Lightweight P, N co-doped graphene / hollow iron-manganese phosphide composite aerogel and preparation method thereof
By preparing lightweight P,N-doped graphene/hollow iron-manganese phosphide composite aerogels, the problems of poor conductivity and weak interfacial bonding of transition metal phosphides were solved, achieving highly efficient electrocatalysis and pollutant molecule adsorption performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- XIAN XINANBO COMPOSITE MATERIALS TECH CO LTD
- Filing Date
- 2026-03-12
- Publication Date
- 2026-06-05
AI Technical Summary
Existing transition metal phosphides have poor conductivity and are prone to aggregation. Traditional graphene composites have weak interfacial bonding, and their preparation process is unsafe. Furthermore, the materials have insufficient specific surface area, which limits their application in electrocatalysis and pollutant molecule adsorption.
A method for preparing lightweight P,N-doped graphene/hollow iron-manganese phosphide composite aerogel was adopted. Through the synergistic effect of hexachlorocyclotriphosphazene and phytic acid solution, hollow iron-manganese phosphide was anchored on graphene sheets to form a three-dimensional hierarchical porous structure. Combined with freeze-drying and gradient annealing processes, conductivity and interfacial interaction were enhanced.
It improves the conductivity and specific surface area of the composite material, solves the problems of insufficient conductivity and easy agglomeration, and enhances the effects of electrocatalysis and adsorption of pollutant molecules.
Smart Images
Figure CN122141560A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of nanoporous composite functional materials technology, specifically relating to a lightweight P,N synchronously doped graphene / hollow iron-manganese phosphide composite aerogel and its preparation method. Background Technology
[0002] Transition metal phosphides (TMPs), due to their hydrogenase-like electronic structure, exhibit excellent hydrogen evolution reaction (HER) activity over a wide pH range, making them a promising catalyst material for hydrogen production via water electrolysis. However, single TMPs suffer from poor conductivity, insufficient exposure of active sites, and the high-temperature phosphating process easily leads to particle agglomeration and volume expansion, severely limiting their practical applications. Combining TMPs with highly conductive carbon matrices such as graphene can effectively alleviate these problems, but traditional graphene still faces challenges in controlling doping levels, interfacial coupling strength, and density. Furthermore, the phosphorus source often uses highly toxic trioctylphosphine or sodium hypophosphite, which easily releases PH3, posing significant safety risks. In addition, the specific surface area of composite materials is limited, making it difficult to guarantee efficient electrochemical mass transfer and strong adsorption capacity. Therefore, it is crucial to develop a green, environmentally friendly, highly interfacially coupled, lightweight, and controllably prepared graphene / TMPs functionalized composite aerogel material, such as the P,N synchronously doped graphene / hollow iron-manganese phosphide composite aerogel in this invention, to leverage its role in electrocatalysis and adsorption of pollutant molecules, but this still faces significant challenges. Summary of the Invention
[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a lightweight P,N synchronously doped graphene / hollow iron-manganese phosphide composite aerogel and its preparation method. This addresses the problems of poor conductivity and easy agglomeration of traditional transition metal phosphides, which limit their catalytic activity, as well as the weak interfacial bonding, toxic and unsafe preparation processes, and insufficient specific surface area of commonly used graphene composite and phosphating methods. This aerogel can enhance the conductivity, specific surface area, and interfacial interactions of the composite material, overcoming the constraints and limitations in its application in electrocatalysis and pollutant molecule adsorption.
[0004] To achieve the above objectives, the present invention employs the following technical solution: A method for preparing a lightweight P,N-doped graphene / hollow iron-manganese phosphide composite aerogel includes the following steps: S1, Graphene oxide is dispersed in N,N-dimethylformamide and sonicated until uniformly dispersed; hexachlorocyclotriphosphazene is added, and the mixture is heated and stirred, then sonicated to obtain solution A; S2, iron salt and manganese salt are added to fumaric acid solution, and mixed solution B is obtained after continuous heating and stirring. Mixed solution B undergoes hydrothermal reaction, and the product of hydrothermal reaction is centrifuged, washed, and dried to obtain product C. S3, place product C in water, stir well, add phytic acid solution, let it stand to react, centrifuge and wash the reaction product, and dry it to obtain sample D; S4, Place sample D in solution A and stir to obtain mixed solution E; S5. The mixed solution E is freeze-dried in a mold and then annealed to obtain a lightweight P,N synchronously doped graphene / hollow iron manganese phosphide composite aerogel. The lightweight P,N synchronously doped graphene / hollow iron-manganese phosphate composite aerogel includes graphene sheets doped with P and N, and hollow iron-manganese phosphate is anchored on the graphene sheets. The hollow iron-manganese phosphate is in the shape of a hollow rod, and the sidewalls of the hollow iron-manganese phosphate have mesopores and micropores.
[0005] A further improvement of the present invention is that Preferably, in S1, the mixing ratio of graphene oxide and N,N-dimethylformamide is (5~20) mg: (5~25) mL, and the mixing mass ratio of graphene oxide and hexachlorocyclotriphosphazene is (5~20) mg: (0.1~0.4) g.
[0006] Preferably, in S1, during the heating and stirring process, the heating temperature is 60~80℃, the stirring time is 12~24h, and the ultrasonic duration is 1~3h.
[0007] Preferably, in S2, the iron salt is either Fe(NO3)3 or FeCl3, the manganese salt is either Mn(CH3COO)2 or MnCl2, the molar ratio of the iron salt to the manganese salt is 1:(0.5~2.8), the heating temperature is 60~80℃, and the stirring time is 5~20min.
[0008] Preferably, in S2, the hydrothermal reaction temperature is 70~150℃ and the reaction time is 2~15h.
[0009] Preferably, in step S3, the product C is placed in water with a concentration of 5-12 mg / mL; the phytic acid solution is added slowly dropwise, with an amount of 0.8-2 mL and a concentration of 0.05-0.2 mol / L.
[0010] Preferably, in step S3, the temperature of the static reaction is 90~120℃, and the static reaction time is 2~5h.
[0011] Preferably, in S4, the mixing ratio of sample D and solution A is (30~70) mg: (5~25) mL.
[0012] Preferably, in S5, the freeze-drying process involves pre-freezing with liquid nitrogen for 5-20 seconds before freeze-drying, and the freeze-drying temperature is -50 to -25°C for 24-48 hours. The specific annealing process is as follows: after holding at 200~350℃ for 1.5~3h, hold at 750~900℃ for 2~3.5h.
[0013] A lightweight P,N synchronously doped graphene / hollow iron-manganese phosphide composite aerogel prepared by any of the above preparation methods includes graphene sheets doped with P and N, wherein the graphene sheets are three-dimensional graphene network structures; hollow iron-manganese phosphides are anchored on the graphene sheets, wherein the hollow iron-manganese phosphides are hollow rod-shaped, and the sidewalls of the hollow iron-manganese phosphides have mesopores and micropores.
[0014] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for preparing a lightweight P,N simultaneously doped graphene / hollow iron-manganese phosphide composite aerogel. The method involves preparing graphene sheets simultaneously doped with P and N, and hollow iron-manganese phosphide, which are then composited. The material of this invention is a lightweight P,N simultaneously doped graphene / hollow iron-manganese phosphide composite aerogel. By uniformly anchoring hollow iron-manganese metal phosphide within P,N simultaneously doped graphene, and then freeze-drying and annealing, a three-dimensional hierarchical porous composite aerogel is formed. This significantly improves the conductivity of the composite structure and synergistically increases the active specific surface area of the material, thereby overcoming the problems of poor conductivity and insufficient exposure of electrochemical active sites in TMP materials. This method for preparing a lightweight P,N simultaneously doped graphene / hollow iron-manganese phosphide composite aerogel material, which combines ultra-low density, high conductivity network, and abundant heterogeneous interfaces, can be widely applied in fields such as hydrogen evolution catalysts for water electrolysis and pollutant adsorption and degradation.
[0015] Furthermore, the use of hexachlorocyclotriphosphazene allows it to serve as both a P and N source, enabling the simultaneous doping of P and N elements into graphene and enhancing its interfacial bonding with hollow iron-manganese phosphides. During the preparation of P- and N-doped graphene sheets, the use of N,N-dimethylformamide as a solvent, combined with synergistic heating, stirring, and ultrasonic treatment of the entire system, ensures the graphene sheets are fully exfoliated and dispersed while simultaneously dissolving the hexachlorocyclotriphosphazene. The use of hexachlorocyclotriphosphazene also serves as a partial phosphorus source, which is beneficial for the subsequent synthesis of phosphide composite materials.
[0016] Furthermore, using phytic acid and hexachlorocyclotriphosphazene as a co-doping system, simultaneous P and N doping is achieved, and POC and NC bonds are formed with the oxygen-containing groups of graphene oxide (GO), which helps to enhance subsequent interfacial coupling and avoids the release of highly toxic PH3. Simultaneously, the phytic acid solution can act as a chelating ligand, and its phosphate groups can undergo coordination reactions with metallic iron / manganese ions to form a P-containing metal ion surface layer. The interior of the crystal lattice is easily etched, thus forming a hollow structure.
[0017] In this invention, compared to single-metal organic framework (MOF) materials, iron-manganese bimetallic MOF precursors can optimize the electronic structure and band gap of subsequent phosphides, and can synergistically improve the electrocatalytic performance of composite materials based on bimetallic active sites. Directional freeze-drying technology combined with gradient annealing can effectively suppress particle agglomeration and aerogel shrinkage, meeting the requirements for flexible and lightweight materials; gradient low-temperature and high-temperature annealing stages can reduce graphene oxide and generate iron-manganese phosphides in situ, ultimately obtaining a lightweight P,N-doped graphene / hollow iron-manganese phosphide (PNG / h-Fe-Mn-P) composite aerogel material.
[0018] In this invention, the lightweight P,N synchronously doped graphene / hollow iron-manganese phosphide (PNG / h-Fe-Mn-P) composite aerogel exhibits a unique three-dimensional hierarchical porous structure. Hollow rod-shaped iron-manganese phosphides are uniformly anchored on the three-dimensional graphene network folds, and mesoporous / microporous features are distributed on the rod-shaped sidewalls. Attached Figure Description
[0019] Figure 1 This is a schematic diagram of the preparation process of the lightweight P,N synchronously doped graphene / hollow iron-manganese phosphide composite aerogel material in this invention. Figure 2 Images of the lightweight P,N synchronously doped graphene / hollow iron-manganese phosphide (PNG / h-Fe-Mn-P) composite aerogel obtained in Example 1 are shown, where (a) is a 10 μm SEM image; (b) is a 2 μm SEM image; (c) is a TEM image; and (d) is a photograph of the actual product. Figure 3 The images show the microstructure and energy spectrum of the P,N synchronously doped graphene (PNG) obtained in Example 1; where (a) is a SEM image, (b) is a TEM image, (c) is a Raman spectrum, and (d) is an EDS energy spectrum. Figure 4 The image shows a SEM image of the lightweight graphene / hollow iron-manganese phosphide (G / h-Fe-Mn-P) composite aerogel material without simultaneous P and N doping obtained in Example 4.
[0020] Figure 5The image shows a SEM image of the lightweight P,N synchronously doped graphene / hollow iron phosphate (PNG / h-Fe-P) composite aerogel material obtained in Example 5.
[0021] Figure 6 The images show the microstructure and energy dispersive spectroscopy (EDS) of the hollow iron-manganese phosphide (h-Fe-Mn-P) obtained in Example 6, where (a) is a SEM image, (b) is a TEM image, and (c) is an EDS energy dispersive spectroscopy (EDS) image. Figure 7 The LSV curves are for the electrocatalytic hydrogen evolution reaction of the products obtained in Examples 1, 4, 5 and 6.
[0022] Specific methods of application The present invention will now be described in further detail with reference to the accompanying drawings: To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.
[0023] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”
[0024] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.
[0025] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.
[0026] This invention provides a lightweight P,N synchronously doped graphene / hollow iron-manganese phosphide composite aerogel and its preparation method. Figure 1This is a schematic diagram of the preparation process of the target sample in this invention. The method of this invention specifically includes the following steps: using hexachlorocyclotriphosphazene as the P and N simultaneous doping material, a uniformly dispersed P and N simultaneous doped graphene mixed solution is prepared; using iron-manganese bimetallic organic frameworks as precursors and phytic acid as phosphorus source and chelating ligand, an iron-manganese phosphate precursor with a hollow structure is prepared; using directional freeze-drying technology combined with gradient annealing process, graphene oxide is reduced and phosphated in situ to generate iron-manganese phosphate, generating a lightweight P and N simultaneous doped graphene / hollow iron-manganese phosphate composite aerogel material with a three-dimensional hierarchical porous network structure. This method uses iron-manganese bimetallic organic frameworks (MOFs) as precursors, phytic acid (PA) as a green phosphorus source, and hexachlorocyclotriphosphazene (HCCP) as an auxiliary nitrogen-phosphorus simultaneous dopant. Combined with a controllable preparation method of low-temperature oil bath-hydrothermal crystallization-freeze-drying-annealing treatment, the process is simple, environmentally friendly, and easy to scale up. The resulting structure has a three-dimensional porous graphene network, and the supported phosphide nanomaterials exhibit a hollow porous rod-like structure. The composite structure has a multi-level pore distribution, which is conducive to rapid mass transfer and gas release in electrochemical reactions and improves the efficiency of hydrogen evolution reaction in water electrolysis.
[0027] Specifically, the method includes the following steps: Step 1: Graphene oxide (GO) is dispersed in N,N-dimethylformamide (DMF) and sonicated until uniformly dispersed; hexachlorocyclotriphosphazene (HCCP) is added, heated and stirred, and then sonicated to obtain a uniformly dispersed brownish-black solution A; The mixing ratio of GO and DMF is (5~20) mg: (5~25) mL, the mixing mass ratio of GO and HCCP is (5~20) mg: (0.1~0.4) g, the heating temperature after heating and stirring and ultrasonic treatment is 60~80℃, the stirring time is 12~24h, and the ultrasonic treatment time is 1~3h.
[0028] In this process, heating and stirring in the DMF solution, combined with ultrasonic treatment, can promote the dissolution of nonpolar hexachlorocyclotriphosphazene and form a uniformly dispersed mixed solution with graphene oxide, reducing its viscosity and facilitating subsequent composite with phosphides, ultimately forming a lightweight P,N synchronously doped graphene / hollow iron-manganese phosphide composite aerogel with a three-dimensional hierarchical porous network structure.
[0029] Step 2: Prepare fumaric acid (FMA) solution, add iron salt and manganese salt in sequence, and stir continuously to obtain mixed solution B; place mixed solution B in a reaction vessel lined with polytetrafluoroethylene for hydrothermal reaction. After the hydrothermal reaction is completed, collect the product to obtain a reddish-brown powder, which is recorded as sample C; wherein, the mass ratio of fumaric acid to metal salt (iron salt and manganese salt) is 1:(2~6.5) mg.
[0030] In this process, the fumaric acid (FMA) solution is composed of fumaric acid and solvent, wherein the ratio of fumaric acid to solvent is (100~160) mg : (15~35) mL, the solvent is either deionized water or DMF, the mass ratio of fumaric acid to metal salt (iron salt and manganese salt) is 1 : (2~6.5) mg, the iron salt is either Fe(NO3)3 or FeCl3 with water of crystallization; the manganese salt is either Mn(CH3COO)2 or MnCl2 with water of crystallization, and the molar ratio of iron salt to manganese salt is 1 : (0.5~2.8). Appropriate amounts of iron salt and manganese salt can ensure that the synthesized iron-manganese bimetallic organic framework precursor material exhibits a regular rod-shaped structure.
[0031] During the heating and stirring process, the heating temperature is (60~80)℃ and the stirring time is (5~20)min.
[0032] In this process, the hydrothermal reaction conditions are as follows: reaction temperature is 70~150℃, reaction time is 2~15h, and the product collection method is to centrifuge the solution after reaction at 8000r / min, wash it with deionized water 3~5 times and ethanol 2 times, and then vacuum dry it at 60℃ for 12h.
[0033] Step 3: Redisperse an appropriate amount of product C in deionized water and stir until a homogeneous solution is formed; add an appropriate amount of phytic acid (PA) solution, allow the reaction to stand, and then collect the powder sample, which is recorded as sample D. In this process, phytic acid molecules, containing six phosphate groups, are multidentate chelating ligands with a strong ability to chelate metal ions. Phytic acid competes for coordination with the metal center in the iron-manganese bimetallic organic framework, disrupting its original structure. As the internal metal center is continuously chelated and dissolved by phytic acid, cavities begin to form inside the crystal, while the outer shell is temporarily retained, forming a hollow or porous structure. This exhibits characteristics such as high specific surface area and abundant pore structure, showing great application potential in fields such as electrochemical catalysis.
[0034] Sample C was redispersed in deionized water to form a mixed solution with a concentration of 5-12 mg / mL. The phytic acid solution was added dropwise slowly, with a volume of 0.8-2 mL and a concentration of 0.05-0.2 mol / L, representing 8%-15% of the total mixed solution volume. The reaction was allowed to stand at 90-120°C for 2-5 hours. The powder sample was collected by centrifuging the solution at 8000 r / min, washing it 3-5 times with deionized water and 2 times with ethanol, and then vacuum drying it at 60°C for 12 hours.
[0035] Step 4: Add sample D to solution A obtained in step 1 and stir to form a uniformly dispersed mixed solution E; wherein the mixing ratio of sample D and solution A is (30~70) mg: (5~25) mL, the stirring temperature is room temperature, and the stirring time is 10~20 min.
[0036] Step 5: Inject solution E into the mold, pre-freeze it with liquid nitrogen, and then quickly transfer it into a freeze dryer for freeze drying. After freeze drying, anneal the resulting product and collect the annealed sample to obtain a lightweight P,N-doped graphene / hollow iron-manganese phosphide (PNG / h-Fe-Mn-P) composite aerogel material.
[0037] The liquid nitrogen pre-freezing time is 5~20s, the freeze-drying temperature is -50~-25℃, the vacuum degree is 5~12Pa, and the drying time is 24~48h. The conditions for annealing the freeze-dried sample are as follows: under an inert atmosphere, the temperature is raised from room temperature to 200~350℃, held for 1.5~3h, then the temperature is raised to 750~900℃, held for 2~3.5h, and the sample is collected after cooling to room temperature with the furnace.
[0038] This invention discloses a lightweight P,N synchronously doped graphene / hollow iron-manganese phosphide (PNG / h-Fe-Mn-P) composite aerogel material, which has a three-dimensional porous network structure. Hollow iron-manganese phosphide is uniformly anchored on P,N synchronously doped graphene nanosheets, forming a unique structure synergistically consisting of a three-dimensional conductive network, a heterogeneous interface, and hierarchical channels. The graphene sheet structure forms a three-dimensional conductive network, with P and N doped on the graphene sheets. The iron-manganese phosphide forms good contact with the graphene sheets and is anchored there, forming a heterogeneous structure. The iron-manganese phosphide is in the form of hollow rods with pores in its walls. In this composite structure, the graphene sheets form a three-dimensional porous network, the hollow rod-shaped structures form secondary channels, and the pores in the hollow tube walls form tertiary channels, collectively forming a hierarchical channel structure.
[0039] In the three-dimensional hierarchical porous composite structure of this invention, the three-dimensional wrinkled graphene network provides a continuous conductive framework and also acts as a flexible "shield" to improve the mechanical / interfacial stability of the composite material. The formation of the hollow porous nanorods facilitates the introduction of lattice distortion and defects, which helps to regulate the band structure and Gibbs free energy of hydrogen adsorption in the active material, thereby enhancing the intrinsic catalytic activity. Furthermore, the multi-level hierarchical porous characteristics of the composite structure are beneficial for rapid mass transfer and gas release in electrochemical reactions, improving the efficiency of hydrogen evolution in water electrolysis.
[0040] In the above process, the coordination and etching reaction of phytic acid solution on the iron-manganese bimetallic organic framework can transform dense microcrystals into hollow and porous Fe / Mn-phytic acid complexes. After the subsequent low-temperature and high-temperature annealing stages, the complexes can be converted into iron-manganese phosphides in situ, while simultaneously releasing gases such as CO2, H2O, and POx and generating lattice defects and slight etching of the framework, so that microporous structures can also be formed on the hollow tube wall.
[0041] The three-dimensional porous network structure of P and N-doped graphene in the composite aerogel was not significantly affected after the annealing process and remained intact.
[0042] The following description, in conjunction with specific embodiments, provides further details.
[0043] Example 1 10 mg of graphene oxide was dispersed in 25 mL of DMF solution and sonicated for 1 h to form a dark brown transparent solution. 0.3 g of hexachlorocyclotriphosphazene (HCCP) was added, and the solution was placed in a 70 °C oil bath and stirred for 24 h. The solution was then sonicated again for 2 h to obtain a uniformly dispersed graphene mixture A. Subsequently, 139 mg of fumaric acid was dissolved in 25 mL of aqueous solution and refluxed in a 75 °C oil bath. After stirring for approximately 10 min, approximately 350 mg of Fe(NO3)3 was added sequentially. 9H2O and 490 mg of MnCl2 Add 4H₂O and continue stirring for 10 min until the metal salt is completely dissolved, forming solution B. Pour solution B into a polytetrafluoroethylene-lined reactor, seal it, and place it in a constant temperature forced-air drying oven at 110 ℃ for 8 h to complete the hydrothermal process. After natural cooling, remove the mixed solution and centrifuge it at 8000 r / min to collect the precipitate. Wash it three times with deionized water and twice with ethanol solution, with each centrifugation time being 5 min. Place the washed and collected precipitate in a vacuum oven at 60 ℃ and vacuum dry for 12 h to obtain a reddish-brown iron-manganese bimetallic organometallic framework powder, denoted as sample C. Disperse approximately 100 mg of powder sample C in 10 mL of deionized water and stir for 10 min to form a homogeneous solution. Slowly add 1 mL (0.1 mol / L) of phytic acid solution dropwise and place it in a 90 ℃ oven to stand for 3 h. The solution was centrifuged (8000 r / min, 5 min), washed thoroughly with deionized water three times and ethanol twice, and then vacuum-dried at 60 ℃ for 12 h. The powder sample was collected and designated as sample D. 50 mg of sample D was added to the graphene mixed solution A prepared in step 1 and stirred at room temperature for 15 min to form a uniformly dispersed black mixed solution E. Solution E was transferred to a 10 mL glass vessel, pre-frozen with liquid nitrogen for 20 s, and immediately placed in a freeze dryer for freeze-drying. The freezing temperature was set to -35 ℃, the vacuum degree to 5 Pa, and the drying time to 36 h. After freeze-drying, the broken glassware was stabilized, the aerogel preform was removed, and annealed. The annealing process was carried out in an argon atmosphere, with the temperature raised from room temperature to 300 ℃ and held for 2 h. Then, the temperature was raised to 800 ℃ and held for 2 h. After cooling to room temperature in the furnace, the black aerogel sample was collected, which is the lightweight P,N synchronously doped graphene / hollow iron manganese phosphide (PNG / h-Fe-Mn-P) composite aerogel material.
[0044] The morphology of the P,N synchronously doped graphene / hollow iron-manganese phosphide (PNG / h-Fe-Mn-P) composite aerogel material obtained in Example 1 was characterized and analyzed. The results are as follows: Figure 2 As shown.
[0045] Figure 2 The images shown are SEM images (ab), TEM images (c), and a photograph (d) of the PNG / h-Fe-Mn-P composite aerogel obtained in Example 1. Figure 2Figure (a) shows that the resulting composite aerogel exhibits a unique three-dimensional interconnected porous network structure. High-magnification SEM images reveal numerous rod-shaped iron-manganese phosphides uniformly anchored on the surface of P,N-simultaneously doped graphene nanosheets, exhibiting a tight composite structure without aggregation. TEM images in Figure (c) further confirm that the aforementioned rod-shaped crystals possess clear hollow cavities embedded within the wrinkled graphene matrix, indicating a distinct hollow structure in the iron-manganese phosphides. The photograph in Figure (d) shows that the resulting aerogel has a black columnar block appearance and exhibits significant lightweight characteristics, remaining stable on the surface of the petals without significant deformation.
[0046] Figure 3 The morphology, defect degree and elemental composition characterization results of the P,N synchronously doped graphene (PNG) obtained in Example 1 are shown. Figure 3 The SEM images in Figure (a) and TEM images in Figure (b) show that the simultaneous P,N doping process did not disrupt the typical wrinkled sheet structure of graphene. The Raman spectroscopy results in Figure (c) indicate that the Ip of PNG... D / I G The increase from 1.089 to 1.113 in GO indicates that the introduced P and N atoms significantly increase in-plane defects, resulting in a higher degree of disorder in the graphene plane, which is beneficial for subsequent interfacial coupling and charge transport. The presence of P and N elements can be found in the EDS energy spectrum of Figure (d), proving that P and N elements have been successfully and simultaneously incorporated into the graphene lattice.
[0047] Example 2 8 mg of graphene oxide was dispersed in 18 mL of DMF solution and sonicated for 1 h to form a dark brown transparent solution. 0.2 g of hexachlorocyclotriphosphazene (HCCP) was added, and the solution was placed in a 75 °C oil bath and stirred for 24 h. The solution was then sonicated again for 2.5 h to obtain a uniformly dispersed graphene mixture A. Subsequently, 150 mg of fumaric acid was dissolved in 15 mL of DMF solution and refluxed in a 75 °C oil bath. After stirring for approximately 10 min, approximately 209 mg of FeCl3 was added sequentially. 6H2O and 136 mg of Mn(CH3COO)2 Add 4H₂O and continue stirring for 10 min until the metal salt is completely dissolved, forming solution B. Pour solution B into a polytetrafluoroethylene-lined reactor, seal it, and place it in a constant temperature oven at 100 °C for 2 h to complete the hydrothermal process. After natural cooling, remove the mixed solution and centrifuge it at 8000 r / min to collect the precipitate. Wash it three times with deionized water and twice with ethanol solution, with each centrifugation time being 5 min. Place the collected precipitate in a 60 °C vacuum oven and vacuum dry it for 12 h to obtain a reddish-brown iron-manganese bimetallic organometallic framework powder, denoted as sample C. Disperse approximately 50 mg of powder sample C in 8 mL of deionized water and stir for 10 min to form a homogeneous solution. Slowly add 0.9 mL (0.1 mol / L) of phytic acid solution dropwise and place it in a 95 °C oven to stand for 3 h. The solution was centrifuged (8000 r / min, 5 min), washed thoroughly with deionized water three times and ethanol twice, and then vacuum-dried at 60 ℃ for 12 h. The powder sample was collected and designated as sample D. 35 mg of sample D was added to the graphene mixed solution A prepared in step 1 and stirred at room temperature for 12 min to form a uniformly dispersed black mixed solution E. Solution E was transferred to a 10 mL glass container, pre-frozen with liquid nitrogen for 16 s, and immediately placed in a freeze dryer for freeze-drying. The freezing temperature was set to -38 ℃, the vacuum degree to 5 Pa, and the drying time to 40 h. After freeze-drying, the broken glassware was stabilized, the aerogel preform was removed, and annealed. The annealing process was carried out in an argon atmosphere, with the temperature raised from room temperature to 320 ℃ and held for 2 h. Then, the temperature was raised to 820 ℃ and held for 2 h. After cooling to room temperature in the furnace, the black aerogel sample was collected, which is the lightweight P,N synchronously doped graphene / hollow iron manganese phosphide (PNG / h-Fe-Mn-P) composite aerogel material.
[0048] Example 3 11 mg of graphene oxide was dispersed in 19 mL of DMF solution and sonicated for 1 h to form a dark brown transparent solution. 0.23 g of hexachlorocyclotriphosphazene (HCCP) was added, and the solution was placed in a 70 °C oil bath and stirred for 24 h. The solution was then sonicated again for 2 h to obtain a uniformly dispersed graphene mixture A. Subsequently, 120 mg of fumaric acid was dissolved in 15 mL of DMF solution and refluxed in a 75 °C oil bath. After stirring for approximately 10 min, approximately 168 mg of FeCl3 was added sequentially. 6H2O and 108 mg of Mn(CH3COO)2 Add 4H₂O and continue stirring for 10 min until the metal salt is completely dissolved, forming solution B. Pour solution B into a polytetrafluoroethylene-lined reactor, seal it, and place it in a constant temperature forced-air drying oven at 75 ℃ for 4 h to complete the hydrothermal process. After natural cooling, remove the mixed solution and centrifuge it at 8000 r / min to collect the precipitate. Wash it three times with deionized water and twice with ethanol solution, with each centrifugation time being 5 min. Place the washed and collected precipitate in a vacuum oven at 60 ℃ and vacuum dry for 12 h to obtain a reddish-brown iron-manganese bimetallic organometallic framework powder, denoted as sample C. Disperse approximately 40 mg of powder sample C in 6 mL of deionized water and stir for 10 min to form a homogeneous solution. Slowly add 0.8 mL (0.1 mol / L) of phytic acid solution dropwise and place it in a 90 ℃ oven to stand for 3 h. The solution was centrifuged (8000 r / min, 5 min), washed thoroughly with deionized water three times and ethanol twice, and then vacuum-dried at 60 ℃ for 12 h. The powder sample was collected and designated as sample D. 30 mg of sample D was added to the graphene mixed solution A prepared in step 1 and stirred at room temperature for 12 min to form a uniformly dispersed black mixed solution E. Solution E was transferred to a 10 mL glass vessel, pre-frozen with liquid nitrogen for 12 s, and immediately placed in a freeze dryer for freeze-drying. The freezing temperature was set to -30 ℃, the vacuum degree to 5 Pa, and the drying time to 42 h. After freeze-drying, the broken glassware was stabilized, the aerogel preform was removed, and annealed. The annealing process was carried out in an argon atmosphere, with the temperature raised from room temperature to 300 ℃ and held for 2 h. Then, the temperature was raised to 800 ℃ and held for 2 h. After cooling to room temperature in the furnace, the black aerogel sample was collected, which is the lightweight P,N synchronously doped graphene / hollow iron manganese phosphide (PNG / h-Fe-Mn-P) composite aerogel material.
[0049] Example 4 15 mg of graphene oxide was dispersed in 25 mL of DMF solution and sonicated for 1 h to form a dark brown transparent solution, yielding a uniformly dispersed graphene solution A. Subsequently, 120 mg of fumaric acid was dissolved in 20 mL of aqueous solution, refluxed in an oil bath at 75 °C, and stirred for approximately 10 min. Then, approximately 300 mg of Fe(NO3)3 was added sequentially. 9H2O and 395 mg of MnCl2 Add 4H₂O and continue stirring for 10 min until the metal salt is completely dissolved, forming solution B. Pour solution B into a polytetrafluoroethylene-lined reactor, seal it, and place it in a constant temperature oven at 120 °C for 6 h to complete the hydrothermal process. After natural cooling, remove the mixed solution and centrifuge it at 8000 r / min to collect the precipitate. Wash it three times with deionized water and twice with ethanol solution, with each centrifugation time being 5 min. Place the washed and collected precipitate in a vacuum oven at 60 °C and vacuum dry for 12 h to obtain a reddish-brown iron-manganese bimetallic organometallic framework powder, denoted as sample C. Disperse approximately 60 mg of powder sample C in 10 mL of deionized water and stir for 10 min to form a homogeneous solution. Slowly add 1 mL (0.1 mol / L) of phytic acid solution dropwise and place it in a 90 °C oven to stand for 2.5 h. The solution was centrifuged (8000 r / min, 5 min), washed thoroughly with deionized water three times and ethanol twice, and then vacuum-dried at 60 ℃ for 12 h. The powder sample was collected and designated as sample D. 40 mg of sample D was added to the graphene solution A prepared in step 1 and stirred at room temperature for 15 min to form a uniformly dispersed black mixed solution E. Solution E was transferred to a 10 mL glass container, pre-frozen with liquid nitrogen for 15 s, and immediately placed in a freeze dryer for freeze-drying. The freezing temperature was set to -35 ℃, the vacuum degree to 5 Pa, and the drying time to 40 h. After freeze-drying, the broken glassware was stabilized, the aerogel preform was removed, and annealed. The annealing process was carried out in an argon atmosphere, with the temperature raised from room temperature to 300 ℃ and held for 2.5 h, then raised to 800 ℃ and held for 2 h. After cooling to room temperature in the furnace, the black aerogel sample was collected, which is the lightweight graphene / hollow iron-manganese phosphide (G / h-Fe-Mn-P) composite aerogel material without simultaneous P and N doping.
[0050] Figure 4 This is a SEM image of the lightweight graphene / hollow iron-manganese phosphide (G / h-Fe-Mn-P) composite aerogel material without simultaneous P and N doping obtained in Example 4. Figure 4 It can be seen that, in Example 4, without the addition of hexachlorocyclotriphosphazene as a P,N simultaneous dopant, the final G / h-Fe-Mn-P composite aerogel material has a microstructure that is basically consistent with the PNG / h-Fe-Mn-P composite aerogel material in Example 1. It also exhibits a unique three-dimensional interconnected porous network structure, with a large number of hollow rod-shaped iron-manganese phosphides uniformly anchored on the surface of the undoped graphene nanosheets, exhibiting a tight composite structure without agglomeration. This indicates that the absence of hexachlorocyclotriphosphazene did not change the microstructure of the composite aerogel in this invention; that is, simultaneous P,N doping has no significant impact on the morphology and structure of the final synthesized composite aerogel material.
[0051] Example 5 12 mg of graphene oxide was dispersed in 25 mL of DMF solution and sonicated for 1 h to form a dark brown transparent solution. 0.25 g of hexachlorocyclotriphosphazene (HCCP) was added, and the solution was placed in a 70 °C oil bath and stirred for another 20 h. The solution was then sonicated again for 3 h to obtain a uniformly dispersed graphene mixture A. Subsequently, 125 mg of fumaric acid was dissolved in 22 mL of aqueous solution and refluxed in a 75 °C oil bath. After stirring for approximately 10 min, approximately 350 mg of Fe(NO3)3 was added. Add 9H₂O and continue stirring for 10 min until the metal salt is completely dissolved, forming solution B. Pour solution B into a polytetrafluoroethylene-lined reactor, seal it, and place it in a constant temperature forced-air drying oven at 115 ℃ for 6 h to complete the hydrothermal process. After natural cooling, remove the mixed solution and centrifuge it at 8000 r / min to collect the precipitate. Wash it three times with deionized water and twice with ethanol solution, with each centrifugation time being 5 min. Place the washed and collected precipitate in a vacuum oven at 60 ℃ and vacuum dry for 12 h to obtain a reddish-brown iron-organic metal framework powder, denoted as sample C. Disperse approximately 80 mg of powder sample C in 10 mL of deionized water and stir for 10 min to form a homogeneous solution. Slowly add 1.2 mL (0.1 mol / L) of phytic acid solution dropwise and place it in a 95 ℃ oven to stand for 2.5 h. The solution was centrifuged (8000 r / min, 5 min), washed thoroughly with deionized water three times and ethanol twice, and then vacuum dried at 60 ℃ for 12 h. The powder sample was collected and designated as sample D. 45 mg of sample D was added to the graphene mixed solution A prepared in step 1 and stirred at room temperature for 15 min to form a uniformly dispersed black mixed solution E. Solution E was transferred to a 10 mL glass container, pre-frozen with liquid nitrogen for 10 s, and immediately placed in a freeze dryer for freeze drying. The freezing temperature was set to -40 ℃, the vacuum degree to 5 Pa, and the drying time to 48 h. After freeze-drying, the broken glassware was stabilized, the aerogel preform was removed, and annealed. The annealing process was carried out in an argon atmosphere, with the temperature raised from room temperature to 350 ℃, held for 2 h, then raised to 850 ℃ and held for 3 h. After cooling to room temperature in the furnace, the black aerogel sample was collected, which is the lightweight P,N synchronously doped graphene / hollow iron phosphide (PNG / h-Fe-P) composite aerogel material.
[0052] Figure 5 This is a SEM image of the lightweight P,N-doped graphene / hollow iron phosphide (PNG / h-Fe-P) composite aerogel material obtained in Example 5. Figure 5As can be seen, in Example 5, when no manganese metal salt source material was added and only a single iron-metal organic framework was used as the precursor material, the resulting PNG / h-Fe-P composite aerogel material had a microstructure that was basically the same as that of the PNG / h-Fe-Mn-P composite aerogel material in Example 1. It also exhibited a unique three-dimensional interconnected porous network structure, with a large number of hollow rod-shaped single iron metal phosphides uniformly anchored on the surface of P and N simultaneously doped graphene nanosheets, exhibiting a tight composite structure without agglomeration. This indicates that the absence of a manganese metal salt source material did not change the microstructure of the composite aerogel in this invention; that is, the iron-manganese bimetallic organic framework as a precursor material had no significant impact on the morphology and structure of the final synthesized composite aerogel material.
[0053] Example 6: There was no step of preparing a uniformly dispersed graphene mixture A or freeze-drying. 139 mg of fumaric acid was dissolved in 25 mL of aqueous solution, refluxed in an oil bath at 75 °C, and stirred for approximately 10 min. Then, approximately 350 mg of Fe(NO3)3 was added sequentially. 9H2O and 490 mg of MnCl2 Add 4H₂O and continue stirring for 10 min until the metal salt is completely dissolved, forming solution B. Pour solution B into a polytetrafluoroethylene-lined reactor, seal it, and place it in a constant temperature forced-air drying oven at 110 ℃ for 8 h to complete the hydrothermal process. After natural cooling, remove the mixed solution and centrifuge it at 8000 r / min to collect the precipitate. Wash it three times with deionized water and twice with ethanol solution, with each centrifugation time being 5 min. Place the washed and collected precipitate in a vacuum oven at 60 ℃ and vacuum dry for 12 h to obtain a reddish-brown iron-manganese bimetallic organometallic framework powder, denoted as sample C. Disperse approximately 100 mg of powder sample C in 10 mL of deionized water and stir for 10 min to form a homogeneous solution. Slowly add 1.5 mL (0.1 mol / L) of phytic acid solution dropwise and place it in a 90 ℃ oven to stand for 3 h. The solution was centrifuged (8000 r / min, 5 min), washed thoroughly with deionized water three times and ethanol twice, and then vacuum dried at 60 ℃ for 12 h. The powder sample was collected and designated as sample D. Sample D was then directly annealed. The annealing process was carried out under an argon atmosphere, with the temperature increased from room temperature to 300 ℃, held for 2 h, then increased to 800 ℃, held for 2 h, and then cooled to room temperature in the furnace. The black powder sample, i.e., the hollow iron-manganese phosphide (h-Fe-Mn-P) composite material, was collected.
[0054] Figure 6 The morphology and composition characterization results of the hollow iron-manganese phosphide powder sample (h-Fe-Mn-P) obtained in Example 6 without simultaneous P and N doping with graphene and without freeze-drying are presented by [the relevant authority / organism]. Figure 6 The SEM image in (a) shows that h-Fe-Mn-P exhibits a uniform rod-like morphology and good dispersibility. Figure 6 (b) TEM images further confirm that it has a clear hollow cavity, and the hollow rod-shaped morphology is completely consistent with the iron-manganese phosphide uniformly anchored on the surface of P,N synchronously doped graphene nanosheets in Example 1. Figure 6 The presence of Fe, Mn and P elements can be found in the EDS spectrum of (d), proving that the iron-manganese bimetallic phosphide material was successfully synthesized.
[0055] Figure 7 The LSV curves for the electrocatalytic hydrogen evolution reaction of the products obtained in Examples 1, 4, 5, and 6 are shown. The results indicate that, in this invention, the hollow iron-manganese bimetallic phosphide is uniformly anchored on P and N simultaneously doped graphene nanosheets, forming a unique structure of "three-dimensional conductive network-heterogeneous interface-hierarchical channels," namely, the lightweight P and N simultaneously doped graphene / hollow iron-manganese phosphide (PNG / h-Fe-Mn-P) composite aerogel material. Compared with other samples (PNG / h-Fe-P composite aerogel, G / h-Fe-Mn-P composite aerogel, and h-Fe-Mn-P powder), it exhibits the lowest overpotential at a certain current density, indicating that it possesses the best HER catalytic performance. For example, at a current density of 50 mA cm⁻¹... -2 At that time, the current densities of each sample were as follows: PNG / h-Fe-Mn-P (201.9 mV) < PNG / h-Fe-P (217.5 mV) < G / h-Fe-Mn-P (241.4 mV) < h-Fe-Mn-P (266.6 mV).
[0056] Example 7 5 mg of graphene oxide was dispersed in 5 mL of DMF solution and sonicated for 1 h to form a dark brown transparent solution. 0.1 g of hexachlorocyclotriphosphazene (HCCP) was added, and the solution was placed in an oil bath at 60 °C and stirred for 12 h. The solution was sonicated again for 1 h to obtain a uniformly dispersed graphene mixed solution A.
[0057] Subsequently, 139 mg of fumaric acid was dissolved in 25 mL of aqueous solution, refluxed in an oil bath at 60 °C, and stirred for about 5 min. Then, approximately 350 mg of Fe(NO3)3·9H2O and 86 mg of MnCl2·4H2O (iron-manganese molar ratio approximately 1:0.5) were added sequentially, and stirring continued for 5 min until the metal salts were completely dissolved, forming solution B. Solution B was poured into a polytetrafluoroethylene-lined reactor, sealed, and placed in a constant-temperature forced-air drying oven at 70 °C for 15 h to complete the hydrothermal process. After natural cooling, the mixed solution was removed, and the precipitate was collected by centrifugation at 8000 r / min. The precipitate was washed three times with deionized water and twice with ethanol solution, centrifuged for 5 min each time. The collected precipitate was placed in a vacuum oven at 60 °C and vacuum dried for 12 h to obtain a reddish-brown iron-manganese bimetallic organometallic framework powder, denoted as sample C.
[0058] Approximately 50 mg of powder sample C was dispersed in 10 mL of deionized water (concentration 5 mg / mL), stirred for 10 min to form a homogeneous solution, and then 2 mL of 0.05 mol / L phytic acid solution was slowly added dropwise. The solution was then placed in a 90 ℃ oven and allowed to stand for 2 h. The solution was centrifuged (8000 r / min, 5 min), washed thoroughly with deionized water three times and ethanol twice, and then vacuum dried at 60 ℃ for 12 h. The powder sample was collected and designated as sample D.
[0059] Add 30 mg of sample D to the graphene mixed solution A prepared in step 1, stir at room temperature for 15 min to form a uniformly dispersed black mixed solution E. Transfer solution E to a 10 mL glass container, pre-freeze with liquid nitrogen for 5 s, and immediately place it in a freeze dryer for freeze drying. Set the freezing temperature to -50 ℃, the vacuum degree to 5 Pa, and the drying time to 24 h.
[0060] After freeze-drying, carefully break the glass container, remove the aerogel preform, and anneal it: under an argon atmosphere, heat from room temperature to 200 ℃, hold for 1.5 h, then continue heating to 750 ℃, hold for 3.5 h, and cool to room temperature with the furnace. Collect the black aerogel sample, which is a lightweight P,N simultaneously doped graphene / hollow iron manganese phosphide (PNG / h-Fe-Mn-P) composite aerogel material.
[0061] Example 8 20 mg of graphene oxide was dispersed in 25 mL of DMF solution and sonicated for 1 h to form a dark brown transparent solution. 0.4 g of hexachlorocyclotriphosphazene (HCCP) was added, and the solution was placed in an oil bath at 80 °C and stirred for 24 h. The solution was then sonicated again for 3 h to obtain a uniformly dispersed graphene mixed solution A.
[0062] Subsequently, 139 mg of fumaric acid was dissolved in 25 mL of aqueous solution, refluxed in an oil bath at 80 °C, and stirred for about 20 min. Then, approximately 350 mg of Fe(NO3)3·9H2O and 480 mg of MnCl2·4H2O (iron-manganese molar ratio approximately 1:2.8) were added sequentially, and stirring continued for another 20 min until the metal salts were completely dissolved, forming solution B. Solution B was poured into a polytetrafluoroethylene-lined reactor, sealed, and placed in a constant-temperature forced-air drying oven at 150 °C for 2 h to complete the hydrothermal process. After natural cooling, the mixed solution was removed, and the precipitate was collected by centrifugation at 8000 r / min. The precipitate was washed three times with deionized water and twice with ethanol solution, centrifuged for 5 min each time. The collected precipitate was placed in a vacuum oven at 60 °C and vacuum dried for 12 h to obtain a reddish-brown iron-manganese bimetallic organometallic framework powder, denoted as sample C.
[0063] Approximately 120 mg of powder sample C was dispersed in 10 mL of deionized water (concentration 12 mg / mL), stirred for 10 min to form a homogeneous solution, and then 0.8 mL of 0.2 mol / L phytic acid solution was slowly added dropwise. The solution was then placed in a 120 ℃ oven and allowed to stand for 5 h. The solution was centrifuged (8000 r / min, 5 min), washed thoroughly with deionized water three times and ethanol twice, and then vacuum dried at 60 ℃ for 12 h. The powder sample was collected and designated as sample D.
[0064] 70 mg of sample D was added to the graphene mixed solution A prepared in step 1 and stirred at room temperature for 15 min to form a uniformly dispersed black mixed solution E. Solution E was transferred to a 10 mL glass vessel, pre-frozen with liquid nitrogen for 20 s, and then immediately placed in a freeze dryer for freeze drying. The freezing temperature was set to -25 °C, the vacuum degree to 5 Pa, and the drying time to 48 h.
[0065] After freeze-drying, carefully break the glassware, remove the aerogel preform, and anneal it: under an argon atmosphere, heat from room temperature to 350 ℃, hold for 3 h, then continue heating to 900 ℃, hold for 2 h, and cool to room temperature with the furnace. Collect the black aerogel sample, which is a lightweight P,N synchronously doped graphene / hollow iron manganese phosphide (PNG / h-Fe-Mn-P) composite aerogel material.
[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for preparing a lightweight P,N-doped graphene / hollow iron-manganese phosphide composite aerogel, characterized in that, Includes the following steps: S1, Graphene oxide is dispersed in N,N-dimethylformamide and sonicated until uniformly dispersed; hexachlorocyclotriphosphazene is added, and the mixture is heated and stirred, then sonicated to obtain solution A; S2, iron salt and manganese salt are added to fumaric acid solution, and mixed solution B is obtained after continuous heating and stirring. Mixed solution B undergoes hydrothermal reaction, and the product of hydrothermal reaction is centrifuged, washed, and dried to obtain product C. S3, place product C in water, stir well, add phytic acid solution, let it stand to react, centrifuge and wash the reaction product, and dry it to obtain sample D; S4, Place sample D in solution A and stir to obtain mixed solution E; S5. The mixed solution E is freeze-dried in a mold and then annealed to obtain a lightweight P,N synchronously doped graphene / hollow iron manganese phosphide composite aerogel. The lightweight P,N synchronously doped graphene / hollow iron-manganese phosphate composite aerogel includes graphene sheets doped with P and N, and hollow iron-manganese phosphate is anchored on the graphene sheets. The hollow iron-manganese phosphate is in the shape of a hollow rod, and the sidewalls of the hollow iron-manganese phosphate have mesopores and micropores.
2. The method for preparing a lightweight P,N-doped graphene / hollow iron-manganese phosphide composite aerogel according to claim 1, characterized in that, In S1, the mixing ratio of graphene oxide and N,N-dimethylformamide is (5~20) mg: (5~25) mL, and the mixing mass ratio of graphene oxide and hexachlorocyclotriphosphazene is (5~20) mg: (0.1~0.4) g.
3. The method for preparing a lightweight P,N-doped graphene / hollow iron-manganese phosphide composite aerogel according to claim 1, characterized in that, In S1, during the heating and stirring process, the heating temperature is 60~80℃, the stirring time is 12~24h, and the ultrasonic duration is 1~3h.
4. The preparation method of a lightweight P,N synchronously doped graphene / hollow iron-manganese phosphide composite aerogel according to claim 1, characterized in that, In S2, the iron salt is either Fe(NO3)3 or FeCl3, the manganese salt is either Mn(CH3COO)2 or MnCl2, the molar ratio of the iron salt to the manganese salt is 1:(0.5~2.8), the heating temperature is 60~80℃, and the stirring time is 5~20min.
5. The method for preparing a lightweight P,N-doped graphene / hollow iron-manganese phosphide composite aerogel according to claim 1, characterized in that, In S2, the hydrothermal reaction temperature is 70~150℃ and the reaction time is 2~15h.
6. The method for preparing a lightweight P,N synchronously doped graphene / hollow iron-manganese phosphide composite aerogel according to claim 1, characterized in that, In S3, product C is placed in water at a concentration of 5-12 mg / mL; the phytic acid solution is added slowly dropwise, with an amount of 0.8-2 mL and a concentration of 0.05-0.2 mol / L.
7. The method for preparing a lightweight P,N-doped graphene / hollow iron-manganese phosphide composite aerogel according to claim 1, characterized in that, In S3, the temperature of the static reaction is 90~120℃, and the static reaction time is 2~5h.
8. The method for preparing a lightweight P,N-doped graphene / hollow iron-manganese phosphide composite aerogel according to claim 1, characterized in that, In S4, the mixing ratio of sample D and solution A is (30~70) mg: (5~25) mL.
9. The method for preparing a lightweight P,N synchronously doped graphene / hollow iron-manganese phosphide composite aerogel according to claim 1, characterized in that, In S5, the freeze-drying process involves pre-freezing with liquid nitrogen for 5-20 seconds before freezing, and the freeze-drying temperature is -50 to -25℃ for 24-48 hours. The specific annealing process is as follows: after holding at 200~350℃ for 1.5~3h, hold at 750~900℃ for 2~3.5h.
10. A lightweight P,N-doped graphene / hollow iron-manganese phosphide composite aerogel prepared by any one of claims 1-9, characterized in that, It includes graphene sheets doped with P and N, wherein the graphene sheets are three-dimensional graphene network structures; hollow iron-manganese phosphate is anchored on the graphene sheets, wherein the hollow iron-manganese phosphate is hollow rod-shaped and has mesopores and micropores on its sidewalls.