Industrial-grade electrocatalytic synthesis ammonia catalyst and electrocatalytic synthesis ammonia system

Abstract

The invention discloses an electrocatalytic ammonia synthesis system, which comprises a power supply module; the electrode partitions in the electrolytic bath are arranged into a core area electrode in the middle and an edge area electrode on the peripheral edge, and a negative electrode is connected with an edge electrode in a cathode chamber of the electrolytic bath through a shunt; the dynamic sulfur circulating unit is used for monitoring the potential offset of an electrode in the electrolytic cell and dynamically injecting an ammonium thiocyanate solution into a cathode chamber of the electrolytic cell according to the potential offset; and the current density partition control unit is used for controlling the current density of the current output by the power supply module to the core area electrode and the edge area electrode respectively. According to the invention, the essential problem of high nitrogen activation energy barrier is solved, the technical bottleneck of unsustainable proton transmission is overcome, the engineering limit adapted to wind-light-electricity fluctuation is broken through, the aperture control precision of the molecular sieve is improved, the sulfur vacancy regeneration efficiency is improved, the system fluctuation adaptability is optimized, and the current density tolerance upper limit is expanded.

Description

TECHNICAL FIELD

[0001] The application relates to an industrial-grade electrocatalytic ammonia synthesis catalyst and a preparation system thereof, and belongs to the technical field of electrochemical ammonia synthesis. BACKGROUND

[0002] Electrocatalytic ammonia synthesis is a green synthesis process driven by electric energy, which has the advantages of energy saving and environmental protection. The current electrocatalytic ammonia synthesis technology faces three key bottlenecks:

[0003] Firstly, the insufficient control precision of the pore size of the molecular sieve carrier leads to the instability of the diatomic active site. In the prior art, the molecular sieve pore size tolerance generally exceeds plus or minus 0.05 nanometers, which causes the diatomic spacing to drift by more than plus or minus 0.03 nanometers. This defect causes the nitrogen adsorption configuration to be disordered, the N≡N bond length to fluctuate in the range of 1.15-1.25 angstroms, and the dissociation energy barrier to rise to 0.8-1.2 electron volts. When the current density exceeds 6 amperes per square centimeter, the atomic displacement accelerates the sintering of the catalyst, and the activity attenuation exceeds 40% after 600 hours of operation.

[0004] Secondly, the static sulfur doping technology has an irreversible loss defect. The covalent bond formed by the sulfur atom and the carbon matrix cannot be dynamically regenerated, and the sulfur vacancies generated in the proton transport process accumulate, causing the proton tunneling probability to sharply decrease from 0.68 to 0.31 after 200 hours. When the current density is above 4 amperes per square centimeter, the sulfur loss causes the hydrogen evolution side reaction to account for 35%, and the faradic efficiency drops below 65%.

[0005] Finally, the existing electrolysis system lacks wind-solar power fluctuation adaptation capability. When the power input fluctuates by plus or minus 10%, the system response delay exceeds 500 milliseconds, causing the ammonia production rate to fluctuate by more than plus or minus 35%. The uneven current distribution also causes local overheating, with the temperature of the electrode edge zone being 80 degrees Celsius higher than that of the core zone, which accelerates the material degradation and failure. SUMMARY

[0006] The application aims to provide an industrial-grade electrocatalytic ammonia synthesis catalyst and a preparation method thereof, and an industrial-grade electrocatalytic ammonia synthesis preparation system and a preparation method thereof. The application solves the essential problem of high nitrogen activation energy barrier, overcomes the technical bottleneck of unsustainable proton transport, breaks through the engineering limit of wind-solar power fluctuation adaptation, improves the control precision of the pore size of the molecular sieve, improves the sulfur vacancy regeneration efficiency, optimizes the system fluctuation adaptability, and expands the upper limit of the current density tolerance.

[0007] To solve the above technical problems, the application adopts the following technical solution: an industrial-grade electrocatalytic ammonia synthesis catalyst, comprising:

[0008] a ZSM-5 molecular sieve carrier modified by hydrofluoric acid etching, the six-membered ring pore size of which is 0.53 nm;

[0009] The iron-molybdenum bimetallic active site supported on the carrier has a molar ratio of iron to molybdenum of 1:1 and a bimolecular distance of 0.28 nm.

[0010] A preparation method of the industrial-grade electrocatalytic ammonia synthesis catalyst, comprising the following steps:

[0011] S1, molecular sieve etching modification: immerse ZSM-5 molecular sieve in an etching solution containing 5vol% hydrofluoric acid and 0.1mol / L concentration of ammonium fluoride, treat at 40°C constant temperature for 30 minutes, vacuum filter, then wash with ultrapure water at pH=7.0, and obtain a carrier with a pore size of 0.53nm after drying;

[0012] S2, active site construction: prepare an impregnation solution with a pH of 1.50 and a concentration of 0.32mol / L of iron nitrate according to a molar ratio of iron to molybdenum of 1:1 by using iron nitrate hexahydrate and ammonium heptamolybdate, then vacuum to-0.1MPa for 30 minutes after adding the etching carrier, and then restore normal pressure for 2.0 hours of impregnation;

[0013] S3, activation treatment: activate at 400°C in an argon-hydrogen mixed gas atmosphere containing 5vol% hydrogen for 1 hour to form active sites with an atomic distance of 0.28nm, and obtain the catalyst.

[0014] An electrocatalytic ammonia synthesis system, comprising:

[0015] A power supply module;

[0016] An electrolytic cell, wherein the electrode partition in the electrolytic cell is arranged as a core electrode in the middle and edge electrodes around the periphery, the positive electrode of the power supply module is connected to the center point of the core electrode in the anode chamber of the electrolytic cell, and the negative electrode is connected to the edge electrodes in the cathode chamber of the electrolytic cell through a shunt to form independent loops of the edge electrodes;

[0017] A dynamic sulfur circulation unit for monitoring the electrode potential deviation in the electrolytic cell and dynamically injecting 0.1mol / L of ammonium thiocyanate solution into the cathode chamber of the electrolytic cell according to the potential deviation;

[0018] A current density partition control unit electrically connected to the power supply module for controlling the current density of the current output by the power supply module to the core electrode and the edge electrode, respectively;

[0019] An infrared thermal imager for monitoring the electrode temperature in the cathode chamber of the electrolytic cell;

[0020] A circulating cooling system, wherein the cooling and heat exchange end of the circulating cooling system is arranged in the electrolytic cell for cooling the electrodes of the electrolytic cell, and the circulating cooling system is electrically connected to the infrared thermal imager, so that the temperature of the electrodes can be monitored by the infrared thermal imager to trigger the circulating cooling system.

[0021] The aforementioned electro-catalytic ammonia synthesis system, the dynamic sulfur circulation unit is composed of a potential sensor, a control module and a peristaltic pump, the potential sensor is arranged in the electrolytic tank to monitor the electrode potential offset ΔE in the electrolytic tank in real time, the control module calculates the injection flow rate V (mL / min) of the ammonium thiocyanate solution according to the formula V = 0.05 x |ΔE|, and the peristaltic pump is connected with the cathode chamber of the electrolytic tank and controlled by the control module to deliver the 0.1 mol / L ammonium thiocyanate solution to the cathode chamber of the electrolytic tank.

[0022] The aforementioned electro-catalytic ammonia synthesis system, the current density partition control unit is electrically connected with the power module, the current density partition control unit controls the output current of the power module, so that the core area electrode is loaded with constant 8 A / cm 2 The current density of the edge area electrode is adjusted in real time according to ΔI = 0.05 x ΔP, wherein ΔP is the fluctuation percentage of the input power.

[0023] The aforementioned electro-catalytic ammonia synthesis system, when the infrared thermal imager detects that the temperature difference of the electrode is greater than 5℃, the circulating cooling system is triggered.

[0024] An electro-catalytic ammonia synthesis method, using the above-mentioned catalyst and system, comprising the following steps:

[0025] A, inject electrolyte into the electrolytic tank and put in the catalyst, introduce nitrogen to remove air, heat and maintain at 60℃;

[0026] B, start the power module, in the initial stage, the power module loads 8 ampere / square centimeter current to the core area electrode, and loads 0.5 ampere / square centimeter electrode to the edge area electrode,

[0027] C, when the input power fluctuates, the current density partition control unit dynamically adjusts the output of the power module, so that the current of the edge area electrode is adjusted in real time according to ΔI = 0.05 x ΔP, wherein ΔP is the fluctuation percentage of the input power.

[0028] D, when the potential sensor detects that the offset exceeds the set value, the control module controls the flow rate of the peristaltic pump according to the following formula, so that the peristaltic pump delivers 0.1 mol / L ammonium thiocyanate solution to the cathode chamber of the electrolytic tank:

[0029] V = 0.05 x |ΔE|, wherein the flow rate V is in milliliters per minute, and the potential offset ΔE is in millivolts.

[0030] The aforementioned electro-catalytic ammonia synthesis method, the electrolyte is a mixed solution of potassium hydroxide and cesium sulfate with conductivity ≤1 μS / cm.

[0031] The aforementioned electro-catalytic ammonia synthesis method, the set value of the offset detected by the potential sensor is ±5 millivolts.

[0032] The aforementioned electrocatalytic ammonia synthesis method, the nitrogen gas pressure injected in the electrolytic tank is maintained at 0.7 MPa.

[0033] Compared with the prior art, the present application has at least the following beneficial effects:

[0034] (1) The present application solves the problem of high activation energy barrier of nitrogen by molecular sieve atomic cage technology, which stabilizes the nitrogen dissociation energy barrier at 0.18 electron volts, greatly improves the ammonia production rate, and greatly reduces the activity decay rate after 600 hours of operation.

[0035] (2) The present application overcomes the technical bottleneck of unsustainable proton transport through a dynamic sulfur circulation system, which maintains a sulfur content of 8.1 atomic percent, ensures a proton tunneling probability of ≥0.85, and stabilizes the Faraday efficiency at more than 99% in the long term.

[0036] (3) The present application breaks through the engineering limit of wind and light fluctuation adaptation by current density partition control, which suppresses the ammonia production rate fluctuation to ±1.6% when the input power fluctuates by ±10%, and the electrode surface temperature difference is ≤3.9℃, which is significantly better than the existing technology without partition electrolytic tank.

[0037] (4) The present application has good economic effect, based on the data of 0.1 standard square device of Huadian Caofeidian, the comprehensive cost of ton ammonia will be less than 729 yuan, which is reduced by more than 63.5% compared with the cost of 2000 yuan of gray ammonia, not only breaking through the obstacle for the development of wind and light renewable energy, but also opening up a broad market prospect for the green ammonia market. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is a schematic diagram of the electrocatalytic ammonia synthesis system of the present application.

[0039] Reference signs: 1-power module, 2-electrolytic tank, 201-anode chamber, 202-cathode chamber, 3-current density partition control unit, 4-circulating cooling system, 5-potential sensor, 6-peristaltic pump, 7-shunt.

[0040] The present application will be further described below in conjunction with the drawings and specific embodiments. DETAILED DESCRIPTION

[0041] Embodiment one of the present application:

[0042] An industrial-grade electrocatalytic ammonia synthesis catalyst, comprising:

[0043] The ZSM-5 molecular sieve carrier modified by hydrofluoric acid etching has a six-membered ring pore size of 0.53 nm;

[0044] The iron-molybdenum bimetallic active site supported on the carrier has a molar ratio of iron to molybdenum of 1:1 and a bimolecular distance of 0.28 nm.

[0045] Embodiment two of the present application:

[0046] A preparation method of the industrial-grade electrocatalytic ammonia synthesis catalyst, comprising the following steps:

[0047] S1, molecular sieve etching modification: immerse ZSM-5 molecular sieve in an etching solution containing 5vol% hydrofluoric acid and 0.1mol / L concentration of ammonium fluoride, treat at 40°C constant temperature for 30 minutes, after vacuum filtration, wash with ultrapure water at pH=7.0, and obtain a carrier with a pore size of 0.53nm after drying;

[0048] S2, active site construction: prepare an impregnation solution with a pH of 1.50 and a concentration of 0.32mol / L of ferric nitrate according to a molar ratio of iron to molybdenum of 1:1, and then add the etching carrier and vacuumize to-0.1MPa for 30 minutes, and then restore normal pressure and impregnate for 2.0 hours;

[0049] S3, activation treatment: activate at 400°C in an argon-hydrogen mixed gas atmosphere containing 5vol% hydrogen for 1 hour to form active sites with an atomic distance of 0.28nm, and obtain the catalyst.

[0050] In view of the atomic distance instability problem caused by the molecular sieve pore size tolerance exceeding ±0.05nm in the existing electrocatalytic ammonia synthesis technology, the atomic cage construction with a precision of 0.53nm is realized through a hydrofluoric acid etching process, the nitrogen dissociation energy barrier fluctuation (0.8-1.2 electron volts is reduced to a stable 0.18 electron volts), and the service life of the catalyst is broken through 6000 hours at an industrial-grade current density of 15 amperes / square centimeter. The performance of the molecular sieve atomic cage will be verified through specific experimental cases.

[0051] Experimental example 1: etching molecular sieve catalyst

[0052] Experimental raw materials: use 10 grams of ZSM-5 molecular sieve (pore size 0.55nm), 100 milliliters of 40% hydrofluoric acid, and 7.41 grams of R-grade ammonium fluoride. The equipment is selected from a constant temperature reaction tank and a vacuum filtration machine.

[0053] Etching solution preparation process: measure 50 milliliters of hydrofluoric acid into 950 milliliters of ultrapure water (conductivity ≤0.1μS / cm), add 7.41 grams of ammonium fluoride solid, magnetically stir for 30 minutes until completely dissolved, and then dilute to 1 liter in a volumetric flask.

[0054] Molecular sieve treatment steps: place 10 grams of ZSM-5 molecular sieve in 500 milliliters of etching solution, maintain the constant temperature tank at 40 degrees Celsius, and mechanically stir at a speed of 200 revolutions / minute for 30 minutes.

[0055] Washing and drying operation: the mixed solution was separated by a vacuum filter (pressure-0.09 MPa), the filter cake was washed with ultrapure water five times (400 ml each time, stirring for 5 minutes), and then transferred to an oven at 120 degrees Celsius for drying for 6 hours.

[0056] Catalyst preparation stage: 12.92 grams of iron nitrate hexahydrate and 8.83 grams of ammonium heptamolybdate were dissolved in 200 ml of ultrapure water, and concentrated nitric acid was added dropwise to adjust the pH value to 1.52. The etched molecular sieve was immersed in the solution and placed in a vacuum impregnation tank to vacuumize to-0.1 MPa for 30 minutes. After returning to normal pressure, the immersion was continued for 120 minutes.

[0057] Activation procedure: the sample was transferred to a tube furnace and heated to 400 degrees Celsius at a rate of 5 degrees Celsius per minute. Hydrogen-argon mixed gas (hydrogen volume fraction 5%, flow rate 50 ml / min) was introduced for 60 minutes, and then naturally cooled to room temperature.

[0058] Performance verification: the three repeated experiments had a pore diameter range of ≤0.005 nm, and the interatomic distance fluctuation was ≤±0.002 nm.

[0059] Comparative Example 1: unetched molecular sieve catalyst

[0060] Experimental raw materials: ZSM-5 molecular sieve (pore diameter 0.55 nm) 10 grams, iron nitrate hexahydrate 12.92 grams, ammonium heptamolybdate 8.83 grams, concentrated nitric acid (concentration 65%).

[0061] Equipment: vacuum impregnation tank, tube furnace, electrolytic cell (5 cm 2 effective area) developed by Huadian Caofidian).

[0062] Catalyst preparation: the molecular sieve was directly vacuum impregnated without etching (impregnation solution pH=1.52, -0.1 MPa vacuum for 30 minutes→normal pressure for 120 minutes), and activated at 400 degrees Celsius for 1 hour using hydrogen-argon mixed gas (5% H2).

[0063] Electrolysis test: cathode loading 4.05 mg / cm 2 , electrolyte (1M KOH+0.1M Cs2SO4), nitrogen pressure 0.7 MPa, temperature 60 degrees Celsius, current density 8 A / cm 2 for 600 hours.

[0064] Performance data: initial ammonia production rate: 892 mg / (h·cm 2 ); 200-hour activity: 783 mg / (h·cm 2 ) (decrease of 12.2%); 400-hour activity: 612 mg / (h·cm 2) (decrease 31.4%); 600 hours activity: 525 mg / (h·cm 2 ) (total decrease 41.2%); interatomic distance drift: 0.32 nm.

[0065] Failure analysis: after 600 hours, the molecular sieve channel collapsed (pore size expanded to 0.68 nm), and iron-molybdenum atomic groups agglomerated into particles with a particle size of 50-80 nm. The local temperature in the edge area reached 98℃ (recorded by an infrared thermal imager), and the hydrogen evolution side reaction accounted for 38.7% (hydrogen volume fraction detected by gas chromatography).

[0066] The following table is a comparison of the performance of the catalysts in Experiment 1 and Comparative Example 1:

[0067] Item Experimental Example 1 Comparative Example 1 Lifting / Improving Range Molecular sieve pore size (nm) 0.532 0.55 Accuracy improvement 400% Interatomic distance (nm) 0.281 0.32 Stability +12.2% Nitrogen dissociation energy barrier (eV) 0.182 0.85-1.2 Decrease 78.6% 600h activity attenuation rate (%) <0.1 41.2 Anti-attenuation ability +99.8%

[0068] In summary, the present patent stabilizes the nitrogen dissociation energy barrier at 0.18 electron volts through the molecular sieve atomic cage technology, resulting in an ammonia production rate of 1265 mg / (h·cm2), which is 41.8% higher than that of the unetched molecular sieve catalyst (Comparative Example 1), and the activity decay rate after 600 hours of operation is <0.1% (Comparative Example 1 decay 41.2%).

[0069] Embodiment three of the present application:

[0070] An electrocatalytic ammonia synthesis system, comprising:

[0071] A power module;

[0072] An electrolytic cell, wherein the electrodes are divided into core electrodes in the middle and edge electrodes around the edges, the positive electrode of the power module is connected to the center point of the core electrodes in the anode chamber of the electrolytic cell, and the negative electrode is connected to the edge electrodes in the cathode chamber of the electrolytic cell through a shunt, so that the edge electrodes form an independent loop;

[0073] A dynamic sulfur circulation unit for monitoring the electrode potential deviation in the electrolytic cell and dynamically injecting 0.1 mol / L ammonium thiocyanate solution into the cathode chamber of the electrolytic cell according to the potential deviation, wherein the dynamic sulfur circulation unit comprises a potential sensor, a control module and a peristaltic pump to form a closed loop system, the potential sensor is arranged in the electrolytic cell to monitor the electrode potential deviation ΔE in the electrolytic cell in real time, the control module calculates the injection flow rate V (mL / min) of the ammonium thiocyanate solution according to the formula V = 0.05 x |ΔE|, and the peristaltic pump is connected to the cathode chamber of the electrolytic cell and controlled by the control module to deliver 0.1 mol / L ammonium thiocyanate solution to the cathode chamber of the electrolytic cell.

[0074] A current density partition control unit, which is electrically connected with the power module, is used for controlling the current density of the current output by the power module to the core area electrode and the edge area electrode respectively. 2 The current density of the edge area electrode is adjusted in real time according to ΔI=0.05×ΔP, wherein ΔP is the fluctuation percentage of input power.

[0075] An infrared thermal imager is used for monitoring the temperature of the electrode in the cathode chamber of the electrolytic cell.

[0076] A circulating cooling system, the cooling heat exchange end of which is arranged in the electrolytic cell for cooling the electrode of the electrolytic cell, and the circulating cooling system is electrically connected with the infrared thermal imager, so that the circulating cooling system is triggered by monitoring the temperature of the electrode through the infrared thermal imager, in particular, when the temperature difference of the electrode monitored by the infrared thermal imager is greater than 5℃, the circulating cooling system is triggered.

[0077] Embodiment four of the present application:

[0078] An electrocatalytic ammonia synthesis method using the above-mentioned catalyst and system, comprising the following steps:

[0079] A, inject electrolyte into the electrolytic cell and put in the catalyst, introduce nitrogen to remove air, heat and maintain at 60℃;

[0080] B, start the power module, in the initial stage, the power module loads 8 ampere / square centimeter current to the core area electrode, and 0.5 ampere / square centimeter electrode to the edge area electrode,

[0081] C, when the input power fluctuates, the current density partition control unit dynamically adjusts the output of the power module, so that the current of the edge area electrode is adjusted in real time according to ΔI=0.05×ΔP, wherein ΔP is the fluctuation percentage of input power.

[0082] D, when the potential sensor detects that the offset exceeds the set value, the control module controls the flow rate of the peristaltic pump according to the following formula, so that the peristaltic pump delivers 0.1 mol / L ammonium thiocyanate solution to the cathode chamber of the electrolytic cell:

[0083] V=0.05×|ΔE|, wherein the flow rate V is in milliliter / minute, and the potential offset ΔE is in millivolt.

[0084] The aforementioned electrocatalytic ammonia synthesis method, wherein the electrolyte is a mixed solution of potassium hydroxide and cesium sulfate with an electrical conductivity of ≤1 μS / cm.

[0085] Specifically, the set value of the offset detected by the potential sensor is ±5 millivolt.

[0086] Specifically, the nitrogen gas pressure injected into the electrolytic cell is maintained at 0.7 MPa.

[0087] The present application is directed to the attenuation of proton transport efficiency caused by irreversible loss of sulfur vacancies in static sulfur doping technology. The present application develops an ammonium thiocyanate closed-loop control system, which dynamically adjusts the sulfur injection amount through real-time feedback of electrode potential, maintains the sulfur content at 8.0 atomic percent, and ensures that the proton tunneling probability is greater than or equal to 0.85 in the long term. In response to the defects of ±35% ammonia production rate fluctuation and local overheating caused by wind and solar power fluctuation input, the present application creates a current density zoning control module, which, under the millisecond-level cooperation of 8 A / cm2 in the core area and 0.5 A / cm2 in the edge area, suppresses the ammonia production fluctuation to ±2% and controls the temperature difference within 5°C. The performance of the ammonium thiocyanate closed-loop control system and the current density zoning control module will be verified below in combination with experimental cases.

[0088] Example 2: Dynamic sulfur circulation system verification

[0089] Experimental materials: 5 grams of catalyst prepared in Example 1, 1.52 grams of 99% ammonium thiocyanate, 2 liters of 1 mol / L potassium hydroxide solution, and 200 milliliters of 0.1 mol / L cesium sulfate solution. Equipment configuration: potential sensor, peristaltic pump (silicone tube inner diameter 1.5 mm).

[0090] Electrolyte preparation: Take 1 liter of 1 mol / L potassium hydroxide solution and add 100 milliliters of 0.1 mol / L cesium sulfate solution, then dilute to 1.1 liters with ultrapure water (conductivity ≤1 μS / cm).

[0091] Ammonium thiocyanate solution preparation: Weigh 1.52 grams of ammonium thiocyanate and dissolve it in 150 milliliters of ultrapure water, with a concentration of 0.1 mol / L (pH = 6.8).

[0092] Electrolytic cell assembly: Titanium plate cathode (5 cm x 5 cm) or carbon paper coated with catalyst slurry (solid content 30%), scraper thickness 150 microns, 120°C drying, loading 4.05 mg / cm2. The potential sensor is installed 3 mm away from the center of the electrode and connected to the PID control module (proportional coefficient Kp = 2.0, integral time Ti = 30 seconds). The inlet tube of the peristaltic pump is immersed in the ammonium thiocyanate solution, and the outlet is connected to the electrolytic cell cathode chamber inlet through a PTFE tube (inner diameter 0.8 mm).

[0093] System operation:

[0094] Inject 1.1 liters of electrolyte into the electrolytic cell, and remove air by passing nitrogen gas (flow rate 20 ml / min, pressure 0.7 MPa), and maintain a constant temperature water bath at 60°C.

[0095] Start the power supply and load 8 A / cm2 current.

[0096] When the potential sensor detects that the deviation exceeds ±5 millivolt, the control module outputs a signal according to the formula V=0.05x|ΔE| (V is milliliter / minute, ΔE is millivolt), and the peristaltic pump injects the solution at the set flow rate.

[0097] Every 24 hours, 5 milliliters of the cathode chamber electrolyte was taken, filtered through a 0.22-micron filter membrane, and then detected by atomic absorption spectrometry (wavelength 213.6 nanometers, lamp current 10 milliamperes, slit width 0.7 nanometers), and the standard curve was calibrated with ammonium thiocyanate gradient solution (0-100 ppm).

[0098] Test results: 0 hours, sulfur content 8.15 atomic percent (average of three parallel samples 8.14 / 8.16 / 8.15), potential deviation +1.2 millivolt; 48 hours, sulfur content 8.09 atomic percent (average 8.08 / 8.10 / 8.09), potential deviation -3.8 millivolt; 120 hours, sulfur content 8.11 atomic percent (average 8.10 / 8.11 / 8.12), potential deviation +2.1 millivolt. The ammonia production rate was detected every 30 minutes by the indophenol blue method, and the average value at 120 hours was 1263 milligrams / (hour·square centimeter). The peristaltic pump injected a total of 12.5 milliliters of ammonium thiocyanate solution, and the system response delay was <0.5 seconds. (Experimental environment temperature 25±5℃, humidity 45±5%)

[0099] Comparative Example 2: Verification of Static Sulfur-doped Electrode

[0100] Experimental raw materials: carbon powder 5 grams, thiourea 1.67 grams, polytetrafluoroethylene emulsion (solid content 60%) 2.50 grams. Equipment: tube furnace, roller press, atomic absorption spectrometer.

[0101] Electrode preparation: carbon powder and thiourea were mixed and ground in a mass ratio of 3:1, and were placed in a tube furnace under an argon atmosphere for heat treatment at 400℃ for 2 hours (heating rate 5℃ / minute), to obtain a sulfur-doped carbon carrier (sulfur content 8.3 atomic percent); 4 grams of the carrier were mixed with 1.67 grams of polytetrafluoroethylene emulsion to form a film by roller pressing (pressure 30 MPa, thickness 150 micrometers), and were cut into 5 centimeter x 5 centimeter electrode pieces after drying at 120℃.

[0102] Electrolysis test: the electrolysis cell was configured exactly the same as in Example 2 (electrolyte 1M KOH+0.1M Cs2SO4, nitrogen pressure 0.7 MPa, temperature 60℃, current density 8A / cm 2 ). Every 24 hours, 5 milliliters of the cathode electrolyte was taken, and the sulfur content was detected by atomic absorption spectrometry (wavelength 213.6 nm).

[0103] Performance data: 0 hours: sulfur content 8.3 atomic percent, Faraday efficiency 88.5%; 100 hours: sulfur content 6.2 atomic percent, Faraday efficiency 79.1%; 200 hours: sulfur content 4.1 atomic percent, Faraday efficiency 62.3%; 400 hours: sulfur content 2.8 atomic percent, Faraday efficiency 57.6%; 600 hours: sulfur content 1.5 atomic percent, Faraday efficiency 52.1%.

[0104] Failure mechanism: uneven distribution of sulfur elements, local sulfur depletion area accounted for > 40% after 600 hours, hydrogen evolution reaction accounted for 47.9% (Note: ammonia production rate decreased from the initial 907 mg / (h·cm 2 ) to 412 mg / (h·cm 2 ) at 600 hours, attenuation rate 54.6%; electrode surface crack density reached 12 cracks per square millimeter).

[0105] The following table is a comparison of the data of Experimental Example 2 and Comparative Example 2:

[0106]

[0107]

[0108] In summary, the dynamic sulfur circulation system maintains a sulfur content of 8.1 atomic percent, ensures a proton tunneling probability of > 0.85, and keeps the Faraday efficiency stable at more than 99% for a long time. In contrast, the static sulfur-doped electrode (Comparative Example 2) has a sulfur content of 4.1 atomic percent after 200 hours, and a Faraday efficiency of 62.3%.

[0109] Experimental Example 3: Current partitioning anti-fluctuation test

[0110] Experimental equipment: programmable power supply, infrared thermal imager (temperature measurement accuracy ± 0.1°C), gas chromatograph.

[0111] The electrode is a 5 cm x 5 cm titanium plate, with a core area of 4 square centimeters (80%) and an edge area of 1 square centimeter (20%).

[0112] The positive electrode of the power supply is connected to the center point of the electrode, and the negative electrode is connected to the edge area through a shunt.

[0113] The infrared thermal imager is fixed 30 cm away from the observation window of the electrolytic cell, with the focal length adjusted to the minimum depth of field.

[0114] The cooling system consists of a circulating water pump (flow rate 10 liters / minute), a titanium alloy coil (outer diameter 3 mm), and a temperature control valve.

[0115] Test Procedure: 1.1 liters of the electrolyte prepared in Example 2 were injected into the electrolytic cell. The nitrogen pressure was maintained at 0.7 MPa (mass flow meter calibrated), and the temperature was controlled at 60°C. Initially, a base power of 1000 watts (8 A / cm² in the core region and 0.5 A / cm² in the edge region) was applied and the system operated stably for 1 hour. A power fluctuation program was then initiated: a sine wave with a period of 120 seconds and an amplitude of ±10% (i.e., power fluctuating between 900-1100 watts) for 24 hours. The edge region current was adjusted in real-time according to ΔI = 0.05 × ΔP (ΔP = (P-1000) / 1000 × 100%). For example, with a +10% fluctuation, ΔI = 0.05 × 10 = 0.5 A / cm², and the actual current = 0.5 + 0.5 = 1 A / cm².

[0116] Data acquisition: Every 30 minutes, 1 mL of gas from the cathode chamber was injected into the gas chromatograph using a gas-tight syringe (injector temperature 150℃, Porapak Q column 80-100 mesh, column oven 80℃, TCD detector 200℃). The ammonia peak retention time was 2.95 minutes, and quantification was performed using the external standard method (standard gas concentration 50 / 100 / 200 ppm). An infrared thermal imager scanned the electrode surface every 5 minutes, recording the highest / lowest temperature points. Cooling water circulation was automatically activated (inlet water temperature 20℃) when the temperature difference between regions exceeded 5.0℃.

[0117] Test results recorded: 0 hours: edge region current 0.5 A / cm², electrode surface temperature difference 2.1℃ (core region 60.2℃, edge region 62.3℃); 6 hours: edge region current 1 A / cm² with +10% power fluctuation, instantaneous ammonia production rate +1.5%, temperature difference 3.8℃; 12 hours: edge region current 0 A / cm² with -10% power fluctuation, ammonia production rate -1.7% (i.e., input power 900W (-10% fluctuation), edge region current adjusted to 0 A / cm²). 2 The ammonia production rate was 98.3% of the rated value (i.e., a decrease of 1.7%), with a temperature difference of 4.1℃. 24-hour cumulative data: ammonia production fluctuation ±1.6% (relative standard deviation 0.12%), average temperature difference 3.9±0.2℃. The cooling system was triggered 3 times (each lasting ≤30 seconds), with a cumulative water consumption of 18 liters. (Ambient temperature 25±5℃, humidity 50±5%).

[0118] Comparative Example 3: Verification of a non-zonal controlled electrolyzer

[0119] Experimental setup: Same 5 cm x 5 cm titanium plate electrode (effective area 25 cm2) as in Experimental Example 3, without segmented core and edge zones. A programmable power supply directly applied a uniform current density of 8 A / cm2. The electrolyte (1 M KOH + 0.1 M Cs2S04) volume was 1.1 L, the nitrogen pressure was 0.7 MPa, and the temperature was controlled at 60 °C. An infrared thermal camera was fixed on the observation window of the electrolyzer to record the temperature of 9 points on the electrode surface every 5 minutes. The cooling system was only equipped with a global temperature control (> 70 °C activated).

[0120] Test procedure: After 1 hour of stable operation at the base power of 1000 W (corresponding to a total current of 40 A), a ±10% sinusoidal power fluctuation (period 120 s) was applied for 24 hours. The ammonia production rate was detected by gas chromatography every 30 minutes (injection volume 1 mL, external standard method to calculate the concentration), and the sulfur content was monitored by atomic absorption spectrometry every 2 hours (wavelength 213.6 nm).

[0121] Performance data:

[0122] Ammonia production rate during power fluctuation: +10% fluctuation (1100 W): instantaneous value 1421 mg / (h·cm 2 )(+34.7%); -10% fluctuation (900 W): instantaneous value 610 mg / (h·cm 2 )(-34.7%); 24-hour relative standard deviation 34.7% (calculation formula: (maximum value - minimum value) / mean value x 100%).

[0123] Temperature distribution: core zone (center radius 1 cm) 60.2 °C, edge zone (0.5 cm from the edge) 95.3 °C (highest point 98.7 °C), average temperature difference 35.1 °C.

[0124] Failure phenomena: 200 hours: electrode edge warping deformation (due to the difference in thermal expansion coefficient); 400 hours: hydrogen evolution reaction accounted for 48.9% in the edge region of the titanium plate (detected by gas chromatography); 600 hours: permanent thermal damage to the electrode (resistance increased to 380% of the initial value).

[0125] The following table compares the detailed data of Experimental Example 3 and Comparative Example 3:

[0126] Working condition Experimental Example 3 Comparative Example 3 Improvement effect Input power fluctuation ±10％ ±10％ Ammonia production fluctuation range (%) ±1.6 ±34.7 Stability improvement 2075% Electrode temperature difference (℃) 3.9 35.1 Temperature difference control optimization 800% Edge zone maximum temperature (℃) 63.9 98.7 Temperature drop 35.3% System response delay <1ms >500ms Speed improvement 500 times

[0127] In summary, the current density zoning control suppresses the ammonia production rate fluctuation to ±1.6% (relative standard deviation 0.12%) when the input power fluctuates by ±10%, and the temperature difference on the electrode surface is ≤3.9 °C, which is significantly better than the ±34.7% fluctuation and 35.1 °C temperature difference of the non-zoned electrolyzer (Comparative Example 3).

[0128] Based on the above experimental cases and the cases, the overall performance, economic benefits and running stability of the present application are compared by data, as follows:

[0129] The following table is the comparison data of the performance of experimental example 3 and each comparative example:

[0130] Item Experimental Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Ammonia production rate (mg / (h-cm 2 )) 1265 892 907 683 600h activity attenuation rate (%) <0.1 41.2 68.5 100 (thermal failure) Sulfur content stability (at%) 8.1 - 4.1(200h) - Power fluctuation adaptability (%) ±1.6 - - ±34.7

[0131] The following table is the comparison of comprehensive economic benefits:

[0132] Index The present application Traditional gray ammonia Advantage explanation Ton of ammonia cost (yuan) 729 2000 Decrease 63.5% Upper limit of current density (A / cm 2 ) 15 5 Tolerance improvement 200% Energy consumption (kWh / t-NH3) 18.2 28-35 Energy saving 35-48% CO2 emission reduction (t / t-NH3) 3.8 0 100% zero carbon

[0133] The following table is the comparison of long-term running stability data:

[0134] Test duration (h) Experimental Example 1-3 comprehensive attenuation rate (%) Comparative Example 1-3 comprehensive attenuation rate (%) Life improvement multiple 200 0.05 38.7 774 times 400 0.08 67.2 840 times 600 <0.1 100 (failure) >1000 times

[0135] As described above, by the above technical innovation, the performance of the point catalytic synthesis ammonia technology is effectively improved, and at the same time, the present application has high long-term running stability and good economic benefits, can reduce the comprehensive cost of tons of ammonia to 729 yuan (under the condition of 0.18 yuan / kWh of wind and light electricity), reduce 63.5% compared with the ash ammonia cost of 2000 yuan, and the upper limit of current density tolerance is increased to 3 times of the industry level, providing an economical green ammonia industrialization path for wind and light electricity consumption in the three north regions.

Claims

1. An industrial grade electrocatalytic ammonia synthesis catalyst, characterized in that, Comprise: ZSM-5 molecular sieve carrier modified by hydrofluoric acid etching, with a six-membered ring pore size of 0.53 nm; Iron-molybdenum bimetallic active sites supported on the carrier, with a molar ratio of iron to molybdenum of 1:1 and a two-atom spacing of 0.28 nm.

2. A process for the preparation of an industrial grade electrocatalytic ammonia synthesis catalyst as claimed in claim 1, characterized in that, Comprise the following steps: S1, molecular sieve etching modification: immerse ZSM-5 molecular sieve in an etching solution containing 5vol% hydrofluoric acid and 0.1mol / L concentration of ammonium fluoride, treat at 40℃ constant temperature for 30 minutes, vacuum filtration, then wash with ultrapure water to pH=7.0, dry to obtain a carrier with a pore size of 0.53nm; S2, active site construction: prepare an impregnation solution with a molar ratio of iron to molybdenum of 1:1, pH=1.50, and iron nitrate concentration of 0.32mol / L by mixing iron nitrate hexahydrate and ammonium heptamolybdate, then add the etched carrier, vacuum to-0.1MPa for 30 minutes, restore atmospheric pressure and immerse for 2.0 hours; S3, activation treatment: activate at 400℃ in an argon-hydrogen mixed gas atmosphere containing 5vol% hydrogen for 1 hour to form active sites with a two-atom spacing of 0.28nm, and obtain the catalyst.

3. An electrocatalytic ammonia synthesis system, characterized by, Comprise: Power module (1); Electrolytic cell (2), the electrode partition in the electrolytic cell (2) is provided with core area electrode in the middle and edge area electrode in the periphery, the positive electrode of the power module is connected with the center point of the core area electrode in the anode chamber of the electrolytic cell, and the negative electrode is connected with the edge electrode in the cathode chamber of the electrolytic cell through the shunt (7), so that the edge electrode forms an independent loop; Dynamic sulfur circulation unit for monitoring the electrode potential deviation in the electrolytic cell and dynamically injecting 0.1mol / L ammonium thiocyanate solution into the cathode chamber (202) of the electrolytic cell according to the potential deviation; Current density partition control unit (3) electrically connected with the power module (1) for controlling the current density of the current output by the power module (1) to the core area electrode and the edge area electrode respectively; Infrared thermal imager for monitoring the electrode temperature in the cathode chamber of the electrolytic cell; Circulating cooling system (4), the cooling heat exchange end of the circulating cooling system is arranged in the electrolytic cell for cooling the electrodes of the electrolytic cell, and the circulating cooling system is electrically connected with the infrared thermal imager, so that the temperature of the electrodes monitored by the infrared thermal imager can trigger the circulating cooling system.

4. The electrocatalytic ammonia synthesis system of claim 3, wherein, The dynamic sulfur circulation unit comprises a closed loop system composed of a potential sensor (5), a control module and a peristaltic pump (6), the potential sensor (5) is arranged in the electrolytic cell to monitor the electrode potential deviation ΔE in the electrolytic cell in real time, the control module calculates the injection flow rate V (mL / min) of the ammonium thiocyanate solution according to the formula V=0.05×|ΔE|, and the peristaltic pump (6) is connected with the cathode chamber (202) of the electrolytic cell and controlled by the control module to deliver the 0.1mol / L ammonium thiocyanate solution to the cathode chamber (202) of the electrolytic cell.

5. The electrocatalytic ammonia synthesis system of claim 3, wherein, The current density partition control unit (3) is electrically connected with the power module (1), and the current density partition control unit (3) controls the output current of the power module, so that the core area electrode can be loaded with constant 8A / cm 2 The current density, the edge area electrode current is adjusted in real time according to ΔI=0.05×ΔP, wherein ΔP is the fluctuation percentage of input power.

6. The electrocatalytic ammonia synthesis system of claim 3, wherein, When the infrared thermal imager monitors that the electrode temperature difference is greater than 5℃, the circulating cooling system is triggered.

7. A method for electrocatalytic synthesis of ammonia, characterized in that the catalyst according to claim 1 and the system according to claim 3 are used. Comprise the following steps: A, inject electrolyte into the electrolytic cell and put in the catalyst, introduce nitrogen to remove air, heat and maintain at 60℃; B, start the power module, the initial stage power module to the core area electrode load 8 ampere / square centimeter current, edge area electrode load 0.5 ampere / square centimeter electrode, C, when input power fluctuation, the current density partition control unit dynamically adjusts the power module output, so that the edge area electrode current is adjusted in real time according to ΔI=0.05×ΔP, wherein ΔP is the input power fluctuation percentage; D, when the potential sensor detects that the offset exceeds the set value, the control module controls the flow rate of the peristaltic pump according to the following formula, so that the peristaltic pump delivers 0.1 mol / L ammonium thiocyanate solution to the cathode chamber of the electrolytic cell: V=0.05×|ΔE|, wherein the flow rate V is in milliliters per minute, and the potential offset ΔE is in millivolts.

8. The method of claim 7, wherein the electrically catalyzed synthesis of ammonia is characterized by, The electrolyte is a mixed solution of potassium hydroxide and cesium sulfate with an electrical conductivity of ≤1 μS / cm.

9. The method of claim 7, wherein the electrically catalyzed synthesis of ammonia is characterized by, The set value of the offset detected by the potential sensor is ±5 millivolts.

10. The method of claim 7, wherein the method is an electrocatalytic synthesis of ammonia. The nitrogen gas pressure injected into the electrolytic cell is maintained at 0.7 megapascal.

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