A two-dimensional porous carbon material, its preparation method and application

Abstract

This invention discloses a two-dimensional porous carbon material, its preparation method, and its application, belonging to the field of water electrolysis for hydrogen production technology. The preparation method of the two-dimensional porous carbon material is as follows: a polyacrylamide solution, a reducing agent, a sulfur-containing compound, and a metal salt are stirred to form a gel-like spatial network structure, followed by a microwave hydrothermal reaction to obtain a precursor; the precursor is dissolved in a water-soluble salt to obtain a mixed solution, which is then freeze-dried to obtain a mixture; the mixture is annealed, and after annealing, it is washed with water to obtain the two-dimensional porous carbon material. The two-dimensional porous carbon material prepared by this invention possesses excellent conductivity and a continuous electron transport path, providing a sufficient electrode / electrolyte interface for the electrocatalytic hydrogen evolution reaction and improving the electrocatalytic efficiency of sulfides.

Description

Technical Field

[0001] This invention relates to the field of water electrolysis for hydrogen production, and more specifically to a two-dimensional porous carbon material, its preparation method, and its application. Background Technology

[0002] With the increasing global demand for clean energy, hydrogen energy is considered a key energy carrier due to its high energy density and pollution-free combustion products. Electrocatalytic water splitting (water electrolysis) is an important pathway to obtain high-purity green hydrogen. The hydrogen evolution reaction (HER), as the cathode half-reaction, has slow kinetics and requires a highly efficient catalyst to reduce the reaction overpotential and improve energy conversion efficiency. Currently, platinum / carbon (Pt / C) catalysts remain the best-performing HER catalysts. Among Pt / C catalysts, Vulcan XC-72 (Cabot Corporation) is the most widely used commercial carbon support, consisting of a mesoporous network formed by the stacking of nanoscale carbon particles (approximately 30 nm to 50 nm).

[0003] In contrast, porous carbon materials have shown great potential in the field of electrocatalysis in recent years due to their unique physicochemical properties. For example, their high specific surface area and abundant pore structure can provide a large number of active site anchoring sites, promoting the mass transfer and diffusion of reactants / products; in existing technologies, heteroatom doping (such as N, S, P, B, etc.) can optimize the charge distribution of the carbon framework, enhancing the adsorption / desorption capacity for reaction intermediates (H*); and promote rapid electron transfer at the electrode interface, reducing reaction impedance. Currently, the synthesis of porous carbon materials mainly relies on the hard template method, that is, using hard templates such as mesoporous silica or zeolite molecular sieves to composite with carbon sources, followed by high-temperature pyrolysis, but the resulting porous carbon still suffers from low electrocatalytic efficiency. Summary of the Invention

[0004] To address the above problems, this invention provides a two-dimensional porous carbon material, its preparation method, and its application. The prepared two-dimensional porous carbon material has excellent conductivity and a continuous electron transport path, providing a sufficient electrode / electrolyte interface for the electrocatalytic hydrogen evolution reaction and improving the electrocatalytic efficiency of sulfides.

[0005] The first objective of this invention is to provide a method for preparing two-dimensional porous carbon materials, comprising the following steps:

[0006] A polyacrylamide solution, a reducing agent, a sulfur-containing compound, and a metal salt are stirred to allow the polyacrylamide molecules to form intermolecular complexes with the sulfur ions in the sulfur-containing compound, creating a gel-like spatial network structure. Then, a microwave hydrothermal reaction is carried out, during which the spatial network structure transforms into a hydrothermal carbon structure to obtain the precursor.

[0007] The precursor is dissolved in a water-soluble salt to obtain a mixed solution, and then the mixed solution is freeze-dried to distribute the precursor in the water-soluble salt crystals, thus obtaining a mixture.

[0008] The mixture is annealed. During the annealing process, metal atoms form metal sulfides under the action of sulfur atoms. The metal sulfides are loaded on the surface of the carbon material. After annealing, the mixture is washed with water to obtain a two-dimensional porous carbon material.

[0009] This invention involves adding a reducing agent, a sulfur-containing compound, and a metal salt to a polyacrylamide solution, stirring to form a gel-like spatial network structure, and then performing a microwave hydrothermal reaction to obtain a precursor. The addition of the reducing agent facilitates the formation of the precursor. Preferably, the reducing agent used in this invention is ascorbic acid; citric acid can also be used.

[0010] The precursor is dissolved in a water-soluble salt to obtain a mixed solution. Using the water-soluble salt as a template, the distribution of the precursor is controlled. The mixed solution is then freeze-dried, resulting in the precursor being distributed within the water-soluble salt crystals, thus obtaining a mixture. The precursor has a gel-like structure. The addition of the water-soluble salt as a template controls the thickness of the two-dimensional carbon material in the subsequent annealing step. The water-soluble salt used in this invention needs to have good water solubility and structural stability; for example, it can be a sodium salt or potassium salt. Preferably, the water-soluble salt used in this invention is sodium chloride. The water-soluble salt used in this invention can be removed by washing with water after the two-dimensional carbon material is formed, avoiding damage to the obtained sample.

[0011] The purpose of freeze drying is to remove the aqueous solution from the microwave hydrothermal solution so that the resulting precursor is evenly distributed on the surface of the water-soluble salt. However, ordinary drying is carried out at 60℃ to 80℃, and the dried sample will shrink to a certain extent, making it impossible to obtain a fluffy precursor structure, which is not conducive to subsequent heat treatment. Therefore, this invention chooses freeze drying.

[0012] The mixture is annealed. During the annealing process, metal atoms form metal sulfides under the action of sulfur atoms. The metal sulfides are loaded on the surface of the carbon material to obtain a two-dimensional porous carbon material.

[0013] In a preferred embodiment of the present invention, the mass ratio of polyacrylamide to sulfur-containing compound is 2:1 to 1.5. It should be noted that an appropriate amount of sulfur source ensures that the added metal ions are fully sulfurized into the target metal sulfide, avoiding the generation of impurity phases such as elemental metals or low-sulfide compounds. If the mass of the sulfur-containing compound is too large, it may cause excessive etching of the initially formed carbon precursor during annealing, damaging the structural integrity of the carbon framework and thus inhibiting the formation of two-dimensional carbon materials.

[0014] In a preferred embodiment of the present invention, the mass ratio of polyacrylamide to metal salt is 2:0.5-0.6. It should be noted that controlling the mass ratio of polyacrylamide to metal salt directly affects the loading, dispersion, and structure of the metal sulfide, as well as the structure of the carbon material itself. Too low a mass of metal salt results in too little total metal sulfide. Although the dispersion may be good, the overall active site density of the material is too low. Conversely, excessive metal ions cannot be effectively isolated and fixed by the network structure of polyacrylamide. During high-temperature annealing, these adjacent metal ions easily migrate and aggregate, forming large, unevenly distributed metal sulfide particles or agglomerates.

[0015] In a preferred embodiment of the present invention, the ratio of polyacrylamide to reducing agent is 2g:5mmol~6mmol. It should be noted that controlling the ratio of polyacrylamide to reducing agent is essentially optimizing the thermodynamic and kinetic environment of the microwave hydrothermal reaction, which is crucial for obtaining a precursor with an ideal microstructure. A weak reducing environment is insufficient to form a stable three-dimensional hydrothermal carbon precursor structure. Conversely, excess reducing agent is also an organic compound, and its decomposition residue will remain in the precursor as an impurity. This may interfere with the carbonization process of polyacrylamide to form a pure carbon skeleton.

[0016] In a preferred embodiment of the present invention, the microwave hydrothermal reaction time is 2 to 3 hours. It should be noted that a shorter microwave hydrothermal reaction time may result in insufficient intermolecular cross-linking reactions and an incomplete gel network structure. In contrast, an over-cross-linked structure may be difficult to effectively graphitize and reconstruct during carbonization, leading to poor conductivity of the carbon material.

[0017] In a preferred embodiment of the present invention, the annealing time is 2 to 2.5 hours. It should be noted that controlling the annealing time is a crucial step in the conversion of the precursor into the final carbon material. A shorter annealing time will prevent the precursor from being completely converted into carbon material, resulting in poor conductivity. Further extending the annealing time, while improving the material's conductivity to some extent through excessive graphitization, leads to an increase in the orderliness of the carbon material, reducing its specific surface area and surface defect sites. Furthermore, under the Ostwald ripening mechanism, the prolonged high temperature provides sufficient energy for the metal sulfide nanoparticles to migrate and fuse, resulting in a significant increase in particle size.

[0018] In a preferred embodiment of the present invention, the mass ratio of polyacrylamide to water-soluble salt is 2:20-30. It should be noted that, theoretically, the effect of water-soluble salt on the carbon layer is through the regulation of precursor concentration distribution. The water-soluble salt acts as a template; when the amount of water-soluble salt is low, the precursor concentration per unit volume is high. During annealing, a large amount of precursor material needs to grow within a relatively limited template surface space, resulting in multi-layer stacking and the formation of a thicker two-dimensional structure. When the amount of water-soluble salt is high, the precursor concentration per unit volume is very low. During annealing, the limited precursor material spreads across the vast total area of ​​the water-soluble salt template, forcing the material to grow in thin layers, forming an ultrathin two-dimensional structure. The thickness of the carbon layer affects the specific surface area, thereby limiting the distribution of metal particles and thus reducing catalytic performance.

[0019] In a preferred embodiment of the present invention, the metal salt is one or more of nickel, cobalt, iron, and rhodium salts; the sulfur-containing compound is ammonium sulfide or thiourea; and the water-soluble salt is sodium or potassium salt. The purpose of selecting transition metal salts such as nickel, cobalt, iron, and rhodium salts, and ammonium sulfide or thiourea as sulfur-containing compounds is to obtain high-performance metal sulfide / carbon composite materials. These specific metal salts are chosen because these sulfides themselves are highly active materials in the field of electrocatalytic hydrogen evolution, directly endowing the composite material with excellent functions. Furthermore, these metal ions can coordinate with the amide groups on the polyacrylamide chain, thereby being uniformly dispersed in the network during the formation of the gel precursor, which lays the structural foundation for the subsequent formation of highly dispersed nano-sulfides. Ammonium sulfide or thiourea is chosen as the sulfur source because they can effectively and controllably provide sulfur. Ammonium sulfide has high reactivity, while thiourea, due to its moderate decomposition temperature and mild process, is more conducive to the formation of uniform sulfides. The synergistic effect of these raw materials enables the in-situ uniform generation of metal sulfides and the precise construction of a two-dimensional porous carbon framework.

[0020] The second objective of this invention is to provide a two-dimensional porous carbon material prepared by the above-described preparation method. In the two-dimensional porous carbon material, the sulfide particles loaded have a particle size of 5 nm to 10 nm. Based on the small size effect of the sulfide nanoparticles, their surface is rich in active sites, which can adsorb and dissociate water molecules and promote the hydrogen evolution reaction.

[0021] A third objective of this invention is to provide the application of the above-mentioned two-dimensional porous carbon material in electrocatalytic water splitting for hydrogen production.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) In the preparation of two-dimensional porous carbon materials, during the stirring and preparation of the reaction solution, polyacrylamide molecules with linear polymer structure are interconnected in the aqueous solution to form a gel-like spatial network structure. The gaps in the structure are filled with abundant sulfur ions. The two-dimensional porous carbon structure is innovatively prepared by microwave method and high temperature annealing. Microwave hydrothermal treatment causes the polymer to undergo dehydrogenation and deoxygenation reactions in the aqueous solution, thereby transforming the spatial network structure into a more stable carbon structure with specific structure and properties, namely hydrothermal carbon structure. The hydrothermal carbon structure is kept unchanged by freeze drying to avoid shrinkage. Then, during the annealing process, metal ions are anchored at sulfur atom sites to form metal sulfide particles in situ, which are dispersed on the surface of the porous carbon material.

[0024] (2) The two-dimensional porous carbon material prepared in this invention is doped with abundant sulfur atoms, and the size of the two-dimensional porous carbon material can be controlled within 5 nm to 10 nm. Thanks to the small size effect of sulfide nanoparticles, its surface is rich in active sites, which can effectively adsorb and dissociate water molecules, promoting the hydrogen evolution reaction. Moreover, the porous carbon structure has high conductivity and continuous electron transport pathways, which can provide sufficient electrode / electrolyte interface for the electrocatalytic hydrogen evolution reaction, improving the electrocatalytic efficiency of sulfides.

[0025] (3) In the prior art, when preparing porous carbon using the hard template method, hydrofluoric acid or strong alkali is required to etch and remove the template, followed by repeated washing, drying, and other post-processing steps. This process has significant drawbacks: the operation is cumbersome and time-consuming, and it involves the use of highly hazardous chemical reagents (such as HF), posing a serious challenge to equipment safety and operator protection. In the preparation process of this invention, water-soluble salt is used as the growth template. Because water-soluble salt has good water solubility, the structure of the obtained two-dimensional porous carbon material is greatly protected during the removal process, avoiding the problem of removing the template with hydrofluoric acid or strong alkali in the prior art. Attached Figure Description

[0026] Figure 1 This is a scanning electron microscope image of the two-dimensional porous carbon material prepared in Comparative Example 1 of this application.

[0027] Figure 2 The image is a transmission electron microscope (TEM) image of the two-dimensional porous carbon material prepared in Comparative Example 1 of this application, with a scale bar of 0.5 μm.

[0028] Figure 3 The image is a transmission electron microscope (TEM) image of the two-dimensional porous carbon material prepared in Comparative Example 1 of this application, with a scale bar of 200 nm.

[0029] Figure 4 This is a transmission electron microscope (TEM) image of the two-dimensional porous carbon material prepared in Comparative Example 2 of this application.

[0030] Figure 5This is a scanning electron microscope image of the two-dimensional porous carbon material prepared in Example 1 of this application.

[0031] Figure 6 Transmission electron microscopy (TEM) image of the two-dimensional porous carbon material prepared in Example 1 of this application, with a scale bar of 0.5 μm.

[0032] Figure 7 The image is a transmission electron microscope (TEM) image of the two-dimensional porous carbon material prepared in Example 1 of this application, with a scale bar of 100 nm.

[0033] Figure 8 The image is a transmission electron microscope (TEM) image of the two-dimensional porous carbon material prepared in Example 2 of this application, with a scale bar of 200 nm.

[0034] Figure 9 The image is a transmission electron microscope (TEM) image of the two-dimensional porous carbon material prepared in Example 3 of this application, with a scale bar of 200 nm.

[0035] Figure 10 The image is a transmission electron microscope (TEM) image of the two-dimensional porous carbon material prepared in Example 3 of this application, with a scale bar of 50 nm.

[0036] Figure 11 The image shows the X-ray spectrum of the two-dimensional porous carbon material prepared in Example 3 of this application. The inset shows the mass fraction of different elements.

[0037] Figure 12 The hydrogen evolution polarization curves are for the two-dimensional porous carbon materials prepared in Examples 2 and 3 of this application.

[0038] Figure 13 Hydrogen evolution polarization curves of the two-dimensional porous carbon materials prepared in Examples 1, 3, 4 and 5 of this application.

[0039] Figure 14 The hydrogen evolution polarization curves are for the samples prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this application. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] The polyacrylamide used in this invention has a molecular weight of 14,000,000 to 16,000,000.

[0042] Example 1

[0043] First, 0.2 g of polyacrylamide was dissolved in 20 mL of deionized water by heating to obtain the first solution. Then, 10 mL of 50 mmol / L ascorbic acid aqueous solution was added to the first solution and stirred until homogeneous to obtain the second solution. Next, 1 mL of 2 mol / L ammonium sulfide aqueous solution was added to the second solution and stirred until homogeneous to obtain the third solution. Finally, 0.05 g of nickel(II) chloride hexahydrate was added to the third solution and stirred until homogeneous to obtain the fourth solution.

[0044] The fourth solution was placed in a microwave hydrothermal reactor and heated at 160°C and 1.4 MPa for 10 minutes, followed by holding at that temperature for 2 hours. A black flocculent sample, i.e., the precursor, was obtained.

[0045] Dissolve 2g of sodium chloride in the precursor and centrifuge at 8000RPM for 3 minutes at 20°C. A black precipitate is obtained. Discard the supernatant, freeze for 24 hours, and then dry in a freeze dryer.

[0046] The obtained sample was crushed and placed in a tube furnace, and heated at 700°C for 2 hours to obtain a black powder sample.

[0047] The black powder sample was added to 50 mL of water to submerge the sample surface. The sample was then sonicated at 100 W for 10 min and centrifuged three times. After centrifugation, the sample was dried overnight in a vacuum drying oven at 60 °C to obtain a two-dimensional porous carbon material.

[0048] Example 2

[0049] First, 0.2 g of polyacrylamide was dissolved in 20 mL of deionized water by heating to obtain the first solution. 10 mL of 50 mmol / L ascorbic acid aqueous solution was added to the first solution and stirred until homogeneous to obtain the second solution. 1 mL of 2 mol / L ammonium sulfide aqueous solution was added to the second solution and stirred until homogeneous to obtain the third solution. Then, 0.05 g of rhodium(III) chloride was added to the third solution and stirred until homogeneous to obtain the fourth solution.

[0050] The fourth solution was placed in a microwave hydrothermal reactor and heated at 180℃ and 1.4MPa for 10 minutes, followed by holding at that temperature for 2 hours. A black flocculent sample, i.e., the precursor, was obtained.

[0051] Dissolve 2g of sodium chloride in the precursor and centrifuge at 8000RPM for 3 minutes at 20°C. A black precipitate is obtained.

[0052] After discarding the supernatant, freeze for 24 hours and then dry in a freeze-drying oven. Grind the obtained sample and place it in a tube furnace, then heat at 600℃ for 2 hours to obtain a black powder sample.

[0053] The black powder sample was added to 50 mL of water to submerge the sample surface. The sample was then sonicated at 100 W for 10 min and centrifuged three times. After centrifugation, the sample was dried overnight in a vacuum drying oven at 60 °C to obtain a two-dimensional porous carbon material.

[0054] Example 3

[0055] First, 0.2 g of polyacrylamide was dissolved in 20 mL of deionized water by heating to obtain the first solution. 10 mL of 50 mmol / L ascorbic acid aqueous solution was added to the first solution and stirred until homogeneous to obtain the second solution. 1 mL of 2 mol / L ammonium sulfide aqueous solution was added to the second solution and stirred until homogeneous to obtain the third solution. Then, 0.05 g of rhodium(III) chloride was added to the third solution and stirred until homogeneous to obtain the fourth solution.

[0056] The fourth solution was placed in a microwave hydrothermal reactor and heated at 180℃ and 1.4MPa for 10 minutes, followed by holding at that temperature for 2 hours. A black flocculent sample, i.e., the precursor, was obtained.

[0057] Dissolve 2g of sodium chloride in the precursor and centrifuge at 8000RPM for 3 minutes at 20°C. A black precipitate is obtained.

[0058] After discarding the supernatant, freeze for 24 hours and then dry in a freeze dryer. Grind the obtained sample and place it in a tube furnace, then heat at 700°C for 2 hours to obtain a black powder sample.

[0059] The black powder sample was added to 50 mL of water to submerge the sample surface. The sample was then sonicated at 100 W for 10 min and centrifuged three times. After centrifugation, the sample was dried overnight in a vacuum drying oven at 60 °C to obtain a two-dimensional porous carbon material.

[0060] Example 4

[0061] First, 0.2 g of polyacrylamide was dissolved in 20 mL of deionized water by heating to obtain the first solution. 10 mL of 50 mmol / L ascorbic acid aqueous solution was added to the first solution and stirred until homogeneous to obtain the second solution. 1 mL of 2 mol / L ammonium sulfide aqueous solution was added to the second solution and stirred until homogeneous to obtain the third solution. Then, 0.05 g of a mixture of rhodium(III) chloride and nickel(II) chloride hexahydrate (rhodium chloride to nickel(II) chloride hexahydrate mass ratio of 5:1) was added to the third solution and stirred until homogeneous to obtain the fourth solution.

[0062] The fourth solution was placed in a microwave hydrothermal reactor and heated at 180°C and 1.4 MPa for 10 minutes, followed by holding at that temperature for 2 hours. A black flocculent sample, i.e., the precursor, was obtained.

[0063] Dissolve 2g of sodium chloride in the precursor and centrifuge at 8000RPM for 3 minutes at 20°C. A black precipitate is obtained. Discard the supernatant, freeze for 24 hours, and then dry in a freeze dryer.

[0064] The obtained sample was crushed and placed in a tube furnace, and heated at 700°C for 2 hours to obtain a black powder sample.

[0065] The black powder sample was added to 50 mL of water to submerge the sample surface. The sample was then sonicated at 100 W for 10 min and centrifuged three times. After centrifugation, the sample was dried overnight in a vacuum drying oven at 60 °C to obtain a two-dimensional porous carbon material.

[0066] Example 5

[0067] First, 0.2 g of polyacrylamide was dissolved in 20 mL of deionized water by heating to obtain the first solution. 10 mL of 50 mmol / L ascorbic acid aqueous solution was added to the first solution and stirred until homogeneous to obtain the second solution. 1 mL of 2 mol / L ammonium sulfide aqueous solution was added to the second solution and stirred until homogeneous to obtain the third solution. Then, 0.05 g of a mixture of rhodium(III) chloride and nickel(II) chloride hexahydrate (rhodium chloride to nickel(II) chloride hexahydrate mass ratio of 5:2) was added to the third solution and stirred until homogeneous to obtain the fourth solution.

[0068] The fourth solution was placed in a microwave hydrothermal reactor and heated at 200°C and 1.4 MPa for 10 minutes, followed by holding at that temperature for 2 hours. A black flocculent sample, i.e., the precursor, was obtained.

[0069] Dissolve 2g of sodium chloride in the precursor and centrifuge at 8000RPM for 3 minutes at 20°C. A black precipitate is obtained.

[0070] After discarding the supernatant, freeze for 24 hours and then put it into a freeze dryer to dry.

[0071] The obtained sample was crushed and placed in a tube furnace, and heated at 700°C for 2 hours to obtain a black powder sample.

[0072] The black powder sample was added to 50 mL of water to submerge the sample surface. The sample was then sonicated at 100 W for 10 min and centrifuged three times. After centrifugation, the sample was dried overnight in a vacuum drying oven at 60 °C to obtain a two-dimensional porous carbon material.

[0073] Example 6

[0074] First, 0.2 g of polyacrylamide was dissolved in 20 mL of deionized water by heating to obtain the first solution. Then, 10 mL of 60 mmol / L ascorbic acid aqueous solution was added to the first solution and stirred until homogeneous to obtain the second solution. Next, 0.7 mL of 2 mol / L ammonium sulfide aqueous solution was added to the second solution and stirred until homogeneous to obtain the third solution. Finally, 0.06 g of ferric chloride hexahydrate was added to the third solution and stirred until homogeneous to obtain the fourth solution.

[0075] The fourth solution was placed in a microwave hydrothermal reactor and heated at 200℃ and 1.2MPa for 10 minutes, followed by holding at that temperature for 3 hours. A black flocculent sample, i.e., the precursor, was obtained.

[0076] Dissolve 25g of sodium chloride in the precursor and centrifuge at 8000RPM for 3 minutes at 20℃. A black precipitate is obtained. Discard the supernatant, freeze for 24 hours, and then dry in a freeze dryer.

[0077] The obtained sample was crushed and placed in a tube furnace, and heated at 600°C for 2.5 hours to obtain a black powder sample.

[0078] The black powder sample was added to 50 mL of water to submerge the sample surface. The sample was then sonicated at 100 W for 10 min and centrifuged three times. After centrifugation, the sample was dried overnight in a vacuum drying oven at 60 °C to obtain a two-dimensional porous carbon material.

[0079] Example 7

[0080] First, 0.2 g of polyacrylamide was dissolved in 20 mL of deionized water by heating to obtain the first solution. Then, 10 mL of 55 mmol / L ascorbic acid aqueous solution was added to the first solution and stirred until homogeneous to obtain the second solution. Next, 1 mL of 2 mol / L thiourea aqueous solution was added to the second solution and stirred until homogeneous to obtain the third solution. Finally, 0.055 g of cobalt chloride hexahydrate was added to the third solution and stirred until homogeneous to obtain the fourth solution.

[0081] The fourth solution was placed in a microwave hydrothermal reactor and heated at 180°C and 1.6 MPa for 10 minutes, followed by holding at that temperature for 2.5 hours. A black flocculent sample, i.e., the precursor, was obtained.

[0082] Dissolve 30g of sodium chloride in the precursor and centrifuge at 8000RPM for 3 minutes at 20℃. A black precipitate is obtained. Discard the supernatant, freeze for 24 hours, and then dry in a freeze dryer.

[0083] The obtained sample was crushed and placed in a tube furnace, and heated at 800°C for 2.3 hours to obtain a black powder sample.

[0084] The black powder sample was added to 50 mL of water to submerge the sample surface. The sample was then sonicated at 100 W for 10 min and centrifuged three times. After centrifugation, the sample was dried overnight in a vacuum drying oven at 60 °C to obtain a two-dimensional porous carbon material.

[0085] Comparative Example 1

[0086] 0.2 g of polyacrylamide was dissolved in 20 mL of deionized water by heating to obtain the first solution. 10 mL of 50 mmol / L ascorbic acid was added to the first solution and stirred until homogeneous to obtain the second solution. Then, 1 mL of 2 mol / L ammonium sulfide was added to the second solution and stirred until homogeneous to obtain the third solution.

[0087] The third solution was placed in a microwave hydrothermal reactor and heated at 180°C and 1.4 MPa for 10 minutes, followed by holding at that temperature for 2 hours. A dark brown flocculent sample, i.e., the precursor, was obtained.

[0088] Dissolve 2g of sodium chloride in the precursor and centrifuge at 8000RPM for 3 minutes at 20°C. A black precipitate is obtained. Discard the supernatant, freeze for 24 hours, and then dry in a freeze dryer.

[0089] The obtained sample was crushed and placed in a tube furnace. Ar gas was introduced and heated at 700°C for 2 hours to obtain a black powder sample.

[0090] The black powder sample was added to 50 mL of water to submerge the sample surface. The sample was then sonicated at 100 W for 10 min and centrifuged three times. After centrifugation, the sample was dried overnight in a vacuum drying oven at 60 °C to obtain a two-dimensional porous carbon material.

[0091] Comparative Example 2

[0092] First, 0.2 g of polyacrylamide was dissolved in 20 mL of deionized water by heating to obtain the first solution. Then, 1 mL of 2 mol / L ammonium sulfide was added to the first solution and stirred until homogeneous to obtain the second solution. Next, 0.05 g of nickel(II) chloride hexahydrate was added to the second solution and stirred until homogeneous to obtain the third solution.

[0093] The third solution was placed in a microwave hydrothermal reactor and heated at 180°C and 1.4 MPa for 10 minutes, followed by holding at that temperature for 2 hours. A black dispersed sample, i.e., the precursor, was obtained.

[0094] Dissolve 2g of sodium chloride in the precursor and centrifuge at 8000RPM for 3 minutes at 20°C. A black precipitate is obtained. Discard the supernatant, freeze for 24 hours, and then dry in a freeze dryer.

[0095] The obtained sample was crushed and placed in a tube furnace. Ar gas was introduced and heated at 700°C for 2 hours to obtain a black powder sample.

[0096] The black powder sample was added to 50 mL of water to submerge the sample surface. The sample was then sonicated at 100 W for 10 min and centrifuged three times. After centrifugation, the sample was dried overnight in a vacuum drying oven at 60 °C to obtain a two-dimensional porous carbon material.

[0097] Figure 1 and Figure 2 The images show scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the two-dimensional porous carbon material obtained in Comparative Example 1, respectively. As can be seen from the figures, this carbon material exhibits a two-dimensional structure with a large specific surface area. (High-magnification TEM image) Figure 3 Further, it was shown that its surface was distributed with a porous structure of varying sizes, which was mainly attributed to the carbon precursor forming a carbon structure under the action of sodium chloride template and the porous features retained after the sodium chloride was removed. Figure 4 The image shows the particulate nickel sulfide structure obtained in Comparative Example 2. The results indicate that introducing a reducing agent into the microwave hydrothermal reaction system promotes the dehydrogenation and deoxygenation reactions of polyacrylamide molecules, thereby generating structurally stable hydrothermal carbon; however, without the addition of a reducing agent, only a particulate nickel sulfide structure can be formed.

[0098] Figure 5 and Figure 6 The images show scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the sample obtained in Example 1, respectively. As can be seen from the images, the sample retains the two-dimensional structural characteristics of carbon materials. (High-magnification TEM image) Figure 7 Further, it was shown that nickel sulfide nanoparticles with a particle size of about 5 nm to 10 nm were uniformly distributed on the surface of the two-dimensional carbon structure. Figure 8 and Figure 9 Transmission electron microscopy (TEM) images of the samples obtained in Examples 2 and 3 are shown respectively, revealing that the two-dimensional carbon structure surface is uniformly loaded with rhodium sulfide nanoparticles with extremely small particle sizes. Figure 10 The image shown is a dark-field transmission electron microscope (TEM) image of the sample obtained in Example 3, indicating that the particle size of the rhodium sulfide nanoparticles on the two-dimensional carbon structure is approximately 3–5 nm. The X-ray energy dispersive spectroscopy (EDS) spectrum is also shown. Figure 11 As can be seen, the mass fractions of carbon, sulfur and rhodium in the sample of Example 3 are 94.5wt%, 4wt% and 1.5wt%, respectively, which further confirms that the composite material is mainly composed of two-dimensional carbon structure, with a small amount of rhodium sulfide nanoparticles uniformly distributed on its surface.

[0099] like Figure 12 As shown, the two-dimensional porous carbon material loaded with rhodium sulfide obtained in Example 3, at a current density of 10 mA / cm², -2The overpotential was 205 mV, lower than that of the two-dimensional carbon material loaded with rhodium sulfide obtained in Example 2 (287 mV). Furthermore, calculations based on the hydrogen evolution polarization curve showed that the Tafel slope of the two-dimensional carbon material loaded with rhodium sulfide obtained in Example 3 was 116 mV dec. -1 The value is far lower than that of the two-dimensional carbon material supported on rhodium sulfide obtained in Example 2 (158 mV dec). -1 The above results indicate that, thanks to the higher annealing temperature, the two-dimensional carbon material supported on rhodium sulfide obtained in Example 3 exhibits superior hydrogen evolution performance of two-dimensional porous carbon materials. Examples 4 and 5 prepared two-dimensional porous carbon materials with supported multi-component sulfide composite structures by adding two different metal salt solutions to the reaction solution. Figure 13 It can be seen that, compared with the two-dimensional porous carbon material loaded with nickel sulfide obtained in Example 1 and the two-dimensional porous carbon material loaded with rhodium sulfide obtained in Example 3, the two-dimensional porous carbon materials loaded with multi-component sulfides prepared in Examples 4 and 5 all exhibited superior hydrogen evolution performance. Among them, the two-dimensional porous carbon material loaded with multi-component sulfides obtained in Example 4 showed better hydrogen evolution performance at a current density of 10 mA cm⁻¹. -2 The overpotential is only 107 mV, which is lower than that of the two-dimensional porous carbon material loaded with multi-component sulfides obtained in Example 5 (187 mV), the two-dimensional porous carbon material loaded with nickel sulfide obtained in Example 1 (359 mV), and the two-dimensional porous carbon material loaded with rhodium sulfide obtained in Example 3 (205 mV).

[0100] like Figure 14 As shown, the two-dimensional porous carbon material obtained in Comparative Example 1 operates at a current density of 10 mA cm⁻¹. -2 The overpotential is 472 mV, indicating that the hydrogen evolution active sites of the two-dimensional porous carbon material loaded with multi-component sulfides mainly originate from sulfide nanoparticles. Furthermore, from... Figure 4 It can be seen that when no reducing agent is added during sample preparation, the sample obtained in Comparative Example 2 is a metal sulfide nanoparticle, not a two-dimensional composite structure, and it exhibits this characteristic at a current density of 10 mA cm⁻¹. -2 The overpotential is 378mV ( Figure 14 The above results indicate that the reducing agent can facilitate the formation of two-dimensional layered carbon materials and effectively inhibit the growth of sulfide nanoparticles, thereby improving their electrocatalytic hydrogen evolution performance.

[0101] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0102] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for producing a two-dimensional porous carbon material, characterized by, Includes the following steps: A polyacrylamide solution, a reducing agent, a sulfur-containing compound, and a metal salt are stirred to allow the polyacrylamide molecules to form intermolecular complexes with the sulfur ions in the sulfur-containing compound, creating a gel-like spatial network structure. A microwave hydrothermal reaction is then carried out, during which the spatial network structure transforms into a hydrothermal carbon structure, yielding the precursor. The microwave hydrothermal reaction is conducted at a temperature of 160℃–200℃, a pressure of 1.2 MPa–1.6 MPa, and a reaction time of 2–3 hours. The metal salt is one or more of nickel, cobalt, iron, and rhodium salts; the sulfur-containing compound is ammonium sulfide or thiourea. The precursor is dissolved in a water-soluble salt to obtain a mixed solution, which is then freeze-dried to distribute the precursor in the water-soluble salt crystals, resulting in a mixture; the water-soluble salt is a sodium salt or a potassium salt. The mixture was annealed. During the annealing process, metal atoms formed metal sulfides under the action of sulfur atoms. The metal sulfides were loaded on the surface of the carbon material. After annealing, the mixture was washed with water to obtain a two-dimensional porous carbon material. The annealing temperature was 600℃~800℃ and the annealing time was 2h~2.5h. The particle size of the loaded metal sulfides in the two-dimensional porous carbon material was 5nm~10nm. Two-dimensional porous carbon materials are used for electrocatalytic water splitting to produce hydrogen.

2. The method for preparing a two-dimensional porous carbon material according to claim 1, characterized in that, The mass ratio of polyacrylamide to sulfur-containing compounds is 2:1 to 1.

5.

3. The method for preparing a two-dimensional porous carbon material according to claim 1, characterized in that, The mass ratio of polyacrylamide to metal salt is 2:0.5 to 0.

6.

4. The method for preparing a two-dimensional porous carbon material according to claim 1, characterized in that, The ratio of polyacrylamide to reducing agent is 2g: 5mmol to 6mmol.

5. The method for preparing a two-dimensional porous carbon material according to claim 1, characterized in that, The mass ratio of polyacrylamide to water-soluble salt is 1:10-15.

6. A two-dimensional porous carbon material prepared by the preparation method according to any one of claims 1 to 5.

7. The application of the two-dimensional porous carbon material according to claim 6 in electrocatalytic water splitting for hydrogen production.

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