A sp&sp 2 Hybrid carbon-supported Ru-N rich in unsaturated coordination centers x / C electrocatalysts, methods of making and using the same

Abstract

The application belongs to the technical field of catalyst materials, and particularly discloses an sp&sp 2 hybrid carbon supported Ru-N x / C electrocatalyst and a preparation method and application thereof. The Ru-N x / C electrocatalyst is prepared by the following steps: dissolving a ruthenium complex in methanol; adding a hydrogen-substituted graphdiyne aerogel to the ruthenium complex solution for soaking, performing vacuum distillation, placing in a joule heating instrument, carbonizing under an argon atmosphere, and cooling to obtain Ru-N x / C. Compared with graphene and other carbon material carriers, the catalyst has abundant sp hybrid carbon and defect sites, enhances the adsorption of nitrogen, and further improves the Ru-N x / C electrocatalytic nitrogen reduction reaction activity. The catalyst has the advantages of adjustable catalytic microenvironment of active sites, strong substrate adsorption and activation capacity, simple synthesis method and good stability, and provides a new material and a preparation method for realizing efficient electrocatalytic nitrogen reduction to synthesize ammonia in an aqueous phase.

Description

Technical Field

[0001] This invention belongs to the field of catalyst material technology, specifically a sp&sp 2 Hybrid carbon immobilized Ru-N rich in unsaturated coordination centers x / C electrocatalysts, their preparation methods, and their application in electrocatalytic ammonia synthesis. Background Technology

[0002] Ammonia is an important chemical with wide applications in chemical engineering, fertilizers, fuels, and energy. However, its industrial production still relies on the traditional Haber-Bosch (HB) process, which consumes large amounts of fossil fuels and emits significant amounts of carbon dioxide. Therefore, developing a new, green, and efficient ammonia synthesis process is imperative. Electrocatalytic nitrogen reduction ammonia synthesis uses green electricity as the driving force and water as the proton source at ambient temperature and pressure to achieve the conversion from nitrogen to ammonia. This method does not use fossil fuels, aligns with the carbon neutrality principle, and is the most promising new ammonia synthesis method to replace the HB process.

[0003] To date, the ammonia yield of electrocatalytic nitrogen reduction synthesis is generally between 10 and 30 μg·h⁻¹. -1 ·mg -1 cat The Faraday efficiency is between 10% and 20%, which is far from industrial application. Designing and constructing efficient and stable electrocatalysts is the key and core to improving the performance of electrocatalytic ammonia synthesis, and is also an essential path to the practical application of the electrocatalytic nitrogen reduction ammonia synthesis process. Currently, among many metal-based catalysts, ruthenium (Ru) is the most promising nitrogen reduction electrocatalyst. However, how to improve its nitrogen reduction activity and effectively suppress the hydrogen evolution side reaction is an urgent problem to be solved. Based on this, we designed and constructed a composite catalyst containing unsaturated coordination centers Ru, namely Ru-N... x It exhibits strong adsorption of N2, effectively activating the N≡N triple bond and inhibiting the hydrogen evolution side reaction. Simultaneously, it contains sp and sp... 2 A novel alkynyl carbon material with hybridized carbon and a highly π-conjugated system, hydrogen-substituted graphdiyne aerogel, was used as a carbon precursor to generate Ru-N x Catalytic active centers are anchored in sites with sp and sp 2 On a hybrid carbon substrate, the aggregation of catalytic active centers is suppressed. Simultaneously, sp and sp 2 The uneven charge distribution on the surface of the hybrid carbon substrate is also beneficial for regulating the electron cloud density of the catalytic active center, generating active sites in the interfacial region that are conducive to the electrocatalytic reduction of nitrogen to ammonia, thereby further improving the catalytic activity.

[0004] Based on the above idea, we selected ruthenium polypyridine complexes with different coordination numbers ([Ru(bpy)2]Cl2 and [Ru(bpy)3]Cl2) and hydrogen-substituted graphdiyne aerogel as precursors, and used joule heating method for carbonization to prepare Ru-N x sp&sp 2 hybridized three-dimensional carbon substrate, and prepared high-efficiency and stable Ru-N x / C composite electrocatalysts, and realized high-efficiency nitrogen reduction to synthesize ammonia at a low potential of-0.1 V (relative to a reversible hydrogen electrode). Ruthenium complexes are various, and ruthenium complexes with different ligands can effectively adjust the type, content and doping of other atoms in N in Ru-N x / C. Therefore, the method has good universality. SUMMARY

[0005] In order to achieve the above purpose, the application provides a preparation method of a high-efficiency Ru-based electrocatalytic nitrogen reduction catalyst which is simple in method and easy to mass-produce, and application of the catalyst in nitrogen reduction to synthesize ammonia. x The hydrogen-substituted graphdiyne aerogel is used as a precursor of a three-dimensional carbon carrier, and a Ru-N x / C composite catalyst with adjustable unsaturated coordination centers is prepared by high-temperature pyrolysis through a joule heating method. A high-efficiency electrocatalytic material preparation method is established, and the application of the material in the field of electrocatalytic nitrogen reduction is researched. x The catalytic activity of the Ru catalytic active center in Ru-N

[0006] The technical scheme of the application is as follows: a sp&sp 2 hybridized carbon-supported Ru-N x / C electrocatalyst, and the preparation method comprises the following steps:

[0007] 1) 1, 3, 5-triaylbenzene and CuCl powder are added into a sample bottle;

[0008] 2) pyridine is added to 1), and the sample bottle is shaken until the solid is dissolved;

[0009] 3) the sample bottle is placed in a constant-temperature water bath for a certain time;

[0010] 4) after the reaction is completed, the sample bottle is sequentially soaked and washed with pyridine, chloroform, ethanol and ultrapure water;

[0011] 5) the hydrogen-substituted graphdiyne aerogel is obtained by freeze-drying;

[0012] 6) A certain amount of ruthenium complex is dissolved in a certain amount of methanol;

[0013] 7) A certain amount of hydrogen-substituted graphdiyne aerogel is added to the solution of step 6) and soaked for a certain time;

[0014] 8) The mixture obtained in step 7) is distilled under reduced pressure to remove methanol while the ruthenium polypyridine complex is uniformly adsorbed on the surface and pores of the hydrogen-substituted graphdiyne aerogel;

[0015] 9) The material obtained in step 8) is placed in a joule heating instrument and carbonized at a specific temperature for a certain time under an argon atmosphere, and then naturally cooled to obtain the product Ru-N x / C.

[0016] The above sp & sp 2 hybrid carbon-supported Ru-N x / C electrocatalyst rich in unsaturated coordination centers, in step 1) and step 2), 1,3,5-triethynylbenzene: CuCl: pyridine is 30 mg: 2-3 mg: 2 mL.

[0017] The above sp & sp 2 hybrid carbon-supported Ru-N x / C electrocatalyst rich in unsaturated coordination centers, in step 3), the reaction temperature of the constant temperature water bath is 60°C, and the reaction time is 72 h.

[0018] The above sp & sp 2 hybrid carbon-supported Ru-N x / C electrocatalyst rich in unsaturated coordination centers, in step 6), the ruthenium complex is dichlorobipyridine ruthenium [Ru(bpy)2]Cl2 or trisbipyridine ruthenium [Ru(bpy)3]Cl2.

[0019] The above sp & sp 2 hybrid carbon-supported Ru-N x / C electrocatalyst rich in unsaturated coordination centers, in step 6), the purity of [Ru(bpy)2]Cl2 is 98%, and the mixing ratio is [Ru(bpy)2]Cl2: methanol = 40 mg: 15-20 mL according to the solid-liquid ratio.

[0020] The above sp & sp 2 hybrid carbon-supported Ru-N x / C electrocatalyst rich in unsaturated coordination centers, in step 7), according to the mass ratio, [Ru(bpy)2]Cl2: hydrogen-substituted graphdiyne = 1:5, and the soaking time is 4-6 h.

[0021] The above sp & sp 2Hybrid carbon supported Ru-N rich in unsaturated coordination centers x / C electrocatalyst, in step 9), the carbonization temperature is 450-600℃, the holding time is 10-30 seconds, and the argon atmosphere.

[0022] The above sp&sp 2 Hybrid carbon supported Ru-N rich in unsaturated coordination centers x Application of the above / C electrocatalyst in electrocatalytic nitrogen reduction.

[0023] The above application, the method is as follows: Ru-N x / C electrocatalytic material as the working electrode, Ag / AgCl electrode as the reference electrode, carbon rod as the counter electrode, Nafion 117 as the proton exchange membrane, and 0.1M Na2SO4 solution saturated with nitrogen as the electrolyte, electrocatalytic nitrogen production of ammonia is carried out in an H-type electrolytic cell.

[0024] The above application, the preparation method of the working electrode is as follows: Ru-N x / C is placed in a centrifuge tube, ultrapure water, ethanol and Nafion solution are added, ultrasonic dispersion is carried out until the mixture is uniform, the dispersion liquid is dropped on the surface of the carbon cloth, and vacuum drying is carried out to obtain the working electrode.

[0025] The beneficial effects of the present application are: a simple and efficient technical method for preparing high-performance Ru-based electrocatalyst (Ru-N x / C) is provided, which can realize efficient electrocatalytic nitrogen reduction synthesis of ammonia, and the synthesis of ammonia efficiency can be comparable to that of single-atom catalyst. The catalytic microenvironment around the Ru catalytic active center, such as the coordination number of Ru, the type and number of nearby heteroatoms, can be adjusted by adjusting the synthesis conditions. Ru-N x / C catalyst activates nitrogen molecules through π-backdonation effect, effectively inhibits the occurrence of hydrogen evolution side reaction, has excellent selectivity and catalytic activity for electrocatalytic nitrogen reduction synthesis of ammonia. In addition, compared with graphene and other carbon materials, the catalyst carrier has abundant sp hybrid carbon and defect sites, which enhances the adsorption of nitrogen, and further improves the Ru-N x / C electrocatalytic nitrogen reduction reaction activity. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a scanning electron micrograph (SEM) of Ru-N x / C.

[0027] Figure 2 and Figure 3 is a transmission electron micrograph (TEM) of Ru-N x / C.

[0028] Figure 4 Ru-N x X-ray photoelectron spectroscopy (XPS) survey spectrum of / C.

[0029] Figure 5 Ru-N x X-ray photoelectron spectroscopy (XPS) high-resolution carbon spectrum of / C.

[0030] Figure 6 Ru-N x Ammonia yield and faradaic efficiency plot of / C for electrocatalytic nitrogen reduction to ammonia reaction. DETAILED DESCRIPTION

[0031] Example 1 A sp&sp 2 Ru-N x / C hybrid catalyst rich in unsaturated coordination centers

[0032] (I) Preparation method, Ru-N x The preparation of / C includes the following steps:

[0033] 1) 30 mg of 1,3,5-tri-alkynylbenzene and 2-3 mg of CuCl powder were added to a sample bottle;

[0034] 2) 2 mL of pyridine was added to 1), and shaken until the solid was dissolved;

[0035] 3) placed in a constant temperature water bath at 60°C for 72h;

[0036] 4) After the reaction was completed, it was sequentially soaked and washed with pyridine, chloroform, ethanol, and ultrapure water for 24h each time;

[0037] 5) freeze-dried to obtain hydrogen-substituted graphdiyne aerogel.

[0038] 6) 40 mg of [Ru(bpy)2]Cl2 was dissolved in 20 mL of methanol;

[0039] 7) 300 mg of self-made hydrogen-substituted graphdiyne aerogel was added to 6), and soaked for 4-6h;

[0040] 8) The methanol in 7) was removed under reduced pressure, and the ruthenium polypyridine complex was uniformly adsorbed in the hydrogen-substituted graphdiyne aerogel;

[0041] 9) The material obtained in step 8) was placed in a joule heating instrument, carbonized at 450°C for 10 seconds under argon atmosphere, and naturally cooled to obtain the product Ru-N x / C.

[0042] (II) Characterization

[0043] Figure 1 Ru-Nx Scanning electron microscope (SEM) image of / C.

[0044] Figure 2 and Figure 3 It is Ru-N x Transmission electron microscopy (TEM) image of / C. Figure 2 This indicates that Ru-N x / C exhibits a two-dimensional nanosheet structure.

[0045] Figure 4 It is Ru-N x The total X-ray photoelectron spectroscopy (XPS) spectrum of / C. Figure 4 This indicates that Ru-N x The compound contains C, N, O, and Ru elements. Ru and N elements originate from the [Ru(bpy)2]Cl2 precursor, while C mainly originates from the hydrogen-substituted graphdiyne aerogel precursor, with some originating from the [Ru(bpy)2]Cl2 precursor. The presence of O is attributed to air adsorption and a small amount of oxygen-containing functional groups generated by alkynyl oxidation. No Cl element was detected in the compound, indicating that Cl was removed during the high-temperature carbonization process.

[0046] Figure 5 It is Ru-N x High-resolution X-ray photoelectron spectra (XPS) of / C in the C1s and Ru 3d regions. Figure 5 This indicates that in Ru-N x / C contains sp 2 There are hybridized C=C bonds and sp-hybridized C≡C bonds. The C=C bonds originate from hydrogen-substituted carbon atoms on the benzene ring of the graphdiyne aerogel, while the C≡C bonds originate from the alkynyl groups of the hydrogen-substituted graphdiyne aerogel. Ru can be divided into elemental Ru and oxidized ruthenium (RuO₂). x ), RuO x The existence of Ru in an intermediate valence state between 0 and +3 after coordination proves that Ru and N are successfully coordinated. Ru-N x The formation of the structure.

[0047] Example 2 Ru-N x Application of / C in electrocatalytic nitrogen reduction

[0048] (I) Preparation of working electrode

[0049] Take 5mg Ru-N x / C powder was mixed with 480 μL ethanol, 500 μL ultrapure water, and 20 μL 5 wt% Nafion solution, and ultrasonically dispersed for 30 min until homogeneous. 30 μL of the dispersion was then evenly dropped onto a 1×1 cm layer of carbon cloth. 2 Dry at 60℃ under vacuum for 12 hours for later use.

[0050] (ii) Ammonia production performance test

[0051] The H-type electrolytic cell was used as the reactor under ambient conditions, and Nafion 117 proton exchange membrane was used to separate the anode and cathode. The electrolyte was 0.1 M Na2SO4 solution, and the volume of the anode and cathode electrolyte was 70 mL. In the three-electrode system, Ru-N x / C was the working electrode, Ag / AgCl electrode was the reference electrode, and carbon rod was the counter electrode. During the experiment, nitrogen was first passed into the electrolyte at a flow rate of 20 mL / min for 30 min to ensure that the N2 in the electrolyte was saturated, and then the electrochemical test was carried out at different potentials for 2 h under the condition of continuous nitrogen flow. The ammonia content in the electrolyte was detected by indigo phenol blue spectrophotometry, and the results are shown in Figure 6 .

[0052] Figure 6 Ru-N x / C in 0.1 M Na2SO4 solution at different potentials. As shown in Figure 6 , the material has the best ammonia synthesis performance at -0.1 V (relative to the reversible hydrogen electrode), and the optimal ammonia production rate is 36.71 μg·h -1 mg -1 cat , and the Faraday efficiency is 33.49%. This ammonia production rate can be comparable to noble metal-based single-atom catalysts. The present application provides a new idea for the design and construction of electrocatalytic nitrogen reduction ammonia synthesis catalysts.

Claims

1. A type of sp&sp 2 Hybrid carbon immobilized Ru-N rich in unsaturated coordination centers x / C electrocatalyst, characterized in that... The preparation method includes the following steps: 1) Add 1,3,5-triynylbenzene and CuCl powder to the sample vial; 2) Add pyridine to 1) and shake until the solid dissolves; 3) Place in a constant temperature water bath and react for a certain period of time; 4) After the reaction is complete, wash the product sequentially with pyridine, chloroform, ethanol, and ultrapure water. 5) Freeze-drying yields hydrogen-substituted graphdiyne aerogel; 6) Dissolve a certain amount of ruthenium dichlorobispyridine [Ru(bpy)2]Cl2 in a certain amount of methanol; 7) Add a certain amount of hydrogen-substituted graphylene aerogel to the solution in step 6) and soak for a certain period of time, according to the mass ratio of [Ru(bpy)2]Cl2: hydrogen-substituted graphylene = 1:5; 8) Distill the mixture obtained in step 7) under reduced pressure to remove methanol while uniformly adsorbing the ruthenium polypyridine complex onto the surface and pores of the hydrogen-substituted graphdiyne aerogel. 9) Place the material obtained in step 8) in a Joule heater and carbonize it at a specific temperature for a certain time under an argon atmosphere, then allow it to cool naturally to obtain the product Ru-N. x / C, the specific carbonization temperature is 450-600 ℃, and the holding time is 10-30 seconds.

2. A sp&sp according to claim 1 2 Hybrid carbon immobilized Ru-N rich in unsaturated coordination centers x / C electrocatalyst, characterized in that: In steps 1) and 2), the ratio of 1,3,5-triynylbenzene:CuCl:pyridine is 30 mg:2-3 mg:2 mL.

3. A sp&sp according to claim 1 2 Hybrid carbon immobilized Ru-N rich in unsaturated coordination centers x / C electrocatalyst, characterized in that: In step 3), the reaction temperature in the constant temperature water bath is 60 ℃ and the reaction time is 72 h.

4. A sp&sp according to claim 1 2 Hybrid carbon immobilized Ru-N rich in unsaturated coordination centers x / C electrocatalyst, characterized in that: In step 6), the purity of [Ru(bpy)2]Cl2 is 98%, and the mixing ratio is [Ru(bpy)2]Cl2:methanol = 40mg:15-20mL.

5. A sp&sp according to claim 4 2 Hybrid carbon immobilized Ru-N rich in unsaturated coordination centers x / C electrocatalyst, characterized in that: In step 7), the soaking time is 4-6 hours.

6. The sp&sp as described in claim 1 2 Hybrid carbon immobilized Ru-N rich in unsaturated coordination centers x Application of / C electrocatalysts in electrocatalytic nitrogen reduction.

7. The application according to claim 6, characterized in that: The method is as follows: Ru-N loaded with carbon cloth x The / C electrocatalytic material was used as the working electrode, the Ag / AgCl electrode as the reference electrode, the carbon rod as the counter electrode, Nafion 117 as the proton exchange membrane, and a nitrogen-saturated 0.1 M Na2SO4 solution as the electrolyte. Electrocatalytic nitrogen to ammonia production was carried out in an H-type electrolytic cell.

8. The application according to claim 7, characterized in that: The working electrode is prepared as follows: Take Ru-N x / C is placed in a centrifuge tube, ultrapure water, ethanol and Nafion solution are added, and ultrasonic dispersion is carried out until the mixture is uniform. The dispersion is then dropped onto the surface of carbon cloth and vacuum dried to obtain the working electrode.

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