Preparation method of Fe single atom and Cu cluster co-doped nitrogen-carbon material and application of Fe single atom and Cu cluster co-doped nitrogen-carbon material in full-pH oxygen reduction electrocatalysis

Abstract

The application discloses a preparation method of Fe single-atom and Cu cluster co-doped nitrogen-carbon material and application of the material in full-pH oxygen reduction electrocatalysis. The ZIF-8 with a three-dimensional and rich pore structure is used as a framework, and Fe@ZIF-8 is prepared by using a solvothermal method. Then, copper acetylacetonate is used as a copper source, and the copper acetylacetonate molecules dispersed in the gas phase are adsorbed on the surface of the ZIF-8 by using the rich pore structure of the ZIF-8 and the low sublimation temperature of the metal acetylacetonate salt. Finally, pyrolysis is carried out under nitrogen or inert atmosphere, so as to form the Fe single-atom and Cu cluster co-doped nitrogen-carbon material. The material is subjected to electrochemical test under acidic, neutral and alkaline conditions, and the material exhibits high oxygen reduction electrocatalysis performance in the full-pH range and has good stability. The material has good performance as a cathode catalyst in a fuel cell, an alkaline / neutral zinc-air battery, and has high application value.

Description

Technical Field

[0001] This invention belongs to the field of carbon materials and electrocatalysis, specifically relating to a method for preparing a nitrogen-carbon material co-doped with Fe single atoms and Cu clusters and its application in full-pH oxygen reduction electrocatalysis. Background Technology

[0002] With socio-economic development, people's demand for energy is increasing day by day. Although traditional fossil fuels have solved people's large-scale energy needs, the limited availability of fossil fuels and the environmental problems caused by their overuse have followed. Developing efficient and clean new energy sources is urgently needed.

[0003] Proton exchange membrane fuel cells (PEMFCs) and zinc-air batteries are novel electrochemical energy conversion devices developed in recent years, attracting widespread attention due to their high energy conversion efficiency and clean, pollution-free operation. Fuel cells, as one of the most promising electrochemical energy conversion technologies, offer numerous advantages, such as high energy conversion efficiency, environmental friendliness, and low noise. In the discharge reaction of zinc-air batteries, the positive electrode undergoes an oxygen reduction (ORR) process, consuming oxygen to generate electricity, while the negative electrode is zinc, abundant in the Earth's crust. This combination offers advantages such as low cost, high power output, and high energy density, making it a relatively ideal power source. However, the cathode OORR reaction in both types of batteries is slow due to kinetic constraints, significantly limiting their practical application. Currently used commercial Pt / C catalysts are not only expensive but also susceptible to poisoning by methanol, carbon monoxide, and other substances, resulting in loss of catalytic activity.

[0004] Nitrogen-doped carbon-based Fe single-atom catalysts are considered the most promising alternatives to commercial Pt / C catalysts due to their low cost and excellent performance. However, the coordination environment and electronic configuration of the Fe single-atom sites in most Fe-NC materials remain controversial, and their activity is significantly lower than that of Pt / C. Furthermore, especially under acidic conditions, Fe sites are susceptible to attack by free radicals generated by the Fenton reaction, which greatly limits their long-term stability. Therefore, further improvements in the activity and stability of iron-based oxygen reduction catalysts remain essential. Summary of the Invention

[0005] This invention discloses a nitrogen-carbon material co-doped with Fe single atoms and Cu clusters (Fe sa Cu nc Preparation method of (NC) and its application in oxygen reduction electrocatalysis across the entire pH range.

[0006] The Fe single-atom and Cu cluster co-doped nitrogen-carbon material has a three-dimensional porous rhombic dodecahedral structure. After Fe coordinates with four N atoms, it is uniformly dispersed in the material in the form of single atoms, while Cu is uniformly distributed on the surface of the material in the form of clusters.

[0007] The preparation method of the Fe single atom and Cu cluster co-doped nitrogen-carbon material is as follows: using three-dimensional Fe@ZIF-8 as a precursor, copper acetylacetonate is vapor-deposited on Fe@ZIF-8 by vacuum gas diffusion method to form FeCu@ZIF-8 precursor, and finally calcined at high temperature in nitrogen or inert gas to obtain the Fe single atom and Cu cluster co-doped nitrogen-carbon material.

[0008] The synthesis method of the three-dimensional Fe@ZIF-8 is as follows: a mixed salt solution of zinc salt and iron acetylacetone is prepared; a 2-methylimidazolium ligand solution is prepared; the mixed salt solution and the ligand solution are mixed and transferred into a reaction vessel for solvothermal reaction; after the reaction is completed, the temperature is lowered to room temperature and centrifuged to obtain the Fe@ZIF-8 precursor.

[0009] The solvents used to prepare the mixed salt solution and ligand solution are selected from one or more of methanol, ethanol, N,N-dimethylformamide, and deionized water.

[0010] The zinc salt is selected from one or more of zinc nitrate, zinc sulfate, zinc chloride, and zinc acetate.

[0011] The temperature of the solvothermal reaction is 90-150℃.

[0012] The specific operation of the preparation method of the FeCu@ZIF-8 precursor is as follows: Fe@ZIF-8 is placed in the center of a tube furnace, and copper acetylacetonate is placed on both sides. The air in the tube furnace is purged with nitrogen or inert gas, and finally evacuated to a vacuum. After heating and holding at a certain temperature, the nitrogen or inert gas flow is turned on to allow the excess copper acetylacetonate volatilization gas to be discharged.

[0013] The mass of copper acetylacetonate placed on each side is 5-20 wt% of Fe@ZIF-8.

[0014] The heating and heat preservation temperature is 250-350℃, and the time is 30-240 minutes.

[0015] The high-temperature calcination is carried out at a temperature of 700-1100℃ for 60-240 minutes, with a heating rate of 2-10℃ / min. -1 .

[0016] The flow rate of the nitrogen or inert gas is 10-100 mL / min. -1 .

[0017] The above-prepared Fe single-atom and Cu cluster co-doped nitrogen-carbon material is used as a cathode catalyst in full-pH oxygen reduction electrocatalysis.

[0018] The Fe single-atom and Cu cluster co-doped nitrogen-carbon materials prepared above are used as cathode catalysts in fuel cells, alkaline zinc-air batteries, and neutral zinc-air batteries.

[0019] This invention uses ZIF-8, a zeolite imidazole ester framework material with a rich three-dimensional porous structure, as a framework. Fe@ZIF-8 is prepared using a solvothermal method. Then, copper acetylacetonate is used as the copper source. Taking advantage of the low sublimation temperature of metallic acetylacetonate salts, copper acetylacetonate molecules dispersed in the gas phase are adsorbed onto the surface of ZIF-8 through its rich porous structure. Finally, pyrolysis is performed under nitrogen or an inert atmosphere to form a co-doped nitrogen-carbon material (Fe@ZIF-8) consisting of Fe single atoms and Cu clusters. sa Cu nc / NC). The copper clusters enhance the oxygen reduction activity and stability of the Fe-N4 active sites under all pH conditions. Electrochemical tests were conducted on this material under acidic, neutral, and alkaline conditions, revealing that the Fe single-atom and Cu cluster co-doped nitrogen-carbon material (Fe...) obtained in this invention... sa Cu nc The NC (non-oxidative oxygen reduction) catalyst exhibits high oxygen reduction electrocatalytic performance across the entire pH range and demonstrates good stability. It performs well as a cathode catalyst in fuel cells and alkaline / neutral zinc-air batteries, showing great practical application value. Attached Figure Description

[0020] Figure 1 The catalyst (Fe) prepared in Example 1 sa Cu nc TEM image (a), spherical aberration electron microscopy image (b), and EDX mapping image (c) of / NC;

[0021] Figure 2 The catalyst (Fe) prepared in Example 1 sa Cu nc / NC), the catalyst prepared in Comparative Example 1 (Fe) sa Synchrotron radiation characterization of Fe (a, b) and Cu (c, d) elements in each standard sample (NC) and standard samples.

[0022] Figure 3 The catalyst (Fe) prepared in Example 1 sa Cu nc Synchrotron radiation fitting diagram of the / NC) site structure;

[0023] Figure 4 The polarization curves (ac) and corresponding Tafel curves (df) of the catalyst prepared in Example 1 and the catalysts prepared in Comparative Examples 1-4 were obtained by electrochemical testing in O2-saturated 0.1M HClO4, 0.1M PBS and 0.1M KOH solutions. The performance comparison graph (gi) of the catalyst prepared in Example 1 and the catalyst prepared in Comparative Example 1 before and after the stability test of 30,000 cycles is also shown.

[0024] Figure 5 The catalyst (Fe) prepared in Example 1 sa Cu nc / NC), the catalyst prepared in Comparative Example 2 (Fe) sa Performance graphs of 20 wt% commercial Pt / C catalysts in proton exchange membrane fuel cells (a), alkaline zinc-air cells (b), and neutral zinc-air cells (c) of Comparative Example 4. Detailed Implementation

[0025] Example 1

[0026] (1) Synthesis of Fe@ZIF-8 by solvothermal method: 793 mg zinc nitrate hexahydrate, 94 mg ferric acetylacetone, and 20 mL methanol were added to a beaker and ultrasonically dispersed for 15 min at room temperature. In another beaker, 875 mg 2-methylimidazole and 10 mL methanol were added and stirred for 15 min at room temperature. The solutions in the two beakers were mixed and stirred at room temperature for 1.5 h until the solution became turbid. The suspension was transferred to a high-pressure reactor and reacted at 120 °C for 4 h. After cooling the product to room temperature, it was centrifuged to obtain a pale yellow product. It was dried in a drying oven at 70 °C for later use.

[0027] (2) Weigh 100 mg of the prepared Fe@ZIF-8 and place it in a porcelain boat, which is then placed in the middle of a tube furnace. Weigh 17 mg of copper acetylacetonate and divide it into two equal portions, placing them in two small porcelain boats on either side of the boat containing Fe@ZIF-8. Use an oil pump to evacuate the air from the tube furnace and introduce argon gas. Repeat this process three times, then evacuate the tube furnace to a vacuum environment. Increase the temperature to 250°C at 10°C / min and maintain it for 90 min. Introduce argon gas into the tube furnace to remove the copper acetylacetonate not loaded on Fe@ZIF-8 from the gas phase using the gas flow, obtaining a pale yellow powdery product, FeCu@ZIF-8.

[0028] (3) FeCu@ZIF-8 was placed in a ceramic boat and then placed in the middle of a tube furnace. Air was extracted from the tube furnace using an oil pump, and argon (Ar) gas was introduced. This process was repeated three times, and the argon gas flow rate was maintained at 50 mL / min. The temperature was increased to 900℃ at a rate of 5℃ / min and held for 2 hours. After natural cooling to room temperature, a black powdery product was obtained, which is the three-dimensional porous carbon-nitrogen composite material (FeCu@ZIF-8) with Fe single atoms and Cu nanoclusters. sa Cu nc / NC).

[0029] Comparative Example 1

[0030] Unlike Example 1, acetylacetone iron was not added in step (1), and the catalyst obtained under the same reaction conditions as in Example 1 was obtained.

[0031] Comparative Example 2

[0032] The catalyst obtained by directly replacing FeCu@ZIF-8 with the product Fe@ZIF-8 from step (1) of Example 1 without going through step (2) is a catalyst obtained by performing step (3).

[0033] Comparative Example 3

[0034] The difference from Example 1 is that the amount of copper acetylacetone was increased to three times, while the other reaction conditions were the same as in Example 1 to obtain the catalyst.

[0035] Comparative Example 4

[0036] 20 wt% commercial platinum carbon.

[0037] Test results:

[0038] (1) TEM images show the catalyst (Fe) prepared in Example 1. sa Cu nc / NC) can maintain the morphology of ZIF-8 very well. Figure 1 a) Aberration-corrected electron microscopy images show that single-atom Fe and Cu nanoclusters were successfully loaded into the catalyst. Figure 1 b) The EDX mapping plot shows that N, Fe, and Cu elements are uniformly distributed in the catalyst. Figure 1 c). The chemical states and coordination environments of Fe and Cu atoms in the catalyst were investigated using X-ray absorption near-edge structure (XANES) and extended-edge X-ray absorption fine structure (EXAFS). Figure 2 As can be seen, the catalyst (Fe) prepared in Example 1 sa Cu nc In the NC spectrum, the valence state of Fe is between +2 and +3. Furthermore, the FT-EXAFS spectrum ( Figure 2 b) In The presence of a main peak at this location indicates Fe-N coordination in the material. No Fe-Fe / Cu coordination was detected on either side, indicating that iron is present in Fe... sa Cu nc Fe exists in an atomically dispersed form within / NC. Furthermore, Fe was analyzed using EXAFS fitting. sa Cu nc The coordination configuration of Fe atoms in / NC. The best-fit results indicate that in the Fe k-edge FT-EXAFS spectrum... The main peak at this location can be well attributed to Fe-N first-shell coordination, with a coordination number of 3.85, further indicating that the Fe site exists in the form of Fe-N4. sa Cu nc In / NC, Cu has the same valence state as metallic Cu, which is 0. Figure 2c) FT-EXAFS spectroscopy in The presence of a main peak at this location indicates Cu-Cu coordination in the material. Figure 2 d) proves the existence of Cu clusters.

[0039] (2) Electrochemical measurements were performed on a CHI 660E or DH7003 electrochemical station using a conventional three-electrode system. A saturated calomel double salt bridge electrode (SCE) and a graphite rod were used as the reference and counter electrodes, respectively. A catalyst-coated platinum-carbon rotating disk electrode (RDE, disk area 0.0707 cm²) was also used. 2 ) or RRDE (disk area is 0.1257cm²) 2 The area of ​​the Pt ring is 0.1885 cm². 2 The working electrode was used as a catalyst ink. All electrolytic cells and electrodes were thoroughly cleaned with chromic acid cleaning solution and deionized water. The catalyst ink was prepared by dispersing 4 mg of Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, or 1 mg of Comparative Example 4 in a 1 mL solution containing 0.685 mL ethanol and 0.295 mL water, and then adding 5 μL of the catalyst ink. 催化剂 -1 Nafion solution was ultrasonically dispersed for 2 hours to form a uniform catalyst ink. The loading of the catalyst ink coated on the glassy carbon electrode in Examples 1, 1, 2, and 3 was 0.6 mg / cm³. -2 The loading in Comparative Example 4 was 0.1019 mg / cm³. -2 Before testing, the electrolyte was purged with pure N2 or O2 for at least 30 minutes to obtain an N2 / O2 saturated solution. Scan rates of 50 mV / s were performed using a three-electrode system in N2 / O2-saturated 0.1 M HClO4, 0.1 M PBS, and 0.1 M KOH at different rotation rates. -1 Cyclic voltammetry (CV) testing and a scan rate of 10 mV / s were performed. -1 Linear sweep voltammetry (LSV) testing was performed. The measured polarization curves were corrected using iR compensation, and then the transformation equation E was used. RHE =E SCE +0.2415 +0.0591 × pH converts to a reversible hydrogen electrode (RHE). Example 1 showed half-wave potentials (E0) of 0.830 V, 0.835 V, and 0.938 V in 0.1 M HClO4, 0.1 M PBS, and 0.1 M KOH, respectively. 1 / 2 ()( Figure 4 Eac) is superior to Comparative Example 1, Comparative Example 2, and Comparative Example 3, respectively. In neutral and alkaline media, Eac 1 / 2 Higher than commercial Pt / C. In Example 1, the Tafel slopes in 0.1M HClO4, 0.1M PBS, and 0.1M KOH were 68.4 mV dec.-1 108.4mV dec -1 and 63.8mV dec -1 Compared with the comparative examples, this demonstrates a significant advantage, revealing that Example 1 exhibits excellent oxygen reduction reaction kinetics in all three media. Figure 4 df).

[0040] Accelerated durability tests (ADTs) were conducted at room temperature on Examples 1 and 2 in O2-saturated 0.1M HClO4, 0.1M PBS, and 0.1M KOH solutions, respectively. The tests were performed at 100mV s⁻¹ within a voltage range of 0.6–1.0V vs. RHE. -1 The scan rate was used for 30,000 cycles, and the ORR curves before and after cycling stability were recorded. Compared with Comparative Example 2, which introduced copper clusters, Example 1 showed better cycling stability in all three electrolytes. ADT results showed that the catalyst prepared in Example 1 had excellent stability. Figure 4 (gi). After 30k ADT cycles, E in 0.1M HClO4, 0.1M PBS and 0.1M KOH solutions in Example 1. 1 / 2 The values ​​decreased by only 16 mV, 0 mV, and 4 mV, respectively, which was better than Comparative Example 2 (which decreased by 42 mV, 3 mV, and 13 mV, respectively, in 0.1 M HClO4, 0.1 M PBS, and 0.1 M KOH solutions).

[0041] The catalyst (Fe) prepared in Example 1 sa Cu nc / NC) and the catalyst prepared in Comparative Example 2 (Fe) sa / NC) was used as the cathode catalyst for proton exchange membrane fuel cell testing. Approximately 30 mg of catalyst was mixed with Nafion solution, isopropanol, and deionized water, and subjected to ultrasonic treatment for 3 hours to obtain a catalyst slurry. The well-dispersed slurry was sprayed onto one side of a Nafion 211 membrane (DuPont) as the cell cathode. The anode used 60 wt% Pt / C with a loading of approximately 0.1 mg. Pt cm -2 The proton exchange membrane was sprayed onto the other side of the proton exchange membrane. The sprayed proton exchange membrane was then hot-pressed with two gas diffusion electrodes (GDEs) at 130°C to obtain a membrane electrode assembly (MEA). The performance of the hydrogen-oxygen fuel cell was tested at a fuel cell workstation under conditions of 80°C and 100% RH. At a back pressure of 0.2 MPa, the catalyst (Fe2+) prepared in Example 1... sa Cu nc / NC) reached approximately 974.1 mW cm -2 Maximum power density value ( Figure 5a) is much higher than that of Comparative Example 2 (476.3 mW cm). -2 ).

[0042] The performance of Examples 1, 2, and 4 in alkaline / neutral liquid zinc-air batteries was evaluated. Polished zinc sheets (0.2 mm thick), 6.0 M KOH + 0.2 M Zn(ac)₂, and 4 M NH₄Cl + 2 M KCl were used as the anode, alkaline electrolyte, and neutral electrolyte, respectively. The cathode was prepared by loading a catalyst onto a 2 × 3 cm² GDE, with the gas diffusion layer on the air side and the catalyst layer on the electrolyte side. The catalyst loading was 2.5 mg cm⁻², and the effective electrode area was 1 cm². The power densities of the alkaline and neutral zinc-air batteries assembled in Example 1 were 234.7 mW cm-2 and 94.9 mW cm-2, respectively, which were higher than those of Comparative Example 2 (the maximum power densities of the alkaline and neutral zinc-air batteries were 215.2 mW cm-2 and 87.8 mW cm-2, respectively) and Comparative Example 4 (the maximum power densities of the alkaline and neutral zinc-air batteries were 170.1 mW cm-2 and 77.3 mW cm-2, respectively).

[0043] Comparative examples and comparative examples show that the introduction of copper clusters can significantly improve the performance of Fe single-atom catalysts as cathode catalysts for oxygen reduction reactions, exhibiting excellent activity and stability in electrolytes across all pH levels. This demonstrates high innovation and practical application potential.

Claims

1. A method for preparing a nitrogen-carbon material co-doped with Fe single atoms and Cu clusters, characterized in that, The specific steps of the preparation method are as follows: using three-dimensional Fe@ZIF-8 as a precursor, copper acetylacetonate is vapor-deposited on Fe@ZIF-8 by vacuum gas diffusion method to form FeCu@ZIF-8 precursor, and finally calcined at high temperature in nitrogen or inert gas to obtain Fe single atom and Cu cluster co-doped nitrogen carbon material. The specific operation of the preparation method of FeCu@ZIF-8 precursor is as follows: Fe@ZIF-8 is placed in the center of a tube furnace, and copper acetylacetonate is placed on both sides. The air in the tube furnace is purged with nitrogen or inert gas, and finally evacuated to a vacuum. After heating and holding at a certain temperature, the nitrogen or inert gas flow is turned on to allow the excess copper acetylacetonate volatilization gas to be discharged. The prepared Fe single-atom and Cu cluster co-doped nitrogen-carbon material has a three-dimensional porous rhombic dodecahedral structure. After Fe coordinates with four N atoms, it is uniformly dispersed in the material in the form of single atoms, while Cu is uniformly distributed on the surface of the material in the form of clusters.

2. The preparation method according to claim 1, characterized in that, The synthesis method of the three-dimensional Fe@ZIF-8 is as follows: a mixed salt solution of zinc salt and iron acetylacetone is prepared; a 2-methylimidazolium ligand solution is prepared; the mixed salt solution and the ligand solution are mixed and transferred into a reaction vessel for solvothermal reaction; after the reaction is completed, the temperature is lowered to room temperature and centrifuged to obtain the Fe@ZIF-8 precursor.

3. The preparation method according to claim 2, characterized in that, The solvents used to prepare the mixed salt solution and ligand solution are selected from one or more of methanol, ethanol, N,N-dimethylformamide, and deionized water.

4. The preparation method according to claim 2, characterized in that, The zinc salt is selected from one or more of zinc nitrate, zinc sulfate, zinc chloride, and zinc acetate.

5. The preparation method according to claim 2, characterized in that, The temperature of the solvothermal reaction is 90-150℃.

6. The preparation method according to claim 1, characterized in that, The heating and heat preservation temperature is 250-350℃, and the time is 30-240 minutes.

7. The preparation method according to claim 1, characterized in that, The high-temperature calcination temperature is 700-1100℃, and the time is 60-240 minutes.

8. The application of the Fe single-atom and Cu cluster co-doped nitrogen-carbon material prepared by the method according to any one of claims 1-7 as a cathode catalyst in full pH oxygen reduction electrocatalysis.

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