A cathode material for low temperature metal fuel cells, its preparation method and use

Abstract

The application discloses a kind of cathode material for low-temperature metal fuel cell and its preparation method and application, preparation nitrogen-doped carbon nanotube as carrier;Utilize the liquid phase oxidation-reduction method of potassium permanganate and manganese sulfate, and introduce cobalt nitrate to carry out one-step hydrothermal synthesis;Utilize the doping effect of cobalt ion to control product crystal phase, and synthesize the rod-shaped structure of MnOOH and CoMn2O4 Nanocomposite on carrier.The obtained cathode material is through the synergistic effect of nitrogen-doped carbon carrier and metal oxide, significantly reduce the energy barrier of low-temperature oxygen reduction reaction.The cathode material has 0.79 V half-wave potential and 5.58 mA·cm ‑2 Limit diffusion current density under-10 ℃ environment;The assembled aluminum-air battery shows 1.56 V open-circuit voltage and 9.71 mW·cm ‑2 Power density under-40 ℃ environment, can be discharged stably for 16.2 h under 2 mA·cm ‑2 Current density, better than commercial Pt / C catalyst.In cold region emergency power supply, polar scientific expedition, military equipment and other extreme low-temperature scenes have significant application value.

Description

Technical Field

[0001] This invention relates to the field of energy materials technology, and more specifically, to a cathode material for a metal fuel cell, its preparation method, and its application. Background Technology

[0002] With the concept of sustainable development gaining widespread acceptance, renewable energy technologies such as fuel cells and metal-air batteries are experiencing accelerated development. Among them, aluminum-air batteries benefit from abundant aluminum resources and a theoretical specific energy of up to 8100 Wh·kg⁻¹. -1 With its advantages such as high energy density, controllable cost, small size, high portability, and excellent safety, aluminum-air batteries are considered one of the most promising next-generation energy storage and power batteries. They use oxygen from the air as the cathode active material, aluminum and its alloys as the anode active material, and an alkaline aqueous solution as the electrolyte. Energy is released through a reduction reaction of oxygen at the solid-liquid-gas three-phase interface of the cathode catalyst layer. Compared to other battery technologies, aluminum-air batteries possess advantages such as high energy density, controllable cost, small size, high portability, and excellent safety, making them irreplaceable in specialized fields such as military equipment, aerospace, and polar research.

[0003] To meet the application needs of aluminum-air batteries in various fields, their low-temperature discharge characteristics have become one of the key performance indicators. In cold regions such as Northeast China and the Qinghai-Tibet Plateau, the average winter temperature remains below -15℃, and in some high-altitude areas it even drops to -30℃. In scenarios such as border outposts in cold regions, polar research stations, and high-altitude meteorological monitoring points, equipment such as emergency lighting, portable communication, and field medical rescue all have strict requirements for the battery's continuous power supply capability in low-temperature environments. Therefore, as a key energy storage component, the discharge stability and reliability of aluminum-air batteries at extreme low temperatures directly determine the operational safety and efficiency of these outdoor devices. However, in low-temperature environments, the oxygen reduction reaction kinetics of the aluminum-air battery cathode slows down significantly, the activity and conductivity of the catalyst decrease, and the transport of electrons and reactants is restricted, resulting in a decline in the overall discharge performance of the battery.

[0004] Currently, research on fuel cell cathode materials mainly focuses on non-precious metal materials, such as transition metal oxide composites and multi-metal alloys, but existing technologies still have significant shortcomings in practical applications. For example, although the prior art (CN201610332586.0) discloses a MnO2-Mn3O4 / carbon nanotube composite catalyst, its preparation process lacks fine control over the crystal phase and microstructure, and the half-wave potential is only 0.66 V, which cannot overcome the performance degradation of fuel cells at low temperatures. In addition, the prior art (CN202010743455.8) prepares a manganese oxide / nitrogen-doped carbon composite catalyst through a cumbersome two-step heat treatment method. The active material and the support only have a weak interfacial bond, resulting in an oxygen reduction half-wave potential of only 0.65 V, which still cannot meet the performance requirements of fuel cells in low-temperature environments. Furthermore, the prior art (CN202411511780.6) proposes a method for preparing high-entropy alloy catalysts by combining solid-phase ball milling with acid etching. Although the material exhibits certain low-temperature tolerance, solid-phase ball milling is difficult to achieve uniform mixing of multiple components at the molecular level, which easily leads to particle agglomeration. Moreover, the long-term acid etching process may also damage the carbon skeleton. Therefore, developing cathode catalysts with high activity, strong conductivity and excellent low-temperature resistance has become a key research direction for improving the low-temperature discharge performance of aluminum-air batteries and expanding their application in extreme environments. Summary of the Invention

[0005] To address the significant decline in discharge performance of aluminum-air batteries at low temperatures, this invention provides a cathode material for low-temperature metal fuel cells and its preparation method. First, a carbon support is surface-oxidized with a strong acid to enhance its hydrophilicity, followed by nitrogen doping. Second, a one-step hydrothermal method is used to grow a rod-shaped nanostructure with a dual-phase coexistence of MnOOH and spinel-type CoMn2O4 on the surface of nitrogen-doped carbon nanotubes, utilizing the lattice regulation effect of cobalt ions. This unique structure not only achieves robust anchoring of the active components on the support but also significantly enhances reaction kinetics through the electronic coupling effect at the dual-phase interface. Compared to traditional high-temperature solid-phase ball milling, heat treatment impregnation, and conventional liquid-phase precipitation methods, this invention offers significant advantages in terms of precise control of active sites, improved structural stability, and reduced process costs. The cathode material of this invention overcomes the shortcomings of existing technologies, exhibits significantly improved catalytic performance, strong stability, and excellent electrocatalytic performance.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A cathode material for low-temperature metal fuel cells and a method for preparing the same, comprising the following steps:

[0008] 1) Carbon nanotubes are immersed in a mixed solution of concentrated nitric acid and concentrated sulfuric acid, ultrasonically dispersed, stirred at room temperature, and then repeatedly washed with deionized water and ethanol. After vacuum drying, they are sealed and stored.

[0009] 2) Add the oxidized carbon nanotubes obtained in step 1) to a mixed solution of ethanol and deionized water, and disperse evenly by ultrasonication. Add melamine, and evaporate the solvent in an oil bath while stirring. Calcine the mixture in a tube furnace under a nitrogen atmosphere.

[0010] 3) Dissolve KMnO4 in deionized water, add MnSO4·H2O, and stir until homogeneous. Then dissolve Co(NO3)2·6H2O in deionized water and slowly add it dropwise to the above solution. Add the nitrogen-doped carbon nanotubes obtained in step 2) and disperse them evenly by ultrasonication. Place the mixture in a polytetrafluoroethylene-lined reactor for hydrothermal reaction. After repeated rinsing with deionized water and vacuum drying, the catalyst is obtained.

[0011] Further, in step 1), the volume ratio of concentrated nitric acid to concentrated sulfuric acid is 1:3. The ultrasonication time is 4-6 h, preferably 4 h. The stirring time is 20-24 h, preferably 24 h.

[0012] Furthermore, in step 2), the volume ratio of deionized water to ethanol or methanol is 1:(1-3), preferably 1:3. The mass ratio of carbon nanotubes to melamine is 1:(1-4), preferably 1:1.

[0013] Furthermore, in step 2), the temperature of the oil bath is 80-100℃, preferably 85℃. The oil bath temperature affects the uniformity of mixing between carbon nanotubes and melamine during solvent evaporation. Preferably, 85℃ can achieve uniform coating of melamine on the surface of carbon nanotubes and effectively avoid component segregation.

[0014] Further, in step 2), the calcination temperature is 750-800℃, preferably 800℃. The calcination time is 1 h. The purpose of calcining at 800℃ for 1 h is to balance the graphitization degree of the carbon framework and the thermal stability of the active nitrogen species, thereby constructing a nitrogen-doped carbon nanotube network with both conductivity and abundant active sites in situ, providing an ideal carrier for the loading of manganese oxides.

[0015] Further, in step 3), the molar ratio of KMnO4, MnSO4·H2O, and Co(NO3)2·6H2O is 1:1.5:(0.25-2.5), preferably 1:1.5:0.5. The mass ratio of nitrogen-doped carbon nanotubes to the total mass of each metal salt is (0.8-1.2):1, preferably 1:1. The amount of Co(NO3)2·6H2O added is used to precisely induce the crystal phase transformation, thereby constructing a biphase composite structure in which MnOOH and CoMn2O4 coexist. Under the preferred stoichiometric ratio, an appropriate amount of cobalt ions can effectively regulate the crystallization kinetics of manganese oxide, promoting close contact between the two crystal phases at the nanoscale and forming abundant heterogeneous interfaces. This unique biphase structure not only optimizes the electronic structure of the active center by utilizing lattice defects, but also significantly enhances the electrical conductivity and oxygen reduction reaction catalytic activity of the material through a synergistic effect.

[0016] Furthermore, in step 3), the hydrothermal reaction temperature is 150-200℃, preferably 180℃. The hydrothermal reaction time is 4-8h, preferably 6h. The purpose of the preferred hydrothermal condition of 180℃ for 6h is to regulate crystal growth kinetics and induce the product to evolve from irregular particles to rod-shaped structures, thereby significantly improving the charge transfer rate and structural stability by utilizing the directional electron transport channels provided by the one-dimensional structure.

[0017] The vacuum drying temperature in the above steps is 60-80℃, preferably 60℃, and the drying time is 6-12 h, preferably 12 h.

[0018] This invention also provides a catalyst prepared using the above method, which uses nitrogen-doped carbon nanotubes as a support. This enhances the electron transport rate and, through synergistic effects with manganese oxides, improves material stability and low-temperature adaptability. The introduction of Co can adjust the band structure of Mn ions, optimize the adsorption energy of oxygen intermediates, introduce oxygen vacancies, further reduce the energy barrier of low-temperature oxygen reduction reactions, and improve catalytic activity and electron conduction performance. The prepared catalyst exhibits a half-wave potential of 0.81 V and a half-wave potential of 6.13 mA·cm⁻¹ at room temperature. -2 The limiting diffusion current density. It still exhibits a half-wave potential of 0.79 V and a current density of 5.58 mA·cm⁻¹ at a low temperature of -10℃. -2 The limiting diffusion current density is achieved. Furthermore, after continuous operation at room temperature for 20,000 s, it still maintains 91.11% of the current density, demonstrating excellent low-temperature resistance and long-term stability.

[0019] This invention also provides the application of a cathode material for low-temperature metal fuel cells in a low-temperature aluminum-air battery, exhibiting excellent electrocatalytic performance in an extreme low-temperature environment of -40°C: the assembled aluminum-air battery achieves an open-circuit voltage of up to 1.56 V and a power density as high as 9.71 mW·cm⁻¹. -2It is significantly superior to the noble metal catalyst Pt / C; at 2 mA·cm -2 It can discharge stably for 16.2 hours at the current density.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] (1) This invention achieves synergistic optimization of catalyst structure and performance by loading manganese oxide onto the surface of nitrogen-doped carbon nanotubes. Nitrogen-doped carbon nanotubes not only provide an excellent conductive network, but also regulate the electronic structure of manganese oxide through the electron donor effect of nitrogen atoms, promoting interfacial charge transfer and adsorption / desorption of reactant intermediates. Simultaneously, after loading manganese oxide, the specific surface area of ​​the catalyst increases significantly, providing more active sites for the reaction process, facilitating sufficient contact and adsorption of reactants, and accelerating reaction kinetics. The synergistic effect of nitrogen-doped carbon nanotubes and manganese oxide enables the composite material to maintain high electron transport efficiency and reactivity at low temperatures, significantly improving the conductivity and low-temperature catalytic performance of manganese oxide.

[0022] (2) This invention introduces Co ions to modulate the band structure of Mn ions while constructing a composite material of nitrogen-doped carbon nanotubes and manganese oxides. The introduction of Co can cause the d-band center of Mn to migrate, thereby effectively changing the strength and electron distribution of the Mn-O bond. This regulation not only optimizes the adsorption energy of the oxygen intermediate, but also promotes the adsorption and activation process of oxygen molecules on the catalytic surface. At the same time, Co doping can also introduce additional oxygen vacancies and electronic structures, providing more active sites for the reaction and further enhancing the interfacial charge transfer capability. Under low-temperature conditions, these structures and electronic regulation effects work synergistically to effectively reduce the energy barrier of the oxygen reduction reaction, accelerate the reaction kinetics, and thus significantly improve the low-temperature catalytic activity, electronic conductivity, and structural stability of the catalyst.

[0023] (3) The cathode material for low-temperature metal fuel cells described in this invention has the advantages of simple process, low cost, high efficiency and low energy consumption in production process. The raw materials used are inexpensive and meet green environmental protection standards. It can achieve large-scale mass production and shows good application prospects. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments and comparative examples of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a scanning electron microscope image of Embodiment 1 of the present invention;

[0026] Figure 2 (a) BET specific surface area and pore size distribution of nitrogen-doped carbon nanotubes prepared in Example 1; (b) BET specific surface area and pore size distribution of Example 1;

[0027] Figure 3 The X-ray diffraction patterns are those of Embodiments 1, 2, and 3 of the present invention and Comparative Examples 1, 2, and 3.

[0028] Figure 4 Linear sweep voltammetry curves at room temperature for Embodiments 1, 2, and 3 and Comparative Examples 1, 2, and 3 of the present invention;

[0029] Figure 5 The linear sweep voltammetry curves of Examples 1, 2, and 3 of the present invention at -10°C are shown.

[0030] Figure 6 The test curves of Example 1 of the present invention and the noble metal catalyst Pt / C at room temperature are shown.

[0031] Figure 7 The open-circuit voltage curve of the aluminum-air battery assembled with the noble metal catalyst Pt / C as the cathode catalyst in Example 1 of this invention at -40 degrees Celsius;

[0032] Figure 8 The power density curve of the aluminum-air battery assembled with the noble metal catalyst Pt / C as the cathode catalyst in Example 1 of the present invention at -40 degrees Celsius;

[0033] Figure 9 The aluminum-air battery assembled in Example 1 of this invention with the noble metal catalyst Pt / C as the cathode catalyst was tested at -40 degrees Celsius at a rate of 2 mA·cm⁻¹. -2 Discharge curve under current density operation. Detailed Implementation

[0034] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. The description of the technical features described below is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples.

[0035] In the following examples, all raw materials used are common commercially available products that can be purchased directly or can be prepared using conventional techniques in the art.

[0036] Room temperature refers to 25±1℃.

[0037] Example 1

[0038] A cathode material for low-temperature metal fuel cells and its preparation method, the specific method comprising the following steps:

[0039] (1) Carrier pretreatment

[0040] 1 g of carbon nanotubes was immersed in 120 ml of a mixed solution of concentrated nitric acid and concentrated sulfuric acid (volume ratio of concentrated nitric acid to concentrated sulfuric acid = 1:3), ultrasonically dispersed for 4 h, and stirred at room temperature for 24 h. Afterwards, it was repeatedly washed with deionized water and ethanol until neutral, and finally dried under vacuum at 70 °C for 24 h to obtain oxidized carbon nanotubes.

[0041] (2) Construction of nitrogen-doped framework

[0042] 0.5 g of the oxidized carbon nanotubes obtained in step (1) were added to a mixed solution of 40 ml of deionized water and ethanol (deionized water:ethanol volume ratio = 1:3) and ultrasonically dispersed until homogeneous. 0.5 g of melamine was added, and the solvent was evaporated in an oil bath at 85 °C with stirring. The mixture was then ground until homogeneous, placed in a corundum crucible, and annealed in a tube furnace under a nitrogen atmosphere at 800 °C for 1 h with a heating rate of 5 °C / min. Nitrogen-doped carbon nanotubes were obtained.

[0043] (3) 7.93MnOOH-2.02Co 1.11 Mn 1.89 Preparation of O4@NCNT

[0044] Dissolve 63.2 mg (0.4 mmol) KMnO4 in 30 ml of deionized water, add 101.4 mg (0.6 mmol) MnSO4·H2O, and stir until homogeneous. Then dissolve 58.20 mg (0.2 mmol) Co(NO3)2·6H2O in 30 ml of deionized water and slowly add it dropwise to the above solution. Next, add 222.8 mg of nitrogen-doped carbon nanotubes obtained in step (2) and ultrasonically disperse until homogeneous. Place the mixed solution in a 100 ml polytetrafluoroethylene-lined reactor and hydrothermally react at 180℃ for 6 h. After the reaction is complete, allow the reactor to cool naturally to room temperature, rinse repeatedly with deionized water, and vacuum dry to obtain the catalyst 7.93MnOOH-2.02Co. 1.11 Mn 1.89 O4@NCNT.

[0045] Example 2

[0046] Compared with Example 1 of the present invention, steps (1) and (2) of Example 2 are the same as those in Example 1. The difference in Example 2 is that in step (3), the amount of Co(NO3)2·6H2O added is 29.1 mg (0.1 mmol), and the specific method is as follows:

[0047] (1) The carrier pretreatment is the same as in Example 1;

[0048] (2) The nitrogen-doped framework was constructed in the same manner as in Example 1;

[0049] (3) Preparation of 0.1Co-MnOOH@NCNT

[0050] Dissolve 63.2 mg (0.4 mmol) KMnO4 in 30 ml of deionized water, add 101.4 mg (0.6 mmol) MnSO4·H2O, and stir until homogeneous. Then dissolve 29.1 mg (0.1 mmol) Co(NO3)2·6H2O in 30 ml of deionized water and slowly add it dropwise to the above solution. Then add 193.7 mg of nitrogen-doped carbon nanotubes obtained in step (2) and ultrasonically disperse until homogeneous. Place the mixed solution in a 100 ml polytetrafluoroethylene-lined reactor and hydrothermally react at 180℃ for 6 h. After the reaction is complete, allow the reactor to cool naturally to room temperature, rinse repeatedly with deionized water, and vacuum dry to obtain the catalyst 0.1Co-MnOOH@NCNT.

[0051] Example 3

[0052] Compared with Example 1 of the present invention, steps (1) and (2) of Example 3 are the same as those in Example 1. The difference in Example 3 is that in step (3), the amount of Co(NO3)2·6H2O added is 87.3 mg (0.3 mmol), and the specific method is as follows:

[0053] (1) The carrier pretreatment is the same as in Example 1;

[0054] (2) The nitrogen-doped framework was constructed in the same manner as in Example 1;

[0055] (3) 6.66MnOOH-5.45Co 1.18 Mn 1.82 Preparation of O4@NCNT

[0056] Dissolve 63.2 mg (0.4 mmol) KMnO4 in 30 ml of deionized water, add 101.4 mg (0.6 mmol) MnSO4·H2O, and stir until homogeneous. Then dissolve 87.3 mg (0.3 mmol) Co(NO3)2·6H2O in 30 ml of deionized water and slowly add it dropwise to the above solution. Next, add 251.9 mg of nitrogen-doped carbon nanotubes obtained in step (2) and ultrasonically disperse until homogeneous. Place the mixed solution in a 100 ml polytetrafluoroethylene-lined reactor and hydrothermally react at 180℃ for 6 h. After the reaction is complete, allow the reactor to cool naturally to room temperature, rinse repeatedly with deionized water, and vacuum dry to obtain the catalyst 6.66MnOOH-5.45Co. 1.18 Mn 1.82 O4@NCNT.

[0057] Comparative Example 1

[0058] Compared with Embodiment 1 of the present invention, steps (1) and (2) of Comparative Example 1 are as described in Embodiment 1. The difference in Comparative Example 1 is that Co(NO3)2·6H2O was not added in step (3), and the specific method is as follows:

[0059] (1) The carrier pretreatment is the same as in Example 1;

[0060] (2) The nitrogen-doped framework was constructed in the same manner as in Example 1;

[0061] (3) Preparation of MnOOH@NCNT

[0062] 63.2 mg (0.4 mmol) KMnO4 was dissolved in 60 ml of deionized water, and 101.4 mg (0.6 mmol) MnSO4·H2O was added and stirred until homogeneous. Then, 0.2 g of nitrogen-doped carbon nanotubes obtained in step (2) were added and ultrasonically dispersed until homogeneous. The mixed solution was placed in a 100 ml polytetrafluoroethylene-lined reactor and hydrothermally reacted at 180 °C for 6 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature, and after repeated rinsing with deionized water and vacuum drying, the catalyst MnOOH@NCNT was obtained.

[0063] Comparative Example 2

[0064] Compared with Example 1 of the present invention, Comparative Example 2 differs in that nitrogen doping of CNTs was not performed, and Co(NO3)2·6H2O was not added. The specific method is as follows:

[0065] (1) The carrier pretreatment is the same as in Example 1;

[0066] (2) Preparation of MnOOH@CNTs

[0067] 63.2 mg (0.4 mmol) KMnO4 was dissolved in 60 ml of deionized water, and 101.4 mg (0.6 mmol) MnSO4·H2O was added and stirred until homogeneous. Then, 0.2 g of the acid-treated carbon nanotubes (oxidized carbon nanotubes) obtained in step (1) was added and ultrasonically dispersed until homogeneous. The mixed solution was placed in a 100 ml polytetrafluoroethylene-lined reactor and hydrothermally reacted at 180 °C for 6 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature, and after repeated rinsing with deionized water and vacuum drying, the catalyst MnOOH@CNTs was obtained.

[0068] Comparative Example 3

[0069] Compared with Embodiment 1 of the present invention, Comparative Example 3 differs in that NCNT was not added, and Co(NO3)2·6H2O was not added. The specific method is as follows:

[0070] (1) Preparation of MnOOH

[0071] 63.2 mg (0.4 mmol) of KMnO4 was dissolved in 60 ml of deionized water, and 101.4 mg (0.6 mmol) of MnSO4·H2O was added and stirred until homogeneous. The mixture was then placed in a 100 ml polytetrafluoroethylene-lined reactor and hydrothermally reacted at 180 °C for 6 h. After the reaction was complete, the reactor was allowed to cool naturally to room temperature, and after repeated rinsing with deionized water and vacuum drying, the catalyst MnOOH was obtained.

[0072] Comparative Example 4

[0073] Compared with Embodiment 1 of the present invention, the difference of Comparative Example 4 is that it uses a physical mixing method to mix the oxide and NCNT, and the specific method is as follows:

[0074] (1) The carrier pretreatment is the same as in Example 1;

[0075] (2) The nitrogen-doped framework was constructed in the same manner as in Example 1;

[0076] (3) Preparation of MnOOH-CoMn2O4

[0077] 63.2 mg (0.4 mmol) KMnO4 was dissolved in 30 ml of deionized water, and 101.4 mg (0.6 mmol) MnSO4·H2O was added and stirred until homogeneous. Then, 58.20 mg (0.2 mmol) Co(NO3)2·6H2O was dissolved in 30 ml of deionized water and slowly added dropwise to the above solution. The mixed solution was placed in a 100 ml polytetrafluoroethylene-lined reactor and hydrothermally reacted at 180 °C for 6 h. After the reaction was complete, the reactor was allowed to cool naturally to room temperature, and after repeated rinsing with deionized water and vacuum drying, MnOOH-CoMn2O4 was obtained.

[0078] (4) Preparation of MnOOH-CoMn2O4@NCNT

[0079] 200 mg of nitrogen-doped carbon nanotubes obtained in step (2) and MnOOH-CoMn2O4 obtained in step (3) were ground and mixed in an agate mortar for 30 minutes to obtain the catalyst MnOOH-CoMn2O4@NCNT.

[0080] Comparative Example 5

[0081] Compared with Embodiment 1 of the present invention, the difference of Comparative Example 5 is that a step-by-step post-processing method is used to introduce the cobalt source, and the specific method is as follows:

[0082] (1) The carrier pretreatment is the same as in Example 1;

[0083] (2) The nitrogen-doped framework was constructed in the same manner as in Example 1;

[0084] (3) Preparation of MnOOH@NCNT;

[0085] 63.2 mg (0.4 mmol) KMnO4 was dissolved in 60 ml of deionized water, and 101.4 mg (0.6 mmol) MnSO4·H2O was added and stirred until homogeneous. Then, 165 mg of nitrogen-doped carbon nanotubes obtained in step (2) were added and ultrasonically dispersed until homogeneous. The mixed solution was placed in a 100 ml polytetrafluoroethylene-lined reactor and hydrothermally reacted at 180 °C for 6 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature, and after repeated rinsing with deionized water and vacuum drying, the catalyst MnOOH@NCNT was obtained.

[0086] (4) Preparation of 0.2Co-MnOOH@NCNT

[0087] The MnOOH@NCNT obtained in step (3) was dispersed in 30 ml of a solution containing 0.2 mmol Co(NO3)2·6H2O, stirred at room temperature for 6 h, dried under vacuum, and then annealed at 300 °C for 2 h in an inert atmosphere in a tube furnace to obtain the catalyst 0.2Co-MnOOH@NCNT.

[0088] Comparative Example 6

[0089] Compared with Embodiment 1 of the present invention, the difference in Comparative Example 6 is that the nitrogen source is replaced with urea, and a one-step hydrothermal method is used to simultaneously perform nitrogen doping and oxide loading. The specific method is as follows:

[0090] (1) The carrier pretreatment is the same as in Example 1;

[0091] (2) Preparation of MnOOH-CoMn2O4@NCNT

[0092] 63.2 mg (0.4 mmol) KMnO4 was dissolved in 30 ml of deionized water, and 101.4 mg (0.6 mmol) MnSO4·H2O was added and stirred until homogeneous. Then, 58.20 mg (0.2 mmol) Co(NO3)2·6H2O was dissolved in 30 ml of deionized water and slowly added dropwise to the above solution, stirring until homogeneous. Subsequently, 500 mg of urea and 200 mg of carbon oxide nanotubes obtained in step (1) were added and ultrasonically dispersed until homogeneous. The mixed solution was placed in a 100 ml polytetrafluoroethylene-lined reactor and hydrothermally reacted at 180℃ for 6 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature, and after repeated rinsing with deionized water and vacuum drying, the catalyst MnOOH-CoMn2O4@NCNT was obtained.

[0093] Comparative Example 7

[0094] Compared with Example 1 of the present invention, the difference of Comparative Example 7 is that a two-step pyrolysis method is used to prepare the nitrogen-doped Vulcan-72XC / carbon nanotube / MnO composite catalyst (reproducing Example 1 in patent CN202010743455.8). The specific method is as follows:

[0095] (1) Preparation of V-CNT-N support: 0.2 g of Vulcan-72XC and 0.05 g of carbon nanotubes (mass ratio 4:1) were weighed, and anhydrous ethanol was added, stirred, sonicated, and dried to obtain a V-CNT mixture. 0.25 g of the above V-CNT mixture and 1 g of urea (mass ratio 1:4) were weighed, and anhydrous ethanol was added, stirred, sonicated, and dried. The mixture was then heated to 600 °C at 5 °C / min and held for 3 h in a tube furnace under a nitrogen atmosphere, and then ground to obtain nitrogen-doped support V-CNT-N.

[0096] (2) Preparation of V-CNT-N / MnO: Weigh 0.5 g of the V-CNT-N support obtained in step (1) and 0.5 g of manganese acetate tetrahydrate (mass ratio 1:1), add anhydrous ethanol, stir, sonicate, and dry. Heat the mixture in a tube furnace under nitrogen atmosphere to 280℃ at 5℃ / min and hold for 3 h, then grind to obtain the composite catalyst V-CNT-N / MnO.

[0097] Phase characterization

[0098] Figure 1 The scanning electron microscope (SEM) image of Example 1 of this invention shows that the oxides exhibit a uniform rod-like structure, evenly dispersed and tightly attached to the surface of carbon nanotubes, forming a wound carrier structure. No obvious aggregation is observed between the oxide particles, indicating that the hydrothermal synthesis process of this invention can effectively control the morphology and dispersibility of the oxides, which is beneficial for the full exposure of active sites and electron transport.

[0099] Figure 2 (a) is a BET specific surface area and pore size distribution diagram of the nitrogen-doped carbon nanotubes prepared in Example 1. As shown in the figure, the nitrogen-doped carbon nanotubes have a BET specific surface area of ​​129.4019 μm. 2 The specific surface area is / g and it exhibits obvious mesoporous structure characteristics, which is conducive to the transport and diffusion of reactants; Figure 2 (b) is a BET specific surface area and pore size distribution diagram of the composite catalyst of Example 1. Compared with nitrogen-doped carbon nanotubes, the specific surface area is further increased to 194.5963 m² after loading with oxides. 2 / g indicates that the introduction of oxides significantly increases the specific surface area of ​​the material, which can expose more active sites, thereby helping to improve the electrocatalytic reaction performance.

[0100] Figure 3The X-ray diffraction patterns of Examples 1, 2, and 3 and Comparative Examples 1, 2, and 3 of this invention are shown. As can be seen from the figures, Example 1 shows the coexistence of two phases, MnOOH and CoMn2O4; the diffraction peaks of Example 2 correspond only to MnOOH; while Example 3 exhibits typical characteristics of a single CoMn2O4 crystalline phase. The presence of different crystalline phases indicates that the amount of Co doping has a significant regulatory effect on the phase composition of the product. The phase results of Comparative Examples 1, 2, and 3 show that, due to the lack of corresponding doping or support regulation, their final products all exhibit a single MnOOH crystalline phase. These results indicate that the synergistic effect of Co doping and nitrogen-doped carbon nanotube support is a key factor in achieving the formation of the MnOOH / CoMn2O4 composite phase, further confirming the effectiveness of phase regulation in the embodiments of this invention.

[0101] Electrochemical performance testing

[0102] Electrochemical performance testing first involved preparing a catalyst ink: 5 mg of catalyst was weighed and added to 490 μL of deionized water, 490 μL of ethanol, and 20 μL of Nafion solution, and ultrasonically dispersed for 1 h to obtain a uniformly dispersed ink. Then, 5 μL of the ink was drop-coated onto the surface of a 5 mm diameter glassy carbon electrode and allowed to air dry. The test employed a standard three-electrode system, with the catalyst-modified rotating glassy carbon electrode as the working electrode, the carbon rod as the counter electrode, and Hg / HgO as the reference electrode. The electrolyte was a 0.1 M potassium hydroxide solution; before testing, oxygen was bubbled into the solution for 1 h to achieve oxygen saturation. During the low-temperature ORR test, the flask containing the electrolyte and electrode system was placed in a cryogenic bath, and the test was conducted after the system reached the set temperature.

[0103] Figure 4 The figures show the linear sweep voltammetry curves of Examples 1, 2, and 3 and Comparative Examples 1, 2, and 3 at room temperature. As can be seen from the figures, Example 1 exhibits the best ORR performance at room temperature, with an onset potential of 0.91 V, a half-wave potential of 0.81 V, and a limiting diffusion current density of 6.13 mA·cm⁻¹. -2 The performance is significantly superior to that of other embodiments and comparative examples. This indicates that the present invention can effectively improve the room-temperature ORR performance of the catalyst by synergistically regulating the oxide composition and carbon support structure.

[0104] To further verify the significant advantages of this invention over the prior art, the key performance indicators of Example 1 of this invention were compared with those of the prior art (Comparative Example 7, reproducing prior art CN202010743455.8), and the results are shown in Table 1. The results show that, compared to the single MnO phase prepared by the cumbersome heat treatment method in the prior art, this invention uses a simple one-step hydrothermal method to construct a two-phase composite structure of MnOOH and CoMn2O4, which greatly enhances the catalytic activity. The half-wave potential of Example 1 is as high as 0.81 V, significantly better than the 0.65 V of Comparative Example 7, fully demonstrating the core advantage of this Co-doped two-phase structure in enhancing reaction kinetics.

[0105] Table 1 Comparison of key indicators between the present invention and existing technologies.

[0106] Comparison Projects Embodiment 1 of the present invention Comparative Example 7 (Prior Art) Preparation method One-step hydrothermal method Heat treatment Active components <![CDATA[MnOOH / CoMn2O4]]> MnO Half-wave potential 0.81 V (actual measurement) 0.65 V (reference value)

[0107] Figure 5 The figures show the linear sweep voltammetry curves of Examples 1, 2, and 3 of this invention at -10°C. It can be seen that Example 1 maintains excellent ORR performance even at low temperatures, with an onset potential of 0.89 V, a half-wave potential of 0.79 V, and a limiting diffusion current density of 5.58 mA·cm⁻¹. -2 This is significantly superior to other embodiments. This indicates that the catalyst prepared by the present invention can maintain high reaction kinetics and electron transport capacity under low temperature conditions, exhibiting excellent low-temperature adaptability.

[0108] Figure 6 The figures show the electrochemical stability test curves of Example 1 of the present invention and the noble metal catalyst Pt / C at room temperature. It can be seen that after continuous operation at 0.7 V (vs. RHE) for 20,000 s, Example 1 still maintains 91.11% of the initial current density, while the noble metal catalyst Pt / C only maintains 76.88%. This proves that Example 1 of the present invention exhibits higher electrochemical stability under long-term operating conditions, which is superior to traditional noble metal catalysts.

[0109] Fuel cell performance testing

[0110] The fuel cell performance was achieved through assembly using a custom-designed mold, followed by coating with a catalyst (1*1 cm). 2 The battery used carbon cloth as the cathode and polished aluminum sheet as the anode, with 7 M KOH solution as the electrolyte. The open-circuit voltage and power density were tested using a Chenhua CHI760E electrochemical workstation in a low-temperature constant-temperature chamber, and a constant-current discharge test was performed using a Xinwei battery testing system.

[0111] Figure 7The figure shows the open-circuit voltage curve of the aluminum-air battery assembled in Example 1 of this invention with the noble metal catalyst Pt / C as the cathode catalyst at -40 degrees Celsius. The results show that the battery assembled using Example 1 has an open-circuit voltage of 1.56 V, which is higher than that of the control battery using Pt / C (1.51 V), and remains stable at -40 degrees Celsius. This indicates that Example 1 of this invention has excellent operating performance and application potential in low-temperature environments.

[0112] Figure 8 The power density curves of aluminum-air batteries assembled using the catalyst prepared in Example 1 of this invention and the noble metal catalyst Pt / C as cathode catalysts are shown at -40°C. As can be seen from the figure, the aluminum-air battery assembled in Example 1 exhibits a power density of 9.71 mW·cm⁻¹. -2 The power density is higher than that of the noble metal catalyst Pt / C, which is 7.23 mW·cm⁻¹. -2 The power density is significantly improved, which fully demonstrates the excellent catalytic performance of the catalyst prepared in this invention under extreme low temperature conditions, and can more efficiently improve the energy output level of aluminum-air batteries.

[0113] Figure 9 The catalyst prepared in Example 1 of this invention and the noble metal catalyst Pt / C were used as cathode catalysts, respectively. After being assembled into an aluminum-air battery, the battery was tested at -40°C and 2 mA·cm⁻¹. -2 Discharge curves under current density conditions. Test results show that under these extreme low temperatures and specific current density conditions, the aluminum-air battery assembled with the catalyst of Example 1 can achieve a stable discharge time of 16.2 h; while the battery assembled with the noble metal catalyst Pt / C only achieves a stable discharge time of 11.4 h. The comparison demonstrates that the catalyst of Example 1 of this invention can significantly extend the effective working time of the aluminum-air battery in low-temperature environments, fully confirming the core advantages of this catalyst in low-temperature application scenarios, and providing crucial support for the reliable operation of the battery in low-temperature scenarios such as emergency power supply in cold regions and power supply for polar scientific research equipment.

[0114] In summary, this invention successfully developed a high-performance cathode material for low-temperature metal fuel cells by achieving synergistic effects, enhancing structural stability, and optimizing process costs. The catalyst prepared in Example 1 of this invention exhibits a half-wave potential of 0.81 V and a half-wave potential of 6.13 mA·cm⁻¹ at room temperature. -2 The limiting diffusion current density. It still exhibits a half-wave potential of 0.79 V and a current density of 5.58 mA·cm⁻¹ at a low temperature of -10°C. -2The limiting diffusion current density was achieved. Furthermore, after continuous operation at room temperature for 20,000 s, it maintained 91.11% of its current density, demonstrating excellent low-temperature resistance and long-term stability. When this catalyst was applied to a low-temperature aluminum-air battery, it exhibited outstanding electrocatalytic performance in an extreme low-temperature environment of -40℃: the assembled aluminum-air battery achieved an open-circuit voltage of 1.56 V and a power density as high as 9.71 mW·cm⁻¹. -2 It is significantly superior to the noble metal catalyst Pt / C; at 2 mA·cm -2 At the specified current density, it can discharge stably for 16.2 hours. The catalyst prepared in this invention possesses the characteristics of high activity, strong stability, low cost, and environmental friendliness, providing reliable technical support for the large-scale commercial application of low-temperature aluminum-air batteries. It demonstrates significant application value in extreme low-temperature scenarios such as emergency power supply in cold regions, polar scientific research, and military equipment.

[0115] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a cathode material for a low-temperature metal fuel cell, characterized in that, Includes the following steps: 1) Carbon nanotubes are oxidized in a strong acid solution, then mixed with a nitrogen source and calcined at high temperature under an inert atmosphere to obtain nitrogen-doped carbon nanotubes. 2) KMnO4, MnSO4·H2O and Co(NO3)2·6H2O are dissolved and mixed sequentially, and the nitrogen-doped carbon nanotubes obtained in step 1) are added and dispersed before hydrothermal reaction. After the reaction is completed, the material is washed and dried to obtain the cathode material.

2. The preparation method according to claim 1, characterized in that, In step 1), the strong acid solution is a mixed solution of concentrated nitric acid and concentrated sulfuric acid with a volume ratio of 1:(1-3); the oxidation process includes ultrasonic dispersion for 4-6 hours and stirring at room temperature for 20-24 hours. The nitrogen source is melamine, wherein the mass ratio of oxidized carbon nanotubes to melamine is 1:(1-4), the high-temperature calcination temperature is 750-800℃, and the holding time is 1-2 hours.

3. The preparation method according to claim 1, characterized in that, In step 2), the molar ratio of KMnO4, MnSO4·H2O and Co(NO3)2·6H2O is 1:1.5:(0.25-2.5).

4. The preparation method according to claim 1, characterized in that, In step 2), the nitrogen-doped carbon nanotubes are multi-walled carbon nanotubes with a diameter of 10-20 nm and a nitrogen mass ratio of approximately 1.8%.

5. The preparation method according to claim 1, characterized in that, In step 2), the ratio of the mass of nitrogen-doped carbon nanotubes to the total mass of each metal salt is (0.8-1.2):

1.

6. The preparation method according to claim 1, characterized in that, In step 2), the hydrothermal reaction temperature is 150-200℃ and the hydrothermal reaction time is 4-8 h.

7. The method for preparing cathode material for low-temperature metal fuel cells according to claim 1, characterized in that, The drying in step 2) is a vacuum drying process at a temperature of 60-80℃ for 6-12 hours.

8. The method for preparing the cathode material for a low-temperature metal fuel cell according to claim 4, characterized in that, The cathode material structure obtained when the molar ratio of KMnO4, MnSO4·H2O and Co(NO3)2·6H2O is 1:1.5:0.5 is a two-phase heterostructure of MnOOH and CoMn2O4.

9. The cathode material for low-temperature metal fuel cells prepared by the preparation method according to any one of claims 1-8, characterized in that, The cathode material includes a nitrogen-doped carbon nanotube carrier and an active component anchored to the surface of the carrier; the active component contains two crystalline phases, MnOOH and CoMn2O4, and the cathode material has a rod-shaped nanocomposite structure.

10. The application of the cathode material according to claim 9 in a low-temperature aluminum-air battery, characterized in that, The material can be used as an air cathode catalytic material in a metal-air battery; the aluminum-air battery has an open-circuit voltage of not less than 1.5 V and a capacitance of not less than 9.0 mW·cm⁻¹ at -40°C. -2 The power density.

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