Preparation method and application of MnO / Mn-N-C catalyst

Abstract

The application provides a preparation method and application of a MnO / Mn-N-C catalyst. The preparation method of the embodiment comprises the following steps: dispersing manganese salt, acrylonitrile (AN) and 2,2-azoisobutyronitrile (AIBN) in an acetone solvent according to a predetermined ratio to obtain a precursor solution; performing photochemical polymerization on the precursor solution under an inert atmosphere by irradiation with ultraviolet light, filtering, washing and drying after the reaction to obtain Mn / PAN; performing pre-oxidation treatment on the Mn / PAN to obtain Mn / PAN-O; and pyrolyzing the Mn / PAN-O under an inert atmosphere to obtain the MnO / Mn-N-C catalyst. The catalyst prepared by the method has high ORR activity and excellent stability, and the gas diffusion electrode (GDE) half-cell and zinc-air battery (ZABs) assembled by using the catalyst both exhibit excellent performance.

Description

Technical Field

[0001] This invention relates to the field of non-precious metal catalysts; more specifically, it relates to a method for preparing a MnO / Mn-NC catalyst for the ORR reaction and its application. Background Technology

[0002] Rapid societal development is accompanied by numerous energy and environmental problems, such as the depletion of fossil fuels, massive greenhouse gas emissions, declining air quality, and severe river pollution. Therefore, green and renewable energy is a necessity of our time. Polymer electrolyte membrane fuel cells (MEFCs) and zinc-air batteries (ZABs) are considered highly efficient energy conversion and storage devices. However, the oxygen reduction reaction (ORR) kinetics at the cathodes of these two types of batteries are very slow, limiting the overall energy conversion efficiency. Therefore, the development of highly active ORR catalysts is needed to accelerate the reaction rate. Pt-based catalysts possess high ORR catalytic activity, but suffer from drawbacks such as scarce Pt resources, high cost, and susceptibility to poisoning, hindering large-scale commercial application. Therefore, the development of high-performance non-precious metal catalysts is of great significance for the practical application of MEFCs and ZABs.

[0003] Transition metal and heteroatom N co-doped MNC (M = Fe, Co, Mn) materials exhibit high activity of MN x With its unique and uniform active sites and abundant transition metal reserves, Mn-NC is a promising ORR catalyst, which is beneficial for reducing catalyst costs. In particular, Mn-NC possesses a unique electronic structure and relatively weak *OH adsorption energy, which can significantly promote ORR activity. Furthermore, manganese oxide (MnO) x It can promote the decomposition of H2O2 during ORR, making the reaction closer to 4-electron transfer, accelerating the reaction rate, and exhibiting excellent ORR performance in alkaline media.

[0004] Polyacrylonitrile (PAN), due to its abundant cyano groups, is a nitrogen-rich carbonaceous precursor that can be used to synthesize ORR catalysts. Furthermore, the pyridine or imine nitrogen and oxygen-containing functional groups generated during PAN oxidation can anchor metal atoms. Currently, PAN materials are mainly prepared through thermal polymerization and electrospinning. However, research on using ultraviolet light to generate free radicals to achieve acrylonitrile (AN) polymerization, while simultaneously doping with Mn metal single atoms to form Mn-NC active sites, has not yet been reported. Summary of the Invention

[0005] The first aspect of the present invention provides a method for preparing a MnO / Mn-NC catalyst. The catalyst prepared by this method has high ORR activity and excellent stability. Gas diffusion electrode (GDE) half-cells and zinc-air batteries (ZABs) assembled based on this catalyst exhibit excellent performance.

[0006] The preparation method of the present invention includes the following steps:

[0007] Manganese salt, acrylonitrile (AN), and 2,2-azobisisobutyronitrile (AIBN) were dispersed in acetone solvent in a predetermined ratio to obtain a precursor solution;

[0008] The precursor solution was subjected to photochemical polymerization under an inert atmosphere and irradiated with ultraviolet light. After the reaction was completed, the solution was filtered, washed, and dried to obtain Mn / PAN.

[0009] Mn / PAN is pre-oxidized to obtain Mn / PAN-O;

[0010] Mn / PAN-O was pyrolyzed under an inert atmosphere for a predetermined time to obtain MnO / Mn-NC catalyst.

[0011] In the above technical solution, under ultraviolet light irradiation, 2,2-azobisisobutyronitrile (AIBN) in the precursor solution decomposes and generates CN(CH3)2C· free radicals, which initiate the polymerization reaction of acrylonitrile (AN). During this process, some Mn in the solution... 2+ It coordinated with AN, and the uncoordinated Mn in the solution 2+ It undergoes photochemical reduction with acetone to produce Mn. 0 .

[0012] Subsequently, the synthesized Mn / PAN underwent a low-temperature pre-oxidation treatment, which helps to stabilize the material, prevent large-area structural collapse during high-temperature pyrolysis, and maintain a high specific surface area. During the high-temperature pyrolysis of Mn / PAN-O, Mn... 2+ The coordination structure with AN generates Mn-N x Active sites, photochemically reduced Mn 0 It is readily oxidized to MnO, and the two active substances synergistically catalyze each other, exhibiting excellent ORR performance.

[0013] According to one specific embodiment of the present invention, the pre-oxidation temperature is 130-330°C, the heating rate is 0.05-2°C / min, and the holding time is 1-3h.

[0014] According to one specific embodiment of the present invention, the pyrolysis temperature is 900-1100℃ and the holding time is 1-3h.

[0015] According to a specific embodiment of the present invention, the volume ratio of acrylonitrile to acetone in the precursor solution is 1:2 to 5, the volume-to-mass ratio of acrylonitrile to 2,2-azobisisobutyronitrile is 1:0.5 to 2, and the concentration of manganese is 0.1 to 0.35 g / L.

[0016] In the preparation method of the present invention, the manganese salt can be any one of manganese acetylacetonate, manganese acetate tetrahydrate, and manganese chloride tetrahydrate.

[0017] In the preparation method of the present invention, the wavelength of the ultraviolet light used in the photochemical polymerization reaction is 254 nm, and the ultraviolet light irradiation time is 1 to 3 h.

[0018] In the preparation method of the present invention, the photochemical polymerization product is filtered and washed sequentially with anhydrous ethanol and ultrapure water.

[0019] In the preparation method of the present invention, the precursor solution can be stirred before and during ultraviolet irradiation.

[0020] In the preparation method of the present invention, the inert atmosphere can be N2.

[0021] The second aspect of the present invention discloses the application of the MnO / Mn-NC catalyst obtained by the above preparation method in the ORR reaction.

[0022] In the preparation method disclosed in this invention, 2,2-azobisisobutyronitrile (AIBN) decomposes under ultraviolet light irradiation, generating CN(CH3)2C· free radicals, which act as initiators for AN polymerization. Since AN is difficult to polymerize under air conditions, a photochemical polymerization reaction needs to be carried out under an inert atmosphere. During this process, some Mn in the solution... 2+ It coordinated with AN, and the uncoordinated Mn in the solution 2+ It undergoes photochemical reduction with acetone to produce Mn. 0 .

[0023] Acetone serves two main purposes: firstly, it acts as a solvent for AN, enabling its polymerization into PAN with a high specific surface area; secondly, under ultraviolet light irradiation, acetone decomposes to generate free radicals, which in turn affect uncoordinated Mn. 2+ Photochemical reduction is performed.

[0024] Pre-oxidation treatment of the synthesized Mn / PAN can make the material more stable, prevent large-area structural collapse during pyrolysis, and help maintain a high specific surface area.

[0025] During pyrolysis, polyacrylonitrile (PAN) is carbonized into nitrogen-doped carbon (NC), and some Mn is also converted. 2+ Mn-N is generated by coordination with N in AN. xActive sites, photochemically reduced Mn 0 It is readily oxidized to MnO, and the synergistic catalysis of the two active substances results in the prepared MnO / Mn-NC catalyst exhibiting excellent ORR performance.

[0026] As detailed below, the MnO / Mn-NC catalyst prepared by the above method exhibits excellent catalytic activity, durability, and methanol tolerance in the ORR reaction. The fuel cell GDE half-cell and zinc-air battery ZABs assembled based on this catalyst both show excellent performance.

[0027] To more clearly illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0028] Figure 1 The images show the XRD patterns of the Mn / PAN, Mn / PAN-O, and MnO / Mn-NC catalysts prepared in Example 1 and the Mn-NC catalyst prepared in Comparative Example 3.

[0029] Figure 2 In the middle: a) XRD patterns of the Mn3O4 / PAN, Mn3O4 / PAN-O, and MnO / NC catalysts prepared in Comparative Example 2; b) XRD patterns of the PAN, PAN-O, and NC catalysts prepared in Comparative Example 1.

[0030] Figure 3 In the image: a is a SEM image of the PAN catalyst prepared in Comparative Example 1; b is a SEM image of the Mn / PAN catalyst prepared in Example 1; c is a SEM image of the Mn / PAN-O catalyst prepared in Example 1; d is a SEM image of the MnO / Mn-NC catalyst prepared in Example 1.

[0031] Figure 4 In the image: a is a TEM image of the MnO / Mn-NC catalyst prepared in Example 1; b is an HR-TEM image of the MnO / Mn-NC catalyst prepared in Example 1.

[0032] Figure 5 In the image: a is a TEM image of the MnO / Mn-NC catalyst prepared in Example 1 without MnO nanoparticles; b is a C element mapping image of the selected region a; c is a N element mapping image of the selected region a; d is a Mn element mapping image of the selected region a; e is a O element mapping image of the selected region a.

[0033] Figure 6In the image: a is the N1s XPS spectrum of the MnO / Mn-NC catalyst prepared in Example 1; b is the Mn 2p XPS spectrum of the MnO / Mn-NC catalyst prepared in Example 1.

[0034] Figure 7 The LSV curves are those of the MnO / Mn-NC catalyst prepared in Example 1, the NC catalyst prepared in Comparative Example 1, the MnO / NC catalyst prepared in Comparative Example 2, and the Mn-NC catalyst prepared in Comparative Example 3.

[0035] Figure 8 This is a comparison chart of the methanol resistance tests of the MnO / Mn-NC catalyst and the Pt / C catalyst prepared in Example 1.

[0036] Figure 9 This is a comparison chart of the stability tests of the MnO / Mn-NC catalyst and the Pt / C catalyst prepared in Example 1;

[0037] Figure 10 In the middle: a is the LSV curve of the MnO / Mn-NC catalyst and Pt / C catalyst prepared in Example 1 assembled into GDE-half cells respectively; b is the stability test curve of the MnO / Mn-NC catalyst and Pt / C catalyst prepared in Example 1 assembled into GDE-half cells respectively.

[0038] Figure 11 In the diagram: a is the open-circuit voltage diagram of the MnO / Mn-NC catalyst and the Pt / C+RuO2 catalyst-based ZABs prepared in Example 1; b is the power density curve of the MnO / Mn-NC catalyst and the Pt / C+RuO2 catalyst-based ZABs prepared in Example 1.

[0039] Figure 12 The graphs show the charge-discharge cycle stability of the MnO / Mn-NC catalyst and the Pt / C+RuO2 catalyst-based ZABs prepared in Example 1.

[0040] Figure 13 This is a flowchart of the preparation method of the present invention. Detailed Implementation

[0041] This invention provides a method for preparing a MnO / Mn-NC catalyst for the ORR reaction. The catalyst prepared by this method exhibits outstanding ORR activity and excellent stability. GDE half-cells and ZABs assembled based on this catalyst both demonstrate excellent performance. Figure 13 As shown, the preparation method of the present invention includes the following steps:

[0042] Manganese salt, acrylonitrile (AN), and 2,2-azobisisobutyronitrile (AIBN) are dispersed in acetone solvent at a predetermined ratio to obtain a precursor solution. The volume ratio of acrylonitrile to acetone in the precursor solution can be 1:2 to 5 (e.g., 1:3), the volume-to-mass ratio of acrylonitrile to 2,2-azobisisobutyronitrile can be 1:0.5 to 2 (e.g., 1:1), and the concentration of manganese can be 0.1 to 0.35 g / L (e.g., 0.25 g / L). The manganese salt can be any one of manganese acetylacetonate, manganese acetate tetrahydrate, and manganese chloride tetrahydrate, preferably manganese acetylacetonate.

[0043] The precursor solution was transferred to a quartz cup, N2 was bubbled into the cup to remove air, and the cup was sealed. The solution was then continuously stirred. The N2 bubbling time could be 2–5 min (e.g., 3 min), and the stirring rate could be 150–300 rad / min.

[0044] Photochemical polymerization was carried out by irradiating a solution in a quartz cup with ultraviolet light. After the reaction was completed, the solution was filtered, washed, and dried to obtain Mn / PAN. The wavelength of the ultraviolet light used in the photochemical polymerization reaction could be 254 nm, and the irradiation time could be 1–3 h. The photochemical polymerization product could be filtered and washed sequentially with anhydrous ethanol and ultrapure water. The drying temperature could be 50 °C, and the drying time could be 4–6 h.

[0045] Mn / PAN is transferred to a tube furnace for pre-oxidation to obtain Mn / PAN-O; wherein the pre-oxidation temperature can be 130-330℃ (e.g., 230℃), the heating rate is 0.05-2℃ / min (e.g., 0.1℃ / min), and the holding time can be 1-3h (e.g., 2h).

[0046] Mn / PAN-O is pyrolyzed under an inert atmosphere (e.g., N2) to obtain MnO / Mn-NC catalyst; wherein the pyrolysis temperature can be 900-1100℃ (e.g., 1000℃) and the holding time can be 1-3h (e.g., 2h).

[0047] The present invention will now be described in more detail with reference to specific embodiments and comparative examples.

[0048] Example 1: Preparation of MnO / Mn-NC catalyst

[0049] 23 mg of manganese acetylacetone, 5 mg of AIBN, and 5 mL of AN were added sequentially to 15 mL of acetone and ultrasonically dispersed to obtain a precursor solution.

[0050] The well-dispersed precursor solution was transferred to a quartz cup, air was purged from the quartz cup by passing N2 through it for 3 minutes, and the cup was sealed. Then, the mixture was stirred continuously at a stirring rate of 200 rad / min.

[0051] The precursor solution was irradiated with 254nm ultraviolet light for 2 hours to induce photochemical polymerization. After the reaction was completed, the solution was filtered and washed with anhydrous ethanol and ultrapure water, and dried at 50℃ for 5 hours to obtain Mn / PAN.

[0052] The Mn / PAN was transferred to a tube furnace and heated to 230°C at a heating rate of 0.1°C / min under an O2 atmosphere, and held at that temperature for 2 hours to obtain pre-oxidized Mn / PAN-O.

[0053] Mn / PAN-O was pyrolyzed at 1000℃ for 2 hours under N2 atmosphere to obtain MnO / Mn-NC catalyst.

[0054] Preparation of NC catalyst (Comparative Example 1)

[0055] The difference between Comparative Example 1 and Example 1 is that no manganese salt was added in Comparative Example 1. The specific steps are as follows:

[0056] 5 mg AIBN and 5 mL AN were added sequentially to 15 mL acetone and ultrasonically dispersed to obtain a precursor solution.

[0057] The well-dispersed precursor solution was transferred to a quartz cup, air was purged from the quartz cup by passing N2 through it for 3 minutes, and the cup was sealed. Then, the mixture was stirred continuously at a stirring rate of 200 rad / min.

[0058] The precursor solution was irradiated with 254nm ultraviolet light for 2 hours to induce photochemical polymerization. After the reaction was completed, the solution was filtered and washed with anhydrous ethanol and ultrapure water, and then dried at 50°C for 5 hours to obtain PAN.

[0059] PAN was transferred to a tube furnace and heated to 230°C at a heating rate of 0.1°C / min under an O2 atmosphere, and held at that temperature for 2 hours to obtain pre-oxidized PAN-O.

[0060] PAN-O was pyrolyzed at 1000℃ for 2 hours under N2 atmosphere to obtain NC catalyst.

[0061] Preparation of comparative 2MnO / NC catalyst

[0062] The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 uses a two-step method. First, Mn3O4 and PAN are synthesized separately, and then both are loaded and subjected to pre-oxidation and pyrolysis. The specific steps are as follows:

[0063] 23 mg of acetylacetone was dissolved in 15 mL of acetone and photochemically reduced by irradiation with 254 nm ultraviolet light for 55 min to obtain Mn3O4.

[0064] PAN was prepared according to the method in Comparative Example 1;

[0065] Mn3O4 and PAN were dispersed in anhydrous ethanol, respectively, and then loaded and stirred for 4 h. After filtration, washing, and drying at 50 °C for 5 h, Mn3O4 / PAN was obtained.

[0066] Mn3O4 / PAN was transferred to a tube furnace and heated to 230℃ at a heating rate of 0.1℃ / min under an O2 atmosphere, and held for 2 hours to obtain pre-oxidized Mn3O4 / PAN-O.

[0067] Mn3O4 / PAN-O was pyrolyzed at 1000℃ for 2 hours under N2 atmosphere to obtain MnO / NC catalyst.

[0068] Preparation of comparative 3Mn-NC catalyst

[0069] The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 subjected the MnO / Mn-NC obtained in Example 1 to acid washing to remove MnO particles. The specific steps are as follows:

[0070] 23 mg of manganese acetylacetone, 5 mg of AIBN, and 5 mL of AN were added sequentially to 15 mL of acetone and ultrasonically dispersed to obtain a precursor solution.

[0071] The well-dispersed precursor solution was transferred to a quartz cup, air was purged from the quartz cup by passing N2 through it for 3 minutes, and the cup was sealed. Then, the mixture was stirred continuously at a stirring rate of 200 rad / min.

[0072] The precursor solution was irradiated with 254nm ultraviolet light for 2 hours to induce photochemical polymerization. After the reaction was completed, the solution was filtered and washed with anhydrous ethanol and ultrapure water, and dried at 50℃ for 5 hours to obtain Mn / PAN.

[0073] The Mn / PAN was transferred to a tube furnace and heated to 230°C at a heating rate of 0.1°C / min under an O2 atmosphere, and held at that temperature for 2 hours to obtain pre-oxidized Mn / PAN-O.

[0074] Mn / PAN-O was pyrolyzed at 1000℃ for 2 hours under N2 atmosphere to obtain MnO / Mn-NC catalyst.

[0075] MnO / Mn-NC was added to 0.5M H2SO4 and kept at 80℃ for 12h to obtain the Mn-NC catalyst.

[0076] Morphology and phase analysis of the examples and comparative examples

[0077] Figure 1The figures show the XRD patterns of the Mn / PAN, Mn / PAN-O, and MnO / Mn-NC catalysts prepared in Example 1, and the Mn-NC catalyst prepared in Comparative Example 3. The figures show that the diffraction peaks at 17.1° and 28.4° for Mn / PAN are characteristic peaks of PAN. After pre-oxidation treatment, the characteristic peaks of PAN gradually transform into carbon peaks. After pyrolysis at 1000°C, the carbon peaks of Mn / PAN-O are significantly enhanced. Meanwhile, the diffraction peaks at 34.9°, 40.5°, 58.7°, 70.1°, 73.7°, and 87.7° correspond well to the (111), (200), (220), (311), (222), and (400) crystal planes of MnO (PDF#07-0230), indicating that MnO was generated during the carbonization process. The Mn-NC obtained after acid washing of MnO / Mn-NC has only two obvious carbon peaks, while the characteristic peaks of MnO have disappeared, indicating that MnO has been successfully removed.

[0078] Figure 2 b is the XRD pattern of the PAN, PAN-O, and NC catalysts prepared in Comparative Example 1. As can be seen from the figure, pure PAN has a strong characteristic peak, which gradually transforms into a carbon peak after pre-oxidation. Finally, after high-temperature pyrolysis at 1000℃, NC shows two obvious carbon peaks, with no other diffraction peaks. Figure 2 XRD patterns of the Mn3O4 / PAN, Mn3O4 / PAN-O, and MnO / NC catalysts prepared in Comparative Example 2 are shown in Figure a. The characteristic peaks of Mn3O4 are difficult to observe in Mn3O4 / PAN. This is mainly due to the poor crystallinity of photochemically synthesized Mn3O4 and its very low content compared to PAN. Furthermore, since no Mn salt was added during the polymerization of AN, pure PAN was synthesized, resulting in stronger characteristic peaks for PAN. The characteristic peaks of PAN in Mn3O4 / PAN-O gradually disappeared after pre-oxidation. After pyrolysis at 1000℃, the diffraction peaks of MnO / NC at 34.9°, 40.5°, 58.7°, and 70.1° correspond well to the PDF card of MnO, indicating the transformation of Mn3O4 into MnO.

[0079] Figure 3 a, 3b, 3c, and 3d are SEM images of the PAN prepared in Comparative Example 1 and the Mn / PAN, Mn / PAN-O, and MnO / Mn-NC catalysts prepared in Example 1. Figure 3 Many small nanospheres in a form combine to form a large PAN nanosphere, and there are obvious pores between these PAN nanospheres. Observation of the morphology of Mn / PAN reveals that... Figure 3Compared to pure PAN, the distribution of nanospheres in Mn / PAN is more irregular. Furthermore, the mass of Mn / PAN collected after the reaction was lower than that of pure PAN, indicating that the addition of Mn salt significantly affects the morphology and polymerization of PAN. During the low-temperature pre-oxidation process at 230℃, the morphology of Mn / PAN-O did not change significantly, maintaining its original structure. SEM images of MnO / Mn-NC show that after pyrolysis at 1000℃, the PAN structure inevitably collapsed somewhat, transforming into nitrogen-doped carbon (NC), and its conductivity improved significantly. However, no obvious MnO nanoparticles were observed in the images, possibly due to the low quantity of MnO or its encapsulation by NC.

[0080] Figure 4 a and 4b are TEM and HR-TEM images of the MnO / Mn-NC catalyst prepared in Example 1, respectively. Figure 4 As can be seen from this, cubic MnO exists on the carbon support, but in small quantities. HR-TEM characterization of other regions of MnO / Mn-NC revealed no metal nanoparticles.

[0081] Figure 5 a, 5b, 5c, 5d, and 5e are TEM images of the MnO / Mn-NC catalyst without MnO nanoparticles prepared in Example 1 and the corresponding mapping images of C, N, Mn, and O elements. It can be seen from the images that the four elements C, N, Mn, and O are all relatively uniformly distributed, with the content of Mn element being relatively low.

[0082] Figure 6 a and 6b are the XPS spectra of N1s and Mn 2p of the MnO / Mn-NC catalyst prepared in Example 1. Figure 6 The five diffraction peaks appearing in a can be attributed to pyridine nitrogen (398.5 eV), Mn-N, and so on. x (399.5 eV), pyrrole nitrogen (400.3 eV), graphitic nitrogen (401.4 eV), and nitrogen oxides (403.5 eV). Figure 6 The two characteristic peaks in b can be attributed to Mn. 2+ The values ​​(641.5 eV, 652.9 eV) indicate the presence of MnO in the catalyst. XPS results show that the catalyst contains Mn-N... x Both MnO and MnO are active species that coexist.

[0083] Catalytic performance testing

[0084] ORR test conditions: The test was conducted using a three-electrode system in an O2-saturated 0.1M KOH solution; the reference electrode was an Ag / AgCl electrode, the counter electrode was a platinum electrode, and the rotating disk electrode (RDE) was the working electrode. Figure 7-10 All potentials in the diagram are the converted standard hydrogen electrode potentials.

[0085] GDE half-cell test conditions: GDE was used as the working electrode, Ag / AgCl as the reference electrode, and a Pt mesh connected by a carbon rod as the counter electrode. The electrolyte was 1M KOH. The test was conducted using an LSV program at 10 mV / s in the range of 0-1.3V (vs. RHE). -1 The LSV polarization curve was obtained by scanning at a specific speed. Then, the stability of the half-cell was tested using the chronoamperometry (it) method, with an initial potential of 100 mA and an LSV curve of 100 cm⁻¹. -2 The potential corresponding to the time.

[0086] ZABs testing conditions: The cathode consists of hydrophilic carbon paper, a gas diffusion layer, and nickel foam, with the catalyst dropped onto the carbon paper as the catalyst layer. The anode is a polished zinc sheet, and the electrolyte is a 0.2M Zn(CH3COO)2 + 6M KOH mixed solution. Both current and power density are normalized to the effective surface area of ​​the air cathode.

[0087] Figure 7 The LSV curves are for the MnO / Mn-NC catalyst prepared in Example 1, the NC catalyst prepared in Comparative Example 1, the MnO / NC catalyst prepared in Comparative Example 2, and the Mn-NC catalyst prepared in Comparative Example 3. The half-wave potentials of MnO / Mn-NC, MnO / NC, NC, and Mn-NC are 0.836V, 0.796V, 0.759V, and 0.787V, respectively. The EV of MnO / Mn-NC is... 1 / 2 The limiting current density is slightly higher than that of Pt / C (0.840). Furthermore, based on the above data, the synthesized NC exhibits some ORR activity, but it still lags significantly behind Pt / C, indicating a lower number of active sites. Compared to NC, MnO / NC shows a significant increase in both onset potential and half-wave potential, while the limiting current density decreases somewhat. This is mainly attributed to the introduction of MnO, which increases the number of active centers and reduces the catalyst's conductivity. MnO / Mn-NC exhibits ORR performance comparable to Pt / C, while the half-wave potential of Mn-NC obtained after acid washing of MnO / Mn-NC is significantly lower, but still better than that of NC. This may be because some Mn-N remains after MnO removal. x Site. Therefore, the excellent ORR activity of MnO / Mn-NC may be due to the interaction of AN and Mn. 2+Coordination occurred during the polymerization process, and Mn-N was obtained after pre-oxidation and carbonization. x Site, and uncoordinated Mn 2+ MnO was formed, and these two active substances worked synergistically to improve ORR performance.

[0088] Figure 8 This is a comparison of the methanol tolerance tests of the MnO / Mn-NC catalyst and the Pt / C catalyst prepared in Example 1. When methanol was injected into the electrolyte at 200 s, the current density of MnO / Mn-NC fluctuated slightly, but returned to its initial state after several tens of seconds, indicating its excellent methanol tolerance. In contrast, the current of Pt / C showed a significant abrupt change after the addition of methanol during the test, jumping into the positive current range. This is likely due to a chemical reaction between Pt / C and methanol, demonstrating its poor methanol tolerance.

[0089] Figure 9 This is a comparison chart of the stability tests of the MnO / Mn-NC catalyst and the Pt / C catalyst prepared in Example 1. The chart shows that after 20,000 s of chronoamperometry testing, MnO / Mn-NC maintained 83.5% of its initial current density, while the current density of Pt / C decreased to 84.1%. This indicates that MnO / Mn-NC has comparable durability to Pt / C.

[0090] Figure 10 a and 10b are the LSV curves and stability test curves of the MnO / Mn-NC catalyst and Pt / C catalyst prepared in Example 1, respectively, assembled into GDE-half cells. Figure 10 It can be observed that after IR compensation, the onset potential of MnO / Mn-NC is close to that of Pt / C, while at 250 mA cm⁻¹... -2 At high current densities, the overpotential of MnO / Mn-NC is 138 mV lower than that of Pt / C, exhibiting superior catalytic performance. Furthermore, from... Figure 10 As observed in Figure a, after 24 hours of testing, the MnO / Mn-NC cell maintained 80.2% of its initial current with a relatively small current decay, while the Pt / C cell's current decreased to 59.3%, showing a rapid decline. This indicates that the GDE half-cell assembled with MnO / Mn-NC exhibits excellent stability.

[0091] Figure 11 a and 11b are the open-circuit voltage and power density curves of the MnO / Mn-NC catalyst and the Pt / C+RuO2 catalyst-based ZABs prepared in Example 1. Figure 11The open-circuit voltage of MnO / Mn-NC-based ZABs can be maintained at 1.46V, significantly higher than that of Pt / C+RuO2-based ZABs (1.40V). (This is based on...) Figure 11 b indicates that the ZABs assembled from MnO / Mn-NC can reach 150mW cm⁻¹. -2 The peak power density is higher than that of Pt / C+RuO2-based ZABs (120 mW cm⁻¹). -2 The current density must be higher than 75 mA / cm². Furthermore, when the current density is greater than 75 mA / cm²... -2 At that time, MnO / Mn-NC based ZABs have a higher discharge voltage.

[0092] Figure 12 This is a charge-discharge cycle stability diagram of the MnO / Mn-NC catalyst and the Pt / C+RuO2 catalyst-based ZABs prepared in Example 1. Figure 12 It can be seen that the voltage of the MnO / Mn-NC assembled ZABs did not show significant decay after 53 hours of charge-discharge testing, while the voltage of the Pt / C+RuO2-based ZABs gradually began to decay after 25 hours of cycling testing. This indicates that the MnO / Mn-NC-based ZABs have superior long-term charge-discharge stability.

[0093] The commercial Pt / C catalyst used in this invention for comparison was purchased from Johnson Matthey. The commercial RuO2 catalyst was purchased from Suzhou Shengernuo Technology Co., Ltd.

[0094] Although the present invention has been described above through specific embodiments, it should be understood that any equivalent improvements made by those skilled in the art in accordance with the present invention without departing from the scope of the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a MnO / Mn-NC catalyst for ORR reaction, characterized in that... Includes the following steps: Manganese salt, acrylonitrile (AN), and 2,2-azobisisobutyronitrile (AIBN) were dispersed in acetone solvent in a predetermined ratio to obtain a precursor solution; The precursor solution was subjected to photochemical polymerization under an inert atmosphere and irradiated with ultraviolet light. After the reaction was completed, the solution was filtered, washed, and dried to obtain Mn / PAN. The wavelength of the ultraviolet light used in the photochemical polymerization reaction was 254 nm, and the irradiation time was 1 to 3 h. The Mn / PAN is pre-oxidized to obtain Mn / PAN-O; wherein the pre-oxidation temperature is 130-330℃, the heating rate is 0.05-2℃ / min, and the holding time is 1-3h. The Mn / PAN-O catalyst is obtained by pyrolysis under an inert atmosphere; wherein the pyrolysis temperature is 900-1100℃ and the holding time is 1-3h.

2. The preparation method according to claim 1, characterized in that: The precursor solution contains acrylonitrile to acetone in a volume ratio of 1:2 to 5, acrylonitrile to 2,2-azobisisobutyronitrile in a volume-to-mass ratio of 1:0.5 to 2, and manganese in a concentration of 0.1 to 0.35 g / L.

3. The preparation method according to claim 1, characterized in that: The manganese salt is any one of manganese acetylacetonate, manganese acetate tetrahydrate, and manganese chloride tetrahydrate.

4. The preparation method according to claim 1, characterized in that: The photochemical polymerization product was filtered and washed sequentially with anhydrous ethanol and ultrapure water.

5. The preparation method according to claim 1, characterized in that: The precursor solution is stirred before and during ultraviolet irradiation.

6. The preparation method according to claim 1, characterized in that: The inert atmosphere is N2.

7. The application of the MnO / Mn-NC catalyst obtained by any one of claims 1-6 in the ORR reaction.

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