Application of molybdenum disulfide-based high-load monatomic iron catalytic electrode in preparation of ammonia by reducing nitrate through electro-catalysis

Abstract

The invention relates to application of a molybdenum disulfide-based high-load monatomic iron catalytic electrode in preparation of ammonia by electro-catalysis nitrate reduction, and belongs to the technical field of high-load monatomic catalysis. The molybdenum disulfide-based high-load monatomic iron catalytic electrode is used as a working electrode to be assembled to obtain a double-chamber three-electrode system; adding an aqueous solution containing nitrate and OH <-> into the anode chamber and the cathode chamber; and applying potential to the cathode to carry out electro-catalysis nitrate reaction. According to the catalytic electrode, the catalyst is loaded on the conductive substrate in an in-situ growth mode, no binder exists, catalyst stacking caused by coating is avoided, and active sites are fully exposed. The monatomic loading capacity of the catalytic electrode reaches 16.45 wt%, and monatomic iron is stably and uniformly dispersed in the molybdenum disulfide nanoflowers in a Fe-S coordination form. The catalytic electrode has excellent selectivity for preparing ammonia by electrocatalytic reduction of nitrate, the maximum Faraday efficiency is 99%, the maximum ammonia yield is 28.59 mg h <-1 > cm <-2 >, and the catalytic electrode has good cycle stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-loading single-atom catalysis, and relates to the application of a molybdenum disulfide-based high-loading single-atom iron catalytic electrode in an electrocatalytic reaction. Background Art

[0002] Ammonia is an important raw material for chemical processes such as fertilizers, and is regarded as the most promising new generation of hydrogen-rich fuel. The traditional Haber-Bosch ammonia synthesis process uses hydrogen and nitrogen as raw materials and reacts under high temperature and high pressure conditions, which is characterized by high cost and high energy consumption. Therefore, in recent years, the electrocatalytic ammonia synthesis process driven by "green electricity" at normal temperature and pressure has received extensive attention. Nitrate wastewater generated by industries such as fertilizers, explosives, metallurgy, and electroplating endangers human health and the ecological environment. Electrochemical reduction of nitrate to ammonia can not only alleviate environmental pollution but also "turn waste into treasure".

[0003] Single-atom catalysts disperse metal elements in the form of single atoms on the substrate catalyst, with an atomic utilization rate of nearly 100%, and are often used in electrocatalysis, photocatalysis, etc. However, during the preparation process, to prevent metal atoms from agglomerating, the single-atom loading is usually very low (<1 wt%), and the number of active sites is limited, resulting in poor selectivity and catalytic activity. At the same time, most single-atom catalysts use carbon nitride materials as the substrate, and the preparation process requires high-energy-consuming and complicated processes such as pickling and calcination, with a high preparation cost. In addition, in an electrocatalytic reaction, the catalyst needs to be loaded on a conductive substrate to form an electrode and a circuit. However, most existing single-atom catalysts are in powder form and need to be coated on the substrate through a Nafion solution, making the catalyst unable to be evenly distributed and covering some active sites. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an application of a molybdenum disulfide-based high-loading single-atom iron catalytic electrode synthesized in situ by one-step hydrothermal method with a carbon material as the substrate in the electrocatalytic reduction of nitrate to ammonia with high activity and high selectivity.

[0005] The technical solution of the present invention is as follows:

[0006] An application of a molybdenum disulfide-based high-loading single-atom iron catalytic electrode in the electrocatalytic reduction of nitrate to ammonia is as follows:

[0007] Step 1: Use the molybdenum disulfide-based high-loading single-atom iron catalytic electrode as the working electrode to assemble a two-chamber three-electrode system;

[0008] Furthermore, in the two-chamber three-electrode system, the counter electrode uses a Pt sheet or a graphite rod; the reference electrode uses Ag / AgCl or Hg / HgO; the cathode and anode chambers are separated by a proton exchange membrane.

[0009] Furthermore, the proton exchange membrane is preferably Nafion 117.

[0010] Step 2: Add an aqueous solution containing nitrate and OH - to both the anodic chamber and the cathodic chamber;

[0011] Further, the aqueous solution needs to be deoxygenated with an inert gas in advance.

[0012] Further, OH - is provided by KOH or NaOH, and the concentration of OH - in the aqueous solution is 1M.

[0013] Further, the concentration of NO 3 - in the aqueous solution is 0.1 - 1M.

[0014] Step 3: Apply a potential of -0.3 to -0.9V vs. RHE at the cathode to carry out the electrocatalytic nitrate reaction.

[0015] Further, when electrocatalytically reducing nitrate to ammonia, the maximum ammonia Faraday efficiency is 99%, and the maximum ammonia production rate is 28.59 mg h -1 cm -2 .

[0016] Further, the preparation method of the molybdenum disulfide-based high-loading single-atom iron catalytic electrode includes the following steps:

[0017] Step 1: After cleaning the carbon material substrate, immerse it in an aqueous solution containing Mo source and S source, take it out after a period of time and perform vacuum drying to obtain a seed layer carbon material substrate;

[0018] Step 2: Hydrothermally react the seed layer carbon material substrate with an aqueous solution containing Mo source, S source and iron salt;

[0019] Step 3: Wait for natural cooling to room temperature, take out the carbon substrate with molybdenum disulfide doped with high-loading single-atom iron grown on it, rinse it repeatedly with deionized water, and dry it thoroughly in a vacuum drying oven to obtain a molybdenum disulfide-based high-loading single-atom iron catalytic electrode.

[0020] Further, in Step 1, the carbon material substrate is carbon fiber cloth, carbon paper or carbon felt, preferably carbon fiber cloth.

[0021] Further, in Step 1, the S source is derived from thiourea or urea, preferably thiourea; the Mo source is derived from sodium molybdate or ammonium molybdate, preferably sodium molybdate dihydrate; the molar concentration of S in the solution is 0.01M - 0.03M, which is 2 - 3 times that of Mo, preferably S: 0.02M, Mo: 0.01M.

[0022] Further, in Step 1, the soaking time is 0.5h - 2h, preferably 1h.

[0023] Furthermore, in step 2, the S source is derived from thiourea or urea, preferably thiourea; the Mo source is derived from sodium molybdate or ammonium molybdate, preferably sodium molybdate dihydrate; the iron salt is derived from ferric sulfate or ferric nitrate, preferably ferric sulfate. The molar concentration ratio of Fe to Mo is 0.25 - 0.5:1, and the molar concentration of S is 0.18M - 0.25M, which is 1.5 - 2.4 times the sum of the molar concentrations of Fe and Mo. Preferably, Fe: 0.047M, Mo: 0.094M, S: 0.23M.

[0024] Furthermore, the hydrothermal reaction temperature is 180 - 220 °C, preferably 200 °C; the hydrothermal reaction time is 18 - 24 h, preferably 20 h.

[0025] The single-atom iron loading of the molybdenum disulfide-based high-loading single-atom iron catalytic electrode prepared by the above method reaches 16.45 wt%.

[0026] The benefits and effects of the present invention are as follows:

[0027] 1. For the catalyst provided by the present invention, the single-atom loading can reach 16.45 wt% (measured by icp), and the single-atom iron is stably and uniformly dispersed in the molybdenum disulfide nanoflowers in the form of Fe-S coordination;

[0028] 2. The present invention adopts an in-situ growth method to load the catalyst on the surface of the conductive substrate without a binder, avoiding the stacking of the catalyst during coating and fully exposing the active sites;

[0029] 3. The high-loading single-atom catalytic electrode provided by the present invention is prepared by a one-step hydrothermal method, with high repeatability, simple steps, short time consumption, and simple raw materials required, which is conducive to industrial application;

[0030] 4. The molybdenum disulfide-based high-loading single-atom iron catalytic electrode provided by the present invention has good cycle stability;

[0031] 5. The molybdenum disulfide-based high-loading single-atom iron catalytic electrode provided by the present invention has excellent electrocatalytic reduction selectivity for nitrate to ammonia, with a maximum Faraday efficiency of 99% and a maximum ammonia production rate of 28.59 mg h -1 cm -2 .

[0032] 6. The molybdenum disulfide-based high-loading single-atom iron catalytic electrode provided by the present invention can also be extended to applications in hydrogen evolution, CO 2 reduction, and photocatalysis and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1These are the results of high-resolution transmission electron microscopy (HRTEM) and elemental mapping (EDS mapping) of a molybdenum disulfide-based high-loading single-atom iron catalyst.

[0034] Figure 2 This is the Fourier transform extended X-ray absorption fine structure spectrum (FT-EXAFS) of iron in a molybdenum disulfide-based high-loading single-atom iron catalyst.

[0035] Figure 3 These are the scanning electron microscopy (SEM) results of a molybdenum disulfide-based high-loading single-atom iron catalytic electrode.

[0036] Figure 4 These are the ammonia production yields and Faraday efficiencies of a molybdenum disulfide-based high-loading single-atom iron catalytic electrode for electrocatalytic reduction of nitrates at different concentrations.

[0037] Figure 5 These are the ammonia production yields and Faraday efficiencies of a molybdenum disulfide-based high-loading single-atom iron catalytic electrode for electrocatalytic reduction of nitrates at different potentials.

[0038] Figure 6 This is the durability test of a molybdenum disulfide-based high-loading single-atom iron catalytic electrode for electrocatalytic reduction of nitrates to ammonia. Detailed implementation manners

[0039] The present invention will be further described in detail below in conjunction with the detailed implementation manners. The examples given are only for clarifying the present invention and not for limiting the scope of the present invention.

[0040] Example 1

[0041] (1) Preparation of a molybdenum disulfide-based high-loading single-atom iron catalytic electrode, the specific steps are as follows:

[0042] Step 1: Cut a carbon fiber cloth to 6×10 cm 2 Soak it in absolute ethanol for 24 h, then take it out, rinse it with deionized water to remove impurities such as surface oil stains and dust, and obtain a clean carbon fiber cloth;

[0043] Step 2: Immerse the clean carbon fiber cloth in a 500 mL aqueous solution containing 1.2 g of sodium molybdate dihydrate and 0.76 g of thiourea. After 1 h, take it out and place it in a vacuum drying oven at 60 °C for 6 h to obtain a carbon fiber cloth with a seed layer;

[0044] Step 3: Stick the carbon fiber cloth with a seed layer to the inner wall of a polytetrafluoroethylene liner, and add a solution containing 1.36 g of sodium molybdate dihydrate, 1.06 g of thiourea, and 0.56 g of iron sulfate (Fe 2 (SO 4 ) 3 ·xH 2After adding 60 mL of aqueous solution of (O), it was placed in a stainless steel autoclave and hydrothermally reacted at 200 °C for 20 h;

[0045] Step 4: Wait for the autoclave to cool naturally to room temperature, take out the carbon fiber cloth with molybdenum disulfide doped with high-loading single-atom iron grown on it, rinse it repeatedly with deionized water, and dry it at 60 °C for 6 h in a vacuum drying oven to obtain a molybdenum disulfide-based high-loading single-atom iron catalytic electrode.

[0046] HRTEM image and EDS mapping of the iron-doped molybdenum disulfide catalyst ( Figure 1 ), verifying the existence and uniform distribution of single-atom iron, and the EXAFS Fourier transform spectrum of iron ( Figure 2 ) verifying that the single atoms are anchored by Fe-S coordination. The SEM image of the molybdenum disulfide-based high-loading single-atom iron catalytic electrode ( Figure 3 ) verifies that the iron-doped nano-flower-like molybdenum disulfide monolayer grows on the surface of the carbon fiber cloth, fully exposing the active sites.

[0047] (2) Application of the molybdenum disulfide-based high-loading single-atom iron catalytic electrode in electrocatalytic reduction of nitrate to ammonia at different nitrate concentrations, the specific steps are as follows:

[0048] Step 1: In a two-compartment three-electrode system, cut the molybdenum disulfide-based high-loading single-atom iron catalytic electrode to make the effective area 1×1 cm 2 , as the working electrode. A 1×1 cm 2 Pt sheet is used as the counter electrode, and Ag / AgCl is used as the reference electrode. The cathode and anode compartments are separated by Nafion 117.

[0049] Step 2: Add 1 M KOH aqueous solutions containing 0.1 M, 0.3 M, 0.6 M, and 1 M KNO 3 that have been deoxygenated with Ar gas for 30 min to both the anode and the cathode.

[0050] Step 3: Apply a potential of -0.73 V vs. RHE at the cathode through an electrochemical workstation CHI660 to carry out the electrocatalytic nitrate reaction for 1 h, record the current density, calculate the Faraday efficiency, and collect the solution after the reaction to analyze the products.

[0051] As Figure 4 shown, the electrode of the present invention has an ammonia Faraday efficiency of >90% at KNO 3 concentrations of 0.1 M - 1 M, with good selectivity and high ammonia yield.

[0052] Example 2

[0053] (1) Preparation of the molybdenum disulfide-based high-loading single-atom iron catalytic electrode is the same as that in Example 1.

[0054] (2) Molybdenum disulfide-based high-loading single-atom iron catalytic electrode, application in electrocatalytic nitrate reduction to ammonia at different cathode potentials, the specific steps are as follows:

[0055] Step 1: The same as Example 1.

[0056] Step 2: Add an aqueous solution containing 0.6 M KNO 3 and 1 M KOH that has been deoxygenated with Ar gas for 30 min to both the anode and the cathode.

[0057] Step 3: Apply a potential of -0.33 V to -0.83 V (vs. RHE) at the cathode through an electrochemical workstation CHI660, conduct the electrocatalytic nitrate reaction for 1 h, record the current density, calculate the Faraday efficiency, and collect the solution after the reaction to analyze the products.

[0058] As Figure 5 shown, the electrodes of the present invention have an ammonia Faraday efficiency of >90% at -0.33 V to -0.83 V (vs. RHE), with good selectivity and a high ammonia yield.

[0059] Example 3

[0060] (1) Preparation of the molybdenum disulfide-based high-loading single-atom iron catalytic electrode, the same as Example 1.

[0061] (2) Durability test of the molybdenum disulfide-based high-loading single-atom iron catalytic electrode for electrocatalytic nitrate reduction to ammonia, the specific steps are as follows:

[0062] Step 1: The same as Example 1.

[0063] Step 2: The same as Example 2.

[0064] Step 3: Apply a potential of -0.73 V (vs. RHE) at the cathode through an electrochemical workstation CHI660, conduct the electrocatalytic nitrate reaction for 1 h, do not change the electrode but replace the fresh electrolyte, repeat the reaction 10 times, record the current density, calculate the Faraday efficiency, and collect the solution after the reaction to analyze the products.

[0065] As Figure 6 shown, the electrodes of the present invention have good durability.

[0066] The above only describes the best embodiments of the present invention, but it should not be construed as a limitation of the claims. The present invention is not limited to the above embodiments, and its specific structure allows for variations. Any variations made within the protection scope of the independent claims of the present invention are within the protection scope of the present invention.

Claims

1. Application of a molybdenum disulfide-based high-load single-atom iron catalytic electrode in electrocatalytic nitrate reduction to produce ammonia, characterized in that: The details are as follows: Step 1: Using a MoS2-based high-load single-atom iron catalytic electrode as a working electrode, a two-chamber three-electrode system is assembled; Step 2: Add nitrate and OH to both the anode and cathode chambers. - Aqueous solution of Step 3: Apply a potential to the cathode to perform an electrocatalytic nitrate reaction.

2. The use of a molybdenum disulfide-based high-load single-atom iron catalytic electrode in electrocatalytic nitrate reduction to produce ammonia according to claim 1, characterized in that: In step 1, in a double-chamber three-electrode system, a Pt sheet or a graphite rod is used as the counter electrode; Ag / AgCl or Hg / HgO is used as the reference electrode; and the cathode and anode chambers are separated by a proton exchange membrane.

3. The use of a molybdenum disulfide-based high-load single-atom iron catalytic electrode in electrocatalytic nitrate reduction to produce ammonia according to claim 1, characterized in that: In step 2, OH - It is provided by KOH or NaOH.

4. The use of a molybdenum disulfide-based high-load single-atom iron catalytic electrode in electrocatalytic nitrate reduction to produce ammonia according to claim 1, characterized in that: In step 2, OH in aqueous solution - The concentration of NO3 in aqueous solution is 1M; - The concentration is 0.1-1M.

5. The use of a molybdenum disulfide-based high-load single-atom iron catalytic electrode in electrocatalytic nitrate reduction to produce ammonia according to claim 1, characterized in that: In step 2, the aqueous solution needs to be deoxygenated by inert gas in advance; in step 3, the potential is -0.3--0.9 V vs. RHE.

6. The use of a molybdenum disulfide-based high-load single-atom iron catalytic electrode in electrocatalytic nitrate reduction to produce ammonia according to claim 1, characterized in that: When electrocatalytically reducing nitrate to ammonia, the maximum ammonia Faraday efficiency is 99% and the maximum ammonia yield is 28.59 mg h -1 cm -2 .

7. The use of a molybdenum disulfide-based high-load single-atom iron catalytic electrode in electrocatalytic nitrate reduction to produce ammonia according to claim 1, characterized in that: The method for preparing the molybdenum disulfide-based high-load single-atom iron catalytic electrode comprises the following steps: Step 1): After cleaning the carbon material substrate, immerse it in an aqueous solution containing a Mo source and a S source, take it out after a period of time and vacuum dry it to obtain a seed layer carbon material substrate; Step 2): hydrothermally reacting the seed layer carbon material substrate with an aqueous solution containing a Mo source, a S source and an iron salt; Step 3): After cooling naturally to room temperature, take out the carbon substrate on which the molybdenum disulfide doped with high-loading single-atom iron is grown, repeatedly rinse with deionized water, and fully dry in a vacuum drying oven to obtain a molybdenum disulfide-based high-loading single-atom iron catalytic electrode.

8. The use of a molybdenum disulfide-based high-load single-atom iron catalytic electrode in electrocatalytic nitrate reduction to produce ammonia according to claim 7, characterized in that: The prepared molybdenum disulfide-based high-loading single-atom iron catalytic electrode has a single-atom iron loading of 16.45wt%.

9. The use of a molybdenum disulfide-based high-load single-atom iron catalytic electrode in electrocatalytic nitrate reduction to produce ammonia according to claim 7, characterized in that: In step 1), the carbon material substrate is carbon fiber cloth, carbon paper or carbon felt; the S source comes from thiourea or urea; the Mo source comes from sodium molybdate or ammonium molybdate; the molar concentration of S in the solution is 0.01M-0.03M, which is 2-3 times that of Mo; the immersion time is 0.5h-2h; in step 2), the S source comes from thiourea or urea; the Mo source comes from sodium molybdate or ammonium molybdate; the iron salt comes from ferric sulfate or ferric nitrate; the molar concentration ratio of Fe and Mo is 0.25-0.5:1, and the molar concentration of S is 0.18M-0.25M, which is 1.5-2.4 times the sum of the molar concentrations of Fe and Mo; the hydrothermal reaction temperature is 180-220°C; and the hydrothermal reaction time is 18-24h.

10. The use of a molybdenum disulfide-based high-load single-atom iron catalytic electrode in electrocatalytic nitrate reduction to produce ammonia according to claim 7, characterized in that: In step 1), the carbon material substrate is carbon fiber cloth; the S source comes from thiourea; the Mo source comes from sodium molybdate dihydrate; the molar concentration of S in the solution is 0.02M, which is twice that of Mo; the immersion time is 1h; in step 2), the S source comes from thiourea; the Mo source comes from sodium molybdate dihydrate; the iron salt comes from ferric sulfate; the molar concentrations of each substance are Fe: 0.047M, Mo: 0.094M, S: 0.23M; the hydrothermal reaction temperature is 200°C; and the hydrothermal reaction time is 20h.

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