Carbon-based difunctional oxygen-electricity composite material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of electrochemical energy conversion, in particular to a carbon-based difunctional oxygen-electricity composite material and a preparation method and application thereof. By controlling the components of the MnO2-Vo nanorods and constructing the interlaced three-dimensional conductive network, the carbon-based difunctional oxygen electrocatalytic composite material is endowed with excellent difunctional oxygen electrocatalytic activity. On one hand, MnO2-Vo nanorods are utilized, trivalent manganese species and oxygen vacancies are enriched on the surfaces of the MnO2-Vo nanorods, on the other hand, MWCNTs are introduced, and the MnO2-Vo nanorods and the MWCNTs are interwoven, wound and mechanically interlocked to form a three-dimensional conductive network, so that rapid electron transfer is ensured, a stable conductive frame is constructed, and the conductivity of the MnO2-Vo nanorods and the MWCNTs is improved. The carbon-based bifunctional oxygen-electricity composite material provided by the invention shows excellent bifunctional catalytic activity, namely excellent ORR and OER catalytic activity, and the performance of the carbon-based bifunctional oxygen-electricity composite material is equivalent to or superior to that of commercial Pt / C, RuO2 and other catalysts.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy conversion technology, and in particular to a carbon-based bifunctional oxygen-electric composite material (denoted as MnO2-Vo / MWCNTs) and its preparation method and application. Background Technology

[0002] Regenerative fuel cells and rechargeable metal-air batteries have attracted much attention as important electrochemical energy conversion and storage devices (EECSDs). To reduce the cost of EECSDs, researchers have used transition metal oxides as catalytic materials. Among them, manganese dioxide (MnO2) has advantages such as abundant reserves and low cost. However, its low electrical conductivity limits its catalytic activity. The slow charge transfer rate during electrocatalysis hinders the timely replenishment and transfer of electrons, making it impossible for MnO2 to effectively demonstrate its catalytic activity.

[0003] Later, researchers enhanced the catalytic activity of MnO2 by combining it with multi-walled carbon nanotubes (MWCNTs), which possess excellent electrical conductivity, large specific surface area, and better chemical stability. However, these materials are mainly used for the electrocatalysis of the oxygen reduction reaction (ORR) or the oxygen evolution reaction (OER), tending to support reactions in one direction and rarely achieving bifunctional oxygen electrocatalysis simultaneously. Therefore, developing a catalytic material with excellent bifunctional oxygen electrocatalytic activity is of significant practical importance. Summary of the Invention

[0004] In view of this, the present invention provides a carbon-based bifunctional oxygen electrochemical composite material, its preparation method and application, and the carbon-based bifunctional oxygen electrochemical composite material provided by the present invention has excellent bifunctional oxygen electrochemical catalytic activity.

[0005] This invention provides a carbon-based bifunctional oxygen-electric composite material, comprising MnO2-Vo nanorods and multi-walled carbon nanotubes; the MnO2 in the MnO2-Vo nanorods is α-MnO2; the multi-walled carbon nanotubes and MnO2-Vo nanorods are intertwined and mechanically interlocked to form a three-dimensional conductive network; the MnO2-Vo nanorods have K-type nanotubes inserted into them. + The 2×2 tunnel structure; the surface of the MnO2-Vo nanorods contains oxygen vacancies and Mn Ⅲ Species; the carbon-based bifunctional oxygen-electric composite material contains a porous structure.

[0006] Preferably, the average diameter of the MnO2-Vo nanorods is 20~20.5 nm; the content of surface oxygen vacancies of the MnO2-Vo nanorods is 40~41%, and the content of MnO2-Vo nanorods is 40~41%. Ⅲ The species content is 44-45%.

[0007] Preferably, the average outer diameter of the multi-walled carbon nanotubes is 12.5~13 nm.

[0008] Preferably, the pore size of the pore structure is 2~160nm.

[0009] This invention also provides a method for preparing the carbon-based bifunctional oxygen-electric composite material described above, comprising the following steps: (1) Multi-walled carbon nanotubes and acid solution are mixed and oxidized to obtain pretreated multi-walled carbon nanotubes; (2) 1-Butyl-3-methylimidazolium tetrafluoroborate (C8H 15 MnO2 nanorods were obtained by mixing N2BF4, manganese sulfate (MnSO4), potassium persulfate (K2S2O8) and water and carrying out a redox reaction. (3) The MnO2 nanorods were mixed with sodium borohydride (NaBH4) and water to carry out a reduction reaction to obtain MnO2-Vo nanorods; (4) The pretreated multi-walled carbon nanotubes are mixed with MnO2-Vo nanorods and water for self-assembly to obtain the carbon-based bifunctional oxygen-electric composite material. There is no requirement for the time order of steps (1) and (2) to (3).

[0010] Preferably, the C8H 15 The volume ratio of N2BF4 to water is 1:95~105; the molar ratio of MnSO4 to K2S2O8 is 1~1.1:1~1.1; the molar ratio of MnSO4 to water is (0.32~0.35) mol:1L.

[0011] Preferably, the mass ratio of the MnO2 nanorods to the molar amount of NaBH4 is 435g:(0.25~1)mol; and the molar amount of NaBH4 to the volume ratio of water is (0.005~0.02)mol:1L.

[0012] Preferably, the mass ratio of the MnO2-Vo nanorods to the multi-walled carbon nanotubes is 1:1.5~9.

[0013] The present invention also provides the application of the carbon-based bifunctional oxygen-electric composite material described in the above-described scheme or the carbon-based bifunctional oxygen-electric composite material obtained by the preparation method described in the above-described scheme in the field of electrochemical energy conversion or storage.

[0014] The present invention also provides a rechargeable zinc-air battery, including an air cathode, wherein the air cathode comprises the carbon-based bifunctional oxygen-electric composite material described in the above-described scheme or the carbon-based bifunctional oxygen-electric composite material obtained by the preparation method described in the above-described scheme.

[0015] This invention provides a carbon-based bifunctional oxygen electrocatalytic composite material. By controlling the composition of MnO2-Vo nanorods and constructing an interwoven three-dimensional conductive network, this invention endows the carbon-based bifunctional oxygen electrocatalytic composite material with excellent bifunctional oxygen electrocatalytic activity. This invention utilizes MnO2-Vo nanorods and enriches their surface with trivalent manganese (MnO2-Vo). Ⅲ On the one hand, it introduces MnO2-Vo species and oxygen vacancies (Vo). On the other hand, it introduces MWCNTs, intertwining and mechanically interlocking MnO2-Vo nanorods with MWCNTs to form a three-dimensional conductive network. This not only ensures rapid electron transfer but also constructs a stable conductive framework, enabling the carbon-based bifunctional oxygen-electric composite material provided by this invention to exhibit excellent bifunctional catalytic activity, namely excellent ORR and OER catalytic activity. Its oxygen reduction reaction half-wave potential (E) is high. 1 / 2 The voltage is 0.79 V, and the oxygen evolution reaction occurs at 10 mA / cm². 2 The potential at the current density is 1.62V, and the bifunctional potential difference ( ΔE OER-ORR That is, the half-wave potential of the oxygen reduction reaction and the oxygen evolution reaction are at 10 mA / cm 2 The potential difference at current density is as low as 0.83V, with performance comparable to or better than commercial catalysts such as Pt / C and RuO2.

[0016] This invention also provides a method for preparing the carbon-based bifunctional oxygen-electric composite material described above. This invention synthesizes MnO2-Vo nanorods via a hydrothermal method and enriches their surface with Mn by sodium borohydride treatment. Ⅲ Species and Vo. Subsequently, MnO2-Vo nanorods are interwoven with MWCNTs to construct a conductive framework. The preparation method provided by this invention is simple, convenient, low-cost, uses inexpensive and readily available raw materials, and is easy to achieve, showing promise for large-scale industrial production.

[0017] This invention also provides the application of the carbon-based bifunctional oxygen-electrochemical composite material described in the above-described scheme or the carbon-based bifunctional oxygen-electrochemical composite material prepared by the above-described scheme in the field of electrochemical energy conversion or storage. The carbon-based bifunctional oxygen-electrochemical composite material provided by this invention can serve as a highly efficient non-precious metal bifunctional oxygen-electrochemical catalyst for use in the field of electrochemical energy conversion or storage, such as rechargeable zinc-air batteries and other EECSDs, with significant cost-effectiveness.

[0018] This invention also provides a rechargeable zinc-air battery (ZAB). Utilizing the carbon-based bifunctional oxygen-electric composite material described above as the air cathode, this invention successfully assembled a rechargeable zinc-air battery. This battery exhibits a high open-circuit voltage, considerable power density, and excellent charge-discharge cycle stability; for example, the open-circuit voltage of the rechargeable zinc-air battery is 1.48V, and the power density is 71.17 mW / cm³. 2After 100 cycles, the voltage difference was only 0.77V, which is comparable to that of commercial Pt / C+RuO2-based zinc-air batteries (open-circuit voltage 1.39V, power density 74.84mW / cm³). 2 Its performance is comparable to that of a voltage difference of 0.87V. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in this 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 some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 The diagram shows the synthesis of carbon-based bifunctional oxygen-electric composite material and the XRD patterns of MnO2 nanorods, MnO2-Vo nanorods, and carbon-based bifunctional oxygen-electric composite material; where a is the synthesis of carbon-based bifunctional oxygen-electric composite material and b is the XRD pattern of MnO2 nanorods, MnO2-Vo nanorods, and carbon-based bifunctional oxygen-electric composite material. Figure 2 XPS test results for MnO2 nanorods and carbon-based bifunctional oxygen-electric composites are shown below. Specifically, a represents the full XPS spectrum of the carbon-based bifunctional oxygen-electric composite; b represents the high-resolution XPS spectrum of C 1s of the carbon-based bifunctional oxygen-electric composite; c represents the high-resolution XPS spectrum of K 2p of the MnO2 nanorods; d represents the high-resolution XPS spectrum of Mn 2p of the MnO2 nanorods; e represents the high-resolution XPS spectrum of Mn 2p of the carbon-based bifunctional oxygen-electric composite; f represents the high-resolution XPS spectrum of Mn 3s of the MnO2 nanorods; g represents the high-resolution XPS spectrum of Mn 3s of the carbon-based bifunctional oxygen-electric composite; h represents the high-resolution XPS spectrum of O 1s of the MnO2 nanorods; and i represents the high-resolution XPS spectrum of O 1s of the carbon-based bifunctional oxygen-electric composite. Figure 3 The figures show the electron paramagnetic resonance (EPR) spectra of MnO2 nanorods and MnO2-Vo nanorods, as well as the N2 adsorption-desorption isotherms and pore size distribution of the MnO2 nanorods and carbon-based bifunctional oxygen-electric composite material; where a is the EPR spectrum of MnO2 nanorods and MnO2-Vo nanorods; and b is the N2 adsorption-desorption isotherm and pore size distribution of the MnO2 nanorods and carbon-based bifunctional oxygen-electric composite material (inset). Figure 4The image shows the SEM, HRTEM, and SEM-EDS elemental analysis results of MnO2-Vo nanorods and carbon-based bifunctional oxygen-electric composites. Image a is the SEM image of MnO2-Vo nanorods; image b is the SEM image of the carbon-based bifunctional oxygen-electric composite; images c-d are the HRTEM images of MnO2-Vo nanorods; images e-f are the HRTEM images of the carbon-based bifunctional oxygen-electric composite; and image g is the SEM-EDS elemental mapping of the carbon-based bifunctional oxygen-electric composite. Figure 5 Electrocatalytic ORR / OER performance tests were performed on MnO2 nanorods, MnO2-Vo nanorods, MWCNTs, carbon-based bifunctional oxygen-electric composites, 20wt% Pt / C, and RuO2. Specifically, a) shows the LSV curves of the samples recorded at 1600 rpm and a scan rate of 10 mV / s in O2-saturated 0.1 M KOH solution; b) shows the Tafel slopes of the samples; c) shows the KL curves of the carbon-based bifunctional oxygen-electric composites at different potentials (the inset shows the electron transfer number n); and d) shows the ORR / OER performance of the samples from MnO2 nanorods, MnO2-Vo nanorods, MWCNTs, carbon-based bifunctional oxygen-electric composites, and 20wt% Pt / C and RuO2. The it curves of Pt / C in O2-saturated 0.1M KOH solution at 0.60V (vs. RHE) and 800rpm are shown in the following figures: e represents the it curves of MnO2 nanorods, MnO2-Vo nanorods, MWCNTs, carbon-based bifunctional oxygen-electric composites, and 20wt% Pt / C in O2-saturated 0.1M KOH solution at 0.60V (vs. RHE) and 800rpm, used to evaluate the ORR tolerance to methanol permeation by it test, with 1.0M and 3.0M methanol added to the electrolyte; f represents the OERLSV curves of the samples recorded at a scan rate of 10mV / s in O2-saturated 0.1M KOH solution; g represents the it curves of MWCNTs and carbon-based bifunctional oxygen-electric composites at 10mA / cm². 2 The Et curves of OER were measured under constant current density; h represents the ΔE values ​​for MWCNTs, carbon-based bifunctional oxygen-electric composites, 20wt% Pt / C, and RuO2. OER-ORR i is a comparison of the bifunctional activities of carbon-based bifunctional oxygen-electric composite materials with those of reported manganese-based and carbon-based catalysts. Figure 6The results show the activity enhancement of MnO2-Vo nanorods, MWCNTs, carbon-based bifunctional oxygen-electric composites, and 20wt% Pt / C. In this figure, a) is the Nyquist plot of the electrochemical impedance spectroscopy (EIS) of MnO2-Vo nanorods, MWCNTs, and the carbon-based bifunctional oxygen-electric composite, with tests conducted in an O2-saturated 0.1M KOH solution; b) is the C value estimated by plotting the current density change. dl ; Figure 7 The ORR / OER catalytic mechanism of carbon-based bifunctional oxygen-electric composite materials; Figure 8 Images show the stability test results of MnO2-Vo nanorods and carbon-based bifunctional oxygen-electric composites; where a is the TEM image of MnO2-Vo nanorods before stability testing; b~c are the TEM images of MnO2-Vo nanorods after stability testing; d~f are the HRTEM images of MnO2-Vo nanorods after stability testing; g is the TEM image of the carbon-based bifunctional oxygen-electric composite before stability testing; h is the TEM image of the carbon-based bifunctional oxygen-electric composite after stability testing; and i is the HRTEM image of the carbon-based bifunctional oxygen-electric composite after stability testing. Figure 9 The diagram shows the structural schematic and test results of the ZAB battery; where a is the structural schematic of the ZAB battery; b is the open-circuit potential of the ZAB battery based on Pt / C+RuO2 and carbon-based bifunctional oxygen-electric composite material; c is the charge-discharge polarization curve and corresponding power density curve of the ZAB battery based on Pt / C+RuO2 and carbon-based bifunctional oxygen-electric composite material; d is the discharge curve of the ZAB battery based on carbon-based bifunctional oxygen-electric composite material at different current densities; and e is the charge-discharge performance of the ZAB battery based on Pt / C+RuO2 and carbon-based bifunctional oxygen-electric composite material. Figure 10 XRD patterns of MWCNTs; Figure 11 A schematic diagram of MnO2-Vo nanorods; Figure 12 SEM images and diameter distributions of MnO2-Vo nanorods and carbon-based bifunctional oxygen-electric composites are shown (statistical analysis was performed using Nano Measurer software). Specifically, a is an SEM image of MnO2-Vo nanorods; b is an SEM image of MnO2-Vo nanorods; c is an SEM image of the carbon-based bifunctional oxygen-electric composite; d is an SEM image of the carbon-based bifunctional oxygen-electric composite; e is the statistical diameter distribution of MnO2-Vo nanorods (239 measured from a and b) obtained based on SEM characterization; f is the statistical diameter distribution of MWCNTs (174 measured from c and d) obtained based on SEM characterization. Figure 13 EDS plot of a selected area for scanning electron microscopy and the weight percentage of elements; Figure 14 ORR LSV curves of carbon-based bifunctional oxygen-electric composites synthesized at different temperatures were recorded in an O2-saturated 0.1M KOH solution at a rotation speed of 1600 rpm and a scan rate of 10 mV / s. Figure 15 ORR LSV curves of carbon-based bifunctional oxygen-electric composites with different oxygen vacancy concentrations were recorded in an O2-saturated 0.1M KOH solution at a rotation speed of 1600 rpm and a scan rate of 10 mV / s. Figure 16 ORR LSV curves of carbon-based bifunctional oxygen-electric composites with different ratios of MnO2-Vo nanorods and MWCNTs were recorded in an O2-saturated 0.1M KOH solution at a rotation speed of 1600 rpm and a scan rate of 10 mV / s. Figure 17 The results of 30 CV pre-scans at a scan rate of 50 mV / s were obtained in an O2-saturated 0.1 M KOH solution before testing for MnO2 nanorods, MnO2-Vo nanorods, MWCNTs, and carbon-based bifunctional oxygen-electric composites. Among them, a represents MnO2 nanorods, b represents MnO2-Vo nanorods, c represents MWCNTs, and d represents carbon-based bifunctional oxygen-electric composites. Figure 18 The CV curves of MnO2 nanorods, MnO2-Vo nanorods, MWCNTs and carbon-based bifunctional oxygen-electric composites were measured at a scan rate of 50 mV / s in an O2-saturated 0.1 M KOH solution. Figure 19 The ORR LSV curves and corresponding uncorrected and background-corrected Tafel plots of the carbon-based bifunctional oxygen-electric composite material were recorded in a 0.1M KOH solution at a rotation speed of 1600 rpm, showing the background (in N2 saturated electrolyte), uncorrected (in O2 saturated electrolyte), and background-corrected values. Specifically, a represents the ORR LSV curves of the carbon-based bifunctional oxygen-electric composite material in a 0.1M KOH solution at a rotation speed of 1600 rpm, showing the background (in N2 saturated electrolyte), uncorrected (in O2 saturated electrolyte), and background-corrected values; b represents the corresponding uncorrected and background-corrected Tafel plots. Figure 20ORR LSV curves of MWCNTs, carbon-based bifunctional oxygen-electric composite material, and 20wt% Pt / C catalyst were measured in O2-saturated 0.1M KOH solution at a scan rate of 10mV / s and different rotation speeds (400, 625, 900, 1225, 1600, and 2025 rpm); where a represents MWCNTs, b represents carbon-based bifunctional oxygen-electric composite material, and c represents 20wt% Pt / C catalyst. Figure 21 KL curves for MWCNTs and 20wt% Pt / C at potentials of 0.2–0.5 V (insets show electron transfer number (n)); where a represents MWCNTs; b represents 20wt% Pt / C; Figure 22 To evaluate the methanol tolerance of carbon-based bifunctional oxygen-electric composite materials in an O2-saturated 0.1M KOH solution, the chronoamperometry was used at 0.60V (vs. RHE) and 800rpm. 6.0M and 10.0M methanol were added to the electrolyte, respectively. Figure 23 The carbon-based bifunctional oxygen-electric composite material, MnO2 nanorods, MnO2-Vo nanorods, MWCNTs, 20wt% Pt / C and RuO2 exhibit a current density of 10 mA / cm² in the OER. 2 The potential at 1.70V and the current density at 1.70V; Figure 24 Tafel slopes for carbon-based bifunctional oxygen-electric composites, MnO2 nanorods, MnO2-Vo nanorods, MWCNTs, 20wt% Pt / C and RuO2OER; Figure 25 The CV curves for MWCNTs, carbon-based bifunctional oxygen-electric composites, and 20wt% Pt / C are recorded at different scan rates (20, 40, 60, 80, 100, and 120 mV / s) within a non-Radius potential window of 1.20–1.30 V (vs. RHE) in O2-saturated 0.1 M KOH solution. Where a represents MWCNTs, b represents carbon-based bifunctional oxygen-electric composites, and c represents 20wt% Pt / C. Figure 26 HRTEM images (a~f) of MnO2-Vo nanorods after stability testing; Figure 27 HRTEM images (a~d) of the carbon-based bifunctional oxygen-electric composite material after stability testing. Detailed Implementation

[0021] This invention provides a carbon-based bifunctional oxygen-electric composite material, comprising MnO2-Vo nanorods and multi-walled carbon nanotubes; the MnO2 in the MnO2-Vo nanorods is α-MnO2; the multi-walled carbon nanotubes and MnO2-Vo nanorods are intertwined and mechanically interlocked to form a three-dimensional conductive network; the MnO2-Vo nanorods have K-type nanotubes inserted into them. + The 2×2 tunnel structure; the surface of the MnO2-Vo nanorods contains oxygen vacancies and Mn Ⅲ Species; the carbon-based bifunctional oxygen-electric composite material contains a porous structure.

[0022] In this invention, the average diameter of the MnO2-Vo nanorods is preferably 20~20.5 nm, more preferably 20.22 nm.

[0023] In this invention, the surface oxygen vacancy content of the MnO2-Vo nanorods is preferably 40-41%, more preferably 40.9%, and Mn Ⅲ The content of species is preferably 44-45%, more preferably 44.7%.

[0024] In this invention, the average outer diameter of the multi-walled carbon nanotubes is preferably 12.5~13 nm, more preferably 12.77 nm.

[0025] In this invention, the pore size of the pore structure is preferably 2~160nm, more preferably 2~80nm.

[0026] The carbon-based bifunctional oxygen-electric composite material provided by this invention has abundant Vo (active sites) and Mn on the surface of MnO2-Vo nanorods compared to MnO2. Ⅲ The species facilitate O2 reduction; the highly conductive MnO2-Vo nanorod entanglements promote efficient charge transport; and the unique nanorod / nanotube porous structure of the carbon-based bifunctional oxygen-electric composite material is beneficial for diffusion mass transfer as a mass transfer channel. The interaction between MnO2-Vo nanorods and MWCNTs is mainly attributed to physical entanglement and mechanical interlocking, resulting from the unique nanorod-nanotube morphology and oxygen-containing functional groups on the MWCNT surface, which improves dispersibility and enhances interfacial contact. In electrocatalysis, this highly interconnected conductive network is crucial for efficient electron transfer and structural stability.

[0027] This invention also provides a method for preparing the carbon-based bifunctional oxygen-electric composite material described above, comprising the following steps: (1) Multi-walled carbon nanotubes and acid solution are mixed and oxidized to obtain pretreated multi-walled carbon nanotubes; (2) C8H 15N2BF4, MnSO4, K2S2O8 and water were mixed and subjected to a redox reaction to obtain MnO2 nanorods; (3) The MnO2 nanorods were mixed with NaBH4 and water to carry out a reduction reaction to obtain MnO2-Vo nanorods; (4) The pretreated multi-walled carbon nanotubes are mixed with MnO2-Vo nanorods and water for self-assembly to obtain the carbon-based bifunctional oxygen-electric composite material. There is no requirement for the time order of steps (1) and (2) to (3).

[0028] This invention involves mixing multi-walled carbon nanotubes with an acid solution and subjecting them to an oxidation reaction to obtain pretreated multi-walled carbon nanotubes. In this invention, the acid solution is preferably nitric acid (HNO3) and sulfuric acid (H2SO4); the mass fraction of the nitric acid is preferably 65-68%, more preferably 66-67%; the mass fraction of the sulfuric acid is preferably 95-98%, more preferably 96-97%; and the volume ratio of the nitric acid to the sulfuric acid is preferably 1-1.2:1-1.2, more preferably 1:1.

[0029] In this invention, the ratio of the mass of the multi-walled carbon nanotubes to the volume of the acid solution is preferably 100 mg: (48~52) mL, more preferably 100 mg: 50 mL.

[0030] In this invention, the temperature of the oxidation reaction is preferably 24-26 degrees Celsius, more preferably 25 degrees Celsius, and the holding time is preferably 8-12 hours, more preferably 10 hours; the oxidation reaction is preferably carried out under the conditions of water bath and stirring.

[0031] In this invention, the oxidation reaction preferably further includes sequentially subjecting the obtained product to a first post-treatment and a first drying; the first post-treatment preferably includes sequentially performing a first solid-liquid separation and a first washing of the obtained solid; the first post-treatment is preferably performed 3 times or more, more preferably 3 to 5 times; the first solid-liquid separation is preferably filtration; the pore size of the qualitative filter paper used for filtration is preferably 10 to 15 micrometers; the first washing is preferably water washing; the water used for water washing is preferably deionized water (DI); the first washing is preferably performed with the pH value of the filtrate reaching 6.5 to 7.5; the temperature of the first drying is preferably 60 degrees Celsius, and the holding time is preferably 8 to 12 hours, more preferably 10 hours.

[0032] Through the above steps, the present invention oxidizes and purifies MWCNTs, removing heavy metals from MWCNTs on the one hand, and generating oxygen-containing functional groups on the surface of MWCNTs on the other hand, laying the foundation for the subsequent formation of oxygen vacancies.

[0033] This invention uses C8H 15N₂BF₄, MnSO₄, K₂S₂O₈, and water are mixed (denoted as the first mixture) and subjected to a redox reaction to obtain MnO₂ nanorods. In this invention, the C₈H₂O₄... 15 The preferred volume ratio of N2BF4 to water is 1:95~105, more preferably 1:100.

[0034] In this invention, the molar ratio of MnSO4 to K2S2O8 is preferably 1~1.1:1~1.1, more preferably 1:1.

[0035] In this invention, the preferred ratio of the amount of MnSO4 to the volume of water is (0.32~0.35) mol:1L, more preferably 0.34 mol:1L.

[0036] In this invention, the temperature of the first mixing is preferably room temperature (20-30 degrees Celsius); the method of the first mixing preferably includes the following steps: mixing C8H 15 N2BF4 was added dropwise to an aqueous solution containing MnSO4 and K2S2O8.

[0037] In this invention, the temperature of the redox reaction is preferably 150-210 degrees Celsius, more preferably 170-190 degrees Celsius, and even more preferably 180 degrees Celsius; the holding time is preferably 3.5-4.5 hours, more preferably 4 hours; and the equipment for the redox reaction is preferably a high-pressure autoclave reactor lined with polytetrafluoroethylene.

[0038] In this invention, the redox reaction preferably further includes cooling the reaction system and then sequentially subjecting the reaction product to a second post-treatment and a second drying. The second post-treatment preferably includes sequentially performing a second solid-liquid separation and a second washing of the resulting solid. The cooling is preferably natural cooling; the final cooling temperature is preferably room temperature (20-30 degrees Celsius); the second post-treatment is preferably performed at least three times, more preferably three to five times; the second solid-liquid separation is preferably filtration; the pore size of the qualitative filter paper used for filtration is preferably 10-15 micrometers; the second washing preferably includes sequentially performing water washing and alcohol washing; the water used for water washing is preferably deionized water; the amount of water used in a single water washing is preferably 5 liters; the alcohol used for alcohol washing is preferably anhydrous ethanol; the amount of alcohol used in a single alcohol washing is preferably 0.5 liters; the temperature of the second drying is preferably 60 degrees Celsius, and the holding time is preferably 24 hours. This invention effectively removes residual ions and impurities through the second post-treatment.

[0039] The present invention synthesizes MnO2 nanorods using the above steps, which have better activity and introduce Mn. III Species.

[0040] After obtaining MnO2 nanorods, this invention involves mixing the MnO2 nanorods with NaBH4 and water to undergo a reduction reaction, yielding MnO2-Vo nanorods. In this invention, the preferred mass ratio of the MnO2 nanorods to the molar amount of NaBH4 is 435 g: (0.25~1) mol, more preferably 435 g: 0.5 mol. By controlling the amount of NaBH4 added, this invention obtains MnO2-Vo nanorods with different oxygen vacancy contents.

[0041] In this invention, the preferred ratio of the amount of NaBH4 to the volume of water is (0.005~0.02) mol:1L, more preferably 0.01 mol:1L.

[0042] In this invention, the temperature of the reduction reaction is preferably room temperature (20~30 degrees Celsius), and the time of the reduction reaction is preferably 4.5~5.5 hours, more preferably 5 hours; the reduction reaction is preferably carried out under stirring conditions.

[0043] In this invention, the reduction reaction preferably further includes a third post-treatment and a third drying of the obtained product; the third post-treatment preferably includes a third solid-liquid separation and a third washing of the obtained solid; the third post-treatment is preferably performed 3 times or more, more preferably 3 to 5 times; the third solid-liquid separation is preferably filtration; the pore size of the qualitative filter paper used for filtration is preferably 10 to 15 micrometers; the third washing preferably includes a water wash and an alcohol wash; the water used for the water wash is preferably deionized water; the amount of water used in a single water wash is preferably 5 liters; the alcohol used for the alcohol wash is preferably anhydrous ethanol; the amount of alcohol used in a single alcohol wash is preferably 0.5 liters; the temperature of the third drying is preferably 60 degrees Celsius, and the holding time is preferably 8 to 12 hours, more preferably 10 hours. This invention effectively removes residual ions and impurities through the third washing.

[0044] After obtaining pretreated multi-walled carbon nanotubes and MnO2-Vo nanorods, the present invention performs self-assembly by mixing the pretreated multi-walled carbon nanotubes with MnO2-Vo nanorods and water (denoted as the second mixture) to obtain the carbon-based bifunctional oxygen-electric composite material. In the present invention, the second mixture preferably includes the following steps: premixing MnO2-Vo nanorods and water to obtain a premixed liquid, and then mixing the pretreated multi-walled carbon nanotubes and the premixed liquid (denoted as mixture A).

[0045] In this invention, the water is preferably deionized water; the premixing is preferably stirred; and the premixing time is preferably 4 hours.

[0046] In this invention, the concentration of MnO2-Vo nanorods in the premixed solution is preferably 190~210 mg / L, more preferably 200 mg / L.

[0047] In this invention, the mass ratio of the MnO2-Vo nanorods to the multi-walled carbon nanotubes is preferably 1:1.5 to 9, and more preferably 1:4.

[0048] In this invention, the mixture A is preferably ultrasound; the power of the ultrasound is preferably 500~600W; and the duration of the ultrasound is preferably 4 hours.

[0049] In this invention, the self-assembly temperature is preferably room temperature (20~30 degrees Celsius), and the heat preservation time is preferably 46~50 hours, more preferably 48 hours; the self-assembly is preferably carried out under alternating stirring and sonication conditions; the time for each stirring or sonication is preferably 2 hours.

[0050] In this invention, the self-assembly process preferably further includes a fourth post-treatment and a fourth drying of the obtained product; the fourth post-treatment preferably includes a fourth solid-liquid separation and a fourth washing of the obtained solid; the fourth post-treatment is preferably performed at least three times, more preferably three to five times; the fourth solid-liquid separation is preferably filtration; the pore size of the qualitative filter paper used for filtration is preferably 10 to 15 micrometers, more preferably 13 micrometers; the fourth washing preferably includes a water wash and an alcohol wash; the water used for the water wash is preferably deionized water; the water volume for a single water wash is preferably 5 liters; the alcohol used for the alcohol wash is preferably anhydrous ethanol; the amount of alcohol used for the alcohol wash is preferably 0.5 liters; the temperature for the fourth drying is preferably 60 degrees Celsius, and the holding time is preferably 24 hours. Through the above post-treatment, this invention effectively removes residual ions and impurities.

[0051] The present invention also provides the application of the carbon-based bifunctional oxygen-electric composite material described in the above-described scheme or the carbon-based bifunctional oxygen-electric composite material obtained by the preparation method described in the above-described scheme in the field of electrochemical energy conversion or storage.

[0052] The carbon-based bifunctional oxygen electrochemical composite material provided by this invention can serve as a highly efficient non-precious metal bifunctional oxygen electrochemical catalyst for use in electrochemical energy conversion or storage fields, such as rechargeable zinc-air batteries and other EECSDs, with significant cost-effectiveness.

[0053] The present invention also provides a rechargeable zinc-air battery, including an air cathode, wherein the air cathode comprises the carbon-based bifunctional oxygen-electric composite material described in the above-described scheme or the carbon-based bifunctional oxygen-electric composite material obtained by the preparation method described in the above-described scheme.

[0054] To further illustrate the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] In a specific embodiment of the present invention, manganese sulfate monohydrate (MnSO4) H2O (99%) was purchased from Macklin; MWCNTs (99%) were purchased from Chengdu Organic Chemical Co., Ltd.; K2S2O8 (≥99.5%), NaBH4 (98%), HNO3 (65.0~68.0 wt%), H2SO4 (95.0~98.0 wt%), potassium hydroxide (KOH, 95%) and zinc acetate (ZnAc2, ≥99.0%) were purchased from Sinopharm Chemical Reagent Co., Ltd.; Nafion (5 wt%), 1-butylPt / C (20 wt%) and RuO2 (≥99.9%) were purchased from Suzhou Xinno Technology Co., Ltd.; the water was deionized water.

[0056] Example This embodiment prepared a carbon-based bifunctional oxygen-electric composite material. The main synthesis route and morphology are as follows: Figure 1 As shown in 'a', the specific steps are as follows: (1) Pretreatment of MWCNTs: 100 mg of MWCNTs were dispersed in a round-bottom flask containing 25 mL of HNO3 and 25 mL of H2SO4. The round-bottom flask was then continuously stirred in a water bath at 25 °C for 10 hours. After the reaction was completed, the collected mixture was filtered through qualitative filter paper (pore size 10-15 μm), washed with deionized water until the pH of the filtrate was 6.5-7.5, and then dried in an oven at 60 °C for 10 hours to obtain pretreated MWCNTs.

[0057] (2) Synthesis of MnO2 nanorods: First, C8H2O2 nanorods were synthesized at room temperature. 15 0.75 mL of N2BF4 was added dropwise to 75 mL of a mixed aqueous solution containing 0.34 M MnSO4 and 0.34 M K2S2O8. The resulting aqueous solution was then transferred to a polytetrafluoroethylene-lined autoclave and reacted at 180 °C for 4 hours. After natural cooling to room temperature, the product was washed sequentially with qualitative filter paper (10–15 μm pore size), 5 L of deionized water, and 0.5 L of anhydrous ethanol. This washing process was repeated five times. The product was then dried in an oven at 60 °C for 24 hours to obtain MnO2 nanorods (denoted as MnO2-180 °C nanorods).

[0058] Keeping all other conditions constant, only changing the reaction temperature to 210 degrees Celsius and 150 degrees Celsius, MnO2-210℃ nanorods and MnO2-150℃ nanorods were obtained, respectively.

[0059] (3) Synthesis of MnO2-Vo nanorods: 435 mg of the prepared MnO2 nanorods were accurately weighed and uniformly dispersed in 50 mL of NaBH4 (0.01 M) aqueous solution. The mixture was continuously stirred at room temperature for 5 hours for reduction reaction. After the reaction was completed, the product was collected by filtration through qualitative filter paper (pore size 10-15 μm). The product was then washed with deionized water (5 L) and anhydrous ethanol (0.5 L), and the filtration and washing were repeated 3 times. The washed product was dried in an oven at 60 °C for 10 hours to obtain MnO2-Vo nanorods.

[0060] Keeping all other conditions constant, only changing the concentration of NaBH4 to 0.005M and 0.02M, MnO2-Vo nanorods were obtained, denoted as MnO2-Vo. l Nanorods and MnO2-Vo h Nanorods.

[0061] (4) Synthesis of carbon-based bifunctional oxygen-electric composite material: First, 20 mg of prepared MnO2-Vo nanorod powder was dispersed in 100 mL of deionized water and stirred continuously for 4 hours. Second, 80 mg of pretreated MWCNTs were uniformly dispersed in the aqueous solution of MnO2-Vo and subjected to ultrasonic treatment at 550 W for 4 hours to obtain a mixed solution. Then, the above mixed solution was treated with alternating stirring (2 hours each time) and ultrasonic treatment (2 hours each time) at room temperature for 48 hours. After self-assembly, the product was filtered and washed with qualitative filter paper (pore size 10~15 μm), deionized water (5 L), and anhydrous ethanol (0.5 L), and the filtration and washing were repeated 3 times. Then, it was placed in an oven and dried at 60 °C for 24 hours to obtain carbon-based bifunctional oxygen-electric composite material, denoted as 20 wt% MnO2-Vo / MWCNTs.

[0062] Keeping all other conditions constant, only changing the mass ratio of MnO2-Vo nanorods to MWCNTs to 1:9 and 1:1.5 respectively, carbon-based bifunctional oxygen-electric composite materials were obtained, denoted as 10wt% MnO2-Vo / MWCNTs and 40wt% MnO2-Vo / MWCNTs respectively.

[0063] Test case 1. Material characteristics: Phase analysis of the samples was performed using an X-ray diffractometer (XRD, D8 Advance, Bruker) equipped with Cu Kα radiation (λ=1.5406). The X-ray diffractometer was operated at 40 kV and 40 mA, with data collected in the 2θ range of 5°–90° in steps of 0.0245° and a counting time of 0.192 seconds per step. Scanning electron microscopy (SEM) imaging was performed using a Zeiss Gemini 360 field emission microscope with accelerating voltages ranging from 0.02 kV to 30 kV. Energy-dispersive X-ray spectroscopy (EDS) analysis was performed using an Oxford UltimMax 40 detector connected to the SEM at an accelerating voltage of 10.0 kV. Elemental plots were obtained at an elevation angle of 32.5° with a real-time acquisition time of 157.3 seconds to ensure reliable elemental identification and distribution analysis. High-resolution transmission electron microscopy (HRTEM) was performed using a Thermo Fisher Scientific Talos F200x instrument operating at an accelerating voltage of 200 kV. For sample preparation, the powdered sample was first ultrasonically dispersed in ethanol for 60 minutes to obtain a well-dispersed suspension. Subsequently, a drop of the suspension was placed on a copper grid covered with an ultrathin carbon film and allowed to dry. The surface chemical composition of the samples was analyzed by X-ray photoelectron spectroscopy (XPS) using a Thermo Scientific ESCALAB Xi+ spectrometer employing a monochromatic Al X-ray source (E = 1486.68 eV). The X-ray source operated at a voltage of 15242.60 V and an emission current of 14.9 mA. All measurements were performed at a baseline pressure below 10 kV. -9The analysis was conducted under ultra-high vacuum conditions at mBar. Spectroscopy was performed using survey scans with a 5.04 eV analyzer work function and a 500 μm X-ray spot size, with the pass energy set to 100 eV, while high-resolution regional spectral collections used a pass energy set to 20 eV. The binding energy was calibrated by referencing an accidental carbon C 1s peak at 284.8 eV. Electron paramagnetic resonance (EPR) spectroscopy was performed on a Bruker MS 5000 spectrometer. N₂ adsorption-desorption isotherms of the samples were analyzed at 77.3 K using a BeiShiDe-PS2-1588 analyzer. Prior to analysis, the samples were degassed under vacuum at 150 °C for 5 h. The Brunauer-Emmett-Teller (BET) method was applied to the adsorption data to determine the specific surface area within a relative pressure (P / P₀) range of 0.04–0.32, while the pore size distribution was obtained from the desorption branch using the Barrett-Joyner-Halenda (BJH) model. Elemental compositional analysis of the samples was performed using an Agilent 5110 inductively coupled plasma optical emission spectrometer (ICP-OES) equipped with a VistaChip II CCD detector. 18.0 mg of sample was collected for acid digestion and then diluted to a final volume of 25.0 mL. Subsequently, optimized instrument parameters were used (RF power: 1150.0 W, plasma current: 12.0 L / min, auxiliary flow rate: 0.7 L / min, nebulizer flow rate: 0.5 L / min).

[0064] II. Electrochemical Measurement: First, 2.5 mg of the sample was dispersed in a solvent mixture of 340 μL ethanol, 150 μL deionized water, and 10 μL Nafion, and then sonicated for 60 minutes to form a uniform ink. Before each test, the surface of the working electrode was thoroughly polished and cleaned. Specifically, an aqueous slurry of alumina powder with progressively smaller particle sizes (1.0 μm, 0.3 μm, and 0.05 μm) was used to polish the glassy carbon working electrode on a velvet pad until a mirror finish was achieved, followed by thorough rinsing with deionized water. Next, 10 μL of the above ink was taken and applied to the glassy carbon disk (4 mm in diameter, corresponding to 0.1256 cm⁻¹) of the working electrode. 2 The geometric surface area and 0.40 mg / cm² 2The catalyst was supported on a rotating disk electrode (RDE) for measurements. The RDE shaft was made of high-purity graphite. The counter electrode (Pt mesh) was placed in the same compartment as the working electrode, without a separator. All potentials were then calibrated to the reversible hydrogen electrode (RHE) scale using the equation (E(vs.RHE)=E(vs.Hg / HgO)+0.098+0.059pH). Prior to measurement, the electrolyte (0.1M KOH) was saturated with high-purity O2 for at least 30 minutes, and 30 cyclic voltammetry (CV) pre-scans were performed to activate the electrode and remove surface impurities. ORR activity was evaluated using linear sweep voltammetry (LSV) at a scan rate of 10 mV / s and a rotation rate of 1600 rpm, while OER LSV measurements were performed under static conditions at a scan rate of 10 mV / s. Chorometric (it) tests for ORR stability were performed for 10 hours at 0.60 V (relative to RHE) and 800 rpm. OER stability was measured using the chronopotential method (Et) at 10 mA / cm. 2 Evaluation was conducted at a constant current density. Methanol tolerance was tested by adding methanol during ORRit measurements. Electrochemical impedance spectroscopy (EIS) measurements were performed using a CHI 760e electrochemical workstation at a constant potential of 0.80 V (relative to RHE) with an AC perturbation amplitude of 5 mV. The double-layer capacitance (C0) was determined from CV scans at different rates (20–120 mV / s) within a non-Radichtal potential window of 1.20–1.30 V (relative to RHE). dl Finally, unless otherwise stated, electrochemical measurements were performed using a CS 300M electrochemical workstation and a three-electrode system.

[0065] Specific requirements: ORR / OER testing should be performed at room temperature using a CS300M electrochemical workstation, employing a standard three-electrode system. Specifically, a Pt mesh should be used as the counter electrode, Hg / HgO (1M KOH) as the reference electrode, and a glassy carbon electrode (rotating disk electrode (RDE), 5 mm in diameter, 0.196 cm²) should be used. 2 The working electrode is [electrode name missing]. Unless otherwise specified, all ORR / OER tests are performed in O2-saturated KOH aqueous solution (0.1M). The following equation is used for calibration relative to the reversible hydrogen electrode potential (the standard electrode potential of the Hg / HgO electrode in alkaline solution is 0.098 V): ; Throughout the testing process, high-purity oxygen was continuously introduced to ensure sufficient oxygen supply. O2 was introduced into the electrolyte for at least 30 minutes before each test. The electrocatalytic activity of OER and ORR was determined using a PINE rotating disk electrode apparatus. The glassy carbon electrode was polished to a mirror finish and thoroughly cleaned before use. Then, to remove surface impurities and activate the electrode, 30 pre-CV scans were performed before testing. CV curves were measured at a scan rate of 50 mV / s. LSV curves were measured at a rotation speed of 1600 rpm and a scan rate of 10 mV / s. Simultaneously, LSV curves were recorded under the same testing conditions in a nitrogen-saturated 0.1 M KOH electrolyte to subtract background current. Impedance testing was performed using a CHI 760E electrochemical workstation at a potential of 0.80 V (vs. RHE), with a frequency range of 100 kHz to 0.1 Hz and an AC perturbation amplitude of 5 mV. A surface area of ​​approximately 0.1256 cm² was used. 2 A glassy carbon electrode was used to ensure uniform catalyst loading. The electric double-layer capacitance was determined by varying the scan rate within a non-Radidatic potential window (1.20–1.30 V (vs. RHE)). The ORR stability of the samples was evaluated by chronoamperometry for 10 hours in an O2-saturated 0.1 M KOH electrolyte at 800 rpm and 0.6 V (vs. RHE). OER stability testing was performed using chronopotentiometry, with the potential range set at 1.4–2.5 V (vs. RHE) and the current density maintained at 10 mA / cm². 2 During the chronoamperometry test, methanol of different concentrations (0.1M, 3.0M, 6.0M, and 10.0M) was added to the electrolyte to conduct a methanol tolerance test.

[0066] The ORR electron transfer number (n) at different electrode potentials was calculated using the Koutecky-Levich (KL) equation: ; Where i is the measured current density, i K and i L Here, n represents the kinetic current density and the limiting current density, respectively; n is the number of transferred electrons; F is the Faraday constant (F = 96485 C / cm); k is the electron transfer rate constant; and C0 is the bulk concentration of O2 (C0 = 1.2 × 10⁻⁶ C / cm²). -3 (mol / L), D0 is the diffusion coefficient of O2 in 0.1M KOH solution (D0 = 1.9 × 10⁻⁶ mol / L). -5 cm / s), v is the kinematic viscosity of the electrolyte (0.01 cm). 2 / s), where ω is the electrode rotation speed.

[0067] III. Assembly and Testing of ZAB Batteries: The assembly process of the ZAB battery is as follows: The anode consists of a 0.6 mm thick zinc plate. The cathode consists of a composite electrode (carbon paper, waterproof and breathable membrane, and nickel foam) comprising the carbon-based bifunctional oxygen-electric composite material prepared in the embodiments of this invention, with a thickness of 0.5 cm. 2 Limited working area and 3mg / cm 2 The catalyst was supported. The electrolyte consisted of a mixed aqueous solution containing 6.0 M KOH and 0.2 M ZnAc2. All electrochemical measurements were performed without an external oxygen supply. For comparison, a mixed air cathode was fabricated using Pt / C and RuO2 at a mass ratio of 1:1. In this invention, all electrochemical performance tests of the ZAB battery were performed using a CS 300M electrochemical workstation.

[0068] IV. Test Results: 1) Characterization results of carbon-based bifunctional oxygen-electric composite materials: Figure 1 The diagram shows the synthesis process of the carbon-based bifunctional oxygen-electric composite material and the XRD patterns of MnO2 nanorods, MnO2-Vo nanorods, and the carbon-based bifunctional oxygen-electric composite material. In the diagram, a is a schematic diagram of the synthesis process of the carbon-based bifunctional oxygen-electric composite material, and b is the XRD pattern of MnO2 nanorods, MnO2-Vo nanorods, and the carbon-based bifunctional oxygen-electric composite material.

[0069] according to Figure 1 As can be seen from 'a' in this invention, MnO2 nanorods were first prepared via a redox reaction. Subsequently, MnO2-Vo nanorods with a surface rich in Vo were obtained by reduction with NaBH4. Then, the MnO2-Vo nanorods and MWCNTs were subjected to repeated sonication and stirring to obtain an intertwined carbon-based bifunctional oxygen-electric composite material.

[0070] according to Figure 1 As can be seen from b, MnO2 nanorods, MnO2-Vo nanorods, and carbon-based bifunctional oxygen-electric composites all exhibit a series of diffraction peaks at 12.8°, 18.1°, 28.8°, 37.5°, and 49.9°, which correspond to the (110), (200), (310), (211), and (411) crystal planes of α-MnO2 (JCPDS No. 44-0141), respectively. This observation indicates that manganese dioxide in the above samples exists in the form of α-MnO2. In addition to the MnO2 diffraction peaks observed in the carbon-based bifunctional oxygen-electric composites, diffraction peaks corresponding to the (002) and (101) crystal planes of carbon (JCPDS No. 41-1487) were observed at 25.7° and 43.1°, respectively. These peaks are consistent with the characteristic peaks of MWCNTs (e.g., ...). Figure 10As shown in the figure, the successful synthesis of carbon-based bifunctional oxygen-electric composite material was confirmed.

[0071] Figure 2 XPS test results for MnO2 nanorods and carbon-based bifunctional oxygen-electric composites are shown below. Specifically, a represents the full XPS spectrum of the carbon-based bifunctional oxygen-electric composite; b represents the high-resolution XPS spectrum of C 1s of the carbon-based bifunctional oxygen-electric composite; c represents the high-resolution XPS spectrum of K 2p of the MnO2 nanorods; d represents the high-resolution XPS spectrum of Mn 2p of the MnO2 nanorods; e represents the high-resolution XPS spectrum of Mn 2p of the carbon-based bifunctional oxygen-electric composite; f represents the high-resolution XPS spectrum of Mn 3s of the MnO2 nanorods; g represents the high-resolution XPS spectrum of Mn 3s of the carbon-based bifunctional oxygen-electric composite; h represents the high-resolution XPS spectrum of O 1s of the MnO2 nanorods; and i represents the high-resolution XPS spectrum of O 1s of the carbon-based bifunctional oxygen-electric composite.

[0072] Table 1. Theoretical and experimental atomic ratios of elements in XPS-based carbon-based bifunctional oxygen-electric composites.

[0073] Note: The theoretical value is based on 20wt% MnO2-V O The overall composition of the nanorods and 80 wt% MWCNTs was calculated, assuming MnO2-V O The stoichiometry of the nanorods is the same as that of MnO2. The difference between the theoretical and experimental values ​​is mainly due to the sensitivity of XPS to the surface and the complex surface morphology of the carbon-based bifunctional oxygen-electric composite material.

[0074] according to Figure 2 The full spectrum of the sample (a) shows that the surface of the carbon-based bifunctional oxygen-electric composite material contains carbon (C) in addition to Mn and O. XPS analysis revealed that the mass ratio of Mn, O, and C in the carbon-based bifunctional oxygen-electric composite material was 8.86:10.62:80.52, values ​​close to the theoretical values ​​calculated based on the composition of 20 wt% MnO2-Vo / MWCNTs and 80 wt% MWCNTs (as shown in Table 1). The lower measured Mn content and higher O content are likely attributed to the surface sensitivity of XPS and the presence of numerous oxygen-containing groups on the sample surface.

[0075] according to Figure 2 b and Figure 2As can be seen from the C1s spectrum, the high-resolution XPS spectra of the carbon-based bifunctional oxygen electrochemical composite clearly show the presence of oxygen-containing functional groups. The three peaks at 291.8 eV, 288.8 eV, and 285.9 eV correspond to O=CO, CO, and C=O, respectively, due to acid oxidation of MWCNTs. These functional groups not only enhance the hydrophilicity and dispersibility of MWCNTs but also play a crucial role in improving the electrocatalytic performance of the carbon-based bifunctional oxygen electrochemical composite. The peak at 284.8 eV is related to CC / C=C, where CC adopts a sp... 2 Hybridization enhances the stability of MWCNTs; on the other hand, the presence of element K can be attributed to the fact that when K₂S₂O₈ is used as a precursor, K… + Ions diffuse into the 2×2 tunnel structure of MnO2-Vo nanorods.

[0076] Table 2 shows the surface percentages of Mn and O elements obtained from XPS spectroscopy.

[0077] according to Figure 2 d and Figure 2 As can be seen from the 'e' value, the two peaks at 642.1 eV and 653.7 eV correspond to Mn2p, respectively. 3 / 2 and Mn 2p 1 / 2 The characteristic peaks of Mn2p were observed; furthermore, the Mn2p spectrum was fitted with four peaks at 640.9 eV, 642.0 eV, 643.2 eV, and 644.5 eV, corresponding to the characteristic peaks of Mn2p. Ⅱ Mn Ⅲ Mn Ⅳ And satellite peaks; through semi-quantitative calculations based on integral area, the surface Mn of carbon-based bifunctional oxygen-electric composites Ⅲ The species content is approximately 44.7%, while the surface Mn content of the MnO2 nanorods is... Ⅲ The species content was approximately 34.7% (as shown in Table 2). These results indicate that a high concentration of Mn exists on the surface of the carbon-based bifunctional oxygen-electric composite material. Ⅲ Species; Mn 3S (ΔE) 3S The bimodal split of ΔE further confirms this; generally, a higher ΔE 3S This indicates that the average oxidation state of Mn is low.

[0078] according to Figure 2 f and Figure 2 As can be seen from g, the ΔE of the carbon-based bifunctional oxygen-electric composite material... 3S (5.01 eV) exceeds the ΔE of MnO2 nanorods. 3S(4.67 eV) indicates that the abundance of low-valence Mn species on the surface of the carbon-based bifunctional oxygen-electric composite material is higher.

[0079] High concentrations of Mn in manganese dioxide Ⅲ Species selection leads to a decrease in the coordination number of manganese, thereby increasing the amount of Vo, which is further confirmed by high-resolution spectra of O. According to Figure 2 h and Figure 2 As can be seen from the i-coefficient, the O 1s spectrum exhibits three distinct peaks at binding energies of 529.6 eV, 531.1 eV, and 533.4 eV, corresponding to lattice oxygen (Lo), oxygen vacancies (Vo), and surface-adsorbed oxygen (So) species, respectively. Based on peak fitting analysis, the Vo content on the surface of the carbon-based bifunctional oxygen-electric composite material is determined to be approximately 40.9%, higher than that of MnO2 nanorods (27.9%, as shown in Table 2). These results indicate that there are more oxygen vacancies on the surface of the carbon-based bifunctional oxygen-electric composite material. This invention further investigates the interaction between MnO2-Vo nanorods and MWCNTs in the carbon-based bifunctional oxygen-electric composite material: high-resolution XPS spectroscopy of C 1s confirms the presence of oxygen-containing functional groups (e.g., CO, C=O, and OC=O) on the surface of the pretreated MWCNTs; however, compared to MnO2 nanorods, no significant binding energy shift was observed in the high-resolution O 1s XPS of the carbon-based bifunctional oxygen-electric composite material, indicating the absence of strong covalent bonds between the two components. Therefore, the interaction between MnO2-Vo nanorods and MWCNTs in carbon-based bifunctional oxygen electrochemical composites is mainly attributed to physical entanglement and mechanical interlocking, resulting from the unique nanorod-nanotube morphology and oxygen-containing functional groups on the MWCNT surface, which improves dispersibility and enhances interfacial contact. This highly interconnected conductive network is crucial for efficient electron transfer and structural stability during electrocatalysis.

[0080] In summary, the schematic diagram of MnO2-Vo nanorods in carbon-based bifunctional oxygen-electric composite materials is shown below. Figure 11 As shown, the 2×2 tunnel is divided by K + Partial insertion, while surface enrichment of Vo and Mn. Ⅲ Species; larger 2×2 tunnels are conducive to O2, OH - The passage of reactants such as H2O helps improve the efficiency of oxygen electrocatalysis; the large amount of Mn present on the surface of MnO2-Vo nanorods... ⅢSpecies and oxygen vacancies can promote O2 adsorption, which is generally considered a key step in ORR; in addition, they are also thought to be associated with enhanced water oxidation activity in OER. It is worth noting that under actual operating conditions, the catalyst surface may undergo reconstruction compared to its original state; however, this particular surface defect engineering is associated with the observed enhanced bifunctional oxygen electrocatalytic activity of MnO2-Vo nanorods.

[0081] Figure 3 The images show the electron paramagnetic resonance (EPR) spectra of MnO2 nanorods and MnO2-Vo nanorods, as well as the N2 adsorption-desorption isotherms and pore size distribution of the MnO2 nanorods and carbon-based bifunctional oxygen-electric composite material. In the image, a represents the EPR spectra of MnO2 nanorods and MnO2-Vo nanorods; b represents the N2 adsorption-desorption isotherms and pore size distribution of the MnO2 nanorods and carbon-based bifunctional oxygen-electric composite material (inset).

[0082] EPR spectroscopy allows for a more in-depth analysis of the surface Vo concentration in a sample. According to... Figure 3 As shown in 'a', compared to MnO2 nanorods, MnO2-Vo nanorods exhibit a stronger EPR signal, indicating a higher concentration of oxygen vacancies on the surface of MnO2-Vo nanorods. This is highly consistent with the X-ray photoelectron spectroscopy (XPS) results. The significant enhancement of the EPR signal can be attributed to the introduction of NaBH4 during the preparation of the carbon-based bifunctional oxygen-electric composite material, which induces the formation of a large number of oxygen vacancies on the surface of MnO2 nanorods. The oxygen vacancies on the surface of MnO2-Vo nanorods can serve as highly active reaction sites. An appropriate concentration of oxygen vacancies can not only enhance the adsorption of O2 molecules on the surface of the carbon-based bifunctional oxygen-electric composite material, thereby promoting the rate-limiting step and accelerating ORR, but also promote the free OH groups in the electrolyte. - The adsorption of ions supports the initial steps of OER.

[0083] according to Figure 3 As shown in Figure b, the specific surface area and pore structure of MnO2 nanorods and carbon-based bifunctional oxygen-electric composites were analyzed using the N2 adsorption-desorption isotherm method. Both exhibited Type IV isotherms with H3 hysteresis loops, indicating that the carbon-based bifunctional oxygen-electric composites should have typical mesoporous and aggregated pore structures. The pore size distribution curves in the inset provide clear evidence for this observation. According to the BJH method, the pore size distribution of the carbon-based bifunctional oxygen-electric composites showed two distinct peaks at approximately 3 nm and 35 nm. In contrast, the pore size distribution curve of MnO2 nanorods showed two relatively broad peaks. Furthermore, the BET specific surface area and BJH average pore size of the MnO2 nanorods were calculated to be 104.6 μm. 2 / g and 24.7nm, while the BET specific surface area and average pore size of the carbon-based bifunctional oxygen-electric composite material are 207.5m² and 24.7nm, respectively. 2 / g and 27.8nm. The above differences mainly stem from the formation of a unique three-dimensional network structure in the carbon-based bifunctional oxygen-electric composite and the NaBH4 treatment. First, the introduction of MWCNTs establishes an effective three-dimensional structural framework in the carbon-based bifunctional oxygen-electric composite, effectively preventing the dense aggregation of MnO2-Vo nanorods. This leads to the formation of a large number of interstitial pores on the order of tens of nanometers, which are formed by the interweaving of MnO2-Vo nanorods and MWCNTs. This microstructure is consistent with the peak pore size distribution observed at 35nm and the increase in average pore size. Furthermore, the introduction of MWCNTs significantly increases the specific surface area of ​​the carbon-based bifunctional oxygen-electric composite. Second, the introduction of a high concentration of oxygen vacancies into the manganese dioxide lattice during the NaBH4 treatment (confirmed by EPR and XPS) simultaneously induces surface etching of the MnO2 nanorods. This process not only generates many small mesopores (corresponding to a sharp 3nm peak) but also establishes a well-defined hierarchical mesopore structure within the carbon-based bifunctional oxygen-electric composite. Conversely, untreated MnO2 nanorods exhibit broad bimodal growth and a low specific surface area. The hierarchical mesoporous structure optimized by NaBH4 treatment plays a crucial role in enhancing the electrocatalytic performance of the bifunctional ORR / OER of the carbon-based bifunctional oxygen-electric composite. On one hand, the small mesopores (~3 nm) ensure sufficient exposure of oxygen vacancy active sites, thereby increasing the local concentration of reactants near these sites. On the other hand, the large mesopores (~35 nm) significantly increase the specific surface area of ​​the carbon-based bifunctional oxygen-electric composite, facilitating efficient electrolyte permeation and enabling rapid diffusion of reactants and products during ORR / OER, thus alleviating diffusion limitations. The synergistic effect between the high-density oxygen vacancies (active sites) and the hierarchical mesoporous structure (mass transfer channels) not only lowers the kinetic energy barrier of the carbon-based bifunctional oxygen-electric composite but also reduces mass transfer resistance, which is essential for promoting multi-step proton-coupled electron transfer processes in ORR and OER.

[0084] Figure 4 The image shows the SEM, HRTEM, and SEM-EDS elemental analysis results of MnO2-Vo nanorods and carbon-based bifunctional oxygen-electric composites. Image a is the SEM image of MnO2-Vo nanorods; image b is the SEM image of the carbon-based bifunctional oxygen-electric composite; images c-d are the HRTEM images of MnO2-Vo nanorods; images e-f are the HRTEM images of the carbon-based bifunctional oxygen-electric composite; and image g is the SEM-EDS elemental mapping of the carbon-based bifunctional oxygen-electric composite.

[0085] according to Figure 4 As can be seen from 'a', the MnO2-Vo nanorods exhibit a smooth surface. According to...Figure 4 As can be seen from b in the image, the SEM image of the carbon-based bifunctional oxygen-electric composite material clearly shows its composite structure. According to... Figure 12 As can be seen, in the carbon-based bifunctional oxygen-electric composite material, MnO2-Vo nanorods exhibit smooth-surfaced nanorods with an average diameter of approximately 20.22 nm; MWCNTs exhibit multi-walled nanotubes with an average outer diameter of approximately 12.77 nm; the MnO2-Vo nanorods are tightly wrapped by flexible MWCNTs, forming a relatively robust three-dimensional network structure. The intertwined morphology of nanorods and nanotubes can be clearly observed in SEM and TEM images. Obviously, the introduction of this composite structure provides more channels for electron and mass transport, thereby promoting efficient electron transport and enhancing mass transfer and diffusion in electrochemical processes.

[0086] according to Figure 4 c and Figure 4 As can be seen from d, the lattice fringes with interplanar spacing of 0.48 nm and 0.31 nm of MnO2-Vo nanorods are clearly visible, corresponding to the (200) and (310) crystal planes of α-MnO2, respectively.

[0087] according to Figure 4 e and Figure 4 As can be seen from f, the interplanar spacing of MnO2-Vo nanorods is measured to be 0.48 nm and 0.24 nm, which correspond to the (200) and (400) crystal planes of α-MnO2, respectively; at the same time, lattice fringes with a spacing of 0.34 nm are also observed, which correspond to the (002) crystal plane of MWCNTs.

[0088] according to Figure 4 As can be seen from g, the SEM-EDS elemental diagram reveals the uniform distribution of C, Mn, O, and K elements in the carbon-based bifunctional oxygen-electric composite material. According to... Figure 13 It can be seen that the atomic ratio of C, O, Mn, and K is approximately 84.89:6.55:8.16:0.41. These results collectively demonstrate the successful integration of MnO2-Vo nanorods with MWCNTs.

[0089] To more comprehensively determine the elemental composition of MnO2-Vo nanorods, ICP-OES analysis was performed on the MnO2-Vo nanorods, and the results are shown in Table 3.

[0090] Table 3. Elemental composition of MnO2-Vo nanorods determined by ICP-OES analysis.

[0091] As shown in Table 3, the mass ratio of Mn, K, B, S, and Na is approximately 50.67:7.34:0.13:0.22:0.33. The high K content is consistent with the analysis results of XPS and EDS, which can be attributed to the K content during the hydrothermal synthesis using K2S2O8. + Ions are embedded in the 2×2 tunnels of the MnO2 nanorods. This characteristic, typical of crypto-KMnO2, may influence electrocatalytic activity by stabilizing the crystal structure and promoting ion transport. Trace amounts of Na, B, and S are derived from NaBH4 reduction treatment and the MnSO4 / K2S2O8 precursor, respectively. Considering their extremely low concentrations, and their relationship with Vo and Mn... Ⅲ Compared to the influence of species and the hybrid structures formed with MWCNTs, their impact on overall oxygen electrocatalytic performance is limited.

[0092] 2) Electrocatalytic ORR / OER performance of carbon-based bifunctional oxygen-electric composite materials: Figure 5 Electrocatalytic ORR / OER performance tests were performed on MnO2 nanorods, MnO2-Vo nanorods, MWCNTs, carbon-based bifunctional oxygen-electric composites, 20wt% Pt / C, and RuO2. Specifically, a) shows the LSV curves of the samples recorded at 1600 rpm and a scan rate of 10 mV / s in O2-saturated 0.1 M KOH solution; b) shows the Tafel slopes of the samples; c) shows the KL curves of the carbon-based bifunctional oxygen-electric composites at different potentials (the inset shows the electron transfer number n); and d) shows the ORR / OER performance of the samples from MnO2 nanorods, MnO2-Vo nanorods, MWCNTs, carbon-based bifunctional oxygen-electric composites, and 20wt% Pt / C and RuO2. The it curves of Pt / C in O2-saturated 0.1M KOH solution at 0.60V (vs. RHE) and 800rpm are shown in the following figures: e represents the it curves of MnO2 nanorods, MnO2-Vo nanorods, MWCNTs, carbon-based bifunctional oxygen-electric composites, and 20wt% Pt / C in O2-saturated 0.1M KOH solution at 0.60V (vs. RHE) and 800rpm, used to evaluate the ORR tolerance to methanol permeation by it test, with 1.0M and 3.0M methanol added to the electrolyte; f represents the OERLSV curves of the samples recorded at a scan rate of 10mV / s in O2-saturated 0.1M KOH solution; g represents the it curves of MWCNTs and carbon-based bifunctional oxygen-electric composites at 10mA / cm². 2 The Et curves of OER were measured under constant current density; h represents the ΔE values ​​for MWCNTs, carbon-based bifunctional oxygen-electric composites, 20wt% Pt / C, and RuO2. OER-ORR; i is a comparison of the bifunctional activities of carbon-based bifunctional oxygen-electric composite materials with those of reported manganese-based and carbon-based catalysts.

[0093] Table 4. catalytic activities of the samples in 0.1M KOH solution at a rotation speed of 1600 rpm, exhibiting ORR and OER catalytic activity.

[0094] Table 5 Summary of catalytic activity of samples

[0095] First, the ORR electrocatalytic activity of carbon-based bifunctional oxygen electrochemical composites synthesized at different temperatures was tested in a 0.1 M KOH electrolyte. The effects of oxygen vacancy concentration and mass ratio on the ORR electrocatalytic activity were also considered. The results are as follows: Figure 14 and Figure 15 As shown. According to Figure 14 It can be seen that the catalytic activity of MnO2 nanorods first increases and then decreases with increasing reaction temperature. The carbon-based bifunctional oxygen-electric composite material prepared at a reaction temperature of 180 degrees Celsius exhibits the best catalytic activity. Surface modification of the MnO2 nanorods yields MnO2-Vo nanorods that exhibit a more positive half-wave potential (e.g., ...). Figure 15 As shown in the figure, an appropriate oxygen vacancy concentration on the surface of MnO2-Vo nanorods can enhance the ORR catalytic activity of MnO2.

[0096] To further enhance the electrocatalytic activity of MnO2-Vo nanorods, MWCNTs were introduced to improve the electron transfer efficiency of the carbon-based bifunctional oxygen-electric composite material. The results are as follows: Figure 16 As shown. According to Figure 16 It can be seen that 20wt% MnO2-Vo / MWCNTs exhibited the highest ORR catalytic activity, indicating that the optimal mass ratio of MnO2-Vo nanorods to MWCNTs in the carbon-based bifunctional oxygen-electric composite material is 1:4. Based on this, this invention conducted an in-depth study on MnO2 nanorods, MnO2-Vo nanorods, and carbon-based bifunctional oxygen-electric composite materials, and systematically evaluated the bifunctional ORR / OER electrocatalytic performance of the three.

[0097] like Figure 17 As shown, to eliminate surface impurities and activate the electrodes, all electrodes underwent 30 CV scans in O2-saturated 0.1M KOH electrolyte. This pretreatment reduced interference from initial conditioning and ensured the stability and reproducibility of the electrochemical behavior. CV curves were obtained using a standard three-electrode system, and the results are shown below. Figure 18 As shown. According to Figure 18It can be seen that, compared with the oxygen reduction peaks of MnO2 nanorods, MnO2-Vo nanorods and MWCNTs, the oxygen reduction peak of the carbon-based bifunctional oxygen-electric composite material shows a significant enhancement and a more positive potential, indicating that the carbon-based bifunctional oxygen-electric composite material may have better ORR activity.

[0098] The activity of the carbon-based bifunctional oxygen-electric composite material was further tested using linear sweep voltammetry (LSV), and the results are as follows: Figure 5 As shown in a. According to Figure 5 As can be seen from 'a', although the ORR catalytic activity of the carbon-based bifunctional oxygen-electric composite material is lower than that of commercial Pt / C (0.86V), it is significantly higher than that of MnO2 nanorods (0.54V), MnO2-Vo nanorods (0.58V), MWCNTs (0.54V), and RuO2 (0.63V). 1 / 2 The half-wave potential of the samples shifted significantly positively (0.79 V) (as shown in Table 4). Since MnO2 nanorods, MnO2-Vo nanorods, MWCNTs, and RuO2 did not exhibit a significant diffusion-limiting current plateau, the current densities of the various samples were compared at a fixed potential of 0.3 V (relative to RHE) to compare the limiting current densities (J / L). Lim This potential lies within the diffusion-controlled region and minimizes interference with the hydrogen evolution reaction. At this potential, the carbon-based bifunctional oxygen-electric composite material provides -5.10 mA / cm². 2 The current density exceeds that of MnO2 nanorods (-2.01 mA / cm²). 2 MnO2-Vo nanorods (-2.94 mA / cm) 2 ), MWCNTs (-3.21mA / cm) 2 Pt / C (-4.60 mA / cm) 2 ) and RuO2 (-4.15mA / cm 2 Furthermore, to enable more reliable comparisons, the catalytic activity of different samples was further evaluated in the kinetically dominant region. (At -1.0 mA / cm²) 2 At the same current density, the potentials of MnO2 nanorods, MnO2-Vo nanorods, MWCNTs, carbon-based bifunctional oxygen-electric composites, Pt / C, and RuO2 were determined to be 0.55V, 0.60V, 0.64V, 0.85V, 0.91V, and 0.76V, respectively, which are consistent with their E values. 1 / 2 The trend remains consistent. The above results indicate that combining MWCNTs with MnO2-Vo nanorods can significantly improve the oxygen reduction catalytic activity. The excellent ORR catalytic activity of the carbon-based bifunctional oxygen-electric composite material can be attributed to: (1) the abundant Vo and Mn on the surface of MnO2-Vo nanorods compared to MnO2.Ⅲ The presence of species helps promote O2 reduction; (2) entangled highly conductive MWCNTs facilitate efficient charge transport; (3) the unique hierarchical mesoporous nanorod / nanotube structure of the carbon-based bifunctional oxygen electrochemical composite material is conducive to diffusion mass transfer. In order to more accurately evaluate the inherent ORR electrocatalytic activity of the carbon-based bifunctional oxygen electrochemical composite material, the LSV curve of the carbon-based bifunctional oxygen electrochemical composite material was measured at 1600 rpm in a 0.1 M KOH solution saturated with N2 to record its background current. The results are as follows. Figure 19 As shown in a. According to Figure 19 As can be seen from 'a' in the figure, after background current correction, the LSV curve of the carbon-based bifunctional oxygen-electric composite material is located at 0.3V (relative to RHE) at J. Lim It shows a slight decrease, from -5.10 mA / cm before correction. 2 It dropped to -4.97 mA / cm 2 Meanwhile, it is located at -1.0 mA / cm. 2 The potential at the current density also showed a slight negative shift, from 0.853 V to 0.846 V. These small decreases in key parameters, and the differences in the sample before and after correction within the 0.8–1.0 V (relative to RHE) potential range (disappearance of reduction characteristics), can be attributed to the systematic elimination of the contribution of non-Radal processes (such as double-layer charge / discharge, non-Radal redox reactions of surface functional groups) to the apparent current during background correction. This allows for a more accurate reflection of the catalyst's intrinsic ORR electrocatalytic activity. Even after eliminating the interference of inactive currents, the carbon-based bifunctional oxygen electropolymer composite still exhibits excellent intrinsic activity. This indicates that its superior ORR performance primarily stems from abundant Mn. Ⅲ The synergistic effect between active sites, high concentrations of oxygen vacancies, and the efficient charge transport network constructed by MWCNTs is not derived from non-reactive processes.

[0099] To investigate the ORR kinetics of carbon-based bifunctional oxygen-electric composites, the Tafel slope was calculated, and the results are as follows: Figure 5 As shown in b. According to Figure 5 As shown in b, the Tafel slope of the carbon-based bifunctional oxygen-electric composite (135.2 mV / dec) is higher than that of the Pt / C catalyst (89.1 mV / dec), but significantly lower than that of MnO2 nanorods (182.2 mV / dec), MnO2-Vo nanorods (153.3 mV / dec), and RuO2 (498.5 mV / dec) (as shown in Table 5). This indicates that the ORR kinetics of the carbon-based bifunctional oxygen-electric composite tend to improve under alkaline conditions. The decrease in the Tafel slope of the carbon-based bifunctional oxygen-electric composite may be attributed to the interaction of Vo and MnO2. ⅢThe presence of species, the improved conductivity of the interconnected MWCNT network, and the synergistic effect of the unique hierarchical porous structure all contribute to enhanced electron and mass transport. Therefore, the composite structure of carbon-based bifunctional oxygen-electric composites favors the promotion of oxygen reduction reactions. However, it should be noted that the Tafel slope can be influenced by various external factors beyond intrinsic kinetics, such as variations in the electrochemically active surface area (ECSA), mass transfer limitations, and surface Mn reduction. Figure 19 As shown in b, after N2 background correction, the Tafel slope of the carbon-based bifunctional oxygen-electric composite material decreased from 135.2 mV / dec to 127.6 mV / dec. This improvement indicates that background correction can effectively eliminate interfering illegal Radaic currents, thereby enabling a more accurate assessment of the intrinsic ORR kinetics. This finding further confirms the excellent electron transfer capability of the carbon-based bifunctional oxygen-electric composite material.

[0100] To further investigate the reaction kinetics of carbon-based bifunctional oxygen-electric composite materials, LSV tests were performed at different rotational speeds to determine the electron transfer number (n) at different potentials. The results are as follows: Figure 20 As shown. According to Figure 20 It can be seen that the current density of different electrodes increases regularly with increasing rotational speed, which can be attributed to the gradual decrease in the thickness of the diffusion layer during rotation. Furthermore, similar to Pt / C, the slope of the KL curve for the carbon-based bifunctional oxygen-electric composite material remains almost constant (e.g., ...). Figure 5 c and Figure 21This indicates that the electron transfer numbers measured at different potentials remain constant for both. The inset shows the electron transfer numbers (n) for different catalysts, with n values ​​ranging from 1.65 to 2.69 for multi-walled carbon nanotubes, indicating that electron transfer in multi-walled carbon nanotubes is primarily dominated by a 2-electron mechanism. Unlike multi-walled carbon nanotubes, the n values ​​for carbon-based bifunctional oxygen-electric composites range from 3.71 to 3.97, which is closer to the n values ​​(3.80–4.28) of commercial Pt / C catalysts (as shown in Table 5). This suggests that the oxygen reduction reaction process in carbon-based bifunctional oxygen-electric composites is primarily dominated by a 4-electron transfer pathway, with less 2-electron reactions occurring. The potential impact of the Nafion binder on the measured ORR selectivity is worth considering. For manganese-containing catalysts, Nafion may not be completely inert, affecting the oxygen reduction pathway and typically promoting a preferential 4-electron transfer process, possibly by lowering the oxidation state of manganese. While the use of Nafion in rotating disk electrode (RDE) measurements is crucial for preparing stable and well-adhered catalyst films, the high 4-electron selectivity of the carbon-based bifunctional oxygen-electric composite material observed in this invention is likely a combined result of this potential Nafion effect and, more importantly, the inherent properties of the catalyst material itself. Specifically, XPS and EPR analyses confirmed the high concentration of MnO in the MnO2-Vo nanorods. Ⅲ Species and Vo are crucial for promoting the direct 4-electron pathway. The synergistic interaction with conductive MWCNTs further ensures an efficient electron supply to the active MnO2-Vo nanorod centers, thereby maintaining the efficient 4-electron reduction of O2. Similarly, the above results demonstrate that the carbon-based bifunctional oxygen-electric composite material prepared in this invention has great potential as a highly efficient ORR catalyst. This is mainly attributed to the synergistic interaction between MWCNTs and MnO2-Vo nanorods; during oxygen reduction, the active centers, primarily composed of MnO2-Vo nanorods, can rapidly acquire electrons transferred from MWCNTs, thus maintaining the efficient reduction of O2 molecules.

[0101] Stability is also one of the key parameters that needs to be evaluated during the research process. In this invention, current-time curves are used to evaluate the oxygen reduction stability of different catalysts, and the results are as follows: Figure 5 As shown by d in the diagram. According to... Figure 5As shown in d, the carbon-based bifunctional oxygen-electric composite material retained 85.3% of its current density after 10 hours of potentiostatic testing (relative to the reversible hydrogen electrode potential of 0.60 V). Compared with commercial Pt / C (83.2%), MWCNTs (54.4%), MnO2-Vo nanorods (68.8%), and MnO2 nanorods (78.3%) (as shown in Table 5), the carbon-based bifunctional oxygen-electric composite material exhibits superior oxygen reduction stability. The excellent stability of the carbon-based bifunctional oxygen-electric composite material can be attributed to its unique intertwined nanorod / nanotube structure. The intertwined tubular structure of MWCNTs immobilizes the active component MnO2-Vo nanorods, making them less prone to aggregation or separation during measurement, which helps maintain the structural integrity of the electrode. Furthermore, methanol resistance is one of the criteria for evaluating catalyst performance. Figure 5 Figure e shows the results of methanol permeation tolerance tests on MnO2 nanorods, MnO2-Vo nanorods, MWCNTs, carbon-based bifunctional oxygen-electric composites, and commercial Pt / C catalysts. Upon injection of 1.0 M methanol, the current density of the Pt / C catalyst dropped sharply, indicating methanol oxidation at the Pt / C electrode. Under the same conditions, the current of the MWCNTs electrode decreased slightly. In contrast, the current densities of the MnO2 nanorods, MnO2-Vo nanorods, and carbon-based bifunctional oxygen-electric composite electrodes remained relatively stable. Furthermore, after injecting 3.0 M methanol into a 0.1 M saturated oxygen KOH electrolyte, the current density of the MWCNTs electrode continuously decreased, while the current densities of the MnO2 nanorods and MnO2-Vo nanorods electrodes decreased only slightly. Notably, the current density of the carbon-based bifunctional oxygen-electric composite electrode remained unchanged. To further investigate the tolerance of the carbon-based bifunctional oxygen-electric composite, the methanol concentration in the electrolyte was increased, and the results are shown below. Figure 22 As shown. According to Figure 22 As can be seen, even at a methanol concentration of 6.0 M, the current-time curve of the carbon-based bifunctional oxygen-electric composite material of this invention maintains a relatively stable overall trend. When the methanol concentration in the electrolyte reaches as high as 10.0 M, the current of the carbon-based bifunctional oxygen-electric composite electrode only decreases slightly. These results demonstrate that, compared with commercial Pt / C, the carbon-based bifunctional oxygen-electric composite material exhibits superior methanol resistance. This excellent stability and high methanol tolerance provide more possibilities for constructing advanced EECSDs.

[0102] For the OER process, LSV curves for various catalysts were obtained using a scan rate of 10 mV / s, and the results are as follows: Figure 5 As shown in f in the figure. According to Figure 5 As can be seen from f, the carbon-based bifunctional oxygen-electric composite material exhibits superior catalytic activity for the oxygen evolution reaction compared to other catalysts. This is demonstrated at a current density of 10 mA / cm².2 At this potential, the carbon-based bifunctional oxygen-electric composite material exhibits a potential of only 1.62 V, significantly lower than that of MnO2-Vo nanorods, MnO2 nanorods, MWCNTs (1.88 V), and Pt / C (1.94 V) catalysts. However, compared to RuO2 (1.61 V), the carbon-based bifunctional oxygen-electric composite material still shows a potential difference of approximately 13 mV (as shown in Table 4). Furthermore, at a potential of 1.70 V, the carbon-based bifunctional oxygen-electric composite material demonstrates the highest current density (27.62 mA / cm²). 2 This exceeds that of MnO2 nanorods (0.26 mA / cm). 2 MnO2-Vo nanorods (0.59 mA / cm) 2 ), MWCNTs (1.54mA / cm) 2 Pt / C (3.54 mA / cm) 2 ) and RuO2 (17.75mA / cm 2 ) current density (e.g. Figure 23 (As shown in Table 4), this indicates that the carbon-based bifunctional oxygen-electric composite material possesses superior catalytic activity for the oxygen evolution reaction (OER). The Tafel curves of various catalysts in the OER are shown in Table 4. Figure 24 As shown in Table 5, the carbon-based bifunctional oxygen-electrode composite exhibits the smallest Tafel slope (166.4 mV / dec), indicating that the oxygen evolution rate (OER) of the carbon-based bifunctional OER composite increases most rapidly with a positive potential shift. This may be attributed to the intertwined MWCNTs enhancing the overall electron transfer rate of the carbon-based bifunctional OER composite. Similar to ORR, factors such as specific surface area, porosity, and the redox behavior of Mn also affect OER performance, and the Tafel slope is not solely determined by reaction kinetics. Nevertheless, the carbon-based bifunctional OER composite still exhibits a low Tafel slope, which, combined with its good LSV performance, indicates that the carbon-based bifunctional OER composite possesses considerable OER reactivity, which can be attributed to the interaction of Vo and Mn. Ⅲ The synergistic effect between species and the conductive MWCNT network enhances charge transfer during the oxygen evolution reaction and contributes to structural stability.

[0103] Using a current density of 10 mA / cm 2 The catalytic stability of OER was evaluated using a potential-time measurement method under the specified conditions, and the results are as follows: Figure 5 As shown in g. According to Figure 5As can be seen from the graph, after 8000 seconds of testing, the potential of the carbon-based bifunctional oxygen-electric composite material increased only slightly by 0.11V, while the potential of MWCNTs increased significantly by 0.50V in a shorter period of 1800 seconds. Notably, MnO2 nanorods and MnO2-Vo nanorods rapidly reached a cutoff voltage of 2.52V within just 24 seconds, a stark contrast to the above results. This indicates that the composite of MnO2-Vo nanorods and MWCNTs can significantly improve the stability of the OER. It is worth mentioning that the carbon-based bifunctional oxygen-electric composite material achieved a potential of 10 mA / cm² as measured by LSV. 2 A significant difference exists between the required potential (1.62 V) and the potential obtained from potential-time measurements (1.7–1.8 V), a phenomenon common in OER electrocatalysis, stemming from fundamental differences between the two measurement techniques. Linear sweep voltammetry (LSV) is a dynamic measurement method affected by non-Faraday capacitance currents, potentially leading to a lower apparent potential at a given current density. In contrast, galvanochronopotentiometry (Et) is a steady-state method where the initial potential must be sufficiently high to charge the electric double layer and sustain the Faraday oxygen evolution reaction. Furthermore, the continuous generation and attachment of oxygen bubbles on the electrode surface during Et testing introduces significant mass transfer resistance; therefore, a higher overpotential is required to maintain the set current density compared to transient LSV scanning. Consequently, the potential recorded in Et testing is higher than that observed in LSV testing.

[0104] To further compare the overall oxygen electrocatalytic activity of different samples, the half-wave potential of ORR and OER at a current density of j=10mA / cm² were calculated. 2 ΔE at time OER-ORR Half-wave potential is a representative indicator of a catalyst's oxygen reduction capability, and j = 10 mA / cm². 2 The potential at which the oxygen evolution reaction (OER) is located is a commonly used reference current density for evaluating the performance of the OER. The results are as follows: Figure 5 As shown in h. According to Figure 5 As can be seen from h, the ΔE of the carbon-based bifunctional oxygen-electric composite material... ORR-OER The value (0.83V) is much smaller than that of MWCNTs (1.34V), Pt / C (1.08V) and RuO2 (1.04V) (as shown in Table 4).

[0105] In addition, the catalytic activity of the carbon-based bifunctional oxygen-electric composite material was compared with that of previously reported catalysts, and the results are as follows: Figure 5 As shown by i in the diagram. According to... Figure 5As can be seen from the figure, compared with most similar catalysts, the carbon-based bifunctional oxygen electrocatalytic composite material prepared in this invention exhibits superior bifunctional electrocatalytic performance in OER / ORR. This performance improvement can be attributed to the abundant Vo and Mn on the surface of the MnO2-Vo nanorods. Ⅲ These species work synergistically to promote oxygen adsorption and hydroxide ion activation. Simultaneously, the conductive MWCNT network facilitates efficient charge transfer and mass diffusion. The carbon-based bifunctional oxygen electrocatalyst exhibits excellent electrocatalytic activity for both ORR and OER, making it a promising bifunctional oxygen electrocatalyst.

[0106] Figure 6 The results show the activity enhancement of MnO2-Vo nanorods, MWCNTs, carbon-based bifunctional oxygen-electric composites, and 20wt% Pt / C. In this figure, a) is the Nyquist plot of the electrochemical impedance spectroscopy (EIS) of MnO2-Vo nanorods, MWCNTs, and the carbon-based bifunctional oxygen-electric composite, with tests conducted in an O2-saturated 0.1M KOH solution; b) is the C value estimated by plotting the current density change. dl .

[0107] To further investigate the reasons for the enhanced activity of the carbon-based bifunctional oxygen-electric composite material, EIS and ECSA tests were performed on the samples. EIS measurements were conducted using a CHI 760E electrochemical workstation at 0.80V (vs. RHE), with a frequency range of 100kHz to 0.1Hz and an AC perturbation amplitude of 5mV. The results are as follows: Figure 6 As shown in Figure a, the equivalent circuit of the electrode can be fitted using a constant-phase element (Q), a semi-circular charge transfer resistance (Rct), and a solution resistance (Rs). The larger the arc, the more difficult the charge transfer between the electrolyte and the catalyst. The fitting data are shown in Table 6.

[0108] Table 6 Impedance fitting data and relative standard error

[0109] Note: The sample area is 0.126 cm². 2 .

[0110] according to Figure 6As shown in a and Table 6, the Rct value of the carbon-based bifunctional oxygen electrocatalytic composite (52.49 Ω) is significantly lower than that of the MnO2-Vo nanorods (173.00 Ω). This indicates that the introduction of MWCNTs effectively improves the conductivity of the carbon-based bifunctional oxygen electrocatalytic composite, which may be one of the key factors in enhancing its oxygen electrocatalytic performance. The slightly higher Rct of the carbon-based bifunctional oxygen electrocatalytic composite compared to MWCNTs (whose charge transfer resistance Rct is 33.16 Ω) is reasonable. This is because MWCNTs, as carbon-based conductors, inherently possess high conductivity, while the introduction of semiconductor-like MnO2 nanorods inevitably increases the interfacial resistance relative to MWCNTs. Importantly, the overall electrocatalytic performance is not solely determined by the charge transfer resistance Rct; it is also influenced by other factors, such as the number of active sites and mass transfer characteristics. The highly conductive MWCNT network combined with Mn-rich... Ⅲ The synergistic effect between the carbon-based bifunctional oxygen-electric composite material provided by the present invention and the MnO2-Vo nanorods with Vo active sites enables the material to exhibit excellent ORR and OER activities, thereby offsetting the slight effect of the slight increase in charge transfer resistance.

[0111] Due to the electrochemical active surface area (ECSA) and the electrochemical double layer capacitance (C... dl It is directly proportional to ), therefore this invention uses C dl The value was used to assess the size of ECSA, and the results were as follows: Figure 6 As shown in b in the figure. Figure 6 b in the figure shows the C of different samples dl This value can be derived from the linear slope of the capacitor current versus the scan rate (e.g., Figure 25 As shown). According to Figure 6 From b, we can see that C dl Pt / C >C dl MnO2-Vo / MWCNTs >C dl MWCNTs (As shown in Table 5), this indicates that carbon-based bifunctional oxygen-electric composites have a larger electrochemical active surface area compared to MWCNTs. Similar to the BET specific surface area, a larger active surface area helps expose more active sites and maintain the good solid-liquid-gas three-phase interface required for the reaction. This is beneficial for improving mass transfer through diffusion, thereby enhancing the electrocatalytic activity of carbon-based bifunctional oxygen-electric composites.

[0112] 3) Exploration of ORR / OER mechanisms: Figure 7 The ORR / OER catalytic mechanism of carbon-based bifunctional oxygen-electric composite materials.

[0113] From the above analysis, it can be seen that Mn contains ⅢThe mechanism by which carbon-based bifunctional oxygen electrochemical composites of species and Vo enhance the electrocatalytic activity of ORR / OER can be attributed to the following factors, such as Figure 7 As shown: (1) The Vo present on the surface of MnO2-Vo nanorods improves the adsorption of oxygen-containing compounds, thereby promoting the electrocatalytic reaction involving oxygen. For ORR, according to the four-step proton-coupled electron transfer reaction mechanism of manganese dioxide (alkaline conditions), the adsorbed O2 replaces OH - The group is considered the rate-limiting step. The presence of Vo enhances the adsorption of O2 molecules on the surface of the carbon-based bifunctional oxygen-electric composite, accelerating the rate-limited oxygen reduction process. For OER, the positively charged Vo enhances the adsorption of free OH groups present in the electrolyte. - Ions also exhibit attraction, which is beneficial for OER. (2) A high concentration of Mn exists in MnO2-Vo nanorods. Ⅲ Species, which helps through Mn Ⅲ Species and Mn Ⅳ Interspecies redox cycles enhance the catalytic activity of ORR and OER. For the oxygen reduction reaction, Mn... Ⅲ Species accelerated O2 2- / OH - The exchange. More precisely, a large portion of Mn... Ⅲ High energy of the d orbital of a species Electrons will transfer to OO Orbit, and Mn Ⅲ Oxidized to Mn Ⅳ This promotes a more stable O2+e - The species replaced the OH on the Mn site. - Ultimately, the increased affinity of carbon-based bifunctional oxygen-electric composites for O2 molecules accelerates the ORR kinetics. For OER, Mn... Ⅲ / Mn Ⅳ It also acts as a mediator. In alkaline solutions, Mn Ⅲ -OH may first be converted to Mn through proton-coupled electron transfer pre-equilibrium. Ⅳ =O, then the two adjacent terminal oxygen atoms couple, releasing O2 molecules. The surface of the carbon-based bifunctional oxygen-electric composite material contains a large amount of Mn. Ⅲ Species also significantly contribute to its oxygen evolution reaction activity. (3) The MnO2-Vo nanorods exhibit a 2×2 tunnel structure with a size of approximately 0.46×0.46 nm. 2 Like O2, OH -Reactants and products such as H2O can be efficiently transported through this tunnel, thereby improving the overall catalytic efficiency of ORR / OER. (4) Intertwined conductive MWCNTs help to achieve efficient charge transport, and can replenish / transfer electrons for the electrocatalytic process in a timely manner, thereby promoting the full development of the catalytic activity of MnO2-Vo nanorods. (5) Carbon-based bifunctional oxygen electrochemical composites have a large active area and a unique hierarchical mesoporous structure, which can promote mass transfer and diffusion. This is beneficial to the contact between the active sites on the surface of carbon-based bifunctional oxygen electrochemical composites and reactants, thereby improving the oxygen electrocatalytic reaction.

[0114] 4) Stability investigation: Figure 8 Images show the stability test results of MnO2-Vo nanorods and carbon-based bifunctional oxygen-electric composites; where a is the TEM image of MnO2-Vo nanorods before stability testing; b~c are the TEM images of MnO2-Vo nanorods after stability testing; d~f are the HRTEM images of MnO2-Vo nanorods after stability testing; g is the TEM image of the carbon-based bifunctional oxygen-electric composite before stability testing; h is the TEM image of the carbon-based bifunctional oxygen-electric composite after stability testing; and i is the HRTEM image of the carbon-based bifunctional oxygen-electric composite after stability testing.

[0115] In addition to excellent catalytic activity, catalysts used in EECSDs also need to possess outstanding durability. To further investigate the reasons for activity degradation, the composition of MnO2-Vo nanorods and carbon-based bifunctional oxygen-electric composite electrodes after long-term stability testing was analyzed. The results are as follows: Figure 8 As shown. According to Figure 8 As can be seen from a to c in the figure, compared with fresh MnO2-Vo nanorods, the surface of the used MnO2-Vo nanorods becomes rough; the original nanorod structure is destroyed, forming many small nanocrystals and ultrathin nanosheets; this is the result of surface reconstruction of MnO2-Vo nanorods in the durability test environment.

[0116] Furthermore, HRTEM analysis was performed on the nanocrystalline region. According to... Figure 8 The observation results clearly show that the interplanar spacing of the nanoparticles in region I is 0.31 nm, corresponding to the (310) crystal plane of α-MnO2. In region II, significant lattice perturbation was observed, with the lattice fringes becoming blurred and the crystallinity significantly reduced. This indicates that the MnO2-Vo nanorods underwent significant electrochemical corrosion under local polarization. During long-term stability testing, a phase transition was observed in the MnO2-Vo nanorods. The initial tunnel-type MnO2 crystal structure gradually evolved into an amorphous state, while a new amorphous phase formed in the surrounding region. Figure 8e and Figure 26 This observation was further confirmed by the images, which showed that the atoms in the nanosheets exhibited an amorphous structure characterized by significant disorder. Compared to the well-defined 2×2 tunnel structure of MnO2 nanorods, the pores in the amorphous MnO2 structure were irregular in shape, varied in size, and poorly interconnected. These pores are a natural result of the disordered stacking and random connection of [MnO6] octahedrons, which share corners or edges. The electrocatalytic activity of amorphous MnO2 is limited by its shorter ion transport channels and lower electronic conductivity. Figure 8 As can be seen from f in the text, in the bulk crystal structure of MnO2-Vo nanorods (Region I), lattice fringes with a spacing of 0.68 nm can still be clearly observed, which corresponds to the (110) crystal plane of MnO2. In Region II, the atomic arrangement lacks long-range order, and the lattice fringes become blurred. ORR / OER is a catalytic process that occurs at the solid-liquid-gas three-phase interface. Therefore, the structural transition from α-MnO2 to the amorphous state on the surface of MnO2-Vo nanorods may be the reason for the observed decrease in activity. The phase transition from α-MnO2 to the amorphous state may be due to disproportionation reaction, electrochemical reaction and Jahn-Teller distortion. This may involve the dissolution of Mn, the formation of dislocations, interlayer breakage and the interlayer intercalation of water molecules or cations. In contrast, compared with fresh carbon-based bifunctional oxygen-electric composites (such as Figure 8 Compared to (as shown in g), no obvious morphological or crystallographic transformations (such as those shown in g) were observed on the surface of the MnO2-Vo nanorods of the carbon-based bifunctional oxygen-electric composite material after stability testing. Figure 8 h and Figure 27 (As shown). Furthermore, according to Figure 8 As shown in Figure i, the HRTEM image of the carbon-based bifunctional oxygen-electric composite material clearly displays lattice fringes corresponding to the (310) crystal plane of α-MnO2 and the (002) crystal plane of MWCNTs. This observation indicates that the stability of MnO2-Vo nanorods in the carbon-based bifunctional oxygen-electric composite material is enhanced upon application of a potential, which can be attributed to the synergistic interaction between MnO2-Vo nanorods and MWCNTs. MWCNTs may play a crucial role in maintaining the electrocatalytic stability of MnO2-Vo nanorods. Compared with MnO2-Vo nanorods, this unique interconnection network effectively improves the stability of the carbon-based bifunctional oxygen-electric composite material. MWCNTs, acting as a buffer layer and support, can effectively mitigate structural transformation, collapse, and aggregation.

[0117] 5) ZAB battery test: Figure 9The diagram shows the structural schematic and test results of the ZAB battery; where a is the structural schematic of the ZAB battery; b is the open circuit potential of the ZAB battery based on Pt / C+RuO2 and carbon-based bifunctional oxygen-electric composite material; c is the charge-discharge polarization curve and corresponding power density curve of the ZAB battery based on Pt / C+RuO2 and carbon-based bifunctional oxygen-electric composite material; d is the discharge curve of the ZAB battery based on carbon-based bifunctional oxygen-electric composite material at different current densities; and e is the charge-discharge performance of the ZAB battery based on Pt / C+RuO2 and carbon-based bifunctional oxygen-electric composite material.

[0118] To evaluate the catalytic performance under practical operating conditions, alkaline ZAB batteries were constructed using carbon-based bifunctional oxygen-electric composite materials and commercially available Pt / C+RuO2 as electrode materials, respectively. The structures are shown below. Figure 9 As shown in a. According to Figure 9 As can be seen from 'a', the composite electrode supported on carbon-based bifunctional oxygen-electric composite material is used as the air cathode, the zinc plate is used as the anode, and a mixed electrolyte composed of 6.0 M KOH and 0.2 M ZnAc2 is used to systematically study the assembled alkaline ZAB battery.

[0119] For comparison, a ZAB cell with Pt / C+RuO2 as the cathode was also constructed. Open-circuit voltage tests were performed on both ZAB cells, and the results are as follows: Figure 9 As shown in b. According to Figure 9 As can be seen from b, the open-circuit voltage of the ZAB battery using carbon-based bifunctional oxygen-electric composite material as the cathode is about 1.48V, which exceeds the 1.39V of the ZAB battery using Pt / C+RuO2 as the cathode.

[0120] The charge / discharge polarization curves and power density curves of the two batteries are as follows: Figure 9 As shown in c in the figure. It is worth noting that the discharge performance of the ZAB battery based on the carbon-based bifunctional oxygen-electric composite material is slightly lower than that of the ZAB battery based on Pt / C+RuO2, but its charging performance is slightly improved in comparison. These factors make the overall charge-discharge performance of the ZAB battery based on the carbon-based bifunctional oxygen-electric composite material comparable to that of the noble metal catalyst, mainly due to the influence of the ORR and OER characteristics of the carbon-based bifunctional oxygen-electric composite material on voltage polarization. The ZAB battery driven by the carbon-based bifunctional oxygen-electric composite material achieves a power density of 71.17 mW / cm². 2 This is comparable to the 74.84 mW / cm² achieved by the ZAB battery based on Pt / C+RuO₂. 2 Quite good. This indicates that the ZAB battery based on carbon-based bifunctional oxygen-electric composite material also exhibits excellent charge-discharge performance.

[0121] also, Figure 9The 'd' in the figure illustrates the discharge stability observed at different current densities. According to... Figure 9 As can be seen from d in the figure, when the current density increases from 10 mA / cm², 2 Gradually increase to 80 mA / cm 2 It dropped back to 10 mA / cm 2 The discharge potential remained stable throughout, with negligible changes observed at each current density stage. This indicates that the ZAB battery based on carbon-based bifunctional oxygen-electric composite material exhibits excellent reversibility.

[0122] Figure 9 The image shows a carbon-based bifunctional oxygen-electric composite material and a Pt / C+RuO2-based ZAB battery at 4 mA / cm². 2 Charge-discharge cycle performance at current density, each cycle consisting of a 10-minute discharge phase followed by a 10-minute charge phase. According to... Figure 9 As can be seen from 'e', ​​after 100 cycles, the charge-discharge voltage difference of the zinc-air battery based on the carbon-based bifunctional oxygen-electric composite material is 0.77V, which is lower than that of the Pt / C+RuO2-based ZAB battery (0.87V). This indicates that the ZAB battery assembled using the carbon-based bifunctional oxygen-electric composite material has superior charge-discharge cycle stability. In summary, the carbon-based bifunctional oxygen-electric composite material of this invention shows promise as a low-cost bifunctional cathode catalyst for replacing noble metal catalysts in the assembly of ZAB batteries.

[0123] In summary, this invention successfully synthesized a carbon-based bifunctional oxygen-electric composite material. In this material, MnO2-Vo nanorods exhibit a 2×2 tunnel structure, and MWCNTs are tightly interwoven with the MnO2-Vo nanorods, forming a strong interconnected conductive network. Furthermore, in alkaline media, compared with MnO2 nanorods, MnO2-Vo nanorods, MWCNTs, and a reference catalyst, the carbon-based bifunctional oxygen-electric composite material demonstrates superior ORR / OER bifunctional electrocatalytic activity and enhanced long-term stability. In the oxygen evolution reaction (OER), the carbon-based bifunctional oxygen-electric composite material exhibits excellent OER / OER bifunctional electrocatalytic activity and enhanced long-term stability at a current density of 10 mA / cm². 2 The overpotential was as low as 0.39V, and after 8000 seconds of operation, the overpotential increased by only 0.12V. In the oxygen reduction reaction, the half-wave potential (E0) of the carbon-based bifunctional oxygen-electric composite material... 1 / 2 The voltage was 0.79V, and after 10 hours of continuous operation, the activity loss was only 14.7%, maintaining excellent stability. Meanwhile, the ZAB battery using a carbon-based bifunctional oxygen-electric composite material as the air cathode achieved a power density of 71.17 mW / cm². 2 Compared with the ZAB battery based on Pt / C+RuO2 (74.84mW / m 2The ZAB battery based on the carbon-based bifunctional oxygen-electric composite material exhibits excellent stability, with a charge-discharge voltage difference of only 0.77V after 100 cycles, significantly lower than the 0.87V of the Pt / C+RuO2-based ZAB battery. These results are consistent with the trends observed in ORR and OER tests of the carbon-based bifunctional oxygen-electric composite material. The superior catalytic activity of the carbon-based bifunctional oxygen-electric composite material can be attributed to the rational composition of the MnO2-Vo nanorods and their composite with MWCNTs. Specifically, the MnO2-Vo nanorods on their surface contain MnO2... Ⅲ Species and Vo promote the exchange of O2 and H in the electrolyte. - Contact and activation. The 2×2 tunnel structure of MnO2-Vo nanorods facilitates rapid ion migration. In particular, this interwoven network structure between MnO2-Vo nanorods and MWCNTs significantly enhances the electron transfer, diffusion mass transfer, and structural stability of the carbon-based bifunctional oxygen-electric composite material. This invention proposes a simple, efficient, and economical preparation method for non-noble metal catalysts to meet the needs of future sustainable energy applications.

[0124] The embodiments of the present invention have been described above; however, these embodiments are merely illustrative and not intended to limit the scope of the invention. Although various embodiments have been described above, this does not mean that the measures in the embodiments cannot be used advantageously in combination. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of the invention, and all such substitutions and modifications should fall within the scope of the invention.

Claims

1. A carbon-based bifunctional oxygen-electric composite material, characterized in that, Including MnO2-Vo nanorods and multi-walled carbon nanotubes; The MnO2 in the MnO2-Vo nanorods is α-MnO2; The multi-walled carbon nanotubes and MnO2-Vo nanorods are intertwined and mechanically interlocked to form a three-dimensional conductive network. The MnO2-Vo nanorods have K inserted into them. + A 2×2 tunnel structure; The surface of the MnO2-Vo nanorods contains oxygen vacancies and Mn Ⅲ Species; The carbon-based bifunctional oxygen-electric composite material contains a porous structure.

2. The carbon-based bifunctional oxygen-electric composite material according to claim 1, characterized in that, The average diameter of the MnO2-Vo nanorods is 20~20.5 nm; The surface oxygen vacancy content of the MnO2-Vo nanorods is 40-41%, and Mn Ⅲ The species content is 44-45%.

3. The carbon-based bifunctional oxygen-electric composite material according to claim 1 or 2, characterized in that, The average outer diameter of the multi-walled carbon nanotubes is 12.5~13 nm.

4. The carbon-based bifunctional oxygen-electric composite material according to claim 1, characterized in that, The pore size of the pore structure is 2~160nm.

5. The method for preparing the carbon-based bifunctional oxygen-electric composite material according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Multi-walled carbon nanotubes and acid solution are mixed and oxidized to obtain pretreated multi-walled carbon nanotubes; (2) 1-Butyl-3-methylimidazolium tetrafluoroborate, manganese sulfate, potassium persulfate and water were mixed and subjected to a redox reaction to obtain MnO2 nanorods; (3) The MnO2 nanorods were mixed with sodium borohydride and water to carry out a reduction reaction to obtain MnO2-Vo nanorods; (4) The pretreated multi-walled carbon nanotubes are mixed with MnO2-Vo nanorods and water for self-assembly to obtain the carbon-based bifunctional oxygen-electric composite material. There is no requirement for the time order of steps (1) and (2) to (3).

6. The preparation method according to claim 5, characterized in that, The C8H 15 The volume ratio of N2BF4 to water is 1:95~105; The molar ratio of MnSO4 to K2S2O8 is 1~1.1:1~1.1; The molar ratio of MnSO4 to water volume is (0.32~0.35) mol:1L.

7. The preparation method according to claim 5, characterized in that, The mass ratio of the MnO2 nanorods to the molar amount of NaBH4 is 435 g: (0.25~1) mol; The ratio of the amount of NaBH4 to the volume of water is (0.005~0.02) mol:1L.

8. The preparation method according to claim 5, characterized in that, The mass ratio of the MnO2-Vo nanorods to the multi-walled carbon nanotubes is 1:1.5~9.

9. The application of the carbon-based bifunctional oxygen-electric composite material according to any one of claims 1 to 4 or the carbon-based bifunctional oxygen-electric composite material obtained by the preparation method according to any one of claims 5 to 8 in the field of electrochemical energy conversion or storage.

10. A rechargeable zinc-air battery, characterized in that, The invention includes an air cathode, wherein the air cathode comprises the carbon-based bifunctional oxygen-electric composite material according to any one of claims 1 to 4 or the carbon-based bifunctional oxygen-electric composite material obtained by the preparation method according to any one of claims 5 to 8.

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