Electrocatalytic ammonia synthesis method and system

Abstract

The invention relates to a method for electrocatalytically synthesizing ammonia, and the method comprises the following steps: enabling an anolyte to enter an anolyte channel; allowing the catholyte to enter the catholyte channel; hydrogen enters the anode gas inlet chamber and enters the anode electrolyte channel through the first gas diffusion layer, nitrogen enters the cathode gas inlet chamber and enters the cathode electrolyte channel through the second gas diffusion layer, and ammonia synthesis reaction is carried out; wherein the catholyte is an electrolyte with low proton concentration. According to the method, the cathode nitrogen reduction reaction and the anode hydrogen oxidation reaction are coupled, sufficient protons are provided for a nitrogen reduction system through introduction of anode hydrogen, the hydrogen evolution competition reaction is inhibited, and the reaction activity and the reaction efficiency are improved; and on the other hand, the catholyte is a low-proton-concentration electrolyte, so that the nitrogen solubility can be improved, the hydrogen evolution competition reaction is further inhibited, and the ammonia yield and the Faraday efficiency of the ammonia synthesis reaction are effectively improved.

Description

Technical Field

[0001] The present invention belongs to the field of ammonia synthesis, and in particular relates to a method and system for electrocatalytic ammonia synthesis. Background Art

[0002] Ammonia is a hydrogen storage medium and a clean fuel with zero carbon emissions, and is widely used in agriculture, medicine, and fine chemicals. The traditional Haber-Bosch ammonia synthesis process uses a homogeneous iron / ruthenium-based catalyst to convert N in the air into hydrogen at high temperature (300-500°C) and high pressure (150-300atm). 2 With H 2 Combined and converted to NH 3 The process is mature, with a total conversion rate of up to 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, a large amount of CO 2 Emissions exacerbate the global greenhouse effect and damage 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 the many new synthetic ammonia technologies explored, electrocatalytic synthetic ammonia technology has the advantages of energy saving, low consumption, green environmental protection, and strong development potential. It is considered to be a promising alternative technology to the HB process. At present, the electrocatalytic synthetic ammonia reaction uses aqueous electrolyte in a single-chamber or double-chamber electrolytic cell, and N is introduced into the cathode. 2 , H 2 O participates in the reaction as a proton source, ammonia is generated on the cathode surface, and oxygen evolution occurs at the anode to generate oxygen. 2 Very stable, with very low solubility in aqueous solution, resulting in N 2 It is not easy to adsorb and activate, and the competitive reaction for hydrogen evolution is fierce, resulting in low ammonia production rate and Faraday efficiency of the current electrocatalytic ammonia synthesis reaction. Summary of the invention

[0004] The object of the present invention is to provide a method and system for electrocatalytic synthesis of ammonia. The method provided by the present invention can improve the reaction activity, increase the solubility of nitrogen and effectively inhibit the competitive reaction of hydrogen evolution, so that the ammonia production rate and Faraday efficiency of the ammonia synthesis reaction are high.

[0005] In order to achieve the above-mentioned object, the present invention provides, in a first aspect, an electrocatalytic ammonia synthesis system, wherein the system comprises an electrolytic cell;

[0006] The electrolytic cell comprises an anode electrolysis chamber and a cathode electrolysis chamber; a proton exchange membrane is arranged between the anode electrolysis chamber and the cathode electrolysis chamber;

[0007] The anode electrolysis chamber is provided with an anode air inlet chamber and an anode electrolyte channel; a first gas diffusion layer is provided between the anode air inlet chamber and the anode electrolyte channel; a first catalytic material layer is provided on a side of the first gas diffusion layer close to the anode electrolyte channel; the first catalytic material layer comprises a hydrogen oxidation catalyst;

[0008] The cathode electrolysis chamber is provided with a cathode air inlet chamber and a cathode electrolyte channel; a second gas diffusion layer is provided between the cathode air inlet chamber and the cathode electrolyte channel; a second catalytic material layer is provided on a side of the second gas diffusion layer close to the cathode electrolyte channel; the second catalytic material layer contains a nitrogen reduction catalyst;

[0009] The hydrogen oxidation catalyst and the nitrogen reduction catalyst are each selected from one or more of a metal catalyst, a two-dimensional material-supported metal catalyst, an oxide-supported metal catalyst, an alloy catalyst and a single metal catalyst.

[0010] Optionally, the system further comprises a DC power supply, a raw gas purification circulation unit and an electrolyte circulation separation unit;

[0011] The nitrogen outlet of the raw gas purification circulation unit is in gas communication with the cathode gas inlet chamber; the hydrogen outlet of the raw gas purification circulation unit is in gas communication with the anode gas inlet chamber;

[0012] The electrolyte outlet of the electrolyte circulation separation unit is communicated with the cathode electrolyte channel and the anode electrolyte channel respectively;

[0013] Wherein, the raw gas purification circulation unit comprises an anode gas purification device, a cathode gas purification device, an anode circulation fan and a cathode circulation fan, and the anode gas purification device and the cathode gas purification device each comprise an acid absorption tank and an alkali absorption tank;

[0014] The electrolyte circulation separation unit comprises an electrolyte storage tank, a heating separator and a circulation pump.

[0015] Optionally, the hydrogen oxidation catalyst and the nitrogen reduction catalyst are each selected from one or more of a metal catalyst, a two-dimensional material-supported metal catalyst, an oxide-supported metal catalyst, an alloy catalyst, and a single metal catalyst;

[0016] The nitrogen reduction catalyst is selected from one or more of a metal catalyst supported by a two-dimensional material, a metal catalyst supported by an oxide, and a metal alloy catalyst; the active metal in the nitrogen reduction catalyst is selected from transition metals, preferably, the active metal is selected from one or more of Fe, V and Mo; the two-dimensional material is selected from MOF, COF, MoS 2, MXene, TMDs, graphene, boron nitride and black phosphorus; the oxide is selected from SnO 2 , WO 3 、CeO 2 and MnO 2 One or more of the following;

[0017] The hydrogen oxidation catalyst is selected from one or more of a metal catalyst, an alloy catalyst and a single metal catalyst; the active metal in the hydrogen oxidation catalyst is selected from a noble metal and / or a transition metal, preferably, the active metal is selected from one or more of Pt, Ni, Au, Ru, Cu and W.

[0018] Optionally, the first gas diffusion layer and the second gas diffusion layer are each selected from one or more of carbon fiber paper, carbon fiber woven cloth, non-woven cloth, carbon nanotubes and graphite;

[0019] The thickness of the first gas diffusion layer and the second gas diffusion layer are each 50 to 400 μm;

[0020] The proton exchange membrane is selected from perfluorosulfonic acid proton exchange membrane and / or sulfonated polysulfone proton exchange membrane.

[0021] 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:

[0022] allowing an anolyte to enter an anolyte channel; allowing a catholyte to enter a catholyte channel;

[0023] Allow hydrogen to enter the anode air inlet chamber and enter the anode electrolyte channel through the first gas diffusion layer, and allow nitrogen to enter the cathode air inlet chamber and enter the cathode electrolyte channel through the second gas diffusion layer to perform nitrogen reduction reaction and hydrogen oxidation reaction;

[0024] Wherein, the cathode electrolyte is a low proton concentration electrolyte.

[0025] Optionally, the proton concentration of the cathode electrolyte is less than 30 wt %; the cathode electrolyte comprises an aprotic solvent and water; the content of water in the cathode electrolyte is 0 to 30 wt %, and the content of the aprotic solvent is 70 to 100 wt %;

[0026] The anode electrolyte and the cathode electrolyte are of the same or different types;

[0027] Preferably, the cathode electrolyte is selected from K 3 PO 4, methanol and phosphine-based ionic liquids, the cathode electrolyte is selected from KOH, tetrahydrofuran and trifluorotoluene, the cathode electrolyte is selected from water, dimethyl sulfoxide and LiFSi; the anode electrolyte is selected from acidic electrolytes or alkaline electrolytes, preferably KOH, Na 2 SO 4 and K 3 PO 4 One or more of the .

[0028] Optionally, the method further comprises: allowing the reaction product to enter a heating separator for heat treatment and gas-liquid separation treatment to obtain circulating electrolyte and synthetic ammonia;

[0029] The temperature of the heat treatment is 70-100°C.

[0030] Optionally, the method further comprises: allowing the circulating electrolyte to enter an electrolyte storage tank and return to the anode electrolyte channel and the cathode electrolyte channel via a circulation pump;

[0031] The circulating nitrogen obtained from the outlet of the cathode air inlet chamber returns to the cathode air inlet chamber via the cathode circulation fan; the circulating hydrogen obtained from the outlet of the anode air inlet chamber returns to the anode air inlet chamber via the anode circulation fan.

[0032] Optionally, the loading amount of the active metal in the hydrogen oxidation catalyst in the first catalytic material layer is 0.1 to 2 mg·cm -2 The loading amount of the active metal in the nitrogen reduction catalyst in the second catalytic material layer is 0.1 to 2 mg cm -2 .

[0033] Optionally, the gas flow rates of the hydrogen and nitrogen are each 10 to 200 ml·min -1 mg -1 ;

[0034] The flow rates of the cathode electrolyte and the anode electrolyte are each 1 to 200 ml·min -1 .

[0035] Through the above technical scheme, the present invention allows hydrogen to enter the anode air inlet chamber, enter the anode electrolyte channel through the first gas diffusion layer, and allows nitrogen to enter the cathode air inlet chamber, enter the cathode electrolyte channel through the second gas diffusion layer, and perform ammonia synthesis reaction. The present invention couples the cathode nitrogen reduction reaction with the anode hydrogen oxidation reaction, and the introduction of anode hydrogen provides sufficient protons for the nitrogen reduction system, inhibits the hydrogen evolution competitive reaction, and improves the reaction activity and reaction efficiency; on the other hand, the cathode electrolyte uses a low proton concentration electrolyte, which can increase the nitrogen solubility, further inhibit the hydrogen evolution competitive reaction, and effectively improve the ammonia yield and Faraday efficiency of the ammonia synthesis reaction.

[0036] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] 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:

[0038] Figure 1 This is a schematic diagram of the process flow of Example 1 of the present invention.

[0039] Figure 2 This is a schematic diagram of the second gas diffusion layer and the second catalytic material layer in Example 1 of the present invention.

[0040] Figure 3 Schematic diagram of the first gas diffusion layer and the first catalytic material layer in Example 1 of the present invention.

[0041] Description of Reference Numerals

[0042] 1. Electrolytic cell; 2. Cathode electrolyte channel; 3. Cathode air inlet chamber; 4. Anode electrolyte channel; 5. Anode air inlet chamber; 6. Electrolyte storage tank; 7. Heating separator; 8. Hydrogen purification device; 9. Nitrogen purification device; 10. Hydrogen circulation fan; 11. Nitrogen circulation fan; 12. Electrolyte circulation pump; 13. DC power supply.

[0043] S1, proton exchange membrane; S2, second gas diffusion layer; S3, first gas diffusion layer; S21, second catalytic material layer; S31, first catalytic material layer. DETAILED DESCRIPTION

[0044] 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.

[0045] A first aspect of the present disclosure provides an electrocatalytic ammonia synthesis system, wherein the system comprises an electrolytic cell;

[0046] The electrolytic cell comprises an anode electrolysis chamber and a cathode electrolysis chamber; a proton exchange membrane is arranged between the anode electrolysis chamber and the cathode electrolysis chamber;

[0047] The anode electrolysis chamber is provided with an anode air inlet chamber and an anode electrolyte channel; a first gas diffusion layer is provided between the anode air inlet chamber and the anode electrolyte channel; a first catalytic material layer is provided on a side of the first gas diffusion layer close to the anode electrolyte channel; the first catalytic material layer comprises a hydrogen oxidation catalyst;

[0048] A cathode air inlet chamber and a cathode electrolyte channel are arranged in the cathode electrolysis chamber; a second gas diffusion layer is arranged between the cathode air inlet chamber and the cathode electrolyte channel; a second catalytic material layer is arranged on the side of the second gas diffusion layer close to the cathode electrolyte channel; the second catalytic material layer contains a nitrogen reduction catalyst.

[0049] The gas diffusion layer provided in the system provided by the present disclosure helps hydrogen and nitrogen to directly reach the electrode surface coated with the catalyst, reduces the limitation of the electrolyte solubility on the reaction, and can increase the solubility of nitrogen, further inhibit the hydrogen evolution competitive reaction, and effectively improve the ammonia yield and Faraday efficiency of the synthetic ammonia reaction.

[0050] In a specific embodiment, the system further includes a DC power supply, a raw gas purification circulation unit and an electrolyte circulation separation unit; wherein the raw gas purification circulation unit includes an anode gas purification device, a cathode gas purification device, an anode circulation fan and a cathode circulation fan, and the anode gas purification device and the cathode gas purification device each include an acid absorption tank and an alkali absorption tank; the electrolyte circulation separation unit includes an electrolyte storage tank, a heating separator and a circulation pump. In the above embodiment, the impurity components in hydrogen and nitrogen are removed by the raw gas purification circulation unit to improve the efficiency of subsequent reactions; the circulating electrolyte, circulating hydrogen, circulating nitrogen and synthetic ammonia are separated by the heating separator, and the circulating electrolyte, circulating hydrogen and circulating nitrogen are recycled, and the electrolyte is heated at the same time to improve the reaction activity, improve the solubility of nitrogen, and effectively inhibit the hydrogen evolution competition reaction, thereby improving the ammonia yield and Faraday efficiency of the synthetic ammonia reaction.

[0051] In the present disclosure, the DC power source is selected from a constant voltage power source, wherein the operating voltage is -0.1 to -1.2 V (vsRHE).

[0052] In a specific embodiment, the nitrogen outlet of the raw gas purification circulation unit is in gas communication with the cathode gas inlet chamber; the hydrogen outlet of the raw gas purification circulation unit is in gas communication with the anode gas inlet chamber;

[0053] The electrolyte outlet of the electrolyte circulation separation unit is communicated with the cathode electrolyte channel and the anode electrolyte channel respectively.

[0054] In a specific embodiment, the nitrogen reduction catalyst and the hydrogen oxidation catalyst are of the same or different types, preferably different. In the above embodiment, according to the catalytic characteristics of the nitrogen reduction reaction and the hydrogen oxidation reaction, the cathode and the anode are respectively loaded with different types of catalysts, which can further improve the catalytic efficiency of the cathode and anode reactions, further promote the reaction, effectively inhibit the hydrogen evolution competitive reaction, and thus improve the ammonia yield and Faraday efficiency of the synthetic ammonia reaction.

[0055] In a further embodiment, the nitrogen reduction catalyst is selected from one or more of a metal catalyst supported by a two-dimensional material, a metal catalyst supported by an oxide, and a metal alloy catalyst; the active metal in the nitrogen reduction catalyst is selected from a transition metal, preferably, the active metal is selected from one or more of Fe, V and Mo; the two-dimensional material is selected from MOF, COF, MoS 2 , MXene, TMDs, graphene, boron nitride and black phosphorus; the oxide is selected from SnO 2 , WO 3 、CeO 2 and MnO 2 One or more of; the hydrogen oxidation catalyst is selected from metal catalysts, which may be one or more of alloy catalysts and single metal catalysts; the active metal in the hydrogen oxidation catalyst is selected from precious metals and / or transition metals, preferably, the active metal is selected from one or more of Pt, Ni, Au, Ru, Pd, Cu and W. In the above embodiment, limiting the type of nitrogen reduction catalyst within the scope of this application can provide more active sites for the reaction system, improve the catalytic activity, and promote the nitrogen reduction reaction; limiting the type of hydrogen oxidation catalyst within the scope of this application can effectively improve the catalytic efficiency, thereby further effectively inhibiting the hydrogen evolution competition reaction, thereby improving the ammonia yield and Faraday efficiency of the synthetic ammonia reaction.

[0056] In a specific embodiment, the first gas diffusion layer and the second gas diffusion layer are each selected from one or more of carbon fiber paper, carbon fiber woven cloth, non-woven cloth, carbon nanotubes and graphite, preferably carbon fiber paper.

[0057] In a specific embodiment, the thickness of the first gas diffusion layer and the second gas diffusion layer are respectively 50-400 μm, preferably 100-200 μm.

[0058] In a specific embodiment, the proton exchange membrane is selected from perfluorosulfonic acid proton exchange membrane and / or sulfonated polysulfone proton exchange membrane.

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

[0060] allowing an anolyte to enter an anolyte channel; allowing a catholyte to enter a catholyte channel;

[0061] Allow hydrogen to enter the anode air inlet chamber and enter the anode electrolyte channel through the first gas diffusion layer, and allow nitrogen to enter the cathode air inlet chamber and enter the cathode electrolyte channel through the second gas diffusion layer to perform nitrogen reduction reaction and hydrogen oxidation reaction;

[0062] Wherein, the cathode electrolyte is a low proton concentration electrolyte.

[0063] The method provided by the present disclosure allows hydrogen to enter the anode air inlet chamber, enter the anode electrolyte channel through the first gas diffusion layer, and allows nitrogen to enter the cathode air inlet chamber, enter the cathode electrolyte channel through the second gas diffusion layer, and perform a synthetic ammonia reaction. The present disclosure couples the cathode nitrogen reduction reaction with the anode hydrogen oxidation reaction, and the introduction of anode hydrogen provides sufficient protons for the nitrogen reduction system, inhibits the progress of the hydrogen evolution competitive reaction, and improves the reaction activity and reaction efficiency; on the other hand, the cathode electrolyte uses a low proton concentration electrolyte, which can increase the nitrogen solubility, further inhibit the hydrogen evolution competitive reaction, and effectively improve the ammonia yield and Faraday efficiency of the synthetic ammonia reaction.

[0064] In a specific embodiment, the proton concentration of the cathode electrolyte is less than 30%, preferably less than 10%; the cathode electrolyte comprises an aprotic solvent and water; the content of water in the cathode electrolyte is 0-30wt%, preferably 0-10wt%, and the content of the aprotic solvent is 70-100wt%, preferably 90-100wt%. In the above embodiment, the cathode electrolyte uses a low proton concentration electrolyte, and the contents of water and aprotic solvent in the cathode electrolyte are controlled within the preferred range of the present application, which can further improve the solubility of nitrogen, further inhibit the hydrogen evolution competition reaction, and effectively improve the ammonia yield and Faraday efficiency of the synthetic ammonia reaction.

[0065] In a preferred embodiment, the cathode electrolyte is selected from K 3 PO 4 , methanol and phosphine-based ionic liquid ([P6,6,6,14][eFAP]); in another preferred embodiment, the cathode electrolyte is selected from KOH, tetrahydrofuran and trifluorotoluene; in another preferred embodiment, the cathode electrolyte is selected from water, dimethyl sulfoxide and LiFSi. In the above embodiments, the cathode electrolyte uses a preferred type combination, which can further improve the nitrogen solubility, further inhibit the hydrogen evolution competition reaction, and effectively improve the ammonia yield and Faraday efficiency of the ammonia synthesis reaction.

[0066] In one embodiment, the anode electrolyte is selected from an acidic electrolyte or an alkaline electrolyte, preferably KOH, Na 2 SO 4 and K 3 PO 4 One or more of, preferably Na 2 SO 4 .

[0067] In a specific embodiment, the method further comprises: allowing the reaction product to enter a heating separator for heat treatment and gas-liquid separation treatment to obtain a circulating electrolyte and synthetic ammonia; the temperature of the heat treatment is 70-100° C., preferably 80-90° C. In the above embodiment, the circulating electrolyte and synthetic ammonia are obtained by separation through a heating separator, and the circulating electrolyte is recycled, and the electrolyte is heated at the same time to improve the reaction activity, improve the nitrogen solubility, and effectively inhibit the hydrogen evolution competition reaction, thereby improving the ammonia yield and Faraday efficiency of the synthetic ammonia reaction.

[0068] In a specific embodiment, the method further comprises: allowing the circulating electrolyte to enter an electrolyte storage tank and return to the anode electrolyte channel and the cathode electrolyte channel via a circulation pump.

[0069] In a specific embodiment, the circulating nitrogen obtained from the outlet of the cathode air inlet chamber is returned to the cathode air inlet chamber via the cathode circulating blower; the circulating hydrogen obtained from the outlet of the anode air inlet chamber is returned to the anode air inlet chamber via the anode circulating blower. In a specific embodiment, the loading amount of the active metal in the hydrogen oxidation catalyst in the first catalytic material layer is 0.1 to 2 mg·cm -2 , preferably 0.2 to 1 mg·cm -2 The loading amount of the active metal in the nitrogen reduction catalyst in the second catalytic material layer is 0.1 to 2 mg cm -2 , preferably 0.2 to 0.8 mg·cm -2 .

[0070] In a specific embodiment, the gas flow rates of the hydrogen and nitrogen are 10 to 200 ml·min respectively. -1 mg -1 , preferably 20 to 80 ml·min -1 mg -1 The flow rates of the cathode electrolyte and the anode electrolyte are 10 to 200 ml / min respectively. -1 , preferably 20 to 100 ml·min -1 mg -1 .

[0071] The present invention is further illustrated by the following examples, but the present invention is not limited thereto.

[0072] Example 1

[0073] The present embodiment provides an electrocatalytic ammonia synthesis system, which includes: a DC power supply 13, an electrolytic cell 1, a raw gas purification circulation unit and an electrolyte circulation separation unit; wherein the electrolytic cell 1 includes an anode electrolysis chamber and a cathode electrolysis chamber; a proton exchange membrane S1 is arranged between the anode electrolysis chamber and the cathode electrolysis chamber; an anode air inlet chamber 5 and an anode electrolyte channel 4 are arranged in the anode electrolysis chamber; a first gas diffusion layer S3 is arranged between the anode air inlet chamber 5 and the anode electrolyte channel 4; a first catalytic material layer S31 is arranged on one side of the first gas diffusion layer S3 close to the anode electrolyte channel 4; the first catalytic material layer S31 contains a hydrogen oxidation catalyst; A cathode air inlet chamber 3 and a cathode electrolyte channel 2 are arranged in the cathode electrolysis chamber; a second gas diffusion layer S2 is arranged between the cathode air inlet chamber 3 and the cathode electrolyte channel 2; a second catalytic material layer S21 is arranged on the side of the second gas diffusion layer S2 close to the cathode electrolyte channel 2; the second catalytic material layer S21 contains a nitrogen reduction catalyst; the proton exchange membrane S1 is a perfluorosulfonic acid proton exchange membrane; the first gas diffusion layer and the second gas diffusion layer are respectively carbon paper, the thickness of the first gas diffusion layer is 200 μm, and the thickness of the second gas diffusion layer is 200 μm; the hydrogen oxidation catalyst is a PtAu alloy catalyst, and the nitrogen reduction catalyst is V / WO 3 Metal catalyst; the loading amount of active metal in the hydrogen oxidation catalyst in the first catalytic material layer is 0.2 mg cm -2 The loading amount of active metal in the nitrogen reduction catalyst in the second catalytic material layer is 0.5 mg cm -2 .

[0074] The gas outlet of the raw gas purification circulation unit is respectively connected to the cathode air inlet chamber and the anode air inlet chamber; the electrolyte outlet of the electrolyte circulation separation unit is respectively connected to the cathode electrolyte channel and the anode electrolyte channel; wherein, the raw gas purification circulation unit includes a hydrogen purification device 8, a nitrogen purification device 9, a hydrogen circulation fan 10 and a nitrogen circulation fan 11, and the anode gas purification device and the cathode gas purification device each include an acid absorption tank and an alkali absorption tank; the electrolyte circulation separation unit includes an electrolyte storage tank 6, a heating separator 7 and an electrolyte circulation pump 12.

[0075] Process flow chart Figure 1 shown.

[0076] This embodiment provides a method for electrocatalytic synthesis of ammonia, and the specific steps are as follows:

[0077] a. allowing the anode electrolyte to enter the anode electrolyte channel; allowing the cathode electrolyte to enter the cathode electrolyte channel; wherein the anode electrolyte is K 3 PO 4 ; The cathode electrolyte includes K 3 PO 4solution, methanol, and [P6,6,6,14][eFAP], the proton concentration of the cathode electrolyte was 5 wt%; the flow rates of the anolyte and cathode electrolyte were 30 ml min -1 .

[0078] b. Allow nitrogen to enter the cathode air inlet chamber and anode air inlet chamber of the electrolytic cell through the nitrogen purification device for 30 minutes at a flow rate of 30 ml / min. -1 , so that the electrolytic cell is in a saturated nitrogen state.

[0079] c. Allow hydrogen to enter the anode air inlet chamber through a hydrogen purification device, and then enter the anode electrolyte channel through the first gas diffusion layer and then disperse and dissolve; allow nitrogen to enter the cathode air inlet chamber, and then enter the cathode electrolyte channel through the second gas diffusion layer and then disperse and dissolve. Connect a DC power supply, apply voltage to the system, and perform nitrogen reduction reaction and hydrogen oxidation reaction at -0.3V (vsRHE) for 120min to obtain a reaction product; wherein the gas flow rate of hydrogen and nitrogen is 20ml·min -1 mg -1 .

[0080] d. The reaction product is passed into a heating separator for heat treatment and gas-liquid separation to obtain circulating electrolyte and synthetic ammonia; the heat treatment temperature is 80°C.

[0081] e. Allow the circulating electrolyte to enter the electrolyte storage tank and return to the anode electrolyte channel and the cathode electrolyte channel through the circulating pump; the circulating nitrogen obtained from the outlet of the cathode air inlet chamber returns to the cathode air inlet chamber through the cathode circulating fan; the circulating hydrogen obtained from the outlet of the anode air inlet chamber returns to the anode air inlet chamber through the anode circulating fan.

[0082] Example 2

[0083] The system and method of Example 1 are used, wherein the only difference in the system is that the first gas diffusion layer and the second gas diffusion layer are each carbon nanotubes; the proton exchange membrane is a sulfonated polysulfone proton exchange membrane; the hydrogen oxidation catalyst is Ru / MoS 2 Catalyst; the nitrogen reduction catalyst is a Fe / MOFs metal catalyst;

[0084] The only difference in the method is that in step a, the cathode electrolyte is water, dimethyl sulfoxide and LiFSi, wherein the content of water in the cathode electrolyte is 5wt%, and the content of the aprotic solvent is 90wt%; the anode electrolyte is KOH, and the flow rate of the cathode electrolyte and the anode electrolyte is 100ml min -1 ;

[0085] In step c, nitrogen reduction reaction and hydrogen oxidation reaction were carried out at -0.1 V (vs RHE) for 60 min; the gas flow rate of hydrogen and nitrogen was 200 ml min-1 mg -1 .

[0086] Example 3

[0087] The system and method of Example 1 are used, except that in step a, the content of water in the cathode electrolyte is 25 wt % and the content of the aprotic solvent is 60 wt %.

[0088] Example 4

[0089] The system and method of Example 1 are used, except that the hydrogen oxidation catalyst and the nitrogen reduction catalyst are of the same type, and a RuCu alloy catalyst is selected.

[0090] Example 5

[0091] The system and method of Example 1 are used, except that in step d, the reaction product is not heat treated.

[0092] Example 6

[0093] The system and method of Example 1 are used, except that the loading amount of the hydrogen oxidation catalyst in the first catalytic material layer is 0.01 mg·cm -2 The loading amount of nitrogen reduction catalyst in the second catalytic material layer is 0.01 mg cm -2 .

[0094] Comparative Example 1

[0095] The system and method of Example 1 are used, except that H is not introduced into the anode. 2 , H is introduced into the anode 2 O, oxygen evolution reaction occurs.

[0096] Comparative Example 2

[0097] The system and method of Example 1 are used, except that the first gas diffusion layer and the second gas diffusion layer are not coated with a catalyst.

[0098] Comparative Example 3

[0099] The system and method of Example 1 are used, except that the proton concentration of the cathode electrolyte is 80 wt %.

[0100] Test Case

[0101] The reaction ammonia yield and Faraday efficiency in Examples 1 to 6 and Comparative Examples 1 to 3 were tested by the following method:

[0102] The NH in the electrolyte after the reaction was measured by UV-visible spectrophotometer using the indophenol blue method. 3 First, draw a standard working curve using a series of different concentrations of standard NH4 Cl solution and the absorbance corresponding to 655nm were plotted to obtain a fitting curve y = 0.3874-0.0006, R2 = 0.9999. Take 2mL of the electrolyte after the reaction of the embodiment and the comparative example, add 2mL of indigo reagent, 200μL of sodium nitroprusside reagent (1wt%) and 50μL of NaClO solution, let it stand in a dark place for 1h, scan it in the wavelength range of 550-800nm ​​with a UV-visible spectrophotometer, and record the absorbance at 655nm.

[0103] The ammonia yield and Faraday efficiency are calculated according to equations (1) and (2):

[0104] Ammonia yield = (c NH3 ×V) / (t×m) formula (1);

[0105] 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;

[0106] Faraday efficiency FE = (3 × F × c NH3 ×V×100%) / (M NH3 ×Q) formula (2);

[0107] 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.

[0108] Table 1

[0109] <![CDATA[Reaction ammonia production rate / μg·h -1 ·mg -1 > Faraday efficiency / % Example 1 261.7 54 Example 2 142.5 38 Example 3 87.3 35 Example 4 185.3 31 Example 5 235.4 50 Example 6 56.8 52.9 Comparative Example 1 23.7 12.5 Comparative Example 2 1.4 2.7 Comparative Example 3 33.6 23

[0110] According to the test results in Table 1, it can be seen that the method and system provided in the present application can effectively suppress the progress of the hydrogen evolution competition reaction and improve the reaction activity and reaction efficiency; and the cathode electrolyte uses a low proton concentration electrolyte, which can increase the solubility of nitrogen and further suppress the hydrogen evolution competition reaction. Compared with comparative examples 1 to 3, the ammonia yield and Faraday efficiency of the ammonia synthesis reaction in Examples 1 to 6 of the present application are higher.

[0111] Since H 2 O 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. 2 Very stable, with very low solubility in aqueous solution, resulting in N 2It is not easy to adsorb and activate, and the competitive reaction for hydrogen evolution is fierce, resulting in low ammonia yield and Faraday efficiency of the ammonia synthesis reaction.

[0112] Since the gas diffusion layer in Comparative Example 2 is not coated with a catalyst, nitrogen and hydrogen enter the cathode and anode electrolyte channels through the gas diffusion layer. Nitrogen reduction reaction and hydrogen oxidation reaction cannot occur in the absence of a catalyst, resulting in extremely low ammonia yield and Faraday efficiency.

[0113] Since Comparative Example 3 uses a cathode electrolyte with a higher proton concentration, N 2 The solubility of the catalyst is poor, and the competitive reaction of hydrogen evolution cannot be effectively suppressed. The efficiency of ammonia synthesis is low, and the ammonia yield and Faraday efficiency are significantly lower than those in Example 1.

[0114] 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.

[0115] 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.

[0116] 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 includes an electrolytic cell; The electrolytic cell comprises an anode electrolysis chamber and a cathode electrolysis chamber; a proton exchange membrane is arranged between the anode electrolysis chamber and the cathode electrolysis chamber; The anode electrolysis chamber is provided with an anode air inlet chamber and an anode electrolyte channel; a first gas diffusion layer is provided between the anode air inlet chamber and the anode electrolyte channel; a first catalytic material layer is provided on a side of the first gas diffusion layer close to the anode electrolyte channel; the first catalytic material layer comprises a hydrogen oxidation catalyst; A cathode air inlet chamber and a cathode electrolyte channel are arranged in the cathode electrolysis chamber; a second gas diffusion layer is arranged between the cathode air inlet chamber and the cathode electrolyte channel; a second catalytic material layer is arranged on the side of the second gas diffusion layer close to the cathode electrolyte channel; the second catalytic material layer contains a nitrogen reduction catalyst.

2. The system according to claim 1, wherein: The system also includes a DC power supply, a raw gas purification circulation unit and an electrolyte circulation separation unit; The nitrogen outlet of the raw gas purification circulation unit is in gas communication with the cathode gas inlet chamber; the hydrogen outlet of the raw gas purification circulation unit is in gas communication with the anode gas inlet chamber; The electrolyte outlet of the electrolyte circulation separation unit is communicated with the cathode electrolyte channel and the anode electrolyte channel respectively; Wherein, the raw gas purification circulation unit comprises an anode gas purification device, a cathode gas purification device, an anode circulation fan and a cathode circulation fan, and the anode gas purification device and the cathode gas purification device each comprise an acid absorption tank and an alkali absorption tank; The electrolyte circulation separation unit comprises an electrolyte storage tank, a heating separator and a circulation pump.

3. The system according to claim 1, wherein: The hydrogen oxidation catalyst and the nitrogen reduction catalyst are each selected from one or more of a metal catalyst, a two-dimensional material-supported metal catalyst, an oxide-supported metal catalyst, an alloy catalyst, and a single metal catalyst; The nitrogen reduction catalyst is selected from one or more of a metal catalyst supported by a two-dimensional material, a metal catalyst supported by an oxide, and a metal alloy catalyst; the active metal in the nitrogen reduction catalyst is selected from a transition metal, preferably, the active metal is selected from one or more of Fe, V and Mo; the two-dimensional material is selected from one or more of MOF, COF, MoS2, MXene, TMDs, graphene, boron nitride and black phosphorus; the oxide is selected from one or more of SnO2, WO3, CeO2 and MnO2; The hydrogen oxidation catalyst is selected from one or more of a metal catalyst, an alloy catalyst and a single metal catalyst; the active metal in the hydrogen oxidation catalyst is selected from a noble metal and / or a transition metal, preferably, the active metal is selected from one or more of Pt, Ni, Au, Ru, Cu and W.

4. The system according to claim 1, wherein: The first gas diffusion layer and the second gas diffusion layer are each selected from one or more of carbon fiber paper, carbon fiber woven cloth, non-woven cloth, carbon nanotubes and graphite; The thickness of the first gas diffusion layer and the second gas diffusion layer are each 50 to 400 μm; The proton exchange membrane is selected from perfluorosulfonic acid proton exchange membrane and / or sulfonated polysulfone proton exchange membrane.

5. A method for electrocatalytically synthesizing ammonia using the system according to any one of claims 1 to 4, wherein: The method includes: allowing an anolyte to enter an anolyte channel; allowing a catholyte to enter a catholyte channel; Allow hydrogen to enter the anode air inlet chamber, enter the anode electrolyte channel through the first gas diffusion layer, allow nitrogen to enter the cathode air inlet chamber, enter the cathode electrolyte channel through the second gas diffusion layer, and perform nitrogen reduction reaction and hydrogen oxidation reaction to obtain reaction products; Wherein, the cathode electrolyte is a low proton concentration electrolyte.

6. The method according to claim 5, wherein: The proton concentration of the cathode electrolyte is less than 30 wt %; the cathode electrolyte comprises an aprotic solvent and water; the content of water in the cathode electrolyte is 0 to 30 wt %, and the content of the aprotic solvent is 70 to 100 wt %; The anode electrolyte and the cathode electrolyte are of the same or different types; Preferably, the cathode electrolyte is selected from K3PO4, methanol and phosphine-based ionic liquids, the cathode electrolyte is selected from KOH, tetrahydrofuran and trifluorotoluene, the cathode electrolyte is selected from water, dimethyl sulfoxide and LiFSi; the anode electrolyte is selected from an acidic electrolyte or an alkaline electrolyte, preferably one or more of KOH, Na2SO4 and K3PO4.

7. The method according to claim 5, wherein: The method further comprises: allowing the reaction product to enter a heating separator for heat treatment and gas-liquid separation treatment to obtain circulating electrolyte and synthetic ammonia; The temperature of the heat treatment is 70-100°C.

8. The method according to claim 7, wherein: The method further comprises: allowing the circulating electrolyte to enter an electrolyte storage tank and return to the anode electrolyte channel and the cathode electrolyte channel via a circulation pump; The circulating nitrogen obtained from the outlet of the cathode air inlet chamber returns to the cathode air inlet chamber via the cathode circulation fan; the circulating hydrogen obtained from the outlet of the anode air inlet chamber returns to the anode air inlet chamber via the anode circulation fan.

9. The method according to claim 5, wherein: The loading amount of the active metal in the hydrogen oxidation catalyst in the first catalytic material layer is 0.1 to 2 mg·cm -2 The loading amount of the active metal in the nitrogen reduction catalyst in the second catalytic material layer is 0.1 to 2 mg cm -2 .

10. The method according to claim 5, wherein: The gas flow rates of the hydrogen and nitrogen are 10 to 200 ml / min respectively. -1 mg -1 ; The flow rates of the cathode electrolyte and the anode electrolyte are each 1 to 200 ml·min -1 .

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