Graphene-based sheet layer porous catalyst and preparation method and application thereof

Abstract

This invention belongs to the field of electrocatalyst technology, and specifically relates to a graphene-based sheet-like porous catalyst, its preparation method, and its application. The preparation method includes: separately preparing an aqueous dispersion of graphene oxide and an aqueous dispersion of nano-melamine-formaldehyde resin, mixing them, and stirring to obtain a mixed dispersion; mixing the mixed dispersion with a hydroxyl-containing compound, adjusting the pH to weakly alkaline, stirring, concentrating, and drying to obtain a dried product; and subjecting the dried product to high-temperature pyrolysis. This method can prepare a sheet-like nitrogen-doped carbon-based non-noble metal electrocatalyst with stable mechanical properties, abundant pore structure, and high nitrogen content. It exhibits excellent electrochemical catalytic performance, has a simple preparation method, mild reaction conditions, and can achieve uniform nitrogen doping.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalyst technology, and specifically relates to a graphene-based sheet-like porous catalyst, its preparation method, and its application. Background Technology

[0002] In recent years, the energy crisis has become increasingly severe, and significant progress has been made in research on sustainable green energy storage and conversion devices. Electrocatalytic reactions such as oxygen reduction, oxygen evolution, and hydrogen evolution are key reactions in various energy storage and conversion devices. Developing highly efficient electrocatalysts is of great importance.

[0003] Carbon-based catalysts have attracted widespread attention in recent years due to their advantages such as good stability, high conductivity, and controllable pore structure. Among them, graphene-based catalysts are a promising type of electrocatalyst. However, the electrocatalytic performance of graphene-based electrocatalysts is unsatisfactory. The π-π interactions between graphene molecules may cause them to recombine, making it difficult to disperse the graphene uniformly, thereby reducing the accessibility of their active sites and resulting in poor electrocatalytic performance. To improve the performance of graphene-based electrocatalysts, researchers have increased the accessibility of active sites through graphene modification, defect engineering, and doping, thereby improving the electrocatalytic performance of graphene-based electrocatalysts and enabling their wider application in energy conversion and storage technologies. For example, patent CN109300701B discloses the preparation of a high-efficiency electrocatalyst composite material of multi-level porous graphene aerogel. It involves reducing and assembling the composite material by adding a reducing agent to obtain a three-dimensional graphene hydrogel with a multi-level porous structure. The three-dimensional graphene hydrogel is then soaked in a metal precursor solution, followed by hydrothermal method, freeze-drying, and pyrolysis to obtain the electrocatalyst. Patent CN202410235078.5 discloses a sulfur-doped graphene material, which is mainly prepared by mixing sublimed sulfur with graphene oxide and then annealing twice.

[0004] However, constructing a reasonable pore structure to solve the mass transfer problem in catalytic reactions, improve the utilization rate of active sites of catalysts, maximize the role of active sites, and thus enhance the performance of graphene-based electrocatalysts remains a technical challenge. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a graphene-based sheet-like porous catalyst, its preparation method, and its applications. This invention provides a novel method for constructing graphene-based sheet-like porous catalysts using templates. The prepared catalyst exhibits stable mechanical properties, abundant pore structure, and high nitrogen content, thereby significantly enhancing the performance of graphene-based electrocatalysts.

[0006] In a first aspect, the present invention provides a method for preparing a graphene-based sheet-like porous catalyst, comprising:

[0007] Aqueous dispersions of graphene oxide and nano-melamine-formaldehyde resin were prepared separately, mixed, and stirred to obtain a mixed dispersion.

[0008] The mixed dispersion was mixed with a hydroxyl-containing compound, and the pH was adjusted to weakly alkaline. After stirring, concentration, and drying, a dried product was obtained.

[0009] The dried product was subjected to high-temperature pyrolysis to obtain a graphene-based sheet-like porous catalyst.

[0010] In some embodiments, the particle size of the nano-melamine-formaldehyde resin is 20–50 nm, for example, any of 20 nm, 35 nm, or 50 nm. Melamine-formaldehyde resin with this particle size range can form mesoporous structures during subsequent pyrolysis and micropores during the pyrolysis process.

[0011] In some implementations, the aqueous dispersion of graphene oxide or the aqueous dispersion of nano-melamine-formaldehyde resin is prepared by adding graphene oxide or nano-melamine-formaldehyde resin to distilled water and then ultrasonically dispersing it using a dispersion device, such as a cell disruptor or mechanical stirring.

[0012] In some embodiments, the weight ratio of graphene oxide to nano-melamine-formaldehyde resin in the mixed dispersion is 1:10 to 40.

[0013] In some implementations, the pH is adjusted to 7-8, and under weakly alkaline conditions, hydroxyl-containing compounds can slowly self-polymerize, thereby achieving the combination of graphene oxide and melamine-formaldehyde resin.

[0014] In some embodiments, the hydroxyl-containing compound is 5,6-dihydroxyindole, 3,4-dihydroxyphenylalanine, dopamine hydrochloride, etc., with dopamine hydrochloride being preferred.

[0015] In some embodiments, the weight ratio of the hydroxyl-containing compound to the nano-melamine-formaldehyde resin in the mixed dispersion and the mixture containing the hydroxyl compound is 1:4 to 20. If the content of the hydroxyl-containing compound is too high, these compounds easily self-polymerize to form microspheres, which act as a link between the graphene oxide and the melamine-formaldehyde resin.

[0016] In some implementations, the two stirring operations are both carried out at room temperature, with stirring times of 2–4 h and 12–24 h, respectively.

[0017] In some implementation schemes, high-temperature pyrolysis involves first holding the resin at 300–400°C in an air atmosphere for 1–3 hours to decompose the nano-melamine-formaldehyde resin, and then holding it at 700–1000°C in an inert gas or nitrogen atmosphere for 1–3 hours.

[0018] Secondly, the present invention provides a graphene-based sheet-like porous catalyst prepared by the aforementioned method.

[0019] Thirdly, the present invention provides the application of the aforementioned graphene-based sheet-like porous catalyst in electrochemical catalysis.

[0020] Compared with the prior art, the preparation method provided by the present invention has the following advantages:

[0021] 1. This invention uses graphene oxide and nano-melamine-formaldehyde resin as templates, respectively. Through hydrogen bonding and self-polymerization of hydroxyl-containing compounds, the two templates are effectively combined to prepare a layered nitrogen-doped carbon-based non-noble metal electrocatalyst with stable mechanical properties, abundant pore structure, and high nitrogen content, exhibiting excellent electrochemical catalytic performance. Graphene oxide provides a good framework structure for the catalyst, while the slow release of ammonia during the pyrolysis of nano-melamine-formaldehyde resin simultaneously achieves pore formation and nitrogen doping, thereby enhancing the performance of the graphene-based electrocatalyst.

[0022] 2. The preparation method is simple and the reaction conditions are low, and the reaction can be carried out at room temperature.

[0023] 3. During the pyrolysis process, melamine undergoes pyrolysis and slowly releases nitrogen-containing gas, which enables uniform doping of nitrogen elements. Attached Figure Description

[0024] Figure 1 The transmission electron microscopy (TEM) energy dispersive spectroscopy (EDS) spectrum of the graphene-based sheet-like porous catalyst prepared in Example 1;

[0025] Figure 2 The adsorption-desorption curves are for graphene-based sheet-like porous catalysts.

[0026] Figure 3 LSV curves for graphene-based sheet-like porous catalysts and Pt / C. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1

[0029] (1) Weigh 2.5 mg of graphene oxide, add 5 mL of distilled water, and sonicate for 30 min using a cell disruptor to obtain a graphene oxide dispersion. Weigh 0.1 g of melamine-formaldehyde resin microspheres with a particle size of 20 nm, add 5 mL of distilled water, sonicate for 3 min using a cell disruptor, and then add them to the graphene oxide dispersion. Stir at room temperature for 2 h.

[0030] (2) Add 5 mg of dopamine hydrochloride to the dispersion obtained in step 1, then add 10 mL of Tris buffer, and continue stirring at room temperature for 12 h, filter, and vacuum dry.

[0031] (3) The dried product obtained in step (2) is first dried at 2℃ for 2 minutes. -1 The temperature was increased to 350℃ at a heating rate, held in air for 2 hours, and then increased at a rate of 2℃ / min. -1 The heating rate was increased to 700℃ in an argon atmosphere and held for 2 hours to finally obtain a sheet carbon material with a mesoporous structure, namely a graphene-based sheet porous catalyst.

[0032] Example 2

[0033] (1) Weigh 100 mg of graphene oxide, add 20 mL of distilled water, and sonicate for 60 min using a cell disruptor to obtain a graphene oxide dispersion. Weigh 1 g of melamine-formaldehyde resin microspheres with a particle size of 50 nm, add 15 mL of distilled water, sonicate for 10 min using a cell disruptor, and then add them to the graphene oxide dispersion. Stir at room temperature for 4 h.

[0034] (2) Add 200 mg of dopamine hydrochloride to the dispersion obtained in step 1, then add 10 mL of Tris buffer, and continue stirring at room temperature for 24 h, filter, and vacuum dry.

[0035] (3) The dried product obtained in step (2) is first dried at 2℃ for 2 minutes. -1 The temperature was increased to 350℃ at a heating rate, held in air for 2 hours, and then increased at a rate of 2℃ / min. -1 The heating rate was increased to 1000℃ in a nitrogen atmosphere and held for 2 hours to finally obtain a sheet carbon material with a mesoporous structure, namely a graphene-based sheet porous catalyst.

[0036] Figure 1 The image shows the transmission electron microscopy (TEM) energy dispersive spectroscopy (EDS) spectrum of the graphene-based sheet porous catalyst prepared in Example 1. It can be seen that the sheet graphene material has a rich pore structure, indicating that the melamine-formaldehyde resin and graphene oxide are effectively combined and form a rich pore structure after pyrolysis.

[0037] Figure 2The adsorption-desorption curves of the graphene-based sheet-like porous catalyst prepared in Example 1 show that the material has a large specific surface area and mesoporous structure.

[0038] Figure 3 The LSV curves of the graphene-based sheet-like porous catalyst and Pt / C show that the oxygen reduction electrocatalytic performance of the non-noble metal catalyst of this invention is close to that of platinum, demonstrating good point catalytic performance.

[0039] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A method for preparing a graphene-based sheet-like porous catalyst, characterized in that, The preparation method includes: Aqueous dispersions of graphene oxide and nano-melamine-formaldehyde resin were prepared separately, mixed, and stirred to obtain a mixed dispersion. The mixed dispersion was mixed with a hydroxyl-containing compound, and the pH was adjusted to weakly alkaline. After stirring, concentration, and drying, a dried product was obtained. The dried product was subjected to high-temperature pyrolysis to obtain a graphene-based sheet-like porous catalyst.

2. The preparation method according to claim 1, characterized in that, The particle size of the nano-melamine-formaldehyde resin is 20-50 nm.

3. The preparation method according to claim 1, characterized in that, In the mixed dispersion, the weight ratio of graphene oxide to nano-melamine formaldehyde resin is 1:10 to 40.

4. The preparation method according to claim 1, characterized in that, The hydroxyl-containing compound is 5,6-dihydroxyindole, 3,4-dihydroxyphenylalanine, or dopamine hydrochloride.

5. The preparation method according to claim 4, characterized in that, The hydroxyl-containing compound is dopamine hydrochloride.

6. The preparation method according to claim 1, characterized in that, In the mixed dispersion and the mixture containing hydroxyl compounds, the weight ratio of the hydroxyl compounds to the nano-melamine-formaldehyde resin is 1:4 to 20.

7. The preparation method according to claim 1, characterized in that, The two stirring operations were carried out at room temperature, with stirring times of 2–4 h and 12–24 h, respectively.

8. The preparation method according to claim 1, characterized in that, The high-temperature pyrolysis is performed by first holding the mixture at 300–400°C in an air atmosphere for 1–3 hours, and then holding it at 700–1000°C in an inert gas or nitrogen atmosphere for 1–3 hours.

9. The graphene-based sheet-like porous catalyst prepared by the method according to any one of claims 1 to 8.

10. The application of the graphene-based sheet-like porous catalyst according to claim 9 in electrochemical catalysis.

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