Zinc-air battery catalyst, preparation method, and recyclable anti-powdering air electrode structure

Abstract

The present invention relates to a zinc-air battery catalyst, a preparation method, and a recyclable, pulverization-resistant air electrode structure, belonging to the technical field of zinc-air battery electrode materials. The present invention relates to a process for adsorbing a magnetic metal-doped catalyst with a magnetic binder. The magnet-controlled zinc-air battery can achieve a long cycle life and address the issue of electrode pulverization. Furthermore, magnetic separation technology can be used to recover spent cobalt catalyst. The recovered catalyst can continue to operate stably in a cycle.

Description

Technical Field

[0001] The invention relates to a zinc-air battery catalyst, a preparation method and a recyclable pulverization-resistant air electrode structure, and belongs to the technical field of zinc-air battery electrode materials. Background Art

[0002] Rechargeable zinc-air batteries (ZABs) are electrochemical energy storage devices with high energy density, excellent safety, and great development potential. However, two key challenges hinder the commercialization of ZABs. First, the catalysts are expensive and contain toxic transition metals that require recycling. Second, the oxygen reduction / evolution reaction (ORR / OER) in the air electrode is kinetically slow, requiring large amounts of catalyst to maintain high kinetic reaction rates. However, the electrocatalysts currently used in ZABs contain heavy metals (such as Pt, Ru, Ir, Co, Mn, Fe, and Ni), and these discarded ZABs leak significant amounts of heavy metals. Second, during the actual charging reaction, the ZAB cathode catalyst is attacked by a large number of O2 bubbles, compromising battery stability. During battery fabrication, conventional ZABs require polymer binders such as Nafion, PTFE, and PVDF. However, these polymer binders are difficult to decompose naturally and are electrically insulating (hindering electron transport in the electrode). These binders are difficult to withstand the persistent attack of the strong alkaline electrolytes used in ZABs and the large number of O2 bubbles generated during the OER. Summary of the Invention

[0003] The present invention develops a process for adsorbing cobalt-doped catalysts with a magnetic binder, which is a simple, controllable and inexpensive ZAB electrode preparation process and recycling strategy. The zinc-air battery controlled by magnets can cycle for 1200 hours (7200 cycles), and in situ observation of a homemade electrolytic cell with an air electrode reveals its resistance to pulverization. In addition, we can use magnetic separation technology to recover the cobalt catalyst in the spent ZAB. The recovered catalyst-loaded ZAB can also be stably cycled for more than 500 hours (ΔE=0.86V). The magnetically controlled electrode designed in this work exhibits excellent battery performance and provides a solution for the recycling and application of catalysts.

[0004] The first object of the present invention is to provide a zinc-air battery catalyst, in which the metal Co as the main catalytic active component exhibits strong magnetism when doped with N and can be fixed by magnetic materials; at the same time, the material also exhibits good multifunctional catalytic performance.

[0005] A zinc-air battery catalyst contains graphite carbon with carbon nanotubes distributed on the graphite carbon. The carbon nanotubes are coated with Co and Co oxides, and the catalyst is doped with nitrogen. The particle size of the catalyst is in the range of 1-2 μm.

[0006] The nitrogen element exists in the form of pyridinic nitrogen, metallic nitrogen, pyrrolic nitrogen or graphitic nitrogen.

[0007] The mass percentage of Co in the catalyst is 10-40 wt%.

[0008] The second object of the present invention is to provide a preparation method for synthesizing the above-mentioned catalyst, wherein the preparation process is to utilize a coordination compound material containing Co, N, and C and calcine it under a reducing atmosphere.

[0009] The preparation method of zinc-air battery catalyst comprises the following steps:

[0010] Step 1: obtaining a coordination compound material containing Co, N, and C, and calcining it under a reducing atmosphere;

[0011] Step 2: The product is treated in dilute acid to dissolve part of the cobalt, and then aged in air to generate cobalt oxide to obtain a catalyst.

[0012] The coordination compound material containing Co, N and C is a cobalt-based MOF material.

[0013] The cobalt-based MOF material is selected from ZIF-67, MOF-74(Co), MOF-24(Co), and MOF-100(Co).

[0014] The reducing atmosphere is a mixture of hydrogen and inert gas in a volume ratio of 1:19.

[0015] The calcination treatment is carried out at 250-400°C for 1.5 hours and then at 600-800°C for 3.5 hours.

[0016] The dilute acid treatment refers to treatment in a 0.5 M dilute acid solution for 12 hours; the aging treatment refers to treatment at 100°C for 1 day.

[0017] A third object of the present invention is to provide an electrode structure for the air electrode in a zinc-air battery. This electrode structure features a design that allows for the adsorption of magnetic catalysts, preventing their loss and allowing for their recovery. Furthermore, since no binder is used during the fixation process, the lifetime degradation of the binder due to oxygen attack is avoided. Furthermore, the arrayed arrangement of the catalysts within the electrode material effectively resists the effects of bubbles on the catalyst layer's stability and prevents pulverization.

[0018] An air electrode structure includes a diffusion layer: one side of the diffusion layer is covered with a catalyst layer, and a portion of the other side is provided with a magnetic material for fixing the catalyst layer by magnetic force. The catalyst layer is used to reduce oxygen; wherein the chemical structure of the catalyst on the catalyst layer contains atoms of magnetic metal; and the catalyst particles in the catalyst layer have a porous structure.

[0019] The areal mass loading of the catalyst on the catalyst layer was 1 mg cm -2 .

[0020] On the side of the diffusion layer containing the magnetic material, there is still an area that can be in direct contact with the air; the size of the pore structure ranges from 1 to 50 μm.

[0021] The catalyst layer does not contain any organic binder.

[0022] The diffusion layer is selected from porous materials, such as foam metal.

[0023] The magnetic metal atoms are one or more of iron, cobalt, nickel, neodymium, samarium, or lanthanide rare earth metals.

[0024] In the catalyst, the mass percentage of magnetic metal atoms in the chemical structure is 10-40wt%.

[0025] The catalyst can be a cobalt-carbon-based catalyst, an iron-carbon-based catalyst, a nickel-carbon-based catalyst, or a ferromagnetic transition metal oxide catalyst (such as Co3O4, Fe2O3, NiO).

[0026] The manufacturing method of the above-mentioned air electrode structure comprises the following steps:

[0027] Step 1, obtaining a diffusion layer;

[0028] Step 2: Mix the catalyst, conductive filler, and solvent to form a slurry, and apply it to one side of the diffusion layer; and simultaneously place a magnetic material on the other side of the diffusion layer to fix the catalyst by magnetic force;

[0029] Step 3: Dry the solvent in the slurry with a sodium lamp.

[0030] The weight ratio of catalyst to conductive filler is 0.5:1, and the concentration of catalyst in the slurry is 10 mg mL -1 . BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1Schematic diagram of the principle of magnetic bonding and magnetic separation of Co-NCNTFs. a) Schematic diagram of the Co-NCNTFs catalyst connected with a magnetically manipulated electrode and a conventional polymer binder under charging conditions. b) Schematic diagram of electron and ion transport in magnetically manipulated Co-NCNTFs under discharge conditions. c) The recycling process of magnetically manipulated Co-NCNTFs batteries and Co-NCNTFs binder batteries.

[0032] Figure 2 Preparation and structural characterization of Co-NCNTFs electrocatalysts. a) Schematic diagram of the Co-NCNTFs synthesis route. b) XRD pattern of Co-NCNTFs, c) SEM and d) magnified SEM images, e) color TEM image, (f, g) HRTEM images, h) STEM-HAADF, and i) elemental scanning images.

[0033] Figure 3 Physicochemical characterization of Co-NCNTFs electrocatalysts. a) Nitrogen adsorption–desorption isotherm, b) Raman spectrum, c) XPS spectrum, d) C 1s, e) N 1s, and f) high-resolution XPS spectra of the Co 2p region.

[0034] Figure 4 Figure 2 shows the ORR and OER electrocatalytic performance. a) ORR curves of Co-NCNTFs, Pt / C, and RuO2 catalysts at 0.1 M KOH concentration and b) the corresponding Tafel slope plots. c) The stability of Co-NCNTFs and Pt / C was tested using the chronoamperometric method at a constant potential of 0.5 V.

[0035] Figure 5 Figure 2. Battery performance of magnetically manipulated electrodes and Nafion binder electrodes. a) Schematic diagram of a magnetically manipulated air electrode battery. b) Charge and discharge polarization curves. c) Discharge polarization curves and corresponding power density. d) Battery discharge capacity at constant current density. e) Battery rate performance of magnetically manipulated Co-NCNTFs and Nafion binder (Pt / C+RuO2). f) Comparison of the anti-powdering performance of different air electrodes at 1, 100, 200, and 300 h of charge. g) Comparison of the anti-powdering performance of different air electrodes at 2 mA cm -2 Comparison of charge-discharge cycle performance of different air electrodes under different current densities.

[0036] Figure 6 The ZABs were subjected to galvanostatic cycling using pristine Co-NCNTF and air-aged Co-NCNTFs electrocatalysts, respectively. Figure 7Recycling of Co-NCNTFs catalysts and quality evaluation. a) Experimental process for magnetically assisted recovery of Co-NCNTFs from waste zinc-air battery air cathodes. b) Cycling performance of a zinc-air battery assembled using recycled Co-NCNTFs. c) Comparison of hysteresis loops of Co-NCNTFs at different cycle times, i.e., 200 and 500 hours of continuous charge and discharge. d) A zinc-air battery assembled using recycled Co-NCNTFs can continuously power an LED light for over 200 hours. DETAILED DESCRIPTION

[0037] The present invention provides a zinc-air battery catalyst comprising a graphite carbon material, carbon nanotubes grown on the graphite carbon, and cobalt and cobalt oxide within and / or at the ends of the carbon nanotubes. The presence of cobalt and cobalt oxide results in excellent ORR and OER performance on the catalyst surface. Furthermore, the magnetic properties of the cobalt-based material allow it to be easily fixed by magnetic materials, thus avoiding the problem of reduced lifespan caused by the need for a binder when manufacturing the catalyst layer of the air cathode. Furthermore, the material is doped with nitrogen to enhance the catalyst's magnetic properties, facilitating its maintenance of a layered structure under the influence of the magnetic material.

[0038] In one embodiment, the present invention provides a carbon composite material of cobalt embedded in nitrogen-doped carbon nanotubes (abbreviated as Co-NCNTFs), and uses a magnet to adsorb the catalyst on the air electrode, which serves as a magnetic control electrode. The zinc-air battery with this magnetic control electrode can have a cycle time of up to 1200 hours (7200 cycles), which is 8 times higher than the cycle time of zinc-air batteries prepared by traditional methods. The Co-NCNTFs catalyst was recovered from discarded ZABs using magnetic separation technology, and the battery performance of the recovered Co-NCNTFs catalyst was demonstrated.

[0039] The air electrode structure in the present invention is covered with a catalyst layer on one side of the diffusion layer, and a magnetic material is provided on a portion of the other side for fixing the catalyst layer by magnetic force. The catalyst layer is used for reducing oxygen. The chemical structure of the catalyst on the catalyst layer contains atoms of magnetic metal. The catalyst particles in the catalyst layer have a porous structure.

[0040] Based on the above structure, when a catalyst containing magnetic metal atoms is used, due to its inherent magnetism, it can be fixed by a magnetic material, thereby avoiding the use of an organic adhesive; the magnetic atoms that can be used here can be one or more of iron, cobalt, nickel, neodymium, samarium or lanthanide rare earth metals, as long as the catalyst can have corresponding catalytic properties on the one hand and magnetism on the other hand; in addition to metal atoms, the catalyst can also be a carbon-based material such as carbon nanotubes, graphite sheets, graphene, etc. in the prior art, or other one-dimensional or two-dimensional materials, as long as the metal catalyst can be loaded and has conductive materials. Among them, cobalt-based materials are preferably used because they have more valence changes and better OER and ORR performance.

[0041] Another key point in the above structure is the pore structure between the catalyst particles. It is precisely because of this morphology that the bubbles generated during operation can move in and out freely without occupying the space of the catalyst layer and causing catalyst pulverization.

[0042] In the above structure, when the magnetic material is located on the other side of the diffusion layer, the area it covers should only be a portion of the area, and the passage for oxygen to enter should not be blocked. Figure 5 As shown in a, when a ring magnet is used, the space inside it allows oxygen to flow in. Of course, a small distance can be separated between the magnetic material and the diffusion layer, as long as the catalyst is magnetically attracted during operation and the structure is stable and oxygen can enter freely.

[0043] Figure 1 Schematic diagram of the process of using magnetic manipulation technology to make zinc-air batteries (ZABs) anti-powdering and recyclable. The generation of bubbles on the electrodes of zinc-air and lithium-air batteries will affect the transfer of energy and mass. In addition, a large number of large bubbles will be generated on the air electrode during charging, which will seriously affect the structural stability of the air electrode. The process of gas escaping from the electrode is usually divided into the stages of bubble nucleation, growth and separation. Figure 1 As shown in a, ordinary cathode catalysts use polymers as binders, but Co-NCNTFs are tightly wrapped by the binder, making it difficult for O2 bubbles to separate from the electrode. Since a large number of bubbles are generated during charging and cannot be discharged, the air electrode is powdered. Figure 1As shown in a and b, when a magnet is used as a binder, the cathode catalyst (Co-NCNTFs) has an array arrangement on the air electrode. This structure is not only conducive to the continuous passage of electrons, ions and oxygen, but also allows O2 bubbles to enter freely, preventing the air electrode from pulverizing. In addition, ordinary (polymer) binders are more expensive than magnetic binders, have difficulty in transmitting electrons, and alkaline electrolytes are prone to deterioration and loss of viscosity when soaked in ZABs for a long time. Therefore, the recycling of waste batteries will become a research focus for the widespread commercial application of ZAB. Figure 1 Figure c shows the process of recovering spent battery cathode catalysts (Co-NCNTFs) from ZABS with conventional (polymer) binders and magnetic binders. Separating the catalyst from the current collector and (polymer) binder is a difficult and time-consuming process during conventional recycling. The cathode catalyst can be easily collected from magnetic binder-based ZABS and recovered simply by removing the magnetic field. The entire recycling process is environmentally friendly and has low consumption costs.

[0044] Considering that cobalt doped with nitrogen-containing composite carbon materials will produce strong magnetism, we use Co-NCNTFs as the catalyst for ZABs magnetically manipulated air electrodes. The preparation process of Co-NCNTFs is as follows: Figure 2 As shown in a.

[0045] Example 1 Co-NCNTFs catalyst synthesis process:

[0046] The synthesis of Co-NCNTFs includes four steps: (1) First, 6.77g of dimethylimidazole powder is dissolved in a mixed solution of 40ml of methanol and 40ml of ethanol. At the same time, 6.9g of Co(NO3)2-6H2O powder is dissolved in a mixed solution of 40ml of methanol and 40ml of ethanol. The two solutions are mixed under stirring for 120 seconds and then stored at room temperature for 20 hours. The mixed solution is then filtered to obtain purple precipitated ZIF-67 crystals, which are washed several times in ethanol and dried at 80°C overnight. (2) The ZIF-67 powder is spread flat in a square porcelain crucible and heated at 350°C for 1.5h in H2 (10%) / Ar gas with a flow rate of 100sccm and a heating rate of 2°Cmin -1 Then, the temperature was raised to 700°C (2°C min -1 ) for 3.5 h and then cooled naturally to room temperature in a tube furnace to collect the black powder Co-NCNTFs. (3) The Co-NCNTs powder was treated in 0.5 M H2SO4 solution at room temperature for 12 h. (4) The acid-treated Co-NCNTFs product was air-aged at 100°C for 2 days and then stored in a glove box.

[0047] The synthesis principle of the above steps is: first, the existing ZIF-67 crystal synthesis method is adopted to obtain ZIF-67 crystals. The consideration of selecting ZIF-67 is its high cobalt content. Some other cobalt-containing coordination compounds can also be used; when continuing to carry out calcination treatment in a reducing atmosphere, the catalytic effect of cobalt can enable the characteristic growth of carbon nanotubes, which can not only serve as a carrier of cobalt but also as a good electron channel; next, the role of acid washing is to remove some excess cobalt; finally, the purpose of air aging is to allow the surface of the cobalt generated by the reduction reaction to continue to be oxidized to generate some cobalt oxides, which are used to improve the oxygen evolution performance of the material.

[0048] Example 2: Fabrication of magnetically bonded air electrodes

[0049] First, the catalyst and acetylene black with a mass ratio of 2:1 were dispersed in a mixed solution containing ethanol to obtain a catalyst concentration of 10 mg mL -1 The catalyst slurry was drop-coated onto one surface of the gas diffusion layer (area mass loading of 1 mg cm) using a ring magnet as a binder. -2 After the solvent evaporated, the air cathode was assembled into a zinc-air battery for further testing.

[0050] Comparative Example 1

[0051] For comparison, the Co-NCNTFs sample obtained in Example 1 was treated in a 2M HCl solution for 5 days to obtain a cobalt-free NCNTFs sample.

[0052] Comparative Example 2: Preparation of a conventional air electrode:

[0053] Preparation process of common polymer binder air cathode: First, the catalyst and acetylene black with a mass ratio of 2:1 were dispersed in a mixed solution of ethanol and Nafion (5%) with a volume ratio of 9:1, and ultrasonicated for 30 minutes to obtain a catalyst concentration of 10 mg / mL. -1 Then, the uniformly dispersed catalyst slurry was drop-coated on the surface of the gas diffusion layer (loading of 1 mg cm -2 The gas diffusion layer, catalyst and nickel foam current collector are pressed into an air cathode using a tablet press.

[0054] Figure 2 b shows the XRD pattern of the as-prepared Co-NCNTFs, confirming the coexistence of graphitic carbon (JCPDS No. 96-101-1061) and metallic cobalt (JCPDS No. 96-901-1619). Figure 2The SEM images of Co-NCNTFs in c and d show a regular diamond dodecahedron structure with clear straight edges, rhombus faces and sea urchin-like surfaces. Figure 2 The transmission electron microscopy (TEM) image of the carbon nanotubes can further observe the coexistence of carbon nanotubes and polyhedrons. Figure 2 f and g show Co, CoO x High-resolution transmission electron microscopy (HRTEM) images of the interface between Co and CNT show that x The particles are surrounded by multiple layers of graphitic carbon. Figure 2 g represents Figure 2 The selected region (dashed line) of f in the metallic Co phase (lattice spacing ) and the presence of amorphous CoOx phase. The morphology and composition were further confirmed using high-angle annular dark field scanning transmission electron microscopy (STEM-HAADF). Figure 2 h and Figure 2 As shown in il, the polyhedral morphology of Co-NCNTF and the corresponding distribution of C, N, Co and O elements on the dodecahedron are demonstrated.

[0055] Through N2 adsorption / desorption tests, it was proved that the pore structure of Co-NCNTFs is a type I (at relatively low and medium pressures) and a type IV (at relatively high pressures) isotherm, with obvious hysteresis loops. Figure 3 As shown in a, the Co-NCNTFS sample has a high BET specific surface area of ​​321 m 2 g -1 and a large pore volume of 2.82 cm 3 g -1 The pore size distribution of Co-NCNTFs samples ( Figure 3 a), the average pore size is 3.8nm, and there are abundant mesopores. The phase composition of the sample was analyzed by Raman spectroscopy. Figure 3 As shown in b, the Raman spectrum of Co-NCNTFs shows 1354 cm -1 and 1587cm -1 The two Raman peaks near the position are defect-type sp 3 Hybridized carbon and graphitized sp 2 Hybrid carbon, the strength ratio between the two can be used to compare the degree of graphitization of carbon materials. d / I g The value is 1.12, which is due to the presence of a large number of structural defects in Co-NCNTFs due to N doping. In order to further understand the chemical composition and electronic structure of the surface of Co-NCNTFs samples, we tested X-ray photoelectron spectroscopy (XPS). XPS images show that Co-NCNTFs contain four elements: C, N, O, and Co ( Figure 3 c), the atomic percentage of each element is 79.5, 9.0, 7.5 and 4.0% respectively. According to the thermogravimetric curve, the Co content in the Co-NCNTFs composite material is about 37wt%. Figure 3 d shows the high-resolution C1s spectrum of Co-NCNTFs, which can be divided into two peaks: CC (284.5eV) and C=N (285.6eV). Figure 3 e), the peaks at 398.5 eV, 399.6 eV, and 401.0 eV are pyridinic nitrogen (or metallic nitrogen), pyrrolic nitrogen, and graphitic nitrogen, respectively. Figure 3 The Co 2p spectrum shown in f has 2p 3 / 2 and 2p 1 / 2 The peaks of the two states are located at 778.49 / 793.09, 779.89 / 795.39 and 781.49 / 797.79 eV, respectively, which can be classified as metallic Co, Co-O and Co-N species. Based on the characterization results, it can be determined that the metallic Co, amorphous Co compounds (CoO x ,CoN x ) and N-doped CNTs coexist, indicating that Co-NCNTFs are magnetic and have good ORR and OER performance.

[0056] To test the electrochemical performance and reaction kinetics of the catalyst, we measured ORR and OER performance on a rotating ring disk electrode (RDE). This work primarily used a three-electrode system with a rotating disk electrode, oxygen-saturated 0.1 mol KOH as the electrolyte, and noble metals Pt / C and RuO2 as ORR and OER references, respectively. The catalyst loading area was 0.25 mg cm -2 The ORR LSV curves of Co-NCNTFs, RuO2 and Pt / C are shown in Figure 2. Figure 4 The ORR half-wave potential (E 1 / 2 ) is 0.82V vs RHE, which is very close to Pt / C (0.81V vs RHE) and much better than RuO2 (0.55V vs RHE). A smaller Tafel slope indicates better ORR performance. Figure 4 The Tafel curve in b shows that the Co-NCNTFs electrocatalyst (81mV dec -1 ) has better ORR performance than Pt / C (84mV dec -1 ) and RuO2(149mV dec -1 ). Test the chronocurrent stability of Co-NCNTFs and Pt / C catalysts at 1600 rpm. Figure 4As shown in Figure c, the current density of the Co-NCNTFs catalyst still maintained 96% of the initial current density after 10 h, while the Pt / C catalyst only maintained 78.2% of the initial current density after 7.1 h.

[0057] The performance of magnetic manipulation electrodes and common binder electrodes as oxygen electrodes in liquid zinc-air batteries was further investigated. Figure 5 As shown in a, the air electrode in the magnetically manipulated ZABs consists of Co-NCNTFs catalyst, nickel foam, air diffusion layer and ring magnet. Figure 5 b shows that the Co-NCNTFs magnetic control battery is at 50 mA cm -2 The potential difference under the condition of magnetic binder is 1.10V, which is slightly lower than the charge and discharge overpotential of the battery with Nafion bonded Pt / C+RuO2 (1.19V). This shows that the magnetic binder battery has better charge and discharge performance. Figure 5 As shown in c, the corresponding power density is proved to be 230 mA cm -2 The maximum power of the magnetically manipulated Co-NCNTFs battery is 158 mW cm -2 , which is better than the Nafion bonded Pt / C+RuO2 battery (160mA cm -2 ; 120mWcm -2 ).like Figure 5 As shown in d, at 10mA cm -2 When the battery is discharged for a long time, the mass of the zinc sheet consumed is calculated and the battery capacity is 795 mAh g -1 , corresponding to an energy density of 954Wh kg -1 , surpassing the Nafion bonded Pt / C+RuO2 battery (721mAh g -1 ;793Wh kg -1 ). Figure 5 The e is shown at current densities of 1, 2, 5, 10, and 20 mA cm -2 When the magnetically manipulated Co-NCNTFs zinc-air battery is used, it exhibits better rate performance than the Nafion-bonded Pt / C+RuO2 zinc-air battery.

[0058] Since the air cathode of the homemade battery is different from the rotating disk electrode in actual situations and can eliminate O2 bubbles, the accumulation of O2 in the air cathode should be fully considered in the actual reaction of the zinc-air battery. In order to prove the effect of O2 bubbles on the cathode reaction of ZABs, we designed an in-situ observable electrolytic cell to observe the charging process. The electrolytic cell mainly consists of an air electrode, a Zn electrode and a KOH electrolyte. Zn is pre-dissolved in the electrolyte. 2+ions to simulate the ionic environment after discharge. To compare the effects of magnetic manipulation and conventional binders on the air electrode, we prepared air electrodes composed of a nickel current collector, a magnetic binder, and a Nafion binder. Detailed electrolytic cell assembly is described in the Experimental section of the Supporting Information. Figure 5 Figure 1 shows a comparison of electrodes loaded with Co-NCNTFs magnetic binder and Co-NCNTFs+Nafion binder at different times (1, 100, 200 and 300 hours) under a current density of 2. The results show that the powdering and shedding of the catalyst on the Co-NCNTFs+Nafion binder electrode were more serious during the 300-hour charging process. However, there was basically no shedding of the catalyst on the magnetically manipulated electrode loaded with Co-NCNTFs. In addition, the O2 accumulation on the Co-NCNTFs+Nafion binder electrode was more obvious than that on the magnetic binder-based air electrode (marked with white circles). This can be attributed to the structures of the two air electrodes. The magnetically manipulated electrode is loose and porous, allowing O2 bubbles to escape freely, while the Nafion binder electrode is flat and has fewer pores, which makes it difficult for O2 bubbles to separate. To demonstrate the stability of the magnetically manipulated Co-NCNTFs battery, we conducted charge and discharge cycle tests under a current density of 2. Figure 5 It can be seen from the g that the Co-NCNTFs connected by magnetic binder have excellent cycle stability and maintain an energy efficiency of 68.1% within 1200 hours. The energy efficiency of the battery with Co-NCNTFs+Nafion binder is 64.3% within 200 hours, and the energy efficiency of the commercial (Pt / C+RuO2) battery is 56.1% within 100 hours. These results show that the magnetically manipulated Co-NCNTFs battery performs better than the ordinary binder battery. It is worth noting that the Co-NCNTFs (containing CoO2) aged in air has a good performance. x ) has a narrow charge-discharge potential gap (ΔE = 0.71 V) and exhibits stable cycle performance for more than 200 h, while the original Co-NCNTFs (without CoO x ) of the battery is polarized significantly within 130h (e.g. Figure 6 ). These results all indicate that CoO x There is a positive impact on ZABs.

[0059] After the cycle is completed, the zinc-air battery with Co-NCNTFs+Nafion binder cannot be recycled. However, the battery with magnetically controlled Co-NCNTFs can be recycled in only three steps, such as Figure 7 First, the air electrode to be recovered is placed in the cathode distilled water, and then ultrasonicated for a few minutes to obtain a concentration of about 10 mg mL -1The Co-NCNTFs black suspension was then prepared. The magnet was then placed on the side of the glass, and the Co-NCNTFs were quickly (approximately 80 seconds) separated from the suspension. Finally, the Co-NCNTFs powder was dried at 80°C for 5 hours. XRD patterns, SEM images, TEM / HRTEM images, XPS spectra, and Raman spectra confirmed that the recovered Co-NCNTFs catalyst maintained its intact structure and morphology. Figure 7 As shown in b, the battery of Co-NCNTFs recovered from waste batteries (which has undergone 1200 hours of cycle test) shows a stable cycle test for more than 500 hours, and the charge and discharge potential gap is narrow (ΔE=0.86V), indicating that Co-NCNTFs has recycling value.

Claims

1. An air electrode structure for a zinc-air battery, characterized in that: The air electrode structure includes a diffusion layer, one side of the diffusion layer is covered with a catalyst layer, and a portion of the other side is provided with a magnetic material, the magnetic material is used to fix the catalyst layer through magnetic force, and the catalyst layer is used for the catalytic reduction reaction of oxygen; wherein, the chemical structure of the catalyst in the catalyst layer contains magnetic metal atoms; the catalyst particles in the catalyst layer have a porous structure; the catalyst layer does not contain an organic binder; the air electrode structure is used to allow O2 bubbles to escape freely; The areal mass loading of the catalyst on the catalyst layer was 0.5–5 mg cm -2 On the side of the diffusion layer containing magnetic material, there is an area that can directly contact the air; the size range of the pore structure is 1-50μm.

2. The air electrode structure according to claim 1, characterized in that: The catalyst layer contains graphite carbon, and carbon nanotubes are distributed on the graphite carbon. Co and Co oxide are coated in the carbon nanotubes, and nitrogen is doped in the catalyst. The particle size of the catalyst is in the range of 0.5-5 μm.

3. The air electrode structure according to claim 1, characterized in that: The nitrogen element exists in the form of pyridinic nitrogen, metallic nitrogen, pyrrolic nitrogen or graphitic nitrogen.

4. The air electrode structure according to claim 1, characterized in that: The diffusion layer is a porous material; the magnetic metal atoms are one or more of iron, cobalt or nickel; the catalyst is a cobalt-carbon-based catalyst, an iron-carbon-based catalyst or a nickel-carbon-based catalyst; in the catalyst, the mass percentage of the magnetic metal atoms in the chemical structure is 10-50%.

5. The air electrode structure according to claim 1, characterized in that: The preparation method of the catalyst includes the following steps: step 1, obtaining a coordination compound material containing Co, N and C, and calcining it under a reducing atmosphere; step 2, treating the product in dilute acid to dissolve part of the cobalt, and then aging it in air to generate cobalt oxide to obtain the catalyst.

6. The air electrode structure according to claim 5, characterized in that: The coordination compound material containing Co, N and C is a cobalt-based MOF material; the cobalt-based MOF material is ZIF-67.

7. The air electrode structure according to claim 5, characterized in that: The reducing atmosphere is a mixture of hydrogen and inert gas, with the volume ratio of hydrogen to inert gas being 1:5-15; the calcination treatment is performed at 250-400°C for 1-3 hours and then at 600-800°C for 2-5 hours.

8. The air electrode structure according to claim 5, characterized in that: The treatment in dilute acid refers to treatment in a 0.1-1M dilute acid solution for 2-20 hours; the aging treatment refers to treatment at 80-120°C for 1-3 days.

9. The method for manufacturing an air electrode structure according to claim 1, wherein: The steps include: Step 1, obtaining a diffusion layer; Step 2: Mix the catalyst, conductive filler, and solvent to form a slurry, and apply it to one side of the diffusion layer; and simultaneously place a magnetic material on the other side of the diffusion layer to fix the catalyst by magnetic force; Step 3, distilling off the solvent in the slurry; The weight ratio of catalyst to conductive filler is 0.5-5:1, and the concentration of catalyst in the slurry is 1-100 mg mL −1 .

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