Application of single-metal Co (at) N-C nanotube with high C and N contents

Abstract

The invention discloses an application of a single-metal Co (at) N-C nanotube with high C and N contents. The Co (at) N-C nanotube is used for a zinc or magnesium metal air battery positive electrode material catalyst. The application of the oxygen reduction catalyst in a primary zinc-air battery, a primary magnesium-air battery and a secondary zinc-air battery is realized. The oxygen reduction catalytic material is characterized by being a monometallic catalyst, and shows relatively high energy density and power density in a metal battery. The half-wave potential of the prepared single-metal catalyst Co (at) NC-1Co (at) NC-1 is 0.85 V, and the half-wave potential exceeds the half-wave potential of commercialized 20% Pt / C; the limit diffusion current density Jd is 5.44 mA cm <-2 >, which is equivalent to that of commercial 20% Pt / C. The power density of a primary zinc air battery taking Co-coated NC-1 as the oxygen reduction catalyst is 202 mW cm <-2 >, and the maximum energy density is 928 Wh kg <-1 > Zn, which is higher than that of a Pt / C-based zinc metal air battery. The catalyst has the advantages of easily available raw materials, simple preparation and low cost, and has potential commercial application value.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, specifically to the application of a high C and N content monometallic Co@NC nanotube as an ORR catalyst. Background Technology

[0002] Metal-air batteries are a special type of fuel cell and are currently one of the most effective green electrochemical energy sources for alleviating energy shortages and environmental pollution. They share the design characteristics of traditional batteries, using a metal as the negative electrode. However, their porous positive electrode structure is similar to that of fuel cells, requiring a continuous supply of oxygen as a reactant, which gives them a very high energy density, approximately 2-10 times that of lithium-ion batteries. Zinc metal-air batteries are characterized by low cost, a relatively high theoretical voltage (1.65V), and a relatively high theoretical energy density (1.36kWh·kg⁻¹). -1 Compared to other metal-air batteries, zinc-air batteries offer advantages such as safe manufacturing processes, low cost, flat discharge voltage, and the use of aqueous electrolytes. As a promising new energy device, zinc-air batteries have received widespread attention and research. Magnesium-air batteries possess high theoretical voltage (3.09V) and high theoretical energy density (2.84kWh·kg⁻¹). -1 ) and high specific capacity (3833mAh.g) -1 With its advantages such as high energy density, it is a green and clean energy source with broad application prospects in portable electronic devices, marine underwater instruments, intelligent autonomous unmanned submarines, and backup energy.

[0003] However, the slow kinetics of the oxygen reduction reaction at the cathode severely hinder the large-scale commercialization of metal-air batteries. High-performance noble metal catalysts are expensive and limited in reserves, significantly restricting the industrialization of air batteries. Therefore, developing high-performance non-noble metal oxygen reduction catalysts is a crucial pathway for the large-scale commercialization of metal-air batteries. Non-noble metal@nitrogen-doped carbon-based materials possess oxygen reduction catalytic activity and are low-cost, making them potential candidates to replace noble metal catalysts.

[0004] In the synthesis of carbon-based catalysts, high-temperature pyrolysis of metal-organic frameworks (MOFs) is an important method for preparing MNC materials. Zeolite imidazole salt frameworks (ZIFs), a subclass of MOFs, combine the characteristics of both zeolites and MOFs, exhibiting an ordered crystal structure, high specific surface area, tunable porosity, and excellent thermal stability. Metal@nitrogen-doped carbon-based MNCs derived from ZIF pyrolysis maintain a three-dimensional porous structure and high surface area, enhancing ORR active sites and catalytic performance. However, single ZIF-derived carbon catalysts often exhibit inherent limitations. For example, ZIF-8-derived carbon-based catalysts suffer from poor conductivity and limited mesopores, while ZIF-67-derived carbon-based catalysts have low nitrogen content, all of which limit further improvements in catalyst performance. Summary of the Invention

[0005] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide an application of high C and N content monometallic Co@NC nanotubes to solve the problems of slow kinetics of positive electrode oxygen reduction reaction and poor conductivity of single ZIF-derived carbon catalysts in existing technologies.

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

[0007] An application of a high C and N content monometallic Co@NC nanotube, wherein the Co@NC nanotube is used as a catalyst in a zinc or magnesium metal-air battery cathode material.

[0008] Preferably, the Co@NC nanotubes are used in the positive electrode catalyst layer.

[0009] Preferably, the positive electrode catalyst layer comprises Co@NC nanotubes, conductive carbon material, Nafion solution, anhydrous ethanol, hydrophilic carbon paper, and an air diffusion layer.

[0010] Preferably, the conductive carbon material is Super P, and the mass ratio of the conductive carbon material to Co@NC nanotubes is 1:1; the concentration of the Nafion solution is 5 wt%.

[0011] Preferably, the Co@NC nanotubes are obtained by the following method:

[0012] A dual ZIF precursor containing Zn and Co was mixed with a nitrogen source and calcined at 300℃-400℃ for 1-2 hours under an inert atmosphere, followed by calcination at 750℃-850℃ for another 2-4 hours to obtain the Co@NC nanotubes.

[0013] Preferably, the dual ZIF precursor is obtained by the following method:

[0014] Cobalt salt, zinc salt, and imidazole compound were dissolved in methanol to obtain corresponding solutions A, B, and C. Solutions A, B, and C were mixed at room temperature and aged for 8-16 hours. The solids were collected and purified to obtain a bis-ZIF precursor containing Zn and Co.

[0015] Preferably, the cobalt salt is cobalt nitrate, the zinc salt is zinc sulfate, and the imidazole compound is 2-methylimidazole; the concentration ratio of the cobalt salt, zinc salt, and imidazole compound is 1:1:(2-5).

[0016] Preferably, the mass ratio of the dual ZIF precursor to the nitrogen source is (5-6):1; the nitrogen source is melamine.

[0017] Preferably, the zinc metal-air battery is prepared as follows: Co@NC nanotubes are ultrasonically dispersed with conductive carbon material, 5wt% Nafion solution, and anhydrous ethanol, and then drop-coated onto hydrophilic carbon paper (the loading of the positive electrode catalyst on the hydrophilic carbon paper is 1 mg cm⁻¹). -2 The zinc metal air battery is assembled by using 6M KOH aqueous solution as the electrolyte and zinc plate as the negative electrode, with the air as the positive electrode.

[0018] Preferably, the preparation method of the magnesium metal-air battery is as follows: Co@NC nanotubes are ultrasonically dispersed with conductive carbon material, 5wt% Nafion solution, and anhydrous ethanol, and then drop-coated onto hydrophilic carbon paper (the loading amount of the positive electrode catalyst on the hydrophilic carbon paper is 1 mg cm⁻¹). -2 The air electrode is used as the positive electrode of the magnesium metal air battery, with 10wt% KCl aqueous solution as the electrolyte and AZ31B magnesium alloy as the negative electrode, and the battery is assembled into a magnesium metal air battery.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The Co@NC nanotubes described in this invention achieve a synergistic effect of high active site density and efficient catalytic pathway. Through the synergistic pyrolysis of a dual ZIF precursor and melamine, a single-metal Co@nitrogen-doped carbon nanotube structure with high carbon content (86.48 atomic%) and high nitrogen content (4.79 atomic%) is formed. The high nitrogen content provides abundant anchoring sites for Co, forming a large number of Co-NC active sites, which are key catalytic centers for the oxygen reduction reaction (ORR). These sites can efficiently adsorb and activate oxygen molecules, promote the four-electron reaction pathway (transfer of 3.72-3.95 electrons, close to the theoretical value), and significantly improve the ORR kinetic rate.

[0021] 2. The Co@NC nanotubes described in this invention possess a porous structure, which facilitates ORR charge transfer. The zinc-containing ZIF-8 in the precursor is reduced to low-boiling-point metallic Zn and volatilizes at high temperatures, endowing the catalyst with abundant porous characteristics. This porous structure not only increases the exposed area of ​​active sites but also provides unobstructed channels for the diffusion of electrolyte ions and oxygen, reducing mass transfer resistance and ensuring the continuous and efficient catalytic reaction, thereby improving the discharge performance of the metal-air battery.

[0022] 3. The staged pyrolysis process of this invention (pretreatment at 300-400℃ followed by carbonization at 750-850℃) and the addition of melamine promote the orderly growth of carbon nanotubes, and the single metal Co is stably anchored on the nitrogen-doped carbon nanotube matrix. Carbon nanotubes have excellent electronic conductivity, which can accelerate charge transfer in catalytic reactions; at the same time, the encapsulation effect of the nitrogen-doped carbon matrix on Co inhibits the aggregation and dissolution of metal particles, enhances the long-term stability of the catalyst, and enables the battery to maintain its performance during cycling or continuous discharge.

[0023] 4. In the Co@NC nanotubes described in this invention, the 3d orbitals of cobalt are not completely filled, making them prone to electron gain and loss. The synergistic effect with nitrogen-doped carbon can modulate its electronic structure and optimize the adsorption energy for oxygen. The pure monometallic Co sites in this invention avoid the difficulty in controlling the electronic structure in bimetallic systems, making the catalytic activity of the Co-NC sites easier to control, ultimately achieving superior ORR performance with a half-wave potential (0.85V) exceeding that of commercially available 20% Pt / C nanotubes.

[0024] 5. This invention enables the application of oxygen reduction catalysts in primary zinc-air batteries, primary magnesium-air batteries, and secondary zinc-air batteries. The oxygen reduction catalyst is characterized as a single-metal catalyst, exhibiting high energy and power densities in metal batteries. The prepared single-metal catalyst Co@NC-1 has a half-wave potential of 0.85 V, exceeding that of commercially available 20% Pt / C; the limiting diffusion current density J... d 5.44 mA cm -2 This is comparable to commercially available 20% Pt / C. The power density of a primary zinc-air battery using Co@NC-1 as the oxygen reduction catalyst is 202 mW / cm². -2 The maximum energy density is 928Wh / kg. -1 Zn This catalyst surpasses Pt / C-based zinc metal-air batteries in its performance. The raw materials are readily available, the preparation is simple, and the cost is low, making it a potential commercial application. The preparation method of the Co@NC nanotubes described in this invention is simple to implement, highly efficient, and easy to control, making it suitable for industrial-scale mass production. Attached Figure Description

[0025] Figure 1 The image shows the XRD pattern of Co@NC-1 prepared in Example 1.

[0026] Figure 2 This is a scanning electron microscope image of Co@NC-1 prepared in Example 1.

[0027] Figure 3 The cyclic voltammetry (CV) curve of Co@NC-1 prepared in Example 1 is shown.

[0028] Figure 4 Linear sweep voltammetry (LSV) curves of Co@NC-1 prepared in Example 1 and Co@NC-2, Co@NC-3 and Co@NC-4 prepared in the comparative examples.

[0029] Figure 5 The open-circuit voltage curve of the zinc metal-air battery assembled with Co@NC-1 prepared in Example 1 is shown.

[0030] Figure 6 The discharge polarization curves and power density curves of the zinc metal-air battery assembled with Co@NC-1 prepared in Example 1 are shown.

[0031] Figure 7 The zinc metal-air battery assembled with Co@NC-1 prepared in Example 1 was tested at 10 mA / cm². -2 Comparison of discharge curves at different current densities.

[0032] Figure 8 The open-circuit voltage is the magnesium metal-air battery assembled with Co@NC-1 prepared in Example 1.

[0033] Figure 9 The discharge polarization curve and power density curve of the magnesium metal-air battery assembled with Co@NC-1 prepared in Example 1 are shown.

[0034] Figure 10 The open-circuit voltage curve of the magnesium metal-air battery assembled with Co@NC-1 prepared in Example 1 is shown.

[0035] Figure 11 The discharge polarization curves and power density curves of the magnesium metal-air battery assembled with Co@NC-1 prepared in Example 1 are shown. Detailed Implementation

[0036] The technical solutions of the present invention will be clearly and completely described in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the present invention are within the scope of protection of the present invention.

[0037] Unless otherwise specified in the specific circumstances, the numerical ranges listed herein include upper and lower limits, as well as all integers and fractions within that range, but are not limited to the specific values ​​listed when the range is defined.

[0038] I. Application of a high-C and N content monometallic Co@NC nanotube

[0039] The Co@NC nanotubes described in this invention are used as catalysts in zinc or magnesium metal-air batteries, particularly as ORR catalysts.

[0040] This invention reveals that while metal-air batteries represent an important direction for green electrochemical energy, the slow kinetics of the oxygen reduction reaction at the cathode severely hinder their large-scale commercialization. High-performance noble metal catalytic materials are expensive and limited in reserves, significantly restricting the industrialization of air batteries. Although non-noble metal@nitrogen-doped carbon-based materials are potential alternatives, these materials, prepared through high-temperature pyrolysis of metal-organic frameworks (MOFs), have limitations. For example, ZIF-8-derived carbon-based catalysts exhibit poor conductivity and limited mesopores, while ZIF-67-derived carbon-based catalysts have low nitrogen content, all of which affect catalytic performance improvement. Therefore, this invention considers improving the cathode catalytic material. Initially, a dual-ZIF substrate was considered, but actual research revealed that zinc only serves as a temporary component in the precursor, volatilizing as a low-boiling-point metal during high-temperature pyrolysis (750-850℃), ultimately forming a pure monometallic Co-anchored nitrogen-doped carbon nanotube structure. This design not only avoids electronic interference between the two metals, making the Co active sites purer, but also makes it easier to regulate their electronic state through the nitrogen-doped carbon matrix. Simultaneously, the co-precipitation method was used to prepare a dual ZIF precursor (ZIF-8@ZIF-67), which is beneficial for forming a bimetallic organic framework with an ordered crystal structure. This precursor retains its three-dimensional porous structure after pyrolysis. Combined with melamine as an additional nitrogen source, it significantly increases the exposed area of ​​active sites, ensuring the prepared material maintains a three-dimensional porous structure and high surface area. Furthermore, this invention involves a staged pyrolysis process: first, calcination at 300℃-400℃ for 1-2 hours for low-temperature pretreatment to remove impurities and perform preliminary shaping; then, heating to 750℃-850℃ and holding for 2-4 hours for high-temperature carbonization, which promotes the ordered growth of carbon nanotubes. This process not only avoids structural damage caused by high temperature alone but also, with the high nitrogen supplementation from melamine, results in a final material with a carbon content of 86.48 atomic% and a nitrogen content of 4.79 atomic%, providing abundant anchoring sites for Co. Ultimately, the Co@NC nanotubes prepared in this invention exhibit a half-wave potential of 0.85 V, exceeding that of commercially available 20% Pt / C catalysts, and a limiting diffusion current density of 5.44 mA / cm². -2It is comparable to commercially available 20% Pt / C; the power density of a primary zinc-air battery using it as an oxygen reduction catalyst is 202 mW / cm². -2 The maximum energy density is 928Wh / kg. -1 Zn content is higher than that of Pt / C-based zinc-air batteries; the assembled magnesium-air battery has an open-circuit voltage of 1.82V and a power density of 62mW / cm³. -2 Furthermore, the catalyst is readily available, simple to prepare, and inexpensive, making it a potential commercial application.

[0041] In some embodiments of the present invention, the Co@NC nanotubes are used in the positive electrode catalyst layer.

[0042] In some embodiments of the present invention, the positive electrode catalyst layer includes Co@NC nanotubes, conductive carbon material, Nafion solution, anhydrous ethanol, hydrophilic carbon paper, and an air diffusion layer.

[0043] In some embodiments of the present invention, the conductive carbon material is Super P, the mass ratio of the conductive carbon material to Co@NC nanotubes is 1:1, and the concentration of the Nafion solution is 5 wt%.

[0044] In some embodiments of the present invention, the Co@NC nanotubes are obtained by the following method:

[0045] A dual ZIF precursor containing Zn and Co was mixed with a nitrogen source and calcined at 300℃-400℃ for 1-2 hours under an inert atmosphere, followed by calcination at 750℃-850℃ for another 2-4 hours to obtain the Co@NC nanotubes.

[0046] In some embodiments of the present invention, the dual ZIF precursor is obtained by the following method:

[0047] Cobalt salt, zinc salt, and imidazole compound were dissolved in methanol to obtain corresponding solutions A, B, and C. Solutions A, B, and C were mixed at room temperature and aged for 8-16 hours. The solids were collected and purified to obtain a bis-ZIF precursor containing Zn and Co.

[0048] In some embodiments of the present invention, the cobalt salt is cobalt nitrate, the zinc salt is zinc sulfate, and the imidazole compound is 2-methylimidazole; the concentration ratio of the cobalt salt, zinc salt, and imidazole compound is 1:1:(2-5).

[0049] In some embodiments of the present invention, the mass ratio of the dual ZIF precursor to the nitrogen source is (5-6):1; the nitrogen source is melamine.

[0050] In some embodiments of the present invention, the zinc metal-air battery is prepared as follows: Co@NC nanotubes and conductive carbon material, 5wt% Nafion solution, and anhydrous ethanol are ultrasonically dispersed evenly, and then drop-coated onto hydrophilic carbon paper (the loading amount of the positive electrode catalyst material on the hydrophilic carbon paper is 1 mg cm⁻¹). -2 The zinc metal air battery is assembled by using 6M KOH aqueous solution as the electrolyte and zinc plate as the negative electrode, with the air as the positive electrode.

[0051] In some embodiments of the present invention, the preparation method of the magnesium metal-air battery is as follows: Co@NC nanotubes and conductive carbon material, 5wt% Nafion solution, and anhydrous ethanol are ultrasonically dispersed evenly, and then drop-coated onto hydrophilic carbon paper (the loading amount of the positive electrode catalyst material on the hydrophilic carbon paper is 1 mg cm⁻¹). -2 The air electrode is used as the positive electrode of the magnesium metal air battery, with 10wt% KCl aqueous solution as the electrolyte and AZ31B magnesium alloy as the negative electrode, and the battery is assembled into a magnesium metal air battery.

[0052] II. Examples and Comparative Examples

[0053] Example 1:

[0054] (1) Weigh 15 mmol of cobalt nitrate hexahydrate and dissolve it in 60 mL of methanol, naming it solution A; weigh 15 mmol of zinc sulfate heptahydrate and dissolve it in 60 mL of methanol, naming it solution B; weigh 60 mmol of 2-methylimidazole and dissolve it in 120 mL of methanol, naming it solution C; pour solution A into solution C and stir to form a homogeneous mixture; then pour solution B into the above mixture and stir for 30 min. Aged the solution at room temperature for 12 h, centrifuged the solution, washed 3 times with methanol, and dried the obtained product overnight in a vacuum oven at 60 °C to obtain a light purple product, which is the bis-ZIF precursor.

[0055] (2) Melamine and precursor in a mass ratio of 1:5 were ground and mixed evenly in a mortar, placed in a crucible, and placed in a tube furnace with Ar flowing through it. The mixture was kept at 350°C for 1 hour, and then heated to 800°C for 2 hours to obtain a single metal cobalt-doped nitrogen carbon nanotube oxygen reduction catalyst, named Co@NC-1.

[0056] Comparative Example 1

[0057] The catalyst was modified from Example 1, except that zinc sulfate heptahydrate was not added in step (1). The other steps were exactly the same as in Example 1, and the catalyst prepared was Co@NC-2.

[0058] Comparative Example 2

[0059] The catalyst was modified from Example 1, except that melamine was not added in step (2). The other steps were exactly the same as in Example 1, and the catalyst prepared was Co@NC-3.

[0060] Comparative Example 3

[0061] The catalyst was modified from Example 1, except that zinc sulfate heptahydrate was not added in step (1) and melamine was not added in step (2). The other steps were exactly the same as in Example 1, and the catalyst prepared was Co@NC-4.

[0062] III. Performance Comparison

[0063] 1. Microscopic characterization

[0064] XRD tests were performed on the Co@NC prepared in Example 1 and the comparative example, and the results are as follows: Figure 1 As shown. Simultaneously, the Co@NC prepared in Example 1 was subjected to electron microscopy scanning, and the results are as follows. Figure 2 As shown, the metal particles are anchored on the carbon nanotubes.

[0065] 2. Electrochemical performance testing

[0066] The Co@NC series catalysts prepared in Example 1 and the comparative example were used as cathode catalysts for metal-air batteries. 1 mg of the metal-air battery cathode catalyst and 1 mg of Super P were weighed using an electronic analytical balance and ultrasonically dispersed in a mixed solution of 20 μL of 5 wt% Nafion solution, 20 μL of isopropanol, and 160 μL of anhydrous ethanol. The mixture was ultrasonically dissolved for 30 min to form a uniform catalyst ink. 19 μL of the catalyst ink was then pipetted in portions and evenly drop-coated onto a pre-polished glassy carbon electrode (with platinum rings), ensuring the suspension evenly covered the entire electrode. The electrode was then allowed to dry naturally at room temperature, yielding a loading of 0.384 mg / cm³. -2 Catalyst thin film electrode.

[0067] The oxygen reduction electrochemical performance of the catalyst was tested using a CHI760E electrochemical workstation in a three-electrode system. The working electrode was a rotating ring-disc electrode with the catalyst supported, the reference electrode was a Hg / HgO electrode, the counter electrode was a carbon rod, and the electrolyte was a 0.1 mol / L KOH solution. The potential was calibrated to the reversible hydrogen electrode potential (RHE) according to the Nernst equation (ERHE = EHg / HgO + 0.0591 × pH + 0.098). Before testing, high-purity O2 was introduced into the electrolytic cell to obtain a gas-saturated electrolyte. During the test, high-purity O2 was continuously introduced at an appropriate flow rate to maintain O2 saturation in the electrolyte. The electrode was first activated by multi-turn CV scans at a scan rate of 10 mV / s. -1The scanning voltage range is 0-1.2V, and the results are as follows. Figure 3 As shown, the LSV polarization curve was then tested at 1600 rpm with a scan rate of 10 mV / s. -1 The scanning voltage range is 0-1.2V, and the results are as follows: Figure 4 As shown. From Figure 3 As can be seen from the curve, within the 0-1.2V vs RHE potential range, Co@NC-1 catalyzes the redox reaction of oxygen, exhibiting a significant current response (j change), proving that Co@NC-1 can drive the electrochemical processes of oxygen adsorption, reduction, and desorption, and possesses oxygen electrocatalytic activity. The "quasi-closed ring" shape of the curve reflects the reversibility of this catalytic reaction, indicating that the redox process can be cyclical, and also reflects that Co@NC-1, as a catalyst, can continuously participate in the oxygen electrochemical reaction within this potential range. Figure 4 It can be seen that, Figure 4 The curves exhibit typical oxygen reduction kinetics. In the low potential range (~0-0.8V vs RHE), the current density (j) is stable and close to a plateau, corresponding to the initial adsorption-reduction phase of oxygen molecules on the catalyst surface. During this phase, the reaction is kinetically controlled, and the catalyst activity determines the reaction rate. In the high potential range (~0.8-1.2V vs RHE), the current density rises rapidly, corresponding to the diffusion-reaction synergistic phase of the oxygen reduction reaction. Driven by the potential, both oxygen diffusion and catalytic reduction rates increase. Furthermore, the starting point of the rapid rise in the curve (initial potential) and the potential at which the current reaches half its peak value (half-wave potential) reflect the activity level of the catalyst. Figure 4 Compared to the comparative example, Example 1 exhibits the lowest onset potential and the most positive half-wave potential (close to the ideal value of 1.0V vs RHE), indicating a favorable thermodynamic trend for oxygen reduction catalyzed by Co@NC-1 and facilitating the reaction. The current density in the high-potential region approaches its limiting value, reflecting the maximum reaction rate of oxygen reduction (limited by oxygen diffusion in the electrolyte). Higher values ​​indicate that the catalyst can utilize oxygen molecules more efficiently at high potentials, corresponding to the battery's performance during high-current discharge.

[0068] 3. Zinc metal air battery

[0069] Weigh 1 mg of Co@NC-1 powder and 1 mg of Super P powder, and ultrasonically disperse them in a mixture of 10 μL of 5 wt% Nafion solution and 190 μL of ethanol. Sonicate for 30 min to form a homogeneous catalyst ink. Distribute the catalyst ink evenly onto a 2.1 cm² plate using a pipette. 2 On hydrophilic carbon paper, 1mg cm -2 The loading capacity was determined. A zinc metal air battery was assembled by combining hydrophilic carbon paper with a supported catalyst and an air permeable layer as the positive electrode, using a zinc plate as the negative electrode and 6M KOH as the electrolyte.

[0070] Using 10mV s -1 The scanning rate was used to record the polarization curve of the battery on an electrochemical workstation (high-purity O2 was continuously introduced at an appropriate flow rate throughout the test to keep the electrolyte saturated with gaseous O2), and then the discharge curve of the battery was tested on a Xinwei battery tester.

[0071] from Figure 5 It can be seen that during the 1000-second test, the zinc metal-air battery assembled with single metal Co@NC-1 as the positive electrode catalyst material can maintain an open-circuit voltage of about 1.6V, which exceeds that of the Pt / C-based primary zinc-air battery (1.52V). This indicates that the battery has a stable initial voltage output capability during the test period, reflecting that when Co@NC-1 is used as the positive electrode catalyst, the potential difference between the positive and negative electrodes of the battery can be maintained stably without significant decay, and the battery system has thermodynamic stability.

[0072] from Figure 6 It can be seen that as the current density increases, the battery voltage continuously decreases, exhibiting polarization. The higher the current, the more significant the voltage loss caused by the battery's internal resistance (ohmic resistance, polarization resistance). The flat section of the curve (low current density region) reflects the battery's thermodynamic stability. Higher voltage indicates better initial activity of Co@NC-1 in catalyzing oxygen reduction; a smaller curve slope indicates a stronger ability of the catalyst to suppress polarization, and a more obvious kinetic advantage of Co@NC-1 driving oxygen reduction. The power density first increases and then decreases with current density, exhibiting a single-peak characteristic. When the current is low, the voltage drop is slow, and the power density increases with increasing current; when the current is too high, the voltage drops rapidly, and the power density decreases because voltage loss > current gain. Peak power density (~1.4V voltage, ~250mA·cm) in the figure. -2 The value corresponding to the current is a key indicator of the maximum output capacity of this zinc-air battery. The optimal catalyst Co@NC-1 based primary zinc-air battery exhibits a 202 mW / cm² output. -2 The maximum power density, and exceeded the maximum power density of the assembled Pt / C-based zinc-air battery (168 mW / cm²). -2 The higher the value, the stronger the power output of the battery under Co@NC-1 catalysis, which is far superior to that of ordinary catalysts. This indicates that Co@NC-1, as a positive electrode catalyst, allows zinc-air batteries to have both stable discharge and high power output capabilities, achieving a performance level suitable for practical application.

[0073] from Figure 7 It can be seen that at 10mA·cm -2 Under constant current density, the battery voltage remains at a high plateau for a long time, except at the end of the discharge phase (specific capacity ~800mAh·g). -1The rapid drop indicates that Co@NC-1 exhibits strong kinetics in catalyzing oxygen reduction, stably driving the reaction during continuous discharge, suppressing polarization (ohmic polarization and concentration polarization), and ensuring stable voltage output. Zinc-air batteries possess long-cycle stable discharge capability, making Co@NC-1 suitable for practical applications of zinc-air batteries (such as portable devices requiring continuous power). The specific capacity at the end of discharge is approximately 800 mAh·g. -1 This value reflects the amount of electricity released per unit mass of zinc electrode; a higher value indicates higher zinc utilization and longer battery life. The energy density, calculated from the voltage plateau and specific capacity, is 928 Wh·kg⁻¹. -1 (n) (Energy density = voltage × specific capacity), this value is much higher than that of ordinary zinc-air batteries (typically ~500-800Wh·kg). -1 (n) It is also higher than Pt / C-based ZAB (885Wh kg). -1 Zn This further confirms its practical application potential. It demonstrates that under Co@NC-1 catalysis, the battery energy conversion efficiency is extremely high, and the chemical energy of zinc can be converted into electrical energy more efficiently.

[0074] 4. Magnesium metal air battery

[0075] Weigh 1 mg of Co@NC-1 powder and 1 mg of Super P powder, and ultrasonically disperse them in a mixture of 10 μL of 5 wt% Nafion solution and 190 μL of ethanol. Sonicate for 30 min to form a homogeneous catalyst ink. Distribute the catalyst ink evenly onto a 2.1 cm² plate using a pipette. 2 On hydrophilic carbon paper, 1mg cm -2 The loading amount. A magnesium metal air battery was assembled by using a composite of hydrophilic carbon paper with a supported catalyst and an air permeable layer as the positive electrode, polished AZ31B magnesium alloy as the negative electrode, and 10wt% KCl as the electrolyte.

[0076] from Figure 8 As can be seen, Co@NC-1 exhibits excellent thermodynamic stability as a positive electrode catalyst, stably establishing the potential difference between the positive and negative electrodes of a magnesium-air battery. It demonstrates excellent initial thermodynamic trend in catalyzing the oxygen reduction reaction, with an open-circuit voltage close to the theoretical voltage of a magnesium-air battery within the reasonable range of ~3.0V. The catalyst shows good compatibility with the battery; the magnesium-air battery system (magnesium negative electrode + Co@NC-1 positive electrode + electrolyte) exhibits no significant side reactions or interface failures. Co@NC-1 can maintain its catalytic activity over a long period, ensuring the battery's basic electrochemical performance. The open-circuit voltage is fundamental to the battery's usable voltage; a stable high-voltage platform (~1.8V) meets the starting voltage requirements of practical applications. Figure 8 The initial electrochemical stability of the Co@NC-1 catalytic magnesium-air battery was verified, which is a key foundation for the practical application of the battery.

[0077] from Figure 9 As can be seen, Co@NC-1 solves the problems of slow oxygen reduction kinetics and severe polarization in magnesium-air batteries, achieving a high voltage platform and high power output. Magnesium-air batteries catalyzed by Co@NC-1 have both low polarization discharge capability and high power output potential, making them suitable for various practical applications of magnesium-air batteries, such as portable batteries.

[0078] from Figure 10 As can be seen, compared with the Pt / C assembled primary magnesium metal-air battery, the Co@NC-1 assembled primary magnesium metal-air battery exhibits a more stable open-circuit voltage, while the Pt / C assembled primary magnesium metal-air battery shows a significant decreasing trend in open-circuit voltage over time. This indicates that Co@NC-1, as a catalyst, performs better in maintaining open-circuit voltage stability in primary magnesium metal-air batteries, possessing excellent performance as a catalyst for this type of battery and the potential to replace Pt / C in magnesium metal-air batteries to improve battery voltage stability.

[0079] analyze Figure 11 As can be seen from the discharge polarization curve (voltage on the left vertical axis), the voltage stability of the Co@NC-1 assembled primary magnesium-air battery is comparable to that of the Pt / C primary magnesium-air battery as the current density increases, indicating that the polarization of the Co@NC-1 assembled primary magnesium-air battery is relatively small at high current densities. From the power density curve (power density on the right vertical axis), the maximum power density of the Co@NC-1 assembled primary magnesium-air battery can reach 62 mW cm⁻¹. -2 The maximum power density is comparable to that of a primary magnesium-air battery assembled with Pt / C, indicating that Co@NC-1, as a catalyst, can give primary magnesium-air batteries an advantage and has the potential to replace Pt / C in improving the power performance of magnesium-air batteries.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. An application of a high-C and N content monometallic Co@NC nanotube, characterized in that, The Co@NC nanotubes are used as catalysts for positive electrode materials in zinc or magnesium metal-air batteries.

2. The application according to claim 1, characterized in that, The Co@NC nanotubes are used in the positive electrode catalyst layer.

3. The application according to claim 2, characterized in that, The positive electrode catalyst layer includes Co@NC nanotubes, conductive carbon materials, Nafion solution, anhydrous ethanol, hydrophilic carbon paper, and an air diffusion layer.

4. The application according to claim 1, characterized in that, The Co@NC nanotubes were obtained by the following method: A dual ZIF precursor containing Zn and Co was mixed with a nitrogen source and calcined at 300℃-400℃ for 1-2 hours under an inert atmosphere, followed by calcination at 750℃-850℃ for another 2-4 hours to obtain the Co@NC nanotubes.

5. The application according to claim 4, characterized in that, The dual ZIF precursor was obtained through the following method: Cobalt salt, zinc salt, and imidazole compound were dissolved in methanol to obtain corresponding solutions A, B, and C. Solutions A, B, and C were mixed at room temperature and aged for 8-16 hours. The solids were collected and purified to obtain a bis-ZIF precursor containing Zn and Co.

6. The application according to claim 5, characterized in that, The cobalt salt is cobalt nitrate, the zinc salt is zinc sulfate, and the imidazole compound is 2-methylimidazole; the concentration ratio of cobalt salt, zinc salt, and imidazole compound is 1:1:(2-5).

7. The application according to claim 4, characterized in that, The mass ratio of the dual ZIF precursor to the nitrogen source is (5-6):1; the nitrogen source is melamine.

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