporous catalytic material layer is 0.3 mg cm -2 .

[0079] The micro-nano bubble generating device is a micro-nano bubble generator; the ammonia separation device comprises a distillation separation unit; and the anode electrolyte separation device is a gas-liquid separator.

[0080] The system further comprises a cathode gas-liquid mixed flow pump 2 , a cathode electrolyte delivery pump 4 , a cathode reflux pump 8 , an anode electrolyte delivery pump 10 , an anode reflux pump 12 and a raw gas pump 13 .

[0081] Process flow chart Figure 1 shown.

[0082] This embodiment provides a method for electrocatalytic synthesis of ammonia, and the specific steps are as follows:

[0083] a. The cathode electrolyte is passed through the cathode gas-liquid mixed flow pump into the micro-nano bubble generator to contact with nitrogen to obtain a cathode electrolyte mixture containing micro-nano N2 bubbles; the cathode electrolyte is a NaSO4 solution (concentration is 1 mol / L), and the flow rate of the cathode electrolyte is 1000 ml min -1 ; The purity of nitrogen is 99.99%, and the gas flow rate of nitrogen entering the micro-nano bubble generator is 500ml min -1 mg -1 The average diameter of the micro-nano N2 bubbles is 0.1-0.2 μm, and the number of micro-nano N2 bubbles in the cathode electrolyte mixture is 10 7 Pieces / ml;

[0084] b. The cathode electrolyte mixture enters the ammonia synthesis reactor through the cathode electrolyte inlet, passes through each level of membrane electrode continuously, contacts with the nitrogen reduction catalyst of the membrane electrode, and undergoes nitrogen reduction reaction. The reaction time is 2 hours to obtain cathode products. The flow rate of the cathode electrolyte mixture entering the ammonia synthesis reactor is 200 ml min -1 ;

[0085] The anolyte enters the ammonia synthesis reactor from the anode side of each level of membrane electrode through the anolyte inlet, contacts with the electrocatalytic oxidation catalyst of the membrane electrode, and undergoes oxygen evolution reaction. The reaction time is 2 hours to obtain the anode product. The anolyte is a NaSO4 solution (concentration is 1 mol / L) with a flow rate of 500 ml min -1 ;

[0086] The reaction conditions of the ammonia synthesis reactor include: the reaction current density is 1A / cm 2 .

[0087] c. The cathode product is discharged from the cathode outlet of the synthetic ammonia reactor into an ammonia separation device for separation to obtain a circulating cathode electrolyte and synthetic ammonia; the circulating cathode electrolyte is returned to the cathode electrolyte inlet of the micro-nano bubble generating device through an optional cathode reflux pump;

[0088] The anode products are discharged from the anode side of each stage and enter the anode electrolyte separation device for separation to obtain circulating anode electrolyte and anode by-products; the circulating anode electrolyte is returned to the anode electrolyte inlet of the synthetic ammonia reactor stack through an optional anode reflux pump.

[0089] Example 2

[0090] The system and method of Example 1 are used, with the only difference being that in step b, the anode performs a glycerol oxidation reaction, the anode electrolyte is a 1 mol / L NaSO4 solution, and the anode reactant is 0.1 mol / L glycerol.

[0091] Example 3

[0092] The system and method of Example 1 are used, except that the electrocatalytic oxidation catalyst is a PtAu alloy catalyst; the nitrogen reduction catalyst is Fe supported by MoS2. The average pore size of the cathode mesoporous catalytic material layer is 30nm, and the porosity is 80%; the average pore size of the anode mesoporous catalytic material layer is 30nm, and the porosity is 80%.

[0093] Example 4

[0094] The system and method of Example 1 are used, except that the loading amount of the electrocatalytic oxidation catalyst in the anode mesoporous catalytic material layer is 0.05 mg·cm -2; The loading amount of nitrogen reduction catalyst in the cathode mesoporous catalytic material layer is 0.05 mg cm -2 .

[0095] Example 5

[0096] The system and method of Example 1 are used, with the only difference being that the average pore size of the cathode mesoporous catalytic material layer is 60 nm, and the porosity is 40%; the pore size of the anode mesoporous catalytic material layer is 70 nm, and the porosity is 45%.

[0097] Comparative Example 1

[0098] The electrolysis was carried out in a single-chamber or double-chamber electrolyzer. The cathode electrolyte and the anolyte electrolyte were both Na2SO4. N2 was introduced into the cathode at a flow rate of 20 ml / min. The cathode used a reduction catalyst supported by carbon paper with an effective area of ​​1 cm 2 , ammonia is generated on the cathode surface; the anode uses a platinum electrode to produce oxygen by oxygen evolution reaction. The electrochemical workstation is used to power the electrolyzer, and the current density is 1A / cm 2 , react for 2h.

[0099] Comparative Example 2

[0100] The system and method of Example 1 are used, except that the system does not include a micro-nano bubble generating device; the cathode electrolyte and nitrogen are mixed in a gas-liquid mixing tank and then enter the cathode inlet of the synthetic ammonia reactor.

[0101] Comparative Example 3

[0102] The system and method of Example 1 are used, except that the average diameter of the micro-nano N2 bubbles is 10-100 μm; the number of the micro-nano N2 bubbles in the cathode electrolyte mixture is 10 4 Pieces / mL.

[0103] Test Example 2

[0104] The reaction ammonia yield and Faraday efficiency in Examples 1 to 5 and Comparative Examples 1 to 3 were tested by the following method:

[0105] The NH3 concentration in the electrolyte after the reaction was measured by UV-visible spectrophotometer using the indophenol blue method. First, a standard working curve was drawn, and a series of standard NH4Cl solutions of different concentrations were plotted against the absorbance corresponding to 655nm, and a fitting curve y=0.3874-0.0006, R2=0.9999 was obtained. 2mL of the electrolyte after the reaction of the embodiment and the comparative example was taken, 2mL of indigo reagent, 200μL of sodium nitroprusside reagent (1wt%) and 50μL of NaClO solution were added, and after standing in a dark place for 1h, a UV-visible spectrophotometer was used to scan in the wavelength range of 550-800nm, and the absorbance at 655nm was recorded.

[0106] The ammonia yield and Faraday efficiency are calculated according to equations (1) and (2):

[0107] Ammonia yield = (c NH3 ×V) / (t×m) Formula (1);

[0108] Among them, c NH3 is the concentration of ammonia in the solution after electrolysis, in μg / mL; V is the volume of the electrolyte, in mL; t is the electrolysis time, in h; m is the catalyst loading, in mg;

[0109] Faraday efficiency FE = (3 × F × c NH3 ×V×100%) / (M NH3 ×Q) formula (2);

[0110] Where F is the Faraday constant, 96485C·mol -1 ;c NH3 is the concentration of ammonia in the solution after electrolysis, in g / mL; V is the volume of the electrolyte, in mL; M NH3 is the molar mass of ammonia, in g / mol; Q is the total charge passing through the electrode, in C.

[0111] Table 1

[0112] <![CDATA[Reaction ammonia yield / mmol·cm -2 ·h]]> Faraday efficiency / % Example 1 1.0 68 Example 2 1.2 73 Example 3 1.6 59 Example 4 0.7 55 Example 5 0.8 60 Comparative Example 1 0.1 31 Comparative Example 2 0.3 45 Comparative Example 3 0.5 34

[0113] As can be seen from Table 1, the method and system provided by the present disclosure can effectively increase the solubility and mass transfer area of ​​nitrogen in the electrolyte, reduce the mass transfer resistance of the nitrogen reduction reaction, effectively promote the efficiency of the nitrogen reduction reaction, improve the Faraday efficiency and ammonia production rate of the synthetic ammonia reaction, and enable the product to be discharged quickly, thereby realizing efficient separation and continuous production of synthetic ammonia.

[0114] By comparing Comparative Example 1 with Example 1, it can be seen that since Comparative Example 1 adopts conventional electrocatalytic ammonia synthesis technology, the solubility of N2 in the solution is extremely low, which makes N2 difficult to adsorb and activate, thereby making the ammonia production rate and Faraday efficiency significantly lower than those of the examples of the present application. In addition, the produced ammonia has an extremely high solubility in the electrolyte and exists in the form of ammonium ions, and high-quality products cannot be obtained, and sustainable and continuous production cannot be achieved.

[0115] By comparing Comparative Example 2 with Example 1, it can be seen that since Comparative Example 2 does not use a micro-nano bubble generating device, the cathode electrolyte and nitrogen enter the gas-liquid mixing tank for mixing and then enter the cathode inlet of the synthetic ammonia reactor stack, which also makes N2 difficult to adsorb and activate, thereby making the ammonia production rate and Faraday efficiency significantly lower than those of the embodiments of the present application.

[0116] By comparing Comparative Example 3 with Example 1, it can be seen that since the average diameter of the micro-nano N2 bubbles in Comparative Example 3 and the number of the micro-nano N2 bubbles in the cathode electrolyte mixture are not within the specified range of the present application, the solubility and mass transfer area of ​​nitrogen in the electrolyte decrease, and the mass transfer resistance of the nitrogen reduction reaction increases, resulting in the Faraday efficiency and ammonia production rate of the synthetic ammonia reaction being lower than those of Examples 1-5 of the present application.

[0117] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0118] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0119] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. An electrocatalytic ammonia synthesis system, wherein: The system comprises a micro-nano bubble generator and a synthetic ammonia reactor; the micro-nano bubble generator comprises a nitrogen inlet, a cathode electrolyte inlet and a mixed liquid outlet; the synthetic ammonia reactor comprises a cathode electrolyte inlet, an anode electrolyte inlet and a plurality of membrane electrode electrolyzers; The cathode electrolyte inlet of the synthetic ammonia reactor is connected to the mixed liquid outlet of the micro-nano bubble generating device; The membrane electrode electrolyzer comprises a membrane electrode, which comprises a diaphragm and a cathode mesoporous catalytic material layer and an anode mesoporous catalytic material layer arranged on both sides of the diaphragm; the cathode catalytic material layer comprises a nitrogen reduction catalyst; and the anode catalytic material layer comprises an electrocatalytic oxidation catalyst.

2. The system according to claim 1, wherein: The system further comprises an ammonia separation device and / or an anolyte separation device; the ammonia separation device comprises a rectification separation unit; the anolyte separation device comprises a gas-liquid separator; The anode product outlet of the synthetic ammonia reactor is connected to the inlet of the anolyte separation device; the circulating anolyte outlet of the anolyte separation device is connected to the anolyte inlet of the synthetic ammonia reactor via an optional anode reflux pump; and / or, The cathode product outlet of the synthetic ammonia reactor is connected to the inlet of the ammonia separation device; the circulating cathode electrolyte outlet of the ammonia separation device is connected to the cathode electrolyte inlet of the micro-nano bubble generating device via an optional cathode reflux pump; Optionally, a cathode electrolyte delivery pump is provided on the pipeline connecting the mixed liquid outlet of the micro-nano bubble generating device and the cathode electrolyte inlet of the synthetic ammonia reactor.

3. The system according to claim 1, wherein: The system also includes a catholyte buffer device and / or an anolyte buffer device; The cathode electrolyte buffer device is arranged on the cathode electrolyte inlet pipeline of the micro-nano bubble generating device; optionally, a cathode gas-liquid mixed flow pump is arranged on the cathode electrolyte inlet pipeline; and / or, The anolyte buffer device is arranged on the anolyte inlet pipeline of the synthetic ammonia reactor. Optionally, an anolyte delivery pump is arranged on the anolyte inlet pipeline.

4. The system according to claim 1, wherein: The number of stages of the synthetic ammonia reactor is 1 to 100; the diaphragm comprises one or more of a perfluorosulfonic acid proton exchange membrane, a Nafion recast membrane, a non-fluorinated polymer proton exchange membrane and a novel composite proton exchange membrane; and the thickness of the diaphragm is 10-200 μm.

5. The system according to claim 1, wherein: The average pore size of the cathode mesoporous catalytic material layer is 2-50nm, and the porosity is 50-90%; the pore size of the anode mesoporous catalytic material layer is 2-50nm, and the porosity is 50-90%; The thickness of the cathode mesoporous catalytic material layer is 50-400 μm; the thickness of the anode mesoporous catalytic material layer is 50-400 μm; Optionally, the nitrogen reduction catalyst comprises one or more of a metal catalyst supported by a two-dimensional material, a metal catalyst supported by an oxide, and an alloy catalyst; the active metal in the nitrogen reduction catalyst comprises a transition metal, preferably, the active metal comprises one or more of Fe, V, Mo, and Cu; the two-dimensional material comprises one or more of a metal organic framework, a two-dimensional carbon material, a polymer, graphene, a transition metal sulfide, and a nitrogen-doped carbon nanotube, and the transition metal sulfide comprises molybdenum disulfide; the oxide comprises one or more of SiO2, WO3, TiO2, and Al2O3; The electrocatalytic oxidation catalyst comprises a metal active component and an optional oxide carrier, wherein the metal active component exists in the form of a metal or an alloy; the metal active component comprises a noble metal and / or a transition metal, and preferably, the metal active component comprises one or more of Au, Pt, Co, Ni and Cu; Optionally, the micro-nano bubble generating device includes a micro-nano bubble generator.

6. A method for electrocatalytically synthesizing ammonia using the system according to any one of claims 1 to 5, wherein: The method includes: The cathode electrolyte is allowed to enter the micro-nano bubble generating device to contact with nitrogen to obtain a cathode electrolyte mixed solution containing micro-nano N2 bubbles; The cathode electrolyte mixture is allowed to enter the ammonia synthesis reaction stack through the cathode electrolyte inlet and contact with the nitrogen reduction catalyst of the membrane electrode to perform a nitrogen reduction reaction to obtain a cathode product; the anode electrolyte is allowed to enter the ammonia synthesis reaction stack through the anode electrolyte inlet and contact with the electrocatalytic oxidation catalyst of the membrane electrode to perform an electrocatalytic oxidation reaction to obtain an anode product; The average diameter of the micro-nano N2 bubbles is 0.01-10 μm, and the number of the micro-nano N2 bubbles in the cathode electrolyte mixture is 10 5 -10 7 Pieces / ml.

7. The method according to claim 6, wherein: The anolyte and the catholyte each independently include one or more of an ionic liquid electrolyte, a salt-like electrolyte, an amino acid electrolyte, and an organic solvent electrolyte; The anolyte and the catholyte are of the same or different types; Preferably, the anolyte includes one or more of NaSO4, KOH, H2SO4, K3PO4, tetrahydrofuran and dimethyl sulfoxide; the catholyte includes one or more of NaSO4, KOH, H2SO4, K3PO4, tetrahydrofuran, dimethyl sulfoxide, propylene carbonate, ethylene carbonate and 1-ethyl-3-methylimidazole chloride.

8. The method according to claim 6, wherein: The method further comprises: allowing the cathode product to enter an ammonia separation device for separation to obtain a circulating cathode electrolyte and synthetic ammonia; allowing the circulating cathode electrolyte to return to the cathode electrolyte inlet of the micro-nano bubble generating device via an optional cathode reflux pump; and / or, allowing the anode product to enter an anode electrolyte separation device for separation to obtain a circulating anode electrolyte and an anode by-product; allowing the circulating anode electrolyte to return to the anode electrolyte inlet of the synthetic ammonia reactor stack via an optional anode reflux pump; Optionally, the electrolyte entering through the cathode electrolyte inlet of the synthetic ammonia reactor stack continuously passes through each stage of the membrane electrode and is finally discharged from the cathode outlet of the stack; the electrolyte entering through the anode electrolyte inlet of the synthetic ammonia reactor stack enters the stack from the anode side of each stage of the membrane electrode, and after the reaction, it is collected from the anode side of each stage and discharged from the circulating anode electrolyte outlet.

9. The method according to claim 6, wherein: The loading amount of the electrocatalytic oxidation catalyst in the anode mesoporous catalytic material layer is 0.1-1 mg·cm -2 The loading amount of the nitrogen reduction catalyst in the cathode mesoporous catalytic material layer is 0.1-1 mg·cm -2 .

10. The method according to claim 6, wherein: The gas flow rate of the nitrogen entering the micro-nano bubble generating device is 500-2500 ml·min -1 ; The flow rate of the cathode electrolyte is 100-30000 ml·min -1 The flow rate of the cathode electrolyte mixture entering the ammonia synthesis reactor is 100-500ml min -1 ; The flow rate of the anolyte is 100-1000ml·min -1 ; The reaction conditions of the ammonia synthesis reactor include: a current density of 0.1-10A / cm 2 .

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