Defective single-atom electrocatalysts and applications thereof

Abstract

The present application relates to a kind of single-atom electrocatalyst containing defects and its application, wherein single-atom electrocatalyst containing defects is prepared by the following method: one, zinc organic salt and a transition metal compound are dissolved in deionized water, forming homogeneous solution;Transition metal is selected from one of Fe, Co, Ni, Cu, Zn;Two, dimethylimidazole is added to the homogeneous solution under ultrasonic condition;Three, ammonia solution is added dropwise to the mixed solution, and stirring is carried out at room temperature, to obtain sample;Four, sample is centrifuged, washed several times, vacuum dried, to obtain solid powder;Five, solid powder is placed in closed state and inert gas is introduced, and single-atom electrocatalyst containing defects is obtained by calcination under inert atmosphere by programmed temperature method.The catalyst prepared by the present application does not use Pt, and such non-noble metal catalyst is low in price and rich in raw materials, which is conducive to the widespread use of zinc-air battery, fuel cell and other energy storage and conversion devices.

Description

Technical Field

[0001] This invention relates to electrocatalysts, and more specifically to a defective single-atom electrocatalyst and its applications. Background Technology

[0002] While fossil fuels based on coal, oil, and natural gas bring convenience to humankind, they also cause severe environmental pollution. Therefore, actively seeking clean and pollution-free renewable alternative energy sources remains a crucial means of achieving sustainable development. Electrocatalytic oxygen reduction (OR) plays a vital role in energy storage and conversion, but its slow kinetics necessitate a large overpotential to drive the reaction. Noble metal catalysts (such as Pt / C and RuO2) possess highly efficient OR activity; however, their high cost and poor stability limit their widespread application. Furthermore, noble metal catalysts suffer from sensitivity to methanol and susceptibility to poisoning by trace amounts of CO potentially carried in fuels. Therefore, replacing noble metals with non-noble metals is one of the development directions in the field of new energy materials.

[0003] Transition metal-nitrogen-doped carbon materials have become one of the most promising types of non-noble metal electrocatalysts due to their excellent electrical conductivity, corrosion resistance, and large specific surface area. Electrocatalysis requires suitable electron transfer and adsorption at the catalytic interface. Defects are good catalytic active centers; introducing defects leads to increased atomic disorder, causing charge asymmetry and altering the adsorption strength of reaction intermediates. Therefore, utilizing defect engineering strategies to modify the single-atom coordination environment is of great significance for improving catalyst activity. Summary of the Invention

[0004] One object of the present invention is to provide a defective single-atom electrocatalyst that addresses the problem that the high cost and poor stability of noble metal catalysts limit their widespread application; a second object of the present invention is to provide applications of such defective single-atom electrocatalysts.

[0005] The technical solution adopted by this invention to solve its technical problem is as follows: This defective single-atom electrocatalyst is formed by the self-assembly of non-noble metal ions and the organic ligand dimethylimidazolium to form a zeolite-like imidazolium ester framework material, followed by the introduction of acetate ions and ammonia water, and high-temperature pyrolysis treatment to form a nitrogen-carbon support with abundant carbon defects; the specific preparation method includes the following steps: Step 1: Dissolve an organic salt of zinc and a transition metal compound in deionized water. The molar ratio of transition metal ions to zinc ions is 1:10~30. The solution is ultrasonically vibrated and then stirred to ensure that the metal salt is fully dissolved and a homogeneous solution is formed. The transition metal is selected from one of Fe, Co, Ni, Cu, and Zn. Step 2: Place the homogeneous solution obtained in Step 1 in an ultrasonic bath, add dimethylimidazole to the homogeneous solution under ultrasonic conditions, sonicate for 1-2 hours, stir for 2-4 hours to form a mixed solution; the molar ratio of all metal ions to dimethylimidazole in the mixed solution is 1:4-20. Step 3: Add the ammonia solution dropwise to the mixed solution and stir at room temperature for 3 to 6 hours to obtain the sample. The introduction of ammonia further introduces defects. The volume ratio between the homogeneous solution and the ammonia solution is 3:1 to 5:1. Step 4: Centrifuge the sample obtained in Step 3, wash it several times with deionized water and ethanol, and vacuum dry it at 60-90℃ for 12-24 hours to obtain a solid powder. Step 5: Place the solid powder in a closed state and introduce an inert gas. Under an inert atmosphere, calcine it using a programmed temperature rise method to obtain a single-atom electrocatalyst containing defects. The calcination temperature is 800-1200℃, the calcination time is 1-6 hours, and the heating rate during calcination is 3-10℃ / min. The inert gas used during calcination is 99.9% Ar or N2. During the high-temperature calcination process, Zn atoms volatilize, leaving nitrogen-containing anchoring sites.

[0006] In the above scheme, the molar concentration of metal ions in the aqueous solution of the transition metal compound is 0.002–0.005 mol / L, and the molar concentration of ions in the aqueous solution of the zinc compound is 0.030–0.095 mol / L.

[0007] In the above scheme, the molar ratio of transition metal ions to zinc ions is 1:14-25; the molar ratio of all metal ions to dimethylimidazole in the mixed solution is 1:6-15.

[0008] In the above scheme, the organic salts and transition metal compounds of zinc are their respective acetates.

[0009] In the above scheme, the ultrasonic time in step one is 1 hour and the stirring time is 2 hours; the stirring time in step three is 4 hours; in step three, the mixture is washed 3 times with deionized water and 2 times with ethanol, and then vacuum dried at 80°C for 12 hours.

[0010] The molar ratio of transition metal ions to zinc ions in the above scheme is 1:16-20; the molar ratio of all metal ions to dimethylimidazole in the mixed solution is 1:8-12.

[0011] In the above scheme, the calcination temperature is 900-1000°C, the heating rate during calcination is 3-10°C / min, and the calcination time is 2-4 hours.

[0012] In the above scheme, the heating rate during calcination is 5℃ / min, the calcination time is 3 hours, the inert gas is 99.9% Ar, and after cooling to room temperature, the catalyst is ground for 10-20 minutes to obtain a single-atom electrocatalyst containing defects.

[0013] The defective single-atom catalysts in the above schemes exhibit excellent catalytic oxygen reduction activity under alkaline conditions, with half-wave potentials reaching 0.89–0.97 V.

[0014] The aforementioned defective single-atom electrocatalyst is a defective iron single-atom electrocatalyst. This defective iron single-atom electrocatalyst is used in a zinc-air battery, with Zn as the negative electrode and the defective iron single-atom electrocatalyst as the positive electrode. The electrolyte is a 6 mol / L KOH and 0.2 mol / L zinc acetate solution. The assembled zinc-air battery exhibits a peak power density of 160–220 mW / cm² in zinc-air battery performance tests. -2 . Beneficial effects

[0015] 1. The method for preparing defective iron single-atom electrocatalysts of this invention is simple and efficient, and can also be used to prepare other non-precious metal single-atom catalysts. Furthermore, this invention does not use Pt-based catalysts; these non-precious metal catalysts are inexpensive and abundant, which is beneficial for the widespread use of energy storage and conversion devices such as zinc-air batteries and fuel cells.

[0016] 2. The defective single-atom catalyst described in this invention anchors metal single atoms and optimizes their activity through a unique coordination environment, and exhibits excellent electrocatalytic performance under alkaline conditions without significant loss or deactivation of metal active sites after the reaction. It also has better resistance to methanol poisoning and corrosion resistance than commercial Pt / C.

[0017] 3. Applying the defective single-atom catalyst described in this invention to a zinc-air battery results in an ultra-long cycle life and high energy density, solving the common problems of poor round-trip efficiency and short cycle life in zinc-air batteries, and providing more possibilities for the practical application of zinc-air batteries.

[0018] 4. This invention utilizes the abundant defects in porous carbon derived from leaf-shaped, zeolite-like imidazole ester framework materials (ZIF-A) as anchoring sites to capture metal atoms and prevent their aggregation. Simultaneously, local structural distortion and electron redistribution can effectively regulate the electronic structure of the metal active center, improving the activity and stability of the electrocatalyst and preparing highly active and durable iron single-atom electrocatalysts. Attached Figure Description

[0019] Figure 1The XRD pattern of the single-atom catalyst prepared according to Example 1 of the present invention; Figure 2 The image shows the SEM pattern of the single-atom catalyst prepared according to Example 1 of the present invention. Figure 3 The TEM image of the single-atom catalyst prepared according to Example 1 of the present invention; Figure 4 The X-ray near-edge absorption structure spectrum of the single-atom catalyst prepared according to Example 1 of the present invention; Figure 5 The linear sweep voltammetry curves of the catalyst prepared in Example 1 and the control sample in 0.1 M KOH are shown.

[0020] Figure 6 The polarization curves and power density curves of zinc-air batteries using the catalyst prepared in Example 1 and the comparative sample Pt / C as the positive electrode are shown. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings: This defective single-atom electrocatalyst consists of isolated, dispersed metallic Fe single atoms anchored on a nitrogen-doped carbon support derived from ZIFs (zeolite imidazolium ester frameworks). The catalyst is formed by the self-assembly of a non-noble metal and an organic salt of Zn with organic ligands to create a zeolite imidazolium ester-like framework. The introduction of acetate and ammonia during high-temperature carbonization significantly increases the carbon defects in the catalyst, providing more effective catalytic active sites. Simultaneously, its porous structure provides a high specific surface area, which is beneficial for mass transfer and improves the electrocatalytic oxygen reduction activity of the air cathode. This preparation method yields readily available and universally applicable materials, and the resulting catalyst material possesses a unique spatial structure and confinement effect, showing great promise for applications in energy storage. Example

[0022] This defective iron single-atom electrocatalyst was prepared by the following method: 1. Dissolve the solid powders of Zn(OAc)₂ zinc acetate (1.9 mmol) and Fe(OAc)₂ ferric acetate (0.1 mmol) in 40 mL of deionized water to form a homogeneous solution.

[0023] 2. Add 24 mmol of 2-methylimidazole to the above mixed solution and sonicate for 1 hour.

[0024] 3. In a fume hood, add 10 ml of ammonia solution dropwise to the mixed solution and stir at room temperature for 4 hours.

[0025] 4. Centrifuge the obtained sample, wash it several times with deionized water and ethanol, and dry it in a vacuum drying oven at 80 °C for 12 hours.

[0026] 5. The synthesized precursor was carbonized in a tube furnace at 950 °C for 3 h under an argon atmosphere, with a heating rate of 5 °C / min. The sample was then collected after grinding.

[0027] VI. Using Zn as the negative electrode and the prepared catalyst as the positive electrode, and the electrolyte being a 6 mol / L KOH and a 0.2 mol / L zinc acetate solution, a zinc-air battery is assembled.

[0028] The catalysts obtained in the above examples were subjected to a series of structural characterizations to verify their structures.

[0029] like Figure 1 The XRD pattern of the catalyst in Example 1 is shown. The figure shows two carbon diffraction peaks at around 24.0° and 44.0°, which correspond to the (002) and (101) crystal planes of graphitic carbon, respectively. No other metal characteristic diffraction peaks are present.

[0030] like Figure 2 The image shown is an SEM image of the catalyst from Example 1, demonstrating that the catalyst obtained in Example 1 is leaf-shaped.

[0031] like Figure 3 The image shown is a TEM image of the catalyst of Example 1, which shows that the catalyst obtained in Example 1 has a leaf-like morphology, a size of 1-2 μm, and is porous.

[0032] like Figure 4 The image shows the Fe K-edge XANES pattern of the catalyst in Example 1, revealing the valence state of a single Fe atom.

[0033] Preparation Example 2: The only difference between this embodiment and Embodiment 1 is that in this embodiment, the amount of Zn(OAc)2 added in step one is 1.875 mmol and the amount of Fe(OAc)2 added is 0.125 mmol.

[0034] Preparation Example 3: The only difference between this embodiment and Embodiment 1 is that in this embodiment, 80 mL of deionized water is added in step one.

[0035] Preparation Example 4: The only difference between this embodiment and Example 1 is that in this embodiment, the amount of 2-methylimidazole added in step two is 16 mmol.

[0036] Preparation Example 5: The only difference between this embodiment and Embodiment 1 is that in this embodiment, dimethylimidazole is dissolved in 40 mL of deionized water to form a solution before being mixed with the solution prepared in step one.

[0037] Preparation Example 6: The difference between this embodiment and Embodiment 1 is that in this embodiment, 8 mL of ammonia solution is added in step three.

[0038] Preparation Example 7: The only difference between this embodiment and Embodiment 1 is that in this embodiment, the stirring time in step three is 6 hours at room temperature.

[0039] Preparation Example 8: The only difference between this embodiment and Embodiment 1 is that in this embodiment, the vacuum drying time in step four is 24 hours.

[0040] Preparation Example 9: The only difference between this embodiment and Embodiment 1 is that in this embodiment, carbonization is carried out in a tube furnace at 950 °C for 2 h in step five, with a heating rate of 5 °C / min.

[0041] Preparation Example 10: The only difference between this embodiment and Embodiment 1 is that in this embodiment, carbonization is carried out in a tube furnace at 1000 °C for 2 h in step five, with a heating rate of 5 °C / min.

[0042] Comparative Example 1: The only difference between this comparative example and Example 1 is that ammonia solution is no longer added in step three of the comparative example.

[0043] Comparative Example 2: The only difference between this comparative example and Example 1 is that ferric acetate is not added in step one of the comparative example.

[0044] Comparative Example 3: The difference between this embodiment and Embodiment 1 is that ferric acetate is not added in step one of the comparative example, and ammonia solution is not added in step three.

[0045] Comparative Example 4: In this example, 5 mg of a commercial Pt / C catalyst (Pt content of 20%) was ultrasonically dispersed for 30 min to obtain a solution.

[0046] To test the catalytic performance of single-atom electrocatalysts, this application also provides application examples and catalyst performance tests.

[0047] Catalyst-catalyzed oxygen reduction reaction and zinc-air battery performance evaluation: 5 mg of catalyst was added to a solution containing 40 μL of 5% Nafion and 960 μL of isopropanol, and the mixture was ultrasonically dispersed to obtain a solution. 11 μL of this solution was drop-coated onto a rotating disk electrode, with a catalyst loading of 0.2 mg / cm³. -2After air drying, a thin-film electrode was obtained; a three-electrode system was formed with an Ag / AgCl electrode as the reference electrode and a Pt wire as the counter electrode. Linear voltammetry was performed at room temperature in an oxygen-saturated 0.1 mol / L KOH solution using an electrochemical workstation, with a scan rate of 10 mV / s and an electrode rotation speed of 1600 r.

[0048] Figure 5 The LSV curves of the catalyst in Example 1 and other comparative samples were measured under alkaline conditions. Under alkaline conditions, the oxygen reduction onset potential was 1.05 V and the half-wave potential was 0.95 V. The measured onset potential and half-wave potential of the oxygen reduction reaction were significantly better than those of commercial Pt / C noble metal catalysts, and the cycle performance was also more stable than that of commercial Pt / C, indicating that it has excellent oxygen reduction catalytic activity. Therefore, the single-atom catalyst prepared in this invention is suitable for use in zinc-air batteries and fuel cell systems.

[0049] Using Zn as the negative electrode and Example 1 as the positive electrode, a zinc-air battery was assembled with a 6 mol / L KOH and 0.2 mol / L zinc acetate solution as the electrolyte.

[0050] like Figure 6 The figures show the polarization curves and power density graphs of the catalyst in Example 1 and Comparative Example 1 with commercial Pt / C. As can be seen from the graphs, the power density of the prepared defective single-atom catalysts is far superior to that of commercial Pt / C, and they have excellent development prospects.

[0051] Non-precious metal ions and the organic ligand dimethylimidazole self-assemble to form a zeolite-like imidazole ester framework material. By introducing acetate ions and ammonia water, a nitrogen-carbon support with abundant carbon defects can be formed under high-temperature pyrolysis treatment, which can be used to provide anchoring sites to capture metal atoms, resulting in metal active centers with high exposure and high loading.

[0052] The non-precious metal catalyst prepared by this invention has electrocatalytic oxygen reduction performance comparable to commercial Pt / C in alkaline electrolyte. When applied to zinc-air batteries, its peak power density surpasses that of most non-precious metal catalysts. Furthermore, this catalyst exhibits excellent charge-discharge cycle stability in zinc-air batteries, and its performance remains stable even after more than 600 hours.

Claims

1. A single-atom electrocatalyst containing defects, characterized in that: This defective single-atom electrocatalyst is formed by the self-assembly of non-noble metal ions and the organic ligand dimethylimidazolium to form a zeolite-like imidazolium ester framework material, followed by the introduction of acetate ions and ammonia water, and high-temperature pyrolysis to form a nitrogen-carbon support rich in carbon defects. The specific preparation method includes the following steps: Step 1: Dissolve the organic salt of zinc and a transition metal compound in deionized water. The molar ratio of transition metal ions to zinc ions is 1:10~30. The solution is ultrasonically vibrated and then stirred to fully dissolve the metal salt and form a homogeneous solution. The transition metal is selected from one of Fe, Co, Ni, and Cu. Both the organic salt of zinc and the transition metal compound are their respective acetates. Step 2: Place the homogeneous solution obtained in Step 1 in an ultrasonic bath, add dimethylimidazole to the homogeneous solution under ultrasonic conditions, sonicate for 1-2 hours, stir for 2-4 hours to form a mixed solution; the molar ratio of all metal ions to dimethylimidazole in the mixed solution is 1:4-20. Step 3: Add the ammonia solution dropwise to the mixed solution and stir at room temperature for 3 to 6 hours to obtain the sample. The introduction of ammonia further introduces defects. The volume ratio between the homogeneous solution and the ammonia solution is 3:1 to 5:

1. Step 4: Centrifuge the sample obtained in Step 3, wash it several times with deionized water and ethanol, and vacuum dry it at 60-90℃ for 12-24 hours to obtain a solid powder. Step 5: Place the solid powder in a closed state and introduce an inert gas. Under an inert atmosphere, calcine it using a programmed temperature rise method to obtain a single-atom electrocatalyst containing defects. The calcination temperature is 800-1200℃, the calcination time is 1-6 hours, and the heating rate during calcination is 3-10℃ / min. The inert gas used during calcination is 99.9% Ar or N2. During the high-temperature calcination process, Zn atoms volatilize, leaving nitrogen-containing anchoring sites.

2. The defective single-atom electrocatalyst according to claim 1, characterized in that: The molar concentration of metal ions in the aqueous solution of the transition metal compound is 0.002–0.005 mol / L, and the molar concentration of ions in the aqueous solution of the organic salt of zinc is 0.030–0.095 mol / L.

3. The defective single-atom electrocatalyst according to claim 2, characterized in that: The molar ratio of the transition metal ions to zinc ions is 1:14–25; the molar ratio of all metal ions to dimethylimidazole in the mixed solution is 1:6–15.

4. The defective single-atom electrocatalyst according to claim 3, characterized in that: In step one, the ultrasonic time is 1 hour and the stirring time is 2 hours; in step three, the stirring time is 4 hours; in step three, the mixture is washed 3 times with deionized water and 2 times with ethanol, and then vacuum dried at 80°C for 12 hours.

5. The defective single-atom electrocatalyst according to claim 4, characterized in that: The molar ratio of the transition metal ions to zinc ions is 1:16-20; the molar ratio of all metal ions to dimethylimidazole in the mixed solution is 1:8-12.

6. The defective single-atom electrocatalyst according to claim 5, characterized in that: The calcination temperature is 900–1000°C, the heating rate during calcination is 3–10°C / min, and the calcination time is 2–4 hours.

7. The defective single-atom electrocatalyst according to claim 6, characterized in that: The calcination process involves a heating rate of 5°C / min, a calcination time of 3 hours, an inert gas of 99.9% Ar, cooling to room temperature, and grinding for 10-20 minutes to obtain a single-atom electrocatalyst containing defects.

8. The defective single-atom electrocatalyst according to claim 7, characterized in that: The defective single-atom catalyst exhibits excellent catalytic oxygen reduction activity under alkaline conditions, with a half-wave potential of 0.89–0.97 V.

9. The application of a defective single-atom electrocatalyst according to any one of claims 1 to 8, characterized in that: The defective single-atom electrocatalyst is a defective iron single-atom electrocatalyst. This defective iron single-atom electrocatalyst is used in a zinc-air battery, with Zn as the negative electrode and the defective iron single-atom electrocatalyst as the positive electrode. The electrolyte is a 6 mol / L KOH and 0.2 mol / L zinc acetate solution. The assembled zinc-air battery exhibits a peak power density of 160–220 mW / cm² in performance tests. -2 .

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