Synthesis method and application of NS-C5 / rGO composite catalyst

Abstract

This invention proposes a synthesis method and application of an NS-C5 / rGO composite catalyst, belonging to the field of electrocatalytic materials technology. First, methyl-3-aminobenzo[b]thiophene-2-carboxylic acid ester is refluxed with sodium hydroxide in a mixed solution of isopropanol and water. The reaction solution is post-treated to obtain a crude product of amino acid sodium salt. Then, formic acid and phenylhydrazine hydrochloride are added, and the reaction is refluxed again. The reaction solution is post-treated to obtain NS-C5, which is then mixed with reduced graphene oxide (rGO) and composited via a π-π stacking method to obtain the NS-C5 / rGO composite catalyst. This invention, by loading NS-C5 onto a reduced graphene oxide support, forms a composite material with clearly defined NS-C5 active centers. This avoids the uncontrollability of nitrogen / sulfur co-doping configuration active centers at the edges of pentagonal carbon defects in traditional pyrolysis and heteroatom doping processes. The resulting NS-C5 / rGO composite catalyst has a well-defined structure and exhibits excellent ORR catalytic activity under both acidic and alkaline electrolyte conditions.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic materials technology, and particularly relates to a synthesis method and application of an NS-C5 / rGO composite catalyst. Background Technology

[0002] With the increasing severity of the global energy crisis and environmental pollution, the development of efficient and clean energy conversion technologies has become a current research hotspot. The oxygen reduction reaction (ORR), as the core cathode reaction in energy devices such as fuel cells and metal-air batteries, is a slow-moving kinetic process that requires efficient catalysts to lower the reaction energy barrier. Currently, commercial ORR catalysts are mainly based on precious metals such as platinum (Pt), but their high cost, scarcity, and limited stability severely restrict the large-scale application of clean energy devices. Non-metallic carbon-based materials, due to their high specific surface area, good conductivity, and tunable structure, have become ideal candidate materials for ORR catalysts. Among them, heteroatom-doped defect carbon materials (such as pentagonal and heptagonal carbon defects) are widely studied for ORR catalytic reactions because they can construct electron-rich active centers and optimize the electronic structure of carbon substrates.

[0003] In recent years, pentagonal carbon defects (C5) have been proven to be highly efficient ORR active sites in carbon-based materials, with their asymmetric local electronic structure promoting O2 adsorption and activation. The introduction of heteroatoms such as N and S can further modulate the electronic microenvironment of C5 sites, enhancing electrocatalytic activity. Our team previously demonstrated through experiments and theoretical calculations that the nitrogen / sulfur co-doped configuration at the edge of pentagonal carbon defects exhibits excellent ORR catalytic activity in acidic media and is considered a promising ORR catalytic active center. However, current mainstream methods for preparing such heteroatom-doped carbon defect catalysts (such as high-temperature pyrolysis and heteroatom doping) have fundamental limitations: the processes are uncontrollable, leading to extremely complex and unclear types, structures, and distributions of active centers in the final product. The coexistence of various defect structures, heteroatom coordination modes, and potentially residual metal catalyst impurities makes it impossible to precisely construct a single, well-defined NS-C5 active site. Consequently, it is difficult to accurately identify the intrinsic catalytic activity and mechanism of action of NS-C5, leading to a long-standing state of ambiguity and controversy regarding whether the NS-C5 configuration truly represents a highly efficient ORR active center, and its intrinsic activity and catalytic mechanism. Therefore, how to accurately construct and clearly identify the active center of this specific structure has become a critical scientific problem and technological bottleneck that urgently needs to be solved in this field. Simultaneously, the lack of systematic regulation of active site density, and the inability to establish a clear "structure-activity-density" relationship, restricts the targeted design and development of high-performance non-metallic ORR catalysts.

[0004] Therefore, developing a preparation method that can accurately synthesize a single NS-C5 active center and systematically regulate the density of active sites is of great significance for revealing the catalytic nature of NS-C5 and promoting the practical application of non-metallic carbon-based ORR catalysts. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a synthesis method and application of an NS-C5 / rGO composite catalyst. This invention can synthesize a well-defined nitrogen-sulfur synergistic pentagonal carbon structure molecule (NS-C5) and confirm that this molecular structure is the highly efficient ORR active center. This fundamentally solves the problem that traditional methods cannot clearly define the configuration of the active center, achieving precise construction of the NS-C5 active center and controllable adjustment of the active site density. At the same time, it verifies the high catalytic performance of this catalyst in ORR, providing a new strategy for the design of non-metallic carbon-based ORR catalysts.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for synthesizing an NS-C5 / rGO composite catalyst, comprising the following steps: (1) Methyl-3-aminobenzo[b]thiophene-2-carboxylic acid ester was refluxed with sodium hydroxide in a mixed solution of isopropanol and water. The reaction solution was post-treated to obtain crude sodium amino acid salt product. (2) The crude sodium salt of the amino acid was dissolved in glacial acetic acid, formic acid and phenylhydrazine hydrochloride were added, and the mixture was refluxed. The reaction solution was post-treated to obtain the organic conjugated molecular product with nitrogen-sulfur-pentagonal carbon structure catalytic active center (NS-C5). (3) The organic conjugated molecular product of the nitrogen-sulfur-pentagonal carbon structure catalytic active center (NS-C5) is mixed with reduced graphene oxide (rGO) and composited in a π-π stacking manner to obtain the NS-C5 / rGO composite catalyst.

[0007] This invention first utilizes the alkaline hydrolysis reaction of esters, taking advantage of the strong alkalinity of sodium hydroxide in an isopropanol-water mixed system, to hydrolyze the ester group of methyl-3-aminobenzo[b]thiophene-2-carboxylic acid ester, generating the corresponding sodium carboxylate salt (crude sodium amino acid salt product), providing a basic organic framework for the subsequent construction of a five-membered carbon ring; then, through a cyclization condensation reaction in an acidic system of glacial acetic acid, formic acid is used as a reaction promoter and phenylhydrazine hydrochloride is used as a condensation reagent, to cyclize with the crude sodium amino acid salt product from the first step, precisely constructing a nitrogen-sulfur co-doped pentagonal carbon structure (NS- C5), this structure is the core site with ORR catalytic activity, which solves the problem of unclear active center in traditional pyrolysis method; the third step utilizes π-π stacked non-covalent interaction to combine NS-C5 (conjugated organic molecule with large area π electron structure) with reduced graphene oxide (rGO, two-dimensional large π conjugated system), so that the aromatic plane of NS-C5 is parallel to the carbon plane of rGO, and the overlap of delocalized π electron clouds generates van der Waals forces, so that NS-C5 is uniformly loaded on rGO, forming a composite catalyst with clear active center, high conductivity and high specific surface area.

[0008] Furthermore, in step (3), NS-C5 and rGO are compounded through a π-π stacking mechanism. The specific process is as follows: NS-C5 is a conjugated organic molecule with a large-area π-electron structure, while rGO is a two-dimensional honeycomb structure composed of a single layer of carbon atoms, covered with six-membered carbon rings. It is the largest π-π conjugated system to date. When the two are mixed, the aromatic plane of NS-C5 tends to be parallel to the carbon plane of rGO. The huge delocalized π-electron clouds of the two will overlap, generating van der Waals forces (i.e., π-π interactions) similar to electron cloud attraction, thus making them fit tightly together.

[0009] Further, in step (1), the volume ratio of isopropanol to water is 9:1.

[0010] Further, in step (1), the molar ratio of sodium hydroxide to methyl-3-aminobenzo[b]thiophene-2-carboxylic acid ester is 4:1.

[0011] Further, in step (1), the ratio of the amount of methyl-3-aminobenzo[b]thiophene-2-carboxylic acid ester to the mixed solution is 1 mmol: 20 mL.

[0012] Further, in step (1), the reflux reaction temperature is 95-105℃ and the time is 1-3h; preferably, the reflux reaction temperature is 100℃ and the time is 2h.

[0013] Further, in step (1), the reaction solution is post-processed as follows: the reaction solution is concentrated under reduced pressure to remove the solvent and obtain the crude product of the amino acid sodium salt.

[0014] Furthermore, the molar ratio of formic acid and phenylhydrazine hydrochloride in step (2) to methyl-3-aminobenzo[b]thiophene-2-carboxylic acid ester in step (1) is 4:1.2:1.

[0015] Furthermore, in step (2), the reflux reaction temperature is 125-135℃ and the reaction time is 2h.

[0016] Further, in step (2), the reaction solution is post-processed as follows: the obtained reaction solution is cooled to room temperature, and then subjected to precipitation, filtration, washing, and drying to obtain the NS-C5.

[0017] Further, in step (3), the mass ratio of the nitrogen-sulfur-pentagonal carbon structure catalytic active center organic conjugated molecular product (NS-C5) to reduced graphene oxide (rGO) is (0.5-6):1, and more preferably, the mass ratio of NS-C5 to rGO is 3:1.

[0018] The present invention also provides an NS-C5 / rGO composite catalyst, which is prepared according to the above preparation method.

[0019] This invention prepares an organic molecular catalyst with a clearly defined NS-C5 active center through controlled organic synthesis and non-covalent composite methods. Furthermore, by uniformly loading NS-C5 onto rGO, a composite catalyst with superior conductivity, NS-C5 / rGO, is obtained. The nitrogen-sulfur co-doped pentagonal carbon structure of NS-C5 serves as a highly efficient ORR active center, while rGO provides the catalyst with a support exhibiting high conductivity and high specific surface area. The π-π stacking composite method ensures the stability and exposure of the active center, giving the catalyst material properties superior to those of traditional carbon-based catalysts.

[0020] This invention also provides an application of the above-mentioned NS-C5 / rGO composite catalyst in the oxygen reduction reaction (ORR). The core principle is based on the matching between the electrocatalytic structure of the NS-C5 / rGO composite catalyst and the ORR reaction mechanism: In the NS-C5 active center, nitrogen (pyrrole) and sulfur (thiophene) synergistically regulate the electronic structure of the carbon site, reducing OOH. The formation energy barrier of the intermediate promotes the adsorption and activation of O2, accelerating the kinetic process of ORR; The high conductivity of rGO ensures rapid electron transport during the catalytic reaction, reducing electron transport resistance. The catalyst exhibits a well-defined active center structure and functions stably in both acidic (0.1 M H₂SO₄) and alkaline (0.1 M KOH) electrolytes. This solves the problem of unclear active centers in the nitrogen / sulfur co-doped configuration at the edges of pentagonal carbon defects in traditional carbon-based catalysts. This lays the theoretical foundation for the design and synthesis of highly efficient non-metallic catalysts for ORR, and the catalyst demonstrates application potential in energy devices such as fuel cells and metal-air batteries.

[0021] Compared with the prior art, the present invention has the following advantages and technical effects: (1) The NS-C5 conjugated organic molecule synthesized in the preparation method of this invention consists of a precisely designed five-membered carbon ring (C5) co-doped with pyrrole (N) and thiophene (S). A conjugated organic molecule (NS-C5) with a clearly defined nitrogen (pyrrole) and sulfur (thiophene) co-coordinated five-membered carbon structure is precisely constructed through an organic synthesis strategy. This molecule is then loaded onto a reduced graphene oxide support to form a composite material with a clearly defined active center, avoiding the uncontrollability of the active center in traditional pyrolysis and heteroatom doping processes. The raw materials used in the method of this invention are readily available, the preparation method is controllable, and the reproducibility is good. Compared with traditional carbon-based electrocatalysts prepared by pyrolysis, the clearly defined active center structure allows for accurate identification of active sites and establishment of structure-activity relationships, thereby elucidating the intrinsic activity and catalytic mechanism of the catalyst's active center. The NS-C5 / rGO composite catalyst of this invention exhibits excellent catalytic activity in ORR reactions under acidic and alkaline electrolyte conditions, and provides new ideas for the design and synthesis of subsequent non-metallic catalysts.

[0022] (2) This invention achieves for the first time the precise construction and activity verification of the NS-C5 structure in the ORR reaction. Through systematic electrochemical testing, in-situ spectroscopic characterization and theoretical calculation, it clearly reveals that the N and S atoms in the NS-C5 structure synergistically regulate the electronic structure of carbon sites, promoting the OOH reaction. The reaction mechanism of intermediate formation significantly enhances ORR catalytic activity. Furthermore, this invention also demonstrates that by systematically adjusting the active site density of NS-C5 recombined on reduced graphene oxide support (NS-C5 / rGO), the catalytic activity of NS-C5 / rGO increases with increasing NS-C5 active site density. When the active site density reaches 30 NS-C5 / rGO, further increases in active site density lead to a gradual decrease in electrocatalytic activity, resulting in a deceleration of reaction kinetics. This verifies the relationship between catalytic activity and active site density, providing a new approach for the precise design and application of highly efficient non-metallic carbon-based catalysts. Attached Figure Description

[0023] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 In Example 1, a is the NS-C5 synthesis route; b is a schematic diagram of the N-C5 molecular structure in Comparative Example 2; c is a schematic diagram of the S-C5 molecular structure in Comparative Example 1; d is a schematic diagram of the complexation of three conjugated organic molecules with rGO; and e is a schematic diagram of the principle of ORR reaction catalyzed by the NS-C5 / rGO composite catalyst. Figure 2 The powder X-ray diffraction (PXRD) characterization results are as follows: NS-C5 and NS-C5 / rGO composite catalysts in Example 1, S-C5, S-C5 / rGO composite catalysts, N-C5, and N-C5 / rGO composite catalysts in Comparative Examples 1-2. Figure 3 The TEM image and C, N, and S elemental distribution diagrams of the NS-C5 / rGO composite catalyst in Example 1 are shown below. Figure 4 The chemical structure and composition analysis results of the NS-C5 / rGO composite catalyst and rGO in Example 1, the S-C5 / rGO composite catalyst in Comparative Example 1, and the N-C5 / rGO composite catalyst in Comparative Example 2 are shown in the figures. a) Raman spectra of NS-C5 / rGO, S-C5 / rGO, N-C5 / rGO, and rGO; b) X-ray photoelectron spectra of NS-C5 / rGO and N-C5 / rGO; c) XPS spectra of NS-C5 / rGO and S-C5 / rGO S 1s; d) X-ray absorption near-edge structure (XANES) spectra of NS-C5 / rGO and N-C5 / rGO; e) K-edge XANES spectra of S atoms in NS-C5 / rGO and S-C5 / rGO; and f) K-edge XANES spectra of C atoms in NS-C5 / rGO, S-C5 / rGO, and N-C5 / rGO. Figure 5 The UV-vis absorption spectra of the NS-C5 and NS-C5 / rGO composite catalysts in Example 1 are shown. Figure 6 IV curves of the NS-C5 / rGO composite catalyst in Example 1, the S-C5 / rGO composite catalyst in Comparative Example 1, and the N-C5 / rGO composite catalyst in Comparative Example 2; Figure 7 LSV performance curves of ORR for 20NS-C5 / rGO composite catalyst, rGO, S-C5 / rGO and N-C5 / rGO composite catalyst under 0.1M H2SO4 electrolyte; Figure 8LSV performance curves of ORR for 20NS-C5 / rGO composite catalyst, rGO, S-C5 / rGO and N-C5 / rGO composite catalyst under 0.1M KOH electrolyte; Figure 9 LSV performance curves of ORR composite catalysts with different active site densities (5NS-C5 / rGO, 10NS-C5 / rGO, 20NS-C5 / rGO, 30NS-C5 / rGO, 40NS-C5 / rGO, 50NS-C5 / rGO, and 60NS-C5 / rGO) under 0.1M H2SO4 electrolyte are shown. Figure 10 LSV performance curves of ORR for composite catalysts with different active site densities (5NS-C5 / rGO, 10NS-C5 / rGO, 20NS-C5 / rGO, 30NS-C5 / rGO, 40NS-C5 / rGO, 50NS-C5 / rGO, and 60NS-C5 / rGO) under 0.1M KOH electrolyte are shown. Figure 11 The in-situ ATR-SEIRAS spectrum of the NS-C5 / rGO composite catalyst is shown. Figure 12 The in-situ ATR-SEIRAS spectrum of the N-C5 / rGO composite catalyst; Figure 13 The in-situ ATR-SEIRAS spectrum of the S-C5 / rGO composite catalyst is shown. Figure 14 The results of DFT calculation models and reaction free energy diagrams for S-C5, N-C5, and NS-C5 are presented. Figure 15 This is a schematic diagram illustrating the clear structure-activity relationship between the NS-C5 configuration of the present invention and its intrinsic ORR activity. Detailed Implementation

[0024] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0025] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0026] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0027] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0028] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0029] This invention provides a method for synthesizing an NS-C5 / rGO composite catalyst, comprising the following steps: (1) Methyl-3-aminobenzo[b]thiophene-2-carboxylic acid ester was refluxed with sodium hydroxide in a mixed solution of isopropanol and water. The reaction solution was post-treated to obtain crude sodium amino acid salt product. (2) The crude product of sodium amino acid salt was dissolved in glacial acetic acid, formic acid and phenylhydrazine hydrochloride were added, and the mixture was refluxed. The reaction solution was post-treated to obtain the organic conjugated molecular product with nitrogen-sulfur-pentagonal carbon structure catalytic active center (NS-C5). (3) The organic conjugated molecular product of the nitrogen-sulfur-pentagonal carbon structure catalytic active center (NS-C5) is mixed with reduced graphene oxide (rGO) and composited in a π-π stacking manner to obtain the NS-C5 / rGO composite catalyst.

[0030] In a preferred embodiment of the present invention, the synthesis method of the NS-C5 / rGO composite catalyst specifically includes the following steps: (1) Disperse methyl-3-aminobenzo[b]thiophene-2-carboxylic acid ester (1 mmol) and sodium hydroxide (4 mmol) in 20 mL of isopropanol / water (9:1, v / v) mixed solvent, stir on a magnetic stirrer and heat to reflux (95-105℃) for 1-3 h. After the reaction is completed, concentrate the reaction solution under reduced pressure to remove the solvent and obtain the crude product of amino acid sodium salt.

[0031] (2) The crude sodium amino acid salt obtained above was dissolved in 10 mL of glacial acetic acid, and formic acid (4 mmol) and phenylhydrazine hydrochloride (1.2 mmol) were added in sequence. The mixture was refluxed in an oil bath at 125-135 °C for 2 h. After the reaction was completed and the mixture was naturally cooled to room temperature, the reaction solution was poured into ice water to precipitate the product. The product was filtered, and the solid obtained was washed with deionized water and dried to obtain the organic conjugated molecular product with nitrogen-sulfur-pentagonal carbon structure catalytic active center (NS-C5).

[0032] (3) The synthesized nitrogen-sulfur-pentagonal carbon structure catalytic active center organic conjugated molecular product (NS-C5) is mixed with reduced graphene oxide (rGO) at a mass ratio of (0.5-6):1 (preferably a mass ratio of 3:1), and the NS-C5 / rGO composite catalyst is obtained by π-π stacking composite.

[0033] This invention also provides an NS-C5 / rGO composite catalyst, prepared according to the above preparation method.

[0034] The present invention also provides an application of the above-mentioned NS-C5 / rGO composite catalyst in the oxygen reduction reaction (ORR). The catalyst has oxygen reduction catalytic activity under both acidic and alkaline electrolyte conditions. Furthermore, the catalyst is used in the cathode catalytic system of fuel cells or metal-air batteries.

[0035] In this embodiment of the invention, room temperature refers to "25±2℃".

[0036] All raw materials used in the embodiments of the present invention were purchased commercially. Specifically, S-C5 used in the comparative example was purchased from Aladdin Company, and N-C5 was purchased from Aladdin Company.

[0037] The technical solution of the present invention will be further illustrated by the following embodiments.

[0038] Example 1 A method for synthesizing an NS-C5 / rGO composite catalyst, specifically including the following steps: (1) Methyl-3-aminobenzo[b]thiophene-2-carboxylic acid ester (1 mmol) and sodium hydroxide (4 mmol) were dispersed in 20 mL of isopropanol / water (9:1, v / v) mixed solvent, stirred on a magnetic stirrer and heated to reflux (100 °C) for 2 h. After the reaction was completed, the reaction solution was concentrated under reduced pressure to remove the solvent and obtain the crude product of sodium amino acid salt.

[0039] (2) The crude sodium amino acid salt obtained above was dissolved in 10 mL of glacial acetic acid, and formic acid (4 mmol) and phenylhydrazine hydrochloride (1.2 mmol) were added in sequence. The mixture was refluxed in an oil bath at 130 °C for 2 h. After the reaction was completed and the mixture was naturally cooled to room temperature, the reaction solution was poured into ice water to precipitate the product. The product was filtered, and the solid obtained was washed with deionized water and dried to obtain the organic conjugated molecular product with nitrogen-sulfur-pentagonal carbon structure catalytic active center (NS-C5).

[0040] (3) 20 mg of the synthesized nitrogen-sulfur-pentagonal carbon structure catalytic active center organic conjugated molecular product (NS-C5) was mixed with reduced graphene oxide (rGO) at a mass ratio of 2:1, and the NS-C5 / rGO composite catalyst (also known as 20NS-C5 / rGO composite catalyst) was obtained by π-π stacking composite.

[0041] Example 2 Same as Example 1, except that in step (3), 5 mg of the synthesized nitrogen-sulfur-pentagonal carbon structure catalytic active center product (NS-C5) and reduced graphene oxide (rGO) are mixed at a mass ratio of 0.5:1 and composited by π-π stacking to obtain the 5NS-C5 / rGO composite catalyst.

[0042] Example 3 Same as Example 1, except that in step (3), 10 mg of the synthesized nitrogen-sulfur-pentagonal carbon structure catalytic active center product (NS-C5) and reduced graphene oxide (rGO) are mixed at a mass ratio of 1:1 and composited by π-π stacking to obtain 10NS-C5 / rGO composite catalyst.

[0043] Example 4 Same as Example 1, except that in step (3), 30 mg of the synthesized nitrogen-sulfur-pentagonal carbon structure catalytic active center product (NS-C5) and reduced graphene oxide (rGO) are mixed at a mass ratio of 3:1 and then composited by π-π stacking to obtain a 30NS-C5 / rGO composite catalyst.

[0044] Example 5 Same as Example 1, except that in step (3), 50 mg of the synthesized nitrogen-sulfur-pentagonal carbon structure catalytic active center product (NS-C5) and reduced graphene oxide (rGO) are mixed at a mass ratio of 5:1 and composited by π-π stacking to obtain a 50NS-C5 / rGO composite catalyst.

[0045] Example 6 Same as Example 1, except that in step (3), 60 mg of the synthesized nitrogen-sulfur-pentagonal carbon structure catalytic active center product (NS-C5) and reduced graphene oxide (rGO) are mixed at a mass ratio of 6:1 and then composited by π-π stacking to obtain a 60NS-C5 / rGO composite catalyst.

[0046] Comparative Example 1 A method for synthesizing an S-C5 / rGO composite catalyst, specifically including the following steps: 20 mg of S-C5 and 10 mg of reduced graphene oxide (rGO) were mixed at a mass ratio of 2:1 and then composited by π-π stacking to obtain the S-C5 / rGO composite catalyst.

[0047] Comparative Example 2 A method for synthesizing an N-C5 / rGO composite catalyst specifically includes the following steps: 20 mg of nitrogen-pentagonal carbon structure catalytic active center product (N-C5) and 10 mg of reduced graphene oxide (rGO) were mixed at a mass ratio of 2:1 and then composited by π-π stacking to obtain N-C5 / rGO composite catalyst.

[0048] Comparative Example 3 Same as Example 1, except that in step (3), 40 mg of the synthesized nitrogen-sulfur-pentagonal carbon structure catalytic active center product (NS-C5) and reduced graphene oxide (rGO) are mixed at a mass ratio of 4:1 and then composited by π-π stacking to obtain a 40NS-C5 / rGO composite catalyst.

[0049] Figure 1 In Example 1, a is the NS-C5 synthesis route; b is a schematic diagram of the N-C5 molecular structure in Comparative Example 2; c is a schematic diagram of the S-C5 molecular structure in Comparative Example 1; d is a schematic diagram of the complexation of three conjugated organic molecules with rGO; and e is a schematic diagram of the principle of ORR reaction catalyzed by the NS-C5 / rGO composite catalyst.

[0050] 1. Crystallographic phase analysis The crystalline phases of the NS-C5 and NS-C5 / rGO composite catalysts in Example 1, and the S-C5, S-C5 / rGO composite catalysts, and N-C5 and N-C5 / rGO composite catalysts in Comparative Examples 1-2 were analyzed using powder X-ray diffraction (PXRD). The PXRD results are shown below. Figure 2As shown, the NS-C5 bulk at 2θ = 7.6°, 9.1°, and 10.3° corresponds to the unique crystal structures of Example 1 and Comparative Examples 1-2, respectively. Since the XRD pattern is mainly affected by rGO, rGO exhibits a characteristic diffraction peak at 2θ = 25.008°. This effect leads to an increase in stacking disorder and molecular arrangement disorder. The absence or significant reduction of sharp peaks in rGO-based compounds further indicates that NS-C5, N-C5, and S-C5 are effectively incorporated into the rGO framework, resulting in a partially amorphous structure.

[0051] 2. Morphology and elemental analysis of the complex The morphology of the NS-C5 / rGO composite catalyst in Example 1 was observed using transmission electron microscopy. The TEM images and elemental distribution maps of the NS-C5 / rGO composite material are shown below. Figure 3 As shown, NS-C5 can be observed to be uniformly distributed on the rGO sheets. Corresponding EDS analysis confirmed the uniform distribution of C, N, and S elements.

[0052] 3. Spectroscopic and electrical analysis The chemical structures and compositions of the NS-C5 / rGO composite catalyst and rGO in Example 1, the S-C5 / rGO composite catalyst in Comparative Example 1, and the N-C5 / rGO composite catalyst in Comparative Example 2 were analyzed using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray absorption near-edge structure (XANES). The results are as follows: Figure 4 As shown, a) are the Raman spectra of NS-C5 / rGO, S-C5 / rGO, N-C5 / rGO, and rGO. It can be seen that the NS-C5 / rGO composite catalyst of Example 1, rGO, the S-C5 / rGO composite catalyst of Comparative Example 1, and the N-C5 / rGO composite catalyst of Comparative Example 2 all show two strong peaks in both the G and D bands. NS-C5 / rGO (1.31), N-C5 / rGO (1.25), and S-C5 / rGO C5 exhibit stronger π-π superposition perturbations, leading to more significant local distortions in the sp2 carbon network of rGO, as indicated by the more pronounced Raman D band enhancement. b) are the X-ray photoelectron spectra of NS-C5 / rGO and N-C5 / rGO. It can be seen that the chemical states of C, N, and S atoms in the NS-C5 / rGO composite catalyst, and the N atoms in NS-C5 / rGO of Example 1 and N-C5 / rGO of Comparative Example 2 are different. The 1s spectrum showed a distinct visible peak at 399.9 eV, confirming the presence of pyrrole-N in the heterocycles of NS-C5 / rGO in Example 1 and N-C5 / rGO in Comparative Example 2. c shows the XPS spectra of NS-C5 / rGO and S-C5 / rGO S 1s, revealing thiophene-S (S 2p... 1 / 2At 164.7 or 165.1 eV, S 2p 3 / 2 The presence of X-ray absorption near-edge structure (XANES) spectra of NS-C5 / rGO in Example 1 and S-C5 / rGO in Comparative Example 1 (163.7 or 163.9 eV) is shown in d. The XANES spectra of the N atom in NS-C5 / rGO of Example 1 and N-C5 / rGO of Comparative Example 2 show a peak at 399.5 eV, representing the energy level from the 1s core level of the N atom to the π level. The electronic transitions to the antibonding state belong to the pyrrole-N species. e represents the K-edge XANES spectra of the S atoms in NS-C5 / rGO and S-C5 / rGO, indicating that the peaks in NS-C5 / rGO of Example 1 and S-C5 / rGO of Comparative Example 1 are mainly located at 2471 eV. This represents the transition of the S atom from its core 1s level to a higher-energy unresolved state, which is related to the bonding interaction between the S atom and adjacent C atoms in the aromatic system, further confirming the presence of thiophene-S in NS-C5 and S-C5. f represents the K-edge XANES spectra of the C atoms in NS-C5 / rGO, S-C5 / rGO, and N-C5 / rGO, where the peak at 284.3 eV is generally associated with the C atom in the benzene ring transitioning from the 1s orbital to the π orbital. The transitions are related to antibonding orbitals. This reflects the electronic structure characteristics of the aromatic system present in COM. Simultaneously, the peak value of 292 eV is related to the 1s-σ transition. This is relevant, and it may correspond to the transition from the carbon 1s energy level to σ. The shift in antibonding orbitals. Specifically, the peak near 292 eV may indicate electronic states associated with the CC, CS, and CN bonds in the NS-C5 / rGO composite catalyst of Example 1, the S-C5 / rGO composite catalyst of Comparative Example 1, and the N-C5 / rGO composite catalyst of Comparative Example 2, reflecting interactions with S- or N- atoms.

[0053] The UV-vis absorption spectra of the NS-C5 and NS-C5 / rGO composite catalysts in Example 1 are shown below. Figure 5 Compared to the original molecular NS-C5 in Example 1, the absorption peak of the NS-C5 / rGO composite material in Example 1 showed a significant red shift, indicating a strong π-π interaction between NS-C5 and rGO.

[0054] The IV curves of the NS-C5 / rGO composite catalyst in Example 1, the S-C5 / rGO composite catalyst in Comparative Example 1, and the N-C5 / rGO composite catalyst in Comparative Example 2 are shown below. Figure 6 As can be seen, the NS-C5 / rGO composite catalyst has higher conductivity compared to other catalysts.

[0055] Application Example 1: ORR Electrochemical Performance Testing (Acidic Conditions) Preparation of catalyst ink: 5 mg of the composite catalyst or raw material rGO obtained in Example 1 or Comparative Examples 1 and 2 were dispersed in a mixed solution of 225 μL deionized water, 225 μL ethanol and 50 μL Nafion (5 wt%) to obtain catalyst ink.

[0056] Electrochemical measurements were performed using a traditional three-electrode electrochemical workstation. The counter electrode was a Pt wire, the working electrode was a glassy carbon electrode, and the reference electrode was an Ag / AgCl (saturated potassium chloride solution) electrode. Linear sweep voltammetry (LSV) was performed using an O2-saturated 0.1M H2SO4 solution as the electrolyte. Figure 7 The LSV performance curves of ORR of 20NS-C5 / rGO composite catalyst, rGO, S-C5 / rGO and N-C5 / rGO composite catalyst under 0.1M H2SO4 electrolyte show that the NS-C5 / rGO composite catalyst prepared in Example 1 has a half-wave potential of 0.72V and has high acid oxygen reduction performance.

[0057] Application Example 2: ORR Electrochemical Performance Testing (Alkaline Conditions) Same as in Application Example 1, except that the electrolyte is a 0.1M KOH solution saturated with O2. Figure 8 The LSV performance curves of ORR of 20NS-C5 / rGO composite catalyst, rGO, S-C5 / rGO and N-C5 / rGO composite catalyst under 0.1M KOH electrolyte show that the NS-C5 / rGO composite catalyst prepared in Example 1 has a half-wave potential of 0.81 V and has high alkaline oxygen reduction performance.

[0058] Following the same method as in Application Example 1 or Application Example 2, the ORR electrochemical performance of the composite catalysts in Examples 1-6 and Comparative Example 3 was tested. Figure 9 The LSV performance curves for ORR of composite catalysts of 5NS-C5 / rGO, 10NS-C5 / rGO, 20NS-C5 / rGO, 30NS-C5 / rGO, 40NS-C5 / rGO, 50NS-C5 / rGO, and 60NS-C5 / rGO are shown in 0.1M H2SO4 electrolyte. Figure 10The LSV performance curves of the ORR composite catalysts 5NS-C5 / rGO, 10NS-C5 / rGO, 20NS-C5 / rGO, 30NS-C5 / rGO, 40NS-C5 / rGO, 50NS-C5 / rGO, and 60NS-C5 / rGO were obtained under 0.1M KOH electrolyte. The results showed that the catalytic activity increased with the increase of active site density, but the growth rate slowed down after the NS-C5 loading exceeded 30 mg.

[0059] Mechanism study: The ORR reaction process of the 20NS-C5 / rGO composite catalyst in Example 1 was monitored using in-situ ATR-SEIRAS technology, and the results are as follows: Figure 11 As shown. A ~890 cm⁻¹ was observed on the surface of the NS-C5 / rGO catalyst. -1 (O) and ~1094cm -1 (OO Characteristic absorption peaks of key intermediates such as ) and their intensities are higher than Figure 12 and Figure 13 Comparative Examples 1-2: N-C5 / rGO and S-C5 / rGO.

[0060] Theoretical calculation and analysis: S-C5, N-C5, and NS-C5 models were constructed using density functional theory calculations, and their ORR reaction free energies were calculated. The results of the DFT calculation models and reaction free energy diagrams are shown below. Figure 14 As shown. OOH on the NS-C5 model. The formation energy barrier of the intermediate (0.56 eV) was significantly lower than that of the S-C5 (0.91 eV) and N-C5 (0.80 eV) models, confirming that the N and S co-coordinated intermediate has superior ORR catalytic activity, and further verifying that NS-C5 is an excellent ORR catalytic active center.

[0061] Figure 15 This diagram illustrates the clear structure-activity relationship between the NS-C5 configuration and its intrinsic ORR activity. It demonstrates the precise synthesis of a novel nitrogen-sulfur coordinated pentagonal (C5) conjugated organic molecule (NS-C5) as an effective metal-free catalyst for the oxygen reduction reaction (ORR). The NS-C5 structure possesses well-defined active sites, exhibiting excellent catalytic activity for ORR. This accurately verifies that NS-C5 is an effective active site for ORR in both acidic and alkaline electrolytes. Furthermore, through rational analysis of the regulation of active site density and the precise construction of the NS-C5 structure, the origin of the unusual activity of NS-C5 is elucidated, and a clear structure-activity relationship between the NS-C5 configuration and its intrinsic ORR activity is established.

[0062] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for synthesizing an NS-C5 / rGO composite catalyst, characterized in that, Includes the following steps: (1) Methyl-3-aminobenzo[b]thiophene-2-carboxylic acid ester was refluxed with sodium hydroxide in a mixed solution of isopropanol and water. The reaction solution was post-treated to obtain crude sodium amino acid salt product. (2) Dissolve the crude sodium salt of the amino acid in glacial acetic acid, add formic acid and phenylhydrazine hydrochloride, reflux the reaction, and then post-treat the reaction solution to obtain the organic conjugated molecular product with nitrogen-sulfur-pentagonal carbon structure catalytic active center. (3) The organic conjugated molecular product of the nitrogen-sulfur-pentagonal carbon structure catalytic active center is mixed with reduced graphene oxide and composited by π-π stacking to obtain the NS-C5 / rGO composite catalyst.

2. The method for synthesizing the NS-C5 / rGO composite catalyst according to claim 1, characterized in that, In step (1), the volume ratio of isopropanol to water is 9:

1.

3. The method for synthesizing the NS-C5 / rGO composite catalyst according to claim 1, characterized in that, In step (1), the molar ratio of sodium hydroxide to methyl-3-aminobenzo[b]thiophene-2-carboxylic acid ester is 4:

1.

4. The method for synthesizing the NS-C5 / rGO composite catalyst according to claim 1, characterized in that, In step (1), the ratio of the amount of methyl-3-aminobenzo[b]thiophene-2-carboxylic acid ester to the mixed solution is 1 mmol: 20 mL.

5. The method for synthesizing the NS-C5 / rGO composite catalyst according to claim 1, characterized in that, In step (1), the reflux reaction is carried out at a temperature of 95-105℃ for 1-3 hours.

6. The method for synthesizing the NS-C5 / rGO composite catalyst according to claim 1, characterized in that, The molar ratio of formic acid and phenylhydrazine hydrochloride in step (2) to methyl-3-aminobenzo[b]thiophene-2-carboxylic acid ester in step (1) is 4:1.2:

1.

7. The method for synthesizing the NS-C5 / rGO composite catalyst according to claim 1, characterized in that, In step (2), the reflux reaction temperature is 125-135℃ and the reaction time is 2h.

8. The method for synthesizing the NS-C5 / rGO composite catalyst according to claim 1, characterized in that, In step (3), the mass ratio of the organic conjugated molecular product of the nitrogen-sulfur-pentagonal carbon structure catalytic active center to the reduced graphene oxide is (0.5-6):

1.

9. An NS-C5 / rGO composite catalyst, characterized in that, It is prepared according to any one of claims 1-8.

10. The application of the NS-C5 / rGO composite catalyst of claim 9 in the oxygen reduction reaction.

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