Ultra-small iridium nitride nanocrystal as well as preparation method and application thereof

Abstract

The invention discloses an ultra-small iridium nitride nanocrystal and a preparation method and application thereof.The particle size of the iridium nitride nanocrystal is 1-2 nm. The preparation method comprises the steps that iridium salt and a reducing agent are mixed and dissolved in an amide solvent, after the mixture is evenly mixed to form a solution, solvothermal reaction is directly conducted, and after the reaction is finished, washing and drying are conducted to obtain the ultra-small iridium nitride nanocrystal. The amide compound is adopted as the nitriding agent, the ultra-small iridium nitride nanocrystal is prepared through the one-step solvothermal method, compared with a traditional precious metal nitride synthesis method, the reaction condition is milder, the product is pure, the process is simple, convenient and easy to implement, operation is convenient, and the obtained iridium nitride is small in particle size, uniform in size and high in yield. The composite material has excellent electro-catalytic performance on acidic oxygen evolution reaction and has a very wide application prospect.

Description

Technical Field

[0001] The present invention relates to a metal nitride and a preparation method and application thereof, and in particular to an ultra-small iridium nitride and a preparation method and application thereof. Background Art

[0002] As a zero-carbon energy carrier with high energy density, hydrogen is considered to be a promising sustainable energy source. The technology of hydrogen production by water electrolysis has attracted widespread attention. OER is the electrocatalytic decomposition of water (2H2O→O2+4H + +4e - ), plays a central role in water electrolysis hydrogen production technology. However, further reducing the overpotential of the water splitting reaction and exploring efficient metal catalysts for water electrolysis remain major challenges.

[0003] Metal nitrides have the characteristics of high melting point, high conductivity and chemical stability, and have broad application prospects in energy-related fields such as electrocatalysis, batteries, and supercapacitors. In 2004, E. Gregoryanz et al. used the laser-heated diamond anvil cell (LH-DAC) high temperature and high pressure technology at a pressure of 40-50 GPa and a temperature above 2000K to artificially synthesize the first binary precious metal nitride, PtN. x The special electronic structure of its crystals has attracted research interest. However, the difficult-to-achieve high-temperature and high-pressure synthesis conditions make the preparation of noble metal nitrides an extremely difficult task. In addition, literature research shows that: (1) N can penetrate into the metal lattice, and because of its small atomic size, it causes the lattice to expand; (2) depending on the difference in electronegativity, significant electron transfer occurs between the doped N atoms and the adjacent noble metal atoms, which can effectively change the charge distribution of the noble metal atoms, improve the adsorption free energy of the catalytic site, and thus significantly change the electrocatalytic performance of traditional iridium-based catalysts.

[0004] The currently reported methods for preparing iridium nitride are relatively limited. They are usually directly synthesized using physical methods under extreme conditions of ultra-high temperature and high pressure. The preparation conditions are very harsh, the operation process is complex, and the yield is low. Summary of the Invention

[0005] Purpose of the invention: The first purpose of the present invention is to provide a method for preparing ultrasmall iridium nitride nanocrystals with simple process and mild conditions; the second purpose of the present invention is to provide ultrasmall iridium nitride nanocrystals prepared by the method; the third purpose of the present invention is to provide the application of the ultrasmall iridium nitride nanocrystals in the acidic anode oxygen evolution reaction.

[0006] Technical solution: The method for preparing ultrasmall iridium nitride nanocrystals of the present invention comprises the following steps: mixing an iridium salt and a reducing agent and dissolving them in an amide solvent, mixing them uniformly to form a solution, directly performing a solvent thermal reaction, and after the reaction is completed, washing and drying to obtain the ultrasmall iridium nitride nanocrystals.

[0007] Amide compounds act as both nitriding agents and solvents. Amide compounds generate highly chemically active free nitrogen at the reaction temperature. During the Ir crystal formation process, the nitrogen atoms combine with Ir atoms and embed themselves into the interstitial spaces of the unit cell, forming ultrasmall iridium nitride nanocrystals. Preferably, the amide solvent is N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), or N,N-dimethylpropionamide (DMP).

[0008] The reducing agent reacts fully with the iridium salt to reduce the iridium salt. Preferably, the reducing agent is ascorbic acid, formaldehyde, or formic acid. Preferably, the molar ratio of the reducing agent to the iridium salt is 6:1 to 12:1.

[0009] During the solvothermal reaction, highly reactive free nitrogen is formed. During the process of reducing the iridium salt to form Ir metal crystals, the free nitrogen combines with some Ir atoms to form iridium nitride. Preferably, the solvothermal reaction temperature is 150-250°C, and the reaction time is 5-15 hours.

[0010] Preferably, the iridium salt is iridium acetate, iridium chloride or iridium acetylacetonate.

[0011] Preferably, the molar concentration of the iridium salt is 1 to 2 mol L -1 .

[0012] The ultra-small iridium nitride nanocrystals prepared by the preparation method of the present invention have a particle size of 1 to 2 nm.

[0013] The iridium nitride nanocrystals self-assemble into spheres. The smaller particle size of the IrN nanocrystals provides abundant active sites, thereby improving catalytic performance.

[0014] The invention relates to the application of the ultra-small iridium nitride nanocrystals in the acidic anode oxygen evolution reaction.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The present invention adopts an amide compound as a nitriding agent and prepares ultrasmall iridium nitride nanocrystals by a one-step solvent thermal method. The particle size is small and uniform. Compared with the traditional noble metal nitride synthesis method, the reaction conditions are milder, the product is pure, the process is simple and easy, and the operation is convenient; (2) The particle size of the iridium nitride nanocrystals of the present invention is 1 to 2 nm, and they self-assemble to form three-dimensional porous nanospheres with an orderly structure; (3) The ultrasmall iridium nitride nanocrystals of the present invention have excellent electrocatalytic performance for acidic oxygen evolution reaction and have very broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a transmission electron microscope (TEM) image of the ultrasmall iridium nitride nanocrystals prepared in Example 1;

[0017] Figure 2 This is a transmission electron microscope (TEM) image of the iridium nanocrystals prepared in Comparative Example 1;

[0018] Figure 3 X-ray photoelectron energy (XPS) spectra of the ultrasmall iridium nitride nanocrystals prepared in Example 1 and the iridium nanocrystals prepared in Comparative Example 1;

[0019] Figure 4 X-ray diffraction (XRD) patterns of the ultrasmall iridium nitride nanocrystals prepared in Example 1 and the iridium nanocrystals prepared in Comparative Example 1;

[0020] Figure 5 X-ray diffraction (XRD) patterns of ultrasmall iridium nitride nanocrystals prepared using different amide molecules as nitriding agents;

[0021] Figure 6 This is a comparison of the electrocatalytic activities of the ultrasmall iridium nitride nanocrystals prepared in Example 1 and the iridium nanocrystals prepared in Comparative Example 1 in the oxygen evolution reaction in 0.5MH2SO4 solution;

[0022] Figure 7 This is a stability (ADT) test curve of the ultrasmall iridium nitride nanocrystals prepared in Example 1 and the iridium nanocrystals prepared in Comparative Example 1 in 0.5MH2SO4 solution. DETAILED DESCRIPTION

[0023] The technical solution of the present invention will be further described below in conjunction with embodiments.

[0024] Example 1

[0025] The method for preparing ultrasmall iridium nitride nanocrystals of the present invention comprises the following steps:

[0026] 10 mg of iridium acetate and 20 mg of ascorbic acid were added to 10 mL of formamide solution and thoroughly ultrasonically mixed. The mixture was then placed in a reactor and reacted at 250°C for 10 hours. After the reaction, the black product was centrifuged, washed four times with ethanol, and freeze-dried to obtain ultrasmall iridium nitride nanocrystals (IrN).

[0027] Example 2

[0028] The difference from Example 1 is that iridium acetate is replaced by iridium chloride, and the rest of the content is consistent with Example 1.

[0029] Example 3

[0030] The difference from Example 1 is that iridium acetate is replaced by iridium acetylacetonate, and the rest of the contents are consistent with Example 1.

[0031] Example 4

[0032] The difference from Example 1 is that ascorbic acid is replaced by formaldehyde, and the rest of the contents are the same as those in Example 1.

[0033] Example 5

[0034] The difference from Example 1 is that ascorbic acid is replaced by formic acid, and the rest of the contents are the same as those in Example 1.

[0035] Example 6

[0036] The difference from Example 1 is that formamide is replaced by acetamide, and the rest of the contents are consistent with Example 1.

[0037] Example 7

[0038] The difference from Example 1 is that formamide is replaced by propionamide, and the rest of the contents are consistent with Example 1.

[0039] Example 8

[0040] The difference from Example 1 is that the reaction temperature of 250° C. is replaced by a reaction temperature of 150° C., and the rest of the contents are the same as those in Example 1.

[0041] Example 9

[0042] The difference from Example 1 is that the reaction temperature of 250° C. is replaced by a reaction temperature of 200° C., and the rest of the contents are the same as those in Example 1.

[0043] Example 10

[0044] The difference from Example 1 is that the reaction time of 10 h is replaced by a reaction time of 5 h, and the rest of the contents are the same as those in Example 1.

[0045] Example 11

[0046] The difference from Example 1 is that the reaction time of 10 h is replaced by a reaction time of 15 h, and the rest of the contents are the same as those in Example 1.

[0047] Example 12

[0048] The difference from Example 1 is that 20 mg of iridium acetate is used, and the rest of the content is the same as that of Example 1.

[0049] Example 13

[0050] The difference from Example 1 is that 13 mg of iridium acetate is used, and the rest of the content is the same as Example 1.

[0051] Example 14

[0052] The difference from Example 1 is that 10 mg of ascorbic acid is used, and the rest of the contents are the same as those in Example 1.

[0053] Comparative Example 1

[0054] On the basis of Example 1, formamide was replaced by water, and other conditions remained unchanged to obtain iridium nanocrystals (Ir).

[0055] Structural characterization

[0056] (1) The ultra-small IrN nanocrystals prepared in Example 1 and the Ir nanocrystals prepared in Comparative Example 1 were physically characterized and compared using a transmission electron microscope (TEM). Figure 1 and Figure 2 shown.

[0057] from Figure 1 It can be seen that the particle size of the IrN nanocrystals prepared in Example 1 is about 1.5 nm, and the IrN nanocrystals self-assemble into spheres. Figure 2 It can be seen that the particle size of the Ir nanocrystals prepared in Comparative Example 1 is 2.5 nm. The particle size of the IrN nanocrystals prepared in Example 1 is smaller than that of the Ir nanocrystals in Comparative Example 1. The smaller particle size provides abundant active sites and improves the catalytic performance.

[0058] (2) X-ray photoelectron spectroscopy (XPS) and X-ray diffraction were used to compare the physical characterization of the ultra-small IrN nanocrystals prepared in Example 1 and the Ir nanocrystals prepared in Comparative Example 1. The results are as follows: Figure 3 and Figure 4 shown.

[0059] Depend on Figure 3 By comparison, it can be found that Ir-N bonds appear in IrN nanocrystals after nitridation, proving the formation of nitride, while Ir-N bonds do not appear in Ir nanocrystals.

[0060] Depend on Figure 4By comparison, it can be found that compared with Ir nanocrystals, the diffraction peak of IrN nanocrystals is obviously shifted to the left, indicating that N is successfully inserted into the Ir nanocrystals, causing lattice expansion.

[0061] (3) X-ray diffraction test was performed on the iridium nitride nanocrystals prepared by using different amide molecules as nitriding agents in Example 1, Example 6, and Example 7 to obtain XRD spectra. The results are as follows: Figure 5 shown.

[0062] Depend on Figure 5 It can be seen that the selected multiple types of amide molecules DMF, DMA, and DMP can all obtain iridium nitride nanocrystals, proving the universality of preparing iridium nitride through amide molecules.

[0063] Performance Characterization

[0064] (1) Commercial IrO2 was used as a reference catalyst, and the oxygen evolution electrocatalytic activity of the ultrasmall iridium nitride nanocrystals (IrN) prepared in Example 1 and the iridium nanocrystals (Ir) prepared in Comparative Example 1 was tested in 0.5 M H2SO4.

[0065] The test method is: using a standard three-electrode system, Shanghai Chenhua CHI 760e electrochemical analyzer at 25 ° C, with a catalyst-modified glassy carbon electrode (d = 3 mm) as the working electrode, a graphite rod as the auxiliary electrode, and a saturated calomel reference electrode (SCE) as the reference electrode. Figure 6 shown.

[0066] Depend on Figure 6 It can be seen that the catalyst prepared in Example 1 has a high -2 The overpotential at 246 mV is superior to that of commercial IrO2 catalyst (316 mV) and comparative Ir catalyst (279 mV). The IrN nanocatalyst exhibits significantly higher oxygen evolution activity in acidic electrolytes than commercial IrO2, primarily due to the fact that the incorporation of nitrogen optimizes the electronic structure of Ir and enhances its catalytic performance.

[0067] (2) The IrN nanocrystals prepared in Example 1 were subjected to a 10 mA cm -2 The ADT is performed for 10,000 scan cycles, and the results are as follows Figure 7 shown.

[0068] Depend on Figure 7 It can be seen that the oxygen evolution curve of IrN nanocrystals only shows a slight positive shift of 12 mV, and the prepared electrocatalyst has good stability in an acidic environment.

Claims

1. A method for preparing ultra-small iridium nitride nanocrystals, characterized in that: The following steps are involved: The iridium salt and the reducing agent are mixed and dissolved in an amide solvent, and after being evenly mixed to form a solution, a solvent thermal reaction is directly carried out. After the reaction is completed, the ultrasmall iridium nitride nanocrystals are obtained by washing and drying.

2. The method for preparing ultrasmall iridium nitride nanocrystals according to claim 1, wherein The amide solvent is N,N-dimethylformamide, N,N-dimethylacetamide or N,N-dimethylpropionamide.

3. The method for preparing ultrasmall iridium nitride nanocrystals according to claim 1, wherein The solvent thermal reaction temperature is 150-250°C.

4. The method for preparing ultrasmall iridium nitride nanocrystals according to claim 1, wherein The reducing agent is ascorbic acid, formaldehyde or formic acid.

5. The method for preparing ultrasmall iridium nitride nanocrystals according to claim 4, wherein: The molar ratio of the reducing agent to the iridium salt is 6:1 to 12:

1.

6. The method for preparing ultrasmall iridium nitride nanocrystals according to claim 1, wherein: The iridium salt is iridium acetate, iridium chloride or iridium acetylacetonate.

7. The method for preparing ultrasmall iridium nitride nanocrystals according to claim 1, wherein: The molar concentration of the iridium salt is 1 to 2 mol L -1 .

8. An ultra-small iridium nitride nanocrystal prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The particle size of the iridium nitride nanocrystal is 1-2 nm.

9. The ultrasmall iridium nitride nanocrystal according to claim 8, characterized in that The iridium nitride nanocrystals self-assemble into three-dimensional porous nanospheres.

10. Use of the ultrasmall iridium nitride nanocrystals according to claim 8 or 9 in an acidic anode oxygen evolution reaction.

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