Asymmetric carbon-based air electrode with wettability gradient as well as preparation method and application of asymmetric carbon-based air electrode

Abstract

The invention discloses an asymmetric carbon-based air electrode with wettability gradient as well as a preparation method and application of the asymmetric carbon-based air electrode. The preparation method comprises the following steps: respectively carrying out ultrasonic dispersion on functionalized fish scale-like hydrophilic graphene nanosheets and functionalized water strider fluff-like hydrophobic multi-walled carbon nanotubes to obtain carbonaceous assembly solutions of carbon-based materials with different structural characteristics; and carrying out carbonaceous assembly under negative pressure by adopting a vacuum suction filtration method, and ensuring that the suction filtration interval of two kinds of carbonaceous assembly liquid does not exceed 1min, so as to obtain the asymmetric air electrode with wettability gradient. The asymmetric air electrode assembled by the Axy-FCNTs-FGNSs through carbonaceous materials has an oxygen transmission channel, an expanded three-dimensional interface enables a positive electrode reaction to have higher active site utilization rate and better structural durability, the peak power density of a zinc-air battery assembled as a positive electrode is up to 239.3 mW cm <-2 >, the specific capacity of the battery is 814.3 mAh gZn <-1 >, and under the circulating current density of 10 mAcm <-2 >, the specific capacity of the zinc-air battery can be greatly improved. Under the condition that the voltage difference is 0.84 V, the excellent cycle life of 3696 times is shown, and good application prospects are achieved.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic materials technology, specifically relating to an asymmetric carbon-based air electrode with a wettability gradient, its preparation method, and its application. Background Technology

[0002] Metal-air batteries are a high-performance emerging green energy source with advantages such as being non-toxic, pollution-free, and having high specific energy. However, the oxygen reduction reaction (ORR) kinetics at the cathode of metal-air batteries are very slow, which greatly limits the energy output of the battery. Current research focuses on developing advanced electrocatalysts for the ORR, with some materials even surpassing commercially available Pt / C catalysts. However, the overall performance of the air electrode depends not only on catalytic activity but also on key factors such as the utilization rate of active components, structural durability, and reactant / product mass transfer efficiency—characteristics essentially determined by the electrode structure design, which are precisely the key factors that most current research has not fully addressed. Traditional homogeneous catalyst layer configurations can only provide a limited two-dimensional three-phase reaction interface, resulting in the underutilization of a large number of catalytic active sites. Furthermore, the cumulative mechanical stress caused by electrolyte flow and repeated bubble aggregation-desorption processes can lead to the gradual peeling off of the catalyst layer, significantly affecting the battery's lifespan. Therefore, it is necessary to fundamentally reconstruct the cathode structure, synergistically improving the reaction kinetics and operational stability of metal-air batteries by expanding the three-phase reaction interface, establishing bidirectional high-efficiency mass transfer channels, and suppressing catalytic component peeling.

[0003] Chinese patent application No. 202311540215.8, entitled "An Asymmetric Air Electrode and Its Preparation Method," describes obtaining the asymmetric air electrode by roll-bonding a charging electrode and a discharging electrode and then calcining them in an inert atmosphere. The charging electrode consists of a metal mesh substrate and an oxygen evolution catalyst prepared in situ on the metal mesh substrate, while the discharging electrode comprises an oxygen reduction catalyst and a hydrophobic material. However, current methods for preparing asymmetric air electrodes are limited, and most require complex preparation methods such as high-temperature calcination and electrodeposition. There is an urgent need to develop a simple, efficient, and universal method to prepare asymmetric air electrodes with a wettability gradient and to study their performance in metal-air batteries. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide an asymmetric carbon-based air electrode with a wettability gradient, its preparation method, and its applications. Specifically, a solvothermal-filtration assembly method is employed, utilizing the wettability characteristics of carbon-based materials with different structures to prepare Asy-FCNTs-FGNSs with a gradient structure, exhibiting excellent wettability gradient properties. This eliminates the need for a carbon paper substrate, expands the three-phase reaction interface, establishes a bidirectional high-efficiency mass transfer channel, and fundamentally reconstructs the cathode structure, demonstrating promising market application prospects.

[0005] To address the problems in the existing technology, the technical solution adopted by this invention is as follows:

[0006] A method for preparing an asymmetric carbon-based air electrode with a wettability gradient includes the following steps:

[0007] (1) Preparation of carbonaceous assembly solution

[0008] Functionalized carbon nanotubes (FCNTs) and functionalized graphene nanosheets (FGNSs) were prepared and processed according to m... 碳质材料 / V DMF The carbonaceous assembly solution 1 and carbonaceous assembly solution 2 were ultrasonically dispersed in an amphiphilic solution at a ratio of 1:1 mg / mL.

[0009] (2) Gradient structure orientation assembly

[0010] First, carbonaceous assembly solution 1, which mimics the hydrophobic properties of water strider hair, is filtered onto a microporous membrane to form a hydrophobic bottom layer. After filtration, vacuum filtration is continued. Under negative pressure, carbonaceous assembly solution 2, which mimics the hydrophilic properties of fish scales, is rapidly filtered to form a gradually transitioning hydrophobic-hydrophilic structural gradient. It is ensured that the filtration interval between the two carbonaceous assembly solutions does not exceed 1 minute. After vacuum drying, an asymmetric air electrode with a wettability gradient is obtained.

[0011] More preferably, the preparation process of the functionalized carbon nanotubes or functionalized graphene nanosheets in step (1) is as follows: 40 mg of carbon nanotubes or graphene nanosheets and 10 mg of iron phthalocyanine are weighed and dispersed in 35 mL of anhydrous ethanol solution, ultrasonically dispersed for 1 h, and then the dispersion is transferred to a 50 mL hydrothermal reactor with a Teflon liner and solvothermally reacted at 180 °C for 12 h. After the reaction is completed, the mixture is washed 3 times with anhydrous ethanol and then placed in a vacuum drying oven and dried at 60 °C for 8 h to obtain ORR-functionalized carbon nanotube electrocatalysts FCNTs or ORR-functionalized graphene nanosheet electrocatalysts FGNSs.

[0012] More preferably, the functionalized graphene nanosheets described in step (1) have a spread of 1 to 3 μm; the functionalized carbon nanotubes are multi-walled carbon nanotubes with a length of 0.5 to 2 μm.

[0013] More preferably, the ultrasonic power in step (1) is 360W, and the ultrasonic treatment lasts for 2 hours.

[0014] More preferably, in step (2), the particle size of the microporous membrane is 0.22 μm; and the range of maintaining the negative pressure is 0.09 to 0.1 MPa.

[0015] More preferably, the dispersant used in step (2) is an amphiphilic solvent, such as DMF, ethanol, or dimethyl sulfoxide (DMSO).

[0016] More preferably, when the carbon-based materials in the carbon-based assembly liquid 1 and carbon-based assembly liquid 2 in step (2) are of equal mass, an asymmetric assembled carbon nanotube-graphene nanosheet (Asy-FCNTs-FGNSs) air cathode is obtained.

[0017] The asymmetric carbon-based air electrode with a wettability gradient prepared by the above method allows functionalized graphene nanosheets to penetrate downwards into the pre-formed carbon nanotube layer under negative pressure, while the functionalized carbon nanotubes fill the carbon-graphene nanosheet network upwards. This forms an interlocking reinforcement structure of carbon nanotubes embedded between graphene sheets in the intermediate transition layer. The hydrophobic layer has a relatively large pore structure, which is conducive to gas diffusion; the hydrophilic layer has a relatively dense sheet stacking structure, which is conducive to electrolyte capillary adsorption and exposure of active sites.

[0018] The above-mentioned asymmetric carbon-based air electrode with wettability gradient is used as a positive electrode catalyst in metal-air batteries.

[0019] Beneficial effects:

[0020] This invention discloses an asymmetric carbon-based air electrode with a wettability gradient, its preparation method, and its application. Employing a solvothermal-filtration assembly method, it utilizes the wettability characteristics of carbon-based materials with different structures to prepare Asy-FCNTs-FGNSs with a gradient structure, exhibiting excellent wettability gradient properties. As an oxygen reduction reaction electrocatalyst, the Asy-FCNTs-FGNSs of this invention demonstrates activity close to that of commercially available 20wt% Pt / C electrocatalysts, while exhibiting superior stability. The asymmetric air electrode assembled from its carbonaceous components possesses oxygen transport channels, and the extended three-dimensional interface results in higher active site utilization and better structural durability for the cathode reaction. When used as the cathode in a zinc-air battery assembly, it achieves a peak power density as high as 239.3 mW / cm². -2 Superior to commercial Pt / C batteries (191mW cm⁻¹) -2 The battery specific capacity is 814.3 mAh g. Zn -1 It is also higher than Pt / C (795mAh g) Zn -1). At 10mAcm -2 At a cyclic current density of 0.84V, the zinc-air battery equipped with Asy-FCNTs-FGNSs cathode material exhibited an excellent cycle life of 3696 cycles, showing promising application prospects. Attached Figure Description

[0021] Figure 1 The images are scanning electron microscope (SEM) images of FGNSs and FCNTs from Example 1.

[0022] Figure 2 The XRD patterns of FGNSs and FCNTs in Example 1 are shown.

[0023] Figure 3 This is a schematic cross-sectional view of the electrode sheet Asy-FCNTs-FGNSs in Example 1.

[0024] Figure 4 This is a cross-sectional SEM image of the electrode sheet Asy-FCNTs-FGNSs in Example 1.

[0025] Figure 5 The COMSOL multiphysics model represents the contact angle of liquid / gas with time and the diffusion of oxygen to the air electrode in the electrode sheet Asy-FCNTs-FGNSs in Example 1.

[0026] Figure 6 The FGNSs and FCNTs prepared in Example 1, as well as commercial Pt / C (20 wt%), were prepared in O2-saturated 0.1 mol L⁻¹ water. -1 LSV curves in KOH electrolyte, scan rate 10 mV s. -1 The rotation speed is 1600 rpm.

[0027] Figure 7 This is the zinc-air battery testing device assembled in Example 1.

[0028] Figure 8 Performance graphs of the zinc-air battery test apparatus assembled in Example 1: Discharge polarization curves and corresponding power densities (a), open-circuit voltage-time curves (b), discharge curves at different current densities (c), and discharge curves at 10 mA / cm² for zinc-air batteries with Asy-FCNTs-FGNSs electrode sheets and commercial Pt / C as the positive electrode. -2 The constant current discharge curve (d) and the long-term charge-discharge cycle performance curve of the zinc-air battery (e) are shown.

[0029] Figure 9 The COMSOL multiphysics model is used to show the contact angle of liquid / gas with time and the diffusion of oxygen to the air electrode in the Asy-FCNTs electrode in Comparative Example 1.

[0030] Figure 10 Performance figures for the zinc-air battery test setup assembled in Comparative Example 1: Discharge polarization curves and corresponding power densities (a), open-circuit voltage-time curves (b), discharge curves at different current densities (c), and discharge curves at 10 mA / cm² for Asy-FCNTs electrode sheets and commercial Pt / C as the positive electrode zinc-air battery. -2 The constant current discharge curve (d) is shown below.

[0031] Figure 11 The COMSOL multiphysics model is used to compare the contact angle of liquid / gas with time and the diffusion of oxygen to the air electrode in the Asy-FGNSs electrode in Comparative Example 2.

[0032] Figure 12 Performance figures for the zinc-air battery test setup assembled in Comparative Example 2: Discharge polarization curves and corresponding power densities (a), open-circuit voltage-time curves (b), discharge curves at different current densities (c), and discharge curves at 10 mA / cm² for zinc-air batteries with Asy-FGNSs electrode sheets and commercial Pt / C as the positive electrode. -2 The constant current discharge curve (d) is shown below.

[0033] Figure 13 The COMSOL multiphysics model is used to compare the contact angle of liquid / gas with time and the diffusion of oxygen to the air electrode in the electrode sheet Asy-FGNSs-FCNTs in Comparative Example 3.

[0034] Figure 14 Performance figures for the zinc-air battery test setup assembled in Comparative Example 3: Discharge polarization curves and corresponding power densities (a), open-circuit voltage-time curves (b), discharge curves at different current densities (c), and discharge curves at 10 mA / cm² for Asy-FGNSs-FCNTs electrode sheets and commercial Pt / C as the positive electrode zinc-air battery. -2 The constant current discharge curve (d) is shown below.

[0035] Figure 15 The following is a performance diagram of the zinc-air battery test device assembled in Comparative Example 4: the discharge polarization curve and corresponding power density of the zinc-air battery with Asy-FGNSs-FCNTs-0.5 electrode sheet as the positive electrode.

[0036] Figure 16 The following is a test performance diagram of the zinc-air battery test device assembled in Comparative Example 5: the discharge polarization curve and corresponding power density of the zinc-air battery with Asy-FGNSs-FCNTs-2 electrode sheet as the positive electrode.

[0037] Figure 17Performance diagram of the zinc-air battery test device assembled in Comparative Example 7: Discharge polarization curve and corresponding power density of the zinc-air battery with Asy-FGNSs-FCNTs-390W electrode sheet as the positive electrode.

[0038] Figure 18 The COMSOL multiphysics model is used to compare the contact angle of liquid / gas with time and the diffusion of oxygen to the air electrode in the electrode plates Asy-FCNTs / FGNSs in Comparative Example 8.

[0039] Figure 19 Performance figures for the zinc-air battery test setup assembled in Comparative Example 8: Discharge polarization curves and corresponding power densities (a), open-circuit voltage-time curves (b), discharge curves at different current densities (c), and discharge curves at 10 mA / cm² for zinc-air batteries with Asy-FCNTs / FGNSs electrode sheets and commercial Pt / C as the positive electrode. -2 The constant current discharge curve (d) is shown below.

[0040] Figure 20 Digital photographs of the electrodes of Example 1(a), Comparative Example 9(b), and Comparative Example 10(c). Detailed Implementation

[0041] To better understand the features and advantages of the present invention, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0042] Example 1: A method for preparing the Asy-FCNTs-FGNSs electrode, comprising the following steps:

[0043] (1) Functionalization of carbon-based materials:

[0044] 40 mg of carbon nanotubes and 10 mg of iron phthalocyanine were weighed and dispersed in 35 mL of anhydrous ethanol solution. The mixture was ultrasonically dispersed for 1 h, and then transferred to a 50 mL hydrothermal reactor with a Teflon liner. The reactor was solvothermally reacted at 180 °C for 12 h. After the reaction, the mixture was washed three times with anhydrous ethanol and then dried in a vacuum drying oven at 60 °C for 8 h to obtain ORR-functionalized carbon nanotube electrocatalysts FCNTs. Similarly, by replacing the carbon nanotubes with graphene nanosheets, ORR-functionalized graphene nanosheet electrocatalysts FGNSs were prepared.

[0045] Figure 1 SEM images of FGNSs and FCNTs show the sheet-like structure of FGNSs and the tubular structure of FCNTs.

[0046] Figure 2The XRD patterns of GNSs and CNTs were compared with standard PDF cards, showing significant peaks corresponding to FePc. Furthermore, the characteristic peak at 26° corresponds to the (002) crystal plane of graphene and carbon nanotubes, while the broad peak shape of CNTs indicates their lower crystallinity.

[0047] (2) Preparation of carbonaceous assembly solution:

[0048] 7.5 mg of FCNTs with hydrophobic properties mimicking water strider villi and 7.5 mg of FGNSs with hydrophilic properties mimicking fish scales were dispersed in a DMF solution, according to m 碳质材料 / V DMF =1:1 mg / mL, and dispersed by sonication at 360W for 2 hours to obtain the corresponding carbonaceous assembly solution 1 and carbonaceous assembly solution 2.

[0049] (3) Gradient structure orientation assembly:

[0050] A carbon-based assembly solution 1, mimicking the hydrophobic properties of water strider fibers, was first filtered onto a microporous membrane (0.22 μm) to form a hydrophobic bottom layer. After filtration of carbon-based assembly solution 1, continuous vacuum filtration was performed. While maintaining a negative pressure (0.09–0.1 MPa), a carbon-based assembly solution 2, mimicking the hydrophilic properties of fish scales, was rapidly filtered to form a gradually transitioning hydrophobic-hydrophilic structural gradient. It was ensured that the filtration interval between the two carbon-based assembly solutions did not exceed 1 minute. After vacuum drying, an asymmetric air electrode Asy-FCNTs-FGNSs with a wettability gradient was obtained. Figure 3 This is a schematic diagram of the fabricated asymmetric electrode.

[0051] Figure 4 The cross-sectional SEM image of Asy-FCNTs-FGNSs shows a clear gradient asymmetry morphology. Figure 4 The scanned images in (bd) sequentially show the morphology of the upper, middle, and lower layers of the Asy-FCNTs-FGNSs cathode. The upper layer of the Asy-FCNTs-FGNSs cathode ( Figure 4 b) exhibits a fish-scale-like flaky surface, indicating it is an FGNSs electrocatalyst, while the lower layer ( Figure 4 d) exhibits hydrophobic bristle-like features, indicating it is an FCNT electrocatalyst. Notably, the FCNT sample surrounds the central region of the FGNSs, suggesting a strong interlayer interaction between the two layers. Figure 4 c).

[0052] Figure 5A COMSOL multiphysics model was used to demonstrate the contact angle of liquid / gas on the electrode surface over time and the diffusion of oxygen to the air electrode. The target electrode sheet, Asy-FCNTs-FGNTs, exhibits a suitable diffusion path, and the solution achieves complete wetting within 120 seconds. Underwater, O2 diffuses completely in just 3500 milliseconds. This electrode exhibits a lower gaseous oxygen transfer resistance, resulting in a higher oxygen concentration in the three-dimensional space within the electrode.

[0053] Electrocatalytic oxygen reduction and zinc-air battery performance testing

[0054] Electrocatalytic oxygen reduction performance was tested using a three-electrode system. FGNSs and FCNTs were loaded onto a rotating disk glassy carbon electrode as the working electrode, with a Pt electrode as the counter electrode, a Hg / HgO electrode as the reference electrode, and a 0.1 mol / L KOH aqueous solution as the electrolyte for electrochemical testing.

[0055] Figure 6 Polarization curves (1600 rpm) for the electrocatalytic oxygen reduction reaction of FGNSs, FCNTs, and commercial Pt / C (20 wt%) are shown. As can be seen from the figure, the limiting current density for FGNSs and FCNTs is 5.4 mA / cm². 2 and 5.6 mA / cm 2 This is higher than the 5.5 mA / cm² of commercial Pt / C. 2 The half-wave potential is 0.86V vs. RHE, which is slightly lower than that of commercial Pt / C (0.84V vs. RHE).

[0056] To evaluate the prospects of Asy-FCNTs-FGNSs in metal-air batteries, performance tests were conducted on zinc-air batteries assembled using the Asy-FCNTs-FGNSs electrode as the positive electrode. Figure 7 Meanwhile, using commercial Pt / C as the positive electrode catalyst, zinc-air cells were assembled using the same method for comparison.

[0057] Figure 8 (a) shows the polarization and power density curves of a zinc-air cell based on an Asy-FCNTs-FGNSs electrode. The peak power density of this zinc-air cell is 239.3 mW cm⁻¹. -2 Superior to commercial Pt / C batteries (191mW cm⁻¹) -2 ).

[0058] Figure 8 (b) is the curve of open circuit voltage versus time. The open circuit voltage of the Asy-FCNTs-FGNSs zinc-air battery gradually increases with time, and after 20 hours it is better than Pt / C, stabilizing at 1.48V.

[0059] like Figure 8As shown in (c), at 10 mAcm -2 At a current density of [value missing], the specific capacity of the Asy-FCNTs-FGNSs zinc-air battery is 814.3 mAh g. Zn -1 This value is higher than that of Pt / C (795mAh g). Zn -1 ).

[0060] At 5, 10, 20 and 50 mA cm -2 At the discharge current density, both Asy-FCNTs-FGNSs and Pt / C air cathode cells exhibited stable discharge voltages that decreased with increasing current density. Figure 8 (d)), Asy-FCNTs-FGNSs batteries at 5, 10, 20 and 50 mAcm -2 The stable voltage values ​​under these conditions are 1.31, 1.29, 1.25, and 1.16V, respectively.

[0061] Long-term cycling tests were conducted on the Asy-FCNTs-FGNSs cathode material to explore its advantages in achieving long-term cycling in rechargeable zinc-air batteries. At 10 mA / cm², [the following parameters were tested]. -2 At a cycling current density of 0.84V, the zinc-air battery equipped with Asy-FCNTs-FGNSs cathode material exhibited an excellent cycle life of 3696 cycles. Figure 8 (e)).

[0062] Comparative Example 1: Preparation and Testing of Sy-FCNTs

[0063] The difference from Example 1 is that in step (2), 15 mg of FCNTs with hydrophobic properties similar to water strider hair and 0 mg of FGNSs with hydrophilic properties similar to fish scales were weighed to prepare carbon assembly solutions, and the obtained electrode sheet was marked as Sy-FCNTs air positive electrode.

[0064] COMSOL multiphysics model images of the liquid / gas contact angle of the sample over time and oxygen diffusion to the air electrode are shown below. Figure 9 As shown, the Sy-FCNTs air electrode remains highly hydrophobic (124°) after 120 seconds. Gas diffusion of the Sy-FCNTs air electrode can be achieved in 300 ms. However, it only has a hydrophobic FCNTs layer, lacking hydrophilic components compared to Example 1, resulting in insufficient electrolyte wettability, difficulty for the electrolyte to penetrate into the electrode interior, and low utilization of active sites; it also lacks a gradient transition layer, resulting in weak gas / electrolyte interface regulation capability.

[0065] Figure 10This is a performance graph of a Sy-FCNTs air electrode and a commercially available Pt / C assembled zinc-air cell. The peak power density of the Sy-FCNTs zinc-air cell is 196.5 mW / cm². -2 The open-circuit voltage is 1.44V, and the specific capacity is 799.2mAh g. Zn -1 At 5, 10, 20, and 50 mA / cm -2 The stable voltage values ​​were 1.23, 1.16, 1.10 and 0.98V, respectively.

[0066] Preparation and testing of comparative example 2Sy-FGNSs

[0067] The difference from Example 1 is that in step (2), 0 mg of FCNTs with hydrophobic properties similar to water strider hair and 15 mg of FGNSs with hydrophilic properties similar to fish scales were weighed to prepare carbonaceous assembly solutions, and the obtained electrode sheet was marked as Sy-FGNSs air positive electrode.

[0068] COMSOL multiphysics model images of the liquid / gas contact angle of the sample over time and oxygen diffusion to the air electrode are shown below. Figure 11 As shown, the liquid can completely wet the Sy-FGNSs air electrode within 120 seconds; underwater, the gas contact angle of the Sy-FGNSs air electrode remains at 115° after 2 seconds. However, it only has a hydrophilic FGNSs layer, lacking hydrophobic components compared to Example 1, resulting in insufficient gas diffusion, difficulty for oxygen to penetrate into the electrode interior, and low utilization of active sites; it also lacks a gradient transition layer, resulting in weak gas / electrolyte interface regulation capability.

[0069] Figure 12 This is a performance graph of the Sy-FGNSs air electrode and a commercially available Pt / C assembled zinc-air cell. The peak power density of the Sy-FGNSs zinc-air cell is 150.2 mW / cm². -2 The open-circuit voltage is 1.43V, and the specific capacity is 800.2mAh g. Zn -1 At 5, 10, 20, and 50 mA / cm -2 The stable voltage values ​​were 1.28, 1.25, 1.21 and 1.10V, respectively.

[0070] Preparation of Comparative Example 3Asy-FGNSs-FCNTs

[0071] The difference from Example 1 is that in step (3), the assembly direction of the air electrode Asy-FCNTs-FGNSs is changed, that is, the FGNSs side with the hydrophilic properties of fish scales contacts the air, and the FCNTs side with the hydrophobic properties of water strider fur contacts the electrolyte. At this time, the electrode sheet is marked as Asy-FGNSs-FCNTs air positive electrode.

[0072] COMSOL multiphysics model images of the liquid / gas contact angle of the sample over time and oxygen diffusion to the air electrode are shown below. Figure 13 As shown, the filtration sequence of the Asy-FGNSs-FCNTs air electrode catalyst material is the reverse of that of the target sample, maximally hindering the permeation of electrolyte and oxygen, resulting in a zinc-air battery assembled with this electrode sheet exhibiting inferior performance compared to Example 1. Figure 14 The peak power density of the Asy-FGNSs-FCNTs zinc-air battery is 129.5 mW / cm³. -2 This is lower than the peak power density of Example 1 (239.3 mW cm⁻¹). -2 The open-circuit voltage was slightly lower than that of Example 1 (1.48V), at 1.43V; the specific capacity was higher than that of Example 1 (814.3mAh g). Zn -1 The performance was poor, at 783.4 mAh g. Zn -1 At 5, 10, 20, and 50 mA / cm -2 The stable voltage values ​​were 1.23, 1.12, 1.01, and 0.81 V, respectively. The voltage drop at high current densities was significant and lower than the rate performance of Example 1. When the assembly orientation of the air electrode Asy-FCNTs-FGNSs was changed, the diffusion of oxygen and electrolyte was no longer suitable for the requirements of a high-performance zinc-air battery.

[0073] Preparation of Comparative Example 4Asy-FGNSs-FCNTs-0.5

[0074] The difference from Example 1 is that step (2) is performed according to m 碳质材料 / V DMF =1:0.5 mg / mL, the functionalized carbon matrix loaded with phthalocyanine iron obtained in step (1) was dispersed in DMF solution. The prepared electrode sheet Asy-FGNSs-FCNTs-0.5 was designated as Comparative Example 4. The smaller amount of DMF resulted in poorer dispersion. The method for assembling the Asy-FGNSs-FCNTs-0.5 electrode sheet into a zinc-air battery was the same as in Example 1.

[0075] Figure 15 The power density of the Asy-FGNSs-FCNTs-0.5 zinc-air battery was tested and found to be 204.67 mW / cm². -2 .

[0076] Preparation of Comparative Example 5: Asy-GNSs-CNTs-2

[0077] The difference from Example 1 is that step (2) is performed according to m 碳质材料 / V DMF =1:2 mg / mL, the functionalized carbon matrix loaded with phthalocyanine iron obtained in step (1) was dispersed in DMF solution. The prepared electrode sheet Asy-FGNSs-FCNTs-2 was designated as Comparative Example 5. The method for assembling the Asy-FGNSs-FCNTs-2 electrode sheet into a zinc-air battery was the same as in Example 1.

[0078] Figure 16 The power density of the Asy-FGNSs-FCNTs-2 zinc-air battery was tested and found to be 199.63 mW / cm². -2 Compared to Example 1, the increased solvent content resulted in greater loss of electrocatalytic material during filtration, leading to a lower content of active material and a lower power density of the battery.

[0079] Comparative Example 6

[0080] The difference from Example 1 is that the ultrasonic power used in step (2) to prepare the carbonaceous assembly solution is 180W. Too low a power cannot disperse the carbon-based material in the DMF solvent, and a large amount of solids settle at the bottom of the solvent, so a well dispersed carbonaceous assembly solution cannot be obtained.

[0081] Comparative Example 7

[0082] The difference from Example 1 is that the ultrasonic power used in step (2) to prepare the carbonaceous assembly solution is 390W, and the prepared electrode sheet Asy-FGNSs-FCNTs-390 is referred to as Comparative Example 7.

[0083] Excessive power causes the phthalocyanine iron in the ORR-functionalized carbon-based material to separate from the carbon-based material, thus destroying the oxygen reduction electrocatalyst. Figure 17 The power density of the Asy-FGNSs-FCNTs-390 zinc-air battery was tested and found to be 86.20 mW / cm². -2 .

[0084] Preparation and testing of comparative examples 8Sy-FGNSs / FCNTs

[0085] The difference from Example 1 is that in step (3), the carbon assembly solution was replaced by a mixture of 7.5 mL of functionalized graphene nanosheet dispersion and 7.5 mL of functionalized carbon nanotube dispersion for one filtration. The obtained sample was labeled as Sy-FGNSs / FCNTs.

[0086] COMSOL multiphysics model images of the liquid / gas contact angle of the sample over time and oxygen diffusion to the air electrode are shown below. Figure 18As shown, the Sy-FGNSs / FCNTs electrode lacks directional diffusion channels for oxygen and electrolyte, resulting in slow electrolyte and oxygen penetration and diffusion. The gas contact angle is 111° after 2 seconds.

[0087] Figure 19 This is a performance graph of a Sy-FGNSs / FCNTs electrode and a commercially available Pt / C assembled zinc-air cell. The peak power density of the Sy-FGNSs / FCNTs cell is 208.1 mW / cm². -2 The open-circuit voltage is 1.43V, and the specific capacity is 812.4mAh g. Zn -1 At 5, 10, 20, and 50 mA / cm -2 The stable voltage values ​​were 1.30, 1.25, 1.18 and 1.06V, respectively.

[0088] Comparative Example 9: Preparation of Asy-FGNSs-FCNTs from carbonaceous assembly solution obtained by stirring

[0089] The difference from Example 1 is that in step (2), the carbonaceous assembly solution of FGNSs and FCNTs is obtained by vigorous stirring at 1500 rpm for 2 hours, and the Asy-FGNSs-FCNTs electrode is obtained by filtration.

[0090] Figure 20 (b) A digital photograph of the Asy-FGNSs-FCNTs electrode prepared by stirring to obtain a carbonaceous assembly solution, compared with Example 1 ( Figure 20 Compared to (a), the stirring method cannot completely disperse the functionalized carbonaceous material, and there are obvious particles on the electrode surface.

[0091] Comparative Example 10: Gradient Air Electrodes Con-FGNSs-FCNTs Obtained by Conventional Drop Casting Method

[0092] The difference from Example 1 is that the vacuum filtration method in step (3) is replaced by the traditional drop casting method for preparing air electrodes. First, 7.5 mL of FCNTs solution is drop-cast, and then another layer of FGNSs carbonaceous assembly solution is drop-cast on top. After vacuum drying, Con-FGNSs-FCNTs electrode is obtained.

[0093] Figure 20 (c) is a digital photograph of the Con-FGNSs-FCNTs electrode. The drop casting method cannot produce a completely smooth electrode sheet, and the structure will be continuously damaged during the drop casting process.

[0094] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an asymmetric carbon-based air electrode with a wettability gradient, characterized in that, Includes the following steps: (1) Preparation of carbonaceous assembly solution: Functionalized carbon nanotubes and functionalized graphene nanosheets were prepared according to m... 碳质材料 / V DMF The carbonaceous assembly solution 1 and carbonaceous assembly solution 2 were ultrasonically dispersed in an amphiphilic solvent at a ratio of 1:1 mg / mL. (2) Gradient structure orientation assembly First, carbonaceous assembly solution 1, which mimics the hydrophobic properties of water strider hair, is filtered onto a microporous membrane to form a hydrophobic bottom layer. After filtration, vacuum filtration is continued. Under negative pressure, carbonaceous assembly solution 2, which mimics the hydrophilic properties of fish scales, is rapidly filtered to form a gradually transitioning hydrophobic-hydrophilic structural gradient. It is ensured that the filtration interval between the two carbonaceous assembly solutions does not exceed 1 minute. After vacuum drying, an asymmetric air electrode with a wettability gradient is obtained.

2. The method for preparing an asymmetric carbon-based air electrode with a wettability gradient according to claim 1, characterized in that, The preparation process of the functionalized carbon nanotubes or functionalized graphene nanosheets in step (1) is as follows: 40 mg of carbon nanotubes or graphene nanosheets and 10 mg of iron phthalocyanine are weighed and dispersed in 35 mL of anhydrous ethanol solution, and ultrasonically dispersed for 1 h. Then, the dispersion is transferred to a 50 mL hydrothermal reactor with a Teflon liner and solvothermally reacted at 180 °C for 12 h. After the reaction is completed, the mixture is washed 3 times with anhydrous ethanol and then placed in a vacuum drying oven and dried at 60 °C for 8 h to obtain ORR-functionalized carbon nanotube electrocatalysts FCNTs or ORR-functionalized graphene nanosheet electrocatalysts FGNSs.

3. The method for preparing an asymmetric carbon-based air electrode with a wettability gradient according to claim 1, characterized in that, The functionalized graphene nanosheets described in step (1) have a spread of 1–3 μm.

4. The method for preparing an asymmetric carbon-based air electrode with a wettability gradient according to claim 1, characterized in that, The functionalized carbon nanotubes are multi-walled carbon nanotubes with a length of 0.5–2 μm.

5. The method for preparing an asymmetric carbon-based air electrode with a wettability gradient according to claim 1, characterized in that, In step (1), the ultrasonic power is 360W and the ultrasonic treatment lasts for 2 hours.

6. The method for preparing an asymmetric carbon-based air electrode with a wettability gradient according to claim 1, characterized in that, The dispersing agent used in step (1) is an amphiphilic solvent, such as DMF, ethanol, or dimethyl sulfoxide (DMSO).

7. The method for preparing an asymmetric carbon-based air electrode with a wettability gradient according to claim 1, characterized in that, In step (2), the particle size of the microporous membrane is 0.22 μm; the range of maintaining the negative pressure is 0.09 to 0.1 MPa.

8. The method for preparing an asymmetric carbon-based air electrode with a wettability gradient according to claim 1, characterized in that, When the carbon-based materials in the carbon-based assembly solution 1 and carbon-based assembly solution 2 are of equal mass in step (2), an asymmetric assembled carbon nanotube-graphene nanosheet (Asy-FCNTs-FGNSs) air cathode is obtained.

9. An asymmetric carbon-based air electrode with a wettability gradient prepared by any one of the preparation methods of claims 1-8, characterized in that, The thickness is 150–300 μm.

10. The application of the asymmetric carbon-based air electrode with wettability gradient according to claim 9 as a positive electrode catalyst in a metal-air battery.

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