Pt nanosheet / pvp-cnt-n-doped graphene aerogel and preparation method and application thereof in flexible battery

Abstract

This invention provides a Pt nanosheet / PVP-CNT-N-doped graphene aerogel, its preparation method, and its application in flexible batteries. The preparation method includes the following steps: adding graphene oxide dispersion and hydrophilic CNT dispersion to a Tris-HCl buffer solution, followed by the addition of a nitrogen source and ultrasonic treatment to obtain a mixed solution; then performing a hydrothermal reaction to obtain a 3D CNT-N-doped graphene aerogel; adding a Pt source aqueous solution to the CNT-N-doped graphene aerogel, adsorbing the excess Pt source aqueous solution, then adding a reducing agent and a dispersant, and performing a hydrothermal reaction to obtain the final product. The material prepared by this invention efficiently catalyzes the oxygen reduction reaction. When used as a positive electrode in a flexible zinc-air battery assembly, it exhibits an open-circuit voltage as high as 1.697V and a high current density of 139.0 mA / cm². 2 It exhibits a high efficiency of 68.5 mW / cm². 2 It has a high power density and a stable discharge voltage.

Description

Technical Field

[0001] This invention belongs to the field of zinc-air battery technology, specifically relating to a Pt nanosheet / PVP-CNT-N-doped graphene aerogel, its preparation method, and its application in flexible batteries; more specifically, relating to a Pt nanosheet / PVP-CNT-N-doped graphene aerogel oxygen reduction reaction (ORR) electrocatalyst, its preparation method, and its application in flexible zinc-air batteries. Background Technology

[0002] Zinc-air batteries have a theoretically high specific energy density (1086Wh / kg). Zn Zinc-air batteries are hailed as a new type of environmentally friendly energy source due to their green, low-cost, and high safety characteristics. Compared to liquid zinc-air batteries, all-solid-state flexible zinc-air batteries have advantages such as smaller size and wearability. Therefore, research on flexible zinc-air batteries has become a hot topic in energy storage devices today.

[0003] Currently, the main factor affecting the performance of flexible zinc-air batteries is the slow kinetics of the oxygen reduction reaction (ORR) in the cathode material, leading to low battery performance. Commercially available ORR catalysts are platinum / carbon containing precious metals. Platinum is expensive, so maintaining catalyst activity and flexibility while appropriately reducing the platinum content is crucial for developing high-efficiency flexible batteries. Summary of the Invention

[0004] To address the shortcomings of existing technologies, reducing the amount of platinum source, using a dispersant that fully disperses platinum, and a carbon substrate that ensures good platinum dispersion, while maintaining flexibility and conductivity, will effectively improve the performance of flexible batteries. Therefore, this invention provides a Pt nanosheet / PVP-CNT-N-doped graphene aerogel, its preparation method, and its application in flexible batteries. This invention uses PVP as a dispersant and a novel carbon substrate CNT-hierarchical porous N-doped graphene aerogel as the substrate, where PVP represents polyvinylpyrrolidone and CNT represents carbon nanotubes. Charge transfer exists between PVP and Pt nanosheets, fixing the Pt nanosheets onto reduced graphene oxide, resulting in smaller size and more uniform dispersion. CNTs possess advantages such as high strength, good conductivity, and flexibility, endowing the composite material with flexibility and stability, and have attracted attention in the field of flexible zinc-air batteries. Hierarchical porous NGA itself has a large specific surface area, allowing the loaded Pt nanosheets to fully expose their active sites, and the N-doped graphene aerogel itself has ORR activity; its large pores ensure efficient mass transfer during the ORR process.

[0005] In short, this invention provides a Pt nanosheet / PVP-CNT-N-doped graphene aerogel oxygen reduction reaction (ORR) electrocatalyst, its preparation method, and its application in flexible zinc-air batteries. This invention synthesizes a novel carbon-based CNT-N-doped graphene aerogel with a 3D (D, dimension) porous structure through hydrothermal processes, freeze-drying, and high-temperature heat treatment. With the participation of PVP, a second hydrothermal process yields a 2D@3D self-supporting structure, where small 2D Pt nanosheets are uniformly distributed on the 3D CNT-N-doped graphene aerogel. The Pt nanosheets mainly expose the (111) crystal plane, exhibiting excellent ORR catalytic activity. As a cathode material in flexible zinc-air batteries, the batteries possess characteristics such as good mechanical flexibility, high open-circuit voltage, and high power density.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing Pt nanosheet / PVP-CNT-N-doped graphene aerogel includes the following steps:

[0008] (1) Add graphene oxide dispersion and hydrophilic CNT dispersion to Tris-HCl buffer solution, then add nitrogen source, and sonicate to obtain a mixture; then carry out hydrothermal reaction, and after the reaction is completed, cool naturally to room temperature, wash, freeze dry and heat treat at high temperature to obtain 3D CNT-N-doped graphene aerogel.

[0009] (2) Add Pt source aqueous solution to 3D CNT-N-doped graphene aerogel, and after adsorption, remove excess Pt source aqueous solution. Then add reducing agent and dispersant PVP to carry out hydrothermal reaction. After the reaction is completed, cool to room temperature, and then wash and vacuum dry to obtain Pt nanosheets / PVP-CNT-N-doped graphene aerogel.

[0010] According to a preferred embodiment of the present invention, the concentration of the Tris-HCl buffer solution in step (1) is 0.1 mol / L and the pH is 8.5; the volume ratio of the Tris-HCl buffer solution to the graphene oxide dispersion is 1 to 5:1.

[0011] According to a preferred embodiment of the present invention, the concentration of the graphene oxide dispersion in step (1) is 2-10 mg / mL, more preferably 5-6 mg / mL; the preparation of the graphene oxide dispersion is a prior art technique, referring to the method in the literature (Xie, B.; Shang, J.; Zhang, R. Preparation and Fluorescence of Ultrafine Graphene Oxide Nanosheets. Science of Advanced Material 2014, 6, 2395-2399.).

[0012] According to a preferred embodiment of the present invention, the concentration of the hydrophilic CNT dispersion in step (1) is 2-10 mg / mL, more preferably 5-8 mg / mL; the mass ratio of graphene oxide to hydrophilic CNT is 1-5:1; the preparation of the hydrophilic CNT dispersion is a prior art, referring to the method in the literature (Cheng, Y.; Lu, S.; Liu, J. Synergistic Effects from Graphene and Carbon Nanotubes Enable Flexible and Robust Electrodes for High-Performance Supercapacitors. Nano Letters, 2012, 12(8), 4206-4211.).

[0013] According to a preferred embodiment of the present invention, the nitrogen source in step (1) is one or more of dopamine, dicyandiamide, chitosan, and urea, and more preferably dopamine; the mass ratio of the nitrogen source to graphene oxide is 1:0.5 to 2.5.

[0014] According to a preferred embodiment of the present invention, the ultrasonic treatment temperature in step (1) is 10-25°C, the ultrasonic power is 300W, and the ultrasonic treatment time is 60-120s.

[0015] According to a preferred embodiment of the present invention, the hydrothermal reaction temperature in step (1) is 160-200°C and the hydrothermal reaction time is 8-20h.

[0016] According to a preferred embodiment of the present invention, the washing in step (1) is washing with deionized water 3 to 10 times; the freeze-drying temperature is -30 to -5°C, and the freeze-drying time is 24 to 60 hours.

[0017] According to a preferred embodiment of the present invention, the high-temperature heat treatment in step (1) is carried out in an Ar atmosphere, the temperature of the high-temperature heat treatment is 500-1000°C, and the time of the high-temperature heat treatment is 2-5 hours.

[0018] According to a preferred embodiment of the present invention, the Pt source in step (2) is one or more of chloroplatinic acid, platinum acetylacetonate, platinum dichloride, and platinum tetrachloride, and is more preferably chloroplatinic acid; the concentration of the Pt source aqueous solution is 1-15 mg / mL; the mass ratio of the added Pt source to the CNT-N-doped graphene aerogel is 1:0.5-2.5, wherein the mass of the added Pt source is the mass of the Pt source added to the 3D CNT-N-doped graphene aerogel before adsorption.

[0019] According to a preferred embodiment of the present invention, the adsorption time in step (2) is 60 to 300 min; the ratio of the volume of excess Pt source aqueous solution adsorbed to the volume of Pt source aqueous solution added before adsorption is 1:1 to 3.

[0020] According to a preferred embodiment of the present invention, the reducing agent in step (2) is one or more of ethylene glycol, ethanol, and benzyl alcohol, and more preferably ethylene glycol; the mass ratio of the reducing agent to the added Pt source is 500 to 2000:1, wherein the mass of the added Pt source is the mass of the Pt source added to the 3D CNT-N-doped graphene aerogel before adsorption.

[0021] According to a preferred embodiment of the present invention, the mass ratio of the dispersant PVP to the CNT-doped graphene aerogel in step (2) is 1 to 10:1.

[0022] According to a preferred embodiment of the present invention, the hydrothermal reaction temperature in step (2) is 100-250°C and the hydrothermal reaction time is 24-80h.

[0023] According to a preferred embodiment of the present invention, the washing in step (2) is to wash with deionized water and anhydrous ethanol 3 to 10 times each; the vacuum drying is to dry at a vacuum of -0.1 to -0.05 MPa and a temperature of 40 to 80°C for 0.5 to 5 hours.

[0024] The present invention also provides a Pt nanosheet / PVP-CNT-N-doped graphene aerogel prepared by the above preparation method; the microstructure of the Pt nanosheet / PVP-CNT-N-doped graphene aerogel is as follows: 2D Pt nanosheets are uniformly distributed on 3D CNT-N-doped graphene aerogel, and the size range of the Pt nanosheets is 1.7 to 3.1 nm.

[0025] According to the present invention, the above-mentioned Pt nanosheet / PVP-CNT-N-doped graphene aerogel is used, but is not limited to, as an electrode material for flexible zinc-air batteries.

[0026] The technical features and beneficial effects of this invention are as follows:

[0027] 1. The material of this invention utilizes a novel carbon substrate—a 3D CNT-N-doped graphene aerogel. CNTs are uniformly distributed on the graphene plane. After high-temperature heat treatment in an inert atmosphere, N atoms are incorporated into both the CNTs and the graphene framework, forming a flexible 3D aerogel porous structure that promotes ion and electron transport. The aerogel possesses characteristics such as large specific surface area, flexibility, high conductivity, and numerous mass transfer channels. Strong intermolecular forces, including π-π stacking interactions, exist between the N-doped graphene and CNTs. The CNTs ensure conductivity and flexibility, while the N-doped graphene itself exhibits ORR activity. This carbon substrate, when used to load 2D Pt nanosheets, avoids their aggregation while ensuring sufficient exposure of their active sites, providing an excellent substrate guarantee for efficient ORR catalysis and improved performance of flexible zinc-air batteries.

[0028] 2. In the material preparation of the present invention, a dispersant is selected to first disperse the Pt source, and then the aggregation of 2D Pt nanosheets is inhibited during the hydrothermal process. The Pt source aqueous solution is subjected to the action of a reducing agent to obtain 2D Pt nanosheets with small size, uniform dispersion and mainly exposed (111) crystal plane, which further ensures that the Pt active catalytic sites are fully exposed.

[0029] 3. The composite material prepared in this invention exhibits near-Pt / C catalytic ORR activity through the synergistic effect of four components: Pt nanosheets, dispersant, CNTs, and N-doped graphene aerogel, achieving the expected goal of high catalytic activity. More importantly, when this Pt nanosheet / PVP-CNT-N-doped graphene aerogel is used as the positive electrode in a flexible zinc-air battery, it exhibits high open-circuit voltage, high power density, and good flexibility (stable discharge voltage at different bending angles), which are superior to those of Pt / C. Attached Figure Description

[0030] Figure 1 Scanning electron microscope (SEM) images of Pt nanosheets / PVP-CNT-N-doped graphene aerogel prepared in Example 1 (a, d), Pt nanosheets / PVP-N-doped graphene aerogel prepared in Comparative Example 1 (b, e), and Pt nanosheets / N-doped graphene aerogel prepared in Comparative Example 2 (c, f), where (ac) is a low-magnification SEM image and (df) is a high-magnification SEM image.

[0031] Figure 2 Transmission electron microscopy (TEM) images of (a) Pt nanosheets / PVP-CNT-N-doped graphene aerogel prepared in Example 1, (b) Pt nanosheets / PVP-N-doped graphene aerogel prepared in Comparative Example 1, and (c) Pt nanosheets / N-doped graphene aerogel prepared in Comparative Example 2.

[0032] Figure 3High-resolution transmission electron microscopy (HRTEM) images of (a) Pt nanosheets / PVP-CNT-N-doped graphene aerogel prepared in Example 1, (b) Pt nanosheets / PVP-N-doped graphene aerogel prepared in Comparative Example 1, and (c) Pt nanosheets / N-doped graphene aerogel prepared in Comparative Example 2.

[0033] Figure 4 The N2 adsorption / desorption isotherms are shown for (a) the Pt nanosheet / PVP-CNT-N-doped graphene aerogel prepared in Example 1, (b) the Pt nanosheet / PVP-N-doped graphene aerogel prepared in Comparative Example 1, and (c) the Pt nanosheet / N-doped graphene aerogel prepared in Comparative Example 2. The inset is a pore size distribution diagram.

[0034] Figure 5 X-ray diffraction patterns of Pt nanosheets / PVP-CNT-N-doped graphene aerogel (PtNPTs / PVP-CNT-NGA) prepared in Example 1, Pt nanosheets / PVP-N-doped graphene aerogel (PtNPTs / PVP-NGA) prepared in Comparative Example 1, Pt nanosheets / N-doped graphene aerogel (PtNPTs / NGA) prepared in Comparative Example 2, and face-centered cubic metal Pt JCPDS standard card (No. 04-0802).

[0035] Figure 6 Thermogravimetric curves of Pt nanosheets / PVP-CNT-N-doped graphene aerogel (PtNPTs / PVP-CNT-NGA) prepared in Example 1, Pt nanosheets / PVP-N-doped graphene aerogel (PtNPTs / PVP-NGA) prepared in Comparative Example 1, and Pt nanosheets / N-doped graphene aerogel (PtNPTs / NGA) prepared in Comparative Example 2 are shown.

[0036] Figure 7 Cyclic voltammetry diagrams of Pt nanosheets / PVP-CNT-N-doped graphene aerogel (PtNPTs / PVP-CNT-NGA) prepared in Example 1, Pt nanosheets / PVP-N-doped graphene aerogel (PtNPTs / PVP-NGA) prepared in Comparative Example 1, and Pt nanosheets / N-doped graphene aerogel (PtNPTs / NGA) prepared in Comparative Example 2.

[0037] Figure 8 Photographs showing the open-circuit voltages of (a) Pt nanosheets / PVP-CNT-N-doped graphene aerogel prepared in Example 1, (b) Pt nanosheets / PVP-N-doped graphene aerogel prepared in Comparative Example 1, (c) Pt nanosheets / N-doped graphene aerogel prepared in Comparative Example 2, and (d) Pt / C as an air cathode catalyst in Comparative Example 3, measured with a multimeter.

[0038] Figure 9The voltage-current density and power-current density curves of the flexible zinc-air batteries assembled with Pt nanosheets / PVP-CNT-N-doped graphene aerogel (PtNPTs / PVP-CNT-NGA) prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 as Pt / C air cathodes are shown.

[0039] Figure 10 Photographs showing the open-circuit voltage of a flexible zinc-air battery assembled with Pt nanosheets / PVP-CNT-N-doped graphene aerogel (PtNPTs / PVP-CNT-NGA) as the air cathode, prepared in Example 1, measured with a multimeter at different bending angles: (a) 0°, (b) 90°, and (c) 180°.

[0040] Figure 11 The discharge voltage curves of flexible zinc-air batteries assembled with Pt nanosheets / PVP-CNT-N-doped graphene aerogel (PtNPTs / PVP-CNT-NGA) prepared in Example 1 and Pt nanosheets / PVP-N-doped graphene aerogel prepared in Comparative Example 1 as air cathodes are shown in the inset. The inset shows photographs of flexible zinc-air batteries with bending angles of 0°, 90°, and 180°.

[0041] Figure 12 Photographs showing the open-circuit voltage of two flexible zinc-air batteries assembled with Pt nanosheets / PVP-CNT-N-doped graphene aerogel as the air cathode, prepared in Example 1, and (b) two household batteries connected in series, as measured by a multimeter.

[0042] Figure 13 A photograph showing two flexible zinc-air batteries assembled in series using Pt nanosheets / PVP-CNT-N-doped graphene aerogel prepared in Example 1 as the air cathode, and driving a 3V motor to rotate a fan.

[0043] Figure 14 The images show two tandem flexible zinc-air batteries assembled using Pt nanosheets / PVP-CNT-N-doped graphene aerogel prepared in Example 1 as air positive electrodes, viewed from angles (a) 0°, (b) 90°, (c) 180°, and (d) 270°, and (e) an image showing the flexible zinc-air battery with the electrode clamps not clamped to the positive and negative electrodes, and (f) an image showing the flexible zinc-air battery with the positive and negative electrodes clamped and the red LED beads lit. Detailed Implementation

[0044] The present invention will be further described below with reference to embodiments and accompanying drawings, but is not limited thereto. Unless otherwise specified, all reagents used in the embodiments are of analytical grade.

[0045] The average molecular weight of polyvinylpyrrolidone (PVP) used in the examples is 55,000.

[0046] Example 1

[0047] A method for preparing Pt nanosheet / PVP-CNT-N-doped graphene aerogel includes the following steps:

[0048] (i) Add 3.7 mL of graphene oxide dispersion with a concentration of 5.4 mg / mL and 1.1 mL of hydrophilic CNT dispersion with a concentration of 6.0 mg / mL to 5.3 mL of Tris-HCl buffer solution (concentration 0.1 mol / L, pH 8.5), stir thoroughly to mix evenly, add 10 mg of dopamine, and sonicate at 15 °C and 300 W for 90 s to obtain a mixture.

[0049] (ii) Transfer all the mixture obtained in step (i) to a hydrothermal reactor and react at 180°C for 12 h. After the reaction is completed, cool naturally to room temperature to obtain polydopamine-CNT-reduced graphene oxide hydrogel. Wash the obtained hydrogel with deionized water 6 times and freeze-dry at -30°C for 36 h to obtain polydopamine-CNT-reduced graphene oxide aerogel.

[0050] (iii) The polydopamine-CNT-reduced graphene oxide aerogel obtained in step (ii) is heat-treated at 800°C for 3 hours in an Ar atmosphere to obtain 3D CNT-N-doped graphene aerogel, denoted as CNT-NGA.

[0051] (iv) Add 1 mL of 10 mg / mL chloroplatinic acid aqueous solution to 10 mg 3D CNT-N-doped graphene aerogel, stir and soak for 2 h, then remove 0.5 mL of excess chloroplatinic acid aqueous solution for recycling.

[0052] (v) Add 16.71 g of ethylene glycol and 40 mg of PVP to the aerogel obtained in step (iv), transfer the resulting suspension to a reaction vessel, and hydrothermally heat at 150 °C for 42 h. After the reaction is completed, allow it to cool naturally to room temperature. Wash the resulting gel 6 times with deionized water and 3 times with ethanol, and then vacuum dry at -0.08 MPa and 60 °C for 2 h to obtain Pt nanosheets / PVP-CNT-N-doped graphene aerogel, denoted as PtNPTs / PVP-CNT-NGA.

[0053] The low-magnification scanning electron microscope image of the PtNPTs / PVP-CNT-NGA prepared in this embodiment is shown below. Figure 1As shown in (a), PtNPTs / PVP-CNT-NGA exhibits a 3D porous structure, as illustrated in the high-magnification scanning electron microscope image. Figure 1 As shown in (d), small-sized Pt nanosheets are uniformly deposited on the CNT-N-doped graphene aerogel through intermolecular forces such as π-π stacking interactions between CNTs and N-doped graphene sheets. Transmission electron microscopy of PtNPTs / PVP-CNT-NGA. Figure 2 As shown in (a), 2D Pt nanosheets are uniformly distributed on CNT-N-doped graphene aerogel, with an average size of 2.4 nm. High-resolution transmission electron microscopy (TEM) of Pt nanosheets / PVP-CNT-N-doped graphene aerogel. Figure 3 (a) indicates that the Pt nanosheets are single crystals with face-centered cubic (111) crystal planes. The N2 adsorption / desorption isotherms and pore size distribution of the Pt nanosheet / PVP-CNT-N-doped graphene aerogel are shown in Figure [Figure number missing]. Figure 4 As shown in (a), the specific surface area of ​​the Pt nanosheet / PVP-CNT-N-doped graphene aerogel is 691.2 m². 2 / g contains mesopores of 2-50nm, with 3.3nm mesopores being the predominant type.

[0054] The X-ray diffraction of the PtNPTs / PVP-CNT-NGA prepared in this embodiment is as follows: Figure 5 As shown, well-crystallized Pt nanosheets exhibit (111), (200), (220), and (311) diffraction peaks, corresponding to the JCPDS standard card (No. 04-0802) for face-centered cubic Pt. The (111) crystal plane is the predominant exposed plane, with an ultrathin thickness perpendicular to this direction of only 4.9 nm. This allows for the full exposure of the (111) crystal plane, which exhibits excellent ORR catalytic activity, effectively improving the utilization rate of the Pt active surface. The thermogravimetric curves of PtNPTs / PVP-CNT-NGA are shown below. Figure 6 As shown, the Pt nanosheet loading was 11.0 wt%. Cyclic voltammograms of PtNPTs / PVP-CNT-NGA ( Figure 7 The results show that the electrochemical active area of ​​PtNPTs / PVP-CNT-NGA is 51.1 m². 2 / g Pt The series resistance of PtNPTs / PVP-CNT-NGA is 4.35Ω, and the charge transfer resistance is 1.10Ω.

[0055] Comparative Example 1

[0056] A method for preparing a Pt nanosheet / PVP-N-doped graphene aerogel is described in Example 1, except that a hydrophilic CNT dispersion is not added in step (i), while other operations remain the same. The Pt nanosheet / PVP-N-doped graphene aerogel prepared in this comparative example is denoted as PtNPTs / PVP-NGA.

[0057] The low-magnification scanning electron microscope image of the PtNPTs / PVP-NGA prepared in this comparative example is shown below. Figure 1 As shown in (b), PtNPTs / PVP-NGA exhibits a 3D porous structure, as illustrated in the high-magnification scanning electron microscope image below. Figure 1 As shown in (e), there is no CNT distribution on the N-doped graphene sheet, and Pt nanosheets are uniformly distributed on the N-doped graphene aerogel.

[0058] Transmission electron microscopy of the PtNPTs / PVP-NGA prepared in this comparative example. Figure 2 (b) shows that the Pt nanosheets have an average size of 4.4 nm and are uniformly distributed on the N-doped graphene aerogel. High-resolution transmission electron microscopy of Pt nanosheets / PVP-N-doped graphene aerogel. Figure 3 (b) indicates that the Pt nanosheets are single crystals with face-centered cubic (111) crystal planes. The N2 adsorption / desorption isotherms and pore size distribution of PtNPTs / PVP-NGA are shown in the figure. Figure 4 As shown in (b), the specific surface area is 242.2 m². 2 / g contains mesopores of 2-50nm, with 3.5nm mesopores being the predominant type.

[0059] The X-ray diffraction of the PtNPTs / PVP-NGA prepared in this comparative example is as follows: Figure 5 As shown, well-crystallized Pt nanosheets exhibit (111), (200), (220), and (311) diffraction peaks, corresponding to the JCPDS standard card (No. 04-0802) for face-centered cubic Pt. The (111) crystal plane is the predominant exposed plane, with a thickness of 5.0 nm perpendicular to this direction. However, the intensity of the (111) peak is less than that of the PtNPTs / PVP-CNT-NGA prepared in Example 1. This is because the N content in PtNPTs / PVP-CNT-NGA is 5.8 at%, while the N content in the PtNPTs / PVP-NGA prepared in this comparative example is 4.1 at%. Higher N content results in more positively charged C atoms adjacent to the N atom, which is beneficial for anchoring more negatively charged chloroplatinate ions, leading to a greater number of Pt nanosheets ultimately loaded after nucleation growth. Thermogravimetric curve of PtNPTs / PVP-NGA (…) Figure 6The results show that the Pt nanosheet loading is 8.1 wt%. This is less than the 11.0 wt% loading in Example 1 with the same Pt ​​source feed amount. Furthermore, PVP disperses and prevents Pt nanosheet aggregation; therefore, the Pt nanosheets without CNTs are not as uniformly dispersed and smaller in size as those in Example 1. Cyclic voltammetry ( Figure 7 This indicates that the electrochemical active area is 25.6 m². 2 / g Pt The series resistance of PtNPTs / PVP-NGA is 4.52Ω, and the charge transfer resistance is 2.31Ω.

[0060] Comparative Example 2

[0061] A method for preparing Pt nanosheet / N-doped graphene aerogel is described in Example 1, except that hydrophilic CNT dispersion is not added in step (i), and PVP is not added in step (v), while other operations remain the same. The Pt nanosheet / N-doped graphene aerogel prepared in this comparative example is denoted as PtNPTs / NGA.

[0062] The low-magnification scanning electron microscope image of the PtNPTs / NGA prepared in this comparative example is shown below. Figure 1 As shown in (c), it exhibits a 3D porous structure, as illustrated in the high-magnification scanning electron microscope image. Figure 1 As shown in (f), there is no CNT distribution on the N-doped graphene sheet. Compared with Example 1 and Comparative Example 1, larger Pt nanosheets are uniformly distributed on the N-doped graphene aerogel.

[0063] Transmission electron microscopy of the PtNPTs / NGA prepared in this comparative example Figure 2 As shown in (c), Pt nanosheets are uniformly distributed on N-doped graphene aerogel, with an average size of 6.3 nm. High-resolution transmission electron microscopy of PtNPTs / NGA. Figure 3 (c) indicates that the Pt nanosheets are single crystals with face-centered cubic (111) crystal planes. The N2 adsorption / desorption isotherms and pore size distribution of PtNPTs / NGA are shown in the figure. Figure 4 As shown in (c), the specific surface area of ​​the Pt nanosheets / N-doped graphene aerogel is 171.9 m². 2 / g contains mesopores of 2-50nm, with 3.4nm mesopores being the predominant type.

[0064] The X-ray diffraction pattern of the PtNPTs / NGA prepared in this comparative example is as follows: Figure 5 As shown, well-crystallized Pt nanosheets exhibit (111), (200), (220), and (311) diffraction peaks, corresponding to the JCPDS standard card (No. 04-0802) for face-centered cubic Pt. The (111) crystal plane is the predominant exposed plane, with a thickness of 9.5 nm perpendicular to this direction. The thermogravimetric curves of PtNPTs / NGA are shown below. Figure 6 As shown, the Pt nanosheet loading in the obtained PtNPTs / NGA was 5.9 wt%. The cyclic voltammogram of PtNPTs / NGA is shown below. Figure 7 As shown, the electrochemical active area of ​​PtNPTs / NGA is 12.8 m². 2 / g Pt The series resistance of PtNPTs / NGA is 4.53 Ω, and the charge transfer resistance is 2.77 Ω. In the PtNPTs / PVP-CNT-NGA prepared in Example 1, the Pt nanosheets are the smallest and most uniformly dispersed, fully exposing the active sites. Therefore, the electrochemically active area is higher than that of the PtNPTs / PVP-NGA prepared in Comparative Example 1 and the PtNPTs / NGA prepared in this comparative example. Compared to PtNPTs / PVP-NGA and PtNPTs / NGA, the addition of CNTs improves the conductivity of the material, thus resulting in the lowest series resistance and charge transfer resistance.

[0065] Comparative Example 3

[0066] The reagent Pt / C (20 wt%) was used as Comparative Example 3.

[0067] Test case

[0068] The Pt nanosheet / PVP-CNT-N-doped graphene aerogel prepared in Example 1, the Pt nanosheet / PVP-N-doped graphene aerogel prepared in Comparative Example 1, the Pt nanosheet / N-doped graphene aerogel prepared in Comparative Example 2, and Comparative Example 3 were subjected to electrochemical performance tests, and were used as air cathodes to assemble planar flexible zinc-air batteries for performance testing. The specific steps are as follows:

[0069] (a) Modified electrode:

[0070] Two mg of the aerogel materials prepared in Example 1, Comparative Example 1, and Comparative Example 2, as well as Comparative Example 3, were dispersed in 985 μL of anhydrous ethanol and 15 μL of 5 wt% Nafion solution, respectively, and sonicated at 300 W for 10 min to obtain four well-mixed sample dispersions. 10 μL of each sample dispersion was uniformly drop-coated onto the surface of a polished rotating disk electrode and dried at room temperature to obtain four modified electrodes.

[0071] (II) Testing of the three-electrode system:

[0072] The modified electrode obtained in step (I) was used as the working electrode, the Pt sheet as the counter electrode, and the Hg / HgO electrode as the reference electrode. The test was conducted in an O2-saturated 0.1 mol / L KOH solution at a scan rate of 5 mV / s to obtain the ORR linear sweep voltammetric curve of the sample.

[0073] (III) Assembly of planar flexible zinc-air batteries:

[0074] The polished zinc foil (0.1 mm thick) was used as the negative electrode. 2 mg of the polished aerogel materials prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were dispersed in 997 μL of anhydrous ethanol and 3 μL of 5 wt% Nafion solution, respectively, and sonicated at 300 W for 10 min to obtain a homogeneous sample dispersion. The sample dispersion was coated onto compacted nickel foam (0.5 mm thick) as the positive electrode material; the sample loading was 2 mg / cm³. 2 The solid electrolyte is potassium hydroxide-polyacrylic acid (KOH-PAA) gel. It is encapsulated with acrylic tape.

[0075] (iv) Open-circuit voltage and power density test of flexible zinc-air batteries:

[0076] For the flexible zinc-air battery assembled in step (iii), the open-circuit voltage was measured with a multimeter, and the power density was measured with a Chenhua electrochemical workstation CHI760E.

[0077] (V) Discharge tests of flexible zinc-air batteries at different bending angles and current densities:

[0078] The flexible zinc-air batteries assembled in Step (III) Example 1 and Comparative Example 1 were subjected to bending angles of 0°, 90°, and 180°, and at speeds of 1, 2, 5, and 10 mA / cm, respectively. 2 Current density was measured using the Blue Battery Testing System to assess discharge performance.

[0079] In a 0.1 mol / L KOH solution, the Pt nanosheets / PVP-CNT-N-doped graphene aerogel prepared in Example 1, the Pt nanosheets / PVP-N-doped graphene aerogel prepared in Comparative Example 1, the Pt nanosheets / N-doped graphene aerogel prepared in Comparative Example 2, and the reagent Pt / C (20 wt%) in Comparative Example 3 were subjected to ORR linear sweep voltammetry curves at 1600 rpm in a three-electrode system. The results showed that the onset potential and limiting diffusion current density of the PtNPTs / PVP-CNT-NGA prepared in Example 1 were 0.92 V and 5.2 mA / cm², respectively. 2 This is higher than the 0.90V and 4.4mA / cm of the comparative example 1PtNPTs / PVP-NGA. 2 Compared with the comparative example 2PtNPTs / NGA, the values ​​were 0.87V and 4.2mA / cm. 2 This is close to the 0.95V and 5.9mA / cm of the comparative example 3Pt / C. 2This is because CNTs have high conductivity, which accelerates electron transfer. PVP acts as a stabilizer and dispersant; the interaction between PVP and Pt nanosheets anchored on graphene ensures uniform dispersion of the Pt nanosheets and prevents further growth, thereby achieving highly efficient ORR catalysis. The ORR linear sweep voltammetric curves of the PtNPTs / PVP-CNT-NGA prepared in Example 1 at different rpm were calculated using the Koutecky-Levich equation, and this sample conforms to the 4-electron transfer mechanism.

[0080] The open-circuit voltage, power density curves, open-circuit voltage after ten bends at different bending angles, and discharge voltages at different bending angles and current densities of the flexible zinc-air battery prepared in Example 1 using PtNPTs / PVP-CNT-NGA as the air cathode are shown below. Figure 8 (a) Figure 9 , Figure 10 , Figure 11 As shown. From Figure 8 (a) It can be seen that the open-circuit voltage of the flexible zinc-air battery with air cathode PtNPTs / PVP-CNT-NGA is 1.697V, which is higher than that of the PtNPTs / PVP-CNT-NGA flexible zinc-air battery. Figure 8 (b) The open-circuit voltage of the PtNPTs / PVP-NGA prepared in Comparative Example 1 is 1.491V. Figure 8 (c) shows the open-circuit voltage of 1.427V for the PtNPTs / NGA prepared in Comparative Example 2. Figure 8 (d) shows the open-circuit voltage of 1.386V corresponding to Pt / C in Comparative Example 3. From Figure 9 As can be seen, the flexible zinc-air battery prepared in Example 1, using PtNPTs / PVP-CNT-NGA as the air cathode, exhibits excellent power density, reaching a high current density of 139.0 mA / cm². 2 The power density is 68.5 mW / cm³. 2 This is far superior to the PtNPTs / PVP-NGA prepared in Comparative Example 1, which corresponds to 89.9 mA / cm². 2 The power density is 43.7 mW / cm³. 2 The PtNPTs / NGA prepared in Comparative Example 2 corresponds to an A / cm² value of 69.9 mA / cm². 2 The power density is 33.3 mW / cm³. 2 The Pt / C ratio obtained in Example 3, compared to air as a positive electrode, is 51.4 mA / cm². 2 The power density is 23.8 mW / cm³. 2 .from Figure 10 It can be seen that the PtNPTs / PVP-CNT-NGA battery with air cathodes at different bending angles of 0, 90, and 180° still maintains a stable open-circuit voltage after being bent ten times. From Figure 11It can be seen that at different bending angles of 0, 90, and 180°, different current densities of 1, 2, 5, and 10 mA / cm² are observed. 2 The air-positive PtNPTs / PVP-CNT-NGA battery exhibits a stable discharge voltage, superior to the corresponding PtNPTs / PVP-CNT-NGA. This is because the highly conductive CNTs impart flexibility to the material, resulting in an assembled battery with excellent mechanical flexibility and high discharge performance.

[0081] Two flexible zinc-air batteries, using PtNPTs / PVP-CNT-NGA prepared in Example 1 as the air cathode, were connected in series, as follows: Figure 12 As shown, the voltage is 3.17V, which is the same as the voltage (3.20V) of two 1.50V commercially available batteries connected in series. From Figure 13 As can be seen, the air positive electrode is connected in series with two PtNPTs / PVP-CNT-NGA batteries, which can drive a 3V motor to rotate the fan. For example... Figure 14 The images show two series-connected flexible zinc-air batteries with an air cathode, PtNPTs / PVP-CNT-NGA, observed at (a) 0°, (b) 90°, (c) 180°, and (d) 270°. Figure 14 e shows a photo of the electrode clamps not clamping the positive and negative electrodes of the flexible zinc-air battery. Figure 14 f demonstrates that the circuit can light up red LED beads when it is turned on, further proving the performance of its flexible battery.

[0082] In summary, regarding the structure and performance, compared to PtNPTs / PVP-NGA and PtNPTs / NGA, the PtNPTs / PVP-CNT-NGA of the present invention can disperse Pt and prevent it from growing further. The (111) crystal plane is the main exposed surface, and its Pt nanosheet active sites are more exposed, resulting in a larger electrochemical active area. The added CNTs improve the conductivity of the composite material, further increase the Pt loading and active sites, and at the same time give the material the flexibility to discharge stably when bent at different angles more times.

[0083] Therefore, the preparation method of the present invention fully utilizes the synergistic effect of each component to obtain a PtNPTs / PVP-CNT-NGA that can efficiently catalyze ORR. This material has a novel structure; when applied to a flexible zinc-air battery, it exhibits excellent discharge performance.

Claims

1. A method for preparing Pt nanosheets / PVP-CNT-N-doped graphene aerogel, comprising the following steps: (1) Add graphene oxide dispersion and hydrophilic CNT dispersion to Tris-HCl buffer solution, then add nitrogen source, and sonicate to obtain a mixture; then carry out hydrothermal reaction, and after the reaction is completed, cool naturally to room temperature, wash, freeze dry, and heat treat at high temperature to obtain 3D CNT-N-doped graphene aerogel; the mass ratio of graphene oxide to hydrophilic CNT is 1~5:1; the nitrogen source is one or more of dopamine, dicyandiamide, chitosan, and urea, and the mass ratio of nitrogen source to graphene oxide is 1:0.5~2.5; after high temperature heat treatment, N atoms are incorporated into both CNT and graphene framework; (2) Add Pt source aqueous solution to 3D CNT-N-doped graphene aerogel, adsorb the excess Pt source aqueous solution, then add reducing agent and dispersant PVP, carry out hydrothermal reaction, cool to room temperature after the reaction is completed, and then wash and vacuum dry to obtain Pt nanosheet / PVP-CNT-N-doped graphene aerogel; the Pt source is chloroplatinic acid, and the mass ratio of the added Pt source to CNT-N-doped graphene aerogel is 1:0.5~2.5; the reducing agent is one or more of ethylene glycol, ethanol, and benzyl alcohol; the mass ratio of the reducing agent to the added Pt source is 500~2000:1; the mass ratio of the dispersant PVP to CNT-N-doped graphene aerogel is 1~10:

1.

2. The preparation method of Pt nanosheets / PVP-CNT-N-doped graphene aerogel according to claim 1, characterized in that, The concentration of the Tris-HCl buffer solution in step (1) is 0.1 mol / L and the pH is 8.5; the volume ratio of the Tris-HCl buffer solution to the graphene oxide dispersion is 1~5:1; and the concentration of the graphene oxide dispersion is 2~10 mg / mL.

3. The preparation method of Pt nanosheets / PVP-CNT-N-doped graphene aerogel according to claim 1, characterized in that, The concentration of the hydrophilic CNT dispersion mentioned in step (1) is 2~10 mg / mL.

4. The preparation method of Pt nanosheets / PVP-CNT-N-doped graphene aerogel according to claim 1, characterized in that, The ultrasonic treatment in step (1) is performed at a temperature of 10~25℃, an ultrasonic power of 300W, and an ultrasonic treatment time of 60~120s. The hydrothermal reaction temperature is 160~200℃, and the hydrothermal reaction time is 8~20h; the washing is performed by washing with deionized water 3~10 times; the freeze-drying temperature is -30~-5℃, and the freeze-drying time is 24~60h.

5. The preparation method of Pt nanosheets / PVP-CNT-N-doped graphene aerogel according to claim 1, characterized in that, The high-temperature heat treatment in step (1) is carried out in an Ar atmosphere, the temperature of the high-temperature heat treatment is 500~1000℃, and the time of the high-temperature heat treatment is 2~5h.

6. The preparation method of Pt nanosheets / PVP-CNT-N-doped graphene aerogel according to claim 1, characterized in that, The concentration of the Pt source aqueous solution in step (2) is 1~15 mg / mL; the adsorption time is 60~300 min; the ratio of the volume of excess Pt source aqueous solution adsorbed to the volume of Pt source aqueous solution added before adsorption is 1:1~3.

7. The preparation method of Pt nanosheets / PVP-CNT-N-doped graphene aerogel according to claim 1, characterized in that, In step (2), the hydrothermal reaction temperature is 100~250℃ and the hydrothermal reaction time is 24~80h; the washing is to wash with deionized water and anhydrous ethanol 3~10 times each; the vacuum drying is to dry at a vacuum degree of -0.1~-0.05MPa and 40~80℃ for 0.5~5h.

8. A Pt nanosheet / PVP-CNT-N-doped graphene aerogel prepared by the method described in claim 1.

9. The application of the Pt nanosheet / PVP-CNT-N-doped graphene aerogel according to claim 8, as an electrode material for zinc-air batteries.

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