NbN nanoparticle composite FeNC catalyst, and preparation method and application thereof

Abstract

This invention relates to an NbN nanoparticle composite FeNC catalyst, its preparation method, and its application. It addresses the problems of single-site concentration and poor catalytic activity in existing FeNC-based ORR catalysts. The catalyst consists of Fe single atoms and NbN nanoparticles supported on a nitrogen-doped carbon support. The nitrogen-doped carbon support has a dodecahedral shape of 100-200 nm, the NbN nanoparticles have a particle size of 5-10 nm, and the Fe is a single-atom Fe-N4 configuration. The preparation method includes: 1. Preparing a ZIF-8 precursor; 2. Adding an additional nitrogen source to the ZIF-8 precursor and pyrolyzing it to prepare NC. N ; 3. To NC N The catalyst was obtained by adding Fe and Nb salts to the dispersion, followed by vacuum drying and pyrolysis. When used in fuel cells, it achieved a peak power density of 1120 mW / cm² under hydrogen-oxygen and hydrogen-air conditions. 2 662 mW / cm 2 It can be used in the field of proton exchange membrane fuel cells.

Description

Technical Field

[0001] This invention belongs to the field of preparation and application of electrocatalysts, specifically relating to a method for preparing and applying an NbN nanoparticle composite FeNC catalyst. Background Technology

[0002] In the face of increasingly serious energy and environmental problems worldwide, developing green, clean, and novel energy conversion devices is of great significance for achieving sustainable development and dual-carbon goals. Proton exchange membrane fuel cells (PEMFCs), as a chemical-to-electrical energy conversion device with great application potential, suffer from a slow-kinetic oxygen reduction reaction (ORR) at the cathode, which limits their overall performance. Although noble metal platinum-based ORR catalysts exhibit excellent performance, their high cost and resource scarcity restrict their large-scale commercial application. Therefore, there is a need to develop inexpensive and abundant non-noble metal alternatives.

[0003] Among non-noble metal-based ORR electrocatalysts, iron-doped carbon (FeNC) materials have attracted much attention due to their excellent ORR activity. Currently, FeNC catalysts mainly focus on the synthesis of single-atom material systems, including high-load single-atom materials or heteroatom-modified single-atom materials. However, the preparation methods for these materials are often complex. For example, the loading of high-density single-atom active sites usually relies on processes such as hierarchical anchoring, increasing the complexity of synthesis. Furthermore, single active sites are easily constrained by linear relationships, limiting catalytic efficiency, and ORR performance needs further improvement. Introducing nanoparticles and single-atom sites into FeNC catalysts to construct composite structures is one approach to improve existing catalyst systems and enhance catalytic activity. However, in this area, existing research mainly focuses on single-atom and nanoparticle composite structures of single metal systems, such as Fe single atoms and iron species nanoparticles, with insufficient research on composite catalytic systems of other elements and metal nitride nanoparticles. Summary of the Invention

[0004] This invention aims to address the problems of single catalytic sites and insufficient catalytic activity in existing FeNC-based ORR catalysts, and provides a FeNC catalyst composed of NbN nanoparticles, its preparation method, and its applications. This invention involves adding Fe salts and Nb salts to a nitrogen-doped porous carbon material derived from a ZIF-8 composite additional N source, followed by pyrolysis to obtain FeNbNC catalysts with a single-atom Fe-N4 structure and NbN nanoparticles supported on the nitrogen-doped carbon material. N The composite catalyst exhibits higher activity and stability than FeNC catalysts without NbN particles. N catalyst.

[0005] The NbN nanoparticle composite FeNC catalyst of this invention comprises Fe single atoms and NbN nanoparticles supported on a nitrogen-doped carbon support. The nitrogen-doped carbon support has a dodecahedral shape of 100-200 nm, the NbN nanoparticles have a particle size of 5-10 nm, and the Fe is in a single-atom Fe-N4 configuration. This catalyst is denoted as FeNbNC. N Composite catalyst.

[0006] The preparation method of the above-mentioned NbN nanoparticle composite FeNC catalyst is carried out according to the following steps:

[0007] I. Preparation of ZIF-8 precursor: First, 2-methylimidazole was dissolved in methanol to obtain solution A; then zinc nitrate hexahydrate was dissolved in methanol to obtain solution B; solution B was poured into solution A, stirred at room temperature for 8-12 h, then centrifuged, and the solid phase was washed with methanol and dried under vacuum to obtain ZIF-8 precursor;

[0008] II. Preparation of Nitrogen-Doped Porous Carbon Materials: The ZIF-8 precursor and the additional nitrogen source were dispersed in a mixed solution of water and ethanol at a mass ratio of (3-5):1. The solution was ultrasonically stirred until homogeneous, then vacuum dried for 10-15 h to obtain a white powder. The white powder was then ground and placed in a tube furnace. Under an inert atmosphere, the temperature was increased to 880-920℃ at a heating rate of 4-6℃ / min and held for 2-3 h for pyrolysis. After cooling, a black powder, denoted as NC, was obtained. N The additional nitrogen source is imidazo[1,2-f]phenanthridine, pyrazine, or o-phenanthroline.

[0009] III. FeNbNC N Preparation of composite catalyst: NC N The solution was added to ethanol and ultrasonically mixed to obtain a dispersion. Then, ethanol solutions of iron salt and niobium salt were added dropwise to the dispersion, and the mixture was stirred at room temperature for 20–24 h. Following this, it was vacuum dried for 10–12 h to obtain a powder. The powder was ground and placed in a tube furnace, where it was pyrolyzed at a heating rate of 4–6 °C / min to 880–920 °C for 2–3 h under an inert atmosphere. After cooling, the NbN nanoparticle composite FeNC catalyst was obtained, denoted as FeNbNC. N Composite catalyst.

[0010] Furthermore, the molar ratio of 2-methylimidazole to zinc nitrate hexahydrate mentioned in step one is (3~5):1.

[0011] Furthermore, in the water and ethanol mixed solution described in step two, the volume ratio of water to ethanol is 1:(1.5~2.5).

[0012] Furthermore, the iron salt mentioned in step three is ferric chloride hexahydrate, and the niobium salt is niobium pentachloride.

[0013] Furthermore, the NC in the dispersion described in step three N The mass concentration is 3~4 mg / ml.

[0014] Furthermore, the concentration of the ethanol solution of the iron salt in step three is 8-9 mg / ml, and the concentration of the ethanol solution of the niobium salt is 4.5-5.5 mg / ml.

[0015] Furthermore, the iron salt and NC mentioned in step three N The mass ratio is (0.1~0.2):1.

[0016] Furthermore, the molar ratio of niobium salt to iron salt in step three is (0.3~1.5):1.

[0017] Furthermore, the drying temperature in step one is 70°C, and the drying time is 6 hours;

[0018] Furthermore, the drying temperature in step two is 80°C, and the drying time is 15 hours.

[0019] Furthermore, the drying temperature in step three is 60°C, and the drying time is 12 hours.

[0020] Furthermore, the inert atmosphere described in steps two and three is Ar.

[0021] The application of the aforementioned NbN nanoparticle composite FeNC catalyst is to use it in the cathode oxygen reduction reaction of a proton exchange membrane fuel cell.

[0022] The advantages of this invention over the prior art are as follows:

[0023] (1) This invention introduces NbN nanoparticles into FeNC, and the two have a synergistic effect in the acidic oxygen reduction reaction. NbN nanoparticles themselves do not possess ORR activity, but Nb forms an electron transport network through N and C atoms, generating a strong interaction with the Fe active center. This reduces the oxidation state and d-band center of Fe, affecting its adsorption degree for ORR intermediates, ultimately promoting the ORR reaction kinetics of Fe-N4 single-atom active sites and improving the electrocatalytic oxygen reduction activity of the catalyst. Specifically, this manifests as the addition of NbN to FeNbNC... N The composite catalyst exhibits a higher half-wave potential, a lower Tafel slope, and a higher kinetic current density in acidic electrolytes.

[0024] (2) This invention adds an additional nitrogen source (imidazo[1,2-f]phenanthridine, pyrazine, o-phenanthroline) to the ZIF-8 precursor to form high-density Fe single atoms (the mass fraction of Fe was 3.6 wt% as measured by inductively coupled plasma (ICP)) and provides sufficient nitrogen to form NbN particles, without the need to use ammonia to form nitrides, thus reducing the risk of synthesis.

[0025] (3) The NbN nanoparticle composite FeNC catalyst of the present invention, when used in a fuel cell, achieves a peak power density of 1120 mW / cm² under hydrogen-oxygen testing conditions. 2 The highest peak power density under hydrogen-air testing conditions reached 662 mW / cm². 2 They are FeNC N The catalyst strength is 1.5 times and 1.6 times that of conventional catalysts. It can be used in the field of proton exchange membrane fuel cells. Attached Figure Description

[0026] Figure 1 It is the FeNbNC prepared in Example 1 N High-resolution transmission electron microscopy (STEM) image of the composite catalyst;

[0027] Figure 2 It is the FeNbNC prepared in Example 1 N Elemental mapping diagram of composite catalysts;

[0028] Figure 3 FeNC prepared in Comparative Example 1 N High-resolution transmission electron microscopy (STEM) image of the catalyst;

[0029] Figure 4 FeNC prepared in Comparative Example 1 N Elemental mapping of the catalyst;

[0030] Figure 5 It is the FeNbNC prepared in Example 1 N Composite catalyst, FeNC prepared in Comparative Example 1 N Aberration-corrected electron micrograph of the catalyst;

[0031] Figure 6 It is the FeNbNC prepared in Example 1 N Composite catalyst, FeNC prepared in Comparative Example 1 N Catalyst, NbNC prepared in Comparative Example 2 N XRD patterns of the catalyst and the FeNbNC catalyst prepared in Comparative Example 3;

[0032] Figure 7 It is the FeNbNC prepared in Example 1 N Composite catalyst, NCN FeNC prepared in Comparative Example 1 N Raman spectra of NC prepared with catalyst and Comparative Example 3;

[0033] Figure 8 It is the FeNbNC prepared in Example 1 N Composite catalyst, FeNC prepared in Comparative Example 1 N XPS plot of the catalyst;

[0034] Figure 9 It is the FeNbNC prepared in Example 1 N Composite catalyst, FeNC prepared in Comparative Example 1 N Schematic diagram of catalyst structure;

[0035] Figure 10 It is the FeNbNC prepared in Example 1 N Composite catalyst, FeNC prepared in Comparative Example 1 N Catalyst, NbNC prepared in Comparative Example 2 N ORR polarization curve of the catalyst;

[0036] Figure 11 It is the FeNbNC prepared in Example 1 N Composite catalyst, FeNC prepared in Comparative Example 1 N Comparison of Tafel slope and kinetic current density of catalysts;

[0037] Figure 12 It is the FeNbNC prepared in Example 1 N Composite catalyst, FeNC prepared in Comparative Example 1 N ORR polarization curves of the catalyst before and after accelerated aging test (ADT) in O2-saturated 0.1 M HClO4 solution at potential ranges of 0.6–0.95 V vs. RHE.

[0038] Figure 13 It is the FeNbNC prepared in Example 1 N Composite catalyst, FeNbNC prepared in Comparative Example 4 DCD ORR polarization curve of the catalyst;

[0039] Figure 14 It is the FeNbNC prepared in Example 1 N Composite catalyst, FeNbNC prepared in Comparative Example 5 N ORR polarization curves and XRD patterns of the -nv catalyst;

[0040] Figure 15 It is the FeNbNC prepared in Example 1 N Composite catalyst, FeNC prepared in Comparative Example 1N Performance diagram of catalyst in fuel cell. Detailed Implementation

[0041] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0042] Example 1: The preparation method of the NbN nanoparticle composite FeNC catalyst in this example is carried out according to the following steps:

[0043] I. Preparation of ZIF-8 precursor: First, 3.24 g of 2-methylimidazole was dissolved in 100 ml of methanol to obtain solution A; then, 2.94 g of zinc nitrate hexahydrate was dissolved in 50 ml of methanol to obtain solution B; solution B was poured into solution A, stirred at room temperature for 12 h, then centrifuged, and the solid phase was washed three times with methanol by centrifugation, and then vacuum dried at 70℃ for 6 h to obtain ZIF-8 precursor;

[0044] II. Preparation of Nitrogen-Doped Porous Carbon Materials: 0.5 g of ZIF-8 precursor and 0.125 g of o-phenanthroline were dispersed in a solution composed of 15 ml of water and 30 ml of ethanol. The solution was ultrasonically stirred until homogeneous, and then vacuum dried at 80 °C for 15 h to obtain a white powder. The white powder was ground and placed in a tube furnace for pyrolysis at a heating rate of 5 °C / min under an Ar atmosphere, and held at 900 °C for 2 h. After cooling, a black powder, denoted as NC, was obtained. N ;

[0045] III. FeNbNC N Preparation of composite catalyst: 36 mg of NC N The solution was added to 10 ml of ethanol and ultrasonically mixed to obtain a dispersion. Then, 700 μl of an ethanol solution of iron salt and 700 μl of an ethanol solution of niobium salt were added dropwise to the dispersion, and the mixture was stirred at room temperature for 24 h. The ethanol solution of iron salt was prepared by dissolving 16.7 mg of ferric chloride hexahydrate in 2 ml of ethanol; the ethanol solution of niobium salt was prepared by dissolving 10 mg of niobium pentachloride in 2 ml of ethanol. The mixture was then vacuum dried at 60 °C for 12 h to obtain a powder. The powder was ground and placed in a tube furnace, where it was pyrolyzed at 900 °C for 2 h under an Ar atmosphere at a heating rate of 5 °C / min. After cooling, the NbN nanoparticle composite FeNC catalyst, denoted as FeNbNC, was obtained. N Composite catalyst.

[0046] FeNbNC obtained in Example 1N High-resolution transmission electron microscopy (STEM) image of the composite catalyst is shown below. Figure 1 As shown; from Figure 1 It can be seen that FeNbNC N The composite catalyst has a dodecahedral shape with a particle size of approximately 100-200 nm, and the carbon support is amorphous with nanoparticles supported on it having a particle size of approximately 5-10 nm. Figure 1 (ab); lattice spacing measurements of nanoparticles were performed, and the results were consistent with the (111) crystal plane of NbN (ab); Figure 1 (c) confirmed the successful loading of NbN nanoparticles on FeNC.

[0047] FeNbNC obtained in Example 1 N Elemental mapping image of composite catalyst as follows Figure 2 As shown; FeNbNC N The uniform distribution of Fe, N, and C elements in the composite catalyst, without particle aggregation, indicates that Fe did not agglomerate, confirming the successful synthesis of single-atom FeNC materials; and the mapping pattern of Nb elements on it matches the shape of nanoparticles, confirming the presence of NbN particles.

[0048] Comparative Example 1: Preparation of FeNC in this Example N The catalyst is prepared using the following specific method:

[0049] I. Preparation of ZIF-8 precursor: First, 3.24 g of 2-methylimidazole was dissolved in 100 ml of methanol to obtain solution A; then, 2.94 g of zinc nitrate hexahydrate was dissolved in 50 ml of methanol to obtain solution B; solution B was poured into solution A, stirred at room temperature for 12 h, then washed with methanol and centrifuged three times. The precipitate was dried under vacuum at 70 °C for 6 h to obtain the ZIF-8 precursor.

[0050] II. NC N Preparation: 0.5 g of ZIF-8 precursor and 0.125 g of o-phenanthroline were dispersed in a solution composed of 15 ml of water and 30 ml of ethanol. The solution was ultrasonically stirred until homogeneous, and then dried under vacuum at 80 °C for 15 h. The dried white powder was ground and placed in a tube furnace, where it was pyrolyzed at 900 °C for 2 h under an Ar atmosphere at a heating rate of 5 °C / min. After cooling, a black powder was obtained, denoted as NC. N ;

[0051] III. FeNC N Catalyst preparation: 36 mg NC NThe iron salt was ultrasonically mixed with 10 ml of ethanol for 1 h, and then 700 μl of an ethanol solution of iron salt was added dropwise while stirring at room temperature for 24 h. The ethanol solution of iron salt was prepared by dissolving 16.7 mg of ferric chloride hexahydrate in 2 ml of ethanol. The mixture was then vacuum dried at 60 °C for 12 h. The resulting powder was ground and placed in a tube furnace, where it was pyrolyzed at 900 °C for 2 h under an Ar atmosphere at a rate of 5 °C / min. After cooling, FeNC was obtained. N catalyst.

[0052] FeNC prepared in Comparative Example 1 N STEM image of the catalyst as follows Figure 3 As shown; FeNC N The catalyst is in the shape of a regular dodecahedron with a particle size of about 100~200nm, and the carbon support is in an amorphous form with no particle aggregation, indicating that no nanoparticle species were formed.

[0053] FeNC prepared in Comparative Example 1 N Elemental mapping image of the catalyst as follows Figure 4 As shown; FeNC N The uniform distribution of Fe, N, and C elements in the catalyst, without particle aggregation, indicates that Fe did not agglomerate, proving the successful synthesis of single-atom FeNC materials.

[0054] Comparative Example 2: This comparative example is for the preparation of NbNC N The catalyst is prepared using the following specific method:

[0055] I. Preparation of ZIF-8 precursor: First, 3.24 g of 2-methylimidazole was dissolved in 100 ml of methanol to obtain solution A; then, 2.94 g of zinc nitrate hexahydrate was dissolved in 50 ml of methanol to obtain solution B; solution B was poured into solution A, stirred at room temperature for 12 h, then washed with methanol and centrifuged three times, and the precipitate was dried under vacuum at 70 °C for 6 h to obtain ZIF-8 precursor;

[0056] II. NC N Preparation: 0.5 g of ZIF-8 precursor and 0.125 g of o-phenanthroline were dispersed in a solution composed of 15 ml of water and 30 ml of ethanol. The solution was ultrasonically stirred until homogeneous, and then dried under vacuum at 80 °C for 15 h. The dried white powder was ground and placed in a tube furnace, where it was pyrolyzed at 900 °C for 2 h under an Ar atmosphere at a heating rate of 5 °C / min. After cooling, a black powder was obtained, denoted as NC. N ;

[0057] III. NbNC N Catalyst preparation: 36 mg NC NThe niobium salt was ultrasonically mixed with 10 ml of ethanol for 1 h, and then 700 μl of an ethanol solution of niobium salt was added dropwise while stirring at room temperature for 24 h. The ethanol solution of niobium salt was obtained by dissolving 10 mg of niobium pentachloride in 2 ml of ethanol. The mixture was then vacuum dried at 60 °C for 12 h. The resulting powder was ground and placed in a tube furnace, where it was pyrolyzed at 900 °C for 2 h under an Ar atmosphere at a rate of 5 °C / min. After cooling, NbNC was obtained. N catalyst.

[0058] Comparative Example 3: In this example, FeNbNC catalyst was prepared without adding an additional nitrogen source. The specific preparation method is as follows:

[0059] I. Preparation of ZIF-8 precursor: First, 3.24 g of 2-methylimidazole was dissolved in 100 ml of methanol to obtain solution A; then, 2.94 g of zinc nitrate hexahydrate was dissolved in 50 ml of methanol to obtain solution B; solution B was poured into solution A, stirred at room temperature for 12 h, then washed with methanol and centrifuged 3 times, and the precipitate was dried under vacuum at 70 °C for 6 h to obtain ZIF-8 precursor;

[0060] II. Preparation of NC: The synthesized white ZIF-8 powder was ground and placed in a tube furnace. Under an Ar atmosphere, it was heated to 900℃ at 5℃ / min for 2 h and then cooled to obtain a black powder, which was denoted as NC.

[0061] III. Preparation of FeNbNC catalyst: 36 mg NC was ultrasonically mixed with 10 ml ethanol for 1 h, and then 700 μl of an ethanol solution of iron salt (16.7 mg ferric chloride hexahydrate dissolved in 2 ml ethanol) and 700 μl of an ethanol solution of niobium salt were added dropwise, and the mixture was stirred at room temperature for 24 h. The ethanol solution of iron salt was prepared by dissolving 16.7 mg ferric chloride hexahydrate in 2 ml ethanol, and the ethanol solution of niobium salt was prepared by dissolving 10 mg niobium pentachloride in 2 ml ethanol. The mixture was then vacuum dried at 60 °C for 12 h. The resulting powder was ground and placed in a tube furnace, and pyrolyzed at 900 °C for 2 h under an Ar atmosphere at a rate of 5 °C / min. After cooling, the FeNbNC catalyst was obtained.

[0062] FeNbNC prepared in Example 1 N Composite catalyst and FeNC prepared in Comparative Example 1 N Aberration-corrected electron micrograph of the catalyst, as shown Figure 5 As shown, spherical aberration electron microscopy can improve resolution and identify single-atom structures by correcting spherical aberration. Because metals have higher conductivity, there is a contrast difference in electron micrographs; metal single atoms or nanoparticles are brighter than nitrogen-doped carbon supports. Figure 5 As shown in a, in FeNbNC NNbN nanoparticles with a lattice spacing of (200) crystal plane can be seen on the composite catalyst, surrounded by Fe single-atom bright spots (circled in cyan), while Figure 5 b shows FeNC N Only single-atom bright spots of Fe were observed on the catalyst (circled in cyan). This result further confirms the effectiveness of the FeNbNC catalyst prepared in Example 1. N Composite catalyst and FeNC prepared in Comparative Example 1 N Successful synthesis of the catalyst.

[0063] FeNbNC prepared in Example 1 N Composite catalyst, FeNC prepared in Comparative Example 1 N Catalyst, NbNC prepared in Comparative Example 2 N The XRD patterns of the catalyst and the FeNbNC catalyst prepared in Comparative Example 3 are shown below. Figure 6 As shown, their XRD patterns all exhibit peaks of amorphous carbon at 26.8° and 42°. FeNbNC prepared in Example 1 N The composite catalyst and NbNC prepared in Comparative Example 2 N The XRD pattern of the catalyst showed several strong diffraction peaks that coincided with the diffraction peaks of NbN, confirming that FeNbNC... N With NbNC N The presence of NbN nanoparticles. Simultaneously, FeNbNC... N Composite catalyst and FeNC N The XRD patterns of the catalysts showed no diffraction peaks for Fe metal, indicating that Fe did not agglomerate and no Fe nanoparticles were present, confirming the single-atom structure of Fe in both catalysts. Notably, the XRD pattern of FeNbNC prepared in Comparative Example 3 showed a lower intensity of the NbN diffraction peak, while diffraction peaks for iron oxides (Fe3O4, Fe2O3) were also present. This indicates that FeNbNC without an additional nitrogen source lacked sufficient N to form NbN nanoparticles, and also lacked N coordination with Fe, leading to the oxidation of Fe clusters into oxides. This result demonstrates that FeNbNC… N Composite catalyst, FeNC N The successful synthesis of the catalyst is consistent with the morphology characterization results described above; it also demonstrates that the addition of an extra nitrogen source serves to form high-density Fe single atoms and provides sufficient nitrogen to form NbN particles.

[0064] FeNbNC prepared in Example 1 N Composite catalyst, NC N FeNC prepared in Comparative Example 1 N Raman spectra of the catalyst and NC prepared in Comparative Example 3, as shown. Figure 7 As shown; ID / I G The NC value reflects the degree of defects and the proportion of graphitization in carbon materials. Adding an additional nitrogen source... N Compared to NC substrates without an additional nitrogen source, the substrate I D / I G The significant increase indicates that the addition of an additional nitrogen source increased the defect level of the carbon substrate. The Ig of the sample after metal addition... D / I G The value decreases because the introduction of metals can increase the degree of graphitization of the carbon substrate, wherein FeNbNC prepared in Example 1 N Composite catalyst and FeNC prepared in Comparative Example 1 N Catalyst compared to I D / I G The value further decreased, indicating that the addition of NbN nanoparticles can further increase the graphitization degree of the catalyst, which is FeNbNC N One of the reasons for the improved stability of composite catalysts.

[0065] FeNbNC prepared in Example 1 N Composite catalyst, FeNC prepared in Comparative Example 1 N XPS plot of Fe 2p orbitals of the catalyst, as shown Figure 8 As shown; XPS spectra can well reflect the composition and valence state of elements, through FeNbNC N Composite catalyst and FeNC N The comparison of catalysts can visually reflect the change in the valence state of Fe with and without NbN particles, thus determining the electron gain and loss. When NbN particles are introduced, FeNbNC... N Fe 2p in composite catalysts 1 / 2 The peaks clearly shift towards lower binding energies, indicating that the introduction of NbN lowers the valence state of Fe. This strongly demonstrates that a strong electronic interaction occurs between NbN particles and Fe single atoms, a process that involves electron transfer through the N-doped C support, ultimately resulting in Fe gaining some electrons and lowering its oxidation state.

[0066] FeNbNC prepared in Example 1 N Composite catalyst, FeNC prepared in Comparative Example 1 N A schematic diagram of the catalyst structure, as shown below. Figure 9 As shown; gray atoms represent C, blue atoms represent N, cyan atoms represent Fe, and purple atoms represent Nb. In FeNbNC N Fe exists as a single atom in the composite catalyst, coordinated with four N atoms and embedded in the carbon support. Nb forms NbN nanoparticles, which play a regulatory role in the Fe active sites near the Fe. Figure 9 a). In FeNCN Fe also exists in single-atom form on the catalyst, coordinated with 4 N atoms and embedded in the carbon support. Figure 9 (b). DFT calculations revealed that the d-band center of Fe decreased significantly after the introduction of NbN particles, from FeNC... N The value of -0.73 eV in FeNbNC decreased to FeNbNC. N The -1.18 eV value, and the decrease in the d-band center, often weakens the adsorption strength of the site for the intermediate, thus favoring the reaction. This strongly suggests that the introduction of NbN particles involves electronic interaction with Fe, altering the adsorption strength of the Fe single-atom active site for the ORR intermediate and thereby enhancing the reaction activity.

[0067] FeNbNC prepared in Example 1 N Composite catalyst, FeNC prepared in Comparative Example 1 N Catalyst, NbNC prepared in Comparative Example 2 N Electrodes were prepared using the catalyst, and ORR polarization curves were measured in 0.1 M HClO4 aqueous solution at room temperature (25 °C). The specific electrode preparation method was as follows: a catalyst coating was formed by dropping catalyst ink onto a 5.6 mm diameter rotating disk electrode (RDE). The catalyst ink was prepared by ultrasonically mixing 5 mg of catalyst, 500 μL of ethanol, and 30 μL of 5 wt% Nafion for 30 min. Hg / Hg₂SO₄ electrode and platinum wire were used as the reference and counter electrodes, respectively. Before each test, the Hg / Hg₂SO₄ electrode was calibrated using a reversible hydrogen electrode (RHE). Linear sweep voltammetry was used to obtain the ORR polarization curves at a rotation speed of 1600 rpm and a scan rate of 5 mV / s, followed by iR correction.

[0068] FeNbNC prepared in Example 1 N Composite catalyst, FeNC prepared in Comparative Example 1 N Catalyst, NbNC prepared in Comparative Example 2 N ORR polarization curves of the catalyst, as shown Figure 10 As shown; in 0.1 M HClO4 solution, compared to NbNC N Catalyst, FeNbNC N Composite catalyst and FeNC N The catalyst exhibits a significantly enhanced half-wave potential, indicating that NbN itself does not possess ORR activity, and the catalyst's activity originates from the Fe active sites; while FeNbNC N Composite catalysts compared to FeNC N The catalyst half-wave potential further increases, indicating that the introduction of NbN has a synergistic effect with the Fe active sites, thereby enhancing the ORR activity of FeNC.

[0069] FeNbNC prepared in Example 1 N Composite catalyst, FeNC prepared in Comparative Example 1 N A comparison of the Tafel slope and kinetic current density of the catalyst is as follows: Figure 11 As shown; the disk current density in the ORR-LSV curve within the kinetic confinement region is independent of the electrode rotation rate and is completely controlled by oxygen reduction kinetics, therefore it is called the kinetic current density (j k The larger the value of j, the faster the dynamic velocity; k A Tafel plot was drawn between the logarithm of the equation and the applied potential. The slope of the linear region is the Tafel slope; the smaller the value, the faster the ORR kinetic reaction rate. Through calculation and fitting, the FeNbNC prepared in Example 1... N Composite catalyst and FeNC prepared in Comparative Example 1 N The Tafel slope of the catalyst is 66.4 mV dec. -1 and 71.7 mV dec -1 The kinetic current densities at 0.8 V vs. RHE are 17.1 mA cm⁻¹. -2 and 8.97 mA cm -2 This indicates that FeNbNC N The composite catalyst exhibits faster ORR kinetics. Based on the above characterization, calculation, and analysis, this is because Nb forms an electron transport network through N and C atoms, which interacts strongly with the surrounding Fe active centers. This reduces the oxidation state and d-band center of Fe, affecting its adsorption degree for ORR intermediates, and ultimately promotes the ORR reaction kinetics of Fe-N4 single-atom active sites, thereby improving the electrocatalytic oxygen reduction activity of the catalyst.

[0070] FeNbNC prepared in Example 1 N Composite catalyst, FeNC prepared in Comparative Example 1 N The catalyst was subjected to accelerated aging tests (ADT) in an O2-saturated 0.1 M HClO4 solution at a potential range of 0.6–0.95 V vs. RHE. The results are as follows: Figure 12 As shown; after 30,000 cycles of aging, FeNbNC N The half-wave potential of the composite catalyst decreased by only 7 mV, compared to FeNC. N The catalyst (10 mV) exhibits better stability.

[0071] Comparative Example 4: This comparative example uses dicyandiamide as an additional nitrogen source to prepare FeNbNC DCD The catalyst is prepared using the following specific method:

[0072] I. Preparation of ZIF-8 precursor: First, 3.24 g of 2-methylimidazole was dissolved in 100 ml of methanol to obtain solution A; then, 2.94 g of zinc nitrate hexahydrate was dissolved in 50 ml of methanol to obtain solution B; solution B was poured into solution A, stirred at room temperature for 12 h, then washed with methanol and centrifuged three times, and the precipitate was dried under vacuum at 70 °C for 6 h to obtain ZIF-8 precursor;

[0073] II. NC DCD Preparation: 0.5 g of ZIF-8 precursor and 0.125 g of dicyandiamide were dispersed in a solution composed of 15 ml of water and 30 ml of ethanol. The solution was ultrasonically stirred until homogeneous, and then vacuum dried at 80 °C for 15 h. The dried white powder was ground and placed in a tube furnace, where it was pyrolyzed at 900 °C for 2 h under an Ar atmosphere at a heating rate of 5 °C / min. After cooling, a black powder was obtained, denoted as NC. DCD ;

[0074] III. FeNbNC DCD Catalyst preparation: 36 mg NC DCD The mixture was ultrasonically mixed with 10 ml of ethanol for 1 h, and then 700 μl of an ethanol solution of ferric salt and 700 μl of an ethanol solution of niobium salt were added dropwise. The mixture was stirred at room temperature for 24 h. The ethanol solution of ferric salt was obtained by dissolving 16.7 mg of ferric chloride hexahydrate in 2 ml of ethanol, and the ethanol solution of niobium salt was obtained by dissolving 10 mg of niobium pentachloride in 2 ml of ethanol. The mixture was then vacuum dried at 60 °C for 12 h. The resulting powder was ground and placed in a tube furnace, where it was pyrolyzed at 900 °C for 2 h under an Ar atmosphere at a rate of 5 °C / min. After cooling, FeNbNC was obtained. DCD Composite catalyst.

[0075] FeNbNC prepared in Example 1 N Composite catalyst, FeNbNC prepared in Comparative Example 4 DCD ORR polarization curves of the catalyst, as shown Figure 13 As shown; dicyandiamide (DCD), melamine, urea, etc., are nitrogen sources widely used in catalyst synthesis, which can release ammonia gas through high-temperature decomposition to achieve the purpose of introducing nitrogen. However, through... Figure 13 Performance comparison revealed that FeNbNC synthesized using dicyandiamide... DCD Composite catalysts compared to FeNbNC NThe performance of composite catalysts deteriorates significantly. This is because while ordinary nitrogen-containing compounds can also serve as N sources, they cover the active sites, leading to a decrease in performance. Nitrogen-containing heterocyclic organic compounds such as imidazo[1,2-f]phenanthridine, pyrazine, and o-phenanthroline have a six-membered ring structure similar to that of carbon supports, which can effectively composite with ZIF-8 and have a strong chelating effect with metals. Therefore, they can not only provide additional N but also more uniformly disperse the metal sites.

[0076] Comparative Example 5: In this embodiment, FeNbNC was prepared by water bath stirring and evaporation when metal was loaded. N The specific preparation method for the -nv catalyst is as follows:

[0077] I. Preparation of ZIF-8 precursor: First, 3.24 g of 2-methylimidazole was dissolved in 100 ml of methanol to obtain solution A; then, 2.94 g of zinc nitrate hexahydrate was dissolved in 50 ml of methanol solution to obtain solution B; solution B was poured into solution A, stirred at room temperature for 12 h, then washed with methanol and centrifuged three times, and the precipitate was dried under vacuum at 70 °C for 6 h to obtain ZIF-8 precursor;

[0078] II. NC N Preparation: 0.5 g of ZIF-8 precursor and 0.125 g of o-phenanthroline were dispersed in a solution composed of 15 ml of water and 30 ml of ethanol. The solution was ultrasonically stirred until homogeneous, and then vacuum dried at 80 °C for 15 h. The dried white powder was ground and placed in a tube furnace, where it was pyrolyzed at 900 °C for 2 h under an Ar atmosphere at a heating rate of 5 °C / min. After cooling, a black powder was obtained, denoted as NC. N ;

[0079] III. FeNbNC N Preparation of -nv catalyst: 36 mg NC N The mixture was ultrasonically mixed with 10 ml of ethanol for 1 h, and then 700 μl of ferric salt-ethanol solution and 700 μl of niobium salt-ethanol solution were added dropwise, and stirred at room temperature for 24 h. The ethanol solution of ferric salt was obtained by dissolving 16.7 mg of ferric chloride hexahydrate in 2 ml of ethanol, and the ethanol solution of niobium salt was obtained by dissolving 10 mg of niobium pentachloride in 2 ml of ethanol. The mixture was then stirred and evaporated to dryness in a 60 °C water bath. The resulting powder was ground and placed in a tube furnace, where it was pyrolyzed at 900 °C for 2 h under an Ar atmosphere at a rate of 5 °C / min. After cooling, FeNbNC was obtained. N -nv composite catalyst.

[0080] FeNbNC prepared in Example 1 N Composite catalyst, FeNbNC prepared in Comparative Example 5 NORR polarization curves and XRD patterns of the -nv catalyst, as follows: Figure 14 As shown; water bath stirring, due to heating the solution to dryness into powder under non-vacuum conditions, may be accompanied by metal agglomeration and oxidation, resulting in FeNbNC N -nv catalyst exhibits reduced limiting diffusion current and improved ORR performance compared to FeNbNC. N The composite catalyst decreased significantly ( Figure 14 (a) Meanwhile, XRD patterns revealed enhanced crystallinity and larger particle size, along with the formation of some niobium oxide impurity phases. Vacuum drying can prevent metal agglomeration and oxidation.

[0081] FeNbNC prepared in Example 1 N Composite catalyst, FeNC prepared in Comparative Example 1 N The performance of catalysts in fuel cells, such as Figure 15 As shown, FeNbNC N The composite catalyst achieved a peak power density of 1120 mW / cm² under hydrogen-oxygen testing conditions in a proton exchange membrane fuel cell. 2 The highest peak power density under hydrogen-air testing conditions reached 662 mW / cm². 2 Significantly higher than FeNC N Catalysts (746 mW / cm) 2 and 409 mW / cm 2 This demonstrates that the synergistic effect of NbN nanoparticles on FeNC is not only applicable to half-cell testing but also enhances performance in fuel cells, further illustrating the effectiveness of the FeNbNC prepared in Example 1. N Composite catalysts have high practical value.

[0082] This invention involves adding Fe and Nb salts to nitrogen-doped porous carbon materials derived from imidazo[1,2-f]phenanthridine, pyrazine, and o-phenanthroline on ZIF-8, followed by pyrolysis to obtain FeNbNC nanoparticles supported on the nitrogen-doped carbon material. NA composite catalyst was developed. The nitrogen source was a nitrogen-containing heterocyclic organic ligand pre-composite with ZIF-8, unlike conventional pyrolysis which involves adding nitrogen-containing compounds, allowing for better anchoring of metal sites. Furthermore, vacuum drying was employed after metal impregnation to prevent metal oxidation. The resulting nitrogen-doped carbon support exhibited a 100-200 nm dodecahedral shape, with approximately 5-10 nm NbN particles and a single-atom Fe-N4 configuration. While the NbN nanoparticles themselves do not possess ORR activity, the Nb forms an electron transport network through N and C atoms, strongly interacting with the Fe active sites. This reduces the oxidation state of Fe and affects its adsorption of ORR intermediates, promoting the ORR reaction at the Fe-N4 single-atom active sites and enhancing the catalyst's electrocatalytic oxygen reduction activity. This is compared to FeNC catalysts without NbN particles. N Compared to other catalysts, FeNbNC N The composite catalyst exhibits improved catalytic activity and stability in acidic ORR. In fuel cell testing, FeNbNC... N The composite catalyst achieved a peak power density of 1.12 W / cm³. 2 .

Claims

1. A NbN nanoparticle composite FeNC catalyst, characterized in that, The catalyst consists of Fe single atoms and NbN nanoparticles supported on a nitrogen-doped carbon support. The nitrogen-doped carbon support has a dodecahedral shape of 100-200 nm, the NbN nanoparticles have a particle size of 5-10 nm, and the Fe has a single-atom Fe-N4 configuration.

2. The method for preparing the NbN nanoparticle composite FeNC catalyst according to claim 1, characterized in that, This method is performed in the following steps: I. Preparation of ZIF-8 precursor: First, 2-methylimidazole was dissolved in methanol to obtain solution A; then zinc nitrate hexahydrate was dissolved in methanol to obtain solution B; solution B was poured into solution A, stirred at room temperature for 8-12 h, then centrifuged, and the solid phase was washed with methanol and dried under vacuum to obtain ZIF-8 precursor; II. Preparation of Nitrogen-Doped Porous Carbon Materials: The ZIF-8 precursor and the additional nitrogen source were dispersed in a mixed solution of water and ethanol at a mass ratio of (3-5):

1. The solution was ultrasonically stirred until homogeneous, then vacuum dried for 10-15 h to obtain a white powder. The white powder was then ground and placed in a tube furnace. Under an inert atmosphere, the temperature was increased to 880-920℃ at a heating rate of 4-6℃ / min and held for 2-3 h for pyrolysis. After cooling, a black powder, denoted as NC, was obtained. N The additional nitrogen source is imidazo[1,2-f]phenanthridine, pyrazine, or o-phenanthroline. III. FeNbNC N Preparation of composite catalyst: NC N The solution was added to ethanol and ultrasonically mixed to obtain a dispersion. Then, ethanol solutions of iron salt and niobium salt were added dropwise to the dispersion, and the mixture was stirred at room temperature for 20–24 h. Following this, it was vacuum dried for 10–12 h to obtain a powder. The powder was ground and placed in a tube furnace, where it was pyrolyzed at a heating rate of 4–6 °C / min to 880–920 °C for 2–3 h under an inert atmosphere. After cooling, the NbN nanoparticle composite FeNC catalyst was obtained, denoted as FeNbNC. N Composite catalyst.

3. The method for preparing an NbN nanoparticle composite FeNC catalyst according to claim 2, characterized in that, The molar ratio of 2-methylimidazole to zinc nitrate hexahydrate mentioned in step one is (3~5):

1.

4. The method for preparing an NbN nanoparticle composite FeNC catalyst according to claim 2 or 3, characterized in that, The iron salt mentioned in step three is ferric chloride hexahydrate, and the niobium salt is niobium pentachloride.

5. The method for preparing an NbN nanoparticle composite FeNC catalyst according to claim 2 or 3, characterized in that, NC in the dispersion described in step three N The mass concentration is 3~4 mg / ml.

6. The method for preparing an NbN nanoparticle composite FeNC catalyst according to claim 2 or 3, characterized in that, The concentration of the ethanol solution of the iron salt mentioned in step three is 8~9 mg / ml, and the concentration of the ethanol solution of the niobium salt is 4.5~5.5 mg / ml.

7. The method for preparing an NbN nanoparticle composite FeNC catalyst according to claim 2 or 3, characterized in that, The iron salt and NC mentioned in step three N The mass ratio is (0.1~0.2):

1.

8. The method for preparing an NbN nanoparticle composite FeNC catalyst according to claim 2 or 3, characterized in that, The molar ratio of niobium salt to iron salt mentioned in step three is (0.3~1.5):

1.

9. A method for preparing an NbN nanoparticle composite FeNC catalyst according to claim 2 or 3, characterized in that, Furthermore, the inert atmosphere described in steps two and three is Ar.

10. The application of the NbN nanoparticle composite FeNC catalyst according to claim 1, characterized in that, This application involves using NbN nanoparticles combined with FeNC catalysts for the cathode oxygen reduction reaction in a proton exchange membrane fuel cell.

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