Preparation method for converting marine polysaccharide into trifunctional carbon-based monatomic catalyst

Abstract

The invention relates to the technical field of electrocatalysts, and particularly discloses a method for preparing a nitrogen and phosphorus doped iron monatomic three-function carbon-based catalyst from marine polysaccharide. The method comprises the following steps: (1) dissolving marine polysaccharide, and fully mixing the dissolved marine polysaccharide with a transition metal salt solution, a template agent and a phosphorus source to prepare a marine polysaccharide-based porous carbon precursor; (2) carrying out carbonization treatment on the porous carbon precursor at 800-1000 DEG C to obtain the marine polysaccharide-based porous carbon material, and (3) mixing the porous carbon material with a nitrogen-containing compound, drying, and carrying out secondary carbonization in an inert atmosphere at 800-1000 DEG C to finally obtain the marine polysaccharide-derived nitrogen and phosphorus-doped iron monatomic three-function carbon-based catalyst. The catalyst has a high specific surface area, a hierarchical pore structure and rich monatomic iron active sites, and shows excellent ORR, OER and HER three-function catalytic activity. The raw materials used in the invention are renewable and low-cost marine polysaccharides (such as chitosan, alginate and agarose) which are rich in source, low in price and easy to obtain, the preparation process is simple, and an effective way is provided for high-value utilization of marine waste resources. The prepared efficient marine polysaccharide-derived three-function carbon-based monatomic catalyst can be widely applied to the fields of energy conversion and storage of fuel cells, metal-air cells, water electrolysis devices and the like.

Description

Technical Field

[0001] This invention relates to the field of transition metal single-atom catalyst preparation technology, and particularly to a method for preparing transition metal single-atom catalysts from marine polysaccharides and their application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Currently, the overexploitation and consumption of petroleum resources has caused a global energy crisis and environmental pollution, severely restricting human survival and development. Developing new green and clean energy technologies is key to solving these problems. Currently, efficient and clean energy sources such as hydrogen-oxygen fuel cells and metal-air batteries have become the main direction for future energy development. However, the slow cathode hydrogen evolution, oxygen evolution, and oxygen reduction reactions limit the efficient utilization of these energy sources. Developing advanced carbon-based catalysts is particularly crucial for the efficient development of clean energy. Transition metal single-atom catalysts, with their high activity and high selectivity, are widely used in electrocatalysis research and have excellent research prospects and application scope.

[0004] Marine polysaccharides are a class of natural high-molecular-weight carbohydrates widely found in marine organisms such as algae, crustaceans, and shellfish. They are characterized by their abundant sources, renewability, good biocompatibility, biodegradability, and structural diversity. These polysaccharides have unique molecular structures and are typically rich in functional groups (such as hydroxyl -OH, carboxylic acid -COOH, amino -NH2, and sulfate ester -OSO3). - Marine polysaccharides contain a large number of heteroatoms (such as sulfur-S and nitrogen-N). Due to their excellent physicochemical properties and biological activity, marine polysaccharides have long been widely studied and applied in many fields such as biomedicine, food industry, environmental protection, agriculture, and cosmetics. However, their in-depth development and utilization in high-value functional materials, especially advanced carbon materials and electrocatalysis and energy catalysis materials, are still insufficient, particularly in the cutting-edge field of single-atom catalysts, where research is still in its early exploratory stages.

[0005] Currently, the mainstream methods for preparing single-atom catalysts mainly include impregnation, co-precipitation, atomic layer deposition, and mass separation-soft landing. These methods have made some progress in achieving atomic-level metal dispersion, but still face the following key bottlenecks: (1) complex and cumbersome processes; (2) high equipment dependence and high cost; (3) low controllable synthesis yield; (4) limited effective metal loading; and (5) limited and costly precursor sources. Therefore, it is of urgent significance to develop novel, simple, efficient, and scalable strategies for preparing single-atom catalysts. Utilizing abundant and structurally tunable biomass (such as marine polysaccharides, lignocellulose, and agricultural waste) as carbon supports and heteroatom sources, high-performance single-atom catalysts can be constructed through optimized thermochemical conversion pathways. This not only breaks through the bottlenecks of traditional methods but also realizes a closed-loop technical route of "waste resource utilization - material functionalization - energy cleanification." This is crucial for promoting the practical application of clean energy technologies such as hydrogen fuel cells, metal-air batteries, and water electrolysis devices. Summary of the Invention

[0006] To address the challenges of complex, expensive, and equipment-intensive traditional methods for preparing single-atom catalysts, this invention provides a method for preparing trifunctional carbon-based single-atom catalysts using renewable marine polysaccharides as a carbon source. This method is simple, environmentally friendly, and fully utilizes marine biomass waste resources. Through a one-step controllable pyrolysis and atomic confinement strategy, it achieves high-performance Fe-N catalysts. x With precise site anchoring, the resulting catalyst possesses triple catalytic functions for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER).

[0007] This invention also provides applications of the aforementioned trifunctional carbon-based single-atom catalyst. The catalyst can be used as an electrode material for various electrochemical devices, particularly suitable for metal-air battery cathodes, bifunctional catalysts for water electrolyzers, and oxygen reduction catalysts for fuel cell cathodes, showing significant industrialization potential in the field of clean energy conversion and storage.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a trifunctional carbon-based single-atom catalyst for the conversion of marine polysaccharides:

[0010] Marine polysaccharides were dissolved by heating, metal salts were added, and the mixture was quickly stirred and dispersed evenly. Then, template agents and phosphorus sources were added, and the mixture was freeze-dried to obtain a phosphorus-doped metal single-atom catalyst precursor derived from marine polysaccharides.

[0011] The phosphorus-doped metal single-atom catalyst precursor derived from marine polysaccharides was carbonized once, washed, and dried to obtain a porous carbon material doped with phosphorus and iron derived from marine polysaccharides.

[0012] The phosphorus and iron-doped porous carbon material derived from the marine polysaccharide was mixed with a nitrogen-containing compound, ground, and then carbonized twice to obtain a transition metal single-atom catalyst.

[0013] This invention develops a novel, efficient, and low-cost strategy for manufacturing carbon-based single-atom catalysts. Using renewable marine polysaccharides (such as seaweed waste and chitosan) as green precursors, and through controlled pyrolysis and impurity self-doping processes, waste biomass is upgraded and transformed into a high-performance trifunctional catalyst. This method simplifies the multi-step preparation process of traditional single-atom catalysts, ensuring the harmless treatment of marine solid waste while converting it into an electrocatalytic material with ORR, OER, and HER triple catalytic functions, providing a sustainable solution for electrode materials in clean energy devices.

[0014] This invention mainly utilizes the functional group coordination metals abundant in marine polysaccharides, and through mixed pyrolysis, after removing the salt template, it is doped with nitrogen-containing compounds and pyrolyzed to synthesize a trifunctional single-atom catalyst with a transition metal-nitrogen-phosphorus structure.

[0015] In some embodiments, the marine polysaccharide is agarose, sodium alginate, chitosan, fucoidan, chondroitin sulfate, etc., and the raw material is selected from at least one of brown algae, red algae, green algae, and shrimp / crab shells.

[0016] In some embodiments, the metal salt is at least one selected from the chloride salt, acetate, nitrate, and sulfate salt of a transition metal;

[0017] In some embodiments, the transition metal is at least one of iron, cobalt, nickel, and zinc.

[0018] In some embodiments, the template agent is at least one of sodium chloride, potassium chloride, sodium carbonate, sodium bicarbonate, and sodium sulfate.

[0019] In some embodiments, the ratio of the marine polysaccharide to the metal salt is 1.5g:0.05-0.1g.

[0020] In some embodiments, the phosphorus source is at least one of sodium phytate, phytic acid, sodium dihydrogen phosphate, sodium metabiphosphite, and sodium hexametaphosphate.

[0021] In some embodiments, the rapid stirring time is 15-45 min, the freeze-drying conditions are -40 to -60°C, 0.1 mPa, and the freeze-drying time is 24 to 48 h;

[0022] In some embodiments, the specific conditions for the primary carbonization are as follows: under an inert atmosphere, the carbonization temperature is 600-800℃, the carbonization time is 5-8h, and the heating program is 2-10℃ / min.

[0023] In some embodiments, the washing temperature is 50-60°C, the washing solution is 0.5-2 mol / L hydrochloric acid, sulfuric acid or nitric acid, and the washing time is 8-24 h.

[0024] In some implementations, the drying temperature after washing is 50-90°C, and the drying time is 8-16 hours.

[0025] In some embodiments, the nitrogen-containing compound is at least one of ammonium chloride, ammonium bromide, ammonium phosphate, urea, thiourea, ammonium dihydrogen phosphate, and melamine.

[0026] In some embodiments, the mass ratio of marine polysaccharide-derived transition metal-doped porous carbon material to nitrogen-containing compound is 1:1-25.

[0027] In some embodiments, the conditions for secondary carbonization are as follows: under an inert atmosphere, the carbonization temperature is 800–1100°C, the carbonization time is 1–5 h, and the heating rate during carbonization is 2–10°C / min.

[0028] In some embodiments, the inert atmosphere is one of nitrogen, argon, carbon dioxide, or an argon-hydrogen mixture.

[0029] More specifically, including:

[0030] Step (1): Heating to dissolve the marine polysaccharide, adding Fe metal salt, template agent, and phosphorus source, stirring rapidly, and freeze-drying. This yields a phosphorus-doped transition metal-doped porous carbon material derived from the marine polysaccharide. The marine polysaccharide is one of agarose, sodium alginate, or fucoidan.

[0031] Step (2): Carbonize the freeze-dried precursor and wash and dry it to obtain marine polysaccharide-derived iron and phosphorus-doped porous carbon material.

[0032] Step (3): Thoroughly mix and grind the iron-doped porous carbon material derived from marine polysaccharides with nitrogen-containing compounds, and carbonize it to obtain a transition metal single-atom catalyst with a metal-nitrogen-phosphorus structure.

[0033] Furthermore, the concentration of the marine polysaccharide solution in step (1) is 2-5 wt%.

[0034] A second aspect of this invention provides the application of a trifunctional carbon-based single-atom catalyst based on marine polysaccharides prepared by the above method in the field of electrocatalysis. The catalyst simultaneously possesses excellent ORR, OER, and HER electrocatalytic activities. Specific applications include, but are not limited to, electrode catalytic materials for the following devices: metal-air batteries (preferably zinc-air batteries), water electrolysis hydrogen production devices, and / or rechargeable zinc-air batteries (possessing both discharge ORR and charge OER functions). The catalytic material is used to improve the efficiency and stability of the corresponding oxygen reduction, oxygen evolution, or hydrogen evolution reactions in the device.

[0035] When marine polysaccharide-based trifunctional carbon-based single-atom catalysts are used as oxygen electrode catalytic materials in zinc-air batteries, 6M potassium hydroxide and 0.2M zinc acetate solutions are prepared as electrolyte solutions for electrochemical performance testing; when used as cathode and anode catalytic materials for water electrolysis to produce hydrogen, 1M potassium hydroxide solution is prepared as electrolyte solutions for electrochemical performance testing.

[0036] This invention utilizes marine polysaccharides as a carbon source and metal chelating agent to prepare a trifunctional carbon-based single-atom catalyst with atomically dispersed metal sites and optimized pore structure through specific conversion processes (metal coordination, controlled carbonization, and single-atom microenvironment regulation). This catalyst exhibits excellent synergistic catalytic activity and stability in electrocatalytic ORR, OER, and HER. This preparation method not only fully utilizes naturally renewable and biocompatible marine biomass resources, achieving a green upgrade from low-value materials to high-performance multifunctional catalytic materials, but also features a green and simple preparation process with low energy consumption, reflecting environmentally friendly principles and conforming to the concept of sustainable green chemistry.

[0037] A third aspect of the invention provides the application of the marine polysaccharide in the preparation of carbon-based single-atom catalysts with highly efficient ORR, OER and HER catalytic activities.

[0038] Beneficial effects of the present invention

[0039] (1) Green and sustainable raw materials, simple and efficient process: This invention uses abundant renewable marine polysaccharides (such as sodium alginate, carrageenan, etc.) as carbon precursors. The raw materials are widely available, naturally degradable, and inexpensive, and avoid the environmental impact of traditional fossil-based precursors. It provides a highly green and environmentally friendly, low-cost preparation route for single-atom catalysts that conforms to the concept of carbon neutrality. The method has simple conversion steps, mild conditions, and controllable process, making it easy to achieve large-scale preparation.

[0040] (2) Polysaccharide structural advantages solve the pain points in the preparation of catalytic materials: This invention makes full use of the unique molecular structure of marine polysaccharides (rich in functional groups such as -OH and -COOH) and their chelation effect to achieve efficient and uniform anchoring of inexpensive transition metal ions. This unique self-assembly ability derived from biological macromolecules effectively inhibits the migration and aggregation of metal atoms during heat treatment, and significantly improves the loading, dispersion uniformity and stability of single-atom metal sites.

[0041] (3) Excellent trifunctional catalytic performance and strong versatility: The carbon-based single-atom catalyst of this invention, prepared by an optimized process using marine polysaccharides, has a unique three-dimensional hierarchical pore structure and high specific surface area. More importantly, its unique active sites and the synergistic effect with the support endow the catalyst with simultaneous and efficient electrocatalytic activity: it not only exhibits excellent ORR activity, but also shows high catalytic activity and long-lasting stability for OER and HER, demonstrating excellent versatility in application.

[0042] (4) Wide range of multifunctional applications: Based on the excellent ORR / OER / HER trifunctional synergistic catalytic performance mentioned above, this catalyst can be widely used as a core catalytic material in the following applications:

[0043] Metal-air batteries (especially rechargeable zinc-air batteries) possess both cathode discharge ORR and charging OER catalytic activities.

[0044] Hydrogen production in water electrolysis units (as a highly efficient bifunctional or trifunctional electrode material for HER and OER).

[0045] Fuel cells (e.g., cathode with ORR activity)

[0046] Other energy conversion devices that require efficient oxygen or hydrogen transfer electrocatalysis.

[0047] (5) Excellent performance for core energy devices: The specific metal-based (such as Fe-, Co-, Ni- single atom, etc.) carbon-based catalysts prepared by this method, as cathode catalysts for metal-air batteries (especially in zinc-air batteries), show excellent performance in terms of catalytic activity and cycle life; at the same time, their excellent HER / OER performance also makes them have great application potential in water electrolysis hydrogen production devices, providing an efficient solution for future renewable energy storage and conversion. Attached Figure Description

[0048] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. Exemplary embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0049] Figure 1 SEM image of the marine polysaccharide-based trifunctional carbon-based single-atom catalyst prepared in Example 1;

[0050] Figure 2 TEM images, annular dark-field scans, and corresponding elemental energy spectra of the marine polysaccharide-based trifunctional carbon-based single-atom catalyst prepared in Example 1;

[0051] Figure 3 Linear sweep voltammetry curves of the marine polysaccharide-based trifunctional carbon-based single-atom catalysts prepared in Examples 1-4, a) ORR, b) OER, c) HER;

[0052] Figure 4 Example 1 and Pt / C were used as electrode catalytic materials for zinc-air batteries, and the cycle stability performance test curves of zinc-air batteries were obtained.

[0053] Figure 5 Linear sweep voltammetry curves for Example 1 and Pt / C+RuO2 used as catalytic materials in water electrolysis electrodes;

[0054] Figure 6 The stability curves of Example 1 and Pt / C+RuO2 used as the catalytic material for water electrolysis electrode are shown at different current densities. Detailed Implementation

[0055] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0056] As described in the background section, due to the high surface energy of a single atom, metal ions are prone to migration and aggregation during pyrolysis, making the development of highly stable single-atom catalysts extremely challenging. At the same time, many published single-atom catalysts are limited by their pore structure or support characteristics, resulting in insufficient exposure of active sites or single catalytic function, which greatly limits their potential for multi-scenario applications.

[0057] Therefore, this invention proposes using marine polysaccharides as the core carbon precursor to prepare carbon-based single-atom catalysts with both high stability and multiple catalytic activities (ORR, OER, HER), with the following main advantages:

[0058] Marine polysaccharides (such as alginate, carrageenan, and agar) possess unique gel network structures and polymer chain characteristics. During pyrolysis preconstruction and carbonization, this structure effectively builds a well-developed pore system and a high specific surface area carbon skeleton. This inherently self-generated porous structure significantly increases the available specific surface area and exposure of active sites, and facilitates mass transport. Unlike other preparation methods that require multiple pretreatment steps, this invention fully utilizes the physicochemical properties of marine polysaccharides to form the desired pores, avoiding complex removal steps, significantly simplifying the process and reducing costs.

[0059] Marine polysaccharides contain a large number of active functional groups such as carboxyl, hydroxyl, sulfate, and amino groups, which have strong coordination / complexation effects on metal cations, enabling them to firmly anchor metal atoms in the early stages of material formation. This strong interaction effectively inhibits the migration and aggregation of metal atoms during subsequent pyrolysis, ensuring that the metal exists in an atomically dispersed state in the final product and significantly improving the thermal stability of the catalyst.

[0060] Achieving Trifunctional Integrated Catalysis: Utilizing the diverse doping of natural heteroatoms and precisely constructed single-atom metal sites (such as Fe, Co, Ni, Zn, etc.), the catalyst obtained in this invention can simultaneously and efficiently catalyze three key reactions: ORR, OER, and HER. This "trifunctional integration" characteristic benefits from the unique atomic-scale coordination environment (MN) induced by marine polysaccharide precursors. x P y O z The synergistic regulatory advantages of carbon substrate properties by atoms and heteroatoms (N, S, O) lay the core foundation for achieving multifunctional integrated applications of single materials.

[0061] Therefore, by using marine polysaccharides as the core carbon precursor and multi-element dopant source, the method of this invention can not only effectively prevent the aggregation of metal atoms and improve the stability and active site exposure of the catalyst, but also construct a trifunctional carbon-based single-atom catalyst integrating high ORR, OER, and HER activity through its abundant natural heteroelements and unique structural regulation capabilities. This invention fully utilizes the advantages of marine polysaccharides, such as their naturalness, sustainability, low cost, and unique composition, providing a promising route for the low-cost, large-scale, and green preparation of high-performance multifunctional single-atom catalysts.

[0062] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0063] Example 1

[0064] A method for preparing a marine polysaccharide-based trifunctional carbon-based single-atom catalyst includes the following steps:

[0065] (1) 1.5 g agarose was added to 50 ml of water and dissolved at 90 °C for 2 h to form a homogeneous solution. Then, 0.075 g FeCl3·6H2O, 1.25 g NaCl, and 25 ml of 25 wt% sodium phytate solution with pH 7.5 were added. The mixture was stirred rapidly for 30 min and then freeze-dried at -60 °C for 48 h to obtain a porous carbon precursor derived from marine polysaccharides and doped with iron and phosphorus.

[0066] (2) The iron and phosphorus-doped marine polysaccharide-derived porous carbon precursor was pyrolyzed at 900℃ under nitrogen atmosphere for 2h (heating rate of 2.5℃ / min), washed with deionized water until no white precipitate was produced after adding silver chloride, and dried at 60℃ for later use to obtain marine polysaccharide-derived iron and phosphorus-doped porous carbon.

[0067] (3) Iron and phosphorus-doped porous carbon derived from marine polysaccharides was mixed and ground with ammonium chloride at a mass ratio of 1:10. After grinding, it was pyrolyzed at 900℃ under a nitrogen atmosphere for 2 hours (heating rate of 5℃ / min) to obtain a nitrogen and phosphorus-doped trifunctional iron single-atom catalyst derived from marine polysaccharides.

[0068] Example 2

[0069] A method for preparing a marine polysaccharide-based trifunctional carbon-based single-atom catalyst includes the following steps:

[0070] (1) 1.5 g agarose was added to 50 ml of water and dissolved at 90°C for 2 h to form a homogeneous solution. Then, 0.075 g FeCl3·6H2O and 1.25 g NaCl were added, and the mixture was stirred rapidly for 30 min. After freeze-drying at -60°C for 48 h, an iron-doped porous carbon precursor derived from marine polysaccharides was obtained.

[0071] (2) The iron-doped marine polysaccharide-derived porous carbon precursor was pyrolyzed at 900℃ under a nitrogen atmosphere for 2h (heating rate of 2.5℃ / min), washed with deionized water until no white precipitate was produced after adding silver chloride, and dried at 60℃ for later use to obtain marine polysaccharide-derived iron-doped porous carbon.

[0072] (3) Iron and phosphorus-doped porous carbon derived from marine polysaccharides was mixed with ammonium chloride at a mass ratio of 1:10 and ground. After grinding, it was pyrolyzed at 900℃ under a nitrogen atmosphere for 2 hours (heating rate of 5℃ / min) to obtain a nitrogen-doped iron single-atom catalyst derived from marine polysaccharides.

[0073] Example 3

[0074] A method for preparing a marine polysaccharide-based trifunctional carbon-based single-atom catalyst includes the following steps:

[0075] (1) 1.5 g agarose was added to 50 ml of water and dissolved at 90°C for 2 h to form a homogeneous solution. Then, 1.25 g NaCl and 25 ml of 25 wt% sodium phytate solution with pH 7.5 were added. The mixture was stirred rapidly for 30 min and then freeze-dried at -60°C for 48 h to obtain a phosphorus-doped porous carbon precursor derived from marine polysaccharides.

[0076] (2) The iron and phosphorus-doped marine polysaccharide-derived porous carbon precursor was pyrolyzed at 900℃ under nitrogen atmosphere for 2h (heating rate of 2.5℃ / min), washed with deionized water until no white precipitate was produced after adding silver chloride, and dried at 60℃ for later use to obtain phosphorus-doped porous carbon derived from marine polysaccharides.

[0077] (3) The phosphorus-doped porous carbon derived from marine polysaccharides was mixed with ammonium chloride at a mass ratio of 1:10 and ground. After grinding, it was pyrolyzed at 900℃ under a nitrogen atmosphere for 2 hours (heating rate of 5℃ / min) to obtain the nitrogen and phosphorus-doped catalyst derived from marine polysaccharides.

[0078] Structural characterization and performance testing:

[0079] Figure 1 This is a SEM image of the marine polysaccharide-based trifunctional carbon-based single-atom catalyst from Example 1.

[0080] Figure 1 The catalyst in question is a nitrogen- and phosphorus-doped trifunctional iron single-atom catalyst derived from marine polysaccharides obtained in Example 1. Figure 1 (a) and (b) clearly show that the nitrogen and phosphorus doped catalysts derived from marine polysaccharides have a distinct honeycomb pore structure. This is because the polysaccharide cross-linking and the action of the template agent endow the catalyst with a rich pore structure during the subsequent pyrolysis process.

[0081] Figure 2 As can be seen from (a) and (b), the nitrogen and phosphorus doped trifunctional iron single-atom catalysts derived from marine polysaccharides have obvious mesopores and micropores, as well as graphene-like sheet structures, indicating that the nitrogen and phosphorus doped trifunctional iron single-atom catalysts derived from marine polysaccharides have well-developed pore structures and a high degree of graphitization.

[0082] Figure 2 (c) A ring dark-field scanning image and its corresponding elemental energy spectrum of the nitrogen- and phosphorus-doped trifunctional iron single-atom catalyst derived from marine polysaccharides prepared in Example 1. On the carbon framework of the nitrogen- and phosphorus-doped trifunctional iron single-atom catalyst derived from marine polysaccharides, carbon, nitrogen, iron, and phosphorus elements are uniformly distributed, indicating that iron exists in the form of single atoms rather than as an element or other oxide.

[0083] Figure 3(a) shows the oxygen reduction, oxygen evolution, and hydrogen evolution activity curves of the marine polysaccharide-derived porous carbon materials prepared in Examples 1-3. Electrochemical tests were performed using an electrochemical workstation with a typical three-electrode system. A Pt sheet was used as the counter electrode, and Ag / AgCl was used as the reference electrode. All voltages were converted to a relatively reversible hydrogen electrode. For the ORR test, before the test, a mixture of 5 mg of carbon material and 1 ml of 0.02% Nafion / ethanol solution was ultrasonically treated to obtain catalyst ink, which was then dropped onto a glassy carbon electrode (5 mm in diameter). Simultaneously, 20 wt% Pt / C ink was prepared as a control to compare and evaluate the catalyst performance. For the OER and HER tests, before the test, a mixture of 5 mg of carbon material and 0.5 ml of 1% Nafion / ethanol solution was ultrasonically treated to obtain catalyst ink, which was then dropped onto nickel foam. Simultaneously, 20 wt% Pt / C ink and RuO2 ink were prepared as controls to compare and evaluate the catalyst performance.

[0084] Example 1: A nitrogen- and phosphorus-doped trifunctional iron single-atom catalyst derived from marine polysaccharides; Example 2: A nitrogen-doped iron single-atom catalyst derived from marine polysaccharides; Example 3: A nitrogen- and phosphorus-doped catalyst derived from marine polysaccharides; from Figure 3 As shown in the oxygen reduction cyclic voltammetry curves of (a), Example 1 has a higher onset potential and half-wave potential than platinum carbon, and its kinetic current is greater than that of commercial platinum carbon; from Figure 3 (b) The cyclic voltammetry curve for oxygen evolution in Example 1 shows that at 100 mA cm⁻¹ -2 At a current density of only 315 mV, its overpotential is significantly better than that of commercial ruthenium dioxide catalysts; from Figure 3 (c) The hydrogen evolution cyclic voltammetry curve of Example 1 shows that at 100 mA cm⁻¹ -2 At a current density of 172mV, its overpotential is only 172mV, demonstrating excellent HER performance. The above indicates that, through the method of Example 1, the marine polysaccharide-derived nitrogen and phosphorus-doped trifunctional iron single-atom catalyst exhibits excellent trifunctional activity.

[0085] Figure 4 The nitrogen- and phosphorus-doped trifunctional iron single-atom catalyst derived from marine polysaccharides prepared in Example 1 was used as the electrode catalytic material for a zinc-air battery. A rechargeable zinc-air battery was fabricated using a dual-electrode structure, with the aforementioned catalyst ink loaded onto carbon cloth as one electrode (i.e., the air cathode, with a loading of 1.5 mg cm⁻¹). -2 Polished zinc foil was used as the other electrode. A solution containing 6M potassium hydroxide and 0.2M zinc acetate was used as the electrolyte. Constant current charge-discharge cycle performance test curves of the zinc-air battery were presented. Figure 4 It can be seen that the assembled zinc-air battery operates at 10 mA / cm². -2It can cycle for 3000 hours during discharge and still has good charge-discharge stability, which is significantly better than commercial Pt / C catalysts (battery fails after 150 hours of cycling).

[0086] Figure 5 The nitrogen- and phosphorus-doped trifunctional iron single-atom catalyst derived from marine polysaccharides prepared in Example 1 was used as the catalytic material for the water electrolysis electrode. A water splitting device was fabricated using a dual-electrode structure, with the above-mentioned catalyst ink loaded onto nickel foam as the cathode and anode, respectively. 1M potassium hydroxide was used as the electrolyte during testing. Figure 5 As shown, the water splitting device assembled in Example 1 has an overpotential of only 1.85V at 50mAcm⁻², which is better than the 1.96V of the Pt / C+RuO₂ assembly, indicating that it can achieve water splitting with lower energy consumption in practical applications.

[0087] Figure 6 The stability test of the nitrogen and phosphorus-doped trifunctional iron single-atom catalyst derived from marine polysaccharides prepared in Example 1 as a catalytic material for water electrolysis electrode was conducted. The results showed that the nitrogen and phosphorus-doped trifunctional iron single-atom catalyst derived from marine polysaccharides could maintain stable charge-discharge performance under different currents.

[0088] Comparative Example 1

[0089] The difference from Example 1 is that sodium phytate solution was not added in step (1). All other steps and parameters were identical to those in Example 1. The resulting sample had an ORR half-wave potential of 0.84 V vs. RHE, reaching 100 mA cm⁻¹ in the OER reaction. -2 The overpotential is 421 mV, reaching 100 mA cm⁻¹ in the HER reaction. -2 The overpotential is 336mV.

[0090] Comparative Example 2

[0091] The difference from Example 1 is that in step (1), the same molar amount of FeCl2·4H2O was used instead of FeCl3·6H2O as the iron source. All other steps and parameters were exactly the same as in Example 1. The resulting sample had an ORR half-wave potential of 0.86 V vs. RHE, reaching 100 mA cm⁻¹ in the OER reaction. -2 The overpotential is 365mV, reaching 100mAcm in the HER reaction. -2 The overpotential is 325mV.

[0092] Comparative Example 3

[0093] The difference from Example 1 is that the pyrolysis temperature in steps (2) and (3) was changed to 800℃ (other heating rates, atmosphere, and time remained unchanged). The resulting sample had an ORR half-wave potential of 0.85V vs. RHE, reaching 100mAcm in the OER reaction. -2 The overpotential is 434 mV, reaching 100 mA cm⁻¹ in the HER reaction. -2 The overpotential is 365mV.

[0094] These comparative examples are designed to reveal the importance of key components or process parameters in Example 1:

[0095] Comparative Example 1 (without sodium phytate): This highlights the crucial role of sodium phytate as a phosphorus source and potential pore-forming / dispersant. Removal of the phosphorus source is expected to lead to a significant decrease in ORR, OER, and HER performance.

[0096] Comparative Example 2 (Fe3+) 2+ Replacement of Fe3+ 3+ The influence of the valence state of the iron source on the formation of Fe single-atom centers was investigated. 3+ It may have stronger coordination ability and precursor cross-linking effect (such as cross-linking polysaccharide chains).

[0097] Comparative Example 3 (lower pyrolysis temperature 800℃): Demonstrates that a higher pyrolysis temperature (900℃) is beneficial for forming a highly graphitized, highly conductive carbon substrate and for forming a stable and efficient Fe-N matrix. x P y The necessity of active centers. Low-temperature treatment often results in numerous structural defects in carbon supports, poor conductivity, insufficient number of active centers, or poor stability.

[0098] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a marine polysaccharide-based trifunctional carbon-based single-atom catalyst, characterized in that, include: Marine polysaccharides were dissolved by heating, and metal salts, template agents and phosphorus sources were added. The mixture was stirred rapidly and then freeze-dried to obtain iron and phosphorus-doped porous carbon precursors derived from marine polysaccharides. The iron and phosphorus-doped porous carbon precursor derived from the marine polysaccharide was carbonized once, washed, and dried to obtain iron and phosphorus-doped porous carbon material. The iron and phosphorus-doped porous carbon material is mixed with a nitrogen-containing compound, ground, and then carbonized twice to obtain a nitrogen and phosphorus-doped trifunctional iron single-atom catalyst derived from marine polysaccharides.

2. The method for preparing a trifunctional carbon-based single-atom catalyst for the conversion of marine polysaccharides as described in claim 1, characterized in that, The marine polysaccharide is one of agarose, chitosan, fucoidan, or sodium alginate, and the raw material is selected from at least one of red algae, blue algae, seaweed, and shrimp / crab shells.

3. The method for preparing a trifunctional carbon-based single-atom catalyst for the conversion of marine polysaccharides as described in claim 1, characterized in that, The metal salt is at least one of the chloride salt, acetate, nitrate, and sulfate salts of transition metals; Alternatively, the transition metal is at least one of iron, cobalt, nickel, and zinc.

4. The method for preparing a trifunctional carbon-based single-atom catalyst for the conversion of marine polysaccharides as described in claim 1, characterized in that, The ratio of marine polysaccharide to metal salt is 1.5g:0.05-0.1g.

5. The method for preparing a trifunctional carbon-based single-atom catalyst for converting marine polysaccharides into a catalyst as described in claim 1, characterized in that, The specific conditions for the first carbonization are as follows: under an inert atmosphere, the carbonization temperature is 600-800℃, the carbonization time is 5-8h, and the heating program is 2-10℃ / min.

6. The method for preparing a trifunctional carbon-based single-atom catalyst for the conversion of marine polysaccharides as described in claim 1, characterized in that, The washing temperature is 50-60℃, the washing solution is 0.5-2mol / L hydrochloric acid, sulfuric acid or nitric acid, and the washing time is 8-24h.

7. The method for preparing a trifunctional carbon-based single-atom catalyst for converting marine polysaccharides into a catalyst as described in claim 1, characterized in that, The nitrogen-containing compound is at least one of ammonium chloride, ammonium bromide, ammonium phosphate, urea, thiourea, ammonium dihydrogen phosphate, and melamine. Alternatively, the mass ratio of the transition metal-doped porous carbon material to the nitrogen-containing compound is 1:1-25.

8. The method for preparing a trifunctional carbon-based single-atom catalyst for converting marine polysaccharides into a catalyst as described in claim 1, characterized in that, The conditions for the secondary carbonization are as follows: under an inert atmosphere, the carbonization temperature is 800-1100℃, the carbonization time is 1-5h, and the heating rate is 2-10℃ / min.

9. The application of the method for preparing marine polysaccharides by means of any one of claims 1-8 into trifunctional carbon-based single-atom catalysts in electrocatalytic oxygen reduction, oxygen evolution, and hydrogen evolution reactions, as well as in energy conversion materials.

Images