A lithium-air battery co-pd diatomic positive electrode catalyst and a preparation method and application thereof

Abstract

The application provides a lithium air battery Co-Pd diatomic positive electrode catalyst and a preparation method and application thereof, and belongs to the technical field of electrochemistry and catalysis. The application comprises the following steps: mixing carbon nanotubes and an alcohol solution to obtain a carbon nanotube solution, mixing the carbon nanotube solution with a cobalt salt and a zinc salt to obtain a cobalt-containing mixture; mixing 2-methyl imidazole and an alcohol reagent to obtain a 2-methyl imidazole solution, mixing the 2-methyl imidazole solution with the cobalt-containing mixture, stirring, centrifuging and drying to obtain CoZn-CNT and the like. The lithium air battery constructed by using the catalyst provided by the application has a low charging platform (3.2 V) and a low overpotential (0.6 V), solves the problem of high overpotential (1.5 V) commonly existing in the lithium air battery, and has a high discharging platform (2.8 V) and a good discharging capacity (15000 mAhg ‑1 ).

Description

Technical Field

[0001] This invention relates to the fields of electrochemistry and catalysis, and in particular to a Co-Pd dual-atom cathode catalyst for lithium-air batteries, its preparation method, and its application. Background Technology

[0002] With the continuous development and utilization of fossil fuels, global reserves are dwindling, and the contradiction between the ever-increasing energy demand for production and daily life and the limited energy reserves is becoming increasingly prominent. Therefore, developing new energy storage systems is of great significance to the sustainable development of modern society. Compared with traditional lithium-ion battery energy storage systems, lithium-oxygen battery systems have an extremely high theoretical energy density (3505Wh*kg). -1 Lithium-oxygen batteries, comparable to oil and environmentally friendly with zero pollution, are considered one of the most promising energy storage systems for solving the energy and environmental crisis. However, research on lithium-oxygen batteries is still in its early stages. They are limited by the lithium negative electrode, the electrolyte, and the air positive electrode, especially the slow ORR / OER reaction kinetics at the positive electrode, resulting in a large overpotential and low cycle life, severely restricting their commercial application. Therefore, rationally constructing a bifunctional catalyst for the positive electrode to improve the ORR / OER reaction kinetic rate is one of the key approaches to solving the problems of lithium-oxygen batteries. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a Co-Pd biatomic cathode catalyst for lithium-air batteries, its preparation method, and its application.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] This invention provides a method for preparing a Co-Pd dual-atom cathode catalyst for lithium-air batteries, comprising the following steps:

[0006] 1) Mix carbon nanotubes with an alcohol solution to obtain a carbon nanotube solution, and then mix the carbon nanotube solution with cobalt salt and zinc salt to obtain a cobalt-containing mixture;

[0007] 2) Mix 2-methylimidazole with an alcohol reagent to obtain a 2-methylimidazole solution. Mix the 2-methylimidazole solution with the cobalt-containing mixture obtained in step 1), stir, centrifuge and dry to obtain CoZn-CNT.

[0008] 3) The CoZn-CNT obtained in step 2) is dispersed in n-hexane, then mixed with a palladium salt solution, stirred, centrifuged, and dried to obtain a solid;

[0009] 4) The solid obtained in step 3) is pyrolyzed to obtain a pyrolyte. The pyrolyte is then treated with hydrochloric acid solution and dried to obtain a Co-Pd biatom cathode catalyst for lithium-air batteries.

[0010] Preferably, in step 1), the mass ratio of carbon nanotubes to the volume ratio of the alcohol solution is 30 mg: 15-40 mL.

[0011] The alcohol solution includes a methanol solution, wherein the methanol solution contains 99.5% methanol by volume.

[0012] Preferably, the volume ratio of the alcohol solution to the cobalt salt and zinc salt in step 1) is 15-40 mL: 0.546 g: 0.558 g;

[0013] The cobalt salt is cobalt nitrate hexahydrate, and the zinc salt is zinc nitrate hexahydrate.

[0014] Preferably, in step 2), the mass ratio of 2-methylimidazole to the volume ratio of the alcohol reagent is 0.616–1.232 g: 15 mL.

[0015] The alcohol reagent includes methanol.

[0016] Preferably, in step 2), the volume ratio of the 2-methylimidazole solution to the cobalt-containing mixture is 1:1;

[0017] The stirring time is 12 hours;

[0018] The centrifugation conditions include: centrifugation and washing with methanol;

[0019] The drying conditions include a temperature of 60–70°C and a time of 12 hours.

[0020] Preferably, in step 3), the mass ratio of CoZn-CNT to the volume ratio of n-hexane is 130 mg: 13 mL.

[0021] The mass ratio of the CoZn-CNT to the volume ratio of the palladium salt solution is 130 mg: 30 μL;

[0022] The palladium salt solution includes a Na2PdCl4 solution, wherein the mass concentration of Na2PdCl4 in the Na2PdCl4 solution is 50 mg / mL;

[0023] The stirring time is 12 hours;

[0024] The centrifugation conditions include: centrifugation and washing with methanol;

[0025] The drying conditions include a temperature of 60–70°C and a time of 12 hours.

[0026] Preferably, the conditions for pyrolysis in step 4) include: a temperature of 900°C, a time of 2 hours, and a heating rate of 2°C / min.

[0027] Preferably, the processing time for step 4) is 12 hours;

[0028] The molar concentration of the hydrochloric acid solution is 0.5 mol / L.

[0029] The present invention also provides a Co-Pd diatomic cathode catalyst for lithium-air batteries prepared by the preparation method described above, wherein the Co-Pd diatomic cathode catalyst for lithium-air batteries has a cobalt mass percentage content of 0.44% and a palladium mass percentage content of 0.52%.

[0030] The present invention also provides the application of the Co-Pd diatomic cathode catalyst of the lithium-air battery described in the above technical solution in lithium-air batteries.

[0031] This invention prepares a cobalt-palladium biatom catalyst, CoPd-N-CNT, by introducing palladium atoms to regulate the D-band of Co-N4. Compared to cobalt single-atom catalysts, the introduction of palladium sites enhances the density of active sites in the catalyst material, regulates the D-band center of cobalt, and optimizes the adsorption of LiO2 intermediates, thereby reducing charge-discharge polarization and lowering overpotential. The composite carbon nanotubes form a 3D conductive cross-linked network, promoting electron and proton transport. The proton-coupled electron transfer at the CoPd-N6 center in CoPd-N-CNT is more active, and the accelerated charge transfer optimizes OER performance. This results in the CoPd-N-CNT catalyst exhibiting excellent ORR / OER bifunctional catalytic performance. Lithium-air batteries constructed using this catalyst exhibit a low charging plateau (3.2V) and low overpotential (0.6V), and a high discharge plateau (2.8V) and good discharge capacity (15000 mAh g⁻¹). -1 ). Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in Embodiment 1 will be briefly described below.

[0033] Figure 1 A comparison of the first charge-discharge curves of the CoPd-N-CNT catalyst prepared in this invention and the Co single-atom catalytic lithium-air battery.

[0034] Figure 2 A comparison of the discharge capacity of the CoPd-N-CNT catalyst prepared in this invention with that of a Co single-atom catalyzed lithium-air battery.

[0035] Figure 3A comparison of the CoPd-N-CNT catalyst prepared in this invention with a Co single-atom catalytic lithium-air battery after 30 cycles;

[0036] Figure 4 This is a schematic diagram of the preparation process of the CoPd-N-CNT catalyst.

[0037] Figure 5 SEM (Scanning Electron Microscopy) image of CoPd-N-CNT;

[0038] Figure 6 TEM transmission electron microscopy morphology, selected area electron diffraction, and EDS energy dispersive spectroscopy (EDS) images of CoPd-N-CNTs.

[0039] Figure 7 A spherical aberration electron microscopy image of CoPd-N-CNT with high-angle ring dark field.

[0040] Figure 8 XRD patterns of CoPd-N-CNT and CoPd-N-CNT;

[0041] Figure 9 Raman spectra of CoPd-N-CNT and CoPd-N-CNT;

[0042] Figure 10 Infrared spectra of CoPd-N-CNT and CoPd-N-CNT;

[0043] Figure 11 XANES spectra and Fourier transforms of CoK-edge and PdK-edge CoPd-N-CNT and control samples. Detailed Implementation

[0044] This invention provides a method for preparing a Co-Pd diatomic cathode catalyst for lithium-air batteries, comprising the following steps:

[0045] 1) Mix carbon nanotubes with an alcohol solution to obtain a carbon nanotube solution, and then mix the carbon nanotube solution with cobalt salt and zinc salt to obtain a cobalt-containing mixture;

[0046] 2) Mix 2-methylimidazole with an alcohol reagent to obtain a 2-methylimidazole solution. Mix the 2-methylimidazole solution with the cobalt-containing mixture obtained in step 1), stir, centrifuge and dry to obtain CoZn-CNT.

[0047] 3) The CoZn-CNT obtained in step 2) is dispersed in n-hexane, then mixed with a palladium salt solution, stirred, centrifuged, and dried to obtain a solid;

[0048] 4) The solid obtained in step 3) is pyrolyzed to obtain a pyrolyte. The pyrolyte is then treated with hydrochloric acid solution and dried to obtain a Co-Pd biatom cathode catalyst for lithium-air batteries.

[0049] This invention involves mixing carbon nanotubes with an alcohol solution to obtain a carbon nanotube solution, and then mixing the carbon nanotube solution with cobalt salts and zinc salts to obtain a cobalt-containing mixture. In this invention, the preferred mass ratio of the carbon nanotubes to the alcohol solution is 30 mg: 15-40 mL. Preferably, the alcohol solution comprises a methanol solution with a methanol volume percentage of 99.5%. The preferred volume ratio of the alcohol solution to the cobalt and zinc salts is 15-40 mL: 0.546 g: 0.558 g. The preferred cobalt salt is cobalt nitrate hexahydrate, and the preferred zinc salt is zinc nitrate hexahydrate. This invention does not have specific limitations on the source of the reagents; commercially available products are acceptable. Preferably, the carbon nanotubes and alcohol solution are mixed under magnetic stirring for 30 minutes at a speed of 600 rpm. In this invention, the carbon nanotube solution is preferably mixed with cobalt salt and zinc salt using magnetic stirring. The magnetic stirring time is preferably 30 minutes, and the magnetic stirring speed is preferably 600 revolutions per minute.

[0050] This invention involves mixing 2-methylimidazole with an alcohol reagent to obtain a 2-methylimidazole solution. The 2-methylimidazole solution is then mixed with a cobalt-containing mixture, stirred, centrifuged, and dried to obtain CoZn-CNT. (Co) 2+ / Zn 2+ Ions are first adsorbed onto carbon nanotubes via electrostatic interactions, then react with dimethylimidazole to form a cobalt-zinc metal-organic framework in situ grown on the carbon nanotubes, labeled CoZn-CNT. In this invention, the mass ratio of 2-methylimidazole to the volume ratio of the alcohol reagent is preferably 0.616–1.232 g:15 mL, and the alcohol reagent preferably includes methanol. In this invention, the volume ratio of the 2-methylimidazole solution to the cobalt-containing mixture is preferably 1:1. In this invention, the stirring time is preferably 12 h. In this invention, the centrifugation conditions preferably include: centrifugation washing with methanol at a speed of 8000 rpm for 10 minutes per cycle, preferably three times at room temperature. In this invention, the drying conditions preferably include: a temperature of 60–70 °C for 12 h.

[0051] In this invention, the obtained CoZn-CNT is dispersed in n-hexane, mixed with a palladium salt solution, stirred, centrifuged, and dried to obtain a solid. Palladium atoms interact with cobalt atoms to form coordination, impregnating the palladium atoms. In this invention, the preferred mass-to-volume ratio of the CoZn-CNT to the n-hexane is 130 mg:13 mL. Preferably, the obtained CoZn-CNT is dispersed in n-hexane and sonicated at room temperature for 1 hour at a power of 0.5 W / cm² and a frequency of 40 kHz. Preferably, the preferred mass-to-volume ratio of the CoZn-CNT to the palladium salt solution is 130 mg:30 μL. Preferably, the palladium salt solution is added dropwise to n-hexane and then sonicated for 10 minutes. Preferably, the palladium salt solution includes a Na₂PdCl₄ solution, and the Na₂PdCl₄ concentration in the Na₂PdCl₄ solution is 50 mg / mL. Preferably, the stirring time is 12 hours, preferably at room temperature, and the magnetic stirring speed is 600 rpm. In this invention, the centrifugation conditions preferably include: centrifugation and washing with methanol, repeated three times. In this invention, the drying conditions preferably include: a temperature of 60–70°C and a drying time of 12 hours.

[0052] This invention involves pyrolyzing a solid to obtain a pyrolyte, which is then treated with hydrochloric acid solution and dried to obtain a Co-Pd diatomic cathode catalyst for lithium-air batteries. The preferred pyrolysis conditions include a temperature of 900°C, a time of 2 hours, and a heating rate of 2°C / min. The pyrolysis is preferably carried out under flowing argon gas. During high-temperature pyrolysis under argon, zinc atoms volatilize and are carried away by the atmosphere, leaving cobalt and palladium coordinated and dispersed in the carbonized matrix. The preferred treatment time is 12 hours. The preferred molar concentration of the hydrochloric acid solution is 0.5 mol / L, selectively removing nanoparticles and clusters. The material obtained by this method has sufficient porosity; the network structure formed by overlapping carbon nanotubes improves the overall conductivity of the catalyst, while also possessing sufficient structural strength to ensure the stability of the material during battery testing.

[0053] The present invention also provides a Co-Pd biatom cathode catalyst for lithium-air batteries prepared by the preparation method described above, wherein the Co-Pd biatom cathode catalyst for lithium-air batteries has a cobalt mass percentage of 0.44% and a palladium mass percentage of 0.52%.

[0054] This invention also provides the application of the Co-Pd diatomic cathode catalyst described in the above-mentioned technical solution in lithium-air batteries. Before assembling the lithium-air battery, a certain amount of catalyst and polytetrafluoroethylene (mass ratio 8:2) are weighed and ground. Then, an appropriate amount of N-methylpyrrolidone (solid powder to liquid ratio of 10mg:1mL) is added. After grinding to a certain extent, the mixture is transferred to a 20mL glass bottle and sonicated for 30min at a power of 0.5W / cm² and a frequency of 40kHz. 30μL of the sonicated slurry is measured with a pipette and dropped onto carbon paper (12mm). It is dried in a forced-air drying oven at 80℃ for 1h, and then transferred to a vacuum drying oven at 120℃ for 12h to obtain the cathode sheet. Subsequently, 2025 coin cells are assembled in an Ar gas glove box (H2O and O2 contents are both below 1ppm). Specifically, the positive electrode used was a pre-prepared positive electrode sheet, the separator was a Whatman glass fiber separator (GF / D), 150 μL of electrolyte (1M LiTFSI / TEGDME) was added, and the negative electrode was a 16 mm diameter lithium metal sheet. Then, the electrochemical performance was tested using a CT2001ALAND battery tester in constant current mode at room temperature.

[0055] To further illustrate the present invention, the following detailed description is provided in conjunction with embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0056] Example 1

[0057] Preparation of CoZn-CNTs:

[0058] 30 mg of carbon nanotubes were weighed into 15 mL of 99.5% methanol solution and magnetically stirred for 30 min at 600 rpm to disperse them evenly. Then, 0.546 g of Co(NO3)2·6H2O and 0.558 g of Zn(NO3)2·6H2O were added, and stirring was continued for another 30 min. 0.616 g of 2-methylimidazole was dissolved in 15 mL of methanol, stirred thoroughly, and then added to the above solution. The mixture was stirred at 600 rpm for 12 h at room temperature. Subsequently, the nanotubes were washed three times with methanol at 8000 rpm for 10 min each time, and then transferred to a vacuum drying oven and dried at 60 °C for 12 h.

[0059] Preparation of CoPd-N-CNTs:

[0060] 130 mg of ZnCo-CNT was weighed and dispersed in 13 mL of n-hexane. The solution was sonicated at room temperature for 1 hour at a power of 0.5 W / cm² and a frequency of 40 kHz. Subsequently, 30 μL of Na₂PdCl₄ (50 mg / mL) was added dropwise to the above solution. -1After sonication for 10 minutes, stirring was continued at room temperature for 12 hours. The impregnated sample was washed by centrifugation with methanol, then transferred to a vacuum drying oven at 60°C for 12 hours. The resulting powder was placed in a tube furnace and dried at 2°C / min under flowing argon gas. -1 The temperature was increased at a rate of [missing information], and the sample was held at 900℃ for 2 hours. It was then allowed to cool naturally to room temperature to obtain the sample. The sample was then treated with 0.5 mol / L hydrochloric acid at room temperature for 12 hours to selectively remove nanoparticles and clusters, followed by centrifugation and drying to obtain the final sample.

[0061] SEM (Scanning Electron Microscopy) morphology of CoPd-N-CNTs, as follows Figure 5 As shown, from Figure 5 It can be concluded that CoPd-CNT consists of rhombic dodecahedrons growing on carbon nanotubes, and retains the rhombic dodecahedron structure after sintering, ultimately forming a 3D conductive network.

[0062] TEM transmission electron microscopy morphology of CoPd-N-CNT, as shown in the figure. Figure 6 As shown, from Figure 6 The results show that a hollow carbon matrix is ​​distributed on the carbon nanotubes, with numerous carbon nanotubes accompanying the hollow matrix. Two uniform carbonized structures were observed, belonging to the carbonized matrix and the carbon nanotubes, respectively. No nanoparticles or other impurity species were observed in the images, indicating the absence of particles in the material, consistent with selected electron diffraction results; only diffuse carbon rings were observed, with no diffraction spots from metal particles. Furthermore, the elemental mapping confirmed that C, N, Co, and Pd elements are uniformly distributed throughout the carbon scaffold.

[0063] High-angle ring dark-field image of CoPd-N-CNT by spherical aberration electron microscopy, as shown Figure 7 As shown, from Figure 7 As can be seen, uniformly distributed paired CoPd diatoms (brighter spots) are clearly observed throughout the carbon matrix. For visual identification, some diatoms are highlighted with white circles. The disite dispersion originates from the adsorption of Pd salt and its binding with adjacent Co nodes. The inset further confirms the coexistence of cobalt-palladium diatoms in the carbon matrix.

[0064] X-ray diffraction pattern of CoPd-N-CNT, such as Figure 8 As shown, from Figure 8 It can be seen that two characteristic peaks belonging to the (002) and (101) crystal planes of carbon appear at 26° and 43°. No characteristic peaks of metallic cobalt, metallic palladium, or compounds are observed, indicating that the metals do not exist in the form of particles in the material.

[0065] Raman spectra of CoPd-N-CNT, such as Figure 9 As shown, from Figure 9 From this, we can conclude that at 1350cm-1 and 1580cm -1 Two peaks appeared, which were attributed to the D band (characterizing structural defects in the graphene sample) and the G band (characterized by sp). 2 Caused by in-plane vibrations of carbon). The ratio of D peak to G peak (I D / I G The coefficient of performance (COP) can characterize the defects and disorder of materials. CoPd-N-CNT (1.061) has a larger proportion than Co-N-CNT (1.021), indicating that a large number of local defects are induced in the carbon matrix of the diatomic system. This will facilitate ion diffusion and may also generate more reactive sites, all of which are beneficial to improving electrochemical performance.

[0066] Fourier transform infrared (FTIR) spectra of CoPd-N-CNT, such as Figure 10 As shown, from Figure 10 It can be concluded that the two samples have similar structures, indicating that palladium adsorption does not disrupt the stability of the matrix framework structure, especially at 3440 cm⁻¹. -1 and 1450cm -1 The broadband band appearing at this point corresponds to the OH vibration of the hydrogen-bonded hydroxyl group, indicating that water molecules are anchored to the catalyst.

[0067] X-ray absorption spectroscopy (XAFS) data of CoPd-N-CNT, such as Figure 11 As shown, from Figure 11 The chemical valence state and coordination environment of the catalyst can be derived from this. (a) The K-edge of Co in the near-edge structure of the X-ray absorption spectrum in the figure proves that the intensity and position of the fingerprint peak are greater than those of the standard sample cobalt powder, which means that the cobalt atoms are in an oxidized state. Fourier transform k in R space 2 Weighted extended X-ray absorption fine structure (FT-EXAFS) spectroscopy indicates that CoPd-N-CNT has only one distinct shell. The corresponding Co-N scattering path is completely different from the Co-Co bond in Co powder. (c) The K-edge of Pd in ​​the figure proves that the intensity and position of the fingerprint peak are greater than those of the standard palladium powder, which means that the palladium atoms are in an oxidized state. Fourier transform k in R space 2 Weighted extended X-ray absorption fine structure (FT-EXAFS) spectroscopy indicates that CoPd-N-CNT has only one distinct shell. This is attributed to Pd-N contributions, and is completely different from the Pd-Pd bonds in palladium powder. Based on the above results, it is fully demonstrated that our catalyst material contains a large number of N-coordinated cobalt-palladium diatoms uniformly dispersed. These unique active sites can also explain their different catalytic behaviors during redox processes.

[0068] Example 2

[0069] Preparation of ZnCo-CNTs:

[0070] 30 mg of carbon nanotubes were weighed into 20 mL of methanol solution and magnetically stirred for 30 min to disperse them evenly. Then, 0.546 g of Co(NO3)2·6H2O and 0.558 g of Zn(NO3)2·6H2O were added, and stirring was continued for another 30 min. 0.616 g of 2-methylimidazole was dissolved in 15 mL of methanol, stirred thoroughly, and then added to the above solution. The mixture was vigorously stirred at room temperature for 12 h. Subsequently, the nanotubes were washed three times by centrifugation with methanol, transferred to a vacuum drying oven, and dried at 60 °C for 12 h.

[0071] Preparation of CoPd-N-CNTs:

[0072] Weigh out 130 mg of ZnCo-CNT and disperse it in 13 mL of n-hexane, then sonicate at room temperature for 1 h. Subsequently, add 30 μL of Na₂PdCl₄ (50 mg / mL) dropwise to the above solution. -1 After sonication for 10 minutes, stirring was continued at room temperature for 12 hours. The impregnated sample was washed by centrifugation with methanol, then transferred to a vacuum drying oven at 60°C for 12 hours. The resulting powder was placed in a tube furnace and dried at 2°C / min under flowing argon gas. -1 The temperature was increased at a rate of [unspecified], and the sample was held at 900℃ for 2 hours. It was then allowed to cool naturally to room temperature to obtain the sample. A portion of the sample was treated with hydrochloric acid for 12 hours, followed by centrifugation and drying to obtain the final sample.

[0073] Example 3

[0074] Preparation of ZnCo-CNTs:

[0075] 30 mg of carbon nanotubes were weighed into 30 mL of methanol solution and magnetically stirred for 30 min to disperse them evenly. Then, 0.546 g of Co(NO3)2·6H2O and 0.558 g of Zn(NO3)2·6H2O were added, and stirring was continued for another 30 min. 0.616 g of 2-methylimidazole was dissolved in 15 mL of methanol, stirred thoroughly, and then added to the above solution. The mixture was vigorously stirred at room temperature for 12 h. Subsequently, the nanotubes were washed three times by centrifugation with methanol and transferred to a vacuum drying oven to dry at 60 °C for 12 h.

[0076] Preparation of CoPd-N-CNTs:

[0077] Weigh out 130 mg of ZnCo-CNT and disperse it in 13 mL of n-hexane, then sonicate at room temperature for 1 h. Subsequently, add 30 μL of Na₂PdCl₄ (50 mg / mL) dropwise to the above solution. -1After sonication for 10 minutes, stirring was continued at room temperature for 12 hours. The impregnated sample was washed by centrifugation with methanol, then transferred to a vacuum drying oven at 60°C for 12 hours. The resulting powder was placed in a tube furnace and dried at 2°C / min under flowing argon gas. -1 The temperature was increased at a rate of [unspecified], and the sample was held at 900℃ for 2 hours. It was then allowed to cool naturally to room temperature to obtain the sample. A portion of the sample was treated with hydrochloric acid for 12 hours, followed by centrifugation and drying to obtain the final sample.

[0078] Example 4

[0079] Preparation of ZnCo-CNTs:

[0080] 30 mg of carbon nanotubes were weighed into 40 mL of methanol solution and magnetically stirred for 30 min to disperse them evenly. Then, 0.546 g of Co(NO3)2·6H2O and 0.558 g of Zn(NO3)2·6H2O were added, and stirring was continued for another 30 min. 0.616 g of 2-methylimidazole was dissolved in 15 mL of methanol, stirred thoroughly, and then added to the above solution. The mixture was vigorously stirred at room temperature for 12 h. Subsequently, the nanotubes were washed three times by centrifugation with methanol, transferred to a vacuum drying oven, and dried at 60 °C for 12 h.

[0081] Preparation of CoPd-N-CNTs:

[0082] Weigh out 130 mg of ZnCo-CNT and disperse it in 13 mL of n-hexane, then sonicate at room temperature for 1 h. Subsequently, add 30 μL of Na₂PdCl₄ (50 mg / mL) dropwise to the above solution. -1 After sonication for 10 minutes, stirring was continued at room temperature for 12 hours. The impregnated sample was washed by centrifugation with methanol, then transferred to a vacuum drying oven at 60°C for 12 hours. The resulting powder was placed in a tube furnace and dried at 2°C / min under flowing argon gas. -1 The temperature was increased at a rate of [unspecified], and the sample was held at 900℃ for 2 hours. It was then allowed to cool naturally to room temperature to obtain the sample. A portion of the sample was treated with hydrochloric acid for 12 hours, followed by centrifugation and drying to obtain the final sample.

[0083] Example 5

[0084] Preparation of ZnCo-CNTs:

[0085] 30 mg of carbon nanotubes were weighed into 15 mL of methanol solution and magnetically stirred for 30 min to disperse them evenly. Then, 0.546 g of Co(NO3)2·6H2O and 0.558 g of Zn(NO3)2·6H2O were added, and stirring was continued for another 30 min. 0.924 g of 2-methylimidazole was dissolved in 15 mL of methanol, stirred thoroughly, and then added to the above solution. The mixture was vigorously stirred at room temperature for 12 h. Subsequently, the nanotubes were washed three times by centrifugation with methanol, transferred to a vacuum drying oven, and dried at 70 °C for 12 h.

[0086] Preparation of CoPd-N-CNTs:

[0087] Weigh out 130 mg of ZnCo-CNT and disperse it in 13 mL of n-hexane, then sonicate at room temperature for 1 h. Subsequently, add 30 μL of Na₂PdCl₄ (50 mg / mL) dropwise to the above solution. -1 After sonication for 10 minutes, stirring was continued at room temperature for 12 hours. The impregnated sample was washed by centrifugation with methanol, then transferred to a vacuum drying oven at 70°C for 12 hours. The resulting powder was placed in a tube furnace and dried at 2°C / min under flowing argon gas. -1 The temperature was increased at a rate of [unspecified], and the sample was held at 900℃ for 2 hours. It was then allowed to cool naturally to room temperature to obtain the sample. A portion of the sample was treated with hydrochloric acid for 12 hours, followed by centrifugation and drying to obtain the final sample.

[0088] Example 6

[0089] Preparation of ZnCo-CNTs:

[0090] 30 mg of carbon nanotubes were weighed into 15 mL of methanol solution and magnetically stirred for 30 min to disperse them evenly. Then, 0.546 g of Co(NO3)2·6H2O and 0.558 g of Zn(NO3)2·6H2O were added, and stirring was continued for another 30 min. 1.232 g of 2-methylimidazole was dissolved in 15 mL of methanol, stirred thoroughly, and then added to the above solution. The mixture was vigorously stirred at room temperature for 12 h. Subsequently, the nanotubes were washed three times by centrifugation with methanol, transferred to a vacuum drying oven, and dried at 70 °C for 12 h.

[0091] Preparation of CoPd-N-CNTs:

[0092] Weigh out 130 mg of ZnCo-CNT and disperse it in 13 mL of n-hexane, then sonicate at room temperature for 1 h. Subsequently, add 30 μL of Na₂PdCl₄ (50 mg / mL) dropwise to the above solution. -1 After sonication for 10 minutes, stirring was continued at room temperature for 12 hours. The impregnated sample was washed by centrifugation with methanol, then transferred to a vacuum drying oven at 70°C for 12 hours. The resulting powder was placed in a tube furnace and dried at 2°C / min under flowing argon gas. -1The temperature was increased at a rate of [unspecified], and the sample was held at 900℃ for 2 hours. It was then allowed to cool naturally to room temperature to obtain the sample. A portion of the sample was treated with hydrochloric acid for 12 hours, followed by centrifugation and drying to obtain the final sample.

[0093] Comparative Example

[0094] Preparation of ZnCo-CNTs:

[0095] 30 mg of carbon nanotubes were weighed into 15 mL of 99.5% methanol solution and magnetically stirred for 30 min at 600 rpm to disperse them evenly. Then, 0.546 g of Co(NO3)2·6H2O and 0.558 g of Zn(NO3)2·6H2O were added, and stirring was continued for another 30 min. 0.616 g of 2-methylimidazole was dissolved in 15 mL of methanol, stirred thoroughly, and then added to the above solution. The mixture was stirred at 600 rpm for 12 h at room temperature. Subsequently, the nanotubes were washed three times with methanol at 8000 rpm for 10 min each time, and then transferred to a vacuum drying oven and dried at 60 °C for 12 h.

[0096] Preparation of Co-N-CNTs:

[0097] The obtained ZnCo-CNT powder was placed in a tube furnace and heated at 2°C for 1 minute under flowing argon gas. -1 The temperature was increased to 900℃ at a certain rate and held for 2 hours. After naturally cooling to room temperature, the sample was obtained. A portion of the sample was treated with hydrochloric acid for 12 hours, followed by centrifugation and drying to obtain the final sample.

[0098] The lithium-air battery assembled using the CoPd-N-CNT catalyst prepared in Example 1 and the Co-N-CNT catalyst prepared in the comparative example achieved a cutoff capacity of 1000 mAh g. -1 100mAg current -1 The constant current charge-discharge curve under the condition, such as Figure 1 As shown, from Figure 1 The results show that CoPd-N-CNT exhibits a lower charging platform (3.2V) and a lower overpotential (0.6V), significantly lower than the overpotential of Co-N-CNT (1.55V). This indicates that cobalt-palladium diatomic batteries offer superior performance compared to cobalt single-atom batteries; the introduction of palladium reduces the overpotential in the OER process and improves catalytic efficiency.

[0099] A comparison of the discharge specific capacity of lithium-air batteries assembled using CoPd-N-CNT catalysts and those prepared in the comparative example during deep discharge, as follows: Figure 2 As shown, from Figure 2It can be concluded that CoPd-N-CNT has excellent discharge specific capacity, with an initial discharge capacity of up to 15000 mAh g. -1 It is far superior to Co-N-CNT (~8000mAh g) -1 )electrode..

[0100] A comparison of the discharge potential of lithium-air batteries assembled using CoPd-N-CNT catalyst and Co-N-CNT catalyst prepared in the comparative example as a function of cycle number is shown in the figure. Figure 3 As shown, from Figure 3 From this, it can be concluded that the Co-N-CNT battery at 200 mAg -1 The discharge / charge cycle curve of the under-charge battery shows severe energy loss, with the OER terminal potential rapidly rising to 4.5V. In stark contrast, the CoPd-N-CNT battery exhibits significant energy loss at 200mAg. -1 The discharge / charge curves under these conditions not only exhibit lower polarization potentials but also maintain stable lithiation and electrolysis potentials, demonstrating superior performance. Compared to cobalt single-atom catalysts, CoPd-N-CNT catalysts show significant advantages in improving overpotential and cycle durability in lithium-air batteries. Therefore, we conclude that cobalt-palladium diatomic catalysts play a decisive role in mitigating charge-discharge polarization, particularly OER overpotential, thereby greatly improving round-trip efficiency, coulombic efficiency, and cycle performance.

[0101] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a Co-Pd diatomic cathode catalyst for lithium-air batteries, characterized in that, The steps are as follows: 1) Mix carbon nanotubes with an alcohol solution to obtain a carbon nanotube solution, and then mix the carbon nanotube solution with cobalt salt and zinc salt to obtain a cobalt-containing mixture; 2) Mix 2-methylimidazole with an alcohol reagent to obtain a 2-methylimidazole solution. Mix the 2-methylimidazole solution with the cobalt-containing mixture obtained in step 1), stir, centrifuge and dry to obtain CoZn-CNT. 3) The CoZn-CNT obtained in step 2) is dispersed in n-hexane, then mixed with a palladium salt solution, stirred, centrifuged, and dried to obtain a solid; 4) The solid obtained in step 3) is pyrolyzed to obtain a pyrolyte. The pyrolyte is then treated with hydrochloric acid solution and dried to obtain a Co-Pd biatom cathode catalyst for lithium-air batteries. In step 1), the mass ratio of carbon nanotubes to the volume ratio of alcohol solution is 30 mg: 15-40 mL. The alcohol solution includes a methanol solution, wherein the methanol solution contains 99.5% methanol by volume. In step 1), the volume ratio of the alcohol solution to the mass ratio of the cobalt salt and zinc salt is 15-40 mL: 0.546 g: 0.558 g. The cobalt salt is cobalt nitrate hexahydrate, and the zinc salt is zinc nitrate hexahydrate; In step 2), the mass ratio of 2-methylimidazole to the volume ratio of the alcohol reagent is 0.616 g: 15 mL. The alcohol reagent includes methanol; In step 2), the volume ratio of the 2-methylimidazole solution to the cobalt-containing mixture is 1:

1. The stirring time is 12 hours; The centrifugation conditions include: centrifugation and washing with methanol; The drying conditions include: a temperature of 60–70°C and a time of 12 hours; In step 3), the mass ratio of CoZn-CNT to the volume of n-hexane is 130 mg: 13 mL. The mass ratio of the CoZn-CNT to the volume ratio of the palladium salt solution is 130 mg: 30 μL; The palladium salt solution includes a Na2PdCl4 solution, wherein the mass concentration of Na2PdCl4 in the Na2PdCl4 solution is 50 mg / mL; The stirring time is 12 hours; The centrifugation conditions include: centrifugation and washing with methanol; The drying conditions include: a temperature of 60–70°C and a time of 12 hours; The conditions for pyrolysis in step 4) include: a temperature of 900℃, a time of 2h, and a heating rate of 2℃ / min. The processing time for step 4) is 12 hours. The molar concentration of the hydrochloric acid solution is 0.5 mol / L.

2. A Co-Pd diatomic cathode catalyst for a lithium-air battery prepared by the method of claim 1, wherein the Co-Pd diatomic cathode catalyst for the lithium-air battery has a cobalt mass percentage of 0.44% and a palladium mass percentage of 0.52%.

3. The application of the Co-Pd diatomic cathode catalyst of claim 2 in lithium-air batteries.

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