Preparation method of graphene-based material

Abstract

According to the preparation method of the graphene-based material provided by the invention, when the prepared graphene-based material is used for fully decomposing water, under the same current density, the graphene-based material has small overpotential in HER and OER reactions and has long-term stability.

Description

Technical Field

[0001] This invention relates to the preparation of graphene-based materials, and particularly to a graphene-based material with a total water splitting catalytic function. Background Technology

[0002] Graphene is an sp2-hybridized single-layer two-dimensional nanomaterial with significant advantages in electrical conductivity, thermal conductivity, surface area, mechanical strength, and chemical stability, making it widely used in sensors, bioengineering, energy production, and storage. However, the poor catalytic performance of pure graphene greatly limits its industrial application. Therefore, researchers have modified the graphene structure to adjust its physical and chemical properties, thereby obtaining electrode materials with high catalytic activity. These modifications include combining it with metal nanoparticles and metal hydroxides, as well as doping the graphene framework with atoms.

[0003] With the depletion of fossil fuels and the worsening of environmental problems, people are prompted to develop clean, pollution-free, and sustainable new energy sources. Hydrogen energy has advantages such as being pollution-free and widely available, making it very suitable as an energy storage and fuel. Furthermore, water electrolysis to produce hydrogen is one of the most environmentally friendly methods currently available.

[0004] For example, CN117364148A discloses a NiFe2O4 / Ni2P@nitrogen-doped graphene tube composite electrocatalyst for total water splitting. First, a NiFe hydroxide precursor grown on the surface of a nitrogen-doped graphene tube is obtained via a hydrothermal method. Then, it is calcined in air in a muffle furnace to generate a NiFe2O4@nitrogen-doped graphene tube electrocatalyst intermediate. Next, the product is placed in a tube furnace, heated to 320°C using sodium hypophosphite as the phosphorus source, and held at that temperature for two hours for in-situ phosphating, yielding a composite electrocatalyst for total water splitting composed of a nitrogen-doped graphene tube and a NiFe2O4 / Ni2P heterostructure grown in situ on its surface. This electrocatalyst exhibits excellent oxygen and hydrogen evolution performance in alkaline media, achieving a current density of 10 mA / cm². Its oxygen evolution overpotential is only 194 mV, and its hydrogen evolution overpotential is 118 mV. Furthermore, as a total water splitting electrocatalyst, it only requires a cell voltage of 1.53 V to achieve a current density of 10 mA / cm², and it operates stably for more than 330 hours without significant changes, demonstrating extremely excellent stability.

[0005] CN116422323A discloses a method for preparing a visible light-driven graphene oxide / rhodium-strontium titanate composite photocatalyst for total water splitting. Strontium chloride, rhodium chloride, and water are stirred for the first time, then tetrabutyl titanate is added, followed by sodium hydroxide. After a second stirring, graphene oxide is added. The autoclave is then heated from room temperature to the reaction temperature. After the reaction is complete, the mixture is washed and dried to obtain graphene oxide / rhodium-strontium titanate precursor powder. Annealing yields graphene oxide / rhodium-strontium titanate powder, which is then used for total water splitting under visible light. This invention, by constructing a graphene / strontium titanate heterostructure, significantly enhances the absorption of visible light by strontium titanate, increases the utilization rate of sunlight, and simultaneously improves the conductivity of strontium titanate, thereby enhancing the total water splitting performance of strontium titanate.

[0006] For example, CN114164445A describes a V-Ni3FeN / Ni@N-GTs electrocatalyst based on a doping and heterojunction strategy. First, a V-doped NiFe precursor is grown on a nitrogen-doped graphene tube support via a hydrothermal method. Then, the substrate is heated to 470°C in a tube furnace, ammonia is introduced, and the substrate is nitrided for 2 hours to obtain an electrocatalyst composed of V-doped Ni3FeN and Ni nanoparticles grown in situ on a nitrogen-doped graphene tube, namely V-Ni3FeN / Ni@N-GTs. Based on the effective regulation of the electronic structure of Ni and Fe in Ni3FeN by V doping, the charge rearrangement induced by the heterojunction interface between V-Ni3FeN and Ni, and the synergistic effect of the good conductivity of the nitrogen-doped graphene tube support, this electrocatalyst exhibits excellent electrocatalytic activity and stability in both hydrogen evolution reaction and oxygen evolution reaction in alkaline medium. Simultaneously, when used as both an anode and cathode catalyst for catalyzing the complete water splitting reaction, it achieves a current density of 10 mA cm⁻² with only a cell voltage of 1.55 V, and demonstrates excellent stability.

[0007] However, the cathode and anode of the electrode have high overpotentials during water electrolysis to produce hydrogen, resulting in low energy utilization. Therefore, it is necessary to develop highly active and stable non-precious metal catalysts to reduce overpotentials and production costs. Summary of the Invention

[0008] Based on the above, this invention provides a method for preparing graphene-based materials. When the prepared graphene-based materials are used for total water splitting, they exhibit small overpotentials in both HER and OER reactions at the same current density and have long-term stability. By changing different catalyst supports and transition metal active centers, highly efficient total water splitting electrocatalyst materials are prepared from the aspects of electrocatalyst heterostructure construction, synergistic effect of nickel phosphide and nickel selenide, active center regulation, and graphene support.

[0009] A method for preparing a graphene-based material includes the following steps: (1) Step 1: Add potassium iodide solution and selenium dioxide to nitric acid to form a purple-black solid and precipitate white crystals. Then filter, deionize and wash, and dry to obtain solid powder. Heat the solid powder to 90-100℃ under an inert atmosphere, keep it for 10-15 min, and grind to obtain powder. (2) Weigh out nickel source, carbon nitrogen source and graphene, grind and mix them and place them in the combustion boat, and then place them in the middle of the T-shaped quartz tube; weigh out the powder prepared in step one and place it in the combustion boat, and place it at the gas inlet on the left side of the T-shaped quartz tube; (3) Weigh the phosphorus source and place it in the combustion boat, and place it at the right air inlet of the T-shaped quartz tube; (4) Inert gas is introduced into the left and right air inlets for 3-5 minutes, then the temperature is increased by setting the program to carry out high-temperature calcination, and then cooled naturally and taken out to obtain the desired graphene-based material.

[0010] The molar ratio of potassium iodide solution to selenium dioxide is 4:1~2, and the amount of nitric acid is 10 wt.%, 75-100 mL.

[0011] The nickel source is nickel oxalate hydrate.

[0012] The carbon and nitrogen source is melamine.

[0013] The graphene in question is thermally expanded graphene.

[0014] The mass ratio of the nickel source, carbon-nitrogen source, and graphene is 1.5:2-3:1.5-2.

[0015] The phosphorus source is sodium hypophosphite, and the dosage is 1-2g.

[0016] The inert gas is argon, and the flow rate is 700-800 sccm.

[0017] The temperature is programmed to rise at 2-5℃ / min to 600-700℃, and then held at that temperature for 2-4 hours.

[0018] A three-dimensional graphene-based material, wherein the three-dimensional graphene-based material uses nitrogen-doped thermally expandable graphene as a substrate, carbon nanofibers are loaded on the surface of the nitrogen-doped thermally expandable graphene, and Ni3P-NiSe is loaded near the carbon nanofibers. x / Ni nanoparticles, wherein the carbon nanofibers have a size of 500-700 nm, and the nitrogen-doped Ni3P-NiSe x / Ni nanoparticles have a size of 30-50 nm.

[0019] The nitrogen-doped Ni3P-NiSe x / Ni nanoparticles are heterogeneous nanoparticles used as catalysts for hydrogen production at all pH levels in electrocatalytic water splitting.

[0020] The three-dimensional graphene-based material obtained 10 mA cm in a 1 mol / L KOH solution. -2 The oxygen evolution overpotential at current density is 173 mV, and the hydrogen evolution overpotential is 95 mV.

[0021] This invention uses thermally expanded graphene as a carrier to impart a high specific surface area to the catalyst; the carbon and nitrogen source is melamine, in which carbon reduces nickel, and nitrogen-doped graphene is obtained after heat treatment to form carbon fibers attached to the graphene surface; hydrated nickel oxalate is used as the nickel source, and after heat treatment, Ni and NiO are obtained. X Then, it reacts with selenium and phosphorus sources in two pipelines to obtain NiSe. x It reacts with Ni3P to form a heterojunction with Ni. The possible reaction formulas are shown below.

[0022] First, potassium iodide solution and selenium dioxide are added to nitric acid, forming a purple-black solid and precipitating white crystals. The mixture is then filtered, deionized, washed, and dried to obtain a solid powder. The solid powder is then heated to 90-100℃ under an inert atmosphere and held for 10-15 minutes, followed by grinding to obtain another powder. The main reaction in this process is: SeO2 + 4KI + 4HNO3 = Se + 2I2 + 2H2O, a liquid-phase reaction that forms a purple-black solid and precipitates white crystals. Impurities are then removed through filtration, washing, drying, and inert treatment, including the removal of iodine by sublimation, to obtain small-particle active Se.

[0023] The hydrated nickel oxalate located at the central convergence point of the T-tube is first dehydrated and then thermally decomposed to obtain nickel oxide. The carbon and nitrogen source, melamine, decomposes to obtain carbon and nitrogen. Some of the carbon reacts with nickel oxide, and some of the carbon decomposes to form carbon fibers. Nitrogen is doped into the graphene support. Raman testing shows that compared to standard graphene ID / IG≈1.15, the catalyst of this invention has ID / IG≈1.23, indicating that thermally expanded graphene undergoes significant doping. However, it cannot be ruled out that the doping occurs in the carbon fibers on the graphene surface. The possible reaction processes involved are as follows.

[0024] C2NiO4·2H2O=C2NiO4+2H2O C2NiO4=NiO+CO↑+CO2↑ 2C + NiO → 2Ni + CO2↑.

[0025] The active Se is placed on the left side of the T-tube, and selenium vapor is obtained at high temperature. The selenium vapor reacts with the nickel in the middle through an inert support to form Ni2Se, NiSe2, or NiSe, i.e., nickel selenium (NiSe). x The compound has the reaction formula Ni + xSe = NiSe. x X = 1 / 2, 1, 2.

[0026] Under high temperature regulation, sodium hypophosphite decomposes and reacts with NiO to form nickel phosphide and nickel: 2NaH2PO2→PH3↑+Na2HPO4; 4PH3+6NiO→Ni3P+3Ni+3P+6H2O.

[0027] Thermally expanded graphene, as a catalyst support, provides extremely high specific surface area and porosity, and its inert nature endows the catalyst with resistance to alkalis and acids. Meanwhile, heterojunction Ni3P-NiSe... x / Ni particles endow the catalytic particles with extremely high conductivity, interfacial properties, and catalytic activity, exhibiting high dispersion on the high graphene surface, which is beneficial for the catalytic reaction of hydrogen evolution and oxygen evolution in water electrolysis.

[0028] Based on the above, this invention obtains a substrate of nitrogen-doped thermally expandable graphene, with carbon nanofibers loaded on the surface of the nitrogen-doped thermally expandable graphene, and Ni3P-NiSe loaded near the carbon nanofibers. x / Ni nanoparticles, wherein the carbon nanofibers have a size of 500-700 nm, and the nitrogen-doped Ni3P-NiSe x / Ni nanoparticles with a size of 30-50nm are used in catalytic powder materials.

[0029] The above-mentioned catalytic powder material and carbon black powder were dispersed in a mixed solvent (the solvent included solution, water, and ethanol), and after ultrasonic homogenization, the prepared catalyst slurry was uniformly coated onto the current collector foam nickel and dried for later use. A three-electrode system was used for testing, with a saturated Ag / AgCl electrode as the reference electrode and a graphite rod as the counter electrode.

[0030] Compared with the prior art, the present invention has the following technical effects: This invention prepares Ni3P-NiSe through bidirectional pyrolysis heat treatment. x / Ni heterogeneous nanoparticles were loaded onto the surface of a nitrogen-doped carbon fiber graphene support, Ni3P-NiSe x Ni nanoparticles, in their small particle form and highly dispersed on the support surface, exhibit a heterojunction structure that significantly reduces the overpotential during hydrogen evolution. Under acidic, neutral, and alkaline conditions, an overpotential of only 92 mV, 113 mV, and 95 mV, respectively, is required to achieve 10 mA / cm². 2 The current density was 10 mA cm⁻¹ in a 1 mol / L KOH solution. -2 The oxygen evolution overpotential at current density is 173 mV. Attached Figure Description

[0031] Figure 1 HER polarization curves for examples and comparative examples.

[0032] Figure 2 10 mA·cm -2Overpotential of current density examples and comparative examples.

[0033] Figure 3 Tafel curves for examples and comparatives.

[0034] Figure 4 Example 2: Stability test of electrode polarization curves before and after 10,000 CV cycles. Detailed Implementation Example 1

[0035] A method for preparing a graphene-based material includes the following steps: (1) Step 1: Add potassium iodide solution and selenium dioxide to nitric acid to form a purple-black solid and precipitate white crystals. Then filter, deionize and wash, and dry to obtain solid powder. Heat the solid powder to 90°C under an inert atmosphere and keep it for 10 min. Grind to obtain powder. The molar ratio of potassium iodide solution to selenium dioxide is 4:1, and the amount of nitric acid is 10 wt.% and 75 mL.

[0036] (2) Weigh out the nickel oxalate hydrate source, melamine carbon nitrogen source, and thermally expanded graphene, grind and mix them, and place them in the combustion boat. The mass ratio of the nickel source, carbon nitrogen source, and graphene is 1.5:2:1.5. Then place them in the middle of the T-shaped quartz tube. Weigh out the powder prepared in step one and place it in the combustion boat. Place it at the air inlet on the left side of the T-shaped quartz tube.

[0037] (3) Weigh 1g of sodium hypophosphite phosphorus source and place it in the combustion boat, and place it at the right air inlet of the T-shaped quartz tube.

[0038] (4) Inert gas is introduced into the left and right air inlets for 3 minutes. The inert gas is argon and the flow rate is 700 sccm. Then, the temperature is set to rise to 600℃ at a program of 2℃ / min. The temperature is kept constant for 2 hours. Then, the material is cooled naturally and taken out to obtain the desired graphene-based material. Example 2

[0039] A method for preparing a graphene-based material includes the following steps: (1) Step 1: Add potassium iodide solution and selenium dioxide to nitric acid to form a purple-black solid and precipitate white crystals. Then filter, deionize and wash, and dry to obtain solid powder. Heat the solid powder to 95°C under an inert atmosphere and keep it for 12.5 min. Grind to obtain powder. The molar ratio of potassium iodide solution to selenium dioxide is 4:1.5. The amount of nitric acid is 10 wt.% and 90 mL.

[0040] (2) Weigh out the nickel oxalate hydrate source, melamine carbon nitrogen source, and thermally expanded graphene, grind and mix them, and place them in the combustion boat. The mass ratio of the nickel source, carbon nitrogen source, and graphene is 1.5:2.5:1.75. Then place it in the middle of the T-shaped quartz tube. Weigh out the powder prepared in step one and place it in the combustion boat. Place it at the air inlet on the left side of the T-shaped quartz tube.

[0041] (3) Weigh 1.5g of sodium hypophosphite phosphorus source and place it in the combustion boat, and place it at the right air inlet of the T-shaped quartz tube.

[0042] (4) Inert gas is introduced into the left and right air inlets for 4 minutes. The inert gas is argon and the flow rate is 750 sccm. Then, the temperature is set to rise to 650℃ at a program of 3℃ / min. The temperature is kept constant for 3 hours and then cooled naturally. The material is then removed to obtain the desired graphene-based material. Example 3

[0043] A method for preparing a graphene-based material includes the following steps: (1) Step 1: Add potassium iodide solution and selenium dioxide to nitric acid to form a purple-black solid and precipitate white crystals. Then filter, deionize and wash, and dry to obtain solid powder. Heat the solid powder to 100℃ under an inert atmosphere and keep it for 15 min. Grind to obtain powder. The molar ratio of potassium iodide solution to selenium dioxide is 4:2, and the amount of nitric acid is 10wt.% and 100mL.

[0044] (2) Weigh out the nickel oxalate hydrate source, melamine carbon nitrogen source, and thermally expanded graphene, grind and mix them, and place them in the combustion boat. The mass ratio of nickel source, carbon nitrogen source, and graphene is 1.5:3:2. Then place it in the middle of the T-shaped quartz tube. Weigh out the powder prepared in step one and place it in the combustion boat, and place it at the air inlet on the left side of the T-shaped quartz tube.

[0045] (3) Weigh 2g of sodium hypophosphite phosphorus source and place it in the combustion boat, and place it at the right air inlet of the T-shaped quartz tube.

[0046] (4) Inert gas is introduced into the left and right air inlets for 3-5 minutes. The inert gas is argon and the flow rate is 800 sccm. Then, the temperature is set to rise to 700℃ at a program temperature of 5℃ / min. The temperature is kept constant for 4 hours and then cooled naturally. The graphene-based material is then obtained.

[0047] Comparative Example 1. A method for preparing a graphene-based material, comprising the following steps: (1) Weigh out the nickel oxalate hydrate source, melamine carbon nitrogen source, and thermally expanded graphene, grind and mix them, and place them in a combustion boat. The mass ratio of the nickel source, carbon nitrogen source, and graphene is 1.5:2.5:1.75. Then place it in the middle of the T-shaped quartz tube. (2) Weigh 1.5g of sodium hypophosphite phosphorus source and place it in the combustion boat, and place it at the right air inlet of the T-shaped quartz tube.

[0048] (3) Inert gas is introduced into the left and right air inlets for 4 minutes. The inert gas is argon and the flow rate is 750 sccm. Then, the temperature is set to rise to 650℃ at a program of 3℃ / min. The temperature is kept constant for 3 hours and then cooled naturally. The material is then removed to obtain the desired graphene-based material.

[0049] Comparative Example 2. A method for preparing a graphene-based material, comprising the following steps: (1) Step 1: Add potassium iodide solution and selenium dioxide to nitric acid to form a purple-black solid and precipitate white crystals. Then filter, deionize and wash, and dry to obtain solid powder. Heat the solid powder to 95°C under an inert atmosphere and keep it for 12.5 min. Grind to obtain powder. The molar ratio of potassium iodide solution to selenium dioxide is 4:1.5. The amount of nitric acid is 10 wt.% and 90 mL.

[0050] (2) Weigh out the nickel oxalate hydrate source, melamine carbon nitrogen source, and thermally expanded graphene, grind and mix them, and place them in the combustion boat. The mass ratio of the nickel source, carbon nitrogen source, and graphene is 1.5:2.5:1.75. Then place it in the middle of the T-shaped quartz tube. Weigh out the powder prepared in step one and place it in the combustion boat. Place it at the air inlet on the left side of the T-shaped quartz tube.

[0051] (3) Inert gas is introduced into the left and right air inlets for 4 minutes. The inert gas is argon and the flow rate is 750 sccm. Then, the temperature is set to rise to 650℃ at a program of 3℃ / min. The temperature is kept constant for 3 hours and then cooled naturally. The material is then removed to obtain the desired graphene-based material.

[0052] Comparative Example 3. A method for preparing a graphene-based material, comprising the following steps: (1) Step 1: Add potassium iodide solution and selenium dioxide to nitric acid to form a purple-black solid and precipitate white crystals. Then filter, deionize and wash, and dry to obtain solid powder. Heat the solid powder to 95°C under an inert atmosphere and keep it for 12.5 min. Grind to obtain powder. The molar ratio of potassium iodide solution to selenium dioxide is 4:1.5. The amount of nitric acid is 10 wt.% and 90 mL.

[0053] (2) Weigh out the nickel oxalate hydrate source and the melamine carbon nitrogen source, grind and mix them and place them in the combustion boat. The mass ratio of the nickel source and the carbon nitrogen source is 1.5:2.5:1.75. Then place them in the middle of the T-shaped quartz tube. Weigh out the powder prepared in step one and place it in the combustion boat. Place it at the air inlet on the left side of the T-shaped quartz tube.

[0054] (3) Weigh 1.5g of sodium hypophosphite phosphorus source and place it in the combustion boat, and place it at the right air inlet of the T-shaped quartz tube.

[0055] (4) Inert gas is introduced into the left and right air inlets for 4 minutes. The inert gas is argon and the flow rate is 750 sccm. Then, the temperature is set to rise to 650℃ at a program of 3℃ / min. The temperature is kept constant for 3 hours. Then, the material is naturally cooled and taken out to obtain the required material.

[0056] As attached Figure 1 Appendix Figure 2 Appendix Figure 3 Appendix Figure 4 As shown, electrochemical tests were performed on the catalyst material using 1 M KOH as the electrolyte in a three-electrode system. Compared with Comparative Examples 1-3, Example 2 prepared Ni3P-NiSe. x / Ni-ni-azide graphene exhibits the best HER catalytic performance. (Comparison at 10 mA·cm⁻¹) -2 The overpotentials at the current densities were 95 mV, 164 mV, 183 mV, and 213 mV for Examples 2 and Comparative Examples 1-3, respectively. The contribution of nitrogen-modified graphene was higher than that of Se and P modification, specifically Ni3P-NiSe. x The synergistic effect of the heterostructure of / Ni is higher than that of Ni3P / Ni and NiSe. x / Ni heterojunction, i3P-NiSe x The heterostructure of / Ni synergistically promotes electron exchange and intermediate conversion processes. Furthermore, this invention employs cyclic voltammetry (CV) at Faraday range for 10,000 cycles to accelerate catalyst degradation. The HER of the electrode is evaluated by comparing the LSV curves before and after cycling, both at 10 mA·cm⁻¹. -2 The displacement was only 7mV, demonstrating extremely high stability.

Claims

1. A method for preparing a graphene-based material, characterized in that... Includes the following steps: (1) Step 1: Add potassium iodide solution and selenium dioxide to nitric acid to form a purple-black solid and precipitate white crystals. Then filter, deionize and wash, and dry to obtain solid powder. Heat the solid powder to 90-100℃ under an inert atmosphere, keep it for 10-15 min, and grind to obtain powder. (2) Weigh out nickel source, carbon nitrogen source and graphene, grind and mix them and place them in the combustion boat, and then place them in the middle of the T-shaped quartz tube; weigh out the powder prepared in step one and place it in the combustion boat, and place it at the gas inlet on the left side of the T-shaped quartz tube; (3) Weigh the phosphorus source and place it in the combustion boat, and place it at the right air inlet of the T-shaped quartz tube; (4) Inert gas is introduced into the left and right air inlets for 3-5 minutes, then the temperature is increased by setting the program to carry out high-temperature calcination, and then cooled naturally and taken out to obtain the desired graphene-based material.

2. The method for preparing a graphene-based material as described in claim 1, characterized in that... The molar ratio of potassium iodide solution to selenium dioxide is 4:1~2, and the amount of nitric acid is 10wt.%, 75-100mL.

3. The method for preparing a graphene-based material as described in claim 1, characterized in that... The nickel source is nickel oxalate hydrate.

4. The method for preparing a graphene-based material as described in claim 1, characterized in that... The carbon and nitrogen source is melamine.

5. The method for preparing a graphene-based material as described in claim 1, characterized in that... The graphene in question is thermally expanded graphene.

6. The method for preparing a graphene-based material as described in claim 1, characterized in that... The mass ratio of the nickel source, carbon-nitrogen source, and graphene is 1.5:2-3:1.5-2.

7. The method for preparing a graphene-based material as described in claim 1, characterized in that... The phosphorus source is sodium hypophosphite, and the dosage is 1-2g.

8. The method for preparing a graphene-based material as described in claim 1, characterized in that... The inert gas is argon, and the flow rate is 700-800 sccm.

9. The method for preparing a graphene-based material as described in claim 1, characterized in that... The temperature is programmed to rise at 2-5℃ / min to 600-700℃, and then held at that temperature for 2-4 hours.

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